Skip to main content
main-content
Top

About this book

Cleaner Combustion and Sustainable World is the proceedings of the 7th International Symposium on Coal Combustion which has a significant international influence. It concerns basic research on coal combustion and clean utilization, techniques and equipments of pulverized coal combustion, techniques and equipments of fluidized bed combustion, basic research and techniques of emission control, basic research and application techniques of carbon capture and storage (CCS), etc.

Professor Haiying Qi and Bo Zhao both work at the Tsinghua University, China

Table of Contents

Frontmatter

Invited Plenary Speeches

Frontmatter

Coal and Clean Coal Technology: Challenges and Opportunities

Globally, there is a growing concern about fuel diversity and security of supply, particularly with regard to oil and natural gas. In contrast, coal is available from a much wider range of sources and has greater price stability. Consequently, coal use is increasing rapidly, and by 2030 may well reach a level of more than 4,500 Mtoe, corresponding to close to a doubling of current levels. However, at the same time, tightening regulations will require better solutions for achieving environmental compliance, for which coal has a number of key issues to address. Most of the coal will be used in the power generation sector. Consequently, the key research challenges are to develop and deploy methods by which coal can be used cleanly, efficiently, and in a sustainable way. These include improvements to existing coal utilisation technologies, particularly to improve operational flexibility and availability, while reducing energy use through higher efficiencies. There is an increasing need to ensure improved emissions control, with the emphasis on achieving ever-lower emissions of particulates, SO

2

and NOx while also introducing control of trace species, particularly mercury. Alongside this, a key challenge is the integration of techniques that can capture CO

2

then transport and store it within secure geological formations, thereby resulting in near zero emissions of CO

2

. From a power plant perspective, the need is to achieve such integration while minimising any adverse impact on power plant efficiency, performance of existing emissions control systems, operational flexibility and availability. At the same time, means to minimize the additional costs associated with such technology must be established.

Andrew Minchener

Ultra-supercritical (USC) Technology—The Best Practical and Economic Way to Reduce CO2 Emissions from Coal Fired Power Plants

China is the largest coal producer and consumer with largest coal power capacity in the world. By the end of 2010, the total installed power capacity in China was 962,190 MWe, in which coal fired power capacity was 706,630 MWe, accounting for over 73.4%. China has been the largest CO

2

emission country as well and its huge coal power capacity is the largest CO

2

emission source. How does China reduce its CO

2

emissions from coal fired power plants is an austere challenge now we are facing.

How does China reduce its CO

2

emissions from coal fired power plants? There are three ways to reduce CO

2

emissions from coal fired power plants: (1) carbon capture and storage (CCS); (2) co-firing biomass with coal; (3) much improvement of efficiency. For the first option of CCS, the technology is still under development and there are still several uncertainties today to be widely used for coal fired power plants in the short term. For the second option of biomass co-firing, it can reduce CO

2

emissions in a way, but it is difficult to implement it in China without strong support of incentive policy. Therefore, the third option of improvement of efficiency is the only but also the best and feasible economic option for China to much reduce CO

2

emissions from coal fired power plants.

This paper will discuss how China to take a active policy to strongly promote the application of supercritical (SC)/Ultra supercritical (USC) technology. Only in 4 years from 2007 to 2010, ordered capacity of coal fired SC/USC units was 482 units with installed capacity of 230,060 MWe, in which, 1,000 MWe USC with 600°C steam parameters was almost 100 units with 100,000 MWe in which 33 units have been in operation. Today, China has been a country with the largest SC/USC units and capacity. The fast application of SC/USC units for coal fired power plants has resulted in energy saving and reduction of emissions. The average coal consumption in China reduced from 366 gce/kWh in 2006 reduced to 335 gce/kWh in 2010, by which coal saving was 240 million tons and the reduction of CO

2

emission was over 400 million tons.

Today, China is going to develop advanced USC with steam temperature of 700°C to reach net efficiency up to over 50%. This paper will introduce a program that before the technology of 700°C USC is available, the development of USC in a special way is underway to use 600°C material and investment for a 1,350 MWe USC unit with net efficiency of >48%, a demonstration plant will be built and hopefully which will be in operation before 2015. By 2020, coal fired power capacity will be 960,000 MWe in China, in which the majority of the capacity will be high efficiency USC units. This will greatly contribute to the remarkable reduction of CO

2

emissions for China.

Jianxiong Mao

CCS: Coal’s Biggest Challenge

Coal, next to oil, is the second most important energy source due to wide distribution and large quantity. Coal is a very economical fuel about $0.50/GJ–$2.50/GJ (NG usually is $6/GJ–$12/GJ. Currently it is $4.03/GJ for July, 2011 delivery). It is the largest fuel source for power generation: 40% world electricity is generated by coal; its shares are about 80% in China and 50% in the U.S. An extensive coal based energy infrastructure has been built up over the years and is in good service.

Ligang Zheng

Coal Utilization in a Carbon Policy Uncertain World—The North America Situation

Both the United State of America and Canada has very high CO

2

/capita emission: 16.53 tonnes for Canada and 18.38 for the U.S. while the world average is at 4.39 and China at 4.91. Canadian economy is heavily intertwined with that of the U.S.: the cross board trading between the U.S. and Canada is valued at more than $2 billion/day. The United State of America is one of the most important coal users in the world and one the key player in climate change issue.

Ligang Zheng

Development of Clean Coal Technologies in Japan

In Japan, we have to import almost of primary energy resources from all over the world. We depend on foreign countries for 96% of our primary energy supply. Following the two oil crises in the 1970s, Japan has diversified its energy resources through increased use of nuclear energy, natural gas and coal as well as the promotion of energy efficiency and conservation.

M. Sato

Mercury Emission, Control and Measurement from Coal Combustion

Coal-fired electric power generation accounts for 65% of U.S. emissions of sulfur dioxide (SO

2

), 22% of nitrogen oxides (NOx), and 37% of mercury (Hg). The proposed Clear Air Interstate Rule (CAIR) and Clean Air Mercury Rule (CAMR) will attempt to regulate these emissions using a cap-and-trade program to replace a number of existing regulatory requirements that will impact this industry over the next decade.

Mercury emissions remain the largest source that has not yet been efficiently controlled, in part because this is one of the most expensive to control

. Mercury is a toxic, persistent pollutant that accumulates in the food chain.

During the coal combustion process, when both sampling and accurate measurements are challenging, we know that mercury is present in three species: elemental, oxidized and particulate. There are three basic types of mercury measurement methods: Ontario Hydro Method, mercury continuous emission monitoring systems (CEMS) and sorbent-based monitoring. Particulate mercury is best captured by electrostatic precipitators (ESP). Oxidized mercury is best captured in wet scrubbers. Elemental mercury is the most difficult to capture, but selective catalytic reduction units (SCRs) are able to convert elemental mercury to oxidized mercury allowing it to be captured by wet flue gas desulfurization (FGD). This works well for eastern coals with high chlorine contents, but this does not work well on the Wyoming Powder River Basin (PRB) coals. However, no good explanation for its mechanism, correlations of chlorine content in coal with SCR performance, and impacts of higher chlorine content in coal on FGD re-emission are available. The combination of SCR and FGD affords more than an 80% reduction in mercury emissions in the case of high chlorine content coals. The mercury emission results from different coal ranks, boilers, and the air pollution control device (APCD) in power plant will be discussed.

Based on this UAEPA new regulation, most power plants that are only equipped with an Electrostatic Precipitator (ESP) have to look for a control method to reduce mercury emission. So far, the most economical method has been active carbon or sorbent injection before the ESP. Active carbon or sorbent injected into the flue gas ducts to oxidize the elemental mercury and then the oxidized mercury will be captured from the flue gas, then the ESP captures the active carbon or sorbent and fly ash simultaneously. Therefore, the long distance transportation of gaseous mercury is eliminated. However, the capture efficiency of mercury is extremely important in order to reduce the increase in ESP load and control the cost. The oxidation and adsorption rate of HBr and fly ash will be discussed in this presentation.

Wei-Ping Pan, Yan Cao, Kai Zhang

Basic Coal Quality and Combustion

Frontmatter

Large-Eddy Simulation of Swirling Pulverized-Coal Combustion

A Eulerian-Lagrangian large-eddy simulation (LES) with a Smagorinsky-Lilly sub-grid scale stress model, presumed-PDF fast chemistry and EBU gas combustion models, particle devolatilization and particle combustion models are used to study the turbulence and flame structures of swirling pulverized-coal combustion. The LES statistical results are validated by the measurement results. The instantaneous LES results show that the coherent structures for pulverized coal combustion is stronger than that for swirling gas combustion. The particles are concentrated in the periphery of the coherent structures. The flame is located at the high vorticity and high particle concentration zone.

L. Y. Hu, L. X. Zhou, Y. H. Luo, C. S. Xu

Evolution of Weak Perturbations in Gas-Solid Suspension with Chemical Reaction

Dynamics of weak finite-amplitude perturbations in two-phase homogeneous medium (gas + solid particles) with non-equilibrium chemical reaction in gas is studied theoretically. Non-linear model of plane perturbation evolution is substantiated. The model takes into account wave-kinetic interaction and dissipation effects, including inter-phase heat and momentum transfer. Conditions for uniform state of the system are analyzed. Non-linear equation describing evolution of plane perturbation is derived under weak dispersion and dissipation effects. The obtained results demonstrate self-organization in the homogeneous system: steady-state periodic structure arises, its period, amplitude and velocity depends on the features of the medium. The dependencies of these parameters on dissipation and chemical kinetics are analyzed.

O. V. Sharypov, I. S. Anufriev

Predicting the Combustion Kinetics of Chinese Coals

The database on the devolatilization of Chinese coals in the English literature represents coals from all ranks and the major Chinese mines. It was mostly acquired with TGAs. There are sufficient datasets from devices that imposed rapid heating rates to bracket combustor behavior. The domains of heating rate, temperature, pressure, and particle size are either directly relevant to combustion conditions, or close enough to manage with modest extrapolations. Whereas the data on ultimate total yields is sufficient to validate a model for any coal type, more detailed product distributions and char compositions would be desirable. Based on the accurate interpretation of this database, there are few unresolved issues surrounding the applicability of FLASHCHAIN® for combustion applications in China. The sub-database on devolatilization under rapid heating conditions represents 34 samples. The predicted yields were within the measurement uncertainties of 4 daf wt. % for 29 of these coals. Among the five ultimate yields that were not accurately predicted, three had measured values less than the proximate volatile matter (PVM), despite the rapid heating rates in the tests. Similarly, the sub-database on devolatilization under slow heating conditions characterizes ultimate devolatilization yields of 30 samples. The predicted yields were within the measurement uncertainties for 22 of these coals. Among the eight that were not accurately predicted, three had measured values that were much lower than the PVM (which is a problem even after accounting for the slow heating rates in the tests) and three were in studies that did not report ultimate analyses for the coals tested. Unfortunately, the database on the combustion behavior of the chars from Chinese coals is insufficient to specify char oxidation kinetics.

Stephen Niksa, Naoki Fujiwara

The Ignition Delay, Laminar Flame Speed and Adiabatic Temperature Characteristics of n-Pentane, n-Hexane and n-Heptane Under O2/CO2 Atmosphere

Oxy-fuel (O

2

/CO

2

) combustion is one of the several promising new technologies which can realize the integrated control of CO

2

, SO

2

, NO

X

and other pollutants. However, when fuels are burned in the high CO

2

concentration environment, the combustion characteristics can be very different from conventional air-fired combustion. Such changes imply that the high CO

2

concentration atmosphere has impacts on the combustion processes. In this paper, the ignition time, laminar flame speed and adiabatic temperature property of C

5

~ C

7

n-alkane fuels were studied under both ordinary air atmosphere and O

2

/CO

2

atmospheres over a wide range of CO

2

concentration in the combustion systems. A new unified detailed chemical kinetic model was validated and used to simulate the three liquid hydrocarbon fuel’s flame characteristics. Based on the verified model, the influences of various parameters (atmosphere, excess oxygen ratio, O

2

concentration, CO

2

concentration, and alkane type) on the C

5

~ C

7

n-alkane’s flame characteristics were systematically investigated. It can be concluded that high CO

2

concentration atmosphere has negative effect on n-pentane, n-hexane and n-heptane flame’s ignition, laminar flame speed and adiabatic temperature. Besides, this work confirms that high CO

2

concentration atmosphere’s chemical effects play a pronounced role on the flame characteristics, especially for the ignition time property.

Ran Zhao, Hao Liu, Xiaojiao Zhong, Zijian Wang, Ziqin Jin, Yingming Chen, Jianrong Qiu

CFD Simulation of Combustion in a 150 MWe CFB Boiler

Eulerian granular multiphase model with meso-scale modeling of drag coefficient and mass transfer coefficient, based on the energy minimization multi-scale (EMMS) model, was presented to simulate a 150 MW

e

CFB boiler. The three-dimensional (3D), time-dependent simulation results were presented in terms of the profiles of pressure, the distributions of carbon and oxygen, as well as the temperature. The EMMS-based sub-grid modeling allows using coarse grid with proven accuracy, and hence it is suitable for simulation of such large-scale industrial reactors.

Nan Zhang, Wei Wang, Jinghai Li

PIV Measurements of the Turbulence Integral Length Scale on Cold Combustion Flow Field of Tangential Firing Boiler

The process of the pulverized coal combustion in tangential firing boiler has prominent significance on improving boiler operation efficiency and reducing NO

X

emission. This paper aims at researching complex turbulent vortex coherent structure formed by the four corners jets in the burner zone, a cold experimental model of tangential firing boiler has been built. And by employing spatial correlation analysis method and PIV (Particle Image Velocimetry) technique, the law of Vortex scale distribution on the three typical horizontal layers of the model based on the turbulent Integral Length Scale (ILS) has been researched. According to the correlation analysis of ILS and the temporal average velocity, it can be seen that the turbulent vortex scale distribution in the burner zone of the model is affected by both jet velocity and the position of wind layers, and is not linear with the variation of jet velocity. The vortex scale distribution of the upper primary air is significantly different from the others. Therefore, studying the ILS of turbulent vortex integral scale is instructive to high efficiency cleaning combustion of pulverized coal in theory.

Wen-fei Wu, Jing-xing Xie, Zhi-jun Gong, Bao-wei Li

Low Temperature Oxidation and Spontaneous Combustion Characteristics of Upgraded Low Rank Coal

The low temperature oxidation and spontaneous combustion characteristics of dried coal produced from low rank coal using the upgraded brown coal (UBC) process were investigated. To this end, proximate properties, crossing-point temperature (CPT), and isothermal oxidation characteristics of the coal were analyzed. The isothermal oxidation characteristics were estimated by considering the formation rates of CO and CO

2

at low temperatures. The upgraded low rank coal had higher heating values than the raw coal. It also had less susceptibility to low temperature oxidation and spontaneous combustion. This seemed to result from the coating of the asphalt on the surface of the coal, which suppressed the active functional groups from reacting with oxygen in the air. The increasing upgrading pressure negatively affected the low temperature oxidation and spontaneous combustion.

H. K. Choi, S. D. Kim, J. H. Yoo, D. H. Chun, Y. J. Rhim, S. H. Lee

Conversion of Different Ash Content Brown Coal in Fluidized Bed

Available equations used to determine combustion specific rate of coal-derived cokes describe the burning of carbon particles well enough but are not accurate in case of ash-containing coke particles combustion. This study is an attempt to account for the influence of both initial ash content and its increase in the course of carbon conversion in specific rate calculations. The results of experimental study of burn-out dynamics of Volchanskiy field (North Urals) brown coal and its coke with different ash content under conditions of fluidized bed combustion at impulse-type non-gradient reactor RSC-1 and dynamic installation Pyrolysis-M are summarized. Diffusion and heterogeneous (kinetic) components of carbon combustion rate are identified separately by using diffusion and kinetics equation with correction for carbon mass fraction in particles. Burning particle overheating values and heterogeneous combustion rate constants at different temperatures are estimated.

P. Osipov, N. Chernyavskiy, A. Ryzhkov, S. Dulienko, A. Remenuk

Slagging Behavior of Upgraded Brown Coal and Bituminous Coal in 145 MW Practical Coal Combustion Boiler

The purpose of this study is to quantitatively evaluate behaviors of ash deposition during combustion of Upgraded Brown Coal (UBC) and bituminous coal in a 145 MW practical coal combustion boiler. A blended coal consisting 20 wt% of the UBC and 80 wt% of the bituminous coal was burned for the combustion tests. Before the actual ash deposition tests, the molten slag fractions of ash calculated by chemical equilibrium calculations under the combustion condition was adopted as one of the indices to estimate the tendency of ash deposition. The calculation results showed that the molten slag fraction for UBC ash reached approximately 90% at 1,523 K. However, that for the blended coal ash became about 50%. These calculation results mean that blending the UBC with a bituminous coal played a role in decreasing the molten slag fraction. Next, the ash deposition tests were conducted, using a practical pulverized coal combustion boiler. A water-cooled stainless-steel tube was inserted in locations at 1,523 K in the boiler to measure the amount of ash deposits. The results showed that the mass of deposited ash for the blended coal increased and shape of the deposited ash particles on the tube became large and spherical. This is because the molten slag fraction in ash for the blended coal at 1,523 K increased and the surface of deposited ash became sticky. However, the mass of the deposited ash for the blended coal did not greatly increase and no slagging problems occurred for 8 days of boiler operation under the present blending conditions. Therefore, appropriate blending of the UBC with a bituminous coal enables the UBC to be used with a low ash melting point without any ash deposition problems in a practical boiler.

Katsuya Akiyama, Haeyang Pak, Yoji Takubo, Toshiya Tada, Yasuaki Ueki, Ryo Yoshiie, Ichiro Naruse

Ignition and Devolatilization of Pulverized Coals in Lower Oxygen Content O2/CO2 Atmosphere

High speed camera is employed to capture the transient images of the burning particle in a flat-flame entrained flow reactor, some information of the burning particle, such as the optical intensity and the residence time, are obtained through analysis of transient images. The ignition and devolatilization behavior of different rank coals at 1,670, 1,770 and 1,940 K over a range of 2–30% O

2

in both N

2

and CO

2

diluent gases are researched. The results indicate that the laws of ignition and devolatilization of pulverized coals in low oxygen O

2

/CO

2

atmosphere are consistent with the literature, which focus on the environments of high oxygen contents (10–30%) or lower temperate (900–1,500 K). With the gas temperature and oxygen content increased, the ignition delay time and devolatilization time for the lower oxygen content cases decreased for both N

2

and CO

2

atmosphere. With the use CO

2

in place of N

2

in low oxygen content, the ignition delay was retarded and the duration of devolatilization was increased. The effect of CO

2

on coal particle ignition is explained by its higher molar specific heat. And the effect of CO

2

on devolatilization results from its effect on the diffusion rates of volatile fuel and oxygen.

Xiaohong Huang, Jing Li, Zhaohui Liu, Ming Yang, Dingbang Wang, Chuguang Zheng

Large-Eddy Simulation of Ethanol Spray Combustion Using a Finite-Rate Combustion Model

Large-eddy simulation of spray combustion is under its rapid development, but the combustion models are less validated by detailed experimental data. In this paper, large-eddy simulation of ethanol-air spray combustion was made using an Eulerian-Lagrangian approach, a subgrid-scale kinetic energy stress model, and a finite-rate combustion model. The simulation results are validated in detail by experiments. The LES obtained statistically averaged temperature is in agreement with the experimental results in most regions. The instantaneous LES results show the coherent structures of the shear region near the high-temperature flame zone and the fuel vapor concentration map, indicating the droplets are concentrated in this shear region. The droplet sizes are found to be in the range of 20–100μm. The instantaneous temperature map shows the close interaction between the coherent structures and the combustion reaction.

K. Li, L. X. Zhou, C. K. Chan

Investigation of a High Pressure Oxy-Coal Process

A study was conducted to investigate the feasibility of an oxy-coal process, which is pressurized to a combustion pressure of 80 bar. At that pressure the water-vapor can be separated economically from the CO

2

/H

2

O flue gases, either by nucleate condensation or by condensation on cooled surfaces in condenser heat exchangers at a temperature of about 300°C. The heat of condensation can be recaptured to preheat the boiler feed water. So the number of economizers is drastically reduced compared to a conventional steam cycle. Another interesting feature of the high pressure oxy-coal process is the fact, that low rank coal with high moisture content can be fired. Such a process at a pressure of about 80 bar is currently investigated by Babcock, USA, as the ThermoEnergy Integrated Power System (TIPS) and will be analyzed in the present paper. A known disadvantage of the oxy-coal processes is the large recirculating flue gas stream to control the combustion temperature, and which need large pipes and heavy recirculation fans. This disadvantage could be avoided if instead of flue gas a part of the condensed water from the condenser heat exchangers is recirculated.

Within the present study both types of processes have been simulated and for an electric power output of about 220 MW. Furthermore, results of CFD simulations of a pressurized 250 MW combustor with a single swirl burner and flue gas recirculation will be presented.

U. Renz

A Preliminary High-Pressure Thermogravimetric Study of Combustion Reactivity of a Collie Coal Char

The effect of pressure(up to 20 bar)on the reactivity of a char(150–160 μm) produced from Western Australian Collie coal has been studied using a high-pressure thermogravimetric analyser (HP TGA). The pressure demonstrated a positive effect in enhancing char combustion reactivities.Kinetic parameters have been determined from the experimental data.The apparent reaction order was found to be approximately 0.7 and the apparent activation energies were 91.0 kJ/mol at atmospheric pressure and 1.5 kJ/mol at an elevated pressure(10 bar),indicating a shift in the control regimes of the reaction at elevated pressures.The lumped effect of the sample size, bulk diffusion,interparticle and intraparticle diffusion at the elevated pressures played an important role in reducing the mass transfer during the HP-TGA experimentation.Thus the activation energy calculated at elevated pressures may not represent the intrinsic activation energy of the char particles but the apparent values of the bulk of the samples.

Yii Leng Chan, Zhezi Zhang, Mingming Zhu, Chao Luan, Changfu You, Dongke Zhang

Dynamic Behavior of Tobacco Waste in the Coal-Fired Fluidized-Bed Boiler

Circulating fluidized bed (CFB) technology is an advanced method for utilizing coal and other solid fuels in an environmentally acceptable manner. During the processing procedure in the nicotiana tabacum plants, lots of tobacco stem wastes are produced, which are normally being dumped to the landfill field. If this kind of waste can be used as a part of the fuel to be added into the coal in a CFB combustor, it will reduce the use of coal and then cut the net carbon emissions. To understand the complicated fluid dynamics of nicotiana tabacum wastes in the coal-fired CFB boiler, the mixing and segregation behavior of tobacco stalk are preliminary measured in a cylindrical fluidized bed. Obvious segregation behavior is found due to distinct differences in density and shape between tobacco stem and coal, which results in poor fluidization quality and bad combustion efficiency. To overcome this disadvantage, a jet with high gas velocity is introduced through the air distributor and a detailed experimental study is conducted in a fluidized bed made up of stem-sand mixture with different solid components at various jet velocities, which greatly improve the mixing performance of stem in the fluidized bed. The above findings are helpful for the technological upgrading of small- or middle-sized CFB boiler with adding tobacco stem into coal.

Kai Zhang, Bangting Yu, Jian Chang, Honggang Chen, Yongping Yang

Numerical Study of Furnace Process of a 600 MW Pulverized Coal Boiler Under Low Load with SNCR Application

Numerical simulation of flow, heat transfer, and combustion process in a 600MW pulverized coal boiler under low load is performed using Computational Fluid Dynamics (CFD) code Fluent. The distributions of temperature and species were obtained and their influences on Selective non-catalytic reduction (SNCR) were analyzed. The results indicate that the furnace temperature changed significantly as the operation load declines. The furnace space with proper temperature for SNCR reaction becomes lower with decreasing of operation load. As the load falls off, the available O

2

concentration for SNCR reactions rises gently and the initial NOx concentration for SNCR reactions debases slightly. These variations can have some influence on the SNCR process. For the upper furnace where the temperature is suitable for SNCR reactions, the CO concentration is close to 0 under different load. Consequently, the SNCR process will not be affected by CO based on the calculation in this work.

Q. X. Cao, Y. Shi, H. Liu, C. H. Yang, S. H. Wu

The Chemical Transformation of Calcium in Shenhua Coal During Combustion in a Muffle Furnace

The chemical reaction characteristics of calcium in three samples of Shenhua coal, i.e. raw sample, hydrochloric acid washed sample and hydrochloric acid washed light fraction, during combustion in a muffle furnace have been investigated in this paper. Ca is bound by calcite and organic matter in Shenhua coal. X ray diffraction (XRD) phase analysis has been conducted to these samples’ combustion products obtained by heating at different temperatures. It has been found that the organically-bound calcium could easily react with clays and transform into gehlenite and anorthite partially if combusted under 815°C, whilst the excluded minerals promoted the conversion of gehlenite to anorthite. Calcite in Shenhua coal decomposed into calcium oxide and partially transformed into calcium sulfate under 815°C, and formed gehlenite and anorthite under 1,050°C. Calcite and other HCl-dissolved minerals in Shenhua coal were responsible mainly for the characteristic that the clay minerals in Shenhua coal hardly became mullite during combustion.

Tian Sida, Zhuo Yuqun, Shu Xinqian, Chen Changhe

Influence of Metal Additives on Pyrolysis Behavior of Bituminous Coal by TG-FTIR Analysis

To study the catalytic effects of alkali, alkaline earth and transition metal additives on coal pyrolysis behavior, bituminous coal loaded NaCl, KCl, CaCl

2

, MgCl

2

, FeCl

3

and NiCl

2

was respectively investigated using Thermogravimetry and Fourier Transform Infrared Spectroscopy (TG-FTIR). Results indicated that the maximum mass loss rate decreased under the metal additives in the primary pyrolysis stage. The total mass loss of pyrolysis was reduced in metals catalyzed pyrolysis except for Na loaded sample. Kinetic analysis was taken for all samples adopting the method of Coats-Redfern. Activation energy of raw coal in the primary pyrolysis stage was 92.15vkJ·mol

−1

, which was lowered to 44.59–73.42 kJ·mol

−1

under metal additives. The orders of catalytic effect for this bituminous coal were Mg > Fe > Ca > Ni > K > Na according to their activation energies. Several investigated volatiles including CH

4

, CO

2

, CO, toluene, phenol and formic acid were identified from FTIR spectra. The yields of CH

4

, CO

2

, toluene, phenol and formic acid were decreased, but the evolution of CO was increased. The presence of metals in the coal samples have been involved in a repeated bond-forming and bond-breaking process, which greatly hindered the release of tars during pyrolysis as the tar precursors were connected to coal/char matrix and were thermally cracked, becoming a part of char.

Wenjuan Su, Mengxiang Fang, Jianmeng Cen, Chao Li, Zhongyang Luo, Kefa Cen

Rate Constant Computation on Some Elementary Reactions of Hg During Combustion

The geometry optimizations of reactants, products and transition states were made by the quantum chemistry MP2 method at the SDD basis function level for Hg, and 6-311++G(3df, 3pd) for others. The properties of stable minimums were validated by vibration frequencies analysis. Furthermore, the microcosmic chemical reaction mechanisms of reactions were investigated by ab initio calculations of quantum chemistry. On the basis of the geometry optimization, reaction rate constants within 298–2,000 K are calculated neither from experimental data nor by estimated, but directly from Quantum Chemistry software–Khimera.

Wang Qing, Yang Bo-wen, Bai Jing-ru

Study on the Basic Properties of Indonesian Oil Sands

The basic properties of three Indonesian oil sands have been investigated. The results show that since the high content of volatile, heating value and oil yield, Indonesian oil sands could be combusted for power generation and retorting for oil refining. Moreover, oil sand ash with the low content of fixed carbon and high content of CaO, could not only be used as solid heat carrier during retorting, but also comprehensively used as construction material. Based on the thermogravimeric analysis (TGA), pyrolysis and combustion behaviors have been identified. As for pyrolysis, 350–520°C could be regarded as the major oil-producing region, the apparent activation energy

E

is not a constant obtained by distributed activation energy model (DAEM). For combustion, 620–800°C is the high-temperature oxidation (HTO) stage. TG-DTG extrapolation method was applied to determine the combustion characteristics parameters such as ignition temperature, burn-out temperature, combustion stability and combustion reactivity, and finally gave a comparison with those of oil shale and coal.

Qing Wang, Qian-qian Jiang, Jing-ru Bai, Jian Sun, Hong-peng Liu

Effects of Fractal Pore on Coal Devolatilization

Coal devolatilization is numerically investigated by drop tube furnace and a coal pyrolysis model (Fragmentation and Diffusion Model). The fractal characteristics of coal and char pores are investigated. Gas diffusion and secondary reactions in fractal pores are considered in the numerical simulations of coal devolatilization, and the results show that the fractal dimension is increased firstly and then decreased later with increased coal conversions during devolatilization. The mechanisms of effects of fractal pores on coal devolatilization are analyzed.

Yongli Chen, Xiaoliang Wang, Liyong Cao, Rong He

Experiment Research of Slag Renovation in the Corner-Fired Boiler

Aiming at serious slag on the water wall around the burner of corner-fired boiler with low-ash-fusion-point coal, cold experimental model has been established. In this experiment, particle image velocimetry (PIV) has been employed to accurately measure aerodynamic field of burner region, and the experimental research of furnace slag renovation has been conducted through changing the burner jet arrangement. The experiment results show that it has significantly effect on aerodynamic field in the furnace by changing burner jet deflection angle. A reasonable actual tangential circle diameter can be formed through adjusting the burner jet deflection angle, to prevent primary air attacking the wall, and further more, to effectively prevent serious slag on the water wall around the burner.

Zhijun Gong, Wenfei Wu

Study on Geochemical Occurrences of REE in Wangqing Oil Shale

Sequential chemical extraction experiment (SCEE) and Float- sink experiment (FSE) have been employed on oil shale research from Wangqing, Jilin province China, in order to determine the binding forms of rare earth elements (REE) in oil shale. The REE contents were determined by the inductively coupled plasma-mass spectrometry (ICP-MS). Wangqing oil shale was screened into specific gravity density level: <1.5g/cm

3

, 1.5–1.6g/cm

3

, 1.6–2.0g/cm

3

, 2.0–2.4g/cm

3

, >2.4g/cm

3

. The mode of occurrences of rare earth elements in Wangqing oil shale was studied by six-step SCEE. FSE results show that REEs in Wangqing oil shale exist mainly in inorganic minerals and more in excluded mineral, while SCEE results show that REEs of Wangqing oil shale is primarily occurred in minerals, including carbonate, Fe-Mn oxide, sulfide, and Si-minerals. FSE and SCEE results fully illustrate excluded mineral is mainly mode of occurrence of REEs in Wangqing oil shale, whereas inorganic minerals and organic matter is not that. The REE distribution pattern curves of FSE density and SCEE fraction products are similar with that of raw oil shale. The REE in different densities products has a close connection with terrigenous clastic rock, and the supply of terrestrial material is stable.

Jing-ru Bai, Qing Wang, Tong Liu, Yan-zhen Wei, Zhang Bai

Study on Trace and Rare Earth Elements in Indonesian Oil Sands

Major, trace elements and rare earth and mineral composition of the oil sand samples (ST1, ST2, ST3) and the oil sand retorting residue (semi-coke: SC1, SC2, SC3) from Indonesian were determined by XFS, ICP-MS and XRD methods. The trace elements content in oil sand is pretty much the same thing in Earth’s Clarke value. The trace element is abundantly in earth’s Clarke, in oil sand yet, for Ti, Mn, Ba, Sr, but these elements are lower enrichment. However, the Cr (EF = 16.8) and Mo (EF = 11.8) are “enrichment” in ST1; the Ni (EF =10.5), Se (EF = 17.5), Sr (EF = 28.7), Mo (EF = 106.5), Sc (EF = 12.8) and U (EF = 43.2) are “enrichment” in ST2; the Se (EF = 12.6), Sr (EF = 18.4), Mo (EF = 47.5), and U (EF = 27.8) are “enrichment” in ST3. Calculations show that trace elements in sime-coke have lower evaporation rate during Fischer Assay. Trace elements in raw oil sand are so stable that trace elements can’t move easily to other pyrolysis product but enrich to sime-coke. After retorting, more elements are EF > 10, such as B, V, Ni, As, Se, Sr, Mo, Hg, Cs and U. It is essential to take the pollution produced by trace elements in sime-coke during the sime-coke utilization into consideration. The REEs content had a high correlation with the ash in oil sand. The REE is closely related to terrigenous elastic rocks.

Jing-ru Bai, Qing Wang, Hong-peng Liu, Zhang Bai

Experimental Study of Rapid Brown Coal Pyrolysis at High Temperature

Rapid coal pyrolysis is a very important step in the early stage of combustion. Rapid pyrolysis experiments of a brown coal at high temperature have been studied on a laminar drop tube furnace. The volatile mass release measured in this study is high for low rank coal. The activation energy and pre-exponential factor of pyrolysis are 19901.22 kJ/mol and 102.71, respectively. The nitrogen distribution between volatile and char is 0.54. With the increase of temperature, the yields of NH

3

decreases, while those of HCN increases, leading the value of HCN/NH

3

to become larger. At high temperature, the main nitrogen- containing species of pyrolysis in volatile is HCN.

Lin Qian, Shaozeng Sun, Shun Meng, Xianyu Meng, Yangzhou Guo

Experimental Validation of Large-Eddy Simulation for Swirling Methane-Air Non-premixed Combustion

Large-eddy simulation of swirling methane-air non-premixed combustion was carried out using a Smagorinsky-Lilly subgrid scale stress model and a presumed-PDF fast-chemistry combustion model. The LES statistical results are validated by PIV, temperature and species concentration measurements made by the present authors. The results indicate that in the present case the presumed-PDF fast-chemistry combustion model is a fairish one. The instantaneous vorticity and temperature maps show clearly the development and the interaction between coherent structures and combustion.

L. Y. Hu, L. X. Zhou, Y. H. Luo, C. S. Xu

Numerical Modeling of Pyrolysis of Sawdust in a Packed Bed

An unsteady, one-dimensional mathematical model has been developed to describe the pyrolysis of sawdust in a packed bed. The sawdust bed was pyrolyzed using the hot gas and an electric heater outside the bed as the source of energy. The developed model includes mass, momentum and energy conservations of gas and solid within the bed. The gas flow in the bed is modeled using Darcy’s law for fluid through a porous medium. The heat transfer model includes heat conduction inside the bed and convection between the bed and the hot gas. The kinetic model consists of primary pyrolysis reaction. A finite volume fully implicit scheme is employed for solving the heat and mass transfer model equations. A Runge–Kutta fourth order method is used for the chemical kinetics model equations. The model predictions of mass loss history and temperature were validated with published experimental results, showing a good agreement. The effects of inlet temperature on the pyrolysis process have been analyzed with model simulation. A sensitivity analysis using the model suggests that the predictions could be improved by considering the second reaction which could generate volatile flowing in the void.

Qingmin Meng, Xiaoping Chen

Volatile Characteristic of Trace Elements During Microwave Pyrolysis of Oil Shale

Oil shale is abundant in the world. Today, the industry of oil shale retorting for producing shale oil is developing owing to high price of oil in the world. In order to study migratory behavior of trace elements in oil shale at microwave pyrolysis, tests were performed in laboratory with oil shale of the Huadian deposit of China at different powers from 400 to 700 W. The trace elements As, Cd, Hg, Mo, Pb, Se, Cr, Cu, Ni, V, Zn, Ba, Co, Mn present in oil shale and shale char were determined by the inductively coupled plasma-mass spectrometry (ICP-MS). By comparing the content of trace elements in oil shale and shale char, distribution characteristics of trace elements at retorting were studied. The overall trends of volatile ratio of trace elements are ascending with higher microwave power and higher than the conventional pyrolysis. The differences in the volatile ratio indicate that the trace elements investigated are bound with the oil shale kerogen and its mineral matter in different manner. So Float-sink experiments (FSE) were performed on oil shale. Huadian oil shale has more included mineral. The volatilization of organic matter is not the main reason for the volatilization of trace elements in oil shale. The trace elements combined with the mineral elements may be also certain volatility.

Jing-ru Bai, Qing Wang, Ling-wen Kong, Zhang Bai

Approximate-Analytical Study on Thermal Preparation and Combustion of a Coal Particle

The main amount of heat and electricity in the world is produced with application of coal. Following development of power engineering plans application of low-grade coals, including those of new deposits (Salomatov VV, Nature conservation technologies at thermal and atomic power plants, Novosibirsk, NSTU, 2006). Massive Shive-Ovoos open-cast is among such low developed deposits of Mongolia. This deposit requires a set of investigations on thermal preparation and combustion of coal, aimed at extensive and efficient energy utilization. Calculation of flame combustion of coals is based on dependences, which determine the whole combustion process of separate coal particles. For particles of natural coals these processes include complex transformations of organic and mineral parts of coal matrix, heating, devolatization, ignition and burning of coke residue. Such detailed elaboration requires complex physical and mathematical simulation.

Five successive stages of thermal preparation and combustion of a coal particle with initial humidity and ash content were distinguished by experimental results:

1.

Heating. The particle is heated; the temperature increases, and the mass stays constant.

2.

Drying. Liquid inside a wet particle evaporates and mass reduces.

3.

Devolatization.

4.

Ignition of slightly dried carbon layer by fuel gases. Residual moisture is still kept in the particle.

5.

Burning. Two successive conditions are considered:

(a)

simultaneous burning of dried carbon layer and evaporation;

(b)

burning of absolutely dry coke residue.

V. V. Salomatov, Kh. Enkhjargal

Fouling Deposition Characteristic by Variation of Coal Particle Size and Deposition Temperature in DTF (Drop Tube Furnace)

One of the major operation obstacles in gasification process is ash deposition phenomenon. In this investigation, experiment was carried out to examine coal fouling characteristics using a laminar DTF (Drop Tube Furnace) with variation of operating condition such as different coal size, and probe surface temperature. Four different samples of pulverized coal were injected into DTF under various conditions. The ash particles are deposited on probe by impacting and agglomerating action. Fouling grains are made of eutectic compound, which is made by reacting with acid minerals and alkali minerals, in EPMA (Electron Probe Micro-Analysis). And agglomeration area of fouling at top layer is wide more than it of middle and bottom layer. The major mineral factors of fouling phenomenon are Fe, Ca, and Mg. The deposition quantity of fouling increases with increasing particle size, high alkali mineral (Fe, Ca, and Mg) contents, and ash deposition temperature.

Hueon Namkung, Li-hua Xu, Youngshin Jeon, Hyungtaek Kim

Drying Kinetics Characteristic of Indonesia Lignite Coal (IBC) Using Lab Scale Fixed Bed Reactor

Recent instability of energy market arouse a lot of interest about coal which has a tremendous amount of proven coal reserves worldwide. South Korea hold the second rank by importing 80 million tons of coal in 2007 following by Japan. Among various coals, there is disused coal. It’s called Low Rank Coal (LRC). Drying process has to be preceded before being utilized as power plant. In this study, drying kinetics of LRC is induced by using a fixed bed reactor.

$$ G(\alpha ) = aN_{{{\rm Re} }}^b{{\left( {\frac{L}{D}} \right)}^c}kt $$

The drying kinetics was deduced from particle size, the inlet gas temperature, the drying time, the gas velocity, and the L/D ratio. The consideration on Reynold’s number was taken for correction of gas velocity, particle size, and the L/D ratio was taken for correction packing height of coal. It can be found that active drying of free water and phase boundary reaction is suitable mechanism through the fixed bed reactor experiments.

TaeJin Kang, DoMan Jeon, Hueon Namkung, DongHa Jang, Youngshin Jeon, Hyungtaek Kim

Experimental Study on the Combustion Characteristics of Liquid Fuel in the Straight Tubes

This study investigates combustion characteristics of liquid hydrocarbon fuel (n-heptane, c7h16) under different operating conditions. In the paper we designed a burner consisting of a stainless steel capillary which is used to dump the fuel and a larger stainless steel tube (or quartz tube) used as a combustion chamber. The inner diameter (ID) of the capillary is 0.24 mm, the inner and external diameter of the larger tube is 4 and 6 mm, respectively. According to the experimental results, the combustion process reaches a stable status after about 100 s. Wall temperature distribution and combustion products are analyzed under conditions with different equivalence ratios, gas flow velocities and materials. As equivalence ratio (ER) whose range is in 0.56–1.08 increases, the wall temperature declines, and wall temperature gradient increases slightly. The range of gas flow velocity is in 0.6–1 m/s, the overall trend of wall temperature distribution is the second point from left boundary as a line, the wall temperature distribution of the four points in the right side increases with the flow velocity increasing, but the left point is rapidly declining. When the burner made of stainless steel, the wall temperature distribution varies slightly due to the larger thermal conductivity of stainless steel than that of quartz, which makes the heat transfer in stainless steel faster and the temperature distribution is more uniform. The thermodynamic calculation software is also used to study the compositions of combustion products. In a word, this structure of the burner shows poor combustion characteristics, we should change the structure and the experimental conditions to achieve better combustion characteristics in the future.

Fei Yang, JunWei Li, ZhaoQiu Zhou, Xin Zhang, NingFei Wang

Slagging and Fouling Evaluation of PC-Fired Boilers Using AshProSM

SmartBurn® applied AshPro

SM

model to two 512 MW Tangential-fired (T-fired) boilers firing US western sub- bituminous coals to evaluate the boiler slagging behaviors with different operating conditions and OFA. The boiler convective pass fouling behaviors with three different coals were also evaluated. The slagging evaluation results indicate that the OFA configuration and air flow distribution have dramatically impacts on the ash impaction rates and slagging patterns on the furnace walls. Deposit growth and strength vary at the different regions of the furnace walls. The fouling evaluation reveals that the tube bank configuration, the amount of incoming ash, the profiles of flue gas temperature, velocity, and species all have significant impacts on fouling deposit formation, growth, and strength development. In addition, the varying ash particle sizes and chemical compositions from different coals also play important roles on the fouling deposit strength development and removal. The investigation demonstrated that AshPro

SM

model can be used to evaluate localized slagging and fouling problems that are related to specific boiler configuration and operating conditions. It can be used to identify the major causes of ash deposition and can guide changes in boiler operation.

Zhanhua Ma, Felicia Iman, Pisi Lu

Emission Control

Frontmatter

Predicting Mercury Retention in Utility Gas Cleaning Systems with SCR/ESP/FGD Combinations or Activated Carbon Injection

This paper presents validations of the Hg speciation predicted by NEA’s MercuRator™ package with an American field test database for 28 full-scale utility gas cleaning systems. It emphasizes SCR/ESP/FGD combinations and activated carbon injection because these two applications present the best long- term prospects for Hg control by coal-burning utilities. Validations of the extents of Hg

0

oxidation across SCRs and of Hg retention in wet FGDs gave correlation coefficients greater than 0.9 for both units. A transport-based FGD analysis correctly assessed the potential for Hg

0

re-emission in one limestone wet FGD. Among the ten stations in the SCR/ESP/FGD validations, the simulations correctly identified 3 of 4 of the relatively high Hg emissions rates; all four of the sites with moderate emissions rates; and both sites with the lowest emission rates. The validations for ACI applications demonstrated that Hg removals can be accurately estimated for the full domain of coal quality, LOI, and ACI rates for both untreated and brominated carbon sorbents. The predictions for ACI depict the test-to-test variations in most cases, and accurately describe the impact of ACI configuration and sorbent type. ACI into FFs is the most effective configuration, although ACI into ESPs often removes 90% or more Hg, provided that there is sufficient residence time and Cl in the flue gas. Brominated sorbents perform better than untreated carbons, unless SO

3

condensation inhibits Hg adsorption.

Balaji Krishnakumar, Chitralkumar V. Naik, Stephen Niksa, Naoki Fujiwara

Structure Optimization of CFB Reactor for Moderate Temperature FGD

The gas velocity distribution, sorbent particle concentration distribution and particle residence time in circulating fluidized bed (CFB) reactors for moderate temperature flue gas desulfurization (FGD) have significant influence on the desulfurization efficiency and the sorbent calcium conversion ratio for sulfur reaction. Experimental and numerical methods were used to investigate the influence of the key reactor structures, including the reactor outlet structure, internal structure, feed port and circulating port, on the gas velocity distribution, sorbent particle concentration distribution and particle residence time. Experimental results showed that the desulfurization efficiency increased 5–10% when the internal structure was added in the CFB reactor. Numerical analysis results showed that the particle residence time of the feed particles with the average diameter of 89 and 9 μm increased 40% and 17% respectively, and the particle residence time of the circulating particles with the average diameter of 116 μm increased 28% after reactor structure optimization. The particle concentration distribution also improved significantly, which was good for improving the contact efficiency between the sorbent particles and SO

2

. In addition, the optimization guidelines were proposed to further increase the desulfurization efficiency and the sorbent calcium conversion ratio.

Yuan Li, Jie Zhang, Kai Zheng, Changfu You

Experiment Study on NOx Reduction Through Biomass Reburning in an Entrained Flow Reactor

The reburning experiments with six kinds of biomass (including rice straw, wheat straw, maize stalk, cotton stalk, rice husk and bagasse,) and one biochar (wheat straw char) was carried out in an entrained flow reactor. The effects of biomass type, stoichiometric ratio in the reburning-zone (SR2), reaction temperature in the reburning-zone (

t

2

), particle sizes of biomass (

d

p

), and reburning fuel fraction (

R

ff

) on NO reduction efficiency analysed. The NO heterogeneous reduction contribute of biochar was also analyzed. The results indicate that NO reduction efficiency behaves a trend of first increase and then decrease with decreasing of SR2 or increasing of

R

ff

. The higher NO reduction efficiency (more than 50%) can be achieved at the range of SR2 = 0.7–0.8 or

R

ff

= 20–26% during reburning with six tested biomass. Cotton stalk with higher volatiles and the highest contents of K, Na alkali metals behaves the best performance of NO reduction. In the range of

t

2

= 900–1,100°C NO reduction efficiency increases with increasing of reburning-zone reaction temperature at the same SR2. NO reduction efficiency increases insignificantly with decreasing of particle size of biomass while

d

p

< 425μm. The contribution of NO heterogeneous reduction by wheat straw char to the total NO reduction is in the higher range of 59–68% while

R

ff

= 10–26%.

P. Lu, Y. Wang, F. Lu, Y. Liu

Adsorption Characteristics of SO2, NO by Steam Activated Biomass Chars

Wheat straw and rice husk collected from the suburb of Nanjing, China, were prepared to different kinds of steam activated biomass-based chars, and the adsorption characteristics of the biomass-based chars was carried out in a fixed bed reactor. The specific surface area and pore structure of different biomass chars were measured by nitrogen adsorption-desorption analysis instrument at 77K. The effects of biomass type, pyrolysis temperature, heating rate, activation temperature and concentration of SO

2

, NO on the adsorption efficiency of SO

2

, NO were analyzed. The results indicated that the steam activation has significant effects on the specific surface area, total pore volume and micro-morphology of biomass chars by improving the internal structure. The adsorption efficiency of SO

2

, NO increased with the decreasing of SO

2

, NO concentration in the experimental range. The optimal condition of char preparation (873K, fast pyrolysis) and steam activation (1,073K) was proposed based on the adsorption efficiency and adsorption volume of SO

2

, NO. It builds a theoretical basis for industrial applications of biomass.

Fei Lu, Tong Shu, Kuan Wang, Ping Lu

Successful Design and Application of SNCR Parallel to Combustion Modification

Various De-NOx methods have been recently adopted in China to control NOx emissions including Selective Non-Catalytic Reaction (SNCR) technology. Usually, the design of SNCR system is carried out after the combustion modification technologies, such as low NOx burner (LNB) and over fire air (OFA), have already been installed and in operation. This article discusses how to design the SNCR system parallel to the combustion modification. The SNCR process design consists of three steps: (1) boiler baseline test, (2) computational fluid dynamics simulation (CFD) facilitated design and (3) SNCR system performance predictions and optimizations. The first step is to conduct boiler baseline test to characterize the boiler operating conditions at a load range. The test data can also be used to calibrate the CFD model. The second step is to develop a three-dimensional boiler coal combustion CFD model to simulate the operation of the boilers at both baseline and post combustion modification conditions. The simulation reveals velocity, temperature and combustible distributions in the furnace. The last step is to determine the position and numbers of the injectors for SNCR reagent. The final field tests upon the project completion have shown that the average SNCR De-NOx efficiency has reached 35.1% with the maximum removal efficiency of 45% on full load. The project also couples the SNCR and SCR (Selective Catalytic Reduction) technologies. The combined removal efficiency of combustion modifications, SNCR and SCR is higher than 82%. This paper shows a successful example for retrofitting aged power-generating units with limited space.

Dongxian Zhao, Leping Tang, Xiaozhen Shao, Derun Meng, Hongjian Li, Wei Zhou, Guang Xu

Study on Pore Structure Properties of Steam Activated Biomass Chars

Wheat straw and rice husk chars were prepared in a fixed bed reactor at different pyrolysis temperatures (673, 873 and 1,073K) and different pyrolysis procedure. The steam activated chars were also prepared in a fixed bed reactor at the following conditions: activation temperature is 1,073K, the flow rate of N

2

is 5L/min, and N

2

and H

2

O molar ratio is 1:1. The specific surface area, pore structure and micro-morphology of different kinds of prepared biomass chars were measured by NOVA1000e analysis instrument and JSM-5610LV scanning electron microscopy (SEM), respectively. Results indicated that the internal structure was improved significantly by steam activation through enlarging the specific surface area and enriching the porosity. The wheat straw char prepared by both rapid pyrolysis at 873K and activation by steam is better than others, whose DR surface area increases from 3.10 to 1099.99m

2

/g. The N

2

adsorption volume of steam activated biomass chars has been significant promoted.

Tong Shu, Fei Lu, Qinchao Wang, Ping Lu

Mercury Speciation and Fine Particle Size Distribution on Combustion of Chinese Coals

Coal combustion is the dominant anthropogenic mercury emission source of the world. Electrostatic precipitator (ESP) can remove almost all the particulate mercury (Hg

p

), and wet flue gas desulfurization (WFGD) can retain a large part of the gaseous oxidized mercury (Hg

2+

). Only a small percentage of gaseous elemental mercury (Hg

0

) can be abated by the air pollution control devices (APCDs). Therefore, the mercury behavior across APCDs largely depends on the mercury speciation in the flue gas exhausting from the coal combustor. To better understand the formation process of three mercury species, i.e. Hg

0

, Hg

2+

and Hg

p

, in gaseous phase and fine particles, bench-scale measurements for the flue gas exhausting from combustion of different types of coal in a drop-tube furnace set-up, were carried out. It was observed that with the limitation of reaction kinetics, higher mercury concentration in flue gas will lead to lower Hg

2+

proportion. The concentration of chlorine has the opposite effect, not as significantly as that of mercury though. With the chlorine concentration increasing, the proportion of Hg

2+

increases. Combusting the finer coal powder results in the formation of more Hg

2+

. Mineral composition of coal and coal particle size has a great impact on fine particle formation. Al in coal is in favor of finer particle formation, while Fe in coal can benefit the formation of larger particles. The coexistence of Al and Si can strengthen the particle coagulation process. This process can also be improved by the feeding of more or finer coal powder. The oxy-coal condition can make for both the mercury oxidation process and the metal oxidation in the fine particle formation process.

Lei Zhang, Michael Daukoru, Sarah Torkamani, Shuxiao Wang, Jiming Hao, Pratim Biswas

The Study of Calcium Sulfate Decomposition by Experiments Under O2/CO2 Atmosphere

Sulphur emission and the effect on ash properties and boiler- tube corrosion in oxy-fuel combustion have received increasing attention in the recent years. Early investigation about calcium- based desulphurization in oxy-fuel, addressed the advantage to reduce the SO

2

emission. This paper, the decomposition of calcium sulphate was characterized by thermogravimetric analyzer. The results showed that the decomposition inhibited by increasing O

2

concentration and SO

2

concentration resulted from recycled flue gas. And CO

2

concentration had the negative effect, which can be solved by changing O

2

concentration through appropriately adjusting recycled flue gas ratio. The kinetics mechanism of calcium sulfate-decomposition in oxy-fuel combustion was further analyzed. Compared with conventional atmosphere, the reaction activation energy was heightened in oxy-fuel conditions, and the difference increased with rising temperature. So it can further confirm the advantage of calcium utilization rate under high temperature in oxy-fuel condition.

Y. Liu, H. Zhou, Y. H. Liu, R. Stanger, L. Elliot, T. Wall, K. F. Cen

Numerical Investigation of Influence Thermal Preparation Coal on Nitric Oxides Formation in Combustion Process

Emissions of nitrogen oxides from coal combustion are a major environmental problem because they have been shown to contribute to the formation of acid rain and photochemical smog. Coal thermalpreparation before furnace delivery is effective method to reduce NOx emissions, shown by experiments in small-scale facilities (Babiy VI, Alaverdov PI, Influence of thermal preparation pulverized coal on nitric oxides outlet for combustion different metamorphized coal. ATI, 1983). This paper presents the mathematical model of burning thermal preparation coal. Validation of the model was carried out on laboratory-scale plant of All-Russia thermal engineering institute. Modeling of low-emissive burner with preliminary heating coal dust is made for the purpose of search of burner optimal constructions which provides low concentration of nitric oxides in the boiler. For modeling are used in-house CFD code “σFlow” (Dekterev AA, Gavrilov AA, Harlamov EB, Litvintcev KY, J Comput Technol 8(Part 1):250–255, 2003).

N. Chernetskaya, M. Chernetsky, A. Dekterev

The Application of Zonal™ Combustion Monitoring and Tuning System to Coal Boilers for Efficiency Improvement and Emissions Reduction

Coal-fired boilers equipped with Low NO

x

Burner (LNB) and Overfire Air (OFA) are challenged with maintaining good combustion conditions. In many cases, the significant increases in carbon monoxide (CO) and unburned carbon levels can be attributed to local poor combustion conditions as a result of poorly controlled fuel-air distribution within the furnace. The Zonal

TM

combustion monitoring and tuning system developed by GE is available to detect and correct the furnace air-fuel distribution imbalance. The system monitors the boiler excess oxygen (O

2

) and combustible gases, primarily carbon monoxide (CO), by using spatially distributed multipoint sensors located in the boiler’s high temperature upper convective backpass region. At these locations, the furnace flow is still significantly stratified allowing tracing of poor combustion zones to specific burners and OFA ports. Using a model-based tuning system, operators can rapidly respond to poor combustion conditions by redistributing airflows to select burners and OFA ports.

By improving combustion at every point within the furnace, the boiler can operate at reduced excess O

2

and reduced furnace exit gas temperature (FEGT) while also reducing localized hot spots, corrosive gas conditions, slag formation, and carbon-in-ash. Benefits include improving efficiency, reducing NO

X

emissions, increasing output and maximizing availability. This chapter presents the results from implementing the Zonal combustion monitoring and tuning system on a 460 MW tangential-fired coal boiler in the Western United States.

Guang Xu, Wei Zhou, Neil C. Widmer, David K. Moyeda

Bench-Scale Studies on Capture of Mercury on Mineral Non-carbon Based Sorbents

A new high-temperature, mineral non-carbon based dispersed sorbent derived from paper recycling products has been shown to capture mercury at high temperatures in excess of 600 °C. The sorbent is consisted of kaolinite/calcite/lime mixtures. Experiments have been conducted on chemi-sorption of elemental mercury in air on a packed bed. The sorption occurs at temperatures between 600 and 1,100 °C and requires activation of the minerals contained within the sorbents. Mercury capture is dominated by temperature and capture on sorbents over long time scales. The capture shows a maximum effectiveness at 1,000 °C and increases monotonically with temperature. The presence of oxygen is also the required. Freshly activated sorbent is the most effective, and deactivation of sorbents occurs at high temperatures with long pre-exposure times. This activation is suspected to involve a solid-solid reaction between intimately mixed calcium oxide and silica that are both contained within the sorbent. Deactivation occurs at temperatures higher than 1,000 °C, and this is due to melting of the substrate and pore closure. The situation in packed beds is complicated because the bed also shrinks, thus allowing channeling and by-passing, and consequent ambiguities in determining sorbent saturation. Sorbent A had significantly greater capacity for mercury sorption than did Sorbent B, for all temperatures and exposure time examined. The effect of SiO

2

on poor Sorbent B is much larger than sorbent A.

Yang Li, Jost O. L. Wendt, Junying Zhang, Chuguang Zheng

Trace Elements Partitioning During Coal Combustion in Fluidized Bed Under O2/CO2 Atmosphere

Experiments were conducted to investigate the effects of temperature and O

2

/CO

2

atmosphere on trace elements (Cr, Mn, Co, Ni, Cd, Pb, Hg, As, Se) partitioning during combustion of Xuzhou bituminous coal in a 6 kWth fluidized bed. Inductively coupled plasma mass spectrometry (ICP-MS) and atomic fluorescence spectrometry (AFS) were used to determine trace elements contents in raw coal, bottom ash, fly ash and flue gas. The results indicate that with bed temperature increase, the relative enrichment of all the trace elements except Cr in bottom ash decreases suggesting that their volatility is enhanced. The relative enrichments of hardly volatile elements, like Cr and Mn in fly ash increase with bed temperature increase while those of partially volatile and highly volatile elements in fly ash are opposite. The relative enrichments of trace elements except Cr and Mn in fly ash are higher than those in bottom ash. Increasing bed temperature promotes elements like As, Se and Hg to migrate to vapor phase, Mn to migrate to fly ash and Cr to migrate to both bottom ash and fly ash. 21%O

2

/79%CO

2

atmosphere improves the volatility of Cr, Mn, Co, Se and their migration to fly ash, while restrains the volatility of As, Ni, Pb. It has little effect on the volatility of Hg but improves its migration to fly ash.

Mass balance ratio was also calculated to observe trace elements distribution in bottom ash, fly ash and flue gas. There is no much difference in trace elements distribution between the two atmospheres. It can be seen that the trace elements proportion in fly ash is much greater, and more than 40% of Hg is distributed in the gas phase. Most of Hg and Se volatilize during combustion. The mass balance ratios are 87 ~ 129% which is considered acceptable.

Haixin Li, Changsui Zhao, Cai Liang, Lunbo Duan, Huichao Chen

Effect of Phosphorous Transformation on the Reduction of PM10 Formation During Co-Combustion of Coal and Sewage Sludge

Co-combustion of Municipal Sewage Sludge with coal will become increasingly widely used, regarded as an important incineration method with the high thermal efficiency, low emissions, low investment and operating costs. However, the presence of phosphorus in fine particle has gained increased attention due to its environmental adverse affection and deactivation of SCR DeNOx catalysts. Therefore, the behavior of phosphorus in fine particles during co-combustion of coal and sewage sludge was investigated in a 25 kW quasi one-dimensional down-fired pulverized coal combustor, where PM

10

was collected from the furnace centerline in the outlet of flue gas cooler by using a two-stage nitrogen-aspirated, water-cooling isokinetic sampling probe followed a 13-stage electric low pressure impactor. Then the formation mechanism of PM

10

was investigated by observing the different fractions of sewage sludge in the coal.

Similar to the coal combustion, the particle-size-distributions (PSD) of PM

10

mass concentration by co-combustion of sewage sludge with coal exhibit two distinct modes separated by a fraction of 0.157–0.263 μm, ultrafine mode and intermediate mode. With the sewage sludge blended sludge up to 15% (thermal ratio), the mass concentration of the total fly ash and PM

10+

(Dp > 10 μm) vastly increased from 1,088 and 547 mg/Nm

3

(during coal combustion) to 5,059 and 4,403 mg/Nm

3

. However, the mass concentration of fine particulates, such as PM

1

, PM

2.5

and PM

10

was maintained at the emission level of coal combustion. When the fraction of sewage sludge less than 15%, the mass concentration of fine particle is higher than the emission during coal combustion, while the growth rate is only by the 3.6, 7.9 and 4.8% of the total concentration of fly ash (5% thermal).

The change of the PSD of mass concentration during co- combustion of sewage sludge and coal, mainly was caused by the interaction between Si、Al and Ca、Fe、K、Na、Mg, which lowed the fusing temperature of the aluminosilicate and silicate, then readily aggregated to form larger particles. Sulphate and phosphate process during the cooling of flue gas will reduced the mass concentration of fine particle, when the fraction of sewage sludge was 15% (thermal), the phosphate and P

2

O

5

will dominantly increased in the ultrafine mode.

J. K. Zhuo, M. Dong, G. D. Li, L. Duan, S. Q. Li, Q. Song, Q. Yao

Experimental Study of Volatile-N Conversion at O2/CO2 Atmosphere in a Drop Tube Furnace

In coal combustion, NOx is largely formed from the oxidation of volatile nitrogen compounds such as HCN and NH

3

. The experiments on the volatile-N conversion to NO at O

2

/CO

2

atmosphere were carried out in a drop tube furnace. The effects of the excess oxygen ratio λ (0.6–1.4), temperature (1,000–1,300 °C), O

2

/CO

2

ratio, and as well as CH

4

/NH

3

mole ratio were investigated. To further understand the importance of NO reburn during volatile combustion, experiments were also performed with different concentrations of background NO (0–950 ppm). The results show that volatile-N conversion to NO is sensitive to excess oxygen ratio λ at strongly oxidizing atmosphere. For volatile combustion, there is an optimal temperature and inlet O

2

concentration to minimize the volatile-N conversion to NO. The CH

4

/NH

3

mole ratio plays an important role on the NO formation under oxidizing atmosphere. High levels of background NO prohibit the volatile-N conversion to NO significantly as the volatile-N conversion ratio decreases by 19–36%. The reburn fractions of recycle NO in fuel-rich and fuel-lean condition are 14.8 and 9.8% at 1,200 °C, respectively.

Huali Cao, Shaozeng Sun, Hao Chen, Xianyu Meng, Dong Wang, Terry F. Wall

Leaching Characteristics of Trace Elements in Desulfurization Gypsum from a Coal-Fired Power Plant

The contents and leaching characteristics of Cr, Cd, As, Pb and Se in FGD gypsum from a 200 MW coal-fired power plant were investigated in this study. Experimental results revealed that: the leaching characteristics of As and Se were similar, both leaching rates were not obviously affected by pH but increased with increase of the liquid-solid ratio. Pb and Cr had similar leaching characteristics, their leaching rates were closely related with the pH of leaching solution and increased with the lowering of pH and both increased with the increasing of solid-liquid ratio. Along with the increase of the liquid-solid ratio, the leaching gradually achieved balance, and the balanced liquid-solid ratio was bigger when pH of leaching solution was lower. Cd content of leaching solution was below detect limit, and thus failed to get its leaching characteristics. The order of trace element content in leaching solution is Pb < Cr < As < Se, and the order of leaching rates is Cr < As < Pb < Se. BCR extraction procedure revealed that trace elements in FGD gypsum were mainly existed as available fraction and migration ability was stronger than that of trace elements in fly ash from coal-fired power plants.

Y. K. Liu, Y. Q. Zhuo, Z. W. Zhu, C. H. Chen

Study on Fine Particles Influence on Sodium Sulfite and Oxygen Gas-Liquid Reaction

Wet limestone scrubbing is the most common flue gas desulfurization process for control of sulfur dioxide emissions from the combustion of fossil fuels, and forced oxidation is a key part of the reaction. During the reaction which controlled by gas-liquid mass transfer, the fine particles’ characteristic, size, solid loading and temperature has a great influence on gas-liquid mass transfer. In the present work is to explain how these factors influence the reaction between Na

2

SO

3

and O

2

and find the best react conditions through experiment. The oxidation rate was experimentally studied by contacting pure oxygen with a sodium sulfite solution with active carbon particle in a stirred tank, and the system pressure drop was record by the pressure sensor. At the beginning the pressure is about 215 kPa and Na

2

SO

3

is about 0.5mol/L. The temperature is 40, 50, 60, 70, 80°C. Compare the results of no particles included, we can conclude that high temperature, proper loadings and smaller particles resulting in higher mass transfer coefficients

k

L

.

Tao Shuchang, Zhao Bo, Wang Shujuan, Zhuo Yuqun, Chen Changhe

Mercury Removal from Coal Combustion Flue Gas by Fly Ash

The effect of physicochemical properties on the mercury adsorption performance of three fly ash samples has been investigated. The samples were tested for mercury adsorption using a fixed-bed with a simulated gas. X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy and other methods were used to characterize the samples. The results indicate that mercury adsorption on fly ash is mainly physisorption and chemisorption. Uncompleted burned carbon is an important factor for the improvement of mercury removal efficiency, especially, the C-M bond may improve the oxidation of mercury, which formed via the reaction of C and Ti, Si and other elements. The higher specific surface areas and smaller pore diameter are all beneficial for the high mercury removal efficiency. The presence of O

2

plays a positive role on Hg adsorption of modified fly ash, while SO

2

has double role of inhibition because of competitive adsorption and promotion to chemisorption. In addition, sample modified with FeCl

3

has a great performance in Hg removal.

Junyan Kuang, Wenqing Xu, Tingyu Zhu, Pengfei Jing

Utilization and Mitigation of VAM/CMM Emissions by a Catalytic Combustion Gas Turbine

A system configured with a catalytic combustion gas turbine generator unit is introduced. The system has been developed using technologies produced by Kawasaki Heavy Industries, Ltd., such as small gas turbines, recuperators and catalytic combustors, and catalytic oxidation units which use exhaust heat from gas turbines. The system combusts (oxidizes) ventilation air methane (less than 1% concentration) and low concentration coal mine methane (30% concentration or less) discharged as waste from coal mines. Thus, it cannot only reduce the consumption of high- quality fuel for power generation, but also mitigate greenhouse gas emissions.

K. Tanaka, Y. Yoshino, H. Kashihara, S. Kajita

Numerical Simulation of Flow in De-NOx Catalyst Honeycomb with NOx Reduction Reaction

The effect of flow behavior in a De-NOx honeycomb with NOx reduction reaction is investigated by direct numerical simulation (DNS). As the inlet flow, fully developed turbulent or laminar flow is given. The results show that the surface reaction is strongly affected by inner flow behavior. The surface reaction rate for the turbulent flow is higher than that for the laminar flow. This is due to the difference of inner flow behavior that the diffusion of NOx in the vicinity of the wall is dominated only by molecular diffusion for the laminar flow, whereas it is enhanced by turbulent motions for the turbulent flow. Moreover, surface reaction is suppressed towards downstream even though inlet flow is turbulent. This is due to the flow transition from turbulent to laminar.

K. Tanno, R. Kurose, H. Makino, S. Komori

Study on Kinetic Parameters and Reductive Decomposition Characteristics of FGD Gypsum

Decomposition characteristics and kinetics of analytical gypsum (AG), dry flue gas desulphurization gypsum (DG) and wet FGD gypsum (WG) were studied by using thermal analyzer in a nitrogen atmosphere. Kinetic parameters (such as activation energy E and frequency factor A) of thermal decomposition of AG, DG and WG were calculated based on TG-DTA curves and Coast-Redfern method. The apparent activation energy of FGD gypsums was much lower than that of AG. The apparent activation energies of tested AG, DG and WG were 214.73, 128.54 and 111.12 kJ/mol, respectively. Reductive decomposition characteristics of analytical gypsum, dry FGD gypsum and wet FGD gypsum were studied by using thermal analyzer. The results indicated that the factors of the final reaction temperature and the reaction atmosphere have significant influences on the decomposition of gypsum, in the condition of 850–1,050°C, the total decomposition rate of three gypsums increases and the time-consumption of reaching decomposition equilibrium of three gypsums decreased with the increasing of the final reaction temperature; in the condition of 0–5% CO, the total decomposition rate of all three tested gypsums increases with increasing of CO volume fraction, and the time-consumption of reaching decomposition equilibrium of three gypsums is shortened with increasing of CO volume fraction; doping of Fe

2

O

3

in the analytic gypsum not only increases the total decomposition rate, but also improves the reaction rate at reasonable doping amount. AG with 5% Fe

2

O

3

doping is more effective based on the total decomposition rate; however, AG with 10% Fe

2

O

3

doping is slightly better on the basis of the decomposition reaction rate.

Jing Zhang, Ping Lu

Investigation on the Transient Enthalpy of Coal Combustion

The transient enthalpy (Δ

h

) of coal/char combustion of the three different coals (including anthracite, bituminous, and lignite) during the process of combustion is determined as a function of burn-off degree by using thermo-gravimetric-differential scanning calorimeter (TG-DSC) simultaneous thermal analyzer, and The error of determining calorific values of coals/chars is less 5% compared the results of TG-DSC with that of an automatic isoperibol calorimeter. It is found that In the initial stage, all the Δ

h

of coals are greater than that of the char pyrolysized from parent coal for many of volatiles contained more a great deal of heat per unit mass oxidized at low temperautre, it also imply that coal is more easily ignited than char corresponded; And in the middle stage, all the Δ

h

of coals is lower than that of the char pyrolysized, so the pyrolysized char oxidation can supply much more of thermo-energy per unit mass. Δ

h

are almost a constant when the burn-off degree is equal to between 0.35/0.15 and 0.95/0.85 for ZCY bituminous coal/char and JWY anthracite/char, between 0.35/0.35 and 0.75/0.9 for SLH lignite/char; In the later stage, the Δ

h

of the coal/char decreased with the burn-off degree, it imply that the activity of the coal/char decreases. Therefore, coal pyrolysis changes not only the structure of char, but also the property of release heat; the transient enthalpy of coal/char combustion has been in change with the burn-out degree.

Pei-fang Fu, Na Wang, Bo Yu, Bin Zhang, Yang Liu, Huai-chun Zhou

Mercury Speciation in Air-Coal and Oxy-Coal Combustion

To study the effect of air-coal and oxy-coal combustion on mercury emission, Xuzhou bituminous coal was burnt in a 6 kWth fluidized bed at 800 and 850°C in four atmospheres: air, 21%O

2

/79%CO

2

, 30%O

2

/70%CO

2

, 40%O

2

/60%CO

2

analysed with an online flue gas analyzer. Ontario Hydro method (OHM) was employed to measure mercury speciation in flue gas. The result indicated that more elemental mercury and oxidized mercury are released when burned in O

2

/CO

2

atmosphere than in air at 800°C, while the situation is just opposite, when coal was burnt at 850°C, less Hg

0

and Hg

2+

in O

2

/CO

2

atmosphere than in air. The concentration of Hg

0

rises as temperature increases both in the conditions of the air combustion and oxy-coal combustion, but the concentration of Hg

2+

increases with the increase of temperature only in the condition of air combustion and decreases in the oxy-coal combustion. With the increase of the oxygen concentration which is in the range of 21–40%, the concentrations of Hg

0

and Hg

2+

decrease first and then increase. When excess air coefficient increases, the oxygen content is higher and the vaporization rate of Hg

0

and Hg

2+

decrease.

Hui Wang, Yufeng Duan, Yongqiu Mao

Study on the Associated Removal of Pollutants from Coal-Firing Flue Gas Using Biomass Activated Carbon Pellets

A pilot-scale multi-layer system was developed for the adsorption of SO

2

/NO

x

/Hg from flue gas (real flue gases of an heating boiler house) at various operating conditions, including operating temperature and activated carbon materials. Excellent SO

2

/NO

x

/Hg removal efficiency was achieved with the multi- layer design with carbons pellets. The SO

2

removal efficiency achieved with the first layer adsorption bed clearly decreased as the operating temperature was increased due to the decrease of physisorption performance. The NO

x

removal efficiency measured at the second layer adsorption bed was very higher when the particle carbon impregnated with NH

3

. The higher amounts of Hg absorbed by cotton-seed-skin activated carbon (CSAC) were mainly contributed by chlorinated congeners content. The simultaneously removal of SO

2

/NO

x

/Hg was optimization characterized with different carbon layer functions. Overall, The alkali function group and chloride content in CSAC impelled not only the outstanding physisorption but also better chemisorptions. The system for simultaneously removal of multi-pollutant-gas with biomass activated carbon pellets in multi-layer reactor was achieved and the removal results indicated was strongly depended on the activated carbon material and operating temperature.

Cuiping Wang, Wanli Yuan, Haiying Qi

Adsorptive Removal of SO2 from Coal Burning by Bamboo Charcoal

Bamboo charcoal (BC) is an environmentally friendly, low-cost and renewable bioresource with porous structure. The adsorption property of bamboo charcoal for sulfur dioxide was investigated through a parametric study conducted with a bench-scale bed and mechanism study by BET, XPS, and temperature pro-grammed desorption (TPD). The varying parameters investigated include particle size of BC, moisture, oxygen, nitric oxide. The experimental data suggest that BC has a good adsorption potential for SO

2

, which removal efficiency is greatly dependent upon the operation conditions. This study provides a good reference for BC to be used for SO

2

removal in the actual flue gas over a wide range of conditions and further provided the preliminary experimental studies and theoretical discussion for bamboo charcoal to be used in multiple pollutants removing.

Zengqiang Tan, Jianrong Qiu, Jun Xiang, Hancai Zeng

Self-Supporting Power Plant – Capturing Evaporated Water and Save Energy a New Source of Water

One of the major challenges of this century is the provision of water for a growing population and industry. The shortage in water resources in arid areas requires the availability of more efficient and cheaper water production processes. In some arid regions water is even more important than electricity. A large source of water is found in the form of evaporated water emitted from different industrial processes. If for example 20% of the evaporated water from the flue gas stream of a coal fired power plant would be captured, the plant would be self-supporting from a process water point of view. This is about 30m

3

of water per hour. The results of the proof of principle project (2001–2008) show that >40% recovery can be achieved. Also an overall energy efficiency improvement can be achieved for industrial plants that reheat their flue gases. Calculations show that this can be about 1% overall efficiency for a coal fired power plant utilizing flue gas reheating. With an installed capacity of more than 600GWe in China, this energy saving results in a very large economic and fuel (coal) impact. This energy efficiency will most likely be the driving force to implement the technology in both water rich and water poor regions. For the capture of evaporated water no chemicals are used, there is no waste water formed and corrosion attack in stacks is mitigated. These results have led to the set up of a large international project named CapWa which aims to produce a membrane modular system suitable for industrial applications within 2–3years. The produced demin water from this system should be competitive with existing demin water technologies. The starting point will be the water vapour selective composite membranes that are developed in the proof of principle project. The CapWa project started in 2010 and consists of 14 partners of which 9 from the EU, 3 from the African continent and 2 from the Middle East.

Ludwin Daal, Frank de Vos, Rob Heijboer, Bert Bekker, Xiu Xiu Gao

Pyrolysis Properties of Potential Biomass Fuels in Southwestern China

The pyrolysis behavior of two biomass fuels (

E. adenophorum

and tobacco stem) and their production were analyzed in this paper using Thermo gravimetric analyzer (TGA) combined with a Fourier transform infrared spectrometer (FTIR). The gaseous phase components derived from the samples decomposing were qualitatively evaluated, and a correlation between the yield of acetic acid and carbon dioxide with heating rate was observed. The global pyrolysis kinetic was determined by DAE method where Miura method was used for obtaining

$$ f(E) $$

, and a fixed pre-exponential factor of 2.2e13 was used to fit DTG curves. CO

2

yield was found increased with the accretion of heating rate, while the other gaseous phase production and acetic acid were decreased simultaneously. The maximum of

$$ f(E) $$

was found around 170–180 kJ/mol.

Ling Qin, Qinghai Li, Aihong Meng, Yanguo Zhang

Experimental Study and Mechanism Analysis of Modified Limestone by Red Mud for Improving Desulfurization

Red mud is a type of solid waste generated during alumina production from bauxite, and how to dispose and utilize red mud in a large scale is yet a question with no satisfied answer. This paper attempts to use red mud as a kind of additive to modify the limestone. The enhancement of the sulfation reaction of limestone by red mud (two kinds of Bayer process red mud and one kind of sintering process red mud) are studied by a tube furnace reactor. The calcination and sulfation process and kinetics are investigated in a thermogravimetric (TG) analyzer. The results show that red mud can effectively improve the desulfurization performance of limestone in the whole temperature range (1,073–1,373K). Sulfur capacity of limestone (means quality of SO

2

which can be retained by 100mg of limestone) can be increased by 25.73, 7.17 and 15.31% while the utilization of calcium can be increased from 39.68 to 64.13%, 60.61 and 61.16% after modified by three kinds of red mud under calcium/metallic element (metallic element described here means all metallic elements which can play a catalytic effect on the sulfation process, including the Na, K, Fe, Ti) ratio being 15, at the temperature of 1,173K. The structure of limestone modified by red mud is interlaced and tridimensional which is conducive to the sulfation reaction. The phase composition analysis measured by XRD of modified limestone sulfated at high temperature shows that there are correspondingly more sulphates for silicate and aluminate complexes of calcium existing in the products. Temperature, calcium/metallic element ratio and particle diameter are important factors as for the sulfation reaction. The optimum results can be obtained as calcium/metallic element ratio being 15. Calcination characteristic of limestone modified by red mud shows a migration to lower temperature direction. The enhancement of sulfation by doping red mud is more pronounced once the product layer has been formed and consequently the promoting effect of red mud becomes greater once the sulfation reaction becomes diffusion controlled. This study indicates that red mud from alumina plant is a favorable additive for improving the desulfurization performance of limestone, and the effect of red mud on limestone’s desulfurization activity is due to superposition of improvement in solid-state ionic diffusion and surface chemical reaction.

Hongtao Liu, Kuihua Han, Shengli Niu, Chunmei Lu, Mengqi Liu, Hui Li

Simulation Analysis of Biomass Gasification in an Autothermal Gasifier Using Aspen Plus

Based on simulation, biomass gasification in an autothermal gasifier is analyzed, the effects of the equivalence ratio (ER), reactor temperature and gasification pressure on the composition and the higher heating values (HHV) of the product gas are also covered. The results indicate that the temperature in the gasifier increases when the ER increases, while the HHV of the product gas decreases. In an autothermal gasifier, the temperature which is controlled by varying ER, has the same influence on the composition and HHV of the product gas as the ER does. Higher gasification pressure slightly increases the temperature in the gasifier and the HHV of the product gas.

Zhongbin Fu, Yaning Zhang, Hui Liu, Bo Zhang, Bingxi Li

Emission and Properties of NOx Generated During Coal Grate-Fired in O2/N2/CO2

With the improvement of environmental protection requirements, the problems of NO

x

emission from industrial boiler become more and more notable. Flue gas recirculation is a low-NO

x

combustion technology. It draws out a part of the flue gas from rear flue and forces it into boiler. So the flue gas can serve the combustion or flow field integration. The drawn flue gas can be forced into the boiler directly, or mixed with the primary air or secondary air. To explore a real effective method of low NO

x

combustion, the article discusses the influence of flue gas recirculation on the formation of NO

x

in the process of coal grate-fired, in the way of using the unit-boiler, measuring the temperature of coal surface and composition and other important influential parameters. Experimental studies show that under the condition of grate-fired, taking Flue gas recirculation in main combustion zone, coke combustion zone and burn-out zone could notably diminish the amount of NO. And with the promotion of flue gas recirculation rate, the effect can be more noticeable.

Li Xu, Jian-min Gao, Lai-fu Zhao, Guang-bo Zhao, Shaohua Wu

Study on the Influence of CaO on NH3 + NO + O2 Reaction System in Pre-calciner

This paper studied the influence of CaO on NH

3

+NO+O

2

reaction system in pre-calciner. Experiments were carried out in a fixed bed reactor. Influence of CaO on NH

3

+NO+O

2

reaction, NH

3

oxidation, NH

3

decomposition and NO reduction by NH

3

at O

2

free condition were studied. NH

3

conversion rates and product selectivities were obtained for each reaction condition. It was proved that the influence of CaO on SNCR performance changed with temperature. CaO promoted SNCR performance at 650°C and changed to inhibit SNCR performance when temperature increased above 700°C. CaO influenced the reaction of NH

3

+NO+O

2

mainly by catalyzing NH

3

oxidation. NH

3

conversion rate and NO selectivity decreased when NH

3

concentration increased. Addition of NO into NH

3

heterogeneous oxidation had little effect on NH

3

conversion rate but decreased NO selectivity. A reaction mechanism for NH

3

NO+O

2

reaction on CaO surface was proposed. Heterogeneous reaction model of NH

3

+NO+O

2

on CaO surface was established based on the proposed reaction mechanism. Numerical results showed that the reaction model in this paper could predict NH

3

oxidation and NH

3

+NO+O

2

reaction on CaO surface very well.

J. S. Tang, Q. Song, S. L. Fu, X. Y. Wu, Q. Yao

Experimental Study on the Desulfurization Performance of Magnesium Slag

An experimental study has been performed on the desulfurization performance of the original magnesium slag (from the process of magnesium production). CaO content is about 50% in the slag, but its conversion rate is below to 30% as desulfurizer directly in the experimental conditions. To enhance the performance of the slag the hydration treatment process is tried. In the hydration process, the slag, additives and water are mixed proportionally in slurry, then dehydrated and dried. By comparing different hydration parameters, the optimal hydration condition is found. The slag performance for desulfurization under different conditions, such as slag types, hydration time, additives and drying temperature, is investigated by TGA. The results show that a much higher calcium conversion rate (about 40%) of the slag is obtained after the hydration process.

By means of XRD, Sorptomtic Instrument and SEM, the related parameters of the original slag and the hydration treated slag are analyzed. It is found that the composition, appearance and surface area changed obviously. The principle is basically studied that the hydration may enhance the desulfurization performance of the slag.

Baoguo Fan, Yan Jin, Xianrong Zheng, Xiaolei Qiao, Xutao Wang

The Emission Characteristic of PAHs During Coal and Sewage Sludge Co-combustion in a Drop Tube Furnace

The emission characteristic of Polycyclic Aromatic Hydrocarbons (PAHs) during coal and sewage sludge co-combustion was performed in a laboratory-scale drop tube furnace. The experimental results demonstrated that the mass percentage of sewage sludge had an important impact on PAHs emission during coal and sewage sludge co-combustion. In generally, the two-ring and five-ring PAHs concentrations decrease as the mass percentage of sewage sludge increase from 0 to 100%. Moreover, it was also found that PAHs from sewage sludge mono-combustion was dominated by the three-ring and four-ring PAHs. As for the coal mono-combustion, the four-ring and five-ring PAHs was the principal components. Meanwhile, the five-rings PAHs was the main contribution for the toxic equivalent (TEQ) concentration during coal and sewage sludge co-combustion. The experiment results also indicated that coal and sewage sludge co-combustion was beneficial to suppress the PAHs TEQ concentration.

Wangsheng Chen, Linbo Qin, Jun Han, Hong Yao

Modeling of Mercury Speciation and Capture in Coal-Fired Flue Gas

A 3D computational fluid dynamics (CFD) modeling tool was developed to model the mercury speciation and capture processes in coal-fired flue gas, including gaseous mercury oxidation and adsorption of mercury by the particulate matter. This CFD modeling tool was then applied to predicting enhanced mercury oxidation and capture by HBr injection in a slipstream reactor. The reaction rate constants of the mercury oxidation by HBr are extracted from the slipstream reactor testing data from the ICSET of Western Kentucky University. The modeling results show good agreement with the testing data and reasonable trends under different conditions. This CFD modeling tool can be either used to design a new mercury control system with higher efficiency and lower operating cost or to improve the performance of an existing system.

Heyang Wang, Zhanhua Ma, Pisi Lu, Yan Cao, Wei-Ping Pan

Catalytic Mechanism of NaY Zeolite Supported FeSO4 Catalyst for Selective Catalytic Reduction of NOx

The experimental results suggested that FeSO

4

-NaY and FeSO

4

-ZSM-5 prepared by impregnation method performed well in NO

x

removal. The NO

x

removal rates of the prepared catalyst were 20–35% higher than those of pure FeSO

4

, The effective temperature window was largely expanded with the best performance temperature shifted from 440 to 340°C. SO

2

and H

2

O in flue gas had no obvious effect on catalyst performance. Mössbauer spectrometry, XPS and in-situ infrared spectra analysis had been employed to investigate the catalytic mechanism of catalysts. It had been found that FeSO

4

, Fe(OH)SO

4

and Fe

2

O(SO

4

) were the major components existing in the prepared catalyst, with their portions related to carrier type and preparing condition. FeSO

4

combined tighter with carriers after de-NO

x

reaction. Fe

2

O

3

and the chemical bond between Fe and Al had been found. Fe(OH)SO

4

was better in terms of NO

x

removal than that of Fe

2

O(SO

4

). NH

3

absorbed on FeSO

4

-NaY catalyst generated the spectra of NH

4

+

and NH

3

, suggesting the Eley-Rideal mechanism. FeSO

4

-ZSM-5 absorbed both NH

3

and NO and the carrier (ZSM-5) itself demonstrated some catalytic effect, indicating a different reaction mechanism.

$$ {\text{SO}}_4^{{2 - }} $$

from FeSO

4

and hydroxyl from carrier jointly enhanced the adsorption of reaction gas. Fe provided the active sites for the reaction between NH

3

and NO.

Wen Ren, Bo Zhao, Yuqun Zhuo, Changhe Chen

Fluidized Bed Combustion

Frontmatter

Research on Coal Pyrolysis and Combustion Poly-generation System

A new poly-generation system combined coal combustion and pyrolysis has been developed for clean and high efficient utilization of coal. Coal is first pyrolyzed in a fluidized bed gasifier and produced gas is then purified and used for MeOH or DME production. Tar is collected during purification and can be processed to extract monocyclic aromatic hydrocarbons, polycyclic aromatic hydrocarbons and to make liquid fuels by hydrorefining. Semi-coke from the gasifier is burned in a CFB boiler for heat or power generation. A 12MW CFB gas, tar, heat and power poly-generation system was erected by Zhejiang University in cooperation with the Huainan Mining Industry (Group) Co., Ltd. in 2007. The experimental study focused on the two fluidized bed operation and characterization of gas, tar and char yields and compositions. The results showed that the system could operate stable, and produce about 0.12Nm

3

/kg gas with 22MJ/Nm

3

heating value and about 10wt.% tar when pyrolysis temperature between 500 and 600°C. The produced gases were mainly H

2

, CH

4

, N

2

, CO, CO

2

, C

2

H

4

, C

2

H

6

, C

3

H

6

and C

3

H

8

. Gas component concentrations were 24.18, 36.29, 7.96, 5.6, 7.84, 11.70 and 3.28%, respectively. The CFB boiler run steadily, whether the gasifier run or not, and produced 12MW power.

Mengxiang Fang, Jianmeng Cen, Chao Li, Qinhui Wang, Shurong Wang, Zhongyang Luo, Kefa Cen, Zhichuan Chao, Xiaoling Zhang, Xingdao Rao, Ganlin Dong, Jiping Wang, Yuan Wang

Numerical Simulation of the Gas-Solid Flow in a Square Circulating Fluidized Bed with Secondary Air Injection

The dynamic behavior of gas-solid flow in an experimental square circulating fluidized bed setup (0.25 m × 0.25 m × 6.07 m) is predicted with numerical simulation based on the theory of Euler-Euler gas-solid two-phase flow and the kinetic theory of granular flows. The simulation includes the operation cases with secondary injection and without air-staging. The pressure drop profile, local solids concentration and particle velocity was compared with experimental results. Both simulation and experimental results show that solids concentration increases significantly below the secondary air injection ports when air-staging is adopted. Furthermore, the flow asymmetry in the solid entrance region of the bed was investigated based on the particle concentration/velocity profile. The simulation results are in agreement with the experimental results qualitatively.

Zhengyang Wang, Shaozeng Sun, Ningbo Zhao, Shaohua Wu, Yufei Tan

Experimental on Fly Ash Recirculation with Bottom Feeding to Improve the Performance of a Circulating Fluidized Bed Boiler Co-burning Coal Sludge

With the aim of reducing carbon content in fly ash, fly ash recirculation with bottom feeding (FARBF) technology was applied to a 75 t/h Circulating Fluidized Bed (CFB) boiler burning mixture of coal and coal sludge. And industrial experiments were carried out to investigate the influence of FARBF technology on the combustion performance and pollutant emission characteristics of the CFB boiler. Results show that as the recirculation rate of fly ash increases, the CFB dense bed temperature decreases while the furnace outlet temperature increases, and the temperature distribution in the furnace becomes uniform. Compared with the conditions without fly ash recirculation, the combustion efficiency increases from 92 to 95% when the recirculation rate increases to 8 t/h, and the desulfurization efficiency also increases significantly. As the recirculation rate increases, the emissions of NO and CO decrease, but the particulate emission increases. The present study indicates that FARBF technology can improve the combustion performance and desulfurization efficiency for the CFB boilers burning coal sludge, and this can bring large economical and environmental benefits in China.

Lunbo Duan, Guiling Xu, Daoyin Liu, Xiaoping Chen, Changsui Zhao

Three-Dimensional Simulation and Experimental Investigation of a Novel Biomass Fast Pyrolysis Reactor

A novel autothermal reactor, named internally interconnected fluidized beds (IIFB), was developed for biomass fast pyrolysis to produce liquid fuels and chemicals. The IIFB reactor includes a pyrolysis bed and a combustion bed to conduct biomass pyrolysis and char burning, respectively. In this study, numerical simulation and experimental studies on volume fraction of particles, solid circulation rate and pressure distribution of the IIFB are reported. The stable flow photographed from the simulations coincides with that in the experiments at the same operating conditions. At the same height, the velocity of gas is twice as larger as the velocity of solid, which is favorable for catalytic reactions. The particles move up unsteadily in the draft tube, and yet they fall down with an almost constant velocity 0.07 m/s in the dipleg. The pressure in the fluidization region is higher than that in the spouted region at H=10mm and it shows an opposite pressure distribution. It is also observed that the experimental value of pressure is in well agreement with that obtained from simulations on the bottom, and yet it shows very different characteristics on the two outlets. Simulation results show that solid circulation rate at different cross-sections converged to 110kg/h which is in well agreement with experimental data of 104.5kg/h.

H. Y. Zhang, S. S. Shao, R. Xiao, Q. W. Pan, R. Chen, J. B. Zhang

Effect of Coal Blending on the Leaching Characteristics of Arsenic and Selenium in Fly Ash from Fluidized Bed Coal Combustion

The capture ability of fly ash to arsenic (As) and selenium (Se) was investigated through the combustion of two single bituminous coals A and B and their mixture (blending ratio of 1:1, wt/wt) in a lab-scale fluidized bed reactor. The leaching characteristics of As and Se in corresponding fly ash were also conducted according to Japanese Industrial Standard (JIS). Speciation of As and Se during fly ash leaching test were predicted from the perspective of thermodynamic equilibrium. The results indicate that, combustion of coal B, containing abundant calcium, possesses a higher capture ability of As and Se than that of coal A through possible chemical reaction between As/Se with CaO. Leaching behavior of As and Se from fly ash is strongly dependent on the pH of the leachate. Free calcium in fly ash generates an alkaline leachate during leaching test and subsequently reduces As and Se leaching, which cause the leaching ratio of As and Se in fly ash derived from the combustion of coal B was much lower, relative to that in coal A. Combustion of blending coal promotes the overall capture ability of the fly ash to As/Se and reduces their leaching from fly ash through the synergy of free CaO between this two kind of fly ash.

F. Jiao, L. Zhang, N. Yamada, A. Sato, Yoshihiko Ninomiya

Mass Balance Performance of A 300 MW CFB Boiler Burning Blend Fuel with Different Mixing Ratio

In order to predict the mass balance of a 300 MWe circulating fluidized bed (CFB) boiler under design process, the ash formation and attrition characteristic of the design fuel mixed with gangue, middling and slime were investigated with Tshinghua own process. In addition, the mass balance in this CFB boiler was simulated with 1D mass balance model, giving the ratio of the ashes, particle size distribution of circulating solid materials and solid circulating rat, Gs. By comparing the residence time distribution and the burn out time required for different size, the minimum bed pressure drop (BPD) or bed inventory in the furnace was determined for different mixing ratio among the three coals.

The results show that under each mixing ratio, the solid circulating flux and solid suspension density in the upper furnace can meet the requirement of heating transfer. However, the minimum BPD or bed inventory required to meet the burn out time of the coarse solids was different. For in the case with the ratio among gangue, middling and slime as 5:3:2, the lowest value is 12 kPa, which will cause serious erosion and more power consumption. Because the middling has lower ash content, higher reactivity and better ash formation, increasing the proportion of the middling (1:5:4) will decrease the BPD greatly to 5 kPa, not only meet the requirements of material balance and burn time for coarse solids easily, but also realize the energy saving operation.

Yang Chen, Junnan Chao, Hairui Yang, Junfu Lv, Hai Zhang, Qing Liu, Guangxi Yue

Measurement of Gas-Solid Flow Pattern in Rectangle Cross-Section in CFB by Electrical Capacitance Tomography

The mal-distribution of solid suspension density in the circulating fluidized bed (CFB) boiler with parallel cyclones is a hot research topic recently. The measurement of gas-solid flow characteristics, including the solid concentration distribution and the velocity profile, is the key to understand such phoneme. Comparing with other measuring methods, such as PIV, LDV, γ-ray attenuation technology, the electrical capacitance tomography (ECT) technology has the features of online monitoring, non-invasive, safe and economically. So far, in most of the studies with ECT measurements, the sensors have circular or square section, which cannot measure the gas flow directly in the rectangle section commonly used in CFB boiler furnace.

Based on the circular section sensor, by modifying the signal acquisition and image reconstruction, an ECT sensor with rectangular section and 8 electrodes was designed and manufactured, which was used to investigate the gas solid flow in a CFB riser with rectangle section (300 mm 80 mm). Meanwhile, the optical fiber probe was employed to measure the particle velocity and the thickness of boundary layer. The results prove that the ECT sensor with rectangle section can acquire the gas-solid flow characteristics.

Jingji Li, Wei Wang, Hairui Yang, Hai Zhang, Qing Liu

The Investigation of the Coal Ignition Temperature in Oxygen-Enriched Atmosphere by TGA

The oxygen-enriched Circulating fluidized bed (CFB) combustion technology is a new method to reduce CO

2

emissions. The coal ignition temperature, T

i

, in an oxygen-enriched CFB boiler is an important parameter for designing the startup burner and for choosing the operating strategy during the startup process. Comparing with the complicated operation in real oxygen-enriched CFB boiler or in a laboratory scale fluidized bed (FBR), thermo gravimetric analyzer is a more simple and convenient method to determine the T

i

, because the TGA results would be related in some way with the field results. Thermo gravimetric analyses of seven different types of coal were operated in air and oxygen-enriched atmosphere (O

2

40%, CO

2

as balance gas), with three different heating rate (10, 20, and 30 K/min). It was found that the T

i

, determined by the DTGA, decreased with the O

2

concentration increasing. The coal with the higher volatile content had a lower ignition temperature. The influence of the heating rate on the T

i

was relatively significant. With 40% O

2

, the coal ignition temperatures firstly increased and then decreased with the increasing heating rate. Compared with the tests results obtained in a laboratory scale FB, the results obtained by these two methods have the same tendencies, and there must be a way to make the TGA results relative to the real coal ignition temperatures in the oxygen-enriched CFB boilers.

Junnan Chao, Hairui Yang, Yang Chen, Junfu Luv, Hai Zhang, Qing Liu

Application of Digital Image Processing Methods on the Cluster Structure at the Wall of a Circulating Fluidized Bed

This paper describes experiments to investigate the cluster structure of gas-particle flow at the wall region of a circulating fluidized bed (CFB). The setup is in a cold scale-model circulating fluidized bed with a riser that has a 0.30 m 0.28 m cross-section and is 2.9 m tall. A video camera was utilized to visualize the cluster structure through a transparent Plexiglas wall. An image processing system was used to analyze images, which were obtained under different superficial gas velocities and solid circulating rates. The results show that distinctly different cluster structures exist in the different operating conditions, which the number, shape and size of the clusters are affected by main air flow.

Li Hai-guang, Zhao Zeng-wu, Li Bao-wei, Wu Wen-fei

Energy and Exergy Evaluation of Product Gas from Coal/Biomass Blend Gasification in a Dual Circulating Fluidized Bed Reactor

Product gas from coal/biomass blend gasification in a dual circulating fluidized bed reactor is studied from energy and exergy aspects. The energy and exergy values of product gases are analyzed, the effects of reactor temperature, steam/fuel ratio and biomass ratio are reported. The energy and exergy values of product gases from coal gasification and biomass gasification increase monotonously when the reactor temperature increases, whereas vary slightly and irregularly when the steam/fuel ratio increases. As the biomass ratio increases from 0 to 1, the energy and exergy values increase first and then decline. On the whole, the exergy values are lower than the corresponding energy values, and keep pace with the energy values. When the reactor temperature and steam/fuel ratio are the same, product gases from biomass gasification show higher energy and exergy values than those from coal gasification.

Yaning Zhang, Zhongbin Fu, Bingxi Li, Hongtao Li, Bo Zhang

Fundamental Study of the Pulverized Coal Char Combustion in Oxyfuel Mode with Drop Tube Furnace

The combustion characteristics of coal char particles in either O

2

/N

2

or O

2

/CO

2

conditions were experimentally investigated. Especially, the char burnout, the char particle temperature and the shrinkage of the char particles were discussed. A Drop Tube Furnace (DTF: whose wall temperature was set at 873, 923 and 973 K) was used as the experimental apparatus. The experimental results revealed that, in equivalent oxygen concentration, the char burnout and the char particle temperature were higher in O

2

/N

2

conditions than those in O

2

/CO

2

conditions. The shrinkage of the char particle did not show the large difference in either O

2

/N

2

or O

2

/CO

2

conditions. Up to 15% of char burnout, the char particle diameters were reduced gradually. Up to 80% of char burnout, the char particle diameters were not changed. This is supposed that the chemical reaction is mainly occurred not on the external surface but on the internal surface of the char particle. Over 80% of char burnout, sudden shrinkage could be seen. Finally, an empirical equation for the prediction of the char particle shrinkage was introduced. Further investigation is required in high operating temperature, where CO

2

gasification may have a large influence on the char burnout.

Takamasa Ito, Makoto Takafuji, Toshiyuki Suda, Toshiro Fujimori

Utilization of Desulfurization Gypsum to Producing SO2 and Cao in Multi-Stage Fluidized Bed

With emission control becomes more and more stringent, flue gas desulphurization (FGD) is commonly employed for desulfurization. However, the product of FGD, gypsum, causes the unexpected environmental problems. How to utilize the byproduct of FGD effectively and economically is a challenging task.

This paper proposed the new technical process to produce SO

2

and CaO by reducing the gypsum in multi-stage fluidized bed reactor with different atmosphere. In addition, some preliminary experiments were carried out in PTGA. The results show that CO concentration has little effect on the initial decomposing temperature, but affect the decomposing rate of phosphogypsum obviously. The decomposing product composed of CaS and CaO simultaneously. The ratio of the two products was determined by CO concentration. Lower CO content benefits to produce more CO product and more SO

2

. The decomposition reaction of phosphogypsum in reducing atmosphere is parallel competition reaction. Therefore, it is necessary to eliminate the effect of CaS and other byproduct efficiently by the new technology, which utilize multi-atmosphere in multistage fluidized bed reactors.

Zhu Miao, Tao Wang, Hairui Yang, Hai Zhang, Xuyi Zhang

Study and Design of Platen Superheater of 300 MW CFB Boiler

In order to avoid overtemperature tube explosion of the platen superheater, the measurements of metal temperatures and the heat transfer coefficients of the platen superheater in a commercial 300 MW Circulating Fluidized Bed (CFB) boiler are conducted in this work. The measured data is analyzed and the theoretical calculation is made. On the basis, the reasonable steam flow path and the value range of heat transfer coefficient of the middle temperature platen superheater are applied for design. Furthermore, based on operation experience from several 300 MW CFB boilers, a design principle of the mass velocity and the arrangement of the platen superheater in the furnace is given.

Zhang Man, Lv Qinggang, Jiang Xiaoguo, Sun Yunkai

Research and Design of 330 MW Circulating Fluidized Bed Boiler

Based on research and manufacture of 210MW circulating fluidized bed (CFB) boiler, the key technologies of large CFB boiler have been Research, the plan design of 330MW CFB boiler have been performed, construction design of key components and scaling up characteristics were analysed, The 330MW CFB boiler designed demonstration project has been put into commercial operation, It is the largest capacity CFB boiler operated in china now, Operation of 330MW CFB boiler was stable and good performance has been proved.

Sun Xianbin, Jiang Minhua, Yu Long, Zhang Yanjun, Shi Zhenghai, Wang Fengjun, Zhang Man, Huang Zhong

3D Full-Loop Simulation of an Industrial-Scale Circulating Fluidized Boiler

In this study, 3D full-loop simulations of a CFB boiler are carried out. FLUENT®6.3 is used as the solver, where an Eulerian multiphase model with EMMS-based drag model is employed. The wide particle size distribution are considered and divided into several groups to better represent the polydisperse behavior of ash particles. The simulation shows that, compared to the conventional drag model, EMMS-based model predicts more reasonable pressure drop of furnace and larger slip velocity at the lower elevations of the furnace. Further work is under way to improve the full-loop simulation.

Bona Lu, Nan Zhang, Wei Wang, Jinghai Li

Experimental Investigation on Secondary Air Jet Penetration Depth in the Dense Zone of a Circulating Fluidized Bed

The secondary air jet penetration depth of dense zone is measured in a 0.25m×0.25m×6.07m circulating fluidized bed. The influence of gas velocities (U

0

), nozzle diameters, jet velocities, nozzle angel and the solids inventory is studied. A modified empirical correlation for calculating the secondary air jet penetration depth in the dense zone is developed. SA jet penetration depth increases with the increase of jet velocity. With the same flow rate, jet penetration depth becomes smaller as the diameter increases. Horizontal jet has the maximum jet penetration depth. The increasing of gas velocities, nozzle angel and solids inventory will reduce the jet penetration depth.

Shaozeng Sun, Ningbo Zhao, Zhengyang Wang, Mingkun Du

DEM-Based Models for Solids Exchange in a Pant Leg Fluidized Bed

Understanding the behaviors of solids exchange between two half beds in a pant leg fluidized bed is crucial in proper design, scale up and operation. DEM models based on Eulerian-Lagrange have shown promise in gaining this understanding. The power spectrum density (PSD) analysis was used to get the dominant frequency of the differential pressure fluctuations in experiments and the difference of particle number in simulations. The experiments were carried out in the pant leg fluidized bed with dimensions of 0.24 m width, 0.02 m depth, 0.8 m height and 0.16 m pant leg height. The black glass particles with diameters of 0.9–1 mm were adopted as bed materials. The effects of fluidization velocity and static bed height on the solids exchange were studied. The amplitudes of fluctuations both in experiments and in simulations show that amount of particles for exchange between two half beds increases with increasing fluidization velocity. The PSD analysis show that two dominant frequencies are gotten at about 0.5–1 Hz and 2.6–3.2 Hz for experiments and 1 and 3 Hz for simulations at higher fluidization velocity. The first and second dominant frequencies correspond to the behavior of solids exchange in the form of clusters or strands and to both bubbling action and solids exchange in the form of single particles respectively. With increasing fluidization velocity, the effect of variations of bed inventory on pressures increases for the simulation cases, while the bubbling action on pressure fluctuations is weakened, and the energy of two dominant frequencies caused by solids exchange only in the form of both clusters and single particles increased. The higher static bed height contributed more particles to exchanging between two half beds in the form of clusters periodically.

Chunzhen Yang, Yufeng Duan, Haitao Hu

Experimental Investigation on a 0.35 MWth Coal-Fired Horizontal Circulating Fluidized Bed Boiler

The capacities of industrial coal-fired boilers are normally less than 20–30 MWe. And these coal-fired boilers of low capacity are facing the severe situation of low efficiency and heavy environmental pollution. Hence, an innovative horizontal circulating fluidized bed (HCFB) boiler was developed to enhance heat efficiency and reduce pollutant emission of industrial boilers in China. The chamber in the HCFB boiler consists of primary combustion chamber, secondary combustion chamber and burnout chamber, which were combined horizontally side by side. To verify the conception of horizontal fluidized circulation and to obtain the characteristic data, a 0.35 MWth coal-combustion HCFB boiler was designed and installed to perform some experiments of combustion and mass circulation. In the boiler there were two mass circulating paths, one is inner circulating through the inertia separator and another was external circulating through the cyclone separator. The connection bottom of the secondary chamber and the burnout chamber was designed as an inertia separator, in which separated and collected solid materials were returned to the primary combustion. In fact the secondary separator was a small cyclone separator connecting to the exit of the burnout chamber. Heat efficiency and separating efficiency of the experimental boiler were measured and analyzed. Furthermore, mass and temperature distribution along the chambers height were also investigated. The results showed that the heat efficiency of the bare boiler was 82%. The mass balance based on ash content was measured and analyzed. Separating efficiency of the inertia separator and cyclone separator was 60 and 99.9%, respectively. It showed that the two stage material separation and circulation enhanced coal combustion in the HCFB boiler and help to minimize the height of the furnace.

Meng Aihong, Li Qinghai, Zhang Yanguo, Wang Zhaojun, Dang Wenda

Raman Spectroscopy and X-ray Diffraction Analysis of the Structural Characteristics of Fluidized Bed Gasification Fly Ash

Previous experiments using thermo-gravimetric analysis (TGA) concluded a high carbon fly ash obtained from a circulating fluidized bed (CFB) gasifier by firing an anthracite coal to be less reactive compared to other high ash content chars that were prepared under laboratory conditions in a drop tube furnace (DTF) from a parent bituminous coal. This fly ash had internal surface (BET) area and pore volume of an order of magnitude larger than the laboratory prepared chars and so a further investigation was carried out by determining the influence of the fly ash residence time (10–20 s) in the CFB on its structural ordering.

The structural analysis was carried out by using Raman spectroscopy and X-ray diffraction (XRD). Raman spectroscopy with a 457.9 nm laser, was used to compare the structural ordering of the fly ash carbon with those of its parent (anthracite) coal; a char prepared from the same parent coal at the same heat treatment temperature as the fly ash but under laboratory conditions; and the other chars prepared from a bituminous parent coal (under laboratory conditions) whose reactivities were found to be higher than the fly ash. It was concluded that the long residence times enhanced the decomposition of the anthracite coal, consumption of the amorphous carbon and the ordering of aromatic units and the crystalline structure as gasification progressed.

The structural behavior of fly ash was also investigated after different conversions in DTF through reactions with oxygen at 5 and 20% concentration at a temperature of 1,300°C. At low residence times, the fly ash became less ordered due to further decomposition and release of loose organic matrix and after longer residence time the fly ash then became more ordered due to aromatic ring growth.

XRD experiments were used to validate the structural analysis result from Raman spectroscopy. The results concluded fly ash and a laboratory char prepared at high temperature to be the most ordered. There was also the linear relationship between the volatile content of the chars including the fly ash when compared with their structural parameters.

L. Kelebopile, R. Sun, X. Zhang, P. Xu

Industrial Applications and Coal Use

Frontmatter

Experimental Investigation on Improving the Removal Effect of WFGD System on Fine Particles by Heterogeneous Condensation

Heterogeneous condensation of water vapor as a preconditioning technique for the removal of fine particles from flue gas was investigated experimentally in a wet flue gas desulfurization (WFGD) system. A supersaturated vapor phase, necessary for condensational growth of fine particles, was achieved in the SO

2

absorption zone and at the top of the wet FGD scrubber by adding steam in the gas inlet and above the scrubbing liquid inlet of the scrubber, respectively. The condensational grown droplets were then removed by the scrubbing liquid and a high-efficiency demister. The results show that the effectiveness of the WFGD system for removal of fine particles is related to the SO

2

absorbent and the types of scrubber employed. Despite a little better effectiveness for the removal of fine particles in the rotating-stream-tray scrubber at the same liquid-to-gas ratio, The similar trends are obtained between the spray scrubber and rotating-stream-tray scrubber. Due to the formation of aerosol particles in the limestone and ammonia-based FGD processes, the fine particle removal efficiencies are lower than those for Na

2

CO

3

and water. The performance of the WFGD system for removal of fine particles can be significantly improved for both steam addition cases, for which the removal efficiency increases with increasing amount of added steam. A high liquid to gas ratio is beneficial for efficient removal of fine particles by heterogeneous condensation of water vapor.

Jingjing Bao, Linjun Yang, Jinpei Yan, Guilong Xiong, Xianglin Shen

Performance Simulations for Co-gasification of Coal and Methane

In the process under development, coal suspended in mixtures of CH

4

, H

2

, and steam is rapidly heated to temperatures above 1,400°C under 5–7 MPa for at least 1 s. The coal first decomposes into volatiles and char while CH

4

is converted into CO/H

2

mixtures. Then the char is converted into CO/H

2

mixtures via steam gasification on longer time scales, and into CH

4

via hydrogasification. Throughout all stages, homogeneous chemistry reforms all intermediate fuel components into the syngas feedstock for methanol synthesis. Fully validated reaction mechanisms for each chemical process were used to quantitatively interpret a co-gasification test series in SRI’s lab-scale gasification facility. Homogeneous reforming chemistry generates equilibrium gas compositions at 1,500°C in the available transit time of 1.4 s, but not at any of the lower temperatures. Methane conversion in the gas phase increases for progressively hotter temperatures, in accord with the data. But the strong predicted dependence on steam concentration was not evident in the measured CH

4

conversions, even when steam concentration was the subject test variable. Char hydrogasification adds CH

4

to the product gas stream, but this process probably converts no more than 15–20% of the char in the lab-scale tests and the bulk of the char is converted by steam gasification. The correlation coefficient between predicted and measured char conversions exceeded 0.8 and the std. dev. was 3.4%, which is comparable to the measurement uncertainties. The evaluation of the predicted CH

4

conversions gave a std. dev. greater than 20%. Simulations of commercial conditions with realistic suspension loadings and no diluents in the feed gave slightly lower conversions of both CH

4

and coal, because hydrogasification accounts for more of the char conversion, and occurs at rates slower than for steam gasification.

Stephen Niksa, J.-P. Lim, D. del Rio Diaz Jara, D. Eckstrom, D. Steele, R. Malhotra, R. B. Wilson

Experimental Study on Low Temperature Pyrolysis of Forestry Residues

Biomass low temperature pyrolysis is a thermo-chemical treatment method that is earmarked by an pyrolysis temperature ranging from 200 to 300°C (under anoxic, heating rates ≤ 50°C/min). This paper investigates the low temperature pyrolysis properties of the raw biomass, including mulberry branch and wood chips, which collected from Jiangsu, China was carried out in a self-designed continuous pyrolysis facility. The experiments were carried out at pyrolysis temperatures of 250 ~ 300°C and residence time of 10 ~ 30 min. The results show that the mass yield of mulberry branch charcoal decreased with the increasing of the pyrolysis temperature and residence time, and the pyrolysis temperature has a significant effect on low temperature pyrolysis than the residence time. The fixed carbon and elemental carbon content of the biomass charcoals increased and volatile matters, hydrogen and oxygen contents of biomass charcoals decreased with the increasing of the pyrolysis temperature and residence time, which results in the decreasing of H/C and O/C ratios. The energy density continues to increase with increase in the pyrolysis temperature and residence time. After the pre-treatment, the biomass charcoal compared with raw biomass gained a high energy density and the improvement of hydrophobicity (OH groups are responsible for hydrogen bonding with water). SEM micrographs of mulberry branch and mulberry branch charcoals show that the porosity and the degree of thermal degradation increase with increasing of the pyrolysis temperature. After based on a systematic consideration, the operating condition of 275°C and 10 min was recommended.

Qinchao Wang, Tong Shu, Fei Lu, Ping Lu

Mathematical Modeling and Optimization of Parameters of Coal-Fired Combined Cycle Unit with Gas-Turbine Cycle Working Medium Heated in Periodic Regenerative Heat Exchangers

Enhancement of efficiency of energy plants on solid fuel is one of the crucial problems in development of energy technologies. Solution to this problem is sought in three main directions:

1.

steam turbine units with ultra-supercritical steam parameters;

2.

combined cycle units with intra-cycle coal gasification;

3.

combined cycle units with coal combustion in pressurized fluidized bed and removal of ash from high-temperature combustion products in ceramic filters.

The increase in energy efficiency of steam turbine units with ultra-supercritical steam parameters is limited by the capabilities of metals available in the energy machine building to operate under high temperatures, and the imperfection of Rankine thermodynamic cycle. The maximum possible efficiency of these units is estimated at 50%.

The efficiency of combined cycle units with intra-cycle coal gasification may reach 52–54%. The main obstacle to the wide- scale use of these units is low reliability and unstable operation of gasifiers on steam-air blast, high price of coal gasifiers on steam-oxygen blast and high auxiliary power consumption.

Energy efficiency of direct-fired coal combustion under pressure is limited by working temperatures of the fluidized bed and ceramic filters that vary in the range of 800–950°C. The efficiency of combined cycle units with direct-fired coal combustion in fluidized bed makes up 40–42%.

Analysis of technologies for electricity production based on solid fuel shows that the optimal combination of reliability and energy and economic efficiency can be achieved through the use of gas-steam binary cycle in combination with coal combustion. However, the technology of coal combustion in the pressurized fluidized bed which is currently applied has considerable disadvantages that decrease greatly its competitiveness.

From our viewpoint a rather promising technology to be studied is the one based on the use of air as a gas-turbine working medium which is heated in cyclic regenerative ceramic heat exchangers by the coal powder combustion products. In this case the working medium can be heated to essentially higher temperatures than at coal combustion in the pressurized fluidized bed. Here only a small amount of ash contained in the coal combustion products settles in the ceramic heat exchanger and then penetrates into the heated air. This makes it possible to provide high air temperature before turbine (1,200–1,300°C) at an acceptable level of ash concentration at gas turbine inlet. The indicated cyclic ceramic heat exchangers have been thoroughly tested on the experimental models of closed-cycle MHD generators which proved them to be serviceable and reliable.

To substantiate the efficiency of this technology it is necessary to perform its optimization studies by using the mathematical model of combined cycle unit with coal combustion and gas- turbine cycle working medium (air) heated in regenerative heaters. The development of such a model and technical studies are the goal of the proposed report.

A. M. Kler, E. A. Tyurina, A. S. Mednikov, E. V. Staheeva

A Improved Fuzzy Analytic Hierarchy Process Application in Prevention High Temperature Corrosion

The mechanism of formation of high temperature corrosion in large scale utility boilers is complex and involves numerous interrelated influencing factors. The fuzzy analytic hierarchy process (FAHP) has been employed in this chapter to make quantitative computations of the factors that influence the formation of the corrosion. When constructing the fuzzy judgment matrix, an affecting degree table of influencing factors was worked out first. Then the score of a pair-wise comparison was computed from a proposed expression

r

ij

=

x

y

+ 0.5. This improved method was applied to the analysis of the high temperature corrosion problem of a 215 MW coal-fired utility boiler, combining with in-site test data. The weights of the influencing factors were determined quantitatively and the main influencing factors were found out. Based on the calculated results, various adjustments to the combustion processes were made and, as a result, high temperature corrosion on the water wall tubes has been found largely reduced on the schedule shutdown of the boiler half year later. Moreover, a real-time high temperature corrosion detection technique can be developed based on the method reported in this chapter.

Haiyu Liu, Houzhang Tan, Xiaohe Xiong, Linzhi Yao, Yanqing Niu, Lin Ma, Tongmo Xu

Prediction of Calorific Value of Coal Using Real Power Plant Data

With the depletion of coal in the world, coal quality fluctuates and deviates greatly from the designed coal in many large scale coal-fired power plants. This increases the coal consumption while reduces the boiler combustion efficiency and stability. Thus, it is very important to conduct real-time measurement to the quality of the coal for optimizing the operation. The calorific value analysis is a significant part of the coal quality analysis, and regular proximate analysis method can’t meet real-time control requirements. In this chapter, an artificial neural network (ANN) model using real plant data for prediction of net calorific value of coal in a China power plant is reported. A three-layer BP neural network has been adopted. The input parameters selection was optimized with a compromise between smaller number of parameters and higher level of accuracy through sensitivity analysis. The activation function selection was also discussed in details. The results indicate that when the pureline was selected as the activation function for hidden layer and logsig was selected as the activation function for output layer, the prediction is most accurate. The results have shown good potential for predicting the net calorific value of coal using the real time data. This information will enhance the performance of the combustion control system for power utilities.

Haiyu Liu, Houzhang Tan, Xiaohe Xiong, Linzhi Yao, Yanqing Niu, Yang Liu, Tongmo Xu

Measurement of CO2 Gasification Rate of Coal Char Under High Pressure and High Temperature Using a Mini Directly-Heated Reactor

A mini directly-heated reactor (mini-DHR) was constructed to measure the gasification rate handily under high CO

2

pressure of ~ 2 MPa in the presence of other gases, such as CO and H

2

, at

T

= ~ 1,200°C. The mini-DHR was made of U-shaped SUS or Pt tubing of 3 mm I.D. The reactor itself was used as a heating element. An electric current of 75–150 A and a few volts were introduced to the reactor to heat up the reactor up to 900–1,200°C. About 1 mg of char was placed in a platinum mesh basket of 1.0 mm I.D. and 10 mm high. The basket with the char sample was placed just above a thermocouple in the reactor. The conversion of char,

X

, was estimated by weighing the remaining char sample. The

X

vs.

t

relationships obtained under various conditions were analyzed to formulate a gasification rate equation in the presence of both CO

2

and CO for a char prepared from an Australian brown coal.

Kouichi Miura, Mitsunori Makino, Eiji Sasaoka, Syunsuke Imai, Ryuichi Ashida

Preliminary Experimental Studies of Waste Coal Gasification

Coal mining is one of Australia’s most important industries. It was estimated that coal washery rejects from black coal mining was approximately 1.82 billion tonnes from 1960 to 2009 in Australia, and is projected to produce another one billion tonnes by 2018 at the current production rate. To ensure sustainability of the Australian coal industry, we have explored a new potential pathway to create value from the coal waste through production of liquid fuels or power generation using produced syngas from waste coal gasification. Consequently, environmental and community impacts of the solid waste could be minimized. However, the development of an effective waste coal gasification process is a key to the new pathway. An Australian mine site with a large reserve of waste coal was selected for the study, where raw waste coal samples including coarse rejects and tailings were collected. After investigating the initial raw waste coal samples, float/sink testing was conducted to achieve a desired ash target for laboratory-scale steam gasification testing and performance evaluation. The preliminary gasification test results show that carbon conversions of waste coal gradually increase as the reaction proceeds, which indicates that waste coal can be gasified by a steam gasification process. However, the carbon conversion rates are relatively low, only reaching to 20–30%. Furthermore, the reactivity of waste coal samples with a variety of ash contents under N

2

/air atmosphere have been studied by a home-made thermogravimetric analysis (TGA) apparatus that can make the sample reach the reaction temperature instantly.

S. Su, Y. G. Jin, X. X. Yu, R. Worrall

Process Simulation and Optimization for Fry Drying of Low Rank Coal

We conducted fry drying process simulations of low rank coal and operation optimization. We set up the operating condition of evaporator so that the coal moisture content would come down from 35 to 10 wt.% during the drying process. Through process simulations, we calculated the heat duty supplied and power consumption under each operating condition. From the simulation results, we calculated operating costs on the basis of prices in Indonesia which is a coal producing place. Cases where thermal energy was reused through MVR showed an effect of reducing operating costs by around 50%. The operating conditions were optimized through operating cost analysis and the results indicated that the optimum operating conditions were evaporator pressure 500 kPa and temperature 168°C

D. H. Chun, S. D. Kim, Y. J. Rhim, N. S. Rho, H. K. Choi, J. H. Yoo, J. H. Lim, S. H. Lee

Effects of the Secondary Oxygen Injection on the Performance of a Staged-Entrained Flow Coal Gasifier

In a staged entrained flow coal-slurry gasifier, the secondary oxygen was injected into the gasifier in order to protect the refractory in the dome region, to improve the mixing process as well as gasification performance. Based on a proposed 3-D numerical model, simulations were conducted for the staged gasifier at different mass flow rates of the secondary oxidizer. The characteristics of the gasification flames were analyzed as well as the influence of the secondary flow on the flow field of the staged gasifier. As the mass flow rate of the secondary oxidizer decreases, the secondary gasification flame curves up according to the backflow region and wall temperature increases. When the mass flow rate of the secondary oxidizer is less than 10% of the total oxidizer mass flow rate, there is an obvious change of the turbulent mixing in the staged gasifier.

Cai Chunrong, WU Yuxin, Zhang Jiansheng, Yue Guangxi, LÜ Junfu, Zhang Hai

Effects of Reducing Conditions on the Properties of Molten Slag in an Entrained Bed Gasifier

The effect of gas composition on the properties of slag generated from high temperature gasification was studied. The proportion of crystalline phase in the slag was measured by X-ray diffraction (XRD) and the microstructure of the slag was quantitatively analyzed by CCSEM. Metal ions in acid-digested slag samples were analyzed by ICP-AES. The results indicate that, in a strongly reducing atmosphere such as 10/90 (volume %) mixtures of CO

2

/H

2

, the Fe content of bulk slag was reduced due to the precipitation of metallic iron in molten slag. The profile of the iron content of the slag was related to the dissolved oxygen transfer in molten slag. In addition, slag generated in mildly gas composition is more stable under than that of strongly atmosphere. Some heavy metals showed the same behavior as iron in the strongly reducing atmosphere were extracted by 1 M/HCl, which results in higher extraction rates for Fe, Zn, and As, Cr.

Y. Wei, H. Li, N. Yamada, A. Sato, Y. Ninomiya, K. Honma, T. Tanosaki, M. Kawaguchie, N. Tatarazakof

Development and Application of Gradient Heat Flux Measurement for Industrial Boiler Furnaces

Brand new heat flux sensors based on artificial heterogeneous structures are created. These sensors are thermo resistive up to 1,000 K and more; therefore, they are the diagnostic aid for furnace processes. The sensors were tested during full-scale experiments.

S. Z. Sapozhnikov, K. A. Grigoryev, V. Yu. Mitiakov, A. V. Mitiakov, Yu. A. Roundyguine, V. V. Osmanov

Calculating Analysis of Firing Different Composition Artificial Coal Liquid Fuels (ACLF) in the Cyclone Primary Furnace

This chapter describes the preparation technologies, results of computer simulation of combustion processes in a cyclone primary furnace during firing of artificial coal liquid fuels prepared from different coal grades and results of live testing. As a result the values of unburned carbon, NO

x

emissions and other concentrations in the outlet section primary furnace were estimated.

A. Tsepenok, Yu. Ovchinnikov, F. Serant

Forecast of Advanced Technology Adoption for Coal Fired Power Generation Towards the Year of 2050

Needs for electricity is growing rapidly in many countries and it is expected the increase of electricity by 2030 is almost double. Fossil fuels, renewables, nuclear energy will play leading parts in the future, but fossil power generation will continue to play a major role. Especially, coal will be used continuously due to its stable supply and lower price. However, global warming countermeasures should be considered for large amount of coal use. High efficient systems and Carbon Capture and Storage (CCS) will be most applicable solution for the problems.

USC, IGCC and A-USC have higher efficiencies, but costs are normally higher. So it is very important to evaluate the future trend of the plants, that is the cost, performance and the share of each plant. It is also essential to evaluate high efficient plants which will be constructed mainly and which system investment should be paid to. But no less important is to evaluate each system from the neutral position. So Japan Coal Energy Center (JCOAL) constructed its own program to expect the future trend of each plant. JCOAL made a basic concept and the programming was done by SRI International of the United States.

The considered systems of coal fired power generation are Supercritical Unit, Ultra Supercritical Unit, Advanced- Supercritical Unit, Integrated Gasification Combined Cycle (IGCC) and Integrated Gasification Fuel Cell (IGFC). In order to compare with the natural gas case, Natural Gas Combined Cycle (NGCC) is included. Evaluation will be done for both without and with CCS cases. This program covers by the year of 2050.

The results are trends of following items: capital cost, operational and maintenance cost, levelized cost of electricity, etc. We can also expect the future share of high efficient coal fired systems by 2050. Here the share will be decided by the levelized cost of electricity. The plant that has the lowest cost will get more share under the scenario of this program.

This chapter summarizes the program and the results of the evaluation.

Keiji Makino

Reduction of Ash Deposition in Pulverized Coal Fired Boilers

This study proposes reduction technology of ash deposition on the heat exchanger tube in pulverized coal fired (PCF) boilers. Thermal spraying technique is adopted to change the surface properties of tube to reduce the ash deposition. As a result, Ni alloy as a thermal spraying material played an effective role to reduce the deposition under both the ash deposition experiments and the actual coal combustion experiments. However, it is necessary to change ash types in order to evaluate that the thermal spraying technology is universally useful or not. If this technology will be applied to the commercialized PCF boilers, additionally, the effectiveness for the long-term will also be studied as well as the theoretical elucidation on the reduction of ash deposition must be discussed. In this study, therefore, four types of coal ash with different melting points were tested as samples for the ash deposition experiments. The long-term ash adhesion experiments were also carried out, using a precise tension tester at high temperature. As the theoretical approaches, the compositions of each ash particle depositing on the tube surface were analyzed by a computer-controlled scanning electron microscope (CCSEM) with electron dispersive spectroscopy (EDS) detector, thereby the interfacial reactions between the ash deposition layer and the heat exchanger tube were discussed. Those results obtained were also compared to the results obtained by the thermal equilibrium calculations.

I. Naruse, R. Yoshiie, Y. Ueki, M. Matsuura, H. Naganuma

Co-firing of Coal with Biomass and Waste in Full-Scale Suspension-Fired Boilers

The energy policy in Denmark has for many years focused on lowering the net CO

2

emission from heat and power production by replacing fossil fuels by renewable resources. This has been done by developing dedicated grate-fired boilers for biomass and waste fuels but also by developing coal-based suspension-fired boilers to accept still higher fractions of biomass or waste material as fuels. This last development has been challenging of many reasons, including pre-treatment of fuels, and solving potential emission and operational problems during the simultaneous development of supercritical steam cycles with steam temperatures close to 600°C, providing power efficiencies close to 50% (Hein KRG, Sustainable energy supply and environment protection – strategies, resources and technologies. In: Gupta R, Wall T, Hupa M, Wigley F, Tillman D, Frandsen FJ (eds) Proceedings of international conference on impact of fuel quality on power production and the environment, Banff Conference Centre, Banff, Alberta, Canada, 29 Sept–4 Oct, 2008).

For 25 years the CHEC (Combustion and Harmful Emission Control) Research Centre at DTU Chemical Engineering, has attained a leading role in research, supporting power producing industry, plant owners and boiler manufacturers to optimize design and operation and minimize cost and environmental impact using alternative fuels in suspension fired boilers. Our contribution has been made via a combination of full-scale measuring campaigns, pilot-scale studies, lab-scale measurements and modeling tools. The research conducted has addressed many issues important for co-firing, i.e. fuel processing, ash induced boiler deposit formation and corrosion, boiler chamber fuel conversion and emission formation, influence on flue gas cleaning equipment and the utilization of residual products.

This chapter provides an overview of research activities, aiming at increasing biomass shares during co-firing in suspension, conducted in close collaboration with the Danish power industry. The research has lead to an improved understanding of the alternative fuels interaction with coal in the boiler chamber. Further, the applied research has provided results with implications for operation of milling and burner equipment, appropriate fuel mixing strategies, minimization of ash deposit formation and corrosion, minimization of NO formation, appropriate operation of SCR catalyst equipment and utilization of residual products.

Kim Dam-Johansen, Flemming J. Frandsen, Peter A. Jensen, Anker D. Jensen

Examination of Oxygen-Enriched Gasification Process for Municipal Solid Wastes in South China

Theoretical and experimental research on the MSW gasification using oxygen is conducted to determine the favorable conditions for the production of increased syngas production of higher heating value. The technology utilizes oxygen enrichment of air for minimum combustion of the waste to increase heating value of the fuel due to decreased amounts of nitrogen in the syngas. The results showed that increase in equivalence ratio (ER) decreased CO and CH

4

content in the syngas while H

2

content increased at ER = 0.25 and then decreased. When the ER is greater than 0.30, the gasification controlled reaction change to combustion controlled. The equivalence ratio of in the range of 0.2–0.3 is the most suitable range for oxygen-enriched gasification. The calculated and experimental results showed good agreement. The equivalence ratio is crucial in oxygen enriched gasification of MSW since it impacts the heating value and gas phase components of the syngas produced.

Hongyu Huang, Haoran Yuan, Noriyuki Kobayashi, Ashwani K. Gupta, Xiong Zuhong, Yong Chen, Kuniyuki Kitagawa

Combustion of Pre-dried Brown Coal in Enriched with Oxygen Atmosphere

Brown coal is considered to be a competitive primary energy source for power generation for many countries. In order to keep its competitive edge, the improvement of the power plant efficiency is absolutely required. This could be accomplished by using clean coal technologies.

The main aspects of the introduction of the clean coal technologies as oxy-combustion are investigation taking into account the fuel characteristics and investigation of coal combustion in atmosphere enriched with oxygen.

An important issue is also the improvement of the fuel quality, which can be achieved by the installation of external brown coal dryers. The influence of pre-drying of the raw fuel in an external dryer is of great importance to the optimization of lignite utilization.

This work is mainly focused on the investigation of the behavior of pre-dried brown coal with different moisture content, during ignition, pyrolysis and combustion in atmosphere at different ratio O

2

/CO

2

is studied. The investigations of ignition time and intensity at selected O

2

/CO

2

ratio for different coal particle size were carried out.

Base on thermogravimetry analysis kinetic data in atmosphere at different ratio of oxygen/carbon dioxide were determined. Also at various moisture content in pre-dried brown coal the tests of oxy-combustion were carried out taking into account the emission pollutants as NO

X

and SO

2

.

H. Pawlak-Kruczek, M. Czerep, J. Długosz, J. Zgóra, M. Ostrycharczyk

Low Temperature Gasification of Biomass Using Ni-Loaded Brown Coal

Catalytic gasification of a woody biomass and a livestock waste were investigated under a prepared nickel-loaded brown coal (LY-Ni) char in a two-stage fixed-bed reactor. The nickel- loaded brown coal was prepared by ion-exchange method with a nickel loading rate of 8.3 wt.%. Nickel species dispersed well in the brown coal, and the LY-Ni char via devolatilization at 600°C showed a great porous property with a specific surface area of 382 m

2

g

−1

. The LY-Ni char was confirmed to be quite active for the biomass volatiles gasification at a relatively low-temperature range from 450 to 650°C. It is noteworthy that almost all the nitrogen-containing products (NH

3

, HCN and N-containing liquids) in biomass waste gasification were converted to N

2

in the case of LY-Ni char. The novel Ni-loaded coal char was also applied as catalyst in an internally circulating fluidized-bed gasifier (ICFG). The results show that ICFG can operate well by using nickel catalysts and LY-Ni char has a better ability and a hopeful prospect for the stability with coking resistance in comparison to the commercial nickel catalyst Ni/Al

2

O

3

.

Takayuki Takarada, Jing-Pei Cao, Xian-Bin Xiao, Kazuyoshi Sato, Yukiko Ogawa

Combined Heat and Power System with Advanced Gasification Technology for Biomass Wastes

The results obtained from an advanced gasification system utilizing high temperature steam are presented here. The results showed successful demonstration of clean syngas production having high calorific value fuel (~10 MJ/m

3

N) using woody biomass wastes in a downdraft type gasifier. The gasification capacity of the plant on dry basis was 60 kg/h. The syngas produced can be utilized in an absorption type chiller for air conditioning. This advanced gasification technology allows one to transform wastes to clean energy at local production sites without any environmental impact and expensive waste transportation costs. The experience gained from the demonstration plant allows one to implement to other industrial applications for use as a decentralized unit and obtain clean syngas for local use. The demonstration conducted here shows that the system is favorable for onsite use of compatible combined heat and power (CHP) system including light oil supported diesel engine power generator. The biomass waste fuel from a lumber mill factory was used in this study. The factory handles a wide forests area of about 50 ha and produces about 2,500 m

3

/year of wood chips from thin out trees and waste lumbers. This translates to a maximum 110 kg/h of wood chips that can be fed to a gasifier. The syngas produced was used for the combined heat and power system. Local use of biomass for fuel reforming reduces the cost of collection and transportation costs so that a sustainable business is demonstrated with profit from the generated electricity and thermal energy. The cost structure incorporates both the depreciation cost and operation cost of the system. Thermal energy from hot water can be used for drying lumbers and wood chips in a cascade manner. The drying process can be adopted for enhancing its productivity with increased variability on the quality of lumber. The results show that the combined heat and power system (CHP) offers good profitable business with much wider application of this technology to a wide range of low grade solid fuels, including plastics, biomass, sewage sludge, and high ash content low grade coals.

S. Mochida, T. Abe, T. Yasuda, A. K. Gupta

CFD and CHD in Random Packing Columns with Seawater Desulfurization

By the volume average method, gas-liquid two-phase flow CFD and CHT model is established to describe the random packing column in seawater desulfurization. By numerical calculation, the flow velocity, porosity distribution, pressure distribution and temperature distribution of seawater are obtained. Pressure loss and the outlet temperature of seawater are compared with experimental data, the prediction results and experimental results are well consistent, is exactly the same trend. Analyzing the results of calculation, a significant “wall flow” phenomena was found, and the reason of its formation is that the porosity of filler near the wall is significantly higher than in the middle region. Analyzing the distribution of seawater temperature, it is found that the distribution of seawater temperature is more uniform on the top of column, the seawater temperature near the wall fluctuated and were gradually more uniform towards the center of the column. Along the direction of the column from top to bottom, the seawater temperature gradually decreased, and the degree of fluctuations gradually reduced and basically does not change at half of the column, which indicated that the heat exchange between the gas and liquid has been basically completed.

Mei-Shan Gao, Shi-He Wang, Xiao-Ming Wang, Ming-Chun Guo

Improvement in Super Heater Deposition of Straw Boiler Based on Numerical Simulation

There is the problem of deposition exits generally in straw boiler super heater due to chlorine and alkalescent substance consists in the straw fuel, which agglomerate combustion material, especially for crops. Deposition does not only behave to raise the tube temperature, but also accelerate corrosion, even hide cartridge igniter trouble. This paper based on the study of some 75 t/h plant to optimize the ash removal system of super heater. According to the CFD simulation, the flue flow situation in tube bundle of super heater diverse along with the position of the tube. Based on the regular of deposit researched from the simulation outcome, this paper propose to optimize the structure of shock wave soot blower of pattern BH-100 used by the plant, which did not performance a proper role.

Lv Tai, Ting-ting Zhou, Hai Wang

Study on Optimizing Proportion of the Briquette with Orthogonal Experiments

Briquette coal is an efficient method in saving fuel energy, decreasing SO

2

and smoke dust emission for civilian boiler. This paper focuses on the study of optimizing composition proportion of briquette of Jilin, which contains Jixi coal, Tuanlinzi coal, coke, as well as peat. The factors influencing combustion characteristics should be taken into account, such as proportion of raw material, and how the composition influences the briquette heat value. The volatile productivity and combustion rate should not be ignored that the experimental outcomes, come from orthogonal experiment that burning briquette in a small capacity boiler, reveal the relationship related to combustion characteristics.

Peng Sha, Ting-ting Zhou, Lv Tai

Experimental Study on the Combustion Characteristics of Liquid Fuel in the Straight Tubes

This study investigates combustion characteristics of liquid hydrocarbon fuel (n-heptane, c7h16) under different operating conditions. In the paper, we designed a burner consisting of a stainless steel capillary which is used to dump the fuel and a larger stainless steel tube (or quartz tube) used as a combustion chamber. The inner diameter (ID) of the capillary is 0.24 mm, the inner and external diameter of the larger tube is 4 and 6 mm, respectively. According to the experimental results, the combustion process reaches a stable status after about 100 s. Wall temperature distribution and combustion products are analyzed under conditions with different equivalence ratios, gas flow velocities and materials. As equivalence ratio (ER) whose range is in 0.56–1.08 increases, the wall temperature declines, and wall temperature gradient increases slightly. The range of gas flow velocity is in 0.6–1 m/s, the overall trend of wall temperature distribution is the second point from left boundary as a line, the wall temperature distribution of the four points in the right side increases with the flow velocity increasing, but the left point is rapidly declining. When the burner made of stainless steel, the wall temperature distribution varies slightly due to the larger thermal conductivity of stainless steel than that of quartz, which makes the heat transfer in stainless steel faster and the temperature distribution is more uniform. The thermodynamic calculation software is also used to study the compositions of combustion products. In a word, this structure of the burner shows poor combustion characteristics, we should change the structure and the experimental conditions to achieve better combustion characteristics in the future.

Fei Yang, JunWei Li, ZhaoQiu Zhou, Xin Zhang, NingFei Wang

Experimental Studies of SO2 Absorption in the Sieve-Plate wet FGD Absorber

Limestone-gypsum wet FGD is the maximum widely applied FGD technology in the world at present, sieve-plate absorber is one of the critical tower in wet FGD processes. This article provides a study on the features of flow field distribution, resistance and desulfurization of sieve-plate FGD absorber through Laboratory-scale experimental FGD system. It is shown that the flow field distribution in sieve-plate FGD absorber is homogeneous, the deviation of velocity distribution of flue gas is 0.4–0.58, whereas the standard deviation of empty absorber is 0.99. In comparison with empty absorber, the pressure loss of sieve-plate absorber increased 30–160%, and following the decreasing of void ratio, the pressure loss of sieve-plate absorber has a tendency of increasing. While the void ratio of sieve-plate is decreasing from 44.3 to 31.5%, the pressure loss increased 16.1–27.6%. The desulfurization efficiency of sieve-plate absorber presents increase first and decrease afterwards following the increasing of void ratio of sieve-plate. In comparison with empty absorber, the desulfurization efficiency increased 8–22.89%. And under the condition of same sieve-plate, the desulfurization efficiency is 3–8% better when the distribution of sieve-plate pores is in square than that in triangle.

Jiancai Sui, Jiajia Deng, Liqiang Zhang, Chunyuan Ma

Study on Pneumatic Conveying Characteristics of Top Discharge Blow Tank of Pulverized Coal

The effects of fluidizing gas flow rate, pressurizing gas flow rate and superficial gas velocity at the riser inlet on the pneumatic conveying characteristics such as pulverized coal mass flow rate, differential pressure, solid-gas ratio, and voidage were investigated in a top discharge blow tank pneumatic conveying system at atmospheric pressure. The results indicate that as the fluidizing gas flow rate increases, the pulverized coal mass flow rate, differential pressure and solid-gas ratio increase at first and then decline, respectively. As the pressurizing gas flow rate increases, the pulverized coal mass flow rate and differential pressure increase gradually, while the solid-gas ratio increases at first and then declines. As the superficial gas velocity at the riser inlet increases, the pulverized coal mass flow rate and differential pressure increase gradually, while the solid-gas ratio increases at first and then declines. The voidage of all the experiments is below 0.95, so the top discharge blow tank system can achieve dense phase conveying.

Guiling Xu, Xiaoping Chen, Cai Liang, Changsui Zhao, Pan Xu

Slagging Gasifier Refractories: A New Pathway to Longer Refractory Life

Solid fuel slagging gasification to convert coal or petroleum coke feedstocks into syngas has rapidly evolved over the last 25 years. The gasifier is a high temperature, high pressure reaction chamber. Operating temperatures are between 1250 and 1575°C. Pressures will be between 20.4 and 68 atm. Syngas has been typically used for chemical feedstocks, fuel for power plants, or for steam and hydrogen generation in other industrial applications.

Ash which comes from the solid fuel during gasification has many impurities. It melts during the gasifier reactor operation forming a liquid that penetrates the refractory lining. Given time, the refractory will wear away from thermal spalling, structural spalling, or overheating of the refractory. In some cases, all three wear mechanisms are seen in the same gasifier lining.

Industry users have identified refractory life as one major limiting factor in worldwide use of this technology. Users have stated if the refractory liner can increase on-line availability of the gasifier operation, more industry acceptance of this technology is possible.

Harbison-Walker Refractories Company will review destructive factors affecting lining life and discuss new refractory materials that have dramatically increased gasifier lining life and reliability. New refractory materials will be presented and supported by field trial results and post mortem analysis.

Mark Schnake

The Influence of Atomizer Internal Design and Liquid Physical Properties on Effervescent Atomizing of Coal-Water Slurry

This study investigated the dependence of effervescent atomizing of coal-water slurry (CWS) on atomizer internal design and fluid properties. Results demonstrate that internal design of atomizer and fluid properties directly affect the two-phase flow pattern inside the atomizer which consequently affects the spray quality. The influence of mixing chamber length on spray quality is not significant at the ALR of 0.15 except for spray 0.75 glycerol/0.248 water/0.002 xanthan mixture. The same trend also found in the effect of angle of aeration holes at

ALR

of 0.15. Large diameter of the inclined aeration holes shows small SMD for water. The consistency index of fluids has no effect on the spray quality and Sauter Mean Diameter (SMD) increases when polymer additions were added to the glycerin-water mixture. The radial profile of SMD for spray water are almost flat, however, the largest SMD can be obtained at the edge of spray for three other fluids.

Meng Liu, Yufeng Duan

Efficient Use of Low Rank Coal: Current Status of Low Rank Coal Utilization

Despite vast reserves, low rank coals are not used as a main fuel in industry because their high moisture content, potential spontaneous combustion in transportation and storage, and the low thermal efficiency during the combustion in conventional power plants. With a view to secure and strengthen low rank coal’s position as high available energy source, in recent years many attempts have been made to develop technologies for an energy-efficient upgrading process. This paper reviews these technologies mainly categorized as drying for reducing moisture, stabilization for decrease self-heating characteristics and cleaning the coal for reducing mineral content of coal. Drying technologies consist of both evaporate and non-evaporative types. There are also highly advanced coal cleaning technologies that produce ash-free coal. The paper discusses some of the promising upgrading technologies aimed at improving these coals in terms of their moisture, ash and other pollutants. Korea’s activity for the drying and stabilization technologies will be introduced in this paper and the utilization of dried low rank coal also introduced.

Sihyun Lee, Sangdo Kim, Hokyung Choi, Donghyuk Chun, Younjun Rhim, Jiho Yoo, Jeongwhan Lim

Influence of Coal Preoxidation on the Porosity of the Activated Carbons with Steam Activation

Activated carbons have been prepared from a low ash content anthracite preoxidized in air to different degrees. Steam has been used as activating agent to prepare different burn-off samples. The preoxidation effect on the physico-chemical characteristics of the resulting chars and activated carbons were comparatively studied. The surface area and porosity of sample was studied by N

2

adsorption at 77 0A0;K. The results show that introduced oxygen in coal structure had a great influence on the carbonization and subsequent activation process. The carbonization of oxidized coal exhibited a broader volatile evolution with respect to temperature, and the resulting chars had a larger microporosity. The porosity of the char is a primary foundation to develop more microporosity upon activation. Activation of char from oxidized coal facilitated development of small scale micropore, however, the micropore widening was also observed at high burn-offs. Compared with development of supermicropore, the evolution of mesoporosity is hindered strongly by preoxidation treatment. The quantity of basic surface sites in activated carbons increased with an increase in oxidation degree, while the quantity of acidic sites appeared equivalent. It seemed that the amount of surface groups and the microporosity mainly developed in a parallel way.

Yuwen Zhu, Jihui Gao, Fei Sun, Yang Li, Shaohua Wu, Yukun Qin

Experimental Study on Drying of Low Rank Coal by Changed Temperature and Particle Size

Nowadays, coal plays an essential role in our global energy mix. With the increasing energy costs and dwindling supplies of petroleum and natural gas, low rank coal has been becoming more and more attractive and practicable, which accounts around 45% of the world’s coal reserves and is cheaper than other fossil fuels. However, low rank coal such as lignite contains 30–60% moisture content and 25–40% volatile matter have kept it from being aggressively exploited until recently. Therefore, how to reduce the moisture content of low rank coal has been an increasingly necessary to solve.

The objective of this paper is to obtain appropriate parameters of drying of low rank coal using the heating method. This drying process is heated by Electronic Moisture Balance (EMB) method through changing temperature and particle size. We choose three different particle sizes as the experimental samples to conduct this experiment at three different temperatures. According to the analysis of this experiment and the TGA results, we conclude that the optimal temperature of causing to a dramatically decrease of moisture content is at 107°C and the drying time of low rank coal is set as 30 min, the three different particle sizes which are chose in this experiment and are less than 3 mm have no distinctive drying effect at 80, 107, 150°C, respectively, the optimal drying temperature range of low rank coal is from 103 to 123°C and the drying rate accelerates with the increasing of the temperature which is in agreement with the theory of convection heat flux.

Xiang-Zhou Yuan, TaeJim Kang, DoMan Jeon, Hueon Namkung, YoungSin Jeon, Hyung-Taek Kim

The Application of Low Rank Coal on IGCC Plant by the Developed Simulation Model

Nowadays, IGCC power plant that uses the gasification technology is emerging in many countries because this system has the characteristic of high efficiency without air pollutant emissions. Though bituminous and sub-bituminous coals are the main feedstock of IGCC in the present years, which only accounts for around 50%, the high consumption of coal will lead to an inevitable tendency that people focus their eyes on low rank coal which holds abundant reserves throughout the world in the future.

In the previous work, the IGCC model based on the Texaco gasification power system has been developed, and the developed model has a good match with the pulverized dry coal. There are five blocks in the simulation model of IGCC plant, such as fuel pretreatment, gasification, ash removal, AGR and combined cycle. Present investigation focuses on the application of low rank coal based on the developed model of 300 MW gasification plant comparing with Illinois#6 (high rank coal). Illinois#6 (IC6) and IBC (Indonesia lignite) are chosen as the feedstock of gasification. To evaluate the application of low rank coal, the evaluating parameters are chosen as cold gas efficiency (CGE) and carbon conversion (CC) of gasifier, composition content of syngas, power output and efficiency of combined cycle. It indicates that IBC coal which has 46.6% of plant net efficiency has relatively superiority over 40.93% of the IC6 under the same evaluating parameters.

Chun-Yang He, Hyung-Taek Kim

Co-Gasification of Oil Sand Coke with Coal

Gasification of oil sand delayed coke with sub-bituminous and lignite coals was performed in an atmospheric entrained flow gasifier using steam and oxygen as gasifying agents. The underlying objective of this work was to assess the effects of the operating variables (i.e. temperature, oxygen and steam concentrations) and coal/coke blending ratio on gasification performance in a high-temperature in order to find the possible synergies in co-gasification of the fuels. Experiments were conducted at 1,400°C, using steam and oxygen to carbon weight ratios of (0.36–1.08) and (0.07–0.2), respectively in N

2

carrier gas. The coke to coal weight ratios of 1/3, 1/2, and 2/3 were used for the blending tests. Particle size of 53–90 μm with d

50

= 75 μm were used. In terms of char reactivity, blending did not show any significant positive effect. Slight deviations from linear additive line are in the order of experiment error. Gasification efficiency was also following a linear additive trend once more pointing out the lack of synergy in entrained flow gasification systems. The results however, showed that higher coke content clearly favored the H

2

production.

Farshid Vejahati, Rajender Gupta

Pulverized Coal Combustion

Frontmatter

Modeling of a Single Char Particle Burning in Oxygen-Enriched O2/N2 and O2/CO2 Environment

The combustion characteristics of pulverized coal in O

2

/CO

2

were reported considerably different from those in conventional air combustion. Properly describing the combustion behaviors of coal particles at elevated O

2

levels in both oxy-firing and air firing is essential for the design and simulation of the advance combustion systems. The objective of the present work is to describe the rate-limit step of coal conversion, i.e., the combustion process of char particles with modeling approach. In order to understand the reasons to cause the differences when replacing N

2

with CO

2

in the oxidant stream, a fundamental model has been developed to describe in detail the combustion of a single pulverized char particle at elevated O

2

mole fractions in either N

2

or CO

2

balance gas. The model includes char oxidation and a kinetic scheme which is coupled with the diffusive properties within the particle and in the boundary layer. The main features of the model include: (1) The properties e.g., thermal conductivity and diffusivities, of the gaseous species in the gas mixture are modeled in detail; (2) The model considers the distributions of carbon reactivity and structure, temperature and gas concentrations within the particle and their evolutions during the conversion process; (3) Thermal annealing and its impact on the evolution of carbon reactivity are considered; (4) The model describes the intra-particle reactions and diffusion as well as the reactions, particularly CO oxidation, and diffusion outside the particle. The model is validated with the comparisons of particle surface temperature between the calculation results and the experimental data of char particle combustion reported in the literature. The oxygen concentration involved covers from normal concentration to up to 100% for both O

2

/CO

2

and O

2

/N

2

combustion. Model results represent that coal particles burned at lower mean temperatures in O

2

/CO

2

than in O

2

/N

2

environments at analogous oxygen mole fractions. Additionally, the model has also been applied to numerically investigate the effects of char property and combustion condition parameters on the combustion process so as to explore the applicability of model in prediction char conversion process in practice.

Y. Chen, C. D. Sheng

Numerical Study on NO Formation in a Pulverized Coal-Fired Furnace Using Oxy-Fuel Combustion

Computational fluid dynamics (CFD) approach was employed to numerically investigate NO formation in a 600 MW wall-fired pulverized coal-fired furnace retrofitted for oxy-coal combustion, aimed at the impacts of flue gas recycle ratio, O

2

staging and recycled NO with the recycled flue gas (RFG) on NO formation and emission. An in-house CFD research code for conventional air combustion was developed and extended to simulate O

2

/RFG combustion with specific considerations of the change of gas properties and its impact on coal particle combustion processes. The extended De Soete mechanisms including NO reburning mechanism were applied to describe transformations of fuel nitrogen. It was shown that CFD simulation represented the significant reduction of NO formation during O

2

/RFG combustion compared to that during air combustion. The in-burner and particularly the in-furnace O

2

staging were confirmed still to play very important roles in NO formation control. Changing the recycle ratio had significant impact on the combustion performance and consequently on NO formation and emission. With the combustion performance ensured, decreasing the flue gas recycle ratio or increasing the inlet O

2

concentration of combustion gas led to reduction of NO formation and emission. Although NO formation and emission was found to increase with increasing the inlet NO concentration of combustion gas, CFD simulation indicated that ~74% of the inlet NO was reduced in the furnace, consistent with the experimental data reported in the literature. This demonstrated the significant contribution of reburning mechanism to the reduction of the recycled NO in the furnace.

Aiyue Zhang, Yuan Chen, Changdong Sheng

The Guidelines for the Design and Layout of Oxy-Fuel Combustor Based on the Experiments of Pulverized Coal Combusted in Ar, N2 and CO2 Respectively

The oxy-fuel combustion technology is going to be a key solution for CO

2

capture and sequestration. And the era of oxy-fuel combustion is approaching. However, the combustion characteristics, such as ignition, flame stability, and combustion duration, have changed because the coal particles are combusted in CO

2

atmosphere. Thus, the novel design technologies of combustor used in oxy-fuel combustion technology are demanded. We have concluded several critical rules from the experiment data obtained from the coal particles combusted in a retrofitted fixed bed reactor in Ar, N

2

and CO

2

respectively. The coal particles are prone to be ignited but take more time to burn up in CO

2

atmosphere at low temperature of 1,000–1,300°C comparing to the data obtained from N

2

and Ar atmospheres under the same conditions. And when at high temperature of 1,600°C, the combustion duration of coal particles combusted in CO

2

is the same with that of Ar and N

2

situation. The NO

x

is prone to released ahead of the carbon combustion at relatively high temperature, and the priority of NO

x

release to Carbon combustion is aggravated as the temperature increases. The overall analysis and comparison among the three atmospheres make the novel design and layout of oxy-fuel combustor feasible. Consequently, the guidelines for these aims basing on those rules conclude from the experimental data and the relative researchers’ work are discussed and a novel design of oxy-fuel burner is put forward and simulated in this paper.

Yu Li, Weidong Fan, Peng Ren, Kang Wang, Junchao Wang

Significant Roles of Inherent Fine Included Mineral Particles in the Emission of PM1–10 During Pulverised Coal Combustion

This study investigates the roles of inherent fine included mineral particles in coal in the formation of inorganic particulate matter (PM) during pulverized coal combustion at 1,400°C. A Western Australia sub-bituminous coal (Collie coal) was used to prepare a raw coal sample of density-separated fraction (1.4–1.6 g/cm

3

) that is narrow-sized (63–90 μm). The raw coal was also washed using dilute acid to prepare an acid washed coal sample that is free of organically-bound inorganic species. Computer-controlled scanning electron microscopy (CCSEM) analysis shows that mineral matter in the raw coal is of included nature, of which ~90% are fine mineral particles <10 m. Combustion of the coal samples produces substantial PM

1–10

that accounts for 20.3–24.8% of total ash collected. The PM

1–10

samples contain abundant fine ash particles that are clearly originated from fine included mineral particles (e.g. quartz) inherent in the coal. The results suggest that liberation and transformation of fine included mineral particles in coal during combustion is a key mechanism responsible for PM

1–10

formation under the combustion conditions. Experimental evidence further suggests that significant coalescence of fine included minerals within a burning coal particle can clearly take place to form large ash particles in the form of agglomerates.

Xiangpeng Gao, Hongwei Wu

Numerical Simulations of a Large Scale Oxy-Coal Burner

Oxy-coal combustion is one of promising carbon dioxide capture and storage (CCS) technologies that uses oxygen and recirculated CO

2

as an oxidizer instead of air. Due to difference in physical properties between CO

2

and N

2

, the oxy-coal combustion requires development of burner and boiler based on fundamental understanding of the flame shape, temperature, radiation and heat flux. For design of a new oxy-coal combustion system, computational fluid dynamics (CFD) is an essential tool to evaluate detailed combustion characteristics and supplement experimental results. In this study, CFD analysis was performed to understand the combustion characteristics inside a tangential vane swirl type 30 MW coal burner for air-mode and oxy-mode operations. In oxy-mode operations, various compositions of primary and secondary oxidizers were assessed which depended on the recirculation ratio of flue gas. For the simulations, devolatilization of coal and char burnout by O

2

, CO

2

and H

2

O were predicted with a Lagrangian particle tracking method considering size distribution of pulverized coal and turbulent dispersion. The radiative heat transfer was solved by employing the discrete ordinate method with the weighted sum of gray gases model (WSGGM) optimized for oxy-coal combustion. In the simulation results for oxy-model operation, the reduced swirl strength of secondary oxidizer increased the flame length due to lower specific volume of CO

2

than N

2

. The flame length was also sensitive to the flow rate of primary oxidizer. The oxidizer without N

2

that reduces thermal NO

x

formation makes the NO

x

lower in oxy-mode than air-mode. The predicted results showed similar trends with measured temperature profiles for various oxidizer compositions. Further numerical investigations are required to improve the burner design combined with more detailed experimental results.

Taeyoung Chae, Sanghyun Park, Changkook Ryu, Won Yang

Simulation of Coal-Dust Combustion in the Boiler Furnace of 800 MW

Have been based on the Euler/Lagrange approach for turbulent reacting gas-particle flows with combusting pulverized coal particles, a comprehensive model for pulverized coal combustion has been developed by incorporating a model of pulverized coal devolatilization and char combustion, a model of NOx formation and a model of ash deposition. Applicability of the comprehensive model has been validated by comparing its predictions with the experimental data. The mathematical model has been applied to a 800-MW tangentially-fired boiler of the Berezovskaya Power Plant to evaluate aerodynamics, heat exchange, formation of nitrogen oxides, and the intensity of local slag formation for different operation regimes and variants of the reconstruction of the furnace-burner device. Numerical data have been used to reconstruction the furnace of the P-67 boiler. The predicted results from the mathematical model are in good agreement with the experimental measurements after reconstruction the furnace.

M. J. Chernetsky, A. A. Dekterv, A. A. Gavrilov, E. S. Tepfer, V. V. Vasilyev

Mitsubishi Latest Coal Fired USC Boiler Technology (CFE Pacifico 700 MW)

Mitsubishi Heavy Industries, Ltd. (MHI) has successfully completed commissioning work for CFE (Comisión Federal de Electricidad) Pacifico 700 MW coal-fired unit in March 2010 which is the first supercritical unit in Latin America. This supercritical boiler was designed with state of the art technologies such as low NOx burners, high fineness pulverizers, advanced vertical furnace wall technology and so on. Especially the advanced vertical furnace wall technology with some improvements is a key technology to realize swift load changes such as 5% load per minute ramping rate with assuring dynamic characteristics. Recently the requirement of the high efficiency and the swift load changes for the power boilers has been increased so that even a coal-fired unit needs flexible operation characteristics for balancing variety of power sources. One of the challenges for the swift load change is to keep the furnace wall metal temperature low during the load change, which the advanced vertical furnace wall could realize. The report describes the features of the unit and commissioning result including load swing test results in details.

T. Hashimoto, K. Sakamoto, M. Fujitab

Comparison of Char Structural Characteristics and Reactivity During Conventional Air and Oxy-Fuel Combustion

The capture and sequestration of CO

2

generated from large- scale stationary power plants is considered to be one of the leading technologies that could potentially have a significant impact on reducing greenhouse emissions. Among these emerging technologies, the oxy-fuel combustion is a near-zero emission technology that can be adapted to both new and existing pulverized coal-fired power stations. The goal of this work is to make a comparative study on char structural characteristics (including char yield, swelling ratio, BET surface area, pore distribution, morphology) and reactivity during conventional air and oxy-fuel combustion. Specific experimental designs include two series. One is carried out in pure N

2

and CO

2

(pyrolysis experiments), and another is prepared in N

2

+ 5%O

2

and CO

2

+ 5%O

2

. Coal samples included raw coal, low density fraction coal and medium density fraction coal in all experiments. The present study is a further effort to extend our knowledge about physical and chemical structural characteristics and reactivity of char in the presence of high concentration CO

2

. Combustion and pyrolysis of a density fractionated China coal at drop tube furnace yielded the following conclusions. Compared to oxy-chars obtained under pure CO

2

atmosphere, the swelling ratios of char obtained in pure N

2

atmosphere are higher. When adding 5%O

2

, experimental results are completely different with those of the pyrolysis experiment. In comparison with the oxy-chars obtained under CO

2

+ 5%O

2

atmosphere, the swelling ratios of the char obtained in N

2

+ 5%O

2

atmosphere are lower. In the pyrolysis experiment, the BET surfaces Area of the oxy-chars are about 10–20 times as much as chars. When adding 5%O

2

, the BET surfaces Area of the oxy-chars are about two to four times as much as chars. During pyrolysis experiment, the total pore volumes of the oxy-chars obtained under pure CO

2

are larger in comparison with chars obtained in pure N

2

. The pore distributions of the oxy-chars are mainly mesopore and the chars have macropore mostly. The micropore and mesopore volume of oxy-chars are about ten times as much as chars separately and the macropore volume of oxy-chars are about two times as much as chars. When adding 5%O

2

, the total pore volumes of the oxy-chars obtained under CO

2

+ 5%O

2

are also larger in comparison with chars obtained in N

2

+ 5%O

2

. In the pyrolysis experiment, the reactivity indexes of oxy-chars obtained under pure CO

2

are lower in comparison with chars obtained in pure N

2

. When adding 5%O

2

, no significant differences can be observed, which may be due to the ordering of carbon microcrystalline structure. In pure CO

2

atmosphere, the oxy-chars have a highly order polycrystalline structure, but chars obtained at pure N

2

atmosphere have a highly disordered carbonaceous structure.

Xiaowei Liu, Minghou Xu, Hong Yao, Ying Gu, Junping Si, Chao Xiong

Low-Temperature Swirl Fuel Combustion: Development and Experience

The promising designs (schemes) of low-temperature swirl furnaces are developed. New schemes are tested in operating plants, confirm its reliability and provided with effective swirl combustion of different kinds of fuel, such as: brown and bituminous coal, peat and natural gas.

K. A. Grigoryev, Yu. A. Roundyguine, V. E. Skuditskii, R. G. Anoshin, A. P. Paramonov, A. A. Trinchenko

Emission of NO and SO2 in a 300 kW Pilot Scale O2/RFG Combustion

The present work was addressed toward the NO and SO

2

emission results on a 300 kW pilot scale facility, and discussed the impact of the different flue gas recycle ratios on the O

2

/RFG coal combustion. In this study, a Chinese lean coal was burned with air and three kinds of O

2

/RFG conditions in the pilot scale oxy-fuel coal combustion facility. The composition of the flue gas was sampled and analyzed by the FT/IR gas analyzer. The ashes were sampled in different place and analyzed to study the burnout rate and the mineral transformation. And in-furnace limestone injection under the air and oxy-fuel condition was used to study the desulfurization efficiency. The comparison was made between the air combustion and O

2

/RFG combustion. It can be seen that NO

x

emissions decrease significantly (296 mg/MJ for air-firing, 80–145 mg/MJ for oxy-firing), compared with the air condition and three kind of oxy-fuel condition. It can be seen that the low NO

x

characteristic of the Oxy-fuel combustion causes lower emission of NO compared with the air combustion. For the emission of SO

2

, Fuel-S to SO

2

conversion rate dropped from 77% in air to 50% under O

2

/RFG condition. And the desulfurization efficiencies of the air combustion and O

2

/RFG combustion were 28.4 and 59.1%, respectively. The contribution of SO

2

enriched in the flue gas to the desulfurization efficiency was more than the contribution of increased reactivity of the limestone. By the analyzing of the ash, it was the similar between the air combustion and O

2

/RFG combustion.

Tai Zhang, Zhaohui Liu, Xiaohong Huang, Jingzhang Liu, Dingbang Wang, Chuguang Zheng

Large-Eddy Simulation of Pulverized Coal Combustion in Swirling Flow

Large-eddy simulation (LES) is applied to both a pulverized coal combustion and non-combustion field in a combustion test furnace with a practical advanced low NO

x

burner called CI-α burner, and investigated the effect to coal combustion on flow field and ignition mechanism. The results show that predicted flow field and coal particle behavior are in general agreement with the experiment. Coal combustion strongly affect flow filed. Primary air jet and swirling flow is enhanced by the burned gas expansion. Moreover, a recirculation flow formed by strong swirling flow is observed near the burner region and keeps stable coal combustion by transporting hot gas and increasing coal particle residence time.

K. Tanno, H. Watanabe, N. Hashimoto, R. Kurose, H. Shirai

Numerical Analysis of Loads Effect on Combustion Performance and NOx Emissions of a 220 MW Pulverized Coal Boiler

This paper presents numerical study on the combustion performance and NO

x

emissions of a 220 MW pulverized coal boiler. Three different loads have been simulated with combusting coal, 200, 170 and 140 MW, respectively. In order to get as precise as possible numerical analysis results, two-step simulation method has been adopted in this work, namely, air supply system simulation and furnace simulation. After air supply system simulation, the results have been taken as the initial and boundary conditions for furnace simulation. The comparison between the measured values and predicted results from 200 MW case shows much better agreement. According to the simulation results, the adopted two-step simulation method is reasonable and suitable for predicting the characters of the flow and combustion process. It is concluded that the distributions of temperature, O

2

and CO concentration inside furnace with different loads shows good similarly. The total NO

x

emissions decreased with the boiler load reducing, and fuel NO

x

has the same trend as total NO

x

, and fuel NO

x

account for about 66% in total NO

x

in all the three cases. More important, thermal NO

x

slowly decreased with the rise of boiler load. More detailed results presented in this paper enhance the understanding of combustion processes and complex flow patterns of front-wall pulverized coal boilers.

Jun Li, Radosław Jankowski, Michał Kotecki, Weihong Yang, Dariusz Szewczyk, Wlodzimierz Blasiak, Artur Brzdekiewicz

Numerical Simulation of Two Phase Flow Characteristic in Dynamic-Static Separator

Dynamic-static coal separator is sensitive in changing the fineness of coal particle that it is available through adjusting the angular velocity of rotation of blades. The paper reveals the flow characteristics of gas-solid two phase in the dynamic-static coal separator respectively using CFD method that how the coal particles of different semi-diameters move under diverse angular velocity of rotation. When simulating the gas turbulent flow situation,

κ-ε

model is selected with semi-implicit method for pressure-linked equations; as to solid phase treatment, it is settled as discrete phase model using uncoupled method to track particle. The result shows the air stream flow pattern and typical particles’ trajectories, as well as velocity pattern of particle and pressure change in the separator, which instructs the practical operation in a valid side.

Lv Tai, Ting-ting Zhou

Modeling of Aerodynamics in Vortex Furnace

At present, the torch burning technology of pulverized-coal fuel in vortex flow is one of the most prospective and environmentally-friendly combustion technologies of low-grade coals. Appropriate organization of aerodynamics may influence stability of temperature and heat flux distributions, increase slag catching, and reduce toxic emissions. Therefore, from scientific point of view it is interesting to investigate aerodynamics in the devices aiming at justification of design and operating parameters for new steam generators with vortex furnace, and upgrade of existing boiler equipment. The present work is devoted to physical and mathematical modeling of interior aerodynamics of vortex furnace of steam generator of thermal power plants.

Research was carried out on the air isothermal model which geometry was similar to one section of the experimental- industrial boiler TPE-427 of Novosibirsk TPS-3. Main elements of vortex furnace structure are combustion chamber, diffuser, and cooling chamber. The model is made from organic glass; on the front wall two rectangular nozzles (through which compressed air is injected) are placed symmetrically at 15° to the horizon. The Laser Doppler Velocimeter LAD-05 was used for non-contact measurement of vortex flow characteristics. Two velocity components in the XY-plane (in different cross- sections of the model) were measured in these experiments. Reynolds number was 3·10

5

.

Numerical simulation of 3-D turbulent isothermal flow was performed with the use of CFD package FLUENT. Detailed structure of the flow in vortex furnace model has been obtained in predictions. The distributions of main flow characteristics (pressure, velocity and vorticity fields, turbulent kinetic energy) are presented.

The obtained results may be used at designing boilers with vortex furnace. Computations were performed using the supercomputer NKS-160.

I. Anufriev, V. Salomatov, Y. Anikin, D. Krasinsky, O. Sharypov, Kh. Enkhjargal

Effect of Oxygen-Enriched Condition on Ignition Favorable Region in High-Temperature Oxygen-Enriched Pulverized Coal Ignition

On the basis of characteristics of high-temperature air oil-free ignition and oxygen-enriched combustion, high-temperature oxygen-enriched ignition was proposed as a new method of pulverized coal ignition for utility boilers, and a device for high-temperature oxygen-enriched ignition was also designed. In order to obtain the law of the effect of oxygen-enriched conditions on pulverized coal ignition in high-temperature oxygen-enriched ignition, the ignition temperatures of design coal for ignition device were obtained in different oxygen concentration conditions by related experiments, and the ignition favorable region was defined. Finally, the effect of oxygen-enriched conditions on the ignition favorable region was obtained by numerical simulation using FLUENT. The results show: temperatures and oxygen concentration of oxygen- enriched gas are two basic factors that affect the size of the ignition favorable region; no larger ignition favorable region appears when the temperature or oxygen concentration is lower; considering the appearance of larger ignition favorable region, the lowest temperature of oxygen-enriched gas decreases with the increase of oxygen concentration; when oxygen concentration is higher than 60%, the temperature of oxygen-enriched gas is the major factor to the size of the ignition favorable region, on the contrary, the oxygen concentration of oxygen-enriched gas becomes the major factor.

Liu Guo-wei, Zhang Yan, Dong Peng, Bie Ru-shan

Different Sorbents in Calcium Looping Cycle for CO2 Capture

Cyclic CO

2

capture using commercial pure micro CaCO

3

and nano CaCO

3

is investigated in this paper which focuses on the different characteristics two different sorbents during high temperature reactions. The results indicate that the nano CaCO

3

sorbent has higher carbonation conversions and carbonation rates than the micro CaCO

3

sorbent in the cyclic reactions. Furthermore, nano sorbent can retain its fast carbonation rates at the beginning dozens of seconds during each cycle. In contrast, the carbonation rates of micro sorbent diminish with the increase of cycle number. But, unfortunately, CaO derived from nano CaCO

3

sorbent sinter much easily. Its grains, which are composed of numerous spherical nanocrystallites, experience dramatic morphological changes during high temperature reactions.

Cong Luo, Ying Zheng, Ning Ding

Analysis on the Influence of Coal Properties on NOx Emissions of Large-Scale Boilers Equipped with Advanced Low-NOx Combustion Systems

The fast development and application of low-NOx combustion technologies have significantly influence on the operation performance of coal-fired utility boilers. With the application of advanced low-NOx combustion technologies, the characteristics of NOx emissions from pulverized coal-fired furnace and the trends of various factors influencing on the emissions may also be different from understandings from the experiences of using the previous technologies. It is well known that coal properties are among the most important factors to affect NOx emission levels. However, the modern low NOx combustion technologies are all based on controlling coal particle combustion process but fitting with the properties of the fired coals. Therefore, the influence of coal properties on NOx emissions of modern large-scale boilers, particularly those equipped with advanced low-NOx combustion systems, is worthy of a further study.

In the present work, extensive in-situ measured NOx emission data as well as coal properties of more than 40 pulverized coal- fired units with the installed capacity of 300–1,000 MW were collected and analyzed to establish the correlation between NOx emission and coal properties. When comparing the impacts of coal volatile content and N content on NOx emission concentrations between different boilers, it was found that, for the boilers burning high volatile bituminous coals, the impacts of coal properties on the NOx emissions of the boilers equipped with advanced low-NOx combustion systems are not long significant. When considering coal properties impact on a certain boiler equipped with advanced low-NOx combustion system, its NOx emission was found in general to decrease with the increases of the coal N and volatile contents. It implies that, for a certain boiler considered, coal properties are still the main factor influencing the NOx emission concentration. The present work presented the further understanding of the influence of coal quality on NOx emission of modern pulverized coal-fired boilers. The data and results will be detailed in the full manuscript.

Shen Yue-yun, Gao Xiao-tao, Zhang Ming-yao

Numerical Simulation of Altitude Impact on Pulverized Coal Combustion

A drop-tube Furnace simulation model has been developed to investigate the pulverized coal combustion characteristics under different altitudes using the commercially available software Fluent. The altitude conditions of 0, 500, 1,000, 1,500 m have been discussed. The results included the fields of temperature, pressure, velocity, the coal burnout, CO burnout and NO emission in the tube furnace. The variation of these parameters with altitude has been analyzed. The coal combustion characteristics were affected by the altitude. The time and space for coal burnout should be increased with the rise of altitude. The valuable results could be referenced in the design of coal- fired furnaces for the high altitude areas.

Pei Xiaohui, He Boshu, Ling Ling, Wang Lei

The Influence Factor Analyses of Non-stable Combustion in the Ignition Process of Gasifier

The pulverized coal gasification technology is large-scale carried out in China for more than 10 years, and more and more coal gasification technology, such as SCGP, GSP, GE, indigenous gasifier, have been widely used in China.

Ignition process is non-stable combustion process, which is the key process in the operation of gasifier. In ignition process of pulverized coal gasifier, the average temperature and pressure will increase to high level (about 800°C and 1 MPa) from the normal condition.

In this paper, the trial furnace experiment have been carried out to study the non-stable flow and combustion characteristics in gasifier. The variety of the temperature and the shape of the flame with the pressure growing have been analyzed. These results show that the average temperature is increasing gradually at atmosphere pressure, while the high temperature region locates 100 mm away from the head of the ignition burner with a spindly shape. As the pressure goes up, the shapes of the flame shorten apparently, while the distance between the high temperature region and the head of the start-up burner decreases. Thereby, it is possible that the head of the start-up-burner will burning-out by the high temperature flame. Therefore, the pressure will tremendously influence the combustion process in gasifier, where the flame will change shortly and unstably.

Kuang Jian-ping, Zhang Shi-cheng, Jie Tao, Cao Feng, Chen Xu-si, Li Hang, Liu Yong-sun

Carbon Particles Mass Concentration Effect on Dusts Ignition and Burning Parameters

High temperature heat and mass transfer of carbon dust was studied numerically. Effect of carbon mass concentration and chemical reactions in pores on burning characteristics was investigated in details. A range of the particles diameters corresponding to maximum fuel burn out was defined. It was shown that in case of porous particles this range is significantly broader and particles ignition critical diameters are smaller. This effect is more pronounced at relatively low gas temperature.

S. G. Orlovskaya, O. N. Zuj, F. F. Karimova

Burning of High-Ash Ekibastuz Coal in the Boiler Furnace of 300–500 MW Power Units

The paper discusses combustion of Ekibastuz black coal in pulverized-coal fired boilers operating in 300–500 MW power units. Main technical solutions related to modernization of combustion system of PK-39 and P-57 boilers manufactured by JSC Machine-Building Factory of Podolsk to reduce nitrogen oxide emissions down to ≤600 mg/nm

3

(at normal conditions and O

2

= 6%). Correctness of these technical solutions is justified by 3D simulation of combustion process.

A. R. Kvrivishvili, A. I. Tsepenok, F. A. Serant, V. V. Gordeev, E. A. Mezhov, A. A. Lavrinenko

Effects on Design and Operation of Coal-Fired Utility Boilers with Changes of Coal Qualities

In recent years, with the development of economic, large-scale coal-fired utility power plants got a rapid development in China. The related utility boilers displays on the new characteristics of large-scale capacity, high parameters, varieties and auto-control in high degree. Nowadays, the situation for the transportation and supply of coal for power plants is still in tense. The actual coal qualities differ much from the design value, which will bring the challenges toward the design, operation and management of the units, together with the decrease of the safe reliability and economic performance. Considered the effects on design and operation of large-scale coal-fired utility boilers with changes of coal qualities, the effects of the different typical coals and the blended coals on combustion characteristics including the ignition, slagging characteristics and tendency were investigated in this paper, especially including the changes of the moisture, volatile, sulfur and ash content. At last, the comprehensive strategies towards the brought effects from the changes of coal qualities were presented, together with the relevant advice and solution.

Cao Yu-chun, Wang Zheng-wei

Syngas Production from Coal Gasification with CO2 Rich Gas Mixtures

Coal gasification with CO

2

rich gas mixture is one of several promising new technologies associated with CO

2

reduction in the atmosphere. Coal gasification with high CO

2

concentration is suitable for producing large amount of syngas. However, an increase in CO

2

concentration will result in lower gas temperature in the reactor. In this paper, a similar gas temperature profile in CO

2

/O

2

mixtures to that of coal gasification in air is predicted by observing the effects of CO

2

concentration. The coal gasification model considered in this calculation is composed of devolatilization model, char gasification model and gas phase reaction model. Reaction rate equation of n-th order type with the Random Pore Model is applied to the char gasification reaction. Influence of inlet particles size is also studied. It is found that 20 μm particles in 21% O

2

/79% O

2

and 100 μm particles in air (21% O

2

/79% N

2

) result in a similar gas temperature profile during coal gasification. The outlet gas mixture with the same calorific value as from air blown coal gasification can be obtained if air is replaced by 50% CO

2

/29% N

2

/21% O

2

mixtures

M. S. Alam, A. T. Wijayanta, K. Nakaso, J. Fukai

Numerical Study on the Stereo-Staged Combustion Properties of a 600 MWe Tangentially Fired Boiler

Numerical study of the combustion process and NO emission of a 600MWe tangentially fired boiler with stereo- staged combustion system were performed by Fluent 6.2 CFD software. The stereo-staged combustion technology is consist of horizontal bias combustion (HBC) burners, separated over fire air (SOFA), horizontal offset secondary air and pulverized coal reburning arrangement. The temperature field and the distribution of combustion species concentration in the furnace were gained as well as the aerodynamic field. The simulation results shows that stereo-staged combustion system can keep good combustion stability and the NOx emission of the boiler reduces significantly when the HBC burners and horizontal offset secondary air are adopted.

Zhengyang Wang, Shaozeng Sun, Lin Qian, Shun Meng, Yufei Tan

Evaluation of Sulfide Corrosion Conditions in Pulverized Coal Fired Thermal Power Plant Boilers

Due to cutbacks in operational costs, many pulverized coal fired thermal power plant boilers have recently been operating under conditions of in-furnace reduction atmosphere enhancement. As a result, stronger in-furnace reduction atmospheres have led to sulfide corrosion. CRIEPI has conducted a study to clarify correlations between boiler operation conditions and sulfide corrosion, and to develop effective sulfide corrosion countermeasures. This report therefore describes experimental and theoretical results of research into evaluation techniques for a sulfide corrosion environment, along with actual applied results of evaluation techniques for a sulfide corrosion environment using an in-furnace of an active boiler.

M. Morinaga, S. Najima, N. Wakabayashi, H. Shirai

Effect of Elbow Structure on Gas-Solid Separation and Flow Field Adjacent to the Exit of the Swirl Burner

An elbow is often used as the solid-gas separator in coal- fired burners. In this paper, four different elbow structures are selected and their effects on the gas solid separation and flow field adjacent to the burner exit are numerically studied. The axial, circumferential velocity distributions, the particle trajectory and the secondary flow are presented and discussed. Based on the simulation results, the solid separation and particle concentration distributions in the radial direction and along circumference remarkably depended on the elbow structure. The secondary flow could be found near the elbow and it also depends on the elbow structure. By modifying the elbow structure, for example, using the guidance plate could improve the elbow performance.

Bo Li, Hai Zhang, Yuxin Wu, Kai Cui, Hairui Yang, Junfu Lu

Numerical Study on the Impact of Varying Operation Conditions on NOx Emissions of Large-Scale Pulverized Coal-Fired Utility Boiler

For complying with the increasingly strengthened regulation on NOx emission from coal fired power plant, newly built large-scale pulverized coal-fired utility boilers are all installed with low-NOx combustion systems to low NOx emissions. Understanding the characteristics of the system is essential for fully utilizing the system without affecting the combustion performance. In the present work, computational fluid dynamics (CFD) approach was applied to simulate the combustion and NOx formation processes in the furnace of 1,000 MW ultra- supercritical boiler equipped with an advanced low-NOx combustion system so as to study the impacts of varying the operation conditions on its NOx emission as well as combustion characteristics. The combustion system is the Mitsuibishi Advanced Combustion Technology system consisting of six levels corner-fired pollution minimum (PM) coal burners and additional air to achieve air staging combustion. With the help of CFD simulation, the distributions of the combustion temperature and CO, O

2

and NO concentrations were calculated and analyzed. The main influential operation parameters studied include coal type, additional air flow rate, excess air level and mill groups in service. The CFD simulations indicated that the main reasons of the low NOx emission from this boiler are on two aspects: rationally organizing the combustion process to achieve relatively uniform temperature distribution and reducing combustion environment in the main combustion zone, and combining the utilizations of the large amount of additional air to achieve deep air stage and the low excess air level as well as PM burners. It was also found that varying the operational parameters had considerable effects on the performance of the combustion system.

Shen Yue-yun, Gao Xiao-tao, Zhang Ming-yao

Results from Trialling Aqueous NH3 Based Post Combustion Capture in a Pilot Plant at Munmorah Power Station: Desorption

Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO) and Delta Electricity have tested an aqueous ammonia based post combustion capture (PCC) process in a pilot plant at Munmorah black coal fired power station. This paper presents and discusses the experimental results obtained and primarily focuses on the desorption section.

A high purity of CO

2

product was obtained at the stripper gas outlet with the CO

2

volumetric concentration generally between 99–100% and the remainder being water and NH

3

. An increase in stripper pressure/temperature can lead to a decrease in NH

3

concentration in the CO

2

product. The NH

3

concentration can be controlled within 200 ppm without wash at a stripper pressure of 850 kPa (the maximum pressure tested) at a stripper gas outlet temperatures of 20–25°C. The solid precipitation occurred in the stripper condenser and reflux lines. Due to the low ammonia content in the solution, CO

2

content in the solution was low and generally more than 50% of regeneration energy was used to heat up the solvent under the pilot plant conditions. The lowest regeneration energy obtained from the pilot plant trials is 4–4.2 MJ/kg CO

2

captured. The effect of various parameters including solvent flow-rate and stripper temperature/pressure in the solvent on the regeneration energy was investigated.

Hai Yu, Scott Morgan, Andrew Allport, Aaron Cottrell, Thong Do, James McGregor, Leigh Wardhaugh, Paul Feron

Carbon Dioxide Capture and Storage (CCS)

Frontmatter

CO2 Capture Performance Using Limestone Modified with Propionate Acid During Calcium Looping Cycle

Limestone was modified with excessive propionate acid solution. The cyclic CO

2

capture performance of the modified limestone during calcium looping cycle was investigated using a thermo-gravimetric analyzer (TGA) and a twin fixed-bed calcination/carbonation reactor system. The results obtained prove that the modified limestone can be an effective sorbent for CO

2

capture at high temperature. The modified limestone exhibits obviously faster carbonation rate, and achieves higher carbonation conversion than the original one under the same reaction conditions. The optimum carbonation temperature for modified limestone is between 680 and 720°C. Higher calcination temperature can aggravate sintering of the sorbent during calcination periods. The modified limestone shows better anti-sintering properties than original one at high calcinations temperature. Long-term CO

2

capture capacity of the sorbent is enhanced by modification using propionate acid, resulting in a carbonation conversion of 0.31 for modified limestone after 100 cycles, while the value for original limestone is only 0.08. The surface morphology of the modified limestone after the first calcination is much more porous and the pores are more connective than that of the original one. A much better pore structure is kept after 100 cycles for modified limestone. It indicates that modified limestone is much more sintering- resistant than original one during cyclic reactions.

Sun Rongyue, Li Yingjie, Liu Hongling, Wu Shuimu, Lu Chunmei

Calcium Looping Technology Using Improved Stability Nanostructured Sorbent for Cyclic CO2 Capture

One of the post-combustion CO

2

capture technologies that have sufficiently been proved to be the best candidates for practical large scale post-combustion application is the calcium looping cycle. However, the CO

2

capture capacity of a calcium-based sorbent derived from natural limestone decays through long-term cyclic utilization; thus, the development of novel sorbents to achieve a high CO

2

capture capacity is an critical challenge for the calcium looping cycle technology. In this paper, we report the preparation and character of a new calcium-based sorbent produced via the combustion of a dry gel. The results show that the novel calcium-based sorbent has a much higher residual carbonation conversion as well as a better performance of anti-sintering when compared with the calcium-based sorbent derived from commercial micrometer grade CaCO

3

and nanometer grade CaCO

3

. It is reasonable to propose that the different final carbonation performances are induced by their different pore structures and BET surface areas rather than by different particle sizes. Compared with the commercial nano CaO, the morphology of the new sorbent shows a more rough porous appearance with hollow nanostructure. During carbonation, CO

2

diffused more easily through the hollow structure than through a solid structure to reach the unreacted CaO. Besides, there is less chance for the hollow nanostructured particles to be merged together during the high temperature reactions.

Cong Luo, Ying Zheng, Ning Ding, Chu-guang Zheng

Validation of CFD-Models for Non-stoichiometric Oxycoal Combustion

To compensate the drawback of high flue gas recirculation rates specific for oxyfuel processes, a new concept based on staged combustion, called controlled staging with non-stoichiometric burners (CSNB) was investigated. A combination of over- and sub-stoichiometric burners avoids inadmissible high flame temperatures even with oxygen concentrations up to 40 vol.-% in the oxidant. The non-stoichiometric burners are arranged in such a way that the overall stoichiometry at the combustion chamber outlet is slightly over-stoichiometric similar to conventional combustion processes, so that full burn out is secured. This concept aims at a more efficient oxyfuel process due to the decreasing effort in the recirculation loop and a new designed, more cost effective, steam generator. For further process optimization of the CSNB concept and the adjacent steam generator layout are validated CFD simulations urgently required. This paper shows first steps in validation of the CSNB combustion concept against state of the art CFD codes. The CFD code was optimized for oxyfuel combustion including a new char combustion and gas radiation model. Experimental investigations and CFD modelling are showing good agreement in concerns of temperature, CO and CO

2

profiles. However the prediction of the oxygen concentration differs significantly between experiment and simulation.

Jan-Peter Bohn, Adrian Goanta, Andreas Baumgartner, Maximilian Blume, Hartmut Spliethoff

Preparation and Application of the SGCS-Made CaO/ZrO2 Sorbent for Cyclic CO2 Capture

Calcium looping method was considered as one of the efficient and cost-effective options to mitigate CO

2

emission from coal combustion and gasification processes. The decay of CO

2

capture capacity for the CaO-based sorbent over multiple carbonation/calcination cycles is of a great concern and hinder its application in the realistic CO

2

capture process. A CaO-ZrO

2

sorbent was synthesized using the novel sol-gel combustion synthesis (SGCS) method and its reaction characteristics were further evaluated under the realistic condition, where the calcination temperature was set as 950°C and the clacination atmosphere adopted was pure CO

2

. The experimental results over 18 looping cycles for the synthetic CaO-ZrO

2

sorbents indicated that the decay of CO

2

capture and conversion under the realistic calcination condition was not avoided due to the severe sintering, and Ca8Zr2 should be preferred in the realistic CO

2

capture process with regard to its reaction characteristics (including its CO

2

capture capacity, conversion and deactivation constant) and economical factor. Finally, observation of the Ca8Zr2 sorbent over 18 cycles by FSEM (field emission scanning electron microscopy) revealed that the decaying of its CO

2

capture capacity was mainly resulted from the closure of mesopores present in the targeted sorbents.

Baowen Wang, Haibo Zhao, Ying Zheng, Zhaohui Liu, Chuguang Zheng

Simulation and Exergy Analysis of a 600 MWe Oxy-Combustion Pulverized Coal-Fired Power Plant

CO

2

emission from pulverized coal-fired power plants (PC) can be efficiently controlled by adopting the oxy-combustion technology, which adds a cryogenic air separation process (ASU) and a flue gas treatment process (FGU) to the conventional combustion process. To understand the thermodynamic properties of the oxy-combustion process, a simulation study and an exergy analysis of a 600 MWe oxy-combustion PC were conducted. The commercial flowsheet software Aspen Plus was used to simulate the process and the simulation results are the basis to perform the exergy analysis. The simulation results show that the CO

2

concentration in the flue gas from the oxy-combustion boiler can be more than 80 mol% and the CO

2

purity from the FGU can reach 99 mol%; the net efficiency of the oxy-combustion system is 10.84% (lower heating value) lower because of the power consumptions of the ASU and FGU processes; the unit power consumption for the oxygen production in the ASU is 0.247 kWh/kg-O

2

. The exergy analysis focused on the boiler models (oxy-combustion and conventional) and each of them was divided to be several parts, such as furnace, heat exchanger. The exergy analysis results show that the exergy efficiency of the oxy-combustion boiler is 0.8% higher than that of the conventional combustion boiler, the primary reason for this is the exergy efficiency of the combustion process in the oxy-combustion boiler is about 4% higher. In addition, water wall and air heater in any boiler model have very low exergy efficiencies.

Jie Xiong, Haibo Zhao, Meng Chen, Chuguang Zheng

The Plant for Co-production of Synfuel and Electricity with Reduced CO2 Emissions

Consideration is given to the prospective technologies for combined production of synthetic fuel (SF) and electricity. The mathematical models of plant for co-production of synfuel and electricity (PCSE) intended for combined production of electricity and synthesis of methanol and dimethyl ether or membrane-based hydrogen production from coal were developed. They were used in the optimization studies on the installations. As a result of the studies, the design characteristics for the plant elements, the relationships between the SF and electricity productions, etc. were determined. These data were used to identify the ranges of SF price for various prices of fuel, electricity and equipment, and estimate the profitability of SF production. Special attention is paid to modeling of CO

2

removal system as part of PCSE and studies on PCSE optimization. The account is taken of additional capital investments and power consumption in the systems.

A. M. Kler, E. A. Tyurina, A. S. Mednikov

Reactor Design, Cold-Model Experiment and CFD Modeling for Chemical Looping Combustion

Chemical looping combustion (CLC) is an efficient, clean and cheap technology for CO

2

capture, and an interconnected fluidized bed is more appropriate solution for CLC. This paper aims to design a reactor system for CLC, carry out cold-model experiment of the system, and model fuel reactor using commercial CFD software. As for the CLC system, the air reactor (AR) is designed as a fast fluidized bed while the fuel reactor (FR) is a bubbling bed; a cyclone is used for solid separation of the AR exit flow. The AR and FR are separated by two U-type loop seals to remain gas sealed. Considered the chemical kinetics of oxygen carrier, fluid dynamics, pressure balance and mass balance of the system simultaneously, some key design parameters of a CH

4

-fueled and Fe

2

O

3

/Al

2

O

3

-based CLC reactor (thermal power of 50 kWth) are determined, including key geometric parameters (reactor cross-sectional area and reactor height) and operation parameters (bed material quantity, solid circulation rate, apparent gas velocity of each reactor). A cold-model bench having same geometric parameters with its prototype is built up to study the effects of various operation conditions (including gas velocity in the reactors and loop seals, and bed material height, etc.) on the solids circulation rate, gas leakage, and pressure balance. It is witnessed the cold-model system is able to meet special requirements for CLC system such as gas sealing between AR and FR, the circulation rate and particles residence time. Furthermore, the thermal FR reactor with oxygen carrier of Fe

2

O

3

/Al

2

O

3

and fuel of CH

4

is simulated by commercial CFD solver FLUENT. It is found that for the design case the combustion efficiency of CH

4

reaches 88.2%. A few part of methane is unburned due to fast, large bubbles rising through the reactor.

Shaohua Zhang, Jinchen Ma, Xintao Hu, Haibo Zhao, Baowen Wang, Chuguang Zheng

The Influence of Included Minerals on the Intrinsic Reactivity of Chars Prepared Under N2 and CO2 Environment

Oxy-fuel technology could be successfully used to retrofit existing coal-fired power plants or alternatively be used to design and build new coal-fired power plants with almost zero emissions. Char reactivity under oxy-fuel conditions will have a significant impact on the coal burnout.

In this paper, two fractions, representing organic-rich particles and organic particles with included minerals, were separated from each of three Chinese coals of different rank. They were then devolatilized at 1,450°C in a drop tube furnace (DTF) under N

2

and CO

2

environment, respectively. The chars were subjected to nitrogen adsorption study, thermogravimetric analysis and XRD analysis.

It was found that char reactivity of all three pairs of chars were increased under CO

2

environment as compared with that under N

2

environment, but with differing trend. For the organic-rich samples the reactivity difference is increased with decreasing rank. On the contrary, for the samples of organic particles with included minerals, the reactivity difference is decreased with decreasing rank.

Mechanism analysis showed that they are resulted not from gasification, but from a combination of changes in surface area and in the orderness of carbon structure in the chars, both of which, in turn, are resulted from the higher heat capacity of CO

2

and the interaction between metastable liquid phase and the included minerals.

Hong Zhang, Huan Li, Jiabao Chen, Bo Zhao, Guangzhou Hu

Comparisons of Ash Particle Properties Under Air and Oxy Coal Combustion in a 25 kW One-Dimensional Down Fired Furnace

A 25 kW one-dimensional down fired furnace was operating in air (O

2

/N

2

) and oxy (O

2

/CO

2

) combustion conditions respectively. A typical Chinese bituminous coal was burned in this experiment. The furnace operation can be switched between air and oxy conditions freely. The real flue gas recycling was performed but not one through system. The recycle ratio defined as the mass fraction of recycled flue gas to the whole flue gas amount is 77.8% (dry basis) here. Comparisons of ash particle properties under these two different combustion conditions were carried out in this work. The particle matters were sampled in flue gas cooling zone (Port 10) by a self-designed two stages nitrogen dilution water cooled sampling probe. The fly ash particle size distribution results measured by mastersizer 2000 show that the fly ash formed under oxy combustion condition is smaller than those formed under air combustion condition. The elements mass fraction of PM

1

show different characteristics under these two conditions. The microscopic analysis confirm differences between air and oxy coal combustion considering burning bulk atmosphere, heat transfer, molecule diffusion and radiation.

G. D. Li, S. Q. Li, M. Dong, R. L. Axelbaum, Q. Yao

Reactivation Properties of Carbide Slag as a CO2 Sorbent During Calcination/Carbonation Cycles

The carbide slag from polyvinyl chloride production as industry hazardous wastes was proposed as CO

2

sorbent at high temperature in calcium looping cycle. The cyclic CO

2

capture behavior and the microstructure characteristics of the carbide slag as one of the typical calcium-based industrial wastes during the multiple calcination/carbonation cycles. Also, the comparisons between the carbide slag and the natural limestone in cyclic CO

2

capture behavior were made. XRD analysis demonstrates that the predominating constituent of the carbide slag is Ca(OH)

2

. The carbonation temperature ranging from 650 to 700°C is favourable to cyclic carbonation of the carbide slag. The cyclic carbonation conversions of the carbide slag is lower than that of the limestone before a certain time, but the situation is converse after that time in a thermogravimetric analyzer. The carbide slag has better cyclic CO

2

capture capacity. The carbonation conversion of the carbide slag retains 0.28 after 100 calcination/carbonation cycles, while the two limestones achieve 0.08 and 0.14 respectively at the same reaction conditions in a dual fixed-bed reactor. The microstructure of the carbide slag by SEM reveals the reason why it possesses better CO

2

capture capacity.

Yingjie Li, Rongyue Sun, Hongling Liu, Chunmei Lu

The Effects of De-humidification and O2 Direct Injection in Oxy-PC Combustion

This study is aimed to derive effects of de-humidification and O

2

direct injection in oxy-PC combustion system. Temperature distribution and flue gas composition were observed for various air and oxy-fuel conditions such as effect of various O

2

concentration of total oxidant, O

2

concentration of primary stream and O

2

direct injection through 0-D heat and mass balance calculation and experiments in the oxy-PC combustion system of 0.3 MW scale in KITECH (Korea Institute of Industrial Technology). Flame attachment characteristic related to O

2

direct injection was also observed experimentally. We found that FEGT (furnace exit gas temperature) of 100% de-humidification to oxidizer is lower than humidification condition; difference between two conditions is lower than 20°C in all cases. The efficiency changing of combustion was negligible in O

2

direct injection. But O

2

direct injection should be carefully designed to produce a stable flame.

C. G. Choi, I. H. Na, J. W. Lee, T. Y. Chae, W. Yang

Progress Update of the Air Blown IGCC and Gasification Plant

From the viewpoint of energy security and global warming issues, the integrated coal gasification combined cycle (IGCC), a highly efficient coal-based power generation system, is regarded as an effective clean coal technology that is close to commercialization. Combination of the IGCC with CO

2

capture and storage technology has been planned; this concept further attracts people looking for ways to reduce CO

2

emissions. As one of the leading company in the field of IGCC reducing CO

2

emission, Mitsubishi Heavy Industries, Ltd. (MHI) is now in a position of actively undertaking its realization with an integration of two stage entrained bed air-blown coal gasifier, which achieves the highest net plant efficiency by using air as the gasification agent, and high temperature combustion turbines. This paper will discuss the latest activities MHI have been taking at the 250 MW IGCC demonstration plant in Nakoso, Japan and air-blown IGCC commercial plant projects using high temperature combustion turbines. As a future vision to the carbon constrained world, MHI’s perspective on upcoming technologies like higher temperature combustion turbines represented by “J”-type, 1,700°C-class will be introduced.

Takao Hashimoto, Koichi Sakamoto, Hiromi Ishii

Photocatalytic Reduction of CO2 Over Sol-Gel Derived Copper-Doped Titania Catalysts

Different doping concentration of copper-doped titania was synthesized by sol-gel method, and the samples were characterized by X-ray diffraction (XRD); Field emission scanning electron microscope (FSEM-EDX); Specific surface area and Pore size analyzer (BET); Thermo gravimetric-differential thermal analyzer (TG-DTA) respectively. The photocatalytic reduction of CO

2

experiments was carried out in a photocatalytic reactor. CO

2

was discharged into a quartz reactor with catalyst suspended in NaHCO

3

solution, and illuminated under UV irradiation at the wavelength of 253.7 nm for 10 h continuously. The results confirmed that in the copper modified TiO

2

samples, the crystalline form of TiO

2

exists as anatase; only on the high CuO loading sample (>10%), the CuO peaks appears obviously; the grain size of all the sol-gel derived CuO-TiO

2

samples were nearly 30 nm, and the copper particles were consistent and dispersed on the surface of TiO

2

. CO

2

can be reduced into methanol in the presence of NaHCO

3

solution over CuO-TiO

2

catalyst. The doping concentration of 5% CuO-TiO

2

performed best catalytic effect, with the methanol yield of 27 mg (g-cata)

−1

in 10 h. With increasing reaction time, yield of methanol was promoted.

Chong Tian, Yongchun Zhao, Junying Zhang, Chuguang Zheng

Comparison of Three Mineral Candidates in Middle and Low-Pressure Condition: Experimental Study

“Greenhouse Effect”, which is scientifically proven to be main caused by the increasing concentration of CO

2

, has become a topic of national and international concern. Mineral carbonation, such as carbonation of alkaline silicate Ca/Mg minerals, analogous to natural weathering processes, is a potentially attractive route to mitigate possible global warming on the basis of industrial imitation of natural weathering processes. In this paper, three typical natural mineral candidates in China, serpentine, olivine and wollastonite, were selected as carbonation raw materials for direct mineral carbonation experiments under middle and low-pressure. A series number of experiments were carried out to investigate the factors that influence the conversion of carbonation reaction, such as reaction temperature, reaction pressure, particle size, solution composition and pretreatment. The solid products from carbonation experiments were filtered, collected, dried and analyzed by X-ray diffraction (XRD) and field scanning electron microscopy equipped with energy dispersive X-ray analysis (FSEM-EDX) to identify the reaction of mineral carbonation. And the method of mass equilibrium after heat decomposition was used to calculate the mineral carbonation conversion. All the XRD and FSEM analysis validate that carbonation reaction was occurred during the experiments and mineral carbonation is one of the potential techniques for carbon dioxide sequestration. The data of mass equilibrium after heat decomposition was collected and then the conversion formula was used to calculate the carbonation conversion of all the three mineral candidates. The mass equilibrium results show that, for all of the three mineral materials, the carbonation conversion increases with the increasing of reaction temperature. But once the temperature increases above 150°C, the conversion of serpentine decreases a little. Reaction pressure is also an important factor to mineral carbonation process. For all of the three mineral materials, the carbonation conversion increases with the increasing of reaction pressure. Decrease of mineral particle sizes and use of heat treatment before carbonation experiments can effectively improve the carbonation conversion of mineral carbonation. And the addition of NaHCO

3

, which had a buffering effect that kept the solution pH in a certain range, can also improve the carbonation conversion. In this paper, a highest carbonation conversion of 89.5% was obtained under the condition of T = 150°C,

$$ {{\text{P}}_{{{\rm{C}}{{\rm{O}}_2}}}} $$

= 4.0 MPa, particle sizes <37 μm in 1 h using wollastonite as the raw material. Compared with serpentine and olivine, wollastonite is the most promising material for carbon dioxide mineral carbonation under middle and low-pressure.

Heng Yan, Jun-ying Zhang, Yong-chun Zhao, Zhi-liang Wang, Xia Pan, Jun Xu, Chu-guang Zheng

Numerical Investigation on IRZ Dimension and Optimization of a 0.3 MWt Swirl Oxy-Firing Flame in High Confinements

In oxy-coal combustion, the Internal Recirculation Zone (IRZ) can effectively improve the flame stability and propagation. Therefore, it is necessary to investigate both the formation of the IRZ and the optimization of the oxy-firing flame in high confinements. The present work investigates the primary four factors which significantly affect the formation of the IRZ and the optimization of the oxy-firing flames. These factors include the V-type flame holder, the secondary stream (SS) swirl number, the recycle ratio, the oxygen pressure fraction in the primary stream (PS). The numerical object is a new swirling oxy-burner for the 0.3 MWt pilot-scale facility in HUST. In the procedure of the numerical investigation, the important chemical reaction scheme needs to be considered for oxy-firing flames, including the four-step global reaction mechanism in the Finite-Rate and Eddy-Dissipation (FRED) model and the gasification reactions with H

2

O and CO

2

. The conclusions are that these four factors significantly affect the formation of the IRZ and the optimization of a 0.3 MWt swirl oxy-firing flame can be obtained in high confinements. Both the pressure fraction of oxygen in PS and the recycle ratio can seriously affect the flame stability and propagation. The V-type flame hold can significantly affect the maximum recirculation rate (

q

mr

/

q

m0

)

max

. The maximum IRZ dimension can significantly keep the flame stability and propagation. Correspondingly, the stabilized flame belongs to the Flame type-II.

Jingzhang Liu, Sheng Chen, Zhaohui Liu, Ke Peng, Nan Zhou, Xiaohong Huang, Tai Zhang, Chuguang Zheng

Thermal Degradation of Ethanolamine in CO2 Capture with SO2

Amine degradation in the absorption/stripping process is one of the concerns in this technology. SO

2

is reported to promote amine degradation in both bench scale and pilot scale. This work investigates the impact of SO

2

on thermal degradation of MEA by preloading additives, which are Na

2

SO

3

, SO

2

and H

2

SO

4

. 7 m (mol/kg H

2

O) MEA with 0.4 CO

2

loading (mol CO

2

/mol MEA) at 135°C is the baseline condition. Initial sulfur concentration is 0.4 m in the experiments with additives. The experiment temperature varied from 120 to 150°C. Neither sulfite nor sulfate has significant impact on MEA degradation rate in thermal condition. There is no different cation product in the samples with additives compared to the baseline experiment. The main process of MEA thermal degradation is still carbamate polymerizing. Ammonium was induced by sulfite. The main organic acid product is formate for all the experiment conditions, while there are new anion products with sulfite. Formate formation was promoted by H

2

SO

4

. Ammonium and formate formation were promoted at higher temperature.

S. Zhou, S. Wang, C. Chen, X. Xu

Effect of Combustion Characteristics on Wall Radiative Heat Flux in a 100 MWe Oxy-Coal Combustion Plant

Oxy-coal combustion exhibits different reaction, flow and heat transfer characteristics from air-coal combustion due to different properties of oxidizer and flue gas composition. This study investigated the wall radiative heat flux (WRHF) of air- and oxy-coal combustion in a simple hexahedral furnace and in a 100 MWe single-wall-fired boiler using computational modeling. The hexahedral furnace had similar operation conditions with the boiler, but the coal combustion was ignored by prescribing the gas properties after complete combustion at the inlet. The concentrations of O

2

in the oxidizers ranging between 26 and 30% and different flue gas recirculation (FGR) methods were considered in the furnace.

In the hexahedral furnace, the oxy-coal case with 28% of O

2

and wet FGR had a similar value of T

af

with the air-coal combustion case, but its WRHF was 12% higher. The mixed FGR case with about 27% O

2

in the oxidizer exhibited the WRHF similar to the air-coal case. During the actual combustion in the 100 MWe boiler using mixed FGR, the reduced volumetric flow rates in the oxy-coal cases lowered the swirl strength of the burners. This stretched the flames and moved the high temperature region farther to the downstream. Due to this reason, the case with 30% O

2

in the oxidizers achieved a WRHF close to that of air-coal combustion, although its adiabatic flame temperature (T

af

) and WHRF predicted in the simplified hexahedral furnace was 103 K and 10% higher, respectively. Therefore, the combustion characteristics and temperature distribution significantly influences the WRHF, which should be assessed to determine the ideal operating conditions of oxy- coal combustion. The choice of the weighted sum of gray gases model (WSGGM) was not critical in the large coal-fired boiler.

S. Park, C. Ryu, T. Y. Chae, W. Yang, Y. Kim, S. Lee, S. Seo

Study of Limestone Thermal Decomposition in O2/CO2 Atmosphere

Oxygen-enriched fluidized bed combustion is a new technology which can realize CO

2

zero emission, enhance the combustion efficiency and reduce pollutants emission. Due to the high concentration of CO

2

, the technology has many different aspects in limestone thermal decomposition and calcium-based desulfurization compared with conventional combustion. In this article, experiments have been done to investigate the behavior and mechanism of limestone thermal decomposition by a thermogravimetric analyser (TGA). It was observed that the limestone specialities of physical properties, pore structure, impurities categories and content have an important influence on the decomposition properties. The present of CO

2

increase the limestone decomposition temperature, and shorten the time length of complete decomposition; especially in low CO

2

concentration atmosphere. When the CO

2

concentration was above 40%, the most probable decomposition mechanism transformed from nuclear producing and growing process (G(α) = [−ln (1 − α)]

3/2

) to fast chemical reaction process (G(α) = (1 − α)

−1

− 1), and the value of E increase linearly with rise in the CO

2

concentration. A rise in heating rate increase the limestone decomposition temperature because of the hysteresis effects of heat transfer, and the effect become more severe with the heating rate increasing. The small limestone particle is easier to decompose completely by the fine heat transfer property in interior of the particle. In the decomposition process, two countering effects of calcination and sintering must be considered in the practical application.

L. N. Tian, H. P. Chen, H. P. Yang, X. H. Wang, S. H. Zhang

Life Cycle Analysis of CO2 Control Technology: Comparison of Coal-Fired Power with Renewable Energy Power

Based on life cycle assessment, the paper assessed the CO

2

avoided cost and cost of electricity (COE) of the power generation technologies, including coal-fired power plant with CO

2

capture and storage (CCS), wind power, solar PV, and biomass-fired power plant. The results show that COE, CO

2

avoided cost of 800 MW USCPC + CCS is competitive comparing with renewable energy power. COE of USCPC + CCS is almost same with that of wind power, and much lower than that of biomass and solar PV. CO

2

avoided cost of USCPC with CCS is a little higher than that of wind power, and much lower than that of biomass and solar PV

Shujuan Wang, Yinying Chen, Ping Zhong, Li Jia, Yingxin Zhu

Dual Phase Sorbents for High Temperature Air Separation

Ceramic sorbents based on combined perovskite/spinel structure have been investigated for their potential use in oxygen- enriched CO

2

stream production. Oxides of strontium and barium doped with cobalt and iron were chosen for this study. X-ray diffraction studies revealed a dual-phase structure containing perovskite and spinel systems. Microstructure observed by SEM showed the spinel phase as intergrowth structure in the dominantly perovskite phase. Thermogravimetric studies show a higher desorption rate and sorption capacity compared to the similar perovskite sorbents which with a lower CO

2

uptake can produce an optimum sorbent material for air separation in oxyfuel power generation. Sintering temperature also showed an effect on oxygen sorptive/desorptive properties. Improved properties can be explained based on the defect chemistry of the new structure.

Mehdi M. Alipour, Rajender Gupta, John Nychka

Prediction of Heat Recovery Characteristics of Oxyfuel Combustion Boiler Using CFD

Oxyfuel combustion is one of the promising technologies to reduce CO

2

emission from pulverized coal fired power plant. In order to apply this technology to the commercial boiler, it is important to predict the boiler performance (especially heat recovery characteristics) in Oxyfuel combustion condition. In this study, prediction of heat recovery characteristics of Oxyfuel combustion boiler using CFD was conducted. As a result, it was shown that the same boiler performance can be achieved in Oxyfuel combustion mode as that in Air combustion mode.

Makoto Takafuji, Toshiyuki Suda, Takamasa Ito, Toshihiko Yamada

Development of Binder-Supported CaSO4 Oxygen Carriers for Chemical Looping Combustion of Methane

Chemical-looping combustion (CLC) has been recognized as an energy-efficient method for CO

2

capture. From thermodynamics point of view, CaSO

4

has a good availability in the cycle of CLC system. The inhibition of the poor mechanical strength and reactivity is fatal to a CLC system based on calcium sulfate (CaSO

4

). In this study, three important parameters (binder, acetic acid, and water) were selected as factors of the L

9

orthogonal experiment designed to investigate the performance of the binder-supported CaSO

4

oxygen carriers by intuitive analysis. Then, the suitable oxygen carriers were comprehensively studied in a fixed bed reactor. The orthogonal experiment results showed that adding binder enhanced the mechanical strength and increased the conversion of the binder-supported CaSO

4

, and the optimal extrusion condition was: 30 g CaSO

4

, 12 g SB powder (sticky pseudo-boehmite), 2.5 ml acetic acid, and 15 ml water. The results of reduction reactivity showed the conversion and mass-based reaction rates of the binder-supported CaSO

4

were obviously enhanced. Moreover, the favorable performance of the binder-supported CaSO

4

was explained by formation of CaAl

2

O

4

. This compound was excellent thermal stability and provided a stable nanosized framework between the crystal grains observed by field emission scanning electron microscope.

Ning Ding, Ying Zheng, Cong Luo, Guan Bian, Peifang Fu, Chuguang Zheng

Effects of SO2/NO on CO2 Capture Characteristics of K2CO3/Al2O3 in a Bubbling Fluidized-Bed Reactor

CO

2

capture from flue gas with SO

2

or NO using K

2

CO

3

/Al

2

O

3

was investigated in a bubbling fluidized-bed reactor. Carbonation and regeneration temperature was 60 and 350°C respectively. The products after carbonation or regeneration process were detected with XRD and barium sulfate gravimetric method. In addition, the physical properties of the sorbent such as granule morphology, S or N element distribution were measured by SEM-EDX. The five cycle test shows that when the carbonation reaction gas contains SO

2

, sulfur compounds were generated, which reduces the utilization ratio of K

2

CO

3

, the amount of CO

2

captured in carbonation process and released in regeneration progress decreased with the circulation times. Element S distributes on the particle surface uniformly and the sulfur content of the product is approximate to the input amount of SO

2

. When the carbonation reaction gas contains NO, the amount of CO

2

captured in carbonation process and released in regeneration progress changed little, XRD and SEM-EDX analysis confirmed that nitrogen compound or element N was not detected in the product. It can be concluded that NO does not react with the sorbent while SO

2

has great effect on the sorbent (K

2

CO

3

/Al

2

O

3

). A 48 times cycle test with different concentration of SO

2

and NO in the carbonation reaction gas was conducted, the failure ratio of the sorbent changed when carbonation reaction gases contains different concentration of the acid gas. After the 48 times circulation test, nitrogen compound or element N was not detected in the products.

Ye Wu, Xiaoping Chen, Chuanwen Zhao, Wei Dong

Cyclic CO2 Capture Performance of Carbide Slag: Parametric Study

In this work, CO

2

capture performance of carbide slag has been investigated in a thermogravimetric analyzer (TGA). Effects of operation parameters including particle size, reaction temperature and reaction duration on CO

2

capture capacity were studied. The experimental results indicate that the increase of particle size ranging from 80 to 180 μm has a positive effect on the CO

2

capture capacity of carbide slag. The sorbent reactivity decreases with an increase of calcination temperature. The prolonged exposure to carbonation conditions has a beneficial effect on sorbent behavior as a function of the number of calcination/carbonation cycles; however, the duration in the calcination step has little effect. Based on the experimental results, the reaction rate constant of carbonation reaction is obtained from Jander equation. It is found that it decreases with the increasing cycles.

Deng-Feng Zhang, Peng-Fei Zhao, Song-Geng Li, Wen-Li Song

Ignition and Combustion Characteristics of Different Rank Coals in O2/CO2 Environments

Previous works on flame stability and stand-off distance under oxy-coal combustion conditions has been conducted with a co-axial turbulent diffusion burner for different rank coals in a 100 kW pulverized coal test rig at the University of Utah. The pilot-scale results indicate that oxygen partial pressure and coal compositions have a significant effect on the ignition and flame stability of coal particles in the oxy-coal combustion. The aim of the present paper is to investigate the ignition and combustion characteristics of three different rank coals at variable oxygen partial pressures in O

2

/N

2

and O

2

/CO

2

environments by Thermo-gravimetric Analyzer (TGA). The experimental results reveal the significant difference of the devolatilization, ignition and combustion properties between three rank coals in O

2

/CO

2

environments. It could provide fundamental understanding on pulverized coal combustion in O

2

/CO

2

environments and elucidate the effect of coal compositions on the ignition and flame stability in pilot-scale oxy-coal combustion.

Yuegui Zhou, Wei Chu, Guangjin Gu, Yangyang Xu, Jost O. L. Wendt

Experimental Study on Efficient Absorption of Carbon Dioxide from Simulation Flue Gas by Rotary Packed Bed

The remove efficiency of carbon dioxide from simulation flue gas containing 15% CO

2

by the aqueous solutions containing methyldiethanolamine (MDEA) and Triethylenetetramine (TETA) in a rotating packed bed was investigated in this study. The absorption efficiency was assessed in terms of rotating speed and packed height that was found to be a strong function. The obtained results indicated that the CO

2

absorption efficiency in a rotating packed bed was observed to be more effective than that in a traditional packed tower, implying a great potential of rotating packed bed applied to the reduction of the greenhouse gas CO

2

from the flue gas.

Lijuan He, Jieqiong Li, Lifeng Chen, Yanling Ni, Gangyi Xu, Yuxiang Zhang, Wenfei Wu

Hydrodynamic Analysis of a Three-Fluidized Bed Reactor Cold Flow Model for Chemical Looping Hydrogen Generation: Pressure Characteristics

Chemical looping hydrogen generation (CLHG) can produce pure hydrogen with inherent separation of CO

2

from fossils fuel. The process involves a metal oxide, as an oxygen carrier, such as iron oxide. The CLHG system consists of three reactors: a fuel reactor (FR), a steam reactor (SR) and an air reactor (AR). In the FR, the fuel gases react with iron oxides (hematite Fe

2

O

3

, magnetite Fe

3

O

4

, wüstite FeO), generating reduced iron oxides (FeO or even Fe), and with full conversion of gaseous fuels, pure CO

2

can be obtained after cooling the flue gas from the fuel reactor; in the SR, FeO and Fe reacts with steam to generate magnetite (Fe

3

O

4

) and H

2

, the latter representing the final target product of the process; in the AR, the magnetite is oxidized back to hematite which is used in another cycle.

A cold flow model of three-fluidized bed for CLHG corresponding to 50 KW hot units has been built. A major novelty of this facility is the compact fuel reactor, which integrates a bubble and a fast fluidized bed to avoid the incomplete conversion of the fuel gas caused by the thermodynamics equilibrium. In order to study the pressure characteristics and the solids concentration of the system, especially in the fuel reactor, the gas velocity of three reactors, gas flow of L-type value, total solids inventory (TSI) and the secondary air of fuel reactor were varied. Results show that the pressure and the solids concentration are strongly influenced by the fluidizing-gas velocity of three reactors. Moreover, the entrainment of the upper part of fuel reactor increases as the total solids inventory increases, and the operating range of the FR can be changed by introducing secondary air or increasing the total solids inventory.

Zhipeng Xue, Wenguo Xiang, Shiyi Chen, Dong Wang

Techno-Economic Analysis of Lignite Fuelled IGCC with CO2 Capture: Comparing Fluidized Bed and Entrained Flow Gasifiers

Integrated coal gasification combined cycle (IGCC) plants with pre-combustion capture of CO

2

represent one of the most promising options for generating low-cost decarbonized power using bituminous coals. This work systematically quantify the effect of coal rank on the efficiency and economics of IGCC systems with CO

2

capture and storage (CCS), with a special focus on comparison of systems using fluidized-bed gasifier (U-GAS) and entrained flow gasifier (Shell). It was found that the Shell IGCCs are little affect by low rank coal after pre-drying in terms of thermal efficiency and the levelized cost of electricity (LCOE) is only increase by 2–6% for lignite cases with and without CCS compared with bituminous coal cases. The specific CO

2

emissions of U-GAS gasifier based lignite fuelled IGCC with CCS is 198 g/kWhe, almost two times of shell gasifier cases, mainly due to lower carbon conversion in the gasifier and the higher methane in the raw gas of gasifier. However, the total capital cost and COE of U-Gas IGCCs are 15–20% less than that of Shell IGCCs because of lower capital cost of gasifier, coal drying units and air separate units per kWe.

Guangjian Liu, Zhen Wu, Haiying Zhang

Study on CO2 Absorption Enhancement by Adding Active Carbon Particles into MEA Solution

The chemical absorption of CO

2

is generally recognized as the most efficient post-combustion technology of CO

2

separation at present. A study on CO

2

absorption enhancement by adding small particles of active carbon into MEA solution is investigated within a self-designed glass stirring tank. Experiments of different particle loadings and different particle sizes have been conducted. When active carbon particle concentration is fewer, compared to the absorption rate of CO

2

gas absorbed by MEA aqueous solution, the role of active carbon adsorption CO

2

gas is negligible. The enhancement efficiency of CO

2

absorption could be improved by 10% to the upmost in this liquid-particle system.

Juan Qian, Rui Sun, Lian Ma, Shaozeng Sun

Comparison of CO2 Fixation in Spent Oil Sand Between Experiment and Simulation

Global Warming caused by the Greenhouse gas has become a serious global issue due to the increasing in the use of fossil fuel and it is being exhausted. Recently, a great deal of research is being carried out to develop alternatives to fossil fuels. The oil sands have become one of the alternative energy sources. However, it is composed of about 10% bitumen and the rest becomes waste. Moreover, oil sands need a large amount of natural gas to provide heat and steam for bitumen extraction. In this study, it has been focused on the satisfaction both CO

2

reduction and waste disposal by using spent oil sand after extraction bitumen from oil sand. Additionally, Aspen Plus was used to simulate to know about its carbonation reactivity. First, we analyzed the analysis of spent oil sand and discovered that it is of mostly composed of SiO

2

, so it needs pretreatment with CaO aqueous solution. After the pretreatment, it is performed by changes in temperature and pressure. The optimum is decided 500°C, 25 atm and reduced rate of mass was calculated 21.92% about carbonation reactivity by using simulation.

Dure Han, Dongha Jang, Yeongshin Jeon, Hyungtaek Kim

Attrition and Cyclic CO2 Capture of CaO Pellets with Aluminates Under Pressurized Carbonation

Recent attempts to improve the attrition resistance and CO

2

uptake of Ca-based sorbent by making pellets with aluminates have succeeded in enhancing their effectiveness. The effects of parameters on sorbent attrition were investigated. Batch experiments were also conducted in a fluidized bed at optimal reaction conditions from previous studies (Carbonation: 0.5 MPa and 700°C in 15% CO

2

/air balance for 15 min; Calcination: 0.1 MPa and 950°C in air for 10 min). The pore structure characteristics (BET, BJH) were measured as a supplement to the attrition and reaction studies. Results showed that the mechanical property of the pellets with the particle size of 1.0–1.43 mm were greatly enhanced, especially for the pellet made from CaO-0.5% CLS. A slow decay in CO

2

capture capacity of the sorbents was observed after making pellets during the first few cycles. It was attributed to attrition of sorbents and the exposure of inner core of the CaO sorbents, which are in favor of CO

2

capture. The pore structure showed that its BJH pore volume and BET surface area did not change much, which benefits CO

2

uptake of the sorbents during the cycling.

H. C. Chen, C. S. Zhao, Y. M. Yang, P. P. Zhang

Application and Demonstration of Oxyfuel Combustion Technologies to the Existing Power Plant in Australia

Oxyfuel combustion is able to directly make the highly concentrated CO

2

from the flue gas of pulverized coal fired power plant and, therefore, is expected as one of the promising technologies for CO

2

capture. We are advancing the Oxyfuel combustion demonstration project, which is called Callide Oxyfuel Project, with the support of both Australian and Japanese governments. Currently the boiler retrofit work is completed and the commissioning in air combustion is going on. In this paper, we introduce the general outline of the Callide Oxyfuel Project and its progress.

Terutoshi Uchida, Toshihiko Yamada, Shuzo Watanabe, Takashi Kiga, Takahiro Gotou, Nobuhiro Misawa, Chris Spero

Backmatter

Additional information