Skip to main content
main-content

2022 | Buch

Clean Coal and Sustainable Energy

Proceedings of the 9th International Symposium on Coal Combustion

herausgegeben von: Prof. Junfu Lyu, Prof. Shuiqing Li

Verlag: Springer Singapore

Buchreihe: Environmental Science and Engineering

share
TEILEN
insite
SUCHEN

Über dieses Buch

This book gathers the proceedings of the 9th International Symposium on Coal Combustion, held in Qingdao, China in July 2019. It provides the latest research results on techniques for pulverized coal combustion and fluidized bed combustion, low-carbon energy and emission controls, and industrial applications. Highlighting research areas that are of great importance in promoting collaboration between related subjects and the technical development of coal-related fields, the book offers a valuable reference guide for researchers and engineers alike.

Inhaltsverzeichnis

Frontmatter

Invited Talks

Frontmatter
Chapter 1. Advances in Two-Fluid LES of Two-Phase Combustion

Recently, large-eddy simulation (LES) was used to study spray-air and coal-air two-phase combustion. Most LES of two-phase combustion takes Eulerian–Lagrangian approach, which needs much more computational time than the Eulerian-Eulerian (E-E) or two-fluid approach. A few studies on E-E LESof two-phase combustion were reported in the literature. In this paper at first previous studies are reviewed. Then, the mathematical models for two-fluid LES of two-phase combustion, proposed by the present author are presented, including filtered controlling equations, specific for full two-fluid and two-fluid-Lagrangian approaches, a two-phase sub-grid scale (SGS) stress model and a SGS combustion model. For the SGS stress model, the present author proposes a two-phase SGS energy equation model, accounting for the interaction between two phases. For the gas-phase combustion model, a second-order moment SGS (SOM-SGS) turbulence-chemistry model, proposed by the present author, is suggested to simulate gas-phase (liquid-fuel vapor or CO and coal-volatile) combustion. Also, for coal combustion, the coal pyrolization and char combustion models are used. These sub-models are separately assessed by comparison with experiments.

L. X. Zhou
Chapter 2. Flexible Operation of High Efficiency Coal Power Plants to Ensure Grid Stability When Intermittent Renewables Are Included

The introduction of intermittent renewables such as wind and solar has created a major integration problem that has to be addressed to ensure operational stability for power generation grid systems. While there is some expectation that large scale batteries may provide a solution, this still appears to be far from commercial viability. Consequently, in most cases coal fired power generation has needed to adapt to a new operating regime so that there is adequate energy system stability. This includes being able to achieve, at low minimum load, rapid ramp rates and cycling together with fast start-up. Flexible operation can have significant impact on a coal power plant with most components being affected. This is because of the increase in thermal and mechanical fatigue stresses in the different parts of the plant, which together with corrosion, differential expansion and other effects, often occurring in synergy, reduce the life time of many plant components. There has been considerable development work undertaken to counter these adverse effects while balancing the grid, including new technologies, processes and skills. There are several means to achieve low minimum load combustion, with the critical need to maintain stable combustion. These include the need to understand and mitigate the technical limitations to low burning rates, such as fire stability, flame monitoring, and minimising unburned coal and CO emissions. Fire stability itself depends on many factors, such as changes in firing rate or fuel quality, inaccurate fuel/air ratio or uneven coal flow. Another impact to consider is the effect of low load operation on downstream NOx control systems and connected equipment. Measures for achieving minimum load include ensuring coal quality, air/fuel flow optimisation and coal fineness, operation with a reduced number of mills or smaller mills, indirect firing, thermal energy storage for feedwater heating, tilting burners, reliable flame scanners and economiser modifications. Start-up procedures are complex and expensive as they usually require auxiliary fuel such as gas or oil, during burners the ignition period. Start-up times in power plants can be shortened through application of reliable ignition, turbine integration, reduced thickness of walls in boiler and turbine design, external heating of boiler thick wall components, measures in the turbine (sliding pressure, advanced sealings, steam cooling of the outer casting), proactive cleaning of boiler deposits plus more effective instrumentation and control. Measures to improve high ramp up rates include exploring mill storage capacity, use of a dynamic classifier instead of a static one; measures in the turbine such as opening of throttled main steam valves, condensate throttling, thermal storage for feedwater heater bypass and HP stage bypass, lower thicknesses of pressure parts, and increased number of headers. Preservation during standby periods is important including targeted plant chemistry management of the boiler and turbine. These and other issues are considered and examples presented.

Andrew Minchener
Chapter 3. Advances in Modeling Coal Pyrolysis, Char Combustion, and Soot Formation from Coal and Biomass Tar

Simulations of pulverized coal boilers and gasifiers have become easier and more complex as computational resources become more available. The improvements in simulations have generally focused on the fluid dynamics and grid resolution, with marginal improvements in treatments of the fundamental coal reactions. In this work, suggestions are made in several areas to improve boiler and gasifier simulations with only relatively small impacts on computational time. New correlations are presented for the elemental composition of coal char and tar as a function of parent coal characteristics, temperature, and heating rate. The importance and correlation of char oxidation effects are discussed. A new generalized model for soot formation, oxidation, and gasification is also discussed.

Thomas H. Fletcher, David O. Lignell, Alex Josephson, Andrew Richards, Troy Holland
Chapter 4. The Change in Bed Materials Size Distribution and Its Effect on CFB Boiler Operation

When burning solid fuels in circulating fluidized bed boilers (CFB), it is important to ensure a large multiplicity of particle circulation along the loop of the furnace–cyclone–return system. The high flow rate of circulating particles determines the uniformity of the temperature field along the height of the furnace, ensures temperature equalization along the bed section, which is especially important for large CFB boilers with a furnace section of 200 and more m2. The size of circulating particles is determined by the efficiency of capture in the cyclone, the higher it is, the smaller the average particle size. It is believed that a well-operated CFB boiler has an average size of circulating particles less than 0.2 and even 0.15 mm. Another factor determining the bed material size distribution is the effective removal of bottom ash, which is especially important for high-ash fuels. The first in Russia large CFB boiler of unit #9 of Novocherkassk TPP has some problems with overly large part of course particles in the bed. The report presents the characteristics of the fuel, bed material and circulating ash compositions. The estimate of circulating flow rate was made. The main characteristics of the boiler, including the temperature field and estimation of circulating flow rate are presented. Special attention is paid to the regimes with the addition of limestone and fly ash. The operating date of changes in the chemical and particle size distribution (PSD) of ash streams is presented. According to results of the study of changes in ash composition, it can be concluded that the composition of fly and circulating ash varies quite rapidly and reaches design values after 10 h (according to CaO). In bottom ash the PSD varies slowly (the order of magnitude is 50 h). It is possible that the fractional composition of bed material also varies slowly. The simplified model for calculation of changes in bed material size distribution after start-up of the boiler is presented. It takes into account the initial composition of sand and coal supplied. The calculation is carried out to determine the specific removal of particles from the bed. The capture efficiency is calculated by dependences of VTI and corrected taking into account published data and results of experiments. According to experimental data, the coefficients of bed material size distribution and the removed bottom ash are introduced. According to the results of calculations, it is shown that for the available fuel fractional composition, the number of large fractions increases over time. The addition of limestone leads to an increase in fractions with sizes of 0.1–0.2 mm. the Best results are obtained when feeding coal with sizes less than 5 mm.

G. A. Ryabov, O. M. Folomeev
Chapter 5. Insights of MILD Combustion from High-Fidelity Simulations

Simulation of coal combustion remains challenging due to the many physical processes involved which span a large range of length and time scales. Although detailed models exist for devolatilization, char oxidation and gas-phase kinetics, most simulation efforts simplify these models considerably to reduce the high cost of simulation. Three mixture fraction-based chemistry models are evaluated, namely, the steady laminar flamelet, equilibrium, and Burke-Schumann models in the scope of coal volatiles combustion. Coal volatiles are assumed to be composed of “light gasses” (CH $$_4$$ 4 , CO, etc.) as well as tar, which refers to the various large aromatic compounds released during the devolatilization process. Here, tar is treated as a single empirical species. Each mixture fraction-based model is evaluated by comparing predicted gas phase properties to computations using finite-rate chemistry with a detailed reaction model. The results indicate that the reconstructions for gas phase temperature and composition from steady flamelet model is the most accurate. The Burke-Schumann chemistry model performed very poorly for predicting the gas phase temperature and composition under stoichiometric conditions. We apply the steady laminar flamelet model to Moderate or Intense Low Oxygen Dilution (MILD) combustion. A key requirement for MILD combustion is that mixing rates are sufficiently fast that gas-phase chemistry occurs nearly volumetrically, eliminating visible flame structures. A Well-stirred reactor assumption is applied to MILD combustion due to its characteristic of volumetric reactions. The necessary conditions to achieve MILD combustion, including recirculation rate of flue gas and heat loss, are determined under various mixture fractions and mass fractions of light gas in the fuel stream. We conclude that the increasing the recirculation rate and heat loss are helpful for achieving MILD regime. Additionally, we observe that the recirculation rate and heat loss values required to achieve MILD combustion increase as the fuel stream is enriched in light gases. Steady flamelet computations reveal that MILD combustion can be achieved when reactants are not well-mixed as long as the scalar dissipation rate is sufficiently large. Our considerations indicate that the steady laminar flamelet model provides a reliable method to model MILD combustion in the absence of well-mixed reactants.

Hang Zhou, Josh McConnell, Terry A. Ring, James C. Sutherland

Basic Coal Quality and Combustion

Frontmatter
Chapter 6. Study on Alkali Metal Migration Characteristics in the Pyrolysis of Naomaohu Coal in CO Atmosphere

The four-step chemical extraction method was used for stepwise extraction to compare the occurrence of alkali metals in Naomaohu coal and the other four types of high alkali coal. The coal sample was placed in a vertical furnace with CO gas atmosphere to study the migration and release law of alkali metal with temperature changing at 400–800 °C. The results show that sodium in the Naomaohu coal is mainly in the form of water-soluble sodium, while potassium is mainly composed of insoluble potassium and organic potassium. The increase of pyrolysis temperature promotes the release of sodium and potassium, and the water-soluble sodium changes to insoluble sodium, and a substitution reaction occurs between sodium and potassium. At 700 °C, the amount of sodium and potassium released from the coal char is relatively reduced, resulting in enrichment.

Peipei Gao, Junjie Fan, Zhiyuan Ren
Chapter 7. Precipitation Characteristics of Alkali/Alkaline Earth Metal in High Alkali Coal

Serious problems of fouling and slagging occurred in combustion of high alkali coal. As the physical and chemical characteristics of coal ash may change at different ashing temperature (AT). The investigation on the precipitation characteristics of alkali/alkaline earth metal (AAEM) in high alkali coal is important for the safety and stable operation of the boilers. To understand the effect of AT on AAEM precipitation characteristics, four different coals were selected as samples. For each coal, three coal ashes were acquired at 200 °C/500 °C/815 °C respectively. X-ray fluorescence spectroscopy (XRF) and Inductively Coupled Plasma Optical Emission (ICP-OES) were applied for the elementary analysis of ash. The test results indicated that ash yields and alkali contents in coal ash decrease while alkaline earth metal content changes little as AT increases. The precipitation temperature of chlorine is lower than 500 °C, and chlorine is substantially completely precipitated before 815 °C. The precipitation characteristic of Na is closely related to the content of chlorine in the coal. Low-temperature ashing will cause carbon burnout problems for high ash coals while the relative error of alkali metal measurement is limited. The test results of ICP-OES on element content in same sample is lower than XRF. However, the elemental content changes with AT are similar between two measurement results. It is recommended to use the ICP-OES test method when measuring AAEM content due to its higher precision.

Hang Shi, Yuxin Wu, Junfu Lyu, Man Zhang, Hai Zhang
Chapter 8. Experimental Study on Removal of Low Concentration Coal Tar in Syngas by Mg-Ca Composite Catalyst

The catalytic cracking of low concentration coal tar in syngas was studied using Mg-Ca composite catalyst. The reaction was carried out in a two-stage fixed bed reactor. The effects of bed temperature (400–800 ℃), catalyst particle size (400–600 μm, 200–400 μm, 100–200 μm, and <75 μm) and catalyst layer height in bed reactor on tar conversion, pyrolysis gas products (CO, H2, CO2, CH4), and the CO2 absorption by CaO in catalyst were investigated. The results showed that the cracking rate of coal tar vapor increased with the increasing of bed temperature, till reaching a maximum of 94% at 700 ℃. The production of H2 also increased with temperature, and the amount of CO2 in the gaseous products decreased between 500 and 700℃ responding to the CO2 absorption capacity of CaO reaching its peak in this temperature range. The absorbed CO2 subsequently released at higher temperatures. The catalytic cracking rate was highest when the catalyst particle size was 100–200 µm, and the catalytic cracking efficiency increased with the increasing of catalyst layer height and reaction time. These results demonstrate that when the catalyst particle size is too small (<75 µm) or the reaction temperature is too high (>700 ℃), the catalyst activity for coal tar cracking is reduced.

Liang Wenzheng, Yan Hao, Li Yanhui, Cui Weiwei, Cong Xiaochun, Wang Cuiping
Chapter 9. Experimental Investigation on Sodium Migration and Mineral Transformation in Ash Deposit During Gasification of Zhundong Coal Using a Drop Tube Furnace

Zhundong coal has attracted an ever-increasing concern due to its super-huge reserve but high content of alkali metals. Volatilized into the gaseous phase during the gasification process, alkali metals are extremely unfavorable for coal utilization. Gasification technology can promote the large-scale utilization of high-alkali coal. However, few efforts, if any, have been conducted on gasification of Zhundong coal. The present study aimed to elucidate the sodium migration and mineral transformation characteristics in coal ash deposition process under different gasification conditions, while the behavior of sodium migration and mineral transformation were further analyzed using Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-OES), X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques. In this paper, the sodium migration characteristics in gasification process under different conditions were investigated by adding three sodium salts (NaCl, Na2CO3 and Na2SO4), kaolin and diatomite into coal, respectively. The effects of ash deposition time on sodium migration and mineral transformation characteristics in ash were also explored. The experimental results showed that the addition of sodium salt could increase the sodium content in the ash to a large extent. Kaolin and diatomite could solidify alkali metals in the gaseous phase during gasification process. As the ash accumulation time increased, the minerals such as chlorine, sulphur, and iron in the gaseous phase were easily bonded to the surface of the ash and reacted to form other crystal phases. The present study can provide guidance for the utilization of Zhundong coal and benefit the development of clean coal technology.

Chengchang Liu, Chang’an Wang, Chaowei Wang, Yongbo Du, Guantao Tang, Guangyu Li, Defu Che
Chapter 10. Study on Characteristics and Influencing Factors of Coal-Water Slurry Pyrolysis

The distribution, composition and yield of coal-water slurry pyrolysis products have an important impact on the efficient combustion/gasification of coal-water slurry. In this paper, the coal-water slurry made of Shenmu coal (bituminous coal) is rapidly pyrolyzed by a high-frequency heating furnace, and the yield, composition and composition of pyrolysis gas were measured and analyzed. The effects of pyrolysis temperature, heating rate and residence time on the pyrolysis characteristics of coal-water slurry were studied. The results have shown that as the temperature increases, the yields of volatile matters and pyrolysis gas continue to increase. The compositions of pyrolysis gas are mainly H2, CO, CH4 and CO2. With the increase of temperature, the yields of H2, CO and CH4 increase first and then decrease, and peaks appear at around 1100 ℃. The CO yield continues to increase with increasing temperature. The rate of temperature increase affects the yield of volatiles. The research results provide a reference for understanding and mastering the formation characteristics of primary pyrolysis products of coal-water slurry.

Fan Feng, Boyang Li, Juan Yu, Yao Zhang, Chen Lin, Zhongxiao Zhang
Chapter 11. Soot Formation in High-Temperature Pyrolysis of Various Coals

Soot formed during high temperature pyrolysis or incomplete combustion, has strong effects on human health and the environment, as well as radiation heat transfer during combustion. Most studies on soot formation are focused on gas combustion, while the studies of soot formation during solid fuel combustion are rarely reported. In this study, the formation and properties of soot particles from coal pyrolysis are investigated in a drop tube furnace at 1000–1300 °C. The soot morphology, number size distribution, ignition characteristics, gas composition and soot-ash composition were characterized with transmission electron microscopy, scanning mobility particle sizer, thermogravimetric analyzer, gas chromatography, and energy disperse spectroscopy. The effect of coal rank on soot formation and yield is mainly discussed. The results show that with the increase of pyrolysis temperature, the soot yield increases. The soot yields show no dependent relationship with the coal ranks. Among the five kinds of coal tested (anthracite, lean coal, bituminous coal, lignite, and high sodium coal), bituminous coal has a much higher soot yield (>7.5%) than that of other coals (0.5–2%). The oxidation reactivity of soot particles from high sodium coal pyrolysis is much higher than that from other coals, because of the high contents of alkali and alkaline earth metals in soot particles.

Shengjie Bai, Yongbing Wang, Gaofeng Dai, Peng Li, Xuebin Wang
Chapter 12. Effect of Microstructures on Char Combustion Reactivity

Reaction of char dominates the combustion of coal in terms of the time scale and heat release, thus study on the reactivity of char is essential. Some researchers found that the coal char combustion reactivity is the function of its microstructure and the devolatilization temperature. However, in the related reported studies, the coal types used in the experiments were limited. Therefore, in this paper series of systematic experiments were conducted with 12 types of coal, including anthracite, bituminous, lean coal and lignite, and the volatile matter content ranges from 5 to 55%. The char samples were prepared in the muffle furnace in ambient atmosphere at 900 °C. The thermogravimetry analyzer (TGA) was employed to evaluate the char combustion reactivity. Moreover, the microstructure of the char was measured by X-Ray Diffraction (XRD). The experimental results indicate that the combustion reactivity of chars decreases with increasing graphitization degree. And an obvious liner relationship between fa and Tmax/E was found.

Jingyuan Li, Lele Feng, Yiqun Huang, Yang Zhang, Lyu Junfu, Man Zhang
Chapter 13. Effect of K2CO3 Addition on CO2 Gasification Characteristics and Ash Sintering Behaviour of a Chinese Lignite at Different Temperatures and Pressures as Examined Using a High-Pressure Thermogravimetric Analyser

The gasification characteristics and the morphology of the residue ash from pressurised K2CO3-catalysed gasification of a Chinese lignite in CO2 was investigated using a High-Pressure Thermogravimetric Analyser operating at pressure of 2.0 or 3.5 MPa and temperature between 750 and 900 °C for at least 2 h, after being heated from room temperature at 10 °C/min. The K2CO3 addition was varied from 0 to 10% w/w. Gasification characteristics of the K2CO3-doped lignite was determined by analysing the weight loss and conversion rate as a function of time whereas the ash morphology was analysed by using SEM–EDS. Results showed that at 3.5 MPa the in-situ weight loss of the lignite increased as K2CO3 addition ratio increased, suggesting that K2CO3 addition promoted lignite gasification. The conversion rate of the lignite correspondingly increased from 61 to 92% as the temperature elevated to 750 °C. An increase in the final temperature to 900 °C significantly promoted lignite gasification when K2CO3 was less than 5%, however this was not obvious for lignite with 10% K2CO3 addition. This is because the conversion rate of the lignite with 10% K2CO3 addition had exceeded 90% before the final temperature of 900 °C was reached. Furthermore, as pressure decreased from 3.5 to 2.0 MPa, the lignite gasification rate slowed down, with or without K2CO3 addition. Conversion rate of the lignite decreased from 61 to 42% while the temperature initially elevated to 750 °C. SEM–EDS analysis revealed that sintering of the lignite ash was not observed at 750 °C, but became apparent at 1% K2CO3 addition. The degree of ash sintering further aggravated at 5 and 10% K2CO3 addition. As the temperature increased from 750 to 900 °C, the ashes of the raw lignite and 1% K2CO3 doped-lignite remained largely similar, whereas the sizes of the 10% K2CO3-doped lignite ash was increased and the particle surfaces became smooth, suggesting an enhanced sintering of the ash. The formation of K-aluminosilicate and Ca-aluminosilicate of low-melting points in the ash was responsible for possible deactivation of the doped catalyst K2CO3 and the observed ash behaviour.

Jianbo Li, Zhezi Zhang, Jian Hao, Jiguang Zhang, Mingming Zhu, Dongke Zhang
Chapter 14. Ash Deposition and Slagging Behavior of Xinjiang High-Alkali Coal in a 20MWth Cyclone Combustion Test Facility

The high content of AAEMs (alkali and alkaline earth metals) in ash as well as its relating serious ash fouling slagging problems are the main reason for the unit boiler, which cannot absolutely fully use high-alkali coal at full generating capacity. In order to fully use those kinds of coal, the cyclone-fired boiler with slagging tap is induced in this paper. The ash melting behavior as well as the migration and transformation characteristics of AAEMs during cyclone-fired process were performed in a 20MWth cyclone combustion test facility. A number of slagging and deposit samples at different locations of boiler were selected and analyzed by using XRF, XRD and SEM–EDX analysis. The experimental results showed that the slag in cyclone burner contains higher content of Fe2O3, around 37.5–52.6 wt%, which is about 2.4 and 3.5 times than that of their parent coal ash. The content of Na2O in slag is around 2.3–8.6 wt%, especially for the slag at location C, D and E, where can provide sufficient reaction time and contact area between flue gas and slag. The main existence form of sodium is Na–Al–Si eutectic compounds and being completely melted in cyclone with smooth surface. For the deposit ash on convective tubes, some Na–Al–Si and Ca–Mg–Si low melting eutectic compounds have a rounded boundary in the main particles due to the low melting temperature and low viscosity, which can adhere to the surface of other ash particles to agglomerate each other.

Xiaojiang Wu, Yigong Zhou, Yezhu Sun, Zhongxiao Zhang, Mingqiang Li, Xiang Zhang, Kai Yan, Yuehua Li, Nan Chen, Xinglei Hu
Chapter 15. Release Characteristics of Alkali Metals in Oxygen-Enriched Combustion of a Single Char Particle with Random Pore Model

Alkali metals released from pulverized coal combustion and gasification are one of the important causes of ash-related problems, such as fouling, slagging, corrosion and atmospheric pollution. To investigate the release characteristics of alkali metals, a theoretical model was developed for the combustion of single char particle based on Random Pore Model (RPM). The particle burnout time, combustion temperature, and NaCl release characteristics of this model were verified with previous experimental results. The combustion of char particle with the size of 50–100 μm was then calculated using this model at the ambient temperature range of 1373 to 1573 K in two different gas atmospheres, i.e. O2/N2 and O2/CO2 atmospheres. The oxygen content in O2/N2 and O2/CO2 atmospheres varied from 21% to 100% and 50% to 100%, respectively. When comparing with char combustion in O2/N2 atmosphere, the particle burnout time and temperature both decreased in O2/CO2 atmosphere, which was also found to be beneficial to the control of alkali metals release. The simulation results showed that smaller particle size, higher temperature, and oxygen-enriched condition promoted char combustion, but in regard of alkali metals release control lower temperature was preferred.

Sibo Qu, Haiming Wang, Changfu You
Chapter 16. Experimental Study on the Influence of Slagging and Fouling for Wall Temperature Distribution

Coal is still the main fossil fuel for power plants in China, and heat resistance ratio of the fly ash slag and fouling layer is the key weight ratio for super-heaters and re-heaters with coal fired boiler. Actually the slagging and fouling layers happened on the fireside surface of tubes are not uniform in the circumferential direction. To explore the influence level of the smoke flow on the slagging and fouling distribution, a tower type furnace facility was established, and the influence of slagging and fouling of a horizontal tube for the wall temperature distribution was studied. Meanwhile, the heat transfer model of clean tube and stained tube was established. A comparative study of clean tube surface and stained tube surface temperature distribution was conducted. The results showed that the wall temperature distribution with slagging and fouling was totally different with the clean condition. And the heat flux distribution of the clean tube was a single-humped curve, but the stained tube showed the double humped curve in the circumferential direction.

Deli Li, Enlu Wang, Jinda Mao, Wei Wu, Kai Li, Qi Wang
Chapter 17. Numerical Investigation of Fly Ash Deposition onto Tube Bundles Inside Coal-Fired Boilers

The particle-laden flow across tube arrays is numerically investigated as a model problem of ash deposition onto the convection heat transfer surfaces inside practical boilers. The transverse pitch ratio is found to significantly affect the impaction efficiency onto each tube. For the frontmost tube, a decrease in the transverse pitch ratio enhances the impaction efficiency of fly ash particle of all sizes. Then, the downstream tubes are more frequently exposed to fine particles. Nevertheless, a small transverse pitch ratio makes it possible for coarse mode particles to reach the second- and third-row tubes in the adjacent column after rebound from the front tube. Finally, a comparison between experiments and simulation implies that the existing sticking/rebound model may overestimate the ash fouling rate.

Yipeng Li, Qian Huang, Lu Duan, Shuiqing Li
Chapter 18. Effect of Refractory Lining Thickness on Slag Layer Behavior in Cyclone Barrel

The cyclone-fired boiler has attracted much attention in recently yeares. The thickness of the refractory lining is closely related to the slag behavior which is of great importance for the operation of the cyclone-fired barrel. In this paper, the slag layer behavior in the cyclone barrel is investagated numerically when the refractory lining thickness is constant or varied. The results show that the refractory lining has a great effect on its surface temperature. Besides, the refractory lining should not be too thick to ensure the presence of the solid slag layer at the high temperature zone of the cyclone barrel. Therefore, in the cyclone barrel, the thickness of the refractory lining of the air inlets sections can be increased to reduce the heat dissipation, whereas the thickness of the refractory lining of the outlet section can be reduced to obtain a solid slag layer thick enough to prevent the erosion of the refractory lining. The proposed scheme with variable thickenss of the refractory lining is proved effective by the numerical simulation.

Chunli Tang, Yueyi Hu, Tao Zhu, Limin Wang, Yanhua Liu, Defu Che
Chapter 19. Characteristics of Alkali Metal Migration and Transformation During Pyrolysis of Naomaohu Coal

The control of Na and K content plays important role on the quality of oil and gas from high alkali coal in Xinjiang. Effect of temperature on the migration and transformation characteristics of alkali metals within Naomaohu coal was investigated on a fixed-bed pyrolysis experimental platform under reducing atmosphere. The results show that Na in the raw coal mainly exists in H2O-soluble form, and K mainly exists in insoluble form. When the pyrolysis temperature is lower than 600 ℃, the H2O-soluble Na changes to insoluble Na as the temperature increases. However, when the temperature is higher than 600 ℃, the proportion of H2O-soluble Na to insoluble Na decreases, and the content of H2O-soluble Na increases with the, the relatively decreasing of insoluble Na. Under lower temperature conditions, the acid-soluble K content increases with the transformation of large numbers of insoluble K in the coal. When the temperature is higher than 600 ℃, the decrease rate of insoluble K becomes slow down, and the content of H2O-soluble K increases. In addition, the released Na and K mainly present in the tar, and the content in the gas is relatively small.

Junjie Fan, Jiaxiao Deng, Zhiyuan Ren, Jianli Wang

Pulverized Coal Combustion

Frontmatter
Chapter 20. Numerical Investigation on Combustion Characteristics and NOx Emission of Double-Reheat Tower Boiler at Different Loads

In this study, a three-dimensional numerical investigation using a finite volume method is presented to obtain the velocity, temperature, and species distributions in a 660 MW double-reheat tower boiler fed with bituminous coal. The refined oxidation model of HCN and NO-char reaction model were used to substitute the default model by the user-defined functions (UDFs). The effects of different loads and excess air ratios on combustion characteristics and NOx emission were studied numerically. The results show that temperature distribution is more uneven at the upper part of the furnace and the NOx emission increases as the load decreases. The temperature distributions in the furnace have little differences under three different excess air ratios. That the oxygen concentration increases significantly as the increase of excess air ratios leads to an increase of NOx emission at the furnace outlet. The minimum NOx concentration at the furnace outlet, 308 ppm, appears under 100% THA with excess air ratio of 1.15. The simulation results in this study can provide reference for optimization of combustion characteristics in double-reheat tower boiler and illustrate a method to reduce NOx emission.

Yan Zhang, Shihao Ma, Jin Guo, Yuesheng Li, Zhengrong Zhu, Jiaqi He, Lei Deng, Defu Che
Chapter 21. Numerical Study on Influence of Platen Super-Heaters on Heat Deviation in a 600 MW Tangentially Fired Pulverized-Coal Boiler

In order to investigate effects of platen super-heaters on the heat deviation in the cross-over pass, numerical simulation of a 600 MW tangentially fired pulverized-coal boiler has been studied. Two cases, building super-heaters or not, were established by FLUENT software in this study. Numerical results agree well with measured data of the utility boiler. Results show platen super-heaters break symmetry of velocity distribution at the furnace outlet. The position where peak temperature occurs is affected by platen super-heaters, while the position where peak velocity occurs is not. Platen super-heaters slightly reduce the temperature deviation at the furnace outlet, and enhances the velocity deviation at the furnace outlet. For this boiler, the velocity deviation is the main reason for the heat deviation in the cross-over pass. The simulation results in this study can provide reference for optimization of temperature deviation and velocity deviation in tangentially fired pulverized-coal boiler.

Kai Chen, Yan Zhang, Lei Deng, Defu Che
Chapter 22. Industrial Experimental and Numerical Simulation Study on the Combustion and NOx Formation Characteristics in a 600MWe Utility Boiler with a Novel Swirl Burner Burning Bituminous Coal

To minimize the NOx formation, a novel low-NOx swirl pulverized-coal combustion technology characterized by the annulus recirculation was proposed by the Harbin Boiler Company Limited. By employing the industrial experiments to study the combustion and NOx formation characteristics in a 600MWe utility boiler burning the bituminous coal, and simultaneously using the Reynolds Stress turbulence model and the Realizable k-ε model to reveal the in-burner flow characteristics and the full-scale combustion characteristics in the 600MWe utility boiler. The numerical results were in good consistent with the experimental results. The results show that an obvious annular recirculation zone is generated in the axial direction at the burner outlet zone. The recirculation zone brings the high-temperature flue gas back to the near burner zone and heats the primary coal/air flow, which promotes the pulverized coal ignition and maintains the flame stability. Additaionaly, the recirculating high temperature gas has the lowest oxygen content, is thus beneficial to the NOx reduction. On reducing the blade angles of the inner and outer secondary air from 65° to 30°. The size of the recirculation zone is gradually reduced, the entraining capacity of the flue gas weakens, the coal ignition is simultaneously delayed. The oxygen contents in the main combustion zone increase, associated with the gradually weakened reducing atmosphere. The NOx content is increased by 8.5%, while the CO content and carbon in fly ash are slightly reduced. While the blade angles becomes larger, the outlet flow field of the burner is easy to fly, and the water wall is prone to coking、high temperature corrosion, etc. It is recommended that the blade angle of the inner and outer secondary air is set to 45° in the actual boiler operation. The numerical results show that due to the combined combustion effect of the secondary air and the pulverized coal, the combustion performance fluctuates. As the newly injected overfire air in the burnout zone, under the combined effects of the oxygen concentration and the high-temperature flue gas, the combustion performance under each case varies less, and the influence degree of adjusting the inner secondary air blade angle is greater than that of the outer secondary air.

Tao Shen, Zhengqi Li, Pisi Lu, Qiang Yu, Xin Song, Jingyu guan
Chapter 23. Distribution of Temperature and Characteristics of Soot Volume Fraction in MILD-OCC Flame

Coal and methane were burnt in the MILD-OCC combustion flame under different combustion conditions to study the temperature distribution and characteristics of soot volume fraction. In this experiment, the flame temperature distribution is measured by thermocouple and the volume fraction (fv) of soot at each sampling point is calculated, then combining with the mass concentration of soot by the filter weighing method to obtain the distribution characteristics of soot in the flame. The results of thermocouple particle densitometry (TPD) show that the formation and oxidation of soot at every point in the flame is related closely to its position and temperature in the flame. The fv of soot in the center of the flame is negatively correlated with the temperature of the flame during the MILD-OCC combustion. The lower temperature region of the flame is conducive to the growth of soot, which leads to higher value of fv. The higher temperature in the center of the flame is beneficial to the oxidation of the soot particles, resulting to lower value of fv. The results of the filter membrane weighing method show that the formation of soot mainly occurs in the central region of the flame. When the radial distance increases, the flame temperature rises, and the soot concentration decreases due to oxidation. On the whole, the distribution of soot measured by the filter membrane weighing method is roughly consistent with that calculated by the TPD, which provides a reference for further research on the MILD-OCC combustion.

Jingwen Lu, Shuwei Zhang, Longhui Tan, Jianyi Lu
Chapter 24. Experimental Investigation of Methane Assisted Pulverized Coal Flames Using an Optical Accessible Combustion Chamber

The formation of inhalabe fine particles (dp $${ \le\,\, 10 \mu {\text{m}}}$$ ≤ 10 μ m ) is an undesirable side effect of solid fuel combustion processes. These particles can accumulate in the human respiratory system and thus cause severe lung damage. Therefore, an understanding of the formation of these particles is of crucial importance to avoid or reduce the amount of fine particulate matter released into the atmosphere. For the investigation of particulate matter formation, a swirled methane assisted pulverized coal combustion test rig was developed, which allows intrusive and non-intrusive measurements to be performed during the combustion process. Within the scope of this work, the developed test rig is described and results of laser Doppler velocimetry (LDV) measurement are presented. The velocity measurements were performed at different height levels of the flame to investigate the flame structure. Within this study, it is shown that the experimental setup achieves stable and reproducible combustion conditions to allow detailed investigations in further works.

C. Axt, D. Zabrodiec, S. Pielsticker, T. Kreitzberg, O. Hatzfeld, R. Kneer
Chapter 25. Ignition Characteristics of Coal/Air Jets from Rectangular Nozzles

The ignition characteristics of pulverized coal-air jets from rectangular nozzles with different aspect ratios (ARs) were studied using a Hencken type entrained flow reactor. High-speed cameras and Mie scattering technique were employed to record the instantaneous flame images and particle motions under different exit velocities and coal concentrations of the primary air flow. The results revealed that similar to the gas flames, the flame length of the coal-air jet first increases and then decreases with increasing Re and finally barely changes when the flow is fully turbulent. For a coal/air flow from a rectangular nozzle, compared with the one from a round nozzle, the transient Re from laminar to turbulent for the rectangular jets is smaller. In the transient region, the flame length is obviously shorter at the same Re. The dissipation of large eddies is faster on the wide side, and the appearance of large eddy structure is delayed on both sides as the coal concentration increases. The simulation results show that for a rectangular nozzle the ignition of the coal jet begins on the two narrow sides, while for a round nozzle, coal jet ignition starts from the surrounding shear layers uniformly.

Lilin Hu, Pengyuan Liu, Yang Zhang, Lele Feng, Yuxin Wu, Junfu Lyu, Hai Zhang
Chapter 26. Numerical Simulation on Pulverized Coal Combustion Chamber with Air Cooling

To investigate the relationship between the temperature distribution in the air-cooled combustor, flame shape and gas distribution ratio, 3D modeling of 14 MW air-cooled combustor and its corresponding furnace was constructed and a series of numerical simulation cases were conducted in this article. The results show that: At the constant excess air ratio, the average temperature in the combustion chamber and the wall temperature both decrease with the increase of internal secondary air ratio. When the internal secondary air ratio is in the range of 0.3–0.4, the wall temperature is relatively high. The highest wall temperature is 930 K, which appears when the internal secondary air ratio is 0.4. When the internal/external secondary air ratio is 0.5/0.5, the flame fullness is at the highest value, which is an appropriate operating condition.

Yongying Wang, Naiji Wang, Shi Yang
Chapter 27. Effect of Inner/Outer Secondary Air Mass Flow Rate on the Airflow Characteristics of the 14-MW Double Cone Burner

The double cone burner is the only coal-fired burner in China that utilizes a annular reverse structure and has been industrialized. Cold airflow experiments on a 1:2 scaled model burner was preformed. Testo 425-hot wire anemometer was used to measure the cold aerodynamic characteristics of the double cone burner. Results show that with increasing the inner secondary air ratio, the length of the recirculation zone has not changed; The width of the recirculation zone does not change substantially without the cone, but it tends to generally increase with increaseing of the inner secondary air ratio with the cone; The shape of the recirculation zone is always a ring structure. When the cone is added, the axial dimensionless mean velocity becomes larger than that without the cone, but the jet profile becomes smaller. In both cases with and without the cone, the axial dimensionless mean velocity near the center of the burner is negative due to the reverse injection of the primary air into the cone.

Nan Jia, Fang Niu, Pengzhong Liu, Pengtao Wang, Jianming Zhou
Chapter 28. Theoretical Analyses on Isolated Particle Ignition of Coal and Biomass

In this paper, an improved transient ignition model is used to study the ignition differences between coal and biomass particles, including ignition time and modes. Using the inflection condition for particle temperature, the heterogeneous ignition time can be determined. Meanwhile, the spatial gas phase temperature distribution can also indicate the homogeneous ignition time. The calculation has evaluated the particle ignition characteristics, with ambient temperature from 1200 to 1800 K, particle diameter from 2000 to 40 μm and oxygen mole fractions in the range of 10–30%. It can be found that heterogeneous ignition always occurs first for the range of coal particles from 40 to 100 μm with temperature increases from 1200 to 1800 K. Compared with small coal particles, 500–2000 μm biomass particle usually ignites homogeneously. The 500 μm biomass particles ignite almost at the same time with coal particles in pc boiler. The changing behavior of ignition temperature is also investigated in this work. The ignition temperatures of small coal particles are all around 1000 K, while ignition temperatures of big biomass particles vary from 650 to 500 K. In the end, the spatial gas temperature and oxygen species distribution are also used to characterize the particle ignition.

Ye Yuan, Hongpei Gao, Zhenghai Shi, Xianbin Sun, Ping Xiao, Shisen Xu, Shuiqing Li
Chapter 29. Numerical Simulation on Combustion Characteristics of Co-Firing Biomass Syngas and Coal in a 660 MW Utility Tower Boiler

Utilize the biomass energy and adopt carbon capture and storage technologies could reduce the CO2 emission effectively. Biomass gasification is an effective ways to use the biomass. Co-firing biomass syngas with pulverized coal under oxy-fuel condition in utility boiler can combine the two advantages to reduce the CO2 emission. In this paper, a new proposed combustion mechanism was used to investigate the combustion characteristics of co-firing different types biomass syngas and coal in a 660 MW double reheat tower boiler. The influence of syngas composition and oxy-fuel condition on temperature distributions and flue gas components was analyzed when total input heat of the boiler was steady. The results show that the temperature and the emission of the NO and CO2 decrease in co-firing conditions, the NO mass concentration reduced up to 10.2% in co-firing cases. Biomass syngas with higher H2 and less CO and CH4 composition contributes to lower CO2 emission and higher boiler temperature, which can improve plant performance. The oxy-fuel condition also affects the combustion characteristics to some extent. With the increase of O2 volume fraction, the temperature increases and the O2 consumption decreases. Moreover, the NO mass concentration increases in oxy-fuel combustion when co-firing biomass syngas and coal with a mixing ratio of 0.1. This study offers reference for boiler’s operation and design optimization for biomass syngas co-firing.

Shihao Ma, Yan Zhang, Zhengrong Zhu, Lei Deng, Defu Che
Chapter 30. Deactivation of V2O5–WO3–TiO2 SCR Catalyst by HF During Co-Firing Electrolytic Aluminum Waste with Coal

Fluorine-containing waste from the electrolytic aluminum industry would cause environmental pollutions if the waste is improperly disposed. It is important and urgent to develop a harmless treatment method for the waste. In this paper, co-firing electrolytic aluminum waste with coal was studied. And the deactivation of V2O5–WO3–TiO2 SCR catalyst by HF was investigated by a lab-scale experimental system. The results show that HF is harmful to the catalyst. The denitrification efficiency of catalyst sample which treated by flue gas with HF is reduced. The denitrification efficiency of sample increases with increasing work temperature and deactivation temperature. When the work temperature is 400 °C, the denitrification efficiency of catalyst sample is higher than 90%. Analysis by temperature programmed desorption of ammonia (NH3-TPD), Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) show the definite dispersion of F on the surface of SCR catalysts. HF would lead to decrease specific surface areas, surface acidity, and oxidation–reduction ability. Although the concentrations of Oβ (surface adsorbed oxygen) increases owing to HF, which may interact with TiO2 to destroy the carrier structure. Meanwhile, there is a chemical deactivation for the influence of HF on V2O5 and WO3.

Zhengrong Zhu, Shihao Ma, Yikun Wang, Yan Zhang, Yuxiao Qiu, Lei Deng, Defu Che
Chapter 31. Numerical Study on Combustion and NOx Emission Characteristics of Co-Firing Semi-Coke and Coal in a Tangentially-Fired Utility Boiler

With the booming coal industry and the increasing production of semi-coke, a large number of small particles and powder pyrolysis semi-coke are urgent to be exploited. Co-firing semi-coke with coal is a potential approach to achieve clean and efficient utilization of such low-volatile fuel. In this paper, the co-combustion performance of semi-coke and coal in a 135 MW tangentially-fired boiler was investigated by numerical simulation. The influences of semi-coke blending ratio, blending mode and injection position on the combustion efficiency and NOx generation characteristics of the utility boiler were extensively analyzed. The simulation results indicated that the NOx emission at the furnace outlet was elevated and the burn-out ratio declined with an increase in semi-coke blending ratio. Different heights of semi-coke injected position could lead to different combustion efficiency and NOx emissions. The semi-coke was recommended to be injected from the middle layer of burners to obtain low carbon content in fly ash. The blending methods (in-furnace versus out-furnace) had certain impacts on the NOx emission and carbon content in fly ash. High burn-out ratio could be obtained when the semi-coke and coal were injected from different burners.

Qinqin Feng, Chang’an Wang, Pengqian Wang, Zhichao Wang, Wei Yao, Lei Zhao, Yongbo Du, Defu Che
Chapter 32. Investigation on NOx Formation Characteristics During Semi-coke Air-Staged Combustion

Semi-coke is the product of low-rank coal by pyrolysis at low temperature. If semi-coke could be used as fuel of industrial pulverized coal boilers, it will widen the fuel range of the industrial pulverized coal boilers and effectively promote the coal staged utilization. As the semi-coke need higher temperature than bituminous coal for its ignition and combustion process, the NOx emission will rapidly increase with the rising of temperature. So, decreasing the NOx is an important task in its utilization. In this paper, the NOx emission rules at the higher fuel-rich zone temperature and properties of semi-coke air-staged combustion were explored by two-stage drop-tube furnace. In the air-staged combustion experiments, the influence of fuel-rich zone temperature and the ratio of air on NOx emission and combustion behavior were investigated. The results indicate that the NOxemission concentration of non-staged combustion rises with fuel-rich zone temperature and the excess air coefficient in its combustion process. The air-staged combustion could visibly reduce the NOx emission in the combustion process. As the Fig. 32.1 shows, the optimum ratio of secondary air is 0.56, at which NOx emission concentration is under 120 mg/m3 and the burn-out rates were above 90%. The conclusions of the burn-out rate and the decrease rate of NOx can be used to guide the industry enlargement experiment in running conditions.

Hui Li, Naiji Wang, Shi Yang, Xin Zhang, Yuhong Cui, Jianming Zhou
Chapter 33. Numerical Investigation on Combustion Stability of Coal Slurry in the Double Cone Burner

Fluent reaction flow has been widely used in the simulation of uniform or non-uniform reaction flow including boilers, gas turbines and rocket engines. Flow field characteristics, material concentration and pollutant generation can be obtained (Travin et al. in Advances in LES of complex flows, vol 65, pp 239–254, 2002). In order to study the combustion stability of coal slurry in the double cone burner, numerical investigation based on Reynolds-Averaged Navier Stokes (RANS) equations (Chen and Ghoniem in Energy Fuels 26:4783–4798, 2012) was explored in this paper. Besides, a reverse jet device for atomization is set up in the pulverized coal double cone reverse jet burner. and a test platform to verify the numerical simulation results is obtained. The simulated data are verified by the experimental data. The results show that a numerical simulation platform for coal slurry combustion process has been established. Based on the test and calculation results obtained, the pulverized coal double cone burner is optimized for the coal slurry combustion. The technical measures include that the diameter of the burner outlet is reduced from 500 to 450 mm, the angle of the front cone is increased from 7° to 9°, the swirling flow strength is increased by 20%, and the preheating temperature of the combustion air is increased from 20 to 150 °C. The simulation results show that after optimization, the temperature in the burner increases by 120 °C, the combustion process is effectively strengthened, and the front cone pressure is reduced. the temperature in the burner can be increased, and the combustion of coal slurry can be more efficient. Therefore, the adoption of technical means can effectively solve the problem of coal slurry combustion organization.

Mo RiGen, Yang Shi, Liu JianHang
Chapter 34. Experimental Study of NOx Emission and Char Characteristics

The NOx emission and char characteristics during coal combustion process in a one-dimension furnace for different air ratios were studied combined with BET, SEM and FTIR analysis. Nitrogen-containing organic compounds in the rapid pyrolysis products of char were determined by pyrolysis chromatography/mass spectrometry (Py-GC/MS). The results obtained shown that when air ratios in the main combustion zone decreased from 0.85 to 0.65, the exit NOx concentration decreased from 315 to 125 ppm. The variation trends of the oxygenic functional group content were contrary to the NOx. The Py-GC/MS experimental results showed that the benzonitrile (BN) released in large amounts from char taken in the primary 400 mm distance. The char specific surface areas (SSA) changed with the coal volatile matters releasing and char burning process along the furnace. With the progress of coal combustion, the numbers of surface micropore first increased and then decreased, following that the macropores appeared, and finally most pores collapsed and chars broke into small particles.

Jialun Wang, Dongfang Wang, Mingming Wang, Mingyan Gu, Yuyu Lin

Fluidized Bed Combustion

Frontmatter
Chapter 35. Study on Penetrability of Central Secondary Air Jet in CFB and Its Influences on Fluidization Characteristics

In this paper, cold-state experiments were conducted in a self-built circulating fluidized bed to study the influences of total air volume, ratio of the volume of secondary air to total air (SAR), velocity of secondary air and the secondary injection height on the penetrability of secondary air, the chamber’s pressure drop, the particle circulating flow rate and the distribution of particle concentration. Results suggest that when the total air volume rises or SAR decreases, the chamber’s overall pressure drop and circulating flow rate increase. Apparent particle concentration increases substantially when total air volume rises and the increase of SAR is capable of promoting particle concentration around the area where the secondary air is injected. Penetration depth of secondary air jet increases with the increase of SAR, jet velocity and injection height while the total air volume alone has little effect on jet’s penetration depth.

Chen Lin, Juan Yu, Yao Zhang, Fan Feng, Zhong-xiao Zhang
Chapter 36. The Fundamental Studies on Combustion of Sintering Flue Gas in Circulating Fluidized Bed

The development of sintering flue gas circulating fluidized bed (CFB) treatment technology is very important because there are many disadvantages in the existing treatment technology. In order to understand this technology, it is necessary to study the combustion of sintering flue gas in a circulating fluidized bed. Experiments were performed to study the combustion characteristics of Zuoyun bituminous coal in this oxygen-deficient atmosphere by a large-capacity TGA (LC-TGA). By changing reaction parameters, the influence of combustion temperature and gas atmosphere on coal combustion were analyzed. The experimental results confirm that the change of oxygen concentration and combustion temperature will greatly affect the combustion of coal in the low oxygen atmosphere. With the increase of oxygen mole fraction and combustion temperature, the combustion rate of coal will gradually accelerate. The presence of CO in the combustion atmosphere will not change this trend, but it does greatly affect the combustion characteristics of coal, which is particularly evident at 800 and 850 ℃. CO has obvious oxygen-grabbing behavior at high temperature, and the influence on coal combustion seems to be closely related to the temperature. The present experimental results will provide the reference for the further development of sintering flue gas circulating fluidized bed technology.

Xin Tao, Lujian Chen, Yiqun Huang, Runxia Cai, Hairui Yang, Shouyu Zhang, Junfu Lyu
Chapter 37. Emission Characteristic of NOx in CFB Boiler at Low Load

In order to study the NOx emission of CFB boiler at low load, a bubbling fluidized bed test was established to investigate the effects of bed temperature, excess air ratio and particle size of ZY coal on NOx emission. A continuous feeder was used to ensure the feeding rate steady, so that the significant parameter excess air ratio can be confirmed. By comparing the NOx emissions of different conditions, the influence law of three parameters can be obtained. The results showed that the bed temperature had a continuous promoting effect on the formation of NOx when bed temperature increased from 700 to 850 °C. At a given temperature, the NOx emission depended mainly on the excess air ratio. With the increasing of excess air ratio, the NOx emission increased first and then decreased. In the same condition, the NOx emission generated in the combustion process of larger particle coal was lower than the value of small particle coal.

Lujian Chen, Xin Tao, Shouyu Zhang, Hairui Yang, Junfu Lyu
Chapter 38. A Method to Measure the Solid Circulation Rate in CFB Boilers

Circulating fluidized bed (CFB) combustion technology is attracting recently due to its low cost in pollution control. Researches show solid circulation rate (Gs) is an important parameter to CFB boiler design and of great significance in pollution control during the operation of CFB boilers. In view of the complex and rough measuring environments such as high temperature and severe abrasion, the measurement of Gs in a CFB boiler remains an unsolved problem in the literature. Thus, this paper proposes a method to quantitatively measure Gs in CFB boilers based on the heat transfer mechanism. In this method, the relation of Gs to the heat transfer coefficient between hot solid particles and heat exchange device was established, and thereby this method can overcome the high temperature and the abrasion problems. Experiments in a hot test rig and numerical simulation using the Barracuda package were conducted to obtain quantitative relation between Gs and heat transfer coefficient, as well as the distribution of the solid particle concentration. Finally, a linear relationship between Gs and the heat transfer coefficient/solid concentration of the cross-section in the standpipe were found and fitting functional formulas were presented as well, proving that the heat transfer method was a feasible and potential way to be applied in actual CFB boilers.

Yangxin Zhang, Lu Cheng, Yang Zhang, Baoguo Fan, Hai Zhang, Junfu Lyu
Chapter 39. Reliability Analysis of 100 MW and Above Circulating Fluidized Bed Boiler Units in China in 2017

In order to demonstrate the overall operation reliability level of circulating fluidized bed (CFB) boiler units in China and provide a useful reference for their operation and development, the statistics of the operation reliability of more than 130 CFB boiler units in China were collected and analyzed. The results show that the 200 MW class units had the longest utilization hours which exceeds 4500 h. The 135 MW class units were most reliable, each of which met 0.65 unplanned outages on average in 2017. The reliability level of the 300 MW class units was comparatively low due to some new units. They met 1.1 and 0.96 planned outages and unplanned outages on average respectively. The unplanned outages occurred twice in the 600 MW supercritical CFB boiler unit in 2017 and had occurred five times in total since its commissioning, three of which were caused by its boiler system. It could be concluded that the boiler systems have the greatest impact on the reliability of the units. The high-temperature heating surface and the combustion system are the main parts of a boiler causing the unplanned outages. The wear and crack are the main kinds of technical faults. In addition, the product quality, maintenance and operation management of the power plants are also very important for the reliability of the CFB boiler units.

Xia Zhou, Jianfeng Li, Yuge Yao, Shujie Chen, Hong Zhou, Qing Liu, Geng Chen
Chapter 40. Development of Advanced Ultra Super Critical Circulating Fluidized Bed Technology by DongFang Boiler

In this paper, the research and development of circulating fluidized bed (CFB) technology by Dongfang Boiler Group Co., Ltd (Dongfang Boiler) in recent years and the understanding of its future development trend are summarized. Based on several decades’ accumulation, Dongfang Boiler has developed two types of supercritical CFB boilers (350 MW and 600 MW, 25.4 MPa/571 ℃/569 ℃), and both types have been in operation. Additionally, supported by major national research and development program (2016YFB0600204), the scheme of 660 MW advanced ultra supercritical (29.4 MPa/605 ℃/623 ℃) CFB boiler has also been completed and is shown in the present work. In order to use the same material as that of pulverized coal fired boiler with similar parameters, one of the most important researches is to reduce the heat deviation in external heat exchanger (EHE). According to the field test on a 600 MW supercritical CFB boiler and simulation of the flow characteristics of EHE, the deviation characteristic is reappeared, and solution to reduce the heat deviation have been proposed. Additionally, with the stringent requirement of pollutant emission from coal-fired units in China, a series of flue gas cleaning technologies can be used. The recommended flue gas cleaning system for a CFB boiler is discussed.

Nie Li, Gong Liming, Xue Dayong, Lu Jiayi, Wei Lixiao, Huang Min
Chapter 41. Cold-Experimental Study About Pressure Resistance of CFB Wind Caps

Air distributor is one of the most important devices to maintain stable and high-efficient operation of circulating fluidized bed boilers. And the pressure drop of the air distributor determine the effect of air distribution and efficiency. The wind caps are the essential parts of air distributors, whose structures determine the pressure drop. Therefore, predicting the resistance of wind caps is one of the most important issues in CFB boiler design. At present, there is little study and theoretical inference about the pressure drop prediction when the diameters of internal structure change. In this study, cold-modelling experiments were made to study the flow characteristics and the resistance regulation as geometry parameters changes qualitatively.

Boheng Tong, Hongyu Zeng, Qingfeng Zhang, Junfu Lyu
Chapter 42. Progress and Main Technical Characteristics of Ultra-supercritical Circulating Fluidized Bed Boiler

The research and development progress of ultra-supercritical circulating fluidized bed boiler in major scientific research institutions and boiler manufacturing plants at home and abroad is described, and the furnace type schemes and technical characteristics of different boilers types are discussed in detail. To research and develop ultra-supercritical CFB boiler technology, main technological difficulties were analyzed from heating surface safety, hydrodynamics safety, maintaining reheat steam temperature at low boiler load and low-cost ultra-low emission technology, and then the solutions to these difficulties were put forward. It guarantees the research and development of ultra-supercritical CFB boiler and provides technical support to continue to maintain the leading position of China’s CFB power technology.

Shengwei Xin, Yingping Li, Peng Zhang, Changhua Hu, Man Zhang, Hu Wang
Chapter 43. Experimental Study on Peaking Performance of 145 MW Circulating Fluidized Bed Boiler Unit with Retrofitting for Low-Vacuum Heat Supply

The peaking performance of 145 MW circulating fluidized bed (CFB) boiler unit with retrofitting for low-vacuum heat supply were studied in this article. Peaking depth, peaking rate, tube wall temperature of superheater and reheater and bed temperature were measured. Unit load curve analysis shows that the peak load capacity of the test unit is significantly reduced after low-vacuum heating reform with the minimum output of 41.4%. The load reduction rate of 0.99 MW/min and the load increasing rate of 0.71 MW/min is relatively small because of the large thermal inertia of CFB boiler. The wall temperature of the superheater and reheater of low load and variable load stages could be higher than that of high load stages, which is easy to cause overheating and tube bursting. The results of bed temperature and furnace negative pressure indicate the excellent combustion stability of CFB boiler at low load.

Xuhui Zhang, Zhonghua Zhao, Gui Long Xiong, Fuxing Cui, Xinguang Dong, Qingchuan Zhao, Ke Liu, Haichao Wang, Jinglong Liu
Chapter 44. The Technology and Application of a New Type of Coal Water Slurry-Fired CFB with High Efficiency and Clean Combustion

This paper introduces the core technology of coal water slurry-fired CFB with high efficiency and clean combustion, based on flow pattern reconstruction. The design of key boiler components and characteristics of boiler and system are also introduced. This technology realizes high desulfurization efficiency as well as less NOx emission at the furnace exit that sharply reduce investment and operating cost. In the last part of the paper, it expounds the application references and development prospects.

Yuping Hao, Ruiguo Li, Yujiao Chen
Chapter 45. Study on Pollutants Control of Circulating Fluidized Bed Boiler Burning Low Calorific Value Coal

In recent years, more and more low calorific value coal such as slime and gangue are used in circulating fluidized bed (CFB) boilers. Under this condition, it is difficult to control pollutants such as SO2 and NOX due to the change of ash content and particle size of coal. Results implied that when low calorific value coal was burnt in a CFB boiler, the change of circulating ash quantity and particle size distribution of CFB boiler cause the fluctuation of furnace bed pressure, as well as the returning blockage of loop seal, and the deterioration of combustion conditions inside furnace leads to a large fluctuation of pollutants emission. The fluctuation of furnace bed pressure is reduced by adjusting the relationship between air and coal volume and introducing bed pressure to modify the control strategy of primary air flow on both sides of the furnace. Effective measures are put forward to deal with the returning blockage of loop seal in the CFB boiler. The influence of operating parameters such as oxygen on pollutants emission and the coupling relationship between SO2 and NOX emission are both studied through experiments. On this basis, the optimization proposal of control strategy of limestone adding system is put forward, which is applied in a 300 MW CFB boiler, and good results are achieved. The results can provide a reference for controlling pollutants of CFB units burning low calorific value coal.

Wanzhu Wu, Ruixin Li, Hu Wang, Congyang Gu

Low Carbon Energy

Frontmatter
Chapter 46. CO2 Adsorption Performance of Na/K-Impregnated MgO

As a carbon dioxide solid sorbents, magnesium oxide has been widely studied due to its wide distribution and low price. But pure MgO under intermediate temperature (250–500 °C) showed a poor CO2 capture capacity. In our study, an effective method for improving the cyclic adsorption stability is to prepare the MgO-based sorbents promoted by sodium/potassium nitrate and citric acid through the mixing-impregnation method. The sorbents were determined by powder X-ray diffraction analyzer (XRD), thermogravimetric analyzer (TGA), and N2 adsorption and desorption were measured at 77 K. The morphology of the sorbents was investigated by scanning electron microscopy (SEM). The results showed that as-prepared composites promoted by sodium nitrate and citric acid exhibited a better adsorption capacity than those modified by potassium nitrate and citric acid, which was 3.9158 mmol/g during the cyclic CO2 adsorption reaction of calcination temperature of 450 °C and carbonation temperature of 350 °C. After 30 cycles of adsorption and desorption, the capture capacity of this sorbents was stable at 3.769 mmol/g. The SEM indicated that the pore morphology of these modified sorbents becomes abundant. Overall, the as-prepared Na/K impregnated MgO sorbent was promising for cyclic intermediate temperature CO2 capture.

Jie Zou, Ning Ding, Cong Luo
Chapter 47. Comprehensive Analyses on Activation Agents of Amines and Nanoparticles for TETA-Based CO2 Capture Absorbents

The issue of climate warming and emissions to the core of global public focus. Chemical absorption is the most possible CCS technology for large-scale commercial application, in which the absorbents were the most critical factor to determine the CO2 capture performance. In this study, TETA-based high-performance absorbents by adding activation agents of nanoparticles and other amines. In this study, TETA-based high-performance absorbents were prepared by adding activation agents with nanoparticles and amines. The ab/desorption performance was tested by a bubble reactor. The critical parameters, such as ab/desorption rate, equilibrium time and CO2-loading, were comprehensively summarized and learned by AHP method. The results proves that Ab/desorption CO2-loading occupies the most important part with the value of 30.77 and 24.36%, respectively. The sequences of amine activation agents is 2.5%PZ > 2.5%DEA > 2.5%MDEA > 2.5%AMP > 2.5%TEA and 5.0%PZ > 5.0%AMP > 5.0%DEA > 5.0%MDEA > 5.0%TEA. For amine activation agents, the addition of PZ shows the optimal overall CO2 capture performance with the value of 0.593 and 0.580. The activation agent of DEA also shows impressive overall CO2 capture performance. The cheap price of 8 k RMB/t gives it the potential for developing high-performance absorbents with the increase of mass fraction, the overall scores of AL2O3-TETA nanofluids increase first and then decrease. The Brown motion of nanoparticles can effectively promote the heat/mass transfer performance of the absorbents.

Jiang Yanchi, Zhang Zhongxiao, Yu Juan, Zhao Ziqi, Fan Junjie, Li Boyang, Jia Mengchuan, Mu Aiwei
Chapter 48. Experimental Study on Carbon Capture Performance of Polyimide Hollow Fiber Membrane in Post-combustion Process

Carbon capture and storage (CCS) technology is effective in mitigating the negative effect of the greenhouse gases. At the same time, membrane-based technology for the capture of CO2 has attracted worldwide attention. In this paper, an experimental study on the carbon capture performance of polyimide (PI) hollow fiber membrane in post-combustion process is carried out to analyze the PI membrane system separation performance of single-stage and two-stage membrane separation methods under different pressure, temperature and gas flow rate conditions. For single-stage membrane separation system, increasing feed gas pressure, feed gas temperature and gas flow rate is beneficial to enhance membrane CO2 permeability. For the two-stage membrane separation system, the feed gas pressure of the first/the second stage pressure, as well as the gas flow rate, can effectively influence the CO2 concentration on permeate side, which can reach up to 91.01%. Furthermore, the two-stage method has 40–60% higher CO2 concentration than single-stage method due to the additional membrane stage.

Liu Yang, Yanchi Jiang, Juan Yu, Ziqi Zhao, Mengchuan Jia, Aiwei Mu
Chapter 49. Simulation Study on Separation of CO2 from Flue Gas in Coal-Fired Power Plant by Membrane Method

A simplified model of membrane separation was improved for predicting the CO2 separation from the flue gas of coal-fired power plant. Simultaneously, a single-stage membrane separation system was built under laboratory conditions that uses a hollow fiber membrane as the separation core module. Different factors affecting the separation effect of the system were experimented and the simulated and experimental values were compared. The comparison results show that the variation trend of the simulated values is basically consistent with the experimental values, and within the allowable error range of the engineering, the simulated values can approximately reflect the experimental values. This model is suitable for the engineering calculation of CO2 membrane separation of flue gas in coal-fired power plants.

Boyang Li, Juan Yu, Fan Feng, Zhongxiao Zhang, Xinwei Guo
Chapter 50. Experimental Study on Slagging and Fouling Behaviors During Oxy-Fuel Combustion of Zhundong Coal Using a Drop Tube Furnace

Zhundong coal featuring high content of alkali metals induces severe slagging and fouling problems during its utilization in utility boilers. Oxy-fuel combustion technology can achieve a large amount of CO2 capture and reduce the NOx emission. Unfortunately, in-depth investigation has been seldom carried out on the process of ash deposition and slagging of high-alkali coal during oxy-fuel combustion. In the present study, the oxy-fuel combustion of high-alkali coals were experimentally studied using a non-cooled sampling probe in a drop tube furnace. The fouling and slagging mechanisms were investigated in various atmospheres, temperatures and different O2 concentrations. In addition, the slag samples were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-ray Spectrometer (EDS). Experimental results indicated that under air and oxy-fuel conditions with the same O2 content, the types of elements and minerals were almost the same. With the temperature increased, the adhesion between the slag samples was strengthened and the pore structure slag was increased. The degree of slag melting and sintering was aggravated at the temperature of 1200 °C and the slag structure was complicated. As the oxygen concentration was increased, some of the spherical particles had completely melted on the surface of the massive ash, resulting in an uneven surface. The present work can provide new insights into the slagging and ash deposition of Zhundong high-alkali coal during oxy-fuel combustion.

Lei Zhao, Chang’an Wang, Yueyi Hu, Ruijin Sun, Guantao Tang, Jin Guo, Zhiming Jiang, Yongbo Du, Defu Che
Chapter 51. Thermodynamic Study on the Utility Oxy-Fuel Boiler with Different Oxygen Volume Fractions

Oxy-fuel combustion technology is one of the most promising technologies for capturing CO2 emitted from coal-fired power plants. For the operation of an oxy-fuel combustion utility boiler, its thermodynamic features should be clarified. For this purpose, a calculation model for oxy-fuel combustion boiler was established, and the thermodynamic characteristics of a 2102 t/h oxy-fuel utility boiler were explored. The results show that at a given oxygen volume fraction, the start-up process of an oxy-fuel boiler can be completed in a short time. Along with the increasing of the oxygen volume fraction, from 22 to 29%, it showed a strong effect on furnace radiant surfaces and furnace volumes. And that variation of CO2 enthalpy played a vital role in the flue gas enthalpy, the oxygen volume fraction was shown to affect the various parts of the furnace differently. The calculations in present research could contribute to the oxy-fuel boiler design and operation.

Kai Li, Enlu Wang, Deli Li, Lifen Wang, Naveed Husnain, Qi Wang

Emissions Control

Frontmatter
Chapter 52. Formation of SO3 in Flue Gas Under SNCR Conditions

Experimental and numerical studies were conducted to investigate the formation of sulfur trioxide (SO3) during the selective non-catalytic reduction (SNCR) process. The effects of the inlet NH3/NO ratio (RAN), reaction temperature, inlet mole fractions of SO2, O2, CO and H2O were assessed. The experiments were conducted using a perfectly stirred reactor (PSR) and SO3 mole fraction was determined using the sulfur balance method. Corresponding numerical simulation was performed using detailed chemistry developed by Mueller and coworkers. Both experimental and numerical results revealed that the SO3 formation was considerably affected by RAN, SO2 and O2 mole fractions. The experimental results demonstrated that under typical SNCR conditions, 0.5 ~ 1.0% of SO2 was converted into SO3, and SO3 mole fraction was 5–10 ppm. The SO3 formation was noticeably enhanced by the addition of NH3 when RAN < 0.5. The conversion rate decreased as the initial SO2 increased. A small amount of O2 could promote the SO3 formation remarkably, but this effect became much weaker as inlet O2 mole fraction ≥1%. The numerical simulation indicated that the increase of the reaction temperature significantly promoted the SO3 formation when the temperature was above 1173 K. A small amount of CO could significantly enhance the SO3 formation. The H2O addition could inhibit SO3 formation. The detailed chemical kinetic analyses showed that the main reaction paths of the SO3 formation were the oxidization reaction of SO2 with O radical via SO2 + O (+M) → SO3 (+ M) (52.3) and the one of SO2 with NO2 via SO2 + NO2 → SO3 + NO (52.4). The effect of the operational parameters, i.e., RAN, reaction temperature, and SO2, O2, CO, H2O mole fractions, could be well explained by the variation of the reaction rates of Eqs. 52.3) and (52.4).

Kang Wang, Wenfeng Shen, Yang Zhang, Yu Peng, Hai Zhang, Hairui Yang, Junfu Lyu
Chapter 53. The Effect of Oxygen-Coal Equivalent Ratio on the Rapid Preparation of Powdered Activated Coke in Low Oxygen Atmosphere

Oxygen is a good activator for the rapid preparation of the powdered activated coke (PAC) in the low oxygen atmosphere, and the oxygen-coal equivalent ratio is an important parameter in the preparation process. In order to obtain the optimal range of oxygen-coal equivalent ratio, it was adjusted by changing the amount of coal supplied under a certain gas distribution (6% O2 and 94% N2).The changes of the SO2 adsorption capacity of the PACs, the burn-off rate of raw coal and the production rate of gas phase products with the equivalent ratio were studied. In addition, the BET and SEM were used to characterize the pore structure of the PACs. The results showed that with the increase of the equivalent ratio, the SO2 adsorption capacity of the PACs increases first and then decreases, reaching the maximum at 0.5, which is 102.2 mg/g; the burn-off rate increases as a whole, but the increment is not obvious, which is in the range of 0.2 ~ 0.4. Combined with the analysis of gas phase products, BET and SEM, it is concluded that the PACs prepared when the oxygen-coal equivalent ratio is in the range of 0.2 ~ 0.5 have relatively developed pore structure. To sum up, the suitable oxygen-coal equivalent ratio range about the preparation of PAC is 0.3 ~ 0.5. This conclusion provides reference for future industrial application.

Binxuan Zhou, Yuan Zhao, Cheng Li, Tao Wang, Ping Zhou, Zhanlong Song, Chunyuan Ma
Chapter 54. Experimental Study on Synergistic Dust Removal of Desulfurization Tower of Coal-Fired Thermal Power Unit

Dust is one of the flue gas pollutants in coal-fired power plants. In coal-fired power plants without wet ESP installed, the synergistic dust removal effect of wet desulfurization tower directly affects the final dust emission concentration. In order to explore the synergistic dedusting effect of wet desulfurization tower and improve the synergistic dedusting performance of wet desulfurization tower, tests were carried out on five 300 MW coal-fired units in actual operation. The reliability and advantages of low pressure impactor (ELPI) measurement method were verified by analyzing and comparing the test results of different measurement methods for particulate matter. Through testing the dust concentration at the entrance and exit of the desulfurization tower, obtained the influence rule of the structure of the wet desulfurization tower on its synergistic dedusting effect, revealed the irregular change of the efficiency of WFGD for PM10 and PM2.5, and expounded that the desulfurization tower measures adopted for ultra-low SO2 emission are helpful to improve the synergistic dust removal effect.

Shen Zhen, Meng Lei, Lyu Junfu
Chapter 55. Analysis of Desulphurization Process in Circulating Fluidized Bed Boiler by Calcium and Sulfur Conservation

During the project of the technical transformation of a 75t/h CFB boiler, the desulphurization rate, the utilization ratio of CaO, the sintered ratio of CaO, etc. can be got, by the calcium conservation and sulfur conservation according to the analysis of coal and ash. In this project, the desulphurization rate in furnace is 14.34% before the technical transformation, and the utilization ratio of CaO is 21.1%, the sintered ratio of CaO is 39.2%. After the technical transformation, the desulphurization rate in furnace is 76.34%, the utilization ratio of CaO is 52.27%, and the sintered ratio of CaO is 23.74%.

Zhang Xin, Wa Naijin, Yang Shi, Li Ting
Chapter 56. Simulation Investigation on NOx Emission Characteristics and Mechanisms During Co-combustion of Fossil Fuels with Different Fuel-Nitrogen Distributions via CHEMKIN

There are over 100 million tons of semi-coke produced in China every year, and use of the semi-coke in utility coal-fired boilers is a promising approach. In this paper, a blending model of semi-coke and bituminous coal was established via CHEMKIN. The NOx emission was investigated by analyses of sensitivity and production rate, while the effects of stoichiometric ratio of main combustion zone, blending ratio, and combustion temperature on migration of fuel nitrogen were further elucidated. The simulation results showed that the conversion ratio of NOx increased monotonically with an increase in the stoichiometric ratio of main combustion zone. The temperature of plug flow reactor (PFR) I exhibited a significant effect on NOx emission, but other reactors had limited influences. The NOx conversion ratio was enlarged with the increase of semi-coke blending ratio. The influence of blending proportion on NOx emission was significant when the stoichiometric ratio of main combustion zone was small. Compared with high blending ratio, the main reactions with low blending ratio had stronger inhibitory effect on the formation of NO. The present study was of guiding significance for reducing NOx emission in the utility boilers co-firing semi-coke.

Chaowei Wang, Chang’an Wang, Lin Zhao, Maobo Yuan, Pengqian Wang, Yongbo Du, Defu Che
Chapter 57. Experimental Study on Combustion of Pulverized Char Preheated by a Circulating Fluidized Bed

The preheating combustion of pulverized char was conducted in a 30 kW test platform, which consists of a circulating fluidized bed (CFB) and a down-fired combustor (DFC). Properties of high-temperature coal gas and preheated char particles were studied under higher air equivalence ratio in circulating fluidized bed, and the fuel gas compositions and temperature distribution along the down-fired combustor were analyzed. It was also found that parameter optimization helped to reduce the NOx emission, the NOx emission was reduced to 109.9 mg/m3(@6%O2) and the combustion efficiency was improved to 97.73% by changing the tertiary gas distribution, which achieved clean and efficient combustion of ultra-low volatile fuel.

F. Pan, J. G. Zhu, J. Z. Liu, Y. Zhang, S. J. Zhu
Chapter 58. Experimental Study on Optimal Adjustment of SCR Ammonia Injection for 1000 MW Coal-Fired Unit Based on Multi-field Cooperative Diagnosis

Taking the SCR flue gas denitrification system of a 1000MW coal-fired boiler in a power plant as the research object, through the coordinated test of the temperature field, flue gas field, NOx concentration field and NH3 concentration field at the entrance and exit of SCR, taking into account the influence of temperature, flow field and concentration field on denitrification reaction comprehensively, the ammonia injection optimization adjustment test was carried out under 900MW load, and the ammonia nitrogen molar ratio distribution at the entrance of SCR was optimized to improve the denitrification reaction. The uniformity of NOx distribution at SCR outlet was improved, and the ammonia escape concentration was reduced. The validation tests were carried out under 750 MW and 500 MW loads, and the NOx concentration distribution and ammonia escape concentration at SCR outlet were tested.

Jinglong Liu, Fanjun Hou, Limeng Zhang, Chuanjun Duan, Haojie Liu, Xudong Zhang, Zhihong Hu, Xingsen Yang
Chapter 59. Effects of High Temperature on NH3/NO Reactions in the Absence of Oxygen

The influence of industrial processing parameters, especially high temperature, on NOx abatement in the absence of oxygen has been experimentally. NOx reduction efficiency is significantly promoted with increasing residence time and NSR and optimal residence time and NSR are 0.7 s and 1.5, respectively, when temperature exceeds 1400 ℃. NOx reduction is strongly dependent on temperature. When temperature is lower than 1000 ℃, NO consumption is hindered due to lack of O radicals. The denitrification efficiency is significantly promoted with the increase of temperature because thermal decomposition of CO2 and NO is quite sensitive to temperature. However, NO formation from pyrolysis of HNO begins plays an important role since temperature exceeds 1400 ℃, which results in decline in NOx reduction efficiency. And the peak value of NO reduction efficiency can reach almost 100% at temperature range of 1300–1400 ℃ with NSR of 1.5. Four chemistry mechanisms have been adopted to simulate NOx reduction by ammonia. Validation shows that results calculated by POLIMI chemistry mechanism agrees better with experimental data than other 3 mechanisms.

Zhixiang Zhu, Degui Bi, Juan Yu, Zhongxiao Zhang, Chen Lin
Chapter 60. Study on Kinetic Model of NOx Reduction Overall Reaction of Fluidized-Bed Flue Gas

There have been a great number of investigations on kinetic model of NOx reduction reaction. However, it was found that it is difficult to apply the reaction model conveniently in the comprehensive numerical simulation of fluidized bed combustion due to the complexity of the kinetic model. Therefore, it is necessary to establish a simplified overall reaction kinetic model to adapt to the complex simulation computation of fluidized bed. In this paper, the Arrhenius coefficients of the overall reaction of NOx reduction were obtained by comparing with detailed mechanism model and optimized by using a genetic algorithm. The result showed that the overall reaction model can predict the change of NOx reduction reaction temperature window, the denitrification efficiency and the ammonia slip accurately.

Yao Zhang, Chen Lin, Juan Yu, Jindong Jiang, Fan Feng, Zhongxiao Zhang
Chapter 61. The Mechanisms and Applications of NOx Reduction by Low-NOx Burner Coupling Deep Air-Staging Technology in Pulverized Coal

In order to reduce the original NOx emission from coal combustion, and lighten the excessive redeucer used in the De-NOx post-treatment which will lead to the corrosion of steam heat exchanger tube and economical efficiency, a new De-NOx technology combined with the De-NOx combustor and the deep air stage combustion was developed, and the technology was testified by theory, numerical simulation, pilot experiment, and industrial experiment. FR/ED (Finite Rate/Eddy Dissipation) model which considering the chemical reactions involved in the gasification process is used in the simulation, and it showed a sufficient accuracy with the experiment results. A strong reductive atmosphere including CO and CH4 was detected with a low stoichiometric ratio both by numerical simulation and experiment in a 7 MW double-cone De-NOx burner, the CO and H2 contents could be 15.457% and 0.992 for SR of 0.456, respectively, while no NOx content was detected at the burner outlet. Method Oxygen-enriched air used in the burner could intensify the reductive atmosphere, and the CO content at the center burner increased form 9.54 to 20.258%, when the oxygen content increased from 21 to 28.3%. For the 7 MW pilot boiler system, the initial NOx emission of the boiler can reach to 159 mg/m3, and the total reduction of NOx generation was more than 70.9%, when the oxygen content in secondary air was 28.3% and the proportion of staged air in tertiary air was 41.2%. Utilization of De-NOx technology in long-term industrial experiment for 40t/h steam boiler showed near no influence on the boiler operation, original NOx of less than 200 mg could be reached at the extreme condition. When the original NOx emission reduced from 697 to 300 mg/m3, the heat loss was less than 0.5%, and more than 50% of ammonia water was saved for SCR, which leading about 1 yuan per ton steam saving of the cost.

Xiaolei Cheng, Naiji Wang, Xin Zhang, Yongying Wang, Long Chen
Chapter 62. Experimental Research on NOx Emission Characteristics Based on Combined Removal Technology of Multi-pollutant with Ash Calcium Recycling

As one of the feasible technologies suitable for industrial boilers and kilns to reduce pollutant emissions to ultra low emission standards, combined removal technology of multi-pollutant is attracting more attention in recent years. As a combined removal technology of multi-pollutant, a low temperature flue gas deep purification technology based on semi-dry method was proposed by China Coal Research Institute. In this article, NO2 absorption characteristics of Ca(OH)2 was investigated in fixed bed and bubbling bed reactor. The composition of reaction products was detected by FTIR method. The result shows that: when the temperature is among 70–80 ℃, oxygen content is 5%, the relative humidity is in the range of 40–60%, the absorption rate in fixed bed test is in the range of 20–30%, nitrate and nitrite exist in the reaction products; while in bubbling bed test, the absorption rate is above 90%. Industrial test of this technology was implemented on a 30 t/h boiler. The result shows that: at the proper operation condition, the absorption rate is in the range of 81–90%. It is found that the absorption rate of NO2 by calcium-based absorbent is as follows: bubbling bed (wet method) ≥ airflow bed (semi-dry method) > fixed bed (close to dry method). The results are mainly affected by the humidification mode.

Ting Li, Naji Wang, Shi Yang
Chapter 63. Selective Catalytic Reduction of NOx with NH3 Using Coal Ash Catalyst

The selective catalytic reduction (SCR) of NOx with NH3 has been investigated with coal ash. Coal samples from different regions of the People Republic of China are taken and processed to be used as the SCR catalysts. The influences of different coal ash catalysts, as well as the influences of calcination temperatures on the NOx conversion of catalysts, are analyzed. The methods of XRF, XRD, and BET are used to characterize the materials. It is found that the calcined sample at 800 °C with Ca: Fe: Al: Si ratio of 0.051: 0.123: 0.511: 1, exhibited good NH3-SCR activity in a broad temperature range of 200–500 °C. As well, the influences of [NH3]/[NO] molar ratio and oxygen concentration on the SCR activity are also studied.

Shagufta Fareed, Enlu Wang, Naveed Husnain, Kai Li, Deli Li
Chapter 64. Effects of Different Precipitants on the De–NO Efficiency of the Fe2O3 Catalyst Synthesized by Co-precipitation Method

Fe2O3 catalysts synthesized by the co-precipitation method with two different precipitants (NH4OH/Na2CO3) were experimentally investigated in the selective catalytic reduction (SCR) of NO with NH3. It was found that the catalyst in which NH4OH was used as precipitant exhibited high NO conversion (above 80% from 250–400 °C). XRD, BET, EDS, and FT-IR characterizations were done to examine the catalysts. The catalyst prepared by using NH4OH precipitant exhibited a lower crystallization degree together with better pore structure, and an increase in the O/Fe ratio, which was helpful for the NH3-SCR reaction. Also, the SO2 tolerance of the catalyst was investigated. The results exhibited that the addition of SO2 gradually decreased the SCR activity. FT-IR analysis of the catalyst exhibited that after the addition of SO2 in the De–NO reaction the development of ammonium sulfate species on the surface of the catalyst caused pore plugging and was responsible for a reduction in the NH3-SCR activity.

Naveed Husnain, Enlu Wang, Shagufta Fareed, Kai Li, Deli Li, Qi Wang
Chapter 65. In Situ Visual Monitoring of Rotary Air Preheater Blockage: Setup and Image Analysis

Blockage of air preheaters has become a common problem in coal-fired power plants due to the formation of sticky ammonium bisulfate. The lack of efficient monitoring technique hinders the efforts to prevent the problem. In this paper, we propose a novel in-situ visual monitoring system on the cold end of the air preheater. The system is inexpensive but powerful enough to reveal the temporal evolution and spatial distribution of blockage fractions. By virtual of 3D printing, we built a lab-scale test structure of the contaminated corrugate plate of the air preheater, and took images under simulating dark environments. We revealed that integrating Gaussian filtration for noise elimination and then K-means clustering for image segmentation exhibits the best performance for images from nearly true circumstances. Moreover, the convolutional neural network manifests its ability to learn the blockage fraction and thus its future applicability for image processing with a well-labeled image dataset.

Cheng Li, Qian Huang, Guanqing Liu, Xiao Sha, Shuiqing Li
Chapter 66. Effect of Chemical Composition on Adsorption and Agglomeration Characteristics of Ash Particles After Sulfuric Acid Adsorption

The low-low temperature electrostatic precipitator has been applied to enhance the efficiency of power plants. In this paper, the influences of chemical constitutions on the adsorption properties of particulate matters with vitriolic acid and the agglomeration after adsorption are researched. Experiments are conducted on a one-dimensional adsorption system, which simulates the working environment of low-low-temperature electrostatic precipitator. The consequences display that the agglomeration between particulate matters in scanning electron microscopy are loose pellets agglomeration together, adhesion of loose pellets to massive particles, and massive particles agglomeration together. For Na and K, the amounts of elements added have little effect on the adsorption of the sulfuric acid by ash particles. For Mg, Fe, and Ca, when the oxide is used as an additive, the adsorption capacity of ash samples to the vitriolic acid was enhanced and the agglomeration phenomenon of the ash granules was more remarkable with increasing elements amounts. In addition, the change of Mg has great impact on vitriolic acid adsorption and granules agglomeration.

Jiahao Jiang, Yu Yan, Jin Guo, Yuesheng Li, Lei Deng, Defu Che
Chapter 67. Characteristics of Hg0 Re-emission Caused by Sulfite in a Wet Flue Gas Desulfurization System

Re-emission of Hg0 caused by sulfite and metal ion in a wet flue gas desulfurization (WFGD) system was investigated experimentally in this study. The effects of SO32− concentration, slurry temperature, pH, O2 concentration, and metal ions on Hg2+ reduction and Hg0 re-emission were studied. The mechanisms of Hg0 re-emission were explored based on the kinetics of mercury reduction and the equilibrium of mercuric-sulfite complexes. The results indicated that Hg2+ was reduced by SO32−, which caused a re-emission of Hg0. It is worth mentioning that increasing SO32− concentration showed an inhibitory effect on Hg0 re-emission because of the formation of Hg(SO3)22−. The reduction of Hg2+ has a positive correlation with slurry temperature. The rate constant of Hg2+ reduction increased by approximately 11 times with temperature increasing from 40 to 60 ℃. A decrease in pH can affect the equilibrium of mercuric-sulfite complexes, thus intensifying Hg0 re-emission. The re-emission amount of Hg0 increased from 0.4 to 23.8 μg with pH decreasing from 6.0 to 4.0. The calculation reveals that the stabilities of HgSO3 and Hg(SO3)22− are weakened at lower pH values, which promots their decomposition to Hg0. Although a secondary release of Hg0 was observed in the presence of O2, Hg0 re-emission was inhibited with increasing O2 concentration. In addition, adding Cu2+ or Fe2+ ions is found to enhance Hg0 re-emission because of the reducing ability of metal ions.

Jialing Xu, Jingjing Bao, Jiguo Tang, Min Du, Zhengyu Mo, Licheng Sun
Chapter 68. Study of the Concentration of Mercury in Coal Used in Combustion, in an Area of Boyacá, Colombia, South America

According to research of the Servicio Geológico Colombiano (SGC by Spanish initials), the Only Plan of Mercury and the Strategic Sector Plan for the elimination the mercury use, a project that studies the occurrence of mercury in the coal in an area of Boyacá is developed as an integral part in the generation of geoscientist knowledge of the subsoil of the national territory. In this context, and in order to establish a baseline of the mercury content in the coals of the area Sogamoso—Tunja and its effect on combustion processes, Characterization and Processing of Minerals and Coals Group carried out 84 samples in front of mines of 16 municipalities of the area, characterizing samples in 24 parameters, physic-chemical and petrographic, obtaining an important input in aspects of: classification, research in combustion, mercury in the combustion cycle, evaluation environmental, social and economic. It includes an analysis of mercury and its relations with the other measured parameters, given its importance in the production of coal energy and the associated environmental impact. The average content of mercury in dried base in analyzed samples is 127 µg/kg. 89% of the coals have values less than 300 µg/kg. According to the results, an acceptable significant direct correlation was identified between the mercury content with Ash, sulfur, pyritic sulfur, and no correlation with chlorine content, which reacts in the combustion.

Sonia Guerra L, Manuel Romero, Daniel Ballen
Chapter 69. An Experimental Study on Ash Deposition Problem of Low-Low Temperature Flue Gas System

In order to achieve the ultra-clean emission standards, many power plants in China have completed the installation of low-low temperature flue gas system. However, during the operation of this system, many problems have emerged, such as the ash deposition problem in the heat exchanger and dry ESP (electrostatic precipitator). In this paper, the fixed adsorption system and entrained flow experimental system were built to study the ash deposition characteristics in low-low temperature flue gas system under different temperatures and particle sizes. The repose angle was measured to evaluate the flowability and adhesion capacity of ash particles. The results show that as the increase of adsorption time, the particle size increased gradually, and the agglomeration effect is attenuated after the particles have reached adsorption saturation. The time at which the ash particles began to agglomerate with each other was defined as the agglomeration threshold. As the adsorption temperature decreased, the particle size growth rate increased. The smaller the size of ash particles, the more significant the agglomeration effect. Large particles were easy to adsorb small particles, but the agglomeration effect between large particles was weak. In addition, in the initial stage of particle agglomeration, it was mainly included the adhesion between smaller particles and the adhesion of smaller particles on the surface of large particles. The followability of the ash particles was greatly reduced after the adsorption and agglomeration process. The repose angle of the ash particles increased as the temperature of the flue gas decreased. The smaller the particle size, the larger the repose angle changes, and the more pronounced the repose angle is influenced by the adsorption temperature. The flue gas temperature cannot be blindly dropped in pursuit of high sulfur oxide removal efficiency and dust removal efficiency.

Yu Yan, Jiahao Jiang, Jin Guo, Yuesheng Li, Lei Deng, Defu Che
Chapter 70. Condensation Characteristic of Sulfuric Acid Vapor on Low-Temperature Surface of Tube Heat Exchanger

In the low-low temperature flue gas system, a part of the H2SO4 vapor is adsorbed by the ash particles, and the other part will condense on the surface of the heat exchanger, resulting in low-temperature corrosion. In this paper, a numerical model for the condensation of H2SO4 vapor on low-temperature surface is constructed. This model combines the thermodynamic phase equilibrium theory, the multicomponent transport theory and the heat transfer theory. The effects of flue gas properties, the size and arrangement of heat exchanger are studied. The results show that, the condensation rate is mainly related to the concentration gradient of H2SO4 vapor near the surface. As the flue gas or surface temperature increases, condensation rate decreases. When the flue gas velocity increases, the mass transfer resistance is reduced, thereby the condensation rate is increased. As the content of H2SO4 in the flue gas increases, the concentration gradient of H2SO4 vapor near the surface increases, and the condensation rate of increases linearly. But the content of water vapor has little effect on the H2SO4 condensation rate. For the tube heat exchanger, when the working conditions keep the same, the smaller the outer diameter of the tube, the greater the condensation rate of the H2SO4 vapor. Compared with the inline arrangement, when the tubes are staggered, the disturbance of flue gas is stronger, and the condensation rate is larger.

Ke Sun, Yu Yan, Fangfang Hu, Lei Deng, Defu Che
Chapter 71. Partitioning Behavior of Arsenic in an Ultra-Supercritical Coal-Fired Power Plant Equipped with APCDs for Ultra-Low Emission

To study the partitioning behavior of arsenic (As) in an ultra-supercritical coal-fired power plant equipped with air pollution control devices (APCDs) for ultra-low emission, the US EPA Method 29 was used to simultaneously sample flue gas before and after selective catalytic reduction (SCR), electrostatic precipitator (ESP), and wet flue gas desulfurization (WFGD). The solid and liquid samples including feed coal, bottom ash, ESP ash, limestone slurry, flush water, WFGD gypsum and wastewater were simultaneously collected in step with flue gas sampling. The mass distribution of As was obtained based on mass balance calculation. Results indicate that the mass balance rate of As is in the range of 78.40–117.68 $$\%$$ % , which is acceptable. At the outlet of air-preheater, particulate-bound As is the dominant species in the flue gas, which accounts for over 98 $$\%$$ % . Most of As were migrated to ESP ash and bottom ash, accounting for 95.19% and 4.28 $$\%$$ % , respectively. Both As5+ and As3+ existed in the feed coal and bottom ash, while As5+ was found to be the major form in the ESP ash, WFGD gypsum and wastewater. The removal efficiency of As by ESP and WFGD is 99.3–99.4 $$\%$$ % , while that by ESP is 99.87–99.90 $$\%$$ % and that by WFGD is 26.32–46.77 $$\%$$ % . The new APCD (mercury absorption device) can oxidize As3+ to As5+ in the flue gas, but somewhat increase the emission concentration of As. As tends to enrich in ESP ash (relative enrichment index  $$=$$ =  1.28) but dilute in bottom ash (relative enrichment index  $$=$$ =  0.23).

Zhipeng Shi, Zhijun Huang, Wei Hua, Lunbo Duan
Chapter 72. A New Scheme for Synergetic Removal of NH3 and SO3 and Particulate Matter in the Flue Gas of Coal-Fired Boiler

In China, coal-fired boilers generally utilize the selective catalytic reduction (SCR) denitration technology to achieve low NOx emission. The SCR catalyst will inevitably convert some of the SO2 in the flue gas into SO3. NH3 escaping from the SCR denitration system can react with SO3 generated in the flue gas to form (NH4)2SO4 and NH4HSO4. NH4HSO4 is highly hygroscopic, viscous and corrosive and easy to induce ash deposition on the heat transfer surfaces at the temperature below its dew point. Since the condensation temperature of NH4HSO4 is just in the operating temperature range of the rotary air preheater (RAPH), the RAPH suffered more serious sticky ash deposition problems seriously impacting the economical and safe operation of the boiler. In this study, a new scheme was proposed for synergetic removal of NH3 slipped from SCR, SO3 and particulate matters in flue gas. The flue gas outlet temperature of the RAPH is raised to the dew point temperature of NH4HSO4 by reducing the heat transfer area, and then NH3 and SO3 in the flue gas can be used as the flue gas conditioning agent to modify the adhesion property and specific resistance of the particles. Therefore, by using this new scheme, not only the particulate matters but SO3 and NH3 escaped from SCR in the flue gas can be removed in the electrostatic precipitator, and the ash deposition corrosion problem on the low temperature heating surface can be greatly alleviated. The key to this new system is the proper parameters design to achieve sufficient adsorption for NH3 and SO3 and the appropriate agglomeration of particulate matters. Therefore, the adsorption and agglomeration characteristics of ash particles were experimentally studied. The results showed that the agglomeration of ash particles can be significantly enhanced by the adsorption reaction, which can increase the mean size of particle matters. The molar ratio between the absorbed N and S contents always maintained in the range of 1.2–1.8. The adsorption of the SO3 and NH3 would interact with the ash particles leading to the morphology changes. Besides, the adsorption of NH3 and SO3 could strengthen the agglomeration of fine ash particles, and produces highly cohesive and relatively large particles, resulting in high collection efficiency due to the reduced rapping losses and re-entrainment. The experimental results initially proved that the proposed system would be a promising approach for the alleviation of the sticky ash deposition and for the synergetic removal of NH3 and SO3 and particulate matters. Further more detailed study would be made to examine the effects of the ratio of NH3 and SO3 in the gas, the adsorption temperature and the particle size on the adsorption rates and adsorption ratio of NH3 and SO3, and the specific resistance of the particles, and the particle agglomeration, in order to obtain proper operating parameters for the synergetic removal system.

Limin Wang, Dechao Li, Yan Yu, Chunli Tang, Lei Deng, Defu Che
Chapter 73. A Population Balance Model for Fine Particle Removal Inside the Electrostatic Precipitator

The electrostatic precipitators (ESP), as the major dust removal devices, requires more advanced designing tools to effectively reduce the fine particulate matter (PM). In this paper a multidimensional population balance model (PBM) is proposed to describe the mechanisms including particle mitigation, coagulation/breakage, nucleation/condensation and deposition/re-suspension inside ESPs. The governing equation is solved after discretizations of space, particle size and velocity. The numerical investigation of a mechanistic lab-scale ESP at Tsinghua shows reasonably good agreements with experimental measured particle size distribution (PSD) and collection efficiencies. Therefore, the model is able to benefit the state-of-the-art design and retrofit of ESPs.

Lu Duan, Qian Huang, Shuiqing Li
Chapter 74. Effect of Calcination Atmosphere on High Temperature H2S Removal of MnxOy/Al2O3 Sorbent in Synthesis Gas

The MnxOy/Al2O3 for high temperature H2S removal were prepared by wet impregnation method with various calcination atmosphere, including N2, H2 and air. The desulfurization and regeneration process were conducted at 850 °C. The result showed that the sorbent calcined in N2 (MN) and sorbent calcined in H2 (MH) had higher sulfur capacity than that of the sorbent calcined in air (MA) during successive desulfurization-regeneration cycles. The characterization result showed that part of Mn3O4 dissolving into the inner of Al2O3 cannot involve the reaction with H2S, which maybe the reason of durability decreasing of desulfurization performance during successive desulfurization-regeneration cycles. In successive desulfurization-regeneration cycles, the tissue structure stability of MN and MH were better than that of the MA, and more active component MN-based oxides were reacted with Al2O3 in MN and MH, the product was beneficial for the H2S removal. However, more Mn3O4 dissolved into the inner of Al2O3 in MA, which cannot react with H2S. These phenomena may be the reason that the higher sulfur capacity of MN and MH than that of MA during successive desulfurization-regeneration cycles.

Li Haifeng, Su Sheng, Liu Lijun, Xu Kai, Hu Song, Wang Yi, Xiang Jun

Design and Operating Experiences

Frontmatter
Chapter 75. A Dataset Analysis of Particular Matter Removal Techniques in China’s Coal-Fired Power Plant

We perform a dataset analysis of particulate matter (PM) removal techniques in China’s coal-fired power plant. The database we built contains 164 units in all regions of China. It covers many typical coal samples and lasts from 2005 to 2019 when the PM emission limit largely reduces from 200 to 10 (or even 5) mg/m3 in China. The most popular primary PM removal technique is the low–low temperature ESP. It is revealed that the specific collection area and inlet flue gas temperature keep adjusting to satisfy the stricter regulation within this period. Usually the use of secondary PM removal technique is necessary for ultra-low emission, with WFGD and demister dominants. The WESP increases the PM removal efficiency, but is always companied with huge electrical costs in operation. We then propose a technology roadmap for the purpose of ultra-low PM emission of coal-fired power plants under different conditions.

Xiaoyu Li, Yu Ni, Hui Long
Chapter 76. Dynamic Characteristics of a Boiler with Low-NOX Combustion

Due to the strictest nitric oxide (NOx) emission limit in the world, a large number of thermal power plants in China have reformed their pulverized coal (PC) boilers with the 3rd generation low-NOx combustion technology which integrates bias combustion burners with separated over fire air (SOFA) nozzles. The 3rd generation low-NOx combustion technology effectively reduces the NOx concentration in flue gas at furnace outlet, from more than 350 mg/m3 to 100–150 mg/m3 in steady states when burning bituminous coal. However, as the utilization of the 3rd generation low-NOx combustion technology, the dynamic process of PC boiler becomes extremely slower than it used to be, on the countrary to the demands of power grid, who expects that the coal fired power plant changes its power load as rapidly as possible. In order to accelerate load changing rate in PC boilers with the 3rd generation low-NOx combustion technology, operating optimization tests, including combustion optimizations in steady states and study on dynamic characteristics during load changing processes, were conducted on a 600 MW commercial boiler. The former works reduce NOx concentration, from 130 to 100 mg/m3, in flue gas at furnace outlet. In addition, the latter works accelerate boiler load changing rate from 1% ECR to 2% ECR, narrowing down the range of steam temperature fluctuation. All these works not only enhance the security of boiler and turbine, but also speed up power load changing process, especially benifit to the flexibility of coal-fired thermal power plant.

Jinjing Li, Lin Yang, Shi Yang, Zhenning Zhao, Yuanyuan Li, Qingfeng Zhang
Chapter 77. Study on Modeling and Control Strategy for Combustion Optimization of Pulverized Coal Boiler

Pulverized coal boilers are often in a state of frequent changes in load, coal type, combustion and other parameters. The generation and removal of nitrogen oxides are closely related to the operating conditions of coal-fired units. Therefore, it is of great economic and environmental significance to study the generation and removal characteristics of nitrogen oxides under full operating conditions of coal-fired units. In this paper, combined with the formation mechanism of nitrogen oxides in coal-fired boilers, the long-term short-term memory neural network model is used to predict the formation of nitrogen oxides in 660 MW front-wall and back-wall pulverized coal fired boilers. Then the optimization of burner switching in variable load process is studied.

Miao Liu, Gengda Li, Xin Wang, Baowei Chen
Chapter 78. Characteristics of RB Control Loop of Large Lignite Power Plant Boiler and Analysis and Comparison

In recent years, lignite has been widely used as an important reserve energy in China. In view of the characteristics of lignite, such as high moisture content, high volatile content and low calorific value, in order to achieve the best expected effect, a plant has carried out many RB experiments. Reasonable use of the boiler itself heat storage, through constant adjustment of water, coal and other inertial links, so that the unit safety and stability to low load. According to the characteristics of lignite boiler, a series of RB logic rationalization control suggestions are put forward.

Y. Zhang, L. Cheng, Q. Zhang, Z. Zhao, M. Gao
Chapter 79. Power Plant Boiler Operation Optimization System Based on CO Control

Based on the characteristics of CO emission from power plant boilers, a CO online monitoring system suitable for power plant boilers was determined through discussion of four aspects: technical principle, flue gas treatment mode, system stability and economy, system installation location. Based on the CO emission value and the relevant operating parameters of the boiler, the boiler economic evaluation indicators were established, including boiler efficiency, superheating and reheat steam temperature, desuperheating water and auxiliary mechanical electrical consumption. According to the evaluation result, the CO emission at the air preheater inlet is controlled within a reasonable range by adjusting the secondary air volume. The application results at a 600 MW power plant show that compared with the original oxygen control method, the power plant boiler operation optimization system based on CO control can reduce the coal consumption of power supply by 2 g/(kW h).

Y. P. Sun, H. J. Cao, Q. F. Zhang, C. Y. Liu
Chapter 80. Technical Measures in Design and Operation of the 1000 MW Supercritical Boiler Burning High-Slagging-Propensity Coal

Centralized coal utilization in large-scale units is still an indispensable part of the energy structure of many developing countries to maintain grid stability. This work is focused on the technical considerations on 1000 MW boiler design and operation for burning high-slagging propensity coals. The design and check coal samples are relatively low in heating values, and exhibit high to severe slagging propensity based on several existing slagging indices. Then the key issues for boiler design are discussed. The use of opposite firing has the advantage of slagging mitigation. Details are provided for the furnace size, burners layout, furnace exit flue gas temperature, furnace arch structure, tube array pitches, and the sootblower deployment. Besides the design considerations, operational optimization is required to reduce the risk of slagging, in which combustion control, slag monitor and effective sootblowing stand out.

Zhou Lyu, Qian Huang, Yuanping Yang, Shuiqing Li
Chapter 81. The Synergistic Performance of Heat and Electricity Studied from the Heating Demand Side and the Supply Side

As the increasingly fast development of cogeneration of heat and power and renewable energy, it is necessary to review the traditional technical route, and develop a more flexible and efficient cogeneration system. The thermal power units on the heating side and the heating users on the thermal demand side, including the whole heat network transmission system, have a great impact on the power grid dispatching. Exploring the regulating potential of the whole heating system can effectively improve the peak regulation of the power grid and the absorption capacity of new energy. Based on the minimum stable combustion load of the boiler, the peak shaving capacity of the cogeneration unit can be increased by 36 million kW compared with the pure condensation operation. In the social energy consumption system, the cogeneration unit can deeply peak-shaving to promote new energy consumption, and save 2.58 million tons of standard coal per year. In addition, different response and delay characteristics of electricity and heat can be utilized to effectively cooperate with frequency modulation operation of power grid and improve power supply quality and operation stability of power grid. At the same time, on the demand side, the adoption of heat storage method can well adjust the peak and valley difference of the power grid.

Pan Zhang, Weiliang Wang, Junfu Lyu
Chapter 82. Effect of Recirculated Flue Gas on 660 MW Double Reheated Boiler

To investigate effect of recirculated flue gas (RFG) on combustion, heat transfer and pollutant emission of double reheated boiler, a three dimension CFD model was established and a scalar equation of mass fraction of RFG was involved to analyze the dispersion of RFG in the furnace. Realizable k-ε model, Euler-Lagrange method, DO model and finite-rate/eddy-dissipation were applied to solve the turbulent flow, dispersion of pulverized coal, radiation and gas-phase turbulent combustion in the furnace. The results show that when the RFG ratio is low, recirculated flue gas was mainly distributed in the central zone of the furnace and spiraled upward in the combustion zone. When the amount of RFG increases, it was diffused around the furnace from the central furnace to the vicinity of the wall, which effectively reduced the temperature. Moreover, NOx emission decreases with the increase of RFG ratio but the carbon burnout decreases apparently when the RFG ratio is larger than 10 $$\%$$ % . The results show that a RFG ratio of 6–10 $$\%$$ % was the best suitable rate for 50 $$\%$$ % THA condition.

H. Xiao, Y. X. Wu, L. L. Feng, C. W. Meng, H. Zhang, M. Zhang, Z. Chai
Chapter 83. Furnace Outlet Temperature Prediction Model of a 350 MW Ultra-Supercritical Boiler

Ultra-supercritical boiler has been widely applied due to its advantages of high combustion efficiency and low pollutant emission. Furnace outlet temperature can indicate the boiler operating status, because of which, related investigations draw various researchers’ attention. Based on a 350 MW design data, this paper established a model for predicting furnace outlet temperature. Comparison of design data and predicted result validates the accuracy of present model. Furnace outlet temperature of different operating parameter (e.g. excess air coefficient) is predicted, which can provide reference for actual operation

Tianyu Zhang, Zhenning Zhao
Chapter 84. Study on the Stability of High Pressure Pneumatic Transport of the Mixture of Pulverized Coal and Extraction Residue of Direct Coal Liquefaction Residue

The use of direct liquefaction residue of coal has been the focus of attention. Due to the liquefaction residue contains more organic compounds, it is necessary to recover these organic compounds by extraction, and then the extraction residue is considered as a feedstock, which mixed with coal into a powder and enter a dry-fed entrained flow coal gasifier for gasification. However, the stability of high pressure pneumatic transport of the mixture of pulverized coal and extraction residue is crucial to the safe and stable operation of dry-fed entrained flow coal gasifiers. In this paper, A set of up to 6.0 MPag high pressure dense phase transport experiments was built, and high pressure pneumatic conveying experiments were carried out using a high-volatile bituminous coal and its mixture with 20 wt% extraction residue of direct coal liquefaction residue (DCLR) in pipes with diameters of 25 mm and 15 mm, respectively, and at back pressures of 1.0–4.0 MPag. By comparing and calculating the relative standard deviations (RSDs) of different signals on the transport stability, the RSD of solid flow rate was selected as an indicator for conveying stability. The result show that the RSDs of both transport stability signals of coal and its mixture with 20 wt% extraction residue of DCLR is less than 4%, which indicated that good stability was found in both the coal and its mixture with 20 wt% extraction residue of DCLR.

B. Z. Peng, X. H. Fang, H. Q. An, Z. Liu, Y. Li, Z. Y. Feng
Chapter 85. Experimental Study of the Flat-Flame Pulverized Coal Gasification Technology

A flat-flame pulverized coal gasification technology is presented and its test results on a 3 t/d gasification test facility are discussed. The test results show that the performance of flat-flame gasification technology is better than the traditional top-placed single-burner technologies, and the test facility is running stably during the test periods. It is revealed that, the flat-flame burner enables higher turbulent intensity and enhances the turbulent mixing between coal particles and oxidant. The overall gasification reaction rate is increased by abovementioned effects. When the mass ratio of O2/coal is 0.8, the carbon conversion, volume fraction of efficient syngas and cold gas efficiency of flat-flame burner were respectively 96.7%, 88.6% and 82.1%, which are completely better than single-burner gasification. Preliminary test results and analysis validates the technical feasibility of flat-flame gasification technology and it is ready for scale-up for industry-scale demonstrations.

H. Q. An, Z. Liu, X. H. Fang, Z. Y. Feng, B. Z. Peng, Y. Li, W. H. Li
Chapter 86. Research on Evaluation of Pulverized Coal Flow Stability in Dilute Phase Pneumatic Conveying Based on Pressure Fluctuation of Resistance Components

By several empirical methods, including pressure drop measurement and electrical capacitance tomography (ECT), flow pattern, pressure drop and pressure fluctuation characteristics of the horizontal bend and venture pipes were investigated. The results showed that, pressure drop signals of venturi is appropriate to evaluate the flow stability. Statistical evaluation indexes, based on effective pressure drop signal of venturi pipe, was constructed to evaluate the powder flow stability. The results showed that, pressure drop signals of venturi is appropriate to evaluate the powder flow stability in different operation conditions.

Yang Shi
Chapter 87. Research on Dense Phase Pneumatic Conveying of the Mixture of Pulverized Coal and Extract Residue of Coal Liquefaction Residue at High Pressure

In order to study on the high pressure dense phase conveying characteristics of extract residue of coal liquefaction residue (hereinafter referred to ER) blending to pulverized coal, the pulverized coal (M1) and the pulverized coal blending 20wt.% extraction residue (M2) were prepared as experimental samples. The conveying experiments were conduct at back pressures (receiver pressure) of 2 and 4Mpag in a pipeline with 25 mm inner diameter. The results showed that at the same superficial gas velocity, there is no significant difference in particles velocity when conveying M1 and M2 samples. The increasing of back pressure reduced the velocity difference between local superficial gas velocity and particles velocity. The conveying phenomena showed that both the mass flow rate and the particle concentration of these two samples increased with the increasing of flow rate of the fluidizing gas. When the fluidization number increased to 2.5, the fluidization effect were good enough to keep the mass flow rate of M1 and M2 stable; when back pressure decreased from 4 to 2Mpag, blending ER to pulverized coal will lead to a decrease in mass flow rate of the mixture powder. The effect of the blending ER to pulverized coal on particle concentration was mainly appeared in the low superficial gas velocity region, in the high gas velocity region, the particle concentration of M1 and M2 was similar during the conveying processes.

X. H. Fang, Z. Liu, H. Q. An, Z. Y. Feng, B. Z. Peng, Y. Li, Y. G. Wang
Chapter 88. The Process of Self-heating Sludge Incineration Based on Granular Heat Carrier

Among the current sludge treatment methods, drying and incineration is one of the most frequently adopted for sludge processing since it works efficiently and can reduce pollution caused by sludge. However, sludge with high moisture content needs a lot of heat for drying before stable burning in the furnace, which increases its cost and causes the stink. This paper introduces a novel process of self-heating sludge incineration based on granular heat carrier as shown in Fig. 88.1. Self-heat incineration means that the process uses self-generating heat for drying and incineration to reduce heat consumption. Free falling particles curtain is used to quickly cool down the flue gas temperature to below 300 °C, to avoid the temperature 300–800 °C that may cause regeneration of dioxin. The particles heated works as heat carrier to dry the wet sludge with water content over 70% in the fluidized bed dryer. The dried sludge is incinerated in the insulated fluidized bed furnace to provide heat to burn other wet sludge directly injected into the furnace. A 240 t/d unit with such process was manufactured and operated in 2017, and the performance is satisfied. SO2 emission is less than 30 mg/Nm3, NOx emission is less than 100 mg/Nm3, PCDD/Fs emission is less than 0.034 ng-TEQ/Nm3 and the investment of this process is less than 250,000 yuan/t/d.

Kong Hao, Miao Miao, Yang Hairui, Zhang Xuyi, Zhang Man
Metadaten
Titel
Clean Coal and Sustainable Energy
herausgegeben von
Prof. Junfu Lyu
Prof. Shuiqing Li
Copyright-Jahr
2022
Verlag
Springer Singapore
Electronic ISBN
978-981-16-1657-0
Print ISBN
978-981-16-1656-3
DOI
https://doi.org/10.1007/978-981-16-1657-0