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2013 Aluminum Keynote: Impurities in the Aluminum Supply Chain


Keynote Session

Raw Material Impurities and the Challenge Ahead

The impurities contained in the raw materials used by the aluminum industry pose challenges that must be managed from various perspectives. These include; product quality, costs, and impact upon the work environment and areas that surround smelters. As the industry continues to grow, impurities, and changes in impurities, will take on greater meaning for process control, equipment design and selection, metal products, and environmental, health, and safety. The author provides his insights into these emerging issues.

Stephen J. Lindsay

Impacts of Impurities Introduced into the Aluminium Reduction Cell

Impurities enter the aluminium reduction process largely through raw materials and operational practices. The declining quality of petroleum cokes, and the steadily increasing efficiency in the capture and recycle of pot fumes, increases impurity burdens with consequent impacts on cell performance and metal quality. Aluminas are a key and quite variable impurity source, with little incentive for producers to drive purity improvements. Beyond metal quality, the critical impacts lie in pot operations where control, or even analysis, of bath chemistry becomes increasingly problematic. Impurities have measureable impacts on current efficiency, and on anode effects, driven by inability to efficiently dissolve alumina. Impurity reduction strategies have been driven by perceived problem elements, for example phosphorus, however these processes generally entail an unacceptable level of collateral alumina loss. It is clear that the alumina contributions to impurity burdens and electrolyte chemistry, are increasingly complex and impact on the way reduction cells are operated.

J. B. Metson, D. S. Wong, J. H. Hung, M. P. Taylor

Changes in Global Refining and Its Impact on Anode Quality Petroleum Coke

The global refining industry has undergone a dramatic upheaval over the past decade. From the mid-2000s when a “Golden Age” was underway, through several years of earnings losses, concerns about ‘peak oil’ to today’s unique crude supply situation in the mid-Continent United States, refiners have never been more challenged in their feedstock supply strategy.

Karl D. Bartholomew

Impact of Higher Vanadium Levels on Smelter Operations

In early 2011, the Rio Tinto — Sebree Works smelter experienced a significant increase (~100ppm) in calcined coke vanadium to levels around 410–440ppm. This was driven by crude oil changes at a refinery supplying one of the primary cokes used in the coke blend supplied to the smelter. The paper discusses the impact of the change on anode quality and carbon consumption and some of the actions taken by the smelter to respond to the change. Data is presented showing the impact on process metrics such as anode consumption, unscheduled anode changes, current efficiency, power consumption, and primary metal quality. The paper shows that changes of this magnitude can be managed with an appropriate understanding of key performance drivers and a focused technical improvement plan.

Chuck Coney, Lew Crabtree, John Gavin, Wes Marcrum, Andrea Weber, Les Edwards

Impact on Smelter Operations of Operating High Purity Reduction Cells

Over the last 15 years New Zealand Aluminium Smelters Limited (NZAS) has developed and implemented technology and operating practices to produce High Purity (Al 99.90+) and Ultra High Purity (Al 99.97+) ingot. In the challenging macro-economic climate of falling LME, weakening exchange rates and increasing power prices, the High Purity strategy has enabled NZAS to maximize value and maintain global leadership in High Purity smelter grade aluminium production.The NZAS journey to High Purity production and the impact that this strategy has had on the complexity of smelter operations are outlined. The operational focus necessary to successfully implement the High Purity strategy is also required to improve all facets of smelter operations. Data will be presented to show the impact recent challenges, such as reducing quality of raw materials, are having on smelter operation and how these are being managed to maintain High and Ultra High purity production economically.

Stewart Hamilton, Ray Cook

Management of Impurities in Cast House with Particular Reference to Ni and V

It is apparent that the concentrations of impurities in raw materials (particularly petroleum coke) are increasing with significant implications for the ability of cast houses to meet customer chemical specifications. A large fraction of the metal content (Ni, V) of the coke and alumina (Fe, Si, Ga, Zn) reports to the Al in the reduction cells. In some smelters the concentration of these impurities is beginning to exceed customer cast product specifications. These impurities can have detrimental effects in certain alloys. In order to formulate control strategies, this paper reviews process options including the classical melt treatment processes of salt fluxing, degassing and filtration for removing impurities in the cast shop. The mechanism of Al boride treatment to remove titanium, chromium, vanadium is examined to get a picture of the possibility of speeding up the process. Those processes used for producing super purity Al are also examined along with refining methods in other non-ferrous metals for potential application to Ni and V control. An investigation into potential for a melt nickel removal process is recapped. We conclude that currently cast house cannot provide a complete solution to the issue of Ni and V control.

M. A. Rhamdhani, J. F. Grandfield, A. Khaliq, G. Brooks

An Initial Assessment of the Effects of Increased Ni and V Content in A356 and AA6063 Alloys

Changes in calcined coke composition associated with different crude oil sources have caused nickel (Ni) and vanadium (V) levels in aluminum to rise. To ensure cast product quality is not compromised an understanding of the effects of these changes is needed. An initial investigation has been conducted for two commonly used alloys, A356 and AA6060/6063. Castings were produced with low typical levels of Ni-V and with high Ni-V levels approaching the maximum P1020 specification of 300ppm each. Micro structural changes were assessed using optical and scanning electron microscopy and tensile properties and corrosion resistance were measured. For as-cast A356 alloy, there was no significant difference in corrosion performance, but adding Ni and V had a small effect on tensile properties. For AA6060/6063 alloy there was no significant difference in the tensile properties of extrusions with low and high Ni-V levels but a small drop in corrosion performance was measured at high Ni-V levels.

John Grandfield, Lisa Sweet, Cameron Davidson, Jason Mitchell, Aiden Beer, Suming Zhu, Xiaobo Chen, Mark Easton

Alumina and Bauxite



Implementation of Logic Control by DCS to Measure the Caustic Concentration in Spent Liquor

In Hydro Alunorte over the years several regression studies have been conducted in order to determine the caustic concentration in spend liquor tanks that feed digestion unit based in temperature, conductivity and density values. A new control is done through multivariable control logic implemented in DCS based on caustic balance in spent liquor storage area. The logic control displays caustic concentration and flows from flash cooling, evaporations and digestion to calculate the soda solution flow required to keep the process parameters. They are part of the instruments control refractometer (PLA), thermocouple and flow meter, which allow the instantaneous measurement of the concentration caustic. The main improvements are stability in caustic control parameters in order to reduce the variability of 53%, reduction in caustic solution consumption, number of analyzed, reduced operator exposure and increase yield

Ayana Oliveira Santos, Aécio Carvalho, Bruno Urakawa, Milton Maciel, E. Antonio Santos

Study of Influences on the Alumina/Caustic (A/C) Ratio and Discharge Digestion (DBO) Caustic of Through Design of Experiments (DOE) Statistic Tool

On the digestion stage of the Bayer process occurs the extraction of alumina contained in to bauxite. The Caustic/Alumina ratio determines the extraction efficiency and stability the digested slurry, as the caustic of discharge digestion determines the digestion delta caustic. Through laboratory experiments at Hydro–Alunorte refinery and the DOE, the influences of the input variables of digestion were evaluated and calculated a statistic model to predict the DBO caustic and A/C ratio. The experiments occurred as the same process conditions of the temperature and pressure by changing the following parameters: weight of bauxite, caustic and temperature digestion, time reaction, CaO and moisture in bauxite, the permutation of these variables totaled 128 reactions. The studies of influences results affirm that the digestion caustic and weight of bauxite are variables of major influence on the A/C ratio and DBO caustic. The statistic model allowed for better monitoring of these variables

Américo Borges, Arthur Monteiro, Ayana Oliveira, Bruno Urakawa, Joel Miranda, Dauton Silva

Particle size distribution model for kinetics of digesting alumina

The kinetic model for leaching process of Chinese diaspore with particle size distribution has been studied. This paper takes into account 1) the irregular shape and rough surface of the natural particles, 2) the residual concentration of Al in particles due to the impurities in natural diaspore, and 3) the particle size distributing in a size range and varying with digesting time. A new kinetic model, PSD+RC+F model, has been developed by the real characteristics of natural bauxite particles in leaching process. The modified gamma distribution function was applied to describe the particle size distribution of diaspore particles. PSD+RC+F model combined with gamma-like distribution function, validated by numerical analysis, shows good agreement with the experimental data.

Li Bao, Ting-an Zhang, Weimin Long, Anh V. Nguyen, Guozhi Lv, Jia Ma, Yan Liu

Fractal kinetic model for digesting alumina

A new kinetic model for diaspore digestion process has been proposed in the view of fractals. Considering characteristics of the natural diaspore particles, this paper introduces two fractal parameters, reactive fractal dimension, DR, and particle size distribution (PSD) fractal dimension, DPSD, to describe the irregular shape and rough surface, and the ruleless particle size distribution, respectively. A piecewise volume cumulative distribution function with PSD fractal dimension has been developed to express the PSD of natural particles varying with digsting time. Combining the piecewise volume cumulative distribution function, the new model, PSD+RC+F model, could express the diaspore digestion process well, by carrying out numerical analysis.

Li Bao, Ting-an Zhang, Anh V. Nguyen, Weimin Long, Jia Ma, Zhihe Dou, Guozhi Lv

MAX HT® Bayer Sodalite Scale Inhibiter: A Green Solution to Energy Consumption

MAX HT® Bayer Sodalite Scale Inhibitor was developed to reduce or eliminate scaling from the evaporator and digester heaters in the Bayer process. This product has been successfully applied in 20 Bayer process plants worldwide, resulting in the significant benefits of increased heat transfer, reduced energy consumption and reduced acid waste from reduced heater cleanings. Based on trial data from a number of plants, the estimated annual savings per ton of alumina produced are 0.26–1.3 Gj energy, resulting in 13–92 kg reduction in CO2 emissions, and 0.9–2.7 kg reduction in acid waste. When these savings are applied to the total alumina production from the 20 plants, this leads to an estimated realized annual savings of 11–56 million Gj energy, 0.54–3.9 billion kg CO2 emissions, and 38–116 million kg of acid waste reduction. For this reason, MAX HT was awarded the 2012 EPA Presidential Green Chemistry Challenge Award.

Morris Lewellyn, Alan Rothenberg, Calvin Franz, Frank Ballentine, Frank Kula, Luis Soliz, Qi Dai, Scott Moffatt


Sodalite Solids Formation at the Surface of Iron Oxide and Its Impact on Flocculation

Sodalite represents the main desilication product (DSP) phase formed from reactive silica during alkaline digestion of bauxite in the Bayer Process. Previous studies into DSP effects on bauxite residue flocculation have focused on flocculant selection or digestion optimisation, not answering a fundamental question: does DSP coat the residue and thereby change surface properties? This study sought to answer that question by contrasting the physicochemical properties of hematite slurries (as a model phase for residue) containing DSP where it was either made in-situ or added as a physical mixture. On the basis of differences found in dewatering behaviour, zeta potential, desilication rates and microscopy of the solids, it is proposed that DSP nuclei initially associate with the hematite surface and subsequently affect flocculant adsorption chemistry, resulting in different extents of flocculant adsorption and smaller aggregates. The practical implications for flocculation processes are discussed.

Alexander Senaputra, Phillip Fawell, Franca Jones, Peter Smith

Improvement on the Operation Management System of Vertical Pressure Filters

Polishing filtration is one of the most crucial step of the Bayer process present in alumina refineries. In Hydro Alunorte, five of the seven production lines use Vertical Pressure Filters (VPF) in the polishing filtration and an excessive consumption of filter cloth was observed. The aim of this paper is present the improvements in the VPF operation management system. The actions were done on the process parameters in order to gain durability of filter cloths used in VPF filters. Process control variables, such as solids in the filtered pregnant liquor, filtration rate and VPF pressure were evaluated and become the limiters for programming the filters operation cycles. An automatic preparation control of the caustic wash solution, used to wash filter cloth at the end of filtration cycle, was also done. The useful life of filter cloth increased by 25% and it means about 12% of reduce in operation costs.

Tatiani Santos, Lucélia Moraes, Aline Sampaio, Milton Maciel, Humberto Lima, Joel Miranda, Alípio Júnior, Juarez Borges

Using a Multivariate Statistical in the Identification of Alumina Loss in Red Mud

The red mud is a residue obtained from the Bayer process for the alumina production and alumina control (gibbsite) present in this important residue, being the limit loss designed is for values below 3.5%. This study used multivariate statistical (Principal Component) to identify the changes of the flow of the plant during the period 2005/2012 that influenced the increase of loss of gibbsite in the red mud residue. This study was conducted in the seven production lines of Hydro-Alunorte, in Pará, Brazil, designed to produce 6.1 million tons of alumina per year. The results confirmed that when the flow of the plant is reduced, there is an increase in the time of contact with the Bayer liquor in decanters and washers, increasing the loss of gibbsite in the red mud. Considering that reducing the flow is a condition inherent to the operation system of a plant, the study recommends adjustments in the routines to reduce operational losses.

Alípio Júnior, Américo Borges, Ayana Oliveira, Humberto Lima, Joaquim Ribeiro, Joel Miranda, Ricardo Podversek

Bevill and the Aluminum Industry

This paper serves as both a primer and an update on the Resource Conservation and Recovery Act (RCRA) statutes and regulations affecting the aluminum industry in the USA. Specifically, this paper will discuss the affect the Bevill Amendment to RCRA has and continues to have on the industry, particularly the import, mining, refining and primary production of aluminum. The paper will cover the development of the RCRA regulations vis-à-vis the aforementioned up-stream aluminum production processes up to the most recent court decisions on applicability of rules to certain of the Bevill “high volume, low toxicity wastes”.

Anthony E. Schoedel

New Development Model for Bauxite Deposits - Dedicated Compact Refinery

An alternative development approach for bauxite deposits proposed in a TMS 2011 paper1 results in a more efficient use of resources and lowers the threshold to develop bauxite & alumina projects.The new approach represents a paradigm shift from “Bigger is Better” to “Smart & Small”, and is based on an alumina refinery with the following characteristics:Dedicated plant design and layout, “designing a greenfield plant as a brownfield expansion”, resulting in lower capital cost per tonne of alumina (tA) capacity;Compact plant production capacity, resulting in a simple and limited scope, further improving capital cost per tA capacity; andSustainability embedded in the design.The current paper explores some aspects of this “DCS-model” such as design basis, plant areas, equipment sparing and layout, applied to a 400,000 t/y alumina refinery. Sustainability will be the subject of a separate paper.

Peter-Hans ter Weer

Red Mud

Automatic Control of Drum Filters Operation

Red mud is the principal waste of Bayer process and must attempt to quality parameters, such as caustic concentration, to not damage disposal environment. In Hydro Alunorte, drum filtration is used for dewatering and washing red mud with filter cloths that retains the cake formed by red mud, recovering part of caustic soda, which returns to the process. The aim of this work was to reduce the consumption of filter cloth with improvement of operation and maintenance by drum filters. After a study of equipment performance, process parameters were adjusted and an automatic control of the drum filter operation was developed, with a complex control loop. The recovery of caustic soda increased and were observed gains on filter cloths durability which means about 40% of reduce in operation costs.

Aline Sampaio, Lucélia Moraes, Tatiani Santos, Humberto Lima, Américo Borges, Juarez Borges

A New Technology for Dry Disposal of Alunorte’s Bauxite Residue

Alunorte uses dry stacking based on the technology of Giulini for bauxite residue storage. The residue is washed and filtered in drum filters. This paper presents a study of a new technology to move from dry stacking to dry disposal for the next implementation phase of Alunorte’s residue disposal area (DRS). A key element is the use of press filters for residue filtration. With this technology will be possible to increase the residue solids content to about 80 wt.-%. This will result in various advantages, such as maximizing the residue storage capacity as a consequence of steeper disposal angles, increasing lifetime of the DRS, lower amount of water within the dump and lower environmental impact.

Marcelo Miranda de Castro, Carlos Roberto Abrunheiro Trindade, Ronaldo Guimarães Pantoja, Eduardo Raimundo Queiroz Alves Junior, Armênio Rabelo Martins

Pilot Test of Bauxite Residue Carbonation with Flue Gas

The Bayer process alumina production generates 0.7 to 2.0 ton of bauxite residue (BR) and an average of 1.0 ton of CO2 per ton of alumina produced. The direct use of exhaust gases to react and reduce the alkalinity of BR may allow a triple gain: improve the storage conditions, open a range of new applications for BR and sequester from 33 to 102 kg of CO2 per ton of alumina. This paper shows a pilot scale reaction of a suspension of bauxite residue in water with flue gas, produced from direct oil burning. Three different types of reactors were used: one spray tower and two packed columns. The inlet and exhaust gases were analyzed using electrochemical and non dispersive infrared sensors. The pH of the suspension was monitored during and after the reaction to evaluate the buffer effect.

Luis C. A. Venancio, José Antonio Silva Souza, Emanuel Negrão Macedo, Fernando Aracati Botelho, Glaucia Costa César

Management of Industrial Waste: The Case of Effective Utilization of Red Mud and Fly Ash at Vedanta Aluminium Limited - Lanjigarh

Red mud is the major waste produced during the production of alumina through Bayer’s process. Its disposal remains a worldwide issue because of huge land requirement and associated environmental concerns. Substantial R&D activities are going on around the world to find its effective utilization, including development of various products and byproducts. At present, the setting up of materials industries is taking place at a rapid pace which necessitates the availability of enormous amounts of raw materials. The use of red mud and fly ash in building material production is one viable option for conservation of natural resources and effective utilization of hazardous industrial effluents.The present paper intends to put forth a perspective view based on real-facts, information and data on the enterprise of VAL’s Refinery towards the utilization of the industrial wastes being generated by the set up with special reference to red mud and fly ash.

Mukesh Kumar, Bimalananda Senapati, C. Sateesh Kumar

Iron Recovery from Red Mud by Reduction Roasting-Magnetic Separation

This work provided an effective method for comprehensive utilization of red mud, which mainly focused on the first step of recovering iron from a high iron content red mud by reduction roasting-magnetic separation. During the reduction, iron oxides were reduced to metallic iron with the aid of sodium sulfate and sodium carbonate. Effects of the dosages of sodium sulfate and sodium carbonate, roasting temperature and roasting time on the metallization ratio of iron of roasted product, total iron grade and iron recovery of magnetic concentrate were primarily investigated. In the presence of 6% Na2SO4, 6% Na2CO3 and optimal reduction roasting-magnetic separation conditions: roasting temperature of 1050 °C, roasting time of 60 min, magnetic separation feed fineness of 90% passing 74 urn and magnetic field intensity of 0.1 T, a magnetic concentrate containing 90.12% iron with iron recovery of 94.95% was obtained from a red mud containing 48.23% total iron, 7.71% Al2O3 and 7.69% SiO2.

Mingjun Rao, Jinqiang Zhuang, Guanghui Li, Jinghua Zeng, Tao Jiang

Removal of Methylene Blue from Aqueous Solutions Using a Novel Granular Red Mud Mixed with Cement

A novel adsorbent was prepared from granular red mud (GRM) mixed with cement and its potential to be a suitable adsorbent for removal of methylene blue (MB) from aqueous solutions was evaluated. By investigating duration of oscillation, dosage of MB, pH and temperature on the adsorption effect, the best experimental condition was obtained: the methylene blue with the dosage of 150 mg/L and a constant pH of 11, after 240 minute oscillation at 303K, the removal of MB and the state balance of absorption capacity up to 86.89 % and 2.6040 mg/g. The equilibrium adsorption was found to increase with increase in temperature of the adsorption process. It was observed that the adsorption isotherms are well represented by both the Langmuir and Freundlich isotherm models. But because the Freundlich isotherm model had a better fitting, the adsorption was attributed to successive multilayer adsorption. Meanwhile, thermodynamic parameters depict the endothermic nature of adsorption and the process is spontaneous. The pseudo-second-order kinetic model was used to correlate the kinetic experimental data and the kinetic parameters were evaluated.

Lu Shuaidan, Thiquynhxuan Le, Shaohua Ju, Peng Jin-hui, Zhang Li-bo

Precipitation and Calcination

Environmentally Safe Operation of Barometric Condensers

Refining alumina from bauxite via the Bayer Process can create environmental liabilities. Many refineries rely on barometric condensers for key unit operations. While barometric condensers offer simple, efficient, and reliable cooling options, they have the ability to discharge contaminated water back to the cooling water source. With tightening environmental regulations worldwide, developing reliable barometric condensers that operate without discharging high pH water is critical to sustaining condenser operations. Alcoa has devised a method to prevent high pH excursions from barometric condenser discharge that has been 100% effective.

Matthew Jacobs

Hatch - ETI Aluminyum Precipitation Modeling

World alumina producers are focusing their efforts on increasing plant efficiency and product quality. The aluminum smelters, the customers of about 90% of the alumina plant product, are requiring a strong and coarse alumina. This demand has lead to more challenging process conditions for the hydrate precipitation process, requiring further fundamental understanding.This paper describes a methodology to predict the Particle Size Distribution (PSD) of hydrate precipitation using SysCAD steady state process modeling. The process model is validated with data from ETI alumina plant. It is shown that Hatch and ETI Aluminyum have implemented a modified hydrate precipitation circuit that employ a classification system for proper distribution of coarse and fine seed, agglomeration stages, and new particle process control strategies which resulted in hydrate product coarsening from approximately 20%, -44µm to 10%-12%, -44 µm and product yield to over 94 gpl Al2O3.

E. Stamatiou, D. R. Chinloy, B. Çelikel, M. Kayaci, E. Savkilioglu

Improve the Classification System in Hydro Alunorte Lines 4/5

Precipitation was the main bottleneck in lines 4 and 5 and had a lower operating factor and yield than the other precipitation lines. The lower operating factor and yield was associated with the following issues: The original flowsheet required the precipitation circuit to be coarse in order to be able to send the produced hydrate to calcination and to limit the amount of fine seed to the Tertiary Thickener system. In addition the Primary Thickeners and Hytanks had frequent pluggages in the underflow and required frequent caustic cleaning. The old circuit limited the solids concentration in the circuit to about 420 gpl. This, together with coarse precipitation circuit and the low operating factor, were the reason for the low production of these lines. The main part of the proposed modifications was upgrade the existing Secondary cyclone system, add an additional Secondary cyclone battery and replace the Primary Thickener and Hydrate Tank with cyclones. In addition to resolving the operational and maintenance issues above, eliminated the precipitation bottleneck and guarantee the budget production expected for this two lines, also there are an expectation to increase production.

Emerson Moraes, Hans Haraldsen, Cleto Junior, Joaquim Ribeiro, Cesar Magro, Jose Chartouni, Everton Santos, Darlan Gomes

Increase in the Stability of Gravimetric Classification System of Precipitation at Hydro Alunorte

After the installation of coarse seed filtration at lines 1, 2 and 3 at Hydro Alunorte, the precipitation productivity was increased, however the effect of higher concentration of solids in the circuit generated some operational problems. Small interruptions in the feed of the filters were responsible for significant production losses resulting from the overload of solids on the classification system caused by the addition of liquor to the chain. In order to improve circuit stability, the underflow streams from the secondary classifier were divided between the first cementator, where the control of supersaturation occurs, and second cementator, where it is fed excess seed. When the seed filter stops, its feed reduces and the flow to second cementator increases, eliminating the flow variation in the chain. Furthermore, statistical modeling was performed to regulate the concentration of solids in the feed of the thickeners, reducing the overload to it.

Victor Cruz, Emerson Moraes, Cleto Azevedo Junior, Denise Rodrigues, Adjane Souza, Alex Furtado, Dauton Silva

“Experience with Commissioning New Generation Gas Suspension Calciner”

Gas Suspension Calciners (GSC) for Alumina have been designed, supplied and commissioned by FLSmidth since 1984 with a nameplate capacity from 820 to 4500 tpd of Smelter Grade Alumina (SGA). Several of these units have been supplied to China using Coal Gas as fuel, and the GSC technology is now used in almost all Chinese refineries build since 2005.The first two (2) of seven (7) new generation GSC units with name plate capacity from 2500 to 3500 tpd SGA is now being commissioned at Rio Tinto Alcan’s Yarwun Refinery in Australia. This paper describes design features of the new generation GSC units and reports the latest operating data with respect to alumina capacity and quality, environmental emissions and energy efficiency.

Susanne Wind, Benny E. Raahauge

Bayer Process Efficiency Improvement

The process efficiency has a great influence on the production yield, energy consumption, investment and operation cost in Bayer process.The factors affecting the Bayer efficiency are particularly discussed in this paper. Reducing the molar ratio of pregnant liquor and raising the molar ratio of spent liquor and the caustic concentration of spent liquor will enhance whole output efficiency in Bayer process. Higher concentration of spent liquor will bring about higher productivity in digestion process and a higher pregnant liquor concentration will be required for reducing energy consumption at evaporation stage as well.The key technology development to improve the Bayer efficiency in Chinese alumina production is revealed.

Gu Songqing

HyClass™ Technology for Improvement of Trihydrate Classification in the Bayer Process

The classification section in the Bayer plants is a critical part of the process. The final separation of the finest hydrate particles from the spent liquor takes place in the tertiary thickener vessels. Efficient capture of trihydrate particles in the classification circuit is essential to improve the productivity of the Bayer process. It is widely accepted that the efficiency of the classification circuit can be improved by the use of additives. Nalco is continually developing new polymer chemistries to improve the efficiency of trihydrate flocculation. A novel hydrate classification technology, HyClass™, was developed by Nalco and field evaluated in the tertiary thickener units of Noranda Alumina. HyClass technology significantly improves the flocculation performance against an industrial standard 85700 with respect to increased hydrate capture, improved settling dose-response, higher underflow densities and most importantly, further improved slurry rheology. The lab development and field evaluation work is summarized in this paper.

Jing Wang, Jaqueline Herrera, Shawn Kostelak, Kody Frederic


Metallic Impurities from the Mine to Metal Products

When it comes to the metallic impurities in alumina, some are of greater importance and concern than others. But, all have maximum levels that can be tolerated by downstream processes and products. This may also be true even when alumina is not the major contributor of a specific impurity, but does significantly contribute to the baseline impurity level. In this paper the author discusses various points of concern related to specific metallic impurities. Conclusions and general guidelines are offered on what acceptable levels will be to most customers of SGA.

Stephen J. Lindsay

The Control of Fluoride Concentration in ETİ Alüminyum Bayer Refinery Liquor

In the ETI Alüminyum Bayer Process liquors, fluoride is evident as an undesirable impurity, because it presents itself as a precipitate of Sodium Fluoride (NaF) in the higher concentration liquors, which has two mal effects, one of which limits the caustic concentration that ETI can attain, and the other is its solid phase presents as scale.Spent liquor from precipitation is fed to evaporators. To improve alumina extraction in autoclave liquor it was decided that the strong liquor caustic concentration be gradually increased. It was noticed that scale formation in the strong liquor pumps and pipelines dramatically increased. XRF and XRD characterized the scale as ‘Villiaumite’ (NaF). Research on Villiaumite found that it started to precipitate at higher caustic concentrations. The solubility of NaF was evaluated and saturation levels were determined. As a result of this study control of NaF precipitation is practiced by ETI.

Esra Savkilioglu, Carl Carton, Serkan Ertugral, Meral Baygul, Kemal Dinc, Seyit Avcu

Beneficiation of High Silica Bauxite Ores of India an Innovative Approach

Many bauxite reserves in India have Al2O3/SiO2 ratio of 4 to 6 and hence pose difficulties in production of alumina through the Bayer process. The extraction of alumina from bauxite in low temperature digestion circuit frequently involves a desilication step in which kaolinite dissolves and reprecipitates as sodalite, a caustic insoluble sodium alumino silicate. Thus formed insoluble sodium alumino silicate gets separated from the process into the red mud, thereby entailing the loss of valuable caustic soda and alumina. The more is the silica, higher is the soda consumption which increases the cost of alumina production.Physical beneficiation techniques are employed to reduce the reactive silica content of bauxite. Based on several investigations it has been made possible to remove ~30% of silica with 92% recovery depending on the characteristics of the ore. The results of detail studies are presented in this paper and it is expected that these findings will lead to improved Alumina Refining practice in the future.

Mukesh Kumar, Bimalananda Senapati, C. Sateesh Kumar

Morphological Investigation of Sodium Oxalate Crystals Grown in Aqueous Sodium Hydroxide Solution

Sodium oxalate crystals grown in aqueous sodium hydroxide solutions with different concentrations were characterized by optical and atomic force microscopy to examine their morphologies. Experimental results indicated that a high concentration of sodium hydroxide had a dramatic effect on reducing the size of sodium oxalate crystals. A nitrogen gas adsorption technique was employed to quantify the change of specific surface area of sodium oxalate. A two dimensional image analysis technique was also employed to estimate surface area and the crystal size distribution of sodium oxalate.

Weng Fu, James Vaughan

Impurities in Raw Gas and Secondary Alumina

It is known that impurities in the secondary alumina tend to accumulate in the finer alumina fractions. Although several treatment methods have been suggested for impurity removal, very few in depth studies are published. In this study, samples of secondary alumina have been split into different fractions using an air classifier. In addition, the secondary alumina has been compared with samples extracted from the raw gas before the dry scrubber. The characterization of the secondary alumina fractions and the raw gas samples are performed by SEM, XRD, EPMA and ICP-MS chemical analysis. Some introductory considerations on acid leaching of the secondary alumina fractions to remove and recover the impurities will also be discussed.

Svetlana Kalyavina, Arne Petter Ratvik, Thor Anders Aarhaug

Low Grade Alumina Sources

Innovative Technology for Alumina Production from Low-Grade Raw Materials

Increasing numbers of research institutes and industrial companies in the world are showing their interest in developing alternative methods for producing alumina from low grade raw materials. This paper examines the advantages and disadvantages of methods proposed by different authors for producing alumina by hydro chemical technology (alkaline and acid) compared with the alkaline sintering technologies.

Alexander Senyuta, Andrey Panov, Alexander Suss, Yuri Layner

Improving Characterization of Low Grade Diasporic Bauxite to be Utilize in Jajarm Alumina Plant

To increase the proportion of lower grade bauxite in the utilized feed and also possibility of increasing A/S ratio in the plant feed (4.66), some investigations on improving A/S ratio of Elburz Bauxite, especially lower grade ones, by gravitational method and flotation has been carried out. To evaluate heavy media separation, using heavy liquids with different specific gravities between 2.8–3.4 (g/cm3) on various size fractions of this bauxite with initial A/S ratio between 1.3–8.5, resulted that a special specific gravity can produce the concentrates (in sunk fractions) with the A/S ratios and productivities which can economically be used as plant feed. Pilot plant tests also carried out on a 25t sample of Bauxite with a A/S ratio of 2.0 and concentrate A/S and recovery in DMS tests were 3.30 and >40%, respectively.

Mohammadtaghi Shadloo, Mohammad Zarbayani, Esmaeil Jorjani, Mojtaba Aram

The Processing of High Quartz Bauxite

Low-grade bauxite refers to bauxite that is high in silica, which is present as kaolin, or quartz, and therefore requires different approaches for processing. With digestion of gibbsitic bauxites the quartz would remain largely undissolved. The nature and hardness of Quartz with respect to other minerals in bauxite will suggest that coarse size fractions will have high quartz content. Whilst designing an alumina refinery designers need to pay special attention to high quartz content slurries as they are abrasive, in addition the non-homogeneity of the resultant mud will mean that the quartz rich particles will settle faster causing segregation within settlers and washers resulting in poor operation. Two options were considered to deal with high quartz bauxite, upstream physical separation during the beneficiation process, or physical separation post bauxite digestion. This paper seeks to explore design and operational considerations whilst designing a greenfield refinery for high quartz content bauxite.

Edgar Gasafi, Alessio Scarsella, Vladimir Hartman, Hans. W. Schmidt

Appropriate Reduction and Fe-Al Separation of High Iron Gibbsite

High iron gibbsite is a Fe-Al composite ore with quite big reserves in China, in which superfine aluminum and ferrous minerals are conjoint with each other. Thus, they are difficult to separate through physical beneficiation. In order to meet iron and aluminum consumption, a new process was proposed, in which gibbsite samples and pulverized coal were mixed uniformly, reduced isothermally at high temperature, cooled rapidly and then dressed by magnetic separation. The effects of reduction conditions, including reduction time, reduction temperature and FC/O (mole ratio), were investigated. The results revealed that regarding samples with 34.68% iron and 23.85% alumina, metallic iron concentrate with 78.23% iron and non-magnetic product with 53.32% alumina were obtained. The yielding ratio of iron and alumina are 89.24% and 86.09% respectively. Metallic iron concentrate can be used as steelmaking burden by further treatment, and alumina can be further extracted from the nonmagnetic product.

Liu Zheng-gen, Chu Man-sheng, Tang Jue, Han Yuan-ting, Wu Xiang-long

Influence of MgO and C/A and Cooling System on Alumina Leaching Properties of Calcium Aluminate Slag

The influences of the content of MgO and C/A (molar ratio of CaO and Al2O3, excluding CaO in 2CaO • SiO2) and cooling system on alumina leaching properties of calcium aluminate slag were investigated by XRD, laser particle size analyzer and chemical analysis. The results showed that when the temperature of taking the sample out from furnace is 1200°C, the alumina leaching rate is gradually decreased from 82.12% to 51.3% with the content of MgO increasing from 0% to 5%.The leaching rate is gradually increased from 51.3% to 74.74% with C/A increasing from 1.71 to 1.85. The leaching rate is gradually increased with the temperature decreasing under 4~5°C/min of cooling rate. When the temperature is 500°C and C/A is 1.85, the main phases of slags are Ca12Al14O33 and r-Ca2SiO4, the self-disintegrating rate is 94.45%, and the alumina leaching rate is 83.69%. The calcium aluminate slag meets alumina leaching requirements.

Zhifang Tong, Yingjie Li, Tao Chen

Calcification - Carbonation Method for Alumina Production by Using Low-Grade Bauxite

Aluminum industry is one of the most important industries in China’s nonferrous metal metallurgy industry. With the development of output in alumina and the improvement of its production technology, China’s high quality bauxite resources are difficult to meet. Under this condition, “Calcification-Carbonation Method” was put forward to deal with middle-low grade bauxite and red mud by Northeastern University, the main purpose of this method is to change the balance phase of red mud into 2CaO•SiO2 and CaCO3 with hydrometallurgical process. Through treatment by “Calcification-Carbonation Method”, A/S of the new structure red mud lowed below to 0.5 and the Na content lowed below to 0.3%, the red mud could be used in cement industry directly. This paper mainly introduced the technological idea and principle of new method, process comparison and typical experiment results is given as well.

Zhang Ting’an, Zhu Xiaofeng, Lv Guozhi, Pan Lu, Liu Yan, Zhao Qiuyue, Li Yan, Jiang Xiaoli, He Jicheng

Basic Research on Calcification Transformation Process of Low Grade Bauxite

Our group put forward a “Calcification-Carbonation” new process use of low grade bauxite to produce alumina based on the problem of bauxite grade are decreasing gradually in china. This paper studies the effect of reaction thermodynamics, kinetics and processing parameters in calcification process. The thermodynamics calculation results show that both calcification reactions of gibbsite and diaspore can proceed within their dissolution temperature range. The study of Non-isothermal kinetics by high-pressure DCS results show that the calcification reaction for gibbsite occur within the temperature range 231.7–248.2°C and 248.2–268.7°C, with an activation energy of 23.7kJ/mol and 18.0kJ/mol respectively; diaspore occur within the temperature range 236.7–255.6°C and 255.6–287.5°C, with an activation energy of 264.9kJ/mol and 118.5kJ/mol respectively. Experimental results show that the appropriate calcification temperature of diaspore and gibbsite are 245°C and 180°C, molar ratio of CaO to SiO2 is 4.69:1; under these condition, silicon phase in minerals transformed hydrogarnet completely.

Zhu Xiaofeng, Zhang Ting’an, Lv Guozhi, Liu Yan, Zhao Qiuyue, Dou Zhihe, Li Yan

Research on the phase transformation and separation performance in calcification - carbonation method for alumina production

With the rapid development of China’s aluminum industry, deficiency of high-quality bauxite reserves has become a bottleneck restricting for the healthy development of China’s aluminum industry. According to these issues, “Calcification-Carbonization Method” was purposed by Northeastern University for alumina production by using low grade bauxite. This paper researched on the transformation and separation performance in the new method. The experiment results indicated that: Al, Fe, Si transformed into hydrated garnet at 180°C and 245 °C through calcification treatment, and silicon phase changed into 2CaO • SiO2 through carbonization treatment. The settling performance of calcification slurry by using gibbsite is near to that of bayer process, when the settling performance by using diaspore get worse because of the solid content is higher than that of bayer process. Under the pressure of 0.18MPa, the filter constant of calcinated slurry are 4.18 × 10-5m2/s and 1.15 × 10-4m2/s for diaspore and gibbsite.

Lv Guozhi, Zhang Ting’an, Zhu Xiaofeng, Pan Lu, Qin Mingxiao, Liu Yan, Zhao Qiuyue, Jiang Xiaoli, Li Yan

Aluminum Alloys: Fabrication, Characterization and Applications


Development and Application

Mechanical Properties of Al-Zn-Mg-Cu Alloys Processed with High-Pressure Torsion

It has been reported that tensile strength of the 7075 alloy, a commercial age-hardenable Al-Zn-Mg-Cu based alloy, is significantly improved by high-pressure torsion (HPT). The present research has been performed to study the effects of alloy compositions and process conditions on mechanical properties in Al-Zn-Mg-Cu alloys processed with HPT. Several Al-Zn-Mg(-Cu) alloys were melted and cast, and disc specimens of 10 mm diameter and 1 mm thick were machined from the homogenized ingots. The disc specimens were solution treated and subjected to HPT with a compression stress of 2 GPa at a rotation speed of 1 rpm. The torque at the steady state increased with increasing amount of alloying elements. The strength after HPT also increased with increasing amount of alloying elements. The tensile strength of Al-10%Zn-2%Mg-2%Cu alloy, in mass %, was increased to about 900 MPa by 10 turns of HPT processing.

Shigeru Kuramoto, Ichiro Aoi, Tadahiko Furuta

High-Performance Be-Al Casting Alloys

Investment casting is a near net shape manufacturing process that typically reduces both the amount of alloy and machining time needed to produce a part. The reductions in these two areas frequently lead to significant decreases in the total cost of the part. Materion has developed procedures for the investment casting of three Be-Al alloys (AlBeCast® 910, 920 and 930). These alloys are composed primarily of Be and Al, and also contain smaller concentrations of other elements (Si, Ge, Ni, Ag, Co and Sr). The Be and Al have very little solubility for one another. Also, they have quite different solidification temperatures (1285 and 660 C respectively). As a result Be-Al alloys solidify with a large mushy zone and form two phases, one being Be and the other Al. In general the alloying elements are selected to improve the mechanical and casting properties of the Al phase, although they also have an impact of the Be phase. X-ray dot maps of alloy cross sections show that the Si, Ge, Ag and Sr tend to stay in the Al phase whereas the Ni and Co forms solid solutions with both the Be and Al. The addition of Ag has the largest impact on the strengths of the alloys due to its tendency to form a Widmanstatten plate, δ’, phase with the Al. Additions of Co and Ni increase strength but also produce a large decrease in thermal conductivity. The high concentrations of Be in these alloys result in high specific modulus values.

Gary Schuster, Charles Pokross

Structure Optimization of Al-Si-Type Alloys for Thermal and Mechanical High Loaded Components

Research and development are a very specific challenge due to the pressure to innovate, to which the automobile industry in particular is subject worldwide. For this reason the development of new materials with improved properties and process-engineering advances were the focus of this project.The targets are to improve properties of aluminum cast alloys by refining the grain size and increasing the heat conductivity. The latter gives better material performance for all applications with local heat maxima. Due to better heat conductivity the maximal material temperature during use will be lower. This yields better local mechanical properties.Therefore a melt treatment with boron was tested, which provides a higher heat and electrical conductivity and yields a better grain structure for improved mechanical properties.This paper describes the development process, the experiments and the results from the examinations. Additionally it gives an outlook on the potential of such aluminum alloys.

Andreas Kleine, Marcel Rosefort, Ansgar Pithan, Christiane Matthies, Hubert Koch

Development of High Strength Aluminium Alloys at BALCO

Aluminium is one metal that makes soft kitchen foil forms the vital high strength parts of aerospace vehicles. To cater to the needs of the aerospace sector and for enhancing market share in the premium products category, BALCO jointly with Vikram Sarabhai Space Centre, ISRO, has established facililities for production of various high strength aluminium alloys for Aerospace and Defence Sectors.Bharat Aluminium Company Ltd. (BALCO) has been closely associated with the growth of Indian aluminium industry. It has played a pivotal role in making aluminium one of the leading metals of the 21st century with myriad uses ranging from house hold and industrial requirements to Defence and Aerospace applications. BALCO has contributed significantly as a primary producer by providing sustenance to vital industries and has proved its mettle by developing and supplying Aerospace grade aluminium alloys to Vikram Sarabhai Space Centre for their Space Launch Vehicles Programmes.

Mausumi Kar, Sachin Prasad, A. K. Paul, P. K. N. Raghavan

Corrosion Resistance Performance

Strength and Failure of Ultrafine Grain and Bimodal Al-Mg Alloy at High Temperatures

Uniaxial tensile tests are conducted at room and high temperatures on a bimodal grain size Al-Mg alloy with an ultrafine grain matrix as the major constituent to evaluate the strength and failure mode of the material. The coarse grain ratio and anisotropy effects are also investigated as parameters that could influence the mechanical behavior. It was found that the strength of the material decreases rapidly with temperature such that at 473 K, it was somewhat weaker than a comparable conventional alloy. Dynamic recovery was observed and found to be dependent on coarse grain ratio. Strength anisotropy was found to be reduced with increasing temperature. No evidence of thermally or mechanically assisted grain growth were observed.

Andrew Magee, Leila Ladani

Process development of AA3103 aluminum alloy for automotive thins

AA3XXX alloys have been widely used to produce automotives thins. First, these thins are drawed, before the condenser production in which it can be used processes as brazing. These alloys can show a large variability of macrostructure due to different cooling rates used after homogenizing whose diffusion mechanism of manganese in solid solution is prevailing. In this work, they were analyzed as-cast samples involving 3 homogenizing temperatures and 3 different cooling rates. Afterwards, samples were rolled until thickness of 200µm and heated to 6 different temperatures to create the annealing curve for each situation. Macro and microstructure analysis was performed as well as electric conductivity. This last showed that the higher treatment temperature and cooling rate are the lower the electric conductivity is. Manganese diffusion from solid solution to precipitated favors the recrystallization and promotes a more homogeneous and fine distribution of grains.

Marcelo Paes, Augusto D. Coelho, Roberto S. Netto, Fernando C. Aguiar

Casting and Solidification

Atom Probe Analysis of Sr Distribution in AlSi Foundry Alloys

The addition of traces of Sr to AlSi foundry alloys induces a flake-to-fibrous transition of the eutectic phase which enhances tensile, impact and thermal shock properties. Since this modification is not always completely homogenous, the underlying mechanisms have to be reviewed. In this work the three dimensional Sr distribution in eutectic Si was analyzed by Laser Pulsed Atom Probe Tomography. Well modified fibers revealed nanometric segregations rich in Al and Sr. These features presented cluster-, planar- and rod-like morphologies which can be related to mechanisms involved in Si growth restriction. This finding reinforces the fact that Sr has a direct influence on the growth mechanism of eutectic Si.

Jenifer Barrirero, Michael Engstler, Frank Mücklich

The Role of Sr on Microstructure Formation and Mechanical Properties of Al-Si-Cu-Mg Cast Alloy

The aim of this paper is to assess the role of Sr modification on eutectic Si, Fe-rich intermetallic phases and porosity and their responses to the mechanical properties of a commercial high pressure die cast alloy Al-Si-Cu-Mg with Fe level up to 1%. Tensile test samples with a variety of coarsenesses, containing different Sr levels were cast using the gradient solidification technique, that enables a study of the solely influence of Sr on micro structure and tensile properties. The modification altered the morphology and size of eutectic silicon, while did not make a significant change on morphology of Fe-rich intermetallic and volume fraction distribution of porosity. The tensile test results indicate that eutectic Si modification is not a guarantee for improved mechanical properties due to the presence of a variety of intermetallics that tend to have a larger role on initiating and propagating cracks leading to premature failures in these commercial alloys.

Mohammadreza Zamani, Salem Seifeddine, Mona Aziziderouei

Modification of the Eutectic Mg2si-Phase of AlMgSi-Cast Alloys

The present work shows a possible method for refining the micro structure of AlMgSi cast alloys in a similar fashion to the method which has been state of the art for many years in the case of hypoeutectic AlSi alloys.

Thomas Pabel, Tose Petkov, Christian Kneissl, Peter Schumacher

The influence of casting speed in the as cast strip mechanical properties of 8079 and 8006 alloys

The influence of casting speed on mechanical properties from twin-rolled cast strip was investigated. Low and high speed coils of 8079 and 8006 alloys were produced from FATA HUNTER twin roll caster of ELVAL.Microhardness and tensile tests of low casting speed coils for both alloys exhibit higher hardness and mechanical properties compared to the higher casting speed coils.Electrical Conductivity measurements and metallographic examinations helped to explain the difference in mechanical properties between the high and low casting speed coils. Increased micro structural knowledge allowed ELVAL to optimize the cold rolling and annealing processes to meet customer specifications.

Dionysios Spathis, John Tsiros

Effect of Cooling Rate on Iron-rich Intermetallic Phases in 206 Cast Alloys

The effect of cooling rate on the solidification characteristics of the iron-rich intermetallics in 206 cast alloys with iron contents up to 0.5 wt% was investigated. The iron-rich intermetallics were analyzed and characterized by using Scanning Electron Microscopy (SEM), Differential Scanning Calorimeter (DSC) and Thermal Analysis (TA). It was found that Chinese script α-Fe and platelet β-Fe phases are the two main iron-rich intermetallics up to 0.3 wt% Fe. With increasing cooling rate, the precipitate temperature increases for a-Fe but decreases for β-Fe and eventually the formation of the β-Fe will be completely suppressed. At 0.5 wt% Fe, two extra iron-rich intermetallics, Chinese script Alm(FeMn) and platelet Al3(FeMn) are experimentally observed. With increasing cooling rate, the Al3(FeMn) or Al6(FeMn) phases that precipitated at relatively low cooling rate can be replaced by Alm(FeMn) and α-Fe. The critical cooling rate to effectively suppress the formation of the platelet β-Fe and obtain dominant Chinese script α-Fe or Alm(FeMn) decreases with increasing iron level.

K. Liu, X. Cao, X.-G. Chen

Effect of Iron in Al-Mg-Si-Mn Ductile Diecast Alloy

The effect of iron on the micro structure and mechanical properties of Al-Mg-Si-Mn alloys has been investigated in high pressure diecast components in association with CALPHAD modelling of the multi-component Al-Mg-Si-Mn-Fe system. It is found that the Fe-rich intermetallic phases solidify in two stages in the high pressure die casting process: one is in the shot sleeve and the other is in the die cavity, showing different morphologies. The compact and star-like intermetallics are identified as α-AlFeMnSi phase with typical composition of Al12(Fe,Mn)3Si. At the increased level of Fe content, β-AlFe is found in the micro structure with a long needle-shaped morphology, which is identified as Al13(Fe,Mn)4Si0.25. The existence of Fe-rich intermetallics in the alloy slightly increases the yield strength, but significantly reduces the elongation. The ultimate tensile strength maintains at similar levels when Fe contents are less than 0.6wt.%, but decreases significantly with the further increased Fe concentration in the alloys.

S. Ji, W. Yang, F. Gao, D. Watson, Z. Fan

Oxidation Behavior of Al2Ca Added Al-5Mg Alloy in the Liquid State

The aim of the present study was to investigate the effect of Al2Ca added Mg addition on the oxidation behavior of Al-5Mg alloy in the liquid state with TGA and melt oxidation test. Results of TG analysis showed that while the weight gain of Al-5Mg was 10%, Al2Ca added Al-5Mg had the weight gain to 0.01%. Comparison between the surface and cross sectional appearance showed that there were a large number of pores and oxide clusters in Al-5Mg alloy, while pore was not observed in Al2Ca added Al-5Mg alloy. SEM and EDS studies revealed that the formation of pores in Al-5Mg alloy was mainly due to the transformation of MgO to MgAl2O4 as the holding time was extended. In the case of Al2Ca added Al-5Mg alloys, the existence of MgAl2O4 was not observed. On the other hand, MgO/CaO mixed layer existed and would act as a protective layer.

Young-Ok Yoon, Seong-Ho Ha, Gil-Yong Yeom, Hyun Kyu Lim, Shae K. Kim

Effect of the Thermal Modulus and Mould Type on the Grain Size of AlSi7Mg Alloy

Thermal analysis has been used for decades for melt control before casting aluminum alloys. However, obtaining a good grain refinement in a standard cup does not ensure that the grain refinement is correct in real parts which may solidify at very different cooling rates. For this study, the effect of cooling rate on AlSi7Mg alloy with different metal qualities in terms of grain refinement was tested. The correlation between grain sizes measured on the standard cup with those obtained in cylindrical test parts with various diameters cast in sand and metallic moulds has been investigated. It was found possible to set up a formula for the grain size of the cylindrical test parts in function of their modulus and of the grain refinement obtained on the standard thermal cups. Corrective actions can then be taken in order to improve the metallurgical quality before casting.

I. Lizarralde, A. Niklas, A. I. Fernández-Calvo, J. Lacaze

Alloy ALSi30 Cast in the Process of Rapid Solidification and Consolidated in the Process of Plastic Forming

AlSi alloys with high Si content have good strength properties at elevated temperatures and resistance to thermal expansion. The main problem in the production of the classic methods of casting AlSi alloys with Si content above 20% is the formation of large precipitates of primary silicon. To prevent the formation of large precipitates of silicon can be used casting methods of rapid solidification and subsequent consolidation in the process of plastic forming. This paper presents the results of structure alloy AlSi30 cast in rapid solidification process on the wheel and consolidated in the process of extrusion and continuous rotary extrusion. The study was conducted on light microscopy and scanning electron microscope. It was found that the entire volume of the alloy is uniformly distributed fine Si particles.

Wojciech Szymański, Marcin Szymanek, Janusz Żelechowski, Mariusz Bigaj, Maciej Gawlik, Bartłomiej Płonka

Thermal Mechanical Processing

Effect of Homogenization Treatment Conditions on the Recrystallization Behavior of Al-1.2Mn Aluminum Alloy Sheets

Aluminum foil is commonly used as a cathode current collector within lithium ion battery. To reduce thickness of the foil, one kind of high strength Al-1.2Mn alloy has been developed. In its fabrication process, the recrystallization structure after intermediate annealing greatly affects the surface topography of foil. In this study, the relationship between recrystallization structure during intermediate annealing after rolling and homogenization treatment conditions of Al-1.2Mn alloys has been investigated. Homogenization was carried out with one step treatment or two steps treatment. It was found that one step homogenization treated cold-rolling sheets had higher recrystallization temperature and finer complete recrystallization grains compared to two steps homogenization treated cold-rolling sheets. This phenomenon can be explained by the relationship between Mn precipitation and recrystallization behavior during intermediate annealing.

Pizhi Zhao, Xinglin Chen, Wei Chen, Yonghao Zhang

Toward a Recrystallized Microstructure in Extruded AA6005A Alloy

The correlation between extrusion processing parameters and chemical compositions on the one hand and the grain structure and mechanical properties on the other hand is studied for an extruded AA6005A alloy. Alloys with different chemical compositions and billet homogenization treatments have been extruded under different processing parameters. Optical microscope observations as well as hardness tests show that a wide range of mechanical properties and microstructures can be obtained. The grain structure can vary from a fibrous, deformed microstructure to a fully recrystallized micro structure. In some cases a mixture of the two is observed. The effects of processing parameters and chemical composition on the grain structure is discussed and used to find the optimized combination of homogenization treatment, pre-heating temperature, cooling rate after deformation, and chemical composition, in order to obtain a homogeneous recrystallized grain microstructure and optimum mechanical strength.

A. Bahrami, A. J. den Bakker, A. Miroux, J. Sietsma

Grain Subdivision and Its Effect on Texture Evolution in an Aluminum Alloy Under Plane Strain Compression

Grain subdivision is widely observed in plastic deformation of aluminum alloys and of practical significance, but characterization of grain subdivision in a scale much larger than the grain size and how it affects texture evolution is still lacking. In this work, we performed channel die compression on an annealed AA1100 aluminum sheet along the normal direction (ND) at medium strains and room temperature. Micro structure and texture were characterized by electron backscatter diffraction (EBSD). The rotation axis and the misorientation angle for the deformation texture variants were calculated. The results show that grain subdivision proceeded in all the grains but in a heterogeneous manner. The <001>∥ND grains present high angle boundaries (HABs) of 15–30° without rotation axis clustering and almost no extra high angle boundaries (EHABs) of 30–60°; while the HABs and the EHABs coexisted in the <011>∥ND and the <112>∥ND grains. The rotation axes of the EHABs preferentially clustered at <011> and <111>. Under plain strain compression, multiple deformation texture variants created by grain subdivision interweaved with each other inside original grains, resulting in the EHABs with rotation axes clustering. In contrast, the HABs generated by grain subdivision via dislocation mechanism showed no rotation axes clustering. Grain subdivision leveraged in the texture component intensity and randomized orientations, resulted in fluctuation of the α-fiber texture.

Q. Ma, W. Mao, B. Li, P. T. Wang, M. F. Horstemeyer

Fatigue Analysis of Ultrafine Grained Al 1050 Alloy Produced by Cyclic Forward Backward Extrusion

In this work, fatigue behavior of ultrafme-grained (UFG) Al 1050 alloy produced by a cyclic forward-backward extrusion (CFBE) was studied. Initial average grain size of 120 urn was reduced to lum, 600nm and 320nm using 1, 2 and 3 cycles CFBE process, respectively. After three CFBE cycles, both yield strength and tensile strength increased about 3.5 and 3 times greater than those of as-received samples. Fatigue tests were carried out under load-controlled mode at a frequency of 15 Hz. Results indicate that grain refinement of Al 1050 samples improved the resistance to fatigue crack nucleation under predominantly high cycle fatigue loading. To explain the formation process of damage surfaces, micro structure changes in the damage surfaces caused by cyclic stresses were studied by scan electron microscopy (SEM).

Hamid Alihosseini, Mohsen Asle Zaeem

Effect of Zn Content and Process Parameters on Corrosion Behaviour of Twin-Roll Cast Aluminum Brazing Alloys

Al — Mn alloys are used as fin materials in various brazing applications of automotive industry. With the addition of Zn, these materials become more prone to corrosion with respect to tube materials and behave sacrificial to protect whole structure. Centerline segregation (CLS), inherently existing feature of Twin-Roll Cast material, is believed to play a role on electrochemical behavior of aluminum alloys. The aim of this study was to reveal contribution of centerline segregation to the overall corrosion behavior of Zn bearing Al-Mn alloys. Influence of casting parameters on magnitude of CLS and Zn content of the alloy is correlated with the open circuit potential measurements and salt spray test results. Complementary studies that aim to elucidate corrosion mechanism operating at the scale of micro structural features was also carried out by employing metallographic techniques and SEM-EDS studies.

Murat Dündar, Mert Günyüz, Cemil Işiksaçan, Anıl Pastirmaci

Solution and Aging

Growth ledges on silver-segregated θ′ (Al2Cu) precipitates

The interfacial structure and composition of θ′ (Al2Cu) precipitates in Al-0.9at.%Cu-0.9at.%Ag alloys were examined using high resolution electron microscopy. High angle annular dark field scanning transmission electron microscope (HAADF-STEM) images showed the presence of a silver(Ag)-rich bi-layer on the coherent (100) θ′-Al interfaces of the precipitates (1). Despite the presence of this layer, growth ledges were observed on the θ′ phase and thickening of the precipitates was able to proceed via ledges of step height 0.5c(θ′).

Julian Rosalie, Laure Bourgeois

On the Aging Behavior of AA2618 DC Cast Alloy

Due to their excellent mechanical properties and dimension stability, Direct Chill (DC) cast ingot plates of AA2618 alloy have been increasingly used for manufacturing large molds. The micro structure of the AA2618 DC cast alloy was examined in as-cast and solution-treated conditions using optical and scanning electron microscopes. The aging behavior of the non-deformed alloy at artificial and natural aging conditions was studied. The precipitation characteristics of the alloy were studied by differential scanning calorimetry and electrical conductivity measurement. The peak-aged conditions of the alloy were attained after aging for 36 h at 175°C, 10 h at 195°C, and 1 h at 215°C with hardness values of 99, 97, and 95 HRF respectively. It was found that the strengthening mechanisms of the natural and artificial aging were differently controlled by the formation of Cu-Mg co-clusters and/or GPB zones and S-Al2CuMg phase respectively.

P. Shen, E. M. Elgallad, X.-G. Chen

The Effect of Cold Work on the Precipitation and Recrystallization Kinetics in Al-Sc-Zr Alloys

Scandium plus zirconium additions to aluminum offer potent alloy strengthening opportunities with enhanced kinetic stability at elevated temperatures, attributable to a favorable sequence of trialuminide precipitation events which occur. This work examines the additional variable of prior cold work on precipitate aging kinetics, and on the recrystallization of the underlying aluminum matrix. Al-0.07Sc-0.08Zr (at%) alloys have been cast, swaged, and isochronally aged over a range of temperatures to quantify hardening response and degree of recrystallization. Cold-worked specimens are compared to as-cast variants; the recrystallization response of the alloy is compared to pure aluminum. These data demonstrate the expanded and optimized properly space attainable via microstructural response to thermomechanical processing.

C. T. McNamara, S. L. Kampe, P. G. Sanders, D. J. Swenson

A Novel Solution Heat Treatment of 7075-Type Alloy

The design of critical aerospace alloys is primarily built on optimizing strength and ductility, both of which can be enhanced by controlling the alloying element additions as well as heat treatment conditions. The 7075 alloy is one such aerospace alloy. The main objective of this study was to optimize the 7075 strength. Several experimental alloys were prepared and tensile test bars were cast using an ASTM B-108 type permanent metallic mold. The as-cast samples were then solution heat-treated at 470°C for times up to 48 hrs. The solution heat-treated bars were also aged in order to improve the alloy strength through precipitation hardening. Line scans for Mg, Cu and Zn were obtained from the various heat-treated alloy samples using an electron probe microanalyzer equipped with EDX and WD S facilities. Peaks corresponding to the Mg, Cu and Zn concentrations in the as-cast samples disappeared after solution treatment, reflecting optimized homogeneity structures. The newly developed versions of the 7075 alloy displayed UTS of ~1 GPa.

M. F. Ibrahim, A. M. Samuel, S. A. Alkahtani, F. H. Samuel

Experimental study of the Al-rich corner of the Al-Si-Ti system at 500 °C

The Al-Si-Ti ternary phase diagram and the correlated thermodynamic database play an important role in material design of high performance alloys for this system. In the present work, we have studied the phase equilibriums of the Al-rich corner of the Al-Si-Ti system at 500°C by means of the diffusion couple technique. The scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) results indicated that four phase layers had formed between two end-members. The X-ray diffraction (XRD) results confirmed that (Al), (Si), Ti7Al5Si12 and Ti(Al,Si)3 phases existed in the diffusion zoon. The confirmed reaction path way can be express as (Al) → Ti7Al5Si12 → Ti(Al,Si)3. Besides, the equilibriums of (Al) + Ti7Al5Si12 and Ti7Al5Si12 + Ti(Al,Si)3 in Al-rich corner at 500°C were identified.

Yang Li, Qun Luo, Jie-Yu Zhang, Qian Li

Emerging Technology

Transient microstructural thermomechanical fatigue and deformation characteristics under superimposed mechanical and thermal loading, in AlSi based automotive diesel pistons

Presently AISi based alloys, consisting up to 12 element systems, are used in the manufacture of automotive pistons for light vehicle (LVD) and heavy (HD) duty diesel engines. The pistons combustion wall is subject to complex superimposed transient mechanical and thermal loading with peak operating temperature representing a homologous temperature range of 0.8–0.9 Thom.Using specialist superimposed thermomechanical bench test apparatus, ‘engine like’ TMF loading has been reproduced and a number of semi in-situ experiments have been carried out to evaluate key micro structure damage mechanisms. The evolution of micro structural damage at the interface between hard Si inclusions and the softer Al matrix has been documented using scanning electron microscopy. The deformation characteristics at the α-Al/ Si interface have been recreated using FEA techniques incorporating non-linear elasto-viscoplastic properties for the matrix material. Comparisons of bench test fatigue lives for transient superimposed high frequency and micro structural TMF loading, with fatigue lives from isothermal mechanical loading are also made.

Roman Morgenstern, Scott Kenningley

Mechanical Behaviour of Cold Formed Metal-Polymer Laminate and the Interaction of Its Layers

This research is aimed at characterising and comparing the mechanical properties of a polymer/metal/polymer laminate and its individual layers. The laminate is cold deep drawn for pharmaceutical packaging, thus the properties were characterised at room temperature. The investigation was needed to understand how the layers contribute to formability in terms of elastic and plastic deformation. Particular attention was given to how the properties of the aluminium alloy layer were enhanced by the addition of each polymer layer. Tensile tests were carried out to determine material strengths, anisotropy and strain-hardening. These properties vary for each layer and the dominating properties in the complete laminate are of strong interest. Cup forming tests were performed to establish the forming depth of the constituent layers, carried out in line with the Erichsen cupping test. Wrinkling of the specimen during these cup forming tests had to be avoided, placing strong emphasis on understanding the stretching mechanism.

Feidhlim Ó Dubhlaing, David J. Browne, Robin Rennicks, Connor Rennicks

Mechanical and Tribological Properties of AA2124-Graphene Self Lubricating Nanocomposite

In this paper AA2124/graphene self-lubricating nanocomposites with different graphene addition of 0.5,3 and 5%wt. were prepared using P/M technique. A combination of cold compaction and hot extrusion (H.E) at ~0.45Tm were employed for fabrication of the nanocomposites. Addition of graphene significantly increased the compressive strength and hardness of the composites, while poor results were obtained for the ductility at room temperature. The microstructures of the composites were studied using OM and SEM. The effects of graphene addition on the friction and wear performances of the nanocomposites at room temperature in air in sliding against plain AA 2124 were investigated for the HE conditions using a pin-on-disk tribometer. Results showed that the wear rates of AA21224 could be remarkably reduced when 3wt% graphene is added and when cold compaction followed by HE at relatively low temperature was employed.

A. Ghazaly, B. Seif, H. G. Salem

Joining Vacuum High Pressure Die Cast A356 Under T4 Treatment to Wrought Alloy 6061

Vacuum high pressure die cast A356 alloy with T4 solution treatment was fusion-joined with wrought alloy 6061 by the Gas Metal Arc Welding (GMAW) process. In the present work, the microstructures of Base metal (T4 A356 and 6061), Heat Affected Zone (HAZ) and Fusion Zone (filler metal ER4043) was analyzed by Scanning Electron Microscopy (SEM) and optical microscopy. The results of tensile testing indicate that the ultimate tensile strength (UTS), yield strength (YS) and elongation (Ef) of T4 A3 56 are relatively low, compared to both wrought alloy 6061 and the filler metal (ER 4043). The microstructure analysis shows that the reduction in the tensile properties of T4 A3 56 should be mainly attributed to the lack of strengthening intermetallic phases (Mg2Si) and coarse grain structure, which resulted from T4 solution treatment.

Meng Wang, Yanda Zou, Henry Hu, Gary Meng, Patrick Cheng, Yeou-Li Chu

General Poster Session

Applications of the Horizontal Squeeze Casting Process for Automotive Parts Manufacturing

In recent years, the Horizontal Vertical Squeeze Casting (HVSC) process has been used with different aluminium alloys to fabricate high integrity automotive parts. In this study, the Horizontal Squeeze Casting (HSC) process is adopted to cast automotive parts using ADC 12 aluminium alloy. To minimize amount of gas porosity inside the squeeze casts, concepts of minimization of ingate velocity and maximization of flow rate along with bottom filling pattern are applied during the cavity filling. The maximum intensification pressure is also applied during solidification in order to ensure the higher cooling rate and minimization of porosities. Based on the experiment, castings can pass a blister test at 490 degree Celsius for 2.5 hours. Then, castings are heat treated by solution treatment at 484 °C for 20 minutes and artificial age at 190 °C for 2.5 hours, respectively. This improves UTS of the heat treated squeeze cast to 254.14 MPa with 1.84% of elongation.

P. Dulyapraphant, E. Kittikhewtraweeserd, P. Kritboonyarit, N. Denmud

Characterization of the Developed Precipitates in Al-2 at.%Zn - x at.%Mg, (x=1.8, 2, 2.4, 3, 4.2)

In the present work, Al-Mg-Zn alloys with compositions of Al- 2 at.% Zn — x at.% Mg, (x=1.8, 2, 2.4, 3 and 4.2) have been investigated. The developed precipitates and their growth have been followed as a function of aging temperature. The precipitates morphology was examined by scanning electron microscope (SEM) and correlated with the microhardness (HV) and differential scanning calorimetry (DSC) of the specimens. The structure of the precipitates has been detected by X-ray diffraction (XRD). Mostly, the precipitates are characterized as T′, T, η′ and η phases. The XRD charts analysis show that T′(Mg32 (Al, Zn)49) and T (Mg32 (Al, Zn)49) are cubic whereas η′ (MgZn2) and η (MgZn2) are hexagonal.η′ andrη phases have had a hexagonal structure of the same composition with slight different lattice parameters .

N. Afify, A. Gaber, Gh. Abbady

Design and Development of a Permanent Mould for the Production of Motor-Cycle Piston in SEDI-Enugu.

This paper demonstrates the possibility of designing and developing a four-cavity low pressure die casting mould in SEDI-Enugu. This research and development included the design of the die blocks and the core box for core production. Furthermore, the die blocks were cast, machined and later heat treated to obtain the desired properties of a mould material. After which the components were assembled and mounted on the Low pressure die casting machine. Emphasis was made on the coating of the mould and crucible pot internal surfaces with a solution of zinc oxide and sodium silicate. This is done prevent iron entrapment in mass of the molten metal as well as to minimize the sticking of castings on the mould during casting operation.

C. E. Ilochonwu, E. I. Nwonye

Development and Research of New Aluminium Alloys with Transition and Rare-Earth Metals and Equipment for Production of Wire for Electrotechnical Applications by Methods of Combined Processing

Development of electrical alloys of system aluminium - rare-earth metals and aluminium-zirconium for production of electrotechnical application wire rod. Design of technological line for their manufacturing.The effect of rare-earth and transition metals on the properties of the aluminium alloys containing such metals is analysed. New alloys with different content of zirconium, cerium, and other components featuring enhanced mechanical and electrophysical characteristics have been proposed. New technologies for production of long round-in-section items involving combined processing methods have been developed. The effects of the processing methods on the structure and properties of semifinished products made of new alloys have been studied and recommendations for the modes of preparing alloys, casting, shaping, and thermal processing have been made for the set of the studied alloys. The method of combined casting and drawing-extrusion is shown to ensure, in laboratory conditions, improved mechanical properties and the required level of electric resistivity.

I. Matveeva, N. Dovzhenko, S. Sidelnikov, L. Trifonenkov, V. Baranov, E. Lopatina

Influence of Machining Parameters on Al-4.5Cu-TiC In-Situ Metal Matrix Composites

With the advent of large number of composite materials, a systematic study of machining characteristics of these new materials is necessary for their rapid adoption in the actual engineering applications. Al-Cu-TiC metal matrix composite is widely used in aeronautical and automobile industries due to their excellent mechanical and physical properties. However machining of these composites is difficult because of the harder reinforcement particles. This paper presents an experimental investigation on the machinability bahavior of Al-4.5Cu-TiC in-situ cast metal matrix composite reinforced with weight percentage of 10% of Titanium Carbide. The experimental studies were conducted under varying process parameters e.g. cutting speed, feed rate and depth of cut. The optimization of machining parameters was done by designing a full factorial (L27) matrix using Taguchi method. The analysis of variance (ANOVA) is employed to investigate the influence of used parameters on surface roughness Ra.

Pradeep Kumar Jha, Anand Kumar, M M Mahapatra

Effect of Mg Contents on Fluidity of Al-xMg Alloys

This study is focused on a basic approach for the fluidity of the Al-Mg binary system. The objective of this study is to investigate the fluidity change of the Al-Mg alloys with increasing Mg content. As a result of fluidity test, pure Al showed the highest value in all the examined alloys. With 2.5%Mg addition, it decreased rapidly. On the other hand, the gain of the flow length was shown with increasing Mg content from 5%Mg addition. The change of the fluidity shown in this study is roughly similar to that reported previously. However, they also showed the difference in the Mg content which has the most viscous fluidity. It is considered that it is attributed to the different experimental conditions. In microstructures, with increasing the Mg content, the dendritic α-Al was developed and the existence of precipitation regarded as β-phase (Mg5Al8) is shown in the grain boundary. This tendency became conspicuous from the 5wt%Mg addition. And then, the grains were refined with the formation of the precipitation.

Nam-Seok Kim, Seong-Ho Ha, Young-Ok Yoon, Gil-Yong Yeom, Hyun Kyu Lim, Shae K. Kim

Effect of Process Parameters on Centrifugally Cast Al-Si FGM

Functionally Graded Materials (FGM) are such kind of materials wherein the properties and structure are varied from one end of the cast to the other intentionally. Centrifuge technique has been used in this study to produce Al-Si FGMs. Several process parameters determine the microstructure and the distribution of phases in the FG casting. These parameters include the size and initial concentration of alloying element, the centrifugal force, solidification rate, cooling rate. In this work an attempt has been made to produce FGMs using three different process variables such as mold temperature, melt temperature and mold rotational speed, their effect on the structure and properties. For this study Al-17wt%Si is used. From the results it is seen that for a particular melt and mold temperatures by increasing the mold rotation speed enhances the segregation of the Si particles at the one end of the casting. Similarly increasing mold or melt temperature only, increases the segregation.

Aithal S. Kiran, Vijay Desai, S. Narendranath, P G Mukunda

Effects of Minor Sc Addition on the Microstructures and Mechanical Properties of Al-Zn-Mg-Cu Casting Aluminum Alloy

Effects of x%(x=0.15, 0.30, 0.45) Sc addition on the microstructures and mechanical properties of metal-mold-casting aluminum alloy Al-6.0Zn-2.8Mg-1.9Cu were studied. It was showed that addition of Sc could reduce α(Al) grain size, modify α(Al)+η(MgZn2) eutectic of the experimental alloy, and eliminate Al7Cu2Fe phase effectively. It was also found that for the heat treatment experimental alloy, addition of minor Sc could make the second phases along α(Al) grain-boundary and η′ meta-stable phase inside α(Al) matrix precipitated more dispersedly, and meanwhile it could promote precipitation of η′ phase and decrease its size effectively. The addition of x% Sc element could improve the room temperature ultimate tensile strength of the experimental alloy, but had little effects on its plasticity. The room temperature UTS of the experimental alloy with the addition of 0.45%Sc could reach to 510MPa, the maximum value, among the three Sc-content alloys. In addition, it was also found that addition of 0.30% Sc would improve the high temperature tensile strength of the experimental alloy more apparently than those with 0.15% and 0.45% Sc.

Yang Guangyu, Liu Shaojun, Jie Wanqi

Microhardness, Corrosion Behaviour and Microstructures of Directionally Solidified Al-Cu Alloys

The aim of this work is to analyze the effect of micro structural parameters (secondary dendritic arm spacings) on the microhardness and corrosion behavior of hypoeutectic Al-Cu alloys. Experimental results include HV microhardness values, corrosion and pitting potential and current density. It was found that high cooling rates during solidification provide finer dendritic spacings, which encourage better mechanical properties. The Vickers microhardness increases as the contents of copper in the alloy increases. The most influencing microstructural variable for corrosion resistance has been found to be the secondary dendrite arm spacing. It has been found that that corrosion resistance decreases with the increasing in secondary spacing until 10wt.% of Cu.

Alicia Ares, Carlos M. Rodriguez, Claudia M. Mèndez, Carlos E. Schvezov, Mario R. Rosenberger

Production of Single Cylinder Engine Components Through High Pressure Die Casting in Sedi Enugu

This research work investigated the casting method employed in the production of aluminium based alloy components of a single cylinder engine in SEDI Enugu. A discussion of the casting processes, especially the die casting process used in the production of single cylinder engine components was carried out.In addition, considerations that lead to the selection of die casting for the project, the main structure and working principles of die casting machine were explained. Besides, this paper treated mould design and mould materials requirement. In conclusion, the alloy analysis of aluminum alloys such as; aluminum-magnesium alloy, aluminum-silicon alloy, aluminum-zinc alloy was discussed. Although all the tests have not been carried out on the components to ascertain their strength and durability, but a functional test has been carried out by test running the component coupled to an engine.

E. I. Nwonye, C. E. Ilochonwu, C. O. Nwajagu

The Effect of Thermomechanical Ageing of Aluminium-Copper Alloy (MATLAB Approach)

The influence of thermomechanical ageing on the mechanical properties of Al-Cu alloy has been investigated. The alloy contains 4.23% of Cu, and was produced by casting process. The casting was warm worked between 0.3Tm–0.5Tm at various temperatures ranging from 300–560°C at 5%, 10%, 15%, and 20% deformation respectively. The results showed that the mechanical properties in terms of hardness, tensile and toughness were improved with increasing percentage at a higher temperature. This was due to the progressive close-up of the voids emanating from casting sample by increasing deformation which is evident from the micrographs. It was concluded that thermo mechanical ageing is beneficial to the mechanical properties of Al-Cu alloy.

Adegbola Adekunle Amos, Ghazali Akeem, Fashina Olugbenga Emmanuel, Omotoyinbo Joseph Ajibade, Olaniran Oladayo

Aluminum Processing


Aluminum Processing I

Surface Crack Characterization of Twin Roll Caster Shells and Its Influence on As-Cast Strip Surface Quality

Caster shells are the most critical components of the twin roll casting process that has significant contribution to the surface quality of the as-cast sheet. Due to their high cost, they also have an impact on the cost structure of as-cast sheet. Twin-roll strip casting is a complex process, which involves high solidification rate and subsequent deformation at the roll bite. Solidified metal exerts enormous mechanical loads on the caster rolls and this results in bending of the caster roll along with the shell. Liquid metal also raises the temperature of the shell considerably at a limited depth and upon leaving the roll bite cooling cycle starts. Heating-cooling cycles at the outer skin of the shell lead to thermal fatigue. Coupled effect of thermal and mechanical fatigue causes surface cracks to appear. These are the features impair the surface properties, even performance of products.Present study aims to elucidate surface crack formation mechanism of caster shells. Metallographic investigations and SEM studies were conducted on the caster shells. The results are correlated with physical and mechanical properties of the shell materials. Studies were extended to aluminum foil and sheet products in which caster shell related defects were observed.

Murat Dündar, Barış Beyhan, Onur Birbaşar, Hatice M. Altuner, Cemil Işıksaçan

Aluminum Processing II

The Effect of Magnesium Content on Microstructure Evolution During Hot Deformation of Aluminum Alloys

Aluminum alloy specimens were tested in tension and compression at temperatures up to 500 °C and strain rates up to 1.0 s−1 to study the microstructures developed during hot working. An AA5182 alloy was hot deformed in tension and subsequently annealed to promote recrystallization, while two Al-Mg alloys (Al-0.5Mg, Al-4.5Mg) were hot deformed in compression and examined as-quenched. The AA5182 alloy showed no signs of dynamic recrystallization, but experienced increased static recrystallization with increasing tensile strain during subsequent annealing. Annealing also resulted in static abnormal grain growth (SAGG) for the AA5182 in regions of light to moderate strain. The Al-4.5Mg alloy, which was tested at faster strain rates and in compression, showed signs of geometric dynamic recrystallization (GDRX) during deformation, while the Al-0.5Mg alloy did not show any signs of recrystallization under the same conditions. Results indicate that increased Mg concentration enhances GDRX and increases SAGG following hot deformation.

Trevor J. Watt, Shinya Yasuda, Koji Ichitani, Ken Takata, Alex Carpenter, Jakub Jodlowski, Eric M. Taleff

High Strength Nanostructured Al-Zn-Mg-Cu-Zr Alloy Manufactured by High-Pressure Torsion

7085 aluminium alloy (Al-7.5 Zn-1.6 Mg-1.5 Cu-0.12 Zr) is processed by high-pressure torsion (HPT) at imposed pressure of 2 GPa and torsion turns of 3, 6, 9 and 12 turns. The microstructures and mechanical properties of 7085 Al alloy under different torsion conditions are systematically investigated, and the refinement mechanism is discussed. The microstructures of the alloy are analyzed by transmission electron microscope (TEM) and scanning electron microscope (SEM). Mechanical properties are studied by tension test and vickers indentation. The results indicate that after HPT treatment, the grains of Al alloy are refined remarkably. Nanometer grains of sizes between 50~250 nm are obtained. The tensile strength and hardness increase obviously and there is some fluctuations in elongation. When the pressure is 2 GPa and the torsion turn is 12 turns, the optimum performance are accomplished, which tensile strength is 699 MPa and microhardness is 260HV0.2.

Chao An, Huimin Lu, Shilai Yuan

Corrosion Behavior of 2024 Aluminum Alloy Anodized in Sulfuric Acid Containing Inorganic Inhibitor

The effects of potassium permanganate, as a corrosion inhibitor, in different concentration on morphology, composition and thickness as well as corrosion resistance of anodic film formed on 2024-T3 aluminum alloy in sulfuric acid were investigated in this paper. Surface morphology and chemical composition of oxide film were studied using field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX). Potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) were conducted to assess the corrosion performance of the coatings. The results showed that presence of potassium permanganate during anodizing process results in more compact and thicker anodic film with smaller pore size. Effects of potassium permanganate increased with concentration. Using permanganate ions improved corrosion resistance of the formed anodic layer, which is about 45% and 94% inhibition for 0.01 and 0.1M permanganate, respectively.

Maysam Mohammadi, Ali Yazdani, Farzad Mohammadi, Akram Alfantazi

Laboratory simulation of wear during hot extrusion of aluminium

The study of the wear of a tribological pair of soft and heated metals in contact with a hard counter body is very demanding. The main difficulty with such studies is the deficiency of reliable experimental data due to the problem of maintaining the prescribed contact pressures for a long time between hot softer metal and hard body. A very important tribological system that belongs to this group of demanding systems is present in aluminium hot extrusion, where temperatures of billets lie in the range 450–500 °C, the contact pressure is up to 30 MPa and the sliding velocity in the range 5–100 m/min. In order to gain a deeper insight into the wear behavior in aluminium hot extrusion, laboratory wear tests on nitrided samples at various contact pressures were carried out. The description of experimental setup and main characteristics of the degradation progress of the tested surfaces are presented.

G. Kugler, M. Terčelj

The Production of Wrought AlSi30Cu1.5Mg1.2Ni1.5Fe0.8 Alloy with Ultrafine Structure

The purpose of this study was to produce by Rapid Solidification process an alloy with Si content exceeding 20%.An ultrafine grained alloy from the AlSi30Cu1.5Mg1.2Ni1.5Fe0.8 system in the form of strips has been fragmented and subjected to the process of consolidation.The paper presents the technological aspect of the process of casting, fragmentation and plastic consolidation of semi-products.

Marcin Szymanek, Bogusław Augustyn, Wojciech Szymański, Dawid Kapinos

The Structure and Properties of Wrought Aluminium Alloys Series 6xxx with Vanadium for Automotive Industry”

The increasing number of vehicle parts, including elements operating in crumple zones, are manufactured from light metal alloys based on aluminum and magnesium. The choice of material for these applications should consider not only the mechanical properties of the alloy, but also its ability to absorb energy.The materials that can offer these properties are wrought aluminum alloys containing vanadium in an amount of 0.05 – 0.5%, characterized by high strength and high toughness. These alloys are also characterized by an adequate capacity to absorb the kinetic energy (low value of the Rp0.2/Rm ratio and very high reduction of area Z).The paper describes structure examinations and testing of mechanical properties using directly extruded round and square bars and forgings made from ingots and bars. The examined material was aluminum alloy from the 6xxx series containing 0.1, 0.2 and 0.3% vanadium.The extruded profiles were characterized by the mechanical properties comparable with the strength parameters of profiles made from a similar alloy from the 6xxx series but without the addition of vanadium, except for the elongation that assumed much higher values. The use of water wave on the press prevented the formation of a rim of coarse crystals on the profile cross-section.

Marzena Lech-Grega, W. Szymański, B. Płonka, S. Boczkal, M. Gawlik, M. Bigaj, P. Korczak

Aluminum Reduction Technology


Cell Design and Performance

In Depth Analysis of Energy-Saving and Current Efficiency Improvement of Aluminum Reduction Cells

In view of the existing aluminum overcapacity and lower aluminum price in China, many companies took measures to reduce the production cost and the energy consumption, but there has been no normalized theory and method defined as yet.To address these issues, this paper puts forward the evident effects of energy-saving and current efficiency improvement in aluminum reduction cells using new thermal insulation pot lining design, application of optimal cathode structure and reduction of horizontal current device. A proper application of new lining materials and combination of relevant process parameters based on the finite element software ANSYS® and thermal field simulation software as the calculation method combining the actual production data are also used. Practice proves that the above-mentioned method combining design, simulation and experiment can become the effective and feasible way to achieve low energy consumption, low cost and high profit.

Yan Feiya, Marc Dupuis, Zhou Jianfei, Ruan Shaoyong

Rio Tinto Alcan AP4X Low Energy Cell Development

High performance AP4X cell technologies have been developed as part of a complete cell development program based on AP30 platform. The latest development for this technology is AP4XLE, which refers to low energy consumption cell technology at more than 400 kA with a target for energy consumption at 12.4 kWh/kg. This technology aims at maximizing the production and the profitability of smelters having limited energy block size. It could be used either for retrofit of existing AP30 cells or for greenfields. Following the Rio Tinto Alcan cell development methodology and using modeling and low ACD operation knowledge, lining and anode assemblies were designed to support smelters amperage creeping. Both St-Jean-de-Maurienne and Alouette smelters are involved in the development process by operating tests on designated booster sections. Excellent energetic and environment performances have been recorded from these trials. Prototype cell performances and future technology development steps are described in this paper.

P. Thibeault, S. Bécasse, A. Blais, P. Côté, L. Fiot, F. Laflamme

Energy Reduction Technology for Aluminum Electrolysis: Choice of the Cell Voltage

In China, all the aluminum smelters are making efforts to reduce the electrical energy consumption of aluminum reduction by decreasing cell voltage. One measure is decreasing cell voltage without any cell structure change. Another measure of decreasing cell voltage is using novel structure carbon cathode. For the first measure, the current efficiency (CE) would be decreased because the anode-cathode-distance is reduced. For the second measure, if the cell voltage is reduced much more, the CE also can be lost. The best choice to decrease energy consumption is that the CE should be maintained when the cell voltage is reduced. It means that the cell should be operated at a reasonable low cell voltage, so that the CE could not be decreased or could be improved. In this paper, the CE and electrical energy consumption of aluminum smelters with different cell voltage operating are shown and the economic benefits are discussed.

Feng Naixiang, Peng Jianping, Wang Yaowu, Di Yuezhong, Liao Xian’an

Advancements of Dubal High Amperage Reduction Cell Technologies

During the past 10 years DUBAL successfully developed its proprietary high amperage DX and DX+ cell technologies that have shown excellent performance. The 40 DX demonstration cells at DUBAL currently operate at 385 kA and the five DUBAL DX+ demonstration cells have been operating at 440 kA since March 2012. Following the commissioning of a sixth rectiformer, EMAL potlines 1 and 2 have increased the amperage of the DX cells to 380 kA. This paper summarizes the performance of both DX and DX+ cells at DUBAL and EMAL. EMAL Potline 3, currently under construction will total 444 DX+ cells with a potline voltage of 2000 V. DUBAL has recently developed a new pot control system (PCS) based on standard PLC hardware architecture which has been selected for EMAL Potline 3. As part of DUBAL’s culture of continuous improvement, further development is in progress towards lower energy consumption, lower PFC emissions and lower capital expenditure.

Michel Reverdy, Abdalla Zarouni, Jean-Luc Faudou, Qassim Galadari, Ali Al Zarouni, Sergey Akhmetov, Kamel Al Aswad, Maryam Al-Jallaf, Walid Al Sayed, Vinko Potocnik

Development of Low-Voltage Energy-Saving Aluminum Reduction Technology

In this study, the representative low-voltage energy-saving techniques for aluminum reduction in recent years in China is reviewed, and two low-voltage energy-saving techniques are described, which include the technique based on innovation of the electrolytic technology and the process control and the one based on comprehensive innovation of cell structure, the electrolytic technology and the process control. The results show that the best energy consumption index can be realized with the application of low-voltage technology and advanced process control technique on the cells designed at the concept of “conventional planar cathode + suitable heat preservation enhancing”.

Li Jie, Lv Xiao-jun, Zhang Hong-liang, Liu Ye-xiang

D18+: Potline Modernisation at DUBAL

Dubai Aluminium commenced operation in 1979 with three potlines utilising Kaiser P69 cell technology. Upgraded to D18 technology, the original potlines have been constantly improved to increase their efficiency and productive output, with amperage increasing from 150 to 202kA.In order to make further significant progress in the original potlines, DUBAL has initiated a project to completely revise and modernise the cell technology. Designated D18+, the new inhouse design incorporates the latest cell technology such as magnetic compensation and proper point feeders within the existing footprint of the original D18 potline infrastructure.Seven D18+ cells were constructed and started-up in March 2012 and are now successfully meeting their key design targets with net specific energy consumption of 12.75 DC kWh/kg Al and anode effect frequency <0.02 /cell/day. The test cells are now currently being fully evaluated before implementing throughout DUBAL’s D18 potlines.

Sergey Akhmetov, Daniel Whitfield, Maryam Mohammad Al-Jallaf, Ali Al-Zarouni, Alexander Arkhipov, Amer Al-Redhwan, Wael Abou Sidou

Industry Test of Perforation Anode in Aluminium Electrolysis Technology

In recent years aluminum industry in China has been developed rapidly. In 2011 China’s electrolytic aluminum output reached 18.06 million tons and has topped the list in the world for 11 consecutive years. However, the energy and environmental issues restrain development of aluminum industry. So it is necessary to promote the use of energy saving technology in the aluminum industry. The composition of the cell voltage is analyzed in this paper. It is reasonable that the cell voltage of ordinary flat cathode cell is about 4.05V. The approximate linear relationships between the bubble layer thickness and the anode width is analyzed. Changing the structure of the anode and adding two rows of the vent on the common anode can reduce the gas running distance below carbon anode, anodal bubble voltage and the work voltage of aluminum reduction cells under the same current efficiency of aluminum reduction cells. Perforated anode technology was tested in small-scale and large-scale industrial cells and the experimental results show that average current efficiency of the test cell is 91.447%, the direct current consumption reaches 12337kwh/T-Al. The anode effect coefficient of the test cell with good thermal balance reduces to an average of 0.185 time /cell–day. The results are consistent with the theory and a comprehensive promotion goal is achieved.

Yingfu Tian, Hesong Li, Longhe Wei, Xi Cao, Jianguo Yin

The First Results of the Indus Trial Application of the Ecosøderberg Technology at the Krasnoyarsk Aluminum Smelter

The RUSAL Engineering & Technology Center has been developing anew EcoSøderberg concept for VSS Søderberg technology since 2005. The concept includes the following:colloidal anode paste with a binder content of less than 26 % (a binder is based on pitch enriched with fine fractions of petroleum coke),a new cathode that allows for the following: a 20 cm lower metal pad and a 1.5% increase in current efficiency (in comparison with conventional cells), anda new gas removal system that provides for better sealing and less fluoride emissions (roof emissions.)There has been a pilot area for testing cells since 2006. Currently there are 20 cells in the pilot area. The main technical solutions (found in the pilot area) have been used in 5 potrooms of the Krasnoyarsk aluminum smelter since March 2010. There are 197 EcoSøderberg cells in operation today. Various tests have proved the efficiency of the new technology. This technology has been chosen as the basis for the conversion of RUSAL’s VSS capacities.

Victor Buzunov, Victor Mann, Evgeniy Chichuk, Vladimir Frizorger, Andrey Pinaev, Evgeniy Nikitin

Fundamentals: Modelling

Unsteady MHD modeling applied to cell stability

In a context of higher energy prices, reducing energy consumption is a top priority for any new technological development. One of the main levers is to reduce Anode to Cathode Distance (ACD), but doing so directly increases Magneto-Hydro-Dynamic (MHD) instabilities and thereby reduces current efficiency. To limit MHD instabilities, Rio Tinto Alcan has carried out an extensive modeling and experimental program with the support of EPFL (Ecole Polytechnique Fédérale de Lausanne) and Coventry University. This article compares the results obtained using the latest unsteady stability model, developed by EPFL, with the lab-scale Coventry experiment and with industrial AP3X operating results. This new model clearly provides a good prediction of instability when metal height and ACD are reduced, at both lab and industrial scales. It overcomes the limitations of the usual shallow-water or linear stability models, for which extensive assumptions have to be made. It opens broad possibilities for investigating new solutions to reduce MHD instabilities.

Renaudier Steeve, Bardet Benoit, Steiner Gilles, Pedcenko Alex, Rappaz Jacques, Molokov Sergeï, Masserey Alexandre

Impact of magnetohydrodynamic and bubbles driving forces on the alumina concentration in the bath of an Hall-Héroult cell

The alumina concentration in the bath plays a fundamental role on cell operation. Local depletion may lead to an anode effect when using carbon anodes. A mathematical model describing the alumina convection-diffusion process in the bath coupled to the cell magneto-hydrodynamic (MHD) in the presence of small bubbles is presented. Small bubbles may be assumed when slotted anodes are used. The relative importance of the velocity fields generated by the magnetic effects and/or the small bubbles on the alumina concentration in the bath is discussed.

René von Kaenel, Jacques Antille, Michel V. Romerio, Olivier Besson

Investigation of Electrolytic Bubble Behaviour in Aluminum Smelting Cell

A 1/4th scale low temperature electrolytic model of the Hall-Heroult cell was constructed to investigate the electrolytic bubble formation mechanism, coalescence and movement under the horizontal anode surface. Geometric and dynamic similarity between the model and real cell was maintained through using similarity criteria. A 0.28M CuSO4+20%H2SO4 solution was selected as an electrolyte where Cu was deposited at the cathode and O2 bubbles were generated underneath the anode, similar to the phenomena of real cell. The bubble generation mechanism, movement, coalescence and detachment under the electrolytic medium were observed using a high speed camera. It was found that electrolytic bubbles generate uniformly under the whole anode surface and grow through gas diffusion and coalescence. At higher current density and higher anode inclination angles, bubbles escape quickly from underneath the anode surface. The bubble layer thickness and bubble sizes were also found to decrease with an increase in anode inclination angle.

Morshed Alam, Yos Morsi, William Yang, Krishna Mohanarangam, Geoff Brooks, John Chen

Mathematical Model Validation of Aluminium Electrolysis Cells at DUBAL

In recent years DUBAL has developed an in-depth mathematical modeling capability for aluminium electrolysis cells, based on commercial software packages, comprising thermo-electric, MHD and mechanical models of the cells as well as CFD models of gas extraction from cells and of potroom ventilation. In order to validate these models a measurement program was initiated, consisting of a group of DX and DX+ cells instrumented for continuous monitoring of cathode lining and potshell temperatures, busbar temperatures and busbar currents. Moreover, special measurement campaigns were carried out for cell voltage breakdown, heat fluxes, freeze profiles, current distribution, magnetic fields, metal velocities, potshell deformation and cell gas exhaust flow rate. The modeling results showed excellent agreement with measured data, allowing the models to now be used with confidence for new cell designs and industrial studies of existing potlines. In this paper, detailed measurement and modeling results shall be discussed.

Abdalla Zarouni, Lalit Mishra, Marwan Bastaki, Amal Al Jasmi, Alexander Arkhipov, Vinko Potocnik

Production Application Study on Magneto-Hydro-Dynamic Stability of a Large Prebaked Anode Aluminum Reduction Cell

The magneto-hydro-dynamic stability of an aluminum reduction cell has an important influence on aluminum electrolysis production. The paper introduces the research theory of magneto-hydro-dynamic stability of a cell and puts forward the concepts of “stationary state” and “transient state” of a reduction cell. A magneto-hydro-dynamic stability software is then used to calculate two different cell conditions. The calculated results prove to be consistent with the actual production, which confirms the model validity.

Ruan Shaoyong, Yan Feiya, Marc Dupuis, Valdis Bojarevics, Zhou Jianfei

MHD of Aluminium Cells with the Effect of Channels and Cathode Perturbation Elements

The industry oriented MHD software for aluminium electrolysis cells is updated to take into account the variation of bottom and top surfaces of the cell cavity. The extended model capabilities include the presence of connected channels, height non-uniformities of the cell bottom affecting the liquid metal hydrodynamics and the electric current passage to the cathode with ridges and variable bottom ledge. The numerical results for 500 kA test cell are used to analyze the cell stability under combination of the effects. Perturbations created by the horizontal current density above the carbon elevations lead to the metal/electrolyte interface wave growth, which is opposed by the increased turbulent damping over the bottom with ridges. Optimization of the cell design permits to improve the cell stability and efficiency.

Valdis Bojarevics

Magnetohydrodynamic Model Coupling Multiphase Flow in Aluminum Reduction Cell with Innovative Cathode Protrusion

The electromagnetic field and the gas bubbles generated beneath anodes in aluminum reduction cells have an important role in the fluctuation of the bath/metal interface. A coupled mathematical model has been developed to investigate the electromagnetic field and the multiphase flow in the aluminum reduction cell with innovative cathode protrusion. As for the electromagnetic field, the finite element method was employed. A transient inhomogeneous multiphase model, the finite volume method, was employed to study the multiphase flow. The results indicated that the electromagnetic field distribution was changed by the innovative cathode protrusion. The electromagnetic force decreased as a result of the optimization of the magnetic field. In addition, the deformation of the meta/bath interface was suppressed significantly, which is beneficial to the reduction of the voltage drop. The innovative cathode protrusion had little effect on the motion of the gas bubbles.

Wang Qiang, Li Baokuan, Wang Fang, Feng Naixiang

Optimization of the Cathode Collector Bar with a Copper Insert Using Finite Element Method

A finite element model of a cathode assembly including a copper insert inside the collector bar was developed. This thermo-electro-mechanical model includes interfaces to simulate the contact between different materials. In order to optimize this model, the authors propose an economic analysis based on the electrical operating cost, the relining cost and the life expectancy of a cell. The geometry of the model is subsequently varied in order to generate a multidimensional response surface based on these economic criteria. Results indicate that substantial economies could be achieved by reducing the resistivity of the collector bar and improving contact at the interface. Also, this model provides some insight in the contact between the different materials of the cathode assembly and its effect on cell performance.

Mathieu Gagnon, Patrice Goulet, Richard Beeler, Donald Ziegler, Mario Fafard

Energy Savings in Aluminum Electrolysis Cells: Effect of the Cathode Design

Non uniform current distribution inside aluminum electrolysis cells is responsible for energy losses, a phenomena impacting on both the economy and the environment. Indeed, non uniform distribution induces premature wear of the cathode surface and triggers magneto-hydro-dynamic instabilities in the molten aluminum of the cell. The present study addresses this problem by examining the effect of the cathode shape and design on the current distribution. A computational methodology based on a finite element method is developed. It is then employed to determine the optimal cathode design, i.e., the design that minimizes the energy losses and maximizes the lifetime of the cell. The effect of various design parameters on the current distribution is highlighted. Their economic impacts on the operation of the cell are also assessed.

Mathieu Blais, Martin Désilets, Marcel Lacroix

Potline Operation I - Smelter Operations

Low Power Operation at Aluminium Dunkerque Smelter

The Aluminium Dunkerque smelter came on stream in 1991 with AP30 technology at 295 kA and since then the technology has been regularly improved to operate around 360 kA nowadays. In mid-2011two successive severe technical incidents took place in the Substation and limited the maximum Substation capacity to 285 kA for several months. To cope with this 20% amperage reduction and limit the risk of smelter stoppage, a major action plan was launched not only in the potrooms but also in the smelter as a whole. After adjustments on both operation and process sides, Aluminium Dunkerque has been able to continue operating the potline for 8 successive months at reduced amperage with satisfactory operating condition and technical results. This demonstrates the robustness and capability of the technology to operate at reduced power and paves the way for flexible power operation at AP Technology™ smelters.

Jean-Michel Peyneau, Laurent Fiot, Stéphane Mermet-Guyenet, Olivier Rebouillat

Maximizing Creeping Value through Rigorous Methodology

Creeping of an existing smelter is often considered cost-effective compared to the development of a greenfield smelter. It indeed permits an increase in metal production and/or a reduction in operating costs with lower investment compared to a greenfield case.In order to minimize issues during the execution phase, a rigorous and thorough preparation is required, including the identification of the creeping impacts on all smelter units, and the proposal of possible solutions to mitigate them.Rio Tinto Alcan Technology group has developed an integrated approach to identify the impacts of creeping, starting at the smelter level and then extending to the different units. Such a method is now available as an AP Technology™ solution.This paper describes the general approach used, and the main tools developed with this aim.

Bénédicte Champel, Nicolas Monnet

The Quick Shut Down and Restarting of 291 kA Pre-Baked Potline at JSC “RUSAL Sayanogorsk» from May to August 2011

Sayanogorsk and Khakas aluminum smelters faced with the serious risk of emergency shut down due to the railway bridge destruction used for the raw materials supplying, after the natural disaster on May 7, 2011. In order to prevent the emergency shutdown UC “RUSAL” decided to reduce temporarily the production volume. As a result, the line amperage was decreased significantly; some amounts of old and sick pots were shunted out in each potline, besides the entire line consisting of 179 pots with a current of 291 kA was disconnected within 2 days. After the resumption of raw materials supply the potline was restarted within 2.5 months. This article describes the sequence of events from the decision to shut down the line to the full production recovery

Victor Buzunov, Andrey Soldatov, Victor Mann, Aleksandr Pavin, Vasily Borisov, Sergey Zatepyakin, Evgeny Shcherbakov, Andrey Guzenkov

Production Growth and Future Challenges in Aluminium Bahrain (Alba)

Aluminium Bahrain B.S.C. (Alba) consistently ranks as one of the largest and most modern Aluminium smelters in the world. Known for its technological strength and innovative policies, Alba enforces strict environmental guidelines, and is widely regarded as one of the top ten performers on a global scale. Commissioned in 1971 with a capacity of 120,000 tons per year, Aluminium Bahrain has steadily progressed and today is one of the world’s top performing and largest Aluminium producers worldwide. Production output has increased stepwise since start-up through numerous technology improvement projects and several major expansions using latest available technology in the market. The current plant capacity is close to 890,000 tons per year. The main strategy adopted by Aluminium Bahrain since the early days has been to sweat the assets by maximizing the production of the electrolytic cells using latest technology, upgrade of technology, expansions with sustaining cost effectiveness position through different programs, maintaining lowest impact on the environment, developing nationals along the way aiming to zero harm as a core principle of the business. This paper describes the strategy adopted by Aluminium Bahrain highlighting the challenges encountered to achieve the key milestones along with the future plans.

Isa Al-Ansari, Abdulla Habib, A. C. Mittal, Nabeel Al-Jallabi

High Frequency Power Modulation - TRIMET smelters provide primary control power for stabilizing the frequency in the electricity grid

The strong growth of renewable energy in Germany leads to high price fluctuations, varying with the availability of these energy resources. To deal with this situation, TRIMET is using the tool “power modulation” since 2008 to compensate these strong price effects.Simultaneously the strong growth of renewable energy sources leads to a need of primary controlreservefor stabilizing the electricity grid at 50 Hz. In this context, TRIMET is the first electricity consumer in Germany, which provides primary control power by modulating a consumer. Traditionally, this source of energy is only provided by power plants or energy storage plants, e.g. pumped energy storage or stationary batteries.

Andreas Lützerath

Autonomous Vehicle and Smelter Technologies

In 2005, the CSIRO automated a forklift-based Hot Metal Carrier to be capable of typical metal transfer operations around a smelter. The project was highly successful and the vehicle has demonstrated hundreds of hours of live autonomous operations to thousands of people from industry and the public. As a result of the exposure of the project, we have expanded its focus to demonstrate how various technology components can be utilised to gain benefits in other areas of smelter automation. These include asset tracking, vehicle usage analysis, pedestrian detection and infrastructure profiling. Each of these components was derived from the core autonomous vehicle technology suite and has shown a high potential for improving safety and efficiency of vehicle operations, metal tracking from pot to furnace, or improved diagnostic processes for measuring deformations of bakes and furnaces. The autonomous vehicle project and its extended technologies are described in this paper.

Ashley Tews, Paulo Borges

Preventive Maintenance of Transport Vehicles is it improving production stability of a smelter?

As a supplier Hencon started maintenance activities in the mid eighties in order to support customers in improving the maintenance on vehicles and getting the cost under control. After 10 years of experience with running state of the art maintenance practices in Russia, India and Mozambique, in this paper we will show what we have learned. Key Performance Indicators will be discussed. Based on that we will present the future of maintenance with the help of today’s ICT.

Maarten Meijer

Fundamentals: Chemistry

Composition and Thermal Analysis of Crust Formed from Industrial Anode Cover

When the anode cover is heated up in the reduction cell, the crust formation from the anode cover commences at the bottom and the process is driven by thermo-chemical processes. It is important to study the composition and thermal stability properties of the crust in order to understand the mechanisms of crust formation and deterioration. Several crust pieces were taken from industrial prebaked anode cells. A number of vertical crust sections were sampled from these pieces, and each section was analyzed for composition and phase change temperature. Results show that the bottom layer is enriched in cryolite, consistent with results published in the literature. The upper region was found to contain more chiolite. Crushed bath-based anode crust has higher CR than alumina based anode crust. The melting of chiolite in the crust leaves substantial macro-porosity there, which contributes to the absorption of NaAlF4 and the penetration of bath through it. The formation conditions of crystalline crust were discussed.

Qinsong Zhang, Mark P. Taylor, John J. J. Chen, David Cotton, Tania Groutzo, Xiaodong Yang

Liquidus Temperatures of Na3AlF6-AlF3-CaF2-KF-LiF-Al2O3 Melts

Temperatures for the primary crystallization of Na3AlF6 in multicomponent electrolyte system of aluminum electrolysis process were determined by thermal analysis. An empirical equation describing liquidus temperatures for the primary crystallization of Na3AlF6 was derived: t/°C= 977.632+32.968 (CR)−25.742ω(Al2O3)−12.507ω(LiF)−2.123ω(KF)−2.040ω(CaF2) +5.300ω(CR)•ω(Al2O3)+1.200•ω(CR)•ω(LiF)−0.114ω(KF)•ω(CaF2)−7.726ω2(CR)+1.085ω2(Al2O3)−0.075•ω2(CaF2), where CR denotes the molar ratio of NaF/AlF3 and ω denotes the mass fraction. CR=2.0–3.0, ω(Al2O3)=2–4 %, ω(LiF)\ ω(KF)\ ω(CaF2)= 0−7 %.

Di Yuezhong, Peng Jianping, Bai Yunbin, Feng Naixiang

The Effect of Calcium Fluoride on Alumina Solubility in Low Temperature Cryolite Melts

The alumina solubility in the KF-NaF-CaF2-AlF3 molten salt system depending on the [NaF]/([NaF]+[KF]) ratio and calcium fluoride concentration was measured in the temperature range from 850 °C to temperature of primary crystallization. The cryolite ratio (CR), calculated as ([KF]+[NaF])/[AlF3], was maintained at 1.3 and 1.5. The calcium fluoride impact on alumina solubility is more significant in electrolytes rich in potassium fluoride.

P. Tingaev, Yu. Zaikov, A. Apisarov, A. Dedyukhin, A. Redkin

Conductivity of KF-NaF-AlF3 System Low-temperature Electrolyte

The continuously varying cell constant (CVCC) technique was applied to measure the conductivity of molten KF-NaF-AlF


electrolyte with ([NaF]+[KF])/[AlF


] ratio (CRT) between 1.2 to 1.5. The investigated temperature range is 750 to 820 °C. The effect of CRT, temperature, NaF and alumina on conductivity was studied. An empirical formula for calculating conductivity of the KF-NaF-AlF


melt was derived:


= 0.1442 × N


+ 0.164 × N + 16.947 × R


− 68.086 × R


+ 91.534 × R + (8.812 × l0




− 0.0874) × A + 1.39 × 10




− 41.1785



is the conductivity, in S·cm


, N is the mole fraction of NaF, R is the CRT of electrolyte, A is the mass fraction of Al






is the temperature of melt in degree centigrade.

Jianhong Yang, Wangxing Li, Hengwei Yan, Dan Liu

Numerical analysis of ionic mass transfer in the electrolytic bath of an aluminium reduction cell

In the Hall-Héroult process, the electrolytic bath is a molten solution of cryolite and alumina. Like all other molten salts, it ends up in different moving ions driven by physical mechanisms such as convection, diffusion and migration. The motion of these ions and their concentration distribution are important because they determine many functional macroscopic parameters of the electrolytic cell like current density distribution, heat generation, back reactions, current efficiency, and mass-transfer controlled reactions at the electrodes. In this study, a numerical model for the fluxes of most important ions in a NaF-AlF3-Al2O3 system has been proposed. The reactions in the bath and the resulted ions have been added to the reactions that take place at the cathode and anode, and a finite element model has been presented for the electrolyte portion of the aluminium reduction cell. The transient motion of the different ions under the migration and diffusion mechanisms have been modelled based on the classical mass transfer equations. The results illustrate the significant role of the migration in the early stages of electrochemical process. This mechanism is also the dominating effect in the motion of nonelectroactive species. For larger time scales, because of the depletion of the consumed species and accumulation of the produced species near the electrodes, the mass transfer is dominated by the diffusion.

Mohsen Ariana, Martin Désilets, Pierre Proulx

Liquidus Temperature of Electrolytes for Aluminum Reduction Cells

In this paper, the liquidus temperatures of the cryolite-alumina melts containing LiF, NaCl and KF were measured. The molar ratio of NaF/AlF3 was in the range of 2.0–3.0. A differential thermal analysis (DTA) apparatus was designed and constructed to measure the liquidus point of cryolite melts. The effect of these additives on the liquidus temperature was discussed. A multiple regression solution was obtained for the liquidus temperature of aluminum electrolytes.

Dong Shi, Bing-liang Gao, Zhao-wen Wang, Zhong-ning Shi, Xian-wei Hu

Effect of LiAlO2 and KF on Physicochemical Properties for Industrial Aluminum Electrolyte

The aluminum electrolytes of 300 kA series cell in a Chinese aluminum plant were investigated. Compositions and physicochemical properties of these electrolyte samples were analyzed, and the effects of contents of additive LiAlO2 and KF on physicochemical properties were studied. The results show that with the increasing content of the LiAlO2 from 0 to 8.52 wt%, the liquidus temperature decreases gradually from 940.7 °C to 917.0 °C, whereas the alumina solubility obtained by oxygen content increases in the initial stage and then reduces. When increasing the content of LiAlO2 up to 3 wt%, the alumina solubility reaches the highest value of 6.44 wt%. The liquidus temperature decreases by 2.3–2.5 °C with per 1 wt% addition of KF, and meanwhile, the alumina solubility increases by 0.05–0.13 wt% correspondingly.

Lv Xiaojun, Chen Shiyue, Lai Yanqing, Tian Zhongliang, Li Jie, Zhang Hongliang

Cell Operations and Process Control

Improvement of Alumina Dissolution Rate through Alumina Feeder Pipe Modification

Aluminum reduction cells use about 1.9 kg of alumina in order to produce 1 kg of aluminum. That is, for modern reduction cells operating in the 350 to 400 kA range, 5000 to 6000 kg of alumina is fed daily. Considering that 5000 to 10000 kg of molten bath is available to dissolve the alumina, the dissolution rate is an important factor in order to avoid muck and enable alumina feed control system to operate within the 2 to 5% alumina concentration. However, on top of cell status, alumina properties have an impact on alumina dissolution rate. Hence, supplier changes and/or segregation of alumina within the delivery system may have negative impact on alumina dissolution rate leading to muck and/or anode effects. This paper discusses modification to an alumina feeder pipe promoting the dissolution rate. Promising results obtained during trial in a pilot plant section are presented and discussed.

Jayson Tessier, Gary P. Tarcy, Eliezer Batista, Xiangwen Wang, Patrice Doiron

Reduction Cell Restart Method Influence on Cell Life Evolution

Low market conditions, power supply limitations, and interruptions in raw material deliveries might cause aluminium smelters to shut down in full or partially, and restart the capacities later. Shutdown circumstances and, more probably, methods of restart have further affect on operational performance and cell life.In the present paper potential mechanisms of cell lining damage caused by different restart techniques are discussed and analysis of restart technique influence on future cell life is made using data from several restarted cell lines.The paper also includes financial assessment of benefits and disadvantages of different restart techniques on a long-term smelter economy.

Mikhail Lukin, Richard Jeltsch

Start of an Aluminum Reduction Cell without Liquid Bath

A successful trial was conducted at Century Aluminum’s Kentucky smelter to determine the best method to start an aluminum reduction cell when liquid bath is not available, as it happens when an idled smelter is restarted. Materials, equipment, and methods critical to the successful dry start are discussed. A newly-lined cell was resistor-baked to target temperature, and dry crushed bath pushed onto the heated cathode surface. The cell voltage decreased over the next 24 hours until the cathode surface temperature stabilized. Ten to 15 centimeters of liquid bath could be seen between the anodes. The anode beam was raised to increase the voltage and heat and melt more dry bath. Eight hours after beam raise, the cell was operating at target voltage and had 35 centimeters of liquid bath. Four hours later the liquid bath reached the metal-addition target temperature, and molten aluminum was added to the cell to complete the dry start.

Kayron F. Lalonde, Brian D. Audie, Willy Kristensen, Timothy M. Snyder

A MIMO Modeling Strategy for Bath Chemistry

The bath chemistry is very complex for analytical modeling due to its sensitivity to disturbances from other processes. The control of the electrolyte also represents a great challenge, provided that any change in the heat and mass balance may affect current efficiency and pot life. In order to test a good control strategy, a process model is very helpful. The model allows process experts to design and test process control strategies without compromising reduction cells. In addition a model allows simulations on the process for a long time. In this work we developed a neural-based strategy to model bath chemistry variables in a Multiple Input Multiple Output (MIMO) approach using a data-driven design. The achieved results are very acceptable for the process engineering staff of the industry where this work was performed.

Fabio M. Soares, Roberto C. L. Oliveira

Cumulative Distributions of Metallic Impurities

Concerns with metallic impurities in aluminium reduction cells are often focused on trend data that offers limited information. The study of the shape and variability of the overall distribution of all reduction cells often offers greater insight into issues with raw materials, process control, or factors such as air-burning that result in bi-modal or more complex distributions. In this paper the author offers insights into how to interpret this information. Conclusions are focused on the value of these interpretations as a tool to manage metal purity and to provide process feedback.

Stephen J. Lindsay

Sodium Content in Aluminum and Current Efficiency — Correlation through Multivariate Analysis

Current efficiency is an important indicator used in the aluminum reduction technology. Values for this indicator are usually determined among potlines and they are not representative of the fluctuations that may occur in a single electrolysis cell. To measure or calculate an accurate value on a monthly basis would be a very interesting tool for process technicians and engineers to help regulate and analyse the performance of the pot. The potential use of the sodium content of aluminum as an indicator of current efficiency is investigated. Many authors discussed its role and indicated a possible correlation with the current efficiency. Aluminerie Alouette Inc. performed some univariate statistical analysis to confirm this correlation on a potline scale. Furthermore, multivariate analysis is performed to strengthen the correlation according to other indicators. Results from these analyses and the possible implementation as an indicator is discussed in this paper.

Lukas Dion, László Kiss, Patrice Chartrand, Gilles Dufour, François Laflamme

Gas-Solid Flow Applications for Powder Handling in Aluminum Smelters Processes

Gas-solid flow occurs in many industrial furnace processes. The majority of chemical engineering unit operations, such as drying, separation, adsorption, pneumatic conveying, fluidization and filtration involve gas-solid flow.Poor powder handling in an industrial furnace operation may result in a bad furnace performance, causing errors in the mass balance, erosion caused by particles impacts in the pipelines, attrition and elutriation of fines, overloading the bag houses. The lack of a good gas-solid flow rate measurement can cause economic and environmental problems due to airborne dust. The paper is focused on the applications of powder handling in relation with furnaces of the aluminum smelter processes such as anode baking furnace and electrolytic furnace (pot cell) to produce primary aluminum.

Paulo Douglas S. de Vasconcelos, André L. Amarante Mesquita

Operational Experience of Advanced Alumina Handling Technology in a Russian Smelter

In 2006 Rusal UC started its new potline in the Khakas Region at the Sayanogorsk Smelter. For this new potline Rusal has chosen two - at that time - new innovative technologies for the alumina handling.The primary alumina is transported pneumatically via the unique and most efficient FLUIDCON conveying system with 135 t/h and 390 m distance from the receiving station to the storage silos.The secondary alumina is distributed via two Aerated Distribution Systems (ADS), each for 168 pots from the day silo to the individual cells based on fluidized aersolide conveyors.In this article these technologies are briefly described to show the uniqueness’s and advantages.The main focus in the article is set on experienced operation and maintenance aspects during the first years of aluminum production and the corresponding measures taken.This paper concludes technical features presented on earlier TMS Annual Meetings [1, 2, 3, 5] and compares them with results from practice.

Jan Paepcke, Arne Hilck, Sergey V. Marshalko

Environment I

Reduction in HF emission through improvement in operational practices

In a prebake aluminium reduction cell, hydrogen fluoride is generated due to the continuous electrochemical oxidation of the hydrogen entrapped in the carbon anode matrix leading to formation of HF emission. Additionally, presence of moisture content in alumina or due to electrochemical generation in anode leads to HF formation due to the following reaction: <math display='block'> <mrow> <mn>2</mn><mi>A</mi><mi>l</mi><msub> <mi>F</mi> <mn>3</mn> </msub> <mo>+</mo><mn>3</mn><msub> <mi>H</mi> <mn>2</mn> </msub> <mi>O</mi><mo>&#x2192;</mo><mi>A</mi><msub> <mi>l</mi> <mn>2</mn> </msub> <msub> <mi>O</mi> <mn>3</mn> </msub> <mo>+</mo><mn>6</mn><mi>H</mi><mi>F</mi> </mrow> </math>$$2Al{F_3} + 3{H_2}O \to A{l_2}{O_3} + 6HF$$ Emissions are known to have adverse impact on human and urban environment. Hence, Dubai Aluminium has adheres to strict performance standards in order to reduce HF emissions via investment in high efficiency Fume Treatment Plants (FTP) which are capable of capturing more than 98% fluoride emissions and revising operational job practise. In D20 technology potline, a reduction in roof HF emissions 30–50% was accomplished after reviewing operational practises. This paper describes the initiatives implemented to reduce roof HF emissions.

H. R. Devadiga, Ali Jassim Banjab, Maryam Mohamed Al Jallaf, Ali H. A. M. Al Zarouni, Kamel Al Aswad, A. Kumar, Gregory Meintjes, S. Gowda, Milton Khan

Trace Element Concentration in Particulates from Pot Exhaust and Depositions in Fume Treatment Facilities

In dry cleaning of pot exhaust, expensive fluorides are captured and returned to production. At the same time impurities are accumulated in the finer fractions of the secondary alumina fed to the cells. While in secondary alumina the impurity content increased in the finer fractions, raw gas revealed a significant increase in impurities for particles with D i > 1 µm. Fume particles were sampled using a cyclone with varying cut-sizes and analyzed with help of HD ICP-MS. A statistical approach is used to identify correlations between element concentrations and particle diameters. Maximum impurity concentrations were recorded for fume fractions with particle size D i > 10 µm. It is expected that an economically feasible way of removing coarse particles from pot exhaust will lead to improved metal quality and increased current efficiency while keeping fluoride losses at a minimum.

Heiko Gaertner, Arne Petter Ratvik, Thor Anders Aarhaug

The Study and Applications of Modern Potline Fume Treatment Plant (FTP)

Primary aluminum reduction is energy and emissions intensive. It is very important for the environment and for business to treat potline fume efficiently. This article discusses how to improve potline fume efficiency from several respects based on CHALIECO GAMI’s experimental studies which were applied successfully in many modern potline’s Fume Treatment Plants (FTP), and also demonstrates the significance of improving alumina injection feeding and flow field inside the bag filter. A new and efficient method for the filter pulse control system is introduced, which is used in Vedanta’s recent Jharsuguda project in India.Based on these studies and applications, as well as new development of pulsing control system, CHALIECO GAMI is now able to control the HF emission concentration and the dust emission concentration respectively below 0.8mg/Nm3 and 5mg/Nm3 at the stack outlet of the FTP.

Deng Xiang, Lv Weining, Liu Xun, Deng Qiyi, Yi Xiaobing

F>C: Combined Treatment of Pot Gases and Anode Baking Furnace Fumes

Dry scrubbing technology is well known and used to treat either gases emitted by the reduction pots (Gas Treatment Centers) or fumes collected from the anode baking furnaces (Fume Treatment Centers). In fewer cases, the treatment of these gases and fumes has been realized by a common dry scrubbing system; fumes emitted by the furnaces are collected and mixed to the gases coming from the reduction pots. The mixed gases and fumes are then scrubbed together by a unique GTC designed and sized accordingly. This paper details the solutions implemented at Aluminium Dunkerque for Rio Tinto Alcan. Technical performances, investment costs and operation costs are detailed and compared with classical solutions, using a GTC and an FTC. Technical and organizational recommendations, necessary to guarantee the success of this solution are given as a conclusion to this paper.

B. Hureiki, C. Lim, A. Periers, E. Bouhabila, G. Girault, M. Leduc, S. Delenclos

Compact Filter Design for Gas Treatment Centers

The footprint occupied by the GTC is an increasing concern since roadways, alumina handling and storage fill the courtyard, the area between pot rooms. This area is further congested by high draft systems and collector ducting. The application of new heat exchangers has been recently discussed because it has the potential to reduce the footprint in two ways 1) by causing a reduction of the actual flow through the filters by eliminating the controlled ingress of dilution air and 2) the reduction in gas temperature reduces the “actual” volumetric flow rate to the baghouse [1].This paper describes a different approach taken by Danieli Corns to develop a compact filter module design that is aimed to reduce the overall footprint and capital costs of a GTC. Dubbed as the “Chinook” module, the design comprises of two low pressure rotating pulse systems combined into a single filter module thereby reducing the total number of modules and required associated equipment. Computational Fluid Dynamic (CFD) modeling was applied and confirms that while maintaining industrial standards on air/cloth ratio and can velocity, the footprint potentially is reduced by 25–30%. Placing the circular bag array of the low pressure pulse system into a square filter housing eliminates any concerns regarding the can velocity since the majority of gas flow migrates to the open areas around the filters. Modules can be upgraded to longer filter bags and/or to filter bags with extended surface without the need to increase the cross sectional area of the module itself. Future developments also include a positive pressure concept to the Chinook module with an exhaust fan upstream of the module and one independent stack on top of each module. Combined with the design aspects discussed, the positive pressure concept has the potential to further reduce the GTC footprint to about 60% in total.

Peter Verbraak, Peter Klut, Travis Turco, Erik Dupon, Edo Engel

An Innovative Compact Heat Exchanger Solution for Aluminum Off-Gas Cooling and Heat Recovery

A new concept of heat exchanger has been developed to cool down exhaust gases of aluminum electrolysis pots before entering a Gas Treatment Center (GTC). It optimizes operating conditions on a GTC, by reducing gas flow rates and enabling energy recovery. A prototype of heat exchanger was installed and tested for 12 months on five pots of the Norsk Hydro aluminum plant in Øvre Årdal, Norway. This prototype consisted of a bundle of finned oval tubes. Off-gas flows cross flow on the external side of the tubes. The oval shape is beneficial in terms of high gas-side heat transfer and low pressure drop. Fins ensure a compact design while being robust to gas-side fouling. Heat transfer characteristics were monitored and are presented. Stable and safe operation has been demonstrated with an early stage heat transfer reduction of approximately 10 to 15% due to fouling, which is lower than theoretical predictions.

El Hani Bouhabila, Erling Næss, Victoria Kielland Einejord, Kolbeinn Kristjansson

Latest Filter Developments Increasing Existing Aluminium Smelter Gas Treatment Centre Capacity and Reducing Emissions

Extended surface filter technology has been used in aluminium smelters around the world to increase the dust collection and fluoride scrubbing capacity of existing GTCs. This has provided an alternative to major capital equipment upgrade and lowered the production cost per tonne of aluminium where GTC capacity limitations were restricting production.As production rates in the smelter increase with capacity creep, so too does the GTC operational temperature. While the proper application of extended surface filters can help compensate for the reduced alumina reaction rate at higher GTC operational temperatures, some smelters increased production demands are now pushing the GTC operation temperatures beyond the limits of the standard polyester filter media. Alternative traditional high temperature filter media is cost prohibitive, and this change in the aluminium smelting industry has created a new cost/solution gap in the market of commercially available filter media.This paper summarises the success of the extended surface filters, and the development of a new and cost effective higher temperature filtration media. This media, when used in conjunction with extended surface filters, will address both increasing GTC operational temperature and the demand for greater capacity from existing GTCs without the need for costly capital equipment upgrades.

Michael Neate, Brad Currell

Reduced Ventilation of Upper Part of Aluminum Smelting Pot: Potential Benefits, Drawbacks, and Design Modifications

Maintaining current draft conditions in the upper part of Al smelting cell requires important electricity consumption for the fans. A reduction of the ventilation rate could significantly diminish the total power requirement at the blowers. However, adverse changes in operating conditions due to this ventilation reduction may disrupt the pot thermal equilibrium. A CFD model was created to investigate the influence of ventilation reduction on pot thermal balance. With the objective of maintaining normal heat losses by the top of the cell, several modifications are simulated, such as using plate fins on the anode assembly, changing hood gap geometry and modifying anode cover thickness. Heat transfer rates are determined for these modified designs, and compared to those currently achieved.

Ruijie Zhao, Louis Gosselin, Mario Fafard, Donald P. Ziegler

Latest developments in potroom building ventilation CFD modelling

In a context of production increases and proactive management of future health regulations, optimised workshop ventilation is necessary. Accurate predictions are required in order to achieve cost-efficient ventilation design including all specific features of the building, and this involves developing complex CFD models. The complexity of the models must, however, be well adjusted. They have to fulfil requirements as different as, for example, providing precise simulation of the impact of ventilation on cell cooling or determination of the positions for roof-vent monitoring equipment. A new approach is now considered, based on the development of several CFD tools of varying sophistication. Depending on project requirements, a combination of tools with the most appropriate level of complexity can be selected so that the trade-off between accuracy and computation time is optimised. This approach, validated through comparison with measurement campaigns, can now be used for cell development and new projects, regardless of building design and local conditions.

Nathalie Menet, Guillaume Girault, Nicolas Monnet, Catherine Turpin, Lionel Soulhac

Potline Operation II - Equipment

Solutions to Address Arc Welding Problems in an Operating Potline

Arc welding in an operating potline has always been problematic, especially repairs to aluminium busbar systems. The modern trend for higher potline amperages both in new and existing plants has led to an increase in these problems. To address this issue an electromagnetic shield has been developed. The shield is described along with modelling and magnetic measurements demonstrating its effectiveness. Further, the shield has been tested by welding cover plates on positive riser bolted joints at full line current. The results are encouraging and demonstrate that voltage drop gains can be made by on line repairs.

Bill Paul, Yann El Ghaoui, Philippe Jadaud, John Anderson, Stephen A. L. Foulds

Replacement of Damaged Electrical Insulators on Live Cross-Over Busbars inside a Tunnel: A Methodology Based on Risk Assessment and Numerical Simulation

With amperage creep, the croscr was severely damaged by excessive temperatures. Its replacement and upgrade was therefore necessary to ensure safe and continued operation of the potline. Electrical hazards, constrained space, heat stress, strong magnetic fields and poor lighting were amongst the challenges.This paper details the methodology developed by the project team to solve the issue.The first success key is that risk analysis was performed at each phase in partnership with the smelter, the original technology supplier and the contractors. The knowledge and experience of the original technology supplier was invaluable in the development of the solution. The second key is that Finite Element Analysis and in situ measurements were used extensively to define an optimized project scope including mitigation measures. The work was then executed with no incident, no damage and no cut-out while on schedule and below budget.

Daniel Richard, André Yelle, Olivier Charette, Andre Felipe Schneider, Jean-François Nadeau, Mickael Glière, Yannick Drouet, Philippe Brème

A Thermal-Mechanical Approach for the Design of Busbars Details

The mechanical behavior of busbars is a complex, displacement-controlled problem intimately linked to the conductors’ temperature. Thermal stresses are generated between two bodies submitted to differential thermal expansion, such as a pair of busbars at different temperatures that are mechanically connected at multiple locations. It can also occur to a single busbar circuit if the system lacks the required flexibility to accommodate the hot conductors-to-cold supports differential thermal expansion.An approach for the thermal-mechanical design of busbars was developed using ANSYS™-based numerical simulation. Special attention is given to specific design features such as weld plates, flexible joints, sliding supports and fixed points positioning for they play a major role on both the thermal expansion’s preferential direction and system’s ability to accommodate it.A test case based on a demonstration busbar system is presented and the impact of geometry and temperature on the thermal-mechanical performance of those specific features is discussed.

Andre Felipe Schneider, Olivier Charette, Daniel Richard, Charles Turcotte

Study of Technology and Equipment on Magnetic Induction Intensity Weaken for Aluminum Reduction Cells Welding in the Condition of Pot Line Current

To solve the welding with powerful magnetic fields in overhauling of cells, a kind of technology and equipment which is used for weakening magnetic induction intensity of welding position just like between collector bar and flex or among the bus bars of 160 ∼ 500 kA aluminum reduction cells in the condition of pot line current was devised. The principle of magnetic field recouped was adopted by the technology. The magnetic induction intensity of welding position can be weakened from more than 100 Gauss to less than 50 Gauss by the technology. According to the technology, magnetic induction intensity weaken equipment which is including magnetic recouped equipment, testing system online of bus bars and expert system of welding process was designed independently by GAMI. Five 350 kA cells have been welded by using the technology and the equipment in Zunyi Aluminum Co., Ltd. and Chinalco Guizhou Aluminum Plant, the welding voltage drop is less than 7.0 mV.

Wang Ziqian, Cao Bin, Yang Tao, Huang Jun, Li Meng

Potline Shutdown and Restart Secured Solutions

Today, on any modern technology for aluminium electrolyse reduction, pot shutdown and restart, planned or unplanned, remain an extremely critical operation, because of the level of energy surrounding the process (electrical and mechanical).Even when using modern reduction technologies, to shut down a pot, the operators have to manually introduce short-circuiting wedges between the electrical conductors to by-pass the current to the following pot and remove them to start the pot. The confined working area located below the floor level puts the operators in an uncomfortable and hazardous situation.Furthermore, wedge extraction speed is of utmost importance. During the restart phase, the high current density may produce some electrical arcs damaging the conductors if the wedges are not removed fast enough. Rhythm of wedges extraction is also a challenge to not compromise the last one integrity (risks of overheating).To reduce conductor maintenance costs but above all to put the operator in a safer working environment, ECL™ along with AP Technology™ teams, designed a remotely-controlled wedge extraction system entirely operated from working floor and connected with the Pot Tending Machine.

Anne-Gaëlle Hequet

Effect of Watering and Non-Watering Cooling Rates on the Mechanical Properties of an Aluminum Smelter’s Potshell

The cooling time of a shutdown aluminum reduction pot depends on the cooling method. Free-convection cooling (non-watering) takes about five to nine days depending on the surrounding environment while watering the pot shortens the cooling time to less than one day. Application of watering cooling rates on the pot from a high temperature can have consequences on the final mechanical property of the potshell. Facilitating a design of a cooling system which optimizes the cooling rate of a shutdown pot without deteriorating the desired mechanical properties of the potshell is required.This study focuses on the effect of different cooling rates on the micro structure and mechanical properties of the potshell material. To this effect, samples of potshell material from a shutdown pot were collected and ASTM standard specimens for mechanical and micro structural examinations were machined. Specimens were heated up to a maximum temperature of 500°C and then cooled at various rates ranging from that of free convection cooling to water quenching cooling. Tensile and micro-hardness tests were carried out to examine the effect of these cooling rates on the mechanical properties of the material. Micro structural analysis was carried out to study the micro structural response of the material to the various cooling techniques. The variation of the thermal and thermo gravimetric properties of the potshell material with temperature has also been measured according to ASTM E1461 Test Method.

Ayoola T. Brimmo, Mohamed I. Hassan, M. O. Ibrahiem, Youssef Shatilla

Mathematical Model of Cooling of a Stopped Pot and Its Validation

In aluminum reduction pot technology, the potshell is used for several generations. After each shut down the potshell is cooled by free convection and radiation. This cooling takes from five to nine days depending on the surrounding temperature. Cooling by spraying water on the potlining is used in some aluminum plants; this reduces the cooling time to less than one day but this method can be harmful for the potshell and for the environment.The aim of this study is to develop a heat transfer model of the aluminum reduction pot in a free convection and radiation environment. A commercial finite element code (FEM), ANSYS®, was used to create the 3D model and solve both the steady state and transient temperature distribution. All material properties and heat transfer coefficients were modeled as functions of temperature. The solidification of aluminum at its phase transformation temperature was included in the model to investigate the behavior of the cooling curve of the various components of the pot during this phase change. The resulting cooling curves are in good agreement with experimental data. This model will be used to design an optimum pot cooling environment.

Mohamed I. Hassan, Ayoola T. Brimmo, M. O. Ibrahiem, Youssef Shatilla

Environment II - PFCs

A Study of Low Voltage PFC Emissions at Dubal

Perfluorocarbon (PFC) emissions are the result of a phenomenon called anode effect (AE), when normal electrolysis is discontinued due to lack of alumina and another reaction takes place leading to generation of PFC gases. Anode effects have been characterized in the industry by measuring their frequency and duration when the cell voltage is above 8 volts. Efforts have been made by the Aluminium Industry to reduce AE frequency and duration leading to considerable reductions in PFC emissions. However, recent independent measurements reported sources of PFC emissions that are “non AE related”. Measurements have been carried out on all DUBAL cell technologies in 2010/2011 and similar occurrences have been observed. DUBAL has initiated a program to identify the possible mechanism of the “non AE related” PFC emissions and to develop new logics for treating it. In this paper, a study of low voltage PFC emissions at DUBAL will be presented.

Abdalla Zarouni, Michel Reverdy, Ali Al Zarouni, K. G. Venkatasubramaniam

Continuous PFC Emissions Measured on Individual 400kA Cells

PFC emissions from the primary aluminium industry have traditionally been linked to anode effects (AE), which are most broadly defined as when the voltage on a cell exceeds 8 Volts for more than 3 seconds. Recent studies however have revealed the existence of continuously generated PFCs, which are not related to a conventionally defined AE. In a study focusing on individual 400kA cells, the continuous generation of PFCs was measured on several pots, was found to vary from one cell to another, and to vary within a number of hours. Generation of these PFCs also varied from one localised region to another within a cell and may be linked to instabilities in local current distribution, as suggested by 20Hz continuous monitoring of individual anode currents. While the study provides further understanding on the characteristics of these PFCs, further work is required to determine the fundamental causes of this emission.

David S. Wong, Jerry Marks

PFC and Carbon Dioxide Emissions from an Australian Aluminium Smelter Using Time-Integrated Stack Sampling and GC-MS, GC-FID Analysis

PFC (CF4, C2F6, C3F8), HFC (CHF3) and CO2 emissions were estimated from two potlines of the Hydro Australia Kurri Kurri aluminium smelter in the Hunter Valley, NSW, in 2009. Emissions were estimated using integrated sampling over a two week period followed by laboratory analysis for PFCs, HFCs and CO2. The PFC emission factors were similar to, but significantly more accurate than, annual PFC emission factors found for other Australian aluminium smelters (Bell Bay, Tasmania; Portland and Pt Henry, Victoria) in 2009, based on in situ PFC data measurements at Cape Grim, Tasmania. The CF4 and CO2 emission factors at Kurri Kurri are significantly larger than the Australian average CF4 and CO2 emission factors reported to the UNFCCC for 2009. C3F8 and CHF3 emissions at Kurri Kurri are low and do not significantly add to GHG emissions from an aluminium smelter.

Paul Fraser, Paul Steele, Mark Cooksey

Investigation on Formation Mechanism of Non-Anode Effect Related PFC Emissions from Aluminum Reduction Cells

Influencing factors on PFC (perfluorocarbon) emission were investigated in Chinese smelters. The formation mechanism of non-anode effect related PFC emissions (short as NAE-PFC) from aluminum reduction cells were discussed. Anodic overvoltage has an obvious influence on NAE-PFC formation, CF4 will emit when anodic overvoltage is higher than 2.55 volts, C2F6 will be generated when anodic overvoltage surpasses 2.68 volts. Alumina concentration in bath with anodic current density also has a clear influence on NAE-PFC formation. Alumina fluctuates in large cells from the metal-tapping-end to the flue-end. Alumina always distributes unevenly in the bath because of bath flow driven by magnetic fields, which will also cause NAE-PFC formation. NAE-PFC will emit when there is not enough alumina under certain anode’s bottom. The limit alumina concentration is 75% of normal level which is 2.0–3.5% in Chinese smelters. Cells will generate NAE-PFC when any anode’s current density is higher than 1.5 times of normal level which is 0.72–0.80A/cm2 in Chinese smelters.

Chen Xiping, Li Wangxing, Zhang Yanfang, Qiu Shilin, Chris Bayliss

On the Mechanism Behind Low Voltage PFC Emissions

Recently there have been several reports on PFC emissions (CF4 + C2F6) during normal operation of aluminium cells. Laboratory recordings of the so-called “critical current density” for the initiation of anode effect on carbon anodes in cryolite-alumina melts can be helpful to understand this phenomenon. When gradually raising the anodic potential, the anodic current density then increases until the alumina concentration at the anode surface approaches zero, whereby the current abruptly drops back to a much lower value, and PFC is being evolved. In an aluminum cell operating at low alumina concentration, alumina depletion may occur at one or more anodes, whereby PFC emission is initiated by this mechanism. Due to the low current density the local ohmic drop decreases, allowing the higher anode polarization needed for PFC evolution. The remaining anodes evolving CO2, may sustain normal electrolysis close to normal cell voltage. How to avoid this harmful condition is discussed.PFC emission at close to normal cell voltage has also been observed in electro winning of neodymium in a fluoride melt.

Jomar Thonstad, Sverre Rolseth, Rudolf Keller

Frequency response analysis of anode current signals as a diagnostic aid for detecting approaching anode effects in aluminum smelting cells

Modern cell control aims to prevent anode effects by controlling the alumina feeding rate based on the change in cell resistance or voltage and the preset limits of these values. Success of this approach depends on the uniform distribution of dissolved alumina across the cell and the anode current distribution. As this is not always the case in practice, the control procedure sometimes fails and the cell undergoes anode effect. Monitoring of the anode current signals has been suggested as an alternative way for early anode effect detection. This paper presents frequency response analysis of anode current signals obtained from an operating cell and shows the ability for early detection of an anode effect. It has been found that the frequency response peak associated with bubble dynamics of the corresponding anode disappears as it undergoes partial anode effect prior to the cell approaching full anode effect. The results show that the analysis can provide further information to identify a localized anode effect which can facilitate cell control for more effective anode effect prevention.

C. Cheung, C. Menictas, J. Bao, M. Skyllas-Kazacos, B. J. Welch

Reduction Strategies for PFC Emissions from Chinese Smelters

Perfluorocarbon (PFC) formation mechanism was investigated and strategies for PFC reduction in China were developed. Alumina concentration in bath has a strong effect on PFC evolution. Anodic overvoltage and current density also have an obvious influence on PFC. Narrow alumina concentration controlling mode, small dose feeding mode, alumina level preestimating and verifying mode were developed in order to reduce PFC emissions. PFC can be reduced by keeping alumina level in bath in the range between 2% and 3%, not low enough to cause anode effect or high enough to deposit in cells. Small dose feeding mode controls both fixed and movable small dose feeders, which can supply alumina into cells at right time. Alumina level preestimating & verifying mode includes pre-estimating modules and verifying modules, which can calculate alumina level by equations related to anodic current density and alumina concentration. If alumina is low, numerical modules will send feeding command to feeders.

Li Wangxing, Chen Xiping, Qiu Shilin, Zhang Baowei, Chris Bayliss

Off-Gas Analysis of Laboratory-Scale Electrolysis Experiments with Anodes of Various Compositions

The sulphur content of industrial anodes in the aluminium industry is usually between 1% and 2%. This sulphur is converted to different sulphuric gases which are released along with the other off gases from the cell. Although wet scrubbers in modern plants are capable of capturing the sulphur before it is released to the atmosphere, the equilibrium dynamics and production kinetics of the sulphurous gases are of vital interest in order to be able to predict acid dew point temperatures and other important parameters for the off gas suction system in a plant.Controlled potential electrolysis with on line gas analysis was utilized to study the compositions of gas species produced in a laboratory cell during regular electrolysis conditions and during anode effects. A three-electrode setup with an Al reference electrode was used to monitor the anodic voltage. The combination of mass spectrometry (MS) and Fourier-transform infrared spectroscopy (FTIR) was used to characterize the off gas.The dominant sulphur containing gas specie in the laboratory cell was COS. CS2 was only observed during anode effect, along with small amounts of SO2.

Ole S. Kjos, Thor Anders Aarhaug, Egil Skybakmoen, Asbjørn Solheim, Henrik Gudbrandsen

Hydrolysis of Carbonyl Sulfide (COS) on Smelting Grade Alumina

Carbonyl sulfide (COS) is present in aluminum smelter off-gas at low ppm concentrations. The primary source of COS is the 2–3 wt% sulfur contained in carbon-based anodes. COS is directly evolved from anode oxidation during aluminum electrolysis. Upon evolution, COS is further oxidized to SO2, while a minor fraction of evolved sulfur is emitted in the form of COS. Very little, if any, of the evolved COS is captured by the dry scrubbing systems.In this work, a series of laboratory experiments was conducted to characterize interactions of COS with smelting grade alumina (SGA) as a function of gas temperature and humidity. The effect of other smelter off-gas components (HF and SO2) was also evaluated. This work suggests that SGA is an efficient catalyst for COS hydrolysis, however, the presence of hydrogen fluoride, SO2 and humidity negatively affects its catalytic activity.

Aleksandr V. Mikhonin, Neal R. Dando, Michael Gershenzon

Cell Fundamentals, Phenomena and Alternatives I (2012)

A Thermodynamic Approach to the Corrosion of the Cathode Refractory Lining in Aluminium Electrolysis Cell: Modelling of the Al2O3-Na2O-SiO2-AlF3-NaF-SiF4 System

The corrosion of the cathode refractory lining in electrolysis cells, partly due to the cryolite bath, can shorten the lifespan of the cell. This corrosion is usually studied with laboratory tests and cathode autopsies of shutdown cells, but the results might not correspond to the reactions taking place in service. The simplified corrosion problem (Al2O3-SiO2 representing the aluminosilicate refractory, NaF-AlF3 representing the cryolite bath) corresponds to the reciprocal system Al2O3-Na2O-SiO2-AlF3-NaF-SiF4. The thermodynamic modelling of this system permits the calculation of complex chemical equilibrium occurring at the service temperature. The reciprocal system has been assessed using the Modified Quasichemical Model in the Quadruplet Approximation (MQMQA), which takes into account both first-nearest-neighbour (FNN) and second-nearest-neighbour (SNN) short-range order (SRO) and allows the modelling of the strongly ordered oxyfluoride liquid solution. A unique set of model parameters is used to reproduce the experimental data. The results of the thermodynamic modelling of the Al2O3-Na2O-SiO2-AlF3-NaF-SiF4 system are presented here.

Guillaume Lambotte, Patrice Chartrand

Effect of Current Density and Phosphorus Impurities on the Current Efficiency for Aluminum Deposition in Cryolite-Alumina Melts in a Laboratory Cell

The current efficiency in industrial Hall-Heroult cells for aluminum production may be up to 96%. [1]. The back reaction between the dissolved metals (aluminum and sodium) and the anode product play the major part in the loss in current efficiency. Also impurities, such as phosphorous, which participate in cyclic red/ox reactions at the electrodes contribute significantly to reduced current efficiency. Phosphorous and other impurities are recycled with secondary alumina. Further potline amperage increase in industrial cells may require higher current densities. Thus the current efficiency dependence on current density and phosphorous content was studied at current density ranging from 0.85 – 1.5 A/cm2 in a laboratory cell. Current efficiencies from 90 – 97% were obtained and increased slightly by increasing cathodic current density. The current efficiency decreased by about 3.8% per 100 ppm of phosphorus in the electrolyte.

Rauan Meirbekova, Gudrun Saevarsdottir, Geir Martin Haarberg, Joseph Prince Armoo

Cast Shop for Aluminum Production


Aluminum Cast Shop I

Very High Purity Ingot — An Endangered Species?

Production of metal that is of very high purity remains at substantial levels globally. But, the changing palette of raw material quality, pot room design factors, and operating conditions that support production of very high metal purity threaten the status quo. Older cell technologies that are quite capable of very high purity production are less competitive. Some technologies, especially in the arena of pollution control, are not as sustainable as they once were. Since the demand for very high purity is not anticipated to diminish, re-alignments of cast house capacity to include small mold lines may become common once again. In this paper the author reviews the key factors that are required to produce very high purity metal and comments upon their sustainability. Conclusions are focused on possible paths forward and how these may impact primary metal cast houses.

Stephen J. Lindsay

The Challenge of Effectively Utilizing Trace Elements/Impurities in a Varying Raw Materials Market

As technology and innovation advances, so do the materials which we use, and in turn, the raw material stream is continually impacted. Today, plants are faced with the challenge of ideally capitalizing on the positive benefits of trace elements when they exist, or following in previous paths of tolerating the increased levels of the elements, and in the worst case, removing the elements at a large expense in production costs. Presented are recent trends observed for various elements, their origins within the raw material stream, and discussions of the need to reexamine how trace elements are handled today and in the future. What is tolerable in certain aluminum alloy products and potential benefits in properties will be explored in addition to the challenges required to remove the elements effectively when needed.

Gyan Jha, Shridas Ningileri, Xiaoxuan Li, Randall Bowers

Energy control in primary aluminium casthouse furnaces

Controlling and reducing the energy consumption in aluminium melting/casting furnaces are key factors influencing the casthouse economy and the carbon foot-print. In order to effectively run a furnace with low energy consumption the burner’s fuel consumption in the different charge stages needs to be monitored. Furthermore, the furnace and burner need to be sufficiently instrumented to continuously measure important furnace parameters and relate these to the resulting melt temperature, and hence the energy consumption.The paper gives operational experience of reducing the melting/casting furnace energy consumption in a Hydro Aluminium primary casthouse.

Inge Johansen, Svenn Ivar Strømhaug

Metal Contamination Associated with Dross Processing

Processing dross to recover the contained metal units has been practiced almost as long as there has been an aluminum industry. While the primary goal is to maximize metal recovery from the dross, other factors are important as well. It is normally desirable to produce metal with a composition similar to the starting alloy. This may not be possible in many instances. This paper will look at the sources and mechanisms for metal contamination. It will also offer suggestions on how the contamination can be minimized.

Ray D. Peterson

Aluminum Cast Shop II

Ultrasonic Degassing and Processing of Aluminum

A commercially and industrially viable ultrasonic system has been developed. This system is being used in an industrial environment. The aim of this paper is to present the experimental method used and results obtained from two different processes. The system was tested on a continuous rod, casting and rolling line. This line is used to make wire rod in pure and alloyed aluminum. The system was also tested in a large scale die casting shop. Each process had its own challenges in how to measure the degassing ability of the system, along with product improvements not related to hydrogen gas. We will present various methods used to measure the dissolved hydrogen and the resulting product improvements after ultrasonic degassing. Additionally we will discuss sampling methods for spectrum analysis and inclusion measurement. Sources of contamination will also be discussed.

Victor Rundquist, Kiran Manchiraju

Kinetics of Ultrasonic Degassing of Aluminum Alloys

Ultrasonic processing was shown to be an efficient means of aluminum melt degassing with benefits of being economical and environment friendly. The fundamental reason for ultrasonic degassing is known to be diffusion of dissolved hydrogen to cavitation bubbles assisted by their pulsation, and their subsequent evacuation from the melt. This paper reports on the kinetics of ultrasonic degassing of an Al-Si casting alloy. The kinetics is studied through interplay of cavitation bubble generation, melt agitation through acoustic streaming, and flotation of gas bubbles to the surface of the melt. Direct measurements of hydrogen concentration in the melt by Foseco ALSPEK-H probe are used along with a reduced-pressure test. The possibility of using short sonication times is discussed.

Noé Alba-Baena, Dmitry Eskin

Removal of Inclusions in Molten Aluminum by Flux Injection Under Counter-Gravity

A new process for removal of oxide inclusions in molten aluminum, namely flux injection under counter-gravity, has been presented in this paper. The molten aluminum to be purified is in the lower holding furnace and is covered with the liquid flux. The molten aluminum is first forced to flow upwards into the crucible which is placed in the upper holding furnace through a feeder tube, followed by the molten flux injecting into the molten aluminum by increasing the pressure in the lower holding furnace. In this way, the flux and the molten aluminum are mixed fully to contact each other, resulting in the transfer of inclusions in the molten aluminum towards the flux because of the absorption of the flux to the inclusions. As the result, the molten aluminum is purified. The injection-backflow procedures can be repeated two or three times to acquire better effectiveness. The experiments were carried out for ADC 12 die casting aluminum alloy with the flux (40% NaCl, 30% KCl, 10% NaF and 20% Na3AlF6). The results show that the inclusion and hydrogen concentration can be decrease significantly after two injection-backflow cycles.

Jianmin Zeng, Hong Gu

Advanced Compact Filtration (ACF): An Efficient and Flexible Filtration Process

Deep bed filters are well known not only for providing efficient inclusion removal that is required for critical products, but also for their relatively high metal hold-up. In multi-alloy casthouses, filtration costs associated with deep bed filters can be considerable due to filter media replacement and scrap metal generation at alloy changes. This paper describes the key components of a new metal filtration technology, the Advanced Compact Filter (ACF) developed and industrialized by Rio Tinto Alcan (RTA). The ACF provides flexible, efficient and robust filtration suited for large product mix environments. This technology was successfully demonstrated on critical products, and is now fully implemented and operated in one Rio Tinto Alcan casthouse. This paper also presents the main benefits for cost reduction provided by this technology.

Francis Breton, Peter Waite, Patrice Robichaud

Electromagnetic Priming of Ceramic Foam Filters (CFF) for Liquid Aluminum Filtration

Commercial Ceramic Foam Filters (CFF) of 30, 50 and 80 Pores Per Inch (PPI) have been primed, using magnetic field strengths of 0.06–0.2T, for periods of 1–10 minutes. The influence of time and field strength on the gas removal from the CFF structure, and the resulting improvements in filter productivity, are discussed. The obtained results are related to Finite Element Modeling (FEM) of the metal flow fields induced by the electromagnetic Lorentz forces. Higher filtration rates were obtained for 50 PPI magnetically primed, than for 30 PPI gravity primed filters. This suggests that electromagnetic priming offers an opportunity to use 50 PPI filters, with a higher overall filtration efficiency than 30 PPI filters, in existing cast house applications where the low productivity/high priming head of these filters would otherwise rule them out. Estimated filtration efficiency of different filter types are presented as functions of velocity and thickness.

Robert Fritzsch, Mark William Kennedy, Jon A. Bakken, Ragnhild E. Aune

Plant Scale Investigation of Liquid Aluminium Filtration by Al2O3 and SiC Ceramic Foam Filters

Plant scale filtration experimentsof 10〝 × 10〝 × 2〝, 30PPi Al2O3 and SiC industrial filters were carried out. Wetting experiments show that the SiC filter wets better with molten aluminium than Al2O3. The assessments by LiMCA II and laser were employed to study the behaviour of the two filters. The Al2O3 filter shows improved time dependent behaviour, increasing filtration efficiency, during one hour filtration. This is not the case for the SiC filter. It decays faster than the Al2O3 one. The SiC filter requires less pressure drop to infiltrate the metal. The result suggests that the SiC can be a new filter choice in the aluminium industry.

Sarina Bao, Martin Syvertsen, Arne Nordmark, Anne Kvithyld, Thorvald Engh, Merete Tangstad

Casting Practices Influencing Inclusion Distributions in Billets

A macro-etching method has been used to analyze the distribution and amount of inclusions along billets and on cross sections. Main parameters that have been varied are holding time before casting and amount of liquid remaining after casting.The result show that short holding times, in the order of 10 minutes, give increased amount of inclusions in the beginning of the billets, but holding times in the range from 30 to 60 minutes do not show any significant differences.If the melt remaining in the furnace after casting is less than about 3000 kg, the inclusion density increases towards the end of the ingots.The distribution of inclusions over the cross section of billets show that most inclusions are found in the centre of the billets, however, at increased total amount of inclusions, they tend to appear evenly over the whole cross sections.The results are discussed based on convection in furnace and settling rates and convection at solidification front.

Ghadir Razaz, Torbjörn Carlberg

Oxidation of Commercial Purity Aluminum Melts: An Experimental Study

Oxidation and dross formation is an undesirable, but unavoidable part of the production of aluminum. Past efforts to minimise dross formation through improved melt processing practices have been hindered by uncertainty in the fundamental behavior of how oxides grow on molten aluminum. The growth of oxide films formed on pure aluminum melts held at various temperatures and exposed to ambient air is investigated. Growth rates (i.e. mass/area as a function of time) were determined by skimming oxide films from laboratory-scale melt surfaces after various exposure times and then processing these films to separate oxide from metal. Collected oxide films were characterized using transmission electron microscopy (TEM) and electron diffraction techniques. γ-Al2O3 appears to be the dominant oxide species and no breakaway oxidation was observed even at 850°C/14h. The micro structural evolution of the films is discussed in light of the results and behavior implications of this work for industrial cast house situations are discussed.

Stephen J. Bonner, John A. Taylor, Ji-Yong Yao, M. Akbar Rhamdhani

Aluminum Cast Shop III

Optimisation of Grain Refinement

Considerable progress has been made in recent years with the optimisation of grain refinement practice. In the past this could only be done by trial and error which is time consuming and far from ideal. More recently it has been possible to study and quantify the various factors affecting grain refinement including melt nucleation level, growth restriction, grain refiner recovery, in line treatments and potency and variation in grain refiners with the help of the Opticast technology which allows data to be generated from sampling the melt in real time. It has been found that whilst it is useful and necessary to quantify the foregoing furnace factors it is equally necessary to control grain refiner variation in order to achieve a fully optimsed result and to support this, a new grain refiner, Optifme, has been developed and introduced in a number casthouses. The results from two casthouses where these techniques have been applied are reviewed.

Rein Vainik, John Courtenay, Bader Saglam

Grain Refiner for Al-Si Alloys

Over the last few decades the grain refinement practice using Ti based chemical additions (Al-Ti-B) is well established for wrought Al alloys, however in the case of Al-Si casting alloys, the practice of adding grain refiners and the impact on castability is not well established in industries, due primarily to chemical instability of conventionally known Ti based grain refiner with Si element in the melt. Research at Brunei University has identified a novel chemical composition that can effectively refine grain structure of Al-Si castings alloys. First, the effect of addition of grain refiner, in the form of powder addition, on micro structural and mechanical properties of LM6 (A423) and LM25 (A356) alloys was investigated. Afterwards, a suitable method to produce the novel grain refiner in the form of master alloy was developed and the effect of addition of master alloy on grain refinement of the previously mentioned Al-Si alloys was studied.

Hari Babu Nadendla, Magdalena Nowak, Leandro Bolzoni

Production of Al-Ti-B Grain Refining Master Alloys from B2O3 and K2TiF6 by Microwave Irradiation

Al-Ti-B master alloys have received much attention in recent years owing to their potential as efficient grain refiners for aluminum foundry alloys. A process involving in-situ reduction of K2TiF6 and B2O3 with excess aluminum in the presence of cryolite flux has been developed for the preparation of Al-Ti-B master alloys using a melt reaction method by microwave irradiation. The microstructure and synthetic process of the master alloy were investigated by optical microscopy and X-ray diffraction. The results show that the master alloy is composed of Al, Al3Ti and TiB2 phases and microwave irradiation method can be used to fabricate Al-Ti-B master alloy in situ from the K2TiF6-2O3-Na3AlF6 and Al system when the aluminum melted. The synthesis mechanisms of the master alloy are as follows: Al3Ti is formed through the reaction between K2TiF6 and Al melt at 850 °C.

Zhou Shu-cai

Effects of Yb Additions on Refinement of Eutectic Si in Al-5Si Alloys

Modification of eutectic Si from platelet to fibrous morphology can be interpreted using impurity-induced twinning (IIT) growth mechanism and twin plane re-entrant edge (TPRE) growth mechanism. According to IIT mechanism, Yb has an exactly fitting radius ratio (1.646). However, to date, the effects of Yb additions on eutectic Si is still very limited. In this contribution, a series of Al-5 wt% Si alloys with Yb additions have been investigated using thermal analysis and multi-scale micro structure characterization techniques. Only a refined plate-like eutectic Si structure was observed. However, in contrast to Sr additions, no fibrous morphology and no significant Si twinning was observed, which is not consistent with the generally accepted IIT mechanisms. We proposed that the morphology change from platelet to fibrous, caused by stronger Si twinning, can be defined as modification; while, the decrease in size, caused by higher nucleation and growth undercooling, should be defined as refinement.

J. H. Li, P. Schumacher

Influence of Vanadium on the Microstructure of A356 Foundry Alloy

Increasing vanadium content in coke used for anodes in aluminium production will lead to rising vanadium concentrations in primary aluminium. Consequently, the vanadium will be found in downstream products such as foundry alloys at levels well above current alloy specifications. The work presented in this article focuses on the effect of different vanadium concentrations on the microstructural features of an as-cast A356 alloy. It is shown that vanadium in excess of 0.2 wt% cause crystals with a distinct polyhedral morphology to precipitate. This phase was identified as Si2V by SEM-EDS measurements. Moreover, traces of vanadium were found in the β-Al5FeSi phase. When the vanadium concentration was increased from 0.06 to 0.8 wt% gradual vanadium enrichment of the β-Al5FeSi from 0.4 to 5.9 wt% occurred. Iron rich particles, which had some solubility for vanadium possessed an almost globular shape and were located within α-Al dendrites or close to the dendrite/eutectic interface.

Thomas H. Ludwig, Paul L. Schaffer, Lars Arnberg

Aluminum Cast Shop IV

Influence of die and casting temperatures and titanium and strontium contents on the technological properties of die-cast A356 in the as-cast and T6 condition

Automobile manufacturers demand downsized components manufactured from materials possessing increased technological properties. To fulfill this, the processing of existing materials must be optimized. In the present study, the individual effects and interactions of the melt’s treatment and process parameters on the mechanical and metallographic properties were investigated in the as-cast and T6-states. This was carried out with the help of the Taguchi method to optimize the technological properties of this much used die-cast A356 alloy. The interaction effects of the parameters considered in this study are hardly addressed in the literature. However, the results of the present investigation show that this aspect is fundamental for optimizing the technical properties of a die-cast A356 alloy. For example, the titanium content of 0.20 wt.%, conventionally used for grain refinement, can be reduced by up to 75 % when the die temperature is relatively low (here: 190 °C). This leads to increased as-cast technological properties and cost savings.

Sebastian F. Fischer, Veronika F. Groten, Johannes Brachmann, Carolin Fix, Thomas Vossel, Andreas Bührig-Polaczek

Horizontal Single Belt Strip Casting (HSBC) of Al-Mg-Sc-Zr Alloys

Scandium containing Al-Mg alloys exhibit significant potential for use in aerospace applications, such as air frames and stiffened panels. Zirconium additions further improve the room temperature (RT) workability, elevated temperature resistance and mechanical properties of these alloys. In this study, the capability of the Horizontal Single Belt Strip Casting (HSBC) technology for casting and processing of Al-Mg-Sc-Zr alloys was investigated. The alloys were strip cast on the horizontal single belt strip caster located in McGill’s Metals Processing Centre (MMPC). Detailed micro-structural characterization of strip-cast Al-Mg-Sc-Zr alloys was conducted via Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and Electron Backscatter Diffraction (EBSD). Additionally, the surface quality of strips was evaluated via 3D profilometry measurements and analyses. Finally, mechanical properties of the cast strip products were evaluated and compared with equivalent cast alloy structures associated with the slower cooling rates specific to direct chill (DC) casting.

Mert Celikin, Donghui Li, Luis Calzado, Mihaiela Isac, Roderick I. L. Guthrie

Electrode Technology for Aluminum Production


Anode Raw Materials

Review of Different Techniques to Study the Interactions Between Coke and Pitch in Anode Manufacturing

The quality of carbon anodes, consumed in electrolysis during the primary aluminum production, has an important impact on the electrolytic cell performance. Coke and pitch are the raw materials used in anode manufacturing. The raw material properties and the process parameters during production determine the anode quality. A plant receives these materials from different sources, and the variability in their properties is usually a major concern during anode production. The interaction between coke and pitch influences strongly the anode properties. Study of coke and pitch individually as well as the interactions between them using different techniques (spectroscopic, optical, etc.) such as XRD, FTIR, XPS, and SEM help identify their compatibility. Each technique gives information on different aspects of the raw materials. In this article, the use of a number of these techniques for studying coke, pitch, and their interactions will be discussed. Results will be presented for a number of cases.

Duygu Kocaefe, Arunima Sarkar, Shipan Das, Salah Amrani, Dipankar Bhattacharyay, Dilip Sarkar, Yasar Kocaefe, Brigitte Morais, Marc Gagnon

Observations on the Coke Air Reactivity Test

The ISO Coke Air Reactivity test has been used by the smelting industry for many years but its use as a calcined coke specification is decreasing. This paper presents a review of previous work published on this test and presents experimental data on a wide range of cokes currently being used for anode production. Coke air reactivities are strongly dependent on coke calcination levels and it is possible to drive air reactivities lower by increasing calcining temperatures. With the general increase in sulfur level of high sulfur cokes used in anode coke blends, higher calcining levels are not desirable due to their negative influence on coke porosity as a result of thermal desulfurization. Many smelters are now adopting lower real density specifications, which runs counter to achieving the low coke air reactivities required to meet coke air reactivity specifications.

Keith Neyrey, Les Edwards, James Marino

Impurity Removal from Petroleum Coke

The question of treating high-impurity coke to enable use in anodes was examined. A mineralogical analysis of different cokes demonstrated that more than 99 % of the particles contained the expected concentrations of sulfur, nickel, and vanadium while a small number of particles contained inclusions of other impurities. A number of potential treatment options were identified and investigated, with thermal desulfurization being studied further. The initial sulfur concentration, residence time and calcination temperature had the highest influence. 45 % sulfur removal was achieved but with significant bulk density loss. Acceptable pilot anode quality was not achievable even with the fines fraction substituted with desulfurized material. Therefore while sulfur removal during calcining is possible, the resulting coke, even in the most promising scenario, is not suitable for anode manufacturing. At this time, an industrial process to remove sulfur and other impurities from petroleum coke is unlikely to be viable.

Alexandre Gagnon, Nigel Backhouse, Hans Darmstadt, Esmé Ryan, Laurence Dyer, David G. Dixon

Calcined Coke Round Robin 19 and the Precision of Bulk Density Tests

Round robins (RR’s) are useful for laboratories to benchmark performance against other labs. RR19 was a collaboration between Rain CII, Hydro Aluminium and R&D Carbon and was organized after the special session on coke bulk density arranged by TMS and ASTM at the 2011 TMS Annual Meeting. Five calcined coke samples representing a range of chemical and physical properties were prepared and sent to 28 laboratories around the world. A key objective was to compare the repeatability and reproducibility of different bulk density and apparent density methods. The paper discusses the organization of RR19 and presents a statistical analysis of the following quality parameters: S, V, Ni, Fe, Ca, Si, Na, P, real density, Lc, VBD, TBD and Hg apparent density. In a companion paper, the properties of bench scale and pilot scale anodes produced with the cokes are presented along with correlations to coke properties.

Marvin Lubin, Les Edwards, Lorentz Petter Lossius

A Method for the Rapid Characterization of Petroleum Coke Microstructure Using Polarized Light Microscopy

Petroleum coke is used for the fabrication of anodes for aluminum reduction cells. There are ever-increasing economic and supply availability pressures for alternative and multiple sources and qualities for fabricating anodes, and therefore for cost effective characterization to make timely adjustments of the anode mixes. One characteristic historically acknowledged as having a significant detrimental influence on anode thermo-mechanical properties is the so-called isotropic structure. Traditionally such characterizations using optical microscopy are exhaustive and therefore cause a throughput concern. A method was developed and successfully applied to green and calcined coke reducing the interpretation time of a sample down to about twenty minutes. The sample preparation and interpretation methodology is described and examples presented, including a case study of how the method was used to guide raw material blend decisions across Rio Tinto Alcan’s North American sites.

Andris Innus, Alain Jomphe, Hans Darmstadt

Improvements of Vibrated Bulk Density Analysis at VM-CBA and Petrocoque S.A

Anodes for aluminum production are composed of coal tar pitch (CTP) and calcined petroleum coke (CPC). The anode composition depends on the reduction technology. For Søderberg anodes, as used by VM-CBA, the coke and pitch contents range from 67 to 79% and from 33 to 21%, respectively. Coke quality control includes sampling and analysis of chemical and physical properties. These tasks are associated with uncertainties, which may lead to wrong decisions. Since 2010, VM-CBA and Petrocoque S.A studied possibilities to reduce the standard deviation (STD) of the vibrated bulk density (VBD) analysis. The result of this work was a reduction of the difference between the VBD results of the two labs from 0.018 to 0.006 g/cm3.

Jean Carlos Pardo, Edinaldo Pereira da Silva, Paulo da Silva Pontes, André Nantes

Influence of GPC Properties on the CPC Quality

A detailed study was carried out on green petroleum coke (GPC) from refineries in different locations in China and the corresponding calcined coke (CPC). The significant influence of GPC properties on the CPC quality was revealed. The content of ash and metal impurities such as Si, V, and Ni etc. increases during calcination, while the sulfur content is reduced. This shows that the sulfur in GPC from the different sources has a quite different reactivity due to the complex nature of sulfur and only a part of the sulfur reacts during calcination. The data revealed inhibition of CPC CO2 activity by sulfur. Sodium and calcium enhance the coke CO2 reactivity, while impurities such as vanadium and nickel promote air reactivity.

Zhao Jingli, Zhao Qingcai, Zhao Qingbo, Yu Lei, Yu Pusheng

Quality of Calcined Petroleum Coke and Its Influence on Aluminium Smelting

This paper reports a study on the structure and porosity of calcined petroleum coke (CPC), the impact on mechanical properties of the corresponding baked anodes; and their behaviour in electrolytic reduction cells, especially the susceptibility towards thermal shock. This work was supported by characterization techniques used by CVG Venalum and PDVSA (Venezuela), such as mercury porosimetry, physisorption, and image analysis by optical microscopy (OM). The results indicated that good CPC quality is reflected by good mechanical anode properties as long as the anode manufacturing process is stable. The anode properties are related to the OTI (optical texture index). It is therefore possible to predict the anode behaviour from the CPC structure and porosity, take appropriate action, and decrease the net carbon consumption (NCC).

José Subero

Paste Plant Operations

A Green Anode Plant Performance Analysis Tool Fully Embedded in the Plant Control System

AMELIOS is an advanced software used to analyze the performance of green anode plants during operation. It helps the plant operators to perform root cause analysis of production breakdowns and guide the process engineers to optimize the anode quality.Because such a tool had also the potential to be used during the commissioning of new green anode plants, the original version was enhanced to fulfill the needs of start-up engineers during the production ramp up and plant fine tuning.It now provides data extraction features that aggregate system recorded parameters with conditional events and has been fully embedded into the green anode plant control system based on state-of-the-art control and information technologies used by most smelters.This paper gives the details of the implementation and beneficial use of AMELIOS during the recent start-up of a new green anode plant in the Gulf.

Xavier Genin, Pasquale Calò

Measures to Prevent Baked Anode Density Drop When Using High Porosity Cokes

In the last years, coke quality has been deteriorating throughout the world. One of the most affected properties is the coke porosity, commonly measured by the Vibrated Bulk Density (VBD). It is well known that the drop in VBD has a direct impact in the Baked Anode properties, especially Baked Apparent Density (BAD). This paper describes some measures taken at Alumar Smelter that enabled the BAD to be kept constant when using low VBD cokes.A complete analysis of the system was carried out and several aspects were considered as potential for improving density. The most significant being the changes made in the fines fraction and optimization of mixing and forming. Whenever applicable, anode properties were compared before and after the changes, in order to estimate each action impact.

Vinicius Piffer, Chin Woo, Fabiana Nicéas, Rafael Bacelar, Jeronimo Araujo, Leonardo Paulino

New Green Anode Plant at EMAL Start-Up & Operation in the First Two Years

EMAL — Emirates Aluminium PJSC, a strategic joint venture between aluminium producer Dubai Aluminium Company Limited, Dubai, UAE and Mubadala Development Company PJSC, Abu Dhabi, UAE, awarded the contract for the supply of a green anode plant and butt crushing facility for the 750,000 tpy EMAL — Emirates Aluminium Smelter project located in the Khalifa Port & Industrial Zone at Al Taweelah, halfway between Abu Dhabi and Dubai, to Outotec GmbH, of Cologne, Germany, in July 2007.Outotec’s scope of delivery covered the engineering, supply and installation on EPC basis of the new green anode plant with two anode production lines, each rated at 50 t/h capacity, along with a crushing plant for recycled carbon materials.It is the first time, that a 100 tph capacity green anode plant was built in one step, utilising continuous mixing and vibro-compacting technologies.Innovative technologies, such as RTO (regenerative thermal oxidisation) for pitch fume treatment, vertical mill for fines production and green reject paste cooling and recycling have been employed.This paper describes the EMAL Green Anode Plant, its preoperational testing, start-up, early operation and the production results in the first year.

Raja Javed Akhtar, Rudolf Gemein, Manfred Beilstein

Improving Anode Baked Density and Air Permeability through Process Optimization and Coke Blending

Dubai Aluminium (DUBAL) has continuously increased aluminium production through improved cell technology and optimizing cell performance at higher amperage. High baked anode density and low air permeability are two key anode characteristics that impact anode performance in the reduction cell. Increasing baked anode density, for instance, will allow a plant to either increase anode shift life or increase potline amperage, without changing anode shift life.To assist DUBAL in its strategic journey of increasing amperage, the DUBAL Carbon Plant management team defined and implemented a 3-year strategic roadmap to improve baked anode density and anode air permeability through process optimization and raw material blending. In this paper, we present the steps taken and the results achieved through implementing this roadmap.

Bienvenu Ndjom, Muhammad Shafik Malik, Amer Al Marzouqi, Tapan Kumar Sahu, Saleh Ahmed Rabba

Development of an Analytical Dynamic Model of a Vibro-Compactor Used in Carbon Anode Production

The carbon anode quality has a significant impact on the production of primary aluminum. Their performance can be evaluated by their various mechanical, electrical, physical, and chemical, properties such as density, electric resistivity, CO2 and air reactivities. The focus of this work is to study the various parameters of the vibro-compaction, which is one of the critical steps in the process of anode manufacturing. In this work, a dynamic model of a vibro-compactor is developed. The vibro-compactor is modeled as a rigid mass suspended on springs and dampers and subjected to harmonic external excitation. This model is used to identify the optimal conditions of the vibro-compacting process. These conditions are obtained through a correlation between the analytical vibro-compaction parameters and data from an industrial vibro-compactor. The use of optimum parameters will help improve the anode performance and, consequently, lead to better productivity and reduction on environmental impact.

Fatma Rebaïne, Mohamed Bouazara, Daniel Marceau, Duygu Kocaefe, Brigitte Morais

Driving Cost Reduction and Carbon Plant Productivity Improvement through Theory of Constraints and Planned Maintenance Capability

Theory of Constraints (TOC) is a management approach that gives clear context for decision-making and can lead to lower cost and more efficient Smelter operations. TOC avoids local (sub) optimization and ensures that actions are aligned with “end-to-end” process performance. When a Smelter TOC operating strategy is cascaded down to the Carbon Plant, and then to the Paste Plant, it provides context for how to best approach Paste Plant operating and maintenance activities. In addition to defining the most appropriate strategy, TOC principles and tools can be applied to activities such as routine maintenance and larger non-routine maintenance projects. For example, Critical Chain Project Management (CCPM) is a TOC technique that increases the speed and quality of these activities and can increase asset reliability and available run time, giving lower cost production runs and greater predictability. This paper describes the cascading of TOC thinking and strategies down through a Smelter, leading to an example of how CCPM can be applied to a Carbon Plant maintenance project.

Keith A. Sinclair, Barry A. Sadler

Optimum Vibration Time for Green Anode Production

Anode forming is one of the most important processes in pre-baked anode production, and most modern plants now use vibro-compactors to produce their green anodes. With a vibro-compactor both vibrating time and vibrating frequency can affect anode quality. Sunstone, the largest anode exporter in China, produces many different sizes of anodes, and therefore has to optimize forming parameters for each anode size produced. In this paper, results are given regarding a technique to optimize vibrating time for green anodes. This method can serve as a guide for any anode plant to determine the proper vibrating time for their anodes and therefore to improve their anode quality.

Shoulei Gao, Chongai Bao, Shoujun Zhang, Huanxue Wang, Joe Woo, Euel Cutshall

Comparison of Mixing Process Methods in Prebaked Anode Production

The continuous, batch, and semi-continuous mixing processes are mainly used for prebaked anode production in China. In recent years, the semi-continuous mixing process is very popular in China. There are three kinds of mixing processes, which are different in construction, equipment configuration, yield, product quality and also varying investment, operation and maintenance cost. Considerations for selecting a mixing process include environment, automation level, staff ability requirement, and adaptability with different raw materials. For a new green anode plant project, the clients always focus on the investment, profit, product quality, operational efficiency, energy consumption and environmental standard, and then choose the proper mixing process method. The three kinds of mixing processes have different advantages according to the project scale, investment, automation level and product quality, and they will all be presented in this paper.

Sun Yi, Guan Huai, Zhou Shanhong, Liu Chaodong, Xu Haifei

Bake Furnace Design and Operation

Hydro Aluminium’s Historical Evolution of Closed Type Anode Baking Furnace Technology

The paper summarizes the historical evolution of the closed anode baking furnace technology from the Riedhammer design to the Hydro Aluminium concept in the Norwegian carbon plants; Àrdal and Sunndal over the last 50 years.The increasing demand for higher production and larger anodes during the last 30 years has required Hydro Aluminium (HAL) to design a proprietary high capacity HAL baking furnace concept. Some major aspects and challenges connected to the rebuilding of the furnaces are described, including maximum utilisation of the existing factory space, allowing a low CAPEX per annual production capacity.Development of new repair and maintenance methods for critical refractory parts were essential in order to maintain a high anode quality and to extend the furnace service life.Main improvements related to the process control, process safety and performance data of the current technological status are presented.

Michal Tkac, Anders Ruud, Inge Holden, Hogne Linga

Use of Mathematical Modelling to Study the Behavior of a Horizontal Anode Baking Furnace

Large numbers of carbon anodes are used in aluminum industry. The manufacture of carbon anodes involves the preparation of a paste (a mixture of coke, pitch, and recycled material), the production of green anodes via mixing and compaction of this paste, followed by cooling and baking of the green anodes. Anode baking is carried out in large furnaces. Any modification to design or operation would require a careful study of its impact on anode quality. In recent years, mathematical models have been used effectively to complement the experimental work in order to improve furnace operation and design. A design model and a process model are being developed to study the behavior of a horizontal anode baking furnace and to determine the necessary improvements. In this article, these models and their use for the study of a furnace will be described, and the results of the numerical simulations will be presented.

Yasar Kocaefe, Noura Oumarou, Mounir Baiteche, Duygu Kocaefe, Brigitte Morais, Marc Gagnon

Study on Anode Baking Parameres in Open-Top and Closed-Type Ring Furnaces

Anode quality has strong impacts on the net carbon consumption in electrolysis cell and subsequently on aluminium production costs. Moreover, inasmuch as baking process is the most expensive step in the anode production and in the other side, anode properties influenced by baking process, therefore furnace selection (open-top or closed-type) and baking process control are always prime priorities that have to be deliberately taken into accounts by smelters. Furthermore, the most important baking parameters are the anode heat-up rate and the baking level, in that the present study deals with the main factors such as influence of firing section on temperature gradient as well as the effect of heat-up duration and anode size on baking level.

Borzu Baharvand, Mohesn Ameri Siahouei, Mohammad Nabi Batoei, Saeb Sadeghi

Energy Efficiency Improvement in Anode Baking Furnaces

Energy Efficiency is currently the biggest challenge in the Aluminum Industry. One of the high energy consumption facilities in a smelter is the Anode Baking Furnace (ABF). Due to unavailability of natural gas in the region, Alumar ABF uses Diesel oil, which increases significantly the energy costs. This paper describes how a different technical approach led to improved energy efficiency and reduced costs. Changes in process parameters, maintenance strategy and operational training were the main enablers.Technology Team worked to improve the draft control in the preheating zone, enabling the Baking Temperature Curve optimization, without compromising anode quality. The new curve allowed the soaking time and the number of fire frames to be reduced, reducing significantly the energy consumption.

Cassio Linhares, Fabiana Niceas, Rafael Bacelar, Helcio Campelo, Marcos A. Silva, Jeronimo Araujo, Raimundo Reis

Anode Baking Process Improvement at ALRO

Along with the partial refractory refurbishment of their three anode baking furnaces, ALRO wanted to reduce their consumption of natural gas and achieve complete combustion of the volatile compounds. Fives Solios proposed its process control expertise and up-to-date technology to upgrade the existing Firing Control System. Advanced software along with CO analysers and high velocity gas injectors were implemented for better combustion control. Port Sealing Ramp and low pressure drop dampers were provided to improve the operating conditions of the furnaces. Additionally, baking profile adjustments, based on CO continuous measurement and balance between the draft and the thermal demand in the heating zones, were jointly conducted by ALRO and Fives Solios resulting in a sustainable reduction of the energy consumption and improved combustion of the volatile compounds while maintaining a consistent anode quality.

Pierre Mahieu, Nicolas Fiot, Arnaud Trillat, Ovidiu Balu, Cristian Stanescu

Operational and Environmental Benefits of the New Baking Furnace at Boyne Smelters by Use of an Advanced Firing Technology

In February 2012, a new baking furnace was commissioned at Boyne Smelters Limited (BSL) on Boyne Island, Australia. This new furnace replaced the production of two existing closed type furnaces and set new benchmarks in production performance.The advanced firing technology is based on latest safety requirements of the Australian Gas Authority (AGA) gas standards. In parallel, new self-recovery network structures behind the wireless network have been developed to maximize the redundancy and availability of the system. Finally, intelligent control modules have been implemented for on-line optimization of the baking process.This paper will outline the special technologies used and demonstrate the results that can be achieved to allow for smarter and cleaner baking cycles in combination with relevant safety standards and system availability.

Andreas Himmelreich, Detlef Maiwald, Domenico Di Lisa, Glenn Cordon, Sathya Moodley

Laser Mapping of Carbon Bake Furnaces

The flue walls in carbon bake furnaces (CBFs) deform over time under cyclic heating and cooling, leading to difficulties in loading/unloading anodes, and inconsistent anode baking. It is useful to regularly measure the deformations to establish the rate of deterioration and assist in the prediction of flue wall life. Boyne Smelters Limited commissioned a new CBF in 2012. During commissioning, CSIRO utilised its 3D laser scanning technology to map the CBF. A sensor payload consisting of a scanning laser rangefinder sensor connected to a logging and processing PC was suspended from a crane and moved over open pits in a pattern to obtain sufficient coverage of internal pit surfaces, as well as some of the CBF floor and walls. The resulting data is useful for comparing the finished CBF to blueprint plans, and serves as a baseline for future scan comparisons to determine deformations of the flue walls and pit floor.

Ashley Tews, Mike Bosse, Robert Zlot, Paul Flick, Meaghan Noonan

Anode Quality and Performance

Pilot Scale Anodes for Raw Material Evaluation and Process Improvement

Primary and secondary raw materials and carbon plant practices are of critical importance for anode quality. Frequent testing of cokes, pitch and production factors in a full scale plant would be feasible, but might be high risk and expensive. It could also be time consuming as the testing would be subject to the demand of production for priority. For over twenty years, Hydro has run systematic pilot scale tests in Årdal, Norway, and since 2005 the facility has been upgraded with intensive mixers and vacuum vibroforming. Today the pilot production simulates full scale operation, and pilot scale results are successfully implemented in carbon plants. The paper discusses the factors that ensure quality practices for pitch level evaluation, aggregate screening curves and baking level control. Examples are from tests of new material sources, a study of secondary raw materials quality related to carboxy reactivity, and studies of production parameters.

Lorentz Petter Lossius, Juraj Chmelar, Inge Holden, Hogne Linga, Michal Tkac

Relationships between Coke Properties and Anode Properties — Round Robin 19

This paper discusses the preparation and production of bench scale and pilot scale anodes with five different calcined coke samples prepared for a world-wide calcined coke round robin (RR). A key objective of the RR and anode testing was to look for relationships between calcined coke properties and anode properties, particularly coke bulk density/apparent density results and anode densities. The calcined coke RR was the 19th organized by Rain CII Carbon, but this time it was a collaborative effort with Hydro Aluminium and R&D Carbon. Calcined coke results for RR19 are discussed in greater detail in another paper in these proceedings. Bench scale anodes with the five cokes were prepared at R&D Carbon and used to select optimum pitch levels for production of pilot scale anodes. This is the first time a RR with such a broad scope has been coordinated and published and it has provided some useful data for the industry.

Lorentz Petter Lossius, Marvin Lubin, Les Edwards, Julien Wyss

Application of the Artificial Neural Network (ANN) in Predicting Anode Properties

Carbon anodes are a major part of the cost of primary aluminum production. The focus of the industry is to minimize the consumption of anodes by improving their quality. Therefore, the determination of the impact of quality of raw materials as well as process parameters on baked anode properties is important. The plants have a large data base which, upon appropriate analysis, could help maintain or improve the anode quality. However, it is complex and difficult to analyze these data using conventional methods. The artificial neural network (ANN) is a mathematical tool that can handle such complex data. In this work, Matlab software was used to develop a number of ANN models. Using published data, linear multi-variable analysis and ANN were applied to assess the advantages of custom multilayered feed-forward ANN. Results are presented which show a number of industrial applications.

Dipankar Bhattacharyay, Duygu Kocaefe, Yasar Kocaefe, Brigitte Morais, Marc Gagnon

A Model for Predicting the Electrical Resistivity of Baked Anodes

Carbon anodes are one of the key components of primary aluminum production. One of the desired properties of the anodes is low electrical resistivity. A proper understanding of the effect of different parameters on electrical resistivity can help produce better quality anodes. A model has been developed to predict the anode electrical resistivity. First, using the Kopelman model for the thermal conductivity of a composite material, the specific electrical resistivity was modeled for the solid part (coke/cokified pitch) assuming coke as the dispersed phase in the cokified pitch matrix. Then, the effects of the anode porosity, distribution of particles, and coke properties are incorporated into the model using an approach based on the work of Shimizu. A factor which is a function of particle size and other properties is introduced. This factor was estimated using the artificial neural network. Published data were used to validate the model.

Dipankar Bhattacharyay, Duygu Kocaefe, Yasar Kocaefe, Brigitte Morais, Marc Gagnon

The Role of Electrode Quality in Metal Purity

Anode quality excursions are well known as factors that can have substantial impact upon metal purity and the ability to produce specific metal products. But, there is more to managing anode quality, as delivered to the pot rooms, than avoiding a major excursion. In this paper the author reviews the key factors from the paste plant through the rodding shop that affect the amount of impurities that are delivered to the metal. Conclusions include a summary of sub-process and design activities that can be managed to minimize the impact of impurities to primary metal production.

Stephen J. Lindsay

Electrochemical Characterization of Carbon Anode Performance

Coke used in the manufacturing of anodes is commonly a mix of cokes from several suppliers to meet the customer’s specifications. This variation in coke composition from suppliers may lead to considerable deviation in anode performance. The present work, still in its early phase, aims to develop a method with which to characterize electrochemical performance of anodes and relate this to the anode material properties. To verify the experimental approach, laboratory anodes were produced from various single cokes with different impurity levels. Voltammetry was performed and polarization curves were recorded to investigate current-voltage characteristics of these anodes. Gas analysis was also executed in order to study the CO2:CO ratio and calculate Pearson-Waddington current efficiencies. The reaction overpotential from polarization curves was found to decrease with increasing total metallic and sulphur impurities, indicating that blended cokes may behave differently on a microscopic scale and between individual anodes in a cell if the anodes come from different production batches. Contrary to the polarization curves, metallic and sulphur impurities were found to not significantly change the CO2:CO ratio or Pearson Waddington current efficiency. Experiments of this type aim to develop fundamental understanding of how single coke properties affect electrochemical performance.

Rebecca Jayne Thorne, Camilla Sommerseth, Espen Sandnes, Ole Kjos, Thor Anders Aarhaug, Lorentz Petter Lossius, Hogne Linga, Arne Petter Ratvik

High Capacity Thermobalance Anode Reactivity Testing

As raw material quality changes and Potline Customer requirements become more onerous, anode reactivity has become an increasingly important quality measure. Conventional anode reactivity testing procedures require dedicated and expensive instruments that have relatively low sample throughputs. Smelters are often unable to test the reactivity of all the core samples they take due to reactivity test capacity imitations. This reduces the ability of plants to identify any changes in anode reactivity that may require countermeasures. A commercially available, multiple sample ThermoGravimetric Analyzer (TGA) has been successfully adapted to measure anode air reactivity. This paper describes the modifications made to the instrument and the standardization of a procedure for anode air reactivity testing. Results obtained from plant anode samples baked under different conditions are also discussed.

Nick Janssen, James Baker, Frank Cannova, Barry Sadler

Diagnosing Changes in Baked Anode Properties using a Multivariate Data-driven Approach

The baked anode quality control scheme used in most carbon plants consists of lab testing of anode core samples and monitoring weekly averaged properties. Both the low anode sampling rate and the averaging hide a significant amount of variability in the anode populations. Additional consideration depending on the sampling procedure needs to be taken into account while analyzing the core sample properties. In previous work, a multivariate latent variable PLS model was developed for predicting individual anode properties at the end of the baking cycle. All the data available at the Alcoa Deschambault smelter were used to build the model. This work investigates how to use this model to learn from data and, in particular, to help diagnose the root cause of variations in the electrical resistivity and LC. Changes in raw material suppliers and non-uniform temperature distribution within the baking furnace were found to contribute to the drifts.

Julien Lauzon-Gauthier, Carl Duchesne, Jayson Tessier

Cathode Materials and Wear

Evolution of the Thermo-Mechanical Properties of Ramming Paste from Ambient to Operating Temperature in a Hall-Heroult Cell

The ramming paste behavior is a key parameter in the cell performance used for the aluminum electrolysis. This anthracite and coal tar pitch mixture bakes during the cell start-up and chemical transformations in the ramming paste are observed. The mechanical properties of the paste are related to these transformations and change with time and temperature during the cell start-up. This paper presents the methodology used to determine the evolution of the mechanical properties of ramming paste, using experimental conditions representative of a cell startup. Experimental results for temperatures from ambient to 960°C are presented and the effects of the test conditions are discussed.

Stephane Tremblay, Lyne St-Georges, Laszlo Kiss, Lyès Hacini, Bénédicte Allard, Daniel Marceau

New Compaction Method for the Production of Large Ramming Paste Samples for 3D Mechanical Characterization

To assess the mechanical behavior of ramming paste, representative laboratory samples must be produced for experimental characterization. Experimental data are necessary to feed three-dimensional creep model where radial strain measurements are required. It is thus imperative to perform measurements on a sample large enough to get significant radial strain amplitude. However, the ISO standard fabrication method is restricted to small-size samples. In the present paper, a different compaction process, adapted from the Proctor method, is proposed in order to get larger cylindrical samples of 100 mm diameter and 200 mm height. The ramming paste samples are produced in multilayer by dynamic compaction, using a falling weight in a circular pattern over the tamped surface. The baked apparent density obtained by X-Ray computed tomography, or CT scan, and the baked mechanical properties such as compressive strength, have been characterized as a function of the number of layers and the number of impacts.

Pierre-Olivier St-Arnaud, Donald Picard, Maxime Noël, Houshang Alamdari, Donald Ziegler, Mario Fafard

Technology for Manufacturing Cathodes for Aluminium Reduction in China

More than 20 manufacturers producing cathode blocks used in aluminum smelters exist in China. The total annual production capacity for the cathodes reaches up to 300 kt, most of which are semi-graphitic cathode blocks and some graphitized cathode blocks as well.The types and quality of the Chinese cathode products and the manufacturing technology for both semi-graphitic and graphitized cathode blocks in China are reviewed in this paper.An energy saving manufacturing technology developed in China for the graphitized cathode block production is also revealed.

Yang Hongjie, Liu Fengqin, Cai Suwei, Yang Xiaopei

The Effect of Cryolite on the Formation of Aluminum Carbide at the Carbon Aluminum Interface

The effect of cryolite on the formation of aluminum carbide was studied by an aluminum-carbon diffusion couple experiment. The interface between the aluminum and carbon was coated by a thin layer of cryolite, and the diffusion couple experiments were performed at 1030 °C in stagnant argon atmosphere. The micro structure of the relatively thick and porous aluminum carbide formed at the solid-liquid interface was investigated by optical and scanning electron microscopy. It was shown that the presence of cryolite has a pronounced effect on the formation of carbide, although fluorides could not be found at the interface after the experiment. The porous and needle like morphology of the carbide layer suggests the mass transport during growth is through the gas or liquid phase. The stability of cryolite and possible gas species involved in the growth process have been analyzed thermodynamically to identify possible gaseous species present at both global equilibrium and metastable conditions.

B. Novak, K. Tschöpe, A. P. Ratvik, T. Grande

Critical Reflections on Laboratory Wear Tests for Ranking Commercial Cathode Materials in Aluminium Cells

The lifetime of high amperage cells with graphitized carbon cathodes is mainly determined by cathode wear. Several attempts have been made to investigate cathode wear in laboratory test cells, but the underlying mechanism is still a matter of discussion. This is reflected in the fact that test methods enabling the ranking of different commercial cathode materials are still to be developed. In the present paper we report on a laboratory test cell where the cathode is directly exposed to the electrolyte, which accelerates the wear rate by an order of magnitude relative to the wear rate in industrial cells. In this study three different commercial carbon cathode materials have been tested; graphitized carbon, high density graphitized carbon, and anthracitic carbon. No significant differences in wear rate could be detected under the test conditions used. Possible reasons for this unexpected result are discussed, and suggestions for modifications of the test cell are provided.

Kati Tschöpe, Anne Støre, Egil Skybakmoen, Asbjørn Solheim, Tor Grande, Arne Petter Ratvik

Model for Excessive Cathode Wear By a “Carbon Pump” at the Cell Bottom

The lifetime of aluminium electrolysis cells is limited by cathode wear, which takes place mainly at the periphery of the cathode. In the present paper it is suggested that excessive wear is due to electrochemical formation and dissociation of aluminium carbide in bath-filled pores within a carbide layer present at the bottom of the cell. The relationship between current and voltage in the pore was established using the Stefan-Maxwell equations on a structure model of the bath, in combination with the calculated reversible voltage and the ohmic voltage drop. A general “wear equation” was derived, describing the relationship between voltage drop along the pore, the thickness and porosity of the carbide layer, and the cryolite ratio. The voltage drop across aluminium carbide layers with different properties is discussed. The model shows that the wear rate will be nearly proportional with the local current density, which is in agreement with practical observations.

Asbjørn Solheim, Kati Tschöpe

Characterization of Porous Structure and its Correlation to Sodium Expansion of Graphite Cathode Materials Using Image Analysis

Graphite cathode materials used in aluminum reduction cells are of porous structure. During aluminum electrolysis, the melt and sodium will penetrate into the cathode block leading to its expansion and deterioration. This work is aimed to give a better understanding of the relationship between the pore structure and the sodium expansion and to improve control of the cathode quality through quantitative image analysis.Experiments with graphite cathode materials were carried out using a modified Rapoport apparatus. Image analysis results indicate that the porosity, pore diameter and pore connectivity after electrolysis can be related to the sodium expansion, while the aspect ratio and the fractal dimension seem to be unchanged. X-ray Diffraction (XRD) measurement for interlayer spacing (d 002) was also found to correlate to the degree of such expansion. Quantitative information on the correlation between the sodium expansion and porous structures can serve both the cathode producer and the smelter for product selection and performance evaluation of cathode blocks.

Xiang Li, Jilai Xue, Tong Chen

Studies on the Resistance to Alkali Metal Penetration of Binders for TiB2-C Composite Cathode Materials

Thermal gravimetric analysis (TGA) and X-ray diffraction (XRD) were used to analyze the pyrolysis of pitch, furan, phenolic aldehyde and epoxy binders. Their micro-structures after carbonization were also studied. The relationship between alkali metal penetration resistance of binders, their pyrolysis activation energy (Ea) and micro-structure after carbonization was investigated. The results show that for binders containing turbostratic graphite or a transitional structure between turbostratic graphite and graphite, the higher the degree of graphitization the better the penetration resistance of the binder. When the binder micro-structure is in a transitional stage from amorphous or other non-graphitic structures to turbostratic graphite, the penetration resistance of the binders deteriorates. For these microstructures, the higher the Ea, the better the penetration resistance. The Ea of pitch, furan, phenolic aldehyde and epoxy are 47.20 kJ/mol, 93.11 kJ/mol, 178.11 kJ/mol and 780.32 kJ/mol respectively.

Fang Zhao, Zhang Kai, Lai Yan-qing, Li Lin-bo, Zhu Jun

Inert Anodes, Cell Materials and Alternative Processes

Mechanically alloyed Cu-Ni-Fe-Y material as inert anode for Al production

In our previous works, we identified the mechanically alloyed Cu65Ni20Fe15 compound as a promising inert anode material for Al production in low temperature (700°C) KF-AIF3 electrolyte. However, further work was required for improving its corrosion resistance. For that purpose, (Cu65 Ni2OFe15)100-xYx materials were prepared by ball milling, consolidated to form dense electrodes and then evaluated as inert anodes for aluminum production. Their morphological, structural and chemical characteristics were studied at different stages of their preparation and after 20 h of electrolysis. The key role played by the element Y on the electrode’s corrosion resistance is highlighted.

V. Ouvarov-Bancalero, D. Guay, L. Roué

Cold Spray deposition of mechanically alloyed Cu-Ni-Fe material for application as inert anodes for aluminum production

Cold spray deposition was evaluated for the production of inert anodes for Al electrolysis from mechanically alloyed Cu-Ni-Fe powders. Cu65Ni20Fe15 (in wt. %) alloy was first prepared from elemental Cu, Ni, Fe powders using an attritor. After 40 h of milling, a nanocrystalline and monophasic Cu(Ni,Fe) solid solution was formed. It was shown that the particle size of the milled powder can be controlled with the addition of stearic acid to the initial powder mixture. In a second step, the cold spray parameters (pressure and temperature of the carrier N2 gas) were optimized in order to maximize the impact velocity of the Cu65Ni20Fe15 particles on the substrate. Then, thick (1100 μm), dense (porosity of 1–2 %) and adherent (adhesion strength of 15 MPa) coatings of Cu65Ni20Fe15 on C63000 substrate (nickel aluminium bronze alloy) were produced. No structural change of the Cu65Ni20Fe15 alloy was observed during cold spray processing.

G. Goupil, S. Helle, E. Irissou, D. Poirier, J. G. Legoux, D. Guay, L. Roué

Initial 1000A Aluminum Electrolysis Testing in Potassium Cryolite-Based Electrolyte

Aluminum electrolysis testing in a 1000A cell at 750°C is described. The cell was fitted with 3 vertically oriented aluminum-bronze anodes and 3 wetted cathodes, maintaining an anode-to-cathode distance of 2.2 cm. The electrodes were immersed in a KF-AlF3 electrolyte with a cryolite ratio of 1.3. Alumina was automatically fed to the cell to maintain a dissolved alumina concentration of 5 wt%, confirmed by analysis. Boron nitride was used as the cell liner material. During electrolysis, the voltage was stable near 4.0 volts at a current density of 0.5 A/cm2. Oxygen gas evolved from the cell was measured with an oxygen sensor. During the 24-hour initial electrolysis test, the anodes were protected by a dense oxide layer.

John Hryn, Olga Tkacheva, Jeff Spangenberger

Electrochemical Behavior of Cermet Anodes in Na3AlF6-K3AlF6-Based Low-Melting Electrolytes for Aluminium Electrolysis

The anodic behavior of 5Cu/10NiO-90NiFe2O4 cermet in Na3AlF6-K3AlF6-based low-melting electrolytes was investigated for use as inert anodes for aluminium electrolysis. The electrochemical techniques, cyclic voltammetry and Tafel anodic polarization analysis, were performed to determine the reactions. Two anodic processes were observed at the cermet anodes: dissolution of Cu and oxygen evolution. The activity of anodic oxide films (CuO) on cermet anodes was calculated as 0.15 using values of the reversible potential obtained from the Tafel analysis, which suggested a lack of surface oxide stabilization. The exchange current density obtained for cermet anodes was 0.19 A cm-2. The porous surface caused by the depletion of Cu during anodic polarization could be the reason for blocking the oxygen evolution on cermet anodes.

Guihua Wang, Xiaofei Sun

Production of Aluminum Sulfide through Carbosulfidation Utilising H2S

Indirect carbothermal reduction of alumina for the production of aluminum utilizes different reducing agents to convert alumina into intermediate aluminum compounds. In the present study, the carbosulfidation route for aluminum production utilizing H2S(g) as the reductant and sulfur source has been investigated, in particular the formation of Al2S3 in the first step of the process. The results of the thermodynamic analysis predicted that conversion of Al2O3(s) to Al2S3(l) significantly increases above 1400°C at 1 atmosphere pressure. Experimental investigations were carried out at temperatures of 1100 to 1500°C using dilute H2S(g) gas in argon. The reaction products were analyzed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), inductively-coupled plasma absorption emission spectroscopy (ICP-AES) and chemical filtration. The X-ray diffraction results confirmed the presence of Al2S3(s). Percentage of conversion from Al2O3 to Al2S3 was found to be over 80% at 1500°C.

Nazmul Huda, M. A. Rhamdhani, G. A. Brooks, B. J. Monaghan, L. Prentice

Microstructural Evolution of Cast Iron Used for Cathode Rodding in Aluminium Electrolysis Cell

The microstructure of cast iron sealed to the steel collector bar through casting process was investigated using optical and scanning electron microscopes equipped with an energy-dispersive X-ray (EDX) analyzer in as cast condition and after 3 and 9 hours electrolysis tests in laboratory scale. Thermodynamic study was also carried out using Factsage software and the results were compared with DSC (Differential Scanning Calorimetry) test to reveal the solidification behavior of the cast iron. The micro structural observation indicated a significant change particularly at the interface of cast iron-steel after the electrolysis tests due to the time dependent diffusion of the elements, mainly carbon and phosphor, from cast iron into the steel. The diffusion zone inside the steel collector bar with pearlitic micro structure can be visually detected and separated from the regular (non diffused) ferritic steel by etching the metallographic samples using Nital reagent.

Alireza Hekmat-Ardakan, Gervais Soucy, Loig Rivoaland

Preparing Al-Sc-Zr Alloys in Aluminum Electrolysis Process

Al-RE Alloys have attracted much attention in recent years due to their great potential in many advanced applications. In this work, Al-Sc-Zr alloys were prepared in a laboratory electrolysis cell. Effects of Sc2O3 and ZrO2 additions and the electrolysis time on Sc-Zr contents and their ratio in the alloys were investigated in Na3AlF6 based melt at 960 °C. SEM and ICP-AES show that Sc and Zr contents in the alloy produced were 0.25–0.32 wt% and 0.26–1.24 wt%. SEM-EDS analysis reveals that Al3(Sc,Zr) particles form in Al alloy prepared by electrolysis. Cyclic voltammetry results demonstrate that Zr4+ proceeds a two-step process electrolysis at -0.7V and -1.05V, respectively, while no single peak appears for Sc deposition.

Yi Qian, Jilai Xue, Qiaochu Liu, Jun Zhu

CBF Environmental & Anode Electrical Connections

Fume Treatment Systems Based on RTO Technology for Carbon Baking Furnaces

Increasing environmental demands, especially for emissions of the carcinogenic PAH (Polycyclic Aromatic Hydrocarbons) require new technologies for the treatment of fumes from carbon anode production plants. Thermal systems have been supplied to several paste plants as well as baking furnaces for the production of anodes, electrodes and cathodes. Due to the specific pollutants such as HF and the behaviour of the sticky condensates, the systems have to be designed properly to ensure a high availability. Pre-filters and preheating avoid clogging of the heat exchanger material of regenerative thermal oxidizers (RTO’s). In addition, stringent health and safety issues as well as a specific fire protection system have to be considered during the design, construction and operation of a new plant. The paper shows the required process steps and the technical solution on the basis of plants for several baking furnaces in Poland and France.

Matthias Hagen, Bernd Schricker

AHEX- A New, Combined Waste Heat Recovery and Emission Control System for Anode Bake Furnaces

Alstom has developed a new Fume Treatment Center (FTC) for improved emission control of Anode Bake Furnaces. The new compact FTC eliminates the conditioning tower with its use of compressed air and water with a patented heat exchanger system (AHEX) specially developed for the anode baking process. The adsorbent (alumina) is injected upstream the AHEX. This eliminates additional reactor stages downstream, and keeps the heat exchanger tubes free from fouling.The AHEX started up in November 2011 at the anode bake plant at Alcoa Mosjøen, Norway and has demonstrated stable operation with gas temperatures cooled down to less than 100°C. Emission measurements document 10–20% less PAH-16 and significantly less HF despite a higher gas to alumina flow ratio in the AHEX system compared to the conventional FTC.In addition, the AHEX system enables up to 5000 kW of thermal energy to be recovered at Alcoa Mosjøen.

A. Sørhuus, S. Ose, G. Wedde

Successful Start-Up of the Fume Treatment Centre at Boyne Smelter Carbon Bake Furnace #4

At Boyne Smelters Limited (BSL) in Queensland Australia, a new carbon bake furnace was built as part of a AUD $337 million development program to replace two existing carbon bake furnaces. The carbon plant was to have a capacity of 200,000 tpy of anodes. It consisted of a Rio Tinto Alcan AP technology furnace, four (4) state of the art fire groups using natural gas, two furnace tending cranes, an anode handling system and a Fume Treatment Centre (FTC). The plant was commissioned in January 2012 and reached full capacity by April 2012. The FTC design incorporated several new features such as newly designed flow distribution system in the baghouse, microfiber filterbags which utilize lime pre-coat for improved filtration and a direct diesel driven emergency draft fan. Similar with the majority of startups there were some challenges to overcome, but the carbon bake furnace and FTC are both fully operational and have achieved operational and process performance guarantees.

Jonathan Higley, Glenn Cordon, Peter Klut, Rick Oliana, Erik Dupon, Travis Turco, Edo Engel

Thermo-electro-mechanical characterization of anode interfaces at operating conditions

A large amount of energy is lost at the interface between materials in electrodes, reducing process energy efficiency. Thus, the characterization of thermo-electro-mechanical behaviour of the interfaces is necessary to support the numerical modelling as an essential step in improving the design of the anode connection. Experiments have been performed on carbon-cast iron-steel samples taken from the anode assembly. The samples have been designed and prepared in such a way that they are representative of the industrial sealing process.Some links between roughness and electrical resistivity have already been established in other studies [1]. In the present investigation, roughness measurements using laser profilometry have been carried out on samples subjected to compressive stress up to 2 MPa. Results have shown that loading effect is negligible on the asperities deterioration between the carbon-cast iron interfaces at this pressure.The obtained values of thermal contact resistance (TCR) and electrical contact resistance (ECR) are in good agreement with the experimental data published in the literature, but still higher than those of the theoretical contact model. This study leads to the development of a new constitutive law for electrical and thermal contact resistance as a function of temperature and pressure.

Hugues Fortin, Marie-Hélène Martin, Nédeltcho Kandev, Guillaume Gauvin, Donald Ziegler, Mario Fafard

A Fully Coupled Thermal-Electrical-Mechanical Transient FEA Model for a 3D Anode Assembly

A fully coupled thermal-electrical-mechanical (TEM) transient model that simulates the rodding and cell operation phases of aluminum smelting in Hall-Héroult cells is presented and discussed. This 3D model of an anode assembly was developed using the commercial finite element analysis code Abaqus, and incorporates (i) temperature-dependent material properties as well as (ii) temperature- and pressure- dependent electrical contact conductance at the anode-thimble interface. The air gap between the anode and thimble is also taken into account through the predictions of (a) its formation during the rodding step, (b) its modification as the anode slides down under gravity on the flutes of the thimble during installation and (c) its partial closure as the components heat up and expand during cell operation. The predictions of the model are found to compare well with known plant measurements of temperatures and voltages for similar systems.

D. R. Gunasegaram, D. Molenaar

Experimental and Numerical Investigation of Voltage Drop in Anode Assemblies

Improving the Hall-Héroult process through reducing voltage drop in the anode assembly is one of the most challenging subjects for the primary aluminum production industry. In this paper, a fully coupled Thermo-Electro-Mechanical (TEM) model of a half carbon block submodel extracted from a full hexapod anode assembly is proposed in order to achieve a better understanding of its multi-physical behavior. This fully parametric Finite Element (FE) model was developed using APDL™ (ANSYS® Parametric Design Language) and was solved using a FESh++ TEM application. Special attention was paid to the good prediction of the contact conditions at the cast iron to carbon interface. First, the model was calibrated using experimental measurements realized by ARDC at Rio Tinto Alcan, and then used to investigate the phenomena taking place in the stub hole region with a focus on the contact at the cast iron to carbon interface.

Ebrahim Jeddi, Daniel Marceau, Laszlo I. Kiss, Lyne St-Georges, Denis Laroche, Lyès Hacini

Optimization of the Anode-Stub Contact: Effect of Casting Temperature, Contact Stress and Temperature and Surface Roughness

In electrolysis of aluminum, the contact between the anode and the anode stub is normally facilitated by cast iron. Important parameters are the effect on the anode stub contact resistance from: Casting temperature of the iron,Temperature of the stub-anode couplingUniaxial stress between carbon and cast ironSurface roughnessIn the current work, standard grey iron was cast at three temperatures, 1430, 1340 and 1250°C, maintaining actual rodding cooling rate, to simulate the tendency of white iron forming during casting. The specimens were subjected to contact resistance measurements with anode carbon at 1 A/cm2 current density, varying the uniaxial stress and temperature. Both stress and temperature increase reduced the contact resistance, while low casting temperature did not affect the resistance significantly. The influence from the surface roughness on the contact resistance was not significant.

Bjarte Oye, Anne Store, Elin Haugland, Jorund Hop

Experimental Investigation of Factors Affecting the Electrical Performance of the Stub to Carbon Connection

A facility has been built and commissioned to enable research into improving the electrical energy efficiency (and reducing associated greenhouse gas emissions) of very large metal-metal and metal-carbon electrical connections used by energy intensive metal-winning processes (aluminium, copper, zinc, ferro-alloys). The facility is able to test large-scale and full-scale industrial electrical connections up to 1000 kg, at up to 5000 A DC and 1200 °C in an inert atmosphere.This paper presents the first results of an experimental investigation using the facility to study the main influencing factors affecting the electrical contact resistance for the stub to carbon connection, which is one of the major electrical connection resistances found in aluminium smelting plants.The investigation clearly shows increasing electrical contact resistance for; (i) decreasing stub diameter, (ii) increasing gap under stub and (iii) stub eccentrically positioned in the stub hole.

D. Molenaar, T. Kilpatrick, A. Montalto


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