Baking Furnace Research Articles

Size Control of ZnO Tetrapod in Gas-phase Synthesis using Flow Restrictor

Abstract Monodispersed tetrapod-shaped ZnO (T-ZnO) particles with rods ranging from 1.3 to 10.5 µm are synthesized by gas-phase reaction of zinc vapor and oxygen gas using a flow restrictor in a single baking furnace. The size control of the T-ZnO particles is accomplished by changing the calcination time and the position of the flow restrictor.

The Technique of Recycling Alkaline Zincate Zinc Plating Waste Liquid in Laboratory

It introduces a kind of technique method that recycling alkaline zincate zinc plating waste liquid in laboratory, involving the fields in electroplating and comprehensive utilization of waste liquid. This method is introduced that with adopting materials such as HCl, NaOH, H2O2, activated carbon, dithiocarbamate diethyl ester, chloroform, ammonia and baking furnace, incinerator, pH test paper, for treatment of the waste liquid through some processes like neutralization, filtration, chemistry precipitation, extraction, distillation, burning, so that some recycled substances in it can be reused such as distilled water, zinc oxide, and as to those can not be recycled, carry on the harmlessization handle by incineration or deep bury.

Sensitivity of Carbon Anode Baking Model Outputs to Kinetic Parameters Describing Pitch Pyrolysis

Carbon anode blocks, used in aluminum electrolysis cells, are usually baked in furnaces for several days, during which they release volatiles due to pitch pyrolysis. Therefore, numerical modeling of anode baking furnaces has to include some representation of pitch pyrolysis via a set of kinetic parameters. These kinetic parameters can vary with raw materials and baking parameters and are tedious to determine experimentally. In this work, we studied how the main outputs of an anode baking model are affected by the variance of the kinetic parameters. Results show that certain model outputs are not considerably influenced by changes in the kinetic parameters (e.g., spatial variation of anode porosity, maximum heating value from volatiles), while others are significantly affected (e.g., time evolution of anode porosity, time of maximum heating value of volatiles, internal pressure of anode), in particular by activation energy variability.

Thermogravimetric Study on Devolatilization Kinetics of Chinalco Anodes during Baking

The production of aluminum requires the use of carbon anodes which are manufactured from coke, pitch, and recycled butts and anodes. Pitch acts as a binder. Green anodes are produced by mixing all these ingredients and then forming them in a compactor. The final step is the baking of green anodes, which determines the final anode properties. During baking, volatiles evolve from the pitch which carbonizes and binds the particulate matter. Anode quality greatly influences the performance of electrolytic cells and has an impact on carbon consumption, energy use, green house gas emissions, and cost.In this project, the effects of the baking conditions on some of the anode properties (air permeability, air and CO2 reactivities) were studied, and the devolatilization kinetics was determined for different cases. The results indicate that the lower heating rates and higher baking temperatures improve the above properties. In this article, the experimental work and the methodology for the determination of the kinetic expressions for devolatilization are described, and the results are presented. The position of volatile evolution in the baking furnace can be determined via these expressions, and this could be effectively used in controlling the volatile combustion to improve the furnace performance.

Intelligent Modeling and Optimization of Carbon Anode Baking Temperature

Coal anode baking temperature system is a MIMO control system which is nonlinear and has cross-coupling and time-delay. The thermal model and flue model before are usually created based on hydrodynamics and heat transfer theory which take long to do the calculation or have ill conditions sometimes. The PID control systems based on the two mechanism models do not yield satisfactory results. In order to control the baking temperature accurately, an intelligent control model based on GA-NN with the aim of improving control precision of baking temperature of carbon anode is established by gathering the real data from anode baking furnace used for initial predictive models. A new GA-NN predictive control system is thus realized for the control of anode baking temperature of which the simulation and real control results showed that the system is efficient and effective with better control precision and robust properties than tradition PID control systems.

Conservação de energia em fornos de cozimento de anodo

A tendência por unidades de produção mais sustentáveis vem obrigando a indústria de alumínio a adotar estratégias para reduzir o consumo de energia e minimizar a geração de resíduos. Procedimentos nesta direção têm sido implementados em fornos de cozimento de anodo, onde alguns aprimoramentos têm permitido a redução no consumo de energia. Entretanto, sabe-se que durante a etapa de queima do anodo, elevada quantidade de calor é ainda dissipada para o ambiente, aumentando os custos com energia. Desta forma, o presente trabalho tem por objetivo apresentar alternativas de redução do consumo de combustível do forno de cozimento de anodo considerando, para isto, o transporte de calor das câmaras de combustão desde as paredes refratárias até o bloco de carbono, passando pelo coque fluido. Os resultados aqui obtidos indicam que uma possível mudança da distribuição do tamanho de partículas do coque, bem como, a adição de uma manta isolante no topo do forno pode aperfeiçoar o desempenho do sistema quando o foco é sustentabilidade e otimização do processo.

Fracture and physical properties of carbon anodes for the aluminum reduction cell

An experimental study with total 504 specimens has been carried out to investigate the fracture and physical properties of the carbon anode materials. The specimens were sampled from anodes produced with machined stub holes. From normal-and Weibull analysis the fracture toughness and the tensile strength showed a clear temperature dependency and orthotropic behavior. It has been found that both the fracture toughness and tensile strength increases with the temperature and are larger for the specimens directed in the horizontal direction than in the vertical direction. The variation in the tensile strength within an anode decreased with the temperature but the variation in the fracture strain increased. The tensile strain appears to be only dependent on the temperature and insensitive to the routine anode properties of the anode material. A multivariate linear regression analyses of the fracture toughness and tensile strength has been conducted and a typical correlation of R 2 = 0.5 ( R is the Coefficient of Determination) to the measured routine anode properties was found. The thermal expansion coefficient is also larger in the vertical anode direction which makes the crack initiation more sensitive to temperatures. The orthotropic studies also showed that the air permeability has a tendency to be larger in the horizontal direction in the upper part of the anode which can induce unnecessary burning from the anode sides. The influence of the processing parameters in the paste plant and baking furnace has not been presented in this paper.

Development of technology for the production of microspherical aluminum oxide supporter for the paraffin dehydrogenation catalyst

For the purpose of improving the mechanical strength and to reduce the abrasive activity of microspherical chromoalumina catalyst for the paraffin dehydrogenation in fluidized bed, technology, using technical aluminum trihydrate as an initial raw material and including consecutive stages of Al(OH)3 dehydration and hydrothermal processing of its product into boehmite, has been developed for the production of highly durable boehmite supporter. As applied to the iso-butane dehydrogenation into iso-butylene, microspherical chromoalumina catalysts, which are synthesized with the use of boehmite supporter, exceed their known industrial analogous in activity, selectivity and physicomechanical properties. The technology of supporter and iso-butane dehydrogenation catalyst is realized at OAO Karpov Mendeleevsk Chemical Plant (Mendeleevsk) for the production with the capacity of 100 t per month. Industrial catalyst lots are under operation at the Synthetic Isoprene Rubber Plant of OAO Nizhnekamskneftechim. The given article consists of two parts. In the first one, investigation results are presented for the changes in technical properties of Al(OH)3 during its dehydration in an industrial continuous baking drum-type furnace. The changes in physicomechanical characteristics of granules at the dehydration stage are caused by phase transformations of gibbsite and boehmite, by crystalline structure rearrangements in the volume of microgranules and do not depend on mechanical loads in a baking furnace and on porous structure changes. The conditions of gibbsite complete phase change into the two-phase boehmite-χ-Al2O3 mixture with minimal reduction in the microgranules strength have been determined: Tav = 435−475°C, νTHA = 170 kg/h, and τav = 0.8 h.

Seleção de refratários para fornos de cozimento de anodo

Nos últimos anos a produção mundial de alumínio tem aumentado e para as empresas continuarem competitivas torna-se necessário que a média do custo de produção do metal seja reduzida. Uma das alternativas é aumentar a vida útil dos refratários usados em fornos de cozimento de anodo, bem como a sua capacidade de produção. Ambas estratégias podem resultar em maior qualidade do anodo e redução no custode manutenção do forno. O presente trabalho tem por objetivo apresentara caracterização termo-mecânica dos tijolos refratários utilizados em fornos de cozimento de anodo e a resistência destes materiais ao ataque químico. Os resultados indicam que a escolha da composição mais adequada depende de uma análise sistêmica das propriedades a alta temperatura, da resistência química e das práticas operacionais do forno.

Seleção de refratários para fornos de cozimento de anodo

Nos últimos anos, a produção mundial de alumínio tem aumentado e para as empresas continuarem competitivas torna-se necessário que a média do custo de produção do metal seja reduzida. Uma das alternativas é aumentar a vida útil dos refratários usados em fornos de cozimento de anodo, bem como a sua capacidade de produção. Ambas estratégias podem resultar em maior qualidade do anodo e redução no custo de manutenção do forno. O presente trabalho tem por objetivo apresentar a caracterização termo-mecânica dos tijolos refratários utilizados em fornos de cozimento de anodo e a resistência destes materiais ao ataque químico. Os resultados indicam que a escolha da composição mais adequada depende de uma análise sistêmica das propriedades a alta temperatura, da resistência química e das práticas operacionais do forno.

Failure Mechanism of Alumino Silicate Refractories in Anode Baking Furnace

Anode baking furnaces is an integral part of aluminium industry. In this furnace, anodes are baked to use in electrolytic reduction. Depending on the design either open top or closed top furnaces are employed. Till date, alumino-silicate refractories are the choicest material due to low cost, low creep under compression, high resistance to thermal cycle, carbon monoxide disintegration and alkali attack. This paper deals with failure mechanism of such type of refractories. Used samples from a Reid Hammer bake oven have been studied to find out the reasons of failure. The failure has occurred due to thermomechanical, pyro-chemical stresses and alkali attack in reducing condition. Out of different reasons of failure, alkali attack in reducing condition is found to be the prime cause for failure.

The effect of the addition of fine andalusite particles in refractory bricks on gaseous corrosion

In the past, the mechanisms of corrosion in refractory materials used in the flue wall of anode baking furnaces have been poorly understood. To better understand the processes of degradation, a study of corroded refractories from anode baking furnaces was conducted. This study found that all refractory bricks contain fine andalusite particles in the matrix and fireclay as aggregates. The first stage of corrosion is the penetration of gaseous sodium, coming from recycled anodes, through the porosity of materials. Then, at high temperature, sodium becomes oxidized and is included in the liquid phase. The sodium-rich liquid phase corrodes the refractory material, in particular mullite networks. To understand why the andalusite mineral is used in the refractory materials, a corrosion test able to simulate the gaseous corrosion of materials at laboratory scale was developed. Several recipes, composed of andalusite or fireclay, were submitted to the corrosion test. The microstructural observations showed that the matrix is more sensitive to corrosion. Thus, the use of a raw material such as andalusite in the matrix is advised in order to reduce the gaseous sodium corrosion of fireclay based bricks.

Hazardous Agents in Anode Manufacture

The aim of this study was to assess to which extent the modernisation of an anode plant had reduced occupational chemical health hazards for jobs with the highest potential of exposure. Periodical measurements of dust and gases were performed at the same workplaces using the same methods, before and after modernisation. These measurements were compared with the recommended standards. Before modernisation the concentrations of total dust, carbon monoxide, carbon dioxide, sulphur dioxide, hydrogen fluoride, benzene, and phenol were above the recommended standards in 56.9 % (74/130) of the samples. After modernisation, only 12.3 % (21/171) of the samples were non-conforming. Before modernisation, workers were exposed to higher concentrations of all agents in all production sections. After modernisation, dust remained the primary pollutant in harmful concentrations in the anode baking furnace (GM=22.1 mg m-3) and in the anode rodding room (GM=22.1 mg m-3), hydrogen fluoride in the anode rodding room (GM=4.2 mg m-3), and sulphur dioxide in all production sections. As plant modernisation has not completely resolved the exposure issue, stringent compliance to safety rules and regular medical checkups are necessary.

Simulating the Heat Transfer Process of Horizontal Anode Baking Furnace

AbstractA transient two‐dimensional mathematical model of a horizontal baking furnace is presented. The model combines complex thermal phenomena in a baking process such as air infiltration, evolution and combustion of volatile matters, combustion of packing coke, and heat losses. The predicted results are in good agreement with measured data. Furthermore, the process is simulated under different operating conditions such as firing cycle time, airflow and air infiltration. The simulated results indicate that the fuel consumption decreases as the firing cycle time decreases, it is also found that reducing the airflow and air infiltration will help to save fuel. The model is proved to be a useful tool for the process optimisation of the baking furnace in the aluminum industry

Simulating the Heat Transfer Process of Horizontal Anode Baking Furnace

AbstractA transient two‐dimensional mathematical model of a horizontal baking furnace is presented. The model combines complicated thermal phenomena in the baking process such as air infiltration, evolution and combustion of volatile matter; combustion of packing coke, and heat losses. The predicted results are in good agreement with measured data. Furthermore, the processes are simulated under different operating conditions such as firing cycle time, airflow and air infiltration. The simulated results indicate that the fuel consumption decreases as the firing cycle time decreases, it is also found that reducing the airflow and air infiltration will assist fuel efficiency. The model has proved to be a useful tool in the process optimization of the baking furnace in the aluminum industry.

Pattern Change of Several Polycyclic Aromatic Furans and Analogous Thiophenes on Oxidative Pyrolysis of Pitches in Flue Gases, and the Relevance to their Quantitative Analysis

Coal tars, coal-tar pitches, and ring-furnace flue gases have been analyzed by GC–MS for several classes of polycyclic aromatic furans and thiophenes and concentration patterns were obtained for benzonaphthofurans, benzonaphthothiophenes, benzobisbenzofurans, and their isomers. During formation of tar in a coke oven battery non-peripheral and alternating polycyclic thiophenes are formed preferentially. Peripheral polycyclic furans were not found in any of the materials. During tar processing the concentrations of minor fractions of peripheral benzonaphthothiophene isomers are reduced substantially. A further reduction occurs during pitch carbonization under oxidative conditions in an annular baking furnace. This largely facilitates quantification of the non-peripheral compounds.

Effect of zinc metal addition on microstructural evolution of Zn 0.22 Cd 0.78 S$ phosphors studied by transmission electron microscopy

The effect of zinc powder addition on the microstructural evolution of fine Zn0.22Cd0.78S:Ag$, Cl phosphor particles was investigated in relation to the luminescent property of phosphors. The phosphor microstructures were analyzed by high-resolution transmission electron microscopy (HRTEM) using the ultramicrotome technique for specimen preparation. The phosphor baking process at 480 °C for 30 min in air results in significant damage to the surface structure of the phosphors due to the decomposition and oxidation of the phosphor itself. The addition of zinc metal powders into the Zn0.22Cd0.78S$ phosphors suppresses the oxidization and decomposition of phosphors by oxidizing zinc metal during the baking process in air. The oxidation of the zinc powders during baking provides the baking furnace with less oxidizing atmosphere for phosphor particles. The structure of phosphors, especially at the surface region, is much less degraded compared to the phosphors baked with no zinc metal addition. © 2000 Kluwer Academic Publishers

Clay alumina brick used in anode baking furnaces

Currently, the choice of refractory for use in the flue walls of a carbon baking furnace is dependent upon the degree of control achieved in the furnace. This article describes how this interrelationship has occurred and describes what refractory systems are in use.

An extended two-dimensional mathematical model of vertical ring furnaces

An extended two-dimensional (2-D+) mathematical model of vertical anode baking furnaces has been developed. The work was motivated by the fact that a previous 2-D model was unable to predict the nonuniform baking in the transverse direction,i.e., perpendicular to the longitudinal axis of the furnace. The modeling strategy based on dividing each section in four zones (underlid, pit, underpit, head wall and fire shaft zones) and introducing two symmetry planes in the exterior pits is explained. The basic heat-transfer relations used are also detailed. Selected results shown include draught and oxygen concentration profiles in the flue, gas and anode temperature distributions and fuel consumption in the back fire ramp. Simulation and experimental results are compared.

95/01797 Waste tar firing system for baking furnaces

95/01797 Waste tar firing system for baking furnaces