230kA预焙阳极铝电解槽设计

应用铝电解工艺优化理论 ,采用新型计算机软件辅助设计 ,将新工艺、新技术、新材料优化组合设计铝电解槽 ,扼要概述电解槽阳极 ,槽膛尺寸、大梁、打壳下料装置 ,内衬及槽壳 ,母线配置等设计。设计获得成功 ,投入系列生产 ,获得预期效果。

我国预焙铝电解槽技术的进展

本文论述了我国预焙铝电解槽设计、控制等技术的最新进展 ,分析讨论了仍然存在的一些问题并对今后的工作提出了一些建议。

Analysis and modeling of alumina dissolution based on heat and mass transfer

A comprehensive heat and mass transfer model of dissolution process of non-agglomerated and agglomerated alumina particles was established in an aluminum reduction cell. An appropriate finite difference method was used to calculate the size dissolution rate, dissolution time and mass of alumina dissolved employing commercial software and custom algorithm based on the shrinking sphere assumption. The effects of some convection and thermal condition parameters on the dissolution process were studied. The calculated results show that the decrease of alumina content or the increase of alumina diffusion coefficient is beneficial for the increase of size dissolution rate and the decrease of dissolution time of non-agglomerated particles. The increase of bath superheat or alumina preheating temperature results in the increase of size dissolution rate and the decrease of dissolution time of agglomerated particles. The calculated dissolution curve of alumina（mass fraction of alumina dissolved） for a 300 k A aluminum reduction cell is in well accordance with the experimental results. The analysis shows that the dissolution process of alumina can be divided into two distinct stages： the fast dissolution stage of non-agglomerated particles and the slow dissolution stage of agglomerated particles, with the dissolution time in the order of 10 and 100 s, respectively. The agglomerated particles were identified to be the most important factor limiting the dissolution process.

Ambient electrical conductivity of carbon cathode materials for aluminum reduction cells

The ambient electrical conductivity (AEC) of carbon cathode materials was investigated in respect to their open porosity, crystal structure and graphite content using hydrostatic method, four-probe technique and X-ray diffraction (XRD), respectively. The AEC is proportional to the specific conductivity (σ0) and the exponential of (1?ε) (ε is porosity) by a quasi-uniform formula based on the percolation theory. Theσ0 can reflect the intrinsic conductivity of the carbon cathodes free of pores, and it depends on the mean crystallite size parallel to the layer (002). The exponentn is dependent on the materials nature of the cathode aggregates, while an averaged value, 4.65, can practically work well with 5 types of cathode materials. The calculation ofσ0 can be extended to the graphitic cathodes containing different aggregates using the simple rule of mixture.

Effect of gas bubble on cell voltage oscillations based on equivalent circuit simulation in aluminum electrolysis cell

A method to investigate the effect of gas bubble on cell voltage oscillations was established. The whole aluminum electrolysis cell was treated as a resistance circuit, and the dynamic simulation of the cell equivalent circuit was modeled with Matlab/Simulink simulation software. The time-series signals of cell voltage and anode current were obtained under different bubble conditions, and analyzed by spectral and statistical analysis methods. The simulation results show that higher bubble release frequency has a significant effect on the cell voltage oscillations. When the bubble coverage of one anode block exceeds 80%, the cell voltage may exceed its normal fluctuation amplitude. The simulation also proves that the anode effect detected by computer in actual production is mainly the whole cell anode effect.

Effects of electrolysis process parameters on alumina dissolution and their optimization

The Box–Behnken design and desirability approach were used to investigate and optimize the process parameters for aluminum reduction cells related to alumina dissolution. The bath temperature, alumina content, current and alumina temperature were chosen as the design parameters. The content of cumulative dissolved alumina(CCDA) and the relative deviation from the target content(RDTC) were adopted as the responses. The interactive influence results show that increasing the bath temperature and alumina temperature, as well as decreasing the alumina content, can increase CCDA. Increasing the bath temperature and lowering the current are beneficial for obtaining a more uniform alumina distribution. The optimal operating parameters were determined to be as follows: bath temperature of 958.8 ℃, alumina content of 2.679 wt.%, current of 300 kA and alumina temperature of 200 ℃.

Footprint of harmful substances in spent pot lining of aluminum reduction cell

Spent pot lining(SPL) from aluminum reduction cells is considered to be hazardous materials due to containing a large amount of soluble fluoride salts and trace toxic cyanides. The distribution of fluorides and cyanide in a 350 kA cell operated for 2396 days was analyzed and the footprint and corrosion mechanism of the harmful substances in SPL were also studied. It is found that the fluorides are mainly concentrated in the cathode carbon block and the layer of dry barrier under the cathodes, which is closely related to permeability of the cathodes and dry barrier the fluorides penetrate in. Cyanide has a low concentration in the cell center and a high concentration in the sidewall, which is positively related to the air amount entering into the areas in the cells.

Carbothermic reduction of chromite fluxed with aluminum spent potlining

Aluminum spent potlining (SPL) was employed as both the fluxing agent and a source of carbonaceous reductant for the carbothermic reduction of chromite, aiming to allow effective separation of alloy from the slag component. The experimental results show that the carbonaceous component of the SPL is more reactive towards chromite reduction compared to graphite. The formation of refractory spinel (MgAl2O4) on chromite particles hinders further reduction and alloy growth. The slag-making components of the SPL (e.g. nepheline and NaF) form molten slags at low temperatures (~1300℃) and partly dissolve the refractory spinel as well as the chromite. Destruction of the spinel layer with enhanced mass transfer greatly improves the alloy growth, which can be further promoted by reduction at a higher temperature (e.g. 1500℃). Ferrochrome alloy particles grow large enough at 1500℃ in the presence of SPL, allowing effective separation from the slag component using elutriation separation.

Simulation of thermal and sodium expansion stress in aluminum reduction cells

Two finite element(FE) models were built up for analysis of stress field in the lining of aluminum electrolysis cells.Distribution of sodium concentration in cathode carbon blocks was calculated by one FE model of a cathode block.Thermal stress field was calculated by the other slice model of the cell at the end of the heating-up.Then stresses coupling thermal and sodium expansion were considered after 30 d start-up.The results indicate that sodium penetrates to the bottom of the cathode block after 30 d start-up.The semi-graphitic carbon block has the largest stress at the thermal stage.After 30 d start-up the anthracitic carbon has the greatest sodium expansion stress and the graphitized carbon has the lowest sodium expansion stress.Sodium penetration can cause larger deformation and stress in the cathode carbon block than thermal expansion.

Numerical simulation of busbar configuration in large aluminum electrolysis cell

Various busbar configurations were built and modeled by the custom code based on the commercial package ANSYS for the 500 kA aluminum electrolysis cell.The configuration parameters,such as side riser entry ratio,number of cathode bars connected to each riser,vertical location of side cathode busbar and short side cathode busbar,distance between rows of cells in potline,the number of neighboring cells,ratio of compensation busbar carried passing under cell and its horizontal location under cell along with large magnetohydrodynamic(MHD) computation based on the custom evaluation function were simulated and discussed.The results show that a cell with riser entry ratio of 11:9:8:9:11 and cathode busbar located at the level of aluminum solution,50% upstream cathode current passing under cell for magnetic field compensation,the distance between rows of 50 m is more stable.

Effect of electromagnetic force and anode gas on electrolyte flow in aluminum electrolysis cell

Based on the commercial computational fluid dynamics software CFX-4.3, electrolyte flow fields in a 156 kA pre-baked anode aluminum electrolysis cell were investigated in three different cases where the electrolyte melt was driven by different kinds of force, i.e. electromagnetic force only, the anode gas drag force only and both of the former two forces. The results show that when electromagnetic force was introduced only, most of the electrolyte moves horizontally; when anode gas drag force was introduced only, the electrolyte flows mainly around each anode with small circulation; when electromagnetic force and anode gas drag force were both introduced together, the structure of the electrolyte flow fields and the velocity of electrolyte are similar to that of the case where only anode gas drag force is used. The electrolyte flow fields are mainly determined by the anode gas drag force.

Application of fiber Bragg grating sensor network in aluminum reduction tank shell temperature monitoring

A fiber Bragg grating temperature sensor network was designed to implement the real-time health monitoring of the aluminum reduction cell. The heat transfer process was simulated using software ANSYS, and an on-line shell monitoring system was established based on optical sensing technology. According to aluminum reduction cell heat transfer theory, the 2D slice finite element model was developed. The relationship between shell temperature and cell status was discussed. Fiber Bragg grating （FBG） was chosen as the temperature sensor in light of its unique advantages. The accuracy of designed FBG temperature sensors exceeds 2 ~C, and good repeatability was exhibited. An interrogation system with 104 sensors based on VPG （volume phase grating） filter was established. Through the long-term monitoring on running state, the status of the aluminum reduction cell, including security and fatigue life could be acquired and estimated exactly. The obtained results provide the foundation for the production status monitoring and fault diagnosis. Long-term test results show good stability and repeatability which are compatible with electrolysis process.

Electric field distribution in 75 kA drained aluminum reduction cell

Current distribution in a drained aluminum reduction cell is critical due to its influence on the current efficiency, electrolysis stability, anodes and cathodes integrity. A finite element model was developed to simulate the electric field in a 75 kA drained aluminum reduction cell. The current distribution and influences of the cathode inclination angle and anode-cathode distance (ACD) were studied. The results show that relatively large horizontal current density appears in the aluminum film, and the maximum value reaches 600 kA/m2. As the cathode inclination angle increases from 2° to 15°, the maximum current density of the metal pad increases by 15%, while the maximum current density of the aluminum-wettable coating layer decreases by 27%. The influence of the ACD on the current distribution is not obvious.

Current Efficiency, Corrosion and Structural Changes in SnO2-Sb2O3-CuO Inert Anodes for Aluminium Electrolysis

A systematic study was conducted on current efficiency （CE）, corrosion and structural changes in SnO2-based inert anodes （made of 96wt%SnO2＋2wt%Sb2O3＋2wt%CuO） on a laboratory Hall-Heroult aluminium cell. The influence of operating parameters and electrolyte composition on the CE and corrosion process were evaluated. The CE was found to be more than 90% and catastrophic corrosion took place at low percent of Al2O3, high percent of LiF, low cryolite ratio and high current densities. From all the structural changes that took place in the SnO2-based inert anodes, we assumed that the most important contribution was due to the migration of CuO towards the outer limits of the constituent grains of SnO2 based ceramic. The complex process occurred during the formation of various phases and their sintering ability both directly depended on Cu/Sb molar ratio.

Resistance optimization of flexes in aluminum reduction cells

The resistance arrangements of the flexes connecting with the cathode bus bar in aluminum reduction cells were generalized as three modes. In each mode the universal method to select proper resistivity of the flexes was induced respectively to insure that the current in local group of flexes was equal. Furthermore, a 350 kA aluminum reduction cell based electric field model was developed by finite element method to evaluate the effect of the method. Suggestions on selection of three modes were also put forward. The results show that the methods of resistance optimization can reduce the current variation about 180 A compared with that in original case.

CFD simulation of effect of anode configuration on gas–liquid flow and alumina transport process in an aluminum reduction cell

Numerical simulations of gas–liquid two-phase flow and alumina transport process in an aluminum reduction cell were conducted to investigate the effects of anode configurations on the bath flow, gas volume fraction and alumina content distributions. An Euler–Euler two-fluid model was employed coupled with a species transport equation for alumina content. Three different anode configurations such as anode without a slot, anode with a longitudinal slot and anode with a transversal slot were studied in the simulation. The simulation results clearly show that the slots can reduce the bath velocity and promote the releasing of the anode gas, but can not contribute to the uniformity of the alumina content. Comparisons of the effects between the longitudinal and transversal slots indicate that the longitudinal slot is better in terms of gas–liquid flow but is disadvantageous for alumina mixing and transport process due to a decrease of anode gas under the anode bottom surface. It is demonstrated from the simulations that the mixing and transfer characteristics of alumina are controlled to great extent by the anode gas forces while the electromagnetic forces(EMFs) play the second role.

Influence of the operating parameters over the current efficiency and corrosion rate in the Hall–Heroult aluminum cell with tin oxide anode substrate material

A systematic laboratory study was conducted on current efficiency and corrosion obtained in cryolite-alumina melts with SnO2-Sb203-CuO ceramic inert anodes. The current efficiency （CE） was determined by measuring the total amount of oxygen evolved at the anode and was found to be ~ 95%. The influence of operating parameters （inter-elec- trode distance, temperature and current density） was evaluated. The quantitative interdependencies as well as the ranges of CE optima[ values were established （2-3 cm, 940-960 ℃ and 0.7-0.8 A.cm 2）. The corrosion process of these anodes was evaluated by the mass loss method. The evaluation also took care of the corrosion data, as the prob- lem of the anode corrosion appeared to be the main obstacle for the use of those anodes in the commercial cells.Low-ering of the ACD up to 2 cm did not aggravate anode corrosion.

Comparison of structure and physical fields in 400 kA aluminum reduction cells

To investigate the differences and the development trends of the 400 kA aluminum reduction cell, four representative cells were deeply analyzed. By using numerical simulation methods in ANSYS software, the structure parameters were firstly compared, and then three-dimensional models of electric-magnetic-flow field were built and solved with finite element method(FEM). The comparison of the structures reveals that the cell bodies are similar while the current flow path and distribution ratio of bus bars are different. It appears that most of the current(70%-80%) in side A are used as the magnetic field compensation current and flow through two ends. The numerical simulation results indicate that the distributions of magnetic fields are different but all satisfy with the magnetohydrodynamics(MHD) stabilization, and the flow patterns are all two or multi vortexes with appropriate velocities. The comparison shows that all studied cells can satisfy with the physical field requirement, and the commercial applications also verify that the 400 kA cells have become the product of the mature and world's leading technology.

Numerical modeling of effect of slot on bubble motion in aluminum electrolytic process

A transient three-dimensional（3 D） model was established to understand the bubble motion in an industrial electrolytic process. An anode with a new design was tested. It incorporates two slots that allow an efficient removal of gas bubbles. The electromagnetic fields were described by solving Maxwell＇s equations. The bubble movement was studied with two-way coupling Euler-Lagrange approach. The interplay of current density and bubble nucleation rate was included. The collision and coalescence of bubbles were considered. Random walk module was invoked for involving the chaotic effect of the turbulence. The numerical results were validated by experimental measurements. The results indicate that the current distribution and the bubble nucleation periodically change. Due to the slot, the bubble elimination heavily increases. The contribution of the slot to the bubble removal exceeds 50% in the case of three currents, and the promotion of the slot decays with increasing the current.

Structure optimization of the dispensing house in a combustion train for a thermal bake-out aluminum reduction cell

The fume bake-out aluminum reduction cell is a novel technology possessing such advantages as easy control for the speed of heating-up, well-distributed temperature, and little cathode and anode oxidation. The key equipment of fume bake-out is a combustion train whose one important part is a dispensing house. This work deals with the numerical model and the flow and temperature fields of the dispensing house, which suggests that uniformity of flow and energy distribution is influenced by the position, shape and direction of the nozzle and cross dimension of dispensing house mainly, but is less influenced by entry speed. The parameters of the dispensing house structure are optimised to satisfy the requirements for a combustion train in fume bake-out, and appropriate dimensions are obtained for a dispensing house structure.