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 cell wall property on compressive performance of aluminum foams

The effects of cell wall property on the compressive performance of high porosity, closed-cell aluminum foams prepared by gas injection method were investigated. The research was conducted both experimentally and numerically. Foam specimens prepared from conditioned melt were tested under uniaxial compressive loading condition. The cell wall microstructure and fracture were observed through optical microscope（OM） and scanning electron microscope（SEM）, which indicates that the cell wall property is impaired by the defects in cell walls and oxide films on the cell wall surface. Subsequently, finite element（FE） models based on three-dimensional thin shell Kelvin tetrakaidecahedron were developed based on the mechanical properties of the raw material and solid material that are determined by using experimental measurements. The simulation results show that the plateau stress of the nominal stress-strain curve exhibits a linear relationship with the yield strength of the cell wall material. The simulation plateau stress is higher than the experimental data, partly owing to the substitution of solid material for cell wall material in the process of the establishment of FE models.

MATHEMATICAL MODELLING OF BUBBLE DRIVENFLOWS IN A NOVEL ALUMINUM ELECTROLYSIS CELL

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Numerical simulation on electrolyte flow field in 156 kA drained aluminum reduction cells

Based on the commercial CFD software CFX-4.3, two-phase flow of electrolyte in 156 kA drained aluminum reduction cells with a new structure was numerically simulated by multi-fluid model and k-ε turbulence model. The results show that the electrolyte flow in the drained cells is more even than in the conventional cells. Corresponding to center point feeding, the electrolyte flow in the drained cells is more advantageous to the release of anode gas, the dissolution and diffusion of alumina, and the gradient reduction of the electrolyte density and temperature. The average velocity of the electrolyte is 8.3 cm/s, and the maximum velocity is 59.5 cm/s. The average and maximum velocities of the gas are 23.2 cm/s and 61.1 cm/s, respectively. The cathode drained slope and anode cathode distance have certain effects on the electrolyte flow.

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.

A method of determining and designing the drained slope in drained aluminum reduction cells

Based on principles of electromagnetic fluid dynamics the exerted forces and movement states of melted aluminum in the traditional reduction cells and the drained cells were compared and analyzed in this paper. And based on the theory of slow movement, a formula in respect of the drained angle was derived, i.e. θ≥(J zB x-J xB z)ρg-(J xB y-J yB x ). It can be seen that the drained slope can be decided by respectively multiplying the area current densities and magnetic induction intensities in three coordinate directions in aluminum reduction cells, and the drained slope is approximate to 0.6% derived from typical data based on measurement and calculation, which implies that the key parameter is obtained in designing of drained cells. The results can be used for a designing basis for drained cathodes.

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.

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.

Effect of electromagnetic force on turbulent flow of molten metal in aluminum electrolysis cells

The standard k-ε model was adopted to simulate the flow field of molten metal in three aluminum electrolysis cells with different anode risers. The Hartman number, Reynolds number and the turbulent Reynolds number of molten metal were calculated quantitatively. The turbulent Reynolds number is in the order of 103 , and Reynolds number is in the order of 104 if taking the depth of molten metal as the characteristic length. The results show that the molten metal flow is the turbulence of high Reynolds number, the turbulent Reynolds number is more appropriate than Reynolds number to be used to describe the turbulent characteristic of molten metal, and Hartman number displays very well that electromagnetic force inhibits turbulent motion of molten metal.

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.

Dynamic self-adaptive ANP algorithm and its application to electric field simulation of aluminum reduction cell

Region partition(RP) is the key technique to the finite element parallel computing(FEPC),and its performance has a decisive influence on the entire process of analysis and computation.The performance evaluation index of RP method for the three-dimensional finite element model(FEM) has been given.By taking the electric field of aluminum reduction cell(ARC) as the research object,the performance of two classical RP methods,which are Al-NASRA and NGUYEN partition(ANP) algorithm and the multi-level partition(MLP) method,has been analyzed and compared.The comparison results indicate a sound performance of ANP algorithm,but to large-scale models,the computing time of ANP algorithm increases notably.This is because the ANP algorithm determines only one node based on the minimum weight and just adds the elements connected to the node into the sub-region during each iteration.To obtain the satisfied speed and the precision,an improved dynamic self-adaptive ANP(DSA-ANP) algorithm has been proposed.With consideration of model scale,complexity and sub-RP stage,the improved algorithm adaptively determines the number of nodes and selects those nodes with small enough weight,and then dynamically adds these connected elements.The proposed algorithm has been applied to the finite element analysis(FEA) of the electric field simulation of ARC.Compared with the traditional ANP algorithm,the computational efficiency of the proposed algorithm has been shortened approximately from 260 s to 13 s.This proves the superiority of the improved algorithm on computing time performance.

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.

Tensile property of Al-Si closed-cell aluminum foam

Al-Si closed-cell aluminum foams of different densities were prepared by molten body transitional foaming process.The tensile behavior of Al-Si closed-cell aluminum foam was studied and the influence of relative densities on the tensile strength and elastic modulus was also researched.The results show that the fracture surfaces of Al-Si closed-cell aluminum foam display quasi-cleavage fracture consisting of brittle cleavages and ductile dimples.The tensile strength and elastic modulus are strictly affected by the relative density of Al-Si closed-cell aluminum foam.With increasing relative density,the tensile strength increases and the strain at which the peak strength is measured also increases;in addition,the elastic modulus increases with increasing relative density.

A Cell Condition-Sensitive Frequency Segmentation Method Based on the Sub-Band Instantaneous Energy Spectrum of Aluminum Electrolysis Cell Voltage

Cell voltage is a widely used signal that can be measured online from an industrial aluminum electrolysis cell.A variety of parameters for the analysis and control of industrial cells are calculated using the cell voltage.In this paper,the frequency segmentation of cell voltage is used as the basis for designing filters to obtain these parameters.Based on the qualitative analysis of the cell voltage,the sub-band instantaneous energy spectrum(SIEP)is first proposed,which is then used to quantitatively represent the characteristics of the designated frequency bands of the cell voltage under various cell conditions.Ultimately,a cell condition-sensitive frequency segmentation method is given.The proposed frequency segmentation method divides the effective frequency band into the[0,0.001]Hz band of lowfrequency signals and the[0.001,0.050]Hz band of low-frequency noise,and subdivides the lowfrequency noise into the[0.001,0.010]Hz band of metal pad abnormal rolling and the[0.01,0.05]Hz band of sub-low-frequency noise.Compared with the instantaneous energy spectrum based on empirical mode decomposition,the SIEP more finely represents the law of energy change with time in any designated frequency band within the effective frequency band of the cell voltage.The proposed frequency segmentation method is more sensitive to cell condition changes and can obtain more elaborate details of online cell condition information,thus providing a more reliable and accurate online basis for cell condition monitoring and control decisions.

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.

Coupled computation method of physics fields in aluminum reduction cells

Considering importance of study on physics fields and computer simulation for aluminum reduction cells so as to optimize design on aluminum reduction cells and develop new type of cells, based on analyzing coupled relation of physics fields in aluminum reduction cells, the mathematics and physics models were established and a coupled computation method on distribution of electric current and magnetic field, temperature profile and metal velocity in cells was developed. The computational results in 82 kA prebaked cells agree well with the measured results, and the errors of maxium value calculated for three main physics property fields are less than 10%, which proves that the model and arithmetic are available. So the software developed can be not only applied to optimization design on traditional aluminum reduction cells, but also to establishing better technology basis to develop new drained aluminum reduction cells.

Cell-structure and mechanical properties of closed-cell aluminum foam

The density, cell size and structure of closed-cell aluminum foam were measured by optical microscopy and image analysis. The properties and the mechanism of compressive deformation that occur in closed-cell aluminum foam were measured and discussed. The results show that the cell size of foam with density of 0.37 mg/m^3 is distributed in the range of 0.5 4.0 mm. The cell size of foam with density of 0.33 mg/m^3 is distributed in the range of 0.55.0 mm. The cell wall thickness of both types is 0.10.3 mm. The closed-cell aluminum foam almost belongs to isotropic one, with a variation of ±15% in elastic modulus and yield strength in longitudinal and transverse direction. Under compressive loading, foam materials show inhomogeneous macroscopic deformation. The site of the onset of local plastic deformation depends on the cell structure. The shape of cell is more important than size in determining the yielding susceptibility of the cells. At early stage of deformation,the deformation is localized in narrow bands having width of one cells diameter, and outside the bands the cell still remains the original shape. The cells within bands experience large permanent deformation. The band normals are usually within 20° of the loading axis.

Physical modeling of gas induced bath flow in drained aluminum reduction cell

A room temperature physical model was used to study the bubble behavior and gas induced bath circulation in a drained aluminum reduction cell. By passing compressed argon through the penetrated Plexiglas box bottom plate immersed in water, gas evolution at the anode bottom surface was simulated. Bubble behavior and liquid flow field were studied and analysis was presented. Bath secondary recirculation was observed in the interpolar gap not the net rising flow as expected. Liquid driven by the bubbles forms small vortices along the interpolar gap with small mean and turbulent velocities and accordingly poor mass transfer. Secondary recirculation also exists between the slot and interpolar gap, part of the flow in the interpolar gap go to the slot with the bubbles and fluid at the bottom of the slot enters the interpolar gap directly without going to the center channel. The existence of the fluid secondary recirculation is very unfavorable to the alumina dissolution and dispersion. Increasing the anode tilt or gas flow rate, or decreasing the anode-cathode distance can make the secondary recirculation in the interpolar gap weak, however, will intensify the secondary recirculation between the slot and interpolar gap.

Effects of cell size on compressive properties of aluminum foam

The effects of cell size on the quasi-static and dynamic compressive properties of open cell aluminum foams produced by infiltrating process were studied experimentally. The quasi-static and dynamic compressive tests were carried out on MTS 810 system and SHPB(split Hopkinson pressure bar) respectively. It is found that the elastic moduli and compressive strengths of the studied aluminum foam are not only dependent on the relative density but also dependent on the cell size of the foam under both quasi-static loading and dynamic loading. The foams studied show a significant strain rate sensitivity, the flow strength can be improved as much as 112%, and the cell size also has a sound influence on the strain rate sensitivity of the foams. The foams of middle cell size exhibit the highest elastic modulus, the highest flow strength and the most significant strain rate sensitivity.

Sound absorption and insulation property of closed-cell aluminum foam

The closed-cell aluminum foams (specimenρ=0.31 g/cm3, diameter of 100 mm, and thickness of 20 mm for sound absorption testing; specimenρ=0.51 g/cm3, length of 1 240 mm, width of 1 100 mm, and thickness of 30 mm for sound insulation testing) were prepared by the method of molten body transitional foaming process. Its sound absorption property under frequency of 160-2 000 Hz and the sound insulation property under frequency of 100-4 000 Hz were tested. The sound absorption results show that the sound absorption property is much better under middle frequencies than that under low and high frequencies. The sound absorption coefficient climbs when frequency increases from 160 Hz to 800 Hz and then drops when frequency is increased from 800 Hz to 2 000 Hz. The function of the sound absorption mainly depends on the Helmholtz resonator, the microphone as well as cracks of closed-cell aluminum foam. The sound insulation experiments show that the sound reduction index (R) is small under low frequencies, and large under high frequencies; the weighted sound reduction index (Rw) and the highest sound reduction index (R) can reach around 30.8 dB and 43 dB, respectively.