Multiphase Flow And Heat Transfer Behavior In Energy-saving Aluminum Electrolytic Cell

Aluminum electrolysis is one of the energy-intensive and big polluting industries,and the sustainable development of the aluminum electrolysis industry will be affected with large amounts of electric energy consumption in the process of aluminum electrolytic production.Therefore,the main goal is to reduce the energy consumption of aluminum reduction cells,and it has a great significant about the study of energy-saving aluminum electrolytic cell.Based on the principle of electrolytic aluminum production and finite volume method,firstly,a three-dimensional physical and transient mathematical model of 300kA traditional anode cell and slotted anode cell has been developed to investigate the impact on the electrolyte(bath)-aluminum melt(metal)interface fluctuation,the escaped rate of gas bubbles and the thickness of the bubble layer in aluminum cell with slotted anode.The volume of fluid(VOF)approach is employed to track the bath-metal interface.Magnetohydrodynamics(MHD)model which is solved by the electrical potential method is used for describing the electromagnetic field.The electromagnetic force(EMF)and surface tension are added into the momentum equation as a source term.The discrete phase model(DPM)is employed to study the motion of gas bubbles in the aluminum electrolytic cells.Secondly,a three-dimensional(3D)transient physical model and mathematical model have been developed to study the heat transfer and flow conditions in the aluminum electrolytic cell.Electrical potential approach was used to obtain electromagnetic fields.electromagnetic force(EMF)and surface tension,which were the source terms in momentum,and Joule heating is added into the energy equation.The volume of fluid(VOF)approach was employed to track the interface of bath and metal.The phase change of molten bath was modeled by an enthalpy method,in which the mushy zone was treated as a porous medium with porosity equal to the liquid fraction.Numerical simulation on magnetohydrodynamics flow and heat transfer of gas bubbles,bath and metal in aluminum cell that explores the stability factors of aluminum electrolytic process and provide theoretical basis for production process optimization which is finally to achieve the goal of saving energy.The results indicate that the bath-metal interface fluctuation in the slotted anode cell is less than that in the traditional anode cell.It is easier for gas bubbles to escape from the cell in slotted anode,and the distance between anode and cathode can be reduce with the bath-metal interface fluctuation decreasing.Meanwhile,the interface fluctuation amplitude increases as the bubble diameter increasing.Gas volume fraction in slotted anode cell is less than that in the traditional anode cell.Moreover,the higher gas volume fraction occurs in the central of the anode bottom about traditional cell and lower in the boundary area and the gas distribution is uniform in the slotted anode cell,it is mainly because that the use of slots can strengthen the escape of gas bubbles and reduce the gas accumulation in the central area.It is accepted that anode with slots reduce gas bubbles layer resistance.The gas escape rate in slotted anode cell is larger than that in traditional anode cell,and the thickness of gas bubble layer in the slotted anode cell and traditional anode cell are about 20mm and 16.5mm,the gas bubble layer is decreased about 3.5mm with slotted anode,therefore,slotted anode has more benefits on reducing gas coverage and energy saving.The whole voltage drop of traditional anode cell and slotted anode cell is about 2.294V,2.170V.Due to the thickness of gas bubble layer has been decreased in bath zone with slotted anode,the voltage drop decreased 0.124V.The current density distribution in slotted anode cell is similar with the traditional anode cell,and the main direction of current is the vertical current because the horizontal current is less than vertical current.It beneficial to reduce the horizontal current density along the X,Y axis direction and increase the vertical current density along the Z axis direction.The bath temperature at the middle of the cell is hotter,that the maximum temperature is about 1226K in traditional anode cell and 1224K in slotted anode cell,while colder at four corners due to the heat transfer in cell side is stronger than in the central of the cell.The distribution of temperature field is similar in the traditional anode cell and slotted anode cell,but the temperature distribution in slotted anode cell is more uniform.The distribution of ledge thickness is similar in the traditional anode cell and slotted anode cell,and the ledge thickness along the X axis direction which is larger than that along the Y axis direction.The frozen ledge thickness along the X,Y axis direction in the side of traditional anode aluminum reduction cell is about 110～180 mm and 180mm-260mm,meanwhile,The frozen ledge thickness along the X,Y axis direction in the side of slotted anode aluminum reduction cell is about 90～155 mm and 145mm～200mm...