Study Of The Horizontal Current In A Large Prebaked Aluminum Reduction Cell

Energy saving is the most issue for aluminum industry,and the research on the electromagnetic field,electrical field and flow field of aluminum electrolysis cell is always a research focus.The production of horizontal current is the result of the synergy of these physical fields and also a direct cause of reducing current efficiency and increasing energy consumption.This dissertation focuses on the horizontal current in a large prebaked aluminum reduction cell,and on the basis of the previous work,an aluminum reduction cell 3D slice electrical model(E model)and 3D thermo-electrical coupled model(TE model)were established.First,combined with the latest achievements of aluminum electrolysis anode gas research,the impact of the anode large bubbles on the horizontal current was investigated for the first time using the E model;Then,the influence of sludge,height of aluminum pad and cathode carbon block,dimension of collector bar,et al.on the horizontal current distribution were also investigated,which enriches and develops the research content of horizontal current in an aluminum reduction cell;Next,the impact of a slotted cathode collector bar on the horizontal current,temperature distribution and voltage drop in cathode were investigated.using the TE model;At last,a type of slotted cathode carbon block was proposed and the influence of the slotted cathode carbon block on the thermo-electrical field in cathode were investigated.The main results are as follows:(1)Because of the high electrical resistance of bubbles,the current will across the electrolyte around the bubble into the aluminum pad,and there is only a few current in the electrolyte located under the large bubble and a local concentration of current at the edge of the large bubble,which causes a big change of the current distribution in the aluminum pad.First,the bubble position will bring different effects on current.For a fixed bubble coverage of 33.3%,when the bubble is located at the left(cell center),it will produce lots of inward horizontal current in the aluminum pad nearby the cell center,and the maximum inward horizontal current in the upper surface of aluminum pad is 8078A/m2 and 0.6m away from the cell center.When the bubble is located at the right(cell side),the maximum horizontal current increases from 13001A/m2(no bubble)to 30174A/m;Second,the bubble coverage has a significant influence on the horizontal current distribution.For a large bubble located in the middle part of carbon anode,the maximum horizontal current will increase with the bubble coverage increasing.When the bubble coverage changes from 33.3%to 100%,the maximum horizontal current in the upper surface of aluminum pad will increase from 20378A/m2 to 37136A/m2 and the location of maximum value shifts to the cell center.Moreover,when the bubble coverage is 100%,it will produce an inward horizontal current up to 35575A/m2 at the cell side.(2)Due to the large resistance of sludge,the current will across the aluminum pad around the sludge into the cathode carbon and there is a local concentration of current at the edge of the sludge.The sludge located in the cell side has a larger influence on horizontal current than that of sludge located in the cell center.The horizontal current will decrease and inward horizontal current will appear in the cell side with the side sludge increasing.(3)Increasing the height of aluminum pad,height of cathode carbon block,or the cross-sectional area of collector bar will reduce the horizontal current.The maximum has decreased by 33.6%,26.1%,and 43.2%,in the case that the height of aluminum pad,height of cathode carbon,or the cross-sectional area of collector bar increases from 20cm to 30cm,450mm to 550mn,and 180×65mm2 to 180×180mm2,respectively.The vertical current distribution at the upper and lower surface of aluminum pad is unchanged with increasing the height of the aluminum pad,and the difference between vertical current in cell center and in cell side at the lower surface of the aluminum pad becomes smaller for the reason that the resistance in cell center and cell side has been equalized with increasing the height of cathode carbon or the cross-sectional area of collector bar.Moreover,the horizontal current will be reduced by 20.5%by changing the assembly of the collector bar from 180×65mm2 into 65 × 180mm2,(4)Because of the slot and insulating material,the traditional collector has been changed into a "double barst" and much more current will go through the bar located under the slot.The closer to the bar upper surface the slot is,the better for the reducing the horizontal current it will be.The horizontal current decreases by 44.1%for a 900mm slot.However,the severe current variation in cathode leads to a 5 3 mV increase in the cathode voltage and a temperature increase in the bar.The bar becomes a "heat source" and the location of the maximum temperature in the bar shifts from the left end to the part nearby the slot.The collector bar will be eroded by the liquid electrolyte if the temperature is higher than the liquid temperature of the electrolyte penetrating into the cathode carbon lowering the cell life.(5)In a slotted cathode carbon block,the slot formed in the cathode carbon block is filled with an insulating material,which is used to equalize current flow in the carbon block to reduce the horizontal current.The longer the slot is,the better for the reducing the horizontal current it will be.For a slot positioned 150mm under the carbon block upper surface,when the length is 400mm,the horizontal current decreases by 50.9%,and cathode voltage increases by 40mV.Moreover,the temperature increase in cathode is very small.