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Industrial Test Study on Newly Structured Cathode Aluminum Reduction Cell

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Tutor: FengNaiXiang
School: Northeastern University
Course: Non-ferrous metallurgy
Keywords: Aluminum electrolytic,Cathode,New structure,Energy consumption,Polar distance
CLC: TF821
Type: PhD thesis
Year:  2009
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Abstract:
In recent years, aluminum electrolytic and technology are advancing by leaps and bounds, the aluminum cell capacity 60kA development from 60 years ago to the current 500 kA current efficiency reached 95%, the level of automation and control technology has also been improved. Aluminum electrolytic power consumption, however, not reduction the electrolyzer at home and abroad DC power consumption is still hovering in the 13000 ~ 13500kWh/T-Al, energy efficiency is less than 50%. Therefore reduce the power consumption of aluminum electrolytic become a primary concern for the aluminum industry workers at home and abroad. A large number of studies have shown that by changing the electrolytic cell structure to achieve a significant reduction in the aluminum electrolytic electricity consumption become a possible way. Thesis drained cathode cell twice a semi-industrial scale pilot study: 1350A Anthracite base TiB2 / C composite layer drained cathode 100 h of electrolytic aluminum reduction cell test and 1850A graphitization base the TiB2 / G composite layer discharge type cathode aluminum reduction cell 140 h electrolysis trial of. The study found that, drained test the electrolyzer from calcined start to normal electrolysis operation with traditional electrolytic cell undifferentiated stable drained electrolyzer cell voltage and grooves working state, and to obtain a higher current efficiency. TiB2 composite layer produced on the drained cathode etching rate is small, and can effectively protect the cathode base member, and is beneficial to prolong the cell life. Aluminum reference electrode technology measured TiB2 / G graphitized drained cathode cell the anode over-voltage and the cathode voltage to follow Tafel equation relationship respectively with the corresponding current density by the instantaneous power failure, its anode voltage and traditional industrial electrolyzer is almost the same, and its cathode overvoltage is about 0.4 V higher than the industrial electrolyzer, which is due to the fluctuations in liquid aluminum is drained electrolyzer does not exist in the vicinity of the cathode surface molecules Bibi the traditional cathode surface of the cell electrolyte molecule is high many cause. Chongqing Tiantai Aluminum Company 168kA series on three electrolyzer industrial test, including the electrolyzer Zhulu of new cathode structure, roasting, start, normal electrolytic production process. Roasting flame a liquid aluminum stages of roasting the new technology, its energy consumption is only the traditional liquid aluminum roasting 1/4 to 1/3, The calcined coke 1/3, to achieve the purpose of energy saving. So far, the new cathode structure electrolytic cell has stable operation 12100kWh/T-Al DC power consumption of an average of one year. Average the past six months, three new cathode structure electrolyzer cell voltage of 3.756V, anode effect coefficient for 0.063d-1, the current efficiency of 93.3% on average, DC consumption to an average of about 12000kWh/T-Al 127 units compared to the same series. the the traditional electrolyzer anode effect coefficient decreases 0.04d-1, the current efficiency of 1.9%, consumption reduced by about 1370 kWh / DC T-Al, a significant reduction in the effect of aluminum electrolytic power consumption. New cathode structure to achieve energy efficient basic principle is: raised in new cathode structure electrolytic cell the cathode surface, the the cathode liquid aluminum velocity field is split, greatly reduce the flow rate of the liquid aluminum weaken the strengthening of gravity waves, the molten aluminum reduce fluctuations. While this projection to make a more uniform cathode current distribution within the liquid aluminum, thereby reducing the source of induced flow of the liquid aluminum. The surface of the projection formed by the smaller horizontal current around the convex forming a circulation of the molten aluminum, can be reduced the the electrolyzer longitudinal direction wave function. Thus making the peak height of the liquid surface of the electrolytic cell cathode aluminum greatly reduced, the effective pole pitch increase of the electrolyzer, so as to achieve the purpose of the cell voltage is reduced by reducing the pole pitch; new groove having a convex cathode surface, the electrolysis of the protrusion formed in the surface of an appropriate level of current, and thus can be around the projection to form a liquid aluminum cycle, this cycle of liquid aluminum is conducive to the dissolution of alumina, new cathode structure can be reduced because of a low alumina concentration of the local anode effect occurs; electrolytic The groove of the aluminum meniscus volatility decreases, enhanced stability, and the decrease in the effective area of ??the liquid surface of the cathode aluminum, so reducing the aluminum secondary dissolved, improving the current efficiency of the aluminum electrolysis cell. Through the the 168kA new cathode structure the electrolyzer and traditional electrolyzer electric balance studies show that: the new cathode structure electrolytic cell pole away from the small, electrolyte voltage drop than the traditional electrolyzer electrolyte voltage drop is small; new cathode structure electrolyzer at lower The cell voltage, reduced energy input, through the side portion and bottom to strengthen insulation, to achieve a lower heat losses, in order to achieve the thermal equilibrium of the electrolyzer. The tests showed that the aluminum cell type insulation can be achieved by heat transformation, to improve energy efficiency. By 168kA new cathode structure of aluminum electrolyzers Surface Stability measurements found: the new cathode energy efficient aluminum cell, with contrast the traditional electrolytic cell of the same series, the cathode the aluminum liquid level of fluctuations with the same cycle and frequency, cycle around in the 50s, and its fluctuation is approximately sinusoidal; different that other energy efficient new cathode aluminum reduction cell with contrasting series electrolyzer compared with smaller fluctuations, indicating that a new type of cathode innovative cathode structure design of energy-efficient aluminum reduction cell, played a reduction wave (site), and the stabilizing role of cathode aluminum liquid level; When contrast the electrolyser cell voltage from 4.10V down to 3.95V, the the equidistant pressure within the anode guide rod drop Ued change margin increased from 0.6 mV to 1.1 mV, fluid and electrolyte aluminum electrolyzer is very unstable, volatility increases, not the normal working of the of proof series compared groove in the lower cell voltage of 3.95V; novel 24 anode current distribution of the standard deviation of the cathode structure electrolyzers in 3.75V groove voltage 0.589kA, to 0.829kA smaller than that of the conventional electrolyzer 4.10V 24 anode current distribution of the standard deviation, and thus can be determined that a new cathode structure electrolytic the test slot 3.75V current distribution is more evenly distributed than of 4.10V the traditional electrolyzer current tank of liquid aluminum is more stable. Corrosion and penetration of electrolyte and a sodium cathode in a laboratory electrolytic cell, the results show that: containing of TiB2 / C cathode electrolyte and sodium permeation, the electrolyte permeate through the cathode porosity, sodium metal can penetrate through the pores, but also exist in the through carbon lattice penetration, using the EDS analysis of the electrolysis after 2h TiB2 / C cathode surface electrolyte TiB2 sparingly soluble in the electrolyte can be observed; the penetration of the metallic sodium in the TiB2 / C cathode in accordance with Fick's Law, which contains 16 sodium penetration depth coefficient for 1.42mm/min1 2% TiB2 cathode sample. Of TiB2 / C composite cathode sodium expansion rate found in the aluminum electrolysis process, TiB2 / C cathode in the aluminum electrolysis process also has sodium expansion characteristics, but its expansion rate is less than in the same experimental conditions carbonaceous cathode sodium expansion coefficient, and with TiB2 component content increases, its expansion rate decreased. By electrolytic corrosion by the liquid exist under the conditions of the non-aluminum cathode Experimental study found that the permeation of sodium penetration occurs after electrolysis electrolyte melt, NaF penetration speed greater than the speed of the cryolite melt infiltration. After electrolysis the conductive properties of the electrolyte melt is changed, and the electrolysis time, the resistance of the electrolyte melt than not before electrolysis an electrolyte resistance of the melt have changed dramatically.
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