In general, the coke bed method has the advantages of being simple, does not require complicated equipment, does not require fuel, has substantially no problem of burning off the cathode carbon block, has a short firing time, and can fire a plurality of electrolytic cells at a time. The gas method has the advantages of uniform temperature distribution, good controllability of heating rate, small vertical temperature gradient, no need to remove coke after startup, no current distribution problem and no effect on the operation of the same series of production tanks. The biggest advantage of the aluminum water method is its simplicity and low smoke volume. However, due to the large thermal shock caused by aluminum filling, the aluminum water with low melting point and low viscosity has preferentially penetrated into the lining crack, and the baking defects of the joint paste cannot be detected after the completion of the roasting and are timely remedied, etc. The aluminum plant has long since not used this method to roast new tanks or overhaul tank linings, but only for secondary firing tanks. Because the coke bed method is a widely used old method, it has a large number of skilled workers and technicians, and has many years of experience, which is another major advantage of its fuel law. In addition, when a fine particle coke bed is used, the coke particles can be burned out in a short period of time after the electrolysis cell is started, without manual removal. The biggest weakness of the coke bed method is that the heating rate is not as good as the gas method and the temperature distribution is not uniform. After using the shunt and the anode soft belt, these weaknesses are greatly improved, but still not comparable to the gas method. In addition, the shunt consumes about 20% of the electrical energy, increasing the cost of roasting. It should also be pointed out that the surface of the cathode carbon block and the anode carbon block should be carefully cleaned before roasting, the coke grain size should be strictly controlled, the coke should be carefully and carefully placed, the anode and the periphery carefully placed, and a sufficient amount of broken and carefully laid. Electrolyte block and cryolite powder, etc. These are also important aspects of achieving good roasting results and should be taken seriously. The first level of the gas law in the promotion process is subject to review and approval by the security department. This takes quite a while in some areas. Although so far, there have been no safety incidents in gas roasting. However, many aluminum electrolysis plants still have concerns about the safety of gas roasting when they choose the roasting method. When using liquefied petroleum gas as fuel, the need for large pressure vessels, which increases the security risk, some of the aluminum reduction plant is also inconvenient, the use of oil as fuel can avoid high-pressure vessel problem, but unfortunately based oil as fuel The roasting equipment is less convenient to operate and control than a gas-fired roasting apparatus. The test to improve the fuel roasting method is still in progress. The aluminum electrolysis plant with natural gas supply is more convenient to use the gas method. For the prebaked tank, how to cover the electrolytic tank for heat preservation and oxidation prevention is another problem encountered by the gas method. The coverage of the self-baking tank is much easier, which is why the gas method is more suitable for the self-baking tank. In addition, it takes time and investment to purchase gas roasting equipment and personnel training. Despite these difficulties, the use of the gas-fired aluminum electrolysis plant in recent years is still on the rise. At present, all or part of the foreign aluminum company/aluminum plant adopts the gas method, such as Alcoa/Reynolds, Elkem, Alusaf, and the like. It should be noted that the method of firing initiation is related to the structure and materials of the carbon lining of the cell. When the gas roasting method is employed, the peripheral caulk paste is sintered at the roasting stage. The large amount of heat and expansion stress generated by the electrolyte and the starting cell can be transferred to the tank through the sides. If the strength of the shell is large enough (this is also the design requirement of modern cell tanks, ie the deformation of the shell should be kept within the elastic range), it will be possible to form a sufficiently large compressive stress in the carbon lining. Since the strength of the joint paste after calcination by the gas calcination method is usually larger than that of other calcination methods, it is possible to exceed the strength of the cathode carbon block. When large stresses are encountered, the carbon block may break and cause the electrolytic cell to break. Therefore, when the gas method and the cathode block with poor thermal shock resistance are used, the formulation of the joint paste should be appropriately adjusted to reduce the strength after baking. When the coke bed roasting method is used, the peripheral paste is usually sintered after the electrolyte is started to start the electrolysis cell. The plasticity of the joint paste and the shrinkage during sintering can alleviate a considerable portion of the expansion stress, so that the compressive stress formed in the liner under the same conditions is smaller than that in the gas calcination method.
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