[China Aluminum Industry Network] In the process of aluminum smelting and processing, a large amount of waste heat has not been properly used, causing huge heat losses. Typical waste heat including exhaust heat from electrolytic aluminum flue gas and waste heat from aluminum smelting, heating, and aging treatment.
The modern aluminum industry uses cryolite-alumina molten salt electrolysis. Molten cryolite is a solvent, alumina as a solute, carbon body as an anode, and aluminum as a cathode. After a strong direct current is passed, an electrochemical reaction is performed at two poles in the electrolytic cell at 950°C-970°C. Electrolysis. Anode products are mainly carbon dioxide and carbon monoxide gas, which contains a certain amount of harmful gases such as hydrogen fluoride and solid dust. The cathode product is aluminum liquid. The aluminum liquid is pumped from the tank by vacuum lifting and sent to the foundry. After being purified and clarified in the holding furnace, it is cast into aluminum ingots or directly processed into wire blanks and profiles. Taking a certain type of electrolytic cell as an example, the average flue gas volume in a single cell is about 10000m3/h. The temperature of the electrolyzer flue gas after mixing with air is about 110~130°C. The electrolysis plant is often composed of dozens or hundreds of electrolytic cells. The potential for the utilization of waste heat from electrolytic flue gas is very large.
During the processing of aluminum, the smelting, standing, and soaking process of aluminum alloy during smelting and casting, the ingot casting, mold heating, aging treatment and quenching during the aluminum alloy extrusion process, and the aluminum surface treatment The process of cleaning, drying, curing, etc. involves the efficient use of thermal energy and has a large space for energy conservation. In particular, the flue gas of various heating furnaces has the characteristics of high temperature and large displacement, and is the main heat loss path, and should be used as the focus of waste heat recovery and utilization. Taking a smelting furnace as an example, only about 25% of the total heat consumption is carried away by the aluminum liquid, and the exhaust heat loss is as high as 42% of the total heat. At the same time, the furnace temperature of each furnace is high and the utility value is high. Taking a smelting furnace as an example, the temperature of the flue gas can reach 1000°C or more when heat recovery is not used. Even if the recovery device is used, the temperature of the final flue gas can reach 150°C or more, which is of continuous use value.
In addition to the above waste heat, other waste heat discharge sites in the aluminum industry plant include boiler flue gas waste heat, boiler condensate waste heat, surface treatment line hot water wash tank waste water waste heat, and surface treatment line workshop air conditioning waste heat. The residual heat of the boiler flue gas is similar to the flue gas emitted from the aluminum smelting and processing process. The flue gas temperature is relatively high and has good use value. In addition to the residual heat of the flue gas, the residual heat discharged by the gaseous medium also includes the ventilation heat of the workshop air conditioning and so on. Although the exhaust heat of the air-conditioning exhaust is low in temperature, it also has great reuse value due to continuous operation and large emission. The waste heat discharged by water as medium has a small amount of emissions, but because the specific heat capacity of water is much larger than that of air, the heat exchange performance is also better than that of air, making the residual heat of boiler condensate water, and the residual heat of the surface treatment line hot water washing tank discharge water also has economic utilization. value.
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