[China Aluminum Network] The application of aluminum contributes to lightweighting, energy saving and emission reduction, but electrolytic aluminum is also a high-energy-consuming industry. In China, the electricity consumption of electrolytic aluminum alone in 2016 accounted for approximately 7.25% of the electricity consumption of the entire society. At the same time, it is regrettable that during the production of aluminum electrolysis, about 50% of the energy input to the electrolyzer was lost in the form of waste heat. Among them, about 35% of the emission of flue gas, about 8% of the upper structure of the electrolytic cell, about 35% of the side of the electrolytic cell, and about 22% of the bottom cathode. Raising the level of energy efficiency in the production of electrolytic aluminum is not only an urgent requirement of the country for energy saving and emission reduction, but also a direction for enterprises to improve operational efficiency and achieve sustainable development.
After more than 10 years of hard work, Cronus Technology AS of Norway has developed a unique aluminum waste heat recovery and active cooling system, which can provide new ideas and efficient solutions for energy saving, emission reduction and elastic production in the electrolytic aluminum industry. .
The technology uses the heat pipe principle. The heat pipe is a heat transfer device and is a super heat conductor. The heat pipe combines the principle of heat conduction and fluid phase change. The working fluid in the heat pipe can be switched between liquid and gas. Its thermal conductivity is 1000 times that of copper.
The active cooling system of aluminum electrolyzer includes four main parts: oil station, collector, control system and pipeline. The low-temperature heat transfer oil in the oil station first enters into the heat collector of the flue gas system through the pipeline, cools the flue gas, collects the heat in the flue gas, and then enters the collector on the side of the electrolytic cell to collect the side of the electrolytic cell. The heat of the wall; then it enters the heat exchanger and converts or uses the collected heat; the cooled oil then enters the petrol station and completes a cycle.
The side collector of the cell is isothermal and does not have thermal stress. The bolts are fixed in the middle of the cradle of the side wall of the electrolytic cell, and there is an insulating layer outside to prevent heat loss.
By controlling the flow rate of the heat transfer oil, the cooling rate of the electrolytic cell can be controlled. Thus, the thickness of the ledge and the heat balance of the cell can be controlled.
In this way, the electrolytic cell can be provided with a stable and controllable working environment, so that its production is not affected by seasonal changes. When the electrolysis cell roast is started, the active cooling system helps to increase the heating rate of the electrolysis cell shell, thereby reducing the thermal expansion of the shell and the refractory material, thereby prolonging the life of the electrolytic cell.
In addition, the active cooling system offers the possibility to adjust the current intensity and cell production. When it is necessary to increase the output, the current can be strengthened, and the cooling rate can be increased at the same time to prevent the electrolytic cell from overheating. When it is necessary to reduce the output, the current intensity can be reduced while the cooling rate can be lowered (the cooling rate can be zero). The device can play a role in insulation (because of the outer insulation layer) and also prevent the cell from being over-cooled.
Under normal production conditions (without adjusting production), this technology can recover about 40% of total heat loss. It is estimated that China currently has approximately 55,000 electrolyzers. In 2016, the output of primary aluminum was approximately 32 million tons, electricity consumption was approximately 433.4 billion degrees, and heat loss was approximately 216.7 billion kilowatt-hours. Assuming that the domestic electrolytic aluminum industry uses this technology, the total amount of heat that can be recovered is approximately 86.6 billion kilowatt-hours, roughly equivalent to the electricity consumption of 170 million urban and rural residents; it can reduce carbon dioxide emissions by approximately 65 million tons, equivalent to the emissions of 23 million vehicles. . This will be a huge potential for energy saving and emission reduction. Of course, the actual energy-saving effect also depends on the way and efficiency of recycling heat energy.
The heat recovered from the electrolyzer is clean energy and can be used for a variety of purposes and energy conversion methods. Including power generation for coal-fired power plants, heating of the steam turbine's feed water; community heating, cooling; low-temperature power generation; and factory heating of materials. The waste heat utilization mode can have different energy reuse patterns based on factors such as the electrolytic aluminum plant's own industrial chain support, the industrial layout of the region, and geographical features.
The technology has undergone more than 10 years of research and development, testing and continuous improvement. In April 2014, this system was installed on a cell in Dubai Aluminum. It has been running smoothly for more than 3 consecutive years without any problems. Groove control and monitoring, heat recovery, system safety and stability have been verified. However, because this cell is one of the entire series, it has not yet been able to verify its intensified current and regulate the actual effect of production. In the next step, this technology is expected to be the first to achieve industrialization in the aluminum industry in China, where the challenge of energy conservation and emission reduction is greater and the capacity is greater. At present, Konas Technology Corporation is conducting exchanges and negotiations with potential partners in China. On the one hand, it promotes the heat recovery function of the system. On the other hand, it further develops and improves the system's function of regulating aluminum production and achieving flexible production.
Konas Technology believes that this technology has multiple meanings and values ​​in China's electrolytic aluminum industry.
First, comprehensive utilization of the heat recovered from this system in various forms can reduce the overall coal-fired and energy consumption of enterprises, improve energy efficiency, and reduce operating costs.
Second, while reducing coal consumption and energy consumption, it has also correspondingly reduced carbon emissions and alleviated the growing environmental pressures faced by electrolytic aluminum companies.
Third, under normal circumstances, by controlling the heat balance of the cell, the current can be strengthened, and the yield per cell can be increased by 20%.
Fourth, when it is necessary to cut production and limit production, it is also possible to reduce the current intensity by controlling the heat balance of the electrolytic cell and achieve a production reduction of about 20% without stopping the tank. This will avoid the loss of production from the stop tanks and the economic losses and the loss of life of the electrolyzers that are brought back to the company. What's more important is to reduce the generation of solid waste caused by stop tanks, reduce unorganized pollutant emissions and greenhouse gas emissions from reopening and abnormal adjustment periods, and reduce environmental pollution.
In short, enterprises can implement limited production or peak production without stopping the production in accordance with environmental protection policy requirements. According to aluminum prices and cost accounting, we can adjust output at any time to achieve flexible production, optimize production organization and improve adaptability. The relevant departments can also monitor the production limits of electrolyzers in real time through the control system.
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