In aluminum smelting, equipment such as rotary kilns, electrolyzers and smelting furnaces require specific refractory materials to withstand factors such as high temperatures, chemical attack and mechanical impact. For example, in rotary kilns, high alumina bricks and magnesia chrome bricks are used as the main refractories materials, while in electrolyzers, materials with good antioxidant properties, such as silicon nitride-bonded silicon carbide bricks, need to be selected. For smelting furnaces, it is necessary to consider properties such as resistance to erosion by liquid aluminum and magnesium vapor, resistance to wear, and resistance to thermal shock. Therefore, these factors must be taken into consideration when selecting refractories materials.
In global non-ferrous metal production, the annual output of aluminum far exceeds that of other non-ferrous metals. The annual consumption of refractory materials by the aluminum industry is much larger than the total amount of refractories materials consumed by copper, lead, and zinc smelting. The production method of metallic aluminum adopts a two-step fixation method: first, alumina is produced from bauxite by wet method; second, metallic aluminum is produced by molten salt electrolysis using industrial alumina as raw material. High-temperature kilns used in the production process include rotary kilns, molten salt electrolyzers, aluminum melting furnaces, etc.
Industrial alkaline substances will seriously corrode the refractories materials in the rotary kiln. During the aluminum smelting process, metallic aluminum has strong penetration ability even at lower temperatures. Once it penetrates into the bricks, it will react with SiO2, causing the Si element to be reduced, destroying the structure of the refractory material, causing the furnace lining to produce a deteriorated layer, becoming loose, peeling and damaged. The reaction equation is: 3SiO2 + 4A1 -2A12O3 + 3SiO2.
Therefore, refractory materials containing SiO2 cannot be used as furnace construction materials for aluminum metal smelting equipment. Generally speaking, in addition to high alumina bricks, It used in aluminum industrial furnaces usually use carbonaceous products.
At present, when producing alumina in our country, we mainly use two methods: sintering method and combined method. This is mainly due to the supply of raw materials. The processing of bauxite usually includes drying and tenderizing, roasting of aluminum hydroxide, etc., and most factories use rotary kilns to carry out these processes.
Rotary kiln is a kiln used for calcining alumina clinker. In the production of alumina, bauxite, soda ash and lime are first prepared in proportion and put into a rotary kiln. After being fired at a high temperature of 1200~1300°C, they are released from the furnace and then processed appropriately to make aluminum hydroxide and mother liquor; Alumina is put into a rotary kiln and calcined at a high temperature of 1200°C. The calcining process in the rotary kiln is as follows: the high-temperature flame and materials move in reverse directions in the furnace. Soda lime bauxite raw material slurry containing 40% water or aluminum hydroxide containing 12% ~ 18% water is added from the end of the kiln. After low-temperature drying, dehydration, heating, and high-temperature calcination, it is discharged from the kiln head, and the high-temperature gas flows from the kiln head to the kiln. Kiln tail flow. Therefore, the kiln is divided into a preheating zone and a high-temperature calcination zone. In order to avoid slurry sticking to the kiln lining during the heating and calcining process and enhance the heat transfer process, chains are also set up between the refractory bricks, which continuously hit the materials and lining bricks during the rotation, affecting the service life of the kiln lining. .
The rotary kilns used in the production of alumina are made of welded steel plate cylinders covered with refractory materials. This kind of refractory material is in a harsh working environment and the working conditions are very harsh. It needs to have the following characteristics: strong resistance to alkali erosion; able to work at high temperatures of 1200~1300°C for a long time without damage; able to withstand the impact of dynamic loads; able to resist the erosion of the charge; Washing by high-temperature airflow. The refractories materials used in rotary kilns are mainly high alumina bricks and magnesia chrome bricks, while low-temperature drying kilns use clay bricks as linings.
