At present, the silicon-calcium smelting process can be divided into mixed feeding method, two-step method, layered feeding method and silicon thermal method.
The layering method is a new process that has been explored after years of practice to neutralize the advantages of the mixed feeding method and the two-step method. It has obvious advantages in reducing power consumption, improving grade rate, reducing original slope consumption, reducing cost, improving element recovery rate, and extending cycle.
1. Preferred Carbonaceous Reducant
Since the production of silicon-calcium alloy requires a larger resistance value of the charge, it is more important to increase the specific resistance and chemical activity of the reducing agent. At the same time, silicon-calcium alloy also requires a certain sinterability of the material surface, so that the material surface of the furnace mouth will not be loose and collapsed when the carbon is too low. Strengthen the sintering of the material surface.
Practice at home and abroad has proved that the use of a variety of reducing agents in silicon-calcium alloys is better, generally divided into three types of reducing agents, including charcoal, wood blocks, bituminous coal, and coke. All three types work well together.
A French company came to China to introduce that they used nearly ten kinds of reducing agents in the production of silicon-calcium alloys. A factory in my country adopted the mixed feeding method. Due to a lot of work on the selection of reducing agents, the power consumption was greatly reduced.
2. Strict requirements on lime and silica
In addition to strictly following the raw material standards to require its main chemical composition, great attention should also be paid to the particle size of the raw material. Lime particle size, the suitable lime particle size for furnaces below 1000 kVA is 20-40 mm, too small and easy to pulverize. In the past, the particle size of 40-60 mm was too large, and better results have been achieved after the particle size is reduced.
Because the particle size is reduced, the surface area can be increased, the chemical reaction speed can be accelerated, and the smelting time in the stage of forming calcium carbide by the layered feeding method can be shortened, which is beneficial to increase production and reduce power consumption.
Silica particle size varies from process to process. The layered feeding method adopts the undersieve of silica 75 silica, with a particle size of 10-25 mm. It can be used as long as the mud and sand are washed clean, and it can be used as waste, which is more beneficial for later annealing.
3. Choose to use appropriate reinforcers
In order to increase production and reduce consumption, it is necessary to make full use of some industrial waste related to Si. SiC, CaC, such as SiC, the alloy slag of silicon 75 produced by graphite electrodes, and so on.
Because these wastes contain such compounds, which are actually intermediate products in the smelting process of silicon-calcium production, the addition and utilization of these products will inevitably reduce the heat energy consumed by the generation of these products, thus reducing power consumption, increasing production, and increasing the production of silicon and calcium recovery rate.