Coke is the main raw material for smelting ferrosilicon, and it is also the reducing agent for smelting ferrosilicon. Therefore, the fixed carbon content in the coke is required to be as high as possible, greater than 84%, and the ash content of the coke is required to be low. When the ash content of coke is high, the amount of slag increases. Since the ash contains about 60% of aluminum oxide (AI2O3), the slag becomes sticky and difficult to remove. In addition, adding coke with high ash content into the furnace will easily cause the material surface to sinter, affecting the air permeability. Therefore, it is required that the ash content of coke should be less than 13%.
Most of the carbon in coke exists in the form of fixed carbon, but a small amount of carbon also exists in the form of hydrocarbons (commonly called volatiles). This part of the hydrocarbons volatilizes away at high temperatures, so the volatile content of the coke should not be greater than 2%.
In addition to the chemical composition requirements of coke, there are also requirements for its physical properties. The greater the resistance of coke at high temperatures, the deeper the electrode is inserted into the charge, which helps to increase the furnace temperature and thereby enlarge the crucible. The large porosity of coke not only has high resistance, but also has a large surface area, which increases the chemical reaction area and accelerates the speed of chemical reactions.
The particle size of coke has a great influence on smelting. When the particle size is too large, the resistance of the charge decreases, and it is difficult for the electrode to be inserted deeply into the charge, resulting in low furnace temperature, small crucible, and abnormal smelting. If the particle size is too small or there is too much powder, the burning loss will be greater, which will easily make the furnace sticky and affect the air permeability of the material surface. Therefore, coke must have a certain particle size. The particle size of coke used in large ferrosilicon electric furnaces is preferably less than 8 mm. The temperature of the small ferrosilicon electric furnace is low. In order to increase the temperature, a "smoldering" process is adopted in the operation. Adding some coke powder can help the sintering of the material surface, so that the electrode can be inserted deeper into the furnace material. Therefore, when smelting in a small-capacity ferrosilicon electric furnace, a small amount of coke powder can be used.
