Why can ferrosilicon be smelted with silica, coke and steel chips after high temperature heating in submerged arc furnace? To know this truth, we must first understand the change law of various raw materials used in smelting ferrosilicon under various high temperature conditions.


The main raw material for smelting ferrosilicon is silica, which contains about 98% silicon dioxide Silicon dioxide is very stable, and the affinity between silicon and oxygen is very strong, so it is not easy to separate. In production, in order to separate and remove oxygen from silica, carbon in coke is used to capture oxygen in carbon dioxide under high temperature conditions in submerged arc furnace, and the higher the temperature, the greater the ability of carbon to capture oxygen. This is because the binding capacity of carbon to oxygen is greater than that of silicon at high temperature. It can be seen that with carbon at high temperature, silica is unstable. At this time, oxygen in silica reacts with carbon to produce gaseous carbon monoxide, which escapes from the furnace mouth through the material layer. After the oxygen in silicon dioxide is taken away by carbon, the remaining silicon and iron form ferrosilicon. Among them, a certain amount of silicon and iron form compounds, such as fesi5, fe2si5 and fesia. Silica reacts with carbon as follows: SiO2 + 2C = Si + 2CO ↑ the above formula is an endothermic reaction. It can be seen from the reaction formula that in order to accelerate the reaction, the electrode should be inserted deeper into the charge to improve the furnace temperature and expand the crucible area. At the same time, the air permeability of the charge surface should be increased to make the carbon monoxide gas escape as soon as possible. If measures such as pricking the vent hole and tamping the furnace are taken, the reaction between carbon dioxide and silicon will be accelerated and ferrosilicon will be generated quickly.


Because there are steel chips and iron in the submerged arc furnace in smelting ferrosilicon, the reduction reaction of silicon dioxide is easier. This is because the reduced silicon and iron form ferrosilicon, which improves the conditions of the reduction process. Therefore, the more iron, the easier the reduction reaction of silicon dioxide. The production also proves this. The lower the silicon content of ferrosilicon, the lower the unit power consumption. For example, the power consumption of smelting 45 ferrosilicon per ton is about 4500 ~ 4800 degrees, and the power consumption per kilogram of silicon is about 11 degrees. The power consumption of smelting 75 ferrosilicon per ton is about 8200 ~ 9000 degrees, and the power consumption per kilogram of silicon is about 12 degrees. The power consumption of smelting each ton of silicon is about 12000 ~ 13000 degrees, and the power consumption per kilogram of silicon is about 13 degrees.


In terms of chemical reaction, it is generally believed that the reaction in which oxygen in oxide is taken away by other substances is called reduction reaction. Substances that capture oxygen are called reducing agents, such as coke. According to the above ferrosilicon smelting principle, it is a reduction process.


In the reaction process, most of the silica in the silica is reduced by carbon. In addition, other impurities and ash brought by coke, such as calcium oxide (CAO), phosphorus pentoxide (P2O5) and aluminum oxide (AI2O3), are also reduced by carbon, and most of phosphorus pentoxide is reduced. Each reaction is as follows: Cao + C = Ca + CO ↑ P2O5 + 5C = 2p + 5cO ↑ AI2O3 + 3C = 2ai + 3Co ↑ the carbon monoxide gas generated in each reaction escapes from the furnace mouth, and other products such as calcium, aluminum and phosphorus enter ferrosilicon. Therefore, it is required to minimize impurities in raw materials to ensure the quality of ferrosilicon.


In the smelting process, a small part of silicon dioxide, aluminum oxide and calcium oxide are not reduced to form slag. The composition of slag contains about sio230 ~ 40%; AI2O345～60﹪; CaO10～20﹪。 The melting point of this slag is about 1600 ~ 1700 ℃ When the amount of slag is large, the power consumption increases, and the over sticky slag is not easy to be removed from the furnace, resulting in the deterioration of the furnace condition. Therefore, better raw materials should be used to reduce the amount of slag and reduce the unit power consumption.


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