2022年7月4日星期一

Why Can a Small Amount of Silicon Carbide be Used in Smelting Ferrosilicon?

Smelting Ferrosilicon


Why Can a Small Amount of Silicon Carbide be Used in Smelting Ferrosilicon?


In order to reduce unit power consumption, some units add a small amount of silicon carbide (SiC) when smelting ferrosilicon, which can save some electric energy. The "silicon carbide" referred to here is not a specific raw material, but the thermal insulation waste of the graphitization furnace when manufacturing graphite electrodes. It contains a lot of silicon carbide, so it is customary to call this waste "silicon carbide". Its ingredients are as follows:

SiC25~40%; SiO220%; C25%; the rest are Al2O3 and CaO, etc. Why adding a small amount of "silicon carbide" during smelting can reduce power consumption.

When ferrosilicon is smelted, the reduction of silicon dioxide is a reaction that absorbs a large amount of heat energy, so this reaction can be carried out intensely at a very high temperature (about 1800-1900 °C), so a large amount of electric energy is consumed. When part of silicon carbide is added to the charge, it reacts with the steel chips in the charge as follows in the furnace:

SiC+Fe= FeSi+C

This reaction is an endothermic reaction, and the heat and reaction temperature it absorbs are lower than those required for the reduction of silica. Therefore, adding part of silicon carbide to the charge can reduce power consumption.

The smelting of 45 ferrosilicon is mainly carried out according to SiC+Fe=FeSi+C due to a large number of steel scraps in the charge, and the destruction reaction of silicon carbide. Therefore, the utilization rate of silicon carbide is higher at this time.

In the smelting of 75 ferrosilicon, due to fewer steel scraps and more silica in the charge, the destruction reaction of silicon carbide will be mainly carried out as follows:

2SiO2+SiC= 3SiO+CO↑

SiO+SiC=2Si+CO↑

Both reactions are carried out at high temperatures above 1800 °C, and gaseous SiO participates in the reaction. On the other hand, since gaseous SiO is more volatile, the reaction of destroying silicon carbide cannot be carried out more safely. It can be seen that the utilization rate of silicon carbide is low when smelting 75 ferrosilicons.

The practice has proved that adding part of silicon carbide when smelting 45 ferrosilicons in a large-capacity submerged arc furnace has a more significant effect. Part of silicon carbide is added when smelting 75 ferrosilicons, and the effect is not significant.

Silicon carbide has a high melting point and strong electrical conductivity. After adding reinforced silicon during smelting, the electrode is not easy to stabilize, the furnace condition is not easy to control, and there is a lot of silicon carbide powder, which affects the air permeability of the material surface, and sometimes stabs are serious. For this reason, it is not easy to add too much silicon carbide during smelting, and the silicon carbide used should be selected to reduce powder.

Experience has proved that when smelting 45 ferrosilicons, each batch of materials (calculated as 300 kilograms of silica) can add 50-70 kilograms of silicon carbide; when smelting 75 ferrosilicons, it is more appropriate to add 20-30 kilograms per batch.

Do not add silicon carbide to the small ferrosilicon submerged arc furnace to prevent the furnace from deteriorating.


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