Operation of Industrial Silicon Smelting (1)

Operation of Industrial Silicon Smelting (1）

The operation method of industrial silicon smelting mainly includes high-temperature smelting, correct charging, sinking and tamping, charge shape and simmering temperature raising, as well as furnace condition judgment and treatment. By accurately controlling the furnace temperature, charge ratio and electrode operation, the smelting process is ensured to be stable to obtain high-quality industrial silicon products. The operation method of industrial silicon smelting and the detailed steps of furnace discharge, furnace condition and pouring are as follows:

1. High-temperature smelting

Compared with ferrosilicon, smelting industrial silicon requires a higher furnace temperature. To produce industrial silicon with a silicon content of more than 95%, the liquidus temperature is above 1410℃, and high-temperature smelting above 1800℃ is required. In addition, since the charge is not equipped with steel scraps, the thermodynamic conditions for SiO2 reduction deteriorate, and the conditions for destroying SiC become more unfavorable. This produces three results: first, the charge is easier to sinter; second, the accumulation of flaky SiC generated in the upper charge is easy to cause the furnace bottom to rise; third, the phenomenon of high-temperature volatilization of Si and SiO is more significant. To this end, the following must be achieved during the smelting process of industrial silicon submerged arc furnace:

1) Control the high furnace temperature.

2) Control the volatilization of Si and SiO.

3) Make the formation and destruction of SiC relatively balanced.

In order to increase the furnace temperature and reduce the volatilization loss of Si and SiO, SiC should basically be kept balanced in the furnace. In the specific operation, heat loss must be reduced by all means, and the crucible must be basically maintained or expanded.

In the production of industrial silicon, the use of petroleum coke with good sintering properties is conducive to the concentration of heat in the furnace, but the material surface is difficult to sink automatically. Similar to the production of 75 ferrosilicon in a small electric furnace, a certain period of simmering and regular centralized feeding can be used.

2. Correct charging

Correct charging is a prerequisite for ensuring stable furnace conditions. This should be emphasized even more for the production of industrial silicon in a small electric furnace. The correct ratio should be determined according to the chemical composition, particle size, water content and furnace conditions of the charge. Special attention should be paid to the proportion and amount of the reducing agent used. The correct ratio should make the charge surface soft and not collapse, with good air permeability, and can ensure the specified simmering time. After the charge ratio is determined, the charge should be accurately weighed, with an error of no more than 0.5%, and mixed evenly before entering the furnace.

Inaccurate charge ratio or uneven charge mixing will cause excessive or insufficient reducing agent in the furnace, affecting the electrode insertion, shrinking the "crucible", and disrupting normal smelting.

3. Sinking and tamping the furnace

In the production of industrial silicon, petroleum coke with good sintering properties is used, and steel scraps are not added to the charge, so the charge is easier to sinter. Therefore, it is difficult for the charge of smelting industrial silicon to sink automatically, and generally forced sinking is required. When the charge in the furnace is simmered for the specified time, the charge under the surface shell is basically burned out, the surface begins to turn white and shiny, the flame is short and yellow, and there is fire and collapse in some areas. At this time, forced sinking operation should be carried out immediately. When sinking, first use the furnace tamping machine to press the shell down from the outer edge of the cone to collapse the material layer. Then use the furnace tamping machine to loosen the bottom of the cone, and push the loosened clinker on the collapsed shell on the spot. Push the large sticky and dead materials that are tamped out to the core of the furnace, and at the same time, shovel the sticky materials on the electrode. When sinking, the high temperature area is exposed, and the heat loss is large. Therefore, the sinking and tamping operation must be carried out quickly.

4. Charge shape and simmering temperature increase

After sinking and tamping, the mixed charge should be quickly concentrated in the core area around the electrode to form a flat-top cone in the furnace and maintain a certain height of the charge surface. It is not allowed to add the charge lopsidedly. The amount of new charge added at one time is equivalent to the amount of charge used for about 1 hour.

After the new material is added, it is simmered. The simmering time is controlled to be about 1 hour. The operation method of simmering and periodically sinking the material is conducive to reducing heat loss, increasing the furnace temperature and expanding the "crucible".

5. Punch holes for ventilation

When adding materials in a concentrated manner, a large amount of raw materials are added to the furnace, which may cause the temperature of the reaction zone to drop slightly. Therefore, in the early stage of adding materials, the furnace temperature is low, the reaction proceeds slowly, and the amount of gas generated will not be too much. After simmering for a period of time, the furnace temperature rises rapidly, the reaction tends to be intense, and the amount of gas generated will also increase sharply. At this time, in order to help the furnace gas escape evenly, it is necessary to "pierce holes for ventilation" at the bottom of the cone.

Petroleum coke has good sintering performance. After concentrated feeding and simmering for a period of time, it is easy to form a hard shell on the material surface, and it is easy to have block materials in the furnace. In order to improve the permeability of the furnace charge, adjust the current distribution in the furnace, and expand the "crucible", in addition to piercing holes for ventilation, a furnace tamping machine or steel rod should be used to loosen the part of the furnace charge with serious cone feet. As for thorough furnace tamping, it is carried out when sinking the material.