At present, there are mainly five production methods for high-quality ferrosilicon in China. One is to use selected furnace materials to produce high-purity ferrosilicon; The method of top-blowing oxygen is used to produce high-purity and low-aluminum ferrosilicon. The fourth is to produce high-purity and low-carbon ferrosilicon by hot flushing slag washing. The fifth is to produce low-aluminum and low-carbon ferrosilicon by selecting furnace materials.
The production of high-purity ferrosilicon by using the method of selecting furnace materials is mainly to smelt and produce raw materials such as quartz stone, petroleum coke, wood block, charcoal and silicon steel sheet, so as to reduce the content of impurity elements in the product. Due to the large fluctuations in the quality of raw materials in this method, some impurities are inevitably brought in during the smelting production process, so that the reduction rate of the impurity content in the product is limited, the product quality is not high, the yield is low, and the production furnace is difficult to maintain. The operation of the furnace mouth is difficult, the production cost and energy consumption of the product are relatively large, and the economic indicators are relatively poor.
The furnace method has a better effect in removing calcium and aluminum, but there are more tail gases, and there are often leakages and chlorine-blowing graphite tubes broken in the production to stop refining, which seriously pollutes the environment, endangers the health of workers, and has a negative impact on production. The equipment is highly corroded.
The method of top blowing oxygen outside the furnace is used for refining outside the furnace, which is also good for removing impurities such as calcium, aluminum and carbon in the product. However, in the process of use, due to the violent tumbling of the molten iron and the large splash loss, the temperature of the molten iron drops rapidly, resulting in sticking and large iron loss, and the statistical loss is 12%-20%. Graphite tubes for oxygen blowing are also often broken and refining is suspended, resulting in low yields and economically uneconomical.
The production of low-aluminum and low-carbon ferrosilicon by the method of selecting furnace materials is mainly to smelt and produce raw materials such as selected reducing agents, such as blue carbon and gas coal coke, so as to reduce the impurity elements in the product, mainly the purpose of aluminum content. Due to the large fluctuations in the composition of raw materials in this method, some impurities are inevitably brought in during the smelting process, so the reduction rate of the impurity content in the product is limited. The aluminum content can generally be reduced to 1.6%, and the maximum can only be reduced to 1.2%. The carbon content 0.2%, only some brands of products can be produced.
The production method of high-quality ferrosilicon comprises the following steps:
1. Screening raw material silica, reducing agent, steel powder or/silicon steel shavings, silica is quartz stone or white silica, black silica, reducing agent is metallurgical coke and gas coal coke, or semi-coke and gas coal coke, semi-coke and petroleum coke and wood blocks, According to the exact component content of various raw materials and the requirements for all element components of the species to be produced, the amount of each raw material is calculated according to known technology, and the ingredients are mixed and filled into the submerged arc furnace for smelting according to the usual conditions and operations for smelting ferrosilicon alloys.
2. Add the calculated amount of pre-melted synthetic slag or/and silica fume, quartz powder, CaF2 or CaO to the refined iron ladle before the furnace is covered with bottom oxygen blowing refining and ferrosilicon is discharged from the submerged arc furnace to adjust the composition of the slag to a weight content of SiO2 > 60 %, CaO < 30%, others < 10%, heat the molten iron ladle and pre-melt the slag and bake it to > 200°C, put it into the submerged arc furnace to release the molten iron, and at the same time blow oxygen or air through the bottom of the ladle, oxygen plus helium , Air plus helium, air plus oxygen for refining outside the furnace, gas pressure > 0.5MPa, gas flow > 6Nm3/h, refining time 30-40 minutes.
3. It is required to remove the silicon carbide (SiC) precipitated on the surface of the ferrosilicon containing C<0.03% and the slag adhered to the surface of the ingot after the ingot is cooled, so as to obtain high-quality ferrosilicon products.
This method mainly has the following advantages:
1. This method has the advantages of wide coverage and strong applicability. It can accurately control the impurity elements according to the quality requirements of various types and grades of ferrosilicon alloys. Using the same method, a series of high-quality ferrosilicon can be produced.
2. Through the scientific and reasonable screening and proportioning of raw materials, the content of impurity elements in the product is controlled, which is beneficial to the maintenance and operation of the submerged arc furnace, reduces consumption, and improves technical and economic indicators.
3. Bottom blowing oxygen refining outside the furnace, high efficiency, sufficient thermodynamic conditions, can effectively control the content of impurity elements in the product, and the refining loss is small, and the equipment is not easy to damage.
4. Oxygen blowing refining has no air pollution, which ensures the health of workers and the safe operation of equipment.
5. Low-temperature casting and surface treatment of ferrosilicon can further reduce the impurity content of the alloy to ensure product quality.