The reduction method is one of the most widely used metallurgical processes in the production of ferroalloys, steel and other metals. The direct reduction process using external hot vertical furnace has many advantages, such as simple process, low energy consumption and high production efficiency, making it increasingly favored.
External hot vertical furnaces use coal or natural gas as the fuel, while reserving carbon, solid reductants, and semi-solid ones. The ore is fed into the upper part of the furnace, and the reductant and ferroalloy are co-fed. The reductant is generally C or SiC. The hot air is pushed from the lower part of the furnace, so that the reaction happens from bottom to top. The hot air converts the reductant and ore into gasified reductant and smoke with some metallic vapor. The self-reduction and reduction of the ore by the reductant happens in all parts of the furnace, then, the final product ferroalloy is discharged from the lower part. The self-reduction occupies the big proportion of the reaction rate. The pre-heated ore is reduced by carbon monoxide and hydrogen when the ore is exposed to the reducing atmosphere of high temperature. The reaction which is accompanied by the temperature and pressure increase occurs in the normal temperature region. The externally heated vertical furnace is operated tightly under sealed atmosphere, in this way, it could decrease the dissipation into the surrounding environment.
The quality of the product can be adjusted by the controlling of the specific process parameters, such as reductant compound rate, ore location, reaction temperature and duration, etc. The reaction temperature is a primary parameter, and it could significantly affect the rate of carbon monoxide reduction and the metallization rate of metallic ions. The ore with high content of oxidized compounds needs higher reaction temperature than the ore with lower oxidized compounds content. The reactions of the ore and reductants are complicated, and the formation and distribution of the compounds affected by reaction temperature also influences the quality and quantity of the product.
Meanwhile, the duration of the heat-retention phase of the external hot vertical furnace is an important factor influencing the reaction rate, product quality and the discharge quantity, which is decided by the increase frequency of the reaction temperature. The close-sealed operation of the external hot vertical furnace helps to minimize or totally avoid the gas leakage.
The external hot vertical furnace is an efficient and environment friendly method in the production of ferroalloys. Continuous technological advances have been made to develop more automated and environment friendly processes. This process is believed to be one of the most promising metallurgical processes in the future.
