Study of the effect of regenerative heat transfer enhancement on the silicothermic reduction process

Abstract

As the main process for industrialized production of crude magnesium, the silicothermic reduction technology has problems such as high energy consumption per ton of magnesium and serious pollution. Under the policy of carbon peak and carbon neutrality, the implementation of energy conservation and pollution reduction technology reform has become an urgent issue in the silicothermic reduction process. Although the thermal conductivity of the briquettes used for magnesium production is low, they will absorb a lot of heat during the reduction reaction. As a result, the heat cannot be transferred quickly enough for the chemical reaction endothermic, leading to a slow magnesium production reaction and low production efficiency. Therefore, in-depth study on the kinetic mechanism of the improved heat transfer coupled chemical reaction is required to decrease the production cycle and increase efficiency. In this work, the effect of filling the voids of briquettes with regenerative particles of different materials on heat transfer process was first studied by means of experiments. It has been discovered that as the thermal conductivity of the filling material increases, the heat transfer process is accelerated, but the endothermic behavior of the regenerative particles at room temperature during the heating process seriously affects the heat transfer to the briquettes. On this basis, the models of heat transfer and magnesium reduction kinetics were combined and the recycling technology of high temperature regenerative particles with different materials was studied by numerical calculation method. The findings demonstrate that the production cycles for filling aluminum oxide, silicon carbide and silicon nitride are reduced to 6, 4 and 1 h, respectively, at the initial temperature of 1373 K for the regenerative particles, compared with the 8 h of the traditional method. However, when the voids of the briquettes are filled with quartz sand with a thermal conductivity close to that of the briquettes, the period increases to more than 10 h. When the initial temperature of the filled regenerative particles decreases, the production cycle also increases. In industrial production, materials with high thermal conductivity should be selected as regenerative particles as far as possible on the basis of considering the cost, and thermal insulation measures should be taken to minimize the heat loss during the recycling of regenerative particles.