Experimental and numerical studies on heat transfer enhancement in the silicothermic reduction process

Currently, the silicon thermal method is the main process to produce primary magnesium, which is controlled by chemical reaction kinetics and the heat transfer process in the retort. However, the unbelievably low thermal conductivity and point contact thermal resistance of the pellets greatly reduce the heat transfer efficiency, resulting in low magnesium production efficiency. To increase productivity, the enhanced heat transfer mechanism was studied in detail by experiments in this paper. The results show that temperature rise may not accurately reflect the enhanced heat transfer effect, thus a synthetical valuation method which took total heat transfer, effective heat transfer ratio and temperature rise into account is proposed. On this basis, a new recycling technique which uses high temperature silicon carbide particles to enhance the heat transfer in the retort is developed. Then a three-dimensional unsteady numerical model incorporating the chemical reaction kinetics and heat transfer was established and used to prove the superiority of this new technique in terms of heat transfer efficiency, magnesium production rate and production cycle. Numerical results show that when the initial temperature of silicon carbide is 1373 K, the instantaneous magnesium production rate can reach 13.2 kg/h within 30 min of heating, which is three times that of the traditional silicothermic process. The production cycle could also be shortened to 240 min, which is half of the original, and the production efficiency can be doubled. This new technique can significantly improve heat transfer efficiency, shorten the production cycle and reduce the production cost. (c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).