The paper describes the development of an automated digital system for monitoring and controlling the thermal regime of gas reverberatory furnaces for fire refining of nickel based on a mathematical model, which accounts for the control of medium-pressure burners. The specific features of the fuel combustion process and accompanying chemical reactions are considered; the chemical composition of the combustion products are analyzed for three different chemical compositions of natural gas; a mathematical modeling of the temperature field distribution is performed; the factors affecting the stability of the combustion process are considered; an algorithm has been developed to optimize the operation of the reverberatory furnace burners. New data were obtained regarding the chemical composition of the combustion products at various content ratios of natural gas and air in the temperature range from 94°C to 316°C. The thermal efficiency of the reverberatory furnace was calculated during the production of nickel alloys. The analytical results were used to derive the dependences of the temperature field distribution on the chemical composition of natural gas, which are necessary for creating an automatic control system for operating a reverberatory furnace based on the optimized control of the air-to-natural gas content ratio at a varying chemical composition of natural gas.