Comprehensive mathematical model of direct reduction for rotary hearth furnaces

A comprehensive mathematical model was established to develop and deeper understand direct reduction technology for rotary hearth furnaces (RHF). The model consists of the overall thermal and chemical balance model, the calculation model of heat balance at different zones, the waste heat recovery process model, the drying model of green pellets, the checking model of furnace box temperature and waste gas dew point, and the RHF process model. The basic process parameters of RHF were calculated by the model. Calculation results show that the overall energy consumption is effected by gas calorific value, waste gas temperature, and the recycling scheme of waste heat recovery. When the gas calorific value increases by 50 kJ·m^-3, the theoretical combustion temperature increases by 22 to 25℃, and the gas consumption decreases by 41 to 47 m³·t^-1. But when the preheating temperature increases by 100℃, the theoretical combustion temperature increases by 35 to 40℃, and the gas consumption decreases by 90 to 103 m³·t^-1. Furthermore, the model can be applied to calculate technical parameters when the raw materials and fuel conditions are different, and the change laws of these technical parameters under different waste heat recovery processes can also be studied by this model.