Numerical simulation of H2-intensive shaft furnace direct reduction process

Abstract

The shaft furnace based H2-intensive direct reduction process has the potential to realize “carbon neutrality” and can significantly reduce the CO2 emission, compared to the traditional blast furnace process. To date, no commercial-scale shaft furnace using H2 has been established, due to the lack of corresponding understanding. In this work, a continuum-based shaft furnace model is developed, which considers the multi-phase flows of gas and solid, heat and mass transfer as well as key chemical reactions in the direct reduction process. It is validated by comparing the simulated performance indicators with those measured in the plant. Using the model, the effects of the pressure at the cooling gas outlet have been studied. The results show that the pressure at the cooling gas outlet has a significant impact on in-furnace gas flow, which should be carefully controlled to separate the reducing and cooling gas effectively. As for the product, the carburization and metallization of direct reduced iron can also be optimized through proper control of the pressure at the cooling gas outlet. On this basis, under the same injection rate, the production using H2 is compared with the normal one using reformed natural gas, under their respectively optimized conditions. It is shown that the production with H2 delivers direct reduced iron with less carburization and metallization. Charging large-sized pellets into the furnace centre can solve the problems to a degree by improving the gas flow distribution in the reducing zone. This work should provide a deeper insight into the cleaner production of the shaft furnace based direct reduction process, particularly that operated with H2.