Operation enhancement of the H2 shaft furnace: a numerical study on the impact of N2 mixing in feed gas

Abstract

Focusing on improving the performance of the hydrogen (H2)-based direct reduction shaft furnace (HSF), the current work was undertaken to evaluate the potential benefits of an operation featuring nitrogen (N2) mixing in feed gas using a computational fluid dynamics (CFD) model that describes the in-furnace gas-solid countercurrent reactive flows. A set of simulation cases was carried out under different N2 flow rates and top pressures. Variation in the latter operating parameter was conducted with the intent to mitigate the issue of H2 dilution caused by N2 mixing. The results showed that the in-furnace thermochemical state deteriorates if the N2 flow rate is inadequate. The state is gradually improved by increasing the N2 flow rate as more sensible heat is delivered into the process, thereby resulting in better degrees of solid reduction and H2 utilization. An increase in the top pressure gives rise to higher gas density that enhances the driving force and thus facilitates the reduction reaction. A higher solid reduction degree is consequently achieved by elevating the top pressure. When the top pressure exceeds 5.0 atm, however, the increase in solid reduction degree becomes marginal, while the energy required for compressing the feed gas continues to rise linearly.