With the intent of exploring feasible options for improving the efficiency of a hydrogen‐operated direct reduction shaft furnace, this study utilizes a computational fluid dynamics model to assess the performance of a retrofitted unit configuration featuring selective gas recycling. In particular, the effects of upper‐row injection level and furnace top pressure are investigated, providing a sufficient upper‐row feed rate of the recycled off‐gas with high reducing potential. The results show that the new configuration is a viable option for enhancing the hydrogen reduction process. A decrease in the upper‐row injection level not only yields a higher solid reduction degree but also causes a larger overall fluidization factor due to the increase in gas pressure drop. Under the conditions where the upper‐row injection level and furnace top pressure are 4.0 m and 150 kPa, the fluidization factor tends to surpass unity, which is the threshold representing the occurrence of particle fluidization. However, the detrimental phenomenon can be effectively suppressed by increasing the top pressure to 250 kPa since the fluidization factor is found to be well below unity. Although the fluidization factor can be further lowered by applying a higher top pressure, the energy demand for compressing the feed gas increases linearly.
Zhao et al. (Fri,) studied this question.