Numerical Investigation of Shaft Gas Injection Operation in Oxygen-Enriched Ironmaking Blast Furnace

Shaft gas injection is considered helpful for realizing an oxygen blast furnace (OBF) to mitigate CO₂ emissions substantially. This paper presents a systematic study of the shaft injection for a 430-m³ industrial OBF using a process model. The OBF is operated at 35, 50, or 100 pct oxygen enrichment. It is combined with the reducing gas injection through blast tuyeres to achieve a reasonable flame temperature. The effects of shaft gas injection rate, shaft gas injection position, and shaft gas injection temperature are studied with fixed hot metal temperature, bosh gas volume, and flame temperature. The results show that the fuel rate decreases as the oxygen enrichment increases. It also decreases with increasing shaft gas injection rate/temperature but increases at a higher injection position. All these changes slow down when the values of the three variables are relatively large. At a higher oxygen enrichment or lower shaft gas injection position/rate, the replacement ratio of coke by the shaft injected gas increases, indicating better utilization of shaft gas energy. However, the replacement ratio increases first to a maximum and then gradually decreases with increasing shaft gas injection temperature, identifying an optimum injection temperature. The inner flow and thermochemical behaviors of OBF are analyzed in detail. It shows that the fuel reduction by shaft injection is a collected effect of decreased carbon consumption by raceway combustion and direct reduction. The former contributor plays a dominating role, benefiting from the pre-heating effect. The latter contributor results from the indirect reduction enhancement because of the intensified reducing atmosphere and increased temperature. These pre-heating and pre-reduction roles are quantified to elucidate the impacts of the flow rate, position, and temperature of shaft injection.