CFD study of charcoal combustion in a simulated ironmaking blast furnace

Abstract

Biomass is a carbon-neutral solid fuel and has the potential to replace coal in pulverised coal injection (PCI) operation of ironmaking blast furnaces (BFs). In this study, a three-dimensional (3D) computational fluid dynamics (CFD) model is used to evaluate the charcoal combustion behaviours under a range of PCI conditions. The key PCI variables include blast temperature, O2 concentration in the blast, mean particle size of charcoal, and charcoal injection rate. In particular, the combustion behaviours are investigated and compared at two locations, namely, along the centreline and over the entire chamber. The simulation results indicate that the final burnout along the centreline is more sensitive to the changes of operational conditions compared to the burnout over the entire chamber under the BF conditions. Furthermore, the effects of key operational variables on the two burnout calculations are identified quantitatively. For example, the increased blast temperature or the reduced mean particle size can improve the two burnouts both, due to the extra energy provided and large surface area, respectively. However, the increased O2 concentration in the blast from 21% to 23% can improve the final burnout only from 64% to 72%, but the further increase of O2 concentration in the blast cannot lead to a further increase for both two burnouts. High blast temperature, high oxygen concentration and fine particle size will allow for a higher burnout. This study provides an effective method of understanding and optimising biomass injection in BF practice.