Three-dimensional modelling of charcoal combustion in an industrial scale blast furnace

Abstract

Charcoal, a biomass-derived fuel, has the potential to replace coal in pulverised coal injection (PCI) in ironmaking blast furnaces (BFs) and enable low-carbon ironmaking. However, the flow and thermochemical in-furnace phenomena related to charcoal combustion are not clear under industrial-scale BF conditions yet. In this study, a three-dimensional (3D) industrial-scale computational fluid dynamics (CFD) model is developed for describing the flow and thermochemical behaviours related to charcoal injection under the real BF conditions. The computational domain includes lance, blowpipe, tuyere, raceway and the surrounding coke bed regions. The model features industrial-scale BF conditions, coke bed around the raceway, non-spherical particle shape of charcoal particles, and modified sub-models of charcoal chemical reactions. The in-furnace phenomena of charcoal injection are simulated. The combustion profile of the charcoal is then compared with two typical PCI coals. The simulation results indicate that their burnout profiles are comparable qualitatively, confirming the potential of charcoal utilisation in PCI technology. Compared to the two typical PCI coals quantitatively, the charcoal combustion process is delayed along the charcoal plume by moisture evaporation but improved in the subsequent recirculation region located above the plume due to its non-spherical particle shape and higher reactivity, indicating the charcoal injection and its control strategy should be re-designed for BF practice, for example, the finer charcoal particles can improve the degree of recirculation and enhance the burnouts. This industrial-scale model is a useful and cost-effective tool for understanding the combustion behaviour of pulverised charcoal and optimising charcoal injection operations for low-carbon ironmaking.