Transient 3D CFD study of pulverised coal combustion and coke combustion in a blast furnace: Effect of blast conditions

Abstract

The pulverised coal combustion and coke combustion in the raceway of an ironmaking blast furnace (BF) is the key to stable and efficient BF operation, especially under various blast conditions, yet their dynamic behaviour is still unknown. In this study, a three-dimensional transient CFD model is developed to investigate the impacts of the variation of key blast conditions on the in-furnace phenomena in an industrial scale BF. This model integrates the two-fluid model and discrete particle model to simulate the dynamic raceway and co-combustion of coke and pulverised coal in the lower part of the BF. A set of blast operating schemes, i.e., blast rate and oxygen enrichment, are numerically examined to illustrate and quantify their influence on the raceway evolution and combustion of coal and coke, respectively. The simulation results show that a higher blast rate benefits the formation of a larger raceway, i.e., with the rising blast velocity, from 90 m/s to 180 m/s, the raceway is expanded in terms of depth (0.4 m to 1.1 m), width (0.13 m to 0.44 m), and height (0.23 m to 0.76 m), which indirectly contributes to enhancing the combustion of coal and coke. The oxygen enrichment operation is also helpful to the co-combustion of coke and coal and increases the internal and surrounding temperature of the raceway, which produces more reducing gas for the BF. The average coal burnout rate is enhanced by 15 % after the blast rate is raised from 90 m/s to 180 m/s and the oxygen mass fraction is raised from 25 % to 35 %. This study offers a cost-effective tool to understand and optimise the blast operations toward stable and efficient BF operation.