Three-dimensional transient modelling of coal and coke co-combustion in the dynamic raceway of ironmaking blast furnaces

Abstract

The blast furnace is a highly efficient but energy-intensive chemical reactor for iron production. Two types of solid fuels, viz. coarse coke particles and fine pulverized coal powders, are combusted simultaneously, forming the dynamic cavities (termed raceway) at the lower part of the blast furnace, and their behaviour affects each other considerably, although this has not been clearly established in the past. In this study, a three-dimensional transient model is developed for describing the complex co-combustion of pulverized coal and coke coupled with the dynamic raceway evolution under industrial-scale blast furnace conditions. The model couples a gas-coke combustion model with a gas-coal combustion model in a transient state by means of two-way coupling scheme. The model is then validated against experimental measurements. The typical transient in-furnace phenomena are illustrated in terms of raceway shape and size, gas-solid-powder flow, temperature fields, gas composition and coal and coke combustion. As time progresses from 0 s to 7.0 s, the raceway size increases in depth, width and height; and the coal burnout slightly increases. At around 7.0 s, the raceway profile and coal and coke combustion approach a relatively stable state. Additionally, the effects of blast rate on the in-furnace phenomena are studied. Under the simulated conditions, when the blast rate is increased from 140 m/s to 180 m/s, a larger raceway is formed and the depth is increased by 22.2%. Subsequently, the average burnout of pulverized coal is improved by 3.6% and the reducing gas, i.e., CO, is increased by 1%. This model offers a cost-effective tool to optimize coke/coal co-combustion in blast furnaces for energy saving and operation stability.