A novel ironmaking decarbonisation technology — co-injection of hydrogen and biochar (CoHB): A CFD study of combustion in the raceway under simulated blast furnace conditions

In this paper, a novel ironmaking decarbonisation technology — co-injection of hydrogen and biochar (CoHB) in blast furnaces (BFs) is proposed for a feasible and sustainable carbon-neutral ironmaking. As the first study, to understand the fundamentals of internal combustion behaviour in the raceway related to CoHB, a three-dimensional (3D) computational fluid dynamics (CFD) model is developed to describe the multiphase reacting flow under simulated BF conditions. Particularly, the present model features a new treatment of volatile matter (VM) and an improved sub-model for hydrogen combustion. The model is successfully validated by the measurements of biochar injection and co-injection of hydrogen and coal, respectively. The typical in-furnace phenomena as well as the interaction between the hydrogen and biochar are analysed comprehensively. The results indicate that the proper injection of hydrogen through the annulus of the fuel lance is beneficial as the high local gas temperatures (1500 K to 1800 K) from the hydrogen combustion provide a biochar burnout enhancement of 6% during the biochar devolatilisation process. However, char reactions are hindered due to the oxygen competition with hydrogen combustion, resulting in a slightly reduced final biochar burnout. This study provides a quantitative insight into the combustion details related to this novel technology and serves as a reference to strive towards the net-carbon ironmaking initiative.