Multi-view feasibility study of the innovative co-injection of H2 and coal in blast furnaces for viable net-zero ironmaking

• A novel strategy for HMB-CFD approach is proposed for H 2 ironmaking. • The upper limit of H 2 injection into a BF is determined to be 31–35 kg/t-HM. • Injection of 10 kg-H 2 /t-HM raises coal burnout by 4 %, lowers CO 2 emissions by 4 %. • Co-injection mitigates the adverse pressure drop associated with H 2 injection alone. Steel industry is highly energy-intensive and emission-intensive, and the co-injection of H 2 and coal in blast furnaces (BFs) is an innovative and cost-effective technology towards carbon-neutrality, but its feasibility is not quantified yet. In this paper, the co-injection of H 2 and coal is, for the first time, studied by combining a heat and mass balance (HMB) model in view of macroscale BF performance and a 3D industrial-scale computational fluid dynamics (CFD) model in view of mesoscale local combustion behaviour. First, the macroscale BF operating window and the key terms applicable to the co-injection of H 2 and coal are designed using the HMB model. It is found that the efficient operations are largely maintained by the “tuyere parameters”, for example, hydrogen injection, whether co-injected with coals or alone, is limited to around 31–35 kg/t-HM. Then the key mesoscale in-furnace local combustion behaviour is investigated using the CFD model, including the combustion efficiency of H 2 and coal, flow field, temperature field and gas species distribution, etc. Further, the effects of coal types and injection rates on the performance of the coals are studied in detail. It is found that the co-injection enhances the performance of both injectants synergistically. Quantitatively, under the conditions studied, the co-injection of coal with 10 kg-H 2 /t-HM helps to increase the final coal burnout by about 4 %, and reduces the CO 2 emissions by about 4 %. Both injection of H 2 alone and co-injection of coal with H 2 will increase bosh gas volume (BGV) and the BF pressure drop; however, the increases with H 2 alone are greater, implying a significant negative impact on BF productivity. The coals with higher volatile matter (VM) are predicted to result in a relatively smaller increase in coal burnout but a larger CO 2 emissions reduction, and vice versa for lower VM coals. This paper provides a useful and cost-effective method for quantifying and designing the co-injection of H 2 and coal for viable ironmaking decarbonisation.