Decarbonisation and hydrogen integration of steel industries: Recent development, challenges and technoeconomic analysis

The steel industry is one of the major sources of greenhouse gas emissions with significant energy demand. Currently, 73% of the world's steel is manufactured through the coal-coke-based blast furnace-basic oxygen furnace route (BF-BOF), emitting about two tonnes of CO2 per tonne of steel produced. This review reports the major technologies, recent developments, challenges and technoeconomic comparison of steelmaking technologies, emphasising the integration of hydrogen in emerging and established ironmaking and steelmaking processes. Significant trials are underway, especially in Germany, to replace coal injected in the tuyeres of the blast furnace with hydrogen. However, it is not clear that this approach can be extended beyond 30% replacement of coke because of the associated technical challenges. Direct smelting and fluidised bed technologies can emit 20%–30% less CO2 without carbon capture and storage utilisation. The implications of hydrogen energy in these technologies as a substitute for natural gas and coal are yet to be fully explored. A hydrogen-based direct reduction of iron ore (DRI) and steel scrap melting in an electric arc furnace (EAF) appeared to be the most mature technological routes to date, capable of reducing CO2 emission by 95% but rely on the availability of rich iron concentrates as feed materials. Shaft furnace technologies are the common DRI-making process, with a share of over 72% of the total production. The technology has been developed with natural gas as the main fuel and reductant. However, it is now being adapted to operate predominantly on hydrogen to produce a low-carbon DRI product. Plasma and electrolysis-based iron and steelmaking are some of the other potential technologies for the application of hydrogen with a CO2 reduction potential of over 95%. However, these technologies are in the preliminary stage of development with a technology readiness level of below 6. There are many technological challenges for the application of hydrogen in steel manufacturing, such as challenges in distributing heat due to the endothermic H2 reduction process, balancing carbon content in the product steel (particularly using zero-carbon DRI), removal of gangue materials and sourcing of cost-competitive renewable hydrogen and high-quality iron ore (65>Fe). As iron ore quality degrades worldwide, several companies are considering melting DRI before steelmaking, possibly using submerged arc technology to eliminate gangue materials. Hence, significant laboratory and pilot-scale demonstrations are required to test process parameters and product qualities. Our analysis anticipates that hydrogen will play an instrumental role in decarbonising steel industries by 2035.