The use of green H2 and sustainable carburization to Fe3C for the direct reduction of iron ore pellets

Abstract

Steel manufacturing is a carbon intensive process, that is responsible for approximately 7% of the total global CO2 emissions. Therefore, TATA Steel IJmuiden aims to lower its carbon emissions. One way to bring down emissions, is to replace the existing blast furnace (BF) CO reduction process with the H2-based direct reduction of iron ore (DRI). The two most widely applied H2-DRI processes around the world are the low pressure MIDREX, abbreviated as MLP, and medium pressure HYL-Energiron, abbreviated as EMP. Since TATA Steel IJmuiden wants to study the switch from BF to H2-DRI steelmaking, it is relevant to gain insight into which gas phase reactions are dominant for both processes, into the direct reduction process itself and into the behaviour of the carburization reactions that improve the steel quality. In the gas phase reactions, it was seen that for the MLP process in situ reforming of natural gas can be a viable option before switching to a 100% H2 process. This may prove to be worthwhile in the early stages of H2-DRI steel production, when green H2 is still scarce and expensive. For EMP, internal reforming seems less of a possibility due to the high reaction rate for the reverse water gas-shift. When comparing both MLP and EMP, reaction rates are generally higher for EMP than for MLP and hence smaller reactor volumes are required for the EMP process to acquire the same amount of output. Direct reduction with H2 has a higher reaction rate than reduction with CO, while for the carburization reactions methane cracking was found to be the dominant reaction. Techno-economic scenarios for 100% H2-based DRI in which green H2 is imported are only feasible when H2-prices fall below €1.80/kg. Meanwhile, a scenario with an on-site electrolyzer powered by grey grid electricity only proves to be worthwhile for electricity prices lower than €20/MWh. The most promising techno-economic scenario, which includes an on-site electrolyzer and the construction of a wind farm just off the coast from the TATA Steel IJmuiden site, assumes an electricity price of €40/MWh.