Hydrogen steelmaking. Part 1: Physical chemistry and process metallurgy

Pushed to the forefront by the objective to drastically reduce the CO2 emissions from the steel industry, a new steelmaking route based on hydrogen and electricity is the subject of a great deal of attention and numerous R&D projects. The first step is to chemically reduce iron ore with H-2, which is produced by electrolysis of water with low-carbon electricity, and then to transform the direct reduced iron into steel in an electric arc furnace. The second step is a conventional one, similar to that used for scrap recycling. The first step is similar to the so-called direct reduction process but would use pure electrolytic H-2 instead of the H-2-CO syngas obtained from natural gas reforming. In this paper, we first show how the reduction by pure H-2 takes place at the microscopic level of the iron oxide grains and pellets. The three-step (hematite-magnetite-wustite-iron) reduction occurs successively in time and simultaneously in the pellets. Secondly, a sophisticated kinetic model of the reduction of a single pellet based on the experimental findings is described. Lastly, we present a mathematical model for the simulation of the reduction by pure H-2 in a shaft furnace, which can be very useful for the design of a future installation. The main results are that using pure hydrogen, the reduction kinetics are faster and can end with full metallization, the direct reduction process would be simpler, and the shaft furnace could be squatter. The gains in terms of CO2 emissions are quantified (85% off) and the whole route is compared to other zero-carbon solutions in Part 2.