Abstract
A new route for making steel from iron ore based on the use of hydrogen to reduce iron oxides is presented, detailed and analyzed. The main advantage of this steelmaking route is the dramatic reduction (90% off) in CO2 emissions compared to those of the current standard blast-furnace route. The first process of the route is the production of hydrogen by water electrolysis using CO2-lean electricity. The challenge is to achieve massive production of H2 in acceptable economic conditions. The second process is the direct reduction of iron ore in a shaft furnace operated with hydrogen only. The third process is the melting of the carbon-free direct reduced iron in an electric arc furnace to produce steel. From mathematical modeling of the direct reduction furnace, we show that complete metallization can be achieved in a reactor smaller than the current shaft furnaces that use syngas made from natural gas. The reduction processes at the scale of the ore pellets are described and modeled using a specific structural kinetic pellet model. Finally, the differences between the reduction by hydrogen and by carbon monoxide are discussed, from the grain scale to the reactor scale. Regarding the kinetics, reduction with hydrogen is definitely faster. Several research and development and innovation projects have very recently been launched that should confirm the viability and performance of this breakthrough and environmentally friendly ironmaking process.
Highlights
Despite the use of the present tense in the title, using just hydrogen as a reductant for ironmaking is not yet an industrial process
In Europe, the HYBRIT project, which aims at building a whole demonstration plant in Sweden, including an iron ore direct reduction unit fed with hydrogen by a water electrolysis plant using fossil-free electricity, is one example [1]
ArcelorMittal announced the start of hydrogen-based ironmaking in its MIDREX direct reduction plant in Hamburg [4]
Summary
Despite the use of the present tense in the title, using just hydrogen as a reductant for ironmaking is not yet an industrial process. The steel industry accounts for between 4% and 7% of global anthropogenic CO2 emissions [6] This results from the almost exclusive use of carbon (coal or coke) for both the energy and the chemical reduction needed along the steelmaking route, the major contributor being the blast furnace, in which the solid iron ore, in the form of sinter or pellets, is transformed into liquid pig iron. 100% of the carbon (monoxide) with H2 could be envisaged This is why most of the current projects mentioned above consider using pure hydrogen in a shaft furnace for ironmaking. Interesting projects are currently ongoing, such as MOE at MIT [9] and SIDERWIN in Europe [10], but these lie outside of the scope of our paper
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