Steel production is associated with a lot of CO2 emissions and it is a very difficult sector to decarbonize. It is estimated that the carbon footprint is ∼ 2 tons of CO2 per tonne of steel produced. In general, there are three stages of steel production - the mining of iron ore, iron ore reduction into iron, and smelting into steel. Compared to other steps in steelmaking, iron ore mining is relatively carbon efficient (0.25 t CO2/t). Finding a method of producing steel that minimizes the harmful effects of its production on the environment is a big challenge. In this context, hydrogen-based steelmaking is currently receiving a lot of attention as it provides an attractive option.
The reduction of iron ore with H2 is nothing new, as the reduction process with H2 takes place in a blast furnace (BF) or a shaft furnace using the direct iron reduction (DRI) method.
Similar to the DRI process, iron ore is reduced by H2 via a gas-solid reaction.
The reduction reaction of iron ore by H2 is represented by the equation
Fe2O3 + 3 H2 → 2 Fe + 3 H2O
The principle of the production process of producing steel using H2 is shown in the picture below. If we want to reduce the carbon footprint of produced steel there is necessary to use fossil-free iron ore pellets for its production. H2 has to be produced via electrolysis of water using renewable electricity. The result of DRI by H2 is sponge iron, which is fed into an electric arc furnace (EAF). After melting and treatment in (EAF), the liquid steel is ready to be used for further processing.
It is estimated that 60-90 kg of green H2 is needed to produce 1000 kg of steel. As can be seen, estimates of the amount of H2 needed vary widely.
It looks like a very promising technology that could reduce the amount of CO2 associated with steel production, right? However, it has several flaws. The steel produced using green H2 is much more expensive compared to steel produced in a blast furnace or in DRI shaft furnace.
Green H2 is and will be very expensive, even the renewable electricity for its production is free. Green hydrogen is expensive due to very high CAPEX for electrolyzer and OPEX for running it. Furthermore, there is a problem with the relatively small capacity factor of PV plants and the average capacity factor of wind farms. Solar and wind are typical intermittent energy resources because they are not constantly available and predictable, so they need a large-scale system to compensate for imbalances between production and demand.
It is obvious green steel production has no chance to compete with fossil steel production unless a carbon tax is set. However, the implementation of the carbon tax to make the fossil steel price equal to green steel would make steel 2-3x more expensive. A lot of people would probably not like that.
