The Carbon Footprint of Different Steel Production Technologies

CO2 emissions of steel production varies widely across different production technologies

Indicative emissions for different steel production technologies in kilogram CO2 per kilogram steel

 

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Without delving into all the technicalities and complexities of both routes, there are two key points worth noting.

Firstly, CCS provides a way to radically lower carbon emissions from the conventional coal-based way of steelmaking. Our indicative calculations point to an 80% emission reduction – an impressive result, given the carbon content of one kilogram of steel is reduced from about 1.87 kilograms of CO₂ to 0.38 kilograms.

Secondly, hydrogen provides a way to radically change the production process in such a way that it hardly emits any CO₂ at all. The carbon content of steel is reduced to nearly zero if ‘fully green’ hydrogen is used – by which we mean hydrogen produced with an electrolyser which is fully powered by zero carbon technologies such as solar panels, wind turbines, hydropower plants, nuclear power plants (or a combination of these).

The definition of green hydrogen implies that the power on which the electrolyser runs comes from renewable sources only (solar and wind energy). In practice, however, this is not yet the case as solar and wind power is not always available and power grids in many countries are still predominantly fossil-based. The 'green' in green hydrogen currently means that the hydrogen is made with renewable electricity and an electrolyser, compared to grey and blue hydrogen which are made from natural gas in a steam methane reformer for the most part.

If the electrolyser is powered by a grid that predominantly runs on gas-fired power plants, the carbon content of the steel is reduced by 30%, from 1.87 kilograms CO₂ per kilogram of steel to 1.28 kilograms. This is a notable improvement – but still worse by far than the conventional coal-based production method using CCS which results in an 80% reduction. Electrolysers that are connected to the power grid will decarbonise in line with the decarbonisation of the entire power system.

Finally, the carbon content of steel increases by more than 50% if the electrolyser is powered by a grid that predominantly runs on coal-fired power plants. So, one has to be careful with hydrogen from electrolysers. Electrolysers and green hydrogen are not green by definition! The power source plays a crucial role, and doing the climate a disservice with traditional fossil-based power sources is a very real possibility at such an early stage in the energy transition.

Hydrogen does not have to be made with electrolysers though. In fact, over 95% of current hydrogen use in the world is produced with natural gas, mostly without CCS (grey hydrogen). In the pursuit of reducing carbon emissions of grey hydrogen, blue hydrogen is needed, which shifts the CCS process from the steel sector to the hydrogen sector. The carbon content from steel made with blue hydrogen is quite similar to conventional coal-based steel with CCS (0.38 kilogram CO₂ per kilogram steel versus 0.22). Blue hydrogen pollutes the environment slightly less than coal-based steel with CCS, as the gas needed to produce it emits less carbon than coal.

Last but certainly not least, steel from grey hydrogen has a much lower carbon footprint compared to conventional coal-based steelmaking. So, steelmakers don’t have to wait until their power systems fully run on solar panels, wind turbines or nuclear power plants. The hydrogen source in the early stage of the sector’s hydrogen transition also shouldn't be too much of a concern, as long as electrolysers are not powered by electricity from coal plants.