Comparing “green steel” technologies: a scorecard based on CO2 reductions

This 4-minute article, based on a longer “Guideline for green steel”, summarizes the current state of steelmaking based objective, quantifiable CO₂ reductions. 

Carbon Capture and Utilization (CCU): 65% CO₂ reduction

There are currently no large-scale commercial CCU processes in the steel industry, but several research studies have indicated great potential. It is possible to capture approximately 65% of the CO₂ emissions and then process them and/or combine them with other gases to make the carbon-based “feedstocks” needed by the chemical industry. The drawback: the same amount of fossil fuels is used, requiring the same extraction impacts, etc.

Carbon Capture and Storage (CCS): 60–70% CO₂ reduction

For CCS, CO2 is compressed, transported, and stored in appropriately selected and managed underground geological reservoirs. The Intergovernmental Panel on Climate Change (IPCC) calculates that, done properly, the reservoirs are “very likely” to retain 99% of the CO₂ for longer than 1,000 years.

That said, there currently are no large-scale commercial CCS facilities in the steel industry. According to the International Energy Agency (IEA), carbon capture is unlikely to be significant by 2030: it estimates that 1% of the annual CO₂ emissions from the steel industry will be captured (16 MtCO₂/year).

Some emissions experts state that CCS reservoirs should be prioritized for industries other than steel – such as plastics or cement – that face large costs and obstacles in developing fossil-free technologies. In these sectors, the carbon dioxide could be reduced by up to 60–70%.  

Scrap steel recycling is already much cleaner than traditional iron-ore based steelmaking since, obviously, you skip the ironmaking process – historically the most CO₂-polluting part of making steel. Since it can be infinitely recycled, it’s not surprising that steel has a 90% recycling rate – the highest of any widespread material. However, recycling can only provide 25% of the current worldwide demand for steel. Current scrap-based steelmaking can be improved by the following practices. 

Low-Carbon DRI: 10–20% CO₂ reduction 

Using low-carbon direct reducted iron (DRI), instead of fossil-based DRI, could reduce the carbon dioxide footprint of scrap-based steelmaking by 10–20%, depending on the amount and type of DRI and on the electricity mix. 

Green Electricity: 50% CO₂ reduction

A complete swap from fossil-fueled to fossil-free electricity could cut current scrap-based steelmaking CO₂ emissions by half. 

Biocoal: up to 40% CO₂ reduction 

Biocoal is produced by the biogreen pyrolysis and carbonization of raw biomass. When made with fossil-free energy and without binders, biocoal is a carbon-neutral fuel. While biocoal can replace pulverized coal injection (PCI), it’s still necessary to use coal to make coke for the blast furnace. In addition, biocoal normally contains a higher amount of Potassium (K) and Phosphorus (P), challenging the quality of the steel. Keeping that in mind, the method could reduce carbon emissions by up to 40%. 

Hydrogen injection: 10–40% CO₂ reduction

Pulverized coal injection in the blast furnace can be partly replaced with hydrogen. The resulting carbon-dioxide decrease is limited, approximately 10–40% depending on the technology. 

Top-gas recycling (TGR): 21–25% CO₂ reduction

The top gases produced during blast-furnace energy production or heating could be recycled by feeding the carbon emissions and hydrogen back to the furnace. The expected carbon reductions are 21–25%. 

Submerged-Arc Furnaces (SAF): CO₂ reductions to be determined

Submerged Arc Furnaces (SAF), or the similar Open Slag Bath Furnaces (OSBF), can replace blast-furnace ironmaking, which would lower the need for coke and coal. A key advantage to these technologies is the possibility to use lower quality iron ore. SAF and OSBF are still under development and they have no large-scale commercial deployment in the steel industry. With further development and innovations, SAF and OSBF could substantially reduce CO₂ emissions in ironmaking. 

Fossil-Based Direct Reduction with Electric Arc Furnaces (EAF): 10–40% CO₂ reduction

Powered by natural gas-based DRI, coal-based DRI, or syngas (a mixture of hydrogen and carbon monoxide), these processes are estimated to reduce carbon-dioxide emissions by 10–40% compared to traditional ironmaking. 

Fossil-Free Direct Reduction (DRI) with Electric Arc Furnaces (EAF): virtually CO₂ free

By far the greatest reduction in CO₂ emissions for iron-ore based steelmaking will come from replacing all major carbon dioxide sources with a green-hydrogen direct reduction process. Fossil-free direct reduction uses hydrogen produced by fossil-free electricity: solar, wind, hydro, etc. The by-product of fossil-free DRI is water, which can readily be reused for hydrogen production, forming a closed loop.

The technological development of fossil-free direct reduced iron for fossil-free steelmaking started in 2016, and produced the world’s first virtually fossil-free steel products in July 2021.

Other promising CO₂-reducing ironmaking technologies

The above summary covers development initiatives that are considered to have “high technology readiness levels.” Additional initiatives with lower technology readiness levels include:

• Fines-based Hydrogen Direct Reduction combined with Electric Arc Furnace (e.g., HyREX, Circored). 
• Fines-based Hydrogen Direct Reduction combined with Smelting Reduction (e.g., SuSteel). 
• Direct electrolysis of iron ore at low temperature (e.g., Ulcowin, Siderwin). 
• Direct electrolysis of iron ore at high temperature (e.g., Ulcolysis, Boston Metal).  

In 2026: commercial quantities of fossil-free steel

Companies across various industries – including automotive – are currently using small amounts of SSAB’s fossil-free steels from its pilot plant to build prototypes. Since our new fossil-free steels have the same properties as our current steels, it comes as no surprise that the adoption by customers has been, so far, very straightforward.