The steel industry accounts for 4% of all the CO2 emissions in Europe and 22% of the industrial carbon emissions in Europe. Several options for its decarbonization are possible: 

• Increasing the efficiency of current production methods.  
• Recycling of steel. But impurities such as copper, which accumulate over time, mean that new steel will always be needed for sectors that require high-quality steel such as cars.  
• Carbon capture and storage (CCS) is likely to play a role in decarbonizing the steel sector. CCS can be used directly at a steel plant or in the production of hydrogen. Hydrogen as a solution to decarbonize industry has been receiving increasing amounts of attention. 

There are two ways in which hydrogen can be used in steel production: 

• Hydrogen can be used as an auxiliary reducing agent in the BF-BOF route (H2-BF) 
• Hydrogen can be used as the sole reducing agent in a process known as direct reduction of iron or DRI (H2-DRI) 

This article will focus on H2–BF, while H2–DRI will be discussed in a future article. 

Using hydrogen in the Blast Furnace – Basic Oxygen Furnace route (BF-BOF)  

Steel production via the BF-BOF route. Source: Bellona Europa, 2019. 

The BF-BOF route, also known as the primary production route, accounts for 60% of steel production in Europe. The majority of the emissions come from the blast furnace and the coke plant. The coke plant produces coking coal, which is used in the blast furnace both as a heat source and to reduce iron. H2-BF has the potential to reduce emissions both in the coke plant and blast furnace because it reduces the amount of coal needed and only forms water after reacting with iron ore instead of carbon dioxide. Today, the most common auxiliary reducing agents are pulverized coal (PC), oil, natural gas, or a combination of these, all of which produce CO2. 

However, due to technical reasons, it is not feasible to only use hydrogen in a blast furnace and therefore, H2-BF is often seen as a transition towards H2-DRI to provide emission reductions in the near-term. Several European steel producers have plans for using H2-BF (table 1). 

Table 1. Projects for hydrogen use in BF-BOF (H2-BF). 

Hydrogen from electrolysis 

Of the several ways hydrogen can be produced, renewable energy coupled to electrolysis should be the priority as it achieves the largest emission cuts, ±21% [1], resulting from hydrogen use in the BF-BOF. Only three projects of the eight that were found state their intention of using green hydrogen from the start: ArcelorMittal in France, Voestalpine in Austria (project H2FUTURE) and TATA in the Netherlands (project H2ERMES). Thyssenkrupp expects to have some green hydrogen by the mid-2020s, but this will depend on how the share of renewables in the electricity grid evolves. If hydrogen is produced via electrolysis using German grid electricity, emissions could increase by 36.7% [2].  

Hydrogen from the reforming of natural gas (grey hydrogen) 

Some companies [3] say they will use green hydrogen when available at reasonable costs and quantities, a claim echoed by many in various industries. Under current policy frameworks the date for these conditions to be fulfilled is unknown, yet unlikely to be in the near-term. In the meantime, they’ll use grey hydrogen. For example, Thyssenkrupp’s Duisburg project announced it will acquire hydrogen through Air Liquide’s regional hydrogen network in the meantime. Considering their H2-production portfolio the hydrogen is likely to be grey. Using grey hydrogen, emissions would be reduced by only ±2.1% [4], ten times less than in the case of green hydrogen. Adding CCS [5] to the reforming process (blue hydrogen) could reduce emission levels similar to green hydrogen (with some residual emissions). This will likely be needed to scale up hydrogen production more quickly. 

Claims and reality of “climate-neutral” steel 

Thyssenkrupp claims it will produce 50,000 tonnes of climate-neutral steel by 2022 using H2-BF. However, as shown, H2-BF can have varying effects on the carbon footprint of steel. But even under optimal conditions, it cannot make steel ‘green’, i.e. climate-neutral [6]. Close attention must be paid to avoid that any emission reductions are automatically equated to “climate-neutral” or “green” steel. Overall, its claim of climate-neutral steel by 2022 is dubious and calls for more scrutiny. Similarly, ArcelorMittal claims it is already delivering green steel even though it does not use H2-DRI nor BF-BOF with CCS at a meaningful scale yet [7]. 

To summarize: 

• At best, injecting green hydrogen into the BF–BOF route can reduce emissions by 21%. 
• Hydrogen from electrolysis with grid electricity can increase emissions of the BF-BOF route by 36.9% depending on the grid emission intensity.  
• Companies state they will use green hydrogen once available, but use grey hydrogen in the meantime. 
• Using grey hydrogen from natural gas reformation can reduce emissions by 2.1%. Blue hydrogen can result in emission reductions similar to green hydrogen.
• Hydrogen BF steel should not be confused with Hydrogen Direct reduction of iron ore, which can indeed go down to very low emissions and produce carbon neutral steel. This technology will be covered in part 2 of this article.

Footnotes 

1. Compared to a reference case of injecting 120 kg PC per tonne of hot metal (1352.3 kgCO2/tHM). It assumes the use of ±28 kg of hydrogen (per tonne of hot metal), which has been deemed optimal. This results in 1063,2 kgCO2/tHM.
2. The German grid emission intensity of 2018 was 469 gCO2eq/kWh. Assuming 60 kWh/kg of hydrogen and 28 kg hydrogen per tonne of hot metal, this would result in an additional 787.9 kgCO2 compared to using green hydrogen. This means that emissions would be 36.9% higher compared to the reference case of injecting 120 kg PC per tonne of hot metal. Applying lifecycle analysis would lead to an even higher value. 
3. The projects in table 1 with no electrolyser. 
4. Values of the carbon footprint of grey hydrogen vary. Here 9.3 kgCO2/kgH2 is used, which is at the lower range of values. It means additional emissions would be 260.4 kg compared to if the hydrogen would be green. 2.1% is relative to the reference case of injecting 120 kg PC per tonne of hot metal. 
5. ArcelorMittal and Air Liquide are in the CCS project Northern Lights, expected to be operational in 2024. 
6. While Thyssenkrupp also has a carbon capture and use (CCU) project Carbon2Chem, in comparison to CCS, CCU does not have significant emissions abatement potential. The pilot plant currently captures 240 Nm3/hour of some two million Nm3/hour of top-gas at the plant in Duisburg or 0.01%, meaning that most of it still enters the atmosphere. Also, the CCU process requires additional hydrogen with similar associated emission risks from its production. 
7. A pilot CCS project started in Dunkirk in 2021, but it is still on a very small scale (0.5 tCO2 per hour). ArcelorMittal is also involved in the Porthos project.