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Introduction

The European steel industry has made tremendous past efforts to reduce its carbon footprint. The CO₂ emissions in conventional steelmaking have been reduced from 3.5 t/tonne of steel down to as low as 1.7 t/tonne. The same effort has been made in electrical steelmaking, leading to huge reductions in energy consumption of up to 50%. Depending on the origin of the electricity, electric arc furnaces emit as little as 1 tonne of CO₂ per tonne of steel. Nevertheless, iron and steel making, with a global production of 1.6 billion tonnes in 2014, remains the biggest industrial emitter of greenhouse gases (GHGs). Unlike the power industry, carbon is not a combustible for iron making, but a reagent for iron ore reduction. In a blast furnace, two atoms of C are required for two molecules of CO to react with one molecule of Fe_xO_y.

Whereas blast furnaces in Europe are now reaching the limits of their technological capabilities in terms of CO₂ reduction, competitors in new economies have retained high emission rates due to obsolete steelmaking facilities, a lack of technological skills and scrap shortages. While the global average of CO₂ emissions per tonne of steel is 2.6 t/t, large steel volumes are produced with emissions of up to 4 t/t. The low emitters are the electric arc furnaces, the natural gas-based iron reduction units and the European steel mills with levels of less than 2 t/t on average. The high emitters of CO₂ are the mills from Eastern Europe, the former Soviet Union and Asia, still at 3.5-4 t/t, the level where Europe used to be in the 1950s.

The story:

The European steel industry faces a two-fold challenge. Not only is energy scarce and very expensive compared to the continents that have their own resources; a second competitive handicap is the carbon tax, enforced by environmental regulations. This carbon tax applies to all steel mills, since the benchmark level, for which free allowances are provided, cannot be obtained by conventional steel producers. The gap from the best to the bench is about 30%.

Compared to other industries, the steel industry has a much lower margin per tonne of CO₂ emitted and will thus be the first to have to stop activities if an overly high carbon tax is imposed. Efforts to re-use CO or CO₂ of fossil origin are not at all rewarded by current legislation. Attempts to produce hydrogen, the only alternative reactant for carbon (for example through high-temperature electrolysis from steel waste heat) are also disadvantaged, because the ETS does not differentiate between industries. So CO₂ taxes are the same for everyone, even when a green alternative exists, and green electrolysis H₂, which generates no CO₂ emissions, stands no chance against steam methane reforming (SMR)-H₂, although the latter emits 10 tonnes of CO₂ per tonne of H₂.

Japanese steelmakers are studying the use of H₂ as a reagent as part of the COURSE 50-project, research which is entirely funded by the Japanese government. But the lack of hydrogen from coke making, and the need for coke as a support for the iron ore in the blast furnace have reduced ambitions to a 30% reduction in CO₂ at the most.

The Zero Emission Plant concept being elaborated by steel producers therefore targets some socially acceptable and possibly economically viable principles. The goal of the project is to separate the CO from the CO₂ in order to use both constituents as feedstock for new industries, thus creating value and employment.

The pure CO and CO₂ gases can be combined with the H₂ from coke oven gas, electrolysis or supplied by a neighbouring industry, because in most industrial zones several thousands of tonnes of hydrogen are still burnt as fatal gases. The fuels and chemicals targeted by these new technologies can replace products derived from fossil fuels or biomass (without indirect land use) such as naphtha, methane, ethanol, methanol, acetone, formic acid, caproic acid and many others. Biochemical fermentation, catalytic reaction or electro-chemical transformation can be used as conversion methods.

In France, the steel industry is collaborating with universities and institutions in the VALORCO-programme to reuse CO₂ for the production of valuable fuels and chemicals

These developments are ongoing, in parallel with the search for cheap hydrogen, which will be the limiting factor. High-temperature electrolysis is particularly interesting in this regard as it reduces electricity consumption by almost 14%. The heat can be derived from waste energy produced through steel making. CO₂-electrolysis, which makes use of the surplus of renewable electricity, is a technology that has been tested in a solar tower. In steel mills, the heat required for the electrolysis cells could come from the waste heat of steel making.

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A more mature technology is the dry reforming of CO₂ with natural gas or coke oven gas. The ULCOS steelmakers’ consortium in Europe previously conducted tests with a 2 MW-plasma torch. This hot syngas can be injected into the furnaces to reduce the iron ore. A direct reduced iron (DRI)-unit using a trial plasma arc, up to 20 MW, is likely to be the next step in the development of this technology.

But CO₂ can also be used without H₂, and can simply be stored in steel slags and minerals that absorb CO₂. Carbonation trials with olivine, serpentine, wollastonite and steel slags have shown a net CO₂-sequestration potential of 15 – 35 weight %. PCC (precipitated calcium carbonate) is the possible end-product of this carbonation, together with other materials which can be used for the construction industry for example. The simple sale of CO₂ to greenhouses is an obvious end-use.

The ambition is to come as close as possible to the predicted volume of reusable anthropogenic CO₂ between 10 and 20%, with the aim of finding a use for at least 25 – 30% of the CO₂ produced from steelmaking. This would also bridge the gap between the best performing EU-mills and the benchmark set out by the European Union.

Conclusion

Given the value created by CO₂ conversion technologies, every industry should be able to afford to capture all of the CO₂ it produces. The revenue generated from the sale of chemicals and fuels produced from part of this CO₂ could cover the cost of making the remainder publically available, for example through a public pipeline, which will in turn attract new industries and create new employment. This would also enable the sufficient and uninterrupted supply of CO₂ that could be liquefied for Enhanced Oil Recovery or storage in a landfill by the state authorities. Consequently, CO₂ conversion should not incur any additional costs for the industry and there will be no financial handicap with regard to competitors that continue to vent their CO₂.