Steel, aluminum, concrete: how to make them without CO2?

The order of magnitude of their contribution is 23% of global greenhouse gas emissions, according to an estimate by UN Environment, the International Energy Agency and sectoral organizations in 2019.

Here is how the three sectors plan to reduce their emissions by 2050, if not eliminate them completely. All plan to use CO2 capture to varying degrees, a technology that is still in its infancy.

Steel

To decarbonize, the global steel industry (around 8% of CO2 emissions) is first betting on the recycling of old scrap metal (car carcasses, beams) in electric furnaces.

Then, it plans to replace the coal in the blast furnaces, initially, with natural gas. Then, when the production capacities of so-called “green” hydrogen (created from renewable, low-carbon energies) are at the level, this hydrogen will replace natural gas.

This then induces a gradual shutdown of the historic blast furnaces replaced by new installations, called “direct reduction” (DRI).

Europe is at the forefront of this development. The Thyssenkrupp conglomerate, responsible for 2,5% of Germany's CO2 emissions, plans to transform its historic Duisburg site, but the gigantic nature of investments and the cost of energy in Europe are weighing on the project.

The world's number two steel maker, ArcelorMittal, acquired 2022% of a factory in Texas in 80 which manufactures deoxidized iron ore briquettes, making it possible to produce steel without coal.

A green steelworks, led by the start-up H2 GreenSteel, should start up in Sweden in 2025: the first new steelworks built in Europe in 50 years.

The International Energy Agency (IEA) recognizes that in 2050, the steel industry will remain one of the last industries still using coal, with not all blast furnaces being able to be converted by 2050.

Steelmakers also plan to resort to capturing excess CO2; ArcelorMittal is testing a pilot system in Dunkirk, France.

Aluminium

It is one of the most consumed metals, both in the old economy, because it makes buildings and cars lighter, and in the new one, linked to the energy transition, because it conducts electricity.

But it is also one of the metals that emits the most greenhouse gases: the production of one ton of aluminum generates between 5 and 25 tons of CO2 equivalent, depending on the origin of the electricity used (not fossil or fossil), indicates the French government's non-energy mineral resources portal.

Direct aluminum emissions are linked to the hydrolysis of alumina, the combustion of the gas necessary for the foundry, and the cooking of graphite anodes, during which the carbon (C) of the electrode recomposes with the oxygen (O2) of the alumina, which releases... CO2.

Indirect emissions depend on the extraction and refining process of bauxite, the initial mineral raw material for alumina. As the stages of transforming ore into metal are often carried out in different countries, indirect emissions linked to transport can also be significant.

These depend above all on the fuel used to produce the gigantic quantities of electricity required: often coal or heavy fuel oil.

To eliminate them, the sector is currently relying mainly on recycling and CO2 capture. It also relies on so-called “inert anode” technology which would not release carbon, but which is far from mature.

Cement + Concrete

Cement and concrete, produced industrially for around 200 years, represent 8% of global CO2 emissions, more than air transport and maritime transport combined, professionals admit. However, with increasing urbanization, global demand is expected to increase by 50% by 2050, according to them.

Cement emits CO2 because fuel must be burned to heat the limestone and clay to 1.450°C in order to obtain the "clinker", the essential binder in cement. The chemical reaction itself generates additional CO2.

A group of industrialists bringing together giants such as the German Heidelberg, the Mexican Cemex and the Swiss Holcim in particular committed on Tuesday to reducing their emissions by 22% by 2050 by reducing the volumes of materials from the design stage of buildings.

Replacing clinker with less emitting binders (calcined clay mixed with crushed limestone, crushed pozzolan, etc.) can reduce emissions by 25%.

The remaining 53% should come from replacing fossil fuels, “the decarbonization of electricity, and the capture and storage of excess CO2”.

This should represent 36% of the reduction in cement emissions globally in 2050, specified the roadmap distributed at COP28 by the GCCA association which brings together 80% of the world's cement manufacturers.