Decarbonizing steel

If the global steel industry were a country, it would be the third largest carbon emitter in the world (after the US and China). The 1,809 Mt of steel produced in 2018 created 3.3 Gt of carbon dioxide, accounting for 9% of the globe’s annual CO2 production. It is therefore clear that in order to meet our carbon reduction targets, we must find alternatives within this “hard to abate” sector.  

MIT’s Professor Donald Sadoway is determined to change how metals are made—to find solutions that are pollution and emissions-free. He is a co-founder of Boston Metal, a company that is already producing steel at a pilot level with zero CO2 emissions.

Traditional steelmaking

Global crude steel production rose tenfold from 189 Mt in 1950 to 1,809 Mt in 2018. As steel is critical for building out our infrastructure, demand is predicted to continue to increase at a rate of 3% per annum to double, reaching 3,700 Mt per year, by 2040.

There are three main steps in traditional steel making,.

  1. The inputs – iron ore, limestone, and carbon – are pre-processed, using energy. The iron ore is crushed into a powder and sintered to form pellets the size of walnuts. The limestone, a flux that removes some of the impurities in the iron ore, is crushed. If the form of carbon used as the reductant is coal, it has to be processed into coke which is more porous and reactive.
  2. The inputs are then heated in a blast furnace to produce molten pig iron and the by-product, slag.
  3. The raw pig iron is too brittle for use and has to go through a process of desulphurisation before it is transformed into useful types of steel in a basic oxygen furnace.

If the desired end product is stainless steel, there is a fourth step of creating an alloy.

While steel is heavily recycled (very little is wasted), the cycle takes about forty years meaning that virgin steel production continues to expand. China dominates this production, accounting for over half of global output.  (Interestingly, emissions from Chinese steel are often lower than from legacy steel produced in Canada or the US, because many Chinese production facilities are newer.)

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