By Noah Beecher Kelk
Metallurgical coal, also called metcoal or coking coal, is a type of coal that is used in the production of steel. It is of a higher purity than thermal coal which is used in energy generation. To make steel, metcoal is heated at around 1100 degrees C to remove water and other chemicals. This is done without the presence of oxygen. The result is a lump of near-pure carbon which is called coke.
The coke is fed into a blast furnace along with ‘raw’ iron ore and some other minerals called fluxes. This produces pig iron. Pig iron is the basic ingredient to produce steel. Coal therefore plays three roles in the production of steel: a reducing agent, to turn the pig iron to coke; a source of energy to drive the process by breaking apart molecular bonds; and a source of carbon for the final product (steel is an alloy of carbon and iron).
The coal industry loves to point out that wind turbines are made of steel, and if you want steel, you need coal. So what are the alternatives?
1. Coal is needed as a reducing agent. “Reduction” is a chemical reaction that turns iron ore (Fe2O3) into pig iron (2Fe). Carbon monoxide (CO) is the crucial ingredient (Fe2O3 + 3CO → 2Fe + 3CO2) and is produced in blast furnaces by burning coal. This also produces carbon dioxide as a waste product.
Alternatively, hydrogen gas (H2) can be used as a reducing agent which results in Direct-Reduced Iron (DRI) and produces only water as a waste product (Fe2O3 + 3H2 → 2Fe + 3H2O). Unfortunately, hydrogen gas is usually manufactured with fossil fuels. There are alternatives, such as electrolysis of water, which are energy intensive. But if these processes used renewable energy sources, there would be no issue in terms of greenhouse gas emissions.
2. A source of energy. This one is obvious – renewables! Blast furnaces need coal, but there is an alternative technology called an Electric Arc Furnace (EAF). This is responsible for approximately 30% of the world’s steel production and does not require coal. But it does require an input of pig iron which does usually require coal. Which brings us to…
3. A source of carbon in the final product. There are other ways to produce carbon for the final alloy. This is obvious, because humans were producing steel long before blast furnaces came around. For example, biochar is a feasible alternative. A wood-based process would also reduce the impacts of coal mining and transport, produce less waste products, and could be sustainably produced with plantations. Moreover, a recent breakthrough by UNSW has seen two million tyres in landfill used as an alternative carbon source.
It’s clear that there are alternatives to coal for each of the three important roles it plays in steel production. Many of the options mentioned in this article would require the steel industry to invest massively in new infrastructure, like on-site renewable electrolysis plants. And that might hurt their profit margins – oh no!
Many of the options discussed above aren’t entirely clean and green. Some of them could easily be picked up as excuses to use natural gas as a “transition fuel” – something the global atmosphere cannot afford. Are there any other options? Well, yes. Steel is super-recycleable. Scrap steel (for example, old fridges) can be recycled, theoretically for ever, with practically zero loss of mass or quality. This can be done with EAFs, running on renewable energy. However, Australia is a big place, and there is scrap steel scattered far and wide. This makes it expensive to collect and recycle. A small amount of public education and funding for steel reclamation could make a big impact on the need for newly produced steel.
But there is another alternative to the current paradigm of steel production. The real issue is about the public obsession with infinite growth. We need to think carefully about what we really need steel for. It might be thought, for example, that wind turbines are a worthwhile use of a limited steel resource, while bombs – for example – are less socially valuable and should be, literally and metaphorically, consigned to the scrap heap.