A New Way to Decarbonise Steel Making?

 by Lucy H

Steel is fundamental to our lives. It is used in our cars, homes, cities and beyond. The steel making industry has been around since their peak in the 1850’s. Unfortunately, the process of converting iron ore into iron, and then iron into steel uses a lot of energy. Because of this, and the fact steel is used in so many things, steelmaking is responsible for over 8% of all global CO2 emissions.  Most of these emissions are created during the industrial process of transforming iron ore - the raw material- into metal. Decarbonising the way iron, and therefore steel, is made could make a significant contribution to reducing global CO2 emissions, and in turn combat climate change. 

The Original Process

The most common practice for steelmaking is as follows: The iron ore is mined and then alloyed with carbon, through the use of coal. Coking coal, a form of coal with a high carbon content, plays three roles, by turning iron ore into iron in a blast furnace,processing iron into steel, and also a fuel that provides power for these processes.

First coking coal is heated in a blast furnace to 110 degrees celsius to produce a pure form of carbon called coke. In turn, coke mixed with limestone, reduces the ore in the blast furnace to iron by reacting with oxygen, releasing carbon monoxide in the process. 

Exemplar diagram of blast furnace with relevant equations:

Next, one molecule of iron reacts with 3 molecules (1:3 molar ratio) of carbon monoxide, leaving two iron atoms and three molecules of CO2 as products. Finally, iron is converted into steel by altering its carbon content in a basic oxygen furnace. Today, globally 90% of steel produced from iron ore is manufactured using this process. As mentioned before, these production processes combined require vast amounts of energy and in turn release greenhouse gases, so large scale manufacturing companies, such as Rio Tinto, are on the hunt for newer ways to produce steel sustainably and renewably, and limit the use of coal. A carbon neutral steel industry could substitute coal in each step of this process but coal remains the most cost effective option in most cases as of date.

So what’s the alternative? 

Rio Tinto, a British -Australian multinational company, the world’s second largest metals and mining corporation (behind BHP), has found a way to “decarbonise steelmaking” after their recent research into BioIron. The company announced its plan to develop the BioIron research and development facility in the Rockingham strategic industrial area just south of Perth, one of the largest iron ore provinces in the world. Instead of coal based blast furnace processing, Rio Tinto’s BioIron process uses raw biomass and microwave energy to convert Pilbara Iron to metallic iron, replacing the need for coal. The main challenge they faced was finding ways to run processing without using coal: “We need to come up with new technologies that don’t rely on coal if we’re going to transition” stated Michael Buckley, Rio Tinto’s steel decarbonisation and BioIron manager. The company partnered with Nottingham University to run a testing facility at a pilot scale, and noted that BioIron had the capacity to reduce greenhouse gas emissions by 95%, and since have been working with agricultural land in WA to sustainably source biomass such as wheat and barley, to provide the raw material and energy for this innovative process. 

Making BioIron

The main reason for bioiron is to use raw biomass as a reductant, instead of coal, discarding the need for fossil fuels, and thus reducing the carbon footprint. 

During manufacturing, the iron ore is blended with fine biomass and fluxes and is fed into a high pressure machine to produce “golf ball” sized briquettes. After, these are layered on a high temperature conveyor belt where biomass pyrolysis gases combust with air to heat the briquettes. Subsequently, microwaves powered by electricity allow the briquettes to absorb energy like a sponge to reach a high enough temperature to turn the ore into directly reduced metallic iron. These microwaves heat the whole bed depth which is a unique and efficient feature not achieved today in the industry. An electric melter then separates impurities from the hot metal which can then be fed into a basic oxygen furnace on site or cast into pig iron and transported to remote steelworks. The prominent feature of this is that the biomass provides most of the energy needed, so BioIron uses less than a third of electricity needed by other new  technologies using hydrogen, for example. However, CO2 is still released, but the emissions are offset by fast growing plants during photosynthesis. Considering how Rio Tinto use, process, produce and transport the biomass too, sustainable research has been conducted, such as avoiding deforestation to clear land for crops, and conserving high value forests. The Pilbar iron has begun its journey into environmentally friendly production with new sustainable technologies, and there is hope very soon that, with further research needing to be carried out, BioIron can be made on an industrial scale, and make its way across the globe, to decarbonise steel production that is so vital to everyday life.