At the moment, a very large proportion of steel production relies on coke. So even though electric-arc furnaces are reasonably energy-efficient (Professor Julian Allwood says that the best ones run at about 50% of the theoretical maximum efficiency, which isn't too bad for a real-world process), even if the supplied electricity was from clean renewable sources, steel production would still be carbon-intensive: in large part from the reduction of iron oxide to iron, but also from the iron-to-steel part of the process.

What are the most promising alternatives, in terms of the economics and scalability, to decarbonise steel production? Both for the reduction of iron oxide to iron, and for the iron-to-steel process?

  • It's not clear why you're saying the process is carbon-intensive even when the electricity is renewable. I know carbon is an ingredient in the steel itself (though not in the form of a greenhouse gas), so is it the process of getting the carbon into the iron that creates CO2 even when electricity is used for the heat? ie does a proportion of the carbon get burnt during the process? – Highly Irregular Jan 18 '15 at 23:30
  • @HighlyIrregular thanks for the prompt - I had a bit of a rummage around, and have corrected and tightened up the question a bit. – EnergyNumbers Jan 19 '15 at 1:08
  • AFAIK over here (GErmany) 90% of scrap iron gets recycled, so you can skip the oxidising step. To go that route, we'd need an economy that needs no additional iron ... – mart Jan 20 '15 at 21:55
  • Can arc furnaces be used for primary iron making? I thought that the basic reaction to make iron was FeO + Coke => Fe + CO2 (Yes various forms of iron oxide) Just getting it hot will not separate the oxygen from the iron. – Sherwood Botsford Feb 19 '16 at 15:17
  • Here is a nice report on this topic. If you have not seen it, I'd suggest flipping through: gov.uk/government/uploads/system/uploads/attachment_data/file/… – Srihari Yamanoor Sep 22 '16 at 5:35

Steel alloys are primarily iron and between 0.002% and 2% carbon. The later is called high carbon steel and is used for heat treated parts. Sometimes other elements are added for strength or other properties, such as silicon and manganese for spring steel or chromium for harder steels.

Replacing carbon with silicon, seeing as the two elements are in the same periodic group, has been tried. Unfortunately, the practical properties of steel (strength, durability, melting point, machinability, and heat-treat-ability) require the carbon atom.

Aluminum alloys are practical too, and have replaced steel in many applications. Aluminum is also more plentiful in the earth's crust than either iron or carbon and is easier to machine, however it is not as strong or durable as steel.

In steel making, carbon is either added or removed to reach some standard percentage of the element in proportion with the other elements. This is done to conform to SAE product standards. Once cannot make steel without carbon.

The steel industry exhales CO2, CO, H2, CH4, and other gasses as a result of the reactions required to meet various specifications. There are a few interesting and potentially practical ways to improve the sustainability of the steel industry.

  1. Recycle steel by SAE number so that the process is mostly removal of surface films and particulate matter, followed by melting and reforming into standard stock.
  2. Reduce consumption by improving engineering and manufacturing processes.
  3. Find ways to minimize the proportion of carbon in the input ore and recycled materials so that the steel making process consumes (rather than produces) carbon based gases.
  4. Use catalytic conversion to convert CO to CO2 and then capture all the CO2 and feed it to plants, phytoplankton, or artificial photosynthesis beds.

This last item is quite a ways down the research and development road, but it is perhaps the most sustainable of the four.

  • This answer suggest that the carbon content of the steel is the issue. I don't think that is very important in relation to the amount of fuel used to make (melt) steel. – Jan Doggen Dec 26 '16 at 19:39
  • @JanDoggen the question itself is not clear on that... – LShaver Dec 29 '16 at 3:59
  • @JanDoggen, my answer is specific to the question and only makes sense in its context. Had the question not used the term decarbonising and mentioned coke in the first sentence, I would not have structured my answer this way. It seemed important to give the questioner some background on the carbon proportions required by SAE standards. I don't think I indicated that carbon in steel anywhere in my answer. I implied the opposite. If you read a little between the lines it will become clear that the REMOVAL of carbon from the metal is what places carbon in the atmosphere in various forms. – FauChristian Dec 31 '16 at 1:37

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