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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?

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  • 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? 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.
    – 410 gone
    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. 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/… Sep 22 '16 at 5:35
1

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?

I'll answer the first:

Direct reduction of iron oxide to iron using hydrogen.

There are several features that make this a promising alternative:

  1. Firstly, renewables installation will eventually reach a phase where the maximum production exceeds the demand for electricity. A wind turbine produces on the average around 30% of its maximum production (for offshore wind power about 45%), and a solar PV array produces on the average around 10-15% of its maximum production depending on the latitude. So when it's really windy or sunny, we have excess power because the systems need to be sized so that average production matches the average consumption. This pushes the price of electricity to zero.
  2. Secondly, unlike solar cells that are a rocket science (solar PV modules by the way cost only around 200 EUR per kilowatt), electrolysis cells are not. So despite the fact that today electrolysis cells cost 1000 EUR per kilowatt, we'll likely see a price below 200 EUR per kilowatt. So electrolysis cells can turn the excess electricity to hydrogen. But it's not ecomonical if continuously done. You need to do it only when electricity is really cheap or free.
  3. Thirdly, hydrogen storage is difficult for the average user, but mandatory if we want to put the excess electricity that is zero-priced to a good use. You need to do it underground because no above-the-ground structure can withstand the high pressures required unless the walls are so thick the costs are prohibitive. So unlike batteries which Elon Musk is promoting as a solution to the energy storage problem (and which they are not due to their limited capacity) and which can be bought by the average home user, hydogen storage needs to be done in an industrial scale under the ground. So a perfect match for a steel-producing plant to act as an electricity grid balancer using hydrogen storage.

The Finnish-Swedish steel company SSAB is planning to use direct reduction of iron oxide to iron using hydrogen on an industrial scale. This ambitious plan will need large amounts of renewable electricity, though, and to be economical it might also need the price of electrolysis cells to decrease from the current expensive levels.

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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.

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  • 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.
    – user2451
    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. Dec 31 '16 at 1:37
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Apparently you do not understand the iron making process. The metallurgical coke serves as physical support of the raw material in the blast furnace, not just as a source of carbon. The support is needed to permit flow of gases up through the furnace . The carbon can be and is supplanted to some degree by addition of nat gas, oil and plastics ( Japan). IRON is produced with the coke , not steel. Steel is produced by blowing oxygen into the molten iron ( no carbon addition) . Once the steel is made you can remelt it for specific use with electric furnaces. Continuous casting has made a substantial reduction in energy consumption in the steel industry.

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Sweden’s H2 Green Steel plant is $4bn green giant fuelled by hydrogen

Decarbonised steel production is becoming a reality in Sweden where H2 Green Steel is building a €2.5bn ($3.9bn) hydrogen powered steel plant that is set to start up in 2024.
H2 Green Steel‘s plant in northern Sweden is to supply European end users with steel produced without fossil fuels and is billed as the world’s largest green hydrogen plant.
...
Instead of producing steel in a blast furnace, green steel is made in an electric arc furnace in a process that produces less than 0.1 tonne of carbon dioxide for 1 tonne of steel.
Green hydrogen employs electrolysis to split water into its two elements of hydrogen and oxygen and the electrolysis process can be powered from low-emission sources like solar.

Could green steel become one of Australia’s most strategic minerals?

Green steel -- likely later than sooner

Green steel, or carbon-neutral steel, would be produced using green hydrogen generated from renewable energy sources rather than fossil fuels, either as an alternative to pulverized coal injection, or PCI, material or as an alternative reductant to produce direct reduced iron, or DRI. The International Energy Agency projected that DRI based solely on hydrogen manufactured via electrolysis will occur as early as 2030.

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  • Generally magazine writers do not understand what they are writing about . I think what he was told is that the 50 year old pelleting enrichment process would be taken much further . Instead of blast furnace gas ( CO , H and methane ) H would be used to reduce oxide content to very low levels like 1 %. Then an electric furnace would be used to melt the iron pellets and the melt would be fluxed to reduce S, P and Si. No clue how they heat the pellets. Ferroalloys would bring the tiny amount of carbon needed along with Mn and any other alloys . It will be interesting to see if it works . Apr 1 at 21:16
  • @blacksmith37 Is this description better?: miningmagazine.com/sustainability/news/1394253/… Apr 1 at 21:38
  • Yes, they are direct reducing pellet ore . But do not say how they heat it. Also fluxing the melted iron to remove impurities is new technology to be developed. I will try to follow developments. Apr 2 at 3:36
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Nothing, Steel is 0.3-2% carbon by mass. Methods for reducing co2 emissions may work. In essence, this process relies on my Tax £'s subsidising wealthy companies so they can charge me more for a product quoting increased production costs that I am subsidising. The world death rate has halved since 1950........So doing my six year old research and maths here..... In 1950 when the world population was 2,300,000,000 with 750,000 vehicles, and considerably less industry than today, the death rate was 19.7 per 1000. Whereas now we have 7,900,000,000 people and 1,200,000,000 cars and considerably more industry, but the death rate is only 9.2 per 1000,. With the much shouted increase, by a factor of 10 by some, in pollution since 1950, but with a death rate that has gone down, I would be looking in another direction than pollution for some answers. Even with the advancements in medical wizardry, that you will no doubt try to quote as the saviour of all mankind, the reduced death rate also has to be balanced against a 1000 fold increase in industrial activity. So the medical advancements and increased activity cancel each other out.

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