Iron ore reduction

[duncan webster 1Participant @duncanwebster1]

<p style=”text-align: center;”>Nothing to do with model engineering, but anogher thread is drifting off into climate change, so i thought I’d ask if anyone knows why this won’t work.</p>
Iron ore is largely converted to iron using coke to rob the oxygen. According to the interweb you can also use methane or syngas, which is a mix of hydrogen and carbon monoxide produced by pyrolysis. Again according to the web you can produce syngas from polythene,  which is composed of carbon and hydrogen. Presumably this would also work with polypropylene and PET. Producing iron this way would still result in CO emession, but less than coal, and it would give a value to waste plastic and so reduce dumping into the sea. So why won’t it work? Even better if you could use the plastic direct, missing out the syngas stage

[SillyOldDufferModerator @sillyoldduffer]

The chemistry works but not the economics.  Problem is the cost of collecting the plastic and transporting it to the furnace.  Doesn’t help that plastic is very light (less Carbon per kilogram than coke), and that some plastics are toxic when heated.

Good news!  There are many ways of reducing Iron ore without coke.   For example, Hydrogen made by electrolysing water with surplus renewable electricity could be used.   The process is clean: electrolysis produces Hydrogen and Oxygen, and reducing Iron Oxide with Hydrogen produces Iron and water.

Dave

 

 

[duncan webster 1Participant @duncanwebster1]

According to my reckoning, 1 kg of coke absorbs 2.67 kg of oxygen, whereas 1 kg of polyethylene absorbs 3.43 kg.

Polythene contains only carbon and hydrogen, ditto polypropylene, PET is polyprop with a carbon, hydrogen and oxygen. Nothing toxic in there. Producing coke from coal produces all sorts of unpleasant stuff

[FulmenParticipant @fulmen]

I don’t think plastics will work in a traditional blast furnace. The charge needs to be porous to allow carbon monoxide to permeate it, soft fuels will simply collapse.That’s one of the reasons for using coke, it allowed for larger furnaces.

With plastics it’s even worse as it will melt, that might turn messy.

[Nigel Graham 2Participant @nigelgraham2]

Arc-furnaces were used for ore smelting in Sweden, Germany and the USA, more than 100 years ago.

The process still needed a reducing-agent and flux. My reference book concentrates on the electrical engineering and does not identify those two reagents, but I guess they were still coke and limestone.

This process demands vast quantities of electricity, but so would electrolysing water to give hydrogen, and it is still necessary to heat the ore.

[FulmenParticipant @fulmen]

Seems like Direct Reduced Iron using syngas has great potential, and syngas from waste is already a thing. So yeah, it’s doable. But they already have competition from the cement industry that has handled waste for decades.

[not done it yetParticipant @notdoneityet]

There was very good reason for using coke, rather than coal in a blast furnace.

The charge is mixed at the top of the furnace and heats as it descends, burning at the hottest part of the ore reduction process.  Any volatiles in the coal would be either volatilised, in the absence of free oxygen, or burned in a surplus of oxygen along with the rest of the coal – in the wrong place in the furnace.  Simple as that.  Coal did not work but coke did.

Clearly, plastics could only be used by ‘firing’ at the point of reduction.  With an arc furnace, there would only be the plastic, plus whatever it is carried into the reactor by, and still the slag to be dealt with.

As soon as oxygen (even from the PET) is available the graphite electrodes may well be rapidly eroded.

Hydrogen, I suspect, is likely far better than plastics, as a reducing agent – because the process control would be protecting the electrodes.

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