How much carbon is produced in the manufacture of a ton(ne) of steel ?

Varies a bit: a COREX plant can be up to 2.2 tons CO2 per ton of hot iron (but some of that will be as export gas), and a modern HIsmelt or DIOS plant might only produce about 1.2 tons of CO2 per ton of hot iron

- but this is at the lowest end.

Say 1.5 - 2.5 tons per ton of rolled steel overall, probably averaging a little under 2 tons CO2/ton steel.

(I have ignored electric smelters, as the electricity to run them has to come from somewhere - if the lekky is carbon-free and natural gas is used as the reductant it might go as low as 0.7 tons CO2/ton steel, but this is impractical)

-- Peter Fairbrother

Peter,

I had to look up Corex, I am a little out of date. Isn't that just iron production, so leaves all the steel production side. Which takes a fair bit of energy, as does the casting, soaking pits, and rolling - I assume you don't just want a 1 tonne ingot ?

Steel plant will include a considerable fraction of recycled steel, so a big fraction of iron stays in circulation once extracted.

I once contacted an organisation (was it the energy saving trust), regarding the benefit of keeping an old car going compared to buying a new more economical model. They came up with a fairly rational answer, and certainly for my regular car it there is no sound environmental reason to dump it even though it is 13 years old.

Steve

Thanks !

Yes, COREX and HIsmelt/DIOS smelters produce "hot iron" (molten iron, usually about 4% carbon) from iron ore and coal - these are usually co-located with steelmaking converters and a steel mill though.

Smelting is the most energy-requiring and CO2 producing part of the steelmaking process.

{ COREX is the major smelting technology used today. HIsmelt and DIOS are the new kids on the block. They replace the old blast furnace and coke oven - the coal is used in the smelters directly, rather than being made into coke, which has many pollution-related and efficiency advantages }

so leaves all the steel production side. Which takes

The input energy for hot iron -> hot steel can be considered to be just pumps, cranes and conveyors.

Conversion gives off a bit of CO2 from burning the carbon in the hot iron though (the heat from which is used to melt the scrap). The export gas from the COREX process, or part of it, may also be used to melt (or usually just preheat) extra scrap, so the ratio of scrap can be higher.

{ steel is produced today by the basic oxygen process, a steelmaking furnace is charged with a mixture of scrap and hot iron and oxygen is blown through it. The 4% carbon in the hot iron burns, the heat from which is used to melt the scrap - the hot iron from the smelter/blast furnace is already molten. }

as does the casting, soaking pits, and rolling

Casting uses little energy (the metal is already molten), soaking pits and rolling can use quite a bit (but less than smelting).

Typically about 20% of the steelmaking converter charge is scrap, the rest is hot iron from the smelter. Larger scrap ratios are possible but unusual in primary steel production.

The process map can be insanely complex (!!), and just talking about single bits of it often doesn't give more than a rough idea of what's going on. Plus a detailed map with figures is going to be a proprietary secret, so you have to estimate a bit.

When you have a combined smelter, converter and steel mill it can get really complex, with various interactions between them like the use of export gas in the soaking pits.

In calculating CO2 release you also have to consider the CO2 from the lime used as flux, the extra steel produced from scrap, the 96% composition of hot iron, the treatments (eg desulphurisation uses magnesium, which costs a whole lot of energy to produce - but the desulphurisation reaction gives off a lot of heat) - and so on.

I have tried my best, without doing lots of research.

A COREX smelter will typically operate at about 1.8 tons CO2/ton hot iron, the converter and mill will use the rest.

About 2.0 tons CO2/ton steel seems a reasonable figure for developed world COREX-based production, and about 1.9 tons CO2/ton steel for HIsmelt/DIOS - but note that the figure for secondary production in the developing world will be higher, sometimes much higher.

Though new large primary plants in China, India etc are often COREX plants.

-- Peter Fairbrother