Coking coal: How energy resides
How carbon strips oxygen from iron in the furnace
What this tab covers The physical form in which the energy is held or carried, where it comes from, the chain of transformations that put it there, and how concentrated it is.Coking coal is bituminous coal whose chemical energy is used twice in a blast furnace: as fuel for heat and as carbon that strips oxygen from iron ore.
Form Chemical energy in carbon-rich fossil plant matter with caking properties Origin Fossil solar (ancient photosynthesis)How it got there
Fusion in the Sun Sunlight Photosynthesis in swamp plants Peat Burial to bituminous rank Mining and washing Baking in coke ovens without air Coke in the blast furnace: heat plus carbon monoxide to reduce iron oreHow concentrated it is
| Measure | Value | Note |
|---|---|---|
| Coking coal, net calorific value | 28.2 (range 24.0 to 31.0) MJ/kg1 | IPCC default; higher than typical steam coal (25.8 MJ/kg). |
| Coke oven coke | 28.2 (25.1 to 30.2) MJ/kg1 | Volatile matter driven off, leaving a hard, porous carbon solid. |
| Quality limits for metallurgical coal | under 1% sulphur, under 8% ash% by weight2 | Typical values cited from the USGS. |
| Coal input per tonne of blast-furnace steel | 800 kg coal per tonne of crude steel3 | Plus about 1,400 kg iron ore and 300 kg limestone. |
Coking coal formed in the same way as other bituminous coal, but its particular mix of volatile compounds lets it soften, swell and re-solidify when heated without air. Coal of this kind, usually a blend, becomes coke: a strong, porous lump of almost pure carbon that can carry the weight of the charge in a blast furnace while letting gases pass through.
In the furnace, coke burns to supply heat. It also forms carbon monoxide, which pulls the oxygen out of iron oxide. So coking coal is a chemical reagent as much as a fuel, which is why it is hard to replace. About 800 kg of coal goes into each tonne of steel made by the blast-furnace route.
Sources
- 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Vol. 2 Energy, Ch. 1 Introduction (Tables 1.2 and 1.4) IPCC, 2006
- Metallurgical Coal: Frequently Asked Questions (R48635) US Congressional Research Service (via EveryCRSReport), 2025
- Fact sheet: Steel and raw materials World Steel Association (copy hosted by Australian Steel Institute), 2018