In some industries, steel, concrete and traditional brick making come to mind, the release of carbon has been inherent to the production process. Bricks in the UK were traditionally made by mixing colliery waste with clay and baking them, the coal waste provided part of the heat energy needed to heat the kiln. In steel production the reduction of the iron oxide in the ores is done using carbon. For most of recorded history this carbon came from charcoal.
So long as the quantity of iron produced was small, the process was sustainable and would not have resulted in CO2 build up. Coppicing was used. That is to say trees were encouraged to grow offshoot stalks close to ground level that could be repeatedly harvested for fuel. Rising demand outstripped what coppicing could supply. By the 18th century so many trees had been cut down to provide charcoal that there was a switch to coal derived coke.
Coppicing was a technique of trimming trees near ground level
to provide a sustainable supply of fuel. In the pre-fossil fuel iron
industry, coppiced charcoal was used to reduce the iron ore.
If the steel industry were to switch back to sustainable charcoal as its source of carbon this would imply a considerable diversion of wood from other potential uses.
However given the amount of wood currently being used as bio-fuel in the UK, this might be possible if the bio-fuel power stations were replaced by wind or atomic ones.
Even doing this implies considerable imports of wood from the Baltic, and the sustainability
of that trade is not clear.
The UK produces about 12 million tons of steel a year. At a carbon utilisation rate of between 2 to 3 tons per ton of output, this implies a use rate of the order of 30 million tons of carbon. It is possible to extract 1 ton of charcoal from 3 tons of dry wood, so that implies that the steel industry would consume around 90 million tons of dry wood in this scenario. A plausible yield per hectare of coppice woodland is 12 tons of dry wood . So for current steel production we would need about 8 million hectare of woods. Bearing in mind the very much higher rate of fixed capital formation required during the green transition, which implies more steel, this is probably an underestimate. For comparison, the Forestry Commission estimated that in 2018 the are of forest in the UK was some 3.1 million hectares.
It is evident, therefore that the idea of reverting a charcoal fueled steel industry is of dubious practicality even here, far less on a world scale. Instead it is likely to be necessary to fundamentally shift from the use of carbon to hydrogen. This has become a pressing concern for the international steel industry. KUSHNIR for example, investigate the implications of shifting the Swedish steel industry to direct hydrogen reduction of ore. The process would involve the use of electric energy to break down water into hydrogen. They report that such a process would involve a great deal more electricity, over 3000KWh extra per ton of electricity. The main use of this is the breakdown of water into hydrogen. This extra electricity would have to be factored into the power plant plan requirements.
To run the UK steel industry that way would require about 2 extra Hinkley Point C power plants.
2 extra Hinkley point plants seem more feasible than tripling the amount of forrest and converting all of that to coppice.
Producing steel by direct reduction of ore
using hydrogen allows CO_2 emissions to be eliminated.