Despite doing a convincing – and carbon-neutral – impersonation of a ‘fossil fuel’, charcoal is largely neglected in the developed world. It has high heating value, low sulphur content, high carbon-to-ash ratio, low inorganic impurities and high surface area. It is lightweight and almost smokeless.
In developing countries charcoal is only really used for heating and cooking, but there are hundreds of potential uses. It forms a rich source of carbon for industrial applications, for example as a reducing agent in blast furnaces or as an adsorbent. It has been used to produce gas to power diesel and gasoline engines.
Some of the most promising applications of charcoal are as a sustainable substitute for coke, petroleum coke, lignite and coal. Charcoal can also be used for soil preparation to promote growth in corn and other crops. In addition, it offers valuable possibilities for carbon sequestration.
Charcoal can replace fossil fuels
Traditional charcoal production is small scale and actually one of our oldest human skills. Burning part of the wood generates the heat needed to dry and carbonise the rest in an oxygen-starved atmosphere.
The major issues have been the relatively low efficiencies of traditional methods (gaining about a ton of charcoal from about 4.5t of dry wood), and the pollution from the smoke given off.
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Both these can be improved by industrial production techniques which, if properly designed and controlled, can yield 1t of charcoal from 3.5t of wood, according to the Food and Agriculture Organization of the United Nations. Brick kilns are usually the most economical, burning the off gases as an extra fuel for carbonisation.
Retort-based industrial systems instead capture the vapours and recover gas and other chemicals by passing them through a condenser. Retort systems, however, need relatively high investments and skilled labour. Liquid effluents have to be carefully handled and disposed of.
After that, the recovered chemicals can be expensive to process before they are suitable for sale. At present they can usually be produced more cheaply from fossil fuels, although those economics may change as fossil fuels further deplete.
Small-scale production has its place
The ‘right’ type of production isn’t always obvious and the choice depends on the balance between capital investment, yield, transport costs for wood and charcoal, the number of jobs created and the ability to recover by-products.
There is still a place for small-scale production, particularly in the developing world. Here, investment capital is scarce, but labour is cheap. It may often be better to use the money to employ local labour to grow more wood, where conditions make that possible.
Traditional processes have their own advantages. They can use large pieces of green wood instead of the small, constant sizes of well-dried wood needed by most industrial systems, which can therefore have the disadvantage of having large wood preparation costs.
Whatever the method of production, the process must be sustainable and have minimum environmental impact. We can’t make the same mistake as with biofuels – cutting down virgin forest to produce it makes no sense.
Forest management instead naturally produces huge volumes of surplus wood, and this can be supplemented by non-woody plant waste.
Given the carbon credits it deserves, charcoal could profitably replace coal as a fuel. As a soil conditioner, it could lock carbon back into the soil for hundreds of years.