Apr 15 Small woodland owners and charcoal – by Gervais Sawyer By Tracy

It is a given fact that small woodland owners are committed to green and environmental activities, so why, I wonder, do they want to get involved in charcoal production? The economics, efficiency and pollution aspects really make no sense.

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Why make charcoal?
So why do you want to make charcoal in the first place? I presume that it is for the purposes of barbecuing your food for the enjoyment of the great outdoors. And what is so special about cooking over charcoal? Does it impart some special flavour? That is not quite logical, because charcoal should be a very pure form of carbon and you might just as well cook over a propane fired grill. But perhaps you are thinking that it will give your food some special smoky flavour? You can achieve this by sprinkling some oak or hickory chips over the glowing charcoal to give you lots of fragrant smoke that will put all sorts of dubious chemicals into your food.

Very pure charcoal is interesting stuff. It can absorb harmful gases and other chemicals. I can’t turn water into wine, but I can turn red wine into white wine by filtering it through active charcoal! Active charcoal is produced from better sources than wood, notably coconut shell.

The best barbecues that I ever experienced were made by my father-in-law, who would light a fire of small hardwood branches laid in a radial pattern. When it was thoroughly hot, he would pull the branches apart to stop the flames and leave plenty of glowing embers in the middle with plenty of smoke from the ember/solid wood interface. So, if it’s charcoal for flavour that you want, partial carbonisation is the answer. My second most memorable barbecue was on a beach in the Scilly Isles. Having no charcoal or driftwood, we built a fire of dry seaweed thrown up by winter storms. It produced a lot of smoke and the result was amazing. Our pork was probably 20% iodine!

What is the charcoal process?
The chemical reactions during pyrolysis depend on the speed of the reaction. Traditional charcoal production is slow pyrolysis. Wood, being a good insulator (and charcoal an even better one) transmits heat slowly to the inside of a piece of wood. This favours reactions producing mostly volatile gases and some tarry residues. (Owners of slow burning wood stoves will know ALL about tar residues in the flue.) If you want to get rid of the tarry component as well, then temperatures must be allowed to rise, burning some of the charcoal in the process. Combustion must then be stopped by cutting off the air supply and allowing to cool.

If the pyrolysis is done very quickly by grinding wood into small chips and injecting them into a hot zone, the products are quite different. Much research effort has been put into this as it yields a large proportion of heavy oil that can be used for heating or diesel fuel.

Environmental aspects.
Charcoal manufacture is wasteful in the extreme. Of the available energy in dry wood, only about 10% comes out as charcoal. The rest of the energy is wasted in firstly drying the wood and subsequently in supplying the energy for the pyrolysis reactions.

Most of the pyrolysis products are volatile such as methane, ethane, methanol, carbon dioxide, carbon monoxide, acetic acid, tars and heavy oils, most of which will be emitted to air through the exhausts. At one time, these volatiles were condensed out and sold for industrial use. However, in the oil age,  the process is uncompetitive.It is therefore hardly surprising that many countries apply strict controls of charcoal burning. However, where manufacture is on a larger scale, requiring considerable capital investment, yields are higher and emissions are burnt to provide the energy for the whole process. Even if small woodland owners were able to cooperate in such a capital investment, the economics of harvesting and transporting thinnings and coppice would be marginal compared with imported charcoal.

Burning charcoal produces carbon dioxide and carbon monoxide. As you are no doubt well aware, carbon monoxide is a lethal poison, and thousands are killed worldwide every year from burning charcoal in confined spaces, and many more hospitalised in ‘near misses’. Indeed, many cases of suicide pacts are accomplished by lighting a barbecue in a closed bedroom. Even use of a barbecue in an indoors fireplace is risky. So we may regard burning charcoal as polluting and wasteful of an already wasteful energy source. The carbon monoxide is a fuel in itself. Those who remember town gas may be surprised to know that it was about 15% carbon monoxide and 50% hydrogen.

Producers of charcoal would like it all to be in nice clean lumps. However, inevitably it also produces quite a lot of fine, dusty material that can either be formed into briquettes or used as a soil conditioner. These fines may comprise particles smaller than 10 micrometres which can penetrate into the lungs if inhaled. Since wood shrinks as it firstly dries and then carbonises, it will break up since the core of the piece is still unshrunk. This is what causes the carcking and dust production. If the wood is firstly cut into small lumps, not only is the carbonisation process quicker, but there are more lumps than dust produced.

Whilst small scale charcoal production can be pursued to supply local markets, it may well be more profitable to concentrate on production of dry fuel wood and thus maximise the energy resource. The growing demand for dry wood chips to supply efficient automatic boilers may well provide the stimulus for a continuous from the small woodland owner.

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