What is woodgas and how does it work?

Woodgas is a gas, think propane. It is produced by partially combusting wood in an oxygen controlled environment. The easiest way to explain the process is to think of the last time you watched a fire burn, if you look closely you should see at least two colors of flame. In fact you may have noticed that the flame on a big fire isn't actually touching the wood. The wood is being transformed from a solid into a gas. The first color you may see, especially at night is blue, the blue flame is almost always invisible during the day. The second color is an orange flame, very noticeable. The third color may not be always present depending on the heat of the fire and it is yellow.

The blue flame is hydrogen. Hydrogen forms water when it combusts and since hydrogen is the strongest attractant of any free oxygen it oxidizes first (burns). The orange flame is carbon monoxide (CO). CO is formed next because there is more carbon (wood) present at this point in the combustion cycle than oxygen. The yellow flame is carbon dioxide (CO2). CO2 is formed when the fire is hot enough that the CO can form a second stage burn, if more oxygen is available.

Woodgas in a usable form must be pulled off the combusting wood before it gets more oxygen. The gas is then filtered, to remove ash and soot and cooled to remove any water that has formed during the combustion cycle. Cooling the gas also increases the BTU content, the gas is denser and the non combustible water has been removed. The filtered, cooled, gas then can be used as fuel. Like propane you can run an internal combustion engine on a gas. When the gas is combusted in a motor or burned like a propane gas, the end emission product is water and carbon dioxide. The beauty of woodgas is that it can claim a negative carbon emission. Any CO2 emissions are equal to the amount of CO2 the donor tree consumed in its life cycle. The ash by-product contains quite a bit of small charcoal (carbon) if the ash is used to enrich your garden soil, that is technically carbon sequestration. Not even an electric car can claim negative emissions, even if it was charged with solar panels, instead of coal based electricity, or even nuclear power. Well I suppose you could charge an electric car with a woodgas powered charging system, but you get the point.

This has been a brief overview of woodgas, and is over simplified. Also please do note that woodgas while a clean, environmentally friendly fuel, does contain carbon monoxide, until it is combusted. Carbon monoxide poisoning from a woodgas system is possible and woodgas should be treated with care and respect, never use woodgas indoors, in a closed garage, or in any poorly ventilated area. If you do decide to attempt to run a vehicle on woodgas, a carbon monoxide detector inside the vehicle would be highly advisable.


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