Biomass fuel and gasification

Biomass is any organic solid fuel (eg. wood, charcoal, cow dung etc.) and gasification is the process of burning it in such a way that the flammable gases are be extracted. These gases, after a complex filtration and cooling process, can be stored or used immediately to power things such as generators or cars. The gasification unit can be built on a trailer, making it possible to produce the gas on the move and supply fuel to a vehicle.

The environmental advantage of using wood or charcoal to run such an engine is that although the engine will still produce potentially harmful exhaust fumes locally, the long term effect on the planet is more sustainable. Fossil fuels can never be replenished as fast as we use them but wood can, if due forethought and consideration is taken. (see: Why burn wood?)

The apparatus needed for the gasification process is however quite complex and does require a lot of welding and metalwork.

The gasification process

When wood, or any biomass fuel burns it releases gasses which under normal conditions will also burn, these are the flames we see on a fire. To extract the gas before it burns it must be starved of oxygen and any source of ignition. This requires a specially designed burner.

The basic principle is to feed just enough air for the first stage of burning that releases the gas in a controlled, air sealed environment. When the aim is to supply fuel to an engine, the draw from the carburetor intake can be used to pull the air through at the required rate. There are also other methods of making this process more efficient. One of which is to feed a little steam in with the air supply regulated by the temperature of the gas produced. The hotter the gas the more steam. The gas can be used to boil the water to produce the steam, making it self regulating. This adds a higher hydrogen content to the gas produced which means the gas contains more energy.

Once the gas is in the pipeline leaving the burner it is essential that everything is kept totally airtight. If oxygen mixes with the gas you've got an explosive mixture!

The next stage is to filter any soot and smoke from the gas and to cool it so your engine doesn't overheat or get clogged up. The best method is a wet filter as this does both jobs. These filters involve trickling water down through gravel or charcoal while drawing the gas is bubbles up through it. The water takes most of the particles out of the gas while cooling it at the same time. It is best to also have extra cooling devices on the engine (eg. radiators). A dry filter may be used as well, even if only to see how dirty it gets and judge the efficiency of your wet filter.

Then, using a choke system to control the flow of gas, it can be fed into the engine (one designed for petrol is simplest to convert) and there you have it!

Last updated: 2009-04-22

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