Posted by Krzysztof Lis on May 8, 2008
Is wood gas a biofuel? Is it renewable?
It sure is, because it is made from renewable feedstock – wood or any other biomass. If it’s made from some other biomass like grass or rice husks, it’d probably be called producer gas though.
Is wood gas a clean fuel?
In most cases, burning wood gas produces almost none harmful substances.
Wood gas combustion produces carbon dioxide, the most important greenhouse gas. But since the wood gas was made from renewable feedstock (biomass), the carbon dioxide cycle closes. It is a commonly accepted rule that combustion of biomass does not produce extra carbon dioxide, because the carbon bound within biomass was taken from the atmosphere by the plants.
As for the sulphur oxides, their emissions negligible compared with the case of burning such as coal. Wood contains a lot less sulphur than coal, so it’s combustion produces a lot less sulphur oxides.
Dust? Also, it can be assumed that emissions of particulate matter is negligibly small, because of two factors. First of all, dust particles are removed from wood gas before it’s fed to the engine. Secondly – from the engine exhaust pipe is located on a small height, so that even if the exhaust gases contain some dust, they fall to the ground soon.
Nitrogen oxides are also emitted in smaller quantities than for petrol or diesel fuel. Wood gas has smaller calorific value (heating value) than petrol / diesel, so peak temperature in combustion chamber is lower than for those two fuels. This leads to lower content of thermal nitrogen oxides in the exhaust gases.
The only not safe component present in wood gas exhaust gases is carbon monoxide. It is an essential component of the wood gas itself, so using this fuel instead of petrol / diesel / LPG will lead to its increased presence in exhaust gases. When wood gas is burned in some burner, for example in central heating boiler, this is not a concern, since there’s enough time for the carbon monoxide to be burnt fully to carbon dioxide.
Producer gas can be produced from many different fuels. It can also be made through gasification of waste that can’t be used for any other purpose. I had the opportunity to visid a plant that makes producer gas out of tannery waste, conaminated with chromium (used in processing of hides). The only left waste from this gasification is ash, that can also be used! It containes the chromium so can be used to make some paints. If not gasified, this waste can be only stored at a specially prepared landfill.
Compared to many so called biofuels, wood gas is quite environment-friendly. It does not require any energy to be used to make this fuel, except for the energy used to make the wood chips fed to the gasifier. You don’t need to use natural gas or coal to distill it, like ethanol, or heat it, like biodiesel.
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