Posted by Krzysztof Lis on March 5, 2008
Wood gas (holzgas in german) is the product of wood gasification. It consists of combustible gases such as carbon monoxide, hydrogen, methane and inert gases – nitrogen, carbon dioxide and water vapor. The composition of the wood gas depends on many factors, e.g. temperature inside the gasifier, moisture content of fuel gasified etc.
Gasification of solid fuels was invented over 200 years ago. In the beginning of 19th century town gas (manufactured from coal) was used to fuel kitchen stoves, industry and street lights. In general any combustible gas manufactured by gasification of solid fuel is described as manufactured gas or producer gas.
Gasification is the process in which the solid fuel is being subject to many termochemical reactions, at the end of those reactions you have combustible gas. This process takes place in a device called gasifier or wood gas generator.
Wood gas can be used for fueling internal combustion engines, both with spark ignition (gasoline fueled) and compression ignition (diesel fueled). The latter case needs some extra explanation.
Wood gas was very popular until the industry started using natural gas as energy source. Prior to development of natural gas supply with pipelines almost all fuel gas was manufactured from coal. Producer gas became popular during World War II, when civil customers couldn’t purchase liquid petroleum derived fuels because of the large military demand. At that time the wood gas renaissance took place.
Volumetric composition of wood gas may be as following :
- carbon monoxide CO – 19%
- hydrogen H2 – 18%
- methane CH4 – 1,25%
- carbon dioxide CO2 – 12%
- water vapor H2O – 2,50%
- nitrogen N2 – rest.
Only three first gases (marked with green color) are combustible. The rest is not combustible and may be considered as impurity, deluting the wood gas and decreasing its heating value. That’s why it’s good idea to remove those gases.One cannot remove the nitrogen from the wood gas (it’s the main component of air which is used as “gasification agent”), removal of water vapor is rather easy (it condenses when gas is being cooled). The carbon dioxide content depends on the temperature iside the gasifier (the higher the temperature, the lower the CO2 content).
Gasification is a way of manufacturing gaseous fuel from biomass like anaerobic digestion (which gives methane), but it is an instant termochemical process in contrast to rather slow biological digestion.
Producer gas is a term more general than wood gas, as I mentioned earlier. Depending on the process which gave the gas and its usage, this gas was also called:
– town gas (illuminating gas) – manufactured from coal in Manufacturing Gas Plants, used as fuel for stoves and streetlights,
– water gas (blue gas) – produced when coal is gasified with steam as gasification agent.
 H.S.Mukunda, S.Dasappa, P.J.Paul, N.K.S.Rajan, U.Shrinivasa – “Gasifiers and combustors for biomass — technology and field studies”
 H.LaFontaine, P.Zimmerman -“Construction of a simplified wood gas generator…”
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