Wood gas

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Wood gasifier on an Opel P4 (1940)
Wood gasifier locomotive in the Bavarian Railway Museum in Nördlingen. The vehicle was built by Deutz in 1916 for the benzene operation and converted by Imbert in Cologne in 1935

Wood gas is a combustible gas that can be obtained from wood; it is produced in wood gasifiers .


In times of war and crisis in particular, when there was a lack of fuel, vehicles were mostly equipped with an improvised wood gasifier on their own initiative. Even the German Reichsbahn tested the use of wood gasifiers of shunting locomotives series Köf II in the 1930s and 1940s (see also: gas engine ).

Wood gas was used, among other things, internal combustion engines of motor vehicles to drive. The generators were built on the outside of the body or carried as trailers. The technical system for this, the wood gasifier, was filled with firewood and functioned as a fixed bed gasifier . The combustible gas mixture (wood gas) escaped from the wood through heating.

At the end of the Second World War there were around 500,000 generator gas vans or wood gas vans in Germany . Generatorkraft , which was subordinate to the Reich Ministry for Armaments and Ammunition , served to supply them - a stock corporation for tank wood and other generator fuels with its associated filling stations.

In the Soviet Union , trucks equipped with wood gasifiers were built in large series, in particular the ZIS-21 models (based on the ZIS-5 ) and the GAZ-42 , of which almost 35,000 were produced between 1939 and 1946. The reason was that, particularly in the far north of the Soviet Union, the fuel supply was not yet secure in the 1930s and 1940s.

Until the early 1950s, a number of small trucks with a special driver's license were in use in Germany for which only tested and approved beech logs could be used. About one liter of gasoline could be replaced by the amount of gas obtained from 3 kg of wood. The wood specially dried for wood gasification and chopped into the right size was called tank wood and was produced and stored in so-called tank wood plants.

In the Schaanwald in Liechtenstein there is a private museum with around 70 wood gas vehicles from motorcycles to tractors. The classic cars are roadworthy and are moved from time to time, using waste from a furniture factory as fuel.

In the context of the discussion about the increasing use of renewable raw materials at the end of the 20th and the beginning of the 21st century, wood gasification and the gasification of other organic substances, especially organic residues, were taken up again to produce gaseous fuels for heat and electricity generation and implemented in individual demonstration systems. Based on this purely energetic use, the use of the product gas as a raw material for the chemical synthesis of biofuels and products of the chemical industry was also targeted and is to be implemented in the near future primarily for BtL fuels , dimethyl ether and methanol . Subsequent methanation and processing enables it to be fed into the natural gas network as Substitute Natural Gas (SNG). High-quality product gases that contain more than 50 percent hydrogen are also referred to as bio - hydrogen .


Wood gas consists of combustible components, mainly of carbon monoxide 34% and methane 13%, as well as smaller proportions of ethylene 2%, hydrogen 2% and resin terpenes , as well as non-combustible components such as nitrogen 1%, carbon dioxide 48% and water vapor. At approx. 1.5 kg / m 3, wood gas is heavier than air under normal conditions . The calorific value of wood gas is around 8.5 MJ / m 3 with conventional autothermal gasification and over 12 MJ / m 3 with allothermal gasification.

The composition of the wood gas can vary greatly depending on the production process. When using air (21% by volume of oxygen, 78% by volume of nitrogen), the product gas contains a very high proportion of nitrogen, which does not contribute to the calorific value of the gas and reduces the hydrogen yield. On the other hand, when using oxygen and water vapor, the product gases do not contain nitrogen and accordingly have a higher calorific value and a high hydrogen yield.

Gas use

The gas produced in the biomass gasification can be used both energetically and materially.

Energetic use through combustion

The current common use for the gas mixture of the biomass gasification is the motor use (in accordance with the petrol or diesel principle), or the combustion in the corresponding combustion plants for production of heat (steam) and electrical power , wherein a cogeneration a very high efficiency of energy conversion is achieved. The wood gas condensate resulting from gas cooling must be properly treated in these systems before it can be fed into a receiving water , as it has a high biochemical oxygen demand. Alternatively, the gas mixture may biomass gasification in solid oxide fuel cells are converted directly to electricity. The active principle was already proven in 2004 in tests.

Use as synthesis gas

In addition, a product gas composed of carbon monoxide and hydrogen can be used as a synthesis gas for the chemical synthesis of various products . The material use of synthesis gas from biomass gasification is still under development; such systems are currently only found on a laboratory and demonstration scale. The large-scale production and use of CO / H 2 synthesis gas accordingly takes place exclusively on the basis of natural gas and other fossil fuels such as coal and naphtha .

The chemical-technical options for use are primarily the production of hydrogen and the subsequent production of ammonia using the Haber-Bosch process , methanol synthesis, various oxo syntheses and the production of biofuels (BtL fuels) and other products via fishermen -Tropsch synthesis :

Process scheme for the production of BtL fuels
  1. in ammonia synthesis using the Haber-Bosch process
  2. in methanol synthesis
  3. in oxo synthesis
  4. in the Fischer-Tropsch synthesis

In addition to these chemical-technical areas of application, synthesis gas can also be used biotechnologically via synthesis gas fermentation . Products of this option can for example be alcohols such as ethanol , butanol , acetone , organic acids and biopolymers . This use is currently still in the development stage and is accordingly not yet used on a large scale.

With all these types of use, it must be taken into account that the water, as part of the process chain, condenses when the gas cools down and is contaminated with organic substances to varying degrees as wood gas condensate ; The proper disposal of this wastewater (about 0.5 liters per kg of wood) is listed here in the BtL scheme as "by-products", but it is an essential part of such systems.


In the production of biofuels, too, the product gas produced in the gasification process is used as synthesis gas in the synthesis processes already described. The focus is on gaseous fuels such as bio-hydrogen, substitute natural gas (methane, SNG) and dimethyl ether, as well as liquid fuels such as methanol and BTL fuels.

Biohydrogen is obtained from the synthesis gas by means of steam reforming , methane can be produced by methanation of the gas. Methanol synthesis is used to produce methanol and dimethyl ether. BtL fuels are produced using the Fischer-Tropsch synthesis, whereby both gasoline and diesel fractions can be produced due to the process parameters.

supporting documents

  1. ^ Ian Byrne: A 1941 map from Generatorkraft. July 2000, online at PetrolMaps.co.uk, accessed January 6, 2017.
  2. ^ Gorkovsky Avtomobilny Zavod (GAZ). On the history of the GAZ-42 and the wood gas drive in the Soviet Union in general. June 15, 2007, online at denisovets.ru, accessed January 6, 2017 (Russian).
  3. Martin Ebner: Put the beech in the tank! In: Südwest Presse Ulm. May 16, 2009, online at martin-ebner.net, accessed on January 6, 2017.
  4. Composition ( Memento from February 22, 2016 in the Internet Archive ) (PDF; 91 kB), on scheffel.og.bw.schule.de, accessed on February 24, 2017.
  5. ^ Hermann Hofbauer, Alexander Vogel, Martin Kaltschmitt: Vergasung. Gasification technology. In: Martin Kaltschmitt, Hans Hartmann, Hermann Hofbauer (Hrsg.): Energy from biomass. Basics, techniques and procedures. Springer Verlag, Berlin / Heidelberg 2009, ISBN 978-3-540-85094-6 , pp. 600–601.
  6. Martin Zeymer, Yves Noel, Roman Schneider: Flue gas emissions from small-scale wood gasification plants - state of the art . In: Hazardous substances - keeping the air clean . tape 75 , no. 5 , 2015, ISSN  0949-8036 , p. 167-171 .
  7. Florian-Patrice Nagel: Electricity from wood through the combination of gasification and solid oxide fuel cells. Dissertation, Eidgenössische Technische Hochschule ETH Zurich, No. 17856, Zurich 2008, online at ethz.ch (English), accessed on January 6, 2017.
  8. ^ Hermann Hofbauer, Alexander Vogel, Martin Kaltschmitt: Vergasung. Gasification technology. In: Martin Kaltschmitt, Hans Hartmann, Hermann Hofbauer (Hrsg.): Energy from biomass. Basics, techniques and procedures. Springer Verlag, Berlin / Heidelberg 2009, ISBN 978-3-540-85094-6 , pp 599-600.


  • T. Metz: Allothermal gasification of biomass in indirectly heated fluidized beds. Dissertation, TU-Munich, 2005, online (PDF; 2.76 MB), on energetische-biomassenutzen.de, accessed on January 12, 2017, VDI-Verlag, 2007, ISBN 978-3-18-355406-5 .
  • A. Vogel: Decentralized electricity and heat generation from biogenic solid fuels. Dissertation, University of Hamburg-Harburg, 2007, IE-Report 2/2007, publisher: Institute for Energy Technology and Environment gGmbH, Leipzig, ISSN  1862-8060 .
  • Hermann Hofbauer, Alexander Vogel, Martin Kaltschmitt : Gasification. In: Martin Kaltschmitt, Hans Hartmann, Hermann Hofbauer (Hrsg.): Energy from biomass. Basics, techniques and procedures. Springer Verlag, Berlin and Heidelberg 2009, ISBN 978-3-540-85094-6 , pp. 599-669.
  • Heinz Hiller among others: Gas Production. In: Ullmann's Encyclopedia of Industrial Chemistry . Wiley-VCH, Weinheim 2005, doi : 10.1002 / 14356007.a12_169.pub2 .

Web links

Commons : Holzgas  - collection of pictures, videos and audio files