Wood gas generator

Gasification was an important and common technology during the 19th and early 20th century. Town gas produced from coal was widely used, mainly for lighting purposes. When stationary internal combustion engines based on the Otto cycle became available in the 1870s, they began displacing steam engines as prime movers in many works requiring stationary motive power. Adoption accelerated after the Otto engine's patent expired in 1886. The potential and practical applicability of gasification to internal combustion engines were well understood from the earliest days of their development.

In 1873, Thaddeus S. C. Lowe developed and patented the water gas process by which large amounts of hydrogen gas could be generated for residential and commercial use in heating and lighting. Unlike the common coal gas, or coke gas which was used in municipal service, this gas provided a more efficient heating fuel.

During the late 19th century internal combustion engines were commonly fueled by town gas, and during the early 20th century many stationary engines switched to using producer gas created from coke which was substantially cheaper than town gas which was based on the distillation (pyrolysis) of more expensive coal.

During World War II, gasoline was rationed and in short supply. Due to the lack of gasoline from petroleum, older people recalled how to build gasifiers for both wood and coal, and how to convert internal combustion engines to run on gaseous fuel, and wood gas generators were in active production. In Great Britain, France, the United States and Germany, large numbers of such generators were constructed or improvised to convert wood and coal into fuel for vehicles. Commercial generators were in production before and after the war for use in special circumstances or in distressed economies. Some World War II era wood gas generators were of the "Imbert" downdraft type, designed around 1920 by French inventor Georges Imbert.

Germany produced Gazogene units for vehicles including cars, trucks, artillery tractors and even tanks, to preserve the limited supplies of fuel.[1] Even in non-combatant countries, such as Sweden or Brazil, gasogene was popular, as oil became hard to obtain. In Brazil, a racer named Chico Landi won at São Paulo's Interlagos circuit in 1944, driving a wood gas-powered Alfa Romeo.[2]

Coal-based town gas production was generally displaced by petroleum-based gas and natural gas. However, Great Britain continued her use of coal-based town gas until the North Sea natural gas discoveries in the 1960s and 1970s.

• 
  Adler Diplomat in WWII with wood gas generator
• 
  Imbert gasifier on a Ford truck converted to a tractor, Per Larssons Antique Tractor Museum, Sweden, 2003
• 
  Demonstration of a working Gohin-Poulenc "gasogene" system in a 1956 Citroën Traction Avant

Saab 99 running on wood gas in Finland. The gas generator is on the trailer.

When oil prices rose there was renewed interest in wood gas generators. The US Federal Emergency Management Agency (FEMA) published a book in March 1989 describing how to build a gas generator in an emergency when oil was not available.[3] It described a design called the "stratified downdraft gasifier" which solves several drawbacks of earlier types.

The European Union sponsored a wood gas project in Güssing, Austria, starting in 2005. This project was an electric power plant with a wood gas generator and a gas engine to convert the wood gas into 2 MW electric power and 4.5 MW heat. There was also an experimental device to use the Fischer–Tropsch process to convert wood gas to a diesel-like fuel. By October 2005, it was possible to convert 5 kg of wood into 1 litre of fuel.

The Democratic People's Republic of Korea (North Korea) is also known to have trucks that run off of wood gas generators. The trucks are common outside of Pyongyang and are in rural villages and smaller towns. These trucks are utilized due to sanctions placed on North Korea regarding imports of oil and gas.[4][5][6][7]

Wood gas generators have a number of advantages over use of petroleum fuels:

• They can be used to run internal combustion engines (or gas turbines, for maximal efficiency) using wood, a renewable resource, and in the absence of petroleum or natural gas, for example, during a fuel shortage.
• They have a closed carbon cycle, contribute less to global warming, and are sustainable in nature.
• They can be relatively easily fabricated in a crisis using materials on hand.
• They are far cleaner burning than a wood fire or a gasoline-powered engine (without emissions controls), producing little, if any soot.
• When used in a stationary design, they reach their true potential, as they are feasible to use in small combined heat and power scenarios (with heat recovery from the wood gas producer, and possibly the engine/generator, for example, to heat water for hydronic heating), even in industrialized countries, even during good economic times, provided that a sufficient supply of wood is attainable. Larger-scale installations can reap even better efficiencies, and are useful for district heating as well.

The disadvantages of wood gas generators are:

• the large specific size
• the relatively slow starting speed; the time to heat the initially cold batch of wood to the necessary temperature level can take many minutes and in bigger plants even hours until the designed power is reached.
• a batch burning operation, that some designs feature, and that regularly interrupts the gas producing process.
• the stop operation out of a high load level is difficult (for example the stop of the engine using the gas): the residual heat still produces gas, which for a certain time leaves the gasifier either without control, or has to be used in a burner
• the primary combustible fuel-gas produced during gasification is carbon monoxide: it is an intentional fuel-product, and is subsequently burned to safe carbon dioxide in the engine (or other application) along with the other fuel-gases; however, continuous exposure to carbon monoxide can be fatal to humans even in small to moderate concentrations.
• the humidity of the wood (usually 15 to 20%) and the water vapor created by the O- and H-atoms of the dry wood itself (about 0.4 liters of water loaded with organic substances per kg of dry wood) condenses during the gas cooling and filtering procedure and yields a liquid (see also wood tar), which needs specific waste water treatment. This treatment requires about 25 to 35% of the created wood gas energy.

When not carefully designed and used, there exists considerable potential for injury or death due to wood gas containing a large percentage of poisonous carbon monoxide (CO) gas. Wood gasifiers of proven design and thoroughly tested construction are considered safe to use outdoors, or in a partially enclosed space, for example, under a shelter open to the air on two sides; they may also be considered relatively safe to use in an extremely well ventilated (e.g. negative pressure) indoor area not connected to any indoor area used for sleeping, equipped with redundant (more than 1), completely independent, battery-powered, regularly tested carbon-monoxide gas detectors. However, prudence must dictate that any sort of experimental wood gasifier design or new construction be thoroughly tested outdoors, and only outdoors, with a "buddy" at all times, and with constant vigilance for any sign of headache, drowsiness, or nausea, as these are the first symptoms of carbon monoxide poisoning.

In addition, mixtures of excessive quantities of air and gas should be avoided as this could lead to the deflagration (explosion) of the gas in question if a combustion source is present. Long-term storage of wood-gas, except through the use of a gasholder-type water-displacement apparatus, should not be attempted, due to the volatile elements present in the gas, which, if allowed to excessively precipitate, will condense in the storage vessel. Under no circumstances should wood-gas ever be compressed to more than 1 bar (15 psi) above ambient, as this may induce condensation of volatiles, as well as lead to the likelihood of severe injury or death due to carbon monoxide or deflagration if the vessel leaks or fails.