A
wood gas generator often known as a gasifier, is a wood-fueled
gasificationGasification is a process that converts carbonaceous materials, such as coal, petroleum, biofuel, or biomass, into carbon monoxide and hydrogen by reacting the raw material, such as house waste, or compost at high temperatures with a controlled amount of oxygen and/or steam. The resulting gas...
reactor mounted on an
internal combustion engineThe internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable...
, to provide a
wood gasWood gas is a syngas also known as producer gas which is produced by thermal gasification of biomass or other carbon containing materials such as coal in a gasifier or wood gas generator or producer gas...
, a form of
syngasSyngas is the name given to a gas mixture that contains varying amounts of carbon monoxide and hydrogen. Examples of production methods include steam reforming of natural gas or liquid hydrocarbons to produce hydrogen, the gasification of coal, biomass, and in some types of waste-to-energy...
. These devices are also known as
gas producers.
History
Gasification was an important and familiar 19th and early 20th century technology, and its potential and practical applicability to
internal combustion engineThe internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable...
s were well-understood from the earliest days of their development. Town gas was produced from coal as a local business, mainly for lighting purposes, at least initially, and experience in the trade was widespread; most practicing technical people would know a good deal about it. When stationary
internal combustion engineThe internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable...
s based on the Otto cycle became available (and especially after the Otto engine's
patentA patent is a set of exclusive rights granted by a state to an inventor or their assignee for a limited period of time in exchange for a public disclosure of an invention....
expired and entered the
public domainThe public domain is a range of abstract materials—commonly referred to as intellectual property—which are not owned or controlled by anyone. The term indicates that these materials are therefore "public property", and available for anyone to use for any purpose...
), internal combustion engines began displacing steam engines as prime movers in many works requiring stationary motive power. Gaseous-fuelled internal combustion engines were commonly fueled by town (lighting) gas during the late 19th century; however, the high price of town gas caused many stationary engine works to switch to using
producer gas-USA:Producer Gas is a generic term referring to:* Wood gas: produced in a gasifier to power cars with ordinary internal combustion engines.* Town gas: manufactured gas, originally produced from coal, for sale to consumers and municipalities....
during the early 20th century. Producer gas has less heat content, but was substantially cheaper to make than town gas was to purchase, due to its generation by partial combustion of coke, a byproduct of coal, rather than through the town-gas process of destructive distillation (pyrolysis) of coal.
By the time
World War IIWorld War II, or the Second World War , was a global military conflict which involved a majority of the world's nations, including all great powers, organized into two opposing military alliances: the Allies and the Axis...
arrived in United States and Great Britain, many internal combustion engines of the Otto type were in use in automobiles; however, they were fueled by petroleum-based gasoline, not coal or wood-based town or producer gas. Due to the war, civilian uses of petroleum were sharply curtailed in both nations. In Great Britain, petroleum shortages and rationing were common; in the United States, petroleum rationing was the law of the land, as all petroleum was diverted to the war effort. 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. Large numbers of such generators were constructed or even improvised; commercial generators were in production before and after the war, for use in special circumstances or in
distressed economiesEconomic shortage is a term describing a disparity between the amount demanded for a product or service and the amount supplied in a market. Specifically, a shortage occurs when there is excess demand; therefore, it is the opposite of a surplus....
. Some World War II era wood gas generators were of the "Imbert" type. They were designed around 1920 by
FrenchFrance , officially the French Republic , is a country located in Western Europe, with several overseas islands and territories located on other continents. Metropolitan France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean...
inventor
Georges ImbertGeorges Christian Peter Imbert born March 25, 1884 in Niederstinzel, Lorraine died February 6, 1950 in Saar Union, Alsace. Around 1920 developed the wood gas generator for the automobile that was commonly used in Europe until petroleum fuel became more economical in the region. He studied chemical...
.
Coal-based town gas production had been displaced by petroleum-based gas and/or natural gas. However, Great Britain continued her use of coal-based town gas until the
North SeaThe North Sea is a marginal, epeiric sea on the European continental shelf. The Dover Strait and the English Channel in the south and the Norwegian Sea in the north connect it to the Atlantic Ocean. It is more than long and wide, with an area of around...
natural gas discoveries in the 1960s and 1970s.
Usually, wood gas generators burn wood, but improvements to efficiency and energy-density are possible, by using
charcoalCharcoal is the blackish residue consisting of impure carbon obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood, sugar, bone char, or other substances in the absence of oxygen...
instead, as charcoal produces a cleaner gas without the tarry volatiles and excessive water content of wood.
There was a rich literature on gas-works, town-gas, gas-generation, wood-gas, and producer gas, that is now in the public domain due to its age.
Modern generators
With rising oil prices, wood gas generators are generating a renewed interest. The US Federal Emergency Management Administration published a book,
Construction of a Simplified Wood Gas Generator for Fueling Internal Combustion Engines in a Petroleum Emergency, in March 1989, describing a different design called the "stratified downdraft gasifier". It solves several drawbacks of earlier types.
The FEMA wood gas generator is (by definition of the FEMA manual) an emergency gasifier. It is designed to be rapidly assembled in a true fuel crisis. While this simplified design and departure from the standard European design does have some distinct benefits (ease of refueling and construction), it also has a host of new problems. The lack of a fixed oxidization zone allows the oxidization zone to creep to a larger area, causing a drop in temperature. The lower temperatures lead to tar production. It also lacks a true reduction zone further increasing this designs propensity to produce tar. Tar in the wood gas stream is considered a dirty gas and tar will gum up a motor quickly, possibly leading to stuck valves, and rings. The FEMA unit does not have a proven track record of being a reliable unit. In fact most successful wood gas generators in use in Europe and the United States are some variation of the imbert. The United Nations produced the FOA 72 document. It has information on wood gas generator design and construction, as does World Bank technical paper 296.
A project about the energy future of Europe was begun in 2005 in
GüssingGüssing is a town in Burgenland, Austria. It is located at , with a population of 3,902 , and is the administrative center of the Güssing district.The Güssing Castle, built in 1157, is the oldest castle in Burgenland and a regional landmark....
,
AustriaAustria , officially the Republic of Austria , is a landlocked country of roughly 8.3 million people in Central Europe. It borders both Germany and the Czech Republic to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the west...
with contribution of
European UnionThe European Union is an economic and political union of 27 Member States, located primarily in Europe. Committed to regional integration, the EU was established by the Treaty of Maastricht on 1 November 1993 upon the foundations of the pre-existing European Economic Community...
research furtherance. The project consisted of a 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. At the wood gas power plant are also two containers for experiments with wood gas. In one container is an experiment to convert wood gas, using the
Fischer-Tropsch processThe Fischer–Tropsch process is a catalyzed chemical reaction in which synthesis gas, a mixture of carbon monoxide and hydrogen, is converted into liquid hydrocarbons of various forms. The most common catalysts are based on iron and cobalt, although nickel and ruthenium have also been used...
, to a diesel-like fuel. By October 2005, it was possible to convert 5 kg wood into 1 litre fuel.
Advantages
- They can be used to run internal-combustion engines (or even 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, say, a wood fire or even a gasoline-powered engine is (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.
Disadvantages
The disadvantages of wood gas generators are their large size, relatively slow starting speed, and batch burning operation, that some designs feature. Also, one of the primary combustible fuel-gasses produced during gasification is
Carbon monoxideCarbon monoxide is a colorless, odorless and tasteless gas, yet very toxic to humans. It consists of one carbon atom and one oxygen atom, connected by a covalent double bond and a dative covalent bond...
: it is an intentional fuel-product, and is subsequently burned to safe
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
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.
Safety
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 monoxideCarbon monoxide is a colorless, odorless and tasteless gas, yet very toxic to humans. It consists of one carbon atom and one oxygen atom, connected by a covalent double bond and a dative covalent bond...
(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 pressureNegative pressure may refer to:*vacuum*negative gauge pressure, a way of expressing pressure measurements below atmospheric pressure*suction*transpirational pull...
) 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 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 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.
Media coverage
In 2008, an example of designing and constructing a working wood gas generator powered truck was shown on the National Geographic Channel's
Planet MechanicsPlanet Mechanics is an English TV programme shown on the National Geographic Channel. The programme was broadcast on Sunday at 7:00pm. Series one has now finished.-Episodes:*1. Air Propelled Sandwich...
in the eighth episode, "Tree Powered Car".
In 2009, another example of designing and constructing a working wood gas powered generator engine was in the TV series
The Colony (TV series)The Colony is a reality television program. The series was filmed in an industrial area bordering the Los Angeles River on the edge of downtown Los Angeles, and follows ten cast members in an environment that simulates life after a global catastrophe. The series first aired on the Discovery Channel...
in the second episode of the first season "Power Struggle".
External links