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Gasification is actually a technology of the 19th and early 20th century. It was during World War II when the technology of wood gasification was first used popularly- because of the rationing of petrol. Gasification has returned to the public interest, this time in a renewed form because of the possibility of cost effectiveness for power generation and the renewable nature of wood... plus once again the scarcity of oil and fuels.
Gas is actually produced when wood burns at high temperatures with a known, but lean or scarce quantity of oxygen. When the supply of oxygen does not reach the burning wood, it transforms into gas. This gas, also known as “producer gas" was used as fuel for engines and hence for motor vehicles during the war.
When wood burns within a temperature range of 395 ° F to 535 ° F, the greater part of the gases are discharged from the wood combined with smoke. The gases contain approximately 50% to 80% of the heat capacity of the wood. This action of wood burning by releasing gas results in a gas blend called "wood gas." Since toxic fumes are released from wood gasification and because of the health risks associated with it, the majority of such items were discarded when oil and gasoline became readily obtainable in 1945.
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Different Zones of a Gasifier
A schematic of downdraft gasifier, as was used on vehicles, consists of four zones. The uppermost zone holds the raw charcoal as fuel through which air and oxygen enter, and it serves as a fuel hopper. The second zone is the region in which the wood fuel reacts with oxygen during transformation. The majority of the explosive constituents of the fuel is burnt in this partition and supplies heat for continuing the transformation. The top is designed to be open to ensure a consistent entrance of air to the transformation region. The third zone contains the charcoal formed in the previous region. Hot incineration gas in the pyrolysis zone reacts with charcoal and transforms the carbon dioxide and water vapor into carbon monoxide and hydrogen. The fourth region is cool, thus ending further reactions. Since the fourth region absorbs heat and oxygen, the zone acts as a buffer where the charcoal is stored. Underneath this region is the scrape, which is protected from high temperatures due to the char and ash.
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Theory of solid firewood gasification
Therefore, gasification aims at transforming the wood (used as raw material) completely into gaseous form leaving behind merely the ashes and static materials. In case of wood gas used as a fuel for inner combustion engines, it is imperative that the gas be created and conserved properly. The usage of such gas should not be until it is added into the engine where it burns properly.
Wood gas formed in a gasifier unit consists of roughly 20% hydrogen (H2), 20% carbon monoxide (CO), and small quantities of methane, all of which are flammable. In addition, it also contains 50 to 60% nitrogen (N2). The nitrogen is noncombustible, diluting the wood gas as it comes in and bums in an engine, but it also acts as a lubricant for the cylinder liners. The products of burning wood gas are carbon dioxide (CO2) and water vapor (H20). Carbon monoxide is a poisonous gas that is also a by-product of wood gasification.
Apart from the apparent fire risk ensuing from the burning processes within the unit, poisoning due to carbon monoxide is the key latent danger during the usual functioning of these basic gasifier units. Even when the engine is shut off, wood gas continues to be produced for around 20 minutes and hence, it is not sensible to remain in the vehicle during this period. The gas formed throughout the shutdown period contains contents of carbon monoxide of 23 to 27% and is very toxic.
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Travis Brock - How-To-Run-Your-car-On-Wood
Georgia Forestry Commission, Wood Gasification, A Unique Method of
Extracting Energy from the Forests of Georgia, The Rome, Georgia Demonstration
E. B. Rogers, Jr. and K. C. Mob - Status of Wood Burning Systems as Sources of Energy (With Emphasis on Wood Gasification), Applied Engineering Company paper, February 1981.
Donath, E.E., "Vehicle Gas Producers,' Processing Technology (3) pp. 141-153