HOME

TheInfoList



OR:

Wood gas is a fuel gas that can be used for furnaces, stoves, and vehicles. During the production process,
biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bio ...
or related carbon-containing materials are gasified within the oxygen-limited environment of a wood gas generator to produce a combustible mixture. In some gasifiers this process is preceded by
pyrolysis The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements '' ...
, where the biomass or coal is first converted to
char Char may refer to: People * Char Fontane, American actress * Char Margolis, American spiritualist * René Char (1907–1988), French poet *The Char family of Colombia: ** Fuad Char, Colombian senator ** Alejandro Char Chaljub, mayor of Barranquill ...
, releasing
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
and
tar Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black bi ...
rich in
polycyclic aromatic hydrocarbon A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. ...
s. In stark contrast with
synthesis gas Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principly used for producing ammonia or methanol. Syngas is combustible and can be used ...
, which is almost pure H2/CO mixture, wood gas ''also'' contains a variety of organic compound ("distillates") that require scrubbing for use in other applications. Depending on the kind of biomass, a variety of contaminants are produced that will condense out as the gas cools. When producer gas is used to power cars and boats or distributed to remote locations it is necessary to scrub the gas to remove the materials that can condense and clog carburetors and gas lines.
Anthracite Anthracite, also known as hard coal, and black coal, is a hard, compact variety of coal that has a submetallic luster. It has the highest carbon content, the fewest impurities, and the highest energy density of all types of coal and is the hig ...
and coke are preferred for automotive use because they produce the smallest amount of contamination, allowing smaller, lighter scrubbers to be used.


History

The first wood gasifier was apparently built by
Gustav Bischof Karl Gustav Bischof (January 18, 1792 – November 30, 1870) was a German chemist, born in Nuremberg. He studied at Erlangen where he became a university lecturer ("Privatdozent") in 1815. In 1819 he was appointed to the position of an extra-O ...
in 1839. The first vehicle powered by wood gas was built by Thomas Hugh Parker in 1901. Around 1900, many cities delivered fuel gases (centrally produced, typically from
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
) to residences.
Natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon d ...
came into use only in the 1930s. Wood gas vehicles were used during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
as a consequence of the rationing of fossil fuels. In Germany alone, around 500,000 "
producer gas Producer gas is fuel gas that is manufactured by blowing a coke or coal with air and steam simultaneously. It mainly consists of carbon monoxide (CO), hydrogen (H2), as well as substantial amounts of nitrogen (N2). The caloric value of the produc ...
" vehicles were in use at the end of the war. Trucks, buses, tractors, motorcycles, ships and trains were equipped with a wood gasification unit. In 1942, when wood gas had not yet reached the height of its popularity, there were about 73,000 wood gas vehicles in Sweden, 65,000 in France, 10,000 in Denmark, and almost 8,000 in Switzerland. In 1944, Finland had 43,000 "woodmobiles", of which 30,000 were buses and trucks, 7,000 private vehicles, 4,000 tractors and 600 boats. Wood gasifiers are still manufactured in China and Russia for automobiles and as power generators for industrial applications. Trucks retrofitted with wood gasifiers are used in
North Korea North Korea, officially the Democratic People's Republic of Korea (DPRK), is a country in East Asia. It constitutes the northern half of the Korean Peninsula and shares borders with China and Russia to the north, at the Yalu (Amnok) and T ...
in rural areas, particularly on the roads of the east coast.


Production

A wood gasifier takes wood chips, sawdust, charcoal, coal, rubber or similar materials as fuel and burns these incompletely in a fire box, producing wood gas, solid ash and
soot Soot ( ) is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolysed ...
, the latter of which have to be removed periodically from the gasifier. The wood gas can then be filtered for tars and soot/ash particles, cooled and directed to an engine or
fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...
.Electricity from wood through the combination of gasification and solid oxide fuel cells
Ph.D. Thesis by Florian Nagel, Swiss Federal Institute of Technology Zurich, 2008
Most of these engines have strict purity requirements of the wood gas, so the gas often has to pass through extensive gas cleaning in order to remove or convert, ''i.e.'', " crack", tars and particles. The removal of tar is often accomplished by using a water
scrubber Scrubber systems (e.g. chemical scrubbers, gas scrubbers) are a diverse group of air pollution control devices that can be used to remove some particulates and/or gases from industrial exhaust streams. An early application of a carbon dioxide sc ...
. Running wood gas in an unmodified gasoline-burning internal combustion engine may lead to problematic accumulation of unburned compounds. The quality of the gas from different gasifiers varies a great deal. Staged gasifiers, where pyrolysis and gasification occur separately instead of in the same reaction zone as was the case in the World War II gasifiers, can be engineered to produce essentially tar-free gas (less than 1 mg/m3), while single-reactor
fluidized bed A fluidized bed is a physical phenomenon that occurs when a solid particulate substance (usually present in a holding vessel) is under the right conditions so that it behaves like a fluid. The usual way to achieve a fluidize bed is to pump pressur ...
gasifiers may exceed 50,000 mg/m3 tar. The fluidized bed reactors have the advantage of being much more compact, with more capacity per unit volume and price. Depending on the intended use of the gas, tar can be beneficial, as well by increasing the heating value of the gas. The heat of combustion of "producer gas"—a term used in the United States meaning wood gas produced for use in a combustion engine—is rather low compared to other fuels. Taylor reports that producer gas has a lower
heat of combustion The heating value (or energy value or calorific value) of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it. The ''calorific value'' is the total energy rele ...
of 5.7 MJ/kg versus 55.9 MJ/kg for natural gas and 44.1 MJ/kg for gasoline. The heat of combustion of wood is typically 15-18 MJ/kg. Presumably, these values can vary somewhat from sample to sample. The same source reports the following chemical composition by volume which most likely is also variable: *
Nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
N2: 50.9% *
Carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
CO: 27.0% *
Hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
H2: 14.0% *
Carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
CO2: 4.5% *
Methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
CH4: 3.0% *
Oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
O2: 0.6%. The composition of the gas is strongly dependent on the gasification process, the gasification medium (air, oxygen or steam), and the fuel moisture. Steam-gasification processes typically yield high hydrogen contents, downdraft fixed bed gasifiers yield high nitrogen concentrations and low tar loads, while updraft fixed bed gasifiers yield high tar loads.Handbook of Biomass Downdraft Gasifier Engine Systems
(Section 5.2 paragraph 2, pg 30), prepared by the Solar Energy Research Institute, U.S. Department of Energy Solar Technical Information Program, Solar Energy Research Institute, 1988
During the production of
charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, ...
for blackpowder, the volatile wood gas is vented. Extremely-high-surface-area carbon results, suitable for use as a fuel in black powder.


See also

*
Biogas Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. It is a ...
*
Biochar Biochar is the lightweight black residue, made of carbon and ashes, remaining after the pyrolysis of biomass. Biochar is defined by the International Biochar Initiative as "the solid material obtained from the thermochemical conversion of ...
- charcoal from biomass * Combined wood gas and biochar production *
Gasification Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (). This is achieved by reacting ...
* Gasification Outdoor Wood Boilers *
Producer gas Producer gas is fuel gas that is manufactured by blowing a coke or coal with air and steam simultaneously. It mainly consists of carbon monoxide (CO), hydrogen (H2), as well as substantial amounts of nitrogen (N2). The caloric value of the produc ...
*
Rocket stove A rocket stove is an efficient and hot burning stove using small-diameter wood fuel. Fuel is burned in a simple combustion chamber containing an insulated vertical chimney, which ensures almost complete combustion prior to the flames reaching th ...
* Water gas


References


External links


Food and Agriculture Organization of the United Nations: ''Wood Gas as Engine Fuel'', 1986
{{DEFAULTSORT:Wood Gas Synthetic fuels Fuel gas Biofuels Automotive engine technologies Pyrolysis Wood products Industrial gases Synthetic fuel technologies