Gasification is a process that converts
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 bi ...
- or
fossil fuel
A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels m ...
-based
carbonaceous
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes up ...
materials into gases, including as the largest fractions:
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 ...
(N
2),
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 simple ...
(CO),
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-toxic, an ...
(H
2), and
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 transpar ...
(). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of
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 as wel ...
and/or
steam
Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization ...
present in the reaction. The resulting gas mixture is called
syngas
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 as ...
(from synthesis gas) or
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 produce ...
and is itself a fuel due to the flammability of the H
2 and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of
renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
if the gasified compounds were obtained from biomass feedstock.
An advantage of gasification is that
syngas
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 as ...
can be more efficient than direct combustion of the original feedstock material because it can be combusted at higher temperatures so that the thermodynamic upper limit to the efficiency defined by
Carnot's rule is higher. Syngas may also be used as the hydrogen source in fuel cells, however the syngas produced by most gasification systems requires additional processing and reforming to remove the contaminants and other gases such as CO and to be suitable for low-temperature fuel cell use, but high-temperature
solid oxide fuel cell
A solid oxide fuel cell (or SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic electrolyte.
A ...
s are capable of directly accepting mixtures of
H2,CO,CO2 steam, and methane.
Syngas is most commonly burned directly in
gas engines, used to produce
methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
and hydrogen, or converted via the
Fischer–Tropsch process
The Fischer–Tropsch process is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen, known as syngas, into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperat ...
into
synthetic fuel
Synthetic fuel or synfuel is a liquid fuel, or sometimes gaseous fuel, obtained from syngas, a mixture of carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass or by refo ...
. For some materials gasification can be an alternative to
landfill
A landfill site, also known as a tip, dump, rubbish dump, garbage dump, or dumping ground, is a site for the disposal of waste materials. Landfill is the oldest and most common form of waste disposal, although the systematic burial of the waste ...
ing and
incineration
Incineration is a waste treatment process that involves the combustion of substances contained in waste materials. Industrial plants for waste incineration are commonly referred to as waste-to-energy facilities. Incineration and other high ...
, resulting in lowered emissions of atmospheric pollutants such as
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 on Eart ...
and
particulates
Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The ter ...
. Some gasification processes aim at refining out corrosive ash elements such as
chloride
The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
and
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
, allowing clean gas production from otherwise problematic feedstock material. Gasification of fossil fuels is currently widely used on industrial scales to generate electricity. Gasification can generate lower amounts of some pollutants as SO
x and than combustion.
History
![Adler Diplomat 3 GS mit Holzgasgenerator-hinten rechts](https://upload.wikimedia.org/wikipedia/commons/3/31/Adler_Diplomat_3_GS_mit_Holzgasgenerator-hinten_rechts.JPG)
Energy has been produced at industrial scale via gasification since the early 19th century. Initially
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 dea ...
and
peat
Peat (), also known as turf (), is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. The peatland ecosystem covers and is the most efficien ...
were gasified to produce
town gas
Coal gas is a flammable gaseous fuel made from coal and supplied to the user via a piped distribution system. It is produced when coal is heated strongly in the absence of air. Town gas is a more general term referring to manufactured gaseous ...
for lighting and cooking, with the first public street lighting installed in Pall
Mall, London on January 28, 1807, spreading shortly to supply commercial gas lighting to most industrialized cities until the end of the 19th century when it was replaced with electrical lighting. Gasification and syngas continued to be used in
blast furnaces
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being "forced" or supplied above atmospheric p ...
and more significantly in the production of
synthetic chemicals where it has been in use since the 1920s. The thousands of sites left toxic residue. Some sites have been remediated, while others are still polluted.
During both
world wars
A world war is an international conflict which involves all or most of the world's major powers. Conventionally, the term is reserved for two major international conflicts that occurred during the first half of the 20th century, World WarI (1914 ...
, especially the
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 vast majority of the world's countries—including all of the great powers—forming two opposin ...
, the need for fuel produced by gasification reemerged due to the shortage of petroleum.
Wood gas generator
A wood gas generator is a gasification unit which converts timber or charcoal into wood gas, a producer gas consisting of atmospheric nitrogen, carbon monoxide, hydrogen, traces of methane, and other gases, which – after cooling and filtering ...
s, called Gasogene or Gazogène, were used to power motor vehicles in
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
. By 1945 there were trucks, buses and agricultural machines that were powered by gasification. It is estimated that there were close to 9,000,000 vehicles running on producer gas all over the world.
Chemical reactions
In a gasifier, the carbonaceous material undergoes several different processes:
![gasification](https://upload.wikimedia.org/wikipedia/commons/e/e1/Gasification.gif)
# The
dehydration
In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
or drying process occurs at around 100 °C. Typically the resulting steam is mixed into the gas flow and may be involved with subsequent chemical reactions, notably the water-gas reaction if the temperature is sufficiently high (see step #5).
# The ''
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 ''py ...
'' (or devolatilization) process occurs at around 200–300 °C. Volatiles are released and
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 Barranquilla ...
is produced, resulting in up to 70% weight loss for coal. The process is dependent on the properties of the carbonaceous material and determines the structure and composition of the char, which will then undergo gasification reactions.
# The ''
combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...
'' process occurs as the volatile products and some of the char react with oxygen to primarily form carbon dioxide and small amounts of carbon monoxide, which provides heat for the subsequent gasification reactions. Letting C represent a carbon-containing
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...
, the basic reaction here is
# The ''gasification'' process occurs as the char reacts with steam and carbon dioxide to produce carbon monoxide and hydrogen, via the reactions
and
# In addition, the
reversible gas phase
water-gas shift reaction
Water gas is a kind of fuel gas, a mixture of carbon monoxide and hydrogen. It is produced by "alternately hot blowing a fuel layer okewith air and gasifying it with steam". The caloric yield of this is about 10% of a modern syngas plant. F ...
reaches
equilibrium very fast at the temperatures in a gasifier. This balances the concentrations of carbon monoxide, steam, carbon dioxide and hydrogen.
In essence, a limited amount of oxygen or air is introduced into the reactor to allow some of the organic material to be "burned" to produce carbon dioxide and energy, which drives a second reaction that converts further organic material to hydrogen and additional carbon dioxide. Further reactions occur when the formed carbon monoxide and residual
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
from the organic material react to form methane and excess carbon dioxide (
). This third reaction occurs more abundantly in reactors that increase the
residence time
The residence time of a fluid parcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor, a lake, a human body). The residence time of a set of parcels is quantified in terms of the frequency distribution ...
of the reactive gases and organic materials, as well as heat and pressure.
Catalysts
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
are used in more sophisticated reactors to improve reaction rates, thus moving the system closer to the reaction equilibrium for a fixed residence time.
Processes
![Gasifier types](https://upload.wikimedia.org/wikipedia/commons/1/12/Gasifier_types.svg)
Several types of gasifiers are currently available for commercial use: counter-current fixed bed, co-current fixed bed,
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 ...
, entrained flow, plasma, and free radical.
Counter-current fixed bed ("up draft") gasifier
A fixed bed of carbonaceous fuel (e.g. coal or biomass) through which the "gasification agent" (steam, oxygen and/or air) flows in counter-current configuration. The ash is either removed in the dry condition or as a
slag
Slag is a by-product of smelting (pyrometallurgical) ores and used metals. Broadly, it can be classified as ferrous (by-products of processing iron and steel), ferroalloy (by-product of ferroalloy production) or non-ferrous/base metals (by-prod ...
. The slagging gasifiers have a lower ratio of steam to carbon, achieving temperatures higher than the ash fusion temperature. The nature of the gasifier means that the fuel must have high mechanical strength and must ideally be non-caking so that it will form a permeable bed, although recent developments have reduced these restrictions to some extent. The throughput for this type of gasifier is relatively low. Thermal efficiency is high as the temperatures in the gas exit are relatively low. However, this means that tar and methane production is significant at typical operation temperatures, so product gas must be extensively cleaned before use. The tar can be recycled to the reactor.
In the gasification of fine, undensified biomass such as
rice hulls
Rice hulls (or rice husks) are the hard protecting coverings of grains of rice. In addition to protecting rice during the growing season, rice hulls can be put to use as building material, fertilizer, insulation material, or fuel. Rice hulls are p ...
, it is necessary to blow air into the reactor by means of a fan. This creates very high gasification temperature, as high as 1000 C. Above the gasification zone, a bed of fine and hot char is formed, and as the gas is blow forced through this bed, most complex hydrocarbons are broken down into simple components of hydrogen and carbon monoxide.
Co-current fixed bed ("down draft") gasifier
Similar to the counter-current type, but the gasification agent gas flows in co-current configuration with the fuel (downwards, hence the name "down draft gasifier"). Heat needs to be added to the upper part of the bed, either by combusting small amounts of the fuel or from external heat sources. The produced gas leaves the gasifier at a high temperature, and most of this heat is often transferred to the gasification agent added in the top of the bed, resulting in an energy efficiency on level with the counter-current type. Since all tars must pass through a hot bed of char in this configuration, tar levels are much lower than the counter-current type.
Fluidized bed reactor
![Gasification facility](https://upload.wikimedia.org/wikipedia/commons/2/29/Gasification_facility_%22Advanced_Methanol_Amsterdam%22.jpg)
The fuel is
fluidized in oxygen and steam or air. The ash is removed dry or as heavy agglomerates that defluidize. The temperatures are relatively low in dry ash gasifiers, so the fuel must be highly reactive; low-grade coals are particularly suitable. The agglomerating gasifiers have slightly higher temperatures, and are suitable for higher rank coals. Fuel throughput is higher than for the fixed bed, but not as high as for the entrained flow gasifier. The conversion efficiency can be rather low due to
elutriation
Elutriation is a process for separating particles based on their size, shape and density, using a stream of gas or liquid flowing in a direction usually opposite to the direction of sedimentation. This method is mainly used for particles smalle ...
of carbonaceous material. Recycle or subsequent combustion of solids can be used to increase conversion. Fluidized bed gasifiers are most useful for fuels that form highly corrosive ash that would damage the walls of slagging gasifiers. Biomass fuels generally contain high levels of corrosive ash.
Fluidized bed gasifiers uses inert bed material at a fluidized state which enhance the heat and biomass distribution inside a gasifier. At a fluidized state, the superficial fluid velocity is greater than the minimum fluidization velocity required to lift the bed material against the weight of the bed. Fluidized bed gasifiers are divided into Bubbling Fluidized Bed (BFB), Circulating Fluidized Bed (CFB) and Dual Fluidized Bed (DFB) gasifiers.
Entrained flow gasifier
A dry pulverized solid, an atomized liquid fuel or a fuel slurry is gasified with oxygen (much less frequent: air) in co-current flow. The gasification reactions take place in a dense cloud of very fine particles. Most coals are suitable for this type of gasifier because of the high
operating temperature
An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
s and because the coal particles are well separated from one another.
The high temperatures and pressures also mean that a higher throughput can be achieved, however thermal efficiency is somewhat lower as the gas must be cooled before it can be cleaned with existing technology. The high temperatures also mean that tar and methane are not present in the product gas; however the oxygen requirement is higher than for the other types of gasifiers. All entrained flow gasifiers remove the major part of the ash as a slag as the operating temperature is well above the ash fusion temperature.
A smaller fraction of the ash is produced either as a very fine dry
fly ash
Fly ash, flue ash, coal ash, or pulverised fuel ash (in the UK) plurale tantum: coal combustion residuals (CCRs)is a coal combustion product that is composed of the particulates (fine particles of burned fuel) that are driven out of coal-fired ...
or as a black colored fly ash slurry. Some fuels, in particular certain types of biomasses, can form slag that is corrosive for ceramic inner walls that serve to protect the gasifier outer wall. However some entrained flow type of gasifiers do not possess a ceramic inner wall but have an inner water or steam cooled wall covered with partially solidified slag. These types of gasifiers do not suffer from corrosive slags.
Some fuels have ashes with very high ash fusion temperatures. In this case mostly limestone is mixed with the fuel prior to gasification. Addition of a little limestone will usually suffice for the lowering the fusion temperatures. The fuel particles must be much smaller than for other types of gasifiers. This means the fuel must be pulverized, which requires somewhat more energy than for the other types of gasifiers. By far the most energy consumption related to entrained flow gasification is not the milling of the fuel but the production of oxygen used for the gasification.
Plasma gasifier
In a
plasma gasifier a high-voltage current is fed to a torch, creating a high-temperature arc. The inorganic residue is retrieved as a glass like substance.
Feedstock
There are a large number of different feedstock types for use in a gasifier, each with different characteristics, including size, shape, bulk density, moisture content, energy content, chemical composition, ash fusion characteristics, and homogeneity of all these properties. Coal and petroleum coke are used as primary feedstocks for many large gasification plants worldwide. Additionally, a variety of biomass and waste-derived feedstocks can be gasified, with wood pellets and chips, waste wood, plastics and aluminium,
Municipal Solid Waste
Municipal solid waste (MSW), commonly known as trash or garbage in the United States and rubbish in Britain, is a waste type consisting of everyday items that are discarded by the public. "Garbage" can also refer specifically to food waste, ...
(MSW),
Refuse-derived fuel
Refuse-derived fuel (RDF) is a fuel produced from various types of waste such as municipal solid waste (MSW), industrial waste or commercial waste.
The World Business Council for Sustainable Development provides a definition:
''"Selected wast ...
(RDF), agricultural and industrial wastes, sewage sludge, switch grass, discarded seed corn, corn stover and other crop residues all being used.
Chemrec has developed a process for gasification of
black liquor.
Waste disposal
![HTCW reactor](https://upload.wikimedia.org/wikipedia/commons/f/f2/HTCW_reactor.jpg)
Waste gasification has several advantages over incineration:
* The necessary extensive flue gas cleaning may be performed on the syngas instead of the much larger volume of
flue gas
Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produc ...
after combustion.
*
Electric power
Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions o ...
may be generated in
engines
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power g ...
and
gas turbine
A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directi ...
s, which are much cheaper and more efficient than the
steam cycle used in incineration. Even fuel cells may potentially be used, but these have rather severe requirements regarding the purity of the gas.
* Chemical processing (
Gas to liquids
Gas to liquids (GTL) is a refinery process to convert natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons, such as gasoline or diesel fuel. Methane-rich gases are converted into liquid synthetic fuels. Two general strategies ex ...
) of the syngas may produce other synthetic fuels instead of electricity.
* Some gasification processes treat ash containing heavy metals at very high temperatures so that it is released in a glassy and chemically stable form.
A major challenge for waste gasification technologies is to reach an acceptable (positive) gross electric efficiency. The high efficiency of converting syngas to electric power is counteracted by significant power consumption in the waste preprocessing, the consumption of large amounts of pure oxygen (which is often used as gasification agent), and gas cleaning. Another challenge becoming apparent when implementing the processes in real life is to obtain long service intervals in the plants, so that it is not necessary to close down the plant every few months for cleaning the reactor.
Environmental advocates have called gasification "incineration in disguise" and argue that the technology is still dangerous to air quality and public health. "Since 2003 numerous proposals for waste treatment facilities hoping to use... gasification technologies failed to receive final approval to operate when the claims of project proponents did not withstand public and governmental scrutiny of key claims," according to the Global Alliance for Incinerator Alternatives. One facility which operated from 2009–2011 in Ottawa had 29 "emissions incidents" and 13 "spills" over those three years. It was also only able to operate roughly 25% of the time.
Several waste gasification processes have been proposed, but few have yet been built and tested, and only a handful have been implemented as plants processing real waste, and most of the time in combination with fossil fuels.
One plant (in
Chiba
Chiba may refer to:
Places China
* (), town in Jianli County, Jingzhou, Hubei
Japan
* Chiba (city), capital of Chiba Prefecture
** Chiba Station, a train station
* Chiba Prefecture, a sub-national jurisdiction in the Greater Tokyo Area on ...
, Japan using the Thermoselect process) has been processing industrial waste with natural gas and purified oxygen since year 2000, but has not yet documented positive net energy production from the process.
In 2007
Ze-gen
Ze-gen, Inc. was a renewable energy company developing advanced gasification technology to convert waste into synthesis gas. Founded in 2004, Ze-gen was a venture-backed company based in Boston, Massachusetts.
The company aimed to develop innovati ...
erected a waste gasification demonstration facility in
New Bedford, Massachusetts
New Bedford (Massachusett language, Massachusett: ) is a city in Bristol County, Massachusetts, Bristol County, Massachusetts. It is located on the Acushnet River in what is known as the South Coast (Massachusetts), South Coast region. Up throug ...
. The facility was designed to demonstrate gasification of specific non-MSW waste streams using ''liquid metal gasification''. This facility came after widespread public opposition shelved plans for a similar plant in
Attleboro, Massachusetts
Attleboro is a city in Bristol County, Massachusetts, United States. It was once known as "The Jewelry Capital of the World" for its many jewelry manufacturers. According to the 2020 census, Attleboro had a population of 46,461.
Attleboro is ...
. Today Ze-gen appears to be defunct, and the company website was taken down in 2014.
Also in the US, in 2011 a plasma system delivered by PyroGenesis Canada Inc. was tested to gasify municipal solid waste, hazardous waste and biomedical waste at the Hurlburt Field Florida Special Operations Command Air Force base. The plant, which cost $7.4 million to construct, was closed and sold at a government liquidation auction in May 2013. The opening bid was $25. The winning bid was sealed.
Current applications
Syngas can be used for heat production and for generation of mechanical and electrical power. Like other gaseous fuels, producer gas gives greater control over power levels when compared to solid fuels, leading to more efficient and cleaner operation.
Syngas can also be used for further processing to liquid fuels or chemicals.
Heat
Gasifiers offer a flexible option for thermal applications, as they can be retrofitted into existing gas fueled devices such as
oven
upA double oven
A ceramic oven
An oven is a tool which is used to expose materials to a hot environment. Ovens contain a hollow chamber and provide a means of heating the chamber in a controlled way. In use since antiquity, they have been us ...
s,
furnace
A furnace is a structure in which heat is produced with the help of combustion.
Furnace may also refer to:
Appliances Buildings
* Furnace (central heating): a furnace , or a heater or boiler , used to generate heat for buildings
* Boiler, used t ...
s,
boiler
A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central h ...
s, etc., where syngas may replace fossil fuels.
Heating value
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 relea ...
s of syngas are generally around 4–10 MJ/m
3.
Electricity
Currently Industrial-scale gasification is primarily used to produce electricity from fossil fuels such as coal, where the syngas is burned in a gas turbine. Gasification is also used industrially in the production of electricity, ammonia and liquid fuels (oil) using Integrated Gasification Combined Cycles (
IGCC), with the possibility of producing methane and hydrogen for fuel cells. IGCC is also a more efficient method of CO
2 capture as compared to conventional technologies. IGCC demonstration plants have been operating since the early 1970s and some of the plants constructed in the 1990s are now entering commercial service.
Combined heat and power
In small business and building applications, where the wood source is sustainable, 250–1000 kWe and new zero carbon biomass gasification plants have been installed in Europe that produce tar free syngas from wood and burn it in reciprocating engines connected to a generator with heat recovery. This type of plant is often referred to as a wood biomass CHP unit but is a plant with seven different processes: biomass processing, fuel delivery, gasification, gas cleaning, waste disposal, electricity generation and heat recovery.
Transport fuel
Diesel engine
The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-call ...
s can be operated on dual fuel mode using producer gas. Diesel substitution of over 80% at high loads and 70–80% under normal load variations can easily be achieved.
Spark ignition engine
A spark-ignition engine (SI engine) is an internal combustion engine, generally a petrol engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug. This is in contrast to compression-ignition engines, ...
s and
solid oxide fuel cell
A solid oxide fuel cell (or SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic electrolyte.
A ...
s can operate on 100% gasification gas. Mechanical energy from the engines may be used for e.g. driving water pumps for irrigation or for coupling with an alternator for electrical power generation.
While small scale gasifiers have existed for well over 100 years, there have been few sources to obtain a ready-to-use machine. Small scale devices are typically
DIY
"Do it yourself" ("DIY") is the method of building, modifying, or repairing things by oneself without the direct aid of professionals or certified experts. Academic research has described DIY as behaviors where "individuals use raw and sem ...
projects. However, currently in the United States, several companies offer gasifiers to operate small engines.
Renewable energy and fuels
![Holzvergaser Güssing](https://upload.wikimedia.org/wikipedia/commons/5/5d/Holzvergaser_G%C3%BCssing.jpg)
In principle, gasification can proceed from just about any organic material, including
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 bi ...
and
plastic waste
Plastic pollution is the accumulation of plastic objects and particles (e.g. plastic bottles, bags and microbeads) in the Earth's environment that adversely affects humans, wildlife and their habitat. Plastics that act as pollutants are catego ...
. The resulting syngas can be combusted. Alternatively, if the syngas is clean enough, it may be used for power production in gas engines, gas turbines or even fuel cells, or converted efficiently to
dimethyl ether
Dimethyl ether (DME; also known as methoxymethane) is the organic compound with the formula CH3OCH3,
(sometimes ambiguously simplified to C2H6O as it is an isomer of ethanol). The simplest ether, it is a colorless gas that is a useful precursor ...
(DME) by methanol dehydration, methane via the
Sabatier reaction
The Sabatier reaction or Sabatier process produces methane and water from a reaction of hydrogen with carbon dioxide at elevated temperatures (optimally 300–400 °C) and pressures (perhaps 3 MPa ) in the presence of a nickel catalyst. It w ...
, or diesel-like synthetic fuel via the
Fischer–Tropsch process
The Fischer–Tropsch process is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen, known as syngas, into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperat ...
. In many gasification processes most of the inorganic components of the input material, such as metals and minerals, are retained in the ash. In some gasification processes (slagging gasification) this ash has the form of a glassy solid with low
leaching
Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). and may refer to:
* Leaching (agriculture), the loss of water-soluble plant nutrients from the soil; or applying a small amou ...
properties, but the net power production in slagging gasification is low (sometimes negative) and costs are higher.
Regardless of the final fuel form, gasification itself and subsequent processing neither directly emits nor traps
greenhouse gases
A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), methane ...
such as carbon dioxide. Power consumption in the gasification and syngas conversion processes may be significant though, and may indirectly cause CO
2 emissions; in slagging and plasma gasification, the electricity consumption may even exceed any power production from the syngas.
Combustion of syngas or derived fuels emits exactly the same amount of carbon dioxide as would have been emitted from direct combustion of the initial fuel. Biomass gasification and combustion could play a significant role in a renewable energy economy, because biomass production removes the same amount of CO
2 from the atmosphere as is emitted from gasification and combustion. While other biofuel technologies such as biogas and
biodiesel
Biodiesel is a form of diesel fuel derived from plants or animals and consisting of long-chain fatty acid esters. It is typically made by chemically reacting lipids such as animal fat (tallow), soybean oil, or some other vegetable oil with ...
are
carbon neutral
Carbon neutrality is a state of net-zero carbon dioxide emissions. This can be achieved by balancing emissions of carbon dioxide with its removal (often through carbon offsetting) or by eliminating emissions from society (the transition to the "p ...
, gasification in principle may run on a wider variety of input materials and can be used to produce a wider variety of output fuels.
There are at present a few industrial scale biomass gasification plants. Since 2008 in Svenljunga, Sweden, a biomass gasification plant generates up to 14 MW
th, supplying industries and citizens of Svenljunga with process steam and
district heating
District heating (also known as heat networks or teleheating) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heating a ...
, respectively. The gasifier uses
biomass fuels such as
CCA or
creosote
Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood or fossil fuel. They are typically used as preservatives or antiseptics.
Some creosote types were ...
impregnated waste wood and other kinds of recycled wood to produces syngas that is combusted on site.
[Gasification allows less emissions, less dust and fuel flexibility](_blank)
– News at Elmia Recycling to Energy 2010, 03.03.11 In 2011 a similar gasifier, using the same kinds of fuels, is being installed a
Munkfors Energys
CHP plant. The CHP plant will generate 2 MW
e (electricity) and 8 MW
th (
district heating
District heating (also known as heat networks or teleheating) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heating a ...
).
Examples of demonstration projects include:
* The 32 MW dual fluidized bed gasification of the GoBiGas project in
Gothenburg
Gothenburg (; abbreviated Gbg; sv, Göteborg ) is the second-largest city in Sweden, fifth-largest in the Nordic countries, and capital of the Västra Götaland County. It is situated by the Kattegat, on the west coast of Sweden, and has ...
, Sweden, produced around 20 MW of
substitute natural gas
Substitute natural gas (SNG), or synthetic natural gas, is a fuel gas (predominantly methane, CH4) that can be produced from fossil fuels such as lignite coal, oil shale, or from biofuels (when it is named Renewable natural gas, bio-SNG) or using e ...
from forest residues and fed it into the natural gas grid since December 2014. The plant was permanently closed due to technical and economical problems in April 2018. Göteborg Energi had invested 175 million euro in the plant and intensive attempts to sell the plant to new investors had failed for a year.
* Those of the Renewable Energy Network Austria, including a plant using dual fluidized bed gasification that has supplied the town of
Güssing
Güssing (; hu, Németújvár, Német-Újvár, hr, Novi Grad) is a town in Burgenland, Austria. It is located at , with a population of 3,578 (2022), and is the administrative center of the Güssing district. For centuries the town occupied an i ...
with 2 MW of electricity, produced utilising
GE Jenbacher
INNIO Jenbacher designs and manufactures gas engines and cogeneration modules in the Austrian town of Jenbach in Tyrol. It is part of the INNIO portfolio of products and is one of their gas engine technologies; the other being Waukesha Engines. ...
reciprocating
gas engine
A gas engine is an internal combustion engine that runs on a gaseous fuel, such as coal gas, producer gas, biogas, landfill gas or natural gas. In the United Kingdom, the term is unambiguous. In the United States, due to the widespread use of ...
s and 4 MW of heat, generated from wood chips, since 2001. The plant was decommissioned in 2015.
* Go Green Gas' pilot plant in Swindon, UK has demonstrated methane production from waste feedstocks at 50 kW. The project has prompted the construction of a £25million commercial facility that aims to generate 22GWh per annum of grid-quality natural gas from waste wood and refuse derived fuel, due for completion in 2018.
*
Chemrec's pilot plant in
Piteå that produced 3 MW of clean syngas from entrained flow gasification of black liquor.
The plant was closed down permanently due to financial problems in 2016
* The High Temperature Winkler (HTW), a pressurized circulating fluidized bed gasification process. During the 1990s HTW was tested with a variety of different feedstocks, including low-rank coals and various forms of biomass; wood, refuse derived fuel (RDF) and municipal solid waste (MSW). The last HTW facility closed permanently in 2002. Since 2015 tests of the process continues at a 0.1 t/h pilot unit at Darmstadt University, while a redesigned full-scale unit is under erection in Amsterdam
See also
*
Coal gasification
*
Fluidized bed combustion
Fluidized bed combustion (FBC) is a combustion technology used to burn solid fuels.
In its most basic form, fuel particles are suspended in a hot, bubbling fluidity bed of ash and other particulate materials (sand, limestone etc.) through which ...
*
History of manufactured gas
The history of gaseous fuel, important for lighting, heating, and cooking purposes throughout most of the 19th century and the first half of the 20th century, began with the development of analytical and pneumatic chemistry in the 18th century. ...
*
Isle of Wight gasification facility
The Isle of Wight gasification facility is a municipal waste treatment plant in southern England. It entered the commissioning phase in autumn 2008, and will be replaced by a new moving grate incinerator in 2019
The facility has been funded as pa ...
*
List of solid waste treatment technologies
The article contains a list of different forms of solid waste treatment technologies and facilities employed in waste management infrastructure.
Waste handling facilities
*Civic amenity site (CA site)
* Transfer station
Established waste treatme ...
*
Plasma arc waste disposal
Plasma gasification is an extreme thermal process using plasma which converts organic matter into a syngas (synthesis gas) which is primarily made up of hydrogen and carbon monoxide. A plasma torch powered by an electric arc is used to ionize g ...
*
Renewable natural gas
Renewable natural gas (RNG), also known as sustainable natural gas (SNG) or biomethane, is a biogas which has been upgraded to a quality similar to fossil natural gas and having a methane concentration of 90% or greater. By increasing the concentr ...
*
Water gas
Water gas is a kind of fuel gas, a mixture of carbon monoxide and hydrogen. It is produced by "alternately hot blowing a fuel layer okewith air and gasifying it with steam". The caloric yield of this is about 10% of a modern syngas plant. F ...
*
Outdoor wood-fired boiler
The outdoor wood boiler is a variant of the classic wood stove adapted for set-up outdoors while still transferring the heat to interior buildings.
Technology
The outdoor wood boiler is a variant on the indoor wood, oil or gas boiler. An outdoor ...
*
Chemical looping reforming and gasification Chemical looping reforming (CLR) and gasification (CLG) are the operations that involve the use of gaseous carbonaceous feedstock and solid carbonaceous feedstock, respectively, in their conversion to syngas in the chemical looping scheme. The typi ...
References
External links
"Biomass Gasification Process""Gasification Technologies Council"
"Thermal Gasification of Biomass, International Energy Agency"Gasification Technology{{fuel gas
Energy conversion
Power station technology
Thermal treatment
Waste treatment technology
Fuel gas
Gas technologies
Synthetic fuel technologies
Sustainable technologies
Pyrolysis
Industrial gases