Jump to: to: navigation navigation,, search search (disambiguation).. For other uses, see see Fuel (disambiguation)
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Wood Wood was one of the first fuels used by humans and is still the primary energy source in much of the world.[citation needed ] Fuel is any material that stores stores energy energy that can later be extracted to perform perform mechanical work in
a controlled manner. A fuel contains energy, mostly heat, that can be released and then reaction in which a manipulated. Most fuels used by humans undergo undergo combustion, combustion, a redox reaction combustible substance releases energy after it ignites and reacts with the oxygen in the air. Other processes used to convert fuel into energy include various other other exothermic chemical reactions reactions or nuclear fusion. fusion. Fuels are also used in the the cells cells of and nuclear reactions, such as as nuclear fission fission or organisms as cellular respiration, respiration, where organic molecules are oxidized to organisms in a process known as release usable energy. energy. Hydrocarbons Hydrocarbons are by far the most common source of fuel used by humans, but many other substances, such as radioactive metals, are currently used as well.
Contents [hide hide]] Chemical 1 Chemical 1.1 Biofuels o Biofuels fuels 1.2 Fossil fuels o Nuclear 2 Nuclear 2.1 Fission o Fission Fusion 2.2 Fusion o
3 trade trade time 4 World Use over time
also 5 See also 6 Footnotes Footnotes References 7 References 8 Further reading reading
[edit] edit] Chemical Chemical fuels are substances that release energy by reacting with substances around them, most notably by the process of oxidation. oxidation.
[edit] edit] Biofuels Main article: article: Biofuel Biofuel
Biofuel Biofuel can be broadly defined as solid, liquid, or gas fuel consisting of, or derived from biomass.. Biomass can also be used directly for heating or power — known known as biomass fuel. biomass Biofuel can be produced from any carbon source that can be replenished rapidly e.g. plants. Many different plants and plant-derived materials are used for biofuel manufacture. Perhaps the earliest fuel employed by humans is wood. Evidence shows controlled fire was used up to 1.5 million years ago at at Swartkrans, Swartkrans, South Africa. Africa. It is unknown which hominid species Homo were present at the sites. sites.[1] first used fire, as both both Australopithecus Australopithecus and an early species of Homo As a fuel, wood has remained in use up until the present day, although it has been superseded for many purposes by other sources. Wood has an an energy density density of 10 – 20 20 MJ / k kg. g.[2] Recently biofuels have been developed for use in automotive transport (for example example Bioethanol Bioethanol and Biodiesel) and Biodiesel), but there is widespread public debate about how carbon efficient these fuels are.
[edit edit]] Fossil fuels Main article: article: Fossil fuel fuel
Fossil fuels are are hydrocarbons, hydrocarbons , primarily primarily coal coal and and petroleum petroleum (liquid petroleum petroleum or or natural gas) gas), [3] animals by exposure to high heat and formed from the the fossilized remains remains of ancient plants and animals crust over hundreds of millions of years. years .[4] pressure in the absence of oxygen in the the Earth' Earth's crust Commonly, the term fossil fuel also includes hydrocarbon-containing hydrocarbon-containing natural resources resources that are not derived entirely from biological sources, such as as tar sands. sands. These latter sources are properly known as mineral fuels.
[edit edit]] Nuclear fuel Main article: article: Nuclear Nuclear fuel
Nuclear fuel is any material that is consumed to derive derive nuclear energy. energy. Technically speaking this definition includes all matter because any element will under the right conditions release nuclear energy, the only materials that are commonly referred to as nuclear fuels though are those that will produce energy without being placed under extreme duress.
[edit] edit] Fission
Nuclear fuel pellets are used to create nuclear energy. fissile elements that can be The most common type of nuclear fuel used by humans is heavy heavy fissile made to undergo undergo nuclear fission fission chain reactions reactions in a a nuclear fission reactor; reactor; nuclear fuel can refer to the material or to physical objects (for example fuel bundles composed of fuel rods) rods) moderating,, or neutron composed of the fuel material, perhaps mixed with structural, structural, neutron moderating 235 and 239Pu Pu,, and the actions of reflecting materials. The most common fissile nuclear nu clear fuels are are U and mining, refining, purifying, using, and ultimately disposing of these elements together make up the nuclear fuel cycle, the cycle, which is important for its relevance to to nuclear power power generation and nuclear weapons. weapons.
edit]] Fusion [edit Fuels that produce energy by the process of nuclear fusion fusion are currently not utilized by man but are the main source of fuel for stars, the most powerful energy sources in nature. Fusion fuels tend to be light elements such as as hydrogen hydrogen which will combine easily. stars that undergo undergo nuclear fusion fusion,, fuel consists of atomic nuclei nuclei that can release energy by the In In stars proton or or neutron neutron.. In most stars the fuel is provided by hydrogen, which can absorption of a a proton combine together to form form helium helium through the the proton-proton chain reaction reaction or by the the CNO cycle. cycle. When the hydrogen fuel is exhausted, nuclear fusion can continue with progressively heavier elements, although the net energy released is lower because of the smaller difference in nuclear binding energy. Once iron-56 or nickel-56 nuclei are produced, no further energy can be obtained by nuclear fusion as these have the highest nuclear binding energies. energies .[5]
edit]] World trade [edit
Fuel imports in 2005 by y the EU and World Bank reported that the USA was the top fuel importer in 2005 followed b [citation needed ] Japan.
[edit edit]] Use over time The first use of fuel was the combustion of wood or sticks by by Homo Homo erectus near 2 million years [6][[ page page needed ] [6] Throughout the majority of human history fuels derived from plants or animal ago.. ago fat were the only ones available for human use. use. Charcoal, Charcoal, a wood derivative, has been used since at least 6,000 BCE for smelting metals. It was only supplanted by by coke, coke, derived from coal, as the forests started to become depleted around the 18th century. Charcoal briquettes are now cooking.[7] commonly used as a fuel for for barbecue barbecue cooking. the steam Coal was first used as a fuel around 1000 BCE in in China. China. With the development of the engine in 1769, coal came into more common use as a power source. Coal was later used to drive engine ships and locomotives. By the 19th century, gas extracted from coal was being used for street lighting in in London. London. In the 20th century, the primary use us e of coal is for the generation of electricity, 2005.[8] electricity, providing 40% of the world's electrical power supply in 2005. Humans have been consuming fossil fuels since the industrial revolution, because they were more readily available then the existing standards such as whale oils, and they were much cheaper to produce. Currently the trend has been towards renewable fuels, such as as biofuels biofuels like alcohols.
fuels Liquid fuels List of energy topics topics management Marine fuel management Propellant Propellant fuel recycled fuel Solid fuel fuel World energy resources and consumption consumption
edit]] Footnotes [edit (2004-03-22). "Bones hint at first use of fire" fire".. BBC News. 1. ^ Rincon, Paul (2004-03-22). http://news.bbc.co.uk/1/hi/sci/tech/3557077.stm http://news.bbc.co.uk/1/hi/sci/tech/3557077.stm.. Retrieved 2007-09-11. (2007). "Chemical Potential Energy" Energy".. The Physics Hypertextbook. 2. ^ Elert, Glenn (2007). http://hypertextbook.com/physics/matter/energy-chem http://hypertextbook.com/physics /matter/energy-chemical/ ical/ . Retrieved 2007-09-11. Novaczek. "Canada's Fossil Fuel Dependency". Dependency" . Elements. 3. ^ Dr. Irene Novaczek. http://www.elements.nb.ca/theme/fuels ents.nb.ca/theme/fuels/irene/novaczek.htm /irene/novaczek.htm.. Retrieved 2007-01-18. http://www.elem fuel".. EPA. Archived from from the original original on 12 March 2007. 4. ^ "Fossil fuel" http://web.archive.org/web/20070312054557/http: ive.org/web/20070312054557/http://oaspub.epa.gov/trs //oaspub.epa.gov/trs/trs_proc_qry.navigate /trs_proc_qry.navigate_term?p_term _term?p_term http://web.arch _id=7068&p_term_cd=TERM.. Retrieved 2007-01-18. _id=7068&p_term_cd=TERM 5. ^ Fewell, M. P. (1995). "The atomic nuclide with the highest mean binding energy". American Journal of 1995AmJPh..63..653F.. doi: doi:10.1119/1.17828. 10.1119/1.17828. 658. Bibcode Bibcode 1995AmJPh..63..653F Physics 63 (7): 653 – 658. Richard (1994). (1994). Origin of Humankind . Basic Books. Books. ISBN ISBN 0465031358 0465031358.. 6. ^ Leakey, Richard http://books http://books.google.com/?id=75-cwH1905QC&pg= .google.com/?id=75-cwH1905QC&pg=PR9&dq=%22first+use PR9&dq=%22first+use+of+Fire%22 +of+Fire%22.. (2007). "Charcoal Briquette" Briquette".. How Products Are Made. 7. ^ Hall, Loretta (2007). http://www.madehow.com/Volume-4/Charcoal-Briquette.html. Retrieved 2007-10-01. Use".. World Coal Institute. 8. ^ "History of Coal Use" http://www.worldcoal.org/pages/content/index.asp?PageID=107.. Retrieved 2006-08-10. http://www.worldcoal.org/pages/content/index.asp?PageID=107
Biogas From Wikipedia, the free encyclopedia
Jump to: to: navigation, navigation, search search "Swamp gas" redirects here. For the obsolete theory of emanations from swamps causing disease.. disease, see see Miasma Miasma theory of disease
gas and condensate Pipes carrying biogas (foreground), (foreground), natural gas Biogas typically refers to a a gas gas produced by the biological breakdown of organic matter matter in the
biofuel. Biogas is absence of oxygen. oxygen. Biogas originates from biogenic material is a type of biofuel. or fermentation fermentation of biodegradable materials such as as biomass biomass,, produced by by anaerobic digestion digestion or [1] manure, sewage, municipal waste, waste, green waste waste,, plant material material and and energy crops. crops. This type of manure, sewage, biogas comprises primarily primarily methane methane and and carbon dioxide. dioxide. Other types of gas generated by use of by gasification gasification of wood or other biomass. This type of gas biomass is is wood gas, gas, which is created by consist primarily of nitrogen, nitrogen, hydrogen, hydrogen, and and carbon monoxide monoxide,, with trace amounts of methane. methane. The gases methane, hydrogen and carbon monoxide can be combusted or oxidized with oxygen. Air Air contains 21% oxygen. This energy release allows biogas to be used as a fuel. Biogas can be used as a low-cost fuel in any country for any heating purpose, such as cooking. It can also be engine,, used in modern modern waste management management facilities where it can be used to run any type of heat engine to generate either mechanical or electrical power. Biogas can be compressed, much like like natural gas,, and used to power gas power motor vehicles. vehicles. In the UK, for example, It is estimated to have the a renewable fuel fuel,, so it qualifies for potential to replace around 17% of vehicle fuel. fuel.[2] Biogas is a renewable energy subsidies renewable subsidies in some parts of the world.
Contents [hide] hide]
History 1 History Production 2 Production 3 Composition Composition 4 Applications Applications Benefits 5 Benefits upgrading 6 Biogas upgrading injection 7 Biogas gas-grid injection Legislation 8 Legislation 9 Development around the world world States 9.1 In the United States o 9.2 In the United Kingdom o Kingdom 9.3 In the Indian subcontinent subcontinent
o
9.4 In developing nations nations
o
also 10 See also 11 References References reading 12 Further reading links 13 External links
[edit edit]] History Ancient Persians observed that rotting vegetables produce flammable gas. In the 13th century, the traveller traveller Marco Polo Polo noted the Chinese used covered sewage tanks to generate power, while biogas technologies were also referred to by 17th century author author Daniel Defoe. Defoe.[3] In 1859, an anaerobic digestion plant was built to process sewage at a Bombay leper colony. Biogas has been used in the UK since 1895, when gas from sewage was used in street lamps across the city of Exeter. Exeter.[4]
[edit] edit] Production Main article: article: anaerobic digestion digestion
Biogas is practically produced as landfill gas (LFG) or or digester digester gas. A biogas plant is the name often given to an anaerobic digester that treats farm wastes or energy crops. Biogas can be produced utilizing anaerobic digesters. These plants can be fed with energy crops such as maize silage or or biodegradable wastes wastes including sewage sludge and food waste. During the process, an air-tight tank transforms biomass waste into methane producing renewable energy that can be used for heating, electricity, and many other operations that use any variation of an internal combustion engine, such as GE Jenbacher gas engines. engines .[5] There are two key processes: Mesophilic processes: Mesophilic and and Thermophilic Thermophilic digestion. digestion.[6] In experimental work at at University of Alaska Fairbanks, Fairbanks, a 1000 litre digester using using psychrophiles psychrophiles harvested from "mud from a frozen lake in Alaska" has produced 200 – 300 300 litres of methane per day, about 20 – 30 30 % of the output [7] from digesters in warmer climates. climates. Landfill gas is produced by wet organic waste decomposing under anaerobic conditions in a landfill..[8][9] The waste is covered and mechanically compressed by the weight of the material landfill that is deposited from above. This material prevents oxygen exposure thus allowing anaerobic microbes to thrive. This gas builds up and is slowly released into the atmosphere if the landfill site has not been engineered to capture the gas. Landfill gas is hazardous for three key reasons. Landfill gas becomes explosive when it escapes from the landfill and mixes with oxygen. The lower explosive limit is 5% methane and the upper explosive limit is 15% methane. methane.[10] The methane contained within biogas is 20 times more potent as a greenhouse gas than carbon dioxide. Therefore uncontained landfill gas which escapes into the atmosphere may significantly
contribute to the effects of global warming. In addition landfill gas' impact in global warming, compounds (VOCs) contained within landfill gas contribute to the formation of volatile organic compounds photochemical smog. smog.
[edit edit]] Composition [11]
Typical composition of biogas biogas Compound Chem % Methane
75 CH4 50 – 75
Carbon dioxide
50 CO2 25 – 50
Nitrogen
10 N2 0 – 10
Hydrogen
H2 0 – 1
Hydrogen sulfide
H2S 0 – 3
Oxygen
O2 0 – 0
The composition of biogas varies depending upon the origin of the the anaerobic digestion digestion process. gas typically has methane concentrations around 50%. Advanced waste treatment Landfill gas [12] 4 CH or
– 75% higher using in situ situ purification technologies produce biogas with 55contains 75% water vapor, techniques[13]can As-produced, biogas also with the fractional water vapor volume a function of biogas temperature; correction of measured volume for water vapor content and thermal expansion is easily done via algorithm. algorithm.[14]
In some cases biogas contains contains siloxanes siloxanes.. These siloxanes are formed from the the anaerobic decomposition of materials commonly found in soaps and detergents. During combustion of decomposition biogas containing siloxanes, siloxanes, silicon silicon is released and can combine with free oxygen or various mostly silica silica (SiO2) or other elements in the the combustion gas. gas. Deposits are formed containing mostly silicates contain calcium, calcium, sulfur sulfur,, zinc, zinc, phosphorus phosphorus.. Such Such white mineral mineral silicates (Si xO y) and can also contain deposits accumulate to a surface thickness of several millimeters and must be removed by chemical or mechanical means. Practical and cost-effective technologies to remove siloxanes and other biogas contaminants are currently available. available.[15]
[edit] edit] Applications
A biogas bus in in Linköping, Sweden Sweden Biogas can be utilized for electricity production on sewage works, works,[16] in a a CHP CHP gas engine, engine, where the waste heat from the engine is conveniently used for heating the digester; cooking; space replace compressed natural gas gas heating; water heating; heating; heating; and process heating. If compressed, it can replace for use in vehicles, where it can fuel an an internal combustion engine engine or or fuel cells cells and is a much more effective displacer of carbon dioxide than the normal use in on-site CHP plants. plants.[2] Methane within biogas can be concentrated via a a biogas upgrader upgrader to the same standards as fossil gas(which itself has had to go through a cleaning process), and becomes biomethane. If natural gas( the local gas network allows for this, the producer of the biogas may utilize the local gas distribution networks. Gas must be very clean to reach pipeline quality, and must be of the water,, hydrogen correct composition for the local distribution network to accept. acc ept. Carbon dioxide, dioxide, water sulfide and sulfide and particulates particulates must be removed if present. If concentrated and compressed it can also be used in vehicle transportation. Compressed biogas is becoming widely used in Sweden, Switzerland, and Germany. A biogas-powered train has been in service in Sweden since 2005..[17][18] 2005 Biogas has also powered automobiles. In 1974, a British documentary film entitled Sweet as a Nut detailed the biogas production process from pig manure, and how the biogas fueled a custom-adapted combustion engine. engine.[19][20]
[edit] edit] Benefits By using biogas, many advantages arise. In North America, utilization of biogas would generate enough electricity to meet up to three percent of the continent's eelectricity lectricity expenditure. In addition, biogas could potentially help reduce global climate change. Normally, manure that is left to decompose releases two main gases that cause global climate change: nitrous dioxide and methane. Nitrous dioxide warms the atmosphere 310 times more than carbon dioxide and methane 21 times more than carbon dioxide. By converting cow manure into methane biogas via digestion, the millions of cows in the United States would be able to produce one anaerobic digestion, hundred billion kilowatt hours of electricity, enough to power millions of homes across the United States. In fact, one cow can produce enough manure in one day to generate three kilowatt hours of electricity; only 2.4 kilowatt hours of electricity are needed to power a single one hundred watt light bulb for one day. day.[21] Furthermore, by converting cow manure into methane biogas instead of letting it decompose, we would be able to reduce global warming gases by ninety-nine million metric tons or four percent. percent .[22] The 30 million rural households in China that have biogas digesters enjoy 12 benefits: saving fossil fuels, saving time collecting firewood, protecting forests, using us ing crop residues for animal fodder instead of fuel, saving money, saving cooking time, improving hygienic conditions, producing high-quality fertilizer, enabling local mechanization and electricity production, improving the rural standard of living, and reducing air and water pollution pollution..[23]
[edit] edit] Biogas upgrading Raw biogas produced from digestion is roughly 60% methane and 29% CO 2 with trace elements of H2S, and is not high quality enough if the owner was planning on selling this gas or using it as fuel gas for machinery. The corrosive nature of H2S alone is enough to destroy the internals of an expensive plant. The solution is the use of a biogas upgrading or purification process whereby contaminants the raw stream are absorbed or upgrading, scrubbed, leaving 98% methane per unit volume of gas.inThere arebiogas four main methods of biogas these include water washing, pressure swing absorption, selexol absorption and chemical treatment. The most prevalent method is water washing where high pressure gas flows into a column where the carbon dioxide and other trace elements are scrubbed by cascading water running counter-flow to the gas. This arrangement could deliver 98% methane with manufacturers guaranteeing maximum 2% methane loss in the system. It takes roughly between 3-6% of the total energy output in gas to run a biogas upgrading system.
edit]] Biogas gas-grid injection [edit Gas-grid injection is the the injection injection of biogas into the the methane grid grid (natural gas grid) grid). Injections [24] power two-thirds of all includes biogas: biogas: until the breakthrough of micro combined heat and power the energy produced by by biogas power plants plants was lost (the heat), using the grid to transport the gas to customers, the electricity and the heat can be used for for on-site generation generation [25] resulting in a reduction of losses in the transportation of energy. Typical energy losses in natural gas transmission systems range from 1 – 2%. 2%. The current energy losses on a large electrical system [26] range from 5 – 8%. 8%.
edit]] Legislation [edit The European Union presently has some of the strictest legislation regarding waste management and landfill sites called the the Landfill Directive. Directive.[citation needed ] The United States legislates against VOCs.. The United States States Clean Air Act Act and Title 40 of the Code of landfill gas as it contains contains VOCs Federal Regulations (CFR) requires landfill owners to estimate the quantity of non-methane organic compounds (NMOCs) emitted. If the estimated NMOC emissions exceeds 50 tonnes per year the landfill owner is required to collect the landfill gas and treat it to remove the entrained NMOCs. Treatment of the landfill gas is usually by combustion. Because of the remoteness of landfill sites it is sometimes not economically econo mically feasible to produce electricity from the gas. However, countries such as the United Kingdom and Germany now has legislation in force that provide farmers with long term revenue and energy security. security.[27][28]
[edit] edit] Development around the world In 2007 an estimated 12,000 vehicles were being fueled with upgraded biogas worldwide, mostly in Europe. Europe.[29]
edit]] In the United States [edit
With the many benefits of biogas, it is starting to become a popular source of energy and is starting to be utilized in the United States more. In 2003 the United States consumed 147 trillion BTU of energy from "landfill gas", about 0.6% of the total U.S. natural gas consumption. consumption.[29] Methane biogas derived from cow manure is also being tested in the U.S. According to a 2008 study, collected by the Science and Children magazine, methane biogas from cow manure would be sufficient to produce 100 billion billion kilowatt hours hours enough to power millions of homes across America. Furthermore, methane biogas has been tested to prove that it can reduce 99 million metric tons of [30] greenhouse gas emissions or about 4% of the greenhouse gases produced by the United States. States. In Vermont, for example, biogas generated on dairy farms around the state is included in the CVPS Cow Power program. The Cow Power program is offered by Central Vermont Pu Public blic Service Corporation as a voluntary vo luntary tariff. Customers can elect to pay a premium on their electric bill, and that premium is passed directly to the farms in the p program. rogram. In Sheldon, Vermont Green Mountain Dairy has provides renewable energy as part of the Cow Power program. It all started when the brothers who own the farm, Bill and Brian Rowell, wanted to address some of the manure management challenges faced by dairy farms, including manure odor, and nutrient availability for the crops they need to grow to feed the animals. They installed an anaerobic digester to process the cow and milking center waste from their nine hundred and fifty cows to produce renewable energy, a bedding to replace sawdust, and a plant friendly fertilizer. The energy and environmental attributes are sold. On average the system run by the Rowell brothers produces enough electricity to power three hundred to three hundred fifty other homes. The generator capacity is about three hundred kiloWatts. kiloWatts.[31] In Hereford, Texas cow manure is being used to power an an ethanol power power plant. By switching to methane bio-gas, the ethanol power plant has saved one thousand barrels of oil a day. Overall, the power plant has reduced transportation costs and will be opening many more jobs for future power plants that will be relying on biogas. biogas.[32]
[edit] edit] In the United Kingdom In the UK, sewage gas electricity production is tiny compared to overall power consumption - a [33] [33][[clarification needed ]
mere 80 MW of generation, compared to 70 GW on the grid. grid. There are currently less than 60 non-sewage landfill plants in the UK, most are on-farm but some larger facilities exist off-farm which are taking food and consumer wastes. wastes.[34] On the 5th October 2010 biogas was injected into the UK gas grid for the first time. Sewage from over 30,000 Oxfordshire homes is sent to Didcot sewage treatment works, where it is treated in an anaerobic digestor to produce biogas, which is then cleaned to provide gas for approximately 200 homes. homes.[35]
edit]] In the Indian subcontinent [edit In Pakistan,India and Nepal biogas produced from the anaerobic digestion of manure manure in smallscale digestion facilities is called called gobar gas; gas; it is estimated that such facilities exist in over two million households in India and in hundreds of thousands in Pakistan, particularly North Punjab,
due to the thriving population of lifestock . It has become popular source of fuel in many parts of Nepal. The digester is an airtight circular pit made of concrete with a pipe connection. The manure is directed to the pit, usually directly from the cattle shed. The pit is then filled with a required quantity of wastewater. wastewater. The gas pipe is connected to the kitchen fireplace through control valves. The combustion of this biogas has very little odour or smoke. Owing to simplicity in implementation and use of cheap raw materials in villages, it is one of the most environmentally sound energy sources for rural needs. One type of these system is the the Sintex Digester.. Some designs use Digester use vermiculture vermiculture to further enhance the slurry produced by the biogas plant for use as compost. compost.[36] The Deenabandhu Model is a new biogas-production model popular in India. ( Deenabandhu means "friend of the helpless.") The unit usually has a capacity of 2 to 3 cubic metres. It is constructed using bricks or by a a ferrocement ferrocement mixture. In India the brick model costs slightly more than the ferrocment model, however ho wever India's Ministry of New and Renewable Energy offers some subsidy per model constructed. Pakistan Dairy Development Company has taken a huge initiative to develop this kind of alterantive source of energy for Pakistani farmers. Biogas is now running diesel engines, gas generators, kitchen ovens, geysers and other utilities in Pakistan. In Nepal, the government provides subsidies to build biogas plant.
edit]] In developing nations [edit Domestic biogas plants convert livestock manure and night soil into biogas and slurry, the fermented manure. This technology is feasible for small holders with livestock producing 50 kg manure per day, an equivalent of about 6 pigs or 3 cows. This manure has to be collectable to mix it with water and feed it into the plant. Toilets can be connected. Another precondition is the temperature that affects the fermentation process. With an optimum at 36 C° the technology technolog y especially applies for those living in a (sub) tropical climate. This makes the technology for small holders in developing countries often suitable.
Simple sketch of household biogas plant Depending on size and location, a typical brick made fixed dome biogas plant can be installed at the yard of a rural household with the investment between 300 to 500 US $ in Asian countries and up to 1400 US $ in the African context. A high quality biogas plant needs minimum maintenance costs and can produce gas for at least 15 – 20 20 years without major problems and re-
investments. For the user, biogas provides clean cooking energy, reduces indoor air pollution and reduces the time needed for traditional biomass collection, especially for women and children. The slurry is a clean organic o rganic fertilizer that potentially increases agricultural productivity. Domestic biogas technology is a proven and established technology in many parts of the world, especially Asia. Asia.[37] Several countries in this region have embarked on large-scale programmes on domestic biogas, such as China[38][39] and India. The Netherlands Development Organisation, SNV,,[40] supports national programmes on domestic biogas that aim to establish commercialSNV viable domestic biogas sectors in which local companies market, install and service biogas plants for households. In Asia, SNV is working in Nepal, Nepal,[41] Vietnam, Vietnam,[42] Bangladesh, Bangladesh,[43] Cambodia, Cambodia,[43] Pakistan[45] and Indonesia, Indonesia,[46] and in Africa in Rwanda, Rwanda ,[47] Senegal, Burkina Faso, Lao PDR, PDR,[44] Pakistan Tanzania,[49] Uganda and Kenya. Ethiopia,,[48] Tanzania, Ethiopia
[edit] edit] See also Sustainable development portal
Energy portal
digestion Anaerobic digestion Biodegradability Biodegradability Bioenergy Bioenergy Biofuel Biofuel Biohydrogen Biohydrogen Landfill gas monitoring monitoring MSW/LFG (municipal solid waste and landfill gas) MSW/LFG gas Natural gas Renewable energy energy gas Renewable natural gas Relative cost of electricity generated by different sources sources utilisation Tables of European biogas utilisation Waste management management
Heat of combustion From Wikipedia, the free encyclopedia
(Redirected from from Calorific value) value) search Jump to: to: navigation, navigation, search the energy energy released as The heat of combustion (ΔHc0) is the as heat heat when a compound undergoes complete combustion complete combustion with with oxygen oxygen under under standard conditions. conditions. The chemical reaction is typically form carbon dioxide, dioxide, water water and heat. It may be expressed a hydrocarbon hydrocarbon reacting with oxygen to form with the quantities:
kJ/mol)) energy / mole mole of fuel (kJ/mol
energy/mass of fuel energy/volume of fuel
The heat of combustion is traditionally measured with a a bomb calorimeter calorimeter.. It may also be 0 calculated as the difference between the the heat of formation (Δ H f ) of the products and reactants.
Contents [hide] hide]
1 Heating value value o value 1.1 Higher heating value 1.2 Lower heating value value o 1.3 Gross heating value o value 1.4 Measuring heating values o values 1.5 Relation between heating values o values o terms 1.6 Usage of terms 1.7 Accounting for moisture o moisture tables 2 Heat of combustion tables 15.4°C) 3 Lower heating value for some organic compounds (at 15.4°C) sources 4 Higher heating values of natural gases from various sources 5 See also also References 6 References 7 External links links
[edit edit]] Heating value substance,, usually a a fuel fuel or or food food (see (see food energy) energy), is The heating value or energy value of a a substance the amount of heat heat released during the combustion of a specified amount of it. The energy value is a characteristic for each substance. It is measured in units of energy energy per unit of the substance, usually mass, usually mass, such as: kJ/kg, kJ/kg, kJ / mol, mol, kcal / / kg, kg, Btu / m³. m³. Heating value is commonly determined by use of a a bomb calorimeter. calorimeter. The heat of combustion for for fuels fuels is expressed as the HHV, LHV, or GHV.
[edit] edit] Higher heating value The quantity known as as higher heating value value (HHV) (or gross energy or upper heating value or gross calorific value or higher calorific value HCV) is determined by bringing all the products of combustion back to the original pre-combustion temperature, and in particular condensing any vapor produced. Such measurements often use a temperature of 25 °C. This is the same as the enthalpy change for the reaction assumes a thermodynamic heat of combustion since the the enthalpy common of the compounds before and after combustion, in which case the water produced temperature by combustion is liquid.
The higher heating value takes into account the the latent heat of vaporization vaporization of water water in the combustion products, and is useful in calculating heating values for fuels where where condensation condensation of the reaction products is practical (e.g., in a gas-fired boiler used for space heat). In other words, HHV assumes all the water component is in liquid state at the end of combustion (in product of combustion).
edit]] Lower heating value [edit The quantity known as as lower heating value value (LHV) (net calorific value or lower calorific value LCV) is determined by subtracting the the heat of vaporization vaporization of the water vapor from the higher heating value. This treats any H2O formed as a vapor. The energy required to vaporize the water therefore is not realized as heat. LHV calculations assume that the water component of a combustion process is in vapor state at value (HHV) (a.k.a. gross calorific the end of combustion, as opposed to the the higher heating value value or gross CV ) which that assumes all of the water in a combustion process is in a liquid state after a combustion process. The LHV assumes that the the latent heat of vaporization vaporization of water water in the fuel and the reaction products recovered. is useful in comparing fuels where condensation ofuse. the combustion products is is not impractical, or It heat at a temperature below 150 °C cannot be put to The above is but one definition of lower heating value adopted by the the American Petroleum Institute (API) and they used a reference temperature of 60 °F (15.56 °C). Institute Another definition — used used by Gas Processors Suppliers Association (GPSA) and originally used by API (data collected for API research project p roject 44) — is is that the lower heating value is the enthalpy enthalpy of all combustion products, minus the enthalpy of the fuel at the reference temperature (API research project 44 used 25 °C. GPSA currently uses 60 °F), minus the enthalpy of the stoichiometric oxygen (O2) at the reference temperature, minus the the heat of vaporization vaporization of the stoichiometric oxygen vapor content of the combustion products. The distinction between the two is that this second definition assumes that the combustion products are all returned back down to the reference temperature but then the heat content from the condensing vapor is considered to be not useful. This is more easily calculated from the higher heating value than when using the previous definition and will in fact give a slightly different answer.
[edit] edit] Gross heating value
Gross heating value (see AR) accounts for water in the exhaust leaving as vapor, and
includes liquid water in the fuel prior to combustion. combusti on. This value is important for fuels like wood or or coal, coal, which will usually contain some amount of water prior to burning. wood
[edit] edit] Measuring heating values
The higher heating value is experimentally determined in a a bomb calorimeter calorimeter by concealing a stoichiometric mixture of fuel and oxidizer (e.g., two moles of hydrogen and one mole of stoichiometric oxygen) in a steel container at 25° is initiated by an ignition device and the combustion reactions completed. When hydrogen and oxygen react during combustion, water vapor emerges. Subsequently, the vessel and its content are cooled down to the original 25 °C and the higher heating value is determined as the heat released between identical initial and final temperatures. value (LHV) is determined, cooling is stopped at 150 °C and the When the the lower heating value reaction heat is only partially recovered. The limit of 150 °C is an arbitrary choice. Note: Higher heating value (HHV) is calculated with w ith the product of water being in liquid form while lower heating value (LHV) is calculated with the product of water being in vapor form.
[edit] edit] Relation between heating values The difference between the two heating values depends on the chemical composition of the fuel. In the case of pure carbon or carbon monoxide, both heating values are almost identical, the difference being the sensible heat content of carbon dioxide between 150°C and 25°C (sensible heat exchange causes a change of temperature. In contrast, heat contrast, latent heat heat is added or subtracted for changes phase changes at constant Examples: Examples:as heat of vaporization vaporization or or heat ofof fusion) fusion For hydrogen the difference is temperature. much more significant it includes the sensible heat water). vapor hydrogen between 150°C and 100°C, the latent heat of condensation at 100°C and the sensible heat of the condensed water between 100°C and 25°C. All in all, the higher heating value of hydrogen is 18.2% above its lower heating value (142 MJ/kg vs. 120 MJ/kg). For For hydrocarbons hydrocarbons the gasoline and and diesel diesel the higher difference depends on the hydrogen content of the fuel. For For gasoline heating value exceeds the lower heating value by about 10% and 7%, respectively, for natural gas about 11%. A common method of relating HHV to LHV is: HHV = LHV + hv x (nH2O,out /nfuel,in) where hv is the heat of vaporization of water, nH2O,out is the moles of water vaporized and [1]
nfuel,in
is the number of moles of fuel combusted. combusted .
Most applications which burn fuel produce water vapor which is not used and thus wasting its heat content. In such applications, the lower heating value is the applicable measure. This is high hydrogen hydrogen content produces much water. The particularly relevant for for natural gas, gas, whose high and power plants plants with with flue gas gross energy value is relevant for gas burnt in in condensing boilers boilers and condensation which condense the water vapor produced by combustion, recovering heat which condensation would otherwise be wasted.
[edit] edit] Usage of terms For historical reasons, the efficiency of power plants and and combined heat and power power plants in Europe is calculated based on the LHV, while in e.g. the US, it is generally based on the the HHV. HHV.
This has the peculiar result that contemporary combined heat and power plants, where where flue gas condensation is implemented, may report efficiencies exceeding 100 % in Europe. condensation Many engine manufacturers rate their engine fuel consumption by the lower heating values. American consumers should be aware that the corresponding fuel consumption figure based on the higher heating value would be somewhat higher. The difference between HHV and LHV definitions causes endless confusion when quoters do 10 % difference for a not bother to state the convention being used. used.[2] since there is typically a 10% power plant on natural gas between the two methods.
[edit] edit] Accounting for moisture Both HHV and LHV can be expressed in terms of AR (all moisture counted), MF and MAF (only water from combustion of hydrogen). AR, MF, and MAF are commonly used for indicating the heating values of coal: AR (As Received) indicates that the fuel heating value has been measured with all
moisture and ash forming minerals present.
MFfuel (Moisture Free) or of that the fuel value has beenforming measured after the has been dried oDry f allindicates inherent moisture butheating still retaining its ash minerals. MAF (Moisture and Ash Free) or DAF (Dry and Ash Free) indicates that the fuel heating value has been measured in the absence of inherent moisture and ash forming minerals.
edit]] Heat of combustion tables [edit Higher (HHV) and Lower (LHV) Heating values of some common fuels fuels[3] kg g HHV HHV BTU / llb b HHV HHV kJ / m mol ol LHV LHV MJ/kg Fuel HHV MJ / k Hydrogen 141.80 61,000 286 121.00 Methane 55.50 23,900 889 50.00 Ethane 51.90 22,400 1,560 47.80 50.35 21,700 2,220 46.35 Propane 49.50 20,900 2,877 45.75 Butane Pentane 45.35 47.30 20,400 44.40 Gasoline 46.00 19,900 41.50 Paraffin 46.20 43.00 Kerosene Diesel 44.80 19,300 Coal Anthracite)) 27.00 14,000 Coal (Anthracite Coal (Lignite Coal Lignite)) 15.00 8,000
Wood
15.00
6,500
Peat (damp) Peat Peat (dry) Peat
6.00 15.00
2,500 6,500
Heat of Combustion for some common fuels (higher value) Fuel kJ / g kcal / / g BTU / llb b 141.9 33.9 61,000 Hydrogen Gasoline 47.0 11.3 20,000 Diesel 45.0 10.7 19,300 Ethanol 29.7 7.1 12,000 49.9 11.9 21,000 Propane 49.2 11.8 21,200 Butane Wood 15.0 3.6 6,000 Coal (Lignite Coal Lignite)) 15.0 4.4 8,000 Coal (Anthracite Coal Anthracite)) 27.0 7.8 14,000 Natural Gas 54.0 13.0 23,000
Higher heating value of some less common fuels fuels[3] kg g BTU / llb b kJ / m mol ol HHV MJ / k
Note that there is no difference between the lower and higher heating values for the combustion of carbon, carbon monoxide and sulfur since no water is formed in combusting those substances.
[edit] edit] Higher heating values of natural gases from various sources These data on higher heating values were obtained from the International Energy Agency: Agency :[4]
Indonesia Indonesia:: 40,600 kJ/m³ Netherlands: Netherlands: 33,320 kJ/m³
Norway:: 39,877 kJ/m³ Norway Russia:: 38,231 kJ/m³ Russia Saudi Arabia Arabia:: 38,000 kJ/m³ Kingdom:: 39,710 kJ/m³ United Kingdom United States: States: 38,416 kJ/m³ Uzbekistan Uzbekistan:: 37,889 kJ/m³
The lower heating values of the above natural gases are about 90 percent of the higher heating values.
Bomb calorimeters
Bomb calorimeter A bomb calorimeter is a type of constant-volume calorimeter used in measuring the heat of combustion of a particular reaction. Bomb calorimeters have to withstand the large pressure within the calorimeter as the reaction is being measured. Electrical energy is used to ignite the fuel; as the fuel is burning, it will heat up the surrounding air, which expands and escapes through a tube that also leadsheat the up airthe outwater of theoutside calorimeter. When air is escaping the copper tube it will the tube. Thethe temperature of thethrough water allows for calculating calorie content of the fuel. In more recent calorimeter designs, the whole bomb, pressurized with excess pure oxygen (typically at 30atm) and containing a known mass of sample (typically 1-1.5 g) and a small fixed amount of water (to absorb produced acid gases), is submerged under a known volume of water (ca. 2000 ml) before the charge is (again electrically) ignited. The bomb, with sample and oxygen, form a closed system - no air escapes during the reaction. The energy released by the combustion raises the temperature of the steel bomb, its contents, and the surrounding water jacket. The temperature change in the water is then accurately measured. This temperature rise, along with a bomb factor (which is dependent on the heat capacity of the metal bomb parts) is used to calculate the energy given out by the sample burn. A small correction is made to account for the electrical energy input, the burning fuse, and acid production (by titration of the residual
liquid). After the temperature rise has been measured, the excess pressure in the bomb is released. Basically, a bomb calorimeter consists of a small cup to contain the sample, oxygen, a stainless steel bomb, water, a stirrer, a thermometer, the rmometer, the dewar (to prevent heat flow from the calorimeter to the surroundings) and ignition circuit connected to the bomb. Since there is no heat exchange ex change between the calorimeter and surroundings → Q = 0 (adiabatic) ; no work performed → W = 0 Thus, the total internal energy change ΔU(total) = Q + W = 0 Also, total internal energy change ΔU(total) = ΔU(system) + ΔU(surroundings) = 0 → ΔU(system) = - ΔU(surroundings) = -Cv ΔT (constant volume → dV = 0)
where Cv = heat capacity of the bomb Before the bomb can be used to determine heat of combustion of any compound, it must be calibrated. The value of Cv can be estimated by Cv (calorimeter) = m (water). Cv (water) + m (steel). Cv (steel) m (water) and m (steel) can be measured; Cv(water)= 1 cal/g.K Cv(steel)= 0.1 cal/g.K In laboratory, Cv is determined by running a compound with known heat of combustion value: C v = Hc/ΔT Common compounds are benzoic acid (Hc = 6318 cal/g) or p-methyl benzoic acid (Hc = 6957 cal/g). Temperature (T) is recorded every minute and ΔT = T(final) - T(initial)
A small factor contributes to the correction of the total heat of combustion is the fuse wire. Nickle fuse wire is often used and has heat of combustion = 981.3 cal/g In order to calibrate the bomb, a small amount (~ 1 g) of benzoic acid, or p-methyl benzoic acid is weighed. A length of Nickle fuse wire (~10 cm) is weighed bo both th before and after the combustion process. Mass of fuse wire burned Δm = m(before) - m(after) The combustion of sample (benzoic acid) inside the bomb ΔH c = ΔHc (benzoic acid) x m (benzoic aicd) + ΔHc (Ni fuse wire) x Δm (Ni fuse wire) ΔHc = Cv. ΔT → Cv = ΔHc/ΔT
Once Cv value of the bomb is determined, the bomb is ready to use to calculate heat of combustion of any compounds by ΔH c = Cv. ΔT [4] [5]
[edit] edit] Calvet-type calorimeters The detection is based on a three-dimensional fluxmeter sensor. The fluxmeter element consists of a ring of several thermocouples in series. The corresponding thermopile of high thermal conductivity surrounds the experimental space within the calorimetric block. The radial arrangement of the thermopiles guarantees an almost complete integration of the heat. This is verified by the calculation of the efficiency ratio that indicates that an average value of 94 % +/1 % of heat is transmitted through the sensor on the full range of temperature of the Calvet-type calorimeter. In this setup, the sensitivity sens itivity of the calorimeter is not affected by the crucible, the type of purgegas, or the flow rate. The main advantage of the setup is the increase of the experimental vessel's size and consequently the size of the sample, without affecting the accuracy of the calorimetric measurement. The calibration of the calorimetric detectors is a key parameter and has to be performed very carefully. For Calvet-type calorimeters, a specific calibration, so called called Joule effect effect or electrical calibration, has been developed to overcome all the problems encountered by a calibration done with standard materials. The main advantages of this type of calibration are as follows: It is an absolute calibration. The use of standard materials for calibration is not necessary. The calibration can be performed at a constant temperature, in the heating mode and in the cooling mode. It can be applied to any experimental vessel volume. It is a very accurate calibration.
An example of Calvet-type calorimeter is the C80 Calorimeter (reaction, isothermal and scanning calorimeter). calorimeter).[6]
edit]] Constant-pressure calorimeter [edit A constant-pressure calorimeter measures the change in in enthalpy enthalpy of a reaction occurring in solution the atmospheric pressure pressure remains constant. solution during which the An example is a coffee-cup calorimeter, which is constructed from two nested nested Styrofoam Styrofoam cups having holes through which a a thermometer thermometer and a stirring rod can be inserted. The inner cup holds the solution in which of the reaction occurs, and the outer cup provides provides insulation. insulation. Then
where
Cp = Specific heat at constant pressure Δ H = Enthalpy of solution ΔT = Change in temperature W = mass of solute M = molecular mass of solute
Advantages
Very large amounts of electricity can be generated in one place using coal, fairly cheaply.
Transporting oil and gas to the power stations is easy.
Gas-fired power stations are very efficient.
A fossil-fuelled power station can be built almost anywhere, so long as you can get large quantities of fuel to it. Didcot power powe r station, in Oxfordshire, has a dedicated rail link to supply the coal.
Disadvantages
Basically, the main drawback of fossil fuels is i s pollution. Burning any fossil fuel produces carbon dioxide, which contributes to the "greenhouse effect", warming the Earth.
Burning coal produces more carbon dioxide than burning oil or gas. It also produces sulphur dioxide, a gas that contributes to acid rain. We W e can reduce this before releasing the waste gases into i nto the atmosphere. More details on 'clean coal technology' from BBC News web site...
Mining coal can be difficult and dangerous. Strip mining destroys large areas of the
landscape.
Coal-fired power stations need huge amounts of fuel, which means train-loads of coal almost constantly. In order to cope with changing demands for power, the station needs reserves. This means covering a large area of countryside next to the power station with piles of coal.
Is it renewable? Fossil fuels are not a renewable renewable energy resource. Once we've burned them all, there isn't i sn't any more, and our consumption of fossil fuels has nearly doubled every 20 years since 1900. This is a particular problem for oil, because we also use it to make plastics and many other products.
Ok, you could argue that fossil fuels are renewable because more coal seams and oil fields will be formed if we wait long enough. However that means waiting for many millions of years. That's a long time - we'd have to wait around for longer than the time that humans have existed so far! As far as we today are concerned, we're using it up very fast and it hardly gets replaced at all - so by any sensible human definition fossil fuels are not renewable