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Name: shah Raj k. Std: viii-b Roll no. : 39 subject: science topic: combustion,flame and fuels |
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The justification for using oxy-fuel is to produce a CO2 rich flue gas ready for sequestration. Oxy-fuel combustion has significant advantages over traditional air-fired plants. Among these are: The mass and volume of the flue gas are reduced by approximately 75%. Because the flue gas volume is reduced, less heat is lost in the flue gas. The size of the flue gas treatment equipment can be reduced by 75%. The flue gas is primarily CO2, suitable for sequestration. The concentration of pollutants in the flue gas is higher, making separation easier. Most of the flue gases are condensable; this makes compression separation possible. Heat of condensation can be captured and reused rather than lost in the flue gas. Because nitrogen from air is not allowed in, nitrogen oxide production is greatly reduced. |
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Coal Advantages Coal can be found in lots of places in the world and there is still plenty in the UK. Coal can be easily transported to the power stations. Coal is a relatively cheap energy source. Disdvantages To dig up coal, we have to create mines which can be dangerous and not very nice to look at. Transporting coal by lorry and train from the mine to the power station causes pollution. Burning coal produces polluting gases like sulphur dioxide which make acid rain. Of all energy sources, burning coal releases the most greenhouse gases which may add to global warming. Coal is a non-renewable source and will run out in about 100 years. Coal miners can be affected by black lung disease or pneumoconiosis and also emphysema if they breathe in too much of the coal dust. |
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Oil and Natural Gas Advantages Oil and natural gas are found in lots of places in the world. We can transport oil and gas in pipes and by using tankers or ships. Disdvantages Environmental damage can be caused when building the rig and by accidental oil spillages. Oil and gas are not renewable, so once the supplies are used, they will run out. Burning these fuels releases greenhouse gases into the air. This may add to global warming. The price of oil and gas will increase because supplies are running out and lots of people will want it Working on an oil or gas rig can be dangerous due to the risk of explosions and bad weather. Nuclear Advantages Nuclear fuel does not make harmful greenhouse gases. You only need a very small amount of nuclear fuel to make a lot of energy Disdvantages The waste that is produced when using nuclear fuel is radioactive and very harmful. It needs to be disposed of carefully Nuclear power stations are at risk from terrorist attack and sabotage. World uranium supplies may run out in about 50 years. |
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The flames caused as a result of a fuel undergoing combustion (burning) Combustion (English pronunciation: /k?m'b?s.t??n /) or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame. Fuels of interest often include organic compounds (especially hydrocarbons) in the gas, liquid or solid phase. In a complete combustion reaction, a compound reacts with an oxidizing element, such as oxygen or fluorine, and the products are compounds of each element in the fuel with the oxidizing element. For example: CH4 + 2 O2 ? CO2 + 2 H2O + energy CH2S + 6 F2 ? CF4 + 2 HF + SF6[discuss] A simple example can be seen in the combustion of hydrogen and oxygen, which is a commonly used reaction in rocket engines: 2 H2 + O2 ? 2 H2O(g) + heat |
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A simple example can be seen in the combustion of hydrogen and oxygen, which is a commonly used reaction in rocket engines: 2 H2 + O2 ? 2 H2O(g) + heat The result is water vapor. aof nitrogen oxides. Complete vs. incomplete See also: pyrolysis In complete combustion, the reactant burns in oxygen, producing a limited number of products. When a hydrocarbon burns in oxygen, the reaction will only yield carbon dioxide and water. When elements are burned, the products are primarily the most common oxides. Carbon will yield carbon dioxide, nitrogen will yield nitrogen dioxide, sulfur will yield sulfur dioxide, and iron will yield iron(III) oxide. |
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Combustion is not necessarily favorable to the maximum degree of oxidation and it can be temperature-dependent. For example, sulfur trioxide is not produced quantitatively in combustion of sulfur. Nitrogen oxides start to form above 2,800 °F (1,540 °C) and more nitrogen oxides are produced at higher temperatures. Below this temperature, molecular nitrogen (N2) is favored. It is also a function of oxygen excess.[1] In most industrial applications and in fires, air is the source of oxygen (O2). In air, each mole of oxygen is mixed with approximately 3.76 mole of nitrogen. Nitrogen does not take part in combustion, but at high temperatures, some nitrogen will be converted to NOx, usually between 1% and 0.002% (2 ppm).[2] Furthermore, when there is any incomplete combustion, some of carbon is converted to carbon monoxide. A more complete set of equations for combustion of methane in air is therefore: CH4 + 2 O2 ? CO2 + 2 H2O 2 CH4 + 3 O2 ? 2 CO + 4 H2O N2 + O2 ? 2 NO N2 + 2 O2 ? 2 NO2 |
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Incomplete combustion will only occur when there is not enough oxygen to allow the fuel to react completely to produce carbon dioxide and water. It also happens when the combustion is quenched by a heat sink such as a solid surface or flame trap. For most fuels, such as diesel oil, coal or wood, pyrolysis occurs before combustion. In incomplete combustion, products of pyrolysis remain unburnt and contaminate the smoke with noxious particulate matter and gases. Partially oxidized compounds are also a concern; partial oxidation of ethanol can produce harmful acetaldehyde, and carbon can produce toxic carbon monoxide. The quality of combustion can be improved by design of combustion devices, such as burners and internal combustion engines. Further improvements are achievable by catalytic after-burning devices (such as catalytic converters) or by the simple partial return of the exhaust gases into the combustion process. Such devices are required by environmental legislation for cars in most countries, and may be necessary in large combustion devices, such as thermal power plants, to reach legal emission standards. The degree of combustion can be measured and analyzed, with test equipment. HVAC contractors, firemen and engineers use combustion analyzers to test the efficiency of a burner during the combustion process. In addition, the efficiency of an internal combustion engine can be measured in this way, and some states and local municipalities are using combustion analysis to define and rate the efficiency of vehicles on the road today. |
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Smoldering
Smoldering is the slow, low-temperature, flameless form of combustion, sustained by the heat evolved when oxygen directly attacks the surface of a condensed-phase fuel. It is a typically incomplete combustion reaction. Solid materials that can sustain a smoldering reaction include coal, cellulose, wood, cotton, tobacco, peat, duff, humus, synthetic foams, charring polymers including polyurethane foam, and dust. Common examples of smoldering phenomena are the initiation of residential fires on upholstered furniture by weak heat sources (e.g., a cigarette, a short-circuited wire), and the persistent combustion of biomass behind the flaming front of wildfires
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Rapid
Container of ethanol vapour mixed with air, undergoing rapid combustion
Rapid combustion is a form of combustion, otherwise known as a fire, in which large amounts of heat and light energy are released, which often results in a flame. This is used in a form of machinery such as internal combustion engines and in thermobaric weapons. Sometimes, a large volume of gas is liberated in combustion besides the production of heat and light. The sudden evolution of large quantities of gas creates excessive pressure that produces a loud noise. Such a combustion is known as an explosion. Combustion need not involve oxygen; e.g., hydrogen burns in chlorine to form hydrogen chloride with the liberation of heat and light characteristic of combustion.
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Turbulent
Combustion resulting in a turbulent flame is the most used for industrial application (e.g. gas turbines, gasoline engines, etc.) because the turbulence helps the mixing process between the fuel and oxidizer.
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Microgravity
Colourized gray-scale composite image of the individual frames from a video of a backlit fuel droplet burning in microgravity.
Combustion processes behave differently in a microgravity environment than in Earth-gravity conditions due to the lack of buoyancy. For example, a candle's flame takes the shape of a sphere.[3] Microgravity combustion research contributes to understanding of spacecraft fire safety and diverse aspects of combustion physics.
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Chemical Equation
Generally, the chemical equation for stoichiometric burning of hydrocarbon in oxygen is
For example, the burning of propane is
Generally, the chemical equation for stoichiometric incomplete combustion of hydrocarbon in oxygen is as follows:
For example, the incomplete combustion of propane is:
The simple word equation for the combustion of a hydrocarbon in oxygen is:
If the combustion takes place using air as the oxygen source, the nitrogen can be added to the equation,as and although it does not react, to show the composition of the flue gas
For example, the burning of propane is:
The simple word equation for this type of combustion is hydrocarbon in air
Nitrogen may also oxidize when there is an excess of oxygen. The reaction is thermodynamically favored only at high temperatures. Diesel engines are run with an excess of oxygen to combust small particles that tend to form with only a stoichiometric amount of oxygen, necessarily producing nitrogen oxide emissions. Both the United States and European Union are planning to impose limits to nitrogen oxide emissions, which necessitate the use of a special catalytic converter or treatment of the exhaust with urea.
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A fire extinguisher is an active fire protection device used to extinguish or control small fires, often in emergency situations. It is not intended for use on an out-of-control fire, such as one which has reached the ceiling, endangers the user (i.e., no escape route, smoke, explosion hazard, etc.), or otherwise requires the expertise of a fire department. Typically, a fire extinguisher consists of a hand-held cylindrical pressure vessel containing an agent which can be discharged to extinguish a fire.
In the United States, fire extinguishers, in all buildings other than houses, are generally required to be serviced and inspected by a Fire Protection service company at least annually. Some jurisdictions require more frequent service for fire extinguishers. The servicer places a tag on the extinguisher to indicate the type of service performed (annual inspection, recharge, new fire extinguisher) and when.
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Fire extinguishers are further divided into handheld and cart-mounted, also called wheeled extinguishers. Handheld extinguishers weigh from 0.5 to 14 kilograms (1 to 30 pounds), and are hence, easily portable by hand. Cart-mounted units typically weigh 23+ kilograms (50+ pounds). These wheeled models are most commonly found at construction sites, airport runways, heliports, as well as docks and marinas.
A flame (from Latin flamma) is the visible (light-emitting), gaseous part of a fire. It is caused by a highly exothermic reaction (for example, combustion, a self-sustaining oxidation reaction) taking place in a thin zone.[1] If a fire is hot enough to ionize the gaseous components, it can become a plasma.[2]
Color and temperature of a flame are dependent on the type of fuel involved in the combustion, as, for example, when a lighter is held to a candle. The applied heat causes the fuel molecules in the candle wax to vaporize. In this state they can then readily react with oxygen in the air, which gives off enough heat in the subsequent exothermic reaction to vaporize yet more fuel, thus sustaining a consistent flame. The high temperature of the flame causes the vaporized fuel molecules to decompose, forming various incomplete combustion products and free radicals, and these products then react with each other and with the oxidizer involved in the reaction. Sufficient energy in the flame will excite the electrons in some of the transient reaction intermediates such as CH and C2, which results in the emission of visible light as these substances release their excess energy (see spectrum below for an explanation of which specific radical species produce which specific colors). As the combustion temperature of a flame increases (if the flame contains small particles of unburnt carbon or other material), so does the average energy of the electromagnetic radiation given off by the flame (see blackbody).
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The chemical kinetics occurring in the flame are very complex and involves typically a large number of chemical reactions and intermediate species, most of them radicals. For instance, a well-known chemical kinetics scheme, GRI-Mech,[4] uses 53 species and 325 elementary reactions to describe combustion of biogas.
There are different methods of distributing the required components of combustion to a flame. In a diffusion flame, oxygen and fuel diffuse into each other; where they meet the flame occurs. In a premixed flame, the oxygen and fuel are premixed beforehand, which results in a different type of flame. Candle flames (a diffusion flame) operate through evaporation of the fuel which rises in a laminar flow of hot gas which then mixes with surrounding oxygen and combusts.
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Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a 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 exothermic chemical reactions and nuclear reactions, such as nuclear fission or nuclear fusion. Fuels are also used in the cells of organisms in a process known as cellular respiration, where organic molecules are oxidized to release usable energy. 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 |
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Chemical
Chemical fuels are substances that release energy by reacting with substances around them, most notably by the process of oxidation.
Biofuels
Main article: 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 as biomass fuel. 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 |
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Fossil fuels
Main article: Fossil fuel
Fossil fuels are hydrocarbons, primarily coal and petroleum (liquid petroleum or natural gas), formed from the fossilized remains of ancient plants and animals[3] by exposure to high heat and pressure in the absence of oxygen in the Earth's crust over hundreds of millions of years.[4] Commonly, the term fossil fuel also includes hydrocarbon-containing natural resources that are not derived entirely from biological sources, such as tar sands. These latter sources are properly known as mineral fuels.
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Nuclear
Main article: Nuclear fuel
Nuclear fuel is any material that is consumed to derive nuclear 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.
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Nuclear fuel pellets are used to create nuclear energy.
The most common type of nuclear fuel used by humans is heavy fissile elements that can be made to undergo nuclear fission chain reactions in a nuclear fission reactor; nuclear fuel can refer to the material or to physical objects (for example fuel bundles composed of fuel rods) composed of the fuel material, perhaps mixed with structural, neutron moderating, or neutron reflecting materials. The most common fissile nuclear fuels are 235U and 239Pu, and the actions of mining, refining, purifying, using, and ultimately disposing of these elements together make up the nuclear fuel cycle, which is important for its relevance to nuclear power generation and nuclear weapons.
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Free-fire zones in the Vietnam War
Initially, the free-fire zone was an area near an airbase which was cleared of civilians to allow aircraft bomb disposal prior to landing.
Returning veterans, affected civilians and others have said that U.S. Military Assistance Command, Vietnam MACV, based on the assumption that all friendly forces had been cleared from the area, established a policy designating "free-fire zones" as areas in which:
Anyone unidentified is considered an enemy combatant
Soldiers were to shoot anyone moving around after curfew, without first making sure that they were hostile. |
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History
When the University of Heidelberg hired Robert Bunsen in 1852, the authorities promised to build him a new laboratory building. Heidelberg had just begun to install coal-gas street lighting, so the new laboratory building was also supplied with gas. The laboratory required heating from the gas as well as illumination. For heating, it was desirable to maximize the temperature and minimize the luminosity. Previous laboratory lamps left much to be desired regarding economy and simplicity, as well as the quality of the flame for a burner lamp.
While his building was still under construction late in 1854, Bunsen suggested certain design principles to the university’s mechanic, Peter Desaga, and asked him to construct a prototype. (Similar principles had been used in an earlier burner design by Michael Faraday as well as in a device patented in 1856 by the gas engineer R W Elsner.) The Bunsen/Desaga design succeeded in generating a hot, sootless, non-luminous flame by mixing the gas with air in a controlled fashion before combustion. Desaga created slits for air at the bottom of the first cylindrical burner, the flame igniting at the top. By the time the building opened early in 1855, Desaga had made fifty of the burners for Bunsen's students. Bunsen published a description two years later, and many of his colleagues soon adopted the design. Bunsen burners are now used in laboratories all around the world.[6]
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Guided by: sandaya mam
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