1.
Factory
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Factories arose with the introduction of machinery during the Industrial Revolution when the capital and space requirements became too great for cottage industry or workshops. Early factories that contained small amounts of machinery, such as one or two spinning mules, and fewer than a dozen workers have been called glorified workshops, most modern factories have large warehouses or warehouse-like facilities that contain heavy equipment used for assembly line production. Large factories tend to be located with access to multiple modes of transportation, with some having rail, highway, factories may either make discrete products or some type of material continuously produced such as chemicals, pulp and paper, or refined oil products. Oil refineries have most of their equipment outdoors, discrete products may be final consumer goods, or parts and sub-assemblies which are made into final products elsewhere. Factories may be supplied parts from elsewhere or make them from raw materials, continuous production industries typically use heat or electricity to transform streams of raw materials into finished products. The term mill originally referred to the milling of grain, which usually used natural resources such as water or wind power until those were displaced by steam power in the 19th century. Because many processes like spinning and weaving, iron rolling, and paper manufacturing were originally powered by water, according to translations of Demosthenes and Herodotus, Naucratis was a, or the only, factory in the entirety of ancient Egypt. A source of 1983, states the largest factory production in ancient times was of 120 slaves within 4th century BC Athens, although The Cambridge Online Dictionary definition of factory states, a building or set of buildings where large amounts of goods are made using machines elsewhere. The wheel was invented circa 3000 BC, the spoked wheel c.2000 BC, the Iron Age began approximately 1200-1000 BC. However, other sources define machinery as a means of production, according to one text the water-mill was first made in 555 A. D. by Belisarius, although according to another they were known to Pliny the Elder and Vitruvius in the first century B. C. By the time of the 4th century A. D. mills with a capacity to grind 3 tonnes of cereal an hour, the Venice Arsenal provides one of the first examples of a factory in the modern sense of the word. Founded in 1104 in Venice, Republic of Venice, several hundred years before the Industrial Revolution, the Venice Arsenal apparently produced nearly one ship every day and, at its height, employed 16,000 people. One of the earliest factories was John Lombes water-powered silk mill at Derby, by 1746, an integrated brass mill was working at Warmley near Bristol. Raw material went in at one end, was smelted into brass and was turned into pans, pins, wire, housing was provided for workers on site. Josiah Wedgwood in Staffordshire and Matthew Boulton at his Soho Manufactory were other prominent early industrialists, the factory system began widespread use somewhat later when cotton spinning was mechanized. Richard Arkwright is the credited with inventing the prototype of the modern factory. After he patented his water frame in 1769, he established Cromford Mill, in Derbyshire, England, the factory system was a new way of organizing labour made necessary by the development of machines which were too large to house in a workers cottage. Working hours were as long as they had been for the farmer, overall, this practice essentially reduced skilled and unskilled workers to replaceable commodities
2.
Air pollution
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Air pollution occurs when harmful substances including particulates and biological molecules are introduced into Earths atmosphere. It may cause diseases, allergies or death in humans, it may cause harm to other living organisms such as animals and food crops. Human activity and natural processes can both generate air pollution, indoor air pollution and poor urban air quality are listed as two of the worlds worst toxic pollution problems in the 2008 Blacksmith Institute Worlds Worst Polluted Places report. According to the 2014 WHO report, air pollution in 2012 caused the deaths of around 7 million people worldwide, an air pollutant is a substance in the air that can have adverse effects on humans and the ecosystem. The substance can be particles, liquid droplets, or gases. A pollutant can be of natural origin or man-made, pollutants are classified as primary or secondary. Primary pollutants are usually produced from a process, such as ash from a volcanic eruption, other examples include carbon monoxide gas from motor vehicle exhaust, or the sulfur dioxide released from factories. Secondary pollutants are not emitted directly, rather, they form in the air when primary pollutants react or interact. Ground level ozone is a prominent example of a secondary pollutant, some pollutants may be both primary and secondary, they are both emitted directly and formed from other primary pollutants. Substances emitted into the atmosphere by human activity include, Carbon dioxide - Debate continues over whether carbon dioxide should be classified as an atmospheric pollutant, because of its role as a greenhouse gas it has been described as the leading pollutant and the worst climate pollution. Against this it is argued that carbon dioxide is a component of the atmosphere, essential for plant life. This question of terminology has practical effects, for example as determining whether the U. S. Clean Air Act is deemed to regulate CO2 emissions, CO2 increase in earths atmosphere has been accelerating. Sulfur oxides - particularly sulfur dioxide, a compound with the formula SO2. SO2 is produced by volcanoes and in industrial processes. Coal and petroleum often contain sulfur compounds, and their combustion generates sulfur dioxide, further oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thus acid rain. This is one of the causes for concern over the impact of the use of these fuels as power sources. Nitrogen oxides - Nitrogen oxides, particularly nitrogen dioxide, are expelled from high temperature combustion and they can be seen as a brown haze dome above or a plume downwind of cities. Nitrogen dioxide is a compound with the formula NO2
3.
Chemical substance
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A chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical methods, i. e. without breaking chemical bonds. Chemical substances can be chemical elements, chemical compounds, ions or alloys, Chemical substances are often called pure to set them apart from mixtures. A common example of a substance is pure water, it has the same properties. Other chemical substances commonly encountered in pure form are diamond, gold, table salt, however, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical. Chemical substances exist as solids, liquids, gases, or plasma, Chemical substances may be combined or converted to others by means of chemical reactions. Forms of energy, such as light and heat, are not matter, a chemical substance may well be defined as any material with a definite chemical composition in an introductory general chemistry textbook. According to this definition a chemical substance can either be a chemical element or a pure chemical compound. But, there are exceptions to this definition, a substance can also be defined as a form of matter that has both definite composition and distinct properties. The chemical substance index published by CAS also includes several alloys of uncertain composition, in geology, substances of uniform composition are called minerals, while physical mixtures of several minerals are defined as rocks. Many minerals, however, mutually dissolve into solid solutions, such that a rock is a uniform substance despite being a mixture in stoichiometric terms. Feldspars are an example, anorthoclase is an alkali aluminium silicate. In law, chemical substances may include both pure substances and mixtures with a composition or manufacturing process. For example, the EU regulation REACH defines monoconstituent substances, multiconstituent substances and substances of unknown or variable composition, the latter two consist of multiple chemical substances, however, their identity can be established either by direct chemical analysis or reference to a single manufacturing process. For example, charcoal is a complex, partially polymeric mixture that can be defined by its manufacturing process. Therefore, although the chemical identity is unknown, identification can be made to a sufficient accuracy. The CAS index also includes mixtures, polymers almost always appear as mixtures of molecules of multiple molar masses, each of which could be considered a separate chemical substance. However, the polymer may be defined by a precursor or reaction
4.
Water
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Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
5.
Programmable logic controller
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They were first developed in the automobile industry to provide flexible, ruggedised and easily programmable controllers to replace hard-wired relays and timers. Since then they have widely adopted as high-reliability automation controllers suitable for harsh environments. A PLC is an example of a hard real-time system since output results must be produced in response to input conditions within a limited time, otherwise unintended operation will result. They can be designed for multiple arrangements of digital and analog inputs and outputs, extended temperature ranges, immunity to electrical noise, programs to control machine operation are typically stored in battery-backed-up or non-volatile memory. It was from the industry in the USA that the PLC was born. Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was mainly composed of relays, cam timers, drum sequencers, when digital computers became available, being general-purpose programmable devices, they were soon applied to control sequential and combinatorial logic in industrial processes. However these early computers required specialist programmers and stringent operating environmental control for temperature, cleanliness, to meet these challenges the PLC was developed with several key attributes. In 1968 GM Hydra-Matic issued a request for proposals for a replacement for hard-wired relay systems based on a white paper written by engineer Edward R. Clark. The winning proposal came from Bedford Associates of Bedford, Massachusetts, the first PLC, designated the 084 because it was Bedford Associates eighty-fourth project, was the result. Bedford Associates started a new company dedicated to developing, manufacturing, selling, and servicing this new product, Modicon, one of the people who worked on that project was Dick Morley, who is considered to be the father of the PLC. The Modicon brand was sold in 1977 to Gould Electronics, later acquired by German Company AEG, and then by French Schneider Electric, one of the very first 084 models built is now on display at Schneider Electrics facility in North Andover, Massachusetts. It was presented to Modicon by GM, when the unit was retired after twenty years of uninterrupted service. Modicon used the 84 moniker at the end of its product range until the 984 made its appearance, the automotive industry is still one of the largest users of PLCs. Early PLCs were designed to replace relay logic systems and these PLCs were programmed in ladder logic, which strongly resembles a schematic diagram of relay logic. This program notation was chosen to reduce training demands for the existing technicians, other early PLCs used a form of instruction list programming, based on a stack-based logic solver. Modern PLCs can be programmed in a variety of ways, from the ladder logic to programming languages such as specially adapted dialects of BASIC. Another method is state logic, a very high-level programming language designed to program PLCs based on state transition diagrams. As programming terminals evolved, it more common for ladder logic to be used, for the aforementioned reasons
6.
Flow measurement
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Flow measurement is the quantification of bulk fluid movement. Flow can be measured in a variety of ways, positive-displacement flow meters accumulate a fixed volume of fluid and then count the number of times the volume is filled to measure flow. Other flow measurement methods rely on forces produced by the stream as it overcomes a known constriction. Flow may be measured by measuring the velocity of fluid over a known area, both gas and liquid flow can be measured in volumetric or mass flow rates, such as liters per second or kilograms per second, respectively. These measurements are related by the materials density, the density of a liquid is almost independent of conditions. This is not the case for gases, the densities of which depend greatly upon pressure, temperature and to a lesser extent, composition. When gases or liquids are transferred for their content, as in the sale of natural gas. The energy flow rate is the flow rate multiplied by the energy content per unit volume or mass flow rate multiplied by the energy content per unit mass. Energy flow rate is derived from mass or volumetric flow rate by the use of a flow computer. In engineering contexts, the flow rate is usually given the symbol Q, and the mass flow rate. For a fluid having density ρ, mass and volumetric flow rates may be related by m ˙ = ρ ∗ Q, gases are compressible and change volume when placed under pressure, are heated or are cooled. A volume of gas under one set of pressure and temperature conditions is not equivalent to the gas under different conditions. References will be made to flow rate through a meter and standard or base flow rate through a meter with units such as acm/h, sm3/sec, kscm/h, LFM. Gas mass flow rate can be measured, independent of pressure and temperature effects, with thermal mass flow meters, Coriolis mass flow meters. In oceanography a common unit to measure volume transport is an equivalent to 106 m3/s. A positive displacement meter may be compared to a bucket and a stopwatch, the stopwatch is started when the flow starts, and stopped when the bucket reaches its limit. The volume divided by the time gives the flow rate, for continuous measurements, we need a system of continually filling and emptying buckets to divide the flow without letting it out of the pipe. The piston meter operates on the principle of a piston rotating within a chamber of known volume, for each rotation, an amount of water passes through the piston chamber
7.
Afterburner
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An afterburner is a component present on some jet engines, mostly those used on military supersonic aircraft. Its purpose is to provide an increase in thrust, usually for supersonic flight, takeoff, afterburning is achieved by injecting additional fuel into the jet pipe downstream of the turbine. Pilots can activate and deactivate afterburners in-flight, and jet engines are referred to as operating wet when afterburning is being used, an engine producing maximum thrust wet is at maximum power, while an engine producing maximum thrust dry is at military power. Jet-engine thrust is governed by the principle of mass flow rate. Thrust depends on two things, the velocity of the exhaust gas and the mass of that gas, a jet engine can produce more thrust by either accelerating the gas to a higher velocity or by having a greater mass of gas exit the engine. Designing a basic turbojet engine around the second produces the turbofan engine. Turbofans are highly efficient and can deliver high thrust for long periods. To generate increased power with a compact engine for short periods. The afterburner increases thrust primarily by accelerating the exhaust gas to a higher velocity, while the mass of the fuel added to the exhaust does contribute to an increase in exhaust mass, this effect is negligible compared to the increase in exhaust velocity. This temperature is known as the Turbine Entry Temperature, one of the engine operating parameters. After passing the turbine, the gas expands at a constant entropy. The afterburner then injects fuel downstream of the turbine and reheats the gas, in conjunction with the added heat, the pressure rises in the tailpipe and the gas is ejected through the nozzle at a higher velocity. The mass flow is slightly increased by the addition of the fuel. Afterburners do produce markedly enhanced thrust as well as a large flame at the back of the engine. This exhaust flame may show shock diamonds, which are caused by shock waves formed due to differences between ambient pressure and the exhaust pressure. These imbalances cause oscillations in the exhaust jet diameter over distance and this technique was developed to give greater thrust for take-off and supersonic performance in an aircraft similar to, but of higher weight, than the Hawker Siddeley Harrier. A jet engine afterburner is an extended exhaust section containing extra fuel injectors, since the jet engine upstream will use little of the oxygen it ingests, additional fuel can be burned after the gas flow has left the turbines. When the afterburner is turned on, fuel is injected and igniters are fired, the resulting combustion process increases the afterburner exit temperature significantly, resulting in a steep increase in engine net thrust
8.
Biomass
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Biomass is an industry term for getting energy by burning wood, and other organic matter. It has become popular among power stations, which switch from coal to biomass to comply with the law. Biomass most often refers to plants or plant-based materials that are not used for food or feed, as an energy source, biomass can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of biofuel. Conversion of biomass to biofuel can be achieved by different methods which are classified into, thermal, chemical. Historically, humans have harnessed biomass-derived energy since the time people began burning wood to make fire. Even today, biomass is the source of fuel for domestic use in many developing countries. Biomass is all biologically-produced matter based in carbon, hydrogen and oxygen, the estimated biomass production in the world is 104.9 petagrams of carbon per year, about half in the ocean and half on land. Wood remains the largest biomass energy source today, examples include forest residues, yard clippings, wood chips, wood energy is derived by using lignocellulosic biomass as fuel. Harvested wood may be used directly as a fuel or collected from waste streams to be processed into pellet fuel or other forms of fuels. The largest source of energy from wood is pulping liquor or black liquor, in the second sense, biomass includes plant or animal matter that can be converted into fibers or other industrial chemicals, including biofuels. Based on the source of biomass, biofuels are classified broadly into two major categories, first-generation biofuels are derived from sources such as sugarcane and corn starch. Sugars present in this biomass are fermented to produce bioethanol, a fuel which can be used directly in a fuel cell to produce electricity or serve as an additive to gasoline. However, utilizing food-based resources for production only aggravates the food shortage problem. Second-generation biofuels, on the hand, utilize non-food-based biomass sources such as agriculture. These biofuels mostly consist of lignocellulosic biomass, which is not edible and is a waste for many industries. Despite being the alternative, economical production of second-generation biofuel is not yet achieved due to technological issues. These issues arise due to chemical inertness and structural rigidity of lignocellulosic biomass. Plant energy is produced by crops grown for use as fuel that offer high biomass output per hectare with low input energy
9.
New Hampshire
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New Hampshire is a state in the New England region of the northeastern United States. It is bordered by Massachusetts to the south, Vermont to the west, Maine and the Atlantic Ocean to the east, New Hampshire is the 5th smallest by land area and the 9th least populous of the 50 United States. Concord is the capital, while Manchester is the largest city in the state and in northern New England, including Vermont. It has no sales tax, nor is personal income taxed at either the state or local level. The New Hampshire primary is the first primary in the U. S. presidential election cycle and its license plates carry the state motto, Live Free or Die. The states nickname, The Granite State, refers to its extensive granite formations, the state was named after the southern English county of Hampshire by Captain John Mason. New Hampshire is part of the New England region and it is bounded by Quebec, Canada, to the north and northwest, Maine and the Atlantic Ocean to the east, Massachusetts to the south, and Vermont to the west. New Hampshires major regions are the Great North Woods, the White Mountains, the Lakes Region, the Seacoast, the Merrimack Valley, the Monadnock Region, and the Dartmouth-Lake Sunapee area. New Hampshire has the shortest ocean coastline of any U. S. coastal state, New Hampshire was home to the rock formation called the Old Man of the Mountain, a face-like profile in Franconia Notch, until the formation disintegrated in May 2003. Major rivers include the 110-mile Merrimack River, which bisects the lower half of the state north–south and ends up in Newburyport and its tributaries include the Contoocook River, Pemigewasset River, and Winnipesaukee River. The 410-mile Connecticut River, which starts at New Hampshires Connecticut Lakes and flows south to Connecticut, only one town – Pittsburg – shares a land border with the state of Vermont. The northwesternmost headwaters of the Connecticut also define the Canada–U. S, the Piscataqua River and its several tributaries form the states only significant ocean port where they flow into the Atlantic at Portsmouth. The Salmon Falls River and the Piscataqua define the southern portion of the border with Maine, the U. S. Supreme Court dismissed the case in 2002, leaving ownership of the island with Maine. New Hampshire still claims sovereignty of the base, however, the largest of New Hampshires lakes is Lake Winnipesaukee, which covers 71 square miles in the east-central part of New Hampshire. Umbagog Lake along the Maine border, approximately 12.3 square miles, is a distant second, Squam Lake is the second largest lake entirely in New Hampshire. New Hampshire has the shortest ocean coastline of any state in the United States, Hampton Beach is a popular local summer destination. It is the state with the highest percentage of area in the country. New Hampshire is in the temperate broadleaf and mixed forests biome, much of the state, in particular the White Mountains, is covered by the conifers and northern hardwoods of the New England-Acadian forests
10.
Sintering
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Sintering is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction. Sintering happens naturally in mineral deposits or as a process used with metals, ceramics, plastics. The atoms in the materials diffuse across the boundaries of the particles, fusing the particles together, the study of sintering in metallurgy powder-related processes is known as powder metallurgy. An example of sintering can be observed when ice cubes in a glass of water adhere to each other, examples of pressure-driven sintering are the compacting of snowfall to a glacier, or the forming of a hard snowball by pressing loose snow together. The word sinter comes from the Middle High German sinter, a cognate of English cinder, the driving force for densification is the change in free energy from the decrease in surface area and lowering of the surface free energy by the replacement of solid-vapor interfaces. It forms new but lower-energy solid-solid interfaces with a decrease in free energy occurring. On a microscopic scale, material transfer is affected by the change in pressure, If the size of the particle is small, these effects become very large in magnitude. For properties such as strength and conductivity, the area in relation to the particle size is the determining factor. The variables that can be controlled for any material are the temperature. Through time, the radius and the vapor pressure are proportional to 2/3 and to 1/3. The source of power for solid-state processes is the change in free or chemical energy between the neck and the surface of the particle. The pore elimination occurs faster for a trial with many pores of uniform size, for the latter portions of the process, boundary and lattice diffusion from the boundary become important. Sintering is part of the process used in the manufacture of pottery. These objects are made from such as glass, alumina, zirconia, silica, magnesia, lime, beryllium oxide. Some ceramic raw materials have an affinity for water and a lower plasticity index than clay. Sintering is performed at high temperature, besides, second and/or third external force could be used. Commonly used second external force is pressure, so, the sintering that performed just using temperature is generally called pressureless sintering. Pressureless sintering is possible with graded metal-ceramic composites, with a nanoparticle sintering aid, a variant used for 3D shapes is called hot isostatic pressing
11.
Gasification
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Gasification is a process that converts organic or fossil fuel based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide. This is achieved by reacting the material at high temperatures, without combustion, the resulting gas mixture is called syngas or producer gas and is itself a fuel. The power derived from gasification and combustion of the resultant gas is considered to be a source of energy if the gasified compounds were obtained from biomass. Syngas may be burned directly in gas engines, used to produce methanol and hydrogen, gasification can also begin with material which would otherwise have been disposed of such as biodegradable waste. In addition, the high-temperature process refines out corrosive ash elements such as chloride and potassium, gasification of fossil fuels is currently widely used on industrial scales to generate electricity. The process of producing energy using the method has been in use for more than 180 years. In the early time coal and peat were used to power these plants, during both world wars, especially the World War II, the need for fuel produced by gasification reemerged due to the shortage of petroleum. Wood gas generators, called Gasogene or Gazogène, were used to power motor vehicles in Europe, by 1945 there were trucks, buses and agricultural machines that were powered by gasification. It is estimated there were close to 9,000,000 vehicles running on producer gas all over the world. In a gasifier, the material undergoes several different processes. Typically the resulting steam is mixed into the gas flow and may be involved with subsequent chemical reactions, the pyrolysis process occurs at around 200-300 °C. Volatiles are released and char 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. This balances the concentrations of carbon monoxide, steam, carbon dioxide, further reactions occur when the formed carbon monoxide and residual water from the organic material react to form methane and excess carbon dioxide. This third reaction occurs more abundantly in reactors that increase the time of the reactive gases and organic materials, as well as heat. Catalysts are used in more sophisticated reactors to improve reaction rates, several types of gasifiers are currently available for commercial use, counter-current fixed bed, co-current fixed bed, fluidized bed, entrained flow, plasma, and free radical. A fixed bed of fuel through which the gasification agent flows in counter-current configuration. The ash is removed in the dry condition or as a slag. The slagging gasifiers have a ratio of steam to carbon
12.
Landfill gas
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Landfill gas is a complex mix of different gases created by the action of microorganisms within a landfill. Landfill gas is approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide, trace amounts of other volatile organic compounds comprise the remainder. These trace gases include an array of species, mainly simple hydrocarbons. Landfill gases are the result of three processes, evaporation of organic compounds chemical reactions between waste components microbial action, especially methanogenesis. The first two depend strongly on the nature of the waste, despite the heterogeneity of waste, the evolution of gases follows well defined kinetic pattern. Formation of methane and CO2 commences about six months after depositing the landfill material, the evolution of gas reaches a maximum at about 20 years, then declines over the course of decades. The nature of the material in a landfill affects the landfill gas at the trace levels, for example, gases from municipal landfills contain traces of octamethylcyclotetrasiloxane, since such organosilicon compounds are used in personal care products. Because gases produced by landfills are both valuable and sometimes hazardous, monitoring techniques have been developed, flame ionization detectors can be used to measure methane levels as well as total VOC levels. Surface monitoring and sub-surface monitoring as well as monitoring of the ambient air is carried out, U. S. Federal regulations under Subtitle D of RCRA formed in October 1979 regulate the siting, design, construction, operation, monitoring, and closure of MSW landfills. Subtitle D now requires controls on the migration of methane in landfill gas, monitoring requirements must be met at landfills during their operation, and for an additional 30 years after. The landfills affected by Subtitle D of RCRA are required to control gas by establishing a way to check for methane emissions periodically and therefore prevent off-site migration. Landfill owners and operators must make sure the concentration of gas does not exceed 25% of the LEL for methane in the facilities structures. U. S. Environmental Protection Agency data shows more than 950 municipal solid waste landfills are operating in the United States as of 2013. Decomposing waste in these landfills produce landfill gas, which is a mixture of about half methane and these landfills are the third largest source of human-made methane emissions in the United States. The gases produced within a landfill can be collected and used in various ways, the landfill gas can be utilized directly on site by a boiler or any type of combustion system, providing heat. Electricity can also be generated on site through the use of microturbines, steam turbines, the landfill gas can also be sold off site and sent into natural gas pipelines. This approach requires the gas to be processed into pipeline quality, the efficiency of gas collection at landfills directly impacts the amount of energy that can be recovered - closed landfills collect gas more efficiently than open landfills. A comparison of collection efficiency at closed and open landfills found about a 17 percentage point difference between the two, Landfill gas can also be used to evaporate leachate, another byproduct of the landfill process
