Information AboutIncinerator |
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.]] Incineration is a ". Incineration of waste materials converts the waste into Ash , Flue Gas es, Particulate s, and Heat , which can in turn be used to generate Electricity . The flue gases are cleaned for pollutants before it is dispersed in the Atmosphere . Incineration with energy recovery is one of several Waste-to-energy (WtE) technologies such as Gasification and Anaerobic Digestion . Incineration may also be implemented without energy and materials recovery. In some countries, incinerators built just a few decades ago often did not include a Materials Separation to remove hazardous, Bulky or Recyclable materials before combustion. These facilities tended to risk the health of the plant workers and the local environment due to inadequate levels of gas cleaning and combustion process control. Most of these facilities did not generate electricity. Modern incinerators reduce the volume of the original waste by 95-96 %, depending upon composition and degree of recovery of materials such as metals from the ash for recycling. Waste to Energy in Denmark , www.zmag.dk, retreived 31.08.07 This means that while incineration does not completely replace Landfill ing, it reduces the necessary volume for disposal significantly. Incineration has particularly strong benefits for the treatment of certain Waste Types in niche areas such as Clinical Waste s and certain Hazardous Waste s where pathogens and toxins can be destroyed by high temperatures. For example in chemical multi-product plants with diverse toxic or very toxic wastewater streams, which cannot be routed to a conventional wastewater treatment plant. Waste combustion is particularly popular in countries such as , The Netherlands , Germany and France . Waste to Energy in Denmark by Ramboll Consult TECHNOLOGY Types of incinerators An incinerator is a Furnace for burning refuse, modern incinerators include pollution mitigation equipment such as flue-gas cleaning. There are various types of incinerator plant design:
Simple incinerators The older and simpler kind of incinerator was a brick-lined cell with a metal Grate over a lower ash pit, with one opening in the top or side for loading and another opening in the side for removing incombustible solids called Clinkers . Many small incinerators formerly found in apartment houses have now been replaced by Waste Compactor s. Fixed or moving grate These are large fixed hearth incinerators, with a moving grate. The moving grate enables the movement of waste through the combustion chamber to be optimised to allow a more efficient and complete combustion. These incinerators are typically used for combustion of Municipal Waste s, and are thus sometimes referred to as Municipal Solid Waste Incinerators (MSWIs). The waste is introduced by a Waste Crane through the "throat" at one end of the grate, from where it moves down over the descending grate to the ash pit in the other end. Here the ash is removed through a water lock. Part of the combustion air (primary combustion air) is supplied through the grate from below. This air flow also has the purpose of cooling the grate itself. Cooling is important for the mechanical strength of the grate, and many moving grates are also water cooled internally. Secondary combustion air is supplied into the boiler at high speed through nozzles over the grate. It facilitates complete combustion of the flue gases by introducing Turbulence for better mixing and by ensuring a surplus of oxygen. According to the European Waste Incineration Directive , incineration plants must be designed to ensure that the Flue Gas es reach a temperature of at least 850 °C for 2 seconds in order to ensure proper breakdown of organic Toxin s. This includes backup auxiliary burners (often fueled by oil), which are fired into the boiler in case the Heating Value of the waste becomes too low to reach this temperature alone. The Flue Gas es are then cooled in the Superheaters , where the heat is transferred to steam, heating the steam to typically 400 °C at a pressure of 40 Bar for the electricity generation in the Turbine . At this point, the flue gas has a temperature of around 200 °C, and is passed to the Flue Gas Cleaning System . A single moving grate boiler can handle up to 35 tonnes of waste per hour, and can operate 8,000 hours per year with only one scheduled 'revision' (inspection and maintenance) of about one months duration Vestforbrænding anlæg 6 - Danmarks største forbrændingsovn , Brochure (in Danish) on the largest incineration line in Europe, 2004. At least in Scandinavia revisions are always performed during summer, where the demand for District Heating is low. Often incineration plants consist of several separate 'boiler lines' (boilers and flue gas treatment plants), so that waste receival can continue at one oven line while the others are subject to revision. Rotary-kiln The Rotary-kiln incinerator Rotary-kiln incinerators An excellent detailed description of rotary-kiln incinerators used by municipalities and by large industrial plants. This design of incinerators have 2 chambers a primary chamber and secondary chamber. The primary chamber in a rotary klin incinerator consist of an inclined refractory lined cylindrical tube. Movement of the cylinder on its axis facilitates movement of waste. In the primary chamber, there is conversion of solid fraction to gases, through volatilization, destructive distillation and partial combustion reactions. The secondary chamber is necessary to complete gas phase combustion reactions The clinkers spill out at the end of the cylinder. A tall Flue Gas Stack , fan, or steam jet supplies the needed Draft . Ash drops through the grate, but many particles are carried along with the hot gases. The particles and any combustible gases may be combusted in an "afterburner". Photos of rotary-kiln incinerators with afterburners. A diagram of a rotary-kiln incinerator can be found here . Multiple/stepped hearth Waste is transported through the furnace by moving teeth mounted on a central rotating shaft. Fluidised bed A strong airflow is forced through a sandbed The air seeps through the sand until a point is reached where the sand particles separate to let the air through and mixing and churning occurs, thus a Fluidised Bed is created and fuel and waste can now be introduced. The sand with the pre-treated waste and/or fuel is kept suspended on pumped air currents and takes on a fluid-like character. The bed is thereby violently mixed and agitated keeping small inert particles and air in a fluid like state. This allows all of the mass of waste, fuel and sand to be fully circulated through the furnace. Specialised incineration Modern furniture factory sawdust incinerators need much attention as these have to handle resin powder and many flammable substances. Controlled combustion, burn back prevention systems are very essential as dust when suspended resembles the fire catch phenomenon of any liquid petroleum gas. Use of heat The heat produced by an incinerator can be used to generate steam which may then be used to drive a Consult. Thus, incinerating about 600 tonnes per day of waste will produce about 17 MW of electrical power and 1200 MWh district heating. Pollution Incineration has a number of outputs such as the ash and the emission to the atmosphere of Flue Gas . Before the Flue Gas Cleaning System , the flue gases may contain significant amounts of Particulate Matter , Heavy Metals , Dioxins , Furans , Sulphur Dioxide , and Hydrochloric Acid . In a study Waste-to-Energy Compared to Fossil Fuels for Equal Amounts of Energy ( Delaware Solid Waste Authority) from 1994, Delaware Solid Waste Authority found that modern incineration plants emitted fewer particles, hydrocarbons and less SO2, HCl, CO and NOx than Coal -fired power plants, but more than Natural Gas fired power plants. According to Germany 's Ministry of the Environment, modern waste combustors reduce the amount of some atmospheric pollutants by substituting power produced by coal-fired plants with power from waste-fired plants Waste incineration a potential danger: bidding farewell to dioxin spouting , Report by Germany's Ministry of the Environment. Gaseous emissions Dioxin and furans The most publicized concerns from environmentalists about the incineration of municipal solid wastes (MSW) involve the fear that it produces significant amounts of , modern incineration plants are no longer significant sources of dioxins and furans. In 1987, before the governmental regulations required the use of emission controls, there was a total of 10,000 grams of dioxin emissions from U.S. incinerators. Today, the total emissions from the 87 plants are only 10 grams, a reduction of 99.9 %. Backyard barrel burning of household and Garden Waste s, still allowed in some rural areas, generates 580 grams of dioxins yearly. Studies conducted by EPA Evaluation of Emissions from the Burning of Household Waste in Barrels , EPA November 1997 demonstrate that the emissions from just one family using a burn barrel produces more emissions than a modern incineration plant disposing of 200 tonnes of waste per day. CO2 As for other complete combustion processes, nearly all of the carbon content in the waste is emitted as CO2 to the atmosphere. MSW contain approximately the same mass fraction of carbon as CO2 itself (27%), so incineration of one tonne of MSW produce approximately 1 tonne of CO2. Alternatively the waste could be Landfill ed. In the landfill, one tonne of MSW would produce approximately 62 m3 Methane by Anaerobic Digestion of the Biodegradable Part Of The Waste . This amount of methane has more than twice the Global Warming Potential than the one tonne of CO2, which would have been produced by incineration. In some countries, large amounts of this Landfill Gas is collected, but still the global warming potential of the lost landfill gas in the US in 1999 was approximately 32 % higher than the amount of CO2 that would have been emitted by incineration.Themelis, Nickolas J. An overview of the global waste-to-energy industry , Waste Management World 2003 In addition, nearly all biodegradable waste has biological origin, and absorbed all of the emitted CO2 during growth. Such considerations are the main reason why several countries administrate incineration of the biodegradable part of waste as . Other emissions Other gaseous toxins in the flue gas from incinerator furnaces include Sulphur Dioxide , Hydrochloric Acid , Heavy Metals and Fine Particles . The Steam content in the flue may produce visible Fume from the stack, which can be perceived as a Visual Pollution . It may be avoided by decreasing the steam content by flue gas condensation, or by increasing the flue gas exit temperature well above its dew point. Flue gas cleaning The quantity of pollutants in the flue gas from incineration plants is reduced by several processes. Particulate is collected by 2006 (in Danish) Acid gas , Sweden (in Swedish) Waste water from scrubbers must subsequently pass through a waste water treatment plant. Sulfur dioxide may also be removed by dry Desulfurisation by injection Limestone Slurry into the flue gas before the particle filtration. NOx is either reduced by catalytic reduction with ammonia in a Catalytic Converter ( Selective Catalytic Reduction , SCR) or by a high temperature reaction with ammonia in the furnace ( Selective Non-catalytic Reduction , SNCR). Heavy metals are often Adsorb ed on injected Active Carbon powder, which is collected by the particle filtration. Solid outputs Incineration produces . At present although some historic samples tested by the incinerator operators' group would meet the being ecotoxic criteria at present the EA say "we have agreed" to regard incinerator bottom ash as "non-hazardous" until the testing programme is complete. Other pollution issues Odour pollution can be a problem with old-style incinerators, but odours and dust are extremely well controlled in a modern incineration plant. They receive and store the waste in an enclosed area with a negative pressure with the airflow being routed through the boiler which prevents unpleasant odours from escaping into the atmosphere. However, not all plants are implemented this way, resulting in inconveniences in the locality. An issue that affects community relationships is the increased road traffic of Waste Collection Vehicle s to transport municipal waste to the incinerator. Due to this reason, most incinerators are located in industrial areas. THE DEBATE OVER INCINERATION Use of incinerators for Waste Management is controversial. The debate over incinerators typically involves business interests (representing both waste generators and incinerator firms), government regulators, environmental activists and local citizens who must weigh the economic appeal of local industrial activity with their concerns over health and environmental risk. People and organizations professionally involved in this issue include the U.S. Environmental Protection Agency and a great many local and national air quality regulatory agencies worldwide. The argument for incineration
The argument against incineration from 1978]]
TRENDS IN INCINERATOR USE The history of Municipal Solid Waste (MSW) incineration is linked intimately to the history of Landfill s and other Waste Treatment Technology . The merits of incineration are inevitably judged in relation to the alternatives available. Since the 1970s, recycling and other prevention measures have changed the context for such judgements. Since the 1990s alternative waste treatment technologies have been maturing and becoming viable. Incineration is a key process in the treatment of hazardous wastes and clinical wastes. It is often imperative that medical waste be subjected to the high temperatures of incineration to destroy Pathogen s and Toxic contamination it contains. Incineration in the United States The first full-scale waste-to-energy facility in the US was the Arnold O. Chantland Resource Recovery Plant, built in 1975 located in Ames, Iowa. This plant is still in operation and produces Refuse-derived Fuel that is sent to local power plants for fuel Arnold O. Chantland Resource Recovery Plant , Ames City Government Homepage. The first commercially-successful incineration plant in the U.S. was built in Saugus, Massachusetts in October 1975 by Wheelabrator Technologies, and is still in operation today Waste-to-Energy: Less Environmental Impact than Almost Any Other Source of Electricity , Integrated Waste Services Association homepage. Several older generation incinerators have been closed; of the 186 MSW incinerators in 1990, only 112 remained by 2003, and of the 6200 medical waste incinerators in 1988, only 115 remained in 2003 Waste Incineration: A Dying Technology . Between 1996 and 2005, no new waste-to-energy plants were built. The main reasons for lack of activity have been:
Despite these problems, there has been renewed interest in waste-to-energy in the U.S. Canada & the UK. Projects to add capacity to existing plants are underway, and municipalities are once again evaluating the option of building modern plants rather than continue landfilling municipal wastes. Incineration in the United Kingdom The technology employed in the UK waste management industry has been greatly lagging behind that of Europe due to the wide availablility of landfills. The Landfill Directive set down by the European Union led to the Government of the United Kingdom imposing Waste Legislation including the Landfill Tax and Landfill Allowance Trading Scheme . This legislation is designed to reduce the release of greenhouse gases produced by landfills through the use of alternative methods of waste treatment. It is the UK Government's position that incineration will play an increasingly large role in the treatment of municipal waste and supply of energy in the UK. Small incinerator units Small scale incinerators exist for special purposes. For example, the small scale Waste Disposal Unit from the homepage of the Indian Centre for Renewable Energy, Appropriate Technology and Environment incinerators are aimed for Hygienically safe destruction of medical waste in Developing Countries . Simple, mobile incinerators are becoming more widely used in developing countries where the threat of avian influenza is high. Small incinerators can be quickly deployed to remote areas where an outbreak has occurred to dispose of infected animals quickly and without the risk of cross contamination. INCINERATORS
SEE ALSO
EXTERNAL LINKS Anti-incineration groups : Anti-incineration Organization based in Syracuse,NY Burn barrels : Burn Barrel Organization : EPA Fact Sheet : Emissions Information EU information : EU Directive on waste incineration : BREF Drafts & Papers International Solid Waste Association position : position papers Overviews : Incineration article : FAQ's on incineration Tutorial : [http://www.sysav.se/upload/flash/sysav.swf Flash presentation of SYSAV], a large incineration plant in Malmö , Sweden . : [http://www.rpi.edu/dept/chem-eng/Biotech-Environ/incinerator.html Incineration Tutorial] from Rensaleer Polytechnic Institute REFERENCES |
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