Incineration
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Incineration is a method of disposing waste by heating it to very high temperatures. Incineration is often described as Thermal Treatment. It can accomplish one of two things. Incineration can actually burn the substance thus decomposing it into other substances. It can also be used to burn off one or more substances in a mixture by taking advantage of different boiling and flash points.
Incineration usually functions as an alternative to landfilling and bioremediation. Incineration reduces the overall volume of the waste stream and, especially for hazardous wastes, is intended to reduce the wastes' toxicity and other hazardous characteristics. It is particularly popular in countries such as Japan where land is a scarce resource.
An incinerator is a furnace for burning refuse. 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 masses called clinkers. Many small incinerators formerly found in apartment houses have now been replaced by trash compacters. The rotary-kiln incinerator used by municipalities and by large factories has a long, slightly inclined passageway through which refuse is moved continuously. In the first section the refuse is dried on moving steps, then moved onto a rocking grate where it is ignited and partially burned. The third and last section is a refractory-lined cylinder where combustion is completed. Clinkers spill out at the end. The heat from the incinerator generates steam in a boiler, producing as much as 100 megawatts of electricity. A high stack, fan, or steam jet supplied from the boiler supplies a draft. Ash drops through the grate, but many particles are carried along with the hot gases. These particles and volatile gases are burned in a combustion chamber fed by several furnaces. In order to control air pollution, the remaining gases are further treated, with acid gas scrubbers to control sulfuric and nitric acid emissions, and bag houses to remove all remaining dust particles, before they are released into the environment.
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Incineration and Waste Management
For the Environmental engineer today Incineration may be used as one of a variety of tools to design and implement a waste management strategy.
Emissions from Incineration
Incineration generates several forms of waste itself, such as the emission of unburned gases and metals in, the hazardous secondary products of combustion, and leftover ash. The health hazards associated with these emissions and incinerator wastes are the subject of intense controversy.
Solids
The volume of solids or ash left after incineration is usually from 30% to 10% of the original quantity of waste. The ash is far more concentrated with pollutants than the original waste. The ash is often regulated as a hazardous waste itself and must be landfilled.
This concentration of pollutants can allow otherwise unrecoverable metals to be recycled. The portion of metals that could not be separated prior to combustion are periodically removed from the boilers and sent to foundries for recycling. 개새끼
Gases
The exhaust gases produced as by products of incineration are a source of concern. The main potential pollutants generated include acid gases hydrogen chloride and sulphur dioxide, also NOx (as nitric oxide and nitrogen dioxide) and carbon dioxide. There is also concern over emissions of persistent organic pollutants such as dioxins and furans which are the subject of ongoing study and debate.
The quantity of hazardous substances in Incinerator exhaust gases is reduced by a technique known as scrubbing
History
The history of municipal waste incineration is linked intimately to the history of landfills and other disposal alternatives. The merits of incineration are inevitably judged in relation to those of the alternatives. Since the 1970s, recycling and other prevention measures have changed the context for such judgements.
The history of hazardous waste incineration is more recent. It is marked by major milestones in environmental regulation, e.g., RCRA, and the ebb and flow of local disputes over the siting and management of incinerator facilities.
The use of incinerators has been on the decline in the United States due in part to high disposal costs. There were 98 such plants in 2002 and 89 in 2004. The reasons for this might be that it is often cheaper to take waste to a landfill, that it is politically difficult to replace aging plants or that emissions standards or public opposition is causing incinerators to be shut down. The difficulties and costs of disposing of hazardous wastes in America are high due to the regulation of waste transport, storage, management and incineration.
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, 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 EPA and AQMD.
The Argument Pro-Incineration
- Much of the debate over incineration has focused on the traces of residual by-products of incineration, some of which are highly toxic in minute amounts. As a result, attention often focuses on non-combustible by-products, such as mercury and dioxin, that are equivalent to far less than 1% of the overall waste stream.
- Incinerators can be used for generating electricity or provide energy in other ways such as generating steam for heat. Such a use is known as waste to energy or energy recovery. However, a significant amount of energy is lost due to "scrubbers", and other methods used to clean up the exhaust. Furthermore, with increased recycling the quality of the garbage as fuel often gets worse (no paper, plastic etc. left) and sometimes additional energy is needed to burn the garbage.
- In densely populated areas, space for landfills is not easily available.
- In processing medical waste, the end product (iebottom ash) is sterile and unrecognisable as medical waste.
The Argument against Incineration
- Concerns over the unknown potential side effects of Dioxins and Furans released into the air.
- The expense of building and running an incinerator.
- Once an incinerator is built, waste is required to run it. This provides a dis-incentive to reducing waste production and reusing waste products.
- The remaining bottom ash must still be dealt with.
Potential technologies
A process that is hoped to end up supplanting incineration of plastics, if proved to be efficient, is thermal depolymerisation. The reality however is, that, unlike the high-temperature incineration, the intermediate-temperature thermal depolymerisation produces almost equal mass of hundreds of chemical compounds, for which there is no application, and many of them are hazardous and harmful.
External links
Burn Barrels
EU Information
Environmental Engineering
ISWA International
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