Incineration
From Wikipedia, the free encyclopedia
- For other forms of waste plant that produce energy see waste-to-energy.
Incineration is a waste treatment technology that involves the combustion of waste at high temperatures.[1] Incineration and other high temperature waste treatment systems are described as "thermal treatment". In effect, incineration of waste materials converts the waste into heat (that can be used to generate electricity), sends gaseous emissions to the atmosphere, and makes residual ash. Incinerators that burn municipal waste may be represented by the acronym MSWI- municipal solid waste incinerator.
A waste-to-energy plant (WtE) is a modern term for an incinerator that burns wastes in high-efficiency furnace/boilers to produce steam and/or electricity and incorporates modern air pollution control systems and continuous emissions monitors. This type of incinerator is sometimes called an energy-from-waste (EfW).
Incineration functions as an alternative to landfilling and biological treatment methods such as composting and anaerobic digestion.
Incineration has particularly strong benefits for the treatment of certain waste types in niche areas such as clinical wastes and certain hazardous wastes where pathogens and toxins must be destroyed by high temperatures.
Modern incinerators are very different from the incinerators that were commonly used until a few decades ago. Old-type incinerators usually did not include a materials separation to remove hazardous or recyclable materials before burning, and tended to risk the health of the plant workers and the nearby residents, and most of them did not generate electricity.
The potential of electricity generation using municipal waste combustion and other non-thermal methods of waste-based energy such as anaerobic digestion are being increasingly looked at as a potential energy diversification strategy.
Incineration is particularly popular in countries such as Japan where land is a scarce resource. Sweden has been a leader in using the energy generated from incineration over the past 20 years. Denmark also extensively uses waste-to-energy incineration in localised combined heat and power facilities supporting district heating schemes.
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[edit] Technology
[edit] 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
- Fixed or moving grate combustion
- Rotary-kiln
- Multiple/stepped hearth
- Fluidised bed
[edit] 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 compactors.
[edit] Fixed or moving grate combustion
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A moving grate enables the movement of waste through the combustion chamber to be optimised to allow a more efficient burn.
[edit] Rotary-kiln
The rotary-kiln incinerator[2] used by municipalities and by large industrial plants has a long, slightly inclined cylindrical tube through which refuse is moved continuously. In the first section, the refuse is dried. In the second section, the dried refuse is 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. 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".[3] To control air pollution, the combustion product gases are further treated with acid gas scrubbers to remove sulfuric acid and nitric acid emissions, and then routed through bag houses to remove particulates before the gases are released into the atmosphere.
[edit] Multiple/stepped hearth
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Waste is transported through the furnace by moving teeth mounted on a central rotating shaft.
[edit] Fluidised bed
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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 fluidized 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 ciculated through the furnace.
[edit] Use of heat
The heat produced by the rotary-kiln incinerator can be used to generate steam which may then be used to drive an electrical generator. The typical range of net electrical energy that can be produced is about 500 to 600 kWh of per ton of waste incinerated.[4] Thus, incinerating about 2,200 tonnes per day of waste will produce about 50 MW of electrical power.
[edit] Pollution
Incineration has a number of outputs such as the ash and the emission to the atmosphere of combustion product gases and particulate matter.
Modern incinerators emit less air pollution than coal plants, but more than natural gas plants.[5] The U.S . EPA has characterized modern incinerators as "producing electricity with less environmental impact than almost any other source of electricity". Germany's Ministry of the Environment in September 2005 published a report stating that modern incinerators reduce the amount of some atmospheric pollutants by substituting power produced by coal-fired plants with power from waste-fired plants. Link: Waste incineration a potential danger: bidding farewell to dioxin spouting
[edit] Gaseous emissions
The combustion product gases exhausted to the atmosphere by incineration are a source of concern. The main pollutants in the exhaust gases include acid gases such as hydrogen chloride, sulphur dioxide, nitrogen oxides (referred to as NOx), and carbon dioxide.
The most publicized concerns from environmentalists about the incineration of municipal solid wastes (MSW) involve the fear that it produces significant amounts of dioxin and furan emissions[6] to the atmosphere. Dioxins and furans are considered by many to be serious health hazards. Older generation incinerators that were not equipped with modern gas cleaning technologies were indeed significant sources of dioxin emissions. Today, however, due to advances in emission control designs and stringent new governmental regulations, modern waste-to-energy incinerators emit virtually no dioxins.
The quantity of pollutants in the emissions from large-scale incinerators is reduced by a process known as scrubbing as well as other processes.
According to the U.S. EPA, modern incinerators 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. waste-to-energy 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 wastes, still allowed in some rural areas, generates 580 grams of dioxins yearly. Studies conducted by the U.S. EPA demonstrate that the emissions from just one family using a burn barrel produces more emissions than a modern incinerator disposing of 200 tons of waste per day.
According to the 2005 report cited above from the Ministry of the Environment of Germany, where there are 66 incinerators, "...whereas in 1990 one third of all dioxin emissions in Germany came from waste incineration plants, for the year 2000 the figure was less than 1%. Chimneys and tiled stoves in private households alone discharge approximately twenty times more dioxin into the environment than waste incineration plants."
[edit] Solid outputs
Incineration produces fly ash and bottom ash just as is the case when coal is combusted. The total amount of ash produced by municipal solid waste incineration ranges from 15% to 25% by weight of the original quantity of waste, and the fly ash amounts to about 10% to 20% of the total ash.[4] The fly ash, by far, constitutes more of a potential health hazard than does the bottom ash because the fly ash contains toxic metals such as lead, cadmium, copper and zinc as well as small amounts of dioxins and furans.[7] The bottom ash may or may not contain significant levels of health hazardous materials. In the United States, and perhaps in other countries as well, the law requires that the ash be tested for toxicity before disposal in landfills. If the ash is found to be hazardous, it can only be disposed of in landfills which are carefully designed to prevent pollutants in the ash from leaching into underground aquifers, but in testing over the past decade, no ash from a U.S. modern waste-to-energy plant has ever been determined to be a hazardous waste; In the UK, fly ash ash is classed as hazardous and must be disposed of in a hazardous waste designated landfill but Incinerator Bottom Ash (IBA) is under investigation by the Environment Agency. 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
[edit] Other pollution issues
Odour pollution can be a problem with old-style incinerators, but it is claimed that odours and dust are extremely well controlled in a modern incinerator. They receive and store the waste in an enclosed area with a negative pressure with the airflow being routed through a boiler which prevents unpleasant odours from escaping into the atmosphere. However, not all plants are implemented this way, resulting in complaints.
An issue that affects community relationships is the increased road traffic of waste collection vehicles to transport municipal waste to the incinerator. Due to this reason, most incinerators are located in industrial areas.
[edit] 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 the U.S. Environmental Protection Agency (U.S. EPA) and a great many local and national air quality regulatory agencies worldwide.
[edit] The argument for incineration
- The concerns over the health effects of dioxin and furan emissions have been significantly lessened by advances in emission control designs and very stringent new governmental regulations that have resulted in large reductions in the amount of dioxins and furans emissions.
- Modern incinerators generate electricity & heat that can be sold to the regional electric grid and can sell steam to district heating systems or industrial customers.
- The ash residue remaining after combustion has been shown to be a non-hazardous solid waste that can be safely landfilled or possibly reused.
- In densely populated areas, finding space for additional landfills is becoming very difficult.
- Countries considered "green" such as Sweden, Denmark, Switzerland and Germany, among others, rely heavily on incinerators, with some countries using incineration to dispose of all of their post-recycling municipal waste.
- Incineration of medical waste produces an end product ash that is sterile and non-hazardous.
[edit] The argument against incineration
- Modern incineration facilities cause environmental harm of a similar magnitude to a modern engineered landfill[8]
- There are still concerns by many about the health effects of dioxin and furan emissions into the atmosphere
- Incinerators also emit heavy metals such as mercury, lead and cadmium, which can be toxic at very minute levels
- The expense of building and operating an incinerator.
- Although waste incineration can be used to generate energy, a portion of that energy is consumed by the use of scrubbers and other methods to clean up the exhaust gases
- The end product ash must still be safely disposed of. SAARC (South Asian Association for Regional Cooperation) countries agree that incineration as well as unproven technologies such as Plasma, should not be considered as an option for the treatment of their municipal solid wastes for low calorific value and environmental pollution potential[9]
[edit] Trends in incinerator use
The history of municipal solid waste (MSW) incineration is linked intimately to the history of landfills 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 pathogens and toxic contamination it contains.
[edit] Incineration in the United States
The first full-scale waste-to-energy incineration 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.[10]
Whereas the construction of modern incinerators plants has increased in Europe, Japan and China during the past 15 years, in the U.S. there have been no new plants constructed since the early 1990s. 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.[11] The main reasons for lack of activity have been:-
- Law. Supreme Court's 1994 ruling in Carbone v. Town of Clarkson, which held that "flow control", or laws that direct where waste should be processed or disposed, violate the Commerce Clause. The effect of this ruling was to make it too risky for private developers to construct new incinerators.
- Economics. With the increase in the number of large inexpensive regional landfills and, up until recently, the relatively low price of electricity, incinerators were not able to compete for the 'fuel', i.e., waste. In Europe, with the ban on landfilling untreated waste, scores of modern design incinerators have been built in the last decade, with more under construction. Recently, a number of municipal governments have begun the process of contracting for the construction and operation of Incinerators. A number of Canadian cities are likewise working toward installation of incinerators.
- Tax Policies. Tax credits for plants producing electricity from waste were rescinded in the 1990s. In Europe, some of the electricity generated from waste is deemed to be from a 'Renewable Energy Source (RES)'. A new law granting tax credits for such plants was implemented in the U.S. in 2004.
- NIMBY (Not in My Backyard). Local opposition together with environmental activists have thwarted projects in major U.S. cities.
- Landfill bias. In Europe and Japan, the public understands the hazards of landfills, but this awareness is less developed in the U.S., where furthermore there is a lot of open land.
Despite these problems, there has been renewed interest in incineration 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.
[edit] 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.
[edit] Incineration in Developing Countries
Mismanagement of health care waste puts health care workers, patients and the community at risk from pathogens and from pollution due to burning in open pits or badly maintained incineration equipment. Primary health facilities require health care waste management systems to minimize the risk of contamination of patients, health workers and the general public from infectious waste. In this regard, a Waste Disposal Unit (WDU) with Small Scale Incinerator (SSI), when used according to Best Practices, can be a cheap and comparatively less hazardous way of disposing of health care waste. 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, Mobile Incinerators, Self sufficient units are ideal for remote areas where fuel and electricity are not available.
[edit] Incinerators
- Allington Incinerator
- Isle of Man Incinerator
- Kirklees Incinerator
- Bukit Tagar Incinerator, Malaysia
- List of incinerators in the UK
- SELCHP
- Sheffield Incinerator
[edit] See also
- Anaerobic digestion
- Biogas powerplant
- Composting
- Gasification
- Human incineration
- Landfill
- List of solid waste treatment technologies
- Mechanical biological treatment
- Pyrolysis
- Thermal treatment
- Waste Incineration Directive
- Waste management
- Waste-to-energy
[edit] External links
Anti Incineration Groups
Burn Barrels
EU Information
International Solid Waste Association Position
- ISWA Working Group on thermal treatment of solid waste
Overviews
Tutorial
- Incineration Tutorial from Rensaleer Polytechnic Institute
- Pictures of small incineration plant
[edit] References
- ^ Overview of incineration Knox, Andrew, An Overview of Incineration and EFW Technology as Applied to the Management of Municipal Solid Waste (MSW), University of Western Ontario, Canada, February 2005
- ^ Rotary-kiln incinerators An excellent detailed description of rotary-kiln incinerators
- ^ Photos of rotary-kiln incinerators with afterburners.
- ^ a b The ABC of Integrated Waste Management
- ^ Waste-to-Energy Compared to Fossil Fuels for Equal Amounts of Energy (Delaware Solid Waste Authority)
- ^ Beychok, M.R., A data base of dioxin and furan emissions from municipal refuse incinerators, Atmospheric Environment, Elsevier B.V., January 1987
- ^ University of Toronto, PhD Thesis Chan, C.C., Behaviour of metals in MSW fly ash during roasting with chlorinating agents, Chemical Engineering Department, University of Toronto, 1997.
- ^ Braathen, N (2007)Instrument mixes addressing household waste, Working Group on Waste Prevention and Recycling, Environment Directorate, Organisation for Economic Cooperation and Development, Retrieved 13.03.07
- ^ Dhaka Declaration (2004)
- ^ Arnold O. Chantland Resource Recovery Plant, www.city.ames.ia.us, Retrieved 29.11.06
- ^ "Waste Incineration: A Dying Technology
