What Is Incineration?
Incineration refers to the enclosed burning of waste. In many places waste is burned in piles, but generally speaking this is not included in the definition of incineration and is not permitted in most developed countries. While some form of combustion chamber is a common feature of incineration, the performance, scale, sophistication and cost of incinerators varies enourmously. The extent to which all organic material is burnt and all emissions are rendered inert, is sometimes said to be a function of time, temperature and turbulence (EPI 1998). This rule of thumb suggests that the longer, hotter and more vigorously material is burnt for, the more effective (and costly) the incinerator. For incineration, as for other waste technologies, there is a clear trade-off: incineration with low adverse health and environmental impacts it is expensive. Conversely, cheap incineration can cause significant impacts on human and environmental health (UNEP, 1998).
High Temperature Incineration
High Temperature Incineration burns waste under controlled conditions to ensure that combustion is as complete as possible. Conditions for complete combustion include high temperatures, excess oxygen, strong mixing and long residence times in the combustion chamber. Strictly speaking, only the organic materials are combusted, but the non-combusted materials can also undergo a transformation under the influence of the heat released. For example, glass melts into slag, chlorine can react with organic material to form mircopollutants (R.Van Berkel pers.comm). Incineration can be set up to recover some of the energy value of the waste and can reduce volumes of by up to 90% and weight by up to 75% (UNEP 1998).
Waste Streams Handled
High Temperature Incineration technology can handle (Waste Inquiry 2000):
- mixed MSW;
- high calorific specific wastes;
- clinical (hospital and laboratory) waste; and
- hazardous waste.
The residue from High Temperature Incineration consists mainly of ash, soot and inert particles and is generally treated and disposed of as a hazardous waste due to the leachable heavy metals and salts (Waste Inquiry 2000).
High Temperature Incineration was the dominant waste disposal option for many years in North America. However, due to the environmental impacts and the public's negative perceptions and vehement opposition to incineration in recent years, it is a much less favourable option. However, High Temperature Incineration remains the dominant form of waste processing in Japan and some parts of Europe (Waste Inquiry 2000).
High Temperature Incineration has long been used to dispose of waste where landfills were not available or the waste was too offensive to landfill. High Temperature Incineration technology has developed to the point that almost complete destruction of waste is achieved with only the ash produced needing to be disposed of in landfill. There are two main types of High Temperature Incineration; single chamber liquid injection systems that are the most common for hazardous wastes, and rotary kiln systems that are versatile enough to accept solid liquid or gaseous waste. There are new High Temperature Incineration technologies developing but they are often experimental in application.
Examples Of Incineration Technologies
In mass burn systems, the refuse is burned in the state it is delivered to the facility (Raggi, 1994). Mass burning requires little or no preprocessing except for the removal of bulky objects in order to maintain efficient fuel flow. Any mixing of the waste in a mass burning facility is limited to mixing in the storage pit during loading of the refuse into the combustion chamber. The technology involves the drying, devolatilization and ignition of waste, similar to the combustion of fossil fuels. Controlled air combustion and excess air combustion are the two most prevalent types of High Temperature Incineration methods. Mass burning plants are available as modular shop assembled units, field erected at the site, or as rotary combustors.
The refuse delivered to RDF facilities is processed so that all non-combustible materials are removed prior to combustion (Raggi, 1994). RDF processing systems give a more homogeneous fuel product than MSW and allow the recovery and recycling of valuable materials contained in the solid waste stream. RDF combustion is a more energy-efficient technique than mass-burning incineration. In general, mechanical processes are used to separate MSW into various components including metal, glass and RDF. These processes have two basic functions: sizing and homogenisation, and separation of the combustible from non-combustibles.
RDF technology is extremely flexible and can be used in varying forms over a wide range of combustion technologies. Even though RDF requires preprocessing, it tends to simplify the fuel burning and emission control functions. Environmentally, RDF technology tends to emit less pollutants into the atmosphere and generates less reduced trace metals and toxic ash for landfilling.
Advantages Of High Temperature Incineration
High Temperature Incineration has the following advantages (Pavoni et al., 1975):
- If land is not available for sanitary landfills or composting facilities within economic haul distances from the center of waste generation, a centrally located incinerator may represent the most economical total system for collection and disposal of refuse;
- The residue produced from incineration constitutes only a small fraction of the charged solid waste and contains only a negligible amount of decomposable materials;
- A properly designed incinerator is capable of accommodating fluctuations of waste quantities and characteristics and also is free from interference by climate and weather; and
- Recovery of materials from incinerator residue and recovery of heat from the incineration process may produce significant incomes.
Disadvantages Of Incineration
The following are disadvantages of High Temperature Incineration (Pavoni et al., 1975; Senate Standing Committee on Environment, Recreation and the Arts, 1994):
- Effect of emissions on public health;
- Risks and hazards;
- Increased traffic;
- Unknown potentially dangerous substances;
- Costs of meeting emission standards;
- Energy recovery is relatively small;
- Incineration is irreversible;
- Potential disincentive to recycling;
- Operating costs are much higher than operational costs fro sanitary landfills because of the requirements for complex and detailed equipment and skilled personnel;
- Refuse incineration is not a complete and ultimate disposal method; and
- A large expenditure of capital funds is required for the design and construction.
- United States Department of Energy (USDOE), 2001, Use of Improved Combustion Technology to Reduce Unburned Carbon, online, available www.netl.doe.gov/publications/proceedings/01/ubc/ralston.pdf, accessed 17/06/2005
- Pavoni, J.L., Heer, J.E. and Hagerty, D.J., 1975, Handbook of Solid Waste Disposal: Materials and Energy Recovery, Van Nostrand Reinhold Company, New York.
- Raggi, A., Technological options and costs of municipal solid waste disposal and recycling, in The Management of MSW in Europe. Economic, Technological and Environmental Perspectives, 1994, A. Quadrio Curzio, L. Prosperetti and R. Zoboldi (Ed)., Elsevier Science, Amsterdam, pp 41-65.
- UNEP (United Nations Environment Program) International Environment Technology Centre, 1998, Solid Waste Management Sourcebook. www.unep.or.jp/ietc/estdir/pub/msw/
- Senate Standing Committee on Environment, Recreation and the Arts, 1994, Waste Disposal, Parliament House, Canberra.
Waste Inquiry (2000) Report of the Alternative Waste Management Technologies and Practices Inquiry.