Incineration
Incineration as a waste disposal process has been an integral part of successful waste management programs in a number of communities. According to the EPA in 1999, there were 110 incinerators in the U.S. that burned MSW. �In 2005 the Commonwealth of Virginia has twelve energy recovery facilities and fourteen regulated medical waste incinerators.
The ability to generate and sell steam and/or electrical power for revenue and charge reasonable tipping fees makes the incineration or waste-to-energy (WTE) technology attractive. However, the problems associated with siting, feasibility studies, and obtaining local public acceptance has complicated the process of building WTE incinerators for project owners.
WTE technology gained a foothold in the U.S. when incineration became economically attractive in comparison to landfills during the oil price increases in the 1970's. WTE technology benefited further from the federal Public Utilities Regulatory Policy Act of 1978 that promoted alternative sources of utility power generation.� Since the above period, the growth of WTE technology as a waste management tool has not been constant. Low landfill disposal prices, low oil and natural gas prices, and localized political opposition, often based on public health fears, are the principal factors determining WTE economic feasibility, and; therefore, private sector investment into this major landfilling alternative.
The two most common WTE incineration technology processes are:
- Mass burn - MSW is burned in the same form as it is generated and collected.
- Refuse-Derived Fuel (RDF) - MSW is processed and/or formed into a usable fuel source.
These processes differ in the extent of pretreatment of the MSW before actual incineration of the MSW. The mass burn incineration technology and the RDF incineration technology require different types of furnaces and incineration conditions.
In a mass burn facility, pretreatment of the MSW includes inspection and separation to remove oversized and noncombustible items and hazardous or explosive materials. The MSW is then fed into an incinerator, where it is supported on a grate or hearth. Air is fed above or below the grate to promote combustion. Mass burn plants range from small modular plants with capacities as low as 25 tons per day to facilities with capacities of 3,000 tons of MSW per day or more.
RDF production also starts with inspection of the MSW in order to remove hazardous waste and noncombustible materials. However, in an RDF facility, the remaining or combustible MSW is then shredded and burned above a traveling grate. Unlike a mass burn facility, RDF preparation and direct firing cannot be performed economically in small plants.
An alternative type of RDF technology involves the processing and compressing of MSW into pellets or cubes for use in conventional furnaces with grates which can be located remote from the RDF processing plant.
Two other WTE technologies include cogeneration of RDF with coal or refuse gasification.� RDF can be effectively mixed with coal and burned in existing coal fired utility boilers to produce electricity. By cogenerating RDF with other fuel sources, the expense of constructing a new incinerator, boiler, air pollution control equipment, and steam turbine and generator to process the RDF can be avoided. In refuse gasification, the MSW is heated to produce a combustible gas that is collected, cleaned, and used as fuel for gas engines, turbines, and industrial boilers.
Within the basic WTE technologies, a number of patented variations exist in the private sector that require differing residuals treatment and differing emission controls.� Factors which have hindered the widespread acceptance of WTE facilities are the high capital and operation and maintenance costs associated with complying with air pollution regulations and requirements. As an air pollution point source, WTE plants are required to meet federal standards set for the following:
- Siting requirements.
- Combustion performance standards.
- Emissions of particulates, cadmium, lead, and mercury.
- Gas emissions for nitric oxides, sulfur dioxides, hydrochloric acid.
- Emissions of ash and fugitive dust.
Construction of WTE incineration facilities are relatively expensive. Therefore, most WTE plants are started by either well capitalized municipalities and authorities, by the private sector, or by a combined partnership. In addition, construction of such facilities often require the assurance or guarantee of high waste stream flows and the future sale of power. Such facilities must be capitalized and depreciated over a substantial period of time. Such an alternative technology requires a long term commitment by a community and decisions to pursue this alternative for waste disposal is complicated due to factors associated with the long time it takes to obtain the return on the investment, etc.
WTE processes often include some form of waste separation. At a minimum, ferrous metals which tend to clog up the incinerator flow, are removed from the MSW and recycled. Often, the WTE facility is co-located with or works in conjunction with a material recovery facility (MRF). The MRF functions either to recover recyclable materials from the raw MSW or to further sort source-separated recyclables and prepare them for transportation to the recycled materials market. The WTE plant can act as a safety valve when recycled material markets are down. That is, recycled materials such as cardboard and paper may be burned as a source of energy if recycling markets do not make it cost effective to separate, sort, and recycle the waste material. The combination WTE & MRF facility allows urban communities to become more self-sufficient with respect to the management of their solid waste and diminish the need for MSW landfills. It should be noted that WTE facilities still require landfilling of the bottom ash and air pollution control ash residues; however, such residues are a small fraction of the original MSW volume.