Incinerators

Brief History of Incineration

Incinerators have evolved greatly since the early 20th century, when open burning of wastes (either in a chimney or outdoors) was the norm for the first half of the 1900s. Incinerators in the 21st century are highly centralized facilities designed to completely combust wastes, produce energy, and minimize and treat the resulting air emissions.

The first waste incinerator was constructed in England in 1874, and the first incinerator in the United States was built in 1885. In the early 20th century, in-house incinerators were very common in the United States, resulting in a remarkably high ash fraction in U.S. garbage (43 percent in 1939). The fast growth of incineration in the United States was halted by a growing environmental movement, which led to both increased legislation and a powerful grassroots movement that fought to keep incinerators from being sited in their communities because of concern about the emissions they produced. Both the Resource Conservation and Recovery Act of 1976 and the Clean Air Act of 1990 set strict standards with which incinerators must comply. Modern incinerators are equipped with various air pollution control devices that treat and minimize the harmful emissions from burning waste. Though popular resistance to waste incineration is strong in the United States, incineration is accepted in other parts of the world; the waste management technology is used widely in Europe and Japan, which combusted 75 and 90 percent of its MSW in 2000, respectively.

Incineration Process

Incineration is the oxidation of materials at a high temperature. During the burning of wastes, moisture evaporates from the fuel and organic compounds are ignited in the presence of oxygen. The incineration process is designed to attain complete combustion of wastes; this means that all carbon in the waste is converted to carbon dioxide (CO2), all the hydrogen to water (H2O), and all the sulfur to sulfur dioxide (SO2). By-products include ash, air emissions, heat, and energy.

For an efficient combustion process, incinerated wastes should have a low moisture content (less than 50 percent) and should have a relatively high heating value (greater than 5 MJ/kg). If moisture contents are higher and heating values are lower, the wastes will require additional fuel to sustain combustion. Wastes that contain inorganic salts, high sulfur or chlorine contents, or radioactive materials must be treated in specially designed facilities. Generally, the two wastes used to produce electricity are MSW, which is unsorted waste, and RDF, which is comprised of a subset of MSW that has a higher average energy content.

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