Sunday, September 12, 2010

Incineration of plastics

Q: What happens inside a modern waste-to-energy facility?
A: The energy value of municipal solid waste (MSW) can be recovered through waste-to-energy incineration. Modern energy recovery facilities burn MSW in special combustion chambers, then use the resulting heat energy to generate steam or electricity. This process reduces the volume of MSW to be landfilled by as much as 90 percent.
Energy recovery facilities are designed to achieve high combustion temperatures, which help MSW burn cleaner and create less ash for disposal. Modern air pollution control devices - electrostatic precipitators, dry and wet scrubbers, and/or fabric filters - are used to remove potentially harmful particulates and gases from incinerator emissions.
Q: Is waste-to-energy incineration safe?
A: Yes. In 1989, the U.S. Conference of Mayors convened an international blue-ribbon panel of experts to discuss the health and safety impacts of waste-to-energy incineration. The symposium participants concluded that a properly equipped, operated and maintained energy recovery facility can operate within existing regulatory standards for human health and safety. The Clean Air Act of 1991 provided for an additional margin of security with tightened emissions standards. Furthermore, many communities are recognizing the importance of removing recyclables, as well as items such as batteries and household hazardous wastes, before incineration to reduce toxic components in incinerator ash.
The symposium participants found that, contrary to popular misconception, there is no evidence to link the incineration of PVC with increased dioxin emissions. Similar conclusions have been reached in a number of sources, including a 1987 study for the New York State Energy Research and Development Authority. Generally speaking, electricity is generated as safely through waste-to-energy incineration as it is through a power plant.
Q: How much waste-to-energy capacity is there?
A: There are 121 energy recovery facilities operating in the United States, with a designed capacity of nearly 97,000 tons per day. An additional five facilities are under construction and 31 are in the planning stages. If all of these facilities come on line as planned, 19 percent of the nation's MSW will be processed by energy recovery facilities by the year 2000.
Q: How do plastics contribute to waste-to-energy incineration?
A: Plastics are derived from petroleum or natural gas, giving them a stored energy value higher than any other material commonly found in the waste stream. In fact, one pound of plastics can generate twice as much energy as Wyoming coal and almost as much energy as fuel oil. When plastics are processed in modern waste-to-energy facilities, they can help other waste combust more completely, leaving less ash for disposal in landfills.
                    Energy Values

Material                                  Btu/pound


PET                                           10,900
HDPE                                        18,700
Other Plastic Containers             16,400
Other Plastics                            17,900
Rubber & Leather                      12,800
Newspaper                                8,000
Corrugated Boxes (paper)          7,000
Textiles                                      9,400
Wood                                       7,300
Average for MSW                     5,900
Yard Wastes                             2,900
Food Wastes                            2,900
Heat Content of Common Fuels
Fuel Oil                                  20,900
Wyoming Coal                        9,600

Courtesy: SPI

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