Data Summary of Municipal Solid Waste Management Alternatives. Volume 1: Report Text Page: 92 of 216
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Modular designs create combustion in two chambers. The solid MSW is fed into a starved-
air chamber (one that contains too little air for complete combustion) that gasifies part of the
waste. The gas is burned in a second chamber with excess air at high temperature for additional
heat recovery and organics destruction. Large plants have a single combustion chamber that uses
In both modular and field-erected units, the heat of combustion may be transferred to water
or steam in tubes that form the chamber of the combustor or the grate in a rotary combustor.
These tubes are called "water walls," and they are highly efficient at heat recovery. Another
variation is to combust the waste in a refractory lined firebox and recover the heat in a waste heat
boiler located farther from the point of combustion.
Finally, in both types of units, the exhaust gases are cleaned. Combinations of devices used
for cleaning may include:
" A scrubber that uses a lime slurry to remove acid gases and often additional
metals and organics as well
" An electrostatic precipitator or baghouse to recover particulates.
Both mass burning and RDF combustion are mature technologies. The first mass burn plant
in the United States that generated electricity for sale was built in New York City in 1902. In
addition, combustion plants with capacities greater than 250 tons per day have been evaluated
more carefully and completely than any other MSW management alternative.
Direct combustion ranks second to landfilling as an MSW management technique in the
United States, accounting for disposal of 17% of all MSW (Kiser, 1991a). Of the 176 municipal
waste combustors (MWCs) operating in the United States in 1991, 149 are mass burn plants
(Kiser, 1991a). Of those, 60 are large, field-erected plants and another 50 are smaller, modular
plants. The other 39 mass burn plants recover no energy.
Because MSW receives minimal or no preprocessing before mass burning, essentially no
energy is required. When mass burning is preceded by separation of recyclables at an MRF, the
energy requirements for materials recovery are assigned to the MRF.
The total energy produced by mass burning is higher than that of any other technology
except shred-and-burn RDF. Energy production from mass burning is often comparable to that
for shred-and-burn RDF, and it may be higher.
Net Energy Balance
For new, larger mass burn facilities, a reasonable estimate of net energy recovery is 525
kilowatt-hours (kWh) per ton of MSW, with a variance of 75 kWh per ton; that is, 3.8 pounds
of MSW generate 1 net kWh (see Appendix A, Attachment 11, page 11-4). Plants that
cogenerate steam and electricity have proportionally higher useful energy recovery, but it is more
difficult to find an appropriate mix of users for the steam.
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SRI International. Data Summary of Municipal Solid Waste Management Alternatives. Volume 1: Report Text, report, October 1992; Golden, Colorado. (https://digital.library.unt.edu/ark:/67531/metadc1310776/m1/92/: accessed May 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.