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• Uncertainty over regulatory requirements
• Major long-term economic risks
• Initially high capital cost tag and frequent cost overruns
• Concern over the effect that a long-term commitment to incineration may have on recy-
cling and other conservation efforts

9.8 REFUSE-DERIVED FUEL

During mass burning of MSW, no processing or separation of the fuel occurs other than simple mix-
ing by the tipping vehicle. In contrast, the refuse-derived fuel (RDF) technology employs a two-
stage production–incineration system. Wastes are processed to produce a higher quality and more
homogeneous fuel product than raw MSW. The input waste is usually shredded to reduce particle
size. Ferrous metals are recovered using magnetic separators. Glass, stones, and soil may be
removed by trommel screening. In some RDF plants, additional equipment is employed to process
the fuel product further, eliminating additional noncombustible materials. The final stages of pro-
cessing may involve air classification to remove the lightest fractions of the charge followed by, in
some cases, densification to produce a fuel in pellet or briquette form. Ideally, the separated, mostly
organic fraction is composed of paper products and nonhalogenated plastics only; however, PVC,
food, and yard wastes also occur. The RDF is either marketed to outside customers or burned on-
site in a so-called “dedicated” furnace.
The practice of selling a solid fuel derived from the physical processing of MSW dates only to
the early 1970s. Since that time a number of processes have been developed for RDF production
and utilization. Several plants are in operation both in the United States and Europe. RDF facilities
represent the smallest portion of the various waste-to-energy facilities studied in a DOE (2001)
report. The RDF-only facility came on line in 1975 and gradually increased in number through
1991. Reaching the peak in 1990/1991 (29 plants), their numbers have since declined. Of the 38
facilities operating since 1975, 15 were still operating in 1998. In addition to combusting RDF only,
however, many more plants burn RDF as a co-fuel, i.e., in a mixture with other solid fuels such as
coal. Co-firing with coal in a ratio of approximately 75:25 coal/RDF is a fairly typical ratio.
The overall benefits of RDF utilization include diverting potentially useful organic materials out
of the landfill, energy recovery from solid wastes, and reduction in a number of gaseous pollutants
compared with the combustion of coal alone.

9.8.1 OVERVIEW OF RDF PREPARATION
Although other methods have been tested, the so-called “dry separation” of RDF from municipal
wastes is by far the most common method of initial preparation. The method may be adapted to pro-
duce various qualities of RDF, depending mostly on the extent of separation of inorganic materials
and the putrescible (i.e., rapidly decomposable and potentially malodorous) components from the
paper and the plastics in the organic fraction. Because waste may undergo processing for other rea-
sons, such as separation of potentially recyclable metals and other inorganics, dry separation is a
logical fit for fuel production.
In order to separate the organic fraction from metals, glass, and other dense components, it is first
necessary to pass the waste through a trommel screen. The incorporation of a screen early in the
waste flow can be used either to avoid the need for air classification of the process stream or to
remove stones, dirt, and putrescible materials before air classification, so that the RDF contains
mostly paper and plastics. Screening may be followed by pulverization in a hammermill or other
shredding device. Separation of ferrous metals by magnetic extraction is a next logical step (see
Chapter 7). Most systems for RDF production include an air classifier to separate the heavy inorganic
components from the largely organic RDF. In some cases, bundled newspaper and cardboard are
manually removed from the incoming waste. Most RDF systems in the United States incorporate all
organics into the fuel, while many developed in Europe separate mainly paper and plastics.