Page 305 - Materials Chemistry, Second Edition

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276 Waste Management Practices: Municipal, Hazardous, and Industrial
9.8.2 GRADES OF RDF
Different grades of RDF can be produced from MSW. The higher the fuel quality, the lower is the
total yield of fuel. For example, if a MRF simply shreds the incoming waste and passes it under a
magnetic separator to remove the ferrous component, the fuel yield may be 90 to 95%, while the
average Btu value may approximate raw MSW. Conversely, producing a pelletized fuel of paper and
plastic may yield 50% of fuel based on the total incoming waste. However, the heating value may
be as much as 14,000 to 15,650 kJ/kg (6500 to 7000 Btu/lb), which is approximately two thirds the
heat value of many Midwest bituminous coal samples. Industry-wide specifications for RDF do not
exist, but RDF has been classified according to the type and degree of processing and the form of
fuel produced. The properties of RDF to consider and incorporate into supply contracts include the
proximate analysis (moisture content, ash content, volatiles, and fixed carbon); ultimate analysis
(C, H, N, O, S, and ash percentage); HHV; and content of chlorine, fluorine, lead, cadmium, and
mercury (Liu and Liptak, 2000).
The types of RDF produced are functions of equipment design, sequence of separation steps, and
operation. The RDF forms fall into the following broad groups: coarse RDF, fluff RDF, powder RDF,
and densified RDF (d-RDF). Details of the various RDF categories are provided in Table 9.7.
A photograph of d-RDF is shown in Figure 9.15.

9.8.3 PROPERTIES OF RDF
The chemical analysis of RDF samples gives an indication of the combustion performance that
might be expected. Heat content (Btu/lb) is obviously one of the top priorities for RDF production.

TABLE 9.7
Major Categories of RDF

RDF-1 (MSW) Raw MSW with minimal processing to remove oversize
bulky waste
RDF-2 ( c-RDF) MSW processed to a coarse particle size with or without
ferrous metal separation such that 95% (by wt) passes
through a 6 in. square mesh screen
RDF-3 (fluff RDF) Shredded fuel derived from MSW processed for the
removal of metal, glass, and other entrained inorganics;
particle size of this material is such that 95% (by wt)
passes through a 2 in. square mesh screen
RDF-4 (p-RDF) Combustible waste fraction processed into powdered form
such that 95% (by wt) passes through a 10 mesh screen
(0.035 in. square)
RDF-5 (d-RDF) Combustible waste fraction extruded (densified or com-
pressed) into pellets, cubettes, briquettes, or similar forms.
This form has become increasing popular owing to the
advantages of ease and cost of transportation and storage
as well as of adaptability to certain types of firing
RDF-6 Combustible waste fraction processed into a liquid fuel
RDF-7 Combustible waste fraction processed into a gaseous fuel

Source: ASTM. Reproduced with kind permission from the American Society for Testing and
Materials.