Page 310 - Materials Chemistry, Second Edition

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Incineration of MSW 281
9.8.6 PROPERTIES OF RDF ASH
As mentioned earlier in this chapter, ash quality from mass-burn incinerator ash is of concern to reg-
ulators and the general public due to the common presence of heavy metals, chlorinated dibenzo-
dioxins, furans, and other toxins. With processing via trommel screens, shredding, magnetic
separation, and air classification, the chemical properties of the waste charge are drastically
changed. Composition of the ash is also correspondingly improved over that of mass-burn inciner-
ator ash. The total elemental analysis of RDF ash is similar to that for coal ash but greatly improved
compared with that of MSW ash.
When leached by the TCLP (U.S. EPA, 1986), concentrations of all TCLP metals and non-
metals as well as reactive sulfide and cyanide are typically well below RCRA limits (Table 9.11;
Pichtel, 1991). The pH of ash tends to vary slightly; however, the majority are in the alkaline range,
a result of the presence of Ca, Mg, Al, Na, and other basic cations in the RDF. In addition, the con-
centration of TCLP extractable and volatile organics, chlorinated dibenzodioxins and furans, and
PCBs are well below the regulatory limits. RDF ash, therefore, can be disposed with much less con-
cern about possible environmental and health impacts as compared with mass-burn incinerator ash.

9.8.7 PLASTICS-DERIVED FUELS

As discussed in Chapter 4, plastics are derived from petroleum and natural gas and are composed
mostly of C, H, and O. Given the high-energy content of plastics, there is interest in using segre-
gated postuse plastics and paper in industrial fuel applications. When such materials derived from
residential, commercial, and industrial sources are used as an industrial fuel, they have been labeled
as process engineered fuel (PEF). Conventional PEF contains 70 to 90% paper and the remaining
percentage is plastic (APC, 1999).
Common reasons for encouraging a higher plastics content include the effect on densified PEF
integrity and high heat value in comparison with conventional fuels. The American Plastics
Council has explored formulations containing in excess of 30% plastics. In the United States, the
7
estimated amount of plastics currently used in PEF is less than 4.54 × 10 kg/year (Fisher and
Tomczyk, 1999).

TABLE 9.11
Analysis for Ignitability, Corrosivity,
Reactivity, and TCLP Metals and
Nonmetals in RDF Ash
Analyte RCRA Limit a Result
o
o
Flash point, F 140 F Negative
Corrosivity, pH 2–12 9.48
Reactive cyanide 250 <10
Reactive sulfide 500 25
Silver 5.0 <0.1
Arsenic 5.0 <0.2
Barium 100.0 0.1
Cadmium 1.0 <0.1
Chromium 5.0 <0.1
Mercury 0.20 <0.05
Lead 5.0 <0.1
Selenium 1.0 <0.2
a All units are in mg/L unless otherwise noted.