Mass Burn and RDF Incinerators

Two main types of waste-to-energy incinerators are mass-burn incinerators and RDF incinerators. Figure 10.9.1 shows the typical structure of a waste-to-energy facility.

The more common mass-burn incinerators burn MSW as received with minimal onsite effort to separate objects that do not burn well or do not burn at all. (For example, bulky, oversized items such as tires, bedframes, fences, and logs are often separated by hand to avoid problems, but glass bottles and metals usually are not.)

RDF incinerators burn MSW that has been pre-processed and sorted (either on the site of the incinerator

(^ Tipping Hall {2} Refuse Bunker (j^ Grapple and Refuse Crane Crane Operator Control Charging Hopper Overfire Air Fan (^ Ram Feed

Ignition Burner Fan Underfire Fan M0 Roller Grate

11 Ash Conveyors to

Materials Recovery (T2 Boiler

(13 Overfire Air Intake (14 Turbine Generator (15 Precipitator

Control Room Deaerator Storage Tank and Heater © Motor Control Center (20 Maintenance Shop (21 Heaters 22 Condenser (23 Switchgear (24 Id Fan (25) Turbine Crane

FIG. 10.9.1 Schematic of a typical waste-to-energy resource recovery facility.

or at separate processing facilities). Noncombustible and recyclable material such as ferrous metals, aluminum, and glass are separated mechanically and collected for processing and future sale or disposal. The combustible portion is converted to a more uniform, pellet fuel through particle reduction (usually 4- to 6-in pellets).

RDF technology is preferred by recycling-oriented users partly for economic reasons (e.g., income from the sale of aluminum), and partly because it cuts the incinerator residues to less than half and thereby reduces the amount of leftover material that must be landfilled. RDF-fired boilers can respond faster to load variations, require less excess air, and can operate at higher efficiencies. Comparisons of mass-burner performance on both raw MSW to simple prepared fuels show that prepared fuel plants have many advantages over the mass-burning technology (Sommer and Kenny 1984). However, RDF technology is still in the development stage. The majority of incinerators under construction are mass-burn. Part of the reason for this lack of development is the complexity of the RDF process, which remains an expensive and maintenance-intensive alternative to mass-burning.

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