Description of Operation of MSW Incinerator

The basic operations involved in the combustion of commingled MSW are identified in Figure 3.41. The operation begins with the unloading of solid wastes from collection trucks (1) into a storage pit (2). The length of the unloading platform and storage bin is a function of the size of the facility and the number of trucks that must unload simultaneously. The depth and width of the storage bin are determined by both the rate at which waste loads are received and the rate of burning. The capacity of the storage pit is usually equal to the volume of waste for two to four days. The overhead crane (3) is used to batch load wastes into the feed (charging) chute (4), which directs the wastes to the furnace (5). The crane operator can select the mix of wastes to achieve a fairly even moisture content in the charge. Large or noncombustible items are also removed from the wastes. Solid wastes from the feed (charging) chute fall onto the grates (6), where

Incinerator Sketch Diagram
FIGURE 3.41 Definition sketch for operation of modern mass-burn incinerator.

they are mass fired. Several different types of mechanical grates are commonly used. Typical physical and chemical characteristics of incinerator solid waste are reported in Table 3.24.

Air may be introduced from the bottom of the grates (under-fire air) by means of a forced-draft fan or above the grates (over-fire air) to control burning rates and furnace temperature. Because most organic wastes are thermally unstable, various gases are driven off in the combustion process taking place in the furnace. These gases and small organic particles rise into the combustion chamber (7) and burn at temperatures in excess of 16000F. Heat is recovered from the hot gases using water-filled tubes in the walls of the combustion chamber and with a boiler

(8) that produces steam that is converted to electricity by a turbine generator

(9). When 30 percent or less of the solid waste is rubbish or when the solid waste contains more than 50 percent moisture, additional supplemental fuel will be needed.

Air pollution control equipment is required on all new incinerators. Air pollution control equipment may include ammonia injection for NOx (nitrogen oxides) control (10), a dry scrubber for SO and acid gas control (11), and a bag house (fabric filter) for particulate removal (12). To secure adequate air flows to provide for head losses through air pollution control equipment, as well as to supply air to the combustor itself, an induced-draft fan (13) may be needed. The end products of combustion are hot combustion gases and ash. The cleaned gases are discharged to the stack (14) for atmospheric dispersion. Ashes and unburned materials from the grates fall into a residue hopper (15) located below the grates where they are quenched with water. Fly ash from the dry scrubber and the bag house is mixed with the furnace ash and conveyed to ash-treatment facilities (16). Details on incinerator design, air pollution control equipment, and ash treatment and disposal may be found in Refs. 2 and 15.

TABLE 3.24 Waste¬ę

Physical and Chemical Characteristics of Incinerator Solid


Percent by Weight (as received)

Proximate analysis


Volatile matter

Fixed carbon


Ultimate analysis








Higher heating value (Btu/lb as received) Without recycling With recycling

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