A state-of-the-art solid waste management system specifies exactly what waste can be burned (based on combustibility and content of the toxic materials and pollutant precursors). It ensures that prohibited materials are detected and removed from the waste. Table 10.9.2 compiles the materials that are prohibited at several MSW incinerators. In addition, stringy wire items, such as fencing and trolling wire, can become entangled in conveyors and should be removed from the MSW feed. Such specifications are stated in contracts between operators and municipalities. Plant operators should prevent prohibited materials from entering the plant or the furnace.
A preliminary view of the waste is recommended when incoming MSW trucks are weighed. Scales, preferably integrated into an automated recording system, should be provided to record the weight of the MSW entering the plant. Tipping floors, which resemble large warehouse floors, are better suited for visual inspection and the removal of unwanted items. State-of-the-art screening includes opening garbage bags on the tipping floor to identify unwanted items inside the bags. Radioactivity sensors are used as screening devices for hospital waste. The MSW is discharged from the tipping floor into the storage pit or directly into the furnace.
The storage provided depends on variations in the rate of truck delivery of MSW to the plant and the planned burning schedule. Storage permits MSW to be retained during peak loads and thus allows the combustion chambers to be sized for a lower average capacity. Large storage areas are generally required for MSW since it is quite bulky, with a bulk density between 250 and 350 lb/cu yd (180 and 240 kg/cu m). Provisions are often made for as much as one week's MSW at small incinerators to allow for downtime and other operating problems; two to three days of MSW storage is more common at larger plants (less than 500 tn/d). Planners should consider seasonable and cyclic variations and unplanned shutdowns in establishing plant storage requirements. The pit size is usually
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