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95 <br />Comprehensive Review of <br />Solid Waste Collection and Disposal Options <br />12.3.3 Modular Combustion <br />A modular incinerator is a type of mass - burning, WTE unit which is prefabricated on a <br />standardized modular basis in a factory Such units are shipped to the site in modules, ranging in <br />design capacity from 10 to 200 tons per day, where they are installed. Several modules can be <br />grouped together at a single location. These "off the shell'' units can often be less costly to <br />fabricate than the larger mass -burn facilities which require more costly field erection. Modular <br />plants can also typically be constructed in some 15 to 20 months. <br />Modular incinerators have been designed and constructed in the United States with different <br />process configurations. Some units have been designed to incinerate solid waste under excess air <br />conditions with either refractory furnaces or waste heat boilers or with waterwalI boilers. A <br />majority of most units, however, have been designed to operate under starved air conditions with <br />refractory furnaces and waste heat boilers. <br />A cross - section view of a typical modular combustion unit is illustrated in Exhibit 12 -2. A <br />majority of modular facilities have a tipping floor and utilize a front loader for simplicity in <br />waste storage and feeding. Combusting takes place in either two or three stages. First, solid <br />waste, which is delivered to the facility, is fed into the initial combustion chamber using a ram - <br />type feeder. A moving ram slides back and forth over fixed steps within the chamber, causing <br />the waste to tumble down one fixed section of the grate to the next fixed section. The waste is <br />then transformed into a low -Btu gas which is then combusted in the secondary chamber, where <br />auxiliary fuel is often fired under excess air conditions. A discharge ram on the back end of the <br />combustion chamber feeds this incinerated waste into an ash quench bath. <br />Exhibit 12 -2. Cross - Section of Typical Modular Facility <br />POLLUTION <br />CONTROL <br />DARY <br />DER <br />IOVAL <br />TEM <br />v2.1 161 10/22/12 <br />