Agenda - Council - 11/25/1980 - Laserfiche WebLink

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- 21 - Bottom ash falling off the end of the 9rate is generally quenched in a water trough and taken to an ash stora9e area prior to disposal. Fine materials (siftings) fall through the grates and are conveyed to a residue collection system. In some designs, siftings are reinjected into the furnace to recover the ~eat loss they represent by not burning to com- pletion. Bottom ash and siftings are usually disposed of in a sanitary landfill. Flue gases leaving t~e boiler may also be passed through an economizer where some waste heat is used to heat the boiler feed water. Economizers improve the thermal efficiency of the unit. The cooled combustion gases are passed through air pollution control devices and, after cleaning, are vented to the atmos- phere through a stack. Modular Incinerators Modular incinerator systems that recover energy are considered to be an effective resource recovery approach for small com- munities or smaller energy users. These units are prefabri- cated and shipped to the site and consequently are suitable for smaller volumes of waste (5 to 30 TPD per unit), although several may be colocated to achieve capacities of up to 160 TPD. Modular units operate as a mass burning incinerator, which does not process the waste before combustion. Extremely large or dangerous objects may be sorted prior to incinera- tion, but the remainder of the noncombustibles are landfilled as part of the residue. The modular ~ncinerators, generally consisting of a primary and a secondary combustion chamber, employ controlled air tech- niques to reduce the amount of air required for combustion in 'the primary chamber and to lower the level of their particu- late emIssions. Ash and other noncombustible residues t~at settle on the hearth of the primary chamber after the combustion process are periodically removed by manually or automatically operated sys- tems. In the manual system, the operator scoops out the ash (by shovel or front-end loader) after the unit has been shut off and cooled down. In the automatic system, the ash is pushed or forced ahead of the burning waste until it exits the chamber, generally through a drop chute lnto a water-sealed p~t or an air-lock chamber.