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Show o The nitrogen oxide emissions remained very low. The highest NO concentration in the flue gas was 120 ppm, which corresponds toXthe emission of 0.11 lb N02/106 Btu input. o No black smoke was observed from the stack. Since the present experiment was conducted only to examine the feasibility of fluid-bed combustion of shredded scrap tires, no detailed experiments were planned. In order to obtain the necessary engineering data for the design of a larger unit, more tests must be conducted to investigate the effects of various operating and design variables on combustion and emission characteristics. However, based on the preliminary results of the present experiment, one should design a fluidized-bed combustor which will burn up all the volatiles in the bed rather than in the freeboard. Such a design may not only improve the carbon combustion efficiency, it certainly will greatly improve sulfur retention by the limestone. A CONCEPTUAL TWO-STAGE FLUIDIZED-BED COMBUSTION TIRE INCINERATOR Based on insights gained from the results of the preliminary tests, a conceptual design of a two-stage fluidized-bed combustion scrap tire incinerator with provisions for heat recovery promises to be the most effective type of FBC device for this type of fuel. A single-stage design with submerged heat transfer surfaces also appears practical, particularly if a coal/tire fuel mix is planned. This concept should, however, be considered more developmental than the two-stage process. Figure 6 is a schematic diagram of the two-stage FBC incinerator concept. Although it is designed to burn shredded scrap tire rubber, with a modified solid handling system it could also burn both whole tires and chopped tires without prior removal of steel beads and steel and/or glass belts. 6.1 Solid Feed Systems Solids handling is an integral part of fluidized-bed combustion. In fact, a considerable amount of investment capital will be tied up in the solids handling system. Whole or chopped tires (with a minimum of size reduction processing) would be fed into the first-stage FBC incinerator through a lockhopper or screw feed system which would maintain the slight in-bed pressure. 6.2 First-Stage Fluidized-Bed Combustion The solid feeder would introduce a mixture of limestone or dolomite and certain amounts of hot bed ash with the chopped tires to the first-stage fluidized-bed combustion chamber. In-bed heat transfer is a possibility, and there would be provisions for water-wall heat adsorption. The function of the first stage would be to break up the tire carcass by the application of intense heat and vigorous physical agitation. Inside the first-stage chamber tire pyrolysis would take place, which would generate combustible gases, vapors, some liquids, and 11-29 |
