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Show o Particulates When scrap tires are burned carbon black and zinc oxide, ZnO, will be emitted as micron size particulates from the incinerator. There are commercially available means to recover the carbon black. The usual practices of particulate recovery are: (1) inertial separators, (2) electrostatic precipitators, (3) bag filters, and (4) wet scrubbers. They can be used to control particulate emission from tire burning. When burning scrap tires, because of the high degree of vigorous mixing demanded by tire incineration, the particulate entrainment may be excessive. It is advisable to install cyclones or other inertial separators as primary particulate separators to reduce the dust load of flue gas prior to secondary recovery. This is a commonly accepted practice. Many textbooks and articles have been written on this subject [e.g., Corey(5)). Zinc oxides can be recovered by electrostatic precipitation combined with wet scrubbing of the flue gas from the tire incinerator. The slurry containing zinc oxide and carbon black, plus some ashes, may be further refined to recover the zinc oxide. Zinc oxide is recovered from tire incineration in Europe; the details of such an operation are available from vendors through appropriate agreements. o Unburned Hydrocarbons There are bound to be some unburned hydrocarbons in the flue gas. The combustion of tires proceeds by two consecutive steps, pyrolysis and combustion. In pyrolysis, the tire is decomposed into gases and liquids. At the same time, competitive reactions are also combining or condensing these decomposed products into compounds of higher molecular weights. It is unavoidable that some of the low molecular weight hydrocarbons may escape; however, this release can be controlled at a level which is environmentally acceptable. Multi-stage combustion is one of the solutions, so most commercial tire incinerators are multi-staged. In FBC, if necessary, the freeboard region of the boiler can be lined with refractory to assure that a high enough temperature is maintained. o Solid Disposal The leaching tests which have been performed on coal-burning fluidized-bed combustion boiler spent bed material have proved it to be benign. The only notable fact is that the leachate has a high pH value of 12. Most oxides of metals are not soluble in water. Furthermore, the spent bed material has been used as a soil conditioner without any unfavorable effects. PRELIMINARY RESULTS FROM THE FLUIDIZED-BED COMBUSTION OF SHREDDED SCRAP TIRES As described earlier, the use of scrap tires as fuel for burning is a process which offers both the promise and the problems of coal. The heating value and chemical composition of scrap tires are comparable to high-volatile bituminous coal. Scrap tires when burned in the conventional manner emit sulfur dioxides, nitrogen oxides, and particulates; in 11-18 |