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Show REVIEW OF TIRE INCINERATION Commercial tire incineration experience makes it clear that environmentally acceptable tire incineration requires different measures than do conventional fuels. Modifications, and sometimes radical changes in conventional incinerator design, are needed to achieve satisfactory incineration of scrap tires. Cox(6), Beckman, et al.(2), have proposed a number of parameters which need to be considered. The following design and operational variables should be closely controlled to insure satisfactory incineration of scrap tires. 4.1 Agitation Sufficient and vigorous agitation to maintain continuous contact between tire and combustion air. In the commercial tire burning equipment, this is accomplished in the following ways: o The primary incineration chamber is designed to rotate and is subject to vigorous vortex agitation (tumbler burner). o A moving arm is provided to stir or poke the fire to insure adequate mixing of fuel (tires) and air (Lucas Cyclone Furnace). o In batch incinerators, such as the Ruthner's Polyma incinerator and the basic incinerator, vigorous mechanical mixing is provided to insure that adequate agitation is achieved. Hot fluidized-bed tests of shredded tire rubber have demonstrated that FBC offers adequate agitation. 4.2 Temperature The process of incinerating scrap tires entails two major steps. The first step is the pyrolysis of scrap tires into their component combustible liquids and gases. The second step is the combustion of the pyrolysis products to carbon dioxide, water, and other final combustion products. Pyrolysis also consists of two consecutive processes: thermal cracking of the rubber into simple hydrocarbons, and condensation of the thermal cracking products into relatively stable compounds. The rates of thermal cracking and final combustion are temperature dependent. Condensation should be reduced by increased temperature. In most tire incinerators, the temperature is high enough to insure fast chemical reaction rates for both pyrolysis and combustion. The temperature required for satisfactory incineration of scrap tires is on the order of 1400°-2000°F. Excessive temperature levels will cause the formation of unacceptable quantities of nitrogen oxides, NO . Temperatures above the fusion temperature of the solid combustion products will cause clinkers to form inside the furnace. Clinkers formed by overly high combustion temperatures have damaged the hearths of tire incinerators and caused operational problems. If the rate of combustion can be sufficiently enhanced without an elevated temperature, it is much preferred. 11-14 |
