TOXIC EMISSIONS FROM BURNING WASTE TIRE CHIPS

摘要

A laboratory investigation is in progress on the emissions from batch combustion of waste tire chips in fixed beds. The goal is to burn this abundant, and rather renewable, solid waste fuel and identify conditions that minimize toxic emissions. Uncontrolled combustion of whole tires generates toxic emissions, such as copious amounts of acrid smoke. Whole tires are often segmented to smaller pieces to facilitate the efficiency of both their transportation (by uncreasing the fuel mass in a given volume) and the feeding of tires to existing furnaces. Technologies for segmenting the tires to small pieces or chips in the order of a centimeter exist. Tire-derived fuel, in the form of chips, is readily available in the market. Recent work in our laboratory examined the batch combustion of tire chips and compared it with the batch combustion of beds of tire crumb and pulverized bituminous coal, under similar conditions. It was shown that soot and polynuclear aromatic hydrocarbon (PAH) emission yields from combustion of tire chips, at a furnace temperature of 1000℃, were significantly higher than those from tire crumb, which in turn were an order of magnitude higher than those from coal. Increasing the mass loading of both tire crumb and pulverized coal in the furnace increased the yields of soot and PAHs. Increasing the segmentation of the tire, at a fixed mass loading, also increased the PAH yields. CO emission yields from batch combustion of TDF were also an order of magnitude higher than those from coal combustion. For both fuels, CO emissions were detected during the combustion of the volatiles only. While CO, PAH and soot emissions from burning tire chips were much higher than those from coal, CO_2, and, especially, NO_x were lower. Current work is addressing techniques for minimizing the toxic organic emissions from burning tire chips. In the experiments reported in this manuscript waste tire chips (0.5-1 cm) are gasified/burned in a horizontal muffle furnace, at gas temperatures in the range of 500-1000℃. This furnace acted as a gasifier and primary combustor. The gaseous effluent of this furnace was mixed with additional air and was channeled in a second furnace where further oxidation took place. With this arrangement of two furnaces in series, with an additional air mixing section in between, a marked reduction in the emissions of organic pollutants, PAH, soot and CO was observed.