CHARACTERIZATION OF SOLID WASTE PRODUCTS FROM CO-COMBUSTION OF TIRE AND COAL

As more utility and industrial facilities are beginning to use tires as a supplemental source of fuel, the study of the chemical composition of solid waste from co-combustion of tires with other fuels is becoming increasingly important. This is due largely to concerns with the potential release of toxic elements through leaching in waste disposal sites. The Wade Utility Plant at Purdue University conducted studies on the solid waste products and the atmospheric emissions from tire co-combustion. This facility combusted both pure coal and a mixture of 95 wt% coal + 5 wt% tire-derived fuel (TDF) in a stoker boiler. The data from this study reveal that the ash from tire co-combustion contains elevated levels of Zn and SO₃ when compared to ash from pure coal combustion. An increase in fly ash As concentration is also observed. In contrast, a 30% drop in Pb concentration for fly ash is observed when the coal + TDF mixture is combusted. Likewise, many other trace metals, such as Ni and Cu, decrease in concentration when TDF is added to coal. This trend is also observed in other studies. Compared to the relatively coarse bottom ash, fly ash from both fuels is enriched in most trace elements; the finer particle sizes of fly ash are effective at capturing volatile trace elements because of their relatively large surface areas. Moreover, X-ray diffraction revealed that in both cases, the finest ash fractions contain lesser amounts of glassy particles than the coarser ash. By investigating these and other trends in the solid waste from tire co-combustion, potential problems caused by the interaction of this waste with humans and the environment may be realized and prevented.