ENVIRONMENTAL IMPACT OF ENERGY RECOVERY FROM WASTE TIRES
This study reports emission data obtained from an experiment carried out at the Purdue University power plant, where two different sets of fuel were combusted at the same conditions. Compared to combustion of pure coal, the use of a mixture of 95 wt% coal + 5 wt% TDF (tire-derived fuel) leads to higher emissions of various metals, most notably Zn (increase from 55 g/h to ~2.4 kg/h). To better characterize the emissions, particulate matter was collected on filter paper that was inserted into the top part of the smokestack. The collected particles thus represent the fly ash fraction that would have escaped into the atmosphere. SEM and TEM investigations revealed that these fugitive particles consist of amorphous (mainly Al-Si-glass) and crystalline material. The crystalline material comprises lime and mullite, and a variety of mostly euhedral S-O phases (inferred to be sulfates), including sulfates of Ca, Pb, Fe-Zn (pure coal), and Zn (TDF+coal). The Zn and Fe-Zn sulfates range in size from a few nm to >100 &mum. The large crystals must have crystallized only after the flue gas has passed through the air pollution control devices within the power plant. Detailed characterization of these particles is essential to assess the interaction between crystals and atmospheric moisture or rain, and thus the environmental impact of tire combustion.