PAH and Soot Emissions from Combustion of Coal and Waste Tire-derived-fuel in Fixed Beds

Abstract

This is a laboratory investigation on the emissions from batch combustion of waste tire-derived-fuel (TDF) and coal in fixed beds. The goal was to compare the magnitude of the emissions of this mode of combustion to that of continuous combustion of streams of particles of the same fuels in pulverized form, conducted previously (Levendis et al., 1996; Levendis et al., 1998). In the experiments herein waste tire chunks (in the range of 3-9 mm), tire crumb (180 212 μm) and bituminous coal (63-75 μm) were burned in a horizontal muffle furnace, at a gas temperature of 1000°C. The fuel mass loading in the furnace was varied; the residence time of the post-combustion gases was 1 s. At the exit of the furnace CO, CO 2 , NO,, polynuclear aromatic hydrocarbon (PAH) and particulate emissions were measured. Results showed that the PAH emissions from batch combustion of tire chunks were higher than those from tire crumb, which in turn were an order of magnitude higher than those from coal, under similar combustion conditions. Increasing the mass loading for both tire crumb and pulverized coal, increased the specific emissions of PAHs. Increasing the segmentation of the tire, at a fixed mass loading also increased the specific PAH emissions. Emissions of particulates closely followed the trend of PAH emissions. Batch combustion of tire chunks resulted in higher particulate yields than tire crumb, with pulverized coal a distant third. Specific CO emissions from batch combustion of TDF were an order of magnitude higher than those from coal combustion. For both fuels, CO emissions were detected during the release and combustion of the volatiles only. On the other hand, specific CO 2 , and, especially, NO x emissions from batch combustion oftire crumb were lower than those from coal. The comparison of the emissions of batch combustion of pulverized fuels in fixed beds with those of continuous combustion of streams of particles was conducted under laminar flow conditions, similar gas temperatures and similar post combustion residence times. Results showed that (i) the PAH and CO emissions of tire crumb were much lower in the latter mode of combustion, even at bulk equivalence ratios as high as 1.4; (ii) to the contrary, for coal the mode of combustion had little influence on the PAH and CO emissions.