Influence of boiler output and type on gaseous and particulate emissions from the combustion of coal for residential heating

Abstract

The study describes gaseous and particulate emissions from the combustion of two types of coal (hard and brown) in three types of boilers (one modern-type and two old-type boilers) used for residential heating. The importance of the heat outputs (nominal and two reduced outputs) for the emission of pollutants was also studied. Three outputs (95-108%, 58-73% and 26-50%) covered the expected operation of these boilers in real households under different outdoor air temperatures in the winter. Gaseous components (NOx, SO2, CO, CO2, OGC) and particulate organic compounds (n-alkanes, poly-cyclic aromatic hydrocarbons, hopanes) were determined in the emissions. In general, the emission factors (EFs) of the products of incomplete combustion were higher from the combustion of coal in old- type boilers than from that in the modern-type boilers. The EFs of particulate matter varied between 11.6 and 17.0 g kg(-1) (hard coal, the oldest-type boiler), and 0.290 and 0.544 g kg(-1) (brown coal, the modern-type boiler). The trends between the EFs of particulate organic compounds and the outputs of boilers were observed only with the automatic boiler (modern-type boiler). Similar trends for old-type boilers were not observed, probably due to the high instability of the combustion process as a result of the old construction of these boilers. Diagnostic ratios of the PAHs and the homohopane index, used for source apportionment of particulate matter in ambient air, were calculated. While the calculated homohopane indexes were similar to those reported in the literature, the calculated diagnostic ratios for PAHs related to coal combustion were different.