Seven small and medium coal-fired boilers were selected to analyze the emission factors and chemical composition characteristics of PM2.5, and the efficiency of the dust collection unit in removing PM2.5, OC, and EC of different particle sizes. At the outlet of the dust collection unit, PM2.5 mass emission factor was around 0.047-0.283 g·kg-1 with an average of (0.146±0.081) g·kg-1. SO42- was the most abundant ionic component, followed by NH4+ and Ca2+. S was the most abundant among all the elements, followed by Al, Ca, and Fe. The contents of OC and EC fluctuated greatly, and the ratio of OC and EC produced by each boiler was greater than one. In the range of the measured particle sizes, the mass concentration of PM2.5 showed a singlet or bimodal distribution, and the peak value appeared at 0.07-0.12 μm and greater than 1 μm in bimodal distribution. The mass concentration of OC showed a bimodal or trimodal distribution, and the peak value appeared at 0.04 μm, 0.20-0.31 μm, and greater than 1 μm in trimodal distribution. The efficiencies of the dust collection unit in removing PM2.5, OC, and EC were 66%, 53%, and 23%, respectively.
Keywords: PM2.5; chemical composition; coal-fired boilers; emission factor; removal efficiency.