Emission characteristics of fine particles from grate firing boilers

Grate firing boilers are the main type of Chinese industrial boilers, which accounts for 85% of the industrial boilers and is one of the most important emission sources of primary air pollutants in China. In this study, five boilers in three cities were selected and tested to measure the emission characteristics of PM_2.5, and gaseous pollutants were applied by a compact dilution sampling system, which was developed for this field study. Results showed that particles mass size distributions for the five industrial boilers presented single peak or double peak, former peaks near 0.14 μm and the later peaks after 1.0 μm; the cyclone dust remover and wet scrubber dust remover had effective removal efficiencies not only to PM_2.5, but also to PM_1.0; and under the condition of same control techniques, grate firing boiler with high capacity has less PM_2.5 emission than the boiler with low capacity. In the PM_2.5 collected from flue gases, SO₄^2- was the most abundant ion, accounted for 20%-40% of the PM_2.5; and C was the most abundant element (7.5%-31.8%), followed by S (8.4%-18.7%). Carbon balance method was applied to calculate the emission factors of these pollutants. The emission factors of PM_2.5, NO_x and SO₂ were in the range of 0.046-0.486 g·kg^-1, 1.63-2.47 g·kg^-1, 1.35-9.95 g·kg^-1 respectively. The results are useful for the emission inventory development of industrial boilers and the source analysis of PM_2.5 in atmospheric environment.