Characteristics of PM and PAHs emitted from a coal-fired boiler and the efficiencies of its air pollution control devices

Sampling and analysis of filterable particulate matter (FPM), FPM_2.5, condensable particulate matter (CPM), polycyclic aromatic hydrocarbons (PAHs), sulfur oxides (SO_x) and nitrogen oxides (NO_x) emitted from a coal-fired boiler equipped with selective catalytic reduction (SCR)+ electrostatic precipitator (ESP) + wet flue gas desulfurization (WFGD) + wet electrostatic precipitator (WESP) as air pollution control devices (APCDs) are conducted. The results show that NO_x concentration emitted from the coal-fired boiler is 56 ± 2.17 ppm (with the NO_x removal efficiency of 47.2%), which does not meet the best available control technology (BACT) emission standard (≤ 30 ppm). On the other hand, the WFGD adopted has a good removal efficiency for SO_x and HCl. Both SO_x and HCl emission concentrations are <1 ppm, and removal efficiencies are >99%. The FPM and FPM_2.5 emitted from the coal-fired boiler are 0.9 ± 0.06 mg/Nm³ and <0.09 ± 0.006 mg/Nm³, respectively. The overall removal efficiency of FPM achieved with ESP+WFGD+WESP+MGGH is 99.98%. However, high concentration of CPM (37.4 ± 6.3 mg/Nm³) is measured, which is significantly higher than FPM and FPM_2.5. The concentrations of 27 PAHs at the WESP inlet and stack are measured as 667 ng/Nm³ and 547 ng/Nm³, respectively while the removal efficiencies of gas- and solid-phase PAHs are 9% and 58%, respectively. The results show that APCDs adopted are not effective in removing PAHs (only 18%), and gas-phase PAHs contribute the most in the total PAH emission. In addition, the benzo(a)pyrene equivalent (BaP_eq) concentration emitted from the stack is 28.8 ng-BaP_eq/Nm³, and most of it is contributed by 4-6 ring PAHs with high toxic equivalent factors (TEFs). Furthermore, the emission factors of air pollutant emitted from coal-fired boilers equipped with different combinations of APCDs are compiled and compared. The results show that except for CPM and NO_x, the emission factors of air pollutant calculated for this coal-fired boiler are lower if compared with other studies.