Chemical composition and size of particles in emissions of a coal-fired power plant with flue gas desulfurization

•Cleaning processes removed over 97% of primary particles that penetrated the ESP.•Particles in the smokestack originated mainly from the desulfurization process.•Gaseous Hg emissions were within the proposed limits in the EU.

Globally more than a quarter of the total primary energy supply is based on coal combustion. The emissions of coal-fired power plants (CFPPs) are regulated in many industrialized countries and therefore power plants use cleaning techniques to minimize emissions such as sulfur dioxide (SO2) and particles. In this study, the particulate emissions from coal combustion were investigated at a CFPP (506 MW) used for combined heat and power production in Helsinki, Finland. Fine particle samples (PM1) were collected after electrostatic precipitator before the desulfurization plant (DSP), including flue gas desulfurization unit (FGD) and baghouse filters, and simultaneously in the smokestack to study the influence of DSP to particulate mass and chemistry. The DSP removed over 97% of particle mass in flue gas. Trace metals were removed efficiently but contribution of some ionic compounds increased in the FGD process. The particle properties were studied in more detail in the smokestack including particle size distribution measurements and size-segregating sampling to study chemical composition and morphology of particles. The particulate emissions from the CFPP were relatively small, consisting mainly of products and reagents of the FGD process (e.g., CaSO4, NaCl) and partly of the primary emissions from the coal combustion (e.g., mineral ash and reaction products of gas phase components). The maximum in particle volume was detected at 0.68 µm. PM1 contributed on average 62 ± 5% to PM10 mass. Besides particulate matter, also the gas-phase emission of mercury was studied because coal combustion is one of the major sources of mercury found in the environment. The mercury emissions were within the proposed limits in the EU.