New particle formation in the fresh flue-gas plume from a coal-fired power plant: effect of flue-gas cleaning

Abstract

Atmospheric emissions, including particle number and size distribution, of a 726 MWth coal-fired power plant were studied experimentally from power plant stack and from flue gas plume dispersing in the atmosphere. Experiments were conducted under two different flue gas cleaning conditions. The results were utilised in a plume dispersion and dilution modelling taking into account nucleation particle precursor (H2SO4 resulted from the oxidation of emitted SO2) formation and assessment related to nucleation rates. The experiments showed that the primary emissions of particles and SO2 were effectively reduced by flue gas desulphurization and fabric filters, especially the emissions of particles smaller than 200 nm in diameter. Primary pollutant concentrations reached background levels in 200–300 seconds. However, the atmospheric measurements indicated that new particles are formed in the flue gas plume, even in the very early phases of atmospheric ageing. The effective number emission of nucleated particles were several orders of magnitude higher than the primary particle emission. Modelling studies indicate that regardless of continuing dilution of the flue gas, nucleation precursor (H2SO4 from SO2 oxidation) concentrations remain relatively constant. In addition, flue gas nucleation is more efficient than natural atmospheric nucleation. Especially, the observation of the new particle formation with rather low flue gas SO2 concentrations changes the current understanding on the air quality effects of coal-combustion. The results can be used to evaluate the optimal ways to achieve better air quality particularly in polluted areas like India and China.