Elemental particle-size emissions from coal-fired power plants: Use of an inertial cascade impactor

Coal-fly-ash particles collected on coated and uncoated impaction substrates were analyzed by scanning electron microscope (SEM) techniques in combination with instrumental neutron activation analysis (INAA) to verify the sizes of particles collected and their elemental composition to estimate the significance of bounce-off and reentrainment onto back-up filters and to evaluate wall and interstage losses for the University of Washington MK III Source Test Cascade Impactor. Particles were analyzed for a total of 39 elements. In samples collected downstream from an electrostatic precipitator (ESP), particles on upper impactor stages were much smaller than indicated by impactor 50% cut-off diameters given for the impactor, which resulted in significant differences in the measured aerosol-distribution parameters of the total particulate mass and of the mass of constituent elements. On the back-up filters, large particles (i.e. aerodynamic diameter ⪢ 2 μm) including those from bounce-off and reentrainment accounted for more than 90% of the total mass, 20–30% of the volatile species of Mo, As, Sb and Se, and all of the refractory elements. Wall and interstage losses of most elements were estimated to be about 40% by mass. Bounce-off and reentrainment onto back-up filters was only slightly reduced for small (aerodynamic diameter <2μm), wet particles collected after a wet scrubber and by use of coated impaction substrates. No significant wall and interstage losses were observed for particles collected downstream from the scrubber.