The evolution of particles in the plume from a large coal-fired boiler with flue gas desulfurization

Airborne measurements were made of gaseous and particulate species in the p lume of a large coal-fired power plant after flue gas desulfurization (FGD) controls were installed. These measurements were compared with measurement s made before the controls were installed. The light scattering and number and volume distributions of plume excess particles were determined by nephe lometry and optical particle counting techniques. The plume impact based on optical techniques was much lower than that observed in earlier measuremen ts. Indeed, plume excess volumes as a function of particle size were of the same magnitude as the variability of the background volume distribution. I n situ excess plume scattering actually decreased with distance from the so urce, in contrast to pre-FGD conditions. The upper limit for the dry rate o f SO2- to-SO42- conversion was estimated from plume excess volume measureme nts to be about 4% hr(-1). This is slightly greater than the upper limit, 3 .5% hr(-1), estimated by earlier researchers, but the same as that estimate d using the present technique with the earlier data. The cross-plume profil e of volume suggests SO2-to-SO42- conversion is highest at the plume edges. The greatest benefit of SO2 reduction on plume excess volume and visibilit y appears to occur far downwind of the source.