10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
A Novel Method Based on Light Scattering for Distinguishing Water and Fly-ash Aerosols in Industrial Stack Emission
Satyanarayanan Seshadri, VIPUL DOGRA, Indian Institute of Technology, Madras
Abstract Number: 1221 Working Group: Low-Cost and Portable Sensors
Abstract Light scattering experiments were performed to understand the difference in behaviour between water and fly-ash aerosols. Our intent is to differentiate liquid droplets from fly-ash found in industrial stack emissions, where liquid carry over is observed when flue gas de-sulphurization is used.
Qualitative differences in measuring spherical (poly styrene latex) and non spherical (talc) were presented using sphericity index as a measure has been proposed and used by [Sachweh, Dick and McMurry,2007]. Their studies were performed in a spherical flow through chamber instrumented with detectors on azimuthal and polar angles. In this study we found that polarization of incident light was altered by both water droplets and fly ash. However at certain polarization angles (ϕp) no scattered light from fly-ash was observed at the detector, while being present for water droplets.
Experiments were performed using fly-ash, mean particle diameter (dp) = 24 µm, collected from biomass combustion exhaust. Fly-ash aerosols, generated using a turntable dust generator, was seeded into a vertical tunnel, where a mean velocity of 8 m/s was maintained. Water droplets with mean droplet size of 15 µm were generated from a pressure jet atomizer. A 532 nm light source was used to illuminate the flow with polarization applied at the source and detector side. Tests were conducted with fly-ash and water droplets alternatively.
Measurements performed at 10 degrees forward scattering angle revealed that the ratio of scattering signatures between ash and water droplets were 5 times lower with change in polarisation settings perpendicular to plane of scattering as compared to in-plane polarisation. Preliminary studies reveal statistically significant differences, enabling quantitative assessment of ratio of water to dust particles in a mixed flow system. Results are compared to standard gravimentric sampling.
Industrial emission stacks currently suffer from over reporting of particulate emission data due to errors from moisture. Liquid carry over can be as high as 6%, confounding traditional CEMS (continuous emission monitoring systems) involving triboelectric or light extintion based measurement systems. With this development, we could propose design of an instrument that could in-situ correct for errors from counting water droplet, thereby reducing false alarms.