AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Optical and Physical Characterization of Coal Fly Ash and Powdered Activated Carbon Agglomerates
TIAN XIA, Herek Clack, University of Michigan
Abstract Number: 673 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract The most mature technology for controlling mercury emissions from coal combustion is the injection into the flue gas of powdered activated carbon (PAC) adsorbents having chemically treated surfaces designed to rapidly oxidize and adsorb mercury. However, carbonaceous particles are known to have low electrical resistivity, which contributes to their poor capture in electrostatic precipitators (ESPs), the most widely used method of particulate control for coal-fired power plants worldwide. Thus, the advent in the U.S. and other countries of mercury emissions standards for power plants has the potential for increased emissions of PAC.
Our previous analyses have provided estimates of PAC emission rates resulting from PAC injection in the U.S. and extrapolated these estimates globally to project their associated climate forcing effect. The present work continues the examination of the potential climate forcing effects of such mercury sorbents by conducting the first comparative measurements of optical scattering and absorption of aerosols comprised of varying mixtures of coal combustion fly ash and PAC. A partially fluidized bed (FB) containing fly ash-PAC admixtures with varying PAC concentrations elutriates aerosol agglomerates. A photo-acoustic extinctiometer (PAX) extractively samples from the FB flow, providing measurements of optical absorption and scattering coefficients of fly ash alone and fly ash-PAC admixtures. Extracted aerosol samples from the FB flow provide particulate loading measurements and SEM images of the collected aerosols provide qualitative insight into size distributions and agglomeration state, useful in determining optical absorption and scattering efficiency values. Soot from an oil lamp flame provides a comparative benchmark. The results indicate that the addition of 1% PAC to fly ash yields agglomerates having ~20 times greater absorption, ~1/5 of the value for soot. Results for optical scattering suggest no significant impact of PAC. These results can enhance optical property data and emissions inventories used in models of climate forcing by particulate carbon.