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NARSTO Workshop on Innovative Methods for Emission Inventory Development and Evaluation University of Texas, Austin October 14-17, 2003 |
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Design Of A Next Generation Dilution Sampling System To Quantify Fine Particulate Emissions From Combustion Systems
Allen L. Robinson, Emily Wietkamp, Eric Lipsky
Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA
Characterizing PM2.5 emissions from combustion systems is difficult because of the high temperatures and moisture content of exhaust gases. Upon exiting the stack the combustion products are rapidly cooled and diluted with ambient air, during which time processes such as coagulation, condensation, and nucleation change the size and composition of the PM emissions. Dilution sampling is a technique that has been developed to examine the influence of rapid cooling and dilution on PM emissions from combustion systems. A dilution sampler rapidly mixes hot exhaust gases with a specified amount of conditioned air and allows for processes such as nucleation, condensation, and coagulation to occur. Understanding the effects of sampling conditions is critical in order to interpret measurements made with a dilution sampler and to optimize sampler design. Although dilution sampling has been widely employed for characterizing emissions from engines, relatively little work has been done using other combustion systems such as power plants. Current samplers such as the Cal-Tech dilution sampler are large and challenging to operate which makes them difficult to deploy in the field.
Design of an improved dilution sampling system for source sampling requires a better understanding of the influence of parameters such as dilution ratio and residence time on the measured PM composition and size distribution. This talk examines the effects of these parameters using measurements made while sampling from a pilot-scale coal combustor, wood stove and diesel engine. Sampling was performed using two different dilution systems: a sampler similar in design to the Cal-Tech dilution sampler (Lipsky et al., 2002), and a much smaller sampler based on porous frit and an eductor pump. Both systems can be operated at dilution ratios between 10 and 100, and allow for aging times up to 1 minute. Measurements include PM2.5 composition (organic and elemental carbon, ions, and metals) and particle number distribution using a scanning mobility particle spectrometer (SMPS). The results indicate that particle number distribution is very sensitive to dilution parameters, especially in the nucleation mode. PM2.5 mass and composition are also sensitive to dilution conditions.
E. Lipsky, C. O. Stanier, S.N. Pandis, A.L. Robinson (2002) Energy and Fuels 16(2): 302-310.