Effects of Dilution Sampling on Fine Particle Emissions from Pulverized Coal Combustion

摘要

A dilution sampler was used to examine the effects of dilution ratio and residence time on fine-particle emissions from a pilot-scale pulverized coal combustor.Measurements include the particle size distribution from 0.003 to 2.5 mum,PM_(2,5)mass,and PM_(2,5)composition(OC/EC,major ions,and elemental).Heated filter samples were also collected simultaneously at stack temperatures in order to compare the dilution sampler measurements with standard stack sampling methodologies.Measurements were made both before and after the bag house,the particle control device used on the coal combustor,and while firing three different coal types and one coal-biomass blend.The PM_(2,5)mass emission rates measured using the dilution sampler agreed to within experimental uncertainty with those measured with the hot-filter sampler.Relative to the heated filter sample,dilution did increase the PM_(2,5)mass fraction of selenium for all fuels tested,as well as ammonium and sulfate for selected fuels.However,the additional particulate mass created by gas-to-particle conversion of these species is within the uncertainty of the gravimetric analysis used to determine the overall mass emission rate.The enrichment of PM_(2,5)selenium caused by dilution did not vary with dilution ratio and residence time.The enrichment of PM_(2,5)sulfate and ammonium varied with fuel composition and dilution ratio but not residence time.For example,ammonium was only enriched in diluted acidic aerosol samples.A comparison of the PM_(2,5)emission profiles for each of the fuels tested underscores how differences in PM_(2,5)composition are related to the fuel ash composition.When sampling after the bag house,the particle size distribution and total particle number emission rate did not depend on residence time and dilution ratio because of the much lower particle number concentrations in diluted sample and the absence of nucleation.These results provide new insight into the effects of dilution sampling on measurements of fine particle emissions,providing important data for the ongoing effort of the EPA and ASTM to define a standardized dilution sampling methodology for characterizing emissions from stationary combustion sources.