Study of Polyaromatic Hydrocarbons Emitted in the Fly Ash from Coal Combustion in a Fluidized Bed Combuster

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Heltsley, Rebecca
thesis / dissertation description
Exposure to Polyaromatic Hydrocarbons (PAHs) has long been identified as an environmental concern because of their carcinogenic and mutagenic effects. The Environmental Protection Agency (EPA) has developed a list of 16 PAHs that are found on the Priority Pollutant List due to the extensive amount of data suggesting the hazards of these compounds. These toxic compounds are often emitted into the atmosphere by anthropogenic sources, such as combustors. Therefore, analysis of these compounds must be conducted during coal combustion. Two 1000-hour coal combustion burns were performed using the 0.1 MWth bench-scale fluidized bed combustor (FBC), which is found in the Combustion Laboratory at Western Kentucky University. The data contained in this thesis were collected from burning coal 97025 and coal 99626 for 1000-hour experiments. The fly ash produced from the combustor was examined as the media for the PAHs. It was collected by an in-situ cyclone sampler that was attached to various ports along the combustor during specific conditions in the combustor. Once the fly ash was collected it was analyzed with two different extraction methods. Solvent extraction was the first method used in this study. Dichloromethane was the solvent used to extract the PAHs in the fly ash. Once the extraction was completed, GC/MS in the selective ion monitoring (SIM) mode was used to analyze the extract. The other method used to extract the PAHs from the fly ash was the thermal extraction method. This method allows direct analysis of the PAHs without any use of a solvent. The GC/TOFMS was used to analyze the samples that were extracted by the thermal extraction method. In this study, the effects of combustion temperature, combustion bed height, sampling height, excess air ratio, and fluidizing velocity were examined to determine how each of these parameters affected the release of PAHs in the fly ash. The results indicated that the parameters investigated have a major influence on the production of PAHs in the combustor. As combustion efficiency decreases, larger PAHs (four to five fused rings) are detected in the fly ash; whereas, during high efficiency combustion, smaller PAHs (two to three fused rings) are more likely to be detected.