(552b) Role of Recycle on Emissions from Oxy-Coal Combustion

Oxy-coal combustion is being touted as a potential means for increasing concentration of carbon dioxide in exhaust gases to help in potential remediation and sequestration. The impact of this modality of combustion on other emissions such as fine particles, trace metals and mercury has been examined in both drop tube and self sustaining coal combustors (Suriyawong et al., 2006). Most of these studies have been conducted by combustion of the coal in a mixture of oxygen and carbon dioxide. However, in a full scale operating scenario, the flue gases will be recycled with only the necessary amount of oxygen added at the inlet with the coal.

In this paper, we will compare the effect of flue gas recycle on fine particle formation and other emissions, to that of the controlled studies performed earlier. Due to the difference in the temperature-time histories and the composition of the flue gases, there are expected to be differences in the combustion characteristics. First, the sub-oxide formation pathways are expected to result in different vaporization rates due to the different time-temperature relationships. It is expected that the more volatile elements such as mercury will not show any differences, however, the chemistry in the gas phase maybe different due to the potential for oxidation to increase. Clearly, the performance of added sorbents ? both micrometer and nanostructured, will be different ? and the results will be reported. Strategies for effective modalities for oxy-coal combustion to minimize emissions of fine particles and other toxic elements such as mercury will be proposed.

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Suriyawong, A., Gamble M., Lee M.H., Axelbaum R. and Biswas P., ?Submicrometer particle formation and mercury speciation under O2 - CO2 Coal Combustion?, Energy and Fuels, 20 (6), 2357-2363, 2006.