An examination of pulverized coal combustion aerosols in air and in retrofit oxy-fired combustion environments

The purpose of this work was to examine how the amount of flue gas recycled and the composition of the recycled flue gas affects aerosol formation and chemistry. Three coals, low sulfur Utah bituminous, high sulfur Illinois basin bituminous, and low sulfur Powder River Basin sub-bituminous coals were examined under air and oxy-fired conditions consistent with a retrofit application. This work focused on oxygen concentrations of 27% and 32% in the combustion environment. Oxy-fired conditions included once through CO2 conditions without recycle to simulate completely cleaned flue gas recycle with all contaminants removed. Flue gas recycle conditions were also examined with various contaminants allowed to be present in the flue gas as well. Aerosols were gathered and analyzed to determine the effect of combustion environment on loss on ignition, particle size distribution, black carbon emissions, and size segregated ash chemistry under a wide variety of oxy-fired combustion conditions at stoichiometry ranging from 0.9 to 1.17. Results were compared to air fired conditions at similar stoichiometric ratios with the primary purpose of understanding how aerosol formation and composition would change in an oxy-fired retrofit application. Results indicated that similar behavior in ignition loss, particle size distribution, and size segregated ash chemistry could be expected across a wide range of coals and oxy-fired combustion conditions. Results also indicated that soot emissions could be significantly reduced under an oxy-fired retrofit combustion condition. No significant aerosol effects that would cause significant harm to a retrofitted pulverized coal boiler were discovered.