Distribution of Organic Compounds in Coal-Fired Power Plant Emissions

The distributions of organic compounds such as methane, non-methane hydrocarbons (NMHCs), and polyaromatic hydrocarbons (PAHs) in the effluent from an ultralow-emission power plant were investigated. The methane and NMHCs in the flue gas were analyzed using a modified portable volatile organic hydrocarbon analyzer according to U.S. EPA method 25A, and a lower boiler load was found to increase the NMHC concentration. The levels of methane and NMHCs in gases evolved from the pyrolysis of solid samples were assessed, and greater amounts of both organic compounds were obtained from bituminous coal. The empirical parameter E was used to represent the amount of organic compounds in the flue gas during combustion as a percentage of the organics obtained from coal pyrolysis. The E values based on methane and NMHCs in the gas phase were below 0.2% at the boiler outlet and less than 0.1% at the stack inlet. The PAHs in solid samples were also analyzed by solvent extraction. The distributions of PAHs in solid samples for slag, selective catalytic reduction (SCR), and electrostatic precipitation were 3, 76, and 21%, respectively. In the slag location, the percentages of five- and six-ring PAHs were higher than those of PAHs with smaller rings. The percentage of three-ring PAHs was the highest in the SCR inlet fly ash in both cases. Mass balance including gas and solid sample calculations indicated that the methane and NMHC levels in the flue gas were less than 0.01 and 0.07% of the amounts obtained from coal pyrolysis, respectively. Results indicated that approximately 99.99% of the methane, 99.77% of the NMHCs, and 99.78% of the PAHs were oxidized during coal combustion in the boiler. The methane, NMHC, and PAH concentrations in fly ash were 0.01, 0.02, and 0.06%, respectively, whereas the slag contained less than 0.01% of each. Overall, less than 0.01% of the methane and 0.07% of the NMHCs were released in the stack. These results confirm the high combustion efficiency obtained from ultra-supercritical pulverized coal-fired boilers incorporating ultralow-emission air pollutant control devices that eliminate organic compounds through oxidation, condensation, and water absorption.