Impact of Coal Chlorine on Mercury Speciation and Emission from a 100-MW Utility Boiler with Cold-Side Electrostatic Precipitators and Low-NO_x Burners

Abstract

Field tests on mercury speciation and emission while burning Kentucky and Illinois coals with different chlorine contents were performed in a 100-MWe pulverized-coal boiler with low-NO x burners. Seven coals were used during the tests and were grouped into two sets for comparison, with the baseline coal being shared between the two sets. The first set of four coals was used to investigate the effect of chlorine in coal on mercury emission and its speciation by selecting coals with similar mercury contents and different chlorine contents. The four coals in the second set were selected to investigate the effect of mercury contents in coal on mercury emission and its speciation by choosing coals with similar chlorine contents and different mercury contents. The mercury concentration and speciation in the flue gas were determined using the American Society for Testing and Materials (ASTM) standard Ontario Hydro Method (OHM) and a PS Analytical Semi-continuous Emissions Monitoring (SCEM) system. Flue gas samplings were performed at two locations: upstream before the electrostatic precipitator (ESP) inlet and downstream after the ESP outlet. A thorough comparison between the two monitoring methods was made. A sampling bias was found in the OHM sampling performed at the ESP inlet, because of the accumulation of ash with a high carbon content on the OHM filter. An ash-free sampling probe should be used with the OHM impinger train for obtaining accurate mercury information whenever ash concentrations are high. Mercury emission and speciation for the seven test coals at the ESP outlet location are described and discussed. Results indicate that the coal chlorine content has an impact on the mercury oxidation processes, which are mitigated by high concentrations of SO2. It is speculated that SO2 limits Cl2 formation.

JV Task 124 - Understanding Multi-Interactions of SO3, Mercury, Selenium, and Arsenic in Illinois Coal Flue Gas

“…The results from pilot-scale testing with a representative Illinois Basin coal support the concept that SO 3 vapor is the predominant factor that impedes efficient mercury removal with activated carbon in an Illinois coal flue gas, while H 2 SO 4 aerosol has less impact on ACI performance. The poisonous effect of SO 3 on activated carbon appears to be from a direct competition between mercury and SO 3 for active sites on the carbon.…”

“…The poisonous effect of SO 3 on activated carbon appears to be from a direct competition between mercury and SO 3 for active sites on the carbon. The resulting effects on mercury capture with ACI can be explained by fundamental mass transfer effects.…”

“…The hypothesis proposed in this work is that the SO 3 vapor generated from combustion of high-sulfur coal reacts with the carbon and hinders its ability to remove mercury. A thorough investigation of the multi-interaction among mercury, SO 3 , and carbon under different flue gas conditions, i.e. temperature, moisture content, and particulate alkali content, was undertaken to explore the hypothesis.…”

“…One possible reason ascribed to this poor sorbent performance with the high-sulfur bituminous coal flue gas is the interaction with SO 2 , where speculated interactions between SO 2 and Cl 2 obstruct chlorine-promoted mercury oxidation and the gas-to-particle conversion of mercury (3). Moreover, SO 2 is capable of impeding mercury adsorption onto particulate matter including AC and other flue gas solids by competing for adsorption sites on the particulate matter (4).…”

“…To determine plant operating conditions that will facilitate mercury control, SO 3 partitioning between vapor and aerosol phases as well as its impact on mercury transformations needs to be understood as a function of flue gas temperature and moisture content. A comprehensive understanding regarding the interactions of SO 3 , mercury, and in-flight alkali and alkaline-earth based particles will facilitate the development of effective mercury control strategies for utility plants burning Illinois coal.…”