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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.

A laboratory scale fluidized bed reactor and a bench scale 0.1 MW th fluidized bed combustor were used to study the effect of operating conditions on the formation of Polycyclic Aromatic Hydrocarbons (PAHs) in fly ash from fluidized bed combustion systems. A high volatile bituminous coal was chosen to investigate PAH emissions during the entire pyrolysis to oxygen-rich combustion process. During the experiments, the fluidized bed reactor was operated at temperatures between 700 °C and 900 °C, while the excess air ratio was varied from 0 to 1.3. An extraction and GC/MS analysis of PAHs was used in this study. Approximately 40 different PAHs were identified during the tests, of which only a few are specified by the U.S. EPA. The experimental results indicate the majority of the PAHs in the solid phase (bed and fly ash) are derived from the breakdown reactions during the processes of combustion and/or pyrolysis in a Fluidized Bed Combustion (FBC) system, although FBC systems have an efficient solidgas mixing process and relatively long residence time. The total amount of PAHs in the fly ash was much higher than that in the raw coal and in the gas phase. Threeand four-ring aromatic compounds were the major PAHs from pyrolysis conditions, while naphthalene (two-rings) is the dominant compound in bed ash collected from oxygenrich combustion conditions. Only naphthalene was detected in the bed ash in the FBC system. High-speed secondary air (air staging) injected into the freeboard of the FBC system is an effective method for minimizing PAH emissions, along with the other benefits including minimizing NO x and SO x emissions.

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