The injection of large quantities of pulverized activated carbon is one method used to remove elemental mercury (Hg 0 ) from flue gas streams. The purpose of this project was to determine whether the unburned carbon that remains in coal fly ash could be used as an inexpensive and effective replacement for activated carbon. Bench-scale tests were conducted at conditions representative of those found in the flue gas trains of coal-fired power plants and municipal waste incinerators. The temperatures and concentrations ranged from 121 to 177 °C and from 0.019 to 11.7 mg of Hg/m 3 . Two types of data were obtained: equilibrium data suitable for obtaining adsorption isotherms and breakthrough data suitable for obtaining adsorption kinetics. Adsorbed-phase concentrations were as high as 600 ppm. Forward adsorption rate constants were ≈0.06-2.3 m 3 /g/s for particle sizes and carbon contents ranging from 59 to 206 µm and from 2% to 36%. Mathematical models were developed to simulate the capture of Hg 0 in flue gas ducts and in baghouses. The results of the simulations indicate that a negligible amount of Hg 0 can be adsorbed by a dilute suspension of fly ash. The best option for controlling Hg 0 emissions using fly ash appears to be injection in pulses prior to a baghouse.

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A mathematical model for the flash calcination of Ca(OH)2 and CaC03 is presented. The model describes the decomposition of the parent material at the reactant-product interface, the diffusion of C02 or H20 through the growing CaO layer, and the sintering of the CaO layer. The model is qualitative, but it provides useful estimates of peak C02 pressures in the CaO layer, relative rates of surface area development and loss for Ca(OH)2 and CaC03, the effect of particle size, and the effects of time and temperature.

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