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Mercury emission compliance is one of the major potential challenges raised by the 1990 Clean Air Act Amendments. Simple ways of controlling emissions have not been identified. The variability in the field data suggests that inherent mercury emissions may be reduced if the source of this inherent capture can be identified and controlled. The key mechanisms appear to involve the oxidation of the mercury to Hg ++ , generally producing the more reactive HgCl 2 , followed by its capture by certain components of the fly ash or char. This research focuses on identifying the rate-limiting steps associated with the oxidation step.Work in this reporting period focused on the development and application of a kinetics model to the oxidation data developed in the present program and literature data under MSW conditions. The results indicate that the pathway Hg+Cl=HgCl followed by HgCl+HCl=HgCl 2 +H predominates over Hg+Cl 2 under high-temperature conditions. This primarily occurs because Cl 2 concentrations are too low under the present conditions to contribute significantly.

The gasification of black liquor, followed by its use in gas turbine engines, is an emerging alternative to the direct firing of the liquor in Tomlinson recovery boilers. Many gasification systems, however, convert the fuel nitrogen present in the liquor into ammonia (NH3) in the fuel gas, which leads to unacceptable NOx emissions in gas turbine combustors. This work uses detailed chemical kinetic modeling to examine the influence of two combustor modifications for the control of NOx emissions from black liquor fuel gas combustion. Availability analysis is also used to evaluate the influence of these NOx control choices on the thermodynamic architecture of the overall system. A rich-quench-lean configuration makes use of air staging. An alternative is to use a hot, rich external precombustor to remove NH3 before the main combustor. Here, the external, rich stage operates at around 30% theoretical air. Adiabatic temperatures are too low to obtain good NH3 reduction, so recuperative heating is necessary.

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