REDUCTION OF INHERENT MERCURY EMISSIONS IN PC COMBUSTION

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{sup 2}, generally producing the more reactive HgCl{sub 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 of oxidation data as a function of temperature and HCl concentration. The temperature range was 800-1200 C. The results show a lower level of oxidation than indicated by the earlier data of Hall et al. (1991). One possible reason for this discrepancy was the preheating of the HCl stream in the Hall experiment, leading to the partial decomposition of the HCl into reactive species. In the present experiments, the HCl was injected as a cold stream. The measured oxidation at these conditions was substantially above that predicted by equilibrium, indicating the dominance of finite rate chemistry. This is to be explored in subsequent work