EVALUATION OF MERCURY EMISSIONS FROM COAL-FIRED FACILITIES WITH SCR AND FGD SYSTEMS
CONSOL Energy Inc., Research & Development (CONSOL), with support from the U.S. Department of Energy, National Energy Technology Laboratory (DOE) and the Electric Power Research Institute (EPRI), evaluated the effects of selective catalytic reduction (SCR) on mercury (Hg) capture in coal-fired plants equipped with an electrostatic precipitator (ESP)-wet flue gas desulfurization (FGD) combination or a spray dyer absorber-fabric filter (SDA-FF) combination. In this program CONSOL determined mercury speciation and removal at 10 bituminous coal-fired facilities; at four of these facilities, additional tests were performed on units without SCR, or with the existing SCR bypassed. This project final report summarizes the results and discusses the findings of the body of work as a whole. Eleven Topical Reports were issued (prior to this report) that describe in great detail the sampling results at each of the ten power plants individually. The results showed that the SCR-FGD combination removed a substantial fraction of mercury from flue gas. The coal-to-stack mercury removals ranged from 65% to 97% for the units with SCR and from 53% to 87% for the units without SCR. There was no indication that any type of FGD system was more effective at mercury removal than others. The coal-to-stack mercury removal and the removal in the wet scrubber were both negatively correlated with the elemental mercury content of the flue gas and positively correlated with the scrubber liquid chloride concentration. The coal chlorine content was not a statistically significant factor in either case. Mercury removal in the ESP was positively correlated with the fly ash carbon content and negatively correlated with the flue gas temperature. At most of the units, a substantial fraction (>35%) of the flue gas mercury was in the elemental form at the boiler economizer outlet. After passing through the SCR-air heater combination very little of the total mercury (<10%) remained in the elemental form in the flue gas; this was true for all SCR catalyst types and sources. Although chlorine has been suggested as a factor affecting the mercury speciation in flue gas, coal chlorine was not a statistically significant factor affecting mercury speciation at the economizer exit or at the air heater exit. The only statistically significant factors were the coal ash CaO content and the fly ash carbon content; the fraction of mercury in the elemental form at the economizer exit was positively correlated with both factors. In a direct comparison at four SCR-equipped units vs. similar units at the same sites without SCR (or with the SCR bypassed), the elemental mercury fractions (measured at the ESP outlet) were lower, and the coal-to-stack mercury removals were higher, when the SCR was present and operating. The average coal-to-stack mercury removal at the four units without an operating SCR was 72%, whereas the average removal at the same sites with operating SCRs was 88%. The unit mercury mass balance (a gauge of the overall quality of the tests) at all of the units ranged from 81% to 113%, which were within our QA/QC criterion of 80-120%.
- Research Organization:
- Consol Energy Inc
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC26-02NT41589
- OSTI ID:
- 893601
- Country of Publication:
- United States
- Language:
- English
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EVALUATION OF MERCURY EMISSIONS FROM COAL-FIRED FACILITIES WITH SCR AND FGD SYSTEMS
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