Emissions, Monitoring and Control of Mercury from Subbituminous Coal-Fired Power Plants PDF Download

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Book Description
The Subbituminous Energy Coalition (SEC) identified a need to re-test stack gas emissions from power plants that burn subbituminous coal relative to compliance with the EPA mercury control regulations for coal-fired plants. In addition, the SEC has also identified the specialized monitoring needs associated with mercury continuous emissions monitors (CEM). The overall objectives of the program were to develop and demonstrate solutions for the unique emission characteristics found when burning subbituminous coals. The program was executed in two phases; Phase I of the project covered mercury emission testing programs at ten subbituminous coal-fired plants. Phase II compared the performance of continuous emission monitors for mercury at subbituminous coal-fired power plants and is reported separately. Western Research Institute and a number of SEC members have partnered with Eta Energy and Air Pollution Testing to assess the Phase I objective. Results of the mercury (Hg) source sampling at ten power plants burning subbituminous coal concluded Hg emissions measurements from Powder River Basin (PBR) coal-fired units showed large variations during both ICR and SEC testing. Mercury captures across the Air Pollution Control Devices (APCDs) present much more reliable numbers (i.e., the mercury captures across the APCDs are positive numbers as one would expect compared to negative removal across the APCDs for the ICR data). Three of the seven units tested in the SEC study had previously shown negative removals in the ICR testing. The average emission rate is 6.08 lb/TBtu for seven ICR units compared to 5.18 lb/TBtu for ten units in the SEC testing. Out of the ten (10) SEC units, Nelson Dewey Unit 1, burned a subbituminous coal and petcoke blend thus lowering the total emission rate by generating less elemental mercury. The major difference between the ICR and SEC data is in the APCD performance and the mercury closure around the APCD. The average mercury removal values across the APCDs are 2.1% and 39.4% with standard deviations (STDs) of 1990 and 75%, respectively for the ICR and SEC tests. This clearly demonstrates that variability is an issue irrespective of using 'similar' fuels at the plants and the same source sampling team measuring the species. The study also concluded that elemental mercury is the main Hg specie that needs to be controlled. 2004 technologies such as activated carbon injection (ACI) may capture up to 60% with double digit lb/MMacf addition of sorbent. PRB coal-fired units have an Hg input of 7-15 lb/TBtu; hence, these units must operate at over 60% mercury efficiency in order to bring the emission level below 5.8 lb/TBtu. This was non-achievable with the best technology available as of 2004. Other key findings include: (1) Conventional particulate collectors, such as Cold-side Electro-Static Precipitators (CESPs), Hot-side Electro-Static Precipitator (HESP), and Fabric Filter (FF) remove nearly all of the particulate bound mercury; (2) CESPs perform better highlighting the flue gas temperature effect on the mercury removal. Impact of speciation with flue gas cooling is apparent; (3) SDA's do not help in enhancing adsorption of mercury vapor species; and (4) Due to consistently low chlorine values in fuels, it was not possible to analyze the impact of chlorine. In summary, it is difficult to predict the speciation at two plants that burn the same fuel. Non-fuel issues, such as flue gas cooling, impact the speciation and consequently mercury capture potential.