NETL- Mercury Emissions Control
Emissions Characterization
In anticipation of the 1990 CAAAs, specifically the draft Title III regarding the characterization of potential HAPs from electric steam generating units, DOE initiated a new Air Toxics Program in 1989. The DOE Mercury Measurement and Control Program evolved as a result of the findings from the comprehensive assessment of hazardous air pollutants studies conducted by DOE from 1990 through 1997. DOE, in collaboration with EPRI, performed stack tests at a number of coal-fired power plants (identified on map below) to accurately determine the emission rates of a series of potentially toxic chemicals. These tests had not been conducted previously because of their cost, about $1 million per test, so conventional wisdom on emissions was based on emission factors derived from analyses of coal. In general, actual emissions were found to be about one-tenth previous estimates, due to a high fraction of the pollutants being captured by existing particulate control systems. These data resulted in a decision by EPA that most of these pollutants were not a threat to the environment, and needed no further regulation at power plants. This shielded the coal-fired power industry from major (tens of millions) costs that would have resulted from further controlling these emissions. However, another finding of these studies was that mercury was not effectively controlled in coal-fired utility boiler systems. Moreover, EPA concluded that a plausible link exists between these emissions and adverse health effects. Ineffective control of mercury by existing control technologies resulted from a number of factors, including variation in coal composition and variability in the form of the mercury in flue gases. The volatility of mercury was the main contributor for less removal, as compared to the less volatile trace elements/metals which were being removed at efficiencies over 99% with the fly ash. In addition, it was determined that there was no reliable mercury speciation method to accurately distinguish between the elemental and oxidized forms of mercury in the flue gas. These two forms of mercury respond differently to removal techniques in existing air pollution control devices utilized by the coal-fired utility industry.
