The Top-Down methodology for determining the BACT is a process whereby all available control technologies are ranked in descending order of control effectiveness. The most stringent or "Top" control technology is established as BACT unless the applicant can demonstrate to the permitting authority that it is not feasible to iomplement it, in which case the next most stringent control technology is examined and so on. The five basic steps of the BACT analysis are:
Acid gas control is becoming an increasingly important issue for the power producing industry. The current principle concern is the control of sulfuric acid (and in some instances resultant acid plumes) generated by the combustion of medium to high sulfur coals and exacerbation of this problem by SO3 generated by SCR systems added for NOx control. A number of compounds added either to the fuel supply, in the furnace, or to the flue gas after it exits the boiler can be used to reduce sulfuric acid concentratinos to acceptable levels. However, some of the SO3 control systems have a negative effect on electrostatic precipitator (ESP) performance, and this undesirable side effect limits the usefulness of these systems.
CleanAir is working with The Electric Power Research Institute (EPRI) to investigate and quantify the impact of various alkaline sorbents on ESP performance through a multi-task effort involving: literature searches and industry surveys, data analysis and correlations, and field and laboratory testing. The findings of this program will be used to calibrate and validate EPRI's Electrostatic Precipitator Model (ESPM). With these changes, ESPM will become an important tool to help EPRI members deal with the consequences of SO3 mitigation strategies. EPRI's members represent over 90% of the electricity generated in the U.S.