The West Virginia Department of Environmental Protection is taking comment until Sept. 6 on an air permit change allowing Allegheny Energy Supply Co. LLC to operate a sorbent injection system for SO3 emissions control at the coal-fired Pleasants plant.
This system would control SO3 formation from Units 1 and 2. In August 2012, Allegheny Energy Supply, a unit of FirstEnergy (NYSE: FE), entered into a consent order to install an SO3 control system to minimize the potential for opacity problems at Pleasants.
Pleasants is a large steam-electric generating station located in Willow Island, W. Va. The facility consists of two coal-fired boilers with a generating capacity of 657 MWe each. These boilers exhaust combustion gases to the atmosphere via separate liners of a common flue stack, following separate trains of air pollution controls including selective catalytic reduction units (SCR), electrostatic precipitators (ESP), and flue gas desulfurization units (FGD).
A side-effect of the use of SCR is enhanced creation of SO3 across the catalyst bed. As the SO3 passes the SCR and cools, it can combine with moisture generated in the scrubbing process to form sulfuric acid aerosols. These aerosols can produce long-lasting visible emissions from the stack.
The sorbent injection system works by injection of a soda ash solution (a base) directly into the flue gas to neutralize acid formation. The solution flash-evaporates and the resulting solids efficiently react with SO3 (and/or SO2) to produce a benign particulate (sodium sulfate) that is removed with the fly ash in the ESP, the agency said.