The U.S. Environmental Protection Agency is proposing to approve a revision to the Indiana State Implementation Plan (SIP) that authorizes temporary alternate opacity limits (TAOLs) at American Electric Power‘s (NYSE: AEP) coal-fired, 2,600-MW Rockport plant during periods of unit startup and shutdown.
This action, said EPA in a notice to be published in the Dec 28 Federal Register, is consistent with the Clean Air Act (CAA) and EPA policy regarding emissions during periods of startup and shutdown. Indiana has provided an air quality analysis demonstrating that this revision will continue to protect the applicable National Ambient Air Quality Standards (NAAQS) for fine particulate matter (PM2.5) in Spencer County, Ind.
Comments on the proposed approval must be received within 30 days after publication in the Federal Register.
In 2002, EPA approved a revision to Indiana’s SIP to include a mechanism to establish TAOLs. Indiana initially submitted TAOLs for 22 power plants with coal-fired boilers that use electrostatic precipitators (ESPs).
On Jan. 13, 2015, Indiana requested a SIP revision to provide a mechanism to establish site-specific TAOLs. This provision was used to establish for Rockport Units 1 and 2 a TAOL during unit startup and shutdown. These two coal-fired boilers are each controlled by an ESP.
The TAOL for unit startup is only allowed until the exhaust temperature reaches 250°F at the ESP inlet, up to a maximum of two hours (20 six-minute averaging periods). The TAOL for unit shutdown is only allowed when the exhaust temperature declines below 250°F at the ESP inlet, up to a maximum of one and one-half (1.5) hours (15 six-minute averaging periods).
To support the SIP revision request, Indiana evaluated COMs data for Units 1 and 2, and air dispersion modeling. Air dispersion modeling was conducted using the AERMOD regulatory dispersion model with five years of meteorological data. The analysis included conservative suppositions for stack temperature and flow rate. Indiana used worst-case emission rates to predict the highest hourly emissions during a cold startup. The modeling results yielded an eighth high 24-hour PM2.5 value of 22.2 micrograms per cubic meter (µg/m3), well below the 24-hour PM2.5 standard of 35 µg/m3. The air quality in the area will remain protected when Units 1 and 2 are operating with TOALs at AEP Rockport.
“EPA has reviewed the COMs data provided in Indiana’s submission on AEP Rockport’s startups and shutdowns from 2001 until the first quarter of 2004,” the agency said. “The AEP Rockport TAOLs appear to be set at appropriate levels, minimizing the TAOL duration.”