The U.S. Environmental Protection Agency (EPA) will say in a notice in the Sept. 30 Federal Register that it is approving a revision to the Indiana State Implementation Plan (SIP), authorizing temporary alternate opacity limits (TAOLs) at American Electric Power’s (NYSE: AEP) coal-fired Rockport plant during periods of boiler startup and shutdown.
This action is consistent with the Clean Air Act (CAA), the Indiana SIP, 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, Indiana. This final rule is effective 30 days after publication in the Federal Register.
AEP operates in Indiana under its Indiana Michigan Power subsidiary.
EPA is approving into the Indiana SIP TAOLs for AEP Rockport Units 1 and Unit 2, which apply only during narrowly-drawn periods of boiler startup and shutdown. These two identical 1,300-MW coal-fired boilers are each equipped with an electrostatic precipitator (ESP) to control PM2.5 emissions, More specifically, Indiana code authorizes AEP Rockport to exceed the applicable SIP opacity limit only under the following circumstances: during startup, for a period not to exceed two hours (twenty six-minute averaging periods), or until the flue gas temperature reaches 250 degrees Fahrenheit at the ESP inlet, whichever occurs first; and during shutdown, once the flue gas temperatures has dropped below 250 degrees Fahrenheit at the ESP inlet, for a period not to exceed one and one-half hours (fifteen six-minute averaging periods).
EPA proposed to approve these alternate limits as revisions to Indiana SIP in December 2015.
EPA has previously approved TAOLs for 22 other Indiana power plants, all of which are controlled with ESPs. These TAOLs contained similar limits, and EPA’s basis for approval was analogous.
EPA has evaluated Continuous Opacity Monitoring System (COMS) data from the AEP Rockport facility and conducted air dispersion modeling in the surrounding area. The COMS data showed that, between 2009 and 2013, AEP’s emissions were in compliance with the SIP opacity rule 99.81% of the time. Conversely, AEP’s emissions exceeded the opacity standards just 0.19% of the time, which includes the startup and shutdown periods covered by the TAOL.
After EPA received public comments in response to the proposal, the Indiana Department of Environmental Management (IDEM) performed an additional air quality analysis in response to specific comments. AEP provided a revised emission profile for PM describing hourly emissions during a 24-hour period, including a startup event, in which the ESP would be entirely shut down during hours 9 and 10. IDEM made the conservative assumption that all of the boilers’ PM10 emissions were 100% PM2.5. The new analysis also considered two scenarios, in which one boiler is starting up while the other boiler is either not operating, or operating at its full, steady rate. Both boilers at Rockport exhaust through a common stack. The two scenarios represent the stack exhaust and dispersion rates for a boiler startup/shutdown event. IDEM modeled one scenario which assumed that the ESP is completely offline for the two hours of highest oil and coal combustion.
The modeling with the background results yielded a 24-hour PM2.5 value of 26.06 micrograms per cubic meter (µg/m3), which is well below the 2012 24-hour PM2.5 NAAQS of 35 µg/m3.
EPA received comment letters from AEP and the Sierra Club, both on Jan. 27, 2016. The AEP comment letter supports this approval into the Indiana SIP. The Sierra Club stated that the fact that AEP Rockport often does not meet applicable opacity limitations is not sufficient to demonstrate that it cannot meet these limits. It asserted that there are numerous options that might be effective in reducing emissions during startup and shutdown periods, including revamping plant maintenance practices, installing baghouses after the ESPs to collect uncontrolled PM, and using a startup fuel other than fuel oil.
EPA responded that the TAOLs at AEP Rockport are needed during startup and shutdown because of temperature limitations of the ESP, which has lowered efficiency at times when temperatures are below 250 degrees. In addition, AEP Rockport has provided data showing that during periods of low temperature when the control technology cannot efficiently control particulates, there may be violations of the SIP opacity limits. During normal operations, however, emission limits are met. The COMs data submitted by AEP Rockport demonstrate that it has operated in a manner consistent with good air pollution control and maintenance practices.
The club suggested that other control devices should be added to the facility, or that there should be a fuel switch. EPA disagreed for several reasons. It said that considering additional controls or changes in fuel is not a criterion in the Indiana SIP for evaluating the approvability of a TAOL. In addition, even if AEP Rockport were to add or modify its control such as by adding a fabric filter (baghouse), similar technical issues could also occur during the low-temperature, low-flow scenario of startups and shutdowns.