EPA proposes new NOX limits for coal-fired Coronado power plant

The U.S. Environmental Protection Agency is proposing to revise part of the Arizona Regional Haze (RH) Federal Implementation Plan (FIP) applicable to the coal-fired Coronado Generating Station.

In response to a petition for reconsideration from the Salt River Project Agricultural Improvement and Power District (SRP), the owner/operator of Coronado, EPA is proposing to replace a plant-wide compliance method with a unit-specific compliance method for determining compliance with the best available retrofit technology (BART) emission limits for NOX from Units 1 and 2 at Coronado. While the plant-wide limit for the NOX emissions from Units 1 and 2 were established as 0.065 lb/MMBtu, EPA said in a notice to be published in the March 31 Federal Register that it is proposing a unit-specific limit of 0.065 lb/MMBtu for Unit 1 and 0.080 lb/MMBtu for Unit 2.

In addition, EPA is proposing to revise the work practice standard in the FIP for Coronado. Finally, it is also proposing to remove the affirmative defense for malfunctions from the Arizona RH FIP, which applies to both Coronado and the coal-fired Cholla Power Plant.

The Arizona Department of Environmental Quality (ADEQ) submitted a RH SIP to EPA Region 9 in 2011. The Arizona RH SIP included BART determinations for NOX, particulate matter (PM), and SO2 for Units 1 and 2 at Coronado. EPA in 2012 proposed to approve ADEQ’s BART determinations for PM and SO2, but to disapprove its determination for NOX at Coronado. EPA proposed a FIP that included a NOX BART emission limit of 0.050 lb/MMbtu for Unit 1 and 0.080 lb/MMbtu for Unit 2 based on a 30-boiler-operating-day (BOD) rolling average. These limits correspond to the use of Selective Catalytic Reduction (SCR) technology to reduce NOX emissions. EPA noted that a consent decree between SRP and EPA required the installation of SCR and compliance with a NOX emission limit of 0.080 lb/MMBtu (30-BOD rolling average) at Coronado Unit 2 by June 1, 2014.

In its comments on that EPA proposal, SRP asserted that a NOX emission rate of 0.050 lb/MMBtu was not achievable at either of the Coronado units, due to their startup/shutdown operating profile. In support of this assertion, SRP submitted reports by two consultants, Sargent and Lundy (S&L) and RMB Consulting and Research (RMB), which indicated that the Coronado units could achieve a rolling 30-day emission rate in the range of 0.053 to 0.072 lb/MMBtu. Specifically, the S&L report examined the effect of multiple startup/shutdown events on emission rates over a 30-day period for Unit 2. The S&L report also examined potential measures to improve the performance of the current SCR design for Unit 2, including installation of a “low load temperature control system.”

EPA received a petition from SRP in February 2013 requesting partial reconsideration and administrative stay of the final rule. EPA Region 9 sent a letter in April 2013 to representatives of SRP informing the company that the agency was granting partial reconsideration of the final rule for the Arizona RH FIP. In particular, EPA stated that it was granting reconsideration of the compliance methodology for NOX emissions from Units 1 and 2 at Coronado and that it would issue a notice of proposed rulemaking seeking comment on an alternative compliance methodology. It also noted that, because EPA initially proposed different NOX emission limits for the two units, it would seek comment on the appropriate emission limit for each of the units. This March 31 Federal Register notice of proposed rulemaking includes each of these elements, and constitutes EPA’s proposed action for the reconsideration.

EPA is proposing a unit-specific compliance method and separate emission limits for NOX on Units 1 and 2 at Coronado. It is also proposing to revise the work practice requirement that applies to Coronado and to remove the affirmative defense for malfunctions that is currently included in the FIP for Coronado and Cholla.

By Coronado unit, EPA found:

  • In evaluating an appropriate limit for Coronado Unit 1, EPA relied primarily upon the information provided in the S&L analysis. This analysis found that an emission rate of 0.065 lb/MMBtu would be appropriate for a scenario consisting of low-load cycling operations (with steam reheat) and three cold startups within a 30-day period. EPA considers this to be a reasonable estimate of SCR performance for Coronado Unit 1. It is therefore proposing a limit of 0.065 lb/MMBtu on a rolling 30-BOD basis.
  • The information provided by SRP supports the assertion that the emission limit in the Consent Decree of 0.080 lb/MMBtu represents BART for Unit 2. In particular, the fact that SRP has already installed a low-load temperature-control system at this unit in order to meet the 0.080 lb/MMBtu limit suggests that a lower limit would not be achievable on a 30-BOD basis. As a result, EPA proposes to set a unit-specific NOX limit for Unit 2 of 0.080 lb/MMBtu, based on a rolling 30-BOD basis.

Coronado is a two-unit, 773-MW plant located near St. Johns in eastern Arizona.

About Barry Cassell 20414 Articles
Barry Cassell is Chief Analyst for GenerationHub covering coal and emission controls issues, projects and policy. He has covered the coal and power generation industry for more than 24 years, beginning in November 2011 at GenerationHub and prior to that as editor of SNL Energy’s Coal Report. He was formerly with Coal Outlook for 15 years as the publication’s editor and contributing writer, and prior to that he was editor of Coal & Synfuels Technology and associate editor of The Energy Report. He has a bachelor’s degree from Central Michigan University.