EPA makes revisions to Arizona haze plan for Coronado, Cholla plants

The U.S. Environmental Protection Agency will publish in the April 13 Federal Register a final rule revising portions of the Arizona Regional Haze Federal Implementation Plan (FIP) applicable to the Coronado Generating Station and the Cholla Power Plant, both of which fire coal.

In response to a petition for reconsideration from the Salt River Project Agricultural Improvement and Power District (SRP), the owner and operator of Coronado, EPA is replacing 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 NOX emissions from Units 1 and 2 was established as 0.065 lb/MMBtu, EPA is now setting a unit-specific limit of 0.065 lb/MMBtu for Unit 1 and 0.080 lb/MMBtu for Unit 2.

In addition, EPA os revising the work practice standard in the FIP for Coronado. Finally, the agency is removing the affirmative defense for malfunctions, which applied to both Coronado and Cholla.

This final rule will be effective 30 days after publication in the Federal Register.

Latest action grew out of a 2011 haze plan from Arizona

The Arizona Department of Environmental Quality (ADEQ) submitted a Regional Haze State Implementation Plan (SIP) to EPA Region 9 on February 28, 2011. The Arizona Regional Haze SIP included BART determinations for NOX, particulate matter (PM), and SO2 for Units 1 and 2 at Coronado. EPA proposed in July 2012 to approve ADEQ’s BART determinations for PM and SO2, but to disapprove its determination for NOX at Coronado.

In the same notice, EPA also 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) and low-NOX burners (LNB) with over fire air (OFA) to reduce NOX emissions. EPA noted that a consent decree between SRP and the 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 the 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, SRP submitted reports by two consultants, Sargent & Lundy (S&L) and RMB Consulting and Research (RMB), which indicated that the Coronado units could achieve a 30-BOD rolling average emission rate in the range of 0.053 to 0.072 lb/MMBtu per unit.

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,” (i.e., steam reheat) which would allow the SCR system to operate during periods of low load.

In the final Arizona Regional Haze FIP, EPA set a plant-wide NOX emission limit for Coronado of 0.065 lb/MMBtu on a 30-BOD rolling average, which SRP could meet by installing a low-load temperature control system on Unit 2 and an SCR system including a low-load temperature control system on Unit 1.EPA structured the compliance determination method for this limit such that, when one of the two units was not operating, its emissions from the preceding 30 boiler operating days would continue to be included in the two-unit average.

In addition, EPA included in the FIP two additional requirements that apply to all affected sources, including Coronado.

  • First, it promulgated a work practice standard that requires that pollution control equipment be designed and capable of operating properly to minimize emissions during all expected operating conditions.
  • Second, it incorporated by reference into the FIP certain provisions of the Arizona Administrative Code (AAC) that establish an affirmative defense for excess emissions due to malfunctions.

SRP asked for changes in final rule

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 EPA was granting partial reconsideration of the final rule for the Arizona Regional Haze FIP. In particular, EPA stated that it was granting reconsideration of the compliance method 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 the agency initially proposed different NOX emission limits for the two units, it would seek comment on the appropriate emission limit for each of the units.

In March 2015, the EPA proposed action on reconsideration of the compliance method and NOX emissions limits for Coronado in the Arizona Regional Haze FIP. In particular, it proposed a unit-specific compliance method and separate numerical emission limits for NOX at Coronado Units 1 and 2. It also proposed 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. Finally, it proposed to determine that these revisions to the FIP would comply with Clean Air Act section 110(l).

EPA proposed to set a separate rolling 30-BOD lb/MMBtu limit for each of the two Coronado units.

In its evaluation of the 2013 S&L report, EPA found that the scenarios examined by S&L were realistic depictions of load profile scenarios historically experienced by the Coronado units. In particular, it found that S&L’s scenario 5c, which consists of low-load cycling operations (with SCR and steam reheat assumed) and three cold startups within a 30-day period was a reasonable and conservative representation of expected future operations at Coronado Unit 1, in light of the number of startup events that have historically occurred and SRP’s expectation that the Coronado units will experience greater periods of operation in load-following service or nonoperation in the future. Accordingly, EPA proposed to find that an emission rate of 0.065 lb/MMBtu, which corresponds to S&L’s scenario 5c, was a reasonable estimate of average SCR performance for Unit 1.

In proposing an emission limit for Coronado Unit 2, EPA considered information provided by SRP concerning Unit 2’s design parameters and the installation of a low-load temperature control system for Unit 2. It found that this information supported SRP’s assertion that the emission limit in the consent decree of 0.080 lb/MMBtu represents BART for Unit 2.

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.