Citing new technical information gleaned from a more modern modeling analysis, the Environmental Protection Agency (EPA) has proposed to withdraw a federal implementation plan (FIP) to control regional haze from four PacifiCorp coal-fired units in Utah and allow the state to revert to conditions set out in a 2015-submitted state implementation plan (SIP).
The agency’s proposed rule issued on Jan. 22 will allow PacifiCorp’s Hunter Units 1 and 2, and Huntington Units 1 and 2, in Emery County, each 430 MW, to use alternatives to selective-catalytic reduction (SCR) technology, which the 2016-issued FIP deems the best available retrofit technology (BART) to control nitrogen oxide (NOx) emissions.
Utah’s SIP revisions submitted in July 2019 contain nearly the same NOx BART Alternative as they did in a partially disapproved SIP the state submitted in June 2015. If finalized, the revised SIP will replace the EPA’s July 2016–issued FIP, which the agency issued because it determined the state’s SIP did not satisfy regional haze program requirements. But the state’s amended SIP now satisfies certain regional haze requirements for the federal program’s first implementation period, the EPA said. The amended SIP will “achieve greater visibility benefits” in Arches, Canyonlands, and seven other National Parks and Wilderness Areas protected as “Class I” areas under the Clean Air Act. “Utah’s plan will reduce overall air emissions by an estimated 1,879 tons per year relative to EPA’s 2016 plan,” the agency added on Wednesday.
A Fresh Look at BART
The EPA’s FIP currently imposes a NOx BART emission limit of 0.07 lb/MMBtu (for a 30-day rolling average) on four BART units, emission reductions that would have required installation and operation of costly SCR technology plus upgraded combustion controls. Comparatively, Utah’s 2015-submitted SIP required that the four units, which are fired with bituminous coal, install a number of combustion control upgrades to reduce sulfur dioxide, NOx, and particulate matter emissions. These include an Alstom TSF 2000 low-NOx firing system and two elevations of separated overfire air (SOFA). At Hunter 3, which the EPA does not consider a BART unit, combustion improvements included upgraded low-NOx burners and overfire air. It also required closure of PacifiCorp’s 172-MW Carbon power plant, which happened as planned in August 2015.
But as the EPA noted on Wednesday, based on “new technical information and a different regulatory test,” the state’s previously submitted NOx BART Alternative—which included the emissions control technologies installed at the four units—actually achieves “greater reasonable progress” than BART. The 2019 SIP revision proposes to incorporate a NOx emission limit of 0.26 lb/MMBtu (30-day rolling average) each for Hunter Units 1 and 2, and Huntington 1 and 2, it said.
In its 2015 SIP, Utah had relied on a “clear-weight-of-evidence test” to demonstrate that the alternative achieves greater reasonable progress than BART, the EPA explained. In the July 2019 submission, the state relies “solely on the application of the two-prong test under 51.308(e)(3) using photochemical grid modeling.”
Photochemical air quality models are gaining traction as tools that are being used more routinely for regulatory analysis and attainment demonstrations by assessing the effectiveness of control strategies. They are essentially large-scale air quality models that simulate the changes of pollutant concentrations in the atmosphere using a set of mathematical equations characterizing the chemical and physical processes in the atmosphere. These models are applied at multiple spatial scales, including local, regional, national, and global.
The air quality modeling at the PacifiCorp units was performed by a contractor using the Comprehensive Air Quality Model with Extensions (CAMx). That photochemical grid model “uses and produces complex scientific data, including emissions from all sources, with a realistic representation of formation, transport, and processes that cause visibility degradation, estimating downwind concentrations paired in space and time,” the agency said. “The EPA’s guidance supports use of this particular model for evaluation of visibility impacts from sources or source categories, such as application of the two-prong test under 40 CFR 51.308(e)(3).” The EPA noted that the CAMx model also simulates air quality “over many geographic scales and treats a wide variety of inert and chemically active pollutants, including ozone, PM [particulate matter], inorganic and organic PM2.5/PM10, and mercury and other toxics,” and the the model has “plume-in-grid and source apportionment capabilities.”
In 2016, the EPA also disapproved particulate matter BART as applied to the emission limitations and control measures associated with the NOx BART Alternative. In December 2019, Utah submitted a supplement to the July 2019 SIP submission that includes an amendment to the monitoring, recordkeeping, and reporting requirements. “Specifically, the amendments require each source to submit a report of any deviation from applicable emission limits and operating practices, including deviations attributable to upset conditions, the probable cause of such deviations, and any corrective actions or preventive measures taken,” the EPA said.
PacifiCorp Mulling Energy Transformation
The news is a victory for PacifiCorp, which currently operates 24 coal units. Under a draft long-term energy plan PacifiCorp announced in September, however, the company intends to retire more than half its fleet by 2030—and up to 20 units by the end of the planning period in 2038. The unit retirements will reduce the company’s coal-fired generation capacity by nearly 2,800 MW by 2030 and by nearly 4,500 MW by 2038.
As Rick Link, PacifiCorp’s vice president of resource planning and acquisitions, noted in a press release in September, the company plans to replace the capacity with new wind, solar, and storage capacity, as well as investments in new transmission. “Coal generation has been an important resource in our portfolio, allowing us to deliver reliable energy to our customers, and will continue to play an important role as units approach retirement dates,” he said. “At the same time, this plan reflects the ongoing cost pressure on coal as wind generation, solar generation and storage have emerged as low-cost resource options for our customers.”
—Sonal Patel is a POWER senior associate editor (@sonalcpatel, @POWERmagazine)