The Colorado Air Quality Control Commission on Dec. 15 approved a regional haze compliance proposal from Tri-State Generation and Transmission that calls for the retirement of early end of coal use at Craig Station Unit 1 and the retirement of the coal-fired, 100-MW Nucla plant.
After the U.S. Environmental Protection Agency approved Colorado’s Regional Haze State Implementation Plan (SIP), WildEarth Guardians and the National Parks Conservation Association (NPCA) challenged portions of the approval by filing suit in the U.S. Tenth Circuit Court of Appeals. As part of that lawsuit, the plaintiffs contested the NOx provisions for Craig Unit 1, which is owned, in part, and operated by Tri-State. In furtherance of settlement of that litigation, in 2014, the commission approved revisions to change the Craig Unit 1 NOx emission limit from 0.28 lb/MMBtu to 0.07 lb/MMBtu, and set the associated compliance deadline for Craig Station Unit 1 as Aug. 31, 2021.
Since the commission approved the 2014 revisions, an agreement was reached involving Craig Unit 1 and Nucla Station. The agreement includes the following commitments:
- Craig Unit 1 will either close by Dec. 31, 2025, or cease burning coal no later than Aug. 31, 2021, with the option to convert the unit to natural-gas firing by Aug. 31, 2023. In the case of a conversion to natural-gas firing, a 30-day rolling average NOx emission limit of 0.07 lb/MMBtu will be effective after Aug. 31, 2021. For both scenarios, Craig Unit 1 will be subject to a NOx emission limit of 0.28 lb/MMBtu, on a 30 day rolling average, effective Jan. 1, 2017 (first compliance date Jan. 31, 2017), until converting to natural gas or permanently shutting down. Craig Unit 1 will be subject to an annual NOx emission limit of 4,065 tons per year effective on Dec. 31, 2019, on a calendar year basis beginning in 2020;and
- Nucla will close on or before Dec. 31, 2022. Nucla will be subject to an annual NOx emission limit of 952 tons per year effective Jan. 1, 2020, on a calendar year basis beginning in 2020.
The agreement reflects a changing industry, economic, and regulatory landscape that does not necessarily favor the installation of costly post-combustion retrofit controls on aging coal-fired electric generating units. Said the commission in a Dec. 15 approval document: “The agreement and these revisions will also result in greater emissions reductions than would result from the previously approved SIP. The Commission’s adoption of these revisions will result in further reductions of visibility impairing pollutants, in addition to providing other environmental co-benefits.”
Tri-State had on Sept. 1 announced this agreement with the Colorado Department of Public Health and Environment, U.S. Environmental Protection Agency, WildEarth Guardians and the National Parks Conservation Association.
Tri-State said the nearby New Horizon Mine, which supplies coal to Nucla, will cease coal production with the retirement of the station. Reclamation efforts at the mine will continue for a time after that.
Additionally, an agreement by the owners of Craig Station Unit 1, regulators and the environmental groups covers the 427-MW Unit 1 at the three-unit, coal-fired Craig facility in Craig, Colorado. The agreement only affects Unit 1 at Craig Station. Craig Station Unit 2 and Unit 3 will continue to operate.
“Tri-State has worked tirelessly to preserve our ability to responsibly use coal to produce reliable and affordable power, which makes the decision to retire a coal-fired generating unit all the more difficult,” said Mike McInnes, CEO of Tri-State, in the Sept. 1 statement. “We are not immune to the challenges that face coal-based electricity across the country.”
Tri-State is the wholesale power supplier, operating on a not-for-profit basis, to 43 electric cooperatives and public power districts that serve more than one million consumers throughout nearly 200,000 square-miles of Colorado, Nebraska, New Mexico and Wyoming.