Duke seeks North Carolina approval for Asheville coal-to-gas repowering

Duke Energy Progress LLC applied Jan 15 at the North Carolina Utilities Commission for a Certificate of Public Convenience and Necessity that covers the $1.1 billion project to construct and operate the Western Carolinas Modernization Project at the existing Asheville Steam Electric Plant in Buncombe County, N.C.

Duke Energy Progress (DEP), a subsidiary of Duke Energy (NYSE: DUK), noted that it will permanently cease operations of all coal-fired generating units at the site on or before the commercial operation date of the generating unit that is the subject of the certificate application. The new natural gas-fired facility has no more than twice the generation capacity as the coal-fired generating units to be retired.

The Western Carolinas Modernization Project will consist of:

  • two new 280-MW (expected winter rating) combined cycle natural gas-fueled units, with fuel oil backup;
  • a contingent natural gas-fueled 186 MW (expected winter rating) simple cycle combustion turbine unit, with fuel oil back up, whose need may be avoided or delayed due to the utilization of other technologies and programs to meet the future peak demand requirements of DEP customers in the region;
  • related onsite transmission facilities; and
  • future new solar generation at the Asheville plant site.

DEP said it is currently in the early stages of formalizing a partnership with communities in Buncombe County, including the City of Asheville, and surrounding communities to explore ways to maximize deployment and effectiveness of programs and innovative energy solutions to reduce energy use in the fast-growing, nine county DEP-Western Region.

The Western Carolinas Modernization Project will enable the early retirement of the 379 MW (winter rating) Asheville 1 and 2 coal units on or before the commercial operation of the new combined cycle units, thereby permanently ceasing operations of all coal-fired units at the site. DEP also has two existing 185 MW (winter rating) combustion turbine units at the Asheville plant site that will continue operation.

The Asheville Combined Cycle units will provide base load generation for DEP’s customers in North Carolina and South Carolina, and are planned for commercial operation in the Fall of 2019. The contingent Asheville Combustion Turbine unit would potentially begin commercial operation in 2023 if the current peak demand growth is not sufficiently reduced by alternative approaches.

The new solar generation facility will be subject to a future CPCN application once the coal unit demolition plans have been sufficiently completed to determine the site configuration that will enable the optimum amount of new solar generation at the Asheville site for the benefit of the company’s customers.

Combined cycle units would be capable of simple cycle operation

The Asheville Combined Cycle project design consists of two power blocks, each with one combustion turbine (CT), one heat recovery steam generator (HRSG), and one steam turbine (ST). The design incorporates a bypass stack damper to allow for simple cycle operation if the steam cycle is not available. The power blocks for the Asheville Combined Cycle units will be sited in the former “1982 Ash Pond” area, which is currently being excavated.

The contingent Asheville CT unit would use one F-frame CT generator to produce electricity. The future CT would be sited near the existing CTs at the Asheville facility.

Natural gas for the Western Carolinas Modernization Project will be provided by a new pipeline and associated facilities being constructed by Public Service Co. of North Carolina (PSNC). PSNC will provide firm transportation service for the Asheville Combined Cycle units. DEP’s partnership with PSNC on the Western Carolinas Modernization Project will bring important additional natural gas supply to Western North Carolina, the utility noted.

The Asheville Combined Cycle units and the contingent CT will be designed with fuel oil backup capability in order to maintain system reliability in the event of an interruption in natural gas supply to the units. In many instances, the loss of multiple units could be mitigated with increased power imports; however the DEP-Western Region has limited transmission import capabilities requiring additional redundancies to protect against import limitations. Without increased transmission import capabilities, the other existing generating options in the region (i.e., hydro facilities, existing CTs) would not be sufficient to provide reliable service and maintain compliance with applicable North American Electric Reliability Corp. (NERC) reliability standards in the event the future units are unavailable during periods of peak demand.

As part of the Western Carolinas Modernization Project, one power block of the new Asheville Combined Cycle project will be connected to the existing 230-kV switchyard with a single 230-kV line. This 230-kV line will be connected from the high side of both the steam turbine generator step-up transformer and the gas turbine generator step-up transformer. The other power block will be connected to the existing 115-kV switchyard with two 115-kV lines. One of the two 115-kV lines will be connected from the high side of the steam turbine generator step-up transformer and the other 115-kV line will be connected from the high side of the gas turbine generator stepup transformer.

Air controls would include selective catalytic reduction

The Western Carolinas Modernization Project will feature highly efficient generation and environmental control technologies. With the associated early retirement of the Asheville coal units, DEP expects to reduce annual emissions of NOx by 35%, reduce annual emissions of S02 by 90%-95%, reduce emissions of CO2 of 60% per megawatt hour, and eliminate mercury emissions.

Operating impacts from pollutants out of the new facility will be addressed through the Western North Carolina Regional Air Quality Agency (WNCRAQA) air quality permit application process. Duke Energy Progress plans to submit a permit application to WNCRAQA on or about Jan. 20. Based upon historical experience for similar permit applications, Duke Energy Progress anticipates that a final air permit should be issued within six months of submitting the application.

The project will use combustion turbines with dry low NOx combustors to meet environmental regulations and permitting requirements. A selective catalytic reduction (SCR) system and oxidation catalyst will be installed in each of the HRSGs and will be operated as necessary to comply with the air permit. Continuous emission monitoring systems (CEMS) will be installed on each turbine’s bypass stack and each combined cycle exhaust stack.

The Asheville Combined Cycle Project will employ cooling towers, which will significantly reduce water withdrawal and remove all thermal impacts to Lake Julian. In contrast, the older Asheville coal units use once-through cooling water systems. Preliminary operating plans include installation of an oil/water separator for treatment of all potential oily waste streams and discharge to the French Broad River along with cooling tower blowdown water, which will be included in the modification of the existing NPDES permit. Other liquid waste streams such as gas turbine wash wastewater will be pumped to tank trucks and hauled off site for treatment.

Project reworked after November termination of supporting power line project

From a total system perspective, the Duke Energy Progress 2015 Integrated Resource Plan (IRP) identifies the need for an additional 1,152 MW of new resources to meet customers’ energy needs by 2020 and 5,099 MW by 2030. The Duke Energy Progress 2015 IRP Short Term Action Plan includes a single 733 MW (winter rating) Asheville combined cycle unit that would serve as a generation system resource as well as the retirement replacement for the existing 379 MW (winter rating) Asheville 1 and 2 coal units and replacement for the previously planned 147 MW (winter rating) Fast Start CTs located in the DEP-Western Region that were identified in the 2014 IRP.

Subsequent to DEP’s filing of its 2015 IRP, the company made the decision to cancel the proposed Foothills Transmission Line project on Nov. 4, 2015. This decision was made in response to extensive community concerns expressed in both South Carolina and North Carolina, and required the development of an alternative configuration that could meet NERC reliability standards, while continuing to satisfy future load growth in the DEP-Western region and also contributing to DEP’s total system reserve requirements. The new proposed configuration includes the new CCs totaling 560 MW that replace the existing 379 MW coal units and eliminate the need for previously-planned 147 MW fast start CTs.

“It is important to note that the addition of these new resources along with all other existing hydro and CT assets in the region are collectively insufficient to meet the area’s peak demand,” Duke wrote in the application. “As a result, the region will continue to require the utilization of imports via the limited transmission options into the DEP-Western Region in order to meet its peak demand requirements. As load continues to grow in the region, the need for more generation, in lieu of new transmission imports, may be required to maintain system reliability. At projected load growth rates without increased participation in [demand side management/energy efficiency] programs, the proposed contingent 186 MW Asheville CT Project will also be required to maintain reliability and meet NERC standards in the region.”

The time and resources necessary to develop and reconfigure the Western Carolinas Modernization Project since the Nov. 4, 2015, decision to cancel the Foothills Transmission Line, combined with the extensive engineering, contracting and construction work necessary to meet the 2019 commercial operation date required for the new CC units, dictate the need to receive CPCN approval from this commission on or before March 1, 2016, Duke wrote. It is asking the commission for a partial waiver of a rule that would speed up the approval process.

North Carolina Electric Membership may take 100-MW stake in the project

The North Carolina Electric Membership Corp. (NCEMC) has an option to purchase and own 100 MW of the Asheville Combined Cycle facility. Duke said it will be working with NCEMC to determine if NCEMC will exercise its ownership option, and if so, how the contract between the parties will be structured. However, the load required to be served by Duke in the DEP-Western region will be the same regardless of the NCEMC ownership decision. Thus, DEP said its need for the combined cycle units is justified by the public convenience and necessity whether DEP owns 560 MW or 460 MW of the generation facility.

The retirement of the Asheville coal units as part of the addition of the Western Carolinas Modernization Project represents an acceleration of approximately 10 years from previous planning assumptions. 

The need for the 186 MW contingent Asheville CT in 2023 resulted from DEP’s decision to cancel the Foothills Transmission Line. Although the 2015 IRP demonstrates the need for this CT unit in 2023 to provide both needed system capacity reserves and satisfy applicable NERC Reliability Standards, beyond the scope of this filing, DEP will work aggressively to transition to a cleaner and smarter energy future through active community engagement, deliberate investment in distributed energy resources (DER), and greater promotion of and access to DSM/EE programs in the DEP-Western Region which may delay or eliminate the need for the contingent Asheville CT unit.

The projected cost of the Western Carolinas Modernization Project is approximately $1.1 billion, with any cost breakdowns from there being kept confidential and not being revealed in public filings.

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.