Duke launches project that could see Cliffside coal unit on 100% natural gas

Duke Energy Carolinas on Oct. 11 notified the North Carolina Utilities Commission of its decision to add Dual Fuel Optionality (DFO) at the coal-fired Rogers Energy Complex in Mooresboro, North Carolina.

This plant, formerly known as the Cliffside facility, is the site of an older, coal-fired Unit 5, and a relatively new, coal-fired Unit 6. The other four coal units at the site were retired earlier this decade as part of an air permitting deal that allowed Unit 6 to be built.

Since no commission approval is required for the DFO project, this Oct. 11 letter was filed for informational purposes. The DFO project will enable up to one hundred percent (100%) natural gas co-firing on Cliffside Unit 6 and 10% gas co-firing on Cliffside Unit 5, resulting in reduced operations and maintenance (O&M) expenses, additional fuel flexibility, operational flexibility, and lower emissions.

The Rogers Energy Complex includes two coal units:

  • the 552-MW subcritical Cliffside Unit 5, which went into commercial operation in 1972; and
  • the newest coal unit for the utility, the 844-MW supercritical advanced clean coal Cliffside Unit 6, which went into commercial operation at year end 2012.

Industry publications have recognized Cliffside as one of the top 10 most efficient coal-fired generating stations, and one of the top 20 for lowest SO2 emission rates, in the United States for 2013 and 2014, the company noted. Even though Cliffside 6 is the newest, most-efficient, steam unit in the Duke Energy Carolinas fleet, the annual capacity factor for Cliffside Unit 6 operating solely on coal can fluctuate materially based upon coal transportation prices, single rail coal transportation, and low market gas costs.

Because of the Cliffside units’ close proximity to the Public Service Co. of North Carolinas’ (PSNC) under-construction intrastate pipeline that connects to the Transco interstate pipeline near Kings Mountain and extends to Asheville, as well as the low gas price environment, Duke Energy Carolinas, conducted an analysis of the benefits of DFO at Cliffside. The company conducted reviews with major boiler original equipment manufacturers, which demonstrated proven technology across the utility industry that added natural gas-fired capability to existing coal units.

Duke Energy Carolinas identified six DFO projects for detailed benchmarking, including projects at supercritical and subcritical stations owned by Southern Co., PSEG and Helios Power Capital LLC. This review identified DFO operational benefits in the form of fuel switching, NOx reductions, O&M reductions, minimum load reductions, smooth unit ramp rates on natural gas, and maintenance flexibility.

Duke Energy Carolinas completed Phase 1 engineering of the Cliffside DFO project in July 2016. In order to modify the existing Cliffside Units 5 and 6 boilers to fire coal and natural gas, the material scope of work includes: burner modifications, ignitor modifications, gas pipings and control system (DCS) additions and logic changes. The DFO is scheduled to be completed by April 15, 2019, at an estimated cost of $56 million.

In addition, Duke Energy Carolinas has entered into an agreement with PSNC for interruptible transport of natural gas via a new pipeline lateral to be constructed off of PSNC’ s Kings Mountain to Asheville instrastate pipeline currently being built. PSNC has filed the pipeline construction and transportation service agreement for commission approval in another docket.

Under DFO, Cliffside Unit 5 will have the ability to burn up to 10% natural gas, while Cliffside Unit 6 will have the ability to burn up to 100% natural gas (or 100% coal, or a blend of the two). Under current and projected short-term (4 to 6 years) natural gas/coal price differentials, natural gas is expected to be the low cost fuel option at Cliffside. Over the long term, the flexibility that DFO provides will help hedge against future coal and gas cost uncertainties and will provide the ability to maximize benefit from short-term (daily/weekly) fuel price variability.

The ability to utilize up to 10% co-firing on Cliffside Unit 5 will also allow the unit to burn lower quality, lower cost coal blends without a loss of capacity that would otherwise occur without the additional gas burn. The DFO project will also substantially reduce fuel oil utilization at Cliffside, by enabling the startup of the units on natural gas.

In addition to lower fixed and variable O&M costs, increased operational flexibility, improved ramp profile, and improved ramp rates, the DFO project will also provide overall environmental benefits, including a 40% reduction of CO2, nearly 100% reduction of mercury and SO2, as well as elimination of ash as a by-product, when running on gas.

Incidentally, Duke Energy Carolinas on Aug. 15 filed a monthly fuel report with the North Carolina commission that shows these July 2015-June 2016 statistics for those units:

  • Cliffside Unit 6, baseload, capacity factor of 30% for the twelve-month period: and
  • Cliffside Unit 5, intermediate, capacity factor of 12% for the twelve-month period.

Duke Energy Carolinas is a unit of Duke Energy (NYSE: DUK).

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.