The Tennessee Valley Authority has put out for comment until May 20 a draft environmental assessment for a Johnsonville Cogeneration Plant, needed to replace to-be-retired coal capacity at a power plant site located near New Johnsonville, Tennessee.
TVA and steam customer DuPont on Jan. 8 had announced the continuation of a partnership to generate power and steam at TVA’s Johnsonville site. The Johnsonville Fossil Plant is the oldest fossil plant in the TVA system. It has 10 coal-fired units which produce approximately 6 billion kilowatt-hours of electricity per year. In April 2011, TVA entered into an agreement with the U.S. Environmental Protection Agency, several states, and three environmental advocacy groups under which it agreed to retire all 10 coal-fired units at Johnsonville by Dec. 31, 2017.
TVA currently provides steam produced by the coal-fired units to an external customer. The existing contract to provide steam will extend to December 2017 when the coal-fired units at Johnsonville are retired. TVA is evaluating actions to continue to provide steam to the steam customer following the retirement of all the coal-fired units. The proposed action is to construct and operate a heat recovery steam generator integrated into an existing combustion turbine (CT) at the site.
TVA added 16 CT units at the plant in the mid-1970s and another four in 2000. The proposed action is to add a heat recovery steam generator (HRSG) onto an existing General Electric 7EA CT (Unit 20). The HRSG would include duct firing to provide the required steam flow. Two auxiliary boilers averaging 300 kilopounds per hour each would be provided for redundancy. All major equipment would be placed on TVA property.
For purposes of this EA analysis, TVA assumes that under the No Action Alternative, the steam customer would install the necessary equipment to provide its own steam. All construction activity would occur on a previously disturbed site adjacent to Johnsonville that is owned by the steam customer. The steam customer has no existing fuel source and would therefore have to construct a new natural gas pipeline to supply gas for auxiliary boilers. The new pipeline could be up to 30 miles long, which is the distance to the nearest existing third-party interstate gas pipeline.
TVA has existing dual-fuel CT units on-site, and construction of the HRSG would not require an additional fuel supply. Two auxiliary boilers would be provided for redundancy as a backup power source in the event that the CT units are off line. Auxiliary boilers would be fired by natural gas only.
Construction is expected to last 18 months with peak construction occurring from April 2016 to October 2016. During the peak construction period, 100 to 200 workers could be employed on site.
“The addition of the cogeneration plant would allow TVA to continue to provide steam to the steam customer after the retirement of the coal-fired units at [Johnsonville] (the Purpose and Need for this proposed action),” said the draft EA. “It would also allow TVA to provide approximately 85 megawatts of baseload electricity to the TVA system with the same process that provides steam to the steam customer. This cogeneration strategy utilizes low emissions equipment and enhances TVA long-term integrated resource planning.”
There are 20 dual-fuel simple cycle CTs at Johnsonville, which includes 16 model GE MS7001B and four model GE PG7121EA. They are operated to meet peak power demands (<3% capacity factor), primarily during the winter and summer. Unit 20 would operate continuously in base load mode after the cogen conversion.