DeCordova nears permit to add combined cycle capability at Texas site

DeCordova II Power Co. LLC is nearing a decision from the Texas Commission on Environmental Quality (TCEQ) on an amendment to an Air Quality Permit and issuance of a Prevention of Significant Deterioration (PSD) Air Quality Permit, which would cover combined cycle optionality for the simple cycle combustion turbine Units 5 and 6.

This subject plant site is located at 4950 Power Plant Court, Granbury, Hood County. This application was submitted to the TCEQ in August 2014, said the commission in a Dec. 22 notice that was posted to its website on Dec. 23.

The TCEQ executive director has determined that the emissions of air contaminants from the proposed facility which are subject to PSD review will not violate any state or federal air quality regulations and will not have any significant adverse impact. All air contaminants have been evaluated, and “best available control technology” will be used to control them. The executive director has completed the technical review of the application and prepared a draft permit which, if approved, would establish the conditions under which the facility must operate.

DeCordova II owns the DeCordova Steam Electric Station, which currently consists of two combustion turbines (CTGs) authorized to operate in simple cycle. The simple cycle operations were authorized in August 2013. The CTGs will be one of two options: General Electric or Siemens.

DeCordova is seeking to augment the generating capacity of this station by adding combined cycle operations. The new project will include an increase in the annual hours of operation for the CTGs, the installation of two duct burner (DB) fired heat recovery steam generators (HRSGs), a steam turbine, an auxiliary boiler, an emergency generator, and a firewater pump.

The DeCordova Station, upon completion of this project, will consist of two natural gas-fired CTGs each equipped with a supplementary DB fired HRSG to operate in either simple cycle or combined cycle modes. The addition of combined cycle capabilities will result in an increase in the annual operating hours. There will be no increase in the currently authorized operating hours for the simple cycle operations. The CTGs will be one of the following model options:

  • Two General Electric Model 7FA CTGs each rated at a nominal gross capacity of 210 MW. Each CTG will have a DB fired HRSG with a maximum heat input of 349.2 million British thermal units per hour (MMBtu/hr).
  • Two Siemens Model SGT6-5000F CTGs each rated at a nominal capacity of 231 MW. Each CTG will have a DB fired HRSG with a maximum heat input of 500 MMBtu/hr.

The CTGs will use either an aqueous ammonia or anhydrous ammonia selective catalytic reduction (SCR) system to control NOx emissions. The system will be comprised of ammonia storage and handling equipment, an ammonia vaporizer, an ammonia injection grid, and catalyst bed modules. The ammonia injection grids and the SCR catalyst beds will be installed in the HRSG housings at locations where exhaust temperatures will facilitate the NOx reduction reactions. 

The natural gas-fired auxiliary boiler will have a maximum heat input of 73.3 MMBtu/hr. The boiler will provide turbine startup steam requirements.

A project contact is: DeCordova II Power Co. LLC, Paul Coon, Air Permitting Manager, Environmental Services, (214) 875-8376.

DeCordova II is an Energy Future Holdings affiliate. In its March 31 annual Form 10-K statement, Energy Future said about new gas capacity permitting: “In 2013 and 2014, the TCEQ granted air permits to Luminant to build two natural gas combustion turbine generation units totaling 420 MW to 460 MW at each of Luminant’s existing DeCordova, Tradinghouse and Lake Creek generation facilities. In 2014 and 2015, Luminant filed air permit applications with the TCEQ to build two natural gas combustion turbine generation units totaling 420 MW to 460 MW at each of its existing Valley and Permian Basin generation facilities. In 2014, Luminant filed air permit applications with the TCEQ to build a combined cycle natural gas generation unit totaling 730 MW to 810 MW at each of its existing Eagle Mountain and DeCordova generation facilities. In 2015, Luminant filed an air permit application with the TCEQ to build two combined cycle natural gas generation units totaling 1460 MW to 1620 MW at its Tradinghouse generation facility. The proposed combined cycle natural gas generation units would be an alternative to the natural gas combustion turbine generation units at DeCordova and Tradinghouse.

“We believe current market conditions do not provide adequate economic returns for the development or construction of these facilities; however, we believe additional generation resources will be needed in the future to support electricity demand growth and reliability in the ERCOT market.”

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.