TVA eyes up to 1,400 MW gas plant to replace Allen coal units

The Tennessee Valley Authority on July 2 invited the public to review and comment on its draft Environmental Assessment for a proposed gas-fired power plant to replace the coal-fired Allen Fossil Plant in Memphis, Tenn.

TVA committed to install new emission controls or retire Allen’s coal units by December 2018 under a 2011 agreement with the U.S. Environmental Protection Agency to reduce emissions across its coal-fired fleet. As part of that agreement, TVA is now determining the best course of action, including retiring some coal units at various plants.

The public comment period for the EA runs from noon July 2 through Aug. 5. An open house will be held July 8 at the Amtrak Central Station’s Boardroom in Memphis.

The Allen Fossil Plant was completed in 1959 by Memphis Light, Gas and Water, and purchased by TVA in 1984. The existing plant has three coal-fired units with a total of 990 MW of capacity that produce approximately 4.8 billion kilowatt-hours of electricity per year.

The proposed action is to construct and operate a new facility fueled by natural gas, which would replace all coal-fired generation. The natural gas-fired facility would be located just south of the existing plant on a 73.3-acre site that TVA currently leases. While a final configuration for the new plant has not yet been determined by TVA, possible configurations for the gas-fired facility include:

  1. Combustion Turbine (CT) plant that would include three or four natural gas-fired CT generators having a total generating capacity of 600 MW to 800 MW, or
  2. Combined Cycle (CC) plant with a generating capacity of 800 MW to 1,400 MW that would include:

  • Either a 2-on-1 or 3-on-1 CC plant consisting of two or three natural gas-fired CT generators and one steam-turbine generator (STG) with the operational flexibility to operate in either simple or combined cycle mode.
  • Two or three heat recovery steam generators (HRSGs) (one per combustion turbine), a mechanical draft cooling tower, and a water-cooled condenser.
  • Aqueous ammonia systems for the selective catalytic reduction (SCR) system.
  • Auxiliary boilers to provide start-up steam for the new CC plant.

Both natural gas-fired CT and CC configurations would include:

  • Construction of a new natural gas pipeline and gas system upgrades to existing infrastructure to connect the plant to an existing gas pipeline.
  • Pond(s) for holding storm water flows from the site.
  • Construction of multiple 161-kV transmission lines (TL) from the proposed natural gas-fired facility to the existing Allen switchyard.
  • Installation of reciprocating engines to combust biogas from the adjacent bio-waste lagoons and produce power.
  • Fuel oil backup tanks and associated backup fuel systems (if required).

Existing Allen gas units may be retained

Depending on final gas plant electrical output, some or all of the existing CT units at the Allen plant would continue to be used for peaking operations. Long-term actions related to this coal unit retirement, such as the potential demolition of the units, are outside the scope of this EA and will be addressed by TVA in the future should the proposed action be implemented.

Operation of the proposed CT/CC facility would require construction and operation of a new natural gas pipeline that would be owned by Memphis Light, Gas, and Water Division (MLGW). Construction and operation of the pipeline is considered a connected action for this National Environmental Policy Act (NEPA) analysis.

The proposed gas pipeline system would include a primary supply line that would be up to 30 inches and built within an existing MLGW gas pipeline corridor right-of-way from the MLGW’s gate station near Airways Boulevard to the west and then north approximately 13 miles to the proposed CT/CC site. This EA is based on the assumption that the proposed pipeline can be fully constructed within MLGW’s existing right of way.

Allen consists of three coal-fired units with a nominal maximum rating of 330 MW each. Under the No Action Alternative, TVA would continue to operate Units 1 through 3 to provide generation needed to meet the real and reactive power needs of the Memphis area. TVA would continue to control emissions of regulated air pollutants at Allen. The plant currently operates SCR units to reduce NOx emissions and electrostatic precipitators to control particulate matter (PM) emissions. Units 1 through 3 burn low-sulfur coal to reduce SO2 emissions.

After April 16, 2015, the units at Allen will be required to comply with the U.S. Environmental Protection Agency’s Mercury and Air Toxics Standards of:

  • 0.030 pounds per million British thermal units (lb/MMBTU) PM;
  • 0.002 lb/MMBTU hydrochloric acid (HCl); and
  • 1.2 pounds per trillion BTU (lb/TBTU) mercury (Hg).

To meet HCl and Hg emission limits, TVA would use limestone and bromide in the pretreatment process of the Powder River Basin coal burned at the plant. If the coal plant continued to operate, TVA would continue using these emission control devices and measures and would limit emissions of SO2 by controlling the sulfur content of the fuel accepted.

Continuing to operate Allen in this configuration would not comply with the EPA clean air settlement agreements and would not meet the purpose and need for this proposed action. However, this alternative is used as a benchmark or baseline to compare the environmental effects of the proposed action alternatives, TVA noted.

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.