TVA seeks comment on shutdown, retrofit options for two Shawnee coal units

The Tennessee Valley Authority put out for comment on Nov. 25 a draft Environmental Assessment of options being considered for the future of the coal-fired Units 1 and 4 at the Shawnee Fossil Plant near Paducah, Ky.

Nearly 90 public comments from the initial scoping phase of the Environmental Assessment process were considered during the development of the current draft. Additional public comments are now being requested before a final recommendation is made to the TVA board of directors. TVA must then communicate a decision to the U.S. Environmental Protection Agency by Dec. 31, 2014. The public comment period on the draft EA runs from Nov. 25 through Dec. 9.

Under a 2011 agreement with the EPA, plus various states and environmental groups, TVA is reducing emissions across its entire coal-fired fleet. At the Shawnee facility, the agreement requires that TVA decide whether to install additional emissions controls on Units 1 and 4, convert those units to biomass, or retire them by Dec. 31, 2017.

There are seven additional operating coal units at Shawnee that are not affected by this proposal and will continue to operate. A remaining unit, the 124-MW Shawnee 10, was retired earlier in 2014. The nine active coal-fired units have a summer net capability of 1,206 MW (about 134 MW each).

The draft Environmental Assessment focuses on two options for Units 1 and 4: installing scrubbers and selective catalytic reduction (SCR) to reduce SO2 and NOx emissions, respectively, or retiring the units. TVA previously examined converting coal units at Shawnee and elsewhere to burn biomass, but it did not prove to be feasible.

The Shawnee Fossil Plant was completed in 1956 and consists of a total of nine active coal-fired units that produce approximately 8 billion kilowatt-hours of electricity per year, enough to supply 540,000 homes. It burns about 9,600 tons of coal a day, which is a blend of about 75% Powder River Basin (PRB) subbituminous coal and 25% Colorado bituminous coal.

These two units not needed for local grid reliability

Shawnee Units 1 and 4 are not needed for reliability purposes in the Paducah area. TVA said it could retire the two units without having to build or obtain replacement capacity to maintain reliable service in the Paducah area. However, the two units do help meet the growing demand for energy and capacity on the TVA system, which enhances their value.

The SCR systems, if installed, would be constructed in the location of the non-operational electrostatic precipitators, which would be removed and sold for scrap metal. The 250-foot tall original emission stacks for Units 1 and 4 would be demolished and the new FGD systems would be located in the area of these stacks.

Additional actions would include potential changes to the dry fly ash piping systems to allow segregation of the new scrubber coal combustion residuals (CCRs), extensions of on-site electrical components, and ancillary facilities such as haul roads, stock piles, and laydown areas.

TVA would conservatively design the FGD system to accommodate a blend of at least 50% higher-sulfur Illinois Basin (ILB) coal and 50% PRB coal. Designing the FGD systems to burn higher-sulfur coal gives TVA the flexibility to switch coals in the future to take advantage of changing market conditions while maintaining compliance with applicable regulations. SHF currently has the ability to receive and blend coal from different sources and a change to use of ILB coal would not require modifications to coal receiving and blending equipment.

TVA operates FGD systems on several of its coal plants; these systems use a wet scrubber process which uses limestone as the reagent mixed with large volumes of water to remove SO2. TVA is currently installing a newer design dry scrubbing system on its Gallatin Fossil Plant and proposes to install dry scrubbing systems at Shawnee.

A dry FGD system, utilizing lime, would be installed to control SO2 and acid gases and toenhance mercury capture by the fabric filter PM control device. Dry scrubber costs havecontinued to decrease, largely because of technical innovations, and are increasingly beingrecognized as an important part of a comprehensive air control program. The following dry FGD systems were evaluated:

  • Spray drying absorber (SDA)
  • Circulating dry scrubber (CDS)
  • Novel integrated desulfurization

TVA identified these three dry scrubber technologies as suitable for Shawnee, and has not yet determined which is preferred. All three systems would utilize lime as the base reagent to remove SO2.

Continued operation of the existing Shawnee Units 1 and 4, with the retrofits, would result in the generation of up to about 180,000 tons per year of CCRs, an increase over the 73,000 tons per year currently produced by Units 1 and 4. The CCRs would consist of comingled FGD residue and fly ash collected in the baghouses, as well as the segregated bottom ash. The quantity of CCRs potentially produced was estimated based on the units running at full load 75% of the time and burning coals with a range of 0.64–3.1 pounds of sulfur per million British Thermal Units. The quantity of bottom ash produced by Units 1 and 4 would not change.

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.