PacifiCorp to alter Naughton Unit 3 NOx output ahead of coal-to-gas conversion

The Wyoming Department of Environmental Quality’s Division of Air Quality is proposing to approve a request by PacifiCorp to revise the 30-day rolling average NOx limit of 0.08 lb/MMBtu to a rate of 0.12 lb/MMBtu for Naughton Unit 3 upon conversion of that coal-fired unit to natural gas.

That intention to approve is out for comment until Oct. 31. A public hearing will be conducted only if in the opinion of the administrator sufficient interest is generated or if an aggrieved party so requests.

The three-unit Naughton Power Plant is located approximately four miles southwest of Kemmerer in Lincoln County, Wyoming.

On July 26, the Division of Air Quality received an application from PacifiCorp to revise the 30-day rolling average NOx limit of 0.08 lb/MMBtu to a rate of 0.12 lb/MMBtu for Naughton Unit 3. A prior air quality permit established the Naughton Unit 3 NOx emission limits following the conversion of the unit from coal to natural gas at 0.75 lb/MMBtu on a 3-hour rolling average basis, 0.08 lb/MMBtu on a 30-day rolling average basis, 250.0 lb/hour on a 30-day rolling average basis, and 519.0 tons/year.

As plans for the conversion of the unit have progressed, it has become apparent that the 0.08 lb/MMBtu limit will not be achievable without the installation of a significant flue gas recirculation system, which would add an estimated $3 million to $5 million of capital expense to this project. To support the economic viability of the gas conversion, PacifiCorp is making efforts to reduce the costs associated with the conversion.

PacifiCorp is requesting that the 30-day rolling average NOx limit of 0.08 lb/MMBtu be modified to a rate of 0.12 lb/MMBtu. The 0.75 lb/MMBtu limit (calculated as a 3-hour rolling average), 250.0 lb/hour limit (calculated as a 30-day rolling average), and the 519.0 tons/year limit will remain unchanged. The 30-day lb/hour limit used for compliance modeling (250.0 lb/hr) will remain the same. The requested 0.12 lb/MMBtu limit will provide operational flexibility and reduce the costs associated with the gas conversion for customers.

In July 2013, an air quality permit was issued to modify the Naughton Power Plant by reducing permitted emissions from Unit 3 and ultimately converting the unit from a coal-fired unit to a natural gas-fired unit in 2018.

Naughton is comprised of three pulverized coal-fired units with a total net generating capacity of 700 MW. Units 1 and 2 will remain on coal after the Unit 3 conversion.

  • Naughton Unit 1 commenced operation in 1963 and has a maximum heat input of 1,850 million British thermal units per hour (MMBtu/hr). The unit generates a nominal 160 MW.
  • Naughton Unit 2 commenced operation in 1968, has a maximum heat input of 2,400 MMBtu/hr, and generates a nominal 210 MW.

The boilers on Units 1 and 2 are tangential fired and equipped with low NOx burners (LNB) and advanced overfire air (AOFA) to control NOx emissions. Each unit is equipped with an electrostatic precipitator (ESP) and a flue gas conditioning system (FGC) to control particulate emissions. SO2 emissions are controlled by sodium-based wet flue gas desulfurization systems (WFGD) installed on each unit.

Naughton Unit 3 commenced operation in 1971, has a maximum heat input of 3,700 MMBtu/hr, and generates a nominal 330 MW. The Unit 3 boiler is tangential fired and retrofitted with ALSTOM LCCFS II low NOx burners with overfire air (OFA) installed in 1999. Particulate emissions are controlled using an ESP with FGC. SO2 emissions are controlled using a two-tower sodium-based WFGD system that was installed in 1997.

PacifiCorp is instituting an interim operating scenario beginning April 1, 2015, and lasting until Jan. 1, 2018, to reduce emissions at Unit 3. The company will limit the heat input to a maximum of 3,145 MMBtu/hour. This is equivalent to 85% of the maximum boiler heat input. The limit is based upon a 24-hour block average hourly heat input. The block average is defined as any 24-hour period between 12:00 midnight and the following midnight during which any fuel is combusted at any time at the steam generating unit. The reduced firing rate was used to establish the unit’s interim pound per hour emission limits.

PacifiCorp will meet the reduced firing rate limit while burning any combination of coal and natural gas. In addition to reducing the heat input for the boiler, the SO2, NOx, and PM emissions rates will be lowered. SO2 emissions from Naughton Unit 3 will be limited to 0.20 lb/MMBtu. NOx emissions will be limited to 0.40 lb/MMBtu. The averaging period for the NOx and SO2 limits will be based on a 30-day rolling average. A PM limit of 0.035 lb/MMBtu will be imposed on the unit.

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.