Public Service Co. of Oklahoma permits Northeastern NOx changes

The Oklahoma Department of Environmental Quality began taking public comment on May 9 on a plan by Public Service Co. of Oklahoma to optimize existing and add new NOx controls at the coal- and gas-fired Northeastern power plant.

Northeastern generates electricity using both combustion and steam turbines. Public Service Co. of Oklahoma (PSO), a unit of American Electric Power (NYSE: AEP), has added low-NOX concentric firing systems (LNCFS, a trademark for Alstom) consisting of low-NOX burners (LNB) and separated overfire air (SOFA) to the coal-fired Units 3 and 4 in advance of the U.S. Environmental Protection Agency’s Cross-State Air Pollution Rule (CSAPR) requirements, under an operating permit modification issued in March 2012. This new permitting is under the prevention of significant deterioration (PSD) program.

“Applicant now requests authority to tune the SOFA units to further decrease NOX emissions,” the DEQ said in a May 6 permitting document. “This is expected to increase [carbon monoxide] CO emissions.”

This application requests tuning of the burners to reduce the stoichiometry within the firing zone. The use of OFA is one of the most common and accepted methods for reducing NOX emissions from tangentially-fired boilers, the DEQ noted. OFA stages the combustion process by injecting a portion of the secondary air above the main firing zone to reduce the initial amount of oxygen available for the fuel. “Tuning, such as changing damper curves, windbox/furnace differentials, O2 curves, etc. to minimize NOX are required after installation of SOFA,” the agency wrote. “Increases in CO will be minimized with the manual yaw adjustment of the SOFA air nozzle tips. Tuning emission increases were not identified in the application for initial installation of SOFA.”

The utility also wants to install low-NOX burners and overfire air (LNB/OFA) on Unit 2, which is a natural gas-fired unit. This is expected to decrease NOX and increase CO emissions, although the manufacturer states that the system will not increase CO emissions, and may actually decrease them, the DEQ said.

The proposed changes are expected to satisfy the Units 3 and 4 Best Available Retrofit Technology (BART) requirements for NOX. They will have no significant effect on BART SO2 requirements.

Northeastern has gas- and coal-fired units

Northeastern Unit 1 has been “repowered,” the DEQ said by way of background. The boiler powering the steam turbine was replaced by two 160 MWe combined cycle gas turbines with heat recovery steam generators (HRSGs). The Unit 1 steam turbine was not removed when the original boiler was removed.

The boiler providing steam to Unit 2 is primarily gas-fueled, with #2 fuel oil as a secondary fuel.

The boilers providing steam for Units 3 and 4 are primarily coal-fired, with natural gas, #2 fuel oil, and co-firing of coal and natural gas as secondary fuels.

Two additional boilers serve as auxiliary gas-fired steam generators, one serving Units 1 and 2 (Auxboiler 1/2), and another serving Units 3 and 4 (Auxboiler 3/4).

The proposed use of petroleum coke (petcoke) is treated in several parts of this permit, the agency said. Units 3 and 4 have always had the ability to burn petcoke as an alternate fuel for coal and it has not been proscribed.

The LNB/OFA project at Unit 2 is expected to reduce NOX emissions from the current 0.386 lb/MMBTU to 0.28 lb/MMBTU and to increase CO from the current 0.059 lb/MMBTU to 0.148 lb/MMBTU.

Additional tuning of the LNCFS at Units 3 and 4 will lead to changes in the emission factors used for NOX and for CO. Applicant expects NOX emissions to decrease from the current 0.386 lb/MMBTU to the BART level of 0.15 lb/MMBTU. Vendor’s data suggests that CO emissions will be at 0.520 lb/MMBTU, up from the current AP-42 equivalent value of 0.0305 lb/MMBTU.

Commission review of utility’s air plan has gone on hold

PSO has since last year been before the Oklahoma Corporation Commission (OCC) for approval of a broad clean-air plan. Under a settlement agreement with various parties – including the U.S. Environmental Protection Agency, the state of Oklahoma and the Sierra Club – the proposed Compliance Plan that the utility filed with the commission last September for Northeastern provides for PSO to:

  • install separated over-fire air systems for NOx control on the coal-fired Units 3 and 4 (total of 930 MW) by the end of 2013;
  • attain a 30-day average SO2 emission rate of 0.65 lb/MMBtu starting in 2014 by burning ultra-low-sulfur coal at both Units 3 and 4;
  • attain a 12-month average SO2 emission rate of 0.60 lb/MMBtu starting in 2015 by burning ultra-low-sulfur coal at both Units 3 and 4;
  • install dry sorbent injection, activated carbon injection and a fabric filter baghouse on Northeastern Unit 3 by April 16, 2016;
  • retire Unit 4 on April 16, 2016, and replace it with a long-term purchase power agreement (PPA);
  • limit the annual capacity factor for Unit 3 to 70% starting in 2021, 60% starting in 2023, and 50% starting in 2025; and
  • retire Unit 3 by the end of 2026.

Said AEP’s April 26 Form 10-Q filing about this delayed case at the Oklahoma commission: “In January 2013, several parties filed testimony with various recommendations. In February 2013, the OCC staff requested a stay in this proceeding, which was granted by the OCC in March 2013. The stay will be in effect until the State Implementation Plan is approved by the Federal EPA, which could be as late as February 2014. If PSO is ultimately not permitted to fully recover its net book value of [Northeastern Station] Units 3 and 4 and other environmental compliance costs, it could reduce future net income and cash flows and impact financial condition.”

As for that SIP, the Form 10-Q added: “In 2011, the Federal EPA proposed to approve in part and disapprove in part the regional haze SIP submitted by the State of Oklahoma through the Department of Environmental Quality. The Federal EPA proposed to approve all of the NOx control measures in the SIP and disapprove the SO2 control measures for six electric generating units, including two units owned by PSO. The Federal EPA proposed a [Federal Implementation Plan] FIP that would require these units to install technology capable of reducing SO2 emissions to 0.06 pounds per million British thermal units within three years of the effective date of the FIP. The Federal EPA finalized the FIP in December 2011 that mirrored the proposed rule but established a five-year compliance schedule. PSO filed a petition for review of the FIP in the Tenth Circuit Court of Appeals and engaged in settlement discussions with the Federal EPA, the State of Oklahoma and other parties. In November 2012, we notified the court that the parties had reached agreement on a settlement that would provide for submission of a revised Regional Haze SIP requiring the retirement of one coal-fired unit of PSO’s Northeastern Station no later than 2016, installation of emission controls on the second coal-fired Northeastern unit in 2016 and retirement of the second unit no later than 2026. The Tenth Circuit Court of Appeals is holding the appeal in abeyance pending implementation of the settlement. A revised regional haze SIP was proposed by the State of Oklahoma and submitted to the Federal EPA for review.”

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.