# Review of New Source Performance Standards for Stationary Combustion Turbines and Stationary Gas Turbines > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2024-27872 ## Record - **Collection:** Federal Register - **Document type:** Proposed Rule - **Published:** December 13, 2024 - **Citation:** 89 FR 101306 ## Text ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 60 [EPA-HQ-OAR-2024-0419; FRL-11542-01-OAR] RIN 2060-AW21 Review of New Source Performance Standards for Stationary Combustion Turbines and Stationary Gas Turbines AGENCY: Environmental Protection Agency (EPA). ACTION: Proposed rule. SUMMARY: The Environmental Protection Agency (EPA) is proposing amendments to the Standards of Performance for new, modified, and reconstructed stationary combustion turbines and stationary gas turbines based on a review of available control technologies for limiting emissions of criteria air pollutants. This review of the new source performance standards (NSPS) is required by the Clean Air Act (CAA). As a result of this review, the EPA is proposing to establish size-based subcategories for new, modified, and reconstructed stationary combustion turbines that also recognize distinctions between those that operate at varying loads or capacity factors and those firing natural gas or non-natural gas fuels. In general, the EPA is proposing that combustion controls with the addition of post-combustion selective catalytic reduction (SCR) is the best system of emission reduction (BSER) for limiting nitrogen oxide (NO X ) emissions from this source category, with certain, limited exceptions. Based on the application of this BSER and other updates in technical information, the EPA is proposing to lower the NO X standards of performance for most of the stationary combustion turbines included in this source category. In addition, for new, modified, and reconstructed stationary combustion turbines that fire or co-fire hydrogen, the EPA is proposing to ensure that those sources are subject to the same level of control for NO X emissions as sources firing natural gas or non-natural gas fuels, depending on the percentage of hydrogen fuel being utilized. The EPA is proposing to maintain the current standards for sulfur dioxide (SO 2 ) emissions, because after reviewing the current SO 2 standards, we propose to find that the use of low-sulfur fuels remains the BSER. Finally, the Agency is proposing amendments to address specific technical and editorial issues to clarify the existing regulations. DATES: Comments. Comments must be received on or before March 13, 2025. Comments on the information collection provisions submitted to the Office of Management and Budget (OMB) under the Paperwork Reduction Act (PRA) are best assured of consideration by OMB if OMB receives a copy of your comments on or before January 13, 2025. For specific instructions, please see the PRA discussion in the Statutory and Executive Order Reviews section of this document. Public Hearing. If anyone contacts us requesting a public hearing on or before December 18, 2024, we will hold a virtual public hearing. See SUPPLEMENTARY INFORMATION for information on requesting and registering for a public hearing. ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-OAR-2024-0419, by any of the following methods: • Federal eRulemaking Portal: https://www.regulations.gov (our preferred method). Follow the online instructions for submitting comments. • Email: a-and-r-docket@epa.gov. Include Docket ID No. EPA-HQ-OAR-2024-0419 in the subject line of the message. • Fax: (202) 566-9744. Attention Docket ID No. EPA-HQ-OAR-2024-0419. • Mail: U.S. Environmental Protection Agency, EPA Docket Center, Docket ID No. EPA-HQ-OAR-2024-0419, Mail Code 28221T, 1200 Pennsylvania Avenue NW, Washington, DC 20460. • Hand/Courier Delivery: EPA Docket Center, WJC West Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004. The Docket Center's hours of operation are 8:30 a.m.-4:30 p.m., Monday-Friday (except Federal Holidays). Instructions: All submissions received must include the Docket ID No. for this rulemaking. Comments received may be posted without change to https://www.regulations.gov, including any personal information provided. For detailed instructions on sending comments and additional information on the rulemaking process, see the SUPPLEMENTARY INFORMATION section below. FOR FURTHER INFORMATION CONTACT: John Ashley, Sector Policies and Programs Division (D243-02), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, 109 T.W. Alexander Drive, P.O. Box 12055 RTP, North Carolina 27711; telephone number: (919) 541-1458; and email address: ashley.john@epa.gov. SUPPLEMENTARY INFORMATION: Participation in virtual public hearing. To request a virtual public hearing, contact the public hearing team at (888) 372-8699 or by email at SPPDpublichearing@epa.gov. If requested, the public hearing will be held via virtual platform. The EPA will announce the date of the hearing and additional details on the virtual public hearing at https://www.epa.gov/stationary-sources-air-pollution/stationary-gas-and-combustion-turbines-new-source-performance. The hearing will convene at 11:00 a.m. Eastern Time (ET) and will conclude at 4:00 p.m. ET. The EPA may close a session 15 minutes after the last pre-registered speaker has testified if there are no additional speakers. The EPA will begin pre-registering speakers for the hearing no later than 1 business day after a request has been received. The EPA will accept registrations on an individual basis. To register to speak at the virtual hearing, please use the online registration form available at https://www.epa.gov/stationary-sources-air-pollution/stationary-gas-and-combustion-turbines-new-source-performance or contact the public hearing team at (888) 372-8699 or by email at SPPDpublichearing@epa.gov. The last day to pre-register to speak at the hearing will be December 26, 2024. Prior to the hearing, the EPA will post a general agenda that will list pre-registered speakers at: https://www.epa.gov/stationary-sources-air-pollution/stationary-gas-and-combustion-turbines-new-source-performance. The EPA will make every effort to follow the schedule as closely as possible on the day of the hearing; however, please plan for the hearing to run either ahead of schedule or behind schedule. Each commenter will have 4 minutes to provide oral testimony. The EPA encourages commenters to submit a copy of their oral testimony as written comments electronically to the rulemaking docket. The EPA may ask clarifying questions during the oral presentations but will not respond to the presentations at that time. Written statements and supporting information submitted during the comment period will be considered with the same weight as oral testimony and supporting information presented at the public hearing. Please note that any updates made to any aspect of the hearing will be posted online at https://www.epa.gov/stationary-sources-air-pollution/stationary-gas-and-combustion-turbines-new-source-performance. While the EPA expects the hearing to go forward as described in this section, please monitor our website or contact the public hearing team at (888) 372-8699 or by email at SPPDpublichearing@epa.gov to determine if there are any updates. The EPA does not intend to publish a document in the Federal Register announcing updates. If you require the services of a translator or a special accommodation such as audio description, please pre-register for the hearing with the public hearing team and describe your needs by December 20, 2024. The EPA may not be able to arrange accommodations without advanced notice. Docket. The EPA has established a docket for this rulemaking under Docket ID No. EPA-HQ-OAR-2024-0419. All documents in the docket are listed in the Regulations.gov index. Although listed in the index, some information is not publicly available, e.g., Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is not placed on the internet and will be publicly available only as pdf versions that can only be accessed on the EPA computers in the docket office reading room. Certain databases and physical items cannot be downloaded from the docket but may be requested by contacting the docket office at (202) 566-1744. The docket office has up to 10 business days to respond to these requests. With the exception of such material, publicly available docket materials are available electronically in Regulations.gov . Written Comments. Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2024-0419, at https://www.regulations.gov (our preferred method), or the other methods identified in the ADDRESSES section. Once submitted, comments cannot be edited or removed from the docket. The EPA may publish any comment received to its public docket. Do not submit to EPA's docket at https://www.regulations.gov any information you consider to be CBI or other information whose disclosure is restricted by statute. This type of information should be submitted as discussed in the Submitting CBI section of this document. Multimedia submissions (audio, video, etc. ) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission ( i.e., on the Web, cloud, or other file sharing system). Please visit https://www.epa.gov/dockets/commenting-epa-dockets for additional submission methods; the full EPA public comment policy; information about CBI or multimedia submissions; and general guidance on making effective comments. The https://www.regulations.gov website allows you to submit your comment anonymously, which means the EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an email comment directly to the EPA without going through https://www.regulations.gov, your email address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the internet. If you submit an electronic comment, the EPA recommends that you include your name and other contact information in the body of your comment and with any digital storage media you submit. If the EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, the EPA may not be able to consider your comment. Electronic files should not include special characters or any form of encryption and be free of any defects or viruses. Submitting CBI. Do not submit information containing CBI to the EPA through https://www.regulations.gov. Clearly mark the part or all of the information that you claim to be CBI. For CBI information on any digital storage media that you mail to the EPA, note the docket ID, mark the outside of the digital storage media as CBI, and identify electronically within the digital storage media the specific information that is claimed as CBI. In addition to one complete version of the comments that includes information claimed as CBI, you must submit a copy of the comments that does not contain the information claimed as CBI directly to the public docket through the procedures outlined in the Written Comments section of this document. If you submit any digital storage media that does not contain CBI, mark the outside of the digital storage media clearly that it does not contain CBI and note the docket ID. Information not marked as CBI will be included in the public docket and the EPA's electronic public docket without prior notice. Information marked as CBI will not be disclosed except in accordance with procedures set forth in 40 Code of Federal Regulations (CFR) part 2. Our preferred method to receive CBI is for it to be transmitted electronically using email attachments, File Transfer Protocol (FTP), or other online file sharing services ( e.g., Dropbox, OneDrive, Google Drive). Electronic submissions must be transmitted directly to the Office of Air Quality Planning and Standards (OAQPS) CBI Office at the email address oaqpscbi@epa.gov, and as described above, should include clear CBI markings and note the docket ID. If assistance is needed with submitting large electronic files that exceed the file size limit for email attachments, and if you do not have your own file sharing service, please email oaqpscbi@epa.gov to request a file transfer link. If sending CBI information through the postal service, please send it to the following address: U.S. EPA, Attn: OAQPS Document Control Officer, Mail Drop: C404-02, 109 T.W. Alexander Drive, P.O. Box 12055, Research Triangle Park, North Carolina 27711, Attention Docket ID No. EPA-HQ-OAR-2024-0419. The mailed CBI material should be double wrapped and clearly marked. Any CBI markings should not show through the outer envelope. Preamble acronyms and abbreviations. Throughout this document the use of “we,” “us,” or “our” is intended to refer to the EPA. We use multiple acronyms and terms in this preamble. While this list may not be exhaustive, to ease the reading of this preamble and for reference purposes, the EPA defines the following terms and acronyms here: ANSI American National Standards Institute ASTM American Society for Testing and Materials BACT best achievable control technology BPT benefit-per-ton BSER best system of emission reduction Btu British thermal unit CAA Clean Air Act CBI Confidential Business Information CDX Central Data Exchange CEDRI Compliance and Emissions Data Reporting Interface CFR Code of Federal Regulations CHP combined heat and power CO carbon monoxide DLE dry low-emission DLN dry low NO X EGU electric generating unit EJ environmental justice EPA Environmental Protection Agency ERT Electronic Reporting Tool FR Federal Register FTP file transfer protocol GE General Electric GHG greenhouse gas GJ gigajoule(s) gr grains HAP hazardous air pollutant HHV higher heating value HRSG heat recovery steam generator ICR information collection request kW kilowatt LAER lowest achievable emission rate lb/MWh pounds per megawatt-hour lb/MMBtu pounds per million British thermal units mg/scm milligrams per standard cubic meter MJ megajoules MMBtu/h million British thermal units per hour MW megawatt MWh megawatt-hour NAICS North American Industry Classification System NEI National Emissions Inventory NESHAP national emission standards for hazardous air pollutants NETL National Energy Technology Laboratory ng/J nanograms per joule NO X nitrogen oxide NSPS new source performance standards NSR New Source Review NTTAA National Technology Transfer and Advancement Act O 2 oxygen O&M operating and maintenance OAQPS Office of Air Quality Planning and Standards OMB Office of Management and Budget PDF portable document format PM particulate matter PM 2.5 particulate matter (diameter less than or equal to 2.5 micrometers) ppm parts per million ppmv parts per million by volume ppmw parts per million by weight PRA Paperwork Reduction Act RACT reasonably available control technology RBLC RACT/BACT/LAER Clearinghouse RFA Regulatory Flexibility Act RIA regulatory impact analysis scf standard cubic feet scm standard cubic meter SCR selective catalytic reduction SO 2 sulfur dioxide SSM startup, shutdown, and malfunction ULSD ultra-low sulfur diesel UMRA Unfunded Mandates Reform Act U.S.C. United States Code VCS voluntary consensus standard VOC volatile organic compound(s) WFR water-to-fuel ratio Organization of this document. The information in this preamble is organized as follows: I. General Information A. Does this action apply to me? B. Where can I get a copy of this document and other related information? II. Background A. What is the statutory authority for this action? B. What is this source category? C. What are the current NSPS requirements? D. What data and information were used to support this action? E. What outreach and engagement did the EPA conduct? F. How did the EPA consider environmental justice in the development of this action? G. How does the EPA perform the NSPS review? H. 2012 NSPS Proposal III. What actions are we proposing? A. Applicability B. NO X Emission Standards C. SO 2 Emission Standards D. Consideration of Other Criteria Pollutants E. Additional Subpart KKKKa Proposals F. Additional Request for Comments G. Proposal of NSPS Subpart KKKKa Without Startup, Shutdown, Malfunction Exemptions H. Testing and Monitoring Requirements I. Electronic Reporting J. Compliance Dates K. Severability IV. Summary of Cost, Environmental, and Economic Impacts A. What are the air quality impacts? B. What are the secondary impacts? C. What are the cost impacts? D. What are the economic impacts? E. What are the benefits? F. What analysis of environmental justice did we conduct? V. Statutory and Executive Order Reviews A. Executive Order 12866: Regulatory Planning and Review and Executive Order 14094: Modernizing Regulatory Review B. Paperwork Reduction Act (PRA) C. Regulatory Flexibility Act (RFA) D. Unfunded Mandates Reform Act (UMRA) E. Executive Order 13132: Federalism F. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments G. Executive Order 13045: Protection of Children From Environmental Health Risks and Safety Risks H. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use I. National Technology Transfer and Advancement Act (NTTAA) and 1 CFR Part 51 J. Executive Order 12898: Federal Actions To Address Environmental Justice in Minority Populations and Low-Income Populations and Executive Order 14096: Revitalizing Our Nation's Commitment to Environmental Justice for All I. General Information A. Does this action apply to me? The source category that is the subject of this proposal is composed of any industry using a newly constructed, modified, or reconstructed stationary combustion turbine as defined in section II.B of this preamble and regulated under Clean Air Act (CAA) section 111, New Source Performance Standards. Based on the number of sources of stationary combustion turbines listed in the 2020 National Emissions Inventory (NEI), most, but not all, are accounted for by the following 2022 North American Industry Classification System (NAICS) codes. These include 221112 (Fossil Fuel Electric Power Generation), 486210 (Pipeline Transportation of Natural Gas), 22111 (Electric Power Generation), 211130 (Natural Gas Extraction), 221210 (Natural Gas Distribution), 325110 (Petrochemical Manufacturing), and 2111 (Oil and Gas Extraction). The NAICS codes serve as a guide for readers outlining the entities that this proposed action is likely to affect. Please see the accompanying Regulatory Impact Analysis (RIA) in the docket for this proposed rulemaking for a complete list of potentially affected sources and their NAICS codes. The proposed standards, once promulgated, will be directly applicable to affected facilities that begin construction, reconstruction, or modification after the date of publication of the proposed standards in the Federal Register . Federal, State, local, and Tribal government entities that own and/or operate stationary combustion turbines subject to existing 40 Code of Federal Regulations (CFR) part 60, subparts GG or KKKK, or proposed 40 CFR part 60, subpart KKKKa, may be affected by these proposed amendments and standards. B. Where can I get a copy of this document and other related information? In addition to being available in the docket, an electronic copy of this action is available via the internet at https://www.epa.gov/stationary-sources-air-pollution/stationary-gas-and-combustion-turbines-new-source-performance. Following publication in the Federal Register , the EPA will post the Federal Register version of the proposal and key technical documents at this same web page. In accordance with 5 U.S.C. 553(b)(4), a summary of this proposed rule may be found at Docket ID No. EPA-HQ-OAR-2024-0419 at https://www.regulations.gov. Memoranda showing the edits that would be necessary to incorporate the changes to 40 CFR part 60, subparts GG and KKKK and 40 CFR part 60, subpart KKKKa proposed in this action are available in the docket. Following signature by the EPA Administrator, the EPA also will post a copy of this document to https://www.epa.gov/stationary-sources-air-pollution/stationary-gas-and-combustion-turbines-new-source-performance. II. Background A. What is the statutory authority for this action? The EPA's authority for this proposed rule is CAA section 111, which governs the establishment of standards of performance for stationary sources. Section 111(b)(1)(A) of the CAA requires the EPA Administrator to list categories of stationary sources that in the Administrator's judgment cause or contribute significantly to air pollution that may reasonably be anticipated to endanger public health or welfare. The EPA must then issue performance standards for new (and modified or reconstructed) sources in each source category pursuant to CAA section 111(b)(1)(B). These standards are referred to as new source performance standards, or NSPS. The EPA has the authority to define the scope of the source categories, determine the pollutants for which standards should be developed, set the emission level of the standards, and distinguish among classes, types, and sizes within categories in establishing the standards. CAA section 111(b)(1)(B) requires the EPA to “at least every 8 years review and, if appropriate, revise” new source performance standards. However, the Administrator need not review any such standard if the “Administrator determines that such review is not appropriate in light of readily available information on the efficacy” of the standard. When conducting a review of an existing performance standard, the EPA has the discretion and authority to add emission limits for pollutants or emission sources not currently regulated for that source category. In setting or revising a performance standard, CAA section 111(a)(1) provides that performance standards are to reflect “the degree of emission limitation achievable through the application of the best system of emission reduction which (taking into account the cost of achieving such reduction and any nonair quality health and environmental impact and energy requirements) the Administrator determines has been adequately demonstrated.” The term “standard of performance” in CAA section 111(a)(1) makes clear that the EPA is to determine both the best system of emission reduction (BSER) for the regulated sources in the source category and the degree of emission limitation achievable through application of the BSER. The EPA must then, under CAA section 111(b)(1)(B), promulgate standards of performance for new sources that reflect that level of stringency. CAA section 111(b)(5) generally precludes the EPA from prescribing a particular technological system that must be used to comply with a standard of performance. Rather, sources can select any measure or combination of measures that will achieve the standard. Pursuant to the definition of new source in CAA section 111(a)(2), standards of performance apply to facilities that begin construction, reconstruction, or modification after the date of publication of the proposed standards in the Federal Register . Under CAA section 111(a)(4), “modification” means any physical change in, or change in the method of operation of, a stationary source which increases the amount of any air pollutant emitted by such source or which results in the emission of any air pollutant not previously emitted. Changes to an existing facility that do not result in an increase in emissions are not considered modifications. Under the provisions in 40 CFR 60.15, reconstruction means the replacement of components of an existing facility such that: (1) the fixed capital cost of the new components exceeds 50 percent of the fixed capital cost that would be required to construct a comparable entirely new facility; and (2) it is technologically and economically feasible to meet the applicable standards. Pursuant to CAA section 111(b)(1)(B), the standards of performance or revisions thereof shall become effective upon promulgation. B. What is this source category? Sources subject to the proposed NSPS are stationary combustion turbines with a design base load rating ( i.e., maximum heat input at ISO conditions) equal to or greater than 10.7 gigajoules per hour (GJ/h) (10 million British thermal units per hour (MMBtu/h)), 1 based on the higher heating value (HHV) of the fuel, that commence construction, modification, or reconstruction after December 13, 2024. A stationary combustion turbine is defined as all equipment, including but not limited to the combustion turbine; the fuel, air, lubrication, and exhaust gas systems; the control systems (except emission control equipment); the heat recovery system (including heat recovery steam generators (HRSG) and duct burners); and any ancillary components and sub-components comprising any simple cycle, regenerative/recuperative cycle, and combined cycle stationary combustion turbine, and any combined heat and power (CHP) stationary combustion turbine-based system. The source is “stationary” because the combustion turbine is not self-propelled or intended to be propelled while performing its function. It may, however, be mounted on a vehicle for portability. 1 The base load rating is based on the heat input to the combustion turbine engine. Any additional heat input from duct burners used with heat recovery steam generating (HRSG) units or fuel preheaters is not included in the heat input value used to determine the applicability of this subpart to a given stationary combustion turbine. However, this subpart does apply to emissions from any HRSG and duct burners that are associated with a combustion turbine subject to this subpart. C. What are the current NSPS requirements? The NSPS for stationary combustion turbines includes standards of performance to limit emissions of nitrogen oxide (NO X ) and sulfur dioxide (SO 2 ). The EPA last revised the NSPS on July 6, 2006, and promulgated 40 CFR part 60, subpart KKKK, which is applicable to stationary combustion turbines for which construction, modification, or reconstruction was commenced after February 18, 2005 (71 FR 38482). Standards of performance for the source category of stationary gas turbines were originally promulgated in 40 CFR part 60, subpart GG (44 FR 52792; September 10, 1979) and only apply to sources that were new prior to 2005. The NO X standards in subpart KKKK are based on the application of combustion controls (as the best system of emission reduction) and allow the turbine owner or operator the choice of meeting a concentration-based emission standard or an output-based emission standard. The concentration-based emission limits are in units of parts per million by volume dry (ppmvd) at 15 percent oxygen (O 2 ). 2 The output-based emission limits are in units of mass per unit of useful recovered energy, nanograms per Joule (ng/J) or pounds per megawatt-hour (lb/MWh). Each NO X limit in subpart KKKK is based on the application of combustion controls as the BSER, but individual standards may differ for individual subcategories of combustion turbines based on the following factors: the fuel input rating at base load, the fuel used, the application, the load, and the location of the turbine. The fuel input rating of the turbine does not include any supplemental fuel input to the heat recovery system and refers to the rating of the combustion turbine itself. 2 Throughout this document, all references to parts per million (ppm) NO X are intended to be interpreted as parts per million by volume dry (ppmvd) at 15 percent O 2 , unless otherwise noted. Specifically, in subpart KKKK, the EPA identifies 14 subcategories of stationary combustion turbines and establishes NO X emission limits for each. The current size-based subcategories include turbines with a design heat input rating of less than or equal to 50 MMBtu/h, those with a design heat input rating of greater than 50 MMBtu/h and less than or equal to 850 MMBtu/h, and those with a design heat input rating greater than 850 MMBtu/h. There are separate subcategories for combustion turbines operating at part load, for modified and reconstructed combustion turbines, heat recovery units operating independent of the combustion turbine, and turbines operating at low ambient temperatures. A specific NO X performance standard is identified for each of the 14 subcategories, and the limits range from 15 ppm to 150 ppm ( see Table 1: NO X Emission Standards; 71 FR 38483, July 6, 2006). The standards of performance for SO 2 emissions in subpart KKKK reflect the use of low-sulfur fuels. The fuel sulfur content limit is 26 ng SO 2 /J (0.060 lb SO 2 /MMBtu) heat input for combustion turbines located in continental areas and 180 ng SO 2 /J (0.42 lb SO 2 /MMBtu) heat input in noncontinental areas. This is approximately equivalent to 0.05 percent sulfur by weight (500 parts per million by weight (ppmw)) for fuel oil in continental areas and 0.4 percent sulfur by weight (4,000 ppmw) for fuel oil in noncontinental areas, respectively. Subpart KKKK also includes an optional output-based SO 2 standard that limits the discharge into the atmosphere of any gases that contain SO 2 in excess of 110 ng/J (0.90 lb/MWh) gross energy output for turbines located in continental areas and 780 ng/J (6.2 lb/MWh) gross energy output for turbines located in noncontinental areas. Thousands of stationary combustion turbines are operating across numerous industrial sectors. In the utility sector alone, there are approximately 3,400 existing stationary combustion turbines. 3 Each of these affected sources is subject to either subpart KKKK or subpart GG. 3 See the U.S. Environmental Protection Agency's (EPA) National Electric Energy Data System database. NEEDS rev 06-06-2024. Accessed at https://www.epa.gov/power-sector-modeling/national-electric-energy-data-system-needs. D. What data and information were used to support this action? The Agency analyzed hourly NO X emissions data reported to the EPA's Clean Air Markets Program Data (CAMPD) under 40 CFR part 75 and other data and information available in the Energy Information Administration's (EIA) and the EPA's databases. In addition, the Agency reviewed other available information sources to determine whether there have been developments in practices, processes, or control technologies by stationary combustion turbines. These include the following: • Air permit limits and selected compliance options from permits that were available online. Not all States provide online access to air permits, but the EPA was able to obtain and review State permits for approximately 70 stationary combustion turbines that are currently subject to subpart KKKK to inform the BSER technology review and obtain other relevant information about the source category, such as monitoring approaches applied. 4 4 See the Research Summary Memo in the docket for this rulemaking for a summary of the results from this State permit search. • Combustion turbine manufacturer specifications sheets for NO X and other criteria pollutant emissions for common combustion turbine makes and models. 5 5 See the Combustion Turbine Manufacturer Specsheet Memo in the docket for this rulemaking for a summary of the review of turbine manufacturers' specification sheets. • Communication with combustion turbine manufacturers, including Siemens, General Electric, Mitsubishi, and Solar Turbines. The Agency also communicated with the Gas Turbine Association (GTA), which represents industries in the affected NAICS categories and their members. Discussions focused on current combustion control technologies to reduce NO X emissions as well as the cost effectiveness of post-combustion SCR for certain sizes and models of turbines. • Search of the Agency's Reasonably Available Control Technology (RACT)/Best Available Control Technology (BACT)/Lowest Achievable Emission Rate (LAER) Clearinghouse (RBLC) database. 6 6 U.S. Environmental Protection Agency (EPA). RACT/BACT/LAER Clearinghouse (RBLC). Available at https://cfpub.epa.gov/rblc/. A variety of sources were used to compile a list of existing facilities constructed in the past 5 years that are subject to subpart KKKK. That list was used to estimate the approximate number of new sources that may be subject to this proposed rulemaking. The list was based on data collected from Form EIA-860, 7 the EPA's National Electric Energy Data System (NEEDS) database, 8 and information collected during the Agency's ongoing work to review the National Emission Standards for Hazardous Air Pollutants (NESHAP) for combustion turbines under 40 CFR part 63, subpart YYYY. Form EIA-860 contains information about currently operating and planned individual electric generators, which includes their location, prime mover, and capacity. NEEDS is an EPA database of electric generators that serves as a resource for modeling the sector. NEEDS includes source information about existing and planned units, information about the combustion turbines themselves, and data about their air emission controls. The list of sources compiled for the EPA's review of the NESHAP only includes combustion turbines that are located at major sources of toxic air emissions. These source lists are included in the docket for this proposal. 7 U.S. Energy Information Administration (EIA). (June 12, 2024). Form EIA-860 data. Available at https://www.eia.gov/electricity/data/eia860/. 8 See the U.S. Environmental Protection Agency's (EPA) National Electric Energy Data System database. NEEDS rev 06-06-2024. Accessed at https://www.epa.gov/power-sector-modeling/national-electric-energy-data-system-needs. E. What outreach and engagement did the EPA conduct? As part of this rulemaking, the EPA engaged and consulted with the public, including communities with environmental justice (EJ) concerns, and industry representatives, through several interactions. The EPA opened a non-regulatory docket 9 and posted framing questions intended to solicit specific public input about ways the Agency could design a broad approach to the regulation of greenhouse gases (GHGs) and other air pollutants from combustion turbines under CAA sections 111 and 112 that protects human health and the environment. Several stakeholders posted comments to the non-regulatory docket pertaining to the review of the NSPS and subpart KKKK. Those comments were reviewed as part of this proposed action. 9 See EPA-HQ-OAR-2024-0135, available at https://www.regulations.gov. The EPA also held a public policy forum on May 17, 2024, at the EPA headquarters in Washington, DC. The forum included a series of panels and interactive discussion sessions that provided an opportunity for the Agency to hear a broad range of views and exchange of ideas concerning upcoming proposed regulations impacting air pollution emissions from stationary combustion turbines. Although the focus of the public policy forum was to discuss the regulation of GHG emissions from stationary combustion turbines in the power sector, there was also some discussion of the 8-year review of the NSPS and standards of performance for criteria pollutant emissions, such as NO X . The forum included a wide range of stakeholders as members of panel discussions, as part of the in-person audience and attending virtually. Key groups represented included: State and local air agencies, Tribal Nations, affected companies, representatives of the EJ community, technology vendors, environmental non-governmental organizations, and electric reliability organizations and industry trade groups. The EPA also consulted with representatives of State and local governments in the process of developing this action to permit them to have meaningful and timely input into their development. The EPA invited the following 10 national organizations representing State and local elected officials to a virtual meeting on August 15, 2024: (1) National Governors Association; (2) National Conference of State Legislatures; (3) Council of State Governments; (4) National League of Cities; (5) U.S. Conference of Mayors; (6) National Association of Counties; (7) International City/County Management Association; (8) National Association of Towns and Townships; (9) County Executives of America; and (10) Environmental Council of States. Also, the EPA invited air and utility professional groups who may have State and local government members, including the Association of Air Pollution Control Agencies; National Association of Clean Air Agencies; American Public Power Association; Large Public Power Council; National Rural Electric Cooperative Association; National Association of Regulatory Utility Commissioners; and National Association of State Energy Officials to participate in the meeting. The purpose of the consultation was to provide general background on the rulemaking, answer questions, and solicit input from State and local governments. The EPA has also engaged with major combustion turbine manufacturers such as Siemens, General Electric, Mitsubishi, and Solar Turbines, as well as with industry trade groups such as the Gas Turbine Association (GTA), for assistance with some of the data collection efforts previously identified in section II.D. Specifically, this included updates on any technology developments and cost estimates that would impact turbine performance and/or criteria pollutant emissions for most new models of available combustion turbines. F. How did the EPA consider environmental justice in the development of this action? Consistent with applicable Executive orders and EPA policy, the Agency carefully considered the potential implications of this proposed action on communities with EJ concerns. As part of the regulatory development process for this rulemaking, and consistent with feedback we received during the development of the final New Source Performance Standards for Greenhouse Gas Emissions From New, Modified, and Reconstructed Fossil Fuel-Fired Electric Generating Units; Emission Guidelines for Greenhouse Gas Emissions From Existing Fossil Fuel-Fired Electric Generating Units; and Repeal of the Affordable Clean Energy Rule ( i.e., the Carbon Pollution Standards), 10 the EPA continued its outreach with interested parties, including communities with EJ concerns. These opportunities gave the EPA a chance to hear directly from the public, including from communities potentially impacted by this proposed rule. The EPA took this feedback into account in the development of this proposal. 10 See 89 FR 39798; May 9, 2024. The EPA's examination of potential EJ concerns in this proposed rule includes a proximity demographic analysis for 130 existing facilities that are currently subject to NSPS subpart KKKK. This represents facilities that might modify or reconstruct in the future and become subject to the proposed requirements in new subpart KKKKa. The locations of newly constructed sources that will become subject to subpart KKKKa are not known, thus, we are limited in our ability to estimate the potential EJ impacts of this rulemaking. As discussed in detail in section IV.F of this preamble, the results of the proximity demographic analysis indicate that the percent of population that is Black, Hispanic/Latino, or Asian living within 50 kilometers (km) of existing facilities with stationary combustion turbines is above the national average. In addition, the percent of population living within 50 km of existing facilities with stationary combustion turbines is also above the national average for linguistic isolation and people with one or more disabilities. Furthermore, within 5 km of the existing facilities with stationary combustion turbines, the percent of population is above the national average for people living below the poverty level and people living below two times the poverty level. However, for the areas located downwind of any stationary combustion turbines that may be covered by new subpart KKKKa, we anticipate the proposed changes to the NSPS will generally reduce the potential emission impacts, in particular NO X emissions. Specifically, for most subcategories of new, modified, and reconstructed stationary combustion turbines, the EPA is proposing combustion controls with SCR as the BSER and, accordingly, is proposing more protective NO X standards of performance for affected sources based on the application of SCR post-combustion control technology and updated information on combustion control efficacy. Although this proposed rule does not preclude the construction of new combustion turbines, and emissions may increase as a result of increased operation of newly-constructed capacity, this proposed rule, if finalized, would ensure that any additional NO X emissions from certain affected sources are reduced to a level consistent with the application of state-of-the-art control technology. Any source that commences construction, modification, or reconstruction after the date of publication of this proposal will be subject to the standards of performance that are ultimately finalized. Further, frontline communities have consistently raised concerns about increases in NO X emissions from newly constructed stationary combustion turbines that plan to co-fire with hydrogen. 11 This proposed rule, when finalized, will help address those concerns by establishing more protective NO X standards for stationary combustion turbines that plan to co-fire hydrogen. 11 See, for example, Docket ID No. EPA-HQ-OAR-2023-0072-0470, Docket ID No. EPA-HQ-OAR-2023-0072-0527, Docket ID No. EPA-HQ-OAR-2023-0072-0658, Docket ID No. EPA-HQ-OAR-2024-0135-0080, and Docket ID No. EPA-HQ-OAR-2024-0135-0114. Additionally, sources that install stationary combustion turbines that meet the applicability of NSPS subpart KKKKa will likely be subject to the New Source Review (NSR) preconstruction permitting program and, more specifically, the requirements of the “major NSR” program. Major NSR permitting requirements can offer protections for communities that are near sources that will experience an increase in NO X and other emissions resulting from the installation and operation of new, modified, or reconstructed stationary combustion turbines. Under the major NSR program, the permitting requirements that apply to a source depend on the air quality designation at the location of the source for each of its emitted pollutants at the time the permit is issued. Major NSR permits for sources located in an area that is designated as attainment or unclassifiable for the National Ambient Air Quality Standards (NAAQS) for its pollutants are referred to as Prevention of Significant Deterioration (PSD) permits. Sources subject to PSD must, among other requirements, comply with emission limitations that reflect the Best Available Control Technology (BACT) for “each pollutant subject to regulation” 12 as specified by CAA sections 165(a)(4) and 169(3) and demonstrate through dispersion modeling techniques that the emissions from the project will not cause or contribute to a violation of the NAAQS or “PSD increments.” 13 Sources can often make this air quality demonstration based on the BACT level of control or, in some cases, may need to accept more stringent air quality-based limitations to model compliance with the ambient standards. Major NSR permits for sources located in nonattainment areas and that emit at or above the specified major NSR threshold for the pollutant for which the area is designated as nonattainment are referred to as Nonattainment NSR (NNSR) permits. Sources subject to NNSR must, among other requirements, meet the Lowest Achievable Emission Rate (LAER) pursuant to CAA sections 171(3) and 173(a)(2) for any pollutant subject to NNSR and must obtain emission “offsets” ( i.e., creditable decreases in emissions) from other sources in the area to compensate for the expected emission increases caused by the new source or modification. These required elements of PSD and NNSR permits can serve to further reduce potential emission impacts from stationary combustion turbines beyond the levels that would be required by the proposed changes to NSPS subpart KKKKa. 12 For the PSD program, “regulated NSR pollutant” includes any criteria air pollutant and any other air pollutant that meets the requirements of 40 CFR 52.21(b)(50). Some of these non-criteria pollutants include greenhouse gases, fluorides, sulfuric acid mist, hydrogen sulfide, and total reduced sulfur. 13 PSD increments are margins of “significant” air quality deterioration above a baseline concentration that establish an air quality ceiling, typically below the NAAQS, for each PSD area. With respect to consideration of specific EJ concerns within the NSR permitting procedures, when the EPA is the issuing authority for the major NSR permit, it has legal authority to consider potential disproportionate environmental burdens on a case-by-case basis, taking into account case-specific factors germane to any individual permit decision. Although the minimum requirements for an approvable State NSR permitting program do not require the permitting authorities to reflect EJ considerations in their permitting decisions, States that implement NSR programs under an EPA-approved State implementation plan (SIP) have discretion to consider EJ in their NSR permitting actions and adopt additional requirements in the permitting decision to address potential disproportionate environmental burdens. Also, the NSR permit review process provides the discretion for permitting authorities to provide enhanced engagement for communities with EJ concerns. This includes opportunities to enhance EJ by facilitating increased public participation in the formal permit consideration process ( e.g., by granting requests to extend public comment periods, holding multiple public meetings, or providing translation services at hearings in areas with limited English proficiency) and taking informal steps to enhance participation earlier in the process, such as inviting community groups to meet with the permitting authority and express their concerns before a draft permit is developed. G. How does the EPA perform the NSPS review? As noted in section II of this preamble, CAA section 111 requires the EPA to, at least every 8 years, review and, if appropriate, revise the standards of performance applicable to new, modified, and reconstructed sources. If the EPA revises the standards of performance, those standards must reflect the degree of emission limitation achievable through the application of the BSER considering the cost of achieving such reduction and any non-air quality health and environmental impact and energy requirements. CAA section 111(a)(1). Section 111 of the CAA requires the EPA to consider a number of factors, including cost, in determining “the best system of emission reduction . . . adequately demonstrated.” CAA section 111(a)(1). The D.C. Circuit has long recognized that “[CAA] section 111 does not set forth the weight that [ ] should [be] assigned to each of these factors;” therefore, “[the court has] granted the agency a great degree of discretion in balancing them.” Lignite Energy Council v. EPA, 198 F.3d 930, 933 (D.C. Cir. 1999). In reviewing an NSPS to determine whether it is “appropriate” to revise the standards of performance, the EPA evaluates the statutory factors identified in the paragraphs above, which may include consideration of the following information: • Expected growth for the source category, including how many new facilities, reconstructions, and modifications may trigger NSPS in the future. • Pollution control measures, including advances in control technologies, process operations, design or efficiency improvements, or other systems of emission reduction, that are “adequately demonstrated” in the regulated industry. • Available information from the implementation and enforcement of current requirements indicating that emission limitations and percent reductions beyond those required by the current standards are achieved in practice. • Costs (including capital and annual costs) associated with implementation of the available pollution control measures. • The amount of emission reductions achievable through application of such pollution control measures. • Any non-air quality health and environmental impact and energy requirements associated with those control measures. The courts have recognized that the EPA has “considerable discretion under [CAA] section 111,” id., on how it considers cost under CAA section 111(a)(1). In evaluating whether the cost of a particular system of emission reduction is reasonable, the EPA considers various costs associated with the particular air pollution control measure or a level of control, including capital costs and operating costs, and the emission reductions that the control measure or particular level of control can achieve. The Agency considers these costs in the context of the industry's overall capital expenditures and revenues. The Agency also considers cost effectiveness analysis as a useful metric and a means of evaluating whether a given control achieves emission reduction at a reasonable cost. A cost effectiveness analysis allows comparisons of relative costs and outcomes (effects) of two or more options. In general, cost effectiveness is a measure of the outcomes produced by resources spent. In the context of air pollution control options, cost effectiveness typically refers to the annualized cost of implementing an air pollution control option divided by the amount of pollutant reductions realized annually. Notably, a cost effectiveness analysis is not intended to constitute or approximate a benefit-cost analysis in which monetized benefits are compared to costs, but rather is intended to provide a metric to compare the relative cost of emissions reductions. The statute does not identify a specific way in which the EPA is to assess cost, and the Agency does not apply a brightline test in determining what level of cost is reasonable. Rather, in evaluating whether the cost of a control is reasonable, the EPA typically has considered cost effectiveness along with various associated cost metrics, such as capital costs and operating costs, total costs, costs as a percentage of capital for a new facility, and the cost per unit of production. In addition, other factors identified in CAA section 111(a) may bear on the EPA's evaluation of cost. For instance, if there is evidence of use of a technology across many of the recently constructed sources in a particular category, such evidence would provide a powerful indication that the cost of that technology is reasonable, or at a minimum, is not excessive. See, e.g., 89 FR 16820, 16864-65; March 8, 2024. After the EPA evaluates the statutory factors, the EPA compares the various systems of emission reductions and determines which system is “best” and therefore represents the BSER. The EPA then establishes a standard of performance that reflects the degree of emission limitation achievable through the implementation of the BSER. In performing this analysis, the EPA can determine whether subcategorization is appropriate based on classes, types, and sizes of sources and may identify a different BSER and establish different performance standards for each subcategory. The result of the analysis and BSER determination leads to standards of performance that apply to facilities that begin construction, modification, or reconstruction after the date of publication of the proposed standards in the Federal Register . Because the NSPS reflect the BSER under conditions of proper operation and maintenance, in doing its review, the EPA also evaluates and determines the proper testing, monitoring, recordkeeping, and reporting requirements needed to ensure compliance with the emission standards. H. 2012 NSPS Proposal On September 5, 2006, a petition for reconsideration of the revised NSPS was filed by the Utility Air Regulatory Group (UARG). The EPA granted reconsideration of subpart KKKK, and, on August 29, 2012, proposed to amend subpart KKKK as well as the original NSPS, subpart GG of 40 CFR part 60. See 77 FR 52554 (2012 NSPS Proposal). The proposed rulemaking addressed specific issues identified by the petitioners as well as other technical and editorial issues. Specifically, the EPA proposed to clarify the intent in applying and implementing specific rule requirements, to correct unintentional technical omissions and editorial errors, and address various other issues that were identified since promulgation of subpart KKKK. The EPA has not taken further action on this proposed rule, and, in this action, proposes in the following section to include applicable clarifications and technical corrections in new subpart KKKKa. III. What actions are we proposing? A. Applicability The source category that is the subject of this proposed action is composed of new stationary combustion turbines with a base load rating (maximum heat input of the combustion turbine engine at ISO conditions) of greater than 10 MMBtu/h of heat input. 14 The standards of performance, proposed to be codified in 40 CFR part 60, subpart KKKKa, once promulgated, would be directly applicable to affected sources that begin construction, modification, or reconstruction after the date of publication of the proposed standards in the Federal Register . The applicability of sources that would be subject to proposed subpart KKKKa is similar to that for sources subject to existing 40 CFR part 60, subpart KKKK. The proposed amendments to subparts GG and KKKK, once promulgated, would be directly applicable to the affected facilities already subject to those subparts. Stationary combustion turbines subject to the proposed standards in new subpart KKKKa would not be subject to the requirements of subparts GG or KKKK. The HRSG and duct burners subject to the proposed standards in subpart KKKKa would be exempt from the requirements of 40 CFR part 60, subpart Da (the Utility Boiler NSPS) as well as subparts Db and Dc (the Industrial/Commercial/Institutional Boiler NSPS), continuing the approach previously established in subpart KKKK. 14 The EPA uses the higher heating value (HHV) when specifying heat input ratings. Proposed subpart KKKKa maintains the NO X exemptions promulgated previously in subparts GG and KKKK. In 1977, in subpart GG, the EPA determined that it was appropriate to exempt emergency combustion turbines from the NO X limits. These included emergency-standby combustion turbines, military combustion turbines, and firefighting combustion turbines. Subpart KKKK further defines emergency combustion turbines as units that operate in emergency situations, such as turbines that supply electric power when the local utility service is interrupted. Additional exemptions in subpart KKKK include (1) stationary combustion turbine test cells/stands, (2) integrated gasification combined cycle (IGCC) combustion turbine facilities covered by subpart Da of 40 CFR part 60 (the Utility Boiler NSPS), and (3) stationary combustion turbines that, as determined by the Administrator or delegated authority, are used exclusively for the research and development of control techniques and/or efficiency improvements relevant to stationary combustion turbine emissions. 1. Revisions to 40 CFR Part 60, Subpart GG and 40 CFR Part 60, Subpart KKKK That Would Also Be Included in 40 CFR Part 60, Subpart KKKKa The EPA is proposing to make two revisions to subparts GG and KKKK that also are proposed to be included in a new subpart KKKKa. Therefore, revised subparts GG and KKKK use similar regulatory text as subpart KKKKa except where specifically stated. This section describes provisions that would be included in all three subparts. The proposed amendments also include updating 40 CFR 60.17 (incorporations by reference) to include additional test methods identified in subpart KKKKa and revising the wording and writing style to clarify the requirements of the NSPS. The Agency does not intend for these editorial revisions to substantively change any of the technical requirements of the existing subparts GG and KKKK. To the extent that the EPA determines that the revisions do have unintended substantive effects, corrections will be made in the final action on the proposed rule. a. Exemptions for Combustion Turbines Subject to More Stringent Standards The EPA is proposing that stationary combustion turbines at petroleum refineries subject to subparts J or Ja of 40 CFR part 60 are not subject to the SO 2 performance standards in subparts GG, KKKK, or those proposed in new subpart KKKKa. The SO 2 standards in subparts J and Ja are more stringent than the SO 2 limits currently in subparts GG, KKKK, or proposed to be included in new subpart KKKKa. This proposed action would simplify compliance for owners or operators of petroleum refineries without an increase in pollutant emissions. The EPA is soliciting comment on whether there are additional source categories of facilities with stationary combustion turbines that are subject to more stringent NSPS that should not be subject to the SO 2 and/or NO X standards in subparts GG, KKKK, or those proposed to be included in new subpart KKKKa. b. Owners/Operators of Combustion Turbines Subject to 40 CFR Part 60, Subpart GG or 40 CFR Part 60, Subpart KKKK Can Petition To Comply With 40 CFR Part 60, Subpart KKKKa The EPA is proposing to allow owners or operators of stationary combustion turbines currently covered by subparts GG or KKKK, and any associated steam generating unit subject to an NSPS, to have the option to petition the Administrator to comply with subpart KKKKa in lieu of complying with subparts GG, KKKK, and any associated steam generating unit NSPS. Since the applicability of subpart KKKKa encompasses any associated heat recovery equipment, owners or operators would have the flexibility to comply with one NSPS instead of multiple NSPS. The Administrator will only grant the petition if they determine that compliance with subpart KKKKa would be equivalent to, or more stringent than, compliance with subparts GG, KKKK, or any associated steam generating unit NSPS. Also, the EPA is clarifying that if any solid fuel as defined in new proposed subpart KKKKa is burned in the HRSG, the HRSG would be covered by the applicable steam generating unit NSPS and not subpart KKKKa. The EPA is not aware of any existing stationary combustion turbines subject to subparts GG or KKKK that burn solid fuel in the HRSG, but the intent of this amendment is to cover only liquid and gaseous fuels. The amendment would prevent a large solid fuel-fired boiler from using the exhaust from a combustion turbine engine to avoid the requirements of the applicable steam generating unit NSPS. 2. Applicability of 40 CFR Part 60, Subpart KKKKa That Is Different From the Applicability of 40 CFR Part 60, Subpart KKKK This section describes applicability provisions proposed in new subpart KKKKa that are different from the applicability provisions in existing subpart KKKK. a. Clarification to Definition of Stationary Combustion Turbine The combustion turbine engine ( i.e., the air compressor, combustor, and turbine sections) is the primary source of emissions from a stationary combustion turbine. In subpart KKKK, the definition of the affected source includes the HRSG and associated duct burners at combined cycle and CHP facilities. See 71 FR 38483; July 6, 2006. This means that the replacement of only the combustion turbine portion of a combined cycle or CHP facility may not constitute a new affected facility. This also means the cost to replace only the combustion turbine engine portion at an existing combined cycle or CHP facility may not constitute most of the costs compared to the replacement of the combustion turbine engine portion and the HRSG portion. This, in turn, is relevant to determining whether an affected source has “reconstructed” because, in general, a reconstructed facility is one that has had components replaced to the extent that the fixed capital costs of the new components exceed 50 percent of the fixed capital costs that would be required to construct a comparable entirely new facility. See 40 CFR 60.15. When the definition of an affected facility was expanded in subpart KKKK, it was not the intent of the EPA to change the determination of whether an existing combustion turbine is “new” or “reconstructed.” The EPA is proposing that it is appropriate that owners or operators of combined cycle and CHP facilities that entirely replace or undertake major capital investments in the combustion turbine engine portion of the facility invest in emissions control equipment as well. In new subpart KKKKa, the EPA is proposing to maintain the definition of the affected source that was promulgated in subpart KKKK. However, to clarify the applicability of this definition when determining whether an existing combustion turbine engine should be considered to be “new” or “reconstructed,” the EPA is proposing to amend the rule language in new subpart KKKKa. The new language would clarify that the test for determining if an affected facility is a new source would be based on whether the combustion turbine portion of the affected facility is entirely replaced. The reconstruction applicability determination would be based on whether the fixed capital costs of the replacement of components of the combustion turbine engine portion exceed 50 percent of the fixed capital costs that would be required to install only a comparable new combustion turbine engine portion of the affected facility. The purpose of the 50 percent cost threshold is to ensure that sources that undertake sufficiently large capital investments as to effectively be “new” sources are required to invest in emissions controls as well, and do not avoid performance standards that would otherwise apply to new sources. In the case of a stationary combustion turbine, which is the regulated source for this source category, a capital investment that amounts to 50 percent of the replacement cost of the combustion turbine engine portion itself is sufficiently major as to make it appropriate to require the owner or operator to invest in emissions controls to meet the requirements in subpart KKKKa. This approach would not consider the costs to replace the HRSG (or its components) when only components of the combustion turbine engine portion are being replaced. This approach to applying the definition of a reconstructed source would ensure that if an existing combined cycle or CHP facility replaces only the combustion turbine engine portion (or its components), then only the replaced portion ( i.e., the combustor) would be considered in a cost analysis to determine whether the source is reconstructed and thus subject to the NSPS performance standards in subpart KKKKa. For example, if a combined cycle turbine engine is replaced at an existing facility subject to subpart KKKK while the HRSG (or its components) is not replaced, then the cost to replace only the combined cycle turbine engine portion would be considered in the applicability determination. If the new turbine engine is determined to be a reconstructed source, then it would be subject to the proposed performance standards for reconstructed combustion turbines in subpart KKKKa. The HRSG at this hypothetical facility would also become subject to subpart KKKKa. It would make no practical difference for a HRSG to remain subject to subpart KKKK while the turbine becomes subject to subpart KKKKa, because the EPA is proposing to maintain the same treatment of the HRSG as in subpart KKKK. In addition, compliance with subpart KKKKa would be minimally impacted by any potential reconstruction of the HRSG. Since the proposed standards in subpart KKKKa are input-based, with optional alternative output-based standards, the efficiency of the HRSG is not essential for demonstrating compliance. Further, the presence of duct burners should not significantly impact the emissions rate since low NO X natural gas-fired duct burners typically contribute 15 ppm to 25 ppm NO X corrected to 15 percent O 2 , and ultra-low NO X duct burners are available that contribute approximately 3 ppm NO X corrected to 15 percent O 2 . Under this approach, the replacement or addition of a new combustion turbine engine to a facility while retaining the existing HRSG would be considered a reconstruction, resulting in the applicability of subpart KKKKa. Likewise, the replacement or addition of a HRSG associated with a combustion turbine engine covered by subparts KKKK or GG would not result in the entire facility being subject to subpart KKKKa. Nonetheless, the Agency emphasizes that this treatment only concerns the meaning of “new” and “reconstruction” for purposes of subpart KKKKa; existing facilities making physical or operational changes must separately evaluate whether those changes constitute “modification” under 40 CFR 60.14 and thereby become subject to subpart KKKKa as a modified source. 15 See sections III.B.4 of this preamble for discussion of the EPA's proposed approach for subcategorization and section III.B.12 for discussion of the proposed emission standards in subpart KKKKa. 15 The EPA proposed a similar approach to reconstruction for subpart KKKK in the 2012 NSPS Proposal. The Agency is not finalizing this change in subpart KKKK and is not altering the approach to reconstruction for purposes of determining the applicability of that subpart. Nonetheless, all existing sources that engage in reconstruction or modification after the date of this proposal would thereby become subject to subpart KKKKa and sources that meet the proposed new or reconstruction test under subpart KKKKa, if finalized, would be subject to subpart KKKKa and would no longer be subject to subpart KKKK. B. NO X Emission Standards 1. Overview This section discusses and proposes requirements for stationary combustion turbines that commence construction, modification, or reconstruction after December 13, 2024. The EPA is proposing that these requirements will be codified in 40 CFR part 60, subpart KKKKa. The EPA explains in section III.B.2 how NO X formation occurs when fuel is burned in a stationary combustion turbine. Section III.B.3 discusses the subcategories the EPA promulgated in subpart KKKK as compared to the subcategory approach being proposed in new subpart KKKKa. Notably, in section III.B.4, the EPA is proposing size-based subcategories that reflect our consideration of the performance of different combustion turbine designs and current NO X control technologies. The proposed BSER for control of NO X emissions for each proposed subcategory of combustion turbines is discussed in sections III.B.7 through III.B.11, and the application of a particular BSER corresponds to the NO X performance standards proposed in section III.B.12. The EPA's determination of the subcategories, BSER, and NO X standards in this action considers multiple factors. These include whether the size of a new, modified, or reconstructed stationary combustion turbine is small, medium, or large ( i.e., base load); whether the affected source would operate at high or low hourly duty cycles; whether the affected source would operate at low, intermediate, or high annual capacity factors; and whether the affected source would burn natural gas, non-natural gas (such as distillate fuels), hydrogen, or a combination of the three. As mentioned previously, in section III.B.7, the EPA describes the NO X emission control technologies it evaluated as part of its review of the NSPS. These include dry combustion controls ( e.g., lean premix/dry low NO X (DLN) systems), wet combustion controls ( e.g., water or steam injection), and post-combustion selective catalytic reduction (SCR). This is followed by a discussion of the EPA's proposed determination of the BSER for each of the subcategories of combustion turbines. To summarize the EPA's proposed BSER determinations for NO X : In general, the EPA is proposing that combustion controls with the addition of post-combustion SCR is the BSER for combustion turbines in the small, medium, and large subcategories. Since subpart KKKK was promulgated in 2006, it has become clear that SCR technology is a widely available and frequently adopted NO X emissions control strategy for a wide range of sizes and types of combustion turbines. In general, and as described in more detail in the sections that follow, the EPA finds that SCR is adequately demonstrated for this source category, is generally cost-effective, and satisfies the other statutory criteria under CAA section 111(a)(1). However, the Agency also recognizes that as the size of a combustion turbine diminishes and/or as the level of operation of a combustion turbine diminishes or becomes more variable, the cost-effectiveness on a per-ton basis and efficacy of SCR technology also diminishes. Thus, at smaller sizes and at lower operating levels, the EPA proposes to establish standards that are based on the use of combustion controls without SCR. Specifically, for small combustion turbines ( i.e., those that have a base load heat input rating of less than or equal to 250 MMBtu/h) that operate at an annual capacity factor 16 less than or equal to 40 percent ( i.e., low and intermediate load combustion turbines), the EPA is proposing that the use of combustion controls alone remains the BSER. For medium combustion turbines ( i.e., those that have a base load heat input rating of greater than 250 MMBtu/h but less than or equal to 850 MMBtu/h) that operate at capacity factors less than or equal to 20 percent ( i.e., low load combustion turbines), the EPA is proposing that combustion controls alone remain the BSER. Likewise, for large combustion turbines ( i.e., those that have a base load heat input rating of greater than 850 MMBtu/h) that operate at capacity factors less than or equal to 20 percent ( i.e., low load combustion turbines), the EPA is proposing that the use of combustion controls alone remains the BSER. 16 Capacity factor is a ratio that measures how often a stationary combustion turbine is operating at its maximum rated heat input. The ratio is based on heat input, or actual heat input, compared to the base load rating, or potential maximum heat input, under specified conditions. As discussed in further detail in the sections that follow, the EPA is requesting comment on several alternative approaches to determining the BSER and appropriate NO X emission standards, particularly for small combustion turbines ( i.e., those that have a base load heat input rating of less than or equal to 250 MMBtu/h). Also, the EPA is taking comment on different ways of defining the size and capacity factor thresholds for establishing the subcategories described in this proposal. In section III.B.13, the EPA explains the proposed BSER and NO X emission standards for modified sources. The EPA is proposing in new subpart KKKKa that the BSER and NO X emission standards for modified stationary combustion turbines are the same as those for certain corresponding new and reconstructed subcategories. For other subcategories, the proposed BSER and NO X emission stanards for modified sources are different. Furthermore, in section III.B.14, the EPA explains its proposed approach to characterize new, modified, and reconstructed stationary combustion turbines that elect to co-fire with a percentage blend of hydrogen (by volume) as either natural gas-fired or non-natural gas-fired sources. Depending on whether the combustion turbine co-fires more or less than 30 percent hydrogen (by volume), it is proposed to be subject to the same BSER and NO X performance standards applicable to either natural gas-fired or non-natural gas-fired combustion turbines in the same size-based subcategory. This section also includes a discussion of the technologies the EPA is proposing as BSER for each of the non-natural gas subcategories and the basis for proposing those controls, and not others, as the BSER. 2. NO X Formation Nitrogen oxides (NO X ) are a group of gases that are produced by stationary combustion turbines when fuel is burned at high temperatures. These gases are a mixture of nitric oxide (NO) and nitrogen dioxide (NO 2 ) and play a major role as precursor pollutants in atmospheric reactions with volatile organic compounds (VOC) that produce ozone ( i.e., smog), particularly on hot summer days. As a precursor pollutant, NO X also reacts with water, oxygen, and other chemicals in the air to form particulate matter (PM) and contributes to acid deposition. NO X is also a criteria pollutant for which there are National Ambient Air Quality Standards (NAAQS). The NAAQS for NO X include a 1-hour standard at a level of 100 parts per billion (ppb) based on the 3-year average of the 98th percentile of the yearly distribution of 1-hour daily maximum concentrations, and an annual standard at a level of 53 ppb. 17 The direct health effects of NO X are primarily respiratory effects, including irritation of the eyes, nose, throat, and lungs. Exposure to low levels of NO X can lead to fluid build-up in the lungs. Inhalation of high levels of NO X can lead to burning, spasms, and swelling of tissues in the throat and upper respiratory tract, reduced oxygenation of the body tissues, and build-up of fluid in the lungs, and death. 18 Elevated concentrations of NO 2 can exacerbate asthma in the short term and may contribute to asthma development in the long term. People with asthma, as well as children and the elderly, are generally at greater risk for the health effects of NO 2 . 19 17 U.S. Environmental Protection Agency (EPA). Nitrogen Dioxide (NO 2 ) Pollution. Available at https://www.epa.gov/no2-pollution/primary-national-ambient-air-quality-standards-naaqs-nitrogen-dioxide. 18 Agency for Toxic Substances and Disease Registry (ATSDR). (March 25, 2014). ToxFAQs for Nitrogen Oxides. Toxic Substances Portal fact sheet. Available at https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsDetails.aspx?faqid=396&toxid=69. 19 U.S. Environmental Protection Agency (EPA). Nitrogen Dioxide (NO 2 ) Pollution. Available at https://www.epa.gov/no2-pollution/basic-information-about-no2#Effects. In addition, environmental effects of NO X pollution include adverse effects on foliage, and, via nitrogen deposition, effects on ecosystems, such as the acidification of aquatic and terrestrial ecosystems and nutrient enrichment. Total NO X emissions are a function of thermal and organic ( i.e., fuel) NO X . Thermal NO X is formed in a well-defined, high-temperature reaction between nitrogen and oxygen from the combustion air. Meanwhile, organic NO X is formed from fuel-bound nitrogen that reacts with oxygen in the combustion chamber. Thermal NO X accounts for the majority of NO X emitted by stationary combustion turbines because natural gas typically does not have a high nitrogen composition. 20 As discussed in more detail below, dry and wet combustion controls reduce the peak flame temperatures, thus limiting NO X emissions, while SCR technology catalytically promotes the conversion of NO X to nitrogen gas (N 2 ) in the exhaust gases of stationary combustion turbines. 20 Our BSER analysis focuses on traditional turbines where the fuel is combusted in air. There is at least one vendor developing new turbines where the fuel is combusted in pure oxygen. In that case, there would be no thermal NO X formed in the combustion process. 3. Subcategorization Approach and NO X Emission Standards in 40 CFR Part 60, Subpart KKKK In subpart KKKK, the EPA lists 14 subcategories of stationary combustion turbines and identifies NO X standards for affected sources in each subcategory based on the application of dry or wet NO X combustion controls. The size-based subcategories include combustion turbines with base load ratings of less than or equal to 50 MMBtu/h of heat input, those with base load ratings greater than 50 MMBtu/h of heat input and less than or equal to 850 MMBtu/h, and those with base load ratings greater than 850 MMBtu/h of heat input. These subcategories are based on the rating of the turbine engine, do not include any supplemental fuel input to the heat recovery system, and are consistent with combustion control technologies (and manufacturer guarantees) available at the time that subpart KKKK was promulgated for different size combustion turbines. Within each size-based subcategory there are individual NO X standards based on whether the combustion turbine is burning natural gas or non-natural gas fuels and reflect the availability of wet or dry low NO X combustion controls for different fuels. There are also separate subcategories in subpart KKKK for modified and reconstructed stationary combustion turbines (reflecting more limited availability of combustion controls); heat recovery units operating independent of the combustion turbine (reflecting the emissions rate of a boiler); combustion turbines operating at part load or operating at low ambient temperatures (or north of the Arctic Circle); and offshore turbines (reflecting the ability of combustion controls to operate under these conditions). See Table 1: NO X Emission Standards (71 FR 38483; July 6, 2006). The NO X standards within these 14 subcategories in subpart KKKK are as low as 15 ppm for combustion turbines firing natural gas with a design heat input rating of greater than 850 MMBtu/h and as high as 150 ppm for sources firing non-natural gas fuels with a design heat input rating of less than or equal to 50 MMBtu/h. 4. Proposed Subcategorization Approach in 40 CFR Part 60, Subpart KKKKa The EPA is proposing three size-based subcategories in subpart KKKKa for stationary combustion turbines that commence construction, modification, or reconstruction after December 13, 2024. The proposed subcategories include combustion turbines with base load ratings of less than or equal to 250 MMBtu/h of heat input, those with base load ratings of greater than 250 MMBtu/h of heat input and less than or equal to 850 MMBtu/h, and those with base load ratings greater than 850 MMBtu/h of heat input. 21 Like subpart KKKK, these subcategories are based on the rating of the turbine engine and do not include any supplemental fuel input to the heat recovery system and are consistent with combustion control technologies (and manufacturer guarantees) currently available for different sized combustion turbines. 21 The EPA is proposing the same BSER regardless of the end use of the combustion turbine—direct mechanical and electric generating applications would be subject to the same emission standards. For the purposes of subpart KKKKa, the EPA refers to stationary combustion turbines as small (base load ratings of less than or equal to 250 MMBtu/h of heat input), medium (base load ratings of greater than 250 MMBtu/h of heat input and less than or equal to 850 MMBtu/h), and large (base load ratings of greater 850 MMBtu/h of heat input), respectively. In addition, the EPA is proposing to further subcategorize small, medium, and large combustion turbines as low load, intermediate load, or base load units depending on 12-calendar-month capacity factors. Low load combustion turbines would be those with a 12-calendar-month capacity factor of less than or equal to 20 percent. Intermediate load combustion turbines would be those with a 12-calendar-month capacity factor of greater than 20 percent but less than or equal to 40 percent. Base load combustion turbines would be those with a 12-calendar-month capacity factor greater than 40 percent. For each of these proposed subcategories, the EPA proposes to carry forward to new subpart KKKKa the current subpart KKKK approach to subcategorize stationary combustion turbines further depending on whether they are natural gas-fired or non-natural gas-fired. In addition, the EPA proposes to carry forward to new subpart KKKKa the current subpart KKKK subcategorization for combustion turbines operating at part loads, combustion turbines located north of the Arctic Circle, combustion turbines operating at ambient temperatures of less than 0 °F, 22 and HRSG units operating independent of the combustion turbine. 22 If any of these conditions are applicable, the combustion turbine would be in this subcategory. a. Size-Based Subcategories This section discusses the EPA's proposals to create size-based subcategories for new, modified, and reconstructed stationary combustion turbines in new subpart KKKKa that are different from the size-based subcategory approach established in existing subpart KKKK. Specifically, the EPA is proposing size-based subcategories for combustion turbines that have base load ratings less than or equal to 250 MMBtu/h of heat input, base load ratings greater than 250 MMBtu/h of heat input and less than or equal to 850 MMBtu/h, and base load ratings greater than 850 MMBtu/h of heat input. The EPA also is proposing to divide these subcategories of combustion turbines further based on their utilization ( i.e., 12-calendar-month capacity factor), depending on whether they operate as low, intermediate, or base load units. The proposed BSER and applicable NO X emission standards would depend on the size of the stationary combustion turbine as determined by its base load rated heat input and on how it is utilized based on its 12-calendar-month capacity factor. The proposed subcategories in subpart KKKKa are based in part on the availability and performance of NO X combustion controls for different designs and sizes of stationary combustion turbines. These factors were also key to determining the size-based subcategories in current subpart KKKK. For example, as discussed previously, subpart KKKK includes a subcategory for combustion turbines with a base load rated heat input of less than or equal to 50 MMBtu/h, and this subcategory was determined to be appropriate because the EPA had found that combustion controls for these size combustion turbines have limited availability relative to larger combustion turbines. Therefore, the EPA further divided this subcategory into electric generating and mechanical drive applications and determined the BSER for electric applications to be water injection and the BSER for mechanical drive applications to be available combustion controls. For combustion turbines in the subcategory of sources with greater than 50 MMBtu/h of heat input and less than or equal to 850 MMBtu/h of heat input, the BSER in subpart KKKK is combustion controls available for aeroderivative combustion turbines, because, when subpart KKKK was proposed in 2005, the largest aeroderivative combustion turbines were less than 850 MMBtu/h. For the subcategory of combustion turbines that are greater than 850 MMBtu/h of heat input, the BSER in subpart KKKK is combustion controls available for frame combustion turbines. The EPA had determined that frame combustion turbines are generally physically larger per amount of output than aeroderivative combustion turbines, given larger areas to stage combustion that results in lower NO X emissions. b. Combustion Turbines Less Than or Equal to 250 MMBtu/h The EPA is proposing in subpart KKKKa to create a subcategory for all new and reconstructed stationary combustion turbines with base load ratings of less than or equal to 250 MMBtu/h of heat input ( i.e., small turbines). The EPA is proposing this size-based subcategory for small stationary combustion turbines based, in part, on a review of available combustion controls and manufacturer guarantees for NO X emissions from these smaller turbine designs. The results of this technology review demonstrate that multiple manufacturers have developed dry combustion controls that can achieve NO X emission rates comparable to the NO X emission rates achieved by larger models of combustion turbines for both electrical and mechanical applications. This subcategory of small combustion turbines with base load ratings of less than or equal to 250 MMBtu/h of heat input also is proposed to be appropriate because it supports consistency across multiple rulemakings and approximately corresponds to the 25 MW threshold for a combustion turbine to be considered an electric generating unit (EGU) in the recently promulgated NSPS for greenhouse gas (GHG) emissions ( i.e., the Carbon Pollution Standards). 23 See 89 FR 39798; May 9, 2024. 23 EGUs are subject to different regulatory criteria outside of the NSPS as compared to small industrial combustion turbines ( e.g., greenhouse gas standards of performance). These other regulatory criteria can be accounted for in the baseline levels of control the EPA uses when evaluating the BSER. In new subpart KKKKa, different from the existing subcategories in subpart KKKK, the EPA is not proposing a subcategory for stationary combustion turbines with base load ratings of less than or equal to 50 MMBtu/h of heat input. The EPA proposes to determine that this subcategory is no longer necessary since multiple manufacturers have developed effective dry combustion controls for nearly all new turbines smaller than 50 MMBtu/h of heat input, and these dry combustion controls are capable of limiting NO X emissions to the same rates as those achieved by larger combustion turbines for both electrical and mechanical applications. According to the subcategory approach proposed in subpart KKKKa, any new or reconstructed stationary combustion turbine with a base load rating of less than or equal to 50 MMBtu/h of heat input would be included in the subcategory of combustion turbines with base load ratings of less than or equal to 250 MMBtu/h of heat input and subject to the same NO X performance standards. Also, the EPA is proposing in new subpart KKKKa that electrical and mechanical applications can apply identical combustion controls and that separate subcategories for these sources are no longer necessary. The EPA also is proposing in new subpart KKKKa to further subcategorize stationary combustion turbines with base load ratings of less than or equal to 250 MMBtu/h of heat input according to capacity factors. Small low load stationary combustion turbines would be those with 12-calendar-month capacity factors of less than or equal to 20 percent, small intermediate load stationary combustion turbines would be those with 12-calendar-month capacity factors greater than 20 percent and less than or equal to 40 percent, and small base load stationary combustion turbines would be those with 12-calendar-month capacity factors greater than 40 percent. According to this subcategorization approach, the EPA is proposing in new subpart KKKKa that all new and reconstructed stationary combustion turbines with base load ratings of less than or equal to 250 MMBtu/h of heat input and that are utilized as low or intermediate load units ( i.e., with 12-calendar-month capacity factors less than or equal to 40 percent) would have a BSER of combustion controls. Furthermore, as discussed in section III.B.12, the EPA is proposing that these small low and intermediate load combustion turbines would be subject to a NO X performance standard based upon application of the proposed BSER and whether they burn natural gas or non-natural gas fuels. The EPA also is proposing in subpart KKKKa that all new and reconstructed stationary combustion turbines with base load ratings of less than or equal to 250 MMBtu/h of heat input that are utilized as base load units ( i.e., with 12-calendar-month capacity factors greater than 40 percent) would have a BSER of combustion controls plus additional post-combustion SCR technology. The EPA proposes in section III.B.12 that these small base load stationary combustion turbines would be subject to a NO X performance standard based upon application of the proposed BSER and whether they burn natural gas or non-natural gas fuels. As for modified stationary combustion turbines with base load ratings of less than or equal to 250 MMBtu/h of heat input, the EPA is proposing in subpart KKKKa that the BSER is combustion controls—regardless of 12-calendar-month capacity factor. All small modified stationary combustion turbines would be subject to a NO X performance standard based application of the proposed BSER and whether they burn natural gas or non-natural gas fuels. In this action, the EPA is soliciting comment on whether the base load rating of less than or equal to 250 MMBtu/h of heat input is an appropriate threshold to distinguish between small and medium stationary combustion turbines for purposes of determining the BSER and proposing NO X standards in subpart KKKKa. For example, as discussed further in section III.B.9, if the EPA were to determine that SCR was not an appropriate BSER for all small stationary combustion turbines, then it may be appropriate to adjust the size-based thresholds such that turbines of greater than 50, 100, or 150 MMBtu/h of heat input should be treated as “medium” turbines. c. Combustion Turbines Greater Than 250 MMBtu/h and Less Than or Equal to 850 MMBtu/h The EPA is proposing to create a subcategory in new subpart KKKKa for new and reconstructed medium stationary combustion turbines, which would be turbines with base load ratings of greater than 250 MMBtu/h of heat input and less than or equal to 850 MMBtu/h. Furthermore, in subpart KKKKa, the EPA is proposing to divide this medium subcategory into low load (12-calendar-month capacity factors of less than or equal to 20 percent), intermediate load (12-calendar-month capacity factors greater than 20 percent and less than or equal to 40 percent), and base load (12-calendar-month capacity factors greater than 40 percent) with separate proposed BSER and NO X emission standards, as discussed in sections III.B.10 and III.B.12. The EPA also is soliciting comment on whether it is appropriate for medium stationary combustion turbines that are EGUs 24 to determine their utilization thresholds according to 12-operating-month electric sales instead of 12-calendar-month capacity factors. Some new and reconstructed stationary combustion turbines that would be subject to new subpart KKKKa also meet the applicability criteria in the Carbon Pollution Standards and are considered EGUs. Determining the utilization thresholds for combustion turbine EGUs based on 12-operating-month electric sales would better align this proposal with the subcategorization approach in the final Carbon Pollution Standards. 24 EGU stationary combustion turbines are those that meet the applicability requirements of proposed subpart KKKKa and also the applicability requirements of subpart TTTTa as described in 40 CFR 60.5509a ( See 89 FR 40036). d. Combustion Turbines Greater Than 850 MMBtu/h In new subpart KKKKa, the EPA is proposing to maintain the subcategory of large stationary combustion turbines with base load ratings of greater than 850 MMBtu/h of heat input, similar to the existing subcategory for large combustion turbines in subpart KKKK. However, the EPA is proposing in subpart KKKKa to further divide these combustion turbines into three subcategories based on the rolling 12-calendar-month utilization. As discussed for the small- and medium-sized combustion turbines, this proposed subcategorization is consistent with the Carbon Pollution Standards and includes subcategories for large combustion turbines with greater than 850 MMBtu/h of heat input that operate at low, intermediate, or base load capacity factors. In terms of capacity factors, the large low load stationary combustion turbines would be those with 12-calendar-month capacity factors of less than or equal to 20 percent, the large intermediate load stationary combustion turbines would be those with 12-calendar-month capacity factors greater than 20 percent and less than or equal to 40 percent, and the large base load stationary combustion turbines would be those with 12-calendar-month capacity factors greater than 40 percent. The EPA also is soliciting comment on whether it is appropriate for large stationary combustion turbines that are EGUs to determine their utilization thresholds according to 12-operating-month electric sales instead of 12-calendar-month capacity factors. Some new and reconstructed large stationary combustion turbines that would be subject to new subpart KKKKa also meet the applicability criteria in the Carbon Pollution Standards and are considered EGUs. Determining the utilization thresholds for combustion turbine EGUs based on 12-operating-month electric sales would better align this proposal with the subcategorization approach in the final Carbon Pollution Standards. e. Natural Gas and Non-Natural Gas Subcategories In subpart KKKK, stationary combustion turbines are categorized as non-natural gas-fired sources when greater than 50 percent of the heat input is from a non-natural gas fuel during part of an hour of operation. The EPA is proposing to maintain that categorization in new subpart KKKKa. In the 2012 NSPS Proposal discussed in section II.H, the EPA proposed to base the emissions standard only on the fuel burned in the combustion turbine engine ( i.e., any fuel combusted in the duct burners of the HRSG would not impact the applicable emissions rate) and to eliminate the 50 percent fuel requirement so that the non-natural gas emissions standard would apply when any amount of non-natural gas fuel is burned in the combustion turbine engine. This proposed change was intended to avoid creating a compliance issue when combustion turbines switch from utilizing gaseous fuels (that can utilize lean premix/DLN combustion) to liquid fuels (that utilize diffusion flame combustion). As previously noted, the EPA took no further action on the 2012 NSPS Proposal. In this action, the EPA is soliciting comment on whether to adopt, in subpart KKKKa, the approach included in the 2012 NSPS Proposal. The EPA believes that this approach could provide a more accurate representation of the performance of applicable control technologies and is soliciting comment on the specifics of co-firing fuels in a combustion turbine engine and how combustion turbines switch fuels. Specifically, the EPA seeks comment on whether multiple fuels can be combusted simultaneously in a combustion turbine engine, which fuels can be combusted in combination, and under what conditions. The EPA also seeks comment on whether it is necessary for a combustion turbine to temporarily cease operation or reduce load to switch from natural gas to distillate oil, or can switch fuels while operating at high loads. Finally, if switching can be done at high loads, the EPA seeks comment on at what point it is necessary to switch from lean premix/DLN combustion, which is only applicable to gaseous fuels, to diffusion flame combustion. Specifically, whether it is necessary to operate using diffusion flame combustion while utilizing natural gas prior to switching to fuel oil, and if this could create a compliance issue for hours during fuel switching. The EPA is soliciting comment on if this issue is technically accurate. A potential issue with removing the 50 percent fuel requirement is that this treatment could create an incentive for an owner/operator to combust a small amount of non-natural gas fuel and thereby obtain a far less stringent emissions standard. Therefore, the EPA is soliciting comment on what mitigating provisions would be necessary to ensure that this treatment only operates in the narrow window where it might be appropriate for legitimate technical reasons. Specifically, if the EPA were to remove the 50 percent fuel requirement, the EPA also solicits comment on limiting the number of hours a combustion turbine may burn multiple fuel types, through longer averaging times for determining compliance, and/or through mass-based caps on the total emissions that are permitted during periods of fuel switching. The EPA is proposing in new subpart KKKKa that the NO X standards are based on the type of fuel being burned in the combustion turbine engine alone. Contrary to subpart KKKK, this would not account for the type of fuel being burned in duct burners associated with the HRSG. In subpart KKKK, the applicable NO X standards are based on the total heat input to the stationary combustion turbine, including any associated duct burners. However, fuel choice impacts combustion turbine engine NO X emissions to a greater degree than it impacts such emissions from a duct burner. Therefore, in subpart KKKKa, the Agency is proposing to include that the NO X standard be based on the type of fuel being burned in the combustion turbine engine alone. The natural gas standard would apply at those times when the fuel input to the combustion turbine engine meets the definition of natural gas, regardless of the fuel, if any, that is burned in the duct burners. The Agency is also proposing to add a provision allowing for a site-specific NO X standard for an owner/operator of a stationary combustion turbine that burns by-product fuels. The owner/operator would be required to petition the Administrator for a site-specific standard using a procedure similar to what is currently required by subpart Db of 40 CFR part 60 (the Industrial Boiler NSPS). The Agency considers it appropriate to propose this provision because new subpart KKKKa covers the HRSG that was previously covered by subpart Db when the site-specific standard was adopted for industrial boilers. The Agency also solicits comment on whether to amend existing subpart KKKK to provide a provision allowing for a site-specific NO X standard for an owner/operator of a stationary combustion turbine that burns by-product fuels. f. Subcategory for Combustion Turbines Operating at Part Loads, Located North of The Arctic Circle, or Operating at Ambient Temperatures of Less Than 0 °F When subpart GG (the original stationary gas turbine criteria pollutant NSPS) was promulgated in 1979, the NO X emission standards and compliance were based on performance testing. Based on subsequent rulemakings, owners/operators of a gas turbine subject to subpart GG with a NO X continuous emissions monitoring system (CEMS) began determining excess emissions on a 4-hour rolling average basis. The 4-hour basis was determined to be the approximate time required to conduct a performance test using the performance test method specified in subpart GG. This 4-hour rolling average became the default for determining the emission rates of gas turbines, and, in 2006, was used in the subsequent review of the stationary combustion turbine criteria pollutant NSPS (subpart KKKK). When subpart KKKK was proposed in 2005, the NO X performance emissions data were again based on stack performance tests, which are representative of emission rates at high hourly loads, rather than on CEMS data. The final NO X standards for high hourly loads were consistent with the performance test data and manufacturer guarantees. Manufacturer guarantees are only applicable during specific conditions, which include the load of the combustion turbine and the ambient temperatures. When combustion turbines are operated at part loads and/or at low ambient temperatures, the identified BSER in subpart KKKK—low NO X combustion controls—were not as effective at reducing NO X from a technical standpoint. 25 At part-load operation and low ambient temperatures, it is more challenging to maintain stable combustion using dry low NO X (DLN) and adjustments to the combustion system are required—resulting in higher NO X emission rates. Therefore, in subpart KKKK, the Agency identified diffusion flame combustion as the BSER for hours of part-load operation or low ambient temperatures. 26 25 The ambient temperature of combustion turbines located north of the Arctic Circle would often be below 0 °F, and these units are included in the low ambient temperature subcategory regardless of the actual ambient temperature. The costs of requiring combustion controls that would rarely be used are determined not to be reasonable. 26 Combustion turbines have multiple modes of operation that are applicable at different operating loads and when the combustion turbine is changing loads. The modes are specific to each combustion turbine model. The identified BSER of diffusion flame combustion also includes periods of operation that use less effective DLN compared to operation at high loads. In subpart KKKK, a part-load hour is defined as any hour when the heat input rate is less than 75 percent of the base load rating of the combustion turbine. If the heat input rate drops below 75 percent at any point during the hour, the entire hour is considered a part-load hour, and the part-load standard is applicable during that hour. Determination of the 4-hour emissions standard is calculated by averaging the four previous hourly emission standards. Under this approach, the high hourly load standard would not be applicable until a minimum of 6 continuous operating hours. The initial and final hours would be startup and shutdown, respectively, and the part-load standard is applicable during those hours. If the combustion turbine were operating at high loads during the middle 4 hours, the high load standard would be applicable to that 4-hour average. The emission standards for the remaining hours would be a blended standard that is between the part-load and high-load standards. This approach was viewed as appropriate to account for the different applicable BSERs. Subpart KKKK also includes a 30-operating-day rolling average standard that is applicable to combustion turbines with a HRSG. The 30-operating-day rolling average was included in subpart KKKK because the HRSG was part of the affected facility and a longer averaging period is necessary to account for variability when complying with the alternate output-based emissions standard. The EPA is proposing to use the same short-term 4-hour standard in new subpart KKKKa along with the blended standard approach. Specifically, the applicable emissions standard would be based on the heat input weighted average of the four applicable hourly emissions standards. However, the EPA is proposing two changes to the part-load subcategory. First, the CEMS data analyzed by the EPA indicates that emissions tend to slowly increase at lower loads, but, in general, combustion turbines are capable of maintaining emission rates at loads of 70 percent and greater rather than at loads of 75 percent or greater, as reflected in subpart KKKK. Therefore, the EPA is proposing in subpart KKKKa that this subcategory applies for any hour when the heat input is less than or equal to 70 percent of the base load rating. The EPA notes that since emission rates increase at lower loads, lowering the part-load threshold would bring more operating periods under the high-load subcategory. It could also result in a higher numeric standard. Longer averaging periods reduce, but do not eliminate, the need for a part-load standard. Even under a 30-operating-day average, combustion turbines will, on occasion, have to operate under part-load conditions for relatively long periods. Establishing an emissions rate that includes all periods of operation and that is achievable decreases the emission reduction required for combustion turbines operating at high hourly capacity factors. 27 Establishing absolute mass-based limits is one potential approach to reduce emissions during all periods of operation. In the Additional Requests for Comment section below, the EPA is soliciting comment on mass-based standards in addition to short-term emission rates to address any regulatory incentive for owners or operators to reduce operating loads so that the part-load standard is applicable. 27 A single emissions standard that applies at all times would presumably need to be set at a numeric level that accounts for the highest hourly emission rates—typically during startup and shutdown. Second, the EPA is proposing a different size threshold for subcategorizing the part-load emission standards. Existing subpart KKKK subcategorizes the part-load emissions standard based on the rated output of the turbine ( i.e., combustion turbines with outputs greater than 30 MW have a more stringent part-load standard than smaller combustion turbines). New subpart KKKKa proposes to subcategorize the part-load standard based on the heat input rating ( i.e., turbines with base load heat input ratings greater 250 MMBtu/h would have a more stringent standard than smaller combustion turbines). In addition to these two proposed changes from subpart KKKK, the EPA is soliciting comment on a number of topics and concerns associated with the part-load subcategory. Currently, there are no limits on the number of hours per year that a combustion turbine could remain in part-load operation and thus gain the benefit of the part-load emissions standard. In this respect, we note that the threshold for the part-load subcategory, even though proposed to be reduced to 70 percent for subpart KKKKa, remains 30 percent higher than what would be considered “base load” operation if measured on an annual basis ( i.e., a 40 percent capacity factor). Further, the BSER for the part-load subcategory is diffusion flame technology, and the associated emissions standards for that BSER are substantially less stringent than the standards that would apply in non-part load operation. In fact, the proposed part-load standard for small combustion turbines of 150 ppm NO X is 50 times less stringent than the 3 ppm standard for such turbines operating at base load on a 12-calendar-month capacity factor basis (which assumes SCR operation in conjunction with combustion controls). Likewise, the proposed part-load NO X standard for medium and large combustion turbines of 96 ppm is 32 times less stringent. The EPA requests comment on measures that can be taken to reduce this discrepancy and/or to narrow the scope of application of the part-load standard so as to eliminate perverse incentives to take advantage of a grossly less stringent emissions standard. The EPA requests comment on a maximum limit to the number of hours per year that the part-load standard can be applied. The EPA requests comment on limiting the part-load standard only to those hours when a combustion turbine is in startup or shutdown mode of operation. The EPA requests comment on longer averaging times coupled with the elimination or shrinking of this subcategory so that the emissions standards are set in such a way that they can be complied with even when combustion turbines are in part-load status. Furthermore, the EPA requests comment on the efficacy of combustion control technology operated in conjunction with SCR when units are in part-load operation. The EPA notes that while there may be some loss in efficiency in combustion controls or in SCR performance in part-load operation, these technologies do not lose all value. Therefore, the EPA requests comment on whether it is appropriate to exclude these technologies from the BSER for part-load operation. If it is not appropriate, then the EPA requests comment on what emissions performance these technologies can achieve in part-load operation. The EPA notes that even if there is some reduction in efficiency, combustion controls in combination with SCR could still achieve emissions rates in part-load operation as low as 9 ppm or 3 ppm, thus calling into question whether emissions rates as high as 96 ppm or 150 ppm would be unjustified to sustain. With respect to the use of longer averaging periods, the EPA believes these could potentially be a part of the solution if the emission standards were set at such a level that they accommodate some part-load hours of operation where there is lower emissions control efficiency. However, under this approach, this may not entirely remove the need for a part-load standard. Even under a 30-operating-day average, combustion turbines will on occasion have to operate under part-load conditions for relatively long periods. Establishing an emissions rate that includes all periods of operation and that is achievable poses an equally concerning request that it would reduce the stringency of the emissions reductions that are required for combustion turbines operating at high hourly capacity factors. With this concern in mind, the EPA also requests comment on whether a mass-based emissions standard set over a longer period, such as monthly or annually, could effectively ensure that part-load operation is kept to a minimum so that an overall environmental result is achieved that is in line with the more stringent emissions rates associated with the EPA's proposed BSER determinations that include combustion controls and SCR. Absolute mass-based limits can incentivize reduced emissions during all periods of operation. In such an approach, a mass-based cap would be established through multiplying an assigned emissions rate that factors in some degree of part-load operation by a reasonable assumption concerning operating levels over the period in question. In the Additional Requests for Comment section, the EPA is soliciting comment on mass-based standards in addition to short-term emission rates. Among the reasons why such an approach may be both environmentally effective and also reduce regulatory burdens, as discussed in that section, is that any such approach could be tailored to effectively address any regulatory incentive for owners/operators to reduce operating loads so that the part-load standard is applicable. Additionally, in subpart KKKKa, the EPA is proposing to maintain the same ambient temperature subcategorization and BSER as in subpart KKKK. If at any point during an operating hour the ambient temperature is below 0 °F, or if the combustion turbine is located north of the Arctic Circle, the BSER is the use of diffusion flame combustion with the corresponding part-load standard. However, many of the same concerns associated with the part-load standard could be of concern with the ambient temperature subcategorization. For instance, it may be that while combustion controls and SCR lose some performance in these cold conditions, they can still effectively reduce emissions to a substantially greater degree than diffusion flame technology alone. Therefore, the EPA similarly requests comment on whether any of the factors or approaches described above in conjunction with limiting the loss in stringency associated with the part-load subcategory could appropriately be applied to the ambient temperature subcategorization. g. Subcategory for HRSG Units Operating Independent of the Combustion Turbine The affected facility under subpart KKKK (and the proposed affected facility under subpart KKKKa) includes the HRSG of combined heat and power (CHP) and combined cycle facilities. Although not common practice, it is possible that the HRSG could operate and generate useful thermal output while the combustion turbine itself is not operating. In subpart KKKK, the EPA subcategorizes this type of operation and bases the NO X emissions standard on the use of combustion controls for a steam generating unit under one of the steam generating unit NSPS. The EPA is proposing to maintain the same approach in subpart KKKKa and to subcategorize operation of the HRSG independent of the combustion turbine engine with the same emissions standard as in subpart KKKK. 5. Form of the Standard The form of the concentration-based NO X standards of performance in subpart KKKK is based on parts per million (ppm) corrected to 15 percent O 2 and the form of alternate output-based NO X standards is determined on a pounds per megawatt hour-gross (lb/MWh-gross) basis. Also, manufacturer guarantees are often reported in ppm and operating permits are often issued in ppm. Aligning the form of the NSPS with common practice simplifies understanding of the emission standards and reduces burden to the regulated community. While not the primary form of the standard, the alternate output-based form of lb/MWh-gross recognizes the environmental benefit of highly efficient generation. In new subpart KKKKa, the EPA is proposing input-based NO X standards in the form of pounds per million British thermal units (lb/MMBtu) and alternate output-based standards in both a gross- and net-output form. As described in the hydrogen combustion section (III.B.14), co-firing hydrogen can increase the NO X emissions rate on a ppm basis when corrected to 15 percent O 2 while absolute NO X emissions may not significantly change. Since actual emissions to the atmosphere are the measure of environmental impacts, the NO X emission standards in the form of lb/MMBtu is a superior measure of environmental performance when comparing emissions from different fuel types. However, throughout this document, the EPA refers to NO X emission rates using ppm for ease of comparison with performance guarantees and permitted emission rates. The actual proposed standards in new subpart KKKKa are in the form of an equivalent lb/MMBtu for a natural gas-fired combustion turbine or a distillate oil-fired combustion turbine for the proposed natural gas- and non-natural gas-fired NO X emission standards, respectively. Consistent with the final Carbon Pollution Standards, the EPA is proposing in subpart KKKKa that the alternate output-based standards be in the form of both gross- and net-output. Net output is the combination of the gross electrical (or mechanical) output of the combustion turbine engine and any output generated by the HRSG minus the parasitic power requirements. A parasitic load for a stationary combustion turbine represents any of the auxiliary loads or devices powered by electricity, steam, hot water, or directly by the gross output of the stationary combustion turbine that does not contribute to electrical, mechanical, or thermal output. One reason for including alternate net-output based standards is that while combustion turbine engines that require high fuel gas feed pressures typically have higher gross efficiencies, they also often require fuel compressors that have potentially larger parasitic loads than combustion turbine engines that require lower fuel gas pressures. Gross output is reported to CAMPD and the EPA can evaluate gross-output based emission rates directly. 28 While this emissions rate is representative of combined cycle turbines without carbon capture and storage (CCS) equipment, the Carbon Pollution Standards require all new base load combustion turbines to install CCS by 2032. To account for the efficiency loss due to CCS, the EPA proposes to use the ratio of the National Energy Technology Laboratory (NETL) combined cycle model plants. Specifically, the achievable gross-output efficiency will be determined by reviewing reported hourly data. The ratio of the NETL combined cycle turbine without CCS gross efficiency will be compared to the NETL combined cycle turbine with CCS gross and net efficiency. These ratios will be multiplied by the reported gross-output emission rate values to determine the proposed alternate output-based standards. As an alternative to continuously monitoring parasitic loads, the EPA is proposing in new subpart KKKKa that estimating parasitic loads is adequate and would minimize compliance costs. A calibration would be required to determine the parasitic loads at four load points: less than 25 percent load; 25 to 50 percent load; 50 to 75 percent load; and greater than 75 percent load. Once the parasitic load curve is determined, the appropriate amount would be subtracted from the gross output to determine the net output. The EPA is requesting comment on this approach and whether a four-load test is appropriate or whether a curve fit of three loads greater than 25 percent load is sufficient. 28 Net output is not reported to CAMPD. 6. Averaging Period As described previously, the NO X emission standards in existing subpart KKKK are based on a 4-hour rolling average for simple cycle turbines and a 30-operating-day average for combustion turbines with a HRSG ( e.g., combined cycle and CHP combustion turbines). For this review of the NSPS, the EPA analyzed hourly emissions data using three averaging periods—a 4-hour rolling average, an operating-day average, and a 30-operating-day average. The EPA is proposing in new subpart KKKKa that the emission standards for all combustion turbines complying with the input-based standard (lb NO X /MMBtu) would be determined on a 4-hour rolling average. According to the EPA's review of hourly emissions data, combustion turbines using combustion controls alone and combustion controls in combination with SCR have a relatively steady emissions profile. The Agency is proposing that shortening the compliance period for combined cycle and CHP units would provide similar levels of environmental protection as the current averaging periods in subpart KKKK. Permits are often based on daily operations and the EPA is soliciting comment on whether aligning these periods could reduce the reporting burden. To avoid situations where the daily average would be based on limited data that does not account for variability, emissions averages would only be determined for operating days with 4 or more hours of CEMS data that are not out-of-control. Data from operating days with fewer than 4 hours of CEMS data that are not out-of-control would be rolled over to the next operating day until 4 or more hours of data are available. A benefit of this approach is that all non-out-of-control emissions data would be used in determining excess emissions. Under the subpart KKKK approach, any 4 operating hours with more than 1 hour of monitor downtime is reported as monitor downtime and the emissions from the remaining hours are excluded. The EPA proposes to carry this approach forward in proposed subpart KKKKa. However, this could potentially exclude reliable monitoring data and complicate determinations that emissions are in or out of compliance with the emissions standards. Thus, in the alternative, the EPA is soliciting comment on basing compliance for all combustion turbines on a 4-hour rolling average basis where only those hours with monitor downtime are excluded. Subpart KKKK currently includes alternate gross output-based standards that owners and operators can elect to comply with instead of the input-based standard. The output-based standard was determined using an efficiency that is representative of a combined cycle turbine, so, in practice, only owners and operators of combined cycle or CHP facilities would elect to use the output-based standard. The EPA is proposing to include output-based standards, on both a gross- and net-output basis, as an alternative to the heat input-based standards. Owners and operators electing to use the output-based standards would demonstrate compliance on a 30-operating-day average. The longer averaging period is appropriate because both the NO X emissions rate on a lb NO X /MMBtu basis and the efficiency of the combustion turbine can vary—increasing the overall variability. 7. Proposed Determinations of the BSER for New, Modified, and Reconstructed Stationary Combustion Turbines in 40 CFR Part 60, Subpart K [Text truncated at 120,000 characters. The full text is on the page linked above.] --- Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2024-27872. Public record. Not legal advice.