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## Chapter **8 Modified Natural Gas**  **- fired Stationary Combustion**  **Tu rbines** 

**Contents** 8.1 General

................................ ................................ ................................ ................................ . 2 8.2 Id entification of BSER

................................ ................................ ................................ ......... 2 8. 2.1 Actions to Trigger Modification

................................ ................................ ........................ 3 Modifications to an Older (e.g. Pre

- 2000) Combined Cycle Unit

................................ .......... 7 Upgrading a Simple Cycle Turbine to a Combined Cycle Unit

................................ ............. 8 8.3 Determination of the Level of the Standard

................................ ................................ ....... 118

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### 8.1 **GENERAL Comment 8.1**  **- 1:**  Commenter 190 stated it is important that EPA not apply the modification provisions of Section 111(b) to existing NGCC units in a manner that results in unintended consequences. According to the commenter, some existing NGCC units may be constrained b y current configurations or operating permit parameters that coul d be addressed by relativel y minor modifications that have the potential to increase emissions on an hourly or annual basis. The commenter stated if the re

- dispatch of these units is intended to displace higher emitting resources or to backstop renewable g eneration under a Section 111(d) program, these potential NGCC emission increases would be offset from the resources they replace. According to the commenter, the possibility that existing NGCC units could become subject to the 111(b) standards b y increasi ng utilization in order to meet the 111(d) requirements could force these units to forego the opportunity to increase output or retire, rather than be subject to the modification provisions (a scenario contemplated by EPA, " [T]hese standards serve another important purpose that may affect a larger number of sources: Providing an incentive, and the information needed, for existing sources to structure their actions to achieve their operating and business goals without triggering the modification or reconstru ction standards. " ). The commenter concluded that the inability to effectuate modifications to these existing NGCC units has the potential to result in stranded investments or require that additional fossil

- fueled generation be constructed, resulting in both a significant cost to customers and an increase in overall emissions. **Response 8.1 -**  **1:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). 

### 8.2 **IDENTIFICATION OF BS ER**  **Comment 8.2 -**  **1:** Commenter 187 suggested EPA that indicate the heat input standard is based on the on the LHV of the fuel, or adjust the heat input standard to a higher value to account for the HHV of the fuel. The commenter is concerned wi th the Agency ' s determination of BSER for modified stationary

combustion turbines for several reasons. According to the commenter, it is not technicall y or economically fea sible to upgrade older stationary combustion turbines to meet the carbon rates of new combustion turbines, and there is no information in the rule

- making docket to support the achievability of the proposed standards for modified and reconstructed units. Ac cording to the commenter, this lack of an EPA technical support document to justify how all older stationary

combustion turbines can be technically and economically

upgraded during a modification to meet the emission rates of new units indicates the Agency itself is not sure they can be achieved. The commenter stated that because a standard of performance must be achievable, EPA should withdraw the Proposed Rule or, at a minimum, expressly exempt any modified combustion turbine that is technologically or ec onomicall y incapable of meeting the performance standard. The commenter also identified a further defect in the proposed definition of BSER as "NGCC technology ." According to the commenter, this definition fails to provide the level of detail8

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required und er Section 111(a) of the Act, and without a clear definition of NGCC technology , sources cannot know what equipment would need to be upgraded if a unit is modified. Moreover, the commenter stated, requiring a simple

- cycle combustion turbine to convert to an NGCC is forcing a change in the basic equipment, which is strictly not allowed under Section 111(b): " [N]othing in this section shall be construed to require, or to authorize [EPA] to require, any new or modified source to install and operate an y particu lar technological s ys tem of continuous emission reduction to comply with an y new source standard of performance. " The commenter stated that simple

- cycle combustion turbines serve a different purpose from combined

- cycle units (i.e., fast response and ramp u p and limited use), and if a simple

- cycle must be converted to an NGCC, then the unit is not suitable for its intended purpose. The commenter stated that simple cycle turbines are primarily employ ed for their fast

- start capability , and requiring a conversi on to a unit that requires more time to start defeats the purpose of using such units and is unlawful. **Response 8.2 -**  **1:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to th e final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **2:** With respect to "modified" simple cy cle combustion turbines, commenter 0206 suggested that EPA drop the standard entirely, as the proposed standard unlawfull y redefines the source and should be deleted. **Response 8.2 -**  **2:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combu stion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **3:** Commenter 0215 stated that EPA failed to distinguish among turbines that were designed and constructed over a period of decades, and thus objects to the Agency 's de termination of BSER. The commenter stated that the definition of "NGCC technology " has implications for evaluating the cost of technology and standard

- setting and without further definition of this term, it is impossible to understand or comment on the pro posal. [ 39476 ] **Response 8.2 -**  **3:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). 

### 8. **2 .1 Actions to Trigger Modification**  **Comment 8.2 -**  **4:** Commenter 0 227 stated they are unaware of any

unit subject to Subpart KKKK that has been alleged to have been "modified" and that subsequently triggered the applicability of an NSP S, but some NGCC facilities have been retrofit with selective catal ytic reactors (SCR) to control NOx emissions, which could have similar impacts as the control device installations that have occurred at Subpart Da units. The commenter stated that accordin g to EPA's data in the companion proposal for existing sources, state

- wide average CO 2 emissions in 2012 for all8

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existing NGCC units in Subpart KKKK exceeded 1,000 lbs/MWh

- net in several states. The commenter stated EPA has not exempted simple

- cycle combus tion turbines from the proposed standard, and not all simple

- cycle facilities could accommodate a conversion to combined cycle operation, which would be necessary to achieve the proposed standards. **Response 8.2 -**  **4:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **5:** Commenter 222 stated EPA must explicitly find that installation of control technology

or changes to comply

with EPA's environmental regulations do not trigger modification or reconstruction requirements under this Rule Proposal or Other Rule Proposals. The commenter supported EPA' s f in ding that changes to install " add

- on control equipment required to meet CAA requirements for criteria and hazardous air pollutants ... would be exempted from the definition of modification unde r the current NSPS regulations." The commenter noted that, howe ver, EPA goes on to add that there are some actions that "could potentially

trigger the modification provisions of CAA section 111(b); " for example, this would include changes in the particulate control equipment that removes limitations on the amount of c oal that can be combusted. According to the commenter, EGU operators should not be penalized for installing newer, larger, and more efficient technologies that allow increased combustion of coal, as that would likely increase efficiency

and lower the emiss ions rate. The commenter stated that any changes that lower the emission rate of CO 2 and any t yp e of heat rate improvement should be explicitly excluded from triggering modification requirements. **Response 8.2 -**  **5:** The EPA is withdrawing the proposed emission standard for m odified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **6:** Commenter 142 stated EPA failed to cor rectl y estimate the number of modifications and therefore dramatically underestimates the cost of the rule. The commenter agreed with EPA's estimate that few units would be reconstruct ed; however, disagreed with EPA' s estimate that few units would be modif ied. According to the commenter, EPA's basis for the estimate is flawed. The commenter stated EPA has not previousl y regulated CO 2 in any NSPS, so any

phy sical changes made to units in the past that resulted in increased CO 2 emissions would not have been c onsidered modifications, as the changes would not have resulted in an increase in emission of a pollutant to which a standard applied. According to the commenter, if the EPA is relying upon other pollutants as a surrogate to estimate the number of modifications, this approach is also flawed. The commenter stated that unlike CO 2 , other pollutants currently regulated under the NSPS ty picall y rel y upon add

- on control devices to control those emissions. The commenter also stated that the NSPS defines an increas e in emissions as an increase that occurs on an hourl y basis. The commenter continued that if a unit has an add

- on control device, the hourly

emission rate of the pollutant subject to regulation can be mitigated by enhanced utilization of the control devic e, yet since no add

- on control devices are currentl y used to control CO 2 emissions, all changes that would result in an hourly increase in CO 2 would be modifications. The commenter estimated that most existing combustion turbines will be modified8

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over the course of their useful life, and upgrades to existing turbines based upon advances in turbine technology

that are designed to increase power output or improve the heat rate are common. Additionally , the commenter stated, Block 1 heat rate improvements requ ired in section 111(d) could actually trigger a modification under section 111(b), because the hourl y emission rate of CO 2 could increase depending upon the heat rate improvements implemented. The commenter also stated heat rate improvement can be achieved when there is a greater increase in output (MW produced) relative to the increase in input (BTU, fuel). **Response 8.2 -**  **6:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **7:** Commenters 0238 and 260 stated EPA should clarify that turbine projects do not constitute modifications within the NSPS context. The commenter cited EPA that it "expects few units would trigger either the modification or the reconstruction provisions." However, the commenter continued, the Agency explains that upgrades to a steam turbine that allow more coal to be combusted in the boiler "could potentiall y trigger the modification provisions of CAA section 111(b)." The commenter stated that EPA's statement is contradictory to NSPS applicability

determinations issued by EPA for electric utility

steam generating units. The commenter provided the following discussion:

" According to NSPS applicability determinations, projects that solely involve the steam turbine do not constitute modifications as defined in 40 CFR section 60.14. For example, in an applicability

determination issued to NRG Energy , EPA stated that ' [t]he analy sis of whether a modification occurs under the NSPS is dependent on phy sical and operational c hanges at the existing facility ' and, ' a turbine is not part of the existing facilit y (i.e., the electric utility steam g enerating unit).' The Agency further explained that turbine changes would fall under the exemption from the modification definition for ' [a]n increase in production rate of an existing facility , if that increase can be accomplished without a capital expend iture. ' According to the Agency , an increase in turbine capacit y that remo ves a bottleneck at the boiler ' would not trigger a capital expenditure at the boilers since the turbine is not part of the electric utility steam generating unit.'" The commenters p rovided a diagram attached to an applicability determination for the Florida Electric Power Coordinating Group which clearl y shows that the turbine is not part of the electric utility steam generating unit. The commenter concluded that given EPA's past app licability determinations on this issue, EPA should clarify in the preamble to the final rule that turbine upgrades at an electric utility steam generating unit would not be considered a modification under the NSPS provisions. Commenter 0255 stated that t urbine upgrades should not be considered a modification. The commenter stated that EPA expresses that few turbine projects would qualify as a modification or reconstruction under the proposed rule but acknowledges that some turbine projects may qualify . Th e commenter stated these statements are not consistent with EPA's historic applicability

determinations where EPA states that the turbine is not part of the electric steam8

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generating unit. The commenter stated EPA should clarify in this rule that turbine u pgrades do not constitute a modification under NSPS. Commenter 0171 stated EPA indicates that upgrades to a steam turbine that allow more coal to be combusted in the boiler "could potentially trigger the modification provisions of CAA section 111(b)". The commenter stated EPA's statement is contradictory to NSPS applicability determinations issued by

EPA for electric utility

steam generating units. The commenter stated according to NSPS applicability determinations, projects that solely involve the steam turbine do not constitute modifications as defined in 40 C.F.R. Section 60.14. The commenter stated EPA should clarify

in final rule that turbine upgrades at an electric utility steam generating unit would not be considered a modification under the NSPS prov isions. Commenter 0238 also stated that as a practical matter, a determination that turbine projects constitute NSR modifications could have negative implications for EPA's Proposed Clean Power Plan. The commenter stated that Building Block I of EPA's Pro posed Clean Power Plan assumes heat rate improvements from existing sources, which will include steam turbine upgrades that also might allow more coal to be combusted in the boiler. According to the commenter, an y compan y contemplating efficiency improveme nts may

be dissuaded from enacting such improvements, which would counteract the Agency's intended goal of lower GHG emissions. The commenter quoted EPA statements that its approach to pollution control and prevention which easil y extends to efficiency gai ns to lower GHG emissions. **Response 8.2 -**  **7:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **8:** Commenter 0190 stated that while it believes that only extremel y unusual circumstances would cause the conversion of an existing coal

- fueled boiler to natural gas to trigger the modification or reconstructi on provisions under Section 111(b), EPA should provide additional clarification on this scenario. The commenter stated that as defined by Section 111, a modification only

occurs if there is an associated emissions increase, noting that under a gas conversi on, CO 2 emissions are reduced b y approximately 50% on a rate basis, and that frequentl y, capacity factor limitations are also imposed, effectivel y ensuring there is no emissions increase. The commenter stated that under the reconstruction provisions under Section 111, the costs of the fixed capital components being replaced must exceed 50% of the costs of the fixed capital components of an entirel y new comparable facility, and as a result, it is highly unlikely that the cost of a coal to natural gas convers ion will trigger the reconstruction provisions. The commenter provided additional information on operating units that have plans to utilize natural gas rather than coal at existing utility boilers, noting one will cease burning coal as a lower cost option to comply with EPA's Mercury

and Air Toxics Standards, and another that will convert to natural gas as a lower cost option to achieve compliance with EPA's Regional Haze Rules. The commenter provided cost information and anal ys is in comparison to the propo sed rule. The commenter noted that the planned coal

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- gas conversions will achieve significant reductions of CO 2 and other emissions and it is critical that these and similar projects at existing8

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units are not disincentivized by EPA's treatment of CO 2 emi ssions under a modification scenario. The commenter suggested that EPA should not subject these converted units to the NSPS under 111(b). The commenter stated that while the new source standards have yet to be finalized, these converted units cannot achiev e the proposed emission rate for natural gas fueled units of 1,000 lb/MWh but they

do provide significant CO 2 benefits. For purposes of Section 111(d), the commenter suggested that converted units should be treated as "other gas" units in EPA's compliance calculation. **Response 8.2 -**  **8:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbin es, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **9:** Commenter 0291 stated that certain replacements or upgrades to steam turbi nes or particulate control devices should not trigger the NSPS modification rule, y et the Proposed Rule will nonetheless become the minimum emission limit that must be achieved b y an EGU if it is to comply

with the PSD New Source Review modification rules specifying BACT application. The commenter stated that EPA must consider the implications of its utility enforcement initiative in its discussion of the NSPS modification rule. The commenter stated that EPA's proposed BSER includes precisel y the kinds of p rojects that are the subjects of its NSR suits

- "equipment upgrades [to] replace existing components with upgraded ones or a more extensive overhaul of major equipment (turbine or boiler)." The commenter stated that EPA must exclude from the NSPS for modif ied sources an y unit that would likely to trigger NSR upon undertaking an HRI improvement. **Response 8.2 -**  **9:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rul e. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Modifications to an Older (e.g. Pre -**  **2000) Combined Cycle Unit Comment 8.2**  **- 10:**  Commenter 0131 expressed reservations about the ability of new N GCCs to meet the 1,000 lbs./MWh limit given the inclusion of all start

- ups and shut downs and cy cling to back up renewables. The commenter stated that EPA now proposes the same standard for modified and reconstructed NGCCs, and as EPA notes in its discussion, the vast majo rity of NGCCs have been built after 2000. According to the commenter, likel y the only NGCCs that would be considered for modification or reconstruction would be those built before 2000. The commenter stated that bringing these machines to this standard wou ld be cost prohibitive and they would likel y be destined for replacement on an economic evaluation. According to the commenter, different standards would be appropriate for different technologies. The commenter stated that they

again would support the appl ication of the alternative standard of matching recent history

as opposed to applying 111(b) standards. **Response 8.2 -**  **10:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule.8

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As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **11:** Commenter 0215 stated that due to changes over time in the design efficiency of NGCC units, it is not possible to bring older comb ustion turbines up to the efficiency levels of modern units. The commenter stated that EPA acknowledges that there is no available method for reducing CO 2 emissions from these units other than applying NGCC technology , and an NGCC unit that triggers recons truction analy sis but cannot meet the proposed NSPS with its current turbine does not have an option of installing add

- on technology and would have to either entirely replace its existing facility with a new modern turbine (and likely a new heat recovery s team generator) or retire it altogether in order to comply . The commenter stated that because it would not be "technologically and economically

feasible" for those units to comply with the Proposed Standards, they would not be considered "reconstructed" an d would not be subject to the standard. **Response 8.2 -**  **11:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct mod ifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **12:** Commenter 0215 disagreed with EPA's assumption that it is technically feasible to upgrade "older" (e.g., especiall y pre - 2000) or even more recent NGCCs to meet the same CO 2 emission rate as moder n technology . The commenter stated that EPA's assumption that such an upgrade "is likely to be cost effective" is unsupported. The commenter disagreed that older units are capable of replacing sufficient equipment to match the emissions performance of a br and

- new NGCC unit on a cost

- effective basis, and stated that EPA has failed to provide an y technical support for basing its Proposed Standards on such an assumption. The commenter stated that without a definition of "NGCC technology ," neither an owner or o perator nor a regulatory

agency would know precisel y what equipment would need to be upgraded if a unit has been determined to have been modified. **Response 8.2 -**  **12:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources ” subject to 111(d). **Upgrading a Simple Cycle Turbine to a Combined Cycle Unit Comment 8.2**  **- 13:**  Commenter 199 stated that if required to convert simple cycle units using NGCC technology , man y units would be forced to shut down. The commenter stated it is not technologicall y feasible to use NGCC technology on a simple cycle unit because doing so requires the addition of a steam generator and steam turbine, which increases the size and characteristics of the plant. The commenter also stated it is not economically feasible bec ause when the characteristics of the plant change, the original purpose for constructing the unit (emergency

and peak loading) is destro ye d. The commenter continued that since NGCC is a cycling or base load energy resource, simple cycle units could possibl y run into trouble if they had to replace multiple rows of turbine and compressor blades and/or have the generator8

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overhauled. The commenter stated that simple cycle units would not be able to achieve the standard as proposed. The commenter stated that a s imple cycle unit's efficiency is approximately

50 to 60 percent lower than a NGCC unit and emits about 1,600 lb CO 2 /MWh, and the only

way to reduce emissions to the levels EPA proposes would be to install NGCC technology . However, according to the commente r, requiring that technology as the BSER for these units is arbitrary

and capricious. **Response 8.2 -**  **13:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **14:** Commenter 214 stated EPA' s BSER determination for modified and reconstructed simple

- cycle units are flawed. According to the commenter, EPA has prov ided no supporting documentation identifying the technical feasibility of altering existing simple

- cy cle CTs to " modern h igh efficiency NGCC technology ." The commenter stated that EPA must provide this documentation for all potentially affected sizes of s i mple

- cycle combustion turbines. The commenter stated that EPA also did not provide the incremental costs incurred at modified or reconstructed simple

- cy cle CTs due to the installation of a HRSG, however, EPA acknowledges potential technical and cost concerns with simple

- cycle CTs installing a HRSG. The commenter referenced the Agency concerns in stating: "if the owner/operator of a simple[

- ]cy cle turbine wishes to make a modification they could do so

- without having to compl y with the requirements of this proposal

- by maintaining an average annual capacity factor of less than one - third. " According to the commenter, EPA, however, cannot substitute an operational limit for an appropriate BSER anal ys is. Commenter 0215 disagreed that NGCC is BSER for a simple cycle turbine and that it would be "technologically

and economically

feasible" to apply , except in very rare situat ions. The commenter stated that such a requirement would violate the statutory prohibition on requiring "an y new or modified source to insta ll and operate any particular technological sy stem of continuous emission reduction to comply with an y new source standard of performance." **Response 8.2 -**  **14:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained i n Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **15:** Commenter 0 165 stated EPA' s BSER conclusion that BSER for a simple cycle combustion turbine is to upgrade the s ys tem to a combined cycle combustion turbine redefines the existing source. According to the commenter, the performance standards under Section 111 of the Clean Air Act are linked to the Best Available Control Technology requirements und er the Prevention of Significant Deterioration program. The commenter stated that Congress specifically linked the two programs together b y stating the Best Available Control Technology

could not be less stringent than the performance standards established under Section 111. Additionally , the commenter stated that the US Supreme Court discussed limitations on EPA's authorit y on appl ying "Best Available Control Technology " and noted the "control technology " could not require a "fundamental redesign" of the f acilit y. According to the8

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commenter, requiring the simple cycle combustion turbine to be upgraded to a combined cycle combustion turbine is a "fundamental redesign" of the existing source. **Response 8.2 -**  **15:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **16:** Commenter 0242 stated concerns regarding the ability for all t ypes of units under all circumstances to be able to achieve NGCC cost

- effectively . The commenter stated that issues may

arise for modified sources that may make it cost

- prohibitive as BSER to apply NGCC depending on the modification that o ccurs. The commenter provided the example that under this rule a simple cy cle may

trigger a modification based on the need for a simple upgrade, and in turn this rule would necessitate conversion to an NGCC which could make the project very cost prohibitiv e. The commenter stated they are particularly

concerned in the context of an energy market that is drasticall y altered through the proposed rule for existing units. The commenter stated that simple cycle units will be utilized more frequentl y due to greate r reliance on intermittent renewable resources and the lack of coal

- fired capacity . According to the commenter, the conversion of a simple cy cle is a complicated and expensive process that will not occur frequentl y, thus possibly leading to electricity

sho rtages, and the U.S. EPA must afford states the ability

in those circumstances to determine emission rates on a case

- by

- case basis. **Response 8.2 -**  **16:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **17:** Commenter 0215 stated that although man y simple cycle units have historically

operated less than 10 per cent of the y ear, there are cases where individual units may need to run much longer to maintain sy stem reliability , either for short or prolonged periods. The commenter stated that converting to a combined cycle facility would not be cost

- effective for mo st, if not all, simple cycle turbine owners, meaning that a simple cy cle turbine that becomes subject to the NSPS for modified sources would be unable to operate, and sy stem reliability would be jeopardized. **Response 8.2 -**  **17:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **18:** Commenter 0176 stated that EPA acknowledges that it is obligated to consider environmental impacts that would flow from the implementation of a proposed NSPS, including impacts to scarce water resources, According to the commenter, NGSC units that are affected b y this rule cannot me et the standard and must convert to a NGCC to meet the standard. The commenter stated that to the extent that the use of NGCC results in depletion of water resources, especially

in water scarce areas, it must be considered by EPA when finalizing the8

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rule, and the fact that NGCC are water intensive provides additional support that a mandate to convert NGSC units to NGCC is not BSER. **Response 8.2 -**  **18:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX. D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **19:** Commenter 0215 stated that EPA should create a separate category or subcategory

for modified high capacit y factor simple cycle turbines, determine an appropriate BSER that does not require conversion to NGCC, anal yz e emissions from units in the subcategory , consider all of the requirements of section 111, and propose a limit that is achievable. **Response 8.2 -**  **19:** The EPA is wi thdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.2 -**  **20:** Commenter 0149 had concerns regarding the ability of all t ypes of units under all circumstances to be able to achieve NGCC cost

- effectivel y. The commenter believes issues may arise for modified sources that may make it cost

- prohibitive as BSER to a pply NGCC depending on the modification that occurs. The commenter stated that under the proposed rule a simple cycle may

trigger a modification based on the need for a simple upgrade, and this would necessitate conversion to an NGCC, which could make the project cost prohibitive. This was particularl y concerning to the commenter in the context of an energy market that is drastically altered through the proposed rule for existing units. **Response 8.2 -**  **20:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). 

### 8.3 **DETERMINATION OF THE LEVEL OF THE STANDAR** **D Comment 8.3**  **- 1:**  Commenter 0150 stated EPA also proposes to establish standards identical to those for new units: 1,000 lb CO 2 /MWh

- gross for large (more than 850 MMBtu/h) units and 1,100 lb CO 2 /MWh

- gross for small (850 MMBtu/h or less) units. According to the commenter, EPA has not provided any record evidence supporting the achievability of these standards, and as such, they

are per se arbitrary

and capricious. **Response 8.3 -**  **1:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Sect ion IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d).8

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**Comment 8.3 -**  **2:** Commenters 0171 and 0254 stated that for modified NGCC, the proposed rule subjects them to the sam e standard as a new NGCC, without any data or explanation that this is appropriate. According to the commenters, EPA's unsupported conclusion is wrong

-- the design of man y units precludes their ability to meet the new

- unit limit, if modified. Commenter 0 215 stated that existing sources generally cannot meet the same emission standard as a new, greenfield source and an anal ys is of existing units demonstrates that a substantial number of units cannot achieve the standards EPA has proposed. **Response 8.3 -**  **2:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources ” subject to 111(d). **Comment 8.3 -**  **3:** Commenters 0195, 0211, 0259 and 0261 stated that EPA should not set identical standards for modified, reconstructed and new units given the technical limitations of modified and reconstructed units. Commenter 0195 also stated that co nsidering that modified units do not experience the same degree of alteration as reconstructed units, the commenter recommends that EPA apply the highest limits included in the proposal, i.e., 1,100 lb CO 2 /MWh for large sources and 1,200 lb CO 2 /MWh for sma ller sources. Commenter 0259 also stated that given that modified units do not experience the same level of phy sical change as reconstructed units, EPA should finalize a higher range than that included in the proposal

- 1,200 lb CO 2 /MWh gross for large mod ified CTs and 1,300 lb CO 2 /MWh gross for smaller modified CTs. Commenter 0211 stated the Proposed Rule improperly imposes identical standards for newl y constructed, modified, and reconstructed natural gas

- fired stationary combustion turbines. The commenter stated existing sources generall y cannot meet the same emission standard as a newl y constructed source. The commenter stated modified or reconstructed NGCC units should be subject to an emission standard that is higher than newly constructed units. The co mmenter also supported the Proposed Rule's rejection of carbon capture and sequestration (CCS) as BSER. Commenter 0261 stated modified combustion turbines should not be forced to comply with the same standards as those for new units given that existing un its were not designed with the technical standards and technology that appl y to new units today. The commenter stated units that are modified cannot take advantage of the same design standards and technology that would allow new units to meet such stringent limits. The commenter stated that due to these technical restrictions, the limits for natural gas

- fired stationary CTs should differentiate between, new, modified, and reconstructed units. The commenter also stated the overl y stringent emission standards , could possibly preclude utilities from making modifications that would improve efficiency , which would reduce the heat rate (Btu/MWh) and the CO 2 emissions rate (lbs/MWh).8

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**Response 8.3 -**  **3:** The EPA is withdrawing the proposed emission standard for modified stationary co mbustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.3 -**  **4:** Commenter 0257 stated that EPA should exempt certain operat ional modes from Subpart KKKK compliance. The commenter stated that EPA's regulations for modified and reconstructed NGCC units should expressly exclude two modes of operation that are not t ypical for NGCC combustion turbines. According to the commenter, m an y combustion turbines are permitted to fire oil as a back

- up fuel for up to 30 day s per y ear, especiall y during periods of curtailment of natural gas when supplies are short, and it is vital that this mode of operation be kept available to ail such units to mitigate risks to reliability . The commenter stated The Agency has provided no emissions data to justify an y NSPS for combined cy cle combustion turbines when they

are firing oil. The commenter suggested that EPA should expressly exclude periods of oper ation when units permitted to do so fire oil as a back

- up fuel. Alternatively , the commenter recommended EPA should further anal yz e CO 2 emissions during oil

- fired operations and propose an NSPS that adequatel y accounts for such periods or re

- evaluate, develop and propose a separate standard for dual

- fuel units. The commenter stated that modifying the standard in these way s would help acco mmodate partial load operations, specific unit design and operational site characteristics, as well as the use of backup fuel. Commenter 0257 also stated that some NGCC units that would be subject to the modified or reconstructed source NSPS have designs that allow the operators to by pass the steam cycle and operate in simple cy cle mode when necessary . The commenter urged EPA to exempt simple cycle mode operations from compliance when an NGCC unit falls below the 33 percent capacit y factor in that mode. **Response 8.3 -**  **4:** Th e EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will remain “existing sources” subject to 111(d). **Comment 8.3 -**  **5:** Commenter 203 stated many of the same concerns expressed for reconstructed units apply

to the Proposal for modified Subpart KKKK units. The commenter provided the following points:

- No technical support document in the rulemaking docket that specifically discusses modified Subpart KKKK EGUs or that contains an y anal ys es of emissions data was found. In particular, anal ys es that would justify the setting of any

emissions limit for modifications are absent. So as to comply

with CAA 307(d)(3 ), EPA should withdraw its proposal until it has developed and included within the rulemaking docket the necessary supporting information;

- Itis even more important for EPA to set a reasonable performance standard for modified Subpart KKKK units, as comp ared to reconstructed units, given the much higher likelihood that future projects could trigger the modification threshold. As there is no explicit requirement in the modification regulations that mirrors the requirement that reconstructions must be techn ologicall y and economically feasible to apply to a given project, a rate limit for8

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modifications equal to the same number for reconstructions arguabl y results in a more stringent limit for the more likely

to occur modification. Given the scope and magnitud e of a triggering project

- much lower than a project costing 50% of a comparable new facility , and instead an increase in hourly

emissions

- if an ything, it would seem that modification performance standards for the same source t ypes should perhaps be some what less stringent that reconstruction standards. Both should be less stringent that performance standards for new KKKK units.

- Because it may

be infeasible for EPA to properl y set performance standards, it could set design, equipment, work practice or o perational standards under 111 (h). Alternatively , here EPA is justified in declining to promulgate performance standards for modified or reconstructed Da or KKKK units, since EPA concludes in its RIA that the Proposal will produce no significant costs or benefits;

- EPA does not have the authority to set source
- specific performance standards for Subpart KKKK units, and instead must hew to the governing parameters of 111 (b). Standards must be set for properl y categorized (or subcategorized source t ypes), and energy efficiency

audits have no place in lieu of the required approach in 111 (b);

- Once EPA develops the required emissions analyses, it should set the standards at a level that provides for 99% compliance;

- Simple cy cle units should be exempt from the rule in all cases. Simple cycle units cannot meet the same standards as NGCC units (see further discussion below);

- When setting the performance standards for modified Subpart KKKK units, EPA must account for the fact that no add

- on equipment is curre ntl y available for CO 2 control, within the parameters of the determined BSER. As previously discussed, unlike many criteria pollutants (NOx, SO 2 or particulates), there is no add

- on equipment currentl y available to reduce CO 2 emissions. Coupled with the fa ct that all equipment degrades over time, becoming less efficient (thus emitting more CO 2 ), if EPA sets CO 2 performance standards for modified units too stringentl y, sources will have no margin for compliance. If a project must be undertaken for continued operations, but the project triggers a NSPS modification, the only choice may

be a permanent shut down of the units. EPA should not establish a NSPS that results in this outcome for modified Subpart KKKK units and, in fact lacks the authority to set such a rigorous standard. **Response 8.3 -**  **5:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct modifications will rema in “existing sources” subject to 111(d). **Comment 8.3 -**  **6:** Commenter 0215 stated that about 10 percent of NGCC units that were designed and built with truly modern high temperature materials cannot meet a 1,000 lb CO 2 /MWh

- gross limit and that only 96 percent of large (more than 850 MMBtu/h) units can meet a 1,100 lb CO 2 /MWh

- gross limit [See: Smith Turbine Report at 2 & 7, Fig. 1; and Attachment A at 3]. The commenter stated that EPA has failed to provide any information to justify that modified units that were constructed in the 1990s can match the emissions8

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performance of new turbines with more efficient designs that were built up to 25 y ears later. The commenter stated that turbine overhauls may allow some older units to approach their original design efficiency

but cannot bring these units up to the level of modern turbines. The commenter stated that an NSPS "establishes what every source can achieve, not the best that a source could do." The commenter stated that EPA should set a limit whereby at least 99 percent of modif ied units should be expected to comply

. **Response 8.3 -**  **6:** The EPA is withdrawing the proposed emission standard for modified stationary combustion turbines, as explained in Section IX.D.3.e of the preamble to the final rule. As a result, combustion turbines that conduct mod ifications will remain “existing sources” subject to 111(d).