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Chapter 7

Reconstructed Natural Gas-fired Stationary Combustion Turbines

The EPA notes that many of the comments in this chapter are similar to comments summarized

in Chapter 7 of the response to comments for the January 2014 proposal. More detailed 

responses are provided in the RTC for the January 2014 proposal. The EPA also notes that many

commenters combined comments for reconstructed and modified units. The responses included 

here are intended to only address reconstructed units.

Contents

7.1 Identification of BSER......................................................................................................... 2

7.1.1 NGCC Technology ............................................................................................................ 2

Technical Feasibility............................................................................................................. 12

Costs...................................................................................................................................... 28

7.2 Determination of the Level of the Standard....................................................................... 29

7.2.1 Large Units Limit of 1,000 lb CO2/MWh; solicited comment on range of 950-1,100 lb 

CO2/MWh ................................................................................................................................. 32

7.2.2 Initial Performance Test in Addition to Ongoing Average.............................................. 33

7.2.3 Load Following/Intermediate vs. Base Load Standard.................................................... 37
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7.1 IDENTIFICATION OF BSER

Comment 7.1-1: Commenter 0215 stated that EPA did not explain why it believes that its 

January 2014 analysis, which focused exclusively on whether new Subpart KKKK units could 

meet its proposed standards, is relevant to the proposed standard's achievability for existing 

turbines that are reconstructed or modified. The commenter stated that the Combustion Turbine 

TSD limited its analysis to emissions data from 2007 to 2011 for units that commenced 

commercial operation after 2000 and completely ignored data from earlier years and older units. 

Response 7.1-1: The EPA relied on the data for NGCC units that commenced operation in 2000

or after to determine what an achievable emission standard for reconstructed NGCC units. As 

discussed in Section IX.D.3.b of the preamble of this final rule, triggering the reconstruction 

provision requires a significant capital investment. It is reasonable to require a reconstructed 

combustion turbine to upgrade the turbine engine, the steam cycle, and integrate the two cycles 

to maximize efficiency. Many upgrade options are available such that reconstructed combustion 

turbines can meet the same standard as new combustion turbines. The standard is based on the 

performance of existing NGCC units and accounts for a wide variety of turbine sizes, operating 

conditions, site-specific conditions, and future degradation.

7.1.1 NGCC Technology

Comment 7.1-2: Commenter 0212 supported EPA's finding that modern, efficient NGCC 

technology is the BSER for stationary combustion turbines. The commenter noted that 

EPA solicited comment on whether the sales exemption in the proposed rule would be sufficient 

to account for the potential increased use of simple cycle combustion turbines due to the 

expected increased percentage of electricity generated from renewable generation in the future.

The commenter believes that the threshold is sufficient. Increasing the exemption for lower 

efficiency units would undermine EPA's BSER determination. 

In the whitepaper, "Meeting the Needs of a Low-Carbon Power Grid: A study of dispatchable 

generation to partner with renewables," that was attached to their comment, the commenter 

discussed the role of simple cycle and combined cycle technologies in accommodating the 

supply fluctuations from increased renewables based on two recent studies. They also provided a 

supplemental analysis of the ERCOT power market. While simple cycle plants provide 

advantages for non-spinning reserve, and are easier to start-up and shutdown, these capabilities 

are not broadly needed to accommodate increased renewables. The reviewed studies show that 

combined cycle plants are projected to be dispatched for longer periods of time than simple cycle 

plants, and to stay online throughout the day, meeting ramping demands through load changes as 

opposed to multiple starts. The ERCOT data show that combined cycle power plants ramp up 

and down to satisfy fluctuating demand; while simple cycle units are used to meet infrequent 

peaks in demand. This will result in lower net generating costs and lower CO2 emissions than 

starting and stopping simple cycle plants multiple times throughout the day. 

Response 7.1-2: The EPA acknowledges the commenter’s support. The EPA notes that for this 

final rule, we erred on the side of caution and finalized a conservative and flexible set of 
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requirements for all combustion turbines, including simple cycle and NGCC, to support the 

continued growth in renewable generation.

Comment 7.1-3: Multiple commenters (0146, 0150, 0187, 0199, 0203, 0275) noted that EPA 

had proposed "NGCC technology" as the BSER for modified and reconstructed natural gas 

combustion turbines, but was vague as to what "NGCC technology" includes. Commenter 0275 

stated that the rulemaking docket does not clearly define "NGCC technology," and without a 

definition of "NGCC technology," an owner, operator or regulatory agency would not know 

precisely what equipment would need to be upgraded if a unit has been determined to have been 

modified or reconstructed. Commenter 0146 stated that precisely what "NGCC technology" may 

be has implications for evaluating the cost of technology and standard-setting. The commenters 

stated that EPA must clarify what it means by "NGCC technology." Commenter 0150 stated that 

NGCC technology varies greatly based on the age and size of the unit, so to give an across the 

board BSER like "NGCC technology" is arbitrary and capricious. Commenter 0203 stated that 

the term was too imprecise to constitute a readily apparent delineation of the BSER for this 

source category.

Commenter 0146 argued that EPA had failed to make any attempt to distinguish among turbines 

that were designed and constructed over a period of decades; consequently, the 

commenter objected to the Agency's determination that it is BSER without further elaboration or 

subcategorization. 

Commenters 0150 and 0203 stated that NGCC technology has evolved over decades and 

continues to improve. Commenter 0150 argued that it is not possible for every NGCC unit to 

achieve the emission rates of NGCC units constructed today, regardless of the work performed. 

Commenter 0199 stated that the EPA's "judgment is to be weighted against its statutory function 

and limitations, the record searched to determine if indeed its decisions and reasons therefore are 

themselves reasoned." See National Lime Ass'n, 627 F.2d 416, 431 (D.C. Cir. 1980), citing 

Essex Chemical, 486 F.2d at 434.

Response 7.1-3: The commenter is mistaken about the purpose of the BSER determination. The 

BSER determination is use by the EPA to determine an appropriate technology to use as a basis 

for the corresponding emission standard. This final rule does not require the use of any particular 

technology. As discussed in Section IX.D.3.b of the preamble of this final rule, triggering the 

reconstruction provision requires a significant capital investment. It is reasonable to require a 

reconstructed combustion turbine to upgrade the turbine engine, the steam cycle, and integrate 

the two cycles to maximize efficiency. Many upgrade options are available such that 

reconstructed combustion turbines can meet the same standard as new combustion turbines. The 

standard is based on the performance of existing NGCC units and accounts for a wide variety of 

turbine sizes, operating conditions, site-specific conditions, and future degradation.

Comment 7.1-4: Commenter 0211 argued that natural gas would be central to whether the 

series of proposed NSPS would be achievable. In its proposed rule for new stationary sources, 

EPA defined a NGCC unit to be BSER for subpart KKKK sources. The commenter stated that 

EPA cited three reasons for its determination: (1) the low carbon dioxide (CO2) emission rate 

associated with NGCC generation; (2) the use of a heat recovery steam generator in combination 

with a steam turbine to increase system efficiency, and (3) the cost-effective operation of such 
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facilities. The commenter stated that in the proposed rule for existing stationary sources, EPA's 

analyses highlight the environmental attributes of NGCC. The commenter stated that EPA 

determined that NGCC units can produce as much as 46 percent more electricity from a given 

quantity of natural gas than steam EGUs and that generation from such units has the benefit of 

the inherently low-carbon content of natural gas. The commenter stated that in the current rule, 

EPA proposed to finalize the same standards for modified and reconstructed natural gas-fired 

stationary combustion turbines as the Agency did for new sources, noting that NGCC technology

is one of the lowest cost forms of baseload and intermediate load electricity generation. While 

the commenter has not endorsed EPA's overall approach to the establishment of GHG standards 

for new units under CAA section 111 (Specifically, ANGA objects to the inclusion of carbon 

capture and sequestration (CCS) technology in the determination of BSER for any EGU) the 

commenter stated that natural gas-fired generation would be a readily-available, cost-effective 

technology to reduce CO2 emissions from the electric generation fleet while maintaining 

reliability. The commenter said that such generation will be a central part of efforts to comply

with any final standard promulgated by EPA on the basis of this proposed rule or the proposed 

rules for new and existing stationary sources. The commenter stated that EPA must avoid 

creating barriers to use of natural gas or imposing measures that could unnecessarily drive up 

compliance costs. The commenter explained the benefits of natural gas to the environment and 

grid stability in comments filed on EPA's proposed rule for new stationary sources and 

specifically referenced and incorporated by reference those comments. 

Response 7.1-4: The EPA acknowledges the commenter’s support.

Comment 7.1-5: Multiple commenters (0224, 0227, 0257) requested that EPA exempt simple 

cycle CTs from the proposed rule. The commenters noted that EPA proposed that modified and 

reconstructed CTs be subject to the same emission standards as applicable to new units, "which 

are based on BSER being efficient NGCC technology." Commenter 0224 argued that it is 

unrealistic to force modified or reconstructed units to comply with the same standards as those 

for new units given the technical constraints existing units face in comparison to new units. 

Commenter 0224 stated that adopting the same NGCC standard would require that a CT 

installing an add-on control, such as SCR to lower NOx emissions, would be effectively forced 

to convert the CT into an NGCC. The commenter stated that the rule cannot be set to favor 

certain technologies and that the appropriate response would be to set higher limits with the 

range for modified or reconstructed CTs as compared to the limits based on a new NGCC in 

recognition of the differences between the two.

Commenter 0224 suggested that EPA consider adopting the CT exemption initially proposed for 

new units. Commenter 0224 stated that, as noted there, simple cycle CT units that supply power 

to the grid are primarily used as peak units, and only infrequently as base or intermediate load 

power. Commenter 0224 stated that because simple cycle CT units serve as peaking units and for 

other system reliability purposes, but not as base load units, these limited and different functions 

distinguish them from NGCC units and other EGUs, which are designed to and regularly serve 

base and intermediate load functions. Commenter 0224 stated that exempting CTs from the 

proposed rules would not have a dramatic impact on emissions levels, even if the CTs, when 

used for peak or reliability purposes, temporarily exceed the proposed standards.
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Commenter 0227 stated that, while it may be theoretically possible to add a heat recovery steam 

generator to any simple cycle turbine, many such units perform specific duty that does not justify

such expense. Commenter 0227 stated that EPA proposed to deal with this through the 

applicability criteria, which limit the applicability of the standards to units whose production 

equals one-third of their potential output. Commenter 0227 cited their comments on the NSPS 

for new units recommending a simple exclusion for simple cycle units from these standards. 

Commenter 0227 stated that simple cycle machines perform valuable functions, and their 

wholesale replacement with combined cycle capacity simply because it is more efficient ignores 

the purposes for which such units were originally constructed. The commenter stated that EPA 

can and should make reasonable distinctions between sizes and types of facilities, and clearly 

propose to exclude simple cycle turbines from these requirements.

Response 7.1-5: The non-base load subcategory provides adequate flexibility for simple cycle 

turbines that reconstruct. When an owner or operator is contemplating reconstruction, they will

determine what percentage electric sales they anticipate in the future. Similar to newly 

constructed units, if they anticipate selling electricity in excess of the percentage electric sales 

threshold, NGCC (or an equivalent technology) will be required to comply with the base load 

subcategory emission standard.

Comment 7.1-6: Commenter 0245 stated that NGCCs need to have the flexibility of operating in 

simple cycle mode where conditions warrant and that those circumstances must be excluded 

from compliance determination calculations. The commenter stated that NGCCs are sometimes 

built in stages, with the heat recovery steam generator and steam turbine added after construction 

and installation of the combustion turbine. The commenter stated that they can also be designed 

to operate in either mode to provide market response flexibility and to provide for continued 

operations during repair or maintenance of the steam turbine.

Response 7.1-6: The EPA disagrees with the commenter that simple cycle operation in an 

NGCC unit should not be counted towards compliance demonstration calculations. The final rule 

does not set separate standards for simple cycle versus combined cycle units. The emission limit 

required for a unit is based on the percentage of the potential electric output sold to the grid.

Further, the base load emission standard includes sufficient flexibility for limited operation of the 

combustion turbine engine without generation from the steam cycle.

Comment 7.1-7: Commenter 0245 argued that EPA had not considered the effect of the 

expected increase in renewables deployment and the resulting effects of increasing cycling of 

combined cycle units to support the integration of variable renewable resources. The commenter 

stated that thirty states have mandatory renewable energy standards with long term and near term 

incremental targets, and that seven states have voluntary programs. The commenter stated that 

new NGCCs will be built in an era that will require increased cycling due to the increased 

intermittency of non-baseload energy sources. The commenter stated that combined cycles 

operate most efficiently and effectively in a steady state while simple cycle units produce the 

lowest emissions during startup and shutdown, and that combined cycle technology is not BSER 

during frequent start and low capacity-factor operation.

Response 7.1-7: In the final rule, NGCC has not been identified as the BSER for non-base load 

unit. NGCC has been identified as the BSER for base load units. As explained in Section 
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IX.C.4.b, the BSER for non-base load units is the use of clean fuels. Therefore, NGCC units that 

cycle, have frequent starts and stops, and operate at part load conditions will only have to comply

with an input-based standard based on the use of clean fuels as long as they remain below the 

percentage electric sales threshold. Our analysis of emissions data demonstrates that the base 

load emission rate of 1,000 lb CO2/MWh-g is readily achievable by NGCC units operating at ase 

load. See Section IX.C.4.b of the final rule preamble for more details on the EPA’s rationale. 

Comment 7.1-8: Multiple commenters (0149, 0157, 0193, 0226, and 0250) argued that EPA has 

not explained how NGCC units, as BSER for modified and reconstructed natural gas turbines, 

can provide the same services as simple-cycle CTs. Commenters 0149 and 0226 stated that 

simple-cycle CTs are designed and built to provide specific grid support services, and argued 

that it is not appropriate to assume that NGCC units can set the standards for simple-cycle CTs 

or always be used to replace simple-cycle CTs. 

Commenter 0193 stated that, while NGCC units are also capable of rapid start and deployment, 

they are not nearly as agile as simple-cycle units and cannot fulfill the same role. Commenter 

0193 stated that because of the added complexity of the associated steam cycle, a combinedcycle plant is unable to respond as quickly and flexibly as a simple-cycle turbine. Commenter 

0193 stated that while many simple-cycle units are capable of multiple start and stop cycles per 

day, frequent start and stop cycles of NGCC facilities also induce significant thermal stress and 

associated operational cost and reliability tradeoffs that must be considered in the plant 

operation. As an example, commenter 0193 noted that an LMS100 simple-cycle gas turbine can 

achieve base load power of 100 MWs within 10 minutes of being called upon by the grid 

operators to fill an energy demand. Commenter 0193 stated that this same turbine could be 

loaded to approximately 25 MW (25 percent load) and any point in between while rapidly

ramping between these load points, and that this fast start and ramping can be done multiple 

times a day to satisfy fluctuating energy demand. Commenter 0193 stated that by comparison, a 

7F combined-cycle plant in a 2 on 1 configuration, in which the 2 gas turbines supply steam to a 

single steam turbine --a very common configuration in the United States--can also start in 10 

minutes and achieve approximately 80 percent of gas turbine load for up to 200 MWs in 10 

minutes. Commenter 0193 stated that the second gas turbine can be started along with the first 

turbine, or soon thereafter. The commenter stated that while starting the gas turbines, the exhaust 

heat is passing through the HRSG and begins generating steam, and that this process requires 

additional warm-up time. Commenter 0193 stated that the steam turbine would follow in load as 

the steam becomes available and can reach full load in roughly 30 minutes for an overnight plant 

shutdown, or take as long as 3 hours if the plant has been shut down for a few days and cooled to 

ambient temperature. Commenter 0193 stated that this illustrates how starting a combined-cycle 

plant is much more complex than starting a simple-cycle gas turbine and why it would not be 

done to satisfy an anticipated shorter term load demand.

Along with the ability for fast and frequent starting, commenter 0193 stated that the size of the 

plant also is a factor in dispatch and optimizing response to operational demand. Commenter 

0193 stated that if a 75 MW load demand is anticipated, an LMS100 would be the most logical 

technology to satisfy that demand, and it would make no sense to start a plant capable of over 

600 MWs to satisfy a relatively small transient anticipated demand. Commenter 0250 concurred, 

stating that NGCC plants are too large to meet their utility's needs for flexibility and redundancy. 

Commenter 0250 stated that even if operated without heat recovery, NGCC plants still have 
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capacities starting at 225 MW for each turbine, far larger than the 100 MW capacity increments 

identified by their utility's system planning process. Commenter 0250 stated that the over-design 

problem worsens with consideration of the full capacity of these plants when operated in 

combined-cycle as they are designed (with heat recovery steam generation), which increases 

their capacity to a range of no lower than 305 MW. Commenter 0250 stated that if such a plant 

were to fail during a period of peak demand, they would not have the redundancy needed to meet 

that demand. Commenter 0250 stated that having multiple units with the proposed design 

configuration (i.e., four turbines at 100 MW capacity each), they can accommodate malfunctions 

or failures in their system (including failure of a unit at MPS), even during periods of peak 

demand, and that he incremental capacity growth of roughly an additional 100 MW per year also 

matches the load and resource needs resulting from expected growth and retirements in their 

utility system, while also spreading out capital requirements.

By building a plant with four GE LMS100 turbines, each with a capacity of 100 MW, 

commenter 0250 said their utility can deploy power over the range of loads needed to meet the 

project objectives while still meeting emission limitations (from 50-400 MW). Commenter 0250 

stated that NGCCs cannot simultaneously provide 50 MW increments of power while also 

meeting emission limitations: At 50% load, the minimum capacity of NGCCs range from 112.5-

169.5 MW, which is significantly greater than the lower range of power output needed for this 

project. Commenter 0250 stated that in order to provide the lower increments needed by their 

utility (50 MW), these NGCCs would need to be operated outside of their design range, which 

means that they would not meet emission limitations and could cause damage. Commenter 0250 

stated that if they were to operate a unit above the level dictated by demand (contrary to prudent 

and accepted practice by a regulated utility) so as to run within emission limits that would still 

lead to wasted fuel and higher emissions (criteria pollutants and GHG). Commenter 0250 stated 

that even when over-producing power at 50% load, NGCCs would be at higher heat rate (lower 

efficiency) than the LMS100s at full load, thus the presumed low heat rates of a NGCC that form 

the basis for the pending proposed rules would not be obtained. Commenter 0250 stated that the 

GHG emissions (lb/MWh) and the heat rate (Btu/kWh) will be very high when NGCCs are 

operated at 50% capacity for longer periods. Commenter 0250 stated that simple-cycle LMS100s 

can be operated very efficiently at low loads (i.e., 50 MW) without damaging the equipment and 

with increased efficiency and lower emissions relative to the NGCCs.

Commenter 0193 stated that the increased flexibility of simple-cycle units in comparison with 

NGCC units is also reflected in the operation of the power market. Commenter 0193 stated that 

NGCC units typically bid in the previous day for generation on the following day, while simplecycle units can bid for generation on the same day--a mere hour ahead of the demand, or even go 

online with full output in less than 10 minutes in response to real-time market demands. 

Commenter 0193 stated that it would be prohibitively expensive for traditional NGCC units to 

bid on the same day. Commenter 0193 stated that while NGCC plants are able to respond to grid 

variability demands, simple-cycle units provide another layer of flexibility for rapid starts, stops, 

and grid fluctuations on a smaller scale than NGCC units can provide, and because these starts 

and stops correlate with lower efficiency and increased CO2 emissions, simple-cycle units used 

in this manner will not be able to meet the proposed standards.
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Commenter 0157 stated that, with regard to reconstructed simple-cycle gas turbines, adding an 

HRSG is a question of space, design, and cost, given that simple-cycle units are designed to 

operate at low capacity factors. Commenter 0157 stated that installing an HRSG on a lowcapacity factor unit, and one that may frequently operate on high-cost fuel oil, makes little 

economic sense. Commenter 0157 stated that EPA is not permitted to redefine the source. 

Commenter 0157 stated that simple-cycle and combined-cycle gas turbines are designed to serve 

different purposes, and that requiring the redesign of a reconstructed simple-cycle CT as a 

combined-cycle CT would frustrate the purpose of the source.

Commenter 0193 noted that CAA section 111 requires EPA to develop a standard of 

performance that reflects the degree of emission limitation achievable through the application of 

BSER, taking into account the cost of achieving such reduction and any nonair quality health and 

environmental impact and energy requirements that the Administrator determines has been 

adequately demonstrated. The commenter argued that the proposed standards are not achievable 

for simple cycle units, are not cost effective, and fail to appropriately consider the other key

factors in a BSER determination. The D.C. Circuit has found that "EPA has a statutory duty to 

promulgate achievable standards." See Nat'l Lime, 627 F.2d at 443. EPA is required to explain 

how the standard is "achievable under the range of relevant conditions which may affect the 

emissions to be regulated, ..." including "under most adverse conditions which can reasonably be 

expected to recur." See Id. at 431 n.46, 432-33. 

According to commenter 0193, the GE LMS100, the most efficient simple cycle gas turbine on 

the market today, would not be able to meet the proposed standard throughout its life. Indeed, it 

is only capable of meeting the proposed standard in a newly installed and nondegraded condition 

and only when operating under optimal operating conditions. The commenter provided a figure 

(from their comments on EPA's January 2014 NSPS), which illustrated some of the factors that 

affect the CO2 emissions performance of the LMS100, including ambient temperature, partial 

load operation, and degradation. The commenter argued that these factors show that even this 

highly efficient unit would be anticipated to have emissions that exceed the proposed rule's 

proposed limit during the lifetime of its operation. Even "as new" and under ideal condition, its 

operation is likely to result in an emission level of 1,020 lb CO2/MWh, which exceeds the 

proposed limits.

While the LMS100's inability to meet the standard is sufficient on its own to show a lack of 

achievability, commenter 0193 noted that the data show that the remainder of available simple 

cycle units also cannot meet the standard. Indeed, the majority of simple cycle gas turbines 

operate at efficiencies less than 43.6 percent--the performance level necessary to reach even the 

upper end of the proposed range. Moreover, because simple cycle units, like combined cycle 

units, may be parked for some periods of time at a low load due to variability in demand, these 

low-load periods must also be taken into consideration in setting the standard. For example, the 

43.6 percent efficiency cited for full load operation is reduced to approximately 36 percent at 50 

percent load, with a corresponding increase in CO2 emissions of approximately 17 percent. 

Similarly, load cycling can also lead to inefficiencies. Finally, during natural gas curtailments, 

the units may be required to operate on fuel oil, leading to increased CO2 emissions.

Commenter 0215 urged EPA to exclude simple cycle combustion turbines explicitly from the 

rule because, as a practical matter, simple cycle turbines cannot achieve the proposed standards 
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for new turbines. The commenter cited 79 Fed. Reg. at 1459 that simple cycle turbines "operate[] 

infrequently" and "only contribute[] small amounts to total GHG emissions," , and are vital to the 

reliable supply of electricity in this nation because they are a cost-effective means of providing 

peak power, especially during hot days. The commenter stated that simple cycle combustion 

turbines are also increasingly important for reliability purposes to support intermittent renewable 

energy sources, such as wind generation, due to their ability to quickly commence operations. 

Commenter 0257 stated that, if modified, high capacity factor, simple cycle turbines are to be 

subject to a GHG NSPS, the Agency should create a separate subcategory for these units, 

determine an appropriate BSER that does not require conversion to NGCC, analyze emissions 

from units in the subcategory, consider all of the requirements of section 111, and propose a limit 

that is achievable.

Multiple commenters (0149, 0226, 0167/0277, 0203, 0257) stated that EPA has created standards 

that effectively prohibit reconstruction and modification of any type of CT. The only way that an 

existing CT of any type can comply with the proposed standards, if it were to exceed the 

proposed applicability threshold, is to become a new NGCC unit. If a unit can only comply with 

standards for modified and reconstructed units by becoming a new unit of a different type, the 

proposed standards are not achievable by that unit.

Commenters 0203 and 0260 did not agree that it is feasible to convert existing natural gas CTs to 

NGCC technology. Commenter 0203 believes it would be highly unlikely that NGCC is BSER 

for a simple-cycle turbine (and that this configuration would be technologically and 

economically feasible, as required by the general reconstruction rule at 40 CFR 60.15(b)(2)). 

This proposed requirement would also violate the statutory prohibition in section 111 against 

requiring any new or modified source to install and operate any particular technological system 

of continuous emission reduction to comply with any NSPS. EPA has failed to provide any 

support for concluding that conversion of existing simple-cycle units to NGCC (i.e., to achieve 

the BSER level of performance--modern, high efficiency NGCC technology) is technically or 

economically feasible across the capacity range of potentially affected simple cycle units. 

Somewhat casually, EPA notes that if a simple cycle CT owner/operator wishes to avoid 

triggering the performance standard for a project, it can simply maintain the current operational 

exclusion. An operational cap unaccompanied by a BSER analysis is not a lawful performance 

standard under the statute. 

Commenter 0260 indicated it is not technically feasible to convert existing CTs to NGCCs 

because there are numerous constraints at existing units, such as physical space (including the 

amount of land comprising the site), water availability limitations, the amount of natural gas 

available to the site during times of high demand, and electric power transmission restrictions. 

Such constraints can be avoided when building a new unit on a greenfield site, but not when 

modifying or reconstructing an existing unit. EPA has failed to perform any analysis of the 

technical feasibility of NGCC conversions at existing units. See id. at 34,989. Commenter 0260 

did agree with EPA that NGCC technology with CCS is not BSER for modified or reconstructed 

combustion turbines. Id. at 34,989-90. An owner/operator of an existing source that is 

undertaking a reconstruction or modification has challenges not faced when building a new 

NGCC unit because the existing unit may be located at a site with space constraints that would 
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make installation of CCS problematic. Id. at 34,989. The commenter further agreed with EPA 

that high efficiency simple cycle aeroderivative turbines are not BSER for modified or 

reconstructed combustion turbines. Id. at 34,989-90

Commenter 0255 did not support EPA's proposal that the BSER for a modified simple cycle 

combustion turbine is to convert the unit to NGCC unit. The commenter stated that requiring 

conversion of a simple cycle turbine to NGCC could create a disincentive to completing a project 

that might improve the efficiency of an existing simple cycle turbine. Secondly, the commenter 

stated that while it is technically feasible to convert some simple cycle turbines to NGCC units, it 

is not necessarily feasible to convert all simple cycle units to NGCC. The commenter 

cited constraints can preempt such a conversion, including water availability, natural gas supply 

constraints, existing power purchase agreements, transmission system interconnection 

agreements and air quality/permitting restrictions. The commenter stated that EPA should 

explicitly exempt simple cycle turbines from being an affected unit as long as the modification 

does not convert it to NGCC.

Response 7.1-8: The commenter is mistaken in stating that the standard for simple cycle units is 

based on the performance of NGCC units. In the final rule, NGCC has not been identified as the 

BSER for non-base load units. NGCC has been identified as the BSER for base load units. As 

explained in Section IX.C.4.b of the preamble, the BSER for non-base load units and multi-fuelfired units is the use of clean fuels. The non-base load subcategory is sufficiently flexible to 

allow for the continued use of simple cycle combustion turbines. See Sections IX.C.4.a.(2) and

IX.C.4.b of the final rule preamble of the for more details..

Comment 7.1-9: Commenter 0250 stated that, because the proposed performance standards have 

only been demonstrated by NGCCs operating at sustained high loads, the proposal effectively 

dictates turbine technology choice. The manufacturer of their simple-cycle LMS100 turbines 

commented in support of the simple-cycle exclusion in the original (withdrawn) proposed rule, 

relaying that the LMS100---its most efficient simple-cycle gas turbine--is only capable of 

meeting combined-cycle performance standards in "newly installed and non-degraded condition 

and under optimal operating conditions." See Letter from Larry A. Boggs, General Electric's 

Director and Senior Counsel of Government Affairs, to EPA, Docket ID. EPA-HQ-OAR-2011-

0660-9978 (June 25, 2012).

Response 7.1-9: The EPA disagrees that the final standard has only been demonstrated for 

NGCC units operating at sustained high loads. An analysis of actual operating data demonstrates 

that the final emission standard is achievable by NGCC units in all base load operating 

conditions. High-efficiency simple cycle turbines like the LMS100 will be subject to the nonbase load emission standard so long as they remain below the percentage electric sales threshold.

Comment 7.1-10: Commenter 0232 agreed with EPA that it is appropriate to base performance 

standards for modified and reconstructed natural gas combustion turbines on the performance of 

NGCC technology. The commenter noted that EPA proposed to determine that NGCC 

technology is the BSER for natural gas combustion turbines, for the same reasons EPA presented 

in the preamble to the proposed carbon pollution standards for new EGUs. As EPA observed in 

the preamble, NGCC is an efficient generating technology that is highly cost-effective and in 

widespread use. However, the commenter does not believe that a performance standard based on 
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NGCC alone reflects the BSER for modified and reconstructed natural gas combustion turbines, 

as section 111 requires. Rather, the BSER for these sources consists of NGCC in addition to the 

requirements of an applicable section 111(d) state plan. As discussed in section I of their 

comments, EPA's proposed goals under section 111(d) reflect four "building blocks" that are 

based on well-established means for reducing carbon pollution from the power sector as a whole. 

The commenter strongly supported EPA's determination in the proposed emission guidelines that 

this system-based approach constitutes the BSER for all EGUs that were existing sources as of 

January 8, 2014, including existing natural gas combustion turbines.2 This system-based 

approach is equally effective and efficient in reducing emissions from existing EGUs that 

subsequently undertake modifications and reconstructions--and better fulfills the statutory

criteria for BSER than any of the proposed alternatives. Indeed, failing to apply this systembased BSER to natural gas combustion turbines that modify or reconstruct would potentially lead 

to increased emissions if those EGUs do not also remain subject to section 111(d) state plans--a 

perverse outcome that would be inconsistent with the structure and purpose of section 111, as 

discussed in section I of their comments. Accordingly, EPA should explicitly provide in the final 

rule that compliance with an applicable section 111(d) state plan, together with an NGCC-based 

emission limitation, represents the BSER for modified and reconstructed natural gas combustion 

turbines. 

The commenter also urged EPA to ensure that the final standards of performance for these 

sources reflect the best emissions performance demonstrated by NGCC facilities. In comments 

filed jointly with other environmental organizations on the proposed carbon pollution standards 

for new EGUs, the commenter argued that they demonstrated that the proposed performance 

standards of 1,000 lb/MWh (for units with heat input greater than 850 MMBTU/h) and 1,100 

lb/MWh (for units with heat input less than 850 MMBtu/h) could be easily achieved by almost 

all NGCC facilities currently in operation. More stringent standards could be cost-effectively

achieved by currently available NGCC technologies, and would have substantially lower 

emissions.

The commenter did not take a position here as to whether EPA should adopt one of the 

alternative characterizations of the BSER that are presented in the proposed emission guidelines, 

but the commenter intended to file comments on this issue in Docket ID No. EPA-HQ-OAR2013-0602.

Response 7.1-10: The EPA is not finalizing the proposed once-in-always-in approach.

Therefore, a reconstructed base load natural gas-fired combustion turbine will have to comply

with an emission standard based solely on modern, efficient NGCC technology and will no 

longer be an existing source subject to a 111(d) state plan.

Comment 7.1-11: Commenter 0192 did not disagree with EPA's conclusion that NGCC 

technology is BSER for natural gas turbines, but they believe the standards of performance 

proposed by EPA do not accurately reflect the emission limits that can be achieved by NGCC 

facilities under real-world operating conditions. To better reflect the emission limits that can be 

achieved in practice by NGCC turbines, the commenter urged EPA to revise the proposed 

standards for modified and reconstructed natural gas turbines.
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Commenter 0214 noted that EPA proposed to require modified and reconstructed NGCC units to 

meet the same standards of performance proposed for new NGCCs, but argued that the 

improvements needed to be made at an existing NGCC unit to achieve the performance of a new 

NGCC unit would likely not be insignificant or cheap, pointing to EPA's statement that "the 

performance of combined cycle technology has improved significantly since 2000." EPA never 

identifies the specific technologies that an existing NGCC can implement to achieve the 

performance of "modern high efficiency NGCC technology." EPA also does not provide the cost 

of implementing these technologies at existing sources

Response 7.1-11: The EPA has concluded that a reconstructed NGCC unit can achieve the same 

emission rate as a new NGCC unit because reconstructed units can essentially be rebuilt as new 

units and because the emission standard both must achieve is conservative and based on the 

performance of a wide variety of existing units. Therefore, the commenters are simply incorrect 

that the EPA has not taken real-world operating conditions into account. The specific 

technologies that a reconstructed turbine can use to improve efficiency are detailed in Section 

IX.D.3.b of the preamble.

Technical Feasibility

Comment 7.1-12: Multiple commenters (0146, 0158, 0189, 0193, 0203, 0212, 0239, 0250, 

0257, 0267) stated that EPA's identification of NGCC technology as BSER for both modified 

and reconstructed natural gas-fired CTs incorrectly assumes that older units can be 

modified/reconstructed to achieve the same standards as new units. Referring to comments from 

UARG, commenter 0239 argued that the expectation that an older combustion turbine can be 

reconstructed to perform at the same level of a state-of-the-art new NGCC unit is flawed and 

therefore the proposed standards for modified and reconstructed natural gas-fired units are 

unachievable.

Commenter 0187 disagreed with EPA that in all instances older natural gas combustion turbines 

will be able to replace sufficient hardware to become effectively a brand new NGCC unit and 

meet the same emission standard. The exhaust gas temperatures and flow rates of different 

natural gas combustion turbine makes and models can vary significantly. Not all combustion 

turbines are suitable for economical NGCC conversion. Furthermore, many combustion turbines 

may not have the space available for the equipment necessary for the NGCC conversion. NGCC 

technology has improved for decades and continues to improve.

Commenter 0212 noted GTA's comments that it would not be appropriate to assume that older 

existing gas turbines can achieve the same levels of performance as a new state-of-the-art 

turbine. Existing units experience a certain amount of unavoidable degradation in performance 

over the gas turbine operating life. While a portion of the degradation can be recovered as a part 

of the turbine upgrade, it is never feasible to recover all of the performance to bring the unit to 

the same level of performance as a new, clean gas turbine installation.

Commenter 0203 questioned whether an existing source, with inherently fewer degrees of 

engineering (design and construction) freedom, can meet the same emissions standard as a new, 

greenfield source. In the absence of specific emissions data or case studies, any presumption 

regarding the appropriate standard should be in favor of setting a higher (i.e., less stringent) 
7-13

standard for reconstructed units than those which are new. The commenter also noted that all 

equipment degrades over time and becomes less efficient. If EPA sets the performance standards 

too stringently, sources that trigger a NSPS (modifications or reconstructions) may have no 

choice but to shut down rather than move forward with a triggering project. The commenter did 

not believe it was the intent of Congress when it passed section 111 (or EPA when it 

promulgated 40 CFR part 60) to force shutdowns of power plants due to NSPS. EPA should be 

careful to avoid this unintended consequence of NSPS set too stringently. Standards must be 

achievable under section 111.

Commenter 0267 stated that the proposed standards for new units are based on ideal operating 

conditions that do not reflect the range of real world operating conditions nor the likely in-use 

degradation that is experienced by every single plant when operating for long periods of time. 

Accordingly, the standards are unlikely to be achievable in the real world. Applying these same 

standards to modified and reconstructed units only compounds the problem. Existing units that 

trigger modification or reconstruction will be older units that are based on earlier designs that do 

not incorporate the design improvements that have made today's turbines highly efficient. While 

modification and reconstruction projects often improve performance, they generally cannot 

restore the unit to the performance on par with a new unit. Existing units that undergo 

modification or reconstruction will also generally not be able to achieve the same standards as 

newly constructed units due to unrecoverable losses in efficiencies from degradation.

Commenter 0257 stated that setting the same emission standards for both new and modified and 

reconstructed sources is anomalous. As a technical matter, older units are not capable of 

replacing sufficient equipment to match the emissions performance of a brand-new NGCC unit 

on a cost-effective basis, and the Agency has not provided any technical support for basing its 

proposed standards on such an assumption. New sources may have several inherent advantages 

over existing, yet-to-be-modified or reconstructed sources that would make less aggressive 

standards for modified and reconstructed sources reasonable. New sources are constructed so 

that all component pa1ts are integrated from the start. Sources that undergo modifications or 

reconstructions, by contrast, must contend with the added expense and technical hurdles of 

adapting new technology to existing infrastructure. Existing, yet-to-be-modified or reconstructed 

sources, by contrast, must work within the confines of their existing sites.

Commenter 0257 noted that an industry group consultant has analyzed emissions data from 248 

NGCC turbines that began operation between 2007 and 2013. The consultant found that about 90 

percent could meet a limit of 1,000 lb CO2/MWh, while 98 percent of large (> 850 MBtu/hr) 

units could meet a CO2 limit of 1,100 lb CO2/MWh. These results are substantially below the 99 

percent achievability target that EPA has historically applied in NSPS rulemakings and would 

require a significant number of NGCC units to retire if they became subject to the proposed 

standards. In order for 99 percent of turbines to comply, EPA would need to finalize an NSPS of 

over 1,400 lb CO2/MWh. The proposed NSPS for modified and reconstructed units would apply

to any existing combustion turbine, including many that commenced operations before 2000. 

EPA has provided no information to justify that modified units constructed in the 1990s can 

match the emissions performance of new turbines with more efficient designs that were built up 

to 25 years later. These older units have no available means to improve heat rate beyond design 
7-14

levels. Older turbines cannot replicate the emissions perfom1ance of modern turbines through 

overhauls or other refurbishments.

Commenter 0189 argued that applying these stringent limits to existing units that are modified 

and reconstructed is not appropriate since it would be more difficult to incorporate retrofits to 

existing units. There is no add-on pollution control technology that is feasible at this time to 

reduce CO2 emissions from modified and reconstructed units, such as would be available for 

compliance with a NOx performance standard. The EPA has not provided justification that these 

proposed CO2 limits are achievable for modified and reconstructed units. For example, the 

commenter has considered as a resource generation option the conversion of an existing simple 

cycle natural gas-fired combustion turbine to a combined cycle at some future time. This 

conversion would serve to lower the current maximum load emission rate of the unit which is

approximately 1,300 lb CO2/MWh to between 1,000 and 1,100 lb CO2/MWh, making it more 

efficient. However , the modified unit could be subject to the more stringent limit in the proposed 

rule of 1,000 lb CO2/MWh for sources with heat input >850 MMBtu/h. Since this modified unit 

would not be able to comply with the EPA's proposed limit, they may not be able to utilize this 

simple cycle conversion to combined cycle as a resource option to meet growing demand.

Commenter 0146 disagreed that an NGCC unit that is 20 or more years old will invariably be 

able to undertake sufficient equipment upgrades to meet the same CO2 emission rate as modem 

technology. To the contrary, as noted in comments of UARG, due to changes over time in the 

design efficiency of NGCC units, it is not possible to bring older combustion turbines up to the 

efficiency levels of modem units. By design, newer NGCC units are capable of operating at 

significantly higher efficiency than older units in the existing NGCC fleet - particularly those 

built before the year 2000. "NGCC technology," as EPA terms it, has been evolving and 

improving for decades and continues to improve. Most newer turbines utilize new hightemperature materials that allow them to achieve higher efficiencies that are not attainable for 

older turbines using other, lower-temperature technologies. See Lowell L. Smith, "Analysis of 

the Proposed Modified and Reconstructed GHG NSPS for Natural Gas Combined Cycle 

Turbines," (Oct. 7, 2014).

Although EPA is always required to ensure that any NSPS is achievable for the entire source 

category, commenter 0146 stated that it is particularly important that EPA provide a sufficient 

margin for achievability here, given that the Agency itself acknowledges that these units have no 

other feasible means to lower their CO2 emissions profiles beyond the rate associated with each 

unit's "NGCC technology." Therefore, an older NGCC unit that is modified or reconstructed but 

cannot meet the proposed NSPS with its current NGCC configuration does not have an option of 

installing add-on technology and would either have to entirely replace its existing facility with a 

new modem turbine (and likely a new heat recovery steam generator) at exorbitant cost or retire 

altogether in order to comply, as noted in the Smith report. An NSPS for these units that is not 

achievable could place a significant portion of the existing generation capacity at risk of forced 

retirement. The commenter owns two NGCC facilities that were constructed in 1986 and 1994, 

and if the units at either of these facilities were deemed to be subject to the proposal, those units 

would be unable to meet a standard based on the emissions performance of NGCC units 

constructed 20 or more years later. Commenter 0158 argued that section 111(b) standards for 

CTs must be achievable at the time of proposal.
7-15

Commenter 0193 noted that they are continually advancing gas turbine technology, investing 

nearly a half billion dollars per year in gas turbine development, with the primary objective of 

improving turbine and plant level efficiency. As a result of these significant investments, today's 

new gas turbines are more efficient than the existing fleet of gas turbines. Through this ongoing 

technology investment, while a 7B gas turbine manufactured in the 1970s generates roughly 60 

MWs with an efficiency of roughly 30.5%, today's state of the art 7HA gas turbine can generate 

330 MWs with an efficiency in excess of 41%. While many of the latest technology

advancements can be retrofitted to improve the performance of existing turbines, the commenter 

argued it is simply not feasible to bring the existing fleet of turbines to the same advanced level 

of performance as a new NGCC plant installed today. Even when retrofitted, existing plants will 

not share the operating capabilities of today's NGCC plants. This includes the fast start 

capabilities built into today's plants. Today's plants are able to start faster than a plant built even 

a decade ago. This faster start capability means less CO2 emissions during start events leading to 

a lower 12-month average emission rate. Heat recovery boilers, and other systems, must be 

specially designed to accommodate the increased thermal stresses resulting from these faster 

starts. These are capabilities that cannot be retrofitted into an existing boiler. Instead, these 

features must be designed into the equipment during initial installation. Because of these factors 

and the unavoidable performance degradation encountered by all operating plants, existing plants 

will have a higher 12-month rolling average CO2/MWh emission rate than a new plant installed 

today.

Commenter 0193 noted that, because modified and reconstructed units are by definition existing 

units, their base level of performance is generally less efficient than a comparable new unit due 

to non-recoverable sources of in-use degradation and the continued improvements in the design 

of new units. While the modification or reconstruction may help bridge this efficiency gap, in 

most instances, it is unlikely to completely change the existing unit so that it operates like a 

newly constructed turbine. Moreover, EPA based its January 2014 BSER determination for new 

units on emissions data from 2007 to 2011 for natural gas-fired (non-CHP) combined cycle units 

that commenced operation on or after January 1, 2000, and that reported complete electric 

generation data, including output from the steam turbine, to EPA. This database, however, does 

not include all existing gas turbines, many of which went into service prior to 2000.

Commenter 0250 noted that the proposed NSPS for GHG emissions from gas-fired stationary

CTs established two subcategories: those with heat input greater than 850 MMBtu/h, and those 

with less. However, no data in the administrative record demonstrates that stationary CTs can 

meet the proposed standard for either category. This is because the proposed standards are 

"based on modern, efficient natural gas combined cycle technology." The Technical Support 

Document for the New NSPS explains that EPA "reviewed the emissions rates of natural gasfired combined cycle units" to determine that "over 96% of these units achieve the proposed 

standards with no excess emissions." See Memorandum from EPA to the EGU NSPS Docket, 

Docket ID No. EPA-HQ-OAR-2013-0495-0082 (Sept. 2013). EPA only found that "because 

over 90 percent of small and large existing [combined-cycle] facilities are currently operating 

below the emission rates of 1,100 lb CO2/MWh and 1,000 lb CO2/MWh, respectively, these rates 

are considered BSER for new [combined-cycle] facilities in those respective subcategories [and] 

[t]hese values represent the emission rates that a modern high efficiency [combined-cycle] 

facility located in the U.S. would be able to maintain over its life." EPA made no such finding 
7-16

for stationary CTs. Accordingly, EPA must set other performance standards, considerate of the 

differences in thermodynamic performance, operating characteristics, and emissions profiles not 

only between NGCCs and SCTs, but also among SCTs. The standards could even consider that 

aeroderivative SCTs are more efficient at low loads.

Commenter 0215 stated that it is contrary to general engineering principles that an existing 

source, with inherently fewer degrees of engineering freedom, could meet the same emission 

standard as a new, greenfield source. The commenter stated that reconstructed NGCC units 

should have a standard that is less stringent than new units. 

In order to demonstrate that its proposed NSPS for reconstructed and modified units are 

achievable, multiple commenters (0146, 0149, 0150, 0189, 0193, 0199, 0201, 0203, 0257, 0267) 

stated that EPA must take into account a number of important factors. The commenters stated 

that EPA must "(1) identify variable conditions that might contribute to the amount of expected

emissions, and (2) establish that the test data relied on by the agency are representative of 

potential industry-wide performance, given the range of variables that affect the achievability of 

the standard." See Sierra Club, 657 F.2d at 377 (citing Nat'l Lime Ass'n, 627 F.2d at 433). In 

other words, the validity of EPA's achievability determination depends on how fully it has 

accounted for the variations among sources in the regulated category that could affect emission 

levels. 

Commenter 0146 noted that courts have repeatedly rejected NSPS that EPA deemed 

"achievable" based on test data from a narrow set of sample sources that did not represent the full 

range of relevant variability among sources to which the standard will apply. See e.g., Nat'l Lime 

Ass'n, 627 F.2d at 432-33; Portland Cement Ass'n, 486 F.2d at 396, 402. In addition, the 

commenter noted that EPA has traditionally set NSPS such that at least 95 percent of units 

subject to the standard would be expected to comply. The commenter stated that this reflects the 

fact that an NSPS "establishes what every source can achieve, not the best that a source could 

do." See Letter from Gary Mccutchen, Chief, New Source Review Section, EPA OAQPS, to 

Richard E. Grusnick, Chief, Air Division, Ala. Dep't of Envtl. Mgmt. at 1 (July 28, 1987) 

("Mccutchen Letter"). Commenters 0150 and 0201 went even further. Commenter 0150 argued 

that accounting for variable conditions generally requires a showing that at least 99 percent of 

new units would be expected to be able to comply with the NSPS. Commenter 0201 argued that 

EPA should modify the proposed standard to account for the operational characteristics of the 

entire gas generation fleet and address the inherent engineering limitations in modifying or 

reconstructing an existing unit as compared to building a new unit. Commenter 0201 said that 

this would address the issue where stationary CTs may not be able to meet the current proposed 

standards under certain operating conditions. The commenter noted that there are instances 

where stationary combustion turbines are needed to support large amounts of intermittent 

renewable energy generation, which requires the units to cycle on and off with much more 

frequency than a plant used to support base load energy needs. A stationary combustion turbine 

that has frequent startup and shutdown periods will have higher CO2 emissions than a unit that 

operates at steady state over the same time frame. In a similar comment, commenter 0149 stated 

that, in order to be achievable, the standards must reflect all operating conditions and anticipate 

that, in the future, NGCC units will be needed to help integrate increasing amounts of variable 

renewable generation into the grid. EPA's proposed section 111(d) guidelines, which 
7-17

contemplate a dramatic increase in the deployment of wind and solar generation, underscore 

these concerns. As more renewables are brought onto the system, NGCC units will ramp up and 

down more frequently, or, will run at lower capacity factors generally, which will degrade heat 

rates and increase emission rates.

Commenters 0193 and 0267 stated that EPA must assure that the final standards for new and 

modified or reconstructed gas turbines are achievable over the lifetime of the facilities 

considering the range of conditions, dispatching needs, capacity loads, in-use degradation, and 

startup, shutdown, and malfunction. The commenters noted that the Sierra Club courts has 

concluded that the standards must be based on reliable information representative of "potential 

industry-wide performance, given the range of variables that affect achievability of the 

standard." See Sierra Club v. Costle, 657 F.2d 298, 377 (D.C. Cir. 1981) (citing Nat'l Lime Ass'n 

v. EPA, 627 F.2d 416, 433 (D.C. Cir. 1980). EPA cannot base the standard on assumed operating 

conditions that are not reflective of how plants operate in practice, and EPA has not justified in 

the record a basis for dictating changes to the way that operators ensure their units are ready to 

come on-line in the event they are needed or ramp down when demand is reduced. EPA should 

revise the standard to ensure that it is achievable for the "industry as a whole" and "for all 

variations of operating conditions being considered anywhere in the country." See Nat'l Lime 

Ass'n. The performance of turbines in use is affected by a number of factors, including a range of 

ambient temperature, water cooling needs and technologies, operating demands, including 

increased load variations, and in-use degradation. Including startup and shutdown emissions in

the standards will also further challenge units in complying with any new standard.

Commenter 0193 noted that, when newly installed, their fleet of gas turbine products is capable 

of achieving the proposed emission limitations at base load operations. Establishing standards 

based on these optimal conditions, however, does not reflect the real world operating conditions 

or account for everyday scenarios where an NGCC unit will not be able to achieve the proposed 

limits. As a result, EPA's proposed limits do not represent BSER for these units. According to 

the commenter, section 111(a)(1) of the CAA requires EPA to establish standards of 

performance that 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." See 42 U.S.C. 7411(a)(1). In 

determining what is achievable and adequately demonstrated, EPA must consider the range of 

current and anticipated operating conditions in the United States. This includes the challenges 

faced by dramatically different physical environments and operational needs in response to 

rapidly changing electricity demands. Any standard that fails to account for these real world 

conditions does not represent BSER because it is not achievable or adequately demonstrated. 

EPA must take into account the following important factors in establishing BSER for new units. 

 Steam turbine condenser cooling: In a NGCC unit, condensing the steam back down to 

water creates a vacuum at the exit of the steam turbine that greatly enhances the steam 

cycle efficiency. The condensing of the steam, however, requires a cooling source, which 

was achieved historically by once-through cooling water drawn and returned to a body of 

water. Given that once-through cooling is now prohibited on new plants in the United 

States, most plants today rely on a cooling tower, or air cooling using an air-cooled 
7-18

condenser. Cooling towers lose a portion of the cooling water through evaporation. At 

sites, notably in arid regions, where water availability is limited, air-cooled condensers 

are used. Unfortunately, air-cooled condensers are not as efficient at creating the vacuum 

at the exit of the steam turbine resulting in a decrease of plant efficiency. As a result, 

plants with air-cooled condensers can be up to 1 percent less efficient than those with 

cooling towers at nominal conditions.

 Ambient temperatures: A gas turbine's energy production and efficiency depend on the 

mass of air that can pass through the turbine. On hot days, air density is lower so less air 

mass can pass through the machine, making the turbine less efficient on hot days 

compared to cold ones. A nominal gas turbine will be 0.5 percent less efficient on a 100-

degree day than a 59- degree International Organization for Standardization (ISO) day. 

Hot temperatures also affect the performance of the air-cooled condensers noted above. A 

plant with a cooling tower will be approximately 4 percent less efficient on a 100-degree 

day than a 59-degree ISO day, while a plant with an air cooled condenser will be closer to 

8 percent less efficient. Thus, a plant located outside of Las Vegas, with an air-cooled 

condenser to limit water usage, could easily have 5 percent higher CO2 emissions than 

the fleet average on hot days. As a result, a plant in a hot arid climate will be significantly

less efficient than a plant in a cooler climate with available water resources. Because of 

these factors, the emission level must be established with sufficient margin to 

accommodate these temperature and design driven efficiency differences.

 Varying Operational Loads: Under the proposed standard, compliance is determined on a 

12-month rolling sum, including all potential operation during that period. NGCC plants 

are most efficient when operating at base load during normal operating conditions. While 

EPA might assume that operators can dictate and adjust their operations to achieve the 

standard or to operate in a particular mode, like base load, this is not the case. A large 

proportion of the installed fleet is operated under an approach referred to as Automatic 

Generation Control (AGC). In AGC mode, the grid operators, not the plant, effectively

control plant operation and load by sending demand signals to the plant with the plant 

automatically adjusting to satisfy that demand requirement. Operational flexibility is a 

core gas turbine attribute. Many plants do not operate consistently at base load, but rather 

may be "parked" at low load during overnight periods. The reason for parking these units 

is to reduce production during times of low demand (e.g., when people are sleeping and 

the lights are out). A parked unit will have higher emissions per MWh but overall lower 

mass emissions (and fuel savings) compared with maintaining base load. A BSER 

determination requires EPA to consider these factors in setting the standard for new units. 

Moreover, any BSER analysis should also take into account expected changes in 

operations to support increased renewable energy. It is expected that grid operators soon 

will require increased operating periods at a part-load or even minimum-load "parked" 

condition. This condition allows the unit to be on "hot standby," thereby enabling the 

plant to respond rapidly to load changes without the time delay and equipment stresses of 

full plant shutdown and startup sequence. The rule must accommodate these future trends 

in operation.

 Start-up and Shutdown Emissions: During a plant startup or shutdown, there are periods 

of fuel burn during which either no energy is being produced or relatively low levels of 

energy are being dispatched to the grid. As a result, during startup and shutdown, the 

mass of CO2 emitted per MWh produced is very high and will certainly exceed 1,000 lb. 
7-19

CO2/MWh limit. Emissions during startup are also variable between installations and can 

vary even at the same plant due to their dependence on site- and time-specific factors, 

such as equipment temperature at the initiation of startup. For example, while a plant that 

has been shut down overnight can start in generally less than an hour because the 

equipment is still warm from previous operation, that same plant may require over three 

hours to achieve full operating temperature if it has been down for a week and the 

equipment is at ambient temperatures. A rapid startup can induce significant thermal 

stresses to the equipment, especially "cold" equipment, which means that the startup 

period must necessarily be longer. This will result in significantly higher CO2 emissions. 

The more startups and shutdowns and the more cold starts, the greater the challenge a 

given unit will have in complying even under otherwise optimal conditions.

 Supplemental Duct Firing: Supplemental duct firing is commonly deployed in NGCC 

plants to increase steam production and boost the plant output during periods of peak 

demand. Supplemental thermal energy is introduced in the ductwork leading into the heat 

recovery steam generator (HRSG) through the use of gas combustors, commonly referred 

to as duct burners. This technology provides essential inexpensive capacity, especially on 

hot days with peak energy demand. The use of supplemental firing to provide peak 

generation, however, reduces overall plant efficiency with a resulting increase in 

CO2/MWh.

 Combined Cycle Power Plant Degradation: Various operational and environmental 

factors will cause NGCC plant performance to degrade over time. Representative causes 

of performance degradation are fouling of the gas turbine compressor, wear of flow seals 

allowing leakage within the gas turbine and steam turbine flow paths, erosion and 

corrosion of heat exchanger surfaces in the HRSG, steam condenser and cooling tower, 

and other performance impacts to ancillary components. This is not an exhaustive list but 

rather illustrates typical causes of unavoidable performance degradation that will be 

encountered at any NGCC plant. While some degradation is partially recoverable through 

maintenance, some degradation is permanent. The most significant cause of power plant 

degradation is fouling of the gas turbine compressor. The rates of both compressor 

fouling and performance loss are a result of the variation in environmental conditions, 

machine operating scenarios, and maintenance practices. Performance loss during normal 

operation is minimized by periodic on-line compressor water washes, in which water and 

cleaning agents are sprayed into the compressor while the turbine is in operation, and offline compressor water washes, in which water and cleaning agents are sprayed into the 

compressor while the unit is not operational, allowing a more thorough compressor 

cleaning. Annual, average plant efficiency would form the best basis to compare 

degradation effects to the 12-month average CO2 emission standard. The level of 

degradation experienced by any individual plant varies greatly depending on site 

conditions, operating level, start frequency, and ambient factors--such as to sea water and 

associated sea salts in the air. Given the wide range of potential degradation causes, it is 

difficult to establish a representative value, although recent permit BACT evaluations 

have included degradation margins as high as 5 to 10 percent to account for the broad 

range of operational effects on NGCC plants.

Thus, in establishing BSER for new, modified, and reconstructed units, commenter 0193 argued 

that EPA must consider the impact of all of these factors on the likely in-use performance of new 
7-20

gas turbines over time. While the commenter's fleet of gas turbines can readily achieve the 

proposed emission standards when operating new at base load steady-state conditions, they

cannot meet the standards if they are used as expected to meet the range of power demands 

needed in today's electricity market. EPA cannot ignore these real world factors and operating 

conditions. Failing to account for these conditions would be inconsistent with CAA section 111, 

and would undermine the rapid deployment of cleaner energy sources, including renewable 

sources. EPA should revisit its approach and develop a final action that is supported by the 

record.

In a similar comment, commenter 0257 questioned whether the proposed emissions standard for 

NGCCs has been adequately demonstrated to be achievable continuously under normal, realworld operating conditions. The inability to meet the 1,000 lb/MWh proposed standard can be 

attributed to several factors. For example, the efficiency of an NGCC unit and the CO2 emissions 

rate are affected by the following factors:

 Operations at part load: Emissions (on an output basis) increase significantly as units are 

operated at partial load for a variety of reasons. Many NGCC units, even those designated 

as "baseload," are required to operate at lower capacities to accommodate integration of 

renewables and other system, grid or electricity market specific needs. Additionally, 

combined-cycle units that have a two-on-one or three-on-one configuration may have 

occasions to operate with one CT out of service for maintenance, which reduces 

efficiency due to reduced heat input into the steam cycle. And as the renewables that are 

mandated by this rule are integrated into the grid, lower and interrupted load service can

be expected for NGCCs, especially the older, smaller units that are not as efficient, 

making their emission rates even higher.

 Use of backup fuel: The proposed standard does not appear to incorporate the use of oil 

as a backup fuel. The use of oil in times of natural gas curtailment (e.g., severe weather 

events, such as hurricanes or interrupted natural gas supply) will increase the average 

CO2 emissions rate. This was vividly demonstrated during the very cold winter of 2013-

2014 when natural gas was in short supply due to pipeline constraints and oil was called 

on to allow CTs to supply the maximum load to the electric grid. Furthermore, given the 

number of NGCCs predicted as the primary technology of choice for new power 

generation and their potential impact on natural gas supply and natural gas infrastructure, 

companies may be required by state commissions or siting authorities to have oil 

available as a back-up fuel in order to support electric reliability.

 Startup and shutdowns: These actions are part of normal operation but do not constitute 

baseload operation and should be exempt from the rule. At start-up, a combustion turbine 

operates essentially as a simple-cycle unit until the steam generator is heated. This is part 

of the design of an NGCC unit. Some NGCC units do not simply follow load, they are 

taken off -line and restarted on a daily basis, increasing the CO2 emission rate based on 

market conditions.

 Performance degradation: While EPA states that it accounted for performance 

(efficiency/heat rate) degradation in setting the proposed standard (based on the design 

performance specification analysis), the standards do not account for the fact that each 

unit is specific in design (e.g., number and efficiency of inlet filters) and operating site 

conditions (dusty open plants, high ambient temperature), and the fact that the percent 
7-21

degradation over time is variable. Referring to the "What You Should Know About 

Design Ratings" document included in the 2012 proposal docket10, ''power and heat rate 

may degrade by 2-6 percentage points during the first 24,000 hours of operation." To the 

extent that some degradation can be recovered, it is not always possible or feasible to 

correct a slightly degraded function immediately, as repairs often involve extended tear 

downs and must be scheduled well in advance.

Multiple commenters (0142, 0146, 0150, 0152, 0203, 0211, 0215, 0226, 0257, 0260) argued that 

EPA had failed to provide the data and analysis demonstrating that the proposed standards are 

achievable by modified and reconstructed units, or explaining how the Agency reached its 

conclusions. Commenter 0211 stated that EPA had not supported its conclusion that modified 

and reconstructed simple cycle units can meet the same standard as NGCC units. Commenter 

0211 stated that EPA posited, without supporting technical information, that simple cycle 

turbines can be modified and reconstructed to become NGCC units. Commenters 0211 and 0142 

stated that a search of the docket does not reveal any TSD for modified or reconstructed natural 

gas-fired combustion turbines, despite such being referenced in the preamble to the proposed rule 

(Commenter 0211 stated that EPA does include a TSD in the docket regarding BSER for 

Reconstructed Steam Generating Units and IGCC facilities and a TSD for the New Source GHG 

NSPS Combustion Turbine Standard, however, the document does not directly refer to or 

consider modified or reconstructed sources). Commenter 0211 stated that no economic analysis 

is provided to support the assertion that when operated at higher capacity factors, conversion of a 

simple cycle unit to an NGCC is cost-effective. While the commenter 0211 believes that cost 

savings may be possible given the relative efficiency of NGCC units, it was not clear that this 

would be true in every instance and, in any event, EPA offered only unsupported, conclusory

statements on this matter. Commenter 0142 stated that without such missing data and related 

materials, States and the public cannot properly determine the basis on which the EPA claims 

that these emission standards are achievable or reasonable. 

In a similar comment, commenter 0203 also stated that the docket does not contain any TSD 

supporting the proposed NSPS for reconstructed subpart KKKK units, but contains only a TSD 

corresponding to the January 2014 proposed NSPS for new units. Commenter 0203 stated that no 

explanation as to why this TSD for new units justifies or is relevant to the proposed performance 

standards for reconstructed or modified units was given. Commenter 0203 stated that EPA's 

analysis of emissions in this TSD in support of its new NGCC unit proposal was restricted to 

CO2 emissions data from 2007 to 2011 for NGCC turbines; data from earlier years for older units 

was ignored. Because the proposal addresses the expected performance of existing units (which 

are then modified or reconstructed), however, commenter 0203 believes data for older units must 

also be included (and properly addressed) in any analysis that determines the capabilities of a 

reconstructed (or modified) unit. Commenter 0203 also noted that EPA failed to provide the 

emissions data that justify the proposed standard and that account for the many variables that 

affect examined emission rates, and without such data, EPA has failed to show that its proposed 

standards are achievable, in derogation of CAA section 307(d)(3).

Similarly, commenter 0257 stated that EPA had not provided any TSD or other information to 

justify that modified units that were constructed in the 1990s can match the emissions 

performance of new turbines with more efficient designs that were built up to 25 years 
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later. Commenter 0257 requested that EPA set a limit whereby at least 99 percent of modified 

units would be expected to comply, consistent with previous NSPS determinations.

Commenter 0150 and 0215 stated that EPA had failed to provide data or analysis in the record 

explaining why EPA believes the emission rates for modified and reconstructed units are 

achievable under the range of operating conditions these units will experience. Commenter 0150 

stated that EPA is required to "(1) identify variable conditions that might contribute to the 

amount of expected emissions, and (2) establish that the test data relied on by the agency are 

representative of potential industry-wide performance, given the range of variables that affect the 

achievability of the standard." See Sierra Club v. Costle, 657 F.2d 298, 377 (1981) (citing Nat'l 

Lime Ass'n, 627 F.2d 416, 433 (D.C. Cir. 1980)). Commenter 0150 stated that This generally 

requires a showing that at least 99 percent of new units would be expected to be able to comply 

with the NSPS, and absent that information, the standards, if finalized, would necessarily be 

arbitrary and capricious.

Commenter 0215 stated that an analysis of existing units performed by a UARG consultant 

demonstrates that a substantial number would likely not be able to achieve the Proposed 

Standards.

Multiple commenters (0149, 0161, 0167/0277, 0193, 0195, 0201, 0214, 0261) argued that the 

standards for modified and reconstructed natural gas CTs should not be the same as the standards 

for new sources. Commenter 0201 stated that a modified and reconstructed unit is different than 

a brand new one because there are inherent limitations on the modifications that can be 

performed on an existing unit. Commenter 0161 stated that the inherent differences between new 

and modified/reconstructed plants justify a higher emission standard for the latter. According 

to commenter 0161, when an existing plant is modified or reconstructed, the process is 

constrained by the layout of the facility, siting issues, compatibility problems between new and 

existing equipment, and other challenges. Commenter 0161 stated that those types of problems 

do not exist when constructing a new plant. Commenter 0161 stated that EPA recognized the 

important differences between new and modified/reconstructed units when it set the emission 

standards for modified and reconstructed coal-fired units. Commenter 0161 cited the New 

Source Proposal, that the emission standard for new coal-fired units is 1,100 lbs CO2/MWh over 

a 12-month operating period or 1,000-1,050 lbs CO2/MWh over an 84-month operating 

period. Commenter 0161 stated that under the modified/reconstructed source proposal, the 

emission standards for reconstructed coal-fired units are 1,900 lbs CO2/MWh for sources 

exceeding 2,000 MMBtu/h and 2,100 lbs CO2/MWh for sources with a heat input rating of 2,000 

MMBtu/h or less. Commenter 0161 stated that the modified source proposal establishes less 

stringent emission standards for modified and reconstructed coal-fired units, as compared to new 

coal-fired units, and that EPA should adopt the same approach for modified and reconstructed 

natural gas-fired units. 

Commenters 0149, 0167 and 0277 stated that setting the same emission standards for both new 

and modified and reconstructed sources is anomalous on its face. Commenters 0149 and 

0167/0277 stated that new sources may have several inherent advantages over existing, yet-tobe-modified or reconstructed sources that would make less aggressive standards for modified and 

reconstructed sources reasonable, and that EPA has recognized this. Commenters 0149 and 
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0167/0277 stated that new sources are constructed so that all component parts are integrated 

from the start, while sources that undergo modifications or reconstructions, by contrast, must 

contend with the added expense and technical hurdles of adapting new technology to existing 

infrastructure. Commenters 0149 and 0167/0277 stated that the potential achievability, costs and 

energy impacts of the standards may differ dramatically for modified and reconstructed sources 

compared to new sources. Commenters 0149 and 0167/0277 stated that new greenfield 

development projects can be sited on plots of land of sufficient size to accommodate required 

emission control technology, while existing, yet-to-be-modified or reconstructed sources, by

contrast, must work within the confines of their existing sites. Commenters 0149, 0167 and 0277 

stated that EPA nowhere indicates that it considered these and other distinguishing factors in 

proposing the same emission standards for new sources as well as modified and reconstructed 

sources.

Commenter 0193 stated that important differences remain between newly constructed units and 

existing units that are modified and/or reconstructed. Commenter 0193 stated that existing units, 

even when reconstructed, face greater physical and technical constraints than new units 

and existing units may trigger modification in response to a number of different physical or 

operational changes. Commenter 0193 stated that these differences should influence the BSER 

determination and the resulting standards for modified and reconstructed units. Commenter 0193 

stated that while EPA correctly requests comment on many of the issues raised in the proposed 

rule for new units regarding the emission standards, neither the statute nor real-world 

considerations require that new and modified and reconstructed unit have the same standards.

Commenter 0195 stated that it is inappropriate for EPA to force modified and reconstructed 

combustion turbines to comply with the same standards as those for new units due to technical 

constraints. Commenter 0193 stated that for newly designed units, manufacturers have access to 

computer modeling that allows for the optimization of the turbine and auxiliary systems design 

so as to assure development of the most efficient unit, whereas modified and reconstructed units 

cannot take advantage of the same design synergies that would allow new units to meet such 

stringent limits.

Commenter 0261 stated that reconstructed combustion turbines should not be forced to comply

with the same standards as those for new units given that existing units were not designed with 

the technical standards and technology that apply to new units today.

Commenter 0214 stated that modified and reconstructed NGCC units and simple-cycle CTs 

would not be able to continuously meet the same performance levels as newly constructed units 

that maintain state-of-the-art technologies. Commenter 0124 stated that EPA has provided no 

factual support for its contrary assertion and should withdraw its proposal to require modified 

and reconstructed NGCC units and simple-cycle CTs to reach the same levels of performance as 

new NGCC units.

Multiple commenters (0150, 0192, 0193, 0195, 0224, 0242, 0253, 0259, 0267) noted that the 

Agency proposed standards of performance for modified/reconstructed units of 1,000 lb 

CO2/MWh-gross for large (greater than 850 MMBtu/hr) units and 1,100 lb CO2/MWh-gross for 

small (less than 850 MMBtu/hr) units. The commenter stated that these standards are identical to 
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EPA's proposed standards for new units. Commenters also noted that EPA requested comment 

on a range of limits for modified/reconstructed stationary combustion turbines: for large units, a 

range of 950-1,100 lb CO2/MWh-gross; for small units, a range of 1,000-1,200 lb CO2/MWhgross. Commenters indicated that the standards for modified/reconstructed stationary combustion 

turbines should be increased to 1,100 and 1,200 lb CO2/MWh, or higher, for large and small 

units, respectively. 

Commenter 0150 argued that existing sources are not likely to be capable of meeting the same 

emission rates as new sources, and that EPA has not provided a basis for proposing otherwise. 

Commenter 0150 stated that unless EPA can provide technical information to the contrary, 

reconstructed NGCC units should have a standard at least 100 lb CO2/MWh-gross higher than 

new units. Commenter 0150 believes that the EPA failed to identify what additional "headroom" 

the NGCC would need where those units are intermittent (mostly wind- following) if the state 

has existing or new renewable energy requirements. Commenter 0150 stated that as NGCC units 

age, they lose efficiency. Commenter 0150 stated that NGCC units that engage in heavy ramping 

for wind following may actually increase their CO2 emissions as those NGCC units age or as 

more intermittent renewables are added. The commenter stated that APPA does not know what 

that headroom should be but that higher CO2 emissions should be anticipated as the 

modified/reconstructed units age.

Commenter 0193 noted that EPA based its January 2014 BSER determination for new units on 

emissions data from 2007 to 2011 for natural gas-fired (non-CHP) combined cycle units that 

commenced operation on or after January 1, 2000, and that reported complete electric generation 

data, including output from the steam turbine, to EPA. The commenter stated that this database 

does not include all existing gas turbines, many of which went into service prior to 2000, and as 

a result, a BSER determination requires EPA to allow up to a 10 percent higher allowable 

emission rate for modified and reconstructed units than the achievable BSER standard of 1,100 

lb/1,200 lb CO2/MWh-gross standard for new gas turbines.

Commenters 0195 and 0224/0253 recommended EPA set limits for modified/reconstructed 

sources at the high end of the range for both the large and small categories, while commenter 

0259 recommended EPA finalize emission limits of 1,200 lb CO2/MWh-gross for large 

combustion turbines and 1,300 lb CO2/MWh-gross for smaller combustion turbines (At least one 

of the CTs in commenter 0259's fleet that has been installed in the last ten years cannot meet the 

currently proposed number for reconstructed CTs). Commenters 0195 and 0259 stated that, for 

newly designed units, manufacturers have access to computer modeling that allows for the 

optimization of the turbine and auxiliary systems design so as to assure development of the most 

efficient unit. Commenters 0195 and 0259 stated that modified and reconstructed units cannot 

take advantage of the same design synergies that would allow new units to meet such stringent 

limits. Commenters 0195 and 0259 stated that given these technical limitations, EPA's standards 

for gas-fired stationary CTs should differentiate between new, modified, and reconstructed units.

Commenter 0224/0253 noted that modified and reconstructed units are constrained by the 

existing unit's design and configuration, while newly built units are not so constrained. 

Commenter 0224/0253 stated that consequently, modified and reconstructed units cannot achieve 

as stringent a level of emission reductions. Commenter 0224/0253 noted that EPA has 
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consistently subjected existing sources to less stringent standards than new sources. Commenter 

0224/0253 stated that applying standards at the high end of a reasonable range of emission limits 

for reconstructed and modified sources would provide the same leeway, recognizing that the 

technical and design constraints of existing sources limit options for reconstruction or 

modification. Commenter 0224/0253 stated that as units get older, they do not run as efficiently

as when they were new, which diminishes their ability to achieve as stringent emission levels as 

new units. Commenter 0224/0253 stated because EPA has established a range of reasonable 

emission limits and setting a limit at the high end still falls within the reasonable range, adopting 

the high end of the range for modified or reconstructed EGUs is permissible.

Commenter 0192 believes that EPA should increase the standard of performance for both large 

and small natural gas turbines by 100 lb CO2/MWh, to 1,200 lb CO2/MWh (HHV) for units less 

than 1500 MMBtu/h and to 1,100 lb CO2/MWh (HHV) for larger units. Commenter 0192 stated 

that these higher standards of performance would better reflect the emission limits that can be 

achieved by natural gas turbines in real-world conditions. Commenter 0192 stated that NGCC 

turbines operate most efficiently when providing baseload power; however, in the real world 

NGCC turbines more commonly provide intermediate load power where operations are less 

efficient and emissions rates increase. Commenter 0192 stated that to account for inefficiency

created by more frequent cycling due to intermediate loads, along with steam turbine condenser 

cooling, changes in ambient temperature, supplemental duct firing, and plant degradation over 

time, it is appropriate to raise the proposed standards of performance by 100 lb CO2/MWh.

Commenter 0267 argued that, given the age distribution of the existing fleet and what turbines 

are likely to achieve in-use over the range of real world operating conditions, BSER for modified 

and reconstructed turbines is an emission limitation of 1,200 lb CO2/MWh for larger units with a 

heat input rate above 1,500 MMBtu/h (HHV) and 1,300 lb CO2/MWh for smaller units with a 

heat input rate equal to or less than 1,500 MMBtu (HHV).

Commenter 0242 did not feel meaningful comments could be formed due to the many variables 

and ranges presented...all compounded by the multitude of changes being considered regarding 

applicability. Commenter 0242 stated that while it is apparent the lower end of the range is not 

achievable, it may be possible the higher end of the range could be achievable for some types of 

units. Commenter 0242 stated that EPA had not provided enough specificity for the commenter 

to determine achievability of the proposed standards of performance and provide meaningful 

comment.

Commenter 0209 requested that EPA increase the emissions limit for modified and 

reconstructed NGCC units from 1,000 or 1,100 lb CO2/MWh to 1,250 lb CO2/MWh to account 

for load following. The commenter stated that while a new NGCC unit would likely meet an 

emission rate limit of 1,000 lb CO2/MWh when utilized for base load generation, it is unclear 

whether NGCC units can sustain that level of efficiency when they are used for load following, 

such as to firm up delivery of wind and other intermittent generation. The commenter stated 

that the Front Range Power Plant is an NGCC plant owned and operated by the commenter's 

utility that began operation in 2002. The commenter stated that analysis of the historic emissions 

data from the part 75 certified CEMS demonstrates rolling 12-month emission rates above 1,000 

lb CO2/MWh for a number of months in 2011. The commenter stated that these slightly higher 
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emissions correspond with lower generation months and an increase in plant cycling. The 

commenter stated that the data also indicated that lb CO2/MWh emission rates were lower during 

time periods of higher generation and reduced plant cycling. The commenter stated that as 

utilities seek to increase reliance on intermittent renewable resources, modest flexibility in the 

emission limit will improve their confidence to expand renewable generation.

Commenter 0226 argued that the proposed standards for modified and reconstructed natural gas 

turbines are not adequately supported and, therefore, should not be applied. The commenter 

stated that the proposed emission standards for modified and reconstructed natural gas-based 

stationary CTs are based on the emission rate EPA asserts is achieved by efficient new natural 

gas combined-cycle units, however there is no evidence offered in the proposal that new units' 

performance would not more easily meet the limits simply because everything is new. The 

commenter stated that the potential achievability, costs and energy impacts of the standards may

differ dramatically for modified and reconstructed sources versus new sources, and the proposal 

does not indicate that there was consideration of these and other distinguishing factors while 

proposing the same emission standards for both new sources and modified and reconstructed 

sources.

Commenter 0213 urged EPA not to allow modified stationary combustion turbines to "elect, as 

an alternative to the otherwise applicable numerical standard, to instead meet a unit-specific 

emission standard that is determined by the CAA section 111(d) implementing authority based 

on implementation." The commenter stated that there is no reason to create a unit-specific 

alternative to the proposed standard of performance for modified stationary combustion turbines. 

The commenter stated that the proposed standard is based on a BSER of efficient combined 

cycle natural gas technology. The commenter stated that CCGT technology provides baseload 

and load-following generation at a relatively low cost compared to other methods of fossil fuel 

combustion, and for many simple cycle turbines, particularly those operating at higher utilization 

rates, "the cost of replacement with a NGCC [CCGT] unit is likely to be cost effective based on 

consideration of fuel savings alone." The commenter stated that given that CCGT is both 

economically reasonable and adequately demonstrated, it would be arbitrary and capricious to 

adopt an emission limit for modified stationary combustion turbines that is less stringent than the 

emission limit achievable through the application of this technology. The commenter stated that 

EPA should not grant sources the option of complying with a unit-specific emission standard to 

be established by state authorities.

Response 7.1-12: The BSER for base load units has been identified as NGCC. The BSER for 

non-base load units has been identified as clean fuels. Whether a unit is classified as a base load 

unit or a non-base load unit depends on the amount of electricity sold to the grid, which is 

derived from a unit’s nameplate design efficiency and calculated as a percentage of potential 

electric output. The EPA notes that the data set used to determine the final base load standard 

includes units that commenced operation on or after 2000. These units represent approximately

90 percent of the existing NGCC capacity. Further, these units would have begun planning on 

construction years prior to that. Therefore, the final base load emission standard has been 

demonstrated for NGCC units using technology that is over 15 years old. Finally, 40 CFR 

60.15(b)(2) provides that if an owner or operator can show that it is not "technologically and 

economically feasible to meet the applicable standards set forth in this part” for a given unit, then 
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the reconstruction provisions will not apply. Therefore, the commenters’ concerns regarding 

technical feasibility are simply not an issue.

See Sections of IX.C.4.a, IX.C.4.b, and IX.C.4.c of the final rule preamble of for a more 

complete discussion of the EPA’s finale rationale for the BSER. See Sections IX.D.3.b, IX.D.3.c, 

and IX.D.3.d of the final rule preamble for a more detailed discussion of the EPA’s final 

regarding the achievability of the final standards.

Comment 7.1-13: Commenter 0193 stated that there was a significant deficiency in EPA's 

historical analysis, specifically the underrepresentation of larger, more efficient simple cycle 

units in the historical database. The commenter's first LMS100 simple-cycle gas turbine power 

plant entered commercial operation in July 2006, thus, it did not even exist for half of the period 

covered in the historical analysis and certainly did not achieve market penetration at that time. 

As described in more detail in the commenter's comments on EPA's January 2014 proposal, the 

LMS100 is the most efficient, and thereby lowest CO2 emitting, simple-cycle turbine available 

today. The commenter stated that since introduction in 2006, LMS100 sales have increased 

dramatically and are likely to continue to increase due to its ability to provide 100 MW of 

efficient and flexible power, plus its rapid start capability that allows it to achieve full power 

within 10 minutes. The commenter stated that in 2013 there was an 82 percent increase in 

operating units (28 to 51). The commenter stated that in Southern California alone, 19 LMS 

100s, came online bringing the total LMS100 count in California to 23, with an additional 5 units 

expected to enter the power generation market by the end of 2015. The commenter stated that 

these 23 units are capable of ramping up 1,200 MW/minute, while offering 2,400 MW of 

generation.

Response 7.1-13: The EPA specifically reviewed the operating data of LMS100 simple cycle 

combustion turbines. While these units tend to run more than traditional simple cycle units, the 

average percentage of electric sales (approximately 10 percent) was still well within the non-base 

load subcategory included in this final rule. In fact, no LMS100 in California has sold more than 

25 percent of its potential electric output. Based on this, we have concluded that the non-base 

load subcategory includes sufficient flexibility for the continued use of high efficiency simple 

cycle turbines.

Comment 7.1-14: Commenter 0176 stated that NGSC units offer significant advantages over 

NGCC units from a water conservation perspective and for that reason should remain as a 

resource for intermediate loads. The commenter stated that NGCC technology is a waterintensive process that can consume hundreds of millions gallons of fresh water per year. The 

commenter stated that a NGCC plant can easily consume more than 270 gallons per MWh of 

cooling water on an annual basis, whereas a NGSC unit consumes only 41 gallons per MWh. See 

Wendy Wilson, Travis Leipzig and Bevan Griffiths-Sattenspiel. Burning our Rivers: The Water 

Footprint of Electricity, River Network (April 2012): Portland, OR. The commenter stated 

that while it is possible to reduce the water requirements of a NGCC by using dry cooling 

methods, such as an air cooled condenser (ACC) instead of an evaporative cooling tower, the use 

of ACC technology can result in significant losses in efficiency and net output. The 

commenter cited a study conducted by EPRI, that "dry cooling imposes a heat rate and lostcapacity penalty on a plant that can range up to 25% during the hottest hour of the year and 

exceed 8% for over 1,000 hours at a hot, arid site. On an annual basis, plant output is reduced by 
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about 2%." See John S. Maulbetsch and Kent D. Zammit, Cost/Performance Comparisons of 

alternative Cooling Systems CEC/EPRI Advanced Cooling Strategies/Technologies Conference 

(June 1-2, 2005). 

The commenter stated that the ACC equipped plant will burn more fuel and increase air emission 

to produce the same net power produced by a NGCC unit using a traditional evaporative cooling 

tower and as demand for energy typically peaks during hot temperatures, this loss of efficiency

would be significant. The commenter stated that "depending on site meteorology, the capital cost 

of the dry cooling system ranges from $21-$26 million for the combined-cycle plant compared to 

$5.7-$6.5 million for wet cooling." 

According to commenter 0176, incentivizing NGCC technology that is water intensive is a 

particularly important consideration in water-starved areas such as Texas. The commenter stated 

that In parts of the country with arid climates that are particularly susceptible to drought 

conditions, excessive reliance on NGCC technology may not be feasible or a desirable option. 

The commenter stated that Texas is experiencing its third year of intense drought conditions, 

with the Texas Panhandle being hit especially hard.

Response 7.1-14: The commenter is mistaken that all combined cycle units consume more water 

than simple cycle units. Combined cycle units that use dry cooling technologies do no consume 

any more water than a comparable simple cycle unit. In fact, it is possible that a combined cycle 

unit uses less water than a simple cycle unit. Simple cycle units often use some type of water 

injection in the turbine itself to enhance performance and high efficiency intercooled simple 

cycle units have a cooling tower for interstage cooling. The EPA specifically review the 

emission rate for NGCC units with dry cooling technologies. The EPA was not able to identify

any impact on performance since these particular units performed just as well as comparable 

units with wet cooling systems. Water constraints are a site specific consideration, and the final 

base load emission standard has been demonstrated as achievable for units using dry cooling 

systems.

See sections of IX.C.4.a, IX.C.4.b, and IX.C.4.c of the final rule preamble of the EGU GHG 

NSPS for EPA’s response to the comments regarding the rationale for BSER.

See sections IX.D.3.b, IX.D.3.c, and IX.D.3.d of the final rule preamble of the EGU GHG NSPS

for EPA’s response to comments regarding rationale and achievability of the final standards.

Costs

Comment 7.1-15: Multiple commenters (0149, 0157, 0226, and 0242) rejected EPA's cost 

argument concerning NGCC technology. Commenters 0149 and 0226 stated that EPA had 

provided no data or analysis to support its assertions that NGCC technology is "likely to be cost 

effective," "likely to be made to return the unit to close to its original operating performance," 

and "pays for itself in fuel savings alone" for all modified and reconstructed CTs---including 

both NGCC and simple-cycle CTs. 

Commenter 0157 stated that EPA erred in claiming that NGCC is one of the lowest cost forms of 

baseload and intermediate load generation. The commenter stated that there are few if any
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baseload NGCC units. The commenter stated that many units operate at high capacity factors, 

but baseload generation is that which is running nearly 100% of the time, and few NGCC units 

meet that criterion. The commenter stated that the low cost of NGCC is a recent phenomenon 

and whether it persists for many years into the future remains to be seen. The commenter stated 

that EPA ignores the historic cost of gas, its price volatility, the fact that supplies are limited by

current infrastructure and that many use natural gas for winter heating, making gas supplies for 

electric generation unreliable enough that many facilities are dual-fueled and operate on fuel oil 

during very cold peaking periods.

Response 7.1-15: The commenter is mistaken that the EPA did not provide a cost analysis. Cost 

models developed by the EIA were used to compare the relative LCOE costs of simple cycle and 

combined cycle units at different percentage electric sales. If natural gas prices were to increase, 

NGCC units would become even more cost-effective relative to simple cycle combustion 

turbines. The multi-fuel-fired subcategory provides adequate flexibility for dual fuel units that 

burn 10 percent or more non-natural gas fuels.

Comment 7.1-16: Commenter 0131 believes EPA needs to expand its definition concerning 

relative cost. The commenter stated that several times EPA refers to the limitation as being 50% 

of the cost of a "comparable entirely new facility", however EPA avoids defining what a 

comparable plant is--this could be 50% of a comparable new plant using the same technology or 

50% of a new plant with comparable power production. The commenter stated that the key point 

for clarification for coal plants is whether EPA means 50% of a new coal plant or 50% of a 

new NGCC with comparable power output. The commenter stated that these are very different 

economic criteria, and EPA needs to define its actual intent and not bury a suggestion of the 

definition in the section describing reasoning as to why no units will actually seek to be 

reconstructed.

Response 7.1-16: This final rule does not amend the reconstruction provisions contained in the 

general provisions or establish subpart specific reconstruction provisions.

7.2 DETERMINATION OF THE LEVEL OF THE STANDARD

Comment 7.2-1: Multiple commenters (0213, 0216, and 0282) argued that EPA's proposed 

standards for modified and reconstructed stationary combustion turbines are too lenient. 

Commenter 0213 noted that EPA's proposed performance standards for these 

modified/reconstructed units are the same as its proposal for entirely new units: smaller units 

(i.e., those with a maximum heat input equal to or less than 850 MMBtu/h) would be required to 

meet a gross-output emission limit of 1,100 lbs CO2/MWh, while larger units (i.e., those with a 

maximum heat input greater than 850 MMBtu/h) are limited to 1,000 lbs CO2/MWh. Commenter 

0213 stated that like the proposed new source rule, the modified/reconstructed rule for stationary

combustion turbines reflects a determination that efficient CCGT technology is the BSER for 

stationary combustion turbines. Commenter 0213 agreed with EPA's BSER determination for 

this category of EGUs, and, in principle, supported the Agency's decision not to distinguish 

between new, modified, and reconstructed units for the purposes of regulating CO2 emissions for 

these sources. Commenter 0213 cited the preamble, that efficient CCGT design is widely 

available and in regular use throughout the electricity sector. Commenter 0213 stated that units 
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that modify or reconstruct should not be allowed to emit at rates greater than those achieved by 

the most-efficient CCGT technologies available. 

However, commenter 0213 argued that the numerical limits the Agency selected--1,100 lbs 

CO2/MWh for smaller units and 1,000 lbs CO2/MWh for larger units on a gross output basis--are 

far too lenient and do not represent the true performance capabilities of the most efficient CCGT 

units currently available and operating. Commenter 0213 referenced comments they submitted 

on the new source standard providing ample documentation regarding emission rates of the 

existing CCGT fleet as well as different design options currently available. Commenter 0213 

stated that a full 94 percent of the CCGT units in existence as of 2011 already satisfy the 

emission limits EPA has selected for its modified/reconstructed rule. Commenter 0213 stated 

that to comport with section 111's technology-forcing mandate, and reduce CO2 emissions from 

modified and reconstructed stationary combustion turbines as the CAA requires, the Agency

must propose limits that reflect the true performance capabilities of the most efficient CCGT 

models on the market.

For the reasons stated in the comment above, commenter 0216 agreed with EPA's determination 

that NGCC technology constitutes the BSER for modified and reconstructed natural gas-fired 

stationary combustion turbines, and with EPA's decision not to distinguish between new, 

modified, and reconstructed units in establishing emission standards for this source category. 

However, commenter 0216 believes that the numerical limits EPA selected in establishing this 

emission standard are not sufficiently stringent because they do not represent the true 

performance capability of the most efficient NGCC units.

Commenter 0282 stated that EPA was correct in setting the standard for modified and 

reconstructed sources at the same level as the proposed 111(b) standard. Commenter 0282 cited 

comments submitted on the section 111(b) proposal that the standard itself is indefensibly lenient 

and must be significantly strengthened. Commenter 0282 supported this by citing the fact that 

EPA has indeed selected it for existing sources that modify or reconstruct but has concluded that 

"the proposed standards will result in minimal emission reductions, costs, or quantified benefits 

by 2025." Commenter 0282 stated that it is unacceptable that the standard EPA proposed for 

existing modified natural gas-fired plants is lower than the section 111(d) standard these plants 

will have to meet if they do not modify.

Commenter 0282 incorporated their section 111(b) comments on the insufficiency of the section 

111(b) natural gas-fired power plants in full, and briefly summarized some of their main points. 

Commenter 0282 stated that by EPA's own account, that proposed new source performance 

standard does not have any discernible effect on greenhouse gas emissions from the power sector 

and will do nothing that EPA's economic projections anticipate will not happen anyway; as such, 

they do not fulfill the Clean Air Act's mandate that emission standards actually reduce emissions. 

Commenter 0282 stated that the proposed standard is so lenient that some 98 percent of existing 

sources already meet it, yet EPA failed to explain why technology that is both adequately 

demonstrated and could achieve greater reductions, such as advanced NGCC or even more 

efficient NGCC technology, has not been selected. Commenter 0282 stated that data in EPA's 

docket demonstrate that a far more stringent emission standard is readily achievable at many 

existing facilities. Commenter 0282 stated that without adequate explanation, EPA decided 
7-31

against requiring partial (let alone anything more than 25%) CCS for natural gas plants, even 

though it found the technology to be adequately demonstrated for boilers and IGCCs. 

Commenter 0282 stated that, in creating standards that favor reliance on natural gas plants for the 

foreseeable future, EPA failed to consider their environmental and non-air consequences, 

including the greenhouse gas and adverse health effects of hydraulic fracturing and other 

nonconventional extraction techniques. Commenter 0282 stated that the proposal, in 

incentivizing increased natural gas extraction, processing, transport and combustion, undercuts 

the only sustainable way of producing energy, which is through renewable energy sources.

Response 7.2-1: As described elsewhere in this final rule, the EPA has concluded that the final 

emission standard for base load units is appropriate considering the universe of units that will be 

subject to the requirements of this rulemaking. Specifically, the base load subcategory includes 

both fast-start NGCC units as well NGCC units designed primarily for steady state operation. 

Comment 7.2-2: Based on commercially available turbines, commenter 0193 stated that the 

correct cut-point between large and small gas turbines for new and modified and reconstructed 

units should be raised to 1,500 MMBtu/h (HHV). As explained in their attached comments to the 

January 2014 proposal for new units, the 850 MMBtu/h (HHV) cut-point was based on NOx 

emissions not CO2. The commenter stated that there are significant differences between these 

two pollutants and the methods and approaches to controlling their emissions. The commenter 

stated that gas turbine NOx emissions are a function of the combustion technology, which is 

dictated by the combustor design while CO2 emissions expressed in terms of lb CO2/MWh are a 

direct function of the overall turbine or plant efficiency. The commenter stated that because the 

design parameters that influence NOx formation fundamentally differ from those that affect CO2

formation, the proposed 850 MMBtu/h cut-point is inappropriate for CO2, and any "consistency" 

benefits of having the same cut-point as subpart KKKK are clearly outweighed by the overriding 

statutory requirement that EPA establish standards that are achievable and account for all source 

types and operations anticipated for the fleet. 

As discussed in the commenter's prior comments, an examination of the performance of all 

commercially available 60 Hz gas turbines (with a heat input of 250 MMBtu/h (HHV) or greater) 

contained in Gas Turbine World 2013 (GTW) shows that the 850 MMBtu/h (HHV) cut-point 

does not provide a logical break point between large and small turbines. The 

commenter reproduced a graph included in their comments on the January 2014 

proposal depicting the estimated CO2 emissions (lb/MWh) of the fleet of commercially available 

gas turbines, when installed in a combined cycle configuration. The commenter stated that the 

vertical lines on the graph show that the 850 MMBtu/h (HHV) cut-point does not logically 

separate higher emitting and lower emitting turbines.

Based on existing data, the commenter stated that a more logical cut-point between large and 

smaller gas turbines is substantially higher. The commenter stated that, as noted by EPA, the data 

show that there are no combustion turbines offered for sale with turbine engine base load ratings 

between 1,300 to 1,800 MMBtu/h. The commenter stated that this range presents a clear datadriven size and performance basis for distinguishing between large and small gas turbines, and 

that a dividing line that falls between these heat input values of 1,300 MMBtu/h (HHV) and 

1,800 MMBtu/h (HHV) would appropriately divide turbines based on their size and emissions 

performance capabilities.
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Commenter 0212 believes that EPA should establish a single performance standard for all 

stationary gas turbines, regardless of turbine size or rated heat input. Commenter 0212 stated that 

separate standards for small and large turbines undermine the incentive for technology

innovation and discourage investment in more efficient technologies. As an alternative to 

increasing the standards of performance for large and small natural gas turbines, commenter 

0192 supported a single performance standard of 1,200 lb CO2/MWh for all modified and 

reconstructed natural gas turbines

Commenter 0213 argued that EPA should not create a separate emission limit for smaller CCGTs 

(i.e., those with a maximum heat input under 850 MMBtu/hr).The commenter stated that if such 

as standard is created it should not exceed 1,000 lbs CO2/MWh. The commenter stated that under 

this scenario, EPA must also provide that multiple smaller units at the same physical site will be 

considered a single source for the purpose of calculating emissions.

Response 7.2-2: For the reasons stated in the preamble to this final rule, we are not finalizing 

size-based subcategories for combustion turbines. The EPA’s rationale for establishing a single 

size category include that the EPA was not able to identify a reasonable cut-point, that any cutpoint has the potential to distort the market, and that the final emission standard is achievable by

both small and large NGCC units.

Comment 7.2-3: Commenter 0149 noted that, in the proposal, EPA solicited comment on 

whether to establish a variable standard that would apply to different operating modes. The 

commenter stated that a variable standard may make sense in theory, but raises many questions 

that EPA has not addressed. The commenter stated that it is difficult to assess a variable standard 

without reference to the actual standard, which EPA has not proposed in the context of this 

rulemaking, and further, EPA has not proposed a time scale over which the different operating 

modes would be measured. The commenter stated that unless and until EPA provides more 

details about a variable standard for new NGCC units--and provides stakeholders sufficient 

notice and an opportunity to comment--the Agency cannot finalize a variable standard for these 

units.

Response 7.2-3: For the reasons discussed in the preamble to this final rule, the EPA is 

finalizing a two-tiered emission standard for non-base load and base load units. Based on 

additional analysis and comments, the base load standard is only applicable when the percentage 

electric sales threshold is exceeded on both an annual and 3-year average.

7.2.1 Large Units Limit of 1,000 lb CO2/MWh; solicited comment on range of 

950-1,100 lb CO2/MWh

Comment 7.2-4: Commenter 0215 stated that based on its analyses of the 2007 to 2013 data 

about 10 percent of NGCC units that were designed and built with truly modern technology

cannot meet a 1,000 lb CO2/MWh-gross limit and that only 96 percent of large (more than 850 

MMBtu/h) units can meet a 1,100 lb CO2/MWh-gross limit (See: Smith Turbine Report at 2 & 7, 

Fig. 1; Attachment A at 3]. The commenter stated that these results are substantially below the 

99 percent achievability target that EPA has historically applied in NSPS rulemakings and would 

require a significant number of NGCC units to retire if they became subject to the Proposed 
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Standards. The commenter stated that in order for 99 percent of turbines with truly modern 

NGCC technology to comply, EPA would need to finalize an NSPS of over 1,400 lb CO2/MWh, 

and although applying a one-third sales criterion to exclude certain turbines did reduce the 

standard that would be required for 99 percent achievability, (see Smith Turbine Report) the 

proposed 1,000 lb CO2/MWh standard was still not achievable for new NGCC units even with a 

one-third sales criterion, thus many more units that are older, which do not have high 

temperature materials, will be unable to meet the proposed limit.

Response 7.2-4: The EPA notes that the commenter is mistaken about how the EPA has 

established emission standards for coal-fired EGUs. In recent NSPS amendments, the EPA first 

identified the best performing units (i.e., the units with the lowest emission rate) and then 

determined the 99 percent confidence level strictly based on the emission rate data from the best 

performing unit(s). 

Comment 7.2-5: Commenter 0215 stated that EPA should analyze emissions from NGCC units 

at least as far back as 1990, explain what such units can realistically accomplish through 

retrofitting newer technology with higher temperature materials (including citing specific 

examples of instances where such work was undertaken), and then re-propose a limit so that the 

commenter can make informed comments on EPA's justification. The commenter stated that 

design efficiencies of NGCC units built before 2000 would need to improve their efficiencies 

from 53 to 55 percent to as much as 60 percent to meet the proposed NSPS, but these units have 

no available means to improve heat rate back to their out-of-the-box design levels, let alone to 

improve their operating efficiencies by 5 to 7 percentage points through overhauls or other 

refurbishments. 39487

Response 7.2-5: While the commenters’ points may e applicable to modified units, the cost 

threshold for reconstructed units would allow the owner or operator to upgrade components 

sufficiently to achieve the final emission rate. 

7.2.2 Initial Performance Test in Addition to Ongoing Average

Comment 7.2-6: Rather than establishing separate performance standards for large and small 

turbines and relying solely on a 12-month average emissions standard, commenter 

0212 recommended a hybrid approach consistent with the approach for which EPA asked for 

comment. The commenter recommended combining (1) an initial performance test with (2) a 12-

month average performance standard. The commenter recommended that within 180 days of 

initial firing following a reconstruction, a combustion turbine facility would demonstrate 

compliance with an initial performance standard while operating at full load, ISO corrected 

conditions. 

The commenter recommended that after demonstrating compliance with the initial performance 

standard, the facility would be subject to an ongoing 12-month average emission standard, 

beginning 365 days after initial firing, like the ongoing performance standard proposed by EPA. 

The commenter stated that the ongoing performance standard would be less stringent than the 

initial performance standard to allow for the diminished efficiency and higher emissions 

associated with increased cycling, part load operation, oil combustion, normal plant degradation, 
7-34

as well as variations in ambient temperature and other environmental factors beyond the control 

of the plant operator.

The commenter stated that there are several advantages of a hybrid approach. The commenter 

recommended an initial performance standard to ensure that companies select high efficiency

generating technologies when making their initial construction or reconstruction decisions. The 

commenter stated that if the initial performance standard for new turbine facilities is set at a level 

of 900-950 lb/MWh, companies can design to this specification and have a high degree of 

confidence that the plant will meet this performance standard at baseload conditions. The 

commenter stated that correcting to ISO conditions would ensure that a plant is not 

disadvantaged by virtue of its high elevation or ambient temperature. The commenter stated 

that duct firing should be excluded during the initial performance test for a standard of 900-950 

lb/MWh to be reasonably achievable. The commenter stated that EPA should recognize that an 

existing modified or reconstructed facility may not be able to achieve the same level of 

performance as a new, state-of-the-art combined cycle facility.

The commenter stated that an ongoing performance standard of 1,100 lb/MWh (with reasonable 

accommodations for alternative fuel use and startup and shutdown) would ensure that a new 

turbine facility plant is operated efficiently and well maintained, while providing a reasonable 

compliance margin if market conditions change and the facility needs to cycle more. The 

commenter expected that EPA would hear concerns from a number of stakeholders regarding the 

potential effects of degradation and cycling on a plant's CO2 emission rate (The California 

Energy Commission (CEC), for example, assumes a 4% heat rate degradation factor for a natural 

gas combined cycle facility over 20 years of operation. See "Comparative Costs of California 

Central Station Electricity Generation," August 2009. The commenter stated that the emission 

rate of a NGCC facility will increase with (1) part load operation, (2) the use of higher carbon 

content backup fuels, (3) startup and shut events, (4) degradation, and (5) other factors like 

higher elevation and ambient temperatures. With the approach the commenter suggested, they

expected a new plant to operate well below the ongoing performance standard because the 

economics of the power sector encourage efficiency and the initial performance standard will 

require companies to invest in high efficiency, combined cycle technologies. The commenter 

stated that in setting an ongoing performance standard for modified and reconstructed facilities, 

EPA should recognize that an existing modified or reconstructed facility may not be able to 

achieve the same level of performance as a new, state-of-the-art combined cycle facility.

The commenter noted that EPA, in its January proposal, suggested that smaller capacity NGCC 

facilities may run in simple cycle mode for short periods of time, increasing their average CO2

emission rate. The commenter stated that this was, in part, the justification for proposing a higher 

performance standard. The commenter stated that a hybrid approach would address this concern. 

The commenter stated that the initial performance test would be conducted in combined cycle 

mode, while the on-going performance test would accommodate simple cycle operation for short 

periods of time.

According to the commenter, reducing the carbon intensity of the electric sector presents a 

unique challenge, which is different from past regulatory efforts aimed at conventional air

pollutants. The commenter stated that the daily emissions performance of the fleet matters less 
7-35

than the industry's performance over many years or even decades, and it is in this context that the 

commenter recommended a hybrid approach with an initial performance standard that will 

ensure that the right investment decisions are made at the outset. The commenter stated that EPA 

asked for comment on this same approach in its proposed rule for new stationary gas turbines: 

"[w]e are considering and requesting comment on requiring an initial performance test for 

stationary combustion turbines in addition to the 12-operating month rolling average standard". 

The commenter stated that requiring an initial compliance test that is numerically more stringent 

than the annual standard for new combined cycle facilities would insure that the most efficient 

stationary combustion turbines are installed, and a less stringent 12-month rolling average 

standard would be set at a level that would take into account actual operating conditions.

The commenter noted that EPA indicated that it received feedback on its January 2014 proposal 

suggesting that the emissions data that it used in developing the natural gas-fired stationary

combustion turbine standards did not completely account for degradation in performance over 

the entire life of an NGCC. Also, the commenter noted that NGCC units are expected to operate 

differently in the future due to the increased percentage of power generated from renewable 

sources, such as wind and solar, and an initial performance test combined with a less stringent 

on-going performance standard would 

Commenter 0232 was concerned that EPA's proposed standards do not include an initial 

performance demonstration to ensure that modified and reconstructed EGUs use the most 

efficient and least-polluting generating technologies available. The commenter stated that the 

proposed standards require only that these EGUs meet the applicable average emission standard 

after the first 12-month compliance period has ended. The commenter stated that for natural gas 

combustion turbines, these average standards do not even reflect the performance of the most 

efficient NGCC facilities currently being operated, let alone the best performance of a NGCC 

facility operating under optimal conditions. The commenter stated that in order to ensure that 

modified and reconstructed EGUs incorporate the most efficient generating technologies 

available, it is essential that EPA augment the average annual performance standards with an 

initial performance test--consistent with their comments on EPA's proposed standards for new 

EGUs. The commenter stated that this is precisely the approach that state permitting authorities 

and EPA have undertaken in recent PSD permits for NGCC facilities, which require that the 

permitted facilities meet a stringent initial CO2 performance standard within 180 days after 

startup (as currently required for other pollutants in the General Provisions of the NSPS. 

The commenter stated that, because the purpose of these initial performance tests is to ensure 

that the facilities are using the lowest-emitting equipment and processes available and therefore 

perform as efficiently as possible under ideal operating conditions, the tests are conducted while 

the facility is operating at 90 to 100% of rated capacity and are normalized for temperature, 

pressure, and other variables. The commenter stated that there are circumstances, such as in the 

case of "peaking" power plants, where normal operation results in variable and on average higher 

emission rates than the plant can achieve under optimal operating conditions. The commenter 

stated that a continuously applicable emission standard for such units would be set at a level that 

reflected this variability. The commenter stated that the incorporation of an initial performance 

test that reflects the emission rate achievable using the best system of emission reduction when a 

plant is operating at optimal conditions ensures that facilities are built, reconstructed, or modified 
7-36

using the lowest-emitting technologies and operating systems available, fulfilling the 

technology-forcing and pollution-minimizing purposes of Section 111. The commenter stated 

that they are an essential component of the carbon pollution standards for newly constructed, 

modified, and reconstructed units, ensuring that the standards fulfill the section 111 statutory

requirements and case law.

According to the commenter, requiring an initial performance test is not only reasonable for 

modified or reconstructed EGUs, it is also fully consistent with similar requirements for other 

pollutants regulated under the NSPS. The commenter stated that subpart KKKK currently 

requires that natural gas combustion turbines complete initial performance tests no later than 180 

days after startup to demonstrate compliance with emission standards for nitrogen oxides and 

sulfur dioxide, and that EGUs covered by subpart Da are similarly required to complete initial 

performance tests within 180 days of startup for particulate matter, sulfur dioxide, and nitrogen 

oxides. The commenter stated that EPA has not explained why it has departed from this timetested requirement in the proposed standards, especially when PSD permits for have shown that 

initial performance tests are both feasible and desirable to ensure that NGCC facilities (and 

potentially other EGUs) incorporate the most efficient available generating technologies.

Multiple commenters (0131, 0193, and 0242) opposed the imposition of an additional annual 

short-term performance test. Commenter 0193 argued that the imposition of a short-term annual 

test, in addition to a 12-month rolling average standard, would add no significant value sufficient 

to offset the increased cost and uncertainty created by the test. Commenter 0192 stated that New 

NGCC units can readily meet EPA's proposed emission standards for new units when operating 

at ideal conditions, specifically when first installed in a new and clean condition, operating at 

baseload and corrected to standardized conditions. Commenter 0193 stated that the challenge is 

in consideration of the 12-month rolling average that encompasses all possible operating 

scenarios encountered by a real world operating facility. Commenter 0193 stated that 

establishing a short-term annual test would impose additional regulatory burden with no 

associated benefit in the form of emission reductions.

Commenter 0131 noted that the rolling average was developed specifically to provide an 

averaging due to conditions like part load and heavy load (optimum) operation. Commenter 0131 

stated that adding an additional short test period does little to provide usable data or verification, 

and that owners will generally seek to make sure their machines are operated and installed using 

best practice. The commenter stated that EPA should recognize that best practice is necessary to 

optimize performance both operationally and economically--the latter driver is the most 

important one.

Commenter 0242 also disagreed with the need for a short term compliance test. Commenter 0242 

was not sure whether EPA was suggesting that a more stringent standard than those proposed 

could later be set based on a short term compliance test, or whether EPA was proposing to set a 

short term limit based on the compliance test. Commenter 0242 questioned whether EPA 

considered that these units will not always be able to operate at their most efficient short term 

rate. Commenter 0242 stated that If EPA continued forward with this proposal, and so few 

sources would be affected as EPA suggested, then states should be able to set the limitation at a 

level that would account for different operating conditions; it should be the state's responsibility
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to set those limits based on each unit's unique circumstances. Commenter 0242 was not in 

agreement with short-term requirements being imposed under this proposal. Commenter 0242 

stated that the proposal addresses CO2 emissions for which there is no basis or reasoning for 

requiring any short-term requirements to limit emissions and provides no logic as to why shortterm limits in addition to long-term limits will address climate change

Commenter 0212 disagreed with EPA on establishing a separate standard for load-following 

(i.e., intermediate capacity factor) NGCC EGUs. The commenter stated that the more stringent 

standard that EPA is considering would apply only during periods of high annual capacity 

factors, and a less stringent standard would apply during periods of intermediate load (e.g., when 

electric sales are between 33 to 60 percent of the potential electric output). The commenter 

believes that an initial performance test combined with an on-going performance standard 

(hybrid approach) would be far simpler to implement and enforce than this approach. The 

commenter believes this issue highlights one of the key advantages of a hybrid approach. The 

commenter stated that there is far less uncertainty regarding the performance of a new NGCC 

facility operating at full load under ISO conditions versus an older facility operating at variable 

load conditions. The commenter stated that in some cases, fast start and hot restart capability can 

result in a slightly lower base load efficiency; however, the effect is modest and would not 

prevent a facility designed for base-load and load-following operation from achieving a standard 

between 900-950 lb/MWh. The commenter stated that by establishing an initial performance 

standard (consistent with EPA's BSER determination), EPA will ensure that companies invest in 

the high-efficiency generating technologies, which in turn, reduces the burden on the on-going 

performance standard to accommodate different levels of cycling and intermediate load 

conditions. The commenter stated that the on-going performance standard can be set at a level 

(like 1,100 lb/MWh) that is reasonably achievable under a wide range of operating conditions, 

while still relying on the initial performance test to drive the best technology choice. The 

commenter stated that the alternative approach that EPA is suggesting, with separate standards 

for different operating conditions, could have the unintended consequence of encouraging less 

efficient technologies and less efficient operation.

Response 7.2-6: While in concept an initial performance test in conjunction with an on-going 

continuous compliance standard appears appealing, the EPA disagrees that is it appropriate for 

the final rule. The universe of NGCC units covered by the base load subcategory includes faststart NGCC units and NGCC units designed for steady state base load operation. An initial 

performance test based on the performance of the latter would preclude the use of fast-start 

NGCC units even though, in their intended role of frequent starting, stopping, and cycling, their 

actual performance may be superior to a NGCC unit designed for steady state operation.

7.2.3 Load Following/Intermediate vs. Base Load Standard

Comment 7.2-7: Commenters 0187 and 0203 supported EPA's proposed approach to establish 

separate standards for load-following NGCC EGUs. Commenter 0187 also believes that 

modified combustion turbines and modified boilers fall into this category. Commenters 0187 

and 0203 stated that this approach would apply a more stringent standard during periods of high 

capacity factors and a less stringent standard during periods of intermediate capacity factors 

(e.g., 33 to 60%). Commenter 0187 noted that many boilers that used to be base-loaded are now 

load-following at times. Commenter 0187 stated that load factor has a significant impact on unit 
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heat rate and the efficiency of units will be less than in the baseline period when they were baseloaded.

Commenter 0193 stated that EPA was correct to examine whether a separate standard should be 

established for load-following (i.e., intermediate capacity factor) NGCC EGUs, but was 

concerned about its implementation and enforcement. The commenter stated that the more 

stringent standard would apply only during periods of high annual capacity factors and a less 

stringent standard would apply during periods of intermediate load (e.g., when electric sales are 

between 33 to 60 percent of the potential electric output). The commenter stated that this 

approach addresses two potential issues with the standards in the January 2014 proposal:

(1) certain NGCC units are designed to be highly efficient when operated as load-following 

units, but these design characteristics reduce the efficiency at base load. Conversely, the NGCC 

units with the highest base load design efficiencies are not necessarily as efficient as NGCC 

designed and intended to be used as load-following EGUs. Therefore, a full-load efficiency

performance test would not necessarily result in the lowest CO2 emissions in practice. 

(2) NGCC units operating as load-following EGUs are inherently less efficient than NGCC units 

operating at base load. Establishing a standard that varies with load would assure that NGCC 

units that are operated as base load units are as efficient as possible and still account for inherent 

lower efficiencies at part-load conditions. 

The commenter noted that gas turbine installations that operate at base-load would generally

demonstrate a higher 12-month average efficiency (i.e. lower CO2/MWh emission rate) than 

load-following installations that operate between 33 and 60 percent capacity factor on average 

when considering the broader range of operational conditions the intermediate/load following 

plant would experience during the 12-month averaging period. The commenter stated that in 

soliciting comments on this proposal, EPA recognized the difficulty of establishing a one-sizefits-all standard for combustion turbines that are increasingly being designed and purchased for 

different power needs. While the commenter supported EPA's exploration of this issue, the 

commenter remained concerned that a load-following standard would be difficult to implement 

and enforce, as annual capacity factors would likely vary significantly from year to year, and in 

fact would quite possibly vary from month to month as the 12-month average is recalculated on a 

30-day basis. The commenter stated that this uncertainty for purchasers, operators and regulators 

may diminish the value of a load-following standard.

Commenter 0195 generally supported EPA's proposed approach to set a separate standard for 

load-following (i.e., intermediate capacity factor) NGCC units, but the commenter also had some 

concerns. The commenter cited the preamble discussion in the proposal, that a more stringent 

standard would apply only during periods of high annual capacity factors and a less stringent 

limit would apply during periods of intermediate load. The commenter stated that EPA explained 

that this approach would address the fact that when NGCC units are designed to be loadfollowing units, these design characteristics will impede efficient operation at base load and vice 

versa, and that NGCC units operating as load-following EGUs are not as efficient as base load 

NGCC units and thus approach would address this situation. On a conceptual level, the 

commenter stated that a flexible standard that accounts for varying efficiencies due to how the 

units are operated is appropriate and reasonable. The commenter felt there was not sufficient 
7-39

specificity in the current proposal on how a flexible standard would work in practice for loadfollowing units. The commenter stated that EPA needs to conduct a supplemental rulemaking to 

provide more detail on this type of standard so that industry can provide meaningful input.

Commenters 0213 and 0232 noted that EPA crafted the modified/reconstructed rule proposal so 

as to exclude units that operate in peaking mode and argued there is no basis in law or policy to 

exempt units from regulation simply because they operate less frequently (and hence less 

efficiently). The commenters stated that section 111(b) expressly permits EPA to create different 

emission limits for different kinds of units within a given regulatory category ("The 

Administrator may distinguish among classes, types, and sizes within categories of new sources 

for the purpose of establishing such standards"). The commenters stated that rather than simply

exempting units from regulation on the basis of how frequently they run over the course of a 

calendar year or on a three-year rolling average basis, the Agency should cover all sources that 

supply (or are designed to supply) any amount of electricity to the grid, and should distinguish 

among these sources on a functional basis. The commenters, therefore, proposed the same threetiered regulatory model for modified and reconstructed stationary combustion turbines that they

discussed in their comments on the new source standard, which recommends that EPA recognize 

three subcategories of NGCC facilities--baseload, load-following/intermediate, and peaking 

EGUs--and establish the following separate performance standards for each: 

 Peaking units (defined as affected EGUs that operate less than 1200 hours per year) 

would be subject to a net output-based emission limit of 1,100 lb CO2/MWh.

 Intermediate/load-following units (defined as EGUs that operate between 1,200 and 

4,000 hours annually) would be subject to a net output-based emission limit of 875 lb 

CO2/MWh.

 Baseload units (defined as EGUs that operate over 4,000 hours annually) would be 

subject to a net output-based emission limit of 825 lb CO2/MWh.

The commenters stated that the recommended standards are based on the reported performance 

of NGCC units in each of these subcategories and are entirely achievable and well within a 

reasonable cost range given the technology that is currently available, and modified and 

reconstructed units should be required to meet them. The commenters referred to their comments 

on the proposed carbon pollution standards for new EGUs. See: EPA-HQ-OAR-2013-0495-

9514.

Commenter 0215 stated that EPA has acknowledged that CO2 emissions increase at lower loads, 

so in principle this might diminish the number of units that cannot meet the Agency's proposed 

NSPS for both reconstructed and modified NGCC units. The commenter stated that EPA adopted 

a similar approach, for similar reasons, in its NSPS for NOx for Subpart KKKK units, setting the 

standard for operations at peak load (100 percent of the manufacturer's design capacity of the 

combustion turbine at ISO conditions). The commenter stated that EPA's suggested approach (as 

well as the similar approach that EPA used in establishing the NSPS for NOx for NGCC Subpart 

KKKK units) results in "little advantage..." [See Smith Turbine Report at 5].

Response 7.2-7: The final applicability criteria included in the final rule include all new and 

reconstructed combustion turbines regardless of actual electric sales. The EPA has finalized 

standards accommodating base load and non-base load operation. The BSER for base load units
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has been identified as NGCC. The BSER for non-base load units has been identified as clean 

fuels. Whether or not a unit is one category or the other is based on the amount of electricity sold 

to the grid, derived from a unit’s nameplate design efficiency calculated as a percentage of 

potential electric output.

Comment 7.2-8: Commenters 0142 and 0242 suggested that if the EPA establishes separate 

standards for load-following NGCC units, the EPA should also establish separate standards for 

coal-fired EGUs based upon how they are dispatched. Both commenters noted that for gas 

turbines, the EPA is soliciting comment on whether a separate standard should be established for 

load-following (i.e. intermediate capacity factor) NGCC EGUs, where the more stringent 

standard would apply only during periods of high annual capacity factors and a less stringent 

standard would apply during intermediate load periods (e.g., when electric sales are between 33 

to 60% of potential electric output). The commenters stated that this would address the fact that 

certain NGCC are designed to be highly efficient when operated as load-following units, but due 

to the design characteristics efficiency is reduced at base load (and vice-versa). The commenters 

stated that NGCC units operating as load-following are inherently less efficient than base load 

units. The commenters agreed that EPA is correct that a unit's dispatch will affect its emissions 

but argued that these concepts are true for most fossil-fuel fired generators, not just NGCC units. 

Commenter 0242 found it difficult to rationalize why such considerations would potentially be 

given to natural gas units and not coal-fired boilers. Commenter 0242 found it particularly 

perplexing when they understood that some coal-fired units may have to trigger the "modify" or 

"reconstruct" definition to achieve compliance with section 111(d) requirements.

Response 7.2-8: The EPA disagrees that tiered emission standards are appropriate for coal-fired 

EGUs. Coal-fired units, unlike natural gas-fired units, have the option to burn fuels with lower 

CO2 emission rates. The use of natural gas or distillate oil would reduce the emission rate of a 

coal-fired EGU by approximately 40 to 20 percent respectively. The use of either of these fuels 

would more than offset any increase in the emission rate that results from operating at part-load 

conditions. A further difference is that stationary combustion turbines include two distinct 

technology choices, simple cycle and NGCC technology, with different emission profiles and 

operating characteristics. This was a factor in determining a separate BSER for non-base load 

and base load units.