MEMORANDUM

TO: Rulemaking docket, "State Implementation Plans: Response to Petition for 

Rulemaking; Findings of Substantial Inadequacy; and SIP Calls to Amend 

Provisions Applying to Excess Emissions During Periods of Startup, Shutdown, 

and Malfunction," ID No. EPA-HQ-OAR-2012-0322 

FROM: Lisa Sutton, Air Quality Policy Division, Office of Air Quality Planning and 

Standards, Office of Air and Radiation, U.S. Environmental Protection Agency 

DATE: May 13, 2013 

SUBJECT: Report of in-person meeting with representatives of the National Environmental 

Development Association's Clean Air Project 

On April 17, 2013, members of the Air Quality Policy Division, Office of Air Quality Planning 

and Standards, Office of Air and Radiation, U.S. Environmental Protection Agency, met in person 

and by conference call with members of the National Environmental Development Association’s 

Clean Air Project (NEDA/CAP). A meeting sign-in sheet is included as an attachment to this 

memorandum. At this meeting, members of NEDA/CAP discussed their concerns with EPA’s 

proposed response to the Sierra Club petition on startup, shutdown, and malfunction provisions in 

state implementation plans. EPA staff encouraged NEDA/CAP to fully restate these concerns in 

their written comments to the docket. 

Following the meeting, Anna Wood of EPA received a related email (including an attachment) 

from Barbara Bankoff, a consultant on environmental and regulatory policy. That email is also 

included as an attachment to this memorandum. 

LS 

Attachments 

From: barbara bankoff

To: Wood, Anna

Cc: Leslie H. Witherspoon; Rising, Bruce W (E ST MOP 3); Leslie Ritts

Subject: Fwd: SSM and gas turbine nsps

Date: Friday, April 19, 2013 6:12:40 PM

Attachments: Final GTA Comments 6_25_12 (3).pdf

Anna -

You had shown some interest in the SSM exemption for gas turbines when we met

on Wednesday. I asked Bruce Rising of Siemens about concerns regarding removing

the current SSM exemption. I am forwarding his recent comments. I have also

attached the Gas Turbine Association comments on the GHG NSPS, which includes a

paragraph about the need for an SSM exemption.

Thank you for the time you and your staff spent with us the other day.

Regards,

Barbara

---------- Forwarded message ----------

From: Rising, Bruce W (NAM RC-US E P-S) <bruce.rising@siemens.com>

Date: Wed, Apr 17, 2013 at 3:23 PM

Subject: RE: SSM and gas turbine nsps

Non-compliance is an issue. Emission controls don’t operate

uniformly at all operating points, especially during the start and

shutdown cycles.

The more starts and stops required by the system, the more time a

specific piece of equipment will be operating without its emission

controls in an optimal range.

The problem is much worse for post combustion emission controls

(like SCR or and FGD on a coal plant) because

those devices have to wait until the base unit reaches a previously

established operating range before “turning on”.

An SCR won’t reduce NOx at temperatures much below 600F, nor above

950F. So the ammonia injection system won’t kick in during those

periods (and hence the catalyst won’t reduce NOx). Likewise CO.

Most CO catalysts work well at low temperatures, and better at high
temperatures. But during the cycling process, the CO catalyst may

not be able to oxidize either CO or unburned hydrocarbons. Those

emissions are highest at the lowest loads. So during the start

cycle (and shutdown), even the CO catalyst, which is pretty

forgiving, will likely have a tough time holding the line.

Then you have the problem of determining the non-compliant level.

It takes 20-30 seconds for combustion gases to leave the gas

turbine, pass through the boiler, then reach the stack. The

sampling system will pump gases back down to the instruments, each

will have a different response time. The data collection system

will sample the data for anywhere from 5 to 15 minutes, then try

and average the data. Now with the emissions going up and down,

it’s not quite clear if the averaging will have any real meaning.

So reported data could be rather misleading.
June 25, 2012 

RE: Environmental Protection Agency 

Docket number EPA-HQ-OAR-2011-0660 

 Proposed Rules for GHG Emissions for Electric Utility Generating Units 

Submitted By: Gas Turbine Association 

 Dr. William H. Day, Managing Director 

 billday3@comcast.net

The Gas Turbine Association (GTA) appreciates the opportunity to comment on EPA’s 

proposed rulemaking to regulate greenhouse gas (GHG) emissions from electric utility 

generating units (EGUs) under the Clean Air Act’s new source performance standards (NSPS) 

program. See 77 Fed. Reg. 22,392 (April 13, 2012). GTA’s comments will be focused on 

emissions from gas turbines, which are highly efficient energy conversion devices with low CO2

emissions normalized to energy production. The success of gas turbines can be measured by 

their market presence. The current installed capacity of combined and simple cycle gas 

turbines represents over 350,000 MW, producing over 20% of the total United States 

generation. Nearly all of the energy production is achieved using natural gas fuel. 

Summary of GTA Recommendations 

• Continue to exclude simple cycle gas turbines 

• Include language that specifically prohibits the NSPS CO2 limit from being adopted as 

the presumptive CO2 BACT level for simple cycle turbines 

• For units other than simple cycle, raise the CO2 level to at least 1,100 lb/MWh to account 

for typical operating scenarios including part-load, rapid ramping and cycling, 

performance degradation and differences in site and atmospheric conditions 

• Include exemption for startup/shutdown and part load operation 

• Allow an alternate method to CEMs for compliance measurement, specifically fuel 

consumption 

• Modify method for computing the 12-month rolling average 

• Exempt combined heat and power units since their exhaust energy is very efficiently 

utilized 

• Allow 500 hours of operation on backup fuel without inclusion in the emission average 
2 | Gas Turbine Association 

Exemption for Simple Cycle Gas Turbines 

The proposed rulemaking recommends that simple cycle gas turbines be excluded from the 

proposed CO2 NSPS in the amended 40 C.F.R. Part 60. See 77 Fed. Reg. at 22,411, 22,431-

32. The rationale laid out in the proposed rulemaking is that simple cycle gas turbines (which 

generally cannot meet the 1,000 lb/MWh rule on any fuel) are primarily used for peak shaving 

duty which is generally viewed to include less than 2,500 hours per year of operation. The 

proposed rulemaking excludes all gas turbines with the justification that most simple cycle gas 

turbines operate less than 2,900 hours per year (less than 1/3 of the total generation capacity). 

The GTA agrees that simple cycle gas turbines should remain completely excluded from the 

rulemaking. GTA strongly supports the exclusion for the reasons EPA identifies, but even 

beyond the rationale EPA identifies, there are at least two additional reasons to exclude simple 

cycle gas turbines. 

First, including simple cycle gas turbines in the NSPS will amount to an effective ban on simple 

cycle in other contexts (e.g. the NSPS level of 1,000 lb/MWh might be used as an upper limit for 

Best Available Control Technology (BACT) calculations if simple cycle gas turbines are 

included). The current Prevention of Significant Deterioration (PSD) GHG rule has a very low 

tons-per-year threshold, which means that PSD could be invoked for a large portion of newly 

installed simple cycle gas turbines in electric power generation that would not otherwise be 

subject to PSD. The Gas Turbine Association is already aware of one state environmental 

protection department that has given such guidance to a customer’s permitting consultant for a 

simple cycle installation. 

The GTA also wishes to emphasize that there is a strong likelihood that, even if simple cycle 

gas turbines are excluded from the proposed rulemaking, the 1,000 lb/MWh limit could be 

considered as a ceiling for BACT for all gas turbines regardless of cycle. If the 1,000 lb/MWh 

level is interpreted as a presumptive BACT for all turbines, such interpretation would effectively 

ban simple cycle gas turbines. Similarly, the proposed rule should not be allowed to be used in 

some way to establish lowest achievable emission rate (LAER). Thus, we request EPA include 

specific language in 40 CFR Part 60 amendment to explicitly prevent the unintended adverse 

impact on simple cycle gas turbines. 

The GTA suggests that 40 CFR § 60.5520 (d) of the proposed rule be amended to add the 

following: 

“Simple cycle combustion turbines are not subject to the requirements 

of this subpart. Further, this subpart and any emissions limits 

included herein is not intended to and shall not be used as a basis for 

establishing for simple cycle combustion turbines either best available 

control technology (BACT) or lowest achievable emission rate 

(LAER). 

Secondly, an effective ban on simple cycle gas turbines could risk the stability of the nation’s 

power grid and hinder the Administration’s goals to advance renewable energy. Increasingly, 

renewable generation resources are being added to the mix of generation assets and are 

forming a much greater percentage of the nation’s electric power generation. The effect of 

increasing renewable generation share is a significant increase in power generation variability 

and thus significantly increased grid instability. The most effective means to mitigate the 

destabilizing effects of renewable additions is the installation of simple cycle gas turbines. 
3 | Gas Turbine Association 

Simple cycle gas turbines can accommodate the very quick start times and rapid ramp rate 

load-following required to stabilize the grid in the presence of significant renewable generation. 

Grid instability may require a significant share of simple cycle gas turbines to run more than 

2,900 hours per year. An effective ban on simple cycle gas turbines would eliminate a crucial 

tool for maintaining grid stability. 

Further, the final rule should clearly state the simple cycle exemption does not impose a 

restriction on simple cycle turbine annual hours of operation. While a majority of current, and 

anticipated future simple cycle turbine installations, operate less than 2900 hours, many 

installations are operate in excess of these number of hours to support grid requirements. The 

facility will be required to operate the number of hours required by electric demand. Limiting 

hours of operation again would restrict the operational flexibility of this fleet of turbines 

necessary ensure reliable and stable electricity supply. 

Finally, the exclusion of simple cycle gas turbines from the NSPS rulemaking would not 

inappropriately favor them over combined cycle gas turbines in the marketplace, nor have the 

unintended effect of delaying the upgrade of simple cycle installations to combined cycle. Cf. 77 

Fed. Reg. at 22,432. The economics of the application always govern the choice between 

simple and combined cycle with capital costs and efficiencies being significantly different 

between the two. Thus anticipated run times (peaking, daily start-stop, or base load), the price 

of fuel, and capital cost of the power plant are the controlling drivers in decision making. 

Because most combined cycle units will have less trouble meeting the proposed regulation, at 

least at high loads, we believe that the proposed regulation will have little effect on the timing of 

upgrade decisions. 

Proposed CO2 Limit 

EPA has proposed a standard of 1,000 lb/MWh for CO2 emissions, but has requested 

comments on a range of 950 to 1,100 lb/MWh. See 77 Fed. Reg. at 22,406. In addition to 

excluding simple cycle turbines entirely, GTA believes the limit should be raised to 1,100 

lb/MWh for other units. 

While the GTA recognizes the 1,000 lb/MWh level may be achievable under certain limited 

conditions – particularly when units are newly installed, clean, with no degradation due to 

thousands of hours of operation, at sea level, under standard day conditions, and running at 

base load – the standard is unlikely sustainable under real world conditions. During real life 

operating scenarios, combined cycle gas turbines (CCGTs) operate in a wide variety of ambient 

conditions (high altitudes, hot weather) with frequent starts and stops and operate across a wide 

load range. Also, gas turbine equipment will experience varying amounts of performance 

degradation due to service. 

An critical attribute of CCGT facilities is the generation flexibility that is essential to ensuring a

stable, secure, reliably energy supply while enabling the deployment of variable renewable 

energy generation. The proposed limit is attainable by most new CCGT facilities, when 

operating at base load, however during variable operation, including frequent starts/stop cycles 

and significant part load operation, many facilities are not able to maintain these emission 

levels. As a result, a more restrictive limit would not result in a lower emitting facility, but would 

result in a constraint in the necessary flexible operation of the CCGT. To ensure and enable 

flexible plant operation, which is essential to the mission of CCGT operation, the GTA 

recommends an emission limit no lower than 1,100 lbs CO2/MW-hr. 
4 | Gas Turbine Association 

Also, various design features and site requirements must also be considered. As example, air 

cooled condenser equipment is often required in arid climates. Air cooled condensers have the 

advantage of reduced water consumption. This benefit comes at a performance penalty. This 

penalty can range from a 1 to 4% percent loss in plant efficiency dependent on site climates and 

design basis. The variable operating conditions and range of design requirements result in 

actual performance below the reference case. 

A recent report by the University of California Center for Energy and Environmental Economics 

reported similar findings regarding only base loaded CCGTs: “The EPA reports that 95 percent 

of these units first operating between 2006 and 2010 would meet the target, and we find a 

similar percentage when looking at predicted emissions based on power plant heat rates. Yet 

we find a lower number at 84 percent based on actual emissions and self-reported generation.”1

 

The study captures only a small amount of real world variability. Analysis for daily start and 

stop, intermediate duty, and power plants operating for a significant period of time at part load 

are not included. Inclusion of such plants would have further reduced the percentage of 

complying power plants. It is, in fact, critical to the management and stability of the electric 

grids in the United States that dispatching authorities have the flexibility to dispatch CCGTs at 

loads from 50% to 100%. Dispatch flexibility is operational flexibility. A limit of 1,000 lb/MWh 

will greatly impede real world operational flexibility and the stability of grids in the United States

will suffer. 

The GTA recommends the emission limit be set at 1,100 lbs CO2/MW-hr. The 1,100 lbs 

CO2/MW-hr level is consistent with levels set in California, Oregon, and Washington. 

 

Exemption for Startup/Shutdown and Part Load Operation 

GTA’s analysis of the operating fleet reveals that part load operation is a very likely operating 

scenario going forward due in significant part to the need for rapid response in support of nondispatchable generation (i.e., wind and solar). Reduced load operations (as well as starts and 

shutdown) can result in a level of CO2 emissions above the proposed level because gas turbine 

efficiency declines significantly at off-design operating loads. CO2 emissions above the 

proposed 1,000 lb/MWh level is expected to also occur with new advanced gas turbines 

entering operation due to the basic physics of turbomachinery. 

Because of the severe penalty encountered with part load operation, GTA recommends that 

CO2 emissions during operations below 50% of maximum continuous rating (of the gas turbine) 

be excluded from the averaging and reporting. 

Continuous Monitoring 

EPA proposes to require compliance monitoring with the NSPS via a CO2 mass rate continuous 

emissions monitoring system (CEMS). 77 Fed. Reg. at 22,409. The GTA believes that fuel 

consumption monitoring should be available as an acceptable alternative to CEMS. 

CO2 mass rate CEMS and associated automatic data acquisition and handling are but one 

technical approach to determine compliance. A CEMs system measures CO2 species 

concentration in the stack as well as stack total and static pressures in the stack. From the data 

 

1

 Kotchen and Mansur, How Stringent is the EPA’s Proposed Carbon Pollution Standard for New Power Plants?, University of 

California Center for Energy and Environmental Economics, April 2012. 
5 | Gas Turbine Association 

the total stack mass flow rate and mass flow rate of CO2 are calculated and then integrated over 

time and normalized, by the electric output in MWh, to determine CO2 lb/MWh over a timeframe. 

While the CEMS method is necessary for criteria pollutants, such as NOx and CO which vary 

widely in emissions characteristics from one engine model and operating condition to another, a 

much simpler and more accurate method is available for CO2. By accurately measuring fuel 

flow over time and assuming that all the carbon in the fuel is oxidized to CO2 (a very accurate 

assumption) the total emission of CO2 may be determined very easily and accurately. EPA has 

relied heavily on fuel consumption monitoring as an alternative to CEMS for its Mandatory 

Reporting of Greenhouse Gases Rule, with three of the four methodological tiers for calculating 

CO2 emissions under that rule relying on fuel consumption data, rather than on CEMS. See 

e.g., 74 Fed. Reg. 56290. EPA should allow fuel consumption monitoring here as well. 

Using fuel consumption monitoring instead of CEMS is far more accurate and avoids the 

challenging problem of measuring emissions during transient periods when stack flow rate 

measurements are inaccurate. During transient operation stack flow conditions may be 

changing rapidly, the kind of conditions that would be difficult for a CEMS to produce accurate 

results. Many combined cycle units that were expected to operate at base load in the United 

States are now found to be operating over a much wider range of loads, with many more starts 

and stops, thus relegating a fuel consumption monitoring method appropriate 

EPA may already have envisioned a fuel consumption monitoring alternative, but an apparent 

drafting error makes that ambiguous. Proposed regulations 40 C.F.R. §§ 60.5535(c) and 

60.5560(c) refer to fuel combustion monitoring. See 77 Fed. Reg. at 22,437, 22,438. Criteria 

for using fuel combustion monitoring method, however, are cross-referenced to a proposed 

provision, § 60.5525(c)(2), which does not exist. GTA urges EPA to correct the oversight and 

make fuel consumption monitoring a widely-available alternative to CEMS. 

Method for Computing the 12-Month Rolling Average 

GTA believes the specified method of averaging will lead to an inaccurate measure of CO2

emissions. Monthly operation of gas turbines can vary widely from a very small capacity factor 

to 100% capacity factor depending on a wide variation in parameters affecting unit dispatch 

such as load demand, periods of overhaul and refurbishment, fuel availability, and amount of 

time spent starting and stopping. Therefore, all months should not be weighted equally, a 

feature of the current methodology specified in § 60.5540. We note further that there is no 

public health reason to compel compliance on a monthly basis. It would be far more accurate, 

at the end of each month, to compute a new rolling average by summing all CO2 emitted in the 

past 12 months and dividing by the total MWh’s generated in the past 12 months. 

Combined Heat and Power (Cogeneration) 

GTA recommends that EPA develop a specific exclusion for Combined Heat and Power (CHP) 

applications. CHP plants operate in a similar manner to the CCGTs that are covered by the 

proposed rule. The thermal energy from CHP plants can be diverted to either energy production 

(kWh) or to thermal loads (heating and cooling). The regulatory challenge of quantifying the 

equivalence of the thermal energy used in terms of kWh to determine compliance with the 

proposed NSPS would be immense and impractical. Because of that complexity, we propose 

that CHP and cogeneration facilities be specifically exempted from the rulemaking. 
6 | Gas Turbine Association 

Backup/Multi-Fuel Operation 

Because of the stringency of the proposed compliance level, GTA requests EPA clarify that the 

NSPS rule only apply during periods of natural gas operation with an exemption for 500 hours of 

operation on backup fuel. During periods of extreme weather events (typically cold winter 

days), plants operating with interruptible gas supplies may be forced to use an alternative or 

backup fuel. Most commonly the backup fuel is number 2 distillate (or similar fuels); which have 

a significantly higher CO2 emission profile.2

 As Figure 1 shows, there is a large difference 

between emission levels based on natural gas and other fuels. An exemption to operate on a 

backup fuel for a period of up to 500 hours per year would accommodate the potential need to 

use a back up fuel. 

Figure 1. CO2 emissions as a function of fuel choice and cycle efficiency (based on Higher Heating Value) 

GTA Member Companies

Alstom Power 

GE Energy 

Florida Turbine Technologies 

Pratt & Whitney Power Systems 

Rolls-Royce 

Siemens Energy 

Solar Turbines Incorporated 

Meggitt Sensing Systems

 

2

 Other liquid backup fuels include diesel, ultra-low sulfur diesel, Jet A, K-1, GT No. 1, No. 2 distillate, and some bio-based fuels 

such as bio-diesel.