April 15, 2013

Mr. Arthur Hofmeister Via Email

EPA Region 4 Hofmeister.Art@epa.gov

Air Permits Section

61 Forsyth St. S.W.

Atlanta, GA 30303 – 8960

Re: Tampa Electric Company 

Polk Power Station 

Polk 2 Combined Cycle GHG PSD Permit 

Dear Mr. Hofmeister, 

During a call on Thursday April, 4 2013, EPA had several questions regarding the GHG PSD 

permit application submitted by Tampa Electric Company (TEC) for the Polk 2 Combined Cycle 

Project. Our responses to these questions are provided below. 

Question 1: What is TEC’s justification for having an annual 3 – hour test certified by the 

CEMS for the following modes of operation, combined cycle on fuel oil, simple cycle on 

natural gas, and simple cycle on fuel oil?

Operation on fuel oil is expected to be infrequent for both combined and simple cycle modes of 

operation since natural gas is significantly lower in cost and is expected to remain lower for the 

foreseeable future. In addition, the draft Florida Department of Environmental Protection 

(FDEP) air construction permit for the Polk 2-5 Conversion Project contains limits on fuel oil 

operating hours; i.e., no more than 750 hours per year per CT (8.5% of the available hours in a 

year) of which no more than 375 hours per year per CT (4.3% of the available hours in a year) 

may be in simple cycle mode. Accordingly, it is expected that use of fuel oil will be limited to 

periods when natural gas is unavailable and brief periods for routine maintenance and readiness 

testing.

Following the conversion to combined cycle mode, operation in simple cycle mode will also be 

infrequent due to the higher fuel costs associated with simple cycle operation. The revised draft 

FDEP air construction permit limits simple cycle hours to no more than 900 hours per year 

(10.3% of the available hours in a year) with a special one-time allocation of 3,480 hours for 

periods when the combined cycle system is unavailable. Operation in simple cycle mode will 

generally be limited to periods when the combined cycle HRSG units and/or common steam 
turbine generator are inoperative due to planned outages or equipment malfunctions and power 

cannot be provided by other more efficient units in Tampa Electric’s fleet of generating units.

Since use of fuel oil and simple cycle mode will be infrequent, it is not possible to predict with 

certainty under what conditions (e.g. loads and ambient temperature) the CTs will operate 

during these infrequent events. For this reason, the proposed GHG BACT limits for the 

infrequent events are referenced to ISO conditions with compliance confirmed on an annual 3-

hour test basis using CO2 CEMS and Part 98 emission factors for CH4 and N2O. 

Question 2: What is the agreement between FDEP and TEC for simple cycle hours of 

operation? Also, what is the justification for the agreed upon hours?

The permit condition that was agreed upon between FDEP and TEC regarding simple cycle 

hours of operation is below. TEC has agreed that this condition allows for maximum flexibility to 

operate the units as required to be able to provide power for our customers in any circumstance 

that it is needed. 

“c. Simple Cycle Operation: Beginning the first full calendar year (CY-1) after demonstrating initial 

compliance in combined cycle mode, the group of four CTGs shall operate in simple cycle mode for no 

more than an average of 900 hours per calendar year per CTG (avg. hours/CY/CTG) except that: 

During CY-1, a one-time special allocation of 3,480 avg. hours/CTG shall be available for use by the 

permittee to provide for events when the steam turbine-electric generator is unavailable, including but not 

limited to planned outages, forced outages and derates; 

If the one-time special allocation of 3,480 avg. hours/CTG is not fully used in CY-1, the balance may be 

carried over into CY-2; 

If the annual allocation of 900 avg. hours/CTG is not fully used in CY-1, the remainder may be added to 

the year-end balance of the special allocation carried over from CY-1 and up to 3,480 avg. hours/CTG 

may be carried over into CY-2; and 

If the annual allocation of 900 avg. hours/CTG is not fully used in CY-3, CY-4, CY-5, CY-6, etc., the 

remainder may be added to the year-end balance of the special allocation carried over from the previous 

year and up to 3,480 avg. hours/CTG may be carried over into subsequent CY-4, CY-5, CY-6, CY-7, etc., 

respectively. 

d. Fuel Oil Usage – CTGs 2A, 2B, 2C and 2D: CTGs 2A, 2B, 2C and 2D shall use ULSD fuel oil for no 

more than 750 avg. hours/CY/CTG of which no more than 375 hours/CY/CTG may be in simple cycle 

mode. The CTGs shall fire ULSD fuel oil no more than 48 hours per day. 

[Rules 62-210.200(PTE) and 62-212.400(BACT), F.A.C.]”

Tampa Electric is an investor owned electric utility regulated by the Florida Public Service 

Commission and subject to the requirements of Chapter 366 of the Florida Statues which include 

an obligation to provide electric service in a reliable and cost effective manner. The request for 

allowable hours of operation contained in the permit application is based upon these 

requirements and necessary to ensure that TEC is in a position to provide the electric service 

should a problem arise with the combined cycle operation necessitating the operation of the 

units in simple cycle mode for an extended period. Although TEC can agree that this contingency 
may not be likely to occur for an extended period, there are many types of possible failures and 

TEC cannot eliminate the possibility that they may occur. TEC and its customers are making a 

significant investment in the damper system to allow flexible use of the CT’s to meet our 

customers’ needs and are seeking to permit a flexible and environmentally sustainable mode of 

operation.

As included in the technical evaluation and preliminary determination, 1050233 – 034 – AC, by 

FDEP, it was agreed between both parties that simple cycle is intended to be a backup mode of 

operation and that TEC would run in combined cycle unless TEC has the need for peaking 

service or the steam turbine – electric generator is derated, in a forced outage, or in a planned 

outage.

TEC needs these simple cycle hours for the following reasons: 

 TEC has a statutory obligation to provide electric service in a reliable and cost effective 

manner

 TEC customers could be subject to significant cost increases due to the possibility of 

having to buy outside power if simple cycle hours on TEC’s system are not available.

 The scenarios requiring > 900 hours of simple cycle operation are possible so they must 

be accommodated.

 Air quality modeling by ECT and FDEP indicate no significant contribution to nonattainment is occurring from the project with any requested mode of operation

FDEP requested that we describe the plausibility of the operating scenario that could interfere 

with the service to our customers. During the past two years, PPS Units 2-5 have averaged over 

900 hours per year per CT and may need to continue utilizing the units in this manner depending 

on the load profile. Figure 1 depicts the actual hours of operation for these units during 2012.

Figure 1 – 2012 Cumulative Operating Hours – PPS 2-5 Simple Cycle Operation

0

200

400

600

800

1000

1200

Hours/year

PPS Units 2-5 2012 Operating Hours

2

3

4

5

Limit in FDEP Revised Draft Permit
This operating profile is a reasonable estimate of required simple cycle operation needs after 

completion of the combined cycle portion of the system. This is supported by considering 

Progress Energy’s 4-on-1 Bartow combined cycle plant with alternative simple cycle operation, 

which has utilized equivalent simple cycle hours when their combined cycle operation did not 

meet their needs.

If a failure preventing combined cycle operation occurred mid-year or later with a limited 

amount simple cycle hours, TEC would not have any simple cycle operating time available and 

would be required to go through the process of requesting permission to operate in simple cycle 

mode. Such a process presents uncertainty in terms of time required to go through the process 

and outcome. These factors would necessitate TEC taking action to secure purchased power very 

quickly after such a failure to ensure power availability to customers. This can and should be 

addressed at this time to avoid this result. 

TEC has also looked into the possibility of a steam turbine failure, as seen below.

There are many different failure risks and failure rates associated with steam turbines, including 

(from Steam Turbine Risk Assessment; Christ et al1):

 Fatigue

 Thermal fatigue

 Erosion

 Stress Corrosion

 Cracking

 Rubbing/distortion 

 Overload

 Material Defect

 Foreign Object Damage

 Wear

 Fretting

 Corrosion

 Electric Discharge

 Creep

 Fouling

 Improper Installation

Many different parts of a turbine could be subject to these failure modes. Most parts of a turbine 

are subject to more than one failure mode. For example, a plug could be subject to erosion, 

fouling, material defect, rubbing distortion, or wear. 
Table 1 describes the top 16 failure modes. The ranks of these failure modes were determined by 

industry experts. These failure modes account for 50% of the basic risk.

Table 1 – Top 16 Steam Turbine Failure Modes

Subcomponent Failure Mechanism When Failure Occurs Rank

Labyrinth seal fixed/rotating Rubbing/Distortion Test & Startup 1

Casing Erosion Outage 2

Labyrinth seal fixed/rotating Rubbing/Distortion Run 3

Stator blading (reaction) Fouling Run 4

Rotor Rubbing/Distortion Test & Startup 5

Stationary Diaphragms Fouling Run 6

Shroud/bands Fatigue Run 7

Blade foils Fouling Run 8

Casing Erosion Run 9

Blade foils Rubbing/Distortion Test & Startup 10

Tenons Fatigue Run 11

Bushings Fouling Run 12

Coupling gear teeth Fouling Run 13

Casing bottling Overload Test & Startup 14

Thrust collar Overload Test & Startup 15

Turbine split line Improper Installation Test & Startup 16

Ancillary equipment such as the generator step up (GSU) transformer can also fail or be 

damaged as a result of extreme weather, rendering the steam turbine generator unavailable. A 

GSU repair can take up to one year to complete. 

Steam turbine failures are not common but there are local examples. Big Bend had a forced 

steam turbine outage in summer 2009 resulting from unavoidable failure. The steam turbine 

tripped during shut down, auxiliary power failed, oil pressure dropped, and the rotor lost 

pressure. The rotor kept spinning as the unit was coming down and destroyed the bearings. 

Overspeed damage can also cause an outage of up to a year or more. Seminole’s Midulla plant 

in Hardee County had a steam turbine and generator failure in 2007 that took over one year to 

repair.

As described above, there are many incidents that could prevent the use of the preferred 

combined cycle mode of operation and TEC is requesting the use of the permit condition that 

was approved by FDEP for simple cycle operation.

 

1 Christ, Timothy J; Drosjack, Michael J; Tanner, G. Mark; “Steam Turbine Risk Assessment – A Tool To Assist 

In Optimizing Inspection And Overhauls Of Industrial Steam Turbines”; Proceedings of the 26th

Turbomachinery Symposium
Question 3: Why are the calendar year (CY) allocations of combined and simple cycle

hours appropriate? 

For the purpose of conservatively estimating potential annual emission rates, the PSD 

application submitted to FDEP used operating scenarios based on 100% loads and ISO 

conditions (i.e., at 59oF). This is considered appropriate for estimating annual potential emission 

rates since emission rates will be lower at lower loads and higher ambient temperatures. 

However, the 100% load scenarios represent the most efficient load for power generation and 

therefore these loads are not suitable for determining a GHG BACT limit in units of lb 

CO2e/MWh on a 12 – month rolling average basis using CO2 CEMS monitoring data if actual 

operating loads will be lower. 

Accordingly, the calendar year allocation of operating scenarios identified for combined cycle 

natural gas – firing represents the expected actual use of the combined cycle system and 

resulting in power generation efficiencies; i.e., actual combined cycle mode heat rates. 

Due to the language that was agreed upon between TEC and FDEP a rolling average is 

inappropriate. As part of the agreement, TEC will get an annual allocation of 900 simple cycle 

hours, which includes both fuel oil and natural gas operation. This annual allocation occurs the 

first calendar year after TEC begins operation in combined cycle mode. In addition, TEC will 

receive a one – time allocation of 3,480 hours to be used when the steam turbine is derated or in 

a planned or forced outage. TEC will then be able to bank left over hours of the 900 hours that 

are not used at the end of each calendar year. However, the one – time allocation bank will 

never exceed 3,480h hours at any time. An example of how this agreement will work can be seen 

below.

Year Annual 

Allocation at 

Beginning of CY

One - Time 

Allocation at 

Beginning of CY

Annual Allocation 

Used 

One – Time 

Allocation Used

CY – 1 900 3,480 500 1,000

CY – 2 900 2,880 500 1,000

CY – 3 900 2,280 500 1,000

A rolling limit for hours will not allow for the banking concept, to build back up the one – time 

allocation, that FDEP and TEC agreed upon. In addition, this will not provide the operational 

flexibility that TEC requires to provide reliable electricity to our customers.

Question 4: Why does TEC have a combined GHG limit for all 4 turbines on combined 

cycle operation and a separate GHG limit for each turbine on simple cycle operation? 

TEC has proposed a GHG limit for the entire 4 – on – 1 combined cycle system instead of a per 

unit basis because it is more accurate. The steam turbine (ST) only has one meter associated 

with measuring the megawatts (MWs) that the ST is generating at any time and this allows for 

only one ST number for all 4 combustion turbines. A mathematically derived number for 

allocating the ST MWs to each combustion turbine would be inaccurate because sometimes not 
all four units are running and during a startup scenario steam from a HRSG unit could be vented 

and the ST bypassed until the steam is hot enough. 

Question 5: Explain the margin used for the proposed GHG BACT limits?

A heat input margin of 10 percent was used in developing the proposed GHG BACT limits in 

units of lb CO2e/MWh, gross. This margin is approximately the same as the margin previously 

used to develop GHG BACT limits in units of Btu/kWh, net with the difference due to expressing 

the GHG BACT limit on a gross rather than net power generation basis. 

Also, attached is the corrected proposed GHG BACT emission limits. 

Please contact myself, 813 – 228 – 4740, or Byron Burrows, 813 – 228 – 1282 if there are any 

additional questions that arise. 

Thank you,

(No Signature Required)

Lyndsey Baldyga

Engineer – Air Programs

Environmental Health & Safety

Tampa Electric Company

EHS/iym/LMB 127 Polk 2 Combined Cycle GHG PSD 

Application EPA Questions