Tetra Tech, Inc.

10306 Eaton Place, Suite 340

Fairfax, VA 22030

phone 703-385-6000

fax 703-385-6007

DATE: January 15, 2009

TO: Paul Shriner and Jan Matuszko, EPA

FROM: Peter Sherman, Tetra Tech and John Sunda, SAIC

SUBJECT: Combined Cycle Power Generation Under 316(b) Phase II 

This memo presents information regarding 

systems, including information 

cooling water and the number 

II rule. 

Cooling Water Use at Combined Cycle Power Plants

Combined Cycle electric power generating systems use a two

process. The most common arrangement is a configurat

by two combustion gas-driven turbine

turbines then being used to produce steam in a single heat

(HRSG). The steam from the HRSG produces electricity 

turbine generator. The overall thermal efficiency of combined cycle generating units is 

50% to 60%. Conventional coal

40%. 

Since the combustion turbine component does 

power generation component produces only about one

generated, combined cycle plants 

67% reduction) as a similar capacity co

2002). Thus, replacing a conventional steam generation system with a combined cycle 

generation system of the same power generation capacity could reduce cooling water 

flow by up to 67%. The data in the EPRI

consistent with this estimate.

MEMORANDUM

10306 Eaton Place, Suite 340

January 15, 2009

Paul Shriner and Jan Matuszko, EPA

Peter Sherman, Tetra Tech and John Sunda, SAIC

Combined Cycle Power Generation Under 316(b) Phase II 

This memo presents information regarding the combined cycle electric power production 

, including information on how combined cycle systems could reduce demand for 

the number of combined cycle systems potentially subject to the Phase 

Cooling Water Use at Combined Cycle Power Plants

Combined Cycle electric power generating systems use a two-stage power generation 

process. The most common arrangement is a configuration where electricity is produced 

driven turbine-generators with the hot exhaust gas from these 

turbines then being used to produce steam in a single heat-recovery steam generator 

(HRSG). The steam from the HRSG produces electricity using a single steam

turbine generator. The overall thermal efficiency of combined cycle generating units is 

50% to 60%. Conventional coal-fired plants have a typical thermal efficiency of 36% to 

Since the combustion turbine component does not require cooling water and the steam 

power generation component produces only about one-third of the total electric energy

generated, combined cycle plants should require about a third as much cooling water (i.e., 

67% reduction) as a similar capacity conventional steam-driven power plant (Micheletti 

conventional steam generation system with a combined cycle 

of the same power generation capacity could reduce cooling water 

The data in the EPRI study presented below appears to be reasonably 

consistent with this estimate.

1

power production 

could reduce demand for 

of combined cycle systems potentially subject to the Phase 

stage power generation 

ion where electricity is produced 

generators with the hot exhaust gas from these 

recovery steam generator 

using a single steam-driven 

turbine generator. The overall thermal efficiency of combined cycle generating units is 

fired plants have a typical thermal efficiency of 36% to 

not require cooling water and the steam 

third of the total electric energy

require about a third as much cooling water (i.e., 

driven power plant (Micheletti 

conventional steam generation system with a combined cycle 

of the same power generation capacity could reduce cooling water 

study presented below appears to be reasonably 
2

According to an EPRI report (2002) addressing water and sustainability,

1

combined cycle 

electric power facilities withdraw approximately 54% to 60% less water than comparable 

facilities that do not use combined cycle technology. In the study, EPRI determined the 

water withdrawal and water consumption rates per unit of power generation for several 

categories of facilities (See Table 1 below). Although this study focused on water 

consumption (loss due to evaporation), it also developed water withdrawal data ranges 

for steam-based and combined cycle facilities using several types of cooling water 

systems. For the facilities using once-through cooling systems, the combined cycle 

system water withdrawal rates were approximately 38%-40% of the water withdrawal 

rates of those facilities using a single cycle (steam) power generation process. Similarly, 

for the facilities using cooling towers, the combined cycle system water withdrawal rates 

were approximately 38%-46% of the water withdrawal rates of those facilities using a 

single cycle power generation process. The facilities using combined cycle technology

and cooling towers had the lowest overall cooling water withdrawal rate.

Table 1. EPRI Report Data on Average Water Withdrawal and Consumption 

Based on Cooling Design

Fuel Prime Mover Cooling 

System

Water Withdrawal 

(gal/MWh)

Water 

Consumption 

(gal/MWh)

Fossil/biomass/waste Steam Once through 20,000 to 50,000 ~ 300

Fossil/biomass/waste Steam Cooling pond 300 to 600 300-480

Fossil/biomass/waste Steam Cooling towers 500 to 600 ~ 480

Nuclear Nuclear steam Once through 25,000 to 60,000 ~ 400

Nuclear Nuclear steam Cooling pond 500 to 1100 400 – 720

Natural gas/oil Combined 

cycle

Once through 7500 to 20,000 ~ 100

Natural gas/oil Combined 

cycle

Cooling towers ~ 230 ~ 180

Natural gas/oil Combined 

cycle

Not specified ~ 0 ~ 0

Coal/petroleum 

residuum

Combined 

cycle

Cooling towers ~ 380 ~ 200

Source: Water & Sustainability (Volume 3): U.S. Water Consumption for Power Production—The Next 

Half Century, EPRI, Palo Alto, CA: 2002. 1006786

Currently, most combined cycle generating systems use natural gas or fuel oil as the fuel 

source (typical new facilities use natural gas). The use of natural gas also results in the 

lowest air emissions of commonly used fuels. The 2009 EIA Energy Outlook (early 

release) projects that natural gas (55%) and renewable sources (22%) will provide most 

of the 255 gigawatts of generating capacity projected to be added between 2007 and 

2030. A new technology in the developmental stage called Integrated Coal Gasification 

Combined Cycle (IGCC) uses coal as the fuel source. These systems first convert coal to 

a gas and then use the gas to generate electricity in a similar manner as conventional 

combined cycle systems. Due to the energy requirements of the additional processes, the 

 

1 Water & Sustainability (Volume 3): U.S. Water Consumption for Power Production—The Next Half 

Century, EPRI, Palo Alto, CA: 2002. 1006786.
3

thermal efficiency of IGCC systems is not quite as high as for conventional combined 

cycle, but may reach up to 50%. Similarly, flow reduction isn’t quite as high - IGCC 

systems use 20-50% less water compared to a conventional (non-combined cycle) coal 

power station of similar size (CCSD 2008). 

There are currently two IGCC plants operating in the US and both have been in operation 

since the mid 1990s and thus are included in EPA’s Phase II plant database. These are 

the Tampa Electric Power Station's 250 MW Polk I IGCC plant that went online in 1996 

(EIA Plant ID #7242) and the Wabash River Repower IGCC project that went online in 

1995 (EIA Plant ID #1010). IGCC is a relatively new technology and, as such, has 

presented issues of reliability, cost, and water pollution in early applications. It is too 

early for this to be considered a mainstream technology. 

Single-cycle power plants using gas, oil or coal as a primary fuel can be retrofitted with a 

heat recovery steam generator (HRSG) that makes combined-cycle operations possible. 

Typically, combined-cycle retrofitting involves retiring the original boiler and replacing 

it with a gas turbine. The original steam turbine and feedwater heaters are usually

retained. Such retrofitting enables a power producer to increase its electrical output 

without building entirely new facilities because of the increased thermal efficiency of 

combined cycle technology. Impediments to such retrofits include the capital costs, as 

well as the higher cost (relative to coal) and availability of natural gas as fuel.

Use of Combined Cycle Power Generation in Phase II

The information presented in Tables 2 and 3 below summarize available DOE EIA data 

for steam generating units at Phase II facilities. The generating capacity data summarized 

is for generating units that use steam as a prime mover in the generating process and 

generating units that are coupled with such units. These include the following prime 

mover codes:

 ST - steam turbine that is not combined cycle;

 CT - combustion turbine component of combined cycle;

 CA - steam turbine component of combined cycle;

 CS - combined cycle generator driven by both steam turbine and combustion gas 

turbine. 

In this analysis, total combined cycle generating capacity is calculated by summing the 

nameplate capacity for all operating facility generating units with prime movers CS, CA, 

and CT. The generating capacity for the steam turbine-only category is calculated by

summing the nameplate capacity for all facility generators with prime mover ST. The 

generating unit nameplate capacity is obtained from the EIA 2006 generator database.

A review of the 2006 EIA generator data indicates that 44 (8%) of the population of 525 

facilities in the Phase II database operate combined cycle generating units. Table 2 

presents the estimated number of facilities in the Phase II universe that operate various 

combinations of the different types of steam generating units. The estimated numbers are 
4

extrapolated from data for the population of 525 facilities in the database to the total 

universe of 536 facilities using facility sample weights. The combined cycle component 

of those facilities with both types of steam generating units ranges from 22% to 95%. 

The 2006 EIA generator database indicated that the steam generating units for six of the 

plants currently included in the Phase II database (Table 2 weighted total = 7) were 

permanently retired. It is possible that the cooling water withdrawal rate for these plants 

may no longer be large enough (i.e., >50 MGD) for them to be considered as in-scope 

Phase II facilities.

Table 2. Estimated Number of Facilities in 

the Phase II Universe by Steam Generation 

Type

Steam Generation 

Type

Estimated Number 

of Facilities

Steam Turbine Only 484

Combined Cycle Only 20

Both Steam Turbine 

and Combined Cycle

25

No Steam (mostly gas 

turbines)*

7

Total Universe - All 

Plants

536

*These plants operated steam turbine generating units in 

2000 and the plants are still in operation but have since 

retired all steam turbine generation units.

Table 3 lists the population of facilities in the Phase II database that operated combined 

cycle generating units in 2006. The table presents total combined cycle generating 

system nameplate capacity for generating units with the prime movers CT, CA, and CS in 

the 2006 EIA generator database. Table 3 also shows the proportion of total steam 

generating capacity (sum of ST, CT, CA, and CS) that is comprised by the combined 

cycle generating system.
5

Table 3. Population of Facilities in the Phase II 

Database with Combined Cycle Generating Units

3 900 34%

201 185 100%

260 1398 50%

399 227 100%

400 604.3 35%

533 654 100%

612 1644 100%

613 1042.4 100%

620 2720 95%

643 619.7 65%

658 30 22%

675 126.5 100%

676 369 38%

689 247 83%

693 58 37%

862 647.3 100%

1007 328 100%

1010 305 26%

1404 226 48%

1588 1744.4 74%

1595 253.6 100%

1904 325 53%

2079 306.8 34%

2406 1186 77%

2465 24.6 49%

2493 360 50%

2539 893.1 100%

2708 102 24%

2951 247 25%

3236 515 100%

3295 547.8 85%

3527 126 100%

3631 189.6 88%

3797 446.6 25%

3804 613 33%

4040 579 100%

6042 1224.6 41%

6043 2448.5 59%

6112 742.6 100%

7242 326.3 100%

10617 107.8 100%

10745 1848.6 100%

54785 192.6 100%

54914 322 100%

Combined 

Cycle 

Nameplate 

Capacity 

(MW)

EIA Facility 

Code

Percent of 

Total 

Steam 

Capacity
6

References

Micheletti, W. Burns, J. Emerging Issues and Needs in Power Plant Cooling Systems.

www.netl.doe.gov/publications/proceedings/02/EUW/Micheletti_JMB.PDF

CCSD. Cooperative Research Centre for Coal in Sustainable Development. IGCC Power 

Generation Fact Sheet. Accessed on December 19, 2008 at website: 

http://www.ccsd.biz/factsheets/igcc.cfm

Wabash River Energy Ltd. Wabash River Coal Gasification Repowering Project - Final 

Technical Report. August 2000. Accessed at website:

http://www.netl.doe.gov/technologies/coalpower/cctc/cctdp/bibliography/demonstration/

pdfs/wabsh/Final%20_Report.pdf

U.S. Department of Energy (U.S. DOE). Energy information Administration (EIA). Form 

EIA-860 Database (2006). Generator Database.