April 17, 2001 

 Review of Potential Efficiency Improvements 

 at Coal-Fired Power Plants 

Introduction

The Clean Air Markets Division, U.S. Environmental Protection Agency requested 

that Perrin Quarles Associates, Inc., perform a review of readily available data on potential 

and actual efficiency improvements at coal-fired utilities. The objective was to identify 

heat rate reductions or efficiency improvements that have taken place due to either 

optimization efforts at existing utility boilers or due to the use of newer advanced 

technologies for coal combustion. 

A unit’s efficiency in this context refers to its thermal efficiency and is defined as a 

percentage determined by the electrical energy export divided by the fuel energy input. 

Fuel energy input can be defined either on a higher heating value (HHV) or lower heating 

value (LHV) basis. HHV is the full energy content of a fuel including the latent heat of 

vaporization of water, while LHV excludes the energy in the water vapor from the fuels 

hydrogen. The HHV will be about 5 to 10 percent higher than LHV. In the United 

States, fuel energy content is generally measured in terms of HHV, and HHV is used 

in Energy Information Agency statistics. Internationally, LHV is more often used. For 

this report, all efficiencies are reported on an HHV basis. Efficiency is also commonly 

represented by the heat rate, which is the reciprocal of the thermal efficiency and is 

described in the units of Btu/kWh. 

This document discusses the range of heat rates and efficiencies associated with 

coal-fired power plants including the improved heat rates that have been achieved at some 

of the more recently constructed state-of-the-art coal-fired facilities. The following is a 

general discussion of this issue in the context of several different types of coal-fired plants. 

Note that the information in this report is based on a search of documents currently 

available on the Internet. More extensive research that may lead to additional data and 

supporting documentation could entail contacting EIA at DOE or individual facilities for 

additional information, particularly with respect to actual heat rates or efficiency 

percentages. 

Conventional Pulverized Coal Plants

Current Heat Rates

Unit efficiency, or heat rate, is a function of unit design, size, capacity factor, the 

fuel fired, maintenance condition of the unit, and operating and ambient conditions (cooling 

water temperature). Existing pulverized coal boilers operating today in the U.S. use 

subcritical or supercritical steam cycles. A supercritical steam cycle normally operates 

above the water critical temperature (705 F) and critical pressure (3210 psia) where water 

can exist only in the gaseous phase. Subcritical systems historically have achieved thermal 

efficiencies of 33 to 34 percent ( 10,300 Btu/kWh to 10,000 Btu/kWh). Supercritical 
systems achieve thermal efficiencies 3 to 5 percent higher than subcritical systems.1

 Table 

1 summarizes heat rate data for the 25 best performing utility coal-fired plants, and 50 best 

performing utility company coal-fired fleets in the U.S. The data were prepared for 

Electric Light and Power’s annual top 100 utility operating report.2

Table 1: Best Coal Fired Heat Rates -- U.S. Utilities

Lowest Reported 

Annual Average 

Heat Rate 

(Btu/kWh)

Highest Reported 

Annual Average 

Heat Rate 

(Btu/kWh)

Average of the 

Reported Annual 

Average Heat Rates 

(Btu/kWh)

25 Best Performing 

Coal-Fired Plants 

8996 9486 9309

50 Best Performing 

Coal-Fired Fleets

9382 10,146 9854

Data on heat rates are taken from Electric Light and Power’s annual top 100 utility operating 

report (EL&P, 1999), and were prepared by Navigant Consulting. Heat rates are from 1998 or 

1997. The report noted that utility methods for determining the heat rate values are 

inconsistent. 

 Heat Rate Improvements at Existing Plants

Many conventional pulverized coal-fired power plants have made improvements to 

their systems that have, in turn, led to improvements in the plant’s efficiency or heat rate. 

The extent to which heat rates can be improved at existing plants is estimated to be at best 3 

to 5 percent.3 This is because heat rate is primarily dependent on unit design, fuel, and 

capacity factor, and the design of a plant can not be changed once built. The literature 

reviewed reported heat rate improvements consistent with the 3 to 5 percent improvement 

estimate. 

 1

Kitto, J.B., Babcock & Wilcox, Developments in Pulverized Coal-Fired Boiler 

Technology, presented to the Missouri Valley Electric Association Engineering Conference, April 

1996. http://www.babcock.com/pgg/tt/pdf/BR-1610.pdf 

2

Burr, M. T., Holding companies rule; top 10 sell 28% of U.S. electricity, Electric Light and 

Power, October 1999. 

3

Levy, E. and N. Sarunac, Technical Review of EPA's Proposed Output Monitoring System, 

Lehigh University Energy Research Center, September 2000. 
Table 2 summarizes some of the potential actions that could be taken to improve 

plant efficiencies. Even though these data are based on the higher moisture "brown coal" 

or lignite typically used only in certain areas, such as Australia, Germany, Russia, and 

certain portions of the U.S., some of the actions may also be applied in the context of the 

lower moisture "black coal" or bituminous that is typically used in the U.S. These actions 

include those that would help restore the plant to its design conditions, change existing 

operational settings, or install retrofit improvements. 

Table 2: Measures that may Improve the Efficiency of Coal-Fired Power Plants4

Action* Efficiency Improvement (%) 

Restore Plant to Design Conditions

Minimize boiler tramp air 0.42

Reinstate any feedheaters out of service 0.46 - 1.97

Refurbish feedheaters 0.84

Reduce steam leaks 1.1

Reduce turbine gland leakage 0.84

Changes to Operational Settings

Low excess air operation 1.22

Improved combustion control 0.84

Retrofit Improvements

Extra airheater surface in the boiler 2.1

Install new high efficiency turbine blades 0.98

Install variable speed drives** 1.97

Install on-line condenser cleaning system 0.84

Install new cooling tower film pack** 1.97

Install intermittent energisation to ESPs 0.32

* Note that the efficiency improvements expected as a result of implementation of these actions may not be 

additive and the feasibility and improvements associated with each action may vary based on plant 

configuration. 

** The expected efficiency improvements associated with these actions may be overestimated. 

 4

Sinclair Knight Merz Pty. Ltd., Integrating Consultancy - Efficiency Standards for Power 

Generation, Australian Greenhouse Office, January 2000, p. 38. 

http://www.greenhouse.gov.au/markets/gen_eff/skmreport.pdf 
Wisconsin Electric Power Company (WEPCO) has implemented a number of 

actions to improve the efficiency or heat rate at certain coal-fired plants, some of which are 

included in Table 2 above. The efficiency improvements as reported in the Climate 

Challenge Participation Accord between WEPCO and the Department of Energy (DOE) are 

summarized in Table 3. Efficiency improvements over a 5 year period ranged from 2.3 

percent to 4.1 percent. In the Accord, WEPCO also committed to other efforts to improve 

heat rates including: various equipment control upgrades such as distributed control 

systems, precipitators and turbine controls; metering upgrades; boiler chemical cleaning; 

feedwater heater improvements; reduced condenser air in-leakage; and reduced thermal 

losses. WEPCO estimated a 0.5 percent annual company-wide heat rate improvement due 

to these additional efforts over a period from 1995 - 2000. 

Table 3: Example Heat Rate Improvements at Wisconsin Electric Plants 

Due to Operational Changes (1990 - 1994)5

Plant

Original 

Heat Rate

(Btu/kWh 

HHV)

Improved 

Heat Rate

(Btu/kWh 

HHV)

Efficienc

y

Increase

(%)

Description of Efficiency 

Improvement Projects

Oak Creek 9,802 9,424 3.9 Variable pressure operation, distributed 

control system, retractable turbine 

packing, variable speed drives on the 

forced and induced draft fans, reduced 

air in-leakage, feedwater heater 

replacements, increased availability and 

capacity factor and precipitator energy 

management system

Pleasant 

Prairie 

11,157 10,796 3.2 Variable pressure operation, unit and 

equipment performance monitoring, 

retractable turbine packing, reduced air 

in-leakage, increased availability and 

variable speed drive make-up water 

pumps 

Presque Isle 11,565 11,089 4.1 Retractable turbine packing, increased 

availability and capacity factor, reduced 

air in-leakage, reduced excess boiler 

O2, boiler chemical cleaning, CO 

monitors on the boiler, improved 

turbine pressure and updated or 

additional instrumentation

Table 3: Example Heat Rate Improvements at Wisconsin Electric Plants

Due to Operational Changes (1990 - 1994) (cont.)

 5

Wisconsin Electric Power Company Climate Challenge Participation Accord (agreement 

with DOE), Appendix A (Wisconsin Energy Emission Reduction/Sequestration Project 

Descriptions), Section 2 - Supply Side Energy Efficiency. 

http://www.eren.doe.gov/climatechallenge/cc_accordxWISCEL.htm 
Plant Original 

Heat Rate

(Btu/kWh 

HHV)

Improved 

Heat Rate

(Btu/kWh 

HHV)

Efficienc

y

Increase

(%)

Description of Efficiency 

Improvement Projects

Valley 13,938 13,623 2.3 Last row turbine blade replacement, 

retractable turbine packing, variable 

speed drives for the forced and induced 

draft fans, superheater surface change, 

reduced air in-leakage, reduced 

pulverizer primary air velocity and 

increased availability and capacity 

factor

PQA has previously reviewed literature for CAMD on NOx reductions and 

efficiency improvements resulting from the installation of combustion optimization 

software, such as NeuSIGHT, ULTRAMAX, and GNOCIS. The software works with a 

boiler's digital control system to optimize and control boiler settings. Efficiency 

improvements from the combustion optimization ranged from 0.3 to 3 percent.6

New Pulverized Coal Plants

 In addition to the potential for efficiency improvements at existing conventional 

pulverized coal-fired plants through operational changes and equipment upgrades, there is 

also the potential for dramatically reduced heat rates through the use of pulverized 

coal-fired power plants built with more advanced technologies. 

A Low Emissions Boiler System (LEBS) based on the direct combustion of 

pulverized coal emphasizes improvements in technology and processes that are already 

widely accepted. These types of facilities include a high-efficiency pulverized coal boiler 

integrated with other more efficient combustion techniques and advancements in emission 

control technologies. The more advanced versions of these facilities may achieve up to 44 

percent efficiency and are expected to be currently commercially available.7

 6

Perrin Quarles Associates, Inc., Review of Utility Coal-Fired Boiler Optimization Papers, 

Appendix, August 2000. 

7

Lester, E., Minimization of Global Climate Change Using Clean Coal Technology, 

American Institute of Chemical Engineers, August 1998, p. 5. 

http://www.aiche.org/government/pdfdocs/cleancoal.pdf 
In the context of these newer units, a 400 MW pulverized coal power plant design 

based on the utilization of pulverized coal feeding a conventional steam boiler and steam 

turbine, as well as state-of-the-art technology and components currently available in the 

market, could achieve heat rates as low as 8,251 Btu/kWh, depending on the specific design 

of the facility. Design data for these types of facilities are summarized in Table 4 below. 

Table 4: Heat Rate Data for Subcritical, Supercritical, and Ultra-Supercritical 

 Coal-Fired Power Plants (Design Data Based on a 400 MW Facility)8

Type of Plant

Steam 

Pressure 

(psig)

Steam 

Temperature (F)

Expected Heat 

Rate (Btu/kWh)

Subcritical (conventional 

pulverized coal plant with 

emission control systems to 

meet current air quality 

standards)

2400 psig 1000F/1000F 9,077

Supercritical (single reheat 

configuration with emissions 

control systems to meet air 

quality standards expected in 

2005)

3500 psig 1050F/1050F 8,568

Ultra-Supercritical (double 

reheat configuration with 

emissions control systems to 

meet air quality standards 

expected in 2010)

4500 psig 1100F/1100F/1100F 8,251

Another source includes data from coal-fired plants in North America, Europe, and 

Japan, and cites the best practice thermal efficiency rates at 37.7 percent and 41.7 percent 

for subcritical and supercritical plants, respectively, for facilities similar in size to those 

referenced above.9

 8

U.S. Department of Energy, Office of Fossil Energy, Market Based Advanced Coal Power 

Systems, Section 3 -- Pulverized Coal-Fired Plants, May 1999, DOE/FE-0400, p. 3.1-5, 3.2-2, and 

3.3-2. 

http://www.fetc.doe.gov/coal_power/special_rpts/market_systems/market_sys.html 

9

Sinclair Knight Merz Pty. Ltd., Integrating Consultancy -- Efficiency Standards for Power 

Generation, Australian Greenhouse Office, January 2000, p. 6. 
An examination of this new generation of coal burning plants internationally have 

revealed that several are capable of achieving efficiencies above 40 percent through the use 

of low condenser pressures, high steam pressures and temperatures, double reheat cycles, 

up to ten stages of feed heating and other changes to station parameters and configuration of 

equipment. These plants and their corresponding efficiencies are summarized in Table 5 

below. 

Table 5 - International "Black Coal" Power Plants 

 with High Design Thermal Efficiencies10

Plant Online

Size 

(MW) Steam Temperature (F)

Design Thermal 

Efficiency (%) HHV

Staudinger 5 1992 550 1004/1040 41.1*

Rostock 1994 550 1004/1040 42

Esbjerg 1992 400 1036/1040 43.2*

Nordjylland-s

vaerket

1998 400 1076/1076/1076

(double reheat cycle)

44.9

Lubeck 1998 440 1076/1112 43.6

Bexbach II 2002

(projected)

750 1067/1103 44.2

* Note that these estimated thermal efficiencies have been confirmed through testing and/or operating 

experience. 

Combined Cycle Operations at Coal-Fired Power Plants

Coal-fired power plants have historically been limited to the simple cycle method. 

However, recent technological developments have led to the capability of powering 

"combined-cycle" generators. Under DOE Initiatives, two new technologies -- 

Pressurized Fluid Bed Combustion and Integrated Gasification Combined Cycle (IGCC) -- 

have allowed for combined cycle operations in the context of coal-fired facilities. These 

facilities have dramatically improved efficiencies or heat rates as compared to conventional 

pulverized coal-fired facilities. 

Pressurized Fluid Bed Combustor

 10Sinclair Knight Merz Pty. Ltd., p. 59. 
One study examined the efficiency benefits of using more advanced technologies 

such as the pressurized fluid bed combustor. Using a standard pulverized coal plant (294 

MW with a heat rate of 9009 Btu/kWh) as a reference point, the efficiency benefits of using 

more advanced technologies were evaluated. A facility similar to the reference plant that 

utilizes a pressurized fluid bed combustor system may be able to achieve heat rates between 

7,040 Btu/kWh and 8,679 Btu/kWh depending on the type of technology. A "bubbling 

bed" pressurized fluid bed combustor could lead to a heat rate of about 8,679 Btu/kWh, 

while a "first generation" or "second generation" pressurized fluid bed combustor could 

lead to heat rates of 8,506 Btu/kWh and 7,040 Btu/kWh, respectively.11 Another DOE 

study also confirms heat rates in this range for a pressurized fluid bed combustor.12

Combustors the size of 70 to 80 MW have been in operation for a number of years. 

Recently, some larger combustors have been constructed. A 350 MW combustor is under 

construction in Japan and the expected efficiency is 41 percent. There is the potential to 

reach 43 percent in future plants. However, based on operational data from one existing 

plant, the overall net efficiency is approximately 38.2 percent.13

Integrated Gasification Combined Cycle

The DOE/Parsons study referenced above also examined the benefits of using an 

Integrated Gasification Combined Cycle (IGCC) system, which is capable of achieving heat 

rates between 7,374 Btu/kWh and 7,581 Btu/kWh, depending again, on the type of 

technology used.14

There have been some successful examples of plants that have recently 

demonstrated the IGCC technology. The Wabash River Coal Gasification Power Plant in 

West Terre Haute, IN and the Polk Power Plant in Polk County, Florida are two IGCC 

systems that have been successful at improving efficiencies. The Wabash River project 

repowered the oldest of six pulverized coal units using a "next-generating" coal gasifier, an 

advanced gas turbine and a heat-recovery steam generator. The 265 MW unit began 

operation in December 1995 and the design heat rate for the repowered unit is 9,034 

Btu/kWh (approximately 38 percent efficiency).15 The Polk Power Plant has a similar 

 11Bonk, D., and M. Freier, U.S. Department of Energy, and Buchanan, et. al., Parsons 

Power, Assessment of Opportunities for Advanced Technology Repowering, p. 3. , Proceedings of 

the Advanced Coal Based and Environmental Systems Conference, Pittsburgh, July 22 - 24, 1997. 

http://www.fetc.doe.gov/publications/proceedings/97/97ps/ps_pdf/PS1-7.PDF 

12Market Based Advanced Coal Power Systems, Section 5 -- Circulating Pressurized Fluid 

Bed Combustor, U.S. Department of Energy, May 1999, p.5-5. 

13Sinclair Knight Merz Pty. Ltd., pp. 59-60, 66-67. 

14Bonk, D. and M. Freier, and Buchanan, et. al., p. 3-4. 

15DOE Fossil Energy Techline, "Fourth Clean Coal Plant to Win Powerplant Award Sets 

Record Operation for Coal Gasifier in Early 1997." February 18, 1997. 

http://www.fe.doe.gov/techline/tl_wab96.html 
efficiency estimated at 39.7 percent and the heat rate is estimated at approximately 8,600 

Btu/kWh.16

 16Clean Coal Today, "Tampa Electric's Greenfield IGCC Ready for Demonstration," Office 

of Fossil Energy, U.S. Department of Energy, DOE/FE-0215 P-24, No. 24, Winter 1996. 
Recent data on actual operational results shows that these facilities have achieved 

efficiencies that are similar to the design values. The overall net thermal efficiency for the 

Wabash River IGCC facility has been 39.7 percent.17 The overall net thermal efficiency 

for the Polk Power Station has been 36.5 percent with an overall heat rate of 9350 Btu/kWh. 

The efficiency for the Polk Station has been slightly lower than expected due to problems 

with the gasifier and low carbon conversion. These and other issues have been recently 

addressed and certain operational changes are expected to lead to a thermal efficiency of 

around 38 percent.18

One study notes that the efficiency of IGCC plants is expected to be around 42 

percent and there is the potential to achieve 49 percent when higher efficiency gas turbines 

become available.19 One DOE study estimates the thermal efficiency of an IGCC plant 

slightly lower at 40.1 percent with a heat rate of 8,522 Btu/kWh. This estimate assumes a 

540 MW facility with a plant configuration based on the technology demonstrated at the 

Wabash IGCC facility but incorporates a new steam turbine. However, this study also 

describes IGCC facilities of similar size based on more advanced technologies (some of 

which of which are not yet commercially available) that could achieve an efficiency and 

heat rate of up to 49.7 percent and 6,870 Btu/kWh, respectively.20

 17"The Wabash River Coal Gasification Repowering Project - An Update," Clean Coal 

Technology, Topical Report #20, September 2000. 

http://www.lanl.gov/projects/cctc/topicalreports/documents/topical20.pdf 

18"Tampa Electric Integrated Gasification Combined-Cycle Project - An Update," Clean 

Coal Technology, Topical Report #19, July 2000. 

http://www.lanl.gov/projects/cctc/topicalreports/documents/topical19.pdf 

19Sinclair Knight Merz Pty. Ltd., pp. 59, 66. 

20Market Based Advanced Coal Power Systems, Section 4 -- Integrated Gasification 

Combined Cycle, DOE, May 1999, p. 4.3-5.