April 17, 2001

Review of Potential Efficiency Improvements

at Coal-Fired Power Plants

Introduction

The Clean Air Markets Division, U.S. Envi ronmental 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 improve ments that have taken place due to either optimization efforts at existing utility boile rs 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 ener gy 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 conten t of a fuel including the latent heat of vaporization of water, while LHV excludes th e 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 term s 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 re ciprocal 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 h eat rates that have be en achieved at some of the more recently constructe d 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 rese arch that may lead to additional data and supporting documentation could entail contacting EIA at DOE or indivi dual facilities for additional information, particularly with re spect to actual heat rates or efficiency

percentages.

Conventional Pulverized Coal Plants

Current Heat Rates

Unit efficiency, or heat rate, is a functi on of unit design, size, capacity factor, the fuel fired, maintenance condition of the unit, and operating and ambi ent 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. Subcritica l systems historically have achieved thermal efficiencies of 33 to 34 percent ( 10,300 Btu/kWh to 10,000 Btu/kWh). Supercriticalsystems achieve thermal efficiencies 3 to 5 percent higher than subcritical systems. 1 Table

1 summarizes heat rate data fo r the 25 best performing utility co al-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 annua l 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 Navi gant 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 pow er plants have made improvements to their systems that have, in turn, led to improveme nts in the plant’s efficiency or heat rate. The extent to which heat rates can be improved at existing plants is esti mated 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 cons istent 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 se ll 28% of U.S. electricity, Electric Light and
Power, October 1999.

3 Levy, E. and N. Sarunac, Technical Review of EPA's Propo sed 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 ar e 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 pl ant to its design cond itions, change existing operational settings, or instal l retrofit improvements.

Table 2: Measures that may Improve the Efficiency of Coal-Fired Power Plants 4

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 impr ovements associated with each action may vary based on plant configuration. ** The expected efficiency impr ovements associated with thes e 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.pdfWisconsin Electric Power Company (WEPCO) has implemented a number of actions to improve the efficiency or heat rate at certain coal-fired plan ts, some of which are included in Table 2 above. The efficiency improvements as reported in the Climate Challenge Participation Accord between WEPC O and the Department of Energy (DOE) are summarized in Table 3. Efficiency improveme nts 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 cont rol upgrades such as distributed control systems, precipitators and tu rbine controls; metering upgrades ; boiler chemical cleaning; feedwater heater improvements; reduced conde nser air in-leakage; and reduced thermal losses. WEPCO estimated a 0.5 percent annual company-wide heat ra te improvement due

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

Table 3: Example Heat Rate Improve ments 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 Ch allenge 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/climate challenge/cc_accordxWISCEL.htmPlant 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 NO x reductions and efficiency improvements resulting from th e installation of co mbustion optimization software, such as NeuSIGHT, ULTRAMAX, and GNOCIS. The software works with a boiler's digital control system to optimize and control boiler sett ings. Efficiency improvements from the combustion optim ization ranged from 0.3 to 3 percent. 6

New Pulverized Coal Plants

In addition to the potential for effici ency improvements at existing conventional pulverized coal-fired plants through operationa l 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 processe s that are already widely accepted. These types of facilities in clude a high-efficiency pulverized coal boiler integrated with other more efficient combus tion techniques and advancements in emission control technologies. The more advanced versio ns 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.pdfIn 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 component s currently available in the market, could achieve heat ra tes as low as 8,251 Btu/kWh, de pending 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 pract ice thermal efficiency rates at 37.7 percent and 41.7 percent for subcritical and supercritical plants, respec tively, 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 -- E fficiency 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 capab le of achieving efficiencies above 40 percent through the use of low condenser pressures, high steam pressu res and temperatures, double reheat cycles, up to ten stages of feed heating and other cha nges to station parameters and configuration of equipment. These plants and their correspond ing efficiencies are summarized in Table 5

below.

Table 5 - International "Black Coal" Power Plants with High Design Thermal Efficiencies 10

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 ha ve 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 Integr ated 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

10 Sinclair 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 simila r 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 le ad to a heat rate of about 8,679 Btu/kWh, while a "first generation" or "second genera tion" pressurized fluid bed combustor could lead to heat rates of 8,506 Bt u/kWh and 7,040 Btu/kWh, respectively. 11 Another DOE study also confirms heat rate s in this range for a pre ssurized fluid bed combustor. 12

Combustors the size of 70 to 80 MW have b een 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 efficien cy is 41 percent. There is the potential to reach 43 percent in future plants. Howeve r, based on operational data from one existing plant, the overall net efficien cy is approximately 38.2 percent. 13

Integrated Gasification Combined Cycle

The DOE/Parsons study referenced above al so 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 improvi ng 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 generato r. The 265 MW unit began operation in December 1995 and the design he at rate for the repowered unit is 9,034 Btu/kWh (approximately 38 percent efficiency). 15 The Polk Power Plant has a similar

11 Bonk, 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 Syst ems Conference, Pittsburgh, July 22 - 24, 1997. http://www.fetc.doe.gov/publications/p roceedings/97/97ps/p s_pdf/PS1-7.PDF

12 Market Based Advanced Coal Power Systems , Section 5 -- Circulating Pressurized Fluid Bed Combustor, U.S. Department of Energy, May 1999, p.5-5.

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

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

15 DOE 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.htmlefficiency estimated at 39.7 pe rcent and the heat rate is estimated at approximately 8,600

Btu/kWh. 16

16 Clean 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 s hows that these facilities have achieved efficiencies that are similar to the design valu es. 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 percen t with an overall heat rate of 9350 Btu/kWh. The efficiency for the Polk Station has been sl ightly lower than exp ected due to problems with the gasifier and low carbon conversion. Th ese and other issues have been recently addressed and certain operationa l changes are expected to lead to a thermal efficiency of around 38 percent. 18

One study notes that the efficiency of IG CC plants is expected to be around 42 percent and there is the potential to achieve 49 percent when higher e fficiency gas turbines

become available. 19 One DOE study estimates the ther mal efficiency of an IGCC plant slightly lower at 40.1 percent with a heat ra te 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 availa ble) that could achieve an efficiency and heat rate of up to 49.7 percen t 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/t opicalreports/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/t opicalreports/documents/topical19.pdf

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

20 Market Based Advanced Coal Power Systems , Section 4 -- Integrated Gasification Combined Cycle, DOE, May 1999, p. 4.3-5.