Plant Monitoring Workstation with Online Determination of Incremental Heat Rate

C. Kona, R. W de Mello, S E . Williams,2 and R.H Leyse3

An online method of determining a unit’s economic characteristics was developed under EPRl’s Power Plant Performance Instrumentation System Project (RP1681/2153). The method, called the Incremental Heat Rate Monitor, will soon be available as part of EPRl’s Plant Monitoring Workstation. Accurate and timely information about a unit’s economic behavior over the load range (that is, the input/output and incremental heat rate curves) is necessary for the economic dispatch of system generating units. Com- monly, a unit’s economic characteristics are deter- mined either from design data or by occasional test. Since a unit’s operation and condition can change from day to day, such information can become quick- ly outdated. The Incremental Heat Rate Monitor con- s t ructs the input/output and incremental heat rate curves periodically, at 15-minute intervals for ex- ample. Therefore, the information that is used for economic dispatch need never be out of date. Fur- ther, the Incremental Heat Rate Monitor accurately reflects the true condition of the unit including the influence of valve loops and the switching of large auxiliaries. While most dispatch algorithms cannot take full advantage of this information, EPRI, a s part of the same project, is developing a dispatch algo- rithm that promises to exploit fully real-time perfor- mance data from generating units.

This article provides a brief description of EPRI’s RP1681/2153 project, a description of t h e EPRI Plant Monitoring Workstation (PMW), and a description of t h e role of the Incremental Heat Rate Monitor within PMW.

EPRI Power Plant Performance Instrumentation System Project

EPRI’s RP1681/2153 project has the broad goals of monitoring plant performance, pinpointing causes of unit deterioration, identifying solutions to deteriora-

’ Power ‘Technologies, Inc. ’ Potomac Electric Power Company .’ Electric Power Research Institute

tion of plant performance, and enhancing the economic dispatch of generating units. The Potomac Electric Power Company (PEPCO) is the host utility for the project, and Morgantown Generating Station Unit 2 is the test unit. The project is divided into three major areas covering the boiler, the turbine-cycle, and system dispatch. Power Technologies, Inc. (PTI) is subcontrac- tor to PEPCO with responsibility for portions of the project relating to turbine-cycle analysis and in- strumentation and software development. The Plant Monitoring Workstation is one of the vehicles chosen to disseminate the project’s results to the electric utility industry.

Plant Monitoring Workstation The EPRI Plant Monitoring Workstation is a VAXO

based collection of programs to monitor, track, trend, troubleshoot, and report plant performance. In addi- tion to providing the real-time performance indices that are useful to unit operations, special attention has been given to the needs of the engineering and management staff by providing interactive access to the perfor- mance calculations, their execution, their configura- tion, and their results.

To be a truly useful tool , t h e information con- tained within a performance monitoring system must be accessible in a variety of ways as t h e needs of operating staff, engineers , managers, and software-support personnel a re all different. The PMW monitors performance and also provides functions t o find, extract , and use da ta . It addres- ses t h e issues of long-term software maintenance and documentat ion, and it provides tools useful for troubleshooting.

The role of performance information for plant operation, t h e so-called operator controllables, is well documented. PMW fills this role by determin- ing attainable operating conditions and t h e cost of deviating from those conditions. The use of perfor- mance information can go well beyond t h e real-time calculat ion of c o s t penal t ies , however. Perfor- mance information, if reliable and easily available,

0895-0156/90/1000-0021 $1.00 0 1990 IEEE O C t O h P r . I 990 21

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Figure 1 . Time plot produced by PMW

is useful in planning for maintenance or identifying problems that might otherwise go unobserved. Thus , a m o n i t o r i n g s y s t e m c a n i m p a c t c a p a c i t y , availability, and maintenance a s well a s day-to- day operat ions. PMW's calculations of equipment performance combined with a built-in historian function provides for t h e long-term storage and retrieval of da ta in addition t o online, periodic calculations.

Figures 1 and 2 show two of t h e ways informa- tion may be viewed with PMW. Both figures show gross turbine-cycle heat ra te and load for a 24- h o u r per iod . In Figure 1 , bo th quant i t ies a r e plot ted against time. In Figure 2 , turbine-cycle heat ra te is plotted against load, making any func- tional relationship between t h e two readily ap- parent . PMW allows any quant i ty (measured o r calculated) t o b e plotted against t ime o r plotted against any o ther quantity. Tabulated d a t a and customized repor t s a re a lso suppor ted .

A performance monitoring program should be viewed a s a living piece of software. In time, performance monitoring software, like all software, will change to ac- commodate changing conditions, whether they be chan- ges in function (additional calculations), changes in the cycle being monitored, changes in instrumentation, or a combination. PMW incorporates techniques of software modularity, reusability, and selfdocumentation that have evolved during the past decade.

At the heart of PMW is a modular collection of cal- culations used to determine performance indices in the power plant. PMW contains all of the calculations that can be viewed as standard or traditional. In addition, at the Morgantown Station, PMW incorporates monitor- ing techniques including the real-time determination of unit incremental heat rate. Among the pioneering ef- forts are:

22 IEEE Computer Applications in Pouier

Figure 2. Scatter plot produced by PMW

Calculation incremental heat rate that determines a unit's actual incremental heat rate versus load c h a r a c t e r i s t i c (A previous par t of t h e RP1681/2153 project pointed out that "errors in incremental heat rate result in errors in dispatch and increases in production cost." With an online incremental heat rate calculation, it is possible to update the information used in the dispatch of the unit on a periodic basis.) Methods of determining turbine condition that attempt to assign loss of turbine performance to leakage, solid particle erosion, foreign material damage, and/or deposits Methods of direct heat rate determination based on measurements of total loss in flue gas Methods of monitoring condenser performance that attempt to assign loss of performance to air inleakage, tube fouling, and/or tube plugging.

Common t o all of t h e performance calculations are functions that determine the thermodynamic and t ransport properties of steam and water. The steam property functions used in PMW solve the 1967 International Formulations for Industrial Use. PMW uses neither approximations of these formula- tions nor curve fits based on these formulations. The extra effort required t o solve the 1967 formula- tions and t h e resulting accuracy are both warranted a n d , with modern compute r s , computat ional ly feasible.

Advantages of the modular nature of PMW's calcula- tions are many, among which are computational ef- ficiency and rigor. Because the building blocks from which performance calculations are implemented are fairly standard (even though there are wide differences in implementation) the effort to base them on first principals of physics and make them computationally

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Figure 3. Rankine cycle model of PEPCO Morgantown unit 2

efficient is justified. Other advantages of the PMWs modular structure are:

w Flexibility (The modular structure of PMW’s software permits great flexibility in the implemen- tation of performance calculations. There is flexibility in using and combining the calculations in PMWs standard library; additionally, new cal- culations are easily added to PMW’s standard library.)

w Maintainabili ty (Per formance ca lcu la t ions should be considered a living piece of software that grows and changes as the unit changes or a s new instrumentation is installed. The same a t t r i b u t e s t h a t g ive PMW’s p e r f o r m a n c e software its flexibility permit new calculations to be implemented or existing calculations t o take advantage of new instruments as they are installed.)

w Software documentation (Keeping documenta- tion current is particularly difficult for software that grows to meet new needs and opportunities. PMWs performance software generates its own documentation of configuration and implementa- tion details. Documentation, therefore, need never be out of date).

w Consistency (PMW’s performance software of- fers consistency of function and use to both operators and engineers. The same set of cal- culations, with input from the same set of in- strumentation, is used by both groups, so the s a m e ca l cu la t ed pe r fo rmance ind ices a r e presented t o both).

PMW’s performance software also offers a consis- tent approach to engineers and managers who are responsible for the performance of several units or plants. Interaction with PMW’s analytical functions (question and answer with menus and help func-

Figure 4. Calculation of unit heat rate function

tions) is uniform, regardless of differences in cycle or instrumentation.

incremental Heat Rate Monitor The online Incremental Heat Rate Monitor has a high

potential for overall system cost savings. Incremental heat rate is the derivative of aunit’s input/output curve. That is, the incremental change in the unit’s input (ad- ditional fuel cost) for an incremental change in the unit’s output (additional electrical power). The in- cremental heat rate is the basis of most dispatch sys- tems in use today.

The Incremental Heat Rate Monitor determines a unit’s input/output curve from online measurements. This is achieved by using a reduced-order Rankine cycle model of the turbinecycle as illustrated in Figure 3. The Rankine cycle model is initialized to the current operat- ing state and, in conjunction with models of turbine, condenser, boiler, and other auxiliaries, used to predict fuel requirements at other loads. Figure 4 illustrates the Incremental Heat Rate Monitor with the Rankine cycle model as one of the monitor’s components.

The Incremental Heat Rate Monitor has been run- ning on unit 2 at Morgantown since November 1988. Figures 5 and 6 show typical results for a 1-hour period. Figure 5 shows thevariations in load and main steam conditions during the period, while Figure 6 shows the resulting unit heat rate as a function of load. The blue line in Figure 6 represents the results obtained with 1-hour average data. The six green lines represent the six 10-minute intervals within the hour. The input/output curve and incremental heat rate curve are derived from the unit heat rate curve. As shown, the monitor is capable of generating the unit’s economic characterist ics for any sampling period.

Oclober 1990 23

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Figure 5. Sample operating parameters for 1 hour of opera- tion (load and main steam conditions)

UHR

GTHR b

Use of the Incremental Heat Rate Monitor closes the loop in dispatch systems by providing feedback regard- ing the true economic characteristics of the unit.

Conclusion The results of EPRl's RP 1681/2153 project are being

made available to the electric utility industry as part of a sof tware product called t h e Plant Monitoring Workstat ion. A significant ach ievement of t h e project is t h e onl ine cleterminatioii of a unit 's economic characteristics: the inputioutput curve and incremental heat rate curve. Both can be useful in optimizing performance, not only at one plant. but system wide.

Acknowledgments VAX is a registered trademark of Digital Equipment

Corporation.

For Further Reading K.J. Kafka. I..H. Fink. N.J. Balu. H.G. ( ' r im, '.An ~\tlvancc.tl L)ispatch

Simulator with Advanced Dispatch r \ l g o r i t h ~ ~ ~ . ' // pliC-cifion.s in Powclr.'' Volume 2. Nunibcr 1. 0ctot)er I W I ,

"Powcr Plant Prrformance Monitoring arid Iini)t-ovement. Volurnc 2, Incremental Heat RateSensitivity.~i;Ilvsis." EPFd CS/EL-I4 15. Electric Power Research Institute. 3412 Hillview Avr.. I'alo l t o . CI\ $Ll:Nj,

"Power Plant Perforinancc Monitoring antl Imprcivcrnciit. Volume :I: Pomw Plant Performance Instrunic.~ i t at ion Svst enis, EPRI (

Eltctric Power Research Institute. 3112 Hillview Ave.. Palo ,\lto.

1: Boiler C)pt i i i i i~~t ioi i ," EPRI C Iristitute. 3412 Hillview Avt,.. Palo Alt(i, C A W : N $ .

"Power Plant Performance Moriitciririg arid Imprcivcmt~nt, V o l u i r i e 1.4413. Electric P o w t ~ r Rrsearch

Sfecirrr Tcihlrs. ASME. 34.5 East 47 th Street. NCM Ycirk. X I ' 1001 7 .

Biographies Carmelo Kona is a senior engineer with the Power

Production Engineering group of Power Technologies. Inc. in Schenectady, NY. He is responsible for the ther- ino/fluid and heat transfer aspects of power plant per-

UNIT LOAD (% OF RATED)

Figure 6. Unit heat rate and gross turbine heat rate using 10-niinute and 1-hour sampling periods

formance. Mr. Kona received a R.S. 111 Mechanical En- gineering from the Milwaukee School of Engineering in Milwaukee, WI and an M.S. in Mechanical Engineering from the Rensselaer Polytechnic Institute in Troy, NY. Mr. Kona is registered as a Professional Engineer with the state of Wisconsin.

Kobert d e Mello has worked for Power Tech- nologies, Inc. since 1975. His primary interests are in the application of computers in power plants. specifi- cally in the areas of monitoring and simulation. Mr. d e M e 1 1 o has i in p 1 em en t e d se ve r a 1 pe r f o r m an c e monitoring systems and is the principal designer of the EPRI Plant Monitoring Workstation. Mr. d e Mello is a graduate of Johns Hopkins University antl Washington University.

Steve Williams graduated from George Washington University in 1977 with a B.S. in Mechanical Engineer- ing. H e is a registered Professional Engineer with the s ta te of Maryland and a member of ASME. H e has been ernployed by the I'otomac Electric Power Com- pany for 10 years. For the past 9 years, he has been in charge of the Central Diagnostic Team, which is responsible for performance testing and diagnostics of PEPCO's steam turbines and auxiliary equipment. H e also spent several years working at PEPCO's Chalk Point and Benning Generating Stations a s a Plant Performance Engineer. Mr. Williams has been actively involved in the EPRI project to evaluate Power Plant Perf or in an c e Instrument a t ion S y s t erns at P EPC 0 ' s Morgaritown Generating Station.

K.H. Leyse is the Project Manager at EPKI in charge of several power plant performance monitoring and irnproveinent projects. H e has initiated and specified large plant test programs at both fossil and nuclear units. H e holds three U S . patents related to this work. He has a R.S. in Chemical Engineering from the Univer- sity of Wisconsin.

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