Fossil Plant Cycle Chemistry

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Fossil Plant Cycle Chemistry

Instrumentation and ControlState-of-Knowledge Assessment

Effective December 6, 2006, this report has been made publicly availaccordance with Section 734.3(b)(3) and published in accordance witSection 734.7 of the U.S. Export Administration Regulations. As a resthis publication, this report is subject to only copyright protection and not require any license agreement from EPRI. This notice supersedesexport control restrictions and any proprietary licensed material noticeembedded in the document prior to publication.


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EPRI Project ManagerK. Shields

ELECTRIC POWER RESEARCH INSTITUTE3420 Hillview Avenue, Palo Alto, California 94304-1338 PO Box 10412, Palo Alto, California 94303-0813 USA

800.313.3774 650.855.2121 [email protected] www.epri.com

Fossil Plant Cycle ChemistryInstrumentation and Control

State-of-Knowledge Assessment

1012209

Final Report, March 2007


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DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS ANACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCHINSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THEORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

(A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I)

WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, ORSIMILAR ITEM DISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESSFOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON ORINTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUAL

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(B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER(INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVEHAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOURSELECTION OR USE OF THIS DOCUMENT OR ANY INFORMATION, APPARATUS, METHOD,

PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT.

ORGANIZATION(S) THAT PREPARED THIS DOCUMENT

Electric Power Research Institute (EPRI)

Scientech, LLC

NOTICE: THIS REPORT CONTAINS PROPRIETARY INFORMATION THAT IS THE

INTELLECTUAL PROPERTY OF EPRI. ACCORDINGLY, IT IS AVAILABLEONLY UNDER LICENSE FROM EPRI AND MAY NOT BE REPRODUCED

OR DISCLOSED, WHOLLY OR IN PART, BY ANY LICENSEE TO ANYOTHER PERSON OR ORGANIZATION.

NOTE

For further information about EPRI, call the EPRI Customer Assistance Center at 800.313.3774 ore-mail [email protected].

Electric Power Research Institute, EPRI, and TOGETHERSHAPING THE FUTURE OF ELECTRICITYare registered service marks of the Electric Power Research Institute, Inc.

Copyright 2007 Electric Power Research Institute, Inc. All rights reserved.


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CITATIONS

This report was prepared by

Electric Power Research Institute (EPRI)3420 Hillview AvenuePalo Alto, CA 94304

Principal InvestigatorsK. Shields

B. Syrett

Scientech, LLC2650 McCormick DriveSuite 300Clearwater, FL 33759

Principal InvestigatorsD. MeilsJ. Witherow

This report describes research sponsored by the EPRI.

The report is a corporate document that should be cited in the literature in the following manner:

Fossil Plant Cycle Chemistry Instrumentation and ControlState-of-Knowledge Assessment.EPRI, Palo Alto, CA: 2007. 1012209.


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v

PRODUCT DESCRIPTION

Effective monitoring of the purity of water and steam is an integral part of a productive cyclechemistry monitoring program. EPRIs cycle chemistry guidelines for fossil plants identify agroup of core monitoring parameters that are considered the minimum requirements. Meeting thecore monitoring requirement is part of EPRIs cycle chemistry benchmarking criteria for plantcycle chemistry programs. In addition to the core parameters, many other chemistry parametersmay be measuredeither routinely or as needed for diagnostic and troubleshooting purposes.

On-line monitoring of cycle chemistry is preferable to grab sample analysis. The EPRI report

Reference Manual for On-Line Monitoring of Water Chemistry and Corrosion: 1998 Update(TR-112024) marked the last time this subject had been addressed. That state-of-art assessmentwas identified as the initial activity in a new project that considers both the need and opportunityfor advancements in monitoring technology.

Results and FindingsThis report describes the available technology options for monitoring a number of cyclechemistry parameters. The main focus is on methods available and in common use at fossilstations; however, information is also provided on a number of recently developed techniques aswell as others that show promise. The report also considers techniques to monitorelectrochemical corrosion potential and corrosion ratetwo parameters not generally monitored

in fossil plants and for which further development could lead to improved monitoring tools forfossil plants in the future.

Challenges and ObjectivesThe real-time monitoring of cycle chemistry supports operator oversight of water and steampurity, minimizing the time needed to 1) identify out-of-specification chemistry conditions and2) implement appropriate corrective actions. It also provides a warning of plant equipmentmalfunction, facilitates the control of chemical additions, optimizes maintenance and repairschedules, and improves corrosion control. Fossil plant personnel involved in the evaluation,selection, operation, and maintenance of chemistry analyzers will find the information in thisreport useful. Information addressing the individual EPRI core monitoring parameters should beof particular value to users whose plants do not currently meet all of the core requirements.

Applications, Value, and UseDespite the many advances in fossil plant cycle chemistry monitoring that have been achievedover the last 30 years, the current techniques have their limitations. In addition, resources neededto obtain, install, operate, and maintain analyzers to provide the information needed to controlcycle chemistry are often an area of concern. Familiarity with the technology involved istherefore important when limited resources are invested in chemistry surveillance and control.


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EPRI PerspectiveChemistry analyzers now in use require that samples be collected and conditioned. Informationprovided by the analyzers is useful for assessing conditions under which the potential exists forcorrosion or other chemistry-related damage to cycle components. However, this information isindirect in that it does not determine the presence or magnitude (that is, rate) of corrosion.

Research efforts are now investigating corrosion in boilers and turbines to enable a betterunderstanding of its mechanisms and root causes in order to further the development of cyclechemistry guidelines. These future guidelines could likely be more effectively implemented ifimproved monitoring techniques were available. Therefore, investigations are planned to identifyand develop monitoring techniques for the direct measurement of chemistry environments inwhich corrosion or deposition activity occurs.

ApproachThe project team collected information from various sources for this report. These included thepublished literature, instrument manufacturer personnel and materials, consultantsknowledgeable in chemistry instrumentation, the Internet, and relevant EPRI reports.

KeywordsCycle chemistryCore monitoring parameterInstrumentationAnalyzerCorrosionSurveillance


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EPRI Proprietary Licensed Material

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CONTENTS

1CYCLE CHEMISTRY MONITORING IN FOSSIL PLANT CYCLES ......................................1-1

1.1 Introduction ....................................................................................................................1-1

1.2 Monitoring Requirements and Choice of Cycle Chemistry.............................................1-1

1.3 Cycle Chemistry Monitoring Approaches .......................................................................1-3

1.3.1 Core Monitoring Parameters ..................................................................................1-3

1.3.2 Diagnostic Monitoring Parameters .........................................................................1-4

1.3 Future Cycle Chemistry Guidelines and Monitoring Approaches...................................1-5

1.4 References.....................................................................................................................1-7

2AIR IN-LEAKAGE ..................................................................................................................2-1

2.1 Effects of Air In-leakage on Unit Performance and Cycle Chemistry.............................2-1

2.2 Monitoring Methods........................................................................................................2-2

2.2.1 Rotameters .............................................................................................................2-2

2.2.2 Early Advanced Air Removal Monitoring Systems .................................................2-3

2.2.3 Multisensor Probe Design ......................................................................................2-3

2.3 References.....................................................................................................................2-7

3CARRYOVER IN DRUM BOILERS........................................................................................3-1

3.1 Introduction to Carryover................................................................................................3-1

3.2 Consideration of Carryover in EPRI Cycle Chemistry Guidelines..................................3-2

3.3 Determination of Total Carryover from Drum Boilers .....................................................3-4

3.4 Sampling and Data Collection Considerations...............................................................3-4

3.5 References.....................................................................................................................3-5

4 CONDUCTIVITY .....................................................................................................................4-1

4.1 Purpose and Use ...........................................................................................................4-1

4.2 Description .....................................................................................................................4-1

4.3 Technical Considerations...............................................................................................4-9


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4.3.1 Cell Constants ........................................................................................................4-9

4.3.2 Cell Constant Determination or Verification..........................................................4-10

4.3.3 Cell Construction and Installation Considerations ................................................4-10

4.3.4 Cell Polarization....................................................................................................4-11

4.3.5 Temperature Effects .............................................................................................4-11

4.3.5.1 Solute Effects................................................................................................4-12

4.3.5.2 Solvent Effects ..............................................................................................4-12

4.3.6 Cation and Degassed Cation Conductivity Temperature Compensation .............4-13

4.3.7 Cation Conductivity Column Connections, Size, Flow and Flow RateConsiderations................................................................................................................4-13

4.3.8 Cation Conductivity Resin Exhaustion, Regeneration and Rinse-in.....................4-13

4.4 Interferences ................................................................................................................4-14

4.4.1 Organic and Strong Acids Interferences...............................................................4-144.4.2 Sample Line Interference .....................................................................................4-14

4.5 Calibration ....................................................................................................................4-15

4.6 Calibration Checks .......................................................................................................4-15

4.7 Alternative Methods for Determining Conductivity .......................................................4-15

4.4 End User Considerations .............................................................................................4-21

4.9 References...................................................................................................................4-21

5 OXYGEN.................................................................................................................................5-1

5.1 Purpose and Use ...........................................................................................................5-1

5.2 Description of Methods...................................................................................................5-1

5.2.1 Galvanic Method.....................................................................................................5-2

5.2.2 Polarographic Method ............................................................................................5-3

5.2.3 Equilibrium Method.................................................................................................5-4


5.3.1 Membrane Replacement ........................................................................................5-5

5.3.2 Electrode Cleaning .................................................................................................5-5

5.3.2.1 Polarographic..................................................................................................5-5

5.3.2.2 Galvanic..........................................................................................................5-6

5.3.2.3 Equilibrium ......................................................................................................5-6

5.3.3 Temperature and Pressure Compensation for Sensors .........................................5-6

5.3.4 Flow Rate Sensitivity ..............................................................................................5-8


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5.3.5 Response Time ......................................................................................................5-8

5.3.5.1 Response Time After Air Calibration...............................................................5-8

5.3.5.2 Response Time Due to Changes in Dissolved Oxygen Concentration inthe Process Stream .....................................................................................................5-9

5.4 Interferences ..................................................................................................................5-95.4.1 Oxygen Contamination ...........................................................................................5-9

5.4.2 Sample Conditioning ............................................................................................5-10

5.4.3 Electrolyte.............................................................................................................5-10

5.4.4 Stray Current ........................................................................................................5-10

5.4.5 Membrane Fouling, Positioning and Tension .......................................................5-10

5.4.6 Hydrogen..............................................................................................................5-10

5.4.7 Other Cycle Chemistry Additives..........................................................................5-11

5.4.8 TDS ......................................................................................................................5-115.5 Calibration ....................................................................................................................5-11

5.5.1 Polarographic .......................................................................................................5-11

5.5.2 Galvanic................................................................................................................5-11

5.5.3 Equilibrium............................................................................................................5-12

5.5.4 Air Calibration for All Sensor Types......................................................................5-12

5.6 Calibration Checks for All Sensor Types......................................................................5-13

5.6.1 Zero Point for All Sensor Types............................................................................5-14

5.6.2 Maintenance for All Sensor Types........................................................................5-155.7 Alternative Methods......................................................................................................5-15

5.7.1 Luminescent Oxygen Sensors [17].......................................................................5-15

5.7.1.1 gkg-1Resolution Optical Sensor to Monitor Dissolved Oxygen ...............5-18


5.9 References...................................................................................................................5-20

6OXIDATION-REDUCTION POTENTIAL................................................................................6-1

6.1 Purpose and Use ...........................................................................................................6-1

6.2 Description of Method ....................................................................................................6-1


6.3.1 Voltmeter Selection ................................................................................................6-4

6.3.2 Reference Electrodes .............................................................................................6-5

6.3.3 ORP Sensing Electrode..........................................................................................6-5


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6.4 Interferences ..................................................................................................................6-7

6.5 Calibration ......................................................................................................................6-7

6.5.1 Calibration Checks .................................................................................................6-9

6.6 End User Considerations ...............................................................................................6-9

6.7 References...................................................................................................................6-10

7 pH ...........................................................................................................................................7-1

7.1 Purpose and Use ...........................................................................................................7-1

7.2 Description .....................................................................................................................7-1


7.3.1 Sensing (Glass) Electrode......................................................................................7-2

7.3.2 Reference Electrode...............................................................................................7-3

7.3.3 Temperature Effects ...............................................................................................7-57.3.3.1 Electrode Effects.............................................................................................7-6

7.3.3.2 Solution Additive Effects .................................................................................7-7

7.4 Interferences ..................................................................................................................7-8

7.4.1 Interfering Ions........................................................................................................7-8

7.4.2 Interfering Stray Currents .......................................................................................7-8

7.5 Calibration ......................................................................................................................7-9


7.7 Alternative Methods for Determining pH ......................................................................7-117.8 End User Considerations .............................................................................................7-14

7.9 References...................................................................................................................7-15

8 SODIUM..................................................................................................................................8-1

8.1 Purpose and Use ...........................................................................................................8-1

8.2 Description of Method ....................................................................................................8-1


8.3.1 Sensing Electrode ..................................................................................................8-4

8.3.2 Reference Electrode...............................................................................................8-7

8.4 Interferences ..................................................................................................................8-8

8.5 Calibration ......................................................................................................................8-9


8.7 Alternative Methods......................................................................................................8-12


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8.9 References...................................................................................................................8-13

9AMMONIA ..............................................................................................................................9-1

9.1 Purpose and Use ...........................................................................................................9-19.2 Description of Methods...................................................................................................9-2

9.2.1 Background ............................................................................................................9-2

9.2.2 Conductivity Approximation....................................................................................9-3

9.2.2.1 Conductivity Approximation Limitations ..........................................................9-3

9.2.3 Ion Selective Electrode...........................................................................................9-4

9.2.4 Colorimetry .............................................................................................................9-5


9.3.1 Ion Selective Electrodes (ISE)................................................................................9-69.3.1.1 Ammonium Sensing Electrode........................................................................9-6

9.3.1.2 Reference Electrode .......................................................................................9-6

9.3.2 Colorimetric Analyzers............................................................................................9-7

9.3.2.1 Colorimetric Limitations...................................................................................9-8

9.3.2.2 Sample Considerations.................................................................................9-11

9.3.2.3 Time Delay....................................................................................................9-11

9.3.2.4 Sample Temperature ....................................................................................9-11

9.3.2.5 Sample Volume ............................................................................................9-129.4 Interferences ................................................................................................................9-12

9.4.1 ISE Interferences..................................................................................................9-12

9.4.2 Colorimetric Interferences ....................................................................................9-13

9.5 Calibration ....................................................................................................................9-13

9.5.1 ISE Calibration......................................................................................................9-13

9.5.2 Colorimetric Calibration ........................................................................................9-14


9.7 Alternative Methods......................................................................................................9-159.7.1 Direct Nesslerization.............................................................................................9-15

9.7.2 Titrimetric Ammonia Determination ......................................................................9-16

9.7.3 ISE Gas Permeable Membrane.........................................................................9-16


9.9 Field Experience...........................................................................................................9-17


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9.9.1 Sample Delivery ...................................................................................................9-17

9.9.2 Analyzer Malfunction ............................................................................................9-18

9.10 References.................................................................................................................9-18

10 CHLORIDE .........................................................................................................................10-110.1 Purpose and Use........................................................................................................10-1

10.2 Description of Method ................................................................................................10-2

10.3 Technical Considerations...........................................................................................10-4

10.3.1 Sensing Electrode ..............................................................................................10-4

10.3.2 Reference Electrode...........................................................................................10-4

10.3.3 Temperature Considerations..............................................................................10-5

10.4 Interferences ..............................................................................................................10-6

10.5 Calibration ..................................................................................................................10-610.6 Calibration Checks .....................................................................................................10-9

10.7 Alternative Methods ...................................................................................................10-9

10.7.1 ASTM D512 Test Method AMercurimetric Titration ........................................10-9

10.7.2 ASTM D512 Test Method BSilver Nitrate Titration .........................................10-9

10.7.3 Standard Methods: Method 4500 - Cl D. Potentiometric Method [11].............10-10

10.7.4 Standard Methods: Method 4500 - Cl E. Automated Ferricyanide Method[11]................................................................................................................................10-10

10.7.5 Ion Chromatography.........................................................................................10-10

10.8 End User Considerations .........................................................................................10-10

10.9 References...............................................................................................................10-11

11 HYDRAZINE.......................................................................................................................11-1

11.1 Purpose and Use........................................................................................................11-1

11.2 Description of Methods...............................................................................................11-2


11.3.1 Colorimetry .........................................................................................................11-2

11.3.1.1 Colorimetric Limitations...............................................................................11-3

11.3.2 Amperometry ......................................................................................................11-4

11.3.2.1 Two Electrode Method................................................................................11-4

11.3.2.2 Three Electrode Method .............................................................................11-5

11.3.3 Iodide Ion Selective Electrode Method...............................................................11-6

11.4 Interferences ..............................................................................................................11-7


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11.4.1 Colorimetry .........................................................................................................11-7

11.4.2 Amperometry ......................................................................................................11-8

11.4.3 Ion Selective Electrode Method..........................................................................11-8

11.5 Calibration ..................................................................................................................11-8

11.5.1 Colorimetry .........................................................................................................11-8

11.5.2 Amperometry ......................................................................................................11-9

11.5.3 Ion Selective Electrode Method..........................................................................11-9

11.6 Calibration Checks ...................................................................................................11-10

11.7 Alternative Methods .................................................................................................11-10


11.8.1 Recognizing Instrument Malfunctions...............................................................11-12

11.8.1.1 Sample Delivery........................................................................................11-12

11.8.1.2 Analyzer Malfunction.................................................................................11-12

11.9 References...............................................................................................................11-13

12 HYDROGEN .......................................................................................................................12-1

12.1 Purpose and Use........................................................................................................12-1

12.2 Discussion of Methods ...............................................................................................12-1

12.2.1 Electrochemical / Polarographic .........................................................................12-2

12.2.2 Thermal Conductivity..........................................................................................12-2

12.2.3 Gas Density Meter ..............................................................................................12-212.3 Technical Considerations...........................................................................................12-3

12.3.1 Electrochemical / Polarographic .........................................................................12-3

12.3.2 Thermal Conductivity..........................................................................................12-5

12.3.3 Gas Density Meter ..............................................................................................12-8

12.4 Calibration ..................................................................................................................12-9

12.5 Calibration Check .......................................................................................................12-9


12.7 End User Considerations .........................................................................................12-1012.8 References...............................................................................................................12-11

13ION CHROMATOGRAPHY ................................................................................................13-1

13.1 Purpose and Use........................................................................................................13-1



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13.2.1 Ion Exchange Chromatography..........................................................................13-3

13.2.2 Ion Exclusion Chromatography ..........................................................................13-7

13.2.3 Ion Pair Chromatography ...................................................................................13-7


13.3.1 Sample Injection .................................................................................................13-7

13.3.2 Column Selection .............................................................................................13-10

13.3.2.1 Concentrator Column................................................................................13-11

13.3.2.2 Guard Column...........................................................................................13-11

13.3.2.3 Separator Column.....................................................................................13-11

13.3.2.4 Eluent Suppressor Column.......................................................................13-12

13.4 Eluent Selection .......................................................................................................13-13

13.5 Detectors..................................................................................................................13-17

13.5.1 Interferences.....................................................................................................13-19

13.6 Calibration ................................................................................................................13-21

13.6.1 Calibration Checks ...........................................................................................13-21

13.7 Alternative Methods .................................................................................................13-21


13.9 References...............................................................................................................13-22

14IRON AND COPPER..........................................................................................................14-1

14.1 Purpose and Use........................................................................................................14-114.2 Description of Methods...............................................................................................14-1


14.3.1 Integrated Sampling ...........................................................................................14-2

14.3.1.1 Wet Chemistry Analysis of Integrated Samples..........................................14-3

14.3.1.2 XRF Analysis of Integrated Samples ..........................................................14-3

14.3.2 Turbidity..............................................................................................................14-4

14.3.3 Particle Counter ..................................................................................................14-5

14.3.4 Dynamic Light Fluctuation Based Particle Monitors ...........................................14-614.3.5 Acoustic Detection..............................................................................................14-6

14.3.6 Colorimetric ........................................................................................................14-7

14.3.6.1 Colorimetric Limitations...............................................................................14-8

14.4 Calibration ..................................................................................................................14-9

14.4.1 Wet Chemistry Analysis......................................................................................14-9


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14.4.2 XRF Analysis ....................................................................................................14-10

14.5 Calibration Check .....................................................................................................14-10

14.6 Alternate Methods ....................................................................................................14-11


14.8 References...............................................................................................................14-12

15 PHOSPHATE......................................................................................................................15-1

15.1 Purpose and Use........................................................................................................15-1



15.3.1 Colorimetric Limitations ......................................................................................15-3

15.3.2 Sample Considerations ......................................................................................15-4

15.3.3 Time Delay .........................................................................................................15-515.3.4 Sample Temperature..........................................................................................15-5

15.3.5 Sample Volume and Introduction of Chemicals..................................................15-5

15.3.6 Light Intensity .....................................................................................................15-5

15.4 Interferences ..............................................................................................................15-6

15.4.1 Particulate Matter ...............................................................................................15-6

15.4.2 Sample Discoloration..........................................................................................15-6

15.4.3 Other Substances...............................................................................................15-6

15.5 Calibration ..................................................................................................................15-715.6 Calibration Check .......................................................................................................15-7


15.8 End User Considerations ...........................................................................................15-8

15.9 Field Experience.........................................................................................................15-8

15.9.1 Sample Delivery .................................................................................................15-9

15.9.2 Analyzer Malfunction ..........................................................................................15-9

15.10 References.............................................................................................................15-10

16 SILICA ................................................................................................................................16-1

16.1 Purpose and Use........................................................................................................16-1



16.3.1 Colorimetric Limitations ......................................................................................16-3


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16.3.2 Sample Considerations ......................................................................................16-4

16.3.3 Time Delay .........................................................................................................16-5

16.3.4 Sample Temperature..........................................................................................16-5

16.3.5 Sample Volume and Introduction of Chemicals..................................................16-5

16.3.6 Light Intensity Check ..........................................................................................16-6

16.4 Interferences ..............................................................................................................16-6

16.4.1 Ortho-phosphate.................................................................................................16-6

16.4.2 Non-reactive Silica..............................................................................................16-6

16.4.3 Particulate Matter ...............................................................................................16-7

16.4.4 Reagent Contamination......................................................................................16-7

16.4.5 Sample Discoloration..........................................................................................16-7

16.4.6 Sample Temperature..........................................................................................16-7

16.5 Calibration ..................................................................................................................16-7

16.6 Calibration Checks ................................................................................................16-8


16.8 End User Considerations ...........................................................................................16-9

16.9 Field Experience.......................................................................................................16-10

16.9.1 Sample Delivery ...............................................................................................16-10

16.9.2 Analyzer Malfunction ........................................................................................16-10

16.10 References.............................................................................................................16-11

17TOTAL ORGANIC CARBON .............................................................................................17-1

17.1 Purpose and Use........................................................................................................17-1

17.2 Forms of Organic Carbon and Description of Method................................................17-2


17.3.1 High Temperature Combustion Method .............................................................17-3

17.3.2 Persulfate Oxidation ...........................................................................................17-4

17.3.3 Conductometric-type TOC..................................................................................17-6

17.4 Calibration ..................................................................................................................17-817.5 Calibration Check .......................................................................................................17-8


17.6.1 Closed-Loop Photocatalytic Oxidation................................................................17-9

17.6.2 TOC Data Comparison.....................................................................................17-11



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17.8 References...............................................................................................................17-12

18ELECTROCHEMICAL CORROSION POTENTIAL ...........................................................18-1

18.1 Purpose and Use........................................................................................................18-1

18.2 Description of Method ................................................................................................18-218.2.1 Use of Reference Electrodes..............................................................................18-3


18.3.1 Reference Electrode Selection ...........................................................................18-4

18.3.2 Quasi-Reference Electrodes Used in Corrosion Rate Probes............................18-5

18.3.3 Reference Electrode Issues ...............................................................................18-6

18.3.4 Voltmeter Selection ............................................................................................18-7

18.4 Calibration and Maintenance Procedures ..................................................................18-7

18.4.1 Reference Electrodes .........................................................................................18-718.4.2 Electrochemical Corrosion Potential Probe ........................................................18-8

18.5 Field Experience.........................................................................................................18-8

18.5.1 ECP Measurements in Condensers ...................................................................18-8

18.5.2 ECP Measurements in Boiling Water Reactors..................................................18-9

18.6 Possible Future ECP Measurements in Fossil Plants................................................18-9

18.7 References...............................................................................................................18-10

19CORROSION RATE...........................................................................................................19-1

19.1 Purpose and Use........................................................................................................19-1

19.2 Description of Traditional Methods.............................................................................19-1

19.3 Advantages of On-Line Corrosion Monitoring ............................................................19-2

19.4 Description of Physical Methods ................................................................................19-3

19.5 Description of Electrochemical Methods ....................................................................19-5

19.5.1 General Considerations......................................................................................19-6

19.5.2 Linear Polarization Resistance (3-Electrode) .....................................................19-8

19.5.3 Linear Polarization Resistance (2-Electrode) ...................................................19-11

19.5.4 Electrochemical Impedance Spectroscopy.......................................................19-13

19.5.5 Coupling Current (Zero Resistance Ammetry) .................................................19-14

19.5.6 Electrochemical Noise......................................................................................19-15

19.5.6.1 Electrochemical Potential Noise ...............................................................19-15

19.5.6.2 Electrochemical Current Noise .................................................................19-17


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19.5.6.3 Electrochemical Noise Resistance............................................................19-18

19.5.7 Galvanic Corrosion Monitoring Using Zero Resistance Ammetry.....................19-18

19.5.8 Coupling Current Between Two or More Metals...............................................19-19

19.5.9 Coupling Current Between Segmented Weld Electrodes.................................19-20

19.5.10 Electrochemical Methods in Combination ......................................................19-20

19.6 Calibration ................................................................................................................19-21


19.8 Possible Future Corrosion Rate Monitoring in Fossil Plants ....................................19-22

19.9 References...............................................................................................................19-22


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LIST OF FIGURES

Figure 2-1 Multisensor Probe.....................................................................................................2-5

Figure 2-2 Multisensor Probe Instrument Schematic .................................................................2-6

Figure 3-1 Representative Drum Boiler Mechanical Carryover..................................................3-3

Figure 4-1 A Typical Cation Conductivity Flow Diagram............................................................4-4

Figure 4-2 Chloride (Cl) Concentration vs. Specific Conductivity ..............................................4-5

Figure 4-3 Sulfate (SO4) Concentration vs. Specific Conductivity..............................................4-6

Figure 4-4 Carbon Dioxide (CO2

) vs. Specific Conductivity .......................................................4-7

Figure 4-5 Typical Degassed Cation Conductivity Schematic Diagram.....................................4-8

Figure 4-6 Relationship Between Ammonia Concentration mg/L (ppm) and Specific

Conductivity (S/cm) at 25C (77F) ................................................................................4-16

Figure 5-1 Typical Oxygen Sensing Probe ................................................................................5-2

Figure 5-2 Solubility of Dissolved Oxygen (mg/L (ppm)) vs. Temperature (C).........................5-7

Figure 5-3 Response of a Polarographic Oxygen Sensor to a 20 g/L (ppb) OxygenAddition Generated by a Faraday Cell .............................................................................5-14

Figure 5-4 Principle of Optical Oxygen Detection Using Fluorescent Dye...............................5-16

Figure 5-5 Fluorescence Density Decay Time as a Function of Oxygen Concentration..........5-16

Figure 5-6 Phase Shift of Modulated Signals...........................................................................5-17

Figure 5-7 Stern-Volmer Calibration Curve..............................................................................5-18

Figure 5-8 Luminescence Sensor Design................................................................................5-19

Figure 7-1 Flowing Junction Reference Electrode Head Cup Configuration..............................7-5

Figure 7-2 Combination Electrode .............................................................................................7-6

Figure 7-3 Standardization (Zero Intercept) Adjustment............................................................7-9

Figure 7-4 Slope (Span) Adjustment........................................................................................7-10

Figure 7-5 Specific Conductivity, Ammonia, pH at 25C..........................................................7-12

Figure 7-6 Ammonia Concentration vs. pH for Various Carbon Dioxide Concentrations.........7-13

Figure 8-1 Measured Sodium Concentration vs. Concentration of Sodium Added....................8-3

Figure 8-2 Response Time of Sodium Ion Selective Sensors: Time vs. SodiumConcentration in g/L (ppb) Before and After Etching .......................................................8-5

Figure 8-3 Elapsed Time After Known Standard Addition: Time vs. SodiumConcentration in g/L (ppb)................................................................................................8-6

Figure 8-4 Sodium Analyzer Response: Elapsed Time After Addition of 20g/L (ppb)Sodium vs. Sodium Concentration.....................................................................................8-7


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Figure 8-5 Calibration Slope (Millivolt Response) of Sodium Ion Selective Electrode atVarying pH Values .............................................................................................................8-9

Figure 8-6 Verification Results Immediately After a 200 and 2,000 g/L (ppb) SodiumCalibration ........................................................................................................................8-10

Figure 9-1 Percent of Ammonia and Ammonium Ions as a Function of Solution pH.................9-3

Figure 9-2 Relationship between Ammonia, Specific Conductivity and pH in the Absenceof Carbon Dioxide at 25C..................................................................................................9-4

Figure 9-3 Chemical Formula and Structure for Phenol ............................................................9-7

Figure 9-4 Chemical Formula and Structure for Salicylic Acid...................................................9-8

Figure 9-5 Absorbance vs. Concentration ...............................................................................9-10

Figure 10-1 Thermo Orion Electrode Reservoir System..........................................................10-5

Figure 10-2 Calibration Curve for Low Level Chloride SIE ......................................................10-8

Figure 11-1 Absorption vs. Concentration ...............................................................................11-4

Figure 12-1 Polarographic Hydrogen Sensing Electrode with Guard Ring............................12-4

Figure 12-2 The Wheatstone Bridge Circuit Showing Schematically How the ReferenceGas Flows Over Filament Resistances R

aand R

c, while the Sample Flows Over

Filament Resistances Rdand R

b. R

a= R

b= R

c= R

dwhen Reference and Sample

Gases have the Same Thermal Conductivity ...................................................................12-6

Figure 12-3 Diagram of Gas Chromatograph with Thermal Conductivity Detector..................12-7

Figure 12-4 Hydrogen Sensor with Thermal Conductivity Detector.........................................12-8

Figure 13-1 Schematic of a Single Column Ion Chromatograph .............................................13-4

Figure 13-2 Illustration of How Ions Elute (Leave the Separator Column) at DifferentRates Resulting in a Separation of Ionic Species in the Flowing Eluent..........................13-5

Figure 13-3 Gradient Separation of Common Anions Using a Hydroxide Gradient.................13-6

Figure 13-4 Anion Analysis Using Ionpac AS17 Separator Column with EluentGenerator; Method 1 ........................................................................................................13-9

Figure 13-5 Anion Analysis Using Ionpac AS17 Separator Column with EluentGenerator; Method 2 ......................................................................................................13-10

Figure 13-6 Chemistry and Ion Movement in Continually Regenerated Eluent

Suppressor.....................................................................................................................13-14

Figure 13-7 The KOH Generator Cartridge Consists of a KOH Generating Chamber andK

+Electrolyte Reservoir Connected by a Cation Exchange Connector .........................13-16

Figure 13-8 Carbonate Removal Device................................................................................13-17

Figure 13-9 Comparison of Spectrum with (Top Spectrum) and without Carbonate

Removal Cevice ............................................................................................................13-18

Figure 13-10 Chromatogram of a Sample Containing 0.022 g/l Sodium and 3000g/lEthanolamine .................................................................................................................13-20

Figure 14-1 Particle Counter Schematic, Illustrating 1 Particle at 3 microns and 2

Particles at 1 micron.........................................................................................................14-5

Figure 14-2 Dynamic Light Fluctuation Schematic ..................................................................14-6

Figure 14-3 Illustration of Self Absorption at High Concentrations ..........................................14-9


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Figure 15-1 Typical Beers Law Absorption (A) vs. Concentration Curve................................15-3

Figure 16-1 Graph Showing 100 Percent Absorption ..............................................................16-4

Figure 17-1 High Temperature Oxidation TOC Analyzer Flow Diagram..................................17-5

Figure 17-2 Persulfate Oxidation, Ultraviolet Lamp TOC Analyzer Flow Diagram...................17-7

Figure 18-1 An Analogy between Measuring Mountain Height with Respect to Sea Leveland Measuring ECP with Respect to a Reference Electrode...........................................18-4

Figure 19-1 Equivalent Electric Circuit (Upper Figure) and Corresponding SchematicDiagram of the 3-Electrode Corrosion Probe Immersed in the CorrosiveEnvironment (Lower Figure)...........................................................................................19-10

Figure 19-2 View of the Exposed End of a Corrosion Probe with Three Concentric Flush-

mounted Electrodes Arranged to Minimize Solution Resistance Errors.........................19-11

Figure 19-3 Equivalent Electric Circuit for the 2-Electrode Corrosion Probe Immersed inthe Corrosive Environment.............................................................................................19-12


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LIST OF TABLES

Table 1-1 EPRI Cycle Chemistry Core Monitoring Parameters for Conventional Fossil

Units ...................................................................................................................................1-3

Table 2-1 Example Diagnostic Capabilities of a Five-Probe Air In-leakage MeasurementSystem ...............................................................................................................................2-6

Table 2-2 MSP Probe Indications for Various Probe Positions..................................................2-7

Table 4-1 Typical Conductivity Range Limits as a Function of Cell Constant............................4-9

Table 4-2 Equivalent Conductances of Separate Ions at Various Temperatures....................4-18

Table 6-1 To Convert ORP or ECP Values Measured Using Reference Electrode #1 toValues on Reference Electrode #2 Scale, Add the Indicated Conversion Factor tothe Measured Potential ......................................................................................................6-6

Table 6-2 Expected ORP Values for Reference Quinhydrone Solutions at pH 4 and pH 7.......6-8

Table 7-1 Various Solution Additive Temperature Correction Factors for Power PlantSteam/Water Cycle pH Measurements..............................................................................7-7

Table 7-2 Example Calculated pH by Differential Conductivity from One InstrumentSupplier ............................................................................................................................7-14

Table 8-1 Typical Results from Known Addition Method for Calibration Check in thenanograms/L (ppt) range..................................................................................................8-12

Table 9-1 Precision Data for Manual Phenate Method Based on Triplicate Analyses ofAmmonium Sulfate.............................................................................................................9-9

Table 9-2 Precision and Bias Data; Direct Nesslerization .......................................................9-15

Table 10-1 Boiler Water Chloride Limits in g/L (ppb) @ 15858 kPa, (2300 psi) ....................10-2

Table 12-1 Some Performance Ranges for Aqueous EC and TC Detectors.........................12-10

Table 17-1 Summary of Some Typical On-Line Instrument Capabilities ...............................17-12

Table 19-1 Typical Examples of the Relationship Between the EPN Fingerprint,

Statistical Parameters, and the Corrosion Mechanism in Progress ...............................19-17


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1CYCLE CHEMISTRY MONITORING IN FOSSIL PLANT

CYCLES

1.1 Introduction

Technology advancements made during the twentieth century enabled substantial improvement

to be made in the efficient and cost effective production of electric power from fossil fuels. In

conventional designs in which steam is produced and expanded in a turbine, the ability to

provide water at higher purity levels than previously possible enabled designers to increase the

operating temperatures and pressures of fossil units. These improvements were accompanied by

increasingly tighter chemistry limits and a need for reliable monitoring approaches that could be

used for surveillance and control purposes. This need shifted the emphasis on chemistry

monitoring from infrequent collection and analysis of grab samples to reliance on analyzers that

provided semi-continuous or real time monitoring of the chemistry parameters of interest.

Also, a trend of reductions in fossil plant staff size and experience levels have dictated increasing

reliance on the performance of chemistry analyzers and the reliability of chemistry monitoring

data. This is of some concern in all situations and, in particular, those where responsibility for

day to day chemistry activities has been assigned to plant operators without extensive relevant

education or training. Advancements in data transmission, display, storage and assessment(including expert systems) as well as general communications have made these changes in

staffing possible. However, effective use of these capabilities remains completely dependent on

the suitability of the cycle chemistry treatments selected and the associated monitoring capability

of the selected analyzers.

1.2 Monitoring Requirements and Choice of Cycle Chemistry

Over the last 20 years EPRI has taken a leadership position in the area of cycle chemistry control

in fossil generating units. The third generation of EPRI Cycle Chemistry Guidelines was

introduced over the period 2001-2005. The guidelines are widely accepted as the de factoworldwide standard; available options for feedwater and boiler water treatment and operational

chemistry target values and action levels for conventional fossil units are summarized in a series

of reports [1-3].

Effective cycle chemistry programs require proper selection of treatments consistent with unit

characteristics. Treatment control and optimization requires provision of sampling and analysis

capabilities consistent with the treatments selected for use. The current guidelines indicate that


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1-2

there are three options for the feedwater treatment and four choices for boiler water treatment.

The feedwater treatments are designated and may be generally characterized as follows.

Reducing all-volatile treatment, AVT(R), in which the feedwater must be dosed with areducing agent to minimize corrosion of copper alloy components

Oxidizing all-volatile treatment, AVT(O), in which no reducing agent is added or neededsince there are no copper alloys in the feedwater system

Oxygenated treatment, OT, in which the feedwater is dosed with oxygen; OT can only beused in cycles where the feedwater meets necessary purity criteria, employs condensate

polishing and no copper alloys are present following the condensate pump discharge.

The available boiler water treatments are identified and generally characterized as follows.

All-volatile treatment [1], AVT, in which the feedwater treatment is either AVT(R) orAVT(O) as appropriate and no further chemical treatment is applied within the boiler.

Phosphate Continuum Treatment [2], PC, in which a drum boiler is dosed principally withtrisodium phosphate (TSP); dosing of the boiler water with sodium hydroxide is also allowed

as a supplement to TSP when needed for pH control. Low and high level TSP dosage

variants of PC, termed PC(L) and PC(H), respectively may be considered depending on the

characteristics and needs of the unit.

Caustic Treatment [2], CT, in which a drum boiler is dosed with sodium hydroxide.

Oxygenated Treatment [3], OT, in which the feedwater dosed with oxygen as needed for OTis used in the boiler without further treatment; OT may be used in cycles with once-through

or drum type boilers, however, with the latter feedwater oxygen dosing must be more

carefully controlled so as to avoid possible corrosion in the boiler.

Additional details concerning selection, use and optimization of each treatment is provided in the

corresponding guideline report. These reports also provide guidance concerning required sample

points and chemistry parameters that should be monitored for the various chemistry treatment

options. This guidance is based on worldwide experience in ensuring minimized levels of

corrosion, impurity ingress and deposition as needed to eliminate chemistry related damage in

boilers and turbines while simultaneously minimizing, or even eliminating, the need for

operational chemical cleaning of boilers.

The chemistry parameters that may be monitored under the cycle chemistry guidelines fit into

two general categories: 1) those parameters which all fossil plants should have for optimum

chemistry control (termed the core parameters) and 2) those parameters which are regarded asdiagnostic parameters that may be monitored as needed for troubleshooting or during

commissioning. The rationale for each important sample point and chemistry parameter

combination is discussed in detail in the individual guideline reports to explain its designation as

an EPRI core or optional (diagnostic) monitoring requirement.

The findings of EPRI cycle chemistry research for conventional fossil plant cycles are also

suitable for application to combined cycle units with heat recovery steam generators since the


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underlying science is the same. A separate guideline report [4] is available that considers

differences in design and operation of combined cycle unit as they effect the chemistry.

1.3 Cycle Chemistry Monitoring Approaches

This report provides a review and discussion of on-line analyzer techniques currently available

and in use in fossil power plants, updating many technical presentations from a 1998 report [5].

The focus is on analyzers used for fossil plant chemistry monitoring as described in the latest

guidelines [1-4]. Monitoring techniques that may be considered for use in future plants are also

presented as a precursor to possible future research being planned by EPRI to address possible

improvements in monitoring and control of cycle chemistry in fossil steam-water cycles.

1.3.1 Core Monitoring Parameters

An overall summary of the EPRI Core Monitoring Parameters and sampling points, adapted from

References 1-3, is provided in Table 1-1 [1-3]. Except in situations where a specific boilerdesign, feedwater chemistry or boiler water chemistry is indicated in the notes, the core

requirements indicated apply to all conventional plant designs and chemistries.

Table 1-1EPRI Cycle Chemistry Core Monitoring Parameters for Conventional Fossil Units [1-3]

Parameter Monitoring Points

Cation Conductivity Condensate Pump Discharge, Condensate Polisher Outlet orEconomizer Inlet, Reheat (or Main) Steam, Boiler Water

a

Specific Conductivity Treated Makeup, Boiler Waterb

pH Boiler Waterc

Dissolved Oxygen Condensate Pump Discharge, Economizer Inlet, Boiler Waterd

Sodium Condensate Pump Discharge, Economizer Inlet, Boiler Watere

Oxidation-Reduction Potential (ORP) Deaerator Inletf

Air in-leakage Condenser Air Removal System Exhaust

Carryover Calculated from Boiler Water and Saturated Steam Readingsg

Notes:

a Drum boiler units only; measured on blowdown for boilers on PC or CT, and either blowdown ordowncomer for boilers on AVT or OTb blowdown of drum boilers on PC and CTc Drum boiler units only; measured on either pH or downcomer of units on AVT; on either blowdown ordowncomer of units on PC or CT; on downcomer of units on OTd Only required in drum boiler units on OT; measured on downcomere Only required in drum boiler units on PC or OT; measured on downcomer

f Only required on units employing AVT(R) as feedwater chemistryg Based on either on-line monitor readings (if available) or analysis results for grab samples


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The Core Monitoring Parameters are considered the minimum level of surveillance needed for

all conventional fossil generating units. They are purposely included as an integral part of the

EPRI Cycle Chemistry benchmarking criteria used to assess individual cycle chemistry

programs. In general, use of on-line analyzers for continuous analysis of chemistry is preferred.

In the ensuing discussions of on-line analyzer technology, greatest emphasis has been placed onthe EPRI Core Monitoring Parameters, which are presented in Sections 2-8 of the report.

Section 2, Air in-leakage

Section 3, Carryover in Drum Boilers

Section 4, Conductivity; includes discussions of specific, cation and degassed cationconductivity

Section 5, Dissolved Oxygen

Section 6, Oxidation-Reduction Potential (ORP)

Section 7, pH Section 8, Sodium

1.3.2 Diagnostic Monitoring Parameters

In customizing their cycle chemistry programs, the organization may elect to monitor one or

more of the diagnostic parameters with on-line analyzers. The more common monitoring

techniques typically used for diagnostic purposes are presented in Sections 9-17 of the report.

These are listed as follows.

Section 9, Ammonia Section 10, Chloride

Section 11, Hydrazine

Section 12, Hydrogen

Section 13, Ion Chromatography; can be used to monitor various ions in water and steam.

Section 14, Iron and Copper; includes a discussion of indirect means of monitoringsuspended solids and particles in water and steam

Section 15, Phosphate

Section 16, Silica

Section 17, Total Organic Carbon

For many of the parameters and techniques more than one approach may be available. In some

instances, particularly when chemistry data are needed for diagnostic purposes, collection of grab

samples for laboratory analysis may be sufficient to satisfy the needs of the operator. These

considerations are included in the Section 2-17 discussions.


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1-6

various parameters which influence deposition. The ultimate aim of this work is to consider

chemical activity under various deposit conditions so as to define the conditions under which

corrosion activity becomes significant.

The latest cycle chemistry guidelines include target values for boiler water in drum-type units

that minimize the risk of corrosion damage. However, these values are empirical in that theyreflect operating experience in fossil plants. Similarly, allowable levels of boiler tube deposition

used to set criteria on the advisability of chemical cleaning are empirical, and represent levels of

waterside solids that field experience suggests will not lead to tube damage and failure.

It is envisioned that future chemistry guidelines will reflect the findings of research by EPRI in

the corrosion and deposition areas. For waterside corrosion, the ultimate chemistry surveillance

capability would be to measure corrosion activity directly in boilers and turbines, the major

components at greatest risk of corrosion damage. However, there is currently no means to

monitor corrosion rates under fossil plant operating conditions, in particular those which exist in

these high temperature components.

Sections 18 (on Electrochemical Corrosion Potential (ECP)) and 19 (on Corrosion) of this report

review the science of corrosion monitoring and requirements for practical use of corrosion

measurement techniques in fossil plants. From inspection of the Section 18 and 19 discussions it

becomes clear that the potential for use of ECP and corrosion monitors in steam-water cycles

exists but this remains a developing area. There are constraints on the applicability and reliability

of available corrosion measurement devices that must be resolved in order to produce

instruments suitable for use in the more demanding components of working fossil plants.

Possible changes in cycle chemistry guidelines to prevent or control corrosion, based on the

currently used indirect direct measurement methods, could initially involve modification of

chemistry limits for impurities in the boiler water. These revised chemistry limits could perhaps

be further refined to reflect the state of deposits on heat transfer surfaces as the effects of

deposits on corrosion activity become more fully understood.

Assuming that a robust corrosion monitor capable of operating in the boiler and/or turbine

environment could be produced, extensive testing would be required as part of the development

process. Location of its use would need further consideration due to concerns about compliance

with design codes, installation costs, and possible consequences of probe damage during service.

These concerns are significant and probably dictate installation of the monitor in a location

external to the unit so it can be reliably isolated if needed. Such an approach may in fact hold

many advantages over use of in situprobes.


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1.4 References

1. Cycle Chemistry Guidelines for Fossil Plants: All-volatile Treatment, Revision 1.EPRI, Palo

Alto, CA: 2002. 1004187.

2. Cycle Chemistry Guidelines for Fossil Plants: Phosphate Continuum and Caustic Treatment.

EPRI, Palo Alto, CA: 2004. 1004188.

3. Cycle Chemistry Guidelines for Fossil Plants: Oxygenated Treatment. EPRI, Palo Alto, CA:

2005. 1004925.

4. Cycle Chemistry Guidelines for Combined Cycle/Heat Recovery Steam Generators (HRSGs).

EPRI, Palo Alto, CA: 2006. 1010438.

5. Reference Manual for On-Line Monitoring of Water Chemistry and Corrosion: 1998 Update,

EPRI, Palo Alto, CA: 1999. TR-112024.


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2AIR IN-LEAKAGE

2.1 Effects of Air In-leakage on Unit Performance and Cycle Chemistry

Fossil unit operation requires that the condenser be operated under vacuum. The air removal

system is designed to remove noncondensable gases from the condenser. In so doing vacuum

conditions are established during fossil unit startup and maintained during unit service.

Excessive air in-leakage rates can result in reduced condenser vacuum, thereby reducing turbine

backpressure and the efficiency of the cycle [1].

Air ingress can also increase the concentration of dissolved oxygen in the steam-water cycle. All

EPRI Cycle Chemistry Guidelines for conventional fossil and combined cycle plants now feature

a Target Value of 10 ppb for dissolved oxygen at the condensate pump discharge [2-5].Meeting the target provides maximum flexibility in treatment and generally ensures that

contamination by carbon dioxide, which contributes to measured cation conductivity, is minimal.

By meeting the target for dissolved oxygen at the condensate pump discharge and by using

ammonia as the feedwater pH conditioning agent, there is generally no need to rely on

techniques other than cation conductivity as the primary indicator of cycle contamination by

inorganic ions such as chloride and sulfate that are of concern in boilers and turbines.

Condensate dissolved oxygen and carbon dioxide levels are affected by the extent and location of

air in-leakage in the condenser and in other parts of the cycle that operate at subatmospheric

pressure. Air in-leakage in excess of that removed by the condenser air removal system will

result in increased condensate dissolved oxygen and carbon dioxide levels, which may cause

corrosion within the condenser. Contamination of the feedwater by oxygen and carbon dioxide

may also lead to an increase in corrosion-product generation within the feedwater part of the

cycle [1]. Effective monitoring and control of condenser air in-leakage is considered so

important that it has been designated a Core Monitoring Parameter in all EPRI cycle chemistry

guidelines [2-5].

Control of condenser air in-leakage to reduce condensate oxygen to 10 ppb is of greatestimportance in those units that must employ AVT(R) so as to minimize corrosion of copper alloysand corrosion product transport in the feedwater part of the cycle. Protection of copper alloys in

the feedwater environment requires that a reducing condition is established and maintained at all

times. EPRI research has shown and field experience has confirmed that use of hydrazine or

another reducing agent to establish a negative oxidation-reduction potential (versus silver/silver

chloride; see Section 6) condition consistent with the requirements of AVT(R) cannot be reliably


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achieved when the condensate oxygen exceeds 10 ppb, regardless of the concentration or type of

reducing agent applied.

In units that employ oxidizing feedwater treatments, maintaining low levels of cycle air in-

leakage is not needed for protection of copper alloys in the feedwater. However, control of this

parameter is desirable to limit dissolved oxygen and carbon dioxide contamination, whichprovides maximum flexibility in control of the feedwater treatment with minimum interference

in measurement of two important chemistry monitoring parameters, namely conductivity and pH.

In fossil unit cycles with condensate polishers, carbon dioxide will be exchanged by the anion

media, potentially increasing the required frequency of regeneration (in deep bed system

designs) or replacement of the precoat media (in precoat filter/demineralizer system designs).

The Heat Exchange Institute recommends that the condenser design restrict air in-leakage to no

more than 1.0 scfm per 100 MW of generating capacity. Constant vigilance must be exercised to

prevent air in-leakage to the cycle from those equipment elements under vacuum. Particular

problem areas include pump seals, valve bonnets, threaded joints, and especially the expansionjoint between the turbine and condenser. Monitoring and limiting the amount of air in-leakage

(condenser air removal system flow) is essential for proper control of dissolved oxygen and

carbon dioxide in the cycle. Such monitoring will determine when an exhaustive effort must be

made to find and fix the source of air leakage. Air in-leakage control is a continual process over

the working life of any steam generating unit. The time and effort required to control air in-

leakage is justified by the beneficial effects on unit startup times, efficiency and compliance with

cycle chemistry guidelines [1].

2.2 Monitoring Methods

The earliest and still most common means of monitoring air removal at the condenser air

removal system exhaust is by means of rotameters. Other monitoring techniques are a

Fossil Plant Cycle Chemistry

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