Surface Condenser Troubleshooting

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Condenser Performance Monitoring Practices

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EPRI Project ManagerJ. Stallings

EPRI 3412 Hillview Avenue, Palo Alto, California 94304 PO Box 10412, Palo Alto, California 94303 USA800.313.3774 650.855.2121 [email protected] www.epri.com

Condenser Performance MonitoringPractices

1007309

Technical Update, September 2002


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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 INTELLECTUALPROPERTY, OR (III) THAT THIS DOCUMENT IS SUITABLE TO ANY PARTICULAR USER'SCIRCUMSTANCE; OR

(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

John L. Tsou Consulting Service

ORDERING INFORMATION

Requests for copies of this report should be directed to EPRI Orders and Conferences, 1355 WillowWay, Suite 278, Concord, CA 94520. Toll-free number: 800.313.3774, press 2, or internally x5379;voice: 925.609.9169; fax: 925.609.1310.

Electric Power Research Institute and EPRI are registered service marks of the Electric PowerResearch Institute, Inc. EPRI. ELECTRIFY THE WORLD is a service mark of the Electric PowerResearch Institute, Inc.

Copyright 2002 Electric Power Research Institute, Inc. All rights reserved.


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CITATIONS

This report was prepared by

John L. Tsou Consulting Service56 Williams LaneFoster City, CA 94404

Principal InvestigatorJ. Tsou

This report describes research sponsored by EPRI.

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

Condenser Performance Monitoring Practices, EPRI, Palo Alto, CA: 2002. 1007309

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ABSTRACT

Steam surface condensers and associated systems cause significant loss of generation and heatrate degradation in both nuclear and fossil-fired power plants. The purpose of this report is toprovide the engineering and operating personnel of the power industry with a guide for selectingand using the practices available for monitoring condenser performance.

Strictly speaking, only condenser backpressure needs to be monitored. However, the cause ofhigh condenser backpressure cannot be determined without monitoring other operatingparameters. Common causes for high condenser backpressure include the following:

High inlet cooling water temperature

Low cooling water flow

Partially filled waterbox

Excessive heat load

Fouled tubes

Excessive air in-leakage

Vacuum equipment problem

Tube bundle design problem

It is not the intent of this paper to address the causes and remedies of high condenserbackpressure. This report does provide details of specialty instruments used in condenserperformance monitoring. References for in-depth studies and sources for obtaining the specialtyinstruments, services and cost are also included.

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CONTENTS

1 INTRODUCTION....................................................................................................................1-1

Background.............................................................................................................................1-1

Purpose...................................................................................................................................1-2

Scope .....................................................................................................................................1-2

Organization of the Report........................................................................................................1-3

Reference................................................................................................................................1-3

2 TEMPERATURE MONITORING PRACTICES .....................................................................2-1

Background.............................................................................................................................2-1

Instruments .............................................................................................................................2-1

Cooling Water Inlet Temperature ..............................................................................................2-2

Cooling Water Outlet Temperature ............................................................................................2-2

Condenser Shell Temperature ...................................................................................................2-4

Hotwell Temperature ...............................................................................................................2-4

Condensate Temperature ..........................................................................................................2-4

References ..............................................................................................................................2-4

3 PRESSURE MONITORING PRACTICES ..............................................................................3-1

Background.............................................................................................................................3-1

Instruments .............................................................................................................................3-1

Cooling Water Inlet Pressure ....................................................................................................3-3

Condenser Backpressure...........................................................................................................3-3

Reference................................................................................................................................3-4

4 FLOW MONITORING PRACTICES ......................................................................................4-1

Background.............................................................................................................................4-1

Instruments .............................................................................................................................4-1

Periodic Cooling Water Flow Measurement ...............................................................................4-2

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Dye Dilution Test................................................................................................................4-2

Velocity Traversing Method.................................................................................................4-3

CW Pump Curves and Total Dynamic Head Method ..............................................................4-5

Heat Balance Method ..........................................................................................................4-5

Continuous Cooling Water Flow Measurement ...........................................................................4-6

Differential Producer Method...............................................................................................4-6

Ultrasonic Time of Travel Method.............................................................................................4-9

Air In-Leakage Flow Monitoring.............................................................................................4-11

Rotameter.........................................................................................................................4-11

Orifice Plate ..........................................................................................................................4-12

Electronic Air In-Leakage Monitor ..........................................................................................4-14

Summary ..............................................................................................................................4-15

References ............................................................................................................................4-17

5 FOULING MONITORING PRACTICES ................................................................................5-1

Background.............................................................................................................................5-1

Instruments .............................................................................................................................5-1

Off-Line Microfouling Monitor.................................................................................................5-2

On-Line Microfouling Monitor .................................................................................................5-3

Bridger Scientific Continuous Side-Stream Reduced-Scale On-Line Microfouling Monitor .......5-3

Bridger Scientific Continuous Small On-Line Microfouling Monitor ............................................5-3

Conco Systems Continuous Side-Stream Reduced Scale On-Line Microfouling Monitor ................5-5

Periodic In-Situ On-Line Microfouling Monitor..........................................................................5-6

EPRI Continuous In-Situ On-Line Microfouling Monitor ............................................................5-6

Taprogge Continuous In-Situ On-Line Microfouling Monitor ......................................................5-7

On-Line Macrofouling Monitor.................................................................................................5-9

Intake On-Line Macrofouling Monitor ..................................................................................5-9

Tubesheet On-Line Macrofouling Monitor ...............................................................................5-10

Summary ..............................................................................................................................5-12

References ............................................................................................................................5-13

6LEVEL MONITORING PRACTICES .....................................................................................6-1

Background.............................................................................................................................6-1

Instruments .............................................................................................................................6-1

Hotwell...................................................................................................................................6-2

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Waterboxes .............................................................................................................................6-2

Intake .....................................................................................................................................6-2

Summary ................................................................................................................................6-5

References ..............................................................................................................................6-6

7DISSOLVED OXYGEN MONITORING PRACTICES............................................................7-1

Background.............................................................................................................................7-1

Instruments .............................................................................................................................7-1

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


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LIST OF FIGURES

Figure 2-1 Circulating Water Discharge Temperature vs. Distance from Inside Edge of Pipe ...............2-3

Figure 2-2 BBC Circulating Water Outlet Temperature Measurement ...............................................2-3

Figure 3-1 Condenser Pressure-Sensing Basket Tip Source: ASME PTC 12.2 ...................................3-2

Figure 3-2 Condenser Pressure-Sensing Guide Plate Source: ASME PTC 12.2..................................3-2

Figure 3-3 The Four-Tap Selector Connects the Basket Tips to the Pressure Transducer andPurge Supply........................................................................................................................3-4

Figure 4-1 Recommended Velocity Traverse Locations Source: ASME PTC 12.2 .............................4-4

Figure 4-2 Water Flow Through Condenser ....................................................................................4-8

Figure 4-3 Flow Through an Abrupt Contraction .............................................................................4-8

Figure 4-4 Elbow Differential Pressure Method ...............................................................................4-9

Figure 4-5 Diagram of Four-Path Ultrasonic Flow Meter ................................................................4-10

Figure 4-6 Schematic of Rotameter ..............................................................................................4-11

Figure 4-7 Orifice Plate Installation..............................................................................................4-12

Figure 4-8 Schematic for Differential Pressure Transmitter Installation ...........................................4-13

Figure 5-1 Conco Heat Transfer Testing Unit ..................................................................................5-2

Figure 5-2 DATS Heat Exchanger Cross-Section View ....................................................................5-3

Figure 5-3 ProDATS Probe and its Schematic .................................................................................5-4Figure 5-4 Conco Portable Test Condenser .....................................................................................5-5

Figure 5-5 On-Line Fouling Monitor ..............................................................................................5-7

Figure 5-6 Taprogge Monitoring System ........................................................................................5-8

Figure 5-7 Typical Cooling Water Intake System ............................................................................5-9

Figure 5-8 Typical Ultrasonic Microfouling Monitoring System .....................................................5-10

Figure 5-9 TVA Tubesheet Macrofouling Monitor.........................................................................5-11

Figure 6-1 Typical Installation of Capacitance Level Monitor ...........................................................6-3

Figure 6-2 Typical Installation of Submersible Differential Pressure Level Monitor............................6-3

Figure 6-3 Typical Installation of Bubbler Level Monitor .................................................................6-4

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LIST OF TABLES

Table 4-1 Circulating Water Flow Monitors ..................................................................................4-15

Table 4-2 Air In-Leakage Flow Monitor ......................................................................................4-16

Table 5-1 Microfouling Monitor ..................................................................................................5-12

Table 6-1 Remote Level Monitors ..................................................................................................6-5

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1INTRODUCTION

Background

Steam surface condensers and associated systems cause significant loss of generation and heat

rate degradation in both nuclear and fossil-fired power plants. The loss of generation due tocondenser backpressure increase can be estimated from a plant turbine thermal kit. The deviation

of heat rate due to condenser backpressure increase is 204 Btu/kWh/in Hg on the utility average

based on an earlier EPRI report[1-1]

. Simply speaking, only condenser backpressure needs to be

monitored. However, the cause of high condenser backpressure cannot be determined withoutmonitoring other operating parameters. Common causes for high condenser backpressure include

the following:

High inlet cooling water temperature

Low cooling water flow

Partially filled waterbox

Excessive heat load

Fouled tubes

Excessive air in-leakage

Vacuum equipment problem

Tube bundle design problem

Some of the causes of high condenser backpressure, such as high inlet cooling water temperature

and excessive heat load, cannot be controlled. Other causes require remedial action. It is not the

intent of this paper to address the causes and remedies of high condenser backpressure. However,any remedial action involves additional cost. To avoid unnecessary cost, it is important to isolate

the true cause of high condenser backpressure. This is the reason that it is essential to monitor theperformance of the condenser on a routine basis to ascertain that it is performing properly based

on current operating conditions. If a condenser is not performing properly, the true cause of the

deficiency most likely can be determined from condenser performance monitoring.

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Introduction

Unfortunately, performance analysis of condenser problems is complicated by the difficulty inmeasuring critical parameters, such as heat rejection rate, and cooling water outlet temperatureand flow rate. Of the three parameters, only two are required for analyzing the performance ofa particular condenser. The heat rejection rate can be calculated from the turbine heat balance.If the heat rejection rate is known, the outlet temperature can be calculated from the flow rate,or the flow rate can be calculated from the outlet temperature. If the heat rejection rate is notknown, then both outlet temperature and flow rate are required. This paper will address commonpractices used in the power industry to monitor and analyze condenser performance.

The performance factor, a.k.a. cleanliness factor or fouling factor, is generally calculated.However, it can also be measured directly with on-line or side-stream specialty instruments.This paper will address various devices available for this purpose.

Local instruments provide adequate data for most of the analysis. Data transmitted to a remotelocation, such as a control room, provide opportunities to record and to trend the data. Trendingprovides additional insight into the causes of performance deficiency.

Purpose

The purpose of this paper is to provide the engineering and operating personnel of the powerindustry with a guide for selecting and using the practices available for monitoring condenserperformance.

It is not the purpose of this paper to evaluate or to recommend practices required for propercondenser performance monitoring. In fact, it is neither necessary nor economically feasible touse all the monitoring practices. However, sufficient information will be provided to allow forchoosing and specifying suitable monitoring practices based on ones needs.

Scope

This paper covers a range of practices used by the power industry to monitor condenserperformance. The monitoring practices for each parameter discussed in this paper are as follows:

Temperature: cooling water inlet and outlet, hotwell and condensate.

Pressure: cooling water inlet and outlet, condenser backpressure.

Flow: cooling water flow, air in-leakage.

Fouling: microfouling and macrofouling, on-line and side-stream.

Level: hotwell, waterboxes and intake.

Dissolved oxygen: condensate.

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Introduction

This report will provide details of specialty instruments used in condenser performancemonitoring. This report will not provide details of commonly used instruments, such as fortemperature and pressure monitoring. A brief evaluation based on the authors own opinion willbe provided. References for in-depth study and sources for obtaining the specialty instruments,services and cost are also provided.

Since this report is not about performance analysis or diagnosis, detailed procedures for thesewill not be included.

Organization of the Report

This report contains seven sections. After the introduction, the subsequent six sections eachcover one monitored parameter.

Each of the sections 2 through 7 contain subsections covering background, instruments,monitoring practices, and references. The objective and purpose of monitoring each parameter

will be provided in the background subsection. Instruments and methods used to monitor theparameters will be briefly discussed in the instrument subsection. Detailed discussion includinginstrument type, monitoring location, source, cost, and authors comments will be provided inthe monitoring practice subsections. References cited in the text will be provided in the referencesubsection.

Reference

[1-1]Heat Rate Improvement Guidelines for Existing Fossil Plants, EPRI Report CS-4554, EPRIMay 1986.

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2TEMPERATURE MONITORING PRACTICES

Background

Cooling water inlet temperature has the greatest impact on condenser performance. It is also theeasiest parameter to be monitored, and every plant does so. If no other problem exists, normalcondenser backpressure can be found from the thermal kit at the particular operating load. Thereis not anything a plant can do if the cooling water source is from a natural body. However, if thecooling water is from a cooling tower, the cooling tower should be investigated for possible

problems.

Cooling water outlet temperature is used to establish terminal temperature difference (TTD),which is the temperature difference between the steam saturation temperature correspondingto the backpressure and the outlet cooling water temperature. TTD is a starting point used indiagnosing many condenser problems. Outlet temperature is also used to establish the differential

temperature (T) between the inlet and outlet cooling water. Higher than normal T indicatesinsufficient cooling water flow. Cooling water outlet temperature is used to calculate heat loadand fouling factors. Unfortunately, accurate cooling water outlet temperature is very difficult todetermine. A workable solution is recommended by the ASME Performance Test Code on SteamSurface Condensers (PTC 12.2 1998)

[2-1].

Condenser shell temperature is not normally measured but is inferred from condenserbackpressure. As mentioned before, it is used to calculate TTD.

Hotwell temperature is compared to shell temperature. A large differential between shelltemperature and hotwell temperature may indicate an excessive steam pressure drop, whichsuggests a condenser design deficiency. Hotwell temperature is also compared to condensatetemperature. A larger than normal difference indicates condensate subcooling, which causeshigher dissolved oxygen and heat rate degradation.

Instruments

Instruments used in condenser temperature monitoring are the same as those used elsewhere inpower plants. Thermometers are used for local temperature monitoring. Thermocouples (TCs),thermistors, and resistance temperature detectors (RTDs) are used remote temperature readings.The ASME Performance Test Code cited above recommends type E thermocouples, 100-ohmplatinum RTDs, and thermistors with a nominal impedance of greater than 100 ohms at 32

oF

(0oC). For RTDs and thermistors the four-wire method is recommended. All temperature

monitors should be calibrated initially and periodically to within 1oF (0.6

oC) using traceable

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Temperature Monitoring Practices

Figure 2-1Circulating Water Discharge Temperature vs. Distance from Inside Edge of Pipe

Figure 2-2BBC Circulating Water Outlet Temperature Measurement

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3PRESSURE MONITORING PRACTICES

Background

The most important pressure to be monitored is the condenser backpressure, which determinesthe condenser performance. Backpressure varies with heat load, cooling water temperature,cooling water flow rate, tube fouling, and other factors, and is monitored by every plant.Condenser backpressure is not difficult to monitor. However, the measured pressure is notalways accurate. Backpressure is used in conjunction with cooling water outlet temperature to

establish TTD.

Another pressure parameter to be monitored is the cooling water pressure. Low cooling waterpressure indicates deficient cooling water flow due to poor cooling water pump performance orlow water level in the intake bay. High cooling water pressure indicates blockage of the flowpass.

Monitoring the differential pressure between the inlet and outlet can indicate blockage of thetubes or tubesheet due to macrofouling. Differential pressure is also used to monitor coolingwater flow. The details will be discussed in the fouling and flow section.

Instruments

Basket tips (Figure 3-1) and guide plates (Figure 3-2) are the most common condenserbackpressure-sensing instruments. Because the guide plates have to be installed parallel to thesteam flow direction, which may be difficult to predict, the author believes the basket tips aremore forgiving and more accurate on average. The pressure measurement device includes non-mercury manometers and electronic absolute pressure transmitters.

Cooling water pressure measurement devices include mechanical pressure gages and electronicpressure transmitters.

Differential pressure measurement devices include mechanical differential pressure gages andelectronic differential pressure transmitters.

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Pressure Monitoring Practices

Figure 3-1Condenser Pressure-Sensing Basket TipSource: ASME PTC 12.2

Figure 3-2Condenser Pressure-Sensing Guide PlateSource: ASME PTC 12.2

Basket tips and guide plates can be ordered from turbine manufacturers and parts vendors. Thebasket tip costs around $500. The guide plate can probably be made in most plant maintenanceshops at considerably less cost. Due to the construction of the basket tip, orientation with steam

flow may be less critical with this device. The guide plate, on the other hand, may be lessaccurate if it is not oriented correctly. However, the guide plates are less likely to be damagedin highly turbulent steam flow areas. The electronic transmitters can be ordered from mostinstrument manufacturers.

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Cooling Water Inlet Pressure

Pressure taps for cooling water pressure measurement should be located in a convenient spotbetween the cooling water pump and the inlet waterbox. Care should be taken to avoid locatingthe measurement point in areas of local high velocity or local flow separation zones. The tap

should be deburred and cleaned on the inside. Isolation valves and fill lines should be installedbetween the sensing point and the gauge or transmitter. The sensing point should be periodicallyback flushed to purge any debris from the sensing point.

Condenser Backpressure

Most plants are equipped with basket tips or guide plates as part of the turbine package. As such,they are located in the transition between the turbine and the condenser. Their location may besubject to higher velocity and pressure variation. ASME PTC 12.2

[3-1]recommends that the

sensing elements be located at least one foot (30 mm) but no more than three feet (90 mm) aboveeach tube bundle. A tube bundle is considered to be all tubes connected to a single-inlet

waterbox. For single-shell and multiple-shell condensers, there should be at least threemeasurement points per tube bundle in each shell. For single-shell multi-pressure condensers,there should be at least two pressure measurement points per tube bundle. If tube bundles arearranged one on top of the other, measurement points need only be provided for the uppermostbundle. Where three measurement points per tube bundle are required, they should be locatedlengthwise near the quarter-points of the tube bundle. Where two measurement points per bundleare required, they should be located lengthwise near the third-points of the tube bundle. In anycase, the lateral position of the measurement points should be as close to the lateral midpoint ofthe bundle as possible.

ASME PTC 12.2[3-1]

requirements are intended to establish rules for performing condenser

acceptance tests. For routine performance monitoring, the code requirements may beunnecessary. If the existing pressure-sensing elements produce acceptable results, nomodification is required.

The second problem with many existing plant pressure-sensing elements is their installation.PTC 12.2

[3-1]recommends that basket tips be installed at an angle of 30 to 60 degrees from the

mean flow direction. The guide plates should be oriented so that the steam flow is parallel to theguide plates. Pressure-sensing piping for pressure measurement should conform to the generalrequirements of subsection 4.3 of PTC 19.2

[3-2].

The third problem with many exist plant sensing elements is the piping leading to the transmitter.If there are any water pockets caused by condensation, they will influence the accuracy of thereading. It is essential to slope the piping from the sensing element to the transmitter in acontinuous upward slope to allow any accumulated condensations to drain naturally to the baskettip.

To further ensure the complete absence of water pockets in the sensing line, EPRI suggests usingautomatic air purging before every reading. The schematic of the setup is shown in Figure 3-3

[3-3].

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Figure 3-3The Four-Tap Selector Connects the Basket Tips to thePressure Transducer and Purge Supply

Reference

[3-1] Performance Test Code on Steam Surface Condensers, ASME PTC 12.2 1998. ASME,New York, 1998.

[3-2] Performance Test Code on Instruments and Apparatus: Pressure Measurement, ASMEPTC 19.2 1987. ASME, New York, 1987.

[3-3]MARK IPerformance Monitoring Products,EPRI ReportGS/EL-5648, September 1989.

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4FLOW MONITORING PRACTICES

Background

As mentioned previously, the cooling water (CW) flow rate is required to analyze condenserperformance. CW flow measurement is the most difficult task because of the large conduit andthe turbulent flow profile. The conduit can be as large as eight to ten feet (2 to 3 m) in diameter.The flow pattern exiting the CW pump is turbulent. The limited straight length of conduit is notlong enough to establish laminar flow. To further complicate the measurement problem, most of

the conduit is buried underground, and access to sensing locations is very limited.

CW flow measurement methods are either periodic or continuous. Periodic CW flowmeasurement methods include the dye dilution test and the velocity traversing method. Periodicmethods are frequently used to calibrate continuous flow measurement instruments. Periodicwater flow measurement is also used to determine the circulating water pump performance.

Over the years, a number of direct and indirect continuous flow measurement methods have beendeveloped. The direct flow measurement methods include the differential producer method andthe ultrasonic time-of-travel method. The indirect flow measurement methods include thecirculating water pump motor load method and the heat balance method.

Air in-leakage may cause high backpressure and increased dissolved oxygen in the condensate,which in turn can increase corrosion potential and oxygen-scavenging chemical consumption.Generally, air in-leakage flow monitoring is performed at the ejector or vacuum pump discharge.The measured flow includes both non-condensible gas and moisture, and needs to be corrected toindicate dry air flow rate.

Instruments

Rhodamine WT fluorescing dye is most commonly used for the dye dilution test. A precisionpositive displacement pump is used to inject the concentrated dye solution, and a calibrated

precision fluorometer is used to measure the dye concentration.

The Fechheimer and Keil Pitot static-type probe, the insertion-type fiber-optic laser Dopplervelocimeter, and the insertion low-drag turbine flow meter are used for velocity traversing.

A precision differential pressure transmitter is used for the differential producer method.Multiple-channel ultrasonic flow meters are employed for the time-of-travel flow measurement.

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Flow Monitoring Practices

Total dynamic head readings are entered into the pump characteristic curve to determine theflow.

The instruments used for air in-leakage monitoring include rotameters, orifice plates, andelectronic air in-leakage monitors.

Periodic Cooling Water Flow Measurement

Dye Dilution Test

The principle of the dye dilution test is that an unknown flow rate can be determined by addinga known quantity of an easily identifiable tracer, mixing fully, and then measuring the resultingconcentration of the tracer in the flow. If this dye is injected at a constant rate, the relationshipbetween the concentration and the flow is as follows:

Q1 C1 = Q2 C2Where: Q1 = dye injection rate

C1 = concentration of injected dyeQ2 = flow rate to be determined

C2 = concentration of diluted dye in water stream

Thus: Q2 = Q1 x C1/C2

C1/C2 is known as the dilution factor (DFt)

Rhodamine WT fluorescing dye is the most commonly used dye because it is non-toxic andexhibits a minimal tendency to be adsorbed onto organic and in-organic surfaces. The dilutionfactor of a solution cannot be measured directly, but it can be determined by comparing itsfluorescence (which is proportional to its concentration) with that of a specially preparedstandard solution of precisely known dilution. This standard solution is prepared by dilutinga sample of the injected dye by approximately the same amount as it will undergo when injectedinto the system. The fluorescence levels of a test sample and of the standard solution aremeasured in a fluorometer, and the dilution factor of the test sample is determined as follows:

DFt = DFs x Fs/Ft

Where: DFt = dilution factor of test sample

DFs = dilution factor of standard solutionFt = fluorescence level of test sample

Fs = fluorescence level of standard solution

The flow to be measured is then:

Q2 = Q1 x DFs x Fs/Ft

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The principle seems simple, but the accuracy of this method depends greatly on the experienceand accuracy of the tester. A detailed test procedure is given in Reference [4-1]. Numerouscompanies provide this type of service.

The dye injection point for the test should be at the circulating water pump inlet. The sampling

point should be as far downstream as possible. A CW piping system with many twists and turnsprovides better mixing and more accurate results. If the sample can be taken at the CWdischarge, then there will be no need to tap into the pipe. Samples from various cross-sectionsof the sampling point should be taken to ensure the dye concentration is uniform. Chemicalinjection, such as chlorine, into the CW must be stopped before the test. The dye should beinjected until the fluorescence level in the sample reaches a steady state before flowdetermination data can be taken. The test sample should be allowed to reach the sametemperature as the standard solution prior to analysis, as the fluorescence intensity of the dyevaries with temperature. A well-conducted test can achieve accuracy within 2%.

Care must be taken to ensure that no flow is introduced or removed during the test. This methodmay not be suitable for a CW system with high concentrations of organic growth and silt.

Additional information and applications can be found in references [4-2] and [4-3]. The methodis widely used in the hydroelectric industry to test the turbine efficiency. Typical costs rangefrom $10,000 to $20,000, depending on geographical location, number of tests, required supportfor test preparations, and desired details of test reports.

Velocity Traversing Method

The velocity traversing method of CW flow measurement actually measures the local velocity ofthe water in the conduit. The average velocity of the entire flow is then calculated based on thelocal velocity on a volumetric weight basis. Since the diameter of the conduit is known, theaverage velocity is used to calculate the water flow rate using the following equation:

Water Flow Rate = Water density x Velocity x Conduit diameter

The PTC 12.2[4-2]

recommends the traverse be taken along at least three equally spaced diameters.The traverse locations should follow the Chebyshef weighing scheme with at least ten pointsalong each diameter (Figure 4-1).

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Figure 4-1Recommended Velocity Traverse LocationsSource: ASME PTC 12.2

The water flow emerging from pumps, elbows, or piping diameter changes is very turbulent.As a result, the velocity profile can be irregular and cannot be accurately measured. The flowgenerally will straighten itself out over a straight length of pipe. PTC 12.2

[4-2]recommends that

the traverse point be located with at least ten diameters of straight, unobstructed piping upstreamand five diameters of piping downstream. In practice, these restrictions may be relaxedsomewhat if the repeatability is good.

The measurement procedure depends on the traverse instruments used. Each instrument has itslimitations. Some work better than others in certain situations. PTC 12.2

[4-2]lists some of these

limitations. Encor-America uses a low-drag insertion turbine flow meter that is believed to workwell without fully developed flow profiles

[4-4].

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Comparing the dye dilution test with the velocity traverse method, one can draw the conclusionthat the dye dilution tests work well with a complex piping system that increases the mixingfactor. On the other hand, the velocity traverse methods work well with a fully developed flowprofile. The dye dilution tests work better with a relatively clean piping system, while organicgrowth and silt have no negative impact on velocity traverse methods. The dye dilution test willhave minimum intrusion into the piping system, but the velocity traverse method requirestapping into the pipe. The velocity traverse method also requires that the pipe be full of waterat the measuring point. The dye dilution test does not have this requirement. Typical costs forvelocity traversing range from $3,000 to $10,000, depending on geographical location, numberof tests, required support for test preparations, and desired details of test reports.

CW Pump Curves and Total Dynamic Head Method

Pump total dynamic head (TDH) is the measure of energy added to the flow by the pump. It isthe algebraic sum of the static discharge head, the velocity head at the measurement point, andthe vertical distance from the measurement point to the water level in the pump bay (lift). TDH

is usually expressed in feet of water.

The static discharge head can be measured with piezometers, manometers, or calibrated pressuregauges. If any of these instruments are located above or below the measurement point, thedistance should be subtracted from or added to the static discharge head. The velocity head iscalculated based on the estimated velocity of the water at the measurement point. The lift can bemeasured with any suitable method, such as measuring tape or a fixed ruler. The computed TDHin feet of water is entered into the pump characteristic curve to obtain the cooling water flow.

This simple method has a minimal need for additional instruments. It accuracy depends on theaccuracy of the pump curve. If the pump impeller is worn, the pump curve will not be accurate.It is recommended that the pump curve accuracy be verified by one of the more accurate flowtests, such as a dye dilution test.

It is possible to make this method a continuous cooling water flow monitoring method byautomating its measurements. The static discharge head can be measured with a pressuretransducer. The velocity head can be estimated. The lift can be measured with a remote-readinglevel gauge (see Section 6 for details). All the data can be fed into a suitable computer orprocessor, and the TDH will be automatically calculated and compared to the built-in pumpcurve to obtain the flow rate. If one automates the system, the costs should be between $2,000and $5,000. Otherwise, the costs are negligible. The verification of pump curves is not includedin this estimate.

Heat Balance Method

This method is not a direct measurement of cooling water flow. Instead, a heat balance isperformed on the turbine cycle to determine the heat rejection rate to the condenser (condenserduty). With the known condenser duty, and the inlet and outlet cooling water temperatures, thecirculating water flow rate can be calculated.

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Since the circulating water flow rate is calculated from the condenser duty and the cooling wateroutlet temperature, the accuracy of the flow rate depends on the accuracy of these twomeasurements. ASME PTC 12.2

[4-2]recommends that the determination of the condenser duty

should be performed according to applicable sections of ASME PTC 6[4-5]

for the testing ofturbines. Because of the complexity of this test, it is recommended that the condenser be testedat the same time as the turbine. The advantage of this method is that the condenser duty isdetermined directly without measurement, and therefore no instrument is required for the coolingwater flow. If the flow rate determined from this method is deemed accurate, this method may beused to calibrate other continuous cooling water flow measurement devices. The cost is minimal,assuming one does not include the turbine test and the cooling water outlet temperaturemeasurement.

Continuous Cooling Water Flow Measurement

Differential Producer Method

Differential-pressure flow meters have been used for decades. They provide a simple, reliablemethod of measuring fluid flow with good results. The simplest meter is the orifice flow meter.The pressure drop across an orifice is measured to determine the flow, which is proportional tothe square root of the differential pressure produced, according to the following equation:

____

W = C x (H)

Where: W = flow rateC = flow coefficient

H = pressure difference

The flow coefficient C depends on the geometry of the flow restriction. If C and the pressure

difference H are known, the flow rate can be calculated.

The pressure difference H can be determined by installing pressure taps upstream anddownstream of the flow restriction and measuring the pressure difference between them.The pressure difference can be measured with any suitable device, such as a manometer oran electronic differential pressure transmitter.

The flow coefficient C must be determined from calibration. To calculate C, one can pass aknown flow rate through the meter and measure the pressure difference H, using the followingequation:

____

C = W (H)

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In condenser applications, the flow rate is determined using either the dye dilution test or thevelocity traverse method.

The traditional differential producer method of flow measurement uses orifice plates, flownozzles, venturi meters, or weir plates. However, none of these are suitable for condenser

applications because of the large size of the conduit and the low pressure head available formeasurement.

Two types of differential producers have been developed for condenser application. The firstuses the condenser outlet waterbox as the location for the differential producer. The second usesany elbow in the conduit. Both types are based on the same operating principle, and only thesensing points are different.

The TVA Engineering Laboratory first investigated the outlet waterbox as a location to producedifferential pressure for CW flow measurement

[4-6]. The schematic plan view and end view of the

setup are shown in Figures 4-2 and 4-3. The approach uses the existing abrupt contraction

created by the changing configuration from waterbox to pipe at the condenser outlet waterbox.Because of the contraction, there is a flow separation in the pipe joining the condenser waterbox.At this point the water pressure will be lower than the pressure in the waterbox. Tapping intothese two points and connecting them to a differential pressure (DP) transmitter provides theflow measurement. The flow will be proportional to the DP between these two points. The flowcoefficient can then be determined on-line using either the dye dilution test or the velocitytraverse method.

The second method is to determine the DP across an elbow. When fluid moves around thecurved path of an elbow, it is subjected to an angular acceleration. The resulting centrifugal forcecreates a DP between the inner and outer radii. The high-pressure tap is on the outside of theelbow and the low-pressure tap is on the inside, as shown in Figure 4-4

[4-4]. This flow measuring

device must also be calibrated on-line.

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Figure 4-2Water Flow Through Condenser

Figure 4-3Flow Through an Abrupt Contraction

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Figure 4-4Elbow Differential Pressure Method

Tests show that the elbow-flow DP method and the waterbox-to-pipe DP method track eachother closely. Both methods require that the measuring point be full of water. The elbow-flowDP method requires that the elbow bend in only one plane. According to one vendor, the elbow-flow DP method has several advantages over the waterbox DP method: (1) a higher DP isavailable for measurement, and (2) the elbow-flow DP method may be applied in the event thewaterbox approach is not feasible. For example, if the condenser has one conduit supplyingwater to two waterboxes/bundles in parallel, it would be easier to take the DP across the elbowbefore the separation. In another case, when the circulating water downstream of a condenser isbelow atmospheric pressure, the outlet waterbox is not a suitable location to measure DP,because it may not be full of water. The elbow in the supply line would be a better location.

The maintenance required for these two DP methods includes routine blowdown of the pressure-sensing line and the periodic calibration of the pressure transmitter. The cost for each of these

systems is in the range of $20,000 to $30,000, including instruments and calibration.

Ultrasonic Time of Travel Method

There are a number of ultrasonic flow meters available on the market. They include the time-of-travel system, the sing-around system, the leading-edge system, and the Doppler system. Onlythe multiple-pass time-of-travel system provides sufficient accuracy for measuring water flow

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through large conduits and open channels such as a circulating water system. This methodinvolves the measurement of travel times of acoustic energy transmitted forward and backwardalong a number of chordal paths (typically four) positioned on an angled acoustic plane across apipe, as shown in Figure 4-5.

Figure 4-5Diagram of Four-Path Ultrasonic Flow Meter

This system uses a high-frequency sonic wave that is beamed at an acute angle across the pipe,as depicted in Figure 4-5. When the wave is transmitted through the water in the direction of theflow, its velocity increases. When the wave is transmitted through the water against the directionof the flow, its velocity decreases. Given the speed of the sound wave in water and the anglebetween its direction and the flow pass, the average water velocity on the flow path can becalculated. Since the velocity in the pipe is not uniform, a four-path system provides an averagewater velocity. The flow rate is calculated from the average velocity.

The ASME PTC 12.2[4-2]

recommends that the metering section should be preceded by at least tendiameters and followed by at least three diameters of straight pipe. In practice, this restrictionmay be relaxed somewhat. In a case where there is a very short straight run (less than five pipe

diameters) upstream of the measuring section, it is likely that the flow will be very turbulent.The manufacturer recommends that a second crossed path be installed at 90 degrees to the firstcrossed path to eliminate the cross-flow error.

To calibrate this system, precise measurements of the distance between the transducers, the angleof the transducers with respect to the centerline of the pipe, and the physical dimension of thepipe are required. No on-line calibration, such as in the dye dilution or velocity traverse tests, isrequired. An accuracy of 1% can be accomplished with this system. Entrained air bubbles in the

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water, silt and other particulate in the water, and a partially full water pipe can all affect theaccuracy.

Periodic cleaning of the transducers is required to prevent algae growth, which in turn affects themeasurement. The transducers can be installed from inside the pipe. However, for ease of

maintenance, tapping into the pipe and mounting the transducers on a flanged, removable plateis desirable.

EPRI tested one ultrasonic flow meter widely used in the hydroelectric industry[4-7]

. Even thoughit was installed in a rectangular channel, favorable results were reported

[4-8]. The cost for this

system is in the range of $100,000 to $150,000.

Air In-Leakage Flow Monitoring

Rotameter

Most plants are equipped with a rotameter for air in-leakage monitoring. The rotameter is avariable-area flow meter. It is composed of a tapered metering tube, mounted vertically with thesmall end at the bottom, and a float that is free to move up and down in the tube. Flow enters therotameter at the bottom, passes around the float and leaves the meter at the top. Figure 4-6 showsa schematic of a typical rotameter.

Figure 4-6Schematic of Rotameter

Under no-flow conditions, the float rests at the bottom of the tapered tube. When flow enters thetube, it passes through an annular space between the float and the tube wall, creating a pressuredrop across the float. This pressure drop raises the float to increase the flow area between thefloat and the tube to reach dynamic equilibrium. At this equilibrium the upward forces on thefloat are balanced by the weight of the float. Any further increase in flow causes the float to risehigher in the tube; a decrease in flow causes the float to drop. For a fluid of a given density andviscosity, the float position corresponds to a unique flow rate. Flow rate is determined by direct

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observation of the position of the float in the metering tube. The tube is marked to indicate theflow rate. The calibration is completed in the factory.

In power plant air in-leakage applications, the rotameter is located at the steam jet ejector orvacuum pump discharge on a bypass line. Normally, the exhaust is vented through the main line.When taking rotameter readings, the main line is closed with a butterfly valve.

Fluctuations in temperature change the fluid density and viscosity, which in turn affect theaccuracy of the rotameter. Therefore, the rotameter provides only an approximate indication ofthe air in-leakage rate. To improve accuracy, temperature and pressure readings may be taken atthe condenser vent connection, and these can be used to correct the air in-leakage rate, accordingto Appendix H of ASME PTC 12.2

[4-2].

The second drawback of the rotameter is that it creates an additional pressure drop when takingthe reading, and thus affects the accuracy of the reading. The third drawback is that the rotameteris read manually. Continuous reading of a rotameter is very difficult, although a magnetictechnique to determine float location has been used to take continuous readings. The advantage

of the rotameter is that it is inexpensive. There will be no cost incurred if the unit is alreadyequipped with a rotameter.

Orifice Plate

The principle of using an orifice plate for flow measurement is similar to using the condenseroutlet waterbox. A differential pressure transmitter may be installed across the orifice plate forcontinuous reading. A schematic of the installation is shown in Figures 4-7 and 4-8.

Figure 4-7Orifice Plate Installation

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Summary

Table 4-1Circulating Water Flow Monitors

Monitor Type Cost Pro Con

Dye dilution test $10K-

$20K

Suitable for complex piping system.

No tapping into the pipe required.

Pipe need not be full of water.

Organic growth and silt a

No flow introduced or re

Not suitable if dye mixin

Not suitable for continuo

Velocity Traversing $3K-

$10K

Not affected by organic growth or silt. Not suitable for complex

Tapping into the pipe req

Pipe must be full of wate


Pump Curves & TDH $5K Minimum additional instruments required.

May be made into a continuous flow monitor.

Accuracy depends on accondition of the pump.

Periodic testing is requirpump curve.

Heat Balance $0 Inexpensive if tested with steam turbine testing.

No additional instruments required.

May be used to calibrate other monitor.

Accuracy depends on ththe outlet water tempera


DP outlet waterbox $20K-

$30K

Inexpensive.

Suitable for continuous monitoring.


On-line calibration requi

DP Elbow $20K-

$30K

Inexpensive.

Higher DP than outlet waterbox method.

Suitable for multiple waterbox/bundle.

More choice of monitoring point.

Suitable for continuous monitoring.


The elbow must bend in

On-line calibration requi

Ultrasonic Flow meter $100K Provides continuous monitoring.

No on-line calibration is required.

Entrained air bubbles, saccuracy.


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Table 4-2Air In-Leakage Flow Monitor

Monitor Type Cost Pro Con

Rotameter $0 - $2K Inexpensive. Less accurate.

Additional pressure drop.

Not suitable for continuous mo

Orifice Plate $7K-$10K More accurate.

Continuous reading.

Additional pressure drop.

More expensive.

Electronic Monitor $20K-$25K

Most accurate.

Continuous reading.

Most expensive.

Maintenance cost may be high

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References

[4-1] Calibration of Dye Dilution Method of Flow Measurement, CEA No. 320 G 396,December 1987

[4-2] Performance Test Code on Steam Surface Condensers, ASME PTC 12.2 1998. ASME,New York, 1998.

[4-3] Schagunn, J., Missimer, J., Demonstration of Dye Dilution for Determining of CirculationWater Flow Rate, Presented at the EPRI/ASME Heat Rate Improvement Conference,Knoxville, TN, 1989.

[4-4] Diaz-Tous, I. A., Leggett, M., Hill, D.,Low-Drag Insertion Turbine Flow MeasurementTechnology for Circulating Water Systems Without Fully-Developed Flow Profiles, EPRI ReportTR-106781, August 1996.

[4-5] Performance Test Code on Steam Turbines, ASME PTC 6 1996. ASME, New York,1998.

[4-6] March, P. A., Almquist, C. W., Technique for Monitoring Flowrate and Hydraulic Foulingof Main Steam Condenser, EPRI Report CS-5942-SR, September 1988.

[4-7]MARK IPerformance Monitoring Products,EPRI ReportGS/EL-5648, September 1989.

[4-8] On-Line Condenser Cooling Water Flow Measurement, EPRI FS-9102, 1991.

[4-9]Measurement of Fluid Flow in Pipe Using Orifice, Nozzle and Venturi, MFC-3M-1989,

ASME, New York, 1990.

[4-10]Instruments and Apparatus: Part II of Fluid Meters, ASME PTC 19.5, ASME, New York,1972.

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5FOULING MONITORING PRACTICES

Background

Fouling reduces the condenser performance in a number of ways. Fouling is further classifiedas microfouling and macrofouling. Microfouling consists of biological fouling, precipitationfouling, particulate fouling, and corrosion fouling. Microfouling forms deposits inside thecondenser tubes. It mainly increases the heat transfer resistance between the steam and waterand in turn decreases the amount of heat that can be dissipated through the cooling water.

Macrofouling consists of marine animals and plants, biological growth, and debris carried overby water. The macrofouling can foul the cooling water system, including the intake system andthe flow conduit, and block the tubesheet flow area. It mainly increases the flow resistance,which in turn reduces the cooling water flow rate and again decreases the amount of heat thatcan be dissipated through the cooling water.

Reducing heat dissipation in the condenser in turn increases the condenser backpressure andturbine cycle heat rate. For this reason, it is important to monitor fouling. When the monitorindicates that the condenser is excessively fouled, appropriate remedial action can be taken.

Using other condenser performance data, including backpressure, heat rejection rate, cooling

water inlet and outlet temperatures, and cooling water flow rate; the condenser performancefactor (also known as the cleanliness factor or fouling factor) can be calculated. This is a methodto monitor condenser performance. However, the reduction in condenser performance may ormay not be solely due to fouling. For this reason, it is desirable to use fouling monitors tomonitor the actual fouling of the condenser tubes or other components in the system.

Instruments

Microfouling monitors can be classified as on-line or off-line monitors. On-line fouling monitorsinclude both in-situ and side-stream monitors. The in-situ fouling monitor also consists of

periodic and continuous monitors. The side-stream fouling monitor includes full-scale andreduced-scale monitors, and is very useful in simultaneous evaluation of treatment options.Off-line fouling monitors are also used to evaluate treatment options and effectiveness. All themicrofouling monitors are specialty products. The operating principles, construction details, andsources will be discussed in the text.

Macrofouling monitors are all on-line. One uses the differential water level between the intakeand the pump bay to monitor macrofouling of the traveling water screen. The other uses the

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Fouling Monitoring Practices

differential water pressure between the inlet and outlet waterboxes to monitor the tubesheetfouling.

Off-Line Microfouling Monitor

Conco Systems (www.concosystems.com) offers an off-line condenser fouling test apparatus(Figure 5-1). This test apparatus consists of four removable tubes (36 inches [91 cm] long) ina shell. Cooling water is circulated through the tubes. Steam is generated in the shell using anelectric heater. Tubes to be evaluated are sent to Conco from the condenser in question. Thesetubes are loaded into the test apparatus. Testing is conducted at the customer specified heat flux,water velocity, and range of water temperature. Comparisons can be made between the asreceived tubes (fouled) and the new, mechanically cleaned or chemically cleaned tubes. Resultsof each test are expressed as overall heat transfer coefficients, fouling factors, and cleanlinessfactors. The costs of the tests are $1,900 for start-up of the apparatus and the first U coefficient,and $500 for each additional U coefficient determination.

Figure 5-1Conco Heat Transfer Testing Unit

Strictly speaking, this apparatus is an off-line fouling test apparatus rather than a fouling

monitor. As such, it is ideal for evaluating the effectiveness of cleaning methods. The drawbackof this method is that it requires removal of a tube from the operating condenser. The removedtube must be representative of the fouling condition, and must also be carefully preserved andpacked for shipping to Conco to prevent a change in fouling condition, such as drying out.

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On-Line Microfouling Monitor

Bridger Scientific Continuous Side-Stream Reduced-Scale On-Line MicrofoulingMonitor

Bridger Scientifics (www.bridgersci.com) DATS side-stream fouling monitor has been inexistence for a long time. This monitor consists of a tube wrapped with an electric heater block(five inches [13 cm]long) (Figure 5-2). A side-stream of cooling water is fed through the tubesection at a controlled rate. The electric heater block surrounding the tube simulates the actualheat load of the condenser tube. Calibrated temperature probes measure both the fluid and heatertemperatures. These data, the flow rate and heat flux are used to automatically calculate the heattransfer resistance. All heat transfer data are then provided as analog output. Changes over timeaccurately reflect the accumulation of the fouling deposit. The cost for the system is $9,500.

Figure 5-2DATS Heat Exchanger Cross-Section View

The advantage of this monitor is that it is relatively small and inexpensive. Since it is off-line, itcan also be used to evaluate other treatment programs. The drawback of this monitor is that theheated section is very small. It is not possible to simulate the fouling of the entire condensertube.

Bridger Scientific Continuous Small On-Line Microfouling Monitor

Bridger Scientifics (www.bridgersci.com) new ProDATS insertion fouling probe is in the finaltesting stage (Figure 5-3). This device consists of two independent sensing assemblies in a singleprobe configuration. The probe may be directly inserted into any pipe two inches (5 cm) orgreater via a hot tap assembly, or it can be operated as a side-stream system with the additionof a clamp-on assembly. The primary sensing element is a heat transfer sensor, which iscomplemented by a secondary magnetic flow sensor. Mounted below the flow sensor are twoidentical 0.25 inch (0.64 cm) tubular sections, each electrically isolated from the other andwound with electrically heated wire. Cooling water flows through these two tube sections.Electric current flowing through the wound wire causes the temperature of the tube to rise, whichcan be accurately monitored by measuring the wire resistance. Cooling water flowing throughthe tubes removes heat from the tubes thereby reducing their temperature rise. Since clean tubes

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will transfer heat to the cooling water with higher efficiency for the same flow rate, the sensingelements will experience a relatively small temperature rise compared to the fouled tube. Bymeasuring the temperature rise of the sensing elements above that of the cooling water, andknowing the flow passage dimensions, a heat transfer value can be calculated which over time isrelated to the fouling deposit buildup on each heated surface. The total fouling can be determinedthis way.

Figure 5-3ProDATS Probe and its Schematic

The second use of this probe is to measure the difference between these two tube sections and inturn determine fouling caused by different mechanisms. There are several ways to make the twosensing sections foul in different modes. One way is to periodically inject chemicals to preventone tube section from microbial fouling. The second way is to generate chlorineelectrochemically in a seawater-cooled system by applying electric currents to one tube section.The two sections will experience the same abiotic fouling (scaling) but different microbialfouling. If one subtracts this component from the untreated sensing element, one will have ameasure of just the microbial component. By using this approach, one can quantify the total

fouling, microbial fouling and abiotic fouling occurring, which can be very useful in developingan overall optimal treatment or control program. The cost for the system is approximately $2,500to $3,000.

The advantages of this monitor are that it is very small, inexpensive and can be inserted on-line.It can also be used to differentiate microbial fouling from scaling. The primary drawback is thatthe heated section is very small. It is not possible to simulate the fouling of the entire condensertube.

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Conco Systems Continuous Side-Stream Reduced Scale On-LineMicrofouling Monitor

Conco Systems (www.concosystems.com) offers a portable test condenser (Figure 5-4). Theportable test condenser is a single-tube (36 inches [91 cm] long), self-contained model

condenser. The portable condenser is installed alongside the unit condenser.

Figure 5-4Conco Portable Test Condenser

The portable test condenser is a shell-and-tube heat exchanger with an integral electric heater.Demineralized water and water vapor occupy the shell space. Air is removed from the shell prior

to startup with a vacuum pump. Cooling water is passed through the test tube section, and theelectric heater is energized to generate steam. Steam is condensed on the tube to transfer heat tothe tube wall and cooling water.

Fouling detection is accomplished by monitoring the initial temperature difference (ITD), whichequals steam temperature minus inlet water temperature. When a tube is fouled, the heat transfercapability of the tube will decrease, causing the steam temperature and, in turn, the ITD toincrease. As with an actual surface condenser, ITD will vary with inlet water temperature.This necessitates the preparation of a calibration curve. A comparison of measured ITD tothe calibration curve allows for detection of fouling and/or relative degree of fouling.

Foulant mass can be quantified by removing the deposit with a mechanical cleaner anddetermination of weight. Fouling can also be determined by comparing the ITD before and aftercleaning with a mechanical cleaner or with chemical cleaning. The portable test condenser canalso be used to evaluate the chemical treatment program. The cost for the system is $12,000 to$18,000, depending on the configuration.

The advantage of this test condenser is that it is portable. A utility can move the monitor aroundand test the fouling tendency in more than one condenser. The foulant mass can easily be

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quantified. It can also be used to evaluate corrosion control optimization and the replacementtube material. The drawback of this test condenser is that the tube is relatively short. It may notduplicate the fouling occurring in the actual condenser.

Periodic In-Situ On-Line Microfouling Monitor

ASME PTC 12.2[5-1]

recommends an in-situ on-line fouling monitor. This monitor uses a pair ofcondenser tubes. During an outage, it is either cemented to the tubesheet or installed on a tubeextension that attaches RTDs or thermocouples to the outlet of this pair of tubes. One tube isthoroughly cleaned. By comparing the performance of these two tubes, the fouling factor can bedetermined. Details of the installation and other requirements are contained in PTC 12.2

[5-1].

Strictly speaking, this is a fouling test rather than a monitoring method.

The advantage of this method is that it is simple and effective with minimal additionalinvestments. It determines the current fouling condition of the entire tube. The major drawbackof this method is that it is not continuous monitoring. It requires an outage to install the

temperature sensors and to clean the reference tube. The existing plant instruments are reliedon for backpressure and cooling water flow rate measurements. These data may or may not beaccurate. If these data were inaccurate, the accuracy of the fouling factor would be inaccurate,although the impact would be proportionally less. The cost of conducting this test depends onwhat needs to be done and whether the tester can complete the test in one trip.

Thermal Engineering Consultants (www.tecus.com) offers a service to conduct fouling tests withthis method.

EPRI Continuous In-Situ On-Line Microfouling Monitor

EPRI funded Bridger Scientific, Inc. in the development of this in-situ on-line fouling monitor(Figure 5-5). This monitor uses a pair of actual adjacent condenser tubes. One tube is designatedas an active tube, and the other is designated as an inactive tube, which is plugged on bothends. The monitor is mounted on the outlet tubesheet of these two tubes. The part of the monitorconnected to the active tube contains the ultrasonic flow sensor and the discharge cooling watertemperature sensor. The part of the monitor connected to the inactive tube contains an inletcooling water temperature sensor and two spring-loaded steam temperature sensors, which areinserted into the tube to measure the steam temperature in the first half and the second half of thetube. The measurements are digitized locally and transmitted to the outside via an RS-485 link toa remote computer through an appropriate opening on the condenser waterbox. A critical featureof this monitor is that the inside diameter of each monitor assembly is machined to precisely

match the condenser tube. Typically, four monitors are used for each condenser to providediversity and redundancy.

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Figure 5-5On-Line Fouling Monitor

Knowing cooling water flow velocity, inlet and outlet cooling water temperature, and steamtemperature, the heat transfer coefficient can be calculated. The calculated heat transfercoefficient is compared to the HEI or ASME theoretically achievable heat transfer coefficientbased on the operating conditions. The fouling factors and cleanliness factors are deducted fromthis comparison. The detailed design of the monitor and the calculation procedure are containedin an EPRI report

[5-2]. The cost for the system is approximately $55,000, including four probes

and software.

The advantage of this monitor is that it directly measures the heat transfer of an entire operatingcondenser tube. The inlet and outlet cooling water temperatures are measured directly. The steamtemperature is measured directly rather than from pressure measurement. Because there is nocooling water flow in the blocked-off tube, the wall temperature comes into equilibrium with thesurroundings and represents the steam temperature at that position of the condenser. The coolingwater velocity is also measured directly and represents the actual cooling water flow through thattube. The drawbacks of this monitor are that it is more expensive, and it requires plugging ofsome tubes and a short outage to install the monitors.

Taprogge Continuous In-Situ On-Line Microfouling MonitorThe Taprogge (www.taprogge.com) condenser monitoring system (Figure 5-6) was developedmainly for monitoring and controlling the Taprogge tube cleaning system, which uses spongeballs circulating through the tubes to clean them. Since the sponge ball will wear out over time,the need to replace these balls is determined by measuring the effectiveness of the sponge ballwiping action. This monitor is also used to measure and control ball circulation.

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Figure 5-6Taprogge Monitoring System

The monitoring system utilizes a row of six tubes in the operating condenser. The two outertubes are used to anchor the sensor probe. One tube is plugged on both ends with spring-loadedthermocouples to measure the steam temperature. Six thermocouples are located at the inlet andoutlet of three tubes to measure the inlet and outlet cooling water temperature. One of these tubesis used to measure the cooling water velocity. This is accomplished by periodically injecting hotwater at the tube inlet end. Measuring the time required for the hot water to travel to the outletend determines the water velocity. The other two tubes are used to measure the effectiveness ofthe sponge balls. This is accomplished by comparing the outlet cooling water temperature ofthese two tubes when a sponge ball enters one of the tubes. The corresponding softwarecalculates the heat transfer coefficient of the individual tubes from the measured temperaturedifference and, in turn, determines the effectiveness of the sponge ball. The cost for the system,including software and four probes, is $150,000 to $200,000, depending on the configuration.

The advantage of this system is that it monitors not only the condenser performance but also theeffectiveness of the sponge ball cleaning system. The major drawback of this system is that it isvery expensive. It would not be cost effective if the condenser in question did not have a spongeball cleaning system. It also requires plugging some tubes and a short outage to install themonitors.

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On-Line Macrofouling Monitor

Intake On-Line Macrofouling Monitor

A typical cooling water intake system is shown in Figure 5-7. Here the trash bars and travelingwater screens are used to protect the condenser and the circulating water system frommacrofouling. However, when the trash bars and traveling water screens are overloaded, thewater level in the pump bay will decrease, providing less net positive suction head (NPSH) andreducing the circulating water pump efficiency, which results in less cooling water flow throughthe condensers. Generally, the macrofouling situation is monitored manually by operatorobservation. The purpose of the on-line macrofouling monitor is to provide early warning aboutany potential problem.

Figure 5-7

Typical Cooling Water Intake System

The principle of the on-line macrofouling monitor is to monitor the water level in the watersource, in the fore bay behind the trash bar, and in the pump bay. Whenever the difference inwater levels between these three places exceeds a preset limit, a warning signal will alert theoperator to take appropriate action. There are a number of ways to measure the water levelremotely, including capacitance, ultrasonic, differential pressure, and bubbler level detectors.The details of these level detectors will be discussed in Section 6. A typical application usingan ultrasonic level detector is shown in Figure 5-8.

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Figure 5-9TVA Tubesheet Macrofouling Monitor

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Summary

Table 5-1Microfouling Monitor

Monitor Type Cost Pro ConConco Tube HT Tester $3.4K Ideal for evaluating cleaning method and

effectiveness.Not a continuousRequires removaRemoved tube mcondition.Removed tube mshipping.

DATS $9.5K Relatively small and inexpensive.Can be used to evaluate water treatmentprogram.

Heated section is

ProDATS $2.5K $3K Very small and inexpensive.Can differentiate microbial fouling and scaling.

Tube diameter asmall.

Portable Test Condenser $12K-

$18K

Portable.

Corrosion and replacement tube evaluation.

Test tube is shor

ASME Method N.A. Minimal additional investment.Measures entire tube.

Not a continuousRequires outagetube.Relies on plant inflow measureme

EPRI On-line Monitor $55K Direct measurement of fouling of an entiretube.Accurate cooling water inlet/outlet and steamtemperature measurement.Accurate cooling water velocity measurement.

More expensive.Requires plugginoutage to install.

Taprogge On-Line Monitor $150K-

$200K

Direct measurement of fouling of an entire

tube.Accurate cooling water inlet/outlet and steamtemperature measurement.Accurate cooling water velocity measurement.Also monitors sponge ball effectiveness.

Most expensive.

Requires plugginoutage to install.


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References

[5-1] Performance Test Code on Steam Surface Condensers, ASME PTC 12.2 1998. ASME,New York.

[5-2] On-line Condenser Fouling Monitor Development, EPRI Report TR-109232, EPRI,December 1997.

[5-3] March, P. A., Almquist, C. W., Technique for Monitoring Flowrate and Hydraulic Foulingof Main Steam Condenser, EPRI Report CS-5942-SR, September 1988.

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6LEVEL MONITORING PRACTICES

Background

In a condenser system, the water level needs to be monitored in four places: the condenserhotwell, the inlet and outlet waterboxes, and the intake.

In the hotwell, the condensate level needs to be maintained to provide net positive suction head(NPSH) for the condensate pump.

In the inlet and outlet waterboxes, the water level needs to be monitored to make sure thewaterboxes are full of water. If the waterboxes are not full, the tubes on the top portion of thetube bundle will not have water flowing through them, and those tubes will not condense steam.Condenser backpressure will suffer as a result.

In the intake, especially the pump bay, the water level needs to be monitored to make sure thereis sufficient NPSH for the circulating water pump. If the NPSH is not sufficient, the pump willcavitate, resulting in a reduction in water rate and possible damage to the pump. See Section 5on Macrofouling Monitoring for more details.

Instruments

Sight glasses are most commonly used to monitor water level locally. Flexible transparent tubesare used to monitor water level in the waterboxes. These are simple devices and need not beelaborated on.

There are a number of ways to measure the water level remotely, including capacitance,ultrasonic, differential pressure, and bubbler level monitors. All of these are suitable formonitoring the water level in the intake.

The capacitance level detectors measure the changes in electric capacitance that occur between

the sensing conductors as the water level changes. A capacitance level measuring system consistsof a probe lowered into the bottom of the water body and connected to a transmitter mounted ona platform above the highest anticipated water level.

Operation of the ultrasonic level detector is based on the time required for a sonic wave to travelfrom a transducer to the water level being measured and back to the transducer. The total traveltime is proportional to the water level. The transducer is mounted on a platform above thehighest anticipated water level.

6-1


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Level Monitoring Practices

Operation of the pressure differential level detector is based on measuring the pressure differencesensed by the unit between its high- and low-pressure sides. The high-pressure side of the unit isconnected to the bottom of the bay and the low-pressure side is open to the atmosphere. Themeasured hydraulic head is directly proportional to the water level. The differential pressuretransmitter is mounted on a platform above the highest anticipated water level.

The bubbler level detector is a differential pressure level detector with an air purge system.Operation of this instrument is based on the differential pressure required for an air flow streamto overcome the liquid head of the water. The pressure reading is proportional to the water level.The air supply transmitter is mounted on a platform above the highest anticipated water level.

Details of these instruments are contained in Reference [6-1].

Hotwell

The hotwell is usually equipped with a sight glass and a float or other suitable liquid level

controller.

Waterboxes

Waterboxes are usually equipped with a sight glass. However, many sight glasses do not reachthe top of the waterbox. If the waterbox is not completely full, the sight glass will not provide thenecessary indication. This situation is especially common with outlet waterboxes, because waterpressure in many outlet waterboxes is below atmospheric pressure. It is recommended that atransparent flexible tube be used to monitor the water level in the inlet and outlet waterboxes.The top connection for the transparent flexible tube should be at the highest point of thewaterbox.

Many sight glasses installed on condenser waterboxes are fouled to the point that the water levelis impossible to observe due to algae growth. It is difficult to clean the sight glass. In comparison,a transparent flexible tube is inexpensive, and one can simply replace it when fouled. It isessential to make sure the flexible tube connection is air tight to prevent air from leaking intothe system, especially if the waterbox is under negative pressure.

Intake

Typical cooling water intake systems, using ultrasonic level indicators and macrofouling

monitoring systems, are discussed in Section 5. Additional typical installations using other leveldetectors are shown in Figures 6-1, 6-2, and 6-3.

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Level Monitoring Practices

Figure 6-1Typical Installation of Capacitance Level Monitor

Figure 6-2Typical Installation of Submersible Differential Pressure Level Monitor

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Summary

Table 6-1Remote Level Monitors

Monitor Type Pro Con

Capacitance No moving parts, minimum maintenance.

Not affected by foam and floating debris.

Grease buildup can affect accurac

Barge traffic will give false reading

Ultrasonic No moving parts, minimum maintenance. Affected by foam and floating deb


Differential Pressure No moving parts, minimum maintenance.

Not affected by foam and floating debris.


Bubbler Not affected by foam and floating debris.

Not affected by barge traffic.

Air supply required.

Pressure regulator, flow controller

Fouling will affect accuracy.


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References

[6-1]Instrumentation Handbook for Integrated Power Plant Water Management, EPRI ReportCS-5873, July 1988.

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7DISSOLVED OXYGEN MONITORING PRACTICES

Background

Dissolved oxygen (DO) in the condensate causes corrosion of power plant components. Oxygen-scavenging chemical consumption increases as the amount of dissolved oxygen increases. It is,therefore, important to monitor oxygen content in the condensate and take appropriate actionwhen needed.

The condenser is the major source of dissolved oxygen in the condensate. The oxygen comesfrom air in-leakage and make-up water. For boiling water reactor power plants, additionaloxygen may come from the reactor. A properly designed condenser and non-condensibleremoval system should be capable of producing condensate with the desired oxygen content(from 7 ppb to

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