return investment analysis economics regular condenser maintenance

7/26/2019 Return Investment Analysis Economics Regular Condenser Maintenance

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W H I T E P A P E R

CONCO SYSTEMS, INC. 530 Jones Street Verona, PA 15147 USA 1-800-345-3476

Return on Investment Analysis:

The Economics of Regular

Condenser Maintenance

Mechanical Tube Cleaning

Air Inleakage Detection

Richard E. PutmanTechnical DirectorConco Consulting Corp.Verona, PA 15147 USA

Absolutely the Best.


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Getting To The Bottom Line

You may already suspect that your plantis not operating at peak performance.You want to incorporate the latest tech-nologies to improve efficiency because

your gut feeling tells you that improv-ing your systems will have a payoff, yetyou need a concrete process to justify aninvestment.

This White Paper summarizes a decadeof research by Conco Systems, Inc. toobtain a better understanding of thebehavior of steam surface condensersand their impact on your plants bottomline. This research was followed by the

development of techniques to modelcondenser performance, with a viewto converting deviations from properbehavior to the equivalent avoidedcosts. Mathematical techniques werealso developed to ascertain the optimumfrequency of condenser cleaning tominimize these avoided costs. The fulldetails of this work are published in abook by ASME Press, New York(1)

entitled, Steam Surface Condensers:Basic Principles, Performance Monitoringand Maintenance.

Minimizing turbogenerator unit heat rateand maximizing generation capacity areamong the guiding principles in powerplant operation strategy. In fossil plants,heat rate is greatly affected by theefficiency with which the fuel is burnt.However, the heat rate of fossil plants,

along with nuclear and combined cycleplants, may also be affected by the stateof the condenser. Its condition is also afactor in determining whether the designMW load can be achieved.

Chapter 8 of Putman(1) outlines the varietyof operating problems to which steamsurface condensers are prone, principalamong these being the fouling of con-denser tubes with its negative impact on

heat transfer rate and turbine back pres-sure. The condenser condition can alsoaffect generation capacity. Air ingressinto the turbine/condenser subsystemhas similarly negative effects.

In this White Paper, we will discuss thethermodynamic considerations that makethe condition of the condenser such animportant element in determining theperformance of the turbogenerator. We

will also outline condenser maintenancestrategies that can be adopted to mini-mize annual unit operating costs and,ultimately, maximize plant revenue.

Condenser operation also has a directimpact on power plant emissions. Theheat rejected by the condenser is asource of thermal pollution; however,if it can be reduced by improved con-

denser maintenance, then the emissionof carbon dioxide and other atmosphericpollutants is also reduced due to thelower consumption of fuel.

Another important condenser mainte-nance problem is the inleakageof cooling water into the condensate,contaminating it chemically (EPRI(2)).However, since it principally affects thecorrosion of boilers and heat exchangers

and since the main topic of thisdocument is the economics and returnon investment as a result of the effectof the condenser on heat rate and/orpower generation, we will not furtheraddress water inleakage here.

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The Condenser/Turbine SubsystemAll nuclear and fossil plants are basedon some variation of the Rankine Cycle the steam/water conditions throughthe low-pressure stage of the turbine fora fossil-fired plant (illustrated in Figure 1).

Here, expansion lines are shown for anumber of loads, steam from the outletof the reheater passing through theintermediate and low pressure stagesof the turbine and expanding finallyinto the condenser.

During the last stage of expansion, thevapor passes through the saturation lineso that the vapor entering the condenseris usually wet. As it becomes condensed,the conditions follow the constant pres-sure line (corresponding to the condenserback pressure) down to the liquid line(not shown). The wetness increases untilthe vapor becomes fully condensed.

The enthalpy of the vapor entering thecondenser depends on condenser backpressure. It should be understood that themagnitude of the enthalpy drop betweenthe reheater outlet and the condenserinlet determines the amount of energy

converted to mechanical work (in thiscase, the generation of power).

If the flow of steam is determined at thesteam generator or boiler(s), as occurs innuclear power or combined cycle unitsoperating in the boiler-follow mode, thenraising the back pressure will reduce theamount of power generated by that fixedamount of steam. This will negatively

affect unit heat rate and, in some cases,will limit the amount of power that canbe generated. Conversely, a drop inback pressure will increase the amountof generated power.

In fossil-fired units, in which the load isdetermined by the setting of the turbinegovernor, an increase in back pressurewill result in more steam having to begenerated to support the load set on the

governor. This, again, has a negativeeffect on heat rate. In severe cases, suchas the back pressure reaching the upperlimit recommended by the turbine manu-facturer, the power setting will have tobe reduced.

The back pressure determines the amountof latent heat (also known as condenserduty) that has to be removed for the

vapor to become condensed, recovered,and then recycled back to the boiler.Meanwhile, in a clean condenser, theback pressure is determined by the duty,and by the cooling water flow rate andits inlet temperature.

Figure 1

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Figure 1 illustrates a design backpressure on which all the appropriateoriginal cycle calculations were based;but the actual back pressure experiencedcan be lower or higher than this. For

instance, it can be lower if the coolingwater inlet temperature is low and thewater flow is at or higher than its designvalue.

If the tubes in the condenser becomefouled, then the thermal resistance causesthe effective heat transfer coefficient ofthe tubes to decrease to the point wherethe back pressure will rise for the sameduty, cooling water flow rate, and inlet

temperature.

Similarly, air ingress increases thethermal resistance of the condensate filmon the outside of the tubes, decreasingthe effective tube heat transfer coefficientand with the same effect on backpressure. The proper management oftube fouling and air inleakage hasimportant consequences on condenser

and unit operating costs, as well as onthe scheduling decisions made by themaintenance department.

Monitoring Condenser

PerformanceThe basic principles used to calculate theperformance of a condenser based onboth design and current operating dataare detailed in Putman.(3) One methodhas been developed by the Heat

Exchange Institute (HEI(4)) and uses thecleanliness factor as the performancecriterion.

The other method is that originallyproposed in ASME PTC 12.2-1983 andupdated in the 1998 revision of that

standard(5). Based upon the sum of ther-mal resistances, the ASME method calcu-lates the clean single-tube heat transfercoefficient as a function of current operat-ing conditions and compares this with

the effective heat transfer coefficient cal-culated from present condenser duty.

One of the uncertainties in condenserperformance monitoring is the actualvalue of the cooling water flow rate.The design value can be affected bythe aging of the pumps or by the effectsof both tube and tube sheet fouling.Putman(6) shows that a reliable estimateof the actual cooling water flow rate

can be obtained from the cooling watertemperature rise, together with thecondenser duty calculated from theturbine thermal kit data.

The conditions that could be expected ifthe condenser were cleaned requires thesolution of a set of nonlinear equationsappropriate to the specific condenserconfiguration and constructing a Newton-

Raphson matrix that reflects the details.

The cost that could be avoided if thecondenser were to be cleaned can beestimated by using this simple equation:

Note that this avoided cost does notdistinguish between the back pressure

that results from fouling or from that dueto any air ingress that may be present.An estimate of the severity of air ingresscan be obtained by calculating the totalchange in heat transfer coefficient due toboth fouling and air inleakage. This canbe obtained by subtracting the present

3


Condenser duty

when fouled

The condenser

duty when clean

Fuel

cost x


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single-tube U-coefficient value (Ueff) from

that calculated if the condenser werecleaned (Uclean).

If this difference is small, all of the esti-mated avoided cost can be attributed tofouling and maintenance plans can bemade accordingly. However, if the differ-ence is substantial, steps should be takento determine the severity of the air inleak-age so the proper maintenance decisioncan be made.

If Rf = thermal resistance due to

foulingRa = thermal resistance due to

air ingress

Then

Clearly, if Rf, Ueffand Uclean are

known, then Ra can be calculated.

Method For Estimating Tube

Fouling ResistanceThe principle of the method developed byBridger Scientific under EPRI sponsorshipfor estimating tube fouling resistance Rf is

described in EPRI(7)

and illustrated inFigure 2 (where tube pairs are used).

One of the pair is a tube with blanked-offends through which no water flows.The other, the fouled tube, not only hassensitive temperature measuring devicesat both ends of the tube, but is alsoprovided with a turbine-type flow meterfor accurate measurement of the waterflow rate through the tube.

The blanked-off tube is used to measurethe mean shell temperature in the vicinity

of the fouled tube so that any vaporpressure loss through the tube bundlescan be accommodated. Several pairs oftubes are placed strategically in differentlocations within the tube bundle(s).

From the data obtained, the mean foulingresistance Rfcan be estimated using themethod outlined in the EPRI(7) report.The value of Ra can then be calculatedusing equation (1) to the left.

(1)

Figure 2

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Types Of Fouling Deposit

A tendency toward condenser tubefouling is a constant problem. Tube corro-sion is also a concern and is sometimesinitiated by fouling, as in under-deposit

corrosion. The maintenance of unitperformance, availability and lifeexpectancy depends on a multi-levelinteraction between tube metallurgy,water chemistry, and the foulingmechanisms involved, together withthe thermodynamics and kinetics of thecondenser system.

In cleaning condensers over a long peri-od of time, at least 1,000 different typesof fouling deposits have been encoun-tered. Each plant has its own idiosyn-crasies and it is not unusual to find eachunit within a plant behaving differently.

Furthermore, different tube materials inthe same condenser also foul in differentways. For example, copper alloys in themain tube bundles foul differently thanthe stainless steel tubes in the air removal

section.

As such, fouling deposits typically fallinto five major categories:

Sedimentary or silt formation Particulate fouling Deposits of organic or

inorganic salts Microbiological fouling Macrobiological fouling

Sedimentary Deposits

Sedimentary fouling occurs whenparticulates entrained in the coolingwater deposit on the tube walls arelower than the design value due to thewater velocity. The remedy is to raise thewater velocity closer to the design value.

Particulate Fouling

For particulate fouling to occur, theremust already be a deposit substrateto which particulates become attached.A common substrate is bacterial slime.

Once the particulates become attached,the deposit layer accumulates rapidly.

Salt Deposition

Salts of various kinds can becomedeposited due to changes in theirconcentrations. This is largely a resultof the increase in water temperature asit passes through the tubes. Examplesof crystalline fouling include calciumcarbonate, silica, calcium sulfate,

manganese, and calcium phosphate.Many of these types of fouling aredifficult to remove once they havebecome deposited. Some salts alsoexhibit an inverse solubility. The solubilitydecreases while the temperature increas-es. This is especially true of calciumcarbonate, the deposits of which oftenincrease toward the tube outlets.

Microbiological FoulingAll sources of power plant cooling watercontain bacteria, many of which exudea gelatinous substance that allows thebacteria to attach themselves to the tubewalls. Because these slimes contain some90 percent water, they have a high resist-ance to heat transfer. The organisms areoften rich in metal compounds, such asthose of manganese, which producean impermeable layer and can cause

under-deposit corrosion, even with stain-less steels. Microbiological fouling is alsosensitive to both velocity and tempera-ture. The deposits tend to increase inthickness as the velocity falls.

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Macrobilogical Fouling

Macrobiological fouling occurs whenmollusks, zebra mussels or similar aquat-ic organisms pass through the screensand attach themselves either to the tube

sheet or to the insides of the tube walls.The reduction in water velocity not onlyincreases the thermal resistance to heattransfer, but can also make the tubessusceptible to other types of fouling. Therate at which these fouling mechanismsdevelop is site-specific and depends onthe chemical treatment methods that areemployed. Aggressive cleaning of tubesand tubesheets is necessary to controlmacrofouling.

Optimizing Condenser Cleaning

FrequencyChapter 7 of Putman(1) discusses thetechnique for calculating the optimumcleaning frequency necessary tominimize the avoided costs incurred byfouling. The site-specific data requiredincludes knowledge of the fouling modelexperienced by that particular unit, as

well as understanding the historicmonthly load profile and the coolingwater inlet temperature profile for theunit over the past 12 months.

Some typical fouling models areillustrated in Figure 3. The mathematicalrelationship between fouling resistanceand time must be generated. A typicalload and inlet temperature profile curveis shown in Figure 4.

Figure 3

Figure 4

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Condenser duty is principally a functionof generator load, cooling water inlettemperature, and its flow rate. It has beenfound that, at a given load, the avoidedlosses are a linear function of the fouling

resistance vs. inlet water temperature, anda different linear function of the foulingresistance vs. load.

Given the load and inlet temperatureprofiles of Figure 4, and a fouling modelsimilar to one of those shown in Figure 3,it is possible to calculate the cost of lossesvs. fouling factor for each of the monthsin that profile. The initial data table for atypical case is shown in Table I.

An optimization program can be used totest the savings to be obtained with onlyone cleaning during the course of theyear, and even establishes the month inwhich it should occur. In then calculates

the savings if there are to be two clean-ings during the year, and establishes themonths in which they should occur. Theprocedure is then repeated for three andfour cleanings per year.

Return on Investment

The results of a typical case are summa-rized in Table II. Note that additionalcleanings always improve performance;but the amount of increase per cleaningdecreases.

The optimum frequency selected is thatwhich causes the incremental return oninvestment to match a threshold criterion

(for example, an ROI of 2). In Table II, theincremental cost of cleaning is shown tobe $13,500, while the correspondingincremental savings (or return on cleaning)are shown in Column 5. The maximumfrequency corresponding to an ROI = 2 is

Table 1 Basic Data

431.41

419.38433.13448.66385.47391.87365.69318.78307.65359.23430.85443.44

50.97

50.0958.9762.9568.8074.6183.6084.4881.9174.7458.4851.84

1740.28

1691.221764.121835.211598.131638.881560.221373.711321.401508.631753.991789.46

1767.43

1716.961795.091869.921629.561674.791599.721407.651352.101540.791784.491818.04

27.15

25.7430.9634.7131.4335.9139.5133.9430.7032.1630.5028.58

31

2831303130313130313031

2019.96

1729.732303.422499.122338.392585.522939.542525.142210.402392.702196.002126.35

2.5000E-05

2.2000E-045.0000E-047.5000E-049.0000E-049.8000E-041.0400E-031.0400E-031.0400E-031.0400E-031.0400E-031.0400E-03

580.74

4,376.2113,244.6921,554.9124,202.3629,138.8135,156.9530,200.6326,436.3828,616.7426,264.1625,431.17

MW

CWtemp,

inDuty,clean

Duty,fouled

Foulinglosses

Daysin

monthSpecific

costFouling

resistance

Costwithoutcleaning

Yearly cost of losses no cleanings $265,203.74

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shown to be three cleanings per year,since four cleanings per year would offeran ROI of


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Since the earlier cleaner designsbehaved as stiff springs, loading thecleaners into the tubes was sometimesrather tedious. To speed up this opera-tion, while also providing the blades

with more circumferential coverage ofthe tube surface, the hexagonal or Hexcleaner shown in Figure 5(b) was devel-oped by Saxon and Krysicki. This designnot only reduced the cleaning time for1,000 tubes, but was also found to bemore efficient in removing tenaciousdeposits like those consisting of variousforms of manganese.

A later development by Gregory Saxoninvolved a tool for removing hardcalcite deposits, which were found to be

difficult to remove even by acid cleaning.This tool is also shown in Figure 5(c),CB, and consists of a Teflon body mount-ed by a number of rotary cutters placedat different angles, and provided witha plastic disk similar to those used topropel other cleaners through tubes.As part of a case study, cleaners of thistype used on a condenser removed 80tons of calcite material. The tool has nowbecome standard whenever hard and

brittle deposits are encountered.

Mechanical cleaners offer the most effec-tive off-line tube cleaning method. Strongenough to remove hard deposits, theycan cut the peaks surrounding pits andflush out the residue at the same time,

thus retarding underdeposit corrosion.Each cleaning tool is custom-made tofit snugly inside a tube having a stateddiameter and gage or wall thickness.This allows the blade contact pressure

to be controlled within tolerances andalso ensures that as much of the tubecircumference as possible is covered asthe cleaner passes down a tube of thecorresponding size.

A special rig has also been developedfor the heat transfer testing of tubes.In the development of these variouscleaners, extensive use of this rig wasmade to determine the effectiveness ofdifferent cleaner designs. Not only couldthe incremental material removed be

established for each successive pass ofthe tool, but the cleaners effect on heattransfer could also be quantified for agiven kind of deposit.

In some plants, it has been commonpractice to use compressed air withwater to propel the cleaners. However,the rapid expansion of the air causesthe cleaner to become a dangerous pro-jectile when the cleaner exits the tube.

The use of water alone never allowsthe cleaner exit velocity to rise above asafe level. Similarly, water supplied ata pressure of 300 psig is much safer topersonnel than at up to 10,000 psig,which is sometimes attained when usinghigh-pressure hydrolasing techniques.

Figure 5(c) CB

Figure 5(d) Brush

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Another advantage of mechanicallycleaning condenser tubes using water asthe cleaner propellant is that the materialremoved can be collected in a plasticcontainer for later drying and weighing

to establish the deposit density (in gramsper square foot). In many cases, X-rayfluorescent analysis of the deposit cake isperformed. Experience has also shownthat properly designed cleaners will notbecome stuck inside tubes unless the tubeis damaged or severely obstructed.

Mechanical cleaners travel through thetubes at a velocity of 10 to 20 ft/s andare propelled by water delivered at 300psig. Some of the members of a well-known family of tube cleaners have thefollowing features:

C4S. The C4S cleaner is general-purpose and may be used to removeall types of obstructions, depositcorrosion, and pitting.

C3S. The C3S cleaner is designedfor heavy duty use and is veryeffective in removing all kinds oftenacious deposits. Its reinforcedconstruction also allows it to removehard deposits, corrosion deposits,

and obstructions.

C2X, C3X. These types of cleanerconsist of two or three hexagonal-bladed cleaner elements, having sixarcs of contact per blade. They areeffective on all types of deposits, butare especially suitable for removingthe thin tenacious deposits of iron,manganese, or silica found on stain

less steel, titanium, or copper-basedtube materials.

C4SS. While the C4SS stainless steelcleaners can be used with all typesof tube materials, they were originally developed for applications usingAL-6XN stainless steel condensertubes; however, they have also beenused for cleaning tubes in highlycorrosive environments.

CB. This tube cleaner was specificallydeveloped to remove hard calciumcarbonate deposits and is designedto break the eggshell-like crystallineform characteristic of these tube-scal-ing deposits. This cleaner has beenfound exceptionally helpful in avoiding the need for alternative and envi-ronmentally harmful chemical clean-ing methods, which were all thatwere previously available for removing these types of hard deposits.

Brushes

Brushes are principally intended toremove light organic deposits, such assilt or mud. They are also useful forcleaning tubes with enhanced surfaces

Figure 6(a) Model 200B Pump System

Figure 6(b) Water Gun

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e.g., spirally indented or finned, or thosewith thin-wall metal inserts or tube coat-ings. The brush (Figure 5(d), Brush)length can be increased for moreeffective removal of lighter deposits.

Cleaning Productivity

in the Field

Using the methods outlined earlier in thissection, it is possible for 5,000 tubes tobe cleaned during a 12-hour shift, utiliz-ing a crew of four operators with twowater guns supplied from one pump.Clearly, an increase in crew size, inthe number of water guns available,or in the number of mechanical cleaners

supplied for the project can increase thenumber of tubes which can be cleanedduring a shift, provided there is adequatespace in the waterbox(es) for the crew towork effectively.

Some Limitations of MechanicalCleaning Methods

Each type of off-line cleaning device hasits own limitations. For instance, brushesmay be effective only with the softestfouling deposits, whereas metal cleanersare more effective against tenaciousfoulants.

However, all methods may needassistance where the deposits have beenallowed to build up and become hard.In such cases, it may still be necessaryto acid-clean, followed by cleaning withmechanical cleaners to remove anyremaining debris.

AIR INLEAKAGE DETECTIONAir inleakage can be inferred from anincrease in the air concentration in thegases drawn off by the air-ejector system.It is often associated with an increase incondenser back pressure. Note that thereis always a minimum air inleakage thatcannot be eliminated.

Westinghouse Electric Corp. used torecommend that air inleakage levels beheld to 1 ft3/min per 100 MW of gener-ation capacity, but other minima aregiven in the ASME and HEI standards.

An increase in the dissolved oxygenconcentration in the condensate canalso indicate that air is leaking intothe suction of the condensate pumpsbelow the condenser hot well.

Tracer gases are used to locate thesource of air inleakage, two of themost common being helium and sulfurHexafluoride (SF6). SF6 was first usedeffectively as an airborne tracer in atmos-

pheric research and demonstrated itsgreater sensitivity as a tracer gas.

Sulfur hexafluoride, discovered in 1900,is a colorless, tasteless, and incom-bustible gas which is practically inertfrom a chemical and biological stand-point. It does not react with water, caus-tic potash, or strong acids and can beheated to 500C without decomposing.

Two of its common uses within the utilityindustry are for arc suppression in high-voltage circuit breakers and the insula-tion of electric cables. SF6 also has manyother uses, such as etching silicon in thesemiconductor industry, increasing thewet strength of kraft paper and protect-ing molten magnesium from oxidation inthe magnesium industry.

The fundamental property of SF6 is thatit can be detected in very low concentra-tions-as low as 1 part per 10 billion(0.1 ppb)-compared with the lowestdetectable concentration of helium of1 part per million above background.It was later found that on-line injectionsutilizing SF6 also allowed leaks as smallas one gallon per day to be detected.

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Analyzer to Detect SF6 in

Condenser Off-Gas

In the early 1980s, EPRI sponsored thedevelopment of an analyzer to detect thepresence of SF6 in condenser off-gas.

Known as the FluorotracerTM

Analyzer, itwas based on mass spectrometer technol-ogy. Figure 7(a), FluorotracerTM Analyzer,is a general view of the SF6 analyzer,while Figure 8 provides a schematic flowdiagram of a sampling system.

For the analyzer to detect the presenceof tracer gas in the received sample, it isimportant that it be free from both mois-ture and free oxygen. This diagramshows how the off-gas sample is firstcooled, then shows how the moisture isremoved in a water trap and passedthrough a dessicant tower to remove anyresidual moisture. The diagrams alsoshow how the sample is finally receivedby the analyzer.

To remove any oxygen contained in thesample from the off-gas system, hydrogengas is introduced into the sample stream,

entering with the sample into the catalyticreactor, where a chemical reactionoccurs between the oxygen and hydro-gen. The moisture is removed by anotherwater trap and dessicant tower.

The dried sample gas is then pumpedinto an electron capture cell, where itpasses between two electrodes and isionized by a radioactive foil. Ionized

nitrogen in the sample supports a currentacross the electrodes, the current levelbeing reduced in proportion to theconcentration of SF6.

Figure 7(a) FluorotracerTM Analyzer

Figure 8

Figure 7(b) SF6 Pak

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An analyzer for use with SF6 as a tracergas is commercially available for use inboth fossil fuel and nuclear generatingstations. The analyzer is also providedwith an SF6 dispenser (shown in Figure

7(b) SF6 Pak.) Weighing approximatelyeight pounds, the flow of the dispensercan be adjusted to obtain the SF6concentration needed to perform theleak detection task under current plantconditions.

Tracer gas leak detection involves atime delay between the injection of thegas and the response shown on the strip

chart recorder connected to the massspectrometer. It should be noted that,while the indicators mounted on the caseof the mass spectrometer display theinstantaneous values of the measure-ments, they are difficult to interpretwithout the addition of a trace from astrip chart recorder. A typical exampleis shown in Figure 9.

The information available from the

recorder chart not only provides a hardcopy for future use, but also tells techni-cians when they are getting close to aleak; when they have passed the leak;when they have located the leak; whetherthe gas is traveling to another leak; or,whether the leak is closer to the outletend. Whether a valve is leaking at thepacking, as opposed to the flange, canalso be determined.

SF6 can be used whenever helium isused; however, the reverse scenario isnot true. The following are among thefactors that go into the choice of tracergas for a given situation:

Air inleakage into the unit.If the unit has more than 10 ft3/minof air inleakage, either tracer gasmay be used. If the inleakage is lessthan 10 ft3/min, then SF6 should

be used.

Dissolved oxygen (DO).The standard procedure for searchingfor the cause of DO leakage belowthe water line is to use SF6.

Unit turbine power. If the unitis running at 20 percent or greaterturbine power, either tracer gas maybe used. If the unit has no turbinepower and cannot be brought up toany level of turbine power, then

helium should be selected.

Unit size. Inspections of units of lessthan 50 MW capacity should alwaysuse helium.

Figure 9

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Air inleakage inspections are best pre-ceded by a test shot to establish the levelof any background contamination andto ensure the instrumentation is function-ing correctly. It is recommended that all

air inleakage inspections begin on theturbine deck, usually starting with therupture disks. When on the mezzaninelevel, the tester should start sprayingtracer gas at the condenser and workoutward along the hood, the expansionjoints, and other potential sources of airinleakage.

It is important to keep track of everythingthat is sprayed with the tracer gas.

During a typical air inleakage inspection,it is not uncommon to spray tracer gason literally hundreds of suspected leak-age paths within the condenser vacuumboundary.

In order to isolate a leak as quickly aspossible, technicians should know wherethey have been and what they haveseen. If a large leak is found on the man-

way on, say, the west side of the turbine,an indication of this must be made on thestrip chart recorder. When the techniciangoes to the west side of the condenserand sprays a suspected penetration intothe condenser on the mezzanine level,the large leak could very well cause anerroneous indication of leakage there.Technicians can also waste a lot ofinspection time searching for a leak thatthey have already found on the turbine

deck. This is another reason the responsetime must be known.

Once the inspection results are in, it isimportant to understand what can andcannot be done with them. A leak detec-tion program is useful only if there is afollow-up repair program. Both SF6 and

helium detectors give readouts, one inmillivolts, the other in an arbitrary scale.

Plant personnel can determine a planof action to repair the leaks after compar-

ing millivolt or scale readouts. These arerelativevalues, not calibrated in engi-neering units such as ft3/min. It is of noimportance to have exact leakage values.

Generating stations already know whattheir totalair inleakage is. Because of themargin of error due to all the variables ofa condenser under vacuum, quantifyingleaks does not add any information towhat the plant personnel already know.

Therefore, it is not cost-effective. What isuseful is the exact location of each leakand its subsequent repair and retest.

When the turbine is not under power, itis very likely that the background concen-tration of the tracer gas will become sohigh that it eliminates any chance ofisolating a leak. Both air inleakage andcondenser tube leakage inspections

require vapor flow to carry the tracergas out of the condenser with the rest ofthe non-condensibles.

If a sprayed tracer gas is sucked into thecondenser, it will begin to accumulate,and the background concentration willrise and saturate the detectors. There aresome occasions when, in an effort tobring a unit back up on-line as soon aspossible, a station has no choice but to

attempt a tracer gas inspection with theunit shut down, and many have beensuccessful in doing so. However, aminimum 20 percent turbine power isrecommended in order to perform atracer gas inspection effectively.

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CONCLUSIONThis White Paper has provided examplesand guidelines to help you understandthe factors that impact a return on invest-ment analysis. These illustrations focus on

the basic components necessary to under-stand a simple ROI analysis when consid-ering the payback for regular condensermaintenance within your plant.

In summary, it is about operating efficien-cy within your plant systems doingmore with less. While it is difficult toassign a hard number to improving yourplants operating performance, you cancertainly calculate how much annual

revenue is at risk should you fail to keepyour systems operating at peakperformance.

When you are ready to investigateregular maintenance systems andoptions, we recommend that a moredetailed assessment be performed specific to your plants uniquerequirements.

REFERENCES

1. Putman, R.E., (2001), Steam SurfaceCondensers: Basic Principles,Performance Monitoring andMaintenance, publ. May 2001,

ASME Press, New York, NY.

2. Condenser Inleakage Guideline, EPRIReport TR-112819, publ. EPRI,January 2000.

3. Putman, R.E. (2001), Ibid, Chapters2 thru 6.

4. HEI (1995), Standards for SteamSurface Condensers, 9th. edition,

publ. Heat Exchange Institute,Cleveland.

5. ASME, (1998) Performance TestCode for Steam SurfaceCondensers, ASME PTC.12.2-1998,publ. American Society ofMechanical Engineers, New York,NY.

6. Putman, R.E. (2001), Ibid, pp. 75-76.

7. EPRI, (1994), Instrumentation of theOn-Line Condenser Fouling Monitor,EPRI Technical Report TR-109232.

CONCO SYSTEMS, INC.

530 Jones StreetVerona, PA 15147 USAPhone: 412-828-1166Fax: 412-826-8255www.concosystems.cominfo@ concosystems.com

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return investment analysis economics regular condenser maintenance

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