che 0611 handle steam more intelligently

8/2/2019 Che 0611 Handle Steam More Intelligently

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The dramatic jump in petroleumand natural prices over the re-cent years has created much im-petus to reduce operating costsat chemical process plants. In

processes that use either oil or gasfor feedstock, such reduction can comeeither from improved energy-usagemethods or from yield improvements.In either case, the plants steam re-

source is often a primary provider ofheat or thermodynamic energy to aprocess. Profit gained from reductionof energy costs through more effectiveuse of steam affects the bottom line inmuch the same manner as the profitgained through production improve-ment.

Indeed, in some cases the relation-ship of productivity improvement isdirectly tied to a more effective useof the steam supplying the process.This relationship can hold for not

merely petrochemical plants but alsofor ones that employ non-petroleumfeedstocks.

Back to basicsThe steam circuit can be divided

into four basic areas;Generation(boiler,waste-heatsteam

generator or flash vessel)Distribution (transportation, tur-binegenerators,andsteam-letdownstrategy)

Use (stripping, process heating,turbine drive, furnace atomization,tracing, flaring, HVAC, other)

Condensate return (recovery of

thermalenergy andtreatedwater;reduction of environmental impactorcostsforsewertreatment)

In todays typical process plants, con-densate return provides an especiallyfruitful opportunity for improving en-ergy efficiency, and much of this ar-ticle focuses on that area.

To be the most effective, steam gen-erally needs to be dry (such as forprocess usage), or superheated (forinstance, for use in turbines). Theserequirements dictate utility-system

operating procedures to generate thehighest quality steam possible, andthen distribute it to the points of usewithout deterioration. Since steambecomes condensate after its heatenergy is expended, strategies mustbe in place to remove condensate asquickly as it is formed, in the steam-supply portion of the circuit and dur-ing steam usage alike.

Furthermore, superheated steam istypically desuperheated by injectinghot condensate into the system. As

a result, excessive wetness can alsooccurdownstreamofthedesuperheat -ing station. In either case, if suchcondensate is not removed from thesteam supply, the negative impact onthe steam system can be substantial.

Possible outcomes of not removingcondensate from a steam supply orprocessincludethefollowing:Lossofyield;entrainedwaterdoes

not carry as much heat to a processas does steam

Damagetonozzles;entrainedwatererodes nozzles, and can adversely af-fect vacuum generation or atomiza-tion

Loss of power; entrained watercauses turbines to operate less effi-ciently

Increase maintenance loading;water hammer can damage equip-ment such as turbine blades andcontrol-valve packing

Increased safety risk; water ham-mer can injure personnel

Poor process control; flooding ex-changescanleadtocontrolswingsAt many plants, the operators ad-

mittedly realize that condensate must

be removed as quickly as it is formed,but a suitable condensate drainage ortransportation system is not in place.In such cases, the condensate is oftenseweredorsenttoafielddrain.Somepossible outcomes of thus removingcondensate but not handling it effec-tively include these;Profit loss due to waste of heated

and treated condensateThe extremely wasteful effect of

opening bypass valves around pro-cess equipment or turbines to pre-

ventwaterloggingordamageA possible increase in system cor-

rosion because too much makeupwatermustbetreated

Condensate is traditionally removedfrom steam systems by steam traps orby equipment combinations involvinglevel pots and outlet control valves. Insomesituationsinwhichhighback-pressurefromthedownstreamportionof the condensate-return system tendsto create a stall, a different systemincorporating both a pump and trapin the design are needed, to drive thecondensate while also trapping thesteam; this process may be referred to

Feature Report

James R. Risko

TLV Corporation

Feature Report

44 ChemiCal engineering www.Che.Com november 2006

With fuel prices at high levels,

the diverse energy-conservation techniques

outlined in this article make more sense than ever Figure 1. Improving the quality ofwaste heat generatoe steam

Handle SteamMore Intelligently


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aspump-trappingorpower-trapping.Because there are thus at least three

condensate-drainage alternatives, itmakes more sense to think in terms ofrequired condensate discharge loca-tions rather than referring to conden-sate removal devices indiscriminatelyas steam traps. This mind-set helpsavoid any predisposition to installsteam traps even in applications thatneed a different type of condensatedrainage solution.

Engineered separator-drains, such

as the one in Figure 1, remove con-densate that is entrained in a mov-ing steamsupply (including flashorregenerated steam). The result ishighest quality steam delivered forplant use. On the other hand, steamtraps remove condensate that has al-ready fallen out of the steam. By theirname, steam traps remove condensateandtrap steam. Level pots canbeusedincertaininstanceswheresteamtraps can not meet the high pressureor capacity requirements.

There can be many situations ina plant where effective condensateremoval requires specialized drain-age designs. For instance, Figures 2a

and2bshowtwooptionsforconden-sate drainage from jacketed pipe thatconveys high-melting-point materials,such as liquid sulfur or high-boilinghydrocarbons

Other examples of specialized appli-cations include options to effectivelydrain steam-heated heat exchangers.

A key consideration is to first deter-minewhetherastallconditionexistsornot;whenitdoes,condensatewillnot drain effectively through a simplesteamtrap.Suchasituationtypically

arises whenmodulating steam pres-sure creates a negative pressure dif-ferential across the condensate draindevice. So-called Type II secondarypressure drainers of the pump-traptypeareusedonequipmentwithneg-ativepressuredifferential(Figure3),whereasType Isecondarypressuredrainers of a pump only type areusedtorecoverandpowercondensateagainst an even higher-backpressurecondition(Figure4).

Stop the bleedingIt has become such a habit in someplants to open bleed valves that it isalmostimpossibletowalkthroughthefacility and not find multiple sourcesof steam being bled to atmosphere.For example, many operators tend toopen bleed lines in an effort to pro-tect equipment from overheating orto obtain higher product throughput,product consistency, or line fluidity.In almost every case, bleeding steam

is a symptom of an improper

drainage design at the givencondensate-discharge loca-tion. There is usually a causal

relationshipwithpooroperationofaprocess. Typical areas to search forsteam bleeds include process heatexchangers (under stall condition),steam tracers on high-temperaturelines or jacketed pipe, and turbinesupply lines.

Hidden bleeding of steam at a pro-cess heat exchanger is usually themostdamaging.Thiscanoccurwhen-ever a bypass line is opened aroundequipment in order to maintain pro-cess throughput. The bleeding may

ChemiCal engineering www.Che.Com november 2006 45

Figure 2. Preferred method to drain jacketedpipe for high temperature fluids such as sulfur

Figure 2. Alternative, practical re-designmethod for existing installations to drain jack-eted pipe for high-temperature fluids such assulfur (No Stall)

Part 1

Figure 3.Trapping steamheat exchangerswith continouspositive pressuredifferential across

drain device


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be invisible to those in the area, but itcontinues daily nevertheless. In suchinstances, the production rate may bemaintained, but the cost of the steam

input is usually far greater thanneeded. Such a losswill often occurcontinuously until an improved designsolution is implemented.

With respect to bleed lines at the in-lets to a turbines, plant personnel are inmany cases so concerned about turbinetripsduetowaterdamagethatthefeelthat opening bleed valves at the inlet isonlywaytoremovepotentiallydamag-ing condensate. As for pipe tracing or

jacketing, in many cases it turns outthat the low-first-cost original design

did shave the installation cost, but attheexpenseoffrequentwaterlogginginthe jackets, so, the bleeders are openedto remove the condensate and improvetheproductflow.

In virtually all cases of bleed steamon the above applications, it is bet-ter to find the cause of the need-to-bleed steam in the first place, so thatan improved drainage solution canbe installed to reduce steam loadingwhilemaintaining or improvingper-formance. Bleed steam is costly.

Incidentally, plant air systems inmany plants incur the ill consequencesof excessive air-bleed loss for similarreasons. Often, the cause of bleedingplant air is that the drainage devicescease operating, due to contaminantsin the system. An improved condensatedrain design for the air system usuallyprovidesnoticeablegains(Figure5).

SteamtrapmanagementHow long should steam traps last?Somecompaniestalkof4%trapfail-

ure rates. For amature plant, how-ever, that figure implies, on average, a25yeartraplife!Isitreallyexpectedthat an entire steam trap populationwillsurvivethechallengingenviron-mentofaprocessplantfor25yearsonaverage?Suchstatementsindicatethe need for a measurable method toquantify trap population life. Onesuch method is to total all replacementtrap purchases over one 12 monthperiod, then add this amount to thechange in trap failures recorded from

theprevioussurvey,while correctingall values to an annual basis. The ad-ditionofnewlyfailedtrapstoreplaced

trapsoverayearperiodwillprovidean estimate of the annual failure rateof a site.

For a site that has not had a pro-active trap management programwith annual surveys and repair, itisnotuncommontohave50%ofthetrappopulation(ormore)inacurrentstate of failure. If those failures areequallydividedbetween failed openorfailedshut,thenabout25%ofthepopulation can be leaking steam.Even with a simple steam-loss es-

timate of $1,500 per trap leakage,multiplying the failed-leaking trappopulation by a leakage estimate canquickly make a good case for remedy-ing the situation. At least one trapmanufacturerprovidessoftwarethatcan clearly estimate the value ofleaking steam from a failed steamtrap.Suchsoftwarecanprovidedatathat will justify the cost of settingup maintenance response on a cost/return basis. Basic summary valuesfrom a condition-monitoring program

Feature Report


Figure 5.Recoveringand ReturningValuable Con-densate to theBoiler

Figure 4. Power-trapping steam heat ex-changers with possible negative pressure differ-ential across drain device (stall)


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for the steam-trap population at oneprocess plant appear in Table 1.Decisions regarding Out of Ser-

vice or No Service traps can bemade based on the expected trap con-dition. If the steam service is turnedon but a given trap is found to havebeen valved out, then that trap isprobablyfailedinaleakingmode(ifthetrapwereinsteadblocked,therewouldusuallybenoneedtovalveitout). If the steam service is insteadturned off (perhaps during a turn-

aroundorwhenwinterizationsteamis not needed) then the trap conditionisunknown.Forunknown-conditiontraps, it is usually common to assumea failure rate comparable to that fortraps of known condition in similarapplication service.Surveyanalysiscanalsobeusedto

select effective maintenance responserecommendations. When setting upsuch a program, the plant manage-ment should assign threshold valuesthatsignalwhenaleakingtrapisto

be replaced, and that also provide anestimate of the replacement valueassociatedwithatrapbeingblocked(Table 2).Then, theplant canapply

the threshold values each individualtraps diagnosis to determine themaintenance decision. Based on suchaprograminaction,Table3demon -strates how a simple spreadsheetanalysis using IF/THEN statementscan provide a recommended actionfor each steam trap location. Thestrategy underlying this spreadsheetanalysisisasfollows:IFthe$Lossis greater than the Threshold Valueon leaking steam traps, THEN re-placethetrap;OTHERWISE,noac -

tion is to be taken.Much attention is focused on re-

placement of leaking traps; and forgood reason. Steam-trap leaks, likeother instances of leaking steam, rep-resentthelow-hangingfruitofaplan -tsite for quick, high return opportu-nity.However,additionalsavingscanbe gained by evaluating the reliabil-ity record of the entire installed trappopulation. At some process plants,historical maintenance and surveyrecords provide adequate data; and

once annual surveys are conducted,therewill bea factual record of thesites trap failures. Then,when thetotal failures (those corrected, plusthose just surveyed but not yet cor-rected) over the testing period add upto the total trap population, then thetrap population has turned one time,in a manner analogous to inventoryturns.Usingsuchamethodwillpro -

vide one method to measure trap life.Such analysismay,of course lead tothereplacementofexistingtrapswith

more-reliable versions.

Dont ignore cold trapsIn light of that the just-mentionedhigh return opportunity with leak-ing traps, plants tend to give higherpriority to replacing such steamtrapsthantodealingwithblockedorcold steam traps. But a cold steamtrap can be a harbinger of an immi-nent disastrous event. There havebeen caseswhere cold traps and,therefore, cold condensate-dischargelocations caused critical turbinesto go out of service, or caused maincompressorstoshutdownaplantfor


Table 1. Condition of installed steam trap population

Cy Qy pc my l

Failed Blowing 124 5.0% $243,025

Leaking 307 12.5% $211,700

Blocked 179 7.3% $0

Low Temp. 294 12.0% $0

Total 904 36.8% $454,725

Good 1180 48.1% $0

Unknown Condition 371 15.1% $0

Total 2455 100.0% $454,725

Table 2. threshold Values for replaCement options withBudget alloCations

Budget replaCement threshold Values

a Bck t rc V $1,500

lk t rc t

Pressure Annual Value $

650 psig $1,600

250 psig $800

150 psig $800

< 50 psig $600

Figure 6. Draining compressed airequipment with contaminants in air line


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days. Keep in mind that the origi-nal designer of the system decidedthat the installed condensatedrainpointwithasteamtrap

to drain was needed to main-tain the desired performance andsafety of the system.

In short, all cold traps should berepaired or replaced. If, in someinstances, it truly seems that atrap is not needed at the intendeddischarge location, then a propermanagement-of-change (MOC)procedure should be executedto permanently remove the trapfrom service. The MOC must care-fully considers all potential conse-

quences of such an action, and assurethat the removal of the drain point isan absolutely safe decision.Keep in mind that technology is notfrozen in time. Plants must increas-ingly develop more-efficient ways tomanage their the steam trap popu-lations. Best practices should be re-viewedandmodified (if appropriate)at once or more often per year to selectthe most effective condensate drainagedevice for the discharge location. Atleast one trap manufacturer offers an

annualservicetoreviewapplications,withup-to-date recommendations forbest practices consideration. Engi-neering consultants may also be fruit-ful sources for improved condensate-drainage practices.Balances and auditsWhile better condensate managementis indeed the most promising strategyfor improving steam-system efficiencyat todays typical process plant, pe-riodic review of the facilitys overall

steam balance can in many cases un-cover unanticipated opportunities forimprovement. For one thing, the steambalancenotonlytracksthesteamflowper se, but also can be useful for spot-tingnewloadimbalancesthatmaybeamenable to re-balancing to save ventsteam.

For example, one primary goal isto always seek a use for otherwisevented/wasted steam. One suchusemight be pre-heating of a nearby fluid.

Another example consists of incorpo-rating pump-trap technology, in orderthatlow-pressuresteambecomessuit-able for some heat exchange equip-

ment that previously could use onlymedium-pressuresteam.Suchpower-trapping the condensate preventsequipment flooding when low pres-sure steam is used, and can improvethe system yield and availability.

In still other applications of the

steam balance, an evaluation of thefirst and second (highest and next-highest) steam pressures can helpidentify expensive missing steam amajorportionofwhichcanoftenbereadily recovered. In many instances,this missing steam is the result ofleaking high-pressure steam traps forwhichanimmediatereplacementor repair can be readily justified at thefirstavailableopportunity(Figure6).

For practical information on settingup and maintaining a steam balance,

seeSteamBalancesSaveMoney,CE,July2004,pp.3641.

A related valuable exercise is an

audit of all the plants condensate.Whereas it may not have been cost-effective to recover certain sources oflost condensate in the past, todayshigh energy prices may have tiltedthe scales. With every rise in energyprices, particularly of Fuel Oil Equiva-

lents(FOES),itbecomesimportanttoevaluate every potentially collectedsource of condensate on a cost/returnbasis, to determine if installing a re-covery system may have become jus-tifiable.

Capital or expense budgets?An all too common situation arises inprocess plants: An energy-efficiencytaskforce uncovers an opportunity,but there is no funding to support therequired improvement project. And in

those caseswhere fundingdoeshap-pen to be available, the money is in amaintenance budget and, therefore,

Feature Report


Table 3. maintenanCe response deCisions

t ac p t r #/. $ l ac

Trap 1 Drip 650 Small Leak 23.2 $1,837 Replace

Trap 2 Drip 650 BLOWING 133.92 $10,605 Replace

Trap 3 Drip 250 BLOWING 77.12 $4,810 Replace

Trap 4 Drip 250 Large Leak 50.46 $3,147 Replace

Trap 5 Tracer 250 Medium Leak 21.21 $1,323 Replace

Trap 6 Drip 150 Small Leak 14.13 $962 Replace

Trap 7 Tracer 50 NOT IN S 0 $0 -

Trap 8 Drip 50 BLOCKED 0 $0 Replace

Trap 9 Drip 50 Large Leak 25.66 $1,011 Replace

Trap 10 Tracer 50 Medium Leak 18.98 $748 Replace

Trap 11 Tracer 50 Small Leak 6.11 $241 -

Trap 12 Drip 25 BLOCKED 0 $0 Replace

Leak ValueBlocked ValueTotals

370.79

$24,684$3,000$27,684

Figure 7. Install Traps DesignedSpecifically for Use on HP Super-heated Steam Lines


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saddledwithvariousconstraintsthatlimit the amount of investment thatcan be made.

One alternative consists of estab-

lishing special energy-improvementbudgetsinstages,withstrictrequire-ments that expected gains be realizedat any given stage before additionalfunds are released. Such a stagegate release approach can providenecessary funds to improve a plantperformance.

A companys financial teams maywanttoevaluateenergyprojectsex-pectedreturnwithotherperformanceprojects to select the best return oninvestment.Somesteam-systemim-

provement projects do meet capital-funds requirements, and can improveaplantsprofitabilitywhileachievinga desired reduction in operating costs.Focused business/energy consultantsand individuals with Certified En-ergyManager (C.E.M.) training canhelp evaluate the financial aspects ofa particular project to determine fea-sibility for the site.

Final thoughtsWell-run process plants consider all

input resources in their operating-cost analyses. Some resource costs,notably plant labor, generally do notincur drastic changes from year toyear. Other resources, like energyor steam, are closely tied to the costof a FOE. While much effort may beexpended to obtain a more economicsupply of fuel or energy, profit canalso be achieved at most plants froma focused effort to improve the steamsystem quality. n

Edited by Nicholas P. Chopey


AuthorJames R. Risko, C.E.M., isthepresidentofTLVCORPO-RATION,13901SouthLakesDrive,Charlotte,NC, 28273;Phone:(704)597-9070;Email:[email protected], vice president forsales, and national salesmanager. He is active in theFluid Controls Institute, andhas previously served as the

organizationsChairman,StandardsChair,andChairoftheSecondaryPressureandSteamTrapSections. Heis adually-certifiedenergyman-ager(A.E.E.&NCSU),andholds twoB.S.de-

greesfromKutztownUniversity,Kutztown,PAin Mathematics/Education and Business Admin-istration/Accounting. He also holds an M.B.A.fromWilkesUniversity,WilkesBarre,PA.

che 0611 handle steam more intelligently

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