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Pag9

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Thefollowingconditionsmustbemaintainedinordertoeliminatethem:

• Ryznarindex= 2 pHs‐pHcbetween6and 7. Where pHsisthe pH ofsaturationand pHc isthetrue level

measuredinthecircuit.

• Theproductofsulphatesand calciumconcentrationinthe ci

rcuitwater,(bothexpressed inmg/lCo3 Ca),

shouldbelessthan500,000.

• Silicacontentshouldbelowerthan150mg/l.

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6.2.1.2 Suspendedsolids.

 These can be brought into the secondary circuit of the cooling tower by the make‐up water, by the air or by

contaminationduringtheproces

s.

 Inthesecondarycircuitofthecoolingtowers,100to150p.p.m.ofsuspendedsolidscanbeadmitted.

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6.2.1.3 Biologicalgrowth

 Theambientconditionsexistinginacoolingtowerfavourbiologicalgrowth.

 It is usually necessary to periodically treat circuits with chlorine and/or other biocides in order to pr

event these

growths.

 Treatmentofthiskindisparticularlynecessarywhenthecircuitmight suffercasual(accidental)pollutioncausedby

processfluids,ashappensinrefineries,sugarrefineries,etc..

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6.2.2 Corrosion

BesideskeepingtheRyz narindexinthestableorslightlycorrosivezone,corrosioninhibitorsmustbeaddedtothesecondary

rcuit.Severalvarietiesarecommerciallyavailableandthemostsuitableshouldbeselectedinconsultationwithspecialized

firms.

Theaboveleadstoalimitationonthemaximumnumberofconcentrationsacceptableinthesecondarycircuit.

Thenumberofconcentrationsiscalled"ConcentrationCycles"andisrepresentedbytheletterN.

Ifwec

all:

E:Evaporatedwaterflowinthetowerasapercentageofnominalwaterflow.

P:Totalblowdown(driftintowerpluslossesincircuit plusdeconcentrationblowdown) asapercentageofnominal water

flow.

Thefollowingratiosareobtained:

Averagemake‐upwaterflowasape

rcentageofcirculatingwaterflow:

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

1

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Totalblowdownneededinthecircuitasapercentageofcirculatingwaterflow:







1

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Whichareusedtocontrolthenumberofconcentrations,usuallydeterminedbydividingtheconcentrationofchloridesinthe 

circuitbythechloridesinthemake‐upwater.

Nvalues(ConcentrationCycles)higherthan5(five)arenotusuallypractical,evenwhenthemake‐upwaterqualityisgood.

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ALWAYS MAKE SURE THAT ANY PRODUCT USED FOR WATER TREATMENT AND CLEANING IS COMPATIBLE, AND IN THE PROPER

CONCENTRATION,WITH THEMATERIALSOFTHEUNIT(GALVANISED STEEL,PP,STAINLESSSTEEL, ETC)ANDWILLNOTDAMAGETHE

COMPONENTSOFTHEUNITITSELF

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 6.3 Electricallocking

Toensurethis,werecommendthatakey‐operatedstopswitchshouldbefitted,makingitimpossibletooperatewhenthekeyisnotin

thelock.

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VERYIMPORTANT!BEFOREREMOVINGTHEFANGUARDORTHEACCESSDOORTOTHEMECHANICALEQUIPMENT,INORDERTOCARRY

OUTMAINTENANCEOPERATIONS,ALWAYSMAKEABSOLUTELYSURETHATTHEFANISSTOPPEDANDTHATITCANNOT BERESTARTED

UNTILTHESEOPERATIONSHAVEFINISHED.

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6.4 Coldweatheroperation

 Coolingtoweroperationattemperaturesbelow0°Cmightgiverisetotheformationoflayersoficeattheairintakes.

 Iceformationcanbereduced,andevenprevented,bytakingthefollowingmeasures:

 • Installheatingresistancesandalevelsensor

 • Addanantifreezesolutionintheprimaryci

rcuit

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