BAC 3985C - Chemical Treatment Requirements

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SERIES 3000 COOLING TOWER
Bleed Rate
Inevaporativecooling,evaporationofasmallportionoftherecirculatingspraywater
asitowsthroughtheequipmentcausesthecoolingeffect.Asthiswaterevaporates,
theimpuritiesoriginallypresentremainintherecirculatingwater.Theconcentrationof
thedissolvedsolidsincreasesovertimeandcanreachunacceptablelevels.Inaddition,
airborneimpuritiesareoftenintroducedintotherecirculatingwater.Iftheseimpurities
andcontaminantsarenoteffectivelycontrolled,theycancausescaling,corrosion,
andsludgeaccumulationsthatreduceheattransferefciencyandincreasesystem-
operatingcosts,potentiallyshorteningtheusefullifeoftheequipment.Thedegreeto
whichdissolvedsolidsandotherimpuritiesbuildupintherecirculatingwatermaybe
denedasthecyclesofconcentration.Specically,cyclesofconcentrationequalthe
ratiooftheconcentrationofdissolvedsolids(forexample-chlorides,sulfates,etc.)inthe
recirculatingwatertotheconcentrationofthesamematerialinthemake-upwater.
• Inordertooptimizeheattransferefciencyandmaximizeequipmentlife,bleedor
blowdownasmallamountofrecirculatingwaterfromthesystem.Thiscontrolsthe
cyclesofconcentrationtomaintainthequalityoftherecirculatingwaterwithinthe
guidelinesgivenin Table 3,onpage 15.
• Replenishthe“bleed”waterwithfreshmake-upwater,therebylimitingthebuild-up
ofimpurities.
• Bleed/blowdown:
– Accomplishthebleedautomaticallythroughasolenoidvalvecontrolledbya
conductivitymeter.Thesetpointisthewaterconductivityatthedesiredcyclesof
concentrationandshouldbedeterminedbyacompetentwatertreatmentexpert.
– Alternatively,useableedlinewithavalvetocontinuouslybleedfromthesystem.
Inthisarrangement,adjusttherateofbleedusingthevalveinthebleedline.
Measuretherateofbleedbyllingacontainerofknownvolumewhilenoting
theduration.Checkthebleedrateandwaterqualityperiodicallytoensurethat
adequatecontrolofthewaterqualityisbeingmaintained.
NOTE: A proper water treatment
program, administered under the
supervision of a competent water
treatment specialist, is an essential
part of routine maintenance to
ensure the safe operation and
longevity of evaporative cooling
equipment, as well as other system
components.
NOTE: The solenoid valve and
conductivity meter must be
supplied by others. Evaporation is
proportional to the load and will
vary seasonally. BAC recommends
the use of a conductivity meter to
maximize water conservation.
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