Essential Essential Cooling Tower Cooling Tower

TreatmentTreatment

Why Treat The Water?Why Treat The Water?

•To Control CorrosionTo Control Corrosion

•To Prevent ScaleTo Prevent Scale

•To Control Algae and Bacterial GrowthTo Control Algae and Bacterial Growth

•To extend equipment life and efficiencyTo extend equipment life and efficiency

What’s Wrong with Water?What’s Wrong with Water?•Water is a natural solvent, it dissolves thing.Water is a natural solvent, it dissolves thing.

•Natural waters contain significant amounts of Natural waters contain significant amounts of minerals like calcium and magnesium.minerals like calcium and magnesium.

•Natural waters typically contain significant amounts Natural waters typically contain significant amounts of oxygen.of oxygen.

•Water, particularly warm water, is a great Water, particularly warm water, is a great environment for living micro-organismenvironment for living micro-organism

What are Solids?What are Solids?•Any material that is or becomes dissolved in water Any material that is or becomes dissolved in water is referred to as a dissolved solid, or is referred to as a dissolved solid, or solidssolids..

Common Dissolved Common Dissolved SolidsSolids

•Calcium and Magnesium Calcium and Magnesium Salts, aka Salts, aka HardnessHardness•IronIron

•CopperCopper

•SulfatesSulfates

•PhosphatesPhosphates

•Silica and SilicatesSilica and Silicates

More about SolidsMore about Solids

Typical Conductivity in parts of Missouri, Typical Conductivity in parts of Missouri, Arkansas and KansasArkansas and Kansas

The measure of all of the solids in a sample of The measure of all of the solids in a sample of water is its Conductivitywater is its Conductivity..

St. LouisSt. Louis 430 micro Siemens430 micro SiemensKCMOKCMO 480480Little RockLittle Rock 440440St. JoeSt. Joe 700700ColumbiaColumbia 480480LenexaLenexa 530530Cape GirardeauCape Girardeau 500500JonesboroJonesboro 540540

Another name for Conductivity Another name for Conductivity is is Total Dissolved SolidsTotal Dissolved Solids. Both . Both are a measure of total mineral are a measure of total mineral content, but they differ in units. content, but they differ in units. TDS is expressed in parts per TDS is expressed in parts per million and Conductivity is million and Conductivity is expressed in micro Siemensexpressed in micro Siemens

Not All Solids Are AlikeNot All Solids Are AlikeSome solids are more problematic than others. Two of the most important Some solids are more problematic than others. Two of the most important solids in water treatment are solids in water treatment are Calcium Carbonate and Magnesium Calcium Carbonate and Magnesium CarbonateCarbonate, aka , aka HardnessHardness

HardnessHardness•Is naturally occurring in most all watersIs naturally occurring in most all waters

•Account of nearly 40% of the Conductivity in natural Account of nearly 40% of the Conductivity in natural waters in the Midwestwaters in the Midwest

•Is the primary component of white scale depositsIs the primary component of white scale deposits

•Becomes less soluble as water gets hotterBecomes less soluble as water gets hotter

Cycles of ConcentrationCycles of Concentration

1 Cycle1 Cycle

When water evaporates is leaves it solids behind. If you completely When water evaporates is leaves it solids behind. If you completely evaporate a sample of water and then refill the container with the same evaporate a sample of water and then refill the container with the same water the mineral content doubles. This is called water the mineral content doubles. This is called Cycling UpCycling Up..

More on CyclesMore on CyclesWhen water evaporates is leaves it solids behind. If you completely When water evaporates is leaves it solids behind. If you completely evaporate a sample of water and then refill the container with the same evaporate a sample of water and then refill the container with the same water the mineral content doubles. This is called water the mineral content doubles. This is called Cycling UpCycling Up..

As cycles increase the amount of solids As cycles increase the amount of solids increaseincrease. .

This means:This means:

•The Conductivity increases.The Conductivity increases.

•The total hardness increasesThe total hardness increases

•The pH will go up as the alkalinity increasesThe pH will go up as the alkalinity increases

•The risk of scale formation increasesThe risk of scale formation increases

Still More on CyclesStill More on CyclesIn a cooling tower system, evaporation is the main means to remove In a cooling tower system, evaporation is the main means to remove heat. This evaporation causes the water to heat. This evaporation causes the water to cycle upcycle up, or increase in , or increase in mineral content. mineral content.

The cycles of concentration in a cooling tower system The cycles of concentration in a cooling tower system are limited via bleed-off. The cycles limit is based on:are limited via bleed-off. The cycles limit is based on:•The Conductivity of the makeup waterThe Conductivity of the makeup water

•The Total Hardness of the makeup waterThe Total Hardness of the makeup water

•The Total Alkalinity (pH) of the makeup waterThe Total Alkalinity (pH) of the makeup water

•The heat load or temperature differential of the systemThe heat load or temperature differential of the system

•The type of water treatment chemistry usedThe type of water treatment chemistry used

Bleed Off is the removal of high Conductivity water in favor of low Bleed Off is the removal of high Conductivity water in favor of low Conductivity makeup. Bleed off generally based on TDS or Conductivity. Conductivity makeup. Bleed off generally based on TDS or Conductivity. This is because the maximum hardness or alkalinity of a given water is This is because the maximum hardness or alkalinity of a given water is relative to its Conductivity. relative to its Conductivity.

Bleed OffBleed Off

A Conductivity Controller and a Bleed Valve are generally A Conductivity Controller and a Bleed Valve are generally used to control cycles. It follows this process:used to control cycles. It follows this process:•Sensor continuously measures the Conductivity of the tower water. Sensor continuously measures the Conductivity of the tower water.

•If the Conductivity is higher than the maximum, the bleed valve is opened. If the Conductivity is higher than the maximum, the bleed valve is opened.

•Bleed off removes high Conductivity water and forces the system to Bleed off removes high Conductivity water and forces the system to makeup low Conductivity raw water. makeup low Conductivity raw water.

•Bleed off continues as it dilutes the Conductivity is the system, until the set Bleed off continues as it dilutes the Conductivity is the system, until the set point is satisfied.point is satisfied.

ScaleScaleScale is the formation of mineral deposits. It can occur in any Scale is the formation of mineral deposits. It can occur in any area that experiences heat transfer or evaporation. Solids area that experiences heat transfer or evaporation. Solids precipitate when they reach the limit of their solubility; when precipitate when they reach the limit of their solubility; when there is more of a solid than the water can keep dissolvedthere is more of a solid than the water can keep dissolved

Common ScalesCommon Scales•Calcium / Magnesium Carbonate - Lime ScaleCalcium / Magnesium Carbonate - Lime Scale•Calcium / Magnesium PhosphateCalcium / Magnesium Phosphate•Calcium / Magnesium SulfateCalcium / Magnesium Sulfate•Calcium / Magnesium SilicateCalcium / Magnesium Silicate•SilicaSilica

Understanding Understanding Scale ControlScale Control

Scale Control works by changing the scaling solids to more Scale Control works by changing the scaling solids to more soluble solids, using water treatment chemistrysoluble solids, using water treatment chemistry

Assuming that the Conductivity is under control, scale Assuming that the Conductivity is under control, scale can be prevented by:can be prevented by:

Converting calcium carbonate to more soluble calcium Converting calcium carbonate to more soluble calcium phosphates and phosphonatesphosphates and phosphonates

Keeping calcium phosphates part or “dispersed” through Keeping calcium phosphates part or “dispersed” through the use of polymersthe use of polymers

Keeping calcium carbonate dispersedKeeping calcium carbonate dispersed

Keeping the pH and alkalinity in checkKeeping the pH and alkalinity in check

Key Points of Key Points of Scale ControlScale Control

Scale Control Hinges on a Few Key IssuesScale Control Hinges on a Few Key Issues

Understanding the mineral content of the raw Understanding the mineral content of the raw waterwater

Proper and complete Bleed OffProper and complete Bleed Off

Maintaining system water alkalinity in “Scale Maintaining system water alkalinity in “Scale Safe” zoneSafe” zone

Consistent addition of scale inhibitorsConsistent addition of scale inhibitors

Consistent addition of scale dispersantsConsistent addition of scale dispersants

Corrosion BasicsCorrosion BasicsCorrosion is the deterioration of a metal due to Corrosion is the deterioration of a metal due to interaction with its environment. Corrosion requires interaction with its environment. Corrosion requires metal, oxygen and water.metal, oxygen and water.

In cooling tower systems, the water contains significant amounts of In cooling tower systems, the water contains significant amounts of air. The oxygen carried by that air reacts with the metal at the air. The oxygen carried by that air reacts with the metal at the surface and starts a corrosion cell. surface and starts a corrosion cell.

IronIron

WaterWateroxygenoxygen

The key to The key to preventing this is preventing this is keeping the oxygen keeping the oxygen from interacting with from interacting with with metal.with metal.

Corrosion ControlCorrosion ControlSince we can’t remove the oxygen from the tower water, Since we can’t remove the oxygen from the tower water, we must create a barrier between the metal and the water we must create a barrier between the metal and the water and oxygen.and oxygen.

IronIron

WaterWateroxygenoxygen

The protective layer The protective layer is thin and can be is thin and can be very delicate. very delicate.

There are three basic kinds of barriersThere are three basic kinds of barriers•PassivePassive

•PrecipitatedPrecipitated

•Film FormingFilm Forming

More on Corrosion ControlMore on Corrosion ControlThe protective barrier prevents the oxygen from The protective barrier prevents the oxygen from contacting the metal. Thereby preventing corrosion.contacting the metal. Thereby preventing corrosion.

Common Corrosion Common Corrosion InhibitorsInhibitors•MolybdateMolybdate

•PhosphatePhosphate

•PhosphonatePhosphonate

•ZincZinc

•AzolesAzoles

•NitriteNitrite

A combination of A combination of inhibitors is usually the inhibitors is usually the best approachbest approach

Crevice and Underdeposit Crevice and Underdeposit CorrosionCorrosion

When the metal is trapped under dirt, debris or scale it does not have When the metal is trapped under dirt, debris or scale it does not have normal access to corrosion inhibitors and the bulk water. This sets up a normal access to corrosion inhibitors and the bulk water. This sets up a specially recognized corrosion cell. Generally, chemical treatment does specially recognized corrosion cell. Generally, chemical treatment does not prevent or cure these corrosion issues.not prevent or cure these corrosion issues.

Hot Spots for Crevice and Underdeposit CorrosionHot Spots for Crevice and Underdeposit CorrosionUnder dirt collected in the sump of the tower or on tube sheetUnder dirt collected in the sump of the tower or on tube sheet

Leaking threadsLeaking threads

Good and bad weld jointsGood and bad weld joints

Under epoxy coatingsUnder epoxy coatings

Under seals and gasketsUnder seals and gaskets

Other Issues in CorrosionOther Issues in CorrosionAside from general corrosion, as previously described, Aside from general corrosion, as previously described, there are other forms of corrosion that are equally there are other forms of corrosion that are equally important.important.

Other Forms of CorrosionOther Forms of Corrosion

Galvanic - Corrosion between Galvanic - Corrosion between dissimilar or incompatible metalsdissimilar or incompatible metals

Stress Crack - Corrosion caused Stress Crack - Corrosion caused by mechanical stress such as by mechanical stress such as vibrationvibration

Flow Related - Cativation, and Flow Related - Cativation, and erosionerosion

None of these forms None of these forms of corrosion can be of corrosion can be controled chemicallycontroled chemically

Essential Cooling Tower TreatmentEssential Cooling Tower Treatment

Good Tower Treatment Good Tower Treatment Starts with :Starts with :Good Conductivity Control Good Conductivity Control Proper selection of treatment Proper selection of treatment chemicals based on makeup chemicals based on makeup water and operating conditionswater and operating conditionsConsistent Chemical Levels Consistent Chemical Levels for Maximum Protectionfor Maximum ProtectionConsistent and timely Consistent and timely monitoring of the water monitoring of the water chemistrychemistry

Good Tower Treatment Good Tower Treatment Ends with :Ends with :Clean condenser tubesClean condenser tubesGood heat transferGood heat transferMinimized corrosion of Minimized corrosion of piping and surfacespiping and surfacesExtended equipment lifeExtended equipment lifeAnnual PM, and CleaningAnnual PM, and Cleaning

Boiler Standby / Summer StorageBoiler Standby / Summer Storage

Proper Boiler Standby Storage IsProper Boiler Standby Storage Is

•Essential for the Longevity of the Boiler Essential for the Longevity of the Boiler

•Prevention of Corrosion during offline periodsPrevention of Corrosion during offline periods

•Preventative Maintenance, but Low MaintenancePreventative Maintenance, but Low Maintenance

•On going during standbyOn going during standby

Proper Boiler Standby Storage Is Proper Boiler Standby Storage Is NOTNOT

•Shutting off the boiler at the end of winterShutting off the boiler at the end of winter

•Draining the boilerDraining the boiler

•Something that is forgotten once startedSomething that is forgotten once started

•Costly or Time ConsumingCostly or Time Consuming

• Reduce treatment levels and blowdown heavily 2 days priorReduce treatment levels and blowdown heavily 2 days prior

• Increase bottom blowdown to remove mudIncrease bottom blowdown to remove mud

• Cool and drain, then wash down and refill (optional)Cool and drain, then wash down and refill (optional)

• Fill boiler to headerFill boiler to header

• Add oxygen scavenger, phosphate and alkalinity boosterAdd oxygen scavenger, phosphate and alkalinity booster

• Fire boiler at low fire until steam begins to formFire boiler at low fire until steam begins to form

• Close headerClose header

• Low fire boiler every 4 to 6 weeks to keep chemicals mixed and activeLow fire boiler every 4 to 6 weeks to keep chemicals mixed and active

Wet StorageWet Storagethe Techniquethe Technique

Wet StorageWet Storagethe Techniquethe Technique

Dry StorageDry Storagethe Techniquethe Technique

• Reduce treatment levels and blowdown heavily 2 days priorReduce treatment levels and blowdown heavily 2 days prior

• Increase bottom blowdown to remove mudIncrease bottom blowdown to remove mud

• Cool and drain, then wash downCool and drain, then wash down

• Open all drain plugs and inspection portsOpen all drain plugs and inspection ports

• Close heater and feedwater valvesClose heater and feedwater valves

• Using a fan circulate air through boiler to completely dryUsing a fan circulate air through boiler to completely dry

• Place trays of desiccate at 10# per 1000 gallons of volumePlace trays of desiccate at 10# per 1000 gallons of volume

• Seal all drain plugs and inspection portsSeal all drain plugs and inspection ports