Cooling Water Fundamentalsdev.chemtreat.com/.../2a-Cooling-Water-Fundamentals... · Cooling Water...

Cooling Water Fundamentals

Steel Industry Water Conference Clearwater Beach FLClearwater Beach, FLSeptember 12‐14, 2012

Raymond M. Post, P.E.Director Cooling Technology

[email protected]

Outline• Types of Cooling Systems

– Once through – Closed Loop– Open‐recirculating

• Cooling TowersCooling Towers– Physical Design– Heat TransferC li C t ti R ti– Cycling or Concentration Ratio

• Issues and Treatment– Depositionp– Corrosion– Microbiological Fouling

2What Cooling topics would YOU like to discuss today?What Cooling topics would YOU like to discuss today?

Property of ChemTreat, Inc. Do not copy without permission.

Cooling Water Systems

R H t (BTU’ )Two Mechanisms:

Remove Heat (BTU’s)

1. Temperature Change “Sensible Heat” “Heat capacity” ‐ Cp = 1 BTU/lb‐oF (1 cal/g‐oC)p y p g

Heat transferred ‐ Q = m x Cp x (Th ‐Tc)

2. Evaporationp “Latent Heat” ‐ LH = 1,000 BTU/lb (556 cal/g)

Heat transferred ‐ Q = m x LH

How do industrial cooling systems use these properties?How do industrial cooling systems use these properties?3


Once ‐ Through System

Cooling Water

g y

Cooling Water Supply

ProcessHeat Load

Cooling Water Discharge or to Mill Water

Q ( Btu/hr.) = Q ( Btu/hr.) = mCpmCp(Tout (Tout ‐‐ Tin) = gpm x 500 (Tout Tin) = gpm x 500 (Tout ‐‐ Tin) Tin) 4


Closed Recirculating System

To HeatTo Heat Sink

Heat E h

ProcessExchanger

Heat Load

Makeup

FromHeat

SurgeSink

SurgeTank

What plant heat exchangers use closed cooling? What plant heat exchangers use closed cooling? 5


Open Recirculating System

Bl d

HotHumid Drift

BlowdownAir

Heat

CoolingTower Cool

Dry HeatLoad

EvaporationDryAir

Makeup Recirculating Pump(s)Recirculating Pump(s)Q = Q = mLHmLH = m x 1,000 Btu/lb = = m x 1,000 Btu/lb = mCpmCp(Tout (Tout ‐‐ Tin)Tin)

6Property of ChemTreat, Inc. Do not copy without permission.

Cooling System ComparisonCooling System Comparison

Once Through Closed Loop Cooling Tower

Pro Con Pro Con Pro ConLowest capital cost Poor chemistry Excellent chemistry Highest sink temp Smaller water Consumes water p y

controly

controlg p

source (~100x) (evaporation)

Lowest operating cost

Large source and water requirements

Corrosion product accumulation

Fairly low temp sink (wet bulb)

Higher operating cost (fan & pump)

L i k Th l di h L h l C lLowest temp sink Thermal discharge Less thermal discharge to water

Concentrates salts

Supplies hot water Fish and plankton entrainment

Good chemistrycontrol

Salt drift

Aquatic Weeds & Potential to reduce AirborneAquatic Weeds & Debris

Potential to reduce wastewater volume

Airborne pathogens


Evaporation Over A Cooling TowerOnly The Pure Water Is Lost

8

Minerals are concentratedMinerals are concentrated


Cycles of ConcentrationCycles of Concentration“Concentration Ratio”“Cycles”, “COC, “CR”, “C”

C = MU IBDBD I

=BD IMU

MU Make p flo I Any ion in BlowdownMU = Makeup flow

BD = Blowdown flow

IBD = Any ion in Blowdown

IMU = Same ion in Makeup


Cooling Tower BalancesCooling Tower BalancesSolving the Cooling Tower Equation

• Mass (Water and Salt Concentration)Mass (Water and Salt Concentration)Makeup = Evaporation + “Blowdown”

• “Blowdown” = BD intentional + Drift + Windage + Leaksg

• Energy (Heat)Q = QQin = Qout

How do we calculate the energy balance?How do we calculate the energy balance?10


Energy (Heat) Balances• Qin = RR * Cp * (TR ‐ TS)

Cp ~ 1.00 Btu/lb‐Fp /

• Qout = E * LH / f LH ~ 1,000 Btu/lb

• E = [ RR * 1.00 * (TR ‐ TS) * f ] / 1,000

E

BD

TR T1 T2

E

Vs. TwbTdb

RH

TS RR

Property of ChemTreat, Inc. Do not copy without permission.11

What is “ f ”?What is “ f ”?

Evaporation Factor (f)

20% RH

1.1

acto

r

1 0 20% RH40% RH60% RH80% RH100% RHtio

n Fa 1.0

0.9

apor

at

0.70.8

20 30 40 50 60 70 80

Eva

0.50.6

20 30 40 50 60 70 80(°F)Wet Bulb Temperature

How do we put this info together into an equation?How do we put this info together into an equation?12


Combined Energy and Mass Balancegy

• E = (RR * (TR ‐ TS) * f)/1,000• MU = BD + EMU = BD + E• C = MU/BD (also, C = ConcBD/ConcMU )

C = (BD+E)/BDBD BD*C = BD+E

BD*C – BD = E BD*(C‐1) = E

BD

E

• BD = E/(C ‐ 1)

RR

TR

MURRTS

If we increase (decrease) cycles, what’s the impact on MU & BD?If we increase (decrease) cycles, what’s the impact on MU & BD?


Effect of Cycles on MU & BD

Tower ParametersTower Parameters

Recirculation Rate 58,824 gpm

Delta T 20 F

Evaporation Factor 0.85

What Cycles do you operate your tower at? What limits the COC?What Cycles do you operate your tower at? What limits the COC?


Definitions ‐ Approach & Range107°F Hot Return H2O

73°F Wet Bulb Air

90°F Air Dry Bulb

84.5°F Cold Sump H2O73 F Wet Bulb Air45% Rel. Humidity

Approach Temperature = 11 5°F Cooling Range (T) = 22 5°F

• The wet bulb temperature is the lowest temperature to which water can be cooled by evaporation

Approach Temperature = 11.5 F Cooling Range (T) = 22.5 F

• The difference between the cold sump temperature and the wet bulb temperature is called the approach

• The temperature difference between the hot return water and the cold t i f d t th li (D lt T)

15

sump water is referred to as the cooling range (Delta T)

What would happen What would happen to to efficiency if we had to efficiency if we had to use Dry Cooling?use Dry Cooling?Property of ChemTreat, Inc. Do not copy without permission.

Cooling Tower DesignsCross‐Flow Induced Draft Counter‐Flow Induced DraftCross‐Flow Induced Draft Counter Flow Induced Draft

Driftli i

AirDrift

Eliminators

Eliminators

Air Louvers


Air flow direction is Counter to Water flowAir flow direction is Counter to Water flowAir flow direction Across the Water flowAir flow direction Across the Water flow

Cooling Tower FillS l h Fill Fil Fill

WATER

Splash Fill Film Fill

WETTEDSURFACE

AIR


Tight Passages Tight Passages –– More EfficientMore EfficientOpen Design Open Design –– Less Prone to FoulingLess Prone to Fouling

Cooling System ReviewCooling System Review

• What are the 3 general types of cooling systems?What are the 3 general types of cooling systems?

• How do cooling towers remove heat?

• What is meant by Cycles of Concentration?What is meant by Cycles of Concentration?– What can happen if “Cycles” get too high?

– Too Low?

• Why is Evaporative cooling more efficient than Dry?

• What is “Approach to the Wet Bulb temperature”What is Approach to the Wet Bulb temperature

• What is high efficiency film fill?– What concern should we have?


COOLINGWATER CHEMISTRYSection 2

COOLING WATER CHEMISTRY


Fundamental Cooling Triangleg g

Corrosion

Control

BioFoulingDeposition

How is each element addressed at your plant?How is each element addressed at your plant?

20

How is each element addressed at your plant?How is each element addressed at your plant?How well is it working?How well is it working?


Depositionp

• What is it?What is it?

• Why should we care?

• How is it measured?How is it measured?

• What factors effect it?

• How is it controlled at• How is it controlled at your mill?

• How well is it working?• How well is it working?


Types of Depositionyp p

• ScalingMi l l–Mineral scale

• FoulingS d d tt– Suspended matter

– Transient corrosion productsproducts

– Process Contamination• Lubricants, mill scale, glycol,

th lid & fl idother process solids & fluids

22

How does scale form?How does scale form?


Scaling ‐ Evaporation Over A Cooling TowerC Th Mi lConcentrates The Minerals

Only the pure water (H2O) is lost by evaporation

23

Only the pure water (H2O) is lost by evaporation

What factors affect scale formation?What factors affect scale formation?Property of ChemTreat, Inc. Do not copy without permission.

Scale Formation

Function of:Cooling Tower pH Chemistry SimplifiedH2O ↔ H+ + OH‐

H+ = Acid = Low pH• Concentration of Ions

• pH

H+ = Acid = Low pHOH‐ = Caustic = High pH

Evaporation concentrates minerals:

• Temperature

• Velocity

HCO3‐ (bicarbonate) → OH‐ + CO2↑

pH increasesHCO3

‐ + OH‐ → H2O + CO3= (carbonate)

Ca++ + CO3= = CaCO3↓

• Presence of Solid Seeding Material

Ca + CO3 = CaCO3↓Calcium carbonate scale

Add sulfuric acid:H2SO4 + 2OH= → H2O + SO4

=

Ca++ + SO4= → CaSO4↓ ?Calcium sulfate scale (gypsum)More soluble than CaCO3, but…

24

What do we mean by “inverse solubility”?What do we mean by “inverse solubility”?


More soluble than CaCO3, but…

Common Scale Forming MineralsInverse Solubility with Temperature and pH

gg gg

ncr

easi

ng

Sol

ubi

lity

ncr

easi

ng

Sol

ubi

lity

ncr

easi

ng

Sol

ubi

lity

ncr

easi

ng

Sol

ubi

lity

In S

Temp

In S

TempIn S

pHIn S

pHTempTemp pHpH

25

Why is inverse solubility a problem?Why is inverse solubility a problem?


Calcium Carbonate Is Inversely Soluble With Temperature (and pH)With Temperature (and pH)

(Process)(Process)

HEATHEAT

CO3‐

Ca+ Ca+ Ca+CO3‐ CO3‐ CO3‐Ca+ Ca+ Ca+CO3‐ CO3‐

Ca+

C

CO3‐Ca+

Ca+ Ca+ Ca+CO3‐ CO3‐ CO3‐

Ca+CO3‐

Ca+ Ca+ Ca+CO3‐ CO3‐

METAL SURFACEMETAL SURFACE HEATHEAT(Process)(Process)

26

(Process)(Process)


Common Mineral ScalesCo o e a Sca es• CaCO3 Calcium Carbonate

• CaSO4 Calcium Sulfate

• Ca3(PO4)2 Calcium Phosphate

• CaF2 Calcium Fluoride

• ZnPO4 Zinc Phosphate4

• Zn(OH)2 Zinc Hydroxide

• Fe2(PO4 )3 Iron Phosphate

• Fe2O3 Iron OxideFe2O3 Iron Oxide

• MnO2 Manganese Dioxide

• SiO2 Silica

• Mg Si O (OH) Magnesium Silicate• Mg3Si4O10(OH)2 Magnesium Silicate

• (AlO)2SiO3 Aluminum Silicate

• CaMgSi2O6 Calcium Magnesium Silicate

27

What is the most common scale?What is the most common scale?


CaCO3 IndicesLSI ‐ Langelier Saturation Index

• LSI = pH – pHs– pH = Actual pH– pHs = Saturation pH

– pHs = function of Calcium, M‐Alkalinity, TDS, & Temp.• M‐Alkalinity or “total alkalinity” is an approximation of the

bicarbonate concentrationbicarbonate concentration

– US Federal Register Aug 27, 1980, p. 57338 Vol 45 (No. 168)

• Interpreting LSI– Negative – calcium carbonate Scale is Not Possible g

– Positive – calcium carbonate Scale is Possible

– >0.5 – Scale is Likely without treatment

– >1.0 – Scale is Probable without treatment

– Typically, operate <2.5 with scale inhibitor

– 3.0 is the max. recommended with heroic treatment

h h h b f h d ?h h h b f h d ?What is the chemistry basis for this index?What is the chemistry basis for this index?


Predicting Mineral Scalingg g

• Proprietary software HH

Safe,No Treatment

NeedsTreatment

Do You Feel Lucky?

OK withTreatment

6 7 8 9

Proprietary software– Write your own– Work with cooperating chemical

or consulting company

pHpH

LSILSI

‐0.5 0.0 0.5 1.0 2.0 2.5 3.0• Commercially available software

– Consider French Creek Software• WaterCycle (Cooling)

H d RO D

LSILSI

SiOSiO

100 150 200 300

• Hyd‐RO‐Dose• DownHole SAT

– PHREEQE– WATEQ4F

SiOSiO22

CaH x SOCaH x SO

1x106 5x106 10x106 40x106

Q• Manufacturer specs.

– First resource• “When all else fails, read the instructions”

T d b i

CaH x SOCaH x SO44

MgH x SiOMgH x SiO

pH 7 – 400,000 pH 8 – 100,000 pH 9 – 20,000


– Tend to be conservative MgH x SiOMgH x SiO22

Controlling Deposit Formation

Chemically Controlling Mineral Scales

WithoutWith

Without Inhibitor

Inhibitor

• “Threshold Inhibition”– Adsorb onto growing crystal embryo– Distort orderly growth patternDistort orderly growth pattern– Encourage dissolution of the embryos into ions– Contrast to Chelation

• Phosphonates (Organic Phosphates)– PBTC, HEDP, AMP, DETPMPA, and others

Generally most effective but are affected by iron and can be degraded by oxidizers and UV light– Generally most effective, but are affected by iron and can be degraded by oxidizers and UV light• Polyphosphates (Inorganic Phosphates)

– Hexametaphosphate primarily– Hydrolyze fairly rapidly to simple “ortho” PO4

• Polymers– Polymaleate, polyacrylate, polymers, copolymers, oligomers– Less effective, but more stable and non‐P– Also used in combination with phosphonates to disperse and distort crystal nuclei 31


Chemically Controlling Mineral ScalesAdvanced Quadrasperse® – Phosphonate Blend

Calcite Supersaturation

• Combination of Quadrasperse®and Phosphonate allows the highest calcium carbonate

300

p

highest calcium carbonate supersaturation

• US Patent 6,645,384

Al t t d f i

200

• Also patented for magnesium silicate control

0

100


Controlling Fouling By Suspended SolidsControlling Fouling By Suspended Solids

• Solid particles enter the cooling systemp g y– Makeup water– Air – airborne dust

Process contamination oils iron glycol– Process contamination – oils, iron, glycol

• Mechanical control– Remove suspended solids from makeup water using appropriate

pretreatment (clarifiers, softeners, and filters)– Install sidestream or full‐flow filters – Re‐design for higher water velocityg g y

• Feed chemical dispersants and/or surfactants to keep them in suspension and prevent them from depositing


Chemical Control of Suspended Solids “Dispersion”Dispersion

Clay particles naturally have a negative surface chargeAnionic polymeric Dispersants adsorb onto suspended solids

...Reinforcing negative chargesAnionic polymeric Dispersants adsorb onto suspended solids...

Causing them to repel

What are some common dispersants?What are some common dispersants?


Typical DispersantsTypical Dispersants

• Homopolymers Polyacrylic acidHomopolymers– PAA, PMA,

• CopolymersSSMA AA/AMPS HPS1 APES t

CH2 CHn– SSMA, AA/AMPS, HPS1, APES, etc.

• Terpolymers– “HSP”, “STP”

COO‐

n

• Quadrasperse®– US Patent 6,645,384

OO

Charged carboxylic acid groupCharged carboxylic acid group


Copolymer Vs. Quadrasperse®Cooler #3 High Temp Heat Exchanger

Gulf Coast Chemical Plant - HX Flow with AA/AMPS Vs ChemTreat Quadrasperse

Cooler #3, High Temp. Heat Exchanger

AA/AMPS Vs. ChemTreat Quadrasperse

5800

6000

w

Copolymer (10 ppm) Quad Polymer (8 ppm)

5400

5600

5800

ater

Flo

wm

)

4800

5000

5200

oolin

g W

(gp m

4600

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56

Week

Co

Cooling water flow top Cooling water flow bottom


Oil Dispersion and Biofilm Penetration - SURFACTANTS -

Polar Non-Polar

OILWater


Can be anionic, nonionic, cationic, amphotericCan be anionic, nonionic, cationic, amphoteric

CorrosionCorrosion

Corrosion

• What is it?

• Why should we care?

• How is it measured?

• What factors effect it?

• How is it controlled?

• How is corrosion controlled at your plant?– How well is it working?


Quantity of Corrosion Products Generated in 2 000 Yards Pipingin 2,000 Yards Piping

Decreases flow Decreases flow –– “Foreign material in pipe”“Foreign material in pipe”

Rambie’, D. Paper Trade Journal, 1984

Increases pressure drop Increases pressure drop –– Increases pumping costIncreases pumping costBlocks critical spray nozzlesBlocks critical spray nozzles


Corrosion Is An Electrochemical Process

Necessary ElementsNecessary Elements

A d• Anode

• Cathode

n Flow Anode

(Zinc case)

Cathode

• Electrolyte

• Electron Flow Electron Cathode

(Carbon rod)

Electrolyte (Conductive paste )E


Corrosion is an Electrochemical ReactionCorrosion is an Electrochemical Reaction

WATER (ELECTROLYTE)

2OHFe(OH)2

Circuit Completed

O

2 ‐

Fe++

ELECTRON

2OH- O2

Fe2O3 (Rust)

O2

2e‐ANODE ELECTRON

FLOWCATHODE

(Metal Loss)

CATHODIC REACTIONSCHEMICAL REDUCTION

Metal (Conductor)

ANODIC REACTIONCHEMICAL OXIDATION CHEMICAL REDUCTION

½ O2 + H2O + 2e‐ 2OH‐

Low pH only: 2H+ + 2e‐ H2 42

CHEMICAL OXIDATIONFe 0 Fe ++ + 2e ‐


What factors affect corrosion?What factors affect corrosion?

Factors Affecting CorrosionFactors Affecting CorrosionConductivity

on R

ate

pH

n R

ate

4 104 pH 104 10

Cor

rosi

o

Cor

rosi

on

4 104 pH 104 10Dissolved Solids(Conductivity)

C

90 F

120 F

90 F

120 F

90 F

120 F

90 F

120 FTemp & Oxygen

sion

Rat

e

48 F

Temp or ppm Oxygen

48 F48 F48 F

Cor

ros

43Are there different forms of corrosion?Are there different forms of corrosion?


Types of Corrosionyp• Uniform• Localized (“pitting”)Localized ( pitting )

– Crevice corrosion– Concentration cellU d d it i– Under‐deposit corrosion

– Stress corrosion cracking– Microbiologically Influenced (“MIC”)– Erosion– Dealloying– Thermal cellThermal cell– Stray current– Galvanic (dissimilar metals)


Uniform CorrosionUniform Corrosion

L t D i• Least Damaging

• Cathodic and Anodic Sites Continuously Changing

• Even Metal LossEven Metal Loss

• Long Time Before Failure

11 mpy 36‐day exposure time

What happens if the anode does not shift randomly?What happens if the anode does not shift randomly?45


Localized Corrosion• Very Detrimental

• Small Amount of Metal Loss

• Short Time Before Failure

• Classic pitting corrosion

Pitting, strictly defined, occurs on a fully exposed surfacePitting, strictly defined, occurs on a fully exposed surface46


Anatomy Of A Pit …Pit Happens…

2e‐WATER (ELECTROLYTE)

Cl‐ OH‐OH‐OH‐

OH

Cl‐ Cl‐

Cl‐

OH‐

OH‐

Cl‐

Cl

2 ( )

H+ H+ H+ H+ H+

Metal (Conductor)

Fe+2 + 2HOH Fe(OH)2 + 2H+

• Rust tubercle behaves like a semi‐permeable membrane• Chloride ions are smaller and diffuse faster than hydroxide ions


Chloride ions are smaller and diffuse faster than hydroxide ions• Pit becomes acidic and concentrated in chlorides• Once a pit forms, the metal is very difficult to re‐passivate

Galvanic CorrosionGalvanic SeriesGalvanic Series

CCoorrrrooddeedd EEnndd((AAccttiivvee)) MMaaggnneessiiuumm CCooppppeerr ZZiinncc BBrroonnzzeess AAll ii CC NNii kk llAAlluummiinnuumm CCooppppeerr--NNiicckkeellSStteeeell TTiittaanniiuumm IIrroonn MMoonneell 330044 SSSS ((AAccttiivvee)) 330044 SSSS ((PPaassssiivvee))330044 SSSS ((AAccttiivvee)) 330044 SSSS ((PPaassssiivvee))331166 SSSS ((AAccttiivvee)) 331166 SSSS ((PPaassssiivvee)) LLeeaadd SSiillvveerr TTiinn GGrraapphhiitteeppBBrraasssseess PPrrootteecctteedd EEnndd

((MMoosstt NNoobbllee))


Stainless Steel Corrosion Behavior

• Active‐Passive Alloy– Chromium in the alloy promotes the formation of a protective hydrous iron oxide film on the surface

– Pits rapidly if a portion of the surface becomes activePits rapidly if a portion of the surface becomes active

• Requirement for maintaining passivity– Oxygen must be continually replenished at the surfaceOxygen must be continually replenished at the surface

– Avoid:• Deposits, especially manganese

• Stagnant conditions (extended wet layup)

• High chlorides

For stainless steel, the deposit control program is your corrosion control program!For stainless steel, the deposit control program is your corrosion control program!


Stainless Steel CorrosionStainless Steel Corrosion• General Corrosion

d– Acids– Reducing environment

• Stress Corrosion Cracking• Stress Corrosion Cracking– Chlorides– High temperature (> ~140 °F or 60 °C)High temperature (> 140 F or 60 C)– Tensile Stress (Residual or Applied)

• Pitting CorrosionPitting Corrosion– Chlorides– Crevices

“What’s a Safe Chloride Level?”“What’s a Safe Chloride Level?”50


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