2a cooling-water-fundamentals-part-1

Cooling Water Fundamentals
Steel Industry Water Conference
Clearwater Beach FLClearwater Beach, FL
September 12‐14, 2012
Raymond M. Post, P.E.
Director Cooling Technology
RayP@chemtreat.com

Outline
• Types of Cooling Systems
– Once through
– Closed Loop
– Open‐recirculating
• Cooling TowersCooling Towers
– Physical Design
– Heat Transfer
C li C t ti R ti– Cycling or Concentration Ratio
• Issues and Treatment
– Depositionp
– Corrosion
– Microbiological Fouling
2
What 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
Process
Heat 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
Process
Exchanger
Heat
Load
Makeup
From
Heat
Surge
Sink
Surge
Tank
What plant heat exchangers use closed cooling? What plant heat exchangers use closed cooling?
5

Open Recirculating System
Bl d
Hot
Humid Drift
BlowdownAir
Heat
Cooling
Tower Cool
Dry Heat
Load
Evaporation
Dry
Air
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)
6

Cooling System ComparisonCooling System Comparison
Once Through Closed Loop Cooling Tower
Pro Con Pro Con Pro Con
Lowest capital cost Poor chemistry Excellent chemistry Highest sink temp Smaller water Consumes water p y
control
y
control
g 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 chemistry
control
Salt drift
Aquatic Weeds & Potential to reduce AirborneAquatic Weeds &
Debris
Potential to reduce
wastewater volume
Airborne
pathogens
7

Evaporation Over A Cooling Tower
Only The Pure Water Is Lost
8
Minerals are concentratedMinerals are concentrated

Cycles of ConcentrationCycles of Concentration
“Concentration Ratio”
“Cycles”, “COC, “CR”, “C”
C =
MU IBD
BD 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
9

Cooling Tower BalancesCooling Tower Balances
Solving 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 = QQin = 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
11
What is “ f ”?What is “ f ”?

Evaporation Factor (f)
20% RH
1.1
actor
1 0 20% RH
40% RH
60% RH
80% RH
100% RH
tionFa
1.0
0.9
aporat
0.7
0.8
20 30 40 50 60 70 80
Eva
0.5
0.6
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)/BD
BD BD*C = BD+E
 BD*C – BD = E
 BD*(C‐1) = E
BD
E
• BD = E/(C ‐ 1)
RR
TR
MU
RRTS
If we increase (decrease) cycles, what’s the impact on MU & BD?If we increase (decrease) cycles, what’s the impact on MU & BD?
13

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?
14

Definitions ‐ Approach & Range
107°F Hot Return H2O
73°F Wet Bulb Air
90°F Air Dry Bulb
84.5°F Cold Sump H2O
73 F Wet Bulb Air
45% 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?

Cooling Tower Designs
Cross‐Flow Induced Draft Counter‐Flow Induced DraftCross‐Flow Induced Draft Counter Flow Induced Draft
Drift
li i
Air
Drift
Eliminators
Eliminators
Air Louvers
16
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 Fill
S l h Fill Fil Fill
WATER
Splash Fill Film Fill
WETTED
SURFACE
AIR
17
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?
18

COOLING WATER CHEMISTRY
Section 2
COOLING WATER CHEMISTRY
19

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?
21

Types of Depositionyp p
• Scaling
Mi l l– Mineral scale
• Fouling
S 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 Tower
C 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?

Scale Formation
Function of:
Cooling Tower pH Chemistry Simplified
H2O ↔ H+ + OH‐
H+ = Acid = Low pH
• Concentration of Ions
• pH
H+ = Acid = Low pH
OH‐ = Caustic = High pH
Evaporation concentrates minerals:
• Temperature
• Velocity
HCO3
‐ (bicarbonate) →  OH‐ + CO2↑
pH increases
HCO3
‐ + 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 Minerals
Inverse Solubility with Temperature and pH
gg
gg
ncreasing
Solubility
ncreasing
Solubility
ncreasing
Solubility
ncreasing
Solubility
In
S
Temp
In
S
Temp In
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 Indices
LSI ‐ 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?
28

Predicting Mineral Scalingg g
• Proprietary software HH
Safe,
No Treatment
Needs
Treatment
Do You
Feel Lucky?
OK with
Treatment
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
29
– Tend to be conservative MgH x SiOMgH x SiO22

Controlling Deposit Formation

Chemically Controlling Mineral Scales
Without
With
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 Scales
Advanced 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
32

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
33

Chemical Control of Suspended Solids
“Dispersion”Dispersion
Clay particles naturally have a negative surface charge
Anionic polymeric Dispersants adsorb onto suspended solids
...Reinforcing negative charges
Anionic polymeric Dispersants adsorb onto suspended solids...
Causing them to repel
What are some common dispersants?What are some common dispersants?
34

Typical DispersantsTypical Dispersants
• Homopolymers
Polyacrylic acid
Homopolymers
– PAA, PMA,
• Copolymers
SSMA AA/AMPS HPS1 APES t
CH2 CH
n– SSMA, AA/AMPS, HPS1, APES, etc.
• Terpolymers
– “HSP”, “STP”
C
OO‐
n
• Quadrasperse®
– US Patent 6,645,384
OO
Charged carboxylic acid groupCharged carboxylic acid group
35

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
aterFlow
m)
4800
5000
5200
oolingW
(gpm
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
36

Oil Dispersion and Biofilm Penetration
- SURFACTANTS -
Polar Non-Polar
OILWater
37
Can be anionic, nonionic, cationic, amphotericCan be anionic, nonionic, cationic, amphoteric

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?
39

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 cost
Blocks critical spray nozzlesBlocks critical spray nozzles
40

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
41

Corrosion is an Electrochemical ReactionCorrosion is an Electrochemical Reaction
WATER (ELECTROLYTE)
2OH
Fe(OH)2
Circuit Completed
O
2 ‐
Fe++
ELECTRON
2OH-
O2
Fe2O3 (Rust)
O2
2e‐
ANODE
ELECTRON
FLOW
CATHODE
(Metal Loss)
CATHODIC REACTIONS
CHEMICAL REDUCTION
Metal (Conductor)
ANODIC REACTION
CHEMICAL OXIDATION CHEMICAL REDUCTION
½ O2 + H2O + 2e‐  2OH‐
Low pH only: 2H+ + 2e‐  H2 42
CHEMICAL OXIDATION
Fe 0  Fe ++ + 2e ‐
What factors affect corrosion?What factors affect corrosion?

Factors Affecting CorrosionFactors Affecting Corrosion
Conductivity
onRate
pH
nRate
4 104 pH 104 10
Corrosio
Corrosion
4 104 pH 104 10
Dissolved Solids
(Conductivity)
C
90 F
120 F
90 F
120 F
90 F
120 F
90 F
120 F
Temp & Oxygen
sionRate
48 F
Temp or ppm Oxygen
48 F48 F48 F
Corros
43
Are there different forms of corrosion?Are there different forms of corrosion?

Types of Corrosionyp
• Uniform
• Localized (“pitting”)Localized ( pitting )
– Crevice corrosion
– Concentration cell
U d d it i– Under‐deposit corrosion
– Stress corrosion cracking
– Microbiologically Influenced (“MIC”)
– Erosion
– Dealloying
– Thermal cellThermal cell
– Stray current
– Galvanic (dissimilar metals)
44

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 surface
46

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
47
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 Corrosion
Galvanic SeriesGalvanic Series
CCoorrrrooddeedd EEnndd
((AAccttiivvee))
MMaaggnneessiiuumm CCooppppeerr
ZZiinncc BBrroonnzzeess
AAll ii CC NNii kk llAAlluummiinnuumm CCooppppeerr--NNiicckkeell
SStteeeell TTiittaanniiuumm
IIrroonn MMoonneell
330044 SSSS ((AAccttiivvee)) 330044 SSSS ((PPaassssiivvee))330044 SSSS ((AAccttiivvee)) 330044 SSSS ((PPaassssiivvee))
331166 SSSS ((AAccttiivvee)) 331166 SSSS ((PPaassssiivvee))
LLeeaadd SSiillvveerr
TTiinn GGrraapphhiitteepp
BBrraasssseess PPrrootteecctteedd EEnndd
((MMoosstt NNoobbllee))
48

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!
49

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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