Evaporative Condenser Passivation
Cameron Klein
Strand Associates, Inc.
Evaporative Condenser Wetted Surface Materials of
Construction
▪ Galvanized Steel
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Protective zinc coating fused to a steel substrate
Zinc layer offers sacrificial protection of steel substrate
Standard construction material
Requires passivation
▪ Stainless Steel
• Upgraded construction material
• Added equipment cost (varies based on size)
• Passivation is not required
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What is White Rust?
▪ White rust is a rapid, localized corrosion attack on zinc
(galvanized) surfaces
▪ Corrosion removes protective zinc layer (pitting)
▪ Waxy feel when wet
▪ Usually occurs on new galvanized surfaces during startup
▪ Can occur on existing galvanized surfaces if exposed to
high pH, high conductivity, or if the surface has been
scraped or aggressively cleaned
▪ Does not occur on stainless steel surfaces
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What is White Rust?
Picture courtesy of Evapco literature
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What is Galvanized Steel Passivation?
▪ Passivation is the process of the zinc layer oxidizing under
controlled conditions
▪ A thin film of zinc oxide is formed on the galvanized surface
▪ Protects the zinc layer which protects the steel substrate
▪ Water chemistry is key
• If the water starts off in the acceptable range for water chemistry,
with evaporation it will not remain in that range without treatment
and blowdown
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Water Chemistry Requirements for Passivation
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Varies by manufacturer but generally:
pH: 7.0 – 8.0
Alkalinity: < 300 ppm
Hardness: > 50 ppm
Conductivity: < 2,400 μS
Chlorides: < 250 ppm
Sulfates: < 250 ppm
All are important, but pH is very important
Ultimately, working with your water treatment supplier is a
critical step in the passivation process
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Passivation Duration
▪ Varies by manufacturer
• BAC: 4-8 weeks
• Evapco: 4-12 weeks
• Marley: minimum of 8 weeks
▪ Varies by climate and water chemistry
▪ No load on system during passivation
• Elevated temperature and changing water chemistry make
passivation very difficult
• Evaporation can concentrate corrosive ions and increase pH
▪ Coordinate with water treatment supplier to create a plan
and to monitor the surfaces to determine when complete
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Visual Difference of Galvanized Surface
▪ Pre-Passivation (new equipment)
• Bright and shiny color
▪ Post-Passivation (ready for loading)
• Dull gray color
Pictures courtesy of Evapco literature
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Evaporative Condenser Expected Useful Life
▪ ASHRAE Service Life Estimate: 20 Years
• Assumed to be fully passivated and water chemistry controlled
during operation
▪ Without passivation and water chemistry controlled,
equipment life estimate drops to 5-15 years
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Considerations
▪ Galvanized steel vs. stainless steel
▪ Project construction schedule
▪ If a passivated surface is damaged, re-passivation of that
surface is critical
▪ Consult the manufacturer literature for requirements
▪ Water treatment vendor involvement
• Passivation involvement
• Ongoing chemical treatment involvement
▪ Not a “set it and forget it” piece of equipment
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Passivation Water Treatment Log
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Questions
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Cooling Tower / Boiler Treatment
& Control
Joe Wenn
IMPURITIES COMMONLY FOUND IN WATER
1. Chemical Formula or Name
2. Difficulties Caused
3. Means of Treatment
HARDNESS
• Calcium and Magnesium salts expressed as CaC03 either Ca+Mg+
• Chief source of scale in heat exchange equipment, boilers, pipelines,
etc. Forms curds with soap, interferes with dyeing.
• Softening, Demineralization, Internal boiler water treatment, Surfaceactive agents.
ALKALINITY
• Bicarbonate (HC03), Carbonate (C03), and Hydrate (OH), expressed <1:5
CaC03
• Foaming and carryover of solids with steam, Embrittlement of boiler steel.
Bicarbonate and carbonate produce CO2 in steam
• Lime and lime-soda softening, Acid treatment, Hydrogen zeolite softening,
Demineralization, Dealkalization by anion exchange.
IMPURITIES COMMONLY FOUND IN WATER
1. Chemical Formula or Name
2. Difficulties Caused
3. Means of Treatment
FREE MINERAL ACID
• Hi-SO, HCl, etc., expressed as CaC03
• Corrosion.
• Neutralization with alkalies.
CARBON DIOXIDE
• CO2
• Corrosion in water lines and particularly steam d condensate lines.
• Aeration, Deaeration, Neutralization with alkalies.
pH
• Hydrogen ion concentration defined as pH + log 1L(H)
• pH varies according to acidic or alkaline solids in water. Most natural
waters have a pH of 6.0- 8.0.
• pH can be increased by alkalies and decreased by acids.
EXTERNAL TREATMENT
Softening -Removal of Calcium and Magnesium
Sodium Zeolite-Most common
• Polystyrene Resins - 32,000 grains/cubic foot
• NaCl - Regenerate .
• Complete Hardness Removal
• Turbidity, Iron, and Oil Detrimental to Resin.
• No Reduction in Alkalinity or Solids
• Increased CO2
• Increase in Corrosion Tendencies due to ·Dissolved Gases 02 and
CO
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Four cycles
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Backwash
Brine Draw
Fast Rinse
Service
- 2.6 Lbs. Salt/Gallon Water - Saturation
- Resin can be cleaned to Remove Iron with
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1). Hydrochloric Acid 2). Citric Acid 3) Sodium Hydrosulfite and Bisulfite
EXTERNAL TREATMENT
Softening -Removal of Calcium and Magnesium
Lime Soda Softening
• Lime and Soda Ash (Sodium Carbonate) or Caustic Soda needed Regenerants 1 - 1 1/2 hours retention time
• Hardness reduced to 10 - 25 ppm Hot Process used for Boiler
Make-up
• Ca+ precipitates CaCO3
• Mg+ precipitates MgOH
• Bicarbonate Alkalinity Converted to Carbonate then CaCO3
• Silica is Precipitated .
• Turbidity is removed (Calcium Hydroxide)
EXTERNAL TREATMENT
Softening -Removal of Calcium and Magnesium
Split Stream Dealkalizer
• Polystyrene Resins Used
• 2 Tanks-Each Regenera!e Separately
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One withNaCI
The other Sulfuric Acid (2--6% Solution)
Zero Hardness Low Alkalinity
Blended Byproduct is Carbonic Acid
Degasifier used to remove excess Carbonic Acid
Demineralized
• Cation - Anion
• Regenerants - Sulfuric Acid and Caustic Soda
• Strong Basic Resin removes Silica
• Aerator needed for CO2 removal
• Used for High Pressure Boiler
EXTERNAL TREATMENT
Softening -Removal of Calcium and Magnesium
Dealkalizers - Chloride Cycle
• One Tank
• Regenerated with NaCl and NaOH
Reverse Osmosis
• Membrane Technology_
• Reduces make-up minerals by 90 to 95%.
• Pretreatment (water softener and carbon filter) typically required
• Substantially reduce boiler blowdown requirements and chemical
usage
White Rust
White Rust
Control
Control
STEAM AND RETURN LINE CORROSION
TYPES AND CAUSES OF CORROSION
Oxygen
• Iron pipe will show pitting
• 4 Fe +6(H20) +3(02) = 4 Fe(OH)3 Iron Ferric Hydroxide
• 02 can increase carbonic acid corrosion lOx
2). Carbon Dioxide
• Iron pipe has grooving or etching usually at elbows or
horizontal runs
• CO2 +H20 = H2CO3 (Carbonic Acid) 2 (HzCO3) +Fe:= Fe
(HCO3)2 + H2 (Ferrous Bicarbonate)
• Boiler Alkalinity converts to CO2
– 1 ppm Bicarbonate Alkalinity evolves to . 79 ppm CO2
– 1 ppm Carbonate Alkalinity evolves to .35 ppm CO2
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100% of Bicarbonate Alkalinity completes reaction at Boiler P .S.I. 0 - 50
10 - 30% of Carbonate Alkalinity completes reaction at Boiler P.S.I. 50- 150
30 - 80% completes reaction at Boiler P.SJ. 150 and over
80 - 100% completes reaction
STEAM AND RETURN LINE CORROSION
TYPES AND CAUSES OF CORROSION
Hydrazine Breakdown from Excessive Use - Ammonia is
formed and in presence of 02 and pH above 8.3 copper is
severely attacked
Ammonium Hydroxide or Ammonia - Will stop carbonic acid
attack but with 02 and pH above 83 copper and brass are
attacked
Sulfite - Will breakdown at high temperature; 1000 degrees F
to Hydrogen Sulfide
Chlorine - From faulty heat exchanger on pool
Coil Leakage
Closed Systems- Boilers
Issues
• Water Volume relative to system Volume
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Madison Water Quality
– High Harness (Scaling)
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Boilers Fail
Solution
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Soft Water
Real World Examples