Evaporative Condenser Passivation. Cameron Klein Strand Associates, Inc.

Transcription

1 Evaporative Condenser Passivation Cameron Klein Strand Associates, Inc.

2 Evaporative Condenser Wetted Surface Materials of Construction Galvanized Steel 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 2

3 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 3

4 What is White Rust? Picture courtesy of Evapco literature 4

5 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 5

6 Water Chemistry Requirements for Passivation Varies by manufacturer but generally: ph: 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 6

7 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 7

8 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 8

9 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 9

10 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 10

11 Passivation Water Treatment Log 11

12 Questions 12

13 Cooling Tower / Boiler Treatment & Control Joe Wenn

14 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.

15 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 ph can be increased by alkalies and decreased by acids.

16 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 Four cycles - Backwash - Brine Draw - Fast Rinse - Service Lbs. Salt/Gallon Water - Saturation - Resin can be cleaned to Remove Iron with 1). Hydrochloric Acid 2). Citric Acid 3) Sodium Hydrosulfite and Bisulfite

17 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 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)

18 EXTERNAL TREATMENT Softening -Removal of Calcium and Magnesium Split Stream Dealkalizer Polystyrene Resins Used 2 Tanks-Each Regenera!e Separately 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

19 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

20 White Rust

21 White Rust

22 Control

23 Control

24 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 100% of Bicarbonate Alkalinity completes reaction at Boiler P.S.I % of Carbonate Alkalinity completes reaction at Boiler P.S.I % completes reaction at Boiler P.SJ. 150 and over % completes reaction

25 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

26 Closed Systems- Boilers Issues Water Volume relative to system Volume Madison Water Quality High Harness (Scaling) Boilers Fail Solution Soft Water

27 Real World Examples