Aqua sai ppt

Details of Water-Cooling Details of Water-Cooling SystemSystem• Cooling towers and ReservoirsCooling towers and Reservoirs• Direct cooling to DiesDirect cooling to Dies• Indirect cooling to oil through Heat Indirect cooling to oil through Heat

ExchangersExchangers• Pre-treatment of Water through Water Pre-treatment of Water through Water

SoftenerSoftener• No Blowdown facility from bottom of water No Blowdown facility from bottom of water

reservoirsreservoirs

WHY DO COOLING WATER PROBLEM WHY DO COOLING WATER PROBLEM EXIST ?EXIST ?

If cooling water left untreated , cooling water If cooling water left untreated , cooling water system provide an environment where the system provide an environment where the four main cooling problems will exist:four main cooling problems will exist:

• CORROSIONCORROSION• SCALESCALE• FOULINGFOULING• MICRO BIOLOGICAL CONTAMINATIONMICRO BIOLOGICAL CONTAMINATION

WHAT ARE THE EFFECTS OF THOSE WHAT ARE THE EFFECTS OF THOSE PROBLEMS ?PROBLEMS ?

• Increased maintenance costIncreased maintenance cost• Reduced heat transfer efficiency and Reduced heat transfer efficiency and

therefore greater energy lossestherefore greater energy losses• Possible production cutbacks or Possible production cutbacks or

shutdownsshutdowns• Direct loss or abandon of plant & Direct loss or abandon of plant &

machineriesmachineries

Methods of Prevention and Control of Methods of Prevention and Control of

ScaleScale • Removal of scale forming minerals by pre-Removal of scale forming minerals by pre-

treatment of makeup water.treatment of makeup water.• Limiting the concentration of scale forming Limiting the concentration of scale forming

minerals by bleed control.minerals by bleed control.• Replacing scale-forming minerals with Replacing scale-forming minerals with

soluble salts by acid dosing.soluble salts by acid dosing.• Controlling the scale forming process Controlling the scale forming process

using scale-inhibiting chemicals.using scale-inhibiting chemicals.

Corrosion Control Corrosion Control ConceptsConceptsThe rate of attack by circulating cooling The rate of attack by circulating cooling

water on steel is a function of temperature water on steel is a function of temperature and pH. It increases with temperature and and pH. It increases with temperature and depression of pH. depression of pH.

Corrosion protection follows two rules:Corrosion protection follows two rules:

High pH promotes scale and inhibits High pH promotes scale and inhibits corrosioncorrosion

Low pH inhibits scale and promotes corrosionLow pH inhibits scale and promotes corrosion

WHAT TYPE OF WATER CHARACTERISTICS AFFECT WHAT TYPE OF WATER CHARACTERISTICS AFFECT CORROSIONCORROSION

• Oxygen and other dissolved gasesOxygen and other dissolved gases• Dissolved or suspended solidsDissolved or suspended solids• Alkalinity or acidityAlkalinity or acidity• VelocityVelocity• TemperatureTemperature• Microbial activityMicrobial activity

WHAT METHODS ARE USED TO PREVENT WHAT METHODS ARE USED TO PREVENT CORROSION ?CORROSION ?

• When designing a new system choose When designing a new system choose corrosion resistant material to minimize corrosion resistant material to minimize

• The effect of an aggressive environment.The effect of an aggressive environment.Adjust pHAdjust pH

• Apply protective coatings such as paints, Apply protective coatings such as paints, metal plating etcmetal plating etc

• Add Protective Film Forming Chemical Add Protective Film Forming Chemical InhibitorsInhibitors..

THE EFFECTS OF SCALE ON HEAT TRANSFER AND THE EFFECTS OF SCALE ON HEAT TRANSFER AND ENERGYENERGY

• EFFECT OF CaCO3 SCALE (OF VARYING THICKNESS) ON EFFECT OF CaCO3 SCALE (OF VARYING THICKNESS) ON OVERALL HEAT TRANSFER  COEFFICIENTOVERALL HEAT TRANSFER  COEFFICIENTScale Thickness, InchesScale Thickness, Inches Overall heat transfer coefficient, BTU per sq ft per Overall heat transfer coefficient, BTU per sq ft per

deg Fdeg FPercent loss in BTU per sq ft per deg Percent loss in BTU per sq ft per deg

FF

0.0000.000 92.7792.77 00

0.0120.012 73.6873.68 20.5820.58

0.0240.024 61.1261.12 34.1234.12

0.0360.036 52.2052.20 43.7343.73

0.0480.048 45.6045.60 55.8355.83

0.0600.060 40.4640.46 56.3956.39

0.0625 (1/16 in.)0.0625 (1/16 in.) 39.5239.52 57.4057.40

THE EFFECTS OF SCALE ON HEAT TRANSFER AND THE EFFECTS OF SCALE ON HEAT TRANSFER AND ENERGYENERGY

EFFECT OF CaSO4 (OF VARYING THICKNESS) ON OVERALL HEAT TRANSFER  EFFECT OF CaSO4 (OF VARYING THICKNESS) ON OVERALL HEAT TRANSFER  COEFFICIENTCOEFFICIENT

Overall heat transfer scale thickness, inchesOverall heat transfer scale thickness, inches Coefficient, BTU per sq ft per deg FCoefficient, BTU per sq ft per deg F Percent loss in BTU per sq ft per deg FPercent loss in BTU per sq ft per deg F

0.0000.000 92.7792.77 00

0.0120.012 63.1063.10 31.9831.98

0.0240.024 47.8147.81 48.4648.46

0.0360.036 38.4938.49 58.5158.51

0.0480.048 32.2032.20 62.0062.00

0.0600.060 27.6927.69 70.0070.00

0.0625 (1/16 in.)0.0625 (1/16 in.) 26.8926.89 71.071.0

PROBLEMS CAUSED BY PROBLEMS CAUSED BY MICROORGANISMSMICROORGANISMS

• HEAT TRANSFER EFFECTSHEAT TRANSFER EFFECTS• FLUID FLOW EFFECTSFLUID FLOW EFFECTS• CORROSION EFFECTCORROSION EFFECT

Parameters to Assess Water QualityParameters to Assess Water Quality

• pHpH

• TDSTDS

• Total HardnessTotal Hardness

• Calcium HardnessCalcium Hardness

• Total AlkalinityTotal Alkalinity

• LSILSI• RSIRSI

What is pH?What is pH?

• pH is a measure of the acidity or basicity a pH is a measure of the acidity or basicity a solution. Solutions with a pH less than seven are solution. Solutions with a pH less than seven are considered acidic, while those with a pH greater considered acidic, while those with a pH greater than seven are considered basic. pH 7 is than seven are considered basic. pH 7 is defined as neutral because it is the pH of pure defined as neutral because it is the pH of pure water at 25 °Cwater at 25 °C

• It should be between 7 and 8.5 for cooling-water It should be between 7 and 8.5 for cooling-water system.system.

What is TDS?What is TDS?

• It means density of “Total Dissolved It means density of “Total Dissolved Solids” in water. To avoid carryover and Solids” in water. To avoid carryover and deposition (due to super saturation) in deposition (due to super saturation) in system, TDS should be maintained within system, TDS should be maintained within 1000 ppm. This can be controlled by blow 1000 ppm. This can be controlled by blow down only.down only.

What is ‘Total Hardness’?What is ‘Total Hardness’?

• Technically, it is the sum of all polyvalent Technically, it is the sum of all polyvalent cationscations

• Practically, it is the amount of calcium and Practically, it is the amount of calcium and magnesium ions, which are the magnesium ions, which are the predominant minerals in natural waterspredominant minerals in natural waters

• This will indicate the amount of scaling This will indicate the amount of scaling load going to system for internal load going to system for internal treatment. treatment.

What is ‘Calcium Hardness’?What is ‘Calcium Hardness’?

• Calcium Hardness is caused by the Calcium Hardness is caused by the presence of calcium ions in the waterpresence of calcium ions in the water

• Calcium salts can be readily precipitated Calcium salts can be readily precipitated from water and high levels of calcium from water and high levels of calcium hardness tend to promote scale formation hardness tend to promote scale formation in the water system. in the water system.

What is ‘Total Alkalinity’?What is ‘Total Alkalinity’?

• Alkalinity is a water's acid-neutralizing Alkalinity is a water's acid-neutralizing capacity capacity

• Alkalinity measures the total amount of Alkalinity measures the total amount of base present and indicates a water base present and indicates a water reservoir’s ability to resist large pH reservoir’s ability to resist large pH changes, or the “buffering capacity.”  changes, or the “buffering capacity.” 

• The most important components of The most important components of alkalinity are carbonates and alkalinity are carbonates and bicarbonates. bicarbonates.

Langelier Saturation IndexLangelier Saturation Index

• The Langelier Saturation Index (LSI;also called Langelier The Langelier Saturation Index (LSI;also called Langelier Stability Index) is a calculated number used to predict Stability Index) is a calculated number used to predict the calcium carbonate stability of water; that is, whether the calcium carbonate stability of water; that is, whether a water will precipitate, dissolve, or be in equilibrium with a water will precipitate, dissolve, or be in equilibrium with calcium carbonatecalcium carbonate

• If LSI is negative: No potential to scale, the water will If LSI is negative: No potential to scale, the water will dissolve CaCO3dissolve CaCO3

• If LSI is positive:  Scale can form and CaCO3 If LSI is positive:  Scale can form and CaCO3 precipitation may occurprecipitation may occur

• If LSI is close to zero: Borderline scale potential. Water If LSI is close to zero: Borderline scale potential. Water quality or changes in temperature, or evaporation could quality or changes in temperature, or evaporation could change the index.change the index.

Ryznar Stabil i ty Index Ryznar Stabil i ty Index (RSI)(RSI)• The Ryznar stability index (RSI) attempts to correlate an The Ryznar stability index (RSI) attempts to correlate an

empirical database of scale thickness observed in water empirical database of scale thickness observed in water systems to the water chemistry. Like the LSI, the RSI systems to the water chemistry. Like the LSI, the RSI has its basis in the concept of saturation level has its basis in the concept of saturation level

• RSI << 6 the scale tendency increases as the index RSI << 6 the scale tendency increases as the index decreasesdecreases

• RSI >> 7 the calcium carbonate formation probably does RSI >> 7 the calcium carbonate formation probably does not lead to a protective corrosion inhibitor filmnot lead to a protective corrosion inhibitor film

• RSI >> 8 mild steel corrosion becomes an increasing RSI >> 8 mild steel corrosion becomes an increasing problem.problem.

Chemical TestingChemical Testing

Chemicals / Chemicals / ParametersParameters

DensityDensity(kg/l i tre(kg/l i tre

))

ColourColour OdourOdour pHpH Increase in Increase in TDS of TDS of

water (1kg) water (1kg) on 1 ml on 1 ml addit ionaddit ion

AST - 6600AST - 6600 1.09 to 1.09 to 1.111.11

Light GreenLight Green PungentPungent 0.1 to 0.30.1 to 0.3 660 to 710660 to 710

AST - 6602AST - 6602 1.12 to 1.12 to 1.131.13

Coca ColaCoca Cola Pungent, Pungent, PhenolicPhenolic

0.5 to 0.70.5 to 0.7 170 to 190170 to 190

AST - 7711AST - 7711 1.04 to 1.04 to 1.051.05

Light BrownLight BrownPhenolicPhenolic

10 to 10.510 to 10.5 4.2 to 4.64.2 to 4.6