Process Cooling water Tower system basics.pptx

Process Cooling Technical

1. WATER AS COOLING FLUID IN INDUSTRIAL PLANTS 1

2. Water as cooling fluid To have good heat transfer, the cooling fluid must be convenient from thermodinamic and cost point of view High Thermal capacity Low specific volume Temperature sufficiently lower then that of the process fluid High availability Low cost 2

3. Water as cooling fluid SPECIFIC HEAT is the measure of how well a substance can absorb heat 1 Kcal/kg°C or 4,18 KJ/kg°C VAPORIZATION HEAT Energy to transform liquid to gaseous 540 Kcal/kg at 100°C 575 Kcal/kg at 40°C 3

4. Water as cooling fluid Main water characteristics k a = thermal conductivity cp = specific heat d = density u = dynamic viscosity v = cinematic viscosity Pr = Prandtl number a = thermal diffusivity

5. Water as cooling fluid However , due to the presence of sevaral impurities , water can cause severe problems to the heat transfer equipment : HEAT TRANSFER BASICS WATER CHARACTERISTICS SCALE FOULING BIOLOGICAL FOULING CORROSION 5

6. Basics of heat transfer 6

7. Basics of heat transfer To understand the impact of water characteristics, is useful to remind the heat transfer laws that help us to recognize the importance of a right treatment CONDUCTION CONVECTION RADIATION 03/06/2024 7

8. Basics of heat transfer Conduction It is the transfer of heat between two areas at different temperature of same material (or different material in contact), due to the heat flux between the molecules without these move from their average position Heat transfer capacity of a material, called thermal conductivity, determine the gradient of temperature accross the material The foundamental law of the conduction is the Fourier law: where 03/06/2024 8 q k = k a (t 2 - t 1 ) / L c q k = heat flux, kcal/h m 2 k a = thermal conductivity, kcal/m h°C (t 2 -t 1 ) = gradient of temperature through a layer of material, °C L c = thickness across which the heat transfer occurs, m

9. Basics of heat transfer Convection It is the heat transfer associated to the transport of mass and energy beteen two points of a fluid or a fluid with a solid 03/06/2024 9 Where: q c = h c A (t 2 -t 1 ) q c = convection heat transfer, kcal/h h c = convection heat transfer coefficient, kcal/hm 2 °C A = heat transfer surface, m 2 (t 2 -t 1 ) = difference of temperature across a fluid film, °C

10. Basics of heat transfer Convection To get high heat transfer value it is needed to reduce as much as possible the limit film layer This can be done by increasing the flow velocity and/or the turbolence of the fluid The ratio between the gradient of temperature inside the fluid in contact with the surface and a reference gradient of temperature is given by the Nusselt Number ( Nu ) The Nu correlates the convection coefficient h, the diameter D and the thermal conductivity k a . 03/06/2024 10 Nu = h c D / k a

11. Basics of heat transfer Convection Reynolds Number ( Re ) indicate if a fluid is moving in the laminar or turbolence region The Re is adimensional and it is proportional directly to the diameter ( D )of the tube, the density ( d ) and velocity ( V ) of the fluid and inverse to the viscosity of the fluid ( u ) Approximatively, for clean tubes Re = D d V / u Re < 2100 laminar motion Re > 2400 turbulent motion

12. Basics of heat transfer Convection According to the convection coefficient ( hc ) , Nusselt number is function of Reynolds number ( Re ) and Prantl number ( Pr ) Where Pr is adimensional and it is given by the relationship A realshionship to calculate the convection coefficient , valid for turbulent region , is given by Dittus and Boelter 03/06/2024 12 Nu = f( Re , Pr ) Pr = c p u / k a h c D / k a = 0.023 Re 0.6 Pr 1/3 u / u w u w = Skin temperature viscosity

13. Basics of heat transfer Radiation It is the heat transfer due to the radiation effect, even in presence of material, between two bodies at different temperature The radiation law is given by Stefan-Boltzman (generalized) 03/06/2024 13 q i = d s e A 1 (T 4 1 - T 4 2 ) where: q i = thermal power of radiation, kcal/h d s = Stefan- Boltzman’s constant, 4,88.10 -8 kcal/m2h°K 4 e = emissivity of the mateiral A 1 = surface, m 2 (T 1 -T 2 ) = differential of temperature across a fluid film, °K

14. Basics of heat transfer Heat transfer in the industrial equipments In the shell&tubes units the heat transfer occurs mainly by conduction and convection In the furnaces and heaters the heat transfer occurs by convection and radiation 03/06/2024 14 Hot Process In Hot Cooling Water Out Cooled Process Out Cold Cooling Water In Kcal's Kcal's SIMPLE HEAT TRANSFER

15. Basics of heat transfer Shell&tubes heat transfer – Water shell side 03/06/2024 15 External deposit External Fluid film Internal deposit Internal Fluid film Wall of tube T 1 T 3 T 2 T 4 T 5 T 6 T 8 T 7 Cold fluid Hot fluid Laminar layer Transition zone Turbulent zone Fluid Outside tube Fluid Inside tube Conduction: T4 - T5 T3 - T4 T5 - T6 Convection: T1 - T3 T6 - T8

16. Water Characteristics 03-Jun-24 16

17. Impact of water characteristics Industrial plants take advantage from the thermodinamic properties of the water as cooling fluid The impurities present in the water can cause severe problems to the heat transfer units It is important to control the operation of heat transfer equipments within the allowed limits of the chemical-physical parameters Water, that become warmer due to the heat transfer, couid cause problems due to the original impurities, their concentration in evaporative units and absorption of pollutants from processes and atmosphere 03/06/2024 17 Scale Deposit Corrosion Fouling

18. Impact of water characteristics Aspect Can be observed materials suspended that could potentially settled on the heat transfer surface These materials could cause deposit, scale, corrosion, erosion, biological foulinf and foam 03/06/2024 18

19. Impact of water characteristics Temperature Specially the skin temperature, represents a significative index of the potential problems that can occurs (scale, corrosion, fouling) The solubility of scaling salts decrease with the increase of the temperature. So, where this is higher the potential precipitation is more critical. Higher potential of scale formation occurs in the hottest areas of the heat transfer unitse (i.e. The inlet of the process where the temperature is higher) 03/06/2024 19

20. Impact of water characteristics pH pH units give the degree of acidity or basicity of water pH represents a very important factor on the development and entity of scale, corrosion and biological fouling phenomena pH is the basic parameter to calssify the corrosiveness of waters 03/06/2024 20

21. Impact of water characteristics Electrical conductivity Electrical conductivity represents the reciprocal of the resistivity to the flowing of the electrical current It is typical for each electrolyte , function of the ion concentration It is an indirect measurement of the dissociated matters present in the water It is an index of the purity and salinity Higher ion concentration increase generally the solubility of the scaling salts Lower resistance increases the aggressivity of the water 03/06/2024 21

22. Impact of water characteristics Total solids (TS) TS represents all the solids present in the water as soluble, colloidal and suspended It is expressed as mg/liter and is determined by evaporation at 180°C High ST value indicates normally poor water quality 03/06/2024 22

23. Impact of water characteristics Total dissolved solids (TDS) TDS are the total dissolved solids in the water It is expressed as mg/liter and are determined by evaporation at 180°C, after filtration at 0.45 micron High TDS value promote the scale and corrosion phenomena 03/06/2024 23

24. Impact of water characteristics Total hardness It represents the amount of alkaline salts, mainly calcium and magnesium salts, that are solubilized in the water It is expressed as mg/liter of Calcium carbonate The presence of hardness cause scale if no tretment is applied to inhibit the precipitation of the scaling salts 03/06/2024 24

25. Impact of water characteristics Temporary hardness It represents the amount of earth-alkaline b i carbonates (calcium and magnesium) in the water It is expressed as mg/liter of Calcium carbonate It is directly responsible for scale formation 03/06/2024 25

26. 03/06/2024 26 Impact of water characteristics Calcium hardness It represents the total content of calcium as bicarbonate, sulfate and possible chloride present in the water UNITS OF HARDNESS RELATION Hardness, °d French, °d German, °D English, °D USA, °d mVal ppm French 1.00 0.56 0.70 0.58 0.20 10.00 German 1.79 1.00 1.25 1.05 0.36 17.85 English 1.43 0.80 1.00 0.84 0.29 14.30 USA 1.71 0.96 1.20 1.00 0.34 17.10

27. Impact of water characteristics Water hardness 03/06/2024 27 Temporary Hardness (carbonatic) Permanent Hardness (non-carbonatic) Calci um carbonat e [ CaCO 3 ] Calci um s ulfate [ Ca S O 4 ] Magnesi um carbonat e [ MgCO 3 ] M agnesi um silicate [ MgS i O 3 ] Calci um bicarbonat e [ Ca(HCO 3 ) 2 ] Calci um chloride [ CaCl 2 ] Magnesi um bicarbonat e [ Mg(HCO 3 ) 2 ] Magnesium sulfate Silicates [ MgSO 4 ]

28. Impact of water characteristics Total alkalinity It represents the total alkaline salts present in the water (bicarbonates, carbonates, hydrates, alkaline phosphates) It is expressed as mg/liter of Calcium carbonate A lkalinity < hardness = total calcium and magnesium bicarbonate temporary hardness / carbonatic hardness Hardness - Al kalinity = non carbonatic alkalinity permanent hardness Al k a linity - Hardness = sodium and potassium bicarbonate 03/06/2024 28

29. Impact of water characteristics 03/06/2024 29

30. Impact of water characteristics 03/06/2024 30

31. Impact of water characteristics Effect of acids on Malkalinity 03/06/2024 31 Acid Degrees Bè %Active ppm required to reduce 1 ppm “M” Alkalinity H 2 SO 4 (Sulfuric) 66 93.35 1.05 NH 2 SO 3 H (Sulfamic) Crystals 99.6 1.95 Granular 93 2.06 HCI (Muriatic) 18 30 2.43 36.5 2.00 HNO 3 (Nitric) 36 52.3 2.41 38 56.5 2.23 40 61.4 2.05 42 67.2 1.87 HC 2 H 3 O 2 (Acetic) 12 99.5 1.20 H 3 C 6 H 4 O 7 (Citric) Crystals 99.5 1.28 HCHO 2 (Formic) - - - 99.5 0.92 H 2 C 2 O 4 2H 2 O (Oxalic) Crystals 99.0 0.91 ppm Acid = 1ppm Alk / PE CaCO3 * PE acido/ %activ acid

32. Impact of water characteristics Alkalinity 03/06/2024 32

33. Impact of water characteristics Alkalinity 03/06/2024 33 CONCENTRA TION BASE ON AL KALINITY M (met hylorange ) e P ( phenolphtalein ) (HCO 3 - ) (CO 3 - ) (OH - ), P = 0 M 2P < M M-2P 2P 2P = M M 2P > M > P 2(M-P) 2P - m P = M M

34. Impact of water characteristics Alkalinity and acidity 03/06/2024 34

35. Impact of water characteristics Chlorides High level of chlorides are corrosive to most of metals, specially SS It is normally considered to calculate the concentration ratio in the open systems compared to that in the make-up water Can be used as indicator for a correct operating of the cooling system It is expressed as mg/liter of Cl 03/06/2024 35

36. Impact of water characteristics Silica Concentration of silica must be under control to avoid severe scaling problem It can precipitate as silica or as magnesium silicate Since the resistivity is high, the impact on heat transfer is very critical Cleaning of silica deposits is very difficult It is expressed as mg/liter of SiO 2 03/06/2024 36

37. Impact of water characteristics Iron It can cause indirect deposition and corrosion High value of iron requires a specific pre-treatment of the water Presence of iron at > 1ppm has significative impact on the scale and corrosion inhibitor by incresing the consumption by adsorption and chelation phenomena It is expressed as mg/liter of Fe 03/06/2024 37

38. Impact of water characteristics Organic matter It could be present in the make-up or adsorbed in the circulating water from the atmosphere or leak process or bacteria proliferation Presence of organic matter could cause foaming, bacteria growth, which can initiate corrosion processes It is expressed as mg/liter of KMnO 4 or mg/liter O 2 03/06/2024 38

39. Impact of water characteristics Dissolved gases (CO 2 / O 2 / H 2 S / NH 3 / light hydrocarbons) Enter in the system with make-up, the atmosphere anf process leaks Could cause severe corrosion problems, high bacteria growth, react with the normal chemical treatments It is expressed as mg/liter of the gas 03/06/2024 39

40. Impact of water characteristics CO 2 Relationship between temperature (°C), pressure and the solubility of carbon dioxide (CO2) in water 03/06/2024 40

41. Impact of water characteristics NH 3 Relationship between percent ammonium ion (NH4+) versus temperature and pH. As the pH and the temperature rise, the fraction of NH 3 in the NH 4 + form increases. 03/06/2024 41

42. Impact of water characteristics Ether extractable Determines the presence of Greases & Oils Could affect the cooling system by promoting the bacteria growth Could create deposits with bacteria growth and initiating corrosion phenomena It is expressed as mg/liter as it is 03/06/2024 42

43. Impact of water characteristics Manganese This element can be normally present in deep waters It is easily oxidized to form deposits, specially in high temperature areas Could initiate galvanic corrosion by deposition of the oxide with high electrochemical potential Presence of Mn at a value exceeding the recommended value, need demanganizing pretreatment It is expressed as mg/liter Mn 03/06/2024 43

44. Impact of water characteristics Copper It is rare to find significative concentration of this element in the make-up waters (< 10 ppb) The source in the circulating water is normally the corrosion process Can be deposited on carbon steel surface to initiate galvanic corrosion It is expressed as mg/liter Cu 03/06/2024 44

45. Impact of water characteristics Microbiological formations Include several different species (bacteria, algae, fungi, yeasts) the proliferate in the ideal cooling water conditions It is expressed as units per milliliter Microbiological growth is one of the most critical factor for the cooling water system Produce bio-fouling with decomposition products Fast reduction of water flow and reduction of the heat transfer Metabolize acidic environment and induced corrosion (MIC) 03/06/2024 45 Microfouling

46. Mineral Salt Scale 03-Jun-24 46

47. Mineral Salt Scale Topics to be covered: Effects of Scale on Process Mechanisms of Scale Formation Factors Affecting Scale Formation Types of Commonly Encountered Scales Prediction of scale potential Scale Inhibition and Prevention Chemical Scale Inhibitors Control of Scale Inhibition Programs Norms and Economics 03/06/2024 47

48. Scale Effect of Scale on Cooling Water Systems Reduces heat transfer efficiency Decreases unit or production capacity Can promote corrosion & microbial growth Increases pump pressure requirements Higher operating costs/decreased profits 03/06/2024 48

49. Scale Impact on heat transfer Scale due to the formation of coherent and hard deposits is the predominant cause of the reduction of heat transfer It is formed with the precipitation of the scaling salts by the effect of temperature increase, high concentration (absolute and relative), pH and alkalinity increase, and critical flu-dynamic conditions 03/06/2024 49

50. Scale Impact on heat transfer From conduction heat transfer equation, is derived the negative impact that deposits have on the efficiency of the heat transfer The thermal resistance is determined by the relationship where The resistance of the water side scale (R de ) reduces the efficiency of the heat transfer equipment 03/06/2024 50 R d = 1 / U d - 1 / U c 1 U d = ____________________________________ 1 / h e + R de + R k + R di A e / A i + A e / A i h i

51. Scale Impact on heat transfer 03/06/2024 51 Type of deposit Thermal Conductivity (W/m°C) Calcium Carbonate 2.25 - 2.94 Calcium Sulfate 2.25 Calcium Phosphate 2.6 Magnesium Phosphate 2.25 Iron oxide 2.94 Biofilm 0.69 Iron metal 61,6

52. Scale Impact on heat transfer 03/06/2024 52 Insulating effect of foulant deposited uniformly on clean heat-transfer surface 0.001 0.01 0.1 10 20 30 40 50 60 70 80 90 100 Heat transfer reduction, % Scale thickness, in SiO2 Clay CaSO4 CaCO3 Al2O3

53. Scale Impact on heat transfer Economic value The thickness of the scale can be monitored by both the increse of the pressure drop and the reduction of the heat transfer The entity of the scale can be measured by periodic computation of the “Global Heat transfer Coefficient (U)” Comparing the value of the actual U with the design U can be valued the loss of efficiency and the increase of energy needed Added costs are: 03/06/2024 53 Higher maintenance frequency Lower shelf life of the equipments – Under deposit corrosion Production loss Out of spec production

54. Scale Impact on heat transfer Economic value – Example 1 03/06/2024 54 Tube diameter = 12.7 mm Deposit thickness = 1.6 mm Water flow rate reduction = 40-50% 1.6 mm 12.7 mm

55. Scale Impact on heat transfer Economic value – Example 2 Having 1 mm thickness of calcium carbonate scale in the inside surface of the tubes in a shell-tubes exchanger – water tube side – with the following design operating conditions: 03/06/2024 55

56. Scale Impact on heat transfer Economic value – Example 2 (cont’d) We can calculate the extra energy cost of pumping to compensate the heat transfer loss: 03/06/2024 56

57. Scale Impact on heat transfer Economic value – Example 2 (cont’d) Calculation of extra water flow needed 03/06/2024 57

58. Scale Chemistry Four Requirements for Scale Formation Ion Supersaturation A Nucleation Site Adequate Contact Time Dissolution & Precipitation 03/06/2024 58

59. Scale Chemistry Factors Affecting Scaling Potential Ion Concentration pH Time Temperature 03/06/2024 59

60. Scale Chemistry Contributing Factors: Hydraulics and Flow Velocities Surface Characteristics Corrosion Fouling Microbial activity System design and operation 03/06/2024 60

61. Scale Chemistry Contributing Factors (cont’d): Presence of Competing ions Latent period of precipitation Total Dissolved Solids (TDS) Total Suspended Solids (TSS) Co-precipitation Post-precipitation 03/06/2024 61

62. Scale Chemistry Commonly Encountered Cooling Water Scales Calcium carbonate Calcium phosphate Iron phosphate Iron oxides Silicates 03/06/2024 62

63. Scale Chemistry Precipitation and crystal growing 03/06/2024 63

64. Scale Chemistry The solubility of calcium carbonate, main component of scale, is function of temperature and partial pressure of carbon dioxide 03/06/2024 64

65. Scale Chemistry Calcium carbonate Solubility as function of temperature 03/06/2024 65

66. Scale Chemistry Calcium sulfate Solubility in high salinity water 03/06/2024 66

67. Scale Chemistry Other Scales found in Cooling Water Systems Magnesium silicate Silica Calcium sulfate Zinc phosphate Aluminum phosphate Calcium fluoride 03/06/2024 67

68. Scale Chemistry 03/06/2024 68 Magnesium silicate Max concentration of Mg and SiO2 in cooling water systems

69. Scale Chemistry 03/06/2024 69 Silica Solubility of different silica state as function of temperature

70. Scale Chemistry 03/06/2024 70

71. Scale Chemistry 03/06/2024 71 Deposit composition in sea water evaporator 10 20 30 40 50 60 70 80 90 100 60 66 71 77 82 88 93 99 104 Evap o rator water temperature, °C Composition of scale CaSO4 CaCO3 Mg(OH)2 Nominal temperature difference - 27 °C Concentration factor = 2

72. Scale Prediction To predict the scaling potential and/or the aggressivity of the waters have been elaborated several indices These are derived from thermodinamic and practical experiences on natural waters These indices have low meaning in case the ionic equilibrium is changed or, in presence of internal chemical treatments that modify the natural precipitation 03/06/2024 72

73. Scale Prediction Calcium carbonate indices 03/06/2024 73

74. Scale Prediction Langelier index (LI), with qualitative meaning, determines the equilibrium pH of saturated water with calcium carbonate, called saturation pH (pHs) This index is expressed by the relationship where: pH = pH actual pH s = pH saturation. 03/06/2024 74 LI = pH - pH s

75. Scale Prediction Langelier index It is calculated with the relationship Where pK' 2 = - log 10 second apparent dissociation constant of carbonic acid pK' sp = - log 10 solubility product of calcium carbonate pCa = - log 10 (Ca) in mols/liter pAlk = - log 10 (alk) in equivalents/liter 03/06/2024 75 pH s = (pK' 2 - pK' sp ) + pCa + pAlk

76. Scale Prediction Ryznar index Proposed by Ryznar, this index, called “Stability index” is computed with the relationship Where pH s = saturation pH pH = actual pH 03/06/2024 76 RI = 2pHs - pH

77. Scale Prediction Ryznar Index 03/06/2024 77

78. Scale Prediction Mineral solubility as function of cycles and pH in a open cooling water system without pH control 03/06/2024 78 9 8 7 6 5 4 3 2 1 Cycles number 5.5 6.0 7.0 6.5 8.0 7.5 9.0 8.5 9.5 10.0 10.5 11.0 CaCO 3 Ca 3 (PO 4 ) 2 (OH) MgSiO 3 SiO 2 FePO 4. H 2 O Soluble area Insol. Sol. Not soluble: FeO(OH) Fe 2 O 3 Fe 3 O 4 pH Sol. Ins.

79. Scale Inhibition Methods Limit the Concentration of Precipitating Ions Alkalinity Reduction pH Reduction Cation Reduction 03/06/2024 79

80. Scale Inhibition Methods (cont’d) Alter system design/operation Velocity Air Rumble Modify Design Metallurgy Lower Heat Flux 03/06/2024 80

81. Scale Inhibition Methods (cont’d) Add Chemical Scale Inhibitors Crystal Modifiers Chelants and Sequestering Agents Conditioners and Dispersants 03/06/2024 81

82. Scale Mechanism of Chemical Scale Inhibitors To control the deposition of the scaling salts are added specific chemicals capable to be absorbed on the surface of micro crystals limiting the growing process The absorption of the ions of these materials represents the most important factor for the control of growing process The kinetic of this process is dependant also from the degree of super saturation of the solution where: 03/06/2024 82 S = (C i - C f ) / C f S = super saturation C i = initial concentration of salt C f = final concentration of salt at the steady state

83. Scale Mechanism of Chemical Scale Inhibitors 03/06/2024 83 Scale of macrocrystal Microcrystal layer (corrosion protective) With inhibitor Micro to macro No inhibitor Stabilization Growth suppression Dispersion Crystal modification A B C Microcrystal solubility Macrocrystal solubility A C B

84. Scale Mechanism of Chemical Scale Inhibitors Crystal modification ( organophosphonates ) Modifies the Nucleation Site, allowing the formation of stable microcrystals Sequestration (polyphosphates, polymers, chelants ) Formation of soluble ion complexes, preventing precipitation reactions Scale conditioners (dispersants, lignins , tannins) Prevent precipitants from depositing 03/06/2024 84

85. Scale Crystal modification 03/06/2024 85

86. Fouling 03-Jun-24 86

87. Fouling Some common foulants are: Silt, Sand, Mud and Iron Dirt and Dust Process contaminants, e.g. Oils, Corrosion Products, Microbio growth 03/06/2024 87

88. Fouling Factors which influence fouling are: Water Characteristics Water Temperature Water Flow Velocity Microbiological Growth Corrosion Process Contamination Environmental (i.e. atmospheric pollutants) 03/06/2024 88

89. Fouling Three levels to address the effects of fouling : 1. Prevention 2. Reduction 3. Ongoing Control Chemical Treatment Charge Reinforcers Wetting Agents 03/06/2024 89

90. Fouling Charge reinforcement mechanism 03/06/2024 90 Slightly Anionic Suspended Particle Suspended Solid Which Has Adsorbed Highly Anionic Chemical Highly Anionic Chemical

91. Fouling Deposit break-up 03/06/2024 91

92. Bio Fouling 03-Jun-24 92

93. Bio Fouling Growth of microorganisms are affected by the following Nutrients Temperature pH Location Atmosphere 03/06/2024 93

94. Bio Fouling Types of Microorganism BACTERIA - need/ do not need Oxygen Aerobic - Slime and Spore former Anaerobic - SRB, Clostridia, etc. Iron bacteria – Gallionella Nitrification - Nitrosomas , Nitrobacter ALGAE - need light, food source FUNGI - destroys wood, reinforces deposits PROTOZOA - feed on bacteria/algae 03/06/2024 94

95. Bio Fouling Microbiological Treatments Common Oxidizing Biocides Chlorine Gas Bleach – Hypochlorite Bromine Tablets Stabilized Chlorine and STABREX Ozone Non- oxidicing Biocides Aldehydes, Quats, Thiazolone , DBNPA Biodispersants do not kill but remove biofilm from surfaces 03/06/2024 95

96. Bio Fouling Mode of Biocidal Action 03/06/2024 96 Isothiazolone DBNPA Glutaraldehyde Quats STABREX Chlorine Oxidants enzyme

97. Bio Fouling pH Effect on Chlorine/Bromine 03/06/2024 97 - Cl + H O HOCl OCl + H 2 2 + 10 20 30 40 50 60 70 80 90 100 4 5 6 7 8 9 10 11 12 pH HOCl or HOBr in % 10 20 30 40 50 60 70 80 90 100 OCl- or OBr- in % HOCl HOBr

98. Bio Fouling Volatility of Common Oxidants Stabilized HOBr 0.1 X HOBr 1 X Bleach - HOCl 1 2 X Chlorine Dioxide 1 1,800 X Ozone 2 160,000 X 1 Blatchley et al ., 1992 2 Montgomery, 1985 03/06/2024 98

99. Bio fouling Impact on heat transfer 03/06/2024 99 Deposits in mm Losses in % Biofilm Calcium carbonate

100. Corrosion 03-Jun-24 100

101. Corrosion Basic discussion Closed systems Open systems Once through 03/06/2024 101

102. Corrosion An electrochemical process in which a metal (i.e. iron, zinc, copper) in it’s elemental form returns to it’s native (i.e., oxidized) state. For example, iron is naturally present as iron oxide (FeO, Fe 3 O 4 , Fe 2 O 3 ). By reduction process it is transformed to native iron (Fe°) In presence of water, the elemental iron tends naturally to transform again to the oxide stat e , normally as combination of Fe 3 O 4 and Fe 2 O 3 03/06/2024 102

103. Corrosion Principles of the corrosion cell The following elements are required for corrosion to occur: a corrodible surface - one with electrons to lose (ANOD) a difference in potential - a driving force for the electrons an electron acceptor - a place for the electrons to go (CATHOD) an electrolyte, to close the circuit - conditions conducive for electron flow 03/06/2024 103

104. Corrosion Principles of the corrosion cell If one of these factors is not available, the corrosion does not occurs Main reactions in neutral-alkaline conditions, are the oxidation of the metal at the anod and the reduction of the oxygen at the cathod Basic principle of the corrosion phenomenon is that the anodic corrosion rate is equal to the cathodic corrosion rate 03/06/2024 104

105. Corrosion Principles of the corrosion cell Chemistry of the corrosion reactions: Anodic reaction Fe°--- Fe +2 + 2e - (oxidation) Cathodic reaction 1/2 O 2 + H 2 O + 2e - --- 2OH - (reduction) At low pH value (<5) the hydrogen ion (H + ) can take the place of the oxygen and close the electric circuit according to the following reaction 2H + + 2e - --- H 2 (reduction) 03/06/2024 105

106. Corrosion Principles of the corrosion cell 03/06/2024 106

107. Corrosion The Type of Corrosion is Determined by the Environment at the Anode: Chemistry Anomalies Differential Ion Cells Different ia l Oxygen Cells Surface Anomalies Deposits Surface Imperfections Dissimilar Metals 03/06/2024 107

108. Corrosion Principles of the corrosion cell 03/06/2024 108

109. Corrosion Impact of corrosion Reduction of the heat transfer efficiency Higher frequency for maintenance and cleaning Equipment replacement Leaks on water and process side Unscheduled shut-down 03/06/2024 109

110. Corrosion Principles of the corrosion cell Polarization Polarization of the anod occurs as the corrosion products form a tick and uniform layer on the metal surface Polarization of the cathod occurs as the hydroxyl ions, the hydrogen or a corrosion inhibitor, form a barrier that impedes a further reduction of the such gases (O 2 ) As these barriers are breaked (depolarization), the corrosion starts again 03/06/2024 110

111. Corrosion Principles of the corrosion cell Depolarization Main factors that can case the depolarization are: Water velocity ( erosion , cavitation ) pH High water velocity can remove the barrier causing the depolarization As the pH drops, the concentration of hydrogen increses . These ions will react with the hydroxyl ions at the cathod that is then depolarized Since at low pH the solubility of the anodic corrosion products increses , also the anod will be depolarized 03/06/2024 111

112. Corrosion Principles of the corrosion cell Polarization 03/06/2024 112

113. Corrosion Principles of the corrosion cell Impact of water velocity 03/06/2024 113

114. Corrosion Principles of the corrosion cell Galvanic corrosion It is a particular type of corrosion that occurs when two different metals are in contact between them and to the electrolyte Is formed a corrosion cell where one metal is the anod and the other is the cathod One example is the copper in contact with the carbon steel where this become the anod because, being less noble, will release more easily the electrons, and copper will be the cathod . Loss of metal occurs at the anod side, then the carbon steel will be corroded 03/06/2024 114

115. Corrosion Principles of the corrosion cell Galvanic corrosion 03/06/2024 115 - Wider cathodic area >> higher corrosion rate Small cathodic area >> lower corrosion rate Wide anodic area >> generalized corrosion - Small anodic area >> pitting corrosion

116. Corrosion Principles of the corrosion cell Galvanic series in sea water 03/06/2024 116 Magnesium Magnesium Alloys Zinc Galvanized Steel Aluminum 1100 Aluminum 6053 Alclad Cadmium Aluminum 2024 (4.5 Cu, 1.5 Mg, 0.6 Mn) Mild Steel Wrought Iron Cast Iron 13% Chromium Stainless Steel Type 410 (Active) 18-8 Stainless Steel Type 304 (Active) 18-12-3 Stainless Steel Type 316 (Active) Lead-Tin Solders Lead Tin Muntz Metal Manganese Bronze Naval Brass Nickel (Active) 76 Ni - 16 Cr - 7 Fe Alloy (Active) Ni - 30 Mo - 6 Fe - 1 Mn Yellow Brass Admiralty Brass Aluminum Brass Red Brass Copper Silicon Bronze 70:30 Cupro Nickel G-Bronze M-Bronze Silver Solder Nickel (Passive) 76 Ni - 16 Cr - 7 Fe Alloy (Passive) 67 Ni - 33 Cu Alloy (Monel) 13% Chromium Stainless Steel Type 410 (Passive) Titanium 18-8 Stainless Steel Type 304 (Passive) 18-12-3 Stainless Steel Type 316 (Passive) Silver Graphite Gold Platinum Passive Passive Passive Active Active Active

117. Corrosion Types of Cooling Water Corrosion General Etch Concentration Cell Corrosion Cracking Mechanical Damage 03/06/2024 117

118. Corrosion Types of Cooling Water Corrosion General Etch Metal loss in which a given area is alternately a cathode and an anode. Metal loss occurs uniformly over the entire surface This is the preferred type of corrosion. 03/06/2024 118

119. Corrosion Types of Cooling Water Corrosion Concentration Cell Corrosion A localized attack caused by a chemical anomaly Crevice Corrosion U nder Deposit Corrosion Tuberculation Biologically Induced Corrosion Acid or Alkaline Corrosion 03/06/2024 119

120. Corrosion Types of Cooling Water Corrosion Tuberculation Highly structured mounds of corrosion products that cap localized regions of metal loss 03/06/2024 120

121. Corrosion Types of Cooling Water Corrosion Cracking Failures caused by the combined effects of corrosion and metal stress. Initiate on the surface exposed to the corrodant , and propagate into the metal in response to the stress state. The critical factors are: Sufficient Tensile Stress A Specific Corrodant 03/06/2024 121

122. Corrosion Types of Cooling Water Corrosion Mechanical Damage Corrosion Fatigue Erosion – Corrosion Cavitation Dealloying 03/06/2024 122

123. Corrosion Principles of the corrosion cell Localized corrosion cell When the metal is exposed to different concentration of a species in solution If the concentration of the oxygen or chloride ion is different close to two areas of the metal surface, can be formed a co rrosion cell This type of cell is called differential aeration cell or differential concentration cell 03/06/2024 123

124. Corrosion Principles of the corrosion cell Differential aeration cell Different oxygen concentration available for different surface area of the metal Deposit formation create the ideal conditions to form the differential aration cell by creating a barrier to the homogeneus oxygen diffusion 03/06/2024 124

125. Corrosion Principles of the corrosion cell Differential aeration cell 03/06/2024 125

126. Corrosion Principles of the corrosion cell Differential Concentration cell Deposit formation can increase pH at the cathod and decrease pH at the anod This phenomenon is called corrosion cell at different ions concentration and occurs in a occluded cell In the occluded cell , a barrier is formed that is permeable only to particular species such as the chlorides or hydrogen (H 2 ) The negative ions of chlorides are accumulated to the anod to balance the cationic Fe++ produced by meta oxidation In the rich hydrogen and chlorides environmental most of the metal are more soluble 03/06/2024 126

127. Corrosion Principles of the corrosion cell Differential ion concentration cell 03/06/2024 127

128. Corrosion Principles of the corrosion cell Differential ion concentration cell 03/06/2024 128

129. Corrosion Principles of the corrosion cell Differential ion concentration cell 03/06/2024 129

130. Corrosion Principles of the corrosion cell Impact on corrosion - Dissolved solids 03/06/2024 130

131. Corrosion Principles of the corrosion cell Impact on corrosion - pH 03/06/2024 131 100 10 5 6 7 8 9 10 Corrosion Rate, Relative Units pH

132. Corrosion Principles of the corrosion cell Impact on corrosion - Dissolved gas Main interesting gases in industrial cooling water systems are carbonic dioxide and oxygen As CO 2 increases , pH will drop causing the depolarization of the cathodic areas In low buffered water (i.e. Condensate or demineralized water), the pH is dropped more easily than in buffered water Sulfuric acid is almost totally ionized as hydrogen sulfate ion and bisulfate ion that cause the depolarization of the anodic areas Ammonia increases the corrosion of copper and alloys of copper by complexing the copper present in the protective layer of copper oxide or copper carbonate 03/06/2024 132

133. Corrosion Principles of the corrosion cell Impact on corrosion - Dissolved gas 03/06/2024 133

134. Corrosion Principles of the corrosion cell Impact on corrosion – Temperature As rule of thumb , each 10°C of water temperature increase , corrosion rate will double This because , increasing the temperature, rises the diffusion rate of the oxygen at the cathod and the kinetic of the cathodic reaction of the oxygen reduction The oxygen corrosion on carbon steel is maximum at 80°C. This beacuse the solubility of oxygen decreases with the increment of the temperature that is in opposition with the kinetic of reaction increment with the temperature 03/06/2024 134

135. Corrosion Principles of the corrosion cell Impact on corrosion – Water velocity If the water velocity is too high, the corrosion products formed at the anod are removed from the metal surface and the protective film cannot be formed In general, corrosion increases with the increment of the water velocity However, more generalized and uniform corrosion occurs with the increment of the water velocity Increment of the water velocity reduce the corrosion of some metals, like the stainless steel and aluminum, that need the oxygen to form the passive film 03/06/2024 135

136. 03/06/2024 136 Factors impact on metal failure Fluid velocity Recommended fluid velocity for tube material in salt water (m/s) < 0.8 0.9-1.5 1.5-1.8 Copper Tube metal 1.8-2.7 2.7-3.6 3.6 Admiralty C70600 C71500 C72200 70-30 2Fe 2Mn SS = good performance = may give good performance, but may require a closer study of the conditions at the site and relationships with other factors = material not performed well

137. Corrosion General Methods for Corrosion Inhibition Use Corrosion Resistant Materials Apply Inert Barrier or Coating Use Cathodic Protection Adjustments to Water Chemistry Application of Corrosion Inhibitors 03/06/2024 137

138. Corrosion Chemical Corrosion Inhibitors Mechanism Principally Anodic Principally Cathodic Both Anodic and Cathodic 03/06/2024 138

139. Corrosion Anodic Inhibitors Function by adjusting the chemistry at the anode (point of high potential) Chromate Molybdate Nitrite Ortho Phosphate (High Dose) Silicate 03/06/2024 139

140. Corrosion Cathodic Inhibitors Function via reactions at the cathode (point of high pH) 03/06/2024 140 electrons O 2 OH - OH - OH - Cathode Zn ++ + 2 OH - Zn(OH) 2 Ca ++ + OH - + HCO 3 - CaCO 3 + H 2 O Ca ++ + OH - + H 2 PO 4 - CaHPO 4 + H 2 O

141. Corrosion Cathodic Inhibitors Zinc Ortho Phosphate (low dose) Polyphosphate Phosphonates Calcium Carbonate 03/06/2024 141

142. Corrosion Both Anodic and Cathodic Inhibitors Soluble Oils Azole Filmers ( copper alloys protection ) Mercaptobenzothiazole (MBT) Benzotriazole (BZT) Tolytriazole (TT) 03/06/2024 142

143. Corrosion Closed systems 03/06/2024 143

144. Corrosion Closed system Operation Medium/High heat flux Use of demineralized water High residence time Presence of multi-metals Low/no water consumption (low/no fresh water / treatments) 03/06/2024 144

145. Corrosion Closed system – Operation Water characteristics Desalinated water quality (demineralized, softened, condensate) is normally used to avoid scale problems However, desalinated water, not buffered, is very aggressive to the metals, specially carbon steel and copper alloys Biological fouling must also be under control to prevent Microbiological Induced Corrosion (MIC) Good metal passivation is absolutely necessary to prevent the damage of the equipments 03/06/2024 145

146. Corrosion Closed system - Metal protection Protection of closed circulating water systems generally features both high pH and high inhibitor levels System pH is most often held at 8,5-9,5 – This reduce the corrosion of mild steel substantially 03/06/2024 146

147. Corrosion Closed system – Metal Protection Treatment (anodic) Must be capable to create a very strong passive barrier by modifying the corrosion potential in the anodic direction 03/06/2024 147 Corrosion current Equilibrium potential Anodic Cathodic Passive potential E Log(i)

148. Corrosion Closed system – Metal Protection Basic treatments Chromates (200 – 1500 ppm) Restricted by envirnmental laws Pump seal failure at high dosage Nitrites (300 – 1500 ppm) Excellent mild steel protection, even for pre-corroded surface Use borax as buffering agent (pH > 8,5) Nitrite is a nutrient for bacteria growth ( Nitrification ) Bacteria produce low pH and slime deposits Molybdates (100 – 200 ppm) Week anodic inhibitor Often combined with nitrites and other agents High risk in case of under-dosing 03/06/2024 148

149. Corrosion Guideline for assessing corrosion* 03/06/2024 149 *Indicated rates apply to general system corrosion mm/year 0 to 0.05 0.05 to 0.075 0.075 to 0.13 0.13 to 0.25 0 to 0.05 0.05 to 0.13 >0.13 0 to 0.03 >0.03

150. Monitoring Detection methods for water problems: 03/06/2024 150