Cooling water treatment (Corrosion) Cooling water treatment (Corrosion) Department: Chemistry Department: Chemistry MS Industrial chemistry 2014 MS Industrial chemistry 2014 M.Kamran ul hassan M.Kamran ul hassan S.Zulfiqar Ali S.Zulfiqar Ali Kapil Dev Kapil Dev Fabiha irfan Fabiha irfan Nida naz Nida naz Faiza iftekhar Faiza iftekhar
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Cooling water treatment (Corrosion)Cooling water treatment (Corrosion)Department: ChemistryDepartment: Chemistry
MS Industrial chemistry 2014MS Industrial chemistry 2014
M.Kamran ul hassanM.Kamran ul hassan S.Zulfiqar AliS.Zulfiqar Ali
Kapil DevKapil Dev Fabiha irfanFabiha irfan
Nida nazNida naz Faiza iftekharFaiza iftekhar
Customer Training WT200C Page 2
Water treatment :Water treatment :
� Pretreatment of water.� Corrosion mechanism� Factor effecting rate of corrosion� Protection of corrosion� Water treatment for corrosion site� Water chemistry� Calculations
Pre-treatment of waterPre-treatment of water
Clarification:A process used to improve water by separating and removing suspended solids from water.Sedimentation :When solid settle out of liquid.
Pre-treatment of water internal Pre-treatment of water internal structure of clarifier:structure of clarifier:
Pre-treatment of water overview Pre-treatment of water overview of clarifier:of clarifier:
Pre-treatment of water weir flow:Pre-treatment of water weir flow:
Customer Training WT200C Page 7
Pre-treatment of water:Pre-treatment of water:
Customer Training WT200C Page 8
Pre-treatment of water:Pre-treatment of water:
Pre-treatment of waterPre-treatment of waterDetention Time (DT):
The time it takes for a drop of water to travel from inlet to outlet.
Typical Design Value 2-3 hrs
Pre-treatment of waterPre-treatment of waterIf the incoming flow rate is too high, then the water will spend less time in the tank (the detention time will be low) and all of the floc may not be removed. If the incoming flow rate is low, the amount of time the water will spend more time in the tank (detention time will be high) and the water treatment plant may not be operating at its optimum capacity
CorrosionCorrosion
� Destruction of plant� increased maintenance costs
� Fouling� loss of efficiency due to increased pumping
costs� loss of heat transfer efficiency
� Increased Biological Nutrients� fouling and health implications
Objectives of Water TreatmentObjectives of Water Treatment� MINIMISE SCALE � MINIMISE CORROSION� MINIMISE FOULING� MINIMISE BIOFOULING� MAXIMUM EFFICIENCY
PROBLEMS OF WATERPROBLEMS OF WATER
� Effect of conductivity
How pH does affect the How pH does affect the system?system?
� Acidic and slightly alkaline water can dissolve metal and the protective oxide film on metal surfaces. More alkaline water favors the formation of the protective oxide layer.
How Oxygen does affect How Oxygen does affect the system?the system?
• Temperature increases diffusion of oxygen to metal surface also increases Promote corrosion.
How Turbidity does affect How Turbidity does affect the system?the system?
How pH does affect the How pH does affect the system?system?
� In general, when pH is below recommended ranges, the chances for corrosion increase and when pH is above recommended ranges, the chances for scale formation increase. The effectiveness of many biocides also depends on pH; therefore high or low pHs may alleviate the growth of microbiological problems
How pH does affect the How pH does affect the system?system?
Corrosive Water Scale-forming Water
low pH high pH
soft or with primarily noncarbonate hardness( Chloride & Sulphate)
hard with primarily carbonate hardness(Carbonates ,Bicabonates 7
Hydroxide)
low alkalinity high alkalinity
Soft: 0 to75 mg/L as CaCO3 Hard: 150 to 300 mg/L as CaCO3 Moderate: 75 to 150 mg/L as CaCO3
Very Hard: Above 300 mg/L as CaCO3
Factors that affect the Factors that affect the corrosion:corrosion:
� P H:� Acidic and slightly alkaline water can
dissolve metal and the protective oxide film on metal surfaces. More alkaline water favors the formation of the protective oxide layer.
� Dissolve gassaes: Oxygen dissolved in water is essential for the cathodic reaction to take place.
Factors that affect the Factors that affect the corrosion:corrosion:
� Temperature:
� Temperature increases diffusion of oxygen to metal surface also increases Promote corrosion.
Factors that affect the Factors that affect the corrosion:corrosion:
� Velocity: � High velocity water increases corrosion
by transporting oxygen to the metal and carrying away the products of corrosion at a faster rate.
� When water velocity is low, deposition of suspended solids can establish localized corrosion cells, thereby increasing corrosion rates
Factors that affect the Factors that affect the corrosion:corrosion:
Microbial growths Microbial growths promote the
formation of corrosion cells in addition; the by products of some organisms, such as hydrogen sulphide from anaerobic corrosive bacteria are corrosive.
Alkalinity:Alkalinity:� In cooling water two forms of
alkalinity play a key role. These are carbonate (CO3) alkalinity and bicarbonate (HCO3) alkalinity. Bicarbonate alkalinity is by far the most common. Alkalinity and pH are related because increase in pH indicates increases in alkalinity and vice versa.
Alkalinity:Alkalinity:
When OH- CO3 HCO3
P=O 0 0 T
2P<T 0 2P T-2P
2P=T 0 2P 0
2P>T 2P-T 2(T-P) 0
How does Alkalinity affect How does Alkalinity affect the system?the system?
� When water with carbonate or bicarbonate alkalinity is heated, the alkalinity is broken down to carbon dioxide. The carbon dioxide released, combines with the water to give carbonic acid, which can cause corrosion of iron or steel equipment. The corrosion products react further with alkalinity and the deposits can build up in the same manner as calcium carbonate scale.
Customer Training WT200C Page 28
How do chemical corrosion How do chemical corrosion inhibitors work?inhibitors work?
Anodic inhibitors :� Form a protective film on the anod.� All oxidizers and promote passivation by
increasing electrical potential of iron.
Customer Training WT200C Page 29
How do chemical corrosion How do chemical corrosion inhibitors work?inhibitors work?
Cathodic inhibitors: � form insoluble precipitate that coat of
protective surface on the cathode.� At cathode of corrosion cell is elevated due to
generation of hydroxide ion..
Customer Training WT200C Page 30
How do chemical corrosion How do chemical corrosion inhibitors work?inhibitors work?
Cathodic inhibitors: � Calcium orthophosphate also cathodic
How do chemical corrosion How do chemical corrosion inhibitors work?inhibitors work?
Mainly anodic: � Chromates, (in absence of oxygen)� Nitrites, (in absence of oxygen)� Orthophosphates & Molybdate (in presence of oxygen)� Mainly cathodic:( Precipitator) p H 7-9� Bicarbonates/ carbonate ( Calcium cabonates)� Metal cations, Zn hydroxide� Polyphosphates (Ca –phospate)
Customer Training WT200C Page 33
How do chemical corrosion How do chemical corrosion inhibitors work?inhibitors work?
� Most closed-loop water systems use a sodium nitrite based inhibitor for corrosion control and a biocide to prevent biological contamination. These inhibitors will protect both the ferrous and non- ferrous materials in your piping system...
Customer Training WT200C Page 34
How do chemical corrosion How do chemical corrosion inhibitors work?inhibitors work?
The major advantages of using nitrite based corrosion inhibitor are as follows:-
� Removes dissolved oxygen by converting the nitrite to nitrate.
� Negligible loss of metal or corrosion. � Excellent heat transferability and flow rate. � Long and extended life of Water without fouling
Customer Training WT200C Page 35
Water treatment Chemicals Water treatment Chemicals for close loop system:for close loop system:
Customer Training WT200C Page 36
Recommended Estimation Recommended Estimation Dosage of chemicals:Dosage of chemicals:
Chemicals Purpose Concetration Consumption kg / day
Scal Trol PDC 9325Cathodic corrosion
inhibitors 1ppm 68
Spectrus NX1104 Non Oxidizing Bioside 60 ppm 178/shock
BetzDearborn AP1120 P Anionic polymer 0.3 ppm 22
Caustic p H & Alkalinity control p H 7.5-8.5 1500-2500
CorrShield NT 4201Anodic corrosion
inhibitors 500-1000 ppm 2.5kg/m3
Customer Training WT200C Page 37
Blowdown & make up Blowdown & make up water calculation:water calculation:
Customer Training WT200C Page 38
Control of ConcentrationControl of Concentration
� The number of times the solids build in the system water is termed the concentration factor (CF).
� CF is controlled by bleed � to increase CF - decrease bleed� to decrease CF - increase bleed
Customer Training WT200C Page 39
Bleed ControlBleed Control� Effect of too much or too little bleed:
� Too much bleed :-� low concentration factor� waste of water � waste of treatment
� Too little bleed:-� high concentration factor� danger of scale and fouling � increased nutrient in system� danger of biofouling
Customer Training WT200C Page 40
1 2 3 4 5 6
xxx
x
x
Concentration Factor
WaterUse
x While increasing concentration factor reduces water use, it also increases nutrients in the system water, encouraging growth of bacteria and slimes. Therefore, we normally run most cooling systems between 2 and 5
Customer Training WT200C Page 41
Non Oxidising BiocidesNon Oxidising Biocides
• Screen water• Select alternating biocide to prevent resistant strains from
developing
• Effective against SRB’s
• Can protect system long after dosing.
• Contain biodispersant
• Higher dosage for kill possible
• Environmentally some have rapid breakdown e.g. DBNPA
Customer Training WT200C Page 42
Non Oxidising BiocidesNon Oxidising Biocides
• Screen water• Select alternating biocide to prevent resistant strains from
developing
• Effective against SRB’s
• Can protect system long after dosing.
• Contain biodispersant
• Higher dosage for kill possible
• Environmentally some have rapid breakdown e.g. DBNPA
Customer Training WT200C Page 43
Non Oxidising BiocidesNon Oxidising Biocides
• Screen water• Select alternating biocide to prevent resistant strains from
developing
• Effective against SRB’s
• Can protect system long after dosing.
• Contain biodispersant
• Higher dosage for kill possible
• Environmentally some have rapid breakdown e.g. DBNPA