Cooling water Treatment presentation

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

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:


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

Corrosion reaction:Corrosion reaction:2Fe + O2 + 2H20 → 2Fe+ + + 4OH-

Anode reaction: 2Fe → 2Fe+ + 2e

Cathode Reaction: O2 + 2H20 + 2e → 4OH-


Corrosion mechanismCorrosion mechanism

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?


� 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


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.


� Temperature:

� Temperature increases diffusion of oxygen to metal surface also increases Promote 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


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.


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.



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..



Cathodic inhibitors: � Calcium orthophosphate also cathodic

inhibitors.� Orthophosphonate dual mechanism anodic

inhibitor & cathodic precipator.



Cathodic inhibitors:� Orthophosphonate dual mechanism anodic

inhibitor & cathodic precipator. HDPE +Fe == Fe Phosphonate (At anod)

� HDPE +Ca == Ca Phosphonate(cathode)



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)



� 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...



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


Water treatment Chemicals Water treatment Chemicals for close loop system:for close loop system:


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


Blowdown & make up Blowdown & make up water calculation:water calculation:


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


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


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


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


Cooling tower Calculation:Cooling tower Calculation:

Parameters Symbol /derivation values

RR RRM3/hrs 2834

System volume Vm3 2967

Hot water temp C 63

cold water temp C 31

Delta -T ∆T 32

Evaporation rate Ev 127

Cycles of concentration Nc =Ev+BD/BD 3

Blowdown rate BD=E/Nc-1 63

Make up rate MU=E+BD 190

Metallurgy MS


Clarifier data:Clarifier data:

Parametrs Values

Clarifier Feed flow 3052m3/hrs

Clarifier Feed inlet temp 73 C

SS OF Feed water 3170ppm

System volume 10732m3


Process water data:Process water data:

Parametrs Values

P H 7-8

TDS <100 PPM

Ca H <35PPM

Total Iron <0.3

T.Aerobic bacteria <10000 cfu/cm

M.Alkalinity <50 ppm

Chloride <25ppm


Make up water& R O data:Make up water& R O data:Parametrs Make up water R O WATER

P H 7-8 7-8

Conductivity 650 <50

Ca H 80 3PPM

Mg H 55 N/A

Total Iron 0.12 N/A

SS 6 N/A

M.Alkalinity 80 ppm <10 ppm

Chloride 90 ppm <15ppm


Pro. Water & MCW data:Pro. Water & MCW data:Parametrs Process water Machinery C.W

P H 7-8 8.5-10.5

Conductivity 200 -250 <3500

Ca H <35 N/A

Total Iron <0.3 <0.3

Total aerobic bacteria <10000 CFU/CM Nil

M.Alkalinity <50 N/A

Chloride <25 ppm N/A


The Ryznar Stability Index formula:

RI Indication (Ryznar 1942)

RI<5,5 Heavy scale will form

5,5 < RI < 6,2 Scale will form

6,2 < RI < 6,8 No difficulties

6,8 < RI < 8,5 Water is aggressive

RI > 8,5 Water is very aggressive

is:


The Ryznar Stability Index formula:

pH

Conductivity in TDS

[Ca2+]

[HCO3-]

Water temperature

RI

is:


Blow down & make up Blow down & make up water calculation:water calculation:


Cooling tower efficiency:Cooling tower efficiency:

� Approach = Cold Water Temperature – Wet Bulb Temperature Range = Hot Water Temperature – Cold Water Temperature

Cooling Tower Efficiency = Range/ (Range + Approach) X 100 32/35*100= 91.43%


What is in your mind ask?What is in your mind ask?

Cooling water Treatment presentation

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