COOLING WATER TREATMENT

ByPrem Baboo

National Fertilizers Ltd.India.Fellow of Institution of Engineers, India

INTRODUCTION• Location- At Vijaipur, Dist-Guna

Around 850km from Mumbai.• Plant details

Unit Vijipur I Vijaypur II

Ammonia Plant MTPD 1520 1520Urea Plant MTPD 2620 2620CPP MW 3 x 17.5 3 x 17.5Raw Material NG NG/NaphthaCommisioning 1987 1998

Details of Cooling Tower.

Ammonia I Urea I Ammonia II Urea IIType Induced

draftCross flow

Induced draft

Cross flow

Induced draft

Cross flow

Induced draft

Cross flow No. Of Cells

6 5 6 5

Delta T 10 10 10 10CR m3/hr 17000 16000 18000 17000System Hold Up

7500 7000 7500 7000

Make up Water QualityParameter UNITS Typical RangepH 7.5 – 8.2Total Hardness Ppm 75 – 120Ca-Hardness Ppm 50 – 80Mg-Hardness Ppm 25 – 40

Silica Ppm 10 – 25Chlorides Ppm 10 – 25M-Alkalinity Ppm 60 – 150Sulphates Ppm 10 – 50TDS Ppm 150 – 200

Re-circulating Water Parameters. Parameter Units Normal Operating

RangepH NTU 6.8 – 7.5Turbidity Ppm 5Total Hardness Ppm 700 – 800TDS Ppm 2200maxSilica Ppm 100maxChlorides Ppm 150 – 250Iron Ppm 1.5maxZinc Ppm 1.0maxTotal PO4 Ppm 4 – 8COC 6-8TBC Counts/ml 1 x 105

SRB Counts/100ml

100

Monitoring Tools1. Corrosion Coupons2. Deposit monitor3. Bio-fouling monitors4. Test heat exchanger5. Microbial counts6. ORP meter7. Inspection of cooler during shut

down

Cooling Systems

• Once-through systems• Closed recirculating systems• Open evaporative recirculating

Simple Cooling Water Diagram

Simple cooling water diagram.

Cooling tower

Blow down

[evaporation]

Return water Coolers

Heat exchangers

Cooling Water Terminology• Cooling water - water used to cool process

fluid, condense steam, cool oil, air, etc• Make-up water - fresh water added to

make-up for loss water• Evaporation - droplets of hot return water

that evaporate taking heat with them cooling the remaining water

• Blow-down or bleed-off - water that is being drained or loss beyond control

Terminology• Cycle of concentration - how many

times concentrated the cooling water is compared to the make up water (dissolved solid concentration)

• Drift loss - loss of water through windage

• Circulation Rate - total circulation pump flow rate

Terminology• Supply temperature - temperature of

the supply water• Return temperature - temperature of

the return water• Delta T (temperature different) - the

difference between return and supply temperature (T return - T supply)

Relationship of various parameters• Cycles Of Concentration C = Concentration in Recirculation Concentration In Make-up

• Evaporation Loss E = 0.0018 x deltaT x R x TF (Tower

Factor)* ( T expressed in oC)

* Tower factor is based on humidity/% contribution of evaporation to delta T

Relationship of various parameters• Windage Loss

W = 0.05 to 0.2 x R / 100

• Blow Down B = E / ( C – 1 ) • Make-up M = E + W + B

Cooling Water Chemistry• pH• Conductivity or Total Dissolved Solid• Turbidity or Total Suspended Solid• Total hardness• Calcium hardness• Alkalinity (p and m)• Chloride• Sulfate• Silica

More Parameters

• Total Iron• Inhibitor residuals (i.e. o-phosphate,

phosphonate, zinc, molybdate, etc.)• Bacteria counts (TBC , SRB, Nitrifying )• Chlorine i.e FRC• ORP• CLO2 levels

pH• Low pH means more hydrogen

ions• Hydrogen ions depolarizes

corrosion cells accelerating corrosion

• High pH means more hydroxyl ions

• Environment for scales formation• Environment for microbiological

activities

Conductivity or TDS

• High values mean more dissolved minerals

• Higher ions movement improves electrical conduction

• Increase the rate of electrochemical corrosion.

Turbidity and Total Suspended Solid

• The content of suspended solid in the water - silt, debris, air-borne materials

• Higher values indicate potential fouling due to deposition of the solid

• The deposition might be combined with microbiological activities - microbiological sludge and MIC

Total Hardness• The contents of permanent hardness -

calcium, magnesium, barium, strontium• Generally indicates the total content of

calcium and magnesium as CaCO3

• Read as CaCO3 due to the molecular weight - 100

• High values indicate potential scales formation when there is a presence of complexing anions

Calcium Hardness• The content of calcium in water

read as CaCO3

• The most common component of scales in water system

• May form calcium carbonate, calcium phosphate and calcium sulfate scales

• High values may also indicate less corrosive (electrochemically) water

Alkalinity• Acid neutralizing ability

• Free mineral acidity - CO2 at pH < 4.2

• M-alkalinity consisting of HCO3- and

CO32- beginning from methyl-orange

point pH >4.2

• P-alkalinity consisting of CO32- and OH-

beginning from phenolpthalien point pH >8.2

Chloride and Sulfate• Corrosive ions - form metal

chloride and sulfate then mineral acids

• Cause pitting corrosion• Chloride - environment for SCC -

stainless steel• Sulfate - required element for SRB

Total Iron

• High values may indicate corrosion activities

• Potential deposition of corrosion products - fouling and under-deposit corrosion

Inhibitor Residuals• Depending of inhibitors used and

control ranges• Inhibitors - phosphate (ortho or total),

phosphonate, zinc, molybdate, toly-triazole

• Low level - insufficient protection• High level - potential scales formation

(precipitative chemistry) and non economical

Why do we treat cooling water?• Corrosion of ferrous and non-ferrous

metals - electrochemical• Precipitation and deposition of

mineral scales• Deposition of suspended solid• Microbiological sludge deposit • Biofilm or microbiological slime• Microbiologically influenced corrosion

Corrosion Scaling

PROBLEMS

Fouling

General Fouling Microbial Fouling

Algae,

Fungi,

CORROSION• Corrosion is an electrochemical

process by which metals return to their native state

• Mild Steel reverts back to Iron Oxide

• This is also true for copper alloys, Zinc, Aluminum etc.

Localised corrosion• c

+ Cathode +

Fe(OH)3

Fe2O3

Fe(OH)2

Fe++

- Anode -

Fe

Metal

e-

e-e-

e-

+ Cathode +OH-

02+H2O

Corrosion Cell 2Fe + O2 + 2H2O ---> 2Fe (OH )2 Ferrous

Hydroxide

2Fe(OH)2+H2O+1/2O2 ->2Fe(OH )3

Hydrated Ferric

Oxide

Prevention Of Corrosion• Condition the metal

– coating (Zinc,Epoxy Resin) .

– Alloy the metal (Stainless Steel)

• Condition the environment Remove Oxygen

• Use corrosion inhibitors

Corrosion Inhibition Mechanisms

• Oxidation• Oxidation with film strengthening• Cathodic polarization• Cathodic precipitants

Anodic InhibitorsAn anodic Inhibitor interferes with the

Anodic process

• Chromate• Molybdate• Phosphate• Nitrite• Phosphonates

Oxidation (With complexation)• .

Fe++

2e--

PO4PO4

Fe3(PO4)2 FePO4

Cathodic Inhibitors A Cathodic inhibitor interferes with the

cathodic process by precipitating an insoluble species onto the cathodic site.

• Zinc• Calcium Carbonate• Polyphosphate• Phosphate• Phosphonates

Cathodic Precipitants• .

Zn

e-

e-

e-

e-

e-

O2

O2

O2

O2

O2

OH-OH-OH-

ZnCa

HCO3HCO3

HCO3HCO3

HCO3

HCO3CaCa

Ca Zn

ZnZn

Zn

Zn(OH)2

HCO3 + OH H2O +CO3

CO3CO3Zn CaCO3

Zinc• Forms zinc hydroxide and zinc

carbonate complexes at cathode• Good for soft water• Above pH 8 will begin to precipitate

in bulk water• Zn is stabilised by phosphonates and

polymers• Levels from 0.25-3.0 ppm used

Poly and Ortho-phosphate• Form complexes with Ca at cathode• Need to formulate stabilizing polymer

with package• Also reacts at anode to form iron

phosphate complex• Levels of 2-15ppm typically used

depending on program

Scaling Caused by crystalline growth of salts on

the system surfaces• CaCO3 (Calcite) : Major Scale • Silica :Amorphous silica precipitates,when

*SiO2 > 150 ppm at pH < 8.0 . > 180 ppm at pH > 8.0

• MgSiO2 :Adsorption of silica on precipitated Mg(OH)2 (Brucite)

• Ca5(PO4)3OH (Hydroxyapatite)• CaF2 (Fluorite) : Potential foulant

Solubilities (20 / 100 deg C)

• Sodium Chloride• Sodium Sulphate• Sodium Carbonate• Sodium Bicarbonate• Sodium Phosphate• Calcium Chloride• Calcium Sulphate• Calcium Carbonate• Calcium Bicarbonate• Calcium phosphate

36% / 39% 16% / 30% 32% / 31% 8% / Dec 11% / Dec 43% / 61% 0.3% / 0.06% 0.005% /0.002% 0.08% / Dec 0.0003%/ 0.0002%

Solubilities ( 20 deg C )

• Silica• Ferrous

Hydroxide• Ferric

Hydroxide

• 0.005%• 0.0007%• 0.0001%

Formation of Hardness scale• Calcium Carbonate has inverse

solubility

• Ca(HCO3)2-------> CaCO3 + H2O + CO2

• Mg(HCO3 )2------> MgCO3 + H2O + CO2

• MgCO3+ H2O-----> Mg(OH)2 + CO2

Scale Formation• CaCO3 precipitates at Saturation pHs

and depends primarily upon:– Level Of calcium hardness– Level Of Bicarbonate alkalinity– pH– TDS– Temperature– Water velocity

Scale Inhibition• Remove hardness salts.

• pH control with Acid

• Dose scale inhibitor

Acid Dosing• Used to limit pH in hard water systems.• Helps in inhibitor selection• Potential for water and treatment savings by

allowing an increase in COC• Each 1ppm M Alkalinity will require:

• 1.0 ppm sulphuric acid• 2.0 ppm Hydrochloric acid• 1.8 ppm Nitric acid

Scale Inhibitors• Added to extend Induction time beyond Retention

time • Induction time decreases with increase in

Saturation level ( Driving force)• Effectiveness of Inhibitor depends on the extent

to which it increases Induction time at lesser dosage

• Inhibitor dosage is increased with increase in Induction time

• If retention time is less than induction time there is very little need of scale inhibitors

Dispersion• A process by which charged particles are

prevented from agglomerating into larger particles rendering them less settleable.

• Most cooling water particulates have a net negative charge. Acrylate dispersants also have a net negative charge. Addition of dispersant increases charge inhibiting agglomeration.

Dispersants• Polyacrylate• Acrylate /Acrylamide• Acrylate terpolymers• Sulfonated styrene• Maleic Acid Homopolymer• Maleic acid co and terpolymers

Bio Fouling• Caused by the excessive growth of

microorganisms.

• Cooling water system-ideal incubator for growth

Problems• Pitting corrosion-depolarising action

of O2 released during their metabolic process.

• Shield metal surfaces from the action of inhibitors

• cause legionella pneumophila disease

Chemical Control• Microbiocides e.g.

Bacteriacides,Fungicides,Algaecides

• Microbiostats e.g.

Bacteriastats,Fungistats,Algaestats

• Surfactants

Microorganisms

• Viruses

– Consists of protein & DNA/RNA (Nucleic acids)

– Survive by multiplying in other host cells - plant or Animals

Cooling Water as a MediumIdeal temperature (200C-600C)pH 6 to 8Often exposed to sunlightSome made of woodNitrogen and phosphorous based

inhibitorsSuspended and airborne debrisGood aerationPresence of process fluids like

ammonia, urea, other organics and sunlight

.• Algae

– Photosynthesis– Uni/Multicellular– Diverse Forms

Filamentous Colonial Plantlike

• Diatoms– A Group of Algae– Organic walls impregnated with silica

.• Blue Green Algae

– Photosynthetic bacteria

• Fungi – Aerobic growth above the waterline– Do not contain chlorophyll

.• Mould

– Fungus which forms visible layer on the surfaces - Wood/Walls/Foods

• Yeast– Unicellular Fungi

• Protozoa– Diverse group of unicellular Microorganisms

Bacteria• Unicellular• Cells may grow attached to each other in

clusters , chains , rods or filaments• Require carbon source for growth• Different shapes

– Rods Bacillus– Spherical Coccus– Spiral Spirill

• Protected by slime• Multiply by cell division

Bacteria (Classification )

• Aerobic Requires O2 & CO2• Anaerobic Grow in O2 free atmosphere• Facultative Grow in both conditions• Autotrophes Inorganic nutrients• Heterotrophes Organic nutrients• Psychrophiles < 22 0c• Mesophiles 22 ~ 45 0 C• Thermophiles > 45 0 C • Planktonic Free floating organisms in .

Water• Sessile Surface attached growing in .

Biofilm

Methods Of Control• Physical

– Nutrient Removal - Remove food or energy source .

e.g. Sunlight , Dead Leaves.Process Contamination.

– Temperature Control - Increase temperature

Not really practical on a Cooling System

Methods Of Control• Chemical

– pH Adjustment• With the help of Acid / Caustic (pH’s Over 10.0 Required)

– Microbiocide Control• Kill Organisms by use of toxic materiale.g. Algaecides,Fungicides, Bacteriacides

Chemical Control• Microbiocides e.g.

Bacteriacides,Fungicides,Algaecides

• Microbiostats e.g.

Bacteriastats,Fungistats,Algaestats

• Surfactants

Biocide Classification• Oxidising Materials

– Have the ability to oxidise organic matter– Irreversibly oxidise protein groups

• Non-Oxidising Materials– Destroy or inhibit normal cell metabolism by

any of the following ways:-• Altering permeability of cell wall• Destroying protein groups• Precipitating protein• Blocking metabolite reaction

Sulphate Reducing Bacteria• Anaerobic and convert dissolved sulphur

compounds to H2S 10 H++ SO4

-2+ 4Fe --> 4Fe+2+H2S +4H2O H2S + Fe+2 --> FeS + H+

• H2S released corrodes Carbon steel and Copper based alloys.

• Localised pH depressions cause further attack

• Exist mainly below deposits devoid of oxygen

• Corrosion rate as high as 100 mpy occurs

Nitrifying / Iron Bacteria• Nitrifying Bacteria :

– Oxidation of Ammonia . NH3 + 2O2 ---> HNO3 + H2O

– Nitrosomonas , Nitrobacter

• Iron Bacteria : – Oxidation of ferrous ions

. ++ .

– Fe + O2 ----> Fe2O3 – Crenothrex

Limitations Of Chlorination• Not effective in alkaline water

Cl + H2O = HOCl + HCl HOCl -> OCl- + H+

OCl- is 1/80 th time as effective as HOCl

Deactivated by the reducing agents H2S ,SO2,,NH3,polyacrylamide, Monoethnolamine,etc.

• Deactivates some Organo phosphonates, Does not penetrate slimes

• Extremely corrosive to many metals-maintenance of chlorinator is difficult.

• Environmental limitations - 0.1 ppm. Free Cl2 can kill fish

• When not effective use bromine compounds,chlorine dioxide,ozone

Chlorine A strong smelling, greenish-

yellow gas with pungent odor which is extremely irritating to mucous membranes.

Chlorine Gas• Hazardous• Heavier than air• Strong oxidizer• Low capital requirements• Produces chlorinated by-

products• Efficacy - pH dependent

Chemistry Chlorination

Chlorine gas dissolves in water and hydrolyses as:

Cl2 + H2O HCl + HOCl (hypoclorous acid)

HOCl ↔ H+ + OCl- – (hypo chlorite ion)

The percentage distribution of hypochlorite ion and undissociated hypochlorous acid can be calculated for various pH values.

The amount of hypochlorite ion becomes appreciable above pH 6 while molecular chlorine is non-existent.

HOCl is about 80 times more effective than OCl- as a biocide

Microbicidal Efficiency• HOCl – the microbicidal efficiency is due to

the relative ease with which it can penetrate cell walls. The penetration is quite comparable to water.

 • OCl- - Poor disinfectant (about 1/80%

efficiency of HOCl). It is unable to diffuse cell wall of microorganisms due to negative electrical charge.

Chlorine EffectivenessAt Various pH

0102030405060708090

100 01020304050607080901004 5 6 7 8 9 10

Percentage HOCl

pH Value

Percentage OCl -

Microbiological Action

• Diffusion of active agent through cell wall and attack the enzymes group whose destruction results in death to the organism. Hence microorganisms are not immune to chlorine

Factors affecting chlorine efficiency:1.Concentration of Free Chlorine2.Contact time3.Temperature4.Types and concentration of organisms5.pH6.Contaminants

Chlorine Di-Oxide• Draw backs of chlorine can be over

come with help of Clo2 mainly in NH3 contaminated water.

• It can be produced on site as• 2NaClO2 + Cl2 2 ClO2 + 2NaCl• ClO2 does not react with ammonia

thus gets effective in controlling microorganisms.

Limitation of Chlorine• Chlorine reacts with organics, hence

exerts a chlorine demand leading to higher chlorine consumption and non-maintenance of residual

• Difficult to handle and dose• Efficacy of chlorine is pH dependent• Chlorine is highly corrosive

Chlorine Reactivity1. With Ammonia- HOCl + NH3 NH2Cl (mono chloramines) +

H2O

- NH2Cl + HOCl NHCl2 (dichloramine) + H2O

- NHCl2 + HOCl NCl3 (trichloramine) + H2OIt means one ppm of ammonia can react with 3 ppm of chlorine, hence will increase chlorine demand

Chlorine Reactivity2. With Organic Nitrogen• Proteins hydrolyzes to amino

acids.• Chlorination chemistry of these

are extremely complex• Because of various hydrolysis

products.• Finally the products are mono/di-

chloramines.

Chlorine Reactivity3. With Urea• Urea hydrolyzes with nitrogen breaking down to

ammonia in presence of urease enzyme. • If the hydrolysis lacks this enzyme, the

formation of NH3 is greatly inhibited. • If significant quantity of urea-N is present and

hydrolysis proceeds at slow rate, unstable residue could result.

• Urea-N would then be reservoir for the production of ammonia.

Chlorine Reactivity4. Inorganic Carbon:C + Cl2 + 2H2O 4 HCl + CO2

This takes place in dechlorination with granular activated carbon.

5. Cyanide:At alkaline pH 8.5 or higher,2Cl2 + 4NaOH + 2NaCN 2NaCNO +

4NaCl + 2H2O

Chlorine Reactivity6. Hydrogen sulphide:H2S + 4Cl2 + 4H2O H2SO4 + 8HCl Here 8.3 ppm of chlorine is required

to oxidize 1 ppm of H2S.

Chlorine Reactivity

9. Hydrocarbons:

Hydrocarbons create high chlorine demand due to high oxidisable organics.

Chlorine Dioxide Application Technology

Chlorine DioxideIntroduction• Strong oxidizer• Not a halogen• Selective reactivity• Generated on site• pH independent• Low capital requirements

Chlorine Dioxide (Contd.)• Rapid acting. Lower contact time for micobiological kill compared to chlorine

• Less corrosive compared to chlorine• Does not hydrolyse to form acid• Does not react to form chloramines• Does not form trihalomethanes with

organic matter like chlorine• Does not produce any chlorinated

compounds

Chlorine Dioxide Mechanism of Kill

Disruption of protein synthesis or lysing of cell

No resistivity by organisms

Chlorine Dioxide Effectiveness at Various

pHs

0102030405060708090

100

4 5 6 7 8 9 10

% Active

pHLb./Equal Performance 1

Chlorine DioxideSafety Considerations

Not handled as a gas Typical use is < 0.3% solutions On-site generator is required

Selection criteria of suitable oxidant• Efficacy • Safety handling• Regulatory reporting• Process contamination• pH dependence

Safety

Sodium Hypochlorite

Sodium BromideChlorine DioxideOzoneBCDMHChlorine Gas

Best

Worst

Reporting Requirements

Chlorine DioxideHypochloriteBromine CompoundOzoneChlorine Gas

Least

Greatest

Performance in Contaminated Systems

Chlorine DioxideOzoneBromine

CompoundsChlorine GasSodium

Hypochlorite

Best

Worst

Performance at Elevated pH

OzoneChlorine DioxideBromine

CompoundSodium

HypochloriteChlorine Gas

Best

Worst

Best Alternative• CHLORINE is still a widely used oxidant

* Inexpensive, historically established, being phased out• HYPOCHLORITE is cheapest alternative

* Similar performance to chlorine, degradation is problem• BROMINE CHEMISTRY, halogen alternative

* Better performance, can be costly, pH dependent• CHLORINE DIOXIDE, non-halogen alternative Cost-effective

broad spectrum, safely fed, pH independent, non-chlorinating agent

• OZONE, New Approach* Capital intensive, strong oxidant, no chemicals

Chlorine Dioxide Generation

Chlorine DioxideAdvantages/Benefits• Gas dissolved in

water• Strong oxidizer• Not a halogen• Selective reactivity

Chlorine DioxideAdvantages/Benefits• Generated on-site• Rapid acting• pH independent• Low capital requirements

Physical Characteristics

Color : Yellow-green

State : Gas

Odor : Similar to chlorine

Solubility: 2.9 gr/L

ClO2 GeneratorGeneration Methods

Chlorine Gas Method Three Pump Method

Precursor Source

WaterInlet

Chlorine

1

2 3

456

7

8

9

10

11

12

13

48"H x 42"W x 17"D

14

ClO2

15

1. Electric Control Box2. Flow Indicator (GPM)3. Hand/Off/Auto Switch4. Ball Valve5. Solenoid Valve6. Pressure Gauge7. In-line Flowmeter8. Ball Check Valve9. Chlorine Eduction10. Chlorine Solenoid Valve11. Chlorine Rotameter12. Precursor Pump13. ClO2 Generator14. Emergency Shutdown Switch15. Loss Of Chlorine Switch

ClO2 GeneratorChlorine Gas Method

ClO2 GenerationGaseous Chlorine Method

2NaClO2 + Cl2 2ClO2 + 2NaCl Sodium Chlorine Chlorine Sodium Chlorite Dioxide Chloride

ClO2 GenerationThree Pump Method

2NaClO2 + NaOCl + 2HCl Sodium Sodium Hydrochloric Chlorite Hypochlorite Acid

2ClO2 + 3NaCl + H2O Chlorine Sodium Water Dioxide Chloride

Hydrochloric Acid SourceSodium Hypochlorite Source

Precursor Source

1

2 3

456

7

8

9

10

48"H x 42"W x 17"D

11

ClO2

9 9WaterInlet

1. Electric Control Box2. Flow Indicator (GPM)3. Hand/Off/Auto Switch4. Ball Valve5. Solenoid Valve6. Pressure Gauge7. In-line Flowmeter8. Ball Check Valve9. Chemical Pumps10. ClO2 Generator11. Emergency Shutdown Switch

ClO2 GeneratorThree Pump Method

ClO2 GeneratorGeneration MethodThree Pump Method

Advantages• Higher

Capacity• High Back-

Pressure Capacities

• Higher Turndown

• No Chlorine Gas Necessary

Disadvantages• Slightly Higher

Cost• Additional

Chemical Storage

• Incompatible Chemicals

Typical ClO2 DosagesRendering Odor Control :2-10 ppmCooling Water Treatment : 0.1-0.5

ppmFood Processing : 2-10 ppmPaper Mill Slime Control :0.25-0.45 lb

ClO2/ton paper

Sodium Chlorite PrecautionsDO NOT allow solution to dry.

DO NOT mix with any other chemicals.

DO NOT use wooden pallets or paddles.

DO NOT wear leather or cloth external clothing.

Normal Shutdown Procedure• Turn operating switch to “Off”• Water flush occurs briefly• Drain unit• If chlorine used, close valve• Drain and flush all chemical

systems

Equipment SiteSurvey Location• Well-ventilated area• Eyewash/shower near generator• Eyewash/shower near bulk

storage• Washdown water source available• Approved drain• Well lighted

Monitoring Tools• Corrosion coupons • Deposit monitor - visual indication of deposit

formation • Biofouling monitor - indicate loss of pressure

due to biofilm • TBC and SRB dip slides• Test heat exchangers• ORP meters • Site Management • Daily reporting

Corrosion Monitoring by Coupons Method

• Corrosion Rate (MPY) = coupons wt loss in gms*365*1000/ Area of coupon in cm2*density of coupon in (gm/cm3)*Exposure period in days*2.54

Also we know that 1 Miles = 0.001 inch =0.0254 mm

Means if corrosion rate is 3 MPY will cause the metal loss (tube thickness reduction) by 0.0762 mm per year.

THANK YOUfor any types of queries

please contact toPrem Baboo

Sr. Manager(Prod)National Fertilizers Ltd, India

Designer for Plant & equipment'spbaboo@hotmail.comPrem.baboo@nfl.co.in

+919425735974