Ammonia CW Case Study 08 Feb 06

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Cooling Water Treatment

-An Experience at GNFC

By N. B. Bhatt and A.M. Vashi


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GNFC AT A GLANCE

Incorporation : May10,1976

Capacity Per Annum Ammonia : 4,45,000 MT

Urea : 5,94,000 MT

Methanol : 1,30,000 MT

Formic Acid : 8,000 MT Acetic Acid : 1,00,000 MT

Weak Nitric Acid : 2,47,500 MT

Conc. Nitric Acid : 66,000 MT

Calcium Amm. Nitrate : 1,42,500 MT Amm. Nitro phosphate : 1,42,500 MT

Captive Power : 50 MW

IT infrastructure : VSAT, Info tower, PKI

NCPL for Aniline and TDI


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GNFC Ammonia Plant

One of the world largest single stream Ammonia-Urea complex

Process Route : Partial oxidation of fuel oil

Ammonia Urea

Capacity 1350 MTPD 1800 MTPD

Capacity Utilization 117 % 118%

Formic acid, Acetic Acid, Aniline, TDI and Methanolplants are dependent on Ammonia plant


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Integration of Ammonia Plant with otherplants

1350 MTPD

UREA

C02

NH3

Nitro Phosphate Unit

NH3

C02

CO

Tail Gas

FORMIC ACID

SYN GAS

H2+CO2+CO

CO2

NCPL

CO

BOILER

CO

ACETIC ACIDMETHANOL 1

METHANOL 2

AMMONIAPLANT

Purge Gas.

P.G.


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Ammonia Cooling Water System

Induced draft CT : 12 no. of cells

CW circulation flow : 34,000 m3/hr

Heat Duty : 352 Mkcal/hr

CW Supply temperature: 33 Deg C.

CW Return temperature: 43 Deg C CW pump capacity : 6800 m3/hr each

CW header pressure : 3.1 barg


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Old In-house CW Treatment

In-house treatment program developedby GNFC was followed before Dec-99

SHMPOrgano-phosphate

Zinc phosphate

BiocidesCOC : 3 ~ 4


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Present Cooling Water TreatmentM/S Chembond Drewtreat treatment:

First introduced in Urea plant in 1992

Since Dec-99 in Ammonia plant

Based on:

Zinc glassy ortho -meta phosphate(KW101)

Organophosphate-PBTC with low molecularwt polymer(KW1002G)

Biocide chemicals :

Chorine Dioxide

Quaternary Ammonium compound

Dichlorophene

DBNP (Di-bromo- nitroso-phenolic comp.

Bio-dispersant (KW-BD)


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CW Treatment Monitoring

Dedicated CW water cell Monitoring of Analysis and supervision of Ammonia

CT by M/s. Chembond

Regular activities:

Daily : Performance evaluation by CW cell

Weekly: CT cells deck algae cleaning

Monthly : Sterilization of side stream filters

Review of exchangers performance

Corrosion rate monitoring

Quarterly: Review with M/s Chembond formodification in treatment; if required

Bio-fouling monitoring

Inspection and cleaning during shut down


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Benefits With better treatment and Modifying the limits

of critical parametersCOC improved to 6~6.5

Saving in CW make up : 11,000,00 m3/year.

Reduction in corrosion rate :

From 3~4 mpy to


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CW parametersMake up

waterCW

circulation

pH 7.0~8.0 6.8~7.2

Conductivity Micro mho 200~400 2500max

TH ppm 70~150 800~825

Mg Hardness ppm 25~70 250~350

Ca Hardness ppm 50~85 450~550

Chloride ppm 10~25 250max

Silica ppm 10~20 100~125

Turbidity NTU 1~2 10


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Typical CW parametersCirculating water

Ortho PO4 ppm 5~6

Poly PO4 ppm 1.5~3.0

Organo PO4 ppm 1.5~3.0

Total PO4 ppm 7~10Zinc ppm 0.5~1

TDS ppm 1500max

NH3 ppm 10TVC per ml 50,000

SRB mpn /100

ml

100


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Ammonia Synthesis Gas

Cooler E706

A case study


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History of E706

Synthesis Gas cooler- a critical

exchanger condenses 50~60% ammoniain synthesis gas loop

Original exchanger started leaking

within a year of service Frequent and severe leakages started

within a short span of time

Cause : Flow induced vibrations Replaced in July-1984 :

A better design exchanger : SS304 tubes

and split flow of CW side installed

F f N S h i G C l


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Features of New Synthesis Gas Cooler

New design exchanger installed in 1984

H.T. Area : 1445 m2

Heat Duty : 14.28 MKcal/hr

Cooling water : Shell side

In/Out temp : 33/43

No of passes : Split flow

CW flow : 1500 m3/hr

MOC : CS

Synthesis gas : Tube side

In /Out temp : 79/ 39

Pressure : 230 bar

No of pass : 2 , U-tubes

No. of tubes : 1095

MOC : SS-304

L k f E706


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Leakage of E706 After 17 years, first leakage noticed in May-2001

Process gas containing 18 % Ammonia leaks to CW side

Gas was coming out with from shell side vent

IN OUT Diff.

pH 7.4 9.1 +1.7

Ammonia 5~10 ppm 15~50 ppm +10~40Conductivity 1240 1150 -90

Ca Hardness 324 272 -52

Chloride 236 208 -32Turbidity 14 16 +4

Total Hardness 664 572 -92

ORP +320 -300 -620


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Leakage of E706Consequences

5 ~10 ppm Ammonia in CW circulationsystem

Elevated pH of CW outlet to 8.5

Chlorination limitation

High microbiological growth - nitrifyingbacteria CW supply pH tends to remain low

Biomass fouling in the exchangers

Gas pocketing in the exchangersBack pressure in the E706, less CW flowthrough it

Scaling in the exchangers of CW system


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Repair of E706 :1In October 2002 S/D

CW side back-flushed:Sludge of ammonia salts was flushed out

Tube bundle Inspected from CW I/L nozzle: Found completely blocked with white sludge

Bundle pulling out was not possible

Chemical cleaning with 5% sulphamic acidResults was not satisfactory

Shell was cut open from one side and cleaned

with high pressure JettingHydro-test at 12 barg was carried out:3 leaky tubes plugged

Leakage Persisted


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Scaling in E706


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E 706 SHELL SIDE SCALING


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Repair of E706 : 2

In Jan 03 S/D

In Jan03 opportunityChemical cleaning with 5% sulphamic acid

Leak test was taken. No leakage identified,

Why? During normal operation, press diff. between

shell and tube is very high 230 bar, cracksopen up at high pressure

Shell is low pressure part Leakage not detectable with hydro test at 12

bar pressure

R i f E706 3


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Repair of E706 : 3In April 03 S/D

A special ammonia test carried outShell plates cut and the bundle cleaned withhydro jetting

Shell pressurised to 1 bar with N2 and furtherto 2 bar with Ammonia

Leakage detected by placing Ammonia testpaper on the tube sheet and observing color

change to blue12 tubes were detected and plugged

However, CW outlet ammonia pick up and pH

still indicated leakage after start-up

o usta n perat ons


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o usta n perat onsChallenging task : To maintain the thermal

performance of E706

E706 performance deteriorated due toscaling and gas back pressure, syn gasoutlet temp increased to 50 deg C from 39deg

Load on down stream refrigeration unit wasincreased, steam consumption increasedby 4 Mt/hr

Measures Taken:

1.0 Local gas release provision

2.0 Managing Micro biological activity

3.0 Managing scaling

1 L l R l


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1. Local Gas ReleaseLocal venting

10 no. of 1 tapping were taken on-line from

the shell and connected to a 4 vent header

Shell side Safety valve was dropped & lineextended up to CT height


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VENT GAS HEADER

E706

SAFETY VALVE LINE


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2.0 Managing Micro biological activityIn presence of ammonia, it is difficult to

achieve free chlorineFor effective microbiological activitycontrol:

Dosing of Chlorine dioxide startedMore stable and effective even athigher pH value

Does not react with Ammonia andorganic comp.

Bromine based biocide was also started


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2.0 Managing Micro biological activity

Additional bio-dispersant dosing wasstarted

Frequency of Sterilization of side stream

filters increased : once a weekCW system and exchangers Monitoring bymeasuring ORP

Nitrate Nitrogen, nitrifying bacteriamonitored


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3.1 Managing Scaling

Measures taken to contain scaling:

1. Local Polymeric Dispersants dosing

Effectiveness checked by analyzingCa-Hardness at CW inlet and Outlet,

before and after dosing


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E706 IN E706 OUT Diff

pH 6.8 8.5 +1.7

Ca H 450 440 -10

TIP 6.7 5.4 - 1.3

Before dosing dispersants

After dosing dispersantsE706 IN E706 OUT Diff

pH 6.8 8.9 +2.1

Ca H 452 448 - 4

TIP 10.3 10.6 +0.3


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3.2 Managing Scaling2. Back flushing:

Loose scale partially removed by theexchanger back flushing during shortinterruptions

3. Nitrogen Bumping:

Twice in a day Low pressure N2blowing for half an hour was done inthe exchanger for removing loose scale

The removal of scale is ensured byanalyzing CW outlet sample indicatingrise in Turbidity by 50 ~90 NTU and risein Ca-Hardness by 10 ~25 ppm.


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Effect of Nitrogen Bumping

E706 Ca-Hardn

ess

Rise in Ca-Hardness

Turbidity Rise inTurbidity

CW Inlet 464 -- 18 --

CW OutletBeforeBumping

460 - 4 28 +10

CW outletAfter

Bumping

480 +20 95 +77


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4. Local CW make up at E706 inlet

To reduce Hardness- a key factor forscaling

CW outlet hardness was reduced from700 ppm to 550 ppm

5. Local Sulphamic acid dosing To reduce local pH

Special arrangement made for dosing


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SULPHAMIC ACIDDOSING TANK

LOCAL WATER MAKE-UP

E706


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Plant Operation could besustained for 3 years till the

replacement of theexchanger in April 2004

with the effective problemspecific treatment


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Conclusion The problems related to cooling water systems

can lead to heavy production and energy loss.This can be effectively handled without affectingproduction and continuity of the plant by thoroughunderstanding of the process as well as CW

chemistry involved. Cooling water treatment is a specialized subject.

A lot of research and improvements are takingplace in this field. This knowledge is available to

industry through experts in the field.

Industry should adopt the relevant features ofadvancements for improvement in the system.


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THANK YOU

Ammonia CW Case Study 08 Feb 06

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