Osama Hasan Intern Engineer

URUT 3 (Plant 2) – Engro Fertilizers

NUST School of Chemical and Materials Engineering

Mentor : Amer Ahmed

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Cooling Tower

Water Quality

Water Borne Problems

Improvement Areas

Case Studies

Conclusion

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Outline

Industrial utility

Provides

Cooling water stream at ambient temperatures

Insights

CW – air evaporative heat transfer interactions

Discharge of unwanted process heat to the atmosphere

Challenges

Qualitative and quantitative maintenance

Minimizing energy and water consumptions

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Cooling Tower

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Water flow

Enven

Type Counter flow / Induced draught

Flow Rate 48000 m3/hr Make up 1500 m3/hr

No of Cells 13 + 1 Blow down 150 m3/hr

CWR T 44 °C Drift Losses 0.01%

CWS T 34 °C Evaporative Losses 1.60%

Wet Bulb 29 °C Filling Splash

Heat Load 4836 MM k cal/h Nozzle polypropylene

CT–4 Design Specs

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Cooling Tower Chemistry

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Challenges

Corrosion

Scaling Microbial Growth

Cooling Tower Challenges

CT chemistry includes:

Identifying sources

Controlling phenomena

Preventive measures

Minimizing effects

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Parameter min max Units Make up C W R

pH 7.5 8.2 7.80 8.10 Conductivity < 2000 - 2500 microS/cm 416 1503 Total hardness ppm CaCO3 175 520 Ca hardness Max 600 ppm CaCO3 120 350 Mg hardness ppm CaCO3 55 170 P-alkalinity 0 ppm CaCO3 0 0 M-alkalinity 50 120 ppm CaCO3 166 88 Chloride < 120 ppm Cl- 16 107 Ortho Phosphate 3.0 4.8 ppm PO4

3- ▒▒▒▒▒▒ 3.56 Total phosphate ppm PO4

3- ▒▒▒▒▒▒ 4.96 Organic Phosphate 1.0 1.5 ppm PO4

3- ▒▒▒▒▒▒ 1.40 Zinc 0.6 1.5 ppm as Zn ▒▒▒▒▒▒ 0.73 Dissolved Fe < 2 ppm Fe2+ 0.07 0.41 Total Fe ppm Fe2+ Silica ppm SiO2

2- TDS < 1200 -1500 ppm 250 902 Suspended solids Max 25 ppm 1 14 Turbidity Max 30 NTU 3 16 Ammonia < 10 ppm ▒▒▒▒▒▒ 4 Nitrites Nil ppm NO3

- ▒▒▒▒▒▒ 0.22 Nitrates Nil ppm NO2

- ▒▒▒▒▒▒ 5.60 Sulphate Max 600 ppm SO4

2- 48 458 Free Chlorine 0.5 1.0 ppm Cl2 ▒▒▒▒▒▒ 0

Water Quality

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Salt concentrations should remain within given ranges for:

Inhibiting corrosion, microbial growth & scaling

Efficient heat transfer

Optimum COC and operation

NEQS limits the disposal of

effluents above the permissible ranges without treatment

Required chemical treatment before disposal is done

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Effluents

Parameters Permissible Range

pH 6 – 9

Ammonia 40 ppm

TSS 200 ppm

TDS 3500 ppm

COD 150 ppm

Grease & Oil 10 ppm

Chloride 1000 ppm

BOD 80 ppm

Iron 8.0 ppm

Zinc 5.0 ppm

Sulphate 600 ppm

Chromium 1.0 ppm

Conductivity 2500 micro S/cm2

Temperature increase ≤ 3°C

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Water Borne Problems

Chemistry

Return of metal to its original state due to an electrochemical potential between cathode and anode sites

Control:

Inhibitors – passivation film prevents O2 diffusion to metal site

Chemisorption; protective filming; reaction

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Corrosion

Ionic migration

Metal ions e.g. Fe ++

Reduction of ions

or oxygen

Anode Cathode Electron migration

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Corrosion

Chromates,

Orthophosphates

Zinc,

Polyphosphates,

Synergic Blends: zinc-chromates chromate-polyphosphates chromate-orthophosphate

Dosing

Zinc and inorganic phosphate (BULAB 9063)

Both anodic and cathodic corrosion protection

Zinc (BULAB 9050)

Protection of mild steel piping and equipment in cooling water systems

Chemistry

Microorganisms : Algae, Fungi, Bacteria

Microbiological Induced Corrosion (MIC)

Deposit Problems

Control

Metabolic poisons; acts rapidly against active cells

Surfactants; rupture the cell walls

Oxidizing agents; oxidize cell components (Cl, Br)

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Microbial Growth

times in a tower but bacterial concentrations may increase by six

Min

era

l salts m

ay

con

cen

trate

six m

illi

on

tim

es

du

rin

g a

n e

qu

al

tim

e s

pan

Dosing

Bromine oxidizing biocide (BULAB 6041)

Used pH above 7.2

Surfactant (BULAB 3847 )

Prevents growth of Bacteria, Fungi, Algae and Sulfate Reducing Bacteria (SRB)

Proven effectiveness in ammonia containing cooling waters

Hypochlorite

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Microbial Growth

will number 281500,000,000 within 2 days. In 3 days the weight of

De

scen

da

nts fro

m a

sing

le b

acte

rium

this

pro

ge

ny

wo

uld

am

ou

nt

to 7

000 t

on

s

Chemistry

Deposits Mineral scales

Corrosion products

Particular matter

Microbiological mass

Types Waterborne salts

Waterborne foulants

Airborne foulants

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Scaling

Dosing

Biodispersant (BULAB 8006)

Designed to inhibit slime build up; enhances the effectiveness of microorganism control

Polymer (BLS 9067 )

Controls the precipitation of calcium phosphate & stabilize the Zinc

Phosphonate and Polymer (BULAB 7024)

Controls the precipitation of calcium carbonate and deposition due to silt or other particulate material

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Scaling

Improving Performance

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Reducing: Water consumption

Chemical dosage

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Performance Improvement

Benefits: Eco efficient

Cost effective

Easy operation

Water Conservation

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Reducing blow down

Increasing COC

Reusing blow down

Avoiding water losses

Leaks

Splashes

Drift losses

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Water Consumption

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Water Consumption

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Option 1 Condensate Recycle in Makeup

For deviated condensate recycle from (PCT of Ammonia-3, PCT of Urea-3) conductivities; the effluent must be routed to CT-4 basin rather than in effluent network

Any steam condensate must be recovered in tower basin rather than in effluent system

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Option 2 Leakages in CT-4

Civil repair at CT-4 is required on immediate basis.

About 35 m3 /h of Water is being lost due to losses from the leakages

Water loss causes:

Dosing wastage

More chemical dosing

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Chemicals Conservation

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Chemicals Conservation

Chemical free platforms – saves money

Alternatives:

1. UV radiation

2. Hydrocavitation

3. Radio frequencies

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Installing UV lights at different headers of CW

Network

UV will kill most of the microbial entities and substantially reduce the quantity of Hypo dosing in the system

Reduced hypo dosing will assist in Lesser chlorides

Less blow down

Lesser chemical consumption

Reduced load on effluent treatment

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Option 1 Using UV Radiation

Golden Circle saves water

and dollars per year through technology switch. The project has ensured:

Reduced chemical consumption

Reduced waste water treatment requirements

Water savings more that

8 ML / year

Option 2 Using Hydrocavitation

0

1

2

3

4

5

6

7

8

COC

Before After

The Golden Circle

hydrocavitation system

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Nasa Marshal Space Flight

Center utilizes radio frequencies to alter the water’s scaling tendencies

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Alternate no. 3: Using Radio Frequency

Cooling System Project Goals: • Increase cycles of concentration to improve water efficiency. • Eliminate scale and bio-fouling in the cooling system. • Eliminate condenser-side chemicals to reduce operating costs

and environmental impacts.

COC = 2 → 5.7 Water savings: 420,808 gal / 8 month

MSFC

Reducing Tower Leakages

Reducing chemical dosing and moving to chemical free platforms is profitable and environment friendly

Project study and technology switch analysis should be initiated for improved performance

Potential Outcome

Reduced operational cost

Eco efficiency

Regional leadership in emerging CT technologies

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Summary

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A school of excellence acting as a precursor for research and development within public and private sector.

Offers undergraduate programmes in twin disciplines of chemical and materials engineering.

Graduate and post graduate programmes in energetics materials and materials and surface engineering.

Key research areas include alternate energy, propulsion systems, smart materials, bio materials, polymers and composites.

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NUST School of Chemical and Materials Engineering