19855321 Water Desalination by Revese Osmosis

8/9/2019 19855321 Water Desalination by Revese Osmosis

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METITO-RO.PPT Slide 1 Printed on 7/31/2010

Module 5.1Module 5.1

WATERWATER

DESALINATIONDESALINATIONBY REVERSEBY REVERSE

OSMOSISOSMOSIS


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Module 5.1.0Module 5.1.0 -- AGENDAAGENDA

Water QualityWater Quality Osmosis & Reverse OsmosisOsmosis & Reverse Osmosis

PretreatmentPretreatment

R.O. MembranesR.O. Membranes

Operation and Plant ControlOperation and Plant Control

TroubleshootingTroubleshooting CleaningCleaning

Flow DiagramFlow Diagram


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Module 5.1.1Module 5.1.1 -- Water Quality 1Water Quality 1

Salt Content

Low Salinity Water (TDS < 500 mg/l)

Rivers Springs

Deep Wells

Brackish Water (TDS 500 - 16,000 mg/l) Heavy Brackish (TDS 16,000 - 30,000 mg/l)

Sea Water (TDS > 30,000 mg/l)


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Module 5.1.2Module 5.1.2 -- Water Quality 2Water Quality 2

W.H.O. Drinking Water Standards 1988

pH 6.0 - 9.6 (7.5 - 8.5 desirable

TDS 1000 mg/l max. (500 max. desirable)

Sodium 200 mg/l max. (20 mg/l desirable)

Hardness 500 mg/l max. (100 mg/l desirable)

Iron 0.3 mg/l max. (None desirable)

Chloride 600 mg/l max. (25 mg/l desirable)


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Module 5.1.2Module 5.1.2 -- Osmosis & Reverse OsmosisOsmosis & Reverse Osmosis

1. Osmosis

Osmosis is a natural occurring

process used by many plant &

animal tissues to transport liquids

across cell walls.


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2. Semi Permeable Membrane

Cell walls are examples of Semi-

Permeable membranes which

allow water to pass through, while

not allowing salts to pass.


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3. Reverse Osmosis

Removal of dissolved salts from the solution by

applying external pressure greater than the

osmotic pressure of the solution and where the

water flows across the membrane from higher

concentration to lower concentration


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4. Osmosis

Pure terS lt Solution

Semi-Permeable Membrane


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5. Reverse Osmosis

Pure WaterSalt Solution

Pr ssur

i-Per eable embrane


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Module 5.1.3.0Module 5.1.3.0 -- PretreatmentPretreatment

Overview Major fouling impurities

Scaling Suspended solids & Colloidal matter

Biological Matter

Metal Oxides

Silica


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Module 5.1.3Module 5.1.3 -- PretreatmentPretreatment

1. Major Fouling Components1. Major Fouling Components Sparingly soluble (scale-forming) salts

Calcium Carbonate

Calcium Sulphate

Barium Sulphate

Strontium Sulphate

Calcium Fluoride

Suspended solids & colloidal matter

Micro-organisms (bacteria & protozoa)

Metal oxides (e.g. Iron & Aluminium)

Silica


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2. Scale Control2. Scale Control Caused by precipitation of sparingly soluble salts :

Calcium Carbonate CaCO3

Calcium Sulphate CaSO4

Barium Sulphate BaSO4

Strontium Sulphate SrSO4

Calcium Fluoride CaF2

Scaling Potential Determined by : Chemical Analysis of Feed Water

R.O. system recovery

Solubility limits of salts


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3. Calcium Carbonate CaCO3. Calcium Carbonate CaCO33 Exists in most waters (as soluble Calcium

Bicarbonate, Ca(HCO3)2)

For Brackish Waters, scaling potential

calculated by Langlier Saturation Index

(LSI)

For Sea Water/Brine water the scaling

potential is calculated by SDI


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4. Suspended Solids & Colloids4. Suspended Solids & Colloids

Suspended Solids - removable settling

Colloids - not removable by settling Negative charges on surface - stable

in water

In R.O. process colloids concentrate at

surface or membrane with salts Leads to colloid destabilization

Colloids coagulate & foul membrane


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4.2 Controlling Colloids Problems4.2 Controlling Colloids Problems

Media Filtration

Coagulation / Flocculation

(On-line or off-line)


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5. Biological Fouling5. Biological Fouling Most water sources contain micro- organisms

Form slime layer on membrane surface

Leads to rapid pressure drop increase

across cartridge filter preceding H.P. Pump

Samples from feed & brine must regularly be tested for

Total Bacterial Count (TBC)


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5.1 Controlling Biological Fouling5.1 Controlling Biological Fouling

Chlorination prior to filtration

stage

WaterMUSTbe de-chlorinated

prior to reaching membranes


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6. Metal Oxides6. Metal Oxides Most common is iron

Frequently encountered in water in

Ferrous (Fe2+) form

In presence of Oxygen, Fe2+ (soluble)

oxidized to Fe

3+

(insoluble) Aluminum can precipitate as

Aluminum Hydroxide


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6.1 Controlling Metal Oxide Fouling6.1 Controlling Metal Oxide Fouling

Oxidation

Chemical Precipitation


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Module 5.1.4.0Module 5.1.4.0 -- Membrane TypesMembrane Types

OverviewOverview

Material

Designs


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1. Materials1. Materials

Cellulose Acetate (Brackish Water)

Cellulose Tri-Acetate (Brackish &Sea Water)

Polyamide (Brackish & Sea Water)

Composite Polyamide TFCL

(Brackish & Sea Water)


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OverviewOverview

Water Quality

Pressures

Recovery

Chemical Addition


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Module 5.1.5Module 5.1.5 -- Operation & Plant ControlOperation & Plant Control

1. Water Quality1. Water Quality

Check that ..

Chlorine in feed is zero

Iron in feed is less than 0.05 mg/l

SDI of feed water is less than 3

TDS of feed water is within R.O.

design criteria


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2. Pressures2. Pressures Check ..

Pump discharge pressure

System pressure (1st stage) Intermediate pressure

Reject (Brine) pressure

Permeate pressure

2nd Stage

R.O.

1st Stage

R.O.Permeate

Brine

H.P.P

Feed Water

Qf


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3.1 Why pressure is important3.1 Why pressure is important Assure plant is running according

to design pressure

Allows normalization of plant

operation to evaluate performance

Indicates fouling when pressure

changes significantly under steady

operating


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4. Important to operate at Design4. Important to operate at Design

Recovery in order toRecovery in order to

Prevent over-saturation ofsparingly soluble salts

Not exceed hydraulic guidelines of

membranes, e.g. min. & max. brinerates, flux etc.

Produce required permeate quality


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5. Chemical Addition5. Chemical AdditionDosing sets include:

Coagulant to reduce colloidal fouling

Acid dosing for pH adjustment to reduce scaling

potential

Chlorine dosing to control microbiological growth

De-chlorinating agent to remove free chlorineprior to membrane

Antiscalant dosing Alkali dosing to adjust permeate water pH to

required level


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Module 5.1.6Module 5.1.6 -- TroubleshootingTroubleshooting

1. Troubleshooting Techniques1. Troubleshooting Techniques Most problems related to fouling

Indicators

Permeate Quality

Permeate Quantity

Salt Rejection

Pressure Differential Accurate operation log is critical for

successful troubleshooting


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2. On2. On--line Investigationsline Investigations Performed while system in operation

Measure the following:

Salt rejection

Product flow

Pressures

Every permeator has to be checked


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3. On3. On--line Investigationsline Investigations

Permeators removed from service

Individual elements identified


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Module 5.1.7Module 5.1.7 -- CleaningCleaning

1. Why Clean?1. Why Clean?

Frequent cleaning is not required

for properly designed and

operated R.O. Systems


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2. When to Clean?2. When to Clean?

Productivity reduced by 10 - 20%

Salt passage increased by 1.5x

Bundle pressure drop (P > 60 psi


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3. How to Clean?3. How to Clean?

Cleaning should be performed after R.O.

data has bee normalized Changes observed not due to changes in operating

conditions

If bacteriological tests show bacteria in

permeate then biocide cleaning is required


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4. Different Cleaning Chemicals4. Different Cleaning Chemicals

Detergent to remove colloidal foulants

Citric acid to remove iron oxide

Formaldehyde for biological control


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5. Cleaning Equipment5. Cleaning Equipment

6

F

3

1

2

5

R . O U N IT

(P E R M E A T O R S )

P E R M E A T E

(P R O D U C T W A T E R )

B R IN E

C LE A N IN G

C A R T R ID G E

F ILT E R

M IX E R

C LE A N IN G T A N K

C LE A N IN G

P U M P S

4


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Reverse OsmosisReverse Osmosis

Importance of FlushingImportance of Flushing

Corrosion rates of stainless steel elements

in stagnant water are very high

Antiscalant, if used, produces a metastable

state with respect to precipitation of

sparingly soluble salts

Upon shutdown, precipitation can occurwithin four hours if the permeators are not

flushed


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Importance of FlushingImportance of Flushing

Upon shutdown, reverse osmosis process

will cease and natural osmosis will occur

Water flows from the fiber bore to the fiber

feed-brine side

If an adequate volume of permeate water at

positive pressure (draw-back tank) is notsupplied, fiber dehydration will occur


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FLUSHING WATER REQUIREMENTSFLUSHING WATER REQUIREMENTS

SPIRAL (5 MINUTES)SPIRAL (5 MINUTES)

Membrane Type Membrane Size Water Quantity

Per Membrane

Vessel with 6 8 inch 30 - 40 GPM

Membranes

Vessel with 6 4 inch 8 - 10 GPM

Membranes


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DRAWBACK REQUIREMENTSDRAWBACK REQUIREMENTS

Membrane Type Size Water Requirement

Twin 8 inch 24 Gallons

Single 8 inch 12 Gallons

Single 4 inch 4 Gallons


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Module 5.1.9Module 5.1.9 RO ConfigurationRO Configuration

RO FEED

WATER

RO REJECTRO PERMEATE

19855321 Water Desalination by Revese Osmosis

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