19855321 Water Desalination by Revese Osmosis
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Transcript of 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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METITO-RO.PPT Slide 2 Printed on 7/31/2010
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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METITO-RO.PPT Slide 3 Printed on 7/31/2010
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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METITO-RO.PPT Slide 4 Printed on 7/31/2010
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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METITO-RO.PPT Slide 5 Printed on 7/31/2010
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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METITO-RO.PPT Slide 6 Printed on 7/31/2010
Module 5.1.2Module 5.1.2 -- Osmosis & Reverse OsmosisOsmosis & Reverse Osmosis
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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METITO-RO.PPT Slide 7 Printed on 7/31/2010
Module 5.1.2Module 5.1.2 -- Osmosis & Reverse OsmosisOsmosis & Reverse Osmosis
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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METITO-RO.PPT Slide 8 Printed on 7/31/2010
Module 5.1.2Module 5.1.2 -- Osmosis & Reverse OsmosisOsmosis & Reverse Osmosis
4. Osmosis
Pure terS lt Solution
Semi-Permeable Membrane
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METITO-RO.PPT Slide 9 Printed on 7/31/2010
Module 5.1.2Module 5.1.2 -- Osmosis & Reverse OsmosisOsmosis & Reverse Osmosis
5. Reverse Osmosis
Pure WaterSalt Solution
Pr ssur
i-Per eable embrane
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METITO-RO.PPT Slide 10 Printed on 7/31/2010
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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METITO-RO.PPT Slide 11 Printed on 7/31/2010
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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METITO-RO.PPT Slide 12 Printed on 7/31/2010
Module 5.1.3Module 5.1.3 -- PretreatmentPretreatment
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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METITO-RO.PPT Slide 13 Printed on 7/31/2010
Module 5.1.3Module 5.1.3 -- PretreatmentPretreatment
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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METITO-RO.PPT Slide 15 Printed on 7/31/2010
Module 5.1.3Module 5.1.3 -- PretreatmentPretreatment
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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METITO-RO.PPT Slide 17 Printed on 7/31/2010
Module 5.1.3Module 5.1.3 -- PretreatmentPretreatment
4.2 Controlling Colloids Problems4.2 Controlling Colloids Problems
Media Filtration
Coagulation / Flocculation
(On-line or off-line)
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METITO-RO.PPT Slide 18 Printed on 7/31/2010
Module 5.1.3Module 5.1.3 -- PretreatmentPretreatment
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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METITO-RO.PPT Slide 19 Printed on 7/31/2010
Module 5.1.3Module 5.1.3 -- PretreatmentPretreatment
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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METITO-RO.PPT Slide 20 Printed on 7/31/2010
Module 5.1.3Module 5.1.3 -- PretreatmentPretreatment
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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METITO-RO.PPT Slide 21 Printed on 7/31/2010
Module 5.1.3Module 5.1.3 -- PretreatmentPretreatment
6.1 Controlling Metal Oxide Fouling6.1 Controlling Metal Oxide Fouling
Oxidation
Chemical Precipitation
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METITO-RO.PPT Slide 22 Printed on 7/31/2010
Module 5.1.4.0Module 5.1.4.0 -- Membrane TypesMembrane Types
OverviewOverview
Material
Designs
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METITO-RO.PPT Slide 23 Printed on 7/31/2010
Module 5.1.4.0Module 5.1.4.0 -- Membrane TypesMembrane Types
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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METITO-RO.PPT Slide 24 Printed on 7/31/2010
Module 5.1.4.0Module 5.1.4.0 -- Membrane TypesMembrane Types
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METITO-RO.PPT Slide 25 Printed on 7/31/2010
Module 5.1.5.0Module 5.1.5.0 -- Membrane TypesMembrane Types
OverviewOverview
Water Quality
Pressures
Recovery
Chemical Addition
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METITO-RO.PPT Slide 26 Printed on 7/31/2010
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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METITO-RO.PPT Slide 27 Printed on 7/31/2010
Module 5.1.5Module 5.1.5 -- Operation & Plant ControlOperation & Plant Control
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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METITO-RO.PPT Slide 28 Printed on 7/31/2010
Module 5.1.5Module 5.1.5 -- Operation & Plant ControlOperation & Plant Control
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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METITO-RO.PPT Slide 30 Printed on 7/31/2010
Module 5.1.5Module 5.1.5 -- Operation & Plant ControlOperation & Plant Control
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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METITO-RO.PPT Slide 31 Printed on 7/31/2010
Module 5.1.5Module 5.1.5 -- Operation & Plant ControlOperation & Plant Control
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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METITO-RO.PPT Slide 32 Printed on 7/31/2010
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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METITO-RO.PPT Slide 33 Printed on 7/31/2010
Module 5.1.6Module 5.1.6 -- TroubleshootingTroubleshooting
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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METITO-RO.PPT Slide 34 Printed on 7/31/2010
Module 5.1.6Module 5.1.6 -- TroubleshootingTroubleshooting
3. On3. On--line Investigationsline Investigations
Permeators removed from service
Individual elements identified
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METITO-RO.PPT Slide 35 Printed on 7/31/2010
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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METITO-RO.PPT Slide 36 Printed on 7/31/2010
Module 5.1.7Module 5.1.7 -- CleaningCleaning
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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METITO-RO.PPT Slide 37 Printed on 7/31/2010
Module 5.1.7Module 5.1.7 -- CleaningCleaning
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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METITO-RO.PPT Slide 38 Printed on 7/31/2010
Module 5.1.7Module 5.1.7 -- CleaningCleaning
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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METITO-RO.PPT Slide 39 Printed on 7/31/2010
Module 5.1.7Module 5.1.7 -- CleaningCleaning
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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METITO-RO.PPT Slide 40 Printed on 7/31/2010
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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METITO-RO.PPT Slide 41 Printed on 7/31/2010
Reverse OsmosisReverse Osmosis
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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METITO-RO.PPT Slide 42 Printed on 7/31/2010
Reverse OsmosisReverse Osmosis
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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METITO-RO.PPT Slide 43 Printed on 7/31/2010
Reverse OsmosisReverse Osmosis
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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METITO-RO.PPT Slide 44 Printed on 7/31/2010
Module 5.1.9Module 5.1.9 RO ConfigurationRO Configuration
RO FEED
WATER
RO REJECTRO PERMEATE