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General
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Seawater is a high Salinity surface water. Seawater normally has a
Total Dissolved Solids (TDS) content between 30,000 to 45,000 ppm. With the increasing demand and limited potable water supply, seawater
desalination has become the single viable alternative and limitless source of fresh
water. The latest developments in membrane
separation technology have made available more advanced membrane
elements with higher flux and superior salt rejection, allowing increased system
recoveries and improved permeate quality at lower operating pressures.
Value engineering has played an important role in reducing cost and
increasing efficiency of the seawater desalination process. With
many energy recovery devices now commercially available, Reverse
Osmosis has become the most economical Seawater Desalting technology,
surpassing the distillation technique even for high capacity
plants. Reverse Osmosis has lower power consumption and operates
at lower temperature compared to other desalting technologies.
Such advantages gives the membrane separation technology a clear edge
over other thermal processes.
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Seawater
Desalination Plants |
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Description |
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Type |
Integrated Seawater RO
Systems (SWRO) |
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Usage |
Seawater
Desalination |
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Applications |
Drinking, Process, Industrial |
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Equipment |
The integrated system can
be a single or multiple-train. Typical integrated SWRO system
consists of three main sections or subsystems; common Pretreatment,
Main Treatment consisting of single or multiple-train RO
subsystem, and a common Post Treatment.
Seawater
Intake and Brine Outfall are typically provided under separate
contracts, under the responsibility of a civil contractor. |
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Capacity |
Varies,
depending on custom requirements and application. Typical
Integrated SWRO Train capacities are as follows: |
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Permeate Flow
500 - 2,000 m3/day
(92 - 367 gpm) |
Operating Pressure
55 - 83 Barg
(800 - 1,200 psig) |
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Features |
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Pretreatment |
Customized,
for conditioning of raw seawater prior to membrane treatment. Typically
consists of Chemical Treatment, Clarification (if required), Media
and Micron Filtration. |
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Main
Treatment |
Reverse Osmosis (RO)
Membrane
Separation System, using high rejection RO membrane elements. |
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Post
Treatment |
Customized
for conditioning of the Main Treatment RO effluent (permeate) to a
final product. Typically consists of,
Chemical
Treatment and Sterilization. |
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Instruments |
Locally
mounted primary
elements. Monitoring and Control Instruments are mounted on the Main Control Panel
(MCP). |
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Controls |
PLC
controlling the entire plant sections. Typically located inside
the MCP |
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Advantages |
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Design |
1.
Simple and reliable.
2. High quality components.
3. Material selection for excellent corrosion resistance.
4. Compact, small equipment footprint.
5. Conservatively designed for consistent, trouble free
operation. |
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Operation |
1.
Reliable, efficient and easy operation requiring little operator
attendance
2. Automatically controlled by micro processor based control
system.
3. Variable control valves to allow flow adjustment for
changing conditions
4. Slow start operation for membrane elements protection.
5. Safety interlocks with "Fail Safe" operation
for extra system protection.
6. All pumps are protected against running dry.
7. Lower capital and operating cost. |
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Performance |
Product
water TDS content of less than 500 mg/l per WHO standards.
Higher quality product water can be obtained by employing a second pass
membrane treatment. |
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Components |
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Pretreatment |
1. Chemical Treatment: Typically includes Disinfectant, Coagulant,
Coagulant Aid, Antiscalant and/ or Acid injection systems.
2. Clarification: Coagulator or Lamella type
clarifiers.
3. Media Filtration: Multi-media filters, FRP or CS housing, epoxy or rubber
lined.
4. Micron Filtration: 5 micron Cartridge filters in
FRP or 316SS Housing |
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Main
Treatment
(RO Train) |
RO High Pressure Pump
(HPP)
Multistage
Centrifugal or Positive Displacement Plunger type. Discharge
pressure up to 1,200 psig |
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1. Membrane Elements: TFC
High Rejection, High Flux 8" x 40" (D x L)
2. Pressure Vessel Assemblies: FRP rated for 1,000-1,200
psig, housing the membrane elements.
3. Support structure Structure: FRP or CS epoxy painted or
powder coated, supporting the pressure vessel assemblies.
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Post Treatment |
Chemical Systems: Alkali, Corrosion Inhibitor injection |
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Piping |
1. Train mounted High Pressure
piping: Fabricated of Sch 40 high
grade SS, Duplex, AL6XN, or 245SMO alloy steel.
2. Train mounted Low Pressure piping: Fabricated of Sch 10
316L SS or Sch 80 PVC.
3. Interconnecting piping: Fabricated of FRP, Sch 80 PVC or
CPVC. |
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Valves |
1. Control Valves:
Modulating, with
Pneumatic or Electrical Actuator.
2. Auto Isolation Valves: Pneumatic or Electrical operator w/ Auto On-Off
control.
3. Manual Valves: High grade SS or Plastic, as required. |
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Instruments |
Provided for
continuous monitoring and control of Flow, Pressure, Temperature,
Level and Analytical parameters, such as pH, Conductivity, ORP,
Turbidity, etc. |
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Controls |
Automatic
control via Programmable
Logic Controller (PLC), mounted inside the Main Control Panel (MCP) |
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Electrical |
Motor
Control Center (MCC), including motor starters and controls;
Local Starter Panels and Junction Boxes; Miscellaneous hardware |
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Options |
1.
Energy Recovery Turbine (ERT)
2. Adjustable Frequency Drive (AFD) for the High Pressure
Pump (HPP)
3. Data Acquisition and Monitoring System (DAQM) |
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