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Desalination
RO systems that produce industrial and drinking water from seawater and brackish water
Process
- Raw
- In process
- Product
- Brine & waste
- Chemical
01Intake screen
Removes floating debris, marine growth and large solids at the seawater intake. A moving screen band lifts the trapped material, and spray water washes it into a debris trough. It is the first step and protects the pumps and filters downstream.
Main components
- Screen band
- Drive motor and gearbox
- Spray header and nozzles
- Debris trough
02Coagulant dosing
Doses coagulant into the raw water ahead of filtration so that fine particles gather into larger flocs. The flocs are then captured easily in the filters downstream. Chemical tanks and metering pumps are supplied together on one skid.
Main components
- Chemical tanks
- Metering pumps
- Discharge piping and valves
- Control panel
03DAF (optional)
Placed ahead of filtration when the raw water carries a lot of algae, oil or fine suspended solids. Water saturated with air is mixed into the raw water, the fine bubbles attach to the flocs and float them up, and a skimmer removes the floated sludge from the surface. It is included or left out depending on the raw water quality.
Main components
- Flotation tank
- Air saturator
- Recycle pump
- Skimmer and sludge trough
04Dual media filter (DMF)
Two layers of media, anthracite and sand, remove turbidity and suspended solids to prepare the water for the UF and RO membranes. Several units run in parallel, and each is backwashed in turn to remove the accumulated solids when the pressure difference rises.
Main components
- Pressure vessel
- Inlet distributor
- Media bed (anthracite, sand)
- Underdrain
05UF
Hollow-fibre membranes with very fine pores remove the fine particles, colloids and bacteria left in the filtered water, reducing fouling of the RO membranes. They are backwashed regularly and cleaned with chemicals when needed.
Main components
- UF modules
- Upper and lower headers
- Rack frame
- Automatic valves
06Cartridge filter
Removes the remaining fine particles just ahead of the high-pressure pump and the RO membranes. The housing holds a number of replaceable filter cartridges. Cartridges are replaced when the pressure difference between inlet and outlet rises.
Main components
- Housing
- Filter cartridges
- Bolted cover
- Differential pressure gauge
07High-pressure pump
Raises the pretreated water above the osmotic pressure of seawater and delivers it to the SWRO pressure vessels. It is the largest power consumer in a desalination plant. Operating pressure is managed with the gauge and valve on the discharge side.
Main components
- Multistage centrifugal pump
- Motor
- Coupling
- Common baseplate
08SWRO
Reverse osmosis membranes inside the pressure vessels pass water and reject salt. The flow leaves as permeate, the product, and concentrate. The vessels are stacked in a rack and connected to feed, permeate and concentrate headers.
Main components
- Pressure vessels
- RO membrane elements
- Feed and concentrate headers
- Rack frame
09Energy recovery device (ERD)
Transfers the pressure of the high-pressure concentrate leaving the SWRO to incoming feed water, reducing the load on the high-pressure pump. In the pressure exchanger type, concentrate and feed exchange pressure directly inside a rotor. The pressurised feed passes a booster pump and rejoins the high-pressure side.
Main components
- Pressure exchangers
- High- and low-pressure manifolds
- Booster pump
- Support frame
102nd-pass BWRO
Treats the first-pass SWRO permeate again by reverse osmosis to lower boron and the remaining salt. It uses brackish water membranes that run at a lower pressure than the first pass. It is added when high purity is needed, such as for boiler make-up water.
Main components
- Pressure vessels
- BWRO membrane elements
- Feed pump
- Header piping
11Product water tank
Stores the product water and sends it to users. It absorbs the difference between production and demand, and a level gauge monitors the water level. pH adjustment or disinfection chemicals are dosed ahead of it when needed.
Main components
- Storage tank
- Level gauge
- Manhole and ladder
- Overflow pipe
Selected deliveries
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01POSCO E&C · 68,000 m³/day · industrial water -
02POSCO E&C · 36,000 m³/day · industrial water -
03POSCO E&C · 32,000 m³/day · industrial water -
04Doosan Heavy Industries · 20,000 m³/day · drinking water -
05Doosan Heavy Industries · 2,800 m³/day · boiler make-up water -
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Desalination plants remove salt from seawater to produce industrial water, drinking water and boiler make-up water. UF or DMF (dual media filters) remove suspended solids and fine particles, SWRO (seawater reverse osmosis) membranes remove the salt, and BWRO (brackish water reverse osmosis) or ion exchange polishes the water to the required quality.
For the Gwangyang seawater desalination plant (POSCO E&C, 2013) we supplied a 32,000 m³/day UF, SWRO and BWRO train. Overseas, we delivered the DMF, SWRO, BWRO and MBE water system for the Cirebon coal-fired power plant in Indonesia (Doosan Heavy Industries, now Doosan Enerbility, 2011).