Ras Al Khair Desalination Plant, Saudi Arabia
Saline Water Conversion Corporation's (SWCC) Ras Al Khair Desalination Plant (formerly Ras Az Zawr Desalination Plant) is a hybrid desalination plant that implements both the multistage flashing (MSF) and reverse osmosis (RO) technologies. The plant is located in the Ras Al Khair Industrial City, 75km north-west of Jubail.
Construction of the desalination plant started in early 2011 and commissioning was held in April 2014. It is the biggest desalination plant of its kind in the world, capable of serving approximately 3.5 billion people in the city of Riyadh.
The plant has a capacity to produce 228 million imperial gallons per day (MIGD) / 728 million litres per day. The project construction cost was SAR27bn (approximately $7.2bn).
The main contractor for plant construction was Doosan and its consortium partner Saudi Archirodon, with Poyry acting as the consultant for the project. The engineering, procurement and construction (EPC) contract involved production and installation of equipment and facilities, as well as testing and commissioning.
The project also includes the building of a 2,650MW combined cycle power plant in the second phase, which will comprise five 600MW combined cycle gas turbine (CCGT) blocks and two 220MW single cycle gas turbines (SCGT) units.
Maaden's alumina refinery will use up to 1,350MW of electricity and 25,000m³ per day of water from the project.
Ras Al Khair desalination project details
The desalination plant consists of eight MSF units and 17 RO units. The MSF units have a capacity to produce 160 MIGD, while the RO units produce 68 MIGD. Three of the MSF units were built at Doosan Heavy Industries Vietnam, while the other five were produced at the Doosan Korea facility.
The project involved construction of an RO building, switchgear buildings, a wastewater treatment plant, a chemical dosing building, as well as installation of a dissolve air floatation unit and two dual media filters. Ground improvement and backfill works were also carried out across the site of the RO and MSF plants.
The offshore elements for the project included the laying of GRP (glass reinforced pipes) discharge pipes measuring three kilometres with end diffusers, construction of an intake channel comprising a dredged channel and two rock breakwaters measuring 1.4km, a seawater intake pump house and a discharge chamber to the pipes.
The desalination plant used approximately 90,000m³ of reinforced concrete, 6,000t of structural steel, 19,000m² of roof and wall cladding and 30,000m² of masonry.
Hybrid treatment tech at the Ras Al Khair facility
The MSF process for desalination involves the heating of seawater to produce steam and then condensing the steam to produce desalinated water.
The process begins with heating the seawater at a high temperature in the brine heater. The heated seawater is conveyed to an evaporator where the pressure is lower, allowing the water to boil rapidly where it flashes into steam. The remaining water then undergoes similar additional stages where the pressure at each stage is lower than the earlier stage.
The vapour generated by the flashing is converted into fresh water by condensing the vapours from the heat exchanger tubings that run through each stage.
Waste heat from the combined cycle power plant will be used to heat the tubes within the distiller unit's brine heaters.
The RO process involves use of pressure to force the seawater through a semi-permeable membrane for the removal of sodium and chloride. The process initially involves pre-treatment by using any of the methods such as coagulation, flocculation, sedimentation and filtration, or even microfiltration (MF) and ultra filtration (UF).
The second stage involves the supply of pressure using pumps to force the water through the membrane. The membrane assembly consists of a pressure vessel and a membrane.
The final stage or the post-treatment stage implements energy recovery devices or energy recovery turbochargers. It involves stabilising the water by removing gases such as hydrogen sulphide, measuring the acidity and alkalinity of the water and preparing it for distribution.
Contractors involved with Saudi Arabia's desalination project
The energy-recovery device (ERD) contract for the RO units was awarded to Fluid Equipment Development Company (FEDCO).
Siemens was contracted to supply 12 SGT6-5000F gas turbines, five SST6-4000 steam turbines, 17 SGen6-1000A generators, ten heat-recovery steam generators and associated electrical equipment and a SPPA-T3000 instrumentation and controls system (I&C). The contract was worth more than $1bn.
Civil and building construction works for the project were carried out by Assad Said under a contract worth SAR213m ($57m). The erection of the steel structure for the pipe bridges at the project site was carried out by Hamte Heavy Industries.
Hyosung supplied 18 types and 154 sets of high-voltage motors, including 4,600KW 14P 13.8KV motors for the desalination plant. Torishima provided six boiler feeds and ten condensate pumps for the combined cycle power plant.
In January 2008, Bahrain-based Energy Central Company (ECC) was awarded a 25-year contract to design, build and operate a seawater desalination plant to serve the irrigation needs of the entire Durrat Al Bahrain development.
The world's second largest seawater desalination plant is being built in Sorek, about 15km south of Tel Aviv, Israel.