Al Khafji Solar Saline Water Reverse Osmosis (Solar SWRO) Desalination Plant

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The world’s biggest solar-powered desalination plant will be located in Al Khafji, Saudi Arabia. Image courtesy of NormanEinstein. AWT and Abengoa joined hands to build the desalination facility. Image courtesy of Advanced Water Technology. The desalination plant will be powered by polycrystalline photovoltaic arrays designed by KACST. Image courtesy of Advanced Water Technology. To be built in Al Khafji City, the Al Khafji desalination plant will be one of the world’s first large-scale solar-powered desalination plants. It will be located to the north-eastern part of Saudi Arabia near the Kuwait border. In January 2015, Advanced Water Technology (AWT) and Abengoa agreed to jointly build the solar-powered plant. AWT is the commercial arm of King Abdulaziz City for Science and Technology (KACST) and is owned by Saudi Company for Development and Technology Investment (Taqnia). The plant is estimated to cost $130m and is expected to be completed by early 2017. It will supply 60,000m³ of desalinated seawater a day to the city of Al Khafji in north-eastern Saudi Arabia, providing a regular supply of water to the region throughout the year. The facility will employ the new solar saline water reverse osmosis (SWRO) desalination method using ultra-filtration (UF) for the pre-treatment process. The solar desalination plant will be built over a 250m x 700m area adjacent to an existing SWRO plant. Solar arrays will be installed on a 90ha area located approximately 1km away from the desalination plant. Construction on the plant is expected to be completed in approximately one year. The desalination plant will include a dissolved air flotation unit (DAF) system, a second-stage ultra-filtration unit (UF), chemical-dosing systems, a reverse-osmosis (RO) unit, and storage tanks for carbon dioxide (CO²), chlorine and lime, as well as a centralised control room for power and water. The RO unit will be divided into six RO trains, which will allow optimum usage of variable solarpower levels. The membranes will be highly resistant to chlorine, salt blockage, and accumulation of bacteria in the RO membrane. The plant will also feature a system to optimise power consumption and a pre-treatment phase to reduce the high levels of salinity, oils, and fats in the region’s seawater. All motors will be controlled with variable frequency drives (VFD) to allow high-variability of operational capacity. The Al Khafji desalination facility will incorporate an ultra-high concentrator photovoltaic (PV) plant to supply power for the desalination plant. The usage of renewable energy will reduce operational costs and harmful gas emissions. The medium-voltage solarpower plant will be fitted with polycrystalline PV solar cells designed by KACST. The plant will have an installed capacity of 15MW and will be connected to both the desalination plant and the national grid. It will produce enough power during peak operation that will be sufficient to sustain the energy requirement of the desalination plant. The Carlsbad desalination project in San Diego County, California, will be the largest desalination plant in the western hemisphere. Water production will be increased during peak power supply from the PV plant. Tracking technology installed at the plant will further maximise the availability of solarpower. Filtration of seawater in Saudi Arabia’s Eastern Region is a complex process due to high salinity, the presence of oils and greases, sea shallowness, seasonal red tides, and jellyfish. The Al Khafji SWRO desalination plant will use ultrafiltration (UF) during pre-treatment and RO to remove dissolved impurities and salts from the ocean water. The pre-treatment technology will prevent clogging of the RO membranes. The SWRO process forces seawater through a polymer membrane using pressure to remove salt. The seawater will pass through an intake tower, where a Jellyfish filter is installed. A 6km pipeline will carry the raw water to the new solar-powered desalination plant for further treatment. A dissolved air flotation (DAF) system will remove oil and other solids from the raw water. This process includes mixing air with water under pressure and releasing at atmospheric pressure in a floatation tank or basin, which results in the formation of tiny bubbles. The suspended matter clings to the air bubbles and floats on the surface of the water from where it will be removed using a skimming device. The UF employed in the second stage will also remove marine organisms and other contaminants from the water.

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