October 2019

WATER INDUSTRY n Solar-powered desalination plant is the world’s largest T he world’s largest solar-powered plant for extracting drinking water from seawater has been commissioned at Al Khai on Saudi Arabia’s Gulf coast. The plant has been built to meet the demand for a reliable supply of drinking water for the growing population of nearby Al Khai City, which has 100,000 residents already. The incoming seawater is processed to produce fresh water using a two-stage, solar- powered reverse osmosis technology. The process uses pressure to reverse the natural process of osmosis to concentrate substances dissolved in the fluid – in this case, salt. Power comes from a nearby solar power plant with a connected capacity of 20MVA. At night, the plant draws power from the public electricity grid. Based on experience elsewhere, the original 34.8kV power supply was reduced to 13.8kV. Key challenges for the project included a tight schedule, and the plant’s large capacity. It can process up to 90,000m 3 of water every day – enough to supply 150,000 people. Although reverse osmosis is a well- established desalination technology, such plants are usually expensive to operate because they need large amounts of electricity. Power can account for up to half of the cost of running such a plant. They also result in high levels of carbon dioxide (CO 2 ) emissions. The efficient use of solar energy in the new plant has reduced the amount of electricity used“significantly”compared to those that rely on power from non-renewable sources, as well as cutting CO 2 emissions. The plant, developed by water desalination experts from Rawafid Industrial and Advanced Water Technology (AWT), was completed in 14 months. To enhance the efficiency of the plant, all of the site’s motors are controlled by variable-speed drives, allowing the motors’ speeds to be altered to suit demand and operating conditions. The drives were supplied by Siemens, which also provided all of the automation, communication, electrification and instrumentation technologies. Having a single supplier simplified vertical and horizontal integration of the electrical components, and is helping to cut operating and maintenance costs. The products used include Sinamics GH180 and G150 converters, Scalance network communications, Sitrans process instrumentation, Sivacon switchgear and Siprotec digital substation protection. Automation functions are performed by a Simatic PCS 7 distributed control system. Most of the control components were off- the-shelf items. “The system is not dedicated to a certain specific process, and it is not customised,” explains Ali Awadallah, CEO and project director at Rawafid. “We can adjust all the parameters by ourselves without calling Siemens for changes in the software.” Since the plant was commissioned, more than a year ago, it has run without a hitch, with an availability of 98%, and is producing better quality water than expected. n The desalination plant makes extensive use of drive technologies ® COMBAT UNPLANNED DOWNTIME optimum SKF bearings for use in the water industry Deep groove ball bearings Angular contact ball bearings Spherical roller bearings www.acorn-ind.co.uk T: 0800 8766 441 E: enquiries@acorn-ind.co.uk split roller bearings Your authorised SKF distributor