A widely used method for desalination is distillation, a thermal process in which seawater is evaporated to obtain fresh water. The downside: distillation is extremely energy intensive. Therefore, most new desalination plants employ reverse osmosis, a process through which fresh water is separated from seawater through semipermeable membranes and applied pressure. An example is a new plant in Al Khafji: Not only does it employ a two-stage reverse osmosis process, it derives its energy from a nearby solar power installation. Turning seawater into freshwater has never been so efficient.
Modern desalination
Drinking water from the sea
It happens every day: water evaporates, makes clouds, and reaches the ground as rain, forming rivers and lakes as a source of drinking water. In desert areas, the rain that falls isn’t enough. An alternative is desalinating water from the ocean, a process that has recently become more efficient.
How to supply a desert population with water?
Latest technology and solar power
A widely used method for desalination is distillation, a thermal process in which seawater is evaporated to obtain fresh water. The downside: distillation is extremely energy intensive. Therefore, most new desalination plants employ reverse osmosis, a process through which fresh water is separated from seawater through semipermeable membranes and applied pressure. An example is a new plant in Al Khafji: Not only does it employ a two-stage reverse osmosis process, it derives its energy from a nearby solar power installation. Turning seawater into freshwater has never been so efficient.
Although the most modern plants have a power consumption of less than four kilowatt hours per cubic meter of water, reverse osmosis is an energy-intensive process. As electricity is produced primarily in Saudi Arabia using fossil fuels, seawater desalination accounts for a large proportion of carbon dioxide (CO2) emissions.
A reliable partner
Saudi Arabian utility company Rawafid Systems built the plant in collaboration with the water desalination experts Advanced Water Technology (AWT). To realize the project within the tight allotted time frame of only 14 months, Rawafid and AWT selected their partners based on reliability and industry expertise.
For the electrical, automation, and instrumentation packages, the project team chose Siemens as the main contractor. “We contracted Siemens as they are a big company in the market of electromechanical supply for power and water production. Moreover, the Siemens control system is universal and utilized in different industries, like oil and gas, petrochemicals, refineries, and water treatment,” says Ali Awadallah, CEO and project director at Rawafid Industrial.
After receiving the order, the Siemens team immediately got to work on designing a comprehensive solution, including transformers; Sivacon switchgear systems; Siprotec protection systems; Sinamics converters; and process instrumentation for monitoring flow, level, pressure, and temperature. Electrical and automation systems are networked using Scalance industrial communication technology.
Energy saving and flexible
The control system for power generation and distribution as well as water processing is based on the Simatic PCS 7 process control system. Not only provides it superior plant availability and efficiency, but also enable central monitoring and control of all plants and systems, thereby supporting operators in their daily work. At the Al Khafji plant, Simatic PCS 7 enables a variable-speed drive powering the high-pressure pump to be automatically adjusted according to the water temperature and salinity, which change according to the season. That saves a great deal of energy compared to conventional flow control by control valve.
Model for further installations
Since startup, the Siemens systems have performed exceptionally. The 37,000 items of equipment, weighing 425 tons, had to be transported to Saudi Arabia and installed on a tight schedule—a major logistical achievement. Siemens engineers showed flexibility accommodating a major change during the project when the power supply was switched from 34.6 kV to 13.8 kV.
Siemens solutions enable seamless vertical and horizontal integration of all electrical components, thus reducing operational and maintenance costs.
These advantages led to a follow-up order: Rawafid and AWT, now part of the A3C consortium with SETE and Al Fatah, commissioned Siemens to equip eight additional reverse-osmosis desalination plants in Saudi Arabia, including all components and commissioning—again on a tight schedule.
A comparison: Distillation and reverse osmosis
Distillation to desalinate seawater consumes extremely high amounts of energy – up to 25 kWh per cubic meter of water produced. An alternative is reverse osmosis. Here, the most advanced plants achieve less than 4 kWh per cubic meter of water produced. Though reverse osmosis is still energy intensive, it does help countries like Saudi Arabia cut their desalination-related CO2 emissions. And when plants are largely powered by photovoltaics — as the new installation in Al Khafji — the CO2 footprint is even smaller.
“When we’re talking about projects that make a big contribution to environmental protection like this solar-powered desalination plant, there’s no time to waste. Our tried-and-tested components are key to coming up with solutions quickly.”