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, however, the rain that falls simply isn’t enough. An alternative is desalinating water from the ocean, a process that has recently become more efficient.

Vast swaths of Saudi Arabia are desert, with low annual rainfall and limited groundwater reserves. To complicate matters even more, the country has no permanent rivers within its borders. The answer to supplying a growing population with fresh water – whether for human consumption, agriculture, or industrial use – is desalination. In fact, desalinated water accounts for about half of the country’s fresh water supply.

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.

The plant with a daily capacity of 60,000 m³ was built by Saudi Arabian utility company Rawafid Systems 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.

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.

“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,” says Markus Wallinger, Project Lead from Siemens. 

Since startup, the Siemens systems have performed extraordinarily well. The equipment consisting of 37,000 items weighing 425 tons had to then be transported to Saudi Arabia and ready for installation according to the tight time plan.

Mastering this logistical challenge was another major achievement of the Siemens team. Furthermore, the Siemens engineers showed their flexibility by accommodating a significant change during the project when the power supply was changed from 34.6 kV to 13.8 kV.

What’s more, the Siemens solutions enable seamless vertical and horizontal integration of all electrical components, thus reducing operational and maintenance costs. 

These advantages and more have led to a follow-up order: Rawafid and AWT, which in the meantime have created the A3C consortium with development company SETE and Al Fatah, have commissioned Siemens to furnish eight further reverse-osmosis desalination plants in Saudi Arabia with electrical equipment. The scope of supply includes all components and commissioning. Again, the project is according to a tight time schedule. But as proven with the installation in Al Khafji, that won’t be an issue.