Desalination plant process.
Desalination plant process.
Desmi DSL double suction pump designed specifically for seawater intake.
Desmi DSL double suction pump designed specifically for seawater intake.

A fresh, clean water supply is a constant challenge around the world. Increasingly, authorities and industrial and agricultural producers are turning to sea water as their source, but desalination is a complex process. One Danish pump system manufacturer, DESMI, understands and provides for those complexities.

Around 70% of the Earth’s surface is covered in water but some 96% of that is sea water. Of the remaining fresh water, only a relatively small proportion is readily available to use as drinking water or to supply other needs, such as production or agricultural needs. Lakes and rivers, for example, contain only around 0.035% of the planet's total water supply. In addition, the pressures of climate change, population growth and increasing affluence are placing a heavy, growing burden on fresh water supplies. 

Desalination in focus
Desalination is the obvious answer to the problem; producing drinking water and service water from seawater. It’s a similar process around the world where sea water is pumped from coastal inlet pipes, processed under high pressure through filters, then pumped onward, usually to reservoirs.

What sounds like a relatively simple process is actually a highly complex one, which Danish pump system manufacturer, Desmi, understands well through its long experience of providing pumps for desalination plants. Desmi provides industrial pumps for many different applications including desalination, with different models and capacities for water purification systems or reverse osmosis (RO) treatment. The company’s DSL double suction pump, for example, is designed specifically for seawater intake and the company has a full range of pumps for brine, recirculation, backwash and transfer.

Efficiency first
Torben Harlev Mai is an application manager at Desmi “It’s absolutely crucial to use highly efficient pumps at each stage of the desalination process,” says Torben. “That’s because it is very expensive to make water in this way. By comparison, pumping up and purifying groundwater uses around 2.7kWh of electricity per cubic metre. But for desalination, it’s 5 to 6kWh – or double the energy consumption. And that’s not good for operating costs or for the environment.” 

Efficiency isn’t the only parameter, however. The salt content of sea water and its varying temperatures around the earth aren’t friendly toward man-made equipment. Desmi’s experience of supplying pump solutions to the maritime industry as its primary business area means the company understand how to deal with such challenges.

“You simply can’t afford to have downtime in an offshore environment,” explains Torben. “Particularly if we’re talking about a pumping system for cooling a ship’s engines. And it’s the same basic pump that we adapt to work dependably in a desalination plant.”

In fact, most of the company’s pumps and related equipment are built to handle even harsher conditions, transferring, for example, heated bitumen or highly abrasive chemicals. For sea water being transferred at temperatures below 15°C (59°F), cast iron is used for the pump’s casing. From 15 to 40°C (59-104°F), nickel alloy is needed. And for pumping sea water at 40 to 60°C (104 to 122°F) in the Middle East, nickel alloy bronze or super duplex is demanded. 

Research and development
The Danish-based manufacturer, whose subsidiaries and distribution network stretch around the globe, gives a high priority to research and development, too. So, while it offers a wide range of standard pumps as a starting point, a growing number of orders are customised to meet specific customer requests.

At the same time, the company welcomes new ideas in the desalination field that can help to alleviate approaching water shortages. And, in recent years, plenty of ideas have surfaced – some short-lived, others holding the promise of better technology in the not-too-distant future.

The pump systems are available to power new solutions, and the company monitors or participates in attempts to arrive at workable, high-flow approaches. But for now, local authorities trying to keep up with fresh water supply requirements must focus on well-proven, high-capacity technologies. 

Averting disaster
Torben is well aware of the issues Desmi is working to solve: “Fresh, clean water supply is an extreme challenge for the world. This has, of course, been known for quite some time, but the situation in Cape Town, South Africa, in the beginning of 2018, shows how big a problem the populations of many different regions of the world may be facing. Answering this challenge, in part, is up to companies like our own that can supply efficient, reliable pumps as key components of the many new desalination plants that need to be planned and commissioned with as little delay as possible.”

For now, Desmi is best able to help by providing its solutions, along with information and advice on pump choices for such plants, and by maintaining high reliability when it comes to providing fresh water to large populations.

Torben adds, “Our office in Dubai is helping the engineers who advise Middle-Eastern utilities and manufacturing companies on water desalination issues to determine the best setup for new investments – discussing pump applications, types, capacities and servicing plans to keep the flow strong and plentiful. The same goes for our offices in China, Singapore, Africa, Denmark etc. Wherever we can help with desalination – we take part”.