Author: Palle Olsen, Application Expert, Danfoss High Pressure Pumps

The scarcity of fresh water resources and the need for additional water supplies is critical in many regions of the world and will be increasingly important in the future. The UN has made availability of water and sanitation for all one of the Global Development Goals.

In order to meet the increasing demand for fresh water supplies, the number of desalination plants continues to grow, and in the quest for fresh water resources, Sea Water Reverse Osmosis (SWRO) has emerged as one of the most efficient solutions.

The process of pumping large amounts of water through desalination membranes is, however, energy intensive, calling for high efficiency pump solutions. And in the race for energy efficiency, Positive Displacement pumps typically outperform centrifugal pumps on most operational parameters in desalination processes.

High energy efficiency. Low life-cycle cost.

Over the last couple of years, the number of desalination plants using positive displacement pumps has grown. These plants have often been seen to return energy savings of 20 % or more compared to traditional centrifugal pumps; and with proven efficiency rates up to 90%, the positive displacement pumps offer the lowest life-cycle costs in the industry.

Today, the desalination industry acknowledges the advantages of parallel-coupled positive displacement pumps when it comes to reliability, uptime and energy efficiency of the system.

This is also the case at a new 3,500 m3/day SWRO plant at a shipbuilding and maintenance yard in Bahrain. Here, six Danfoss APP 30 pumps are mounted in parallel to achieve the required flow capacity. The multiple pump train ensures that the capacity can be increased incrementally according to the need for water at any given time. During operation, the production of water can be adjusted to consumption by changing only the speed of the pump to harvest additional energy savings. The same excellent solution could today have been achieved by using two APP 78 pumps.

Even when one of the pumps is down for maintenance, the system runs uninterruptedly giving great flexibility and reliability of supplies 24/7/365. The simple construction of the axial piston pump with few moving parts enables easy service and maintenance. Furthermore, the robust and simple design of the APP pumps allows them to run for minimum a year between service intervals.

The conclusion of the Bahrainian shipyard is clear: even though the upfront cost of six APP pumps compared to one CF pump might be seen as is a higher investment, the low cost of ownership throughout the lifetime of the plant and the predictable payback time bring significantly improved profit margins over the lifetime of the desalination plant.

Large Positive Displacement pumps open new opportunities onshore and offshore

The growing trend toward modularity for mid-size SWRO plants opens new opportunities for use of parallel-coupled positive displacement pumps in onshore and offshore desalination applications. The larger Danfoss APP 53- 86 pumps have turned out to be an excellent choice for operators who want the advantages of axial piston technology in high output plants. The larger pumps are particularly well suited for parallel-coupled trains in SWRO plants with a capacity of up to 30,000 m3/day or even more.

“The larger APP pump sizes that offer flows between 53 and 86 m3/hour have fast become favorites in land-based, medium/large-sized SWRO plants. However, the compact and light-weight design is also attractive in offshore applications where both space and reliability is of vital importance”, says Jesper Bentzen, Sales Director at Danfoss.

With the launch of the APP 53 to 86, Danfoss high-pressure pumps now cover flow rates from 0.6 to 86 m3/hour. Danfoss is committed to supporting the desalination industry with energy efficient solutions that can help bring clean water supplies to people across the world. The constant research in new technologies and development of new positive displacement pumps will contribute to fulfilling the global development goal of safe and affordable drinking water for all by 2030.

Facts about Danfoss APP 53-86 pumps:

• Available in sizes from 53 m3/h to 86 m3/h for use in medium/

large-sized SWRO facilities

• Optimized for SWRO applications

• Energy savings up to 20%

• Efficiency rates of up to 90%

• Oil free

• Compact footprint and low weight

• Few parts, reliable operation and easy maintenance