One source for RO equipment

By Fred Grondhuis, Flowserve

As the number of projects is expected to pick up in 2010 and beyond, dealing with only one supplier is a major benefit to contractors. With the acquisition of Calder AG, Flowserve has now become the one company that can supply all flow control equipment for reverse osmosis (RO) plants. This includes energy recovery devices, pumps, mechanical seals and valves.

The reverse osmosis process has become increasingly popular in the last 15 years. There are many factors contributing to that popularity, including the increased efficiency of membranes and the increased efficiency of energy recovery devices. These devices are designed to reclaim the energy in the brine reject stream from the membranes. The energy is transferred to the raw seawater, thereby reducing the amount of energy needed for the high-pressure membrane feed pumps. This reduced need for energy makes RO one of the most efficient processes for converting seawater to potable water.

The ever increasing need for reliable fresh water, a growing world population and industrialization are driving the construction of salt water conversion plants in arid regions around the planet. Many of these plants are located in the Middle East, around the Mediterranean Sea, and in the Asia/Pacific region. Global Water Intelligence¹ has estimated that the total installed capacity will nearly double by 2016 to 83 million m³/day (20,700 MGD). Because there are economies of scale in plant construction and operation, the plants have become much larger in the last 10 years. Today, 99% of the plants produce 61% of the water. By 2016, it is estimated that 99% of the plants will produce 47% of the water.¹ This means plants are getting larger and capacities of 300,000 m³/d or 75 MGD are common.

The early RO plants used reverse running pumps to capture the energy from the membrane reject stream. These pumps were quickly upgraded to hydraulic (Pelton) turbines, incorporating rotating elements specifically designed to maximize the energy recovered, but still using the same basic configuration. The typical efficiency achieved with these machines today is 88 - 90%. The turbines are a proven technology that is easy to operate and maintain and still quite popular for large installations.

Energy is the second largest expense in operating RO plants. That fact led to the development of isobaric machines. In the 1980s DWEER Tech developed the Dual Work Exchanger Energy Recovery (DWEER™). The first unit was installed in Grand Cayman in 1989. This machine consists of two long vessels that feature a floating piston that separates the process fluids. The brine reject stream fills vessel one from the right. The high-pressure liquid pushes the piston, thereby transferring the pressure to the liquid that already is in the vessel, which is raw seawater. The energy is transferred to seawater which is then boosted to overcome small losses and combines with seawater from the membrane feed pumps into the membranes. Meanwhile, the second vessel is operating in the reverse direction. The energy from the brine is spent and raw water pushes the piston back to the right, where the brine is ejected to the sea. Controlling the motion of the pistons is the patented LinX™ valve. On the other side of the vessels is a pair of check valves for each vessel. To view an animation of the operation, please visit: www.calder.ch/htm/start.htm.

The beauty of the system is that there are no rotating parts that can wear out. In fact, at full speed the pistons are only cycling up to five times per minute. The system is adjustable for speed, which means that it can start very gradually, eliminating over-pressurization and water hammer. Also, due to the low speed, the noise levels are well below OSHA recommended levels of 85 dBa. The DWEER has been well accepted in the industry and has been used in some of the largest installations to date, such as Ashkelon, Israel, at 330,000 m³/d (82 MGD). The main reason for the success of the DWEER is the outstanding efficiency of the system, which can reach 96 - 98%. This affects the overall energy consumption of the plant.

Two publications attributed the success of achieving low energy rates to the DWEER:

• After one year of operation, Australia's Gold Coast SWRO plant reports that its energy consumption is about 15% lower than anticipated. The plant employs a Flowserve/DWEER energy recovery device.²
• CWCO improved its operating performance last year. With its ultra low energy design, the Blue Hills SWRO plant boasts the world's lowest specific energy consumption for an equivalent sized plant.³

Flowserve Corporation manufactures centrifugal pumps, valves and mechanical seals that have been widely used in Oil & Gas, Power, Water and Chemical industries. For over 50 years, Flowserve has supplied pumps to the desalination industry. One of the trademarks of Flowserve equipment is the reliability and high efficiency of its pumps.

The acquisition of Calder complements the total package that Flowserve can now offer the industry. For energy recovery devices, Flowserve now offers both the DWEER and the ERT hydraulic turbine. In addition to worldwide sales and manufacturing, Flowserve also operates a network of over 150 Quick Response Centers, with locations in Saudi Arabia, Dubai and Abu Dhabi. The QRCs are designed to offer service and repair for Flowserve equipment. The combination of highly efficient new equipment backed by a network of service centers makes Flowserve the one source for RO equipment in this industry.

References:

1. Global Water Intelligence - Desaldata reports -Fall 2008

2. Water Desalination Report, Volume 46 (2010), Issue 10 - page 4

3. Water Desalination Report, Volume 46 (2010), Issue 12 - page 2