Energy Recovery Spins Out Energy Savings for Desalination

Energy Recovery Inc. (ERI), a company based in San Leandro, California, has developed technology that reduces the amount of energy required for desalination.

The technology does not directly relate to filtering water, but instead harnesses the pressure in the wastewater stream of reverse osmosis systems and transfers that pressure to the incoming feed stream to reduce the energy required to run the desal process.

According to ERI’s web site, the technology in its PX device (pictured above) has led to seven U.S. patents and international patents.

Tim Dyer, the company’s CTO, commented on ERI’s IP. ”We innovate and create intellectual property along the way to address existing and emerging industrial energy recovery needs. Our strategy drives our IP, and our IP drives our strategy.”

U.S. Patent No. 7,201,557 (’557 Patent) relates to some of ERI’s fundamental innovations. Entitled “Rotary pressure exchanger,” the ’557 Patent is directed to a pressure exchange apparatus for transferring the pressure of a high pressure fluid stream to a lower pressure fluid stream.

The rotary pressure exchanger (11) has a housing (13) containing a rotor (15) with a plurality of channels (16). A low pressure seawater feed stream from a reverse osmosis system is pumped through a straight inlet conduit (39) and fills an inlet passageway (41).

At the same time, high pressure brine from the reverse osmosis system is pumped through an elbow conduit (51), fills a plenum chamber (53) and enters axial channels (16), causing the rotor (15) to spin.

As the rotor (15) spins, there is periodic alignment of each channel (16) with the opening to a discharge seawater passageway (65) in an upper end cover (19). According to the ’557 Patent, whenever this alignment occurs the seawater in the channels is instantly pressurized.

Thus, the pressurized seawater is caused to flow out of the channels, fill an upper plenum chamber (45) and exit through an elbow discharge conduit (43).

Similarly, when a rotor channel (16) is aligned with the opening to the seawater inlet passageway (63) and the opening to the brine discharge passageway in the lower end cover (21), the seawater forces the low pressure brine out of the pressure exchanger (11) through the straight discharge conduit (49).

ERI’s pressure exchanger has the advantage of simplicity, with the rotor being the only moving part. The rotor and associated components seal the high pressure portion of the reverse osmosis process by keeping high and low pressure separate without the need for pistons.

According to ERI’s web site, the PX device makes desalination more economical and less energy intensive by reducing the amount of energy required by up to 60%.

Eric Lane is a patent attorney at Luce, Forward, Hamilton & Scripps in San Diego and the author of Green Patent Blog. Mr. Lane can be reached at elane@luce.com.