|Massive savings on Energy Utilization
|New Energy Recovery System - now makes it possible to
produce high quality potable water at less than half the price.
The Desalination Story:
Seawater desalination plants have produced potable water for many years.
However, until recently desalination had been used only in extreme circumstances
because of the very high-energy consumption of the process.
Early desalination plants utilized various evaporation technologies. The most
advanced seawater evaporation systems using multiple stages have an energy
consumption of over 9.0 kWh per cubic meter (34 kWh per 1,000 gallons) of potable
water produced. For this reason large seawater desalination systems were initially
constructed in locations with very low energy costs, such as the Middle East or next
to process plants with available waste heat.
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In the 1970s the seawater reverse osmosis process was developed which made
potable water from seawater by forcing it under high pressure through a tight
membrane thus filtering out salts and impurities.
These salts and impurities are discharged from the SWRO device as a concentrated brine solution in a
continuous stream, which contains a large amount of energy. Most of this high-pressure energy can be
recovered with a suitable device. Many early SWRO plants built in the 1970s and early 1980s had an energy
consumption of over 6.0 kWh per cubic meter (23 kWh per 1,000 gallons) of potable water produced, due to
low membrane performance, pressure drop limitations and the absence of energy recovery devices.
The Search for Energy Savings:
In 1985 Filmtec (Dow Chemical Co.) developed the first commercial low pressure, single stage SWRO
element. At the same time pump manufacturers were adapting existing technology such as reverse running
turbines and Pelton wheel devices to SWRO plants in order to recover energy. The new membrane
technologies and first generation energy recovery devices made possible seawater desalination with energy
consumption of slightly less than 4.0 kWh/m³. The rotating machinery of these first generation energy
recovery devices were made of metal parts which often exhibited high corrosion, wear and maintenance
problems when placed in a marine environment.
By 1990 a second generation of energy recovery devices came to market which used high alloy wear parts
such as 904L stainless steel. At around this time the hydraulic turbo charger was also developed. These
innovations improved reliability and reduced maintenance, but still suffered from the limitation of recovering
only 50 to 80 percent of the energy in the high-pressure brine stream from SWRO plants because of various
Over the past 20 years various inventors have attempted to develop advanced commercial energy recovery
devices to overcome these efficiency limitations. These devices have used combinations of pistons, bladders,
valves and timers, and some worked well initially, but suffered high maintenance problems. Others were fitted
with artificial intelligence programs only to suffer an early demise in an industry where the prevalence of
unskilled operators demands simplicity.
In 1992 "Energy Recovery, Inc." began the development of a relatively simple ducted rotor that could
transfer the pressure energy directly from the SWRO brine to the incoming feedwater stream. Five years and
several million dollars later, the idea evolved into a 4-inch diameter, patented commercial device, the
The PE devices were first sold commercially in 1997. The all-ceramic moving and mating parts of the PE
have shown exceptionally low, and even zero wear in high-pressure SWRO brine applications and the
material is not susceptible to the pitting and stress corrosion of steel and bronze components in similar
applications. The slow rotating PE (1,500 RPM) has proven to be a low maintenance component in
commercial desalination plants.
Since the PE transfers energy directly from the brine to the feed without high-speed rotating shaft
inefficiencies, the PE achieves actual efficiencies of 91 to 95 percent within a broad flow range.
Reduced energy and capital costs mean that for the first time ever it is possible to produce potable water
from seawater at a cost below $1 per cubic meter in many locations worldwide.