POWER August 2017 - 29

WATER AWARD
1. The purification process. The
Desalitech closed circuit reverse osmosis
(CCRO) system, shown here, is used to demineralize
water at the Grapeland Generating
Station, a peaker plant located in Rancho Cucamonga,
California. Courtesy: Southern California
Edison
(CCRO) system from Desalitech (Figure 1).
In a CCRO system, the water flows in a loop,
so there is only one stage that repeats. Filtered
water flows out in a continuous stream,
while the water with the contaminants-
known as brine-is recirculated back to the
front of the membrane array using a circulation
pump. Once the desired recovery is
achieved, the brine flush valve is opened and
concentrated brine is purged from the system
without stopping the production of filtered
water, and releasing only a small amount of
pressure. Maintaining pressure in the system,
rather than releasing it to discharge the brine,
is a key element in lowering energy use.
The Desalitech CCRO system allows the opfailure
combined to make them an unattractive
option in the long run.
RO, RO, RO Your Boat
A reverse osmosis (RO) system offered a
more permanent solution. In an RO system,
water is forced under pressure through a permeable
membrane to separate contaminants.
But traditional RO systems have a number of
disadvantages.
For one thing, traditional RO systems
use more water to flush away contaminants,
meaning greater water use overall. They
typically have a multi-stage filtering process,
requiring more pumping to push the water
through each stage, and thus, they use more
energy. Finally, the first membrane in the
process tends to get fouled the most, requiring
more maintenance.
Every stage of the traditional RO process
is comprised of multiple sequential membranes,
and each can only achieve 50% recovery
of contaminants. It takes two stages to
achieve 75% recovery, creating 25% waste.
Even so, this is the standard configuration of
most industrial and municipal RO systems.
Enter a new solution-a closed circuit RO
erator to specify the filtration rate for automatic
operation. Once the desired rate is entered on
the control panel, the system automatically
purges the brine when that rate is reached.
Rates up to 98% have been achieved with fullscale
systems, according to Desalitech.
This closed circuit approach (Figure 2)
can reduce wastewater by 50% to 80% compared
to a traditional RO system, with 20% to
35% less energy, lower brine disposal costs,
and fewer membranes to become clogged
and replaced.
An Industry First
To conserve water and cut costs, SCE adopted
Desalitech's innovative CCRO process
with mixed-bed polishers at the five gas-fired
power plants mentioned previously. This was
the first implementation of CCRO technology
in the power generation industry. The systems
operate at 91% recovery in a single-stage design,
producing a guaranteed water purity of
less than 10 microsiemens per centimeter.
Kishore Billapati of SCE expects that
switching from mobile demineralization
trailers to CCRO at the company's five
peaker plants will save 44 million gallons of
water per year, improve reliability, and cut
2. CCRO layout. Desalitech invented a unique way of operating crossflow RO membranes
in a highly efficient and flexible simple filtration device. At a software-based setpoint, the system
automatically flushes out all the concentrate, and then returns to its normal operation
mode. Courtesy: Desalitech
Standard reverse osmosis membranes
High-pressure
pump
Permeate
Pretreated
feedwater
Cartridge
filter
Brine flush
valve
August 2017 | POWER
Circulation
pump
www.powermag.com
POWER POINTS
Winning Attributes
Southern California Edison's
use of patented closed circuit
reverse osmosis (CCRO) water
purification is a first for the power
generation sector.
CCRO offers substantial cash, water,
and waste savings for power
plant operations, saving 44 million
gallons of water per year, improving
reliability, and cutting annual
water operating costs by 85%.
CCRO offers a model for the
thousands of other combustion
turbines in operation around the
world.
annual water operating costs by 85%, which
amounts to more than $1 million in savings
per plant. Most of the dollar savings comes
from no longer renting and maintaining the
mobile trailers. SCE still has other plants that
use mobile trailers, and the company plans
to keep mobile systems on call, in case the
CCRO systems are unavailable.
Reduced water use was not a big moneysaver
for SCE, said Billapati, but it is still
important because SCE strives to be a " good
corporate citizen " in drought-parched Southern
California.
The switch will reduce SCE's water disposal
costs, because the brine can be disposed
of in a lower-cost brine disposal
facility. Some of SCE's combustion turbine
plants do not have access to a sewer line, so
wastewater must be taken offsite via truck.
Others have access to a special " brine line "
operated by sewage districts, which directs
very salty wastewater from industrial processes
to a special treatment process, keeping
it out of freshwater bodies like rivers, lakes,
and groundwater.
While the water and dollar savings were
important, Billapati said, the reliability benefits
might be the greatest positive. " When the mobile
trailers were exhausted, the plant couldn't
run, " Billapati pointed out. " You are at the mercy
of the vendor to send you the trailers. With
CCRO you are manufacturing your own water,
so there should not be any interruption. "
For pioneering a better way to manage the
water needs of its power plants and for managing
water in a more sustainable manner,
SCE is a worthy recipient of POWER's 2017
Water Award. ■
-Bentham Paulos is a freelance
writer and consultant specializing in
energy issues.
29

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POWER August 2017

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