“Valves in a desalination facility are dealing with water rather than hazardous materials,
although saltwater is still corrosive. The real difference is in the size of the valves. They’re a lot
larger than in, say, a chemical plant because we’re dealing with large quantities of water," says
Ben Lee, product manager for a line of valves suitable for use in desalination.
which lowers your capital costs.”
The ultimate cost of producing
desalted water “depends on the local
conditions,” Morgan says. Decker
agrees, noting that while efficiency is
improving monthly and technology
makes it possible to produce water for
$1 per 1,000 gallons, "most plants are
not achieving that figure right now." A
CM2H Hill survey noted that seawater
is now being desalted in Southern California at an estimated $2.41 per 1,000
gallons and in Tampa Bay at $2.08,
while worldwide figures range from
$1.89 in Israel to $2.76 in Cyprus.
Coastal sites are not the only U.S.
areas which today are actively exploring
water desalination. “In fact, there isn’t
much seawater desalination going on in
the U.S.,” observes ITT’s Morgan.
“Only California and Tampa have seawater plants in operation, though others
are in the works. Most of the desal
activity in the U.S. is with brackish
groundwater treatment.”
And Decker notes, “Many metro
areas, like San Antonio and Albuquerque, are looking into desalination.”
Last year the federal Bureau of Reclamation opened its Brackish Groundwa-
ter National Desalination Research
Facility in Alamogordo, NM.
Then, too, desalting water is becoming
more competitive with other sources of
water simply because the cost of those
other sources is going up as availability
goes down. “Though desalination can’t
be competitive with nearby surface
water,” Decker explains, “there are
areas which are running out of water
options. Unless we see a spike in electricity costs, desalination is competitive.”
Valve Considerations
Costs are a prime concern for Ed Davis,
facilities manager for the $158 million
Tampa Bay Seawater Desalination Plant.
Opened in January 2008 on an 8.5-acre
site, its daily capacity of 25 million gallons makes it the largest SWRO plant in
North America. And while the costs of
that capacity are large, “we're upbeat
because the price of desalted water keeps
dropping as membrane technologies keep
getting better.”
As for flow control, Davis continues,
the pre- and post-treatment areas of the
Tampa facility “have the same requirements as any surface water plant.” But
because the desal plant is holding sea-
water, his team must constantly fight
salt corrosion and biological growths
such as barnacles. “We can spray for
barnacles and other biologicals,” he
points out, “but not for salt corrosion.
That’s why valves in the low-pressure
part of the plant must be good—
including the little things, like screws, so they
don’t keep corroding and have to be
replaced all the time.”
In the high-pressure areas where seawater is forced at perhaps 900 psi
through the RO membranes, Davis says,
“Valves must be reliable. I look for
value more than price. Desalination is
maintenance-intensive, so we look for
anything that will lessen our maintenance load. We also want to know, if we
have a critical situation then how quickly can the valve be replaced?”
After treatment, desalted water is
blended with water from less expensive
sources, including groundwater and surface water, to make the supply more
affordable. As for disposal of briny
wastewater, an official statement from
Tampa Bay Water declares, “The concentrated seawater left over from the
desalination process will not significantly alter Tampa Bay’s salinity, because it
is diluted with up to 1. 4 billion gallons
per day of power plant cooling water.“
Yet Decker of CH2M Hill believes,
“We can only throw the concentrated
brine back into the ocean for a limited
time. What if everybody started doing it
tomorrow? Or what if you’re an inland
city and don’t have an ocean nearby?”
Current alternatives include drying
beds, deep-well injection and out-filtra-tion. “But researchers are working on
new uses for leftover brine,” notes
Decker, “as well as reducing the amount
of reject water. It’s gone from 50/50 or
60/40, to where RO systems can now
produce 80% usable water and only
20% waste.”
While companies such as ITT make
RO membranes, and firms such as
CM2H Hill are involved in planning and
engineering, Flowserve Corporation is a
valve and pump manufacturer that has
become active in the water desalination
market. Based in Dallas, Flowserve
offers nearly 70 products for use in
