POWER July 2022 - 24

WATER AWARD
Harnessing Cooling Tower
Plumes to Provide Purified Water
Courtesy: Infinite Cooling
A novel technology that is surprisingly simple in principle promises to significantly
reduce water consumption in evaporative cooling tower systems by capturing water
from cooling tower plumes.
Sonal Patel
C
ooling towers at power plants are
essentially heat rejection systems
that use significant quantities of
water to dissipate heat from recirculating
water. In wet cooling towers, the
process involves evaporating a portion
of the circulating water, producing heat
transfer through both sensible heat of air
and latent heat of evaporation.
A longstanding concern in the power
industry involves the amount of water
loss from cooling towers. Water is
mainly lost through evaporation, which
involves vapor dissipation into the ambient
air during the heat rejection process.
But it also occurs during blowdown,
when the water has to be removed
from the tower and replaced to prevent
fouling and scale formation. Some water
is also lost due to drift, which occurs
when tiny droplets are entrained with
the exiting air or vapor flow, though drift
losses are typically minimal, comprising
less than 1% of consumption.
Water losses can be substantial. The
U.S. Environmental Protection Agency
(EPA) suggests that regardless of cooling
tower operating efficiency, about 1.8 gallons
of water are evaporated for every tonhour
of cooling. " Traditional wet-cooled
power plants lose 60% to 90% of their
incoming water via cooling tower evaporation
or drift, " noted Dan Sampson, a principal
technical consultant at HDR.
In
addition
to
being
costly,
these
losses have other side effects. Because
water evaporation requires continuous
makeup from a water source, current
and future water scarcity concerns may
24
1. Schematic demonstrating location and use of Infinite Cooling's retrofittable solution. Courtesy:
Infinite Cooling / National Energy Technology Laboratory (NETL)
www.powermag.com
POWER | July 2022
directly affect power plant reliability and
viability. In 2017, two doctoral students
from the Massachusetts Institute of
Technology (MIT), Maher Damak and
Karim Khalil, and MIT Professor of Mechanical
Engineering Kripa Varanasi set
out to address this pressing issue with a
concerted focus on power plant plumes.
The Quest for Plume Abatement
When vapor leaves a cooling tower, it
may, under certain ambient conditions
(usually when ambient air is cold or humid),
condense and form a plume of fog,
the researchers observed. Plumes have
long posed another concern for the power
industry, the researchers noted. They
can be a nuisance and even dangerous.
" Regulatory requirements relating to
safety (drifting plumes can reduce visibility
on roads and airports) and aesthetics,
force some cooling towers to be
equipped with plume abatement systems,
which generally heat the exiting
vapor and decrease its moisture content,
either by heat exchangers or by blowing
hot dry air and mixing it with the exiting
vapor, thereby preventing the formation
of fog droplets at the outlet of the tower, "
they said.
While these abatement systems can
remove the appearance of a plume, a
power plant using them may still consume
the same amount of water and suffer
lowered overall net energy efficiency,
owing to added heat requirements redirected
to the cooling tower outlets. And
while some devices have been designed
to collect exiting vapor from cooling towers
for reuse in the cycle, most methods
rely on liquid or solid sorption, requiring
significant energy or costly equipment.
Under a project fostered by the MIT
Varanasi Research Group, the research

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POWER July 2022

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