POWER March 2017 - 29

WATER & WASTEWATER
1. Turning tides. More efficient cooling towers reduce the amount of water withdrawn
from lakes, rivers, or the ocean for thermal power plant cooling needs. Courtesy: GE Water &
Process Technologies
Stress on Freshwater Supplies " in this issue
of POWER). This was the case for a client of
GE Water & Process Technologies.
" Our customers were asked to use municipal
gray water. This is the wastewater from
a municipal plant. When they were zoned
and started up they could not use fresh water
from the river or the lake, and these are very
tough to treat waters, " Peter Macios, executive
product manager for the company, said.
GE Water & Process Technologies offers
a wide range of customizable chemical and
equipment treatment options for generators
dealing with difficult waters. " We were able
to develop and design programs that allowed
our customers to-number one-operate as
efficiently [as possible] with the use of that
water and negate all the effects on ... microbiological
controls, disposition, and corrosion, "
Macios said.
surface to the air, resulting in a much more
efficient transfer of heat.
However, film fill isn't without its disadvantages.
As noted, while splash fill works
to break water into droplets by-as the name
suggests-making it splash off relatively
wide-set bars within the tower, film fill directs
the water through small funnels. Unfortunately,
and unsurprisingly, most cooling
towers aren't running with filtered water. The
water being used in these towers is generally
pretty dirty, full of mineral and biological
sediment that can easily clog the fill with
microbiological growth, fouling, or scaling.
Rough Waters
While splash fill is at a disadvantage to more
modern fill styles in cooling efficiency, it's
not without its upsides. Splash fill is less
dense, and thus more forgiving of difficult
water. Water heavy in sediment can clog film
fill far more easily than splash fill, but in general,
the tradeoff is not worth it as chemical
treatments to help deal with difficult water
are advancing quickly.
The four main water quality issues power
generators face in keeping their towers running
in top shape are corrosion, scaling, fouling,
and microbiological activity.
Corrosion occurs when chemicals in the
water eat away at the components of the
cooling tower. This can result in a loss of heat
transfer, and in turn decreased efficiency.
Corrosion can also lead to equipment failure,
which in turn can lead to plant downtime and
equipment replacement costs.
Scaling is the buildup of dissolved minerals
on equipment. This too can result in the
reduction of the heat exchange ability of the
March 2017 | POWER
system as the scale can act as insulation,
making it much more difficult for the system
to effectively cool.
Similar to scaling, fouling is the buildup
of suspended particles. While scaling is limited
to minerals, however, fouling applies
to anything from organic matter to oils. At
best, fouling inhibits heat transfer the same
way scaling does, by acting as an insulator.
At worst, fouling can completely plug fill,
reducing the evaporative areas of the system,
dealing a blow to the efficiency of the system.
Finally,
microbiological activity refers to
the impact that any microorganism living in
the system has on the plant. The microorganism
can be suspended in the water or may
grow on the surfaces of the cooling tower
equipment, again resulting in reduced heat
transfer due to the insulation and blockage of
the fill material.
Cooling towers use massive amounts of
water, so it's no surprise that municipalities
and states have in many cases delegated
the lowest quality of the resources for use
by power generators. In 2010, water withdrawals
for thermoelectric power accounted
for 45% of total withdrawals in the United
States, according to the U.S. Geologic Survey's
most recent national water use report.
However, water usage for thermoelectricpower
generation has been on the decline
(Figure 1), the report notes. Between 2005
and 2010 water withdraws in that category
decreased 20%.
To preserve freshwaters, some areas of
the country require cooling towers to use
municipal gray water or to cycle their towers
more (see " Reclaimed Water Reduces
www.powermag.com
Chemical treatment of cooling tower water
is a complex balancing act. Unfortunately,
many chemical treatments to address one issue
negatively impact chemical treatments
to address another. Fortunately, GE believes
it has found the right balance, developing
chemical treatments that do not adversely
interact.
" With traditional programs, when you
set a biocide or microbiological control, it
always degraded the corrosion inhibition
and deposit control, " Macios said. " In other
words, the programs are always at odds with
one another. At GE, we're able to keep both
microbiological deposit control and corrosion
in check without affecting any of the
programs. "
GE's GenGard water treatment technology
works across the pH spectrum to inhibit
corrosion, while GE's Spectrus microbiological
control agent keeps microbial species,
including bacteria, algae, yeast, and fungi,
under control. Unlike other chemical treatment
options, the two technologies can be
used together. " The beauty of the program is
they're synergistic. The oxidizer [Spectrus]
doesn't degrade the GenGard program. Spectrus
doesn't have an effect on the GenGard, "
Macios said.
Moving Parts
Even when a cooling tower's fill is clean and
operating efficiently, inefficiencies may still
be lurking. One efficiency issue that often
receives little attention is the performance of
the spray nozzles at the top of the tower.
It has generally been accepted that a water
spray is going to take the shape of an umbrella,
resulting in a circular spray pattern.
The problem with that is that it is difficult
to line up circles to evenly distribute water
over a surface. If the circles are lined up to
just touch, entire areas of the fill media are
29

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POWER March 2017

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