POWER July 2014 - 35

ENVIRONMENTAL CONCERNS
steam plant's water consumption, according
to the NETL report, but it would increase
an IGCC plant's consumption by only about
37%. Still, said Zammit, the " penetration
and impact [of CCS] will be unit- and sitespecific. "
Another
impact on water resources could
come from biomass generation. While inplant
water consumption is comparable to
coal plants, growing biomass fuel may require
significant amounts of water, particularly
if it is grown specifically for use in a
power plant. This is a concern in areas where
agricultural water supplies are already under
stress, such as China, India, and the U.S. central
plains.
Biomass is not the only fuel with an effect
on water resources. Natural gas from shale is
projected to constitute 53% of the U.S. gas
supply by 2040, according to the EIA. While
the water consumed by hydraulic fracturing
is small compared to agricultural use, much
shale gas development is taking place in areas
under water stress, such as Texas. Shale
gas, as a new industry, must compete with
existing demands on water resources, something
that has caused controversy in many
areas. It is worth noting as well that, unlike
water used in agriculture, most of the water
used in hydraulic fracturing is permanently
lost from the hydrological cycle. Waterless
methods, though currently limited, are likely
to grow in importance.
The Way Forward
There is clearly pressure-political, social,
and environmental-to reduce the power sector's
load on water resources. Most of these
pressures will be experienced in areas such as
India and China, where both electricity and
water supplies are constrained.
Zerrenner believes one key is better coordination
between power and water suppliers.
" The power sector and the water sector need
a better understanding of how they impact
each other, " she said. " A crucial first step is
for power and water engineers to start collaborating.
They can then work with regulators
and legislators to reveal novel conservation
strategies. Everyone in the chain in both
sectors needs to understand the interconnection. "
For
existing plants, a focus on improving
efficiency-of both water and plants-will
be key. A 2010 NETL study reviewed various
methods that have been employed globally,
among them:
■ Replacing/retrofitting with modern, more
efficient plant systems.
■ Switching to higher-quality coal.
■ Use of waste heat to dry high-moisture
coals.
July 2014 | POWER
4. Nifty shades of gray. The Sand Hill Energy Center in Austin, Texas, began using treated
wastewater from a nearby wastewater treatment plant for cooling in 2006, which allowed it
to reduce its use of municipal potable water by 80%. Courtesy: Austin Energy
■ Retrofitting dry cooling.
■ Retrofitting cogeneration.
■ Purification/desalination of brackish water
and saltwater.
■ Dry bottom ash handling.
■ Dry emissions scrubbing.
■ Recycling and reusing wastewater.
■ Improved monitoring of water consumption.
The use of alternative sources of water deserves
special attention, since it can have the
most direct impact on a plant's consumption
of local water resources. One facet of this can
include capturing wastewater streams, such
as cooling tower blowdown, and using these
for processes that do not require high water
quality. Cascading wastewater from higherto
lower-quality needs enables extensive reuse.
Many plants in water-stressed areas have
already implemented such recycling measures.
Making degraded water sources more
cost-effective for cooling is another area with
future possibilities, according to Jessica Shi,
a senior technical leader at EPRI.
Where large quantities of water are needed
for wet cooling, municipal wastewater has
proven useful as a replacement for freshwater.
A number of new plants in the U.S., such
as the Sand Hill Energy Center in Austin
(Figure 4) and the Empire Generating Plant
in Rensselaer, N.Y., have leveraged such supplies.
Doing so, however, requires special
measures because of the potential for generating
airborne pathogens.
For high-quality water needs, purification
and desalination of water resources
that are not suitable for agriculture or other
competing uses-whether seawater or lowquality
groundwater-is an option. While
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expensive and energy intensive, it can be
made cost-effective if a desalination plant is
co-located with the power plant in an area
where freshwater is at a premium (that is,
where it can be sold to recapture some costs)
and waste heat can be captured for use in the
desalination process (see " Adding Desalination
to Solar Hybrid and Fossil Plants " in
the May 2010 issue). Advanced membrane
distillation technology could also greatly reduce
the costs of desalination.
Going forward, new technologies will
be necessary to further improve efficiency
and reduce costs for closed-cycle cooling,
as well as improving overall plant water
efficiency. " We have technologies today
that can reduce water consumption for new
plants, " said Zammit. However, " research is
still needed to address the cost and O&M
impacts of such technologies. In addition,
research into technologies such as the thermo-syphon
cooler and more cost-effective
water treatment options could help conserve
water at existing plants. "
EPRI and several partners inaugurated the
Water Research Center at Georgia Power's
Plant Bowen in Cartersville, Ga., in 2012
with the goal of generating industry-wide
insights that will help generators minimize
their impact on water resources. (See " Research
Center Dedicated to Power Plant Water
Use Opens " in the November 2012 issue,
and " Advanced Cooling and Water Treatment
Technology Concepts for Power Plants " in
the April 2014 issue.) Specialized research
such as this is certain to be key. ■
-Thomas W. Overton, JD is a POWER
associate editor (@thomas_overton, @
POWERmagazine).
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POWER July 2014

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