POWER April 2012 - 55

WATER MANAGEMENT
to install a zero-liquid discharge system
where most all of the wastewater is reused,
consumed, and/or evaporated on-site, " Byers
said. " While this serves to maintain the
stream's water quality, it also reduces its
flow, and therefore may be counterproductive
to addressing other water scarcity issues. "
The EPA is expected to finalize its proposed
new cooling water intake rulemaking
for existing facilities by July 2012, Byers
explained. Because the cooling water intake
flow applicability threshold was dropped to 2
million gallons per day, this rule as proposed
will regulate not only power plants with oncethrough
cooling but also some with closed
cycle cooling tower systems. Depending upon
the final requirements, many power plants
may be able to achieve compliance by upgrading
their intake design and operations to minimize
impacts to fish and aquatic species.
" The final regulations, however, may
force some plants to convert from oncethrough
cooling to closed cycle cooling towers,
which, in addition to being costly, will
5. Cutting water use in power generation. New technological developments in
power generation are helping to reduce water use. For example, much of the new power generation
in the arid Southwest has been from natural gas combined cycle units with air cooling,
which reduces utility water use per net MWh. Courtesy: EPRI
70,000
60,000
50,000
40,000
30,000
20,000
10,000
also result in a reduction of plant efficiency
and power output, " Byers said.
Before the EPA released its proposed rule
in March 2011, many analysts who had assumed
the rule would require all power plants
with once-through cooling systems to convert
to closed loop cooling towers forecasted that
the associated costs would force a significant
number of plants to shut down entirely. Byers
pointed out that " while the rule as currently
proposed may still (alone or in conjunction
with other EPA regulatory drivers) induce
some plants to retire, the proposed rule's requirements
provide more options for continued
operation, and in any event, the five-year
phase-in period for compliance, would not
force those decisions until closer to the end
of the current decade. "
Trends in the Power Sector's
Water Usage
Zammit explained that water resources vary
" dramatically from watershed to watershed,
depending on current uses, allocation (overallocation),
changes in land use and runoff,
overdraw of groundwater aquifers, and the
aforementioned climate changes. "
Although EPRI has water management
1950
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2000
6. A range of water footprints. Water use varies widely among the different power
plant types. For example, nuclear power generation is the most water-intensive, while solar
photovoltaic and wind energy use no water to generate electricity. Analysis assumes closed
cycle wet cooling towers are used. Courtesy: EPRI
Boiler makeup
CT injection
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400
300
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Nuclear Coal
April 2012 | POWER
Oil
Gas
Simple
CT
Combined
cycle
IGCC Solar
thermal
Solar PV Wind Biofuel
www.powermag.com
Scrubbing
Fuel processing
Ash handling
Cooling
Inlet air cooling
risk analysis tools that can be used to examine
sector water requirements, sustainability
goals, and conservation options for a given
watershed, it is difficult to predict what impacts
will be related to each sector. For instance,
much of the new power generation
in the arid Southwest has been natural gas
combined cycle units with air cooling, which
reduces utility water use per net megawatthour.
Zammit added that " this trend is expected
to continue with lower natural gas
prices. Also, wind and solar photovoltaic are
playing roles in reducing power sector water
use. Municipal demands are growing, but so
is effluent reuse " (Figures 5 and 6).
Developing Generation
Technologies That Conserve Water
NETL's advanced cooling technology projects
are attempting to increase the efficiency of
cooling processes, including using less water
and making dry cooling less power intensive.
Carney pointed out that " water recovery from
power plants has been most successful in condensing
the water from the flue gas and not
only capturing this water but also capturing
some of the energy lost with the water and
putting it back into the power cycle. "
Traditionally, power plants are located
next to large rivers, and water is withdrawn
as needed for cooling, Carney said. Newer
sources of water are reclaimed wastewater,
underground mine pool water, produced water
from oil and natural gas production, and
other sources that may need treatment prior
55
Water use (gallons/MWh)
Water use (gallons/MWh)

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POWER April 2012

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