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Universities Council on Water Resources
Journal of Contemporary Water Research & Education
Issue 143, Pages 30-34, December 2009
An Electric Power Industry Perspective
on Water Use Efficiency
John R.Wolfe1, Robert A. Goldstein2, John S. Maulbetsch3, and Charles R. McGowin2
1
C
Limno Tech, Inc., Ann Arbor, MI; 2Electric Power Research Institute (EPRI), Palo Alto, CA;
3
Maulbetsch Consulting, Menlo Park, CA
lean, fresh water has become a critical
resource in the U.S. with growing
demand due to increases in population
and economic activity, exacerbated by population
shifts to more arid regions. At the same time, goals
of environmental protection and enhancement
require improvements in water quality to sustain
wildlife and recreation. While local impacts of
global climate change are uncertain, its overall
impact is expected to be a further reduction in
water availability.
The southwestern U.S. is especially vulnerable
to water shortages because of rapid population
growth and low rainfall, but growth in other
regions may also lead to warm-weather shortages.
Roy et al. (2005) estimated that water sustainability
concerns will be greatest in the west, and that many
regions in the eastern U.S. may also require new
water supplies by 2025 unless existing patterns of
water use can be modified.
Water availability has become a contentious
siting issue for thermoelectric power plants,
which must compete with the growing demands
of municipalities, agriculture, and industry for
surface water and groundwater supplies. This
can constrain development in water-poor regions,
and affects the topology of the national grid that
transmits electricity between regions. Power
plants currently account for about 3 percent of the
freshwater consumed in the U.S., in contrast with
agriculture, which consumes about 40 percent (U.S.
Geological Survey 2004). In fact, thermoelectric
power generation accounts for about 40 percent
of all U.S. freshwater withdrawals because about
half of U.S. plants still use once-through cooling
technology – water withdrawn from an ambient
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water body moves only once through the cooling
system before being discharged back into the
environment. If a thermoelectric power plant
cannot meet its withdrawal requirements, it will
have to either reduce its power output or shut down.
Growing Electric Power and Water
Demands: Consequences and Solutions
The competition over limited water supplies has
put pressure on the electric power sector to use less
water, and on regional authorities to manage water
resources more intensively. There is also increasing
attention to energy conservation in the water sector,
especially in water-poor areas that require the most
pumping, conveyance, and treatment to meet needs
(U.S. Department of Energy 2006).
Viewed as a problem of sustainability, the
challenge is to maintain steady growth in living
standards, including electric power sufficient to
support that growth, while also continuing to serve
needs that can only be met by clean and ample
water resources. If to meet current needs, water
supplies are exhausted or fouled, they become
unavailable for future uses. In today’s climate
of diminishing water availability, sustainable
regional development requires the planning of
water and energy infrastructures to be integrated.
The pressure on water supplies can be reduced,
however, through applications of innovative
approaches to water conservation. These include
both regional planning tools and measures to reduce
water consumption by thermoelectric plants.
The choice of cooling technology and other
decisions affecting water use are part of an overall
siting and plant design process in which demand
Journal of Contemporary Water Research & Education
An Electric Power Industry Perspective on Water Use Efficiency
location, fuel availability, and transmission
infrastructure historically have been more
powerful drivers than water availability (Electric
Power Research Institute 2007). In the future,
water considerations are likely to play a major
up front role in the overall siting and planning
process. Cooling systems with water-conserving
technologies will be considered for locations where
water is less available or more costly to obtain and
use.
A brief discussion of water requirements of
thermoelectric plants can provide insight into
water conservation opportunities. Water use by a
simple steam cycle generation plant is dominated
by cooling. In a simple steam cycle, there exists
a closed loop of water flow referred to as boiler
water. Heat converts liquid water to steam in a
boiler. The heat is usually created by burning a fuel
such as coal, nuclear, or gas, although the source of
heat could also be biomass, solar, or geothermal.
The steam, under pressure, flows from the boiler
to a turbine where it expands and spins the turbine,
which in turn spins a generator, which produces
electricity. Steam exiting the turbine goes to a
condenser, where cooling water flowing external
to the boiler water loop converts the steam back to
liquid and further cools it. The cooled boiler water
flows back to the boiler and begins the boiler water/
steam cycle anew. The heated cooling water leaving
the condenser must now either be discharged to an
ambient water body and replaced by uptake of a
new flux of cool water (once through cooling), or
cooled by a cooling tower and recycled back to the
condenser (closed cycle cooling).
A cooling tower cools primarily by evaporation.
A fraction of the water being recycled by a cooling
tower system must be discharged to prevent salts
from reaching a level of concentration that would
produce significant scaling problems. The flux of
discharged water is called blowdown. The flux of
water that must be taken up to replace blowdown
and evaporative losses is called make-up water.
Combined cycle plants are more water efficient
than single steam turbines, because the combination
of gas and steam turbines has a higher conversion
ratio of thermal to electrical energy. A combined
cycle plant uses two turbines, each driving a
separate generator. The first turbine is driven
directly by the expansion of burning natural gas.
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31
The hot gas outflow from this first turbine is then
used to heat a boiler which produces steam cycle
that spins the second turbine.
Although plant type is the most important
determinant, water requirements also depend on
climate, regulations, source water quality, and inplant water management systems. For example,
in warm, humid environments, mechanical draft
cooling towers must be larger and use more fan
power than would otherwise be the case.
Opposition to power plant siting frequently
focuses on water use, especially (but not
exclusively) in water-short regions, and can lead to
delays or denial of project approval. Regulations
governing intake and discharge of cooling water
under the Clean Water Act have also led to the
adoption of closed-cycle cooling instead of oncethrough cooling at nearly all new plants. This has
enabled the electric power industry to reduce its
water withdrawals per unit of power generated by a
factor of three, at the same time that it has increased
its output of electric power by a factor of 15 (U.S.
Geological Survey 2004). However, because
cooling towers cool principally by evaporation,
the shift to cooling towers has increased water
consumption per unit of power generated.
The imposition of water quality discharge
limitations through state National Pollution
Elimination Discharge Elimination System permits
and air quality regulations, such as those limiting
particulate emissions from cooling towers, can
affect water use by constraining the choice of
cooling technology. The use of low quality source
water in cooling towers may increase the amount of
blowdown and thus decrease water use efficiency.
This can be countered by either pre-treating the low
quality source water or post-treating the cooling
tower blowdown and recycling.
Technological Solutions to Water Scarcity
A wide variety of processes are already employed
in power plants to recover, recycle, and reuse water.
Water is treated to isolate contaminants and send
fresh water back for cooling or other uses, reducing
the amount of fresh water required for make-up at
the front end. A first step in water reuse is to route
cooling water blowdown to disposal ponds, from
which the resultant supernatant liquid is treated
and recycled back into the plant. Slurry from flue
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Wolfe, Goldstein, Maulbetsch, and McGowin
gas controls and ash handling can also be routed
to disposal ponds as a first treatment step. Water
treatment processes commonly used to promote
water reuse and zero liquid discharge include
reverse osmosis and evaporation.
Dry and hybrid cooling are technologies
that offer major opportunities for saving water
(McGowin 2007). Dry cooling uses air instead of
water to remove heat and cool condensers. Dry
cooling dramatically reduces water consumption
and increases the flexibility of power plant siting,
but comes with higher capital costs than wet
cooling and reduces power plant performance
during hot-weather. Wind effects can also reduce
the efficiency of dry cooling systems. Hybrid
systems are essentially dry systems with just
enough wet cooling to maintain needed generation
efficiency during the hottest days of the year.
Lesser but still significant additional water savings
can be attained in coal plants by employing water
conserving technologies to remove SO2 from flue
gas and mechanical systems that do not use water
to capture and convey bottom ash (Electric Power
Research Institute 2008).
The use of degraded water sources (e.g.,
sewage treatment plant effluent, saline or brackish
groundwater, agricultural runoff, abandoned mine
drainage, and water produced in connection with oil
and gas extraction) can conserve fresh surface and
groundwater sources. Nationally, about 8 percent
of municipal wastewater is currently reclaimed,
and the remainder represents a huge untapped
resource of relatively clean water; however, it
is important to recognize that this percentage is
highly variable based on locality. As population
grows, the amount of waste water effluent will
grow, and likely the demand to use the effluent will
increase. The rate of increase will be moderated
by conservation measures and public acceptance.
Challenges in using municipal wastewater for
cooling may include treating lower quality effluent
to meet plant operation and discharge regulatory
needs, long transport distances between municipal
discharge points and the power plant intakes, and
possible sudden changes in municipal treatment
plant effluent quality.
Technological challenges with respect to other
degraded water sources can include controlling
scaling from high-salinity waters, and meeting
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regulatory discharge requirements as a result
of nutrients in agricultural runoff, organics in
produced waters from oil and gas extraction, and
metals and low pH in abandoned mine drainage.
One tangible benefit of water conservation to
power generators is reduced cost of acquiring,
delivering, and treating water for use in the plants
(Electric Power Research Institute 2004). Of these
costs, water treatment costs can be the highest,
ranging from about $0.10 - 4.00 per thousand gallons
(kgal), depending on type and degree of treatment
required. Delivery costs depend on distance, mode
of delivery (e.g., pipeline), and routing, especially
in the case of urban areas. Delivery cost can be
negligible or range as high as $1.20/kgal. The cost
of water acquisition can likewise be negligible or
range to about $0.50/kgal, depending on regional
supply and demand, and also on the legal system
governing allocation of water rights, which varies
by state. Because costs can vary widely from one
location to another, the attractiveness of alternative
water-saving technologies can also vary widely
across locations and regions. The creation and
development of new technologies to increase water
use efficiency and conservation provides more
opportunity for decision-makers to reduce water
costs and more flexibility to site plants with respect
to their electricity markets or fuel sources.
Plants using simple steam cycles account for the
great bulk of U.S. power generation, but are not
the only power generation facilities that require
reliable water supplies to meet community needs.
Hydroelectric power accounts for about 5-10
percent of U.S. power generation, with the output
depending on precipitation and resulting runoff and
snowmelt. However, hydropower generation shares
water resources with other users of the same water
bodies, and when water levels decline, all users
suffer, and power generators must compete for a
scarce resource (Energy Information Administration
2004). Unlike thermoelectric facilities, for whom
dry cooling is an available alternative, hydropower
generators are completely dependent on water to
generate power, as dictated by annual weather
conditions and longer term weather fluctuations and
climate change. The sustainability of hydropower
generation under conditions of variable and limited
flows requires rational planning and collaborative
resource allocation among stakeholders, supported
Journal of Contemporary Water Research & Education
An Electric Power Industry Perspective on Water Use Efficiency
by reliable forecasts of available flows, along with
a sound understanding of the uncertainties in those
forecasts.
Benefits of Investment in Technology
Interviews and workshops conducted with
Electric Power Research Institute member
company representatives identified high-priority
water resource issues and areas of research offering
tangible benefits (Electric Power Research Institute
2007). There was strong nationwide support for
development of technologies to further reduce
water use. These include capture of evaporation
through condensation; reduction in blowdown
losses through development of cooling system
materials that are more resistant to scaling,
corrosion, and fouling; and reductions in water
losses from scrubbing, by recovering evaporative
losses, or increasing the removal efficiency of
dry scrubbing. For illustrative purposes, the
potential annual savings in water-related costs
from reducing all three of these loss processes for
a typical 350 MW coal-fired plant were estimated
to range from $875,000 to $2,700,000. Most
of those savings would be from reductions in
blowdown and evaporative losses, while savings
from elimination of wet scrubbing would be less
because scrubbing consumes much less water than
cooling or blowdown.
Research allowing greater use of nontraditional
waters was also strongly supported in the interviews.
A wet surface air cooler is one technology with the
potential to use degraded waters without extensive
pretreatment. If treatment costs could be reduced
by just $0.25-0.75/kgal, the annual saving in waterrelated costs to a 350 MW coal-fired plant would
range from about $370,000 to $1,100,000.
As discussed above, air and hybrid cooling
technologies exist but have cost and efficiency
disadvantages. There was strong support in
the interviews for research to overcome these
disadvantages. If hot weather inefficiencies could
be reduced through improved design, such as
advanced hybrid cooling systems, the potential
annual savings for a 350 MW coal-burning plant
could range from about $500,000 to $1,000,000.
Sound investment decisions also require
good information about the current and future
availability and cost of water for cooling, and about
Journal of Contemporary Water Research & Education
33
the sufficiency of flow for hydropower generation.
There was strong support from hydropower
generators and users of ground and surface waters
for improved planning tools in regions that are
affected by droughts. During the severe 2003
heat wave in France, the nation’s hydropower
capacity decreased by 20 percent because of
reduced surface water flow. If 20 percent of U.S.
hydropower capacity were lost for 5 weeks due
to drought, the value of the lost power would be
about $1.6 trillion. With planning tools in place
to accurately forecast droughts, to allocate water
among competing uses, and to plan replacement
of lost power by peak load generators, some or all
of that potential economic loss to consumers of
electric power could be avoided.
Aggregate benefits from an aggressive program
of water sustainability research for the electric
power industry have also been estimated (Electric
Power Research Institute 2007). While existing
plants can benefit from water saving technologies,
the greatest potential gain is for new facilities,
where new technologies can be more easily
integrated into the plant, and the payback period
for investment in these technologies is longer.
Even if it is assumed that new technologies will be
adopted only at new plants, the aggregate potential
savings are very substantial. Based on estimates
of new capacity to be added between 2010 and
2030 (Energy Information Administration 2006),
the present discounted value of potential savings
for coal-fired baseload plants alone is estimated
to be about $760 million, based on the estimated
savings for individual plants discussed above, and
assuming that each new water saving technology
is adopted by only 10 percent of new plants.
Improvements in forecasting and planning tools
would provide additional potential benefits to
producers and consumers.
Realization of these potential gains will require
the commitment of resources to the evaluation
and development of emerging technologies and
planning tools, testing of those technologies at
pilot and field scales, and sharing of findings
among power generators and other water resource
stakeholders. In addition, as water availability
becomes more limiting, it will be vital that water
availability be a primary determinant in siting. The
more technological information that can be made
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Wolfe, Goldstein, Maulbetsch, and McGowin
available to all stakeholders, along with reliable
information on water supplies, costs, and economic
benefits of adopting new technologies, the more
successful communities will be in planning and
siting new capacity to use regional water supplies wisely.
has been a private consultant to government and
industry. Most of his work has been on water use and
conservation in electric power production. He can be
reached at 770 Menlo Avenue; Suite 211, Menlo Park,
CA 94025, email: [email protected].
Conclusions
Charles R. McGowin is currently responsible for
managing the Electric Power Research Institute’s
advanced power plant cooling and wind power R&D
projects and preparation of the annual EPRI Renewable
Energy Technical Assessment Guide. He can be reached
at 3420 Hillview Avenue, Palo Alto, CA 94304, email:
[email protected].
Although water supplies are constrained in many
areas of the country, there is great potential to relieve
these constraints by increasing water conservation
and water use efficiency. Through scientific and
technical research, this potential can be enhanced
and the cost associated with its realization reduced.
The relative benefits of individual technologies
and practices to conserve water and increase water
use efficiencies are site dependent; hence, there is
value in creating a toolbox of these technologies
and practices for stakeholders to choose from.
Finally, it is critical to recognize that increased
efficiency and conservation are necessary but not
sufficient conditions for sustainability. Sustainable
development requires that aggregate water and
energy demands are balanced against available
resources, and that the management of energy and
water assets is integrated.
References
Electric Power Research Institute EPRI. 2008. Water
Use for Electric Power Generation. Palo Alto, CA.
Electric Power Research Institute EPRI. 2007. Program
on Technology Innovation: An Energy/Water
Sustainability Research Program for the Electric
Power Industry. Palo Alto, CA.
Electric Power Research Institute. 2004. Comparison
of Alternative Cooling Technologies for U.S. Power
Plants. Palo Alto, CA.
Energy Information Administration. 2006. Annual
Energy Outlook 2006 with Projections to 2030.
Acknowledgements
Energy Information Administration. 2004. Annual
Energy Review 2003.
The support of the Electric Power Research
Institute to authors Wolfe and Maulbetsch as main
authors of the EPRI reports cited below is gratefully
acknowledged.
McGowin, C. J., J .S. Maulbetsch, and R. Goldstein.
2007. Increasing Thermoelectric Generation Water
Use Efficiency. Presented at the First Western Forum
on Energy & Water Sustainability, University of
California, Santa Barbara, California.
Author Bios and Contact Information
John R. Wolfe, Ph.D., P.E., DEE, Vice President,
LimnoTech, Inc. has expertise in fate and transport
modeling of contaminants and environmental economics.
He manages projects in water resource issues for energy
production, contaminated sediment, and water quality
protection. He can be reached at 501 Avis Drive, Ann
Arbor, Michigan 48108, email: [email protected].
Robert A. Goldstein, Senior Technical Executive, EPRI
is currently managing research on Total Maximum Daily
Loads, electric power/water resource sustainability, and
climate change impacts on water resources. He can be
reached at 3420 Hillview Avenue, Palo Alto, CA 94304,
email: [email protected].
Roy, S. B., P. F. Ricci, K. V. Summers, C-F Chung, and R.
A. Goldstein. 2005. Evaluation of the sustainability
of water withdrawals in the United States, 1995 to
2025. Journal of the American Water Resources
Association 41 (5): 1091-1108.
U.S. Department of Energy. 2006. Energy Demands
on Water Resources: Report to Congress on the
Interdependency of Energy and Water.
U.S. Geological Survey. 2004. Estimated Use of Water
in the United States, 2000. USGS Circular 1268.
Denver, CO.
Since 1999, John S. Maulbetsch, Maulbetsch Consulting,
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Journal of Contemporary Water Research & Education