Clean, fresh water has become a critical

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1 30 Universities Council on Water Resources Issue 143, Pages 30-34, December 2009 An Electric Power Industry Perspective on Water Use Efficiency John R.Wolfe 1, Robert A. Goldstein 2, John S. Maulbetsch 3, and Charles R. McGowin 2 1 Limno Tech, Inc., Ann Arbor, MI; 2 Electric Power Research Institute (EPRI), Palo Alto, CA; 3 Maulbetsch Consulting, Menlo Park, CA Clean, 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of all U.S. freshwater withdrawals because about half of U.S. plants still use once-through cooling technology water withdrawn from an ambient water body moves only once through the cooling system before being discharged back into the environment.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

2 An Electric Power Industry Perspective on Water Use Efficiency 31 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. 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

3 32 Wolfe, Goldstein, Maulbetsch, and McGowin 32 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 SO 2 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 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 $ 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

4 An Electric Power Industry Perspective on Water Use Efficiency 33 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 $ /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 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

5 34 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. Conclusions 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. Acknowledgements 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. 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, jwolfe@limno.com. 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, rogoldst@epri.com. 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, maulbets@sbcglobal.net. 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, cmgowin@epri.com. References Electric Power Research Institute EPRI Water Use for Electric Power Generation. Palo Alto, CA. Electric Power Research Institute EPRI Program on Technology Innovation: An Energy/Water Sustainability Research Program for the Electric Power Industry. Palo Alto, CA. Electric Power Research Institute Comparison of Alternative Cooling Technologies for U.S. Power Plants. Palo Alto, CA. Energy Information Administration Annual Energy Outlook 2006 with Projections to Energy Information Administration Annual Energy Review McGowin, C. J., J.S. Maulbetsch, and R. Goldstein Increasing Thermoelectric Generation Water Use Efficiency. Presented at the First Western Forum on Energy & Water Sustainability, University of California, Santa Barbara, California. Roy, S. B., P. F. Ricci, K. V. Summers, C-F Chung, and R. A. Goldstein Evaluation of the sustainability of water withdrawals in the United States, 1995 to Journal of the American Water Resources Association 41 (5): U.S. Department of Energy Energy Demands on Water Resources: Report to Congress on the Interdependency of Energy and Water. U.S. Geological Survey Estimated Use of Water in the United States, USGS Circular Denver, CO. Since 1999, John S. Maulbetsch, Maulbetsch Consulting,