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lectric power generation requires The S Tory in B rief reliable access to large volumes o Optimizing the consumption, use, and discharge o water, primarily or cooling o thermal power plants. Tis need comes at water represents a signicant challenge or power a time o declining supply, when even temperate climates are experiencing water generation acilities. A new research center and constraints due to population growth, preadvanced research across several ronts are aimed cipitation uctuations, and changing demand patterns. A 2010 EPRI study at nding new technologies and methods to ound vulnerability to water shortages in all U.S. regions, with decreasing stream improve water use eciency, lower withdrawal ows in some areas, declining groundwater levels, increasing surace water temlevels, and reduce pollutant discharges. peratures, and variable precipitation. Such water constraints could aect uture generation technology selection, plant siting, design and engineering study or the research Ash pond runo can be used or y ash and plant operation. inrastructure. Construction is scheduledto wetting (dust control). Wastewater treatstart in the spring, with the center expected ment research might allow or even greater Water Research Center to begin testing by midyear. recycling and reuse. A major ocal point or uture research will A signicant amount o water is lost be the new Water Research Center, being Water Reuse through power plant stacks (ue gas rom developed by Georgia Power (a subsidiary Monitoring inrastructure already has ossil plants contains 8%–13% moisture as o Southern Company) in collaboration been installed at Plant Bowen or water a by-product o combustion) and cooling with EPRI and supported by 12 electric modeling and balancing research. “Older tower plumes. Moisture recovery rom ue generating companies. Located at Georgia power generation acilities, which were gas would be signicant i proven to be Power’s Plant Bowen, near Cartersville, built when water was not an issue, typi- economically viable. Te recovered water Georgia, the center will provide insights on cally do not have instrumentation on di- can be used elsewhere in the plant, and the best practices or sustainable water man- erent ow streams,” said Jay Wos, South- recovered heat can be used to reduce the agement and meeting wastewater restric- ern Company’s manager or the Water plant’s heat rate. Research at the center and tions. It also will be used to evaluate tech- Research Center. “We recently installed elsewhere will evaluate new moisture nologies or reduced water consumption metering technology that gives us a more recovery technologies, including ue gas and improved wastewater treatment. precise idea o how much water the plant coolers, water-selective membranes, con“Te Water Research Center will be a is using, how the water is used, and what’s densing heat exchangers, and membrane rst-o-its-kind, industrywide resource or in the water. Knowledge o all ows may wet electrostatic precipitators. conducting power company water enable us to develop plant-specic models Water conservation and reuse eorts, research,” said George Oen, EPRI project or water balancing and identiy reuse together with uture more stringent dismanager or the center. “Electric generat- options at dierent levels o cleanliness.” charge limits, are spurring interest in zero ing companies, research organizations, and Power plants today employ many prac- liquid discharge systems or treating FGD vendors will have access to ull-scale inra- tices to reuse water. Water typically is “cas- wastewater. “Zero liquid discharge systems structure, treatable water, monitoring and caded” rom one use to another, depend- are the allback when wastewater cannot be analysis acilities, and specialist sta to ing on the water quality needed or each cost-eectively treated and discharged. Terenable plant-based water research studies.” process. For example, reshwater is treated mal zero liquid discharge systems use energy According to Oen, research projects will and used or boiler eedwater, resulting in to evaporate the water in order to separate include advanced cooling-water technolo- a wastewater stream. Wastewater rom the out dissolved solids, producing both solids gies, biological and inorganic wastewater water treatment system can be used as or landll disposal and high-quality reusable treatments, zero liquid discharge options, makeup in the ue gas desulurization water, thereby discharging no liquid,” said solid landll water management, and water (FGD) system. Boiler blowdown can be Paul Chu, EPRI project manager. conservation (including moisture recovery used as makeup in cooling-water systems. Tese systems begin with pretreatment, rom ue gas). Te EPRI collaborative will Cooling tower blowdown also can be used which includes dealkalization/metal removal guide acility development to ensure that it as makeup in the FGD system. FGD and clarication, and oten are ollowed by meets industry needs. EPRI is sponsoring a blowdown can be used or ash sluicing. sotening, which converts calcium chloride
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to the more easily handled sodium chloride. A brine concentrator reduces wastewater volume, and a crystallizer produces solids or disposal and reclaims the water. Very ew zero liquid discharge installations are operating to treat the complex and highly corrosive FGD scrubber blowdown; more applications are ocused on other waters, such as cooling tower blowdown. In addition to the signicant capital, energy, and chemical costs, many power companies are concerned with reliability issues related to scaling and corrosion. Because zero liquid discharge operations appear highly dependent on water chemistry and proper design, more independent research is needed to understand their operation on a range o water constituents and parameters. According to Chu, EPRI is documenting the operating experience o the limited number o plants with zero liquid discharge systems or FGD wastewaters and helping plan possible laboratory studies at the Water Research Center.
ard Breckenridge, EPRI projectmanager. One such alternative is dry cooling. It uses air rather than water to condense the steam, which is piped rom the turbine to air-cooled condensers. Since 1999, nearly 20 GW o new U.S. capacity has come into service equipped with direct dry cooling. “Although dry coolingsystems achieve large water savings,” said Breckenridge, “their initial cost is three to ve times that o wet cooling systems, their operating power requirements or cooling-system pumps and ans are 1.5 to 2.5 times higher than those o wet cooling systems, and they impose a 3%–15% thermal eciency penalty on the power plant, depending on ambient conditions.” EPRI research is addressing operational and cost issues associated with air-cooled condensers. High and gusty winds can cause stalling o the airow in leading-edge ans, creating a sudden drop in cooling capacity. A recent EPRI study, conducted with Électricité de France, perormed wind tunnel tests on scale modelso power plants with air-cooled condensers to determine Reducing Cooling Water how wind aects airow around and within A key to curtailing power plant water con- condenser cells. Te study also evaluated sumption is to reduce the largest single use: mitigation approaches. cooling water. EPRI also is exploring hybrid cooling sysPower plants typically arecooled by using tems, which congure dry and wet loops in either once-through cooling or recirculating parallel, to cool the recirculating condenser cooling. Once-through systems withdraw water. Tese systems reduce cooling-water water rom a natural source (typically a lake, volume by using dry cooling during cooler river, or ocean), use it to extract waste heat periods and wet cooling during hotter perirom the steam cycle, and then return it to ods, when dry systems cannot maintain low the water body at a slightly elevated tem- turbine-exhaust pressure. Eight hybrid sysperature. In the United States today, more tems are operating in the United States— than 1,200 generating units (about 40% o three on coal-red steam plants, two on U.S. capacity) use once-through cooling. gas-red combined-cycle plants, and three Recirculating cooling (sometimes called wet on waste-to-energy plants. cooling) cools water in a tower or pond and “o date, little public inormation has recirculates the water to the condenser. been available on the design, cost, and perCooling is accomplished by evaporation o ormance o hybrid systems,” said Brecka small raction (1%–2%) othe water. enridge. “Results o a recent EPRI study “EPRI’s Advanced Cooling echnology that surveyed existing hybrid systems project is investigating methods to reduce the showed that they are typically sized to coneciency penalty o switching rom these sume 30%–70% less water than a closedconventional cooling approaches to systems cycle wet cooling system and can be that have lower water consumption and is expected to cost 75%–90% o an all-dry evaluating their cost-eectiveness,” said Rich- system with an air-cooled condenser.”
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EPRI’s Advanced Cooling echnology project recently developed sotware that allows utilities to project the operational impacts o installing hybrid cooling. Another option or reducing reshwater consumption is to use degraded water sources. Power plants have used such sources or years, particularly sewage efuent. A recent study identied 57 U.S. acilities that use reclaimed municipal wastewater or cooling. I located close enough to a power plant, this source is attractive because o its year-round availability, relatively low treatment cost, and minimal plant impacts. o increase the use o degraded water rom other sources, EPRI has identied needed research on better and cheaper treatment options, wastewater disposal options, and coatings to prevent scaling and ouling. Potential Breakthr ough Technologies EPRI’s echnology Innovation (I) program is exploring early-stage technologies that could be alternatives to current wet cooling options. In early 2011, EPRI released a Request or Inormation to researchers and developers pursuing waterecient technologies with potential power industry applications. From more than 70 responses, EPRI selected our projects. One is a technology developed by Argonne National Laboratory or enhancing thermophysical properties o heat transer uids used inwet cooling towers. Te process adds heat-absorptive nanoparticles to the coolant stream,enabling the same volume o coolant toabsorb more heat in the condenser and to dissipate the increased heat in the cooling tower. Te potential is there to reduce water use at both existing and new steam-electric plants by as much as 20% and decrease coolant ow rates by about 15%, lowering pumping loads and parasitic losses. Also under investigation are an absorption chiller, which supplements a dry-cooling-type technology with a rerigerant cycle or evaporative cooling to temperatures lower than those attainable with dry cooling; dew point cooling, under devel-
George Offen is a senior
opment by the Gas Research Institute, technical executive, ocused which would cool water to the dew point, on the reduction o air pollutgaining cooling eciency and using twoants rom coal-red power plants, including development thirds less water; and a thermosiphon, developed by Johnson Controls, which and optimization o controls or mercur y, CO2, employs a rerigerant in a gravity-eed and SO2. Beore joining EPRI in 1985, he was manager o energy engineering at Acurex cycle to reduce evaporative losses. Corporation and earlier held teaching positions “Te issue with current alternatives to at Stanord and Santa Clara Universities and water-based cooling, such as dry cooling, is carried out research assignments at Chevron that they’re costly and haveoperational draw- Research and the French Institute o Petroleum. backs,” said Sean Bushart, EPRI program Oen received B.S. and Ph.D.degrees rom manager. “We know the technologies in the Stanord University and an M.S. rom MIT, all in I Program will take a lot o work to develop, mechanical engineering. but they also have huge potential . With these Richard Breckenridge is a projects, we’re pushing the envelope to nd senior project manager in the game-changing technologies that would Generation Sector, ser ving as the technical lead in water achieve signicant water reduction while also management technologies being operationally desirable.” This article was written by Jonas Weisel. Background information was provided by George Offen,
[email protected], 650.855.8942; Richard Breckenridge,
[email protected], 704.595.2792; Paul Chu,
[email protected], 650.855.2362; and Sean Bushart,
[email protected], 650.855.8752.
and in the development o the Water Research Center. Prior to joining EPRI, Breckenridge was the corporate chemist at Arizona Public Service Company and worked many years in the consulting eld or specialty chemical companies, including Calgon Corporation, Nalco, and Applied Specialties, Inc. Breckenridge earned his B.S. degree rom Northern Arizona University in earth science, chemistry, and mathematics.
Paul Chu is a senior project manager in the Environment Sector, with current research activities ocused on air and water toxics issues. Beore joining EPRI in 1992, he worked at Babcock & Wilcox, where he was involved in various development projects related to fue gas cleanup o SO2, NOx, and particulates. Chu received a B.S. degree in chemical engineering rom the University o Arkansas and an M.S., also in chemical engineering, rom the University o Texas at Austin. Sean Bushart is senior program manager or the Land and Groundwater program, with current activities ocused on innovative applications related to power plant and transmission and distribution environmental issues. He also manages EPRI’s Water Technical Innovation program and is the lead or EPRI’s cross-sector water initiative. Prior to joining EPRI in 1999, Bushart was director o microbiology/chemistry laboratory servicesat CytoCulture. He holds B.S. and Ph.D. degrees in biology rom Rensselaer Polytechnic Institute.
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