Water in Power Plants - EPRI

7/22/2019 Water in Power Plants - EPRI

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lectric power generation requiresreliable access to large volumes owater, primarily or cooling o

thermal power plants. Tis need comes ata time o declining supply, when eventemperate climates are experiencing water

constraints due to population growth, pre-cipitation uctuations, and changingdemand patterns. A 2010 EPRI studyound vulnerability to water shortages inall U.S. regions, with decreasing streamows in some areas, declining groundwa-ter levels, increasing surace water tem-peratures, and variable precipitation. Suchwater constraints could aect uture gen-eration technology selection, plant siting,and plant operation.

Water Research CenterA major ocal point or uture research willbe the new Water Research Center, beingdeveloped by Georgia Power (a subsidiaryo Southern Company) in collaborationwith EPRI and supported by 12 electricgenerating companies. Located at GeorgiaPowers Plant Bowen, near Cartersville,Georgia, the center will provide insights onbest practices or sustainable water man-agement and meeting wastewater restric-tions. It also will be used to evaluate tech-

nologies or reduced water consumptionand improved wastewater treatment.

Te Water Research Center will be arst-o-its-kind, industrywide resource orconducting power company waterresearch, said George Oen, EPRI projectmanager or the center. Electric generat-ing companies, research organizations, andvendors will have access to ull-scale inra-structure, treatable water, monitoring andanalysis acilities, and specialist sta toenable plant-based water research studies.

According to Oen, research projects willinclude advanced cooling-water technolo-gies, biological and inorganic wastewatertreatments, zero liquid discharge options,solid landll water management, and waterconservation (including moisture recoveryrom ue gas). Te EPRI collaborative willguide acility development to ensure that itmeets industry needs. EPRI is sponsoring a

design and engineering study or the researchinrastructure. Construction is scheduled tostart in the spring, with the center expected

to begin testing by midyear.

Water ReuseMonitoring inrastructure already hasbeen installed at Plant Bowen or watermodeling and balancing research. Olderpower generation acilities, which werebuilt when water was not an issue, typi-cally do not have instrumentation on di-erent ow streams, said Jay Wos, South-ern Companys manager or the WaterResearch Center. We recently installed

metering technology that gives us a moreprecise idea o how much water the plantis using, how the water is used, and whatsin the water. Knowledge o all ows mayenable us to develop plant-specic modelsor water balancing and identiy reuseoptions at dierent levels o cleanliness.

Power plants today employ many prac-tices to reuse water. Water typically is cas-caded rom one use to another, depend-ing on the water quality needed or eachprocess. For example, reshwater is treatedand used or boiler eedwater, resulting ina wastewater stream. Wastewater rom thewater treatment system can be used asmakeup in the ue gas desulurization(FGD) system. Boiler blowdown can beused as makeup in cooling-water systems.Cooling tower blowdown also can be usedas makeup in the FGD system. FGDblowdown can be used or ash sluicing.

Ash pond runo can be used or y ashwetting (dust control). Wastewater treat-ment research might allow or even greater

recycling and reuse.A signicant amount o water is lost

through power plant stacks (ue gas romossil plants contains 8%13% moisture asa by-product o combustion) and coolingtower plumes. Moisture recovery rom uegas would be signicant i proven to beeconomically viable. Te recovered watercan be used elsewhere in the plant, and therecovered heat can be used to reduce theplants heat rate. Research at the center andelsewhere will evaluate new moisture

recovery technologies, including ue gascoolers, water-selective membranes, con-densing heat exchangers, and membranewet electrostatic precipitators.

Water conservation and reuse eorts,together with uture more stringent dis-charge limits, are spurring interest in zeroliquid discharge systems or treating FGDwastewater. Zero liquid discharge systemsare the allback when wastewater cannot becost-eectively treated and discharged. Ter-mal zero liquid discharge systems use energyto evaporate the water in order to separateout dissolved solids, producing both solidsor landll disposal and high-quality reusablewater, thereby discharging no liquid, saidPaul Chu, EPRI project manager.

Tese systems begin with pretreatment,which includes dealkalization/metal removaland clarication, and oten are ollowed bysotening, which converts calcium chloride

The STory in Brief

Optimizing the consumption, use, and discharge o

water represents a signicant challenge or power

generation acilities. A new research center and

advanced research across several ronts are aimedat nding new technologies and methods to

improve water use eciency, lower withdrawal

levels, and reduce pollutant discharges.

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to the more easily handled sodium chloride.A brine concentrator reduces wastewatervolume, and a crystallizer produces solids ordisposal and reclaims the water.

Very ew zero liquid discharge installa-tions are operating to treat the complex

and highly corrosive FGD scrubber blow-down; more applications are ocused onother waters, such as cooling tower blow-down. In addition to the signicant capi-tal, energy, and chemical costs, manypower companies are concerned with reli-ability issues related to scaling and corro-sion. Because zero liquid discharge opera-tions appear highly dependent on waterchemistry and proper design, more inde-pendent research is needed to understandtheir operation on a range o water con-

stituents and parameters. According toChu, EPRI is documenting the operatingexperience o the limited number o plantswith zero liquid discharge systems orFGD wastewaters and helping plan possi-ble laboratory studies at the WaterResearch Center.

Reducing Cooling WaterA key to curtailing power plant water con-sumption is to reduce the largest single use:cooling water.

Power plants typically are cooled by usingeither once-through cooling or recirculatingcooling. Once-through systems withdrawwater rom a natural source (typically a lake,river, or ocean), use it to extract waste heatrom the steam cycle, and then return it tothe water body at a slightly elevated tem-perature. In the United States today, morethan 1,200 generating units (about 40% oU.S. capacity) use once-through cooling.Recirculating cooling (sometimes called wetcooling) cools water in a tower or pond andrecirculates the water to the condenser.Cooling is accomplished by evaporation oa small raction (1%2%) o the water.

EPRIs Advanced Cooling echnologyproject is investigating methods to reduce theeciency penalty o switching rom theseconventional cooling approaches to systemsthat have lower water consumption and isevaluating their cost-eectiveness, said Rich-

ard Breckenridge, EPRI project manager.One such alternative is dry cooling. It

uses air rather than water to condense thesteam, which is piped rom the turbine toair-cooled condensers. Since 1999, nearly20 GW o new U.S. capacity has come into

service equipped with direct dry cooling.Although dry cooling systems achieve largewater savings, said Breckenridge, their ini-tial cost is three to ve times that o wetcooling systems, their operating powerrequirements or cooling-system pumpsand ans are 1.5 to 2.5 times higher thanthose o wet cooling systems, and theyimpose a 3%15% thermal eciency pen-alty on the power plant, depending onambient conditions.

EPRI research is addressing operational

and cost issues associated with air-cooledcondensers. High and gusty winds cancause stalling o the airow in leading-edgeans, creating a sudden drop in coolingcapacity. A recent EPRI study, conductedwith lectricit de France, perormed windtunnel tests on scale models o power plantswith air-cooled condensers to determinehow wind aects airow around and withincondenser cells. Te study also evaluatedmitigation approaches.

EPRI also is exploring hybrid cooling sys-

tems, which congure dry and wet loops inparallel, to cool the recirculating condenserwater. Tese systems reduce cooling-watervolume by using dry cooling during coolerperiods and wet cooling during hotter peri-ods, when dry systems cannot maintain lowturbine-exhaust pressure. Eight hybrid sys-tems are operating in the United Statesthree on coal-red steam plants, two ongas-red combined-cycle plants, and threeon waste-to-energy plants.

o date, little public inormation hasbeen available on the design, cost, and per-ormance o hybrid systems, said Breck-enridge. Results o a recent EPRI studythat surveyed existing hybrid systemsshowed that they are typically sized to con-sume 30%70% less water than a closed-cycle wet cooling system and can beexpected to cost 75%90% o an all-drysystem with an air-cooled condenser.

EPRIs Advanced Cooling echnologyproject recently developed sotware thaallows utilities to project the operationaimpacts o installing hybrid cooling.

Another option or reducing reshwateconsumption is to use degraded wate

sources. Power plants have used suchsources 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 apower plant, this source is attractive becauseo its year-round availability, relatively lowtreatment cost, and minimal plant impactso increase the use o degraded water romother sources, EPRI has identied neededresearch on better and cheaper treatmenoptions, wastewater disposal options, and

coatings to prevent scaling and ouling.

Potential BreakthroughTechnologiesEPRIs echnology Innovation (I) program is exploring early-stage technologiesthat could be alternatives to current wecooling options. In early 2011, EPRIreleased a Request or Inormation toresearchers and developers pursuing water-ecient technologies with potential poweindustry applications.

From more than 70 responses, EPRIselected our projects. One is a technologydeveloped by Argonne National Laboratoryor enhancing thermophysical properties oheat transer uids used in wet cooling towers. Te process adds heat-absorptivenanoparticles to the coolant stream, enablingthe same volume o coolant to absorb moreheat in the condenser and to dissipate theincreased heat in the cooling tower. Tepotential is there to reduce water use at bothexisting and new steam-electric plants by amuch as 20% and decrease coolant owrates by about 15%, lowering pumpingloads and parasitic losses.

Also under investigation are an absorption chiller, which supplements a dry-cooling-type technology with a rerigerancycle or evaporative cooling to temperatures lower than those attainable with drycooling; dew point cooling, under devel


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opment by the Gas Research Institute,which would cool water to the dew point,gaining cooling eciency and using two-thirds less water; and a thermosiphon,developed by Johnson Controls, whichemploys a rerigerant in a gravity-eed

cycle to reduce evaporative losses.Te issue with current alternatives towater-based cooling, such as dry cooling, isthat theyre costly and have operational draw-backs, said Sean Bushart, EPRI programmanager. We know the technologies in theI Program will take a lot o work to develop,but they also have huge potential. With theseprojects, were pushing the envelope to ndgame-changing technologies that wouldachieve signicant water reduction while alsobeing 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.

George Offen is a seniortechnical executive, ocused

on the reduction o air pollut-

ants rom coal-red powerplants, including development

and optimization o controls or mercury, CO2,

and SO2. Beore joining EPRI in 1985, he was

manager o energy engineering at Acurex

Corporation and earlier held teaching positionsat Stanord and Santa Clara Universities and

carried out research assignments at Chevron

Research and the French Institute o Petroleum.

Oen received B.S. and Ph.D.degrees rom

Stanord University and an M.S. rom MIT, all inmechanical engineering.

Richard Breckenridge is asenior project manager in the

Generation Sector, serving asthe technical lead in water

management technologies

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 consult-

ing eld or specialty chemical companies,

including Calgon Corporation, Nalco, and

Applied Specialties, Inc. Breckenridge earnedhis B.S. degree rom Northern Arizona University

in earth science, chemistry, and mathematics.

Paul Chu is a senior projectmanager 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 devel-

opment projects related to fue gas cleanup o

SO2, NOx, and particulates. Chu received aB.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 Bushartis senior pro-gram manager or the Landand Groundwater program,

with current activities ocused

on innovative applications

related to power plant and transmission and

distribution environmental issues. He also manages

EPRIs Water Technical Innovation program and isthe lead or EPRIs cross-sector water initiative. Prior

to joining EPRI in 1999, Bushart was director o

microbiology/chemistry laboratory services atCytoCulture. He holds B.S. and Ph.D. degrees in

biology rom Rensselaer Polytechnic Institute.

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Water in Power Plants - EPRI