Power Industry Guide

FLOWSERVE C

Power Industry GuideValtek Control Products

ORPORATION, VALTEK CONTROL PRODUCTS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Conventional Subcritical Coal-fired Power Plant . . . . . . . . . . . . . . . . . . 6

Condensate System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Condenser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Makeup Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Water Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Condensate Pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Feedwater System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Boiler Feedpump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Feedwater Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Deaerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Boiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Economizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Air Heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Drum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Superheaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Reheater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Attemperator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Super-critical Power Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Sliding Pressure Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Nuclear Power Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Moderator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Nuclear Reactor Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Boiling Water Reactor (BWR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Pressurized Water Reactor (PWR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Breeder Nuclear Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Boiling Water Reactor Safety Systems . . . . . . . . . . . . . . . . . . . . . . . . . 18

Systems for Normal Plant Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Reactor Water Cleanup System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Shutdown Cooling Function of the Residual Heat Removal System . . 18

Systems for Abnormal Plant Operations . . . . . . . . . . . . . . . . . . . . . . . . 18

Standby Liquid Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Reactor Core Isolation Cooling System . . . . . . . . . . . . . . . . . . . . . . . . . 18

High Pressure Core Spray System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Low Pressure Core Spray System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Residual Heat Removal System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Gas Turbines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Combined Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Flowserve Power Industry GuideTable of Contents

FLOWSERVE CORPORATION, VALTEK CONTROL PRODUCTS 3

IntroductionElectric power can be generated by a number of differ-ent processes, systems and components; however,most electricity is generated through the use of a rotatingelectric generator. An electric generator operates onthe principle that a small electric current can be gener-ated in a wire by passing it through a magnetic field. Byusing many wires in a coil, the currents are added to oneanother to generate usable electric current.

Commercial power generation can be broken down intothree categories based upon the energy source used:thermal (coal, gas, and oil), renewable (hydro, biomass,geothermal, solar, and wind), and nuclear. Total genera-tion in 1996 by U.S. electric utilities was 3,077 billionkilowatt-hours. Of the total generation, 68 percent wasthermal, 10 percent renewable, and 22 percent nuclear.Coal fired units accounted for 84 percent of the thermalgeneration or 57 percent of the total. Non-utility genera-tors produced 383 billion kilowatt hours in 1995. Ap-proximately 76 percent of the non-utility generation isthermal and 24 percent renewable. Natural gas ac-counts for 74 percent of the thermal generation or 56percent of the total non-utility generation.

Consumption of electricity worldwide is estimated at11.4 trillion kilowatt-hours and expected to grow to 20trillion kilowatt-hours by 2015. This represents approxi-mately a three percent increase in power consumption.

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In a conventional thermal process, a steam turbineconverts steam energy into usable, rotational energy toturn the generator. Boilers produce steam to operatethe turbine. Windmills, water turbines, internal combus-tion engines and other motive forces can be used inplace of the steam turbine to turn the generator.

Although coal is the most common fuel to fire a boiler ina power plant, natural gas, oil or even biomass can beutilized as fuel to replace the coal to fire the boiler, andthe majority of the process remains unchanged.Exhaust gas and ash disposal systems are dependenton the type of fuel being used. Figure 1 provides anoverall view of a coal- fired power plant and the powergeneration process.

This guide offers the reader a general understanding ofthe major systems in a power plant utilizing a conven-tional boiler fired by coal, oil, gas or biomass to producesubcritical steam, which drives a steam turbine con-nected to a generator. A brief discussion of variationsof this process such as nuclear, gas turbine, and super-critical plants are also described and covered individu-ally under their own section. Rather than give a com-plete description of each of these variations, the majordifferences between them and the conventional ther-mal processes are explained.

Figure 1: Coal-fired Power Plant

SubstationTransformer

CoolingTower

MakeupPumps Pump

TurbineGenerator

Water to

Boiler

Condensate Pump

Condenser

Feed Pump High

PressureHeaters

LowPressureHeaters

Steam Water From High PressureHeaters

Air H

eaters

Stack

InducedDraft Fan

SO2Particulate Collector

CombustionAirForced

DraftFan

Primary Air Fan

Boiler

Burner

CoalPulverization

Coal Supply

5

Conventional Subcritical Coal-Fired Power Plant
Actual power generation facilities are very complex andinvolve numerous processes and components. Steampower plants can be classified as subcritical and super-critical. If a plant operates below the critical point ofwater (3208.2 psia) , it is classified as subcritical.
This section is intended to provide a description of theprocesses and major components in a subcritical powerplant (see Figure 2). Although similar in many ways, thesuper-critical power plant has some variations that arecovered in greater detail in a separate section.

The conventional power generation process is a con-tinuous cycle; therefore, discussion can begin at any

6

point in the cycle. Because each part of the cycle buildsupon the previous process in a continuous loop, theentire power generation cycle must be explained beforeeach process becomes clear.

This discussion begins at the condenser. Water fromthe condenser is heated and the pressure increasesthrough the feedwater system. The boiler adds moreheat energy, and the superheated steam expandsthrough a series of turbine blades that turn the gen-erator. The expanded steam exits the turbine to thecondenser, and the cycle continues.

Low Pressure Turbine

Condenser(2.1 in. Hg Abs)

CondensatePump

256.8P109.0F

68.2

P

43.9

P12

.77P

5.61

P

Boiler FeedPump

Turbine3 in

. Hg

Abs

ToCondenser

163.6F

163.6F

5.16P158.6F159.3F

169.3F

11.75P

200.9F10F

Low Pressure Feedwater Heaters

205.9F

195.9F40.4P

267.9F10F

262.9F

272.9F

62.8P

295.7F

290.7F

DeaeratingHeater

BoilerFeedPump

3018 P

369.0F

171.2P

377.1F

High Pressure Feedwater Heaters

387.1F

406.3F

262.4P406.3F

415.3F

482.0F

576.7P485.0F

Fuel In Eco

nom

izer

/Fur

nace

/Sup

erhe

ater

Reh

eate

r

AirHeater

ForcedDraftFan

InducedDraftFan

Flue Gas OutAir In

High PressureTurbine

2400 psig1000F

546.3P 1000F

IntermediatePressureTurbine

607.

0P

285.

2P18

0.2P

Figure 2: Heat Balance for a Subcritical Power Plant

P = psig

F = Farenheit


Figure 3: Condensate System

Condensate System

Condensate Pump

FeedwaterTo LP Heaters

Condenser

Generator

LP Turbine

Exhaust Steam

Hotwell

Circulation Pump

Cooling Water

Cooling Tower

CondenserThe condenser operates on the principle that a mass ofliquid occupies significantly less space than an equalmass of gas. For example, a pound of steam at 212° Fand atmospheric pressure would occupy 26.8 cubicfeet. The same pound of steam, if condensed, wouldoccupy only about 0.017 cubic feet. That is a volumetricreduction of almost 99.94 percent. In a condenser, theexhaust steam from the turbine is passed through aheat exchanger where cool water running through tubescondenses steam into a liquid. This reduction in volumeforms a vacuum in the condenser. Reducing the pres-sure in the condenser allows the steam from the turbineto condense at a lower temperature. The lower thepressure and temperature that can be achieved in thecondenser, the greater the overall efficiency of the plant.

Cooling water is brought into the condenser throughtubes and the exhaust steam passes by them. In thismanner, the heat is transferred from the steam to thecooling water and the steam condenses and is col-lected in the 'hotwell' to be used again as feedwater.The warm cooling water is then circulated to a coolingtower where it is cooled to near ambient conditions(Figures 3 and 4).

Makeup WaterA power plant is a continuous cycle; therefore, theoreti-cally, very little water should have to be added. In everysystem, however, leaks and evaporation occur, requir-ing a small amount of water to be added to the system.This water is referred to as makeup water.


Water TreatmentImpurities in feedwater can cause serious corrosionproblems and adversly affect the efficiency and opera-tion of a power plant. Pure water rarely exists naturally;thus, raw water for makeup needs to be treated toreduce contaminants that cause corrosion and leavedeposits throughout the system. No water treatment iscompletely effective in removing impurities. Thoseimpurities not removed from the makeup water prior toentering the system concentrate in the feedwater andboiler. These impurities are often removed in a processreferred to as 'blowdown.' Blowdown can be either acontinuous or intermittent process and involves using avalve to release water from the boiler.

Water contains both dissolved and suspended solids ofvarious types and concentrations, depending upon itssource. Suspended solids can be removed by filtrationor settling. Dissolved solids cannot be removed byfiltration and are in solution with water. Examples ofsuspended solids include mud, silt, sand, clay, organicmatter and some metallic oxides. Examples of dissolvedsolids include iron, calcium, silica, magnesium andsodium.

If left in the system, dissolved solids form scale on theboiler internal surfaces and reduce heat transfer. Thiscan result in overheating of the tubes and failure ordamage of other downstream equipment. Dissolvedsolids can be removed from the system using a varietyof processes including evaporation, ion exchange,reverse osmosis, electrodialysis and ultrafiltration.

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Figure 4: Condenser Condensate Outlet

Main Expansion Joint

Boiler Feed PumpTurbine ExhaustDuct

Water Box

Non-condensableOfftakes

CirculatingWater InletNozzles

Tubes

Extracting Piping

Feedwater Heatersin Condenser Neck

Steel VacuumContainingShell

CirculatingWater Outlet

Load Carrying Members

Main Steam Inlet▼ ▼

Hotwell

Condensate Outlet

Tube Support Plates Cou

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Condensate PumpCondensate collected in the hotwell will be at the samepressure as the condenser (approximately 0.5 psia)and must be pressurized before moving on to thefeedwater system. During start-up, little if any flow iscirculating through the system. For this reason, it isnecessary for the condensate pump to have a recircu-lation system similar to the main feedpump. In thecondensate pump case, however, the water to berecirculated is at significantly lower pressure and tem-perature than the main feedpump. Recirculation pre-vents overheating and cavitation of centrifugal pumps.

8

A control valve known as the condensate pump recircu-lation valve provides the required minimum flow. Afterpassing through the condensate pump, the condensateenters the feedwater system.

In order to make usable energy to turn the steamturbine, water needs to be pressurized and heated untilit vaporizes into steam. After vaporizing, the steamtemperature is elevated (superheated) to maximize theenergy content of the steam and to protect the turbinefrom water damage. The boiler provides the energy tovaporize and superheat steam. The boiler is also usedto reheat steam between turbine sections.

Major water quality problems associated with boiler systemsFeedwater High-pressure Super- Steam-Using Condensate

Major Problem Deaerator System Boiler Boiler Turbine heater Equipment SystemScale Hardness X X SiO2 X XCorrosion Oxygen X X X X X X Alkalinity/CO2 X X X X X Ammonia X Chelate X XDeposits Metal Oxides X X X Organics X X XCarryover Entrained liquids X X X XDissolved solids X X X


Figure 5: Feedwater System

Feedwater SystemTo Boiler

High PressureHeaters Boiler

Feedpump

Deaerator

Low PressureHeaters

From Condenser

The feedwater system provides the boiler with water inthe proper volume and at the design pressure andtemperature. The feedwater system includes the lowand high pressure feedwater heaters, deaerator andboiler feedpump (see Figure 5). If the feedwater isdelivered at the incorrect temperature or pressure, theboiler tubes and downstream equipment can be dam-aged. Improper temperatures also adversely affect theefficiency and reliability of the process. In a typicalsubcritical plant, the feedwater is delivered to the boilerat approximately 2400 - 3200 psig and 300 - 500° F.Too low of a flow to the boiler can result in overheatingof the tubes, while too high of a flow can result in wetsteam entering the turbine, causing water damage tothe turbine blades.

Boiler FeedpumpPressurization of the feedwater is accomplished throughthe use of a boiler feedpump that is commonly steamdriven. Large plants may have a smaller motor-drivenfeedpump for start-ups. Also, smaller power plants mayutilize a motor-driven main feedpump. Boiler feedpumpsrequire a minimum flow to protect against overheatingand cavitation. Minimum circulation for the feedpumpsis provided by a feedwater recirculation system. Therecirculation system diverts the minimum flow from thedischarge of the pump back to either the condenser orthe deaerator. Because both the condenser and thedeaerator are at relatively low pressures as comparedto the high discharge pressures of the pump, severecavitation can be expected in the valve diverting thisflow. This valve is referred to as the 'boiler feedpumprecirculation valve,' 'feedpump minimum bypass valve'or 'automatic recirculation control valve' and is one ofthe most severe applications in the power plant.During normal plant operation, sufficient flow is pass-ing through the feedpump to the boiler without anyrecirculation, so the valve will be closed. Figure 6 isa steam driven, boiler feedpump.


Feedwater HeatersIn the feedwater system, water passes through a seriesof heaters referred to generically as feedwater heaters,which utilize steam extracted from various stages of theturbine to raise the temperature of the boiler feedwater.The heat energy from the steam is transferred to thefeedwater in these heaters through a tube and shelltype heat exchanger or through direct mixing of thesteam and the feedwater. Feedwater heaters that mixthe steam and water are referred to as 'open' whilethose utilizing a tube and shell type heat exchanger are'closed.' A closed type feedwater heater is depicted inFigure 7.

Open feedwater heaters serve a dual function of feed-water heating and removing non-condensable gases.The function of removing non-condensable gases iscovered in greater detail in the Deaerator section.

Feedwater heaters are further categorized as either lowor high pressure. The difference between the two isthat the low-pressure units are heating water that hasnot yet passed through the boiler feedpump or the

Figure 6: Boiler Feedpump

9

Feedwater Outlet

ImpingementPlate

Steam Inlet Desuperheating Zone

Shroud

ShellBaffles/

Supports TubesDrainsInlet Head

Impingement Baffle

Orifice(Typ)

Subcooling Zone Inlet

Drains SubcoolingZone

Drains Outlet

FeedwaterInlet

Partition Cover

Figure 7: Closed Feedwater Heater

To Economizer

485°F

415°F 577psia 387°F 262 psia

406°F

Heater Drain ValveEmergency

Heater DrainValve(s)

To Condenser 1 psia

Heater Drain Valve

To Deaerator170 psia

Feedwater from BoilerFeed Pump 377°F

Extraction SteamExtraction Steam

Heater DrainValve

Heater DrainValve

Heater DrainValve

To Condenser 1 psia

EmergencyHeater DrainValve(s)

Feedwater fromCondensate Pump 105°F

273°F 63 psia 206°F 40 psia 169°F 12 psia 115°F 5 psia

6 psia164°F

Extraction Steam

159°F

Extraction Steam

13 ps ia201°F

Extraction Steam

44 psia268°F

196°F263°F

Extraction Steam

68 psia296°F

To Deaerator

291°F

High Pressure Heater Drain SystemSubcritical, 2400 psig turbine

Low Pressure Heater Drain SystemSubcritical, 2400 psig turbine

Figure 8: Low and High Pressure Heater Drain Systems

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deaerator. High-pressure feedwater heaters are lo-cated after the main feedpump and are closed while thelow-pressure heaters can be either open or closed.

Steam for the low-pressure heaters is commonly ex-tracted from the low pressure section of the turbine.High-pressure heaters are located downstream of theboiler feed pump and utilize steam extracted from thehigh or intermediate pressure sections.


In closed feedwater heaters, as the steam gives up itsheat to the feedwater it loses energy and often con-denses. Control valves referred to as 'heater drainvalves' control the condensate level in each of theheaters. Condensate from one heater is cascadeddown to the next heater. Condensate from the heaterscan be returned to the condenser, deaerator or mixedwith the feedwater, depending upon the plant design(see Figure 8).

Figure 9: Deaerator

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Feedwater Inlet Gas Vent Relief Valve

Feedwater to Feedpump

SteamInlet

Gas Vent

DeaeratorAfter the feedwater leaves the last of the low-pressureheaters, it is directed to a device known as the deaeratorto remove the non-condensable gases in the feedwa-ter. The deaerator operates on the principle that hotwater can hold considerably less dissolved gases thancold water. Using extraction steam, the feedwater isheated in the deaerator to near saturation tempera-tures, and the water releases the dissolved gaseswhich are then vented off. The deaerator is actually anopen feedwater heater.

Feedwater is a combination of makeup water and watercondensed from steam that has passed through theboiler and into the condenser. Because the condenser

is operated at a vacuum, some atmospheric gasescan leak into the system. Also, water holdsdissolved gases such as oxygen and nitrogen thatare referred to as non-condensable. These gasesdo not condense at the same temperature assteam, and if they are not removed they can buildup in the condenser , causing the pressure to rise.Also, dissolved gases left in the system can leadto corrosion of the boiler and piping. If the pres-sure rises in the condenser, the plant will not runefficiently and the turbine could be damaged.

11

The boiler converts the energy in the fuel to heat andtransfers this heat energy to the feedwater, combustionair and steam. Heat transfer in the boiler takes place inthe economizer, air heater, boiler tubes, drum, super-heaters and reheater.

EconomizerThe economizer is a bank of tubes through which thefeedwater passes before it goes into the main tubesection of the boiler. Heat that is remaining in thecombustion gases in the boiler after passing throughthe tubes, superheaters and reheaters is directed throughthe economizer. The economizer reduces energy con-sumption and thermal strain on the boiler tubes.

Air HeaterThe air heater or 'pre-heater' heats the combustion airto the boiler in order to improve efficiency and improve

Boiler

12

combustion. The air heater is the last heat exchangermechanism in the boiler before the flue gases arevented. Because the flue gas is relatively low intemperature by the time it reaches the air heater, a largesurface area is often required in the air heater tofacilitate heat transfer.

DrumAfter the boiler feedwater has passed through theeconomizer, it is directed to the boiler tubes and drumwhere it finally becomes steam. The drum provides anarea where the steam separates from the feedwater.The drum is connected to many sections of tubes thatcirculate the feedwater in the boiler. These steel tubesare arranged to maximize the exposure to the heat fromthe boiler. As steam bubbles form, they collect in thedrum before passing further on. It is important to keepa constant liquid level in the upper drum to provide the

Figure 10: Carolina Type 455 MW Boiler

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proper quality of steam. Control valves called feedwa-ter regulator valves, control the liquid level in the drum.Requirements for the feedwater can vary greatly so theflow rate to the drum must be constantly adjusted.Modern boilers have high heat rates and if new feedwa-ter is not introduced, they can actually boil dry anddamage boiler tubes in a matter of a few minutes.

SuperheatersSuperheaters are used to raise the temperature of thesteam coming from the drum to the design temperatureof the turbine. To understand the reason for increasingsteam temperature, one must first understand how themaximum thermal efficiency of a power plant is affectedby the maximum and minimum operating temperatures.Energy is proportional to absolute temperature somaximum efficiency can be calculated with:

E =

Because these temperatures are absolute tempera-tures, you must add 460 to degrees Fahrenheit to getthe absolute temperature in degrees Rankine. As anexample, for a plant that operates with a maximumtemperature of 500° F and a minimum temperature of160° F, the maximum thermal efficiency would be:

E = = 35.4%

If the maximum temperature were to be raised to1000° F and the minimum temperature remained thesame, the maximum thermal efficiency becomes:

E = = 57.5%

This example demonstrates the benefit from operatingat higher temperatures and a major reason for adding asuperheater. In reality, power plants have significantinefficiency and even the best conventional steampower plants have an actual efficiency of about 40percent.

The superheater consists of alloy steel tubes throughwhich the steam from the drum passes. These tubes arelocated in the boiler in the path of the hot gases. As thesteam passes through these tubes it is heated to atemperature higher than the saturation temperature itachieved in the drum. In addition to improving thethermal efficiency of the plant, adding a superheateralso helps insure that the steam does not condense inthe lower pressure stages of the turbine and causedamage. It is not uncommon for the boiler to include twosets of superheaters called the primary and secondarysuperheaters.

960 - 620960

1460 - 6201460

T1-T2

T1


ReheaterIn addition to the superheaters, steam is often returnedto the boiler to be reheated after it has passed throughthe high-pressure or intermediate stages of the turbine.Besides a considerable drop in pressure, steam leavingthe high-pressure stages of the turbine has also cooledsignificantly. By returning the steam to the boiler, thereheater brings the steam temperature back up tonearly the same temperature as it was before enteringthe high-pressure stage of the turbine. By reheating, theefficiency of the lower pressure stages of the turbinecan be significantly improved.

Figure 11: Spray Attemperator

Water Flow

Spray Nozzle

Venturi Mixing

Steam Line

Thermal Sleeve

Steam Flow

AttemperatorAttemperators are used to control the temperature ofthe steam to the turbine. Allowing too high of a tempera-ture can cause turbine overheating, while too low oftemperature affects plant efficiency and can result inwater droplets forming in the lower pressure stages ofthe turbine. Water droplets will quickly erode the turbineblades.

Several types of attemperators are available but mostcontemporary power plants utilize some type of sprayattemperator. Spray attemperators function by addinghigh purity water to the steam through a spray nozzlelocated at the throat section of a venturi in the steamline.

Attemperators are normally located between the pri-mary and secondary superheaters and also before thereheat superheater. Placing the attemperators in theselocations helps protect the turbine from water that maynot vaporize immediately upon spraying it into thesteam (see Figure 11).

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Turbine

Figure 12: Steam Turbine Generator

The turbine is essentially a complex windmill or fan withmany blades that converts the thermal energy of thesteam to useful mechanical energy. Steam turbines inthermal generating plants can range in generatingcapacity from 1 megawatt to more than 1,000 mega-watts. As high-energy steam passes through the vari-ous stages of the turbine, its energy is converted torotating the turbine. It is common for a turbine to haveboth high and low pressure sections with a reheat cyclein between. An intermediate stage can also be in-cluded, which may or may not include an additionalreheat cycle.

After passing through the high-pressure section of theturbine, the steam may be returned to the boiler reheatsuperheater to increase the steam temperature beforeentering the next turbine section. This is done toimprove the efficiency of the turbine and to reduce the

14

potential of condensate forming in the lower pressurestages of the turbine. The reheat steam is heated toapproximately the same temperature as the super-heated steam entering the high-pressure turbine. How-ever, the reheat steam pressure is much lower than thatof the main steam. Superheated steam pressures mightbe as high as 2700 psi while reheat steam pressuresmight be below 600 psi. Steam is also extracted atvarious points in the turbine for use in other areas of theplant for heating feedwater, operating auxiliary equip-ment, and space heating. Figure 2 is an example of aplant employing high, low and intermediate pressureturbines with one reheat cycle.

After exiting the low-pressure turbine, the steam returnsto the condenser. At this point, one complete cycle inthe power generation process has been completed.

Figure 13: Cutaway view of Steam Turbine

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Super-critical Power Plants
A variation of the conventional power generationprocess is the super-critical or 'once-through' boiler.Super-critical plants operate at pressures exceedingthe critical point of water. The term 'once through'comes from the identifying feature of the super-criticalboiler which has no drum for the separation of thesteam and water. While all super-critical plants areonce-through, not all once-through plants are super-critical.
The main difference between a conventional and super-critical boiler is that the super-critical boiler is designed toproduce steam at temperatures and pressures higherthan the super-critical temperature and pressure ofwater. Figure 14 is a heat balance for a typical super-critical power plant. Operating in the super-criticalregion increases thermal efficiency, reduces fuel con-sumption and produces fewer emissions. Because of


the higher operating pressures and temperatures, equip-ment construction, operation and reliability becomeeven more important factors for super-critical plants.

Once-through boilers lack a drum for steam and waterseparation and heat storage. For this reason, they havea start-up system that includes either a flash tank orseparators. The flash tank or separators serve muchthe same function as a drum while the boiler is comingup to operating temperature, pressure and flow. Figure15 shows a simplified schematic of a Babcock & WilcoxUniversal Pressure Boiler Bypass System.

After start-up of the once-through boiler, the flash tankis bypassed and flow through the plant is as shown inthe schematic pictured in Figure 14. Notice that theschematic now becomes similar to a conventionalthermal power cycle except that the pressures andtemperatures are higher.

Low Pressure Turbine

Condenser(2 in. Hg Abs)

CondensatePump

101.1F

50.8

P28

.8P

14.3

P6.

3PBoiler Feed

PumpTurbine2.

5 in

.Hg

Abs

ToCondenser

112.0F

102.0F5.92P

174.5F

169.5F

Low Pressure Feedwater Heaters

164.5F13.56P

208.0F

203.0F

213.0F

27.1P

244.5F

239.5F

DeaeratingHeater

BoosterPump278.9F525P

278.1F

47.7P

288.9F

High Pressure Feedwater Heaters

361.9F

407.6F

269.5P

351.9F

137.9P

Boiler FeedPump425.0P

430.3F

502.0F

693.4P

502.0F

Fuel In Eco

nom

izer

/Fur

nace

/Sup

erhe

ater

Reh

eate

r

AirHeater

ForcedDraftFan

InducedDraftFan

Flue Gas OutAir In

High PressureTurbine

3500 psig1000F

664.8P1000F

8

IntermediatePressureTurbine

714.

9P

142.

2P28

6.7P

Figure 14: Heat Balance for a Super-critical Power Plant

P = psig

F = Farenheit

15

Z

Boiler Primary Superheater 200

201

201A207 205

242

240

Secondary Superheater

210

Turbine

Condenser

CondensatePump

241

Flash Tank

230

DeaeratorStorage

BoilerFeedPump

Deaerator231

220

H.P. Heaters

I.P. Heaters

CondensatePolishing

Equipment

202

Figure 15: Pressure Control of Power Plants

Sliding Pressure ControlA term heard frequently when referring to once-throughboilers is “sliding pressure control.” Surplus powergenerating capacity, and the inclusion of many nuclearplants as base load units increased the necessity ofthrottling once-through power plants during low demandtimes. Sliding pressure control was developed as amethod of allowing once-through boilers to cycle theirload during off-peak hours.

Regulating the pressure of the steam entering the tur-bine controls the generator speed. Turbine control valves,located on the inlet of the turbine, normally perform thisfunction for moderate changes in demand. However, ifdemand swings often or widely, a different controlstrategy is necessary to protect the turbine.

Flow through a valve can be considered a constantenthalpy (h - btu/lbm) process. By referring to the steamtables it can be easily demonstrated that when thepressure is reduced through a valve, in order to maintainthe same enthalpy, the temperature of the outlet steammust also be reduced. This means that large demandswings can result in significant steam temperaturechanges that can cause turbine damage and reduce thethermal efficiency of the plant.

Sliding pressure control allows the turbine load to varywith demand while supplying the turbine with constanttemperature steam. This is accomplished by openingthe turbine control valve and controlling the turbine with

16

a control valve located between the primary andsecondary superheaters. Even though the steamtemperature downstream of the sliding pressurecontrol valve may vary as a result of its throttling, thesecondary superheater can smooth out the resultingtemperature changes of the steam prior to enteringthe turbine. Figure 16 illustrates normal and slidingpressure control.

Figure 16: Pressure Control

TurbineTurbineThrottleValve


SlidingPressureControlValve

Primary Superheater

Boiler

Sliding Pressure Control of once-through Power Plants

Boiler Primary Superheater


TurbineThrottle

Valve Turbine

Conventional Control of once-through Power Plants


Although not currently as popular as some alternatives,nuclear power plants can be found in 32 countriesworldwide and account for over 20 percent of the powergenerated in these countries.

Nuclear power plants utilize a controlled chain reactionof fissionable material to produce heat. This reactiontakes place in the nuclear core. A nuclear core andsteam generator can be used to replace the boiler andassociated systems and the rest of the power genera-tion cycle would be similar to a conventional thermalpower plant. Nuclear generating units range in sizefrom 75 megawatts to more than 1,400 megawatts.

ModeratorConventional nuclear reactors utilize water around thecore as a moderator. The moderator serves two func-tions. First, it slows down the neutrons so when theycollide with fuel molecules they will be absorbed andcause them to fission. Second, as the fission processoccurs, the heat of the core rises. The moderator isused to transfer this heat from the core to producesteam. The moderator in all water modulated plants is'heavy water' or deuterium oxide. Deuterium is ahydrogen isotope that has an extra neutron. Theincreased size of the nucleus of the deuterium oxidemakes it more effective than normal water in slowingdown the fission neutrons.

Nuclear Power Plants


NUCLEAR REACTOR TYPES

Boiling Water Reactor (BWR)Some nuclear power plants heat the moderator until itbecomes steam. This type of nuclear plant is referredto as a "Boiling Water Reactor" or BWR. The steamproduced in the BWR core is then used to turn theturbine. One disadvantage of this type of system is thatthe steam is radioactive and the equipment it comes incontact with becomes radioactive. An advantage of theBWR is its simplicity and ability to operate at slightlyhigher steam temperatures than alternative designs.Figure 17 is a cutaway of a BWR reactor.

Pressurized Water Reactor (PWR)Nuclear power plants that use water as a moderator butdo not boil it are referred to as a “Pressurized WaterReactor” or PWR. PWR’s pressurize the moderatorso it does not boil at the high core temperatures. Themoderator is then circulated through a heat exchangerwhere the process water/steam is heated (seeFigure 18).

Most operating nuclear reactors are PWR’s and usethe moderator to heat the process steam by means ofa heat exchanger. This keeps the process steamseparate from the radioactive water surrounding thenuclear core.

Figure 17: Cutaway view of a BWR Reactor

17

Nuclear power plants operate at lower temperaturesand pressures than typical fossil powered units andtherefore have some subtle differences. Because ofthe lower temperatures and pressures in the nuclearsteam cycle, the limits on oxygen and other non-con-densable gases in the feedwater are less stringent andcan normally be controlled through condenser hotwelldeaerators. For this reason, most U.S. nuclear plantfeedwater systems are totally enclosed and do notincorporate a classic deaerating heater.

Breeder Nuclear ReactorsThe conventional nuclear reactor requires a highlyrefined uranium-235 or plutonium fuel and accounts forvirtually every commercial nuclear power plant in opera-tion. Uranium-235 accounts for less than one percent ofthe naturally occurring uranium. Most uranium exists asthe isotope uranium-238. Breeder reactors were devel-oped to utilize the more plentiful uranium-238 as fuel.Breeder reactors get their name from their characteristicof actually producing more fissionable material thanthey use. This is accomplished by building a core offissionable plutonium-239 with an outer layer of ura-nium-238. As the plutonium-239 undergoes the fissionprocess, it releases neutrons that when added to thenucleus of a uranium-238 atom, transform it to pluto-nium-239. The plutonium can then be used in the fissionprocess.

Because plutonium is used to make nuclear weapons,has a half-life of 24,000 years and is extremely toxic,breeder reactors have been the center of much contro-versy. Breeder reactors also require liquid sodium asa core coolant. Liquid sodium is very reactive andactually is flammable in contact with air or water. A

Figure 18: Nuclear Reactor

SubstationTransformer

CoolingTower

MakeupPumps Pump

TurbineGenerator

Water to

BoilerCondensate Pump

Condenser

Feed Pump High

PressureHeaters

LowPressureHeaters

Steam

Primary CoolantPump

ReactorVessel

PrimaryConcrete

Shield

Pressurizer

SteamGenerator

Core

18

problem with leaks of sodium at existing breeder reac-tors has also slowed the expansion of this technology.

Boiling Water Reactor Safety SystemsIn addition to the typical systems used in power genera-tion, nuclear power plants utilize many auxiliary sys-tems specific to nuclear power generation. Theseauxiliary systems can be broken into two general cat-egories: systems necessary for normal operations andsystems that provide backup or support during upsetconditions. Brief descriptions of some of the auxiliarysystems for a BWR are given below. Although specificto a BWR, many identical or similar systems would befound in a PWR.

SYSTEMS FOR NORMAL PLANTOPERATIONS

Reactor Water Cleanup SystemThe reactor water cleanup system provides continuouspurification of a portion of the reactor coolant in order toreduce the concentration of fission products.

Shutdown Cooling Function of theResidual Heat Removal SystemThe shutdown cooling function of the residual heatremoval system removes heat from the nuclear systemduring shutdown and prior to refueling.

SYSTEMS FOR ABNORMAL PLANTOPERATIONS

Standby Liquid Control SystemThe standby liquid control system is a redundant controlsystem capable of shutting the reactor down from ratedpower operation to the cold condition. Operation of thissystem has not been required in any commercial boilingwater reactor. This system consists of a large storagetank filled with sodium pentaborate, pumps, valves,piping and instrumentation. This equipment injects thesodium pentaborate into the reactor core and shutsdown the reactor without the use of additional systems.

Reactor Core Isolation Cooling SystemThe reactor core isolation cooling system maintainssufficient water in the reactor pressure vessel to coolthe core in the event the vessel becomes isolated fromthe turbine steam condenser accompanied by a loss offeedwater flow. The system also allows for completeplant shutdown under conditions of loss of the normalfeedwater system. This is accomplished by maintain-ing the necessary reactor water inventory until thereactor vessel is depressurized, allowing the operationof the shutdown cooling function of the residual heatremoval system.


Figure 19: Residual Heat Removal System

Drywell

Reactor Vessel

Containment Vessel

Pull FlowBypass

PressureReducingValve

RCICPump Suction

HeatExchange

Service Water

RCICPump Suction

SupressionPool System

Pumps

High Pressure Core Spray SystemThe high pressure core spray system depressurizesthe nuclear boiler system and provides makeup waterin the event of a loss of reactor coolant. It also preventsfragmentation of the nuclear core in the event the corebecomes uncovered.

Low Pressure Core Spray SystemThe low pressure core spray system prevents fragmen-tation of the nuclear core in the event the core isuncovered by loss of coolant by directing jets of waterdown into the fuel assemblies.


Residual Heat Removal SystemThe residual heat removal system removes post-powerenergy from the nuclear boiler under normal and abnor-mal conditions. The residual heat removal systemconsists of several subsystems, including low pressurecoolant injection, suppression pool cooling, contain-ment spray cooling, reactor steam condensing andnuclear boiler shutdown cooling. A simplified sche-matic of the residual heat removal system is shown inFigure 19.

19

Gas turbines are often utilized to turn the generatorrather than a steam turbine. Due to an abundance ofinexpensive natural gas, a relatively easy permittingprocess, and a short construction cycle, gas turbineshave become a very popular way of adding generatingcapacity. Gas turbines have quick start-up times and asa result are popular for peaking, remote, emergencyand reserve power requirements. Gas turbines areavailable in a variety of sizes and configurations withmodern turbines being delivered with generating ca-pacity in excess of 200 MW and firing temperaturesexceeding 2000° F.Gas turbines can be designed and built specifically forpower generation purposes or may be adapted fromother applications. An example of an adapted turbine isthe aeroderivative turbine. An aeroderivative turbine isone that was originally designed for aviation use thathas been converted for power generation.

Gas Turbines

20

Combined CycleOften, in order to increase efficiency of a gas turbine, aheat recovery steam generator (HRSG) is utilized tomake use of the waste heat in the turbine exhaust togenerate steam. The steam generated can then berouted through a steam turbine and associated cycle togenerate even more power. In this case, the waste heatfrom the gas turbine provides the same function as thecoal, oil or gas, while the remainder of the processremains relatively unchanged. When a HRSG is uti-lized, the turbine is referred to as operating as a “com-bined cycle." A typical HRSG is illustrated in Figure 21.

Gas turbines without heat recovery boilers are called“simple cycle," while those operating with heat recoveryare “combined cycle” (see Figure 22). Valve applica-tions for a combined cycle installation have most of thesame engineering challenges and concerns as those

Figure 20: Gas Turbine

Cou

rtes

y of

Mits

ubis

hi H

eavy

Ind

ustr

ies


Figure 21: HRSG

Cou

rtes

y of

Del

tak


found in a conventional fossil-fuel power plant. Inaddition to the control valves found on the HRSG, theturbine requires valves for fuel control and shut-off. It isnot uncommon for gas turbines to operate under a 'dualfuel' control scheme that allows the use of either liquidor gaseous fuel. Dual fuel systems allow power genera-tors to utilize inexpensive natural gas when it is avail-able and switch over to petroleum when the natural gasis unavailable or higher in cost than the alternativepetroleum fuel.

Gas turbines also often use control valves to inject DI(deionized) water or steam for power augmentation oras a means of controlling NOx emissions. Gas turbinecontrol valves are usually specified by the turbinemanufacturer and commonly have hydraulic or electricoperators. For additional information on gas turbinesand associated control valve applications, contact theFlowserve specialist assigned to the specific gas tur-bine manufacturer.

Figure 22: Combined Cycle Schematic

Compressor

Air

Fuel

Combustor

Gas Turbine

Generator

Pump

SteamGenerator

Condenser

Generator

Steam Turbine Cooling Water

Turbine Exhaust

21

GlossaryAir Heater A heat exchanger for the recovery of

energy from the flue gas. Preheats combustionair prior to entering the boiler. This is last heatexchanger in the flue gas prior to the stack.

Attemperator A device that controls steam tempera-ture by diluting high temperature steam with lowtemperature water.

Atom The smallest component of an elementhaving all the properties of the element, consist-ing of an aggregate of protons, neutrons, andelectrons such that the number of protonsdetermines the element.

Baseload The minimum amount of electric power ornatural gas delivered or required over a period oftime at a steady rate. The minimum continuousload or demand in a power system over a givenperiod of time usually not temperature sensitive.

Biomass Organic material such as wood waste orgarbage.

Blowdown Water that is bled from the boiler drumor steam supply system to control the concentra-tion of total solids in the boiler water.

Boiling Water Reactor (BWR) A nuclear reactorthat utilizes the moderator as the primaryprocess fluid.

Boiler A device for generating steam for power,processing or heating purposes or for producinghot water for heating purposes or hot watersupply.

Boiler Feedpump The main pump in a power plant.Breeder Nuclear Reactor A nuclear reactor that

utilizes Uranium-238 in the fission process andas a result produces fissionable plutonium.Because they create more fuel than they use,they are given the name breeder.

Closed Feedwater Heater A feedwater heaterincorporating a tube and shell type heatexchanger to prevent direct mixing of thefeedwater and extracted steam.

Cogeneration When a power plant produces bothsteam and electricity as end products.

Combined Cycle The combination of one or moregas turbine and steam turbines in an electricgeneration plant.

Condenser An extended surface heat exchange forthe purpose of extracting the heat of a fluid.

Condensate Polishing The process removingminerals from the condensate.

Constant Enthalpy Process A process in which theenthalpy of the fluid at the beginning of theprocess is equal to the enthalpy of the fluid at theend of the process.

Condensate The liquid resulting when a vapor issubjected to cooling and/or pressure reduction.

Deaerator An open feedwater heater used to removenon-condensable gases from the feedwater.

22

Deionization The removal of all charged atoms ormolecules from some material such as water.The process commonly employs one resin thatattracts all positive ions and another resin tocapture all negative ions.

Dissolved Solids Mineral impurities in the conden-sate, feedwater or makeup water that are insolution.

Drum A large vessel in the boiler where steam isseparated from the water.

Economizer A heat exchanger prior to the air heaterfor preheating feedwater.

Evaporation The change of state from liquid to vapor.Electron An elementary subatomic particle having a

rest mass of 9.107 x 10-28g and a negative chargeof 4.802 x 10-10 statcoulomb. Also known asnegatron. A subatomic particle of identicalweight and positive charge is termed a positron.

Electrodialysis A method of purifying water wherean applied electrical charge draws impuritythrough permeable membranes.

Extracted Steam Steam that is extracted from theturbine at intermediate locations between theentrance and the exit to the condenser.

Feedwater Heater A device used to preheat feedwa-ter prior to entering the boiler.

Flash Tank A device, similar to a drum, used onstart-up systems for once-through boilers toseparate water and steam.

Flue Gases The products of combustion in the boiler.Fossil Fuel Fuel such as coal, crude oil or natural gas,

formed from fossil remains of organic material.Generator A machine that converts mechanical

energy into electrical energy. Generally rated interms of real power (megawatts) and reactivepower (Megavars) output or in terms of realpower (megawatts) and power factor. Genera-tors require a source of mechanical energyoutput (typically a turbine) and ancillary equip-ment to interface with the transmission network.

High Pressure Feedwater Heater A feedwaterheater located after the main pump.

Half-life The time span necessary for the atoms of anuclide to disintegrate by one-half.

Hotwell The area in a device such as a condenseror feedback heater where condensate collects.

Ion Exchange A demineralization process in whichthe cations in solution are replaced by hydrogenions and the anions in solution are replaced byhydroxide ions.

Isotope Any of two or more forms of a chemicalelement, having the same number of protons inthe nucleus, or the same atomic number, buthaving different numbers of neutrons in thenucleus, or different atomic weights.


Kilowatts A unit of electrical power equal to onethousand watts.

Kilowatt-Hour (kWh) One thousand watt hours.Low Pressure Feedwater Heater A feedwater

heater located prior to the main pump.Makeup Water Treated raw water added to the

system to compensate for that lost due toleakage, process requirements, evaporation,sampling, venting or blowdown.

Megawatt A unit of electrical power equal to onemillion watts or one thousand kilowatts.

MW Abbreviation for Megawatt.Non-Condensable Gas Gases such as nitrogen

and oxygen that do not condense at condenserpressures and temperatures.

NOx Abbreviation for Nitrous Oxide.Nucleus The positively charged core of an atom; it

contains almost all of the mass of the atom butoccupies only a small fraction of its volume.

Nuclear Power Plant A facility in which heat pro-duced in a reactor by the fissioning of nuclearfuel is used to drive a steam turbine.

Nuclear Reactor A device in which a fission chainreaction can be initiated, maintained and con-trolled. Nuclear reactors are used in the powerindustry to produce steam for electricity.

Neutron An elementary particle having no charge,mass slightly greater than that of a proton, andspin of 1/2.

Open Feedwater Heater A feedwater heater thatuses direct mixing of the feedwater with ex-tracted steam.

Peaking When a facility is operated on a cyclic basisto provide for fluctuating demand.

Plutonium A fissionable material used in nuclearpower plants and weapons.

Preheater A heat exchanger for the recovery ofenergy from the flue gas. Preheats combustionair prior to entering the boiler. Located prior tothe preheater and after the superheaters andreheaters.

Pressurized Water Reactor (PWR) A nuclearreactor that separates the moderator from theprocess through the use of a heat exchanger.

Proton An elementary atomic particle of massnumber 1 and a positive charge equal in magni-tude but opposite in sign to the charge on anelectron.

Recirculation System Systems designed to providecentrifugal pumps with a minimum flow to preventoverheating, cavitation and damage.

Reheater A heat exchanger, where steam that hasalready passed through part of the turbine, isreheated.


Reverse Osmosis A method of purifying water byapplying hydraulic pressure to an impure streamand forcing it through a semipermeablemembrane.

Rankine An absolute scale of temperature in whichthe degree intervals are equal to those of theFahrenheit scale in which 0° Rankine equals-459.7° F.

Saturation Temperature The temperature at whichvaporization takes place at a given pressure(saturation pressure).

Saturation Pressure The temperature at whichvaporization takes place at a given temperature(saturation temperature).

Scale Mineral deposits on the inner walls of boilerpiping.

Separator A device used on start-up systems for once-through boilers to separate water and steam.

Simple Cycle When gas turbines are used to gener-ate electricity without heat recovery and steamgeneration, they are operating in a "Simple Cycle."

Sludge Boiler water solids which settle out in head-ers, drums and boiler surfaces.

Subcritical Operating temperatures and pressuresare below the critical point of water (3203.6 psia.)

Super-Critical Operating temperatures andpressures are above the critical point of water(3203.6 psia.)

Superheat The process of raising the steam tem-perature above the saturation temperature.

Superheater A heat exchanger where main steam isheated beyond the saturation temperature.

Suspended Solids Mineral or organic impurities inthe condensate, feedwater, or makeup water thatare not dissolved.

Turbine The part of a generating unit usually consistof a series of curved vanes or blades on a centralspindle, which is spun by the force of water,steam or hot gas to drive an electric generator.Turbines convert the kinetic energy of such fluidsto mechanical energy through the principles ofimpulse and reaction, or a measure of the two.

Ultrafiltration A method of purifying water by forcingit through a filtering membrane.

Uranium-235 A highly refined and rare isotope ofUranium. Uranium-235 is the primary fissionmaterial for boiling water and pressurized waterreactors.

Uranium-238 The most plentiful isotope of Uranium.Venturi A constricted area in the flow passage

vacuum that causes an increase in fluid velocityand a corresponding decrease in pressure.

Watthour (Wh) An electrical energy unit of measureequal to 1 watt of power supplied to, or takenfrom, an electrical circuit steadily for 1 hour.

23

Flowserve Corporation has established industry leadership in the design and manufacture of its products. When properly selected, thisFlowserve product is designed to perform its intended function safely during its useful life. However, the purchaser or user of Flowserveproducts should be aware that Flowserve products might be used in numerous applications under a wide variety of industrial serviceconditions. Although Flowserve can (and often does) provide general guidelines, it cannot provide specific data and warnings for allpossible applications. The purchaser/user must therefore assume the ultimate responsibility for the proper sizing and selection, installa-tion, operation and maintenance of Flowserve products. The purchaser/user should read and understand the Installation OperationMaintenance (IOM) instructions included with the product, and train its employees and contractors in the safe use of Flowserve products inconnection with the specific application.While the information and specifications contained presented in this literature are believed to be accurate, they are supplied for informativepurposes only and should not be considered certified or as a guarantee of satisfactory results by reliance thereon. Nothing containedherein is to be construed as a warranty or guarantee, express or implied, regarding any matter with respect to this product. BecauseFlowserve is continually improving and upgrading its product design, the specifications, dimensions and information contained herein aresubject to change without notice. Should any question arise concerning these provisions, the purchaser/user should contact FlowserveCorporation at any of its worldwide operations or offices.

For more information, contact:

©1998 Flowserve Corporation. Flowserve and Valtek-Kammer are registered trad24

For more information about Flowserve Corporation,contact www.flowserve.com or call USA 972 443 6500

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Quick Response CentersValtek Houston5114 Railroad StreetDeer Park, TX 77536 USATelephone 281 479 9500Facsimile 281 479 8511

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