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Turbine VacuumSystem

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Presentation outline Why Vacuum system is required ?

Parts of Vacuum system?

Steam Ejectors

Vacuum Pumps

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Why is it required? The steam turbine itself is a device to

convert the heat in steam to mechanical

power.

Enthalpy drop across the turbine decides

the work output of the turbine. For

increasing this enthalpy drop across the

turbine we need effective condenservacuum system.

http://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Power_%28physics%29http://en.wikipedia.org/wiki/Power_%28physics%29http://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Steam_turbine

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By condensing the exhaust steam ofturbine, the exhaust pressure is brought

down below atmospheric pressure,

increasing the steam pressure drop

between inlet and exhaust ofsteam turbine.This further reduction in exhaust pressure

gives out more heat per unit weight of

steam input to the steam turbine, for

conversion to mechanical power.

http://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Atmospheric_pressurehttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Atmospheric_pressurehttp://en.wikipedia.org/wiki/Atmospheric_pressurehttp://en.wikipedia.org/wiki/Atmospheric_pressurehttp://en.wikipedia.org/wiki/Steam

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Parts of Vacuum System

Condenser

CW system

Ejectors/Vacuum pumps

Gland Sealing System

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CondenserSteam from last stage

of LPT Exhausts on

condenser tube

condensation of

steam takes place

Water collected in hot

well

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Shell of the Condenser

The shell is the outer most body of the condenser shell is fabricated from fairly thick carbon steel plates.

Due to its large size the shell is sufficiently

strengthened or stiffened internally with carbon steel

plates to give sufficient rigidity for the shell proper. The shell also gives support to number of intermediate

support plates for the long tubes, depending on the size

of the condenser.

At the same time the intermediate tube support platesallow for the free movements of tubes in all directions

particularly lengthwise due to expansion and

contraction occurring during operation.

http://en.wikipedia.org/wiki/Carbon_steelhttp://en.wikipedia.org/wiki/Expansionhttp://en.wikipedia.org/wiki/Contractionhttp://en.wikipedia.org/wiki/Contractionhttp://en.wikipedia.org/wiki/Expansionhttp://en.wikipedia.org/wiki/Carbon_steelhttp://en.wikipedia.org/wiki/Carbon_steelhttp://en.wikipedia.org/wiki/Carbon_steel

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The whole condenser is supported on heavy springs,

mounted on steel sole plates at suitable places on theconcrete foundation

At the bottom of the shell where the condensate isallowed to collect, a sump (often referred to as the

hotwell) is provided. This sump is common to both the halves but separated

by a partition wall in the middle up to the height of thebottom row of tubes.

The inside of shell and outside the tubes as a whole

remains undervacuum under normal operatingconditions. Inside the tubes the cooling or circulatingwater passes through.

http://en.wikipedia.org/wiki/Spring_%28device%29http://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Spring_%28device%29

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Air Zone Inside the shell, a central or side portion

longitudinally is separated by an outershield except at the bottom. This partitionis called the Air zone.

All the gases released in the condenserdue to cooling are taken out via these airzone tubes.

From a suitable portion of this air zoneinside the shell an air vent pipe is takenout and brought out of the shell forconnection to an airextraction device.

http://en.wikipedia.org/wiki/Extractionhttp://en.wikipedia.org/wiki/Extraction

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Tube Sheets At each end of the shell, tube sheet of sufficient

thickness is provided, with holes for the tubes

to be inserted and rolled. To take care of length wise expansion of tubes

some designs have expansion joint between the

shell and the tube sheet allowing the latter to

move longitudinally.

http://en.wikipedia.org/wiki/Tubehttp://en.wikipedia.org/wiki/Tubehttp://en.wikipedia.org/wiki/Expansionhttp://en.wikipedia.org/wiki/Butterfly_valvehttp://en.wikipedia.org/wiki/Butterfly_valvehttp://en.wikipedia.org/wiki/Expansionhttp://en.wikipedia.org/wiki/Tubehttp://en.wikipedia.org/wiki/Tube

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Water Boxes The tube sheet at each end with tube ends rolled, for

each half condenser is enclosed in a fabricated boxknown as water box.

These water boxes on inlet side will also have big size

flanged connections for cooling water inlet at lowerlevel forbutterfly valves.

small vent pipe with hand valve for air venting athigher level, and hand operated drain valve at bottomto drain the water box for maintenance.

Similarly thermometerpockets are located at inlet andoutlet pipes for local measurements cooling watertemperature.

http://en.wikipedia.org/wiki/Valvehttp://en.wikipedia.org/wiki/Thermometerhttp://en.wikipedia.org/wiki/Brasshttp://en.wikipedia.org/wiki/Cupro_nickelhttp://en.wikipedia.org/wiki/Cupro_nickelhttp://en.wikipedia.org/wiki/Brasshttp://en.wikipedia.org/wiki/Thermometerhttp://en.wikipedia.org/wiki/Valvehttp://en.wikipedia.org/wiki/Valvehttp://en.wikipedia.org/wiki/Valve

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Tubes Generally the tubes are made of brass,

aluminum brass, cupro nickel, stainless steel ortitanium depending on the cooling water

chemistry. The lengths are fixed at about 20 ft (6 m) (for the

200 MW device mentioned above), dependingon the size of the condenser.

The outer diameter is limited to a maximum ofone inch for ease of handling and ease ofinsertion through the shell tube holes and forrolling at both ends.

http://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Titaniumhttp://upload.wikimedia.org/wikipedia/en/2/25/Dores-Cond-diag1.pnghttp://localhost/var/www/apps/conversion/Documents%20and%20Settings/Siva/Desktop/2BE3%20how%20it%20works.swfhttp://localhost/var/www/apps/conversion/Documents%20and%20Settings/Siva/Desktop/2BE3%20how%20it%20works.swfhttp://upload.wikimedia.org/wikipedia/en/2/25/Dores-Cond-diag1.pnghttp://upload.wikimedia.org/wikipedia/en/2/25/Dores-Cond-diag1.pnghttp://upload.wikimedia.org/wikipedia/en/2/25/Dores-Cond-diag1.pnghttp://en.wikipedia.org/wiki/Titaniumhttp://en.wikipedia.org/wiki/Titaniumhttp://en.wikipedia.org/wiki/Titaniumhttp://en.wikipedia.org/wiki/Stainless_steel

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CW system

CW pumps supply cooling

water to condensers

CW maintains vacuum in

condensers

CW flows through

condensers tubes

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STEAM EJECTORS Air and water vapor are removed from the

main steam condenser, enter the 1st stageejector and are compressed to the interstagepressure by means of the high pressure

motive steam. The load and motive steam are discharged

to the inter condenser and a portion of thewater vapor load and motive steam are

condensed by condensate from the maincondenser.

Non-condensibles and associated watervapor are removed from the inter condenser

by the 2nd stage ejector.

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STEAM EJECTORS

Motive

steam

Non condensibile gases and

water vapour from condenser

Convergent

divergent

diffuser

Nozzle

D

ischargeto

co

ndenser

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STEAM EJECTORS Multistage condensing ejector systems can be

designed to operate at any condenser pressure and

designs are not limited by the available cooling

water temperature to the intercondenser

(condensate cooled systems are common).

These systems have no moving parts, are the most

reliable, require the least maintenance of all venting

systems, and are the least expensive in initial cost.

Once equipment is built for a given motive steampressure that pressure must be maintained or the

ejector will become unstable and lose vacuum.

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STEAM EJECTORS

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EJECTORS MAIN AIR EJECTOR

STARTING AIR EJECTORS

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Ejectors

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VACUUM PUMPS The liquid-ring vacuum pump is a specific form of

rotary positive-displacement pump utilizing liquidas the principal element in gas compression.

The working parts of the liquid ring vacuum pumpconsist of a multi-bladed impeller mountedeccentrically in a round casing which is partlyfilled with liquid. As the impeller rotates, theliquid is thrown by centrifugal force to form a

liquid ring which is concentric with the peripheryof the casing.

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LRVPSuction port

Impeller

Gas vapour

mixture Liquid ring

Casing

Discharge port

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LRVP In addition to being the compressing

medium, the liquid ring absorbs the heatgenerated by compression and friction,absorbs any liquid slugs or vapor enteringwith the gas stream, and condenses watervapor entering with the gas.

A closed loop (or total recirculation) sealsystem is commonly used. The seal watertemperature warmer than the cooling waterto the pump heat exchanger, which isnormally taken from the same source as thecondenser cooling water (CW or ARCW).

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LRVPSeparator

vent

Non condensible gases and

water vapour from condenser

Cooling

water

Liquid ring vacuum pump system

Seal water

LRVP

Seal cooler

Makeup

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LRVP The vacuum attainable by a liquid ring vacuum pump is

limited by the vapor pressure of the seal fluid.

As the operating vacuum approaches the vaporpressure of the seal, more and more of the seal fluid willflash into vapor.

The capacity of the liquid ring vacuum pump is reducedas more of the impeller space is occupied by vapor fromthe seal fluid, leaving less space available to accept theincoming load.

If allowed to continue, cavitation will occur inside thepump, resulting in damage to internal surfaces, andpreventing the pump from achieving greater vacuumlevels.

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