Turbine Vacuum System in Thermal Power Plant

8/13/2019 Turbine Vacuum System in Thermal Power Plant

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26 December 2013 PMI Revision 00 1

Turbine VacuumSystem




Presentation outline

Why Vacuum system is required ?

Parts of Vacuum system?

Steam Ejectors

Vacuum Pumps




Why is it required?

• The steam turbine itself is a device to convert theheat in steam to mechanical power .

• Enthalpy drop across the turbine decides thework output of the turbine. For increasing thisenthalpy drop across the turbine we needeffective condenser vacuum system.

http://en.wikipedia.org/wiki/Steam_turbine

http://en.wikipedia.org/wiki/Heat

http://en.wikipedia.org/wiki/Steam

http://en.wikipedia.org/wiki/Power_%28physics%29

http://en.wikipedia.org/wiki/Power_%28physics%29


http://en.wikipedia.org/wiki/Heat







•

By condensing the exhaust steam of turbine, theexhaust pressure is brought down belowatmospheric pressure , increasing the steampressure drop between inlet and exhaust of steamturbine . This further reduction in exhaust pressuregives out more heat per unit weight of steam inputto the steam turbine , for conversion to mechanicalpower.


http://en.wikipedia.org/wiki/Atmospheric_pressure






















Parts of Vacuum System

• Condenser• CW system• Ejectors/Vacuum pumps• Gland Sealing System







Condenser

Steam from last stageof LPT Exhausts on

condenser tube

condensation ofsteam takes place

Water collected in hotwell




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 sufficientrigidity for the shell proper.

• The shell also gives support to number of intermediate supportplates for the long tubes, depending on the size of the condenser.

• At the same time the intermediate tube support plates allow for thefree movements of tubes in all directions particularly lengthwisedue to expansion and contraction occurring during operation.

http://en.wikipedia.org/wiki/Carbon_steel

http://en.wikipedia.org/wiki/Expansion

http://en.wikipedia.org/wiki/Contraction

http://en.wikipedia.org/wiki/Contraction








• The whole condenser is supported on heavy springs , mounted on

steel sole plates at suitable places on the concrete foundation• At the bottom of the shell where the condensate is allowed 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 the bottom row oftubes.

• The inside of shell and outside the tubes as a whole remainsunder vacuum under normal operating conditions. Inside thetubes the cooling or circulating water passes through.

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

http://en.wikipedia.org/wiki/Vacuum

http://en.wikipedia.org/wiki/Vacuum

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




Air Zone• Inside the shell, a central or side portion

longitudinally is separated by an outer shieldexcept at the bottom. This partition is called theAir zone.

•

All the gases released in the condenser due tocooling are taken out via these air zone tubes.• From a suitable portion of this air zone inside the

shell an air vent pipe is taken out and brought outof the shell for connection to an air extraction device.

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

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




Tube Sheets

• At each end of the shell, tube sheet of sufficientthickness is provided, with holes for the tubes to beinserted and rolled.

• To take care of length wise expansion of tubes somedesigns have expansion joint between the shell and thetube sheet allowing the latter to move longitudinally.

http://en.wikipedia.org/wiki/Tube



http://en.wikipedia.org/wiki/Butterfly_valve

http://en.wikipedia.org/wiki/Butterfly_valve







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

condenser is enclosed in a fabricated box known as water box.• These water boxes on inlet side will also have big size flanged

connections for cooling water inlet at lower level for butterflyvalves .

•

small vent pipe with hand valve for air venting at higher level, andhand operated drain valve at bottom to drain the water box formaintenance.

• Similarly thermometer pockets are located at inlet and outlet pipesfor local measurements cooling water temperature .

http://en.wikipedia.org/wiki/Valve


http://en.wikipedia.org/wiki/Thermometer

http://en.wikipedia.org/wiki/Brass

http://en.wikipedia.org/wiki/Cupro_nickel

http://en.wikipedia.org/wiki/Cupro_nickel

http://en.wikipedia.org/wiki/Brass

http://en.wikipedia.org/wiki/Thermometer







Tubes• Generally the tubes are made of brass , aluminum brass,

cupro nickel , stainless steel or titanium depending onthe cooling water chemistry.

• The lengths are fixed at about 20 ft (6 m) (for the 200MW device mentioned above), depending on the size ofthe condenser.

• The outer diameter is limited to a maximum of one inchfor ease of handling and ease of insertion through theshell tube holes and for rolling at both ends.

http://en.wikipedia.org/wiki/Stainless_steel

http://en.wikipedia.org/wiki/Titanium

http://upload.wikimedia.org/wikipedia/en/2/25/Dores-Cond-diag1.png

http://localhost/var/www/apps/conversion/Documents%20and%20Settings/Siva/Desktop/2BE3%20how%20it%20works.swf

http://localhost/var/www/apps/conversion/Documents%20and%20Settings/Siva/Desktop/2BE3%20how%20it%20works.swf







http://en.wikipedia.org/wiki/Stainless_steel







CW system

CW pumps supply cooling

water to condensers

CW maintains vacuum incondensers

CW flows throughcondensers tubes




STEAM EJECTORS•

Air and water vapor are removed from the mainsteam condenser, enter the 1st stage ejector and arecompressed to the interstage pressure by means ofthe high pressure motive steam.

• The load and motive steam are discharged to theinter condenser and a portion of the water vaporload and motive steam are condensed bycondensate from the main condenser.

• Non-condensibles and associated water vapor are

removed from the inter condenser by the 2nd stageejector.




STEAM EJECTORS

Motive

steam

Non condensibile gases andwater vapour from condenser

Convergentdivergentdiffuser

Nozzle

D

i s c

h a r g e

t o c o

n d e n s e r




STEAM EJECTORS• Multistage condensing ejector systems can be designed to

operate at any condenser pressure and designs are not limitedby the available cooling water temperature to theintercondenser (condensate cooled systems are common).

• These systems have no moving parts, are the most reliable,require the least maintenance of all venting systems, and arethe least expensive in initial cost.

• Once equipment is built for a given motive steam pressure thatpressure must be maintained or the ejector will becomeunstable and lose vacuum.




STEAM EJECTORS




EJECTORS• MAIN AIR EJECTOR

• STARTING AIR EJECTORS




Ejectors




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

positive-displacement pump utilizing liquid as the principalelement in gas compression.

• The working parts of the liquid ring vacuum pump consist

of a multi-bladed impeller mounted eccentrically in a roundcasing which is partly filled with liquid. As the impellerrotates, the liquid is thrown by centrifugal force to form aliquid ring which is concentric with the periphery of thecasing.




LRVPSuction port

Impeller

Gas vapourmixture Liquid ring

Casing

Discharge port




LRVP• In addition to being the compressing medium, the

liquid ring absorbs the heat generated bycompression and friction, absorbs any liquid slugsor vapor entering with the gas stream, and

condenses water vapor entering with the gas.• A closed loop (or total recirculation) seal system iscommonly used. The seal water temperature warmerthan the cooling water to the pump heat exchanger,which is normally taken from the same source as the

condenser cooling water (CW or ARCW).




LRVP

Separator

vent

Non condensible gases andwater vapour from condenser

Cooling

water

Liquid ring vacuum pump system

Seal water

LRVP

Seal cooler

Makeup




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 vapor pressure of the

seal, more and more of the seal fluid will “flash” into vapor.• The capacity of the liquid ring vacuum pump is reduced as more of

the impeller space is occupied by vapor from the seal fluid, leavingless space available to accept the incoming load.• If allowed to continue, cavitation will occur inside the pump,

resulting in damage to internal surfaces, and preventing the pumpfrom achieving greater vacuum levels.




TH NK YOU

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