Turbine Vacuum
System
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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?
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• The steam turbineThe steam turbine is a device to
convert the heatThe steam turbine is a device to
convert the heat in steamThe steam turbine 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 condenser vacuum system.
• By condensing the exhaust steamBy condensing
the exhaust steam of turbine, the exhaust
pressure is brought down below atmospheric
pressureBy condensing the exhaust steam of
turbine, the exhaust pressure is brought down
below atmospheric
increasing the
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Parts of Vacuum System
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Condenser
CW system
Ejectors/Vacuum pumps
Gland Sealing System
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Power Loss Due to Excess Back
Pressure
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CONDENSER
The functions of condenser are:
•To provide lowest economic heat rejection temperature
for the steam. Thus saving on steam required per unit of
electricity.
•To convert exhaust steam to water for reuse for thus
saving on feed water requirement.
•De-aeration of make-up-pump water introduced in the
condenser.
•To form a convenient point for introducing make up
water.
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Steam Condenser
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Steam condenser is a closed space into which steam exits the turbine
and is forced to give up its latent heat of vaporization.
It is a necessary component of a steam power plant because of two
reasons.
It converts dead steam into live feed water.
It lowers the cost of supply of cleaning and treating of working fluid.
It is far easier to pump a liquid than a steam.
It increases the efficiency of the cycle by allowing the plant to operate
on largest possible temperature difference between source and sink.
The steam’s latent heat of condensation is passed to the water flowing
through the tubes of condenser.
After steam condenses, the saturated water continues to transfer heat
to cooling water as it falls to the bottom of the condenser called,
hotwell.
This is called subcooling and certain amount is desirable.
The difference between saturation temperature corresponding to
condenser vaccum and temperature of condensate in hotwell is called
condensate depression.
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A Device to Convert Dead Steam into
Live Water
Dead Steam
Water ready to take
Rebirth
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Two-Pass Surface Condenser
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Thermal Processes Occurring in
Condensers
• The condenser never receives pure seam from the turbine.
• A mixture of steam and non-condensable gases (Air-steam
mixture) enters the condenser.
• The ratio of the quantity of gas that enters the condenser to the
quantity of steam is called the relative air content.
•The value of ε, depends on type, capacity, load and design dimensions
of the condenser plant.
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Condenser
•Steam from last stage of
LPT Exhausts on
condenser tube
• condensation of steam
takes place
•Water collected in hot
well
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Inside a Shell and tube
condenser
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Surface Condenser ( shell and tube)
A surface condenser is basically a shell and tube
heat exchanger with phase change. The main parts
of a condenser are as follows.
• 1-SHELL
• 2-TUBES
• 3-TUBE SHEETS
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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 plates allow for the
free movements of tubes in all directions particularly lengthwise
due to expansionAt the same time the intermediate tube support
plates allow for the free movements of tubes in all directions
particularly lengthwise due to expansion and contraction occurring
during operation.
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CONDENSER SUPPORT
• 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 of
tubes.
• The inside of shell and outside the tubes as a whole remains
under vacuum under normal operating conditions. Inside the
tubes the cooling or circulating water passes through.
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InInorder
ordertotoallow
allow
expansion along the
expansion along the
height,
height,the
thecondenser
condenser
isissupported
supportedon
on
springs
springsspecially
specially
design
designtototake
takeofofload
load
fig.
fig.5.9
5.9
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Air Zone
• Inside the shell, a central or side portion
longitudinally is separated by an outer shield
except at the bottom. This partition is called the
Air zone.
• All the gases released in the condenser due to
cooling 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 out
of the shell for connection to an air extraction
device.
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Tube Sheets
• At each end of the shell, tubeAt 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 expansionTo 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.
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Condenser tubes are
secured to the end
tubes plates
expanding and
flanging of tube ends
which provides very
good arrangement
against penetration of
circulating water in to
the steam space.
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 butterfly
valves.
• small vent pipe with hand valve small vent pipe with hand valve
for air venting at higher level, and hand operated drain valve at
bottom to drain the water box for maintenance.
• Similarly thermometer pockets are located at inlet and outlet pipes
for local measurements cooling water temperature.
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The tubes have
been so
arranged that
there is equal
distribution of
steam on the
tube nest with
minimum
resistance to
steam flow.
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Condenser tubes…..
Non-condensable gases are continuously sucked with
the help of steam ejectors With a view to allow a
relative expansion between tubes and the body of the
lower part, lens type compensator has been provided
in the body it self at rear water box end. This
arrangement prevents deformation of the body and
damage to connections between tubes and end
plates
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Condensate Depression
• The temperature of condensate is always a few degrees
lower than the coincident condensing steam
temperature.
• Subcooling of condensate is undesirable on two accouts:
• It lowers the thermodynamic efficiency of the power
cycle.
• It enhances the propensity of the condensate to
reabsorb non-condensibles.
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Condenser Pressure, mm of Hg
Effect of Air Leakage on Condenser Pressure
Air pump controlling the back pressure
Condenser controlling the back pressure
Air pump controlling the back pressure
Condenser controlling the back pressure
10
30
40
50
20
Cooling water Inlet Temperature
CONDENSER
• Evolution of Tube material
Cu-Zn
Cu-Ni
SS304 / Titanium : Inert to all kind of
Water
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LIMITATIONS
•Corrosion
•Expansion
•Arrangement
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TYPES OF FAILURES IN
CONDENSER
• Impingement attack :Erosion due to high inlet
water velocity or high localized water velocity
• Bio Fouling
• Stress Corrosion
• Corrosion Fatigue
• Deposit attack
• Steam Side Ammonia Corrosion
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ONLINE CLEANING
OF
CONDENSER
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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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Hot water in (95°F)
Fan motor
Air in 95°F dry bulb,
78°F wet bulb
Air out
Cooled water out (85°F)
Mechanical Draft Cooling Tower
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STEAM EJECTORS
• Air and water vapor are removed from the main
steam condenser, enter the 1st stage ejector and are
compressed to the interstage pressure by means of
the high pressure motive steam.
• The load and motive steam are discharged to the
inter condenser and a portion of the water vapor
load and motive steam are condensed by
condensate from the main condenser.
• Non-condensibles and associated water vapor are
removed from the inter condenser by the 2nd stage
ejector.
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STEAM EJECTORS
Discharge to condenser
Nozzle
Convergent
divergent
diffuser
Motive
steam
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Non condensibile gases and
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water vapour from condenser
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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 steam pressure 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
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The liquid-ring vacuum pump is a specific form of rotary
positive-displacement pump utilizing liquid as the principal
element in gas compression.
• The working parts of the liquid ring vacuum pump consist
of a multi-bladed impeller mounted eccentrically in a round
casing which is partly filled with liquid. As the impeller
rotates, the liquid is thrown by centrifugal force to form a
liquid ring which is concentric with the periphery of the
casing.
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LRVP
Suction port
Discharge port
Casing
Impeller
Gas vapour
mixture
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Liquid ring
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LRVP
• In addition to being the compressing medium, the
liquid ring absorbs the heat generated by
compression and friction, absorbs any liquid slugs
or vapor entering with the gas stream, and
condenses water vapor entering with the gas.
• A closed loop (or total recirculation) seal system is
commonly used. The seal water temperature warmer
than the cooling water to the pump heat exchanger,
which is normally taken from the same source as the
condenser cooling water (CW or ARCW).
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LRVP
vent
Non condensible gases and water
vapour from condenser
Separator
Makeup
LRVP
Cooling
water
Seal water
Seal cooler
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LiquidPMI
ring
vacuum pump system
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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 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, leaving
less 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 pump
from achieving greater vacuum levels.
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THANK YOU
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