performance analysis of power plant condensers p m v subbarao professor mechanical engineering...
TRANSCRIPT
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Performance Analysis of Power Plant Condensers
P M V SubbaraoProfessor
Mechanical Engineering DepartmentI I T Delhi
A Device Which makes Power Plant A True Cycle..A Device Which set the limit on minimum cycle
pressure…..
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T-S Diagram : Rankine Cycle with FWHs.
?,, exitcondincond pp
inCWT ,outCWT ,
?TTD
exhaustturbinep ,
hoodp
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Two-Pass Surface Condenser
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T-S Diagram : Rankine Cycle with FWHs.
?.steamsatcond pp
inCWT ,outCWT ,
?TTD
exhaustturbinep ,
hoodp
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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.
sc
air
m
m
,
•The value of , depends on type, capacity, load and design dimensions of the condenser plant.
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Variation of Steam-air Mixture Parameters
airsc mm
,
steampiinc pp ,,
steampep ,
airpep ,
satT
steameexitc TT ,,
exit
airpisteampiinc ppp ,,,
airpesteampeexitc ppp ,,,
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• Using Dalon’s Law: asc ppp
sssssaaaaa TRmvpTRmvp &
622.0
s
a
s
a
s
a
m
m
R
R
p
p
622.01 c
s
pp
s
ssss
a
aaaa p
TRmv
p
TRmv
Gas laws:
Volumes and temperatures are same.
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• At the entry to condenser the relative content of air is very low and partial pressure of steam is almost equal to condenser pressure.
• As air-steam mixture moves in the condenser, steam is condensed and the relative content of air increases.
• Accordingly, the partial pressure of steam drops down.• The total pressure in the bottom portion of condenser is lower than
that of the top portion.• The pressure drop from inlet to exit of condenser is called steam
exhaust resistance of a condenser.
• The partial pressure of air at the bottom of the condenser cannot be neglected.
exitcincc ppp ,,
airpesteampeexitc ppp ,,,
cairpesteampeinc pppp ,,,
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• The temperature of steam is a function of condenser pressure.
• As the air-steam mixture moves through the condenser and the steam is condensed, its temperature decreases owing to decreasing partial pressure of saturated steam.
• This is due to increase in relative content of air in the mixture.
• The pressure also decreases due to resistance to flow of steam.
• The zone of intensive condensation.• The zone of cooling of air-steam mixture.
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Variation of Steam Partial Pressure & Saturation Temperature
0
10
20
30
40
50
60
70
1 2 3 4 5 6
Inlet exit
Saturation Temperature, 0C
Steam Partial Pressure, kPa
Tcw,in
Tcw,out
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Condenser with Air Removal Pump : A practicable Concept
ambinCW TT ,
exitCWT ,
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s
a
m
m622.01
condensersat
pp
Combined Condensation & Air Pumping Action:
value.finite a tocontrolled beCan
zero. todecreasesy Continuosl : & decreasesSlowly :
sa mm
Air Pumping Action Vs Condensing Action !!!
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Effect of Air Leakage on Condenser Pressure
Cooling water Inlet Temperature
10 3020 40 50
Inle
t C
onde
nser
Pre
ssur
e, m
m o
f H
g
Condenser controlling the back pressure
Air pump controlling the back pressure
Air pump controlling the back pressure
Condenser controlling the back pressure
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Power Loss Due to Excess Back Pressure
What is Techno-economically Viable value of TTD ?
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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.