# Indian Institute of Technology Delhi by mikesanye

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```									    Performance Analysis of Power Plant
Condensers

P M V Subbarao
Professor
Mechanical Engineering Department
I I T Delhi

A Device Which makes Power Plant A True Cycle..
A Device Which set the limit on minimum cycle
pressure…..
T-S Diagram : Rankine Cycle with FWHs.

pturbine ,exhaust
phood
pcond,in  pcond,exit ?
TTD  ?
TCW ,out                               TCW ,in
Two-Pass Surface Condenser
T-S Diagram : Rankine Cycle with FWHs.

pturbine ,exhaust
phood

TTD  ?        pcond  psat .steam ?

TCW ,out                                TCW ,in
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.


m air
       
m c,s
•The value of , depends on type, capacity, load and design dimensions
of the condenser plant.
Variation of Steam-air Mixture Parameters
        
mc , s  m air
pc ,in  p pi ,steam              Tsat
pc ,in  p pi ,steam  p pi ,air



pc ,exit  p pe,steam  p pe,air
p pe,steam                                       exit
p pe,air    Tc,exit  Te,steam
• Using Dalon’s Law:          pc  ps  pa
Gas laws:            pa va  ma RaTa & ps vs  ms RsTs
                    

Volumes and temperatures are same.

ma RaTa        
ms RsTs
va 
             vs 

pa             ps

 
pa  Ra   m a 
        0.622
ps  Rs   m 
   s

pc
ps 
1 0.622
• 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.

pc  pc ,in  pc ,exit
• The partial pressure of air at the bottom of the condenser cannot be
neglected.
pc ,exit  p pe,steam  p pe,air

pc,in  p pe,steam  p pe,air  pc
• 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.
Variation of Steam Partial Pressure & Saturation Temperature

70

60

50                                   Saturation Temperature, 0C
Tcw,out
40

30                                                       Tcw,in

20
Steam Partial Pressure, kPa
10

0
1      2        3        4            5            6

Inlet                                        exit
Condenser with Air Removal Pump : A practicable
Concept

TCW ,in  Tamb
TCW ,exit
pcondenser       
                   ma 
psat                      
1 0.622         ms 
 
Combined Condensation & Air Pumping Action:

                           
m a : Slowly decreases & m s : Continuosly decreases to zero.
  Can be controlled to a finite value.

Air Pumping Action Vs Condensing Action !!!
Effect of Air Leakage on Condenser Pressure
Inlet Condenser Pressure, mm of Hg

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
Power Loss Due to Excess Back Pressure

What is Techno-economically Viable value of TTD ?
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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