Learning Center
Plans & pricing Sign in
Sign Out

Indian Institute of Technology Delhi


									    Performance Analysis of Power Plant

                     P M V Subbarao
            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
T-S Diagram : Rankine Cycle with FWHs.

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

                    pturbine ,exhaust

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

                          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
                        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
• 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



   50                                   Saturation Temperature, 0C

   30                                                       Tcw,in

                                        Steam Partial Pressure, kPa

           1      2        3        4            5            6

        Inlet                                        exit
    Condenser with Air Removal Pump : A practicable

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
                                                       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
• Subcooling of condensate is undesirable on two accouts:
• It lowers the thermodynamic efficiency of the power
• It enhances the propensity of the condensate to
  reabsorb non-condensibles.

To top