2488 Aguk Zuhdi MF VCPC by fhSiUpI

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									KARAKTERISTIK BEBERAPA
 SISTEM TERMODINAMIKA


  Vapor and
Combined Power
  Cycles (2)
8.2 The carnot vapor cycles
                   Energy reservoir at
                   high temperature, TH

                   2                     3
                             Boiler

                                                    W
       Feed pump


           W                          Turbine

                            Condenser
                   1                            4

                       Energy reservoir at
                       low temperature, TL
8.2 The carnot vapor cycles

                       QIN




                               WTURBINE



          WPUMP         QOUT
8.2 The carnot vapor cycles

                       QIN
                              High temperature
                              heat addition, TH
                                                      Turbine to obtain
                                                      work by expansion
                                                      of working fluid.

Work input to
compress working
fluid


                                                             WTURBINE


                                        Low temperature
                                        heat rejection, TL
            WPUMP       QOUT
8.2 The carnot vapor cycles


              Energy reservoir at
              high temperature, TH
                              Q1=Q23

                                    Wnet=W34-W12

                              Q2=Q41

              Energy reservoir at
              low temperature, TL
8.2 The carnot vapor cycles


                                        Process
  T
                                        1-2 Adiabatic compression
                                        (work input to system, W1)
                   Q1=QH
                                        2-3 Isothermal expansion
TH         2               3


      W1                       W4       (heat added, Q1)

 TL                                     3-4 Adiabatic expansion
               1           4

                   Q2=QL                (work out from system, W4)

                                    s   4-1 Isothermal compression
                                        (heat rejected, Q2)
8.2 The carnot vapor cycles



       Efficiency of the Carnot cycle,
             work out     wnet
                      
           net supplied    q1
             q2    TL
         1  1
             q1    TH
8.2 The carnot vapor cycles

 1. Limiting of heat transfer which severely limits the
    maximum temperature that can be used in the cycle and
    the thermal efficiency (Higher power requirement)

 2. Not practical to design a compressor that handles
    two phases (Not homogeneous)
3. Difficult to control the condensation process at the
   desired quality.

4. High quality of steam decrease or high contents of
   liquid droplets cause erosion and wear at turbine
   blades
8.2 Rankine cycle : the ideal cycle for vapor power cycles

  Elimination of impracticalities of Carnot
                   cycle


Superheating the steam in the boiler and
condensing it completely in the condenser


                    Rankine cycle
8.2.2 Rankine cycle : the ideal cycle for vapor power cycles


                                Process
                                1-2 Isentropic compression
                                    in a pump
                                2-3 Isobaric heat addition
                                    in a boiler
                                3-4 Isentropic expansion in
                                    a turbine
                                4-1 Isobaric heat rejection
                                    in a condenser
8.2.2 Rankine cycle : the ideal cycle for vapor power cycles


                                            3*
      T                                3


              2



              1                        4    4*

                                             s

          All processes are internally reversible.
8.2.2 Rankine cycle : the ideal cycle for vapor power cycles

                                                                     Isentropic
               Reversible constant                                   expansion to
               pressure heat addition                           3*   produce work
       T                                                    3
               (2  3)                                               (3  4) or
                                                                     (3*  4*)


                  2
 Isentropic
 compression
 (1  2)
                  1                                         4   4*
                                  Reversible constant
                                  pressure heat rejection        s
                                  (4  1)



           All processes are internally reversible.
8.2.2 Rankine cycle : the ideal cycle for vapor power cycles

 h                                 3            Kinetic energy
               Qin
                                                and potential
                                        Wturb   energy changes
      Wpump2
                                   4
                                                are usually small
           1
                         Qout                   and can be
                                                neglected.
                                        s
For steady flow energy equation per unit mass of steam (From first
law of Thermodynamics) reduces to

     qin  qout   win  wout   he  hi           kJ/kg 
8.2.2 Rankine cycle : the ideal cycle for vapor power cycles


   For feed pump (q  0)
   wpum p  h2  h1  v( P2  P )
                               1              kJ/kg
   where h1  h f @ P1        and        v  v f @ P1


   For Boiler ( w  0)
   qin  h3  h2               kJ/kg
8.2.2 Rankine cycle : the ideal cycle for vapor power cycles

      For turbine (q  0)
      wturb  h3  h4       kJ/kg

      For condenser( w  0)
      qout  h4  h1     kJ/kg

     Thermalefficiency of Rankine cycle,
            wnet      qout
      th        1
            qin       qin
      where wnet  qin  qout  wturb  wpum p   kJ/kg
8.2.2 Rankine cycle : the ideal cycle for vapor power cycles
                            Increased
                            average
             h              temperature of       3*
                            heat addition

                         QH
                                                          WOUT
                 WIN 2
                                             4
                                    QC
                     1
                                                      s
        wturb  wpum p
   
             qin                             
      h3*  h4   h2  h1                     0
   
                 h3*  h2
                                             h3*
8.3.3 Deviation of actual vapor power cycles from the
    idealized ones
                                                    Pressure drop in boiler
    Irreversibility in the
                                  Ideal cycle
    pump (heat loss)                                (fluid friction)


           T
                                                3
                                                               Actual cycle
                        2


                                                4
                   1
                                                    s

     Pressure drop in condenser                     Irreversibility in the
     (fluid friction)                               turbine (fluid friction)
8.2.3 Deviation of actual vapor power cycles from the
    idealized ones
                             Isentropic efficiency for pump

                                   ws h2 s  h1
                              P    
                                   wa h2 a  h1

                              Isentropic efficiency for turbine

                                   wa h3  h4 a
                              T    
                                   ws h3  h4 s
8.2.3 Deviation of actual vapor power cycles from the
    idealized ones
Example
  Steam is the working fluid in an Ideal Rankine cycle. Saturated
  vapor enter the turbine at 80 bar and saturated liquid exits the
  condenser at a pressure of 0.08 bar. The turbine and the pump
  each have an isentropic efficiency 85%. Determine

a. Thermal efficiency
b. Mass flow rate of steam in kg/hr for a net power output 100 kW
c. Rate of heat transfer into working fluid as it passes through the
   boiler (MW)
d. Rate of heat transfer from condensing steam as it passes
   through the condenser (MW)
e. Mass flow rate of the condenser cooling water in kg/hr if
   cooling water enter the condenser at 15oC and exits as 35oC
8.2.3 Deviation of actual vapor power cycles from the
    idealized ones
Solution
8.2.3 Deviation of actual vapor power cycles from the
    idealized ones
Solution
8.2.3 Deviation of actual vapor power cycles from the
    idealized ones
Solution
8.2.3 Deviation of actual vapor power cycles from the
    idealized ones
Example
     Superheated steam at 30 bar and 360oC enter the
     turbine of steam power plant operating at steady
     state and expands to a condenser pressure 1.0 bar.
     Assume the isentropic efficiencies of the turbine
     and pump 85% and 80% respectively. Determine

a.   The thermal efficiency
b.   The heat rate
c.   The steam supply to deliver 1000kW
d.   The corresponding Rankine efficiency
8.2.3 Deviation of actual vapor power cycles from the
    idealized ones
Solution
8.2.3 Deviation of actual vapor power cycles from the
    idealized ones
Solution
8.2.3 Deviation of actual vapor power cycles from the
    idealized ones
Solution
8.2.4 How can we increase the efficiency of the Rankine
    cycle

   Usage of steam power plants :
   production of most electric power in the world


   Basic idea of increasing the thermal efficiency
   of the steam power plants :
 1.Increase the average temperature in the boiler
 2.Decrease the average temperature in the
   condenser
3.4 How can we increase the efficiency of the Rankine
    cycle
Lowering the condenser pressure (Lower Tlow,avg)
                                 P  mean T ,
    Steam in saturated mixture                 re
                                 thus temperatu of the heat is rejected
       during condensation
                                        Increase in net work output


                                  And also the heat input requirements (2
                                    to 2’) but small compare to Wnet



                                 Condenser operating pressure is limited by
                                  the temperature of the cooling medium


                                  Could cause air leakage to condenser and
                                 moisture content of the steam in the turbine
8.2.4 How can we increase the efficiency of the Rankine
    cycle
Superheating the steam to high temperatures (Increases
Thigh,avg)
                            Steam is superheated at P constant (3 to 3’)
                               which increase the net work output.


                            Decreases the moisture content of the steam
                                        at the turbine exit.




                             Steam superheated temperature is
                                 limited by metallurgical
                           considerations and material limitation
8.2.4 How can we increase the efficiency of the Rankine
    cycle
Increasing the boiler pressure (Increases Thigh,avg)



                          Pboiler increase which will automatically
                                raises the boiling temperature


                          Instead of increase the net work output,
                           it also increase the moisture content in
                                          the turbine
8.2.4 How can we increase the efficiency of the Rankine
    cycle
Example
  Consider a steam power plant operating on the ideal
  Rankine cycle. Steam enters the turbine at 3MPa and 350oC
  and is condensed in the condenser at a pressure of 75kPa.
  Determine
a. The thermal efficiency of this power plant
b. The thermal efficiency of this power plant if the condenser
   pressure decrease to 10kPa.
c. The thermal efficiency if steam is superheated to 600oC
   instead of 350oC
d. The thermal efficiency if the boiler pressure is raised to
   15MPa while the turbine inlet temperature is maintained at
   600oC
8.2.4 How can we increase the efficiency of the Rankine
    cycle
Solution
8.2.4 How can we increase the efficiency of the Rankine
    cycle
Solution
8.2.4 How can we increase the efficiency of the Rankine
    cycle
Solution
8.2.5 The ideal reheat Rankine cycle

Objective of reheat the Rankine cycle :
Increase the net work output and thus the thermal
efficiency without the problem of excessive moisture at
the final stage of the turbine

Two possible solutions :
1. Superheat the steam to very high temperature before it
   enters the turbine (limited by metallurgical
   consideration)
2. Expand the steam in the turbine in two stages, and
   reheat it in between.
 8.2.5 The ideal reheat Rankine cycle
            qprim ary            wturb I                    1-2 Isentropic compression
                                                 wturb II
                                                                in pump
                                                            2-3 Isobaric heat addition in
                                                                boiler
                                qreheat                     3-4 Isentropic expansion in
                                                                high pressure turbine
                                                            4-5 Isobaric heat addition in
                                                                boiler (reheat)
qin  qprimary  qreheat  h3  h2   h5  h4           5-6 Isentropic expansion in
wturb out  wturb I  wturb II  h3  h4   h5  h6         low pressure turbine
qout  h6  h1                                              6-1 Isobaric heat rejection in
wpum p  h2  h1                                                condenser
8.2.5 The ideal reheat Rankine cycle
                   wturb I                                              1-2 Isentropic compression
                                                   qreheat
                                                             wturb II       in pump
                                                                        2-3 Isobaric heat addition in
       qprim ary                         wturb I
                                                                            boiler
                                                      wturb II
                                         qreheat                        3-4 Isentropic expansion in
wpum pin
                                                                            high pressure turbine
                             qprim ary
                                                                        4-5 Isobaric heat addition in
                                                                            boiler (reheat)
                                                                        5-6 Isentropic expansion in
              wturb I  wturb II  wpump
    th                                                                    low pressure turbine
                        qprimary  qreheat                              6-1 Isobaric heat rejection in
                                                                            condenser
8.2.5 The ideal reheat Rankine cycle


                              Increase the number of
                              expansion and reheat
                              stage is limited by :
                              Superheated exhaust
                              which increase the
                              temperature for the heat
                              rejection process
                              (decrease the thermal
                              efficiency)
8.2.5 The ideal reheat Rankine cycle
Example
  Steams are the working fluid in an ideal Rankine cycle with
  superheat and reheat. Steam enters the first stage turbine at
  80 bar 480oC and expands to 7 bar. It is then reheated to
  440oC before entering the second stage turbine where it
  expand to the condenser pressure of 0.08 bar. The net power
  output is 100 MW. Determine

a. The thermal efficiency of the cycle
b. The mass flow rate of steam in kg/hr
c. The rate of heat transfer Qout from the condensing steam as
   it passes through the condenser in MW.
8.2.5 The ideal reheat Rankine cycle
Solution
8.2.5 The ideal reheat Rankine cycle
Solution
8.2.5 The ideal reheat Rankine cycle
Solution
3.6 The ideal regenerative Rankine cycle
                           Feed water : liquid that living the
                           pump
                           Regeneration : heat transfer from
                           the expanding steam in a
                           counterflow heat exchanger built in
                           the turbine
          Regeneration
                           Regenerator : or a feedwater heater
                           (FWH) is a device where heat
                           transfer occur

                           Usage of regeneration : improves
                           cycle efficiency

                           Type of FWH : Open type and
                           Closed type
8.2.6 The ideal regenerative Rankine cycle
Open Feedwater Heaters        a mixing chamber of steam and
                              feedwater

                             1-2 Isentropic compression to saturation
                                  temperature in pump I.
                             2-3 Mixing of Feedwater from pump
                             6-3 with steam from turbine.

                             3-4 Isentropic compression to the boiler
                                  pressure in pump II.
                             4-5 Isobaric heat addition in boiler.
                             5-6 Isentropic expansion to intermediate
                                  pressure (y portion to FWH).
                             5-7 Isentropic expansion to the condenser
                                  pressure.
                             7-1 Isobaric heat rejection in condenser.
8.2.6 The ideal regenerative Rankine cycle
Open Feedwater Heaters
8.2.6 The ideal regenerative Rankine cycle
Closed Feedwater Heaters         Heat transfer without mixing
                                 taking place

                             1-2 Isentropic compression in pump I.
                             2-9 Regeneration (only heat transfer)
                             3-4 Isentropic compression in pump II
                             9/4-5 Mixing of feed water and steam
                             5-6 Isobaric heat addition in boiler.
                             6-7 Isentropic expansion to intermediate
                                  pressure (y portion to FWH).
                             6-8 Isentropic expansion to the condenser
                                  pressure.
                             7-3 Regeneration (only heat transfer)
                             8-1 Isobaric heat rejection in condenser.
8.2.6 The ideal regenerative Rankine cycle
Closed Feedwater Heaters
8.2.6 The ideal regenerative Rankine cycle

                                              yh6  1  y h2  h3
                                              yh6  h2  yh2  h3
                                                              h3  h2
                                                           y
                                                              h6  h2


                                              qin  h5  h4

                                              qout  1  y h7  h1 
h5  wturb  yh6  1  y h7             wpump  wpump I  wpump II
h5  wturb  yh6  h7  yh7
                                          wpump  1  y h1  h2   h3  h4 
wturb  h5  h6   1  y h6  h7 
8.2.6 The ideal regenerative Rankine cycle
Example
  A steam power plant operates on an ideal regenerative
  Rankine cycle. Steam enters the turbine at 6MPa and 450oC
  and is condensed in the condenser at 20kPa. Steam is
  extracted from the turbine at 0.4 MPa to heat the feedwater
  in an open feedwater heater. Water leaves the feedwater
  heater as a saturated liquid. Show the cycle on a T-s
  diagram, and determine

a. The net work output per kilogram of steam flowing through
   the boiler
b. The thermal efficiency of the cycle
8.2.6 The ideal regenerative Rankine cycle
Solution
8.2.6 The ideal regenerative Rankine cycle
Solution
8.2.6 The ideal regenerative Rankine cycle
Solution
8.2.6 The ideal regenerative Rankine cycle
 Example
   A regenerative vapor power cycle with one open feedwater heater.
   Steam enters the turbine at 80 bar 480oC and expands to 7 bar,
   where some of the steam is extracted and diverted to the open
   feedwater heater operating at 7 bar. The remaining steam expands
   through the second stage turbine to the condenser pressure 0.08
   bar. Saturated liquid exits the open feedwater heater at 7 bar. The
   isentropic efficiency of each turbine stage is 85% and each pump
   operates isentropically. If the net power output of the cycle is 100
   MW. Determine

1. The thermal efficiency
2. The mass flow rate of steam entering the first turbine stage in
   kg/hr
8.2.6 The ideal regenerative Rankine cycle
Solution
8.2.6 The ideal regenerative Rankine cycle
Solution
8.2.6 The ideal regenerative Rankine cycle
Solution
8.2.6 The ideal regenerative Rankine cycle
 Example
  A steam power plant operates on an ideal reheat-regenerative
  Rankine cycle and has a net power of 80MW. Steam enters the
  high pressure turbine at 10MPa and 550oC and leaves at 0.8MPa.
  Some steam is extracted at this pressure to heat the feedwater in an
  open feedwater heater. The rest of the steam is reheated to 500oC
  and is expanded in the low pressure turbine to the condenser
  pressure of 10kPa. Show the cycle on a T-s diagram with respect to
  saturation lines, and determine

1. The mass flow rate of steam through the boiler
2. The thermal efficiency of the cycle
8.2.6 The ideal regenerative Rankine cycle
Solution
8.2.6 The ideal regenerative Rankine cycle
Solution
8.2.6 The ideal regenerative Rankine cycle
Solution
8.2.7 combined gas-vapor cycles

 Combined cycle of Brayton gas power cycle and
         Rankine vapor power cycle

Purpose of combination :
        To achieve higher thermal efficiency


 Gas turbine engine            Regeneration, 500oC
  (Temperature limit 1500oC)
                                  Steam turbine engine
                                     (Temperature limit 620oC)
8.2.7 combined gas-vapor cycles
8.2.7 combined gas-vapor cycles
 Example
   The gas turbine portion of a combined gas-steam power plant has a
   pressure ratio of 16. air enters the compressor at 300K at a rate of
   14kg/s and is heated to 1500K in the combustion chamber. The
   combustion gases leaving the gas turbine are used to heat the steam to
   400oC at 10MPa in a heat exchanger. The combustion gases leave the
   heat exchanger at 420K. The steam leaving the turbine is condensed
   at 15kPa. Assuming all the compression and expansion processes to
   be isentropic, determine

a. The mass flow rate of the steam
b. The net power output
c. The thermal efficiency of the combined cycle

For air, assume constant specific heats at room temperature.
8.2.7 combined gas-vapor cycles
Solution
8.2.7 combined gas-vapor cycles
Solution
8.2.7 combined gas-vapor cycles
Solution
8.2.7 combined gas-vapor cycles
 Example
   Consider a combined gas-steam power cycle. The topping cycle is a
   simple Brayton cycle that has a pressure ratio of 7. Air enters the
   compressor at 15oC at a rate of 10kg/s and the gas turbine at 950oC.
   The bottoming cycle is a reheat Rankine cycle between the pressure
   limits of 6MPa and 10kPa. Steam is heated in a heat exchanger at a
   rate if 1.15 kg/s by the exhaust gases leaving the gas turbine and the
   exhaust gases leave the heat exchanger at 200oC. Steam leaves the
   high-pressure turbine at 1.0MPa and is reheated to 400oC in the heat
   exchanger before it expands in the low pressure turbine. Assuming
   80% isentropic efficiency for all pumps and turbine, determine

a. The moisture content at the exit of the low pressure turbine
b. The steam temperature at the inlet of high pressure turbine
c. The net power output and the thermal efficiency of the combined
   plant
8.2.7 combined gas-vapor cycles
Solution
8.2.7 combined gas-vapor cycles
Solution
8.2.7 combined gas-vapor cycles
Solution

								
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