TITLE.PM5

592 ENGINEERING THERMODYNAMICS

dharm

\M-therm\Th12-4.pm5

60 bar, 450°C

1kg^1

2 ¢

Boiler

Turbine

3barmkg

5 5

Feed

heater

Pump Pump

4

4 Out

Condenser

In

Water

3 ¢

0.07 bar

(1–m) kg

Alternator

üýþ

3- supplyf

( ) Schematic arrangement of the steam power planta

s

T

60 bar

1 (60 bar, 450°C)

2 ¢

2

3 3 ¢

5

4

( )bT-sdiagram (Neglecting pump work)

s

h

h 3 ¢

h 3

h 2 ¢

h 2

h 1 1

60 bar

3 bar

0.07 bar

Sat

.cur

3 ¢ ve

3

2

2 ¢

( )ch-sdiagram

2 ¢

Fig. 12.38

∴ h 3 = 2165 kJ/kg

Again, ηturbine = 0.87 =

hh

hh

23

23

′− ′

′− or 0.87 =

2697

2697 2165

−′ 3

−

h

∴ h 3 ′ = 2234 kJ/kg
From steam tables, corresponding to pressures 3 bar and 0.02 bar, the saturated liquid heats
at points 4 and 5 are :
hf 4 = 163.4 kJ/kg ; hf 5 = 561.4 kJ/kg.
(i) The steam bled per kg of steam supplied to the turbine, m :
Considering the energy balance for feed heater we have ;
m(h 2 ′ – hf 5 ) = (1 – m) (hf 5 – hf 4 )
or m(2697 – 561.4) = (1 – m) (561.4 – 163.4)
or 2135.6 m = 398 (1 – m)
∴ m = 0.157 kJ/kg of steam generated. (Ans.)