TITLE.PM5

VAPOUR POWER CYCLES 595

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(ii) The boiler generating capacity :

If ms is the mass of steam supplied to the power plant per second, then the work developed is

given by :

ms(h 1 – h 2 ) + ms(1 – m) (h 3 – h 4 ) = 110 × 10^3

or, ms(2985 – 2520) + ms(1 – 0.172) (3170 – 2555) = 110 × 10^3

or, ms(465 + 509.22) = 110 × 10^3

∴ ms = 112.91 kg/s or 406.48 tonnes/hour (Ans.)

(iii) Thermal efficiency of the cycle, ηthermal :

ηthermal =

Output / kg of steam

Input / kg of steam

= −+− −

−+− −

()()()

()()()

hh mhh

hhf mhh

12 34

132

1

2 1

= −+− −

−+− −

()(.)()

(.)(.)( )

2985 2520 1 0 172 3170 2555

2985 697 1 1 0 172 3170 2520

=974 22

2826 1

.

.

= 0.3447 or 34.47%. (Ans.)
Example 12.25. A steam power plant equipped with regenerative as well as reheat arrange-
ment is supplied with steam to the H.P. turbine at 80 bar 470°C. For feed heating, a part of steam is
extracted at 7 bar and remainder of the steam is reheated to 350°C in a reheater and then expanded in
L.P. turbine down to 0.035 bar. Determine :
(i)Amount of steam bled-off for feed heating,
(ii)Amount of steam supplied to L.P. turbine,
(iii)Heat supplied in the boiler and reheater
(iv)Cycle efficiency, and
(v)Power developed by the system.
The steam supplied by the boiler is 50 kg/s. (B.U. Dec., 2000)
Solution. The schematic arrangement is the steam power plant of shown in Fig. 12.40 (a)
and the processes are represented on h-s diagram as shown in Fig. 12.40 (b).

1

Boiler

H.P.

6 6

Condenser

Alternator

üýþ

3- supplyf

( ) Schematic arrangement of the steam power planta

80 bar,

470°C

1kg

1kg

80 bar

Superheater

L.P.

Reheater

(1–m) kg 3

4 0.035 bar

(1–m) kg

5

Regenerator (1–m) kg

5

mkg 2

7 bar