Power Plant Engineering

STEAM TURBINE 215

Vb

A E

C D

Vr 0

Vr 1

V 1

Va 0 V^0 Va 1

Vr 0 Vt 1

B

35° 20° 20° 35°

F

Power = m × Vb ×^10

(V V )

1000

tt− kW

= 4.54 × 67 ×

212

1000

= 64.47 kW

at 1.373 bar, dry saturated

Vs = 1.259 m^3 /Kg (from steam table)

Now m = πD × D ×

V

V

a

s

× 10

From velocity triangle,

Va = 50 m/s

D^2 = 4.54 × 1.259 ×

10

p× 50

= 0.3

D = 0.5477 m

h = 5.477 cm

Heat drop required =

74.47

0.8

= 80.58 kJ/kg.

EXERCISE

1.Steam is supplied to a turbine at a pressure of 58.42 bar abs and tetnperature of 440°C. It is

expanded in a H.P. turbine to 6.865 bar abs., the internal efficiency of the turbine being 0.85.

The steam is then reheated at constant pressure upto 300°C. Its is then expanded to 0.049 bar

abs. In L.P. turbine having internal efficiency of 0.80. If the mechanical efficiency of the

turbine is 98% and alternator efficiency is 96%, calculate the amount of steam generated by

the boiler per kWh output. [Ans. 3.68 kg/hr]

2.A steam power plant working on regenerative heating cycle utilizes steam at 41.2 bar and

400°C and the condenser pressure is 0.944 bar vacuum. After expansion in the turbine to 4.90

bar, a part of steam is extracted from the turbine for heating feed water from condenser in the

open heater. Draw the cycle on T-0 diagram and find thermal efficiency of the plant. Assume

the heat drop to be isentropic and the atmospheric pressure may be taken as 1.013 bar.

[Ans. 38.89%]