Steam enters the turbine of a simple vapor power plant with

Steam enters the turbine of a simple vapor power plant with a pressure of 10 MPa and a temperature of 580 degree C and expands adiabatieally to 6 kPa. The isentropic turbine efficiency is 85 %. Saturated liquid exits the condenser at 6 kPa and the isentropic pump efficiency is 82 %. The quality of steam leaving the turbine is nearly 0.81 0.85 0.90 0.95 The turbine work output per kilogram of steam circulated is nearly 1247.7 kJ/kg 1347.7 kJ/kg 1467.9 kJ/kg 1367.9 kJ/kg

Solution

at 580 C and 10 MPa

h1 = 3580 kJ/kg

s1 = 6.85 kJ/kg-K

a) at 6 kPa and s2 = s1 = 6.85 kJ/kg-K from steam tables

we get quality = 0.81   (option a is correct)

b) at 6 kPa and x = 0.81

     h2 = 2110 kJ/kg

     Therefore actual work output of turbine = 0.85 * (h1 - h2)   = 0.85 * (3580 - 2110) = 1249.5 kJ/kg

     Therefore option a is correct.