Question

Rankine cycle operates on boiler pressure 15 MPa and condenser pressure of 30 kPa. Superheated steam enters the high-pressure turbine at 450°C. The high-pressure turbine expands the steam and enters the re-heater at 2.5 MPa. The steam is reheated until temperature reaches 450°C before being expanded in low-pressure turbine to condenser pressure of 30 kPa. Assume the isentropic efficiency of the low-pressure and high-pressure turbines are 94% and 89% respectively, and pump is working isentropically. Neglect the change in kinetic energy, potential energy and pressure drops in boiler and condenser. The net power produced by the plant is 10 MW. Determine the followings: (a) Net heat supplied by boiler (in kJ/kg). [10 Marks] (b) Net heat rejected in condenser (in kJ/kg). [6 Marks] (c) Thermal efficiency of the cycle. [2 Marks] (d) Mass flow rate of the cycle (in kg/s). [1 Mark] (e) Thermal efficiency of the cycle if both turbines replaced with isentropic turbine. [6 Marks] (f) T-s diagram of the cycle with respect to the saturation lines. [5 Marks]

Answer 1

The rankine cycle with perfect reheating improves the efficiency when compare to rankine cycle without reheater.

Actually reheater will increases the turbine workoutput with constant heat supplied tge efficiency will increase in it.

But in this problem the high pressure and low pressure turbines are not isentropic then the efficiency is 35.94% and if they are isentropic the efficiency will increase to 38.39%.

The enthalphy values for all the states in T-S diagram are taken from the steam tables S.C Jain by Birla publications Pvt.ltd.

ASSUMPTIONS :

1. Kinetic and potential energies are negligible.

2. All the process of rankine cycle are taking place in open systems.

3. Neglect pressure drops in boiler and condenser.