Repeat Problem 9.58 for a closed feedwater heater where the extraction steam is pumped to the boiler pressure before being combined with the condenser feedwater, as shown in Fig. 9.18. Assume isentropic turbines and pumps.

Fig 9.18

Problem 9.58

A regenerative Rankine cycle operates with a first-stage turbine inlet state of 800° C and 5MPa and a second-stage exhaust pressure of 0.01 MPa. A single open feedwater heater, as shown in Fig. 9.17, is used with an extraction pressure of 0.7MPa. Assume the exit states of condenser and of the feedwater heater are both saturated liquid. The turbine and pump efficiencies are 100%. Determine the first-law thermal efficiency for the cycle and the total turbine work rate per unit boiler mass flow rate (kJ/kg).

 Fig. 9.17

m Boiler Morn Mixing Champer (1-y) m m Pump 2 yin Closed feed- water heater 8 lym (1-y) m (a) 5 Pump 1 Turbine (1-y) m Condenser Temperature, T 8 in y m (1-y) m Entropy, s (b) 5 3 m (1-y) m