Question

Water is the working fluid in a regenerative Rankine cycle with one closed feedwater heater. Steam enters the turbine at 1400 lbf/in.² and 1000°F and expands to 120 lbf/in.², where some of the steam is extracted and diverted to the closed feedwater heater. The remaining steam expands through the second-stage turbine to the condenser pressure of 3.5 lbf/in.² Each turbine stage and the pump have isentropic efficiencies of 85%. Flow through the condenser, closed feedwater heater, and steam generator is at constant pressure. Condensate exiting the feedwater heater as saturated liquid at 120 lbf/in.² undergoes a throttling process as it passes through a trap into the condenser. The feedwater leaves the heater at 1400 lbf/in.² and a temperature equal to the saturation temperature at 120 lbf/in.² The net power output of the cycle is 1 x 10⁹ Btu/h.


Determine for the cycle:

(a) the mass flow rate of steam entering the first stage of the turbine, in lb/h.

(b) the rate of heat transfer, in Btu/h, to the working fluid passing through the steam generator.

(c) the percent thermal efficiency.

Answer 1