Mid-term Exam: Steam Cycle (with solution)

Q3.  Steam Cycle  (12 points)

 A small-scale power plant uses a steam cycle with reheat, having a high-pressure turbine (HP) section and a low-pressure turbine (LP) section driving an electrical generator on a single shaft. There is only one steam extraction from the turbine toward a feedwater tank (FWT) operating at 15 bar. There are no other feedwater preheaters in the cycle, only the FWT.

Calculate the electrical power output and the electrical efficiency of the cycle. 
Disregard any pressure losses or thermal losses. Neglect the pump work.  

The given input parameters are listed below:  

Total steam mass flow                                    200 kg/s       
Steam superheat pressure & temperature    160 bar / 550 ^oC 
Steam reheat pressure & temperature          10 bar / 550 ^oC 
Steam extraction pressure for the FWT         15 bar 
Condenser pressure                                       0.05 bar 
Isentropic efficiency of HP turbine section     85 % 
Isentropic efficiency of LP turbine section      90 % 
Mechanical efficiency of turbine shaft            96 % 
Electrical Generator efficiency                       92 % 
Boiler thermal efficiency                                 88 %