Thermodynamic efficiency in a power plant

Example 4.10 Thermodynamic efficiency in a power plant A steam power plant produces 65 MW electricity with an efficiency of 70%. It uses steam (stream 1) at 8200 kPa and 550°C. The discharged stream (stream 2) is at 75 kPa. If the expansion in the turbine is adiabatic, and the surroundings are at 298.15 K, determine  

Assume that kinetic and potential energies are negligible, and the system is at steady state. 

If the turbine operates at isentropic conditions, then we have 

Therefore, the discharged steam is wet steam, and the vapor fraction xs (the quality at isentropic operation) is 

Therefore, the final state is superheated steam at 75kPa and between 125 and 15°C. Using the linear interpolation of the values from the steam table, we have 

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