1. A Rankine cycle operates with a closed feed water heater (without a trap). The turbine...

 

 

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1. A Rankine cycle operates with a closed feed water heater (without a trap). The turbine inlet pressure is 15 MPa and the exit pressure is 200 kPa. Steam is extracted from the turbine for the feed water heater at a pressure of 10 MPa. The total amount of heat added in the boiler is known to be 100MW. The inlet temperature into the boiler is known to be 300 C. The inlet temperature into the high pressure turbine is known to be 1200 C. (i) Show the cycle in a T-s diagram with properly labeled states. Draw a properly labeled schematic for the feed water heater(s) and write down the associated First law(s). (ii) Calculate the mass flow rate of water that is "bled-off" through the feedwater heater (kg/sec) and through the power plant (kg/sec). Hint: There will be two unknowns - one of them an enthalpy value and the other will be the bled-off steam mass flow rate. Solve for the bled-off steam mass flow rate by eliminating the unknown enthalpy. (iii) Calculate the efficiency of the cycle if the high pressure turbine has an isentropic efficiency of 0.75 while the low pressure turbine has an isentropic efficiency of 0.82. (iv) Calculate the quality of the steam at the exit of the low pressure turbine (v) Do the feed water heater(s) violate the 2nd Law? Explain. 1. A Rankine cycle operates with a closed feed water heater (without a trap). The turbine inlet pressure is 15 MPa and the exit pressure is 200 kPa. Steam is extracted from the turbine for the feed water heater at a pressure of 10 MPa. The total amount of heat added in the boiler is known to be 100MW. The inlet temperature into the boiler is known to be 300 C. The inlet temperature into the high pressure turbine is known to be 1200 C. (i) Show the cycle in a T-s diagram with properly labeled states. Draw a properly labeled schematic for the feed water heater(s) and write down the associated First law(s). (ii) Calculate the mass flow rate of water that is "bled-off" through the feedwater heater (kg/sec) and through the power plant (kg/sec). Hint: There will be two unknowns - one of them an enthalpy value and the other will be the bled-off steam mass flow rate. Solve for the bled-off steam mass flow rate by eliminating the unknown enthalpy. (iii) Calculate the efficiency of the cycle if the high pressure turbine has an isentropic efficiency of 0.75 while the low pressure turbine has an isentropic efficiency of 0.82. (iv) Calculate the quality of the steam at the exit of the low pressure turbine (v) Do the feed water heater(s) violate the 2nd Law? Explain.