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Rankine Cycle

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Consider a Rankine cycle with reheat. Compressed water enters the boiler at 21 bars and is heated to 500C. Due to frictional effects there is a pressure loss of 1 bar in the boiler. At the exit of the boiler 40% of the steam produced is extracted for an external chemical process. The exhaust pressure of the first turbine is 5.0 bars. The steam is then reheated to 440C. The condenser operates at one bar. Make-up is added at the condenser. Determine:
(a) thermal efficiency of the cycle
(b) second law effectiveness

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I assume Boiler Feed Water ( BFW ) is at 1 bara and 25 degrees C. Let's call this state 1.

State 1 : Water is subcooled ; h1= 104 KJ/Kg s1 = 0.37 KJ/( Kg*K )

Water is pumped using a centrifugal pump that increase pressure to 21 bara. Let's call this state 2.

State 2 : Water is subcooled ; h2 = 106 KJ/Kg s2 = 0.37 KJ/( Kg * K )

After this water enter the boiler, where is produced steam at 20 bara and 500 degrees F. Let's call this state 3.

State 3 : Steam is overheated ; h3 = 3468 KJ/Kg s3 = 7.43 KJ/( Kg * K )
The steam saturation temperature is 212.4 degrees C.

40% of the steam goes to a Chemical Process ( I suppose for thing like heating, but not for ...

Solution Summary

This solution explains how to find the thermal efficiency and second law effectiveness of a boiler by considering it as a rankine cycle undergoing reheat.

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Thermodynamics Rankine cycle efficiency problem

An ideal reheat Rankine cycle operates between the pressure limits of 20 kPa and 8 MPa, with reheat occurring at 3 MPa. The temperature of steam at the inlets of both turbines is 500°C, and the enthalpy of steam is 3104 kJ/kg at the exit of the high-pressure turbine, and 2385 kJ/kg at the exit of the low-pressure turbine. Disregarding the pump work, the cycle efficiency is:

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