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Rankine Cycle

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

Solution Preview

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.