Steam Power Plant: Solve Home Work Task

[simonre7]

Hi guys been given the following as some home work, haven't got a clue really its a bit confusing!

Steam ar 40 bar and 400C enters the high pressure turbine of a steam power plant at a rate of 20kg/s and explands to a pressure of 3 bar at which point it is just dry saturated. at this point part of the steam is re heated to 400C and then expands in the low pressure turbine to a condenser pressure of 0.05 bar with an isentropic efficiency of 88%. the remainder passes directly to asingle 'open' feed heater. the water leaving the condenser is raised to the feed heater pressure which it enters at a temp of 50C

1) Draw a schematic diagram of the plant and a corredponding cycle diagram on a temperature-entropy axes

2) neglecting feed pump work inputs, find:
a) the mass flow rates of steam and water entering the feed heater
b) the plnats power output and heat input
c) the plants thermal efficiency

Thank you in advance

 

[Astronuc]

Use steam tables.

"Steam at 40 bar and 400C" is a thermodynamic statepoint with which is associated a specific enthalpy. One must know if it is superheated or otherwise.

"3 bar, dry saturated" is another statepoint - key here is 'dry saturated'. What is the saturation temperature of water at 3 bar?

The inlet conditions of the LP turbine (assuming negligible pressure drop across the reheater) is 400 C at 3 bar.

Then one must determine the liquid vs steam proportions based on "condenser pressure of 0.05 bar with an isentropic efficiency of 88%".

 

[simonre7]

i'm not sure if it is super heated or not, all i have is the information i posted.

From my basic knowledge of steam tables i think the saturation temp of water at 3bar is about 133.5C

and to be honest from then on I am lost with where to look and what to do...



Pain in the bum Thermodynamics!