A power plant is connected to a supply of 150 psia steam at 500 degrees F. The l

Question

A power plant is connected to a supply of 150 psia steam at 500 degrees F.

The load is constant and requires throttling to 100 psia between points 1 and 2 in order to hold the load.

The turbine exhausts to 2 psia.

In order to conserve energy, it is desired to bleed off a fraction of the steam at point 3 (which is at 30 psia)

for feed water heating so that the throttle can be fully open without changing the load.

The isentropic efficiency in both turbine stages is 86%.

a.) What is the maximum percentage of steam that can be bled without reducing the work output?

b.)What is the maximum temperature to which returned water at 60 psia and 60 degrees F can be heated?

If you cant see image of problem heres a link http://imgur.com/xFoNlOn

I already found all the h's (enthalpy) and all the properties for each state. I just need a equation or somthing for part a

A power plant is connected to a supply of 150 psia steam at 500 degrees F. The load is constant and requires throttling to 100 psia between points 1 and 2 in order to hold the load. The turbine exhausts to 2 psia. In order to conserve energy, it is desired to bleed off a fraction of the steam at point 3 (which is at 30 psia) for feed water heating so that the throttle can be fully open without changing the load. The isentropic efficiency in both turbine stages is 86%. What is the maximum percentage of steam that can be bled without reducing the work output? What is the maximum temperature to which returned water at 60 psia and 60 degrees F can be heated? If you cant see image of problem heres a link http://imgur.com/xFoNlO

Explanation / Answer

in part a you need to find out the quality of steam

first find s at point 2 from T=500 and P=100psia

s2=s3 so with s3 and p=30psia we find T3s

isoentropic efficeiency of high turbine=(T2-T3a)/(T2-T3s)=0.86

T2=500 degree

T3s calculated above we find T3a

with T3a and p=30psia we find s3a

with s3a and p=2psia
we find T4s,

0.86=(T3a-T4a)/(T3a-T4s)

find T4a in this equation

let y be bled out

work of turbine=(h2-h3a)+(1-y)*(h4a-h3a)

h4a and h3a can be found out from T3a and T4a

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