Steam Turbine Efficiency and Steam Bleeding

[PieD94]

Homework Statement

[/B]
Steam is expanded from 90 bar, 412°C to 4.5 bar saturation in a high pressure turbine, after-which a certain percentage of the steam is bled off to a feed heater. The remaining steam is then expanded through a low pressure turbine to 1.0 bar and dryness fraction of 0.93. All ‘steam’ entering the feed pumps shall be a saturated fluid. Produce a schematic diagram of the system, together with appropriate T-s diagram. Using steam tables only, calculatea) the isentropic efficiencies of both turbines

b) the percentage of steam bled of to the feed heater

c) the power generated by the turbines per unit mass of steam leaving the boiler

d) the energy available for low grade heating from the condenser


Neglect feed pumps and state any assumptions made

Homework Equations

The Attempt at a Solution

(a) Isentropic Efficiency = (h1-h2/h1-h2s)

= (3152-2745)/(3152-2525)

=407/627

= 0.6491

Isentropic Efficiency for high pressure turbine= 65%

(b) Assuming that the open feedwater heater is adiabatic.

Im not sure if a is right and as for the other questions, I am stumped. any help is appreciated. I am getting 0.63/0.64 for question b) however I've a feeling that is far too high

 

[rock.freak667]

For part a) how did you go about calculating the dryness fraction at after the the superheated steam to the 4.5 bars ?Also, you should try to start off with the schematic and the T-s diagram as it will help a lot.