28.02.2013 Views

Handbook of Turbomachinery Second Edition Revised - Ventech!

Handbook of Turbomachinery Second Edition Revised - Ventech!

Handbook of Turbomachinery Second Edition Revised - Ventech!

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

flow path will continue to be developed and see an increasingly larger role in<br />

the design and retr<strong>of</strong>itting <strong>of</strong> large steam turbines.<br />

Improvements in turbine exhaust hoods and/or last-row blade<br />

performance can have some substantial consequences. Reducing hood loss<br />

will increase leaving loss and may increase the loss in last-row exit turning<br />

because <strong>of</strong> jet deflection. Only a fraction <strong>of</strong> the reduced hood loss in the last<br />

rotating row can be recovered. Similarly, increased blading efficiency also<br />

results in increased exit jet velocity and consequently higher hood loss.<br />

Neither <strong>of</strong> these trade<strong>of</strong>fs implies that there is no improvement in turbine<br />

performance.<br />

7. Moving to advanced steam conditions. Challenges to the integrity<br />

<strong>of</strong> the steam path will result from the constant push toward more aggressive<br />

operating conditions such as higher temperatures associated with advanced<br />

steam plants. Such advanced steam conditions may lead to higher<br />

thermodynamic efficiencies utilizing combined cycles employing cooling <strong>of</strong><br />

the gas turbine blades with steam from the steam turbine (approaching 60%<br />

Rankine cycle efficiencies) (Fig. 71). However, moving toward advanced<br />

steam conditions will tend to exacerbate many <strong>of</strong> the damage types currently<br />

affecting the steam path, thus imposing greater requirement for the<br />

evaluation and control <strong>of</strong> damage.<br />

Figure 71 Combined Rankine and Brayton cycles for improved overall cycle<br />

efficiency.<br />

Copyright © 2003 Marcel Dekker, Inc.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!