Page 335 - Steam Turbines Design, Applications, and Rerating

Chapter
15

Elliott Shortcut Selection Method

for Multivalve, Multistage

Steam Turbines

Manufacturers and their computers are usually available to assist the
user with turbine selection. Using these resources, the purchaser
should be able to evaluate the options available for each application.
Blade stresses, thrust loads, stage pressures, temperatures, and other
pertinent information are speedily determined with the computer’s
help (see later). Many manufacturers, in fact, use the computer to cal-
culate the efficiency of each stage and of the entire turbine. In other
words, every stage of every machine is completely defined before a pro-
posal is made. The user is thus assured of getting the most reliable tur-
bine at the highest possible efficiency.
In the early stages of planning, the engineer may want to do some
approximate turbine selecting of his own. A Mollier diagram and some
examples are included to enable you to:

1. Estimate full and part load steam rates
2. Find stage pressures and temperatures
3. Estimate an extraction turbine

15.1 Approximate Steam Rates

Figures 15.1 and 15.2 can be used to determine an approximate tur-
bine efficiency when horsepower, speed, and steam conditions are
known. In many instances an approximate efficiency may well serve
the purpose since the parameters mentioned may change.

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