Page 349 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Chapter 8
Steam Turbines and

Turboexpanders *

Special Purpozre Steam Tlrrbines

While much attention has been devoted to new high-power, high-speed
centrifugal compressors, steam turbine drives have more often been the
cause of plant downtime.
Initially, problems peculiar to process drives were not given enough
thought. Unplanned shutdowns resulted. The combined requirements of
high speed, high power, and variable speed, associated with process
drives, have led to some rethinking by steam turbine manufacturers.
Rigorous operating conditions demand careful optimization between
process requirements and mechanical considerations when selecting,
maintaining, and operating a special purpose steam turbine such as is illus-
trated in Figure 8- 1.
Steam turbine types and applications are shown in Tables 8-1 and 8-2.
The second table shows that all types of steam turbines have a place in
process plants.
In some instances where the reason for the type in use is not clear-cut,
the back-pressure turbine may be favored because it is:

Lowest in capital cost.
Most suitable for high speeds.
Simplest in construction . . . and hence more reliable.

Condensing Tbrbine Disadvantages. The condensing turbine has several
disadvantages compared to the back-pressure turbine.

* Material related to special purpose steam turbines is edited from information furnished
by Wtinghouse Canada, Inc., Hamilton, Ontario, Canada. By permission.

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