Page 352 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Steam Turbines and Turboexpanders 331

Figure 8-1. Multivalve special purpose steam turbine.

Larger blades due to high steam volumes. Therefore low blade natu-
ral frequencies and increased risk of blade excitation exist.
Lower over-all reliability because of the need to provide a condenser,
ejectors, extraction pumps, etc.
High first cost caused by two factors:

a. A larger turbine due to high specific volumes
b. The extra cost of condenser, etc.

Poor operating cost because about two-thirds of the steam heat con-
tent is used in heating condenser cooling water.
Difficulty in measuring performance on site because of problems in
finding the steam energy at exhaust.
More costly boiler feedwater treatment to remove chlorides, salts
and silicates which would otherwise produce deposits or corrosion of
the blades.
Blade failures are more likely. The last few rows of blades are sub-
ject to erosion by the water droplets which are present in condensing
steam.