Page 48 - Steam Turbines Design, Applications, and Rerating

Chapter
2

Turbine Casing and Major

Stationary Components

Mechanical drive steam turbines for compressors and pumps, as well
as cogeneration turbine-generator sets, can be designed for inlet steam
conditions ranging from 2000 psig/1005°F (138 bar/541°C) down to
nearly atmospheric pressures with saturated inlet temperatures.
These turbines can also have multiple provisions for the admission or
extraction of steam for various process uses. Uncontrolled steam
extractions are often used for feedwater heating where the pressure
and energy of the extracted steam is approximately proportional to the
flow of steam through the turbine. When controlled steam pressure or
flow is required, automatically regulated extraction valve gear assem-
blies are provided within the turbine casings to maintain a constant
pressure or flow at the extraction point.
The various steam inlet and exhaust schemes obviously call for dif-
ferent casing configurations. Associated with casings are a number of
different valve geometries, stationary dividing walls, or guide blades
directing steam flow to rotating blades, etc.
For purposes of clarity of presentation, our text deals with this col-
lectively under the umbrella heading stationary components as
opposed to the turbine rotor that rotates.

2.1 Casing Design
Based on capable manufacturers’ experience in developing casing
materials and construction for high inlet steam conditions, designs
employ either a single- or double-shell construction. Both of these shell
configurations have been used on many applications and have accu-
mulated years of operation. These construction methods facilitate the

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