Page 375 - Compression Machinery for Oil and Gas

356 SECTION II Types of Equipment

FIG. 7.44 Bearing housing.

Journal bearings—Journal bearings provide a means to support the rotating
rotor radially on an oil film. Bearings are typically made of steel backing with a
layer of lead-tin babbitt to help with wear and reduce journal scoring and dam-
age during start-up and low load conditions. Major journal bearing designs
include liner, tilting pad, and spherical seat tilting pad, flexural pivot. Also,
there are different styles of lubrication including flooded design and direct
injected designs. Bearing instrumentation includes use of thermocouples and
RTD (resistance temperature detectors)’s to measure bearing metal tempera-
ture. In addition, bearing housings and drains are outfitted with thermowells
to measure specific bearing oil throw-off temperatures (Fig. 7.45).
Thrust bearing—Thrust bearings serve to manage a steam turbine rotor axial
thrust by providing a lubricated surface for the rotor to thrust against. Two main
categories of thrust bearings designs include, self-leveling designs which con-
sist of a base ring, leveling links, and individual pads with pivot on back and
fixed ring designs with tapered lands which are often found in with older
designs. The self-leveling feature aids in matching pads with the changing
thrust disk location and perpendicular relationship to steam turbine axis. Bear-
ings are typically made of steel backing with a layer of lead-tin babbitt to help
with wear and reduce journal scoring and damage. Also, there are different
styles of lubrication including flooded design, and direct injected designs. Bear-
ing instrumentation includes use of thermocouples and RTD’s to measure bear-
ing metal temperature as well as load cells to measure thrust load (Fig. 7.46).

Selection

The selection process for a mechanical drive steam turbine depends on the type
of process, the available steam conditions, the required power, and the speed
range. In addition, there may be steam rate and possibly casing connection size
requirements.
Basic steps for ideal back pressure turbine:
1. Establish a TSR (from inlet, exhaust steam conditions, and required power).
2. Determine isentropic heat drop across turbine.