Page 83 - Steam Turbines Design, Applications, and Rerating

64 Chapter Three

Figure 3.16 Advanced tilting-pad bearing design with Spray Bar Blockers ® and
Bypass Cooling ® . (RMT, Wellsville, N.Y.)

ating temperatures, was effective in reducing bearing metal tempera-
tures from 235 to 200°F. This design also employs offset pivoted pads to
further reduce pad operating temperatures.
Figure 3.16 is a photo of an advanced evacuated housing design with
babbitted chrome-copper pads. Since the chrome-copper material’s
heat transfer properties are a factor of six greater than those of steel,
they are very effective in taking the heat away from the babbitt. This
effect is amplified by the heat transfer grooves located on the back of
the pads. Cool inlet oil is injected into these grooves, carrying the heat
away from the pad body. This ByPass Cooling ® oil does not participate
in lubricating the bearing. Instead, it is routed out of the heat transfer
grooves and directly into the oil drain.
Another feature of the bearing shown in Fig. 3.16 is the Spray Bar
Blocker . This device sprays cool inlet oil directly into the pad’s leading
®
edge, shielding it from the hot oil that exits the preceding pad’s trailing
edge. It also effectively blocks much of the hot oil carryover from the
upstream pad, preventing it from entering the leading edge of the
downstream pad. The hot oil is then allowed to exit the bearing. This
advanced evacuated housing bearing is extremely effective in reducing
bearing operating temperatures, enabling operation at extremely high
surface velocities of up to 400 ft/s, and thus allowing steam turbines to
operate at much higher speeds.