Page 165 - Compression Machinery for Oil and Gas

Integrally Geared Compressors Chapter 4 153

Large gear
Increased pitch line velocity

→
Pinion power

Small gear

Pinion rotational speed →
FIG. 4.16 Effect of pinion speed and gear size on pinion power.

2 b
u B
P ¼ p B 2u pl (4.5)
πn d B
In the lower part of Fig. 4.16, it is shown why thrust forces originating from
different pressures acting on the impellers also have an impact on the bearing
reactions, F BT . A resulting gas thrust, F gas , has to be counteracted by a thrust
collar force, F TC . Since the contact of the thrust collar with the corresponding
surface on the bull gear is not in the pinion shaft centerline, the thrust collar
force F TC creates a moment which tries to turn the pinion shaft around an axis
perpendicular to the axis of rotation. Additional bearing reaction forces, F BT ,
inhibit this movement.
Because the bearing reactions to weight force, gear tooth force, and thrust
collar moment are not necessarily in the same plane, the resulting bearing reac-
tions for any pinion may point in different directions, even upward if the tooth
force is large in comparison to the weight of the pinion. As the tooth force and
the gas thrust are dependent on the operating point of the compressor, so are the
bearing reaction force magnitudes and directions. This changes the bearing
stiffness and damping so that the rotordynamic behavior of any pinion of an
IGC has to be verified for different loads.

Lubrication
In addition to lubricating the journal and axial bearings like in all other com-
pressors, an IGC also requires lubrication and cooling for the gear meshes
and thrust collars. Since the bearing load in an IGC is much higher than in inline