Page 299 - Compression Machinery for Oil and Gas

284 SECTION II Types of Equipment

FIG. 6.33 Power versus mole weight for oil flooded screw compressors.

However, this is a good representation of the consistency of these behaviors. It
can be seen that for both machine sizes, the power consumption and flowrate are
almost completely independent of the gas mole weight.

Power Consumption Versus v i for Oil-Flooded Screw Compressors

As mentioned previously, some oil-flooded screw compressors have a fixed v i ,
while others have the ability for the v i to be varied. In either case, it is important
to consider the working v i of the machine in the context of the working pressure
ratio of the machine. The v i should be selected or set such that the final internal
pressure of the machine matches the discharge header pressure as closely as
possible. Fig. 6.34 demonstrate this for oil-flooded screw compressors. In addi-
tion to the impact on power consumption, a large mismatch between internal
and external pressures can lead to operating problems as mentioned previously
in the Overcompression section.

FIG. 6.34 Power versus vi for oil flooded screws.