Page 295 - Compression Machinery for Oil and Gas

280 SECTION II Types of Equipment

9000
Suction volume flow (m 3 /h) 7000
8000

6000
5000
4000
3000
100% tip speed
2000
75 % tip speed
1000
50% tip speed
0
1 1.5 2 2.5 3 3.5 4 4.5 5
Discharge pressure (bar abs)
FIG. 6.26 Flow versus discharge pressure for a dry screw compressor.

FIG. 6.27 Flow versus discharge pressure for an oil flooded screw compressor.

Power Consumption Versus Discharge Pressure
Fig. 6.28 shows the power consumption versus discharge pressure with different
built-in volume ratios v i . Compressor speed, gas molecular weight, and suction
pressure are kept constant. For constant suction pressure the power consump-
tion increases linearly with the discharge pressure. For a small built-in volume
ratio, the slope of the power curve is steep resulting in a rapid growth of power
consumption with increasing pressure ratio. For a large built-in volume ratio v i,
the slope is much less than for a small v i but on the other hand the power