Page 298 - Compression Machinery for Oil and Gas

Screw Compressors Chapter 6 283

The second important gas property is the isentropic exponent k. A high isen-
tropic exponent leads to high discharge temperatures due to internal compres-
sion as described in Chapter 2. If the discharge temperature exceeds the design
limits of the compressor, then a liquid injection into the suction nozzle may be
used to cool the gas.

Actual Suction Volume Flow and Power Consumption Versus
Molecular Weight for Oil-Flooded Screw Compressors

Figs. 6.31 and 6.33 demonstrate these relationships for oil-flooded screw com-
pressors. The 50% rotor diameter machine in this example has a lower tip speed
limit than the 100% rotor diameter machine, so the flowrate is quite a bit lower.

10,000
9000
Suction volume flow (m 3 /h) 7000 100% rotor diameter
8000

6000
50% rotor diameter
5000
4000
3000
2000
1000
0
10 20 30 40 50
Molecular weight (kg/kmol)
FIG. 6.31 Volume versus mole weight for oil flooded screw compressors.

3000

Power consumption (kW) 2000 100% rotor diameter
2500

1500
50% rotor diameter
1000

500

0
0 10 20 30 40 50
Molecular weight (kg/kmol)
FIG. 6.32 Power versus mole weight for dry screw compressors.