Page 161 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

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Compressor Best Practices Be st Practice 3.7

Fig 3.7.13 Oil separation system (Courtesy of Man/GHH)

K-1
action, unfortunately, is taken after installation of the com- T 2 P 2 ð K Þ

pressor. These facts are presented in Figure 3.7.14. T 1 ¼ P 1
Figure 3.7.15 deﬁnes the performance relationships used for
screw compressors.
In phase 1 of project:
Conﬁrm compatibility of oil with process
Conﬁrm oil will not be degraded by process gas
Visit installations to conﬁrm vendor claims
Screw compressor performance relationships
3
CFM = (RPM) (DM ) (L/DM) (C 0 ) where:
Fig 3.7.14 Flooded screw reliability DM = male rotor diameter – inches
L/DM = length to diameter ratio of male rotor
C 0 = rotor proﬁle constant
4 + 6 proﬁle = 15.853
Performance relationships 3 + 4 proﬁle = 18.082
4 + 6 ‘A’ proﬁle = 17.17
All screw compressors are positive displacement compressors. 4 + 6 ‘D’ proﬁle = 16.325
Performance of screw compressors is calculated using the adi- 3 + 4 ‘A’ proﬁle = 19.372
abatic process. An adiabatic compression process assumes that 6 + 8 ‘D’ proﬁle = 10.364
no heat is lost in the compression process. The path of com-
pression is deﬁned by: Fig 3.7.15 Performance relationships

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