Page 143 - Compression Machinery for Oil and Gas

130 SECTION II Types of Equipment

TABLE 3.3 Trigger Points for Restage Parameters

Percent
Change <25% 25%–50% >50%
<15% 15%–31% >31%
Φ 1
<5% 5%–19% >19%
Ψ 1
<5% 5%–15% >15%
P 1
HP <3% 3%–13% >13%

coefficient, the trigger point for restage consideration for next overhaul is when
the parameter drifted 5%–15%. If they drifted more than 15%, that is, the trigger
for immediate restage consideration. The flow coefficient trigger points are
25% for next overhaul and 50% for immediate consideration.
The other general rule is that a compressor restage is recommended when the
efficiency is less than 6% of peak efficiency and power is a limiting factor.
Q 1
Φ 1 ¼ 3 is the inlet flow coefficient, for compressors, using the first
ð D 2 Þ N
compressor inlet flow coefficient.
H isen
Ψ isen ¼ is the isentropic head coefficient for single body compres-
ð D 2 NÞ 2 k 1
P 2
sor, Ψ isen ¼ Cp T 1 2 k 1 for compressors using the total pressure
ð D 2 NÞ
P 1
ratio and the first compressor speed and impeller tip diameter.
References

[1] T. Allison, J. Moore, A. Rimpel, J. Wilkes, R. Pelton, K. Wygant, Manufacturing and testing
experience with direct metal laser sintering for closed centrifugal compressor impellers, in: Proc.
of 43rd Turbomachinery & 30th Pump Users Symposia, September 23–25, Houston, TX, 2014.
[2] J. Sorokes, Selecting a Centrifugal Compressor, 2013.
[3] R. Kurz, The Physics of Centrifugal Compressor Performance, PSIG, Palm Springs, CA, 2004.
[4] V. Huetten, T. Krause, V.A. Ganesan, C. Beer, S. Demming, VSDS motor inverter design con-
cept for compressor trains avoiding interharmonics in operating speed range and verification,
in: Turbosymposium 2013, Tutorial 10, 2013.
[5] Fluid Sealing Association Gasket Division Members, A guide to gasketing principles and best
practices, in: Proceedings of the Forty-First Turbomachinery Symposium, September 24–27,
2012, Houston, TX, 2012.
[6] J.M. Vance, B. Murphy, F. Zeidan, Machinery Vibration and Rotordynamics, Wiley, Hoboken,
NJ, 2010.
[7] API Recommended Practice 684, API Standard Paragraphs Rotordynamic Tutorial: Lateral
Critical Speeds, Unbalance Response, Stability, Train Torsional and Rotor Balancing, second
ed., American Petroleum Institute, Washington, DC, 2005.