Page 445 - Compression Machinery for Oil and Gas

424 SECTION III Applications

operating power cost of the selected single-stage rotary screw compressor with
a 1100-hp/4160-3-60 motor and a three-stage reciprocating compressor with a
700-hp/460-3-60 motor. The client provided variables for the project electrical
cost, operational hours per year at various suction pressures (over range of 20–
60psig). The result was quite interesting, because the three-stage reciprocating
compressor had an annual power cost savings of over $90,000 per year, even
though it required a suction pressure regulator to maintain the minimum suction
pressure of 20 psig to prevent rod loading at higher suction pressures. It did not
have any other capacity control. There was about a 15% premium initial cost for
the reciprocating compressor, plus additional electrical cost savings for not hav-
ing to bring in 4160/3/60 power that the rotary screw motor would have
required. So, the client opted to select the reciprocating compressor.
Additional FGC power cost savings are available if the turbine has a range of
fuel gas pressure requirements, based on the combustion air temperature or
some other performance variable. This would require the turbine manufacturer
to provide a 4-20-mA signal from the turbine PLC control panel to the FGC PLC
control panel with the required fuel gas pressure. The FGC PLC control panel
can be programmed to automatically adjust the FGC discharge pressure set
point to match the actual fuel gas pressure required by the turbine. The FGC
energy savings is due to not having to always operate at the highest fuel gas
pressure. The FGC PLC program should default to the highest required dis-
charge pressure, in case the signal from the turbine PLC panel is lost, to avoid
nuisance FGC and turbine trips.
The FGC is a unique and growing downstream compressor application. By
considering the various points outlined in this chapter, the design engineer can
make several contributions to the overall fuel gas system reliability and
efficiency.

References

[1] E. Worrell, C. Galitsky, Energy Efficiency Improvement and Cost Saving Opportunity for
Petroleum Refineries, LBNL-56183, Ernest Orlando Lawrence Berkeley National Laboratory,
Berkeley, CA, 2005.
[2] H. Bloch, Application considerations, in: Compressors and Modern Process Applications, John
Wiley & Sons, Inc., Hoboken, NJ, 2006.
[3] C.B. Meher-Homji, T. Matthews, A. Pelagotti, H.P. Weyermann, LNG turbomachinery,
in: Proceedings of the 1st Middle East Turbomachinery Symposium (METS-I), Feb 13–16,
2011, Doha, Qatar, 2011.
[4] API Standard 617, Axial and Centrifugal Compressors and Expander-Compressors for Petro-
leum, Chemical and Gas Industry Services, seventh ed., American Petroleum Institute,
Washington, DC, 2002.
[5] J.M. Sorokes, J.A. Kopko, High inlet relative Mach number centrifugal compressor impeller
design, in: Proceedings of ASME Turbo Expo 2007 Power for Land Sea and Air, Montreal,
Canada, Paper No. GT2007-27864, 2007.