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Analyzing Compressor Performance

"Performance" thus involves several characteristics, most notably energy consumption of the compressor in this current age of
energy short supply.  Performance is largely achieved by the equipment vendors, but fully maintained by the plant site.  
Damage to performance occurs naturally in normal "wear and tear" from long term running of the equipment, as well as from
accidental or inadvertent damage from incidents such as compressor surge and vibration, due to speed or flow control
problems and rotor/impeller imbalances.

From the air compressor performance data shown, several points can be noted.  First, the compressor did fairly closely
perform, but did not exactly perform according to design efficiencies at initial start-up.  A lot of considerations can come into
play in analysis of these differences, including ambient conditions, required final discharge pressure, the condition of
inter-coolers, etc.  The biggest point would be that the 4th stage never met design efficiency expectations.  (This was true of
the original equipment before revamp too, thus the incremental efficiency improvement was achieved with the compressor
retrofit project.)

There are mild "inconsistencies" in the compressor performance data.  Efficiency of stages should not increase over time.  
Sometimes this appears to occur, particularly for two reasons.  First, of course, there may be slight error in the temperature
and pressure test data that represents the operating efficiency of the machine.  Second, the compressor can operate in an
"envelope" of varying efficiencies, dependent upon the operating capacity and impeller speed through individual sections of the
machine.  (Example, Stage 2 at 1 service month)  The loss of compressor efficiency from normal wear and tear due to
continuous operation, typically can amount to approximately 1 percentage point efficiency decrease per year.
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