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MONITORING COMPRESSOR
EFFICIENCY FOR MAXIMUM
PERFORMANCE
Presented at PowerGen 2007By Tina L. Toburen, P.E.
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Gas turbines, Compressors
and Air Density
PV=nRT
Increase mass flow by
Increasing Pressure
Increasing Volume
Reducing Temperature
m=PV / ZRT
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Impact of Compressor Performance
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Impact of
1% Lost Compressor Efficiency
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Isentropic Compressor Efficiency
( )kk
processsP
P
T
T
Z
Z1
1
2
2
1
2
1
,
=
Isentropic Process Efficiency
Isentropic Work Efficiency( )
==
2
1
1
2
1
1
2
,,
1
1
Z
Z
T
T
P
P kk
workaworks
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Compressor Efficiency Polytropic Work Efficiency
where
( )
=
=
1
1
1
1
2
1
1
2
1
1
2
,
n
n
k
kor
Z
Z
TT
P
P
p
n
n
workp
=
21
1
TP
TPln
PPln
n2
1
2
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Parameters to Monitor for Compressor
Performance Compressor inlet temperature and pressure
Compressor discharge temperature and pressure
Rotor Speeds (HP and LP, if applicable)
Operating mode of unit (base, part load, T3control, T48 control, etc.)
Auxiliary systems in use (inlet cooling, SPRINT,
bleed heat, etc.)
m=PV / ZRT
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Factors that Impact Compressor
Performance
Inlet temperature
Pressure Ratio Humidity
m=PV / ZRT
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Expected Changes to Compressor
Discharge Temperature
40%
50%
60%
70%
80%
90%
100%
110%
120%
130%
30% 40% 50% 60% 70% 80% 90% 100% 110% 120% 130%
Pressure Ratio (as percent of Design)
ExpectedCOT(aspercentofDesign)
CIT=40
CIT=60
CIT=80
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Compressor Performance Ratio Step 1: Calculate current operating compressor
efficiency
Step 2: Determine expected compressordischarge temperature (CDT) at current operating
conditions Step 3: Determine expected compressor
efficiency based on calculated CDT
Step 4: Calculate compressor performance ratioas measured divided by expected efficiency
Step 5: Trend performance ratio over time
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Using Compressor Efficiency
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Optimizing Water Wash Schedules
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Conclusions Compressor performance has a significant impact
on overall plant performance
There are multiple means of calculatingcompressor efficiency pick one
A real-time performance monitoring system is notrequired to trend compressor efficiency. Planned periodic manual calculations can lead to a greater
understanding of expected efficiencies and fouling rates
Monitoring compressor efficiency can lead tooptimized water washes, resulting in: Higher output Lower heat rate Lower CO2 emissions
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MONITORING COMPRESSOR
EFFICIENCY FOR MAXIMUM
PERFORMANCE
For more information, contact:
Tina L. Toburen, P.E.
425-821-6036
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