Steady-State Power Operation of a Supercritical Carbon Dioxide Brayton Cycle Bechtel Marine Propulsion Corporation Bettis Atomic Power Laboratory West Mifflin, PA Page 1 Supercritical CO 2 Power Cycles Symposium September 9-10, 2014 Eric Clementoni Timothy Cox
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Steady-State Power Operation of a
Supercritical Carbon Dioxide Brayton Cycle
Bechtel Marine Propulsion CorporationBettis Atomic Power LaboratoryWest Mifflin, PA
Page 1Supercritical CO2 Power Cycles Symposium September 9-10, 2014
Eric Clementoni
Timothy Cox
Presentation Summary
• S-CO2 Brayton Cycle Integrated Systems Test (IST)
Overview
• System Operational Overview
– Loop startup
– Normal Operating Conditions
• Operational Test Results
Page 2Supercritical CO2 Power Cycles Symposium September 9-10, 2014
• Operational Test Results
– Normal Power Generation
– Maximum Power Operation
• 100 kWe IST has been main S-CO2
development focus of BMPC
• Simple Brayton cycle
– Single variable speed turbine-compressor
– Single constant speed turbine-generator
IST Overview
Page 3Supercritical CO2 Power Cycles Symposium September 9-10, 2014
– Single constant speed turbine-generator
– Single recuperator
• Focus on system control
– Rapid startup
– Power changes
– Shutdown
CompressorTurbine
Heat
Source
Generator Turbine
Recuperator
Precooler
Sea WaterCooling
Water
IST Physical Layout
Hot Oil System
Turbo-Compressor
Recuperator
Turbine Throttle Valves
Compressor Recirculation Valve
Page 4Supercritical CO2 Power Cycles Symposium September 9-10, 2014
Turbo-Generator
Precooler
Leakage Collection Compressors
IST Physical Layout
Turbo-Generator
Page 5Supercritical CO2 Power Cycles Symposium September 9-10, 2014
Recuperator
Precooler
Turbo-Compressor (not
visible)
IST Turbomachinery
Turbo-Generator
Thrust Bearing
Page 6Supercritical CO2 Power Cycles Symposium September 9-10, 2014
Turbo-Compressor
Compressor/Diffuser Turbine
Thrust Bearing
Loop Startup
• Heat up system to supercritical conditions and
achieve normal system mass
• Start up both turbomachines to 37,500 rpm
• Heat up system to normal turbine inlet
Page 7Supercritical CO2 Power Cycles Symposium September 9-10, 2014
• Heat up system to normal turbine inlet
temperature
– Transition TG from motoring to generating
• Establish normal compressor inlet conditions
Normal Power Operation
• Turbine-generator operates at fixed speed
with load regulated to maintain speed
• Turbine-compressor thermal-hydraulically
balanced
Page 8Supercritical CO2 Power Cycles Symposium September 9-10, 2014
balanced
– Turbine power = compressor power + losses
• Power level changed by position of
compressor recirculation valve
– Valve nearly full closed at maximum system power
IST Power Limitations
• TG output voltage droops as power is increased
• Voltage droop affects speed and rotor position
algorithm causing delay in firing of IGBTs and
degradation of power factor
Page 9Supercritical CO2 Power Cycles Symposium September 9-10, 2014
degradation of power factor
– Limited to 24 kWe DC (~30 kWe AC) @ 55,000 rpm
• Permanent magnet rotor remagnetized to
increase output voltage
– Resulted in higher power capability
– New target ~50 kWe AC @ 60,000-65,000 rpm
Maximum Power OperationNovember 2013
**40 kW on power
Page 10Supercritical CO2 Power Cycles Symposium September 9-10, 2014
**40 kW on power
analyzer
0
10
20
30
40
50
Po
we
r (k
W)
or
Eff
ieci
en
cy (
%)
TG Power
TC Power
Brayton Power
Brayton Efficiency
System Up-Power
Page 11Supercritical CO2 Power Cycles Symposium September 9-10, 2014
-10
500 1000 1500 2000 2500 3000 3500 4000
35000
40000
45000
50000
55000
60000
500 1000 1500 2000 2500 3000 3500 4000
Sp
ee
d (
rpm
)
Time (seconds)
TC Speed
2
4
6
8
10
12
Flo
w (
lbm
/s)
TG Turbine
TC Turbine
Compressor
Compressor Recirc
System Mass Flow Rates
Page 12Supercritical CO2 Power Cycles Symposium September 9-10, 2014
0
35000
40000
45000
50000
55000
60000
500 1000 1500 2000 2500 3000 3500 4000
Sp
ee
d (
rpm
)
Time (seconds)
TC Speed
Compressor Map
Model Prediction for
Design Operating Conditions
Page 13Supercritical CO2 Power Cycles Symposium September 9-10, 2014
Test Data
Summary
• IST continuing to make progress towards the
purpose of demonstrating controllability of
the S-CO2 Brayton cycle
• System operation up to 40 kWe AC has been
Page 14Supercritical CO2 Power Cycles Symposium September 9-10, 2014
• System operation up to 40 kWe AC has been
demonstrated with good agreement with
model predictions
• Normal power operation over range of power
levels up to ~50 kWe planned
Acknowledgements
• This paper summarizes work that has been
performed a number of devoted engineers,
scientists, technicians, and support personnel
at the Bechtel Marine Propulsion Corporation
Page 15Supercritical CO2 Power Cycles Symposium September 9-10, 2014
at the Bechtel Marine Propulsion Corporation
and our subcontractors. This paper would not
be possible without the efforts of this team.
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