Page 1Supercritical CO2 Power Cycles Symposium March 29-31, 2016
Initial Transient Power Operation of a
Supercritical Carbon Dioxide Brayton Cycle
with Thermal-Hydraulic Control
Eric Clementoni
Timothy Cox
Martha King
Bechtel Marine Propulsion CorporationBettis Atomic Power LaboratoryWest Mifflin, PA
Page 2Supercritical CO2 Power Cycles Symposium March 29-31, 2016
Presentation Summary
• sCO2 Brayton Cycle Integrated Systems Test
(IST) Overview
• System Control
• System Operating Conditions
• Operational Test Results
Page 3Supercritical CO2 Power Cycles Symposium March 29-31, 2016
• 100 kWe IST has been main sCO2 development
focus of BMPC
• Simple Brayton cycle
– Single variable speed turbine-compressor
– Single constant speed turbine-generator
– Single recuperator
• Focus on system control
– Rapid startup
– Power changes
– Shutdown
IST Overview
CompressorTurbine
Heat
Source
Generator Turbine
Recuperator
Precooler
Sea WaterCooling
Water
Page 4Supercritical CO2 Power Cycles Symposium March 29-31, 2016
IST Physical Layout
Hot Oil System
Turbo-Generator
Turbo-Compressor
Recuperator
Precooler
Turbine Throttle Valves
Compressor Recirculation Valve
Leakage Collection Compressors
Page 5Supercritical CO2 Power Cycles Symposium March 29-31, 2016
IST Physical Layout
Turbo-Generator
Recuperator
Precooler
Turbo-Compressor (not
visible)
Page 6Supercritical CO2 Power Cycles Symposium March 29-31, 2016
IST Turbomachinery
Turbo-Generator
Turbo-Compressor
Compressor/Diffuser Turbine
Thrust Bearing
Page 7Supercritical CO2 Power Cycles Symposium March 29-31, 2016
Cycle Control Overview
• Turbine-generator speed fixed (60,000 rpm)
• Power level controlled via turbine-compressor speed
– Speed setpoint via lookup table
• Compressor recirculation valve position also function
of system power level
– More open at low power, nearly closed at max power
– Maintains adequate surge margin
• IHX outlet temperature and compressor inlet
temperature controlled via PI control of heater
power and cooling water flow, respectively
Page 8Supercritical CO2 Power Cycles Symposium March 29-31, 2016
Thermal-Hydraulic Control
IHX
GenMot/
Gen
Pre
coo
ler
Recuperator
Load regulated to
maintain 60,000 rpm
shaft speed
No load
PI control
regulates
TC shaft
speed
TC speed
setpoint
function of
TG load
setpoint
T T C
Page 9Supercritical CO2 Power Cycles Symposium March 29-31, 2016
IST Operating Conditions
• Maximum power limited to 40 kWe by motor-
generator controller performance
• Turbine inlet temperature reduced to 440°F
– Achieve max power with CCV4 nearly closed
• Compressor inlet of 96°F and ~1310 psia
– Stable compressor inlet density for small changes
in parameters
– Fixed total system mass � small changes in
pressure with power level due to cavity conditions
Page 10Supercritical CO2 Power Cycles Symposium March 29-31, 2016
System Power Transients
0
5
10
15
20
25
30
35
40
45
0 1000 2000 3000 4000 5000
TG
Lo
ad
(%
Po
we
r)
Time (seconds)
Generator Output
Load Setpoint
Page 11Supercritical CO2 Power Cycles Symposium March 29-31, 2016
Turbine-Compressor Speed Control
40000
42000
44000
46000
48000
50000
52000
54000
56000
0 1000 2000 3000 4000 5000
Turb
ine
-Co
mp
ress
or
Sp
ee
d (
rpm
)
Time (seconds)
Turbine-Compressor Speed
Speed Setpoint
Page 12Supercritical CO2 Power Cycles Symposium March 29-31, 2016
Compressor Recirculation Valve Response
0
10
20
30
40
50
60
0 1000 2000 3000 4000 5000
Co
mp
ress
or
Re
circ
ula
tio
n V
alv
e P
osi
tio
n (
% O
pe
n)
Time (seconds)
Page 13Supercritical CO2 Power Cycles Symposium March 29-31, 2016
Compressor Recirculation Valve Resistance
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 1000 2000 3000 4000 5000
Co
mp
ress
or
Re
circ
ula
tio
n V
alv
e C
v
Time (seconds)
Page 14Supercritical CO2 Power Cycles Symposium March 29-31, 2016
Summary
• IST operated over range of power transients
between 5% and 40% of design rating
• Thermal-hydraulic control strategy works very
well for transients evaluated to date
• Overall system response is very stable despite
large oscillations in compressor recirculation
valve position
Page 15Supercritical CO2 Power Cycles Symposium March 29-31, 2016
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
and our subcontractors. This paper would not
be possible without the efforts of this team.
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