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.