goals of the workshop and targets for sco2 power cycle integration with thermal … ·...

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Goals of the workshop and targets for sCO2 power cycle integration with thermal energy storage

Dr. Rajgopal Vijaykumar, Technology Manager

USDOE sCO2 Workshop 2019

October 31, 2019


Focus: sCO2 Power Block Integrated with TES

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Example Power Block: RCBC

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• Make Utility Operators Comfortable with sCO2 Power Block Integration with TES

• TES is a Critical Feature that Decouples Energy Collection from Discharge to Grid, but no Operational Experience

• Need to Gain Experience by Operating at Temperatures of Today’s Plants

• Overcome Operator O&M Concerns by developing an Integrated Power Block and Robust Control Strategy

Commercialization Pathway for sCO2 Power Cycle

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• While Working on 700°C, in order to gain experience:

• Target TIT down to 550°C - 620°C (Piping not high-nickel alloy)

• Materials for Piping, tanks, ready, available and not very costly

• For turbomachinery, easier casing, impeller and seal design and fabrication

• Focus on integrated operation of turbomachinery/heat exchangers and TES for ≥1,000 hours; utility operators comfort

• Interaction of Materials, Temperature and SubComponentDesign still to be resolved

sCO2 Integration with Power Plants: Materials Issues

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Compressor

Pre-Cooler

HT Recuperator

Seals Expander

PHX

Piping Tank

Comfort Zone for Fabrication and Testing


• Current generation plants use Nitrates as TES

• 60-40 NaNO3/KNO3; not an eutectic

• Liquidus = 222°C

• Temperature Limit ~600°C

• Low Vapor Pressure

• Reasonable Specific Heat (1.545 kJ/kg°C) and Density (>1,700 kg/m3)

• GEN3: Chloride Salt and Solid Particles for 700°C

Thermal Energy Storage Fluid

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• Similar for Parabolic Trough and Power Tower

• General Dimensions 120’(D) X 40’(H)

• getting bigger (Noor 153’ X 46’) ~18,000 m3; 2,700 MWt

• Limits on H & D Set by Soil Bearing Load (for H) and by 1.5” thickness for Steel Plates, no Heat Treat (for D)

• Bruce counts 82 Tanks built so far

• 290°C Carbon Steel Cold Tank and 565°C Stainless Steel Hot Tank Operating Temperatures

TES Tank Design for Nitrate Salt

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• Specific Requirement for CSP: Molten Salt->sCO2

• Approach Temperatures of 15-20°C Indicated

• For ~250 MWT, Shell and Tube Heat Exchangers can be quite expensive

• MicroChannel Heat Exchangers Have Not been Developed to Even Facility Scale

• Differences Between Molten Salt and sCO2 Channels for Pressure, Thermal Conductivity.

Primary Heat Exchanger

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Major Issue for sCO2 Power Block Integration with TES

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T-S Cycle Plot for Turbine Inlet temperature = 550 C



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P-h Cycle Plot for Turbine Inlet temperature = 550 C

150°C



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Mismatch between ΔT for TES and Optimized ΔT for sCO2 Cycle

565°C

290°C

550°C

400°CsCO2


• Dagget, CA • Denver, CO

Ambient Air Temperatures at Representative CSP Sites

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-10

0

10

20

30

40

50

0 2000 4000 6000 8000 10000

Tem

per

atu

re (

°C)

Hour of the Year -20

-10

0

10

20

30

40

0 1728 3456 5184 6912 8640

Am

bie

nt

tem

pe

ratu

re, °C

Hour of the Year


• Ambient Temperature + PreCooler Design Sets Compressor Inlet Temperatures

• Large Swings in Ambient temperature, both, on a Daily basis and Seasonal Basis

• Traditional A-Frame Air Coolers: Can they Can Maintain Compressor Inlet Temperature in the 35-40°C?

• MicroChannel ACHEs have not Been Designed

• Reduced PreCooler approach Temperatures and ΔP Needed for Maximum Cycle Efficiency.

Operating sCO2 Cycles with Air Coolers

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• Steady State Cycle Efficiency Decreases with Increasing Ambient Air Temperature

• Compressor Head Flow Curve and impact on wide range Performance

Ambient Air Temperatures at Representative CSP Sites

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0.38

0.385

0.39

0.395

0.4

0.405

0.41

0.415

0.42

0.425

0.43

20 25 30 35 40 45 50

Cyc

le E

ffic

ien

cy

Ambient Temperature, °C


• Realized that Cost Competitive sCO2 cycles will need to be at higher Turbine Inlet Temperatures

• Lower capital costs due to simplicity and smaller size; addressed by Nate in a following presentation

• Lower (or zero) use of water, due to compatibility with dry cooling

• 4X more compact design or footprint (permitting more operational flexibility, rapid startup and shutdown)

sCO2 Cycles Need to be Competitive with Steam

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System Temperature (oC) Conversion Efficiency Capital Cost ($/kWe)

Super-critical Steam 540 – 620 ~40-45% 1,200

Super-critical CO2 550 - 649 ~41-46% <900


sCO2 Cycles Need to be Competitive with Steam

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Dostal V., Driscoll M. J., P. Hejzlar and N. E. Todreas, A Supercritical Carbon Dioxide Cycle for Next Generation Nuclear Reactors, MIT-ANP-TR-100, March (2004).


• Higher Turbine Inlet Temperature (Equivalent to Higher HTF Temperature)

Means to Higher Power Cycle Efficiency

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0.43

0.44

0.45

0.46

0.47

0.48

0.49

0.5

500 550 600 650 700 750 800

Po

wer

Cyc

le E

ffic

ien

cy

HTF Inlet Temperature into PHX

UA=2000 UA=3000

Power Cycle Efficiency as a Function of HTF inlet Temperature, for Varying Recuperator UA; Compressor

Inlet Temperature = 40°C; Turbine Efficiency = 91%; Main Compressor, Recompressor Efficiency = 85%


• Higher recuperation is Probably not as effective


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0.42

0.43

0.44

0.45

0.46

0.47

0.48

10000 15000 20000 25000 30000 35000 40000

Effi

cien

cy

UA (kW/K)

T_HTF=574 T_HTF=600 T_HTF=625 T_HTF=650

Power Cycle Efficiency as a Function of Recuperator UA, for a range of HTF temperatures Compressor

Inlet Temperature = 40°C; Expander Efficiency = 91%; Compressor(s) Efficiency = 85%


• Turbine Efficiency has a Significant Impact


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Power Cycle Efficiency as a Function of Expander Efficiency, for Varying HTF Temperature;

Compressor Inlet Temperature = 40°C; Main Compressor, Recompressor Efficiency = 85%;

UA = 3,000 kW/K

0.41

0.42

0.43

0.44

0.45

0.46

0.47

0.84 0.85 0.86 0.87 0.88 0.89 0.9 0.91 0.92

Cyc

le E

ffic

ien

cy

Turbine Efficiency

T_HTF = 574 T_HTF = 600 T_HTF = 620

Current SOA


• Compressor efficiencies somewhat Less So


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Power Cycle Efficiency as a Function of Compressor Efficiency, for HTF Temperature of

574°C; Compressor Inlet Temperature = 40°C; Expander Efficiency = 91%; UA = 3,000

kW/K

0.43

0.435

0.44

0.445

0.77 0.78 0.79 0.8 0.81 0.82 0.83 0.84 0.85

Cyc

le E

ffic

ien

cy

Compressor Efficiency

MC Efficiency RC Efficiency

Current SOA


• Higher Expander Efficiency requires Careful Turbomachinery Packaging and Reduced Expander Leakage

• Compressor and Expander development at a stage that Single Shaft/Single Casing Designs can Be Considered

• Packaging and reduction of seal count easier at 550 C than 700 C; give vendors breathing room

• Robust Control Strategy

Integrated Turbomachinery

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• Determine the scope of the Conceptual Research Effort

• Size of the Power Block

• Size of TES

• Ultimate Heat Sink Definition: Air Cooling Only or Cold Storage to Allow a Broader testing Program

• Turbomachinery Enhancements Considering the Narrowed Scope of Turbine Inlet Temperature (550-620°C)

• Heating the TES Fluid: FiredGas Heater or Pumped Thermal or Electrical?

• If a broader TIT (550-620 C) considered, methods for heating sCO2

Goals of the Workshop (1)

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• Turbomachinery Panel

• Breakout Panel Discussion discuss Steps beyond the current vendor efforts and STEP program

• Expander and Compressor Design Improvements

• Packaging Turbomachinery

• Dry Gas Seals and Bearing Subcomponents

• Power Block Size and testing hours in the Facility for Utility Operator Comfort

• O&M Reduction

• “Autonomous” Control Systems (?)


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• Heat Exchanger Panel

• Panel discussions with Vendors in the morning

• Heat Exchanger Breakout

• Recuperators

• Primary heat exchanger design unknowns

• Air Cooler design unknown

• For Wide Range Testing Program of Compressor-PrecoolerIntegration, look at Cold Storage?


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• Thermal Energy Storage

• Presentation on CSP experience with TES

• Facilities

• Experience in Existing Facilities Design and Operation

• Breakout Session on TES

• Nitrate Salt or ?

• Integration with sCO2 cycle a big Question mark

• How to heat the TES? Fired Heater or Grid-Heated?

Goals for this Workshop (4)

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Questions?Rajgopal Vijaykumar

[email protected] Manager, CSP, SETO

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