supercritical carbon dioxide brayton cycle for power...

Supercritical Carbon Dioxide Brayton cycle for power generation:

Major R & D efforts and directions

Pradip DuttaDepartment of Mechanical EngineeringDepartment of Mechanical Engineering

Indian Institute of Science, Bangalore, India

Green Power - Challenges & Innovation, NTPC Energy Technology Research Alliance (NETRA) June 08– June 09, 2017

Major advantages of CSP in Indian context

What is concentrating solar power (CSP)?

• Concentrated energy → heat up a fluid → produce steam → activate turbines → electricity

• PV : Directly converts sunlight into electricity

Major advantages of CSP in Indian context

• High conversion efficiency possible• Possibility of thermal storage, hybridization• Scalability; grid compatibility• Easy to establish indigenous manufacturing• Vast indigenous experience in thermal power technology

Main components of a CSP plant

SOLAR FIELD POWER PLANT

Parabolic Trough Technology

Compact Linear FrenselReflector Technology

Power Tower Technology

Different collector technologies

Conventional Steam based Solar Thermal Plant

C

Thermal Storage

Boiler /

D

4

Steam turbine2

3

Solar field

B

Pump 2

Boiler / Heat Exchanger

Pump 1A

1

Condenser

De-aerator

Pump 3

5

6

7

Line Focus & Single Axis Tracking Point Focus & Dual Axis Tracking

Parabolic DishParabolic Trough

Present Collector Technology Options

Solar TowerLinear Fresnel

•High capital expenditure (bulky power block)•Water intensive •Expansion into two-phase region, leading to blade corrosion; water treatment issuesLow thermal efficiency (2 phase heat addition;

Problems and Limitations of Steam-based Rankine Cycle Power Plants

12 June 2017 7

corrosion; water treatment issues•Low thermal efficiency (2 phase heat addition; limitation of turbine inlet temperature) •Not easily scalable: Viable for large scale only (> 50 MW)

CSP cost Arithmetic

Solar field cost ~ 60%

Solar field Power Plant

Aim: decrease cost (low cost structure, tracking, optics, coating materials)

Aim: increasecycle efficiency

coating materials)

Develop new cycles, new engines

Develop “disruptive” technologies

Resources

High insolationModerate insolation

Potential Technology innovations for distributed CSP

1) High Efficiency CO2 Brayton cycles (100 kW – 5 MW)Supercritical CO2 Brayton cycle: >50% cycle efficiency even at 700°C receiver temperature

• also being developed for next generation nuclear power plantsplants

2) Organic Rankine Cycle (ORC) systems (25 kW -1 MW)Challenge: scale down penalty

Brief Description of Brayton cycle

Closed Brayton cycle

Constant pressure heat addition andrejection.

Efficiency of Brayton cycle dependsonly on pressure ratio

Closed cycle gas turbines are simple,

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Closed cycle gas turbines are simple,compact, less expensive and have shorterconstruction periods:

→ Better overall economics.

Simple Recuperated Closed Brayton Cycle

T-S, Recuperated Closed Brayton Cycle

CO2 Brayton Cycles: New concept

power generation =20 kW compressor OD=1.5 cm

Sandia National Labs

Supercritical

Transcritical (2-phase heat rejection)

Transcritical (1-phase heat rejection)

Sub-critical (1-phase

Supercritical CO2 Brayton: >50% cycle η even at 700ºC

Smaller vol. flow rates, low compression work, compact power block

Sub-critical (1-phase heat rejection)

S-CO2 Thermodynamic Cycle

Supercritical CO2 (S-CO2)

Major advantages:• Very high cycle efficiency (~50%)• Compact power block• Dry cooling (waterless operation)

Heat source temp: 500-700°C

Heliostat field Schematic of S-CO2 Power Plant with Solar Field

Turbine

Regenerator

Compressor Air Pre Cooler

3

4 6

1

2

5

5Air inlet

Air exit

High Pressure

Low PressureReceiver

Solar Heat Input

Heliostat Field

• Dry cooling (waterless operation)• Versatile (solar, waste heat, nuclear)

Relative sizes of Steam and SCO2 turbine

Performance studies of Brayton cycles

1

10

100

1000

0 200 400 600 800 1000 1200

Pre

ssu

re (b

ar)

Enthalpy (kJ/kg)

1TN

2′TN 3′TN

4′TN6TN

5TN1S

2′S 3′S

4′S6S

5S

308 K 873 K

1SN

2′SN 3′SN

4′SN6SN

5SN

Transcritical (TN)

Supercritical (S)

Subcritical (SN)

Turbine

Regenerator

Boiler

1

5

2

3

6

4

iHTFoHTF

850

950

3′SN3′TN3′S873 K

P-h diagram

13

CompressorGas cooler

1 26

Parametric studies•Turbine expansion ratio•Low side pressure•Heat source temp. range

Outcome of studies• Cycle efficiency• Heat recovery• Flow rates• Entropy generation• Optimization

Working fluids studied• Air, CO2

250

350

450

550

650

750

850

0.5 1 1.5 2 2.5 3 3.5 4

Tem

per

atu

re (K

)

Entropy (kJ/kg K)

1SN

2′SN

6SN

5SN4′SN

1TN

2′TN 6TN

5TN

4′TN

1S

2′S6S

5S

4′S

308 K

T-s diagram

Thermal Efficiency and its optimization

15

20

25

30

35

Ov

era

ll th

erm

al e

ffic

ien

cy (%

)

Turbine inlet temp = 873 K

p1= 1 bar

p1= 85 bar

p1= 75 bar

p1= 70 bar

p1= 40 bar

Air, p1 = 1 bar

1

10

100

1000

Pre

ssu

re (b

ar)

1TN

2′TN 3′TN

4′TN6TN

5TN1S

2′S 3′S

4′S6S

5S

308 K 873 K

1SN

2′SN 3′SN

4′SN6SN

5SNTurbine eff= 75 %

Compressor eff= 80 %

Subrcritical CO2

Transrcritical CO2

supercritical CO2

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SN-CO2 cycle, TN-CO2 cycle, ∆ S-CO2 cycle,Key Conclusions

• S-CO2 performs the best.

• Ratio of regenerator heat recovery to externally supplied ~3

• Hence, proper design of regenerator a major challenge

10

1 2 3 4 5

Expansion ratio

Turbine inlet temp = 873 K1

0 200 400 600 800 1000 1200

Enthalpy (kJ/kg)

1SN 4′SN6SN

[1] Garg et al , Supercritical carbon dioxide Brayton cycle for concentrated solar power, J. Supercritical Fluids, 2013[2] Garg et al., Comparison of CO2 and Steam in Transcritical Rankine Cycles for Concentrated Solar Power, Energy Procedia, 2014

CO2 vs Steam

350

450

550

650

750

850

950

Tem

per

atu

re (

K)

2′TC

5TC

3′TC

(873 K)

3′

4′

2′

4

2

4′TC

iHTF

oHTF

350

450

550

650

750

850

950

1050

1150

Tem

per

atu

re (

K)

3′ (873 K)

3′

4′2′

42

1

iHTF

o

CO2 Transcritical Condensing cycle Supercritical Steam cycle

15

250

350

0.5 1 1.5 2 2.5 3Entropy (kJ/kg K)

1TC

2′TC

300 K

2

1

6TC

250

350

0 2 4 6 8 10

Entropy (kJ/kg K)

12′ 300 K

4′

oHTF

• More heat source temperature required for the same turbine inlet temperature for steam.• Easier choice of Heat transfer fluid (HTF) for CO2 .

S-CO2 has potential to replace steam in

Conventional power plant

Solar thermal power plant

Nuclear power plant

• Year 2012: US DOE awarded 10 MWe S-CO2 R&D solar plant to a consortium consisting of NREL, Sandia, Abengoa Solar, Echogen Power Systems, U. of Wisconsin and EPRI.• US Department of Energy's S-CO2 initiatives: $44 million proposed in 2016 Budget for R&D

International status: Recent highlights

S-CO2 to replace steam in

Conventional power plant

Solar thermal power plant

Nuclear power plant

Challenges of S-CO2

PCHE etched Plates

Development of turbo expander, compressor & generator

High speed equipments

Compact turbine

Development of Recuperator (PCHE)

Thermal hydraulic Design,

Mechanical Design

Fabrication Aspects

Metallic materials suitable for long term operation at

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PCHE Channels

PCHE Block Section

Metallic materials suitable for long term operation at high temperature in CO2 environment

Materials available for temperatures less than 550 0C.

Compatibility of materials with heat transfer fluid of solar plant

Fabrication aspects:

First chemically etching flow channels into plates

CO2 Brayton: Critical thermal challenges

• High T high P receivers for CO2.

• Heat exchangers: Regenerator, pre-cooler

• High T thermal energy storage system : molten salt, PCM,

particles?

• Ideally, receivers and storage systems would need an integrated • Ideally, receivers and storage systems would need an integrated

approach in design

Test loop at Sandia National Labs (for Nuclear)

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S-CO2 test loop at IISc(for Solar)

Supercritical CO2 Brayton Cycle test loop at IISc

CAD Layout • High side temperature: 550°C

• High side pressure: 140 bar.

• Nominal flow rate of C02: 11 Kg/min.

• Two stage heating 100 +45 kW

To be integrated with solar receiver

Actual loop

S-CO2 Solar Receiver Configurations

Directly heated, closed-loop supercritical CO2 Brayton

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Indirectly heated, closed-loop supercritical CO2 Brayton

Possible Solar Receivers

Cavity

Volumetric

12-Jun-17 Indian Institute of Science, Bangalore 22

Tubular

Volumetric

Falling Particle

Some Existing Receiver Designs

Pressurised air receiver REFOS - Volumetric Pressurised air receiver HiTREC, DLR, 1995


Pressurised air receiver REFOS - Volumetric cavity receiver, 1996

Pressurised air receiver HiTREC, DLR, 1995

Direct Steam Generation,

Ivanpah 2014

Molten Salt, Solar Two, California,

1999

S-CO2 Receivers : Major Issues & Challenges

Tubular Receiver

Volumetric Receiver

Falling Particle Receiver

High tube wall thickness, limitation

on allowable heat flux, high losses

Window sealing and cooling, Structural failure of absorber

Particle flow control and additional heat exchanger design


Common Issues

Coatings : Durability at high

temperature, compatibility

with s-CO2

Response to transients and

provision of inbuilt storage

Reduction in strength of

materials at high temperature

High and uneven thermal

expansion

Falling Particle Receiver

Falling particle receiver at Sandia National Lab Conceptual design of a s-CO2 falling particle receiver

•High temperature heat transfer to working fluid•Efficient absorption; no flux limitation as in tubular•Possibility of cost effective storage (e.g. sand particles)•Scalable• Specific heat : 1.5-2 kJ/kg.K; density ~ 3000 kg/m3.

Concept 1: Straight Tubular receiver

Integrated optical-thermal modelRay Trace Model with Receiver Concept

Prototype of High Temperature CO2 Receiver (Sandia, , IISc, IITB) CSP 1

Ray Trace Model with Heliostat Field and Target

Bladed receiver design tested at SandiaBladed Panel Receiver

Flat Panel Receiver

Prototype manufacturing at Sandia

Concept 2: Helical coil cavity receiver

Irradiation Entering Cavity

Small scale model (~1 kWth) tested with compressed air and Fresnel lens test rig at IISc

Prototype of High Temperature High CO2 Receiver (Sandia, , IISc, IITB) CSP 1

Temperature distribution using air

Scaled up prototype (~10 kWth) being developed; On-sun test rig with 32 m2 Schefflerdish close to S-CO2 loop

Flux characterization using PHLUX method: Approx flux ~10 kW

Small scale module; Testing and

S-CO2 Volumetric Solar Receiver (BHEL, IISc) CSP Core 2

Development of CFD tools for volumetric receiver •Discrete Ordinates Method (DOM) for radiation heat transfer modelling coupled with FVM in ANSYS Fluent

QUARTZ GLASS – Successful demonstration with compressed air, no failure due to thermal effects

29

Small scale module; Testing and validation for radiation properties, window material and sealing qualifications

Summary:1. Quartz based ceramic closed volumetric air receiver

successfully demonstrated2. Scalability of design to larger scales, higher pressures

with s-CO2 identified as potential challenges

Indirect heating of s-CO2 using ceramic based Air-s-CO2 HEX with inbuilt storage being exploredcurrently

Modeling and Experimental Evaluation of Air–Ceramic Heat Transfer and Thermal Storage Dynamics

Experimental setup and test sample

Mullite, hexagonal channels with a wall thickness of 1 mm, geometric porosity 40 %

Flow rate ~ 0.0038 kg/sT1- T5: K-type thermocouplesMass of sample: 0.450 kg

CHARGING Inlet ~873 KDISCHARGING Inlet ~300 K

SampleDensity

(kg/m3)

Specific

heat

(J/kgK)

Thermal

Conductivit

y

(W/mK)

Mullite

(3Al2O3 2SiO2)3130 1000 1.25

Chromite

(FeCr2O4)3750 1200 1.4

Numerical Simulation was performed using ANSYS Fluent to study the effects of the following parameters on heat storage

:

Channel shapes

•Square

•Hexagon

Flow rates (kg/s)

•0.001, 0.0015

•0.002

Individual Channel area (mm2)

•4, 16, 36, 64

0.001 kg/s, 300 seconds, square 4 mm2

Sample Temp Distribution

Conclusions

• New thermodynamic cycles required for addressing CSP performance issues under different design conditions

• s-CO2 is a promising working fluid for high temperature application: but issues with materials, thermophysicalproperties, heat exchanger design, high peed properties, heat exchanger design, high peed torbomachinery

• Receiver design for high pressure and high temperature very crucial

• Challenges in Recuperator heat exchanger design and mnufacuring - PCHE

Thank you

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supercritical carbon dioxide brayton cycle for power...

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