heat transfer fluids & innovative r+d subjects for of june ... · •indirect storage: 7.5 h,...

Dr. Rocío Bayón Concentrating solar systems, CIEMAT-PSA e-mail: [email protected]

7th SFERA Summer School Heat Transfer Fluids & Innovative R+D Subjects for

Concentrating Solar Systems. Almería, 9-10th of June 2016

Latent heat thermal storage

7th SFERA Summer School Almería, 9-10 June 2016

Contents

1. Importance of thermal storage in CSP

2. Commercial CSP plants with thermal storage

3. CSP plants with DSG

4. Latent heat storage

1. Materials, requirements & drawbacks

2. Innovative solutions & strategies for improving materials performance

5. Examples of storage integration in DSG plants

6. Further applications of thermal storage

7. Conclusions


Importance of thermal storage in CSP

• Power generation becomes independent from solar resource availability

– Overcome transient periods of clouds

– Extend timeframe of power generation

• Solar field must be enlarged and new components must be added

• Increases the capacity factor

Favors electrical production under nominal conditions

Increases the annual performance yield of the power block

Allows other renewables to be integrated in the energy mix

3


Importance of thermal storage in CSP

Thermal storage makes

CSP DISPATCHABLE 4


Commercial CSP plants with thermal storage Parabolic trough collectors

• HTF: thermal oil (293º-393ºC) • Indirect storage: 7.5 h, molten salts in 2 tanks (290º-390ºC) • Salt-oil HX

5


Commercial CSP plants with thermal storage: Parabolic trough collectors

Andasol-1,2 y 3

http://www.grupocobra.com/business/project/central-termosolar-andasol-1/

• Aldiere (Granada) • Grupo ACS/Cobra • 50 Mwe • 7 h storage

6









Commercial CSP plants with thermal storage: Central receiver

• HTF: molten salts (285º-565ºC) • Direct storage in 2 tanks • Higher storage density

7


Commercial CSP plants with thermal storage: Central receiver

Gemasolar • Fuentes de Andalucía (Sevilla) • Torresol Energy • 20 MWe • 15 h storage

http://www.torresolenergy.com/TORRESOL/inicio/es 8

http://www.torresolenergy.com/TORRESOL/inicio/es


CSP plants with direct steam generation (DSG)

Only one fluid is used Water is the HTF of the solar field

and also power cycle fluid The steam temperature of the

turbine can be increased up to 550 °C (superheated)

No steam generator is required The overall plant efficiency is

increased Good control of two-phase fluid is

required

DSG plants can only become economical competitive if a cost effective storage systems is available

9


Commercial CSP plants with DSG

Tower: PS10 and PS20 • Sanlúcar la Mayor (Sevilla) • Abengoa Solar • 10/20 MWe • HTF: water liquid/vapor (300ºC) • Storage: 1 h RUTHS ACCUMULATOR

http://www.abengoasolar.com/

http://www.novatecsolar.com

Fresnel: Puerto Errado 1 & 2 • Calasparra (Murcia) • Novatec Solar España S.L. • 1.4/30 MWe • HTF: water liquid/vapor (140-270ºC) • Storage: 0,5 h RUTHS ACCUMULATOR

Tower

Fresnel

10

http://www.abengoasolar.com/

http://www.novatecsolar.com/


Steam accumulators (Ruths) in DSG plants

R. Tamme, IEA ECES Annex 19. Final report. July 2010

Direct storage

Store latent heat as sensible heat in saturated liquid water under pressure

Turbine has to work at lower pressure conditions 50 bar vs 100 bar for PS-10

Too expensive for large capacities

Low storage capacity Only for transient conditions

Discharge: 90 kg of sat. steam per m3 @ 55 bar

11

Thermal storage of large capacity for DSG plants remains unsolved


Thermal storage implementation in DSG plants

~60% ~20% ~20%

12

preheating

(SENSIBLE)

superheating

(SENSIBLE)

condensation/evaporation

(LATENT)

POWER

BLOCK

• Power block turbine works with superheated steam

• Latent heat (60%) combined with sensible heat (40%)


Fundamentals of latent storage

• Charge:

• Vapor condensation (HTF from solar field)

• PCM: Solid to liquid transition

• Discharge:

• PCM: Liquid to solid transition

• Vapor generation (HTF to power block)

• There is a temperature gap in HTF between charge and discharge (T)

0.0 0.2 0.4 0.6 0.8 1.0

Tem

pe

ratu

re

Q/Q

Charge

HTF from solar field

Tm

PCM: SolidLiquid

0.0 0.2 0.4 0.6 0.8 1.0

Tem

pe

ratu

re

Q/Q

Discharge

HTF to PB

Tm

PCM: Liquid Solid

0.0 0.2 0.4 0.6 0.8 1.0

Tem

pe

ratu

re

Q/Q

Charge/Discharge

HTF to PB

T

HTF from solar field

• Storage option for the condensation/evaporation process of the HTF

• Storage medium undergoes a phase change (usually solid to liquid) at constant Tphase

Phase change material (PCM)

• Q=Q1-Q2=mPCM Hphase (>0 in charge, <0 in discharge)

Storage capacity depends on the latent enthalpy: Hphase

• Heat transfer by conduction Controlled by thermal conductivity of the PCM

• Indirect storage HTF≠PCM

13


What defines Tphase?

• The process in which the latent storage system is going to be implemented

1. For energy production in CSP plants with DSG (Rankine):

• Fresnel collectors: Tphase < 270ºC (~55bar)

• Parabolic troughs: Tphase < 310ºC (~100bar)

• Central receivers: Tphase < 345ºC (~155bar)

2. For energy production in other CSP plants working at high temperatures

• HTF= air or s-CO2 (Brayton): Tphase 600-800ºC

• Parabolic dishes: Tphase 700-800ºC

3. For power block dry-cooling:

• Ambient night temperature <Tphase< Power block condensing temperature

14


PCM kinds & requirements (I)

High phase change enthalpy: Hfus

Phase change temperature (Tphase) suitable for the DSG process A. Hoshi et al. Solar Energy 79 (2005) 332

Sugar alcohols

Organic materials

Inorganic salts single or eutectic

Metals

15


Reversible melting/freezing process with low supercooling

Supercooling Difference between the onset temperatures of melting and freezing

Most materials exhibit some supercooling behavior (between 1ºC to 50ºC)

It is usually magnified in DSC measurements since sample mass is low

DSC Melting: 168 ºC Frezing: 107 ºC

Furnace cycles are more reliable since they are closer to the reality

PCM kinds & requirements (II)

60 80 100 120 140 160 180 200 220

-140

-120

-100

-80

-60

-40

-20

0

20

40

60

2nd

Tpeak

=168.8 ºC

Hfus

=284.9 kJ/kg

Tpeak

=168.8 ºC

Hfus

=280.6 kJ/kg

Tpeak

=107.7 ºC

Hfus

=212.1 kJ/kg

Tpeak

=107.7 ºC

Hfus

=214.4 kJ/kg

DS

C [

mW

/mg

]

Temperature [ºC]

1st

10ºC/min0 50 100 150 200 250 300 350

100

110

120

130

140

150

160

170

180

190

Supercooling

1st cycle

8th cycle

50th cycle

Te

mp

era

ture

[ºC

]Arbitrary time [min]

D-manntiol

melting interval

New species?

D-Mannitol

61 ºC supercooling!!! 16


D-Mannitol

Example of degradation after 1 week @ 180ºC in air

PCM kinds & requirements (III)

Thermal stability in the working temperature range No sublimation or vaporization No degradation Stability upon melting/freezing cycles

Hydroquinone

Example of vaporization & degradation upon melting

Salicylic acid

Example of vaporization upon melting

Tmelt = 173 ºC Hmelt = 215 kJ/kg Tmelt = 159 ºC

Hmelt = 199 kJ/kg

Tmelt = 168 ºC Hmelt = 292 kJ/kg

Be careful with PCM candidates proposed in the literature!!!

17


PCM kinds & requirements (IV)

PCMs for high temperatures

Pure inorganic salts

Eutectic mixtures

Electrical discharge power decreases with time

Thermal conductivity <1W/mK High thermal resistance

Thermal conductivity

18


Reducing thermal resistance (I)

• PCM packing in a matrix with high k Composites: Graphite + salt Metallic foams

Carbon fibbers

Metallic shell (+ Foams) (CSP2 Project, KU Leuven (B) &Co )

19


• Macro-encapsulation of PCMs with high k materials

Metallic shells Sacrificial material + Clay + Metal Shell

Reducing thermal resistance (II)

Additional Problems: ∆V/V high Corrosion

Porous PCM pellets +

Metallic coating

Clean Energy Research Center, University of South Florida & SunBorneEnergy 20


• METALLIC alloys as PCMs

– AlSi12 :Hphase=560J/g: Tm=577ºC => supercritical steam + NaK as HTF (Stellenbosch U.)

– Mg (49%)-Zn(51%): Tm=340ºC ; Hphase=138 - 180 kJ/kg

– Mg-Zn-Cu-Ni (285-330ºC / Hphase=150-170 kJ/kg) (Tecnalia -SP)

Reducing thermal resistance (III)

21


Reducing thermal resistance (IV)

•Heat pipes

University of Connecticut

•Heat transfer structures

DLR

22


Reducing thermal resistance (V)

• Special geometry (spiral)

Saturated steam

Saturated liquid

TES acts as separator

Drainage is

promoted from

external to

internal channels

Vapor exit is

promoted from

external to

internal channels

Efficient heat transfer Low pressure losses Manufacturing at workshop PSA, Ciemat

23


Improving storage efficiency

High-temperature PCMs

Challenges Static heat transfer enhancement + corrosion protection

MgCl2 (714ºC & 452kJ/kg) with graphite foam/composites

eu-NaCl-Na2CO3 (635ºC & 308kJ/kg) compatibility tests with SS316 under minimized O2 atmosphere

eu-(Ba-K-Na)-Cl (530ºC & 211kJ/kg) encapsulated with a fly-ash based geopolymer shell

(Argonne N. Lab & Illinois University) (South Australia University & QUT )

8 h @200ºC

8 h@600ºC

24


Moving the PCM: HX approach

•Decoupling heat transfer area from storage capacity

25

• Screw heat exchanger from Fraunhofer ISE

• Solid PCM is crushed and transported as it forms Self-cleaning

• For high pressure the flights design must be improved

• PCMflux concept from DLR

• Thin liquid layer connects PCM and HTF piping

• PCM: eu-NaNO2-NaNO3

• Thin liquid layer: HITEC®


CIEMAT approach Use of liquid crystals (LCs) as PCMs since they can absorb/release energy when they undergo a change between two liquid phases

Moving the PCM: material approach

PCM slurries to transport latent heat and enhance heat transfer in fluids

Main challenge Microencapsulation of high-temp PCMs

US 4911232 A (1990)

26


LCs as storage materials

• Organic molecules with anisotropic shape

• Fluids with some solid state properties

o 3-D lattice

o Orientation

o Solid

CRYSTAL

o 2, 1-D or no lattice

o Orientation

o Fluid

LIQUID CRYSTAL (MESOPHASES)

o No lattice

o No orientation

o Fluid

LIQUID

At least two transitions: 1.Crystal to mesophase Melting temperature 2.Mesophase to liquid Clearing temperature

What are liquid crystals? • Liquid crystals are materials that present intermediate behavior between crystalline solid and isotropic liquid Mesophase

27


Thermal properties of LCs (I)

Advantages Energy exchange takes place by convection Power curve is constant with time during both charge and discharge Sensible heat can be stored as well They can be used not only for heat storage but also for heat transport

Melting point Clearing point

28


Thermal properties of LCs (II)

R. Bayón, R. Rojas. International Journal of Energy Research 2013; 37: 1737-1742 29

Acree W. E., Chickos J. S.: Phase change enthalpies and entropies of liquid crystals. Journal of Physical and Chemical Reference Data 2006; 35: 1051-1330.

It is possible to find liquid crystals that display clearing transitions with high values of enthalpy in the temperature range of latent storage for DSG applications

PCM Tphase Hphase

eu-NaNO3/KNO3 222 ºC 100 kJ/kg

eu-NaNO3/Ca(NO3)2 230 ºC 110 kJ/kg

NaNO3 306 ºC 178 kJ/kg

KNO3 334 ºC 98 kJ/kg


DSG-CSP plant with LCs-based storage S

ola

r fie

ld

Power block

Charge

Discharge

Steam

Liquid

water

Direct steam generation power plant with two tank liquid crystal storage

Steam

Liquid water

Heat

exchanger

Condenser/

evapora

tor

Hot tank:

isotropic liquid

Cold tank:

liquid crystal

All storage systems could be gathered in a joint two-tank system (Single tank configuration under study)

R. Bayón, E. Rojas. International Journal of Energy Research 2013; 37: 1737-1742 30


Biphenyl benzoic acid derivatives They form intermolecular H-bonds in the mesophase High clearing temperatures and enthalpies are expected

1. R. Bayón et al. European Conference on Liquid Crystals, September 2015 2. R. Bayón et al. Applied Sciences 2016, 6(5), 121

First results with LCs as PCMs

Promising results at lab scale Tclear =251ºC ΔHclear = 55 kJ/kg Viscosity = 0.18-0.6 Pas Cp mesophase =2.4 kJ/kgK

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7 8 9 101112131415161718100

125

150

175

200

225

250

275

300

325

350 Nematic

Smectic

Solid

Tem

pe

ratu

re [

oC

]

Carbon atoms of alkyl groups [n]

Enthalpy

H

cle

arin

g [kJ/k

g]

Rather low stability upon melting due to high reactivity of acid group

31


Examples of storage integration in a DSG plant

preheating

(SENSIBLE)

superheating

(SENSIBLE)

condensation/evaporation

(LATENT)

POWER

BLOCK

• Power block turbine works with superheated steam

• At least a high temperature sensible storage is required 32


Latent + sensible regenerative storage

• Test modules installed in a coal power plant in Carboneras (Spain) by DLR and other partners

• Latent heat module: PCM NaNO3 (Tm=306 ºC) • Sensible heat regenerative module: Concrete

Sensible storage

Latent storage

33


Latent + 2 sensible: regenerative & thermocline

Three stage storage system (CEA-LITEN & ALSOLEN) 1. Low-temp storage: pressurized liquid water in a thermocline tank 2. Latent heat storage: NaNO3/fins 3. High-temp storage: air/brick regenerator

34


Latent + 3 sensible

3-tank sensible storage with solar salt

1-tank latent storage with NaNO3

35 M. Seitz, S. Hübner and M. Johnson, SolarPACES 2015, Cape Town (SA)


Applications of latent storage with high-temp PCMS (I)

Parabolic dish with PCM storage (Sandia Labs)

Cu-Si-Mg (700-800ºC / 462 kJ/kg)

Al2O3, Y2O3 and MgAl2O4 identified as candidate coatings to contain the PCM STEALS project (NREL)

Solar Thermoelectricity via Advanced Latent heat Storage

36


Applications of latent storage with high-temp PCMS (II)

37

• Substitution of a sensible storage by a cascade latent storage

University of South Australia Tower plant with HFT=s-CO2

CO2-Brayton


Applications of latent storage with high-temp PCMS (III)

38

• Air receivers protection against cloud transients – PCM: Li2CO3 (723 ºC) + Copper (1080 ºC) for enhancing thermal

conductivity

CNRS-PROMES


Power block dry-cooling

39

PCMs + air condensers for locations with low water availability and large temperature differences between night and day Deserted areas

Charge during turbine operation Regeneration phase at night

Ambient night temperature <Tphase< Temperature of steam from turbine

Saturated steam from turbine 30ºC-40ºC


Conclusions

Latent thermal storage is crucial for the development of CSP plants with DSG

No cost-effective solution has been found yet

Latent storage is under strong development

Technical optimization of concepts & materials

Still uncertainties in the reliability & scalability of some of them

Innovative concepts for latent storage should be developed in terms of new materials, configurations & applications

Please think different and use your imagination!!


The end…

INTERESTED IN A POSTDOCTORAL POSITION IN THERMAL

STORAGE? Marie Skłodowska-Curie Actions (H2020-MSCA-IF-2016) Deadline: 14 September 2016 17:00:00 (Brussels time)

More General Info: http://ec.europa.eu/research/participants/portal/desktop/

en/opportunities/h2020/topics/2226-msca-if-2016.html Contact (before 15th August 2016):

[email protected]

http://ec.europa.eu/research/participants/portal/desktop/en/opportunities/h2020/topics/2226-msca-if-2016.html








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