thermal storage for ste plants - sfera - solar facilities...

Thermal Storage for STE Plants

3rd SFERA Summer School, Almería, June 27-28 2012

Markus EckGerman Aerospace CenterInstitute of Technical Thermodynamics

www.DLR.de/TT • slide 2 > Thermal Storage for STE Plants > Markus Eck > 3rd SFERA Summer School > Almeria >June 28, 2012

Outline

Introduction / Motivation

Technical Options for Thermal Energy Storage (TES)

Current Developments

Conclusions / Questions

Source: Solar Millennium


Motivation / IntroductionReview: What are Solar Thermal Power Plants?

- Pure solar operation

- Additional back-up capacities required in the grid

Electr.

Solar Field Power Block GridSolar-

IrradiationHeat



- Solar electricity production

- Integrated fossil back-up capacity for power on demand

Electr.

Fuel

Solar-Irradiation

Solar Field Power Block GridHeat



Electr.

Solar-Irradiation

Heat

- Solar electricity production

- Integrated storage for increased capacity factor and electricity on demand

- Additional fossil back-up

Fuel

Storage

Solar Field Power Block Grid


Motivation / IntroductionStorage Makes the Difference

Higher solar annual contribution

Reduction of part-load operation

Power management Dispatchable power

Storage is necessary to increase the share of renewable energy


Motivation / IntroductionEconomic effect of integrated thermal storage capacity?

Storage Capacity in Full Load Hours

Rel

ativ

e LC

OE

[%]


Technical Options for Thermal Energy StorageAdaptation to Receiver System and Power Block

Tmax < 500°C 500°C < Tmax < 1000°C

Working fluids: thermal oil air steam molten salt …


Technical Options for Thermal Energy StorageAdaptation to Receiver System and Power Block

storagesystem

ONE single storage technology will not meet the unique requirements of different solar power plants

Heat Transfer Fluid Collector System Pressure Temperaturesynthetic oil trough/Fresnel 15 bar 400°Csaturated steam tower/Fresnel 40 bar 260°Csuperhaeted steam trough/Fresnel 50-120 bar 400-500°Cmolten salt tower/trough 1 bar 500-600°Cair tower 1 bar 700-1000°Cair tower 15 bar 800-900°C

new concepts

Heat EngineORC

steam turbinegas turbine

Stirling engineothers


Technical Options for Thermal Energy StorageClassification of Storage Systems

Sensible Heat Latent Heat

Stor

age-

med

ium Liquid

Phase Change Material (PCM)

Solid Steam Accumulator

coldhotp TTcVQ shVQ


Capacity Potential off-sun operation hours

Power Duration of charging and discharging

Temperature level Efficiency of heat engine / spec. storage density

Response time Flexibility

Parasitic loads Efficiency of storage system

Thermal losses Efficiency of storage system

Comparison of storage concepts requires consideration of all relevantevaluation criteria

Technical Options for Thermal Energy Storage (TES)Classification of Storage Systems


Technical Options for TESSensible Heat – Liquid Media (direct)


Stor

age-

med

ium Liquid


SolidSteam

Accumulator

Cold tank290°C

Hot tank565°C

Steam Generator

Turbine

Generator

Receiver

Source: Homepage Torresol Energy

Heat transfer fluid and storage medium are the same

1st system: Solar Two Project Storage capacity 90 MWh (3h) 1,400 t of nitrate salts

(60% NaNO3 + 40% KNO3) 2 tanks: 12 m Ø, 8 m high

2nd commercial tower system at Gemasolar plant (Spain):

Storage capacity 700 MWh (15h)

7,000 t of nitrate salts


Technical Options for TESSensible Heat – Liquid Media (direct)


Stor

age-

med

ium Liquid


SolidSteam

Accumulator

Heat transfer fluid and storage medium are the same

1st system: Solar Two Project Storage capacity 90 MWh (3h) 1,400 t of nitrate salts

(60% NaNO3 + 40% KNO3) 2 tanks: 12 m Ø, 8 m high

2nd commercial tower system at Gemasolar plant (Spain):

Storage capacity 700 MWh (15h)

7,000 t of nitrate salts Source: Gemasolar


Technical Options for TESSensible Heat – Liquid Media (indirect)


Stor

age-

med

ium Liquid


SolidSteam

Accumulator

Heat transfer fluid and storage medium are NOT the same

1st system: Andasol I plant (Spain) with

storage capacity 1,010 MWh (7.7 h)


2 tanks 34 m Ø, 15 m high

Several indirect systems with parabolic troughs are in operation (Spain)


Technical Options for TESSensible Heat – Liquid Media (indirect)


Stor

age-

med

ium Liquid


SolidSteam

Accumulator

Heat transfer fluid and storage medium are NOT the same

1st system: Andasol I plant (Spain) with

storage capacity 1,010 MWh (7.7 h)


2 tanks 34 m Ø, 15 m high

Several indirect systems with parabolic troughs are in operation (Spain)

Source: Solar Millennium


Technical Options for TESSensible Heat – Solid Media – Regenerator Storage


Stor

age-

med

ium Liquid


SolidSteam

Accumulator

Regenerator storage as storage option for air Simple setup, allows use of low-cost storage materialsDirect contact air / storage materialCan be used up to very high temperatures

1,5 flh demo storage at 1.5 MWe experimental Solar Tower Plant in Jülich, Germany

-Source: Kraftanlagen München


Technical Options for TESLatent Heat – Steam Accumulator – PS-10


Stor

age-

med

ium Liquid


SolidSteam

Accumulator

Example: PS-10

Saturated steam at 250°C50 min storage operation at 50% load

Source: Abengoa Solar

Source: Abengoa Solar

water storage system


Steam Discharging

Isolated Pressure Vessel

Liquid Phase

Steam

Steam Charging

Liquid water Charging / Discharging

Charging process:raising temperature inliquid water volume bycondensing steam

Discharging process:generation of steamby lowering pressure insaturated liquid water volume

→ Buffer storage for peak power

→ Inefficient and economically not attractive for high pressures and capacities

Technical Options for TESLatent Heat – Steam Accumulator – PS-10


Stor

age-

med

ium Liquid


SolidSteam

Accumulator


Evaporation 65%

Preheating 16%Super-heating

19%

Parabolicsolar field

Fresnelsolar field Solar towerSolar Receiver

260°C – 400°C 107 bar

Technical Options for TESLatent Heat – PCM Storage for DSG Systems


Stor

age-

med

ium Liquid


SolidSteam

Accumulator


Technical Options for TESLatent Heat – PCM Storage


Stor

age-

med

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SolidSteam

Accumulator

Nitrate salt represent possible PCMs for applications beyond 100 °C

Important PCM criteria: thermal conductivity, melting enthalpy, thermal stability, material cost, corrosion, hygroscopy

0

50

100

150

200

250

300

350

400

100 150 200 250 300 350Temperature [°C]

Enth

alpy

[J/g

]

KNO3

NaNO3NaNO2

KNO3-NaNO3

LiNO3-NaNO3

KNO3-LiNO3

KNO3-NaNO2-NaNO3

LiNO3

0

50

100

150

200

250

300

350

400

100 150 200 250 300 350Temperature [°C]

Enth

alpy

[J/g

]

KNO3

NaNO3NaNO2

KNO3-NaNO3

LiNO3-NaNO3

KNO3-LiNO3

KNO3-NaNO2-NaNO3

LiNO3




Stor

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SolidSteam

Accumulator

solid

liquid

Fluid

solid

liquid

Fluid

Heat transfer coefficient is dominated by the thermal conductivity of the solid PCM

→ Low thermal conductivity is bottleneck for PCM

Heat carrier: water/steam


Tube

Fins

schematic PCM-storage concept

Finned Tube Design

effective λ > 10 W/mK

Source: DLR




Stor

age-

med

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SolidSteam

Accumulator

Phase change materialDemonstrated at DLR:

NaNO3 - KNO3 - NaNO2 142°CLiNO3 - NaNO3 194°CNaNO3 - KNO3 222°CNaNO3 306°C

Experimental validation5 test modules with 140 – 2000 kg PCMWorlds largest high temperature latent heat storage with 14 tons of NaNO3 (700 kWh) operating 2010-11

Source: DLR


PCM-Evaporator module: Capacity ~ 700 kWh PCM: NaNO3 Melting point: 306°C Salt volume: 8.4 m³ Total height 7.5 m Inventory ~ 14 t

Concrete Superheatermodule: Capacity ~ 300 kWh Concrete: 22 m³ 144 tubes Length 13.6 m

- Source:

DLR

Technical Options for TESLatent and Sensible Heat – Combined System


Stor

age-

med

ium Liquid


SolidSteam

Accumulator


Technical Options for TESLatent Heat – Filling of Granular Salt


Stor

age-

med

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SolidSteam

Accumulator


180

200

220

240

260

280

300

320

340

11:30 12:30 13:30 14:30 15:30 16:30 17:30Time

Tem

pera

ture

in °C

0

200

400

600

800

1000

1200

1400

1600

Hea

t Flo

w in

kW

ThPCM TcPCM T_PCM-1 T_PCM-2 T_PCM-3 Q*ChPCM Q*DChPCMCharge

100 – 125 bar 100 - 77 bar

Discharge

- 305

Discharge time 2:00 h

Technical Options for TESLatent Heat – Cycling with Sliding Pressure


Stor

age-

med

ium Liquid


SolidSteam

Accumulator


Current Developments


Salt systems

Corrosion

Thermal stresses / growth

Construction & Commissioning

Thermal losses / salt freezing

Improve understanding of molten salt systems

Current DevelopmentsCrucial Aspects for 2-Tank Molten Salt Storage Design


Stor

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SolidSteam

Accumulator


Salt Composition[kg]

Density at 300°C

[kg/m³]

Spec. Heat Cap. at 300°C

[kJ/(kg*K)]

Melting Temp.1

[°C]

Max operation Temp.1

[°C]

Solar Salt 60 % NaNO3

40 % KNO3

1899 1.495 220 600

HitecTM 7 % NaNO3

53 % KNO3

40 % NaNO2

1640 1.56 142 535

Hitec XLTM 7 % NaNO3

45 % KNO3

48 % Ca(NO3)2

1992 1.447 120 500

Multi ComponentSalts

Molten Nitrates / Nitrides

65-852,3

5602,3

established research

Current DevelopmentsSensible Heat – Identification of Improved materials


Stor

age-

med

ium Liquid


SolidSteam

Accumulator


Current DevelopmentsSensible Heat – Identification of Improved materials


Stor

age-

med

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SolidSteam

Accumulator

Demand for… …higher thermal stabilities of molten salts 700 °C …Lower melting points < 140 °C …improved thermo-physical properties

Research on new salt mixtures:

Ternary system Ca(NO3)2-KNO3-NaNO3

Quaternary system Li, Na, K // NO2,NO3

- Source: DLR


+ Cost reduction potential:approx. 33 %

- No long term experiencehave been published so far

3h charging cycle

Current DevelopmentsSensible Heat – Thermocline Storage


Stor

age-

med

ium Liquid


SolidSteam

Accumulator


+ Only one tank necessary

- Nearly the same amount of salt as in 2-Tank storage

-Source: SENER, INGENIERIA Y SISTEMAS, S.A.

Current DevelopmentsSensible Heat – Thermocline Storage w. floating barrier


Stor

age-

med

ium Liquid


SolidSteam

Accumulator


Source: Fabrizi, F., 2007, ENEA

Source: Weizmann Institute of Science

Current DevelopmentsSensible Heat – Thermocline Storage w. embedded HTX


Stor

age-

med

ium Liquid


SolidSteam

Accumulator


Storage system Power blockC

olle

ctor

fiel

d

Heat transfer fluid and storage medium are different Low cost storage material with integrated heat exchanger No risk of solidification Modular and scalable design Economic and reliable TES (< 35 € / kWh TES capacity) Flexible to large no. of sites and construction materials

Source: DLR

Source: DLR

Current DevelopmentsSensible Heat – Alternative Storage Media – Concrete


Stor

age-

med

ium Liquid


SolidSteam

Accumulator


400 kWh pilot storage in

operation since May 2008

Storage capacity:

0.65 kWh/(m3·K)

Over 10,000 operation hours

No indication of any

degradation effects

- 2nd Generation Pilot Storage built 2008 by

Source: DLR

Source: ZÜBLIN

Current DevelopmentsSensible Heat – Alternative Storage Media – Concrete


Stor

age-

med

ium Liquid


SolidSteam

Accumulator


Current DevelopmentsSensible Heat – Solid Media


Stor

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med

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SolidSteam

Accumulator

Durability of inexpensive storage materials

Containment technology and HT-insulation

Thermo-mechanical issues

Even flow distribution through storage material


Current DevelopmentsLatent Heat – PCM


Stor

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med

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SolidSteam

Accumulator

Cost-effective production and assembly

Free flow path in vertical direction => no risk with volume change during phase change

Controlled distribution of heat in the storage

Concept optimized by FEM analysis

Successful demonstration in lab-scale

Major cost reduction expected

Enhanced heat transfer by extruded longitudinal fins

Source: DLR


Liquid Storage Media (Molten Salt) Solid Storage Media (Concrete)

Molten Salt 49% Heat Exchanger 57%

Structure of capital costs

Limited potential for further cost reductions due to physical constraints New Basis Concept required

Current DevelopmentsAnalysis of Existing Concepts


Large heat transfer surfaces(short path length for heat conduction within solid storage material) Direct contact between storage medium and working fluid

(no expensive piping / coating) Storage volume at atmospheric pressure

(no expensive pressure vessels)

solid state storage media

-cost effective-no freezing

Requirements

Current DevelopmentsDevelopment of New Basic Storage Concept


Problem:Low volume specific energy density of air

large pressure losses part load operation difficult

Stor

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volu

me

closed air cycle

Heat exchanger

Fan

from solar field

to solar field

Current DevelopmentsAir is used as an intermediate HTF – CellFlux Concept


Stor

age-

med

ium Liquid


SolidSteam

Accumulator


Current DevelopmentsCellFlux - Concept


Stor

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SolidSteam

Accumulator

Source: DLR


(n-1).storage cell

Stor

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Air cycle

Heat exchanger

CellFlux Storage Unit

Parabolicsolar field

n.storage cell

Stor

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volu

me

Air cycle

Heat exchanger

1.storage cell

Stor

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Air cycle

Heat exchanger

2.storage cell

Stor

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Air cycle

Heat exchanger

Fresnelsolar field Solar towerSolar Receiver

Prim

ary

heat

tran

sfer

flui

d

Prim

ary

heat

tran

sfer

flui

d

Power blockG

Current DevelopmentsCellFlux - Integration into STE Plant


Stor

age-

med

ium Liquid


SolidSteam

Accumulator


Solar Institute Jülich/DLR


Stor

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SolidSteam

Accumulator

Current DevelopmentsSand Storage

Challenges:

Heat transfer air-sand Sand transport

Source: DLR


Aim: Separation of power characteristic from storage level in latent heat storage Solid granular salt and molten salt are stored in separate tanks Transport of PCM through screw heat exchanger (SHX) Phase change inside SHX

SHE

Granular material

Molten material


Stor

age-

med

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SolidSteam

Accumulator

Current DevelopmentsLatent Heat Storage with external HX - Principle

Charging


PCM material transport Self cleaning effect

St eam / Wat er Inlet

St eam / Wat er Out l et

St eam / Wat er nlet

Out l et

St orage M at erial Ou t let

Hollow t rou ghHol lowf li ght s

St orage M at erial Inlet

Hollow shaf t

St eam / Wat er In let

St eam / W at er Ou t let

St eam / W at er Inlet

Ou t let

St o rage M at erial Out let

Hol low t ro ughHo llowf l igh ts

St o rage M at erial Inl et

Hol low sh af t




Out l et




Hollow shaf t




Out l et




Hollow shaf t




Ou t let




Hol low sh af t




Ou t let




Hol low sh af t


Stor

age-

med

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SolidSteam

Accumulator

Current DevelopmentsLatent Heat Storage with external HX - SHX


Proof of conceptalready yielded Qth = 10 kW

Outlook Process and material

optimisation Two prototype setups to

be installed at Fraunhofer ISE labs: 1st Prototype using

thermal oil as HTF 2nd prototype using steam

as HTF Concept for upscaling

Molten salt

SHX

Granular salt

Salt inlet


Stor

age-

med

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SolidSteam

Accumulator

Current DevelopmentsLatent Heat Storage with external HX – Proof of Concept


Molten salt inlet

Obtained salt granules

Cristallization of salt

Piece of salt


Stor

age-

med

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SolidSteam

Accumulator

Current DevelopmentsLatent Heat Storage with external HX – Details


Teq[1 bar]

°C

∆H [1 bar]

kJ/mol

Capacity* Solid onlykWh/m3

Capacity*All

reactantskWh/m3

CapacityGravimetric

kWh/t

521 100 410 323 373

Objectives Thermal Storage for T > 300°C Use of industrial process heat

Power generation (e.g. solar thermal plants)

Reaction: Ca(OH)2 ↔ CaO + H2O

-

*Porosity of 0.5


Stor

age-

med

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SolidSteam

Accumulator

Current Developments – Long TermThermo-chemical Heat Storage – Gas-Solid Reactions


Different technical approaches for different process requirements available

Proven options:

Two-Tank molten salt storage up to 560oC and 1010 MWhth

Demonstrated options:

PCM storage up to 100 bar and 700 kWhth

Pecked bed storage up to 700oC and 1,5 Mwhe

Several improvements are conceivable

Cost reduction of proven and demonstrated systems

New Concepts are investigated

Thermoclines

Air as intermediate heat transfer fluid

PCM w. external heat exchanger

Thermo-Chemical Storage

Conclusions

thermal storage for ste plants - sfera - solar facilities...

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