Experimental Study of Phase Change Materials for Thermal Storage in the Temperature Range of

300-400

o C

R. Adinberg, D. Zvegilsky, M. Epstein E2C 2013 October 27-30, 2013 Budapest, Hungary

2

Discussion Topics



Thermal Energy Storage (TES) for Concentrating Solar Power (CSP) plants



Selection of Phase Change Materials (PCM) for Solar TES



Thermal analysis of PCM and Main results



Reflux Heat Transfer Storage (RHTS) experimental system



TES prototype design



Conclusions

3

Solar-Fossil Hybrid Power System Q R SOLAR POWER CSP System Q 0 Q 2 Q 1 Q F FOSSIL FUEL Power Block Q L ~ Electricity Grid Q 3 Power Control System: Q 0 …....Q

L (HTF flow), E S Thermal Storage Operation



Buffering during transient weather conditions



Dispatchability / time-shifting into peak/night hours



Achieve full load operation of the steam turbine cycle



Increase of annual capacity factor 20 to 40/50%

4 State of the art Thermal Storage Technology 2-tank Molten Salt System

Andasol, Spain Solar Power Plant 50 MWe

14 m height Tank Size 38 m diameter Amount 28,500 tons Capacity 1010 MWh Molten Salt (K-Na)NO 3 Temperature 250-400 o C Method Effect Phase Temperature

300-400

o C (Parabolic Trough CSP) Sensible Heat Latent Heat Thermo Chemical

Δ

H T C P

Δ

T @ Tmelt

Δ

H R (Endo-Exo thermal reaction) Liquid Solid/Liquid Solid Gas Materials Thermal oil Molten salt Pressured water PCM: Molten Salts Metal Alloys CaO/H 2 O NH 3

→

N 2 + H 2

5 Reflux Heat Transfer Storage -RHTS Key Features PCM-HTF Direct Contact HTF Vapor Natural Convection & Liquid Reflux Heat Exchanger External to PCM To Steam Generator 

Challenge : PCM-HTF Compatibility

 PCM HTF

Diphyl

 Temp

.

Selected Materials:

Zn Alloys, Molten Salts Diphenyl Oxide + Biphenyl (Dowtherm A; Therminol VP-

1)

< 400 o C PCM HTF Boiling Design Specifics Isothermal Process: Overall Thermal Conductivity: Energy density by volume: Pressure-tight tank: T steam PCM m.p. PCM-to-Steam Thermosyphon 2-5 times of 2-tank MS system 5-10 bar

6 HTF Diphyl PCM-HTF Thermo-Chemically Stable Systems PCM

Zn70Sn30

Melting Temp.

370

o C Density (solid)

7.

g/ cm 3 Latent Heat

107

J/g Max Test Temperature

400

o C

Zn95Al5 KNO 3 (K/NA/Li) 2 CO 3 384 334 392/7 7.

2.

2.5

101 110 280 400 360 400

TGA/DTA Q600 TA Instruments Thermal Analysis Applied DSC DSC 4000 PerkinElmer FTIR Tensor 27 Bruker Optics Calorimetric results for the 3C-Diphyl chemical system including a few sequential heating-cooling cycles between 350 to 420 o C Time

7 RHTS Lab-scale Experimental System Multiple Cycles

Stirrer Insulation Water-filled Condenser (4 L) Metering Valve Pressure Sensor HTF Flow HTF: Diphyl 0.25 L Sample Pan 1 2 3C-PCM 0.9 kg Sample Vessel Electric Furnace Thermocouples K, T

Cross section of the sample pan containing 3C PCM after the long-term test

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RHTS Prototype Design Calculated parameters of a thermal storage tank PCM for a 50MWe solar power plant Amount PCM, ton

KNO 3 17,000

Amount HTF, ton Height, m

ca. 2,000 20 3C 14,000 ca. 1,000 20

Diameter, m Thermal capacity, MW th h

32 500 24 1000

Fig. 7.

Schematic design of a thermal storage tank where Diphyl is used as HTF in both the storage and solar collector.

Thermal Storage for 7 operational hours (solar capacity factor 0.4) Number of tanks 2 1

Experimental Study of Phase Change Materials for Thermal Storage in the Temperature Range of 300-400oC SUMMARY  RHTS is a synergistic process that integrates the PCM solid–liquid and HTF liquid–vapor reversible phase change effects for respectively storing and transferring heat in the thermal storage system.

 The experimental results of this work show that the -Diphyl ( K/Na/Li) 2 CO3 storage medium is thermally and chemically stable and suitable for RHTS up to 400 o C .

 The experimental system has been demonstrated quite heat transfer effective in for improving the performance of thermal storage systems.

 A feasibility study is currently being done on integration of 3C Diphyl RHTS module into a 50 MW solar thermal electric power plant.