High Temperature Thermochemical Heat Storage:Operation Modes of a 10kW Pilot Reactor based

on CaO/Ca(OH)2

Matthias Schmidt, Christian Roßkopf, Marc Linder, Antje Wörner

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Content

- Introduction to thermochemical energy storage based on CaO/ Ca(OH)2

- Material properties

- Reactor design and test bench development

- Experimental results of different operation modes

- Summary and outlook

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Thermochemical Heat Storage reaction system CaO/Ca(OH)2

- Loss free storage of chemical potential

- Adjustable storage temperature

- Possibility of heat transformation

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CaO(s) + H2O(g) ⇌ Ca(OH)2(s) + ΔH

endotherm

exotherm

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.70.001

0.01

0.1

1

10

Temperatur 1000 / T [1/K]

pga

s [b

ar]

Ca(OH)2(s)

CaO(s)

636727 560 496 441 394 352 315

Temperature [°C]

H2O(g)

H2O(g)

From a reaction system to a heat storage systemoperation principle

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Reactor DesignGashandling

Process integration:

ReactionMaterial

Properties

Material Properties - CaO/Ca(OH)2

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Thermophysical properties:

- Fine powder (d50 ~ 5 µm)

- low permeability

- Low thermal conductivity (0.1 – 0.4 W/mK)

F. Schaube et al., Thermochimica Acta, 2012

Ca(OH)2 (4 Cycl) commerical available Ca(OH)2

Chemical properties:

- Reversible reaction (400-600°C)

- Sufficiently fast rates of reaction

- No chemical degradation observed

Pilot Reactor Design (10kW; 25 kg Ca(OH)2)indirectly operated fixed bed

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Source: DEG Eingineering

Reaction Gas Handlingvapor pressure holder(10mbar – 3bar)

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Multifunctional Pilot Plantoverall experimental set up for CaO/Ca(OH)2 reactor

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Multifunctional Pilot Plantoverall experimental set up for CaO/Ca(OH)2 reactor

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Multifunctional Pilot Plantoverall experimental set up for CaO/Ca(OH)2 reactor

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Multifunctional Pilot Plantoverall experimental set up for CaO/Ca(OH)2 reactor

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M. Schmidt et al., Applied Thermal Energy 62 (2014)

Multifunctional Pilot Plantoverall experimental set up for CaO/ Ca(OH)2 reactor

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M. Schmidt et al., Applied Thermal Energy 62 (2014)

0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00 400.00250

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600

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1.00

T_air_outlet

T_air_inlet

Conversion

Time [min]

Tem

per

atu

re [

°C]

Co

nve

rsio

n

Charging Modedehydration of Ca(OH)2 at ph2O = 100mbar

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0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00 180.00 200.00300

350

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550

T_air_inlet

T_R_01

T_R_05

T_R_11

T_R_13

time [min]

Tem

per

atu

re [

°C]

Buffer Storage Modedroping inlet temperature, hydration of CaO at 1 bar vapor

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Tequilibrium = 490°C@ (ph2O ~ 1bar)

Heat Generation ModeHydration of CaO, starting temperature of 350°C

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0.00 50.00 100.00 150.00 200.00 250.00330

350

370

390

410

430

450

470

490

0.00

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0.20

0.30

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0.90

1.00

T_air_inlet

T_air_outlet

Conversion

time [min]

Tem

per

atu

re [

°C]

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nve

rsio

n

Summary and Outlook

CaO / Ca(OH)2 combines low material costs with high storage density

Reactor for 25kg (10 kWh) and 10 kW in operation

Charging at temperatures >400°C demonstrated

Discharging at adjustable temperatures (400-600°C) and in different operation modes possible

- Development of integration strategies(CSP and other applications)

- Performance evaluation through system modeling

- Material modifications to improve conveyance

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Thank you!

Matthias SchmidtGerman Aerospace Center (DLR)Institute of Technical Thermodynamics

matthias.schmidt@dlr.dewww.DLR.de

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