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Folie 1 > Latent Heat Storage for Process Heat Applications > Jochen Buschle Latent Heat Storage for Process Heat Applications Jochen Buschle DLR – German Aerospace Center Institute of Technical Thermodynamics – Stuttgart Co-Authors: Wolf-Dieter Steinmann, Rainer Tamme The Tenth International Conference on Thermal Energy Storage, Atlantic City, 31. May – 2. June 2006

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Folie 1 > Latent Heat Storage for Process Heat Applications > Jochen Buschle

Latent Heat Storage for Process Heat ApplicationsJochen Buschle

DLR – German Aerospace CenterInstitute of Technical Thermodynamics – Stuttgart

Co-Authors: Wolf-Dieter Steinmann, Rainer Tamme

The Tenth International Conference on Thermal Energy Storage, Atlantic City, 31. May – 2. June 2006

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Content

Presentation is presenting first results obtained in the national project PROSPER dealing with industrial process steam storage. Possible contribution of Germany to planed new Annex 19.

Project partners are XELLA AG and SGL Technologies GmbH Duration 07/2004 – 06/2007

The project is funded by the Federal Ministry of Economy (BMWi) under the contract FKZ 032736017

Latent heat steam storage in process heat applicationsComparsion macro-encapsulation and external arrangementSimulation resultsConcepts to increase the power density of the storageConclusion

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Gas concrete manufacturing process

Hardening of gas concrete (steam atmosphere; max 13 bar)Batch process, 2 cycles per day155 kg steam at 13 bar for 1 m³ gas concrete = 100 kWhth

Xella Porenbeton GmbH (300.000 m³/a corresponds to 30 GWhth/a)

weighing and mixing

hardeningcuttingbulking

0

4

8

12

pres

sure

[bar

]

0 1 2 3 4 5 6 7 8 9 10

time [h]

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varying-pressure accumulator - „Ruths storage“

Charging pipe

Discharging pipe

Water feed pipe

Steam

Water

Pressure vessel

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Process description - State of the art

varying-pressure accumulators2 Ruths steam accumulators70% of the required steam per cycle

is produced in the boiler

live steam; 70%

overflow; 10%

Ruths-low pressure;

15%

Ruths-high pressure; 5%

boiler autoclave 5-8 bar3-5 bar

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Potential for introducing latent heat steam storageIsothermal steam accumulators withPhase Change Material (PCM)2 PCM enhanced steam accumulators(Tm = 152°C and 171°C)40% of the required steam per cycle is produced in the boiler

live steam; 40%

overflow; 10%

Latent-high pressure; 25%

Latent-low pressure; 25%

Latent heatstorage

Latent heatstorage

8 barboiler autoclave 5 bar

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Macro encapsulation

PCM Gas

Stiff encapsulation requiredDefinition of minimal gas volume inside capsules

Compensation of volume variation PCMAvoidance of significant pressure variations⇒ Gas volume requires about 20% of theinternal volume of the capsules

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External arrangement of PCMPCM

Additional required:Headers for the tube registerUnpressurised containment forthe PCMPump for circulation required

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Comparison macro encapsulation and externalarrangement

PCM steam

Boundary conditionstemperature step: 10 Kelvinpipe diameter: 40 mmheat transfer coefficient to the steam: neglectedthermal conductivity PCM: 0.5 W/mKdensity PCM: 2000 kg/m³same amount of PCM

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Macro encapsulation vs. external arrangement

40

60

80

100so

lidifi

edPC

M m

ass

[%]

External arrangement

Macro encapsulation20

00 500 1000 1500 2000 2500 3000 3500

time [s]

External arrangement shows higher power level assuming the sameamount of pipe material

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Macro encapsulation vs. external arrangement

Outside pressure load demands higher wall thickness than insidepressure load due to buckling

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

2 6 10 14 18 22 26 30

pressure [bar]

wal

l thi

ckne

ss [m

m]

externally arranged PCM

encapsulated PCM

External arrangement

Macro encapsulation

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Comparison steam accumulator concepts

varying-pressureaccumulator

Macro-encapsulatedPCM

externally arrangedPCM

pressure vessel:diameter: 1m; height: 3m; volume: 2.36 m³; water level: 80%

PCM enhancement:diameter tube: 4 cm; mass PCM: 1250 kg; thermal conductivity: 0,5 W/(m K)

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Simulation modell

ramp

I

Pump 1

true -1000Po...

5050

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Results simulation

1000 2000 3000 4000 5000

020406080

100

1000 2000 3000 4000 5000

0

14

28

42

56

kW

time [s]

time [s]

Power

Provided heat

kWh

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Required thermal conductivity

0

200

400

600

800

1000

1200

0 5 10 15 20 25 30

k [W/mK]

time

[sec

.]

h = 100000 W/(m²K)

h = 10000 W/(m²K)

h = 1000 W/(m²K)

thermal conductivity above 5 W / (m K) is advantageous

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Basic concepts to increase the power density of thermal energy storage tested at DLR

Increase of the effectivethermal heat conductivity Increase of the heat transfer area

PCM - Composite Integretion of fins

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PCM Composite

Solution: Compression of Salt and expanded graphite

Advantages expanded graphite:Hight thermal conductivityCorrosion resistancematerial can be machined

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Integration of Fins

Solution: Foils made of expandedgraphite

Advantages graphite foils:Hight thermal conductivity(approx. 150 W/mK)Corrosion resistanceArrangement of foils verticalto the axis of the heattransfer pipes is optimal with respect to theanisotropic heatconductivity of expandedgraphite

PCMPCM PCM

PCMPCM PCM

Graphite-foil

PCM

Steam pipe

10 mm

0,5 mm

Graphite-foil

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Lab scale experiments at DLR

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Conclusion

Isothermal energy storage is important especially for steam processesExternal arrangement of PCM is advantageousThermal conductivity of 5 W / (m K) is required

Future work:

Lab scale experiment for validation of modelsSystem simulation of gas concret production process with latent heatsteam accumulator

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Thank Youfor Your Attention

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Latent heat steam accumulator