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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
Folie 2 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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
Folie 3 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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]
Folie 4 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
varying-pressure accumulator - „Ruths storage“
Charging pipe
Discharging pipe
Water feed pipe
Steam
Water
Pressure vessel
Folie 5 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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
Folie 6 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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
Folie 7 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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
Folie 8 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
External arrangement of PCMPCM
Additional required:Headers for the tube registerUnpressurised containment forthe PCMPump for circulation required
Folie 9 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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
Folie 10 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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
Folie 11 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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
Folie 12 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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)
Folie 13 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
Simulation modell
ramp
I
Pump 1
true -1000Po...
5050
Folie 14 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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
Folie 15 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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
Folie 16 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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
Folie 17 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
PCM Composite
Solution: Compression of Salt and expanded graphite
Advantages expanded graphite:Hight thermal conductivityCorrosion resistancematerial can be machined
Folie 18 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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
Folie 19 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
Lab scale experiments at DLR
Folie 20 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
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
Folie 21 > Latent Heat Storage for Process Heat Applications > Jochen Buschle
Thank Youfor Your Attention