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Latent heat storage above 120°C for applications in the industral process heat sector and solar power generation

Tamme, Rainer and Bauer, Thomas and Buschle, Jochen and Laing, Doerte and Müller-Steinhagen, Hans and Steinmann, Wolf-Dieter (2008) Latent heat storage above 120°C for applications in the industral process heat sector and solar power generation. International Journal of Energy Research, 32 (3), pp. 264-271. John Wiley & Sons Ltd. DOI: 10.1002/er.1346. ISSN 0363-907X.

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Official URL: http://www.interscience.wiley.com

Abstract

This paper is focussed on thermal storage technologies using phase change materials (PCMs) in the temperature range of 120-300 °C for solar thermal power generation and high temperature process heat. As state-of-the-art reference system a steam accumulator is described, which typically has a volume-specific thermal energy density of 20-30 kWh/m³. Regarding efficiency, a fundamental demand on thermal storage is the minimization of temperature differences between working fluid and storage medium. This requires isothermal storage systems for processes using water/steam. An obvious solution is, therefore, the application of PCMs. The selection of the PCMs depends strongly on the operation conditions of the respective application. At present, the main emphasis is directed to alkali metal nitrates and nitrites and their mixtures. For example, the eutectic mixture of the binary system KNO3-NaNO3 has been identified as an excellent system to be used for processes using saturated steam at around 25 bar. At around 5 bar the ternary system KNO3-NaNO2-NaNO3, commonly used as heat transfer fluid, can also be used as a PCM. To overcome the low thermal conductivity of the salt systems, approaches of increased surfaces area and increased thermal conductivity using expanded graphite (EG) have been investigated. Using EG/PCM-composites the effective thermal conductivity can be increased from below 0.5 W/(mK) to 3-20 W/(mK). Three design concepts have been developed. In the macro-encapsulated design, the PCM is enclosed in metal tubes, giving a short distance for heat transfer and increasing the heat transfer area. In the second design, the heat exchanger tubes are embedded in EG/PCM-composite storage material. The third design option uses graphite foils arranged perpendicularly onto the heat exchanger tubes and a suitable salt system filled in between. The upgrade of existing steam accumulators using these PCM concepts is also proposed.

Document Type:Article
Title:Latent heat storage above 120°C for applications in the industral process heat sector and solar power generation
Authors:
AuthorsInstitution or Email of Authors
Tamme, RainerUNSPECIFIED
Bauer, ThomasUNSPECIFIED
Buschle, JochenUNSPECIFIED
Laing, DoerteUNSPECIFIED
Müller-Steinhagen, HansUNSPECIFIED
Steinmann, Wolf-DieterUNSPECIFIED
Date:March 2008
Journal or Publication Title:International Journal of Energy Research
Refereed publication:Yes
In ISI Web of Science:Yes
Volume:32
DOI:10.1002/er.1346
Page Range:pp. 264-271
Publisher:John Wiley & Sons Ltd
ISSN:0363-907X
Status:Published
Keywords:Phase Change Materials, Thermal Energy Storage, Steam Storage, Process Heat, Solar Power Generation
HGF - Research field:Energy
HGF - Program:Efficient Energy Conversion (old)
HGF - Program Themes:E EV - Energy process technology (old)
DLR - Research area:Energy
DLR - Program:E EV - Energy process technology
DLR - Research theme (Project):E - Thermochemische Prozesse (old)
Location: Stuttgart
Institutes and Institutions:Institute of Technical Thermodynamics > Thermal Process Technology
Deposited By: Dörte Laing
Deposited On:28 Feb 2008
Last Modified:27 Apr 2009 14:05

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