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Thermal Storage
Latent heat storage 18.1.2017

Picture of an electric arc furnace. The potential for integrating heat storages in electro-steel plants was analysed.
© Badische Stahl-Engineering GmbH

Increasing efficiency of power plants and electric arc steelworks

How can energy efficiency in industry and thermal power

plants be increased by using thermal energy storages? Researchers are studying

the integration of thermal storage in different industrial and CHP processes.

The focus is on high temperature storages with a storage temperature above 200

°C. A highlight of the project TESIN is the development, design, build,

commissioning and operation of a latent heat storage unit in the operating CHP

plant in Wellesweiler, Saarland of STEAG New Energies.

Project status Storage Integration
Type of storage Latent heat storage, Molten salt
Storage construction Valves, fast relay switches, control technology
Temperature type High temperature
Storage/Charging Indirect
Storage time Medium (weeks to months), short
Number of cycles Variable – depending on standby use frequency, weekly to monthly
Charge temperature Up to 350 °C
Discharge temperature 300 to 350 °C
Storage capacity 1,5 MWh
Energy storage density ~180*MJ/m³
Project duration Mai 2013 until January 2018

The main goal of the TESIN project is the increase of energy efficiency in industry and energy supply by using thermal energy storages. BSE and DLR analyzed energy flows to determine the possibilities for integrating energy storages in the BSW electric arc steel plant in Kehl. A reference concept was created and the market potential investigated. STEAG New Energies (SNE) identified the market potential for the integration of storages in their generation systems in Germany an DLR analyzed storage concepts for these systems.

  • Aerial photo of the Wellesweiler CHP plant with a photomontage of the storage unit, showing details of the storage unit design © F. W. Brökelmann GmbH & Co. KG
  • Simulation of the storage integration of a two-tank molten salt storage combined with a Clausius-Rankine cycle in an electric arc furnace © DLR
  • Geographic locations of the SNE plants © STEAG New Energies GmbH
  • Schematic of the integration of the latent heat storage unit in the SNE cogneration plant Wellesweiler, Saarland © DLR
  • High power level extended fin designed and produced for the TESIN storage unit in an aluminium extrusion process and mounted with spring steel clips © F. W. Brökelmann GmbH & Co. KG
  • Latent heat storage unit shows during construction with mounted thermocouples © DLR

DLR developed a high performance latent heat storage, designed specifically for the cogeneration process in Wellesweiler of SNE with a high discharge power. The special heat transfer structures needed for that were developed together with FWB.The research storage unit that has been designed will be built, integrated in a running standby process and, after running an extensive test program, transferred into real operation. For the estimation of the possibilities for energy storages in industrial processes in general, a systematic method of analysis was developed at DLR and realized in a suitable software tool. With the data from electric arc steel production and the thermal power plant, a large field of applications can be confirmed. In the future, processes can be analysed with this tool more quickly and the best integration possibilities for storages can be recognized. The commisioning of the research storage unit is scheduled for winter 2017/2018.

Analysis of industrial and cogeneration processes

In this project, different industrial and CHP processes are analyzed regarding a possible storage unit integration. The focus is on high temperatures storages with storage temperature above 200 °C. A highlight of the project is the development, design, build, commissioning and operation of a latent heat storage unit in an operating CHP plant.

Within the project, the possible technical and economical potentials for storage unit integration in electric arc furnaces and CHP plants were determined. Measurements were conducted in the steel plant and the theoretical potential estimated using commercially available systems analysis software packages for both the steel plant and the CHP plants. In parallel, a large research storage unit is being integrated in a CHP plant of SNE.

Assess potential and then integrate the storage

In the CHP plant in Wellesweiler, Saarland, it was analyzed if the integration of a thermal energy storage unit in the process can eliminate the need for a constant firing of a standby boiler, with a concurrent significant reduction in the use of fossil fuels. Since the technical and economical estimation of the potential requires experience from the actual assembly, build and operation of the storage, the economical evaluation of the storage is a later part of this project.

In the case of the storage integration in electric arc steel plants, a detailed analysis of the energy uses was being conducted as a first step. The goal of this analysis is the identification of heat sources for which energy storage is technically and economically feasible. In parallel, processes which can serve as heat sinks for this energy are being identified. The concepts for integration were developed and involve the extraction of energy from the flue gas of the electric arc furnace to a two-tank molten salt storage. The storage is continuously discharged to a Clausius-Rankine steam process producing electricity. This steam can either be used by the plant or fed into the electricity grid

In parallel, the generation systems of SNE were being analyzed for integration possibilities for thermal energy storage. This research showed that the integration of energy storages technically and economically more feasible in the planning of new processes, in which the charging and discharging parameters are considered.

Work packages of the TESIN project

  • Reference concept und potential analysis for the use of storages in electric arc steelworks

The flow of energy in the electric arc steel production was determined and based on that, the possible improvements from integrating ideal storages was determined. Different concepts for storage, transfer and use of waste heat for the chosen variants were studied and compared and a reference concept developed. For the reference concept, a rough layout and an estimation of investment costs were made. The profitability of the integration of storages in the plant in Kehl were calculated. In addition, the main differences between different electric arc steelworks and their influence on storage solutions were identified.

  • Analysis of the potential for the use of storages in power plants

The power plants owned and/or operated by SNE that produce process steam, electricity and/or have back-up function for energy supply were investigated and energy flows analyzed. In order to determine other important parameters for the use of storages, a comparison to the cogeneration plant in Wellesweiler was carried out.

  • Further development of latent heat thermal energy storages for high power density and superheating

To replace the standby boiler in the cogeneration plant Wellesweiler, which runs at a constant minimal load, a latent heat storage unit must produce the required superheated steam for a short time (about 15 minutes). Previous storages in other projects were built for longer discharge times – about 1-2 or 6-8 hours – and for lower power levels. In addition, superheated steam, as opposed to saturated steam, is required from the storage unit. To this end,  further development of this technology was conducted. A fin design was developed and analyzed and simulations of the storage design und various operating conditions carried out.

  • Construction and integration of a PCM storage in a cogeneration plant

A storage system for the cogeneration plant Wellesweiler was designed in detail with the manufacturer and the rough layout for pipelines, valves and a wiring diagram were made, as well as a general plan for commissioning during operation. The required measurement techniques in the storage and the system were defined.
The build, test and delivery of the storage system are in process. In parallel to that, the necessary permits for operating the thermal energy storage in the cogeneration plant Wellesweiler have been requested. The system has been detailed and partially built, further build will occur after the delivery of the storage unit.

  • Commissioning and running of the PCM storage system in the cogeneration plant Wellesweiler

Cold and hot commissioning of the storage system and the partial systems is to be conducted. This is done to test the partial and total system. The storage will be filled with the salt inventory during the commissioning. Tests regarding heat losses, power performance characteristics and partial charging and discharging loads will be conducted. When the optimization of operation is finished and a secure storage operation can be guaranteed, the storage will be transferred to normal operation, during which data will be evaluated.

  • Development of an analysis methodology for using storages in industrial processes

Development and testing of a software tool for conceptional representation of industrial processes as a combination of energy sources, energy sinks,  energy conversion processes, storage elements and the temporally changing flows of energy was carried out.

  • Cooperation in the IEA Implementing Agreement ECES

The DLR is the operating agent in Annex 30 of the IEA Implementing Agreement ECES (Energy Conservation through Energy Storage) and contributes both in this role as well as technically. The title of the Annex is “Thermal Energy Storage for Cost-Effective Energy Management and CO2 Mitigation”. The research and results of the TESIN project are a part of the Annex.

Supported by: The Federal Government on the basis of a decision by the German Bundestag


2. April 2019
10th Batterietagung 2019

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Research funding

The information system EnArgus provides information on research funding, including on this project (German only).