Thermal Storage for Eco-Efficient Processes – STEEP

To set up a PCM storage system, several technological and economic challenges are identified and guide the STEEP project:
• The storage materials development at low prices and long lifetime;
• Improvement of thermal, physical and chemical characteristics of these materials: mainly kinetic of crystallization and thermal conductivity;
• Integration of the material in the storage system and design of the tank and \ or heat exchanger.
• Integration of the storage system in a thermal processes and regulation, and control of the whole system.
To carry out this research, collaborative work is done at several scales: from a few milligrams of PCM in laboratory calorimeters, to tons in the preindustrial system through the few kilos of laboratory-scale prototype. This experimental work is coupled to a numerical study which results are expressed in terms of energy efficiency, economic viability and environmental impact.

The first mains results of the project are:
• Identification of industrial processes;
• Obtaining, in our temperature range, two appropriate PCM in terms of cost and life time;
• The finalization of the laboratory thermal storage test bench.

The final prospects of the project is the development and the medium-term marketing of an optimized thermal energy storage system for waste heat recovery in the industry. The impacts of this technology are numerous.
This system will allow energy savings. Indeed, by recovering industrial waste heat, we will reduce the power demand and increase the overall energy efficiency of industrial processes. Although the addition of a storage system generates an additional investment cost, it will be made profitable considering the energy savings realized in the long term.
On the other hand the energy storage will reduce the peak consumption. The storage of thermal energy in industrial processes allow smoothing curves of loads by reducing the maximum power demand (ie peak shaving) on electric and heating networks.
Finally, saving energy will permit to reduce the emission of greenhouse gas.

A presentation was done in the ECOS conference, in Pau (30 June to 3 July 2015).

Sacha Rigal, Didier Haillot, Stéphane Gibout, Erwin Franquet and Jean-Pierre Bédécarrats, Latent Thermal Energy Storage System for Heat Recovery: Experimental and Numerical Investigations, 28th ECOS conference, Pau, France

This oral communication focused on the modeling of the thermal storage system.

A large amount of energy is rejected by the industry at low temperature level (between 0 and 150 ° C). Indeed, considering all the French industrial processes, the amount of energy lost in this temperature range is estimated at 75 TWh / year. In order to improve the overall energy efficiency of these processes, it is possible to re-use this waste heat.

However, in a large number of industrial processes, there is time delay between the process step at which the energy is lost and the process step at which this energy could be recovered. A thermal storage system should then be integrated in the process to match the energy demand and the production. This would lead to a reduction in the consumption of primary energy.

The thermal energy storage technology included Phase Change Material (PCM) appears particularly attractive in this particular application. It combines large volume and mass storage capacity and constant charge and discharge temperature. These two parameters are particularly suitable for heat recovery in batch processes.

However, the implementation of these storage systems is determined by scientific and technological bottleneck. These are at different levels: thermal storage material, system and its command control, integration in industrial processes….

Within a framework of industrial research, the objective of the project Thermal Storage for Eco-Efficient Process (STEEP) is to develop a storage system based on solid-liquid PCM technology in a temperature range between 80 and 140 ° C. The consortium to develop this system is composed of two laboratories and three companies. The project coordinator is the Laboratory of Thermal Energy and Processes (LaTEP) specializes in energy storage systems by latent heat. Other partners include the Eco Efficiency and Industrial Processes Department of EDF, the Institute of Materials, Microelectronics and Nanosciences de Provence (IM2NP), the R & D department of CRISTOPIA Company, and the R&I center of the Industrial Thermal Applications Company (CIAT).

STEEP project aims to demonstrate the technical and economic feasibility of a storage system adapted to the energy recovery in industrial process and using a solid-liquid PCM technology. It revolves different tasks ranging from materials development to their implementation in a pilot plant. The numerical evaluation of the performance of an industrial process incorporating a storage module for PCM will also be done. These performances will be expressed in terms of energy, economic and life cycle analysis (LCA).