Research. The system that stores and restores heat thanks to zeolites

These are very small balls, the color of light sand, which flow between the fingers. “Zeoliths exist in their natural state, but these are synthetic, produced on an industrial scale from sources of silica and aluminium. It is a material easy to implement on a large scale, not very expensive, already widely used in the field of petrochemicals. It’s from the same family as what you find in the little sachets placed in new shoes,” explains Simona Bennici. Director of CNRS research in energy optimization at the Institute of Materials Science of Mulhouse (IS2M) where she arrived at the end of 2016, this Italian has been studying the thermochemical storage of heat for more than ten years. From 2017, and thanks to the connection operated by the Carnot-MICA Institute

it has started a collaboration with RCUA (Urban heat networks of Alsace). Joint subsidiary of RGDS and Primeo Energie, this energy company operates 24 heating and cooling networks, on the scale of a district or a city, in the Eurometropolis as well as in the Mulhouse conurbation. About 30,000 homes are heated thanks to these so-called “virtuous” networks supplied mainly by renewable energies (biomass, geothermal energy, solar, etc.), with fossil fuels providing extra fuel only during peak consumption periods in very cold weather. “RCUA’s goal is to switch to 100% renewable energy, so the company is looking for ways to store the excess heat produced at certain times, and to release it when necessary,” notes the researcher. This is where zeolites come in. Because these little balls have amazing properties. “When you hydrate them, they heat up on their own. We can then recharge this heat by dehydrating them,” sums up Simona Bennici. And this hydration-dehydration cycle can be repeated almost endlessly without the material degrading, including when it is subjected to the usual atmospheric pollutants, whether indoor or outdoor.

“Develop this technology for all networks” of RCUA

To be able to make the most of these precious properties, it was necessary to develop a high-performance technology. With the help of Elliott Scuiller, in a Cifre thesis (industrial agreement for training through research), remunerated by RCUA, and other colleagues from IS2M, the research group led by Simona Bennici has thus developed a thermochemical heat storage demonstrator, funded by the Carnot-MICA Institute: not a prototype, but “a pilot system, which allows us to model the storage system, to acquire data under conditions close to those of a heating network”, explains the researcher.

The next step is approaching. “Within a year, a year and a half,” she estimates, “we will be able to set up an industrial demonstrator for RCUA that will work with a few tons of materials. » « We are going to validate all this on the heating network of the autonomous port of Strasbourg, which is supplied by the fatal heat of the Blue Paper paper mill, confirms Hervé Lamorlette, general manager of RCUA. On this industrial scale, we will be the first. The idea is then to develop this technology on all of our networks. »

The disadvantage of this technology, because there are bound to be some, “is that each system must be adapted to its specific application”, indicates Simona Bennici. But in this period when all the alternatives to fossil fuels – and in particular to Russian gas – are on the rise, this first application should lead to others. “Today, I have a lot of requests from manufacturers who work in energy, particularly in heat pumps and who are looking for new storage systems”, rejoices the researcher.

The Carnots form a network of 39 French public research structures, recognized and labeled, to carry out partnership research projects in the service of business innovation. The Carnot label was created in 2006, it is awarded by the Ministry of Higher Education, Research and Innovation.

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