Industrial Waste Heat : Valorisation by Thermocline Storage

Waste heat is heat that is generated but not used, and is therefore released into the atmosphere. It is particularly prevalent in various industrial sectors such as ceramics, metallurgy, glassmaking, food processing, construction, etc. Part of the heat lost in these industrial sectors is in the form of hot fumes. Depending on the sector and the industrial process, rejected fumes have different characteristics in terms of temperature, composition, flow rate and intermittence of emission. To date, little use has been made of industrial waste heat.

One potential solution is to recover industrial waste heat using thermocline storage. This is a storage system consisting of an insulating envelope filled with a thermal storage material. During the charging phase, the hot fumes generated by an industrial site pass through this envelope and transfer heat to the storage material. A temperature gradient zone (thermocline zone) is formed within the storage material, delimiting the hot and cold zones. This thermocline gradually moves towards the outlet of the storage envelope. During the discharge phase, a fluid at ambient temperature (e.g. air) circulates through the system and recovers the stored heat, generating a hot fluid at the outlet. This hot fluid is used to recover waste heat.

This article presents the sources of waste heat available in France and around the world, and the solutions for recovering them, in particular the thermocline storage solution. Heat transfer fluids and thermal storage materials are discussed. An example of a recent industrial application to recover fumes from a ceramics production site is presented.