2024-01-25 07:30:48
Industry loses around 20% of the energy it consumes in the fumes it releases into the atmosphere. Among the solutions known to date, the recovery and valorization of industrial waste heat via thermocline storage is relevant and has already been commercialized.
An extract from “Industrial fatal heat: recovery through thermocline storage” by Doan PHAM MINH, Yasmine LALAU, Thibaut ESENCE
Historically, high-temperature massive heat storage has mainly been developed for thermodynamic solar power plants. Storage makes it possible to absorb variations in sunlight and control the conversion of heat into electricity. The technology that has established itself in the power plants currently in operation is two-tank thermal storage. A heat transfer fluid circulates between two tanks, one called a “hot tank” and the other “cold tank”. During the charging phase, the fluid circulates from the cold tank to the hot tank, recovering heat from the source located between the two tanks. In the discharge phase, the fluid circulates in the opposite direction and returns the heat to the point of consumption. Heat recovery and restitution can be carried out directly, in contact with the source, or indirectly, via an exchanger. Thermocline type thermal storage can be seen as an evolution of two-tank storage. It consists of making hot and cold fluids coexist in a single tank. The separation then takes the form of a “thermocline zone”.
What is thermocline storage?
This type of system consists 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 this material, which delimits the hot and cold zones. This thermocline gradually moves towards the exit 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 and thus the waste heat is recovered.
Thermocline storage can occur in two forms.
- Without packing: the tank is entirely occupied by the heat transfer fluid, which also acts as a thermal storage material. The fluid is therefore a liquid selected for its high volumetric heat capacity. In practice, the storage liquid must have low thermal conductivity to limit heat exchange between the hot and cold zones.
- With packing: the tank is occupied by a fixed bed of storage material. Part of the heat transfer fluid is therefore replaced by a solid, whose performance in terms of energy density and/or cost is more advantageous. These storage systems have been studied since the 1980s for their use in solar power plants and more recently for waste heat recovery applications.
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