The development of a bench-scale fluidized bed reactor for thermochemical energy storage under partial vacuum

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A significant portion of Canadian residential space heating and hot water needs can be met with solar thermal energy; however, the penetration of solar thermal technology in Canada is currently limited by the sizable thermal storage systems that are required during the heating season when solar insolation is low. In comparison to the conventionally large tanks required for storing sensible heat in liquid water, thermochemical reactions between solid adsorbent materials and water in the gas phase possess much higher energy storage densities, providing a more compact and loss-free thermal storage solution. Thermochemical storage via sorption is indirect, where enthalpy is released when water vapour bonds with the surface of an adsorbent during adsorption. Subjecting the saturated material to an equal amount of heat as that released during adsorption will break those bonds (desorption), regenerating the material to undergo further adsorption-desorption cycles. Adsorbents including synthetic zeolites have been investigated using fixed bed reactors at atmospheric pressure and promising results have been obtained with respect to the high energy storage densities and long life cycle of these materials. This research program will follow recommendations made for future work identified during a successful NSERC Engage period, and will explore the effects of pressure and fluidization on the sorption of zeolite 13X for the application of low-temperature thermal energy storage. It is expected that faster desorption at a lower reactor temperature can be achieved under a partial vacuum in the reactor, and that a gradual reduction of pressure in the reactor will prolong the release of heat during adsorption. As an extension of the fixed bed design, it is expected that heat and mass transfer between the gas and solid will be improved with fluidization. After a comprehensive model of a bench-scale fluidized bed reactor has been simulated in a multiphysics software, an apparatus will be constructed for an experimental phase in which the adsorption and desorption of fluidized zeolite 13X will be observed under positive and negative (vacuum) gage pressure respectively.