Experimental assessment of radio frequency-driven desorption of zeolite 13X for application in thermal energy storage systems

Thermal energy storage systems are essential parts of an energy mix in which renewables are a significant part, with targets of the share of renewable electricity at national level higher than 50 %. In order to reach this target, different types of energy storage are needed, including both centralized and decentralized ones. Among the various technologies that can be applied, a promising solution could be the use of thermochemical energy storage systems in which the charging process involves direct heating of the storage material, using electro-magnetic fields. In the present work, the technical feasibility in the use of radio-frequency for the desorption of zeolites under the typical operating conditions of a thermal energy storage was evaluated. Several adsorbents were evaluated and, ultimately, tests were carried out using commercial zeolite 13X from UOP, in three morphologies. The main goal of the activity was to characterize the temporal evolution of the temperature of the material, thus identifying the dynamic trend and, at the same time, defining the efficiency of the process, in order to compare it with indirect charging methods. Using 0.25 W/g power for the RF generator, all three morphologies reach the target temperature of 150 °C: the cylindrical pellets are the faster, followed by the spherical beads with larger diameter, whereas the smaller beads are the slowest. The temperature increase, for all the materials, is exponential. Comparing the results of the tests with the theorical energy needed for the desorption of the material, it is possible to notice that the efficiency in charging process is in the range 94–97 %.