Performances and modelling of a circular moving bed thermochemical reactor for seasonal storage

A novel thermochemical reactor was designed, built, and tested at Besol's and CEA-INES' labs. Its circular shape and its vibrating bed allow to move the solid hydrate constantly, therefore increasing turbulence in the moist air heat and mass transfer region. A reactor model was developed and identified in order to calculate its performances over a wide range of operating conditions and to understand what are the key factors leading to increased performances, especially regarding the specific behavior of the composite material made of calcium chloride incorporated in a silica gel matrix. New kinetic equations were developed while combining sorption and porous medium physical phenomena. The model was further refined with a 10 layers solid bed spatial discretization. However vibrations actually mix those layers, which would require a more detailed approach. Nevertheless, outlet parameters were predicted in both modes with a deviation lower than 0.72 K equivalent.

Test results in realistic conditions showed an average 356 W heating power with an air temperature elevation of +6.0 K, while desorption cooling power was 278 W with an average 4.5 K temperature decrease. The usable energy density with this 0.163 m3 uninsulated reactor was 200.4 W h per kg of 9% hydrated solid composite, which is adapted to seasonal storage since it is close to the 207.8 W h per kg theoretical target. Electrical consumption for air circulation is only about 10 W, but vibration accounts for almost 70 W, which still needs to be reduced. Detailed results showed that a continuous solid flow and a counter current configuration would lead to further increase average outlet temperature.