Experimental investigation of CaCO3/CaO in a spiral coil reactor for thermochemical energy storage

Abstract Simultaneously offering sufficient heat and mass transfer is a significant challenge for the reactor design in the field of thermochemical energy storage owing to either a low thermal conductivity or a low permeability of the solid reactants. This paper proposes a spiral coil reactor based on combination of pneumatic transmission and secondary flow for thermochemical energy storage. The CaCO3/CaO is selected as reaction medium. The gas-solid flow behavior, energy charging and discharging are investigated by the experimental methods. The results show that CaCO3 conversion is around 2–5% during the energy charging experiments and CaO conversion is around 60–68% during the energy discharging experiments. The CaO conversion is a little higher than that in the fluidized bed under the same condition. Both the unstable gas velocity and the fluctuation of pressure drop in the spiral coil reactor due to particles agglomeration and sintering at high charging reaction temperature account for the low CaCO3 conversion. In addition, the energy discharging experiments also indicate that the flow rate and reaction temperature have large effects on the CaO conversion. An increase in the gas velocity relieves CaO sintering, consequently resulting in a higher CaO conversion. Moreover, the reaction rate can be improved at higher energy discharging temperature which leads to enough residence time and higher CaO conversion. Overall, this paper provides a novel insight for gas-solid reactor design in the field of thermochemical energy storage.