Analysis of thermal deposition of MgCl2·6H2O hydrated salt in the sieve-plate reactor for heat storage

Hydrated salt thermochemical energy storage which utilizes reversible gas-solid reactions to store heat for charging and release heat for discharging has a promising application in the energy utilization system. A novel sieve-plate hydrated salt thermochemical energy storage system (TCES) with the reactive porous bed of MgCl2·6H2O is investigated, and the mathematical equations describing the heat and mass transfer for the TCES are developed to analyze the effects of the geometric parameters of reactor and operating conditions on the thermal decomposition of MgCl2·6H2O salt during charging (dehydration). The rises of the sieve plate number and length within a certain degree cause the shorten time to reach the equilibrium extent conversion at input temperature. The δ, ratio of channel width h1 to reactive bed thickness h0, needs to be optimized to achieve higher dehydration efficiency. More residence time of heating gas and more heat storage can be achieved with the relatively higher input temperature. The kinetic factor needs to be above Rkin = 1 · 10−3 s−1 to avoid lower extent conversion and larger time length for the reactive bed to reach the equilibrium phase at input temperature. The dehydration efficiency in the reactive bed and the heat utilization rate of heating gas in the charging are related to the heating gas velocity. The simulations agree with the published TGA-DSC testing results. For the current mode, the reactor with a 6 sieve plates of L0 = 24-26 cm and a δ = 0.8 flow channel as well as the relatively higher thermal conductivity and operating temperature within a certain degree in the reactive bed are proposed.