A scaling procedure for designing thermochemical energy storage system

Abstract

Thermochemical energy storage (TCES) technology offers a promising avenue for achieving prolonged thermal energy storage through reversible gas-solid reactions. In the present work, a scaling analysis approach is presented to derive the relevant length and time scales for heat charging and discharging processes occurring inside a porous reactor bed of a TCES system. The processes involved are vapour flow through the porous bed, coupled heat and mass transfer, and heat and mass absorption/release in conjunction with reaction kinetics, for the case of water vapour and potassium carbonate as the gas-solid pair. This analysis employs an order-of-magnitude approach on mass, momentum, and energy conservation equations. The scaling analysis of continuity and momentum equations derives the scale for critical vapour penetration depth. It signifies the length scale beyond which pressure drop becomes significant, leading to a significant reduction in the reaction rate. Similarly, a critical thermal diffusion length scale is derived from the scaling analysis of the energy equation. This scale signifies the length beyond which the reaction rate drops significantly due to limited thermal diffusion. The derived scales characterize the performance of the energy storage bed and help in determining bed dimensions for an effective flow of heat and water vapour through the bed.