Thermal transport model of a packed-bed reactor for solar thermochemical CO₂ capture

A 1 kW_th dual-cavity solar thermochemical reactor concept is proposed to capture carbon dioxide via the calcium oxide based calcination-carbonation cycle. The reactor design is refined using a numerical heat and fluid flow model for the calcination step. The Monte Carlo ray-tracing and net radiation methods are employed to solve for radiative exchange in the inner cavity, coupled with a computational fluid dynamics analysis to solve the mass, momentum, and energy equations in the concentric reaction zone modeled as a gas-saturated porous medium consisting of optically large particles. The cavity diameter and length-to-diameter ratio are varied to study their effects on pressure drop, temperature distribution, and heat transfer in the reactor. The Monte Carlo ray-tracing and net radiation methods are compared for accuracy and computation time. The net radiation method reaches convergence 1.5 times faster than the Monte Carlo ray-tracing method and provides a smoother radiative flux distribution. Increasing the cavity diameter and length-todiameter ratio at a fixed volume of the reaction zone decreases the radial temperature gradients across the cavity wall and within the reaction zone. However, it also results in increased pressure drop and reduced heat transfer to the reaction zone.