(355c) A Numerical Model of Transient Thermal Transport Phenomena in a High-Temperature Solid-Gas Reacting System for CO2 Capture Applications

A numerical model coupling transient radiative, convective and conductive heat transfer and mass transfer to chemical kinetics of heterogeneous solid−gas reactions has been developed for a semi-transparent, non-uniform, and non-isothermal particle undergoing cyclic thermochemical transformations.  The thermochemical calcination−carbonation reaction pair is selected as the model cycle because of its suitability for solar-driven CO₂capture:

 Solar, endothermic step:              CaCO₃ → CaO + CO₂

Non-solar, exothermic step:          CaO + CO₂ → CaCO₃

Mass and energy conservation equations are solved numerically for the solid and gas phases using the finite volume method and the explicit Euler time integration scheme. The solid phase is modeled as an emitting, absorbing and anisotropically scattering porous medium. Rosseland diffusion approximation with non-gray medium radiative properties is used to model the internal radiative transport. A volumetric reaction model is employed for both the calcination and carbonation reactions. Time-periodic boundary conditions for high-flux solar irradiation and the external gas species concentrations are applied. The model predicts the time-dependent temperature distribution, extents of the calcination and carbonation reactions, and consequently the overall amount of CO₂ captured by the single particle over repeated cycles as a function of solar concentration ratio, CO₂ partial pressure in the ambient gas, and particle size. Results support the potential of calcium based sorbent for CO₂ capture, and provide input to solar-driven implementation of the process.