Cross-Scale Transfer and Reaction Coupling during CO₂ Capture: A Novel DEM-PNM-Based Pore-to-Reactor-Scale Model

Abstract

The mesoscale packing structure and its coupling with the gas flow and heterogeneous reaction kinetics are key for CO2 capture using CaO-based sorbents. A series of packing structures were constructed based on the discrete-element method (DEM), and the accuracy was verified by electronic computer X-ray tomography (CT). It was found that the random particle filling structure based on the DEM can accurately reflect the coordination number and connectivity between pores. Further, a two-dimensional pore network model (PNM) including the effects of packing structure evolution and diffusion–reaction kinetics was developed to study the multiscale coupling among gas flow, energy transport, and carbonation reactions in packed-bed reactors. The calculated results were validated by comparison with experimental data from thermogravimetric analyzer (TGA) tests during the CO2 capture process. The short-circuit flow of the reactive gas caused by the inhomogeneous packing structure of the binary composite packing bed was not linearly correlated with the mass percentage of the binary particles. The differences in the CO2 capture efficiency and sorbent utilization induced by the packing structure characteristics were demonstrated numerically to decrease gradually with the Peclet number at an inlet velocity of 0.8 m/s. Moreover, a dimensionless Thiele modulus was introduced to assess the effect of internal diffusion. This model and the obtained results can be used for the optimization and design of packed-bed reactors with gas–solid uncatalyzed reactions.