Local dynamics of CO2 adsorption in a discrete packing contained in a thin tube was assessed by 3D modelling. Thin tube packed bed adsorbers are currently used over tube structures in thermochemical energy storage systems and atmospheric revitalization of confined spaces. Driven by interplays between key factors such as the exothermicity and the fluid flow, the advective transport was found less effective than the diffusive one on the breakthrough trends of CO2 which displayed significant concentration gradients at both inter- and intra-particle scales. The lack of angular symmetry inside the particles by the reduction in resistance to mass transfer in area of solid particles exposed to high velocities led to greater convective transports from bulk of the gaseous phase to the pores. The result of the modelling agreed with the experimental data obtained at the exit of the adsorber, helping reduction in reliance on the empirical dispersion models used in the one-dimensional modelling.