A Computational Fluid Dynamics MacroModel for the Design of Bed Adsorbers

Abstract

A new three-dimensional (3D) multiphase computational fluid dynamics (CFD) model for adsorption physics in packed beds of spherical beads is developed and validated. The model is constituted at a macroscopic scale that integrates new volumetric source terms in the multi-species gas transport and energy conservation equations. These new terms, for the first time, take into account the impact of pores adsorption occupation rate (PAOR), or gas loading. Transient 3D simulations are performed at an atmospheric pressure of about 1.02 bar for different CO2-He gas mixture feed-in compositions (100%, 50%, and 15% CO2). The 3D model validation is conducted through quantitative comparisons with experimental data from the literature for CO2 adsorption on porous Zeolite-13X beads in a cylindrical fixed-bed. Results demonstrate the new model's ability to accurately predict the breakthrough curves and the thermal front propagation inside the bed. Finally, the new CFD model is applied to investigate CO2 capture in a new 3D design of fixed-bed adsorbers of equivalent adsorbent material volume. The new design outperformed the reference cylindrical design thanks to its new geometry with higher surface area. This allows to shorten the adsorption periods in pressure and temperature swing adsorption processes and thus increase the overall gas separation process productivity.

Figures (15)

• Figure 1: A schematic representation of the effect of the new introduced terms $(1-\varepsilon_p)\Gamma_Y$ of equation \ref{['equ:DeltaYspeciesConservation']} and $(1-\varepsilon_p)\Gamma_T$ of equation \ref{['equ:DeltaTenergyConservation']}. (a) Present two source terms modeling take into account the impact of PAOR (Pores Adsorption Occupation Rate) inside the adsorbing particles or beads/pellets in the new present 3D CFD model thus assuming ${{\partial q} \over {\partial \bf{x}}} \neq 0$. (b) The two terms assumption in old macro-model formulations as presented in the literature that assume ${{\partial q} \over {\partial \bf{x}}}=0$. $q$ is the adsorbed quantity inside the particle of volume $V_p$ and porosity $\varepsilon_p$.
• Figure 2: New volumetric source terms ($\Gamma_Y$ and $\Gamma_T$) as function of the CO2 feed-in percentage. (a) $\Gamma_Y$; (b) $\Gamma_T$.
• Figure 3: A perspective view of the 3D CFD computational domain of the fixed-bed adsorber. (a) bed dimensions; (b) the mesh topology with boundary mesh layers close to the external wall of the bed.
• Figure 4: Validation of the present 3D CFD model results against the experimental data of Wilkins et al. 2019 wilkins2019measurement. Case at 100% CO2 feed-in and $5.83 \cdot 10^{-6} m^3/s$ flow rate, $p=1.02$ bar. Temperature profile corresponds to the centerline local position ($r=0$) located at $z=52 mm$ away from the bed inlet. (a) Outlet CO2 mass fraction (Y) as a function of time in seconds; and (b) local temperature T at $r=0$ and $z=52 mm$ inside the bed as function of time in seconds.
• Figure 5: Validation of the present 3D CFD model results against the experimental data of Wilkins et al. 2019 wilkins2019measurement. Case at 50% CO2 50% He feed-in and $5.25 \cdot 10^{-6}~m^3/s$ flow rate, $p=1.02$ bar. Temperature profile corresponds to the centerline local position ($r=0$) located at $z=52~mm$ away from the bed inlet. (a) Outlet CO2 mass fraction (Y) as a function of time in seconds; and (b) local temperature T at $r=0$ and $z=52~mm$ inside the bed as function of time in seconds.