Dynamic behavior of CO2 adsorption from CH4 mixture in a packed bed of SAPO-34 by CFD-based modeling

Abstract

Abstract In this work, a dynamic non-isothermal adsorption process of CH4 and CO2 in a fixed bed of SAPO-34 particles was modeled by coupled DEM-CFD. This Euler–Lagrange method gives access to specification of each adsorbent pellet including location, temperature and concentrations, and facilitates study of phenomena like adsorption. Transport phenomena including heat and mass transfer in fluid and between solid and gas were taken into account. Eventually the model was validated by experimental results of breakthrough curve. Especially near wall channeling effect and the role of inlet feed velocity on the bed efficiency were addressed in this work. Local and bulk porosity values calculated using DEM model showed an acceptable agreement with previous empirical equations. Results indicated that this coupled method can be applied as a promising tool to study the mass transfer zone and efficiency of the adsorption process. The results revealed that as the feed continues to flow into the column, the lower layers of the adsorbent particles become practically saturated and then the mass transfer zone starts moving upward to a region of fresher adsorbent in the column. Also, the results showed that, at a low inlet velocity with a low Peclet number (Pe = 0.195), channeling effect is reduced and the diffusion mechanism controls the mass transfer. However, HETP enhances with increase in the feed gas velocity (Pe = 2.25) as well as increase in deviation from plug flow regime, and consequently the adsorption efficiency decreases. HETP decreases drastically at the beginning with increase in interstitial velocity. Increase in the interstitial velocity beyond a particular value of 0.5 cm s−1 leads to increase in the HETP value. This trend and presence of a minimum in this graph were explained based on Van Deemter concept.