Effects of Particle Stratification on Fixed Bed Absorber Performance

Abstract

The effects of adsorbent particle size distribution (PSD) and the layering of particles in stratified and reverse stratified modes on the performance of fixed bed adsorber were investigated. Using trichloroethylene as the adsorbate and granular activated carbon as the adsorbent, experimental studies were conducted in stratified beds for different flow rates and influent concentrations. The homogeneous solid diffusion model was modified to take into account PSD and was used to simulate breakthrough curves. The PSD-based model was validated using experimental data and was found to be more accurate in predicting the breakthrough curves than the non-PSD-based model. The validated model was used to conduct simulations to examine the effects of key variables on performance in the stratified and reverse stratified modes. In the reverse stratified mode, the adsorbent particle size decreases gradually in the direction of flow. Model simulations indicate that this mode of operation increases breakthrough time, decreases the time to reach saturation, and thereby increases the overall adsorbent capacity utilization. The mass transfer zone for the reverse stratified bed was found to be narrower and sharper than that for the stratified bed. These model predictions have important ramifications to the water and wastewater industry in terms of reducing the overall cost of treatment using granular activated carbon adsorption.