A numerical model for predicting adsorption behaviour in small activated carbon beds

Abstract

A Reynolds-Averaged Navier-Stokes (RANS) model to describe the adsorption of volatile organic compounds on activated carbon beds was developed, using the Dubinin-Radushkevich adsorption isotherm with a Linear Driving Force (LDF) kinetic model. The model was validated using experimental breakthrough data for cyclohexane. The model was then used to predict the impact of adsorption kinetics in small activated carbon beds. The adsorption showed two distinct phases: an initial period where contaminant very rapidly penetrated into the bed, followed by a period where the contaminated front advanced at a slow, constant pace. The initial distance penetrated into the bed was shown to be inversely proportional to the LDF kinetic constant, a trend the same as that predicted using a common plug-flow mass-balance model. The velocity distribution after this initial phase showed some small variations with kinetic constant. This suggests that the kinetic constant may have an impact on the speed of the advance of the contaminated front, an effect not seen in plug-flow models.