Modeling VOC adsorption in lab- and industrial-scale fluidized bed adsorbers: Effect of operating parameters and heel build-up

Abstract

Scale-up and optimization of fluidized beds are challenging due to the difficulty in accounting for the interrelated effect of various phenomena, which are typically described by empirical and/or semi-empirical equations. In this study, a two-phase model was introduced to simulate the adsorption of VOCs on beaded activated carbon (BAC) in a lab-scale fluidized bed adsorber. The model assumes the presence of a bubble phase free from adsorbent particles, and an emulsion phase composed of the adsorbent particles and interstitial gas. The versatility of the proposed model was then evaluated using data from an industrial scale adsorber with different operating conditions, adsorbent properties, and bed geometry. The response of the model to the operating conditions (adsorbent feed rate, air flow rate and initial concentration) showed better agreement with the experimental lab-scale data when the emulsion gas in two-phase model was considered in plug flow than in perfectly-mixed flow (R2 = 0.96 compared to 0.91). To simulate the performance of BACs with different service lifetimes (degree of exhaustion as a result of heel developed inside their pores), the main characteristics of the BACs (pore diameter, porosity, and adsorption capacity) were first correlated to their apparent densities. The model could accurately predict the experimental lab-scale VOC concentrations in each stage (R2 = 0.92) as well as overall removal efficiencies (R2 = 0.99) for BACs ranging from virgin to fully-spent. Finally, the model was used to predict the performance of an industrial-scale fluidized bed adsorber for VOC removal at different operating conditions and apparent densities. Predicted and measured VOC removal efficiencies were in good agreement (R2 = 0.94). Although the model was verified for adsorption of VOCs on BAC, the modeling approach presented in this study could be used for describing adsorption in different adsorbate-adsorbent systems in multistage counter-current fluidized bed adsorbers.