Modeling the effect of humidity and temperature on VOC removal efficiency in a multistage fluidized bed adsorber

Abstract

The competitive adsorption of volatile organic compounds (VOCs) and water vapor onto beaded activated carbon (BAC) in a fluidized bed adsorber is developed in the form of a two-phase model using the Manes method. The Manes method uses as input single component adsorption isotherms described by the Langmuir model for adsorption of VOCs and the Qi-Hay-Rood (QHR) model for adsorption of water vapor. The effect of temperature is accounted for using the linear van’t Hoff relationship for Langmuir affinity coefficient. The effects of relative humidity (RH) and temperature in the simulations are validated using experimental data, with very good agreement observed (e.g. R2 = 0.98 comparing overall removal efficiencies). Humidity begins to have an effect on the adsorption of 1,2,4-trimethylbenzene (TMB) on BAC starting at 70% RH in the form of a reduction in overall removal efficiency due to fewer available adsorption sites. The overall removal efficiency decreases from 93.0% at 70% RH to 85.4% at 90% RH, and then plateaus with further increase in RH up to 100%. In dry air, temperature variation has a small effect on removal efficiency, showing a reduction in modeled overall removal efficiency from 93.0% to 90.2% when the adsorption temperature increases from 22 to 50 ˚C. On the other hand, at high RH values, temperature has a larger and positive effect on removal efficiency due to RH change. Increasing the temperature of a stream of humid air (RH = 95%) from 22 to 27 °C increases the TMB removal efficiency by 6.9% from 85.3% to 92.2%. Taking into account the effect of humidity and temperature, the model can be used to help optimize fluidized bed adsorber operations in industrial applications.