Equilibrium theory analysis of thermal regeneration of a humid adsorption column: Selection of optimal hot purge gas temperature

Abstract

A Thermal Swing Adsorption (TSA) process has been widely commercialised for its application to air drying. In designing an air-drying TSA, zeolite 13X is chosen as a desiccant when required to produce a very low dew point dry air due to its highly nonlinear, favourable isotherm. It is essential to make use of an external hot purge gas in producing such an extremely low dew point dry air, as the column has to be regenerated thoroughly for the next adsorption step. In case of the externally heated TSA, usage of a hot purge gas gives rise to huge energy consumption. Also the cycle time has to be made as short as possible to enhance the bed productivity. To optimise this energy-intensive process, it is crucial to find an optimal hot purge gas temperature at which the column can be regenerated as quickly as possible with less energy *Manuscript Click here to view linked References consumed. In this study, Equilibrium Theory approach was taken to analyse the thermal regeneration breakthrough of a zeolite 13X column saturated with a water vapour in which the equilibrium isotherm is estimated by Toth or Aranovich-Donohue isotherms. As a result of Equilibrium Theory analysis, it was found that the trailing front of a thermal regeneration breakthrough would exhibit a transition of the shape from simple wave to shock wave with increasing purge gas temperature. The purge gas temperature has to be chosen so that after thermal regeneration the targeted water vapour concentration remaining in the column lies within the concentration range occupied by the shock wave. A useful correlation that relates the targeted dew point of the remaining water vapour with the purge gas temperature was proposed. The presence of the optimal hot purge gas temperature estimated by Equilibrium Theory was validated by both full numerical simulation and ideal work consumption.

Modeling of Water Vapor Adsorption and Desorption in an Industrial Medical Air Dryer

“…However, further examination and comparison of experimental breakthrough curves with our model predictions revealed that this assumption was not entirely accurate in this study. Moreover, in the capillary condensation region, the adsorption and desorption breakthrough behaviors differ from each other. − This is due to the fact that in this region, the pores of the adsorbent fill with water molecules, which leads to a decrease in the available adsorption sites. As a result, the adsorption capacity of the adsorbent decreases while the desorption capacity increases.…”

Modelling of an Adsorption Heat Storage System and Study of Operating and Design Conditions

“…Kuznyk et al [47] took data from Bales [43] and fit a model based on the Langmuir isotherm, a linear contribution in the transition zone and capillary condensation. Ahn [48] uses experimental data from Wang [46] and combines the FHH and Aranovich-Donohue (AD) models. In the works cited, a good agreement is found between experimental and simulated data.…”

“…To pursue our model, we have selected the simulated isotherms from Ahn [48], which are also available in Figure 3. Simulated data agrees with the fitted experimental data from Wang [46].…”

Equilibrium Theory Analysis of Vacuum Swing Adsorption for Separation of Ethanol from CO2 in a Beverage Dealcoholization Process

“…Equilibrium Theory has since been developed further to analyse various adsorption systems, e.g. a PSA system with linear isotherm 27,28 , a PSA system with nonlinear isotherms 29,30 , effect of incomplete purge in a PSA system 31 , adiabatic temperature swing adsorption system 32 , etc.…”

“…While the process performances are affected by both adsorption equilibrium and kinetics, analysis of an adsorption process can be simplified greatly by equilibrium theory in which adsorption kinetic effects is neglected . The equilibrium theory has since been developed further to analyze various adsorption systems, e.g., a PSA system with linear isotherms , and a PSA system with non-linear isotherms, , the effect of incomplete purging in a PSA system, an adiabatic temperature swing adsorption system, etc.…”