Experimental study of thermal phenomenon in PSA air dehumidification

Abstract

A bench scale adiabatic PSA apparatus using a pair of vacuum-jacketed columns was constructed to study the non-isothermal effects involved in PSA air dehumidification with silica gel adsorbent. The thermal phenomenon coupled with the operating parameters, including half-cycle time, pressure ratio and velocity ratio of purge to feed, have been investigated systematically. A V-shaped temperature variation with time and a humped axial temperature distribution were observed for long cycle time due to thermal breakthrough. The temperature propagation speed and the local adsorption rate were obtained numerically from the experimental temperature distribution. The temperature propagation speed was greater than that for the mass because of the higher adsorption capacity of silica gel. The cycle time had no relation to the temperature propagation speed. A higher pressure ratio led to a faster temperature propagation, while the maximum temperature rise was almost the same. When the velocity ratio of purge to feed gas was less than 1.0, the desorption could not proceed completely and thus the mass transfer zone dispersed along the column. Recommendations for the design and operation of air drying PSA were also discussed on the basis of the above interpretation.