The dynamics of a packed gas absorber by the pulse response technique

Abstract

AbstractThe dynamic response of a packed gas absorber to inlet gas composition changes was investigated by the pulse response technique for the case where absorption was accompanied by pseudo first‐order irreversible chemical raction.The solute‐carrier‐solvent system was carbon dioxide‐air‐0.07 normal aqueous sodium hydroxide solution. The column used was 6.5 in. I.D. Plexiglass packed to a height of 6.15 ft. with either ¼‐in. Raschig rings or ¾‐in. Berl Saddles. Gas flow rates ranged from 1.5 to 10 lb.‐moles/hr./sq.ft. and liquid flow rates ranged from 0 to 200 lb.‐moles/hr./sq.ft. A pulse of carbon dioxide was injected into the inlet air stream and monitored as it entered the packed section. The outlet gas and liquid phase concentrations were continuously monitored as the resulting pulses left the packed section. The pulse response data were reduced to frequency response by digital computer calculations. Reliable data could be obtained over the frequncy range 0 to 5 radians/second.The experimental results were compared with theoretical predictions from the slug flow, axial diffusion, and mixing cell models. Both the mixing cell model and the axial diffusion model satisfactorily predicted the experimental frequency responses over the entire frequency range covered. The slug flow model was found unsatisfactory for predicting gas‐phase amplitude ratios at high frequencies, where axial mixing affected the amplitude ratios. Gas‐phase particle Peclet numbers and overall mass transfer coefficients based on the gas‐phase driving force determined in the present absorption system were in reasonable agreement with the values reported in the literature.