Mass transfer in structured packing

Erasmus, Andre Brink (1999-10)

Thesis (M.Ing.) -- University of Stellenbosch, 1999.

Thesis

ENGLISH ABSTRACT: Distillation forms the core of all liquid mixture separation processes. It is the benchmark to which all new separation processes are compared. In the design of these columns, especially those containing structured packing, design engineers still rely on rules of thumb or data interpolation, which lead to the addition of huge safety margins. This study is a contribution towards establishing a dependable mass transfer model for structured packing. It is based on the analogy between a short wetted wall column and the flow passages found inside structured packing. The two-film theory was used to separate the total resistance to mass transfer in a gas side- and a liquid side resistance. A gas phase mass transfer correlation was developed by evaporating several pure liquids in a short wetted wall column. The effect that the complex surface of the structured packing, Mellapak 350Y, has on the gas phase mass transfer rate was investigated. It was found that the liquid surface profile created by this surface causes higher mass transfer rates than measured for the smooth surface. The liquid side resistance to mass transfer was investigated by evaporating binary mixtures in the wetted wall column. No substantial liquid side resistance was found. Significant enhancement of the gas phase mass transfer was observed for mixtures where there were a difference between the surface tension of the solvent and solute. The gas phase mass transfer correlations based on the wetted wall experimental work for both the smooth and complex surfaces was used to predict the separation efficiency of the structured packing, Mellapak 350Y, in binary total-reflux distillation. The complex surface correlation proved to be more accurate. It was found that the predicted packed height is sensitive towards the estimation of the binary gas phase diffusion coefficient.

AFRIKAANSE OPSOMMING: Distillasie is die proses wat die meeste gebruik word vir die skeiding van vloeistofmengsels. Alle nuwe skeidings prosesse word direk hiermee vergelyk ten einde die effektiwitiet daarvan te bepaal. In die ontwerp van distillasie kolomme, veral die wat gestruktureerde pakking bevat, gebruik ontwerpingenieurs meestal duimreels of data interpolasie. Dit lei tot baie konserwatiewe ontwerpe met groot veiligheidsfaktore. Hierdie werk is 'n bydrae tot die skepping van 'n betroubare massa-oordragsmodel vir gestruktureerde pakking. Dit is gebaseer op die analogie tussen 'n kort benatte wand kolom en die kanale wat in gestruktureerde pakking gevind word. Die twee-film teorie was gebruik om die totale weerstand teen massa-oordrag te skei in 'n gasfase- en 'n vloeistoffase weerstand. 'n Gasfase massa-oordragskorrelasie is ontwikkel gebaseer op die verdamping van 'n paar suiwer vloeistowwe in 'n kort benatte wand kolom. Die effek wat die komplekse oppervlak van die gestruktureerde pakking, Mellapak 350Y, op die gasfase massa-oordrag het, is ondersoek. Daar is gevind dat die vloeistofoppervlakprofiel wat deur die komplekse oppervlak gegenereer word 'n hoer massa-oordrag tempo veroorsaak in vergelyking met die gladde oppervlak. Die vloeistoffase weerstand is ondersoek deur binere mengsels in die benatte wand kolom te verdamp. Geen betekenisvolle weerstand is gevind nie. 'n Beduidende verhoging in die gasfase massa-oordrag is waargeneem vir die binere sisteme waar daar 'n verskil in die oppervlakspanning van die komponente is. Die gasfase massa-oordragskorrelasies, gebaseer op die benatte wand eksperimentele werk vir beide die gladde- en die komplekse oppervlak, is gebruik om die skeidingsdoeltreffendheid van die gestruktureerde pakking, Mellapak 350Y, te voorspel in totale terugvloei binere distillasie. Die korrelasie vir die komplekse oppervlak was meer akkuraat. Daar is gevind dat die voorspelde pakkingshoogte baie sensitief is vir die beraming van die binere gasfase diffusiekoeffisient.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/51336
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