A mass transfer model for structured packing

Kawesha, David Mukuma (2002-12)

Thesis (MScEng) -- Stellenbosch University , 2002.

Thesis

ENGLISH ABSTRACT: The distillation process is the most widely used separating process in the chemical process industry. The optimal design of the distillation units can lead to reduced capital costs and improved energy utilisation. This is particularly the case for structured packed distillation column where design methods tend to over-predict the column efficiency. This work seeks to contribute to the development of a reliable mass transfer model for structured packing. A gas phase mass transfer correlation was developed based on the evaporation of pure components into an air stream. The mass transfer rates were measured in a short triangular wetted wall channel with a corrugated surface wall. The influence that the geometric configuration as well as surface structure has on the mass transfer rates was investigated. The channel geometry and surface wall structure resembled that of the structured packing (Flexipac 350Y). The influence of the channel geometry on the gas mass transfer rates was not significant except at low flow conditions. The liquid phase resistance was investigated for binary mixtures in the triangular wetted wall channel. It was found that the overall mass transfer rate decreased with increasing composition of the volatile component. The enhancement of the gas phase mass transfer rate masked the presence of the liquid resistance. ii The gas phase mass transfer correlations were used in the mass transfer model to predict the separation efficiency of a structured packed distillation column. The structured packing used to validate the mass transfer model was high-capacity Flexipac 350Y and normal Flexipac 350Y. The binary distillation experiments were done at total reflux conditions for the pressure range O.33-1atm. The accuracy of the separation efficiencies of the mass transfer model improved with increasing pressure for both materials. The mass transfer model was able to predict the variation of separation efficiencies with column loadings.

AFRIKAANSE OPSOMMING: Distillasie is die skeidingsmetode wat die meeste in die chemiese industrie gebruik word. Die optimale ontwerp van distillasie eenhede kan lei tot verlagings in kapitaalkostes en 'n verbeterde gebruik van energie. Dit is veral waar in die geval van kolomme met gestruktureerde pakking waar huidige ontwerpsmetodes, die kolomeffektiwiteit nie akkuraat beskryf nie. Hierdie studie het ten doelom 'n bydrae te lewer tot die ontwikkeling van 'n betroubare massa-oordragsmodel vir gestruktureerde pakking. 'n Gasfase massa-oordragskorrelasie is ontwikkel gebaseer op metings van die verdampingstempo van suiwer komponente in 'n lugstroom. Die massaoordragstempos is gemeet in 'n kort driehoekige benatle wand kanaal waarin die wand 'n bepaalde oppervlakprofiel het. Die invloed van beide die kanaalgeometrie en die oppervlakprofiel is ondersoek. Die geometrie en oppervlakprofiel is soorgelyk aan die van Flexipac 350Y gestruktureerde pakking. Die invloed van die kanaalgeometrie op die gasfase massaoordragstempos is slegs beduidend by lae vloeitempos. Die vloeistoffase weerstand vir binêre mengsels is ondersoek in die driehoekige kanaal. Dit is gevind dat die algehele massa-oordragstempo verlaag met 'n verhoging in die konsentrasie van die vlugtige komponent. Die verhoging in die gasfase massa-oordragstempo verberg die invloed van die vloeistoffase weerstand. Die gasfase massa-oordragskorrelasies is in 'n massa-oordragsmodel gebruik om die skeidingseffektiwiteit van gestruktureerde pakking in "n kolom te voorspel. Metings op hoë-kapasiteit Flexipac 350Y en normale Flexipac 350Y is gebruik om die modelvoorspellings te evalueer. Die binêre distillasies is by totale terugvloei gedoen in die drukbereik 0.33 - 1.0 atm. Daar is gevind dat die model meer akkuraat is by hoër drukke. Die massa-oordragsmodel is in staat om die variasie in skeidingseffektiwiteit met veranderende kolomlading te voorspel.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/52647
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