Thesis (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Structured packing is a popular column internal for both distillation and absorption
unit operations. This is due to the excellent mass transfer characteristics and low
pressure drop that it offers compared to random packing or trays. The main
disadvantage is the lack in reliable models to describe the mass transfer
characteristics of this type of packing. The recent development of the non-equilibrium
model or rate based modelling approach has also emphasized the need for accurate
hydraulic and efficiency models for sheet metal structured packing.
The main focus of this study was to develop an accurate model for the mass transfer
efficiency of Flexipac 350Y using a number of experimental and modelling
techniques. Efficiency is however closely related to hydraulic capacity. Before
attempting to measure and model the efficiency of Flexipac 350Y, the ability of
existing published models to accurately describe the hydraulic capacity of this
packing was tested. Holdup and pressure drop were measured using air/water and
air/heavy paraffin as test systems. All experiments were performed on pilot plant
scale 200mm ID glass columns. Satisfactory results were obtained with most of the
models for determining the loading point and pressure drop for the air/water test
system. All of the models tested predicted a conservative dependency of capacity on
liquid viscosity for the air/paraffin test system. Efficiency and pressure drop were
measured using the chlorobenzene/ethylbenzene test systems under conditions of
total reflux in a 200mm ID glass column. Widely differing results were however
obtained with the different models for the efficiency of Flexipac 350Y. Experiments
were subsequently designed and performed to measure and correlate the vapour
phase mass transfer coefficient and the effective surface area of Flexipac 350Y
independently. The vapour phase mass transfer coefficient was measured and
correlated by subliming naphthalene into air from coatings applied to specially
fabricated 350Y gauze structured packing. The use of computational fluid dynamics
(CFD) to model the vapour phase mass transfer coefficient is also demonstrated. The
effective surface area for vapour phase mass transfer was measured with the
chemical technique. The specific absorption rate of CO2 into monoethanolamine
(MEA) using n-propanol as solvent was determined in a wetted-wall column and used
to determine the effective surface area of Flexipac 350Y on pilot plant scale (200mm
ID glass column). The efficiency of Flexipac 350Y could be modelled within an
accuracy of 9% when using the correlations developed in this study and ignoringliquid phase resistance to mass transfer for the chlorobenzene/ethylbenzene test
system under conditions of total reflux.
The capacity and efficiency of the new generation high capacity packing Flexipac
350Y HC was also measured and compared with that of the normal capacity packing
Flexipac 350Y. An increase in capacity of 20% was observed for the HC packing for
the air/water system and 4% for the air/heavy paraffin system compared with the
normal packing. For the binary total reflux distillation the increase in capacity varied
between 8% and 15% depending on the column pressure. The gain in capacity was
at the expense of a loss in efficiency of around 3% in the preloading region. / AFRIKAANSE OPSOMMING: Gestruktureerde pakking is 'n populêre pakkingsmateriaal en word algemeen gebruik
in distillasie en absorpsie kolomme. Dit is hoofsaaklik as gevolg van die goeie
massa-oordragseienskappe en lae drukval wat dit bied in vergelyking met 'random'
pakking en plate. The hoof nadeel is egter die tekort aan akkurate modelle om die
massa-oordrags eienskappe te bepaal. Om modelle te kan gebruik waar die massaoordragstempo
direk gebruik word om gepakte hoogte te bepaal, word akkurate
kapasiteits- en effektiwiteitsmodelle vir gestruktureerde plaatmetaalpakking benodig.
Die hoof doelwit van hierdie studie was om 'n akkurate model te ontwikkel vir die
massa-oordragseffektiwiteit van die plaat metaal pakking Flexipac 350Y deur gebruik
te maak van verskillende eksperimentele- en modelleringstegnieke. Effektiwiteit is
egter direk gekoppel aan hidroliese kapasiteit. Bestaande modelle in die literatuur is
eers getoets om te bepaal of hulle die hidroliese kapasitiet van Flexipac 350Y
akkuraat kan voorspel. Vir die doel is vloeistofterughou en drukval gemeet deur
gebruik te maak van die sisteme lug/water en lug/swaar parafien. Alle eksperimente
is in loodsaanlegskaal 200mm ID glaskolomme uitgevoer. Meeste van die modelle
was relatief akkuraat in hulle berekening van die ladingspunt en die drukval vir die
lug/water toets sisteem, maar was konsertief in voorspellings van die groothede vir
die lug/swaar parafien sisteem. Effektiwiteit en drukval was gemeet deur gebruik te
maak van die binêre toetssisteem chlorobenseen/etielbenseen onder totale
terugvloei kondisies in 'n 200mm ID glaskolom. Daar is 'n groot verskil in die
effektiwiteitsvoorspelling deur die verskillende modelle. Vervolgens is eksperimente
ontwerp en uitgevoer om die dampfase massaoordragskoeffisiënt en die effektiewe
oppervlakarea vir Flexipac 350Y onafhanklik te meet en te korreleer. Die dampfase
massaoordragskoeffisient is gemeet en gekorreleer deur naftaleen te sublimeer
vanaf spesiaal vervaardigde 350Y gestruktureerde pakking van metaalgaas. Die
gebruik van numeriese vloeimeganika (CFD) om die dampfase
massaoordragskoeffisient te bereken word gedemonstreer. Die effektiewe
oppervlakarea vir dampfase massaoordrag is bepaal deur van 'n chemiese metode
gebruik te maak. Die spesifieke absorpsietempo van CO2 in monoetanolamien (MEA)
met n-propanol as oplosmiddel is gemeet in a benatte wand kolom en gebruik om die
effektiewe oppervlakarea van Flexipac 350Y te bepaal op loodsaanlegskaal (200mm
ID). Die effektiwiteit van Flexipac 350Y kon met 'n akkuraatheid van binne 9%gemodelleer word deur vloeistoffaseweerstand te ignoreer en van die korrelasies
gebruik te maak wat in hierdie studie ontwikkel is.
Die effektiwiteit en kapasiteit van die nuwe generasie hoë kapasiteit pakking Flexipac
350Y HC is ook gemeet en vergelyk met die normale kapasiteit pakking Flexipac
350Y. 'n Verhoging in kapsiteit van 20% is gemeet vir die HC pakking in vergelyking
met die normale kapasiteit pakking vir die lug/water sisteem en 'n 4% verhoging in
kapasiteit vir die lug/swaar parafien sisteem. Die verhoging in kapasiteit het gevarieër
tussen 8% en 14% in die binêre totale terugvloei distillasie toetse en was afhanklik
van die kolom druk. Die verhoging in kapasiteit was ten koste van 'n verlaging in
effektiwiteit van ongeveer 3% onderkant die ladingspunt.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16045 |
| Date | 12 1900 |
| Creators | Erasmus, Andre Brink |
| Contributors | Nieuwoudt, I., University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xxviii, 148 leaves : ill. |
| Rights | University of Stellenbosch |
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