Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Distillation column design and operation require understanding of both the hydrodynamic
and thermodynamic behaviour and limitations. One of the hydrodynamic aspects that
negatively influence separation efficiency in the distillation column is entrainment of the
liquid with the rising vapour or gas. Inaccurate entrainment predictions will lead to poor
separation efficiencies in the column and consequently over design of the column diameter
and/or height has to be incorporated. This has a significant impact on the capital cost due to
the size and scale of industrial columns. Therefore, small improvements in entrainment
prediction will lead to large savings in capital investment.
Previous research published in the open literature focused primarily on the influence of gas
and liquid flow rates and, tray geometry on entrainment for the air/water system.
Consequently the non-air/water database is small and consists of data obtained from
various tray and column geometries. As a result the accuracy of current entrainment
prediction models is questionable for systems other than air/water. Therefore, the first
objective of this work was to investigate whether current prediction models perform well
for systems other than air/water. To prove this air/water, air/ethylene glycol and air/silicon
oil data were measured and compared with current prediction correlations. It was found
that current prediction models perform poorly for the air/ethylene glycol and air/silicone oil
systems. At the same time a new observation was made with regard to froth development
and behaviour inside the column. The observation shows that liquid flow rate has a nonmonotonic
influence on entrainment, caused by the short (475mm) tray flow path.
The second objective was to examine the influence of gas physical properties on
entrainment. New entrainment data were measured by individually contacting air, CO2 and
SF6 with water and ethylene glycol, while n-butanol was contacted with CO2 and SF6. The
data was compared with current prediction models which performed poorly for SF6 results.
This shows the inability of these models to predict entrainment for gas systems with high
densities. Modified Reynolds and Froude numbers were developed to show the influence of
gas physical properties on entrainment. Low modified Reynolds numbers and large modified
Froude numbers resulted in high entrainment.
The third objective was to determine the influence of liquid physical properties on
entrainment. New entrainment data were measured using CO2 with Isopar G, n-butanol,
water, silicone oil and ethylene glycol. Current prediction models compared poorly to the
data and did not include the influence of liquid viscosity on entrainment. It was found that
viscosity had an intricate non-monotonic influence on entrainment.
The fourth and final objective was to correlate the influence of gas and liquid properties on
entrainment as determined by the previous two objectives. To make the dataset more
complete, entrainment was measured for four tray spacings using CO2/Isopar, CO2/nbutanol,
air/ethylene glycol, CO2/ethylene glycol, air/silicone oil and CO2/silicone oil (over
1700 data points). Two new correlations are presented to predict the fraction of liquid
entraining with the rising gas (L’/G with R2 = 85%) and the fraction of liquid entering the tray
that entrains (L’/L with R2 = 92%). The performance of the L’/G correlation (R2 = 85%) is
vastly superior to two other prominent correlations (R2 = 61% and 23%). This correlation can
be implemented to predict entrainment successfully for different tray geometries by
combining the predicted influence of tray geometry, by Kister and Haas (1988), with results
from the newly developed correlation. All four objectives are presented as manuscripts for
journal publication and serve as alone standing documents. / AFRIKAANSE OPSOMMING: Distillasie kolom ontwerp en bedryf vereis begrip van beide die hidrodinamiese en
termodinamiese gedrag en beperkings. Een van die hidrodinamiese aspekte wat skeiding
doeltreffendheid negatief beïnvloed in die distillasie kolom is meesleuring van die vloeistof
met die stygende dampe of gas. Onakkurate meesleuring voorspellings sal lei tot swak
skeiding doeltreffendheid in die kolom en gevolglik word die ontwerp van die kolom
deursnee en / of hoogte beinvloed. Dit het 'n beduidende impak op die kapitale koste as
gevolg van die grootte en skaal van industriële kolomme. Klein verbeterings in meesleuring
voorspelling sal dus lei tot groot besparings in kapitaal belegging.
Vorige navorsing gepubliseer in die oop literatuur het hoofsaaklik gefokus op die invloed van
gas- en vloeistof vloeitempos en plaat geometrie op meesleuring vir die lug/water sisteem.
Gevolglik is die nie-lug/water databasis klein en bestaan van die data wat verkry is uit
verskeie plaat en kolom-geometrieë. As gevolg is die akkuraatheid van die huidige
meesleuring voorspelling modelle vir stelsels anders as lug/water te betwyfel. Daarom is die
eerste doel van hierdie werk om ondersoek in te stel of die huidige voorspelling modelle
goed presteer vir stelsels anders as lug/water. Om dit te bewys was lug/water,
lug/etileenglikol en lug/silikon olie data gemeet en vergelyk met die huidige voorspelling
korrelasies. Daar is bevind dat die huidige voorspellings modelle swak presteer vir die
lug/etileenglikol en lug/silikon olie. Op dieselfde tyd was 'n nuwe waarneming gemaak met
betrekking tot dispersie ontwikkeling en gedrag binne die kolom. Die waarneming toon dat
vloeistof vloeitempo 'n nie-monotoniese invloed op meesleuring het, veroorsaak deur die
kort (475mm) plaat vloei pad lengte.
Die tweede doelwit was om die invloed van gas fisiese eienskappe op meesleuring te
ondersoek. Nuwe meesleuring data was gemeet deur individuele kontak van lug, CO2 en SF6
met water en etileenglikol, terwyl n-butanol slegs met CO2 en SF6 inkontak gebring was. Die
eksperimentele resultate word vergelyk met die huidige voorspellings modelle wat swak
presteer invergelyking met SF6 resultate. Dit toon die onvermoë van hierdie modelle om
meesleuring vir gas stelsels met hoë digthede te voorspel. Gemodifiseerde Reynolds en
Froude getalle was ontwikkel om die invloed van gas fisiese eienskappe op meesleuring aan
te toon. Lae gemodifiseerde Reynolds getalle en groot gemodifiseerde Froude getalle lei na
hoë meesleuring.
Die derde doelwit was om die invloed van vloeistof fisiese eienskappe op meesleuring te
bepaal. Nuwe meesleuring data is gemeet deur gebruik te maak van CO2 met Isopar G, nbutanol,
water, silikon olie en etileenglikol. Huidige voorspellings modelle vergelyk swak
met die data en sluit nie die invloed van vloeistof viskositeit op meesleuring in nie. Daar is
gevind dat viskositeit 'n ingewikkelde nie-monotoniese invloed op meesleuring het.
Die vierde en finale doelwit was om die invloed van die gas en vloeistof eienskappe op
meesleuring soos bepaal deur die vorige twee doelwitte te korreleer. Om die datastel meer
volledig te maak, is meesleuring vir vier plaat spasiërings met CO2/Isopar, CO2/n-butanol,
lug/etileenglikol, CO2/ethylene glycol, lug/silikon olie en CO2/silikon olie (meer as 1700 data
punte gemeet). Twee nuwe korrelasies word aangebied om die fraksie vloeistof wat
meegesleur word met die stygende gas (L’/G met R2 = 85%) en die fraksie vloeistof wat die
plaat binnetree wat meegesleur word (L’/L met R2 = 92%) te voorspel. Die prestasie van die
L’/G korrelasie (R2 = 85%) is aansienlik beter as twee ander prominente korrelasies (R2 = 61%
en 23%). Hierdie korrelasie kan suksesvol geïmplementeer word om meesleuring vir
verskillende plaat geometrieë te voorspel deur die voorspelde invloed van plaat geometrie
deur Kister en Haas (1988), met die resultate van die nuut ontwikkelde korrelasie te
kombineer. Al vier doelwitte word as manuskripte vir joernaal publikasie aangebied en dien
as alleenstaande dokumente.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/71668 |
| Date | 12 1900 |
| Creators | Uys, Ehbenezer Chris |
| Contributors | Knoetze, J. H., Burger, A. J., Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 315 p. : ill. |
| Rights | Stellenbosch University |
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