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Wax deposition from kerosene onto cooled surfaces Ghedamu, Michael Abraha
Abstract
Wax fouling is a major problem in some oil refineries. The main objective of this project was to test different surfaces with the aim of eliminating or at least reducing wax deposits in heat exchangers. Wax is separated in oil refineries by cooling the wax-laden petroleum stream in chillers and then scraping off the deposited wax mechanically from the surfaces of the heat exchangers (chillers). The solid wax is separated from the liquid petroleum stream by means of filters. An experimental test rig was set up to study ways of eliminating or reducing wax deposits by changing some of the operating conditions as well as the surface type of the heat transfer area. A double pipe heat exchanger 0.72 m long with inner tube (ID=9.96 mm, OD=12.45 mm) and outer pipe (ID=25.4 mm) was used. The solution tested was wax dissolved in kerosene, which flowed through the annular section while the cooling water flowed countercurrently in the inner tube. The effects of flow velocity of waxkerosene, of bulk temperature, of wax-kerosene concentration and of heat transfer surface type have been studied. Two types of wax were used: refined wax and slack wax. The surfaces used were: uncoated stainless steel, sand-blasted stainless steel, chrome-plated stainless steel, n-C18 silane-coated chrome-plated stainless steel, Heresite Si 57 E coated stainless steel (shiny), Heresite P-400/L-66 coated stainless steel (dull) and n-C18 silane coated stainless steel. The cloud point for each wax-kerosene concentration investigated (5, 10, 15 and 20 wt. % wax) was measured using ASTM procedures. The rheology of wax-kerosene was also investigated to determine if the mixtures were Newtonian or non-Newtonian. All mixtures were found to be Newtonian. The mixture viscosity was determined at temperatures from the cloud point upwards at each concentration. A Kern-Seaton (1959) equation was used to determine R*[sub f] and Θ[sub c] from the resistance vs. time experimental data. The wax deposit showed a decrease in R*[sub f] with increasing Re, with increasing T[sub b] and with decreasing concentration. Similar results were found by Bott and Gudmundsson (1977b). From the plots of R*[sub f] vs. Re, the hierarchy in increasing R*[sub f] was found to be: Heresite-coated stainless steel (dull and shiny) < n-C18 silane coated stainless steel < n-C18 silane-coated chrome-plated stainless steel < chrome-plated stainless steel < uncoated stainless steel < sand-blasted stainless steel. A similar hierarchy with four of the seven tubes was shown with respect to R*[sub f] vs. T[sub b]. That plastics show a lower wax deposit compared to metal surfaces has been shown by previous investigations. After some deposition had occurred, the removal of wax chunks from the surface and occasional bare patches were visually observed on all tubes except the two Heresite-coated tubes and the sand-blasted stainless steel. The phenomenon of deposit sliding was observed on the chrome-plated stainless steel, where the sliding velocity was recorded. The concentration and bulk temperature of a petroleum stream may be fixed by refinery conditions. However, a lower wax deposit on heat transfer surfaces can be obtained by using a smooth surface material which has a low affinity for wax, and high flow velocity or turbulence.
Item Metadata
Title |
Wax deposition from kerosene onto cooled surfaces
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1995
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Description |
Wax fouling is a major problem in some oil refineries. The main objective of this
project was to test different surfaces with the aim of eliminating or at least reducing wax
deposits in heat exchangers. Wax is separated in oil refineries by cooling the wax-laden
petroleum stream in chillers and then scraping off the deposited wax mechanically from the
surfaces of the heat exchangers (chillers). The solid wax is separated from the liquid
petroleum stream by means of filters.
An experimental test rig was set up to study ways of eliminating or reducing wax
deposits by changing some of the operating conditions as well as the surface type of the
heat transfer area. A double pipe heat exchanger 0.72 m long with inner tube (ID=9.96
mm, OD=12.45 mm) and outer pipe (ID=25.4 mm) was used. The solution tested was
wax dissolved in kerosene, which flowed through the annular section while the cooling
water flowed countercurrently in the inner tube. The effects of flow velocity of waxkerosene,
of bulk temperature, of wax-kerosene concentration and of heat transfer surface
type have been studied. Two types of wax were used: refined wax and slack wax. The
surfaces used were: uncoated stainless steel, sand-blasted stainless steel, chrome-plated
stainless steel, n-C18 silane-coated chrome-plated stainless steel, Heresite Si 57 E coated
stainless steel (shiny), Heresite P-400/L-66 coated stainless steel (dull) and n-C18 silane
coated stainless steel.
The cloud point for each wax-kerosene concentration investigated (5, 10, 15 and
20 wt. % wax) was measured using ASTM procedures. The rheology of wax-kerosene
was also investigated to determine if the mixtures were Newtonian or non-Newtonian. All
mixtures were found to be Newtonian. The mixture viscosity was determined at
temperatures from the cloud point upwards at each concentration.
A Kern-Seaton (1959) equation was used to determine R*[sub f] and Θ[sub c] from the
resistance vs. time experimental data. The wax deposit showed a decrease in R*[sub f] with
increasing Re, with increasing T[sub b] and with decreasing concentration. Similar results were
found by Bott and Gudmundsson (1977b). From the plots of R*[sub f] vs. Re, the hierarchy in
increasing R*[sub f] was found to be: Heresite-coated stainless steel (dull and shiny) < n-C18
silane coated stainless steel < n-C18 silane-coated chrome-plated stainless steel <
chrome-plated stainless steel < uncoated stainless steel < sand-blasted stainless steel. A
similar hierarchy with four of the seven tubes was shown with respect to R*[sub f] vs. T[sub b]. That
plastics show a lower wax deposit compared to metal surfaces has been shown by
previous investigations.
After some deposition had occurred, the removal of wax chunks from the
surface and occasional bare patches were visually observed on all tubes except the two
Heresite-coated tubes and the sand-blasted stainless steel. The phenomenon of deposit
sliding was observed on the chrome-plated stainless steel, where the sliding velocity was
recorded.
The concentration and bulk temperature of a petroleum stream may be fixed by
refinery conditions. However, a lower wax deposit on heat transfer surfaces can be
obtained by using a smooth surface material which has a low affinity for wax, and high
flow velocity or turbulence.
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Extent |
6333096 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-01-19
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0058574
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1995-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
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Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.