U.S. patent application number 14/278513 was filed with the patent office on 2015-11-19 for integrated process for reducing solids from the product of solvent extraction of oil sands bitumen.
This patent application is currently assigned to SYNCRUDE CANADA LTD. in trust for the owners of the Syncrude Project, as such owners exist now and. The applicant listed for this patent is SYNCRUDE CANADA LTD. in trust for the owners of the Syncrude Project, as such owners exist now and. Invention is credited to SUJIT BHATTACHARYA, XIN ALEX WU.
Application Number | 20150329786 14/278513 |
Document ID | / |
Family ID | 54538000 |
Filed Date | 2015-11-19 |
United States Patent
Application |
20150329786 |
Kind Code |
A1 |
WU; XIN ALEX ; et
al. |
November 19, 2015 |
INTEGRATED PROCESS FOR REDUCING SOLIDS FROM THE PRODUCT OF SOLVENT
EXTRACTION OF OIL SANDS BITUMEN
Abstract
A method is provided for producing a marketable bitumen product
having low solids and essentially no water. The method can be
integrated into existing solvent extraction processes for
extracting bitumen from mined oil sand. A high-solids diluted
bitumen is produced from a solvent extraction process and then
mixed with a light solvent (LS) stream in at least a first mixer to
produce a diluted bitumen-LS mixture. The diluted bitumen-LS
mixture is subjected to separation in at least a first separator to
produce low-solids diluted bitumen and high-solids asphaltene-rich
tails. The LS is removed from the low-solids diluted bitumen to
produce the marketable bitumen product.
Inventors: |
WU; XIN ALEX; (Edmonton,
CA) ; BHATTACHARYA; SUJIT; (Edmonton, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SYNCRUDE CANADA LTD. in trust for the owners of the Syncrude
Project, as such owners exist now and |
Fort McMurray |
|
CA |
|
|
Assignee: |
SYNCRUDE CANADA LTD. in trust for
the owners of the Syncrude Project, as such owners exist now
and
Fort McMurray
CA
|
Family ID: |
54538000 |
Appl. No.: |
14/278513 |
Filed: |
May 15, 2014 |
Current U.S.
Class: |
208/390 |
Current CPC
Class: |
C10G 1/047 20130101;
C10G 1/045 20130101 |
International
Class: |
C10G 1/04 20060101
C10G001/04 |
Claims
1. A method of producing a marketable bitumen product having low
solids and essentially no water from an oil sand/solvent slurry
produced in a solvent extraction process of mined oil sand,
comprising: (a) subjecting the oil sand/solvent slurry to a first
solid-liquid separation step to produce a high-solids diluted
bitumen stream and a first solids stream; (b) mixing the
high-solids diluted bitumen with a light solvent (LS) stream in at
least a first mixer to produce a diluted bitumen-LS mixture; (c)
subjecting the diluted bitumen-LS mixture to separation in at least
a first separator to produce low-solids diluted bitumen and
high-solids asphaltene-rich tails; (d) recovering the LS from the
low-solids diluted bitumen in a diluent recovery unit to produce
the marketable bitumen product; (e) washing the high-solids
asphaltene-rich tails with LS and combining the washed high-solids
asphaltene-rich tails with the first solids stream to produce a
second solids stream; and (f) drying the second solids stream in a
dryer to recover the LS and produce dry tailings.
2. The method of claim 1, wherein the solvent extraction process
comprises contacting mined oil sand with a high-flash point HS and
a LS-rich stream to produce the oil sand/solvent slurry.
3. The method of claim 2, wherein the first solids stream is fed to
a repulper for mixing with a LS-dominant stream and subjected to a
second solid-liquid separation step prior to being combined with
the washed high-solids asphaltene-rich tails.
4. The method of claim 3, wherein the second solid-liquid
separation step produces a first filtrate stream and a second
filtrate stream.
5. The method of claim 4, wherein the first filtrate stream is used
in the solvent extraction process as the LS-rich stream and the
second filtrate stream is sent to the repulper as the LS-dominant
stream.
6. The method of claim 1, wherein in step (b), the LS is a
paraffinic C.sub.6-C.sub.7 solvent.
7. The method of claim 1, wherein in step (b), the LS is a
paraffinic C.sub.5-C.sub.8 solvent
8. The method of claim 7, wherein in step (b), the LS to diluted
bitumen mass ratio in the diluted bitumen-LS mixture ranges from
about 2.5 to about 4.0.
9. The method of claim 8, wherein in step (c), the low-solids
diluted bitumen comprises less than about 500 mg/kg solids and
about 1000 mg/kg water on dry bitumen basis.
10. The method of claim 9, wherein in step (d), the LS is recovered
in the diluent recovery unit by flashing off the LS from the
low-solids diluted bitumen.
11. The method of claim 10, wherein in step (d), a first portion of
the recovered LS is recycled to the first mixer, and a second
portion of the recovered LS is recycled to the solvent extraction
process.
12. The method of claim 11, wherein in step (d), the marketable
bitumen product comprises less than 500 mg/kg solids on dry bitumen
basis.
13. The method of claim 12, wherein the marketable bitumen product
further comprises HS.
14. The method of claim 13, wherein the HS is a light gas oil.
15. The method of claim 14, further comprising recovering the
HS.
16. The method of claim 1, wherein the combined bitumen recovery is
greater than about 90 wt %.
17. The method of claim 1, wherein the solvent extraction process
comprises contacting mined oil sand with a LS-rich stream to
produce the oil sand/solvent slurry.
18. The method of claim 17, wherein the first solid-liquid
separation step comprises passing the oil sand/solvent slurry
through a top-loading filter, whereby the first solids stream is a
filter cake.
19. The method of claim 18, wherein, in step (b), the LS is a
paraffinic C.sub.5-C.sub.8 solvent.
20. The method of claim 19, wherein, in step (b), the LS to bitumen
mass ratio in the diluted bitumen-LS mixture ranges from about 1.2
to about 2.0.
21. The method of claim 20, wherein, in step (d), the LS is
recovered in the diluent recovery unit by flashing off the LS from
the low-solids diluted bitumen.
22. The method of claim 21, wherein in step (d), a first portion of
the recovered LS is recycled to the mixer, and a second portion of
the recovered LS is recycled to the solvent extraction process.
23. The method of claim 1, wherein, in step (d), the marketable
bitumen product comprises less than 400 mg/kg solids on dry bitumen
basis.
24. The method of claim 1, wherein the combined bitumen recovery is
greater than about 88 wt %.
25. The method of claim 1, wherein the mixer comprises a high
energy-dissipation impeller.
26. The method of claim 25, wherein the impeller is a Rushton
turbine.
27. The method of claim 26, wherein the duration of mixing ranges
from about 1 minute to about 10 minutes.
28. The method of claim 1, wherein the separator is a gravity
settler.
29. The method of claim 1, wherein the separator is any
conventional solid-liquid separator.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to methods of
reducing solids content in high-solids diluted bitumen produced by
an existing solvent extraction process of mined oil sand.
BACKGROUND OF THE INVENTION
[0002] Oil sand deposits such as those found in the Athabasca
Region of Alberta, Canada, generally comprise water-wet sand grains
held together by a matrix of viscous heavy oil or bitumen. Bitumen
is a complex and viscous mixture of large or heavy hydrocarbon
molecules which contain a significant amount of sulfur, nitrogen
and oxygen. Oil sands processing involves either Clark hot water
extraction or solvent extraction to produce diluted bitumen which
is further processed to produce synthetic crude oil and other
valuable commodities. Clark hot water extraction technology or its
variants require large amounts of water and generate a great
quantity of wet tailings. Part of the wet tailings becomes mature
fine tailings which contain approximately 30% fine solids and are a
great challenge for tailings treatment. In addition, certain
problem oil sands, often having high fines content, yield low
bitumen recoveries in the water-based extraction process. This
leads to economic losses and environmental issues with bitumen in
wet tailings.
[0003] In contrast, solvent extraction of bitumen from mined oil
sands uses little or no water, generates no wet tailings, and can
achieve higher bitumen recovery than the exiting water-based
extraction. Solvent extraction usually produces diluted bitumen
product containing less than about 0.5 wt % water without any
additional treatment step such as centrifugation or deasphalting.
Solvent extraction is thus potentially more robust and more
environmentally friendly than water-based extraction.
[0004] Solvent extraction is conducted using either a single
solvent or mixture of solvents. One process uses paraffinic
solvents and rejects a significant amount of asphaltene (see for
example, Canadian Patent Application No. 2,715,301 and Canadian
Patent Application No. 2,724,806). This process yields a low-solids
product similar to a paraffinic froth treatment product, which
contains less than about 0.1 wt % water and solids and is
pipelinable and marketable. The diluted bitumen product is produced
with low solids content through a fines capture process with
asphaltene precipitation. Product of less than about 0.04 wt % (400
mg/kg) solids on dry bitumen basis with significant deasphalting
has been reported. However, this process does not recycle the
asphaltene-rich tails. Product of less than about 0.1 wt % (1000
mg/kg) solids on dry bitumen basis with significant deasphalting
has also been reported. However, mixing the asphaltene-rich tails
with the oil sand-solvent slurry causes the release of the captured
fines back into the hydrocarbon product, defeating the purpose of
product cleanup by deasphalting. The combined bitumen (maltene and
asphaltene) recovery for solvent extraction processes with
significant asphaltene rejection is estimated below about 88%,
considering about 6% loss of bitumen in the extraction itself.
[0005] Another solvent extraction process uses aromatic and
paraffinic solvents, and rejects little asphaltene (see for
example, Canadian Patent Application No. 2,761,555 and Canadian
Patent Application No. 2,751,719). Bitumen recovery greater than
about 95% can be achieved. However, this process normally produces
a high-solids product similar to a naphtha froth treatment product,
which is not marketable without upgrading. The diluted bitumen
product typically contains about 0.2-0.5 wt % of solids on dilbit
basis and about 0.4-1 wt % on dry bitumen basis. The solids are
almost exclusively fines which are difficult to remove by settling
or centrifugation. Bitumen may be lost in the centrifuge tails. The
product must be locally upgraded by coking to be pipelinable and
marketable.
[0006] Accordingly, there is a need for a method of producing
low-solids marketable bitumen at a reasonably high bitumen
recovery.
SUMMARY OF THE INVENTION
[0007] The current application is directed to a method of producing
a low solids, essentially water-free bitumen product from an oil
sand/solvent slurry produced by an existing solvent extraction
process of mined oil sand. It was surprisingly discovered that by
conducting the method of the present invention, one or more of the
following benefits may be realized:
[0008] (1) The invention may be integrated with an existing solvent
extraction process in which diluted bitumen is extracted from oil
sand using either a single solvent (e.g., a light solvent such as
C.sub.3-C.sub.9 paraffinic solvent) or a combination of solvents
(e.g., a high-flash point heavy solvent and a light solvent).
[0009] (2) The quality of the diluted bitumen product is enhanced
by sufficient mixing. There is about 35% improvement of the product
quality by using a high energy-dissipation impeller as compared to
a low energy-dissipation impeller.
[0010] (3) High-solids asphaltene-rich tails produced by the
invention are further treated without releasing captured fines in
the solvent extraction process.
[0011] (4) Light solvent recovered by the invention is recycled in
both the solvent extraction process and the bitumen solids content
reduction process of the invention.
[0012] (5) One solvent extraction process uses a combination of a
heavy solvent and a light solvent. Using the method of the
invention, a low-solids, water-free stream is produced which
comprises predominantly bitumen and heavy solvent which may be a
light gas oil. The stream may contain less than about 500 mg/kg
solids on dry bitumen basis. The stream may be pipelined either to
a distillation unit for heavy solvent recovery prior to sale, or to
market directly as "synthetic bitumen" or "synbit" including the
heavy solvent as a diluent. The synbit has a filterable solids
content of less than about 300 mg/kg which is considered fungible
in refineries. [0013] (6) One solvent extraction process uses only
a light solvent. Using the method of the invention, a low-solids,
water-free stream is produced which comprises predominantly
bitumen.
[0014] Use of the present invention improves reduction of water and
solids content in a final bitumen product, thereby in turn
producing a low-solids marketable bitumen product with a reasonably
high bitumen recovery. The bitumen recovery in the final bitumen
product is generally greater than about 90% including the bitumen
loss in the solvent extraction process.
[0015] Thus, broadly stated, in one aspect of the invention, a
method of producing a marketable bitumen product having low solids
and essentially no water from an oil sand/solvent slurry produced
in a solvent extraction process of mined oil sand is provided,
comprising: [0016] subjecting the oil sand/solvent slurry to
solid-liquid separation to produce a high-solids diluted bitumen
stream and a first solids stream; [0017] mixing the high-solids
diluted bitumen with a light solvent (LS) stream in at least a
first mixer to produce a diluted bitumen-LS mixture; [0018]
subjecting the diluted bitumen-LS mixture to separation in at least
a first separator to produce a low-solids diluted bitumen stream
and high-solids asphaltene-rich tails; [0019] recovering the LS
from the low-solids diluted bitumen in a diluent recovery unit to
produce the marketable bitumen product; [0020] washing the
high-solids asphaltene-rich tails with LS and combining the washed
high-solids asphaltene-rich tails with the first solids stream to
produce a second solid stream; and [0021] drying the second solid
stream in a dryer to recover the LS and produce dry tailings.
[0022] In one embodiment, the LS is a paraffinic C.sub.6-C.sub.7
solvent. In one embodiment, wherein both a heavy solvent (HS) and a
light solvent (LS) are used in solvent extraction, the LS to
bitumen mass ratio ranges from about 2.5 to about 4.0.
[0023] In one embodiment, the LS is a paraffinic C.sub.5-C.sub.8
solvent. In one embodiment, wherein only LS is used in solvent
extraction, the LS to bitumen mass ratio ranges from about 1.2 to
about 2.0.
[0024] In one embodiment, the bitumen recovery is greater than
about 90 wt %. In another embodiment, the bitumen recovery is
greater than about 88 wt %.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Referring to the drawings wherein like reference numerals
indicate similar parts throughout the several views, several
aspects of the present invention are illustrated by way of example,
and not by way of limitation, in detail in the figures,
wherein:
[0026] FIG. 1 is a diagram showing, in general, one embodiment of a
bitumen solids content reduction process of the present
invention.
[0027] FIG. 2 is a diagram showing, in general, one embodiment of a
bitumen solids content reduction process of the present
invention.
[0028] FIG. 3 shows two graphs of the solids concentration in
dilbit (mg/kg) versus settling time (minutes).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The detailed description set forth below in connection with
the appended drawings is intended as a description of various
embodiments of the present invention and is not intended to
represent the only embodiments contemplated by the inventor. The
detailed description includes specific details for the purpose of
providing a comprehensive understanding of the present invention.
However, it will be apparent to those skilled in the art that the
present invention may be practiced without these specific
details.
[0030] The present invention relates generally to a method of
reducing solids content in high-solids diluted bitumen produced by
solvent extraction of mined oil sand. Reduction of bitumen water
and solids content improves bitumen product quality, thereby in
turn producing a low-solids marketable bitumen product with a
reasonably high bitumen recovery. The method of the present
invention is integrated with an existing solvent extraction
process. High-solids asphaltene-rich tails produced by the method
of the invention are further treated without releasing captured
fines in the solvent extraction process. Light solvent recovered by
the method of the invention is reused in the solvent extraction
process and in the bitumen solids content reduction process of the
invention. The method of the invention thus imparts environmental
and economic benefits.
[0031] Several embodiments of the method for reducing solids
content in high-solids diluted bitumen produced by an existing
solvent extraction process are described herein. The solvent
extraction process may be, but is not limited to, one described
below or one described in the background section. The embodiment of
the invention shown in FIG. 1 integrates the solvent extraction
process as described in Canadian Patent Application No. 2,751,719,
wherein bitumen is extracted from oil sand using a combination of
high-flash point heavy solvent (HS) and light solvent (LS). The
embodiment of the present invention shown in FIG. 2 integrates a
solvent extraction process wherein bitumen is extracted from oil
sand using only LS.
[0032] As used herein, the term "heavy solvent" or "HS" refers to a
solvent with a typical boiling range of 177-480.degree. C. and
generally includes hydrocarbon liquids in the C.sub.10 to C.sub.30
range such as light gas oil and diesel.
[0033] As used herein, the term "light solvent" or "LS" means a
solvent with a typical boiling range of 36-126.degree. C. and
generally includes hydrocarbon liquids in the C.sub.5 to C.sub.8
range such as pentane, hexane, cyclohexane, heptanes and
octane.
[0034] FIG. 1 shows one embodiment of the method of the present
invention integrated with an existing solvent extraction process
which uses a combination of HS and LS. The solvent extraction
process is shown separated with a dashed line in FIG. 1. The oil
sand is delivered in a dry form from a mine to a slurry preparation
and conditioning unit (e.g., a tumbler/crusher circuit) which is
located in an extraction plant. The oil sand is prepared,
conditioned, crushed, and mixed with a HS and a LS-rich in two
stages to form an oil sand/solvent slurry 100. As used herein, a
"LS-rich stream" is defined as a stream containing more than about
50 wt % LS. The oil sand/solvent slurry 100 is passed through a
first solid-liquid separator 10, e.g., a filter, to produce a
high-solids diluted bitumen stream or high-solids "dilbit" 105 and
a filter cake 101.
[0035] The filter cake 101 is fed to a repulper 11 in which it is
vigorously mixed with a LS-dominant stream pumped into the repulper
11. As used herein, a "LS-dominant stream" is defined as a stream
containing more than about 80 wt % LS. The repulper 11 may be a
baffled tank agitated with impellers. After repulping, the repulped
filter cake 102 is passed through a second solid-liquid separator
12, e.g., a top-loading filter, to produce a first filtrate stream
130 and a first filter cake 103a. The first filter cake 103a is
then washed with a pure LS stream and a second filtrate stream 132
and a second filter cake 103b are separated from the second
solid-liquid separator 12. It is understood that the second
filtrate stream 132 and second filter cake 103b could be produced
in a third, separate, solid-liquid separator. The first filtrate
stream 130 and the second filtrate stream 132 may be recycled back
to the solvent extraction process as the LS-rich stream to produce
the oil sand/solvent slurry and the repulper 11 as the LS-dominant
stream, respectively. The filter cake 103b is dried in a solids
dryer 13 to recover the LS and to produce dry tailings 104 for
disposal.
[0036] The high-solids diluted bitumen 105 contains about 1 wt %
solids on dry bitumen basis. The high-solids diluted bitumen 105 is
sufficiently mixed with a LS stream 110 in a suitable mixer 14 to
produce a diluted bitumen-LS mixture 106. In one embodiment, the LS
stream 110 comprises C.sub.6-C.sub.7 paraffins. In another
embodiment, the LS stream 110 comprises C.sub.5-C.sub.8
paraffins.
[0037] The flow rate of LS stream 110 is adjusted so that the mass
ratio of LS stream 110 to high-solids diluted bitumen 105 is
controlled to be in the range of about 0.5 to about 1.0. Since the
high-solids diluted bitumen 105 in this embodiment already contains
LS, the mass ratio of LS to bitumen is about 2.5 to about 4.0 in
the diluted bitumen-LS mixture 106. At such a ratio, only moderate
asphaltene precipitation occurs due to the presence in high-solids
diluted bitumen 105 of an aromatics-rich HS, a light gas oil
fraction produced from an oil sand bitumen upgrading unit.
[0038] In one embodiment, the diluted bitumen-LS mixture 106 is fed
to a separator 15 in which it is subjected to separation to produce
low-solids diluted bitumen 107 and high-solids asphaltene-rich
tails stream 108. Since the solids and asphaltene from the diluted
bitumen-LS mixture 106 settle in the separator 15, the low-solids
diluted bitumen 107 may contain less than about 500 mg/kg
filterable solids and about 1000 mg/kg water on dry bitumen basis.
In one embodiment, separator 15 is a gravity settler. In another
embodiment, separator 15 is a general solid-liquid separator that
includes a bank of centrifuges.
[0039] The low-solids diluted bitumen 107 is fed to a diluent
recovery unit 16 to recover the LS stream 110. Any manner of
recovering the LS stream 110 from the low-solids diluted bitumen
107 may be used. In one embodiment, the LS stream 110 is recovered
by flashing off from the low-solids diluted bitumen 107. The
recovered LS stream 110 can be recycled in both the method of the
invention and the solvent extraction process.
[0040] In one embodiment, a greater portion of the recovered LS
stream 110 is reused in the mixer 14, while a lesser portion 111 of
the recovered LS stream 110 is reused in the solvent extraction
process.
[0041] Removal of the LS stream 110 from the low-solids diluted
bitumen 107 produces a low-solids, water-free stream 109 comprising
predominantly bitumen and HS. In one embodiment, the stream 109
(also referred to herein as the marketable bitumen product)
contains less than about 500 mg/kg solids on dry bitumen basis. In
one embodiment, the HS is a light gas oil. The stream 109 may be
pipelined either to a distillation unit for HS recovery prior to
sale, or to market directly as synthetic bitumen or "synbit"
including the HS as a diluent. In one embodiment, the synbit has a
filterable solids content of less than about 300 mg/kg which is
considered fungible in refineries.
[0042] At this stage, the method of the invention is integrated
with the existing solvent process. The high-solids asphaltene-rich
tails stream 108 enters the solvent extraction process downstream
of the repulper 11 to avoid liberating the captured fines through
agitation. The tails stream 108 is fed to the second solid-liquid
separator 12 only after passage of filtrate stream from the
repulped slurry 102 through the second solid-liquid separator 12
and formation of a filter cake 103, which is a precursor of first
filter cake 103a. The liquids of the tails stream 108 drain through
the filter cake 103, while highly viscous asphaltene fine-solids
tails are retained by the top layer of the filter cake 103 to form
first filter cake 103a. The filter cake 103a is washed at least
once with LS, for example light paraffinic solvent 111. After
washing and draining, the solids in tails stream 108, now mixed
with first filter cake 103a to form second filter cake 103b, are
relatively dry. Second filter cake 103b is further dried in the
solids dryer 13 to recover LS as part of the solvent extraction
process. The subsequent dry tailings 104 thus include the
asphaltene-fine solids tails and spent oil sand solids. The heat
duty to recover the LS from tails stream 108 is minimized following
this integration.
[0043] In one embodiment, the total hydrocarbon loss including
maltene, asphaltene and HS after the treatment of the tails stream
108 is less than about 5 wt % on oil sand bitumen basis. Taking
into account a typical hydrocarbon loss of about 4 wt % on oil sand
bitumen basis for the existing solvent extraction process, the
combined bitumen recovery is greater than about 90%.
[0044] FIG. 2 shows one embodiment of the method of the present
invention integrated with an existing solvent extraction process
wherein bitumen is extracted from oil sand using only LS. However,
the method of the invention is generally the same as that shown in
FIG. 1.
[0045] The solvent extraction process is shown separated with a
dashed line in FIG. 2. The oil sand is delivered in a dry form from
a mine to a slurry preparation and conditioning unit (e.g., a
tumbler/crusher circuit) which is located in an extraction plant.
The oil sand is prepared, conditioned, crushed, and mixed with a
LS-rich stream to form an oil sand/solvent slurry 300. The oil
sand/solvent slurry 300 is passed through a solid-liquid separator
30, e.g., a top-loaded filter, to separate high-solids diluted
bitumen or high solids "dilbit" 303 and a first filter cake 301a.
The first filter cake 301a is then washed with a pure LS stream. A
second filtrate stream 332 and a second filter cake 301b are
separated from the solid-liquid separator 30. Second filtrate
stream 332 may be recycled back to the solvent extraction process,
e.g., an oil sand/solvent slurry preparation unit, as the LS-rich
stream. The second filter cake 301b is dried in a solids dryer 31
to recover the LS and to produce dry tailings 302 for disposal.
[0046] The high-solids diluted bitumen 303 is sufficiently mixed
with a LS stream 308 in a mixer 32 to produce a diluted bitumen-LS
mixture 304. In one embodiment, the LS stream 308 comprises
C.sub.5-C.sub.8 paraffins.
[0047] The mass ratio of LS to bitumen in stream 304 is controlled
to be in the range of about 1.2 to about 2.0 by adjusting the flow
rate of the LS stream 308.
[0048] The diluted bitumen-LS mixture 304 is fed to a separator,
e.g., a gravity settler, 33 in which it is subjected to separation
to produce low-solids diluted bitumen 305 and high-solids
asphaltene-rich tails stream 306. In one embodiment, the separator
33 is a general solid-liquid separator that includes a bank of
centrifuges.
[0049] The low-solids diluted bitumen 305 is fed to a diluent
recovery unit 34 to recover the LS stream 308. Any manner of
recovering the LS stream 308 from the low-solids diluted bitumen
305 may be used. In one embodiment, the LS stream 308 is recovered
by flashing off from the low-solids diluted bitumen 305. The
recovered LS stream 308 is recycled in both the method of the
invention and the solvent extraction process. In one embodiment, a
greater portion of the recovered LS stream 308 is reused in the
mixer 32, while a lesser portion 309 of the recovered LS stream 308
is reused in the solvent extraction process.
[0050] Removal of the LS stream 308 from the low-solids diluted
bitumen 305 produces a low-solids, essentially water-free stream
307 comprising predominantly bitumen. In one embodiment, the stream
307 contains less than about 400 mg/kg solids on dry bitumen
basis.
[0051] At this stage, the method of the invention is integrated
with the existing solvent process. The high-solids asphaltene-rich
tails stream 306 enters the solvent extraction process downstream
of any slurry preparation/conditioning unit to avoid liberating the
captured fines through agitation. The tails stream 306 is fed to
the solid-liquid separator 30 only after passage of the liquid in
the oil sand/solvent slurry 300 through the solid-liquid separator
30 and formation of a filter cake 301, which is a precursor of
first filter cake 301a. The liquids of the high solids tails stream
306 drain through the filter cake 301, while highly viscous
asphaltene fine-solids tails are retained by the top layer of the
filter cake 301 to form first filter cake 301a. The first filter
cake 301a is washed at least once with fresh LS. After washing and
draining, the solids in the high-solids tails stream 306, now mixed
in second filter cake 301b, are relatively dry. Second filter cake
301b is further dried in the solids dryer 31 to recover LS as part
of the solvent extraction process. The subsequent dry tailings 302
thus include the asphaltene-fine solids tails and spent oil sand
solids. The heat duty to recover the LS from high-solids tails
stream 306 is minimized following this integration.
[0052] In one embodiment, the total hydrocarbon loss including
maltene and asphaltene after the treatment of the tails stream 306
is less than about 6 wt % on oil sand bitumen basis. Taking into
account a typical hydrocarbon loss of about 6 wt % on oil sand
bitumen basis for the existing solvent extraction process, the
combined bitumen recovery is greater than about 88 wt %.
[0053] In the embodiments shown in FIGS. 1 and 2, the mixer 14 and
32 may comprise a high energy-input impeller. In one embodiment,
the impeller comprises a Rushton turbine which is a radial flow
impeller having a flat disk upon which flat, concave, or
semi-circular blades are vertically mounted. Preferably, the Ruston
turbine is run at a speed that causes the mixed liquid to be in a
fully turbulent regime in order to enhance collision and
aggregation between individual asphaltene particles and asphaltene
particles-fine solids. The duration of mixing may range from about
1 minute to about 10 minutes.
[0054] In the embodiments shown in FIGS. 1 and 2, the gravity
settler 15 and 33 may comprise any suitable apparatus which
facilitates gravity settling including, but not limited to, a
gravity settling vessel and an inclined plate separator ("IPS"). An
IPS refers is an apparatus comprising a plurality of stacked
inclined plates onto which a mixture to be separated may be
introduced so that the mixture passes along the plates in order to
achieve separation of components of the mixture.
[0055] Exemplary embodiments of the present invention are described
in the following Examples, which are set forth to aid in the
understanding of the invention, and should not be construed to
limit in any way the scope of the invention as defined in the
claims which follow thereafter.
Example 1
[0056] A dilbit product of about 620 g containing approximately 33
wt % bitumen, 33 wt % virgin light gas oil and 34 wt % heptane was
mixed with additional heptane using various impellers at 50.degree.
C. The hydrocarbon mixture of about 1000 g contained approximately
20 wt % bitumen, 20 wt % virgin light gas oil and 60 wt % heptane.
The mixed hydrocarbon sample was allowed to settle in a vessel at
50.degree. C.
[0057] FIG. 3 shows the filterable solids concentration reduction
in the top 1-2 cm of the mixed hydrocarbon sample during settling.
"RT" stands for Rushton turbine which is an impeller with high
levels of energy dissipation; "PBT" stands for pitched blade
turbine which is a medium energy-dissipation impeller; and "A310"
is a hydrofoil which is a relatively low energy-dissipation
impeller. The mixing time was 5 minutes, except for one RT mixing
case of 10 minutes. The average filterable solids concentrations at
20 minutes settling time are shown in Table 1. There is about 35%
improvement of the product quality by using a high energy-input
impeller (RT) as compared to the low energy-input impeller
(A310).
TABLE-US-00001 TABLE 1 Solids concentration Solids concentration on
dry bitumen Impeller Type in dilbit (mg/kg) basis (mg/kg) RT 90 450
PBT 113 565 A310 140 700
Example 2
[0058] An oil sand sample containing 8.9 wt % bitumen and 38% fines
in its solids was extracted with two solvents: virgin light gas oil
and heptane in a batch apparatus. The oil sand/solvent slurry
proceeded through four filtration stages with a repulping step
between the second and third stages. An asphaltene and solids-rich
tails sample from Example 1 was added to the top of the filter cake
after the third stage filtration. Alternately, the tails sample was
added to the repulper before the third stage filtration. The tails
sample mass is about 5% of the oil sand mass.
[0059] Table 2 shows the filterable solids concentrations in four
filtrates for three cases: the control (i.e., no tails addition);
addition of tails after repulping and third stage filtration; and
addition of tails during repulping. The first and second stage
filtrates varied slightly in their solids contents due to the
variation in oil sand feeds. The post-third stage tails addition
shows no significant change of the solids concentrations in the
third and fourth stage filtrates as compared to the control case,
indicating that captured fines in the tails sample were retained by
the filter cake. The tails addition during repulping shows drastic
increase of the solids concentration in the third stage filtrate,
indicating that captured fines in the tails sample were released
during repulping. Since all filtrates except the first stage
filtrate are recycled in the process, the released solids will
eventually reach the first stage filtrate (product) which is
undesirable.
TABLE-US-00002 TABLE 2 Post-Third Stage Tails Addition No Tails
Addition Tails Addition During Repulping Filtrate (mg/kg) (mg/kg)
(mg/kg) First Stage 2270 3600 3360 Second Stage 1750 2120 2120
Third Stage 390 320 10530 Fourth Stage 100 150 840
[0060] Table 3 shows the variations in filter #2 process rate
including third and fourth stage filtrations and total hydrocarbon
(bitumen, light gas oil and asphaltene) loss as a result of adding
a tails stream on post-third stage filter cake. The results
indicate about 15% reduction in filter process rate and 3% increase
(on oil sand bitumen basis) in hydrocarbon loss compared to the
control case (i.e., no tails addition). This sample of oil sand was
aged and poorer in quality than typical fresh oil sands, which
resulted in higher hydrocarbon loss in the control case.
TABLE-US-00003 TABLE 3 No Tails Post-Third Stage Parameter Addition
Tails Addition Filter #2 Process Rate (t/m.sup.2h) 14.1 11.9
Hydrocarbon Loss on Oil Sand 8.5 11.3 Bitumen Basis (wt %)
[0061] The scope of the claims should not be limited by the
preferred embodiments set forth in the examples, but should be
given the broadest interpretation consistent with the description
as a whole.
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