Note: Descriptions are shown in the official language in which they were submitted.
CA 02895118 2015-06-15
DOCKET NO.: NS-515
DUAL-SOLVENT EXTRACTION OF OIL SAND BITUMEN
INVENTORS: WU, Xin Alex; BHATTACHARYA, Sujit
ASSIGNEE: SYNCRUDE CANADA LTD.
Field of the Invention
[0001] The present invention relates to a solvent extraction process
which uses
at least two different solvents for extracting bitumen from mined oil sands.
Background of the Invention
[0002] The present commercial bitumen extraction process for mined oil
sands is
Clark hot water extraction technology or its variants that use large amounts
of water and
generate a great quantity of wet tailings. Part of the wet tailings becomes
fluid fine tailings
(FFT), 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] An alternative to water-based extraction is solvent extraction of
bitumen
from mined oil sands, which uses little or no water, generates no wet
tailings, and can
potentially achieve higher bitumen recovery than the existing water-based
extraction,
especially for the aforementioned problem oil sands. Therefore, solvent
extraction is
potentially more robust and more environmentally friendly than water-based
extraction.
[0004] The majority of solvent extraction processes taught in the prior
art use a
single solvent or a solvent mixture having a fixed composition throughout the
process.
This solvent may be a light solvent with a typical boiling range of 36-110 C,
an
intermediate solvent with a typical boiling range of 66-205 C, or a heavy
solvent with a
typical boiling range of 177-343 C. However, the use of any light or
intermediate solvent
poses a fire hazard during the initial contact of solvent with oil sands in a
vessel that is not
adequately purged or deoxygenated with an inert gas. Effectively purging such
a vessel is
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a challenge due to the sticky nature of oil sands that may not allow effective
use of air
locks for the feed. If the oil sands are transported from a deoxygenation unit
to a solvent
contact unit through a semi-open port, solvent vapor may travel from the
solvent contact
unit to the deoxygenation unit and mix with air and/or the inert gas, thereby
posing a fire
hazard and causing solvent loss. Oil sands may be fed through a bath of liquid
such as
water to deoxygenate, as disclosed in Canadian Patent No. 2,815,132. However,
this
process may add excessive water which is problematic for solvent recovery.
Further, the
oil sand-volatile solvent mixture is fed through multiple slurry conditioning
units which are
not gas-tight, allowing leakage of solvent vapor.
(0005] Attempts to solve the above issues by using two solvents
sequentially
encounter solid/liquid separation problems and issues with higher solvent
demand and
operating costs. A non-volatile light gas oil and bitumen mixture for initial
slurry
preparation is disclosed in Canadian Patent No. 2,751,719. Inert gas
blanketing is
provided in the contact vessel in case light hydrocarbon contaminant is
present in the
mixture. Minimizing contaminant through proper operation of a distillation
unit may
decrease solvent vapor release in semi-sealed slurry conditioning units.
However, this
process requires a second light volatile solvent to facilitate solvent-diluted
bitumen
separation and solvent recovery from solids.
[00061 Processes for extracting oil sand bitumen using two solvents are
disclosed in Canadian Patent Nos. 2,751,719 and 2,761,555 and United States
Patent
Nos. 3,117,922 and 3,131,141. Such processes yield two hydrocarbon streams.
The first
stream is generated from the first separation of diluted bitumen from solids,
and contains
bitumen at a high concentration and one or two solvents. The second stream is
generated
from a subsequent separation of diluted bitumen and wash liquid from solids
and contains
bitumen at a lower concentration and two solvents at a different ratio
compared to that in
the first stream. The second stream cannot be directly recycled at the initial
slurry
preparation stage due to the presence of the second (volatile) solvent and the
safety/solvent loss issues mentioned above. These two streams necessitates two
separate
flash/distillation units for separation, complicating the process and
incurring greater
operational costs compared to a single-solvent extraction process which allows
direct
recycling of low bitumen streams at the slurry preparation stage and requires
only one
flash/distillation unit for its product. Combining these two streams as in
United States
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Patent No. 3,117,922 reduces the bitumen concentration in the product and
increases the
size and cost of the flash/distillation unit to process the diluted product.
[00071 After slurry preparation and conditioning, diluted bitumen is
typically
separated from any solids through gravity settling, filtration, or other
techniques. To speed
up the separation rate, water may be added to bind fine solids and coarse sand
to reach a
total water to solids (W/S) mass ratio ranging between about 0.08 to 0.15 in
slurry (i.e.,
"solids agglomeration" as disclosed in Canadian Patent Nos. 2,724,806,
2,740,468 and
2,740,481, and United States Patent Nos. 4,057,486 and 4,719,008). In order to
completely recover solvent from spent solids to meet the environmental
requirements, the
W/S ratio needs to be reduced to at least 0.02 and involves energy-intensive
operations
that increase greenhouse gas emissions. As an example, processing oil sands at
8000 t/h
requires drying water at the rate of about 680 t/h in addition to solvent
vaporization,
assuming 85 wt% solids content in oil sands and W/S=0.12. Drying the
relatively wet
agglomerates using multiple dryers is an energy-intensive, uneconomical
operation.
[00081 In summary, none of the prior art solvent extraction processes
can
resolve all of the following issues:
1. Fire hazard and solvent loss at initial contact of solvent with oil sands
in an extraction
process using a single volatile solvent;
2. Complicated flow sheet and greater operational costs for multiple
flash/distillation units
in an extraction process using two solvents; and
3. Conflicting requirements of water addition to satisfy fast solid-liquid
separation and
drying of spent solids for solvent recovery.
[0009] There is a need for a solvent extraction process that is safe,
operable and
economical.
Summary of the Invention
/000/0] The present invention relates to a solvent extraction process
which uses
at least two different solvents for extracting bitumen from mined oil sands.
It was
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surprisingly discovered that by using the process of the present invention,
one or more of
the following benefits may be realized:
(1) The solvent extraction process of the present invention provides
greater
flexibility in the choices of heavy solvent (HS) and light solvent (LS), and
the ranges of
HS/LS mass ratios. The HS/LS mass ratio may vary from the first to the last
separation
stage within the process to optimize bitumen recovery and separation rate.
(2) The process improves safety and minimizes solvent vapor loss. After
initial
contact with a high-flash point HS to form dense slurry for oil sand
deoxygenation and
before mixing with LS and solids flocculation, the dense slurry is passed
through an airlock
to isolate oxygen-free and LS-containing atmosphere downstream from oxygen-
containing
and LS-free atmosphere upstream, thereby reducing fire hazard or solvent loss.
(3) Solids flocculation is achieved using a relatively intense mixer, e.g.
an
unconventionally designed baffled tank agitated with impellers, allowing for
use of a
relatively low water to solids (W/S) mass ratio. The W/S mass ratio in slurry
may be less
than about 0.1, preferably less than about 0.08.
(4) The process combines multiple LS streams into a second slurry
preparation
and conditioning unit, and recycles the LS for use in bitumen dissolution and
solids
flocculation. Recycling these LS streams does not reduce the bitumen
concentration in
the final product. A single hydrocarbon stream is thereby generated in the
process so that
a single distillation unit can be used for component separation without
reducing the total
solvent use efficiency. The process provides a less complex flow sheet and
minimizes
operational costs.
1000111 Use of the present invention achieves good bitumen recovery, good
solvent recovery, and cleaner dry tailings. Thus, broadly stated, in one
aspect of the
present invention, a process for extracting bitumen from oil sand is provided,
comprising:
= contacting mined oil sand with a high-flash point heavy solvent (HS) to
produce a
dense oil sand slurry;
= mixing the dense slurry with a first light solvent (LS) stream and a
second LS
stream to give a heavy solvent to light solvent (HS/LS) mass ratio of about
75/25 to
about 40/60;
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= subjecting the HS/LS-diluted oil sand slurry to a first stage solid-
liquid separation to
produce a first liquids stream containing bitumen and a first solids stream;
= washing the first solids stream with a mixed solvent having a HS/LS mass
ratio of
about 50/50 to about 20/80 and subjecting the solids and the mixed solvent to
a
second stage solid-liquid separation to produce a second liquids stream and a
second solids stream.
[00012] In one embodiment, the process further comprises mixing the dense
slurry and LS streams with a minimal amount of water to give a total water to
solids (W/S)
mass ratio less than about 0.1 to flocculate solids.
[00013] In one embodiment, the process further comprises passing the
dense oil
sand slurry for deoxygenation through an airlock after initial contact with
the high-flash
point HS to minimize the risks of fire hazard or solvent loss.
[00014] In one embodiment, the process further comprises mixing the
second
solids stream and LS in a repulper prior to being subjected to a third stage
solid-liquid
separation to produce a third liquids stream and a third solids stream. In one
embodiment,
the process further comprises washing the third solids stream with LS and
subjecting the
solids and LS stream to a fourth stage solid-liquid separation to produce a
fourth liquids
stream and a fourth solids stream. The fourth liquids stream is predominantly
LS and is
used in repulping. The fourth solids stream is dried in a solids dryer to
produce dry
tailings.
[00015] In another aspect of the invention, solids flocculation is
conducted using a
baffled tank agitated with one or more impellers while the dense slurry is
being mixed with
LS streams. Water is added into this tank to give a total water to solids
(W/S) mass ratio
less than about 0.1. In one embodiment, the one or more impellers comprise 45
pitched
blade turbines having a diameter ranging from about 0.55 to about 0.7 of the
tank
diameter. In one embodiment, the bottom clearance ranges from about 0.01 to
about 0.15
of the tank diameter. In one embodiment, the power input by the one or more
impellers
ranges from about 1 W/kg to about 15 W/kg of slurry.
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Brief Description of the Drawings
[00016] The invention will now be described by way of an exemplary
embodiment
with reference to the accompanying simplified, diagrammatic, not-to-scale
drawings:
[00017] FIG. 1A (Prior Art) and FIG. 1B are graphs of heavy solvent to
light solvent
ratio (HS/LS) (from 0/100 to 100/0) versus bitumen concentration in
hydrocarbons (from
high to low).
[000181 FIG. 2 is a schematic process flow diagram of one embodiment of
the
solvent extraction process.
[00019] FIG. 3 is a schematic diagram which clarifies the structural
differences
among flocs, microagglomerates, and pellets as set out in the prior art
(Meadus and
Sparks, 1983).
[00020] FIG. 4A (Prior Art) and FIG. 4B are schematic diagrams of baffled
tanks
agitated with impellers.
Detailed Description of Preferred Embodiments
[00021] 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
inventors. 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 practised without these specific
details.
[00022] The present invention relates generally to a solvent extraction
process
which uses at least two different solvents for extracting bitumen from mined
oil sands. A
conventional process is disclosed in Canadian Patent No. 2,751,719 (CA '719)
which uses
a combination of a heavy solvent (HS) and a light solvent (LS). Compared to
this prior art
process, the present invention provides a greatly improved process.
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[00023] Without being bound to theory, the principle behind using a
combination
of a heavy solvent (HS) and a light solvent (LS) is illustrated in FIGS 1A (CA
'719) and 1B
which show plots of heavy solvent to light solvent ratios (HS/LS) from 0/100
to 100/0 on
the Y axis versus bitumen concentration in hydrocarbons (from high to low) on
the X-axis.
The X-axis also represents the progression of extraction from left to right.
The shaded
area shows the region of asphaltene precipitation.
[00024] Each filled circle represents a stage of mixing and/or
separation. The first
circle represents the initial mixing of dry oil sand and heavy solvent to form
a dense slurry.
This stage is the same in both the CA '719 process and the process of the
present
invention.
[00025] The second circle represents the conditions in the first stage of
the first
solid-liquid separator. In the CA' 719 process, the mass ratio of HS/LS is
controlled to be
in the range of about 70/30 to about 50/50, preferably 60/40, to ensure little
to no
asphaltene precipitation. Similarly, in the process of the present invention,
the mass ratio
of HS/LS is controlled to be in the range of about 75/25 to about 40/60 to
ensure little to no
asphaltene precipitation. Aside from the slight variation in the ranges for
the mass ratio of
HS/LS, this stage is essentially the same in both the CA '719 process and the
process of
the present invention.
[00026] The third circle represents the conditions in the second stage of
the first
solid-liquid separator. At this stage, there are significant differences
between the CA'719
process and the process of the present invention. In the CA '719 process, the
mass ratio
of HS/LS is adjusted from being within a range of about 70/30 to about 50/50
(preferably
about 60/40) to within a range of about 75/25 to about 55/45 (preferably about
65/35). The
HS/LS mixture is thus adjusted to have a significant proportion of HS. The HS
concentration is increased while the LS concentration is decreased to avoid
asphaltene
precipitation. At a HS/LS mass ratio ranging from about 75/25 to about 55/45,
little
asphaltene will precipitate out since the HS concentration is sufficiently
high to dissolve
any asphaltene precipitate. However, this causes higher HS loss to spent
solids as the
elevated HS concentration in liquid trapped in solids at the third circle must
be brought
down to a low value in the next two stages of washing/separation, which
ideally should be
zero. This is schematically shown by the fifth circle in FIG. 1A being
substantially higher
than the dashed base line, which is not the case with the fifth circle in FIG.
1B.
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[00027] In the process of the present invention, the mass ratio of HS/LS
is
adjusted from being within a range of about 75/25 to about 40/60 to within a
range of about
50/50 to about 20/80. The HS/LS mixture is thus adjusted to have a significant
proportion
of LS (in contrast to the greater proportion of HS in the CA '719 process).
The HS/LS
mixture has a decreased concentration of HS and an increased concentration of
LS, but
results in asphaltene precipitation. Despite the high LS concentration, this
stream still
contains some HS, which makes the asphaltene precipitate soft and non-sticky
so that the
chance of plugging and fouling is minimized. More importantly, the asphaltene
precipitate
is recycled back into a second slurry preparation and conditioning unit
(represented by the
second circle in FIG. 1B) where it is easily re-dissolved. The re-dissolution
of asphaltene
precipitate minimizes oil loss.
[00028] The increase of LS concentration at the third circle of FIG. 1B
compared
to the third circle of FIG. 1A (the CA '719 process) has two main advantages.
First, the
more gradual decrease of HS proportion shown in FIG. 1B allows a complete LS
countercurrent wash scheme: 5th (circle)->4th >3rd ¨nd
>2without the need of a flash drum
to process any of these streams. In comparison, the CA '719 process only
allows two
.
"broken" countercurrent wash schemes: 5th (circle) ->4th -> 2nd and 3rd
(circle) ->flash drum
->1st due to the requirement of high HS concentration at the third circle.
Therefore, the
present invention simplifies the flow sheet and increases the solvent use
efficiency since
the flash drum in the CA '719 process removes some HS and LS from the roles of
bitumen
dissolution and solids flocculation in the second slurry preparation and
conditioning unit
(second circle). The streams in the process of the present invention are thus
predominantly LS streams which are ultimately directed into the second slurry
preparation
and conditioning unit. Second, because the HS concentration has been reduced
at the
third circle, the amount of HS loss to the spent solids has been reduced
compared to that
in the CA '719 process. This is schematically shown by the fifth circle
touching the dashed
base line in FIG. 1B, unlike in FIG. 1A (prior art).
[00029] The next stage is the same in both the CA '719 process and the
process
of the present invention. The solids produced in the first separator will have
a low bitumen
concentration and can be further treated with light solvent to reduce the
heavy solvent
present in the solids in a second separator to produce tailings having little
or no bitumen
and little or no heavy solvent (fourth and fifth circles). In the second
separator, the amount
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of bitumen is low enough that the addition of light solvent will not result in
a significant
amount of asphaltene precipitation.
[00030] Compared to the CA '719 process, the solvent extraction process
of the
present invention provides greater flexibility in the choice of heavy and
light solvents and
the range of HS/LS ratios. Further, the process improves safety by minimizing
fire hazard
and solvent vapor release through inclusion of an airlock. Solids flocculation
is achieved
by ensuring optimal water to solids ratio in a baffled tank agitated with
impellers.
Surprisingly, by recycling multiple streams containing a light solvent into a
second slurry
preparation and conditioning unit for use in bitumen dissolution and solids
flocculation, a
single hydrocarbon product stream is thereby generated in the process for
component
separation in a single distillation unit without reducing the bitumen
concentration in the
product or the total solvent use efficiency. Overall, the process of the
present invention
achieves good bitumen recovery, good solvent recovery, and cleaner dry
tailings.
[00031] The heavy solvent used in the present embodiment is a light gas
oil
stream, i.e. a distillation fraction of oil sand bitumen, of mixed C9t0 C32
hydrocarbons with
a boiling range within about 130-470 C. The light end boiling is below about
170 C. The
contaminant content originating from a naphtha stream in the upgrader is less
than about 5
wt%. It has a flash point of about 90 C in air.
[00032] The light solvent is a hydrocarbon stream C6-C10 with a boiling
range of
69-170 C, which light solvent is available from bitumen upgrading units. The
preferred LS
is aliphatic C6-C7 with a boiling range of 69-110 C.
[00033] Turning to the specific embodiment shown in FIG. 2, cold oil sand
10 is
mixed with hot HS 12 with a temperature range of about 70-200 C from conduit
14 and
optionally, with water 16 from conduit 18, in a first slurry preparation and
conditioning unit
20. The unit 20 may comprise a rotating tumbler followed by a two-stage
sizer/crusher.
Longitudinal lifters may be present in the tumbler to assist in the
comminution of large oil
sand lumps by lifting and dropping them on other oil sand lumps. The solids
content in the
dense slurry in the slurry preparation and conditioning unit 20 is about 60-75
wt%. The
dense slurry temperature is preferably around 50 C, the source of heat being
primarily
from the hot HS 12 from conduit 14.
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[00034] The bitumen concentration in the dense slurry in the slurry
preparation
and conditioning unit 20 is about 25-65 wt%. In one embodiment, the HS-
dominant stream
12 contains about 70 wt% HS and about 30 wt% recycled bitumen. The bitumen
concentration in the dense slurry is about 50 wt%. In one embodiment, the HS-
dominant
stream 12 is pure HS. The bitumen concentration in the dense slurry is about
30 wt%.
[00035] Preparation of the dense slurry in the unit 20 also deoxygenates
the oil
sand by filling its air pockets. An inert gas, e.g. nitrogen, may be used to
continuously
purge the unit 20. Some residual oxygen can be tolerated in the unit 20 since
the HS and
the bitumen are not flammable at the slurry temperature. The inert gas purge
in the unit
20 acts as first-stage oxygen reduction that helps in maintaining a safe
oxygen-free
atmosphere downstream. Alternatively, air may be used to ventilate the unit 20
to reduce
the hydrocarbon vapor concentration below its low flammable limit. The vented
air may be
used in combustion in solids dryer 22 to prevent the release of hydrocarbon
vapor to the
atmosphere. Inert gas purge may be limited to the area in vicinity to an
airlock 28.
[00036] The dense slurry stream 24 exits the unit 20 via conduit 26, and
passes
through an airlock 28 and into a second slurry preparation and conditioning
unit 30. In one
embodiment, the dense slurry stream 24 flows by gravity from the unit 20,
through the
airlock 28, and into the unit 30. The airlock 28 provides an atmosphere
substantially free
of oxygen downstream of it. In one embodiment, the airlock 28 comprises a
rotary valve
and seals to separate the oxygen-containing atmosphere in the unit 20 from the
inert
atmosphere downstream. The hydrocarbons in the dense slurry provide additional
sealing
and prevent solids from sticking within the airlock 28.
[00037] Fines liberation into the hydrocarbons should be minimized to
keep the
solid-liquid separation rates sufficiently high. Addition of water to the oil
sand causes
aggregation of fines with sand grains that minimizes the fines liberation.
According to
Meadus and Sparks (1983; FIG. 3), the amount of water added can influence the
type of
aggregated solids. The types of aggregated solids are distinguished as
"flocs",
"microagglomerates" or "pellets". The process to form "flocs" is thus called
"solids
flocculation" and the process to form "microagglomerates" or "pellets" is
called "solids
agglomeration".
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[00038] With regard to solids flocculation, the aggregation of fines with
sand
grains forms "flocs" which are characterized as having a pendular structure
with few water
molecules filling the spaces among the solids, and loosely bridging the solids
together.
The percentage of pore filling by the bridging water ranges from about 0.5% to
about 50%.
[00039] With regard to solids agglomeration, the aggregation of fines
with sand
grains forms "microagglomerates" which are characterized as having a funicular
structure
with a greater amount of water molecules filling the spaces among the solids,
and more
securely bridging the solids together. The percentage of pore filling by the
bridging water
ranges from about 45% to about 95%.
[00040] The second slurry conditioning unit 30 substantially completes
bitumen
dissolution and solid flocculation Compared to solids agglomeration, solids
flocculation
requires much less water. For solids flocculation, the water to solids (W/S)
ratio is typically
less than about 0.1, preferably less than about 0.08 (refer to Examples 1-3).
For solids
agglomeration, the water to solids ratio is greater than 0.08 (United States
Patent No.
4,719,008) and typically greater than 0.1 to be functional (refer to Example
3). Solids
flocculation is preferred over solids agglomeration since less water is
required, enabling
less heat duty in spent solids drying and better recovery of LS from solids,
thereby saving
energy and generating cleaner dry tailings.
[00041] The second slurry preparation and conditioning unit 30 may
comprise a
static or dynamic mixer. Preferably, the mixer is a baffled tank agitated with
impellers. A
conventional mixer has an impeller diameter of about 0.33-0.5 of the tank
diameter and a
bottom clearance of about 0.33 of the tank diameter (FIG. 4A; Paul et al.
(ed.) "Handbook
of Industrial Mixing ¨ Science and Practice," John-Wiley and Sons: Hoboken NJ
2004, pp.
157), but it does not provide effective solids flocculation. In comparison,
the mixer of the
present invention with large diameter impellers placed at a low clearance is
configured to
induce solids flocculation (FIG. 4B). In one embodiment, the impellers are 45
pitched
blade turbines having a diameter ranging from about 0.55 to about 0.7 of the
tank
diameter. The bottom clearance ranges from about 0.01 to about 0.15 of the
tank
diameter. In one embodiment, the bottom clearance ranges from about 1 cm to
about 5
cm for any tank diameter. The power input by the impellers ranges from about 1
VV/kg to
about 15 W/kg of slurry.
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(000421 In the second slurry preparation and conditioning unit 30, the
slurry 24 is
dosed with a minimal amount of water 16 or an aqueous solution (e.g., water
from oil
sands tailing ponds) having a pH of about 8-8.5 from conduit 32. Water or
aqueous
solution is added to yield a total water to solids mass ratio (W/S) of less
than about 0.1,
preferably less than about 0.08.
(00043] The slurry 24 is further mixed with a LS-rich stream 34 from
conduit 36,
and a LS-dominant stream 38 from conduit 40 in the slurry preparation and
conditioning
unit 30. The LS-rich stream 34 may contain LS in an amount ranging from about
45 wt%
to about 65 wt%. The LS-dominant stream 38 may contain LS in a greater amount
ranging
from about 70 wt% to about 90 wt%.
(00044] The mass ratio of HS/LS in the LS-diluted slurry is controlled to
be in the
range of about 75/25 to about 40/60 by adjusting the flow rates in conduits 36
and 40 to
ensure little to no asphaltene precipitation and to facilitate the subsequent
solid-liquid
separation. The solids content in the mixed slurry in the slurry preparation
and
conditioning unit 30 is about 45-60 wt%. The bitumen concentration in the
mixed
hydrocarbon phase in the slurry preparation and conditioning unit 30 is about
15-40 wt%.
(000451 In one embodiment wherein the HS-dominant stream 12 contains
recycled bitumen, the HS/LS ratio ranges from about 55/45 to about 45/55 in LS-
diluted
slurry. The bitumen concentration in the mixed hydrocarbon phase in unit 30 is
about 25-
40 wt%.
(00046J In one embodiment wherein the HS-dominant stream 12 comprises
pure
HS, the HS/LS ratio ranges from about 72/28 to about 62/38 in LS-diluted
slurry. The
bitumen concentration in the mixed hydrocarbons in unit 30 is about 15-30 wt%.
[000471 All LS-containing streams in the process are combined into
streams 34
and 38 and reused in the second slurry preparation and conditioning unit 30 to
reduce the
solids concentration in the dense slurry 24 to a suitable level for proper
bitumen
dissolution, floc formation and subsequent solid-liquid separation. The use of
the "waste"
LS-containing streams reduces the total HS and LS to oil sand bitumen mass
ratios to
about 1 and 3, respectively, for the process with bitumen recycle in stream
12. In
comparison, the CA '719 process requires these ratios to be about 1.3 and 3.5,
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respectively, to achieve similar solids and bitumen concentrations in streams
throughout
the process. This improvement of solvent use efficiency is achieved by
eliminating the
flash drum in CA '719 process that removes some HS and LS from the process
after
merely one washing step.
[00048] The LS-diluted slurry 42 is then fed onto a first solid-liquid
separator 44.
In one embodiment, the first solid-liquid separator 44 may comprise a top-
loading filter
such as, for example, an enclosed pan filter. The first solid-liquid separator
44 contains at
least two stages which are shown separated with a dashed line in FIG. 2. The
first-stage
separation generates a first liquids stream 46 and a first solids stream 48.
The first liquids
stream 46 is sent to a distillation unit 50 via conduit 52 to recover LS 54
and HS 56,
removed via conduits 58 and 60, respectively, and to produce bitumen 62, which
is
removed via conduit 64. Recovered HS and LS flow into tank 66 and tank 68,
respectively.
Tank 68 receives another recycled LS stream 70 via conduit 72. Tank 68 also
receives a
LS makeup stream 132 via conduit 134. The HS makeup is produced internally by
distilling
the product bitumen in the unit 50 since the HS here is a fraction of bitumen.
The HS
makeup is included in the recovered HS stream 56 from conduit 60. In one
embodiment,
the distillation unit 50 includes multiple distillation columns. LS may be
recovered in one
column and HS in the next column. In one embodiment, the recovered HS stream
56
comprises about 20-40 wt% recycled bitumen and 60-80 wt% HS. In one
embodiment, the
recovered HS stream 56 is pure HS.
(00049] If the first liquids stream 46 is untreated, the bitumen 62 may
contain
about 1 wt% solids, similar to the product of naphtha-based froth treatment in
a water-
based extraction process. If the stream 46 is partially deasphalted, the
bitumen 62
contains less than about 500 mg/kg solids.
[00050] After the first-stage separation, the first solids stream 48 from
the
separator 44 receives a LS-dominant stream 74 from conduit 76 for washing, and
goes
through a second-stage solid-liquid separation to generate a second liquids
stream 34 and
a second solids stream 78. The LS-dominant stream 74 contains about 70 wt% to
about 90
wt% LS. The mass ratio of HS/LS in this washing liquid is maintained in the
range of about
50/50 to about 20/80. This HS/LS ratio happens to be the value in a downstream
liquids
stream 96 that is partially recycled here. After using stream 74 for washing,
the second
liquids stream 34 also has a relatively high LS proportion compared to HS and
can be
WSLegah 053707 \ 00453 \ 12065702v1 13
CA 02895118 2015-06-15
recycled directly into a second slurry preparation and conditioning unit 30
without upsetting
the HS/LS ratio in unit 30. The streams in the process of the present
invention are thus
predominantly LS streams which are ultimately directed into the second slurry
preparation
and conditioning unit 30. Compared to the prior art CA '719 process, the
reduced HS/LS in
the washing liquid stream 74 enables direct recycle of the stream 34 without
the need of
further processing with a flash drum and also reduces the HS concentrations in
solids so
that the HS loss to spent solids is reduced.
[000511 In one embodiment, the second solids stream 78 is a filter cake
discharged from the pan filter. Some asphaltene may precipitate from the
second liquids
stream 34. Because of the presence of HS in the second liquids stream 34, the
precipitated asphaltene is in the form of soft loose solids that can be pumped
through a
pipe without causing plugging. When the second liquids stream 34 arrives at
the unit 30,
the solvent chemistry there re-dissolves the precipitated asphaltene to
minimize oil loss.
[00052] In one embodiment, the second solids stream 78 flows out of the
first
separator 44 into a repulper 80. In one embodiment, the repulper 80 is a
baffled tank
agitated with impellers. In one embodiment, the tank and impellers have an
unconventional configuration shown in FIG. 4B. A LS-dominant stream 82 from
conduit 84
is pumped into the repulper 80 as well. The repulper 80 provides vigorous
mixing of the
solids stream 78 and a predominantly LS stream 86 from conduit 88 to dissolve
any
trapped bitumen and HS. The predominantly LS stream 86 contains about 80 wt%
to
about 99 wt% LS. After repulping, the slurry 90 is fed via conduit 92 onto a
second solid-
liquid separator 94. The solids content in the slurry 90 in the repulper 80 is
about 50-65
wt%.
(00053) The second solid-liquid separator 94 contains at least two stages
(third
and fourth stages) which are shown separated with a dashed line in FIG. 2. In
one
embodiment, the second solid-liquid separator 94 may comprise a top-loading
filter such
as, for example, an enclosed pan filter. The third-stage solid-liquid
separation generates a
third liquids stream 96 and a third solids stream 98. The third liquids stream
96, which
comprises primarily light solvent, is removed via conduit 100 to be split
through a splitter
110 into stream 38 for reuse in the second slurry preparation and conditioning
unit 30;
stream 74 for reuse in the separator 44; and stream 82 for reuse in the
repulper 80. In one
WSLegal',053707 \ 00453 \ I2065702 14
CA 02895118 2015-06-15
embodiment, the split ratio is about 33%, about 48% and about 19% for streams
38, 74,
and 82, respectively.
[00054] After the third-stage separation, the third solids stream 98 in
the separator
94 receives a pure LS stream 112 from conduit 114 for washing and goes through
a fourth-
stage solid-liquid separation to generate a fourth liquids stream 86 and a
fourth solids
stream 116. The fourth liquids stream 86, which comprises predominantly LS, is
removed
via conduit 88 for reuse in the repulper 80. In one embodiment, the solids
stream 116 is a
filter cake discharged from the pan filter.
[00055] The spent solids 116 from the separator 94 are removed via
conduit 118
into the solids dryer 22. In one embodiment, the conduit 118 may be a jacketed
screw
conveyor to preheat the spent solids 116 with steam in the jacket. In one
embodiment, the
dryer 22 comprises a super-heated steam dryer. The solids are heated to about
100 C
and discharged as dry tailings 120. In one embodiment, the LS content in dry
tailings 120
is less than about 300 mg/kg LS, equivalent to VOC emissions of less than 3.8
bbl/kbbl of
bitumen produced. In one embodiment, the LS content is less than about 100
mg/kg,
equivalent to VOC emissions of less than 1.3 bbl/kbbl of bitumen produced.
[00056] In one embodiment, the dry tailings 120 may be further mixed with
fluid
fine tailings (FFT) that are produced in water-based processes and typically
contain about
30 wt% solids, at a mass ratio of about 1:0.25 to make a trafficable solids
mixture
containing about 85 wt% solids. This mixture, which is more consolidated and
less dusty
than loose dry solids, can be transported to a land reclamation site for
disposal.
[00057] The recovered vapors (LS and H20) 122 flow via conduit 124 to a
condenser/separator 126. The cooling medium used in condenser/separator 126
may be
cold recycle cooling water. Condensed LS 70 flows out via conduit 72 to the LS
tank 68.
There may be a trace amount of HS condensed in the LS stream 70. Condensed
water
128 flows out via conduit 130 and could be recycled for steam generation if
needed. The
bitumen and LS recoveries in this process are about 95% and about 99%,
respectively.
This bitumen recovery includes small loss of HS to spent solids that is
deducted from the
product bitumen in distillation as HS makeup. The HS recovery, if calculated
separately, is
about 99%.
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CA 02895118 2015-06-15
Example 1
[00058] Table 1 shows the relationship of water-to-solids mass ratios
(W/S) in
slurry and filtration rates for a test oil sand (#1) containing 9.3 wt%
bitumen, 2.1 wt% water
and 88.6 wt% solids. The fines (<44 pm) content in the solids was 21 wt%. This
oil sand
was relatively dry, so by varying the water dosage, the W/S could be adjusted
in a wider
range. The hydrocarbon phase in the slurry prior to the first filtration step
comprised about
30 wt% bitumen, 35 wt% virgin light gas oil and 35 wt% heptane. The solids
content in the
slurry was about 58 wt%. The solids were flocculated in a baffled dished-
bottom mixing
tank of 13 cm in diameter (T) at 50 C. The impeller was a 6-blade 45 PBT of
7.6 cm in
diameter (D). The bottom clearance (C) was about 1.5 cm. Thus, D/T = 0.58 and
UT =
0.12. The down-pumping axial impeller was operated at 600 rpm for 4 minutes,
providing
a power input of about 6 W/kg of slurry. The mixed slurry was transferred to a
top-loading
batch filter with about 70 kPa (absolute) pressure inside its filtrate
receiver. The filter cake
thickness was kept around 4.4 cm. One stage of drainage and one stage of
washing were
carried out on this filter. The filter cake was removed for repulping with a
high-LS-content
solution. One stage of drainage and one stage of washing were carried out on
the same
filter after repulping. The second filter cake was the spent solids for drying
and solvent
recovery. Filter process rate refers to the oil sand throughput per filter
area (including both
filters before and after repulping) per hour in a hypothetical continuous
operation. Initial
filtrate flux refers to the average flux of the first filtrate prior to air
breakthrough.
[00059] Table 1
W/S Mass Ratio in Slurry 0.046 0.052 0.057 0.068
Filter Process Rate (t/m2h) 6.6 7.0 8.0 8.5
Initial Filtrate Flux (L/m2s) 4.9 5.9 8.5 10.2
[00060] Using a dual-solvent extraction process including solids
flocculation and
repulping, even the lowest filter process rate of 6.6 t/m2h is sufficient for
a commercial pan
filter to operate efficiently. The data indicate that with proper flocculation
conditions and
apparatuses, the filtration step may be scaled up to a commercial operation
with a W/S
ratio below about 0.07.
WSLega11053707 \ 00453 \ 12065702v1 16
CA 02895118 2015-06-15
Example 2
(00061] Two samples of oil sands #1 and #2 having 9.3 wt% and 9.7 wt%
bitumen, 2.1 wt% and 6.2 wt% water and 21% and 28% fines in solids,
respectively, were
extracted with dual solvents under similar conditions as described in Example
1. The test
for oil sand #2 had zero water addition. Oil sand connate water was the sole
source of
water for solids flocculation. Both samples went through four stages of
filtration with
repulping between stages 2 and 3. The filter cake thickness was kept around
4.3 cm. All
wash liquids were prepared based on their compositions and flow rates in a
continuous
process. Table 2 shows the extraction performance.
(00062] Table 2
Oil sand Initial Filtrate Filter Process Bitumen* W/S Mass
Flux Rate Recovery Ratio in
(L/m2 s) (t/m2 h) (%) Slurry
#1 5.9 7.0 96.9 0.052
#2 11.1 8.5 94.1 0.074
= Bitumen recovery here includes small loss of HS to spent solids that can
be deducted from the
product bitumen in distillation as HS makeup.
(00063] The bitumen recoveries for oil sands #1 and #2 in water-based
extraction
are 88% and 55%, respectively. The data indicate that using the dual-solvent
extraction
process including solids flocculation, filter process rates above 7 t/m2 h,
bitumen recovery
around 95% and W/S below 0.08 can be achieved even for a relatively wet oil
sand #2.
Example 3
(00064] Tests were conducted to compare the filter process rates and
bitumen
recoveries achieved using a solids agglomeration method of the prior art which
involved a
drum agglomerator verses the solids flocculation method of the present
invention which
involved the mixing tank/impeller described in Example 1. The two solvents
used in
extraction and the slurry compositions were identical in these two tests and
similar to those
in Example 1. An oil sand (#3) used in both tests contained about 10 wt%
bitumen, 5 wt%
water and 85 wt% solids. The fines (<44 pm) content in the solids was 28 wt%.
The solids
contents in the slurry for the agglomeration and flocculation tests were about
45 wt% and
52 wt%, respectively. The filter cake thicknesses used in the agglomeration
and
flocculation tests were 10.2 cm and 4.7 cm, respectively. The agglomeration
data have
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been converted based on a hypothetical filter cake thickness of 4.7 cm to be
comparable
with the flocculation data. Table 3 shows the comparison of extraction
performance.
[00065] Table 3
Method Flocculation Agglomeration (Prior Art)
W/S in Slurry 0.07 0.08 0.08 0.095 0.11 0.12
0.14
Filter Process Rate 5.0 7.1 0 4.1 4.3 4.2 4.4
(tlrin2h)
Initial Filtrate Flux 3.6 7.2 0 3.2 3.6 4.1 5.1
(Lies)
Bitumen Recovery (%) 93.0 92.4 N/A 91.0 91.4 91.3
87.2
* Bitumen recovery here includes small loss of HS to spent solids that can be
deducted from the
product bitumen in distillation as HS makeup.
(00066) The filter process rate and initial filtrate flux obtained from
the solids
flocculation method of the present invention ranged from 5.0 to 7.1 t/m2h and
3.6 to 7.2
L/m2s, respectively, with lower water content (W/S mass ratio between 0.07 to
0.08),
compared to those from the solids agglomeration method of the prior art, 4.1
to 4.4 t/m2h
and 3.2 to 5.1 L/m2s, respectively, with higher water content (W/S mass ratio
between
0.095 to 0.14). At W/S=0.08, the solids agglomeration method caused filter
plugging thus
making the filter process rate zero. Filter plugging implies failure of the
method to
effectively bind fines with coarse sand grains.
(00067) Similarly, the bitumen recovery was higher for the flocculation
method
(over about 92%) at lower water content (W/S mass ratio between 0.07 to 0.08)
compared
to bitumen recovery for the agglomeration method (about 91%) at higher water
content
(W/S mass ratio between 0.095 to 0.12). Bitumen recovery plummeted to 87% at
even
higher water content (W/S mass ratio around 0.14). The bitumen recovery for
oil sand #3
in water-based extraction is 81%.
[00068] In summary, the present invention involving solids flocculation
was
superior to the prior art involving solids agglomeration, yielding higher
filter process rates
and bitumen recovery in a low water content regime where the agglomeration
method no
longer functions. Lower water content is preferred in the process since higher
water
content interferes with downstream solvent recovery from spent solids.
[00069] The previous description of the disclosed embodiments is provided
to
enable any person skilled in the art to make or use the present invention.
Various
Vv'SLegal\ 053707 \00453 12065702v1 18
CA 2895118 2017-05-02
modifications to those embodiments will be readily apparent to those skilled
in the art, and
the generic principles defined herein may be applied to other embodiments
without
departing from the spirit or scope of the invention. Thus, the present
invention is not
intended to be limited to the embodiments shown herein, but is to be accorded
the full
scope consistent with the claims, wherein reference to an element in the
singular, such as
by use of the article "a" or "an" is not intended to mean "one and only one"
unless
specifically so stated, but rather "one or more". All structural and
functional equivalents to
the elements of the various embodiments described throughout the disclosure
that are
= known or later come to be known to those of ordinary skill in the art are
intended to be
encompassed by the elements of the claims. Moreover, nothing disclosed herein
is
intended to be dedicated to the public regardless of whether such disclosure
is explicitly
recited in the claims.
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Blackbourn, R.L.; Bott, R.A.; Giles, S.P.; Komishke, B.D.; Ling, Y.; Ploemen,
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Veen, B.C.M. Closed loop solvent extraction process for oil sands. Canadian
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Delude, SO.; Giles, S.P. and Visser, C.M. A method for removing oxygen from an
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=
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