U.S. patent application number 12/874025 was filed with the patent office on 2012-03-01 for extraction of oil sand bitumen with two solvents.
This patent application is currently assigned to SYCRUDE CANADA LTD.. Invention is credited to GEORGE CYMERMAN, GEORGE JONES, XIN ALEX WU.
Application Number | 20120048781 12/874025 |
Document ID | / |
Family ID | 45695722 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120048781 |
Kind Code |
A1 |
WU; XIN ALEX ; et
al. |
March 1, 2012 |
EXTRACTION OF OIL SAND BITUMEN WITH TWO SOLVENTS
Abstract
A process for extracting bitumen from oil sand using a
combination of heavy solvent and light solvent is provided
comprising contacting mined oil sand with a non-flammable heavy
solvent (HS) to produce a dense oil sand slurry; mixing the dense
slurry with a light solvent (LS) to give a heavy solvent to light
solvent (HS/LS) mass ratio of about 70/30 to 50/50 and subjecting
the diluted oil sand slurry to a first stage solid-liquid
separation to produce a first liquids stream containing bitumen and
a first solids stream; mixing the solids stream with a mixed
solvent having a HS/LS mass ratio of about 75/25 to 55/45 and
subjecting the diluted solids stream to a second stage solid-liquid
separation to produce a second liquids stream and a second solids
stream; rinsing the solids stream with a countercurrent flow of LS
to recover the HS and produce spent solids; and drying the spent
solids to LS concentration of less than 160 g/tonne solids.
Inventors: |
WU; XIN ALEX; (Edmonton,
CA) ; JONES; GEORGE; (Calgary, CA) ; CYMERMAN;
GEORGE; (Edmonton, CA) |
Assignee: |
SYCRUDE CANADA LTD.
Fort McMurray
CA
|
Family ID: |
45695722 |
Appl. No.: |
12/874025 |
Filed: |
September 1, 2010 |
Current U.S.
Class: |
208/390 |
Current CPC
Class: |
C10G 1/045 20130101;
C10G 2300/44 20130101 |
Class at
Publication: |
208/390 |
International
Class: |
C10G 1/04 20060101
C10G001/04 |
Claims
1. A process for extracting bitumen from oil sand, comprising: (a)
contacting mined oil sand with a non-flammable heavy solvent (HS)
to produce a dense oil sand slurry; (b) mixing the dense slurry
with a light solvent (LS) to give a heavy solvent to light solvent
(HS/LS) mass ratio of 70/30 to 50/50 and subjecting the diluted oil
sand slurry to a first stage solid-liquid separation to produce a
first liquids stream containing bitumen of the highest
concentration and a first solids stream; (c) mixing the solids
stream with a mixed solvent having a HS/LS mass ratio of 75/25 to
55/45 and subjecting the diluted solids stream to a second stage
solid-liquid separation to produce a second liquids stream and a
second solids stream; (d) reusing the second liquids stream after
removing its LS component in step (a); (e) rinsing the second
solids stream with a countercurrent flow of LS to recover the HS
and produce spent solids; and (f) drying the spent solids to LS
concentration of less than 160 mg/kg solids.
2. The process of claim 1, wherein the recovered HS from step (e)
that is rich in LS is reused in either the first-stage separation
[step (b)], the second-stage separation [step (c)], or both.
3. The process of claim 1, wherein the HS is a non-volatile,
high-flash point virgin light gas oil, distilled from oil sand
bitumen, having a boiling range of about 220-480.degree. C.
4. The process of claim 1, wherein the LS is mixed C.sub.6-C.sub.7,
produced from an oil sand bitumen upgrading unit, having a boiling
range of about 66-101.degree. C.
5. The process as claimed in claim 3, wherein the boiling range is
about 220-330.degree. C.
6. The process as claimed in claim 4, wherein boiling range is
about 85-101.degree. C.
7. The process of claim 1, wherein the diluted oil sand slurry is
transported to the first-stage separation though a pipeline.
8. The process of claim 1, wherein the ratio of HS/LS continuously
varies from the first to the last separation stage to optimize
bitumen recovery and separation rate.
9. The process of claim 1, wherein a dryer removes and recovers
about 99.9% of LS from the spent solids.
10. The process of claim 1, wherein the oil sand contains at least
about 40% fines in solids and bitumen recovery is at least about
95%.
11. The process of claim 1, further comprising: (g) integrating the
process with an existing water-based extraction process to maximize
economic return, minimize total energy input and convert wet
tailings produced from the water-based extraction process to
trafficable solids.
12. A process for extracting bitumen from oil sand using a
combination of heavy solvent and light solvent, comprising: (a)
contacting mined oil sand with a non-flammable heavy solvent (HS)
to produce a dense oil sand slurry; (b) mixing the dense slurry
with a light solvent (LS) to give a heavy solvent to light solvent
(HS/LS) mass ratio of about 70/30 to 50/50 and subjecting the
diluted oil sand slurry to a first stage solid-liquid separation to
produce a first liquids stream containing bitumen and a first
solids stream; (c) mixing the solids stream with a mixed solvent
having a HS/LS mass ratio of about 75/25 to 55/45 and subjecting
the diluted solids stream to a second stage solid-liquid separation
to produce a second liquids stream and a second solids stream; (d)
rinsing the solids stream with a countercurrent flow of LS to
recover the HS and produce spent solids; and (e) drying the spent
solids to LS concentration of less than 160 g/tonne solids.
13. The process of claim 12, wherein the recovered HS from step (d)
that is rich in LS is reused in either the first-stage separation
[step (b)], the second-stage separation [step (c)], or both.
14. The process of claim 12, wherein the HS is a non-volatile,
high-flash point virgin light gas oil, distilled from oil sand
bitumen, having a boiling range of about 220-480.degree. C.
15. The process of claim 12, wherein the LS is mixed
C.sub.6-C.sub.7, produced from an oil sand bitumen upgrading unit,
having a boiling range of about 66-101.degree. C.
16. The process as claimed in claim 14, wherein the boiling range
is about 220-330.degree. C.
17. The process as claimed in claim 15, wherein boiling range is
about 85-101.degree. C.
18. The process of claim 12, wherein the diluted oil sand slurry is
transported to the first-stage separation though a pipeline.
19. The process of claim 12, wherein the ratio of HS/LS
continuously varies from the first to the last separation stage to
optimize bitumen recovery and separation rate.
20. The process of claim 12, wherein a dryer removes and recovers
about 99.9% of LS from the spent solids.
21. The process of claim 12, wherein the oil sand contains at least
about 40% fines in solids and bitumen recovery is at least about
95%.
22. The process of claim 12, further comprising: (f) integrating
the process with an existing water-based extraction process to
maximize economic return, minimize total energy input and convert
wet tailings produced from the water-based extraction process to
trafficable solids.
Description
FIELD OF INVENTION
[0001] The present invention relates to a solvent extraction
process for extracting bitumen from mined oil sand.
BACKGROUND OF THE INVENTION
[0002] Most commercial bitumen extraction processes for mined oil
sand are water-based processes that consume large amounts of water
and generate a great quantity of wet tailings.
[0003] An alternative to water extraction is solvent extraction of
bitumen from mined oil sand, which uses little or no water,
generates no wet tailings and can potentially achieve higher
bitumen recovery than the existing Clark hot water extraction
process or its variants. Solvent extraction is potentially more
robust and more environmentally friendly than water 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. For example, solvent could be a
light solvent with a typical boiling range of 36-110.degree. C.,
e.g. C.sub.5-C.sub.6 (U.S. Pat. No. 4,347,118 and U.S. Pat. No.
4,752,358), cyclohexane (U.S. Pat. No. 4,189,376), toluene (U.S.
Pat. No. 4,416,764), heptane/toluene mix (U.S. Pat. No. 4,448,667),
or chlorinated C.sub.1-C.sub.2 (U.S. Pat. No. 4,532,024 and U.S.
Pat. No. 6,207,044). However, the main problem with the use of any
hydrocarbon light solvent is the fire hazard it poses in a mining
environment. An additional problem with using light solvents such
as pure toluene is that they are usually not available in large
quantities to oil sand bitumen producers.
[0005] The most readily available solvent to oil sand bitumen
producers is a mixed aliphatic C.sub.5-C.sub.7 solvent (light
naphtha). However, light naphtha is a poor solvent for bitumen and
asphaltenes tend to precipitate out after bitumen dilution, which
would trap bitumen and solvent in the spent solids, thereby making
the recoveries of both components low. Chlorinated light solvents
are even less likely to be used in bitumen extraction. Although
they are reportedly non-flammable and safe to operators and the
environment, they are detrimental to downstream upgrading and
refining processes and the cost due to solvent loss is
prohibitively high.
[0006] Another single solvent which could be used for bitumen
extraction would be a heavy solvent with a typical boiling range of
177-343.degree. C., e.g. kerosene (U.S. Pat. No. 4,094,781) or
diesel (Canadian Patent No. 1,048,432). However, the main problem
with the heavy solvents is the poor solvent recovery. To fully
recover the heavy solvents, high-energy input operations such as
retorting or coking the spent solids are required. Energy used to
heat the spent solids in these operations is usually
unrecoverable.
[0007] Alternatively, an intermediate solvent such as naphtha with
a typical boiling range of 66-205.degree. C. could be used in the
extraction (Canadian Patent No. 1,190,877 and U.S. Pat. No.
5,534,136). Naphtha is generally a better solvent for bitumen
compared to most light solvents. However, the heavy fractions in
naphtha that contribute to good bitumen solubility are also the
cause of difficulty in solvent recovery. The energy requirement
(temperatures near or over 200.degree. C.) needed for the solvent
recovery from spent solids usually makes the process uneconomical.
In addition, the light fractions in naphtha would create the same
safety issue in a mining environment as the light solvents.
[0008] It has been suggested that using two solvents sequentially
may overcome some of the problems encountered with the use of
single solvents (U.S. Pat. No. 3,131,141, U.S. Patent Application
No. 2006/0076274 and U.S. Pat. No. 3,117,922). For example, a
heavy, aromatics-rich and non-flammable solvent may be used for
bitumen extraction, which would ensure safe operations such as ore
wet crushing in a mining environment and no asphaltene
precipitation. Subsequently, a light solvent (usually aliphatic) is
used for the extraction of the heavy solvent from the spent solids.
Solvent recovery from spent solids would be relatively easy after
the light solvent replacement.
[0009] The solvent switch (from heavy to light) generally occurs
after the near complete extraction of bitumen. Hence, the light
solvent could be a very poor bitumen solvent, e.g. liquefied
propane/butane. However, since heavy solvents usually have high
viscosities by themselves, separating heavy solvent-diluted bitumen
from a sand matrix requires high heavy solvent-to-bitumen (HS/B)
ratio to lower the diluted bitumen viscosity to an acceptable
level. In addition, oil sand is preferably transported to
extraction plants in a form of solvent-based slurry through
pipelines. This requires even higher HS/B ratio, e.g., about 5:1.
Further, heavy solvents require higher temperature (over
300.degree. C.) to distill and recycle. Thus, a high HS/B ratio
would likely make the process uneconomical. Furthermore, these
processes also require almost the same amount of light solvent as
the heavy solvent, which greatly increases the cost of solvent
storage, handling and recycle.
[0010] U.S. Pat. No. 4,389,300 teaches feeding oil sand, presumably
dry-crushed, into a single vertical column containing both
countercurrent heavy solvent wash and light solvent wash at
different depths. Light solvent after countercurrent wash was not
completely withdrawn from the column and was allowed to mix with
heavy solvent at the point of initial mixing with oil sands.
However, in a commercial-scale operation, it is difficult to crush
dry oil sands to a lump size amenable to extraction without the aid
of solvent or hot water. In addition, the ratio of the two solvents
cannot be precisely controlled or varied in various locations of a
column without discrete stages. Thus, the proportion of light
solvent might be either too small, thereby failing to lower the
HS/B ratio significantly, or could be too large, thereby causing
asphaltene precipitation.
[0011] In summary, it is likely that the prior art solvent
extraction processes failed to become commercially viable due to
one or more of the following unresolved issues:
1. Hazard of handling flammable solvents in mining environment
where sealing and operating equipment under inert atmosphere are
difficult to implement. 2. Poor solvent recovery from spent oil
sand generates high volatile organic compound (VOC) emission
levels. 3. Light solvents that are easy to recover from solids are
usually poor solvents for bitumen and cause asphaltene
precipitation. 4. Attempts to solve the above issues by
sequentially using a heavy solvent and a light solvent greatly
increase the operating cost. 5. Being inherently more complicated
in bitumen-sand separation and solvent recovery, any solvent
extraction process appears uneconomical compared with the existing
water-based extraction process.
[0012] There is a need for a solvent based extraction process that
is both safe, economical and yields both high bitumen and solvent
recoveries.
SUMMARY OF THE INVENTION
[0013] In accordance with a broad aspect of the invention, there is
provided a solvent extraction process which uses at least two
different solvents and controlled solvent mix ratios during solvent
extraction.
[0014] In one embodiment, a non-flammable heavy solvent (HS) may be
used for initial oil sands mixing and crushing in mining
operations. A heavy/light solvent mixture with significant
proportion of light solvent (LS) may be used for the oil sands
slurry transportation and the first stage of solid-liquid
separation, at which time the bitumen concentration is sufficiently
high that the presence of light (poor) solvent would not induce
asphaltene precipitation. A heavy/light solvent mixture with
relatively more HS may be used for the second stage of separation
to prevent asphaltene precipitation. Finally, a LS-dominant mixture
may be used for the subsequent stages of separation, at which point
most of the bitumen has been removed and the amounts of
precipitated asphaltene are minimal. Hence, the spent solids would
subsequently become almost HS-free. The light solvent would be
readily recovered from the spent solids using a thermal/stripping
method.
[0015] "Heavy solvent" or "HS" as used herein means a solvent with
a typical boiling range of 177-343.degree. C. and generally include
hydrocarbon liquids in the C.sub.10 to C.sub.20 range such as
kerosene and diesel.
[0016] "Light solvent" or "LS" as used herein means a solvent with
a typical boiling range of 36-110.degree. C. and generally include
hydrocarbon liquids in the C.sub.5 to C.sub.7 range such as
pentane, hexane, cyclohexane and toluene.
[0017] In another broad aspect of the invention, a process for
extracting bitumen from oil sand using a combination of heavy
solvent and light solvent is provided, comprising: [0018]
contacting mined oil sand with a non-flammable heavy solvent (HS)
to produce a dense oil sand slurry; [0019] mixing the dense slurry
with a light solvent (LS) to give a heavy solvent to light solvent
(HS/LS) mass ratio of about 70/30 to 50/50 and subjecting the
diluted oil sand slurry to a first stage solid-liquid separation to
produce a first liquids stream containing bitumen and a first
solids stream; [0020] mixing the solids stream with a mixed solvent
having a HS/LS mass ratio of about 75/25 to 55/45 and subjecting
the diluted solids stream to a second stage solid-liquid separation
to produce a second liquids stream and a second solids stream;
[0021] rinsing the solids stream with a countercurrent flow of LS
to recover the HS and produce spent solids; and [0022] drying the
spent solids to LS concentration of less than 160 g/tonne
solids.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a graph of heavy solvent to light solvent ratio
(HS/LS) (from 0/100 to 100/0) versus bitumen concentration in
hydrocarbons (from high to low).
[0024] FIG. 2 is a schematic process flow diagram of one embodiment
of the solvent extraction process.
[0025] FIG. 3 is a schematic drawing showing the integration of an
embodiment of the solvent bitumen extraction process of the
invention with a water-based bitumen extraction process.
DESCRIPTION OF VARIOUS EMBODIMENTS
[0026] The present invention attempts to exploit the different
properties of various solvents to allow for good bitumen recovery
(reduced asphaltene precipitation), good solvent recovery and
improved safety. Without being bound to theory, the principle
behind using a flexible combination of a heavy solvent (HS) and a
light solvent (LS) is illustrated in FIG. 1. FIG. 1 shows a plot 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 shaded area shows the region of
asphaltene precipitation.
[0027] Each filled circle represents a stage of mixing and/or
separation, as discussed in more detail below. The first circle
represents the initial mixing of dry oil sand and heavy solvent.
The second circle represents the addition of light solvent to the
heavy solvent/oil sand slurry to produce a mixture of the HS/LS
around 60/40, which facilitates slurry transport through a
pipeline, conditioning of the oil sand slurry therein to release
bitumen, digest lumps of oil sand, etc. The same circle also
represents the conditions in the first stage of the first
solid-liquid separator. The third circle represents the conditions
in the latter stage of the first separator where the HS/LS ratio is
slightly increased to about 70/30. At this solvent mix ratio, very
little asphaltene will precipitate out.
[0028] 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. In the second separator, the amount of
bitumen is low enough that the addition of light solvent will not
result in a significant amount of asphaltene precipitation.
[0029] The heavy solvent used in the following embodiment is a
virgin light gas oil, i.e. a distillation fraction of oil sand
bitumen, C.sub.12-C.sub.32 with a boiling range within about
220-480.degree. C., which would not fall under the Volatile Organic
Compounds (VOCs) regulations with respect to air quality in Canada.
The preferred boiling range is about 220-330.degree. C. The HS
contains approximately 30-50% aromatic compounds and is able to
dissolve bitumen asphaltene. It has a flash point more than
10.degree. C. above the process temperature, which is within the
range of 20-80.degree. C., preferably around 50.degree. C.
[0030] The light solvent in the present embodiment could be mixed
C.sub.6-C.sub.7 with a boiling range of 69-101.degree. C., which
light solvent is available from bitumen upgrading units. The
preferred LS is aliphatic C.sub.7 with a boiling range of
85-101.degree. C.
[0031] FIG. 2 shows one embodiment of flexibly combining two
solvents in a commercially viable way to achieve the solvent mix
ratio changes as shown in FIG. 1. Cold oil sand 10 is mixed with
0-2 wt % hot water from conduit 11, generally having a temperature
in the range of 50-90.degree. C., and hot HS with a temperature
range of 140-190.degree. C. from conduit 12, which hot HS may
contain small amounts of bitumen, in a slurry preparation unit 30,
which slurry preparation unit 30 may comprise a
tumbler/crusher/pumpbox circuit, and which may be located on the
mine site. Longitudinal lifters (not shown) may be present in the
tumbler to assist in the comminution of large oil sands lumps by
lifting and dropping them on other oil sand lumps. Preferably, the
mass ratio of HS to bitumen is 1-1.5. The solids content in the
dense slurry in unit 30 is 65-75 wt %.
[0032] The tumbler/crusher/pumpbox circuit may also include an
integral rotary screen (not shown) for screening the oil
sand/water/HS slurry prior to its passage into the pumpbox.
Screened oversize may be crushed to pumpable size and also passed
into the pumpbox. In one embodiment, the slurry preparation unit 30
operates at a temperature of about 50.degree. C., the source of
heat being primarily from the hot HS from conduit 12.
[0033] The dense slurry in the pumpbox may be further mixed with a
LS stream, which may contain a small amount of HS, from conduit 17
to make the slurry pumpable, e.g., having solids content of 55-65
wt %. In one embodiment, the mass ratio of HS/LS in the slurry is
controlled to be in the range of 70/30 to 50/50, preferably about
60/40, by adjusting the flow rate in conduit 17 to ensure no
asphaltene precipitation and to facilitate the subsequent
solid-liquid separation.
[0034] The slurry is then pumped out via conduit 13 to a slurry
pipeline 31, which may connect the mine and the extraction plant.
Apart from transportation, the slurry pipeline 31 may also serve as
a slurry mixer, lump digester and conditioner, thereby aiding the
bitumen extraction from the interstices of the sand matrix to the
liquid hydrocarbon phase.
[0035] The slurry from pipeline 31 is fed into a first multi-stage
separator 32, which also receives an LS stream containing small
amount of HS from conduit 23 and pure HS from conduit 3 for
countercurrent washing. Two liquid streams and one solid stream are
produced in the first separator 32. The mass ratio of HS/LS in the
washing liquid, i.e. the combined stream from conduits 3 and 23, is
maintained in the range of 75/25 to 55/45 by adjusting the flow
rate in conduit 3 to make the mass ratio of HS/LS in the wash
product in conduit 19 about 70/30. At this solvent mix ratio, there
is little or no asphaltene precipitation.
[0036] The first product stream of first separator 32 is sent to a
distillation unit 40 via conduit 18 to recover LS and HS, removed
via conduits 25 and 26, respectively, and to produce bitumen, which
is removed via conduit 1. Recovered HS and LS flow into tank 42 and
tank 43, respectively. The second (or wash) product stream from the
first separator 32 is withdrawn via conduit 19 and is sent to a
flash drum 41 to remove LS, which is cooled and recycled through
conduit 24 into tank 43, and produce hot HS, which is removed via
conduit 12 and used in the slurry preparation step (slurry
preparation unit 30).
[0037] The solid stream flows out of first separator 32 via conduit
14 to a second multi-stage separator 33, which also receives pure
LS from conduit 2 for countercurrent washing. In separator 33, the
mass ratio of HS/LS in the hydrocarbons drops from about 70/30 to
almost pure LS. Because most of the bitumen has been removed from
the solids, the amount of precipitated asphaltene at this stage is
minimal. The addition of LS at this stage results in spent solids
that are almost HS-free and the light solvent can be readily
recovered from the spent solids using a thermal/stripping
method.
[0038] The product stream from second separator 33, which comprises
primarily light solvent, is removed via conduit 20 to splitter 36,
where the product is split at a ratio in the range of 50/50 to
90/10 into streams 17 and 23 for reuse in the slurry pipeline 31
and the first separator 32, respectively.
[0039] The first and second separators (32 and 33) are preferably,
although not limited to, vacuum belt filters with multi-stage
countercurrent wash capability and gas-tight enclosure, likely
filled with an inert gas, e.g., CO.sub.2. The spent solids (filter
cakes) from the second separator 33 are removed via conduit 15 into
a dryer 34, preferably a rotary indirect dryer, with an inert
stripping gas operating at a solids temperature around 100.degree.
C., where the spent solids are dried to the LS content of less than
160 mg/kg of solids. This usually requires a low moisture content
of less than 0.5 wt % in the solids. The recovered vapors (LS and
H.sub.2O) and the inert stripping gas, e.g., CO.sub.2, flow to a
condenser/separator 35. The cooling medium used in
condenser/separator 35 may be cold oil sand process water.
[0040] The hot process water produced after heat exchange in
condenser/separator 35 may be used in water-based bitumen
extraction process, which may be running in parallel with the
solvent-based process, as described in more detail below. Condensed
LS flows out via conduit 22 to the LS tank 43, which also receives
a LS makeup via conduit 27. Condensed water flows out via conduit
21 and could be recycled for steam generation if needed. The inert
gas is recycled after water and solvent condensation.
[0041] The dry tailings are removed via conduit 16 and may be
further mixed with mature fine tailings (MFT) that are produced in
water-based processes and typically contain 33 wt % solids, at a
mass ratio of 1:0.28 to make a trafficable solids mixture
containing 85 wt % solids. This mixture, which is more consolidated
and less dusty than loose dry sand, is transported to a land
reclamation site for disposal. Alternately, the MFT proportion may
be significantly higher to make a non-segregated composite
tailings, containing 55-65 wt % solids, to be pumped to a field for
drying in ambient air. The non-segregating nature of the composite
tailings generally makes it dry within a short period of time. The
dry tailings may also be sprayed with water and disposed as
trafficable solids if MFT is not available.
[0042] As previously mentioned, the preferred mass ratio of HS to
bitumen is, although no limited to, around 1-1.5 based on the mass
flow rate of solvent in conduit 3 and the mass flow rate of bitumen
in conduit 1. The preferred mass ratio of LS to bitumen is,
although no limited to, 2-4 based on the total mass flow rate of
solvent in conduit 2 and the mass flow rate of bitumen in conduit
1. The resulting bitumen recovery is about 95% or greater for
Athabasca oil sands containing 40% fines (less than 44 .mu.m) in
solids. The recoveries of heavy solvent and light solvent are about
97% and 99.9% or greater, respectively.
[0043] It should be noted that the commercial water-based
extraction process is generally not capable of processing oil sands
with 40% fines without blending with low-fines oil sands. Thus, the
present invention also comprises a method of integrating the
aforementioned solvent extraction process into the existing
water-based extraction process to substantially improve the
economic return and reduce wet tailings production. The integration
includes the following three aspects: ore segregation, energy
sharing, and wet tailings reduction and sequestration.
1) Ore Segregation
[0044] With reference now to FIG. 3, a dual-solvent extraction
train (below) is running in parallel with a significantly larger
water-based extraction train (above). All "problem" oil sands,
defined as oil sands causing low bitumen recovery in the
water-based extraction, are segregated during mining and sent to
the smaller solvent extraction train. All "normal" oil sands,
defined as oil sands causing reasonably high bitumen recovery in
the water-based extraction, are processed in the existing
water-based extraction train. For a hypothetical mine containing
1/8 (12.5%) problem oil sands (ay. grade 8.9%) and 7/8 (87.5%)
normal oil sands (ay. grade 11.5%), the bitumen recovery for the
problem oil sands portion following this ore segregation procedure
is improved by approximately 11% from the base case, i.e. 100%
water-based extraction to process both (problem+normal) oil sands
with some blending.
[0045] Furthermore, the bitumen recovery for the normal oil sands
portion is improved by approximately 6% from the base case since
the feed to water-based extraction is not contaminated with the
problem oil sands. The economical benefit from the latter is about
5 times of the benefit from the former. Therefore, the ore
segregation method increases the economic return by a factor of 5.
This would make the solvent extraction process economically viable
despite its large capital investment. This ore segregation can be
achieved in the truck-and-shovel mining, since problem oil sands
are present in certain ore facies previously characterized by mine
geologists.
2) Energy Sharing
[0046] The largest operating cost for solvent extraction is in the
solvent recovery from spent solids. Recovery of LS to the point
that is in compliance with VOC emission regulations usually
requires evaporation of almost all naturally present and added
water from the tailings in the process. Therefore, large energy
input is needed to supply the latent heat for water and solvent
vapors. However, the hot vapors subsequently need to be condensed
using cooling water. With an integrated system, the resulting hot
water can then be used in the parallel water-based extraction
process, which requires heated or hot water. Thus, through such
energy sharing, the operating cost for solvent extraction can be
reduced.
3) Wet Tailings Reduction and Sequestration
[0047] Problem oil sands are usually high-fines oil sands.
Depending on the compositions of ore bodies, processing 1/8 (12.5%)
of the oil sands in a mine through solvent extraction can reduce
the amount of mature fine tailings (MFT) generation by about 18-30%
(100% being the total amounts of MFT generated in the same mine if
all oil sands are processed with water-based extraction). Further,
sequestration of the existing MFT from water-based extraction with
dry tailings from solvent extraction will make aforementioned
trafficable solids or quick-drying composite tailings, thereby
further reducing the amounts of MFT in inventory.
Example 1
[0048] A vacuum filtration test was performed using an oil sand
sample containing 8.5% bitumen, 4.6% water and 86.6% solids. The
fines (less than 44 .mu.m) content was 40% in solids. This oil sand
sample had been previously tested in a water-based extraction pilot
and yielded 0% bitumen recovery. The filter opening was 180 .mu.m
and the vacuum was around 0.7 bar. The filtration temperature was
50.degree. C. The boiling range of the virgin light gas oil (HS)
used was 177-424.degree. C. The light solvent (LS) was n-heptane.
The filtration rates are shown in Table 1.
TABLE-US-00001 TABLE 1 Bitumen conc. in Mass Test hydrocarbons
ratio of Filtration rate* no. (wt %) HS/LS (gpm/ft.sup.2) 1 29.7
.infin. (no LS) 0.19 2 34.6 3 0.15 3 34.6 1.5 0.46 *Average rate
including a very slow tail. Rate without the tail is usually twice
as fast.
[0049] Table 1 shows an example of the filtration performance in
the first stage separation. When no light solvent was used (test
no. 1), the filtration rate was slow even at somewhat lower bitumen
concentration. When the HS/LS ratio was 3 (test no. 2), the
filtration rate was slow as well. However, when the HS/LS ratio
reached 1.5, i.e. 60/40, the filtration rate was significantly
improved. Therefore, lowering the HS/LS ratio to 1.5 as shown in
test no. 3 will likely result in a faster separation process than
some of the prior art where no LS was involved in the first-stage
separation as shown in test no. 1. No asphaltene precipitation
occurred during the test.
Example 2
[0050] 100 g of the oil sand sample of Example 1 was rinsed with
five solvent mixtures: (1) 2.4 g bitumen+15 g HS+10 g LS; (2) 12 g
HS+4 g LS; (3) 2.5 g HS+10 g LS; (4) 10 g LS; and (5) 10 g LS and
then filtered under the same conditions mentioned above. The spent
filter cake was heated to 95.degree. C. and stripped with argon at
500 ml/min for 20 min. The recoveries of all hydrocarbons are shown
in Table 2.
TABLE-US-00002 TABLE 2 Bitumen Virgin light gas oil* Heptane**
96.4% 98.9% 99.92% *Based on a hypothetical HS/bitumen mass ratio
of 1.2. **Based on a hypothetical LS/bitumen mass ratio of 2.
This example simulated two stages of washing/filtration at
different HS/LS ratios in a first hypothetical separator, followed
by three stages of countercurrent washing/filtration with a light
solvent in a second hypothetical separator, and followed by solids
drying to recover almost all residual light solvent.
Example III
[0051] Spent filter cakes of 5 cm in thickness containing
approximately 7 wt % heptane and 4 wt % water were stripped with
argon at 95.degree. C. Stripping was stopped at various moisture
contents in solids. The residual heptane concentrations in solids
are shown in Table 3.
TABLE-US-00003 TABLE 3 Water conc. in solids Heptane conc. in
solids Test no. (wt %) (mg/kg) 1 1.32 496 2 0.56 163 3 0.19 29
This example showed that the moisture content in packed spent
solids must be below 0.5 wt % to achieve the light solvent
concentration lower than 160 mg/kg based on data interpolation.
[0052] 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 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.
* * * * *