U.S. patent application number 14/245653 was filed with the patent office on 2014-08-07 for closed loop solvent extraction process for oil sands.
This patent application is currently assigned to Shell Oil Company. The applicant listed for this patent is Shell Oil Company. Invention is credited to Robert Lawrence BLACKBOURN, Reinhard Alfred BOTT, Steven Paul GILES, Bernardus Cornelis Maria IN' T VEEN, Bradley Dean KOMISHKE, Yicheng LONG, Ingmar Hubertus Josephina PLOEMEN.
Application Number | 20140216985 14/245653 |
Document ID | / |
Family ID | 43781867 |
Filed Date | 2014-08-07 |
United States Patent
Application |
20140216985 |
Kind Code |
A1 |
BLACKBOURN; Robert Lawrence ;
et al. |
August 7, 2014 |
CLOSED LOOP SOLVENT EXTRACTION PROCESS FOR OIL SANDS
Abstract
The present invention is directed to a method which includes the
steps of: contacting an oil sand with a suitable solvent to
generate a solvated oil sand slurry; separating solvent-diluted
bitumen from the solvated oil sand slurry to generate (a) a
solvent-diluted bitumen and (b) a slurry with increased solids
concentration; filtering the slurry with increased solids
concentration; dropping the solids into a pressure reduction vessel
wherein the pressure in the pressure reduction vessel is a pressure
below a vapor pressure of the solvent; and drying the solids
removed from the pressure reduction vessel to produce solids having
dry tailings. The method of the present invention may be used to
produce a low ash bitumen product and dry tailings from oil
sands.
Inventors: |
BLACKBOURN; Robert Lawrence;
(Houston, TX) ; BOTT; Reinhard Alfred; (Waldbronn,
DE) ; GILES; Steven Paul; (Damon, TX) ;
KOMISHKE; Bradley Dean; (Calgary, CA) ; LONG;
Yicheng; (Calgary, CA) ; PLOEMEN; Ingmar Hubertus
Josephina; (Amsterdam, NL) ; IN' T VEEN; Bernardus
Cornelis Maria; (Amsterdam, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Shell Oil Company |
Houston |
TX |
US |
|
|
Assignee: |
Shell Oil Company
Houston
TX
|
Family ID: |
43781867 |
Appl. No.: |
14/245653 |
Filed: |
April 4, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12887352 |
Sep 21, 2010 |
|
|
|
14245653 |
|
|
|
|
Current U.S.
Class: |
208/390 |
Current CPC
Class: |
C10G 1/04 20130101; C10G
1/045 20130101 |
Class at
Publication: |
208/390 |
International
Class: |
C10G 1/04 20060101
C10G001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2009 |
CA |
2679908 |
Claims
1. A method for extracting bitumen from an oil sand, the method
comprising: contacting an oil sand with a solvent to generate a
solvated oil sand slurry; separating solvent-diluted bitumen from
the solvated oil sand slurry to generate (a) a solvent-diluted
bitumen and (b) a slurry with increased solids concentration;
filtering the slurry with increased solids concentration to produce
a solids and a filtrate output; dropping the solids into a pressure
reduction vessel wherein the pressure in the pressure reduction
vessel is a pressure below a vapor pressure of the solvent;
removing solids from the pressure reduction vessel; and drying the
solids removed from the pressure reduction vessel to produce solids
having dry tailings.
2. The method of claim 1, further comprising size-reducing the oil
sand to produce a size-reduced oil sand feed and contacting the
size-reduced oil sand feed with the solvent to generate the
solvated oil sand slurry.
3. The method of claim 1 wherein the solvent is a C3 to C9
paraffinic solvent, or a mixture thereof.
4. The method of claim 1 wherein the solvent is a C5 solvent.
5. The method of claim 1 wherein the separating step is carried out
in a settler.
6. The method of claim 1 further comprising producing solids and a
filtrate during the filtering step.
7. The method of claim 6 further comprising drying the solids.
8. The method of claim 6 wherein at least some of the solvent in
either or both of the solids and the filtrate is recovered and
recycled to either or both of the contacting step and the filtering
step.
9. The method of claim 6 wherein at least some of the filtrate is
recycled to the contacting step.
10. The method of claim 6 further comprising heating the solids
during the filtering step.
11. The method of claim 1 wherein at least some of the solvent in
the solvent-diluted bitumen is recovered and recycled to either or
both of the contacting step and the filtering step.
12. The method of claim 1 further comprising feeding overflow from
the separating step to a second separating step.
13. A method for extracting bitumen from an oil sand, the method
comprising: reducing the size of an oil sand feed to produce a
size-reduced oil sand feed; adding to the size-reduced oil sand
feed to form a slurry a solvent; feeding the slurry to a separation
device; allowing the slurry to be separated in the separation
device into a solvent-diluted bitumen and an underflow; feeding the
underflow to a filtration unit; recovering a filtrate from the
filtration unit; recovering solids from the filtration unit;
reducing the pressure on the solids in a reduced pressure vessel to
a pressure below the vapor pressure of the solvent to remove some
solvent from the solids; and recovering additional solvent from the
solids from the reduced pressure vessel by drying the solids
wherein dry tailings are produced.
14. The method according to claim 13, wherein at least some of the
solvent in either or both of the solids and the filtrate is
recovered and recycled to either or both of the step of adding
solvent to the size-reduced oil sand feed to form a slurry, and the
filtration unit.
15. The method according to claim 13, wherein at least some of the
filtrate is recycled to the step of adding solvent to the
size-reduced oil sand feed to form a slurry.
16. The method of claim 13 further comprising heating the solids in
the filtration unit.
17. The method according to claim 13, wherein at least some of the
solvent in the solvent-diluted bitumen is recovered and recycled to
either or both of the step of adding solvent to the size-reduced
oil sand feed to form a slurry and the filtration unit.
18. The method of claim 13 further comprising desolventising the
underflow within the filtration unit.
19. The method of claim 13 comprising adding solvent to the oil
sand feed using a rotary breaker.
20. The method of one of claim 13 wherein the solvent is selected
from the group consisting of C3 to C9 solvents and mixtures
thereof.
21. The method of claim 13 wherein the solvent is a C5 solvent.
22. The method of claim 13 further comprising purging with an inert
gas while introducing the oil sand into a hydrocarbon
atmosphere.
23. The method of claim 13 further comprising feeding the solvent
diluted bitumen from the separation device to a second separation
device.
24. The method of claim 13 wherein the underflow fed to the
filtration unit comprises about 60 to about 85% weight of
solids.
25. The method of claim 13 wherein the separation device comprises
a settler.
26. The method of claim 1 wherein at least a portion of solvent
vapour is added above the filter bed and condenses in the filter
bed.
27. The method of claim 26 further comprising the step of
condensing at least a portion of the solvent vapor that was
introduced above the filter bed.
Description
RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
application Ser. No. 12/887,352, filed on Sep. 21, 2010, which
claims priority to Canadian patent application 2,679,908, filed on
Sep. 29, 2009.
FIELD OF THE INVENTION
[0002] This invention relates to a solvent-based process for the
extraction of bitumen from oil sands. The process can be used to
generate a low-ash bitumen product and dry tailings.
BACKGROUND OF THE INVENTION
[0003] In a typical surface-mined oil sand processing operation to
produce bitumen, the oil sand is usually crushed to reduce the size
of oil sand lumps. The crushed oil sand is mixed with water (e.g.
in a rotary breaker) to form a slurry of bitumen, mineral solids
and water, as well as to remove lumps of clay, rocks and unablated
oil sand over a specified size (e.g. 2'' diameter). Then the
ore/slurry is conditioned, for example, in a hydro-transportation
pipeline or other conditioning means. The conditioned slurry is
introduced into a primary separation vessel in which aerated
bitumen droplets are separated from a bottom stream consisting
primarily of water and solids. The aerated bitumen droplets are
recovered as bitumen froth. The bottom stream is treated to recover
as much water as possible from the final process outlet stream that
is generally referred to as tailings.
[0004] The bitumen froth typically contains about 60% by weight
bitumen. The remainder is mainly made up of water and solids. The
froth is typically treated by adding a solvent and/or other agents,
which promotes the separation of bitumen from the other components
of the froth. For example, in paraffinic froth treatment processes,
the bitumen froth may be mixed with a paraffinic solvent (e.g.,
pentane or hexane or a mixture of both) in a multi-stage
counter-current decantation (CCD) process circuit (see, for
example, Canadian Patent Application Nos. 2,350,907 and 2,521,248,
the disclosures of which are incorporated herein by reference,
which describe paraffinic froth treatment processes including CCD).
In a CCD process, the bitumen froth is typically separated
into:
1) a dilute bitumen phase (dilbit), mainly comprising solvent and
high value components of the bitumen, known as maltenes, and
dissolved asphaltenes; 2) an aqueous phase, comprising mainly
water, water-soluble materials and dispersed fine solids, such as
clays; 3) an inorganic particulate phase, mainly comprising sand;
and 4) an organic particulate phase, mainly comprising precipitated
asphaltenes, with water and clays incorporated into the aggregate
structure of the asphaltenes.
[0005] A dilute bitumen phase which is partially deasphalted and
substantially free of mineral solids and water is produced as
overflow in the CCD process. An aqueous phase comprising water,
mineral solids, and rejected asphaltenes may be withdrawn from the
CCD circuit as underflow.
[0006] The underflow obtained from the CCD process, the CCD
tailings, also contains solvent. The solvent can be recovered from
the CCD tailings in a tailings solvent recovery unit and the
remaining underflow containing water, mineral solids and
precipitated asphaltenes is deposited into a tailings pond.
[0007] Most oil sands processing operations generally result in
substantial volumes of wet tailings. The wet tailings require
significant handling expenditures and severely constrain overall
mine planning flexibility. In addition, wet tailings present an
environmentally challenging situation. In many current open-pit
mining operations, waste streams are disposed of by pipelining the
waste stream slurry to an external tailings confinement facility or
pond, also known as a tailings pond, which is essentially a
man-made pond enclosed within a dyke system that contains the waste
material. Poor settling characteristics of fine inorganic solids in
the containment facility or pond create an uppermost solids layer
that has limited bearing capacity. The low bearing capacity of the
top layer of the tailings ponds presents a technical barrier to
reclaiming mined surfaces because the top layer cannot be covered
with overburden using heavy earth moving machinery.
[0008] In addition to problems associated with wet tailings, many
of the oil sands processing operations currently being employed use
large amounts of input water. The input water is usually drawn from
natural sources such as rivers that must also provide sufficient
volumes to meet the competing needs of nearby communities and
industrial entities. Therefore, it would be desirable to use a
process for extracting bitumen from oil sands which does not employ
large quantities of water.
[0009] Since as early as the 1920s, there have been many attempts
to develop a non-aqueous extraction process that could be used in
the oil sands mining industry. A non-aqueous extraction process
could potentially reduce or eliminate the need for added process
water, and result in the production of dry tailings. Dry tailings
are more amenable to land reclamation efforts as compared to wet
tailings. However, none of the proposed non-aqueous extraction
processes have proven to be commercially viable or have addressed
certain technical limitations inherent in each proposed
solution.
SUMMARY OF THE INVENTION
[0010] According to an aspect of the present invention, a method is
provided comprising: contacting an oil sand with a suitable solvent
to generate a solvated oil sand slurry; separating solvent-diluted
bitumen from the solvated oil sand slurry to generate (a) a
solvent-diluted bitumen and (b) a slurry with increased solids
concentration; filtering the slurry with increased solids
concentration; dropping the solids into a pressure reduction vessel
wherein the pressure in the pressure reduction vessel is a pressure
below a vapor pressure of the solvent; and drying the solids
removed from the pressure reduction vessel to produce solids having
dry tailings. The method of the present invention may be used to
produce a low ash bitumen product and dry tailings from oil
sands.
[0011] According to one embodiment of the present invention, there
is provided a method for extracting bitumen from an oil sand, the
method comprising reducing the size of an oil sand feed; adding a
suitable solvent to the size-reduced oil sand feed to form a
slurry; feeding the slurry to a separation device; allowing the
slurry to be separated into a solvent-diluted bitumen and an
underflow; feeding the underflow to a filtration unit; recovering a
filtrate from the filtration unit; recovering solids from the
filtration unit; and recovering solvent.
BRIEF DESCRIPTION OF FIGURES
[0012] FIG. 1 is a flow scheme of an example of a solvent based
extraction process comprising two settlers in series and a
filtration unit according to one embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The present invention relates to a method and process for
extracting bitumen from oil sands using a combination of
conditioning, solvation, primary liquid/solid separation (using,
for example, settlers or hydrocyclones) and filtration unit
operations. It has been observed that by using a method involving
these processing steps, a low-ash bitumen product may be produced,
along with dry, substantially solvent-free tailings. For example,
low ash bitumen may comprise less than 0.1 weight % ash. Producing
a bitumen product with low ash content has considerable advantages
as it enables the use of high value adding hydro-processing
upgrading operations in the refinery operations downstream of the
extraction process. The dry tailings may be backfilled into the
mine directly. By "dry", it is meant that the tailings are
substantially free of solvent and water.
[0014] A rotary breaker is generally used in oil sands processing
operations to reduce the size of some of the larger oil sand lumps
to more processable material, and to exclude or reject some of the
larger lumps and rocks that may hinder downstream processing.
Generally, the breaker also solvates and conditions the
size-reduced oil sand feed.
[0015] Other equipment of comparable functionality to a rotary
breaker can also be used, such as, for example, a rotary scrubber,
screw washer, mechanical mixer, spiral classifier, log washer, or
vibrating screener. The solvent-diluted oil sand slurry from the
rotary breaker would generally be a rather thin slurry (e.g. low in
solids concentration). If a thin slurry from a rotary breaker would
be fed to a filtration unit directly, solids segregation or
"classification" may occur. Classification, as would be understood
by a person skilled in the art, means that the slurry separates in
two phases, a layer of coarse solid particles at the bottom and a
layer of supernatant liquid with dispersed fine particles at the
top. The fines in this supernatant liquid layer may lead to the
formation of a layer of fine solids on top of the filter bed during
filtration, which may lead to plugging of the filter bed or
strongly reduced filtration rates. A thick slurry, which has a high
concentration of solids, may reduce or eliminate the creation of
this supernatant liquid layer with dispersed fines and lead to
improved filtration rates by helping to prevent plugging of the
filter bed. Accordingly, a pre-treatment of the oil sand slurry
before feeding to the filtration unit is desirable to increase the
concentration of slurry solids so as to produce a thick slurry. In
the present invention, this pre-treatment may be accomplished by
the use of a solids-liquid separation device such as a settler
following the rotary breaker. The settling operation could
optionally be performed by hydrocyclones.
[0016] The use of filters has been suggested (see, for example,
U.S. Pat. No. 3,475,318 and U.S. Pat. No. 3,542,666). However, many
of these filters suffer from fines classification during
filtration, leading to prolonged filtration times, the need for
additives to enhance filtration times, and unrealistic equipment
sizes and/or uneconomical numbers of filters. Also, the filtrate
product from filters known to date would not generally be low in
ash content and, as a result, would require post-treatment to
produce a final bitumen product with a low ash content.
[0017] On the other hand, the complete absence of a filter in the
process may necessitate a CCD-type process or moving-bed process to
achieve sufficient washing of the bitumen from the oil sand slurry.
It is believed that a CCD-type process would require a large number
of stages to achieve sufficient washing and a moving-bed process
may not be feasible at the large scale required in oil sands
operations.
[0018] The combination of a settler and a filtration unit in series
may be used in the production of a low ash bitumen from a solvated
oil sand slurry. The use of the combination of a settler and a
filtration unit in series may result in high bitumen recovery, the
production of a bitumen product with low ash content and the
removal of solvent from the oil sands. A special advantage of the
proposed method is that for oil sands with a low bitumen content
higher bitumen recovery may be achieved than with the conventional
water based extraction technology.
[0019] The filtration unit operation also serves as a combined
washer/desolventiser of the process stream. A filtration unit can
both wash the bitumen away from the solid materials, and also
partially desolventise the solids, i.e. the filter cake. If the
majority of solvent is not removed from the solids as a liquid,
excessive amounts of vapour may be generated during drying of the
solids material by evaporation downstream. The excessive vapour may
cause severe erosion problems in the drying equipment. Moreover,
evaporating large amounts of solvent generally requires high energy
consumption. A filtration unit can be used to provide a continuous
processing option to extract the majority of the solvent as liquid
during the filtration operation, thereby addressing problems
associated with excessive vapour during the drying stage.
[0020] Feeding a thick slurry to the filtration unit helps to
ensure that the slurry is homogeneous and may assist in preventing
blockage of the filter bed. Ideally, the solids content in the
slurry should be high enough to ensure that classification does not
take place after loading the slurry into the filtration unit.
Coarse solid particles in the slurry tend to settle at lower solids
concentrations, and thereby leave a layer of supernatant liquid
with dispersed fine particles on top. The fine particles in this
supernatant liquid layer may block the filter bed during
filtration. A thick slurry would be less likely to classify when
being loaded on the filter medium. The filter medium may be a layer
of cloth or screen that lays on the filter pan, and which has a
nominal opening for passage of the filtrate from the thick slurry.
For example, a filter medium may have a 10-500-micron opening
through which the thick slurry would be separated into a filtrate
and a solids portion or filter cake that remains on the filter
medium.
[0021] A thick slurry may generally be a non-classifying slurry and
therefore, suitable for use in filtration operations. A person
skilled in the art would be able to determine a suitable solids
content for the oil sand slurry. The solids content may, for
example, depend on the type and duration of the subsequent
filtration step and the particle size distribution of the oil sand.
A person skilled in the art would be able to determine suitable
solids content through routine experimentation. For example, a
solids content of 65 to 85% weight/total mass may be fed to the
filtration unit to help prevent classification of solids.
[0022] The oil sands extraction processes of the present invention
may employ C3 to C9 paraffinic solvents, isomers and/or
combinations thereof. For example, solvents such as pentane or
hexane may be used. Non-paraffinic solvents, such as aromatic or
halogenated solvents, which can dissolve all asphaltenes, would
generally not be suitable. When the asphaltenes are dissolved,
there will likely be a dispersion of many fine clay particles.
Accordingly, using non-paraffinic solvents such as aromatic or
halogenated solvents would likely result in extremely low settling
rates making producing a low ash product in the settler unfeasible.
Also, filtration behaviour may be negatively influenced through the
large amount of very fine clay particles.
[0023] In one embodiment, a C5 solvent or mixtures of C5 solvents
may be used.
[0024] The solvent-to-bitumen (S/B) mass ratio at the overflow of
the first stage settler may play a role in the subsequent
filtration performance of the solvated oil sand slurry and in
overall bitumen recovery. Lower S/B ratios may lead to higher
dissolution of asphaltenes, and less aggregation of clay particles
with decreased settling and filtration performance. Higher S/B
ratios may increase equipment size and energy consumption in the
solvent/bitumen separation step. Higher S/B ratios may also result
in the recovery of less asphaltenes into the final bitumen product.
An S/B ratio of 1.0 to 5 may be used. In one embodiment, a ratio of
1.5 to 3 may be used. The skilled person will be able to determine
whether a solvent or mixture of solvents is suitable, and whether
the S/B ratio is suitable, through routine experimentation, which
will depend in part on the availability of particular solvents.
1. Primary Size Reduction
[0025] The method and process of extracting bitumen according to
the present invention usually begins with a primary size reduction
step, which may be used in order to reduce the size of the mined
oil sands and deliver the material suitable for further processing
(size reduction, classification, extraction) to the closed loop
extraction process. The primary size reduction can be carried out
in a rotary crusher on a very large scale. Crushers are used
extensively in the oil sands processing industry for reducing the
size of the fresh mined ore. Generally, the ore may be reduced in
size to about 8''. The size-reduced material from the crusher may
be conveyed to a surge bin(s) for further processing.
2. Entry of Solids into the System
[0026] The primary size-reduced oil sands are then fed from a
primary surge bin into a hydrocarbon-containing environment for
extraction. The oil sands are added in a controlled fashion to the
hydrocarbon environment while reducing the oxygen content of the
sands to a point where it would not exceed flammable limits. The
problems relating to reducing the oxygen content and preventing
escape of hydrocarbon vapours to the atmosphere may be addressed by
purging with an inert gas, utilizing solids feeders and optionally
an intermediate or secondary surge chamber with inert gas
purge.
[0027] As a person skilled in the art would appreciate, the primary
surge bin and secondary chamber may generally be operated on level
control by adjusting the feed rate into and/or the discharge rate
from the bin such as to maintain a certain desired level of solids
in the bin. Inert gas (such as nitrogen) or other non-combustible
gas (such as flue gas) may be added to the bin and/or the secondary
chamber below the solids level in the chamber. A vent located above
the solids level may be used to purge the oxygen content to
acceptable concentrations, as would be known to one skilled in the
art. An oxygen analyzer located in the vent stream may be used to
control the flow of non-combustible gas into the secondary
chamber.
[0028] The size-reduced, oxygen-depleted oil sands may be fed by
level control through a second solids feeder to a conveyor and then
to a hydrocarbon environment. In the present invention, the
hydrocarbon environment may be provided in a rotary breaker where
solvation occurs. A secondary oxygen analyzer (which, for example,
may be positioned in the conveyor leading from the secondary or
surge chamber to the rotary breaker) can be used to measure the
oxygen content and to control the inert gas to the bin and/or the
secondary chamber.
3. Solvent/Ore Contact-Mixing-Extraction/Further Size
Reduction/Rejection of Larger Material in a Rotary Breaker
[0029] The rotary breaker may perform several functions,
including:
[0030] Contacting the primary size-reduced oil sands with
extraction solvent to solvate bitumen. As described below, C3 to C9
paraffinic solvents, which may be freshly added and/or recycled
from later processing steps, may be used.
[0031] Further reducing the size of lumps in oil sands containing
bitumen during the extraction process in the rotating vessel.
[0032] Excluding large lumps. The rotating drum will have holes,
and the holes may be sized to optimize performance with respect to
extraction/overall recovery and to help with the rejection of
larger lumps that may disrupt the uniform slurry needed for
filtration, efficient washing, and primary drying stages described
below.
[0033] Rotary breakers are common in the coal and oil sands
industries for size exclusion mainly in water environments.
However, the current process may be carried out in a hydrocarbon
environment where extraction of the bitumen from the oil sands,
size reduction of the primary sized material, and size exclusion
all take place. Recycled solvent containing bitumen from a
filtration unit operation located downstream of the settler may be
used as the solvent for the incoming bitumen in the rotary breaker.
Optionally, a portion of fresh solvent may also be added to the
rotary breaker.
[0034] The pressure and temperature of the rotary breaker may
generally be set so as to keep the solvent in the liquid state. The
temperature of the operation can be carried out from about
-10.degree. C. to 100.degree. C. depending on the solvent employed.
For example, the process may be carried out using C5 solvent at
about 0 to 30.degree. C. and close to atmospheric pressure. The
residence time may be about 1 to 30 minutes. Rotation speed and
residence time can be changed within normal design parameters. The
hole size can be from 5-50 mm
[0035] Oil sand lumps exhibit a large variation in ability to
disintegrate. Some lumps disintegrate within a minute without any
agitation, even at temperatures below 0.degree. C., while others do
not disintegrate at all without agitation. The lumps that
disintegrate quickly would leave the equipment quickly, decreasing
the volume flow downstream of the rotary breaker and providing more
residence time and agitation to the lumps that do not break down as
easily. This makes the rotary breaker a suitable device for
efficiently disintegrating oil sand lumps and enabling further
extraction of bitumen from the sand.
[0036] The rotary breaker may be equipped with internals, such as
breaker bars or lift plates, to deliver higher energy dissipation
to assist in the breakdown of ore lumps, the separation of bitumen
from the ore lumps and dissolution of bitumen in solvent. A person
skilled in the art would understand suitable screen size holes,
residence times and energy input in the breaker to achieve
this.
[0037] Optionally, to enhance dissolution of bitumen and
disintegration of any remaining lumps before the slurry is fed to
the settler, an additional unit operation (not shown) may be
included downstream of the rotary breaker and upstream of the
settler. This additional unit operation may perform the following
functions: (a) increase contact time between solvent, bitumen and
ore; and (b) introduce additional shear/mixing energy to
disintegrate any remaining oil sand lumps. For example, one or more
vessels, active or passive mixing devices, pumps and/or pipelines
may be used to enhance the dissolution of bitumen before the slurry
is fed to the settler.
[0038] Optionally, water can be added during slurrying in the
rotary breaker to increase filtration rates as explained in U.S.
Pat. No. 3,542,666. Adding a base to this water to maintain a
certain minimum pH may also be beneficial.
4. Transport to Next Unit Operation
[0039] A commercially-available slurry pump (centrifugal, disc,
positive displacement or other) may be used to transport the output
from the breaker, which comprises a slurry of dissolved bitumen in
solvent and solids, to a conventional settler (sometimes called a
clarifier or thickener). Material which has been size excluded
(e.g. particles larger than the hole size of the rotary breaker)
will exit the breaker through another outlet. The rejected
particles will mainly consist of lumps and stones/rocks.
5. Liquid/Solid Primary Separation
[0040] A primary solids/liquid separation may take place in a
solids-liquid separation device such as a conventional settler.
Hydrocyclones may be used as an alternative for the primary
liquid/solvent separation. The settler may serve multiple purposes
including:
[0041] Providing residence time for the solids and liquids to
separate.
[0042] Producing an overflow comprising solvent-diluted bitumen
having a low ash concentration. The low ash concentration of the
bitumen is beneficial for pipeline transport and for certain types
of downstream upgrader bitumen processing such as
hydrocracking.
[0043] Providing an underflow that has been concentrated in solids
(i.e. thickened). This underflow is suitable in the filtration step
because it does not classify into coarse solids and a
fines-containing liquid phase.
[0044] The first-stage settler underflow may be transported to a
filtration unit for washing the sands and for further removal of
bitumen and desolventisation, i.e. removal of solvent.
[0045] Optionally, a second-stage settler can be employed to
produce a higher quality bitumen product. Overflow from the first
settler may be sent to a second settler, where it is further
separated into a second overflow and an underflow. The underflow of
the second settler can be mixed in homogeneously with either the
first-stage settler feed or filter feed or dealt with in a tailings
solvent recovery unit. The presence of a second settler may also
allow for the first settler to be a much smaller size and enable
utilization of much simpler settler equipment such as a deep cone
settler without any moving internal parts.
[0046] The solvent-to-bitumen (S/B) ratio for the second settler
can be kept consistent with the primary settler overflow S/B ratio
or can optionally be increased through addition of fresh solvent in
the second settler feed so as to induce more asphaltene
precipitation. Asphaltene precipitation is known to aid in the
removal of fine particles. The temperature of the second-stage
settler can optionally be increased in comparison to the first
stage to enhance settling rates, thus allowing for smaller
equipment sizes. Heating up this stream is relatively easy since
the bulk of the solids have been removed upstream.
6. Filtration--Solids/Liquid Separation, Washing,
Desolventisation
[0047] The filtration unit may comprise several parts, including
but not limited to, peripheral equipment such as a slurry feeding
system, a filtrate receiver, one or more pressure vessels, feed
control valves, and/or pumps. The "filtration unit" as used in the
present invention includes any equipment located between the output
of the settler and to the point where the filter cake is reduced in
pressure and transported to the next unit operation. For example,
the filtration unit may allow for solvent washing of the filter
cake, and for solvent vapour desolventisation as described
herein.
[0048] The filtration unit includes a filter. A feed slurry is
deposited as a filter cake into the filter, on top of a filter
medium. The filter cake comprises the layer of solids on top of the
filter medium. The majority of the solids cannot pass through the
filter medium, while liquids can pass through the filter medium.
Fresh solvent and/or solvent vapour and/or other gases may be
passed through the filter cake by means of an applied pressure
difference between the space above the top of the filter cake and
the space below the filter cake. Following passage through the
filter medium, a filtrate is produced comprising a liquid stream
with a certain amount of dispersed fine solids. The solids or
filter cake are retained on the filter medium.
[0049] A filtration unit may serve many functions, including:
[0050] Washing the extracted oil sands and removing the remaining
maltenes. The final bitumen material is upgraded by leaving behind
a portion of unwanted, undissolved, asphaltenes in the solids.
[0051] Desolventising, i.e. removing solvent from the sand as a
liquid.
[0052] Heating up the solids to facilitate the downstream drying
operation.
In the filtration step, a thickened slurry which is produced as
underflow from the settler is pumped into the filtration unit.
[0053] After loading the thickened slurry into the filtration unit,
recycled solvent (or fresh make-up as required) may be fed to the
filtration unit for removal of entrained bitumen left after the
settling step. Counter-current washing in multiple stages may be
applied to enable washing at low fresh solvent consumption.
[0054] Solvent vapour (e.g. generated during solvent recovery in
the solvent recovery unit) may be introduced above the filter bed.
The solvent vapour introduction can serve multiple purposes. First,
the vapour can drive the majority of the solvent from the filter
bed as a liquid. Second, a condensation front can be created where
the solvent vapour condenses on the filter cake. This condensation
front of clean solvent may be pushed through the filter cake and
results in additional washing of the filter cake, and further
recovery of remaining bitumen. Third, the condensing vapour may
also heat up the sand in the filter cake. Fourth, after vapour
breakthrough through the filter bed, vapour velocity will increase
and more solvent will be removed from the bed as small liquid
droplets.
[0055] Optionally, in a subsequent step, the pressure underneath
the filter cake can be decreased to further reduce the solvent
content of the filter cake by flashing off more solvent.
Alternatively, water steam under pressure may be applied above the
filter cake to heat up the filter cake and reduce the remaining
solvent content. In another embodiment of the invention, solvent
vapour and steam could be consecutively applied. Finally, nitrogen
gas can optionally be purged through the filter bed to even further
reduce the solvent content by stripping out more solvent.
[0056] Experiments on filtration using nitrogen gas pressure to
drive the solvent from the filter bed reduced solvent content from
20 wt % in the settler underflow to about 8-12 weight %.
[0057] Removing the majority of the solvent as a liquid in the
filter may also help to minimize downstream erosion. Any solvent
vapour generated in the filter itself will not result in erosion
problems as the solids are fixed in a filter cake.
[0058] Feeding hot material from the filtration unit into the
subsequent drying step simplifies the downstream drying equipment,
since it should be unnecessary to introduce large amounts of heat
to the solids stream. Alternative methods to heat large solids
streams such as by gas flow or through direct heat exchange usually
require large and potentially very expensive equipment.
[0059] The filtrate may be recycled directly to the rotary
breaker.
[0060] The described filtration process could be executed in a
filter (e.g. a rotary pan filter) under overpressure.
7. Transport to Drying
[0061] The solids exiting the filtration unit under pressure are
transported to a dryer, which can be operated at lower pressure to
facilitate evaporation of solvent. This requires reducing the
pressure of the solids, and several ways of accomplishing this
would be known to a person skilled in the art. For example, the
solids may be dropped directly into pressure reduction vessels.
These vessels may be operated in parallel in a semi-batch mode. For
example, one chamber may be filling with solids from the filter
while another vessel is closed to the filter. A vent valve in the
chamber allows for depressurization, following which the material
may be removed for final-stage drying. The vapour may be condensed,
or alternatively, recovered by a scrubber or other means, and
recycled to the process. The pressure inside the vessels is reduced
compared to the higher-pressure within the filter, so that the
pressure is below the vapour pressure of the remaining solvent in
these vessels. The solids can then be unloaded from the pressure
vessel onto a conveyor belt or other means of transport to the
dryer.
[0062] In another example only one pressure reduction vessel is
used, with an upstream storage vessel to allow for the
discontinuous operation of the pressure reduction vessel.
[0063] In yet another example, dense phase conveying is used to
combine the depressurization and transporting functions into one
unit operation.
8. Final Solids Drying
[0064] In Canada, economic and regulatory regulations require that
for water-based extraction processes, only 4 barrels of solvent can
be lost per 1000 barrels of bitumen production. Similar
requirements likely apply to non-water based extraction processes.
Accordingly, it is beneficial to employ processes wherein the
solvent is recycled.
[0065] The solids material is transported into a dryer. An inert
stripping gas, such as N2, flue gas or steam, is used to remove the
residual solvent from the sand. Vent produced in the dryer may be
sent through a scrubber or other solvent recovery unit to recover
solvent, which is recycled to the process. Entrained solids in this
vent may be removed through a cyclone, bag filter or other
appropriate means. Inert gas may also be recycled in this drying
process. Water in the vent stream is collected separately and
removed from the process.
[0066] A second-stage drying step may optionally be used to remove
the residual solvent in the tailings to acceptable
concentrations.
9. Reclamation: Exit of Solids from System
[0067] The dried tailings can be transported back into the original
mine site or stored at another location. A small amount of water
can be sprayed onto the tailings if dust becomes an issue. As is
well known in the art, an issue with wet tailings is achieving
sufficient consistency to enable final reclamation through covering
the tailings with overburden.
[0068] The sand, which is produced as a result of this extraction
process, may be used directly for landfill. This allows for faster
and potentially less expensive mine backfilling. The solids may
also be mixed or agglomerated with wet mature fine tailings (MFT)
from the existing water-based process, thereby reducing the
proportionate amount of MFT and producing a material that may be
acceptable for backfilling.
10. Solvent Recovery
[0069] The bitumen product can be recovered from the
solvent-diluted bitumen overflow of the settler through
conventional means like distillation or flashing. The bitumen
produced must meet pipeline specifications, with regard to
characteristics such as viscosity. To achieve these specifications,
some solvent may be left in the bitumen product. Heat integration
techniques can be applied, as will be appreciated by those skilled
in the art. Where the solvent used for pipelining is different from
the solvent used in the extraction process, solvent swap may be
required.
[0070] FIG. 1 shows an embodiment of the present invention. In an
oil sands extraction process, mined oil sands (5) from a mining
operation, for example, are trucked or conveyed to a primary
crusher, which may be, for example, a rotary crusher (10). The
primary size reduction may be carried out by the rotary crusher on
a very large scale, for example. The crusher may reduce the size of
the oil sand particles or lumps to about 8-12'' or less. From the
crusher, the size-reduced oil sand material is conveyed via a
conveyor (20) into one or more surge bins (30) and is ready for
further processing.
[0071] The output from the primary surge bin (30) comprises primary
size-reduced oil sands. The primary size-reduced oil sands are fed
into a secondary chamber or intermediate surge chamber (45) via a
solids feeder (40), which may be, for example, a Posimetric.TM.
feeder, manufactured by Pennsylvania Crusher Corporation of
Broomall, Pa. The primary surge bin (30) and the secondary chamber
(45) may be operated on standard level control by controlling the
feed into and out of the chamber. To reduce the oxygen content of
the oil sands to a point that will not exceed flammable limits as
the size-reduced oil sands are introduced into secondary chamber
(45), the secondary chamber may be equipped with an inert gas purge
(55) through which inert gas such as nitrogen, flue gas or other
inert gas is added into the secondary chamber (45). The primary
surge bin (30) and the secondary chamber (45) may be operated on
standard level control.
[0072] The inert gas (55) may be added below the solids level and a
vent (46) which may be located above the solids may be used to
purge the oxygen content to acceptable concentrations. A person
skilled in the art would be able to determine suitable oxygen
concentrations without undue experimentation. An oxygen analyzer
located in the vent stream may be used to control the flow of
non-combustible gas to the secondary chamber.
[0073] As a result of the inert gas purge, the primary size-reduced
oil sands that exit the secondary chamber (45) will be
oxygen-depleted. The oxygen-depleted, primary size-reduced oil
sands exiting the secondary chamber (45) are then fed by level
control through a second solids feeder (50) to a conveyor (60). The
second solids feeder (50) may be, for example, a Posimetric.TM.
feeder. A secondary oxygen analyzer may be used to measure the
oxygen content during conveying, before introduction into the
solvent environment within the rotary breaker (80). For example,
the secondary oxygen analyzer may be present in a conveyor (60)
which may lead from the secondary feeder (50) to the rotary breaker
(80).
[0074] The output from conveyor (70) may be fed into a rotary
breaker (80), which may be, for example, a rotating drum-like
vessel with size exclusion/classifying capability. The size
exclusion/classifying capability may be accomplished by holes
within the drum, which rejects lumps larger than the hole size. For
example, lumps and rocks larger than about 2'' or larger may not
pass through the holes and are rejected from the primary material.
In one embodiment, lumps larger than about 0.5'' in diameter are
not passed through the breaker and are rejected from the primary
material. A person skilled in the art would be able to determine
the hole size to optimize performance and ensure uniform slurry for
later processing steps.
[0075] Following the classification through the breaker, larger
lumps and rocks (e.g., >0.5'') are rejected (105) and may be
sent to a dryer (320), while the output from the breaker (90)
comprising dissolved bitumen in solvent and smaller sands may be
sent to the next unit operation via a slurry pump (100). Recycled
solvent (115) containing bitumen and which has been recycled from
the filtration unit operation may be injected into the rotary
breaker (80). Optionally, a portion of recycled or fresh solvent
(125) can also be added to the rotary breaker (80). The target S/B
ratio of the solvent-diluted bitumen for the process may be set at
the overflow of the primary settler (135). For example, a target
S/B ratio of 1 to 5 may be used. As would be appreciated by a
person skilled in the art, the target S/B ratio may be determined
by on-line analysis.
[0076] In order to keep the solvent in the rotary breaker in liquid
state, temperature and pressure may be controlled. The temperature
may be, for example, about -10 to about 100.degree. C. depending on
the solvent. For example, with a C5 mixture, the process may be
carried out close to atmospheric pressure, or a temperature of
about 0 to about 30.degree. C. The residence time may be about 1 to
30 minutes. A person skilled in the art would be able to determine
suitable pressure, temperature and residence times.
[0077] Optionally, water (126) can be added during slurrying in the
rotary breaker to increase filtration rates as explained in U.S.
Pat. No. 3,542,666. A base may also be added to the water to
maintain a certain pH.
[0078] The output from the rotary breaker (90) which comprises
bitumen dissolved in solvent may be transported via a slurry pump
(100) which may be, for example, a centrifugal, disc, positive
displacement or other device, to a conventional settler (120) via
line (110). The settler (120) may also be referred to as a
clarifier or thickener.
[0079] Primary solids/liquid separation may take place in a
solids-liquid separation device such as a settler (120). The
settler can also produce solvent-diluted bitumen as overflow (135).
This overflow usually has a low ash concentration. The settler can
also produce an underflow (130) that may be concentrated in solids,
such as a thick slurry. The thickened underflow may assist in
subsequent filtration steps by preventing classification.
[0080] The first-stage settler underflow (130) may be transported
by a slurry pump (140), which may be, for example, a centrifugal,
disc, or positive displacement pump to a filtration unit (160) for
washing the oil sands for removal of additional bitumen and
solvent, prior to further solids desolventisation.
[0081] Optionally, the overflow (135) of the primary settler (120)
can be sent to a second stage settler (195). When a second settler
is used, the primary settler (120), or alternatively a
hydrocyclone, may remove the majority of the solids through the
underflow (130), while the secondary settler may be used to produce
a higher quality overflow product which is lower in ash content.
The underflow of the second settler can be mixed in homogeneously
with either the primary settler feed or filter feed, or dealt with
in a tailings solvent recovery unit.
[0082] Optionally, chemical addition may be introduced into the
first and/or second settler to aid in sequestering fines and
asphaltenes.
[0083] The filtration unit (160) may comprise a filter (170)
suitable for filtration of thick slurries, such as a moving belt,
moving pan filter or a rotary filter.
[0084] After loading the thickened slurry into the filtration unit
(160), recycled solvent from tank (410) (or fresh make-up (400)
from tank (370) to account for any solvent losses in the process if
required) may be fed to the filtration unit (160) to assist in the
removal of entrained bitumen left in the thick slurry following the
settling step. The filtration step can also be staged and carried
out in a counter-current fashion. Following addition of solvent
(220), solvent vapour generated during solvent recovery (228) in
the solvent recovery unit (460) may be introduced above the filter
bed.
[0085] Optionally, the filter system may comprise separate pieces
of equipment. The first piece of equipment (i.e. the first stage
filter) would allow for the filtrate cake to be washed. The output
from the first-stage filter, which may comprise hot material, may
discharge into a second-stage filter or optional piece of equipment
that would allow for solvent vapour desolventisation. In the
filtration unit (160), the thick slurry (130) exiting the settler
(120) may be separated into a solids portion (180) and a filtrate
output (115). The filtrate output (115) from the filtration unit
may be recycled directly to the rotary breaker as the solvent
feed.
[0086] The solids (180) may exit the filtration unit (160) under
pressure and be dropped into one or more pressure reduction vessels
(182). The solids may enter the chambers by gravity through a
valve, for example, and exit the chamber after pressure reduction
by gravity through a second valve located on the bottom of the
pressure reduction vessels (182). Valves (175) which may be
suitable for this application include a Dome Valve.TM. produced by
Macawber Engineering Inc. of Maryville, Tenn.
[0087] Inside the vessels, the pressure may be reduced from a
higher-pressure environment such as in the filtration unit to a
pressure below the vapour pressure of the remaining solvent. The
number of vessels required to accomplish this depends on the size
of the application. The person skilled in the art would be able to
determine a suitable number of vessels with routine
experimentation. The vapour may be condensed, for example in a
condenser (380) with accumulator (390), or alternatively recovered
by a scrubber, and recycled for further use. The solids can then be
conveyed by belt (184) or other means to a final dyer (250) and
introduced to the dryer via a solids feeder.
[0088] As an alternative to the pressure reduction vessels,
continuous rotary valves may be used, or a column of solids to seal
between the high and low-pressure environments may be used. In all
cases, the depressurized material would be removed for final-stage
drying.
[0089] In another example, dense phase conveying is used to combine
the depressurization and transporting functions into one unit
operation.
[0090] The final dryer (250) may remove solvent from solids to very
low concentrations (<400 ppmw) and produce dry tailings. A
commercially available Wyssmont Turbofan Dryer.TM. may be used for
the final drying step.
[0091] The vent from the dryer may be sent through a standard
cyclone (255) and/or dust filter to remove entrained solids from
the solvent/inert gas stream. The material may then be sent through
a scrubber (260) or other solvent recovery unit to recover the
solvent and recycle the inert gas for further use. For example, the
inert gas may also be recycled to the secondary chamber (45). The
scrubber (260) bottoms containing the solvent and scrubbing medium
is sent to a distillation column (270) where solvent is recovered
as the overhead product and recycled to the process. The solvent is
condensed and recovered in accumulator (280). Water can be
collected in a boot on the accumulator (280) and removed from the
process or used for dust prevention in reclamation. Recovered
solvent (350) may be sent to solvent recovery tank (410). The
column bottoms are returned to scrubber (260).
[0092] The depressurized solids material may exit the dryer (250)
through a feeder (330). Alternatively, large rotary valves, or a
column of product above a feeder to seal the low differential
pressure may be used.
[0093] The overflow (135) from the primary settler, or optionally
the overflow (198) from the secondary settler, may be sent to a
solvent recovery column (460), which may be a conventional
distillation column, for example. The overhead-recovered solvent
produced from the column can be recycled to the filtration unit, as
a vapor (228). Condensed material is collected in an accumulator
(440) equipped with a boot for water removal from the process. The
recovered solvent (420) may also be recycled via recovered solvent
tank (410). The bottoms material from the column (455) contains the
low-ash bitumen product.
[0094] The dry tailings (340) are produced following the final
stage of drying. Additional water (360) may be added to the
tailings to control dust.
[0095] The dry tailings may be conveyed by belt or trucked to the
original mine site for introduction into the mine site. Alternative
conveying methods such as dense or dilute phase conveying may also
be used.
EXAMPLES
1) Use of Settler
[0096] A number of settling experiments were performed to
illustrate that a bitumen product with low ash content can be
produced. Two different sets of experiments were conducted.
[0097] In the first set of experiments, a single-stage settler
line-up was simulated. First, a bitumen-preloaded solvent was
prepared to mimic the solvent/bitumen mixture from the filter that
is used for contacting the ore in the rotary breaker in the process
described above. This preloaded solvent was poured directly into a
glass settling cylinder of 2.2 m length and 50 mm diameter and an
amount of fresh ore was added to this solvent.
[0098] The solvent/ore within the settling cylinder was then mixed
through rotating the cylinder around its central axis, in an
end-over-end fashion, for 5 minutes until adequate mixing was
achieved. After the mixing, the rotation was stopped and the solids
were allowed to settle. Referring to Table 1, a series of samples
was taken via a series of valves along the side of the settling
cylinder. All samples were taken from a selected valve chosen for
close proximity to the liquid just above the interface between
coarse sand and liquid with fines. The liquid level in the settling
cylinder dropped with each sampling. A settling velocity was
calculated based on the distance between the top liquid level and
the sampling valve and the time at which the sample was taken. When
sampling began the liquid was murky due to the presence of fines,
but by the time that sample 3.3 was taken in the first experiment
(see below), sufficient time had elapsed for the fines to settle
and the liquid was generally clear.
[0099] Table 1 shows the results of three experiments performed for
different ore grades and at different S/B ratios of the final
solvent/bitumen mixture. As is apparent from the results, in all
cases bitumen with low ash content was produced. Settling
velocities from about 3-11 cm/min may result in bitumen with ash
content below 0.1 wt %.
TABLE-US-00001 TABLE 1 Settling of bitumen, solvent, solids
mixtures from different ore grades at different solvent to bitumen
ratios. Settling velocity to Ash achieve Ore Settling measurement
<0.1 wt S/B grade Sample Time velocity ASTM D482 % ash Wt wt %
No (min) cm/min % w cm/min 4.1 5.6% 3.1 7.0 8.4-6.6 8.290 3.0-4.8
3.2 7.6 6.6-4.8 5.700 3.3 8.2 4.8-3.0 0.199 3.5 8.8 3.0-1.2 0.042
3.6 9.3 <1.2 0.046 2.8 10.6% 4.1 5.0 10.1-8.3 0.15 4.6-8.3 4.2
5.7 8.3-6.5 0.039 4.3 6.4 6.5-4.6 0.103 4.4 7.1 4.6-2.8 0.04 4.5
7.8 2.8-1.0 0.065 4 10.6% 5.1 5.0 11.0-9.0 0.195 7.1-11.0 5.2 5.5
9.0-7.1 <0.001 5.3 6.0 7.1-5.1 0.037 5.4 6.5 5.1-3.1 0.024 5.5
7.0 3.1-1.1 0.035 5.6 7.5 <1.1 0.018
[0100] In a second series of experiments, a two-stage settler
line-up was simulated. Oil sand was mixed with solvent (C5) in a
flask with the aim of achieving a set S/B ratio. After mixing, the
coarse solids settled and the solvent/bitumen mixture was poured
off. A limited amount of the coarse solids were included with the
liquid to help ensure that all fines in the supernatant liquid were
maintained in the liquid that was poured off. This liquid was then
poured into a polycarbonate cylinder of 2 m length and 25 mm
diameter, the top of the cylinder was closed and the solvent, and
fines and coarse material were re-dispersed by agitating the
cylinder. The cylinder was then positioned vertically. The cylinder
lid was removed and samples were taken from the top using a
sampling tube.
[0101] In the first experiment, samples of the liquid were taken
near the top of the liquid level in the cylinder after 5, 15, 30,
45 and 60 minutes of settling. Initially, the liquid was murky but
cleared following settling of the fines. The top liquid level
dropped by 30 cm at each sampling due to the withdrawal of the
sample. In the second experiment, samples were taken with the
sample tube placed just above the liquid/solid interface level in
the cylinder after 5, 10, 15, 20 and 35 minutes of settling. The
results are shown in the Table 2. Bitumen with low ash content was
produced. In both experiments settling velocities are above the
maximum measurable in the given set-up, i.e. 6 cm/min in the first
experiment and 26 cm/min in the second experiment. However, the
results in Table 2 illustrate the added utility of the two-stage
settler line-up.
TABLE-US-00002 TABLE 2 Bitumen recovery from different ore grades
using a two-stage settler simulation. Ash Ore Settling measurement
grade Sample Time velocity ASTM D482 Experiment S/B wt % No. (min)
cm/min % w 1 2.3 10.6% 4.1 5 >6 0.0316 4.2 15 2-6 0.0328 4.3 30
1-2 0.0324 4.4 45 0.67-1 0.0367 4.5 60 <0.5 0.0391 2 5.3 10.6%
5.1 5 >26 0.0250 5.2 10 26-11 0.0184 5.3 15 11-6 0.0202 5.4 20
6-4 0.0227 5.5 30 4-2 0.0130 5.6 35 2-1 0.0375
2) Filtration Experiments
[0102] While a low ash bitumen product may be produced from a
settler alone, the underflow of the settler still contains sand,
solvent and bitumen, which may be further separated in order to
recover additional bitumen. Thus, additional experiments using
filtration were conducted.
i) Influence of Slurry Solids Concentration and Filter Outlet
[0103] It was observed during experiments that filtration rates
were sometimes lower due to high filtration resistance or the
filter cake becoming blocked. Closer investigation revealed that
the solids concentration in the slurry can have an influence on the
filtration performance. Due to the settling behaviour of the coarse
material in the slurry, classification may take place almost
immediately after slurry feeding on top of the filter surface. The
fines dispersed in the liquid layer above the coarse solids can
form a layer on top of the filter cake with a much higher
filtration resistance than the coarse sediment; this can lead to
very slow filtration rates or even complete blocking of the filter
cake.
[0104] Another parameter that may be of importance depending
factors such as ore quality is whether the outlet of the filter is
open or closed during feeding the slurry. It has been observed that
having an open filter outlet can enable surplus liquid present in
the slurry to pass more readily through the filter medium, thus
helping to prevent building up a supernatant liquid layer with
fines and eventually a blocking layer of fines on top of the filter
cake.
Table 3 shows the results of filtration experiments on two
different feed types. In Table 3, "t1" represents the time from
beginning of feeding until the filter cake becomes visible. "t
Wash" represents the time between filling in of wash liquid until
the filter cake becomes visible again. The pressure difference
across the filter cake was applied by pressurized gas above the
filter cake.
TABLE-US-00003 TABLE 3 Filtration experiments using two different
types of filter feed. Test No. A B C D Sand/g 401 400 402 400
Solvent/g 171 170 145 144 Solvent type C5 C5 C5 C5 Slurry Input/g
562.9 560 541.7 440.8 Dp/bar 0.3 0, 3 . . . 0.3 0.3 tl/s ? 5 >
300 66 <5 Wash solvent/g 81 Wash not -- -- possible t Wash/s
10.7 -- -- -- Mass 94.7 Decantate/g Slurry solids 59.1% 59.1% 61.9%
75.0% content/wt % S/B 3.5 3.5 3.5 3.5 Sand Type a2 a2 Bench
11.05.09 Bench 11.05.09 Filter outlet Open Closed Open Open Comment
Blocked Very long cake formation time tl, very low filtration
rate
[0105] As experiment C demonstrates, almost complete blockage of
the filter occurred, with very long cake formation time and a very
low filtration rate (even though the outlet was open during
filling). Increasing the slurry solids concentration (experiment
D), however, resulted in improved filtration performance.
Experiment B demonstrated that at a slurry solids content of 59.1%
blocking of the filter cake occurred; however, this blocking was
avoided in a subsequent run at the same solids concentration by
opening the filter outlet during slurry filling (experiment A).
ii) Solvent Type
[0106] Table 4 shows the results of filtration experiments with
different solvents. Table 4 illustrates that filtration with the
paraffinic solvents was successful while filtration using an
aromatic solvent exhibited slow filtration rates and high ash
content in the filtrate. Aromatic solvents resulted in all of the
asphaltenes being dissolved. Paraffinic solvents only partially
dissolved the asphaltenes. Non-dissolved asphaltenes may aid in
agglomeration of the fine particles, and thereby improve the
filtration behaviour.
[0107] Open funnel vacuum filtration experiments were conducted
with a 0.025 .mu.m filter element. Filtration was undertaken with
slurry mixtures using ore of 5.6 wt % bitumen content and toluene,
pentane or heptane, at ambient conditions:
TABLE-US-00004 TABLE 4 Bitumen production using different solvents.
Ash*** ASTM FD* Ore Solvent Filtration D482 Test Mm Solvent gr Gr
SD** results % w 1 47 Toluene 25 11 Very slow but no blocking 2 47
Pentane 25 11 Runs, no 0.0232 blocking 4 90 Toluene 50 22 Very
slow, 0.3920 16 hours 5 90 Pentane 25 50 y Runs, no blocking 6a 90
Heptane 25 50 y Good 0.0251 6b 90 Heptane 25 50 y Good *FD = Filter
diameter **SD = Solvent decanted ***= Ash measurement
[0108] Although the foregoing invention has been described in some
detail by way of illustration and example for purposes of clarity
of understanding, it is readily apparent to those of ordinary skill
in the art in light of the teachings of this invention that certain
changes and modifications may be made thereto without departing
from the spirit or scope of the appended claims.
[0109] The citation of any publication, patent or patent
application is for its disclosure prior to the filing date and
should not be construed as an admission that the present invention
is not entitled to antedate such publication, patent or patent
application by virtue of prior invention.
[0110] It must be noted that as used in the specification and the
appended claims, the singular forms of "a", "an" and "the" include
plural reference unless the context clearly indicates
otherwise.
[0111] Unless defined otherwise all technical and scientific terms
used herein have the same meaning as commonly understood to one of
ordinary skill and the art to which this invention belongs.
* * * * *