Note: Descriptions are shown in the official language in which they were submitted.
CA 02753811 2011-09-29
METHOD OF PROCESSING TAILINGS FROM
SOLVENT-BASED HYDROCARBON EXTRACTION
FIELD
[0001] The present disclosure relates generally to the field of hydrocarbon
extraction
from mineable deposits, such as bitumen from oil sands. More particularly, the
present
disclosure relates to the processing of tailings from solvent-based
hydrocarbon extraction.
BACKGROUND
[0002] Oil sands are sand deposits which, in addition to sand, comprise clays,
connate water, and bitumen. Depending on the geographic location, bitumen may
be
recovered by mining and extraction methods or by in-situ recovery methods.
[0003] Oil sands ore in a mining and extraction operation is typically
processed using
mechanical and chemical techniques to separate the bitumen from the sands. In
general,
water-based extraction and solvent-based extraction are the two processes that
have been
proposed or used to extract bitumen from mined oil sands. In the case of water-
based
extraction, water is the dominant liquid in the process and the extraction
occurs by having
water displace the bitumen on the surface of the solids. In the case of
solvent-based
extraction, the solvent is the dominant liquid and the extraction of the
bitumen occurs by
dissolving bitumen into the solvent.
[0004] The commercial application of a solvent-based extraction process has,
for
various reasons, eluded the oil sands industry. A major challenge to the
application of
solvent-based extraction to oil sands is the tendency of fine particles within
the oil sands to
hamper the separation of solids from the bitumen extract. Solvent extraction
with solids
agglomeration is a technique that has been proposed to deal with this
challenge. The
original application of this technology was coined Solvent Extraction
Spherical Agglomeration
(SESA). A more recent description of the SESA process can be found in Sparks
et al., Fuel
1992(71); pp 1349-1353.
[0005] Previously described methodologies for SESA have not been commercially
adopted. In general, the SESA process involves mixing oil sands with a
hydrocarbon
solvent, adding a bridging liquid to the oil sands slurry, agitating the
mixture in a slow and
controlled manner to nucleate particles, and continuing such agitation to
permit these
nucleated particles to form larger multi-particle spherical agglomerates for
removal. The
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bridging liquid is preferably water or an aqueous solution since the solids of
oil sands are
mostly hydrophilic and water is immiscible with hydrocarbon solvents. It has
been found that
the bridging liquid used in the process can be water with both a high fines
and salt content.
In fact, in certain embodiments of the SESA process, it may be preferable to
have aqueous
bridging liquid with either high fines content and/or high dissolved solid
content.
[0006] The SESA process described by Meadus et al. in U.S. Patent No.
4,057,486,
involves combining solvent extraction with solids agglomeration to achieve dry
tailings
suitable for direct mine refill. In the process, organic material is separated
from oil sands by
mixing the oil sands material with an organic solvent to form a slurry, after
which an aqueous
bridging liquid is added in the amount of 8 to 50 wt% of the feed mixture. By
using controlled
agitation, solid particles from oil sands come into contact with the aqueous
bridging liquid
and adhere to each other to form macro-agglomerates of a mean diameter of 2 mm
or
greater. The formed agglomerates are more easily separated from the organic
extract
compared to un-agglomerated solids. The organic extract free agglomerates can
be sintered
at high temperatures to make useful construction material. For example, halide
salts such as
NaCl, KCI, and CaCl2 can be dissolved in the aqueous bridging liquid to form
agglomerates
that, when sintered at elevated temperatures, produce very strong aggregates.
[0007] The oil sands industry has become relatively adept at handling aqueous
tailings streams from water-based bitumen extraction. These tailings are
sorted by size in a
variety of operations, and bitumen and minerals can then be extracted. For
instance, settlers
and cyclones are currently used for aqueous tailings to separate particular
streams by
particle size distribution; the coarser fraction can be pumped into place and
rapidly drained,
making it an excellent construction material.
[0008] Oil sands tailings are unique among mining tailings in that they
comprise
residual hydrocarbons. They often also comprise metals, clays, and sands. In a
water-
based extraction process, oil sand tailings comprise water. Because of this
water content,
the tailings are pumpable and easily fed into separation units common in the
oil industry. In
this way, metals can be extracted from the aqueous tailings, bitumen can be
skimmed from
floating mats on tailings ponds, and coarse and fines fractions can be
separated by gravity or
enhanced gravity separation All of these separations of aqueous tailings
currently take
place in the oil sands industry.
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[0009] While one solution to treating solid tailings could be to wet the
tailings and
subject them to the same processes as aqueous tailings this solution greatly
diminishes the
value of a process that produces dry tailings in the first place.
[0010] Outside of the oil sands mining industry, solids handling and
separation is
common in the mining industry. In particular, several mechanisms exist for the
dry
beneficiation of coal, as described by Lockhart, "Dry Beneficiation of Coal",
Powder
Technology 40 (1984) 17-42 and also by Dwari and Rao, "Dry Beneficiation of
Coal - A
Review", Mineral Processing and Extractive Metallurgy Review 28 (2007) 177-
234. These
techniques are applied to ores, which are routinely separated and classified,
and the
methods listed above, such as cyclones, sieves, magnets, etc., are established
technologies.
[0011] B. D. Sparks and F. W. Meadus, "A Combined Solvent Extraction and
Agglomeration Technique for the Recovery of Bitumen from Tar Sands", Canadian
Chemical
Engineering Conference, Calgary: Energy Processing: Tar Sands Technology, 1979
describes the production of solid agglomerates, and refers to the storage of
these materials
without containment.
[0012] U.S. Patent Publication No. 2010/0258478 Moran et al. describes a
method
for separating aqueous oil sand tailings into a bitumen rich stream and a dry
mineral stream,
but separation of the dry mineral stream is not mentioned.
[0013] Newman and Arnold, in "Dry stack tailings design for the Rosemont
Copper
project", Proceedings of the 14th International Conference on Tailings and
Mine Waste 2010,
Vail, Colorado, describe a dry tailings project requiring a buttress and a
cover requirement for
the tailings facility.
[0014] Lupo and Hall, in "Dry stack tailings - design considerations", ibid,
describe
that tailings could be distributed in a stack based on their moisture content
exiting the
extraction process to reduce flow of fluid tailings and dyke strength
requirements. No
separation is mentioned; instead, drier tailings resulting from the primary
process are
deposited in one way while process upset tailings are deposited in another.
[0015] U.S. Patent No. 4,240,897 (Clarke) describes a method of producing dry
tailings and recommends that these tailings be mixed with overburden and used
as backfill
for reclamation. No separation of tailings is mentioned.
[0016] U.S. Patent No. 7,695,612 (Erasmus) describes a method of recovering
heavy
minerals from aqueous oil sands tailings.
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SUMMARY
[0017] Described is a method of processing a bituminous feed. The bituminous
feed
is solvent extracted to form a bitumen-rich stream and a bitumen-lean stream.
Solvent is
recovered from the bitumen-rich stream to form a bitumen product. Solvent and
water are
recovered from the bitumen-lean stream to form dry tailings with a moisture
content of less
than 40 wt.%. The dry tailings are separated into at least two streams, each
stream having a
moisture content of less than 40 wt.%, based on at least one physical or
chemical property.
At least one of the at least two streams is then used at an oil sands mine
site. In this way,
the dry tailings may be used more effectively.
[0018] Other aspects and features of the present disclosure will become
apparent to
those ordinarily skilled in the art upon review of the following description
of specific
embodiments in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Embodiments of the present disclosure will now be described, by way of
example only, with reference to the attached figures.
[0020] Fig. 1 is a schematic illustrating a disclosed embodiment.
[0021] Fig. 2 is a schematic illustrating a disclosed embodiment.
[0022] Fig. 3 is a schematic illustrating a disclosed embodiment.
[0023] Fig. 4 is a schematic illustrating a disclosed embodiment.
DETAILED DESCRIPTION
[0024] As used herein, the term "bituminous feed" refers to a stream derived
from oil
sands that requires downstream processing in order to realize valuable bitumen
products or
fractions. The bituminous feed is one that comprises bitumen along with
undesirable
components. Such a bituminous feed may be derived directly from oil sands, and
may be,
for example, raw oil sands ore. Further, the bituminous feed may be a feed
that has already
realized some initial processing but nevertheless requires further processing.
Also, recycled
streams that comprise bitumen in combination with other components for removal
as
described herein can be included in the bituminous feed. A bituminous feed
need not be
derived directly from oil sands, but may arise from other processes. For
example, a waste
product from other extraction processes which comprises bitumen that would
otherwise not
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have been recovered, may be used as a bituminous feed. Such a bituminous feed
may be
also derived directly from oil shale oil, bearing diatomite or oil saturated
sandstones.
[0025] As used herein, the term "agglomerate" refers to conditions that
produce a
cluster, aggregate, collection or mass, such as nucleation, coalescence,
layering, sticking,
clumping, fusing and sintering, as examples.
[0026] As used herein, the term "dry tailings" refers to tailings with a
moisture content
of less than 40 wt.%.
[0027] Dry tailings are not common in the oil sands industry. Where produced,
dry oil
sands tailings have been seen as an end state rather than as a composition
suitable for
further processing and use. Additionally, solid-solid separation is not common
in the oil
sands industry. As described herein, dry tailings from solvent-based
extraction may be
processed for advantageous use.
[0028] As described in the summary section, the present disclosure relates to
a
method of processing a bituminous feed. The bituminous feed is solvent
extracted to form a
bitumen-rich stream and a bitumen-lean stream. Solvent is recovered from the
bitumen-rich
stream to form a bitumen product. Solvent and water are recovered from the
bitumen-lean
stream to form dry tailings with a moisture content of less than 40 wt.%. The
dry tailings are
separated into at least two streams, each stream having a moisture content of
less than 40
wt.%, based on at least one physical or chemical property. At least one of the
at least two
streams is then used at an oil sands mine site.
[0029] Suitable solvent-based extraction processes may include solvent-based
extraction processes that uses an aqueous stream in the extraction process.
Exemplary
solvent-based extraction processes include, but are not limited to, those
described in the
background section, those described below, and those described in Canadian
Patent
Application Serial No. 2,724,806 ("Adeyinka et al.") filed December 10, 2010
and entitled
"Process and Systems for Solvent Extraction of Bitumen from Oil Sands".
[0030] Summary of Processes of Solvent Extraction Described in Adeyinka et
al. One method of extracting bitumen from oil sands in a manner that employs
solvent
extraction with solids agglomeration is described by Adeyinka et al. In this
process, a solvent
is combined with a bituminous feed derived from oil sands to form an initial
slurry.
Separation of the initial slurry into a fine solids stream and a coarse solids
stream may be
followed by mixing a bridging liquid with the fine solid stream and
agglomeration of solids
from the fine solids stream to form an agglomerated slurry. The agglomerated
slurry can be
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CA 02753811 2011-09-29
separated into agglomerates and a low solids bitumen extract. Optionally, the
coarse solids
stream may be reintroduced and further extracted in the agglomerated slurry. A
low solids
bitumen extract can be separated from the agglomerated slurry for further
processing.
Optionally, the mixing of a second solvent with the low solids bitumen extract
to extract
bitumen may take place, forming a solvent-bitumen low solids mixture, which
can then be
separated further into low grade and high grade bitumen extracts. Recovery of
solvent from
the low grade and/or high grade extracts is conducted, to produce bitumen
products of
commercial value. The agglomerates may be sent to a tailings solvent recovery
unit to
recover solvent and water, leaving dry tailings. Additional details of a
solvent-based
extraction process are described below.
[0031] Processing of Tailings from Solvent-Based Extraction
[0032] Dry tailings from solvent-based bitumen extraction may be separated
into at
least two streams, each stream having a moisture content of less than 40 wt.%.
These
streams may be suitable for different uses. At least one stream may be
suitable for use at the
oil sands mine site, or another oil sands mine site, including an water-based
bitumen
extraction mine site. The separation is effected by leveraging a physical or
chemical property
of the tailings.
[0033] Characteristics to be leveraged for the dry oil sands tailings
separation may
include, but are not limited to size, density, dipole moment, permeability,
shape, magnetism,
adhesiveness, wettability, attrition, strength, solubility, inductiveness, and
electric charge.
[0034] Suitable methods or devices for separating dry oil sands tailings may
include,
but are not limited to a screen, a sieve, a blower (for instance an air
blower), gravity
separation or enhanced gravity separation (for instance using a cyclone,
centrifuge, or settler),
filtration, electrostatic precipitation, a magnet, a shaker, a grinder,
milling, and rolling.
[0035] Separation may also be achieved naturally without using a device, i.e.
by
consolidation over time. In one embodiment, the dry tailings are rolled down
an incline such
as a hill or mine face. The tailings separate themselves according to size
and/or density.
Materials at the top are of a lighter density and/or a smaller size. In
another embodiment, first
and second streams are separated from one another by a sieve, screen, or a
blower. In
another embodiment, the tailings are separated in a cyclone. In another
embodiment, they
are separated according to their electrostatic charge. In another embodiment,
they are
separated by a magnetic field. In another embodiment, the tailings are
separated by their
tendency to cling to a surface. In another embodiment, the tailings are
separated by their
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strength. In another embodiment, the tailings are separated by being
selectively crushed in a
mill.
[0036] A first of the separated streams may be used as a construction material
while a
second is used for mine backfill. In this embodiment, the first stream may be
a coarser
stream. The second stream may be comprised of a finer fraction of particles.
The separation
into these streams would allow the coarser stream to be mixed with water
because it would
rapidly drain. The coarser material could subsequently be pumped into place,
allowing
construction according to the general practice in the industry, for instance
for construction of a
mine form at the oil sands site, such as a dyke or a road.
[0037] At least one of the at least two streams may be used drainage, as
foundation,
as a road, for reclamation, or as a dyke, at the oil sands mine site, or is
used in a deposit for
growing vegetation.
[0038] A stream of finer particle sized tailings may be separated from a
stream of
coarser particle sized tailings. The finer particles are used in the lining of
a tailings cell to
reduce its permeability to water. The tailings could be placed at the bottom
of, along the walls
of, and/or on the cap of a tailings deposit.
[0039] The streams may be separated by charge or magnetism. An incoming
tailings
stream is subjected to a magnetic moment or an electrostatic charge. The
portion of the
incoming tailings stream that responds to this force is captured separately
from the portion
that does not respond to the force. The mineral composition of the tailings
being different, one
of the tailings streams, rich in one or more minerals, is used in a mineral
extraction process to
recover the valuable minerals. Another stream is used for mine backfill. In
another
embodiment, the mineral poor stream is placed in a deposit closer to potential
contact with
water. The mineral rich tailings are placed farther away from potential
contact with water. In
another embodiment, the mineral rich stream is placed under water, and the
mineral poor
stream is placed in or over the water table.
[0040] The separation may be used to produce streams of differing sizes or
densities,
which can be used in different capacities in mine backfill. The lighter stream
may be more
prone to dusting, and may be covered with another material, such as a coarser
stream of
tailings. The heavier stream may be used as a capillary barrier. In this
application, the
coarser stream has a low hydraulic wicking potential while dry as compared to
the finer
stream. A material may be selectively moved from the deposit based on its
materials
properties.
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[0041] The tailings may be separated into streams that differ by their
chemical
composition into a chemically active stream and a chemically inert stream. The
tailings may
be separated into a stream that can be heat treated to form a cementitious
material. The
tailings may be separated into a stream that can be mixed with a chemical
binder and another
stream that is not mixed with a chemical binder.
[0042] As described above, the term "dry tailings" refers to tailings with a
moisture
content of less than 40 wt.%. In another embodiment, the dry tailings may have
a moisture
content of less than 30 wt. %.
[0043] Figure 1 illustrates an embodiment using airblowing to separate dry
tailings
cyclonically. Tailings (100) may be dried (101) to form dry tailings (102).
The drytailings
(102) are airblown in a cyclone (104) for separation by particle size and/or
density. The
cyclone produces a lighter stream (106) and a heavier stream (108). The
lighter stream (106)
may comprise mainly clays and may be suitable as an impermeable layer, such as
a clay liner.
The heavier stream (108) may be a coarser material and may be suitable for use
as a
construction material, such as for roads or containment. In an example where
both streams
are used at the mine site, as illustrated in Figure 1, the heavier stream
(108) may be used as a
containment structure (110) and the lighter stream (108) may used as an
impermeable layer
(112), for containing aqueous tailings (114).
[0044] Figure 2 illustrates an embodiment leveraging the magnetic dipole
moment
present in some of the dry tailings. Tailings (200) may be dried (201) to form
dry tailings
(202). The dry tailings (202) are separated using a magnet (204) into a higher
dipole moment
containing stream (206) which may have a higher concentration of metals, and a
lower dipole
moment containing stream (208). The higher dipole moment containing stream
(206) may be
further processed to reclaim metals. The lower dipole moment containing stream
(208) may
be used as mine backfill.
[0045] Figure 3 illustrates an embodiment where dry tailings (302) are passed
to a
blower (304) to separate the dry tailings (302) according to how prone they
are to being
carried by the wind. The coarser fraction (306) drops out faster than the
finer fraction (308).
The coarser fraction (306) may be deposited in a windy area, or on a higher
elevation than the
finer fraction (308). Alternatively, the finer fraction (308) may be placed
first and then covered
by the coarser fraction (306) to reduce dusting.
[0046] Figure 4 illustrates an embodiment where an induced dipole moment (404)
separates dry tailings (402) according to the availability of minerals
containing a dipole
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CA 02753811 2011-09-29
moment. The tailings (400) and dryer (401) are also illustrated. The material
containing a
higher dipole moment (406) is more prone to acid rock drainage and may be
placed in a
subaqueous environment to mitigate its oxidation. This layer may be covered
with the
material containing a lower dipole moment (408). Alternatively, the material
containing a
higher dipole moment (406) may be placed away from an aqueous material (410),
and is
insulated with the material containing a lower dipole moment (408). The mine
pit (412) is also
illustrated.
[0047] For dry sands tailings, many uses may favor a particular fraction of
the tailings
rather than the whole tailings. Furthermore, some fractions of the tailings
may be preferred
over other fractions of the tailings. Examples include construction materials
for dykes or
roads, as backfill within the mine, or as a recycle stream to aid in
extraction. An example of a
recycle stream aiding in the extraction process is as follows. It has been
previously shown
that increasing the solids content, or more preferably the fines content, of a
slurry may
improve the solvent extraction with solids agglomeration process. Thus, a
fines solids stream
produced by a process described herein may be redirected back to the solvent
extraction
process to aid in solids agglomeration. More uses can be envisioned, such as
mineral
extraction from a mineral rich stream, as a pH buffer in a tailings pond, or
as an absorption
stream to enhance the solids content of fluid tailings, as described above.
One example is to
use the fines streams as an impermeable layer. Such an impermeable layer can
be used as
liner for mature fine tailings produced in an aqueous-based extraction
process.
[0048] The moisture content of the tailings may be reduced prior to
separation, for
instance by drying, extraction, or agglomeration.
[0049] At least one of the at least two streams may be mixed with an additive
comprising a polymer, gypsum, alum, or a resin.
[0050] At least one of the at least two streams may be mixed with tailings
generated
from an aqueous-based bitumen extraction process.
[0051] At least one of the at least two streams may be grinded.
[0052] One or more heavy metals may be recovered from at least one of the at
least
two streams. The heavy metals may be titanium, strontium, or vanadium, or a
combination
thereof.
[0053] At least one of the at least two streams may be recycled into the
solvent
extraction of step a).
[0054] The dry tailings may have a water : solids mass ratio of less than
0.15:1.
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[0055] The oil sands mine site may be mine site employing aqueous-based
bitumen
extraction or a mine site employing solvent-based bitumen extraction.
[0056] Description of one Solvent-Based Extraction Process Using
Agglomeration:
[0057] Agglomeration. In one embodiment, the formed agglomerates are sized on
the order of 0.1-1.0 mm, or on the order of 0.1-0.3 mm. In one embodiment, at
least 80 wt.%
of the formed agglomerates are 0.1-1.0 mm, or 0.1 to 0.3 mm in size. The rate
of
agglomeration may be controlled by a balance between intensity of agitation
within the
agglomeration vessel, shear within the vessel which can be adjusted by for
example changing
the shape or size of the vessel, fines content of the slurry, bridging liquid
addition, and
residence time of the agglomeration process. The agglomerated slurry may have
a solids
content of 20 to 70 wt %.
[0058] Agitation. Agglomeration is assisted by some form of agitation. The
form of
agitation may be mixing, shaking, rolling, or another known suitable method.
The agitation of
the feed need only be severe enough and of sufficient duration to intimately
contact the
emulsion with the solids in the feed. Exemplary rolling type vessels include
rod mills and
tumblers. Exemplary mixing type vessels include mixing tanks, blenders, and
attrition
scrubbers. In the case of mixing type vessels, a sufficient amount of
agitation is needed to
keep the formed agglomerates in suspension. In rolling type vessels, the
solids content of
the feed is, in one embodiment, greater than 40 wt.% so that compaction forces
assist
agglomerate formation. The agitation of the slurry has an impact on the growth
of the
agglomerates. In the case of mixing type vessels, the mixing power can be
increased in
order to limit the growth of agglomerates by attrition of said agglomerates.
In the case of
rolling type vessels the fill volume and rotation rate of the vessel can be
adjusted in order to
increase the compaction forces used in the comminution of agglomerates. These
agitation
parameters can be adjusted in the control system described herein.
[0059] Extraction Liquor. The extraction liquor comprises a solvent used to
extract
bitumen from the bituminous feed. The term "solvent" as used herein should be
understood
to mean either a single solvent, or a combination of solvents.
[0060] In one embodiment, the extraction liquor comprises a hydrocarbon
solvent
capable of dissolving the bitumen. The extraction liquor may be a solution of
a hydrocarbon
solvent(s) and bitumen, where the bitumen content of the extraction liquor may
range
between 10 and 70 wt%, or 10 and 50 wt%. It may be desirable to have dissolved
bitumen
CA 02753811 2011-09-29
within the extraction liquor in order to increase the volume of the extraction
liquor without an
increase in the required inventory of hydrocarbon solvent(s). In cases where
non-aromatic
hydrocarbon solvents are used, the dissolved bitumen within the extraction
liquor also
increases the solubility of the extraction liquor towards dissolving
additional bitumen.
[0061] The extraction liquor may be mixed with the bituminous feed to form a
slurry
where most or all of the bitumen from the oil sands is dissolved into the
extraction liquor. In
one embodiment, the solids content of the slurry is in the range of 10 wt% to
75 wt%, or 50 to
65 wt%. A slurry with a higher solids content may be more suitable for
agglomeration in a
rolling type vessel, where the compressive forces aid in the formation of
compact
agglomerates. For turbulent flow type vessels, such as an attrition scrubber,
a slurry with a
lower solids content may be more suitable.
[0062] The solvent used in the process may include low boiling point solvents
such
as low boiling point cycloalkanes, or a mixture of such cycloalkanes, which
substantially
dissolve asphaltenes. The solvent may comprise a paraffinic solvent in which
the solvent to
bitumen ratio is maintained at a level to avoid or limit precipitation of
asphaltenes.
[0063] While it is not necessary to use a low boiling point solvent, when it
is used,
there is the extra advantage that solvent recovery through an evaporative
process proceeds at
lower temperatures, and requires a lower energy consumption. When a low
boiling point
solvent is selected, it may be one having a boiling point of less than 100 C.
[0064] The solvent selected according to certain embodiments may comprise an
organic solvent or a mixture of organic solvents. For example, the solvent may
comprise a
paraffinic solvent, an open chain aliphatic hydrocarbon, a cyclic aliphatic
hydrocarbon, or a
mixture thereof. Should a paraffinic solvent be utilized, it may comprise an
alkane, a natural
gas condensate, a distillate from a fractionation unit (or diluent cut), or a
combination of
these containing more than 40% small chain paraffins of 5 to 10 carbon atoms.
These
embodiments would be considered primarily a small chain (or short chain)
paraffin mixture.
Should an alkane be selected as the solvent, the alkane may comprise a normal
alkane, an
iso-alkane, or a combination thereof. The alkane may specifically comprise
heptane, iso-
heptane, hexane, iso-hexane, pentane, iso-pentane, or a combination thereof.
Should a
cyclic aliphatic hydrocarbon be selected as the solvent, it may comprise a
cycloalkane of 4 to
9 carbon atoms. A mixture of C4-C9 cyclic and/or open chain aliphatic solvents
would be
appropriate.
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[0065] Exemplary cycloalkanes include cyclohexane, cyclopentane, or a mixture
thereof.
[0066] If the solvent is selected as the distillate from a fractionation unit,
it may for
example be one having a final boiling point of less than 180 C. An exemplary
upper limit of
the final boiling point of the distillate may be less than 100 C.
[0067] A mixture of C4-C10 cyclic and/or open chain aliphatic solvents would
also be
appropriate. For example, it can be a mixture of C4-C9 cyclic aliphatic
hydrocarbons and
paraffinic solvents where the percentage of the cyclic aliphatic hydrocarbons
in the mixture is
greater than 50%.
[0068] Extraction liquor may be recycled from a downstream step. For instance,
as
described below, solvent recovered in a solvent recovery unit, may be used to
wash
agglomerates, and the resulting stream may be used as extraction liquor. As a
result, the
extraction liquor may comprise residual bitumen and residual solid fines. The
residual
bitumen increases the volume of the extraction liquor and it may increase the
solubility of the
extraction liquor for additional bitumen dissolution.
[0069] The solvent may also include additives. These additives may or may not
be
considered a solvent per se. Possible additives may be components such as de-
emulsifying
agents or solids aggregating agents. Having an agglomerating agent additive
present in the
bridging liquid and dispersed in the first solvent may be helpful in the
subsequent
agglomeration step. Exemplary agglomerating agent additives include cements,
fly ash,
gypsum, lime, brine, water softening wastes (e.g. magnesium oxide and calcium
carbonate),
solids conditioning and anti-erosion aids such as polyvinyl acetate emulsion,
commercial
fertilizer, humic substances (e.g. fulvic acid), polyacrylamide based
flocculants and others.
Additives may also be added prior to gravity separation with the second
solvent to enhance
removal of suspended solids and prevent emulsification of the two solvents.
Exemplary
additives include methanoic acid, ethylcellulose and polyoxyalkylate block
polymers.
[0070] Bridging Liquid. A bridging liquid is a liquid with affinity for the
solids
particles in the bituminous feed, and which is immiscible in the solvent.
Exemplary aqueous
liquids may be recycled water from other aspects or steps of oil sands
processing. The
aqueous liquid need not be pure water, and may indeed be water containing one
or more
salt, a waste product from conventional aqueous oil sand extraction processes
which may
include additives, aqueous solutions with a range of pH, or any other
acceptable aqueous
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CA 02753811 2011-09-29
solution capable of adhering to solid particles within an agglomerator in such
a way that
permits fines to adhere to each other. An exemplary bridging liquid is water.
[0071] The total amount of bridging liquid added to the slurry may be
controlled in
order to optimize bitumen recovery and the rate of solid-liquid separation. By
way of
examples, the total amount of bridging liquid added to the slurry may be such
that a ratio of
bridging liquid plus connate water from the bituminous feed to solids within
the agglomerated
slurry is in the range of 0.02 to 0.25, or in the range of 0.05 to 0.11.
[0072] The bridging liquid may be added in a concentration of less than 50 wt%
of the
oil sands feed, or less 25 wt%.
[0073] In one embodiment, the bridging liquid may comprise fine particles
(sized less
than 44 pm) suspended therein. These fine particles may serve as seed
particles for the
agglomeration process. In one embodiment, the bridging liquid has a solids
content of less
than 40 wt.%.
[0074] Ratio of Solvent to Bitumen for Agglomeration. The process may be
adjusted to render the ratio of the solvent to bitumen in the agglomerator at
a level that
avoids precipitation of asphaltenes during agglomeration. Some amount of
asphaltene
precipitation is unavoidable, but by adjusting the amount of solvent flowing
into the system,
with respect to the expected amount of bitumen in the bituminous feed, when
taken together
with the amount of bitumen that may be entrained in the extraction liquor
used, can permit
the control of a ratio of solvent to bitumen in the agglomerator. When the
solvent is assessed
for an optimal ratio of solvent to bitumen during agglomeration, the
precipitation of
asphaltenes can be minimized or avoided beyond an unavoidable amount. Another
advantage of selecting an optimal solvent to bitumen ratio is that when the
ratio of solvent to
bitumen is too high, costs of the process may be increased due to increased
solvent
requirements.
[0075] An exemplary ratio of solvent to bitumen to be selected as a target
ratio during
agglomeration is less than 2:1. A ratio of 1.5:1 or less, and a ratio of 1:1
or less, for example,
a ratio of 0.75:1, would also be considered acceptable target ratios for
agglomeration. For
clarity, ratios may be expressed herein using a colon between two values, such
as "2:1 ", or
may equally be expressed as a single number, such as "2", which carries the
assumption
that the denominator of the ratio is 1 and is expressed on a weight to weight
basis.
[0076] Measurement of the solvent and bitumen content of the extraction liquor
and/or bitumen extract could occur directly or by proxy. Direct measurement of
solvent and
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CA 02753811 2011-09-29
bitumen content could involve evaporating off the solvent and measuring the
mass of both
liquids, or use of a gas chromatograph, mass balance, spectrometer, or
titration. Indirect
measurement of solvent and bitumen content could include measuring : density,
the index of
refraction, opacity, or other properties.
[0077] Slurry System. The slurry system may optionally be a mix box, a pump,
or a
combination of these. By slurrying the extraction liquor together with the
bituminous feed,
and optionally with additional additives, the bitumen entrained within the
feed is given an
opportunity to become extracted into the solvent phase prior to agglomeration
within the
agglomerator.
[0078] The resulting slurry from the slurry system may have a solid content in
the
range of 20 to 65 wt%. In another embodiment, the slurry may have a solid
content in the
range of 20 to 50 wt%. In another embodiment, the slurry may have a solid
content in the
range of 40 to 65 wt%. In the case of mixing type vessels, a lower solid
content may be
preferred since that will assist in the proper mixing of the bridging liquid
and reduce the
mixing energy needed to keep the slurry well mixed. In the case of rolling
type vessels, a
higher solid content may be preferred since that will increase the compaction
forces used in
the comminution of agglomerates. Additionally, the increased compaction forces
may reduce
the amount of hydrocarbons that remain in the agglomerates and produce
stronger
agglomerates.
[0079] The preferred temperature of the slurry is in the range of 20-60 C. An
elevated slurry temperature is desired in order to increase the bitumen
dissolution rate and
reduce the viscosity of the slurry to promote more effective sand digestion
and agglomerate
formation. Temperatures above 60 C are generally avoided due to the
complications
resulting from high vapor pressures.
[0080] Residence Time. The residence time of the extraction process may be
greater than 5 minutes, or may be greater than 10 minutes, or may be greater
than 15
minutes, or may greater than 30 minutes. Depending on the desired level of
agglomeration,
the residence time of the agglomeration process may be in the range of 15
seconds to 10
minutes. In order to maximize bitumen recovery, the residence time of the
agglomeration
process may be in the range of 1 to 5 minutes.
[0081] Solid-Liquid Separator. As described above, the agglomerated slurry may
be separated into a low solids bitumen extract and agglomerates in a solid-
liquid separator.
The solid-liquid separator may comprise any type of unit capable of separating
solids from
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liquids, so as to remove agglomerates. Exemplary types of units include a
gravity separator,
a clarifier, a cyclone, a screen, a belt filter or a combination thereof.
[0082] The system may contain a solid-liquid separator but may alternatively
contain
more than one. When more than one solid-liquid separation step is employed at
this stage of
the process, it may be said that both steps are conducted within one solid-
liquid separator, or
if such steps are dissimilar, or not proximal to each other, it may be said
that a primary solid-
liquid separator is employed together with a secondary solid-liquid separator.
When a
primary and secondary unit are both employed, generally, the primary unit
separates
agglomerates, while the secondary unit involves washing agglomerates.
[0083] Non-limiting methods of solid-liquid separation of an agglomerated
slurry are
described in Canadian Patent Application Serial No. 2,724,806 (Adeyinka et
al.), filed
December 10, 2010.
[0084] Secondary Stage of Solid-Liquid Separation to Wash Agglomerates. As a
component of the solid-liquid separator, a secondary stage of separation may
be introduced
for countercurrently washing the agglomerates separated from the agglomerated
slurry. The
initial separation of agglomerates may be said to occur in a primary solid-
liquid separator,
while the secondary stage may occur within the primary unit, or may be
conducted
completely separately in a secondary solid-liquid separator. By
"countercurrently washing", it
is meant that a progressively cleaner solvent is used to wash bitumen from the
agglomerates. Solvent involved in the final wash of agglomerates may be re-
used for one or
more upstream washes of agglomerates, so that the more bitumen entrained on
the
agglomerates, the less clean will be the solvent used to wash agglomerates at
that stage.
The result being that the cleanest wash of agglomerates is conducted using the
cleanest
solvent.
[0085] A secondary solid-liquid separator for countercurrently washing
agglomerates
may be included in the system or may be included as a component of a system
described
herein. The secondary solid-liquid separator may be separate or incorporated
within the
primary solid-liquid separator. The secondary solid-liquid separator may
optionally be a
gravity separator, a cyclone, a screen or belt filter. Further, a secondary
solvent recovery
unit for recovering solvent arising from the solid-liquid separator can be
included. The
secondary solvent recovery unit may be a conventional fractionation tower or a
distillation
unit.
CA 02753811 2011-09-29
[0086] When conducted in the process, the secondary stage for countercurrently
washing the agglomerates may comprise a gravity separator, a cyclone, a
screen, a belt
filter, or a combination thereof.
[0087] The solvent used for washing the agglomerates may be solvent recovered
from the low solids bitumen extract, as described in Canadian Patent
Application Serial No.
2,724,806 (Adeyinka et al.). A second solvent may alternatively or
additionally be used as
described in Canadian Patent Application Serial No. 2,724,806 (Adeyinka et
al.) for additional
bitumen extraction downstream of the agglomerator.
[0088] Recycle and Recovery of Solvent. The process may involve removal and
recovery of solvent used in the process.
[0089] In this way, solvent is used and re-used, even when a good deal of
bitumen is
entrained therein. Because an exemplary solvent:bitumen ratio in the
agglomerator may be
2:1 or lower, it is acceptable to use recycled solvent containing bitumen to
achieve this ratio.
The amount of make-up solvent required for the process may depend solely on
solvent
losses, as there is no requirement to store and/or not re-use solvent that has
been used in a
previous extraction step. When solvent is said to be "removed", or
"recovered", this does not
require removal or recovery of all solvent, as it is understood that some
solvent will be
retained with the bitumen even when the majority of the solvent is removed.
[0090] The system may contain a single solvent recovery unit for recovering
the
solvent(s) arising from the gravity separator. The system may alternatively
contain more than
one solvent recovery unit.
[0091] Solvent may be recovered by conventional means. For example, typical
solvent recovery units may comprise a fractionation tower or a distillation
unit. The solvent
recovered in this fashion will not contain bitumen entrained therein. This
clean solvent is
preferably used in the last wash stage of the agglomerate washing process in
order that the
cleanest wash of the agglomerates is conducted using the cleanest solvent.
[0092] The solvent recovered in the process may comprise entrained bitumen
therein, and can thus be re-used as the extraction liquor for combining with
the bituminous
feed. Other optional steps of the process may incorporate the solvent having
bitumen
entrained therein, for example in countercurrent washing of agglomerates, or
for adjusting
the solvent and bitumen content prior to agglomeration to achieve the selected
ratio within
the agglomerator that avoids precipitation of asphaltenes.
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[0093] The agglomerates may be sent to a tailings solvent recovery unit to
recover
solvent and water, leaving dry tailings.
[0094] Dilution of Agglomerator Discharge to Improve Product Quality. Solvent
may be added to the agglomerated slurry for dilution of the slurry before
discharge into the
primary solid-liquid separator, which may be for example a deep cone settler.
This dilution
can be carried out in a staged manner to pre-condition the primary solid-
liquid separator feed
to promote higher solids settling rates and lower solids content in the solid-
liquid separator's
overflow. The solvent with which the slurry is diluted may be derived from
recycled liquids
from the liquid-solid separation stage or from other sources within the
process.
[0095] When dilution of agglomerator discharge is employed in this embodiment,
the
solvent to bitumen ratio of the feed into the agglomerator is set to obtain
from about 10 to
about 90 wt% bitumen in the discharge, and a workable viscosity at a given
temperature. In
certain cases, these viscosities may not be optimal for the solid-liquid
separation (or settling)
step. In such an instance, a dilution solvent of equal or lower viscosity may
be added to
enhance the separation of the agglomerated solids in the clarifier, while
improving the quality
of the clarifier overflow by reducing viscosity to permit more solids to
settle. Thus, dilution of
agglomerator discharge may involve adding the solvent, or a separate dilution
solvent, which
may, for example, comprise an alkane.
[0096] In the preceding description, for purposes of explanation, numerous
details
are set forth in order to provide a thorough understanding of the embodiments.
However, it
will be apparent to one skilled in the art that these specific details are not
required.
[0097] The above-described embodiments are intended to be examples only.
Alterations, modifications and variations can be effected to the particular
embodiments by
those of skill in the art without departing from the scope.
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