Note: Descriptions are shown in the official language in which they were submitted.
BITUMEN RECOVERY FROM COARSE SAND TAILINGS
BACKGROUND
Field of Disclosure
[0001] The disclosure relates generally to the field of oil sand tailings.
Description of Related Art
[0002] This section is intended to introduce various aspects of the art,
which may be
associated with the present disclosure. This discussion is believed to assist
in providing a
framework to facilitate a better understanding of particular aspects of the
present disclosure.
Accordingly, it should be understood that this section should be read in this
light, and not
necessarily as admissions of prior art.
[0003] Modern society is greatly dependent on the use of hydrocarbon
resources for fuels
and chemical feedstocks. Hydrocarbons are generally found in subsurface
formations that can
be termed "reservoirs". Removing hydrocarbons from the reservoirs depends on
numerous
physical properties of the subsurface formations, such as the permeability of
the rock
containing the hydrocarbons, the ability of the hydrocarbons to flow through
the subsurface
formations, and the proportion of hydrocarbons present, among other things.
Easily harvested
sources of hydrocarbons are dwindling, leaving less accessible sources to
satisfy future energy
needs. As the costs of hydrocarbons increase, the less accessible sources
become more
economically attractive.
[0004] Recently, the harvesting of oil sand to remove heavy oil has become
more
economical. Hydrocarbon removal from oil sand may be performed by several
techniques.
For example, a well can be drilled to an oil sand reservoir and steam, hot
air, solvents, or a
combination thereof, can be injected to release the hydrocarbons. The released
hydrocarbons
may be collected by wells and brought to the surface.
[0005] In another technique, strip or surface mining may be performed to
access the oil
sand, which can be treated with water, steam or solvents to extract the heavy
oil.
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[0006] Oil sand extraction processes are used to liberate and separate
bitumen from oil
sand so that the bitumen can be further processed to produce synthetic crude
oil or mixed with
diluent to form "dilbit" and be transported to a refinery plant. Numerous oil
sand extraction
processes have been developed and commercialized, many of which involve the
use of water
as a processing medium. Where the oil sand is treated with water, the
technique may be
referred to as water-based extraction (WBE). WBE is a commonly used process to
extract
bitumen from mined oil sand.
[0007] One WBE process is the Clark hot water extraction process (the
"Clark Process").
This process typically requires that mined oil sand be conditioned for
extraction by being
crushed to a desired lump size and then combined with hot water and perhaps
other agents to
form a conditioned slurry of water and crushed oil sand. In the Clark Process,
an amount of
sodium hydroxide (caustic) may be added to the slurry to increase the slurry
pH, which
enhances the liberation and separation of bitumen from the oil sand. Other WBE
processes
may use other temperatures and may include other conditioning agents, which
are added to
the oil sand slurry, or may operate without conditioning agents. This slurry
is first processed
in a Primary Separation Cell (PSC), also known as a Primary Separation Vessel
(PSV), to
extract the bitumen from the slurry.
[0008] In one bitumen extraction process, a water and oil sand slurry is
separated into
three major streams in the PSC: bitumen froth, middlings, and a PSC underflow
(also known
as primary separation tailings or coarse sand tailings (CST)).
100091 Regardless of the type of WBE process employed, the process will
typically result
in the production of a bitumen froth that requires treatment with a solvent.
For example, in
the Clark Process, a bitumen froth stream comprises bitumen, solids, and
water. Certain
processes use naphtha to dilute bitumen froth before separating the product
bitumen by
centrifugation. These processes are called naphthenic froth treatment (NFT)
processes. Other
processes use a paraffinic solvent, and are called paraffinic froth treatment
(PFT) processes, to
produce pipelineable bitumen with low levels of solids and water. In the PFT
process, a
paraffinic solvent (for example, a mixture of iso-pentane and n-pentane) is
used to dilute the
froth before separating the product, diluted bitumen, by gravity. A portion of
the asphaltenes
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in the bitumen is also rejected by design in the PFT process and this
rejection is used to
achieve reduced solids and water levels. In both the NFT and the PFT
processes, the diluted
tailings (comprising water, solids and some hydrocarbon) are separated from
the diluted
product bitumen.
[0010] Solvent is typically recovered from the diluted product bitumen
component before
the bitumen is delivered to a refining facility for further processing.
[0011] The PFT process may comprise at least three units: Froth Separation
Unit (FSU),
Solvent Recovery Unity (SRU) and Tailings SRU (TSRU). Mixing of the solvent
with the
feed bitumen froth may be carried out counter-currently in two stages in
separate froth
separation units. The bitumen froth comprises bitumen, water, and solids. A
typical
composition of bitumen froth is about 60 wt. % bitumen, 30 wt. % water, and 10
wt. % solids.
The paraffinic solvent is used to dilute the froth before separating the
product bitumen by
gravity. The foregoing is only an example of a PFT process and the values are
provided by
way of example only. An example of a PFT process is described in Canadian
Patent No.
2,587,166 to Sury.
[0012] From the PSC, the middlings, comprising bitumen and about 10-30 wt.
% solids,
or about 20-25 wt. % solids, based on the total wt. % of the middlings, is
withdrawn and sent
to the flotation cells to further recover bitumen. The middlings are processed
by bubbling air
through the slurry and creating a bitumen froth, which is recycled back to the
PSC. Flotation
tailings (FT) from the flotation cells, comprising mostly solids and water,
are sent for further
treatment or disposed in an external tailings area (ETA). CST may be, for
instance, released
directly to tailings ponds or be subjected to a combination of flotation and
hydrocyclone
processes to recover bitumen and then desand the mixture.
[0013] In ETA tailings ponds, a liquid suspension of oil sand fines in
water with a solids
content greater than 2 wt. %, but less than the solids content corresponding
to the Liquid
Limit are called Fluid Fine Tailings (FFT). FFT settle over time to produce
Mature Fine
Tailings (MFT), having above about 30 wt. % solids.
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[0014] It would be desirable to have an alternative method of recovering
bitumen from
coarse sand tailings (CST).
SUMMARY
[0015] According to one aspect, there is provided a method including
providing a coarse
sand tailings stream (CST) comprising sand, fines, clay, water, and bitumen;
mixing the CST
to liberate the bitumen from the sand and disperse the bitumen in the water to
form a mixed
CST stream; and separating the sand from the bitumen to form a bitumen-rich
stream.
[0016] The foregoing has broadly outlined the features of the present
disclosure so that
the detailed description that follows may be better understood. Additional
features will also
be described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] These and other features, aspects and advantages of the disclosure
will become
apparent from the following description, appending claims and the accompanying
drawings,
which are briefly described below.
[0018] It should be noted that the figures are merely examples and no
limitations on the
scope of the present disclosure are intended thereby. Further, the figures are
generally not
drawn to scale, but are drafted for purposes of convenience and clarity in
illustrating various
aspects of the disclosure.
[0019] Figure 1 is a schematic of a bitumen extraction method including a
method for
recovering bitumen from coarse sand tailings (CST).
[0020] Figure 2 is a chart of the effect of mixing on bitumen recovery from
CST.
[0021] Figure 3 is a chart of the effect of mixing on the percentage of
undigested bitumen
in CST.
DETAILED DESCRIPTION
[0022] For the purpose of promoting an understanding of the principles of
the disclosure,
reference will now be made to the features illustrated in the drawings and
specific language
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will be used to describe the same. It will nevertheless be understood that no
limitation of the
scope of the disclosure is thereby intended. Any alterations and further
modifications, and
any further applications of the principles of the disclosure as described
herein are
contemplated as would normally occur to one skilled in the art to which the
disclosure relates.
It will be apparent to those skilled in the relevant art that some features
that are not relevant to
the present disclosure may not be shown in the drawings for the sake of
clarity.
[0023] At the outset, for ease of reference, certain terms used in this
application and their
meaning as used in this context are set forth below. To the extent a term used
herein is not
defined below, it should be given the broadest definition persons in the
pertinent art have
given that term as reflected in at least one printed publication or issued
patent. Further, the
present processes are not limited by the usage of the terms shown below, as
all equivalents,
synonyms, new developments and terms or processes that serve the same or a
similar purpose
are considered to be within the scope of the present disclosure.
[0024] Throughout this disclosure, where a range is used, any number
between or
inclusive of the range is implied.
[0025] A "hydrocarbon" is an organic compound that primarily includes the
elements of
hydrogen and carbon, although nitrogen, sulfur, oxygen, metals, or any number
of other
elements may be present in small amounts. Hydrocarbons generally refer to
components
found in heavy oil or in oil sand. However, the techniques described are not
limited to heavy
oils but may also be used with any number of other reservoirs to improve
gravity drainage of
liquids. Hydrocarbon compounds may be aliphatic or aromatic, and may be
straight chained,
branched, or partially or fully cyclic.
[0026] "Bitumen" is a naturally occurring heavy oil material. Generally, it
is the
hydrocarbon component found in oil sand. Bitumen can vary in composition
depending upon
the degree of loss of more volatile components. It can vary from a very
viscous, tar-like,
semi-solid material to solid forms. The hydrocarbon types found in bitumen can
include
aliphatics, aromatics, resins, and asphaltenes. A typical bitumen might be
composed of:
19 weight (wt.) aliphatics (which can range from 5 wt. % - 30 wt. %, or
higher);
19 wt. % asphaltenes (which can range from 5 wt. % - 30 wt. %, or higher);
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30 wt. % aromatics (which can range from 15 wt. % - 50 wt. %, or higher);
32 wt. % resins (which can range from 15 wt. % - 50 wt. %, or higher); and
some amount of sulfur (which can range in excess of 7 wt. %), based on a
weight of the
bitumen.
In addition, bitumen can contain some water and nitrogen compounds ranging
from less than
0.4 wt. % to in excess of 0.7 wt. %, based on a weight of the bitumen. The
percentage of the
hydrocarbon found in bitumen can vary. The term "heavy oil" includes bitumen
as well as
lighter materials that may be found in a sand or carbonate reservoir.
[0027] "Heavy oil" includes oils which are classified by the American
Petroleum Institute
("API"), as heavy oils, extra heavy oils, or bitumens. The term "heavy oil"
includes bitumen.
Heavy oil may have a viscosity of about 1,000 centipoise (cP) or more, 10,000
cP or more,
100,000 cP or more, or 1,000,000 cP or more. In general, a heavy oil has an
API gravity
between 22.3 API (density of 920 kilograms per meter cubed (kg/m3) or 0.920
grams per
centimeter cubed (g/cm3)) and 10.00 API (density of 1,000 kg/m3 or 1 g/cm3).
An extra heavy
oil, in general, has an API gravity of less than 10.0 API (density greater
than 1,000 kg/m3 or
1 g/cm3). For example, a source of heavy oil includes oil sand or bituminous
sand, which is a
combination of clay, sand, water and bitumen. The recovery of heavy oils is
based on the
viscosity decrease of fluids with increasing temperature or solvent
concentration. Once the
viscosity is reduced, the mobilization of fluid by steam, hot water flooding,
or gravity is
possible. The reduced viscosity makes the drainage or dissolution quicker and
therefore
directly contributes to the recovery rate.
[0028] "Fine particles" or "fines" are generally defined as those solids
having a size of
less than 44 microns (um), that is, material that passes through a 325 mesh
(44 micron).
[0029] "Coarse particles" are generally defined as those solids having a
size of greater
than 44 microns (m).
[0030] "Clays" are generally defined as those solids having a size of less
than 2 microns,
but some clays may be larger. Clays may include ceramics like aluminum and
silicon oxide
species like kaolinite and illite, and they may also include fine particles of
other species such
as iron oxides and quartzes.
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[0031] A "bitumen extract" is generally defined as bitumen that has been
extracted from
oil sand.
[0032] A "bitumen product stream" or "bitumen product" is generally defined
as a high
grade bitumen product that may be suitable for transport within pipelines and
processing
within downstream refineries. A high grade bitumen product stream may have a
solids
content of less than 1 wt. %, or less than 0.1 wt. %, on a dry bitumen basis.
[0033] The term "solvent" as used in the present disclosure should be
understood to mean
either a single solvent, or a combination of solvents.
[0034] The terms "approximately," "about," "substantially," and similar
terms are
intended to have a broad meaning in harmony with the common and accepted usage
by those
of ordinary skill in the art to which the subject matter of this disclosure
pertains. It should be
understood by those of skill in the art who review this disclosure that these
terms are intended
to allow a description of certain features described and claimed without
restricting the scope
of these features to the precise numeral ranges provided. Accordingly, these
terms should be
interpreted as indicating that insubstantial or inconsequential modifications
or alterations of
the subject matter described and are considered to be within the scope of the
disclosure.
[0035] The articles "the", "a" and "an" are not necessarily limited to mean
only one, but
rather are inclusive and open ended so as to include, optionally, multiple
such elements.
[0036] "At least one," in reference to a list of one or more entities
should be understood to
mean at least one entity selected from any one or more of the entity in the
list of entities, but
not necessarily including at least one of each and every entity specifically
listed within the list
of entities and not excluding any combinations of entities in the list of
entities. This definition
also allows that entities may optionally be present other than the entities
specifically identified
within the list of entities to which the phrase "at least one" refers, whether
related or unrelated
to those entities specifically identified. Thus, as a non-limiting example,
"at least one of A
and B" (or, equivalently, "at least one of A or B," or, equivalently "at least
one of A and/or
B") may refer, to at least one, optionally including more than one, A, with no
B present (and
optionally including entities other than B); to at least one, optionally
including more than one,
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B, with no A present (and optionally including entities other than A); to at
least one,
optionally including more than one, A, and at least one, optionally including
more than one, B
(and optionally including other entities). In other words, the phrases "at
least one," "one or
more," and "and/or" are open-ended expressions that are both conjunctive and
disjunctive in
operation. For example, each of the expressions "at least one of A, B and C,"
"at least one of
A, B, or C," "one or more of A, B, and C," "one or more of A, B, or C" and "A,
B, and/or C"
may mean A alone, B alone, C alone, A and B together, A and C together, B and
C together,
A, B and C together, and optionally any of the above in combination with at
least one other
entity.
[0037] A method may comprise: providing a coarse sand tailings stream (CST)
comprising sand, fines, clay, water, and bitumen; mixing the CST to liberate
the bitumen from
the sand and disperse the bitumen in the water to form a mixed CST stream; and
separating
the sand from the bitumen to form a bitumen-rich stream.
[0038] By "liberate", it is meant to detach bitumen from sand.
[0039] By "disperse" it is meant to distribute liberated bitumen in the
water.
[0040] The mixing may be any suitable mixing which liberates the bitumen
from the sand
and disperses the bitumen in the water to form a mixed CST stream, to a
sufficient extent to
that the mixed CST may be separated in the separation step. By "mixing", it is
meant to
provide sufficient shear in the aqueous slurry to liberate bitumen from the
sand and increase a
concentration of air bubbles in the system to facilitate bitumen flotation.
The shear may be,
for instance, 2000-14000 s-1. The mixing may comprise mixing in an inline
mixing unit, a
mixing tank, or a length of pipe with pumps.
[0041] The method may further comprise adding a dilution water stream to
the CST prior
to or during the mixing to further disperse the bitumen. Dilution water is
added to further
reduce density and viscosity of the CST stream. The dilution water stream may
be added to
the CST in any suitable amount, for instance 10-30 vol. %, or about 20 vol. %,
based on a
volume of the CST.
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[0042] The method may further comprise adding a gas to the CST prior to or
during the
mixing to further liberate the bitumen from the sand. The method may further
comprise
adding a gas to the mixed CST prior to of during the separating to further
liberate the bitumen
from the sand. The gas may be any suitable gas, and may comprise air, a
nitrogen rich
stream, CO2, a flue gas, or a combination thereof. The air may be dissolved in
water or
injected as a vapor.
[0043] The separating may comprise separating in any suitable unit, for
instance a
flotation vessel, a fluidized bed, an aerated fluidized bed, a hydrocyclone,
or a combination
thereof.
[0044] The bitumen-rich stream may comprise 0.1 to 4 wt. % bitumen.
[0045] The method may further comprise concentrating the bitumen-rich
stream to form a
concentrated bitumen-rich stream. The concentrating may be effected by any
suitable means,
for instance by flotation. The concentrating may be effected using any
suitable unit, for
instance a mechanical flotation cell, a flotation column, or a downcomer-type
flotation unit.
[0046] The CST may have a sand content of 40 to 80 wt. %, or 50 to 70 wt.
%. The CST
may have a D50 of 150-350 microns, or 200 to 300 microns. The CST may have a
temperature of 45 to 55 C. The CST may have a bitumen content of 0.05 to 4 wt.
%, or 0.1 to
3 wt. %. The CST may be from a bottom of a primary separation vessel (PSV).
[0047] Fig. 1 is a schematic of a bitumen extraction method including a
method for
recovering bitumen from coarse sand tailings (CST). An oil sand slurry stream
(102)
comprising mined bituminous ore and water is introduced into a primary
separation vessel
(PSV) (104). The PSV produces bitumen froth (106) for further processing,
middlings (108),
and coarse sand tailings (CST) (110). The middlings (108) are introduced into
flotation cells
(112) producing fine tailings (FT) (114) and recycle froth (116). The FT are
passed through
thickeners (118 and 120) forming thickened tailings (122 and 124), which are
sent to tailings
ponds (126). A recycle stream (128) is also formed, combined with the recycle
froth (116),
and recycled to the PSV (104).
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[0048] The coarse sand tailings stream (CST), comprising sand, fines, clay,
water, and
bitumen, is mixed in a mixer (130) to liberate the bitumen from the sand and
disperse the
bitumen in the water to form a mixed CST stream (132), and is passed to a
separation unit
(134) separating the sand from the bitumen to form a bitumen-rich stream.
[0049] Lab-scale experiments were conducted to investigate the effect of
mixing on
bitumen recovery. A known amount of CST was diluted with 20 vol. % process
water. The
mixture was then exposed to shear for 5 to 10 minutes in a mixing cell
equipped with
impellers. The mixture was then exposed to 5 to 10 minutes of air injection
and mixing in the
same tank. The recovered bitumen in the froth layer was then removed from the
top of the
vessel for bitumen content analysis. The remaining of the mixture was removed
from the
bottom for bitumen content analysis. This test was conducted at two different
mixing rate.
The purpose of the mixing is to disperse the bitumen in the water so that the
bitumen follows
the water through the separation step. The results are illustrated in Figures
2 and 3. Figures 2
is a chart of the effect of mixing on bitumen recovery from CST. Figure 3 is a
chart that
shows the effect of mixing on the percentage of undispersed bitumen in CST.
Higher shear
increases bitumen liberation and decreases the amount of undispersed bitumen.
The benefit of
mixing for this purpose is illustrated by Figure 3.
[0050] It should be understood that numerous changes, modifications, and
alternatives to
the preceding disclosure can be made without departing from the scope of the
disclosure. The
preceding description, therefore, is not meant to limit the scope of the
disclosure. Rather, the
scope of the disclosure is to be determined only by the appended claims and
their equivalents.
It is also contemplated that structures and features in the present examples
can be altered,
rearranged, substituted, deleted, duplicated, combined, or added to each
other. The scope of
the claims should not be limited by particular embodiments set forth herein,
but should be
construed in a manner consistent with the specification as a whole.
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