Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM AND METHOD FOR TREATING TAILINGS
TECHNICAL FIELD
A system and a method for treating tailings resulting from processes for
recovering
bitumen from oil sand.
BACKGROUND OF THE INVENTION
Oil sand is essentially a matrix of bitumen, solid mineral matter, and water.
The bitumen component of oil sand consists of viscous hydrocarbons which
behave
much like a solid at normal in situ temperatures and which act as a binder for
the other components
of the oil sand matrix.
The solid mineral matter component of oil sand consists of sand, rock, silt
and clay.
Coarse solid material is generally considered to include solid mineral matter
having a particle size
greater than or equal to about 44 microns, while fine solid material is
generally considered to
include solid mineral matter having a particle size less than about 44
microns. Sand and rock are
therefore generally present in oil sand as coarse solid material, due to the
relatively large size of
individual particles of sand and rock. Silt and clay are generally present in
oil sand as fine solid
material, due to the relatively small size of individual particles of silt and
clay.
The water component of oil sand consists essentially of a film of connate
water
surrounding the sand in the oil sand matrix, and may also contain particles of
solid mineral matter
within it.
A typical deposit of oil sand will contain about 10% to 12% bitumen and about
3%
to 6% water, with the remainder of the oil sand being made up of solid mineral
matter. Of the total
amount of solid mineral matter, good quality oil sand deposits typically
contain about 14% to 20%
fine solid material and about 80% to 86% coarse solid material. Poorer quality
oil sand deposits
may contain 30% or more fine solid material. Oil sand extracted from the
Athabasca area near
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Fort McMurray, Alberta, Canada averages about 11 % bitumen, 5% water and 84%
solid mineral
matter, with about 15% to 20% of the solid mineral matter being fine solid
material.
Oil sand deposits are mined for the purpose of recovering bitumen from the oil
sand, which bitumen is then upgraded to synthetic crude oil. Several different
approaches to
recovering the bitumen from the oil sand have been developed.
A conventional approach to recovering bitumen from oil sand is the use of a
"hot
water process" in which aggressive thermal action, aggressive chemical action
and aggressive
mechanical action are used to liberate and separate bitumen from the oil sand.
The hot water process includes several steps. In a first step, oil sand is
conditioned
by mixing the oil sand with hot water in a conditioning vessel which
vigorously agitates the
resulting slurry in order to completely disintegrate the oil sand. Sodium
hydroxide (caustic) may
be added to the slurry during conditioning to maintain a slightly basic pH in
the conditioning
vessel, which enhances the disintegration of the oil sand by chemically
dispersing the fine solid
material contained in the oil sand.
In a second step, the slurry of disintegrated oil sand undergoes a primary
separation
process in a primary separation vessel. The primary separation process
separates the slurry into
three streams. A solids stream, containing relatively large amounts of coarse
solid material and
relatively small amounts of bitumen and fine solid material, settles out from
the slurry and is
withdrawn from a lower portion of the primary separation vessel. A bitumen
froth stream,
containing relatively large amounts of air entrained bitumen and relatively
small amounts of solid
mineral matter, floats to the top of the slurry and is withdrawn from an upper
portion of the
primary separation vessel. A middlings stream, containing a relatively small
amount of bitumen
and a relatively large amount of fine solid material, is withdrawn from an
intermediate portion of
the primary separation vessel.
In a third step, the middlings stream is treated or scavenged, typically by
froth
flotation techniques, to recover a portion of the bitumen contained therein.
The bitumen which is
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recovered from the middlings stream may be returned to the primary separation
process or may be
combined with the bitumen froth stream.
In a fourth step, the bitumen froth stream is subjected to a froth treatment
process in
which solid mineral matter and water is separated from the bitumen froth to
produce a "clean" and
"dry" bitumen froth.
Tailings resulting from processes to recover bitumen from oil sand generally
contain water, solid mineral matter, small amounts of residual bitumen, and
other substances as
further impurities. Such tailings may generally be described as "coarse
tailings" if they contain a
relatively high ratio by weight of coarse solid material relative to fine
solid material, and such
tailings may generally be described as "fine tailings" if they contain a
relatively low ratio by
weight of coarse solid material relative to fine solid material.
The various steps of the hot water process result in the production of both
coarse
tailings and fine tailings. Coarse tailings are produced by the primary
separation process as the
solids stream which is withdrawn from the lower portion of the primary
separation vessel, fine
tailings are produced by the froth treatment process as froth treatment
tailings, and fine tailings are
also produced by the treatment or scavenging of the middlings stream as
middlings tailings.
The management of tailings resulting from processes to recover bitumen from
oil
sand presents significant challenges. Although coarse tailings may be
effectively dewatered and
disposed of as backfill or in berms, fine tailings (particularly those
produced from the middlings
stream) tend to be resistant to dewatering and difficult to dispose of in an
environmentally
appealing manner due to the small particle size of fine solid material and the
complexities of the
behaviour of clays and silts. These problems are exacerbated by the virtually
complete
disintegration of oil sand that occurs during the hot water process, which
includes both physical
and chemical dispersal of the fine solid material contained in the oil sand.
Conventionally, most fine tailings produced by the hot water process are
deposited
in tailings ponds, where they undergo a limited degree of settling to form
mature fine tailings
("MFT"), a stable suspension of fine tailings having a solids content by
weight of no greater than
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about 30 percent. Mature fine tailings are not sufficiently solid to support
most uses of the land
occupied by the tailings ponds. In addition, due to their relatively low
solids content (and thus
high water content), mature fine tailings trap large amounts of valuable
process water.
Another approach to recovering bitumen from oil sand is directed at "solids
rejection" as a primary separation technique, in which oil sand is separated
into a bitumen froth
stream and a solids stream, without the production of a middlings stream.
One example of the solids rejection approach is described in Canadian Patent
Application No. 2,030,934 (Strand), Canadian Patent Application No. 2,124,199
(Strand),
Canadian Patent No. 2,123,076 (Strand et al), Canadian Patent Application No.
2,512,106 (Strand),
and Canadian Patent Application No. 2,524,110 (Strand), all of which are
assigned to Bitmin
Resources Inc. (the "Bitmin Process").
In the Bitmin Process, a countercurrent separator drum containing a spiral
ribbon
and mixer elements is utilized for primary separation of the oil sand. Oil
sand is gently rolled from
one end to the other end of the separator drum while warm water circulates in
the opposite
direction. The pH of the warm water in the separator drum is maintained at no
greater than about 7
in order to limit the chemical dispersal of fine solid material contained in
the oil sand.
Two streams are then removed from the opposite ends of the separator drum. A
solids stream containing solid mineral matter (including coarse solid material
and a small amount
of fine solid material), water and a small amount of residual bitumen is
removed from one end of
the separator drum, and a bitumen froth stream containing bitumen, solid
mineral matter (including
fine solid material and a small amount of coarse solid material) and water is
removed from the
other end of the separator drum.
The solids stream, representing coarse tailings, is filtered using a
horizontal belt
filter apparatus to produce dewatered coarse tailings which may be disposed of
as backfill, in
berms, or in some other manner. The bitumen froth stream is further processed
to produce
bitumen froth as a product stream and fine tailings. The fine tailings are
dewatered in a thickener,
following which all or a portion of the dewatered fine tailings may be co-
filtered with the coarse
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tailings to produce non-segregating tailings comprising the coarse tailings
and the fine tailings, or
the fine tailings may be disposed of in some other manner.
A second example of the solids rejection approach is described in Canadian
Patent
No. 2,332,207 (Lavender et al) and Canadian Patent No. 2,358,805 (Lavender et
al), both of which
are assigned to TSC Company Ltd. (the "TSC Process").
In the TSC Process, an assembly of three hydrocyclone packs or clusters
arranged
countercurrently in series are utilized for primary separation of the oil
sand. Two streams are
removed from the hydrocyclone assembly. A solids stream containing solid
mineral matter
(including coarse solid material and some fine solid material), water and a
small amount of
bitumen is removed as an underflow stream from the third hydrocyclone, and a
bitumen froth
stream containing bitumen, solid mineral matter (including fine solid material
and some coarse
solid material) and water is removed as an overflow stream from the first
hydrocyclone.
The solids stream, representing coarse tailings, is filtered using a
horizontal belt
filter apparatus to produce dewatered coarse tailings. The bitumen froth
stream is further
processed in a "product separator" to produce bitumen froth as a product
stream and fine tailings.
The fine tailings are recycled back to the hydrocyclone assembly for further
processing in the
hydrocyclone assembly.
Other approaches to recovering bitumen from oil sand may be based upon
variations of the hot water process, the Bitmin Process and the TSC Process,
or may be based upon
other technologies.
Regardless of the approach which is used to recover bitumen from oil sand, the
production of fine tailings as a result of the recovery process has thus far
been virtually inevitable,
due to the complex composition of oil sand and the challenges faced in
efficiently and effectively
recovering bitumen from oil sand.
As a result, there continues to be a need for processes and systems for
treating
tailings resulting from processes for recovering bitumen from oil sand. There
is a particular need
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for processes and systems for dewatering fine tailings to recover process
water therefrom and to
provide dewatered fine tailings having improved chemical and physical
properties.
SUMMARY OF THE INVENTION
The present invention is directed at systems and methods for treating tailings
resulting from processes for recovering bitumen from oil sand.
The invention includes the use of chemical treatment and a high density
thickener
apparatus for the purpose of producing dewatered fine tailings from partially
dewatered fine
tailings. The invention may also include systems and methods for producing
partially dewatered
fine tailings from fine tailings. The invention may also include systems and
methods for
separating tailings into fine tailings and coarse tailings. The invention may
also include systems
and methods for dewatering coarse tailings to produce dewatered coarse
tailings. The invention
may also include methods for disposing fine tailings and coarse tailings.
Tailings resulting from processes for recovering bitumen from oil sand may
have a
pH above 7 and may contain relatively high concentrations of carbonate ions
and bicarbonate ions.
The purpose of the chemical treatment is to provide the tailings with a water
chemistry which is
favourable for processing of the tailings. For example, the chemical treatment
may remove
carbonate ions and bicarbonate ions from the tailings in order to reduce the
concentration of
carbonate ions and bicarbonate ions in the tailings, and/or the chemical
treatment may lower and/or
neutralize the pH of the tailings.
The chemical treatment may be applied to partially dewatered fine tailings.
The
chemical treatment may be comprised of facilitating cation exchange in the
partially dewatered
fine tailings in order to reduce the activity of clay particles contained
within the partially dewatered
fine tailings. Facilitating cation exchange in the partially dewatered fine
tailings may be comprised
of adding a suitable cation to the partially dewatered fine tailings. The
added cation may be
calcium ions.
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The chemical treatment may be comprised of adjusting the pH of the partially
dewatered fine tailings to a substantially neutral pH and/or maintaining the
pH of the partially
dewatered fine tailings at a substantially neutral pH. The substantially
neutral pH may be between
about 6.5 and about 7.5.
The chemical treatment may be comprised of reducing the pH of the partially
dewatered fine tailings to less than about 6 in order to remove carbonate ions
and bicarbonate ions
from the partially dewatered fine tailings. The chemical treatment may be
comprised of reducing
the pH of the partially dewatered fine tailings to about 4 in order to remove
substantially all
carbonate ions and bicarbonate ions from the partially dewatered fine
tailings.
The chemical treatment may be comprised of reducing the pH of the partially
dewatered fine tailings to produce acidic partially dewatered fine tailings in
order to remove
carbonate ions and bicarbonate ions from the partially dewatered fine tailings
and then increasing
the pH of the acidic partially dewatered fine tailings to a substantially
neutral pH in order to
produce neutralized partially dewatered fine tailings.
The removal of carbonate ions and bicarbonate ions from the partially
dewatered
fine tailings may result in carbon dioxide being evolved from the partially
dewatered fine tailings.
The evolved carbon dioxide may be collected. The collected evolved carbon
dioxide may be
sequestered or may be used or disposed in some other manner.
The pH of the partially dewatered fine tailings may be reduced in any suitable
manner. For example, the pH of the partially dewatered fine tailings may be
reduced by adding an
acid to the partially dewatered fine tailings. The acid may be any suitable
acid, such as for
example sulphuric acid or sulphamic acid.
The pH of the partially dewatered fine tailings may be increased in any
suitable
manner. For example, the pH of the partially dewatered fine tailings may be
increased by adding a
base to the partially dewatered fine tailings.
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The base may be comprised of the cations which are added to the partially
dewatered fine tailings so that adding the base to the partially dewatered
fine tailings results both
in adding the cations to the partially dewatered fine tailings and in
increasing the pH of the
partially dewatered fine tailings. The base may therefore be comprised of an
alkaline substance
containing calcium ions, such as lime (i.e., calcium oxide or calcium
hydroxide).
A flocculant may be added to the chemically treated partially dewatered fine
tailings
in order further to facilitate production of the dewatered fine tailings in
the high density thickener
apparatus.
The high density thickener apparatus may be comprised of any thickener type
apparatus which is capable of producing an underflow stream having a
relatively high solids
content by weight in comparison with the underflow stream produced by a
conventional thickener.
For example, the high density thickener apparatus may be a deep cone paste
thickener.
In a first embodiment, the invention is a method of producing dewatered fine
tailings from partially dewatered fine tailings resulting from a process for
recovering bitumen from
oil sand, the method comprising:
(a) providing the partially dewatered fine tailings, wherein the partially
dewatered fine
tailings are comprised of water, fine solid material and coarse solid
material,
wherein the partially dewatered fine tailings have a ratio by weight of coarse
solid
material to fine solid material of less than about 2 to 1;
(b) reducing the pH of the partially dewatered fine tailings to less than
about 6 in order
to remove carbonate ions and bicarbonate ions from the partially dewatered
fine
tailings, thereby producing acidic partially dewatered fine tailings;
(c) adding calcium ions to the acidic partially dewatered fine tailings in
order to
facilitate cation exchange in the acidic partially dewatered fine tailings
whereby the
calcium ions are exchanged into the acidic partially dewatered fine tailings;
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(d) increasing the pH of the acidic partially dewatered fine tailings to
between about 6.5
and about 7.5, thereby producing neutralized partially dewatered fine tailings
having a substantially neutral pH;
(e) adding a flocculant to the neutralized partially dewatered fine tailings;
and
(f) dewatering the neutralized partially dewatered fine tailings in a high
density
thickener apparatus, thereby producing the dewatered fine tailings.
Preferably the partially dewatered fine tailings have a solids content by
weight
which is at least about 25 percent. Alternatively, preferably the partially
dewatered fine tailings are
froth treatment tailings resulting from the treatment of bitumen froth
produced by the hot water
process.
The pH of the partially dewatered fine tailings may be lowered to about 4 in
order
to facilitate removal of substantially all of the carbonate ions and the
bicarbonate ions from the
partially dewatered fine tailings.
The partially dewatered fine tailings may have a ratio by weight of coarse
solid
material to fine solid material of between about 0.1 to 1 and about 2 to 1.
The partially dewatered
fine tailings may have a ratio by weight of fine solid material to fine solid
material plus water of
between about 0.25 to 1 and about 0.35 to 1. The partially dewatered fine
tailings may have a
density of between about 1250 kg/m3 and about 1450 kg/m3. The partially
dewatered fine tailings
may have a solids content by weight of between about 25 percent and about 50
percent.
The dewatered fine tailings may have a ratio by weight of fine solid material
to fine
solid material plus water of between about 0.45 to 1 and about 0.60 to 1. The
dewatered fine
tailings may have a density of between about 1550 kg/m3 and about 1800 kg/m3.
The dewatered
fine tailings may have a solids content by weight of between about 50 percent
and about 75
percent.
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In a second embodiment, the dewatered fine tailings of the first embodiment
are
produced from fine tailings. As a result, the partially dewatered fine
tailings are first produced
from the fine tailings, and the dewatered fine tailings are then produced from
the partially
dewatered fine tailings.
In the second embodiment, the invention is therefore a method of producing
dewatered fine tailings from fine tailings resulting from a process for
recovering bitumen from oil
sand, the method comprising:
(a) providing the fine tailings, wherein the fine tailings are comprised of
water, fine
solid material and coarse solid material and wherein the fine tailings have a
ratio by
weight of coarse solid material to fine solid material of less than about 2 to
1;
(b) partially dewatering the fine tailings to produce partially dewatered fine
tailings,
wherein the partially dewatered fine tailings have a solids content by weight
of at
least about 25 percent;
(c) reducing the pH of the partially dewatered fine tailings to less than
about 6 in order
to remove carbonate ions and bicarbonate ions from the partially dewatered
fine
tailings, thereby producing acidic partially dewatered fine tailings;
(d) adding calcium ions to the acidic partially dewatered fine tailings in
order to
facilitate cation exchange in the acidic partially dewatered fine tailings
whereby the
calcium ions are exchanged into the acidic partially dewatered fine tailings;
(e) increasing the pH of the acidic partially dewatered fine tailings to
between about 6.5
and about 7.5, thereby producing neutralized partially dewatered fine tailings
having a substantially neutral pH;
(f) adding a flocculant to the neutralized partially dewatered fine tailings;
and
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(g) dewatering the neutralized partially dewatered fine tailings in a high
density
thickener apparatus, thereby producing the dewatered fine tailings.
The pH of the partially dewatered fine tailings may be lowered to about 4 in
order
to facilitate removal of substantially all of the carbonate ions and the
bicarbonate ions from the
partially dewatered fine tailings.
The fine tailings may have a ratio by weight of coarse solid material to fine
solid
material of between about 0.1 to 1 and about 2 to 1. The fine tailings may
have a ratio by weight
of fine solid material to fine solid material plus water of between about 0.05
to 1 and about 0.25 to
1. The fine tailings may have a density of between about 1100 kg/m3 and about
1250 kg/m3. The
fine tailings may have a solids content by weight of between about 15 percent
and about 30
percent.
The fine tailings may be partially dewatered in any manner which results in
the
production of partially dewatered fine tailings having the required
composition as set out above.
For example, the fine tailings may be partially dewatered in a conventional
thickener apparatus.
The conventional thickener apparatus may be comprised of one or more
conventional thickeners.
In a third embodiment, the dewatered fine tailings of the first embodiment are
produced from tailings. As a result, the tailings are first separated into
fine tailings and coarse
tailings, the partially dewatered fine tailings are then produced from the
fine tailings, and the
dewatered fine tailings are then produced from the partially dewatered fine
tailings.
In a method aspect of the third embodiment, the invention is therefore a
method of
producing dewatered fine tailings from tailings resulting from a process for
recovering bitumen
from oil sand, the method comprising:
(a) providing the tailings, wherein the tailings are comprised of water, fine
solid
material and coarse solid material;
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(b) separating the tailings into fine tailings and coarse tailings, wherein
the fine tailings
have a ratio by weight of coarse solid material to fine solid material of less
than
about 2 to 1, and wherein the coarse tailings have a ratio by weight of coarse
solid
material to fine solid material of at least about 20 to 1;
(c) partially dewatering the fine tailings to produce partially dewatered fine
tailings,
wherein the partially dewatered fine tailings have a solids content by weight
of at
least about 25 percent;
(d) reducing the pH of the partially dewatered fine tailings to less than
about 6 in order
to remove carbonate ions and bicarbonate ions from the partially dewatered
fine
tailings, thereby producing acidic partially dewatered fine tailings;
(e) adding calcium ions to the acidic partially dewatered fine tailings in
order to
facilitate cation exchange in the acidic partially dewatered fine tailings
whereby the
calcium ions are exchanged into the acidic partially dewatered fine tailings;
(f) increasing the pH of the acidic partially dewatered fine tailings to
between about 6.5
and about 7.5, thereby producing neutralized partially dewatered fine tailings
having a substantially neutral pH;
(g) adding a flocculant to the neutralized partially dewatered fine tailings;
and
(h) dewatering the neutralized partially dewatered fine tailings in a high
density
thickener apparatus, thereby producing the dewatered fine tailings.
The pH of the partially dewatered fine tailings may be lowered to about 4 in
order
to facilitate removal of substantially all of the carbonate ions and the
bicarbonate ions from the
partially dewatered fine tailings.
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In a system aspect of the third embodiment, the invention is therefore a
system for
producing dewatered fine tailings from fine tailings resulting from a process
for recovering
bitumen from oil sand, the system comprising:
(a) an apparatus for partially dewatering the fine tailings in order to
produce partially
dewatered fine tailings;
(b) a chemical treatment subsystem for chemically treating the partially
dewatered fine
tailings, the chemical treatment subsystem comprising:
(i) a station for reducing the pH of the partially dewatered fine tailings to
less
than about 6 in order to remove carbonate ions and bicarbonate ions from
the partially dewatered fine tailings, thereby producing acidic partially
dewatered fine tailings;
(ii) a station for adding calcium ions to the acidic partially dewatered fine
tailings in order to facilitate cation exchange in the acidic partially
dewatered fine tailings whereby the calcium ions are exchanged into the
acidic partially dewatered fine tailings;
(iii) a station for increasing the pH of the acidic partially dewatered fine
tailings
to between about 6.5 and about 7.5, thereby producing neutralized partially
dewatered fine tailings having a substantially neutral pH; and
(iv) a station for adding a flocculant to the neutralized partially dewatered
fine
tailings; and
(c) a high density thickener apparatus for dewatering the neutralized
partially
dewatered fine tailings to produce the dewatered fine tailings.
The station for reducing the pH of the partially dewatered fine tailings may
reduce
the pH of the partially dewatered fine tailings to about 4 in order to
facilitate removal of
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substantially all of the carbonate ions and the bicarbonate ions from the
partially dewatered fine
tailings.
The coarse tailings may have a ratio by weight of coarse solid material to
fine solid
material of between about 20 to 1 and about 30 to 1. The coarse tailings may
have a ratio by
weight of fine solid material to fine solid material plus water of less than
about 0.10 to 1. The
coarse tailings may have a density of between about 1650 kg/m3 and about 1750
kg/m3. The
coarse tailings may have a solids content by weight of between about 60
percent and about 80
percent.
The tailings may be separated into the fine tailings and the coarse tailings
in any
suitable manner. For example, the tailings may be separated into the fine
tailings and the coarse
tailings by passing the tailings through a cyclone apparatus. The cyclone
apparatus may be
comprised of one or more cyclones and/or stages of cyclones. The cyclone
apparatus may be
comprised of a first stage cyclone and a second stage cyclone.
Separating the tailings into the fine tailings and the coarse tailings may be
comprised of passing the tailings through the first stage cyclone, thereby
producing a first overflow
stream and a first underflow stream and passing the first underflow stream
through the second
stage cyclone, thereby producing a second overflow stream and a second
underflow stream.
The fine tailings may be comprised of the first overflow stream. The fine
tailings
may be further comprised of the second overflow stream. The coarse tailings
may be comprised of
the second underflow stream.
The high density thickener apparatus which is used to dewater the partially
dewatered fine tailings may produce an underflow stream comprised of the
dewatered fine tailings
and an overflow stream. At least a portion of the overflow stream from the
high density thickener
apparatus may be combined with the first underflow stream from the first stage
cyclone before the
first underflow stream is passed through the second stage cyclone.
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The dewatered fine tailings and the coarse tailings may be transported in any
suitable manner for any desired purpose. For example, the dewatered fine
tailings may be
transported in separate pipelines. The dewatered fine tailings and the coarse
tailings may be
transported by separate pipelines to a tailings disposal area.
A flocculant may be added to the coarse tailings at an upstream end of the
pipeline
carrying the coarse tailings in order to inhibit the separation of the fine
solid material and the
coarse solid material in the pipeline.
The density and/or solids content by weight of the coarse tailings may be
adjusted
before the coarse tailings are transported by pipeline. As one example, the
density of the coarse
tailings may be adjusted to be no greater than about 1750 kg/m3 before the
coarse tailings are
transported by pipeline. As a second example, the solids content by weight of
the coarse tailings
may be adjusted to be no greater than about 70 percent before the coarse
tailings are transported by
pipeline.
The density and/or solids content by weight of the coarse tailings may be
adjusted
in any suitable manner. For example, the density and/or solids content by
weight may be adjusted
by diluting the coarse tailings with water. The coarse tailings may be diluted
with water obtained
from the method of the invention or from some other source. For example, the
coarse tailings may
be diluted with at least a portion of the overflow stream from the high
density thickener apparatus.
The bulk fluid velocity of the coarse tailings while being transported through
the
pipeline carrying the coarse tailings may be maintained at or above a minimum
bulk fluid velocity.
The minimum bulk fluid velocity of the coarse tailings being transported
through the pipeline may
be about 3 meters per second.
The coarse tailings may be transported through the pipeline carrying the
coarse
tailings in any suitable manner, having regard to the solids content by weight
and the viscosity of
the coarse tailings. As one example, in some embodiments the coarse tailings
may potentially be
transported through the pipeline carrying the coarse tailings using one or
more centrifugal pumps.
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As a second example, in other embodiments the coarse tailings may be
transported through the
pipeline carrying the coarse tailings using one or more positive displacement
pumps.
Where flocculant is added to the coarse tailings in order to inhibit the
separation of
the fine solid material and the coarse solid material in the pipeline, the
flocculant is preferably
added downstream of the pump or pumps.
Similarly, the dewatered fine tailings may be transported through the pipeline
carrying the dewatered fine tailings in any suitable manner, having regard to
the solids content by
weight and the viscosity of the dewatered fine tailings. As one example, in
some embodiments the
dewatered fine tailings may potentially be transported through the pipeline
carrying the dewatered
fine tailings using one or more centrifugal pumps. As a second example, in
other embodiments the
dewatered fine tailings may be transported through the pipeline carrying the
dewatered fine tailings
using one or more positive displacement pumps.
The invention may also involve methods of disposing dewatered fine tailings
and
coarse tailings resulting from processes for recovering bitumen from oil sand.
The methods of
disposing may be performed using dewatered fine tailings and/or coarse
tailings produced using
the method of the invention, or may be performed using dewatered fine tailings
and/or coarse
tailings which have been produced using some other method or methods.
In a first method of disposing dewatered fine tailings and coarse tailings,
the
invention is a method of disposing dewatered fine tailings and coarse tailings
resulting from a
process for recovering bitumen from oil sand, the method comprising:
(a) providing the dewatered fine tailings, wherein the dewatered fine tailings
are
comprised of water, fine solid material and coarse solid material, wherein the
dewatered fine tailings have a ratio by weight of coarse solid material to
fine solid
material of less than about 2 to 1, and wherein the dewatered fine tailings
have a
solids content by weight of at least about 50 percent;
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CA 02707197 2010-06-21
(b) providing the coarse tailings, wherein the coarse tailings are comprised
of water,
fine solid material and coarse solid material, wherein the coarse tailings
have a ratio
by weight of coarse solid material to fine solid material of at least about 20
to 1, and
wherein the coarse tailings have a solids content by weight of at least about
60
percent;
(c) providing a tailings disposal area; and
(d) depositing the dewatered fine tailings and the coarse tailings in the
tailings disposal
area in alternating layers.
The dewatered fine tailings may have a ratio by weight of fine solid material
to fine
solid material plus water of between about 0.45 to 1 and about 0.60 to 1. The
dewatered fine
tailings may have a density of between about 1550 kg/m3 and about 1800 kg/m3.
The dewatered
fine tailings may have a solids content by weight of between about 50 percent
and about 75
percent.
The coarse tailings may have a ratio by weight of coarse solid material to
fine solid
material of between about 20 to 1 and about 30 to 1. The coarse tailings may
have a ratio by
weight of fine solid material to fine solid material plus water of less than
about 0.10 to 1. The
coarse tailings may have a density of between about 1650 kg/m3 and about 1750
kg/m3. The
coarse tailings may have a solids content by weight of between about 60
percent and about 80
percent.
The dewatered fine tailings may have been subjected to chemical treatment
before
being deposited in the tailings disposal area. The chemical treatment may have
been similar to the
chemical treatment of partially dewatered fine tailings according to other
embodiments of the
invention. The dewatered fine tailings may have been subjected to chemical
treatment during their
production or following their production.
The dewatered fine tailings may therefore contain a relatively low
concentration of
carbonate ions and bicarbonate ions, may have a substantially neutral pH, and
may have been
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CA 02707197 2010-06-21
subjected to cation exchange whereby suitable cations have been exchanged into
the dewatered
fine tailings in order to reduce the activity of clay particles contained in
the dewatered fine tailings.
The suitable cations may be calcium ions.
The dewatered fine tailings and the coarse tailings may have similar and/or
compatible water chemistry when they are deposited in the tailings disposal
area, in order to avoid
adverse chemical reactions between the dewatered fine tailings and the coarse
tailings following
their deposition in the tailings disposal area. For example, the coarse
tailings may contain a
relatively low concentration of carbonate ions and bicarbonate ions. The
coarse tailings may also
have a relatively neutral pH. The coarse tailings may also contain suitable
cations for cation
exchange.
The similar and/or compatible water chemistry of the coarse tailings may be
achieved by subjecting the coarse tailings to some or all of the chemical
treatment which is applied
to the partially dewatered fine tailings according to other embodiments of the
invention. The
coarse tailings may be subjected to chemical treatment either during their
production or following
their production.
Alternatively, water recovered from the partially dewatered fine tailings in
the
course of production of the dewatered fine tailings in accordance with the
methods of the invention
may be added to the coarse tailings in order to achieve some degree of similar
and/or compatible
water chemistry of the coarse tailings, by diluting the coarse tailings with
water from chemically
treated partially dewatered fine tailings.
Achieving a similar and/or compatible water chemistry for the dewatered fine
tailings and the coarse tailings and/or subjecting the coarse tailings to some
or all of the chemical
treatment which is applied to the partially dewatered fine tailings may also
cause the coarse tailings
to flow more easily when deposited in layers in the tailings disposal area and
may also cause the
coarse tailings to exhibit a relatively lower angle of repose in the tailings
disposal area so that the
coarse tailings deposit in the tailings disposal area as a nearly flat layer
over the underlying layer of
dewatered fine tailings.
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The chemical treatment of the coarse tailings may therefore be comprised of:
(a) reducing the pH of the coarse tailings to less than about 6 in order to
remove
carbonate ions and bicarbonate ions from the coarse tailings, thereby
producing
acidic coarse tailings;
(b) adding calcium ions to the acidic coarse tailings in order to facilitate
cation
exchange in the acidic coarse tailings whereby the calcium ions are exchanged
into
the acidic coarse tailings; and
(c) increasing the pH of the acidic coarse tailings to between about 6.5 and
about 7.5,
thereby producing neutralized coarse tailings having a substantially neutral
pH.
A flocculant may be added to the coarse tailings in order further to
facilitate
dewatering of the coarse tailings in the tailings disposal area. Where coarse
tailings which have a
suitable water chemistry or which have been subjected to chemical treatment
are transported in a
pipeline, the flocculant may be added downstream of the pump or pumps.
The first method of disposing dewatered fine tailings and coarse tailings may
be
further comprised of collecting drained water which is drained over time from
the dewatered fine
tailings and the coarse tailings in the tailings disposal area.
The collection of drained water may be performed in any suitable manner. For
example, the tailings disposal area may be provided with a drainage grid
positioned in a lower
portion of the tailings disposal area, and/or the tailings disposal area may
be provided with vertical
drains extending substantially vertically in the tailings disposal area.
The alternating layers of the dewatered fine tailings and the coarse tailings
each
have a thickness. The thickness of the alternating layers may be selected to
enhance the further
dewatering of the dewatered fine tailings. For example, the ratio of the
thickness of the layers of
the dewatered fine tailings to the thickness of the layers of the coarse
tailings may be less than
about 1 to 1 or may be less than about 0.5 to 1.
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In a second method of disposing dewatered fine tailings and coarse tailings,
the
coarse tailings may be dewatered to produce dewatered coarse tailings. The
coarse tailings may be
dewatered in any suitable manner. For example, the coarse tailings may be
dewatered by filtering
using a horizontal belt filter apparatus to produce the dewatered coarse
tailings and belt filter
filtrate. A flocculant may be added to the coarse tailings before the coarse
tailings are filtered.
The belt filter filtrate may be recycled, may be further processed or may be
disposed
or used for some other purpose. For example, all or a portion of the belt
filter filtrate may be
combined with the first underflow stream from the first stage cyclone.
The dewatered coarse tailings may have a solids content by weight of between
about 6 percent and about 12 percent.
The dewatered coarse tailings may be combined with the dewatered fine tailings
in
order to produce combined dewatered tailings. The dewatered coarse tailings
and the dewatered
fine tailings may be combined in any desired proportion to produce the
combined dewatered
tailings.
The combined dewatered tailings may be used as backfill or in berms or may be
used or disposed in some other manner.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the invention will now be described with reference to the
accompanying drawings, in which:
Figure 1 is a process flow diagram depicting a first embodiment of the
invention in
which partially dewatered fine tailings are processed to produce dewatered
fine tailings.
Figure 2 is a process flow diagram depicting a second embodiment of the
invention
in which fine tailings are processed to produce dewatered fine tailings.
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Figure 3 is a process flow diagram depicting a third embodiment of the
invention in
which tailings are processed to produce dewatered fine tailings and coarse
tailings.
Figure 4 is a schematic vertical section drawing of a tailings disposal area
according
to a first method for disposing dewatered fine tailings and coarse tailings in
which dewatered fine
tailings and coarse tailings are deposited in the tailings disposal area in
alternating layers.
Figure 5 is a schematic plan view of the tailings disposal area of Figure 4.
Figure 6 is a process flow diagram including the third embodiment of the
invention
depicted in Figure 3, and a second method for disposing the dewatered fine
tailings and coarse
tailings in which coarse tailings are dewatered to produce dewatered coarse
tailings and in which
the dewatered fine tailings and dewatered coarse tailings are combined to
produce combined
dewatered tailings.
Figure 7 is a theoretical material balance for the process flow diagram of
Figure 1,
wherein the partially dewatered fine tailings are froth treatment tailings.
Figure 8 is a theoretical material balance for the process flow diagram of
Figure 2,
wherein the fine tailings are mature fine tailings.
Figure 9 is a theoretical material balance for the process flow diagram of
Figure 2,
wherein the fine tailings are fine tailings produced by the Bitmin Process.
Figure 10 is a theoretical material balance for the process flow diagram of
Figure 2,
wherein the fine tailings are fine tailings produced by the TSC Process.
Figure 11 is a theoretical material balance for the process flow diagram of
Figure 3,
wherein the tailings are middlings tailings produced by the hot water process.
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Figure 12 is a theoretical material balance for the process flow diagram of
Figure 6,
wherein the tailings are middlings tailings produced by the hot water process.
DETAILED DESCRIPTION
The present invention is directed at methods and systems for treating tailings
resulting from processes for recovering bitumen from oil sand. The invention
may involve the
dewatering of partially dewatered fine tailings to produce dewatered fine
tailings. The invention
may also involve the partial dewatering of fine tailings to produce the
partially dewatered fine
tailings. The invention may also involve the separation of tailings into fine
tailings and coarse
tailings. The invention may also involve the disposal of dewatered fine
tailings, coarse tailings
and/or dewatered coarse tailings.
As used herein, "bitumen" is the hydrocarbon material typically contained in
oil
sand deposits. As used herein, a "bitumen recovery process" includes any
process by which
bitumen is recovered or separated from a material which contains bitumen and
non-hydrocarbon
material such as solid mineral matter, water, etc.
As used herein, "coarse solid material" is solid mineral matter having a
particle size
greater than or equal to about 44 microns, while "fine solid material" is
solid mineral matter
having a particle size less than about 44 microns.
As used herein, "ratio by weight of coarse solid material to fine solid
material" is
the weight of coarse solid material contained in tailings relative to the
weight of fine solid material
contained in the tailings, expressed as a ratio.
As used herein, "fine tailings" are tailings which result from a process to
recover
bitumen from oil sand and which contain a relatively low ratio by weight of
coarse solid material
relative to fine solid material. The ratio by weight of coarse solid material
to fine solid material for
fine tailings may be any ratio which represents that a significant proportion
of fine solid material
relative to coarse solid material is contained in the tailings, such that the
properties of the tailings
are significantly affected by the fine solid material contained therein.
Although the ratio by weight
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CA 02707197 2010-06-21
of coarse solid material to fine solid material for fine tailings may be as
high as about 10 to 1, the
ratio is preferably less than about 6 to 1, and more preferably is less than
about 2 to 1.
As used herein, "coarse tailings" are tailings which result from a process to
recover
bitumen from oil sand and which contain a relatively high ratio by weight of
coarse solid material
relative to fine solid material. The ratio by weight of coarse solid material
to fine solid material for
coarse tailings may be any ratio which represents that a relatively
insignificant proportion of fine
solid material to coarse solid material is contained in the tailings, such
that the properties of the
tailings are not significantly affected by the fine solid material contained
therein.
As used herein, "solids content" is the combined weight of fine solid material
and
coarse solid material contained in tailings relative to the total weight of
the tailings, expressed as a
percentage.
As used herein, "ratio by weight of fine solid material to fine solid material
plus
water" is the weight of fine solid material contained in tailings relative to
the combined weight of
fine solid material and water which is contained in the tailings, expressed as
a ratio.
Several embodiments of the invention are described in the description that
follows,
with reference to Figures 1-12. Where a particular feature of the invention is
common to two or
more embodiments of the invention, the feature is identified by the same
reference number in the
description of such embodiments contained herein.
Referring to Figure 1, there is depicted a process flow diagram for a first
embodiment of the invention in which partially dewatered fine tailings are
processed to produce
dewatered fine tailings.
In the first embodiment depicted in Figure 1, partially dewatered fine
tailings (20)
resulting from a process for recovering bitumen from oil sand are provided as
a feed material. The
partially dewatered fine tailings (20) are comprised of water, fine solid
material and coarse solid
material and have a ratio by weight of coarse solid material to fine solid
material of less than about
2 to 1, and preferably have a solids content by weight of at least about 25
percent.
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In a particular application of the first embodiment, the partially dewatered
fine
tailings (20) may be comprised of froth treatment tailings resulting from the
treatment of bitumen
froth produced by the hot water process. Such froth treatment tailings
typically have a ratio by
weight of coarse solid material to fine solid material of less than about 2 to
1, but may have a
solids content by weight less than 25 percent. The first embodiment of the
invention may be
suitable for use with froth treatment tailings despite a relatively low solids
content by weight due
to the particular composition of froth treatment tailings. For example, froth
treatment tailings may
contain relatively lower amounts of clay particles as fine solid material and
relatively higher
amounts of heavy minerals as fine solid material in comparison with other fine
tailings which may
result from the processing of oil sand, which may reduce the effect of clay
chemistry upon froth
treatment tailings relative to other fine tailings which may result from the
processing of oil sand.
If particular tailings (other than froth treatment tailings) do not meet the
requirements of the partially dewatered fine tailings (20) with respect to the
ratio of coarse solid
material to fine solid material or solids content, they may be processed in
accordance with the
second embodiment of the invention, as described below.
The partially dewatered fine tailings (20) are delivered to a station (22) for
reducing
the pH of the partially dewatered fine tailings (20) to less than about 6,
thereby producing acidic
partially dewatered fine tailings (24). The station (22) may be comprised of
any structure, device
and/or apparatus which is suitable for reducing the pH of the partially
dewatered fine tailings (20).
In the first embodiment depicted in Figure 1, the station (22) is comprised of
an
apparatus (26) for adding an acid to the partially dewatered fine tailings
(20). The acid is
preferably sulphuric acid or sulphamic acid. As depicted in Figure 1, the
station (22) is also
comprised of a mixer (28) for mixing the acid with the partially dewatered
fine tailings (20).
The partially dewatered fine tailings (20) will typically contain equilibrium
amounts
of carbonate species such as carbon dioxide, carbonic acid, carbonate ions and
bicarbonate ions as
a carbonate system. Reducing the pH of the partially dewatered fine tailings
(20) will shift the
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CA 02707197 2010-06-21
equilibrium of the carbonate system and will likely result in the liberation
of carbon dioxide from
the acidic partially dewatered fine tailings (24).
The acidic partially dewatered fine tailings (24) may therefore optionally be
delivered to an apparatus (30) for collecting carbon dioxide (32) which
evolves from the acidic
partially dewatered fine tailings (24). The apparatus (30) for collecting
carbon dioxide (32) may be
comprised of a carbon dioxide collection vessel (not shown), and may be
further comprised of a
compressor (not shown) for compressing the collected carbon dioxide (32)
and/or a condenser (not
shown) for separating water vapour from the collected carbon dioxide (32).
The acidic partially dewatered fine tailings (24) are then delivered to a
station for
adding calcium ions to the acidic partially dewatered fine tailings (24) and
to a station for
increasing the pH of the acidic partially dewatered fine tailings (24) to
between about 6.5 and 7.5,
thereby producing neutralized partially dewatered fine tailings (34) having a
substantially neutral
pH. The stations may be comprised of any structure, device and/or apparatus
which is suitable for
performing the required functions.
The purpose of adding calcium ions to the acidic partially dewatered fine
tailings
(24) is to facilitate cation exchange in the acidic partially dewatered fine
tailings (24) whereby
calcium ions are exchanged into the acidic partially dewatered fine tailings
(24). In most
circumstances, the acidic partially dewatered fine tailings (24) will contain
large amounts of
sodium as a cation which is adsorbed to the fine solid material, and the
addition of calcium ions
will result in the calcium ions being substituted into the acidic partially
dewatered tailings (24) in
place of the sodium ions. This in turn will lower the activity of the clay
particles in the acidic
partially dewatered fine tailings (24) and enhance the ability to dewater the
neutralized partially
dewatered fine tailings (34).
The reason for increasing the pH of the acidic partially dewatered fine
tailings is
that the neutralized partially dewatered fine tailings (34) will be more
readily dewatered than the
acidic partially dewatered fine tailings (24).
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The stations for adding calcium to the acidic partially dewatered fine
tailings (24)
and for increasing the pH of the acidic partially dewatered fine tailings (24)
may be separate
stations or may be comprised of a single station. Furthermore, adding calcium
ions to the acidic
partially dewatered fine tailings (24) and increasing the pH of the acidic
partially dewatered fine
tailings (24) may be comprised of separate acts or a single combined act.
In the first embodiment depicted in Figure 1, adding calcium ions to the
acidic
partially dewatered fine tailings (24) and increasing the pH of the acidic
partially dewatered fine
tailings (24) is performed as a single combined act at a single station (36)
by adding to the acidic
partially dewatered fine tailings (24) an alkaline calcium containing
substance such as lime (i.e.,
calcium oxide and/or calcium hydroxide), which simultaneously adds calcium
ions to the acidic
partially dewatered fine tailings (24) and increases the pH of the acidic
partially dewatered fine
tailings (24). In the first embodiment, the station (36) is therefore
comprised of an apparatus (38)
for adding lime to the acidic partially dewatered fine tailings (24). The
station (36) may be further
comprised of a mixer (not shown) for mixing the lime with the acidic partially
dewatered fine
tailings (24).
Following addition of the lime, the neutralized partially dewatered fine
tailings (34)
will have a water chemistry which is favorable for dewatering of the
neutralized partially
dewatered fine tailings (34) by flocculation.
The neutralized partially dewatered fine tailings (34) are therefore delivered
to a
station (40) for adding a flocculant to the neutralized partially dewatered
fine tailings (34). The
flocculant may be comprised of any suitable flocculant and may be added in any
suitable amount.
The station (40) may be comprised of any structure, device and/or apparatus
which is suitable for
adding a flocculant to the neutralized partially dewatered fine tailings (34).
In the first embodiment, the station (40) is comprised of an apparatus (42)
for
adding the flocculant to the neutralized partially dewatered fine tailings
(34). The station (40) may
be further comprised of a mixer (not shown) for mixing the flocculant with the
neutralized partially
dewatered fine tailings (34).
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CA 02707197 2010-06-21
As described above and as depicted in Figure 1, the flocculant is added to the
neutralized partially dewatered fine tailings (34) after the calcium ions have
been added to the
acidic partially dewatered fine tailings (24) and after the pH of the acidic
partially dewatered fine
tailings (24) has been increased to provide the neutralized partially
dewatered fine tailings (34).
These three acts could, however be performed in any order and, referring to
Figure
1, a single mixer (44) may be provided for mixing both the lime and the
flocculant with the acidic
partially dewatered fine tailings (24) after their addition to the acidic
partially dewatered fine
tailings (24).
The station (22) for lowering the pH of the partially dewatered fine tailings
(20), the
combined station (36) for adding calcium ions to the acidic partially
dewatered fine tailings (24)
and for increasing the pH of the acidic partially dewatered fine tailings (24)
and the station (40) for
adding a flocculant to the neutralized partially dewatered fine tailings (34)
therefore comprise a
chemical treatment subsystem (45) which chemically treats the partially
dewatered fine tailings
(20) to prepare them for dewatering.
As a result, after passing through the mixer (44) the neutralized partially
dewatered
fine tailings (34) are delivered to a high density thickener apparatus (46)
for dewatering of the
neutralized partially dewatered fine tailings.
The high density thickener apparatus (46) may be comprised of any apparatus or
combination of apparatus which is capable of producing an underflow stream
which has a
relatively high solids content by weight relative to the underflow stream
typically produced by a
conventional thickener apparatus. Typically a high density thickener apparatus
(46) will exhibit a
relatively large height to diameter ratio relative the height to diameter
ratio of a conventional
thickener apparatus.
The high density thickener apparatus (46) may be comprised of an apparatus of
the
type used to produce paste consistency material from tailings, where paste
consistency material or
"paste" is defined as a mixture of coarse solid material, fine solid material
and water which has a
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CA 02707197 2010-06-21
relatively high solids content, exhibits very little water bleed, and is
relatively non-segregating.
Such apparatus are often referred to as a deep cone paste thickener.
One exemplary deep cone paste thickener is the EIMCOTM Deep ConeTM Thickener,
which is manufactured by FLSmidth Dorr-Oliver Eimco. Features of the EIMCOTM
Deep ConeTM
Thickener are described in U.S. Patent No. 5,718,510 (Farmery et al) and U.S.
Patent No.
5,806,977 (Farmery et al). The EIMCOTM Deep ConeTM Thickener is described as
having an
ability to accommodate up to 20 times the solids mass flow and 10 times the
hydraulic loading of
conventional thickener apparatus.
The EIMCOTM Deep ConeTM Thickener is described as a deep cylindrical tank
which is designed to maintain a deep bed of settled solids and to maximize
gravity compression,
thereby achieving discharge solids concentrations which can approach the
limits of flowability.
The EIMCOTM Deep ConeTM Thickener is provided with a mechanical rake mechanism
which is
designed to meet unusually high torque requirements which are necessitated by
the deep bed of
settled solids and by the high viscosity of the underflow as it approaches a
paste consistency. The
rake mechanism is also designed to keep thickened solids flowing toward the
discharge outlet of
the thickener and to assist with the releasing of water from the deep bed of
settled solids.
A second exemplary deep cone paste thickener is the E-CATTM Clarifier-
Thickener,
also manufactured by FLSmidth Dorr-Oliver Eimco. The E-CATTM Clarifier-
Thickener is
described as a deep cylindrical tank with a steep-sided bottom cone which
serves as a compaction
zone for flocculated solid material. The E-CATTM Clarifier-Thickener has no
moving parts. Free
water which is displaced from the solids bed in the compaction zone is
directed to a central
dewatering cone and recycle column where it rises to be returned to the inlet
feedwell to provide
influent dilution.
The high density thickener apparatus (46) is preferably an apparatus of the
type
referred to as a deep cone paste thickener. Although a deep cone paste
thickener is a preferred
high density thickener apparatus (46) for use in the invention, it is noted
that the purpose of the
invention and of the high density thickener apparatus (46) is not to produce a
paste as defined
above and having the properties listed above, but to produce an underflow
stream which has a
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relatively high solids content by weight relative to the solids content by
weight which is achievable
using a conventional thickener apparatus.
The high density thickener apparatus (46) therefore produces an underflow
stream
which is comprised of dewatered fine tailings (48). Referring to Figure 1, the
high density
thickener apparatus (46) also produces an overflow stream (50) which is
comprised of water and
small amounts of residual bitumen and fine solid material.
The underflow stream comprising the dewatered fine tailings (48) will
typically
have a solids content of at least about 50 percent and will typically have a
ratio of fine solid
material to fine solid material plus water of at least about 0.45 to 1. The
dewatered fine tailings
(48) may be disposed in a manner as described below, and due to the water
chemistry of the
dewatered fine tailings (48), further dewatering of the dewatered fine
tailings (48) may be achieved
following disposal of the dewatered fine tailings (48).
Depending upon its composition, the overflow stream (50) may be recycled as
make-up process water for the bitumen recovery process, may be used as a
diluent in the bitumen
recovery process or in the process of the invention, or may be used or
disposed of in some other
suitable manner.
The overflow stream (50) may optionally be further processed before use and/or
disposal in order to remove residual bitumen or other impurities therefrom.
Further processing of
the overflow stream (50) is desirable where the overflow stream (50) contains
appreciable amounts
of residual bitumen.
The overflow stream (50) from the high density thickener apparatus (46) may
also
be comprised of two separate streams (not shown), wherein a relatively less
dense overflow stream
contains appreciable amounts of residual bitumen and other less dense material
and wherein a
relatively more dense overflow stream is comprised of relatively "clean"
water. Such a two-phase
overflow stream may be particularly desirable where the feed material for the
first embodiment is
froth treatment tailings, since froth treatment tailings typically contain an
amount of hydrocarbon
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CA 02707197 2010-06-21
solvent or diluent and/or diluted residual bitumen which is preferably
separated from the overflow
stream (50).
Referring to Figure 2, there is depicted a process flow diagram for a second
embodiment of the invention in which fine tailings are processed to produce
dewatered fine
tailings (48).
In the second embodiment depicted in Figure 2, fine tailings (60) resulting
from a
process for recovering bitumen from oil sand are provided as a feed material.
The fine tailings
(60) are comprised of water, fine solid material and coarse solid material,
and have a ratio by
weight of coarse solid material to fine solid material of less than about 2 to
1. The fine tailings
(60) which are provided as the feed material for the second embodiment of the
invention will
generally have a lower solids content than the partially dewatered fine
tailings (20) which are
provided as the feed material for the first embodiment of the invention. In
other words, the fine
tailings (60) will generally have a solids content by weight which is less
than about 30 percent.
The fine tailings (60) may result from any process for recovering bitumen from
oil
sand. For example, the fine tailings (60) may be comprised of or be a
component of middlings
tailings resulting from the hot water process, may be comprised of mature fine
tailings (MFT)
produced by the hot water process or some other process, or may be comprised
of tailings
produced by treating the bitumen froth stream obtained in a solids rejection
process such as the
Bitmin Process or the TSC Process. If such tailings do not meet the
requirements of the fine
tailings (60) with respect to the ratio of coarse solid material to fine solid
material, they may be
processed in accordance with the third embodiment of the invention, as
described below.
The essential difference between the second embodiment of the invention as
depicted in Figure 2 and the first embodiment of the invention as depicted in
Figure 1 is that the
second embodiment accepts fine tailings (60) as a feed material, while the
first embodiment
requires partially dewatered fine tailings (20) as the feed material. The
second embodiment
therefore provides a two stage process which involves partial dewatering of
fine tailings (60) to
produce partially dewatered fine tailings (20), followed by processing of the
partially dewatered
fine tailings (20) to produce dewatered fine tailings (48), while the first
embodiment provides a
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one stage process which involves processing of partially dewatered fine
tailings (20) to produce
dewatered fine tailings (48).
The partial dewatering of the fine tailings (60) to produce the partially
dewatered
fine tailings (20) may be performed using any dewatering process and/or
apparatus which is
suitable for producing partially dewatered fine tailings (20) having a solids
content by weight of at
least about 25 percent from the fine tailings (60).
Preferably, the partial dewatering of the fine tailings (60) is performed
using a
thickener apparatus (62). As depicted in Figure 2, the partial dewatering of
the fine tailings (60) is
performed using a conventional thickener apparatus as the thickener apparatus
(62).
As used herein, a "conventional thickener apparatus" is comprised of a
separation
vessel which provides a relatively large settling/flotation area relative to
the depth of the solids bed
and which typically includes a rake mechanism for aiding in dewatering of the
solids bed and/or
for directing the solids toward the solids outlet of the vessel. A
conventional thickener is
distinguished from a deep cone paste thickener in that a conventional
thickener is typically capable
of producing an underflow stream which has a relatively lower solids content
than the underflow
stream produced by a deep cone paste thickener, but is well suited for
partially dewatering feed
streams which have a relatively low initial solids content.
The fine tailings (60) may optionally be processed to recover residual bitumen
therefrom before being subjected to partial dewatering to produce the
partially dewatered fine
tailings (20). The residual bitumen may be recovered using any suitable
process and/or apparatus.
Referring to Figure 2, the fine tailings (60) may optionally be delivered to a
flotation apparatus
(64) where the fine tailings may be subjected to froth flotation to recover
residual bitumen
therefrom.
The necessity or desirability of recovering residual bitumen from the fine
tailings
(60) will depend upon the origin of the fine tailings (60) and upon economics.
For example, if the
fine tailings (60) are comprised of mature fine tailings (MFT) or some other
type of tailings which
may contain economically significant amounts of residual bitumen, it may be
desirable to recover
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residual bitumen from the fine tailings (60) before subjecting the fine
tailings (60) to partial
dewatering.
Following the optional flotation apparatus (64), the fine tailings (60) are
delivered
to a station (66) for adding a flocculant to the fine tailings (60). The
flocculant may be comprised
of any suitable flocculant and may be added in any suitable amount. The
station (66) may be
comprised of any structure, device and/or apparatus which is suitable for
adding a flocculant to the
fine tailings (60).
In the second embodiment, the station (66) is comprised of an apparatus (68)
for
adding the flocculant to the fine tailings (60). The station (66) is also
comprised of a mixer (70)
for mixing the flocculant with the fine tailings (60).
After passing through the mixer (70), the fine tailings (60) are delivered to
the
thickener apparatus (62) for partial dewatering of the fine tailings (60).
The thickener apparatus (62) produces an underflow stream which is comprised
of
the partially dewatered fine tailings (20). The thickener apparatus (62) also
produces an overflow
stream (72) which is comprised of water and small amounts of bitumen and fine
solid material.
The underflow stream comprising the partially dewatered fine tailings (20)
will
typically have a solids content of at least about 25 percent and will
therefore be suitable for
dewatering in accordance with the first embodiment of the invention as
depicted in Figure 1. If,
however, the underflow stream does not have a solids content of at least about
25 percent, the
underflow stream may be further processed to achieve a solids content of at
least about 25 percent
before being dewatered in accordance with the first embodiment of the
invention as depicted in
Figure 1.
Depending upon its composition, the overflow stream (72) may be recycled as
make-up process water for the bitumen recovery process, may be used as a
diluent in the bitumen
recovery process or in the process of the invention, or may be used or
disposed of in some other
manner. The overflow stream (72) may be particularly valuable as make-up
process water for the
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bitumen recovery process because it may contain significant amounts of heat
and because it may
have a water chemistry which is similar to and/or compatible with the water
chemistry of the
bitumen recovery process.
Optionally, the overflow stream (72) may be further processed to recover
residual
bitumen therefrom or to further clarify the water comprising the overflow
stream (72) before using
or disposing of the overflow stream (72). For example, the overflow stream
(72) may be subjected
to froth flotation in a flotation apparatus (74) in order to recover residual
bitumen therefrom.
Referring to Figure 3, there is depicted a process flow diagram for a third
embodiment of the invention in which tailings are processed to produce
dewatered fine tailings
(48).
In the third embodiment depicted in Figure 3, tailings (80) resulting from a
process
for recovering bitumen from oil sand are provided as a feed material. The
tailings (80) are
comprised of water, fine solid material and coarse solid material. The
tailings (80) which are
provided as the feed material for the third embodiment of the invention will
generally have a
relatively higher ratio by weight of coarse solid material to fine solid
material than the fine tailings
(60) or the partially dewatered fine tailings (20) which are provided as the
feed material for the
second embodiment and the first embodiment of the invention, respectively. In
other words, the
tailings (80) will generally have a ratio by weight of coarse solid material
to fine solid material
which is greater than about 2 to 1.
The tailings (80) may result from any process for recovering bitumen from oil
sand.
For example, the tailings (80) may be comprised of middlings tailings
resulting from the hot water
process.
The essential difference between the third embodiment of the invention as
depicted
in Figure 3 and the second embodiment of the invention as depicted in Figure 2
is that the third
embodiment accepts tailings (80) as a feed material, while the second
embodiment requires fine
tailings (60) as the feed material. The third embodiment therefore provides a
three stage process
which involves separation of the tailings (80) into fine tailings (60) and
coarse tailings, partial
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dewatering of the fine tailings (60) to produce partially dewatered fine
tailings (20), followed by
processing of the partially dewatered fine tailings (20) to produce dewatered
fine tailings (48).
The separation of the tailings (80) into the fine tailings (60) and the coarse
tailings
may be performed using any process and/or apparatus which is suitable for
separating the tailings
(80) to produce fine tailings (60) having a ratio by weight of coarse solid
material to fine solid
material of less than about 2 to 1 and coarse tailings having a ratio by
weight of coarse solid
material to fine solid material of at least about 20 to 1.
Preferably, the separation of the tailings (80) into the fine tailings (60)
and the
coarse tailings is performed by passing the tailings (80) through a cyclone
apparatus (82). As
depicted in Figure 3, the separation of the tailings (80) into the fine
tailings (60) and the coarse
tailings is performed using a first stage cyclone (84) and a second stage
cyclone (86) as the cyclone
apparatus (82). The cyclone apparatus (82) may be comprised of fewer than two
cyclones or more
than two cyclones as long as the cyclone apparatus (82) is capable of
producing the fine tailings
(60) and coarse tailings which have the required ratios of coarse solid
material to fine solid
material.
The cyclones (84,86) may be comprised of any suitable cyclone or hydrocyclone
apparatus which is capable of producing an underflow stream comprising
relatively coarse tailings
and an overflow stream comprising relatively fine tailings.
Referring to Figure 3, the tailings (80) are delivered to the first stage
cyclone (84).
The tailings (80) are passed through the first stage cyclone (84) to produce a
first overflow stream
(88) and a first underflow stream (90).
The first underflow stream (90) is delivered to the second stage cyclone (86).
The
first underflow stream (90) is passed through the second stage cyclone (86) to
produce a second
overflow stream (92) and a second underflow stream (94).
All or a portion of the overflow stream (50) from the high density thickener
apparatus (46) may be added to the first underflow stream (90) before the
first underflow stream
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(90) is passed through the second stage cyclone (86), to dilute the first
underflow stream (90) in
order to improve the operation of the second stage cyclone (86) and/or to
impart to the first
underflow stream (90) a water chemistry which is similar to and/or compatible
with the water
chemistry of the dewatered fine tailings (48).
All or a portion of the overflow stream (72) from the thickener apparatus (62)
may
also be added to the first underflow stream (90), in order to dilute the first
underflow stream (90).
The first overflow stream (88) and the second overflow stream (92) are
combined to
provide a combined overflow stream (96). Typically this combined overflow
stream (96) will have
a ratio by weight of coarse solid material to fine solid material which is
less than about 2 to 1 and
will therefore be suitable for processing in accordance with the second
embodiment of the
invention as depicted in Figure 2. If, however, the combined overflow stream
(96) does not have a
ratio by weight of coarse solid material to fine solid material which is less
than about 2 to 1, the
combined overflow stream (96) may be further processed to achieve a ratio by
weight of coarse
solid material to fine solid material which is less than about 2 to 1 before
the combined overflow
stream (96) is processed in accordance with the second embodiment of the
invention as depicted in
Figure 2.
If the combined overflow stream (96) has a ratio by weight of coarse solid
material
to fine solid material which is less than about 2 to 1, the fine tailings (60)
will be comprised of the
first overflow stream (88) and the second overflow stream (92) and will be
processed in
accordance with the second embodiment of the invention as depicted in Figure
2.
The second underflow stream (94) will typically have a ratio by weight of
coarse
solid material to fine solid material which is at least about 20 to 1. If,
however, the second
underflow stream (94) does not have a sufficiently high ratio by weight of
coarse solid material to
fine solid material, the second underflow stream (94) may be further processed
to achieve a ratio
by weight of coarse solid material to fine solid material which is at least
about 20 to 1.
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If the second underflow stream (94) has a ratio by weight of coarse solid
material to
fine solid material which is at least about 20 to 1, the coarse tailings (98)
will be comprised of the
second underflow stream (94).
The third embodiment of the invention as depicted in Figure 3 will therefore
result
in the production of the dewatered fine tailings (48) having a ratio by weight
of coarse solid
material to fine solid material which is less than about 2 to 1 and a solids
content by weight which
is at least about 50 percent. Preferably the dewatered fine tailings (48) will
also have a ratio by
weight of fine solid material to fine solid material plus water of at least
about 0.45 to 1.
The third embodiment of the invention as depicted in Figure 3 will also result
in the
production of the coarse tailings (98) having a ratio by weight of coarse
solid material to fine solid
material which is at least about 20 to 1. Preferably the coarse tailings (98)
have a solids content by
weight of at least about 60 percent.
The dewatered fine tailings (48) and the coarse tailings (98) may be used or
disposed of in any manner, either separately or together.
For example, the coarse tailings (98) can be used and/or disposed of as
backfill or in
berms, and the dewatered fine tailings could be deposited in a tailings
disposal area such as a
tailings pond.
Preferably, however, the dewatered fine tailings (48) and the coarse tailings
(98) are
used and/or disposed of together according to one of two alternate methods.
A first method of disposing the dewatered fine tailings (48) and the coarse
tailings
(98) will be described with reference to Figures 3-5. A second method of
disposing the dewatered
fine tailings (48) and the coarse tailings (98) will be described with
reference to Figure 6.
The first method of disposing the dewatered fine tailings (48) and the coarse
tailings
(98) may be used with any fine tailings having a ratio by weight of coarse
solid material to fine
solid material of less than about 2 to 1 and a solids content by weight of at
least about 50 percent,
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and with coarse tailings having a ratio by weight of coarse solid material to
fine solid material of at
least about 20 to 1 and a solids content by weight of at least about 60
percent.
Preferably the first method of disposing is used with dewatered fine tailings
(48)
which contain relatively low amounts of carbonate ions and bicarbonate ions,
which have been
subjected to cation exchange whereby calcium ions have been exchanged into the
dewatered fine
tailings (48) in order to reduce the activity of clay particles contained in
the dewatered fine tailings
(48) and which have a substantially neutral pH.
Preferably the first method of disposing is used with coarse tailings (98)
which have
a water chemistry which is similar to and/or compatible with the water
chemistry of the dewatered
fine tailings (48) and/or with coarse tailings (98) which have been subjected
to some or all of the
chemical treatment which may be applied to partially dewatered fine tailings
(20) according to
other embodiments of the invention. In other words, preferably the coarse
tailings (98) contain
relatively low amounts of carbonate ions and bicarbonate ions. The coarse
tailings (98) may also
contain amounts of a suitable cation for cation exchange into the dewatered
fine tailings (48) and
may have a substantially neutral pH.
In Figures 3-5 and the description which follows, the first method of
disposing is
used with dewatered fine tailings (48) and coarse tailings (98) which have
been produced using the
third embodiment of the method of the invention.
Referring to Figures 3-5, the first method of disposing the dewatered fine
tailings
(48) and the coarse tailings (98) involves depositing the tailings (48,98) in
a tailings disposal area
(110). The first method utilizes the coarse tailings (98) to provide
compressive loading on the
dewatered fine tailings (48) in the tailings disposal area (110) to assist in
achieving further
dewatering of the dewatered fine tailings (48) in the tailings disposal area
(110).
Referring to Figure 3, the method according to the third embodiment of the
invention may be performed some distance from the tailings disposal area
(110). As a result, it
may be necessary to transport the dewatered fine tailings (48) and the coarse
tailings (98) to the
tailings disposal area (110).
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The tailings (48,98) may be transported to the tailings disposal area (110) in
any
suitable manner, such as, for example by truck or by rail. Preferably,
however, the tailings (48,98)
are transported to the tailings disposal area (110) by a fine tailings
pipeline (112) and by a coarse
tailings pipeline (114) respectively.
The dewatered fine tailings (48) have a ratio by weight of coarse solid
material to
fine solid material of less than about 2 and therefore do not contain large
amounts of coarse solid
material. In addition, the dewatered fine tailings (48) will probably have a
solids content by weight
of between about 50 percent and about 70 percent. As a result, the dewatered
fine tailings (48)
may be pumped through the fine tailings pipeline (112) using a fine tailings
pump (116). It is
expected that the dewatered fine tailings (48) will exhibit relatively low
viscosity and/or shear
strength and may exhibit shear thinning. As a result, it is expected by way of
example that the fine
tailings pump (116) may be comprised of one or more centrifugal pumps operated
in the laminar
flow regime.
The coarse tailings (98) have a ratio by weight of coarse solid material to
fine solid
material of at least about 20 to 1 and a solids content by weight exceeding
about 60 percent. The
composition of the coarse tailings (98) therefore presents potential
challenges for transporting the
coarse tailings (98) through the coarse tailings pipeline (114).
As one example, if the solids content by weight of the coarse tailings (98)
exceeds
about 70 percent, the coarse tailings (98) may be difficult to pump. As a
result, if the solids
content by weight of the coarse tailings (98) exceeds about 70 percent, the
coarse tailings (98) may
be diluted with water to reduce their solids content. Preferably the coarse
tailings (98) are diluted
with at least a portion of the overflow stream (50) from the high density
thickener apparatus (46),
since the overflow stream (50) will have a water chemistry which is similar to
the water chemistry
of the dewatered fine tailings (48).
As a second example, if the bulk velocity of the coarse tailings (98) through
the
coarse tailings pipeline (114) is too low, some coarse solid material and fine
solid material may
settle out from the coarse tailings (98) in the coarse tailings pipeline
(114), thereby clogging the
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coarse tailings pipeline (114). As a result, the bulk velocity of the coarse
tailings (98) through the
coarse tailings pipeline (114) is preferably maintained to be at least about 3
meters per second.
The coarse tailings (98) are pumped through the coarse tailings pipeline (114)
using
a coarse tailings pump (118).
In order to further limit the amount of coarse solid material and fine solid
material
which settles out from the coarse tailings (98) in the coarse tailings
pipeline (114), and in order to
control the deposition angle of the coarse tailings (98) in the tailings
disposal area (110), a station
(120) for adding a flocculant to the coarse tailings (98) is preferably
provided downstream of the
coarse tailings pump (118). The flocculant may also further facilitate
dewatering of the coarse
tailings (98) in the tailings disposal area (110). The flocculant may be
comprised of any suitable
flocculant and may be added in any suitable amount. The station (120) may be
comprised of any
structure, device and/or apparatus which is suitable for adding a flocculant
to the coarse tailings
(98).
In the third embodiment, the station (120) is comprised of an apparatus (121)
for
adding the flocculant to the coarse tailings (98). The station (120) may be
further comprised of a
mixer (not shown) for mixing the flocculant with the coarse tailings (98).
By controlling the solids content by weight of the coarse tailings (98) and
the
tendency of coarse solid material and fine solid material to settle out from
the coarse tailings (98),
it is expected by way of example that the coarse tailings pump (118) may be
comprised of one or
more centrifugal pumps.
Once the dewatered fine tailings (48) and the coarse tailings (98) have been
transported to the tailings disposal area (110), they may be deposited in the
tailings disposal area
(110).
Referring to Figure 4 and Figure 5, the tailings disposal area (110) is
comprised of a
tailings pond (122). The tailings disposal area (110) is further comprised of
a collection system
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(124) for collecting drained water which drains from the dewatered fine
tailings (48) and the coarse
tailings (98) in the tailings disposal area (110).
The collection system (124) may be comprised of any structure, device or
apparatus
which is capable of collecting the water which is drained from the tailings
(48,98). As depicted in
Figure 4 and Figure 5, the collection system (124) is comprised of a drainage
grid (126) and a
system of vertical drains (128).
The drainage grid (126) is comprised of a network of interconnected drains
(130)
and pipes (132) which is positioned in a lower portion (134) of the tailings
disposal area (110).
The drains (130) communicate with the tailings pond (122) and are spaced so
that they are
distributed relatively evenly throughout the planar area covered by the
tailings pond (122). The
pipes (132) collect drained water from the drains (130) into one or more
drainage conduits (136)
which facilitate removal of the drained water from the tailings disposal area
(110). The drainage
conduits (136) are connected with other conduits (not shown) and/or water
storage facilities (not
shown) which enable recycling of the drained water back to the bitumen
recovery process, to the
methods of the invention, or to other uses.
Each of the vertical drains (128) extends substantially vertically in the
tailings pond
(122). The system of vertical drains (128) is arranged so that the vertical
drains (128) are
distributed relatively evenly throughout the planar area covered by the
tailings pond (122). The
vertical drains (128) provide permeable vertical channels in the tailings pond
(122) which enhance
the ability of drained water to move vertically downward through the tailings
pond (122) toward
the drainage grid (126).
The first method of disposing the dewatered fine tailings (48) and the coarse
tailings
(98) is comprised of depositing the dewatered fine tailings (48) and the
coarse tailings (98) in the
tailings pond (122) in alternating layers. As depicted in Figure 5, the
alternating layers begin with
a layer of the coarse tailings (98) in the lower portion (134) of the tailings
disposal area (110)
which cover the drainage grid (126) so that the coarse tailings (98) provide a
relatively permeable
area in the immediate vicinity of the drainage grid (126).
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The thicknesses of the alternating layers of dewatered fine tailings (48) and
coarse
tailings (98) will depend upon the composition and properties of the dewatered
fine tailings (48)
and the coarse tailings (98), upon the relative amounts of dewatered fine
tailings (48) and coarse
tailings (98) which are available, and upon the objectives for the tailings
disposal area (110) with
respect to further dewatering of the dewatered fine tailings (48) and the
coarse tailings (98).
Preferably the thickness of the layers of the dewatered fine tailings (48) is
less than
the thickness of the layers of the coarse tailings (98). More preferably, the
ratio of the thickness of
the layers of the dewatered fine tailings (48) to the thickness of the layers
of the coarse tailings (98)
is less than about 0.5 to 1. By providing relatively thin layers of the
dewatered fine tailings (48),
further dewatering of the dewatered fine tailings (48) may be enhanced, and by
providing relatively
thick layers of the coarse tailings (98), the compressive loading of the
coarse tailings (98) upon the
dewatered fine tailings (48) can also be enhanced.
For example, the thickness of the layers of the dewatered fine tailings (48)
may be
about 1 meter and the thickness of the layers of the coarse tailings (98) may
be about 2.5 meters.
The coarse tailings (98) will be very permeable due to the relatively high
ratio by weight of coarse
solid material to fine solid material contained therein. The dewatered fine
tailings (48) will be
relatively permeable due to the addition of the calcium ions and resulting
cation exchange and due
to the substantially neutral pH of the dewatered fine tailings (48).
As a result, the weight of the relatively thick layers of coarse tailings (98)
upon the
relatively thin layers of the dewatered fine tailings will result in further
dewatering of the
dewatered fine tailings (48) as well as further dewatering of the coarse
tailings (98). The drained
water which drains from the dewatered fine tailings (48) and the coarse
tailings (98) will drain
downward to the drainage grid (126), assisted by the system of vertical drains
(128) extending
substantially vertically through the tailings pond (122).
It is expected that the first method for disposing the dewatered fine tailings
(48) and
the coarse tailings (98) will over a relatively short period of time
substantially increase the solids
content by weight of both the dewatered fine tailings (48) and the coarse
tailings (98).
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It is also expected that by combining at least a portion of the overflow
stream (50)
from the high density thickener apparatus (46) with the first underflow stream
(90) from the first
stage cyclone (84), and/or by diluting the coarse tailings (98) with at least
a portion of the overflow
stream (50) from the high density thickener apparatus (46) as depicted in
Figure 3, the water
chemistry of the coarse tailings (98) will be very similar to the water
chemistry of the dewatered
fine tailings (48), with the result that the dewatered fine tailings (48)
should not experience any
significant degradation of their ability to be further dewatered due to
contact with the coarse
tailings (98).
Referring to Figure 6, the second method of disposing the dewatered fine
tailings
(48) and the coarse tailings (98) involves dewatering the coarse tailings (98)
and then combining
the dewatered fine tailings (48) and the dewatered coarse tailings to produce
combined dewatered
tailings, so that the dewatered fine tailings (48) and the coarse tailings
(98) can be disposed of
together as the combined dewatered tailings.
In the second method of disposing the dewatered fine tailings (48) and the
coarse
tailings (98), the dewatered fine tailings (48) and the coarse tailings (98)
are produced in
accordance with the third embodiment of the invention as depicted in Figure 3.
In the second method of disposing the dewatered fine tailings (48) and the
coarse
tailings (98), the coarse tailings (98) may first be delivered to a station
(150) for adding a
flocculant to the coarse tailings (98). The flocculant may be comprised of any
suitable flocculant
and may be added in any suitable amount. The station (150) may be comprised of
any structure,
device and/or apparatus which is suitable for adding a flocculant to the
coarse tailings (34).
As depicted in Figure 6, the station (150) is comprised of an apparatus (152)
for
adding the flocculant and may be further comprised of a mixer (not shown) for
mixing the
flocculant with the coarse tailings (98).
Depending upon the properties of the coarse tailings (98), the addition of the
flocculant to the coarse tailings (98) may not be required, in which case the
station (150) for
adding a flocculant to the coarse tailings (98) either may not be provided or
may be bypassed.
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In either case (i.e., either with or without a flocculant), the coarse
tailings (98) are
delivered to a horizontal belt filter apparatus (154). The coarse tailings
(98) are filtered by the
horizontal belt filter apparatus (154) to produce dewatered coarse tailings
(156) and belt filter
filtrate (158).
The belt filter filtrate (158) may be recycled back to the bitumen recovery
process
or to the method of the invention, may be further processed, and/or may be
disposed or used for
some other purpose. As depicted in Figure 6, the belt filter filtrate (158) is
recycled and combined
with the first underflow stream (90) from the first stage cyclone (84),
thereby diluting the first
underflow stream (90) and enhancing the performance of the second stage
cyclone (86).
The dewatered coarse tailings (156) will typically have a solids content by
weight of
at least about 85 percent. The dewatered coarse tailings (156) are transported
in a suitable manner,
such as by conveyor or by truck, to a tailings mixing facility (160).
The dewatered fine tailings (48), comprising the underflow stream from the
high
density thickener apparatus (46), are also transported in a suitable manner to
the tailings mixing
facility (160). As in the first method of disposing the dewatered fine
tailings (48) and the coarse
tailings (98), the dewatered fine tailings (48) may, for example, be
transported to the tailings
mixing facility (160) using the fine tailings pump (116).
The tailings mixing facility (160) may be comprised of any area or structure
which
is suitable for combining the dewatered coarse tailings (156) and the
dewatered fine tailings (48).
For example, the tailings mixing facility (160) may be comprised simply of a
tailings pile where
the tailings (48,156) can be mixed together using loaders and/or other
earthmoving equipment, or
the tailings mixing facility (160) may be comprised of a mixing apparatus.
The dewatered coarse tailings (156) and the dewatered fine tailings (48) are
mixed
together at the tailings mixing facility (160) in suitable proportions to
produce combined
dewatered tailings (162). The suitable proportions of the dewatered coarse
tailings (156) and the
dewatered fine tailings (48) is dependent upon the relative amounts of the
dewatered coarse
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tailings (156) and the dewatered fine tailings (48) which are available and
upon the desired
properties and use of the combined dewatered tailings (162). Leftover
dewatered coarse tailings
(156) and/or dewatered fine tailings (48) may be disposed of according to the
first method of
disposing described above or may be used and/or disposed in some other manner.
Due to the high solids content by weight of the dewatered coarse tailings
(156) and
the relatively high solids content by weight of the dewatered fine tailings
(48), the combined
dewatered tailings (162) will typically not be saturated, and will therefore
typically undergo only
minimal additional drainage.
The combined dewatered tailings (162) may be disposed of as fill material or
in
berms or may be used and/or disposed in some other manner.
As can be seen, the first method of disposing the dewatered fine tailings (48)
and
the coarse tailings (98) offers the potential of further dewatering of the
dewatered fine tailings (48)
and thus recovery of additional drained water, while the second method of
disposing the dewatered
fine tailings (48) and the coarse tailings (98) offers the potential of
reducing or eliminating the
need for a dedicated tailings disposal area (110).
Theoretical material balances for the first embodiment, the second embodiment,
the
third embodiment and for the first and second methods for disposing the
dewatered fine tailings
(48) and the coarse tailings (98) are provided in the following examples, with
reference to Figures
7-12.
Example 1
Example 1 relates to the first embodiment of the invention.
The process flow diagram for Example 1 is provided in Figure 1. A theoretical
material balance for Example 1 is provided in Figure 7.
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In the first embodiment of the invention, the feed material is partially
dewatered
fine tailings (20). In Example 1, the partially dewatered fine tailings (20)
are froth treatment
tailings produced by a froth treatment process in conjunction with the hot
water process for
recovering bitumen from oil sand. The material quantities in Example 1 are
based upon the
estimated quantity of froth treatment tailings which would result from the
processing of 5000
tonnes per hour of oil sand using the hot water process.
In Example 1, the overflow stream (50) from the high density thickener
apparatus
(46) is comprised of two separate streams, wherein one of the streams contains
appreciable
amounts of residual bitumen and the other of the streams is comprised of
relatively clean water.
Example 2
Example 2 relates to the second embodiment of the invention.
The process flow diagram for Example 2 is provided in Figure 2. A theoretical
material balance for Example 2 is provided in Figure 8.
In the second embodiment of the invention, the feed material is fine tailings
(60).
In Example 2, the fine tailings (60) are mature fine tailings (MFT) resulting
from the hot water
process for recovering bitumen from oil sand. The material quantities in
Example 2 are based
upon the processing of 3000 m3/hour of mature fine tailings.
In Example 2, the fine tailings (60) are subjected to froth flotation in the
flotation
apparatus (64) before being delivered to the thickener apparatus (62), in
order to recover residual
bitumen which is contained within the mature fine tailings.
Example 3
Example 3 relates to the second embodiment of the invention.
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The process flow diagram for Example 3 is provided in Figure 2. A theoretical
material balance for Example 3 is provided in Figure 9.
In Example 3, the fine tailings (60) are fine tailings resulting from the
Bitmin
Process for recovering bitumen from oil sand. The material quantities in
Example 3 are based
upon are based upon the estimated quantity of fine tailings which would result
from the processing
of 5000 tonnes per hour of oil sand using the Bitmin Process.
In Example 3, the fine tailings (60) are not subjected to froth flotation in
the
flotation apparatus (64) before being delivered to the thickener apparatus
(62), since the fine
tailings (60) do not contain significant amounts of residual bitumen (in
comparison with the
mature fine tailings of Example 2).
Example 4
Example 4 relates to the second embodiment of the invention.
The process flow diagram for Example 4 is provided in Figure 2. A theoretical
material balance for Example 4 is provided in Figure 10.
In Example 4, the fine tailings (60) are fine tailings resulting from the TSC
Process
for recovering bitumen from oil sand. The material quantities in Example 4 are
based upon are
based upon the estimated quantity of fine tailings which would result from the
processing of 5000
tonnes per hour of oil sand using the TSC Process.
In Example 4, the fine tailings (60) are not subjected to froth flotation in
the
flotation apparatus (64) before being delivered to the thickener apparatus
(62), since the fine
tailings (60) do not contain significant amounts of residual bitumen (in
comparison with the
mature fine tailings of Example 2).
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Example 5
Example 5 relates to the third embodiment of the invention and to the first
method
of disposing dewatered fine tailings (48) and coarse tailings (98).
The process flow diagram for Example 5 is provided in Figure 3. A theoretical
material balance for Example 5 is provided in Figure 11.
In the third embodiment of the invention, the feed material is tailings (80).
In
Example 5, the tailings (80) are middlings tailings resulting from the hot
water process for
recovering bitumen from oil sand. The material quantities in Example 5 are
based upon are based
upon the estimated quantity of fine tailings which would result from the
processing of 5000 tonnes
per hour of oil sand using the hot water process.
In Example 5, the tailings (80) are processed to produce dewatered fine
tailings (48)
and coarse tailings (98). In Example 5, the overflow stream (72) from the
thickener apparatus (62)
is subjected to froth flotation in the flotation apparatus (74) to recover
residual bitumen. In
Example 5, the fine tailings (60) are comprised of the first overflow stream
(88) from the first
stage cyclone (84) and the second overflow stream (92) from the second stage
cyclone (86). In
Example 5, the first underflow stream (90) from the first stage cyclone (84)
is diluted before
entering the second stage cyclone (86) with all or a portion of the overflow
stream (50) from the
high density thickener apparatus (46) and with a portion of the overflow
stream (72) from the
thickener apparatus (72). In the theoretical material balance of Figure 11,
all of the overflow
stream (50) from the high density thickener apparatus (46) is used to dilute
the first underflow
stream (90) from the first stage cyclone (84).
In Example 5, the dewatered fine tailings (48) and the coarse tailings (98)
are
disposed using the first method of disposing the dewatered fine tailings (48)
and coarse tailings
(98), by being deposited in alternating layers in the tailings disposal area
(110). The dewatered
fine tailings (48) and the coarse tailings (98) undergo further dewatering in
the tailings disposal
area, thereby producing the settled coarse tailings and the settled fine
tailings referred to in Figure
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11, and thereby facilitating the reclamation of additional water from the
dewatered fine tailings
(48) and the coarse tailings (98).
Example 6
Example 6 relates to the third embodiment of the invention and to the second
method for disposing dewatered fine tailings (48) and coarse tailings (98).
The process flow diagram for Example 6 is provided in Figure 6. A theoretical
material balance for Example 6 is provided in Figure 12.
In the third embodiment of the invention, the feed material is tailings (80).
In
Example 6, the tailings (80) are middlings tailings resulting from the hot
water process for
recovering bitumen from oil sand. The material quantities in Example 6 are
based upon are based
upon the estimated quantity of fine tailings which would result from the
processing of 5000 tonnes
per hour of oil sand using the hot water process.
In Example 6, the tailings (80) are processed to produce dewatered fine
tailings (48)
and coarse tailings (98). In Example 5, the overflow stream (72) from the
thickener apparatus (62)
is subjected to froth flotation in the flotation apparatus (74) to recover
residual bitumen. In
Example 6, the fine tailings (60) are comprised of the first overflow stream
(88) from the first
stage cyclone (84) and the second overflow stream (92) from the second stage
cyclone (86). In
Example 6, the first underflow stream (90) from the first stage cyclone (84)
is diluted before
entering the second stage cyclone (86) with all or a portion of the overflow
stream (50) from the
high density thickener apparatus (46) and with all of the belt filter filtrate
(158). In the theoretical
material balance of Figure 12, all of the overflow stream (50) from the high
density thickener
apparatus (46) is used to dilute the first underflow stream (90) from the
first stage cyclone (84).
In Example 6, the dewatered fine tailings (48) and the coarse tailings (98)
are
disposed using the second method of disposing the dewatered fine tailings (48)
and coarse tailings
(98), by producing the dewatered coarse tailings (156) and then combining the
dewatered fine
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tailings (48) and the dewatered coarse tailings (156) to produce the combined
dewatered tailings
(162).
The invention therefore provides for the production of dewatered fine tailings
(48)
having a relatively high solids content by weight and a potential for further
dewatering using
conventional dewatering techniques, through the use of chemical treatment and
specific methods
and combinations of apparatus.
While not intending to be bound by theory, it is believed that the chemical
treatments which are used in producing the dewatered fine tailings (48)
facilitate the production of
non-interacting flocs of fine solid material having reduced face to face
repulsion and less tendency
to adopt edge to face "house of cards" structures.
As a result, such non-interacting flocs may be relatively more dense and
compact in
comparison with flocs produced using conventional dewatering methods, and
dewatered fine
tailings comprising such non-interacting flocs may potentially be further
dewatered. It is estimated
that following further dewatering of the dewatered fine tailings which are
produced using the
invention, the final solids content by weight of the fine tailings may be
about 80 percent.
The invention also provides for the production of dewatered fine tailings (48)
from
tailings (80), from fine tailings (60) or from partially dewatered fine
tailings (20) resulting from
processes for the recovery of bitumen from oil sand. The invention also
provides for the
production of coarse tailings (98) from tailings (80) and for the production
of dewatered coarse
tailings (156) from coarse tailings (98). Finally, the invention provides for
the disposal of
dewatered fine tailings (48) and coarse tailings (98) in a single tailings
disposal area (110) and for
the production and disposal of combined dewatered tailings (162) comprising
dewatered coarse
tailings (156) and dewatered fine tailings (48).
The methods for disposing the dewatered fine tailings (48) and the coarse
tailings
(98) involve either depositing the dewatered fine tailings (48) and the coarse
tailings (98) in
alternating layers or dewatering of the coarse tailings (98) to produce
dewatered coarse tailings
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(156) and combining the dewatered coarse tailings (156) and the dewatered fine
tailings (48) to
produce combined dewatered tailings (162).
In either method for disposing, it is believed to be desirable that the coarse
tailings
(98) have a water chemistry which is similar to and/or compatible with the
water chemistry of the
dewatered fine tailings (48). The similar and/or compatible water chemistry
may be achieved by
diluting the coarse tailings (98) with water recovered in the course of
producing the dewatered fine
tailings (48) using the methods of the invention or by chemically treating the
coarse tailings (98).
It is believed that similar and/or compatible water chemistry is desirable for
at least
two reasons.
First, a similar and/or compatible water chemistry reduces the potential for
adverse
chemical reactions between the dewatered fine tailings (48) and the coarse
tailings (98). For
example, it is believed that under anaerobic conditions, clays contained in
the dewatered fine
tailings (48) and the coarse tailings (98) may disperse if the coarse tailings
(98) contain relatively
high amounts of carbonate ions and bicarbonate ions relative to the dewatered
fine tailings (48).
Second, a similar and/or compatible water chemistry may improve the handling
properties of the coarse tailings (98). For example, the coarse tailings (98)
may flow relatively
more easily and may exhibit a relatively low angle of repose, which is
particularly advantageous
for the first method of disposing the dewatered fine tailings (48) and the
coarse tailings (98).
In this document, the word "comprising" is used in its non-limiting sense to
mean
that items following the word are included, but items not specifically
mentioned are not excluded.
A reference to an element by the indefinite article "a" does not exclude the
possibility that more
than one of the elements is present, unless the context clearly requires that
there be one and only
one of the elements.
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