Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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RELOCATABLE COUNTERCURRENT DECANTATION SYSTEM
The present invention relates generally to a process and a circuit for
producing a first product comprising bitumen, fines and water and a second
product comprising coarse solids, fines and water, from oil sand. More
particularly, the present invention relates to a process and a circuit
comprising a
countercurrent decantation assembly having a plurality of sand/liquid
separators
that may be mobile or relocatable.
BACKGROUND OF THE INVENTION
Oil sand, such as is mined in the Fort McMurray region of Alberta,
generally comprises water-wet sand grains held together by a continuous matrix
of viscous bitumen. It lends itself to liberation of the sand grains from the
bitumen, preferably by slurrying the oil sand in hot process water, allowing
the
bitumen to move to the aqueous phase. Oil sand slurrying generally takes place
in large, stationary slurry preparation or mixing towers. Once oil sand slurry
is
formed, the slurry is pumped through a pipeline at least 2.3 km long to the
bitumen extraction facility.
During pipelining of oil sand slurry to extraction facility, the oil sand
slurry
undergoes conditioning, namely, ablation of oil sand lumps, liberation of
bitumen
from the oil sand, entrainment of the bitumen by air bubbles, and the
coalescence of bitumen droplets. This allows the bitumen to be separated out
more readily. The conditioned slurry is then temporarily retained under
quiescent
conditions in a large gravity separation vessel (referred to as the "PSV")
housed
at the bitumen extraction facilities, where the sand settles and is removed as
an
underflow, together with some bitumen and water, and the aerated bitumen,
contaminated with water and solids, including fines, rises and is recovered as
froth.
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These deep cone PSVs are very large, approximately 30 meters in
diameter, so as to provide the large separation area required to process 8000
tonne per hour oil sand. The PSV is also 35 meters tall to assure free flow of
coarse solids to the centrally located bottom discharge. When filled with oil
sand
slurry, each PSV weighs up to 25,000 tonnes and is suspended on 12 friction
piles extending -40 meters below grade.
Bitumen extraction facilities housing these large PSVs have traditionally
been located removed from the actively mined mine sites. Further, as the
actively mined mine sites become more remote as the mine faces recede, the
distance that the oil sand slurry must travel from the mine face to extraction
and
the distance that the separated sand must travel to sand disposal sites
frequently
exceeds 10 km. It is expensive to transport massive quantities of sand over
long
distances by pipeline, considering the high energy requirement per ton/km, the
high cost of maintenance due to abrasion, as well as the capital cost of
pipelines,
pumps and auxiliary equipment.
The present invention uses a countercurrently operating assembly
comprising a plurality of sand/liquid separators, which assembly is preferably
relocatable, to separate out sand from bitumen, which may be configured so as
to minimize the distance of sand transportation. Further, the present
invention
recycles water from tailings deposits thereby conserving water and reducing
the
need for heated water.
The present invention provides at least one of the following benefits:
1. reduced cost of sand transportation;
2. increased bitumen recovery from oil sand; and
3. reduced heat energy requirement, due to the displacement of warm
middlings in the tailings stream with cold "beach run-off", i.e., water from
tailings deposition ponds.
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SUMMARY OF THE INVENTION
In accordance with one broad aspect of the invention, there is provided a
process line for separating oil sand slurry comprising coarse solids, fine
solids
(fines), bitumen and water into a first product comprising bitumen, fines and
water and a second product comprising coarse solids, fines and water, said
process line having:
= a pipeline for transporting and conditioning oil sand slurry;
= a plurality of countercurrently operating solid/liquid separators arranged
in
series along the pipeline, each separator operatively connected to the
pipeline and to each other, and each separator producing an underflow
and an overflow, wherein the underflow of one separator is fed to the next
separator in series and the overflow of each separator is fed to the
preceding separator, the underflow of the last separator being the second
product and the overflow from the first separator being the first product;
and
= a tailings deposition pond for receiving the second product, whereby,
when the coarse solids settle out from the water in the tailings deposition
pond, the water is recycled back to the last separator.
In one embodiment the process line further has a bitumen cleaning means
operative to receive the first product and remove a portion of the fines and
water
therefrom to produce clean bitumen froth. In one embodiment, the bitumen
cleaning means comprises a gravity separation vessel such as a primary
separation vessel (PSV), wherein the bitumen floats to the top of the vessel
to
form clean bitumen froth and the fines settle to the bottom of the vessel. In
another embodiment, the bitumen cleaning means comprises an inclined plate
settler and a flotation cell in series, each producing an overflow and an
underflow
and operatively interconnected so that the flotation cell receives the
underflow
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from the inclined plate settler and the overflow from the flotation cell is
recycled
back to the inclined plate settler, the overflow from the inclined plate
settler being
the clean bitumen froth.
In accordance with another broad aspect of the invention, there is
provided a process line for separating oil sand slurry comprising coarse
solids,
fine solids (fines), bitumen and water into a first product comprising
bitumen,
fines and water and a second product comprising coarse solids, fines and
water,
said process line having:
= a pipeline for transporting and conditioning oil sand slurry; and
= a plurality of countercurrently operating solid/liquid separators arranged
in
series along the pipeline, each separator operatively connected to the
pipeline and to each other, and each separator producing an underflow
and an overflow;
wherein the underflow of one separator is fed through the pipeline for further
conditioning to the next separator in series and the overflow of each
separator is
fed to the preceding separator, the underflow of the last separator being the
second product and the overflow from the first separator being the first
product.
In accordance with another broad aspect of the invention, there is
provided a circuit for producing a first product comprising bitumen, fines and
water and a second product comprising coarse solids, fines and water, from
mined oil sand, said circuit having:
= a slurry preparation unit for mixing mined oil sand with hot water to
produce an oil sand slurry comprising coarse solids, fines, bitumen and
water;
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= a pipeline operatively connected with the slurry preparation unit for
receiving the oil sand slurry and transporting it while simultaneously
conditioning it;
= a countercurrently operating assembly comprising a plurality of solid/liquid
separators in series, each separator forming a lighter overflow and a
heavier underflow, operatively connected to the pipeline for separating
most of the coarse solids from the bitumen, wherein the overflow from the
first separator in the series is the first product and the underflow from the
last separator in the series is the second product; and
= a tailings deposition pond for receiving the second product, whereby,
when the coarse solids settle out from the water in the tailings deposition
pond, the water is recycled back to the last separator in the series.
In one embodiment, the circuit is located at the mine site. The phrase
"mine site" refers to an area of land presently undergoing open pit mining to
excavate oil sand (mine pit) and which has one or more mine faces and one or
more tailings retention facilities or tailings deposition ponds, which may be
dike-
enclosed areas or mined-out pits. In another embodiment, the circuit is
located
at the mine face. In a further embodiment, the slurry preparation unit and the
solid/liquid separators are of a transportable size and relocatable using
skids or
the like, so that the slurry preparation unit, pipeline and solid/liquid
separators are
all capable of moving closer to the mine face as the mine face recedes.
In one embodiment, the countercurrently operating assembly comprises at
least two separators in series, the separators being selected from a group
consisting of gravity settlers, inclined plate settlers, cycloseparators,
hydrocyclones, or combinations thereof. In another embodiment, the
countercurrently operating assembly comprises at least three separators in
series, the separators being selected from the group consisting of gravity
settlers,
inclined plate settlers, cycloseparators, hydrocyclones, or combinations
thereof.
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In accordance with another broad aspect of the invention, there is
provided a process for separating oil sand slurry comprising coarse solids,
fines,
bitumen and water, into a first product comprising bitumen, fines and water
and a
second product comprising coarse solids, fines and water, having the steps of:
= providing in series at least two solid/liquid separators, each separator
having an inlet, an overflow outlet and an underflow outlet and each
separator producing a lighter overflow stream and a heavier underflow
stream;
= feeding oil sand slurry to the inlet of the first separator in the series
and
removing the overflow stream through the overflow outlet of the first
separator to produce the first product;
= removing the underflow stream of the first separator through its underflow
outlet and feeding it to the inlet of the next separator in the series;
= recycling the overflow of said next separator and each subsequent
separator to the inlet of the preceding separator and feeding the underflow
of said next separator and each subsequent separator to the inlet of the
following separator;
= removing the underflow of the iast separator to produce the second
product and depositing the second product into a tailings deposition pond;
and
= allowing the solids to separate from the water and recycling the water from
the tailings deposition ponds back to the inlet of the last separator in the
series.
In one embodiment, the process further has the step of removing most of
the fines in the first product by gravity separation to produce cleaned
bitumen
froth. In one embodiment, fines are removed from the first product using a
gravity separation vessel such as a primary separation vessel (PSV). In
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another embodiment, fines are removed using in series an inclined plate
settler and a flotation cell.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic showing one embodiment of a process line for
separating oil sand slurry into a first product comprising bitumen, fines and
water
and a second product comprising coarse solids, fines and water.
FIG. 2 is a schematic showing another embodiment of a process line for
separating oil sand slurry into a first product comprising bitumen, fines and
water
and a second product comprising coarse solids, fines and water.
FIG. 3 is a schematic showing one embodiment of a circuit for producing a
first product comprising bitumen, fines and water and a second product
comprising coarse solids, fines and water, from mined oil sand.
FIG. 4 is a schematic showing another embodiment of a circuit for
producing a first product comprising bitumen, fines and water and a second
product comprising coarse solids, fines and water, from mined oil sand.
FIG. 5 is a side view of a cycloseparator, which may be used in the
process line and circuit of the present invention, showing the internal
section of
the vortex finder in dotted lines.
FIG. 6 is a sectional side view showing and inclined plate settler.
FIG. 7 is a perspective view of a rotary digester, which may be used in the
circuit to form oil sand slurry.
FIG. 8 is a view similar to FIG. 7, showing part of the drum wall broken
away to display internal lifters.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention is exemplified by the following embodiments.
With reference first to FIG. 1, process line 1 comprises a series of
countercurrently operating separators. More particularly, the separators used
are
inclined plate settlers 20, 21, 22, one of which is shown in more detail in
FIG. 6.
Process line 1 further comprises pipeline 10, which pipeline is divided into
three
pieces 10a, 10b and 10c. Pipeline 10b interconnects first inclined plate
settler 20
to second inclined plate settler 21 and pipeline 10c interconnects second
inclined
plate settler 22 to third inclined plate settler 23.
Pipeline 10a feeds oil sand slurry to inclined plate settler 20, the first
settler in the series. Overflow 30 is produced, which is referred to herein as
the
first product, which first product comprises bitumen, fines and water and is
often
referred to as lean froth. If desired, much of the fines and water in overflow
30
can be removed by delivering it to inclined plate settler 40 to produce an
overflow
50 of clean bitumen froth and an underflow 52, also referred to in the
industry as
middlings. Underflow 52 is then delivered to a flotation cell 41 where most of
the
bitumen still remaining will float and be removed as overflow 51, or flotation
froth.
Overflow 51 is recycled back to inclined plate separator 40 to ensure that
virtually
all of the bitumen is recovered as a clean froth product. Underflow 53 can be
disposed of either in tailings deposit 60 or further processed into thickened
fine
tails or paste, using a fine tails thickener (not shown).
Underflow 33 from inclined plate settler 20 is optionally aerated and
pumped via pump 70 through pipeline 10b to second inclined separator 21.
Further conditioning of the underflow oil sand slurry occurs in pipeline 10b
and
thus additional bitumen is released, aerated and coalesced. Overflow 31 from
second inclined separator 21 is recycled back to first inclined separator 20
and
underflow 34 is again optionally aerated and pumped via pump 72 through
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pipeline 10c for further conditioning to a third inclined plate settler 22.
Overflow
32 from the third inclined plate settler 22 is recycled back to the second
inclined
plate settler 21 and underflow 35, the second product, which comprises washed
coarse sand, fines and water, is pumped via pump 74 and deposited into
tailings
deposit 60. Water 62, also referred to as beach run-off, can be recycled back
to
the third inclined plate settler 22, thereby conserving water and reducing
heat
losses, as described in more detail below.
Separation of solids from bitumen and water can be understood more
clearly with reference to FIG. 6, showing first inclined plate settler 20 as
an
example. The oil sand slurry (or underflow) is fed into the bottom inlet 99 of
inclined plate separator 20 from pipeline 10 (not shown). As the inclined
plate
settler 20 fills with slurry, the coarse solids or sand start to separate out
due to
gravity and the coarse solids drop along the internal plates 101 to the bottom
of
the settler. Coarse solids are then withdrawn through the outlet 102 as
underflow. The bitumen, fines and water, leave through the top outlet 103 as
overflow.
FIG. 2 is a schematic of another embodiment of a process line of the
present invention. Process line 2 comprises, in series, countercurrently
operating separators, more particularly, two inclined plate settlers 20, 21,
and a
centrifugal cycloseparator 44, which cycloseparator is shown in more detail in
FIG. 5. With reference now to FIG. 5, cycloseparator 44 is generally a
cylindrical,
hollow vessel 147 having an internal chamber 150, tangential inlet 153 at the
upstream end, and central vortex finder outlet 156 (for overflow) and
peripheral
outlet 159 (for underflow) at the downstream end.
With reference again to FIG. 2, underflow 34 from the second inclined
plate settler 21 is optionally aerated and pumped via pump 72 to the inlet of
cycloseparator 44. Underflow 34 spins as it advances longitudinally through
the
cycloseparator's vessel chamber. The heavier fraction concentrates outwardly
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and leaves the vessel chamber as an underflow stream 135 (second product
comprising mainly sands, fines and water) through the peripheral outlet.
Underflow stream 135 is then deposited into tailings deposit 62. The lighter
fraction (comprising mainly water and fines and some residual bitumen)
concentrates inwardly and leaves as overflow 132 through the vortex finder
outlet
and is recycled back to the second inclined plate settler 21.
FIG. 3 presents a conceptual flow-diagram of a circuit for producing a first
product comprising bitumen, fines and water and a second product comprising
coarse solids, fines and water, from mined oil sand, using relocatable
equipment
located at the mine site 304. Mine site 304 comprises mine pit 306, mine face
300 and tailings deposit 302. The circuit involves strip mining oil sand 301
at one
side of the mine site 304 and producing an oil sand slurry with hot water in a
relocatable slurry preparation unit 308, located close to mining face.
A relocatable slurry preparation unit useful in the present invention is a
rotary digester shown in more detail in FIG. 7 and FIG. 8. Rotary digester 91
is a
rotatable drum having internal lifters 93, drive means 94 and a trommel screen
95. The oil sand and water are fed into a feed box 96 and are tumbled within
the
drum 92 to mix them and condition the produced slurry. The screen 95 removes
oversize and the screened slurry is pumped through a pipeline by pump 97.
Referring again to FIG. 3, the oil sand slurry prepared in slurry preparation
unit 308 is pumped through pipeline 310, which comprises pipeline pieces 310a,
310b, 310c, which pipeline 310 is within the mined-out-pit and configured
along
the shortest practical route, to a sand storage site or tailings deposition
pond
302. It is understood that for a few initial years, tailings must be deposited
outside the mined-out pit. However, as soon as the mined out pit becomes large
enough, tailings are stored in the pit.
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Considering the scale of mining and tailings storage operations, the slurry
pipeline will extend several kilometres. The countercurrently operating
assembly
312 comprises three separators 314, 316, 318, which separators can be gravity
settlers, inclined plate settlers, cycloseparators, hydrocyclones or
combinations
thereof. The first separator 314 is preferably situated at least 2.0 to 2.5 km
away
from the slurry preparation unit 308 to maximize the benefits of pipeline
conditioning and thus pipeline 310a is preferably at least 2.0 km. However,
the
circuit provides an opportunity for further conditioning and bitumen recovery
in
pipelines 310b and 310c. To take best advantage of the additional pipeline
conditioning, the last separator 318 should be located close to the tailings
deposition pond 302. As mining faces and tailings deposition ponds advance,
the last separator 318 is relocated to the front end of the countercurrently
operating assembly and the pipeline is rearranged accordingly.
In operation, using as an example a countercurrently operating assembly
comprising three separators as shown in FIG. 3, wherein each separator
produces an underflow stream and an overflow stream, pipeline conditioned
slurry is mixed with the overflow stream of the second separator 316 and
introduced into the first separator 314, where coarse solids, rocks,
undigested
lumps and bitumen/sand aggregates are concentrated to form first stage
underflow, along with some middlings and un-aerated bitumen. A first stage
underflow pump (not shown) transfers the first stage underflow stream to the
second separator 316 and controls its rate. The rate of the first stage
overflow is
the difference between the feed and the underflow rates and it comprises the
excess middlings, finer solid fractions, most I ibe rated/ae rated bitumen, as
well as
some un-aerated, small bitumen droplets that normally follow middlings.
The first stage underflow is mixed with the third stage overflow of the third
separator 318 and fed into the second separator 316, where settling coarse
solids and other large objects, along with some middlings and bitumen, are
withdrawn as second stage underflow and passed to the third separator 318.
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The middlings and bitumen overflow of the second separator 316 is then passed
to the first separator 314.
The second stage underflow stream from the second separator 316 is
then mixed with water from the tailings deposition pond 302, which water is
also
referred to as cold beach run-off, and passed to third separator 318. The
third
stage underflow from third separator 318 is then pipelined to tailings
deposition
pond 302, where coarse sand settles and excess liquid run-off pools at the
foot of
the tailings pile. Run-off is held in a small pool equipped with a floating
run-off
pumping barge. It is important to limit the size of the pool as to avoid the
formation of large volumes of Mature Fine Tails.
All fines and bitumen that failed to be captured in the settled coarse sand
within a few days of storage are collected with the run-off and mixed with the
second stage underflow to feed the third separator 318. Hence, the second
stage underflow is diluted with cold run-off, resulting in the bitumen content
and
temperature being reduced. However, the third stage overflow becomes
enriched in bitumen and warmed up by comparison with the beach run-off. This
process of dilution of warmer/bitumen-richer middlings from a previous stage
with
colder/bitumen-leaner overflow from a subsequent stage enables very high
recoveries of heat and bitumen, which is controlled mostly by the efficiency
of
liquid/solid separation in the separators and volumetric ratio of run-off to
middlings content in underflow streams.
By way of example, assuming modest bitumen recoveries of 70% at each
stage, the overall bitumen recovery would exceed 97%, with all recovered
bitumen and most heat concentrated in the first stage overflow stream, which
passes to further processing. This ability to achieve high overall bitumen
recovery despite modest individual stage recoveries, allows the use of much
smaller and less efficient separators, which may include hydrocyclones,
cycloseparators or gravity settlers.
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The first stage overflow or first product, which is also referred to as lean
froth, may be further upgraded at froth cleaning plant 330. Here, most of the
fines and excess water are separated from the bitumen to form clean bitumen
froth. The fines may optionally be thickened in fine tails thickener 332 prior
to
being deposited into tailings deposition pond 302. As previously mentioned,
froth
cleaning units such as PSVs, inclined plate settlers, flotation cells or
combinations there of may be used to produce clean bitumen froth.
FIG. 4 is a schematic of another embodiment of a process line of the
present invention. Process line 4 comprises, in series, countercurrently
operating separators, more particularly, three centrifugal cycloseparators
440,
442 and 444. In this embodiment, overflow from each cycloseparator 440, 442
and 444 leaves through vortex finder outlets 450, 452 and 454, respectively,
and
is collected in pump boxes 420, 422, and 424, respectively. Overflow in pump
box 422 is pumped back to a tangential inlet of cycloseparator 440 and
overflow
in pump box 424 is pumped back to a tangential inlet of cycloseparator 442.
Overflow from the first cycloseparator is collected in pump box 420 as first
product (lean froth) comprising bitumen, fines and water, which is then
pipelined
to a froth cleaning plant (not shown).
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