Note: Descriptions are shown in the official language in which they were submitted.
CA 02227667 1998-O1-22
1 FIELD OF THE INVENTION
2 This invention relates to an assembly and process for forming an
3 aqueous oil sand slurry, screening it to remove oversize solids,
mechanically
4 agitating it and conditioning it, to produce a slurry ready for pipelining.
6 BACKGROUND OF THE INVENTION
7 Tree McMurray oil sands of Alberta constitute one of the largest
8 deposits of hydrocarbons in the world. The oil sands are first mined at a
mine
9 site and then transported to an extraction plant in order to extract the
bitumen.
In recent years the preferred mode of transport of mined oil sands has been
11 by way of a slurry pipeline. The oil sand is mixed with water to form a
slurry
12 that is capable of being pumped down a pipeline to the extraction plant.
13 One needs to provide a suitable means for slurrying the oil sand with
14 water and entraining air to produce a slurry that is suitable for pumping
down
the pipeline. The as-mined oil sand contains a variety of lumps including
16 rocks, clay and oil sand lumps. Therefore a mixer means is required that
not
17 only slurries the oil sand but also ensures that oversize lumps that are
18 unsuitable for pumping and feeding into the pipeline are rejected. A
typical
19 aqueous slurry comprises the following: bitumen froth, sand, smaller lumps
of
oil sand, clay andlor rocks (between 0 and 2 inches in diameter) and larger
21 lumps of oil sand, clay andlor rock (between 2 and 4 inches in diameter).
22 In United States patent No. 5039227, issued to Leung et al and
23 assigned to the owners of the present application, one mixer circuit for
this
24 purpose has been disclosed.
2
CA 02227667 2002-06-13
1 In the Leung et al mixer circuit, an oil sand stream is dropped from the
2 end of a conveyor into a mixer tank. The mixer tank is open-topped, has a
3 cylindrical body and conical bottom and forms a central bottom outlet. A
4 swirling vortex of slurry is maintained in the tank and the incoming oil
sand
and added water is fed into it. Slurry leaves the tank through the bottom
6 outlet, is screened using vibrating screens to reject oversize, and is
7 temporarily collected in an underlying pump box. Some of the slurry in the
8 pump box is withdrawn and pumped back through a return line to be
9 introduced tangentially into the mixer tank to form the swirling vortex. The
balance of slurry in the pump box is withdrawn and pumped into the pipeline.
11 In Canadian patent 2,227,667, a second-generation mixer circuit in the
12 form of a vertically oriented stack of components, functions to slurry the
oil
13 sand with water. The oil sand is initially dropped from the end of a
conveyor
14 and is contacted in mid-air with a stream of water. The mixture drops into
a
downwardly slanted trough and the water and oil sand mixes as they move
16 turbulently through the open-ended trough. The slurry is deflected as it
leaves
17 the trough and is spread in the form of a thin sheet on an apron. It is
then fed
18 over screens to reject oversize lumps. The screened slurry drops into a
pump
19 box where it is temporarily retained. The rejected lumps are comminuted in
an impactor positioned at the end of the screens. The comminuted oil sand is
21 screened to remove remaining oversize lumps and the screened comminuted
22 oil sands are delivered into the pump box. The slurry in the pump box is
23 withdrawn and pumped into the pipeline.
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CA 02227667 1998-O1-22
1 Both of the prior art mixer circuits routinely produce a slurry that
2 contains lumps ranging from 0 to 4 inches in diameter. Before the slurry is
3 pumped 1:o the pipeline, it is temporarily stored in a pump box. The pump
box
4 is restricted to a certain volume because if the volume of retained slurry
is too
great, settling of the sand and lumps will occur. As a result, the residence
6 time of the slurry in the pump box is relatively short (in the order of 1
minute)
7 and the slurry is quickly pumped from the pump box to the pipeline.
8 As. the slurry travels down the pipeline, slurry conditioning or digestion
9 takes place. Adequate conditioning is critical for good bitumen recovery in
a
downstream separation vessel and is especially important when extracting
11 bitumen from low grade oil sand. Basically what conditioning means is that
12 the larger oil sand lumps are ablated into smaller lumps and bitumen flecks
13 coalesce and coat or attach to air bubbles. The lumps need to be dispersed
14 in water to promote the release of oil droplets and the attachment of air.
Conditioning also benefits from turbulent pipeline flow and is dependent upon
16 the length of the pipeline, hence, the length of time that the slurry
resides in
17 the pipeline before reaching the separation vessel. The larger the oil sand
18 lumps, the more time required to digest or ablate these lumps to release
the
19 bitumen flecks. Therefore if a slurry is routinely produced that contains
large
lumps, there will be a need for long pipelines or residence time.
21 An ideal slurry for fast conditioning (i.e. under 10 minutes) would be
22 one that consists of lumps that are less than 2 inches in diameter. But
23 producing such a slurry is impractical due to limitations of the prior art
mixer
24 circuits. For example, in the second-generation mixer circuit, slurry
routinely
2.5 contains lumps that are 2 to 4 inches in diameter. This is as a result of
4
CA 02227667 1998-O1-22
1 limitations in the mixer circuit with respect to the screening process.
These
2 circuits roust accommodate large throughputs of oil sand. Therefore, the
3 screen openings must be considerably larger than 2 inches, hence, larger
4 lumps (i.~~. 2 to 4 inches in diameter) are introduced into the pipeline.
This
means that the pipeline has to be a certain length to ensure sufficient
6 residencE~ time of such a slurry (preferably a minimum of 4 km to give a
7 residencE: time of approximately 12 to 15 minutes) for proper conditioning
to
8 occur.
9 There may be times, however, when it is unnecessary to have such a
long pipeline. But if the pipeline is too short, the residence time of the
slurry in
11 the pipeline will be too short for proper conditioning of the slurry to
occur.
12 This will result in a decrease in bitumen recovery. However, a pump box can
13 be designed whereby the harder to digest 2 to 4 inch lumps are segregated
14 from the rest of the slurry and are directed to an impactor where they are
comminuted to small lumps. Therefore the length of the pipeline becomes
16 less critical.
17 SUMMARY OF THE INVENTION
18 This invention relates to an assembly and process for forming an
19 aqueous oil sand slurry whereby the slurry contains preferably lumps that
are
about 2 inches or less in diameter prior to the slurry being pumped to the
21 pipeline.
22 In the prior art, a pump box is used to temporarily store the aqueous
23 slurry prior to being pumped through the pipeline. In the current
invention, the
24 cross-sectional area of the pump box is increased relative to what was
conventional and a mixing means is added to the pump box. This
5
CA 02227667 1998-O1-22
1 accomplishes two things. First, the slurry is separated into two phases: a
2 suspendE=d slurry with lumps 2 inches in diameter or less and larger lumps
3 that cannot be suspended and therefore settle to the bottom of the pump box.
4 In a preferred feature, the larger lumps that settle to the bottom are
pumped
out of the pump box, directed to a 2 inch screen deck and the reject lumps are
6 comminuted in an impactor. The comminuted product is delivered back to the
7 pump bo:x. Over time, the overall effect is that the slurry being introduced
into
8 the pipeline contains only lumps that are about 2 inches or less. Hence,
9 conditioning of the slurry occurs much faster, thereby eliminating the need
for
long pipelines for conditioning.
11 Second, the actual residence time of the slurry in the pump box is
12 increased relative to the prior art due to the fact that the cross-
sectional area
13 of the pump box has been increased relative to the prior art. Therefore,
some
14 conditioning of the slurry will take place in the pump box itself, rather
than in
the pipeline. Both the volume of the pump box and the flow rate of the slurry
16 will determine the residence time of the slurry in the pump box. The
following
17 equation can be used to determine the residence time:
18 volume (m3) I flow rate (m3lmin) = residence time (min).
19 In practice, it is desirable to keep the slurry flow rate relatively
constant.
Thereforf~, the optimal way to increase residence time is to increase the
21 volume of the pump box. This can be achieved by increasing the cross-
22 sectional area of the pump box.
6
CA 02227667 2002-06-13
1 In one broadly stated aspect of the invention, a process is
2 provided for producing an aqueous slurry of oil sand, suitable for
introduction
3 into a pipeline, comprising:
4 ~ mixing oil sand and water to form an aqueous slurry containing
lumps;
6 ~ screening the slurry to remove oversize lumps and produce a
7 screened slurry containing undersize lumps;
8 ~ temporarily retaining the screened slurry in a pump box for a pre-
9 determined retention time;
~ mechanically agitating the slurry contained in the pump box; and
11 ~ withdrawing slurry from the pump box and pumping it into a
12 pipeline.
13 In another broadly stated aspect of the invention, a downwardly
14 sequenced assembly is provided for producing an aqueous slurry of oil sand,
ready for introduction into a pipeline, comprising:
16 ~ means for mixing oil sand with water to produce a slurry containing
17 lumps;
18 ~ means for screening oversize lumps from the slurry to produce a
19 screened slurry containing undersize lumps suitable for pumping
through a pipeline; and
21 ~ a pump box for receiving the screened slurry, said pump box having
22 means for mechanically agitating the slurry within the pump box,
23 said pump box being associated with a means for withdrawing
24 slurry from the pump box and pumping it into a pipeline.
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CA 02227667 1998-O1-22
1 More specifically, in a preferred form, the downwardly sequenced
2 assembly for producing an aqueous slurry of oil sand, ready for introduction
3 into a pipeline, comprises:
4 ~ A conveyor having a discharge end for delivering a continuous
stream of oil sand that falls through air into a trough;
6 ~ A pipe for delivering a stream of water which contacts and wets the
7 falling oil sand in mid-air;
8 ~ The trough being downwardly slanted, open-topped and positioned
9 in spaced relation below the conveyor discharge end and the water
pipe. The trough is operative to receive the mixture of oil sand and
11 water and confine it temporarily to allow the oil sand and water to
12 turbulently mix and form a slurry. stream as they flow along its
13 length and discharge from its open lower end;
14 ~ An upstanding wall positioned adjacent the trough's lower end and
spaced therefrom so that the slurry stream hits it and is deflected,
16 with the result that its direction of flow is changed and further mixing
17 is induced;
18 ~ An apron providing a broad surface for receiving the deflected
19 stream, whereby the stream is spread out and thinned to form a
slurry sheet adapted to efficiently utilize the screen area;
21 ~ A first screen assembly for receiving and screening the slurry sheet
22 to reject oversize and produce a screened slurry stream;
23 ~ A pump box for receiving and temporarily retaining the screened
24 slurry;
8
CA 02227667 1998-O1-22
1 ~ A mechanical agitator in the pump box for separating the screened
2 slurry into two phases, the slurry containing suspended lumps and
3 the larger lumps that cannot be suspended; and
4 ~ A means for withdrawing suspended slurry from the pump box and
delivering the slurry into the pipeline.
6 In a preferred extension of the invention, the rejected oversize lumps
7 from the first screen assembly are fed directly into an impactor and
8 comminuted. The comminuted product is screened by a second screen
9 assembly to reject remaining oversize. The comminuted, screened product is
then delivered into the mechanically agitated pump box.
11 In a second preferred extension of the invention, the mechanically
12 agitated pump box is equipped with a means for recycling lumps reaching the
13 bottom of the pump box, preferably by withdrawing them tangentially from
the
14 bottom of the pump box. These lumps are delivered to a third screen which
may be attached to the first screen assembly. The rejected oversize lumps
16 are then fed directly into the impactor to be comminuted in the impactor.
The
17 comminuted product is then delivered into the mechanically agitated pump
18 box.
19
DESCRIPTION OF THE DRAWLNGS
21 Figure 1 is a schematic side view showing the preferred embodiment of
22 the invention.
9
CA 02227667 1998-O1-22
1 DESCRIPTION OF THE PREFERRED EMBODIMENT
2 As-mined oil sand to be pipelined is first crushed before conveying it to a
3 mixer circuit 1. This is commonly done by passing it through a set of double
4 rolls, producing 24-inch product. This pre-treatment (which forms no part of
the
invention;l is done to break down the very large contained lumps.
6 The crushed oil sand contains lumps of varying size and composition.
7 The mixer circuit 1 comprises a series of downwardly arranged
8 components.
9 The uppermost component is a conveyor 2 for continuously delivering a
stream of crushed oil sand 3. The oil sand cascades or falls from the
discharge
11 end 4 of the conveyor 2 - it drops downwardly through an air space 5.
12 A horizontal pipe 6 is positioned opposite to the conveyor discharge end
13 4. The pipe discharges a stream 7 of water into the falling oil sand in mid-
air at
14 a sufficient rate so that the water/oil sand ratio is equivalent to that of
the
pipeline slurry. Typically this ratio is about 1:3 by weight. The stream 7
16 contacts ~:he downwardly descending oil sand and is distributed through it
and
17 wets it.
18 The oil sand and water drop into a downwardly slanted, open-topped,
19 open-ended trough 8. The trough is formed of plate steel.
As the oil sand and water move through the trough, they mix turbulently
21 and form a slurry.
22 A solid, vertical wall 10 formed of steel is positioned adjacent the lower
23 end 11 of the trough 8. The wall 10 is spaced from the trough's lower end
11
2.4 and extends across the trajectory path of the slurry stream 13 discharging
from
the trough.
CA 02227667 2002-06-13
i A downwardly slanted apron 14 extends downwardly from the wall 10 in
2 a direction opposite to that of the trough 8.
3 The slurry stream 13 hits the wall 10, is deflected and changes its
4 direction of movement, being discharged onto an apron 14. In the course of
these movements, further turbulent mixing of the oil sand and water occurs. On
6 reaching a second apron 31, the slurry spreads out laterally and is thinned,
to
7 form a slurry sheet 15 of comparable width to the screen 16.
8 The slurry sheet 15 flows from the second apron 31 onto a contiguous
9 first vibrating screen 16. It is sized to retain +4 inch material.
The oversize lumps 20 retained by the vibrating screen 16 are delivered
11 into an impactor 24. The lumps 20 are largely oii sand in composition and
12 many disintegrate when impacted by the rotating arms of the impactor,
13 producing comminuted product 27. This product discharges from the outlet of
14 the impactor onto a second vibrating screen 30. The oversize lumps retained
by screen 30 are discarded. The screened comminuted product, containing
16 undersize lumps that passed through the screen 16, is discharged into pump
17 box 18.
18 Pump box 18 is equipped with a vertical shaft agitator 21 that
19 mechanically agitates the collected screened slurry such that a vortex 22
is
created. The pump box is further equipped with at least one vortex breaker
21 plate 23 positioned so as to allow the vortex 22 to form at the bottom of
the
22 pump box. Much of the slurry remains in suspension and only the larger
lumps
23 25 (between 2 and 4 inches in diameter) settle to the bottom of the pump
box
24 18. The larger lumps are pumped from a tangential outlet 26 and are
delivered
to a third vibrating screen 28 that is sized to retain +2 inch material. The
SEross7as.~oc;i}11
CA 02227667 2002-06-13
1 oversize lumps 29 retained by the screen 28 are delivered into the impactor
24.
2 Most of the oversize lumps are disintegrated when impacted by the rotating
3 arms of the impactor 24. The comminuted product is discharged into the pump
4 box 18. Ultimately, the suspended slurry in the pump box is pumped from an
outlet 19 into a pipeline.
6 The foregoing describes our best mode of carrying out the invention.
7 As will be realized, the invention is capable of other and different
8 embodiments and its several details are capable of variation, all without
9 departing from the invention. The scope of the invention is established in
the
claims now following.
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