Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02015784 1999-10-22
1 FIELD OF THE INVENTION
2 In one aspect, this invention relates to a
3 modification of the conventional hot water process for
extracting bitumen from mined oil sand, to produce bitumen
froth. In a preferred aspect of the invention, this modified
extraction process is linked with a novel process for
7 purifying the obtained froth.
$ BACKGROUND OF THE INVENTION
g Oil sands in Alberta are currently being mined and
processed at two separate commercial operations . Each such
11 "operation" involves a sequence of steps, namely;
12 - strip mining the oil sand;
13 - transporting the mined oil sand to an
14 extraction plant;
- extracting the bitumen from the oil sand using
16 the hot water process, to produce bitumen
17 froth;
lg - diluting the bitumen froth with a light
lg hydrocarbon diluent, typically with naphtha,
2~ and separating contained water and solids from
21 the diluted froth using two stages of
22 centrifugation, to produce purified bitumen;
23 and
24 - upgrading the bitumen in a refinery to produce
synthetic crude.
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- CA 02015784 1999-10-22
Oil sand itself comprises sand grains which are
encapsulated in thin sheaths of connate water. Fine clay
3 like solid particles are present in the water. The bitumen
4 or oil is present in the interstices between the water-wet
sand grains.
The hot water process comprises first dispersing
7 the bitumen from the solids and then recovering the bitumen
8 separately. The first step of this process involves the
following, which will be referred to as "conditioning":
- The as-mined oil sand is fed into and moved
11 through the length of a rotating,slightly-
12 inclined-from-horizontal drum or tumbler. Hot
13 process water and a small amount of caustic
14 are mixed with the oil sand in the tumbler .
The temperature of the added hot water is
16 about 95°C. The amount of process water
1~ added is in the order of 20~ by weight of the
18 oil sand or less. The water:solids ratio is
19 therefore about 0.2 or less. The amount of
caustic used is about' 0.03$ by weight of the
21 oil sand. Steam is injected into the mixture
22 along the length of the tumbler, in an amount
suf f is Tent to trim the slurry temperature to
24 ensure that it is at about 80oC when it leaves
the Fumbler . The retention time in the
26 tumbler is typically about 3 minutes. The
product is a slurry of porridge-like
28 consistency.
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- CA 02015784 1999-10-22
There are several mechanisms going on together during
2 conditioning. These include:
- That the caustic reacts with acidic moieties
4 of the bitumen to create surfactants that
assist the bitumen to separate from the
6 solids;
- That the process water heats the bitumen,
8 thereby reducing its viscosity, so that it can
9 more easily separate from the solids;
- That the process water provides a medium
11 into which the bitumen may be dispersed away
12 from the solids, in the form of minute flecks;
13 - That the combination of the heat, obtained
14 from the water and steam, and the mechanical
energy, supplied by rotation of the tumbler,
16 together work to induce ablation of the oil
sand lumps. This ablation is of particular
18 importance in winter, when the as-mined oil
19 sand contains many frozen chunks. A screen is
positioned at the outlet from the tumbler .
21 This screen removes remaining over-size lumps
22 from the slurry and the lumps are discarded as
23 tailings. If ablation is not complete, then
24 the oversize reject rate increases . This
becomes a problem, as bitumen is lost with the
26 rejects; and
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CA 02015784 1999-10-22
1 - That the agitation of the slurry assists in entraining air bubbles,
2 which play a necessary part in the flotation step which follows
3 conditioning.
4 Broadly stated then, the known conditioning step of the hot water
process involves: mixing the oil sand with hot water using mechanical energy
fi for sufficient time to disperse the bitumen from the solids and into the
water,
7 ablate oil sand lumps and entrain air bubbles, to produce a conditioned
slurry.
8 It is useful at this point to give some explanation as to why the industry
9 has commonly combined:
- the use of sufficient hot process water having a temperature of
11 about 95°C; and
12 - the provision of trim steam;
13 to ensure a slurry temperature of about 80°C at the tumbler outlet.
If the
14 slurry is at about 80°C, the density differential between the
bitumen and water
is at a maximum. This has long been felt to be desirable for the subsequent
16 flotation step. In addition, the high temperature assists in achieving
complete
17 ablation in a short retention time.
18 Now, the industry has long appreciated that it would be desirable to
19 carry out conditioning at a lower temperature. The heat that is added by
way
of the process water and steam is not recovered, so any diminution in its
21 consumption would be desirable as long as the process die not otherwise
22 suffer side effects of such severity as to make the change impractical.
5
CA 02015784 1999-10-22
1 However, while the desirability of conducting conditioning at a lower
2 temperature was self-evident, no one, to our knowledge, has taught a
3 combination of conditions that would enable reduction of temperature to be
4 achieved in the extraction without suffering an unacceptable degree of side
effects. It is an objective of this invention to provide such a combination.
5a
CA 02015784 1999-10-22
1 After leaving the tumbler and being screened, the
slurry is diluted by the addition of more hot water. More
particularly, the water content of the slurry is increased to
give a water/solids ratio of about 1:1 (which equates with a
total water content of about 50~ based on the weight of the
6 oil sand). This dilution is a step referred to in the
industry as "flooding".
8 The diluted slurry is retained under quiescent
conditions in an open-topped vessel having a cylindrical
upper portion and a conical lower portion. The vessel is
11 termed a primary separation vessel or "PSV". In the PSV, the
12 sand sinks, is concentrated by the cone, and is discharged as
13 tailings from the base of the cone. The bitumen becomes
14 attached to air bubbles and rises to form a froth. The froth
is recovered by overflow into a launder extending around the
16 rim of the vessel. This froth is termed "primary froth" and
17 typically analyzes at:
18 66.4 bitumen
8.9~ solids
24.7 water
21 Between the froth layer at the top and the sand
22 layer at the bottom of the PSV contents, there exists an
23 intermediate water layer containing fine solids and some non-
24 buoyant bitumen. This layer is referred to as "middlings".
A slipstream of the middlings is withdrawn and introduced
26 into sub-aerated flotation cells, wherein the feed is
2~ agitated and copiously aerated to produce a "dirty" froth,
28 referred to as "secondary froth" . The secondary froth is
29 recovered and typically analyzes at:
6
CA 02015784 1999-10-22
1 23.8$ bitumen
2 . 17.5$ solids
58.7 water
4 The underflow from the secondary flotation cells is
discarded as tailings.
Because the spontaneously-produced primary froth is
7 cleaner than the secondary froth produced by forced aeration,
8 it is a fundamental objective in the strategy applied to the
hot water process to maximize the production of primary froth
and minimize the production of secondary froth.
1.1 The secondary froth is partially upgraded by
12 holding it in a tank for a period of time to allow some of
13 the contained water and solids to settle out. The produced
14 cleaned secondary froth is then combined with primary froth
15 to yield a "combined froth", stream which is the product from
16 the extraction circuit.
17 In the conventional process, the combined froth is
lg diluted with naphtha, to increase the difference in specific
19 gravity of the hydrocarbon phase relative to the water phase.
2~ This is done to facilitate separation of the phases by
21 gravity forces.
22 The diluted froth is then processed in a scroll-
23 type centrifuge to remove contained coarse sand. The
24 hydrocarbon-rich product from the scroll centrifuge is
25 treated in a disc-type centrifuge to remove contained water
26 and fine solids. The so-purified product typically analyzes
27 at:
7
CA 02015784 1999-10-22
59.4$ $ by wt. bitumen
2 37.5 ~ by wt. naphtha
3 4.5$ $ by wt. water
0.4 $ by wt. solids
This purified product is suitable for upgrading in
a refinery-type facility to produce various hydrocarbon
products. The entire process, as described, is commonly
referred to as the hot water process. It is the object of
9 this invention to modify the conditioning step, including
lowering the temperature at which it is conducted, but
11 without significantly lessening the primary froth and total
~2 bitumen recoveries, relative to the conventional recoveries.
13 SUMMARY OF THE INVENTION
14 More particularly, we have discovered a novel
combination of conditions which, when applied to the
16 conventional hot water process, cause the so-modified process
17 to produce a comparable yield of primary bitumen froth with
~g less heat consumption. The conditions involved relate to the
g conditioning step. They comprise:
- Conducting the conditioning step without the
2~ addition of steam and adding sufficient hot
22 process water to the tumbler to supply all of
23 the heat required to yield an oil sand slurry
24 having a temperature in the range of 40oC to
55oC; and
26 - Increasing the retention time of the slurry in
%7 the tumbler to within the range of about 7-12
28 minutes.
8
CA 02015784 1999-10-22
1 Therefore, in a broad aspect of the invention, the known conditioning
2 step of the hot water process is modified by mixing sufficient hot water
with
3 the oil sand to supply all of the heat required to yield an oil sand slurry
having
4 a temperature in the range of 40 - 55°C, said hot water being
essentially the
only source of heat supplied to the slurry; and maintaining the mixing time
6 within the range of about 7 - 12 minutes.
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CA 02015784 1999-10-22
1 By "hot process water" is meant water of such
2 temperature as to give, when mixed with the oil sand feed, a
3 slurry of the desired temperature. Usually the water will
4 have a temperature in the range 70°C to 95°C.
In a preferred form of the invention, the amount of
6 hot process water added in the conditioning step is in the
range of about 25-35~ by weight of the oil sand and the
8 amount added, including the flooding step, is in the range of
9 about 45- 65$.
From the foregoing, it will be noted that:
11 - No steam is used in the tumbler;
12 - The temperature of the slurry leaving the
13 tumbler is reduced relative to that of the
14 slurry produced in the conventional process;
and
16 - More water than is conventional is used in the
17 conditioning step but the total amount of hot
18 process water used in the combination of the
19 conditioning and flooding steps of the
modified process is substantially the same as
21 used in the conventional process.
22 As supported by the examples following below, the
23 modified extraction process is characterized by a recovery of
24 bitumen, in the form of primary froth, generally equivalent
to that obtained using conventional conditions. In addition,
26 the extent of lump ablation, as indicated by the amount of
27 bitumen lost with the rejects, is also generally equivalent.
9
CA 02015784 1999-10-22
1 The resulting process is characterized by the following
2 advantages:
3 - That the elimination of using steam reduces
4 capital and operating costs; and
- That while consumption of mechanical energy is
6 increased by use of the invention, its cost is
7 less than the use of heat needed to operate at
8 80°C. Surprisingly, we have discovered that the
9 separation of bitumen is more responsive to
mechanical energy than it is to thermal energy.
11 More particularly, our work has shown that 0.45
12 kJ of mechanical energy has the same effect as 61
13 kJ of thermal energy. This enables improvement
14 of the extraction process even though the
retention time and mechanical energy consumption
16 are increased.
17 Broadly stated, the invention is an improvement in the
18 hot water process of extracting bitumen from as-mined oil sand,
19 some of which is present in the form of lumps, wherein the oil
sand is mixed with hot water and a surfactant-producing caustic
21 process aid, in a rotating tumbler in a conditioning step,
22 whereby the lumps of oil sand are ablated, the slurry produced
23 from the tumbler is diluted with additional hot water in a
2looding step, and the diluted slurry is temporarily retained in
a primary separation vessel to produce primary bitumen froth by
26 spontaneous flotation. The improvement comprises: admixing in
27 the tumbler an amount of hot water sufficient to combine with
28 the oil sand and process aid to yield a slurry having a
29 temperature at the tumbler outlet in the range of 45° - 55°C,
said
CA 02015784 1999-10-22
1 hot water being essentially the only source of heat supplied to the slurry;
and
2 maintaining the retention time of the slurry in the tumbler within the range
of
3 about 7 to 12 minutes; whereby the quanta of recovery of bitumen as primary
4 froth and the rejection of over-sized lumps of oil sand are generally
equivalent
to those which would have been obtained if the process had been operated
6 with a slurry exit temperature of about 80°C and transfer retention
time of
7 about 3 - 4 minutes.
8 In another statement of the invention, it is an improvement in the
9 conditioning step of the hot water process for extracting bitumen from oil
sand, wherein oil sand is mixed with hot water using mechanical energy for
11 sufficient time to disperse the bitumen from the solids and into the water,
12 ablate oil sand lumps and entrain air bubbles, to produce a conditioned
slurry.
13 The improvement comprises: mixing sufficient hot water with the oil sand to
14 supply all of the heat required to yield an oil sand slurry having a
temperature
in the range of 45 - 55°C, said hot water being essentially the only
source of
16 heat supplied to the slurry; and maintaining the mixing time within the
range of
17 about 7 - 12 minutes.
18
19 DESCRIPTION OF THE DRAWING
Figure 1 is a schematic showing the pilot plant extraction circuit used to
21 develop the first aspect of the invention.
22
23 DESCRIPTION OF THE PREFERRED EMBODIMENT
24 The invention is exemplified and delineated by the following examples.
l0a
CA 02015784 1999-10-22
1 EXAMPLE I
2 -. T.his example describes the processing of an average
3 grade oil sand in a pilot plant extraction unit shown in Figure
4 1.
The oil sand composition was as follows:
6 12% by wt. bitumen
7 3.1% by wt. water
8 84.9% by wt. solids
9 Three runs are reported. In run A, no steam was used
in the tumbler, retention time was extended to 8 minutes, and the
11 tumbler slurry temperature was 50°C. In run B, the same
12 conditions were used as in run A, except that the retention time
13 was increased to 12 minutes. Run C was conducted in accordance
14 with prior art conditions.
~ The pilot plant used was designed to process about 2.5
16 tons per hour of oil sand, in comparison to one train in
17 assignees' cozxmercial operation that is designed to process about
18 3250 tph. However, the pilot plant has previously been proven
19 to yield similar results to those of the commercial train when
the hot water process was practiced in the two units under
21 substantially the same conditions with substantially the same oil
22 sand feed.
23 . The pilot glant comprised a feeder 1 for feeding oil
24 sand to a tumbler 2. Hot water (95°C), caustic and steam could
25, be introduced into the tumbler through suitable lines. The
26 tumbler product passed through a 1/2 inch screen 3 to remove
27 oversize material. The screened product dropped into a pump box
/i
CA 02015784 1999-10-22
1 4 where it was diluted with additional hot water. The product
2 from the pump box was fed to a PSV 5 to produce a primary froth
3 product, a tailings underflow, and a middlings stream. The
4 middlings stream was fed to a bank of induced air flotation cells
6. The flotation cells produced a secondary froth stream and a
6 tailings underflow. The secondary froth stream was fed to a tank
7 7 to settle out water and solids and produce secondary froth.,
8 Following is the data relating to runs A. R anr~ ~.
9 R~ P,~ _B C_
Conditioning Time (minute) 8 12 4
11 Ore Feed rate (G/S) 639 639 639
12 Slurry Water (Wt%) 25 25 20
13 Tumbler Speed (RPM) 13.90 13.70 13.70
14 Caustic Addition (Wt%) 0.03 0.03 0.03
Tumbler Slurry Temp. (C) 50 50 80
16 Flooded SLurry Temp. (C) 60 60 80
17 Total Water Addition (Wt%) 65 65 65
/ ~L
CA 02015784 1999-10-22
1 Prime Froth Density (G/mL) NA 0.75 0.92
2 Ore Sample ~ Bitumen 12.0
3 ~ Water 3.1
4 ~ Solids 84.9
~ Fines 11.5
6 PSV Froth Rate (G/S) 101 98 106
PSV Froth ~ Bitumen 67.8 71.7 65.5
8 $ Water 21.1' 17.5 25.8
9 ~ Solids 11.0 10.8 8.8
PSV Middlings Rate (G/S) 205 198 158
11 PSV Middlings ~ Bitumen 0.8 0.5 1.7
12 ~ Water 82.2 82.3 81.1
13 ~ Solids 17.0 17.2 17.1
14 pSV Tails Rate (G/S) 675 714 697
PSV Tails $ Bitumen 0.3 0.2 0.3
16 ~ Water 33.2 34.4 35.0
17 ~ Solids 66.5 65.4 64.7
18 Reject Rate (G/S) 7 8 9
19 (W/W)$ 1.1 1.3 1.4
Reject ~ Bitumen 5.9 6.0 5.2
21 $ Water 0.2 23.5 11.1
22 ~ Solids 87.0 70.6 83.8
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CA 02015784 1999-10-22
1 Cleaner Froth Rate (G/S) 5 9 16
2 Cleaner Froth ~ Bitumen 50.3 14.1 35.5
3 $ Water 36.0 69.6 49.7
~ Solids 13.8 16.2 14.8
Secondary Tails Rate (G/S) 200 189 142
6 Secondary Tails ~ Bitumen 0.3 0.3 0.3
7 ~ Water 83.6 84.3 84.9
8 ~ Solids 16.1 15.5 14.8
9 Combined Froth $ Bitumen 66.97 66.90 61.57
~ Water 21.80 21.84 28.93
- ~ Solids 11.13 11.25 9.59
11
12 PSV Froth Bitumen (G/S) 68.48 70.27 69.43
13 PSV Tails Bitumen (G/S) 2.03 1.43 2.09
14 Cleaner Froth Bitumen (G/S) 2.52 1.25 5.0'8
Cleaner Tails Bitumen (G/S) 0.60 0.57 0.43
16 Rejects Bitumen (G/S) 0.41 0.48 0.47
17 Primary Recovery (~) 92.50 94.96 88.90
18 Secondary Recovery (~) 3.40 1.70 7.27
19 Combined Recovery (~) 95.90 96.66 96.18
Primary Tails Loss (~) 2.74 1.93 2.68
21 Secondary Tails Lcss (~) 0.81 0.77 0.55
22 Reject Loss ($) 0.56 0.65 0.60
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CA 02015784 1999-10-22
1 Primary Recovery (Rej-Free) 93.02 95.58 89.44
2 Secondary Recovery (Rej-Free) 3.42 1.71 7.32
3 Combined Recovery (Rej-Free) 96.43 97.29 96.76
Primary Tails Loss (Rej-Free) 2.75 1.94 2.69
Secondary Tails Loss (Rej-Free) 0.82 0.77 0.55
6 From the foregoing data it will be noted that:
7 - The warm slurry runs A and B yielded primary
8 froth and total bitumen recoveries which were
9 better or comparable to those from the hot
slurry run C;
11 - The bitumen losses with the tumbler and PSv
12 tailings were comparable for the warm and hot
13 slurry runs;
14 - The oversize reject rates from the three runs
were comparable, indicating that the extent of
16 ablation was about the same;
17 - The total hot water consumption for the thee
18 runs was the same, yet the recoveries for the
1g runs mere comparable; and
- As shown by comparing the data of runs A and
21 B, there is little improvement obtained in
22 increasing the tumbler residence time from 8
23 to 12 minutes when the slurry is only warm.
CA 02015784 1999-10-22
EXAMPLE II
2 This example demonstrates that operation of the hot
3 water process by reducing only the temperature of the slurry
in the conditioning step gives reduced yields of primary and
combined froth.
6 Hot water process runs were conducted, using the
7 pilot plant and conditions described in Example I, on two
g distinct oil sand feeds. In one case, the process was
g operated at 80oC and in the other it was operated at 50oC.
The relevant data was as follows:
Oil Sand Type Estuarine Marine
~2Bitumen in feed (~) 8.1 8.9
13Mean primary recovery
14at 80oC 80.3 37.2
15at 50oC 65.9 37.0
16Mean combined recovery
at 80C 86.2 77.5
~8at 50oC 81.1 67.9
19 EXAMPLE III
20This example shows the advantage of redistributing
2~the total hot increase the amount used in
water used, the
to
22tumbler. The the amount bitumen lost with
effect is that of
23tumbler rejects is reduced the slurry having
in the case
of
24increased water content in
the tumbler.
All results
were for
25a slurry having a temperature of 50oC.
16
CA 02015784 1999-10-22
1 Residence Slurry Water Oil Sand Bitumen lost
2 time (min) as proportion feed rate to reject ($
3 of oil sand (g/s) based on bitumen
( ~S ) in feed )
6.16 17 445 2.34
6 5.78 22 445 1.47
7 5.45 27 445 0.55
8 4.56 17 639 3.16
9 4.30 22 639 2.29
4.07 27 639 1.42
11 3.70 17 833 3.98
12 3.50 22 833 3.11
13 3.33 27 833 2.24
14 Such reductions are not notice d at 80oC because
reject rates ar e always low. At 50oC the reject rate has
a
16 tendency to be high but can reduced by using more of
be the
17 total water in the tumbler as slurry water.
Thereafter,
a
lg proportionately lower amount of water needed as flood
is
lg water for the resulting dilu ted slurry to give the same
separation in be achieved from conventional
the PSV as would
21 water distribution.
17
