Note: Descriptions are shown in the official language in which they were submitted.
CA 02493677 2005-01-21
1 "CIRCUIT AND PROCESS FOR CLEANING DEAERATED
2 BITUMEN FROTH"
3
4 FIELD OF THE INVENTION
The present invention relates to cleaning deaerated bitumen froth by
6 separating contained water and solids contaminants from the bitumen.
7
8 BACKGROUND OF THE INVENTION
9 For many years now, bitumen has been recovered from the Athabasca
oil sands formation in Alberta using a water-based extraction and air
flotation
11 technique. In greater detail:
12 = the as-mined oil sand is mixed with heated water to produce a
13 slurry containing entrained air bubbles; and
14 = contained bitumen is recovered from the slurry in the form of a froth,
by flotation.
16 The froth contains varying concentrations of water and particulate
17 solids contaminants. The solids comprise coarse sand and fine clay
particles.
18 A typical froth might comprise:
19 bitumen - 60 % by wt.
water - 30 % by wt.
21 solids - 10 % by wt.
22 It is necessary to "clean" the froth by removing as much of the water
23 and solids as one can feasibly manage, to prepare it for downstream
24 upgrading.
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1 Before it is cleaned, the froth is substantially deaerated to render it
2 pumpable.
3 The present invention is directed to providing a circuit and process for
4 cleaning deaerated bitumen froth.
6 SUMMARY OF THE INVENTION
7 As previously indicated, the invention is applied to deaerated bitumen
8 froth, such as that produced by an extraction plant associated with an oil
9 sands facility.
The deaerated bitumen froth comprises bitumen, water and coarse and
11 fine solids components, present as a partially emulsified mixture.
12 The purpose of the invention is to maximize recovery of the bitumen
13 from the froth as a discrete product, while simultaneously removing water
and
14 solids.
The difficulty in achieving this objective lies in the fact that, with some
16 of the mixture, it is relatively easy to separate the components, while
with the
17 balance it is progressively more difficult to effectively carry out the
separation.
18 Otherwise stated, there exists a spectrum of emulsion and a corresponding
19 progressively increasing difficulty in separating the bitumen from the
other
components.
21 In a broad sense, the invention presents a countercurrent separation
22 circuit and process wherein:
}
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1 = the deaerated bitumen froth undergoes two stages of gravity settling, in
2 primary and secondary inclined plate separators ("IPS's"), followed by
3 one or more stages of cyclonic separation;
4 = coupled with addition of a light hydrocarbon diluent (preferably
naphtha) to each of the gravity settling stages and, optionally, to the
6 cyclonic stage(s) as well.
7 In connection with this process design, the concentration of diluent,
8 expressed as diluent/bitumen ratio ("D/B ratio"), is greater in the
secondary
9 gravity settling step than it is in the primary gravity settling step. In
other
words, the D/B ratio is progressively increased as the water and solids in the
11 emulsion being treated is more tightly bound with the bitumen. In
conjunction
12 with increasing the D/B ratio, the separation force applied is increased,
as the
13 froth is subjected initially to gravity settling (1g) and then to cyclonic
14 separation (100's of g's).
By having the capability to deliver diluent separately to each of the
16 stages, it is possible to split the overall diluent addition needed for the
process
17 between the stages. As a result, more diluent can be allocated to a later
18 stage if the emulsion being treated in the later stage is proving difficult
to
19 separate. This provides flexibility to the process.
In one embodiment of the invention, a countercurrent process is
21 provided for recovering bitumen from deaerated bitumen froth containing a
22 mixture of bitumen, water and coarse and fine solids, comprising: providing
a
23 froth cleaning process circuit of units comprising primary and secondary
24 inclined plate separators ("IPS's") and a primary cyclone, said units being
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1 connected in sequence for enabling three successive stages of separation;
2 providing a source of light hydrocarbon diluent connected to supply diluent
as
3 required to each of the units; feeding froth, diluent and a recycled
secondary
4 overflow from the secondary IPS to the primary IPS and controlling the rate
of
diluent addition to the primary IPS so as to provide a pre-determined primary
6 diluent/bitumen ("D/B") ratio in the primary IPS, and subjecting the
resulting
7 mixture to gravity settling in the primary IPS so as to produce an overflow
8 product and a primary underflow; feeding primary underflow, diluent and a
9 recycled cyclone overflow from the primary cyclone to the secondary IPS and
controlling the rate of diluent addition to the secondary IPS so as to provide
a
11 secondary D/B ratio in the secondary IPS greater than the primary D/B
ratio,
12 and subjecting the resulting mixture to gravity settling in the secondary
IPS so
13 as to produce secondary overflow and secondary underflow; feeding
14 secondary underflow to the primary cyclone and subjecting it therein to
cyclonic separation to produce primary cyclone overflow and primary cyclone
16 underflow; recycling at least part of the secondary IPS overflow to the
primary
17 IPS; and recycling at least part of the primary cyclone overflow to the
18 secondary IPS.
19 In another embodiment, a deaerated bitumen froth cleaning process
circuit is provided comprising: a source of deaerated bitumen froth; a source
21 of light hydrocarbon diluent; a primary inclined plate separator ("primary
IPS")
22 having an inlet, an outlet for circuit product and an outlet for primary
IPS
23 underflow; means, connecting the froth source with the primary IPS inlet,
for
24 supplying froth thereto; means, connecting the diluent source with the
primary
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1 IPS inlet, for supplying diluent thereto; a secondary inclined plate
separator
2 ("secondary IPS") having an inlet, an outlet for secondary IPS overflow and
an
3 outlet for secondary IPS underflow; means, connecting the primary IPS
4 underflow outlet with the secondary IPS inlet, for supplying primary IPS
5 underFlow thereto; means, connecting the secondary IPS overflow outlet with
6 the primary IPS inlet, for recycling secondary IPS overflow thereto; means,
7 connecting the diluent source with the secondary IPS inlet, for supplying
8 diluent thereto; a primary cyclone having an inlet, an outlet for primary
cyclone
9 overflow and an outlet for primary cyclone underflow; means, connecting the
secondary IPS underflow outlet with the primary cyclone inlet, for supplying
11 secondary IPS underflow thereto; means, connecting the primary cyclone
12 overflow outlet with the secondary IPS inlet, for supplying primary cyclone
13 overflow thereto; and means, connecting the diluent source with the primary
14 cyclone inlet, for supplying diluent thereto.
16 DESCRIPTION OF THE DRAWING
17 Figure 1 is a simplified schematic flow diagram of a circuit in
18 accordance with the invention; and
19 Figure 2 is a schematic flow diagram of a test circuit used to provide
the experimental run data set forth hereinbelow.
21
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1 DESCRIPTION OF THE PREFERRED EMBODIMENT
2 The invention is based on a process circuit and a combination of steps
3 applied to a specific feedstock (deaerated bitumen froth) for a specific
4 purpose (cleaning the froth).
There is an underlying preferred scheme with respect to operating the
6 circuit and process, which is now described:
7 The overall objective of the process is to produce a desired flow rate of
8 clean bitumen for consumption by an upgrader. A naphthenic diluent
9 preferably is used in this process for cleaning bitumen froth, as it
provides
optimum operating conditions and easy recovery in an upgrader. The design
11 of an upgrader limits the acceptable range of variability in the
composition of
12 the naphtha-diluted bitumen (its feed). The composition includes diluent,
13 water and solids in addition to the most important component, bitumen.
14 The amount of diluent is significant with respect to the amount of
bitumen. In fact, to ensure that product specification is met, the mass flow
of
16 diluent is ratioed to the mass flow of bitumen. This is called a D/B ratio.
This
17 key parameter is used in this froth treatment process to control the
overall
18 addition of diluent. That is, a desired flow rate of bitumen (froth) is set
and the
19 required diluent (to meet the product D/B ratio) is calculated and
subsequently
fed. Note that the product D/B ratio is equal to the primary IPS D/B ratio
21 because only the primary IPS produces product.
22
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1 In the design, the overall D/B ratio is in the range 0.5 - 0.8 and
2 preferably is in the range 0.65 - 0.75. As previously stated, the primary
D/B
3 ratio in the primary IPS will closely correspond with the selected overall
D/B
4 ratio. The secondary D/B ratio is not set, but will fall in a broad range of
1.0 -
4.0, preferably in the range 1.4 - 2Ø These ranges are selected with the
6 objective of achieving a product containing 0.5 - 2% by wt. water and 0.2 -
7 1.5% by wt. solids.
8 It is desirable to directly measure the mass flow of bitumen in the froth.
9 However, due to limitations in instrumentation, it is often necessary to
measure the flow of diluted froth (i.e. after the primary diluent flow has
been
11 added) and then back-calculate the amount of bitumen. This is easily done
12 with computer control systems in a fraction of a second. Through repeated
13 calculations, the diluent addition is adjusted to zero in on the desired
D/B
14 ratio.
The process allows the addition of diluent in various locations (e.g.
16 feed to the primary IPS, feed to the secondary IPS and feed to the primary
17 cyclone). Note that regardless of where the diluent is added it will
eventually
18 and substantially come out as product. Therefore, for each volume of
diluent
19 that is added to one of the feed locations, a similar volume must be
subtracted
from another feed location in order to ensure that the product D/B ratio
21 remains essentially constant. Note that the larger the change in diluent
flows,
22 the longer it will take for the process to re-establish steady-state.
23
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1 It is desirable under most conditions to split the diluent addition
2 between the primary and secondary IPS's. While it is technically possible to
3 control the D/B ratio in the secondary IPS (as is done in the primary IPS),
it is
4 not practical. The reason is that the feed to the secondary IPS is variable
(possibly highly variable if the froth feed composition is changing).
Therefore,
6 it is easier to control the split ratio of diluent to the primary versus
secondary
7 IPS's. Note that a desired split ratio is first calculated based on expected
flow
8 and compositions of the secondary IPS feed. This ratio is then adjusted to
9 zero in on a desired secondary IPS D/B ratio (without causing any
significant
deviation in the primary IPS product quality).
11 When operating the primary IPS at the desired froth feed rate and D/B
12 ratio, the underflow is drawn away from the IPS at a specific rate. That
rate is
13 a ratio of the underflow to feed rates. Any diluted froth/bitumen that is
not
14 drawn off as underflow is pushed over the top and is collected as diluted
bitumen product. Note that it is desirable to fine tune the underflow of the
16 primary IPS to draw the emulsion out the bottom for additional treatment
17 rather than allowing it to migrate up and into the product. The emulsion
(level
18 and thickness) is monitored using a segmented capacitance probe which
19 shows the percentage of water at various heights in the IPS. Note that the
absence of an emulsion layer would be represented by a sharp change in
21 capacitance from a low number representing predominately hydrocarbon to a
22 high number representing predominately water. Conversely, a thick emulsion
23 layer would be represented by a gradual change in capacitance from a low
24 number to a high number.
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1 Having reference now to Figure 1, it shows a process circuit in broad
2 and simplified outline. The invention was tested in a corresponding test
circuit
3 1, which is shown in greater detail in Figure 2. This Figure 2 test circuit
will
4 now be described, followed by a Table setting forth the composition
analyses,
D/B ratios and results of an experimental run. It will be noted that neither
6 Figure 1 or Figure 2 show equipment such as pumps, valves or meters. It is
7 expected that one skilled in the art will insert such equipment as required.
8 The test circuit 1 comprised a primary IPS 2, a secondary IPS 3, a
9 primary cyclone 4 and an optional secondary cyclone 5 which could be used
in or closed out of the circuit. These units were connected in sequence for
11 enabling three or, if desired, four successive stages of separation. The
circuit
12 was countercurrent in design. It was adapted to clean deaerated bitumen
13 froth 6 in stages by separating the hydrocarbons (bitumen and diluent) from
14 the water and solids components to separately recover a diluted bitumen
product 7, containing small residual amounts of water and solids, and a water
16 and solids tailings 8, containing a small content of residual hydrocarbons.
17 A source 10 of deaerated bitumen froth 6 was provided. This source
18 was a bitumen extraction plant in an oil sands facility. The froth 6
comprised
19 a partly emulsified mixture of bitumen, water and particulate solids
comprising
coarse sand and clay fines.
21 The froth source 10 was connected by line 11 with a primary mixer 12.
22 The mixer 12 was connected by line 9 with the inlet of the primary IPS 2.
23 A source 13 of hydrotreated naphtha was connected by a line 14 with
24 the primary mixer 12, for supplying primary diluent 13a thereto.
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The overflow 18 from the secondary IPS 3 was recycled through line
17 to the primary IPS 2.
The primary mixer 12 was equipped with an impellor and functioned to
blend the viscous froth 6 and primary diluent 13a. Recycled secondary IPS
5 overflow 18 was added to produce a resulting mixture 15 fed to the primary
IPS 2 through line 9.
The primary IPS 2 was conventional in design. It contained a plate
pack 21 of 96 parallel plates of size 3150 x 610 mm spaced apart 38 mm and
angled at 55 . The vessel was sized to accommodate a feed rate up to
10 47m3/h. Overflow was controlled by a weir.
The primary IPS was operated by controlling the D/B ratio of the feed
15, the feed flow and the underflow. The D/B ratio was controlled with the
objective of ensuring that the product was within the specification for
contaminants. The feed flow was controlled with the objective of ensuring that
the IPS loading rate was low enough so that the desired froth cleaning was
realizable. And the underflow was controlled with the objective of ensuring
that the water, solids and emulsions were drawn away from the product. The
overflow was not directly controlled as the liquid level was set by the
overflow
weir. In addition it was an objective to keep the top level of the emulsion
zone
below the bottom of the plate pack 21, using the information from a
capacitance probe positioned in the IPS.
The primary diluted bitumen product 7 was produced as overflow from
the primary IPS 2 through line 16.
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1 The primary IPS underflow 20 was conveyed through line 23 to a
2 secondary mixer 24. Secondary diluent 22 was pumped through line 25 to the
3 secondary mixer 24. And primary cyclone overflow 26 was recycled through
4 line 27 to the secondary mixer 24. The three streams were blended in the
mixer and the resulting mixture 28 was fed through line 29 to the inlet of the
6 secondary IPS 3.
7 The secondary IPS 3 was identical to the primary IPS 2.
8 The secondary IPS was operated by controlling the primary/secondary
9 diluent split with the objective of ensuring that a D/B range within the
desirable
range previously given was achieved. The underflow was controlled with the
11 objective of ensuring that the water, solids and emulsions were drawn down.
12 The overflow was not directly controlled as the liquid level was set by the
13 overflow weir. In addition it was an objective to keep the top level of the
14 emulsion zone below the bottom of the plate pack, using the information
from
a capacitance probe positioned in the IPS.
16 As previously mentioned, the secondary IPS overflow 18 was recycled
17 to the primary IPS 2.
18 The secondary IPS underflow 30 was conveyed through line 31 to the
19 inlet of a tertiary mixer 32. Tertiary diluent 33 could be fed through line
34 to
the mixer 32. And overflow 35 from the secondary cyclone 5 was recycled
21 through line 36 to the mixer 32. These three streams were blended in the
22 mixer 32 and the resulting mixture 37 fed through line 38 to the inlet of
the
23 primary cyclone 4.
24 The primary cyclone 4 was a Krebs g-Max (trade-mark) cyclone.
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1 The primary cyclone 4 was operated by controlling the feed pressure.
2 Maintaining a target feed pressure maintained g forces, which enhanced
3 emulsion breaking and rejection of unwanted water and solids to the
4 underflow.
As previously indicated, the overflow 26 from the primary cyclone 4
6 was recycled to the secondary IPS 3.
7 The underflow 40 from the primary cyclone 4 could be fed directly
8 through line 41 to the inlet of the secondary cyclone 5, which was similar
to
9 the primary cyclone 4. The secondary cyclone overflow 35 was recycled to
the primary cyclone 4 and its underflow was produced as circuit tailings 8.
11 The secondary cyclone was also operated by controlling the feed
12 pressure.
13 An experimental run was conducted in the test circuit 1 and yielded the
14 following data:
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Stream Stream Flow Water Bitumen Diluent Mineral D/B
# Description t/h wt % wt % wt % wt % Ratio
6 Froth Feed 13.17 34.21 62.31 0 3.48 0
Total Diluent 5.22 0.10 0 99.10 0 n/a
13a Primary Diluent 2.00 0.10 0 99.10 0 n/a
Diluted Froth Feed 15.17 29.71 54.09 13.18 3.02 0.24
15 Primary IPS Feed 23.32 20.24 48.55 29.07 2.15 0.60
7 Primary IPS Overflow 13.42 0.65 60.69 38.34 0.32 0.63
Product
20 Primary IPS Underflow 9.90 46.80 32.09 16.50 4.62 0.51
22 Secondary Diluent 3.20 0.10 0 99.10 0 n/a
28 Secondary IPS Feed 18.29 33.13 26.17 37.08 3.62 1.42
18 Secondary IPS Overflow 8.15 2.63 38.23 58.62 0.52 1.53
30 Secondary IPS Underflow 10.14 57.65 16.47 19.78 6.10 1.20
33 Tertiary Diluent 0.02 0.10 0 99.10 0 n/a
37 Primary Cyclone Feed 15.31 42.61 23.03 29.57 4.78 1.28
26 Primary Cyclone Overflow 5.19 27.46 31.03 37.57 3.94 1.21
40 Primary Cyclone Underflow 10.12 50.38 18.93 25.47 5.22 1.35
Secondary Cyclone Feed 10.27 51.14 18.64 25.08 5.14 1.35
35 Secondary Cyclone Overflow 5.14 12.94 36.10 48.76 2.19 1.35
8 Secondary Cyclone 5.14 89.33 1.17 1.41 8.09 1.20
Underflow
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