Note: Descriptions are shown in the official language in which they were submitted.
CA 02612791 2007-11-29
PROCESS FOR SELECTIVE RECOVERY OF BITUMEN
FROM OIL SANDS SLURRIES BY COLUMN FLOTATION
FIELD OF THE INVENTION
[0001] This invention applies to the fields of flotation and bitumen
extraction
from oil sands.
BACKGROUND OF THE INVENTION
[0002] Conventional oil sands processing consists of vigorous mixing with
warm water at 30-50 C. This slurry is fed to a primary separation vessel (PSV)
where a bitumen froth product is obtained, along with a tails stream and a
middlings
stream. The middlings stream contains some bitumen that is normally recovered
by
froth flotation in columns or mechanical cells [Godard & Cleyle, 2004;
Mankowski
et al, 1999; Wiwchar et al, 2004; Cleyle & Lee, 2006]. Flotation froth is
normally
recycled back to the primary separation vessel.
[0003] The bitumen froth product from the PSV must meet targeted bitumen
and solids contents. Bitumen froth product typically has a bitumen content of
55%
and a solids content of 15% [Mankowski et al, 1999]. Clearly, these targets
are
influenced by the composition of feed material to the PSV, including the
recycled
flotation froth from the middlings circuit. To date, limited attempts have
been made
to control the composition of such feeds because they are viewed to be outside
operational control.
1
CA 02612791 2007-11-29
100041 The current operating practice in oil sands middlings circuits is to
maximize bitumen recovery. The problem with this operating philosophy is that
solids fines are also recovered with the bitumen in the flotation froth. These
fines
make their way back to the PSV and can be carried over to bitumen froth
product.
SUMMARY OF THE INVENTION
100051 In the present invention a flotation column is used for the flotation
of
an oil sands slurry, for example oil sands middlings where bitumen is
separated
from mineral particles. Bitumen, which is hydrophobic, adheres to rising air
bubbles to make a bitumen concentrate (flotation froth). Solids being mostly
hydrophilic, report to the column underflow as flotation tails. In particular,
the
present invention provides a method or a process for obtaining flotation froth
with a
pre-determined solids content by manipulating the bias of a column cell.
[00061 In contrast with conventional operating practise, the method of this
invention recovers bitumen within a solids recovery constraint, i.e. solids
deportment to the flotation froth is constrainted to be within a predetermined
limit.
According to one aspect, this is done by maintaining the column bias at or
above a
predetermined value, such as for example -0.015 cm/s.
[00071 Column bias or bias rate is based on water balance and in its simplest
form compares water in the concentrate, resulting from the froth flotation, to
wash
water. Zero bias is when the net difference of water between these streams is
zero.
In other words, wash water simply replaces the volume of water in the
concentrate
at zero bias. Positive bias is when wash water exceeds water in the
concentrate.
The difference can be expressed as volume of water per unit time per unit area
of
column, or as a superficial velocity. This is particularly important and best
2
CA 02612791 2007-11-29
visualized at the upper end of the column. An equivalent measure for bias is
the net
difference of water flow between the tailings resulting from the froth
flotation and
the feed to the column.
100081 As a close approximation for overall low solids density operations, all
slurry stream volumes can be expressed in terms of water volumes or flows, the
solids assumed to be negligible. At zero bias, the concentrate (water) flow
rate
equals the wash water flow rate; and, therefore, the feed (water) flow rate
would
equal the tails (water) flow rate. It follows that the tails flow rate would
exceed
feed flow rate for positive bias. For this invention, we compared the
difference
between the tails slurry rate and the feed slurry rate to calculate bias.
Therefore, the
bias rate of a flotation column is closely approximated and calculated by
subtracting
the flow rate of column feed from the flow rate of the column tails. In
effect, the
bias is a measure of the net downward flow of water at the upper part of the
flotation column, measured in volumetric units per cross-sectional area of
column
over time, typically in cm3 per cm2 per second, or cm/s. If the only water fed
to a
column is that in the column feed, the bias is clearly negative: feed flow is
the sum
of concentrate and tails flow. If sufficient water is added in the froth water
wash,
then the bias can be positive: water wash flow equals or exceeds the
concentrate
flow. For the tests done in relation to this invention, wash water was added
as froth
underwash. Froth underwash is the introduction of wash water into a column
below
the bitumen froth layer so that the bitumen bubble aggregates rise through a
layer of
clean (solids-free) water.
[00091 In the process of this invention, the solids deportment from oil sand
slurry to flotation bitumen froth is preferably kept below 10% with respect to
the
feed to the column by maintaining the column bias, for example, at about -
0.015
cm/s or higher. Results from test work show that a more negative bias than
this
value results in very high solids deportments to flotation froth concentrate.
This due
3
CA 02612791 2007-11-29
to the higher net upwards flow of water inside the column carrying suspended
solids
to the froth and entrainment of solids particles in the froth.
[0010] To summarize, the present invention identifies the column bias rate as
a key parameter in the separation of solids from bitumen.
[0011] According to one aspect of the invention, the objective is to limit
solids recovery to the flotation froth to 10% with respect to the feed to the
column
or less by adjusting the column bias rate.
[0012] The preferred practise is to operate a column flotation cell in a
manner
such that the calculated net overall downward flow of water within the upper
part of
the column above the feed point (column bias rate) is above about -0.015 cm/s.
According to another aspect of the invention, the range of bias rate is
between about
-0.015 and 0.5 cm/s.
[0013] This method is applicable to separation of bitumen from oil sand
slurry that is composed of bitumen, mineral solids and water. The method can
be
applied in secondary recovery where bitumen is recovered from an oil sands
middlings stream. The method can also be applied to tertiary recovery, where
bitumen is separated from oil sands tailings, such as cyclone overflow.
[0014] According to another aspect of the invention, froth underwash is used
in the column and the flow rates of feed, wash water as underwash, flotation
froth,
and flotation tails are adjusted to meet the range of bias rates mentioned
above.
[0015] According to another aspect of the invention, overhead wash water is
used in the column and the flow rates of feed, wash water, flotation froth,
and
flotation tails are adjusted to meet the range of bias rates mentioned above.
4
CA 02612791 2011-08-12
Alternatively, wash water may be added in the froth.
[0016] The main advantage of this method is that it defines an operational
parameter that is relatively easy to adjust and control. Although column bias
is a known
concept in the metallurgical field, it is novel and new to the oil sands
industry. No such
method is described in the literature for limiting solids recovery to
flotation froth in the
recovery of bitumen from oil sands.
[0016a] In a further embodiment of the present invention there is provided a
process for the recovery of bitumen from an oil sand slurry, the oil sand
slurry
comprising bitumen, mineral solids and water. The process may include:
subjecting the oil sand slurry to flotation in a flotation column; and
selectively controlling a column bias of the flotation column to produce
flotation
tailings and a flotation bitumen froth having a predetermined solids content
of about 10
% by weight or less resulting from a controlled deportment of the mineral
solids from the
oil sand slurry to the flotation bitumen froth, the flotation column being
operated in a
manner so as to modulate a net difference of water flow between the flotation
tailings and
the oil sand slurry.
[0016b] The column bias may be maintained at a value of at least about -0.015
cm/s.
[0016c] The column bias may be maintained at a value of about -0.015 cm/s to
about 0.5 cm/s.
[0016d] In a further embodiment of the present invention, the process may
further
include selectively controlling the column bias further to include operating
the flotation
column in a manner such that a net overall downward flow of water within an
upper part
of the flotation column at a location above a feed point of the oil sand
slurry to the
flotation column is above about -0.015 cm/s.
CA 02612791 2011-08-12
[0016e] The oil sand slurry may be obtained from an oil sand-derived primary
stream, an oil sand-derived middlings stream or an oil sand-derived tailings
stream.
[0016f] The oil sand slurry may be obtained from an oil sand tailings cyclone
overflow.
[0016g] The process may further include applying wash water above the
flotation
bitumen froth as overhead wash water, into the flotation bitumen froth, or
below the
flotation bitumen froth as underwash.
[0016h] The process may further include a flow rate of the oil sand slurry, a
flow
rate of wash water, a flow rate of the flotation bitumen froth, a flow rate of
the flotation
tailings or a combination thereof being adjusted to control the column bias.
[0016i] In a further embodiment of the present invention, there is provided a
process for the recovery of bitumen from an oil sand slurry, the oil sand
slurry
comprising bitumen, mineral solids and water. The process may include:
subjecting the oil sand slurry to flotation in a flotation column; and
selectively controlling a column bias of the flotation column to produce
flotation
tailings and a flotation bitumen froth having a predetermined solids content
of about 10
% by weight or less resulting from a controlled deportment of the mineral
solids from the
oil sand slurry to the flotation bitumen froth, the flotation column being
operated in a
manner such that a net overall downward flow of water within an upper part of
the
flotation column at a location above a feed point of the oil sand slurry to
the flotation
column is above about -0.015 cm/s.
[0016j] In yet a further embodiment of the present invention there is provided
a
process for the recovery of bitumen from an oil sand slurry, the oil sand
slurry
comprising bitumen, mineral solids and water. The process may include:
subjecting the oil sand slurry to flotation in a flotation column; and
selectively controlling a column bias of the flotation column to produce
flotation
tailings and a flotation bitumen froth having a predetermined solids content
of about 10
5a
CA 02612791 2011-08-12
% by weight or less resulting from a controlled deportment of the mineral
solids from the
oil sand slurry to the flotation bitumen froth, the flotation column being
operated in a
manner so as to modulate a difference between a flow rate of wash water to the
flotation
column and a flow rate of water in the flotation bitumen froth from the
column.
[0016k] The column bias may be maintained at a value of at least about -0.015
cm/s.
[00161] The column bias may be maintained at a value of about -0.015 cm/s to
about 0.5 cm/s.
[0016m] In a further embodiment of the present invention, the process may
further
include selectively controlling the column bias further to include operating
the flotation
column in a manner such that a net overall downward flow of water within an
upper part
of the flotation column at a location above a feed point of the oil sand
slurry to the
flotation column is above about -0.0 15 cm/s.
[0016n] The slurry may be obtained from an oil sand-derived middlings stream.
[0016o] The slurry may be obtained from an oil sand-derived tailings cyclone
overflow.
[0016p] The process may further include a froth underwash being applied in the
flotation column and wherein a flow rate of the oil sand slurry may be fed to
the column,
a flow rate of the froth underwash, a flow rate of the bitumen flotation
froth, a flow rate
of flotation tailings or a combination thereof may be adjusted to control the
column bias.
[0016q] The process may further include an overhead wash water being used in
the
flotation column and wherein a flow rate of the oil sand slurry may be fed to
the column,
a flow rate of the overhead wash water, a flow rate of the bitumen flotation
froth, a flow
rate of the flotation tailings or a combination thereof may be adjusted to
control the
column bias.
5b
CA 02612791 2011-08-12
[0016r] In a further embodiment of the present invention, there is provided an
apparatus for the recovery of bitumen from an oil sand slurry, the oil sand
slurry
comprising bitumen, mineral solids and water. The apparatus may include:
means for subjecting the oil sand slurry to flotation in a flotation column;
and
means for selectively controlling a column bias of the flotation column to
produce
flotation tailings and a flotation bitumen froth having a predetermined solids
content of
about 10 % by weight or less resulting from a controlled deportment of the
mineral solids
from the oil sand slurry to the flotation bitumen froth, the flotation column
being
operated in a manner so as to modulate a net difference of water flow between
the
flotation tailings and the oil sand slurry.
[0016s] The column bias may be maintained at a value of at least about -0.015
cm/s.
[0016t] The column bias may be maintained at a value of about -0.015 cm/s to
about 0.5 cm/s.
[0016u] The apparatus may further include the means for selectively
controlling
the column bias further including means for operating the flotation column in
a manner
such that a net overall downward flow of water within an upper part of the
flotation
column at a location above a feed point of the oil sand slurry to the
flotation column may
be above about -0.015 cm/s.
[0016v] The oil sand slurry may be obtained from an oil sand-derived primary
stream, an oil sand-derived middlings stream or an oil sand-derived tailings
stream.
[0016w] The oil sand slurry may be obtained from an oil sand tailings cyclone
overflow.
[0016x] The apparatus may further include means for applying wash water above
the flotation bitumen froth as overhead wash water, into the flotation bitumen
froth, or
below the flotation bitumen froth as underwash.
5c
CA 02612791 2011-08-12
[0016y] The apparatus may further include a flow rate of the oil sand slurry,
a flow
rate of wash water, a flow rate of the flotation bitumen froth, a flow rate of
the flotation
tailings or a combination thereof being adjusted to control the column bias.
[0016z] In a further embodiment of the present invention, there is provided an
apparatus for the recovery of bitumen from an oil sand slurry, the oil sand
slurry
comprising bitumen, mineral solids and water. The apparatus may include:
means for subjecting the oil sand slurry to flotation in a flotation column;
and
means for selectively controlling a column bias of the flotation column to
produce
flotation tailings and a flotation bitumen froth having a predetermined solids
content of
about 10 % by weight or less resulting from a controlled deportment of the
mineral solids
from the oil sand slurry to the flotation bitumen froth, the flotation column
being
operated in a manner such that a net overall downward flow of water within an
upper part
of the flotation column at a location above a feed point of the oil sand
slurry to the
flotation column is above about -0.015 cm/s.
[0016aa] In a further embodiment of the present invention, there is provided
an
apparatus for the recovery of bitumen from an oil sand slurry, the oil sand
slurry
comprising bitumen, mineral solids and water. The apparatus may include:
means for subjecting the oil sand slurry to flotation in a flotation column;
and
means for selectively controlling a column bias of the flotation column to
produce
flotation tailings and a flotation bitumen froth having a predetermined solids
content of
about 10 % by weight or less resulting from a controlled deportment of the
mineral solids
from the oil sand slurry to the flotation bitumen froth, the flotation column
being
operated in a manner so as to modulate a difference between a flow rate of
wash water to
the flotation column and a flow rate of water in the flotation bitumen froth
from the
column.
[0016bb] The column bias may be maintained at a value of at least about -0.015
cm/s.
5d
CA 02612791 2012-06-01
[0016cc] The column bias may be maintained at a value of about -0.015 cm/s to
about 0.5 cm/s.
[0016dd] The means for selectively controlling the column bias further may
include
means for operating the flotation column in a manner such that a net overall
downward
flow of water within an upper part of the flotation column at a location above
a feed point
of the oil sand slurry to the flotation column is above about -0.015 cm/s.
[0016ee] The slurry may be obtained from an oil sand-derived middlings stream.
[0016ff] The slurry may be obtained from an oil sand-derived tailings cyclone
overflow.
[0016gg] The apparatus may further include a froth underwash being applied in
the
flotation column and wherein a flow rate of the oil sand slurry may be fed to
the column,
a flow rate of the froth underwash, a flow rate of the bitumen flotation
froth, a flow rate
of flotation tailings or a combination thereof may be adjusted to control the
column bias.
[0016hh] The apparatus may further include an overhead wash water being used
in
the flotation column and wherein a flow rate of the oil sand slurry may be fed
to the
column, a flow rate of the overhead wash water, a flow rate of the bitumen
flotation froth,
a flow rate of the flotation tailings or a combination thereof being adjusted
to control the
column bias.
[0016ii] In a further embodiment, there is provided a process of producing
bitumen
from an oil sand slurry. The process may include
introducing the oil sand slurry proximate to an upper end of a flotation
column at
a slurry feed rate, wherein the oil sand slurry comprises at least three
phases including
bitumen, minerals and water;
providing wash water into the upper end of the flotation column at a wash
water
rate;
5e
CA 02612791 2012-06-01
providing air proximate to a lower end of the flotation column, the air
comprising
an upwardly mobile carrier phase, wherein the bitumen included in the oil sand
slurry
interacts with the upwardly mobile carrier phase;
monitoring and selectively controlling a column bias of the flotation column
to
produce in the lower end of the column flotation tailings including minerals
and water,
the flotation tailings flowing at a tailings flow rate, and a flotation
bitumen froth in the
upper end of the column, the flotation bitumen froth having a predetermined
solids
content of about 10 % by weight or less resulting from a controlled deportment
of the
minerals from the oil sand slurry to the flotation bitumen froth, the
flotation bitumen
flowing at a concentrate flow rate;
discharging the tailings from the flotation column at the tailings flow rate,
and
producing the flotation bitumen from the flotation column at the concentrate
flow
rate.
[0016jj] The monitoring and selectively controlling the column bias may
include
operating the flotation column in a manner so as to modulate a net difference
of water
flow between the flotation tailings and the oil sand slurry.
[0016kk] The monitoring and selectively controlling the column bias may
further
include maintaining the column bias at a value of at least about -0.015 cm/s,
or of of
about -0.015 cm/s to about 0.5 cm/s.
[001611] The monitoring and selectively controlling the column bias may
further
include operating the flotation column in a manner such that a net overall
downward flow
of water within an upper part of the flotation column at a location above a
feed point of
the oil sand slurry to the flotation column is above about -0.015 cm/s.
[0016mm] The monitoring and selectively controlling the column bias may
further
include operating the flotation column in a manner so as to modulate a
difference
between a flow rate of wash water to the flotation column and a flow rate of
water in the
flotation bitumen froth from the column.
5f
CA 02612791 2012-06-01
[0017] Further objects and advantages of the invention will become apparent
from the description of preferred embodiments of the invention below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The invention will now be described, by way of examples, with reference
to the accompanying drawings, in which:
[0019] Figure 1 is a diagrammatical illustration of the operation of a froth
flotation column as applied to the flotation of a oil sands slurry;
[0020] Figure 2 is a simplified process flow diagram illustrating the
operation of a
demonstration plant for the recovery of bitumen from an oil sand slurry by
column
flotation;
[0021] Figure 3 is a graphical illustration showing solids recovery (i.e.
deportment of solids to flotation froth) in a flotation column as a function
of column bias
rate;
[0022] Figure 4 is a graphical illustration showing solids recovery as a
5g
CA 02612791 2007-11-29
function of column bias rate in a flotation column not operated under the
conditions
of the present invention;
[0023] Figure 5 shows plots of bitumen-solids selectivity for different bias
ranges in a flotation column; and
[0024] Figure 6 shows a plot of bitumen-solids selectivity for different bias
ranges in a flotation column not operated under the conditions of the present
invention.
[0025] Figures 7a and b, respectively, show bitumen and solids recovery to
overflow as a function of pulp residence time in a flotation column;
[0026] Figure 8 is an illustration of bitumen flotation selectivity against
solids
for low-grade and high-grade feeds in a flotation column;
[0027] Figures 9a and b, respectively, show flotation froth bitumen/solids
ratio and bitumen grade as functions of bitumen recovery in a flotation
column; and
[0028] Figures 10a and b, respectively, show bitumen and solids recovery to
overflow as a function of pulp residence time in a flotation column not
operated
under the conditions of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] In the following description, certain specific details are set forth in
order to provide a thorough understanding of various embodiments of the
invention.
However, one skilled in the art will understand that the present
apparatus/method
6
CA 02612791 2007-11-29
has additional embodiments, and/or may be practiced without at least some of
the
details set forth in the following description of preferred embodiment(s). In
other
instances, well known structures associated with the technology have not been
described in detail to avoid unnecessarily obscuring the descriptions of the
embodiments of the invention.
[0030] The operation of a flotation column for the flotation of an oil sands
slurry for the separation of bitumen from mineral particles is illustrated in
Figure 1.
This separation is based on the bitumen and mineral particles having different
surface hydrophobicities. Oil sands slurry (feed) 1, flows into the column 2
near,
but not at, the top, while air bubbles 3 are forced in near the bottom of the
column 2.
Hence, there are two carrier phases: air bubbles 3 moving up, and aqueous feed
I
moving down. Bitumen, naturally hydrophobic, adheres to rising air bubbles and
forms a froth 4 that overflows 5 to a launder at the top of the column 2. The
mineral
particles, being hydrophilic, remain in aqueous suspension and flow down and
out
the bottom of the column 2. The froth 4 that overflows the column, carrying
mostly
bitumen, is termed flotation concentrate. The underflow pulp 6 carrying mostly
undesired mineral, or "gangue", is termed flotation tails. Wash water 7 is
introduced
in the column 2, above the froth 4 as overhead wash, or in the froth 4, or
below the
froth 4 as underwash, as desired.
[0031] The invention is illustrated by the following example based on a
demonstration plant run using the equipment as show in Figure 2. This plant
included, among the various unit operations, two columns 12 and 14 for bitumen
flotation. Figure 2 shows a process flow diagram for the demonstration plant.
Oil
sands material was passed through a roll sizer 16 and fed to a countercurrent
drum
separator 18 where it was mixed with warm water. Lean froth containing bitumen
overflowed from the ore feed end 20, and wet sand exited at the other end 22.
Wet
sand exiting the drum 18 was dried in a belt filter 24. Bitumen in the lean
froth was
separated in a primary separation cell (PSC) 26. PSC overflow was piped to a
tank
7
CA 02612791 2007-11-29
farm 29 for the temporary storage of bitumen froth product. PSC tails 28 were
fed
to the flotation column 12. Overflow 30 from the column 12 was fed back to the
PSC while the underflow 32 was fed to a thickener 34 for water recovery.
Thickener overflow 36 was fed to the flotation column 14 for flotation of
trace
bitumen. Clean water in the underflow 3 8 of the column 14 was reheated and
fed
back to the drum separator 18.
[00321 Column 12 was a 9.2-m-tall, 2.7-m-diameter (50 m) SGS Minnovex
column with an internal launder. Principal feed to the column was underflow
from
the PSC. Feed composition varied within the ranges of. 0.01-0.81% bitumen
content, 1.5-15.1 % solids content, and 84.4-98.3% water content. On occasion,
the
column 12 operated with froth underwash. Flows ranged from 149 to 215 m3/h for
PSC underflow, and 0.8 m3/h for underwash. Forced aeration within the column
12
was in the order of 0.5 cm/s superficial gas velocity (Jg). Gas holdup volume
was
approximately 10%. The purpose of this column was to recover residual bitumen
from PSC tails 28.
[00331 Column 14 was a 9.2-m-tall, 2.0-m-diameter (27 m) SGS Minnovex
column with an internal launder. Sole feed to the column was thickener
overflow
36, with flows ranging from 107 to 184 m3/h. Feed composition varied in the
ranges of. 0-0.33% bitumen content, 0-2.3% solids content, and 97.7-99.9%
water
content. The column 14 had no froth underwash. Forced aeration within the
column was in the order of 0.5 cm/s superficial gas velocity (Jg). Gas holdup
volume was approximately 10%. The purpose of column 14 was to remove all
residual bitumen from thickener overflow 36 prior to sending the water (column
underflow 38) back to the water heater sump 40.
[00341 Figure 3 shows a plot of column bias rate versus solids recovery to
froth flotation in the column 12. In this specification solids recovery refers
to the
8
CA 02612791 2007-11-29
amount, proportion or percentage of solids that deports the flotation froth.
Note
how the solids recovery remains below 10% at column bias rates above -0.015
cm/s. At bias rates lower than -0.015 cm/s, the solids recovery increases,
sometimes
exceeding 40%.
[0035] Figure 4 shows a plot of column bias rate versus solids deportment to
froth flotation in the column 14. This column was operated with no froth
underwash and with a minimum froth depth. Hence, the bias rate was more
negative than for column 12 and never surpassed -0.025 cm/s. Note that the
solids
recovery was consistently above 10% and sometimes reached 100%.
[0036] The operating ranges recommended are a bias rate of -0.015 cm/s or
higher. Within this range, rates between -0.015 and 0.5 cm/s are preferred.
Bias
rates above 0.5 cm/s require substantial wash water or froth underwash flow
rates
that may not be practical. In effect, a range of -0.015 to 0.05 cm/s is deemed
sufficient to limit solids recovery within the 10% value. Optimal bias rate
will vary
with various feed materials and other solids recovery levels can be selected
as
desired.
[0037] The forced aeration rate of the flotation column 12, 14 should be
maintained such that the superficial gas velocity within the column falls in a
range
of 0.2 to 3.0 cm/s.
[0038] Figure 5 shows plots of solids recovery as a function of bitumen
recovery for cases where the bias rates were above or below -0.015 cm/s in
column
12. These bitumen-solids selectivity plots help to gauge and compare bitumen-
solids separation efficiencies. The diagonal line represents no separation,
i.e. equal
recoveries of bitumen and solids. Both data sets lie below the diagonal line,
indicating that there was separation, i.e. bitumen recovery to flotation froth
9
CA 02612791 2007-11-29
concentrate was greater than solids recovery. The higher bias (>-0.015cm/s)
data
set is further below the line than the lower bias (<-0.015 cm/s) data set,
indicating
higher flotation selectivity and therefore higher degree of separation at bias
rates
greater than -0.015 cm/s.
[00391 In effect, the higher bias gave higher quality flotation products. In
general, bitumen froth quality is based on the bitumen-solids ratio. This is
analogous to the grade recovery relationships used in mineral processing.
Figure 6
shows grade-recovery plots for the different bias rates in the flotation froth
concentrate of the column 14.
[00401 Column 14 was operated with bias rates below the ranges
recommended by this invention. Indeed, the bitumen-solids selectivity plot
shown
in Figure 6 indicates that there was little separation between bitumen and
solids;
namely, the data points fall on both sides of the equidistant line.
[00411 Column 14 was operated at low bias rates because its primary purpose
was to recycle bitumen-free water to the water heater 40. Hence, the lack of
bitumen-solids separation was inconsequential. Column 14 was run with a
minimum froth depth. The flotation froth concentrate carried large amounts of
solids as well as bitumen.
[00421 Figures 7a and b show the flotation kinetics for bitumen and solids,
respectively. In this specification, recovery is defined as the portion of
bitumen (or
solids) fed to the column 12 that reported to concentrate (or overflow) 30.
Recoveries to overflow 30 are plotted against estimated pulp residence times
in the
column 12. The pulp residence times are estimates based on pulp flows because
no
residence time distribution tracer tests were done. Pulp residence time
estimates
assumed a gas holdup volume of 10% based on pulp flow velocities approximating
CA 02612791 2007-11-29
1 cm/s, thus giving an effective pulp volume of 45 m3 inside the column 12.
Two
sets of data are shown in Figures 7a and b: one set corresponds to feed
bitumen
grades of 1-6% and another corresponding to feed bitumen grades of 6-19%. It
is to
be noted that bitumen grades and bitumen contents are not the same. These
terms
are defined as follows:
content = bitumen x 100% (1)
bitumen + solids + water
grade = bitumen x 100% (2)
bitumen + solids
[00431 The reason for considering grade as defined in Equation 2 is based on
the concept that water is a carrier phase in column flotation. Separation is
based on
the differential hydrophobicity of particles (be they solids or bitumen) and
their
subsequent attachment to air bubbles. Hence, only bitumen droplets and solid
particles participate in the separation. In mineral processing terminology,
grade is
defined as the desired mineral divided by the desired mineral plus gangue, or
impurities. When that definition is applied to bitumen flotation, the solids
are the
obvious impurities.
100441 Figures 7a and b shows that the difference between bitumen and solids
recovery at a given residence time was greater (more effective separation) in
the low
grade feeds (1-6%), than in the high grade feeds (6-19%). Although in both
cases
bitumen floated much faster than the solids, bitumen recoveries were higher
with
lower grade feeds. Solids deportment to concentrate was faster in the high
grade
feeds than the low grade feeds. Another method to gauge and compare separation
efficiencies is to draw bitumen/solids selectivity plots, as shown in Figure
8.
100451 Figure 8 shows plots of solids recovery as a function of bitumen
recovery. The diagonal line represents no separation, i.e. equal recoveries of
11
CA 02612791 2007-11-29
bitumen and solids. Both data sets lie below this line, indicating that there
was
separation, i.e. bitumen recovery to overflow was greater than solids
recovery. The
low grade data set is further below the line than the high grade data set,
indicating
higher flotation selectivity and therefore higher degree of separation at
lower feed
grades. In effect, the lower grade feeds gave higher quality flotation
products. In
general, bitumen froth quality is based on the bitumen/solids ratio. This is
analogous to the grade recovery relationships used in mineral processing.
100461 Figures 9a and b, respectively, show bitumen/solids curves and grade
recovery curves for column 12 flotation froth. It can be seen that the charts
in
Figures 9a and b are virtually identical. They both illustrate the trade-off
relationship between recovery and product quality. As more bitumen is
recovered,
froth quality necessarily decreases. An extreme example of this is that 100%
bitumen recovery would be achieved by simply having 100% of the column feed
going to overflow (no separation). The grade recovery curve (or ratio recovery
curve) allows the operation of a column for optimal recovery and froth
quality. For
example, according to Figures 9a and b, if a 60% bitumen grade (bitumen/solids
ratio of 1.5) were desired, the column 12 would have had to be operated such
that
the bitumen recovery were about 84% for low grade feeds and about 60% for high
grade feeds. According to Figures 7a and b, this would have been achievable by
having a pulp residence time of 13.5 minutes for low grade feeds, and 13
minutes
for high grade feeds.
[00471 Figures IOa and b, respectively, show the flotation kinetics for
bitumen and solids in column 14. Recoveries to overflow are plotted against
estimated pulp residence times in the column. Pulp residence times were
estimated
assuming a gas holdup volume of 10%. The data shown in Figures 10a and b
correspond to feed bitumen grades that were between 8 and 63%.
12
CA 02612791 2007-11-29
[0048] Figures IOa and b show that bitumen and solids had nearly identical
flotation kinetics in column 14. Indeed, as already mentioned, the bitumen
versus
solids recovery data shown in Figure 6 indicates that there was no flotation
selectivity between bitumen and solids. The data points fall on both sides of
the line
of no separation.
[0049] Bitumen/solids separation took place in the first scavenger flotation
column 12 but not in the second scavenger flotation column 14. This was likely
due, in part, to the feed compositions in the two columns (see Table 1).
Compared
to column 12, the feed to column 14 had very little solids, almost all of it
fines (<44
m). These fines would have been entrained and carried with froth water to the
bitumen froth concentrate. Note that the error values in Table 1 represent 26
from
the mean values.
13
CA 02612791 2007-11-29
Table 1. Feed composition of column feeds
Column 12 Column 12 Column 14
(low grade) (high grade)
Bitumen grade, % 3.1 3.4 10.4 9.6 36.7 42.5
Solids content, % 7.1 8.2 6.6 8.3 0.6 1.7
Fines in solids (<44 m), 63.8 35.9 58.6 41.2 93.8 17.6
[00501 The lack of bitumen/solids separation in column 14 was
inconsequential to the plant because the purpose of column 14 was to scavenge
bitumen from recycle process water prior to heating. That was in contrast to
column
12, where efficient bitumen/solids separation was necessary.
[00511 Column flotation froth proved very unstable, with violent bubble
bursting and bitumen splashing if a froth layer was allowed to form at the top
of the
columns 12 and 14. To overcome this problem, the columns 12, 14 were run with
minimal froth depths. The froth instability may be explained by the operating
temperatures that ranged between 50 and 60 C for both columns. At these
temperatures, the decreased surface tension of water promotes bubble
coalescence,
resulting in very large bubbles. Operating the columns 12, 14 as scavengers
resulted
in increased carryover of water to the bitumen froth concentrate.
100521 One operational difference between the columns 12 and 14 was that
froth underwash was used in column 12 but not in column 14. This meant that
column 14 always ran with a negative bias while column 12 sometimes ran with a
positive bias, depending on flows. As mentioned, bias refers to the net
downward
flow of water through the flotation froth. When underwash flow is sufficiently
high
that the column underflow is higher than the feed flow, then the column is
said to
14
CA 02612791 2007-11-29
run with a positive bias.
[00531 A number of common flotation parameters were not measured in the
tests. These include froth velocity and lip carrying capacity; pulp residence
time
distribution for detection of short-circuiting; gas dispersion and holdup;
bubble size;
and bubble surface area flux to determine carrying capacity.
[0054] To summarize, the following conclusions can be drawn from the tests:
100551 Bitumen/solids separation in column 12 was successful at 50-60 C,
with feeds having bitumen grades between 1 and 19%, and where the solids had
about 60% fines. Bitumen/solids separation did not occur in column 14 at 50-60
C,
with feeds having bitumen grades between 8 and 63%, and where the solids had
about 90% fines. The lack of separation was likely due to high solids
entrainment in
the flotation froth.
[00561 Bitumen column flotation data can be analyzed and interpreted by
adopting mineral processing principles. Flotation kinetics can be deduced by
plotting bitumen or solids recovery as functions of residence time. Flotation
performance can be evaluated and predicted by plotting bitumen grade (or
bitumen/solids ratio) as a function of bitumen recovery. Bitumen/solids
separation
(or selectivity) can be evaluated and predicted by plotting solids recovery as
a
function of bitumen recovery. Interpretation of bitumen flotation data becomes
very
straightforward when bitumen grade is described only in terms of bitumen
content
and solids content, with the water portion being excluded. Water can be
considered
simply as a carrier phase. These same mineral processing principles used for
column cells are also applicable to bitumen flotation in mechanical cells.
CA 02612791 2011-08-12
[00571 Unless the context requires otherwise, throughout the specification and
claims which follow, the word "comprise" and variations thereof, such as
"comprises"
and "comprising" are to be construed in an open, inclusive sense, that is as
"including but
not limited to."
[00581 Although specific embodiments of the invention have been described and
illustrated, such embodiments should not be construed in a limiting sense.
Various
modifications of form, arrangement of components, steps, details and order of
operations
of the embodiments illustrated, as well as other embodiments of the invention,
will be
apparent to persons skilled in the art upon reference to this description. It
is therefore
contemplated that the appended claims will cover such modifications and
embodiments
as fall within the true scope of the invention. In the specification including
the claims,
numeric ranges are inclusive of the numbers defining the range. Citation of
references
herein shall not be construed as an admission that such references are prior
art to the
present invention.
16
