Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS F'OR RECOVERING HYDROCARBONS
FROM TAR SANDS
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
[0001] The present invention relates to an improved process of recovering
hydrocarbons
from tar sands and like minerals and, mare specifically, to the use of
hydrogen peroxide for such
recovery.
DESCRIPTION OF THE PRIOR ART
[0002] Tar sands (which are also known by other names such as oil sands,
bituminous sands
etc.) are sand deposits that are impregnated with dense, viscous petroleum.
One of the largest
deposits of tar sands is in the Athabasca region of Alberta, Canada. This
region is believed to
contain more petroleum than the combined known reserves of the entire world.
Unfortunately,
due to the physical characteristics of these tar sands oil reserves, and their
mixture with sand and
minerals, extraction of the desired hydrocarbons involves a higher cost that
makes this source of
oil less attractive.
[0003] Various solutions have been developed for improving the efficiency of
hydrocarbon
recovery from tar sands. One of these methods is the "hot water process",
wherein tar sands are
first subj ected to steam and alkali treatment to form an aqueous slurry. The
heat treatment
initially serves to separate a hydrocarbon portion comprising the mare
volatile components.
Also, by forming the tar sands into a slurry, the viscosity of the hydrocarbon
material is reduced
so as to facilitate its transport. The slurry is then subjected to a frothing
step wherein the heavier
hydrocarbon material, also referred to as bitumen or bituminous material, is
collected in the froth
and later separated. This process, however, can result in a lower than desired
yield of
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hydrocarbons as some of the bituminuous material is lost in the tailings,
which is comprised
mainly of sand particles. Apart from the reduced hydrocarbon yield, the
resulting sand cannot be
easily discarded due to environmental concerns.
[0004] Canadian patent number 1,275,063 teaches an improved hot water process
wherein
tar sands are treated with an oxidizing agent such as hydrogen peroxide to
facilitate extraction of
the heavier hydrocarbon materials. A similar method is taught in Canadian
patent application
number 2,177,018. Another tar sands treatment process is taught in US patent
number
6,251,290. Although having improved hydrocarbon extraction efficiency, these
methods involve
additional cost that may render the process economically unattractive. In
addition, these
references relate mainly to batch processes and do not provide guidance on
continuous processes.
The references also do not teach any means of optimizing the use of the H2OZ
oxidant for
achieving efficient and economic operation.
[0005] Notwithstanding the improvements to the hot water process discussed
above, there
exists still a need for a more improved hydrocarbon extraction process wherein
a higher, faster
and more cost effective hydrocarbon recovery is obtained and wherein the use
of the oxidizing
agent is made in an effective manner.
SUMMARY OF THE INVENTION
[0006] In accordance with a preferred embodiment, the present invention
provides a process
for recovering hydrocarbons from tar sands comprising:
- forming a heated slurry of said tar sands by mixing said tar sands with
water;
- pumping the slurry to a separation vessel;
- diluting said slurry with water and mixing said slurry with an oxidizing
agent, said
oxidizing agent being capable of generating gas bubbles when contacted with
said slurry;
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- generating a first froth layer in said separation vessel to entrain a first
hydrocarbon
fraction containing hydrocarbons in said slurry;
- separating the slurry in said separation vessel into said first froth layer,
a tailings layer,
and a middlings layer, said tailings layer comprising solid components of said
slurry and said
middlings layer comprising liquid and fines components of said slurry;
- removing and transporting said first froth layer to a froth treatment
station;
- removing and transporting said tailings layer to a coarse tailings treatment
station; and,
removing and transporting said middlings layer to a flotation tank.
[0007] In accordance with another embodiment, the present invention provides a
process for
recovering hydrocarbons from tar sands comprising:
- forming a heated slurry of said tar sands by mixing said tar sands with
water;
- pumping the slurry to a separation vessel;
- diluting said slurry with water;
- generating a first froth layer in said separation vessel to entrain a first
hydrocarbon
fraction containing hydrocarbons in said slurry;
- conducting a primary hydrocarbon separation in said separation vessel, said
separation
resulting in said first hydrocarbon rich froth layer, a hydrocarbon lean
tailings and a middlings
layer;
- removing said middlings layer and transporting said layer to a flotation
tank, said
flotation tank including an inlet for addition of an oxidizing agent; the
oxidizing agent being
capable of generating gas bubbles when contacted with the middlings;
- generating a second froth layer in said flotation tank to entrain
hydrocarbons contained
in said middlings;
- separating and removing said second froth layer; and,
- removing the remaining contents in said flotation tank.
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[0008] In accordance with another embodiment, the present invention provides a
process for
recovering hydrocarbons from tar sands comprising:
- forming a heated slurry of the tar sands by mixing the tar sands with water;
- pumping the slurry to a separation vessel;
- diluting the slurry to increase the water to ore ratio;
mixing, or injecting, the slurry with an oxidizing agent, the oxidizing agent
being
capable of generating gas bubbles when contacted with the slurry;
- separating the slurry in said separation vessel into a first froth layer, a
tailings layer, and
a middlings layer, the first froth layer comprising a first hydrocarbon
fraction of the
hydrocarbons contained in the slurry, the tailings layer comprising the solid
components of the
slurry and the middlings layer comprising liquid and fines components of the
slurry;
- removing and transporting the first froth layer to a froth treatment
station;
- removing and transporting the tailings layer to a coarse tailings treatment
station;
- removing and transporting the middlings layer to a flotation tank, the
flotation tank
including a froth generating means comprising air sparging andior injection of
hydrogen
peroxide;
- generating a second froth in the flotation tank to entrain a second
hydrocarbon fraction
containing hydrocarbons in the middlings;
- removing and transporting the second froth layer either back to the
separation vessel or
directly to the froth treatment station;
- removing and transporting the remaining portion in the flotation tank to a
fine tailings
treatment station or back into the bottom of the separation vessel.
[0009] In accordance with yet another embodiment, the invention provides a
process for
recovering hydrocarbons from tar sands comprising:
- forming a heated slurry of the tar sands by mixing the tar sands with water,
the slurry
having a water to ore ratio of about 0.2 to 0.5 by weight;
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- pumping the slurry to a separation vessel with a hydrotransport system;
- diluting the slurry to a water to ore ratio of about 0.5 to I .6 by weight;
- mixing the slurry with hydrogen peroxide;
- separating the slurry in said separation vessel into a first froth layer, a
tailings layer, and
a middlings layer, the first froth layer comprising a first hydrocarbon
fraction of the
hydrocarbons contained in the slurry, the tailings layer comprising solid
components of the slurry
and the middlings layer comprising liquid and fines components of the slurry;
- removing and transporting the first froth layer to a froth treatment
station;
- removing and transporting the tailings layer to a coarse tailings treatment
station;
- removing and transporting the middlings layer to a flotation tank, the
flotation tank
including a froth generating means comprising air sparging and/or injection of
hydrogen
peroxide.
- generating a second froth in the flotation tank to entrain a second
hydrocarbon fraction
containing hydrocarbons in the middlings;
- removing and transporting the second froth layer either back to the
separation vessel or
directly to the froth treatment station;
- removing and transporting the remaining portion in the flotation tank to a
fine tailings
treatment station or back into the bottom of the separation vessel.
BRIEF DESCRIPTION OF THE DRAW1NGS
[0010] These and other features of the preferred embodiments of the invention
will become
more apparent in the following detailed description in which reference is made
to the appended
drawings wherein:
[0011] Figure 1 is the schematic drawing of a tar sands treatment process
according to a
preferred embodiment of the invention.
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[0012] Figure 2 is a graph illustrating the average effects of extraction
variables on primary
recovery of hydrocarbons from tar sands according to the present invention.
[0013] Figure 3 is a graph illustrating the average effects of extraction
variables on total
recovery of hydrocarbons from tar sands according to the present invention.
[0014] Figures 4 and 5 are graphs illustrating the effect of peroxide addition
point on primary
plus secondary recovery.
[0015] Figure 6 is a graph illustrating froth recovery as a function of time.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] In the following description, it will be understood that the term "tar
sands" will be
used to refer to tar sands, oil shales and other such naturally occurring
material wherein
hydrocarbons are bound or mixed with sand or other mineral deposits. Further,
the terms "oil",
"bitumen" or "hydrocarbons" will be used to refer to any hydrocarbon material
that is contained
in tar sands and which is to be recovered.
[0017] One of the objects of the present invention is to provide an improved
process for
hydrocarbon extraction from tar sands that results in a high hydrocarbon
recovery with a reduced
cost. In one of its embodiments, the present invention provides a process that
has a lower
demand for an oxidizing agent, such as hydrogen peroxide (HZOZ). As will be
understood, such
reduction in oxidant will reduce the cost associated with the hydrocarbon
extraction process. In
the course of this study, it has been found that one of the key factors
associated with improving
extraction efficiency lies in the point at which the oxidant ("peroxide") is
added. It has also been
found that with a select addition point of the oxidant, a lower concentration
can be used.
Furthermore, it has been found that the addition of hydrogen peroxide not only
improves the
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recovery yield but also increases the recovery rate, i.e. the velocity with
which bitumen froth can
be recovered from tar sands. The following description discusses these aspects
of the invention
in more detail.
[0018] In most of the known tar sands treatment systems, the following
treatment steps are
followed: digestion; flotation; and scavenging (secondary flotation). In the
digestion step, the tar
sands are formed into a slurry and heated and mixed. It is at this stage in
the prior art that an
oxidant, such a hydrogen peroxide, is added to the slurry. During this step,
the viscosity of the
hydrocarbon material is reduced and the oxidant serves to support the release
of bituminous
material from the sand or mineral components. Once the slurry is formed, it is
subjected to one
or more frothing processes to entrain the hydrocarbon material released from
the sand. The sand
is then discarded as known in the art.
[0019] In the prior art, for example US Patent No. 6,251,290, it leas been
postulated that the
addition of an oxidant to the tar sands slurry serves to partially oxidize the
hydrocarbon material
and to break any polar bonds between such components and sand particles.
However, the
present study has concluded that the beneficial action of the peroxide lies
with its in-situ
decomposition on the surfaces of the solids and the generation of oxygen
bubbles, which, in turn,
support the vertical flotation of oil to the surface. Once a free gas bubble
is formed, the
interfacial characteristics of the gas/water and bitumen/water interfaces make
attachment of the
oil to the bubble favourable and thus support the mechanical separation of the
hydrocarbon
material from the sand. A particular advantage of an in-situ bubble generating
oxidant over
sparged air is that gas bubbles are generated right at the bitumen/solid
interface and the
association of the bubbles with bitumen is enhanced by the proximity of newly
formed bubbles
to bitumen. These bubbles begin as microbubbles and grow to a range of sizes,
which eventually
provide sufficient lift to float the attached oil. Furthermore, the reaction
of peroxide with the
solid surfaces renders the solids more water wet, which hinders reattachment
of separated
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bitumen. As such, the present invention provides an improved process wherein
separation within
the slurry is increased and accelerated by, among other means, the addition of
an oxidizing agent
at specific locations and at specif.c concentrations to maximize its
functional efficiency.
[0020] Figure 1 schematically illustrates a process in accordance with the
preferred
embodiment of the invention. As shown, the system includes three stages
labelled as I, II and
III. The first stage, I, comprises the digestion or "conditioning" phase. At
this stage, the tar
sands are combined with preferably hot water to form a heated slurry. This
step brings the tar
sands into a pumpable state and reduces the viscosity of the slurry. During
this stage, any
volatile hydrocarbons may be released from the stream with known technologies.
[0021] Digestion of the tar sand slurry progresses as the slurry is
transported with one or
more pumps 12 to the second stage discussed below. In the preferred
embodiment, transport of
the slurry is achieved using a hydrotransport system, which is k~zown in the
art. Further, in the
preferred embodiment, the water to ore (w/o) ratio of the slurry in this
digestion phase is about
0.2 to 0.5 on a weight basis. This results in a generally thicker slurry than
that of the prior art.
For example, in US Patent 6,251,290, a w/o ratio of between 0.5 and 1.0 is
taught. Due to the
low water to ore ratio, high sheax forces are introduced and turbulent mixing
takes place in the
pipeline that breaks up clumps of sand and liberates the bitumen as the slurry
is pumped to the
second stage. Such high mechanical force present in a hydrotransport system
especially serves
to initiate the separation of the heavy hydrocarbon components from the
mineral or sand
components. In the preferred embodiment, the digestion stage is carried out in
the
hydrotransport pipeline while the tar sand slurry is transported from the mine
site to a separation
facility at a different location.
[0022] In the prior art, as discussed above, an oxidizing agent (i.e. hydrogen
peroxide) is
normally added at this digestion stage on the assumption that the partial
oxidation of the
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hydrocarbon components results in a greater hydrocarbon separation. However,
according to the
invention, no oxidant is added until the next stage or just ahead of the next
stage discussed
below. Instead, the present invention uses internally generated shear forces
during the pumping
process to initiate the hydrocarbon separation.
[0023] The second stage, stage II, is refe~yed to as the flotation stage. At
this stage, the
digested slurry is pumped into a first flotation vessel 14, also known as a
primary separation
vessel (PSV) or separation cell. At this stage, the slurry is further diluted
by addition of water 16
to result in a slurry with a water to ore (w/o) ratio in the range of about
0.5 to 1.6, which again is
a higher ratio than that taught in the prior art. In a preferred embodiment,
especially for
industrial scale equipment, the slurry is further diluted to result in a
slurry with a water to ore
(w/o) ratio of 0.6 to 1.1 by weight. This higher water content serves to aid
in the formation of
layers of froth, middlings and tailings. Along with the water 16, the desired
oxidant 18 is also
added to the slurry at this stage as well as any known flotation aids or
agents. Such flotation aids
generally include alcohols (e.g. methyl isobutyl carbinol, MIBC), caustic
(NaOH), sodium
bicarbonate (NaHC03), kerosene and other components as are apparent to persons
skilled in the
art. In the preferred embodiment, the oxidant is hydrogen peroxide primarily
due to its lower
cost. However, as discussed below, various other oxidants can be used with the
invention as will
be apparent to persons skilled in the art. As illustrated in Figure 1, the
oxidant, dilution water
and other flotation aids can be injected in-line just ahead of vessel 14 (as
shown by stream 13) or
into the aqueous middlings stream of the vessel 14, below the bitumen-laden
froth layer (as
shown by stream 15). Addition of the oxidant and water ahead of the vessel 14
(i.e. via stream
13) offers a few advantages. Firstly, from a process point of view, it is
easier to mix the oxidant
and water into the slurry when done in-line as opposed to directly into the
vessel 14. Further,
better mixing and more efficient dilution of the slurry is achieved when the
oxidant is introduced
in-line. The hydrogen peroxide is preferably added to result in an oxidant
concentration less than
0.5%, and preferably between 0.01 % and 0.1 % by weight in the aqueous phase.
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[0024] In the vessel 14, the slurry is agitated to enhance the formation of a
primary froth 20
on the surface of the slurry. During this phase, the solids 22 (i.e. send
etc.) settle to the bottom
of the vessel. As known in the prior art, the froth 20 entrains the
hydrocarbon material released
from the tar sands. Once settling of the solids 22 is complete, the sand,
which is essentially free
of hydrocarbons, is removed as coarse tailings and taken 23 to a tailings
treatment step 24, to be
discarded in a manner as known in the art. The froth 20 is extracted and
passed to a separate
froth treatment process 26 for extracting the hydrocarbon material entrained
therein. Such froth
treatment methods are commonly known in the art and typically include the
mixing of a
paraffinic solvent (e.g. naphtha) with the froth to lower the viscosity of the
bitumen, so that it can
be cleaned of water and solids by centrifuging, hydrocycloning or settling.
The remaining
aqueous phase 28, referred to as the middlings layer, of the vessel 14 is
transported to the third
phase of the system, which involves the "scavenging" process or "secondary
flotation" as
discussed below. The primary separation vessel 14 is generally maintained at
about 25°C or
higher, to allow enough heat for the hydrogen peroxide to decompose. In the
preferred
embodiment, the temperature of the vessel 14 is maintained at about 25°
to 65°C. This
temperature range offers optimal conditions for the decomposition of I-IZO2.
Although
temperatures higher than 65°C may be utilized, the energy cost to raise
the temperature to such
level would not be recouped. The heat of the slurry from stage I would
normally be sufficient to
~ maintain the desired temperature conditions and, as such, no additional
heating system is
required, thereby allowing costs to be minimized.
[0025] As discussed above, one of the aspects of~ the present invention is to
increase bitumen
recovery of the tar sand. In the preferred embodiment, the oxidant added to
the slurry during the
flotation stage is one that results in the generation of a gas when added to
the slurry (i.e. in-situ
generation). According to a preferred embodiment, the oxidant is hydrogen
peroxide (HZO2). It
is known that hydrogen peroxide decomposes, upon contact with the mineral and
solids fraction
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of the tar sands slurry, into oxygen gas and water. ~.Tnder normal
circumstances the
decomposition is sufficiently catalyzed by the mineral and solids fraction of
the tar sand and, as
described ahove, the temperature of the separation vessel 14 is maintained at
a value to ensure
such decomposition. However, in on.e embodiment of the invention, additional
HZO2
decomposition catalysts such as caustic soda (I~laOH), sodium bicarbonate
(NaHCO3), lime
(Ca(OH)2) or heavy metal ions, preferably ferric/ferrous (Fe2+i3+) or cupric
ions (Cu2+) can be
added in low amounts to accelerate the decomposition kinetics. As indicated
above, although
temperatures of about 25°C can be used, another embodiment of the
invention involves the
temperature of the slurry being raised, preferably up to 35° to
65°C in order to accelerate the
decomposition of hydrogen peroxide. Further, it is known that the oxygen
resulting from the
decomposition of HZOZ is initially formed as very small diameter bubbles
("microbubbles")
having generally uniform dimensions. It has been found in the present study
that the generation
of these gas bubbles greatly increases and accelerates the recovery of the
hydrocarbon material
contained in the slurry, more so than the application of an agitating force
alone. Once free gas
bubbles are formed, the interfacial characteristics of~ the gas/water and
bitumen/water interfaces
make attachment of the bitumen to the bubbles favourable. Exposure to hydrogen
peroxide also
renders the solid surfaces more hydrophilic and water wet so that reattachment
of separated
bitumen to dispersed solids is hindered. These features altogether support the
mechanical
separation of the hydrocarbon material from the sand and other mineral
components. As the
bubbles grow in size they entrain the hydrocarbon components and carry them to
the surface
where the froth is formed.
[0026) With an agitator alone, wherein air rnay be sparged into the slurry,
gas bubbles are
generated in a single location (i.e. the base of the vessel) and in a narrow
range of sizes and then
rise upwardly. As such, their maximal effect is localized in a certain portion
of the vessel.
Furthermore, their effect is limited upon the number of successful collisions
between rising
bubbles and oiI droplets in the suspension. On the other hand, with the
addition of hydrogen
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peroxide according to the invention, gas bubbles are generated irz-situ
throughout almost the
entire volume of the separation vessel. Even more important is the fact that
they are generated
right at the bitumen/solid interface (that is, where they have maximum contact
with bitumen)
thereby eliminating the requirement of successful collisions and maximizing
the separation
effect. The mechanistic advantage of in-situ generated oxygen bubbles over
externally
introduced air therefore lies in the higher probability of attachment of
bubbles to bitumen
droplets as a result of the proximity of newly formed bubbles to bitumen and
the alteration in the
wettability of the solid surfaces.
[0027] In the prior art, as discussed above, the oxidant is normally added
upstream of the
separation vessel, during the digestion phase. As such, the efficiency of the
oxidant would not
be maximized in such an approach since oxygen bubbles formed during digestion
would not
have a chance to float attached bitumen to the surface. A significant amount
of bubbles would
even be destroyed due to the high shear forces present in a hydrotransport
line. The present
invention, therefore, provides an improvement over the prior art by adding the
oxidant at the
most efficient location.
[0028] The third stage of the process, indicated as III in Figure 1, involves
the scavenging
(secondary flotation) of any remaining hydrocarbon material in the middlings
28 from the
primary separation vessel 14. It will be understood that the third phase of
the process is a
preferred embodiment. The middlings 28 generally comprise the liquid phase of
the slurry and
include water in which mineral fines are suspended. The middlings 28 are
transported to a
second flotation tank, or secondary vessel, 30 and subjected to a further
frothing step for
removing any remaining hydrocarbon material. In this step, the frothing is
achieved by known
sparging methods. Optionally, in another embodiment, a second hydrogen
peroxide solution 32
can be added to enhance the froth generation as described with reference to
stage II. The
peroxide solution 32 may be added together with or instead of air sparging.
The froth 34 from
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this step, referred to as the secondary froth, is retrieved and transported 36
to the froth treatment
facility 26. In another embodiment, all or a portion of the froth 34 may
optionally be returned 38
to the primary separation vessel 14 to repeat the flotation process and
improve froth quality. The
remaining liquid and solids in the tank 30 are removed as fine tailings, 40,
and taken to a fine
tailings treatment step 25, to be treated in a manner known in the art.
~ptionally, in another
embodiment of the present invention, clean flotation effluent from the
flotation tank 30 is
injected into the bottom of the primary separation vessel (PSV) 14, as shown
by stream 31, to
displace bitumen-bearing material to the middlings stream of the vessel 14.
[0029] As indicated above, the use of the flotation tank 30 is a preferred
embodiment of the
invention. It will be understood that the hydrocarbon recovery of the primary
vessel 14 will be
generally greater than that of the secondary vessel 30 due to the higher
hydrocarbon
concentration in the slurry. Extraction of hydrocarbons in the secondary tank
30 is more difficult
since the middlings stream entering the tank 30 is considerably leaner than
the feed stream to the
primary vessel 14. For this reason, as explained above, the present invention
provides an
improved secondary tank 30 wherein H202 is provided as a froth generating
means. The action
of the peroxide, as explained above, provides an efficient hydrocarbon removal
system.
[0030] The following examples are provided to illustrate the present invention
and are not
intended to limit the invention in any way.
Examples
Example 1
[0031] Various tests were carried out in a batch extraction unit (BEU) using
the process of
the present invention and the data from such tests are provided in the tables
below. The tests
were conducted to determine if hydrogen peroxide would assist in the recovery
of bitumen from
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a sample of poorly processing Athabasca oil sand, which had been taken from
the Albian Sands
Energy Inc. lease, northeast of Fort McMumay, Alberta, Canada. ~i1 sand from
this particular
stockpile had been associated with poor processing during 20-ton per hour
pilot runs on the
Albian lease.
[0032] Baseline primary recoveries from this oiI sand, without peroxide as a
process aid,
ranged from 20 to 47%, depending on the operating conditions used. Primary
recovery typically
should be in the range of 80% for a typical oil sand having 8.5% bitumen
content.
[0033] The results of a sensitivity analysis, as shown on Table 1 and in
Figures 2 and 3,
illustrate the aspects of the present invention. For this purpose several
independent extraction
variables were selected and a high and a low level defined for each variable.
Then, a factorial
design of test program was conducted to determine the significance of effects
of hydrogen
peroxide on extractability and to compare the magnitude of those effects to
the impact of other
variables. Figure 2 illustrates the average mp 'marX recovery efficiencies,
which are the recovery
rates of hydrocarbons after the Stage II step (after "primary flotation") for
all experiments
conducted at a low and a high level of each extraction variable. Figure 3
illustrates the average
total recovery efficiencies, after both the Stage II and III steps (after
"scavenging") for all
experiments conducted at a low and a high level of each extraction variable.
[0034] From the results, it is first noted that primary and total recoveries
increased by
increasing the peroxide dosage from 0.1 to 0.5% in water. Primary recovery
increased on
average from 30.5 to 46.6% and total recovery on average from 45.4 to 56.6%
(see Figures 2 and
3). As well, the results show that it was much more effective to add the
peroxide just prior to the
flotation step (Stage II) rather than during digestion (Stage I). In fact, the
point in the process at
which the peroxide was added was more important than the quantity, within the
range of
peroxide used. The average primary recovery increased from 26.9 to 50.3% and
the average
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total recovery from 40.1 to 61.9% as the point of addition was moved from
digestion (Stage I) to
flotation (Stage II). The sensitivity analyses also revealed that only the
point of addition and the
peroxide concentration had an average effect on recovery at the 95% confidence
level. The
effects of other extraction variables were insignificant or significant at
much lower statistical
confidence levels (e.g. temperature).
[0035] Further analyses relating to froth quality revealed that the peroxide
had no measurable
effect on either the amount of solids or amount of water that floated with the
bitumen.
Bitumen/solids ratios and % Bitumen contents in the primary froth and combined
froths (i.e.
primary + secondary) were used as measures of these attributeso
[0036] The results of additional head-to-head comparisons, where all other
variables were
fixed except for peroxide addition - i.e. either no peroxide added, peroxide
added only during
digestion, peroxide added only during flotation, or peroxide added at both
stages - are shown in
Table 2. It is noted that increases in primary and total recovery were
generally higher when
peroxide was added at the flotation stage alone or when it was added at both
stages, flotation and
digestion, as compared to addition at only the digestion stage. The average
benefit in primary
recovery for adding peroxide just prior to flotation rather than during
digestion was 8.4 % and in
total recovery, 9.2 %. Given the precision of the method, the results in Table
2 confirm the
results of the factorial design of experiments (Table 1). On average, primary
and total recovery
increased from 22.2 and 37.1% respectively for the "no peroxide runs" to 38.7
and 51.2%
respectively for the "peroxide runs". When the average of runs where 0.1 %
peroxide was used is
compared to the average of runs where 0.5% peroxide was used, then average
primary recovery
was found to increase from 30.5% to 46.7%, and average total recovery from
35.7°/~ to 56.0%.
By all measures of froth quality, that is % bitumen in primary and total
froths, % solids in
primary froth (shown in Table 2) and bitumen/solids ratio in the primary and
total froths, there
was only a marginal deterioration as a result of peroxide addition in the
flotation stage.
TOOSl3-0004-CA
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CA 02428544 2003-05-09
Example 2
[0037] In the next series of tests the process aids hydrogen peroxide and
sodium hydroxide
were compared. Furthermore, it was intended to determine the impact of
peroxide if it was added
prior to scavenging (Stage III). In addition to the poorly processing Albian
oil sand, an oxidized
ore from the Athabasca Aurora site was processed. First, a baseline test with
no process aids was
conducted. Second, a "caustic" run was carried out using an amount required to
produce a
digestion slurry of pH 8.5. Then, additional two runs were made using one half
and 1.5 times of
this "optimum" amount of caustic. Third, a 2-level, full factorial experiment
was carried out, in
which the H202 addition point (prior to flotation versus prior to scavenging),
the peroxide
amount and the presence of induced air during scavenging were varied. Finally,
two additional
runs were made in which hydrogen peroxide was added prior to flotation and
prior to an
additional post-scavenging stage (see Table 3 and 4). This post-secondary
recovery stage was
carried out as a means of determining if there would be any benefit to
increasing residence time
at the end of the process to make use of any ongoing oxygen bubble formation.
[0038] The recovery data from the two series of runs are presented in Table 3
and 4. The
comparison below shows that the "optimum" caustic process and the peroxide
process yield
similar recoveries both after the typical scavenging stage (column: Primary
plus Secondary
recovery) and after the "post-scavenging" stage (column: Total Recovery). Both
processes,
however, yield significantly higher recoveries than the baseline runs without
a process aid.
Comparison of Optimized Caustic and Peroxide Recoveries:
Run Prianary ~ Prymary plus Total Recovery
Recover Secondary Recover
Albian Ore
Baseline 20.0 45.1 58.8
Optimum Caustic 45.0 70.2 79.4
T00573-0004-CA
144899-3209.57
TDO-RED X8194326 v. I
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CA 02428544 2003-05-09
Peroxide (Flotation)- 61.6 - 70.3 74.5
Peroxide (Scavenging)16.6 69.5 76.7
Aurora Ore
Baseline 24.2 61.4 85.0
Optimum Caustic 52.3 86.8 92.3
Peroxide (Flotation)74.7 86.7 91.2
Peroxide Scavenging)30.4 84.1 90.1
[0039] The comparison indicates that even if total recovery is equivalent for
the optimum
caustic and hydrogen peroxide case, recovery could be moved forward to the
primary flotation
S stage. Consequently, on a commercial scale, there is a potential for either
increased throughput
or smaller sizing of vessels to achieve equivalent recoveries.
[0040] As a result of using a factorial experiment design, it was possible to
isolate the effect
of using peroxide prior to flotation (primary recovery) versus prior to
scavenging. Figures 4 and
S show that in only one out of eight head-to-head comparisons was there a
significant benefit of
adding peroxide prior to primary flotation rather than prior to scavenging.
However, by virtue of
the fact that in all eight cases, recovery was slightly better by adding
peroxide prior to primary
flotation, there may be a small benefit to adding the peroxide in time to take
advantage of the full
extent of bubble formation.
[0041] Although primary recovery increased dramatically with peroxide addition
just prior to
that stage, changes in froth quality were marginal. For the Albian oil sand,
the average bitumen
content in the primary froth decreased from an average of 14.4% to an average
of 12.6% when
peroxide was used. The change in solids was not significant - the use of
peroxide was associated
with a minor decrease in solids content from 38.6% to 38.1%.
Example 3
T00513-0004-CA
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CA 02428544 2003-05-09
[0042] Another series of tests was carried out in a laboratory hydrotransport
loop to better
measure the effect of hydrogen peroxide on total recovery and, in particular,
on recovery
kinetics. This continuous flow loop is intended to simulate the digestion
process during slurry
transport. The operation of the loop however differs from a commercial slurry
transport design
because the recovery vessel is built into the loop so that bitumen can be
recovered even before
digestion is complete. The internal diameter of the loop was 2 inches. The
slurry - controlled at
50 °C - was comprised of 1 kg of oii sand and 3 kg of water. It was
pumped for sixty minutes
around the loop using a progressing cavity pump. A calculated amount of
hydrogen peroxide was
either charged in a single dose immediately at the beginning of the run (t= 0
min) or split in half
and added in two portions at the beginning (t=0 min) and after 30 min into the
run. In addition,
the same calculated amount of hydrogen peroxide was continuously metered into
the flow loop
over 60 minutes. A baseline run without any additive and a run with caustic as
a process aid (pH
8.5} were conducted as well for comparison purposes.
[0043] Results of the loop tests are shown in Table 5 and Figure 6. The
recovery profiles
depicted in Figure 6 reveal that all runs approach a total (cumulated)
recovery between 80 and
90% after 60 minutes. Differences in recovery are marginal after this length
of time. This
similarity in recoveries is most probably attributed to the fact that all of
the tests were carried to
extinction after 60 minutes. However, analysis of the prof les within the
first 20 minutes of the
test show recovery increases in the range of 10- 20% for the "peroxide runs"
versus the "no
additive" and "caustic" run. Figure 6, therefore, clearly demonstrates that
peroxide addition
improves the rate of recovery during the early stage of the extraction
process. Closer
examination of the recovery data of the "no additive", "single" and "double"
dosage runs with
hydrogen peroxide suggests a linear relationship between the initial recovery
rate (at t=0 min)
and the hydrogen peroxide concentration.
T00513-0004-CA
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TDO-RED #8194326 v. I
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CA 02428544 2003-05-09
[0044] The above-mentioned improvements in $°ecovery kinetics obtained
with hydrogen
peroxide are unprecedented in tar sands extraction and have not been mentioned
in the prior art.
These unexpected findings have significant economic implications for large-
scale industrial
operations. If they occur on a commercial scale, there is a potential for
either faster processing
and increased throughput of ore in existing installations or smaller sizing of
vessels for newly
designed extraction plants.
[0045] Although the invention has been described with reference to certain
specific
embodiments, various modifications thereof will be apparent to those skilled
in the art without
departing from the spirit and scope of the invention as outlined in the claims
appended hereto.
T00513-0004-CA
144899-320957
TDO-RED #t$19432G v. l
-19-
CA 02428544 2003-05-09
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