Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SEPARATION OF BITUMEN FROM
_AR SANDS BY FLOTATION
This invention relates to a flotation method for
improved separation of bitumen from aqueous slurries in a
tar sands extraction process.
The invention is particularly useful in conjunction
with the Hot Water Process for the extraction of bitumen
from tar sands, because in this process a number of
flotation operations are or can be performed.
Deposits of tar sands, also known as oil sands and
bituminous sands, have been identified in many parts of
the world including four major deposits in Alberta,
Canada.
The Alberta tar sands typically contain between 70
and 90 percent by weight of mineral solids, 5 and 20 per
cent of viscous petroleum having a 6 to 10 API gravity
and specific gravity of about 1.0 commonly referred to as
bitumen, and from about 1 to 10 percent of water. The
mineral solids usually referred to as "coarse" are mostly
quartz sand over 45 microns in particle size, whereas those
referred to as "fines" are mostly clay, silts and fine
sands having ~article size less than 45 microns. The
content of fines has been generally found to increase with
the decrease in bitumen content in the tar sands. The
usually accepted physical arrangement of the sand-bitumen-
water mixture that constitutes the tar sands depicts an
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aqueous phase which envelops the hydrophilic sand
grains and separates them from the bitumen phase. The
key requirement for the production of bitumen is a fast
and complete separation of the bitumen from the mineral
solids. Various techniques for separating the bitumen
from mined tar sands have been developed to different
degrees in the last several decades. These include:
direct coking, solvent extraction, cold water separation
process, spherical agglomeration and a sand reduction
process just to mention a few. These methods are not
being used on commercial scale due to a variety of
reasons, such as material handling problems, low bi-tum0n
recoveries, hi~h energy requirements, solvent 109ses, etc.
The present commercial plants, Suncor and Syncrude,
are based on the Hot Water Process which was initiated in
the 1920's by The Research Council of Alberta led by
K. A. Clark.
An excellent write-up on tar sands and on bitumen
recovery technology is presented by Donald Towson in
Kirk-Othmer Encyclopedia of Chemical Technology, Third
Edition, pages 602-627.
In the Hot Water Process, the mined tar sands are
treated in a tumbler with hot water, steam and additives,
usually caustic, to break down the lumps and produce a
slurry at approximately 80C-90C. The slurry is diluted
with hot water to approximately 50% solids, then pumped
into a gravity separation cell where entrained air causes
the bitumen to float. The flotation process produces the
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primary froth, middlings and an underflow, which
constitutes the primary tailings.
The secondary froth, which is produced from the
middlings by air flotation, con-tains approximately twice
the amount of solids and water as compared to the
primary froth. Tailings from the secondary circuit join
the primary tailings to form the extraction plant tailings.
Following de-aeration and heating, the combined froth
stream is further treated by dilution and centrifuging to
remove the solids and water from the bitumen in preparation
for the upgrading or coking process. The solids and water
removed togethe.r with residual hydrocarbons consti-tute the
froth trea-~ment plan-t tailings.
Since the early stages of development of the Hot Water
Process, it has been recognized that lower grade ore, with
its higher percentage of fines and lower bitumen content,
results in lower bitumen recovery in the primary separation
stage and increased load (total middlings flow and solids
content) in the secondary air flotation circuit. Since the
secondary separation produces froth with high, mainly ine
solids content, the total solids and water content may
surpass the handling capability of th~ froth treatment
plant. Consequently, large amounts of bitumen are lost in
; the extraction plant tailings. A more efficlent separation
of bitumen from the middlings stream is highly desirable if
a high level of bitumen recovery is to be achieved. This
may also allow for reduced cut-off grade of tar sands ore
at the mine and increase the total tar sand resource
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available for processing.
Many improvements of the Hot Water Process have been
proposed which could be classified under two headings:
1. Improved control to increase bitumen recovery
and separation efficiency of the existing
plants;
2. Development of methods for the recovery of
the residual hydrocarbons from the tailings
and for improving the settling characteristics
of the sludge.
Some of these proposals seem to be more ef~ective
than others, however, most are not cost effective because
they require major modifications to the existiny plants.
It is, therefore, the object of the present invention
to provide a novel flotation method whereby a high
quality froth with high bitumen recoveries is obtained
and this without requiring major modifications to the
existing installations. This object is achieved by using
a solid hydrocarbon, such as coke or coal, as collector.
It is already known to use solid hydrocarbons, such
as coke or coal, to improve bitumen recovery in tar sands
operations, as disclosed for example in Canadian Patent
No. 1,088,445 of October 28, 1980 by A. Frederick Sirianni
and John A. Ripmeester, or ln Canadian Patent No.
1,107,216 of August 18, 1981 by William H. Hill. These
are agglomeration processes wherein the solid hydrocarbon
amalgamates or unites with the bitumen and the so formed
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organic phase is then separated from the aqueous phase.
In contrast to the above, the present invention relates
to the use of a solid hydrocarbon, such as coke or coal as
a collector in a flotation method enhancing the collection
of bitumen in the form of froth. The solid hydrocarbon
collector also acts as a depressant for the minerals by
preventing the surface active agents in the pulp to act as
a collector for such minerals.
The novel method can be used in any system that
utilizes flotation for the extraction of bitumen, but it is
particularly useful in conjunction with the Hot Water Pro-
cess where it can be employed, with advantage, at various
stages, such as :
1. Tumbler feed
2. ~qiddlings stream
3. Tallings stream
~. Tailings pond
5. Any combination of the above.
In this regard, it should be noted, however, that if
the novel process is used in the tumbler feed and/or
~iddlïngs stream stages, certain modifications of the ex-
traction and froth treatment plants would be required. On
the other hand, its use at the tailings stream and/or
tailings pond stages would require the construction of a
flotation plant with minor modifications to the existing
process .
hus, according to the present invention, the addiLion
of a solid hydrocarbon as a collector to the tar sands pulp
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to float the bitumen and depress the minerals results in
a significant improvement in froth quality (i.e. lower
solids content). The solid hydrocarbon may, for example,
be coke or coal, which is comminuted to the extent that it
can act as collector and it will preferably have a particle
size between about 0.07 mm and 1.0 mm. The amount of the
solid hydrocarbon to be added may vary depending on the
actual process or treatment in which it is employed; how-
ever, it will be an amount suitable for the solid hydro-
carbon to act as a collector for the liquid hydrocarbon~bïtumen) droplets extracted during the process: the most
suitable amount can be readily established by those familiar
with the art of flotation and, preferably, such collector is
used ïn an amount of 0.1~-6~ by weight with reference to the
pulp (slurry) on wet basis. In thls regard, the collector
can be added prior to or during the flotation proper or by
stages and, in fact, staged addition of the coke, for
example, can decrease the required dosage significantly.
It has also been surprisingly found that the concen-
tration of surface active agents in the pulp is signifi-
cantly reduced by the use of such collector. This reduc-
tion decreases the ability of such surface active agents to
act as a collector for the minerals present in -the pulp.
The minerals are thereby effectively depressed and, thus,
the solid hydrocarbon collector also acts as a depressant
for the mineral particles.
The flotation can be carried out with air, or with an
ïnert gas such as nitrogen, or with combustion gas if it is
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readily available. However, it has been found that C02
is particularly suitable as flotation gas and results in a
further increase in separation efficiency, producing
higher grade froth.
This process can also be applied for upgrading a
typical secondary froth by adding to it solid hydrocarbon
as collector and re-floating the same.
Further advantages of the novel method reside in the
finding that the tailings from this method can be readily
flocculated to produce a faster settling sludge. Also, the
presence of the solid hydrocarbon collector in the froth
enhances the ease of further separation of the remaining
solids from the bitumen. In this regard, it should be
pointed out that the amount oE solids and watex in the
recovered bitumen should be as low as possible and the
lower the concentration of bitumen in the slurry, the
higher the solids recovery for a given bitumen recovery.
For example, in the existing process, with bitumen concen-
tration of about 2%-22% in the middlings pulp, the cut-off
li`mit for solids contained in the bitumen phase is usually
2% for a 30% solids slurry. Above this limit, the separa-
tïon of such sollds would present too much difficulty and
is ~nacceptable on industrial scale.
Thus, it is often the solids content (mineral finesj
i`n the recovered bitumen that controls the permissible per-
centage of bitumen separation itself.
The invention will now be further described with
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reference to some non-limitative examples and with refer-
ence to the appended drawings in which:
Figure l shows comparative values of bitumen recovery
versus froth grade;
Fïgure 2 shows comparative values of bitumen recovery
versus froth quality;
Figure 3 shows comparative values of bitumen recovery
versus froth quality on diluted middlings; and
Figure 4 shows comparative curves of solids recov
eries and bitumen recoveries versus flotation time.
EXAMPLES
1. Tests were conducted on middlings samples which
contain 55% wt. solids, 3.6~ wt. bitumen and wa~er. 4.5 Kg
samples were heated in a flotation cell and kept at 80C.
Flotation tests were conducted with air, with CO2, wi-th air
and collector, and with CO2 and collector. Collector dosage
was 4.5% by weight relative to the slurry and the collector
was added at various stages of the flotation process. Froth
was collected after l, 3, 6 and 12 minutes of flotation.
The results for the tests with 210 grams of fluid coke addi-
ti`on into the middlings before flotation are presented in
Ti~ures l and 2 in comparison with air flotation and CO2
flotation. By using CO2 and fluid coke as a collector, the
ini`ti`al recovery of bitumen after 3 minutes increased from
~ 25 39.5% to 81.9% with froth grade increasing from 18% to 31%,
; froth grade being defined as bitumen/(bitumen + minerals
water~, % wt. in the cumulative froth. The minerals to
bltumen mass ratio in the froth is improved from 1.55 to
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0.54. Other collector dosages between 0.4% and 5~ byweïght relative to the slurry were tested in the same
manner and gave similar advantageous results~
2. Tests conducted on diluted middlings to 30~ wt.
solids and 2% wt. bitumen (with other conditions being
the same as in Example 1) resulted in similar bitumen re-
covery rates but with significant improvement in the
separation efficiency; mineral to bitumen ratios dropped
from 0.62 to 0.39 at the 90% bitumen recovery level, as
illustrated in Figure 3.
3. Rate tests were conducted on secondary circuit
slurry con-taining 30% solids and 2% bitumen by weight at
80-82C. The curves in Figure ~ yive the results obtained.
The two bottom curves indicate results of recovery of
solids in the ~roth without addition to collector (broken
curve) and with 4.5~ coke addition as collector(solid curve).
The two upper curves indicate bitumen recovery under the
same circumstances.
It is obvious from this figure that, with a solids
cutoff at 2~ and without addition of the coke collector,
only about 50% of bitumen recovery is achieved, ~hereas
with the addition of the coke collector, about 77% of bitu-
men recovery is realized, an increase of 54%.
The above examples clearly demonstrate the effective-
ness of the novel method. When applied to the Hot WaterProcess plants, the method can be employed mostly with
existing equipment (i~e. flotation circuit) with only minor
process~modifications. The fact that coke is readily
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available in such plants as by-product is another signifi-
cant advantage. The important benefits of the process
include higher bitumen recoveries with lower solids content;
better control in case of variations ln feed stock quality;
higher recycle ratio of process waters; reduction in
tailings pond requirements and altogether lower cost per
barrel of bitumen produced.
The invention is not limited to the specific embodi-
ments described above and any modifications obvious to those
lQ skilled in the art are included therein.
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