Note: Descriptions are shown in the official language in which they were submitted.
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Patent
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Elevated Temperature Treatment of Bitumen Froth
By Yicheng Long and Tyler Smith
Field of the Invention
[0001] The invention relates to a method and apparatus for treatment of
bitumen froth to enhance
separation of solids and water as well as partial asphaltene rejection.
Background
[0001] Oil sand is essentially a matrix of bitumen, mineral material and
water, and possibly
encapsulated air. The bitumen component of oil sand consists of viscous
hydrocarbons which
behave much like a solid at normal in situ temperatures and which act as a
binder for the other
components of the oil sand matrix. Oil sand will typically contain about 10%
to 12% bitumen
and about 3% to 6% water, with the remainder of the oil sand being made up of
mineral matter.
The mineral matter component in oil sand may contain about 14% to 20% fines,
measured by
weight of total mineral matter contained in the deposit, but the amount of
fines may increase to
about 30% or more for poorer quality deposits. Oil sand extracted from the
Athabasca area near
Fort McMurray, Alberta, Canada, averages about 11% bitumen, 5% water and 84%
mineral
matter, with about 15% to 20% of the mineral matter being made up of fines.
Oil sand deposits
are mined for the purpose of extracting bitumen from them, which is then
upgraded to synthetic
crude oil.
[0002] A widely used process for extracting bitumen from oil sand is the
"water process." In
this process, both aggressive thermal action and aggressive mechanical action
are used to liberate
and separate bitumen from the oil sand. An example of the water process is the
hot water process.
In the hot water process, oil sand is first conditioned by mixing it with hot
water at about
95° Celsius and steam in a conditioning vessel which vigorously
agitates the resulting
slurry in order to disintegrate the oil sand. Once the disintegration of the
oil sand is complete,
the slurry is separated by allowing the sand and rock to settle out. Bitumen,
with air entrained in
the bitumen, floats to the top of the slurry and is withdrawn as a bitumen
froth. The remainder of
the slurry is then treated further or scavenged by froth flotation techniques
to recover bitumen
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that did not float to the top of the slurry during the separation step. The
froth is further treated to
separate solids and water from liquid hydrocarbons. Such a process is
suggested in US patent no.
5,645,714, the disclosure of which is incorporated herein.
[0003] US patent no. 5,236,577 suggests a high temperature process for
treating bitumen froth
where a froth is contacted with a diluent at a temperature in the range of 80
to 300 C. Examples
of diluents are naphtha, Varsol, and natural gas condensate. The higher
temperature is indicated
to improve the rate of separation, and to improve the ultimate product
quality, as measured by
decreasing the solids and water content of the treated froth.
[0004] Canadian patent no. 2,232,929, the disclosure of which is incorporated
herein, discloses
an improvement to the hot water process that utilizes a paraffinic solvent to
extract bitumen from
the bitumen froth.
[0005] US patent no. 6,214,213, suggests a process for treatment of a bitumen
froth wherein
hydrocarbons solvents are utilized to separate water and solids from the froth
to produce bitumen.
The hydrocarbon solvent, when combined with the froth, causes the froth
emulsion to invert.
Summary of the Invention
[0006] A method is provided to separate a bitumen product from an oil sand
compositions
wherein the oil sand composition comprises bitumen containing asphpaltenes,
the method
comprising the steps of. contacting an oil sand composition with water to form
a water and oil
sand slurry; separating the water and oil sand slurry into a froth comprising
mineral solids, water
and a hydrocarbon phase, and an underflow stream comprising solids, water, and
entrained
hydrocarbons; contacting, at a temperature above 120 C, the froth with a
sufficient amount of a
paraffinic solvent to reach at least partial asphaltene precipitation;
separating the solvent-diluted
froth into a hydrocarbon phase containing a majority of the paraffinic
solvent, a majority of the
hydrocarbons from the solvent-diluted froth, and a tailings stream containing
a majority of solids
and a majority of the water present in the froth wherein at least a portion of
the asphaltenes from
the oil sand are not in the hydrocarbon phase; and separating the hydrocarbon
phase into the
bitumen product and a recyclable solvent stream.
[0007] The paraffinic solvent may comprise butane, pentane, hexane, heptanes,
or mixtures
thereof. A portion of asphaltenes present in the froth are partitioned from
the hydrocarbon phase
into a separate asphaltene phase resulting in a bitumen product that is more
readily transported
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and processed. Separation of the asphaltene phase from the hydrocarbon phase
is considerably
more efficient at elevated temperatures. Additionally, solubility of
asphaltenes in solvent-diluted
bitumen is lower at elevated temperatures of the present process compared to
prior art processes.
The lower solubility results in considerably less solvent being needed to
produce a similar
quality of produced bitumen with asphaltenes partially removed. For example,
compared to a
typical solvent contacting temperature of about 80 C, operation at 140 to 180
C permits
lowering of the solvent to bitumen ratio by about 40% with five and/or six
carbon number
paraffinic solvent to result in a 50% reduction in asphaltene content of the
bitumen product
compared to the bitumen present in the oil sand composition. Lowering the
amount of solvent
required considerably reduces operating costs and because the size of the
equipment required is
decreased, capital costs are also reduced. Because, in prior art solvent
processes, solvent is
removed from the bitumen and the tailings streams by heating the respective
streams, the present
invention does not require significant additional heating for the feeds of the
solvent recovery unit.
Due to the reduced solvent to bitumen ratio, total energy required to recover
solvent from
solvent-diluted bitumen is significantly reduced by reduction of the amount of
solvent required.
[0008] Separation of the froth and solvent mixture into a hydrocarbon phase
and heavier phases
is enhanced at elevated temperatures. Although the present invention is not to
be limited by the
theory or mechanism, it is believed that at a temperature above 120 C the
asphaltenes exceed a
softening point and are no longer solids. Separation of solids from a solvent-
diluted bitumen
liquid phase is dictated by settling, which is very dependent on the size and
structure of the
asphaltenic particles. When beyond asphaltene softening point, the separation
of the
hydrocarbon (solvent-diluted bitumen) and heavy phases (water, mineral solids,
and precipitated
asphaltenes) becomes more like liquid-liquid separation.
[0009] Optionally, amounts of solvent similar to those used in prior art
paraffinic solvent
processes could be used and the present invention would result in reduced
asphaltene content of
the bitumen product.
Brief description of the Figure
[0010] The Figure is a process flow drawing for the process of the present
invention.
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Detailed Description of the Invention
[0011] Referring now to the Figure, an oil sand ore stream, 101, is contacted
with water 102 in a
mixer 120, to form a water and oil sand slurry 103. The oil sand ore can be a
mined bitumen ore
from a formation such as oil sands found in the Athabasca area near Fort
McMurray, Alberta,
Canada. The ratio of oil sand ore to water may be, for example, in the range
of 1 to 6 or 1 to 2.
The oil sands may contain between 75 and 95 percent by weight of mineral
solids, and may
contain between 10 and 20 percent by weight hydrocarbons. The hydrocarbon
portion of the oil
sands may have a gravity of between 7 and 10 API and may contain from 10 to
25 percent by
weight of asphaltenes. Other components of the hydrocarbon portion of the oil
sand ore may be
to 40 percent by weight aliphatics, 5 to 20 percent by weight aromatics, and
10 to 50 percent
by weight polar compounds. The mixer may agitate the slurry to break up solids
and to increase
the area of contact between the solids and the water. The mixer may also heat
the slurry to a
temperature of, for example, between 40 and 90 C to enhance separation of the
hydrocarbons
from the solids. Air and chemicals such as caustic or surfactants maybe added
to the slurry to
further enhance separation of the hydrocarbons from the solids. Alternatively,
liberation of
hydrocarbon from mineral material may be accomplished in a slurry conditioning
transportation
line. The water and oil sand slurry optionally may be screened in a screener
121 to remove
larger solids 104 from a remaining slurry stream 105.
[0012] Remaining slurry stream 105 may be further processed to provide an
initial solids
separation in a first separator 123 producing an underflow stream 114,
containing solids and
water with some bitumen, and a froth 106. The froth contains a majority of the
hydrocarbons
from the oil sands stream, along with entrained water and solids. Typically,
the froth contains
about 60 weight percent bitumen, about 30 weight percent water, and about 10
weight percent
mineral solids. The first separator may include additional steps and
equipment, such as, for
example, flotation cells, to increase the bitumen recovery and de-aerators to
remove excessive air.
[0013] Froth, 106, from the first separator may be contacted with a paraffinic
solvent, 108 to
form a solvent-diluted froth mixture 107. The solvent at elevated temperature
may cause
demulsification , and also cause at least some of the asphaltenes present in
the froth to partition
from the hydrocarbon phase into a separate asphaltene phase.
[0014] The paraffinic solvent may contain between about 80 and 100 percent by
weight of
saturated hydrocarbons that do not contain rings. The paraffinic solvent may
contain less than
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about 2 percent by weight of aromatic hydrocarbons and less than about 8
percent by weight
cycloparaffins. The paraffinic solvent may include more than 90 percent by
weight
hydrocarbons having from four to seven carbon atoms, or optionally five or six
carbon atoms. In
one embodiment of the present invention, the solvent is more than 90 percent
by weight pentane.
[0015] The solvent-diluted froth 107 may be brought to a temperature of
between 120 C and
200 C or optionally between about 120 C and 180 C, or between 140 C and 180 C.
These
temperatures may be above the softening point of the precipitated asphaltenes
under the process
conditions. The solvent-diluted froth could be brought to the desired
temperature by heating
with heat exchangers, direct contact with steam, furnaces, combinations of
these, or by other
known means. One or more of the solvent and froth streams could be heated
sufficiently prior
to being mixed so that the combined stream would be in the desired temperature
range. The
solvent-diluted froth may be held in the desired temperature range for a
residence time of
between about 1 second and about 30 minutes, or optionally between about 1
second and about
five minutes. The froth and solvent may be intimately contacted, for example,
by a static mixer
or a stirred vessel, either prior to being heated to the desired temperature
range, or within the
desired temperature range.
[0016] A benefit of increased temperatures for contacting froth with the
paraffinic solvent is that
similar bitumen product asphaltene contents may be achieved with considerably
lower ratios of
solvent to bitumen. For solvents that are at least ninety percent by weight of
pentane, hexane, or
mixtures thereof, a ration of solvent to bitumen in the froth may be between
1.1 and 2.2. When
butane is utilized as the paraffinic solvent, for example when more than fifty
percent by weight
of the paraffinic solvent is butane, or more than ninety percent by weight
butane, the ratio of
solvent to bitumen in the may be between 0.7 and 1.7. When the paraffinic
solvent comprises at
least fifty percent paraffins having a carbon number greater then 7, the
ration of paraffinic
solvent to bitumen in the froth may be between 1.5 and 3Ø
[0017] The solvent-diluted froth stream 107 may be routed to a second
separator, 124, the
second separator effective to separate the solvent-diluted froth into a
hydrocarbon phase 110 and
a tailings stream 111. The hydrocarbon phase contains a majority of the
solvent present in the
solvent-diluted froth feed, optionally at least 60 percent of the solvent in
the solvent-diluted froth
feed. The hydrocarbon phase also contains a majority of the non-asphaltene
hydrocarbons
present in the froth. Optionally, the hydrocarbon phase may contain at least
70 percent to the
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non-asphaltene hydrocarbons present in the froth stream. Separation of the
solvent-diluted froth
into the hydrocarbon phase and the tailings stream may be done while the
streams are in the
temperature range of between 120 C and 200 C, optionally between 120 C and 180
C, or
between 120 C and 160 C. The tailings stream may contain a majority of the
inorganic solids
and a majority of the water present in the froth. In some embodiments of the
invention, the
tailings stream contains more than 95 percent of the solids present in the
froth, and optionally at
least 99 percent of the solids from the froth.
[00181 Asphaltenes may be partially partitioned from the hydrocarbon phase
into a separate
asphaltene phase and at least partially rejected into the tailings, or
recovered as a separate stream
from the second separator. This partitioning may be useful when decreasing the
asphaltene
content of the bitumen increases options for marketing the bitumen. For
example, the
asphaltenes removed from the bitumen and not recovered with the bitumen
product may be
between ten and eighty percent of the asphaltenes present in the oil sand
composition.
[0019] For simplicity, a single second separator is shown in the Figure,
although it is to be
understood that the second separator could be a series of separation stages
optionally including
counter-current contacting with solvent. The second separator may optionally
be a process that
produces three or more products. The three or more products could be the
hydrocarbon stream
essentially as described above, a stream that contains a majority of the
inorganic solids in the
solvent-diluted froth and water, and the precipitated asphaltenes. The
tailings stream of the
present invention would be a combination of the stream containing a majority
of the inorganic
solids and the stream concentrated in asphaltenes. The second separator can be
tank separator(s),
hydrocyclone(s), inclined plate separator(s), or their combinations. The
second separator may
have internals to enhance separation.
[0020] Recycle solvent 109 may be recovered from the hydrocarbon stream 110 in
a solvent
recovery unit 125, leaving a bitumen product 112. The bitumen product may have
less than
about 15 percent by weight asphaltene content, and less than 1 percent by
weight water content.
Some solvent may optionally remain in the bitumen product, for example, to
facilitate pipeline
transportation of the bitumen product.
[0021] Tailings 111 may be processed in a tailings solvent recovery unit 127
to remove at least a
portion of the solvent present in the tailings stream 113 and a solvent free
tailings stream 115.
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The recovered solvent from the tailings solvent recovery unit 113 may be
combined with recycle
solvent and make-up solvent 116 to form the solvent stream 108.
[0022] The solvent recovery unit 125 may use known methods to remove more
volatile
hydrocarbons from less volatile hydrocarbons such as distillation and
supercritical solvent
separation. The tailings solvent recovery unit may utilized known methods to
remove volatile
hydrocarbons from solids and/or aqueous streams such as using the heat present
in the tailings
stream for vaporization of the solvent.
[0023] Water in the tailings may be at least partially separated from the
solids and recycled, for
example, to the slurry of oil sand slurry 103. Recycling water from the
tailings reduces the need
to provide additional water 102. Recycling this water as hot water also
provides additional heat
to the front- end water extraction process and improves energy efficiency of
the overall process.
Alternatively, at least a portion of the heat in the tailing stream 115 can be
recovered using heat
exchangers before the tailings stream 115 is sent to the tailings pond.
[0024] The invention also includes the apparatus capable of performing the
method.
[0025] The concentration of asphaltenes in the bitumen product may be below
about 15 percent
by volume, or below about 10 percent by volume, or between 6 and 12 percent by
volume.
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