Note: Descriptions are shown in the official language in which they were submitted.
CA 02755637 2011-10-19
TH4058
SOLVENT TREATMENT OF PARAFFINIC FROTH TREATMENT
UNDERFLOW
Field of the Invention
The invention relates to a method and apparatus for treatment of bitumen froth
treatment
underflow to recover asphaltenes.
Background
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.
The "water process" is a process for extracting bitumen from oil sand. In this
process,
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.degree 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top of the slurry and is withdrawn as a bitumen froth.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 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. An example of a hot water process is suggested in US
patent no. 5,645,714,
the disclosure of which is incorporated herein.
US patent no. 5,236,577 suggests a high temperature process for treating
bitumen froth
where a froth is further processed by contact 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 elevated
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.
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Canadian patent number 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. The paraffinic solvent may be a five or six
carbon number
paraffin. The paraffinic solvent will dilute the bitumen, but also cause a
portion of asphaltenes
present in the bitumen to precipitate from the hydrocarbon phase.
Precipitation of a portion of the
asphaltenes reduces the hydrocarbon yield of the process, but provides for an
improved quality
bitumen product. The amount of asphaltenes precipitated may be controlled by,
for example,
altering the ratio of solvent to bitumen. Typically, enough asphaltenes are
precipitated to result in a
bitumen product that contains less than about ten percent by weight
asphaltenes, resulting in
removal of five to ten percent of the bitumen as precipitated asphaltenes.
Canadian patent application 2682,109 suggests a process to recover asphaltenes
from
tailings produced by a paraffinic solvent froth treatment process. Solvent in
the underflow stream
from the paraffinic solvent froth treatment is first removed in a tailings
solvent recovery unit
(TSRU), and then two solvents are added sequentially in the TSRU underflow.
First a cyclic
solvent is added, and then a polar and non-polar solvent is added to extract
hydrocarbons from the
tailings stream. The polar-non-polar solvent may be a mixture of alkanes such
as three to ten
carbon number alkanes, and either ketones or alcohols or a combination of
ketones and alcohols. A
hydrocarbon phase is formed that contains the solvents and extracted
hydrocarbons. The
hydrocarbon phase is then separated into recyclable solvents and an asphaltene
product.
Summary of the Invention
A method is provided to recover a composition comprising asphaltenes from an
oil sand
compositions, 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 the froth with a sufficient amount of a
paraffinic solvent to
reach at least partial asphaltene precipitation to form a solvent diluted
froth; 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; contacting the tailings
stream with a cyclic
solvent to form a diluted tailings stream comprising an hydrocarbon phase; and
separating at least a
portion of the hydrocarbon phase from the diluted tailings stream wherein the
hydrocarbon phase is
a composition comprising asphaltenes. The composition comprising asphaltenes
may also contain
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non-asphaltenes bitumen components, and could also contain some of the
aromatic and/or
paraffinic solvent components, but asphaltenes may be the dominate component
in this composition.
A paraffinic solvent used in paraffinic froth treatment step 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 and processed. The cyclic solvent used in underflow
treatment may be,
for example, benzene, toluene, xylene, reformate or mixtures thereof. The
suitable solvent could
comprise cycloparaffins, for example, cyclopentane, cyclohexane or
methycyclohexane. The
weight ratio of cyclic solvent to recovered asphaltenes may be between about 3
to I or about 15 to
1. Recovery of an asphaltene product according to the present invention
provides a product that
can either be used as a fuel, or sold, and also removes this component from
the tailings stream that
is disposed of in, for example, a tailings pond.
Recovery of asphaltenes from the tailings stream directly from the froth
separation rather
than from the tailings from a tailings solvent separation unit decreases the
solvent volume to be
processed in the tailings solvent recovery unit, and utilizes solvent
remaining with the froth
separation tailings to reduce the amount of cyclic solvent required. Removal
of at least a portion of
bitumen and asphaltenes remaining in the tailings from the froth separation
prior to the tailings
being processed in the tailings solvent recovery unit according to the present
invention also
improves the operation of the tailings solvent recovery unit because bitumen
and asphaltenes, when
present in the tailings, tend to hold solvent, and increase temperatures
needed to vaporize solvent as
well as solvent volume to be vaporized.
Brief description of the Figure
The Figure is a process flow drawing for the process of the present invention.
Detailed Description of the Invention
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 I to 6 or I 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 'A PI 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 10 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
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CA 02755637 2011-10-19
TH4058
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.
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.
Froth, 106, from the first separator may be contacted with a paraffinic
solvent, 108 to form
a solvent-diluted froth 107. The solvent may cause at least some of the
asphaltenes present in the
froth to precipitate and to partition from the liquid hydrocarbon phase into a
separate solid
hydrocarbon phase.
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
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.
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 I11. 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 non-
asphaltene
hydrocarbons present in the froth stream. The tailings stream may contain a
majority of the
inorganic solids and a majority of the water present in the froth along with
at least a portion of any
precipitated asphaltenes. 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.
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Asphaltenes may be partially partitioned from the hydrocarbon phase into a
separate
asphaltene phase and at least partially rejected into the tailings. This
partitioning may be useful
when decreasing the asphaltene content of the bitumen product 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.
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 can be tank
separator(s),
hydrocyclone(s), inclined plate separator(s), or their combinations. The
second separator may have
internals to enhance separation and material handling.
Recycle solvent 109 may be recovered from the hydrocarbon stream l 10 in a
solvent
recovery unit 125, leaving a bitumen product 112. The bitumen product may have
less than about
percent by weight asphaltene content, and less than I percent by weight water
content. Some
15 solvent may optionally remain in the bitumen product, for example, to
facilitate pipeline
transportation of the bitumen product.
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 utilize 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.
Tailing stream 111 may be contacted with cyclic solvent 118 in contactor 126
to form a
diluted tailings stream 117. The weight ratio of cyclic solvent to asphaltenes
in the tailings may
between 15 to I and 3 to 1. The amount of cyclic solvent used will generally
be the amount
necessary to provide sufficient contact between the cyclic solvent and the
tailings stream rather
than the amount needed based on solubility of the asphaltenes in the cyclic
solvent. Thus, the
weight ratio of cyclic solvent to total tailings stream may be between 1.3 to
I and 0.2 to 1.
The cyclic solvent may be, for example, an aromatic such as, for example,
benzene, toluene,
xylene, or reformate, a cycloparaffin such as cyclopentane, cyclohexane, or
methylcyclohexane, or
mixtures thereof. The contactor could be, for example, a static mixer, mixing
valve, mixing vessel
with internals, or pump. Alternatively, the contactor may be a length of pipe
within which the
solvent contacts the tailings sufficiently to cause at least a portion of the
asphaltenes to dissolve in
the cyclic solvent. At least a portion of any paraffinic solvent that remained
with the tailings
stream would also be incorporated into the cyclic solvent. . The paraffinic
solvent in the tailings
stream may marginally reduce the amount of cyclic solvent needed to
effectively remove
precipitated ashphaltenes from the tailings stream.
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The diluted tailings 1 l7 may be processed in a tailings separator 128 to
separate the diluted
tailings into a hydrocarbon composition 131 and a deasphaltened tailings
stream 133. The tailing
separator may be, for example, a tank settler, cyclone, inclined plate
separator, or centrifuge, or a
combination thereof.
The deasphaltened tailings stream 133 may be processed in a tailings solvent
recovery unit
129 to remove at least a portion of the solvent present in the tailings
stream, producing an aromatic
and paraffinc solvent stream 113, and a solvent free tailings stream 115. The
recovered solvent
from the tailings solvent recovery unit 113 may be combined with stream 131
and fed into
distillation unit 127
The tailings solvent recovery unit 129 may be a flash vessel wherein the
solvent is
vaporized and recovered as paraffinic solvent stream 113. Stripping steam may
be sparged into the
flash vessel to provide a deeper removal of solvent. Optionally, the tailings
solvent recovery unit
129 may be modified to remove the cyclic solvent and the paraffinic solvent as
separate streams,
for example, by removing the cyclic solvent as a side draw to a stipper which
may include a
reboiler to provide removal of at least a portion of the paraffinic solvent
present in the side draw.
Because the present invention reduces the amount of solvent remaining in the
tailings stream, it
may be economical to either eliminate the tailings solvent recovery unit, or
produce one solvent
stream that could be recycled either to the paraffinic solvent or the cyclic
solvent, or used as diluent
for either produced bitumen or the produced asphaltenes stream.
The hydrocarbon composition 131, and optionally the aromatic and paraffinic
solvent
stream 113 from the tailings solvent recovery unit 129, may be processed in a
distillation unit 127
to recover solvents. A paraffinic solvent 130 may be recovered and recycled
back to froth
treatment, and a cyclic solvent stream 135 may be recycled back to contactor
126. An asphaltene
product stream 132 may also be produced. In an embodiment where the paraffinic
solvent
comprises pentanes, and the cyclic solvent comprises toluene, the separation
of the two solvents by
distillation is readily accomplished because of the significant separation in
boiling points of the
solvents. Alternatively, the aromatic and paraffinic solvent stream 113 could
be combined with
cyclic solvent stream 135 and recycled directly to contactor 126. The presence
of some paraffinic
material in the cyclic solvent stream is not harmful to the process because
the amount of cyclic
solvent used is limited by the need to obtain good contact between the solvent
and the tailings, and
therefore more cyclic solvent is needed than what would be dictated by the
solubility of the
asphaltenes in the cyclic solvent.
The asphaltene product stream 132 may be utilized as a fuel, gasified, or sold
for other end
uses for which asphaltenes are known to be useful. The present invention
results in the production
of the additional asphaltene product, and removes this material from the
tailings stream that is
ultimately disposed of in, for example, a tailings pond.
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Distillation unit 127 could be multiple distillation columns, or could be a
column with a
side draw and optionally a stripper to remove at least a portion of the more
volatile solvent from the
side draw stream.
Water in the tailings stream 115 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.
The invention also includes the apparatus capable of performing the method.
Example
Froth from a commercial oil sands facility using a water process for initial
separation of
mineral components from bitumen, was processed in a pilot paraffinic froth
treatment facility
where the froth treatment underflow was collected. The composition of the
froth treatment
underflow was 7% bitumen, 7% paraffinic solvent (pentanes and hexanes are the
main constituents)
and water + solids of 86%, all by mass.
A cyclic solvent, in this case toluene, was added to the froth treatment
underflow, at a ratio
of 0.6/1 toluene to underflow by volume. The mixture was homogenized, at
ambient temperature,
using a pitch blade turbine type impeller duel mixer, with baffles in the
mixing container.
Homogenization lasted for 3 minutes with an impeller rotation speed of 600
rpm. After
homogenization, the mixture was allowed to settle for 30 minutes. After
settling, samples of the top
hydrocarbon mixture and bottom aqueous material were collected for analysis.
The composition of
the hydrocarbon phase and the aqueous phase are contained in the tables below
Hydrocarbon Phase Composition by Mass (%)
Solvent (paraffinic + Bitumen Water Ash
toluene)
86.7 11.0 0.7 1.6
Aqueous Phase Composition by Mass (%)
Paraffinic Solvent Toluene Bitumen Water + Solids
0.9 4.0 0.6 94.5
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The bitumen recovery of this treatment is 93%.
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