Note: Descriptions are shown in the official language in which they were submitted.
CA 02640914 2010-12-23
A MULTI-STAGE PROCESS FOR TREATING BITUMEN FROTH
USING A PARAFFINIC DILUENT
TECHNICAL FIELD
A process for treating a bitumen froth to remove solid mineral material and
water therefrom.
BACKGROUND OF THE INVENTION
Bitumen is typically extracted from surface-mined oil sands by using water-
based extraction processes. The mined oil sands are first mixed with hot or
warm water to
create a slurry, which is then conditioned in a piece of rotary equipment or
in a slurry pipeline.
Subsequently, the bitumen is separated from the bulk of the mineral material
tailings and water
in one or more separation vessels to produce bitumen froth.
A typical good quality bitumen froth may be comprised of between about 50
percent and about 70 percent bitumen by weight, between about 10 percent and
about 20
percent solid mineral material by weight, and between about 20 percent and
about 35 percent
water by weight. A typical poor quality bitumen froth may be comprised of
relatively less
bitumen and relatively more solid mineral material and/or water.
Bitumen froth requires further processing to yield a bitumen product which is
an
acceptable feedstock for bitumen upgrading processes or for pipeline transport
to an upgrading
facility.
The treatment of bitumen froth in preparation for upgrading or transport is
known as "froth treatment" and is carried out using a froth treatment process.
The objective of
any froth treatment process is to maximize the recovery of bitumen from the
bitumen froth and
to maximize the rejection of solid mineral material and water from the bitumen
froth. Bitumen
recovery is the proportion of the bitumen contained in the bitumen froth which
is contained in
the bitumen product which results from the froth treatment, and is typically
expressed as a
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fraction, decimal or percentage. Rejection of solid mineral material and water
is typically
expressed as the percentage by weight of residual solid mineral material and
water which is
contained in the bitumen product or the "BS&W" (bottom solids and water)
content of the
bitumen product. The effectiveness of a froth treatment process is therefore
often measured
with reference to bitumen recovery and the BS&W content of the bitumen
product.
There are currently two different types of froth treatment processes which are
used in the oil sands industry. One type of froth treatment process is the
naphthenic process,
which has been used commercially for several decades. The other type of froth
treatment
process is the paraffinic process, which has been developed more recently.
Both types of froth
treatment use a solvent to produce a diluted bitumen product (i.e., dilbit)
which is diluted with
the solvent.
In the naphthenic process, a naphtha solvent is used to dilute the bitumen
contained in the bitumen froth. A naphtha solvent consists of or contains
significant amounts
of one or more aromatic compounds. Asphaltenes are readily soluble in a
naphtha solvent. As
a result, in the naphthenic process, both the maltenes and the asphaltenes
contained in the
bitumen are dissolved in the naphtha solvent and the naphtha solvent dilutes
both the maltenes
and the asphaltenes.
In the naphthenic process, the separation of solid mineral material and water
from the diluted bitumen is enhanced by the increased difference in specific
gravity between the
phases which results from the dilution of the bitumen (both maltenes and
asphaltenes) by the
naphtha solvent.
The naphthenic process typically results in a relatively high bitumen recovery
from the bitumen froth, but also typically results in a relatively high BS&W
content in the
resulting bitumen product, so that the diluted bitumen product is not
particularly "clean". The
bitumen recovery using the naphthenic process is typically about 98 percent.
The BS&W
content of a diluted bitumen product produced by the naphthenic process is
typically between
about 1.5 percent by weight and about 5 percent by weight (i.e., a solid
mineral material content
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of between about 0.5 percent by weight and 1 percent by weight and a water
content of between
about 1 percent by weight and about 4 percent by weight). The fine tailings
resulting from the
naphthenic process are comprised of fine sands, silts, clays and some residual
bitumen and
solvent.
In the paraffinic process, a paraffinic solvent is used to dilute the bitumen
contained in the bitumen froth. A paraffinic solvent consists of or contains
significant amounts
of one or more relatively short-chained aliphatic compounds (such as, for
example, C4 to C8
aliphatic compounds).
Asphaltenes generally exhibit less solubility in paraffinic solvents than in
naphtha solvents, and asphaltenes tend to exhibit greater solubility in longer
chain paraffinic
solvents than in shorter chain paraffinic solvents.
In the paraffinic process, the addition of the paraffinic solvent to the
bitumen
froth appears to destabilize the asphaltenes contained in the bitumen froth,
some of which
precipitate out as clusters or aggregates while simultaneously trapping
maltenes, solid mineral
material and water within the clusters and aggregates. The precipitation of
asphaltenes
therefore has the effect of separating solid mineral material and water from
the bitumen, while
the increased difference in specific gravity between the phases which results
from the dilution
of the bitumen (including both maltenes and un-precipitated asphaltenes) by
the paraffinic
solvent enhances the separation of the remaining solid mineral material and
water from the
diluted bitumen.
The amount of asphaltenes which precipitate in the paraffinic process, the
rate of
asphaltene precipitation, and the BS&W content of the resulting diluted
bitumen product are a
function of the composition of the paraffinic solvent, the concentration by
weight of the
paraffinic solvent in the bitumen froth (typically expressed as the solvent to
bitumen ratio or
S:B ratio), and the temperature at which the process is carried out. In
general, the extent of
precipitation of asphaltenes in paraffinic solvents increases as the chain
length of the paraffinic
solvent decreases. In general, the extent of precipitation of asphaltenes in
paraffinic solvents
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increases as the solvent to bitumen ratio in the bitumen froth increases. In
general, the extent of
precipitation of asphaltenes in paraffinic solvents appears to increase as the
temperature of the
bitumen/solvent system increases.
Typically, the paraffinic process is performed in a manner so that between
about
40 percent and about 50 percent by weight of the asphaltenes contained in the
bitumen froth are
precipitated in order to produce a diluted bitumen product which has a
relatively low BS&W
content.
Although the paraffinic process typically results in a relatively lower BS&W
content in the resulting diluted bitumen product in comparison with the
naphthenic process, the
paraffinic process also typically results in a relatively lower total bitumen
recovery in
comparison with the naphthenic process due to the relatively high amount of
asphaltene
precipitation, whereas the relatively low entrapment of maltenes within the
asphaltene clusters
or aggregates results in maltene recoveries in the paraffinic process which
are comparable with
the naphthenic process. The loss of bitumen in the paraffinic process presents
both economic
and environmental concerns.
In summary, there is a need for a paraffinic process for froth treatment which
provides both a relatively high bitumen recovery and a relatively low BS&W
content in the
resulting diluted bitumen product (i.e., dilbit).
SUMMARY OF THE INVENTION
References in this document to orientations, to operating parameters, to
ranges,
to lower limits of ranges, and to upper limits of ranges are not intended to
provide strict
boundaries for the scope of the invention, but should be construed to mean
"approximately" or
"about" or "substantially", within the scope of the teachings of this
document, unless expressly
stated otherwise.
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The present invention is a paraffinic froth treatment process for treating a
bitumen froth comprising bitumen, solid mineral material and water. The
bitumen is comprised
of maltenes and asphaltenes. The solid mineral material may be comprised of
fine mineral
material such as silt, clay and heavy metals and/or may be comprised of coarse
mineral material
such as sand and rock. Typically, the solid mineral material is comprised
primarily of fine
mineral material.
The bitumen froth which may be processed using the invention may be
comprised of any material which is comprised of bitumen, solid mineral
material and water. As
one example, the bitumen froth may be comprised of or consist of a typical
good quality
bitumen froth which may be comprised of between about 50 percent and about 70
percent
bitumen by weight, between about 10 percent and about 20 percent solid mineral
material by
weight, and between about 20 percent and about 35 percent water by weight. As
a second
example, the bitumen froth may be comprised of or consist of a low quality
bitumen froth
which may be comprised of relatively less bitumen and relatively more solid
mineral material
and/or water than a good quality bitumen froth. As a third example, the
bitumen froth may be
comprised of or consist of a waste material from bitumen extraction, such as
for example pond
oil. Some or all of the bitumen contained in the bitumen froth may be oxidized
bitumen.
The bitumen component of the bitumen froth is comprised mainly of maltenes
and asphaltenes. The process provides for a controlled precipitation and/or
rejection of
asphaltenes from the bitumen froth in order to achieve a relatively high
bitumen recovery and a
relatively low solid mineral material and water (BS&W) content. The amount of
precipitation
and/or rejection of asphaltenes from the bitumen froth is generally dependent
upon the
composition of the paraffinic solvent, the solvent to bitumen ratio in the
bitumen froth, and the
temperature at which the bitumen froth is processed.
In particular, the process provides for first gravity separation in a first
gravity
separation apparatus of a first mixture comprising bitumen froth and a first
amount of a
paraffinic solvent into a first overflow stream and a first underflow stream,
wherein the first
mixture is comprised of first mixture asphaltenes, and wherein the first
underflow stream is
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comprised of between about 5 percent and about 40 percent of the first mixture
asphaltenes by
weight. Stated otherwise, between about 5 percent and about 40 percent of the
first mixture
asphaltenes by weight are precipitated or are otherwise rejected from the
first mixture so that
the first overflow stream is comprised of between about 60 percent and about
95 percent of the
first mixture asphaltenes by weight.
In some embodiments, the range of the amount of the first mixture asphaltenes
which may be precipitated or otherwise rejected from the first mixture may be
more narrow
than between about 5 percent and about 40 percent by weight. The lower limit
may be greater
than about 5 percent and the upper limit may be less than about 40 percent,
depending upon the
characteristics of the bitumen froth being processed, the operating conditions
of the process,
and the BS&W content and bitumen recovery which is sought to be achieved using
the process.
For example, in some embodiments, between about 5 percent and about 25
percent of the first mixture asphaltenes by weight may be precipitated or
otherwise rejected
from the first mixture so that the first underflow stream may be comprised of
between about 5
percent and about 25 percent of the first mixture asphaltenes by weight and so
that the first
overflow stream may be comprised of between about 75 percent and about 95
percent of the
first mixture asphaltenes by weight.
As a result of the cleaning effects of the controlled precipitation and/or
rejection
of the asphaltenes, the first overflow stream may have a solid mineral
material and water
(BS&W) content which is less than or equal to about 0.5 percent of the first
overflow stream by
weight. In some embodiments, the first overflow stream may have a solid
mineral material and
water (BS&W) content which is less than or equal to about 0.25 percent of the
first overflow
stream by weight. In some embodiments, the first overflow stream may have a
solid mineral
material and water (BS&W) content which is less than or equal to about 0.1
percent of the first
overflow stream by weight.
The first underflow stream may be further processed in order to recover
bitumen
therefrom and thereby increase the bitumen recovery from the bitumen froth. In
some
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embodiments, the first underflow stream may be further processed so that the
bitumen recovery
from the bitumen froth is greater than or equal to about 94 percent. In some
embodiments, the
first underflow stream may be further processed so that the bitumen recovery
from the bitumen
froth is greater than or equal to about 96 percent. Generally, the overall
bitumen recovery from
the bitumen froth may be increased if the first underflow stream is subjected
to a single stage of
further processing, and may be increased even further if the first underflow
stream is subjected
to a plurality of stages of further processing, where warranted.
The first underflow stream may be further processed in any suitable manner in
order to recover bitumen therefrom. In some embodiments, the first underflow
stream may be
further processed using one or more gravity separation techniques in one or
more stages of
gravity separation. In some embodiments, a second mixture comprising the first
underflow
stream and a second amount of a paraffinic solvent may be further processed by
second gravity
separation in a second gravity separation apparatus, thereby producing a
second overflow
stream and a second underflow stream. In some embodiments, a third mixture
comprising the
second underflow stream and a third amount of a paraffinic solvent may be
further processed by
third gravity separation in a third gravity separation apparatus, thereby
producing a third
overflow stream and a third underflow stream.
The first mixture has a first solvent to bitumen ratio. The paraffinic
solvent, the
first solvent to bitumen ratio, and the temperature at which the first gravity
separation is carried
out are selected to precipitate or otherwise reject the desired amount of
asphaltenes from the
bitumen froth and thereby provide a desired amount of cleaning of the bitumen
froth without
unduly rejecting asphaltenes from the bitumen froth.
In some embodiments, the temperature at which the first gravity separation is
carried out may be between about 20 degrees Celsius and about 90 degrees
Celsius. In some
embodiments, the temperature at which the first gravity separation is carried
out may be
between about 50 degrees Celsius and about 90 degrees Celsius. In some
embodiments, the
temperature at which the first gravity separation is carried out may be
between about 75 degrees
Celsius and about 90 degrees Celsius.
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The second mixture has a second solvent to bitumen ratio. The paraffinic
solvent, the second solvent to bitumen ratio, and the temperature at which the
second gravity
separation is carried out are selected to facilitate recovery of bitumen from
the second mixture
by increasing the difference in density between the bitumen and the other
components of the
second mixture.
In some embodiments, the temperature at which the second gravity separation is
carried out may be between about 20 degrees Celsius and about 90 degrees
Celsius. In some
embodiments, the temperature at which the second gravity separation is carried
out may be
between about 50 degrees Celsius and about 90 degrees Celsius. In some
embodiments, the
temperature at which the second gravity separation is carried out may be
between about 75
degrees Celsius and about 90 degrees Celsius.
The third mixture, where applicable, has a third solvent to bitumen ratio. The
paraffinic solvent, the third solvent to bitumen ratio, and the temperature at
which the third
gravity separation is carried out are selected to facilitate further recovery
of bitumen from the
third mixture by increasing the difference in density between the bitumen and
the other
components of the third mixture.
In some embodiments, the temperature at which the third gravity separation is
carried out may be between about 20 degrees Celsius and about 90 degrees
Celsius. In some
embodiments, the temperature at which the third gravity separation is carried
out may be
between about 50 degrees Celsius and about 90 degrees Celsius. In some
embodiments, the
temperature at which the third gravity separation is carried out may be
between about 75
degrees Celsius and about 90 degrees Celsius.
The second solvent to bitumen ratio is greater than the first solvent to
bitumen
ratio. Where applicable, the third solvent to bitumen ratio is greater than
the first solvent to
bitumen ratio. In some embodiments, the third solvent to bitumen ratio is
greater than the
second solvent to bitumen ratio.
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In one aspect the invention is a process for treating a bitumen froth
comprising
bitumen, solid mineral material and water, the process comprising:
(a) subjecting a first mixture comprising the bitumen froth and a first amount
of a
paraffinic solvent to first gravity separation in a first gravity separation
apparatus, thereby producing a first overflow stream and a first underflow
stream, wherein the first mixture has a first solvent to bitumen ratio,
wherein the
first mixture is comprised of first mixture asphaltenes, and wherein the first
gravity separation is performed so that the first underflow stream is
comprised of
between 5 percent and 40 percent of the first mixture asphaltenes by weight;
and
(b) subjecting a second mixture comprising the first underflow stream and a
second
amount of the paraffinic solvent to second gravity separation in a second
gravity
separation apparatus, wherein the second mixture has a second solvent to
bitumen ratio and wherein the second solvent to bitumen ratio is greater than
the
first solvent to bitumen ratio, thereby producing a second overflow stream and
a
second underflow stream.
In some embodiments, the process may be further comprised of subjecting a
third mixture comprising the second underflow stream and a third amount of the
paraffinic
solvent to third gravity separation in a third gravity separation apparatus,
wherein the third
mixture has a third solvent to bitumen ratio and wherein the third solvent to
bitumen ratio is
greater than the first solvent to bitumen ratio, thereby producing a third
overflow stream and a
third underflow stream. In some embodiments, the third solvent to bitumen
ratio may be
greater than the second solvent to bitumen ratio.
The paraffinic solvent is comprised of at least one paraffinic compound,
wherein
a paraffinic compound is an aliphatic hydrocarbon compound. The paraffinic
solvent is
comprised of a sufficient amount of one or more paraffinic compounds so that
the paraffinic
solvent exhibits the properties of a paraffinic solvent. The paraffinic
solvent may therefore be
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comprised of a single paraffinic compound or may be comprised of a mixture of
paraffinic
compounds. The paraffinic solvent may also be comprised of a mixture of one or
more
paraffinic compounds and one or more other substances.
In some embodiments, the paraffinic solvent may be comprised of a paraffinic
compound selected from the group of paraffinic compounds consisting of butane,
pentane,
hexane, heptane, octane, and mixtures thereof. In some embodiments, the
paraffinic solvent
may be comprised of a mixture of paraffinic compounds such as a mixture of
pentane ' and
hexane. In some embodiments, the paraffinic solvent may be comprised of one or
more natural
gas liquids derived from natural gas.
In some embodiments, the same paraffinic solvent may be used for the first
gravity separation, the second gravity separation and, where applicable, the
third gravity
separation. In some embodiments, different paraffinic solvents may be used for
the first gravity
separation, the second gravity separation, and/or where applicable, the third
gravity separation.
As used herein, "gravity separation" includes any technique which utilizes
gravity in order to achieve separation of a mixture of substances having
different densities, but
does not include "enhanced gravity separation techniques" such as centrifuge
techniques,
cyclone techniques etc. which may utilize other forces such as centrifugal
forces in substitution
for or in addition to forces due to gravity. Enhanced gravity separation
techniques are generally
not preferred for use in the invention because the relatively large forces
used to effect
separation may unnecessarily disrupt and/or interfere with components of the
bitumen froth,
such as clustered or aggregated asphaltenes.
One or more different gravity separation techniques may be used to perform the
gravity separation in the invention. Preferably the gravity separation
techniques used in the
invention are relatively low intensity processes so that disruption and/or
interference with
components of the bitumen froth (such as clustered or aggregated asphaltenes)
is minimized.
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The gravity separation techniques used in the invention may be performed using
any suitable gravity separation apparatus or suitable combination of suitable
gravity separation
apparatus.
Preferably, gravity settling vessels and/or inclined plate settlers are used
as the
gravity separation apparatus to perform the gravity separation in the
invention.
Gravity settling vessels are typically comprised of tanks or other vessels
into
which a material to be separated may be introduced in order to facilitate
separation of the
material due to gravity into two or more components having different
densities. Gravity settling
vessels may be any shape, size and/or configuration which is suitable for
achieving the desired
gravity separation. Gravity separation vessels may include internal structures
such as weirs,
sumps, launders, baffles, distributors etc. and may include internal
mechanical devices such as
rakes, conveyors, augers etc.
Inclined plate settlers are typically comprised of a plurality of inclined
plates into
which a material to be separated may be introduced in order to facilitate
separation due to
gravity into two or more components having different densities. The material
to be separated is
typically introduced at an upper end of the inclined plate settler. Product
streams are typically
removed from the inclined plate settler at both the upper end and the lower
end of the inclined
plate settler, with the lower density product stream being removed at the
upper end and the
higher density product stream being removed at the lower end.
Inclined plate settlers may be preferred over gravity settling vessels in
circumstances where space is limited, since the plurality of plates provides
an increased
effective area over which relative settling of components and separation of
the material can
occur relative to gravity settling vessels.
Inclined plate settlers may also be preferred over gravity settling vessels in
circumstances where the anticipated vertical settling rates of the components
to be separated
may be relatively small, since inclined plate settlers typically require less
vertical settling
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distance of components in order to be effective relative to gravity settling
vessels. As a general,
non-limiting guide, inclined plate settlers may be preferred in circumstances
where the
anticipated vertical settling rate is less than about 100 millimeters per
minute, while gravity
settling vessels may be more suitable for use in circumstances where the
anticipated vertical
settling rate is greater than about 100 millimeters per minute.
In some embodiments, inclined plate settlers which are used in the invention
may be comprised of inclined plates which have been adapted to minimize or
eliminate the
accumulation of bitumen on the inclined plates.
In some embodiments, the inclined plates may be coated with a non-sticking
material. Non-limiting examples of non-sticking materials which may be
suitable for coating
the inclined plates include polytetrafluoroethylene (PTFE), perfluoroalkoxy
(PFA), and
fluorinated ethylene propylene (FEP), all of which are manufactured by DuPont
and sold under
the Teflon TM trademark.
In some embodiments, the inclined plates may be constructed of a non-sticking
material. An example of a non-sticking material which may be suitable for
construction of the
inclined plates is stainless steel, such as austenitic stainless steel.
In some embodiments, the gravity separation of the invention may be performed
exclusively using gravity settling vessels. In some embodiments, the gravity
separation of the
invention may be performed exclusively using inclined plate settlers. In some
embodiments,
the gravity separation of the invention may be performed using any combination
of gravity
settling vessels and inclined plate settlers. In some embodiments, the first
gravity separation
may be performed using an inclined plate settler. In some embodiments, the
second gravity
separation may be performed using an inclined plate settler. In some
embodiments, the second
gravity separation may be performed using a gravity settling vessel. In some
embodiments,
where applicable, the third gravity separation may be performed using a
gravity settling vessel.
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The determination of whether a particular stage of gravity separation of the
invention is performed using a gravity settling vessel or an inclined plate
settler may be based
in whole or in part upon the anticipated vertical settling rate which can be
expected in the
gravity separation.
Due to the relatively low amount of asphaltene precipitation and/or rejection
which results in the first gravity separation, the anticipated vertical
settling rate of the rejected
material may be less than about 100 millimeters per minute. As a result, the
use of an inclined
plate settler for the first gravity separation may be advantageous.
Due to the progressively higher solvent to bitumen ratios which may
potentially
be provided in the second gravity separation and the third gravity separation
respectively, the
anticipated vertical settling rate of the rejected material may be greater
than about 100
millimeters per minute. As a result, the use of an inclined plate settler for
the second gravity
separation and/or the third gravity separation may not be as advantageous as
it may be for the
first gravity separation.
The first gravity separation, the second gravity separation, and where
applicable,
the third gravity separation, may be performed in distinct stand-alone stages,
may be integrated
and performed in a co-current manner, or may be integrated and performed in a
countercurrent
manner.
In some embodiments, the process is performed in a countercurrent manner
whereby the second overflow stream is added to the first mixture and whereby,
where
applicable, the third overflow stream is added to the second mixture. As a
result, where the
process is performed in a countercurrent manner the first overflow stream
represents a single
diluted bitumen product stream and the final underflow stream represents a
single diluted froth
treatment tailings stream.
The paraffinic solvent may be introduced at any or all of the stages of the
process. In some embodiments, the paraffinic solvent may be introduced at each
of the first
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gravity separation, the second gravity separation, and where applicable, the
third gravity
separation.
In some embodiments, the paraffinic solvent is introduced only to the last
stage
of gravity separation. As a result, in some embodiments where the process is
comprised of first
gravity separation and second gravity separation, the second overflow stream
is comprised of
the paraffinic solvent so that the first amount of the paraffinic solvent is
provided by the second
overflow stream. As a result, in some embodiments where the process is
comprised of first
gravity separation, second gravity separation and third gravity separation,
the third overflow
stream is comprised of the paraffinic solvent so that the second amount of the
paraffinic solvent
is provided by the third overflow stream.
The process of the invention thereby provides for a controlled amount of
precipitation and/or rejection of asphaltenes from the bitumen froth in order
to utilize the
cleaning effects of asphaltene precipitation and/or rejection to separate
solid mineral material
and water from the bitumen while limiting the amount of bitumen rejection. The
process of the
invention also provides for further processing of the first underflow stream
containing the
rejected bitumen in one or more stages of separation in order to recover
bitumen therefrom.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the invention will now be described with reference to the
accompanying drawings, in which:
Figure 1 is a schematic process flow diagram of an embodiment of the
invention.
Figure 2 is a table of experimental conditions for one-stage laboratory
settling
tests conducted in connection with the invention.
Figure 3 is a table of one-stage laboratory settling test results conducted in
connection with the invention, using pentane as the paraffinic solvent.
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Figure 4 is a table of one-stage laboratory settling test results conducted in
connection with the invention, using hexane as the paraffinic solvent.
Figure 5 is a table of one-stage laboratory settling test results conducted in
connection with the invention, using heptane as the paraffinic solvent.
Figure 6 is a table of one-stage laboratory settling test results conducted in
connection with the invention, using a 1:1 mixture of pentane and hexane by
weight as the
paraffinic solvent.
Figure 7 is a graph depicting the amount of asphaltenes contained in a diluted
bitumen product produced from a bitumen froth in one-stage laboratory settling
tests using
pentane, hexane, heptane and a 1:1 mixture of pentane and hexane by weight as
the paraffinic
solvent, as a function of the solvent to bitumen ratio.
Figure 8 is a graph depicting asphaltene rejection from a bitumen froth
treated in
one-stage laboratory testing tests using pentane, hexane, heptane and a 1:1
mixture of pentane
and hexane by weight as the paraffinic solvent, as a function of the solvent
to bitumen ratio.
Figure 9 is a table of two-stage pilot plant test results conducted in
connection
with testing of the invention on a good quality bitumen froth, using pentane
as the paraffinic
solvent, and using two gravity settling vessels as the gravity separation
apparatus.
Figure 10 is a table of two-stage pilot plant test results conducted in
connection
with testing of the invention on a good quality bitumen froth, using pentane
as the paraffinic
solvent, and using gravity settling vessels as the gravity separation
apparatus.
Figure 11 is a table of two-stage pilot plant test results conducted in
connection
with testing of the invention on a good quality bitumen froth, using pentane
as the paraffinic
solvent, and using two gravity settling vessels as the gravity separation
apparatus.
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Figure 12 is a table of two-stage pilot plant test results conducted in
connection
with testing of the invention on a good quality bitumen froth, using a 1:1
mixture of pentane
and hexane by weight as the paraffinic solvent, and using two inclined plate
settlers as the
gravity separation apparatus.
Figure 13 is a table of three-stage pilot plant test results conducted in
connection
with testing of the invention on a good quality bitumen froth, using a 1:1
mixture of pentane
and hexane by weight as the paraffinic solvent, and using two inclined plate
separators and one
gravity settling vessel as the gravity separation apparatus.
Figure 14 is a table of three-stage pilot plant test results conducted in
connection
with testing of the invention on a good quality bitumen froth, using a 1:1
mixture of pentane
and hexane by weight as the paraffinic solvent, and using two inclined plate
separators and one
gravity settling vessel as the gravity separation apparatus.
Figure 15 is a table of three-stage pilot plant test results conducted in
connection
with testing of the invention on a good quality bitumen froth, using a 1:1
mixture of pentane
and hexane by weight as the paraffinic solvent, and using two inclined plate
separators and one
gravity settling vessel as the gravity separation apparatus.
Figure 16 is a table of two-stage pilot plant test results conducted in
connection
with testing of the invention on a good quality bitumen froth, using pentane
as the paraffinic
solvent, and using two gravity settling vessels as the gravity separation
apparatus.
Figure 17 is a table of two-stage pilot plant test results conducted in
connection
with testing of the invention on a good quality bitumen froth, using pentane
as the paraffinic
solvent, and using two gravity settling vessels as the gravity separation
apparatus.
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Figure 18 is a table of two-stage pilot plant test results conducted in
connection
with testing of the invention on a good quality bitumen froth, using pentane
as the paraffinic
solvent, and using two gravity settling vessels as the gravity separation
apparatus.
Figure 19 is a table of two-stage pilot plant test results conducted in
connection
with testing of the invention on a poor quality bitumen froth, using a 1:1
mixture of pentane and
hexane by weight as the paraffinic solvent, and using one inclined plate
settler and one gravity
settling vessel as the gravity separation apparatus.
Figure 20 is a table of two-stage pilot plant test results conducted in
connection
with testing of the invention on a poor quality bitumen froth, using a 1:1
mixture of pentane and
hexane by weight as the paraffinic solvent, and using two gravity settling
vessels as the gravity
separation apparatus.
DETAILED DESCRIPTION
The present invention is directed at a process for treating bitumen froth
which
provides for first gravity separation of a first mixture comprising the
bitumen froth and a first
amount of a paraffinic solvent into a first overflow stream and a first
underflow stream, wherein
the first mixture is comprised of first mixture asphaltenes, and wherein the
first underflow
stream is comprised of less than or equal to about 40 percent of the first
mixture asphaltenes by
weight. Stated otherwise, the first gravity separation results in
precipitation and/or rejection
from the first overflow stream of less than or equal to about 40 percent of
the first mixture
asphaltenes by weight.
As a result, the process of the invention may be distinguished from typical
commercial paraffinic froth treatment processes which typically provide for
between about 40
percent and about 50 percent asphaltene precipitation and/or rejection by
weight in a first
separation stage.
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The relatively lower amount of asphaltene precipitation and/or rejection which
is
provided by the invention results in the loss of lower amounts of bitumen in
the first separation
stage and requires the use of relatively less solvent in comparison with
typical commercial
paraffinic froth treatment processes.
The diluted bitumen product (i.e., dilbit) which is produced by the invention
typically has a solid mineral material and water (BS&W) content which is less
than or equal to
about 0.5 percent by weight. In some applications of the invention, the
diluted bitumen product
which is produced by the invention may have a BS&W content which is less than
or equal to
about 0.1 percent by weight. As a result, the BS&W content of the diluted
bitumen product
which is produced by the invention is similar to the BS&W content of the
diluted bitumen
product which is produced by typical commercial paraffinic froth treatment
processes.
Figure 1 provides a schematic flow diagram of an embodiment of a system (20)
for performing an embodiment of the process of the invention. As depicted in
Figure 1 and
described below, the system (20) is configured to be operated on a continuous
basis. However,
the system (20) could be configured, and the method of the invention could be
performed, on a
semi-continuous or batch basis.
Referring to Figure 1, the system (20) comprises a first gravity separation
apparatus (30) having a first mixture inlet line (32), a first overflow stream
outlet line (34), and
a first underflow stream outlet line (36). The first gravity separation
apparatus (30) is
comprised of an inclined plate settler due to the relatively low amount of
asphaltene
precipitation and/or rejection (and the resulting relatively low vertical
settling rate) which is
intended to occur in the first gravity separation apparatus (30). A first
mixer (38) precedes the
first gravity separation apparatus (30) and is connected with the first
gravity separation
apparatus (30) via the first mixture inlet line (32). The first mixer (38) may
be comprised of
any suitable mixing device or apparatus, including an in-line mixer.
The system (20) further comprises a second gravity separation apparatus (40)
having a second mixture inlet line (42), a second overflow stream outlet line
(44), and a second
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underflow stream outlet line (46). The second gravity separation apparatus
(40) is comprised of
either a gravity settling vessel or an inclined plate settler, depending in
part upon the vertical
settling rate which is anticipated in the second gravity separation apparatus
(40). A second
mixer (48) precedes the second gravity separation apparatus (40) and is
connected with the
second gravity separation apparatus (40) via the second mixture inlet line
(42). The second
mixer (48) may be comprised of any suitable mixing device or apparatus,
including an in-line
mixer.
The system (20) further comprises a third gravity separation apparatus (50)
having a third mixture inlet line (52), a third overflow stream outlet line
(54), and a third
underflow stream outlet line (56). The third gravity separation apparatus (50)
is comprised of
either a gravity settling vessel or an inclined plate settler, depending in
part upon the vertical
settling rate which is anticipated in the third gravity separation apparatus
(40). A third mixer
(58) precedes the third gravity separation apparatus (50) and is connected
with the third gravity
separation apparatus (50) via the third mixture inlet line (52). The third
mixer (58) may be
comprised of any suitable mixing device or apparatus, including an in-line
mixer.
A bitumen froth feed line (70) is connected with the first mixer (38). The
first
underflow stream outlet line (36) is connected with the second mixer (48). The
second
underflow stream outlet line (46) is connected with the third mixer (58).
The third underflow stream outlet line (56) is connected with a tailings
solvent
recovery unit or TSRU (72) for recovering paraffinic solvent from the third
underflow stream.
The first overflow stream outlet line (34) is connected with a solvent
recovery
unit or SRU (74) for recovering paraffinic solvent from the first overflow
stream.
An optional final cleanup tank (80) and an optional final cleanup bypass line
(82) may be interposed in the first overflow stream outlet line (34) between
the first gravity
separation apparatus (30) and the SRU (74). An optional cleanup tank underflow
stream outlet
line (84) may extend between the final cleanup tank (80) and the third mixer
(58).
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A solvent addition line (90) is connected with the third mixer (58). The
solvent
addition line (90) is provided with paraffinic solvent via a TSRU recovered
solvent line (92)
which is associated with the TSRU (72), via an SRU recovered solvent line (94)
which is
associated with the SRU (74), and via a solvent makeup line (96) which is
associated with a
source of makeup solvent (not shown).
The second overflow stream outlet line (44) is connected with the first mixer
(38). The third overflow stream outlet line (54) is connected with the second
mixer (48).
The system (20) is therefore arranged in a three-stage countercurrent
configuration.
In operation of the system (20) to perform an embodiment of the process of the
invention, bitumen froth is delivered to the first mixer (38) via the bitumen
froth feed line (70)
and a second overflow stream is delivered to the first mixer (38) via the
second overflow stream
outlet line (44). The second overflow stream contains a first amount of the
paraffinic solvent.
The bitumen froth and the second overflow stream are mixed in the first mixer
(38) to provide a first mixture comprising the bitumen froth, the first amount
of the paraffinic
solvent, and the second overflow stream. The first mixture is delivered to the
first gravity
separation apparatus (30) via the first mixture inlet line (32). The first
mixture is comprised of
first mixture asphaltenes which represent a portion of the bitumen which is
contained in the
bitumen froth and in the second overflow stream. The first mixture has a first
solvent to
bitumen ratio.
The first mixture is separated by first gravity separation in the first
gravity
separation apparatus (30) into a first overflow stream and a first underflow
stream. The first
overflow stream represents a diluted bitumen product stream which is delivered
to the SRU
(74) via the first overflow stream outlet line (34).
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The paraffinic solvent, the first solvent to bitumen ratio, and the
temperature at
which the first gravity separation is performed are selected so that the first
overflow stream
contains between about 60 percent and about 95 percent of the first mixture
asphaltenes by
weight and so that the first underflow stream contains between about 5 percent
and about 40
percent of the first mixture asphaltenes by weight.
The first mixture asphaltenes which are contained in the first underflow
stream
effectively trap and/or carry a large proportion of the solid mineral material
and water which are
contained in the first mixture so that the first overflow stream has a BS&W
content which is
less than or equal to about 0.5 percent by weight. The first underflow stream
may also contain
a relatively small amount of maltenes from the first mixture.
The first underflow stream is delivered to the second mixer (48) via the first
underflow stream outlet line (36) and a third overflow stream is delivered to
the second mixer
(48) via the third overflow stream outlet line (54). The first underflow
stream and the third
overflow stream together contain a second amount of the paraffinic solvent.
The first underflow stream and the third overflow stream are mixed in the
second mixer (48) to provide a second mixture comprising the first underflow
stream, the
second amount of the paraffinic solvent, and the third overflow stream. The
second mixture is
delivered to the second gravity separation apparatus (40) via the second
mixture inlet line (42).
The second mixture is comprised of bitumen (including both maltenes and
asphaltenes) which
is contained in the first underflow stream and in the third overflow stream.
The second
mixture has a second solvent to bitumen ratio. The second solvent to bitumen
ratio is greater
than the first solvent to bitumen ratio.
The second mixture is separated by second gravity separation in the second
gravity separation apparatus (40) into the second overflow stream and a second
underflow
stream. The second overflow stream typically contains a relatively large
proportion of the
bitumen which was contained in the second mixture and is delivered to the
first mixer (38) for
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further processing, as described above. The second underflow stream typically
contains a
relatively small proportion of the bitumen which was contained in the second
mixture.
The second underflow stream is delivered to the third mixer (58) via the
second
underflow stream outlet line (46), a cleanup tank underflow stream is
optionally delivered to the
third mixer via the optional cleanup tank underflow stream outlet line (84),
and a solvent
addition stream containing paraffinic solvent is delivered to the third mixer
(48) via the solvent
addition line (90). The second underflow stream, the optional cleanup tank
underflow stream
and the solvent addition stream together contain a third amount of the
paraffinic solvent.
The second underflow stream, the optional cleanup tank underflow stream and
the solvent addition stream are mixed in the third mixer (58) to provide a
third mixture
comprising the second underflow stream, the third amount of the paraffinic
solvent, and
optionally the cleanup tank underflow stream. The third mixture is delivered
to the third
gravity separation apparatus (50) via the third mixture inlet line (52). The
third mixture is
comprised of bitumen (including both maltenes and asphaltenes) which is
contained in the
second underflow stream and in the optional cleanup tank underflow stream. The
third mixture
has a third solvent to bitumen ratio. The third solvent to bitumen ratio is
greater than the first
solvent to bitumen ratio. The third solvent to bitumen ratio is also greater
than the second
solvent to bitumen ratio.
The third mixture is separated by third gravity separation in the third
gravity
separation apparatus (50) into the third overflow stream and a third underflow
stream. The
third overflow stream includes a relatively large proportion of the bitumen
which was contained
in the third mixture and is delivered to the second mixer (48) for further
processing, as
described above.
The third underflow stream represents a diluted froth treatment tailings
stream
which is delivered to the TSRU (72) via the third underflow stream outlet line
(56). The third
underflow stream includes a very high proportion of the solid mineral material
and water which
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were contained in the bitumen froth and typically a very small amount of the
bitumen which
was contained in the bitumen froth.
As indicated above, the final cleanup tank (80), the final cleanup bypass line
(82) and the cleanup tank underflow stream outlet line (84) are optional in
the system (20)
depicted in Figure 1 and may be omitted if the first overflow stream
constitutes a sufficiently
clean diluted bitumen product stream. Alternatively, the final cleanup tank
(80) may be
included in the system (20) depicted in Figure 1, but the final cleanup bypass
line (82) may be
utilized to bypass the final cleanup tank (80) if the first overflow stream
constitutes a
sufficiently clean diluted bitumen product stream.
As indicated, the invention provides for a BS&W content of less than or equal
to
about 0.5 percent by weight, so that the first overflow stream should
constitute a sufficiently
clean diluted bitumen product stream for most purposes. If, however, the
required BS&W
content of the diluted bitumen product stream is less than that provided by
the invention, the
final cleanup tank (80) may be included and/or utilized to reduce the BS&W
content of the first
overflow stream to a desired amount.
The final cleanup tank (80) may also be used to reduce the BS&W content of a
portion of the first overflow stream, and the final cleanup bypass line (82)
may be used to
bypass the final cleanup tank (80) for the remaining portion of the first
overflow stream. The
overflow stream from the final cleanup tank (80) may thus be combined with the
bypass stream
from the final cleanup bypass line (82) to provide the diluted bitumen product
stream which is
delivered to the SRU (74) via the first overflow stream outlet line (34).
The third underflow stream is processed in the TSRU (72) to recover a portion
of the paraffinic solvent therefrom, which paraffinic solvent may then be
recycled for use in the
process of the invention via the TSRU recovered solvent line (92).
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The first overflow stream is processed in the SRU (74) to recover a portion of
the paraffinic solvent therefrom, which paraffinic solvent may then be
recycled for use in the
process of the invention via the SRU recovered solvent line (94).
Pilot plant testing of the invention in a three-stage countercurrent
configuration
similar to Figure 1 has achieved a bitumen recovery of about 96 percent or
higher and a BS&W
content of about 0.10 percent by weight in the first overflow stream.
The schematic process flow diagram of Figure 1 and the above description of
the
embodiment of the process of the invention utilizing the system (20) of Figure
1 has been
developed based upon laboratory testing and pilot plant testing of the
principles of the
invention. This laboratory and pilot plant testing is now described with
reference to Figures 2-
20.
LABORATORY TESTING
Froth Composition
Blended bitumen froth extracted from medium to low grade oil sand was
characterized for its composition and the bitumen contained therein was
analyzed for its
viscosity, density, asphaltene content, and metals content. The bitumen froth
was found to
contain about 54.5 percent bitumen by weight, about 11.9 percent solid mineral
material by
weight, and about 33.5 percent water by weight.
One-Stage Laboratory Settling Tests
Suitable froth treatment conditions, including paraffinic solvent composition,
concentration of the paraffinic solvent (i.e. solvent to bitumen ratio or S:B
ratio), and operating
temperature at which a bitumen product having a bottom solids and water (BS&W)
content of
less than or equal to about 0.5 percent by weight can be produced while
minimizing asphaltene
precipitation and/or rejection, were defined by a number of autoclave tests
using pentane,
hexane, and heptane as solvents.
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One-stage autoclave settling tests were conducted using n-pentane, n-hexane,
heptane, and a 1:1 mixture of n-pentane and n-hexane by weight as the
paraffinic solvent.
Figure 2 lists the experimental conditions for one-stage settling tests
conducted in an autoclave.
Pentane as the Paraffinic Solvent
The results of one-stage autoclave settling tests conducted using n-pentane as
the
paraffinic solvent are summarized in Figure 3.
The amount of asphaltene precipitation and/or rejection observed in the
laboratory testing summarized in Figure 3 ranged between about 17.9 percent
and about 20.5
percent by weight.
The water content in each of the diluted bitumen products was below about 0.1
percent by weight after one hour of settling. At a sufficiently high S:B
ratio, asphaltene
precipitation occurs. The precipitating asphaltenes form aggregates with the
solid mineral
material and the water contained in the bitumen froth. The aggregates "sweep"
a large portion
of the solid mineral material and water from the bitumen froth, resulting in a
very clean
product.
The solid mineral material content in each of the diluted bitumen products was
measured as ash content, which includes all mineral solids and metals
contained in the diluted
bitumen product. It is common knowledge that most of the solid mineral
material contained in
bitumen froth remains with the water phase during froth treatment, and that
reducing the water
content during froth treatment also reduces the solid mineral material
content. In the paraffinic
process, solid mineral material can be removed almost completely by the
effects of asphaltene
aggregation. As can be seen in Figure 3, the solid mineral material content
decreased to below
about 0.1 percent by weight, which was found principally to represent the
contribution of
metals contained in the bitumen.
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The solid mineral material and water (BS&W) content of the diluted bitumen
products resulting from the settling tests summarized in Figure 3 ranged from
about 0.09
percent to about 0.11 percent by weight.
Hexane as the Paraffinic Solvent
The results of one-stage autoclave settling tests conducted using n-hexane as
the
paraffinic solvent are summarized in Figure 4.
The amount of asphaltene precipitation and/or rejection observed in the
laboratory testing summarized in Figure 4 ranged between about 6.8 percent and
about 32.1
percent by weight.
The water content in each of the diluted bitumen products after settling for
one
hour was below about 0.1 percent by weight for the settling tests with initial
S:B ratios of about
1.8 and about 2.0, regardless of the operating temperature. At an initial S:B
ratio of about 1.6
the water content in the diluted bitumen product after settling for one hour
varied from about
0.7 percent to about 0.1 percent by weight, depending on the temperature.
The solid mineral material (ash) content in each of the diluted bitumen
products
was below about 0.1 percent by weight except for the first test summarized in
Figure 4, in
which the solid mineral material content was about 0.11 percent by weight.
Heptane as the Paraffinic Solvent
The results of one-stage autoclave settling tests using heptane as the
paraffinic
solvent are summarized in Figure 5.
The amount of asphaltene precipitation and/or rejection observed in the
laboratory testing summarized in Figure 5 ranged between about 2.6 percent and
about 24.2
percent by weight.
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The water content in each of the diluted bitumen products after settling for
one
hour was below about 0.1 percent by weight.
The solid mineral material (ash) content was about 0.35 percent by weight for
the settling test which provided an asphaltene precipitation and/or rejection
of about 2.6 percent
by weight. The solid mineral material content for the other two settling
tests, which both
provided an asphaltene precipitation and/or rejection above about 5 percent by
weight, was
below about 0.1 percent by weight.
1:1 Pentane/Hexane Mixture as the Paraffinic Solvent
The results of one-stage autoclave settling tests conducted using a 1:1
mixture of
n-pentane and n-hexane as the paraffinic solvent are summarized in Figure 6.
The amount of asphaltene precipitation and/or rejection observed in the
laboratory testing summarized in Figure 6 ranged between about 7.4 percent and
about 22.3
percent by weight.
The water content in each of the diluted bitumen products was below about 0.1
percent by weight after one hour of settling.
The solid mineral material content was about 0.18 percent by weight for the
settling test which provided an asphaltene precipitation and/or rejection of
about 7.4 percent by
weight. The solid mineral material content for each of the other settling
tests summarized in
Figure 6 was below about 0.10 percent by weight.
The settling test results summarized in Figure 6 demonstrate that a very clean
diluted bitumen product can be produced under the conditions tested, even when
asphaltene
precipitation and/or rejection is as low as about 8.4 percent by weight and as
high as about 22.3
percent by weight.
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Additional Comments Relating to the Laboratory Settling Tests
Figures 2-6 include material balance summaries for the one-stage settling
tests
which are summarized in Figures 2-6.
The settling rates for all tests should be considered as approximate
estimations.
In the autoclave, the interface between asphaltene clusters or aggregates and
overflow diluted
bitumen product cannot be measured.
The settling rate can only be estimated from measurements of water content at
different time intervals. A sudden drop in the water content of the diluted
bitumen product
indicates that asphaltene aggregates, including trapped solid mineral material
and water, have
passed through the sampling level during the sampling time interval, thereby
providing an
estimate of the settling time for settling over the distance between the
surface and the sampling
level. In the laboratory experiments summarized in Figures 2-6, the sampling
level was about
8.5 centimeters from the surface. The settling time was estimated by
regression of the initial
points (water content as a function of time) and calculating the time required
for the water
content to reach zero from the regression equation. The calculated data for
all tests are
provided in Figures 2-6.
The underflow from each laboratory settling test was analyzed for its
composition by Dean-Stark extraction. Since only bitumen, solid mineral
material and water
percentages are determined by the Dean-Stark procedure, the paraffinic solvent
content in the
underflow was obtained from the difference between 100 percent and the sum of
the
percentages of bitumen, solid mineral material and water. As a result, any
experimental errors
and uncertainties in determining the bitumen, solid mineral material and water
contents are
accumulated in the determination of the paraffinic solvent content.
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The experimental data show that the underflow from each of the one-stage
autoclave settling tests contained between about 14 percent and about 22
percent bitumen by
weight, depending on the S:B ratio.
The paraffinic solvent content of the underflow for each of the one-stage
autoclave settling tests typically ranged between about 14 percent by weight
and about 27
percent by weight, except in the case of two tests involving heptane as the
paraffinic solvent at
S:B ratios greater than about 2Ø In these two tests, the paraffinic solvent
content was greater
than about 34 percent by weight, as indicated in Figure 5.
The total bitumen loss (i.e., both maltenes and asphaltenes) to the underflow
for
each of the one-stage autoclave settling tests ranged between about 13 percent
by weight and
about 25 percent by weight, with maltene losses constituting between about 55
percent and
about 75 percent of the total bitumen loss.
These results suggest that the bitumen recovery from a one-stage froth
treatment
process is not acceptable for commercial application, despite the fact that
the diluted bitumen
product has a sufficiently low BS&W content to be satisfactory for pipeline
transportation
and/or for use as an upgrading feedstock. The amount of bitumen loss resulting
from one-stage
froth treatment in accordance with the invention, even where asphaltene
precipitation and/or
rejection is reduced in comparison with the conventional paraffinic process,
suggests a need for
additional processing of the underflow stream to recover portions of the
bitumen contained
therein.
The data contained in Figures 2-6 demonstrates that the BS&W content in the
diluted bitumen product is dependent primarily upon the amount of asphaltene
precipitation
and/or rejection, which in turn is dependent upon the composition of the
paraffinic solvent, the
concentration of the paraffinic solvent (i.e., the solvent to bitumen ratio or
S:B ratio), and
operating temperature.
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Referring to Figures 2-6, in each settling test in which the amount of
asphaltene
precipitation and/or rejection was greater than or equal to about 5 percent by
weight, the
resulting BS&W content was less than or equal to about 0.5 percent by weight,
and more
particularly, was less than or equal to about 0.25 percent by weight.
The effect of operating temperature upon the BS&W content of the diluted
bitumen product appears to depend upon the S:B ratio. When the S:B ratio is
sufficiently high
to provide at least about 5 percent asphaltene precipitation and/or rejection
by weight, the
BS&W content does not appear to be particularly dependent upon the operating
temperature.
At lower S:B ratios where there is little or no asphaltene precipitation
and/or rejection, the
effect of operating temperature upon the BS&W content becomes more
significant.
Specifically, as the operating temperature increases, the BS&W content in the
diluted bitumen
product decreases.
As previously indicated, the amount of asphaltene precipitation and/or
rejection
is dependent on the composition of the paraffinic solvent, the concentration
of the paraffinic
solvent (i.e., solvent to bitumen ratio or S:B ratio) and the operating
temperature. From the
data contained in Figures 2-6, it appears that the amount of asphaltene
precipitation and/or
rejection is dependent primarily upon the composition of the paraffinic
solvent and the S:B
ratio.
Figure 7 is a graph depicting the asphaltene content in diluted bitumen
product
as a function of S:B ratio for the paraffinic solvents used in the laboratory
testing, without
regard to the effects of operating temperature. Figure 8 is a graph depicting
the percentage of
asphaltene precipitation and/or rejection as a function of the S:B ratio for
the different
paraffinic solvents which were used in the laboratory testing. Figure 7 and
Figure 8 indicate a
clear trend for the effects of the type of paraffinic solvent and the S:B
ratio on the amount of
asphaltene precipitation and/or rejection.
In generating the data used in Figure 7 and Figure 8, the S:B ratio for each
paraffinic solvent was varied with very narrow ranges. Within these narrow
ranges of S:B ratio,
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the amount of asphaltene precipitation and/or rejection varied with the values
of S:B ratio
almost linearly for each paraffinic solvent. It should be noted that these
linear relationships
should not be extended without supporting experimental data because the linear
relationships
may not be valid throughout wider ranges of S:B ratios.
Figure 7 and Figure 8 also demonstrate graphically that the extent of
asphaltene
precipitation is greater in shorter chain paraffinic solvents (i.e. pentane)
than in relatively longer
chain paraffinic solvents (i.e., heptane). As would be expected, the lines in
Figure 7 and Figure
8 for the 1:1 mixture of n-pentane and n-hexane is located intermediate
between the line for n-
hexane and the line for n-pentane.
Graphical representations similar to Figure 7 and Figure 8 may provide a very
useful guideline for the selection of paraffinic solvent and for the selection
of a corresponding
S:B ratio to obtain a desired amount of asphaltene precipitation and/or
rejection. In order to
achieve a specific amount of asphaltene precipitation and/or rejection, a
specific combination of
paraffinic solvent and S:B ratio can be selected from Figure 7 and Figure 8 or
from similar
graphical representations.
For example, in order to produce a diluted bitumen product having a BS&W
content less than or equal to about 0.5 percent by weight, the minimum
asphaltene precipitation
and/or rejection should be around 5 percent by weight. Referring to Figures 2-
6, an amount of
asphaltene precipitation and/or rejection of at least about 15 percent by
weight appears
consistently to provide a BS&W content of less than or equal to about 0.2
percent by weight.
In Figure 8, a dashed horizontal line has been provided at the level of about
15
percent asphaltene precipitation and/or rejection by weight. The intersection
between this
dashed line and a line provided on Figure 8 for a particular paraffinic
solvent indicates the S:B
ratio which is needed to achieve about 15 percent asphaltene rejection by
weight for, the
particular paraffinic solvent.
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Accordingly, the precipitation and/or rejection of about 15 percent
asphaltenes
by weight with pentane as the paraffinic solvent requires an S:B ratio of
about 1.25, with a 1:1
mixture of pentane and hexane as the paraffinic solvent an S:B ratio of about
1.4, with hexane
as the paraffinic solvent an S:B ratio of about 1.7, and with heptane as the
paraffinic solvent an
S:B ratio of about 2Ø
As a result, based upon the data contained in Figures 2-6 and upon the graph
in
Figure 8, the S:B ratio indicated above for each paraffinic solvent which is
required to provide
about 15 percent by weight asphaltene precipitation and rejection may be the
minimum S:B
ratio which is required to produce a diluted bitumen product having a BS&W
content which is
consistently less than or equal to about 0.2 percent by weight.
PILOT PLANT TESTING
Pilot Plant Testing with Good Quality Froth
Figures 9-18 provide summaries of pilot plant testing of continuous two-stage
and three-stage countercurrent paraffinic froth treatment processes
illustrating features of the
invention using good quality bitumen froth as a feed material.
The good quality bitumen froth was comprised of between about 62 percent and
about 67 percent by weight bitumen, between about 6 percent and about 9
percent by weight
solid mineral material, and between about 26 percent and about 30 percent by
weight water.
The paraffinic solvent used in the pilot plant testing of the good quality
bitumen
froth was either n-pentane or a 1:1 mixture of n-pentane and n-hexane by
weight.
Several different equipment configurations were tested, including gravity
settling
vessels, inclined plate settlers, and combinations of both gravity settling
vessels and inclined
plate settlers.
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Two-Stage Testing, Pentane Solvent, Two Gravity Settling Vessels
Material balances for two-stage pilot plant tests using pentane as the
paraffinic
solvent with two gravity settling vessels in a countercurrent configuration
are presented in
Figures 9-11.
Referring to Figure 9, the S:B ratio in the diluted bitumen product was about
1.33, resulting in precipitation and/or rejection of about 21.43 percent by
weight of the
asphaltenes contained in the Stage 1 feed stream. The solid mineral material
content and the
water content in the diluted bitumen product were each about 0.05 percent by
weight so that the
BS&W content was about 0.10 percent by weight. The total bitumen recovery
(maltenes and
asphaltenes) in the diluted bitumen product was about 96.27 percent. The
paraffinic solvent
recovery in the diluted bitumen product was about 96.1 percent. The operating
temperature for
Stage 1 was about 77 degrees Celsius and the operating temperature for Stage 2
was about 86
degrees Celsius.
Referring to Figure 10, the S:B ratio in the diluted bitumen product was about
1.57, resulting in precipitation and/or rejection of about 30.77 percent by
weight of the
asphaltenes contained in the Stage 1 feed stream. The solid mineral material
content and the
water content in the diluted bitumen product were each about 0.00 percent by
weight so that the
BS&W content was also about 0.00 percent by weight. The total bitumen recovery
(maltenes
and asphaltenes) in the diluted bitumen product was about 94.32 percent. The
paraffinic
solvent recovery in the diluted bitumen product was about 98.5 percent.
Referring to Figure 11, the S:B ratio in the diluted bitumen product was about
1.65, resulting in precipitation and/or rejection of about 40.00 percent by
weight of the
asphaltenes contained in the Stage 1 feed stream. The solid mineral material
content and the
water content in the diluted bitumen product were each about 0.05 percent by
weight so that the
BS&W content was about 0.10 percent by weight. The total bitumen recovery
(maltenes and
asphaltenes) in the diluted bitumen product was about 94.03 percent. The
paraffinic solvent
recovery in the diluted bitumen product was about 96.3 percent.
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Two-Stage Testing, Pentane/Hexane Solvent, Two Inclined Plate Settlers
A material balance for a two-stage pilot plant test using a 1:1 mixture of
pentane
and hexane by weight with two inclined plate settlers in a countercurrent
configuration is
presented in Figure 12.
Referring to Figure 12, the S:B ratio in the diluted bitumen product was about
1.62, resulting in precipitation and/or rejection of about 18.18 percent by
weight of the
asphaltenes contained in the Stage 1 feed stream. The solid mineral material
content and the
water content in the diluted bitumen product were each about 0.05 percent by
weight so that the
BS&W content was about 0.10 percent by weight. The total bitumen recovery
(maltenes and
asphaltenes) in the diluted bitumen product was about 96.80 percent. The
paraffinic solvent
recovery in the diluted bitumen product was about 93.3 percent. The operating
temperature for
Stage 1 was about 85 degrees Celsius and the operating temperature for Stage 2
was about 76
degrees Celsius.
Three-Stage Testing, Pentane/Hexane Solvent, Two Inclined Plate Settlers and
One Gravity
Settling Vessel
Material balances for three-stage pilot plant tests using a 1:1 mixture of
pentane
and hexane by weight as the paraffinic solvent, with inclined plate settlers
in the first stage and
second stage and a gravity settling vessel in the third stage, in a
countercurrent configuration,
are presented in Figures 13-15.
Referring to Figure 13, the S:B ratio in the diluted bitumen product was about
1.59, resulting in precipitation and/or rejection of about 5.56 percent by
weight of the
asphaltenes contained in the Stage 1 feed stream. The solid mineral material
content and the
water content in the diluted bitumen product were each about 0.05 percent by
weight so that the
BS&W content was about 0.10 percent by weight. The total bitumen recovery
(maltenes and
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asphaltenes) in the diluted bitumen product was about 98.36 percent. The
paraffinic solvent
recovery in the diluted bitumen product was about 96.5 percent.
Referring to Figure 14, the S:B ratio in the diluted bitumen product was about
1.52, resulting in precipitation and/or rejection of about 7.69 percent by
weight of the
asphaltenes contained in the Stage 1 feed stream. The solid mineral material
content and the
water content in the diluted bitumen product were each about 0.05 percent by
weight so that the
BS&W content was about 0.10 percent by weight. The total bitumen recovery
(maltenes and
asphaltenes) in the diluted bitumen product was about 98.44 percent. The
paraffinic solvent
recovery in the diluted bitumen product was about 97.0 percent. The operating
temperature for
Stage 1 was about 75 degrees Celsius and the operating temperature for Stage 3
was about 83
degrees Celsius.
Referring to Figure 15, the S:B ratio in the diluted bitumen product was about
1.48, resulting in precipitation and/or rejection of about 17.39 percent by
weight of the
asphaltenes contained in the Stage 1 feed stream. The solid mineral material
content and the
water content in the diluted bitumen product were each about 0.05 percent by
weight so that the
BS&W content was about 0.10 percent by weight. The total bitumen recovery
(maltenes and
asphaltenes) in the diluted bitumen product was about 97.71 percent. The
paraffinic solvent
recovery in the diluted bitumen product was about 96.0 percent.
A comparison of the results in Figures 13-15 with the results in Figures 9-11
suggests that the total bitumen recovery from bitumen froth can possibly be
increased to about
96 percent or about 98 percent for a three-stage process according to the
invention from about
94 percent or about 96 percent for a two-stage process according to the
invention.
If the results in Figures 13-15 are accurate, and do not result from artifacts
in the
mass balance reconciliation process, it would appear from the results in
Figures 9-11 that any
significant increase in total bitumen recovery for a three-stage process in
comparison with a
two-stage process would likely be attributable to an increase in asphaltene
recovery, since a
two-stage process appears to achieve a very high maltene recovery.
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However, it is difficult to reconcile increased asphaltene recovery in the
third
stage with the operating conditions in the third stage. In particular,
referring to Figures 13-15,
the S:B ratio in the third stage is significantly higher than in the first and
second stages, with the
result that asphaltenes are likely to be less soluble in the third stage than
in the first and second
stages and are therefore less likely to be recovered in the third overflow
stream produced by the
third stage.
As a result, further investigation is required in order to determine
conclusively
whether a three-stage process according to the invention can provide a
significantly higher total
bitumen recovery than a two-stage process according to the invention.
In practice, selecting between a two-stage process and a three-stage process
will
likely depend on overall project economics, including a consideration of the
possibility that
total bitumen recoveries might be increased by using a three-stage process
according to the
invention in comparison with a two-stage process according to the invention.
Two-Stage Testing, Pentane Solvent, Two Gravity Settling Vessels, High
Asphaltene Rejection
Material balances for two-stage pilot plant tests using pentane as the
paraffinic
solvent with two gravity settling vessels in a countercurrent configuration
are presented in
Figures 16-18. In each of the material balances presented in Figures 16-18,
the amount of
asphaltene precipitation and/or rejection in Stage 1 exceeds about 40 percent
by weight. As a
result, the material balances presented in Figures 16-18 represent
applications of a typical
paraffinic froth treatment process instead of applications of the process of
the invention.
Referring to Figure 16, the S:B ratio in the diluted bitumen product was about
1.96, resulting in precipitation and/or rejection of about 42.86 percent by
weight of the
asphaltenes contained in the Stage 1 feed stream. The solid mineral material
content and the
water content in the diluted bitumen product were each about 0.00 percent by
weight so that the
BS&W content was also about 0.00 percent by weight. The total bitumen recovery
(maltenes
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and asphaltenes) in the diluted bitumen product was about 89.91 percent. The
paraffinic
solvent recovery in the diluted bitumen product was about 99.0 percent.
Referring to Figure 17, the S:B ratio in the diluted bitumen product was about
2.09, resulting in precipitation and/or rejection of about 45.45 percent by
weight of the
asphaltenes contained in the Stage 1 feed stream. The solid mineral material
content and the
water content in the diluted bitumen product were each about 0.00 percent by
weight so that the
BS&W content was also about 0.00 percent by weight. The total bitumen recovery
(maltenes
and asphaltenes) in the diluted bitumen product was about 93.02 percent. The
paraffinic
solvent recovery in the diluted bitumen product was about 97.7 percent.
Referring to Figure 18, the S:B ratio in the diluted bitumen product was about
1.73, resulting in precipitation and/or rejection of about 46.67 percent by
weight of the
asphaltenes contained in the Stage 1 feed stream. The solid mineral material
content and the
water content in the diluted bitumen product were each about 0.00 percent by
weight so that the
BS&W content was also about 0.00 percent by weight. The total bitumen recovery
(maltenes
and asphaltenes) in the diluted bitumen product was about 91.40 percent. The
paraffinic
solvent recovery in the diluted bitumen product was about 96.1 percent.
As can be seen from Figures 16-18, a paraffinic froth treatment process which
results in precipitation and/or rejection of more than 40 percent by weight of
the asphaltenes
contained in the bitumen froth is capable of producing a very clean diluted
bitumen product
having a very low BS&W content, but this very clean product is produced at the
expense of
total bitumen recovery, which is significantly less than the bitumen
recoveries which are
achievable using the process of the invention.
Pilot Plant Testing with Poor Quality Froth
Figure 19 and Figure 20 provide summaries of pilot plant testing of continuous
two-stage countercurrent paraffinic froth treatment processes illustrating
features of the
invention using poor quality bitumen froth as a feed material.
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Two-Stage Process, Pentane/Hexane Solvent, One Inclined Plate Settler and One
Gravity
Settling Vessel
A material balance for a two-stage pilot plant test using a 1:1 mixture of
pentane
and hexane by weight as the paraffinic solvent, with one inclined plate
settler and one gravity
settling vessel in a countercurrent configuration, is presented in Figure 19.
The poor quality bitumen froth which was used in the test relating to Figure
19
was comprised of about 58 percent by weight bitumen, about 12 percent by
weight solid
mineral material, and about 30 percent by weight water.
Referring to Figure 19, the S:B ratio in the diluted bitumen product was about
1.84, resulting in precipitation and/or rejection of about 33.33 percent by
weight of the
asphaltenes contained in the Stage 1 feed stream. The solid mineral material
content and the
water content in the diluted bitumen product were each about 0.05 percent by
weight so that the
BS&W content was about 0.10 percent by weight. The total bitumen recovery
(maltenes and
asphaltenes) in the diluted bitumen product was about 95.89 percent. The
paraffinic solvent
recovery in the diluted bitumen product was about 95.5 percent. The operating
temperature for
Stage 1 was about 72 degrees Celsius and the operating temperature for Stage 3
was about 75
degrees Celsius.
Two-Stage Process, Pentane/Hexane Solvent, Two Gravity Settling Vessels
A material balance for a two-stage pilot plant test using a 1:1 mixture of
pentane
and hexane by weight as the paraffinic solvent with two gravity settling
vessels in a
countercurrent configuration is presented in Figure 20.
The poor quality bitumen froth which was used in the test relating to Figure
20
was comprised of about 46 percent by weight bitumen, about 16 percent by
weight solid
mineral material, and about 38 percent by weight water. The poor quality
bitumen froth was
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extracted from aged low-grade oil sand ores which were kept in storage for
several months at
the extraction site. The bitumen froth had also aged from prolonged storage in
a holding tank at
the extraction site prior to being transported to the froth treatment facility
for testing.
This poor quality bitumen froth was considered to be waste material and plans
had been made to dispose of the bitumen froth at a tailings facility. It was
decided, however, to
subject the bitumen froth to paraffinic froth treatment in an effort to
recover a diluted bitumen
product therefrom in a manner similar to that used with good quality bitumen
froth. The
purpose of testing this poor quality bitumen froth was to evaluate the
potential for treating
waste materials such as pond oil using the process of the invention.
Referring to Figure 20, the S:B ratio in the diluted bitumen product was about
1.74, resulting in precipitation and/or rejection of about 40.00 percent by
weight of the
asphaltenes contained in the Stage 1 feed stream. The solid mineral material
content and the
water content in the diluted bitumen product were each about 0.05 percent by
weight so that the
BS&W content was about 0.10 percent by weight. The total bitumen recovery
(maltenes and
asphaltenes) in the diluted bitumen product was about 95.31 percent. The
paraffinic solvent
recovery in the diluted bitumen product was about 95.5 percent. The operating
temperature for
Stage 1 was about 76 degrees Celsius and the operating temperature for Stage 3
was about 77
degrees Celsius.
As can be seen from Figure 20, a high quality diluted bitumen product was
obtained from this poor quality bitumen froth, suggesting that the process of
the invention may
be useful for recovering bitumen from waste materials.
In this document, the word "comprising" is used in its non-limiting sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the elements is present, unless the context
clearly requires that
there be one and only one of the elements.
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