Note: Descriptions are shown in the official language in which they were submitted.
CA 02573633 2007-01-10
BITUMEN FROTH TREATMENT PROCESS
FIELD OF INVENTION
The present invention relates to a process for treating a bitumen froth
comprising
bitumen, water and a mineral material using a diluent and gravity separation
techniques.
BACKGROUND OF INVENTION
Oil sand is essentially a matrix of bitumen, water and mineral material. The
bitumen component of oil sand consists of viscous hydrocarbons, including
asphaltenes, 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. The mineral material component of oil sand
typically
consists largely of sand, but may also include rock, silt, clay and heavy
metals. Sand and rock
are considered to be coarse mineral material, while clay and silt are
considered to be fine
mineral material, where fines are defined as mineral material having a
particular size of less
than 44 microns. The water component of oil sand consists essentially of a
film of connate
water surrounding the sand in the oil sand matrix, and may also contain
particles of fine mineral
material within it.
A typical deposit of oil sand will contain about 10% to 12% bitumen and about
3% to 6% water, with the remainder of the oil sand being made up of mineral
material.
Typically the mineral material component in oil sand will contain about 14% to
20% fines,
measured by weight of total mineral material 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 material, with about 15% to 20% of the mineral material being
made up of
fines.
Oil sand deposits are mined, and oil sand extraction processes are performed,
for
the purpose of liberating or separating the bitumen from the oil sand, which
bitumen may
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subsequently be upgraded to produce synthetic crude oil. Accordingly, various
oil sand
extraction processes have been developed for separating the bitumen from the
oil sand.
One well known oil sand extraction process is the Clark Process, which is
often
referred to as the "hot water process". The hot water process utilizes both
aggressive thermal
action and aggressive mechanical action to liberate and separate bitumen from
the oil sand and
is typically a three step process which produces a number of product streams.
In the hot water process, the oil sand is first conditioned by mixing it with
hot
water at about 95 Celsius and steam in a conditioning vessel which vigorously
agitates the
resulting slurry in order to completely disintegrate the oil sand. Once the
disintegration is
complete, the slurry undergoes a primary separation process. The primary
separation process
separates the slurry by allowing the sand and rock to settle out to provide a
"coarse tailings"
stream, while the bitumen, having air entrained within it, floats to the top
of the slurry and is
withdrawn as a "bitumen froth stream". The remainder of the slurry, which is
referred to as the
"middlings stream", 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 primary
separation process. The
bitumen recovered from the middlings stream may be returned to the primary
separation
process or may be combined with the bitumen froth stream.
Various alternative oil sand extraction processes have been developed,
including
but not limited to the inventions described in: Canadian Patent No. 1,085,761
issued on
September 16, 1980 to Rendall; United States of America Patent No. 4,512,956
issued on April
23, 1985 to Robinson et al; United States of America Patent No. 4,533,459
issued on August 6,
1985 to Dente et al; United States of America Patent No. 4,414,117 issued on
November 8,
1983 to Yong et al; United States of America Patent No. 4,225,433 issued
September 30, 1980
to Liu et al.; Canadian Patent Application No. 2,030,934 published on May 28,
1992 by Strand;
Canadian Patent Application No. 2,124,199 published on June 11, 1992 by
Strand; and
Canadian Patent No. 2,123,076 issued November 17, 1998 to Strand et. al.
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Regardless of which oil sand extraction process is used, such processes
typically
produce a bitumen froth stream which is comprised of bitumen, water and
mineral material.
The bitumen froth stream from the oil sand extraction process is typically
subjected to further
processing in order to remove amounts of water and mineral material in order
to produce a
bitumen product which is suitable either for upgrading or for pipelining to an
upgrading facility.
For example, in order to be suitable for upgrading, the bitumen product may be
required to contain at least about 95 percent hydrocarbons by weight, while in
order to be
suitable for pipelining, the bitumen product may be required to contain at
least about 99.5
percent hydrocarbons by weight.
Thus, the bitumen froth stream obtained from an oil sand extraction process
must typically undergo one or more treatment processes in order to remove
water and mineral
material therefrom. A number of different bitumen froth treatment processes
have been
proposed in the prior art.
Canadian Patent No. 1,239,371 issued July 19, 1988 to Angelov et. al. provides
a process for de-emulsifying and de-asphalting a heavy oil/water emulsion. The
emulsion is
first mixed with a solvent comprising a paraffinic composition, whereby the
oil is dissolved by
the solvent while the water and asphaltics coalesce as fast settling
particles. The particles are
then separated from the oil/solvent phase for further treatment.
Canadian Patent No. 1,267,860 issued April 19, 1990 to Hann describes a
process in which the bitumen froth is diluted with a light hydrocarbon diluent
prior to the
passing of the diluted bitumen froth through an inclined plate separator. The
inclined plate
settler is controlled by varying the underflow withdrawal rate from the
separator in response to
the hydrocarbon content of the separator overflow. Subsequently, the settler
underflow is
conducted to a "conventional" centrifuge treatment circuit, while the settler
overflow, after
diluent recovery, is conducted to an upgrading process.
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Canadian Patent No. 1,293,465 issued December 24, 1991 to Shelfantook et. al.
relates to a counter-current process for treating bitumen froth which utilizes
three stages of
inclined plate separators. In particular, the bitumen froth is passed through
a circuit of the
serially connected inclined plate settlers, while a light hydrocarbon diluent
moves
countercurrently through the circuit.
Canadian Patent No. 2,012,305 issued March 21, 1995 to Lechnick et. al.
describes the preparation of a tar sands extract comprising bitumen, a "non-
specific" solvent
capable of dissolving all of the bitumen components and mineral fines, and
mixing the extract
with a "specific" solvent which is generally not capable of dissolving all of
the bitumen
components such as the asphaltenes, in order to form agglomerates comprising
asphaltenes and
mineral fines. The agglomerates are then gravitationally separated from the
balance of the tar
sands extract using a "lamella separator."
Canadian Patent Application No. 2,000,068 by Hall, published April 2, 1991
relates to a bitumen froth treatment process which involves separating bitumen
from the froth
using gravity settling. The bitumen is removed from the bitumen froth
utilizing a gravity
separator which is heated to a temperature of between about 250 F and about
450 F while
maintaining the froth under sufficient pressure to prevent the vaporization of
the water and
bitumen. The process is intended to be performed without the addition of
diluent to the
bitumen froth.
Canadian Patent No. 2,021,185 issued September 15, 1998 to Tipman et, al.
relates to a process which passes the bitumen froth through a plurality of
separation stages in
series for gravity separation of the water and solids from the bitumen. Each
separation stage
further involves the heating of the bitumen froth to a temperature of between
about 80 C to
about 300 C under a sufficient pressure to maintain the hydrocarbon component
in a liquid
state. Further, a low molecular weight hydrocarbon diluent may be mixed with
the bitumen
froth for preconditioning of the froth prior to each gravity separation stage.
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Canadian Patent No. 2,217,300 issued August 20, 2002 to Long et. al. and
Canadian Patent No. 2,149,737 issued March 2, 1999 to Tipman et. al. both
provide methods
for the cleaning of a bitumen froth. The methods include adding a sufficient
amount of a
paraffinic solvent to the froth to induce inversion, mixing the froth and the
solvent for a
sufficient time to disperse the solvent in the froth, and subjecting the
mixture to gravity or
centrifugal separation.
Canadian Patent No. 2,400,258 issued January 11, 2005 to Madge et. al. and
Canadian Patent Application No. 2,527,058 by Garner et. al., published March
19, 2004
describe froth treatment circuits in which a bitumen froth feed stream is
diluted with a solvent
and supplied to a primary inclined plate separator stage. The underflow from
the primary
inclined plate separator is further processed by a primary cyclone stage, a
secondary inclined
plate separator stage and a secondary cyclone stage. The solvent or diluent
may be naphtha or a
paraffinic or alkane hydrocarbon solvent. The expressed intention of the
circuits is to treat the
bitumen froth without the need for centrifuge equipment.
Canadian Patent Application No. 2,435,113 by Walker et. al., published January
11, 2005 describes the treatment of a bitumen-water emulsion, such as a
bitumen froth, with a
mixture comprised of a naphtha and a light solvent, particularly a C3 or C4
aliphatic
hydrocarbon. The treatment destabilizes the emulsion and results in the
precipitation of some
of the asphaltenes in the bitumen. The amount of precipitation is controlled
to produce a
product of a specified asphaltene content. More particularly, the asphaltene
content is
controlled by adjusting the ratio of the naphtha to the light solvent and/or
the ratio of the light
solvent to the bitumen. The combined bitumen froth and mixture of naphtha and
light solvent
are fed to a phase separator.
Canadian Patent Application No. 2,493,677 by Romero et. al., published June
28, 2005 utilizes a counter-current bitumen froth treatment circuit. The
treatment circuit
includes a primary inclined plate separator, a secondary inclined plate
separator and a primary
cyclone connected in series. A diluent is added to each of the primary and
secondary inclined
plate separator stages, and a diluent is optionally added to the cyclone
stage.
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United States of America Publication No. US2005/0150844 Al by Hyndman et.
al., published July 14, 2005 describes a process for treating a bitumen froth
which includes
adding a diluent solvent to the bitumen froth to produce a diluted bitumen
froth. The diluted
bitumen froth is subjected to a separating step to separate the bitumen from
the remaining
diluted tailings component. The separating step is performed by a separator
apparatus
comprised of first and second separator vessels connected in series and
configured to operate in
a countercurrent manner, wherein the diluent solvent is added to the bitumen
froth in the second
separator vessel. Further, the solvent is subsequently recovered from the
diluted tailings
component such that it may be recycled within the process.
There remains a need for an alternative process for treating bitumen froth
which
requires relatively low energy input to operate and which provides for a
relatively efficient use
of diluent.
SUMMARY OF INVENTION
The present invention is a process for treating a bitumen froth comprising
bitumen, water and a mineral material. The process is comprised of subjecting
the bitumen
froth and a diluent to gravity separation.
More particularly, the process is comprised of a plurality of stages of
gravity
separation. In a first stage of gravity separation, a mixture comprising the
bitumen froth and a
first added amount of the diluent is subjected to gravity separation. In
subsequent stages of
gravity separation, mixtures comprising streams derived from the bitumen froth
and further
added amounts of the diluent are subjected to gravity separation. The added
amounts of the
diluent at each stage of gravity separation are controlled in order to control
the amount of the
diluent which is present in each of the mixtures which are subjected to
gravity separation.
In one preferred aspect, the process is comprised of three stages of gravity
separation. In another preferred aspect, the process is comprised of four
stages of gravity
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separation. The invention may, however, be comprised of fewer than three
stages of gravity
separation or more than four stages of gravity separation.
In a particular preferred aspect, the invention is a process for treating a
bitumen
froth comprising bitumen, water and a mineral material, the process
comprising:
(a) subjecting a first mixture comprising the bitumen froth and a first added
amount
of a diluent to first gravity separation in a first gravity separation
apparatus,
thereby producing a first overflow stream and a first underflow stream;
(b) subjecting a second mixture comprising the first underflow stream and a
second
added amount of the diluent to second gravity separation in a second gravity
separation apparatus, thereby producing a second overflow stream and a second
underflow stream; and
(c) subjecting a third mixture comprising the second underflow stream and a
third
added amount of the diluent to third gravity separation in a third gravity
separation apparatus, thereby producing a third overflow stream and a third
underflow stream.
The mixtures which are subjected to gravity separation in the practice of the
invention each have a diluent-to-bitumen ratio.
The bitumen which is contained in the mixtures may be present as maltenes,
dissolved asphaltenes, and precipitated asphaltenes. Diluent-to-bitumen ratio
as used herein is
the ratio by weight of the amount of diluent in the mixture to the amount of
bitumen in the
mixture, wherein the amount of bitumen includes maltenes and dissolved
asphaltenes, but does
not include precipitated asphaltenes.
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The diluent-to-bitumen ratio of each of the mixtures is controlled in the
practice
of the invention in order to provide a desired result for each of the stages
of gravity separation,
preferably while avoiding the use of excessive amounts of diluent.
Preferably there is a trend toward increasing the diluent-to-bitumen ratio of
successive mixtures which are subjected to the gravity separation. Preferably
a first diluent-to-
bitumen ratio of the first mixture is between about 0.5 and about 1.1.
Preferably a second
diluent-to-bitumen ratio of the second mixture is between about 2 and about 4.
Preferably a
third diluent-to-bitumen ratio of the third mixture is between about 3 and
about 8.
As used herein, "gravity separation" includes any process which utilizes
gravity
in order to achieve separation of a mixture of substances having different
densities, and is
therefore distinguishable from other separation processes such as molecular
sieve processes,
absorption processes, adsorption processes, magnetic processes, electrical
processes, etc.
As used herein, "gravity separation" is also distinguishable from "enhanced
gravity separation processes" such as centrifuge processes, cyclone processes
etc. Enhanced
gravity separation processes are generally not suitable for use in the
invention because they may
unnecessarily disrupt or interfere with the components of the bitumen froth,
resulting in less
selective separation, and because they generally require higher energy input
than gravity
separation processes.
One or more different gravity separation processes may be used to perform the
gravity separation in the invention. Preferably the gravity separation
processes used in the
invention are relatively low intensity processes, thereby minimizing
disruption and/or
interference with the components of the bitumen froth and minimizing the
required energy
input.
The gravity separation processes may be performed using any suitable gravity
separation apparatus or suitable combination of gravity separation apparatus.
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Preferably, gravity settling vessels and/or inclined plate settling apparatus
are
used as the gravity separation apparatus to perform the gravity separation.
Gravity settling vessels are typically comprised of tanks or other vessels
into
which a material to be separated may be introduced for a residence time in
order to facilitate
separation of the material due to gravity into two or more components having
different
densities. Gravity settling vessels may have any shape, size and/or
configuration which is
suitable for achieving gravity separation. Gravity settling 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 settling apparatus are typically comprised of a plurality of
inclined
plates onto which a material to be separated may be introduced so that the
material flows
downward along the plates in order to facilitate separation due to gravity
into two or more
components having different densities.
Inclined plate settling apparatus may be preferred over gravity settling
vessels in
circumstances where space is limited and a relatively small "footprint" for
the gravity
separation apparatus is required.
In preferred embodiments, a combination of gravity settling vessels and
inclined
plate settling apparatus are used as the gravity separation apparatus to
perform the gravity
separation.
An objective of each of the stages of gravity separation is to produce an
overflow stream and an underflow stream, wherein the overflow stream contains
a relatively
higher amount of bitumen than the underflow stream and wherein the underflow
stream
contains a relatively higher amount of water and mineral material than the
overflow stream.
Each of the stages of gravity separation is performed for a length of time
which
is sufficient to provide an effective amount of separation having regard to
the limitations of the
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gravity separation apparatus, the bitumen froth and the diluent. Preferably
each of the stages of
gravity separation is designed to achieve a balance between a desired amount
of separation and
the time required to achieve the desired amount of separation.
Where the gravity separation apparatus is comprised of a gravity settling
vessel,
preferably the average residence time of the mixture in the gravity settling
vessel is at least
about 30 minutes. Where the gravity separation apparatus is comprised of an
inclined plate
settling apparatus, the apparatus may be sized to provide a desired level of
separation at a
desired throughput of material to be separated.
The diluent may be comprised of any diluent which is suitable for use in
treating
a bitumen froth. For example, the diluent may be comprised of what is
recognized in the art as
a naphtha diluent or may be comprised of what is recognized in the art as a
paraffinic diluent.
Naphtha diluents may include aromatic compounds while paraffinic diluents may
include
relatively short-chain aliphatic compounds (such as, for example, C5 to C8
aliphatic
compounds).
Preferably the diluent is either a naphtha type diluent or a paraffinic type
diluent.
A naphtha type diluent is comprised of a sufficient amount of a naphtha
diluent (or an
equivalent thereof) so that the naphtha type diluent essentially exhibits the
properties of a
naphtha diluent. A naphtha type diluent may therefore be comprised of a
mixture of a naphtha
diluent and one or more other substances.
A paraffinic type diluent is comprised of a sufficient amount of a paraffinic
diluent (or an equivalent thereof) so that the paraffinic type diluent
essentially exhibits the
properties of a paraffinic diluent. A paraffinic type diluent may therefore be
comprised of a
mixture of a paraffinic diluent and one or more other substances. One
exemplary diluent which
may be suitable for use as a paraffinic type diluent is natural gas
condensate, which may be
comprised of a large percentage of relatively short-chain aliphatic compounds
together with
small amounts of other hydrocarbons which may include naphtha compounds.
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An important distinction between naphtha diluents and paraffinic diluents is
that
asphaltenes are generally soluble in naphtha diluents, while asphaltenes
exhibit a tendency to
precipitate in paraffinic diluents under certain conditions. In particular,
asphaltenes tend to
precipitate in paraffinic diluents when the diluent-to-bitumen ratio is at or
above a critical
asphaltene precipitation diluent-to-bitumen ratio. At diluent-to-bitumen
ratios above the
critical asphaltene precipitation diluent-to-bitumen ratio, the extent of
asphaltene precipitation
in paraffinic diluents generally increases as the diluent-to-bitumen ratio
increases.
The critical asphaltene precipitation diluent-to-bitumen ratio varies
depending
upon the composition of the bitumen, the composition of the diluent, and other
conditions such
as temperature and pressure. The critical asphaltene precipitation diluent-to-
bitumen ratio for a
particular combination of bitumen and diluent may be determined
experimentally, but is
typically about 1.1.
It is known that asphaltenes tend to attract each other and agglomerate
together
as they precipitate. During this process, water and mineral material become
associated with the
asphaltenes and tend to precipitate with the asphaltenes. As a result,
precipitation of
asphaltenes has been found to produce a cleaning effect on bitumen froth by
assisting in the
separation of bitumen from the water and mineral material which are components
of the
bitumen froth.
Furthermore, it is generally recognized that asphaltenes which include the
highest concentrations of undesirable constituents such as sulphur and heavy
metals are most
susceptible to precipitation in paraffinic diluents and are therefore the
first asphaltenes to
precipitate in paraffinic diluents. Consequently, although precipitation of
asphaltenes generally
results in a loss of hydrocarbons from the bitumen, precipitation of a small
amount of
asphaltenes also assists in removing undesirable constituents from the
bitumen.
As a result, the cleaning effects of asphaltene precipitation in paraffinic
diluents
are twofold. First, precipitation of asphaltenes assists in separating water
and mineral material
from the bitumen due to the agglomeration of asphaltene particles. Second,
precipitation of a
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small amount of asphaltenes removes undesirable constituents such as sulphur
and heavy
metals from the bitumen.
In some aspects of the invention, the diluent is preferably a naphtha type
diluent.
In other aspects of the invention, the diluent is preferably a paraffinic type
diluent. In either
case, the amount of the diluent which is present in each of the mixtures which
are subjected to
gravity separation (i.e., the diluent-to-bitumen ratio) may be controlled in
order to achieve a
specific result from the gravity separation. Where the diluent is a naphtha
type diluent, the
amount of the diluent may be controlled to achieve a desired composition of
the overflow
streams and the underflow streams. Where the diluent is a paraffinic type
diluent, the amount
of the diluent may be controlled to selectively avoid the precipitation of
asphaltenes or to cause
the precipitation of asphaltenes, as well as to achieve a desired composition
of the overflow
streams and the underflow streams.
In either case, one of the functions of the diluent is to dilute the bitumen
which
is contained in the bitumen froth, thereby increasing the mobility of the
bitumen and reducing
the density of the combined diluent and bitumen so that it is more easily
separated from the
water and mineral material which are contained in the bitumen froth.
Each of the overflow streams produced by the invention is comprised of an
overflow amount of bitumen, diluent, water and mineral material. Similarly,
each of the
underflow streams produced by the invention is comprised of an underflow
amount of bitumen,
diluent, water and mineral material.
Where the diluent is a naphtha type diluent, a first goal of the first gravity
separation is to produce a first overflow stream which is an acceptable
bitumen product, and a
second goal of the first gravity separation is to limit to an acceptable
amount the amount of
bitumen and diluent which is contained in the first underflow stream.
In order to achieve the first goal of the first gravity separation using a
naphtha
type diluent, the first diluent-to-bitumen ratio is preferably selected having
regard to the other
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operating parameters of the process and the characteristics of the gravity
separation apparatus
so that the water and the mineral material in the first overflow stream
together comprise less
than about 10 percent by weight of the first overflow amount. The first
diluent-to-bitumen ratio
is more preferably selected so that the water and the mineral material in the
first overflow
stream together comprise less than about 7 percent by weight of the first
overflow amount. The
first diluent-to-bitumen ratio is most preferably selected so that the water
and the mineral
material in the first overflow stream together comprise less than about 5
percent by weight of
the first overflow amount.
In order to achieve the second goal of the first gravity separation using a
naphtha
type diluent, the first diluent-to-bitumen ratio is preferably selected having
regard to the other
operating parameters of the process and the characteristics of the gravity
separation apparatus
so that the bitumen and the diluent in the first underflow stream together
comprise less than
about 25 percent by weight of the first underflow amount. The first diluent-to-
bitumen ratio is
more preferably selected so that the bitumen and the diluent in the first
underflow stream
together comprise less than about 20 percent by weight of the first underflow
amount. The first
diluent-to-bitumen ratio is most preferably selected so that the bitumen and
the diluent in the
first underflow stream together comprise less than about 15 percent by weight
of the first
underflow amount.
Where the diluent is a naphtha type diluent, a goal of the second gravity
separation is to recover additional bitumen from the second mixture.
In order to achieve this goal of the second gravity separation, the diluent-to-
bitumen ratio of the second mixture may be increased relative to the diluent-
to-bitumen ratio of
the first mixture, thereby increasing the density differential of the combined
diluent and
bitumen relative to the water and mineral material and decreasing the bitumen
concentration in
the combined diluent and bitumen.
More particularly, in order to achieve this goal of the second gravity
separation
using a naphtha type diluent, the second diluent-to-bitumen ratio is
preferably selected having
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regard to the other operating parameters of the process and the
characteristics of the gravity
separation apparatus so that the water and the mineral material in the second
overflow stream
together comprise less than about 10 percent by weight of the second overflow
amount. The
second diluent-to-bitumen ratio is more preferably selected so that the water
and the mineral
material in the second overflow stream together comprise less than about 8
percent by weight of
the second overflow amount. The second diluent-to-bitumen ratio is most
preferably selected
so that the water and the mineral material in the second overflow stream
together comprise less
than about 6 percent by weight of the second overflow amount.
More particularly, in order to achieve this goal of the second gravity
separation
using a naphtha type diluent, the second diluent-to-bitumen ratio is
preferably selected having
regard to the other operating parameters of the process and the
characteristics of the gravity
separation apparatus so that the bitumen and the diluent in the second
underflow stream
together comprise less than about 20 percent by weight of the second underflow
amount. The
second diluent-to-bitumen ratio is more preferably selected so that the
bitumen and the diluent
in the second underflow stream together comprise less than about 18 percent by
weight of the
second underflow amount. The second diluent-to-bitumen ratio is most
preferably selected so
that the bitumen and the diluent in the second underflow stream together
comprise less than
about 15 percent by weight of the second underflow amount.
Where the diluent is a naphtha type diluent, a goal of the third gravity
separation
is to maximize the amount of bitumen which is contained in the third overflow
stream and thus
minimize the amount of bitumen which is contained in the third underflow
stream. This goal is
particularly important where the third gravity separation is the last stage of
gravity separation,
since the third underflow stream will in such circumstances represent a
tailings stream, with the
result that bitumen contained in the third underflow stream will be lost to
the tailings stream.
As a result, selective rejection of water and mineral material is typically
less important than
bitumen recovery in the performance of the third gravity separation.
In order to achieve this goal of the third gravity separation, the diluent-to-
bitumen ratio of the third mixture may be increased relative to the diluent-to-
bitumen ratio of
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the second mixture, thereby increasing the density differential of the
combined diluent and
bitumen relative to the water and mineral material and decreasing the bitumen
concentration in
the combined diluent and bitumen.
More particularly, in order to achieve this goal of the third gravity
separation
using a naphtha type diluent, the third diluent-to-bitumen ratio is preferably
selected having
regard to the other operating parameters of the process and the
characteristics of the gravity
separation apparatus so that the water and the mineral material in the third
overflow stream
together comprise less than about 10 percent by weight of the third overflow
amount. The third
diluent-to-bitumen ratio is more preferably selected so that the water and the
mineral material in
the third overflow stream together comprise less than about 8 percent by
weight of the third
overflow amount. The third diluent-to-bitumen ratio is most preferably
selected so that the
water and the mineral material in the third overflow stream together comprise
less than about 6
percent by weight of the third overflow amount.
More particularly, in order to achieve this goal of the third gravity
separation
using a naphtha type diluent, the third diluent-to-bitumen ratio is preferably
selected having
regard to the other operating parameters of the process and the
characteristics of the gravity
separation apparatus so that the bitumen and the diluent in the third
underflow stream together
comprise less than about 15 percent by weight of the second underflow amount.
The third
diluent-to-bitumen ratio is more preferably selected so that the bitumen and
the diluent in the
third underflow stream together comprise less than about 13 percent by weight
of the second
underflow amount. The third diluent-to-bitumen ratio is most preferably
selected so that the
bitumen and the diluent in the third underflow stream together comprise less
than about 10
percent by weight of the third underflow amount.
Where the diluent is a paraffinic type diluent, the process is preferably
further
comprised of subjecting a fourth mixture comprising the first overflow stream
and a fourth
added amount of the diluent to fourth gravity separation in a fourth gravity
separation
apparatus, thereby producing a fourth overflow stream and a fourth underflow
stream.
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CA 02573633 2007-01-10
Each of the mixtures which is subjected to gravity separation is comprised of
bitumen. The bitumen is comprised of asphaltenes and maltenes. All or a
portion of the
asphaltenes may be present as dissolved asphaltenes.
Dissolved asphaltenes are asphaltenes that are dissolved in the diluent and/or
the
maltenes. Where the diluent is a paraffinic type diluent, a general goal of
the process is to
control the precipitation of dissolved asphaltenes during each of the stages
of gravity separation
in order to achieve a very high quality bitumen product and an efficient use
of the diluent.
Where the diluent is a paraffinic type diluent, a goal of the first gravity
separation is to separate a large portion of the water and mineral material
from the bitumen
without causing any, or any significant precipitation of the first mixture
dissolved asphaltenes
which are contained in the first mixture.
In order to achieve the goal of the first gravity separation using a
paraffinic type
diluent, the first diluent-to-bitumen ratio is selected so that it is less
than the critical asphaltene
precipitation diluent-to-bitumen ratio, thereby minimizing precipitation of
the first mixture
dissolved asphaltenes when the first mixture is subjected to the first gravity
separation.
Where the diluent is a paraffinic type diluent, a first goal of the fourth
gravity
separation is to produce a fourth overflow stream which is a high quality
bitumen product, and
a second goal of the fourth gravity separation is to limit to an acceptable
amount the amount of
bitumen and diluent which is contained in the fourth underflow stream.
In order to achieve these goals of the fourth gravity separation using a
paraffinic
type diluent, the fourth diluent-to-bitumen ratio is selected to be greater
than the critical
asphaltene precipitation diluent-to-bitumen ratio in order to take advantage
of the bitumen
cleaning effects of asphaltene precipitation, but is preferably controlled so
that a desired amount
of the fourth mixture dissolved asphaltenes are precipitated when the fourth
mixture is
subjected to the fourth gravity separation.
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CA 02573633 2007-01-10
The desired amount of asphaltene precipitation will depend upon the desired
quality of the bitumen product (which is enhanced by asphaltene precipitation)
and the desired
level of bitumen recovery (since the precipitation of asphaltenes results in
lost bitumen).
The fourth diluent-to-bitumen ratio is preferably selected so that no greater
than
about 70 percent by weight of the fourth mixture dissolved asphaltenes are
precipitated when
the fourth mixture is subjected to the fourth gravity separation. This limit
will provide a very
high quality bitumen product at the expense of bitumen recovery. The fourth
diluent-to-
bitumen ratio is more preferably selected so that no greater than about 20
percent by weight of
the fourth mixture dissolved asphaltenes are precipitated when the fourth
mixture is subjected
to the fourth gravity separation. This limit will provide significant cleaning
effects from
asphaltene precipitation with significantly lower bitumen loss.
In addition, the fourth diluent-to-bitumen ratio is preferably selected so
that at
least about 5 percent by weight of the fourth mixture dissolved asphaltenes
are precipitated
when the fourth mixture is subjected to the fourth gravity separation, in
order to achieve some
measurable cleaning effects from asphaltene precipitation. In particular,
precipitation of at least
about 5 percent by weight of the fourth mixture dissolved asphaltenes should
typically result in
the removal of a large percentage of the water and minerals with the
precipitated asphaltenes
and will also result in removal from the bitumen of at least some of the
asphaltenes which
contain the highest concentrations of undesirable constituents.
Stated in other terms, the fourth diluent-to-bitumen ratio is preferably
between
the critical asphaltene precipitation diluent-to-bitumen ratio and about 1.8.
The fourth diluent-
to-bitumen ratio is more preferably between the critical asphaltene
precipitation diluent-to-
bitumen ratio and about 1.5. The fourth diluent-to-bitumen ratio is most
preferably between the
critical asphaltene precipitation diluent-to-bitumen ration and about 1.2.
Where the diluent is a paraffinic type diluent, a goal of the second gravity
separation is to dilute further and selectively clean the second mixture by
providing a combined
density of the diluent and bitumen which is reasonably favourable for
selective bitumen
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CA 02573633 2007-01-10
recovery and by utilizing further the cleaning effects of asphaltene
precipitation. As a result,
the second diluent-to-bitumen ratio is preferably greater than the fourth
diluent-to-bitumen
ratio. Controlling the amount of asphaltene precipitation during the second
gravity separation is
less important than in the fourth gravity separation since the amount of
asphaltenes contained in
the second mixture is relatively small in comparison with the amount of
asphaltenes contained
in the fourth mixture. As a result, more asphaltene precipitation may
typically be tolerated
during the second gravity separation than during the fourth gravity
separation.
In order to achieve this goal of the second gravity separation using a
paraffinic
type diluent, the second diluent-to-bitumen ratio is preferably selected so
that no greater than
about 80 percent by weight of the second mixture dissolved asphaltenes are
precipitated when
the second mixture is subjected to the second gravity separation. The second
diluent-to-
bitumen ratio is more preferably selected so that no greater than about 30
percent by weight of
the second mixture dissolved asphaltenes are precipitated when the second
mixture is subjected
to the second gravity separation. The second diluent-to-bitumen ratio is more
preferably
selected so that no greater than about 20 percent by weight of the second
mixture dissolved
asphaltenes are precipitated when the second mixture is subjected to the
second gravity
separation.
Stated in other terms, the second diluent-to-bitumen ratio is preferably
between
the critical asphaltene precipitation diluent-to-bitumen ratio and about 3.
The second diluent-
to-bitumen ratio is more preferably between the critical asphaltene
precipitation diluent-to-
bitumen ratio and about 2.5.
Where the diluent is a paraffinic type diluent, a goal of the third gravity
separation is to dilute further and selectively clean the third mixture by
providing a combined
density of the diluent and bitumen which is favourable for bitumen recovery
and by utilizing
even further the cleaning effects of asphaltene precipitation. As a result,
the third diluent-to-
bitumen ratio is preferably greater than the second diluent-to-bitumen ratio.
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CA 02573633 2007-01-10
Controlling the amount of asphaltene precipitation during the third gravity
separation is less important than in either the fourth gravity separation or
the second gravity
separation since the amount of asphaltenes contained in the third mixture is
relatively small in
comparison with the amount of asphaltenes contained in either the fourth
mixture or the second
mixture. As a result, more asphaltene precipitation may typically be tolerated
during the third
gravity separation than during either the fourth gravity separation or the
second gravity
separation.
In order to achieve this goal of the third gravity separation using a
paraffinic type
diluent, the third diluent-to-bitumen ratio is preferably selected so that no
greater than about 80
percent by weight of the third mixture dissolved asphaltenes are precipitated
when the third
mixture is subjected to the third gravity separation. The third diluent-to-
bitumen ratio is more
preferably selected so that no greater than about 40 percent by weight of the
third mixture
dissolved asphaltenes are precipitated when the third mixture is subjected to
the third gravity
separation.
Stated in other terms, the third diluent-to-bitumen ratio is preferably
between the
critical asphaltene precipitation diluent-to-bitumen ratio and about 6.
One or more of the gravity separation stages may be assisted with the use of
one
or more suitable process aids. Suitable process aids may include, but are not
limited to,
flocculants and coalescing agents. In preferred embodiments, an amount of a
flocculant may be
used to assist the gravity separation stages. The flocculant may be comprised
of any suitable
substance or combination of substances.
The process of the invention may be configured to produce a plurality of
bitumen product streams and/or a plurality of tailings streams.
Preferably, however, the process of the invention is configured to produce a
single bitumen product stream and a single tailings stream. Where the process
is comprised of
three gravity separation stages which are configured as described above, the
bitumen product
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CA 02573633 2007-01-10
stream is preferably the first overflow stream and the tailings stream is
preferably the third
underflow stream. Where the process is comprised of four gravity separation
stages which are
configured as described above, the bitumen product stream is preferably the
fourth overflow
stream and the tailings stream is preferably the third underflow stream.
As a result, preferably the second overflow stream and the third overflow
stream
are each recycled so that they are added to one or more of the mixtures which
are subjected to
gravity separation. Where the process is comprised of four gravity separation
stages, preferably
the fourth underflow stream is also added to one or more of the mixtures for
further processing
by gravity separation.
The second overflow stream and the third overflow stream may be added to any
of the mixtures. Preferably, however, the second overflow stream is added to
the first mixture
so that the first mixture is further comprised of the second overflow stream,
and the third
overflow stream is added to the second mixture so that the second mixture is
further comprised
of the third overflow stream.
Similarly, the fourth underflow stream may be added to any of the mixtures.
Preferably, however, the fourth underflow stream is added to the second
mixture so that the
second mixture is further comprised of the fourth underflow stream.
Either or both of the bitumen product stream and the tailings stream may be
subjected to diluent recovery in order to recover at least a portion of the
diluent therefrom.
Where the bitumen product stream is the first overflow stream, the first
overflow stream may
therefore be subjected to diluent recovery. Where the bitumen product stream
is the fourth
overflow stream, the fourth overflow stream may therefore be subjected to
diluent recovery.
Where the tailings stream is the third underflow stream, the third underflow
stream may
therefore be subjected to diluent recovery.
The process of the invention may be performed at any suitable temperature,
pressure or combination of temperature and pressure. In preferred embodiments,
the gravity
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CA 02573633 2007-01-10
separation stages are performed at or near ambient (atmospheric) pressure,
thus eliminating the
need for the gravity separation apparatus to be certified as pressure vessels.
Preferably the gravity separation stages are performed at a relatively
elevated
temperature, since separation may be enhanced at elevated temperatures due to
reduced
viscosity of the bitumen froth and increased coalescence of particles. In
preferred embodiments
at ambient (atmospheric) pressure, the gravity separation stages are
preferably performed at an
elevated temperature of between about 60 Celsius and about 120 Celsius or
more preferably
at an elevated temperature of about 80 Celsius.
All or portions of the process of the invention may alternatively be performed
at
a pressure exceeding ambient (atmospheric) pressure, thus facilitating higher
elevated
temperatures and further improved separation due to further reduced viscosity
of the bitumen
froth and further increased coalescence of particles.
SUMMARY OF DRAWINGS
Embodiments of the invention will now be described with reference to the
accompanying drawings, in which:
Figure 1 is a process flow diagram of a first preferred embodiment of a
process
for treating a bitumen froth according to the invention, wherein the process
includes three
stages of gravity separation.
Figure 2 is a theoretical material balance prepared using preferred operating
parameters for the process flow diagram of Figure 1, wherein the diluent is a
naphtha type
diluent.
Figure 3 is a process flow diagram of a second preferred embodiment of a
process for treating a bitumen froth according to the invention, wherein the
process includes
four stages of gravity separation.
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CA 02573633 2007-01-10
Figure 4 is a theoretical material balance prepared using preferred operating
parameters for the process flow diagram of Figure 3, wherein the diluent is a
paraffinic type
diluent.
DETAILED DESCRIPTION
The present invention is a process for treating a bitumen froth using a
diluent
and gravity separation techniques. The bitumen froth to be treated may be
obtained from any
oil sand extraction process, and is comprised of bitumen, water and mineral
material. The
bitumen is comprised of maltenes and asphaltenes.
Referring to Figure 1, there is depicted a process flow diagram for a first
preferred embodiment of the invention which includes three stages of gravity
separation.
Referring to Figure 3, there is depicted a process flow diagram for a second
preferred
embodiment of the invention which includes four stages of gravity separation.
The first preferred embodiment and the second preferred embodiment may both
be performed using any suitable diluent. The first preferred embodiment is,
however,
particularly suited to be performed using a naphtha type diluent, while the
second preferred
embodiment is particularly suited to be performed using a paraffinic type
diluent.
As a result, the first preferred embodiment will be described in part with
reference to a theoretical example using a naphtha type diluent and the second
preferred
embodiment will be described in part with reference to a theoretical example
using a paraffinic
type diluent.
Referring to Figure 1, a process flow diagram for the first preferred
embodiment
of the invention is provided.
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CA 02573633 2007-01-10
A bitumen froth (1) is delivered to a first mixer to produce a first mixture
(3)
which comprises the bitumen froth (1) and a first added amount (2) of the
diluent. The first
mixture (3) is delivered to a first gravity separation apparatus (4) which
comprises an inclined
plate settling apparatus. The first mixture (3) is subjected to gravity
separation in the first
gravity separation apparatus (4) to produce a first overflow stream (6) and a
first underflow
stream (11).
In the first preferred embodiment as depicted in Figure 1, the first overflow
stream (6) is a bitumen product stream. The bitumen product stream may be
subjected to
diluent recovery in a solvent recovery unit (SRU) or in another suitable
process or apparatus
(not shown) in order to recover all or a portion of the diluent from the
bitumen product stream.
The recovered diluent may be recycled for reuse in the process of the
invention. Depending
upon the final composition of the bitumen product stream following diluent
recovery therefrom,
the bitumen product stream may be transported by pipeline or in some other
manner to a
bitumen upgrading process or facility (not shown).
The first underflow stream (11) is delivered to a second mixer to produce a
second mixture (14) which comprises the first underflow stream (11) and a
second added
amount (13) of the diluent. The second mixture (14) is delivered to a second
gravity separation
apparatus (15) which comprises a gravity settling vessel. The second mixture
(14) is subjected
to gravity separation in the second gravity separation apparatus (15),
preferably for an average
residence time of at least about 30 minutes, to produce a second overflow
stream (5) and a
second underflow stream (16).
The second overflow stream (5) is recycled so that the first mixture (3) is
further
comprised of the second overflow stream (5). The second underflow stream (16)
is delivered to
a third mixer to produce a third mixture (18) which comprises the second
underflow stream
(16) and a third added amount (17) of the diluent. The third mixture (18) is
delivered to a third
gravity separation apparatus (19) which comprises a gravity settling vessel.
The third mixture
(18) is subjected to gravity separation in the third gravity separation
apparatus (19) , preferably
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CA 02573633 2007-01-10
for an average residence time of at least about 30 minutes, to produce a third
overflow stream
(20) and a third underflow stream (21).
The third overflow stream (20) is recycled so that the second mixture (14) is
further comprised of the third overflow stream (20). The third underflow
stream (21) is a
tailings stream. The tailings stream may be subjected to diluent recovery in a
tailings solvent
recovery unit (TSRU) or in another suitable process or apparatus (not shown)
in order to
recover all or a portion of the diluent from the tailings stream. The
recovered diluent may be
recycled for reuse in the process of the invention. The tailings stream may be
further processed
in a thickener or in another suitable process or apparatus (not shown) before
disposal or may be
directly disposed of.
Referring to Figure 3, a process flow diagram for the second preferred
embodiment of the invention is provided.
A bitumen froth (1) is delivered to a first mixer to produce a first mixture
(3)
which comprises the bitumen froth (1) and a first added amount (2) of the
diluent. The first
mixture (3) is delivered to a first gravity separation apparatus (4) which
comprises an inclined
plate settling apparatus. The first mixture (3) is subjected to gravity
separation in the first
gravity separation apparatus (4) to produce a first overflow stream (6) and a
first underflow
stream (11).
In the second preferred embodiment as depicted in Figure 3, the first overflow
stream (6) is delivered to a fourth mixer to produce a fourth mixture (8)
which comprises the
first overflow stream (6) and a fourth added amount (7) of the diluent. The
fourth mixture (8)
is delivered to a fourth gravity separation apparatus (9) which comprises an
inclined plate
settling apparatus. The fourth mixture (8) is subjected to gravity separation
in the fourth gravity
separation apparatus (9) to produce a fourth overflow stream (10) and a fourth
underflow
stream (12).
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CA 02573633 2007-01-10
In the second preferred embodiment, the fourth overflow stream (6) is a
bitumen
product stream. The bitumen product stream may be subjected to diluent
recovery in a solvent
recovery unit (SRU) or in another suitable process or apparatus (not shown) in
order to remove
all or a portion of the diluent from the bitumen product stream. The recovered
diluent may be
recycled for reuse in the process of the invention. Depending upon the final
composition of the
bitumen product stream following diluent recovery therefrom, the bitumen
product stream may
be transported by pipeline or in some other manner to a bitumen upgrading
process or facility
(not shown).
The first underflow stream (11) is delivered to a second mixer to produce a
second mixture (14) which comprises the first underflow stream (11) and a
second added
amount (13) of the diluent. The fourth underflow stream (12) is also delivered
to the second
mixer so that the second mixture (14) is further comprised of the fourth
underflow stream (12).
The second mixture (14) is delivered to a second gravity separation apparatus
(15) which
comprises a gravity settling vessel. The second mixture (14) is subjected to
gravity separation
in the second gravity separation apparatus (15), preferably for an average
residence time of at
least about 30 minutes, to produce a second overflow stream (5) and a second
underflow stream
(16).
The second overflow stream (5) is recycled so that the first mixture (3) is
further
comprised of the second overflow stream (5). The second underflow stream (16)
is delivered to
a third mixer to produce a third mixture (18) which comprises the second
underflow stream
(16) and a third added amount (17) of the diluent. The third mixture (18) is
delivered to a third
gravity separation apparatus (19) which comprises a gravity settling vessel.
The third mixture
(18) is subjected to gravity separation in the third gravity separation
apparatus (19), preferably
for an average residence time of at least about 30 minutes, to produce a third
overflow stream
(20) and a third underflow stream (21).
The third overflow stream (20) is recycled so that the second mixture (14) is
further comprised of the third overflow stream (20). The third underflow
stream (21) is a
tailings stream. The tailings stream may be subjected to diluent recovery in a
tailings solvent
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CA 02573633 2007-01-10
recovery unit (TSRU) or in another suitable process or apparatus (not shown)
in order to
recover all or a portion of the diluent from the tailings stream. The
recovered diluent may be
recycled for reuse in the process of the invention. The tailings stream may be
further processed
in a thickener or in another suitable process or apparatus (not shown) before
disposal or may be
directly disposed of.
In the first preferred embodiment and the second preferred embodiment of the
invention, the gravity settling vessels and the inclined plate settling
apparatus are selected as the
gravity separation apparatus because they both provide suitable settling
performance without
unnecessarily disrupting or interfering with the components of the bitumen
froth and because
they require significantly less energy input than enhanced gravity separation
apparatus such as
centrifuges and cyclones.
Alternate embodiments of the invention may include interchanging of the
gravity
settling vessels and the inclined plate settling apparatus and/or substitution
of the gravity
settling vessels and the inclined plate settling apparatus for other gravity
separation apparatus.
Inclined plate settling apparatus may be preferred over gravity settling
vessels where available
space for the gravity separation apparatus is limited.
In all embodiments of the invention, the stages of gravity separation are
preferably performed at a relatively elevated temperature of between about 60
Celsius and
about 120 Celsius, or more preferably at a temperature of about 80 Celsius,
in order to
enhance the separation during the stages of gravity separation. Alternatively,
one or more of
the gravity separation stages may be performed at pressures exceeding ambient
(atmospheric)
pressure and at further elevated temperatures, in order to provide further
enhanced separation.
In all embodiments of the invention, each of the added amounts of the diluent
is
controlled in order to provide a desired result at each of the stages of
gravity separation. In the
preferred embodiments, each of the added amounts of the diluent is controlled
with the goal of
achieving a desired diluent-to-bitumen ratio during each of the stages of
gravity separation.
Having regard to the commingling of streams from the various gravity
separation stages due to
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CA 02573633 2007-01-10
recycling etc., the desired diluent-to-bitumen ratio may be achieved by
monitoring the actual
diluent-to-bitumen ratios in the gravity separation apparatus and by providing
suitable feedback
control to control the added amounts of the diluent.
In the preferred embodiments of the invention, the actual diluent-to-bitumen
ratios in the gravity separation apparatus may be monitored by constantly or
periodically
measuring the densities (absolute or relative) of the mixtures, which
densities may be used to
determine the relative proportions of diluent and bitumen in the mixtures,
based upon known
properties of the diluent and the bitumen froth.
In the preferred embodiments of the invention, the amounts of the added
diluent
for each of the stages of gravity separation are individually controlled so
that each of the stages
of gravity separation may be performed at a desired diluent-to-bitumen ratio
for the particular
stage, thus providing for increased opportunity to optimize the treatment of
the bitumen froth.
In all embodiments of the invention, process aids may be used in one or more
stages of gravity separation in order to assist the gravity separation. The
need for process aids
may be assessed, and the selection of appropriate process aids may be made
using criteria
known in the art of bitumen processing.
Figure 2 and Figure 4 are theoretical material balances which represent
theoretical examples relating to the first preferred embodiment and the second
preferred
embodiment of the invention respectively. Figure 2 is an example based upon
the use of a
naphtha type diluent in conjunction with the process flow diagram of Figure 1.
Figure 4 is an
example based upon the use of a paraffinic type diluent in conjunction with
the process flow
diagram of Figure 3.
Example 1
Example I is depicted in Figure 2. Referring to Figure 2, a theoretical
material
balance is provided for the first preferred embodiment of the invention,
wherein preferred
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CA 02573633 2007-01-10
operating parameters using a typical naphtha type diluent have been applied to
the process flow
diagram of Figure 1. The theoretical material balance in Figure 2 has been
prepared using
typical operating characteristics for apparatus of the type depicted in Figure
1.
In Example 1, 330 tonnes per hour of bitumen froth are processed in three
stages
of gravity separation to provide a bitumen product stream of about 324.9
tonnes per hour as the
first overflow stream (6).
The general goal in Example 1 is to maximize bitumen recovery from the
bitumen froth while providing a first overflow stream (6) which is reasonably
clean (i.e., which
contains a reasonably low concentration of water and mineral material).
Pursuant to this general goal, the bitumen recovery in Example 1 is about
98.50
percent, and the bitumen product stream, comprising bitumen, diluent, water
and mineral
material, contains about 4.5 percent water and mineral material by total
weight of the bitumen
product stream. The bitumen product stream in Example 1 may be suitable for
processing in a
bitumen upgrading facility, but may not be suitable for pipeline transport to
a bitumen
upgrading facility, due to the relatively high amount of water and mineral
material contained
therein.
In Example 1, the naphtha type diluent functions essentially to assist in
liberating the bitumen from the water and mineral material and to dilute the
bitumen in order to
enhance the ability to separate the diluent and bitumen from the water and
mineral material. In
Example 1, the cleaning effects resulting from asphaltene precipitation are
not realized due to
the use of the naphtha type diluent.
The effectiveness of gravity separation using a naphtha type diluent with
respect
to both bitumen recovery and rejection of water and mineral material is
dependent upon the
diluent-to-bitumen ratio. As a result, desired compositions of the overflow
streams (6,5,20) and
the underflow streams (11,16,21) produced by the three stages of gravity
separation may be
achieved by regulating the diluent-to-bitumen ratio of the mixtures (3,14,18).
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CA 02573633 2007-01-10
In Example 1, the diluent-to-bitumen ratio of the first mixture (3) is
regulated by
controlling the first added amount (2) of the diluent, the diluent-to-bitumen
ratio of the second
mixture (14) is regulated by controlling the second added amount (13) of the
diluent, and the
diluent-to-bitumen ratio of the third mixture (18) is regulated by controlling
the third added
amount (17) of the diluent. The diluent-to-bitumen ratios are regulated so
that each of the three
stages of gravity separation will provide an overflow stream and an underflow
stream having a
desired composition which will assist in achieving the general goal of Example
1.
As a result, in Example 1, the diluent-to-bitumen ratios of the mixtures
(3,14,18)
are increased for each successive stage of gravity separation so that bitumen
recovery is more
aggressive in each successive stage of gravity separation, while the diluent-
to-bitumen ratio of
the first mixture (3) is regulated so that the first overflow stream (6)
provides an acceptable
balance between bitumen recovery and rejection of water and mineral material.
Example 2
Example 2 is depicted in Figure 4. Referring to Figure 4, a theoretical
material
balance is provided for the second preferred embodiment of the invention,
wherein preferred
operating parameters using a typical paraffinic type diluent have been applied
to the process
flow diagram of Figure 3. The theoretical material balance in Figure 4 has
been prepared using
typical operating characteristics for apparatus of the type depicted in Figure
3.
In Example 2, 330 tonnes per hour of bitumen froth are processed in four
stages
of gravity separation to provide a bitumen product stream of about 320 tonnes
per hour as the
fourth overflow stream (10).
The general goal in Example 2 is to minimize the amount of water and mineral
material which is contained in the bitumen product stream while providing a
reasonable level of
bitumen recovery from the bitumen froth.
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CA 02573633 2007-01-10
Pursuant to this goal, the bitumen recovery in Example 2 is about 97.00
percent,
and the bitumen product stream, comprising bitumen, diluent, water and mineral
material,
contains about 0.11 percent water and mineral material by total weight of the
bitumen product
stream. The bitumen product stream in Example 2 is suitable for processing in
a bitumen
upgrading facility and is likely also suitable for pipeline transport to a
bitumen upgrading
facility. The very low concentration of water and mineral material in the
bitumen product
stream in Example 2 relative to Example 1 is achieved at the cost of a lower
bitumen recovery
in Example 2 relative to Example 1.
In Example 2, the very low concentration of water and mineral material in the
bitumen product stream is achieved by selectively utilizing the phenomenon of
asphaltene
precipitation which occurs when bitumen is combined with paraffinic type
diluent, due to the
cleaning effects of asphaltene precipitation.
The phenomenon of asphaltene precipitation and the amount of asphaltene
precipitation which is experienced using a paraffinic type diluent are
dependent upon the
diluent-to-bitumen ratio. As a result, desired amounts of asphaltene
precipitation during the
four stages of asphaltene precipitation may be achieved by regulating the
diluent-to-bitumen
ratios of the mixtures (3,8,14,18).
In Example 2, the diluent-to-bitumen ratio of the first mixture (3) is
regulated by
controlling the first added amount (2) of the diluent, the diluent-to-bitumen
ratio of the second
mixture (14) is regulated by controlling the second added amount (13) of the
diluent, the
diluent-to-bitumen ratio of the third mixture (18) is regulated by controlling
the third added
amount (17) of the diluent, and the diluent-to-bitumen ratio of the fourth
mixture (8) is
regulated by controlling the fourth added amount (7) of the diluent. The
diluent-to-bitumen
ratios are regulated so that each of the four stages of gravity separation
will provide a desired
amount of asphaltene precipitation.
In Example 2, the first gravity separation is intended to separate a large
portion
of the water and mineral material from the bitumen without causing any, or any
significant
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CA 02573633 2007-01-10
precipitation of the first mixture dissolved asphaltenes. As a result, in
Example 2, the first
gravity separation is performed by regulating the diluent-to-bitumen ratio of
the first mixture
(3) so that it is less than the critical asphaltene precipitation diluent-to-
bitumen ratio. In
Example 2, the diluent-to-bitumen ratio of the first mixture is therefore
about 0.80 and results
in essentially no precipitation of the first mixture dissolved asphaltenes.
In Example 2, the fourth gravity separation is intended to produce a bitumen
product stream as the fourth overflow stream (10) which has a relatively low
concentration of
water and mineral material contained therein. Preferably the bitumen product
stream also has a
relatively low concentration of undesirable constituents such as sulphur and
heavy metals. As a
result, in Example 2, the fourth gravity separation is performed by regulating
the diluent-to-
bitumen ratio of the fourth mixture (8) so that it is greater than the
critical asphaltene
precipitation diluent-to-bitumen ratio, but results only in a moderate amount
of precipitation of
the fourth mixture dissolved asphaltenes. In Example 2, the diluent-to-bitumen
ratio of the
fourth mixture (8) is therefore about 1.10, which results in precipitation of
about 8.00 percent
by weight of the fourth mixture dissolved asphaltenes.
In Example 2, the second gravity separation is intended to dilute further and
selectively clean the second mixture (14) by providing a combined density of
bitumen and
diluent which is reasonably favourable for selective bitumen recovery and by
causing further
precipitation of the second mixture dissolved asphaltenes from the second
mixture (14).
Increased precipitation of the second mixture dissolved asphaltenes relative
to precipitation of
the fourth mixture dissolved asphaltenes may be tolerated in the second
gravity separation
because the amount of bitumen contained in the second mixture (14) is
significantly lower than
the amount of bitumen contained in the fourth mixture (8). As a result, in
Example 2, the
second gravity separation is performed by regulating the diluent-to-bitumen
ratio of the second
mixture (14) so that it is higher than the diluent-to-bitumen ratio of the
fourth mixture (8), and
results in a higher amount of precipitation of the second mixture dissolved
asphaltenes than was
experienced by the fourth mixture dissolved asphaltenes. In Example 2, the
diluent-to-bitumen
ratio of the second mixture (14) is therefore about 2.17, which results in
precipitation of about
16.10 percent by weight of the second mixture dissolved asphaltenes.
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In Example 2, the third gravity separation is intended to dilute further and
selectively clean the third mixture (18) by providing a combined density of
bitumen and diluent
which is favourable for bitumen recovery and by causing further precipitation
of the third
mixture dissolved asphaltenes from the third mixture (18). Increased
precipitation of the third
mixture dissolved asphaltenes relative to precipitation of the second mixture
dissolved
asphaltenes may be tolerated in the third gravity separation because the
amount of bitumen
contained in the third mixture (18) is significantly lower than the amount of
bitumen contained
in the second mixture (14). As a result, in Example 2, the third gravity
separation is performed
by regulating the diluent-to-bitumen ratio of the third mixture (18) so that
it is higher than the
diluent-to-bitumen ratio of the second mixture (14), and results in a higher
amount of
precipitation of the third mixture dissolved asphaltenes than was experienced
by the second
mixture dissolved asphaltenes. In Example 2, the diluent-to-bitumen ratio of
the third mixture
(18) is therefore about 5.07, which results in precipitation of about 33.30
percent by weight of
the third mixture dissolved asphaltenes.
As indicated above, the first preferred embodiment of the process of the
invention as depicted in Figure 1 is particularly suited to be performed using
a naphtha type
diluent, while the second preferred embodiment of the process of the invention
as depicted in
Figure 3 is particularly suited to be performed using a paraffinic type
diluent.
The second preferred embodiment is particularly suited to be performed using a
paraffinic type diluent because the second preferred embodiment provides for
the first overflow
stream (6) to be subjected to the fourth gravity separation under conditions
which provide for a
carefully controlled amount of asphaltene precipitation, thus providing the
additional cleaning
effects of asphaltene precipitation to the relatively clean first overflow
stream (6).
Since naphtha type diluents do not typically provide the cleaning effects
associated with paraffinic type diluents, the fourth gravity separation
provided for in Figure 3 is
not as advantageous where naphtha type diluents are used. Similarly, omitting
the fourth
gravity separation of Figure 3 where paraffinic type diluents are used does
not provide the
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significant benefits of the further cleaning of the first overflow stream (6)
using the
phenomenon of asphaltene precipitation.
Despite these considerations, the treatment of bitumen froth in a plurality of
stages of gravity separation with a diluent under conditions where the diluent-
to-bitumen ratio
is regulated for each stage provides significant advantages regardless of the
type of diluent
which is used, in terms of energy input to the process, efficient use of
diluent, and properties of
the resulting bitumen product stream.
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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