Note: Descriptions are shown in the official language in which they were submitted.
CA 02901786 2015-08-26
PARAFFINIC FROTH TREATMENT
BACKGROUND
Field of Disclosure
[0001] The disclosure relates generally to the field of oil sand
processing. More
specifically, the disclosure relates to processing bitumen froth.
Description of Related Art
[0002] This section is intended to introduce various aspects of the art,
which may be
associated with the present disclosure. This discussion is believed to assist
in providing a
framework to facilitate a better understanding of particular aspects of the
present disclosure.
Accordingly, it should be understood that this section should be read in this
light, and not
necessarily as admissions of prior art.
[0003] Modern society is greatly dependent on the use of hydrocarbon
resources for
fuels and chemical feedstocks. Hydrocarbons are generally found in subsurface
formations
that can be termed "reservoirs." Removing hydrocarbons from the reservoirs
depends on
numerous physical properties of the subsurface formations, such as the
permeability of the
rock containing the hydrocarbons, the ability of the hydrocarbons to flow
through the
subsurface formations, and the proportion of hydrocarbons present, among other
things.
Easily harvested sources of hydrocarbons are dwindling, leaving less
accessible sources to
satisfy future energy needs. As the costs of hydrocarbons increase, the less
accessible sources
become more economically attractive.
[0004] Recently, the harvesting of oil sand to remove heavy oil has
become more
economical. Hydrocarbon removal from oil sand may be performed by several
techniques.
For example, a well can be drilled to an oil sand reservoir and steam, hot
air, solvents, or a
combination thereof, can be injected to release the hydrocarbons. The released
hydrocarbons
may be collected by wells and brought to the surface. In another technique,
strip or surface
mining may be performed to access the oil sand, which can be treated with
water, steam or
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solvents to extract the heavy oil. Where the oil sand is treated with water,
the technique may
be referred to as water-based extraction (WBE). WBE is a commonly used process
to extract
bitumen from mined oil sand.
[0005] In an example of WBE, mined oil sands are mixed with water to
create a slurry
suitable for extraction. Caustic may be added to adjust the slurry pH to a
desired level and
thereby enhance the efficiency of the separation of bitumen.
[0006] Regardless of the type of WBE employed, the extraction process
will typically
result in the production of a bitumen froth comprising bitumen, water and fine
particles and a
tailings stream comprising coarse particles and some fine particles and water.
The tailings
stream may consist essentially of coarse particles and some fine particles and
water. A typical
composition of bitumen froth may be about 60 weight (wt.) % bitumen, 30 wt. %
water, and
wt. % solids. The water and solids in the froth are considered as
contaminants. The
contaminants may be substantially eliminated or. reduced to a level suitable
for feed to an oil
refinery or an upgrading facility, respectively. Elimination or reduction of
the contaminants
may be referred to as a froth treatment process. Elimination or reduction of
the contaminants
may be achieved by diluting the bitumen froth with a solvent. The solvent may
comprise any
suitable solvent, such as an organic solvent. For example, the organic solvent
may comprise
naphtha solvent and/or paraffinic solvent. Diluting the bitumen with solvent
(also referred to
as dilution) may increase the density differential between bitumen and water
and solids.
Diluting the bitumen with solvent may enable the elimination or reduction of
contaminants
using multi-stage gravity settlers. Use of the multi-stage gravity settlers
may result in a
"diluted bitumen froth" and froth treatment tailings. The froth treatment
tailings may
comprise residual bitumen, residual solvent, solids and water. The froth
treatment tailings
may be further processed to recover residual solvent, for instance in a
tailings solvent
recovery unit (TSRU).
[0007] Certain processes use naphtha to dilute bitumen froth before
separating the
product bitumen by centrifugation. These processes are called naphthaneic
froth treatment
(NFT) processes. Other processes use a paraffinic solvent, and are called
paraffinic froth
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treatment (PFT) processes, to produce pipelineable bitumen with low levels of
solids and
water. In the PFT process, a paraffinic solvent (for example, a mixture of iso-
pentane and n-
pentane) is used to dilute the froth before separating the product, diluted
bitumen, by gravity.
A portion of the asphaltenes in the bitumen is also rejected by design in the
PFT process and
this rejection is used to achieve reduced solids and water levels. In both the
NFT and the PFT
processes, the diluted tailings (comprising water, solids and some
hydrocarbon) are separated
from the diluted product bitumen.
[0008] Solvent is typically recovered from the diluted product bitumen
component
before the bitumen is delivered to a refining facility for further processing.
[0009] One PFT process will now be described further, although variations
of the
process exist. The PFT process may comprise at least three units: Froth
Separation Unit
(FSU), Solvent Recovery Unit (SRU) and Tailings Solvent Recovery Unit (TSRU).
Two
FSUs may be used, as shown in Fig. 1.
[0010] With reference to Fig. 1, mixing of solvent with the feed bitumen
froth (100) is
carried out counter-currently in two stages: FSU-1 and FSU-2, labeled as Froth
Separation
Unit 1 (102) and Froth Separation Unit 2 (104). The bitumen froth comprises
bitumen, water,
and fine solids (also referred to as mineral solids). A typical composition of
bitumen froth is
about 60 wt% bitumen, 30 wt% water, and 10 wt% solids. The paraffinic solvent
is used to
dilute the froth before separating the product bitumen by gravity. Examples of
paraffinic
solvents are pentane or hexane, either used alone or mixed with isomers of
pentanes or
hexanes, respectively. An example of a paraffinic solvent is a mixture of iso-
pentane and
n-pentane. In FSU-1 (102), the froth (100) is mixed with the solvent-rich oil
stream (101)
from the second stage (FSU-2) (104). The temperature of FSU-1 (102) is
maintained at, for
instance, about 60 C to about 80 C, or about 70 C, while the solvent to
bitumen (SB) ratio
may be from 1.4:1 to 2.2:1 by weight or may be controlled around 1.6:1 by
weight for a 60:40
mixture of n-pentane:iso-pentane. The overhead from FSU-1 (102) is the diluted
bitumen
product (105) (also referred to as the hydrocarbon leg) and the bottom stream
from FSU-1
(102) is the tailings (107) comprising water, solids (inorganics),
asphaltenes, and some
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residual bitumen. The residual bitumen from this bottom stream is further
extracted in FSU-2
(104) by contacting it with fresh solvent (109), for instance, in a 25 to 30:1
(w/w) SB ratio at,
for instance, about 80 C to about 100 C, or about 90 C. Examples of operating
pressures of
FSU-1 and FSU-2 are about 550 kPag and 600 kPag, respectively. The solvent-
rich oil
(overhead) (101) from FSU-2 (104) is mixed with the fresh froth feed (100) as
mentioned
above. The bottom stream from FSU-2 (104) is the tailings (111) comprising
solids, water,
asphaltenes and residual solvent, which is to be recovered in the Tailings
Solvent Recovery
Unit (TSRU) (106) prior to the disposal of the tailings (113) in an ETA. The
recovered
solvent (118) from TSRU (106) is directed to the solvent storage (110).
Solvent from the
diluted bitumen overhead stream (105) is recovered in the Solvent Recovery
Unit (SRU)
(108) and passed as solvent (117) to Solvent Storage (110). Bitumen (115)
exiting the SRU
(108) is also illustrated. The foregoing is only an example of a PFT process
and the values
are provided by way of example only. An example of a PFT process is described
in Canadian
Patent No. 2,587,166 to Sury.
[0011] It would be desirable to provide an alternative or improved
process for treating
bitumen froth.
SUMMARY
[0012] It is an object of the present disclosure to provide alternative
or improved
methods for processing bitumen froth.
[0013] Disclosed is a process including feeding a diluted bitumen froth
into a settler to
form a hydrocarbon-rich layer and a water-rich layer, and an interface layer
therebetween, and
raising and lowering the interface layer by controlling diluted bitumen froth
feeding,
underflow outflow, or overflow outflow, or a combination thereof, for
improving separation.
[0014] The foregoing has broadly outlined the features of the present
disclosure so
that the detailed description that follows may be better understood.
Additional features will
also be described herein.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0015] These and other features, aspects and advantages of the disclosure
will become
apparent from the following description, appending claims and the accompanying
drawings,
which are briefly described below.
[0016] Figure 1 is a prior art paraffinic froth treatment (PFT) process.
[0017] Figure 2 is a flow chart of a bitumen froth processing.
[0018] Figure 3 is a schematic of a bitumen froth processing.
[0019] Figure 4 is a schematic of a bitumen froth processing.
[0020] It should be noted that the figures are merely examples and no
limitations on
the scope of the present disclosure are intended thereby. Further, the figures
are generally not
drawn to scale, but are drafted for purposes of convenience and clarity in
illustrating various
aspects of the disclosure.
DETAILED DESCRIPTION
[0021] For the purpose of promoting an understanding of the principles of
the
disclosure, reference will now be made to the features illustrated in the
drawings and specific
language will be used to describe the same. It will nevertheless be understood
that no
limitation of the scope of the disclosure is thereby intended. Any alterations
and further
modifications, and any further applications of the principles of the
disclosure as described
herein are contemplated as would normally occur to one skilled in the art to
which the
disclosure relates. It will be apparent to those skilled in the relevant art
that some features
that are not relevant to the present disclosure may not be shown in the
drawings for the sake
of clarity.
[0022] At the outset, for ease of reference, certain terms used in this
application and
their meaning as used in this context are set forth below. To the extent a
term used herein is
not defined below, it should be given the broadest definition persons in the
pertinent art have
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given that term as reflected in at least one printed publication or issued
patent. Further, the
present processes are not limited by the usage of the terms shown below, as
all equivalents,
synonyms, new developments and terms or processes that serve the same or a
similar purpose
are considered to be within the scope of the present disclosure.
[0023] Throughout this disclosure, where a range is used, any number
between or
inclusive of the range is implied.
[0024] A "hydrocarbon" is an organic compound that primarily includes the
elements
of hydrogen and carbon, although nitrogen, sulfur, oxygen, metals, or any
number of other
elements may be present in small amounts. Hydrocarbons generally refer to
components
found in heavy oil or in oil sand. However, the techniques described are not
limited to heavy
oils but may also be used with any number of other reservoirs to improve
gravity drainage of
liquids. Hydrocarbon compounds may be aliphatic or aromatic, and may be
straight chained,
branched, or partially or fully cyclic.
[0025] "Bitumen" is a naturally occurring heavy oil material. Generally,
it is the
hydrocarbon component found in oil sand. Bitumen can vary in composition
depending upon
the degree of loss of more volatile components. It can vary from a very
viscous, tar-like,
semi-solid material to solid forms. The hydrocarbon types found in bitumen can
include
aliphatics, aromatics, resins, and asphaltenes. A typical bitumen might be
composed of:
19 weight (wt.) % aliphatics (which can range from 5 wt. % - 30 wt. %, or
higher);
19 wt. % asphaltenes (which can range from 5 wt. % - 30 wt. %, or higher);
30 wt. % aromatics (which can range from 15 wt. % - 50 wt. %, or higher);
32 wt. % resins (which can range from 15 wt. % - 50 wt. %, or higher); and
some amount of sulfur (which can range in excess of 7 wt. %).
In addition, bitumen can contain some water and nitrogen compounds ranging
from less than
0.4 wt. % to in excess of 0.7 wt. %. The percentage of the hydrocarbon found
in bitumen can
vary. The term "heavy oil" includes bitumen as well as lighter materials that
may be found in
a sand or carbonate reservoir.
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[0026] "Heavy oil" includes oils which are classified by the American
Petroleum
Institute ("API"), as heavy oils, extra heavy oils, or bitumens. The term
"heavy oil" includes
bitumen. Heavy oil may have a viscosity of about 1,000 centipoise (cP) or
more, 10,000 cP or
more, 100,000 cP or more, or 1,000,000 cP or more. In general, a heavy oil has
an API
gravity between 22.3 API (density of 920 kilograms per meter cubed (kg/m3) or
0.920 grams
per centimeter cubed (g/cm3)) and 10.00 API (density of 1,000 kg/m3 or 1
g/cm3). An extra
heavy oil, in general, has an API gravity of less than 10.0 API (density
greater than 1,000
kg/m3 or 1 g/cm3). For example, a source of heavy oil includes oil sand or
bituminous sand,
which is a combination of clay, sand, water and bitumen. The recovery of heavy
oils is based
on the viscosity decrease of fluids with increasing temperature or solvent
concentration. Once
the viscosity is reduced, the mobilization of fluid by steam, hot water
flooding, or gravity is
possible. The reduced viscosity makes the drainage or dissolution quicker and
therefore
directly contributes to the recovery rate.
[0027] "Fine particles" are generally defined as those solids having a
size of less than
44 microns (m), that is, material that passes through a 325 mesh (44 micron).
[0028] "Coarse particles" are generally defined as those solids having a
size of greater
than 44 microns (1,im).
[0029] The term "solvent" as used in the present disclosure should be
understood to
mean either a single solvent, or a combination of solvents.
[0030] The terms "approximately," "about," "substantially," and similar
terms are
intended to have a broad meaning in harmony with the common and accepted usage
by those
of ordinary skill in the art to which the subject matter of this disclosure
pertains. It should be
understood by those of skill in the art who review this disclosure that these
terms are intended
to allow a description of certain features described and claimed without
restricting the scope
of these features to the precise numeral ranges provided. Accordingly, these
terms should be
interpreted as indicating that insubstantial or inconsequential modifications
or alterations of
the subject matter described and are considered to be within the scope of the
disclosure.
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[0031] The articles "the", "a" and "an" are not necessarily limited to
mean only one,
but rather are inclusive and open ended so as to include, optionally, multiple
such elements.
[0032] The term "paraffinic solvent" (also known as aliphatic) as used
herein means
solvents comprising normal paraffins, isoparaffins or blends thereof in
amounts greater than
50 wt. %. Presence of other components such as olefins, aromatics or
naphthenes may
counteract the function of the paraffinic solvent and hence may be present in
an amount of
only 1 to 20 wt. % combined, for instance no more than 3 wt. %. The paraffinic
solvent may
be a C4 to C20 or C4 to C6 paraffinic hydrocarbon solvent or a combination of
iso and normal
components thereof. The paraffinic solvent may comprise pentane, iso-pentane,
or a
combination thereof The paraffinic solvent may comprise about 60 wt. % pentane
and about
40 wt. % iso-pentane, with none or less than 20 wt. % of the counteracting
components
referred above.
[0033] In current commercial practice, each Froth Settling Unit (FSU), is
operated as
a continuous process. The interface level at each FSU is maintained at the
same level by
adjusting the flow rates of the underflow and the overflow according to the
feed rate and its
corresponding composition. The velocity of the process fluid is non-zero.
Therefore,
hydrodynamically, some solvent will be entrained by the solids to the
underflow, and some
solids will be entrained by the bitumen product and solvent to the overflow.
[0034] As described herein, the settler is operated semi-continuously and
the interface
level of the settler(s) is adjusted during operation. Operating in this way
may assist bitumen
(maltene) recovery and/or reduce solvent loss. Figure 2 is a flow chart of
bitumen froth
processing. As seen in Figure 2, disclosed is a process including feeding a
diluted bitumen
froth into a settler to form a hydrocarbon-rich layer and a water-rich layer,
and an interface
layer therebetween (202), and raising and lowering the interface layer by
controlling diluted
bitumen froth feeding, underflow outflow, or overflow outflow, or a
combination thereof, for
improving separation (204).
[0035] Figure 3 is a schematic showing filling up of a settler (302).
Suppose that at the
beginning of the process, the interface level (304) between the
bitumen/solvent-rich region
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(306) and the water-rich region (308) is at a low level. In this instance, a
flow controller (not
shown) (for instance a valve or pump) for the underflow (310) is at the closed
or off position.
As the froth feed (312) is introduced to the settler (302), the solids
(mineral solids and
asphaltene flocs) together with the water will settle towards the settler
bottom due to
buoyancy (higher density compared to bitumen and solvent). Consequently, the
interface level
rises as seen in the second (302b) and third (302c) settlers of Figure 3. This
feeding and
settling process may be continued until the interface level reaches a desired
level, which may
be below inlet pipes feeding the bitumen froth. The desired level may
alternatively be above
these inlet pipes. When the desired level is reached, a flow controller for
the underflow is
opened or turned on. This operation allows drainage of the water-rich region.
The overflow
(314) is also shown, as described above.
[0036] Figure 4 is a schematic showing draining of the settler. The
draining may be
continued until the interface level (404) reaches a desired level in the
settler. Numerals are
not repeated in Figures 3 and 4 because only the interface levels change.
[0037] While no promises are made, the following potential benefits will
now be
discussed.
[0038] When the underflow is not flowing, the solids have the opportunity
to compact
in the water-rich region, creating a denser bed. As the solids compact,
solvent in between the
asphaltene flocs and mineral solids is squeezed out, thereby allowing the
solvent to float to
the overflow, enhancing the solvent recovery and reducing solvent losses.
[0039] When the underflow is not flowing, additional residence time is
provided for
the solvent to separate from the asphaltene flocs, mineral solids, and water.
[0040] The water-rich region is more quiescent compared to a continuous
process.
Therefore, there is less flow disturbance, which causes the solids to be
recycled upwards,
increasing the risk of releasing settled fines to the overflow. The result may
be improved
solids separation.
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v
[0041] By controlling the underflow flow rate, the density of the
underflow can also
be controlled. Therefore, one can control the separation process depending on
the froth feed
quality.
[00421 By increasing solvent recovery, maltene recovery may also
be increased.
[0043] The paraffinic solvent may be any suitable paraffinic
solvent. For instance, the
paraffinic solvent may comprise greater than 50 vol % pentane.
[0044] The paraffinic solvent may have greater than 50 wt. % of n-
pentane, iso-
pentane, or a combination thereof, based upon total weight of the solvent.
[0045] The settler may be any suitable settler. The settler may
be a froth settling unit
(FSU), as described above. Where two or more separators are used, they may be
arranged in
series or in parallel. While the froth feed is illustrated into the side of
the settler, the froth
feed may also be fed into the middle of the settler and may include any
suitable number of
entry ports.
[0046] Underflow recirculation pumps that recycle the solids to
disrupt the FSU cone
bottom bed and improve hydrocarbon-water exchange may be used.
[0047] Water injection at different locations (e.g. feed barrels,
cone bottom, cone
boot, etc.) in the FSUs may be used.
[0048] Solvent may be recovered from the overflow to produce a
bitumen product.
For example, the overflow may be passed through a solvent recovery unit (SRU)
or other
suitable apparatus in which the solvent is flashed off and condensed in a
condenser associated
with the solvent flashing apparatus and recycled/reused in the process. The
SRU may be any
suitable SRU, such as but not limited to a fractionation vessel. Any suitable
amount of solvent
may be removed.
[0049] The underflow may be sent to a second separator, for
instance as described
above as a second FSU. A second paraffinic solvent may be added to the
underflow followed
by gravity separating the underflow.
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[0050] A feed time during which the diluted bitumen froth is fed into the
settler may
be between 5 and 120 minutes. A drain time during which the underflow is
drained from the
settler may be between 5 and 120 minutes.
[0051] Part of the underflow may be recycled back into the settler for
improving
separation. A volume ratio of diluted bitumen froth: recycled underflow may be
1:1 to 5:1.
A recirculation pump may be used for this purpose. The recirculation pump
along with the
flow may impart shear on the underflow being recycled, breaking up asphaltenes
aggregates,
and thereby releasing intra-particle solvent.
[0052] Water may be injected into a bottom cone section of the settler
for improving
separation. The rate of water injection may be 10 m3/hr, 30 m3/hr, 50 m3/hr,
100 m3/hr, 150
m3/hr, 200 m3/hr, or up to 250 m3/hr.
[0053] Additives may be added to the settler for lowering surface
tension, breaking
emulsions, or promoting release of solvent, especially during the fill
process, where solids
settle in the vessel.
[0054] The scope of the claims should not be limited by particular
embodiments set
forth herein, but should be construed in a manner consistent with the
specification as a whole.
It is also contemplated that structures and features in the present examples
can be altered,
rearranged, substituted, deleted, duplicated, combined, or added to each
other.
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