Note: Descriptions are shown in the official language in which they were submitted.
CA 02866923 2014-10-10
METHODS FOR PROCESSING DILUTED BITUMEN FROTH OR FROTH
TREATMENT TAILINGS
BACKGROUND
Field of Disclosure
[0001] The disclosure relates generally to the field of oil sand
processing. More
specifically, the disclosure relates to methods for processing diluted bitumen
froth or froth
treatment tailings.
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
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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
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 another tailings stream. The another tailings
stream may be
commonly referred to as the froth treatment tailings. The froth treatment
tailings may
comprise residual bitumen, residual solvent, solids and water. The froth
treatment tailings
stream may be further processed to recover residual solvent, for instance in a
tailings solvent
recovery unit (TSRU). If the solvent is paraffinic solvent, the froth
treatment tailings may be
referred to as "paraffinic froth treatment tailings".
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[0007] It is desirable to reduce the amount of bitumen and solvent in the
diluted
bitumen froth or the froth treatment tailings sent to gravity settlers, such
as gravity settlers
positioned after the first gravity settler of the multi-stage gravity
settlers, and to the TSRU. In
particular, the quantity of bitumen and solvent in the diluted bitumen froth
and froth treatment
tailings directly impacts the amount of bitumen and solvent lost to tailings
and has a
substantial impact on the design requirements of the TSRU. Bitumen in the
tailings is either
lost, impacting overall bitumen recovery of the bitumen recovery process, or
requires
additional processing equipment to recovery bitumen from the tailings. The
size and cost of
processing equipment to recover solvent from the tailings is directly related
to the quantity of
solvent in the tailings. The performance of a TSRU may be improved by reducing
the
fraction of solvent in the froth treatment tailings. The gravity settlers
positioned after the first
gravity settler of the multi-stage gravity settlers may be referred to as
subsequent gravity
settlers.
[0008] Existing schemes to reduce the amount of bitumen and solvent in
froth
treatment tailings generally rely on additional gravity settling stages or
large recycle loops to
reduce the bitumen and solvent carry-under from the gravity settlers to the
TSRU. Additional
gravity settling stages have high capital, operating, and maintenance costs.
Large recycle
loops increase pump power requirements, increase piping sizes, increase
erosional wear,
increase the downward flux rate of the settlers and decrease residence time in
the settlers. The
downward rate may be a nominal downward velocity from an inlet of the settler
to a bottom
outlet of the settler. Residence time may be an average amount of time that an
average
particle resides within a settler prior to exiting a bottom of the settler.
Increased downward
flux rate and lower residence time have negative implications on performance
and vessel
sizing requirements.
[0009] In view of the aforementioned disadvantages, there is a need for
alternative or
improved methods for processing diluted bitumen froth or froth treatment
tailings.
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SUMMARY
[0010] It is an object of the present disclosure to provide methods for
processing
diluted bitumen froth or froth treatment tailings.
[0011] Disclosed is a method for processing diluted bitumen froth or
froth treatment
tailings comprising bitumen and solvent. The method may comprise forming a
settler
overflow and a settler underflow by gravity separating the diluted bitumen
froth or the froth
treatment tailings in a settler; forming a hydrocyclone overflow and a
hydrocyclone
underflow by separating the settler underflow in a hydrocyclone; and recycling
the
hydrocyclone overflow to the settler.
[0012] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] 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.
[0014] Figure 1 is a flow chart of a method for processing diluted
bitumen froth or
froth treatment tailings.
[0015] Figure 2 is a flow chart of a method for processing diluted
bitumen froth or
froth treatment tailings.
[0016] 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.
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DETAILED DESCRIPTION
[0017] 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.
[0018] 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
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.
[0019] Throughout this disclosure, where a range is used, any number
between or
inclusive of the range is implied.
[0020] 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.
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[0021] "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.
[0022] "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 10.0 API (density of 1,000 kg/m3 or 1
g/cm3). An extra
heavy oil, in general, has an API gravity of less than 10.00 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.
[0023] "Fine particles" are generally defined as those solids having a
size of less than
44 microns (um), that is, material that passes through a 325 mesh (44 micron).
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[0024] "Coarse particles" are generally defined as those solids having a
size of greater
than 44 microns (m).
[0025] The term "solvent" as used in the present disclosure should be
understood to
mean either a single solvent, or a combination of solvents.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] A settler can separate diluted bitumen froth or froth treatment
tailings,
comprising bitumen and solvent, by gravity, into a settler overflow and a
settler underflow.
The settler overflow has a higher liquid content (by weight) and a lower solid
content (by
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weight) than the settler underflow. Settlers may be arranged in series with a
settler underflow
from one settler passed as a feed to the next settler in the series. A settler
underflow flow-rate
may be controlled to maintain a hydrocarbon continuous ¨ aqueous slurry
interface level in
the settler. Controlling the aqueous slurry interface level in the settler may
be maintained in
conjunction with processing a settler underflow from a final settler in a
hydrocyclone. A final
settler may be a settler last in a series of settlers. The hydrocyclone may
produce a
hydrocyclone overflow and a hydrocyclone underflow. The hydrocyclone overflow
has a
higher liquid content (by weight) and a lower solid content (by weight) than
the hydrocyclone
underflow. The hydrocyclone overflow flow-rate may be controlled to a fixed
flow-rate or
flow ratio with respect to the hydrocyclone underflow flow-rate. The fixed
flow-rate or flow
ratio may be optimized to balance equipment, piping size requirements, piping
wear, and/or
pump power requirements, with incremental recovery of solvent and bitumen from
the
tailings. The hydrocyclone inlet flow-rate may be maintained at a fixed volume
flow-rate.
The hydrocyclone inlet flow-rate may be maintained at the fixed volume flow-
rate by
modulating the hydrocyclone overflow flow-rate. The hydrocyclone inlet flow-
rate may be
maintained at the fixed volume flow-rate by adding water to the underflow from
the final
settler vessel. Maintaining the hydrocyclone inlet flow-rate at the fixed
volume flow-rate
may be advantageous because a fixed speed pump may be used upstream of the
hydrocyclone
and the hydrocyclone geometry may be optimized for a single inlet flow- rate.
Control of the
overflow, underflow, and water flow-rates may be achieved using control
valves, variable
speed pumps, or a combination thereof.
[0030]
Figures 1 and 2 are flow charts of a method for processing diluted bitumen
froth or froth treatment tailings. The diluted bitumen froth or froth
treatment tailings (1) may
be the result of WBE followed by dilution by solvent, and froth separation in
the case of the
tailings. For example, mined oil sand may undergo WBE to form bitumen froth.
The
bitumen froth may be diluted with solvent and, in the case of the tailings,
undergo froth
separation by gravity in a settler (referred to herein as a preliminary
settler). An overflow
from the preliminary settler may comprise bitumen and solvent and may be
passed to solvent
recovery. An underflow from the preliminary settler may form the froth
treatment tailings
(1). The froth treatment tailings (1) may comprise water, mineral matter,
precipitated
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asphaltenes, solvent, and/or some unrecovered bitumen. The froth treatment
tailings may
comprise precipitated asphaltenes if the solvent is paraffinic. Where two or
more preliminary
settlers are used, they may be arranged in series or in parallel.
[0031] The method may comprise forming (202) a settler overflow (3) and a
settler
underflow (5) by gravity separating the diluted bitumen froth or froth
treatment tailings (1) in
a settler (2). The settler (2) may be any suitable gravity settler. The
settler (2) may comprise
a vertical tank (14) above a conical bottom (15). The settler underflow (5)
may be withdrawn
from the bottom of the settler (2). The bottom of the settler (2) may be
within the conical
bottom (15). Where two or more settlers (2) are used, they may be arranged in
series or in
parallel.
[0032] Solvent may be recovered from the settler overflow (3). For
example, the
settler overflow (3) 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.
[0033] Due to the structure of asphaltene aggregates, when the solvent is
paraffinic, in
the diluted bitumen froth or froth treatment tailings (1) and the incremental
recovery of
solvent and solvent-soluble bitumen from the settler underflow (5) (described
below), the
settler underflow (5) may approach a maximum packing ratio of a transportable
slurry. As the
maximum packing ratio is approached, a pressure drop may increase through a
hydrocyclone
(6) and piping leading into and out of the hydrocyclone (6), which may
decrease solid-liquid
separation efficiency in the hydrocyclone (6). Water (4) may be added to the
settler
underflow (5) to reduce the packing ratio. For example, water (4) may be added
to the settler
underflow (5) in a water: settler underflow volume ratio of 1:5 or less, or of
1:50 to 1:5. The
amount of water (4) that may be added may depend on the water content of the
diluted
bitumen froth or froth treatment tailings (1). The water content of the
diluted bitumen froth or
froth treatment tailings (1), may vary depending for instance on the oil sand
composition
and/or WBE parameters. The addition of the water (4) may reduce the bulk
viscosity of the
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settler underflow (5). Reducing the bulk viscosity of the settler underflow
(5), may improve
separation efficiency in the hydrocyclone (6).
[0034]
The method may comprise forming (204) a hydrocyclone overflow (7) and a
hydrocyclone underflow (8) by separating the settler underflow (5) in a
hydrocyclone (6).
The settler underflow (5) may be pumped into the hydrocyclone (6) using a pump
(10). This
pumping of the settler underflow (5) may increase a pressure of the settler
underflow (5).
Increasing the pressure of the settler underflow (5) may allow for overcoming
pressure losses
in the hydrocyclone (6). Increasing the pressure of the settler underflow (5)
may enable the
hydrocyclone overflow (7) to be recycled back to the settler (2).
Where two or more
hydrocyclones (6) are used, they may be arranged in series or in parallel.
Solvent may be
recovered from the hydrocyclone underflow (8), for example in a subsequent
TSRU of a
tailings solvent recover unit (TSRU) (9). The hydrocyclone (6) reduces the
bitumen and
solvent content in the settler underflow (5). Reducing the bitumen and solvent
content in the
settler underflow (5) may reduce the amount of bitumen and solvent in tailings
which may be
sent to the subsequent gravity settler or the TSRU (9).
[0035]
Cyclonic separation of the diluted bitumen froth or froth treatment tailings
(5)
may increase bitumen and solvent recovery by using centrifugal force rather
than gravity.
Due to the enhanced separation of bitumen and solvent in the hydrocyclone (6),
bitumen and
solvent recovery may be improved in the settler (2) without an unacceptable
increase in a
downward flux rate in the settler (2). Due to the enhanced separation of
bitumen and solvent
in the hydrocyclone (6), bitumen and solvent recovery may be improved in the
settler (2)
without inducing a detrimental circulation pattern in the settler (2). A
detrimental circulation
pattern is a flow pattern internal to the settler (2) that results in either
(a) solids and/or water
being carried-over into the settler overflow (3) or (b) higher entrainment of
solvent and
solvent-soluble bitumen into the settler underflow (5).
[0036]
The method may comprise recycling (206) the hydrocyclone overflow (7) to
the settler (2). The hydrocyclone overflow (7) has a higher hydrocarbon liquid
(bitumen and
solvent) content than the settler underflow (5). The hydrocyclone overflow (7)
may be kept
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_
to, for example but not limited to 10-30 wt. % hydrocarbon liquid, for
assisting bitumen and
solvent recovery. The hydrocarbon liquid may be combined bitumen and solvent.
By
limiting the hydrocarbon liquid content in the hydrocyclone overflow (7) from
the
hydrocyclone (6) to, for instance 10-30 wt. %, separation of the lighter
hydrocarbon liquid
from the water and solids may be improved. In particular, drawing more water
and solids into
the hydrocyclone overflow (7) may reduce the amount of lighter hydrocarbon
liquid in the
hydrocyclone underflow (8), in contrast to trying to achieve the most
efficient separation in
both the hydrocyclone overflow (7) and the hydrocyclone underflow (8).
Adjusting the
overflow rate from the hydrocyclone (6) may permit optimization of solvent and
bitumen
recovery in the settler (2).
[0037] The settler (2) may recover bitumen and solvent-soluble
bitumen from the
hydrocyclone overflow (7) that is recycled. The hydrocyclone overflow that is
recycled may
be referred to a recycled hydrocyclone overflow. The hydrocyclone overflow (7)
may be
introduced into the settler (2) below an inlet for receiving the diluted
bitumen froth or froth
treatment tailings (1). The hydrocyclone overflow (7) may be recycled adjacent
and above
the conical bottom of the settler (2). The hydrocyclone overflow (7) may be
pumped into the
settler (2) using a pump (11). Pumping the hydrocyclone overflow (7) into the
settler (2) may
overcome pressure losses in the hydrocyclone (6) to enable the recycling of
the hydrocyclone
overflow (7) to the settler (2).
[0038] 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.
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