U.S. patent application number 13/464574 was filed with the patent office on 2012-08-30 for optimizing heavy oil recovery processes using electrostatic desalters.
Invention is credited to Michael F. Raterman, Arun K. Sharma.
Application Number | 20120217187 13/464574 |
Document ID | / |
Family ID | 41446123 |
Filed Date | 2012-08-30 |
United States Patent
Application |
20120217187 |
Kind Code |
A1 |
Sharma; Arun K. ; et
al. |
August 30, 2012 |
Optimizing Heavy Oil Recovery Processes Using Electrostatic
Desalters
Abstract
The invention relates to improved bitumen recovery processes and
systems. The process may include providing a bitumen froth feed
stream, separating the stream in a froth separation unit to produce
a diluted bitumen stream, treating the diluted bitumen stream in an
electrostatic desalter to produce a treated bitumen stream, and
separating the treated bitumen stream into a solvent recycle stream
and a bitumen product stream. The system may include a combined
AC/DC desalter with a control unit for optimizing the treatment
process to produce a product bitumen stream using less solvent and
smaller separators than conventional bitumen froth treatment plants
and processes.
Inventors: |
Sharma; Arun K.; (Missouri
City, TX) ; Raterman; Michael F.; (Doylestown,
PA) |
Family ID: |
41446123 |
Appl. No.: |
13/464574 |
Filed: |
May 4, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12464724 |
May 12, 2009 |
|
|
|
13464574 |
|
|
|
|
61133270 |
Jun 27, 2008 |
|
|
|
Current U.S.
Class: |
208/390 |
Current CPC
Class: |
C10G 2300/206 20130101;
C10G 2300/805 20130101; C10G 1/047 20130101; C10G 1/045 20130101;
C10G 33/02 20130101; C10G 2300/44 20130101; C10G 1/002 20130101;
C10G 2300/4081 20130101 |
Class at
Publication: |
208/390 |
International
Class: |
C10C 3/08 20060101
C10C003/08 |
Claims
1. A method of recovering hydrocarbons, comprising: providing a
bitumen froth inlet stream including a volume of paraffinic
solvents, a volume of water, and asphaltenes; settling out at least
a portion of the asphaltenes in a froth separation unit to produce
at least a first settled out asphaltenes stream (a first tailings
stream) and a diluted bitumen stream; separating the volume of
paraffinic solvents from the diluted bitumen stream in a solvent
recovery unit configured to produce a product bitumen stream and a
solvent recycle stream; and treating at least one of the diluted
bitumen stream and the product bitumen stream in at least one
electrostatic desalter to produce a treated bitumen stream.
2. The method of claim 1, wherein the electrostatic desalter is
configured to remove at least about 10 percent (%) to about 50% of
the solids from the at least one of the diluted bitumen stream and
the product bitumen stream.
3. The method of claim 2, further comprising settling out at least
a portion of the asphaltenes from the first tailings stream in a
second froth separation unit configured to receive the first
tailings stream and produce at least a second diluted bitumen
stream and a second tailings stream containing asphaltenes
separated from the first tailings stream.
4. The method of claim 3, wherein the electrostatic desalter is
configured to receive at least a portion of the second diluted
bitumen stream.
5. The method of claim 4, wherein the electrostatic desalter
further comprises: an inlet flow conduit operatively connected to a
fresh water inlet configured to deliver a fresh water stream to the
inlet flow conduit and a chemical inlet configured to deliver a
chemical stream to the inlet flow conduit, wherein the inlet flow
conduit is configured to deliver the diluted bitumen stream to the
electrostatic desalter; a mixing valve operatively connected to the
inlet flow conduit, wherein the mixing valve is configured to
impart mixing energy to the diluted bitumen stream and a second
stream selected from the group consisting of the fresh water
stream, the chemical stream, and any combination thereof; and an
oil outlet configured to produce the treated bitumen stream.
6. The method of claim 5, further comprising: receiving at least
one data input; and controlling at least one process condition to
configure a composition of the treated bitumen stream based on the
at least one data input.
7. The method of claim 6, wherein the at least one data input is
selected from the group comprising: a flow rate of the diluted
bitumen stream, a flow rate of the fresh water inlet stream, a flow
rate of the chemical inlet stream, a composition of the diluted
bitumen stream, a composition of chemicals flowing through the
chemical inlet, an electrostatic field characteristic, a
temperature inside the electrostatic desalter, a mixing valve
pressure, a mixing valve intensity, a temperature of the diluted
bitumen stream, a thickness of an emulsion layer, and any
combination thereof.
8. The method of claim 7, wherein the at least one process
condition is selected from the group comprising: the flow rate of
the diluted bitumen stream, the flow rate of the fresh water inlet
stream, the flow rate of the chemical inlet stream, a solvent
content of the diluted bitumen stream, the composition of chemicals
flowing through the chemical inlet, the electrostatic field
characteristic, the temperature inside the electrostatic desalter,
the mixing valve pressure, the mixing valve intensity, the
temperature of the diluted bitumen stream, the thickness of an
emulsion layer, and any combination thereof.
9. The method of claim 4, further comprising configuring the at
least one electrostatic desalter as a plurality of desalting units
in a configuration selected from the group consisting of: at least
one two-stage train and at least two parallel single-stage
units.
10. The method of claim 5, wherein the chemical inlet stream
includes a chemical demulsifier.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of U.S.
application Ser. No. 12/464,724, entitled OPTIMIZING HEAVY OIL
RECOVERY PROCESSES USING ELECTROSTATIC DESALTERS, filed on May 12,
2009, which claims the benefit of U.S. Provisional Application No.
61/133,270, filed Jun. 27, 2008.
FIELD OF THE INVENTION
[0002] The present invention relates generally to producing
hydrocarbons. More specifically, the invention relates to methods
and systems for upgrading bitumen in a solvent based froth
treatment process using electrostatic desalting for optimization of
the process.
BACKGROUND OF THE INVENTION
[0003] The economic recovery and utilization of heavy hydrocarbons,
including bitumen, is one of the world's toughest energy
challenges. The demand for heavy crudes such as those extracted
from oil sands has increased significantly in order to replace the
dwindling reserves of conventional crude. These heavy hydrocarbons,
however, are typically located in geographical regions far removed
from existing refineries. Consequently, the heavy hydrocarbons are
often transported via pipelines to the refineries. In order to
transport the heavy crudes in pipelines they must meet pipeline
quality specifications.
[0004] The extraction of bitumen from mined oil sands involves the
liberation and separation of the bitumen from the associated sands
in a form that is suitable for further processing to produce a
marketable product. Among several processes for bitumen extraction,
the Clark Hot Water Extraction (CHWE) process represents an
exemplary well-developed commercial recovery technique. In the CHWE
process, mined oil sands are mixed with hot water to create slurry
suitable for extraction as bitumen froth.
[0005] After extraction, the heavy oil slurry (e.g. bitumen froth)
may be subjected to a paraffinic froth treatment process. In such a
process, the slurry or froth may be introduced into a froth
separation unit (FSU) wherein the froth is separated into a diluted
bitumen stream and a tailings stream. The diluted bitumen stream
may be directed to a solvent recovery unit (SRU) for flashing or
other processing to produce a hot bitumen product stream and a
solvent stream. The hot bitumen product stream may be sent to a
pipeline for production and the solvent stream may be recycled in
the treatment process.
[0006] Electrostatic desalters/dehydrators have been utilized in
the oil field and at refineries for the purpose of removing
contaminants in the oil being processed. This generally results in
reduced corrosion and fouling, control of trace metal content, and
improved wastewater treatment. See, e.g. SAMS, GARY W. AND WARREN,
KENNETH W., New Methods of Application of Electrostatic Fields,
AIChE Spring National Meeting, New Orleans, La., April 2004. Such
units may be used in a variety of configurations. See, e.g. U.S.
Pat. No. 6,860,979. Electrostatic desalters may also be used to
treat heavy oils. See, e.g. THOMASON, WILLIAM H., ET AL, Advanced
Electrostatic Technologies for Dehydration of Heavy Oils, SPE
97786, November 2005.
[0007] Methods to optimize the efficiency of settlers can
significantly impact the efficiency of heavy hydrocarbon (e.g.
bitumen) recovery processes. There exists a need in the art for a
low cost method to produce pipeline quality hydrocarbons from heavy
oil or bitumen.
SUMMARY OF THE INVENTION
[0008] In one aspect of the invention, a system of recovering
hydrocarbons is provided. The system includes a bitumen froth inlet
stream including bitumen, water, solids, and at least one
paraffinic solvent; a froth separation unit configured to receive
the bitumen froth inlet stream and produce at least a diluted
bitumen stream and a first tailings stream; a solvent recovery unit
configured to receive the diluted bitumen stream and produce a
product bitumen stream and a solvent recycle stream; and at least
one electrostatic desalter configured to receive at least one of
the diluted bitumen stream and the product bitumen stream and
produce a treated bitumen stream. The system may also include a
second froth separation unit to produce a second diluted bitumen
stream to the electrostatic desalter and a control unit for
optimize operation of the desalter in the system.
[0009] In another aspect of the invention, a method for recovering
hydrocarbons is provided. The method includes providing a bitumen
froth inlet stream including a volume of paraffinic solvents, a
volume of water, and asphaltenes; settling out at least a portion
of the asphaltenes in a froth separation unit to produce at least a
first settled out asphaltenes stream (a first tailings stream) and
a diluted bitumen stream; separating the volume of paraffinic
solvents from the diluted bitumen stream in a solvent recovery unit
configured to produce a product bitumen stream and a solvent
recycle stream; and treating at least one of the diluted bitumen
stream and the product bitumen stream in at least one electrostatic
desalter to produce a treated bitumen stream. The method may
further include providing a second diluted bitumen stream to the
desalter from a second froth separation unit and may also include
controlling certain process conditions to optimize the performance
of the desalter in the process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The foregoing and other advantages of the present invention
may become apparent upon reviewing the following detailed
description and drawings of non-limiting examples of embodiments in
which:
[0011] FIG. 1 is a schematic of a heavy hydrocarbon treatment plant
layout according to at least one aspect of the present
disclosure;
[0012] FIG. 2 is a flow chart of an exemplary heavy hydrocarbon
treatment process including at least one aspect of the present
disclosure;
[0013] FIG. 3 is an illustration of an exemplary electrostatic
desalting unit for use in the plant of FIG. 1 and/or the process of
FIG. 2;
[0014] FIG. 4 is a schematic of an alternative exemplary bitumen
froth treatment plant layout including at least one aspect of the
present disclosure; and
[0015] FIG. 5 is a schematic of yet another alternative exemplary
bitumen froth treatment plant including at least one aspect of the
present disclosure.
DETAILED DESCRIPTION
[0016] In the following detailed description section, the specific
embodiments of the present disclosure are described in connection
with preferred embodiments. However, to the extent that the
following description is specific to a particular embodiment or a
particular use of the present disclosure, this is intended to be
for exemplary purposes only and simply provides a description of
the exemplary embodiments. Accordingly, the disclosure is not
limited to the specific embodiments described below, but rather, it
includes all alternatives, modifications, and equivalents falling
within the true spirit and scope of the appended claims.
[0017] The term "asphaltenes" as used herein refers to hydrocarbons
which are the n-heptane insoluble, toluene soluble component of a
carbonaceous material such as crude oil, bitumen or coal. One
practical test to determine if oil is an asphaltene is to test
whether the oil is soluble when blended with 40 volumes of toluene
but insoluble when the oil is blended with 40 volumes of n-heptane.
If so, the oil may be considered an asphaltene. Asphaltenes are
typically primarily comprised of carbon, hydrogen, nitrogen,
oxygen, and sulfur as well as trace amounts of vanadium and nickel.
The carbon to hydrogen ratio is generally about 1:1.2, depending on
the source.
[0018] The term "bitumen" as used herein refers to heavy oil. In
its natural state as oil sands, bitumen generally includes
asphaltenes and fine solids such as mineral solids.
[0019] The invention relates to processes and systems for
recovering hydrocarbons. In one aspect, the invention relates to a
system for recovering hydrocarbons. The system may include a plant
located at or near a bitumen (e.g. heavy hydrocarbon) mining or
recovery site or zone. The plant may include at least one froth
separation unit (FSU) having a bitumen froth inlet for receiving
bitumen froth (or a solvent froth-treated bitumen mixture) and a
diluted bitumen outlet for sending diluted bitumen from the FSU.
The plant also includes a solvent recovery unit for separating
bitumen from solvent to produce a solvent recycle stream and a
bitumen product stream. The plant further includes at least one
electrostatic desalter configured to treat either or both of the
diluted bitumen stream and the bitumen product stream. Where the
desalter is configured to treat the diluted bitumen stream, the SRU
will be configured to separate the treated bitumen stream. The
plant may also include at least one tailings solvent recovery unit
(TSRU), solvent storage unit, pumps, compressors, and other
equipment for treating and handling the heavy hydrocarbons and
byproducts of the recovery system.
[0020] In another aspect, the invention is a process to partially
upgrade a bitumen or heavy crude and is particularly suited for
bitumen froth generated from oil sands which contain bitumen,
water, and asphaltenes. The process includes providing a bitumen
froth inlet stream having asphaltenes, paraffinic solvents, and
water, settling out at least some of the asphaltenes in a froth
separation unit (FSU) to produce a diluted bitumen stream and a
tailings stream, separating the solvents from the diluted bitumen
stream in a solvent recovery unit (SRU) to produce a bitumen
product stream and a solvent recycle stream, and treating either or
both of the diluted bitumen stream and the bitumen product stream
in an electrostatic desalter to produce a treated bitumen stream.
In the case where the treatment is of the diluted bitumen stream,
the separation step separates the treated bitumen stream rather
than the diluted bitumen stream.
[0021] Referring now to the figures, FIG. 1 is a schematic of an
exemplary paraffinic froth treatment system including certain
aspects of the present disclosure. The plant 100 receives bitumen
froth 102 from a heavy hydrocarbon recovery process. The bitumen
froth 102 includes bitumen, water, and at least one paraffinic
solvent and is fed into a first froth separation unit (FSU) 104. A
diluted bitumen stream 106 and a tailings stream 114 are produced
from the FSU 104. The diluted bitumen stream 106 may be wholly or
partly diverted to an electrostatic desalter 134 via stream 130.
The desalter 134 produces a treated bitumen stream 136, which is
sent to a solvent recovery unit (SRU) 108, which separates bitumen
from solvent to produce a bitumen product stream 110 and a solvent
recycle stream 112. If a portion of the diluted bitumen stream 106
is not diverted, then it may be delivered to the SRU 108 via stream
106' without treatment in the desalter 134. In one optional
embodiment, the bitumen product stream 110 is sent to an
electrostatic desalter 142 via line 140 for treatment. Treatment in
the desalter 142 may be in addition to or in lieu of treatment in
desalter 134. Further, desalter 134 may be the same unit as
desalter 142 in some embodiments. Note that the SRU 108 may be
configured to separate solvent from the diluted bitumen stream 106
or the treated bitumen stream 136, depending on the location of the
desalter 134 or 142.
[0022] In one exemplary embodiment of the present invention, the
desalters 134 and 142 include a fresh water inlet stream 131a
having a control valve and a chemical inlet stream 131b with a
control valve (only shown on desalter 134). The streams are
connected to the diluted bitumen stream 130 for addition to stream
130. The desalters 134 and 142 also preferably include a mixing
valve or other such device 132 for mixing the diluted bitumen
stream 130 with either or both of the fresh water inlet stream 131a
and the chemical inlet stream 131b. This exemplary embodiment may
further include a control unit 138 having input/output lines
139a-139x for obtaining data from sensors in the system 100 and
sending control signals to various parts of the plant 100. The
control unit 138 is preferably an automated unit, but may include
some manual operability such as a manual override, or be completely
manually operated. This exemplary embodiment may further include a
heating unit to raise the temperature of the diluted bitumen stream
130 (or product bitumen stream 110) to at least about 115 degrees
Celsius (.degree. C.) up to about 150.degree. C.
[0023] The control unit is configured to receive at least one data
input and modify at least one process condition to optimize a
composition of the treated bitumen stream 136. The data input may
be one or more of the following: a flow rate of the diluted bitumen
stream, a flow rate of the fresh water inlet stream, a flow rate of
the chemical inlet stream, a composition of the diluted bitumen
stream, a composition of chemicals flowing through the chemical
inlet, an electrostatic field characteristic, a temperature inside
the electrostatic desalter, a mixing valve pressure, mixing valve
intensity, a temperature of the diluted bitumen stream, a thickness
of an emulsion layer, and any combination thereof. The process
condition may be one or more of: the flow rate of the diluted
bitumen stream, the flow rate of the fresh water inlet stream, the
flow rate of the chemical inlet stream, a solvent content of the
diluted bitumen stream, the composition of chemicals flowing
through the chemical inlet, the electrostatic field characteristic,
the temperature inside the electrostatic desalter, the mixing valve
pressure, the mixing valve intensity, the temperature of the
diluted bitumen stream, the thickness of an emulsion layer, and any
combination thereof.
[0024] In another embodiment, the desalters 134 and 142 may be
configured as multiple desalting units. The desalting units 134 and
142 may be arranged as a multi-stage train such as a two stage
train, or may be operated in parallel, such as by having two
parallel single-stage units. Any number of units may be used, which
will depend on cost, availability, desired capacity and other
operational factors that are best addressed by a person of ordinary
skill in the art on a case-by-case basis.
[0025] In an exemplary embodiment of the plant 100, the bitumen
froth 102 may be mixed with a solvent-rich oil stream 120 from FSU
116 in FSU 104. Additionally, the solvent recycle stream 112 may be
mixed with tailings 114 from the first FSU 104 and fed into a
second froth separation unit 116. The second FSU 116 produces a
solvent rich oil stream 120 and a second tailings stream 118. The
solvent rich oil stream 120 is mixed with the incoming bitumen
froth 102 and the tailings stream is sent to a tailings solvent
recovery unit 122, which produces a third tailings stream 124 and a
solvent stream 126. In a conventional paraffinic froth treatment
(PFT) plant, the temperature of FSU 104 may be maintained at about
60 to 80 degrees Celsius (.degree. C.), or about 70.degree. C. and
the target solvent to bitumen ratio of such prior art systems is
about 1.4:1 to 2.2:1 by weight or about 1.6:1 by volume on average.
In the disclosed plant 100, the target solvent to bitumen ratio is
reduced by 10 to 50% from those listed above. This ratio will vary
depending on the solids concentration in the bitumen, types of
solvents used, composition of the bitumen, and other factors.
However, it is expected that the desalters 134 or 142 are expected
to reduce the solids concentration (in parts per million) by about
half. This solvent reduction makes operation of the plant 100 more
cost efficient, permits utilization of smaller FSU's 104 and 116,
and a smaller SRU 108 to treat an equivalent amount of produced
bitumen.
[0026] The bottom stream 114 from FSU 104 is the tailings
substantially comprising water, mineral solids, asphaltenes, and
some residual bitumen. The residual bitumen from this bottom stream
is further extracted in FSU 116 by contacting it with fresh solvent
(from e.g. 112 or 126). The bottom stream 114 of the plant 100 has
a lower flow rate than the bottom stream of a conventional PFT
plant and the solvent to bitumen ratio is also lower. In addition,
FSU 116 may be smaller relative to the amount of bitumen recovered
in stream 102.
[0027] The solvent-rich overflow 120 from FSU 116 may be mixed with
the bitumen froth feed 102. The bottom stream 118 from FSU 116 is
the tailings substantially comprising solids, water, asphaltenes,
and residual solvent. The bottom stream 118 is fed into a tailings
solvent recovery unit (TSRU) 122, a series of TSRUs or by another
recovery method. In the TSRU 122, residual solvent is recovered and
recycled in stream 126 prior to the disposal of the tailings in the
tailings ponds (not shown) via a tailings flow line 124. Exemplary
operating pressures of FSU 104 and FSU 116 are respectively about
550 thousand Pascals gauge (kPag) and about 600 kPag mixed pentane
solvents. Other solvents may require a higher pressure to prevent
boiling or allow for operation at lower pressures. FSUs 104 and 116
are typically made of carbon-steel but may be made of other
materials.
[0028] FIG. 2 is an exemplary flow chart of a process for
recovering hydrocarbons utilizing at least a portion of the
equipment disclosed in FIG. 1. As such, FIG. 2 may be best
understood with reference to FIG. 1. The process 200 includes
providing a bitumen froth inlet stream having water, asphaltenes,
and solvent 204. Next, the asphaltenes are settled out in a froth
separation unit (FSU) to produce a tailings stream and a diluted
bitumen stream 206. The solvent is separated from the diluted
bitumen stream in a solvent recovery unit (SRU) to produce a
solvent recycle stream and a bitumen product stream 208. Either or
both of the diluted bitumen stream and the bitumen product stream
are treated in an electrostatic desalter to produce a treated
bitumen stream 210. Note, that certain steps may be repeated and
the order of the steps may be altered. For example, the treatment
step 210 may come before the separation step 208, after the
separation step 208, or both. In the case where the treatment step
210 comes prior to the separation step 208, the SRU separates the
treated bitumen stream rather than the diluted bitumen stream.
Optionally, the process 200 may include receiving at least one data
input 212 and controlling at least one process condition to
configure a composition of the treated bitumen stream bas on the
data input 214.
[0029] Still referring to FIGS. 1 and 2, the step of providing the
bitumen froth 204 may include a thermal extraction method such as
the clark hot water extraction (CHWE) method, steam assisted
gravity drainage (SAGD), vapor extraction (VAPEX), sliding
reservoir bitumen recovery (SRBR), fluidized, in-situ, reservoir
extraction (FIRE), cold, heavy oil production (CHOPS) or some
combination of these methods. An exemplary composition of the
resulting bitumen froth 102 is about 60 wt % bitumen, 30 wt % water
and 10 wt % solids, with some variations to account for the
extraction processing conditions. In such an extraction process oil
sands are mined, bitumen is extracted from the sands using water
(e.g. the CHWE process or a cold water extraction process), and the
bitumen is separated as a froth comprising bitumen, water, solids
and air. During extraction, air is added to the bitumen/water/sand
slurry to help separate bitumen from sand, clay and other mineral
matter. The bitumen attaches to the air bubbles and rises to the
top of the separator (not shown) to form a bitumen-rich froth 102
while the sand and other large particles settle to the bottom.
Regardless of the type of oil sand extraction process employed, the
extraction process will typically result in the production of a
bitumen froth product stream 102 comprising bitumen, water and fine
solids (including asphaltenes, mineral solids) and a tailings
stream 114 consisting essentially of water and mineral solids and
some fine solids.
[0030] In the process 200 solvent 120 is added to the bitumen-froth
102 after extraction and the mixture is pumped to another
separation vessel (froth separation unit or FSU 104). The addition
of solvent 120 helps remove the remaining fine solids and water.
Put another way, solvent addition increases the settling rate of
the fine solids and water out of the bitumen mixture. Because of
the treatment step 210 of the present process 200, less solvent is
used and fewer asphaltenes and other solids are settled out of the
bitumen mixture. The treatment step 210 removes many of these
solids in addition to dehydrating the bitumen stream, removing
salts, and other impurities. In one embodiment of the recovery
process 200 a paraffinic solvent is used to dilute the bitumen
froth 102 before separating the product bitumen by gravity in a
device such as FSU 104. Where a paraffinic solvent is used (e.g.
when the weight ratio of solvent to bitumen is greater than 0.8), a
portion of the asphaltenes in the bitumen are rejected thus
achieving solid and water levels that are lower than those in
existing naphtha-based froth treatment (NFT) processes. In the NFT
process, naphtha may also be used to dilute the bitumen froth 102
before separating the diluted bitumen by centrifugation (not
shown), but not meeting pipeline quality specifications.
[0031] As would be expected with any process, the preferred
conditions seek to produce the greatest amount of bitumen product
110 with the least amount of expense (e.g. from energy use,
chemical use, etc.). Variables that could be configured include,
but are not limited to: flow rate of the diluted bitumen stream,
flow rate of the fresh water inlet stream, flow rate of the
chemical inlet stream, solvent content of the diluted bitumen
stream, composition of chemicals flowing through the chemical
inlet, electrostatic field characteristics, temperature inside the
electrostatic desalter, mixing valve pressure, mixing valve
intensity, temperature of the diluted bitumen stream, thickness of
an emulsion layer, and any combination thereof. Configuring the
preferred conditions may be accomplished by obtaining data 212
related to the process 200 and controlling process steps 214 like
those listed above via manual or automated control systems such as
controller 138.
[0032] FIG. 3 is an exemplary illustration of an electrostatic
desalting unit for use in the plant of FIG. 1 and/or the process of
FIG. 2. As such, FIG. 3 may be best understood with reference to
FIGS. 1 and 2. The desalting unit 300 may include a tank 302, an
inlet distributor (also called a spreader) 304, an oil collector
306, electrodes 308, and a power unit 310 operatively connected to
the electrodes 308. In addition, the desalter 300 includes an inlet
flow line 312, a chemical injection line 314, fresh water injection
line 316, a mixing valve 318, and oil outlet 320 operatively
attached to the oil collector 306, and a water outlet 322. During
standard operation, the desalter 300 may contain at least three
layers of fluids: a water layer 324 at the bottom, an emulsion
layer 326 above that, and an oil layer 328 on top of the emulsion
layer 326. In addition, when treating heavy oil having particulates
such as mineral solids and asphaltenes, the solids may settle at
the bottom of the tank. The desalting unit 300 may be either of the
desalters 130 or 142 and may be utilized in parallel with other
desalting units or may be configured in stages with other
units.
[0033] Although all types of electrostatic desalters are within the
scope of the present disclosure, one preferred type of
electrostatic desalter 300 utilizes a combined alternating current
(AC)/direct current (DC) field. Depending on the composition of the
bitumen feed 102, it may be preferable to utilize a modulated high
voltage DC field with AC (MHVDC/AC) type of desalter, bi-modal
field modulation (BFM) type of desalter, or another type. See, e.g.
SPE 97786, supra, which is hereby incorporated by reference for
further description of these desalter types. The basic electrode
308 configuration is the same for all of these types of
desalters.
[0034] In operation, the desalter 300 mixes the feed stream 312
and/or 130 with fresh "wash water" 314 and/or 131a and a chemical
agent 316 and/or 131b. The combined stream is then mixed in the
valve mixer 318 and/or 132 to form an emulsion. In general, the AC
field is established between the bottom of the electrodes 308 and
the oil/water interface and promotes initial water droplet
coalescence. The DC field is generated between each pair of
oppositely charged electrodes 308 establishing an electrostatic
voltage field between the electrodes 308. This field is a
significant factor in the dipole force, electrophoretic force, and
the di-electrophoretic force, which are often referred to as
"coalescence forces," which directly affect the amount of
separation of water from oil droplets.
[0035] Some exemplary factors that affect desalter operation and
performance include the feed rate and quality of the feed
composition, temperature/viscosity/density relationships,
electrical field intensity, wash water rate and quality, flow
configuration, emulsion formation (e.g. by pumps, exchangers,
valves, and mixers, etc.), control of water level and emulsion
layers, demulsifier chemicals addition rate, and others. Treatment
of heavy oils having asphaltenes and mineral solids provide
additional challenges and may require specific solutions such as
increasing the temperature of the desalter to lower the viscosity
of the heavy hydrocarbon, increasing the amount of chemical
demulsifier to destabilize the solids-stabilized emulsion, and
enhanced degassing techniques. Also, sludge drains and mud washing
techniques may be utilized to prevent accumulation of solids in the
desalter tank 304. Another optional feature is the use of a highly
sensitive level probe to sense the water content of the oil/water
interface layer. These and other factors and techniques are
discussed in greater detail in WARREN, KENNETH W. AND ARMSTRONG,
JOHN, Desalting Heavy Crude Oils--The Venezuelan Experience, found
at: natcogroup.com under Technical Papers, December 2001, which is
hereby incorporated by reference for said technical
disclosures.
[0036] FIG. 4 is an exemplary schematic of an alternative bitumen
froth treatment plant of FIG. 1 utilizing the process of FIG. 2,
including the desalter of FIG. 3. As such, FIG. 4 may be best
understood with reference to FIGS. 1-3. The plant 400 includes a
bitumen froth input stream 402 (which may also be mixed with a
solvent-rich stream 424) is input to a froth separation unit (FSU)
404, which separates stream 402 into a diluted bitumen component
406 comprising bitumen and solvent and a froth treatment tailings
component 412 substantially comprising water, mineral solids,
precipitated asphaltenes (and aggregates thereof), solvent, and
small amounts of unrecovered bitumen. The tailings stream 412 may
be withdrawn from the bottom of FSU 404, which may have a conical
shape at the bottom, and sent to a second FSU 420, which produces a
second diluted bitumen stream 422 and a second tailings stream 426.
The second diluted bitumen stream 422 may be combined with the
first diluted bitumen stream 406, with the bitumen feed stream 402,
or sent directly to the SRU 408. In the preferred case where at
least a portion of the second diluted bitumen stream 422 is
combined with the first diluted bitumen stream 406, the combined
stream is sent via line 440 to an electrostatic desalter 300a for
treatment before going to the SRU 408 for separation via line 442.
In one alternative embodiment, the product stream 410 may be at
least partially diverted to an electrostatic desalter 300b via line
444 then produced via line 446.
[0037] The SRU 408 may be a conventional fractionation vessel or
other suitable apparatus in association with other suitable
equipment for this purpose in which the solvent 414 is flashed off
and condensed in a condenser 416 associated with the solvent
flashing apparatus and recycled/reused in the process 400. The
solvent free bitumen product 410 is then stored or transported for
further processing (e.g. via pipeline) in a manner well known in
the art or sent to the electrostatic desalter 300b. Froth treatment
tailings component 412 may be passed directly to the tailings
solvent recovery unit (TSRU) 430 or may first be passed to a second
FSU 420.
[0038] In one embodiment, FSU 404 operates at a temperature of
about 60.degree. C. to about 80.degree. C., or about 70.degree. C.
In one embodiment, FSU 404 operates at a pressure of about 700 to
about 900 kPa, or about 800 kPa. Diluted tailings component 412 may
typically comprise approximately 50 to 70 wt % water, 15 to 30 wt %
mineral solids, and 5 to 25 wt % hydrocarbons. The hydrocarbons
comprise asphaltenes (for example 2.0 to 12 wt % or 9 wt % of the
tailings), bitumen (for example about 7.0 wt % of the tailings),
and solvent (for example about 8.0 wt % of the tailings). In
additional embodiments, the tailings may comprise greater than 1.0,
greater than 2.0, greater than 3.0, greater than 4.0, greater than
5.0, greater than 10.0 wt % asphaltenes, or about 15.0 wt %
asphaltenes.
[0039] Still referring to FIG. 4, FSU 420 performs generally the
same function as FSU 404, but is fed the tailings component 412
rather than a bitumen froth feed 402. The operating temperature of
FSU 420 may be higher than that of FSU 404 and may be between about
80.degree. C. and about 100.degree. C., or about 90.degree. C. In
one embodiment, FSU 420 operates at a pressure of about 700 to
about 900 kPa, or about 800 kPa. A diluted bitumen component stream
422 comprising bitumen and solvent is removed from FSU 420 and is
either sent to FSU 404 via feed 424 for use as solvent to induce
asphaltene separation, is at least partially diverted to the
electrostatic desalter 300a via line 440 for treatment, or is
passed to SRU 408 via feed 425 or to an another SRU (not shown) for
treatment in the same way as the diluted bitumen component 406. The
ratio of solvent: bitumen in diluted bitumen component 422 may be,
for instance, about 10:1 to 40:1, or about 20:1. Alternatively,
diluted bitumen component 422 may be partially passed to FSU 404
via line 424 and partially passed to SRU 408 via line 425, or to
another SRU (not shown). Solvent 414 from SRU 408 may be combined
with the diluted tailing stream 412 into FSU 420, shown as stream
418, or returned to a solvent storage tank (not shown) from where
it is recycled to make the diluted bitumen froth stream 402. Thus,
streams 422 and 418 show recycling. In the art, solvent or diluted
froth recycling steps are known such as described in U.S. Pat. No.
5,236,577.
[0040] In the exemplary system of FIG. 4, the froth treatment
tailings 412 or tailings component 426 (with a composition similar
to underflow stream 412 but having less bitumen and solvent), may
be combined with dilution water 427 to form diluted tailings
component 428 and is sent to TSRU 430. Diluted tailings component
428 may be pumped from the FSU 420 or FSU 404 (for a single stage
FSU configuration) to TSRU 430 at the same temperature and pressure
in FSU 420 or FSU 404. A backpressure control valve 429 may be used
before an inlet into TSRU 430 to prevent solvent flashing
prematurely in the transfer line between FSU 420 and TSRU 430.
[0041] Flashed solvent vapor and steam (together 434) is sent from
TSRU 430 to a condenser 436 for condensing both water 438 and
solvent 440. Recovered solvent 440 may be reused in the bitumen
froth treatment plant 400. Tailings component 432 may be sent
directly from TSRU 430 to a tailings storage area (not shown) for
future reclamation or sent to a second TSRU (not shown) or other
devices for further treatment. Tailings component 432 contains
mainly water, asphaltenes, mineral matter, and small amounts of
solvent as well as unrecovered bitumen. A third TSRU (not shown)
could also be used in series and, in each subsequent stage, the
operating pressure may be lower than the previous one to achieve
additional solvent recovery. In fact, more than three TSRU's could
be used, depending on the quality of bitumen, pipeline
specification, size of the units and other operating factors.
[0042] FIG. 5 is yet another exemplary alternative embodiment of a
heavy oil treatment plant in accordance with the present invention.
The plant shares many of the components with the plant of FIG. 4,
utilizes the process of FIG. 2, and includes the electrostatic
desalter of FIG. 3. as such, FIG. 5 may be best understood with
reference to FIGS. 2-4. The plant 500 generally includes three
portions, the froth separation portion 501, the solvent recovery
portion 503, and the tailings solvent recovery portion 505. Similar
to the plant 400, the plant 500 includes at least one desalting
unit 300, which may be located in one or all of the locations 300a,
300b, and 300c.
[0043] As noted, plant 500 includes many similar components as the
plant 400 and to the extent the schematics look the same, they may
be considered equivalent. For example, the froth separation portion
501 includes FSU's 404 and 420, but shows a slightly different flow
configuration and a heating unit 507. Additional alternative flow
schemes are shown between the froth separation portion 501, the
solvent recovery portion 503, and the tailings recovery portion
505. These flow lines include additional heaters like 507 as well
as separation/accumulation tanks such as 509a and 509b. The solvent
recovery portion 503 includes a solvent recovery unit 408 as well
as a vacuum system 511 and a steam generation unit 513. These
additional units (e.g. 511 and 513) may also be included in plant
100 and plant 400, but were not shown for simplicity. They are
shown in plant 500 for illustrative purposes and as just one
example of a layout for a process plant for treating bitumen froth.
The plant 500 also more specifically contemplates a high
temperature bitumen treatment process.
[0044] While the present disclosure may be susceptible to various
modifications and alternative forms, the exemplary embodiments
discussed above have been shown only by way of example. However, it
should again be understood that the disclosure is not intended to
be limited to the particular embodiments disclosed herein. Indeed,
the present disclosure includes all alternatives, modifications,
and equivalents falling within the true spirit and scope of the
appended claims.
* * * * *