U.S. patent application number 12/530078 was filed with the patent office on 2010-05-27 for process for recovering solvent from ashphaltene containing tailings resulting from a separation process.
Invention is credited to Ken Sury.
Application Number | 20100126906 12/530078 |
Document ID | / |
Family ID | 38561390 |
Filed Date | 2010-05-27 |
United States Patent
Application |
20100126906 |
Kind Code |
A1 |
Sury; Ken |
May 27, 2010 |
Process For Recovering Solvent From Ashphaltene Containing Tailings
Resulting From A Separation Process
Abstract
A process for recovering paraffinic solvent from tailings
produced in the treatment of bitumen froth comprising introducing
the tailings into a tailings solvent recovery unit (TSRU), the TSRU
having internals, and distributing the tailings over the internals.
An inert gas or steam is then introduced below the internals and
above the liquid pool for enhancing the vaporization of the
contained solvent. Solvent is vaporized from asphaltene
agglomerates. In one embodiment, the process is affected in the
absence of mechanical means used to substantially break up
asphaltene agglomerates or to prevent the agglomeration of
asphaltene. In another aspect, the process comprises introducing
the tailings into a first TSRU as described above and then into a
second TSRU operated at a lower pressure. In another aspect,
internals are optionally present and steam or inert gas is injected
in the liquid pool.
Inventors: |
Sury; Ken; (Calgary,
CA) |
Correspondence
Address: |
EXXONMOBIL UPSTREAM RESEARCH COMPANY
P.O. Box 2189, (CORP-URC-SW 359)
Houston
TX
77252-2189
US
|
Family ID: |
38561390 |
Appl. No.: |
12/530078 |
Filed: |
March 27, 2008 |
PCT Filed: |
March 27, 2008 |
PCT NO: |
PCT/US08/04024 |
371 Date: |
September 4, 2009 |
Current U.S.
Class: |
208/30 |
Current CPC
Class: |
C10G 1/045 20130101 |
Class at
Publication: |
208/30 |
International
Class: |
C10G 73/02 20060101
C10G073/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 3, 2007 |
CA |
2587166 |
Claims
1. A process for recovering paraffinic solvent from froth treatment
tailings produced in the treatment of bitumen froth comprising:
introducing the froth treatment tailings into a tailings solvent
recovery unit (TSRU), the TSRU having internals, and distributing
the froth treatment tailings over the internals to increase the
surface area of the froth treatment tailings; introducing inert gas
or steam below the internals so that it flows counter currently to
the froth treatment tailings and heats the froth treatment tailings
to vaporize at least a portion of the paraffinic solvent; and
removing the vaporized solvent from the TSRU; wherein: the froth
treatment tailings contain asphaltenes; and the at least a portion
of the solvent is vaporized from asphaltene agglomerates.
2. The process of claim 1, wherein the process is affected in the
absence of mechanical means used to substantially break up
asphaltene agglomerates or to prevent the agglomeration of
asphaltene.
3. The process of claim 1, wherein the TSRU has an absolute
pressure of about 100 and about 200 kPa.
4. The process of claim 1, wherein the internals comprise a
plurality of interior, vertically spaced shed decks.
5. The process of claim 1, wherein the internals are coated with an
asphaltene fouling resistant coating to mitigate fouling or
plugging in the TSRU.
6. The process of claim 1, wherein the froth treatment tailings
contain at least 1.0 wt % asphaltenes.
7. The process of claim 1, wherein the froth treatment tailings
contain at least 5.0 wt % asphaltenes.
8. The process of claim 1, wherein the inert gas or steam
introduced below the internals is introduced above a liquid level
that forms in the bottom of the TSRU.
9. The process of claim 1, wherein the paraffinic solvent is a
C.sub.4 to C.sub.6 paraffinic hydrocarbon solvent.
10. The process of claim 1, wherein the paraffinic solvent is
pentane, iso-pentane, or a combination thereof.
11. The process of claim 1, wherein the temperature of the TSRU is
about 75 to about 100.degree. C.
12. The process of claim 1, wherein the TSRU has an absolute
pressure of about 120 to about 170 kPa.
13. The process of claim 1, wherein the inert gas is nitrogen,
methane, carbon dioxide, argon, steam or any other inert gas that
is not reactive under process conditions.
14. The process of claim 1, wherein the inert gas or steam to froth
treatment tailings mass ratio is about 1:1 to about 10:1.
15. The process of claim 1, further comprising feeding tailings
from the TSRU into a second TSRU maintained at an absolute pressure
that is lower than the pressure of the TSRU recited in claim 1, the
second TSRU having internals, and distributing the tailings from
the TSRU over the internals to increase the surface area of the
tailings from the TSRU; introducing inert gas or steam below the
internals of the second TSRU so that it flows counter currently to
the tailings from the TSRU and heats the tailings from the TSRU to
vaporize at least a portion of the paraffinic solvent; and removing
the vaporized solvent from the second TSRU.
16. The process of claim 15, wherein the second TSRU has an
absolute pressure of about 20 to about 200 kPa.
17. A process for recovering paraffinic solvent from froth
treatment tailings produced in the treatment of bitumen froth
comprising: introducing the froth treatment tailings into a first
tailings solvent recovery unit (TSRU), the first TSRU having
internals; distributing the froth treatment tailings over the
internals to increase the surface area of the froth treatment
tailings; introducing inert gas or steam below the internals so
that it flows counter currently to the froth treatment tailings and
heats the froth treatment tailings to vaporize at least a portion
of the paraffinic solvent; removing the vaporized solvent from the
first TSRU; feeding tailings from the first TSRU into a second TSRU
maintained at an absolute pressure that is lower than the pressure
of the first TSRU, the second TSRU having internals; distributing
the tailings from the first TSRU over the internals of the second
TSRU to increase the surface area of the tailings from the first
TSRU; introducing inert gas or steam below the internals of the
second TSRU so that it flows counter currently to the tailings from
the first TSRU and heats the tailings from the first TSRU to
vaporize at least a portion of the paraffinic solvent; and removing
the vaporized solvent from the second TSRU.
18. The process of any one of claims 22 to 25, wherein the froth
treatment tailings contain asphaltenes; wherein the at least a
portion of the solvent is vaporized from asphaltene agglomerates;
and wherein the process is effected in the absence of mechanical
means used to substantially break up asphaltene agglomerates or to
prevent the agglomeration of asphaltene.
19. A process for recovering paraffinic solvent from froth
treatment tailings produced in the treatment of bitumen froth
comprising: introducing the froth treatment tailings into a
tailings solvent recovery unit (TSRU); introducing inert gas or
steam into a liquid pool formed in the bottom of the TSRU to
vaporize at least a portion of the paraffinic solvent; and removing
the vaporized solvent from the TSRU; wherein: the froth treatment
tailings contain asphaltenes; and the at least a portion of the
solvent is vaporized from asphaltene agglomerates.
20. The process of claim 19, wherein the TSRU is substantially free
of internals.
21. The process of claim 19, wherein the process is effected in the
absence of mechanical means used to substantially break up
asphaltene agglomerates or to prevent the agglomeration of
asphaltene.
22. The process of claim 19, wherein the froth treatment tailings
contain at least 1.0 wt % asphaltenes.
23. The process of claim 19, wherein the froth treatment tailings
contain at least 5.0 wt % asphaltenes.
24. The process of claim 19, wherein the TSRU has an absolute
pressure of about 20 and about 200 kPa.
25. The process of claim 19, wherein the paraffinic solvent is a
C.sub.4 to C.sub.6 paraffinic hydrocarbon solvent.
26. The process of claim 19, wherein the paraffinic solvent is
pentane, iso-pentane, or a combination thereof.
27. The process of claim 19, wherein the temperature of the TSRU is
about 75 to about 100.degree. C.
28. The process of claim 19, further comprising feeding tailings
from the TSRU into a second TSRU maintained at an absolute pressure
that is lower than the pressure of the TSRU recited in claim 19.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Canadian patent
application number 2,587,166 which was filed on May 3, 2007.
FIELD OF THE INVENTION
[0002] The present invention relates generally to an improved
process for recovering solvent from asphaltene containing tailings
resulting from a separation process. More particularly, the
invention relates to recovering paraffinic solvent from such
tailings.
BACKGROUND OF THE INVENTION
[0003] The extraction of bitumen from mined oil sands involves the
liberation and separation of 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 a
well-developed commercial recovery technique. In the CHWE process,
mined oil sands are mixed with hot water to create slurry suitable
for extraction. Caustic is added to adjust the slurry pH to a
desired level and thereby enhance the efficiency of the separation
of bitumen. Recent industry developments have shown the feasibility
of operating at lower temperatures and without caustic addition in
the slurrying process.
[0004] Regardless of the type of water based oil sand extraction
process employed, the extraction process will typically result in
the production of a bitumen froth product stream comprising
bitumen, water and fine solids (also referred to as mineral matter)
and a tailings stream consisting of essentially coarse solids and
some fine solids and water. A typical composition of bitumen froth
is about 60 wt % bitumen, 30 wt % water and 10 wt % solids, with
some variations to account for the extraction processing
conditions. The water and solids in the froth are considered as
contaminants and must be either essentially eliminated or reduced
to a level suitable for feed to an oil refinery or an upgrading
facility, respectively. The contaminants rejection process is known
as a froth treatment process and is achieved by diluting the
bitumen froth with a sufficient quantity of an organic solvent such
as naphtha. There are two commercial approaches to reject the froth
contaminants, namely naphtha based and paraffinic solvent based.
Solvent addition (dilution) increases the density differential
between bitumen and water and solids and as well enable the
contaminants rejection using multi-stage gravity settling units.
The separation schemes generally result in a bitumen diluted
product and another tailings stream, commonly referred to as the
froth treatment tailings, containing residual bitumen, residual
solvent, solids and water. The froth treatment tailings stream must
be processed further to recover the residual solvent and be
suitable for disposal. Residual solvent recovery is dictated by
both environmental and economic reasons. This recovery operation is
referred to as a tailings solvent recovery process.
[0005] In the naphtha based separation, the resulting bitumen
product contains 1 to 3 wt % water and <1.0 wt % solids and is
not suitable for transporting through a common pipeline carrier.
The addition of sufficient amounts of paraffinic solvent results in
asphaltene precipitation, formation of aggregates with the
contaminants (entrained water and carryover solids in the froth)
and a rapid settling to provide a solids free dry bitumen product
suitable for transportation in a common carrier and to
refineries.
[0006] The addition of paraffinic solvent to bitumen froth and the
resulting benefits are described in Canadian Patents Nos. 2,149,737
and 2,217,300. According to Canadian Patent No. 2,149,737, the
efficiency (rate and extent) of removal of water and solids
generally increases as (i) the carbon number or molecular weight of
the paraffinic solvent decreases, (ii) the solvent to froth ratio
increases, and (iii) the amount of aromatic and naphthene
impurities in the paraffinic solvent decreases. The inventors
further demonstrated that the separation of water and solids from
the bitumen is achieved at temperatures above 30.degree. C. The
effect of temperature on bitumen recovery and bitumen product
quality obtainable in this separation process was studied in a
scale up pilot using natural gas condensate (NGC) which contains
about 83% paraffin. While bitumen recovery was higher (97.6 vs.
83.8 wt %) if the run was conducted at 117.degree. C., the product
quality obtained was significantly lower (99.2 vs. 90.6 wt %) than
obtained at 50.degree. C. In accordance with the one of the
discoveries stated above, the inventors used a relatively high
solvent/froth ratio to obtain a better product quality with NGC in
a continuous process but this test was done at 50.degree. C.
Although the inventors obtained a satisfactory product quality
using pure paraffinic solvents at laboratory conditions and up to
80.degree. C., it was not obvious such a result would be duplicated
at a pilot scale continuous test unit due to uncertain
hydrodynamics as well as increasing solubility of water in
hydrocarbon at higher temperatures. In general, in a continuous
separation, product quality and yield are inter-related and
judicious fine-tuning of process parameters is required to
establish optimum quality for a given yield. As discussed above,
the froth treatment process must have a reliable and economic
technique for solvent recovery from the tailings. However, the
unique nature of the solvent-containing tailings makes solvent
removal a challenge to the industry. Various processes have been
devised for recovering solvent from solvent-containing tailings,
some of which will now be described.
[0007] Canadian Patent No. 1,027,501 describes a process for
treatment of tailings to recover naphtha. The process comprises
introducing the tailings into a distributor at the upper end of the
chamber of a vacuum flash vessel or tower maintained at 35 kPa, in
order to flash the naphtha present in the tailings. The vessel is
also equipped with a stack of internal shed decks for enhancing
contact between stripping steam and the tailings feed. The steam is
introduced at a point above the liquid pool in the vessel and below
the stack of shed decks. The steam is intended to heat the flashed
tailings as they pass down through the shed decks, to vaporize
contained solvent and some water, for recovery as an overhead
stream. In practice, however, this process results in only 60 to
65% recovery of the solvent; hence, a large amount of solvent is
still being released to the environment.
[0008] Canadian Patent No. 2,272,045 describes a method for
recovery of hydrocarbon solvent from tailings produced in a bitumen
froth treatment plant comprising introducing the tailings into a
steam stripping vessel maintained at near atmospheric pressure, the
vessel having a plurality of interior, vertically spaced shed
decks, and distributing the tailings over said shed decks. Steam is
introduced below the shed decks for vaporizing the major portion of
the contained solvent and some water. However, the tailings are
free of asphaltenes according to page 4, lines 11 to 13. Canadian
Patent No. 2,272,035 describes a process for recovery of
hydrocarbon solvent from tailings produced in a bitumen froth
treatment plant comprising introducing the tailings into a vacuum
flash vessel maintained at a sufficiently low sub-atmospheric
pressure to vaporize the major portion of the contained solvent and
some water. The residuals then pool near the bottom of the flash
vessel. Steam is then introduced into the tailings pool for
vaporizing residual solvent and some water. However, as with
Canadian Patent No. 2,272,045, discussed above, the tailings are
free of asphaltenes according to page 4, lines 12 to 15. Thus, the
inventors of these two patents did not have to contend with the
challenges associated with having asphaltenes in the tailings.
Certain of such challenges are discussed below with reference to
Canadian Patent No. 2,353,109 and Canadian Patent Application No.
2,454,942.
[0009] Canadian Patent No. 2,353,109 describes a process for
treating an underflow stream (or tailings) containing water,
solvent, asphaltenes and solids, from one of the last separation
steps in a paraffinic solvent process for separating bitumen from
an oil sands froth, wherein a) the stream is introduced to a
solvent recovery vessel that is substantially free of internals
wherein the temperature and pressure are such that the solvent is
normally a vapor; b) a pool of liquid and solids is maintained in
the lower part of the vessel at a controlled level for sufficient
time to allow the solvent to vaporize; c) the pool is agitated to
the point where the asphaltenes are dispersed, submerged and
prevented from re-agglomerating and the solids are maintained in
suspension; d) the solvent is recovered as an overhead vapor
stream; and e) the solvent depleted remainder of the stream is
removed from the bottom of the vessel as a liquid slurry. Agitation
is preferably effected by means of an impeller. An alternate
agitation means is a pump-around circuit to pump the slurry from
the top of the liquid pool to the lower part of the liquid pool or
vice versa. The typical composition of this underflow stream is
described as about 40 to 60 wt % water, about 15 to 35 wt % mineral
solids (sand and clay), about 5 to 15 wt % entrained solvent, and
about 10 to 15 wt % asphaltenes and unrecovered bitumen. Page 3,
second full paragraph of that patent describes (a) that
conventional solvent technology employs vessels with internals such
as trays, packing and baffles; (b) that such internals provide the
residence time required for the necessary solvent vaporization to
take place; (c) that vessels with such internals are not practical
for an underflow stream having the aforementioned composition; (d)
that the aforementioned conventional approach is unworkable because
of the accumulation of inorganic and organic solids and the fouling
or plugging of vessel internals, lines and valves; and (e) that in
that invention, the necessary residence time is achieved by having
a liquid pool form in the lower part of the vessel. The invention
teaches that agitation must be provided in or around the solvent
recovery unit primarily to disperse or prevent the growth of
aggregates of precipitated asphaltenes thereby enhancing the
release of solvent from the precipitated asphaltenes to the vapor
phase. In one embodiment, first and second stage solvent recovery
vessels are used, where the second stage vessel is typically
operated at a reduced pressure relative to the first stage vessel
to reduce any amount of foam that may still be associated with the
liquid slurry removed from the bottom of the first stage vessel.
The second stage vessel is mechanically identical to the first
stage vessel.
[0010] Canadian Patent Application No. 2,454,942 describes a
process for solvent recovery from froth treatment tailings
comprising water, particulate solids, and precipitated asphaltenes.
According to the inventors, recycling a pre-determined portion of
the solvent recovered tailings stream to the solvent recovery
apparatus is necessary to maintain downward flux in the apparatus
which inhibits accumulation of asphaltene mat in the solvent
recovery unit and suppress the formation of foam. Furthermore,
shearing conditions (provided by pumps, mixers or another
apparatus) is preferably provided in the recycle circuit first, to
break up asphaltene flocs/aggregates and second, to enhance
recovery of solvent from the tailings. There is no introduction of
steam or inert gas to vaporize solvent from the asphaltenes.
[0011] Thus, Canadian Patents Nos. 2,272,045 and 2,272,035 deal
with solvent recovery from tailings that are free of asphaltenes.
Canadian Patent No. 2,353,109 deals with solvent recovery without
the use of internals. Canadian Patent Application No. 2,454,942
deals with solvent recovery without the introduction of steam or
inert gas to vaporize solvent from the asphaltenes. Both of
Canadian Patent No. 2,353,109 and Canadian Patent Application No.
2,454,942 deal with solvent recovery from tailings containing
asphaltenes using agitation or shearing in or around the recovery
vessel, so that the asphaltenes are dispersed, submerged and
prevented from re-agglomerating.
SUMMARY OF THE INVENTION
[0012] It is an object of the present invention to obviate or
mitigate at least one disadvantage of previous processes.
[0013] In a first aspect, the present invention provides a process
for recovering paraffinic solvent from froth treatment tailings
produced in the treatment of bitumen froth comprising: introducing
the froth treatment tailings into a tailings solvent recovery unit
(TSRU), the TSRU having internals, and distributing the froth
treatment tailings over the internals to increase the surface area
of the froth treatment tailings; introducing inert gas or steam
below the internals so that it flows counter currently to the froth
treatment tailings and heats the froth treatment tailings to
vaporize at least a portion of the paraffinic solvent; and removing
the vaporized solvent from the TSRU; wherein the froth treatment
tailings contain asphaltenes; and wherein the at least a portion of
the solvent is vaporized from asphaltene agglomerates.
[0014] Within this first aspect, the following embodiments may be
included. The process may be affected in the absence of mechanical
means used to substantially break up asphaltene agglomerates or to
prevent the agglomeration of asphaltene. The TSRU may have an
absolute pressure of about 100 and about 200 kPa. The internals may
comprise a plurality of interior, vertically spaced shed decks. The
internals may be coated with an asphaltene fouling resistant
coating to mitigate fouling or plugging in the TSRU. The froth
treatment tailings may contain at least 1.0 wt % asphaltenes, or at
least 5.0 wt % asphaltenes. The inert gas or steam introduced below
the internals may be introduced above a liquid level that forms in
the bottom of the TSRU. The paraffinic solvent may be a C.sub.4 to
C.sub.6 paraffinic hydrocarbon solvent. The paraffinic solvent may
be pentane, iso-pentane, or a combination thereof. The temperature
of the TSRU may be about 75 to about 100.degree. C. The TSRU may
have an absolute pressure of about 120 to about 170 kPa. The inert
gas may be nitrogen, methane, carbon dioxide, argon, steam or any
other inert gas that is not reactive under process conditions. The
inert gas or steam to froth treatment tailings mass ratio may be
about 1:1 to about 10:1. The process may further comprise: feeding
tailings from the TSRU into a second TSRU maintained at an absolute
pressure that is lower than the pressure of the TSRU recited above,
the second TSRU having internals, and distributing the tailings
from the TSRU over the internals to increase the surface area of
the tailings from the TSRU; introducing inert gas or steam below
the internals of the second TSRU so that it flows counter currently
to the tailings from the TSRU and heats the tailings from the TSRU
to vaporize at least a portion of the paraffinic solvent; and
removing the vaporized solvent from the second TSRU. The second
TSRU may have an absolute pressure of about 20 to about 200 kPa.
The internals of the second TSRU may comprise a plurality of
interior, vertically spaced shed decks. The inert gas or steam
introduced below the internals in the second TSRU may be introduced
above a liquid level that forms in the bottom of the second TSRU.
The second TSRU may have an absolute pressure of about 35 kPa to
about 125 kPa, or about 35 kPa to about 100 kPa. The temperature of
the second TSRU may be about 75 to about 100.degree. C.
[0015] In a second aspect, the present invention provides a process
for recovering paraffinic solvent from froth treatment tailings
produced in the treatment of bitumen froth comprising: introducing
the froth treatment tailings into a first tailings solvent recovery
unit (TSRU), the first TSRU having internals; distributing the
froth treatment tailings over the internals to increase the surface
area of the froth treatment tailings; introducing inert gas or
steam below the internals so that it flows counter currently to the
froth treatment tailings and heats the froth treatment tailings to
vaporize at least a portion of the paraffinic solvent; removing the
vaporized solvent from the first TSRU; feeding tailings from the
first TSRU into a second TSRU maintained at an absolute pressure
that is lower than the pressure of the first TSRU, the second TSRU
having internals; distributing the tailings from the first TSRU
over the internals of the second TSRU to increase the surface area
of the tailings from the first TSRU; introducing inert gas or steam
below the internals of the second TSRU so that it flows counter
currently to the tailings from the first TSRU and heats the
tailings from the first TSRU to vaporize at least a portion of the
paraffinic solvent; and removing the vaporized solvent from the
second TSRU.
[0016] Within this second aspect, the following embodiments may be
included. The TSRU may have an absolute pressure of about 100 and
200 kPa and the second TSRU may have an absolute pressure of 20 to
200 kPa. The internals may comprise interior, vertically spaced
shed decks. The insert gas or steam introduced below the internals
may be introduced above a liquid level in the first and second
TSRU's. The froth treatment tailings may contain asphaltenes, at
least a portion of the solvent may be vaporized from asphaltene
agglomerates, and the process may be affected in the absence of
mechanical means used to substantially break up asphaltene
agglomerates or to prevent the agglomeration of asphaltene. The
froth treatment tailings may contain at least 1.0 wt % asphaltenes,
or at least 5.0 wt % asphaltenes. The paraffinic solvent may be a
C.sub.4 to C.sub.6 paraffinic hydrocarbon solvent. The paraffinic
solvent may be pentane, iso-pentane, or a combination thereof.
[0017] In a third aspect, the present invention provides a process
for recovering paraffinic solvent from froth treatment tailings
produced in the treatment of bitumen froth comprising: introducing
the froth treatment tailings into a tailings solvent recovery unit
(TSRU); introducing inert gas or steam into a liquid pool formed in
the bottom of the TSRU to vaporize at least a portion of the
paraffinic solvent; and removing the vaporized solvent from the
TSRU; wherein the froth treatment tailings contain asphaltenes; and
wherein the at least a portion of the solvent is vaporized from
asphaltene agglomerates.
[0018] Within this third aspect, the following embodiments may be
included. The TSRU may be substantially free of internals. The
process may be affected in the absence of mechanical means used to
substantially break up asphaltene agglomerates or to prevent the
agglomeration of asphaltene. The froth treatment tailings may
contain at least 1.0 wt % asphaltenes, or at least 5.0 wt %
asphaltenes. The TSRU may have an absolute pressure of about 20 and
about 200 kPa. The paraffinic solvent may be a C.sub.4 to C.sub.6
paraffinic hydrocarbon solvent. The paraffinic solvent may be
pentane, iso-pentane, or a combination thereof. The temperature of
the TSRU may be about 75 to about 100.degree. C. The process may
further comprise feeding tailings from the TSRU into a second TSRU
maintained at an absolute pressure that is lower than the pressure
of the TSRU recited above.
[0019] Other aspects and features of the present invention will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific embodiments of the
invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Embodiments of the present invention will now be described,
by way of example only, with reference to the attached Figure,
wherein:
[0021] FIG. 1 is a schematic of a diluted bitumen froth treatment
process, including a tailings solvent recovery process according to
an embodiment of the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0022] Generally, the present invention provides, in one aspect, a
process for recovering paraffinic solvent from tailings produced in
the treatment of bitumen froth comprising introducing the tailings
into a tailings solvent recovery unit (TSRU), the TSRU having
internals, and distributing the tailings over the internals. An
inert gas or steam is then introduced below the internals for
enhancing the vaporization of the contained solvent. Solvent is
vaporized from asphaltene agglomerates. In one embodiment, the
process is affected in the absence of mechanical means used to
substantially break up asphaltene agglomerates or to prevent the
agglomeration of asphaltene. In another aspect, the process
comprises introducing the tailings into a first TSRU as described
above and then into a second TSRU operated at a lower pressure.
[0023] It has been shown that prior art methods of agitation or use
of shearing devices in the recovery of solvent from diluted
tailings containing asphaltene agglomerates actually results in
significant increase in operability problems such as plugging and
fouling as well as lower solvent recovery.
[0024] FIG. 1 is a schematic of a diluted bitumen froth treatment
process, including a tailings solvent recovery process according to
an embodiment of the present invention. The paraffinic solvent
diluted bitumen froth (2) enters froth separation unit FSU (4).
[0025] The diluted bitumen froth (2) may be produced in a number of
ways known in the art and comprises bitumen, asphaltenes, mineral
solids, water, and a paraffinic solvent.
[0026] The diluted bitumen froth (2) contains a paraffinic solvent
because such a solvent has been added to a bitumen froth to induce
precipitation of a portion of the asphaltenes present in bitumen,
aggregation with water droplets and solids present in froth and
settling rapidly in a gravity settler (FSU).
[0027] The term "paraffinic solvent" (also known as aliphatic) as
used herein means solvents containing normal paraffins,
isoparaffins and blends thereof in amounts greater than 50 wt %.
Presence of other components such as olefins, aromatics or
naphthenes counteract the function of the paraffinic solvent and
hence should not be present more than 1 to 20 wt % combined and
preferably, no more than 3 wt % is present. The paraffinic solvent
may be a C.sub.4 to C.sub.20 paraffinic hydrocarbon solvent or any
combination of iso and normal components thereof. In one
embodiment, the paraffinic solvent comprises pentane, iso-pentane,
or a combination thereof. In one embodiment, the paraffinic solvent
comprises about 60 wt % pentane and about 40 wt % iso-pentane, with
none or less than 20 wt % of the counteracting components referred
above.
[0028] By using a blend of pure paraffins and operating at a
temperature range of 70 to 90.degree. C. in a continuous separation
unit as shown in FIG. 1, it is possible to achieve both a high
quality (containing <0.01 wt %, or at least <0.5 wt. %,
water+solids) and a high yield (98 wt %) bitumen product.
[0029] With the addition of a sufficient amount of paraffinic
solvent, and by way of gravity settling, the diluted bitumen froth
(2) separates in FSU (4) into a diluted bitumen component (6)
comprising bitumen and solvent and a froth treatment tailings
component (8) comprising mainly of water, mineral matter,
precipitated asphaltenes, solvent, and very small amounts of
unrecovered bitumen. The tailings stream (8) may be withdrawn from
the bottom of FSU (4), which may be conical. In one embodiment, FSU
(4) operates at a temperature of about 60.degree. C. to about
80.degree. C., or about 70.degree. C. In one embodiment, FSU (4)
operates at a pressure of about 700 to about 900 kPa, or about 800
kPa.
[0030] Diluted bitumen component (6) is passed through a solvent
recovery unit, SRU (10), such as a conventional fractionation
vessel or other suitable apparatus in which the solvent (12) is
flashed off and condensed in a condenser associated with the
solvent flashing apparatus and recycled/reused in the process. The
solvent free bitumen product (14) is then stored or transported for
further processing in a manner well known in the art.
[0031] Froth treatment tailings component (8) may be passed
directly to the tailings solvent recovery unit, TSRU, (16) or may,
as shown in FIG. 1, first be passed to a second FSU (18). Diluted
tailings component (8) may typically comprise approximately 50 to
70 wt % water, 15 to 25 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 further embodiments, the tailings
comprise greater than 1.0, greater than 2.0, greater than 3.0,
greater than 4.0, greater than 5.0, or greater than 10.0 wt %
asphaltenes.
[0032] Tailings component (8) is a tailings stream generated in a
paraffinic-based bitumen froth treatment process or other
separation process and while certain means resulting in a froth
treatment tailings component have been described above, the present
invention is not limited thereby.
[0033] FSU (18) performs generally the same function as FSU (4).
The operating temperature of FSU (18) may be higher than that of
FSU (4) and may be between about 80.degree. C. and about
100.degree. C., or about 90.degree. C. In one embodiment, FSU (18)
operates at a pressure of about 700 to about 900 kPa, or about 800
kPa. A diluted bitumen component stream (20) comprising bitumen and
solvent is removed from FSU (18) and is either sent to FSU (4) feed
for use as solvent to induce asphaltene separation or is passed to
SRU (10), or to another SRU, for treatment in the same way as the
diluted bitumen component (6). The ratio of solvent:bitumen in
diluted bitumen component (20) may be, for instance, 1.4 to 30:1,
or about 20:1 in the configuration shown in FIG. 1. Alternatively,
diluted bitumen component (20) may be partially passed to FSU (4)
and partially passed to SRU (10), or to another SRU. Solvent (12)
from SRU 10 may be combined with the diluted tailing stream (8)
into FSU (18), shown as stream (22), or returned to a solvent
storage tank (not shown) from where it is recycled to make the
diluted bitumen froth stream (2), thus, streams (20) and (22) show
recycling. In the art, solvent or diluted froth recycling steps are
known such as described in Canadian Patent No. 2,021,185.
[0034] The froth treatment tailings (8) or tailings component (24)
(with a composition similar to underflow stream (8) but having less
bitumen and solvent), is combined with dilution water (25) to form
diluted tailings component (26) and is sent to TSRU (16). The
dilution water may be at about 70.degree. C. to about 95.degree.
C., or about 90.degree. C. and the addition rate may vary between
0.5 to 2.0 times the mass of the tailings stream (8) or (24).
Diluted tailings component (26) may be pumped from the FSU (18) or
FSU (4) (for a single stage FSU configuration) to TSRU (16) at the
same temperature and pressure in FSU (18) or FSU (4), as the case
may be. A backpressure control valve may be used before an inlet
into TSRU (16) to prevent solvent flashing prematurely in the
transfer line between FSU (18) and TSRU (16). The operation of TSRU
(16) is discussed in more detail below.
[0035] Flashed solvent vapor and steam (together 27) is sent from
TSRU (16) to a condenser (28) for condensing both water (30) and
solvent (32). Recovered solvent (3) may be reused in bitumen froth
treatment. Tailings component (34) may be sent directly from TSRU
(16) to a tailings storage area for future reclamation or, as shown
in FIG. 1, may be sent to TSRU (36). Tailings component (34)
contains mainly water, asphaltenes, mineral matter, and small
amount of solvent as well as unrecovered bitumen. Solvent vapor and
steam (together 38) are sent from TSRU (36) to a condenser (40).
Water (42) and solvent are condensed in the condenser (40)
resulting in recovered solvent (44). As with recovered solvent
(32), recovered solvent (44) may be reused in the same manner as
stream (32). Tailings (47) from TSRU (36) may be further treated or
may be sent to a tailings storage area for future reclamation.
[0036] TSRU (16) and TSRU (36) will now be discussed in further
detail. TSRU (16) is a flash vessel or drum maintained at an
absolute pressure of about 100 to about 200 kPa (or about 120 to
about 170 kPa, or about 140 kPa). This TSRU may be operated at a
temperature of about 75.degree. C. to about 100.degree. C., and has
internals 46. In FIG. 1, the internals (46) are illustrated as a
plurality of interior, vertically spaced shed decks. Internals (46)
(and internals (50) described below) may alternatively be trays,
packing, baffles or other such internals known in the art. The
diluted tailings component (26) is distributed over the internals
(46) to increase the surface area of the diluted tailings component
(26). Below the internals (46) is a ring (not shown) having a
plurality of openings for the release of inert gas or steam (48).
The inert gas or steam (48) counter currently contacts the downward
flowing diluted tailings component (26) distributed over the
internals 46 and provide both the necessary heat for vaporizing the
solvent and a driving force for the vaporized solvent to the vapor
phase. The internals (46) ensure that the diluted tailings stream
is spread relatively uniformly over a large surface area that can
be subsequently exposed to inert gas or steam. A distributor (not
shown), having a plurality of openings, may be used to evenly
distribute diluted tailings component (26) over the internals (46).
The surface of the internals (46) may be covered with a suitable
coating, such as an asphaltene fouling resistant coating, to
mitigate or eliminate fouling and plugging.
[0037] An inert gas or steam (48) is introduced below the internals
(46), and above a tailings liquids pool in the bottom of TSRU (16),
so that it flows counter currently diluted tailings component (26)
and heats diluted tailings component (26) to vaporize the
paraffinic solvent and some water. The mass of inert gas or steam
addition rate may vary between 1 to 10 times the mass of the
solvent depleted tailings flow from TSRU (16). Vaporized solvent
and steam (together 27) is removed from the TSRU (16) as discussed
above.
[0038] As the solvent depleted slurry leaves the last layer of
internals (46), it is collected in a conical section of TSRU (16)
to allow for pumping from the bottom of TSRU (16) at a steady flow
rate to either a final disposal area or to TSRU (36) for additional
solvent recovery. The conical arrangement creates a pool of liquid
slurry. The slurry is removed from the TSRU, as tailings component
(34), using a pump in a conventional manner to the final disposal
area or TSRU (36). Tailings component (34) may have about the same
composition of diluted tailings component (26) minus the solvent
recovered (32).
[0039] TSRU (36) operates in generally the same manner as TSRU (16)
but is maintained at an absolute pressure of about 20 to about 200
kPa (or about 35 to about 125 kPa, or about 35 to about 100 kPa, or
about 50 kPa). The operating pressure of TSRU (36) is lower than
the pressure of TSRU (16). That is, TSRU (36) may be operated below
atmospheric pressure. TSRU (36) may be operated at about 75.degree.
C. to about 100.degree. C., or about 82.degree. C. to about
90.degree. C., or about 85.degree. C. to about 90.degree. C., or
about 90.degree. C. Because TSRU (36) may be operated at lower
pressures and at below atmospheric pressure, TSRU (36) may be
operated at lower temperatures, for instance about 65.degree. C. to
about 80.degree. C., or about 70.degree. C. As with TSRU (16), the
internals (50) of TSRU (36) are illustrated as a plurality of
interior, vertically spaced shed decks. Inert gas or steam (52) may
be introduced below the internals (50), and above a tailings pool
in the bottom of TSRU (36).
[0040] A third TSRU 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.
[0041] In one embodiment, one, two, or more than two TSRU's are
used where the froth treatment tailings solvent recovery is
affected in the absence of "mechanical means used to substantially
break up asphaltene agglomerates or to prevent the agglomeration of
asphaltene". The term "agglomerates" as used herein is not limited
by shape and includes flocs and aggregates. The term
"substantially" is used here to exclude means that does not, to a
substantial extent, mechanically break up asphaltene agglomerates
or prevent the agglomeration of asphaltene. Non-limiting examples
of "mechanical means used to substantially break up asphaltene
agglomerates or to prevent the agglomeration of asphaltene" are the
agitation means described Canadian Patent No. 2,353,109 where the
tailings pool is agitated to the point where the asphaltenes are
dispersed, submerged and prevented from re-agglomerating and the
solids are maintained in suspension. In that patent, agitation may
be effected by a mechanical impeller, or an alternate agitation
means, such as a pump-around circuit to pump the slurry from the
top of the liquid pool to the lower part of the liquid pool or vice
versa. Another non-limiting example of such means are the shearing
conditions provided by pumps, mixers or other apparatuses,
described in Canadian Patent Application No. 2,454,942, which are
said to be preferably provided in the recycle circuit first, to
break up asphaltene flocs/aggregates and second, to enhance
recovery of solvent from the tailings. The "mechanical means used
to substantially break up asphaltene agglomerates or to prevent the
agglomeration of asphaltene" does not include means, the purpose of
which is unrelated to breaking up asphaltene agglomerates or to
preventing agglomeration of asphaltenes, such as a pump disposed
before or after the TSRU as shown herein.
[0042] Water may be recovered from the solvent depleted tailings
stream (34 or 47) downstream of the slurry pump and may be recycled
for re-use upstream of the tailing solvent recovery unit in order
to recover valuable heat contained in the water, thus reducing the
energy requirements of the process. For example, recovered water
may be combined with the dilution water (25) upstream of the
tailings solvent recovery unit but this is not to provide
additional agitation to the unit.
Example 1
[0043] In a small scale pilot test, a run was operated at about
atmospheric pressure without shearing or agitation in or around
TSRU (16) with internals (46) and successfully resulted in solvent
loss of less than 2.8 bbl per thousand barrels of bitumen product
(6). The addition of steam resulted in a further reduction to less
than 1.0 bbl of solvent loss per thousand barrels of bitumen
product. A typical TSRU (16) tailings (34) sample was then
subjected laboratory scale vacuum separation tests to simulate the
performance of the second stage TSRU (36). These results are shown
in Table 1.
TABLE-US-00001 TABLE 1 Solvent Recovery Performance Pressure
Average solvent Solvent Loss (bbl/ (atm abs) content (wt %) 1000
bbls of bitumen) 1.00 0.028 1.18 0.79 0.024 0.97 0.59 0.015
0.63
[0044] Pumps are used to maintain a specified level in each TSRU
and the vessels are sized to maintain a high downward velocity of
the slurry.
[0045] As discussed herein, it has been discovered that recovery of
solvent from asphaltene agglomerates in a TSRU is effective without
agitation in or around the TSRU. Thus, mechanical means used to
substantially physically break up asphaltene agglomerates or to
prevent the agglomeration of asphaltene may be omitted. In addition
to the embodiments discussed herein using internals, in another
embodiment, there is provided a process for recovering paraffinic
solvent from froth treatment tailings produced in the treatment of
bitumen froth comprising: introducing the froth treatment tailings
into a tailings solvent recovery unit (TSRU) (which may or may not
have internals); introducing inert gas or steam into a liquid pool
formed in the bottom of the TSRU to vaporize at least a portion of
the paraffinic solvent; and removing the vaporized solvent from the
TSRU; wherein the froth treatment tailings contain asphaltenes; and
wherein the at least a portion of the solvent is vaporized from
asphaltene agglomerates. In one embodiment, the process is affected
in the absence of mechanical means used to substantially physically
break up asphaltene agglomerates or to prevent the agglomeration of
asphaltene.
[0046] The phrase "to vaporize at least a portion of the paraffinic
solvent" is used herein to make clear that not all of the solvent
is necessarily vaporized. In certain embodiments, the percentage,
by volume, of solvent that is vaporized is: at least 70%, at least
80%, at least 90%, at least 95%, at least 98%, at least 99%, at
least 99.5%, at least 99.9%, or at least 99.9%.
[0047] In the preceding description, for purposes of explanation,
numerous details are set forth in order to provide a thorough
understanding of the embodiments of the invention. However, it will
be apparent to one skilled in the art that these specific details
are not required in order to practice the invention
[0048] The above-described embodiments of the invention are
intended to be examples only. Alterations, modifications and
variations can be effected to the particular embodiments by those
of skill in the art without departing from the scope of the
invention, which is defined solely by the claims appended
hereto.
* * * * *