Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR TREATING BITUMEN USING DEMULSIFIERS
This invention relates to a froth treatment process for
treating bitumen using demulsifiers.
BACKGROUND
Bitumen froth is an intermediate material, produced in a
water-based oil sands extraction process, and is typically a
mixture of bitumen, water, and mineral solids. Bitumen
froth treatment processes are designed to remove
contaminants (water and mineral solids) from the froth and
to produce high-quality bitumen.
Various techniques have been described to recover the
bitumen from oil sand froth, including in Canadian Patent
No. 2,149,737, describing a process in which a paraffinic
solvent is mixed with oil sand froth and fed to a first
settler in which gravity separation is used to recover
dilute bitumen product.
The paraffinic bitumen froth treatment process also removes
a portion of asphaltenes in the froth from the bitumen.
In paraffinic froth treatment processes, the bitumen froth
may be mixed with a paraffinic solvent (e.g., pentane or
hexane or a mixture of both) in a multi-stage counter-
current decantation (CCD) process circuit (see, for example,
Canadian Patent Application Nos. 2,350,907 and 2,521,248,
which describe paraffinic froth treatment processes
including CCD). A solvent diluted bitumen (dilbit),
substantially free of solids and water, and partially
deasphalted is produced as overflow in the CCD process. The
underflow comprises water, mineral solids, and rejected
asphaltenes which may be withdrawn from the CCD circuit.
The underflow obtained from the CCD process contains a
certain amount of solvent and maltenes; the solvent can be
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recovered in a tailings solvent recovery unit (TSRU) and may
then be sent to a tailings pond.
A separation assembly for a CCD process may comprise
multiple settlers (see, for example, Canadian Patent
Application No. 2,350,907). Each settler may have an upper
outlet, for removal of an overflow stream, located at or
near the top of the settler, a lower outlet, for removal of
an underflow stream, located at or near the bottom of the
settler, and an inlet, for the feed stream, located between
the bottom and top of the settler. The feed stream to a
first settler comprises oil sand froth that has been
contacted with a solvent bearing stream. The feed stream to
each settler after the first settler comprises the underflow
stream from the previous settler that has been contacted
with a solvent bearing stream. The streams are contacted
using mixing means.
When an oil sand froth is mixed with an effective amount of
a solvent such as a paraffinic solvent, a transformation is
initiated, resulting in the formation of different phases of
material, and typically at least four distinct phases of
material.
The four phases can broadly be described as follows:
1) a dilute bitumen phase (dilbit), mainly comprising
solvent and high value components of the bitumen, known
as maltenes;
2) an aqueous phase, mainly comprising water, water-
soluble materials and dispersed fine solids, such as
clays;
3) an inorganic particulate phase, mainly comprising sand;
and
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4) an organic particulate phase, mainly comprising
precipitated asphaltenes, with water and clays
incorporated in the aggregate structure of the
asphaltenes.
Each of the four phases is generally present in each settler
of the paraffinic froth treatment process. The difference
in density between each of the phases is such that gravity
Oeparation can take place in each of the settlers. Because
t,!he density of the dilute bitumen phase is less than that of
dhe other phases, it can be withdrawn as an overflow stream.
Because the density of the other phases is greater than that
di the dilute bitumen phase, they tend to sink in the dilute
bitumen phase and can be withdrawn as an underflow stream
from each settler. Each of the other phases exhibit a
tendency to sink that varies according to its density and
particle size.
When multiple settlers are used in a CCD process, the
Underflow stream from a first settler is fed to the next
Settler in series in which further gravity separation
dccurs. The underflow stream may be mixed with additional
dolvent.
Two, three or more settlers may be employed until the
underflow stream from the last s,ettler no longer contains
sufficiently high recoverable amounts of maltenes. The
overflow stream from each settler, other than the first
settler, may be mixed with, and become the source of solvent
for, the underflow stream fed to an upstream settler.
The above-described process can be carried out over a range
of temperatures and pressures. If the process is carried
out at a temperature of about thirty degrees Celsius and at
atmospheric pressure, sometimes called the low temperature
froth treatment (LTFT) process, then typically three or more
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settlers may be needed to recover essentially all of the
maltenes from the oil sand froth.
If the process is carried out at higher temperatures and
pressures, sometimes called the high temperature treatment
(HTFT) process, the separation typically proceeds at a
higher rate and therefore fewer separations may be required
to recover essentially all of the maltenes from the oil sand
froth. In the high temperature froth treatment process,
t'!ypically two settlers are used, and the temperature in each
Settler is normally fifty or seventy-five degrees Celsius or
higher.
In a froth treatment CCD process, settler feeds to settlers
are mixed via settler feed mixers. The mixers can be in-
line static mixers and/or impeller tank mixers, for example.
Mixing facilitates the dissolution of bitumen in the
solvent, in order to achieve an efficient bitumen recovery
to the CCD overflow.
~owever, the mixing also creates emulsification and
dispersion of water droplets in the dilbit phase. The water
dlroplets may be stabilized by the surfactants that originate
from bitumen (e.g., naphthenic components), clays, and
asphaltenes. The water droplets can lead to a dilbit-
continuous underflow, and a significant amount of dilbit can
remain in the CCD underflow if the droplets are stable and
do not coalesce rapidly. High dilbit in CCD underflow is
not desirable as it results in lower CCD bitumen recovery
and higher solvent content in TSRU feed.
The paraffinic froth treatment process rejects a portion of
bitumen asphaltenes into CCD underflow. As a consequence,
the potentially adhesive asphaltenic solids may deposit and
accumulate in CCD settlers. Asphaltenic solids deposition
is more likely to occur when the CCD settler underflow is
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not water continuous. When the CCD settler underflow is not
water continuous, the asphaltenic solids are not well
dispersed in water and subsequently are not carried out of
settlers with the underflow water phase.
Therefore, in separating bitumen from oil sand froth in a
CCD process, it is desirable that the water droplets
coalescence at a sufficient rate so that the amount of
dilbit in the CCD underflow is minimized and so that a
water-continuous underflow may form.
SUMMARY
According to an aspect of the present invention, there is
provided a method for separating an oil sand froth in a
paraffinic froth treatment process, the method comprising
adding a demulsifier to a multi-stage counter-current
decantation (CCD) circuit.
In one embodiment of the present invention, there is
provided a method for separating an oil sand froth
comprising mixing the oil sand froth with a paraffinic
solvent to form a fluid mixture; feeding the fluid mixture
into a settler having a lower fluid outlet near a bottom
thereof and an upper fluid outlet near a top thereof;
feeding a demulsifier into the settler; inducing the fluid
mixture to be separated by gravity separation in the settler
into a bitumen enriched, water and solids depleted, upper
fluid fraction and a bitumen depleted, water and solids
enriched, lower fluid fraction; inducing the bitumen
enriched, water depleted, upper fluid fraction to flow into
the upper fluid outlet and inducing the water enriched,
bitumen depleted, lower fluid fraction to flow into the
lower fluid outlet; and agitating the fluid mixture with
mixing means such that the bitumen depleted, water and
solids enriched, lower fluid fraction within the settler
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comprises a substantially homogeneous mixture of solids and
liquids.
In another embodiment of the present invention, there is
provided a method for separating an oil sand froth
comprising: (a) mixing the oil sand froth with a paraffinic
solvent to form a fluid mixture; (b) feeding the fluid
mixture into a first settler having a lower fluid outlet
near a bottom thereof and an upper fluid outlet near a top
thereof, and optionally adding a demulsifier to the first
settler; (c) inducing the fluid mixture to be separated by
gravity separation in the settler into a bitumen enriched,
vi ater and solids depleted, upper fluid fraction and a
bitumen depleted, water and solids enriched, lower fluid
fraction; (d) inducing the bitumen enriched, water depleted,
upper fluid fraction to flow into the upper fluid outlet and
inducing the water enriched, bitumen depleted, lower fluid
f',raction to flow into the lower fluid outlet; (e) agitating
the fluid mixture with mixing means such that the bitumen
epleted, water and solids enriched, lower fluid fraction
ithin the settler comprises a substantially homogeneous
ixture of solids and liquids; (f) feeding a fluid mixture
omprising the bitumen depleted, water and solids enriched,
l!ower fluid fraction via the lower fluid outlet into a
second settler having a lower fluid outlet near a bottom
thereof and an upper fluid outlet near a top thereof, and
optionally adding a demulsifier to the second settler via
the lower fluid outlet of the first settler; (g) inducing
the fluid mixture to be separated by gravity separation in
the second settler into a bitumen enriched, water and solids
depleted, upper fluid fraction and a bitumen depleted, water
and solids enriched, lower fluid fraction; (h) inducing the
bitumen enriched, water depleted, upper fluid fraction to
flow into the upper fluid outlet of the second settler;(i)
inducing the water enriched, bitumen depleted, lower fluid
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fraction to flow into the lower fluid outlet of the second
settler; (j) feeding a fluid mixture comprising the bitumen
depleted, water and solids enriched, lower fluid fraction
via the lower fluid outlet of the second settler into a
third settler having a lower fluid outlet near a bottom
thereof and an upper fluid outlet near a top thereof; and
optionally adding a demulsifier to the third settler via the
lower fluid outlet of the second settler; (k) inducing the
fluid mixture to be separated by gravity separation in the
t,hird settler into a bitumen enriched, water and solids
lepleted, upper fluid fraction and a bitumen depleted, water
and solids enriched, lower fluid fraction; (1) inducing the
b,itumen enriched, water depleted, upper fluid fraction to
fllow into the upper fluid outlet of the third settler; (m)
inducing the water enriched, bitumen depleted, lower fluid
fraction to flow into to the lower fluid outlet of the third
settler; and wherein a demulsifier is added to at least the
first, second or third settler.
BRIEF DESCRIPTION OF FIGURES
F!,igure 1 is a flow scheme of three settlers in a LTFT
pirocess for separating bitumen from an oil sand froth
according to an embodiment of the invention.
Figure 2 is a flow scheme of two settlers in a HTFT process
for separating bitumen from an oil sand froth according to
an embodiment of the invention.
DESCRIPTION
It has been observed that a demulsifier may be added to
reduce the amount of dilbit in the underflow and to help
reduce accumulation of asphaltenes in the settlers.
Suitable demulsifiers are surface-active chemicals
(!surfactants), which tend to preferentially stay at the
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interface of water droplets in the underflow and
subsequently facilitate coalescence of water droplets. The
coalesced water droplets may thus form a water-continuous
CCD settler underflow with asphaltenic solids dispersed
therein.
Demulsifiers that may be used in the present invention are
not particularly limited. Any demulsifier that aids in
water coalescence in the underflow may be suitable for use
iln the present invention, including commercially available
demulsifiers. The suitability of any particular demulsifier
rrlay be readily determined by a person skilled in the art
through routine experimentation. Whether a particular
demulsifier is suitable may depend on a number of
conditions, such as, for example and without limitation,
process temperature; froth characteristics, such as the
composition of the froth, including the presence of surface
active fines or natural organic surfactants in the froth;
niixing conditions; amount of asphaltene rejection during
froth treatment; and the use of other process aids upstream
qf the froth treatment circuit.
f demulsifier to be added varies, depending on
'~ he amount o
factors such as the type of demulsifier, the type of mixer
aind intensity of mixing, which froth treatment process is
tised (HTFT or LTFT), and other factors, including those that
influence choice of demulsifier. For instance, amounts of
demulsifier in the range of about 10 ppm to about 1000 ppm
may be used, including any intermediate value or range. By
way of further example, a dosage range of about 30 ppm to
about 200 ppm may be suitable in some embodiments of the
present invention, including any intermediate value or
range. The skilled person will be able to determine whether
a demulsifier is suitable and in what amount through routine
experimentation.
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A demulsifier may be added to any or all of the settlers,
including directly into the settler feeds (e.g., to a first
settler feed, a second settler feed, etc.) at any stage of a
CCD process.
Addition of a suitable demulsifier in an effective amount
can decrease the formation of stable water droplets in the
dilbit phase, and facilitate coalescence of the water
droplets before dispersion in the dilbit. The water
droplets in the settler feeds may then coalesce and a water-
continuous underflow may then be obtained. The faster
formation of a water-continuous underflow in a settler may
then minimize the entrained dilbit. For example, there may
then be minimal entrained dilbit at the upper interface of
settler underflow. This means that the entrained dilbit in
settler underflow will be reduced as the underflow exits the
bottom of the settler.
Addition of an effective amount of demulsifier to a CCD
process to aid in the formation of a water-continuous
underflow can assist in dispersion of asphaltenic solids in
water of the underflow, which solids may then be carried out
of the settler by the underflow. This helps to mitigate the
problem of asphaltenic solids deposition and accumulation in
dCD settlers.
I!n one embodiment of the invention, a low temperature froth
treatment (LTFT) process may be used comprising a three-
stage CCD. In such a process, first stage settler feed is a
mixture of froth and second stage overflow. A second stage
settler feed is a mixture of first stage underflow and third
stage overflow. The third stage settler feed is a mixture
of second stage underflow and fresh solvent. The LTFT
process is typically operated at about 30 C.
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In another embodiment of the present invention, a high
temperature froth treatment (HTFT) process may be used
comprising a two-stage CCD. In this process, a first stage
settler feed is a mixture of froth and second stage
overflow. The second stage settler feed is a mixture of
first stage underflow and fresh solvent. The HTFT process
dosign temperature is typically above 50 C, and usually
lout 75 C.
F'gure 1 shows an embodiment of the invention comprising an
a sembly of three stage settlers (1), (2), (3) in a LTFT
process. In each settler (1), (2) and (3), an oil sand
froth is separated into a bitumen enriched, water and solids
depleted, upper fluid fraction, and a bitumen depleted,
water and solids enriched, lower fluid fraction.
The first settler (1) comprises a fluid inlet (4), an upper
fl;uid outlet (5) and a lower fluid outlet (6).
The second settler (2) comprises an upper fluid outlet (7),
al,lower fluid outlet (8) and a fluid inlet (9), which is
Onnected to the lower fluid outlet (6) of the first settler
(]~) .
TAe third settler (3) comprises an upper fluid outlet (10),
a lower fluid outlet (11) and a fluid inlet (12), which is
connected to the lower fluid outlet (8) of the second
settler (2) and to a paraffinic solvent supply conduit (35).
Each fluid inlet (4), (9) and (12) may be equipped with a
mixer (13), (14) and (15) for mixing a stream comprising
froth, solvent and demulsifier in the case of mixer (13) and
for mixing streams comprising underflow from the preceding
mixer, solvent and demulsifier in the case of mixers (14)
and (15). Solvent need not be recycled solvent as shown in
Figure 1. Solvent introduced into feed streams may be
recycled solvent from downstream mixers, and/or may be
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solvent newly introduced into CCD process. As the skilled
person will appreciate, it may not be necessary to add
demulsifier to each feed stream. Also, demulsifier may be
added directly into the settlers, rather than into feed
streams. Other chemical agents (such as, for example and
without limitation, an asphaltene dispersant used to prevent
asphaltene deposition in the CCD settlers) could also be
added to feed streams and/or settlers. Chemical addition
(including addition of demulsifier) may be made at any time
in the process, including before or after addition of
sOlvent to feed streams, or directly to solvent prior to
mixing with froth or underflow streams.
Pumps (17) and (18) may be arranged in fluid inlet (9) and
(12) of second and third settlers (2) and (3). A pump may
also be arranged in the fluid inlet of first settler (1).
Pumps (20) ,(21) and (22) may be arranged in fluid outlets
(7) and (10) of the first, second and third settlers
(1), (2) and (3). A pump (19) may be arranged in lower fluid
outlet (11) of third settler (3).
The mixing of the demulsifier with the settler feeds may be
ac$complished by mixers (13) to (15). Mixing may also be
aclcomplished within pumps (17) to (19) and/or when the
d mulsifier and settler feeds are travelling to the
s ttlers.
The bitumen-enriched fractions flowing through the fluid
outlets (7) and (10) of the second and third settlers (2)
and (3) may be re-injected partly into the inlets (4) and
(9) of the first and second settlers (1) and (2), as
illustrated by arrows (26) and (27). A solvent-diluted
bitumen (dilbit) substantially free of solids and water, and
partially deasphalted, is produced and can be recovered from
outlet (5) of the first settler, shown by arrow (36).
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A demulsifier may be added to fluid inlet (4) into the first
settler (1) as illustrated by arrow (28). Alternatively or
additionally, a demulsifier may be added to fluid inlet (9)
into the second settler (2), as illustrated by arrow (29).
Alternatively or additionally, a demulsifier may be added to
fluid inlet (12) into the third settler (3), as shown by
arrow (30). In an embodiment, a demulsifier is added to
only one fluid stream and in another embodiment the
demulsifier is added to one or more of fluid inlet streams
(4), (9) or (12). In other embodiments, the demulsifier may
be added directly into one or more of settlers (1), (2) or
(3), or the demulsifier may be added into one or more fluid
streams and directly into one or more settlers. Figure 1
shows the added demulsifier being mixed with fluid streams
by mixer(s) (13), (14) or (15).
Arrow (37) shows removal of bitumen depleted, water and
solids enriched, underflow obtained from the third settler
(3), which underflow may be sent to a TSRU for solvent
rQcovery.
Fi.gure 2 shows another embodiment of the present invention
cgmprising an assembly of two settlers (41) and (42) in a
H~FT process.
In each separation vessel (41) and (42), an oil sand froth
isi, separated into a bitumen enriched, water and solids
depleted, upper fluid fraction, and a bitumen depleted,
water and solids enriched, lower fluid fraction.
The first settler (41) comprises a fluid inlet (44), an
upper fluid outlet (45) and a lower fluid outlet (46). The
bitumen enriched upper fluid fraction flowing through the
upper fluid outlet (45) can be recovered and injected into a
first overflow drum (70).
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The second settler (42) comprises an upper fluid outlet
(47), a lower fluid outlet (48) and a fluid inlet (49),
which is connected to the lower fluid outlet (46) of the
first settler (41). The bitumen enriched upper fluid
fraction flowing through the upper fluid outlet (47) may be
recovered and injected into a second overflow drum (71) and
can then be re-injected to the oil sand froth slurry in the
fluid inlet (44) of the first settler (41), as illustrated
by arrow (60).
Mixers (61) and (62) can be arranged in the fluid inlets
(44) and (49) of the first and second settlers (41) and
(42). Pump (64) may be arranged in the fluid inlet (49) of
se''cond settler (42). A pump may also be arranged in the
fluid inlet of first settler (41). Pumps (65) and (66) can
be arranged in the fluid outlets of overflow drums (70) and
(7,l) , and a pump (67) can be arranged in the fluid outlet of
seicond settler (42).
A Illdemulsifier may be added into fluid inlet (44) into the
filrst settler (41), as illustrated by arrow (80).
Alternatively or additionally, a demulsifier may be added
i to fluid inlet (49) into the second settler (42), as
il,ilustrated by arrow (81). In another embodiment, a
demulsifier may be added directly to either or both the
fi,rst settler (41) and second settler (42), optionally
toigether with addition of demulsifier to either or both
fluid inlets (44) or (49)
Mixer (61) mixes the feedstock entering the first settler
(41), which comprises the froth, solvent, demulsifier and
optionally additional chemical agents. Mixer (62) serves to
contact the feedstream entering the second settler (42),
which comprises underflow stream from the first settler
(42), solvent, demulsifier and optionally additional
chemical agents.
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The mixing of the demulsifier with the settler feeds may be
accomplished by mixers (61) and (62). Mixing may also be
accomplished within pump (64) and/or when the demulsifier
and settler feeds are travelling to the settlers.
Solvent introduced into the feed stream entering the first
settler (41) may be recycled solvent from settler (42),
and/or may be solvent newly introduced into CCD process. As
the skilled person will appreciate, it may not be necessary
to add demulsifier to each feed stream. Also, demulsifier
may be added directly into the settlers, rather than into
feed streams. Other chemical agents (such as, for example,
anasphaltene dispersant) may also be added to feed streams
and/or settlers. Chemical addition (including addition of
demulsifier) may be made at any time in the process,
including before or after addition of solvent to feed
streams, or directly to solvent prior to mixing with froth
or underflow streams.
Arrow (75) shows removal of a bitumen depleted, water and
solids enriched, underflow from lower fluid outlet (48) of
se;cond settler (42), which underflow may be sent to a TSRU,
fo~ example.
Examples
A froth treatment pilot process was used to test the effect
of chemical addition on an oil sand froth. The pilot
process used a 5" internal diameter glass pressure column as
one of the CCD settlers. With proper illumination, the
behaviour of the CCD underflow was observed visually. In
particular, the velocity of the underflow was determined by
selecting distinct water droplets and solids in the
underflow and determining the time for the selected water
droplets to travel a known distance.
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When the CCD process was operated without demulsifier
addition, distinct water droplets were observed in the CCD
underflow after being in the CCD underflow for several
minutes. In comparison, when demulsifier was added water
droplets coalesced within a few seconds. A larger downward
moving velocity of the water droplets in the upper portion
of the CCD settler underflow was also observed compared to
when demulsifier was added. (As used in this Example, the
"upper portion" of the CCD settler refers to the about 10%
of the total underflow phase in the settler which is closest
to the dilbit phase.) The settler underflow was observed to
be dilbit-continuous. As a consequence, the CCD underflow
contained a large amount of entrained dilbit.
It was observed that the moving velocity of the water
droplets generally conformed to the following equation:
olul - 02u2
where 0 is the volume fraction of the dispersed water phase
and uis the downward moving velocity of the water droplets.
The equation essentially states the principle of equal
flluxes at locations 1 and 2.
The downward velocity of the water droplets in the upper
portion of the CCD was observed to be as high as 2 times the
dotwnward velocity as compared to the velocity that would be
expected if all droplets were coalesced (i.e., water-
continuous underflow).
The velocity (v) of the water-based underflow may be
calculated using the mass flow of the underflow (MF). The
mass flow of a water-continuous underflow, at the CCD
outlet, can be obtained based on the mass balance. The
column internal area (A) and the underflow density are known
va',lues. MF is related to v by the following equation:
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MF = A x v x (underflow density)
This equation applies to the underflow composition. If the
mass flow of a water-continuous underflow is used (from the
mass balance calculation), the resulting velocity of a
water-continuous underflow may be determined.
When the CCD process was operated with demulsifier addition,
no stable water droplets were observed. As soon as the
droplets settled at the upper interface of the settler
underflow, fast (i.e., almost instantaneous) coalescence of
the droplets was observed to take place with a water-
continuous underflow. The fast formation of a water-
continuous underflow in settler minimizes the entrained
dilbit, as there was reduced entrained dilbit in settler
underflow as the underflow exited the bottom of the settler.
Asphaltenic solids were dispersed in water and carried out
of settler by the water-continuous underflow.
When the CCD process was operated with demulsifier addition,
reduced asphaltenic solids deposition was observed.
Asphaltenic solids were dispersed in water and carried out
of settler by the water-continuous underflow.
The formation of small stable water droplets is also
affected by the mixing intensity of the settler feed. In
general, larger water droplets were observed with lower
mixing intensity. The second and/or third stage mixers of
the LTFT process and the second stage mixer of the HTFT
process may be absent (or, the mixers could be otherwise
disengaged) in order to reduce underflow solvent content.
However, overall bitumen recovery to the CCD overflow may be
compromised if mixing intensities of CCD settler feeds are
insufficient.
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Although the foregoing invention has been described in some
detail by way of illustration and example for purposes of
clarity of understanding, it is readily apparent to those of
ordinary skill in the art in light of the teachings of this
invention that certain changes and modifications may be made
thereto without departing from the spirit or scope of the
appended claims.
The citation of any publication, patent or patent
application is for its disclosure prior to the filing date
and should not be construed as an admission that the present
invention is not entitled to antedate such publication,
patent or patent application by virtue of prior invention.
It must be noted that as used in the specification and the
appended claims, the singular forms of "a", "an" and "the"
include plural reference unless the context clearly
indicates otherwise.
Unless defined otherwise all technical and scientific terms
usFd herein have the same meaning as commonly understood to
one of ordinary skill and the art to which this invention
belongs.
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