Note: Descriptions are shown in the official language in which they were submitted.
CA 02809956 2013-03-18
APPARATUS, SYSTEM AND METHOD FOR PUMPING GASEOUS FLUID
BACKGROUND OF THE INVENTION
[001] 1. FIELD OF THE INVENTION
[002] Embodiments of the invention described herein pertain to the field of
electric submersible
pumps.
[003] More particularly, but not by way of limitation, one or more embodiments
of the invention
enable an apparatus, system and method for pumping gaseous fluid in electric
submersible pump
down-hole applications.
[004] 2. DESCRIPTION OF THE RELATED ART
[005] Fluid, such as gas, oil or water, is often located in underground
formations. In such situations,
the fluid must be pumped to the surface so that it can be collected,
separated, refined, distributed
and/or sold. Centrifugal pumps are typically used in electric submersible pump
applications for
lifting well fluid to the surface. Centrifugal pumps impart energy to a fluid
by accelerating the fluid
through a rotating impeller paired with a stationary diffuser. The rotation
confers angular momentum
to the fluid passing through the pump. The angular momentum converts kinetic
energy into
pressure, thereby raising the pressure on the fluid and lifting it to the
surface. Multiple stages of
impeller and diffuser pairs may be used to further increase the pressure.
[006] Conventional centrifugal pumps are designed to handle fluid consisting
mainly of liquids.
However well fluid often contains gas in addition to liquid. Currently
available submersible pump
systems are not appropriate for pumping fluid with a high gas to liquid ratio.
Particularly,
submersible pump systems need to be better suited to manage gas contained in
well fluid. When
pumping gas laden fluid, the gas may separate from the other fluid due to the
pressure differential
created when the pump is in operation. If there is a sufficiently high gas
volume fraction, typically
around 10% to 15%, the pump may experience a decrease in efficiency and
decrease in capacity or
head (slipping). If gas continues to accumulate on the suction side of the
impeller it may entirely
block the passage of other fluid through the impeller. When this occurs the
pump is said to be "gas
locked" since proper operation of the pump is impeded by the accumulation of
gas. As a result,
careful attention to gas management in submersible pump systems is needed in
order to improve the
production of gas laden fluid from subsurface formations.
[007] A typical impeller of a centrifugal pump is shown in FIGs. lA and 1B. In
FIG. 1A, closed
impeller 100 is shown with six evenly spaced conventional vanes 105. For
illustration purposes
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only, upper conventional shroud 110 and lower conventional shroud 115 are
shown in FIG 1B, but
are not shown in FIG. 1A. FIG. 1B shows a cross sectional view of closed
impeller 100 with two
conventional shrouds, upper conventional shroud 110 and lower conventional
shroud 115. In FIG.
1B, conventional hub 125 is long and hollow and connected to lower
conventional shroud 115, upper
conventional shroud 110 and conventional vanes 105. Conventional hub 125
slides over
conventional shaft 130 and is keyed to conventional shaft 130, which causes
closed impeller 100 to
rotate with conventional shaft 130. Closed impeller 100 rotates
counterclockwise or clockwise with
shaft 130. Apertures 120 (shown in FIG. 1A) balance the pressure on each side
of closed impeller
100. Conventional closed impeller 100 has a suction specific speed of about
6000.
[008] Closed impeller 100 is paired with a conventional stationary diffuser,
such as that shown in
FIG 2, such that each impeller rotates within (inward of) the diffuser to
which it is paired. The
diffuser does not rotate, but is mounted co-axially with the impeller and
nests on the diffuser of the
previous stage. Typically there is a clearance gap between the diffuser and
impeller to which it is
paired. This conventional clearance gap is typically about 0.015 inches to
about 0.02 inches in width
for conventional semi-open impellers.
[009] Currently, gas separators are sometimes used in an attempt to address
the problems caused by
gas in produced fluid. Gas separators attempt to remove gas from produced
fluid prior to the fluid's
entry into the pump. However it is often infeasible, costly or too time
consuming to ascertain the
correct type of pump and separator combination which might be effective for a
particular well, and
even if the correct arrangement is ascertained, the separator may not remove
enough gas to prevent a
loss in efficiency and/or prevent gas locking.
[0010] In the case of an electric submersible pump (ESP), a failure of the
pump or any support
components in the pump assembly can be catastrophic as it means a delay in
well production and
having to remove the pump from the well for repairs. A submersible pump system
capable of
homogenizing produced gaseous fluid would be an advantage in all types of
submersible assemblies.
[0011] Currently available pump assemblies do not contain components to
satisfactorily
homogenize gas laden fluid and prevent gas locking. This shortcoming decreases
the efficiency and
overall effectiveness of the pump assembly. Therefore, there is a need for an
apparatus, system and
method for pumping gaseous fluid in electric submersible pump applications.
BRIEF SUMMARY OF THE INVENTION
[0012] One or more embodiments of the invention enable an apparatus, system
and method for
pumping gaseous fluid.
2
[0013] An apparatus, system and method for pumping gaseous fluid are
described. The impeller
of an illustrative embodiment comprises an increased inlet area. In some
embodiments, the
increased inlet area is between about 1.75 and about 2.5 times the size of an
inlet area of a
conventional impeller. In some embodiments, the impeller comprises a single
shroud located on a
bottom side of the impeller. In some embodiments, at least two untruncated
vanes extend
substantially upstream from the single shroud, and at least two truncated
vanes extend substantially
upstream from the single shroud, wherein each truncated vane sits at a mid-
pitch location between
untruncated vanes starting from the bottom side of the impeller. In some
embodiments, the
truncated vanes are between about 50% and about 75% of the chord length of the
untruncated
vanes. In some embodiments, the single shroud extends radially about a hub. In
certain
embodiments the suction specific speed of the impeller is between about 8000
to about 12000.
[0014] The centrifugal pump of an illustrative embodiment comprises an
impeller inward of a
diffuser and an increased clearance gap between the impeller and the diffuser,
the impeller
comprising a top side and a bottom side, wherein the top side is open to the
diffuser, and wherein
the impeller further comprises a single shroud located on the bottom side of
the impeller and
arranged radially about a hub, an untruncated vane extending substantially
upstream from the
single shroud, and a truncated vane extending substantially upstream from the
single shroud. In
some embodiments there are at least two untruncated vanes, wherein a truncated
vane sits at a mid-
pitch location between the at least two untruncated vanes starting from the
bottom side of the
impeller. In certain embodiments, the increased clearance gap is between about
0.060 inches and
about 0.180 inches wide.
[0015] The method of an illustrative embodiment may include a method for
pumping gaseous fluid
comprising placing a centrifugal pump into a well containing gaseous fluid,
operating the pump to
induce the fluid to flow towards the surface of the well, causing at least a
portion of the fluid to
flow through an increased clearance gap between an impeller and a diffuser,
and minimizing phase
separation of the fluid by reducing a pressure differential between a pressure
side and a suction
side of an impeller vane. In some embodiments the phase separation of the
fluid is minimized by
an impeller with an increased inlet area. In some embodiments, the inlet area
is increased by
replacing an impeller vane with a truncated vane.
10015a1 In another illustrative embodiment, a semi-open impeller for an
electric submersible pump
(ESP) assembly includes a single shroud coupled to a bottom side of an
impeller. A top side of
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the impeller is open to a diffuser. The semi-open impeller further includes at
least two untruncated
vanes extending substantially upstream from the single shroud, and at least
two truncated vanes
extending substantially upstream from the single shroud. Each truncated vane
sits at a mid-pitch
location between untruncated vanes starting from the bottom side of the
impeller.
[0015b] In another illustrative embodiment, an electric submersible pump (ESP)
assembly
includes an impeller inward of a diffuser. The impeller includes a top side
and a bottom side. The
top side is open to the diffuser. The impeller further includes a hub, and a
single shroud coupled
to the bottom side of the impeller and arranged radially about the hub. The
impeller further
includes an untruncated vane extending substantially upstream from the single
shroud, and a
truncated vane extending substantially upstream from the single shroud. The
truncated vane
extends from an outer circumference of the single shroud and is between about
50% and about
75% of a chord length of the untruncated vane as measured from the hub. The
impeller further
includes a clearance gap between the impeller and the diffuser, wherein the
clearance gap is
between about 0.06 inches and about 0.18 inches wide.
[0015c] In another illustrative embodiment, an improved system for pumping
gaseous fluids from
a well employing an electric submersible pump (ESP) includes an ESP assembly
including an
impeller inward of a diffuser. The impeller includes a top side and a bottom
side. The top side is
open to the diffuser. The impeller includes a hub, and a single shroud located
on the bottom side
of the impeller and arranged radially about the hub. The impeller further
includes an untruncated
vane extending substantially upstream from the single shroud, and a truncated
vane extending
substantially upstream from the single shroud. The impeller further includes
an increased inlet
area of the impeller. The increased inlet area is between about 1.75 and about
2.5 times the inlet
area of a conventional inlet area. The ESP assembly is placed into a well
containing gaseous fluid
and operated such that at least a portion of a liquid and a gas in the gaseous
fluid are homogenized.
[0016] In further embodiments, features from specific embodiments may be
combined with
features from other embodiments. For example, features from one embodiment may
be combined
with features from any of the other embodiments. In further embodiments,
additional features may
be added to the specific embodiments described herein.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above and other aspects, features and advantages of the
illustrative embodiments will be
more apparent from the following more particular description thereof,
presented in conjunction with
the following drawings wherein:
[0018] FIG. lA illustrates a plan view of an impeller of the prior art.
[0019] FIG. 1B illustrates a cross sectional view of an impeller of the prior
art.
[0020] FIG. 2 illustrates a perspective view of a diffuser of the prior art.
[0021] FIG. 3 illustrates one embodiment of an exemplary electric submersible
pump (ESP)
system.
[0022] FIG. 4A illustrates a perspective view of one embodiment of a semi-open
impeller.
[0023] FIG. 4B illustrates a perspective view of one embodiment of a semi-open
impeller.
[0024] FIG. 5 is a partial cross sectional view taken along line 5-5 of FIG. 3
of one embodiment of
an impeller.
[0025] FIG. 6 is a cross sectional view taken along line 6-6 of FIG. 3 of one
embodiment of a
centrifugal pump.
[0026] FIG. 6A is an enlarged view of one embodiment of the inlet area of a
centrifugal pump.
[0027] FIG. 7 is a flow chart illustrating an exemplary method of pumping
gaseous fluid.
[0028] While the invention is susceptible to various modifications and
alternative forms, specific
embodiments thereof are shown by way of example in the drawings and may herein
be described in
detail. The drawings may not be to scale. It should be understood, however,
that the embodiments
described herein and depicted in the drawings are not intended to limit the
invention to the particular
form disclosed, but on the contrary, the intention is to cover all
modifications, equivalents and
alternatives falling within the scope of the present invention as defined by
the appended claims.
DETAILED DESCRIPTION
[0029] An apparatus, system and method for pumping gaseous fluid will now be
described. In the
following exemplary description, numerous specific details are set forth in
order to provide a more
thorough understanding of embodiments of the invention. It will be apparent,
however, to an artisan
of ordinary skill that the present invention may be practiced without
incorporating all aspects of the
specific details described herein. In other instances, specific features,
quantities, or measurements
well known to those of ordinary skill in the art have not been described in
detail so as not to obscure
the invention. Readers should note that although examples of the invention are
set forth herein, the
claims, and the full scope of any equivalents, are what define the metes and
bounds of the invention.
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[0030] As used in this specification and the appended claims, the singular
forms "a", "an" and "the"
include plural referents unless the context clearly dictates otherwise. Thus,
for example, reference to
a vane includes one or more vanes.
[0031] "Coupled" refers to either a direct connection or an indirect
connection (e.g., at least one
intervening connection) between one or more objects or components. The phrase
"directly attached"
means a direct connection between objects or components.
[0032] "Bottom" or "lower" side of an impeller refers to the substantially
downstream side of an
impeller.
[0033] "Top" or "upper" side of an impeller refers to the substantially
upstream side of an impeller.
[0034] "Downstream" refers to the direction substantially with the primary
flow of fluid when the
centrifugal pump is in operation.
[0035] "Upstream" refers to the direction substantially opposite the primary
flow of fluid when the
centrifugal pump is in operation.
[0036] One or more embodiments of the invention provide an apparatus, system
and method for
pumping gaseous fluid for use in electric submersible pump applications. While
the invention is
described in terms of an oil or water production embodiment, nothing herein is
intended to limit the
invention to that embodiment.
[0037] The invention disclosed herein includes an apparatus, system and method
for pumping
gaseous fluid. In some embodiments, after intake into the pump assembly, gas
laden fluid may be
rotated by a centrifugal pump including a semi-open impeller. In some
embodiments, the semi-open
impeller includes only a single shroud arranged radially about a hub. In some
embodiments, a
truncated vane and an untruncated vane, which may be arranged
circumferentially about the hub,
may extend substantially upstream from the single shroud. In some embodiments,
the truncated vane
may be located at a mid-pitch location between two untruncated vanes starting
from the bottom side
of the impeller. In certain embodiments, the impeller may include two, three
or four of each
truncated and untruncated vanes which alternate around the hub. In some
embodiments, the impeller
may include an increased inlet area. In some embodiments, there may be an
increased clearance gap
between the impeller and a diffuser, through which the fluid may flow. The
features of the invention
may minimize phase separation of the fluid by reducing the pressure
differential between the
pressure side and suction side of an impeller vane. This may homogenize the
liquid and gas in the
fluid, increase the efficiency and performance of the pump, prevent gas
locking and reduce the
producing well's downtime.
[0038] In some embodiments, the vanes of the present disclosure are arranged
such that there is a
CA 02809956 2013-03-18
larger inlet area of the impeller than in conventional impeller designs.
Specifically, the reduction in
the number of untruncated vanes and addition of one or more truncated vanes of
the present
disclosure provide for additional open space in the inlet region of the
impeller. The impeller of an
illustrative embodiment may have between about 1.75 and 2.5 times the size of
the inlet area of a
conventional impeller. The additional open space may reduce the velocity of
the fluid passing
through the impeller, which assists in maintaining high positive pressure at
the impeller inlet. The
impeller of the present disclosure is capable of operating with higher suction
specific speed as
compared to conventional impellers. In some embodiments, the impeller of the
present disclosure
may operate at about 8000 to about 12000 suction specific speed.
[0039] The invention includes a centrifugal pump for electric submersible pump
(ESP) systems.
FIG. 3 illustrates one embodiment of an exemplary ESP assembly for use in the
system of the
invention. This assembly may be located in an underground well during
operation. In FIG. 3, the
centrifugal pump of an illustrative embodiment comprises ESP charge pump 200,
which is located
downstream of ESP intake 210. As shown in in FIG. 3, fluid enters the ESP
assembly through fluid
intakes 215 on ESP intake 210. ESP charge pump 200 may homogenize fluid prior
to the fluid
entering ESP primary pump 220.
[0040] In some embodiments, a gas separator (not shown) may be located between
ESP intake 210
and ESP charge pump 200 to reduce the gas content of the fluid prior to the
fluid entering ESP
primary pump 220. When used, the gas separator may be the intake surface for
the ESP pump
system. In certain embodiments, the centrifugal pump of the present disclosure
eliminates the need
for a gas separator. In some embodiments, the centrifugal pump of an
illustrative embodiment may
be used in conjunction with a gas separator.
[0041] ESP primary pump 220 and production tubing string 225 are downstream of
ESP charge
pump 200. In some embodiments, motor lead extension 230 may plug into ESP
motor 250 at one
end and may be spliced to another larger cable than runs the length of the
well bore to a junction box
and/or a control panel on the surface of the well site. Production tubing
string 225 may be a conduit
for the produced well fluid to flow from the reservoir towards the surface.
ESP seal 240 sits between
ESP motor 250 and ESP intake 210 and may protect ESP motor 250 from well
fluid.
[0042] FIGs. 4A and 4B illustrate perspective views of one exemplary
embodiment of a semi-open
impeller of an illustrative embodiment. Impeller 30 may include single shroud
300 arranged radially
about hub 310. Truncated vane 320 and untruncated vane 330 may extend
substantially upstream
from single shroud 300. In some embodiments, truncated vane 320 sits at a mid-
pitch location
between two untruncated vane 330 starting from the bottom side of impeller 30.
In certain
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embodiments, truncated vane 320 alternates with untruncated vane 330, which
vanes 320, 330 are
circumferentially disposed about hub 310. In some embodiments there are two,
three or four of each
truncated vane 320 and untruncated vane 330 disposed about hub 310. Greater or
fewer number of
vanes 320, 330 may also be used. In certain embodiments, the number of
truncated vane 320 varies
from the number of untruncated vane 330 and/or the vanes 320, 330 may not
strictly alternate. In
FIG. 4B, balance holes 340 are also shown on impeller 30 and assist in
equalizing the pressure on
each side of impeller 30. In some embodiments, impeller 30 may operate at
about 8000 to about
12000 suction specific speed. In some embodiments, truncated vane 320 may
increase the
performance of a pump's head flow and efficiency and maintain high net
positive suction pressure,
without sacrificing suction performance.
[0043] FIG. 5 is a partial cross sectional view taken along line 5 _____ 5 of
FIG. 3 of one illustrative
embodiment of an impeller for a centrifugal pump. FIG. 5 illustrates one
embodiment of single
shroud 300 and the arrangement of vanes 320, 330 disposed about hub 310 of
impeller 30. In some
embodiments, truncated vane 320 is between about 50% and 75% the chord length
of untruncated
vane 330 (as judged from hub 310 and extending from the outer circumference of
single shroud
300). In certain embodiments, truncated vane 320 may be shorter or longer but
always shorter in
chord length than untruncated vane 330. In some embodiments, a centrifugal
pump of an illustrative
embodiment may include abrasion resistant trim, such as busing 560 and flanged
sleeve 570 (shown
in FIG. 6) to increase the lifespan of the centrifugal pump in the instance
that solids are also present
in the produced well fluid.
[0044] In some embodiments the arrangement of vanes 320, 330 create inlet area
610 of impeller 30
between about 1.75 and about 2.5 times the size of the inlet area of a
conventional impeller. One
embodiment of inlet area 610 is illustrated in FIG. 6A. As shown in FIG. 6A,
the size of inlet area
610 may be calculated using the formula:
Inlet Area .27rRH ¨ B
where R is mean inlet radius 620 as measured from centerline 640, H is inlet
vane height 630 and B
is the vane blockage. The vane blockage may be calculated as follows:
Vane Blockage = -
sinfl
where N is the number of untruncated vane 330 in impeller 30, H is inlet vane
height 630, T is vane
thickness 350 (shown in FIG. 5) and (3 is the inlet vane angle (shown in FIG.
5).
[0045] As truncated vane 320 do not contribute to vane blockage, the
arrangement of vanes 320,
330 of an illustrative embodiment reduce the vane blockage and thereby
increase inlet area 610.
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[0046] FIG. 6 is a cross sectional view taken along line 6.-6 of FIG. 3 of one
embodiment of a
centrifugal pump of an illustrative embodiment. Impeller 30 may be keyed to
shaft 540 at hub 310,
such that impeller 30 rotates with shaft 540. Impeller 30 is paired with
diffuser 510. FIGs. 6, 6A
show untruncated vane 330 for illustration purposes, but truncated vane 320
may also be included in
impeller 30 in addition to or instead of untruncated vane 330, for example as
shown in FIGS. 4A, 4B
and/or FIG. 5. In some embodiments, no shroud is present on top side 550 of
impeller 30. Single
shroud 300 is located on the bottom side of impeller 30.
[0047] Gap 530 is between untruncated vane 330 and/or truncated vane 320
(shown in FIG. 5) of
impeller 30 and diffuser 510. In some embodiments, gap 530 is an increased
clearance gap. The
width of gap 530 may be increased by machining the face of diffuser 510 that
sits parallel to the face
of impeller 30. In some embodiments, increased clearance gap 530 is between
about 0.060 inches
and about 0.180 inches wide, as required for various gas to liquid ratios. In
certain embodiments,
increased clearance gap 530 may be wider or narrower depending on the size of
the pump and type
of well and/or fluid being pumped. In some embodiments, increased clearance
gap 530 is at least
wider than about 0.020 inches. Increased clearance gap 530 allows the high
pressure fluid to
circulate and mix with low pressure fluid. Balance holes 340 assist in
equalizing the pressure on
each side of impeller 30.
[0048] In some embodiments, bushing 560 and flanged sleeve 570 located
upstream and/or
downstream of hub 310 assist in stabilizing impeller 30 and/or holding
impeller 30 in place during
operation. ln some embodiments, bushing 560 and flanged sleeve 570 are located
directly upstream
and downstream of hub 310. Bushing 560 and/or flanged sleeve 570 may assist in
carrying at least a
portion of the axial thrust load on impeller 30, such as upthrust and/or
downthrust. Bushing 560
and/or flanged sleeve 570 may be made of tungsten carbide, silicon carbide or
any other material
having similar properties. In some embodiments, bushing 560 and flanged sleeve
570 comprise
abrasion resistant trim.
[0049] As shown in FIG. 6, when impeller 30 is in operation, fluid may flow
downstream and/or
upwards through passage 580 towards successive stages of impeller 30 and
diffuser 510 pairs and
then to ESP primary pump 220, eventually passing through production tubing 225
to a pipe, conduit,
tank, collection container or other desired location.
[0050] In some embodiments, ESP charge pump 200 comprises multiple stages of
impeller 30 and
diffuser 510 pairs, which are stacked on shaft 540. In certain embodiments,
ESP charge pump 200
includes between about 10 and about 100 stages of impeller 30 and diffuser 510
pairs. In some
embodiments, impeller 30 may be employed in ESP primary pump 220.
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[0051] FIG. 7 is a flow chart illustrating an exemplary method of pumping
gaseous fluid of an
illustrative embodiment. At step 710 a centrifugal pump, such as ESP primary
pump 220 and/or ESP
charge pump 200, is placed into a well containing gaseous fluid. The pump may
then be operated to
induce the fluid to flow towards the surface of the well at step 720. At least
a portion of the fluid
may flow through increased clearance gap 530 between truncated vane 320 and/or
untruncated vane
330, and a diffuser 510, at step 730. At step 740, phase separation of the
fluid may be minimized by
reducing the pressure differential between the pressure side and suction side
of truncated vane 320
and/or untruncated vane 330. In some embodiments, the fluid flow may be caused
by rotating an
impeller comprising truncated vane 320 and at least two untruncated vane 330
extending
substantially upstream from a single shroud 300, wherein a truncated vane 320
sits at a mid-pitch
location between untruncated vane 330 starting from the bottom side of
impeller 30. In some
embodiments, the pressure differential between the pressure side and suction
side of truncated vane
320 and/or untruncated vane 330 may be reduced by increasing impeller inlet
area 610. Fluid may
then be lifted towards the surface, a transport conduit, pipe, tank,
collection container, or any other
desired location at step 750.
[0052] The centrifugal pump of the invention may be suitable for a variety of
types of submersible
stages known in the art for use in submersible pumps. For example, mixed flow
submersible pump
stages, as well as radial flow submersible pump stages, may make use of the
centrifugal pump of the
invention. Both these and other submersible stages suitable for use with an
ESP system may benefit
from the centrifugal pump of the present disclosure.
[0053] Various embodiments of the invention may comprise various numbers and
spacing of
truncated vane 320. ESP primary pump 220 and/or ESP charge pump 200 may
benefit from the
centrifugal pump of the invention. One or more pump stages within ESP primary
pump 220 and/or
ESP charge pump 200 may benefit from the centrifugal pump of the invention. In
some
embodiments the invention described herein may be suitable for pumping fluid
having a gas to liquid
ratio of up to about 50% by volume. The impeller of the invention may have
between about 1.75 and
2.5 times the size of the inlet area of a convention impeller. In some
embodiments, the impeller of
the invention may operate at about 8000 to about 12000 suction specific speed.
[0054] While the invention herein disclosed has been described by means of
specific embodiments
and applications thereof, numerous modifications and variations could be made
thereto by those
skilled in the art without departing from the scope of the invention set forth
in the claims. The
embodiments described in the foregoing description are therefore considered in
all respects to be
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CA 02809956 2013-03-18
illustrative and not restrictive. The scope of the invention is indicated by
the appended claims, and
all changes that come within the scope thereof are intended to be embraced
therein.
