Note: Descriptions are shown in the official language in which they were submitted.
CA 02897179 2015-07-07
DOCKET NO.: NS-533
IMPELLER FOR A CENTRIFUGAL SLURRY PUMP
Inventors: Yeu (John) Tieu; Daniel MacNeil; Stefano Chiovelli; Khaled Obaia
Assignee: Syncrude Canada Ltd. In Trust for the Owners of the Syncrude Project
FIELD OF THE INVENTION
[0001] The present invention relates to an improved impeller for a centrifugal
slurry pump.
BACKGROUND OF THE INVENTION
[0002] A conventional centrifugal slurry pump generally includes an impeller
having multiple
vanes and which is mounted for rotation within a volute casing. The slurry
pump imparts
energy to the slurry through the centrifugal force produced by rotation of the
impeller. The
slurry enters into the impeller through an intake conduit positioned in line
with the rotating
axis and is accelerated by the impeller, flowing radially outward into the
volute casing and
subsequently exiting through a discharge conduit. A suction sideliner is
positioned a
predetermined short distance away from the impeller suction side, the distance
being so small
as to substantially preclude slurry flow between the impeller and the suction
sideliner.
[0003] Slurries are two-phase mixtures of solid particles and fluids in which
the two phases
do not chemically react with each other and can be separated by mechanical
means. Slurries
are typically characterized as either non-settling or settling in accordance
with the size of the
solid particles suspended within the fluid. Non-settling slurries include fine
particles (less
1
CA 02897179 2015-07-07
than 50 m) which form stable homogeneous mixtures. Settling slurries include
coarse
particles (greater than 50 p.m) which form an unstable heterogeneous mixture.
Examples of
slurries include oil/water; tailings/water; and coke/water slurries. Such
slurries can cause
abrasion, erosion, and corrosion, resulting in significant wear to pump parts.
[0004] Attempts have been made to reduce wear of the pump parts, particularly
the impeller,
volute casing, and suction sideliner. A slurry pump operating at low speeds
outlasts a faster
running pump. Slower running pumps generally have heavier, larger diameter
impellers to
spread the energy which causes the wear over a larger area. Various
modifications related to
the configuration, thickness, number, and arrangement of impeller vanes have
been described.
For example, thicker impeller vanes are capable of handling an abrasive slurry
and
minimizing wear, but necessitate a reduction in vane number to avoid narrowing
the
passageways through which the slurry flows.
[0005] Pump parts have been formed of various hard metals, elastomeric, or
metal-reinforced
elastomeric materials to suit the material being pumped. Rubber-lined pumps
are often used
for pumping non-settling slurries since the resilience of the rubber can
absorb and return the
energy generated by the impact of the particles to the slurry; however, rubber-
lined pumps can
be damaged by sharp, large particles or degraded by hydrocarbons. Metal slurry
pumps are
suitable for pumping abrasive, settling slurries, with 28% chrome iron being
the most
common material and stainless steel being used for corrosive slurries. The
performance of a
chrome impeller may be enhanced by laser cladding which deposits an alloy
coating to the
surfaces of the impeller.
2
CA 02897179 2015-07-07
[0006] Among all pump parts, the impeller greatly influences the flow patterns
of the slurry
and the rate of wear. The average lifespan of an impeller is about 1,500 to
2,000 hours, which
approximates only half the lifespan of the slurry pump itself. During
manufacture, an impeller
is typically cast as one piece; thus, for replacement, an entirely new
impeller needs to be
installed. The maintenance hours and downtime of the pump are time and cost
consuming.
Increasing the lifespan of the impeller would be greatly beneficial in
maintaining pump
performance and meeting production targets.
[0007] Accordingly, there is a need for an improved impeller for a centrifugal
slurry pump.
SUMMARY OF THE INVENTION
[0008] In one aspect, the invention may comprise an impeller for a centrifugal
slurry pump,
which may comprise:
= a top shroud; a bottom shroud; and a middle portion therebetween, said
middle
portion having at least one substantially vertical wall defining a slurry flow
channel, wherein the top shroud, bottom shroud and middle portion are
configured as one piece to together define a first unitary body;
= at least one vane nose positioned at a leading edge of the at least one
substantially vertical wall;
= an inner retaining ring mounted over the top shroud to secure the vane
nose
within the body; and
= an outer wear ring mounted on a periphery of the top shroud.
3
T CA 02897179 2015-07-07
[0009] In one embodiment, the first unitary body, the at least one vane nose,
the inner
retaining ring, and the outer wear ring are manufactured as four separate
pieces. In another
embodiment, the at least one vane nose and the inner retaining ring are
configured as one
piece to together define a secondary unitary body and, thus, the impeller
consists of a first
unitary body, a second unitary body, and an outer wear ring, each manufactured
separately
from the other and assembled together to form the impeller.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Referring to the drawings wherein like reference numerals indicate
similar parts
throughout the several views, several aspects of the present invention are
illustrated by way of
example, and not by way of limitation, in detail in the figures, wherein:
[0011] FIG. 1 is a cutaway sectional view showing a centrifugal pump for
mineral slurry
within which the impeller of the present invention can be used.
[0012] FIG. 2 is a sectional side view of one embodiment of an impeller
comprising multiple
components.
[0013] FIG. 3 is a detailed view of a bottom shroud and middle portion of one
embodiment of
the impeller as shown in FIG. 2, without a vane nose attached.
[0014] FIG. 4 is a view of the vane nose of the impeller as shown in FIG. 2.
[0015] FIG. 5 is a bottom view of the inner retaining ring of the impeller as
shown in FIG. 2.
[0016] FIG. 6 is a sectional side view of a portion of the inner retaining
ring of FIG. 4 when
fastened to the top shroud.
4
CA 02897179 2015-07-07
[0017] FIG. 7 is a detailed view of a bottom shroud and middle portion of
Figure 3, with a
vane nose attached.
[0018] FIG. 8 is a sectional side view of a vane nose and tail formed of
different materials.
[0019] FIG. 9 is a perspective view of the inner retaining ring when mounted
over the vane
nose and body of the impeller as shown in FIG. 7.
[0020] FIG. 10 is a perspective view of another embodiment of a vane nose
useful in an
impeller of the present invention.
[0021] FIG. 11 is a perspective view of another embodiment of an impeller
comprising
multiple components.
[0022] FIG. 12 is a perspective view of the impeller as shown in FIG. 11 where
the vane nose
and inner retaining ring have been removed.
[0023] FIG. 13 is a side view of the vane nose and inner retaining ring
configured as one
piece to define a unitary body.
[0024] FIG. 14 is a perspective view of an alternative embodiment of the
present invention,
including an outer wear ring.
[0025] FIG. 15 is a perspective view of yet another alternative embodiment of
the present
invention, including an outer wear ring.
[0026] FIG. 16 is a perspective view of yet another alternative embodiment of
the present
invention, including an outer wear ring.
= CA 02897179 2015-07-07
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] In one aspect, the invention comprises an impeller which is assembled
from multiple
components, rather than casting the impeller as a single component as is
commonly done.
Each component may thus be individually tailored to its specific function in
the impeller.
[0028] The components of the impeller may be readily and conveniently
connected or
detached for inspection, reinsertion or replacement if necessary. This
obviates the current
need to replace an entirely new impeller; decreases the maintenance hours and
downtime of
the pump; and increases the lifespan of the impeller.
[0029] The present invention relates generally to an impeller for use in a
centrifugal slurry
pump. An embodiment of a centrifugal slurry pump 100 wherein an impeller of
the present
invention can be used is shown in cross-section in FIG. 1. The centrifugal
pump 100 is driven
by a motor (not shown), such as electric motor, turbine, etc., that is
connected to an impeller
of the present invention by a shaft 172. The impeller 110 is provided in a
volute casing 174.
An intake conduit 176 is provided in the volute casing 174 to route liquid
into the pump 100,
where the liquid will be subsequently discharged from the pump 100 through a
discharge
conduit 178 provided in the volute casing 174. A suction sideliner 180 is
provided to allow
access to the inside of the volute casing 174. Rotation of the impeller 110
causes slurry
within the volute casing 174 to be accelerated radially from the intake
conduit 176 and
discharged circumferentially at increased pressure at pump outlet, discharge
conduit 178, in a
manner well understood by those skilled in the art.
6
CA 02897179 2015-07-07
[0030] One embodiment of an impeller 10 of the present invention is shown in
FIGS. 2 to 9.
Impeller 10 includes a body 12, at least one vane nose 14, and an inner
retaining ring 16. The
body 12 has an annular and cylindrical shape which defines various directions
with respect to
the shape. As used herein, the term "radially" refers to a direction which is
generally along an
imaginary radius of the annular and cylindrical shape. As used herein, the
term "axially"
refers to a direction which is generally parallel to the axis of rotation. As
used herein, the
term "circumferentially" refers to a direction which is generally along an
imaginary
circumference of the annular and cylindrical shape.
[0031] The body 12 has a top shroud 18, a bottom shroud 20, and a middle
portion 22
sandwiched between the top and bottom shrouds 18, 20. The body 12 defines an
axially-
disposed eye 24. As used herein, the term "eye" means the center of the
impeller 10 where the
slurry enters. The eye 24 is coaxial with the central axis which is the axis
of rotation of the
impeller 10.
[0032] The top shroud 18 comprises a disc which defines at least one vane tail
26. Multiple
vane tails 26 are spaced circumferentially about the central axis, and evenly
apart from each
other. The top shroud 18 has at least one hole 28 dimensioned to receive a
fastener 30 which
is inserted to secure the retaining ring 16 to the top shroud 18. In one
embodiment, the
retaining ring 16 is secured to the top shroud 18 using screw fasteners and
also bonded with
an epoxy. Alternatively, the retaining ring 16 may be secured to the top
shroud 18 by brazing
or hot isostatic pressing. Multiple holes 28 may be spaced circumferentially
and evenly apart
from each other. The top shroud 18 defines a first recess 32 which is
configured to receive
and accommodate a corresponding protrusion 34 of the retaining ring 16. The
dimensions of
7
CA 02897179 2015-07-07
=
the first recess 32 are not essential to the invention and are dictated by the
size of the
protrusion 34.
[0033] The bottom shroud 20 comprises a disc having an axially-disposed hub 36
extending
from the bottom shroud 20. The hub 36 is operatively connectable to a drive
shaft (not
shown) for causing rotation of the impeller 10 about its central axis.
[0034] The middle portion 22 comprises at least one wall 38 which defines a
passageway 40
through which the slun-y flows. The wall 38 defines a second recess 42 which
is configured to
receive and accommodate the vane nose 14. The dimensions of the second recess
42 are not
essential to the invention and are dictated by the size and configuration of
the vane nose 14.
[0035] The vane nose 14 comprises a nose body 44 and upper and lower ends 46,
48,
respectively, at opposite ends of the nose body 44. The nose body 44 is
preferably curved in
order to direct slurry flow. In one embodiment, the nose body 44 is
substantially rectangular
in shape. The upper end 46 defines a tab 50 which extends upwardly to engage a
complementary slot 52 defined within the retaining ring 16. An elongate side
tab 54 projects
from the nose body 44 beyond each of the upper and lower ends 46, 48 to insert
into the
second recess 42 defined by the wall 38. The configuration of the vane nose 14
may be varied
so as to ensure that it inserts into, and is retained, by the second recess
42. In one
embodiment, the side tab 54 is substantially square or rectangular. The vane
nose 14 is
positioned in an orientation that is inclined at an angle less than 90 degrees
relative to the
bottom shroud 20. The angle may range from about 45 degrees to less than about
90 degrees
8
CA 02897179 2015-07-07
[0036] The inner retaining ring 16 comprises a disc having a top side 56, an
underside 58, and
defining an opening 60. The retaining ring 16 defines at least one slot 52
sized and configured
to engage the corresponding tab 50 of the vane nose 14. In one embodiment, the
retaining
ring 16 has four slots 52. The retaining ring 16 has at least one aperture 62
through which a
fastener 30 can extend into contact with a corresponding hole 28 of the top
shroud 18 to
secure the retaining ring 16 to the top shroud 18. Multiple apertures 62 may
be spaced
circumferentially and evenly apart from each other.
[0037] On the top side 56, the retaining ring 16 has at least one vane tail
extension 64 which
aligns with a corresponding vane tail 26 of the top shroud 18 to complete the
length of the
vane tail 26. The vane tail 26 may also be referred to as an expeller vane.
The expeller vanes
26 may provide some additional pump efficiency and assist in moving particles
out from
between the impeller and the suction liner.
[0038] On the underside 58, the retaining ring 16 has at least one protrusion
34 sized and
configured to fit securely within the first recess 32 of the top shroud 18.
When mounted to the
top shroud 18, the protrusion 34 surrounds the upper end 46 of the vane nose
14 to restrain the
vane nose 14 within the body 12.
[0039] Suitable fasteners include, any suitable system or component that can
be driven,
screwed, or otherwise forced through the holes 28 and apertures 62 to attach
the retaining ring
16 to the top shroud 18, including without limitation, bolts, screws, rivets,
or any other
fasteners commonly used in construction. Although less preferred, it is also
contemplated that
the retaining ring 16 may be attached to the top shroud 18 via other means,
such as for
9
CA 02897179 2015-07-07
example, other fastening mechanisms or adhesives. If desired, the retaining
ring 16 can be
permanently attached such as by brazing, hot isostatic pressing or other
suitable means known
to those skilled in the art.
[0040] The impeller 10 can be constructed from any material or combination of
materials
having suitable properties such as, for example, mechanical strength; erosion,
corrosion and
wear resistance; ability to withstand severe applications; and ease of
machining. The body 12,
vane nose 14, and retaining ring 16 may be formed of cermets (such as but not
limited to
tungsten carbide), metal matrix composites (such as but not limited to
tungsten carbide in a
metal matrix), hard metal alloys, metal-reinforced elastomers, ceramic-
reinforced elastomers
(such as but not limited to alumina or tungsten carbide in a urethane or
rubber) or elastomers.
Suitable materials include, but are not limited to, aluminum, brass, bronze,
cast iron,
composite, plastic, rubber, stainless steel, titanium, or other appropriate
materials known to
those skilled in the art.
[0041] It is well known that the leading edges of impeller vanes are most
severely worn
among all components of a typical centrifugal slurry pump. As used herein, the
tenn "leading
edge" means the surface which faces in a direction of rotation of the
impeller. As used herein,
the term "trailing edge" means the surface which faces in a direction that is
opposite the
direction of rotation of the impeller. In one embodiment, the vane nose 14 is
preferably
formed of tungsten carbide, while the wall 38 is formed of chromium white
iron. In one
embodiment, the body 12 is formed of chromium white iron. Thus, by being able
to make the
vane nose 14 of a stronger material than the single body 12, which includes
wall 38, longer
wear life of the impeller can be expected.
CA 02897179 2015-07-07
[0042] The "inner circle" of the top shroud of common impellers is greatly
prone to damage
and wear. The retaining ring 16 protects this portion of the impeller 10. In
one embodiment,
the retaining ring 16 is formed of chromium white iron.
[0043] The fasteners 30 such as for example, screws, pins, or bolts, may be
formed of steel,
for example, stainless steel, and strength-bearing materials.
[0044] It will be appreciated that the impeller 10 is simple but rugged in
construction that it
can be made at low cost and easily fabricated. The body 12 is preferably of
one-piece
construction combining the top shroud 18, bottom shroud 20, and middle portion
22, and may
be foinied by any suitable manufacturing process including, but not limited
to, casting,
machining, hot isostatic pressing, cast infiltration and other processes known
in the art. In a
casting processõ liquid material of which the body 12 is to be formed is fed
into a mold
cavity where it cools and hardens to the configuration of the cavity. Once the
material has
hardened, the finished body 12 is released from the mold. Casting is a
relatively simple and
rapid process for producing the body 12. The retaining ring 16 may be
manufactured similarly
to the body 12. Machining may be used to form the holes 28, apertures 62, and
recesses 32,
42. In one embodiment, the vane nose 14 may be formed by sintering or hot
isostatic
pressing, whereby powdered material is held in a mold and heated to fuse the
material
together into a single piece.
[0045] During assembly of the impeller 10, the vane nose 14 is mounted within
the body 12
by inserting the side tab 54 into the second recess 42 (FIG. 6). Multiple vane
noses 14 are
inserted within the body 12 so as to be spaced circumferentially about the
central axis, and to
11
CA 02897179 2015-07-07
define flow channels 66. Positioning of the vane noses 14 between the eye 24
and outside
diameter of the impeller 10 allows the vane noses 14 to direct slurry flow.
[0046] The retaining ring 16 is mounted over the top shroud 18 to fit the
protrusion 34 within
the first recess 32, to align the slot 52 with the tab 50 of the vane nose 14,
and to align the
apertures 62 with the corresponding holes 28 of the top shroud 18 (FIG. 8). At
least one
fastener 30 is passed through the aperture 62 and hole 28 to attach the
retaining ring 16 to the
top shroud 18, thereby securing the vane nose 14 in place within the middle
portion 22 of the
body 12 (FIG. 5). The retaining ring 16 can be readily attached to or released
from the top
shroud 18 of the body 12 as needed.
[0047] In another embodiment, the vane nose 14 can be manufactured without
tabs 50 and 54
and the body 12 will not have slot 52 sized and configured to engage the
corresponding tab 50
or slot 42 sized and configured to engage the corresponding tab 54. This
embodiment is
shown in FIG. 10, where vane nose 114 comprises a nose body 144 and upper and
lower ends
146, 148, respectively, at opposite ends of the nose body 144. The front
surface 141 may be
curved in order to direct slurry flow. The back surface 143, however, is
essentially planar, so
that the vane nose 114 can be attached to a now flat surface of body 12, which
no longer has
slot 52, by glue such as epoxy and the like. Similarly, upper end 146 is
essentially planar or
slightly concave so as to be able to be attached to the surface of body 12,
which no longer has
slot 42, by glue such as epoxy and the like. Other means for fastening two
pieces of metal
together, such as but not limited to brazing or hot isostatic pressing, as
known in the art can
also be used. In one embodiment, the vane nose 14 or 114 is manufactured as a
single body.
12
CA 02897179 2015-07-07
[0048] Another embodiment of an impeller of the present invention is shown in
FIGS. 11-13.
Impeller 210 includes a body 212, at least one vane nose 214, and an inner
retaining ring 216.
The body 212 has an annular and cylindrical shape which defines various
directions with
respect to the shape. The body 212 (shown independently in FIG. 12) has a top
shroud 218, a
bottom shroud 220, and a middle portion 222 sandwiched between the top and
bottom shrouds
218, 220. The body 212 defines an axially-disposed eye 224. The top shroud 218
comprises a
disc which defines at least one vane tail 226. Multiple vane tails or expeller
vanes 226 are
spaced circumferentially about the central axis, and evenly apart from each
other.
[0049] In one embodiment, the top shroud 218 defines a first recess 232 which
is configured
to receive and accommodate inner retaining ring 216.
[0050] The bottom shroud 220 comprises a disc having an axially-disposed hub
236 (shown
in FIG. 12) extending from the bottom shroud 220. The hub 236 is operatively
connectable to
a drive shaft (not shown) for causing rotation of the impeller 210 about its
central axis. The
bottom shroud also comprises a cut-out portion 221 for accommodating a vane
nose assembly
290, which assembly is shown in FIG. 13. The middle portion 222 comprises at
least one wall
238 which defines a passageway 240 through which the slurry flows. The wall
238 is
designed to accommodate the vane nose 214 of vane nose assembly 290.
[0051] With reference specifically to FIG. 13, the vane nose assembly 290 is a
unitary body
comprising vane nose 214, retaining ring 216 and hub cover 215, which hub
cover 215 is
designed to fit into cut-out portion 221 of bottom shroud 220. The vane nose
assembly 290 is
designed to be set, for example, by epoxy, into body 212. Thus, in this
embodiment, vane
13
CA 02897179 2015-07-07
=
nose assembly 290 can be made from a stronger material than body 212. Thus,
the regions of
the impeller that are generally more greatly exposed to the abrasive slurry
can be
manufactured as a single unit out of stronger wear-resistant material. Thus,
the slurry pump
life-time can be greatly extended.
[0052] In another embodiment, wear and damage to the expeller vanes 26 or 226
may be
mitigated by different strategies. In one example, the expeller vanes 26 226
may be protected
using attached wear elements such as carbide tiles or coating the expeller
vanes with a wear-
resistant coating, such as by thermal spraying, laser cladding, hot isostatic
pressing or other
techniques well known to those in the art.
[0053] In one embodiment, the expeller vanes 26 or 226 may be eliminated and
the retaining
ring 16 may comprise a hard or wear-resistant material. The retaining ring 16
may be formed
from a plurality of carbide tile segments 301 which are assembled to form a
complete ring, as
is shown in Figure 14.
[0054] In one embodiment, where expeller vanes are eliminated, an outer wear
ring 302 may
be attached or otherwise formed into the impeller. The outer wear ring may
also be formed
from a plurality of carbide tile segments 303, as is shown in Figure 14.
[0055] Hard or wear-resistant material may include such materials as ceramic
or non-ceramic
carbides such as chromium carbide, tungsten carbide, or a cen-net such as
sintered tungsten
carbide. Sintered tungsten carbide, also known as cemented carbide, is a
composite material
comprising tungsten carbide powder mixed with a binder metal such as cobalt or
nickel,
compacted in a die and then sintered at a very high temperature. Wear-
resistant materials may
14
CA 02897179 2015-07-07
also include various ceramic materials such as alumina or a nitride such as
silicon nitride. As
used herein, a ceramic material is an inorganic, non-metallic, oxide, nitride
or carbide
material, which may or may not be crystalline. Suitable hard or wear-resistant
materials are
well known in the art and are readily commercially available.
[0056] In an alternative embodiment, as shown schematically in Figure 15, the
impeller may
include an inner retaining ring 16 formed from a plurality of segments 401
which are
separated by small gaps and a outer wear ring 402 also formed from a plurality
of segments
403, also separated by small gaps. The gaps of the inner ring 16 and the gaps
of the outer ring
402 are connected by grooves 404 formed in the top shroud 18 to form channels
which mimic
the function of expeller vanes.
[0057] In another embodiment, as shown in Figure 16, the inner and outer rings
may be
dimensioned to abut each other, such that the top shroud is completely covered
and not
exposed. Alternatively, the inner and outer rings may be combined into a
single wear resistant
disk which covers the top shroud 18. The element which covers the top shroud,
whether
formed from abutting inner and outer rings, or a unitary element, may comprise
expeller vanes
or grooves which mimic the function of expeller vanes. This single wear
resistant disk may
be formed by hot isostatic pressing, cast infiltration or a similar suitable
technique.
Definitions and Interpretation
[0058] The singular forms "a," "an," and the include plural reference unless
the context
clearly dictates otherwise. It is further noted that the claims may be drafted
to exclude any
optional element. As such, this statement is intended to serve as antecedent
basis for the use
CA 02897179 2015-07-07
of exclusive terminology, such as "solely," "only," and the like, in
connection with the
recitation of claim elements or use of a "negative" limitation. The terms
"preferably,"
"preferred," "prefer," "optionally," "may," and similar terms are used to
indicate that an item,
condition or step being referred to is an optional (not required) feature of
the invention.
[0059] The term "and/or" means any one of the items, any combination of the
items, or all of
the items with which this term is associated.
[0060] As will also be understood by one skilled in the art, all language such
as "up to", "at
least", "greater than", "less than", "more than", "or more", and the like,
include the number
recited and such terms refer to ranges that can be subsequently broken down
into sub-ranges
which fall within the broader range. In the same manner, all ratios recited
herein also include
all sub-ratios falling within the broader ratio.
[0061] One skilled in the art will also readily recognize that where members
are grouped
together in a common manner, such as in a Markush group, the invention
encompasses not
only the entire group listed as a whole, but each member of the group
individually and all
possible subgroups of the main group. Additionally, for all purposes, the
invention
encompasses not only the main group, but also the main group absent one or
more of the
group members. The invention therefore envisages the explicit exclusion of any
one or more
of members of a recited group. Accordingly, provisos may apply to any of the
disclosed
categories or embodiments whereby any one or more of the recited elements,
species, or
embodiments, may be excluded from such categories or embodiments, for example,
as used in
an explicit negative limitation.
16
CA 02897179 2015-07-07
[0062] As will be apparent to those skilled in the art, various modifications,
adaptations and
variations of the foregoing specific disclosure can be made without departing
from the scope
of the invention claimed herein. The various features and elements of the
invention described
herein may be combined in a manner different than the specific examples
described or
claimed herein without departing from the scope of the invention. In other
words, any
element or feature may be combined with any other element or feature in
different
embodiments, unless there is an obvious or inherent incompatibility between
the two, or it is
specifically excluded.
17
