Note: Descriptions are shown in the official language in which they were submitted.
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DOCKET NO.: NS-431
AN IMPROVED IMPELLER FOR A CENTRIFUGAL SLURRY PUMP
FIELD OF THE INVENTION
The present invention relates to an improved impeller for a centrifugal slurry
pump.
BACKGROUND OF THE INVENTION
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.
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 than 50
[tm) which form stable homogeneous mixtures. Settling slurries include coarse
particles
(greater than 50 vim) 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.
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 aiTangement of impeller vanes have been
described. For
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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.
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 sluiTy; however, rubber-lined
pumps can be
damaged by sharp, large particles or degraded by hydrocarbons. Metal sluiTy
pumps are
suitable for pumping abrasive, settling slurries, with 28% chrome iron being
the most common
material and stainless steel being used for conosive slurries. The performance
of a chrome
impeller may be enhanced by laser cladding which deposits an alloy coating to
the surfaces of
the impeller.
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.
Accordingly, there is a need for an improved impeller for a centrifugal slurry
pump.
SUMMARY OF THE INVENTION
The current application is directed to an improved impeller for a centrifugal
slun-y
pump. It was surprisingly discovered that by using the impeller of the present
invention, one or
more of the following benefits may be realized:
(1) Rather than casting the impeller as a single component as is commonly
done,
the impeller comprises multiple components which are formed separately and
assembled
together to form the completed impeller. Each component may thus be
individually tailored to
its specific function in the impeller.
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(2) 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.
In one aspect, an improved impeller for a centrifugal slurry pump is provided,
comprising:
= 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; and
= at least one vane nose positioned at a leading edge of the at least one
substantially vertical wall.
In one embodiment, the impeller further comprises:
= a retaining ring mounted over the top shroud to secure the vane nose
within the
body.
In one embodiment, the first unitary body, the at least one vane nose and the
inner
retaining ring are manufactured as three 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 comprises a first unitary body
and a second
unitary body, each body manufactured separately from the other.
BRIEF DESCRIPTION OF THE DRAWINGS
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:
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.
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FIG. 2 is a sectional side view of one embodiment of an impeller comprising
multiple
components.
FIG. 3 is a side view of the body of the impeller as shown in FIG 2.
FIG 4 is a front view of the vane nose of the impeller as shown in FIG 2.
FIG 5 is a bottom view of the inner retaining ring of the impeller as shown in
FIG 2.
FIG. 6 is a sectional side view of a portion of the inner retaining ring of
FIG. 4 when
fastened to the top shroud.
FIG 7 is a side view of the vane nose when assembled into the body of the
impeller as
shown in FIG. 2.
FIG 8 is a sectional side view of a vane nose and tail formed of different
materials.
FIG 9 is a side view of the inner retaining ring when mounted over the vane
nose and
body of the impeller as shown in FIG. 2.
FIG 10 is a front view of another embodiment of a vane nose useful in an
impeller of
the present invention.
FIG 11 is a side view of another embodiment of an impeller comprising multiple
components.
FIG 12 is a side view of the impeller as shown in FIG 11 where the vane nose
and inner
retaining ring have been removed.
FIG 13 is a side view of the vane nose and inner retaining ring configured as
one piece
to define a unitary body.
FIG. 14a shows a new prior art impeller.
FIG. 14b shows the wear pattern of the prior art impeller of FIG. 14a at 1000
hours and
20000 hours.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The detailed description set forth below in connection with the appended
drawings is
intended as a description of various embodiments of the present invention and
is not intended to
represent the only embodiments contemplated by the inventor. The detailed
description
includes specific details for the purpose of providing a comprehensive
understanding of the
present invention. However, it will be apparent to those skilled in the art
that the present
invention may be practiced without these specific details.
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.
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.
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
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slurry enters. The eye 24 is coaxial with the central axis which is the axis
of rotation of the
impeller 10.
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. 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 the first recess 32 are not essential to the
invention and are dictated
by the size of the protrusion 34.
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.
The middle portion 22 comprises at least one wall 38 which defines a
passageway 40
through which the slurry 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.
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.
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
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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.
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.
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.
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 example,
other fastening mechanisms or adhesives. If desired, the retaining ring 16 can
be permanently
attached.
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 hard metal alloys, metal-
reinforced
elastomers, or elastomers including, but 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.
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 term
"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
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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.
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.
The fasteners 30 such as for example, screws, pins, or bolts, may be formed of
steel, for
example, stainless steel, and strength-bearing materials.
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 formed by
any suitable manufacturing process including, but not limited to, casting,
machining, and other
processes known in the art. Briefly, 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,
whereby powdered material is held in a mold and heated to fuse the material
together into a
single piece.
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 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 sluny flow.
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
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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.
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 suth 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 as
known in the art can also be used.
In one embodiment, the vane nose 14 or 114 is manufactured as a single body.
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 226 are spaced
circumferentially about the central axis, and evenly apart from each other. In
one embodiment,
the top shroud 218 defines a first recess 232 which is configured to receive
and accommodate
retaining ring 216.
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
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290, whieh 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.
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 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.
Example 1
FIG. 14a shows a prior art impeller which has been cast as a single unit (one
piece) from
chrome white iron.
FIG 14b shows the wear pattern of the prior art impeller after 1000 hours of
use with oil
sand slurries and 2000 hours of use with oil sand slurries. It can be seen
that the vanes (walls)
located between the top shroud and the bottom shroud have been essentially
worn away after
2000 hours. It was discovered by the applicant that the average life span of a
slurry pump
having an impeller cast as a single piece from chrome white iron used with oil
sand slurries,
which are very abrasive, have an average life span of about 1500 hours. By
providing vane
noses of the present invention made separately from a more wear resistant
material such as
sintered tungsten carbide with increase the average life span significantly.
Furthermore, the
individual vane noses can be replaced where significant wearing occurs without
having to
replace the entire impeller. Thus, downtimes, replacement frequencies, and
costs for new
impellers are all reduced.
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