Note: Descriptions are shown in the official language in which they were submitted.
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DECANTER CENTRIFUGES AND RELATED METHODS OF USE TO DEWATER
MATURE (FLUID) FINE TAILINGS
TECHNICAL FIELD
[0001] This document relates to decanter centrifuges and related methods
of use, for
example to dewater mature fine tailings (MFT), also known as fluid fine
tailings (FFT).
BACKGROUND
[0002] Decanter centrifuges such as the ALFA LAVALTM LYNX 1000Tm are used
to
dewater oil sands tailings. The LYNX 1000Tm has a radial feed discharge, a
conical beach, a
cylindrical pond, and a solid fighting conveyor.
SUMMARY
[0003] Decanter centrifuges are disclosed. In one case a decanter
centrifuge is
disclosed for the purpose of dewatering MFTs. The centrifuge may comprise an
accelerator,
an axial flow passage within conveyor fighting, and redirection nozzles
connected to the
feed chamber, as a package for economically processing large volumes of MFTs.
[0004]= A decanter centrifuge comprising: a bowl forming a sedimentation
chamber
with a cake discharge and a centrate discharge; a screw conveyor within the
sedimentation
chamber, the screw conveyor having a conveyor body, such as a cylindrical tube
with or
without a conical beach section, and a flight, the screw conveyor defining an
axial flow
passage between the conveyor body and a radially inward facing edge of the
flight; a feed
conduit connected to supply a feed mixture of solids and liquids to a feed
chamber formed
within the conveyor body; and a feed redirection nozzle that is structured to
direct the feed
mixture from the feed chamber toward the axial flow passage.
[0005] A method is disclosed of continuously processing a feed mixture
within a
decanter centrifuge, the decanter centrifuge having a bowl and a screw
conveyor, the bowl
forming a sedimentation chamber with a cake discharge and a centrate
discharge, the feed
mixture comprising solids and liquids, the method comprising: supplying the
feed mixture
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through a feed conduit into a feed chamber formed by a conveyor body of the
screw
conveyor; directing the feed mixture into the sedimentation chamber with a
feed redirection
nozzle, in which the nozzle directs the feed mixture toward an axial flow
passage defined
between the conveyor body and an inner edge of a flight mounted to the
conveyor body;
rotating the bowl and the conveyor body to effect at least a partial phase
separation of the
solids and liquids of the feed mixture; and discharging solids through the
cake discharge, and
discharging liquids through the centrate discharge.
[0006] A decanter centrifuge is disclosed comprising: a bowl forming a
sedimentation chamber with a cake discharge and a centrate discharge, in which
the cake
discharge is at or near a first axial end of the bowl, and the centrate
discharge is at or near a
second axial end of the bowl; a screw conveyor within the sedimentation
chamber, the screw
conveyor having a conveyor body and a flight, the screw conveyor defining an
axial flow
passage between the conveyor body and a radially inward facing edge of the
flight; a feed
conduit connected to supply a feed mixture of solids and liquids to a feed
chamber formed
within the conveyor body at an intermediate location between the first axial
end and the
second axial end of the bowl, the feed mixture in some cases comprising mature
fine tailings
produced from an oil sands process; a feed redirection nozzle structured to
direct the feed
mixture from the feed chamber toward the axial flow passage; and an
accelerator within the
feed chamber for increasing the angular velocity of the feed mixture prior to
entering the
sedimentation chamber.
[0007] A decanter centrifuge is disclosed comprising: a bowl forming a
sedimentation chamber with a cake discharge and a centrate discharge, in which
the cake
discharge is at or near a first axial end of the bowl, and the centrate
discharge is at or near a
second axial end of the bowl; a screw conveyor within the sedimentation
chamber, the screw
conveyor having a flight; a feed conduit connected to supply a feed mixture of
solids and
liquids to a feed redirection nozzle; and the feed redirection nozzle being
structured to direct
the feed mixture from the feed chamber toward the second axial end of the
bowl.
[0008] A decanter centrifuge is disclosed comprising: a bowl forming a
sedimentation chamber with a cake discharge and a centrate discharge; a screw
conveyor
within the sedimentation chamber, the screw conveyor having a conveyor body
and a flight;
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a feed conduit connected to supply a feed mixture of solids and liquids to a
feed chamber
formed within the conveyor body, the feed chamber communicating with, for
example
connected to, the sedimentation chamber via a feed injection port in the outer
surface of the
conveyor body, the feed mixture comprising mature fine tailings produced from
an oil sands
process; and an accelerator within the feed chamber for increasing the angular
velocity of the
feed mixture prior to entering the sedimentation chamber.
[0009] A decanter centrifuge is disclosed comprising: a bowl forming a
sedimentation chamber with a cake discharge and a centrate discharge; a screw
conveyor
within the sedimentation chamber, the screw conveyor having a conveyor body
and a flight,
the screw conveyor defining an axial flow passage between the conveyor body
and a radially
inward facing edge of the flight; a feed conduit connected to supply a feed
mixture or solids
and liquids to a feed chamber formed within the conveyor body, the feed
chamber
communicating with the sedimentation chamber via a port in the outer surface
of the
conveyor body, the feed mixture comprising mature fine tailings produced from
an oil sands
process.
[0010] A decanter centrifuge is disclosed comprising: a bowl; a conveyor;
a feed
tube; a feed chamber; an accelerator in the feed chamber; and a feed
redirection nozzle; in
which the decanter centrifuge is structured so that, in use, a feed mixture
passes through the
feed tube and into the feed zone where the angular velocity of the feed
mixture is increased
by the accelerator, the feed mixture then passes out of the feed zone, is
redirected by the
nozzle in an axial direction into a sedimentation chamber within the bowl, and
the rotation of
the conveyor and the bowl cause sedimentation within the bowl, to separate
solids and
liquids in the feed mixture.
[0011] A decanter centrifuge may be provided having a conveyor design
with; 1) an
inlet or feed chamber in which rotational energy may be applied to the feed
slurry before the
feed flows through the inlet apertures and discharges into the space between
the conveyor
body and the internal side of the bowl where the separation of the solid
constituents is
achieved, 2) a part that redirects the feed flow direction towards the liquid
end hub as it
discharges from the inlet into the space between the conveyor body and the
bowl wall. And
3) window ports are cut into the fighting or the fighting is modified such
that it is elevated
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on posts to provide a space for the redirected flow of the feed to travel
unimpeded axially
towards the liquid end hub between the conveyor tube body and the top of the
flights. The
feed flow is now travelling axially towards the liquid end hub with a
relatively reduced
velocity, a relatively reduced turbulence and a more laminar flow pattern.
Such structure is
expected to provide for relatively less turbulent flow than in a centrifuge
such as the LYNX
1000TM that has solid fighting and no redirection nozzles. The stated
structure is expected
to allow for greatly improved settling of the suspended solids in the feed,
and to minimize
shear and hence reducing polymer dosage and centrifuge rotating assembly
maintenance
requirements.
[0012] Redirection nozzles may be fastened, for example bolted, over
inlets (feed
zone discharge) to redirect the flow ninety degrees with respect to the feed
zone from a radial
direction to an axial flow direction in the sedimentation chamber towards the
pond hub
(clarification section) of the bowl. Such a configuration may reduce
turbulence that would
otherwise be caused by the influent being introduced radially from the feed
zone and heading
axially directly toward the bowl wall. Such is expected to eliminate or reduce
wear occurring
on the conical section. The caulk strips on the bowl extension may have a
longer life as well.
Conventional larger bowl machines such as the LYNX 1000TM incorporate solid
fighting,
axial feed ports into the sedimentation chamber, and limited to no means for
increasing the
angular velocity of the feed mixture prior to supply into the sedimentation
chamber, and are
used for municipal waste streams. By contrast, MFTs have been found to exhibit
excessive
wear on conventional centrifuges, thus requiring frequent servicing, decreased
clarification,
and increased polymer costs.
[0013] In various embodiments, there may be included any one or more of
the
following features. The nozzle is mounted over an outer surface of the
conveyor body, with
the nozzle communicating with the feed chamber via a port in the conveyor
body. The nozzle
defines a hood that forms an elbow-shaped flow passage that connects the port
to an axially
facing nozzle opening defined by the hood. An outer diameter of the
redirection hood is
smaller than an inner diameter of the flight. The cake discharge is at or near
a first axial end
of the bowl, the centrate discharge is at or near a second axial end of the
bowl, and the
nozzle is structured to direct the feed mixture toward the second axial end of
the bowl. The
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axial flow passage defines an axial flow path that extends from the nozzle to
the second axial
end. The bowl comprises a conical beach section defining the first axial end
and a cylindrical
pond section defining the second axial end, and the flight forms a windowless
helix whose
inner edge is fused to the conveyor body continuously along a length of the
flight throughout
the beach section. Plural nozzles radially spaced around the feed chamber. The
flight is
helically mounted to an outer surface of the conveyor body via a plurality of
radial posts
such that the helical flight is radially spaced from the conveyor body to
define the axial flow
passage. A replaceable wear liner is internally mounted to the nozzle to
protect the nozzle
from abrasion from the feed mixture. The feed chamber is defined between
axially spaced
plates mounted within the conveyor body. An accelerator within the feed
chamber for
increasing the angular velocity of the feed mixture prior to entering the
sedimentation
chamber. The accelerator comprises an impellor with plural vanes. The feed
conduit is
connected to supply feed mixture to the feed chamber through a port in a first
axial end wall
of the feed chamber, and the impellor is fixed to a second axial end wall of
the feed chamber.
The nozzle, or a port that supplies the nozzle and is defined in the outer
surface of the
conveyor body, is located radially outward of the impellor in a plane,
perpendicular to a
centrifuge axis, defined by the impellor. The feed chamber comprises a
plurality of lobes
radially spaced from one another about the second axial end wall within the
feed chamber to
define a radial feed passage to the nozzle. The radial feed passage has side
walls defined by
the plurality of lobes and the side walls each mount a replaceable wear liner.
A drive
connected to simultaneously rotate the screw conveyor and the bowl at
different angular
velocities relative to one another. The feed mixture comprises mature fine
tailings produced
from an oil sands process. The feed mixture supplied to the feed chamber
comprises a
flocculant. The axial flow passage is defined by a plurality of axial windows
in the flight.
The mature fine tailings comprise solids of 10-45 % by weight of the feed
mixture.
Operating the decanter centrifuge to effect a phase separation of the solids
and liquids in the
feed mixture, and producing solids through the cake discharge, and liquids
through the
centrate discharge. Supplying the feed mixture from a tailings pond, in which
the feed
mixture comprises mature fine tailings produced from an oil sands process. The
feed mixture
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prior is flocculated to supplying the feed mixture through the feed conduit.
The decanter
centrifuge is supported for rotation by oil bath bearings.
[0014] These and other aspects of the device and method are set out in the
claims,
which are incorporated here by reference.
BRIEF DESCRIPTION OF THE FIGURES
[0015] Embodiments will now be described with reference to the figures, in
which
like reference characters denote like elements, by way of example, and in
which:
[0016] Fig. 1 is a perspective view of a conveyer for a decanter
centrifuge.
[0017] Fig. 2 is a side elevation view and schematic of a centrifuge
connected to
process mature fine tailings (MFT) from a tailings pond.
[0018] Fig. 3 is a section view taken along the 3-3 section lines in Fig.
2 and
illustrating a feed tube positioned within the conveyor body.
[0019] Fig. 3A is a section view taken along the 3A-3A section lines in
Fig. 3.
[0020] Fig. 3B1 is a section view taken along the 3B-3B section lines in
Fig. 3.
[0021] Fig. 3B2 is a perspective view of the portion of the centrifuge as
shown in
Fig. 3B1.
[0022] Fig. 3C1 is a section view taken along the 3C-3C section lines in
Fig. 3.
[0023] Fig. 3C2 is a perspective view of the portion of the centrifuge as
shown in
Fig. 3C1.
[0024] Fig. 3D1 is a section view taken along the 3D-3D section lines in
Fig. 3.
[0025] Fig. 3D2 is a perspective view of the portion of the centrifuge as
shown in
Fig. 3D1.
[0026] Fig. 4 is a perspective view of a feed redirection nozzle assembled
with a
wear liner.
[0027] Fig. 5 is an exploded perspective view of the nozzle and wear liner
of Fig. 4.
[0028] Fig. 6 is atop plan view of the nozzle of Fig. 4.
[0029] Fig. 7 is a front elevation view of the nozzle of Fig. 4.
[0030] Fig. 8 is a side elevation view of the nozzle of Fig. 4.
[0031] Fig. 9 is a top plan view of one half of the wear liner of Fig. 4
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[0032] Fig. 10 is a bottom perspective view of one half of the wear liner
of Fig. 4.
[0033] Fig. 11 is an end view of the liquids discharge of the centrifuge
of Fig. I.
[0034] Fig. 12 is an end view of the steel inner plate forming the cake
discharge ports
at the beach section of the bowl.
[0035] Fig. 13 is a section view of an oil bath bearing assembly
supporting the first
axial end of the centrifuge of Fig. 2.
DETAILED DESCRIPTION
[0036] Immaterial modifications may be made to the embodiments described
here
without departing from what is covered by the claims.
[0037] Oil sands may comprise water-wet sand grains held together by a
matrix of
viscous heavy oil or bitumen. The oil sands may comprise a mixture that is
approximately
10% bitumen, 80% sand, and 10% fine tailings. Bitumen is a complex and viscous
mixture of
large or heavy hydrocarbon molecules, which may contain a significant amount
of sulfur,
nitrogen and oxygen. The extraction of bitumen from sand using hot water
processes yields
large volumes of fine tailings composed of fine silts, clays, residual bitumen
and water. Fines
in such mixtures include clay mineral suspensions or emulsions, predominantly
kaolinite and
illite.
[0038] An example fine tailings suspension has 85% water and 15% fine
particles by
mass. Dewatering of fine tailings occurs very slowly by gravity settling. When
first
discharged in ponds, the very low density material is referred to as thin fine
tailings. Oil
sands tailings ponds are engineered dam and dyke systems that contain a
mixture of salts,
suspended solids and other dissolvable chemical compounds such as acids,
benzene,
hydrocarbons, residual bitumen, fine silts and water. The Syncrude Tailings
Dam or Mildred
Lake Settling Basin is a tailings pond that was, by volume of construction
material, the
largest earth structure in the world in 2001.
[0039] After a few years when the fine tailings have reached a solids
content of about
30-35%, they are referred to as fluid or mature fine tailings (MFTs), which
behave as a fluid-
like colloidal material. The fact that MFTs behave as a fluid and have very
slow
consolidation rates at 1 g significantly limits options to reclaim tailings
ponds. In fact, fine
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tailings will likely never fully settle in these tailing ponds. It is believed
that the electrostatic
interactions between the suspended particles, which are still partly
contaminated with
hydrocarbons, prevent settling from occurring. These tailing ponds have become
an
environmental liability for the companies responsible. A challenge facing the
industry
remains the removal of water from the fluid fine tailings to strengthen the
deposits so that
they can be reclaimed and no longer require containment. Many studies and
project have
been undertaken to address tailings pond remediation.
[0040] Tailings deposited in a tailings pond may contain primarily water,
hydrocarbons and solids, which may include mineral material, such as rock,
sand, silt and
clay. The process described in this document may be useful in reclaiming these
ponds by
separating the liquid portion from the solid tailings, and using the separated
portions to
return land to its natural state. However, the apparatus and method may also
be applied to
any fluid having components to be separated, such as a sewage or solid-liquid
mixture. The
fluid to be treated may comprise tailings from deep within a tailings pond,
without dilution,
so long as the tailings are pumpable. If the tailings are not pumpable, they
may be made
pumpable by dilution with water.
[0041] Decanter centrifuges are used in the mechanical separation process
of MFTs
from the water in which the tailings are suspended. A centrifuge is a device
that employs a
high rotational speed to separate components of different densities. A
decanter centrifuge
separates solid materials from liquids in a slurry. The operating principle of
a decanter
centrifuge is based on separation via buoyancy. Naturally, a component with a
higher density
will fall to the bottom of a mixture, while the less dense component will be
suspended above
it. A decanter centrifuge increases the rate of settling through the use of
continuous rotation,
producing relatively high g-forces, for example forces equivalent to between
1000 to 4000 g-
forces. Such acceleration reduces the settling time of the components by a
large magnitude,
for example permitting a mixture to settle in seconds in contrast to the same
mixture settling
in hours, days, years, or longer under ambient g-forces.
[0042] Through the use of decanter centrifuges, settling may be
accelerated by
flocculating the MFT clay particles, for example using polyacrylamides, and
exposing the
flocculated feed mixture to relatively high g-force in a decanter centrifuge,
such as 1400 g or
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higher, to effect phase separation. In such centrifuges, data suggests that
the tailings feed
creates internal turbulence along the length of the bowl resulting in lessened
separation
efficiency, increased solids caking along the pond section of the bowl, liquid
influx into the
beach section of the bowl, and increased wear etching and damage likely from
the abrasive
sand in such mixtures.
[0043] Referring to Figs. 1-3, a decanter centrifuge 10 is illustrated,
having a bowl
12, a screw conveyor 14, and a feed conduit 30. Referring to Fig. 3, bowl 12
forms a
sedimentation chamber 33 with a cake discharge 24 and a centrate discharge 26.
The screw
conveyor 14 is located within the sedimentation chamber 33. The screw conveyor
14 is the
part that conveys solid material, which is in the process of settling or has
settled in
sedimentation chamber 33, to move towards the cake discharge 24. The conveyor
14 may
have a conveyor body 50, for example a central hub coaxial with the bowl 12 as
shown. The
conveyor 14 may have a suitable conveying part, such as a scroll, auger, or
helical flight 60.
The flight 60 may be helically mounted to an outer surface of the conveyor
body. The feed
conduit 30 is connected to supply a feed mixture of solids and liquids, for
example a feed
mixture of MFT, into the sedimentation chamber 33. During use, feed mixture is
continually
supplied to the sedimentation chamber 33 while the bowl 12 and screw conveyor
14 are
rotated. Rotation imparts a centripetal settling force upon feed mixture
within the
sedimentation chamber 33 to effect at least a partial phase separation between
the liquids and
solids in the feed mixture.
[0044] Referring to Figs. 2, 3, 3A, and 11, bowl 12 and conveyor 14 may be
oriented
for co-current or counter-current flow, the latter of which is shown.
Referring to Fig. 3, the
bowl 12 may be divided into a pond section 37, which may be a straight
cylinder, and a
beach section 35, which may have a conical shape, for example the shape of a
truncated
cone. The sedimentation chamber 33 may be defined by an internal encircling
wall 32 of
bowl 12, a first end plate 34A at a first axial end 34 of rotatably journaled
drum or bowl 12,
a second end plate 36B at a second axial end 36 of the pond section of the
bowl 12. Where a
conveyor body 50 is present, the sedimentation chamber 33 is also defined
between the
conveyor body 50 and the internal encircling wall 32 of bowl 12.
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[0045] In a counter-current model as shown, the cake discharge 24, for
example
radial ports 40, is at or near first axial end 34, while the centrate
discharge 26, for example
axial ports 42, is at or near second axial end 36. Referring to Figs. 3 and
11, centrate
discharge ports 42 may be radially spaced about an axis of rotation 38 of bowl
12. Ports 42
may be positioned to open, and hence drain liquid from, a radius 39A, defined
from axis 38,
selected to achieve a specific pond depth 39B, defined as radial distance from
internal
encircling wall 32, within the bowl 12. The selection of the pond depth 39B
means the ports
42 act as a weir that takes off a top layer of liquid from fluids in the bowl
12. Referring to
Figs. 1, 2 and 3, cake discharge ports 40 may be defined by the spaces between
axial
projections 41 in a ring plate 34A, for example a steel inner (Fig. 12). The
ring plate 34A
may be mounted to an axial end of the beach section 35.
[0046] Referring to Figs. 1 and 3, the screw conveyor 14 may be structured
to permit
axial flow of fluids, for example along an upper surface 63 of feed mixture,
in the
sedimentation chamber 33. In one case axial flow is permitted radially inward
of (as shown),
or axially through, flight 60. Referring to Figs. 3, 3C1, and 3C2, an axial
flow passage 65
may be defined between the conveyor body 50 and a radially inward facing edge
68B of
flight 60, for example pond flight 60B. The axial flow passage 65 may define
axial flow path
or paths 65 that extend across the pond section 37, for example from a feed
inlet such as feed
redirection nozzles 98, to the second axial end 36 of bowl 12.
[0047] Permitting axial flow may improve laminar flow of liquids in the
chamber 33
and reduce turbulence and fluid velocity. With a solid fighting system, the
liquid portion of
the slurry must wind its way around the helix of the flight 60 to reach
centrate discharge 26.
Referring to Fig. 3, by contrast, data suggests that when MFT is processed
using a solid
helical flight 60 (not shown) in the pond section 37, the liquid is forced to
travel, around the
helical flow channel defined by the flight 60, toward end 46. Liquids passing
around the
helix create turbulence that tends to upset settling of the solids in the MFT,
carrying such
solids all the way up to the second axial end 46 of the pond in some cases.
Turbulence may
also reduce polymer (floc) size, decreasing settling efficiency and increasing
the amount, and
hence cost, of flocculant added. Thus, by permitting quasi or fully axial flow
of liquids
toward the centrate discharge 26, such turbulence is reduced, leading to solid
drop out and
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settling along the pond section 37, after which conveyor 14 then carries such
solids towards
the beach section 35.
[0048] Referring to Figs. 1 and 3, in the example shown, axial flow of
fluids is
achieved by mounting the ribbon flight 60 to an outer surface 52 of the
conveyor body 50 via
a plurality of radial gussets or posts 62. Thus, the helical flight 60 is
radially spaced from the
conveyor body 50 to define the axial flow passage or passages 65. A stiffener
part, such as a
helical bar 72, may be mounted to flight 60 to increase the rigidity of flight
60. In some cases
the flight 60 may be mounted on an outer edge of a series of vanes (not shown)
that extend
parallel to axis 38 and are radially spaced about the conveyor body 50. In
further cases,
windows (not shown) may be cut through the flight 60 to provide axial flow.
The gaps 66
between posts 62, conveyor body 50 and inner edge 68B, or the use of windows
in flight 60,
may permit quasi or fully axial laminar flow, for example from the feed inlet
to the centrate
discharge 26.
[0049] Referring to Figs. 1 and 3, the axial flow feature described here
is provided on
the pond section 37 only in some cases. As shown, the flight 60, for example
the part 60A of
flight 60 that extends across the beach section 35, may form a windowless
helix (solid) that
hugs the conveyor body 50, for example by having inner edge 68A of flight 60A
fused to the
conveyor body 50 continuously along a length, for example the entire length as
shown,
throughout the beach section 35. In such cases, axial surface flow of liquids
is permitted only
in pond section 37, but not in beach section 35. A baffle, such as a baffle
ring or disc 70,
may encircle conveyor body 50A in the beach section 35 to act as a weir that
blocks axial
and helical travel of liquids toward first axial end 36.
[0050] Referring to Figs. 1 and 3, a feed redirection nozzle or plurality
of nozzles 98
may be provided to direct feed mixture, entering the sedimentation chamber 33
from the feed
conduit 30, in an axial direction, for example towards axial end 36 and/or
toward the axial
flow passage 65. Referring to Fig. 3, feed conduit 30 may be connected to
supply the feed
mixture to a feed zone or chamber 76, which may be formed within the conveyor
body 50.
The feed conduit 30 may be a non-rotating pipe extended within and coaxial
with a rotating
internal cylindrical shell 31 formed by the conveyor body 50. In some cases
the feed conduit
30 is mounted to rotate. In some cases the feed conduit 30 is mounted to rifle
the feed
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mixture as it passes through the conduit 30. Each nozzle 98 may be structured
to receive feed
mixture from the feed chamber 76 via a respective port, such as a radial port
96, in the outer
surface 52 of the conveyor body 50, for example in between adjacent rows of
fighting 60 as
shown. Referring to Fig. 3D2, plural nozzles 98 may be radially spaced about
an outer
circumference of the conveyor body, for example equidistant from one another
to provide a
balanced influx of feed mixture, around the feed chamber 76, for example
around the
conveyor body 50.
[0051] Referring to Figs. 3, 3C2, and 3D2, each nozzle 98 may be mounted
over, in
some cases integrally projected in a radial direction out of, an outer surface
52 of the
conveyor body 50. Referring to Figs. 3 and 4, the nozzle 98 may define a hood
102, for
example that is positioned over the outer surface 52 and forms an elbow-shaped
flow
passage 101 (Fig. 4) that extends from a radial base opening 110 to an axially
facing nozzle
opening 100. Referring to Fig. 3, the radial base opening 110 may be aligned
with the radial
port 96 in the conveyor body 50 in use. Thus, feed mixture passes into the
nozzle 98,
changes direction, for example from radial to an axial direction, and exits
the nozzle 98,
heading toward the second axial end 36 of the bowl 12.
[0052] With MFT applications, feed mixture supplied via radially directed
ports 96
directly into the sedimentation chamber 33 (no nozzles 98), appears to create
turbulence,
upsetting settled solids passing from the pond to the beach, and in some cases
leading to
wear in the internal encircling wall 32 of the bowl 12. By contrast, nozzles
98 redirect the
feed mixture away from the bowl 12 wall 32 to initiate axial flow in feed
supplied to the
chamber 33, and thus may reduce disruption to settled solids passing to the
beach. The
nozzles 98 shown supply feed mixture directly into the pond. Where axial flow
paths 65 are
defined by the flight 60 and used in combination with nozzles 98, laminar flow
may be
further improved, and wear on the bowl 12 may be reduced as the jet of feed
mixture
supplied to the sedimentation chamber 33 passes into the pond, where the
energy of the
redirected jet is dissipated. Where the nozzles 98 are mounted to the conveyor
body 50 and
the paths 65 are axially aligned with the openings 100 in the nozzles 98 (Fig.
3), the
conveyor body 50, nozzles 98, and paths 65 rotate together and thus always
remain in
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alignment, avoiding or reducing wear on adjacent posts 62 or sides of flight
60 if windows
are used in flight 60.
[0053] Referring to Fig. 3, an outer diameter 107 of the redirection hood
102 is
smaller than an inner diameter 64 of the flight 60B.. Therefore, the
redirected fluids travel
along axial paths that are radially inward of the flight 60B towards the
liquid end hub. In one
case, a minimum or average radius 69 of the radially inward facing edge 68B of
the flight 60
may be greater than or commensurate with a maximum radius 107 of the discharge
opening
100 in the hood 102. Both embodiments may reduce or eliminate the effect of
the incoming
feed mixture jet causing wear on the flight 60, by providing a reduced radial
footprint for the
nozzle 98. In one design configuration the radius 107 is the maximum radial
height of the
hood 102 itself. In some cases the distance of the radius 107 is less than or
equal to half the
radial distance or height 109 of the pond itself The shorter the radial
extension of the hood
102 into the sedimentation chamber 33, the less negative effect, if any, of
the hood 102 on
settled solids being conveyed from the pond to the beach.
[0054] Referring to Figs. 4-10, an embodiment of a nozzle 98 is
illustrated in which a
replaceable wear liner 114 is internally mounted to the nozzle 98 to protect
the nozzle 98
from abrasion from the feed mixture. The internal flow passage 101 of the
nozzle 98 may
mount the replaceable wear liner 114. Referring to Figs. 4, 5, and 7, the hood
structure of the
nozzle 98 may be defined by spaced side walls 104, a rear wall 106, a top wall
108, which
may or may not curved, slanted, or curved and slanted, in order to achieve a
directional
change in the internal flow passage 101. The nozzle 98 may be mounted to the
conveyor
body 50 by a suitable mechanism, for example fasteners such as bolts (not
shown) passed
through bolt holes 105 into the conveyor body 50.
[0055] The wear liner 114 may or may not conform to the shape of some or
all of the
inner surfaces of the nozzle 98 that define the flow passage 101. In the
example shown the
wear liner is a tungsten carbide insert that is divided into two identical
halves 116, though
other configurations and number of parts may be used. The wear liner 114 may
also have a
pair of spaced side walls 118, a rear wall 119, and a top wall 117. The wear
liner 114 may be
formed of a wear resistant material that acts as a sacrificial part that
protects the nozzle 98
13
CA 02932188 2016-06-07
from fluid breakout, and that may be replaced periodically at a lesser expense
than
replacement of the entire nozzle 98.
[0056] Referring to Figs. 3, 3D1, and 3D2, an accelerator, such as an
impellor 80,
may be provided within the feed chamber 76 for rifling or increasing the
angular velocity of
the feed mixture prior to entering the sedimentation chamber 33. An impellor
80 may have
plural fins or vanes 84, for example formed as a series of flat plates as
shown originating
from a common point coaxial with the rotational axis 38 of the centrifuge 10.
[0057] A nose, such as truncated cone or rounded knob 82 may project
coaxial with
the axis 38 in order to divide the incoming feed mixture radially outward, and
the rotating
vanes 84 may act to induce a vortex or other suitable rotating action on the
feed mixture to
bring the mixture up to a relatively higher angular velocity prior to
sedimentation. By
shaping the nose knob 82 as a truncated cone whose pointed end faces the feed
conduit 30,
air occurring in the feed or having become entrained by the feed while flowing
into the inlet
may be passed away along the periphery of the knob, thereby preventing an air
cushion from
occurring in the inlet which may interfere with the intended flow. With the
stated design of
the projection any liberated air may flow along the periphery of the
projection and leave the
inlet through the axial bore 79A. The baffle knob may protrude towards the
inlet pipe. Such
structure may provide for improved control of the inflowing feed when it
changes from
being an axial flow to being a radial flow by softening or reducing feed zone
material
acceleration.
[0058] In some embodiments the projection or knob 82 may have substantially
radial, longitudinal ribs, such as vanes 84, uniformly distributed around the
periphery of the
knob 82, for example in a cross-hair configuration. In some cases (not shown)
there may be
one or more substantially radial ribs (not shown) following helices along the
periphery of the
projection. A larger momentum may thus be transferred to the liquid in the
feed chamber 76
in case the free liquid surface approaches the periphery of the knob 82,
because the rate of
flow of the feed increases. By altering the shape of the ribs, from
rectilinear ribs to ribs that
are curved around the projection following a helix, the flow may be directed
more strongly
towards the ports 96, thereby obtaining an improved axial distribution of the
feed. By
altering the radial extension of the ribs it may be possible to ensure that
the free surface of
14
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the liquid may not approach such a small radius that the liquid back flows out
of the feed
chamber 76 into the overflow chamber 78 through the annulus defined between
the outer
wall of the feed tube 30 and the axial bore 79A of the plate 77.
[0059] Referring to Fig. 3, the feed chamber 76 may be defined by a
radially
confining wall (conveyor body encircling wall 52), a first axial end wall,
such as a plate 79,
and a second axial end wall, such as a plate 77. Referring to Fig. 3C2, the
feed chamber 76
may receive feed mixture through a port 79A in plate 79, for example connected
to feed
conduit 30. Referring to Figs. 3, 3D1, and 3D2, the impellor 80 may be
mounted, for
example fixed, to the plate 77. If fixed, impellor 80 will rotate with
conveyor body 50, thus
inducing vortex action within feed chamber 76 during use.
[0060] Referring to Fig. 3D1, the vanes 84 may, in isolation, be
structured to increase
the velocity of the feed mixture only part of the way up to the angular
velocity of feed
mixture in sedimentation chamber 33 (Fig. 3). The ribs or vanes 84 may extend
a radial
distance 84A from the axis of the impellor 80 (as shown the impellor axis is
coaxial with the
bowl axis 38 so only the axis 38 is illustrated). The radial distance 84A may
be selected to be
a portion, for example less than half, of the radial distance 84B from the
axis 38 to the
convey conveyor body 50 wall 52. The vanes 84 may be radial ribs uniformly
distributed
along the periphery of the baffle knob 82. The ribs may extend along straight
lines or helical
lines or other suitable shapes. The vanes 84 may impart a sufficient rotation
to the feed in the
inlet with the view of obtaining a stable circulation flow in the inlet
cavity.
[0061] Referring to Figs. 3D1 and 3D2, the feed chamber may comprise a
plurality
of lobes 88 radially spaced from one another about the plate 77 to define
radial feed passages
90. For example, lobes 88 may be formed in, for example mounted to, the plate
77. The
lobes 88 may project out of the plate 77 from respective positions around a
circumference of
plate 77, for example a peripheral portion 89 of plate 77, and be radially
spaced to define
radial feed passages 90. Each passage 90 may extend to a respective nozzle 98.
The side
walls 93 of each lobe 88 in use act upon the feed mixture to further increase
the angular
velocity of the feed mixture beyond what is achieved with the accelerator. The
side walls 93
may be structured, for example curved as shown, to reduce the shock imparted
on the feed
mixture in transitioning from lower to higher angular velocities. By
positioning lobes 88
CA 02932188 2016-06-07
about the periphery 89 of plate 77, the impellor blades 84 are mounted
radially inward of the
lobes 88 such that the lobes 88 and vanes 84 complement but do not interfere
with one
another.
[0062] In the example shown in Fig. 3D1, each side wall 93 of a lobe 88
has the
shape of the top surface of an airfoil. For example, each side wall 93 has a
sharp, for
example planar trailing curve 93B, which may form an obtuse angle with the
inside surface
of the wall 52 of the conveyor body 50. Each side wall 93 may also have a
rounded leading
curve 93A, which may wrap back around itself to form an acute angle with the
wall 52 of the
conveyor body 50. As the conveyor body rotates, the feed mixture, after coming
into contact
with the impeller and being redirected, is contacted by the leading curve 93A,
whose curve
imparts rotational force upon the feed mixture in a gentler fashion than would
a wall whose
surface follows a radius of the feed chamber 76. Each passage 90 may also
expand in width
up to the discharge port 96 to nozzle 98, in order to create a pressure drop
that further
accelerates the feed mixture. The side walls 93 may each mount a replaceable
wear liner 94,
for example made of a suitable sacrificial material, such as tungsten carbide.
Other shapes
may be used for side walls 93 and liners 94.
[0063] Data suggests that while processing MFT with a traditional decanter
centrifuge lacking an accelerator, the feed enters the chamber 33 at a
relatively low angular
velocity relative to that of materials in the chamber 33, and receives a
significant excess
amount of energy, resulting in turbulent flow. Such turbulence may be large
enough to shear
flocculating polymers, reducing polymer size and requiring relatively large
amounts of
flocculant to achieve the desired agglomerating effect. When an accelerator is
used, the
incoming feed mixture causes relatively less turbulence, and hence polymer
shearing, despite
the fact that the incoming feed may not have attained the same angular
velocity as the
conveyor 14 (in some cases 80% of the bowl 12 speed is achieved). In addition
the
comparatively long path of flow in the thick liquid layer adjacent the nozzle
98 may permit
excess energy to be dissipated in a manner as to prevent or reduce the
occurrence of
turbulent flows from liquids moving in a helical fashion around flight 60 to
the centrate
discharge.
16
CA 02932188 2016-06-07
[0064] Referring to Fig. 3, the nozzle 98, or a port 96 that supplies the
nozzle 98 and
is defined in the outer surface 52 of the conveyor body 50, may be located
radially outward
of the impellor 80 in a plane, perpendicular to a centrifuge axis 38, defined
by the impellor
80. Thus, the feed mixture enters the feed chamber 76, changes from an axial
to a radial
direction under acceleration, and exits the feed chamber 76. Such a
configuration causes less
turbulence and wear than a configuration where the feed enters the chamber
moving in a first
axial direction and is forced to change to a second axial direction opposite
the first axial
direction prior to discharge from the feed zone into the sedimentation
chamber, or vice versa.
[0065] Referring to Fig. 2, various parts may be provided to operate the
centrifuge
10. For example, a drive, such as a motor and gearbox 22 may be mounted to
rotate the bowl
12 and conveyor 14. The gearbox 22 may connect to simultaneously rotate the
journaled
screw conveyor 14 and the bowl 12 at different angular velocities relative to
one another, for
example through respective drive shafts (not shown). By rotating the bowl 12
at a different
speed, for example 1-100 rpm faster than the conveyor 14 (Fig. 3), the
conveyor 14 applies a
relatively gentle conveying effect to move settled solids towards the cake
discharge 24. In
some cases, the drive comprises plural drive motors and gearboxes that each
drive and
support a respective one of the conveyor 14 or bowl 12, for example if each
drive were
mounted on a respective axial end 34, 36. One or both the first and second
axial ends 34 and
36 may each be mounted to a respective bearing unit 20, such as an oil bath or
grease bearing
unit, and the bowl 12 and conveyor 14 may rotate around a common axis 38. The
centrifuge
may be mounted on a suitable structural frame 16, with or without a removable
hood or
casing 28.
[0066] Referring to Figs. 3, 3B1, 3B2, 3C1, and 3C2, a buffer or overflow
chamber
78 may be provided in association with feed chamber 76. The purpose of the
overflow
chamber 78 is to provide an alternate route for feed mixture to enter the
sedimentation
chamber 33 in the event that the feed chamber 76 becomes plugged or
restricted, for example
as a result of over feeding. In the example shown the overflow chamber 78 is
axially closer
to axial end plate 34A, such that feed mixture travels from conduit 30,
through a port 81A in
a plate 81, axially through the overflow chamber 78, and through port 79A in
plate 79 to
enter the feed chamber 76.
17
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[0067] Overflow chamber 78 may incorporate one or more of the features
disclosed
in this document for feed chamber 76 and nozzles 98. The overflow chamber 78
is shown
with purely radial outlets 124, although nozzles (not shown) may be mounted
over such
outlets 124, and in some cases radially staggered so as not to be interfered
with by the
position of nozzles 98 of feed chamber 76. The plate 77 may incorporate axial
lobes 120
whose side walls define radial passages 122 to ports 124. Thus, if feed
chamber 76 becomes
plugged, back pressure builds, forcing incoming feed mixture to pass through
passages 122
and ports 124 into chamber 33, rather than traverse feed chamber 76. The
overflow chamber
78 is intended to provide a temporary solution to plugging without locking the
system up
completely and causing a potentially damaging high pressure situation.
[0068] Referring to Figs. 2 and 3, centrifuge 10 may be used in a
continuous process
to effect a phase separation of a feed mixture. As above, feed mixture, such
as including
MFTs produced from an oil sands process, may be supplied through a feed
conduit 30 into a
feed chamber 76. Nozzles 98 may be used to direct the feed mixture into the
sedimentation
chamber 33, in which the nozzle directs the feed mixture toward an axial flow
passage 65
defined between the conveyor body 50 and an inner edge 68B of a conveyor
flight 60. The
bowl 12 and conveyor body 50 may be rotated to effect at least a partial phase
separation of
the solids and liquids of the feed mixture. Solids may be discharged through
the cake
discharge 24, and liquids discharged through the centrate discharge 26.
[0069] Feed mixture may be supplied to chamber 33 via feed conduit 30 by a
suitable
pumping mechanism, and in a continuous fashion. For example, feed conduit 30
may enter
the centrifuge by passing through a bearing unit 20 in one of the axial ends
34, 36, and
connecting to the internal feed box or chamber 76 (Fig. 3). In some cases the
feed mixture
may comprise mature fine tailings produced from an oil sands process, for
example if the
feed conduit 30 is connected to receive such a feed mixture. In the example
shown, a pump
136 draws MFT from a tailings pond 134, at a level sufficiently below the pond
surface 132
to access MFT. In other cases, other types of fluids from tailings pond 134
may be accessed.
The MFT is pumped via line 130 to feed conduit 30. Other pre-centrifuge
processing steps
may be carried out, for example to heat or dilute the MFT by addition of
water.
18
CA 02932188 2016-06-07
[0070] The feed mixture supplied to the feed chamber 76 may also comprise
a
suitable flocculant. In flocculation, a chemical is added to agglomerate
particles, which may
be destabilized by addition of a coagulant, into relatively large particles
colloquially called
flocs, whose relatively large molecular weight causes an increase in density
and drop out
from the liquid phase. Flocculants include relatively high molecular weight,
water soluble
organic polymers. A flocculant may be added from a suitable source, such as a
tank 138,
using machinery such as an addition pump 140 and a mixer in some cases (not
shown).
[0071] Phase separated materials, such as liquids and solids discharged
from
centrifuge 10, may be subject to further processing or disposal as desired.
For example,
solids from cake discharge 24 may be ejected onto a conveying device 142,
which may
transport same to a disposal area 144. Liquids remove from centrate discharge
26 may be
transported via a line 146 to a suitable disposal site, such as the tailings
pond 134 where the
feed mixture was taken from. Oil and water separation may be carried out on
centrate to
remove entrained bitumen. Connections and communication between parts may
occur
through intermediate components. Radial ports 96 may have a suitable position
and shape,
for example such may be spaced radially and axially from one another, in a
helical fashion.
Ports 96 may be circular, oval, or other suitable shapes.
[0072] Referring to Fig. 13, an example of an oil bath bearing assembly 20
is
illustrated supporting the first axial end 34 of the centrifuge. A similar oil
bath bearing unit
may support the other axial end of the centrifuge. The bearing assembly 20 may
rest on an
external part or ledge of the casing 28 as shown, below a lid 150 of the
casing, and may
receive a rotating shaft 152 extended from bowl 12. The feed conduit (not
shown) may
extend through the interior of the shaft 152 in use to supply feed mixture to
the centrifuge.
Inboard and outboard seals, such as labyrinth seals 158A, and 158B,
respectively may be
positioned on either axial end of a pillow block 162, which sits over top a
bearing 160 and
defines an oil bath chamber 164. Bearing 160 receives oil from a nipple 162,
and oil drain
=
ports 162 may be located at the base of the chamber 164 for removing oil from
the oil bath
chamber 164.
[0073] Labyrinth seals 158A and 158B may not contact the shaft 152, and
may be
provided with sufficiently close tolerance to shaft 152 such that the ingress
of cake into the
19
CA 02932188 2016-06-07
bearing 20 is reduced relatively to a conventional grease bearing. Also, the
provision of the
oil bath bearing 20 outside the casing 28 reduces ingress of cake into the
unit. Moreover, the
cycling of an oil bath through the unit acts to flush out particulates that
find their way into
the unit 20, further extending part life. It is believed that such bearings
may have a field life
of five or more years, as opposed to the relatively shorter life span of an
internal grease
bearing, particularly in the context of processing highly abrasive MFT cake.
[0074] There may be provided a close fit between an outer edge 71 of
flight 60 and
the bowl 12, such as 1-2 mm or other distances. More than one flight 60 may be
provided,
for example a double helix. Flights 60A and 60B may be separate or connected
flights. Bowl
12 speeds of 800 - 4000 rpm may be used or other suitable speeds. Conveyor
fighting 60
may have a suitable rake, such as a positive, negative, or neutral (as shown)
rake.
[0075] A centerless conveyor may be used, for example without a central
conveyor
body 50. Centrifuge 10 may be used in applications other than processing MFT
from oil
sands, such as processing tailings from a mining process. MFTs may comprise
solids of 10-
45 % by weight of the feed mixture, although other ranges may be used. A
vertical or
horizontal centrifuge may be used. A co-current or counter-current flow may be
used. A
solid bowl 12 may be used with a conical, cylindrical, and cylindrical-conical
configuration.
[0076] The centrifuge 10 may be used to effect a liquid-gas-solid, liquid-
liquid, gas-
liquid separation, or other suitable arrangements. Nozzles 98 may impart a
direction change
of ninety degrees to the feed mixture. In some cases the nozzles 98 may direct
the feed
mixture in an axial direction, which may be a vector with a dominant axial
scalar component,
and forming an angle with respect to axis 38 of less than forty five degrees,
for example less
than ten degrees and in some cases zero degrees. The conveyor body 50 may be
solid or
hollow as shown.
[0077] The mouth of the inlet apertures (for example nozzles) may be
located on a
radius greater than the radius to the outlet openings, such that a peripheral
area of the inlet
outwardly defined by the radius to the inlet apertures is free of carriers,
inwardly extending
projections. Parts of the centrifuge 10 may be arranged to inherently balance
the device, for
example by uniformly distributing nozzles, feed passages, and other parts
radially about the
circumference of conveyor body 50. Weight balance may be achieved by arranging
CA 02932188 2016-06-07
components to have a center of gravity along axis 38 during use. The impellor
80 and the
lobes 88 may be fastened to the plate 77, for example in a removable fashion
to permit
removal in case such was not needed with the particular feed mixture
processed, or in order
to replace a worn part.
[0078] Plates or hubs 34A and 36A (Fig. 3) may each have an axial opening
44, 46,
respectively, for various purposes such as receiving the feed conduit 30
and/or mounting
drive shafts or bearings. Beach part 50B of conveyor body 50 may be shaped in
a conical
fashion to follow the shape of the beach section 35 of bowl 12. In one
embodiment the inlet
pipe or feed conduit 30 may be repositioned, for example along the axis 38 to
adjust the
distance between the outlet of the feed conduit 30 and the knob 82 or
accelerator. Thus, the
diameter of the feed jet at the baffle knob 82 may be altered by displacement
of the feed
conduit, thereby making it possible to adapt the flow in the feed chamber 76
to the type of
feed and/or the rate of flow thereof. The impellor 80 may be geared to rotate
faster or slower
than the rotation of conveyor body 50. Flocculant may be added to the feed
mixture before,
during, or after (by injection into the sedimentation chamber) the feed
mixture is supplied to
the sedimentation chamber section. Radially spaced may refer to the fact that
parts are
spaced about a circumference of an object, whether the circumference is taken
by a cross-
section or is projected into a plane.
[0079] In the claims, the word "comprising" is used in its inclusive sense
and does
not exclude other elements being present. The indefinite articles "a" and "an"
before a claim
feature do not exclude more than one of the feature being present. Each one of
the individual
features described here may be used in one or more embodiments and is not, by
virtue only
of being described here, to be construed as essential to all embodiments as
defined by the
claims.
21
