NOZZLE FOR DISC CENTRIFUGE BOWL

BUSE DESTINEE AU BOL D'UNE CENTRIFUGEUSE A PLATEAU

English Abstract

The nozzle has a longitudinal bore comprising two
straight segments joined by an elbow. The surface of the bore
is smoothly curved and continuous through the change of
direction, to prevent the eddying associated with prior art
change-of-angle linear junctions of the segments. Erosion of the
nozzle is diminished by this change.

French Abstract

La buse est constituée d'un alésage longitudinal comprenant deux segments rectilignes joints par un coude. La surface de l'alésage est continue et courbée régulièrement pendant le changement de direction pour empêcher la turbulence associée aux raccordements linéaires du changement d'angle du modèle antérieur des segments. Ce changement permet de diminuer l'érosion de la buse.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A nozzle for use in the bowl of a disc centrifuge
machine comprising:
a duplex nozzle body comprising an inner sleeve,
forming a longitudinally extending passageway, and a contiguous
outer sleeve forming a sheath supporting the inner sleeve along
most of its length;
the passageway consisting of an inlet segment and an
outlet segment joined by an elbow segment, the centerlines of the
inlet and outlet segments being angularly disposed in an obtuse
angle orientation;
the surface of the elbow segment being smoothly curved
and continuous with the surfaces of the inlet and outlet
segments, free of change-of-angle linear junction lines.

Description

~ , ~O~
1 FIELD OF ~HE INVENTION
2 This invention relates to a restrictive nozzle for use
3 in the outlet of a bowl of a disc centrifuge.
4 BACKGROUND OF ~HE :[NVENTION
The present invention was conceived in response to
6 inade~uate nozzle service li~e in disc centrifuges. rrhese
7 centrifuges are machines which were originally used to separate
cream from milk in the dairy industry. They were pressed into
9 service in the oil sand plants o~ Alberta for the purpose o~
treating de-sanded bitumen froth, to separate the contained water
11 and fine solids from the bitumen. However, when used in this
12 service, severe wear and short operating life, of both the
13 nozzles and the bowl with which they were associated, were
14 e~perienced.
More particularly, a disc centrifuge comprises a
16 stationary conical casiny, within which is arranged a spinning
17 distributor, stack of closely spaced, conical discs and a
18 containing bowl. Bitumen froth is fed from above into the center
19 o~ the hollow spinning distributor. The froth leaves the
distributor and enters the spaces between the discs. Inertial
21 forces cause water ana solids to migrate outwardly toward the
22 spinning bowl wall. Bitumen works its way inwardly and
23 accumulates near the center of the stack, from whence it is
~4 removed as the light phase discharge. The water and solids are
discharged from the spinning bowl through a plurality o~ radial
26 apertures formed by the bowl wall. Flow through these apertures
27 is controlled by restrictive nozzles mounted in them.

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1 Ln the operation of the disc centrifuge, there is an
2 interface between separated oil and separated water and solids
3 in the space between a pair of adjacent discs. This interface
4 is referred to as the equilibrium line or "E-line". The nozzle
controlling the r~te of discharge of water and solids from the
6 space affects the location of the E-line. If the bore of the
7 nozzle is too large, then the rate of discharge from the space
8 is excessive, the E-line moves toward the nozzle, and oil begins
9 to be lost with the water and solids. This is an obviously
undesirable result.
11 In service, the noz~les are subjeat to high wear rates,
12 with consequent enlargement of the nozzle bore. In the early
13 days of the technology,-the nozzles would only last 4 to 12 hours
1~ before the location of the E-line would be deleteriously
affected. In addition, enlargement of the bore outlet would
16 increase the diameter of the erosive stream issuing from the
17 nozzle. The stream could contact the outer surface of the bowl
18 wall and cause it to wear. So, in addition to the costly loss
19 of oil with the water and solids, nozzle bore enlargement would
lead to significant replacement and repair costs.
21 The throughput rates of the plant circuits have been
22 gradually pressed upwardly over the years of operation. During
23 the early days of the plant, the disc centrifuges would process
24 10 - 25 million barrels o~ dry bitumen (oil). Today they process
about 80 million barrels. This has subjected the nozzles of the
26 centrifuges, which have remained constant in number in
27 applicant's plant, to ever increasing wear.

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1 The materials and design of the nozzles have evolved
2 and improved over the 20 year life of applicant's plant. Prior
3 to the present invention, average nozzle life had been extended
4 to about 560 hours.
Im~ediately prior to the present invention, ~he nozzle
6 design had evolved to that illustrat:ed in Figure 1. The nozzle
7 a comprised an outer sleeve b formed of stainless steel. An
8 inner sleeve c formed from sintered tungsten carbide powder was
9 contained and supported by the outer sleeve. The innex sleeve
formed a bore d created by machininy. This bore had an anyular
11 deviation from linear, the nozzle outlet e being typically
12 disposed at an angle of 110~ relative to the bore inlet.
13 The bore d was created by utilizing an inner sleeve c
14 comprising inner and outer separate segments g, h which met to
create the elbow of the inner sleeve, forming the segments around
16 generally cylindrical sand cores and machining the rough bores
17 produaed to finely controlled dimensions. Thus the finished bore
18 d was machined from two different angular orientations meeting
19 at the elbow i of the deviation. The surface of the finished
bore at the slbow was characterized by angular changes involving
21 linear junction lines j.
22 SUMMARY OF THE INVENTION
23 The present invention is based on the discovery that
2~ the sharp angular changes in the bore surface of the prior
n~zzles induced erosive eddies in the flow stream. By changing
26 to a bore having a smoothly curved surface at the elbow, the flow
27 pattern of the stream has been altered with significant reduction
28 in wear.

2 ~ 7 '~
1 I~ summary then, the present i.nvention provides a
2 nozzle for use in association with an outls-t of a disc centrifuge
3 bowl, comprising:
4 - a duplex nozzle body comprising an inner sleeve,
forming a longitudinally extending passageway, and
6 a contiguous outer slaeve forming a sheath
7 supporting the inner sleeve along most of its
8 length;
9 - the passageway consisting of an inlet segment and
an outlet segment joined by an elbow segment, the
11 centerlines of the inlet and outlet segments being
12 angularly disposed in an obtuse angle orientation;
13 - the surface of the elbow segment of the passageway
14 being smoothly curved and continuous with the
surfaces of the inlet and outlet segments, free
16 of change-of-angle linear junction lines.
17 DESGRIPTION OF THE DRAWINGS
18 Figure 1 is a cross-sectional view of a prior
19 embodiment of a nozzle having linear junction lines at the elbow
of the passayeway or bore;
21 Figure 2 is a cross-sectional view of the nozzle of
22 Figure 1 provided with a smoothly curved bore at its elbow
23 segment;
24 Figure 3 is a plot comparing the increase in nozzle
bore dimension over time for the nozzles of Figures 1 and 2.

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1 DESCRIPTION OF THE PREFERRED EMBODIMENT
2 As illustrated in Figure 2, the nozzle 1 comprises a
3 duplex body 2 formed by an inner sleeve 3 and a contiguous outer
4 sleeve ~ forming a sheath which supports the inner sleeve 3 along
S most of its length. The inner sleeve 3 is formed of titanium
6 carbide and the outer sleeve 4 o~ stainless steel.
7 The inner sleeve 3 forms an internal longitudinal bore
8 5 comprising an inlet segment 6 and outlet segment 7 joined by
9 an elbow segment 8. The inlet and elbow seyments 6, 8 are
tapered and the outlet segment 7 is cylindrical. The diminishing
11 diameters of the inlet and elbow segments 6, 8 are therefore
12 larger than that of the outlet segment 7, the nozzle 1 therefore
13 being restrictive in nature. The centerlines of the inlet and
14 outlet segments 6, 7 are angularly disposed in an obtuse angle
orientation.
16 The surface of the elbow segment 8 is curved and
17 smooth, being free of linear junction lines at the joinder of
18 ~ore surfaces disposed at different angles.
19 Figure 3 provides test data showing i.ncreasing relative
bore enlargement of two nozzles, one provided in accordance with
21 Figure 1 and the other in accordance with Figure 2. The two
22 nozzles were identical except for the shape of the elbow segment
23 and they were tested in the same disc centrifuge at the same
24 time.

Representative Drawing