Note: Descriptions are shown in the official language in which they were submitted.
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1
THREE-PHASE ROTARY SEPARATOR
BACKGROUND OF THE INVENTION
This invention relates generally to separation of three fluid phases-
gas, oil and water, and more particularly concerns achieving such separation
using rotating separator apparatus. In addition, the invention concerns
methods
of operating rotary separator apparatus in relation to scoop means immersed in
a liquid ring on the rotary separator. Solids entrained in the flow must also
be
separated.
In existing non-rotary methods, a large gravity separation tank is
required to be used, and only partial separation of oil and water phases is
achievable. Therefore, additional treatment is required for separating those
constituents. Secondary treatment methods require expenditure of large
amounts of power, as for example via high speed centrifuges.
Another advantage is the size and weight of the required vessels.
For offshore oil and gas productions, the large separation vessels require
large,
expensive structures to support their weight.
From US-A-4,087,261 there is known a rotating separator
apparatus which shows scoops fully submerged in the apparatus to remove
separated liquids. As shown, the flowrate from a fully submerged scoop is
fixed
by the liquid velocity and the scoop inlet area. Increases in flowrate would
cause
the liquid entering a particular submerged scoop to overflow it and go into
another scoop. Decreases in flowrate would cause the scoop to take in
additional liquid from another zone.
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SUMMARY OF THE INVENTION
it is a major object of the invention to
provide a simple, effective method and appa.ratus meeting
the above needs.
According to the present invention, there is provided a method of
operating a rotating separator apparatus, to which fluid including gas and
liquid
is supplied in a fluid jet as via a nozzle , the method comprising the steps
of
providing at said apparatus an outlet for flowing li(juid A of higher density,
and
providing at said apparatus an outlet for flowing liquid B of lesser density,
said
liquids A and B having a stable interface location determined by the relative
locations of said outlets, providing at least one of said outlets in the form
of a
scoop immersed in at least one of said liquids collecting as a centrifugally-
induced liquidous ring travelling relative to the scoop, and further
a) separating the liquids from the gas in said stream, at a first zone within
said rotating apparatus,
b) separating the liquids into liquids of differing density at a second zone
within said apparatus,
c) said separating including providing a scoop immersed in at least one of
said liquids traveling relative to the scoop, the method being characterised
by
the further step of
d) providing a movable inlet barrier in association with the scoop to block
entry of gas into the scoop.
According to the present invention, there is also provided a rotating
separator apparatus comprising means as a nozzle to supply a fluid including
gas and liquid to the separator, the separator further comprising an outlet
for
flowing liquid A of higher density, and an outiet for flowing liquid B of
lesser
density, said liquids A and B having a stable interface location determined by
the
relative locations of said outlets, at least one of said outlets having the
form of a
scoop immersed in at least one of said liquids collecting as a centrifugally-
CA 02305407 2005-04-21
2a
induced liquidous ring travelling relative to the scoop, the apparatus further
camprising
a) means for separating the liquids from the gas in said stream, at a first
zone within said rotating apparatus,
b) means for separating the liquids into liquids of differing density at a
second zone within said apparatus,
c) means for said separating including a scoop immersed in at least one of
said liquids travelling relative to the scoop, and being characterized by
d) a movable inlet barrier in association with the scoop to block entry of gas
into the scoop.
it is another object to provide method and
apparatus to achieve complete separation of- gas, oil,
water, and solids. It operates either by the two-phase'
fluid energy or by a supplementary motor drive. It has
a self-regulating featuze to handle widely varying ratios
of gas, oil and water with no externa:L controls.
A further olaject concerns removal from the
fluid jet of entrained solid parti.cles, the method
including providing a solids removal passage in" the
rotating-separator apparatus, and including separating
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i J . . , = , . . .
t . 1'= . a r . ' ' i ' . t i ' , t '.
~the particles which are separated. by transfer to the
passage.
Yet another object includes provision at the
rotating separator apparatus of a passage for receiving
a liquid A of higher density, providing at the apparatus
an outlet for liquid A, and providing at the apparatus an
outlet for liquid B of lesser density, the liquids A and
B having a stable interface location determined by the
relative locations of the outlets and passage, such that
substantially complete separation of flowing liquids A
and B occurs for a relatively wide range of flows. At
least one of the outlets may advantageously be in the
form of a scoop immersed in at least one of the liquids
flowing as in a liquidous ring relative to the scoop. A
movatie barrier may be provided in association k ith
the scoop to block entry of gas into the scoop.
An additional object includes supporting the
barrier for movement in response to changes in force
applied to the barrier by at least one of the liquids
flowing relative to the scoop.
A still further object includes providing one
or more of the outlets at the rotating separator
apparatus to have the form of an open weir, and flowing
liquid via that weir to a passage leading to a liquid
nozzle, as will be described.
Finally, it is an object of the invention to
provide for liquid leaving the nozzle in the form of a
jet producing thrust, and including transferring the
thrust to the rotating separator apparatus.
ey
These and other objects and advantages of the
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invention, as well as the details of an illustrative embodiment, will be more
fully
understood from the following specification and drawings, in which:
DRAWING DESCRIPTION
Fig. 1 is a sectional view, i.e., an axial radial plane, of three-phase
rotary apparatus incorporating the invention;
Fig. 1 a is a view like Fig. 1;
Fig. 2 is a fragmentary section showing details of a scoop having
an entrained immersed in a rotating ring of liquids, and taken in a plane
normal
to the axis of separator rotation;
Fig. 3 is a fragmentary section taken on lines 3-3 of Fig. 2;
Fig. 4 is a view like Fig. 2 showing a modification;
Fig. 5 is a view taken on lines 5-5 of Fig. 4; and
Fig. 6 is a fragmentary section showing an open weir outlet to a
liquid nozzle.
DETAILED DESCRIPTION
Fig. 1 shows a version of the three-phase rotary separator
structure 32. A mixture of oil, gas and water is expanded in nozzle 17. The
resulting gas and liquid jet 1 is well collimated. The jet impinges generally
tangentially onto a moving (rotating) surface
CA 02305407 2005-04-21
2. As shown in U.S. Patent 5,385,446, the surface is solid with holes 3, to
permit
drainage of the liquids and solids. Surface 2 is defined
by the inner side of a rotating separator annulus 2a
connected as by rotor 8 and structure 31 to a rotating
shaft 19 of structure 32. Shaft bearings are shown at=
locations l3a. The moving surface may alternatively be
comprised of the separated liquid, in which case no solid
surface 2 is required. -
The centrifugal force field acting on the gas
and liquid jet, when it impacts the moving surface,
causes an immediate radially inward separation of the gas
from the liguids. The separated gas flows through gas
blades 3 in the Yotor 8, transferring power to the rotor
and shaft 19. The gas leaves through an exit port 18.
Blades 9 are.spaced about the rotor axis 19b.
The oil and water, and any particulate solids,
flow into the. space between the outer wall 20 and the
separating surface 2, in the, centrifugal force field.
The grea-ter density of water causes it to acquire a
radial outwar-d velocity and separate from the oil f low 4.
Separated water is indicated at S. The separating oil
and water flow axially through slots at location 3a in
the rotor, toward the oil outlet 10, and toward the water
outlet 13, respectively.
If the tangential velocity of the gas and
liquid jet 1 impinging on the separating surface 2 i s
greater than the rotating surface speed, the liquids wi.3_l..
be slowed by frictional forces transferring power to the
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separating surface and hence to the rotor and shaft. Zf
the tangential velocity of the jet is lower than the
desired rotating surface speed, external power must be
transferred to the shaft, and hence rotor and separating
surface, to drag the slower liquids up to the speed of
the rotating surface. The power can be transferred, for
example by a motor, or by the shaft of another rotary
separator.
The solids, being heavier than the water, are
thrown to the inner side of the wall 20. The solids are
collected at the farthest radial position 6 of that wall,
and flow at 21 with a small amount of water into a volute
22 from which they are discharged.
A barrier 12 to the balance of the water and
cll- flow-ng --g'tGFardlV_.,_..: s tile water to flow through
structure-defined passages 23 located below (outwardly
of ) the water-oil interface 7, formed by the centrifugal
force field.
The relative placement of the oil outlet 10 in
the oil collection zone 10a, and the water outlet 13, in
the water collection zone 13a beyond barrier 12 causes
the oil-water interface 7a to form at a location radially
outward of both the oil outlet and the water outlet, but
which is radially inward from the water passages 23.
This location of the rotating interface at 7a effects
separation of the oil and water. Note that interface 7a
intersects barrier 12, and that 2ones 10a and 13a are at
opposite axial sides of barrier 12. The interface radial
location is determined by the following relation, listing
dimensions as shown in Fig. 1a:
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poW ( r2s - r2o )= P~,m ( r't2_r2~ )
where p, = oil density
põ = water density
m = rpm of surface 2
ri = radius to oil - water interface
r, = radius to oil outlet
rõ = radius to water outlet
The interface location is independent of the
relative amounts of water and oil, so long as the
pressure drop of liquid in flowing from the interface
location to the outlets is small compared to the large-
centrifugally-induced head from the rotating liquids.
The liquid outlets are typically.open scoops of the type
shown in Figs. 2, 3,=4, and S.
In Fig: 2 a rotary separator is show-n at 110
and having an annular portion 111 with a surface llla
facing radially inwardly toward the separator axis 112 of
rotation (the same as axis 19b in Fig. 1). A liquid film
or layer builds up-as a-ring 113 on the rotating surface
and is shown to have a thickness "t". Such liquid may
typically be supplied in a jet, as from a two-phase
nozzle. The nozzle, jet'and separator elements are
schematically shown in Fig. 5. See also U.S. P atent
5,385,446, incorporated herein by reference, and wherein
the momentum of the jet is transferred to the separator
at its inner surface llla, inducing.rotation.
A scoop or diffuser structure is provided at
114 for removing liquid in the ring 113. The scoop has
an entrance 115 defined by radially separated inner and
outer lips 115a and 115b presented toward the relatively
~-' CA 02305407 2000-03-30
PCT/N097/00267
,' .
oncoming liquid in the ring. Lip 115b is immersed"In the
liquid ring; and lip 115a is located radially inwardly of
the inner surface 113a of the liquid ring. Ring liquid
at 113b, radially inwardly of the scoop lip 115b, enters
the scoop at 113c, and flows via a passage 116 in the
scoop toward outlet 117. The scoop is normally non-
rotating, i.e., fixed, or it may rotate, but at a slower
rate than the separator.
Gas that has separated from the liquid that
builds up as layer 113 collects in the separator
interior, as at 118. Since lip 115a lies inwardly of the
liquid ring inner surface 113a, there is a tendency for
separated gas to enter the scoop at region 120, due to
the drag effect of the rotating liquid ring upon the gas
adjacent the liquid surface 113a.
Barrier structure is provided, and located
proximate the scoop entrance or inlet, to block gas
exiting to the scoop. one such barrier structure is
indicated at 121, and as having a-barr-ier surface 121a
projecting radially outwardly of the scoop inner lip
115b, i.e., toward the liquid ring, whereby liquid on the
ring travels relatively past barrier surface 121a to
enter the scoop at its inlet. The barrier surface has a
doctor tip extent, indicated at 121b, controlling the
radial thickness at t2 of the liquid ring that enters the
scoop. In this regard, tz is normally less than tl. The
doctor tip extent 121b is also normally of a width
(parallel to axis 112) about the same as that of the
scoop inlet.
The barrier surface is shown to have taper in
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,~. CA 02305407 2000-03-30
PCT/NO97/00267
' .; ,9 , .", ,". ,='= ''~.- , ; ; ; ; : ; ;
the direction of relative travel of liquid that enters
the scoop, and that taper is preferably convex, to
minimize or prevent build up of liquid in a turbulent
wake at the scoop entrance. Note in Fig. 3 that the
scoop inlet width w is of lesser extent than the liquid
in the ring, i.e., ring liquid exists at widthwise
opposite sides of the scoop, as at 113e and 113f.
Accordingly, separated gas is prevented, or
substantially prevented, from entering the scoop to flow
to the outlet, and an efficient gas-liquid separation is
achieved.
Another aspect concerns the provision of means
for effecting controllable displacement of the barrier
structure toward the liquid ring, whereby the thickness
t2 of the liquid layer entering the scoop is controlled.
In the Fig. 2 and Fig. 3 example, such barrier
displacement control means is shown in the form of a
spring 125, positioned to urge the barrier structure
toward the liquid ring. A balance is achieved between
the force of the spring acting to urge the barrier toward
the liquid ring, and the force of liquid impinging on the
convex surface 121a of the barrier, to position the
barrier radially as a function of separator rotary speed,
liquid ring. rotary speed, and liquid viscosity, whereby
a controlled rate of liquid ingestion into the scoop to
match liquid supply to the ring is achieved, and without
air ingestion, i.e., the inlet is left open to liquid
inflow, but is blocked for gas.
Guide structure is also provided for guiding
such displacement of the barrier structure as it moves in
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. , . . ,,. , , . ,. . ,,. ,.
direction toward and away from the liquid ring. See for
example engaged relatively sliding surfaces 129 and 130
of the barrier and scoop stem 131, attached to the scoop
and sliding in the bore in a sleeve 129a attached to the
scoop. A stop 134 on the stem is engageable with the end
133a of the sleeve to limit radially outward movement of
the barrier structure, and its doctor tip, as referred
to.
Figs. 4 and 5 show use of a foil 40 or foils
immersed in the liquid and angled relative to the
direction of liquid ring travel, to receive liquid
impingement acting to produce a_force component in a
radially outward (away from axis 12) direction. That
foil is connected to the barrier structure 121, as via
struts.42, to exert force on the barrier acting to move
it into or toward the liquid. Such force countered by
the force exerted on the barrier convex surface, as
referred to above, and a balance is achieved, as referred
to. No spring is used in this example.
The advantage of these types of outlets for the
three-phase separator are that large changes in liquid
flow rate can be accommodated with only small changes in
liquid height. This enables large changes in oil flow or
water flow to be swallowed by the outlet without large
increases in the pressure drop or location of the oil-
water interface 7.
Another form of outlet is shown in Fig. 6. An
open outlet passage 50 is placed at the location of the
desired radially inwardly facing oil level 51. The oil
flows into the passage and forms a gas-oil interface 43
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51, at the location where the jet flow 45, from a liquid (oil) nozzle 44,
which is
produced by the centrifugally-induced head from that interface location,
equals
the incoming oil flow. Nozzle 44 is spaced radially outwardly from outlet
passage
50, and connected thereto by a duct 54 (an open weir), which rotates with the
rotor. The nozzle opening is preferably sized for the maximum possible oil
flow.
Flows less than that maximum cause the interface 43 to move more radially
outward, reducing the head, and hence flow from the nozzle.
A similar arrangement is shown for the water outlet 52. The
principles are the same as described for the oil outlet. See water radially
inwardly facing level 62, gas-water interface 63, flow 65 from liquid (water)
nozzle 64, and duct 70 (an open weir).
The provision of these outlets enables additional power to be
generated from the reaction forces of the water and oil jets emanating from
the
associated nozzles. The outlet flows can be collected in volutes similar to
that
previously shown in Fig. 1 a.
Either type of outlet can be used for either liquid, independently of
the type of outlet chosen for the other liquid.
