EP0777531A1

EP0777531A1 - Separator

Info

Publication number: EP0777531A1
Application number: EP95930742A
Authority: EP
Inventors: Bjorn Christiansen; Karl Petter Loken
Original assignee: Den Norske Stats Oljeselskap AS; Kvaerner Process Systems AS
Current assignee: Fjords Processing AS; Equinor ASA
Priority date: 1994-08-31
Filing date: 1995-08-30
Publication date: 1997-06-11
Also published as: NO943226D0; NO180258C; NO943226L; WO1996006683A1; NO180258B; AU3400795A; CA2198697A1

Abstract

In order to prevent gas from being involved in the liquid phase in a separator in the form of a hydrocyclone, a device is used with a tapered inlet section (6), which can be hollow or blocked with a cylindrical plain plate, which is attached to a straight, cylindrical tube (7) which can be plugged, or is run out through the cyclone's side walls or bottom.

Description

Separator

The invention concerns a separator device comprising a preferably hollow section having decreasing diameter from the preferably open top towards a closed bottom, or preferably attached to a straight cylindrical tube, which may be closed at the bottom and which is arranged concentrically inside a tapered section of a hydrocyclone, having preferably the same shape as the invention, for separating gas or vapour from a liquid, or alternatively two other fluids with differing densities, i.e. oil/water. The invention can either be attached to the hydrocyclone walls using fixed connections such as stay rods and the like, or the device can be allowed to rotate, either by means of a motor or by arranging turbine blades at the outlet of the invention's tube section.

The device should not be confused with conventional core stabilizors which are placed at the centre of the cyclone's lower outlet cross section, e.g. described in US patent 2,757,581. These usually consist of a solid cylindrical object with a diameter which is much smaller than the diameter of the lower outlet cross section.

Furthermore, the device should not be confused with "classifiers" which have the objective to separate solid particles of different diameters, or different densities, from a continuous liquid- or gas fluid. "Classifiers" represent actually an integrated two stage cyclone separator. The second stage separation chamber, removing the small/light particles, might at first hand look similar to the invention described in this patent application, i.e. US patent 2,706,045, but it has a completely different function.

Finally, the device must not be confused with "dollar plates" which are used for gas scrubber cyclones, utilized to separate small fractions of liquid (< 5 vol%) from a continuous gas phase. These usually consist of a circular plate arranged in the lower end of a cylindrical separator vessel. Their function is to prevent the up-flowing gas vortex from re-entraining already separated liquid from the lϊee liquid surface formed in the bottom of the vessel. A physical analogue situation is the cyclone tornado which is capable of "sucking" large objects like houses up into the air.

The main object of the invention is to prevent gas from being entrained in the liquid phase in cases where it is desirable to separate gas and liquid. A secondary object of the device is the ability to impart the gas-free liquid phase a substantial centrifugal field in order to achieve liquid/liquid (e.g. oil/water), or liquid/particle separation.

The invention is described with reference to the drawings, in which:

fig. 1 shows a side view of a conventional hydrocyclone containing a device which is according to the invention,

fig. 2 shows a top view example of how the upper tapered part of the device may be affixed to the hydrocyclone's outer wall, and

fig. 3 illustrates an example how the lower part of the device's tube section may be affixed to the cyclone's tapered outlet section.

fig. 4 shows as an example a "cup" formed shape of the device.

fig. 5 illustrates a practical arrangement of the invention inside a hydrocyclone for gas/liquid separation when the cyclone liquid outlet is submerged beyond a free liquid surface, i.e. cyclone used as an inlet device inside gravity separators.

fig. 6 illustrates another practical arrangement of the invention inside a hydrocyclone for gas/liquid- or liquid/liquid separation where the cyclone body diameter is reduced in two or more sections. The invention is used inside the last tapered section of the cyclone.

In the following description a "tapered" section means a section decreasing from a large diameter towards a smaller diameter. The shape of the tapered section can be conically, as shown in Fig. 1, or any suitable shape, e.g. as illustrated in Fig. 4.

The working principle for the separator device is described in the following:

The preferably conically shaped annulus in Fig. 1 (can also have other shapes such as shown in fig. 4) which is formed by the tapered cyclone inner wall 5 and the tapered section of the device 6 will create a back pressure in the flow and thus build up a pressure in the center of the separation chamber 1 allowing the lighter phase (i.e. the gas) to be forced through the vortex finder 4. This backpressure is developed according to the nature law of maintaing rotational momentum. When moving from the cross section A-A to B-B in fig 1, the tangential component of the flow will increase substantially due to the decrease in cross-sectional diameter. The pressure from cross sections A-A to B-B will then decrease proportionally in order to maintain the total energy of the separated denser phase.

The tapered inlet section of the device 6 must thus be arranged in the cyclone's tapered section 5 in order to achieve this effect. Fig. 1 shows the highest reccomended axial location of the device 6 where the inlet of the device 6 is at the same axial height as the start of the cyclone's tapered section 5. The lowest reccomended location is determined by the cross- sectional inlet area of the formed annulus, which should preferably be larger than the cross-sectional area of the lower outlet pipe 10 of the cyclone. The tapered inlet section 6 of the device should have a diameter greater than 0.9X the diameter of the cyclone's lower outlet pipe 10, and smaller than 0.99X the diameter of the cylindrical section 1 of the cyclone.

Although a conical section 6 is a preferred geometry of the device, it should be noted that it might have any shape when it is decreased from a large diameter to a smaller diameter. Fig. 5 shows a cup shaped geometry as an example. Furthermore, the preferred attached tube 7 shown in fig. 1 can be removed.

One embodiment of the invention is now described in detail with reference to the drawings:

Fig. 1 illustrates a hydrocyclone consisting of a cylindrical section 1, a tangential inlet 2, a circular top plate 3 with a through-going pipe 4 for extraction of the gas phase, a section 5 where the cyclone body diameter is decreased from a large diameter to a smaller diameter and preferably a discharge pipe 10 for extraction of the liquid phase. These parts are considered to be according to the prior art. The invention comprises a device which is attached inside the cyclone's tapered section 5 consisting of a tapered section 6, having preferably a conical shape, which might be closed at the bottom or attached to a tube 7. The top of the tapered section 6 should preferably be open, but can be closed with a cylindrical plane plate as well. The optional tube 7 can be plugged at the lower end or it can be run out of the hydrocyclone through side walls or the bottom. There are various ways of attaching the device to the hydrocyclone. Fig. 1 illustrates how the invention is attached by stay rods 8 and 9 in a standard hydrocyclone.

Fig. 2 illustrates how the invention's tapered section 6 is attached to the hydrocy clone's tapered section 5 with stay rods 8.

Fig. 3 illustrates how the invention's tube section 7 is attached to the hydro- cyclone's outlet pipe 10 by stay rods 9.

Fig. 4 shows as an example a "cup" formed shape of the device.

Fig. 5 illustrates a practical arrangement of the invention inside a hydrocyclone for gas/liquid separation when the cyclone liquid outlet is submerged beyond a free liquid surface 1 1, i.e. the cyclone being used as an inlet device inside gravity separators.

Fig. 6 illustrates another practical arrangement of the invention inside a hydrocyclone for gas/liquid- or liquid/liquid separation where the cyclone body diameter is reduced in two or more sections. The invention is used preferably inside the last tapered section of the cyclone.

Claims

PATENT CLAIMS

1. A gas-/liquid separator in the form of a hydrocyclone, characterized in that in the tapered section of the hydrocyclone there is placed a device comprising a hollow section with decreasing diameter from the top, which preferably is open, towards the bottom, which preferably is closed.

2. A gas-/liquid separator of claim 1, characterized in that the bottom of the device is open and attached to a straight cylindrical tube, which can be plugged at the bottom, or is run out through the cyclone's side walls or bottom.

3. A gas-/liquid separator of claim 1 , characterized in that the device in the tapered section of the hydrocyclone is closed at the top and closed at the bottom.

4. A gas-/liquid separator of claim 1, characterized in that the device either is attached to the hydrocyclone through fixed connections such as stay rods and the like, or that the device is rotatable by means of bearings which are attached to the cyclone through fixed connections such as stay rods and the like, the rotary energy either being supplied by means of a motor or by arranging turbine blades at the outlet of the device's pipe section.

5. A gas-/liquid separator of claim 1, characterized in that the cyclone body diameter is reduced in two or more sections, and the device is used preferably inside the last tapered section of the cyclone.

AMENDED CLAIMS

[received by the International Bureau on 5 February 1996 (05.02.96); original claims 1-5 replaced by new claims 1-7 (1 page)]

1. A flow modifier for a hydrocyclone for separating a first fluid from a second fluid, the density of the first fluid being greater than the density of the second fluid, the flow modifier having a cross-section arranged, when in use, to increase the rotational momentum of the first fluid within a tapered section of the hydrocyclone so as to increase the pressure within a core of the hydrocyclone, and thereby increase the flow of the core to an overflow.

2. A flow modifier as claimed in claim 1, wherein the hydrocyclone has a cylindrical section and an outlet section, and the flow modifier has a first end having a first diameter less than 99% of the diameter of the cylindrical section and greater than 90% of the minimum diameter of the outlet section

3. A flow modifier as claimed in claim 1, wherein the cross-section of the flow modifier is tapered.

4. A flow modifier as claimed in claim 1, wherein the cross-section of the flow modifier is substantially funnel-shaped.

5. A flow modifier as claimed in claim 1, wherein the second end of the flow modifier is closed so as to form an open cavity.

6. A flow modifier as claimed in claim 3, wherein the flow modifier is axially located substantially between the axial ends of the tapered section of the hydrocyclone.

7. A flow modifier as claimed in claim 4, wherein the tapered portion of the flow modifier is axially located substantially between the axial ends of the tapered section of the hydrocyclone.