WO2000074810A1

WO2000074810A1 - Multiphase separator

Info

Publication number: WO2000074810A1
Application number: PCT/NO2000/000193
Authority: WO
Inventors: Martin SØRENSEN; Johan Collett
Original assignee: Kongsberg Offshore A.S
Priority date: 1999-06-03
Filing date: 2000-06-02
Publication date: 2000-12-14
Also published as: NO992718D0; AU5115500A; NO992718L; NO311789B1

Abstract

Multiphase separator for separation of a fluid flow (30) comprising several fluid components, preferably for separation of hydrocarbons and water, and arranged in a tank (20) in connection with plants for petroleum production, comprising an inlet (13) for the fluid flow (30) to a preferably horizontal cyclone (10) having separated outlets for liquid and gas, respectively, to the tank (20). The inlet is located at a first end (11) of the cyclone (10). An outlet (14) for gas is located centrally and axially directed at a second, opposite end (12) of the cyclone (10). An outlet (15) for liquid from an outer annular space (IV) in the cyclone (10) is located at the second, opposite end of the cyclone (10). The outlet (15) for liquid leads to an open channel (16) which communicates with the desired inflow area of the tank (20).

Description

MULTIPHASE SEPARATOR

Introduction

The present invention relates to a multiphase separator for separating a fluid flow comprising several fluid components, preferably for separating hydrocarbons and water, and arranged in a tank in connection with plants for petroleum production, comprising an inlet for the fluid flow to a cyclone arranged horisontally or vertically and hav separate outlets for liquid and gas, respectively, to the tank.

Prior art

Cyclones of a conventional type for separation of a fluid flow in fractions with mutual different densities are generally arranged in a vertical position. In such cyclones, light-weight fractions in the fluid flow are normally removed through the top, and heavier fractions in the fluid flow are normally removed trough the bottom.

Such cyclones may also be oriented horizontally. However, each of the light-weight fractions and heavier fractions in the fluid flow are still discharged from different ends of the cyclone. EP Al 028.996 is a cyclone arranged horizontally, which is adapted to separation of fluids and particles in a suspension. A high voltage electrode is arranged in and along the longitudinal axis to contribute to the particle separation.

US 4,820,414 discloses a horizontally oriented cyclone having a tangential inlet and outlets for light-weight fluid and heavier fluid arranged at the same end. However, the primary outlet for light-weight fluids is arranged in the opposite end of the outlet for heavier fluids. This cyclone is mainly adapted for separation for liquids having mutually different densities.

A number of cyclones being arranged in tanks for the separation of liquid and gas. The purposes of these cyclones are to separate gas from liquid at the inlet and reduce the velocity of the fluid flow, direct the liquid flow in a desired direction or to a specific outlet area in the tank, together with degradation of foam. Several problems are involved in connection with such cyclones. Firstly, conventional inlet cyclones having an outlet for gas in the top and an outlet for liquid in the liquid volume of the tank sensitive to variations the gas/liquid rate of the fluid flow. Secondly, the liquid separation may be severely disturbed if a gas plug coming through the system is pressed down into the liquid volume of the tank. Thirdly, conventional inlet cyclones often have high shear forces at the outlet which may cause formation of very small drops and emulsions, which again leads to longer separation time for the liquid fractions.

GB 2.191.424. shows a horizonal cyclone arranged in a separation tank for gravitational separation of fluid mixtures of gases and liquids. However, the cyclone is of a conventional type, where gas and liquid each are discharged from different ends of the cyclone.

EP A2 58 484 relates to a vertical cyclone separator and is adapted for separation of fractions having different densities in a fluid comprising solid matter. This cyclone separator is primarily a particle separator.

WO 90/05591 describes an apparatus for centrifugal separation of a mixture of components, wherein at least one or more of the components have a specific weight being different from each other. The apparatus is a horizontal centrifugal separator having a relatively long middle portion (throat) and an adjustable throttle valve element for adjusting the gap between the diffusor wall and the throttle valve element . In conformity with conventional inlet cyclones, an object of the present invention is to separate gas from the fluid flow at the inlet of the tank, which may be a separator tank or a buffer tank.

In addition, an object of the multiphase separator is to eliminate the possibility of a possible gas plug flowing into a separator to be pressed down into the residence volume of the tank. Briefly, this is achieved by arranging both the outlets for gas and liquid in the same end, above the residence volume of the tank. Another object of the present invention is to obtain separation of the liquid fractions primarily in the multiphase separator and discharging generally in separate flows, with a degree as high as possible of laminar flow for avoiding degradation of droplets and formation of emulsion. An additional function intended is to draw a side flow comprising generally water and particles from the multiphase separator, wherein the particles can be led to a collecting chamber in the tank. Yet another object of the present invention is to provide a highly efficient separator requiring less residence volume, thus being smaller and having a lower weight. These are preferable properties, especially for floating installations, seabed installations and downhole installations.

Summary of the invention

The present invention is briefly explained a multiphase separator of a fluid flow comprising several fluid components, preferably for separation of hydrocarbons and water, and arranged in a tank in connection with plants for petroleum production, comprising an inlet for the fluid flow to a cyclone being arranged horizontally or vertically and having separate outlets for liquid and gas, respectively, to the tank. The novel and distinctive features of the invention is that the inlet is located at a first end of the cyclone, that an outlet for gas is located centrally and axially directed at a second, opposite end of the cyclone, that an outlet for liquid from an outer annular space in the cyclone is located at the second, opposite end of the cyclone, and that the outlet for liquid leads to an open channel which communicates with the desired inflow area of the tank.

In one embodiment of the invention, the cyclone has a throat between a first section of the cyclone and a second section of the cyclone, wherein the first section is adapted to set and maintain the fluid flow in a rotary motion; the second section is adapted to reduce the rotation velocity. In another embodiment the multiphase separator comprises an axially oriented inlet, and guide vanes may also be arranged in the first section of the cyclone for setting the fluid flow in a rotary motion. In a further embodiment of the invention, the cyclone comprises a tangentially oriented inlet, and the inlet may also be of a shape similar to a snail shell.

In yet another embodiment the outlet for liquid from the cyclone is adapted to normally be partly filled with liquid, so that any possible excess of gas may freely escape through the outlet together with the liquid.

Description of the drawings

The invention will be described in more detail in the following, with reference to the attached drawings. Figure la shows a vertical section in the axial direction of an embodiment of the multiphase separator according to the invention arranged horizontally in a tank. Figure lb shows a vertical section in the axial direction of another embodiment of the multiphase separator according to the invention arranged vertically in a tank. Figure 2 shows a vertical section in the axial direction of a multiphase separator according to the invention having axial inlet and guide vanes.

Figure 3 shows a view of the multiphase separator according to the invention at a first end of a cyclone. Figure 4 shows a view similar to figure 3, wherein the inlet is of a shape similar to a snail shell. Figure 5 is a vertical section in the axial direction showing flow conditions in the outlet for liquid at a second end of the cyclone. Figure 6 is a section of the second end of the cyclone wherein division plates are arranged at the outlet for liquid.

Figure 7 is a section of the second end of the cyclone wherein guide plates are arranged at the outlet for liquid. Description of the preferred embodiments

Figure la shows a multiphase separator according to the invention arranged in a tank 20, such as a separation tank. The multiphase separator comprise a preferably horizontal cyclone 10 having a first end 11 and a second, opposite end 12, wherein an inlet 13 is arranged at the first end 11 of the cyclone 10, for supply of a fluid flow 30, and separate outlets 14 and 15, wherein the outlet 15 leads to an open channel 16 communicating with the desired inflow area in the tank 20. The cyclone 10 may be divided into four main sections, where a first section I is located at the first end 11, a second section II is located between the first section I and a throat 103, a third section III lies between the throat 103 and a fourth section, or outer annular space, IV, and the outer annular space is located at the second end 12.

In a preferred embodiment of the invention the outlet 14 is located centrally and axially directed at the second, opposite end at the second, opposite end 12 of the cyclone 10, primarily for discharge of the gas fraction 31 in the fluid flow 30. In addition, the outlet 15 from the outer annular space IV in the cyclone 10 is located at the second, opposite end 12 of the cyclone 10, primarily for discharge of the liquid fraction 12 of the fluid flow 30. The outlet for gas 14 and the liquid outlet 15 is in other words arranged at the same end of the cyclone 10, as opposed to conventional cyclones arranged in tanks.

The outlet for liquid 15 leads to a channel 16 being open for pressure equalising to the rest of the tank 20. Firstly, the possibility for gas cutting into the layers of liquid in the tank 20 is reduced. Secondly, the multiphase separator becomes less sensitive to possible gas plugs which may arise in the fluid flow 30. ZAnother purpose of the open channel is to create as stationary and laminar flow conditions as possible, so that separation of the liquid components is maintained in the highest possible degree. Clearly, a horizontal orientation of the multiphase separator is favourable, but it will be apparent to skilled persons that a vertical orientation of the multiphase separator is possible. A vertically oriented embodiment of the multiphase separator is shown in figure lb and has analogous function as the embodiment shown in fig. la.

As shown in figures la and 2, the cyclone 10 may in a preferred embodiment of the invention have a throat 103 between a first section 101 of the cyclone 10 and a second section 102 of the cyclone 10. The first section of the cyclone 10 is adapted to maintain the fluid flow 30 in a rotary motion. In the second section 102 the diameter increases with increasing diameter along the axis of the flow direction in the cyclone 10. The increasing diameter is intended to reduce the velocity of the fluid flow 30 to minimize turbulence and shear forces in the fluid flow 30.

Appearing from figure 2, the inlet 13A may be axially arranged. In this embodiment according to the invention guide vanes, preferably in two separate stages 101A/101B is arranged in the first section 101A/101B to induce rotary motion of the fluid flow 30.

In another embodiment, as shown in figure 3, the inlet 13 may be generally tangentially arranged in the first section 101 of the cyclone 10, so that the fluid flow 30 is set in a rotary motion in the cyclone 10. The inlet may also be of a shape 13B similar to a snail shell, as shown in figure 4, which may boost the rotary motion in the first section 101 of the cyclone 10, thus giving a larger degree of separation between liquid 32 and gas 31.

The outlet for liquid 15 is adapted to normally be partly filled with liquid, as shown in figure 5, such that possible excess of gas, may freely escape through the outlet together with the liquid 15, which further will flow into the open channel 16.

Figure 6 shows that at least one, preferably three, division plate (s) 19A may be arranged at the outlet for liquid 15 for stepwise discharge of the liquid fractions 32 in the fluid flow 30. The division plates 19A may be curved in accordance with the layers of liquid in the cyclone 10, they may cover the whole circumference to a tubular shape, so that the cross section has a circular form, or be of in another suitable shape. The division plates 19A may in a preferred embodiment be arranged with stepwise decreasing radial distance from the axis of the cyclone 10. The division plates 19A may possibly also be arranged in equal radial distance from the axis of the cyclone. In figure 7, a plurality of guide plates 19B is arranged at the outlet 15 for liquid for primarily reducing the flow motions in the liquid 32 in front of the open channel 16. A combination of division plates 19A and guide plates 19B may be considered if at least one of the guide plates 19B is prolonged in the downstream direction (shown in dashed lines) to form the divisional plate (s) 19A.

If the tank 20 is a separation tank, the outlet 17 of the open channel 16 may be arranged in the layers of liquid, so that the liquid 32 being discharged from the outlet 15 for liquid of the cyclone 10 to the inflow area of the tank 20 forms a water layer 33A and an oil layer 34A, separated by an interface, wherein the water layer 33A is generally led to a water layer 33B in the tank 20 and the oil layer is generally led to an oil layer 34B in the tank 20. This is shown in figure 1 and in more detail in figure 6.

In figure la a coalescer element 40 is shown arranged in the open channel 16. Arranged in a separation tank 20, such a coalescer element 40 has the advantages of an increased degree of separation of the liquid fractions 33A and 34A by acting as a "demister" , and reducing the flow motions in the liquid. A second coalescer element 50 is shown in another, more common location in the tank 20. Coalescer elements to be used in this connection is previously known. In another embodiment of the invention at least one outlet 18 for discharge of generally particles may be arranged preferably at a middle portion of the cyclone 10. The outlet 18 may be led to a collection chamber 60 being arranged in the tank for discharge of essentially particles. It should be pointed out that according to the present invention, the tank is not limited to separation tanks, but may, e.g., also comprise buffer tanks for controlling the fluid flow in a plant, or pipe sections functioning similar to a tank. Because the tank also may be substituted with a pipe section functioning as a tank, the present invention may also have uses in downhole installations.

A horizontal cyclone may be mounted with a slight fall for draining purposes, e.g, having an angle of divergence from the horizontal plane of up to 10-15°.

A tangential inlet 13 as shown in figure 3 may be located in a plane being somewhat slanted from a purely radial plane, to give the flow a certain component also in the axial direction. The slanted plane is indicated with an angle α, as indicated in figure 4.

Claims

C l a i m s

1. Multiphase separator for separating a fluid flow (30) comprising several fluid components, preferably for separating hydrocarbons and water, and arranged in a tank (20) in connection with plants for petroleum production, comprising an inlet (13) for the fluid flow (30) to a cyclone (10) being arranged horizontally or vertically and having separate outlets for liquid and gas respectively to the tank (20) , c h a r a c t e r i z e d i n that the inlet (13) is located at a first end (11) of the cyclone (10) , that an outlet (14) for gas is located centrally and axially directed at a second, opposite end (12) of the cyclone (10) , that an outlet (15) for liquid from an outer annular space (IV) in the cyclone (10) is located at the second end of the cyclone (10) , and that the outlet (15) for liquid leads to an open channel (16) which communicates with the desired inflow area in the tank (20) .

2. Multiphase separator according to claim 1, c h a r a c t e r i z e d i n that the cyclone (10) has a throat (103) between a first section (101) of the cyclone (10) and a second section (102) of the cyclone (10) , the first section (101) is adapted to maintain the fluid flow (30) in a rotary motion, and that the diameter of the second section (101) increases with increasing diameter along the axis of the flow direction in the cyclone (10) .

3. Multiphase separator according to claim 1 or 2 , c h a r a c t e r i z e d i n that the inlet (13A) is arranged axially at the first end (11) of the cyclone (10) .

4. Multiphase separator according to claim 3, c h a r a c t e r i z e d i n that guide vanes (101A / 101B) , preferably in two separate sections, is arranged in the first section (101) of the cyclone (10) for inducing rotary motion of the fluid flow (30) .

5. Multiphase separator according to claim 1 or 2 , c h a r a c t e r i z e d i n that the inlet (13) is arranged generally tangentially at the first end (11) of the cyclone (10) .

6. Multiphase separator according to claim 5, c h a r a c t e r i z e d i n that the inlet (13B) similar to a snail shell .

7. Multiphase separator according to anyone of the preceding claims, c h a r a c t e r i z e d I n that the outlet (15) for liquid is adapted to normally be partly filled with liquid, so that possible excess of gas may freely escape through the outlet (15) together with the liquid.

8. Multiphase separator according to anyone of the preceding claims, c h a r a c t e r i z e d i n that at least one, preferably three, division plate (s) (19A) is (are) arranged at the outlet (15) for liquid for discharge of the liquid fractions in the fluid flow (30) .

9. Multiphase separator according to claim 8, c h a r a c t e r i z e d i n that the division plates

(19A) are arranged at a stepwise decreasing radial distance from the axis of the cyclone (10) .

10. Multiphase separator according to claim 1-7, c h a r a c t e r i z e d i n that a plurality of guide plates (19B) are arranged at the outlet (15) for liquid for primarily reducing the flow motions in the liquid (32) before the open channel (16) .

11. Multiphase separator according to claim 8 and 10, c h a r a c t e r i z e d i n that at least one of the guide plates (19B) is prolonged in the downstream direction for formation of said division plate (s) (19A) .

12. Multiphase separator according to anyone of the preceding claims, where the tank is a separation tank, c h a r a c t e r i z e d i n that the outlet (17) from the open channel (16) is arranged in the liquid layers of the tank (20) in such a manner that the liquid (32) being led from the outlet (15) for liquid of the cyclone (10) to the inflow area of the tank (20) forms a water layer (33A) and an oil layer (34A) , separated by an interface, wherein the water layer (33A) is led generally to a water layer (33B) in the tank (20) and the oil layer (34A) is led generally to an oil layer (34B) in the tank (20) .

13. Multiphase separator according to anyone of the preceding claims, c h a r a c t e r i z e d i n that a coalescer element (40) is arranged in the open channel (16) .

14. Multiphase separator according to anyone of the preceding claims, c h a r a c t e r i z e d i n that at least one outlet (18) for discharge of generally particles is arranged preferably at a middle portion of the cyclone (10) .

15. Multiphase separator according to anyone of the preceding claims, c h a r a c t e r i z e d i n that the outlet (14) for gas is arranged above the liquid level of the tank (20) .