WO1999040993A1

WO1999040993A1 - Separator for three-phase mixture to be used under the sea

Info

Publication number: WO1999040993A1
Application number: PCT/FR1999/000327
Authority: WO
Inventors: Maurice Waintraub; Chantal Rigaill
Original assignee: Prosernat
Priority date: 1998-02-16
Filing date: 1999-02-15
Publication date: 1999-08-19
Also published as: EP0975406A1; FR2774924A1; FR2774924B1

Abstract

The invention concerns a separator for three-phase mixture such as a liquid-liquid-gas mixture to be used under the sea, particularly for separating the constituents of an oil/water/gas mixture, comprising a chamber (1) provided with intake means (2; 14, 15, 16, 17, 18, 19) for the three-phase mixture, first discharge means (3; 9, 10) and second discharge means (4), and a coalescing device comprising two sub-assemblies (5, 11; 7, 12) of sloping plates (6; 8). The invention is characterised in that the first discharge means (9, 10) consist of a barrier-plate (9) substantially perpendicular to the plates of said sub-assemblies (11, 12) and extending from the chamber lower wall (26) up to a height (h2) greater than the height (h1) of the plates of said sub-assemblies (11, 12), and of a discharge orifice (10) located on the barrier-plate (9) side opposite to the one where the sub-assemblies (11, 12) are located.

Description

SEPARATOR FOR THREE-PHASE MIXTURE TO BE USED UNDER SEA LEVEL

The invention relates to a separator for a three-phase mixture of the liquid-liquid-gas type intended to be used below sea level, in particular for separating the constituents of an oil / water / gas mixture.

STATE OF THE ART

French patent No. 2,707,890 has proposed a separator for a three-phase liquid-liquid-gas mixture comprising means for admitting the mixture, a packing structure made up of thin fluted sheets pierced with orifices and stacked so as to forming grooves, and means of evacuation. This separator has satisfactory efficiency, but it cannot be used for a long time without human intervention being necessary.

The applicant has therefore continued research with a view to developing a separator which can be placed at the bottom of the sea in a crude oil production installation. In addition to being able to withstand underwater conditions, in particular having good mechanical strength and good corrosion resistance, such a separator must perform good separation of the constituents of the mixture and maintain this good quality of separation over a long period of time. period, without human intervention being necessary.

SUMMARY OF THE INVENTION

The plaintiff thus succeeded in developing a separator fully achieving the objectives it had set for itself. More specifically, the applicant has invented a separator for a three-phase liquid-liquid-gas mixture, of the type comprising an enclosure provided with means for admitting the three-phase mixture, first means of evacuation and second means of evacuation, as well as a coalescing device comprising:

- a first subset of plates spaced from each other and arranged substantially parallel to each other, - a second subset of plates spaced from each other and arranged substantially parallel to each other,

- Said first and second sub-assemblies being close to each other and arranged so that each plate of the first sub-assembly is substantially symmetrical, with respect to a substantially vertical plane, to a plate of the second sub-assembly,

the upper faces of the plates of the first subassembly forming a salient angle α with the upper faces of the plates of the second subassembly, the intake means comprising an orifice,

- the first means of evacuation comprising an orifice,

- the second evacuation means comprising an orifice and being located at the lower part of the enclosure,

- Said first and second subassemblies being arranged between the intake means and the first and second discharge means and oriented so that a current can flow from the admission means to the first and second discharge means passing through the spaces formed between the different plates.

This separator is characterized in that the first evacuation means consist of: - a barrier plate substantially perpendicular to the plates of said subassemblies and extending from the bottom wall of the enclosure to a height (h ₂ ) greater than the height (hi) of the plates of said subsets, and

- an evacuation orifice located on the side of the barrier plate opposite to that where the sub-assemblies are located.

The essential advantage of such a separator is that it provides good separation of the liquid components and that it can operate for a period of the order of 25 years without human intervention.

Other advantages and characteristics of the invention will emerge on reading the following description, to which are annexed, by way of illustration only, FIGS. 1 to 5.

SUMMARY DESCRIPTION OF THE FIGURES

Figure 1 shows schematically, in partial section and in perspective, a separator according to the invention.

FIG. 2 schematically represents, in section, a variant of the separator of FIG. 1.

FIG. 3 schematically represents, in front view in section, a part of the inlet means of the separator of FIG. 2. FIG. 4 schematically shows, in view from the left in section, a part of the inlet means of the separator of FIG. Figure 2.

FIG. 5 shows schematically, in partial section and in perspective, the separator of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

The separator according to the invention is illustrated in general in Figure 1, where it can be seen that it comprises an enclosure 1 having a substantially cylindrical shape, arranged horizontally and whose ends are closed by two hemispherical parts.

This enclosure is provided with inlet means 2 for the three-phase mixture, first evacuation means 3 and second evacuation means 4.

Between the intake means 2 and the discharge means 3, 4 there is a first subset 5 of plates 6 arranged parallel to each other and spaced from each other and a second subset 7 of plates 8 also arranged parallel to each other and spaced from each other.

These sub-assemblies 5,7 are close to each other and and arranged so that each plate 6 of the first sub-assembly 5 is substantially symmetrical, with respect to a substantially vertical plane, to a plate 8 of the second subset 7.

The upper faces of the plates 6 of the first sub-assembly 5 form a salient angle α with the upper faces of the plates 8 of the second sub-assembly 7. The plates 6.8 are of generally rectangular shape, preferably regularly spaced, smooth and wavy to present more surface in a given volume. They are held in place at their ends by blades 29, 30. A central space located between the plates 6 of the first sub-assembly 5 and the plates 8 of the second sub-assembly 7 allows the vertical passage of the fluids.

The two sub-assemblies 5,7 do not rest on the lower wall of the enclosure, they are slightly raised so as to leave a space allowing the circulation of fluids.

The intake means 2 include an orifice located in the wall of the enclosure 1.

The first evacuation means 3 include an orifice located in the wall of the enclosure 1.

The second discharge means 4 comprise an orifice located in the wall of the enclosure 1, at its lower part.

The plates 6,8 are oriented with respect to the intake 2 and discharge 3,4 means so that a current of three-phase mixture can circulate passing through the spaces formed between the different plates of the coalescence assembly . 4

The general operation of the separator according to the invention can therefore be explained as follows ^• the three-phase mixture enters the enclosure 1 through the intake means 2 and then flows to the first and second discharge means 3,4 , by circulating between the plates 6 and between the plates 8, that is to say in a substantially horizontal direction, in the longitudinal direction of the cylinder constituting the enclosure 1.

During this flow, the heavy liquid goes down, while the light liquid goes up or stays in the upper part of the current, because the two subsets 5,7 of plates 6,8 form a coalescence device, that is to say a device allowing the droplets of liquids to gather and form drops which will then separate from the other liquid

The light liquid is then evacuated by the first evacuation means 3 and the heavy liquid by the second evacuation means 4

The gas contained in the mixture is evacuated directly by the evacuation means 3

According to an advantageous variant illustrated in FIG. 2, the first evacuation means comprise

- A barrier plate 9 substantially perpendicular to the plates of the sub-assemblies 11, 12 and extending from the lower wall 26 of the enclosure to a height h ₂ greater than the height hi of the plates of the sub-assemblies 11.12,

- a discharge orifice 10 located on the side of the barrier plate 9 opposite to that where the sub-assemblies are located 11,12

The barrier plate 9 is fixed to the enclosure in a sealed manner on all its sides, except for the upper side, which means that only the light supernatant liquid can pass over it and then be evacuated through port 10.

In addition, the enclosure preferably comprises a second barrier plate 13, situated between the orifice 10 and the barrier plate 9 and substantially parallel to the latter. This second barrier plate 13 extends from a height h ₃ greater than the height h ₂ of the barrier plate 9, up to a height ru situated above the lower wall 26 of the enclosure, so as to leave an opening 29. This arrangement allows the volume between the two barrier plates 9 and 13 to constitute a buffer reserve which flows through the opening 29 towards the orifice 10 when the flow rate decreases at the inlet. Thus, the flow rate of the fluids at the outlet of the separator is regulated.

Advantageously, as can also be seen in Figures 3, 4 and 5, the intake means include ^• 5

a supply pipe 14 connecting a wall of the enclosure to a location located inside the enclosure, at a point situated in the upper part of the enclosure, above the sub-assemblies 11, 12 of plates,

a chamber 15 without an upper wall and into the lower wall from which the supply pipe 14 opens, and

- an obstacle 16 disposed inside the chamber 15, opposite the outlet of the pipe 14

The supply pipe 14 preferably crosses the wall of the enclosure at a point located in the lower part of the hemispherical end of the cylinder constituting the enclosure

As is apparent from Figures 3 and 4, the obstacle 16 consists of V-shaped angles arranged parallel to each other in a plane perpendicular to the axis of the pipe 14, spaced from each other so as to be able to pass the fluid between them Each angle is preferably oriented so that the point of the "V is located at the bottom of the angle

In addition, the angles are preferably distributed over several levels along the axis of the pipe 14, the angles of one level then preferably being offset with respect to those of the neighboring level, so that the fluid passing between two angles of a level collides with an angle of the upper level

Thus, the fluid coming from the pipe 14 cannot pass directly through the obstacle 16 because it must somehow zigzag between the angles. The flow of the resulting fluid generally ensures a tranquilization of the flow of the fluid on its arrival in the enclosure of the separator Preferably, two parallel walls 18, 19 of the chamber 15 extend upwards and maintain a second obstacle 17 which may be similar to the obstacle 16

As can be seen by referring again to Figure 2, it is advantageous to set up a wave barrier 31 between the intake means 14, 15,16,17,18,19 and the sub-assemblies 11.12 of plates This anti-wave barrier may be a plate arranged parallel to the barrier plate 9 and extend from the bottom wall 26 of the enclosure to a height less than the height hi of the subassemblies 11 , 12

Sand removal means can be provided They are formed from pipes 20,21 and discharge orifices 22,23 The pipes 20,21 are pierced along their length with projection orifices and they extend horizontally between the sub-assemblies 11, 12 and the lower wall 26 of the enclosure They each have a bent portion 24.25 which passes through the wall 26 of the enclosure and by means of which 6 pressurized water can be introduced. This water is then projected by the projection orifices arranged along the conduits 20 and 21 and it carries the sand deposited on the wall 26 towards the evacuation orifices 22, 23.

Of course, it is possible, as is apparent from FIGS. 2 and 5, to put in series in the direction of flow of the mixture of fluids to be separated, one or more other coalescing devices similar to the first

Thus, thanks to its constitution, the separator according to the invention is not likely to retain deposits or to clog over time In addition, the pressure drop it causes is limited is less than 1 bar

During normal operation, the level N of the liquid in the enclosure is close to the obstacles 16 and 17 of the intake device (FIG. 2), due to the existence of the barrier plate 9 or, where appropriate, of the second barrier plate 13 The coalescence device is therefore below the level of the liquid The fluids flow is carried out at low speed and on smooth surfaces As a result, the separation is effective

As it is generally made of a metallic material such as stainless steel, the mechanical resistance of its elements is very high and consequently, its resistance over time is ensured. Furthermore, the intake means 14, 15, 16, 17, 18, 19 can be used with any type of separator

Uses The separator according to the invention can be used to remove water from oil / water / gas mixtures in which water sometimes represents up to 80% of the mixture

Under its normal operating conditions, i.e. temperatures of 50 to 65 ° C and a pressure of 35 to 105 bars, its separation power is such that the water removed generally contains less than 1000 ppm of petroleum This is an advantage important because the water removed is usually reinjected into the rock and the oil it contains contributes to clogging the rock, which is why it is important to minimize its oil content

The separator according to the invention can thus be installed at a depth of up to 1000 m below sea level, and even more if the mechanical dimensioning of the enclosure is provided for this purpose.

Claims

7 CLAIMS

1. Separator for three-phase liquid-liquid-gas mixture, of the type comprising an enclosure (1) provided with inlet means (2; 14, 15, 16, 17, 18, 19) of the three-phase mixture, first means of evacuation (3; 9, 10) and second evacuation means (4), as well as a coalescing device comprising:

- a first sub-assembly (5, 11) of plates (6) spaced apart from one another and arranged substantially parallel to each other, - a second sub-assembly (7, 12) of plates (8) spaced apart from each other and arranged substantially parallel to each other,

- said first and second sub-assemblies (5, 1 1; 7, 12) being close to one another and arranged so that each plate (6) of the first sub-assembly (5, H) is substantially symmetrical, with respect to a substantially vertical plane, to a plate (8) of the second sub-assembly (7,12),

the upper faces of the plates (6) of the first sub-assembly (5, 11) forming a salient angle α with the upper faces of the plates (8) of the second sub-assembly (7,12),

- the intake means (2; 14,15,16, 17, 18,19) comprising an orifice (2), - the first evacuation means (3; 9, 10) comprising an orifice (3),

- the second discharge means (4) comprising an orifice (4) and located at the level of the lower part of the enclosure (1),

- said first and second sub-assemblies (5,7) being arranged between the intake means (2; 14, 15, 16,17,18,19) and the first and second discharge means (3; 4; 9, 10) and oriented so that a current can flow from the intake means (2; 14, 15, 16, 17, 18, 19) to the first and second discharge means (3; 4; 9 , 10) passing through the spaces formed between the different plates (6,8); this separator being characterized in that the first evacuation means (9, 10) consist of:

- a barrier plate (9) substantially perpendicular to the plates of said subassemblies (11, 12) and extending from the lower wall (26) of the enclosure to a height (h ₂ ) greater than the height (hi) of the plates of said subassemblies (11, 12), and - of a discharge orifice (10) located on the side of the barrier plate (9) opposite to that where the subassemblies are located ( 11.12). 8

2. Separator according to the preceding claim, characterized in that the first evacuation means (9,10) further comprise a second barrier plate (13) located between the orifice (10) and the barrier plate (9) and substantially parallel to the latter, extending from a height (h ₃ ) greater than the height (h ₂ ) of the barrier plate (9), to a height (ru) situated above the bottom wall (26) of the enclosure, so as to leave an opening (29).

3. Separator according to any one of the preceding claims, characterized in that the enclosure (1) has a substantially cylindrical shape closed at its ends by hemispherical parts.

4. Separator according to the preceding claim, characterized in that the enclosure (1) is arranged horizontally.

5. Separator according to any one of the preceding claims, characterized in that the plates (6,8) are corrugated plates.

6. Separator according to any one of the preceding claims, characterized in that the plates (6,8) are regularly spaced.

7. Separator according to any one of the preceding claims, characterized in that the intake means (14,15,16,17,18,19) comprise:

a supply line (14) for the three-phase mixture from a wall of the enclosure to a location inside the enclosure, above the sub-assemblies of plates (11,12),

a chamber (15) devoid of an upper wall and into the lower wall from which opens said feed pipe (14), and

- An obstacle (16) arranged inside this chamber (15) opposite the outlet of said supply pipe (14).

8. Separator according to the preceding claim, characterized in that a second obstacle (17) is arranged above the chamber (15).

9. Separator according to claim 8 or claim 9, characterized in that the obstacles (16,17) consist of V-shaped angles arranged parallel to each other in a plane perpendicular to the axis of the supply pipe ( 14), spaced from one another so as to allow the fluid to pass between them and distributed over 9 several levels along the axis of the supply pipe (14), the angles of a level then being offset from those of the neighboring level.

10. Separator according to any one of the preceding claims, characterized in that it further comprises an anti-wave barrier (31) disposed between the intake means (14,15,16,17,18,19) and the subsets (11,12) of plates.

11. Separator according to any one of the preceding claims, characterized in that it also comprises means for eliminating (20,21,22,23) of the sand deposited at the bottom of the enclosure.

12. Separator according to any one of the preceding claims, characterized in that it comprises one or more other coalescing devices similar to the first.

13. Use of a separator according to any one of the preceding claims for removing water from an oil / water / gas mixture.