GB2280619A

GB2280619A - The use of a distillation and absorption column packing in a three-phase separator

Info

Publication number: GB2280619A
Application number: GB9414669A
Authority: GB
Inventors: Maurice Lionel Waintraub
Original assignee: PROCEDES ET SERVICES PROSER SA
Current assignee: PROCEDES ET SERVICES PROSER SA
Priority date: 1993-07-20
Filing date: 1994-07-20
Publication date: 1995-02-08
Anticipated expiration: 2014-07-20
Also published as: GB9414669D0; FR2707890A1; NO942705L; NO942705D0; GB2280619B; FR2707890B1; NO307958B1

Abstract

The invention relates to the use in a separator for a three-phase liquid-liquid-gas mixture of a packing structure (Fig. 4, not shown) which is normally used in distillation columns or in absorption columns, the structure being constituted by thin fluted sheets pierced with orifices and stacked in such a way as to form channels open at their ends, the channels of one and the same sheet being offset angularly in relation to those of the immediately contiguous sheets. In separator 1, the three-phase mixture enters via pipe 2, is divided into two streams by divider 26 and passes down a sequence of steps 7. The packings are suspended from the top of the separator at 8a and 8b and suppress foaming. Heavy liquid (e.g. water) is removed via connection 4, the lighter liquid (e.g. oil) via 5 and gas via outlet 6. Further packings 12a, b, c are used to dampen resonance in the liquid which could arise from motion (e.g. or a marine installation). <IMAGE>

Description

THE USE OF A DISTILLATION AND ABSORPTION COLUMN LINING IN A THREE-PHASE SEPARATOR AND A THREE-PHASE SEPARATOR EQUIPPED WITH SUCH A LINING The present invention relates to the use, in a threephase separator, particularly a separator disposed at the outlet from oil wells and intended for the separation of mixtures of the water-gas-petroleum type, of a lining normally used in distillation and absorption columns. The invention likewise relates to a three-phase separator equipped with such a lining and intended more particularly to be shipped on floating oil platforms.

It is known that at the outlet from oil wells, a three Xquld phase mixture of the S iquid-gas type is recovered which consists essentially of water, petroleum (still referred to as oil in the industry) and gas, which it is necessary to separate. This situation is found equally in the case of land-based and marine oil fields. However, in this latter case, the problems posed are more complex by virtue of the limited space available and even more so on board floating installations, with a need to balance these installations and dampen the rolling pitching phenomena inside the separators.

In practice, it is normal practice to use as separators, on both land and sea, cylindrical, horizontal or vertical enclosures the dimensions of which are calculated in such a way as to ensure a sufficient dwell time for the three-phase mixture so that separation of the various phases can be carried out by decantation, coalescence, filtration or the like, and so that entrainment of a minority phase into a majority phase is minimised. The cylindrical enclosure has an inlet for three-phase mixture and draw-off outlets disposed at various levels for the three phases which are to be separated, the lowest outlet being used to draw off the water, a midway outlet for the extraction of the oil while the outlet situated at the highest level is used for extraction of the gases.

However, this type of separator is not suitable for crude foaming petroleum because, when the pressure drops, there is a formation of foam and the resulting mixture does not have sufficient time to separate satisfactorily before extraction via the various outlets.

In order to resolve this problem, the Applicants have already proposed using in these three-phase separators a static structure which to a considerable degree consists of an assembly of plates, corrugated or honeycomb in form, which offer a large area of contact with the mixture to be separated and which are coated with a surfactant product the surface tension coefficient of which is very much lower than that of the foaming liquids in the mixture (see FR-A-2 551 357).

The present invention seeks to achieve a similar result, in other words that of breaking up the foams which are likely to form in a separator of a three-phase liquid-liquid-gas mixture, but by using a static structure which does not entail any coating with a surfactant product.

Another aim of the invention is to propose the use of such a static structure to stabilise a separator of a threephase mixture which is carried by a floating installation.

The studies carried out by the Applicants have indeed enabled them to establish that structures normally used as linings of distillation or absorption columns can be used in separators of three-phase mixtures both for breaking up the foams produced and for stabilising the separator.

These linings comprise thin fluted sheets, possibly provided with orifices and stacked in such a way as to form channels which are open at their ends, the channels in one and the same sheet being offset angularly in relation to those of the immediately adjacent, or contiguous sheets in the stack, the various channels being inclined in relation to the axis of the absorption or distillation column. Linings of this type are marketed for example by companies of the SULZER group under the registered trade mark MELLAPAK, in particular MELLAPAK (250Y) and SPP, and they are described for example in the commercial literature of that company.

Surprisingly, such lining structures, disposed in a separator of a three-phase mixture, in the upper part thereof, that is to say in contact with at least the gaseous phase, have been found capable of effectively breaking up foams which have formed.

Therefore, a first aspect of the invention is the use of a lining structure of the type mentioned hereinabove in a separator of a three-phase liquid-liquid-gas mixture and which is disposed in the separator in such a way as to be in contact with the gaseous phase with a view to breaking up any foams which are likely to form.

The Applicants have also established that such lining structures, disposed in a separator of a three-phase liquidliquid-gas mixture, in contact with at least one of the liquid phases, reinforce the stability of such a separator when it is disposed on a floating installation, dampening the pitching and eliminating or deadening the frequency of the jolting or resonance in the liquid.

A second aspect of the invention is therefore the use in a separator of a three-phase liquid-liquid-gas mixture intended to equip a floating installation, of a lining structure of the type referred to hereinabove, disposed in such a way as to be in contact with at least one of the liquid phases of the mixture in order to reinforce the stability of the separator and deaden the pitching of it.

It will be noted that the lining structures of distillation or absorption columns for which the present invention proposes a novel usage, are lightweight structures disposed as a replacement for heavier structures, and which substantially lighten the mass of the three-phase separators. The tests conducted by the Applicants have proved the tremendous efficiency of these lining structures in breaking up foam, because they have succeeded in establishing that the effective life of foams produced during the separation of three-phase water-oil-gas mixtures was reduced to less than half.

Another aspect of the invention is constituted by a separator of a three-phase liquid-liquid-gas mixture of the type comprising a substantially cylindrical enclosure disposed horizontally or vertically, and provided with means for the inlet of the three-phase mixture and means for drawing off respectively the three separate phases of this mixture, said draw off means being offset in height over the separator, the means of drawing off the heaviest liquid phase being disposed in the bottom part of the separator, the means of separating the lighter liquid phase being disposed at an intermediate level and the means of drawing off the gaseous phase being disposed in the upper part, this device being characterised in that it comprises at least one lining structure of the type referred to hereinabove, in contact with the gaseous phase and/or at least one of the liquid phases separated from the mixture.

In a preferred embodiment of such a separator, which will be described in greater detail hereinafter, the separator which is of substantially cylindrical form, is disposed horizontally and it has two halves which are substantially symmetrical in respect of a median plane at right-angles to its axis. The three-phase mixture inlet means is situated in the upper part of the separator, substantially in the median plane at right-angles to its axis while the means of drawing off the two liquid phases are situated at levels which are staggered in this same median plane while the means of drawing off the gaseous phase comprise two draw-off pipes disposed in the upper part of the separator, at the two ends of this latter.

Advantageously, the three-phase mixture to be separated, which is introduced into the separator, is poured onto a deflector in the form of a dihedron, the edge of which is disposed substantially in the median plane at right-angles to the axis while the two surfaces are inclined symmetrically downward, in order to divide the flow of mixture into two substantially equal fractions. These two fractions symmetrically assume a stepped form like the treads of a staircase, which brake without impact the progression of the mixture in the direction of the two ends of the separator, where the two liquid phases are poured onto the bottom to separate by decantation into a heavy phase (water) which will be evacuated by the draw-off means provided in the bottom part, and a lighter phase (oil), which will be removed by the draw-off means provided at the midway level.

As it progresses over the deflector and over the staircase type of structure, the mixture is decelerated without suffering any shocks and the gaseous phase is thus able to separate from the liquid phases without any excessive formation of foam. Before using the gas draw-off means, they advantageously pass through a drying system employing chicanes or the like which make it possible to separate the last traces of the liquid phases and to draw them off through a drain towards the bottom of the separator.

To break up the foam, which nevertheless is likely to form, lining structures of the type defined hereinabove are disposed in the upper part of the separator, above the stepped structure.

To dampen the rolling and pitching phenomena and in order thus to enhance the stability of the separator, when it is supported by a floating installation, two means are advantageously used jointly: - on the one hand, on the surface of the treads of the stepped structure, edges project upwardly, for example parallel with the axis of the separator, in such a way as to counteract the phenomenon of rolling; - on the other, in the bottom part of the separator, lining structures of the type described above are at least partially embedded in the liquid phases in order to oppose the pitching phenomena and avoid the frequencies of resonance.

At least one tube traversing the separator from top to bottom may be provided to allow passage of a radioactive probe known in the prior art in this arrangement and performing this function, allowing the detection of the levels and at least one breather traversing one of the steps of the stepped structure to allow the passage towards the top part of the separator of the gas which is separated from the liquid phases in the bottom part.

Further characteristic features and advantages of the invention will become apparent from the ensuing description of a preferred embodiment of such a decanting apparatus. In this description, reference will be made to the appended drawings, in which: Fig. 1 is a longitudinal half-section through a vertical plane of the separator taken on the line I-I in Fig.2 Fig. 2 is a cross-section taken on the line II-II in Fig. 1; Fig. 3 combines two transverse half-sections respectively on the lines III-III (part a) and III'-III' (part L) of Fig. 1; Fig. 4 shows on an enlarged scale a perspective view of a lining structure for which the present invention proposes a novel application.

The separator shown in Figs. 1 to 3 comprises a cylindrical body 1 intended to be disposed horizontally in the position of use and comprising two halves which are substantially symmetrical in relation to a vertical plane at right-angles to its axis.

A duct 2 for supplying three-phase mixture which is to be separated discharges through a hood 3 in the central upper part of the body 1 while in the central bottom part of the body there is a discharging pipe 4 for drawing off the water phase and at the intermediate level, still in the central part of the body 1, there is a pipe 5 for drawing off the oil phase. In the vicinity of the two ends of the body, pipes 6 for drawing off the gaseous phase open out into the top part of the body.

At right-angles to the three-phase mixture supply pipe 2 there is a deflector 26 in the form of a dihedron, the edge of which is disposed horizontally at right-angles to the axis of the body 1 and of which the two faces diverge in the direction of the bottom part of the body 1. The object of this deflector 26 is on the one hand to receive the flow of mixture to be separated without imposing on it any sudden shock likely to lead to the formation of a substantial volume of foam and on the other, to divide the flow of mixture into two substantially equal fractions which are dispersed in the direction of the two opposite ends of the body 1. The three-phase mixture flows off, assuming a structure resembling descending steps 7, and which connects with the base of the deflector 26. The steps 7 avoid the three-phase mixture undergoing any abrupt drop towards the bottom of the separator and so likewise contribute to avoidance of the formation of a substantial volume of foam.

Furthermore, the steps 7 afford the mixture which is to be separated a substantial surface area for exchange, allowing the major part of the gas present to become separated from the liquid phases. The lowest step 7 plunges directly into the upper liquid phase, so avoiding any sudden contact between the mixture and the liquid phase.

Disposed above the steps 7 are lining structures 8a and 8b normally used in distillation or absorption columns.

These lining structures, shown in Fig. 4, consist of a stack of fluted sheets 9, in which the edges of the flutes are offset angularly from one sheet to the other. These fluted sheets are pierced by orifices 10. The object of these linings, in the distillation columns or in the absorption columns, is to ensure intimate contact between the gas and the liquid present in order to enhance the efficacy of distillation or absorption. In the present case, the Applicants have established that these lining structures have the capacity to "break down" the foams which form in the separator by very effectively separating the gaseous phase from the liquid phases. These structures can be made from metal or from plastics material and typically they are of a metal/propylene/metal complex. They are not very heavy and therefore do not substantially increase the weight of the separator. The structures 8g and 8k are suspended directly from the inside surface of the top wall of the body 1.

The pipe 6 for drawing off gases discharges into an enclosure 11 comprising chicanes or the like, in which the traces of liquid present in the gaseous phase complete their separation from this latter and are drawn off through a drain 11 traversing the stepped structure 7, towards the bottom part of the separator.

In this bottom part, lining structures 12a, 12b, 12c similar to the structures 8a, 8b are supported by the bottom wall of the body 1 and are at least partially immersed in the liquid phases. The purpose of the structures 12g, 12, 12c is to stabilise the separator when it is used on a floating platform, and to suppress the resonance frequencies and dampen the pitching of the separator.

In order to dampen rolling, the steps 7 have edges 13 which project in their upper part parallel with the axis of the body 1.

A breather pipe 14 supported by one of the steps 7 and communicating through this latter with the bottom part of the separator allow the gases which become separated from the liquid phases in the bottom of the separator to be drawn off towards the upper part of this latter.

Tubes 15 traversing the separator from top to bottom provide passage for radioactive probes adapted to detect the levels in operation.

AS can be seen from Fig. 2, the pipe 5 intended for recovery of the oil phase, does not discharge directly into the separator but is connected to a collector or manifold 16 in which there are ports 17, which is disposed crosswise in the body 1, substantially horizontally. This drawing also shows that the hood 3 is supported by U-shaped channel sections 18 disposed transversely and horizontally within the body 1 and the ends of which rest on cups 19 fixed to the inner surface of the body 1.

A separator of this type, weighing less than the conventional separators, proves to be extremely effective in preventing the formation of foams and the destruction of such foams since their effective life is on average twice as short than with conventional separators. Furthermore, it is particularly suitable for use on floating installations because it offers considerable stability, effectively combats the phenomena of rolling and pitching and eliminates resonance phenomena.

Claims

1. Use in a separator of a three-phase liquid-liquid-gas mixture of a lining structure normally used in distillation or absorption columns, the structure being constituted by thin fluted sheets in which there are orifices and which are stacked in such a way as to form channels open at their ends, the channels of one and the same sheet being offset angularly in relation to those of the immediately adjacent sheets, this lining structure being disposed in the separator in such a way as to be at least partially in contact with the gaseous phase in order to break up any foams which are likely to form.

2. Use in a separator for a three-phase liquid-liquid-gas mixture and intended to be mounted on a floating installation of a lining structure normally used in distillation or absorption columns, the structure consisting of thin fluted sheets possibly pierced with orifices, stacked in such a way as to form channels which are open at their ends, the channels of one and the same sheet being offset angularly in relation to those of the immediately adjacent sheets, this lining structure being disposed in the separator in such a way as to be at least partially in contact with at least one liquid phase in order to enhance the stability of the separator and to dampen pitching.

3. A separator of a three-phase liquid-liquid-gas mixture of the type comprising a substantially cylindrical enclosure disposed horizontal or vertically and provided with three-phase mixture inlet means and discharge means respectively for the three phases separated from the mixture, said draw-off means being offset in height with respect to the separator, the means of drawing off the heavier liquid phase being disposed in the bottom part of the separator, the means of separating the light liquid phase being disposed at a midway level and the means of drawing off the gaseous phase being disposed in the upper part, wherein the device comprises, in at least partial contact with the gaseous phase and/or at least one of the liquid phases, a lining structure normally used in distillation columns or in absorption columns, the structure being constituted by thin fluted sheets pierced with orifices and stacked in such a way as to form channels which are open at their ends, the channels of one and the same sheet being offset angularly in relation to those of the immediately contiguous sheets.

4. A separator according to claim 3, comprising a substantially cylindrical body disposed horizontally, characterised in that it comprises two halves substantially symmetrical in relation to a median plane perpendicular to its axis, the three-phase mixture inlet means being situated in the upper part of the separator, substantially in the median plane at right-angles to its axis, while the means of drawing off the two liquid phases are situated at levels which are offset in this same median plane, the means of drawing off the gaseous phase comprising two pipes disposed in the upper part of the separator at its two end.

5. A separator according to claim 4, characterised in that the three-phase mixture inlet means is disposed in line with a deflector in the form of a dihedron, the edge of which is disposed substantially in the median plane at right-angles to the axis and of which the two faces are inclined symmetrically downwardly in order to divide the flow of mixture into two substantially equal fractions.

6. A separator according to claim 5, characterised in that the lateral surfaces of the separator connect with a descending stepped structure over which the mixture to be separated flows.

7. A separator according to claim 6, characterised in that the steps comprise edges which project at their upper surface, preferably parallel with the axis of the body in order to dampen rolling phenomena.

8. A separator according to one of claims 3 to 7, characterised in that the gas draw-off means discharge into an enclosure in which there are chicanes and which is capable of separating the entrained traces of liquids from the gases.

9. A separator according to claim 8, characterised in that the enclosure is equipped with means for drawing off in the direction of the liquid phase traces of liquid entrained by the gases.

10. A separator according to one of claims 6 to 9, characterised in that lining structures are disposed above the stepped structure.

11. A separator according to one of the claims 6 to 10, characterised in that lining structures are disposed beneath the stepped structure and are at least partially immersed in one or both liquid phases in order to dampen pitching phenomena.

12. A separator according to one of claims 6 to 11, characterised in that at least one of the steps of the stepped structure comprises a breather pipe traversing the said step and discharging into the upper part of the separator.

13. A separator substantially as hereinbefore described with reference to the accompanying drawings.

14. Use of a separator substantially as hereinbefore described with reference to the accompanying drawings.