GB2037602A - Separating two immiscible liquid phases of different densities - Google Patents

Abstract

A liquid comprising two immiscible liquid phases (e.g. hydrocarbon in water) is introduced continuously into a separating chamber through an inlet 26 which directs the liquid between two baffle walls 24 and 25 which are orientated obliquely to the inflow direction, the inlet 26 being opposite the lower wall 25. The separating chamber may be a half annular chamber defined between outer and inner cylindrical walls 22 and 23 and vertical partitions 27 and 39 in which case walls 24 and 25 are semi-frustoconical in shape. The light phase is removed via valved outlet 34 while the heavier phase still containing an emulsion of the light phase passes downwardly into a lower part annular chamber containing a plurality of half ring shaped coalescing fins 28. The liquid then flows through pipe 29 into a central outlet chamber from where the coalesced light phase is removed through outlet 33 and the heavier phase through outlet 32. <IMAGE>

Description

SPECIFICATION Separating two immiscible liquid phases of different densities The present invention relates to the separation of two immiscible liquid phases of different densities which are mixed with one another and in continuous flow.

The invention has particular application to the separation of hydrocarbons contained in water to be discharged, for example industrial water to be discharged or ballast water, complying with the specifications contained in Resolution A 393 passed by the IMCO (Inter-Governmental Maritime Consultative Organization) on the 14th November 1977 and which provides that the content of hydrocarbons in effluents discharged from places where machinery is accommodated and from tanks must not be higher than 100 ppm.

According to the invention there is provided apparatus for separating two immiscible liquid phases of different densities, comprising a decanting chamber provided with an inlet for introducing a liquid to be treated and opening out between walls which are oriented obliquely with respect to the direction of introduction, the said walls constituting two deflectors located one below the other, and the inlet being opposite the lower deflection.

Preferably, the deflectors respectively adjoin two opposite walls of the chamber and cooperate with them to form a baffle. According to another preferred feature of the invention, the top of the lower deflector is located substantially at the same level as the bottom of the upper deflector.

A separator which has a decanting chamber provided with an inlet for introducing the liquid to be treated and which opens out between walls which are oriented obliquely with respect to the direction of introduction has been described in U.S. Patent 1,920,468.

The invention will be described in more detail, by way of example, with reference to the drawings in which:~ Figure 1 is a basic schematic diagram of a separator embodying the invention; Figure 2 is a vertical section of an actual separator embodying the invention; Figure 3 is a horizontal section through the separator of Figure 2 in the plane LLL-LLL of Figure 2, and Figure 4 is a perspective view of the separator of Figure 2 which is restricted to certain elements.

The separator shown diagrammatically in Figure 1 comprises an enclosure 1 within which there are an inlet chamber 2, a transfer chamber 3, and an outlet chamber 4.

The inlet chamber 2 is provided with two deflectors 5 and 6 which form between them a space 7 into which opens an inlet 8 through which the liquid to be treated is introduced into the separator.

The deflectors 5 and 6 are inclined walls which are inverted with respect to the direction of introduction of the liquid and which form with this direction of introduction 9 (assumed to be horizontal) identical or different opposite accute angles a and b, preferably between 450 and 20 , better still between 350 and 250 and optimally in the vicinity of 300.

Preferably, the bottom 10 of the upper deflector 5 is located substantially level with the top 11 of the lower deflector 6 as shown, and the inlet 8 is disposed just below the bottom 10.

The liquid to be treated is, for example, ballast water (the heavy phase) containing a hydrocarbon (the light phase) which is to be separated so as to reduce the hydrocarbon content of the water to a tolerable level before discharging the water into the sea.

The major part of the separation is achieved by decantation (gravity separation) in the inlet chamber 2.

In fact, the deflectors 5 and 6 and the walls 12 and 13 of the chamber which respectively adjoin them constitute a baffle having an upper exit section 14 through which the separated light phase is evacuated towards the top of the inlet chamber and a lower exit section 15 through which the heavy phase, still containing an emulsion of the light phase, is evacuated downwardly. The light phase which accumulates at the top of the chamber 2 can be removed by any suitable means (indicated diagrammatically by the arrow 16), while the heavy phase (the path of which is indicated diagrammatically by the arrow 17) flows into the transfer chamber 3.

The chamber 3, which is located at a level lower than that of the inlet chamber, is provided with means promoting coalescence of the emulsion of the light phase which is still contained in the heavy phase, these means, for example, being constituted simply by a system of fins 18, the axes of which are horizontal, but which are themselves either horizontal or inclined (as seen in a transverse plane). These fins are slightly spaced one from another, for example with an interval of less than 10mm, but nevertheless sufficient for a suitable flow of liquid. By way of indication, an interval of 7 mm is suitable for a flow of 500 litres per hour.

The fins have the effect of multiplying the area of contact with the fluid and of reducing the distance of decantation of the drops of the light phase. These will naturally rise and apply themselves against the fin located immediately above. They will coalesce with each other at the surface of the fin, which, when it is sufficiently saturated, will release the light phase at the outlet in the form of large drops, which will decant easily in the outlet stage 4.

The outlet stage or chamber 4 is provided with an evacuation outlet 19 for the light phase at the top and with an evacuation outlet 20 for the heavy phase at the bottom; preferably, a screen 21 disposed between the coalescing chamber 3 and the outlet 20 prevents the outlet being a direct extension of the fins 18 and creates a vertical speed reversal favourable to decantation.

Figure 1 is only a basic view in the assumed case of a prismatic apparatus with rectangular chambers.

Figures 2 to 4 relate to an apparatus of the cylindrical type.

The apparatus shown in Figures 2 to 4 comprises two vertical cylindrical walls 22 and 23 which define an annular space between them.

The inlet 26 for the liquid to be treated opens into the upper part of this space below a collar 24 adjoining the outer cylindrical wall 22 and facing a collar 25 adjoining the inner cylindrical wall 23. These collars, which are halves only of truncated cones (see Figure 4), perform the functions of the deflectors 5 and 6, respectively, of the embodiment of Figure 1.

The heavy phase descends into a lower zone of the annular space on one side of a vertical partition 27 and makes its way horizontally towards the other side of this partition, passing through a set of horizontal fins 28 constituted by half discs and which perform the function of the fins 18 of the embodiment of Figure 1. When the liquid arrives on the other side of the partition 27, it passes into a tube 29, the inlet of which is in the bottom part of the annular space. This routeing of the liquid from one side of the partition 27 to the other is shown diagrammatically by the curved line 30 in Figure 3.

The pipe 29 opens out inside the space 31 within the inner wall 23, where the heavy phase is evacu atedthrough a bottom outlet 32, while the light phase is evacuated through atop outlet 33. The space 31 constitutes the outlet chamber.

Moreover, the light phase which has been separated by the action of the collars 24 and 25 is extracted through an outlet 34 at the top of the annular space.

The light phase outlets 33 and 34 may be under the control of valves 35 and 36 operated by level detectors 37 and 38.

Figure 4 shows only the walls 22 and 23, the collars 24 and 25, some of the fins 28, the vertical partition 27 and the other vertical partition 39 against which the collars starting from the partition 27 terminate.

It is to be noted that the coalescing chamber is of particularly simple design and does not present the inconveniences of apparatus having a coalescing cartridge. This is permitted by the fact that the coalescing chamber has to treat only a mixture which contains no more than residues of hydrocarbons, the major part of the hydrocarbons having been separated in the decanting chamber.

For example, a mixture containing 25% of hydrocarbons (by weight) in water, injected at the inlet of the illustrnt#d apparatus can give a heavy phase (water) containing less than 50 ppm of hydrocarbons (by weight) after passing through the apparatus. If this mixture were sent directly into the coalescing chamber, the working of this chamber would be stopped.

The present invention is not restricted to the embodiments which have been described.

Claims (16)

1. Apparatus for separating two immiscible liquid phases of different densities, comprising a decanting chamber provided with an inlet for introducing a liquid to be treated and opening out between walls which are oriented obliquely with respect to the direction of introduction, the said walls constituting two deflectors located one below the other, and the inlet being opposite the lower deflector.

2. Apparatus according to claim 1, in which the deflectors respectively adjoin two opposite walls of the chamber and cooperate with them to form a baffle having a bottom exit and a top exit.

3. Apparatus according to claim 1 or 2, in which the top of the lower deflector is substantially at the same level as the bottom of the upper deflector.

4. Apparatus according to claim 1, 2 or3, in wh.ch the defectors comprise inclined walls inverted with respect to the direction of introduction of the liquid and which form with this direction identical or different opposite acute angles.

5. Apparatus according to claim 4, in which the acute angles are each between 450 and 200.

6. Apparatus according to claim 4, in which the acute angles are each between 350 and 250.

7. Apparatus according to claim 4, in which the acute angles are each in the vicinity of 300.

8. Apparatus according to any preceding claim, in which the deflectors are substantially planar.

9. Apparatus according to any preceding claim, in which the deflectors are portions of a frustoconical shape.

10. Apparatus according to any preceding claim, and comprising a coalescing chamber which receives the heavy phase from the decanting chamber and contains means for causing any light phase which still accompanies the heavy phase to coalesce, in which the coalescing means comprise fins having a substantially horizontal axis.

11. Apparatus according to claim 10, in which the coalescing means comprise fins in the form of portions of discs.

12. Apparatus according to claim 10 or 11, further comprising an outlet chamber which receives the liquid from the coalescing chamber.

13. Apparatus according to claim 12, in which the outlet chamber is located in a space circumscribed by a cylindrical wall and this cylindrical wall is surrounded by another cylindrical wall with which it forms an annular space, the upper part of which constitutes the decanting chamber and the lower part of which constitutes the coalescing chamber, these two chambers being defined by vertical partitions.

14. A separator substantially as herein described with reference to the drawings.

15. A method of separating two immiscible liquid phases of different densities, comprising flowing the liquid through a separator in accordance with any preceding claim.

16. A method according to claim 15, in which the liquid phases comprise hydrocarbons and water respectively.