WO1999043439A1

WO1999043439A1 - Device and method for the separation of fluids

Info

Publication number: WO1999043439A1
Application number: PCT/NO1999/000055
Authority: WO
Inventors: Jan Fredrik Michelet
Original assignee: Read Process Engineering A/S
Priority date: 1998-02-24
Filing date: 1999-02-22
Publication date: 1999-09-02
Also published as: NO980767L; AU2552799A; NO980767D0; NO308199B1; EP1073526A1

Abstract

A hydrocyclone for the separation of two fluids having different densities and which are immiscible, comprising a conical tube (1) having an inlet for the fluids to be separated in proximity to the widest end of the tube, an axial outlet (10) for the fluid having the lowest density close to the fluid inlet, an outlet (14) for the fluid having highest density at the narrowest end of the tube (1) and wherein in the inlet there are provided means, such as guide vanes or inlet openings (9) which are approximately tangential to the inner diameter of the tube to set the fluid mixture in substantially rotational motion, wherein in the tube (1) at one or more points at a distance from the inlet there are provided means for converting axial motion into rotational motion. A method for the separation of fluids using the improved cyclone is also described.

Description

DE VI CE AND METHOD FOR THE SEPARATION OF FLUIDS

The present invention relates to an improved hydroflotation cyclone for the separation of fluids of different densities which are immiscible, such as, for example, oil and water, and also a method for the separation of a fluid mixture.

Hydroflotation cyclones or hydrocylcones have been used for a long time for a rapid and efficient separation of fluids having different densities which are immiscible, such as oil and water. Hydrocyclones have been extensively used on oilfields for a rapid and efficient separation of oil and water, especially for cleaning sufficient oil from the water, so as to give the water an oil content that is low enough to meet the pollution authorities' requirements with respect to discharge of the water.

A hydrocyclone consists in principle of an elongate, internally conical tube wherein the fluid mixture to be separated is passed in at great pressure and correspondingly high velocity through the approximately tangential inlet of the inner peripheral tube in proximity to the widest end of the tube. The heaviest phase will then be collected against the tube walls, whilst the light phase will float in towards the centre of the tube, from where it is removed through an outlet in the centre of the apparatus at or in proximity to the top, that is to say at the widest end of the tube. The heaviest phase, that is to say the water in the case of the cleaning of oil and water, will then flow out through the narrowest end of the hydrocyclone.

A hydrocyclone of this kind is described in Norwegian Patent No. 177613. A hydrocyclone of this type is used for cleaning water with an oil content of less then 1% in order to reach on oil content of, for example, 40 ppm or 15 ppm, which is sufficient for either reinjection of the water into an oilfield and/or gas field or discharge of the water into the surroundings.

When the oil content in the water is higher, the viscosity of the liquid mixture increases, which in turn results in the radial motion necessary to obtain a purifying effect in the hydrocyclone becoming an axial flow at a relatively short distance from the inlet of the liquid mixture in the hydrocyclone. The purifying effect on such a mixture is thus not optimal, and the mixture must, if possible, run through several such separation cycles before the water reaches the desired level of purity. The object of the present invention is to provide a hydrocyclone which overcomes the said problem.

According to the present invention, this is achieved by a hydrocyclone for the separation of two fluids having different densities and which are immiscible, comprising a conical tube having an inlet for the fluids which are to be separated in proximity to the widest end of the tube, an axial outlet for the fluid having the lowest density in proximity to the inlet for the fluids, an outlet for the fluid having the highest density at the narrowest end of the tube, and wherein in the inlet there are provided means, such as guide vanes or inlet pipes which are approximately tangential to the inner diameter of the tube, to set the fluid mixture in a substantially rotational motion, wherein in the tube at one or more points at a distance from the inlet there are provided means to convert the axial motion into rotational motion.

A method for the separation of two fluids which are immiscible and which have different densities is also provided wherein the mixture of the fluids is introduced into a hydrocyclone, wherein the fluid mixture at the top is set in rotational motion, wherein the fluid having the lowest density is passed out through an axial outlet in proximity to the inlet end of the hydrocyclone, and the fluid having the highest density is discharged at the opposite end of the hydrocyclone, wherein the fluid mixture which flows through the hydrocyclone is again set in rotational motion one or more times downstream of the fluid mixture inlet.

According to the invention, in order to overcome the problem that the desired radial motion leads to and becomes a non-purifying axial motion, means such as guide vanes are provided in the hydrocyclone to set the liquid mixture in radial motion at a distance from the liquid mixture inlet which is such that the radial motion has become too much of an axial motion. In this way, the liquid mixture is again made to spin in order to ensure additional purifying effect in the hydrocyclone.

In connection with the means for setting the liquid mixture in rotation again, i.e., upstream and/or downstream of the means, there is also provided at the central axis of the hydrocyclone an outlet for the light phase, such as, for example, oil. Depending on the expected composition of the liquid mixture, the purification requirements and the like, such means may be placed at one or more points along the length of the hydrocyclone for setting the liquid stream in radial motion again. During the operation of the present hydrocyclone, the liquid mixture introduced will first undergo a coarse separation at the top, i.e., the widest end of the hydrocyclone, wherein the light phase which is separated there is removed at or in proximity to the top through an axial outlet. The use of the above-mentioned axial outlets in conjunction with the means for setting the liquid mixture in rotation again will allow a larger portion of the light phase or oil to be removed in this way for every step, thereby ensuring that the heavy phase which flows out through the narrow end of the hydrocyclone has a purity which is sufficient for reinjection or discharge.

The oil in the first oil outlet has the least intermixture of water, whilst the water content of the subsequent oil outlets rises with each step. In fact, in order to discharge an oil having an acceptable purity, the oil/water mixture from the last oil outlet or outlets may be recirculated to the inlet and undergo another separation.

The present invention will now be described with reference to the attached figures, wherein:

Figure 1 shows a longitudinal section through an embodiment of the present invention;

Figure 2 shows a section through a vane body with vanes;

Figure 3 shows a section through an alternative vane body with vanes;

Figure 4 shows a section through an alternative vane body with vanes; and

Figure 5 shows a partially cut-away model of the embodiment shown in

Figure 4.

Figure 1 shows a preferred "three-step" embodiment of the present improved hydrocyclone. The present hydrocyclone comprises a conical tube which in its turn, for production-technical reasons, may be composed of several tube sections.

Although the tube 1 in the illustrated embodiment is approximately linearly conical, in some cases it may in fact be preferable to have a non-linear conical shape. The tube 1 in the illustrated embodiment is surrounded by a jacket 2 which is divided into a plurality of chambers, in the illustrated embodiment an inlet chamber 3, oil outlet chambers 4 and 5 and a water outlet chamber 6, which are defined by radial walls 7 running radially from the outer wall of the tube 1 to the inner wall of the jacket 2.

A plurality of hydrocyclones may optionally be connected in parallel relation in a common jacket 2, in order to increase total capacity.

The liquid to be separated enters the inlet chamber 3 through liquid inlet 8. From inlet chamber 3, the liquid flows into the tube 1 through inlet openings 9 which enter the interior of the tube 1 approximately tangentially to the interior wall of the tube in proximity to the widest end of the tube. The liquid which is under high pressure, for example, in the order of 2-10 bars, is then set in vigorous rotation, whereby the lightest phase of the liquid mixture floats in towards the tube axis and is withdrawn through the primary oil outlet 10. Because of the high viscosity of the liquid, the radial motion of the liquid decreases and the motion of the liquid gradually becomes a more axial motion.

To set the liquid in radial motion again, a vane 11 is installed in the tube, at a distance from the top where computations indicate that the radial motion has become so low that no more separation takes place. In the embodiment shown in Figure 1, two vanes have been installed, at about 1/3 and 2/3 of the way along total length of the tube, respectively. The vane 11 is arranged on a vane body 12, in which vane body there is bored a secondary oil outlet 13 through which liquid can be withdrawn from the centre of the tube in the downstream end of the body 12, and passed out into the oil outlet chambers 4 and 5 respectively. The vanes 11 and the vane body 12 are normally positioned in a sleeve 21. The secondary outlet 13 runs from the downstream end of the vane body up through the vane body and from there runs out radially through the vane body 12, the vane 11, the sleeve 21 and the tube 1 to lead into and empty its contents into the surrounding outlet chamber 4 or 5.

The liquid in the oil outlet chambers 4 and 5 can be emptied through the oil draw-off points 15 and 16 respectively.

The remaining liquid, which consists essentially of water, is ultimately emptied out through water outlet 14 in the narrow end of the tube 1, where it passes out into water outlet chamber 6 and can be drawn off through water draw-off point 17. The liquid which passes out through the oil outlets 13 into oil outlet chambers 4 and 5 respectively, is collected in these chambers and can, if the level of purity is not high enough, be recirculated into liquid inlet 8 for another separation. It is especially the liquid in the oil outlet chamber 5 which may still have a large water content that is

5 circulated, whilst the liquid in the oil outlet chamber 4 can flow out together with the liquid from the primary oil outlet 10. Since the pressure in the liquid inlet 8 and the inlet chamber is considerably greater than the pressure in the outlet chamber 5, a non- illustrated recirculation pump is provided between the oil draw-off point 16 and the liquid inlet 8. The water which exits into the water outlet chamber 6 is drawn off l o through water draw-off point 17.

The vane body 12 may be of various designs and may have a disc 18 fitted on the downstream end so that the turbulence downstream of the vane is limited to the space formed between the vane 11 and the disc 18. The disc 18 also presses the liquid out is towards the periphery of the tube so that its velocity increases, which in turn increases the separation capacity of the hydrocyclone.

In the hydrocyclone shown in Figure 1 two vanes are installed to increase the radial velocity. However, depending upon the oil mixture that is to be purified, from one to a

20 plurality of vanes may be installed in the hydrocyclone. The more viscous the liquid that is to be separated, the faster it loses its radial motion. Thus, for a highly viscous liquid it is necessary to install more vanes spaced apart at smaller intervals than if the liquid to be separated is less viscous. The apparatus can therefore have from one to several secondary, tertiary etc. oil outlets, where the content of the heavy phase, i.e., in

25 the illustrated example water, in the light phase, i.e. oil, is higher the further from the inlet in the hydrocyclone it is. The liquid which is withdrawn in the last oil outlet before the water outlet 14 will thus contain relatively large amounts of water and may to advantage be recirculated to the liquid inlet 8.

30 In the illustrated example, inlet openings 9 are used to set the liquid mixture in motion in the inlet end. However, these inlet openings 9 may also be replaced by vanes. Moreover, the vanes 1 1 and the vane body 12 may be replaced by a body having guide holes which again set the liquid to be separated in radial motion.

35 The jacket 2, the inlet chamber 3, the outlet chambers 4 and 5 and the water outlet chamber 6 may be omitted and replaced by directly connected pipes or hoses. The vanes 11 and the vane body 12 may be of various designs. Figures 2, 3, 4 and 5 show both different designs of the vanes 11 and the vane bodies 12 and different locations of the axial outlets 13, 19 and 20. In the embodiment described above, an axial outlet 13 was placed in the vane body 12 at the downstream end of the vane body 12.

Figures 4 and 5 show an embodiment wherein two axial outlets are bored in the vane body 12, one outlet 20 in the upstream end and one outlet 19 in the downstream end. These two outlets 19 and 20 both empty out into outlet chambers 4 and 5 respectively, as described above. Depending on the specifications of the liquid to be separated, the diameter of the outlets 19 and 20 can be adjusted so that a correct amount of the light liquid is drawn off axially and that the ratio of discharge upstream to discharge downstream is adjusted so as to give optimal separation.

As can be seen from Figures 2 - 5, the design of the vanes may also be different depending on the need in question. In the embodiments shown in Figures 2 and 3 the vanes 11 make less than one revolution on the vane body 12, whilst each vane in the embodiment shown in Figures 4 and 5 make several revolutions on the vane body 12.

Example

A hydrocyclone essentially as shown in Figure 1 was produced and was used for a series of tests using different mixtures of oil and water and under different operating conditions.

The hydrocyclone tube was about 1.5 metres long with a diameter at the inlet end of about 70 mm and a diameter at the water outlet 14 of about 15 mm. The primary oil outlet, which was an axial bore in the top of the tube has a diameter of about 4 mm.

Two vane bodies were installed at about 0.5 and 1 metre respectively from the liquid inlet. The secondary and tertiary oil outlets were axial bores in the countercurrent end of the vane bodies connected to radial ducts which ran out into the oil outlet chambers.

The table below shows the results from representative tests using this three-step hydrocyclone. w

Test No. P in P ORI ^P OR2 ^P OR3 P WR Oil stream Water stream Water in Water Water Water Oil in (mVh) (m³ /h) % ORl (%) OR2 (%) OR3 (%) WR

1 6.5 0 0.25 0 4.5 1.75 3.2 66 24 33 83 15ppm

2 2.5 0 0.25 0.5 2 1 2 81 19 73 97 15ppm

3 2.8 0 1.75 2 2.25 1 1.5 71 16 62 99 15ppm

4 6.5 0 6.5 6.25 6 0.9 1 5 . 63 19 87 99 40ppm

5 6.25 1 0 0 4.5 1.6 2.8 67 18 30 94 0.5%

6 6 1 0 0 4 1.1 3.4 76 11 57 96 <1%

7 6 1 2 0 3.75 1.2 3.4 76 14 77 > 99 40ppm

8 6 1 3 3.2 4.5 1 3 80 14 60 97 <1%

P stands for pressure in bars in stands for inlet

OR stands for oil reject, oil reject 1, 2 and 3 respectively

WR stands for water reject

O

H

O o o o in tΛ

Claims

P a t e n t c l a i m s

1.

A hydrocyclone for the separation of two fluids having different densities and which are immiscible, comprising a conical tube (1) having an inlet for the fluids to be separated in proximity to the widest end of the tube, an axial outlet (10) for the fluid having the lowest density close to the inlet for the fluid, an outlet (14) for the fluid having the greatest density at the narrowest end of the tube (1), and wherein in the inlet there are provided means such as guide vanes or inlet openings (9) which are approximately tangential to the inner diameter of the tube, in order to set the fluid in substantially rotational motion, characterised in that in the tube (1) at one or more points at a distance from the inlet there are provided means for converting axial motion into rotational motion.

2.

A hydrocyclone according to claim 1 , characterised in that in connection with the means for converting axial motion to rotational motion one or more axial outlets (13, 19, 20) are provided for the fluid having the lowest density.

3.

A hydrocyclone according to claim 1 or 2, characterised in that the means for converting axial motion to rotational motion are static vanes (11).

4. A hydrocyclone according to claim 3, characterised in that the vanes (11) are positioned on a vane body (12) which is mounted in the hydrocyclone.

5.

A hydrocyclone according to claim 4, characterised in that the axial outlet or outlets (13, 19, 20) are one or more axial bores in the vane body (12).

6.

A hydrocyclone according to claim 5, characterised in that there is provided an axial outlet (13, 19) in the downstream end of the vane body relative to the direction of flow of the fluid in the hydrocyclone.

7.

A hydrocyclone according to claim 6, characterised in that in addition there is provided an axial outlet (20) in the upstream end of the vane body (12).

8.

A method for the separation of two fluids which are immiscible and which have different densities, wherein the mixture of the fluids is introduced into a hydrocyclone wherein the fluid mixture at the top is set in rotational motion, wherein the fluid having lowest density is passed out through an axial outlet (10) close to the inlet end of the hydrocyclone and the fluid having the highest density is passed out at the opposite end of the hydrocyclone, characterised in that the fluid mixture flowing through the hydrocyclone is again set in rotational motion one or more times downstream of the inlet of the fluid mixture.

9.

A method according to claim 8, characterised in that more of the fluid having the lowest density is withdrawn in .onnection with the points where the fluid is again set in rotational motion.

10 Amended Claims

[received by the International Bureau on 01 July 1999 (01.07.99); original claims 1-5 amended; remaining claims unchanged (1 page)]

1.

A hydrocyclone for the separation of two fluids having different densities and which are

5 immiscible, comprising a conical tube (1) having a wider end and a narrower end and having an inlet (9) for the fluids to be separated in proximity to the widest end of the tube (1), an axial outlet (10) for the fluid having the lowest density close to the inlet (9) for the fluid, an outlet (14) for the fluid having the greatest density at the narrowest end of the tube (1), and means such as tangentially inlet openings and guide vanes (11) to set o the fluids in substantially rotational motion in the tube (1), characterised in that the guide vanes (11) in the tube (1) are formed on a central vane body (12) having an axially outlet (13,19,20) for the fluid having the lowest density.

2. 5 A hydrocyclone according to claim 1, characterised in that there is provided an axial outlet (13, 19) in the downstream end of the vane body relative to the direction of flow of the fluid in the hydrocyclone.

3. o A hydrocyclone according to claim 2, characterised in that in addition there is provided an axial outlet (20) in the upstream end of the vane body (12).

4.

A hydrocyclone according to any of the claims 1-3, characterised in that the vane body 5 (12) is fixed in a surrounding sleeve (21) by means of the vanes (11), said sleeve being fixed in the conical tube (1).

5.

A hydrocyclone according to any of the claims 1-4, characterised in that the conical tube 0 (1) is mounted in a housing (2) which by means of radial walls (7) is divided into a first end space (3) at a supply (8) for the fluids, one or more spaces (4,5) connected with the axial outlet/outlets (13,19,20) through the vane bodies (12) and with outlets (15,16), respectively, for the fluid having the lowest density, and a second end space (6) connected with the outlet (14) for the fluid having the greatest density, and having an 5 outlet (17) for the fluid having the greatest density.