Electrohydrodynamic separation device for separating fluids in a mixture and associated method

Abstract

The invention relates to an electrohydrodynamic separation device comprising: a storage reservoir (2), a separation chamber (4) with at least two outlets (5a, 5b), and means (6) for generating an electric field including at least one electrode (7) and adjustment means (8) for creating a variable field that guides the droplets. The invention utilises the effects produced by a non-uniform electromagnetic field on a droplet. It can be used to separate non-polar liquids.

Description

DESCRIPTION Title: Electro-hydrodynamic separation device for separating fluids in a mixture and associated process technical field

[0001] The present invention relates to an electrohydrodynamic separator for separating fluids, particularly a water-oil mixture. The present invention will find its main application in fluid separation within the petroleum industry.

[0002] However, the present invention can also be used for the separation of other types of fluids and can also advantageously be used for the separation of fluids in more distant fields, particularly in the chemical industry. Technological background

[0003] Various techniques are used to separate two fluids; one particularly effective technique is based on coalescence. This technique involves causing droplets to clump together, becoming increasingly larger, and then being separated from the rest of the fluid by gravity or centrifugal force.

[0004] To induce this fusion of droplets, one of the most common techniques is to subject the fluid to an electric field. When the electric field is applied, the fluids react differently depending on the polarity or non-polarity of their constituent molecules. In practice, if it is a polar fluid, the droplets will coalesce; if it is a non-polar fluid, the electromagnetic force will have no effect on this fluid, which behaves like a dielectric.

[0005] A first drawback of this electromagnetic field coalescence technique is that it does not allow for the efficient separation of two polar fluids from each other, even when these two fluids have different dipole moments.

[0006] A second drawback is that this technique does not allow for changing the relative speed of the fluids separated from each other.

[0007] A third drawback is that this technique does not allow the drops to be directed in a particular direction, the movement of the drops in the fluid depends only on external forces such as gravity and centrifugal force, which strongly conditions the geometry of the devices and in particular the orientation of the fluid collectors at the outlet and the length of the main tube in which coalescence takes place.

[0008] A fourth drawback arising in particular from the third one mentioned above is that, given the non-orientation of the drops, it is often necessary to carry out several successive separation steps to obtain a satisfactory separation rate. Summary of the invention

[0009] The present invention relates to an improvement in fluid separation techniques using a magnetic field and aims to overcome the aforementioned drawbacks. A primary objective of the present invention is to resolve all or part of the technical problems associated with the aforementioned prior art by providing an electro-hydrodynamic separation device for separating polar and non-polar fluids from each other, or for separating polar fluids from each other, and allowing control of the orientation and / or velocity of the droplets in the flow.

[0010] Another objective of the present invention is to propose an electrohydrodynamic separation device for fluid separation allowing for various geometries and orientations of outlet tubes.

[0011] Another objective of the present invention is to propose an electrohydrodynamic separation device for fluid separation allowing fluids to be separated without the need for gravitational separation or with the aid of a centrifugal effect after coalescence.

[0012] Another objective of the present invention is to propose an electrohydrodynamic separation device for fluid separation that can be adapted to existing separation installations.

[0013] Another objective of the present invention is to provide a reliable and easy-to-implement electrohydrodynamic separation device for fluid separation.

[0014] The invention aims to protect an electro-hydrodynamic separation device for separating fluids in a mixture comprising a storage tank for the mixture connected to a separation chamber opening onto at least two fluid outlets and means for generating an electric field, comprising at least one electrode and such that said means for generating the electric field include adjustment means for generating a variable field in the separation chamber capable of generating an electro-hydrodynamic potential difference at the level of drops of the mixture allowing their guidance.

[0015] The present invention also aims to protect a separation method for implementing the device as described above. Brief description of the figures

[0016] Other features and advantages of the present invention will become apparent from the description of the specific and non-limiting embodiments of the present invention below, with reference to the attached Figures 1 to 3, in which:

[0017] [Fig. 1] illustrates a schematic embodiment of a device according to the invention, in perspective view,

[0018] [Fig. 2a] represents a schematic view of the separation chamber according to a first example conforming to the invention,

[0019] [Fig. 2b] represents a schematic view of the separation chamber according to a second example in accordance with the invention,

[0020] [Fig. 3] schematically illustrates a schematic view of the separation chamber according to a second example of the invention comprising accumulation zones. Detailed description

[0021] The present invention relates to an electro-hydrodynamic separation device. Referring primarily to Figure 1, a perspective view of this separation device is shown.

[0022] This separation device 1 comprises a storage tank 2 for a mixture of fluids 3 to be separated. The storage tank 2 is connected to a separation chamber 4 in which the separation will take place.

[0023] The separation chamber 4 opens onto at least two outlets 5a, 5b allowing the flow of the separated fluids.

[0024] According to one aspect of the invention, the separation device 1 comprises means for generating an electric field 6, comprising at least one electrode 7, suitable for enabling coalescence and / or guidance of the drops.

[0025] This electrode 7 can have a variable shape depending on the characteristics of the fluid or the geometry of the separation chamber 4. According to the advantageous embodiment illustrated in Figure 1, at least one electrode 7 has a substantially flat shape.

[0026] These means for generating the electric field 6 include adjustment means 8 for generating a variable field in the separation chamber 4. When the liquids flow into the separation chamber 4 in a given direction or along a principal axis, the electrodes 7 will be positioned on either side of the chamber 4 along this principal axis with a variable angle 01 or 02 as shown in Figures 2a and 2b.

[0027] This variable field will create an electro-electrohydrodynamic potential difference at the droplet level. Indeed, the electrical stresses are proportional to the square of the electric field intensity E, generated by the generation means 6, according to Maxwell's stress tensor. For a spherical droplet, the net force driving the electro-electrohydrodynamic flow is proportional to the electrical stress at the droplet's surface, the scale of which is as follows:

[0028] F e oc E 2

[0029] Since the electric field is not uniform, the stress distribution can vary across the droplet surface, but the magnitude of the driving force generally depends on E 2

[0030] In addition to electrical stress, other forces are exerted, including viscous resistance which opposes the movement of the drop and surface tension, which helps to maintain the shape of the drop.

[0031] The viscous drag opposing the movement of the drop depends on the terminal velocity V, as well as the viscosity of the fluid p and the diameter of the drop D.

[0032] For a spherical droplet moving in a viscous fluid, the drag force is given by a form of Stokes' law:

[0033] F d oc DV

[0034] At terminal velocity, the drag force exactly balances the driving force due to the electric field:

[0035] DE oc E 2

[0036] By rearranging the expression, we obtain the general dependence of the speed:

[0038] We can write it more precisely by starting with the electric force:

[0039] F e = k E 2

[0040] with k as a constant depending on the geometry of the droplet, the dielectric properties of the fluids and the distribution of surface charges.

[0041] The viscous drag force acting on the droplet, according to Stokes' law for a spherical object in a viscous medium, is given by: F d = k2 / J.DV where: p is the dynamic viscosity of the surrounding fluid, D is the diameter of the drop, V is the terminal velocity and k2 is a geometric constant.

[0042] At terminal velocity, the electrical force and the viscous drag force are balanced.

[0043] k t E 2 = k2 / j.DV [ L 0044] J Thus we have [ L 0045] J And so

[0046] As shown in the attached figures, when the electrodes 7 are tilted, a non-uniform electric field is generated in the separation chamber 4. The electric field is stronger below the drop and weaker at the top, resulting in an asymmetry of the electro-hydrodynamic forces acting on the drop.

[0047] In the present invention, the inclination of the electrodes 7 introduces an effective vertical component of the electric field, which can be described by the angle 9 between the electrodes and the vertical axis and as shown in Figure 2a - 2b.

[0048] The vertical component of the electric field causing the movement is therefore reduced by a factor of cos9:

[0050] It can be deduced from this equation that when the angle of inclination increases (i.e., the electrodes become more horizontal), the intensity of the effective vertical electric field on the drops increases, which increases the terminal velocity.

[0051] Thus, at 9° (perfectly horizontal electrodes), the terminal velocity is maximum. At 9° (perfectly vertical electrodes), the vertical component of the electric field approaches zero, and the terminal velocity decreases accordingly.

[0052] According to a first application, the separation device 1 is used to separate dielectric or imperfect dielectric liquids. That being said, the separation device 1 can also allow the separation and guidance of a mixture of polar / nonpolar liquids or between two polar liquids, except when these liquids are miscible.

[0053] As an example, device 1 is used for separating oil droplets dispersed in water produced on offshore platforms. In this application, the oil droplet separation is achieved through the non-uniformity of the electric field, which is controlled by the electrode's tilt and the electric field strength. This application typically represents a final stage in the separation process, after most of the oil has already been removed by other methods, such as gravity separators. The fine separation at this stage often requires additional volumetric force, and in our case, we propose using the electric field for this purpose.

[0054] The potential difference at the level of the drops can be adjusted by the adjustment means 8 provided at the level of the means for generating the electric field 6 allowing their guidance as explained above.

[0055] According to the embodiment shown in the accompanying figures, these adjustment means 8 comprise a variable-angle electrode support 9. The electrode support 9 both supports the electrode 7 and allows its inclination relative to the separation chamber 4 or relative to the main axis of movement of the mixed fluid. In the illustrated example, the support 7 consists of a motorized plate 19.

[0056] The movement of the platform 10 can be achieved in various ways commonly used in the field of lifting and including, but not limited to, the movement of hydraulic cylinders, or motorized worm gears or air cushions.

[0057] In the embodiment described above, a single electrode 7 is provided in the longitudinal direction of the separation chamber 4, however, depending in particular on the length of the separation chamber 4, the size of the electrodes 7 or the type of guidance to be exerted, the separation device 1 may in an alternative embodiment include at least two electrodes 7 placed in series, each electrode 7 being arranged on a support with variable inclination 9.

[0058] Advantageously, the angle of inclination of the electrode support 9 is between 0 and 90 degrees, allowing the effect on the droplets to be modified from a minimum, corresponding to an inclination of zero degrees (electrode 7 placed parallel to the main axis of the separation chamber 4), to a maximum, corresponding to an angle between 80 and 90 degrees, at which point the force differences exerted on the droplets will be greatest between the top and bottom of the droplets being guided. This, however, corresponds to the case where the droplet remains spherical; in the event of droplet deformation, the optimal angle for optimal entrainment will be different and determined empirically.

[0059] According to one embodiment, the pivot point is positioned not at one end of the support as shown in Figure 1, where the pivot is at the lower end of the support 9, but on the support 9 itself, specifically approximately at the midpoint of the motorized platform 10. This arrangement allows the support 9 to be rotated so that the electrode 7 induces a stronger electric field on the droplets towards the outlet of the separation chamber 4, or conversely, a stronger field towards the inlet of the chamber 4 by rotating the variable-angle support 9 in the opposite direction. In the example shown in Figures 2a and 2b, the electrodes 7 have opposite angles of inclination with respect to the axis of the chamber 4, and the direction of the droplets in the mixture 3 is also opposite (vector u).

[0060] According to the invention, the means for generating an electric field 6 comprise a current generator 11 and control means 12 for said current generator 11. The current generator 11 may be chosen from the very varied range of current generators on the market according to the electrical power characteristics and the adjustment requirements for the control of the generator.

[0061] The control means 12 ensure both the control of the current to be generated and the inclination of the electrode support(s) 9 7. The association between the characteristics of the generated current and the inclination of said at least one electrode 7 allows the control of the induced electro-hydrodynamic force and consequently the guidance of the drops.

[0062] As mentioned above, the electro-hydrodynamic separation device guides the droplets in position and velocity, allowing outlets 5a and 5b to be placed in various locations, not just downstream of the flow in separation chamber 4. This feature is particularly advantageous as it enables different orientations for each fluid. Once the different fluids are separated in orientation, it becomes possible to create accumulation zones Za for each fluid. To this end, separation chamber 4 is designed to include at least one deflector 13.

[0063] Referring this time to figure 3, we see a separation chamber 4 comprising a set of deflectors 13 allowing the creation of accumulation zones Za of one of the fluids of the mixture.

[0064] The invention also aims to protect a method for implementing the device 1 as described above, in which a step is provided for tilting the supports 9 according to the required speed of movement of the drops from the control means 12. According to an advantageous feature, the control performed by the control means 12 to obtain a setpoint speed V on the adjustment means 8 and the generation means 6 is given by the relation:

[0065] V = CE 2 COS 2 (TT / 2 — 0)

[0066] The separation device 1 and the associated method described above allow for the guidance of droplets within the mixture, with control over their speed and direction. However, other features within the grasp of a person skilled in the art could also have been considered without departing from the scope of the invention as defined in the following claims.

Claims

DEMANDS 1. Electro-hydrodynamic separation device for separating fluids in a mixture (3) comprising a storage tank (2) of the mixture connected to a separation chamber (4) opening onto at least two fluid outlets (5a, 5b) and means for generating (6) an electric field, comprising at least one electrode (7) characterized in that said means for generating (6) the electric field comprise adjustment means (8) for generating a variable field in the separation chamber capable of generating an electro-hydrodynamic potential difference at the level of drops of the mixture allowing their guidance.

2. Electro-hydrodynamic separation device for fluid separation according to claim 1 in which the adjustment means (8) comprise an electrode support (9) with variable inclination.

3. Electro-hydrodynamic separation device for fluid separation according to claim 2 in which the electrode support (9) is a motorized plate (10) allowing the inclination of the electrode (7) to be changed relative to the main axis of movement of the fluid.

4. Electro-hydrodynamic separation device for separating fluids according to any one of the preceding claims in which the device (1) comprises at least two electrodes (7) placed in series, each electrode (7) being arranged on an electrode support (9), with variable inclination.

5. Electro-hydrodynamic separation device for separating fluids according to any one of claims 2 to 4 wherein the angle of inclination of the electrode support (9) is between 0 and 90 degrees.

6. Electro-hydrodynamic separation device for fluid separation according to any one of claims 2 to 5 wherein the means for generating an electric field (6) comprise a current generator (11) and control means (12) for the current generator enabling the inclination of the electrode supports (9) to be associated with the characteristics of the generated current to allow the guidance of the drops.

7. Electro-hydrodynamic separation device for separating fluids according to any one of the preceding claims in which the separation chamber (4) includes at least one deflector (13) for creating accumulation zones (Za) of one of the fluids of the fluid mixture (3).

8. Method for implementing the device according to claim 6 or claim 7 related to claim 6, wherein a step is performed of tilting the electrode supports (9) as a function of the speed of movement to be obtained at the level of the drops from the control means (12).

9. Method for implementing the device according to the preceding claim in which the control signal issued by the control means (12) to obtain a setpoint speed V on the adjustment means (8) and the generation means (6) of an electric field is given by the relation:

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