Abstract:
The present invention relates to a device for separating an effluent comprising phases of different density and conductivity, the device comprising a pair of electrodes ( 12, 13 ), means ( 10 ) for introducing the effluent between said electrodes, means intended for separation ( 3 ) and discharge ( 4 ) of said separated phases. The separation means comprise at least one centrifugation element including a helical channel ( 19 ) in which the effluent is centrifuged after passing between the electrodes. An opening extends over the entire periphery of said centrifuged effluent so as to discharge part of the centrifuged effluent. The discharge means further comprise sealing means for limiting discharge of the less dense phase through said opening.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the field of emulsified effluent processing, notably petroleum effluents from production wells. The emulsions concerned are those whose disperse phase is electrically conducting, unlike the continuous phase, for example water dispersed in an organic phase such as oil.  
           [0002]    It is important to separate the water from the effluent produced so as to improve the quality, therefore the market value, of the effluent and to limit the size of the processing and transport equipments. After passage of the emulsified effluent through conventional water/oil separators, the effluent still contains about 1 to 5% emulsified water in the oil. The goal of the present invention is to decrease these residual amounts of water and salts in order to meet the technical requirements of the downstream processes.  
         BACKGROUND OF THE INVENTION  
         [0003]    Document U.S. Pat. No. 5,647,981 describes a device which combines the principle of an electrocoalescer with centrifugation.  
           [0004]    Water-in-oil emulsions can be “broken” by coalescence of the water drops through the action of an electric field. However, in order to increase the efficiency of these electrostatic separators, one tries to increase the electric potential between the electrodes, with a real risk of appearance of breakdown phenomena between electrodes. On the other hand, considering the residence time required between the electrodes, the effluent flow rate that can be treated is low, unless an installation of disproportionate size is used.  
           [0005]    Document FR-2,824,489 discloses a combination between an electrocoalescer of determined shape and centrifugation and separation means specific to said coalescer.  
           [0006]    The present invention aims to improve the separation means described in document FR-2,824,489.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention thus relates to a device for separating an effluent comprising phases of different density and conductivity. The device comprises a pair of electrodes, means for introducing the effluent between said electrodes, a helical channel in which said effluent is centrifuged, after passage between said electrodes, so that the phases are separated, and means intended for discharge of the separated phases. The discharge means comprise an opening extending over the periphery of said centrifuged effluent to discharge part of the centrifuged effluent. The device is characterized in that the discharge means further comprise sealing means for limiting discharge of the less dense phase through said opening.  
           [0008]    The sealing means can comprise a mask closing said opening and leaving an orifice so that the denser phase distributed in the lower part of said channel is discharged through said orifice and the less dense phase distributed in the upper part of said channel is kept inside the discharge means by said mask.  
           [0009]    The sealing means can comprise a surface converging towards the inside of the discharge means, so that part of the effluent discharged through said opening is collected by said surface and fed into the discharge means. This surface can be truncated-cone-shaped.  
           [0010]    The orifice can extend over an angular portion ranging between 20° and 180°.  
           [0011]    The helical channel can consist of at least one helical wall arranged in an annular space. The end of the helical wall coincides with an edge of the orifice. The orifice can also extend on either side of the end of said helical wall.  
           [0012]    The helical wall is in contact with the internal tube but it can provide a clearance with the wall of the external tube.  
           [0013]    The helical channel can consist of a helical tube.  
           [0014]    The electrodes can have the shape of cylinders arranged along the same axis.  
           [0015]    The section of flow of said helical channel can be so determined that the velocity of the effluent increases in relation to the velocity of the effluent in the vicinity of said electrodes.  
           [0016]    According to the invention, the less dense phase can be discharged through an axial line.  
           [0017]    According to the invention, the discharge means can comprise a cyclone and an axial orifice for discharge of at least part of the centrifuged phase. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0018]    Other features and advantages of the present invention will be clear from reading the description hereafter of a non limitative example, with reference to the accompanying drawings wherein:  
         [0019]    [0019]FIG. 1 diagrammatically shows the principle of the invention,  
         [0020]    [0020]FIG. 2 diagrammatically shows the outlet of the separator according to the invention,  
         [0021]    [0021]FIG. 3 is a developed view of a part of the invention,  
         [0022]    [0022]FIG. 4 shows in detail an element of the separator outlet,  
         [0023]    [0023]FIG. 5 illustrates a variant of the centrifuge,  
         [0024]    [0024]FIG. 6 shows the distribution of the oil and water phases at the separator outlet. 
     
    
     DETAILED DESCRIPTION  
       [0025]    The general layout of an example of embodiment of a device according to the invention meets the following requirements:  
         [0026]    the fluid is preferably fed under pressure between two cylindrical and concentric walls, the tangential inlet is not essential but preferably maintained,  
         [0027]    the electrocoalescer has a determined geometry allowing to obtain a sufficient residence time for the effluent. For example, its length can be about 1 m and the annular space is such that the residence time of the fluid is 10 seconds at a flow rate of 500 l/h. The distance between the cylinders is therefore 7.86 mm (radius difference between a 2-inch tube (50.8 mm) and a 1-inch tube (25.4 mm)),  
         [0028]    a centrifuge is arranged after the electrocoalescer, whose motive element is one or more helical surfaces arranged between two concentric cylinders over, for example, a length of 500 mm. For information, the distance between the cylinders has been reduced to 6.35 mm (radius difference between a 1.5-inch tube and a 1-inch tube) in order to increase the velocity of the fluid as it flows through the centrifuge,  
         [0029]    the centrifuge opens onto a separator proper. This part is essential and of delicate design in order to prevent the intense turbulence developed at the centrifuge outlet from dispersing the water droplets again.  
         [0030]    In FIG. 1, which shows the whole of device  1  according to the invention, reference numbers  2 ,  3  and  4  respectively refer to the coalescer, centrifuge and separator parts. Arrow  5  shows the inflow of the effluent containing the emulsion into the device, arrow  6  shows the outflow of the dehydrated effluent sent to transport and refining installations  8 , arrows  7  show the various outflows of the essentially aqueous phase sent to discharge processing installations  9 .  
         [0031]    The means for feeding the emulsified effluent into the coalescer are such that the fluid is fed tangentially into annular space  11  delimited by the outside of electrode  12  and the inside of shell  13 . The dimensions of the electrocoalescer, diametral and longitudinal, are so determined that, considering the rate of injection of the effluent through means  10 , the residence time in the air gap of the electrodes is such that the coalescence of the water drops is optimum. Electrodes  12  and  13  are electrically connected to an electric field generator  14 . Electrodes  12  and  13  are preferably cylindrical in shape. At the end of the coalescer, electric insulating means  15  separate the electrodes from the inlet means of centrifuge  3 .  
         [0032]    Centrifuge  3  consists of an external cylindrical tube  16 , preferably vertical, an internal tube  17  in continuation with central electrode  12  of the coalescer, and a helical wall  18  in contact with the inside of tube  16  and the outside of tube  17  so as to form a continuous helical channel  19  around the longitudinal axis of the device. The shape of this channel  19  is such that the effluent at the coalescer outlet is led to be centrifuged over the total length of centrifuge  3 . This length is furthermore determined to optimize the centrifuging effect. Conical connection means  20  can be used between the coalescer and the centrifuge in order to reduce the main section of flow of the effluent so as to increase the velocity of flow of the fluid in the centrifuge. The higher the velocity, the better the centrifugation and therefore the phase separation.  
         [0033]    In an equivalent way, the centrifuge can be obtained from a line of suitable section with a helical shape for centrifugation of the fluid. At least one tube can for example be helically wound around a tube.  
         [0034]    Without departing from the scope of the invention, centrifuge  3  can comprise several helical channels.  
         [0035]    [0035]FIG. 5 shows a variant of the centrifuge wherein helical wall  18  is not in contact with the inner wall of external tube  16 . Clearance d allows formation of a layer of the centrifuged phase which can freely flow also in the longitudinal direction, i.e. downwards when the device is arranged vertically, which is generally preferable.  
         [0036]    A separation element  4  is fastened to the end of the centrifuge. Its purpose is to collect the water drops which are in contact with the outer wall by centrifugation. A conical part  20  forming a continuation of the centrifuge produces a cyclone type separation, the centrifuged phase being discharged through orifice  21 , the lighter phase (organic phase) being discharged in the direction of the axis of the cone through the inner space of tube  17  extended by the inner line of electrode  12 . Separation element  4  furthermore comprises a lateral opening surface  22  allowing to separate the major part of the aqueous phase in contact with the inner wall of tube  16 .  
         [0037]    [0037]FIG. 2 shows more in detail the separation means. The same reference numbers as in FIG. 1 are used in FIG. 2. Channel  19  is delimited by two helical walls  18   a  and  18   b  separated by a distance h corresponding to the height of channel  19 . At the end of centrifuge  3 , channel  19  opens into an annular volume  30  defined between the inner surface of tube  16  and the outer surface of tube  17 . Volume  30  communicates with collection volume  31  through opening  22  provided in tube  16 . The collection volume is delimited by the outside of tube  16  and by divergent tube  35 . It can be noted that end  23  of tube  17  is extended after opening  22 . Opening  22  is preferably a complete ring extending over the periphery of tube  16  so that the major part of the centrifuged aqueous liquid is discharged through this opening. Opening  22  can be made by cutting out a portion of tube  16  between two planes. Thus, tube  16  is separated into two distinct sections: a section extending upstream from opening  22  and a section extending downstream from opening  22 .  
         [0038]    Under the effect of centrifugation, the water, denser than oil, tends to spread and to circulate in the lower part of channel  19  whereas the oil tends to spread and to circulate in the upper part of channel  19 . FIG. 3 shows channel  19  developed in a plane. The lower part of channel  19  rests on helical surface  18   a.  The upper part of channel  19  is delimited by helical surface  18   b  separated by height h from surface  18   a.  The phases of the effluent at end  29  of channel  19  are separated. The water represented by the dotted volume circulates in the lower part of channel  19  over height h 1 . The oil represented by the hatched volume circulates in the upper part of channel  19  over height h 2 .  
         [0039]    [0039]FIG. 2 shows two means  32  and  33  intended to allow passage, through opening  22 , mainly of aqueous liquid only and to keep the oil in volume  30 .  
         [0040]    First means  32  consists of a surface extending in volume  31 , for example a truncated cone converging towards the inside of tube  16 . Truncated cone  32  allows to collect part of the effluent that has passed through opening  22  and to feed it back into tube  16 . Under the effect of centrifugation in channel  19 , the oil phase that has flowed through opening  22  in the direction shown by arrow F 1  is collected by truncated cone  32 , then it is fed back into the inner volume of tube  16 . The aqueous phase, denser than the oil phase, circulates mainly in the direction shown by arrow F 2 . The aqueous phase is not affected by truncated cone  32  and it is discharged from volume  31  through an outlet  7 .  
         [0041]    Second means  33 , shown in dotted line in FIG. 2 and in detail in FIG. 4, consists of a mask which closes part of opening  22 . Mask  33  can be a tube portion inserted inside or outside tube  16 . Mask  33  leaves an orifice  34 . The position and the geometry of orifice  34  are so selected that the water circulating in the lower part of channel  19  is discharged through orifice  34  and the oil circulating in the upper part of channel  19  is kept in annular volume  30  by mask  33 . For example, orifice  34  extends over an angular portion θ ranging between 20° and 180° and over a height H ranging between 10% and 100% of the height h of channel  19 . Orifice  34  can be positioned in relation to the end of helical surface  18  marking the end of channel  19 . For example, angular portion θ of orifice  34  is distributed on either side of the end of helical surface  18 . Or the end of helical surface  18  coincides with an edge of orifice  34 , orifice  34  extending over an angular portion θ from this edge in the direction of rotation of the helix of channel  19 .  
         [0042]    [0042]FIG. 3 also shows mask  33  developed in a plane. Orifice  34  is so positioned in relation to channel  19  that channel  19  mainly leads the aqueous phase to orifice  34 .  
         [0043]    One of the first and second means  32  and  33  can be used independently of the other. First and second means  32  and  33  can be used simultaneously.  
         [0044]    Operation of the device according to the invention was simulated with the FLUENT fluid mechanics code. FIG. 6 shows the end of the separator. The numerical simulation results can be seen in FIG. 6: the distribution of the oil and of the water forming a petroleum effluent that circulates in the device according to the invention.  
         [0045]    It can be observed in FIG. 6 that, on the one hand, the water  40  is distributed above surface  18  (i.e. in the lower part of channel  19 ) and, on the other hand, the oil  41  is distributed below surface  18  (i.e. in the upper part of channel  19 ).  
         [0046]    Implementation of surface  32  or of mask  33  according to the invention allows to increase the value of the separated water fraction by about 25% in relation to the device provided with opening  22  without surface  32  and without mask  33 .