Abstract:
An electrostatic separator intended for separation of liquid phase systems, made up of mixtures of liquids of various electrical permittivity. In particular, the separator is intended for separation of an oil-and-water emulsion. The electrostatic separator contains a vessel, inside which there is suspended a system of electrodes energized from an external voltage source. The electrode system comprises at least one pair of conducting plates ( 8 ), which is attached to a supporting frame ( 7 ) and electrically connected with the high voltage winding of a feeding transformer ( 9 ), which is placed in the supporting frame ( 7 ). The supporting frame ( 7 ) is preferably a casting of an insulating material. The conducting plates ( 8 ) of the electrode system are preferably connected to the winding of the feeding transformer ( 9 ) through a capacitive electrical connection.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to Polish patent application 351182 filed 13 Dec. 2001 and is the national phase under 35 U.S.C. §371 of PCT/IB02/05358. 
   1. Technical Field 
   The present invention relates to an electrostatic separator intended for separation of liquid phase systems, which are mixtures of liquids of different electrical permittivity. In particular, the electrostatic separator contains a vessel, inside which there is suspended a system or set of electrodes energised by means of an external voltage source. 
   Since the invention is particularly applicable to electrostatic separators for separation of water from oil in oil-and-water emulsions, it will be described with reference to such an application. However, it should be understood that the invention is applicable to all kinds of electrostatic separation applications intended for separation of liquid phase systems. 
   BACKGROUND OF THE INVENTION 
   Electrostatic separation of liquid phase systems is commonly used in the chemical industry, especially in petroleum industry. Such separation consists in the use of the forces of an electric field generated by means of electrodes immersed in the liquid environment subjected to the separation process. There are known solutions wherein the electrodes are energised with both DC and AC current. 
   The commonly known separators are vessels of various shapes, which are filled with liquid subjected to the separation process. When connected to a voltage source, the electrodes, which are immersed in the liquid, cause the formation of an electric field. Phase separation takes place as a result of many processes connected with the presence of the electric field, such as polarisation and dipole interaction or electrophoresis. For a water-in-oil emulsion, wherein the dispersed phase is water, fine droplets of the dispersed phase coalesce to form bigger droplets, which fall down to the tank bottom due to gravity. The separated phases of the mixture are removed from the tank through outlets suitably located in the vessel. Separator vessels can be divided into a number of chambers, in which different separation techniques are applied depending on the percentage composition of the mixture to be separated into its components or phases. Mixture separation employs electrodes made of conducting elements, to which an external source of high voltage is connected through a transformer located outside the vessel. If the electrodes are supplied with direct current, the power supply system contains a rectifier. Due to the danger of arcing between the electrodes, the power supply units are often provided with protecting systems, which restrict the current. 
   2. Prior Art 
   For example, from U.S. Pat. No. 3,674,677 there is known a device intended for water-and-oil emulsion separation. This device contains a cylindrical, horizontally situated vessel, having an emulsion inlet opening located at a certain level at one end of the vessel, an oil drain located at the other end of the vessel, and a water drain located in the vessel bottom. Inside the vessel there is placed vertically one set of electrodes supplied with high voltage and another set of electrodes grounded inside the vessel. The electrodes in both sets have the form of conducting plates, concentrically curved with respect to the longitudinal axis of the vessel. The high voltage electrodes are placed between the earthed electrodes and the earthed internal wall of the vessel. The vertical high voltage electrode plates are attached to a horizontal plate, which is suspended from the walls of the upper part of the vessel by means of many insulated hangers, and which is electrically coupled, through an insulated feeder, to an external source of high voltage. The vertical plates of the earthed electrodes are attached to internal metal parts of the vessel. 
   From U.S. Pat. No. 4,702,815 there is known a device for desalting and dehydrating of oil by means of an electrostatic separation process. The device contains a vessel provided with adequate inlet openings for oil and diluting water, and outlet openings for the separated products. An electrode system for the generation of an electric field, suspended vertically in the upper part of the vessel and attached to said vessel by insulated hangers, is composed of a number of composite plates placed parallel to each other, and these plates consist of a conducting part that is located centrally in the framing of another part, which does not conduct electric current. Voltage is supplied to the conducting part from an external source of alternating current, whereby the high voltage winding of a transformer located outside the vessel is connected to the electrodes in such a manner that adjacent plates are supplied with opposite charges, or that supply voltage is fed to alternate plates, and each non-supplied plate is earthed. 
   The presented solutions of prior art demonstrate basically two types of electrostatic separation devices. One type, presented in U.S. Pat. No. 3,674,677, represents a separator with an electrode arrangement, which is usually supplied by means of a DC source, and another type presented in U.S. Pat. No. 4,702,815 represents a separator with a system of insulated electrodes, normally supplied with alternating current. There are further known solutions, which have both types of electrode arrangements placed in one vessel, e.g. the solution known from U.S. Pat. No. 4,308,127. 
   In all above mentioned solutions the source of high voltage supply is located outside the electrostatic separator vessel, and the elements used to attach the electrode system inside the vessel require the use of special insulated connections between the high voltage winding of the feeding transformer and individual electrodes, placed in the separator vessel wall. Thus, prior art electrostatic separators show a complicated and voluminous construction, and are also difficult to maintain. 
   THE OBJECT OF THE INVENTION 
   It is an object of the invention to present an electrostatic separator containing a vessel, which separator has a construction that is considerably simpler and more compact compared to prior art separators. The electrostatic separator shall also be operatively reliable and promote an easy maintenance thereof. 
   BRIEF DESCRIPTION OF THE INVENTION 
   The object of the invention is achieved by means of an electrostatic separator containing a vessel, such as a gravity separator tank, inside which there is suspended a system or set of electrodes energized by means of an external voltage source, characterised in that the electrode system comprises at least one pair of conducting plates, which is attached to a supporting frame arranged inside the vessel, and electrically connected to a high voltage winding of a feeding transformer, which is located in the supporting frame. 
   Preferably, the supporting frame is in the form of a casting made of an insulating material. 
   Preferably, the supporting frame casting is made of epoxy resin. 
   Preferably, the conducting plates of the electrode system are connected to the feeding transformer winding through a capacitive electrical connection. 
   Preferably, the capacitive electrical connection has a form of a conducting element insulated inside the supporting frame, and the end of the conducting plate of the electrode system is placed near the conducting element. 
   Preferably, the conducting plates of the electrode system are coated with a layer of an insulating material. 
   Preferably, the operating frequency of the feeding transformer is higher than 50 Hz. 
   The advantage of the inventive separator is the possibility to construct a device in which all high-voltage elements are completely insulated inside the supporting frame, and the power supply from the external power supply source, delivered to the feeding transformer through the separator vessel wall is low voltage supply. Placement of the feeding transformer in the supporting frame, especially a frame made of an insulating material, and the location of the electrode system in this frame, considerably simply the construction of the separator. 
   Further features and advantages of the present invention are presented in the following detailed description of the inventive electrostatic separator. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Below, preferred embodiments of the electrostatic separator according to the present invention will be described more in detail with reference to the appended drawings. in which: 
       FIG. 1  schematically shows a longitudinal cross sectional view of a first embodiment of the inventive separator, 
       FIG. 2  shows a cross-section according to A—A in  FIG. 1 , 
       FIG. 3  schematically shows a developed detail “a” in  FIG. 2 , 
       FIG. 4  schematically shows a cross-section of a second embodiment of the inventive separator, and 
       FIG. 5  schematically shows a developed detail “b” in  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a schematic view showing an electrostatic separator according to one embodiment of the invention. The electrostatic separator contains a vessel, which is a metallic, cylindrical, horizontally oriented drum, filled with a water-and-oil emulsion  2 . Filling of the vessel  1  is made through an inlet  3 . located in the upper part of the vessel. Normally, the separator vessel is divided by means of suitable baffles into several chambers or compartments. in which the successive separation stages are realised. In the embodiment example in the drawing one baffle  4  is shown, and the vessel is divided into two compartments. In the first compartment, containing the inlet  3  for emulsion  2  and a water drain  5 , which is used to remove the water phase  6  from the vessel  1 , there is attached a supporting frame  7  to the Inner upper wall of the vessel  1  by means of a support structure not shown in the drawing. In the second compartment of the vessel  19  located behind the baffle  4  (as seen in the main flow direction through the vessel  1 ), there is a drain opening  15  for separated pure oil. To the supporting frame  7  there are attached conducting plates of an electrode system, which are connected to an outer voltage source located outside the vessel  1 . The supporting frame  7  is a casting made of insulating material, preferably epoxy resin, with a transformer  9  arranged on the inside thereof The transformer  9  is completely insulated on the outside and its ends of the low voltage winding  10  are leading out of the frame  7  and connected to a low voltage terminal  11  arranged at the outside of the vessel  1 . The conducting plates or electrodes  8  are suspended generally vertically from the supporting frame  7  and arranged in parallel with each other at fixed distances so as to substantially cover the cross sectional area of the vessel, especially the cross sectional area of the water-and-oil emulsion. The conducting plates further have a certain extension in the length direction of the vessel depending on for example the specific separation condition. 
   As can be seen in more detail in  FIGS. 2 and 3 , according to a first embodiment of the invention, one end of the low voltage winding of the transformer  9  is connected to an external low voltage terminal  11 , while the other end is connected with the vessel wall. The ends of the high voltage winding  12  of the transformer  9  are connected via voltage busbars  13 , which are embedded in the material of the frame  7 , with conducting elements  14  made of flat channel bars, by electric connection of the channel back with the appropriate bus. In each conducting element  14 , which is located in the insulating material of the frame  7 , in the gap formed between the flanges of the channel bar and in a groove located in the frame  7 , directly under the gap of the channel, there is placed a conducting plate  8  of the electrode system. Between the outer surface of this plate and the inner surface of the conducting element  14  there is an insulating layer of the frame  7 , whose thickness corresponds to the difference in the transverse dimensions between the width of the groove made in the frame  7 , corresponding to the conducting plate  8  thickness, and the distance between the flanges of the channel section in the conducting element  14 . In the electrode system, each of the electrodes is made of a conducting material, in the form of an uninsulated conducting plate  8 , or this plate can be continuously coated with an insulating layer  8   a . The electrical connection between the conducting element  14  and the conducting plate  8 , or a conducting plate with the insulating layer  8   a , is in both cases a capacitive electrical connection. The ends of the high voltage winding  12  are connected with the plates of the electrode system in such a way that the adjacent plates are supplied with high voltage of opposite sign. which is shown in  FIG. 3 . In the device operating conditions, any number of conducting plates  8  can be made as conducting plates with the insulating layer  8   a . The conducting plates  8  and the conducting plates with the insulating layer  8   a  can be installed in the same system of electrodes fixed in the frame  7 . The selection of the type of electrodes depends on the manner of power supply and on the supply voltage level. The outside shape of the supporting frame  7  is adjusted to suit the shape of the separator vessel  1 . 
   In a second embodiment of the invention, as shown in  FIGS. 4 and 5 , a system or set of electrodes is fixed in the conducting elements  14  in the frame  7 , which are supplied with high voltage of the sane sign. One end of the high voltage winding  12  is connected, through a busbar  13  and the conducting element  14 , with conducting plates  8  or with conducting plates with an insulating layer  8   a , while the second end is connected to a coupling element  16 , located inside the frame  7 , in close proximity of the vessel wall, so that the capacitance between the coupling element  16  and the wall of the vessel  1  is greater than the capacitance between each pair of the conducting plates  8  of the electrode system, formed by the conducting plate  8  or the conducting plate with the insulating layer  8   a , and an earthing electrode  17 . The earthing electrodes  17  in the form of substantially vertically arranged plates or sheets are located between the conducting plates  8  or supply electrodes and they are connected with the vessel wall through a connector  18 , as for example schematically shown in  FIG. 4 . 
   In the first embodiment of the invention, as schematically shown in  FIGS. 2 and 3 , the electric field generated in the water-and-oil emulsion  2  between conducting plates  8  or conducting plates with an insulated layer  8   a  requires the plates to be power supplied from a source of AC voltage. Voltage is supplied to the conducting plates  8  or conducting plates with the insulated layer  8   a  in a contactless manner through a capacitive coupling in the following way. The plates  8  are placed in the grooves of the supporting frame  7 . These plates can be all made of a conducting material or they can have a conducting core surrounded by the insulating layer  8   a . The supporting frame  7  is a casting of an insulating material, inside which there are embedded conducting elements  14 . which are located in the immediate proximity of the grooves with the plates  8 . The conducting elements  14  are alternately connected to the ends of the high voltage secondary winding  12  of a feeding transformer  9  by means of busbars  13 . The conducting elements  14  are coupled in a capacitive way with the conducting plates  8  or the conducting layers of the plates coated with the insulating layer  8   a , which causes that voltage generated in the secondary winding  12  of the transformer  9  is supplied in a contactless way to the conducting plates  8 , also in an alternating way. One end of the primary winding  10  of the feeding transformer  9  is connected to the vessel  1  casing, and the other end of the primary winding  10  is connected with a low voltage terminal  11 . The operating frequency of the feeding transformer  9  is higher than 50 Hz, which allows a reduction of the size of the transformer  9 . 
   In the second embodiment of the invention, as schematically shown in  FIGS. 4 and 5 , inside a vessel  1  there are placed two sets of an electrode system. In one set, each conducting plate  8 , or conducting plate with an insulating layer  8   a , is placed in the groove of a supporting frame  7 . The supporting frame  7  is a casting of an insulating material. inside which there are embedded conducting elements  14 , which are located in the immediate proximity of the grooves with the plates  8 . The conducting elements  14  are connected with one end of the high voltage secondary winding  12  of a feeding transformer  9 . by means of a bus bar  13 . The conducting elements  14  are coupled in a capacitive way with the conductive plates  8 , or the conductive layers of the plates enveloped in the insulating layer  8   a , which causes that voltage generated in the secondary winding  12  of the transformer  9  is supplied in a contactless manner to the conducting plates  8 . Between the plates  8  there are arranged metallic plates  17  of the second set of electrodes, which are connected with one another and with the vessel  1  casing through a connector  18 . The other end of the secondary winding is connected with a coupling element  16  placed inside the supporting frame  7  in the Immediate vicinity of the vessel wall, thus ensuring a capacitive coupling with the vessel wall, whose potential is the reference potential. One end of the primary winding  10  of the feeding transformer  9  is connected to the casing of the vessel  1 , while the second end of the primary winding  10  is connected with a low voltage terminal  11 . The operating frequency of the feeding transformer  9  is higher than 50 Hz, which permits a reduction in the size of the transformer. 
   It should be realised that the above presentation of the invention has been made by way of example, and that alternative embodiments will be obvious for a person skilled in the art. However, the scope of protection claimed is defined in the patent claims supported by the description and the appended drawings. 
   LIST OF REFERENCE NUMBERS USED IN THE FIGURES 
   
       
         1 . Vessel 
         2 . Oil-and-water emulsion 
         3 . Inlet 
         4 . Baffle 
         5 . Water drain 
         6 . Water phase 
         7 . Supporting fame 
         8 . Conducting plates,  8   a —conducting plates with an insulating layer 
         9 . Feeding transformer 
         10 . Low voltage winding 
         11 . Low voltage terminal 
         12 . High voltage winding 
         13 . Voltage busbars 
         14 . Conducting element 
         15 . Oil drain 
         16 . Coupling element 
         17 . Earthing electrodes 
         18 . Connector