Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05F—STATIC ELECTRICITY; NATURALLY-OCCURRING ELECTRICITY
  • H05F3/00—Carrying-off electrostatic charges
  • H05F3/04—Carrying-off electrostatic charges by means of spark gaps or other discharge devices

Definitions

• the invention relates to a static eliminator intended in particular to improve the treatment of polymers.
• polymers are very insulating products from the electrical point of view and they can retain static electricity on their surface for periods of several weeks.
• the generation of electrostatic charges by friction always accompanies the operations " necessary for the production of these polymers, and in particular the pneumatic transport. This latter operation is made necessary because the polymerization reactors are, for safety reasons, away from staff workstations, the polymer comes out in the form of granules and is conveyed, most often by pneumatic transport, to bagging stations or bulk filling of containers.
• This transport produces a partial abrasion of the granules, which produces fines, and a partial fusion, by heating, of granules entrained along the walls.
• the streaks left by the molten product solidify in the form of filaments called "angel hair" which have a diameter of the order of a tenth of a millimeter and a length of a few centimeters, or in the form of strands which have a diameter of several millimeters and a length of more than 10cm.
• Fine, angel hair and tow are waste products which degrade the quality of the product and which should, in principle, be separated from the granules by ventilation devices. But, the friction of the products on the walls of the installation generate electrostatic charges both on the granules and on the waste.
• a static eliminator comprising at least one nozzle having a body limiting a supersonic nozzle for the expansion of a compressed gas, a corona tip located at near the nozzle neck and an electrical supply circuit connected to the corona tip.
• the eliminator object of French patent n ° 80 21 977, repeats previously known arrangements, and in particular the creation, in the vicinity of the neck of a supersonic nozzle, of nanometric aerosols of ice formed by condensation of water vapor. on ions produced by a corona discharge, as well as the entrainment of these aerosols by a supersonic jet.
• the essential characteristic of the aforementioned patent resides in the process which makes it possible to obtain in the jet, in the case where the metal tip which produces the corona discharge is supplied with alternating current, equal positive and negative currents, which ensures electrical neutrality. of the mixture of ions supplied by the nozzle. This neutrality is ensured, on the one hand thanks to the insulating coating of the throat of the nozzle and of the part of the nozzle external to the nozzle, and on the other hand by the insertion of a capacitor in the supply circuit of The point.
• the invention provides for this purpose a static eliminator of the type defined in the introduction, which incorporates basic characteristics of the invention of French patent No. 80 21 977, but adds essential characteristics to achieve the goals mentioned above above and allow an application, in particular in the field of treatment or production of polymers.
• the corona tip (or crown tip) is constituted by a surgical needle made of chrome steel, the tip of which has a diameter of less than 30 micrometers.
• such a surgical needle has the advantage of being readily available commercially and of being able to be replaced easily for maintenance.
• the supersonic nozzle is composed of a metal insert comprising a hollow cylindrical part extended towards the front by a conical part ending in a bead oriented inwards, the assembly being molded in a epoxy insulation so as to cover the conical part and its bead with insulation, both outside and inside, and the front of the cylindrical inner part.
• the hollow cylindrical part composing the metal insert of the nozzle is provided at its rear part with an internal thread and has an external wall having the same diameter as a cylindrical metal tube which protects a front part of the nozzle. and which is located adjacent to the metal insert.
• the needle is advantageously supported by an insulating tube or sleeve having a threaded front part adapted to be screwed into the internal thread of the rear end of the metal insert of the nozzle.
• the eliminator advantageously comprises a metal ring arranged to slide with gentle friction over the rear part of the nozzle and on the cylindrical metal tube and to be fixed there in a position chosen so as to ensure conductive contact between the metal insert of the nozzle and metal tube.
• the insulating tube or sleeve is internally provided with a fixing device which is formed by two metal rings pierced with an opening to allow the passage of compressed gas, at least one of these metal rings being provided with a thread.
• the needle is then fixed in a threaded support arranged to be screwed or unscrewed in the fixing device in order to effect an approximate adjustment of the position of the point of the needle relative to the neck of the nozzle.
• the relative position of the needle tip and the nozzle neck can be adjusted quickly and precisely, without disassembly of the nozzle, by screwing or unscrewing the nozzle on the front end of the insulating tube or sleeve. defined above, which surrounds the support of the needle.
• the needle advantageously comprises a conical recess fitted at a rear end opposite the point.
• the rear end of the needle can be engaged inside a hollow cylinder-shaped recess arranged at the front of this metal support in the form of a cylinder, this recess having a diameter greater than a few hundredths of a millimeter to that of the needle, the rear end of the needle being fixed in the cylindrical recess by widening the walls of the conical recess of the needle due to the crushing of its walls between the inner wall of the holder and a ball of ballpoint pen of appropriate diameter.
• the device comprises a metal T-connector allowing the introduction of the compressed gas into the nozzle, this connector being interposed between the metal tube which protects the front of the nozzle and another metal tube. which protects one rear of the nozzle, so as to make contact with the tubes to ensure the continuity of the conductive connection between the front and the rear of the nozzle.
• the metal tube which protects the rear of the nozzle is in contact with a metal fixing device intended to anchor a coaxial cable to bring it from a high voltage to the needle, this metallic fixing device being in contact itself with a metallic shielding of this cable, which is connected to earth.
• the electrical supply circuit of the corona needle comprises two components in series between the needle and the secondary of a transformer which supplies it with high voltage, namely a capacitor with a value between 20 pF and 200 pF, and a resistance of value between 1 M ⁇ and 100 M ⁇ ;
• the capacitor and the resistor are located in an insulating envelope comprising openings made for the passage of input and output connections which are covered with an insulating thermosetting polymer to prevent the penetration of humid air into the envelope;
• the coaxial cable bringing the high voltage is terminated on the side of an electrical supply circuit by a high voltage plug, passes through the central opening of a metallic piece of revolution, called a plug, which has a flat side located in vis-à-vis the high-voltage device, with a milled housing adapted to the installation of an O-ring around this central opening, this part of revolution having an outside diameter larger than that of the high-voltage plug, then that the central opening has a diameter smaller than that of this plug;
• the eliminator comprises a waterproof plastic conduit arranged around the coaxial cable bringing the high voltage to the nozzles, the sealing being completed by the installation of two cable glands, one of which is placed around the inlet cable in the nozzle and the other is placed at one entrance to the part of revolution;
• the part of revolution has a cylindrical extension threaded on the side facing the supply device, this extension penetrating, through an opening of diameter greater than that of the high-voltage plug, into a cabinet which encloses the electrical supply, the seal O-ring being applied in leaktight manner to an outer wall of this cabinet by screwing a threaded ring on this threaded extension;
• the electrical supply circuit of the nozzle (s) includes high voltage transformers whose primary is connected to the output of a synchronous static relay powered by an AC voltage source, for example from the mains;
• the application of the primary voltage to the static relay is controlled by a time relay whose coil is supplied from a pressure switch connected to the compressed gas distribution network supplied to the nozzle (s);
• the nozzle (s) is (are) supplied with compressed air of pressure between 12 and 5 bars, at a dew point between -19 "C and -40 'C.
• the eliminator comprises an even number of nozzles, each group of two nozzles being formed of nozzles having voltage-current characteristics as similar as possible, each of the two nozzles being connected to an opposite polarity of an alternating supply; and for each group of two nozzles, the primary of the high voltage transformer supplying a first nozzle and the primary of the high voltage transformer supplying a second nozzle are in phase opposition.
• FIG. 1 is a side view of a static eliminator according to the invention showing more particularly the structure of the nozzle ;
• FIG. 2 is a partial sectional view showing the nozzle, the insulating sleeve cooperating with the nozzle, as well as the needle and its support arranged inside the sleeve;
• FIG. 3 is a sectional view of the nozzle of Figure 2;
• - Figure 4 is a sectional view of the insulating sleeve of Figure 2;
• FIG. 5 is a sectional view of the support and the needle of Figure 2;
• FIG. 6 is an enlarged view of the tip of the needle
• FIG. 7 is a sectional view on an enlarged scale, of the rear end of the needle and of a ball;
• FIG. 9 shows two envelopes for receiving respectively an electrical resistance and a capacitor forming part of the power supply of the tip
• FIG. 10 illustrates means for connecting the nozzle to a power supply and control cabinet
• FIG. 11 is a block diagram of the power supply and control cabinet of Figure 10; and Figure 12 schematically illustrates the power supply of two nozzles according to the invention.
• FIG. 1 shows a static eliminator designated as a whole by the reference 10.
• This eliminator comprises a generally elongated nozzle body comprising a metal tube 12 which constitutes the front of the body nozzle and which ends in a nozzle 14 through which the aerosol is ejected under the effect of a supersonic jet as designated by the reference 16.
• the metal tube 12 is connected to its rear part, by by means of a demountable conductive assembly 18, to a T-shaped connector 20 which has a lateral tube 22 for the supply of a gas under pressure, here compressed air from a compressed air source 24.
• the connector 20 is connected to a metal tube 26 which constitutes the rear of the nozzle body and which is connected to a fixing device 28.
• the latter is connected to a coaxial cable 30 serving for the supply of the tip (described below) that houses the nozzle, from a high-voltage power source 32.
• the metal part of the nozzle body is connected to earth as shown by the reference 34.
• the nozzle 14 internally houses a needle 36 terminated by a tip 38, also called “corona tip” located near an inner neck 40 which defines the nozzle.
• the rear end of the needle 36 is connected to a threaded support 42 which is itself connected to a resistor 44 and a capacitor 46, both housed inside the metal tube 26 ( Figure 1). These two components are connected to the coaxial tube 30 mentioned above.
• the support 42 is mounted inside an insulating sleeve 48 which is itself housed inside the tube 12.
• a cylindrical ring 50 (FIG. 1) is arranged to slide with gentle friction over the rear part of the nozzle 14 and on the cylindrical metal tube 12 to be fixed in a chosen position so as to ensure conductive contact between the nozzle and the metal tube. This conductive contact is effected with a metal insert 52 (FIGS. 2 and 3) which comprises the nozzle 14 and which will be described later.
• the corona tip is constituted by a surgical needle 36 made of chrome steel, the tip 38 of which has a diameter of less than 30 micrometers (FIG. 6).
• the radius of curvature of the tip 38 is advantageously between 10 and 20 micrometers.
• the needle ends in a circular base carrying a conical opening 54 (FIG. 7) used for mounting the needle in the support 42, as will be seen below.
• the metal insert 52 comprises a hollow cylindrical part 56 extended forwards by a conical part 58 terminated by a bead 60 oriented inwards. .
• the assembly is molded in a cylindrical shape 62 of insulating material, in the example of epoxy material, so as to cover with insulation the conical part 58 and the bead 60, both outside and inside , and the front of the cylindrical inner part.
• the shape of the mold must be such that this insulator covers the converging part 64 of the nozzle and its neck 60, the diverging part 66 of the nozzle being formed in a cylindrical epoxy extension having the same outside diameter D as the metal insert 42
• the appropriate shapes of the converging part and of the diverging part of the nozzle are obtained during molding by the choice of the shape of the mold.
• a rectification of the insulating material by means of cutters can possibly improve the profile of the supersonic nozzle.
• the thicknesses of insulation inside the nozzle 14 are chosen so that the maximum voltage applied to the needle is less than the breakdown voltage of the insulation.
• the nozzle 14 has a flat outer face 67 obtained by milling the cylindrical shape 62 obtained by molding.
• the hollow cylindrical part 56 constituting the metal insert 42 of the nozzle is provided at its rear part with an internal thread 68 and has an external wall 70 having the same diameter D as the metal tube 12 (FIG. 1) which protects the part front of the nozzle and which is located adjacent to the metal insert.
• the insulating sleeve 48 (FIG. 4) has a threaded front part 72 adapted to be screwed into the internal thread 68 of the rear end of the metal insert. This insulating sleeve thus makes it possible to electrically isolate the needle from the body of the nozzle. As already indicated, the insulating sleeve 48 is surrounded by the metal tube 12, the ring 50 sliding with gentle friction on the insert 52 of the nozzle and on the metal tube 12.
• the insulating sleeve 48 has an internal thread 74 into which are screwed two metal rings 76 and 78 intended to carry the metal support 42 of the needle.
• the ring 76 has a passage 80 for the metal support, while the ring 78 includes a threaded passage 82 to cooperate with the external thread 84 ( Figure 5) of the metal support 42.
• the two metal rings are pierced with openings (not shown) to allow the passage of compressed gas.
• the threaded support 42 which carries the needle 36 is arranged to be screwed or unscrewed in the fixing device formed by the rings 76 and 78 in order to effect an approximate adjustment of the position of the point 38 of the needle 36 relative to at the neck 40 of the nozzle. Furthermore, the relative position of the tip of the needle and the neck of the nozzle can be adjusted quickly and precisely, without dismantling the nozzle, by screwing or unscrewing the threaded part 72 of the insulating sleeve 48.
• FIG. 7 the rear end of the needle 36 is engaged inside a recess 86 in the form of a hollow cylinder arranged at the front of the metal support 42, this recess having a diameter a few hundredths of a millimeter greater than that of the needle.
• the rear end of the needle is fixed in the cylindrical recess 86 by widening the walls of the conical recess 54 of the needle as a result of the crushing of these walls between the inner wall of the support and a ball 88 of ballpoint pen, diameter appropriate.
• This assembly is carried out by crimping in the following manner. The needle is held vertically in a vice with the tip down.
• the ball 88 is placed on the needle and the support 42 is pressed onto the assembly so as to surround the ball and the needle.
• the support is then struck vertically with a light hammer blow, so that the ball sinks into the housing and crushes the walls of the conical part 54 of the needle against the interior walls of the support 42. This process allows '' obtain a light and undeformable whole.
• the capacitor 46 ( Figure 2) must be able to withstand a DC voltage of 16 kilovolts across the terminals while the protective resistor 44 must have a value between 1 M ⁇ and 100 M ⁇ .
• These two components are arranged in series in two insulating envelopes (FIG. 9), the insulating envelope 90 of the capacitor 46 and the insulating envelope 92 of the resistor 44 being assembled end to end.
• the assembly is sealed at passages 94 and 96 of the connections by insulating varnish so as to protect these components against the humidity of the air circulating in the nozzle.
• the two envelopes 90 and 92 are housed inside the metal tube 26 shown in FIG. 1.
• the connector 20 (FIG. 1) makes electrical contact with the tubes 12 and 26 to ensure the continuity of the conductive connection between the front and the rear of the nozzle.
• the cylindrical ring 50 which surrounds the metal insert 52 and the front of the tube 12 makes it possible to maintain the insert at the potential of the mass of the nozzle, that is to say at the potential of the earth, although the nozzle is screwed on the insulating sleeve.
• the body of the nozzle is connected by the removable assembly 18 to the connector 20 by which the compressed air is introduced.
• the metal tube 26 is a cylindrical tube of sufficient diameter to contain the resistor and the capacitor and their respective envelopes.
• the tube 26 is in electrical contact with the T-connector 20.
• the metal tube 26 which protects the rear of the nozzle is in contact with the fixing device 28 which is used for anchoring the coaxial cable 30.
• This metal device is itself in contact with a metal shield (not shown) of the cable that is connected to earth.
• the coaxial cable 30 is terminated, on the side of the high voltage electrical supply circuit 32, by a high voltage plug 100 capable of fitting to a high voltage base 102 (FIG. 10).
• the cable is surrounded by a waterproof plastic conduit 104, here a corrugated conduit, fixed to the nozzle by means of a cable gland 106 to seal the assembly (FIG. 1).
• the cable 30 passes through the central opening 107 of a metallic piece of revolution 108 (called a "plug"), for example made of stainless steel, which has a flat side 110 located opposite a wall 112 of a high voltage device 114, for example a high voltage cabinet (FIG. 10).
• the flat side 110 comprises a milled housing 116 in the form of a circular groove suitable for the installation of an O-ring 118 around the central opening.
• This piece of revolution 108 has a larger outside diameter than that of the high-voltage plug 100, while the central opening 107 has a diameter smaller than that of the plug.
• the tightness of the conduit 104 disposed around the coaxial cable 30 is completed by the installation of a second cable gland 120 placed at the entrance to the part of revolution 108.
• the part of revolution 108 has a cylindrical threaded extension 122 of the side facing the feeder 114, this extension penetrating through an opening 124 of diameter greater than that of the high-voltage plug 100 in the wall 112 of the cabinet 114 which encloses the electrical supply.
• the seal 118 is applied in leaktight manner to the external wall of this cabinet by screwing a threaded ring 126 on this threaded extension.
• the electrical supply circuit of the nozzle (s) includes high voltage transformers 128 whose primary is connected to the output of a synchronous static relay 130 supplied by a voltage source alternative for example by the sector.
• the application of the primary voltage to the static relay 130 is controlled by a time relay 132, the coil of which is supplied from a pressure switch 134 connected to the compressed gas distribution network supplied to the nozzle (s).
• each nozzle is supplied with compressed air from the source 24 and through a supply valve 136 which controls a conduit 138 connected to the tube 22 of the T-connector 20.
• the needle of the or the nozzles is supplied with high voltage of between 6000 and 9000 volts by a box containing the transformers 128 which raise the voltage from the network voltage.
• Each nozzle is connected to a transformer fully enclosed in an appropriate insulator. The voltage is brought to the nozzle via the coaxial cable 30 which ends with the plug 100 adaptable on the base 102.
• the output connections of the transformers are connected one to earth, the other to the base assigned to the corresponding nozzle.
• the nozzles are protected against overcurrents by fuses inserted in the circuit connected to the primary of the transformers 128.
• the synchronous static relay 130 plays a predominant role. Indeed, the coaxial cable connected to the nozzle behaves like a delay line for fast signals, so that these signals undergo a reflection at the end of the line. The impedance corresponding to a corona tip being very high (open line), this reflection is carried out without change of sign.
• a step of 10,500 volts is applied to the level of the base / plug assembly, a reflected signal of 10,500 volts is superimposed almost instantaneously on this step, the set plug / receptacle being then subjected to a voltage of 21,000 volts, which causes a bypass arc and a short circuit to ground.
• the synchronous static relay 130 makes it possible to close the primary circuit which supplies the transformer only when the mains voltage crosses zero. This avoids the random closing produced by a mechanical switch, closing which can occur at any moment of the cycle and which produces a step of input voltage in the coaxial line, step which can possibly correspond to the secondary to the voltage peak (i.e. 10,500 volts for a secondary supplying 7,000 volts in effective value).
• the presence of this static relay is essential to ensure the safety and reliability of the operation of the installation.
• the time relay 132 plays an essential role. Because the nozzle is located in an explosion risk zone, it must in no way present risks of initiation of electric shocks at the nozzle. However, this is defined to work without priming under normal pressure conditions which correspond to the nominal flow regime. Consequently, if these conditions are not established, the relay 132 is closed, which applies the mains voltage to the primary of the transformers.
• the pressure switch 134 records the nominal pressure before this pressure is obtained at the nozzles, the relay 132 is timed, which makes it possible to apply the voltage to the nozzles only after obtaining the nominal flow rate of the compressed air.
• the choice of the corresponding delay is evaluated according to the structure of the pneumatic circuit associated with the eliminator, but it is not very constraining to choose a delay much greater than the few seconds which correspond to the time of establishment of the permanent regime of the flow d compressed air in the pneumatic circuit associated with the eliminator.
• the assembly shown in FIG. 10 makes it possible to connect the coaxial cable 30 (plug 100 and base 102) inside the cabinet 114, which is protected against dust and water jets.
• This cabinet is advantageously made of composite material or stainless steel.
• the arrangement of the part of revolution 108 with the seal 118 and the ring 126 allows easy removal of the nozzle.
• the part 108 closes the opening 124, the seal 118 being strongly supported on the outside wall of the cabinet by screwing the ring 126 on the threaded cylinder 122 which penetrates inside the wardrobe.
• the assembly is therefore sealed by the seal 118, and by the two cable glands 106 and 120.
• To disassemble the nozzle it suffices to separate the plug 100 from the base 102 and unscrew the ring 126, which frees the part 108 and leaves a large passage to the plug 100 connected to the end of the coaxial cable.
• the or each nozzle is supplied with compressed air of pressure between 12 and 5 bars, at a dew point between -19 ° C and -40 ° C.
• the compressed air used must, once it is relaxed, contain neither too much nor too little moisture. Too humid air leads to the condensation of a film of water on the insulating parts which support the needle holder and causes a short circuit to the corona peak earth. Too dry air does not achieve the expected performance of the process, since the transport of electrical charges by the supersonic jet requires a sufficient number of carriers formed by the condensation of ice on the ions by the corona discharge, and this number decreases very quickly below a certain humidity.
• the optimal conditions of current transported through the nozzle by the aerosols correspond to a dew point of -19 "C. These conditions are obtained for example in a refrigeration dryer fed by compressed compressed air at a pressure of 6 bars, the coil of which is traversed by water at a temperature of 3 ° C. For a dew point of -40 ° C., the intensity of the current transported is halved.
• the eliminator comprises at least one group of two nozzles 10A and 10B supplied from two transformers 128A and 128B. These two transformers have respective primaries 140A and 140B supplied in phase opposition.
• the simplest method consists in using an even number of paired nozzles so as to have emission characteristics (currents depending on the high voltage applied) as similar as possible. This is achieved by connecting, for each group of nozzles, a first nozzle to a phase of the AC high voltage supply and the second nozzle to the opposite phase.
• each group of nozzles being formed of nozzles having voltage-current characteristics as similar as possible, each of the two nozzles being connected to an opposite polarity of an alternating supply.
• the invention finds a very particular application in the treatment of polymers.

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• Elimination Of Static Electricity (AREA)
• Electrostatic Spraying Apparatus (AREA)

Applications Claiming Priority (2)

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• 2004
  • 2004-05-07 FR FR0404941A patent/FR2870082B1/fr not_active Expired - Fee Related
• 2005
  • 2005-04-26 JP JP2007512249A patent/JP2007536719A/ja active Pending
  • 2005-04-26 RU RU2006121132/28A patent/RU2325791C2/ru active
  • 2005-04-26 EP EP05762436A patent/EP1743509A1/fr not_active Withdrawn
  • 2005-04-26 US US10/577,927 patent/US20080278879A1/en not_active Abandoned
  • 2005-04-26 CN CNA200580001567XA patent/CN1906980A/zh active Pending
  • 2005-04-26 WO PCT/FR2005/001027 patent/WO2005122653A1/fr not_active Application Discontinuation

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