EP0750450B1 - Plasma torch having an essentially axisymmetrical general structure - Google Patents

Description

The present invention relates to plasma torches, in particular, but not exclusively, to non-transferred arc torches.

Generally, a plasma torch of this type comprises two coaxial tubular electrodes, in extension of one another and arranged each in a support surrounding it. Means are provided to produce striking an electric arc between the two electrodes, as well as means to inject a plasma gas, such as air, into a chamber between the electrodes. In each electrode support are also provided means electrode cooling.

In addition, advantageously, the plasma torch is provided with means for move the attachment foot of the electric arc on the upstream electrode, consist of an electromagnetic coil surrounding the support of said upstream electrode.

More precisely still, the invention applies more particularly to a plasma torch, the ignition of the electric arc of which is achieved by a short circuit temporary established between the electrodes through displacement momentary of the upstream electrode in contact with the downstream electrode, using a cylinder device, called choke cylinder.

To illustrate more precisely this type of plasma torch to which refers more particularly to the present invention, reference may be made to usefully in the embodiment of FIG. 4 of the document FR-A-2,654,294.

This embodiment relates to a compact plasma torch and of reduced size intended in particular to be mounted in furnaces vitrification of waste.

This torch generally comprises a tubular casing in which are housed said upstream and downstream electrodes, as well as the system plasma gas injection system, the electrode cooling system, the upstream electrode displacement cylinder device for starting purposes and the arc foot displacement field coil.

Said envelope is connected, at its proximal end, to a block of connections, ensuring fluid and electrical connections with the outside of the torch, which is fixed to the wall of an oven by a clamping system height of the junction between said tubular casing and the connector part rear, the tubular casing part, commonly called a naked torch, being engaged in the oven.

The design of this type of plasma torch is complex and does not allow not the easy realization of naked torches of different lengths likely to meet specific industrial needs.

In addition, the cooling of the electrodes is not optimal and the complexity of the cooling circuit leads to pressure drops important requiring the use of high operating pressures, for example example of the order of 12 bars.

In addition, this high pressure affects the pressure required to control of the displacement cylinder of the upstream electrode, at start-up, since during the retraction of the upstream electrode, following the said actuator must overcome the downstream thrust exerted by the fluid cooling on the upstream electrode. This is how commonly a pressure of the order of 160 bars is necessary for actuating said cylinder.

Finally, this type of torch does not offer good accessibility to parts torch wear (upstream and downstream electrodes) as well as adjustments, for example example of position and stroke of the choke cylinder. You have to practically completely disassemble the torch.

By document US 5 362 939, we know a plasma torch convertible comprising two coaxial tubular outer casings serving as leads respectively to a cooling fluid and to a plasma gas, however the internal structure is too complex to allow adaptation in simple length of the torch without having to upset said internal structure.

The present invention aims to overcome the various drawbacks mentioned above of this type of plasma torch and more generally of plasma torches non-transferred arc type or transferred arc type, regardless of system of starting used, by proposing a torch with a simplified general architecture, almost entirely axi-symmetrical and therefore facilitating both the realization of the torch and its maintenance.

• une partie tubulaire dite torche nue dans laquelle sont disposées une électrode unique dite amont ou une paire d'électrodes coaxiales dites amont et aval, les électrodes étant tubulaires et refroidies par un circuit de refroidissement approprié, une bobine dite de champ de déplacement du pied d'arc et des moyens pour injecter un gaz plasmagène en aval de l'électrode amont ou entre l'électrode amont et l'électrode aval, des moyens étant en outre prévus pour assurer le démarrage de la torche, et
• une structure dite externe, solidaire de la torche nue à son extrémité proximale et dans laquelle sont regroupées les liaisons fluidiques et électriques avec l'extérieur de la torche,

caractérisée en ce que ladite torche nue comporte une structure porteuse formée de trois enveloppes coaxiales se recouvrant au moins partiellement, solidaires de ladite structure externe, à savoir une enveloppe externe métallique, une enveloppe intermédiaire métallique définissant avec l'enveloppe externe le circuit de retour du fluide de refroidissement de la ou des électrodes et de la bobine, et une enveloppe interne définissant avec l'enveloppe intermédiaire le circuit d'admission du gaz plasmagène auxdits moyens d'injection et canalisant par sa face interne le flux entrant du fluide de refroidissement en direction de l'électrode amont, de la bobine de champ et éventuellement de l'électrode aval, en sorte que ladite structure porteuse à trois enveloppes puisse être dimensionnée à la longueur désirée tout en incorporant des organes internes de le torche en adaptant simplement la longueur des éléments de liaison desdits organes à ladite structure externe.To this end, the subject of the invention is a plasma torch with a generally axi-symmetrical general structure, of the type comprising:

• a tubular part called naked torch in which are disposed a single electrode called upstream or a pair of coaxial electrodes called upstream and downstream, the electrodes being tubular and cooled by an appropriate cooling circuit, a coil called field of displacement of the foot d arc and means for injecting a plasma gas downstream of the upstream electrode or between the upstream electrode and the downstream electrode, means being furthermore provided for ensuring the starting of the torch, and
• a so-called external structure, integral with the naked torch at its proximal end and in which are grouped the fluidic and electrical connections with the exterior of the torch,

characterized in that said naked torch comprises a support structure formed of three coaxial envelopes overlapping at least partially, integral with said external structure, namely a metallic external envelope, a metallic intermediate envelope defining with the external envelope the return circuit of the coolant for the electrode (s) and the coil, and an internal envelope defining with the intermediate envelope the circuit for admitting the plasma gas to said injection means and channeling by its internal face the incoming flow of the cooling fluid direction of the upstream electrode, of the field coil and possibly of the downstream electrode, so that said support structure with three envelopes can be dimensioned to the desired length while incorporating internal organs of the torch by simply adapting the length elements for connecting said members to said external structure.

Such an arrangement makes it possible to reduce the number of parts of the torch and above all to give it the length you want, in relation to that of successive envelopes, the naked torch receiving, whatever its length, standard internal components, i.e. the electrode (s), the coil field, the plasma gas injection system, the circuit separators cooling and starting means.

According to a particular application of the invention to a plasma torch at non-transferred arc provided with a starting device comprising a said cylinder choke acting on the upstream electrode to momentarily bring it closer to the downstream electrode, said choke cylinder is disposed outside the body of said external structure and comprises a rod which runs right through the cylinder, is connected to the upstream electrode by a connecting rod extending in the body of the external structure and inside said internal envelope and has a section allowing said incoming flow of cooling fluid to exert on said cylinder rod a back pressure tending to counterbalance the pressure of said fluid on the upstream electrode, while the outer end of the cylinder rod is provided with means for adjusting the stroke of this rod.

The structure according to the invention also makes it possible to simplify substantially the cooling circuit which presents pressure losses much lower than those of the known torch cooling circuit, thus allowing, with equal cooling capacity, to significantly reduce the pressure required for the fluid, for example from 12 to 6 bars, with the consequence advantageous indirect, in the case of torches with non-transferred arc and cylinder starting choke, a reduction in proportion to the pressure required to operate the choke cylinder.

• Figure 1 est une vue en perspective schématisée d'une torche à plasma conforme à l'invention ;
• Figure 2, fractionnée respectivement en 2a,2b et 2c à des fins de lisibilité, est une demi-vue en coupe axiale de la torche de la figure 1 ;
• Figure 3 est une demi-vue partielle en section sagittale de la partie de la torche à hauteur de la liaison électrique entre l'électrode amont et la tige de connexion, et
• Figure 4 est une demi-vue partielle en section sagittale de la partie de la torche à hauteur du système d'injection de gaz plasmagène.

Other characteristics and advantages will emerge from the description which follows of an embodiment of a plasma torch according to the invention, description given by way of example only and with reference to the appended drawings in which:

• Figure 1 is a schematic perspective view of a plasma torch according to the invention;
• Figure 2, respectively divided into 2a, 2b and 2c for readability, is a half view in axial section of the torch of Figure 1;
• FIG. 3 is a partial half-view in sagittal section of the part of the torch at the height of the electrical connection between the upstream electrode and the connection rod, and
• Figure 4 is a partial half-view in sagittal section of the part of the torch at the level of the plasma gas injection system.

FIG. 1 shows a plasma torch according to the invention, usable for example in a waste vitrification oven, consisting of two essential parts, namely a front part called naked torch 1 of shape general cylindrical and a rear part called connector 2 formed by a external structure ensuring the fluidic and electrical connections of the torch with outside and allowing the transport and handling of the torch.

The naked torch 1 has a distal end or nose 3, of diameter slightly reduced, however that structure 2, called external because it remains at outside the oven when the naked torch 1 is introduced into the latter by a suitable opening in the wall, consists of a tubular body 4 coaxial with the naked torch 1, provided at its ends with two flanges 5 in the form of rhombus and bearing at their ends of the lifting pins 6, at the in known manner, from the torch to a lifting beam (not shown).

The naked torch 1, according to a characteristic of the invention, comprises a supporting structure (Figure 2) formed by three overlapping coaxial envelopes partially, namely a metallic external envelope 7, an envelope metallic intermediate 8 and an inner casing 9 of insulating material electrically.

The casing 7 is cylindrical, extends over the entire length of the torch bare 1 and is connected at its proximal end to the tubular body 4 of the structure external 2 by an annular connecting piece 10.

The envelope 8 is also cylindrical, extends substantially over the length of the largest diameter casing 7, as well as inside the body 4 to which it is tightly fixed, by a threaded crown 11, approximately in the central area.

Between the two envelopes 7,8 is thus formed an annular space 12 communicating with an annular space 13 defined between the body 4 and the envelope 8.

The space 13 communicates by a passage, represented at 14 in FIG. 1 and symbolized by the same reference numeral in Figure 2, with a coolant return line (not shown), the occurrence of demineralized water, the hot part of the torch.

At its distal end, the intermediate envelope 8 serves to support a annular separator 15 of the cooling circuit of the downstream electrode 16 which is a conventional annular electrode whose distal end is fixed to the torch nose.

The distal end of the intermediate envelope 8 also serves, as as will be seen later, at the attachment of the plasma gas injection system 17 and from the distal end of the upstream electrode 18 which is an annular electrode also conventional coaxial, like the downstream electrode 16, to axis 19 of the torch.

The casing 9 is a cylindrical tube which extends substantially between the proximal end of the upstream electrode 18 and a location on the body 4 slightly behind the part 11 while being fixed to said body 4 by a crown threaded 20.

The tube 9 thus defines with the intermediate envelope 8 an annular space 21 communicating, structure side 2, with an annular space 22 internal to the body 4 and communicating, by a passage shown at 23 in FIG. 1 and only symbolized by the same reference numeral in Figure 2, with a pipeline (not shown) for supplying plasma plasma fluid, in this case the air.

The distal end of the internal envelope 9 is in tight contact with the end of an annular separator 24 of the cooling circuit of the upstream electrode 18.

A tubular electromagnetic coil called field 25, also conventional and intended, in known manner, to move the arch foot over the upstream electrode 18 externally envelops this electrode.

The distal end of the separator 24 is connected to the distal end of the intermediate casing 8 by means of an annular connecting piece 26 in electrically insulating material, support for gas injection system plasmagen 17.

This injection system (see also Figure 4) includes an open grid ring 27, of electrically insulating material, arranged in the interval between electrodes 16,18 and on the external face of which is formed a chamber homogenization 28, performed in part 26.

The chamber 28 communicates through holes 29 passing through the room 26 with the space 21. The holes 29, six in number (cf. FIG. 4 on which a section complete of part 26 is shown in perspective) are regularly distributed and their axes 30 do not intersect the axis of the part 26 in order to create a vortex effect when air enters through holes 29 in the chamber homogenization 28.

In addition, the part 26 is pierced with a series of holes 31 with axes parallel to the axis of the part 26, that is to say the axis 19 of the torch, in order to ensure continuity of the cooling circuit, successively of the upstream electrode 18 and of the field coil 25, then of the downstream electrode 16.

In FIG. 2, it can be seen that the holes 31 make an annular space 32 defined between the separator 24 and a separator tube 33 remotely enveloping the field coil 25 and an annular space 34 delimited between the separator 15 and the downstream electrode 16.

At the proximal end of the downstream electrode 16, opposite the electrode upstream 18, is fixed a stop pin 35 called ignition.

At its proximal end the upstream electrode 18 is fixed to the end a metal rod 36, for example of copper, itself fixed at the end a transmission axis 37 of electrically insulating material, of large section and the end of which is slidably mounted in a bore 38 of a flange 39 attached to the outer end of the body 4.

Said sliding end of axis 37 is integral with a rod 40 extending inside a hollow rod 41 of a choke cylinder 42 fixed to the flange 39, outside the body 4.

The hollow rod 41 passes completely through the jack 42 and is integral, at its outer end of the rod 40 via a pair 43 of nut and lock nut. At its other end, the rod 41 bears against a washer 44 secured to the rod 40, by means of a damping spring 45.

A screw stop 46, adjustable in position on the cylinder rod 41, allows, by modification of its distance from the end of the jack 42, adjust the stroke of the cylinder rod.

The rod 36 carries a metal sleeve 47 mounted sliding and integral of the field coil support 25 to the winding of which is connected said socket 47.

A socket 49 for electrical connection to the coil 25 is fixed to the end of an electrical connection rod 50, parallel to the axis 19, extending opposite the internal tubular envelope 9 and passing through the body 4 to be attached to the flange 39, the material of which is of course non-conductive electricity.

The rod 50 is connected to an electrical connection terminal 51 (plus pole), the minus pole being constituted by the connection terminal 52, connected to the body metallic 4.

The electrical circuit for supplying the electrodes therefore comprises the rod 50, part 49, field coil 25 which is mounted in series, part 47, the rod 36, the upstream electrode 18, the downstream electrode 16, the nose of the torch, the outer casing 7 and the body 4.

The internal envelope 9 is in contact by its internal face with a space 53 delimited by the body 4 and in the axis of which the rods 36 and 37 extend.

This space 53 communicates by a passage, represented at 54 in the figure 1 and only symbolized by the same reference numeral in FIG. 2, likely to be connected to a water supply pipe (not shown) torch cooling.

The cooling water circuit thus consists of space 53, which communicates through holes 48a in the part 47 with a space annular 48b formed between the tip 48c of the upstream electrode 18 and a annular deflector 48d forming a venturi, integral with the coil 25 and channeling water to the space between the upstream electrode 18 and the field coil 25. Then, the water passes into the space between the coil 25 and the tube 33, into the space 32 (via perforations 55 at the proximal end of the tube 33), in the passages 31, in space 34, then in space 12 and finally in space 13. This circuit thus licks the parts completely and as directly as possible electrically conductive 50,49,47, the upstream tip 48c, then the external face of the upstream electrode 18, the two sides of the field coil 25, the system injection 17, the external face of the downstream electrode 16 and finally the external face of the naked torch 1, over its entire length.

Such a circuit is relatively simple in comparison with those of traditional torches. It optimally cools the hot parts of the torch, as well as all of its outer casing 7, which allows the torch to face without damaging the temperatures prevailing in an oven of vitrification and which can largely exceed 1600 ° C, even reach 2000 ° C.

In addition, the pressure losses of the cooling circuit are reduced compared to those of conventional circuits, which lowers the operating pressure of the torch cooling water source. This is how that for a type of arc torch not transferred from the Applicant, the pressure cooling water was reduced from 12 to 6 bars.

It is important to note that the design in the form of envelopes concentric tubular 7,8 and 9 of the structure carrying the essential organs (electrodes, injector, field coil) of the torch and connecting them to the block connection 2, allows great freedom in determining the length of the naked torch 1.

To be convinced, it suffices to refer, in FIG. 2, to the zone of the torch at the height of the rod 36, to find that the length modifications of the naked torch will simply have an impact on the length of the envelopes 7,8,9 and rods 36,37,50.

Thus naked torches of different lengths can be equipped internally from the same organs (electrodes, injector, field coil, separators, electrical connection parts, etc.), fluid circulation (air and water) being provided in the same way through the spaces provided between the different envelopes 7,8,9.

According to another important characteristic of the invention, the mounting particular of the choke cylinder 42, completely outside the body 4, with the rod connection 37 with large section immersed in cooling water at the inlet torch, allows, on the one hand, an adjustment of the cylinder stroke and a easy maintenance and, on the other hand, to control the jack 42 with a fluid reduced pressure compared to usual starter cylinders.

Indeed, the upstream electrode of torches of this type being cooled on outside, the water pressure creates a strong push on the electrode downstream.

However, at start-up, the upstream electrode 18 is brought, by the jack 42, to the contact with the stop pin 35 at start-up.

The duration of this contact must be just sufficient to avoid harmful consequences of a direct short circuit with very high amperage. So he is necessary to send the choke cylinder the power suitable for retraction sudden upstream electrode, which power must overcome said thrust downstream caused by the cooling water.

By providing, in accordance with the invention, a very large section to the connecting rod 37, practically compensating for said downstream thrust, so that less effort is required from the actuator 42.

Thus, instead of a usual pressure of the order of 160 bars, the jack 42 can only be supplied at a pressure that is largely half that.

If the pressure necessary for the choke cylinder can even be sufficient lowered, for example up to 7 bars, one can consider using to operate the cylinder the cooling water of the torch.

Furthermore, the concentric structure of the envelopes 7,8,9, allows a easy access to the interior of the torch, starting by depositing the envelope external 7, for example to replace the electrodes or any other part or for any maintenance or repair operation.

In this regard, it should be noted that the end of the connecting rod electric 50 is simply plugged in, via the connecting piece 49, on connection and / or centering pins 56 integral with the coil 25 and separator 24.

It should also be noted that the distal end of the envelope 9 is not integral with the separator 24, which allows extraction from the torch of the envelope 9 alone, to access the fixing (11) of the intermediate envelope 8.

The mutual positioning of the envelopes 7,8,9 is ensured for example by simple guide pads 57.

The invention is obviously not limited to the embodiment shown and described above, but on the contrary covers all variants, in particular as regards the arrangement of the plasma gas injector system 17, the arrangement of the field coil 25, the control means of displacement of the upstream electrode at start-up, or the arrangement of the external structure 2.

Finally, the invention applies generally to all types of non-transferred arc plasma torches, whatever the starting system, as well as all types of plasma torches with transferred arc.

Claims (5)

1. Plasma torch with an overall structure which is substantially axisymmetric, of the type comprising:

   a tubular part referred to as the bare torch (1) in which there is disposed a single so-called upstream electrode or a pair of electrodes referred to as upstream (18) and downstream (16), the electrodes being tubular and cooled by a suitable cooling circuit, a so-called field coil (25) for moving the foot of the arc and means (17) for injecting a plasmagenic gas downstream of the upstream electrode or between the upstream electrode (18) and the downstream electrode (16), means (42) also being provided to start up the torch, and

   a so-called external structure (2), fixed to the bare torch (1) at its proximal end and in which there are grouped together the fluid and electrical connections with the exterior of the torch,

   characterised in that said bare torch (1) comprises a carrying structure formed by three coaxial casings overlapping at least partially, fixed to said external structure (2), namely a metallic external casing (7), a metallic intermediate casing (8) defining with the external casing (7) the return circuit for the cooling fluid for the electrode or electrodes (18, 16) and the coil (25), and an internal casing (9) defining with the intermediate casing (8) the circuit for admitting plasmagenic gas to said injection means (17) and, by means of its internal face, channelling the incoming flow of the cooling fluid in the direction of the upstream electrode (18), the field coil (25) and possibly the downstream electrode (16), so that said carrying structure with three casings can be sized to the desired length while incorporating the internal components (16, 17, 18, 25, 42) of the torch simply by adapting the length of the connecting elements (36, 37, 50) for said components to said external structure (2).
2. Torch according to Claim 1, of the non-transferred arc type, provided with a start-up device having a so-called starter ram (42) acting on the upstream electrode (18) in order to bring it momentarily closer to the downstream electrode (16), characterised in that said starter ram (42) is disposed exterior to the body (4) of said external structure and comprises a rod (41) which passes right through the ram, is connected to the upstream electrode (18) by a connecting rod (37) extending in the body (4) of the external structure and inside said internal casing (9) and provides a cross-section enabling said incoming flow of the cooling fluid to exert on said rod (41) of the ram a counterpressure tending to counterbalance the pressure of said fluid on the upstream electrode (18), while the external end of the rod (41) of the ram is provided with means (46) for adjusting the travel of this rod (41).
3. Torch according to Claim 1 or 2, characterised in that the field coil (25) surrounds the upstream electrode (18) externally, is cooled on its internal and external faces and is electrically connected on the one hand by a plug-in connection (49, 56) with an electrical connection rod (50) disposed inside said internal casing (9) and connected at its other end to an electrical terminal (51) of the external structure (2), and on the other hand to the upstream electrode (18) by a sliding-contact connection with the connecting rod (36, 37) between the starter ram (42) and said upstream electrode (18).
4. Torch according to one of Claims 1 to 3, characterised in that the spaces (12, 21, 53) delimited respectively between the external casing (7) and the intermediate casing (8), between the intermediate casing (8) and the internal casing (9) and inside the internal casing (9), communicate respectively with a first annular space (13), a second annular space (22) and a third space (53), all three provided in said external structure (2), said third and first spaces (53, 13) communicating respectively with an inlet (54) and an outlet (14) for the torch cooling fluid, whilst said second space (22) communicates with a source (23) of plasmagenic gas.
5. Torch according to one of Claims 2 to 4, characterised in that the plasmagenic gas injection means (17) is disposed inside the intermediate casing and consists of an annular piece (26) provided with passages (29) in the direction of a homogenisation chamber (28) arranged on the internal face of said piece (26) and passages (31) coaxial with the axis (19) of the torch, providing continuity of the cooling circuit for the external faces of the upstream (18) and downstream (16) electrodes and a perforated injection grille (27) opposite said homogenisation chamber (28), arranged in the gap between said electrodes (18, 16).

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