FR2601441A1 - PLASMA ROTATING OVEN WITH MATERIAL SUPPLY TO BE TREATED WITH MECHANICAL DRIVE - Google Patents

Abstract

THE INVENTION RELATES TO A ROTARY PLASMA OVEN. THE OVEN INCLUDES AT LEAST ONE PLASMA TORCH LOCATED NEAR ONE END OF THE OVEN BODY 1 AND THE ROTATION AXLE D. THE OVEN IS EQUIPPED AT THE OTHER END OF THE OVEN BODY 1 WITH FEED MEANS 2 ALLOWING TO ESTABLISH A SUPPLY FLOW OF MATERIAL TO BE TREATED, SENSITIVELY COAXIAL WITH THE ROTATION SHAFT D WITH A VIEW TO OBTAINING A SUPPLY OF THE OVEN WITH MATERIAL BY SINGLE MECHANICAL DRIVE, ARRANGED ON A SECOND TORCH OR A PERMIT ELECTRODE TO ESTABLISH THE OVERLAPPED OR TRANSFERRED PLASMA ARC. APPLICATION TO ROTARY PLASMA OVENS FOR THE PROCESSING OF MATERIALS SUCH AS ALUMINA, MAGNESIA OR SIMILAR REFRACTORY MATERIALS.

Description

2'601441

  The present invention relates to a plasma rotary furnace with feed material

  treat by mechanical drive.

  Rotary plasma furnaces used for the treatment at high or very high temperature of pulverulent or granular materials, has been the subject of much work to date. Among the most recent, we can cite, in particular, in the publication J.F.E. No. 3, published in March-April 1979, the article by David Yerouchalmi entitled "High temperature rotary kiln heated axially by arcs plasma for melting and product development.

ultra-refractory and metals ".

  The profitable operation of the rotary plasma furnaces currently used, furnaces as described in the aforementioned article, passes through a continuous supply of material to be treated. For this purpose, as is moreover schematically represented in FIG. 1, the furnace itself or furnace body is inclined with respect to its initial horizontal position, the furnace body being rotated by a motor system G, and the product to be treated is introduced from a loading hopper Q disposed at the upper end of the furnace body, the casting of the high temperature treated material being carried out at the other end. An axial superimposed plasma is generated between the plasma electrodes A, B, the torch B being substantially axially disposed with respect to the axis of rotation and the torch A being shifted relative to this axis or translated thereto. ci, so as to allow the casting of the treated material. The power supplies D and F of the torches A and B make it possible to create two plasma jets which, by joining in the axis of the furnace, form a

  column of ionized gas conducting electricity.

  The power supply E is used to superimpose an electric arc on this gas column. Since the temperature of the plasma arc reaches the greatest potential and can even exceed 10,000 K, the plasma flows exhibit a high viscosity at such temperatures, the degree of viscosity thereof being an increasing function of temperature. Because of this high viscosity of the plasma arc, the penetration by simple gravity of the powder is almost impossible in the arc itself and the introduction of the material to be treated in the furnace or furnace body presents significant difficulties, the introduction of the material into the furnace body is in fact carried out so that the material reaches the lower part of the refractory chamber of the furnace body. In order to obtain such methods for introducing the material to be treated into the oven, it is necessary to provide a carrier gas flow of the powdery or granular material to be treated, the material thus penetrating into the furnace body via An injection nozzle S under the effect of gravity and the carrier gas stream. Although some difficulties may arise in the case where a lip of molten material is formed on the flow edge of the nozzle introduction, preventing the introduction of the material, in the pulverulent state or

  granular, the previously described system is satisfactory for low material flow rates.

  In order to achieve much higher flow rates, using the device as described above, it would be necessary to increase the dimensions of the introduction nozzle and / or greatly increase the flow and pressure of the current of

  carrier gas of the material to be treated.

  The increase in the values of the above-mentioned parameters can not be validly envisaged because of a corresponding decrease in the energy efficiency of the furnace, following a modification of the plasma formation conditions in particular. A significant increase in the flow rate of the carrier gas, the flow rates of plasma gas being very low, appears in particular excluded, an inadvertent extinguishing or blowing of the plasma may even be caused by a too large carrier gas flow. In any case, a significant flow of carrier gas

  effect a parasitic consumption of heat by it, which is detrimental to obtaining a good performance of the oven.

  The object of the present invention is to remedy the aforementioned drawbacks by using a rotary plasma furnace in which the introduction of the

  material to be treated in the furnace is ensured, in the absence of any carrier gas flow, by only mechanical drive.

  Another object of the present invention is the implementation of a rotary plasma furnace for treatment at high or very high temperature

  industrial scale or granular materials, with material flow rates of the order of 0.5 to 1 cubic meter per hour.

  Another object of the present invention is the implementation of a plasma rotary kiln of simplified design, a plasma torch being suppressed, the operating parameters of the furnace 5 can be adapted to ensure conditions of

appropriate operation.

  The rotary plasma furnace having a furnace body rotatable about an axis and at least one plasma torch disposed adjacent one of the two ends of the furnace body and the axis of rotation thereof is remarkable in that the oven is provided

  material feed means to be treated to establish a feed stream substantially coaxial with the axis of rotation to obtain a supply of the furnace material by the single mechanical drive.

  The invention finds application to the treatment of pulverulent, granular or pasty materials such

  in particular, alumina, magnesia, refractory materials.

  Other characteristics and advantages of the rotary plasma furnace which are the subject of the invention will become apparent on reading the description and on the observation of the following drawings in which, in addition to the FIG. 25 1 relating to the prior art,

  FIG. 2 shows in section a general view of an oven object of the present invention, FIG. 3 represents, in section, an alternative embodiment of the oven object of the present invention, FIG. 4 represents, in section in a plane of longitudinal symmetry, a detail of embodiment of the furnace object of the invention corresponding to the

Z601441

  FIG. 5a shows, also in section, a detail of the device shown in FIG. 2 and FIGS. 5b and 5c respectively represent an enlarged view of the Achimed screw of the device of FIG. Figure 5a and a sectional view

  according to a sectional plane AA of Figure 5b.

  The rotary plasma furnace, object of the invention, will first be described in connection with the

  Figure 2. In all the figures, the same references designate the same elements.

  As previously described, the rotary plasma furnace, object of the invention, comprises a furnace body 15, noted 1, rotatable about an axis, the furnace body 1 being as described above set in motion around of the axis by means of drive means denoted G. It furthermore comprises

  at least one plasma torch denoted A, B in FIG. 2, a plasma torch disposed in the vicinity of one end of the furnace body 1 and of the axis of rotation a.

  In accordance with the invention, the plasma furnace is provided at one end of the furnace body 1 with means 2 noted for supplying material to be treated, so as to establish a supply flow of the furnace of material to be treated. , substantially coaxial with the axis of rotation ,. These means make it possible to supply the furnace with material to be treated coaxially with the axis of rotationA, the supply of material taking place by the only mechanical stretching of the latter, in the absence of any

  carrier gas stream of the material.

  As it also appears in FIG. 2, the supply means 2 and the plasma torch denoted B are arranged at the same end of the furnace body 1. The supply means 2 and the plasma torch denoted B are as shown in FIG. 2, concentric and admit the same axis of

revolution, the axis of rotation.

  As it also appears in Figure 2, and will be described in more detail later

  in the present description, the feeding means 2 may advantageously be constituted by

  a hollow Archimedean screw, the plasma torch B being disposed in the hollow part of the screw. The feed means 2 are of course connected to a hopper

  loading device denoted Q, as previously described in the description. So, the concentric character

  of the plasma torch denoted by B and feed means 2 previously described makes it possible to ensure a supply of material to be treated continuously, under suitable conditions of operation and efficiency of the furnace, the carrier gas stream of the material being totally suppressed and losses of heat energy due to the presence of the gas current

  bearer in the prior art are also deleted.

  According to an advantageous variant of the rotational furnace 25 with plasma object of the invention shown in FIG. 2, the supply means 2 and the plasma torch denoted A can be arranged at the opposite ends of the furnace body 1. The supply means 2 and the plasma torch A then admit for the same axis of revolution the axis of rotation of the furnace body. In this case, as it appears in particular in FIG. 3, the supply means 2 of material to be treated are also constituted by an Archimedean screw admitting, for axis of revolution, the axis of rotation A of the furnace body. Of course, the Archimedean screw constituting the supply means 2 as shown in FIG. 4 is also connected to a loading hopper denoted Q. The embodiment of FIG. 3 appears particularly advantageous insofar as it authorizes the implementation of a plasma rotary kiln design significantly simplified in o o according to an object of the invention, one of the plasma torches, the torch B, can then be suppressed. For this purpose, the end of the feed means 2 made of material is advantageously provided with an anode-forming wear part 20, this wear part being more particularly intended to act as a counter-electrode for the plasma torch A disposed in the vicinity of the opposite end of the furnace body 1. The wear part 20 may advantageously be made of a very thin material.

  good conductor of electricity, such as a beryllium bronze or copper or copper alloys for example.

  As can be seen in particular in FIGS. 3 and 4, the feed means 2 of material may advantageously be adjustable in position with respect to the corresponding end of the furnace body 1, the adjustment in position consisting of a translational adjustment T along the axis of rotation of the furnace body. The translation adjustment means symbolically represented by T in FIGS. 3 and 4 may advantageously be constituted by support slides allowing translation of the assembly constituted by the feed means 2 and the hopper Q in the direction to be the axis of rotation of the furnace body 1. The translation adjustment means have not been shown in Figures 3 and 4 so as not to impair the clarity of the disclosure of the subject of the invention. Advantageously, the aforementioned translation adjustment makes it possible to obtain, according to the parameters of use of the furnace, object of the invention, and in particular of the nature of the body or material to be treated, the temperature to be attained for the treatment. of it in the enclosure 10 of the furnace body an optimum setting of the plasma jet length generated between the torch A and the wear part forming anode. noted 20 in Figure 4. The

  The operating parameters of the furnace are then adapted or optimized accordingly.

  As is also apparent in FIG. 4, the Archimedean screw can advantageously be provided with a double-walled envelope, denoted 201, 202, in order to allow the circulation between the aforementioned walls of a cooling fluid. The cooling fluid can advantageously be constituted by deionized water. The Archimedean screw, as shown in FIG. 4, may advantageously comprise, in the double-walled envelope 201, 202 mentioned above, a propeller 210, mounted on a propeller body 211, the assembly being mounted in a part centering 212, in a self-lubricating material. The propeller 210 thus defines a helicoidal chamber 200, in which the material to be treated is transported by mechanical drive, by setting the Archimedean screw in motion. The double-body envelope 201, 202 comprises, at the end of the screw located in the furnace body 1, an opening 204 placing in communication the helicoidal chamber 200 of the screw and the inside of the furnace body 1 in the vicinity of the axis. The opening 204 then allows the introduction of the material into the furnace body, substantially by gravity, independently substantially of the viscosity

of the plasma jet.

  As will be further noted in FIG. 4, the wear part 20 forming anode may advantageously comprise a housing denoted 2000, substantially annular, intended to receive a permanent magnet in the form of a torus, the permanent magnet in operation. of the furnace being intended to cause, by electromagnetic interaction, a precession movement of the plasma jet around the axis to, so as to obtain a wear-averaging effect, on the contact surface of the

the wear part 20.

  It will be understood that in the embodiment described in FIGS. 3 and 4, the rotary plasma furnace which is the subject of the invention allows the introduction of pulverulent or granular material into the rotary furnace, via the means feed 2 support of the anode cooled in the total absence of carrier gas of the material to be treated. This introduction of course is carried out continuously, with the advantages of optimum operating conditions of the furnace as previously described. In addition, as will be seen in FIG. 4, the propeller body 211 may advantageously be provided with an axial orifice denoted 2110, this axial orifice 2110 emerging at the level of the wear part, on an outlet orifice noted in 2010 and in which, in operation, a jet of gas is generated by the intermediary of an auxiliary source not shown in the drawing, in order to establish, after appropriate supply of the entire device electrical energy by means of generators D, E, F previously described, a superpolarized plasma arc between the wear part for 10 mantle anode 20 and the torch disposed facing A. A gas jet thus created opening from the orifice 2010, then makes it possible to establish the desired electric arc between the wear part forming anode 20 and the torch A described above. The plasma arc thus formed can then be stretched by translational displacement of the supply means 2 shown in FIG. 4 so as to define a desired plasma arc length in function

the application in question.

  The rotary plasma furnace previously described makes it possible in particular to mechanically introduce the material to be treated into the furnace, in the absence of any carrier gas with a great improvement in the thermal efficiency of the furnace. The amount of gas required to protect the electrode and support the plasma arc in the furnace is in any case small and corresponds to the normal operating conditions and establishment of the plasma arc in

the oven.

1 1

  Another embodiment of the rotary plasma furnace object of the invention as shown in particular in Figure 2, will be described in more detail

  in conjunction with Figures 5a, 5b, 5c.

  It will of course be understood in accordance with the embodiment of FIG. 5a that the propeller body 211 itself is hollow, the central space of the propeller body 211 accommodating the plasma torch noted B as it is represented in this figure. The Archimedean screw formed by the propeller 210 and the propeller body 211 are inside a double-walled cylindrical envelope noted.

  201, 202 and turn around the torch noted B by driving the material to be treated from the hopper 15 noted Q to the exit end noted 204.

  The supply of material to be treated is then substantially axial, the axes of the furnace or furnace body 1, the screw formed by the screw body 211 and the propeller 210 and the torch B being then merged and

  corresponding to the axis & rotation of the furnace body 1.

  The end of the assembly formed by the plasma torch B, the propeller body 211 and the double-walled envelope 201, 202, fits into the flange of the furnace body 1 in rotation and is susceptible to be subjected to the radiation of the molten material and to the temperature which prevails near the plasma which is

  It will be recalled for the record that the temperature of the plasma arc in the vicinity of the axis of rotation a can commonly reach and even exceed temperatures above 10,000 K.

  sequence, it is necessary to cool all of the aforementioned parts and -the double-walled casing 201, 202 is traversed by a coolant flow rate, such as deionized water and the Archi5 screw itself , constituted by the screw body 211 and the propeller 210 is also traversed by a coolant flow of the same kind. The deionized water constituting the refrigerant for example, enters through the helix which is itself hollowed out and exerted by the screw body 211, the screw body 211 being itself constituted by a double-walled body. In view of the fact that the propeller body 211 and the propeller itself 210 are moving parts with respect to the axis A, the circulation of water or cooling fluid in the propeller and in the propeller body 211, can advantageously be made from two rotating joints noted respectively 2101 and 2110. The rotary joint 2101 allows the supply of the propeller 210, proper cooling fluid, then that the rotary joint 2110 allows on the contrary the evacuation of the cooling fluid from the propeller body 211. The two rotary joints 2101 and 2110 mentioned above are advantageously arranged upstream of the loading hopper Q, which is of course integral with the double wall outer shell 201, 202, and in direct communication with the helical chamber 200. The arrangement of the aforementioned rotary joints will not be described in detail in FIG.

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  the measure o the supply by rotating joint in a fluid, such as a cooling fluid, of rotating systemsconcentriquesis within the scope of skill in the art and is not within the scope of the present invention. Figures 5b and 5c allow better

  understand the detail of the relative arrangement of the propeller body 211 and the propeller 210 with respect to the circulation of cooling fluid.

  In FIG. 5b in particular, it will be noted that the propeller 210 in fact forms a circulation channel for the cooling fluid, the aforementioned circulation channel being in communication at its end with the double-walled propeller body 211. , the double wall thus constituting a return pipe of the cooling fluid to the exhaust rotary joint 2110 supra. In FIG. 5b in particular, the arrows indicate the direction of circulation of the cooling fluid. In addition, a substantially annular partition 2112 may be provided at the end of the double-walled screw body 211,

  end located in the vicinity of the aforementioned torch B.

  By substantially annular partition is meant a ring-shaped partition having an opening for the passage of cooling fluid, the latter being further guided at the communication orifice with the double-walled propeller 211, by an extension of the ring directed along a generating line of the double wall envelope. The substantially annular partition may optionally adopt other forms, that represented by the

  FIGS. 5b and 5c being given by way of example only.

  This partition 2112 has the effect of allowing the cir-

  culation of the cooling fluid along a substantially peripheral path materialized by the arrows shown in FIG. 5c, in the vicinity

  of the aforementioned end of the propeller body 211.

  The helix 210 constituting the Archimedean screw may be formed or made of a stainless steel for example, and the double-walled envelope 201, 202 may advantageously be made of a softer material, so that the latter undergoes preferentially abrasion wear brought by

the operation.

  Of course, both in the case of the embodiment of FIG. 2 and in that of FIG. 3, the rotary plasma furnace which is the subject of the invention also comprises a device for guiding and supporting the screw, as well as its drive system which can conventionally be constituted by an input ring on which meshes a pinion or a belt driven by an electric motor. The guiding device having been described in the case of the embodiment of FIG. 3, this guiding device thus making it possible, as previously described, to adjust the position in translation of the supply means 2 along the axis of rotation a as previously described, the drive system consisting of conventional elements of the

  technique will not be described in detail.

  A rotary plasma furnace has thus been described which makes it possible both to obtain an improvement in the thermal efficiency of the furnace and a very considerable increase in the treatment flow rates of the material to be treated. The furnaces of the prior art allowing at most treatment rates of the order of 150 l / h, it was thus possible to obtain a flow rate increase of the order of a factor of three by the implementation of rotary kilns to plasma according to the present invention. The aforementioned furnaces, in particular because of their greater processing capacity, can be used without disadvantage.

  on an industrial scale for the treatment of the most diverse projects.

Claims (12)

  1. A rotary plasma furnace comprising a furnace body (1) rotatable about an axis (A) and at least one plasma torch (A, B) disposed in the vicinity of one end of the furnace body ( 1) and the axis of rotation (A), characterized in that said furnace is provided at one end of the furnace body (1) with means (2) for supplying a material feed flow to be treated substantially coaxial with the axis of rotation (), in order to obtain a supply of the material furnace by the single mechanical drive. 2. Oven according to claim 1, characterized in that said supply means (2) and the plasma torch (B) are arranged at the same end of the furnace body (1), the supply means (2) ) and the plasma torch (B) being concentric and   admitting the same axis of revolution, the axis of rotation (A).   3. Oven according to claim 2, characterized in that said feeding means (2) are constituted by a hollow Archimedean screw, said plasma torch (B) being disposed in the hollow portion. of the screw.   4. Oven according to claim 1, characterized in that the supply means (2) and the plasma torch (A) are arranged at the opposite ends of the furnace body (1), said supply means (2) and the plasma torch (A) admitting for the same axis of   revolution the axis of rotation (a) of the furnace body.   5. Oven according to claim 4, characterized in that the supply means (2) of material to be treated are constituted by an Archimedean screw admitting for axis of revolution the axis of rotation () of the furnace body. 6. Oven according to claim 5, characterized in that the end of the feed means (2) of material is provided with a wear part (20) forming anode, said wear part (20) forming anode 10 being intended to act as a counter-electrode for the plasma torch (A) disposed in the vicinity of   the opposite end of the furnace body.   7. Oven according to one of claims 4 to   6, characterized in that said supply means (2) of material are adjustable in position, relative to the corresponding end of the furnace body (1), in translation (T) along the axis of rotation (a. ) from the body oven.   8. Oven according to one of claims 3 to 7, characterized in that the Archimedes screw is provided   a double-walled envelope (201,202) to allow the circulation, between the walls, of a fluid cooling.   9. Oven according to claim 8, characterized in that said casing comprises at the screw end located in the furnace body an opening (204) placing in communication the helical chamber (200) of the screw and the inside of the body of the body. oven in the vicinity of the axis of rotation (,), said opening (204) per30 putting the introduction of the material into the body of oven by gravity. 6 0 1 4 4 1   10. Oven according to claim 9, characterized in that the helical chamber (200) of the Archimedes screw is fed with material from a hopper (Q).   Oven according to one of claims 6 to   , characterized in that the helix (210) of the Archimedean screw is a hollow helix, the propeller body (211) being further constituted by a double-walled body to ensure the circulation of a fluid refri10 manager, said fluid entering through the hollow propeller (210)   and emerging through the double-walled body (211).   Oven according to one of claims 6 to   11, characterized in that the helix (210) of the screw   Archimedes is made of stainless steel, the veloppe being made of a softer material.