EP0338927B1 - Process and apparatus for the destruction of chemical stable waste - Google Patents

Abstract

- The torch (1) is of the nontransferred arc plasma type; - the nozzle (3) of the said torch (1) is pointed towards an orifice (8) so that the axis (4) of the said nozzle and the axis (6) of the said orifice are at least approximately coinciding; and - a flow (20) of the said waste is passed through the said orifice (8) so that it moves forward towards the said torch (1). <IMAGE>

Description

The present invention relates to a method and a device for the destruction of chemically stable waste, and in particular radioactive waste and / or presenting significant dangers for the environment and living beings.

Are already known, for example from US-A-3841239, EP-A-105866 and EP-A-112325, devices for destroying waste by pyrolysis using at least one plasma torch. In these known devices, the waste is brought, generally from top to bottom by the action of gravity, towards a zone heated by said torches, arranged laterally with respect to the path followed by the waste.

Such devices do not allow an optimal transfer of energy from the plasma to the waste, so that certain particularly stable waste, such as cyanide and organo-chlorinated organic waste, cannot be treated by known plasma devices. Thus, this particularly dangerous waste must be stored deep in the ground, for example in salt mines, or in warehouses, pending the discovery of a process allowing its elimination.

The present invention relates to a method and a device allowing the total destruction by pyrolysis of the most stable waste.

• ― ladite torche est du type à plasma d'arc non transféré;
• ― on dirige la buse de ladite torche vers un orifice, de façon que l'axe de ladite buse et l'axe dudit orifice soient au moins approximativement confondus; et
• ― on fait passer un flux desdits déchets à travers ledit orifice, de façon qu'ils s'avancent vers ladite torche.

To this end, according to the invention, the process for the destruction by pyrolysis of chemically stable waste by means of at least one plasma torch is remarkable in that:

• - Said torch is of the non-transferred arc plasma type;
• - Directing the nozzle of said torch towards an orifice, so that the axis of said nozzle and the axis of said orifice are at least approximately coincident; and
• - Passing a stream of said waste through said orifice, so that they advance towards said torch.

By "plasma torch of non-transferred arc" is meant here, which is the usual meaning, a plasma torch comprising two fixed electrodes, on which the feet of the arc are hung.

Thus, according to the invention, the plasma dart attacks at the end (and no longer transversely as in the prior art) the stream of waste passing through said orifice. As a result, the transfer of thermal energy is optimal and it is possible to obtain the destruction of very stable bodies, such as cyanide or organochlorine organic compounds.

Experience has shown that it was advantageous, with regard to heat transfer, for the diameter of said orifice to be slightly greater, on the order of 2 to 3 times, than the diameter of the nozzle of said torch.

Indeed, the entire section of the waste stream passing through said orifice is thus subjected to the action of the plasma dart. Also, by adjusting the energy of the plasma torch, the distance between said torch and said orifice and / or the speed of advance of said waste stream through said orifice, it is possible to adjust the amount of energy per unit of time received. by said waste through said orifice, that is to say the quality of the destruction of said waste.

In an advantageous embodiment of the invention, the axes at least approximately coincident of said nozzle and said orifice are at least approximately vertical and the flow of waste moves, at least in the vicinity of said orifice, from bottom to top . In this case, the dart of the plasma torch is therefore directed downwards.

When, in addition, said orifice is the end of a tubular waste injector, it can then be seen that the upper part of said injector can serve as a crucible for the end part of said waste stream, which is in the state liquid.

Preferably, said nozzle and said orifice are arranged in an expansion chamber, in which the gases from the liquid end of the stream of said waste are burned. Means may be provided for introducing oxygen and / or energy inside said expansion chamber, in order to facilitate the combustion of said gases.

In an alternative embodiment of the invention, the axes at least approximately coincident of said nozzle and said orifice are slightly inclined relative to the vertical, in the direction of said expansion chamber, so that part of the end liquid from said waste stream can spill into said expansion chamber. This liquid part is then treated and burned in said expansion chamber, possibly with an additional supply of oxygen and / or energy.

Whatever the state, liquid or gaseous, of the waste when it is introduced into the expansion chamber, only a gaseous phase remains at the downstream part of said expansion chamber. Optionally, to prevent liquid particles of waste being projected too far inside said expansion chamber by the plasma dart, which would harm the quality of the combustion of said liquid particles and their transformation into gas, it is possible to providing baffles inside said expansion chamber, just opposite said nozzle and said orifice. Such an expansion chamber can be a rotary kiln.

Thanks to the quality of the pyrolysis treatment carried out by the present invention, before being discharged into the atmosphere and / or used as a heat source, the gases resulting from combustion in the expansion chamber can undergo only one simple treatment. Preferably, they are simply washed in a washing tower, after having undergone a thermal quenching.

The waste to be destroyed by the implementation of the invention may, initially, be in gaseous or liquid form. However, they can also be in solid form.

To this end, in order to be able to feed said orifice with a waste stream, treatment is provided to transform said solid waste into a paste which can be extruded through said orifice. Such treatment may include shredding, grinding, and / or wetting operations. The dough can then be moved by pumping means.

Preferably, between said pumping means and said orifice, there is provided, for the flow of waste to be destroyed, a guide duct, in the form of a siphon. Thus, any gas rise in the direction of said pumping means is avoided.

• La figure 1 est un schéma synoptique d'un exemple de réalisation du dispositif conforme à la présente invention.
• La figure 2 illustre le processus de fonctionnement du dispositif de la figure 1.
• La figure 3 montre schématiquement une variante de réalisation du dispositif de la figure 1.
• La figure 4 illustre en coupe, plus en détail, une partie du dispositif de la figure 3.
• La figure 5 est une coupe partielle d'une autre variante de réalisation.

The figures of the appended drawing will make it clear how the invention can be implemented. In these figures, identical references designate similar elements.

• Figure 1 is a block diagram of an exemplary embodiment of the device according to the present invention.
• Figure 2 illustrates the operating process of the device in Figure 1.
• FIG. 3 schematically shows an alternative embodiment of the device of FIG. 1.
• FIG. 4 illustrates in section, in more detail, part of the device of FIG. 3.
• Figure 5 is a partial section of another alternative embodiment.

The device, according to the invention and shown in FIG. 1, comprises a plasma torch 1, capable of emitting a plasma dart 2 at the outlet of its nozzle 3. This torch is of the known type with non-transferred arc. In known manner and not shown, it can be composed of two coaxial tubular electrodes, cooled, which are joined by an injection chamber of the plasma gas and by a part ensuring the electrical insulation of the two electrodes. The arc foot can be rotated by a magnetic field coil for the upstream electrode, and by the action of the vortex in the downstream electrode. The nominal operating characteristic of the torch can be 500 kW electric and the adjustment of the power of the torch is preferably carried out continuously between 250 kW and 500 kW.

The plasma torch 1 is arranged so that its axis 4 is at least substantially vertical, the nozzle being directed downwards.

Opposite the nozzle 3, the device in FIG. 1 comprises a tubular injector 5, the axis 6 of which is at least substantially vertical and coincides with the axis 4 of the torch 1. The tubular injector 5 is supplied with waste to be destroyed by its lower end 7. This waste leaves said injector 5 through the upper orifice 8 thereof, arranged opposite the nozzle 3. Preferably, the diameter D of the tubular injector 5 is equal to a few times (2 or 3) the diameter d of the nozzle 3. In one embodiment, the diameter D of the injector 5 was equal to 100 mm.

At least the lower part of the nozzle 3 and the upper part of the tubular injector 5 are arranged in a valve system 9, giving access to a gas expansion chamber 10.

The embodiment of the device according to the invention, shown in FIG. 1, is more particularly intended for the destruction of solid waste. The waste to be destroyed is for example contained in drums and, in order to reduce the costs of processing said waste, the device of FIG. 1 makes it possible to destroy said drums at the same time as the waste they contain.

To this end, the device comprises a device 11 for prior treatment of said waste comprising a shredder-shredder 12 fed by a hopper 13, and which is optionally associated with a finisher shears (not shown), a mixer-feeder 14 provided with an inlet fluid 14, and a pump 16.

The outlet of the pump 16 is connected to the lower part 7 of the injector 5 by a guide duct 17 forming a siphon. Preferably, a safety member 18, for example a knife gate valve, is provided between the pump 16 and the guide duct 17.

The barrels 19 of waste to be destroyed are introduced into the hopper 13 and led to the shredder-shredder 12, the knives of which grip, shear, tear and compress said barrels and their container. The possible finishing shear makes it possible to reduce the final particle size of the comminuted materials to a dimension which is, for example, 10 × 20 mm maximum.

The whole process is carried out in a cascade by gravity, without manual intervention in a relatively slow manner to avoid any production of sparks which could ignite the product. In addition, all the equipment can be put under vacuum, to avoid any toxic gas emission.

The ground materials, thus reduced in size, flow by gravity to the mixer-feeder 14 whose role is to compact the materials (the pasty parts with the foreign bodies) by pushing them into the transfer pump 16.

The pump 16 is for example of the known type (PUSTMASTER) with hydraulic cylinders and allows a regular supply flow of the heterogeneous mixture and under high pressure (80 to 100 bars), thus ensuring excellent compaction.

It is possible to add to the gas mixer 14, via the inlet 15, either water or oily products which it is desirable to get rid of, this in order to improve the pumpability of the ground materials and their resistance to form.

Thus, at the outlet of the pump 16, the ground waste (with their containers) is in a pasty form. The pump 16 pushes this pasty material (through the safety member 18) in the guide duct 17, up to the injector 5. In the guide duct 17 and the injector 5, the pasty material therefore forms a flange 20 which advances towards the nozzle 3.

The siphon shape of the guide duct 17 prevents any liquid or gas rising towards the pump 16.

In the injector 5, the tube 20 progresses from bottom to top and its upper end part is subjected to the action of the plasma stinger 2, which attacks it at the end (see FIG. 2). Thus, the upper part of the flange 20, constantly renewed, is nibbled by the plasma dart 2 (the temperature of which is around 4000 to 5000 ° C) and goes into the molten liquid phase (see reference 21), which itself gives rise to a gaseous phase 22 in the opening system 9. An intermediate semi-molten pasty phase 23 is established between the upper zone 21 of the liquid phase and the pasty roll 20.

It will be noted that the liquid phase of zone 21 forms a sort of crucible constituting thermal and chemical protection of the injector 5.

The gas phase 22 appearing in the opening system 9 is evacuated towards the expansion chamber 10, in which it finishes destroying itself completely under the effect of the temperature which prevails there (for example of the order of 1800 ° C). Self-combustion occurs, which can be promoted by the introduction of air or oxygen (at 24). The expansion chamber 10 can be designed for the substoichiometric combustion of chlorinated liquid effluents and it can be provided with an internal coating of the "CHROMCOR" type.

Thanks to the coaxial arrangement of the nozzle 3 and the injector 5, the free upper end of the flange 20 is in intimate and prolonged contact with the dart 2 and undergoes in the vicinity of the upper orifice 8 of said injector, a very sharp rise in temperature; the molecules of the material of the pasty sausage are then completely dissociated into more or less ionized elementary particles.

The combustion gases generated in the expansion chamber are treated by a system 25, which, because of the excellent performance of the device according to the invention, can be uncomplicated. Thus, the system 25 may include a quenching device 26 making it possible to lower the temperature of the gases and followed by a washing tower 27. thus neutralizes residual products, such as chlorine for example, and the gases can then be led to a chimney 28, for their evacuation to the atmosphere.

Optionally, these gases can be introduced into a boiler for energy recovery.

In the variant embodiment of the device according to the invention, illustrated in FIG. 3, there are the different elements 1 to 20 and 25 to 28, described above. However, in this case, the axes 4 and 6, of the torch 1 and of the injector 5 respectively, are inclined relative to the vertical, so that at least part 29 of the liquid phase 21 of the flange 20 (see FIG. 2) can flow into the expansion chamber 10. It is then advantageous for the latter to be produced in the form of an inclined rotary kiln 30 capable of mixing the non-gaseous elements coming from the injector 5 and which will eventually destroy themselves on their way to the lower downstream part of said rotary kiln 30, thanks to the high temperature prevailing in said rotary kiln 30. To facilitate this destruction, air can be introduced (at 31) under pressure in the latter. Burners can also be provided (not shown) in order to provide additional energy (symbolized by arrow 32), to said rotary kiln.

The downstream part 33 of the rotary kiln 30 then forms a post-combustion chamber for the gaseous products. In this post-combustion chamber, there are no more non-gaseous products.

In Figure 4, there is partially shown an industrial embodiment of the device of Figure 3. It can be seen there the rotary kiln 30, whose longitudinal axis XX is inclined downward from the opening system 9 towards the post-combustion chamber 33, in order to facilitate the progression (during which they will be completely gasified) of the molten materials 29, from upstream to downstream. This rotary kiln is supported by rollers 34 and rotated by a motor 35, by means of a rotary roller 36. The connection between the opening system 9 and the rotary kiln 30 is made by a piece of fixed adaptation 45.

FIG. 4 also shows that the injector 5, for example made of tantalum, has a double wall structure, inside which a cooling fluid can circulate. To this end, said injector 5 is connected to a circuit 37 for circulating coolant.

In known manner and not shown, the plasma torch 1 is associated with a cooling group, a group for producing plasma gas (for example air) and a power supply.

The bottom 38 of the opening system 9 can be tilted to promote the flow of the molten material 29 to the furnace 30.

From the above, it is easily understood that one can adjust the quality of the destruction of the waste contained in the tube 20, by adjusting the speed of advance thereof, the power of the torch 1 and / or the distance separating the dart 2 from the orifice 8 of the injector 5.

The speed of advance of the flange 20 is obviously controllable by controlling the pump 16. Likewise, the power of the torch 1 is electrically adjustable in a known manner.

As regards the variation of the distance between the sting 2 and the orifice 8, an appropriate device has been shown in FIG. 5. Torch 1 is slidably mounted on along its axis 4; in its sliding, it is guided by a column 39 with which a slider 40 cooperates. The slider 40 is movable by a motor system 41 and screws 42. A bellows 43 seals between the torch 1 and the opening system 9.

Furthermore, in the device of FIG. 5, baffles 44 are provided, forming baffles, arranged in the adaptation piece 45, to prevent the projection of particles torn from the rod 20 by the plasma, at too great a distance from inside said oven. The deflectors 44 thus allow the particles to be treated as close as possible to the plasma jet.

Claims (16)

1. Method for the destruction of chemically stable waste (19) by pyrolysis by means of at least one plasma torch (1), characterized in that:

― said torch (1) is of the non transferred arc plasma type;

― the nozzle (3) of said torch (1) is directed towards an orifice (8), so that the axis (4) of said nozzle and the axis (6) of said orifice merge at least approximately; and

― a flow (20) of said waste is caused to pass through said orifice (8), so that it advances towards said torch (1).

2. Method according to claim 1, characterized in that the diameter of said orifice (8) is equal to a few times the diameter of the nozzle (3) of said torch.

3. Method according to one of claims 1 or 2, characterized in that at least the distance between said torch (1) and said orifice (8) is adjustable.

4. Method according to one of claims 1 to 3, characterized in that the at least approximately merged axes of said nozzle (1) and of said orifice (8) are at least approximately vertical and in that the flow (20) of waste moves from bottom to top, at least in the vicinity of said orifice (8).

5. Method according to one of claims 1 to 4, characterized in that the gaseous and/or liquid products resulting from the action of said torch (1) on said flow (20) of waste are subjected to expansion and combustion.

6. Method according to claim 5, characterized in that said gaseous products resulting from said expansion and said combustion are dipped, then washed.

7. Method according to one of claims 1 to 6, applied to solid waste, characterized in that said solid waste is transformed into a paste extrudable through said orifice (8).

8. Device for the destruction by pyrolysis of chemically stable waste (19) using at least one plasma torch (1), characterized:

― in that said torch (1) is of the non transferred arc plasma type;

― in that it comprises an injector (5) for a flow (20) of said waste; and

― in that the axis (4) of the nozzle (3) of the torch (1) is at least approximately merged with the axis (6) of the outlet orifice (8) of said injector (5).

9. Device according to claim 8, characterized in that the outlet orifice (8) of said injector (5) is directed upwards.

10. Device according to one of claims 8 or 9, characterized in that said nozzle (3) and said orifice (8) are disposed in an expansion and combustion chamber (10, 30).

11. Device according to claim 10, characterized in that means are provided for introducing oxygen and/or energy inside said expansion chamber (10, 30).

12. Device according to claim 11, characterized in that the at least approximately merged axes of said nozzle and of said orifice are slightly slanted with respect to the vertical, in the direction of said expansion chamber (10, 30).

13. Device according to one of claims 11 or 12, characterized in that baffles (44) are provided inside said expansion chamber (10, 30), just opposite said nozzle and said orifice.

14. Device according to one of claims 11 to 13, characterized in that said expansion chamber is a rotary oven (30).

15. Device according to one of claims 8 to 14, characterized in that it comprises means (11) for transforming solid waste into a paste extrudable through said orifice (8).

16. Device according to one of claims 8 to 15, having means (16) for causing said waste to advance, characterized in that between said advancing means (16) and said injector (5), a duct (7) is disposed, in the form of a siphon, for guiding said waste.

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