EP0277862A1 - Process and apparatus for the destruction of solid waste by pyrolysis - Google Patents

Abstract

- Method and device for the destruction of solid waste by pyrolysis, in which a column (10) of such waste is traversed at least partially, from bottom to top, by a hot gas stream blows at the base of said column. - According to the invention, said hot gas stream is generated by at least one plasma jet. - Destruction of unburnt materials and improvement of the flow of molten residues.

Description

The present invention relates to a method and a device for the destruction and treatment of solid waste, in particular waste of hospital and / or industrial origin.

It is known that solid waste, such as hospital waste for example, is generally destroyed in grate ovens, in which the combustion temperature is maintained at a high value by fossil fuel burners. The ashes and bottom ash are removed in solid form, because fossil fuels do not allow to reach temperatures high enough to fluidize them, and contain a lot of unburnt materials which present a danger to the environment and clog the pipes. evacuation. In addition, such combustion requires an excess of air.

It is also known that, to avoid such drawbacks, solid waste can also be destroyed by pyrolysis using a wind of hot air making it possible to obtain high temperatures and to ensure combustion in the absence of air. A pyrolysis oven is used for this purpose, which is generally in the form of a vertical cylinder (or several truncated cones). The waste is placed in the upper part and is heated and pyrolyzed, as it descends into the oven, by hot gases, originating from pyrolysis, which circulate against the current, that is to say climbing. The hot air wind is blown at the bottom of the oven. It provides part of the heat energy necessary for operation and the oxygen ensuring the combustion of part of the waste, thus producing additional heat energy. With such a pyrolysis oven, the ash and bottom ash are removed at high temperature in a pasty form, but the metals are not fully melted and the flow of this very viscous material is difficult and uncertain. In addition, known pyrolysis ovens do not allow satisfactory control of the temperature of the molten residues.

The object of the present invention is to remedy the drawbacks of known pyrolysis ovens. It makes it possible to solve the problem of unburnt materials contained in the residues originating from the destruction of solid waste and to improve the flow of these molten residues.

To this end, according to the invention, the process for the destruction of solid waste by pyrolysis, according to which a column of such waste is traversed at least partially, from bottom to top, by a hot gas stream blown at the base of said column , is remarkable in that said hot gas stream is generated by at least one plasma jet, and preferably by a plurality of plasma jets distributed at the periphery of said column of waste, in the vicinity of the base thereof. this.

Thus, the hot gas blown at the base of the pyrolysis oven and passing through the waste column is no longer air, but a gas produced by one or more plasma generators (torches), which makes it possible to control the temperature molten residue.

The plasma jet is preferably directed to the base of the waste column, where it enters the molten slag bath. It thus completes the fusion of the waste which has undergone pyrolysis and it increases the temperature of the slag, thus giving it the fluidity required for good flow.

It is then advantageous, for this purpose, that the direction of each plasma jet is inclined, from top to bottom, with respect to the horizontal, towards the base of said column.

In order to allow the choice, for example depending on the nature of the waste, of the location of the point of impact of the plasma torch sting on a section of said column, provision is made for the direction of each plasma jet relative to the 'horizontal is adjustable.

Furthermore, in order to allow greater efficiency and greater freedom in the choice of the point of impact of the darts of the plasma torches on the base of the waste column, provision is made for the direction of each plasma jet to be inclined relative to to the direction of the corresponding radius of the waste column and that this direction is adjustable.

• a) en réglant la puissance et/ou l'enthalpie du plasma et/ou en choisissant la nature du gaz plasmagène, on règle l'apport d'oxygène au four, donc la quantité de matière oxydée et par voie de conséquence, la quantité de chaleur dégagée ;
• b) en réglant la puissance de la ou des torches, génératri­ces de plasma, on règle la puissance thermique introduite dans le four en complément de l'énergie dégagée par la pyrolyse ;
• c) en réglant l'angle d'inclinaison de la ou des torches sur l'horizontale, on peut diriger le dard préférentielle­ment sur les déchets ou sur le laitier et faire varier ainsi la répartition de la chaleur apportée aux déchets et au laitier ;
• d) en réglant l'orientation de la torche par rapport à l'axe du four, on crée des mouvements de convection du laitier qui favorisent l'homogénéisation de sa température et de sa fluidité.

As a result, thanks to the invention, the following advantages can be obtained:

• a) by regulating the power and / or the enthalpy of the plasma and / or by choosing the nature of the plasma gas, the oxygen supply to the oven is adjusted, therefore the quantity of oxidized material and consequently, the quantity heat released;
• b) by adjusting the power of the plasma-generating torch or torches, the thermal power introduced into the furnace is adjusted in addition to the energy released by the pyrolysis;
• c) by adjusting the angle of inclination of the torch or torches on the horizontal, it is preferable to direct the dart at the waste or at the slag and thus vary the distribution of the heat supplied to the waste and to the slag;
• d) by adjusting the orientation of the torch relative to the axis of the furnace, convection movements of the slag are created which promote the homogenization of its temperature and its fluidity.

Any suitable plasma gas can be used.

For the implementation of the method according to the invention, there is provided a device for the destruction of solid waste by pyrolysis, comprising a vertical wall in which is guided a column of such waste, means for blowing a hot gas jet arranged at the lower part of said wall and means for the evacuation of hot gases arranged in the upper part of said wall, this device being remarkable in that said means for blowing hot gaseous jet consist of at least one plasma generator.

Preferably, said gas jet blowing means are constituted by a plurality of plasma generators distributed at the periphery of said lower part of said wall.

Advantageously, said plasma generators are adjustable in orientation around a horizontal axis and / or around a vertical axis.

Although it can be collectively adjusted in orientation, said plasma generators are preferably individually adjustable.

When, in known manner, said device comprises a pouring orifice for molten slag provided in the bottom of said device, there is at least one of said plasma generators at least substantially perpendicular to said pouring orifice.

It will be noted that the plasma jet participates, on the one hand, in the vertical stability of the charge and, on the other hand, in the clearance of the pouring orifice (thus avoiding the passage of non-pyrolyzed material).

Thanks to the invention, it can therefore be seen that all kinds of solid waste can be destroyed, even when mixed with pasty waste.

• La figure 1 est une coupe verticale schématique d'un four à pyrolyse conforme à la présente invention.
• La figure 2 est une coupe horizontale schématique, correspondant à la ligne II-II de la figure 1.
• La figure 3 illustre schématiquement en coupe un détail du montage d'une torche à plasma sur un four à pyrolyse conforme à la présente invention.

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 schematic vertical section of a pyrolysis oven according to the present invention.
• Figure 2 is a schematic horizontal section, corresponding to the line II-II of Figure 1.
• Figure 3 schematically illustrates in section a detail of the mounting of a plasma torch on a pyrolysis oven according to the present invention.

The pyrolysis oven, according to the invention and shown in Figures 1 and 2, comprises a refractory crucible 1, surmounted by a vertical envelope in two parts 2 and 3, the upper part 3 of said envelope being itself surmounted through a hopper 4.

Under the hopper 4, in the upper part 3 of the envelope, an airlock 5 is provided, delimited between an upper register 6 and a lower register 7.

A pipe 8 for the evacuation of the gases is provided at the junction of the two envelope parts 2 and 3.

Plasma torches 9 are arranged at the periphery of the crucible 1 and directed towards the interior thereof.

The waste to be destroyed is loaded into the oven through the hopper 4 and passes through the airlock 5, which seals with the outside.

The upper part 3 of the envelope, the cross section of which advantageously goes downwards in order to avoid jams, guides the waste column 10 in its descent by gravity.

The upper part 10a of the waste column contained in the upper part 3 of the envelope (under the register 7) protects the airlock from direct contact of the gases leaving the oven through the pipe 8. The combustion of these gases in a post-combustion, their cooling and their treatment are not described below, because outside the scope of the present invention.

The lower part 2 of the envelope, advantageously cooled by a water jacket 11, guides the downward descent of the middle part 10b of the waste column 10.

The section of the envelope 2 also increases in a downward direction in order to avoid jams. The waste contained in this zone 10b is gradually dried, decomposed and pyrolyzed by the hot gases which come from the lower part of the oven.

The crucible 1, constituting the base of the furnace, is entirely coated with refractory elements resistant to very high temperatures. The waste enters there through the upper part and comes to rest on the bottom 12 in the slag 13.

The liquid slag 13 flows through an orifice 15 passing through the bottom 12 of the crucible 1, falls into a well 16 and cools in a tank 17 filled with water.

The point of impact 14 of the plasma jets of the torches 9 on the base 10c of the waste column 10 can be adjusted by adjusting the angle a of the torches 9 with the horizontal. If we decrease a , point 14 moves to the still solid waste; on the other hand, if the angle a increases, the point 14 moves towards the slag 13.

The angles a may be different for each torch 9, thus making it possible to distribute the energy supplied horizontally as well as possible, which promotes stirring movements. One of the torches 9 is advantageously in the vertical plane of the taphole 15 so as to release the latter.

As can be seen in FIG. 2, the torches 9 are not directed towards the axis 18 of the crucible 1, but form with the corresponding radius 20 an angle b which can be adjusted according to the intended application and even vary in order to give a rotational movement to the molten slag and thus homogenize its temperature.

The torches 9 are supplied with electric current and with plasmogenic gas in a known manner and not shown. Under the effect of the stabilized electric arc in the torches, the gas is transformed into plasma (for example between 3000 ° C and 7000 ° C) and constitutes a dart 19 at very high temperature.

By increasing the power of the plasma torches, the temperature in the crucible is increased and therefore the temperature of the slag which thus becomes more fluid.

By choosing a wide angle has torches with the horizontal, one preferentially directs the plasma jet towards the slag, and one thus increases its temperature.

Part of the thermal energy is brought to the system by the enthalpy of the plasma. The other part is provided by the combustion of a fraction of the waste in contact with the oxygen brought in by the plasma; by increasing the flow of gas supplied to the torches, the quantity of waste oxidized by the oxygen in the plasma is increased, therefore the thermal energy released by the combustion of the waste is increased. It is then possible to use in return the corresponding energy of the plasma to raise the temperature of the slag, for example by increasing the angle a .

Thus, by varying the power of the torches, the plasma gas flow and the inclination of the torches, it is possible to modify the temperature of the slag in order to obtain a liquid of viscosity compatible with good flow.

In addition, it is possible to obtain sufficiently high slag temperatures so that the base metals are fully melted.

Finally, at the high temperatures obtained in the slag (1500 ° C. for example), it is ensured that all the risks of contamination, in particular pathogenic in the case of hospital waste, are eliminated. Experience shows that the residues collected do not contain unburnt materials and are perfectly inert.

In Figures 1 and 2, there is shown an embodiment in which the angles a and b are fixed once and for all, at an optimal value depending on the particular structure and application of the oven.

On the contrary, in Figure 3, there is shown the adjustable mounting of a torch 9. In the embodiment shown, said adjustable mounting is of the ball joint type.

As can be seen in this figure 3, each torch 9 is secured to a frame 25, by means of fixing means 26. The nozzle 27 of said torch 9 passes through the frame 25 and an internal seal 28 ensures the seal between the latter and said nozzle. The mount 25, by means of a seal 29, can rotate in a spherical bearing 30 in order to pivot around a center of rotation 31. The spherical bearing 30 is formed in a flange 32, for example hollow to form a channel 33 for circulation of a cooling fluid, which is fixed to the periphery of an orifice 34, passing through the side wall 35 of the crucible 1. A rear support 36, secured to the flange 32 by spacers 37, has a spherical bearing surface 38 in contact with a stud 39, integral with the rear of the torch 9 and provided with a spherical end capable of sliding on the bearing surface 38. Elastic means 40, provided between the frame 25 and the torch 9 allow to apply the seal 29 against the spherical bearing 30 and the stud 39 against the spherical bearing 38. The seals 28 and 29 are for example made of copper or stainless steel.

It is thus seen that, thanks to the assembly of FIG. 3, it is possible to orient a torch 9 around the center 31 to give the angle a and / or the corresponding angle b any desired value, and even to vary these angles continuously. The pivoting of a torch 9 around the center 31 can be ensured by any mechanical, pneumatic, electrical, ... or even manual means (not shown).

Claims (14)

1 - Process for the destruction of solid waste by pyrolysis, according to which a column (10) of such waste is traversed at least partially, from bottom to top, by a hot gas stream blown at the base of said column, characterized in that said hot gas stream is generated by at least one plasma jet. 2 - Method according to claim 1,
characterized in that said hot gas stream is generated by a plurality of plasma jets distributed at the periphery of said column (10) of waste, in the vicinity of the base thereof. 3 - Method according to one of claims 1 or 2,
characterized in that the direction of each plasma jet is inclined from top to bottom, with respect to the horizontal, in the direction of the base of said column. 4 - Process according to claim 3,
characterized in that the direction of each plasma jet relative to the horizontal is adjustable. 5 - Method according to any one of claims 1 to 4,
characterized in that the direction of each plasma jet is inclined relative to the direction of the corresponding radius of the waste column (10). 6 - Process according to claim 5,
characterized in that the direction of each plasma jet relative to said radius is adjustable. 7 - Device for destroying solid waste by pyrolysis, comprising a vertical wall (1,2,3) in which is guided a column (10) of such waste, means for blowing a hot gaseous jet disposed at the part bottom of said wall and means (8) for the evacuation of hot gases arranged in the upper part of said wall,
characterized in that said hot gas jet blowing means consist of at least one plasma generator (9). 8 - Device according to claim 7,
characterized in that said gas jet blowing means consist of a plurality of plasma generators (9) distributed around the periphery of said lower part (1) of said wall (1,2,3). 9 - Device according to claim 8,
characterized in that said plasma generators (9) are adjustable in orientation about a horizontal axis. 10 - Device according to claim 8,
characterized in that said plasma generators (9) are adjustable in orientation around a vertical axis. 11 - Device according to any one of claims 9 or 10,
characterized in that said plasma generators (9) are individually adjustable in orientation. 12 - Device according to any one of claims 8 to 11, comprising a pouring orifice for the molten slag provided in the bottom of said device,
characterized in that at least one of said plasma generators (9) is at least substantially perpendicular to said pouring orifice (15). 13 - Device according to claims 9 and 10,
characterized in that said plasma generators (9) are mounted on said wall (1,2,3) by means of ball joints (25,32). 14 - Device according to claim 13,
characterized in that the elements (25,32) of each of said ball joints are pressed elastically against each other.

Images