WO1994000252A1 - Method and machine for compacting waste containing thermoplastic materials - Google Patents

Abstract

Industrial waste containing thermoplastic materials, possibly mixed with other solids, is compacted to enable storage in a non-bulky form, particularly in drums. The compacting machine comprises an induction furnace (2) with a vessel containing a rotary eccentric mixer (7) for mixing, crushing and grinding the waste as it is heated in the vessel. The crushed solids are then coated with the molten or softened thermoplastic materials. The softened mass flows out through an opening at the bottom of the furnace and into a drum (10) in a preheating receptacle (9). The drum may be vibrated. Said machine may be used for processing any waste containing thermoplastic materials, including low-level radioactive waste such as protective equipment from nuclear facilities.

Description

METHOD AND MACHINE FOR COMPACTING WASTE CONTAINING THERMOPLASTIC MATERIALS

The present invention relates to a process for compacting waste containing thermoplastic materials, in particular waste in the form of flexible films or sheets, this process comprising a mixing and heating step in a tank equipped with an eccentric rotary mixer, to soften the thermoplastics for packaging in a compact form.

The invention also relates to a compacting machine for implementing this process, this machine comprising a tank of substantially circular section with vertical or inclined axis, provided with an inner peripheral wall, with a filling orifice for waste and a discharge orifice, a mixer with a parallel axis and eccentric with respect to the axis of the tank and heating means associated with said tank.

More and more people are trying to recover used thermoplastics in order to recycle them into new products. However, there are many cases where such recovery is not economically possible, for example if the materials are too polluted or altered to be reused, or if they are mixed with other materials and sorting would be too expensive. Waste of this kind must then be packaged in containers for transport and / or storage. This generally requires compaction, since the waste has a very low bulk density which results in excessive volume and too many containers.

A typical example of waste containing thermoplastic materials is the case of waste resulting from maintenance operations in the nuclear industry. This waste is mainly composed of bags or protective clothing in vinyl, boots, various PVC films, mixed with textile articles or cellulosic materials such as paper, cardboard, cotton etc, as well as wood waste, glass wool. This waste is likely to present a certain radioactivity and must be sorted according to its class of activity. Weakly radioactive residues, for example having an activity of less than 200 mrem, are generally packaged in metal drums for storage. The quantities of waste thus produced are relatively large and the problem of storage volume is often difficult to solve. This is why this waste is subjected to compaction which ultimately makes it possible to obtain a higher density inside the barrels.

To date, the following processes are used industrially, but their performance is still insufficient:

- the shredding processes make it possible to reach densities between 0.3 and 0.5 t / m2, these are the processes currently in force for compacting low-level radioactive waste;

- The most efficient methods of compacting thermoplastic materials, using a melting or softening of these materials, offer compacting possibilities up to a density of 0.8 to 0.9 t / m2.

Such a compacting device is described in publication FR-A-2 429 665. This device uses an eccentric roller press which grinds the previously shredded waste, then discharges it through an outlet orifice close to the inlet orifice, using a scraper. In this device, a preparation of the waste before grinding is necessary and the evacuation of this waste after grinding is often done in an unsatisfactory manner in particular because of the risk of jamming. Indeed, the axis of the discharge orifice is located in a horizontal plane which does not promote a natural evacuation of said waste. The subject of the present invention is a method and a machine of the kind indicated in the preamble, making it possible to achieve a greater degree of compaction of the waste, than the aforementioned known methods, with simple means, usable easily even if the waste is slightly radioactive. and very reliable.

For this purpose, the method according to the invention is characterized in that the waste is heated during the mixing at a temperature between 60 ° C and 100 ° C for a period necessary for their softening, and in that the 'this fluidized waste is removed, during the kneading-heating phase, by gravitational flow in a container placed under said tank.

Thus, a mixing of the waste is carried out simultaneously, having the effect of crushing the solid elements which they contain and of compressing them to eliminate voids, and a heating which softens or melts the thermoplastic materials, which are kneaded by the mixing and which therefore tend to fill the voids still remaining in the mass. This heated mass becomes fluid and can then be packaged at a maximum density, in particular be poured into a container.

In an advantageous form of the method, a vibration is applied to said container while it receives the waste.

For the implementation of this method, another aspect of the invention relates to a thermo-mechanical compacting machine for waste containing thermoplastic materials, characterized in that the machine includes heating means for heating the waste during mixing. for a time necessary for their softening, in that the tank has a substantially cylindrical upper part provided with a filling orifice and extended at its lower part by a frustoconical sector provided with an evacuation orifice, in that the mixer has a part cylindrical upper part and a frustoconical lower part arranged in such a way that the walls of this mixer roll on the corresponding internal walls of the tank, crushing and kneading said waste in the space between the walls of the mixer and those of the tank, and that the machine comprises receiving means arranged below the discharge orifice to receive by gravity the hot fluidized waste leaving the tank during the mixing-heating phase.

A preferred embodiment of the machine comprises orbital displacement means producing a circular displacement of the axis of the mixer around the axis of the tank during the rotation of the mixer.

Another embodiment of the machine may include orbital displacement means producing a circular displacement of the axis of the tank around the axis of the mixer during the rotation of the mixer.

The mixer can advantageously be supported by a console movable in translation parallel to the axis of the tank and supporting the means for driving the mixer in rotation.

Preferably, said peripheral wall of the tank is metallic and said heating means are of the induction type.

In a particular embodiment, the tank is movable in translation parallel to its axis. The receiving means may include a heating shell arranged to contain a removable barrel below the drain opening of the tank. Preferably the heating shell comprises an induction heating, the removable barrel being a metallic barrel. This heating shell can be movable horizontally between a working position where the barrel is located below the tank and a loading position where the barrel can be introduced and / or removed over the shell. The barrel can rest on a vibrating device provided in the bottom of the shell.

Other characteristics and advantages of the present invention will appear in the following description of an embodiment of a compacting machine according to the invention, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic elevation view showing the compacting machine in a high position,

FIG. 2 is a view similar to FIG. 1, showing the compacting machine in a working position,

FIG. 3 is a view similar to FIGS. 1 and 2, showing the compacting machine in a rest position with minimal bulk,

FIG. 4 is a schematic view illustrating the operation of the machine in its working position and,

Figure 5 is a plan view of a part of the machine, illustrating the kinematics and the drive means of the mixer.

Referring to Figures 1 to 3, the thermo-mechanical compacting machine mainly comprises the following sub-assemblies: a frame 1; an induction furnace 2 comprising a metal tank 3 provided with a feed hopper or filling orifice 4 and with a lower evacuation orifice 5, the tank 3 having a vertical axis 6; a mixer 7 rotating about a vertical axis 8 eccentric with respect to the axis 6 of the tank; a preheating shell 9 for a metal drum 10 intended to contain the compacted waste; and a set of controls 11 ensuring the overall operation of the machine. The mixer 7 is suspended from a bracket comprising a telescopic drum 12 and a console 13 which contains the drive means of the mixer 7 and which can go up or down with the mixer. In this example, the oven 2 is also movable in vertical translation along the barrel 12, as will be described later. The preheating shell 9 is movable horizontally between its working position of FIG. 2, below the oven 2, and one or more loading positions where the barrel 10 can be extracted upwards and replaced by an empty barrel .

Figures 4 and 5 show in more detail the main elements of the tank 3 of the induction furnace and the mixer 7 working in this tank. The tank 3 comprises a peripheral wall 20 of steel comprising a cylindrical part 20a and a frustoconical lower part 20b ending in a discharge orifice 21. The wall 20 and the orifice 21 are centered on the axis 6 of the tank and are surrounded by an induction heater 22 which allows the wall 20 to be heated to a well-determined temperature. The control, supply and regulation members of such a device are well known; they are housed in the control unit 11.

The rotary mixer 7 of circular section is driven in rotation about its axis 8 eccentric relative to the tank 20, while the axis 8 of the mixer describes a circle around the axis 6 of the tank. Thus, part of the peripheral surface of the mixer 7 is located near the peripheral wall 20 of the tank, in a mixing and crushing zone 23 where the interval between these two walls is very reduced. To this end, the surface of the mixer 7 comprises a cylindrical part 7a and a frustoconical part 7b whose vertical profiles correspond respectively to those of the parts 20a and 20b of the wall of the tank. Above the cylindrical part 7a, the wall of the mixer has a frustoconical part 7c flared downwards and forming an inlet bias 24 for the materials to be ground. The mixer 7 may consist of compacting rollers fixed on a vertical shaft mounted in cantilever in the console 13. Figure 5 schematically shows the. kinematics of the mixer 7, seen from above, relative to the position of the axis 6 and of the wall 20 of the tank. The mixer and its drive members are supported by a structure of the console 13 comprising two parallel arms 26 and a horizontal base plate 27 fixed to the arm 26.

The shaft 25 of the mixer is rotated in the direction indicated by the arrow A by means of a first motor 28 and a floating reduction gear 29. In order that it does not rotate, the latter is provided with an arm 30 connected to the base plate 27 by a link 31 provided with articulations 32 and 33, which allows the reduction gear 29 to follow the displacement of the eccentric axis 8 around the axis 6. This displacement is produced by means of 'a ring gear 34 driven in the direction of arrow B by a second motor 35 by means of a fixed reduction gear 36. Thus, the mixer 7 performs, inside the stationary tank, an orbital movement during from which the grinding zone moves all around the tank. Preferably, the speed of rotation of the mixer in the direction of arrow A is slightly greater than the speed resulting from its movement in the direction of arrow B, so that the kneaded and crushed materials are subjected to shearing.

The machine works as follows. The receiving barrel 10, for example an ordinary 200 liter steel barrel, is inserted vertically into the induction preheating shell 9, where it is brought to a temperature of the order of 60 to 90 ° C. The main purpose of this preheating is to maintain the future contents of the barrel at a temperature where the thermoplastics are viscous. For example, for materials based on vinyl, this temperature is between 60 and 90 ° C. The barrel 10 is then brought under the oven 2 placed in the working position of FIG. 2.

The waste, sorted beforehand and packed in bags, is introduced into the hopper 4 for loading the oven, the wall 20 of which is heated to a temperature equal to or greater than the softening point of the thermoplastics contained in the waste, that is to say generally say between 60 and 100 ° C. In the tank 3, the rotary and orbital movement of the mixer 7 catches the waste, crushes it against the heated wall 20 and ensures its compaction as explained above, while the waste gradually descends by gravity to the orifice discharge 21 to fall into a pasty state in the barrel 10. Preferably, the barrel rests on a vibrating device at the bottom of the shell 9, which ensures the distribution of the pasty mass in the barrel and the elimination of bubbles gases that could be there. It will be noted that the upper edges of the barrel 10 can be connected to the discharge orifice 21 of the tank by a flexible sleeve (not shown) allowing recovery of any emanation of gas or dust, in particular in the case of treatment of products. slightly radioactive.

Thus, we note that the machine according to the invention combines the use of two waste treatment methods:

a melting or softening of all waste based on thermoplastic materials (for example PVC, polyethylene, elastomers, etc.) which makes it possible to reduce these materials in the form of a wafer whose density is close to the density of the materials they - same, generally from 1, 3 to 1, 5 t / m3;

mixing and grinding of all of the waste components and in particular of non-thermoplastic materials, such as glass or cellulosic materials (paper, blotters, rags, cardboard, wood, textiles, various fibers, etc.) including ground materials are trapped in the matrix of molten thermoplastic material.

Consequently, it is possible to obtain a complete filling of the barrel 10, with a mass whose density can be of the order of 1, 3 to 1, 5 t / m3, that is to say approximately four times higher than the density obtained with conventional methods.

The present invention is not limited to the example réalisatione embodiment described above, but it extends to any modification or variant obvious to a person skilled in the art. In particular, it will be noted that the stationary position of the tank 3 of the oven 2 during work makes it possible to close this tank by a cover 40 (FIG. 2) fixed to the console 13, to avoid any dissemination of polluting products liable to be released. during heating and mixing. If such a risk is not to be feared, a mechanically simpler variant can be provided, in which the mixer 7 does not have an orbital movement, its axis 8 being fixed, while it is the axis 6 of the tank which performs a circular movement around the axis of the mixer. Many other particular embodiments of the machine can be provided according to specific applications, in particular for extruding through a die the pasty mass at the outlet of the oven, for example to make it into profiled elements or granules. In all cases, the combination of mixing and heating makes it possible to treat the waste at temperatures much lower than those necessary for a simple melting.

Claims

claims 1. Method for compacting waste containing thermoplastic materials, in particular waste in the form of flexible films or sheets, this process comprising a mixing and heating step in a tank equipped with an eccentric rotary mixer, characterized in that it is heated this waste during mixing at a temperature between 6θ ° C and 100 ° C for a period necessary for their softening, and in that this fluidized waste is removed during the mixing-heating phase, by gravitational flow in a container placed under said tank. 2. Method according to claim 1, characterized in that a vibration is applied to said container while it receives the waste. 3. thermomechanical compacting machine for waste containing thermoplastic materials, for the implementation of the method according to claim 1, this machine comprising a tank (3) of substantially circular section with vertical axis (6) or inclined, provided with an inner peripheral wall (20), a filling orifice (4) for the waste and an evacuation orifice (21), a mixer (7) with a parallel axis and offset from the axis of the tank and heating means associated with said tank, characterized in that the machine comprises heating means (22) for heating the waste during mixing for a period necessary for their softening, in that the tank has an upper part substantially cylindrical (20a) provided with a filling orifice (4) and extended at its lower part by a frustoconical sector (20b) provided with a discharge orifice (21), in that the mixer (7) comprises a e cylindrical upper part (7a) and a frustoconical lower part (7b) arranged in such a way that the walls of this mixer roll on the corresponding internal walls (20) of the tank, crushing and kneading said waste in the space between the walls of the mixer and those of the tank, and in that the machine comprises receiving means (9. 10) arranged below the discharge orifice (21) to receive by gravity the hot fluidized waste leaving the tank during the mixing-heating phase. 4. Machine according to claim 3, characterized in that it comprises means of orbital displacement producing a circular displacement of the axis (8) of the mixer around the axis (6) of the tank during the rotation of the mixer ( 7). 5 »Machine according to claim 3, characterized in that it comprises means of orbital displacement producing a circular displacement of the axis (6) of the tank around the axis (8) of the mixer during the rotation of the mixer ( 7). 6. Machine according to claim 4 or 5, characterized in that the mixer is supported by a console (13) movable in translation parallel to the axis of the tank and supporting the means for driving the mixer in rotation. 7. Machine according to one of claims 3 to 6, characterized in that said peripheral wall (20) of the tank is metallic and in that said heating means (22) are of the induction type. 8. Machine according to one of claims 3 to 7, characterized in that the tank (3) is movable in translation parallel to its axis. 9. Machine according to claim 3, characterized in that the receiving means comprise a heating shell (9) arranged to contain a removable barrel (10) below the orifice for discharging the tank. 10. Machine according to claim 9, characterized in that the heating shell (9) comprises an induction heating, the removable barrel (10) being a metal barrel. 11. Machine according to claims 8 and 9, characterized in that the heating shell (9) is movable horizontally between a working position where the barrel (10) is located below the tank (3) and a loading position where the barrel can be introduced and / or evacuated over the shell. 12. Machine according to one of claims 9 to 11, characterized in that the barrel (10) rests on a vibrating device provided in the bottom of the shell (9).