FR2573340A1 - Process for separating and treating plastic waste with a view to reusing it and device for its implementation - Google Patents

Abstract

The invention relates to a process for treating plastic waste, comprising the grinding of the waste, the separation of the plastic and foreign matter, especially for selective decantation (settling), and a device for its implementation. The ascending-flow decantation (settling) column includes, in its bottom part, a zone 11 of reduced cross-section and is fitted over its entire height with a fixed screw.

Description

The present invention relates to a process for the separation and treatment of plastic waste with a view to its reuse, and a device for its implementation
The plastic waste to be reused after its separation and treatment are plastics of industrial and domestic origin, that is to say mixtures of pre-separated plastics and associated with various foreign bodies, for example plastics from selective collections of bottles (mineral water, fruit juice, milk, wine, ...) containing polyethene, polyvinyl chloride, polyethylene terephthalate, polystyrene, aluminum, glass, paper, organic materials or plastics from dehulling telephone or electrical cables containing polyethylene, PVC and rubber, copper.

The present invention therefore relates to a process for the separation and treatment of plastic waste with a view to its reuse, characterized in that it comprises the following steps a) grinding of the waste and the dispersion of the ground material into
aqueous phase, b) selective decantation of the ground material dispersed in phase
aqueous, c) recovering the fractions of the dispersed ground material
loaded with material for reuse.

 The plastic waste is passed through grinders to reach a particle size of approximately 3 to 15 mm. If the waste is loaded with ferrous materials, the crushed material then undergoes a deferrization step according to a conventional method.

 If the waste is loaded with cellulosic materials, for example the labels of the bottles, the ground material then undergoes a step of destruction of these cellulosic materials making it possible to break the structure of the fibers and to reduce them into elements dispersible in the aqueous phase.

In a particular embodiment of the invention, the step of destroying the cellulosic materials present on the plastics, is done by simple mechanical treatment by violent agitation of the dispersion in a turbomixer, for example, this in order to break the structure cellulosic fibers and reduce them to dispersible elements in the aqueous phase. However, it may be preferable to make a prior maceration of the dispersion, in the presence of an alkali, for example a sodium hydroxide solution or preferably a solution of sodium hypochlorite. The separation according to the process is carried out in the aqueous phase.

 if the treatment has not hitherto required any prior treatment in the aqueous phase, in the case for example if the waste does not contain cellulositic material, it may be necessary to ensure the wetting of the particles of the ground material to avoid fixing of air bubbles by the particles to be separated, by treating with hydrotope agents. The hydrotope agents, that is to say wetting agents, non-foaming agents used in the wetting phase are low molecular weight alcohols.

 The dispersion in the aqueous phase of the ground material, that is to say the carrier fluid loaded with plastic particles and heavy products is then treated in a selective decantation device.

 The present invention also relates to a selective decantation device for the implementation of the process, composed of an ascending flow separation column, with a substantially vertical axis comprising, in its lower part, a zone of reduced section and below the reduced section area, a carrier fluid inlet pipe, and above the reduced section area, a supply line for dispersed comminuted material to be decanted and at the bottom of the column, a de-fueling valve for heavy products , and at the top of the column, a pipe for discharging the carrier fluid loaded with plastic particles, the column being provided with a coaxial helix with an angle at least equal to approximately 600.

This column makes it possible to separate the glasses, stones and other heavy products which descend by sedimentation and are evacuated by the valve from the plastic particles carried by the fluid which is evacuated from above. This device makes it possible to avoid convection movements and thereby the retention of heavy products and plastic particles to be separated.

 It can be useful for different reuse of heavy plastics (polyvinyl chloride, polyethylene, tetraphthalate, polystyrene, for example) and light plastics (polyolefin for example), to separate the particles of heavy and light plastics. , one can use downstream of the selective decantation device, a decanter with fixed fins whose walls of the lower part of the decanter are inclined towards a low point and whose walls of the upper part of the decanter are inclined towards a high point and, which comprises at mid-height a supply line for loaded carrier fluid, provided with a device for agitating the loaded carrier fluid, and a screw extractor at the low point, and a screw extractor at the high point, and at mid height opposite to the supply pipe, a pipe for discharging the discharged carrier fluid, the fixed fins of which are substantially parallel and arranged perpendicular to the main direction of the stream of fluid ide carrier and leave a free passage area to the main stream of carrier fluid between the supply and outlet pipes.

 This device makes it possible to separate the crushed fractions loaded with plastic particles slightly heavier and lighter than the carrier fluid.

You can choose the density at which you want to cut, between 1 and about 1.4, by adjusting the density of the carrier fluid to the desired cutting density; for this, mineral salts, for example Caca2 or NaCl, are added to the carrier fluid.

 The plastic particles are then separated from the carrier fluid by wringing, washed to rid them of the various salts, alkalis and wetting agents optionally added to the carrier fluid, then dried.

Fine particles of heavy products which would have been entrained with the plastic particles in the selective decantation can then be eliminated by fine sieving (0.2 to 0.8 mm) or elutriation
The carrier fluid and the washing effluents can be recycled and / or purified before their recycling.

 Other characteristics and advantages of the invention will appear during the following detailed description of the process and the devices, and in the drawings which are appended.

 The figure gives a schematic sectional representation of the selective settling column, without the coaxial propeller.

 Figure 1b gives a schematic sectional representation of the area A of the selective settling column provided with the propeller.

 Figure 2 gives a schematic sectional representation of the static settling device.

 The plastic waste to be reused is crushed in mechanical crushers, until reaching a particle size of 3 to 15 mm, and the ferrous materials contained in this crushed material are eliminated by a deferrization treatment, according to a conventional method of magnetization.

This ground material is then mixed with water loaded with sodium hypochlorite. The ground material is left to macerate in the aqueous phase before passing through a turbomixer where it undergoes vigorous stirring until the cellulose fibers pulled from the plastics are reduced to dispersed elements in the aqueous phase, - of dimensions less than 1 mm - .

Maceration facilitates the subsequent destruction of cellulosic fibers. In this particular embodiment, it is not necessary to treat the dispersion with wetting agents, before it arrives in the settling phase, - in the settling column.

 As shown in FIG. 1 a, which gives a simplified representation in section of the decanting column, said decanting column comprises a zone of reduced section 11 in its lower part, below the zone 10 in its upper part. The dispersion in the aqueous phase of the ground material, that is to say the carrier fluid loaded with plastic particles and heavy products is introduced at a concentration of products to be separated of between 1 and 20 e in the column, above the reduced-section area 11 via the pipe 12, the dimensions of which are chosen to avoid any deposit before arriving in the separation column. The supply of carrier fluid, via the supply pipe 13, makes it possible to adjust the flow rates in the column so that the speed of the carrier fluid is less than the speed of sedimentation of the heavy products which are discharged by the valve 14, and greater than the speed of sedimentation of the plastic particles, discharged with the carrier fluid by the pipe 15 evacuation.

 Finally, the column is provided, substantially over its entire height, with a helix of the same axis as the column, with an angle at least equal to 600, consisting of a helical blade 16 carried by a fixed shaft 17, the connection between the shaft and the blade being provided by welding.

 In order not to overload FIG. 1 a, this propeller is not shown there, which appears in FIG. 1 b representing, on another scale, zone A of the column provided with the propeller.

 The pipe 15 for evacuating the carrier fluid, loaded with plastic particles, leads said carrier fluid loaded to the finned settling tank 1 represented in FIG. 2.

 The carrier fluid loaded with plastic particles borrows the supply line 21 of the finned decanter provided with an agitator 22, and the loaded carrier fluid is thus homogenized before entering the decanter, at a concentration of plastic particles. from 1 to 20%.

 In the decanter, the walls 30, 31, 32 and 33 of the enclosure are inclined at an angle of approximately 450 towards the collectors at the low point 23 and at the high point 24.

The fixed fins 26 allow the separation of heavy and light plastic particles, with a minimum of disturbing movements of the carrier fluid. They leave a zone 29 of free passage to the main stream of carrier fluid.

 The plastic waste is extracted at the high point 24 and at the low point 23 by means of screw extractors 27 and 28. They are separately wrung in continuous wringers, washed and dried for re-use.

 The carrier fluid evacuated by the extractors and by the pipe 25 for evacuating the discharged carrier fluid, as well as the washing effluents, are purified by a treatment with polyelectrolytes. The agglomerates formed by the polyelectrolytes and the particles of impurities are separated from the carrier fluid in a basin, and treated in a specialized treatment station.

Claims (10)

 loaded with material for reuse.  aqueous phase, c) recovering the fractions of the dispersed ground material  in the aqueous phase, b) selective decantation of the ground material dispersed in  1, Process for the separation and treatment of plastic waste with a view to its reuse, characterized in that it comprises the following stages a) the grinding of the waste and the dispersion of the ground material 2. Method according to claim 1, characterized in that it comprises, after grinding and before decantation, a deferrization step. 3. Method according to claim 1, characterized in that it comprises, after grinding and before decantation, a step of destruction of the cellulosic materials. 4. Method according to claim 3, characterized in that the cellulosic materials are destroyed by violent agitation of the dispersed ground material, optionally preceded by maceration of the dispersed ground material in the presence of an alkali. 5. Method according to claim 4, characterized in that sodium hydroxide or sodium hypochlorite is used for the maceration of the dispersed ground material. 6. Method according to claim 1. characterized in that the dispersed ground material is treated before selective decantation with a wetting agent. 7. Method according to claim 1, characterized in that the selective decantation comprises the passage of the ground material dispersed in a decantation column, optionally followed by a static decantation. 8. Method according to claim 7, characterized in that in the static decantation step, a cut is made at a density between 1 and 1.4, determined by the amount of mineral salts previously added to the carrier fluid. 9. Device for the selective settling of a dispersion for the implementation of the method according to one of claims 1 to 8, composed of a separation column with ascending flow with vertical-axis separation comprising, in its lower part, a zone of reduced section (11) and below the zone of reduced section, a pipe (13) for carrying carrier fluid, and above the zone of reduced section, a pipe (12) for supplying dispersed slurry to be decanted and at the bottom of the column, a valve (14) for unloading heavy products, and at the top of the column, above the zone (10), a pipe (15) for evacuating the carrier fluid loaded with plastic particles, the column being provided with a coaxial propeller (16) with an angle at least equal to about 604. 10. Device according to claim 9 characterized in that it comprises, downstream of said separation column, a static decantation device of the fin decanter type whose walls of the lower part of the decanter are inclined towards a low point (23 ) and whose walls of the upper part of the decanter are inclined towards a high point (24) and which comprises at mid-height a pipe (21) for supplying charged carrier fluid provided with a device (22) for agitating the fluid loaded carrier, and a screw extractor (27) at the low point (23), and a screw extractor (28) at the high point (24) and halfway up, opposite the pipe (21) of supply, a pipe (25) for discharging the discharged carrier fluid, and the fixed fins (26) of which are substantially parallel and disposed perpendicular to the main direction of the stream of carrier fluid and leave a zone (29) of free passage to the main stream of carrier fluid between the pipes (21), (25) supply and discharge.