BACKGROUND OF THE INVENTION This invention relates to a method and an apparatus for washing and separating plastics materials - coming from domestic and/or industrial waste that is milled or reduced into small pieces - from various types of contaminant. The plastics pieces to be processed can come, for example, from containers, bottles, films and other post- consumption objects, and once they have been decontaminated they are ready for reuse as regenerated material.

The contaminants to be eliminated can comprise earth, sand, gravel, various types of dirt, labels or elements of other material remaining adhering to plastics pieces. PRIOR ART

In the field of treatment to recover plastics materials, washing systems are known that provide one or more washing tanks or containers, inside which the material is made to transit with which the contaminant to be eliminated aggregates.

From IT 1326462, an apparatus is known that is configured for continuous washing of recovery material previously reduced into pieces, which is subjected to successive washing steps in a plurality of reactors that are serially connected to one another, inside which washing water is made to flow continuously, and a given quantity of recovery material.

Other systems are disclosed in US 4.196.019, EP 0 094 282, US 4.073.661, EP 0 129 518, and EP0359106. In particular, the object of US 4.196.019 is an apparatus for washing plastics material in pieces of small dimensions, in which the apparatus comprises an elongated tank, which is suitable for being filled up to a preset level with a washing bath, provided with a blade stirrer that extends horizontally just below the upper level of the washing bath, to generate a stirring state; the plastics pieces flow to a horizontal channel from which they are discharged by a rotating drum.

A similar apparatus is disclosed in US 4.073.661 : the plastics material in pieces of small dimensions is inserted into a water bath of a washing tank comprising a horizontal stirrer; the pieces of plastics material that float in the tank are removed by being dragged by a screw conveyor, which is positioned partially above the washing bath and along an upwardly oriented discharge channel. EP 0 094 282 discloses a recovery system comprising a plurality of washing tanks that are serially connected and communicate with one another by labyrinth passages, in which the single washing tanks are provided with normal blade stirrers; the pieces of plastics material that float in the water bath are pushed along a discharge channel by a plurality of rotors that are suitably spaced apart along a discharge channel, and extracted from the bath by a blade wheel.

None of the currently known systems, including those disclosed above, is able to solve a problem disclosed below. In order to separate the contaminants from the plastics material, the different specific weight thereof is generally exploited. Pieces of plastics material with specific weight that is about the same or less than the washing water are in a floating condition, whereas the contaminants with a specific weight generally greater than that of the water should precipitate to the bottom of the containers or washing tanks.

Unfortunately, in practice, conditions occur that adversely affect this principle of selection by specific weight, greatly reducing the efficiency of the entire separating process. More precisely, when recycling low-density materials, thus materials with a lower specific weight than that of the washing fluid, a significant volume of product is generated that has to be processed. In the separating tank, agglomerates of plastics material tend to be generated that act as "rafts" of floating material that affect the separating quality of the heavy materials. Basically, such floating agglomerates, in addition to not allowing thorough washing of the individual pieces of plastics, act as a support for the aggregated contaminants, preventing the precipitation thereof downwards.

Simply adopting blades that are suitable for pushing the material below the water surface to promote sinking of the heavy contaminants is not sufficient inasmuch the agglomerates tend to remain cohesive and compact.

As the commercial value of the recovery material is closely connected to the degree of cleanliness and purity thereof, is thus linked to the percentage of residual contaminants that remain at the end of washing, the great need to overcome the problem disclosed above and thus to obtain a more efficient washing and separating process is evident.

OBJECTS OF THE INVENTION

One object of the invention is to improve current washing systems for plastics materials.

Another object of the invention is to provide a solution that, in addition to being constructionally and functionally simpler, enables higher levels of purity and decontamination of plastics materials to be achieved.

In particular, one object of the invention is to provide a solution that is able to solve the problem of floating agglomerates of plastics material that prevent thorough washing of the pieces and complete precipitation of the heavier contaminants.

SHORT DESCRIPTION OF THE INVENTION

These and further objects and advantages are achievable by a method according to claim 1, and an apparatus according to claim 10. In particular, owing to the conveying unit comprising disaggregating-propelling means, which in one embodiment comprises screw conveying means, the problem of floating agglomerates of plastics material is solved.

The agglomerates of plastics are subjected, by the screw conveying means, to an intense disaggregating, opening and singling action, and are forced to descend deep down the tank. The agglomerates are projected forcibly downwards in the fluid inside the separating tank to be effectively separated from the contaminants. The single parts of plastics material can have an enormous increase in volume that advantageously leads to having greater separation from the contaminants. With the same volume of water used, it is possible to process greater quantities of plastics, with clear economic advantages and a reduction of the environmental impact that arises therefrom.

The action performed by the conveying unit greatly reduces the influence of the phenomenon of undesired floating caused by the microbubbles that adhere to the surfaces of the particles and which in general is normally addressed by chemical additives.

Owing to the drawing and recirculating means that in particular comprises a variable flowrate pump, from the bottom of the tank a recirculation flow is drawn that contributes to regulating the separating efficiency of the material with density that is also very near that of the washing fluid used.

Further, the screen unit enables the contaminants to be retained that are pumped by removing means and the washing water to be recirculated in the separating tank, thus reducing the consumption of process water, and simplifying the system significantly.

SHORT DESCRIPTION OF THE DRAWINGS

These and further features and advantages of the method and of the washing and separating apparatus will be clearer from the following description, with reference to the drawings, in which:

Figures 1 and 2 are two different views of a washing and separating apparatus according to the present invention;

Figure 3 is a longitudinal section according to line ΠΙ- ΙΠ of figure 2;

Figure 4 is another longitudinal section, in a perspective view, according to line IV- IV of figure 2;

Figure 5 shows an enlarged detail of figure 4;

Figure 6 is a top view of the apparatus according to the invention;

Figure 7 is a block flow diagram relating to the washing and separating method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION With reference to the attached figures, an apparatus 1 is disclosed below for washing a plastics material P and separating therefrom contaminating substances C.

The apparatus 1 comprises a washing container 2, provided with stirrer means 3, and suitable for receiving a first flow F _IN of a washing fluid W together with the plastics material P containing the contaminants C to be subjected to a first action of separating.

The stirrer means 3 is configured for generating a turbulent stirring action to detach from the plastics material P, by mechanical action, the part of contaminating material C adhering thereto.

The washing container 2 is bounded below by a first bottom portion 4 suitable for receiving a first fraction XI of the heavier contaminants C. The washing container 2 is provided below with a removing device 13 of valve or pump type acting to remove periodically the first fraction XI of the contaminants C that settles on the first bottom portion 4. The apparatus 1 comprises, downstream of the washing container 2, a separating tank Vs comprising a first chamber 5 and a second chamber 7 placed in succession one after the other. The first chamber 5 is shaped for receiving by overflowing a second flow F2 of washing fluid W with floating plastics material P coming from the washing container 2 to be subjected to a second separating action.

The first chamber 5 can be provided internally with further stirrer means 12 arranged for generating a turbulent action for detaching mechanically possible further contaminants C adhering to the pieces of plastics material P.

The first separating chamber 5 comprises below a second bottom portion 6 suitable for receiving a second fraction X2 of precipitating contaminants C.

The first separating chamber 5 can be provided with a respective removing device 14 of valve or pump type suitable for drawing periodically the second fraction X2 of contaminants C from the aforesaid second bottom portion 6. The second chamber 7 is shaped for receiving a third flow F3 of washing fluid W with floating plastics material P coming from the first chamber 5, to be subjected to a third separating action.

On the second chamber 7 an outlet port 1 1 is obtained through which an outgoing flow F _OUT of washing fluid W with processed plastics material P' is evacuated by overflowing.

The apparatus 1 is provided with rotating means 9 configured for facilitating the advancement of the plastics material P in a floating condition from the first chamber 5 to the second chamber 7 and from the second chamber 7 to the outlet port 1 1.

The rotating means in particular comprises a plurality of roller or drum elements 9 with a horizontal axis, arranged transversely to the advancement path of the floating plastics material P.

The roller elements 9 are distributed evenly along the longitudinal dimension D _L of the separating tank Vs.

The roller elements 9 comprise a plurality of baffles 10 that, in rotation, penetrates slightly below the free surface L to push the floating plastics material P along the advancement path. The apparatus 1 is provided with a conveying unit Gc arranged for advancing the third flow F3 from the first chamber 5 to the second chamber 7.

The conveying unit Gc comprises disaggregating-propelling means 15 configured for disaggregating the floating agglomerates of plastics material P and for pushing the third flow F3 by force downwards inside the second chamber 7 to separate further a third fraction X3 of the contaminants C from the plastics material P.

The disaggregating-propelling means, more precisely, comprises a plurality of screw conveying units 15 that are rotatable around rotation axes A _R that are tilted with respect to an axis that is vertical and drivable by respective motors 18.

The screw conveying units 15 are contained in respective conduits 16 that protrude inside the second chamber 7. The screw conveying units 15 and the respective conduits 16 are distributed along an entire width dimension Dw of the separating tank Vs, so as to define, astride the first chamber 5 and the second chamber 7, an obligatory transit front for the third flow F3 of water and plastics material P. The apparatus 1 comprises drawing and recirculating means 17 suitable for drawing, below the separating tank Vs, a recirculation flow F _R comprising washing fluid W and precipitated contaminants C, and a screen unit Us suitable for receiving the aforesaid recirculation flow F _R to retain the contaminants C thereof and return the washing fluid W to the separating tank Vs.

The drawing and recirculating means 17 comprises a variable flowrate pump 19 and a recirculation circuit 20 that extends from a bottom zone of the separating tank Vs to an upstream zone 21 placed above the screen unit Us, and from a downstream zone 22 of the screen unit Us to a summit zone 23 placed above the separating tank Vs.

In particular, the recirculation circuit 20 comprises a first conduit 20A that extends from the third bottom portion 8 to the upstream zone 21, and a return conduit 20B that protrudes from the downstream zone 22 of the screen unit Us to the aforesaid summit zone 23.

With the help of the block diagram of figure 7, the washing and separating method according to the invention is disclosed, which is actuated by the apparatus 1 that has just been disclosed.

The plastics material P coming from pre-washing and milling of post-consumption plastics waste, which waste is reduced into small pieces (dimensions from a few mm to a few cm) and containing contaminants C, is loaded together with an incoming flow FI of washing fluid W, such as water with possible additives, inside the washing container 2 (block S I).

Inside the container 2 there is a first separation (block S2), with precipitation of a first fraction XI of the contaminants C onto the first bottom portion 4 and transfer of a second flow F2 of water W with plastics material to the first separating chamber 5 (block S4).

The first fraction XI of the contaminants C deposited on the first bottom portion 4 is evacuated periodically by the removing device 13 of valve or pump type (block S3).

During the process, the roller or drum elements 9 are driven, at a rotation speed that is suitable for advancing the plastics material P, maintaining the plastics material P inside the washing container 2 and inside the separating tank VS for the time that is necessary to obtain the desired degree of purity and decontamination.

The incoming F _IN and outgoing F _0UT flows are adjusted according to the required degree of "refresh" for the washing fluid W.

The right degree of "refresh" is determined by taking account of both the degree of purity and decontamination aimed for and the specific economy needs to be met.

The speed of the roller or drum elements 9 can be adjusted according to the incoming/outgoing fluid flowrates and the degree of purity that it is desired to obtain for the processed plastics material P.

In the case of operation with a high degree of change of the washing fluid W, thus with high inlet and outlet flowrates and strong overflow effect, the roller elements 9 act to slow the flow of outgoing plastics material with respect to the outgoing flow of fluid W, contrasting the dragging hydrodynamic action of the fluid and gradually enabling the plastics material P to advance from one chamber to the next chamber to the outlet port 11. In the case of operation with reduced inlet and outlet flowrates of the fluid W, and thus less overflow and dragging effect, the roller elements 9 perform a dragging effect that helps the plastics material to advance to the outlet port 11.

Inside the first chamber 5, a second fraction X2 of the contaminants precipitates that can be periodically eliminated by the removing device 13 of valve or pump type

(block S5).

The plastics material P washed further is transferred (block S6) from the first chamber 5 to the second chamber 6 by the conveying unit Gc disclosed above. The screw conveying units 15, which is rotatable at rotation speeds that are settable from about 100 rpm to about 150 rpm, on the basis of specific process needs and of the features of the material to be processed, act to break up the floating agglomerates of plastics material that inevitably tend to form during the process. The blocks of floating plastics material are vigorously disaggregated and opened up, and are propelled with force to a depth in the second chamber 7, facilitating the depositing of the contaminants C on the bottom whereas the plastics material with a lesser specific weight rise to the surface to be then evacuated by overflowing from the outlet port 11.

The agglomerates of floating plastics material, owing to the intense action of the screw conveying units 15, are reduced into single pieces (so-called "flakes" or "chips") which can benefit from a larger contact surface with the washing fluid, with advantages from the point of view of the degree of cleanliness that is achievable. Naturally, this enables greater quantities of plastics material P to be processed with the same quantity of water used, or vice versa, it is possible to reduce the quantity of water necessary for processing appropriately a certain volume of plastics material P. In all cases, the resulting economic advantage is evident.

The block S7 shows the washing fluid W drawing, filtering and recirculating step.

The variable flowrate pump 19 draws from the bottom of the separating tank (in this case from the third bottom portion 8 of the second separating chamber 7) the recirculating flow F _R , contributing to regulating the separating efficiency of the material with density that is also very near that of the washing fluid used.

The recirculating flow F _R , containing the third fraction X3 of the contaminants, is sent to the screen unit Us, which is made to vibrate.

The screen unit Us retains the contaminants C whereas the filtered fluid W is returned, by the return conduit 20B, inside the separating tank VS. Owing to this configuration that ensures a constant elimination of the contaminants C from the washing bath, thus maintaining the quality of the washing fluid W high, the water consumption necessary for the washing process is reduced significantly. From what has been disclosed and shown in the drawings, it is clear that the method and the washing and separating apparatus according to the invention achieve the set objects successfully. The method and the apparatus disclosed above enable high levels of purity to be easily obtained in the recovery plastics material in reduced process time, owing to the immediate continuous removal of the contaminants C from the washing container 2 and from the chambers 5 and 7 of the separating tank Vs. Owing to the fragmentation of the floating "rafts" of plastics material P performed by the screw conveying units 15, there is a significant increase in the efficacy of opening, washing and separation of the single pieces of plastics material P from the contaminants. Propelling water and plastics material downwards promotes depositing of the contaminants C on the bottom of the tank Vs, whereas the pumping action of the pump 19, combined synergically with the filtering action of the screen unit Us, ensures constant and continuous removal of the contaminants C, maintaining the washing bath in excellent operating conditions.

The objects are thus achieved of providing a solution that is functionally and constructively simple but is able to reduce general process costs and ensure great efficiency in separating contaminants from plastics materials to be recycled. It is understood that what has been said and shown with reference to the attached drawings has been given merely by way of illustration of the general features of the method and of the washing and separating apparatus; thus other modifications or variations can be made to the method, to the entire apparatus, or parts thereof, whilst remaining within the context of the claims. In particular, the geometric conformation, dimensions, position and materials that make up one or several parts of the washing apparatus can be selected and/or optimized suitably on the basis of specific operating needs and materials to be processed.