WO2001008281A1

WO2001008281A1 - Method for recycling electric cables

Info

Publication number: WO2001008281A1
Application number: PCT/FR2000/002097
Authority: WO
Inventors: Hubert Juillet
Original assignee: Bright Co Ltd.
Priority date: 1999-07-23
Filing date: 2000-07-21
Publication date: 2001-02-01
Also published as: FR2796750A1

Abstract

The invention concerns a method for chemically stripping used electric cables with PVC insulating sheath, so as to recuperate the metal and the PVC transformed into film. First, the used electric cables (2) are introduced into an autoclave-cylinder (3) wherein is also fed a specific solvent as well as a shielding gas. After being mixed in said cylinder the PVC is dissolved in the solvent, leaving the electric cable completely stripped but not in any way split as a result of being crushed. The PVC solution is refined and purified through a centrifugal decanter (30), a filter press (34) and a compounder (37). The resulting refined solution is then conveyed to a calendering spreader (55) whereon it is transformed into a solid film. The solvent is extracted from said film by absorption in a gas and then restored by desorption and continuously recycled in the process.

Description

METHOD FOR RECYCLING ELECTRIC CABLES

The subject of the present invention is, as a new industrial product, a method of stripping used electrical cable, the sheath of which is made of PVC, for recycling. Polymer solutions are already known which cover in their industries a very broad spectrum of use, and this because they often constitute a necessary step during synthesis, purification such as fractionation, or precipitation but also because they have original macroscopic properties exploited in many fields of applications. The description of such systems is based on two essential themes:

Solubility and conformation, which are intimately linked to the concept of sequence. Indeed, the connection between adjacent elements constituting the macromolecular chain will cause a reduction in the degree of freedom of these elements and induce the existence of interactions at more or less long distance which will give polymer solutions quite specific properties. , compared to those of small molecules.

The process of mechanically stripping electrical cables is also known, a process which involves grinding or shredding followed by separation on a densimetric table of the metal fraction and the PVC fraction. This process has the following drawbacks:

Grinding or shredding are expensive operations due to their high energy consumption on the one hand and the wear of the material on the other hand. In addition, crushing and shredding have the undesirable effect of embedding metallic particles in the PVC decortica, and, in multi-stranded conductive cables, the pollution rate can amount to more than ten% by weight, d 'where an equivalent loss of metal. The densimetric table does not ensure an absolute separation of the two fractions, namely metal and PVC, at least if one wishes to work at acceptable rates. And in fine particles the presence of PVC in the metal can reach almost three% by weight, at least if sufficiently low passage speeds are desired. The presence of PVC in the metal being harmful for melting downstream of said metal, since it generates carbonates and chlorides which must be got rid of by different operations, each of which has its cost. On the other hand, the metal obtained by mechanical shelling is in the form of fragmented particles and it is always difficult, especially in small particles - to quickly realize the degree of purity of a considered fragmentation. 5 This difficulty in examining a batch of metal quickly leads to innumerable disputes between customers and suppliers, one claiming that his product is impeccable, the other claiming the opposite. Finally the husk released by this method is a product which poses many environmental problems and therefore it must be landfilled which results in a cost.

The present invention aims to remedy these drawbacks and relates to a chemical process for the stripping of the used electric cable with PVC sheath, which operates by dissolving said PVC in a solvent, then in restoring said PVC by absorption of said solvent in a gas followed by desorption of said solvent in a condenser, said solvent then being reused in the process. The present process has many advantages over the conventional mechanical method used universally today as well: 0 - it is low in energy consumption

- it returns a clean metal free of any pollution

- it restores a whole unmilled metal that is easy to inspect visually to ensure its quality

- it avoids the landfill of PVC with the costs that this entails

- it increases profitability due to the possible marketing of the PVC obtained

- it is part of the improvement of industrial processes with a view to reducing their effects on the environment 0 The invention will be better understood by referring to the description below as well as to the accompanying drawings, in which:

FIG. 1) is a view of the first phase of the cycle of the present process, namely the dissolution of the PVC sheaths. FIG. 2) is a view of the second phase of the cycle of the present process, namely the refining of the PVC solution.

FIG. 3) is a view of the third phase of the cycle of the present process, namely the separation of the solvent and the PVC.

Figure 4) is an overview of the installation according to the present method. 0 Thus in (1) a truck loaded with used electrical cables (2) dumps its load into a drum (3) through an opening (4) provided with an access door (5), said drum being an isolated autoclave and thermally regulated. Said drum ends with a shaft mounted on a geared motor 5 (6) in said shaft is provided a cavity in which are arranged four pipes leading to a rotary junction (7), said pipes extending beyond said rotary junction. Each of these pipes fulfills its own function, thus the pipe (8) is used to introduce the solvent or the solution into the drum (3), the pipe (9) is used to extract them.

The pipe (10) brings the gas into the drum and the pipe (11) is used to extract it.

A pump (12) is used to pump said gas and another pump (13) is used to pump said solution and said solvent. In (14) is shown a gas tank in the gaseous state, and in (15) a tank for the same gas but in the liquid state. In (16) is shown a gas pressure regulator.

In (17) is shown a tank containing fresh solvent and in (18) a tank containing solvent concentrated in PVC. In (19) are shown a series of valves. In (20) is represented the entry of the liquid gas. From (21) to (28) are shown intermediate boiler tanks containing a solution increasingly loaded with PVC, the tank (21) contains a new solvent and the tank (28) a very concentrated solution close to saturation.

In (29) is shown a pipe which brings the concentrated solution of

PVC contained in the tank (18) in a centrifugal decanter

(30).

Said settling tank has three outlets, one of which is an underflow (31) of the settling tank, the other is an overflow (32) of said settling tank while the third is a median outlet (33) of said settling tank, the latter is directed towards a filter press (34) which in turn has two outlets and one of which (35) is a drain outlet and the other (36) is used to bring the solution to a counter-rectifier (37).

Said counter-rectifier has two inputs, one of which (40) is a manual input and the other (41) an input connected to three ingredient tanks (40), (43), (44). In (45) is shown a pipe which goes towards the soaking tank of a coating machine in which a bubbling cylinder (47) soaks which moistens a transmitting cylinder (48) which in turn moistens a calender (49) whose surface is smooth or embossed as desired. A stripper cylinder (50) is placed against said calender at a distance from said transmitter cylinder.

A sealed tunnel (51) extends the coating, the PVC film (52) which leaves said tunnel passes over a deflection cylinder (53), then it is wound by a winder (54). Said coating machine and said tunnel are placed in a hermetically sealed enclosure (55) in which circulates against the current, a hot gas coming from the pipe (56).

The hot gas comes from an air heater (57) which is provided with a precise thermal regulator.

Said gas enters said tunnel through an opening (58) and exits through another opening (59), the outlet of the hot gases (59) is directed towards a condenser (60) cooled by the ambient air. Said condenser has an outlet connected to a pipe which is directed towards a decanter (61) the latter in turn has two outlets one of which (62) is connected to a pipe which is directed towards the tank (17) of solvent ( 9) of the method and the other of which is directed towards an air heater (57) whose outlet is directed towards the entrance of the tunnel (51). On the drum door (3) is also arranged a relief valve (63).

The installation according to the present method also comprises a programmable automaton which, by means of sensors and power relays, controls the whole of the control of said installation. Furthermore, all the tanks and reservoirs of the present process containing liquids are boilers.

The installation according to the present process operates as follows: The operation is cyclical and a cycle comprises several times, this is valid for the first phase of the process. Initially the drum (3) is brought into a vertical position and its access door (5) is open.

A dump truck then dumps a quantity of used electric cables into it, then said access door is closed. At this stage, the reservoirs (21) to (28) are filled with PVC solutions, the least concentrated of which is located on the far left (21) and the most concentrated of which is located on the right (18), this distribution being the does previous cycles of the process.

At the second stage of the cycle, the air present in the drum (3) is swept, and for this purpose compressed gas supplied by the pipe (10) is injected there. The valve (63) allows the evacuation of said ^air -

At the third stage of the cycle and when the air present in said drum has been completely removed, said drum is tilted (64).

At the fourth stage of the cycle, the PVC solvent contained in the tank (28) is introduced into said drum, it is the most concentrated solution of PVC of all the tanks (21) to (28).

This introduction is ensured by the pump (13).

At the fifth time of the cycle the drum (3) is rotated and it does not stop until the end of the cycle.

The bubbling of said used cable into said solution results in a dissolution of part of the PVC sheaths thereof, and -5-

this has the effect of further increasing the concentration of said solution.

After a certain mixing time, said solution is so concentrated that its solubilizing action is almost entirely stopped.

At the sixth time of the cycle, the drum is emptied of its liquid fraction, either of said concentrated solvent and the latter is then directed by gravity into the tank (18) or of that which contains the solution most charged with this first phase. of process. At the start of the seventh cycle time, the drum is empty of liquid, and the tank (28) also. The contents of the reservoir (27) are then injected into said drum, and the bubbling of the cable resumes. After a certain time the liquid content of said drum is emptied into the tank (28). The following times are repeated in the same way with each time the drum is emptied into a tank emptied at the previous time and the introduction into said drum of increasingly lean solution, coming from the tanks upstream. At the last time of the cycle, the filling is done with new solvent coming from the tank (17).

The cable which is in the drum is then completely rid of its PVC sheath, and it no longer has any trace of said PVC, its appearance being impeccable. At the last time of the cycle and after the last emptying of said drum, the latter stops rotating then it pivots to find itself in a vertical position, its access door located downwards.

Said door then opens and the stripped metal cable which is in the drum pours onto a truck (20) placed under it.

Once the cycle is complete, the truck then heads for the foundry. In parallel with the cycle described above, operations of a continuous nature take place which do not depend chronologically on said cycle.

Thus, the first phase of these operations consists in refining the PVC solution obtained with a view to its use for the manufacture of finished or semi-finished products.

The purpose of this refining is to remove all the impurities which could have mixed with said solution, then to readjust the latter, as to its color, as well as to the content of its various constituents such as talc, plasticizers, stabilizers. This refining comprises several stages, the first of which is intended to remove from the solution all the particles which are heavier, or those which are lighter than said solution.

This is done in a centrifugal decanter (30), so the solution arrives in the decanter through the pipe (29) and the centrifugation extracts the 5 heavy particles by an underflow (31) which go to the drain, and it also extracts light particles through the outlet (32) which also leaves for emptying.

At the outlet (35) of the decanter, the solution is perfectly pure, but to ensure total safety, this solution is directed to a filter press which still extracts any particles which may have escaped from the decanter.

Once purified of its impurities, the solution is adjusted and rectified with regard to some of its parameters.

This second operation is done by a counter. It is a mixer into which a quantity of said solution is introduced cyclically, then of the required ingredients.

The ingredients in question are stored in tanks (42)

(43) (44), connected to the counter by a pipe (41) and by means of valves (19). A manual input (40) is arranged on said counter for ad hoc adjustments.

Finally, a last operation of the present process consists in separating the solvent from the PVC while transforming the PVC into a film.

This operation is carried out on a coating machine, on the shell of which a liquid film of the solution is deposited.

The solvent of this film being absorbed in a gas, which has the effect of transforming said liquid film into a solid PVC film free of solvent.

The operation takes place as follows: The solution is directed to a tank (46) of the coating machine, this tank has a thermal regulation and a level regulator.

A bubbler cylinder (47) takes a quantity of solution from said tank. This is deposited by a transmitting cylinder (48) on an absorption grille (49), which also has thermal regulation.

This coating machine is placed under a bell and a strong current of hot gas scans its enclosure so that the solvent present in said enclosure is absorbed by said gas.

On said calender (49) a film is then formed, which is peeled off by the stripper cylinder (50), then said film passes through a tunnel (51) to restore all of the solvent that it still contains, and finally it leaves the tunnel and is returned to a winder (54) via a return cylinder (53).

The coil thus obtained is ready to be marketed. The hot gas in which the solvent has been absorbed is pumped to the condenser (60) where it is cooled thus causing the desorption of the solvent it contains, the latter is then collected in a settling tank (61), then it returns by gravity to the stock of new solvent (17) and is therefore recycled indefinitely, with the exception of process losses. The solvent according to the present process works in a closed cycle, and therefore it is never in contact with the atmosphere, and therefore does not cause any odor in the ambient air.

As for the gas, at the outlet of the condenser, stripped of its solvent then returns to the enclosure of the coating machine, after having been heated by the air heater (57), and a circuit is thus definitively ensured by this gas.

The various fluids which circulate in the installation according to the present process are, the service of the drum in solvent and solution, they are ensured by the piping (7) and (8).

The gas circulation in the absorption and desorption system is ensured by the piping (56) and (63).

The gas flow from the drum (3) is ensured by the piping

(10) and (11), connected to the piping (56) and (63) and it thus benefits from the desorption of the condenser (60) which makes it possible to remove any trace of solvent in said drum after the last time of each cycle, or before the opening of the door of said drum for its unloading.

The return of the desorbed solvent to the tank of new solvent is ensured by the piping (62).

The parameters of the present process are as follows:

- The raw material to be treated is used electrical cable, the insulation sheath of which is made of PVC, and the conductors of CU and AL or both. - the objectives are the separation of PVC and metals with a respectively high degree, and the transformation of said PVC into a thin film of adjustable thickness between 50 to 300 microns, directly marketable, and finally the restitution of a metal not altered and unfractionated. - the chemical formula of the chemical solvent is (C ₆ H ₁₂ O) 92% + (H ₂ O) 8%

- the boiling point of this solvent is 128 ° C

the absorption temperature in the gas of said solvent is 115 ° C.

the desorption temperature of said solvent for said gas is less than 25 ° C.

the temperature for dissolving said PVC in said solvent is 95 ° C.

- the pumping and storage temperature of said solution is 90 ° C - the absorption and desorption gas is: N _2l it is also used for inerting the interior volumes of the process

- the PVC of electric cables is conventional PVC, of formula H ₂ C = CHCI

- the maximum PVC temperature is limited to 95 ° C. - the overpressure of N ₂ in the installation is 150g / cm ² - the color to obtain PVC is a dark gray

- the color of the PVC in the counter is adjusted using white pigments and black pigments

- the duration of the time for dissolving the PVC in the solvent is 6 hours for the first time and 15 minutes for the last time

- the number of successive solutions in a cycle is 12

- the duration of a complete cycle is recommended over a 24-hour period.

In the present process it is easy to understand that the metal CU and AL obtained is of excellent chemical quality, since no aggressive agent has come to alter their state.

This, however, insofar as the required parameters have been respected.

For PVC, its passage to the dissolved state can raise questions as to its final quality.

However given the current knowledge in terms of polymer dissolution, and especially considering the original mode of dissolution implemented in the present process, it appears that the PVC thus recycled has not only the characteristics of the original PVC in many respects, but even exceeds the latter, in some of its performances. This is explained by the fact that the PVC compount, due to its dissolution undergoes a homogenization operation, in fact the different elements which compose it are more intimately in the presence of each other during the duration of the state dissolved. The extraction of said PVC by absorption in a gas makes it possible to carry out the separation and recycling of said solvent at relatively low temperatures, and in all cases below its boiling point.

As a result, the solvent does not undergo degradation due to the passage to a possible vapor phase, and its recycling can be considered thus ad infinitum, minus the minimum losses of the process. The present description is not exhaustive and constitutes only an example to which numerous modifications can be made, without however departing from its scope.

Claims

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1) Process for the treatment of electric cables whose sheath is made of PVC in order to separate said PVC from the metal contained in said characterized cable,

5 in that said method comprises chemical means which ensure said separation, and in that said chemical means are constituted by the placing in the fluid state of said PVC, and in that said fluid state of said PVC is obtained by its solubilization in a solvent, and in that said solubilization operates hot, and in that said solubilization operates in an autoclave, and in that said autoclave is placed under inert gas, and in that said autoclave is rotary and forms a drum. 5 2) Method according to claim 1) characterized in that said autoclave is filled and then drained several times during a process cycle, and in that the drained solutions are stored in intermediate tanks, 0 and in that said solutions stored in the intermediate tanks are reused in the counter-current process, and in that the complete cycle, due to said counter-current reuse of said solutions, releases at one end of said intermediate tanks, a concentrated solution of PVC, and at the other end a solution very poor in PVC, and in that the first step of each cycle is carried out with the most concentrated solution of PVC in order to saturate it, and in that the last step of each cycle is carried out with fresh solvent. 0 3) Method according to claims 1) and 2) characterized in that said saturated PVC solution undergoes a refining operation, and in that said refining operation consists in subjecting said solution to the action of a centrifugal decanter, 5 and in that said refining operation further consists in subjecting said solution to the action of a filter press, and in that said refining operation further consists in adjusting and rectifying said PVC solution by a passage in a counter where various additives are mixed and kneaded there. 0 4) Method according to claims 1) 2) and 3) characterized in that it 1 also comprises, -1 1 -

means for separating the two constituents of said saturated PVC solution, and in that said means are constituted by the absorption of said solvent from said solution in a gas, and in that said absorption is effected by transforming said solution into a film on a calender, by licking said gas, and in that said film formed on said calender is directed in a tunnel, and in that said licking takes place in this tunnel against the flow of the direction of the unwinding of said film, and in that once loaded by said absorption said solvent is. desorbed in a condenser, and in that said solvent collected in said condenser is then reintroduced into the process, and this indefinitely, and in that the PVC film thus obtained in the installation is wound in a coil.

5) Process according to claim 1) 2) 3) and 4) characterized in that the process parameters are: the separation of PVC and metals with a respective high degree, and the transformation of said PVC 0 into a thin film of an adjustable thickness between 50 to 300 microns, directly marketable, and finally the restitution of an unaltered and unfractionated metal, the chemical formula of the chemical solvent is

(C ₆ H ₁₂ 0) 92% + (H ₂ O) 8%, 5 the boiling temperature of this solvent is 128 ° C, the absorption temperature in the gas of said solvent is 115 ° C, the desorption temperature of said solvent for said gas is less than 25 ° C, the temperature for dissolving said PVC in said solvent is 0 to 95 ° C, the pumping and storage temperature for said solution is

90 ° C, the absorption and desorption gas is N ₂ , it is also used for inerting the interior volumes of the process, 5 the PVC of electric cables is conventional PVC, of formula

H ₂ C = CHCI, the maximum temperature of PVC must be limited to 95 ° C, the removal of N ₂ in the installation is 150g / cm ^2, the color to obtain from PVC is a dark gray, 0 adjustment the color of the PVC in the counter is made using white pigments and black pigments, the duration of the time for dissolving the PVC in the solvent is

6 hours for the first time and 15 minutes for the last time, the number of successive solutions in a cycle is 12.45 hours the duration of a complete cycle is 24 hours.