CONTINUOUS FEEDING DEVICE FOR A PLASTIC PYROLYSIS SYSTEM

Abstract

The present invention relates to a fuel production system by pyrolysis from shredded plastics, of the type comprising a reactor fed with molten plastics by a feed device (1b), and a distillation column, the feed device (1b) being heated by the circulation of a heat transfer fluid. This system is characterized in that the distillation column is connected to the feed device (1b) by an inlet duct (18b) which recovers the waxes produced during distillation in the distillation column and circulates them as a heat transfer fluid in said feed device (1b). Figure for the abstract: Fig. 5

Description

Title of the invention: Continuous feeding device for a plastics pyrolysis system

[0001] The present invention relates to a device for continuously feeding a system for the pyrolysis treatment of plastic materials with a view to their transformation into fuel and in particular into diesel.

[0002] Numerous devices are known for treating plastic materials by pyrolysis, but these devices have the disadvantage of being complex to implement and having relatively low yields.

[0003] Furthermore, from application FR 1904370 in the name of the EARTHWAKE Association, a system for treating plastic materials is known in which the latter undergo degradation by pyrolysis and, depending on the specific conditions of this treatment, this process makes it possible to achieve yields that are hitherto unequalled since, from, for example, 100 kg of polyethylene waste, it makes it possible to produce 70 kg of diesel, 15 kg of gasoline and a sufficient quantity of methane to provide the energy necessary for the operation of this system.

[0004] It is understood that it is interesting to operate such a system continuously.

[0005] A first difficulty arises from the fact that a continuous supply must be carried out without any admission of air into the reactor of the system in operation, otherwise there is a risk of the latter exploding.

[0006] A second difficulty arises from the fact that it is also imperative that the vapors cannot escape from the reactor, otherwise there is a risk of their ignition.

[0007] The present invention aims to provide a means for ensuring continuous operation of this type of feed device, without any admission of air into the reactor or any exit of vapors from the latter.

[0008] The present invention thus relates to a device for supplying molten plastic elements to a reactor of a fuel production system by pyrolysis of these plastic materials, using a distillation column, this device being traversed by a heat transfer fluid, characterized in that this fluid is constituted by the waxes supplied by the distillation column.

[0009] In this text, wax will be understood to mean the product forming the heavy fraction at the bottom of the distillation column.

[0010] More precisely, this feeding device will be characterized in that:

[0011] - it comprises a set of two coaxial metal tubes, namely a tube external and an internal tube which form between them a circulation volume closed at its two ends,

[0012] - it comprises a central and coaxial tube which is arranged inside the internal tube,

[0013] - the plastic elements are admitted at one end, called the end proximal, and circulate in the volume between the internal tube and the central tube to exit through the opposite end, called the distal end,

[0014] - the proximal end of the circulation volume is in communication with the distal end of the internal volume of the central tube by a conduit which is at least partly external,

[0015] - the proximal end of the internal volume of the central tube is in communication with outside through an outlet duct,

[0016] - it comprises a wax intake duct in communication with the end distal to the circulation volume.

[0017] In one embodiment of the invention, the above-mentioned outlet duct may extend partly inside the central tube.

[0018] In one embodiment of the invention, the conduit for connecting the proximal end of the circulation volume with the distal end of the internal volume of the central tube passes through the central tube, substantially in its middle, as well as the external and internal tubes, to extend axially in the latter towards its distal end and to be interrupted at a short distance from a bottom thereof.

[0019] In another embodiment, the conduit for connecting the proximal end of the circulation volume with the distal end of the internal volume of the central tube passes through, substantially at its distal end, the external and internal tubes, to open into the bottom, or distal end, of the central tube.

[0020] The feed device may comprise an axial conveying screw whose proximal end will be fed with crushed plastic materials and which will be driven in rotation by a motor equipped with means for managing its rotation speed and which will feed crushed plastic materials to the volume between the internal tube and the central tube.

[0021] The diameter of the external tube may be between 80 mm and 200 mm and preferably be around 170 mm.

[0022] The diameter of the internal tube may be between 50 mm and 160 mm and preferably be around 140 mm.

[0023] The diameter of the central tube may be between 20 mm and 100 mm and preferably be around 60 mm.

[0024] In addition, the exchange surface area between the walls carrying the heat transfer fluid and the plastic materials to be melted may be between 0.4 m2 and 1.5 m2 and preferably be close to 1 m2.

[0025] According to the invention, a helical turn may be arranged over the entire height of the annular space between the outer tube and the inner tube, this turn being joined to the outer surface of said tubes.

[0026] In one embodiment of the invention, the distal end of the supply device may be provided with a valve.

[0027] The present invention also relates to a system for producing fuel by pyrolysis from crushed plastic materials comprising a distillation column associated with a reactor and a device for supplying said reactor with said crushed plastic materials, comprising means for melting the latter as described previously, said melting means will comprise a circuit conveying a heat transfer fluid consisting of waxes recovered at the outlet of the lower stage of the distillation column.

[0028] This fuel production system may comprise means for loading the feed device comprising means for grinding the plastic materials and means for blowing into said device for feeding the ground plastic materials.

[0029] Embodiments of the present invention will be described below, by way of non-limiting example, with reference to the appended drawing in which:

[0030] [Fig-1] is a schematic principle view of a production facility for fuel by pyrolysis of plastic materials comprising a supply device according to the invention,

[0031] [Fig.2] is a vertical and diametrical sectional view of a first mode of implementation implementation of the feeding device according to the invention,

[0032] [Fig.3] is a schematic principle view of the installation according to [Fig.l], supplemented by means of grinding plastic materials,

[0033] [Fig.4] is a vertical and diametrical sectional view of a second mode of implementation implementation of the feeding device according to the invention,

[0034] [Fig.5] is a vertical and diametrical sectional view of a third mode of implementation implementation of the feeding device according to the invention,

[0035] [Fig.6] is a perspective view of the feeding device shown in the [Fig.5].

[0036] [Fig.l] shows a schematic diagram of a feed device according to the invention in the context of its essential use, namely the continuous feed of molten plastic materials without the supply of oxygen to a reactor belonging to a system ensuring the transformation by pyrolysis of said plastic materials into fuels and in particular diesel.

[0037] In this diagram, the feed device 1 is arranged close to a reactor 3 to which it delivers plastic materials ground in the molten state, this reactor 3 being heated at its lower part by a gas ramp 4 which is capable of bringing its internal temperature to a value necessary to ensure the pyrolysis of the plastic materials introduced, in particular of the order of 450°C. This reactor ensures the operation of a distillation column 5 from which the distillates are recovered in the form of diesel, gasoline and methane.

[0038] According to the invention, the base of the distillation column 5 is joined to the base of the feed device 1 by an inlet conduit 7 which recovers the “wax” produced during distillation in the column 5 and which is usually returned to the latter after having been cooled, this arrangement being explained below. Furthermore, a second conduit 9 recovers the reflux of the wax at the bottom of the column 5 to return it to the reactor 3.

[0039] The feed device 1 receives at its upper part, in a hopper 10, plastic materials in ground or crushed form and delivers them at its lower part to the reactor 3 after having been heated so that they are admitted into the reactor 3 in a pasty molten form, this feeding of the reactor being done under the effect of their simple weight.

[0040] As shown in [Fig.2], the supply device 1 comprises several concentric vertical tubes. First of all, a pair of tubes close to each other, namely an external tube 11 with a diameter D of the order of 170 mm and an internal tube 12 with a diameter d of the order of 140 mm. These two tubes are closed at their upper part and end at their lower part with a double convergent 13, with a conicity of the order of 40%, which is also closed at its base so that the volume between the external 11 and internal 12 tubes forms a circulation volume V, making it possible to ensure the passage of a heat transfer liquid as explained below.

[0041] The two tubes 11 and 12 terminate at their upper part in a flange 14 which allows them to be connected to a device supplying plastic chips, in particular the hopper 10, as explained below, and at their lower part in a flange 16 which allows the outlet of the supply device 1 to be connected to the reactor 3.

[0042] The volume between the two tubes 11 and 12 which form the double convergent 13 is in communication with a horizontal conduit 18 provided with a connecting flange 20 which allows it to be connected, via the conduit 7, to the wax outlet of the distillation column 5. It is understood that thus the wax penetrates, as heat transfer fluid, into the circulation volume V between the external 11 and internal 12 tubes.

[0043] The feed device 1 also comprises an axial tube 22 which extends over the entire length of the tubes 11 and 12, i.e. from the upper flange 14 to a distance close to the lower outlet, substantially up to halfway up the double convergent 13 and which ends in a convergent 23 and is closed at its upper part by a shutter 24 and at its lower part by a bottom 25.

[0044] In order to allow passage of the heat transfer fluid inside the circulation volume V defined by the tubes 11 and 12, the upper part of said circulation volume V is connected to a conduit 26 external to the supply device, and of smaller diameter than the tube 22. This conduit descends substantially to mid-height of said tube 22 then passes through the latter as well as the tubes 11 and 12 to extend axially downwards inside the tube 22 to near its bottom 25.

[0045] Furthermore, another axial conduit 28 of the same diameter as the conduit 26 originates at the upper part of the tube 22, descends inside the latter and emerges horizontally from the feed device, substantially in the middle of the latter after having passed through the tube 22 and the tubes 11 and 12. This outlet conduit ends with a flange 30 which allows it to be connected by a conduit 32 to the distillation column 5 with the interposition of an exchanger 8 allowing the cooling of the wax to be completed if necessary.

[0046] In the embodiment described herein, the supply of plastic chips to the feed device 1 according to the invention is ensured, as shown schematically in [Fig. 3], by a grinder 34 into which the plastic elements to be treated are introduced, such as for example bottles, which is associated with a propulsion device, such as for example a fan 36, which propels the plastic chips, via a tube 38, into the hopper 10 whose outlet is in communication with the inlet of the feed device 1 via its connecting flange 14. A vent 40 is provided to relieve pressure from the system in the event of overpressure generated by the fan 36.

[0047] Under these conditions, the operation of the supply device 1 according to the invention is established as described below.

[0048] The plastic shavings are admitted through the so-called proximal end of the device via the hopper 10 into the annular cross-section space between the internal tube 12 and the axial tube 22 where they are heated both on the internal surface of the internal tube 12 and on the external surface of the axial tube 22. These two surfaces thus constitute the exchange surfaces of the feed device, as explained below.

[0049] The plastic materials are melted during the passage through the device and exit from it through its so-called distal end, i.e. through the double convergent 13, from which they are delivered to the reactor 3.

[0050] The waxes coming from the distillation column 5, which constitute the heat transfer fluid, are introduced through the conduit 18 and circulate in the circulation volume V comprised between the walls of the outer 11 and inner 12 tubes to exit at the top of this volume through the conduit 26 from which they are directed by the latter inside the first axial tube 22 to exit the conduit 26 and rise in the axial tube 22 to the top of the latter where they enter the second axial conduit 28 and exit the feed device at the flange 30 to return to the distillation column 5 after passing through the exchanger 8 intended to cool them to a temperature preferably comprised between 220°C and 300°C and in particular of the order of 270°C. The circuit traveled by the waxes inside the feed device 1 is shown in [Fig.2] by continuous line arrows, while the path taken by plastic materials is shown by arrows in bold dotted lines.

[0051] The use of wax as a heat transfer fluid is particularly interesting from the point of view of energy saving because, on the one hand, a heat transfer fluid is used which does not need to be heated since it leaves the distillation column at a temperature sufficient to melt the plastics and, on the other hand, the wax used which should in any case be cooled before returning to the distillation column 5 are cooled here, at least in part, due to the quantity of heat which they have given up to ensure the heating and melting of the plastics.

[0052] It was found by the applicant that by using wax as a heat transfer fluid and by providing the feed device with an exchange surface of 1 m2, it was able to supply the reactor 3 with a quantity of plastic materials in the molten state of the order of 40 kg per hour.

[0053] In one embodiment of the present invention, the annular space between the outer tube 11 and the inner tube 12 receives a helical turn, not shown in the drawing, which extends from the top to the bottom of this space and which connects the facing surfaces of these two tubes 11 and 12. This turn makes it possible to force the heat transfer fluid to follow a helical path, which has the effect of improving the heat exchanges between the heat transfer fluid and the inner wall 12 and the axial tube 22 with which it is in contact and which ensure the heating of the plastic materials.

[0054] This helical coil will be fixed to the internal wall of the external tube 11 and the external wall of the internal tube 12 in particular by welding means. The cross-section of this coil may be circular or, preferably, rectangular.

[0055] Furthermore, in order to avoid heat losses between the external tube 11 and the exterior of the supply device 1, the external wall of the external tube 11 as well as the external conduit 13 can advantageously be insulated. For reasons of clarity of the drawing this insulation is not shown in the figures.

[0056] As shown in Figures 1 and 3, the outlet of the molten plastic material which is introduced into the reactor 3 can be closed at its distal part by a valve 21, which makes it possible, when the system is stopped, to maintain the tightness of the reactor by preventing the entry of air into it and also preventing the exit of vapors from this reactor.

[0057] The present invention is particularly interesting in that it makes it possible to deliver the molten plastic material to the reactor 3 of a unit for transforming plastic materials into fuel as shown schematically in [Fig. 1], without, on the one hand, there being an input of oxygen into the reactor which could cause it to explode and, on the other hand, without there being an exit of vapors from this same reactor which could risk catching fire on contact with the ambient air.

[0058] Indeed, if we consider the path of the plastic materials from the proximal end of the feed device 1 (i.e. the top of the latter in the present example) to the distal end of the latter (i.e. the bottom in the present example) we see that at the level of the hopper 10 the plastic materials are in the state of chips, therefore in a state where air is admitted between them and that, progressively when descending into it, these plastic materials leave their rigid state to progressively pass into the molten state. Under these conditions, it is understood that when these plastic materials pass into the molten state, the remaining air bubbles will be expelled towards the top of the mixture then towards the outside of the feed device.

[0059] The present embodiment is more interesting in that the conduits 18 and 28 through which the wax enters and exits the device respectively by crossing the path taken by the plastic materials are respectively distant from the inlet and the outlet of the device, which makes it possible to avoid the formation of obstructive plugs at these levels.

[0060] [Fig.4] shows a second example of implementation of a continuous feed device according to the invention.

[0061] In this example, the elements providing the same function as in the first example have retained the same numerical references with the addition of an index a.

[0062] Like the previous one, this feed device 1a operates vertically and comprises two coaxial tubes 11a and 12a ending at their base in a double convergent 13a and which are closed at their upper part and at their lower part so as to form a circulation volume V a. The latter is in communication with a conduit 18a through which the waxes ensuring the heating of the device are admitted. It also comprises an axial internal tube 22a which extends substantially over the entire the length of tubes 11a and 12a, from the proximal end of the device to its distal end, and which is closed at its upper part.

[0063] This tube 22a opens at its base onto a conduit 26a which horizontally crosses the tubes 11a and 12a to extend outside the device to the upper or proximal part of the latter where it opens into the circulation volume V a.

[0064] As in the previous example, the plastic materials are admitted to the upper, or proximal, part of the device in the hopper 10a and descend by gravity into the annular cross-section space between the tubes 22a and 12a.

[0065] The heating waxes which are admitted through the conduit 18a enter the circulation volume V a and rise in the latter to exit at the top through the conduit 26a and move therein towards the base of the axial tube 22a in which they rise to exit through the conduit 28a and return to the distillation column through the conduit 32.

[0066] In this embodiment, it is understood that the plastic materials are here subjected to a heating gradient increasing from top to bottom. Such an embodiment is interesting in that it is easier and faster to construct.

[0067] Figures 5 and 6 show a third embodiment of the present invention, in which the crushed plastic materials are no longer fed by gravity.

[0068] In this example, the elements providing the same function as in the previous examples have retained the same numerical references with the addition of an index b.

[0069] The device 1b with a horizontal longitudinal axis comprises two coaxial tubes 11b and 12b ending in a double convergent 13b and forming between them a circulation volume V h.

[0070] It also comprises an axial tube 22b closed at its two ends which extends substantially from the middle of the convergent 13b to approximately half the length of the tubes 11b and 12b.

[0071] It also comprises a conduit 26b and a conduit 28b which are arranged functionally as well as the respective conduits 26 and 28 of the first example.

[0072] As mentioned previously, in this embodiment, the plastic shavings are not fed by gravity but mechanically. To do this, the flange 14b arranged at the inlet of the tubes 11b and 12b is connected to a flange 44 of a tubular body 46 containing an endless conveyor screw 48 arranged on an axis 50 which is driven in rotation by a motor 52 whose rotation speed is controlled by servo means 54. The plastic materials enter the body 46 at the proximal end of the device via a hopper 10b and their exit is at its distal end via the convergent 13b.

[0073] This device, as well as that described with regard to [Fig.4], may comprise in the annular cross-section space between its external wall 11b and its internal wall 12b a helical coil making it possible to promote heat exchanges.

[0074] Such an implementation method is interesting in that it allows the quality of the plastic materials that it accepts to be taken into account. Thus, depending on the hardness of the latter, the device allows the speed with which they move inside it to be adjusted and controlled, by adjusting the rotation speed of the conveying screw 48 using the servo-control means 54. Thus, for resistant plastic materials, a lower rotation speed will be adjusted than for less resistant plastic materials.

[0075] Furthermore, in this embodiment, the power supply device is more easily accommodated when its location is limited in terms of height, which is particularly the case when, for example, it is desired to place it in a container.

Claims

Claims

1. System for producing fuel by pyrolysis from crushed plastic materials, of the type comprising a reactor (3) supplied with molten plastic materials by a feed device (1, 1a, 1b), and a distillation column (5), the feed device (1, 1a, 1b) being heated by the circulation of a heat transfer fluid, characterized in that the distillation column (5) is in communication with the feed device (1, 1a, 1b) by an inlet duct (7, 18, 18a, 18b) which recovers the waxes produced during distillation in the distillation column (5) to circulate them as heat transfer fluid in said feed device (1, 1a, 1b).

2. Fuel production system according to claim 1, characterized in that it comprises means for loading the feed device (1) comprising means for grinding (34) the plastic materials and means for blowing (36) the ground plastic materials into said feed device (1).

3. Fuel production system according to claim 1 or 2, characterized in that the supply device comprises: - a set of two coaxial metal tubes, namely an outer tube (11, 11a, 11b) and an inner tube (12, 12a, 12b) which form between them a circulation volume (V, Va, Vb) closed at its two ends, - a central and coaxial tube (22, 22a, 22b) which is arranged inside the inner tube (12, 12a, 12b), the plastic materials being admitted at one end, called the proximal end, and circulating in the volume between the inner tube (12, 12a, 12b) and the central tube (22, 22a, 22b), to exit through the opposite end, called the distal end, the proximal end of the circulation volume (V, Va, Vb) being in communication with the distal end of the internal volume of the central tube (22, 22a, 22b) by a conduit (26, 26a, 26b) at least partly external, the proximal end of the internal volume of the central tube (22,22a, 22b) being in communication with the outside by an outlet conduit (28, 28a, 28b), the supply device comprising a wax intake duct (18, 18a, 18b) in communication with the distal end of the circulation volume (V, Va, Vb).

4. Fuel production system according to claim 3, characterized in that the aforesaid outlet conduit (28, 28b) extends partly inside the central tube (22, 22b).

5. Fuel production system according to one of claims 3 or 4, characterized in that the conduit (26) for connecting the proximal end of the circulation volume (V) with the distal end of the internal volume of the central tube (22) passes through the latter substantially in its middle, as well as the external (11) and internal (12) tubes, to extend axially in the latter towards its distal end and to be interrupted at a short distance from a bottom (25) thereof.

6. Fuel production system according to claim 3, characterized in that the conduit (26a) for connecting the proximal end of the circulation volume (Va) with the distal end of the internal volume of the central tube (22a) passes, substantially at its distal end, through the external (11a) and internal (12a) tubes to open into the bottom, or distal end, of the central tube (22a).

7. Fuel production system according to one of claims 3 or 4, characterized in that it comprises an axial conveying screw (48) whose proximal end is supplied with crushed plastic materials which is driven in rotation by a motor (52) equipped with means (54) for managing its rotation speed and which circulates the crushed plastic materials in the volume between the internal tube (12b) and the central tube (22b).

8. Fuel production system according to any one of claims 3 to 7, characterized in that the diameter of the external tube (11, 11a, 11b) is between 80 mm and 200 mm and is preferably close to 170 mm.

9. Fuel production system according to any one of claims 3 to 8, characterized in that the diameter of the internal tube (12, 12a, 12b) is between 50 mm and 160 mm and is preferably close to 140 mm.

10. A fuel production system according to any one of claims 3 to 9, characterized in that the diameter of the tube central (22, 22a, 22b) is between 20 mm and 100 mm and is preferably close to 60 mm.

11. Fuel production system according to any one of claims 3 to 10, characterized in that the exchange surface between the walls of the tubes (11b, 12b) carrying the heat transfer fluid and the plastic materials to be melted is between 0.4 m2 and 1.5 m2 and is preferably close to 1 m2.

12. Fuel production system according to any one of claims 3 to 11, characterized in that a helical turn is arranged over the entire height of the annular space between the outer tube (11, 11a, 11b) and the inner tube (12, 12a, 12b), this turn being joined with the outer surface of said tubes.

13. Fuel production system according to any one of claims 3 to 12, characterized in that its distal end is provided with a valve (21).

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