SYSTEM FOR CLEANING METALLIC SCRAPS FROM ORGANIC COMPOUNDS

Abstract

An installation for melting metallic scraps, and particularly adapted for melting aluminium scraps, includes a system for cleaning the metallic scraps, and in particular for cleaning the scraps from organic compounds.

Claims

1. A system for cleaning metallic scraps from organic compounds comprising: a first chamber provided with an inlet for the scraps and a second chamber provided with an outlet for the scraps, a device for controlling the atmosphere in the first chamber and in the second chamber, the oxygen content in the second chamber being above the oxygen content in the first chamber; a temperature controller for heating the first chamber at a temperature adapted to provide pyrolysis of at least a part of the organic compounds and for heating the second chamber at a temperature adapted to provide burning of at least a part of residues of the pyrolysis; a conveying assembly for conveying scraps from the inlet for scraps in the first chamber toward the outlet for scraps in the second chamber; the conveying assembly comprising: a first linear guiding mechanism for conveying substantially longitudinally scraps in the first chamber and a second linear guiding mechanism for conveying substantially longitudinally scraps in the second chamber, a transversal chute between the first chamber and the second chamber, wherein the scraps freely fall from the first chamber in the second chamber; a driving device for driving the first linear guiding mechanism and the second linear guiding mechanism at adjustable speed, the driving device being capable of driving the first guiding mechanism at a different speed than the second linear guiding mechanism, so that the thickness of the layer of scraps in the second chamber is adjustable with regards to the thickness of the layer of scraps in the first chamber.

2. A system according to claim 1, wherein at least one of the first linear guiding mechanism and the second linear guiding mechanism comprises an endless conveying belt upon which the scraps can be conveyed.

3. A system according to claim 1, wherein at least one of the first linear guiding mechanism and the second linear guiding mechanism comprises vibrating plates upon which the scraps can be conveyed.

4. A system according to claim 1, comprising a height adjustment device for adjusting the transversal dimension of the chute.

5. A system according to claim 1, wherein the device for controlling the atmosphere comprises a gases recirculation system comprising an outlet for the gases in the first chamber connected to an inlet for the gases in the second chamber, the temperature controller controlling the temperature and the a device for controlling the atmosphere controlling the content of oxygen of the gases before they enter the second chamber.

6. A system according to claim 1, comprising thickness sensors for sensing the thickness of the scraps on the first linear guiding mechanism and/or on the second linear guiding mechanism.

7. A system according to claim 1, wherein at least one of the first guiding mechanism and the second guiding mechanism is gas-permeable.

8. A system according to claim 1, especially dedicated to the cleaning of aluminium scraps.

9. A system according to claim 1, further comprising a melting furnace connected to the outlet for the scraps of the system for cleaning, so that the scraps flow from the second chamber of the system for cleaning into the melting furnace.

10. A system according to claim 8, further comprising a scraps crusher connected to the inlet for scraps of the system for cleaning, so that the scraps are crushed before entering the first chamber.

11. A method for cleaning metallic scraps by use of a system for cleaning according any of claim 1, comprising: feeding the scraps by an inlet for the scraps in the first chamber of the system for cleaning; conveying the scraps substantially longitudinally through the first chamber; falling of the scraps in a second chamber along a chute; conveying the scraps substantially longitudinally through the second chamber; removing the scraps by an outlet for the scraps; the method being characterized in that it comprises: determining a target thickness for the scraps on a linear guiding mechanism in the second chamber; and adjusting the speed of first linear guiding mechanism in the first chamber and/or of the second linear guiding mechanism in order to reach the target thickness on the second linear guiding mechanism.

12. A method according to claim 11, wherein the target thickness for the scraps on the second linear guiding mechanism is below the thickness of the scraps on the first linear guiding mechanism.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Other effects and advantages will appear in the following description of preferred embodiments accompanied with the drawings wherein.

[0040] FIG. 1 is a schematic representation of an installation for melting metallic scraps comprising a system for cleaning scraps according to a first embodiment.

[0041] FIG. 2 is similar to FIG. 1, with a system for cleaning metallic scraps according to a second embodiment.

[0042] FIG. 3 is a diagram illustrating the evolution of the rate of mass change (continuous line) and of the content of dioxygen (discontinuous line) depending on temperature in the system for cleaning metallic scraps of FIG. 1 or FIG. 2.

DETAILED DESCRIPTION

[0043] FIGS. 1 and 2 each illustrates schematically an embodiment of an installation 100 for the melting of metallic scraps, and more precisely particularly adapted for melting aluminium scraps. The installation 100 comprises a system 1 for cleaning the metallic scraps, and in particular for cleaning the scraps from organic compounds. The system 10 comprises: at least a first chamber 2 provided with an inlet 3 for the scraps and at least a second chamber 4 provided with an outlet 5 for the scraps, a device 6 for controlling the atmosphere in the first chamber 2 and in the second chamber 4, the oxygen content in the second chamber 4 being above the oxygen content in the first chamber 2; a temperature controller 7 for heating the first chamber 2 at a temperature adapted to provide pyrolysis of at least a part of the organic compounds and for heating the second chamber 4 at a temperature adapted to provide burning of at least a part of residues of the pyrolysis; a conveying assembly 8 for conveying scraps from the inlet 3 in the first chamber 2 toward the outlet 5 in the second chamber 4.

[0044] The conveying assembly 1 comprises at least: a first linear guiding mechanism 9 for conveying substantially longitudinally scraps in the first chamber 2 and a second linear guiding mechanism 10 for conveying substantially longitudinally scraps in the second chamber 4, a transversal chute 11 between the first chamber 2 and the second chamber 4, wherein the scraps freely fall from the first chamber 2 in the second chamber 4; a driving device 12 for driving the first linear guiding mechanism 9 and the second linear guiding mechanism 10 at adjustable speed, the driving device 12 being capable of driving the first guiding mechanism 9 at a different speed than the second linear guiding mechanism 10, so that the thickness of the layer of scraps in the second chamber 4 is adjustable with regards to the thickness of the layer of scraps in the first chamber 2.

[0045] More generally, the installation 100 also comprises a scraps supply, for instance from a feeder 101, connected to the inlet 3 for the scraps of the system 1. For instance, scraps come from consumer products, such as beverage cans, but also from building sector, such as aluminium profiles. If needed, in order to ensure an efficient treatment in the system 1 for cleaning, the installation 100 can comprises a crusher 102 upstream from the inlet 3 for the scraps in the system 1, so that the scraps are crushed to present an optimal size for the cleaning. By crusher, we refer here to any device able to reduce the initial size of the scraps. The installation 100 also comprises a melting furnace 103 connected to the outlet 5 for the scraps of the system 1, so that once the scraps are cleaned, they can be melted in the same installation, as required.

[0046] An embodiment of the operations will now be described with reference to FIG. 1 in particular.

[0047] The scraps fall from the inlet 3 for the scraps of the system 1 in the first chamber 2, onto the first linear guiding mechanism 9. According to the embodiment of the description, the first linear guiding mechanism 9 is an endless conveying belt, here after referred to as the first belt 9. The belt is preferentially, but not necessarily, gas-permeable. For instance, the belt is meshed.

[0048] The scraps are conveyed by the first belt 9 in a first substantially longitudinal direction, that is to say that the point where the scraps arrive on the first belt 9 is longitudinally shifted from the point where the scraps leave the first belt 9. Practically, the longitudinal direction corresponds to the horizontal direction.

[0049] We define here after a horizontal direction and a vertical direction by reference to the natural directions relatively to the force of gravity: a horizontal direction is a direction transverse to the force of gravity, the vertical direction being parallel to the force of gravity.

[0050] Alternatively, the first belt 9 can be inclined downward or upward, without impacting the operation of the system 1.

[0051] The scraps leave the first belt 9 at a longitudinal end of the first belt 9, where they fall freely along the transversal chute 11. More precisely, the chute is an area where the scraps move substantially transversally with no support, that is to say they move vertically downward, under the effect of the gravity on their mass. The scraps can be guided transversally partially along the chute 11. However, the scraps are at least free to fall transversally so that they undergo aeration, as it will be explained further here under.

[0052] The scraps fall from the first belt 9 along the chute 11 to the second chamber 4 on the second linear guiding mechanism 10. According to the described embodiment, the second linear guiding mechanism is an endless conveying belt, here after referred to as the second belt 10. The second belt 10 can present, but not necessarily, the same features as the first belt 9. According to the described embodiment, the second belt 10 convey the scraps in the same longitudinal direction as the first belt 9. In other words, the second belt 10 is transversally shifted from the first belt 9, and the scraps are conveyed in the same direction from the input 3 for scraps to the output 5 for scraps.

[0053] The transverse distance between the first belt 9 and the second belt 10 is adjustable. More precisely, the system 10 comprises a height adjusting device in order to adjust the transversal dimension of the chute 11. Accordingly, the time during when the scraps fall freely along the chute, and consequently the time of aeration and agitation of the scraps can be adjusted.

[0054] The scraps are conveyed by the second belt 10 to the outlet 5 for scraps, where they are for instance conveyed to the melting furnace 103.

[0055] The driving device 12 is set to control the speed of the first belt 9 that the scraps undergo a pyrolysis in the first chamber 2, and to control the speed of the second belt 10 so that the scraps undergo a char-removal treatment in the second chamber 4, as it will be explained further here under. The speed of each belt 9, 10 is adjusted in order to get a targeted residence time in each chamber. The speed of each belt can be adjusted independently from each other, so that the pyrolysis stage and the char-removal stage can be considered, in term of residence time, independently.

[0056] FIG. 3 illustrates schematically the rate of mass change of the scraps and the dioxygen level of oxygen in the gases in the system 10 for cleaning, depending on the temperature. In the pyrolysis stage, in the first chamber 4, the level of dioxygen should be as low as possible, even null if possible. When the temperature reaches around 350 C., the organic compounds volatilized, so that the rate of the mass change of the scraps increase to reach a first value. Hydrocarbons residues remain on the scraps. In the second chamber 1, during char-removal stage, the level of dioxygen is enough to provide combustion of the residues, so that the rate of the mass change increase to reach a second value, typically lower than the first value.

[0057] The system 1 also comprises a gases recirculation system, for recirculating the gases from an inlet 13 for gases in the second chamber 4 toward an outlet 14 for gases in the first chamber 2, and from the outlet 14 for gases toward the inlet 13 for gases. The device 6 for controlling the atmosphere comprises a dioxygen feeder in order to enrich the gases in dioxygen before they enter at the inlet 13 for the gases in the second chamber 4. More precisely, the gases circulate in a loop the device 6 for controlling the atmosphere is placed between the outlet 14 for gases and the inlet 13 for gases, according to the flow direction of the gases, so that the gases at the inlet 13 for gases contain dioxygen at a controlled level, adapted to provide char-removal in the second chamber 4, and to provide pyrolysis in the first chamber 2. More precisely, the level of dioxygen provided by the device 6 for controlling the atmosphere is adjusted so that nearly all the dioxygen is consumed in the second chamber 4 during char-removal, and so that the level of oxygen in the first chamber is nearly null, or as low as possible. Indeed, the char-removal stage is basically a combustion reaction, requiring the presence of dioxygen. On the contrary, the pyrolysis stage requires a level of dioxygen as low as possible. The gases circulation from the second chamber 4 toward the first chamber 2, with an initially controlled level of dioxygen, at counter-flow with the scraps, provides the required conditions in the first chamber 2 and the second chamber 4 for an efficient cleaning of the scraps.

[0058] The device 6 for controlling the atmosphere is also able to provide a control on the pressure of the gases before they enter the second chamber 4.

[0059] The speed of the second belt 10 can be adjusted advantageously with respect to the speed of the first belt 10 so that the thickness of the scraps on the second belt is below the thickness of the scraps on the first belt 9. Indeed, char-removal stage is basically a combustion reaction, requiring a contact between the gases rich in dioxygen and the scraps. The pyrolysis stage is basically an increase in temperature, and the contact between the scraps and the gases is not relevant. Then, the thickness on the second belt 10 should be advantageously as low as possible, with a compromise regarding production requirements. By adjusting the speed of the second belt 10 with respect to the speed of the first belt 9, the thickness of the scraps on the second belt is easily adjusted. In that event, the system 1 can comprises sensors for measuring the thickness of the scraps in each chamber 2, 4, and for adjusting the speed of each belt 9, 10 accordingly.

[0060] Moreover, the chute 11 between the first belt 9 and the second belt 11 provides an advantageous aeration and agitation of the scraps before they fall on the second belt. It has been observed that such aeration and agitation increase the efficiency of the cleaning. It is supposed that such aeration and agitation provide at least two effects:

[0061] First, the organic compounds volatilized during the pyrolysis stage could remain trapped in the layer of scraps on the first belt 9; when they fall along the chute 11, they are freed, so that they are eliminated from the scraps more efficiently; second, the scraps are aerated, no surface of the scraps being in contact with a support, so that most of the surface of each scrap is in contact with the gases, increasing the liberation of volatilized organic compounds and improving the contact with the gases for instance for finishing char-removal stage if dioxygen has not already been totally consumed in the second chamber 10; it results that the level of dioxygen in the first chamber 2 can be as low as possible.

[0062] Moreover, the temperature controller 7 comprises a burner 7a placed between the outlet 14 for gases and the inlet 13 for gases, and before the device 6 for controlling the atmosphere according to the flow direction of the gases, so that the gases exiting the system 1 enter the burner 7a where the volatilized organic compounds from the pyrolysis can be burnt. The gases, cleaned at least partially from the volatilized organic compounds, are consequently heated by the burning process in the burner, and can be sent back in the system 1, in the second chamber 4. In the event that the temperature of the gases after the burner 7a is not adapted for the char-removal in the second chamber 4, the temperature controller 7 can comprises a heat exchanger 7b.

[0063] For instance, if the temperature of the gases is too high after the burner 7a, and even after the dilution by dioxygen from the device 6 for controlling atmosphere, the heat exchanger 7b can advantageously cool the gases, and in the same time recover part of the heat.

[0064] The level of dioxygen and the temperature of the gases at the inlet 13 for gases depend in particular on the sizing of the system 1, and the required residence time in each chamber 2, 4. For instance, set points for dioxygen level and set points for temperature at the inlet 13 for gases and at the outlet 14 for gases can be determined, and the device 6 for controlling the atmosphere and the temperature controller 7 can be set accordingly. Temperature sensors and dioxygen measuring devices can be implemented in the system 10 in order to provide an increase control.

[0065] The gases can be vented by a fan 15 allowing the circulation of the gases. Part of the gases can be rejected to the atmosphere through a stack 16. A second heat exchanger 17 could be placed upstream to the stack 16 for heat recovery consideration. Alternatively, a cleaning device can also be implemented before releasing the gases to the atmosphere.

[0066] FIG. 2 illustrates another embodiment of the system 1 represented on FIG. 1 and as described here above. In this embodiment, all the other features being identical to those of the embodiment of FIG. 1, the conveying direction of the second belt 9 is contrary to the conveying direction of the first belt 9. Consequently, the second belt 10 extends under the first belt 9, so that the dimension in the longitudinal direction is reduced when compared with the embodiment of FIG. 1.

[0067] According to another embodiment, not represented, the system 1 for cleaning comprises three linear guiding mechanisms, that is to say, when compared to the embodiments of FIGS. 1 and 2, that a third linear guiding mechanism is implemented between the first linear guiding mechanism 9 and the second linear guiding mechanism 10. A chute, as the chute 11 already described, can be implemented between each linear guiding mechanism, so that the system 1 comprises two chutes. With a third, intermediate linear guiding mechanism, an intermediate zone can be created as a transition between the pyrolysis stage and the char-removal stage. The efficiency of the pyrolysis can be increased, as more dioxygen can be consumed in the intermediate zone. Moreover, by providing two chutes, the effects of agitation and aeration are also increased.

[0068] The linear guiding mechanisms could comprise any other mechanism than the endless belt, providing a linear displacement in the longitudinal direction with a control on the speed of displacement of the scraps. For instance, they could comprise vibrating plates or walking plates. The linear guiding mechanisms could also include the formation of a fluidized or semi-fluidized bed, favouring the contact between the scraps and the gases.