EP4256096A1

EP4256096A1 - Method for the recovery of aluminium from aluminium scrap, and multichamber melting furnace

Info

Publication number: EP4256096A1
Application number: EP21819852.1A
Authority: EP
Inventors: Rukiye GÜLTEKIN; Dominikus Schröder
Original assignee: LOI Thermprocess GmbH
Current assignee: LOI Thermprocess GmbH
Priority date: 2020-12-03
Filing date: 2021-11-26
Publication date: 2023-10-11
Also published as: MX2023006409A; DE102020132240A1; WO2022117466A1; US20240011122A1; CA3200561A1

Abstract

The invention relates to a method for the recovery of aluminium from aluminium scrap with adhering organic deposits in a multichamber melting furnace (1), at least comprising the following method steps: - batchwise charging of the hearth (7) of the scrap chamber (2) with aluminium scrap (6), - thermal pre-treatment of the aluminium scrap (6) in a scrap chamber (2) during a first pre-treatment phase at a specified first temperature and in an atmosphere which is substantially free of oxygen in order to transform the organic deposits adhering to the aluminium scrap into a pyrolysis gas, - thermal pre-treatment of the aluminium scrap (6) in the scrap chamber (2) during a second pre-treatment phase at a specified second temperature, wherein the scrap chamber (2) is heated up to the spontaneous ignition temperature of the pyrolysis gas, wherein at least one air stream (L) is provided in the scrap chamber (2) in order to produce an ignitable sub-stoichiometric pyrolysis-gas/combustion-air mixture, which is made to react in the scrap chamber (2) in a combustion process, and - transferring the atmosphere from the scrap chamber (2) to a post-combustion process. The invention also relates to a corresponding multichamber melting furnace.

Description

Process for the recovery of aluminum from aluminum scrap and multi-chamber melting furnace

The invention relates to a method for recovering aluminum from aluminum scrap that has organic adhesions, in a multi-chamber melting furnace, with a scrap chamber that is set up to receive melt, the scrap chamber having a batch loadable with the aluminum scrap hearth, which is above of the level (N) of the melt and wherein a loading door is arranged in the wall of the scrap chamber and with at least one heating chamber which is designed to receive melt and which has at least one combustion device, at least with the following process steps:

- Batch loading of the hearth (7) of the scrap chamber (2) with aluminum scrap (6),

- thermal pretreatment of the aluminum scrap (6) in the scrap chamber (2) during a first pretreatment phase at a predetermined first temperature and in an atmosphere free of oxygen in order to convert the organic adhesions on the aluminum scrap into a pyrolysis gas.

Furthermore, the invention relates to a multi-chamber melting furnace for the recovery of aluminum from aluminum scrap which has organic adhesions, comprising:

- a scrap chamber which is set up to receive melt, the scrap chamber having a hearth which can be loaded in batches with the aluminum scrap, which is located above the level (N) of the melt and a loading door is arranged in the wall of the scrap chamber, the scrap chamber is set up for the thermal pre-treatment of the aluminum scrap and wherein, during a first pre-treatment phase, at a predetermined first temperature in an atmosphere free of oxygen, the organic Adhesives on the aluminum scrap can be converted into a pyrolysis gas and

- At least one Hei zkammer, which is set up for receiving Schmel ze and has at least one combustion device.

A multi-chamber melting furnace is understood to mean a melting furnace system with a plurality of chambers that are separate from one another. The individual chambers can be spatially separated from one another or in a single furnace housing or be formed a common wall. A two-chamber furnace known per se has two chambers, specifically a scrap chamber into which aluminum scrap is introduced in batches for thermal pretreatment and a heating chamber for heating the melt located in the heating chamber.

The heat required for melting in both chambers is provided in the heating chamber by means of at least one combustion device. As a rule, several burners, in particular gas burners, are used. At least part of the heat required for the pre-treatment is introduced into the scrap chamber by a recirculating flow of melt and atmosphere exchange from the heating chamber.

The scrap aluminum can be scrap cans, for example. Scrap cans are either used aluminum beverage cans or return material from industrial production. However, the aluminum scrap can also be any other type of scrap that is to be melted, e.g. B. scrap in the form of shredder material, profiles or other returns.

Aluminum scrap is often contaminated or shows some organic contamination on the surface. The aluminum scrap can be contaminated with oils, greases, paints, coatings or other organic contaminants. the buildup, e.g. B. the coatings of beverage cans, usually consist of long-chain hydrocarbon compounds.

It is known from practice to subject aluminum scrap to a thermal pre-treatment in order to remove the buildup as far as possible. Due to its practical feasibility, thermal pre-treatment in the form of pyrolysis has become established.

During a first pre-treatment phase, at a predetermined first temperature in an atmosphere free of oxygen, i. H. where the oxygen content is so low that there is no free oxygen available for oxidizing aluminum, most of the organic buildup is pyrolyzed.

After the pre-treatment, however, the scrap still has organic adhesions on the surface, namely less volatile adhesions, such as e.g. B. in the form of elemental carbon. If these adhesions are introduced into the melting process in the heating chamber, the carbon reacts with the aluminum to form aluminum carbide. Residues of non-pyrolyzed adhesions react with the melt and lead to dross formation. This leads to metal loss.

In other words, interactions between organic buildup and the melt lead to high metal losses.

The object of the invention is accordingly to provide a remedy here and to create a possibility of avoiding dross formation during the recovery of aluminum from aluminum scrap in a multi-chamber melting furnace and of increasing the metal yield. This object is achieved by a method with the method steps according to claim 1 and a multi-chamber melting furnace with the features of claim 12.

The method according to the invention has at least the following steps:

- batchwise loading of the hearth of the scrap chamber with aluminum scrap,

- Thermal pre-treatment of the aluminum scrap in the scrap chamber during a first pre-treatment phase at a predetermined first temperature and in an atmosphere that is free of oxygen in order to convert the organic adhesions on the aluminum scrap into a pyrolysis gas,

- Thermal pre-treatment of the aluminum scrap in the scrap chamber during a second pre-treatment phase at a predetermined second temperature, the scrap chamber being heated to the self-ignition temperature of the pyrolysis gas, at least one air flow being provided in the scrap chamber in order to create an ignitable sub-stoichiometric pyrolysis gas/combustion air mixture to generate, which is reacted in the scrap chamber in a combustion process and

- Transferring the atmosphere from the scrap chamber to afterburning.

The process steps are carried out in the order shown. However, one or more of the method steps can also be carried out simultaneously, one after the other and/or at least partially in parallel.

The loading of the hearth of the scrap chamber with aluminum scrap in batches is preferably carried out by means of a special charging machine, in particular by means of a charging machine that is sealed off from the melting furnace, so that during loading because the entry of oxygen into the scrap chamber is largely avoided. If oxygen should be introduced into the scrap chamber during loading, it is eliminated during, preferably at the end of, the loading process step, preferably by means of a brief combustion step.

In other words, the following process step is additionally carried out before the second pre-treatment phase:

- Combustion of the oxygen introduced into the scrap chamber during loading.

Experience has shown that combustion between approx. 30 seconds and two minutes is sufficient to largely eliminate the oxygen that has entered the scrap chamber during loading. Then the first pre-treatment phase begins.

During a first pre-treatment phase at a predetermined first temperature, the organic adhesions on the aluminum scrap are converted into a pyrolysis gas by means of pyrolysis.

The first pre-treatment phase takes place at a first temperature, which is up to about 550°C, in an atmosphere which does not contain free oxygen, i. H. whose oxygen content is so low that oxidation of the aluminum scrap is avoided during pre-treatment.

Depending on the alloy, the melting temperature of aluminum is between 600 and 650°C and thus above the pyrolysis temperature, which is a maximum of 550°C.

During the second pre-treatment phase, the scrap chamber is heated to at least the self-ignition temperature of the pyrolysis gas, which is around 750°C. The predetermined second temperature is approximately 850°C. Preferably the second temperature is between 750°C and 900°C. The one in the junk room The air flow introduced supplies the oxygen required for a sub-stoichiometric combustion reaction. The pyrolysis gas/air mixture is reacted sub-stoichiometrically in order to avoid oxidation of the aluminum scrap. During the reaction, those hydrocarbons are largely eliminated which, in the form of adhesions on the aluminum scrap, would react with the melt and lead to dross formation.

After the second phase of pre-treatment, the aluminum scrap is inserted and melted in the liquid melt that surrounds the hearth.

The method according to the invention has the advantage that metal loss in the melt product is avoided.

Advantageous refinements of the method and of the multi-chamber melting furnace are specified in the dependent patent claims. The features listed individually in the dependent patent claims can be combined with one another in any technologically sensible manner and further developments of the invention can be defined.

During the second pretreatment phase, the air stream is preferably provided in such a way that a pyrolysis gas/combustion air mixture with an air ratio (X) in the range from 0.3 to 0.6, preferably 0.5, is achieved. A control/regulation unit is used for this.

Preferably, the melt recirculates between the heating chamber and the scrap chamber to heat the melt in the scrap chamber.

Due to the recirculation of the melt between the heating chamber and the scrap chamber, the melt, which is heated in the heating chamber by means of the combustion device, is introduced into the scrap chamber and is used there to heat the scrap after the second pre-treatment phase scrap is pushed into the melt until it has melted down.

A circuit line between the heating chamber and the scrap chamber could be used for recirculation. The melt is advantageously conveyed from the heating chamber into the melting chamber by means of a line in which a pump is located. Alternatively, a stirrer can ensure the circulation of the melt between the chambers if suitable openings are provided in the intermediate wall in the area of the melt.

An advantageous embodiment is characterized in that the following method step is additionally carried out during the second pretreatment phase:

- if the temperature in the scrap chamber is lower than the self-ignition temperature of the pyrolysis gas, generating at least one flame in the scrap chamber by means of a burner to which fuel and combustion air are supplied.

The burner serves to ignite the air/pyrolysis gas mixture when the temperature in the scrap chamber is lower than the self-ignition temperature of the pyrolysis gas. When the self-ignition temperature of the pyrolysis gas in the scrap chamber is reached, the burner is switched off because the reaction between the oxygen in the air stream and the pyrolysis gas takes place without an ignition source.

An essential further development of the method according to the invention is characterized in that the atmosphere is transferred from the scrap chamber into the heating chamber for post-combustion and that the combustion device is preferably operated with excess air. Consequently, the air ratio (X), which puts the actually available air mass in relation to the necessary air mass, which is theoretically required for complete combustion, is greater than 1 , 0 . In other words, the combustion device is operated over-stoichiometrically in order to provide the combustion air for the combustible parts of the atmosphere from the scrap chamber. The combustion air for the post-combustion is thus supplied to the atmosphere in a simple manner by means of the combustion device.

The aluminum scrap has different amounts of organic adhesions. If there are large amounts of buildup, there is a risk that afterburning in the heating chamber will be overloaded. In the method according to the invention, overloading of the post-combustion in the heating chamber is avoided because part of the hydrocarbons is already burned in the scrap chamber during the second pretreatment phase. It is also advantageous that the combustion reaction during the second pre-treatment phase causes heating, in particular uniform heating of the charge of aluminum scrap.

A characteristic value for the mixing ratio or the air ratio of the gas/air mixture in the heating chamber is measured and, depending on the deviation of the measured value of the characteristic value from a target value, a signal is generated for supplying more or less fuel and/or combustion air to the combustion device, preferably using a control -/control unit .

Conclusions about the course of combustion can be drawn from the characteristic value. If the proportion of hydrocarbons in the atmosphere that is supplied to the heating chamber for post-combustion should be extremely high, the fuel supply to the combustion device could also be completely interrupted, so that only combustion air flows out of the combustion device. Within the scope of the invention, a manipulated variable for providing and/or terminating the provision of the air flow in the scrap chamber could be generated from the measured characteristic value, preferably by means of the control/regulating unit.

A particularly advantageous development of the invention consists in that a manipulated variable for providing and/or terminating the provision of the air flow in the Scrap chamber and / or derived for generating the flame in the scrap chamber.

The oxygen content of the exhaust gas is preferably measured by means of the sensor. Alternatively, other parameters for the mixing ratio of the gas/air mixture in the heating chamber could also be measured.

The method according to the invention is further characterized in that in the second pre-treatment phase the air flow is provided by directing the air flow between the loading door and aluminum scrap into the scrap chamber or by directing an air flow between the loading door and aluminum scrap into the Scrap room is addressed.

The area between the loading door and the aluminum scrap charge is the coldest area in the scrap chamber. Due to the reaction of the pyrolysis gas with the oxygen from the air flow directed into this area, the temperature in this area is raised to such an extent that the deposits that are still on the aluminum scrap are evenly converted into the gaseous state and can be burned. Preferably, the flame is generated adjacent to the airflow provided in the scrap chamber, preferably with the distance between flame and airflow being chosen such that the flame heats the airflow, and preferably with the flame and airflow being directed into the scrap chamber in the same way. In other words, the flame and the air flow are directed in the same direction into the scrap chamber.

Within the scope of the invention, the atmosphere inside the scrap chamber can be circulated by means of a circulation channel which is connected to the scrap chamber with an inlet opening and an outlet opening, preferably parallel to the partition wall in the scrap chamber, preferably by means of a fan. The air flow and/or the flame in the flow of the circulated atmosphere in the outlet opening between the loading door and the aluminum scrap are preferably directed into the scrap chamber.

A particularly advantageous development of the invention is that the air flow in the scrap chamber is provided by means of the burner, which is operated with excess air when the temperature in the scrap chamber is lower than the self-ignition temperature of the pyrolysis gas and/or its fuel supply is interrupted and its Combustion air supply is reduced so that a sub-stoichiometric pyrolysis gas / combustion air t mixture is generated in the scrap chamber when the temperature in the scrap chamber has reached or exceeds the self-ignition temperature of the pyrolysis gas.

If the temperature in the scrap chamber is lower than the

Auto-ignition temperature of the pyrolysis gas is determined in the

Scrap chamber by means of the fuel supply to the burner flame generated. The combustion air is provided with the excess air in order to produce an ignitable sub-stoichiometric pyrolysis gas/combustion air mixture in the scrap chamber.

When the temperature in the scrap chamber reaches or exceeds the autoignition temperature of the pyrolysis gas, a flame is no longer needed for ignition purposes. The air flow that has to be provided in the scrap chamber to generate an ignitable sub-stoichiometric pyrolysis gas/combustion air mixture is supplied by the combustion air supply to the burner and passes through the burner into the scrap chamber.

The invention also includes a multi-chamber melting furnace for the recovery of aluminum from aluminum scrap which has organic adhesions, comprising:

- a scrap chamber which is set up to receive melt, the scrap chamber having a hearth which can be loaded in batches with the aluminum scrap, which is located above the level of the melt and a loading door is arranged in the wall of the scrap chamber, the scrap chamber for thermal pretreatment of the aluminum scrap is set up and during a first pretreatment phase, at a predetermined first temperature in an atmosphere that is free of oxygen, the organic buildup on the aluminum scrap can be converted into a pyrolysis gas,

- at least one heating chamber which is set up to receive melt and which has at least one combustion device,

- at least one air inlet in the wall of the scrap chamber for providing at least one air flow in the scrap chamber during a second pre-treatment phase at a predetermined second temperature, the scrap chamber can be heated to the self-ignition temperature of the pyrolysis gas,

- A control/regulating unit that is set up to provide the air flow in the scrap chamber in such a way that an ignitable substoichiometric pyrolysis gas/combustion air mixture is produced in the scrap chamber, which can be reacted in a combustion process in the scrap chamber and

- An atmosphere outlet in the wall of the scrap chamber for discharging the atmosphere from the scrap chamber to an afterburning.

During the first pretreatment phase, pyrolysis takes place at the predetermined first temperature. This is a conversion process in which organic compounds are split in the absence of oxygen (air ratio X essentially = 0). The exclusion of oxygen prevents the aluminum scrap from oxidizing.

The atmosphere is free of oxygen. This means that the oxygen content is extremely low, so that pyrolysis and no oxidation or combustion takes place.

During the second pre-treatment phase, the scrap chamber is heated to at least the self-ignition temperature of the pyrolysis gas, which is approx. is 750 °C. The predetermined second temperature is about 850 °C. Preferably the second temperature is between 750°C and 900°C. The air flow introduced into the scrap chamber through the air inlet supplies the oxygen required for a sub-stoichiometric combustion reaction. The pyrolysis gas/air mixture is reacted sub-stoichiometrically in order to avoid oxidation of the aluminum scrap. During the reaction, those carbon Hydrogen sulfide is largely eliminated, which would react with the melt in the form of buildup on the aluminum scrap and would lead to dross formation if the aluminum scrap, after pre-treatment, was inserted into the liquid melt surrounding the hearth and melted.

According to a further advantageous feature of the invention, the multi-chamber melting furnace is characterized in that there is a partition wall between the scrap chamber and the heating chamber and that the partition wall has at least one opening for recirculating the melt between the heating chamber and the scrap chamber to heat up the melt in the scrap chamber. The scrap chamber and the heating chamber are arranged horizontally one behind the other, next to one another or in an L-shape and are separated from one another by the partition.

The atmosphere outlet is preferably designed as a connecting line between the scrap chamber and the heating chamber in order to transfer the atmosphere from the scrap chamber into the heating chamber for post-combustion, and the combustion device can preferably be operated with excess air in order to supply the atmosphere with the combustion air for post-combustion by means of the supply combustion device. The connecting line between the scrap chamber and the heating chamber preferably has a blower/fan.

According to a further feature of the invention, the scrap chamber has at least one burner to which fuel is supplied by means of a fuel supply and combustion air is supplied by means of a combustion air supply and the burner is set up to initiate the combustion process of the pyrolysis gas/air mixture by means of a flame. if the

temperature in the scrap chamber is lower than the ent Ignition temperature of the pyrolysis gas. The combustion reaction can thus be initiated at the earliest possible point in time and the process can thus be accelerated.

According to a further advantageous feature of the invention, the multi-chamber melting furnace is characterized in that the air inlet is designed as an air lance and/or that the burner is arranged next to the air inlet, that preferably the distance between the air inlet and the burner is selected such that the flame of the burner heats the air flow from the air inlet and that preferably the burner and the air inlet are equally directed into the scrap chamber between the loading door and the aluminum scrap.

In other words, the flame from the burner and the air flow from the air inlet are directed in the same direction into the scrap chamber in the form of an air lance.

Starting from opposite walls of the scrap chamber, an air lance is preferably directed into the scrap chamber between the loading door and aluminum scrap. This embodiment has proven to be particularly effective. The arrangement should be chosen in such a way that the flame and airflow are not directed at the scrap but next to it.

A particularly advantageous development of the invention is that the burner forms the air inlet and that the control/regulation unit is set up to operate the burner with excess air when the temperature in the scrap chamber is lower than the self-ignition temperature of the pyrolysis gas and/or around the Shut off the fuel supply to the burner and reduce its combustion air supply when the temperature in the scrap chamber has reached the self-ignition temperature of the pyrolysis gas or exceeds it. For this purpose, the fuel supply and the combustion air supply have corresponding control elements.

If the temperature in the scrap chamber is lower than the self-ignition temperature of the pyrolysis gas, a flame is generated in the scrap chamber by means of the burner. The burner is operated with excess air in order to use the excess air to provide the air flow that is required in the scrap chamber in order to produce an ignitable substoichiometric pyrolysis gas/combustion air t mixture.

When the temperature in the scrap chamber has reached the self-ignition temperature of the pyrolysis gas, a flame is no longer required for ignition. Consequently, the fuel supply to the burner is interrupted. Because the burner is no longer supplied with fuel, the combustion air supply can be reduced accordingly, so that only enough combustion air is supplied to produce an ignitable substoichiometric pyrolysis gas/combustion air mixture in the scrap chamber.

A preferred embodiment is characterized in that at least one circulation duct is connected to the scrap chamber in order to circulate the atmosphere within the scrap chamber, preferably by means of a fan, so that the inlet opening of the circulation duct is in the wall of the scrap chamber adjacent to the Partition wall and the exit opening of the circulation zkanals preferably located in the wall of the scrap chamber between the loading door and the stove and that preferably the air inlet and / or the burner is located within the exit opening or. are .

The air inlet designed as an air lance is preferably designed in such a way that the air exit speed is relatively high in order to ensure an even distribution of the air in the area between the loading door and the charge with aluminum scrap receive . The exit velocity from the burner is also high to obtain an even temperature distribution between the door and the scrap charge. The exit speed of the burner is preferably between 60 m/s and 130 m/s and/or the exit speed of the air flow from the air inlet is between 30 m/s and 60 m/s.

The invention, further advantages and the technical environment are explained in more detail below using preferred embodiments by way of example with reference to the accompanying drawings. The invention should not be restricted by the exemplary embodiments shown. It is also possible to combine partial aspects of the features explained in the figures with other features from other figures and/or the description.

They show in a schematic representation:

FIG. 1 shows a multi-chamber melting furnace for recovering aluminum from aluminum scrap in a sectional view from above;

FIG. 2 shows the multi-chamber melting furnace from FIG. 1 in a lateral sectional representation;

FIG. 3 shows the multi-chamber melting furnace from FIG. 1 in a frontal sectional view;

FIG. 4 shows a further embodiment of the multi-chamber melting furnace according to the invention in a sectional representation from above;

FIG. 5 shows a further embodiment of the multi-chamber melting furnace according to the invention in a lateral sectional representation. In all figures, the same components have the same reference numbers. FIG. 1 shows a sectional representation, seen from above, of a multi-chamber melting furnace 1 designed as a two-chamber melting furnace for the recovery of aluminum from aluminum scrap which has organic adhesions. FIG. 2 shows a sectional view from the side and FIG. 3 shows a sectional view over the width of the multi-chamber melting furnace seen from the end face. Only the components of the multi-chamber melting furnace 1 that are essential to the invention are shown.

In FIGS. 1 to 4 it is shown schematically that the multi-chamber melting furnace 1 has a scrap chamber 2 and a heating chamber 3 with a wall 4 which is closed with respect to the outside atmosphere and has walls 4a and 4b.

The scrap chamber is set up for pre-treating the aluminum scrap before it is melted. The scrap chamber 2 has a closable loading door 5 on the front side, through which the scrap chamber 2 can be loaded in batches with the aluminum scrap 6 . The loading door 5 can be moved horizontally and extends essentially over the entire width of the scrap chamber 2 or the multi-chamber melting furnace 1 . In the scrap chamber 2 there is a hearth 7 which is loaded with the aluminum scrap 6 . The aluminum scrap 6 is put together as a batch. The hearth 7 is at least partially sloping and borders the liquid melt 8 under production conditions, the hearth 7 being arranged above the level N of the melt 8 . After the pre-treatment, the aluminum scrap is manually pushed into the liquid melt 8 and melted.

Viewed from the loading door 5, the heating chamber 3 extends behind the scrap chamber 2 over the entire width of the multi-chamber melting furnace 1 liquid melt 8 and has a combustion device 9 and an exhaust gas outlet 10 . The combustion device 9 is designed as a gas burner which is directed into a heating zone 3a above the melt 8 in the melting chamber. Several combustion devices 9 in the form of gas burners are used, of which only one combustion device 9 is shown in FIG.

The scrap chamber 2 and the heating chamber 3 are arranged one behind the other in the longitudinal direction and are separated from one another by means of a partition wall 11 . Alternatively, the chambers can also be arranged next to each other or in an L-shape. For example, it can be a hanging partition. The partition wall 11 protrudes into the melt 8 under operating conditions. The partition wall 11 has at least one opening 12 or channel below the level N or the surface of the melt 8 for recirculating the melt 8 between the heating chamber 3 in the scrap chamber 2 in order to heat the melt in the scrap chamber 2 and thus the scrap chamber 2 to heat.

The hearth 7 of the scrap chamber 2 is loaded in batches with aluminum scrap by means of an automatic charging machine (not shown) or a bucket wheel loader. A charging machine is used here that is sealed off from the melting furnace so that the entry of oxygen into the scrap chamber during charging is largely avoided. If the oxygen input cannot be completely avoided during loading into the scrap chamber, the oxygen is eliminated before the first pre-treatment phase, preferably by means of a short-term incineration step. Experience has shown that combustion between 30 seconds and two minutes is sufficient to largely eliminate the oxygen that enters the scrap chamber during loading. The scrap chamber 2 is initially by means of recirculation the melt 8 from the heating chamber 3 into the scrap chamber to a predetermined first temperature, preferably 550° C., is heated. The heating could be accelerated by means of a suitable external heating.

No oxygen is supplied to the scrap chamber during the first pre-treatment phase. The aluminum scrap is treated at the predetermined first temperature in a reducing atmosphere, i. H. an atmosphere substantially free of oxygen to convert the organic buildup on the aluminum scrap into a pyrolysis gas.

"Oxygen-free" is understood to mean the absence of oxygen, so that the air ratio X is essentially 0. A large part of the buildup is converted into the gas phase during this first pretreatment phase.

In the walls 4a, 4b of the scrap chamber 2 there is an air inlet 13a, 13b each for providing an air flow L in the scrap chamber 2 in order to produce an ignitable pyrolysis gas/air mixture in the scrap chamber in a second pretreatment phase.

During the second pre-treatment phase, the provision of the air flow L is controlled in such a way that the air ratio of the pyrolysis gas/air mixture in the scrap chamber 2 is between 0.3 and 0.6, preferably 0.5.

In the two exemplary embodiments, starting from opposite walls 4a and 4b of the wall 4 of the scrap chamber 2, one air inlet 13a, 13b each in the form of an air lance is arranged in such a way that the air flow L from each air inlet 13a, 13b into the scrap chamber 2 between Loading door 5 and aluminum scrap 6 is directed. This is intended to the air flow in the coldest area of the scrap chamber 3 in the To provide proximity to the aluminum scrap 6, the air flow is not directed directly at the aluminum scrap 6 in order to avoid the melting of the metal and thus metal erosion. In addition, an equalization of the temperature distribution in the melting chamber 3 is achieved.

During the second pre-treatment phase, the scrap chamber 2 is heated to the self-ignition temperature of the pyrolysis gas. In Figures 2 and 3, a control / regulation unit 14 is shown, which is set up to control or regulate the provision of the air flow from the air outlets 13a, 13b in the scrap chamber 2 such that in the scrap chamber 2 an ignitable sub-stoichiometric air t / pyrolysis gas mixture is formed, which reacts in the scrap chamber 2 in a combustion process to form a combustion gas. The sub-stoichiometric combustion ensures that there is no unwanted oxidation of the aluminum scrap.

The scrap chamber has on opposite walls 4a, 4b je a burner 15a, 15b to initiate the combustion process during the second pre-treatment phase when the temperature in the scrap chamber 2 is lower than the self-ignition temperature of the pyrolysis gas. These burners are used to remove oxygen, which may be introduced into the scrap chamber during loading, from the scrap chamber during or immediately after loading by means of a combustion reaction before the first pre-treatment phase begins. The scrap chamber is fed by means of the burners only as much fuel until an ignitable mixture is formed with the oxygen present in the scrap chamber, which mixture is ignited.

Each burner 15a, 15b is associated with an air inlet 13a, 13b. The distance between each air inlet 13a, 13b and a burner 15a, 15b is preferably so small that that in each case the flame of the burner heats the adjacent air flow L from the air inlet. Adjacent burners and air outlets are directed into the scrap chamber 2 in the same direction, preferably substantially parallel to each other. The exit speed of the air streams L from the air outlets 13a, 13b is between 30m/s and 60m/s. This ensures that an optimal mixture of air and the combustible components of the pyrolysis gas is achieved. The exit speed of the burners 15a, 15b is between 60m/s and 130m/s.

The embodiment according to FIG. 4 shows that the scrap chamber 2 has a circulation channel 16a, 16b on both sides, each with a fan 17a, 17b, in order to circulate the atmosphere inside the scrap chamber 2. The atmosphere is circulated in the longitudinal direction of the scrap chamber between the partition wall 11 and the front loading door. Each circulation channel 16a, 16b has an inlet opening 18a, 18b and an outlet opening 19a, 19b in the walls 4a, 4b. The inlet openings 18a, 18b are arranged adjacent to the partition wall 11. The outlet opening 19a, 19b is located in the walls 4a, 4b between the front loading door and the hearth 7, respectively. The air inlet 13a and the burner 15a are arranged inside the outlet opening 19a and the air inlet 13b and the burner 14b are arranged inside the outlet opening 19b.

FIG. 5 shows an embodiment in which the burners 15a', 15b' also serve as air outlets. Each burner has a fuel supply 22a, 22b and an air supply 23a, 23b. Each burner 15a', 15b' is operated with excess air as long as the temperature in the scrap chamber 2 is lower than the self-ignition temperature of the pyrolysis gas. By means of the control / regulating unit 14, the fuel supply is 22a, 22b interrupted to the burner and the combustion air supply 23a, 23b reduced such that in the Scrap chamber 2 is a sub-stoichiometric pyrolysis gas / combustion air t mixture is generated when the temperature in the scrap chamber 2 has reached the self-ignition temperature of the pyrolysis gas or exceeds it. In this operating state, which is shown in FIG. 5, only air flows out of the burners 15a', 15b'. Because there is no need for air lances, this embodiment is structurally particularly simple.

FIG. 2 shows that there is a connecting line 20 which has a blower 21 between the scrap chamber 2 and the heating chamber 3 in order to feed the atmosphere from the scrap chamber 2 to post-combustion in the heating chamber. The atmosphere includes the exhaust gas from the combustion reaction during the second pretreatment phase and unburned pyrolysis gas. The thermal energy generated during post-combustion is used to heat the heating chamber.

The combustion device 9 is connected to a fuel line 24 and a combustion line 25 . The combustion device 9 in the heating chamber 3 is set up for over-stoichiometric operation, so that the combustion air for post-combustion in the heating chamber is supplied to the atmosphere from the scrap chamber 2 by means of the combustion device 9 . This is a structurally particularly simple solution for providing combustion air for post-combustion. However, the combustion air required for post-combustion could also be supplied to the atmosphere in the heating chamber 3 by means of an air line.

In other words, the combustion air line 26 of the combustion device 9 in the heating zone 3a of the melting chamber 3 is set up in the heating zone 3a in addition to the combustion air for the fuel that the combustion device device is supplied by means of the fuel line 25 to provide combustion air for post-combustion of the atmosphere from the scrap chamber 2 .

A sensor 26 (FIG. 2) for measuring the oxygen content in the exhaust gas outlet 10 of the heating chamber 3 is arranged in the exhaust gas outlet 10 of the heating chamber 3 . The oxygen content represents a characteristic value for the mixing ratio of the gas/air mixture in the heating chamber 3 . Depending on the deviation of the measured oxygen content from a target value, the control/regulating unit 14 generates a signal for supplying more or less fuel and/or combustion air to the combustion device 9 .

A manipulated variable for providing and/or terminating the provision of the air streams L in the melting chamber is also derived from the measured characteristic value or from the signal as a function of the deviation of the measured characteristic value from the desired value. A signal for generating the flame in the scrap chamber ( 2 ) could also be derived within the scope of the invention.

During afterburning, the atmosphere from the scrap chamber 2 is afterburned in the heating chamber 3 in a safe and environmentally friendly manner with a long residence time and high temperatures. The exhaust gases from the heating chamber 3 finally pass through the exhaust gas outlet 10 to a special exhaust gas cleaning process, in which the exhaust gas is cleaned of dust and harmful gas components.

After the end of the second pre-treatment phase, the pre-treated aluminum scrap charge 6 is pushed into the melt in the scrap chamber 2 .

According to the invention, optimal pretreatment conditions are created in order to remove organic buildup as completely as possible to convert the gas phase. This leads to reduced dross formation and thus to an increased metal yield while at the same time saving energy.

The embodiments described above are to be understood as examples. The features that are described together with other features also individually define essential components of the invention, regardless of whether they are disclosed in the description, the claims, the figures or otherwise. Modifications are readily possible within the scope of the invention. Thus, the multi-chamber melting furnace can have more than two chambers. Within the scope of the invention, only a single air inlet/burner combination or also several air inlet/burner combinations can be provided. Finally, it is pointed out that the term "comprising" does not exclude any components or elements, that reference signs in the claims do not represent any limitation and that "a" or "an" includes a plurality.

Reference List

1 More Chamber Furnace

2 scrap room

3 heating chamber

3a heating zone of the heating chamber

4 wall

4a, 4b wall

5 loading door

6 aluminum scrap

7 stove

8 melt

9 combustion device

10 exhaust outlet

11 partition

12 opening

13a, 13b air inlet

14 control unit

15a, 15b burners

15a' 15b burner

16a, 16b circulation channel

17a, 17b fan

18a, 18b entrance opening

19a, 19b outlet opening

20 Atmosphere outlet/connecting line

21 blowers

22a, 22b fuel supply

23a, 22b combustion air supply

24 fuel line

25 Combustion ventilation duct

26 sensors

X air count

L air flow

N level of the melt

Claims

Process for the recovery of aluminum from aluminum scrap, which has organic adhesions, in a multi-chamber melting furnace (1), with a scrap chamber (2) that is set up to receive melt, wherein the scrap chamber (2) has an aluminum scrap (6 ) chargeable in batches (7), which is above the level (N) of the melt and wherein in the wall (4) of the scrap chamber (2) is a loading door (5) and with at least one heating chamber (3), the is set up to receive melt and has at least one combustion device (9), at least with the following method steps:

- thermal pretreatment of the aluminum scrap (6) in the scrap chamber (2) during a first pretreatment phase at a predetermined first temperature and in an atmosphere that is free of oxygen in order to convert the organic buildup on the aluminum scrap into a pyrolysis gas,

- Thermal pre-treatment of the aluminum scrap (6) in the scrap chamber (2) during a second pre-treatment phase at a predetermined second temperature, the scrap chamber (2) being heated to the self-ignition temperature of the pyrolysis gas, with at least one air flow (L ) is provided in order to produce an ignitable substoichiometric pyrolysis gas/combustion air t mixture which is reacted in the scrap chamber (2) in a combustion process and - Converting the atmosphere from the scrap chamber (2) to an afterburning. Method according to Claim 1, characterized in that during the second pre-treatment phase the air flow (L) is provided in such a way that a pyrolysis gas/combustion air mixture with an air ratio (X) in the range from 0.3 to 0.6, preferably 0. 5, is reached. Method according to Claim 1 or 2, characterized in that the melt is recirculated between the heating chamber (3) and the scrap chamber (2) in order to heat the melt in the scrap chamber (2). Method according to at least one of the preceding claims, characterized in that the following method step is additionally carried out during the second pre-treatment phase: - if the temperature in the scrap chamber (2) is lower than the self-ignition temperature of the pyrolysis gas, generating at least one flame in the scrap chamber by means of a Burner (15a, 15b, 15a', 15b') to which fuel and combustion air are supplied. Method according to at least one of the preceding claims, characterized in that the atmosphere from the scrap chamber (2) is transferred to the heating chamber (3) for post-combustion and that the combustion device (9) in the heating chamber (3) is preferably operated with excess air. Method according to Claim 5, characterized in that a characteristic value for the mixing ratio of the gas/air mixture in the heating chamber (3) is measured by means of a sensor (26) in an exhaust gas outlet (10) of the heating chamber (3) and as a function of the If the measured characteristic value deviates from a target value, a signal for supplying more or less fuel and/or combustion air to the combustion device (9) is generated. Method according to Claim 6, characterized in that a manipulated variable for providing and/or terminating the provision of the air flow (L) in the scrap chamber is derived from the measured characteristic value, preferably the oxygen content, or from the signal as a function of the deviation of the measured characteristic value from the target value (2) and/or for generating the flame in the scrap chamber (2). Method according to at least one of the preceding claims, characterized in that the air flow (L) is provided in the second pre-treatment phase by directing the air flow (L) between the loading door (5) and aluminum scrap (6) into the scrap chamber (2) or by from opposite walls (4a, 4b) of the scrap chamber (2), a current of air (L) between the loading door (5) and aluminum scrap (6) is directed into the scrap chamber (2). Method according to one of Claims 4 to 8, characterized in that the flame is generated next to the air flow (L) provided in the scrap chamber (2) and that the distance between the flame and the air flow (L) is preferably selected in such a way that the flame Air flow (L) heated and that preferably the flame and the air flow (L) are directed in the same way in the scrap chamber (2). Method according to any one of claims 4 to 9, characterized in that the air flow (L) in the scrap chamber is provided by means of the burner (15a', 15b) which is operated with excess air when the temperature in the scrap chamber (2) is lower than the self-ignition temperature of the pyrolysis gas and/or its fuel supply is interrupted and its combustion air supply is reduced in such a way that a sub-stoichiometric pyrolysis gas/combustion air mixture is generated in the scrap chamber when the temperature in the scrap chamber (2) has reached the self-ignition temperature of the pyrolysis gas or exceeds it. Multi-chamber melting furnace for the recovery of aluminum from aluminum scrap containing organic residues, comprising :

- a scrap chamber (2) which is set up to receive melt, the scrap chamber (2) having a hearth (7) which can be loaded in batches with the aluminum scrap (6) and which is located above the level (N) of the melt and wherein in a loading door (5) is arranged on the wall (4) of the scrap chamber, the scrap chamber (2) for the thermal pre-treatment of the aluminum scrap (6) 30 is set up and wherein during a first pretreatment phase, at a predetermined first temperature in an atmosphere that is free of oxygen, the organic buildup on the aluminum scrap (6) can be converted into a pyrolysis gas,

- at least one heating chamber (3) which is designed to receive melt (8) and which has at least one combustion device (9),

- at least one air inlet (13a, 13b) in the wall of the scrap chamber to provide at least one air flow (L) in the scrap chamber (2) during a second pre-treatment phase at a predetermined second temperature, the scrap chamber (2) being heatable to the self-ignition temperature of the pyrolysis gas is,

- A control / regulating unit (14) which is set up to provide the air flow (L) in the scrap chamber (2) in such a way that in the scrap chamber (2) an ignitable substoichiometric pyrolysis gas / combustion air t mixture is formed, which can be brought to react in the scrap chamber (2) in a combustion process and

- An atmosphere outlet (20) in the wall of the scrap chamber for discharging the atmosphere from the scrap chamber to afterburning. Multi-chamber melting furnace according to Claim 11, characterized in that there is a partition (11) between the scrap chamber (2) and the heating chamber (3) and that the partition (11) has at least one opening (12) for recirculating the melt between the heating chamber ( 3) and the scrap chamber (2) and/or that the atmosphere outlet (20) is designed as a connecting line between the scrap chamber (2) and the heating chamber (2) in order to convey the atmosphere from the scrap chamber (2) into the heating chamber 31 mer (3) for post-combustion and that preferably the combustion device (9) can be operated with excess air in order to supply the combustion air for post-combustion by means of the combustion device (9) to the atmosphere. Multi-chamber melting furnace according to one of claims 11 or 12, characterized in that the scrap chamber (2) has at least one burner (15a, 15b, 15a', 15b'), the fuel by means of a fuel supply (22a, 22b) and combustion air by means a combustion air supply

(23a, 23b) and that the burner (15a, 15b, 15a', 15b') is preferably set up to initiate the combustion process of the pyrolysis gas/air mixture by means of a flame when the temperature in the scrap chamber is lower than that Auto-ignition temperature of the pyrolysis gas. Multi-chamber melting furnace according to Claim 13, characterized in that the air inlet (13a, 13b) is designed as an air lance and/or that the burner (15a, 15b) is arranged next to the air inlet (13a, 13b), that preferably the distance between the air inlet (13a, 13b) and the burner (15a, 15b) is selected such that the flame of the burner (15a, 15b) heats the air flow (L) from the air inlet (13a, 13b) and that preferably the burner (15a, 15b) and the air inlet (13a, 13b) are directed in the same way into the scrap chamber (2) between the loading door (5) and aluminum scrap (6). Multi-chamber melting furnace according to Claim 13 or 14, characterized in that the burner (15a', 15b') forms the air inlet (13a, 13b) and that the control/regulating unit (14) is set up to control the burner (15a' , 15b') 32 to be operated with excess air if the temperature in the scrap chamber (2) is lower than the self-ignition temperature of the pyrolysis gas and/or to interrupt the fuel supply to the burner (15a', 15b') and to reduce its combustion air supply if the temperature in the scrap chamber (2) has reached or exceeded the self-ignition temperature of the pyrolysis gas. Multi-chamber melting furnace according to one of Claims 11 to 15, characterized in that at least one circulation channel (16a, 16b) with an inlet opening (18a, 18b) and an outlet opening is connected to the scrap chamber (2) in order to circulate the atmosphere inside the scrap chamber ( 2) to circulate, preferably by means of a fan (17a, 17b) and that the outlet opening (19a, 19b) is preferably located in the wall (4) of the scrap chamber (2) between the loading door (5) and the hearth (7) and that preferably the air inlet (13a, 13b) and/or the burner (15a, 15b, 15a', 15b') is or are arranged within the outlet opening (19a, 19b) and/or that the burner (15a, 15b, 15a' , 15b') is set up in such a way that its exit speed is between 60m/s and 130m/s and/or that the air inlet (13a, 13b) is set up in such a way that the exit speed of the air flow is between 30m/s and 60m/s.