Triple-chamber melting furnace for aluminum scrap and operating method

Abstract

A melting furnace (200) for melting aluminum scrap (S) contaminated by volatile organic compounds (VOCs) comprises a cold chamber (222), at least a first hot chamber (224a) and a second hot chamber (224b), at least one regenerative burner group (228) configured to perform a combustion in said first hot chamber (224a) and second hot chamber (224)b, and at least one regenerator group (230) configured to draw fumes from said first hot chamber (224a) and second hot chamber (224), superheat a storage structure by said fumes, and introduce heated air from said storage structure into the cold chamber (222).

Description

TRIPLE-CHAMBER MELTING FURNACE FOR ALUMINUM SCRAP ANDOPERATING METHODField of the invention

[0001] The present invention belongs to the field of systems for manufacturing aluminum; in particular, the present invention relates to a triple-chamber melting furnace for aluminum scrap .Background of the invention

[0002] Following modern environmental protection and sustainability policies , the processes for the recovery and transformation of aluminum scrap have become widespread . Recycling aluminum scrap in the melting process indeed allows significantly decreasing the consumption of aluminum mineral and the related emissions associated with the transformation process .

[0003] However, melting aluminum scrap has some drawbacks , mainly due to the fact that the single scrap pieces do not only contain aluminum parts . Indeed, in the single piece, along with the aluminum part , there can be parts made of organic materials , usually referred to as VOCs (Volatile Organic Compounds ) , such as paint , polymer materials , glues , adhesives , and other compounds derived from hydrocarbons , which are inseparably associated with the metal parts . For example, in the scrap originatingfrom the recovery of fixtures , the aluminum part s , such as a window frame, are painted and provided with glued gaskets .

[0004] During the scrap melting process , the volatile organic compounds generate unhealthy fumes . Therefore, the need exists to adequately burn such fumes , both to neutralize them and avoid dispersing harmful substances into the environment and to utilize the calorific value of such compounds and promote the melting of the scrap .

[0005] Some combustion processes attempting to meet such a need exist .

[0006] For example, melting furnaces are known, referred to as SCMF ( indicated as suitable especially for scrap with VOCs < 1% ) , ECOMELT PR ( indicated as suitable for scrap with 1% < VOCs < 5% ) and ECOMELT PS ( indicated as suitable especially for scrap with VOCs > 5% ) fromHertwich Engineering Gmbh . WASTOX® combustion processes and AIROX® combustion technology from LINDE AG are also known .

[0007] Examples of melting furnaces are shown in US 2001 / 028136 Al and CN 206 583 290 U .

[0008] Figure 1 diagrammatically shows a melting furnace of the prior art (two standard chamber furnace ) , suitable for treating aluminum scrap having a low fraction of volatile organic compounds (VOCs < 1% ) . Access inside themelting furnace 1 is by means of a door 2 , beyond which there is a dry floor 3 on which scrap 4 to be melted in arranged . In front of the dry floor 3 is a tank 5 in which there is bath 6 . A wall 7 vertically extending above the free surface of bath 6 separates the inside of furnace 1 into a cold chamber 8 , where there is one part of bath 6a, and it is provided with a door 2 and the dry floor 3 , and a hot chamber 9, where there is the other part of bath 6b, and it is provided with a burner group 10 . Wall 7 is further provided with an opening 15 which puts the hot chamber 9 and the cold chamber 8 in communication . The burner group 10 comprises burners 11 , 12 which operate in the hot chamber 9 . The hot chamber 9 is provided with a fume outlet 13 ; sometimes , the cold chamber 8 is also provided with a fume outlet 14 .

[0009] Scrap 4 is preheated in the cold chamber 8 due to the heat coming from the burners 11 , 12 , which operate in the hot chamber 9; in other words , the heat generated in the hot chamber 9 by the burners 11 , 12 is directly used to preheat the scrap 4 in the cold chamber 8 . The preheated scrap 4 is immersed in bath 6a, where the melting occurs . The fumes resulting from the volatile organic compounds generated in the cold chamber 8 pass into the hot chamber 9, where they can be combusted by means of the excess air of the burners 11 , 12 and suckedby the fume outlet 13 .

[0010] However, the combustion of fumes resulting from volatile organic compounds is not always optimal . The highly contaminating scrap releases an increased amount of volatile organic compounds , with emissions often concentrated in a step of the dry scrap preheating process ( scrap temperature between 250 ° and 450 ° C) . In the presence of increased amounts of volatile organic compound in standard dual chamber furnaces , it is not possible to burn all the incombustibles because there is a need for an increased amount of air which cannot be introduced as excess air into the burners (the burners cannot operate with air / gas ratios beyond a design limit , usually equal to air / gas=15 ) . There is also a need for a strong turbulent mixture to complete the combustion of the unburned volatile organic compound and the regenerative burners of the standard dual chamber furnaces are not designed to efficiently introduce the excess air . In addition, the fumes produced by this type of combustion contain toxic substances .Object of the invention

[0011] It is the object of the present invention to provide a triple-chamber melting furnace for aluminum scrap which is particularly effective and efficient in treating aluminum scrap contaminated by volatile organiccompounds , thus improving the processes and systems currently available . In particular, it is the object of the present invention to provide a triple-chamber furnace which allows loading highly contaminated scrap, extracting the entire volatilizable component of the scrap, and utilizing all or almost all of the calorific value of the volatile organic compound in the furnace, thus drastically reducing the consumption of natural gas .

[0012] Such an object is achieved by a melting furnace according to claim 1 and the operating method according to claims 16 and 17 . The dependent claims describe further advantageous embodiments of the invention .Brief description of the Figures

[0013] Figure 1 shows a standard double-chamber melting furnace, according to the prior art .

[0014] The features and advantages of the three chamber melting furnace and operating method according to the present invention will become apparent from the following description, given by way of non-limiting example, according to the further figures in the accompanying drawings , in which :- Figure 3 diagrammatically shows a three chamber and dual regeneration melting furnace, according to the present invention;Figure 3 is a comparative table between the specificconsumption of the furnace according to the prior art and of the furnace according to the present invention . Description of the inventionTriple-chamber and dual regeneration melting furnace

[0015] With reference to Figure 2 , a triple chamber melting furnace (three chamber melting furnace ) for aluminum scrap is indicated by reference numeral 200 as a whole ; such scrap can also comprise a fraction of volatile organic compounds (VOCs ) . The furnace is particularly adapted to treat aluminum scrap having a fraction of volatile organic compounds between 2 and 5% by weight ( 2 < VOCs <5% ) .

[0016] The melting furnace 200 comprises an inner compartment preferably having a rectangular plan characterized by a length L and a width W, where the length L is greater than the width W . For example, according to an embodiment , length L is 15 meters and width W is 9 meters .

[0017] The inner compartment is accessible from a main access 202 , preferably positioned in the direction of the width W of the inner compartment , by opening a door 204 . On the side opposite to the main access 202 , the compartment is delimited by a bottom wall 206 ; finally, laterally, the inner compartment is delimited by side walls 208 , 210 .

[0018] Furnace 200 further comprises a dry floor 212 positioned in the inner compartment , behind the main access 202 . The dry floor 212 is adapted to support the aluminum scrap S, preferably divided into scrap portions Psi, with i = 1 . . . n, where P si is the scrap portion that entered first and Psn is the scrap portion that entered last .

[0019] Furnace 200 further comprises a tank 214 containing the molten metal bath B, positioned between the dry floor 212 and the bottom wall 206 of furnace 200 .

[0020] Furnace 200 further comprises a primary partition wall 220 arranged in the inner compartment , between the dry floor 212 and the bottom wall 206, extending above the free surface of bath B, and delimits a cold chamber222 , on the side of the main access 202 , and a hot region223 , on the side of the bottom wall 206, in the inner compartment .

[0021] Furnace 200 further comprises a secondary partition wall 225 arranged in the hot region 223 , extending between the bottom wall 206 and the primary partition wall 220 , above the free surface of bath B, thus identifying a first hot chamber 224a and a second hot chamber 224b .

[0022] In particular, the cold chamber 222 comprises a part of tank 214 , that from the dry floor 212 to the primarypartition wall 220 , so that a part Be of the molten metal bath B is in the cold chamber 222 , and the dry floor 212 . The hot region 223 instead comprises the other part of tank 214 , that from the primary partition wall 220 to the bottom wall 206 ; this other part of tank 214 is partly in the first hot chamber 224a, so that another part Bha of the molten metal bath B is in the first hot chamber 224a, and partly in the second hot chamber 224b, so that a last part Bhb of the molten metal bath B is in the second hot chamber 224b .

[0023] In other words , the three portions of molten bath Be, Bha, Bhb in the three chambers 214 , 224a, 224b are in communication by means of openings in the partition walls below the free surface .

[0024] The primary partition wall 220 further has at least a first opening 226a, preferably a plurality of first openings , for example comprising a plurality of calibrated holes distributed over the primary partition wall 220 , which puts the cold chamber 222 and the first hot chamber 224a in communication .

[0025] The primary partition wall 220 further has at least a second opening 226b, preferably a plurality of second openings , for example comprising a plurality of calibrated holes distributed over the primary partition wall 220 , which puts the cold chamber 222 and the secondhot chamber 224b in communication .

[0026] The melting furnace 100 includes a regenerative system comprising a regenerative burner group 228 and a regenerator group 230 .

[0027] As anticipated, the furnace 200 further comprises a regenerative burner group 228 operating between the hot chambers 224a, 224b and configured to perform a combustion in said hot chambers 224a, 224b . The burner group 228 comprises a first regenerative burner 228a operating in the first hot chamber 224a and a second regenerative burner 228b operating in the second hot chamber 224b, cooperating with each other . Each regenerative burner 228a, 228b comprises respectively a burner body and a regenerator body . Furthermore, each regenerative burner 228a, 228b comprises respectively an accumulation structure 228a ' , 228b ' , suitable for accumulating and heating the air to be heated and sending the thus heated air and combustible gas to the respective burner 228a, 228b to perform combustion in the hot chambers 224a, 224b .

[0028] For example, the first burner 228a is arranged on the bottom wall 206 of the first hot chamber 224a, in front of the primary partition wall 220 , and the second burner 228b is arranged on the bottom wall 206 of the second hot chamber 224b, in front of the primarypartition wall 220 .

[0029] As anticipated, the furnace 200 further comprises a regenerator group 230 operating between the hot chambers 224a, 224b and the cold chamber 222 . The regenerator group 230 comprises a first regenerator 230a operating between the first hot chamber 224a and the cold chamber 222 , and a second regenerator 230b operating between the second hot chamber 224b and the cold chamber 222 . Each regenerator 230a, 230 is provided with a storage structure 230a ' , 230b' , for example made of ceramic, suitable for taking heat from the hot fumes of the hot chambers 224a, 224b, storing it and accumulating heat from the hot fumes and for releasing the accumulated heat to the air to be heated in the cold chamber 222 . It is important to note that the regenerators 230a, 230b of the regenerative system are not directly connected to the burners 228a, 228b .

[0030] The first regenerator 230a is connected to an air inlet pipe 232 , to a first air outlet pipe 234a, which leads into the cold chamber 222 , preferably at the dry floor 212 , to a first fume inlet pipe 236a, which draws fumes from the first hot chamber 224a, and to a fume outlet pipe 238 .

[0031] The second regenerator 230b is instead connected to an air inlet pipe 232 , to a second air outlet pipe 234b,which leads into the cold chamber 222 , preferably at the dry floor 212 , and a second fume inlet pipe 236b, which draws fumes from the second hot chamber 224b, and to the fume outlet pipe 238 .

[0032] During a first operating step, the fumes taken from the first hot chamber 224a overheat the storage structure 230a ' of the first regenerator 230a allowing thermal energy to be stored; air to be heated is sent to the storage structure 230a' , which air, once heated, is sent to the cold chamber 222 by means of the first air outlet pipe 234a . Advantageously, the use of regenerators and the storage structures of the regenerators allows thermal energy to be stored and accumulated to heat air to be sent to the cold chamber and to reduce the emissions of toxic substances that are generated with traditional regenerative burners .

[0033] At the same time, to the accumulation structure 228a' the first burner 228a, superheated in the previous operating step, air to be heated is sent , which air, once heated, is mixed with combustible gas and feeds the combustion in the first hot chamber 224a .

[0034] At the same time , fumes drawn from the second hot chamber 224b are sent to a storage structure 230b' of the second regenerator 230b to superheat said storage structure 230b' .

[0035] Moreover, at the same time, fumes drawn from the second hot chamber 224b are sent to the accumulation structure 228b' of the second burner 228b to superheat said storage structure .

[0036] During the first operating step, the fumes of the first hot chamber 224a transit in the cold chamber 222 , participating in the heating of the scrap, and the fumes of the cold chamber 222 transit in the second hot chamber 224b, participating in the combustion and therefore in the melting of the metal .

[0037] During a second operating step, to the storage structure 230b' of the second regenerator 230b, superheated in the previous operating step, air to be heated is sent to the storage structure, which air, once heated, is sent to the cold chamber 222 by means of the second air outlet pipe 234b .

[0038] At the same time, to the accumulation structure 228b' of the second burner 228b, superheated in the previous operating step, air to be heated is sent to the storage structure, which air, once heated, is mixed with combustible gas and feeds the combustion in the second hot chamber 224b .

[0039] At the same time, fumes drawn from the first hot chamber 224a are sent to the storage structure 230a' of the first regenerator 230a to superheat said accumulationstructure 228a' .

[0040] Moreover, at the same time, the fumes drawn from the first hot chamber 224a are sent to the accumulation structure 228a' of the first burner 228a to superheat said accumulation structure 228a' .

[0041] During the first operating step, the fumes of the first hot chamber 224a transit in the cold chamber 222 , participating in the heating of the scrap, and the fumes of the cold chamber 222 transit in the second hot chamber 224b, participating in the combustion and therefore in the melting of the metal .

[0042] Furnace 200 further comprises electronic management means , for example comprising an electronic board or a microchip, operatively connected to the furnace components for managing the operating steps .

[0043] According to constructional variant , furnace 200 comprises at least a further burner 240 operating in the cold chamber 214 , or at least a further burner 241a operating in the first hot chamber 224a or at least a further burner 241b operating in the second hot chamber 224b, mainly for the purpose of increasing the temperature in the cold chamber 222 or in one of the hot chambers 224a, 224b when required .

[0044] Scrap S located on the dry floor 212 of the cold chamber 222 is initially heated by the hot environment( radiation by temperature 750 ° C) and by said at least a further burner 240 . Upon reaching a temperature indicatively equal to 200 ° C, scrap S will start emitting an organic volatile compound which will be at least partially burned by the air introduced by the regenerator group 230 , thus generating heat such as to partially self-sustain the process of heating the scrap itself .

[0045] Moreover, the portions Psi of scrap S are immersed in the part Be of bath B of the cold chamber 222 in time sequence . In other words , portion Psi is first immersed, which entered first and is close to tank 214 ; once portion Psi is immersed, the other portions Ps2 . . . Psn advance from the main access 202 towards tank 214 and the further portion Psn+1 is introduced into the furnace . By fractioning the loading, the release of volatile organic compound of the scrap loaded into the cold chamber 222 is thus distributed . Each load of portion Psi emits volatile organic compound according to a curve including a climbing ramp, a peak stage, and a decreasing stage . Since there are several loads on the dry floor, there will be scrap in a different emission step, thus it is possible to ensure an overall more homogeneous distribution of the release of the volatile organic compound .

[0046] A sufficiently heated scrap portion is thus immersedin the bath, indicatively at about 550 ° C, to ensure the almost complete volatilization of the volatile organic compounds .

[0047] In the cold chamber 222 , the air exiting from each regenerator 230a, 230b reacts with the fumes produced by the combustion of the volatile organic components , creating a sort of "distributed burner" in the cold chamber 222 , i . e . the fumes obtained in the hot chambers 224a, 224b preheat the air in the cold chamber 222 . In other words , it is possible to extract thermal energy from the fumes exiting from the hot chambers 224a, 224b, store it in the storage structures 230a ' , 230b' of each regenerator 230a, 230b and transfer it to the air entering the cold chamber 222 .

[0048] Moreover, according to a constructional variant , furnace 200 comprises a first lance group 250a comprising at least one oxygen lance, configured to introduce oxygen into the first hot chamber 224a, for example through said openings 226a of the primary partition wall 220 , and a second lance group 250b, comprising at least one oxygen lance, configured to introduce oxygen into the second hot chamber 224b, for example through said openings 226b of the primary partition wall 220 .

[0049] In particular, in the first operating step, the fumes found in the cold chamber 222 pass into the secondhot chamber 224b and preferably oxygen is introduced into the second hot chamber 224b by operating the second lance group 250b so as to have a combustion in the second hot chamber 224b of the fumes originating from the cold chamber 222 , containing volatile organic compound not yet burned .

[0050] In the second operating step, the fumes found in the cold chamber 222 pass into the first hot chamber 224a and preferably oxygen is introduced into the first hot chamber 224a by operating the first lance group 250a so as to have a combustion in the first hot chamber 224a of the fumes originating from the cold chamber 222 .

[0051] Moreover, in a constructional variant , furnace 200 comprises a further fume outlet pipe operating in the first hot chamber and the second hot chamber for part of the fumes to exit from the first hot chamber and the second hot chamber towards the treatment system .

[0052] Therefore, according to the invention, part of the fumes of the hot chamber is used, by means of a regenerator group, to preheat air to be introduced into the cold chamber . Such air aims to completely or partially burn the volatile organic compound emitted by the scrap by recovering the heat thereof directly in the cold chamber and partially self-sustaining the heating of the scrap itself . The fumes of the cold chamber,containing part of the unburned volatile organic compound, pass then into the hot chamber where the combustion of the volatile organic compound is completed with the oxygen lances (triple-chamber and dual regeneration furnace ) . The unburned emissions are thus abated and all the heat available in the volatile organic compound is recovered in the furnace .

[0053] Innovatively, the triple-chamber melting furnace according to the present invention achieves the aforesaid object ; such a furnace is indeed particularly effective and efficient in treating aluminum scrap polluted by volatile organic compounds .

[0054] In this respect , the table in Figure 3 , including partly experimental data and partly data originating from mathematical models , shows the specific consumption of natural gas and oxygen in the melting step in three types of melting furnace : a furnace of the prior art (Figure 1 , standard double-chamber) and a triple-chamber and dual regeneration furnace (Figure 2 ) .

[0055] The table highlights that the standard dual chamber furnace, for melting aluminum scrap containing a VOC fraction between 1 and 3% , has a specific consumption of 60 Nm3 of natural gas (NG) per ton of molten metal and no consumption of oxygen . The triple chamber and dual regeneration furnace according to the present invention,for melting aluminum scrap containing a VOC fraction between 2 and 5% , has a specific consumption from 34 to 17 Nm3 of natural gas (NG) per ton of molten metal and a specific consumption from 7 to 30 Nm3 of oxygen (02 ) per ton of molten metal .

[0056] Advantageously, the triple-chamber furnace according to the invention further ensures that the scrap is immersed in the aluminum bath after performing the complete removal of the volatile organic compounds . This eliminates the release of black smoke upon the immersion of the contaminated scrap and significantly reduces the slag on the bath generated by the organic component in liquid phase, thus increasing the metal yield of the furnace, i . e . , the ratio between dripped aluminum and loaded aluminum .

[0057] Advantageously, the regenerative system of the triple-chamber furnace object of the present invention allows to transfer thermal energy from the hot chamber to the cold chamber without transferring material ( fumes or liquid) between the chambers .

[0058] It is clear that a technician in the field, in order to satisfy contingent needs , could make modifications to the double-chamber furnace described above, all of which are contained within the scope of protection defined by the following claims .

Claims

Claims1. A melting furnace (200) for melting aluminum scrap (S) , comprising:- a cold chamber (222) , accessible from a main access (202) for introducing the scrap (S) , a dry floor (112; 212) for supporting the scrap (S) to be preheated and a part of a tank (214) for containing molten metal (B; Be) up to a free surface;- at least a first hot chamber (224a) comprising another part of the tank (214) for containing the molten metal (B, Bha) , and a second hot chamber (224b) comprising another part of the tank (214) for containing the molten metal (B, Bhb) , said first hot chamber (224a) and second hot chamber (224b) being separated from the cold chamber (222) above the free surface of the molten metal by a primary partition wall (220) provided with at least a first opening (226a) for the passage of fumes from the cold chamber (222) to the first hot chamber (224a) and at least one second opening (226b) for the passage of fumes from the cold chamber (222) to the second hot chamber (224b) ;- at least a regenerative burner group (228) comprising an accumulation structure (228a' , 228b' ) and configured to perform a combustion in said first hot chamber (224a) and second hot chamber (224b) ;- at least a regenerator group (230) comprising a storage structure (230a' , 230b' ) and configured to draw fumes from said first hot chamber (224a) and second hot chamber (224b) , superheat said storage structure (230a' , 230b' ) by said fumes, and introduce heated air from said storage structure (230a', 230b' ) into the cold chamber (222) .

2. A melting furnace (200) according to claim 1, comprising at least one additional burner (240) adapted to operate in the cold chamber (222) , preferably arranged on the ceiling of the cold chamber (222) .

3. A melting furnace (200) according to claim 1 or 2, comprising at least one additional burner (241a, 241b) adapted to operate in said at least one hot chamber (224a, 224b) , preferably arranged on the ceiling of the at least one hot chamber (224a, 224b) .

4. A melting furnace (200) according to any one of the preceding claims, comprising at least one lance group (250a, 250b) configured to introduce oxygen into the at least one hot chamber (224a, 224b) .

5. A melting furnace (200) according to any one of the preceding claims, comprising a fume outlet pipe (142) operating in the at least one hot chamber (224a, 224b) for at least one part of the fumes found in said at least one hot chamber (224a, 224b) to exit towards a fume treatment system.

6. A melting furnace (200) according to any one of the preceding claims, comprising a fume outlet pipe (238) operating in the cold chamber for at least one part of the fumes found in the cold chamber (222) to exit towards a fume treatment system.

7. A melting furnace (200) according to any one of the preceding claims, wherein the first hot chamber (224a) and the second hot chamber (224b) extending from the primary partition wall (220) to a bottom wall (206) and being separated from each other above the free surface of the molten metal by a secondary partition wall (225) .

8. A melting furnace according to claim 1, wherein the burner group (228) comprises a first regenerative burner (228a) operating in the first hot chamber (224a) and a second regenerative burner (228b) operating in the second hot chamber (224b) , cooperating with each other.

9. A melting furnace according to claim 8, wherein the first burner (228a) is arranged on the bottom wall (206) of the first hot chamber (224a) and the second burner (228b) is arranged on the bottom wall (206) of the second hot chamber (224b) .

10. A melting furnace according claim 1, wherein the regenerator group (230) comprises a first regenerator (230a) and a second regenerator (230b) , wherein- the first regenerator (230a) is connected to an airinlet pipe (232) and a first air outlet pipe (234a) , which leads into the cold chamber (222) at the dry floor (212) , and a first fume inlet pipe (236a) , which draws fumes from the first hot chamber (224a) , and a fume outlet pipe (238) , and- the second regenerator (230b) is connected to an air inlet pipe (232) and a second air outlet pipe (234b) , which leads into the cold chamber (222) at the dry floor (212) , and a second fume inlet pipe (236b) , which draws fumes from the second hot chamber (224b) , and a fume outlet pipe (238) .

11. A method of operating a melting furnace (200) for aluminum scrap (S) , wherein the furnace (200) comprises a cold chamber (222) accommodating the scrap (S) , a first hot chamber (224a) , and a second hot chamber (224b) , comprising the following recursive steps:- in a first operating step: i) feeding air to be heated to a previously superheated accumulation structure (228a' ) of a first regenerative burner (228a) and sending the air thus heated and combustible gas to the first burner (228a) to have a combustion in the first hot chamber (224a) ; ii) feeding air to be heated to a previously superheated storage structure (230a' ) of a first regenerator (230a) and sending the air thus heated to the cold chamber(222) ; iii) sucking fumes from the second hot chamber (224b) to superheat a accumulation (228b' ) structure of a second regenerative burner (228b) ; iv) sucking fumes from the second hot chamber (224b) to superheat a storage structure (230b' ) of a second regenerator (230b) ; v) allowing the fumes to transit from the first hot chamber (224a) to the cold chamber (222) and from the cold chamber (222) to the second hot chamber (224b) ;- in a second operating step: i) feeding air to be heated to the previously superheated accumulation structure (228b' ) of the second burner (228b) and sending the air thus heated and combustible gas to the second burner (228b) to have a combustion in the second hot chamber (224b) ; ii) feeding air to be heated to the previously superheated storage structure (230b' ) of the second regenerator (230b) and sending the air thus heated to the cold chamber (222) ; iii) sucking fumes from the first hot chamber (224a) to superheat the accumulation structure (228a' ) of the first burner (228a) ; iv) sucking fumes from the first hot chamber (224a) to superheat the storage structure (230a' ) of the firstregenerator (230a) ; v) allowing the fumes to transit from the second hot chamber (224b) to the cold chamber (222) and from the cold chamber (222) to the first hot chamber (224a) .

12. An operating method according to claim 11, comprising the following step:- in the first operating step between step iv) and step v) : iva) feeding air and combustible gas to at least one additional burner (140) operating in the cold chamber (222) .

13. An operating method according to claim 11 or 12, comprising the following step:- in the first operating step following step v) : vi) feeding oxygen to an oxygen lance (250b) operating in the second hot chamber (224b) to burn at least part of the fumes entering the second hot chamber (224b) .

14. An operating method according to any one of claims 11 to 13, comprising the following step:- in the second operating step following step v) : vi) feeding oxygen to an oxygen lance (250a) operating in the first hot chamber (224a) to burn at least part of the fumes entering the first hot chamber (224a) .

15. An operating method according to any one of claims 11 to 14, wherein the scrap (S) arranged in the cold chamber(222) comprises separate scrap portions (Psi, with i 1 n) and said scrap portions are introduced in time sequence into the cold chamber (222) from the environment outside the furnace, a first portion (Psi) being the scrap portion introduced first and an n-th portion (Psn) being the scrap portion introduced last.

16. An operating method according to any one of claims 11 to 15, wherein the scrap (S) arranged in the cold chamber (222) comprises separate scrap portions (Psi, with i = 1 n) and said scrap portions are introduced in time sequence into the molten metal bath (Be) of the cold chamber (122; 222) , a first portion (Psi) being the scrap portion introduced first and an n-th portion (Psn) being the scrap portion introduced last.

17. A method of operating a melting furnace (200) for aluminum scrap (S) , wherein the furnace (200) comprises a cold chamber (222) accommodating the scrap (S) and at least one hot chamber (224a) , wherein the scrap (S) arranged in the cold chamber (222) comprises separate scrap portions (Psi, with i = 1 ... n) , and said scrap portions are introduced in time sequence into the cold chamber (122; 222) from the environment outside the furnace, a first portion (Psi) being the scrap portion introduced first and an n-th portion (Psn) beingthe scrap portion introduced later, and said scrap portions are introduced in time sequence into the molten metal bath (Be) of the cold chamber ( 222 ) , the first portion (Psi ) being the scrap portion introduced first and the n-th portion (Psn) being the scrap portion introduced later .

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