WO2025120453A1

WO2025120453A1 - Double-chamber melting furnace for aluminum scrap and operating method

Info

Publication number: WO2025120453A1
Application number: PCT/IB2024/061927
Authority: WO
Inventors: Bruno Mancini; Roberto Albertoni; Valerio BATTAGLIA; Massimo Moschini
Original assignee: COMETAL ENGINEERING SpA
Current assignee: COMETAL ENGINEERING SpA
Priority date: 2023-12-04
Filing date: 2024-11-27
Publication date: 2025-06-12
Anticipated expiration: 2026-06-04
Also published as: IT202300025821A1; WO2025120455A1

Abstract

A melting furnace (100) for melting aluminum scrap (S) contaminated by volatile organic compounds (VOCs) comprises a cold chamber (122), at least one hot chamber (124), at least one regenerative burner group (128) configured to perform a combustion in said at least one hot chamber (124), and at least one regenerator group (130) configured to draw fumes from said at least one hot chamber (124), superheat a storage structure by said fumes, and introduce heated air from said storage structure into the cold chamber (122).

Description

DOUBLE-CHAMBER MELTING FURNACE FOR ALUMINUM SCRAP AND

OPERATING METHOD

Field of the invention

[0001] The present invention belongs to the field of systems for manufacturing aluminum; in particular, the present invention relates to a double-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 originating from 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% ) from

Hertwich 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 the melting 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 sucked by 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 double-chamber melting furnace for aluminum scrap which is particularly effective and efficient in treating aluminum scrap contaminated by volatile organic compounds , thus improving the processes and systems currently available . In particular, it is the object of the present invention to provide a double-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 double-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 2 diagrammatically shows a two chamber and dual regeneration melting furnace, according to the present invention;

Figure 3 is a comparative table between the specific consumption of the furnace according to the prior art and of the furnace according to the present invention . Description of the invention

Double-chamber and dual regeneration melting furnace

[0015] With reference to Figure 2 , a double chamber melting furnace (two chamber melting furnace ) for aluminum scrap is indicated by reference numeral 100 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 1 and 3% by weight ( 1 < VOCs <3% ) .

[0016] The melting furnace 100 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 14 meters and width W is 9 meters .

[0017] The inner compartment is accessible from a main access 102 , preferably positioned in the direction of the width W of the inner compartment , by opening a door 104 . On the side opposite to the main access 102 , the compartment is delimited by a bottom wall 106 ; finally, laterally, the inner compartment is delimited by side walls 108 , 110 . [0018] Furnace 100 further comprises a dry floor 112 positioned in the inner compartment , behind the main access 102 . The dry floor 112 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 100 further comprises a tank 114 containing the molten metal bath B, positioned between the dry floor 112 and the bottom wall 106 of furnace 100 .

[0020] Furnace 100 further comprises a primary partition wall 120 arranged in the inner compartment , between the dry floor 112 and the bottom wall 106, extending above the free surface of bath B, and divides the inner compartment into a cold chamber 122 , on the side of the main access 102 , and a hot chamber 124 , on the side of the bottom wall 106 .

[0021] In particular, the cold chamber 122 comprises part of tank 114 , that from the dry floor 112 to the primary partition wall 120 , so that a part Be of the molten metal bath B is in the cold chamber 122 , and the dry floor 112 . The hot chamber 124 instead comprises the other part of tank 114 , that from the primary partition wall 120 to the bottom wall 106, so that another part Bh of the molten metal bath B is in the hot chamber 124 . [0022] The primary partition wall 120 further has at least one opening 126 which puts the cold chamber 122 and the hot chamber 124 in communication .

[0023] The melting furnace 100 includes a regenerative system comprising a regenerative burner group 128 and a regenerator group 130 .

[0024] As anticipated, the melting furnace 100 comprises a regenerative burner group 128 operating in the hot chamber 124 , and configured to perform a combustion in said hot chamber 124 . The burner group 128 comprises a first regenerative burner 128a and a second regenerative burner 128b cooperating with each other . Furthermore, each regenerative burner 128a, 128b comprises respectively an accumulation structure 128a ' , 128b ' , suitable for accumulating and heating the air to be heated and sending the thus heated air and combustible gas to the respective burner 128a, 128b to perform combustion in the hot chamber 124 .

[0025] For example, the first burner 128a is arranged on one of the side walls 108 of furnace 100 , close to the bottom wall 106, while the second burner 128b is arranged on the other side wall 110 , close to the primary partition wall 120 .

[0026] According to a constructional variant (not shown ) , the first burner 128a and the second burner 128b are arranged on the bottom wall 106 .

[0027] As anticipated, furnace 100 further comprises a regenerator group 130 operating between the hot chamber 124 and the cold chamber 122 . The regenerator group 130 comprises a first regenerator 130a and a second regenerator 130b, each regenerator 130a, 130b being provided with a storage structure 130a' , 130b' , for example made of ceramic, suitable for drawing heat from hot fumes of the hot chamber 124 , storing it and transferring the stored heat to air to be heated in the cold chamber 122 . It is important to note that the regenerators 130a, 130b of the regenerative system are not directly connected to the burners 128a, 128b .

[0028] Each regenerator 130a, 130b is connected to an air inlet pipe 132 , to an air outlet pipe 134 , which leads into the cold chamber 122 , preferably at the dry floor 112 , to a first fume inlet pipe 136, which draws fumes from the first hot chamber 124 , and to a fume outlet pipe 138 , connected to a fume treatment system .

[0029] During a first working phase, the fumes from the hot chamber 124 overheat the storage structure 130a ' , 130b' of each regenerator 130a, 130b, allowing thermal energy to be stored; the air thus heated is sent to the cold chamber 122 . 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 .

[0030] In a second operating step, the storage structure 130a ' , 130b' heats the incoming cold air by means of the stored thermal energy and the air thus heated is introduced into the cold chamber 122 to preheat the aluminum scrap S . While the first regenerator 130a is in the first operating step, the second regenerator 130b is in the second operating step, and vice versa .

[0031] In the hot chamber 124 , in a first operating step, the first burner 128a is fed with air and combustible gas , e . g . , natural gas or a mixture of combustible gases . The incoming air is heated by the storage structure of the first burner 128a . The first burner 128a carries out the combustion of the gas/heated air mixture . At the same time, the second burner 128b sucks the fumes from the hot chamber 124 and superheats the storage accumulation 128b' of the second burner 128b .

[0032] In the second operating step, the first burner 128a sucks the fumes from the hot chamber 124 and superheats the storage structure 128a' of the first burner 128a . At the same time, the second burner 128b is fed with air and combustible gas ; the incoming air is heated by the accumulation structure 128b' of the second burner 128b .

The second burner 128b carries out the combustion of the gas/heated air mixture . While the first burner 128a is in the first working phase, the second burner 128b is in the second working phase, and vice versa .

[0033] Furnace 100 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 .

[0034] According to a constructional variant , furnace 100 comprises at least a further burner 140 operating in the cold chamber 122 , preferably arranged on the ceiling of the cold chamber, mainly for the purpose of increasing the temperature in the cold chamber 122 when required .

[0035] Scrap S located on the dry floor 112 of the cold chamber 122 is initially heated by the hot environment ( radiation by temperature >750 ° C) and by said at least a further burner 140 . 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 130 , thus generating heat such as to partially self-sustain the process of heating the scrap itself .

[0036] Moreover, the portions Psi of scrap S are immersed in the part Be of bath B of the cold chamber 122 in time sequence . In other words , portion Psi is first immersed which entered first and is close to tank 114 ; once portion Psi is immersed, the other portions Ps2 . . . Psn advance from the main access 102 towards tank 114 and the further portion Psn+1 is introduced into the furnace . In this way, by dividing the loading, the release of volatiles from the scrap loaded into the cold chamber 122 is 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, in this ay it is possible to ensure an overall more homogeneous distribution of the release of the volatile organic compound .

[0037] A sufficiently heated scrap portion is thus immersed in the bath, indicatively at about 550 ° C, to ensure the almost complete volatilization of volatile organic compounds .

[0038] In the cold chamber 122 , the air exiting from each regenerator 130a, 130b reacts with the fumes produced by the combustion of the volatile organic components , creating a sort of "distributed burner" in the cold chamber 122 , i . e . the fumes obtained in the hot chamber 124 pass into the cold chamber through the air outlet duct 134 and preheat the air in the cold chamber 122 . In other words , it is possible to extract thermal energy from the fumes exiting from the hot chamber 124 , store it in the storage structures 130a ' , 130b' of each regenerator 130a, 130b and transfer it to the air entering the cold chamber 122 .

[0039] Moreover, the fumes found in the cold chamber 122 , containing also the fumes generated by the combustion of the volatile organic compounds , pass into the hot chamber 124 through opening 126 and contribute to heating the bath . Any volatile organic compounds still unburned are burned in the hot chamber 124 with the excess air of the burner group 128 .

[0040] Moreover, during the operation of the furnace, the concentration of oxygen 02 and carbon dioxide CO2 is monitored by means of probes in both the cold chamber 122 and the fumes exiting from the hot chamber 124 . In particular, the management means manage the flow rate of air introduced into the cold chamber 122 by the regenerator group 130 to maintain an oxygen concentration close to 0 and a target value of specific residual CO2 for each type of scrap loaded . It is thus possible to regulate the excess air of the burner group 128 to complete the combustion of the volatile organic compound passing into the hot chamber 124 through opening 126 . The complete combustion is checked by the probes in the fumes exiting from the hot chamber 124 .

[0041] Moreover, in a constructional variant , furnace 100 comprises a further fume outlet pipe 142 operating in the hot chamber 124 , preferably behind the bottom wall 106, for part of the fumes to exit towards the treatment system .

[0042] 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 excess air of the regenerative burner group (double-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 .

[0043] Innovatively, the double-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 .

[0044] 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 double-chamber and dual regeneration furnace (Figure 2 ) .

[0045] 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 . On the other hand, the dual chamber and dual regeneration furnace according to the present invention, for melting aluminum scrap containing a VOC fraction between 1 and 3% , has a specific consumption ranging from 55 to 40 Nm3 of natural gas (NG) per ton of molten metal and no consumption of oxygen .

[0046] Advantageously, the double-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 .

[0047] Advantageously, the regenerative system of the double-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 .

[0048] 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

1. A melting furnace (100) for melting aluminum scrap (S) , comprising:

- a cold chamber (122) , accessible from a main access (102) for introducing the scrap (S) , a dry floor (112) for supporting the scrap (S) to be preheated and a part of a tank (114) for containing molten metal (B; Be) up to a free surface;

- at least a hot chamber (124) comprising another part of the tank (114) for containing the molten metal (B, Bh) , said at least one hot chamber being separated from the cold chamber (122) above the free surface of the molten metal by a primary partition wall (120) provided with at least one opening (126) for the fumes to transit from the cold chamber (122) to the at least one hot chamber (124) ;

- at least a regenerative burner group (128) comprising an accumulation structure (128a', 128b' ) and configured to perform a combustion in said at least one hot chamber (124; 224a, 224b) ;

- at least a regenerator group (130) comprising a storage structure (130a', 130b' ) and configured to draw fumes from said at least one hot chamber (124) , superheat said storage structure (130a', 130b' ) by said fumes, and introduce heated air from said storage structure (130a', 130b' ) into the cold chamber (122) .

2. A melting furnace (100) according to claim 1 comprising at least one additional burner (140) adapted to operate in the cold chamber (122) , preferably arranged on the ceiling of the cold chamber (122) .

3. A melting furnace (100) according to any one of the preceding claims, comprising a fume outlet pipe (142) operating in the at least one hot chamber (124) for at least one part of the fumes found in said at least one hot chamber (124) to exit towards a fume treatment system.

4. A melting furnace (100) according to any one of the preceding claims, comprising a fume outlet pipe (138) operating in the cold chamber (122) for at least one part of the fumes found in the cold chamber (122) to exit towards a fume treatment system.

5. A melting furnace (100) according to any one of the preceding claims, comprising a single hot chamber (124) extending from the primary partition wall (120) to a bottom wall (106) .

6. A melting furnace (100) according to claim 1, wherein the burner group (128) comprises a first regenerative burner (128a) and a second regenerative burner (128b) cooperating with each other.

7. A melting furnace (100) according to claim 6, wherein the first burner (128a) is arranged on a side wall (108) of the furnace, close to the bottom wall (106) , and the second burner (128b) is arranged on another side wall (110' ) , close to the primary partition wall (120) .

8. A melting furnace (100) according to claim 6, wherein the first burner (128a) and the second burner (128b) are arranged on the bottom wall (106) .

9. A melting furnace (100) according to any one of claims 5 to 8, wherein the regenerator group (130) comprises a first regenerator (130a) and a second regenerator (130b) , each regenerator (130a, 130b) being connected to an air inlet pipe (132) and an air outlet pipe (134) , which leads into the cold chamber (122) , and a fume inlet pipe (136) , which draws fumes from the hot chamber (124) , and a fume outlet pipe (138) .

10. A method of operating a melting furnace (100) for aluminum scrap (S) , wherein the furnace (100) comprises a cold chamber (122) accommodating the scrap (S) and a single hot chamber (124) , comprising the following recursive steps:

- in a first operating step: i) feeding air to be heated to a previously superheated accumulation structure (128a' ) of a first regenerative burner (128a) and sending the air thus heated and combustible gas to the first burner (128a) to have a combustion in the hot chamber (124) ; ii) sucking fumes from the hot chamber (124) to superheat an accumulation structure (128b' ) of a second regenerative burner (128b) ; iii) sucking fumes from the hot chamber (124) to superheat a storage structure (130a' ) of a first regenerator (130a) ; iv) feeding air to be heated to a previously superheated storage structure (130b' ) of a second regenerator (130b) and sending the air thus heated to the cold chamber (122) ;

- in a second operating step: i) feeding air to be heated to the previously superheated accumulation structure (128b' ) of the second burner (128b) and sending the air thus heated and combustible gas to the second burner (128b) to have a combustion in the hot chamber (124) of the furnace (100) ; ii) sucking fumes from the hot chamber (124) to superheat the accumulation structure (128a' ) of the first burner (128a) ; iii) sucking fumes from the hot chamber (124) to superheat the storage structure (130b' ) of the second regenerator (130b) ; iv) feeding air to be heated to the previously superheated storage structure (130a' ) of the first regenerator (130a) and sending the air thus heated to the cold chamber (122) ;

- during the first operating step and the second operating step, allowing the fumes to transit from the cold chamber (122) to the hot chamber (124) .

11. An operating method according to claim 10, comprising the following step:

- in the first operating step following step iv) : v) feeding air and combustible gas to an additional burner (140) operating in the cold chamber (122) .

12. An operating method according to any one of claims 10 to 11, wherein the scrap (S) arranged in the cold chamber (122) comprises separate scrap portions (Psi, with i = 1 n) and said scrap portions are introduced in time sequence into the cold chamber (122) 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.

13. An operating method according to any one of claims 10 to 12, wherein the scrap (S) arranged in the cold chamber (122) 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) , a first portion (Psi) being the scrap portion introduced first and an n-th portion (Psn) being the scrap portion introduced last.

14. A method of operating a melting furnace (100) for aluminum scrap (S) , wherein the furnace (100) comprises a cold chamber (122) accommodating the scrap (S) and at least one hot chamber (124) , wherein the scrap (S) arranged in the cold chamber (122) comprises separate scrap portions (Psi, with i = 1 ... n) , and said scrap portions are introduced in time sequence into the cold chamber (122) 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 later, and said scrap portions are introduced in time sequence into the molten metal bath (Be) of the cold chamber (122) , the first portion (Psi) being the scrap portion introduced first and the n-th portion (Psn) being the scrap portion introduced later.