WO2023170721A1

WO2023170721A1 - Feed apparatus for feeding a metal charge to a melting furnace

Info

Publication number: WO2023170721A1
Application number: PCT/IT2023/050069
Authority: WO
Inventors: Enrico RIGA; Marco Ansoldi; Emanuele TRUCILLO; Luigi Testa
Original assignee: Danieli & C. Officine Meccaniche S.P.A.
Priority date: 2022-03-10
Filing date: 2023-03-09
Publication date: 2023-09-14

Abstract

Feed apparatus (10) for feeding a metal charge (C) toward a melting furnace (100), wherein the apparatus (10) comprises a conveying channel (11) and a fixed hood (12) which is configured to hermetically close the upper part of the conveying channel (1 1) in such a way as to define an internal tunnel (13) having a longitudinal axis (X) and extending from an inlet end (15) for the introduction of the metal charge (C) to an outlet end (16) configured to be disposed adjacent to the melting furnace (100).

Description

“FEED APPARATUS FOR FEEDING A METAL CHARGE TO A MELTING FURNACE”

FIELD OF THE INVENTION The present invention concerns a feed apparatus for feeding a metal charge, understood here as a load of metal material such as scrap iron, to a melting furnace, for example an electric arc furnace, of a steel plant. In particular, the feed apparatus can be used to feed the metal charge continuously, preferably by preheating it before introducing it into the melting furnace. BACKGROUND OF THE INVENTION

The feeding, or loading, of a metal charge, which can even weigh several tons, into an electric arc furnace of the known type, can take place both in a discontinuous manner, for example by means of suitable charge baskets, and also by means of a continuous charging system, also known by the English term “Endless Charging System”, or simply ECS.

Known continuous charging systems substantially consist of a feed apparatus, even a few tens of meters long, which comprises a conveying channel and a cover, or hood, which seals the latter hermetically, thus defining an internal tunnel in which the metal charge is made to advance from an inlet end to an outlet end disposed adjacent to the melting furnace.

The internal tunnel of known feed apparatuses usually has a cross section which remains constant along the entire longitudinal development of the apparatus itself.

Normally, the conveying channel is provided with, or associated with, a known movement system, for example functioning with eccentric masses, which allows the metal charge to advance from the inlet end toward the melting furnace.

Furthermore, during the advance of the metal charge, the high temperature melting fumes, exiting from the melting furnace, are sucked inside the tunnel of the feed apparatus to flow counter-current with respect to the metal charge, in order to preheat the latter before it enters the melting furnace itself. One disadvantage of known feed apparatuses is that only the upper layer of the metal charge, that is, the layer which is directly hit by the flow of melting fumes, can be adequately heated, while the lower part of the metal charge remains cold, or in any case very much less heated than the upper one. Among the known documents, US 4.676.742 A is known, which describes a feed and preheating apparatus for a metal charge having an internal chamber with a rectangular cross section which varies linearly in height and in width from the inlet end to the outlet end. The inlet end, from which the metal charge is introduced, has a smaller section than the outlet end, so as to avoid compression of the material when it is pushed toward the outlet. Both the bottom wall as well as the upper wall of the chamber are inclined by respective angles, which are different from each other. Furthermore, the upper wall has a linear longitudinal profile, and the bottom wall has a profile with inclined steps provided with apertures through which the fumes for heating the metal charge are introduced.

Document EP 3.149.421 Al describes an apparatus for feeding a metal charge to a melting furnace in which the metal charge is pre-heated by the heating fumes which flow in the opposite direction to that of the feed of the metal charge. The feed apparatus comprises an internal chamber having a height that varies from the inlet end to the outlet end, more specifically the inlet end has a smaller cross section than the outlet end. The bottom wall has a stepped longitudinal profile which determines the variation in height, wherein the steps are provided with apertures for the circulation of the heating fumes. The upper wall has a linear longitudinal profile. Document CN 112501383 A describes a tunnel-type continuous feed preheating device with an internal chamber having a cross section that varies in height. The bottom wall has a stepped longitudinal profile which determines the variation in height, while the upper wall has a linear longitudinal profile.

It follows that, in the state of the art, a considerable fraction of the energy content of the fumes is not adequately exploited to heat the metal charge, in particular in the zone close to the inlet end of the feed apparatus.

There is therefore a need to perfect, or provide, a feed apparatus for feeding a metal charge to a melting furnace, which can overcome at least one of the disadvantages of the state of the art. To do this, it is necessary to solve the technical problem of guaranteeing a preheating of the metal charge that is uniform and as high as possible along the entire length of the internal feed tunnel, which can even be several tens of meters long. In particular, one purpose of the present invention is to provide a feed apparatus for feeding a metal charge substantially continuously, which can even weigh several tons, to a melting furnace, which allows to adequately preheat the entire metal charge to a high temperature, before it enters the melting furnace, using the fumes exiting from the furnace.

Another purpose of the present invention is to provide a feed apparatus for feeding a metal charge to a melting furnace which can exploit to the utmost the energy content of the fumes exiting the furnace, so that the energy consumption of the melting furnace is also optimized. Another purpose of the present invention is to provide a feed apparatus for feeding a metal charge to a melting furnace which is simple to manufacture, and which has low manufacturing and operating costs.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claim. The dependent claims describe other characteristics of the present invention or variants to the main inventive idea. In accordance with the above purposes, and to resolve the technical problem disclosed above in a new and original way, also achieving considerable advantages compared to the state of the prior art, a feed apparatus according to the present invention for feeding a metal charge toward a melting furnace comprises a conveying channel and a hood configured to close the upper part of the conveying channel in such a way as to define an internal tunnel having a longitudinal axis and extending from an inlet end for the introduction of the metal charge to an outlet end configured to be disposed adjacent to the melting furnace, wherein the cross section of the tunnel varies from a minimum section in correspondence with the inlet end to a maximum section in correspondence with the outlet end. In accordance with another aspect of the present invention, the hood comprises at least one covering wall having a longitudinal profile with a serrated shape.

The fact of providing a serrated-shaped profile in the upper wall of the conveying tunnel that conveys the metal charge has the advantage of increasing the vorticity and turbulence of the heating fumes fed in the opposite sense to the metal charge, so as to induce them to enter more deeply into the latter. This allows to optimize the heat exchange between the fumes and the metal charge.

In accordance with one aspect of the present invention, the hood has an internal height which varies from a minimum height, disposed toward, or in correspondence with, the minimum section, to a maximum height, disposed toward, or in correspondence with, the maximum section.

In accordance with another aspect of the present invention, the covering wall, having said longitudinal profile with a serrated shape, has an internal height which increases in a substantially linear manner from the minimum height, in correspondence with the inlet end, to the maximum height, in correspondence with the outlet end.

In accordance with another aspect of the present invention, the hood is made in a single body. In accordance with another aspect of the present invention, the hood comprises two or more modules disposed adjacent to each other along the longitudinal axis.

In accordance with another aspect of the present invention, each of the modules has a longitudinal profile such that it has a lower height and a greater height. Moreover, the module which is in correspondence with the inlet end has a lower height equal to the minimum height, and the module which is in correspondence with the outlet end has a greater height equal to the maximum height.

In accordance with another aspect of the present invention, the modules are connected to each other in such a way that the lower height of each of the modules is in correspondence with the greater height of another module adjacent thereto. In accordance with another aspect of the present invention, the greater height of each of the modules is greater than the lower height of the module adjacent thereto and disposed toward the outlet end, in such a way as to obtain a longitudinal profile with a serrated shape.

In accordance with another aspect of the present invention, the hood comprises upper lateral walls disposed and/or shaped in such a way as to define a variable width at least in one part of the hood, so as to cause localized accelerations in the fumes at exit from the melting furnace and directed toward the inlet end of the tunnel. In accordance with another aspect of the present invention, in correspondence with the vertical segments of the serrated-shaped profile of the hood, corresponding apertures are made in order to make air or other gasses enter into the tunnel in a controlled manner, and with which there are possibly associated respective hatches which are, if necessary, able to be selectively opened.

DESCRIPTION OF THE DRAWINGS

These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein: - fig. 1 is a schematic and partly sectioned lateral view of a feed apparatus for feeding a metal charge toward a melting furnace, in accordance with a first embodiment of the present invention;

- fig. 2 is a schematic and partly sectioned lateral view of a feed apparatus for feeding a metal charge toward a melting furnace, in accordance with a second embodiment of the present invention;

- fig. 3 is a section view of a first detail of the apparatus of fig. 1 ;

- fig. 4 is a section view of a second detail of the apparatus of fig. 1 ;

- fig. 5 is an enlarged detail of the second detail of fig. 4;

- fig. 6 is a front view of a cross section taken at an inlet end of the apparatus of figs. 1 and 2;

- fig. 7 is a front view of a cross section taken at an outlet end of the apparatus of figs. 1 and 2;

- fig. 8 is a schematic top view of the feed apparatus according to another embodiment; - fig. 9 is a schematic top view of the feed apparatus according to an additional embodiment.

We must clarify that in the present description the phraseology and terminology used, as well as the figures in the attached drawings also as described, have the sole function of better illustrating and explaining the present invention, their function being to provide a non-limiting example of the invention itself, since the scope of protection is defined by the claims.

To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can be conveniently combined or incorporated into other embodiments without further clarifications. DESCRIPTION OF SOME EMBODIMENTS OF THE PRESENT INVENTION

With reference to fig. 1, a feed apparatus 10 according to the present invention is designed and able to be used to feed a metal charge C, as defined above, toward a melting furnace 100 of a known type, for example an electric arc furnace, of an iron and steel plant, which is not shown in the drawings.

In particular, the melting furnace 100 is disposed downstream of the apparatus 10, according to a direction of advance, or loading VI of the metal charge C, and it is provided with a lateral loading aperture 101 through which the apparatus 10 can continuously feed the metal charge C.

The apparatus 10 essentially comprises a conveying channel 11 along which the metal charge C is made to advance, and a fixed cover, or hood, 12, which is configured to hermetically close the upper part of the conveying channel 11 , in such a way as to define an internal tunnel 13 having a rectilinear development along a longitudinal axis X, and which extends from an inlet end 15 for the introduction of the metal charge C to an outlet end 16 configured to be disposed adjacent to the loading aperture 101 of the melting furnace 100.

In correspondence with the outlet end 16, the apparatus 10 is provided with a connection device 17, or mobile hood, substantially of a known type, which can possibly be opened for inspections or to extract obstructions, which is selectively mobile between an idle, or contracted, position and an operating, or extended, position in which it is at least partly inserted into the loading aperture 101 of the melting furnace 100 for the introduction of the metal charge C. The selective movement of the connection device 17 is obtained by means of a trolley movement system, of a known type and not shown in the drawings.

The advance of the metal charge C toward the melting furnace 100 occurs in the direction of advance V 1 along the longitudinal axis X and is achieved in any known manner whatsoever, for example through a longitudinal vibrational and oscillatory movement of the conveying channel 11 which is generated by a vibration and movement device 18 disposed below and/or laterally, and generally upstream, but it could also be toward the middle, of the conveying channel 11 , that is, toward the inlet end 15. For example, the vibration and movement device 18 exploits an eccentric mass mechanism of a known type and not shown in the drawings.

The apparatus 10 also comprises an auxiliary suction duct 19, disposed in correspondence with the inlet end 15, with which there are associated extraction means 20 of a known type, such as a suction system for example. These extraction means 20 have the function of extracting, or drawing, the preheating fumes F produced by the melting inside the melting furnace 100 in order to make them exit through the tunnel 13 toward a fumes disposal plant, of a known type and not shown in the drawings, in order to preheat the metal charge C before it is introduced into the melting furnace 100. Please note that the fumes are drawn into the tunnel 13 in a direction of suction V2 opposite to the direction of advance VI of the metal charge C.

The conveying channel 11 has a substantially U-shaped cross section and comprises a base wall 21 which defines a substantially horizontal rest surface 22, on which the metal charge C rests, and two substantially vertical, or slightly flared, lower lateral walls 23 and 25, which are specular to each other with respect to a substantially median and vertical longitudinal plane PL (figs. 6 and 7) which extends along the longitudinal axis X of the apparatus 10.

The hood 12 comprises two substantially vertical upper lateral walls 26 and 27 which are specular to each other with respect to the longitudinal plane PL, and a covering wall 29. In the example given here, the covering wall 29 has a slightly arched shape. However, according to other embodiments not shown in the drawings, the covering wall 29 can also be flat or have other suitable shapes.

As shown schematically in figs. 8 and 9, each lower lateral wall 23 and 25 is associated with the corresponding upper lateral wall 26 and 27 by means of respective sealing means 28, of a known type, which have the function of preventing the escape of the fumes F in transit inside tunnel 13.

Along the longitudinal axis X, the hood 12 (figs. 1 and 2) is divided into two zones, that is, into a first zone, distal with respect to the melting furnace 100 and which extends from the inlet end 15, and a second zone, proximal to the melting furnace 100 and which extends until the outlet end 16. The first zone comprises, or consists of, a plurality of refractory lining panels 30, while the second zone comprises, or consists of, cooled panels 31 , generally consisting of side by side pipes for the passage of a cooling fluid. Both the refractory panels 30 and also the cooled panels 31 are of a known type and therefore are not described in detail. Clearly, it is possible to make the entire paneling with cooled panels, or with refractory material.

In accordance with one aspect of the present invention, the cross section of the tunnel 13 varies from a minimum section SI in correspondence with the inlet end 15, to a maximum section S2 in correspondence with the outlet end 16.

Moreover, at least a part of the hood 12 has an internal height H which varies from a minimum height Hl, disposed toward, or in correspondence with, the minimum section SI, to a maximum height H2, disposed toward, or in correspondence with, the maximum section S2.

In the example given here, the minimum section SI of the tunnel 13 coincides with the inlet section of the inlet end 15, while the maximum section S2 of the tunnel 13 coincides with the outlet section of the outlet end 16.

Please note that the minimum height Hl and the maximum height H2 are considered, or calculated, starting from the upper part of the conveying channel

11 , in correspondence with the longitudinal plane PL. In this way, it is possible to define the same reference points both in the minimum section S 1 and also in the maximum section S2 of the tunnel 13.

Moreover, by varying the internal height H of the hood 12 between the minimum height H 1 and the maximum height H2, it follows that the internal height of the tunnel 13 itself also varies between an inlet height HG, in correspondence with the minimum section SI, and an outlet height HU, in correspondence with the maximum section S2. In particular, the inlet height HG (fig. 6) is defined by the sum of a constant height HC of the conveying channel 11 and the minimum height Hl, while the outlet height HU (fig. 7) is defined by the sum of the constant height HC and the maximum height H2.

In accordance with possible embodiments of the present invention, the hood 12 (fig. 1) comprises, or consists of, a plurality of modules M_i, with i = 1 , ..., n, which are disposed adjacent to each other, without a break in continuity, along the longitudinal axis X.

In accordance with another aspect of the present invention, each module M_i has a longitudinal profile such as to have a height that grows linearly along its respective longitudinal development, passing from a lower height HMIN.I to a greater height H_MAX,i. Moreover, the module M_i disposed in correspondence with the inlet end 15, referred to as module M_i , has a lower height H_MIN,i, that is, H_MIN,i, equal to the minimum height Hl of the hood 12, and the module M_i in correspondence with the outlet end 16, referred to as module M_n, has a greater height H_MAX,i, that is, H_MAX,n, equal to the maximum height H2.

Please note that, also in this case, the maximum height H_MAX,i and the minimum height H_MIN,i of each module M_i are considered along the longitudinal plane PL. Furthermore, the modules M_i can have different lengths, depending on the specific operational needs. In particular, the modules M_i are connected to each other in such a way that the lower height H_MIN,i of each of the modules M_i corresponds to the greater height H_MAX,i of another module M_i adjacent thereto.

As shown in fig. 1, the hood 12, viewed laterally, is therefore formed by a plurality of modules M_i, each having a longitudinal section having the shape of a rectangular trapezoid, in which the smaller base is defined by the respective lower height H_MIN,i, the larger base is defined by the respective greater height H_MAX,i, and the oblique side is defined by a respective portion 32 of the covering wall 29.

In accordance with a first embodiment of the present invention, shown in fig. 1 , the greater height H_MAX,i of each module M_i is greater than the lower height H_MIN,i of the module M_i adjacent to it and disposed toward the outlet end 16, so as to obtain a longitudinal profile of the covering wall 29 of the hood 12 with a serrated shape.

This serrated-shaped longitudinal profile comprises a plurality of inclined longitudinal segments, which are defined by the respective portions 32 of the covering wall 29 of each module M_i, and which are joined to each other, in correspondence with the respective ends, by substantially vertical segments, the extension of which is given by the difference between the greater height H_MAX,i of a certain module M_i and the lower height H_MIN,i of the module M_i that follows it, in the direction of advance VI of the metal charge C.

Furthermore, according to one embodiment, the greater heights H_MAX,i and the lower heights H_MIN,i of the modules M_i are not constant along the longitudinal axis X of the hood 12, but they grow in a substantially linear manner from the inlet end 15 to the outlet end 16.

In fact, the first module M_i (fig. 3), that is, the one in correspondence with the inlet end 15, has a lower height H_{MIN, I} equal to the first height Hl and a certain greater height H_MAX.I ; the last module M_n (fig. 4), that is, the one in correspondence with the outlet end 16, proximal to the melting furnace 100, has a certain lower height H_MIN.n which is greater than the lower height H_{MIN. I,} of the first module M_i and a greater height H_MAX,n which is equal to the maximum height H2.

In the example shown in fig. 1 , the growth of the greater heights H_MAX,i and of the lower heights H_MIN,i of the modules M_i is not perfectly linear, but substantially with certain steps, wherein within a same step there is a group of modules M_i, which are adjacent to each other, having the same lower heights H_MIN,i and greater heights H_MAX,i. In the example given here and without limits to generality, there are three steps which are defined by.

- a first step comprising three initial modules M_i having the same lower and greater heights H_MIN,i and H_MAX,i, wherein the lower height H_MIN,i is equal to the minimum height Hl ;

- a second step comprising two intermediate modules M_i having the same lower and greater heights H_MIN,i and H_MAX,i, which are larger than those of the first group; and

- a third step comprising five final modules M_i having the same lower and greater heights H_MIN,i and H_MAX,i, which are greater than those of the second step, and wherein the greater height H_MAX,i is equal to the maximum height H2.

In other embodiments, not shown in the drawings, only in some points, or zones, along the longitudinal development of the hood 12, the lower height H_MIN,i of a certain module M_i and the greater height H_MAX,i of the next module M_i are the same.

At the points of disconnection, that is, along the discontinuity surfaces, between each module M_i and another one adjacent to it, there can be sealing means, of a known type and not shown in the drawings, which have the function of preventing the entry of air from the outside into the tunnel 13. For example, these sealing means comprise, or consist of, flexible sealing members, of the adaptable type and having a longitudinal extension parallel to the longitudinal axis X.

According to another possible embodiment of the present invention, the hood 12 is made in a single body.

In accordance with a second embodiment of the present invention, shown in fig. 2, the hood 12 is made in a single body and the covering wall 29 has a longitudinal profile with a serrated shape. Also in this case, the covering wall 29 with such longitudinal profile has an internal height H which increases in a substantially linear manner from the minimum height Hl to the maximum height H2.

The variation of the cross section of the tunnel 13 along the longitudinal axis X, making the internal height H of the hood 12 increase from the minimum height H1 to the maximum height H2, has the advantage that the speed of the fumes F inside the tunnel 13 increases progressively as these gradually proceed toward the inlet end 15. The increase in such speed generates turbulence in the fumes F which allows to improve the heat exchange between the fumes F and the metal charge C present in the tunnel 13.

Moreover, using a hood 12 having a covering wall 29 with a serrated-shaped longitudinal profile (figs. 1 and 2) has the advantage of further increasing the swirling and turbulence of the fumes F, so as to make them enter deeper into the metal charge C. This allows to optimize the heat exchange between the fumes F and the metal charge C even in correspondence with the inlet end 15, that is, the zone furthest away from the melting furnace 100, consequently also significantly improving the efficiency of the melting furnace 100, because an on average hotter metal charge C will enter it.

One aspect to consider with the use of a hood 12 that has a covering wall 29 with a serrated-shaped longitudinal profile is that in correspondence with one or more convergence zones ZC (fig. 5) inside the tunnel 13, that is, in proximity to the comers where the inclined longitudinal segments and the substantially vertical segments of each serration converge, concentrations, or accumulations, AC of potentially explosive gases can form in the fumes F, such as accumulations of carbon monoxide CO for example, which could be very dangerous.

In order to reduce the danger of such accumulations AC, in correspondence with the substantially vertical segments of the serrated-shaped profile of the hood 12, corresponding apertures 35 can be advantageously made, with which respective hatches 36 are associated, with commanded opening for example, or controlled inlets for air or other gasses, which are able to be selectively opened, when necessary, and are configured to make air or other gases, such as pure oxygen for example, enter the tunnel 13 in a controlled manner. The controlled entry of gas into the tunnel 13, in addition to diluting the formations of accumulations AC in the fumes F, advantageously allows to generate additional heat, since it takes the CO present in the fumes F to oxidation.

In addition, it can be useful to also inject liquids from the apertures, such as nebulized water or steam for example, useful for reducing the temperatures of the gases, limiting the formation of NOX.

In accordance with other embodiments of the present invention, shown in figs.

8 and 9, the upper lateral walls 26 and 27 of the hood 12 are disposed and/or shaped in such a way as to define a variable width at least in one part of the hood itself, so as to cause localized accelerations in the fumes F at exit from the melting furnace 100 and directed toward the inlet end 15 of the tunnel 13, that is, toward the suction duct 19.

In particular, the variation in width can be achieved both in a linear manner (fig. 8), with the width of the hood 12 growing linearly from the inlet end 15 to the outlet end 16, and also in a non-linear manner, for example with symmetrical narrowings and/or widenings (fig. 9). According to other embodiments of the present invention not shown in the drawings, the narrowings and/or widenings can be made asymmetrically with respect to the longitudinal axis X.

It is clear that modifications and/or additions of parts may be made to the feed apparatus 10 as described heretofore, without departing from the field and scope of the present invention, as defined by the claims.

For example, according to other embodiments, not shown in the drawings, it is possible to insert additional narrowing means inside the tunnel 13, each having the function of reducing the internal cross section of the apparatus 10, so as to create further increases in the speed of the fumes F by means of a Venturi type effect.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art will be able to achieve other equivalent forms of feed apparatuses for feeding a metal charge toward melting furnaces, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

In the following claims, the sole purpose of the references in brackets is to facilitate their reading and they must not be considered as restrictive factors with regard to the field of protection defined by the same claims.

Claims

1. Feed apparatus (10) for feeding a metal charge (C) toward a melting furnace (100), wherein the apparatus (10) comprises a conveying channel (11) and a hood (12) configured to close the upper part of said conveying channel (11) in such a way as to define an internal tunnel (13) having a longitudinal axis (X) and extending from an inlet end (15) for the introduction of said metal charge (C) to an outlet end (16) configured to be disposed adjacent to said melting furnace (100), wherein the cross section of said tunnel (13) varies from a minimum section (SI) in correspondence with said inlet end (15) to a maximum section (S2) in correspondence with said outlet end (16), characterized in that said hood (12) comprises at least one covering wall (29) having a longitudinal profile with a serrated shape.

2. Apparatus (10) as in claim 1, characterized in that said hood (12) has an internal height (H) which varies from a minimum height (Hl), disposed toward, or in correspondence with, said minimum section (SI), to a maximum height (H2), disposed toward, or in correspondence with, said maximum section (S2).

3. Apparatus (10) as in claim 1 or 2, characterized in that said covering wall (29) has an internal height (H) which increases in a substantially linear manner from said minimum height (Hl), in correspondence with said inlet end (15), to said maximum height (H2), in correspondence with said outlet end (16).

4. Apparatus (10) as in any claim hereinbefore, characterized in that said hood (12) is made in a single body.

5. Apparatus (10) as in claim 1, 2 or 3, characterized in that said hood (12) comprises two or more modules (M_i) disposed adjacent to each other along said longitudinal axis (X).

6. Apparatus (10) as in claim 5, characterized in that each of said modules (M_i) has a longitudinal profile such that it has a lower height ( H_MIN,i) and a greater height (H_MAX,i), and in that the module (M_i) which is in correspondence with said inlet end (15) has a lower height ( H_MIN,i) equal to said minimum height (Hl), and the module (M_i) which is in correspondence with said outlet end (16) has a greater height ( H_MAX,i) equal to said maximum height (H2).

7. Apparatus (10) as in claim 6, characterized in that said modules (M_i) are connected to each other in such a way that the lower height ( H_MIN,i) of each of said modules (M_i) is in correspondence with the greater height (HMAXJ) of another module (M_i) adjacent thereto.

8. Apparatus (10) as in claim 7, characterized in that the greater height (HMAXJ) of each of said modules (M_i) is greater than the lower height (HMINJ) of the module (M_i) adjacent thereto and disposed toward said outlet end (16), in such a way as to obtain a longitudinal profile with a serrated shape.

9. Apparatus (10) as in any claim hereinbefore, characterized in that said hood (12) comprises upper lateral walls (26, 27) disposed and/or shaped in such a way as to define a variable width at least in one part of said hood (12), so as to cause localized accelerations in fumes (F) at exit from said melting furnace (100) and directed toward said inlet end (15) of said tunnel (13).

10. Apparatus (10) as in any claim hereinbefore, characterized in that in correspondence with the vertical segments of said serrated-shaped profile of said hood (12) corresponding apertures (35) are made for the controlled entry of air or other gasses into said tunnel (13) and with which respective selectively openable hatches (36) are associated.