Heat exchange apparatus and annealing plant for a metal strip

Abstract

A heat exchange apparatus comprising at least one bridle roll for exchanging heat with a metal strip advancing along a plant, said at least one bridle roll comprising: - a hollow cylindrical body (1) defining a longitudinal rotation axis (X); - an outer shell (2) fastened on the outer lateral surface of said hollow cylindrical body (1) and defining an outer cylindrical radial surface of said roll, coaxial to said axis (X), for partially winding the metal strip around said outer shell (2) during the advancement thereof; - at least one inner channel (3) obtained by the coupling between the outer lateral surface of said hollow cylindrical body (1) and an inner cylindrical radial surface of the outer shell (2); wherein at least one lateral end portion (5) of said hollow cylindrical body (1) comprises a respective annular gap (6) adapted to contain a heat-transfer fluid and to distribute said heat-transfer fluid in said at least one inner channel (3); wherein there is provided a hollow transmission element (7) to which said at least one lateral end portion (5) is connected to receive the transmission of a rotating motion around said longitudinal axis (X), said hollow transmission element (7) comprising an inner duct (8) for feeding said heat-transfer fluid in said annular gap (6).

Description

[0001] HEAT EXCHANGE APPARATUS AND ANNEALING PLANT FOR A METAL STRIP

[0002] Field of the invention

[0003] The present invention relates to a heat exchange apparatus for exchanging heat with a metal strip, for example made of steel, advancing along a plant, in particular an annealing plant such as for example, a hot-dip galvanizing line (HDGL) or a continuous annealing line (CAL).

[0004] Background art

[0005] In galvanizing lines, the strip is annealed in specific furnaces before being galvanized and / or painted. Indeed, since the strip becomes hard and fragile during cold rolling, annealing is performed to reduce the hardness and improve the formability of the material.

[0006] Moreover, annealing helps to eliminate any surface defects on the strip, ensuring a more uniform and better quality surface before galvanizing.

[0007] During this process, the strip is heated in annealing furnaces, which generally use fossil fuels and more recently, have begun employing induction furnaces and / or furnaces with electric heating elements in order to partially or completely replace fossil fuels.

[0008] Such an operation in any case involves bringing a strip from substantially room temperature to about 950-1000°C, with consequent energy consumption.

[0009] When it is finished, the annealing process releases a hot strip ready to be galvanized, but it is sufficient to have a strip temperature of about 500°C for galvanizing. Therefore, much of the thermal energy conferred to the strip during the annealing process is subsequently lost.

[0010] Further thermal energy is lost downstream of the galvanizing operation when the strip - after it has transited in the liquid zinc tank - passes through the air blades and the cooling area, which cause the zinc coating to solidify.

[0011] The need is therefore felt to reduce the energy consumption associated with heating the strip inside annealing furnaces, in particular in the initial preheating steps which bring the material from room temperature to the target temperature. Given that it is also necessary to cool the strip downstream of the annealing treatment, the need is also felt to recover at least part of this heat to reconfer it to the strip being heated.

[0012] Heat exchange apparatuses provided with at least one roll capable of achieving a heat exchange between transiting strip and said roll, are known. Disadvantageously, these heat exchange rolls are subjected to stress following contact with the strip under tension and the crossing of a heat-transfer fluid therein, which can reach high temperatures with the risk of causing part of the roll structure to be deformed. To avoid these deformations, the known rolls have a complex design and / or considerable weight to ensure structural stability.

[0013] Therefore, the need is felt to make an innovative heat exchange apparatus allowing these needs to be met, while also obtaining the subsequent advantages in terms of reducing energy consumption, and therefore an equivalent reduced impact on the environment.

[0014] Summary of the invention

[0015] It is the object of the present invention to make a heat exchange apparatus provided with at least one bridle roll having a simple design and considerably reduced weight while maintaining increased stability considering the stresses to which it is subjected following contact with the strip under tension and the crossing of a heat-transfer fluid therein, which can reach high temperatures with the risk of causing part of the roll structure to be deformed.

[0016] It is another object of the present invention to make a heat exchange apparatus in which said at least one bridle roll is capable of achieving an optimal heat exchange between transiting strip and said bridle roll, in particular to perform a controlled cooling, or a controlled preheating, of the strip which is partially wound around said at least one roll.

[0017] It is a further object of the present invention to make a heat exchange apparatus positionable in proximity of, upstream and / or downstream, of an annealing plant, or incorporated in said annealing apparatus, in order to at least partially recover the thermal energy subtracted from the annealed metal strip in a controlled cooling step and to reuse it, transferring this recovered energy to the metal strip entering the annealing apparatus by means of a heat-transfer fluid, preferably diathermic oil, thus obtaining a preheating of the product to be annealed, with apparent advantages for the environment and the reduction of the furnace operating costs. Therefore, the present invention proposes to achieve the objects discussed above by making a heat exchange apparatus comprising at least one bridle roll for exchanging heat with a metal strip advancing along a plant, said at least one bridle roll comprising

[0018] - a hollow cylindrical body defining a longitudinal rotation axis X;

[0019] - an outer shell fastened on the outer lateral surface of said hollow cylindrical body and defining an outer cylindrical radial surface of said roll, coaxial to said longitudinal axis X, for partially winding the metal strip around said outer shell during the advancement thereof;

[0020] - at least one inner channel made by the coupling between the outer lateral surface of said hollow cylindrical body and an inner cylindrical radial surface of the outer shell; wherein at least one end portion of said hollow cylindrical body comprises, in the axial direction, a respective annular gap adapted to contain a heat-transfer fluid and to distribute said heat-transfer fluid in said at least one inner channel; wherein said annular gap is delimited by at least two parallel walls of said hollow cylindrical body, orthogonal to the longitudinal axis X; wherein there is provided a hollow transmission element to which said at least one end portion is connected to receive the transmission of a rotating motion around said longitudinal axis X, said hollow transmission element comprising an inner duct for feeding said heat-transfer fluid in said annular gap; wherein said at least one end portion has a plurality of through holes having a respective axis parallel to the longitudinal axis X and defining a respective tubular reinforcing element inside said annular gap.

[0021] A further aspect of the invention relates to an annealing plant for a metal strip advancing along a direction, said plant comprising in sequence

[0022] - at least one preheating section;

[0023] - at least one heating section;

[0024] - at least one temperature maintaining section;

[0025] - at least one cooling section; wherein there is provided a first heat exchange apparatus as described above in said at least one preheating section; wherein there is provided a second heat exchange apparatus as described above in said at least one cooling section; and wherein there is provided a heat-transfer fluid closed circuit configured to cross both said second heat exchange apparatus to subtract thermal energy from the metal strip by conduction, thus obtaining a high temperature heat-transfer fluid, and said first heat exchange apparatus to transfer thermal energy to the metal strip by conduction, thus obtaining a low temperature heat-transfer fluid.

[0026] The dependent claims describe preferred embodiments of the invention.

[0027] Brief description of the Figures

[0028] Further features and advantages of the invention will become more apparent in the light of the detailed description of preferred but not exclusive embodiments of the solution of the invention illustrated, by way of non-limiting example, with reference to the accompanying drawing tables, in which:

[0029] Figure 1 shows a perspective view of a bridle roll of the apparatus according to the invention;

[0030] Figure 2 shows a side view of two bridle rolls of the apparatus according to the invention;

[0031] Figure 3 shows a side section view of a first embodiment of the bridle roll;

[0032] Figure 4 shows a first perspective view of part of the bridle roll of Figure 3;

[0033] Figure 5 shows a side section view of a second embodiment of the bridle roll;

[0034] Figure 6 shows a first perspective view of part of the bridle roll of Figure 5;

[0035] Figure 7 shows a second perspective view of part of the bridle roll of Figure 3;

[0036] Figure 8 shows a second perspective view of part of the bridle roll of Figure 5;

[0037] Figure 9 shows a side, partial section view of certain components of the bridle roll according to the invention;

[0038] Figure 9a shows a side, partial section view of an alternative variant of said components of the bridle roll;

[0039] Figure 10 shows a perspective view of a first component of the bridle roll according to the invention; Figure 11 shows a perspective view of a second component of the bridle roll according to the invention;

[0040] Figure 12 shows a perspective view of a detail of Figure 9;

[0041] Figure 13 shows a diagram of an annealing apparatus comprising bridle rolls according to the invention;

[0042] Figure 14 shows a perspective view of a preferred configuration of an apparatus according to the invention;

[0043] Figure 15 shows a diagram of a cooling section of said annealing apparatus;

[0044] Figure 16 shows a diagram of a preheating section of said annealing apparatus.

[0045] The same reference numerals in the Figures identify the same elements or components.

[0046] Detailed description of preferred embodiments of the invention

[0047] With reference to Figures 1 to 12, they depict some embodiments of a bridle roll of the heat exchange apparatus according to the invention, which is specifically designed to exchange heat with a metal strip advancing along a plant.

[0048] In general, bridle rolls are rolls adapted to modify the tension of the strip in rolling plants for flat metal products due to the known change in direction they apply on the metal strip, thus defining, for example, a serpentine path of the strip, constraining the strip so as to control the tension thereof.

[0049] The heat exchange apparatus of the present invention reuses this technology, applying it in a cold rolling train for flat products, preferably in the plant area upstream of the galvanizing in a hot-dip galvanizing line (HDGL) or in a continuous annealing line (CAL) in order to achieve an optimal heat exchange between transiting strip and bridle rolls, in particular to perform a controlled cooling, or a controlled preheating, of the strip which is partially wound around said bridle rolls.

[0050] As is known, the metal strip is a product that has one dimension, i.e., the thickness, which is considerably smaller than the other two dimensions, that is the length and the width.

[0051] In all the embodiments of the invention, the heat exchange apparatus comprises at least one bridle roll for exchanging heat with a metal strip advancing along a plant. Said at least one bridle roll comprises (Figures 1 and 3-8):

[0052] - a hollow cylindrical body 1 defining a longitudinal rotation axis X; - an outer shell 2 fastened on the outer lateral surface of the hollow cylindrical body 1 and defining an outer cylindrical radial surface of the roll, or outer lateral surface of the roll, coaxial to said axis X, for partially winding the metal strip around the outer shell 2 during the advancement thereof;

[0053] - at least one inner channel 3 obtained by the coupling between the outer lateral surface of the hollow cylindrical body 1 and an inner cylindrical radial surface, or inner lateral surface, of the outer shell 2.

[0054] Advantageously, considering the axial direction, i.e. , the direction along axis X, at least one lateral end portion 5 of the hollow cylindrical body 1 comprises therein a respective annular gap 6 adapted to receive a heat-transfer fluid and to distribute it in the at least one inner channel 3. A hollow transmission element 7 is arranged along the longitudinal axis X and is rigidly connected, for example by means of keying, to said at least one lateral end portion 5 to transmit a rotating motion to the bridle roll around axis X. Said hollow transmission element 7 comprises an inner duct 8 for feeding the heat-transfer fluid in said annular gap 6.

[0055] The configuration described above allows achieving an optimal heat exchange between transiting strip, which is partially wound around the bridle roll, and heattransfer fluid which flows in the at least one peripheral inner channel 3 of the bridle roll.

[0056] In a preferred variant, the seal between the cylindrical body 1 and the outer shell 2 is achieved by means of external lateral welding in a circumferential direction, avoiding the use of costly O-rings suitable for the seal of the heat-transfer fluid. This external lateral welding is provided at a circumferential area 90 (indicated in Figure 6), for example.

[0057] In greater detail, a welding seam is provided at both ends of the bridle roll, considering the axial direction of the roll, in an outer circumferential boundary area between the cylindrical body 1 and the outer shell 2.

[0058] Preferably, the seal between cylindrical body 1 and outer shell 2 is made exclusively by means of said welding.

[0059] The annular gap 6 is delimited along a radial direction by a, preferably cylindrical, outer lateral surface of said hollow transmission element 7 and by an inner annular end surface of the hollow cylindrical body 1. The annular gap 6 is further delimited, along a direction parallel to axis X, by at least two parallel walls, for example only two parallel walls, orthogonal to the longitudinal axis X.

[0060] Preferably, the annular gap 6 of the end portion 5 of the hollow cylindrical body 1 is delimited by two circular-shaped parallel walls which are an integral part of the structure of the hollow cylindrical body 1 , for example made in a single piece with the hollow cylindrical body (Figures 4 and 6).

[0061] Said end portion substantially constitutes a base of the hollow cylindrical body 1 , said base having a flat, hollow cylindrical shape. The inner volume of said base is the volume of said annular gap 6.

[0062] In a preferred variant of the invention, in said at least one bridle roll, there are provided:

[0063] - a plurality of first radial holes 9, made in the thickness of the hollow transmission element 7 and connecting said inner duct 8 to the annular gap 6;

[0064] - and a plurality of second radial holes 10, made in the thickness of a radially peripheral part of said at least one lateral end portion 5 and connecting the annular gap 6 to said at least one inner channel 3.

[0065] Preferably, said at least one inner channel 3 comprises two or three helical channels, preferably connected in parallel, delimited by a respective helical groove 4, made on the outer lateral surface of the hollow cylindrical body 1 , and by the cylindrical inner radial surface of the outer shell 2.

[0066] The possibility of providing a single inner helical channel 3, or more than three inner helical channels, is not excluded.

[0067] Advantageously, as illustrated in Figures 3-4 and 7, said at least one lateral end portion 5 has a plurality of through holes 11 defining a respective axis parallel to the longitudinal axis X, and preferably arranged along a circumference coaxial to said longitudinal axis X, so that the volume of the respective annular gap 6 inside the lateral end portion 5 is reduced. Said through holes 11 , for example cylindricalshaped, define corresponding tubular reinforcing elements inside the annular gap 6, thus ensuring also an increased structural stability.

[0068] Preferably, the number and size of said tubular reinforcing elements are designed to reduce the volume of said annular gap 6 (Figure 7) by at least 20%, preferably at least 50%. Preferably, the number of said through holes 11 varies from three to nine. The example in Figure 7 provides six, mutually equal, through holes 11 in the lateral end portion 5.

[0069] Preferably, the distance between the two parallel walls delimiting the annular gap 6 is in a range from 50 to 350 mm, for example from 100 to 350 mm.

[0070] In an alternative variant of the bridle roll shown in Figures 5-6 and 8, there are instead provided:

[0071] - radial reinforcing elements 12, preferably angularly equally spaced apart from one another, arranged between the two parallel walls so as to divide the annular gap 6 into a plurality of sectors 60, preferably corresponding to circular sectors equal to each other;

[0072] - at least one first radial hole 9, for example only one radial hole 9, connecting the inner duct 8 to a respective sector 60, and at least one second radial hole 10 connecting said respective sector 60 to at least one inner channel 3.

[0073] Preferably, the number of the radial reinforcing elements 12, for example radial bars, and therefore the number of sectors 60, varies from four to eight. The example in Figure 8 provides six radial reinforcing elements 12, and therefore six mutually equal sectors 60, in the lateral end portion 5.

[0074] Preferably, the distance between the two parallel walls delimiting the annular gap 6 is in a range from 40 to 100 mm, for example from 40 to 90 mm.

[0075] In both variants of the bridle roll described above, the simple design and the reduced weight of the bridle roll - which is almost empty inside - in any case allow a high roll stability to be maintained, considering the stress to which it is subjected following contact with the strip under tension and the crossing of a heat-transfer fluid therein, which can reach high temperatures with the risk of causing part of the roll structure to be deformed.

[0076] In particular, the first variant of the bridle roll allows a high structural stability due to the presence of the through holes 11 which determine corresponding tubular reinforcing elements inside the annular gap 6 and a consequent reduced volume for the heat-transfer fluid transiting in the annular gap. This configuration allows also using a simple first lateral hub 7 as hollow transmission element. A second lateral hub 7’ can be provided at a second lateral end portion 5’ of the hollow cylindrical body 1 , opposite to the lateral end portion 5 (Figure 3).

[0077] Instead, the second variant of the bridle roll allows a high structural stability despite a greater manufacturing simplicity of the lateral end portions 5, 5’, in particular if an at least partially hollow through-axis hub 7, crossing the roll along the longitudinal axis X and on which both the lateral end portions 5, 5’ are connected, were used as transmission element (Figure 5).

[0078] In a first embodiment of the heat exchange apparatus of the invention, partially illustrated in Figures 3, 5 and 9, the heat-transfer fluid enters the bridle roll at a first lateral end portion 5 and exits the bridle roll at a second lateral end portion 5’, opposite to the first lateral end portion 5.

[0079] Both lateral end portions 5, 5’ of the hollow cylindrical body 1 comprise a respective annular gap 6, 6’.

[0080] A first annular gap 6 of the first lateral end portion 5 is adapted to receive the heattransfer fluid from the inner duct 8 of a first lateral hub 7, or of a through-axis hub, and to distribute said heat-transfer fluid in said at least one inner channel 3.

[0081] In particular, first radial holes 9 connect the inner duct 8 to the first annular gap 6, and second radial holes 10 connect said first annular gap 6 to the at least one inner channel 3.

[0082] A second annular gap 6’ of the second lateral end portion 5’ is instead adapted to receive the heat-transfer fluid from said at least one inner channel 3 and to convey said heat-transfer fluid into a further inner duct 8’ of a second lateral hub 7’, or of said through-axis hub, on which said second lateral end portion 5’ is connected.

[0083] In particular, third radial holes 10’ connect said at least one inner channel 3 to the second gap 6’, and fourth radial holes 9’ connect said second gap 6’ to the further inner duct 8’.

[0084] First annular gap 6 and second annular gap 6’ are each delimited by two respective parallel walls, orthogonal to the longitudinal axis X.

[0085] Preferably, the annular gaps 6, 6’ of the respective end portions 5, 5’ of the hollow cylindrical body 1 are delimited by two circular-shaped parallel walls which are an integral part of the structure of the hollow cylindrical body 1 , for example made in a single piece with the hollow cylindrical body. Said end portions constitute substantially the two bases of the hollow cylindrical body 1 , said bases having a flat, hollow cylindrical shape. The inner volume of said bases is the volume of the respective annular gap 6, 6’.

[0086] In the case of the first variant of the bridle roll (Figures 3-4 and 7), both lateral end portions 5, 5’ have a respective plurality of through holes 11 defining a respective axis parallel to the longitudinal axis X, and preferably arranged along a circumference coaxial to said longitudinal axis X so that the volume of the respective annular gap 6, 6’ is reduced. Said through holes 11 define corresponding tubular reinforcing elements inside the respective annular gap 6, 6’, thus ensuring also increased structural stability.

[0087] Preferably, the number and size of said tubular reinforcing elements are designed to reduce the volume of the respective annular gap 6, 6’ by at least 20%, preferably at least 50%.

[0088] Preferably, both lateral end portions 5, 5’ are provided with a respective outer covering panel 20. Said outer covering panels 20 are held integral to the respective end portion 5, 5’ and held integral to each other by means of a plurality of tie rods 21 , each tie rod 21 passing through a respective through hole 11 of each end portion 5, 5’.

[0089] The outer covering panels 20 are arranged preferably orthogonal to the longitudinal axis X.

[0090] Advantageously, this configuration with outer covering panels and tie rods allows an optimal covering and thermal shielding of the bridle roll to be obtained, thermally isolating the roll from the external environment while keeping the heat inside. In particular, the tie rods hold the structure in position, ensuring the panels remain firmly fastened and aligned, further optimizing the thermal shielding.

[0091] In a variant of the invention, the outer covering panels 20, for example discshaped, are made of metal material.

[0092] There is provided, between each covering panel 20 and the respective end portion 5, 5’ of the bridle roll, a further annular gap 74 (Figure 4), much less extended along the longitudinal axis X with respect to the adjacent annular gap 6, 6’ which is crossed by the heat-transfer fluid. The tubular reinforcing elements, defined by the through holes 11 , are sized so as to also reduce the volume of said further annular gap 74, given that an outer end of said tubular reinforcing elements is in close contact with the corresponding covering panel 20. Preferably, said further annular gap 74 is filled with an insulating material, for example rock wool or other suitable material.

[0093] In a further variant, at least one layer of insulating material is also arranged on the inner part of the tubular reinforcing elements, i.e. , on the inner wall of the through holes 11 , and / or on the inner part of the hollow cylindrical body 1 .

[0094] Each substantially circular-shaped covering panel 20 can be formed by a single piece or by at least two or three pieces, for example three pieces each defining a center angle of 120°.

[0095] In the case of the second variant of the bridle roll (Figures 5-6 and 8), both lateral end portions 5, 5’ have respective radial reinforcing elements 12 between the two parallel walls such as to divide the first annular gap 6 into a plurality of first sectors 60 and the second annular gap 6’ into a plurality of second sectors, respectively. There are also provided:

[0096] - at least one radial hole 9 connecting the inner duct 8 to a respective first sector 60;

[0097] - at least one second radial hole 10 connecting said respective first sector to the at least one inner channel 3;

[0098] - at least one third radial hole connecting said at least one inner channel 3 to a respective second sector;

[0099] - and at least one forth radial hole connecting said respective second sector to the further inner duct 8’.

[0100] Preferably, both lateral end portions 5, 5’ are provided with a respective outer covering panel 20.

[0101] In a preferred variant of the heat exchange apparatus of the invention, upstream of the at least one bridle roll, there are provided:

[0102] - a fixed pipe 24 for a passage of heat-transfer fluid;

[0103] - a hollow drive shaft 15 provided therein with a tube 16 integral therewith and coaxial to the longitudinal axis X, and integrally connected to the first lateral hub 7, or to the through-axis hub, so that tube 16 and inner duct 8 of the lateral hub 7 define a rotating pipe 16, 8; - a rotating joint 18 connecting the fixed pipe 24 to said rotating pipe 16, 8.

[0104] Preferably, the rotating joint 18 comprises a fixed part 25, connected to the fixed pipe 24, and a rotating duct 17 inside said fixed part 25 and communicating with the rotating pipe 16, 8.

[0105] In a preferred variant, the rotating joint 18 further comprises a flange 26 with conical coupling arranged on the rotating duct 17 and fastened to the hollow drive shaft 15, for example by means of screws arranged along the periphery of the flange and inserted in corresponding peripheral holes of the hollow drive shaft 15. Thereby, the integral rotation of rotating duct 17 and rotating pipe 16, 8 is ensured. Hydraulic sealing elements can be provided at the connection between said rotating duct 17 and said rotating pipe 16, 8, and also between tube 16 and inner duct 8.

[0106] Preferably, upstream of the at least one bridle roll, there are further provided:

[0107] - at least one support 19 of the hollow drive shaft 15, with bearings interposed between said support 19 and said hollow drive shaft 15;

[0108] - and a plurality of cooling fins 22, projecting from the hollow drive shaft 15 and arranged between said at least one support 19 and a first end of the hollow drive shaft 15 connected to the first lateral hub 7, or through-axis hub.

[0109] Since heat is transmitted towards the outside by the heat-transfer fluid, which flows inside the lateral hub 7, or through-axis hub, and other heat can also be generated during the rotation in the coupling area between hollow drive shaft 15 and said hub, these cooling fins 22 allow the heat to be dissipated, avoiding the bearings from overheating.

[0110] The connection between hollow drive shaft 15 and hub 7 can be achieved by means of a flanged coupling, as illustrated in Figures 9-11. As illustrated in Figure 9, the hydraulic rotating joint 18 is therefore packed with the hub 7.

[0111] Moreover, it is preferable to also provide a obstacle connection between hollow drive shaft 15 and hub 7, for example by means of a tab, grooved profiles or longitudinal pins.

[0112] Figures 10-11 show, for example, a groove 23, 23’ partly made on the hub 7 and partly made inside the drive shaft 15, where a tab (not shown) is inserted. The tab carries out the connection, transmitting the stress onto the lateral walls of the groove, while a clearance radially exists; therefore, said tab acts as an obstacle, preventing the relative rotating motion.

[0113] In a further preferred variant, tube 16 is provided in the thickness thereof with an annular air chamber 16’, coaxial to axis X, for reducing the transmission of heat from the heat-transfer fluid towards the outside, and in particular towards the aforesaid bearings.

[0114] The hollow drive shaft 15 can be operated by a motor 13 arranged along an axis parallel to, and distinct from, the longitudinal axis X.

[0115] Preferably, there is provided a chain drive 14, optionally with a planetary gear reducer, connecting the motor 13 to an end of the hollow drive shaft 15 connected to the rotating joint 18.

[0116] In a preferred variant, there is provided an adjustment system for adjusting the tension of the chain of said chain drive 14, for example a mechanical or pneumatic or hydraulic actuator. Figures 1-2 show an example of a mechanical actuator 81 comprising a screw adjustment system.

[0117] In a second embodiment of the heat exchange apparatus of the invention, partially illustrated in Figure 9a, the heat-transfer fluid instead enters and exists the bridle roll from the same side, i.e. , at the first lateral end portion 5.

[0118] The annular gap 6 of the first lateral end portion 5 of the hollow cylindrical body 1 is divided into two adjacent and parallel portions 91 , 93 separated by an intermediate wall 92, preferably parallel to the two parallel walls indicated above.

[0119] The hollow transmission element 7, in the shape of lateral hub or through-axis hub, comprises an inner duct 8 for feeding the heat-transfer fluid, entering the roll, in a first portion 91 of said annular gap 6. Said first portion 91 is adapted to receive the heat-transfer fluid from the inner duct 8 of the first lateral hub and to distribute said heat-transfer fluid in said at least one inner channel 3.

[0120] A first series of first radial holes 9 connects the inner duct 8 to said first portion 91 of the annular gap 6.

[0121] A first series of second radial holes 10 connects the first portion 91 of the annular gap 6 to an inlet section of the at least one inner channel 3.

[0122] Said at least one inner channel 3 is configured to allow the heat-transfer fluid to reach the second lateral end portion 5’ of the hollow cylindrical body 1 and to return towards the first lateral end portion 5. For example, said at least one inner channel 3 is configured to allow the heat-transfer fluid to reach a second annular gap 6’ of the second end portion 5’ and to return towards the first gap 6.

[0123] A second series of second radial holes 10 therefore connects an outlet section of the at least one inner channel 3 to the second portion 93 of the annular gap 6.

[0124] A second series of first radial holes 9 finally connects said second portion 93 of the annular gap 6 to a further inner duct 80 of the hollow transmission element 7.

[0125] Preferably, the further inner duct 80 is arranged coaxially to, and inside, said inner duct 8.

[0126] The further inner duct 80 has a suitable extension crossing both the tube 16 and the rotating duct 17 of the rotating joint 18.

[0127] According to a further aspect of the invention, herein described is an annealing plant for a metal strip advancing along a direction, comprising at least two heat exchange apparatuses, as the one described above.

[0128] In particular, this annealing plant comprises in succession (Figure 13):

[0129] - at least one preheating section 30;

[0130] - at least one heating section 31 ;

[0131] - at least one temperature maintaining section 32;

[0132] - at least one cooling section 33.

[0133] Advantageously, there are provided a first heat exchange apparatus in said at least one preheating section 30; a second heat exchange apparatus in said at least one cooling section 33; and a heat-transfer fluid closed circuit configured to cross both the second heat exchange apparatus to subtract thermal energy from the metal strip by conduction, thus obtaining a high temperature heat-transfer fluid, and the first heat exchange apparatus to transfer thermal energy to the metal strip by conduction, thus obtaining a low temperature heat-transfer fluid.

[0134] It is preferable to provide only one preheating section 30, only one heating section 31 , only one temperature maintaining section 32, and only one cooling section 33. Therefore, in steady state operation, the heat-transfer fluid allows the thermal energy that is removed from the annealed metal strip in the cooling section 33 to be completely or partially recovered and reused by transferring it to the metal strip in the preheating section 30, at the inlet of the plant, thus obtaining a preheating of the product to be annealed, with obvious advantages for the environment and the reduction of the operating costs of the heating section 30.

[0135] Preferably, the first heat exchange apparatus comprises a plurality of heating bridle rolls 34 for the advancement of the metal strip; the second heat exchange apparatus comprises a plurality of cooling bridle rolls 35 for the advancement of the metal strip; and the heat-transfer fluid closed circuit crosses in series both the cooling bridle rolls 35, provided in the cooling section 33, and the heating bridle rolls 34, provided in the preheating section 30. The bridle rolls 34, 35 are as the bridle roll described above in one of the variants thereof.

[0136] As illustrated in Figure 14, a preferred configuration of each heat exchange apparatus provides that the heating bridle rolls 34 and the cooling bridle rolls 35 be arranged in such a manner that each bridle roll is wound by the metal strip by at least 190°.

[0137] Preferably, there are provided, in both heat exchange apparatuses, an even number of bridle rolls 34, 35, preferably six, which are arranged one after the other, in groups of two bridle rolls at different heights from one another, preferably only two different heights, along a conveying direction A of the metal strip.

[0138] As illustrated in Figures 2 and 14, considering each group of two bridle rolls, a preferred variant provides that the difference in height between the two bridle rolls equal to each other, be determined by the difference in height of the respective support frame 82. By virtue of the adjusting system for adjusting the tension of the chain of the chain drive 14, it is possible to position the motors 13 substantially at the same height on the respective support frames 82, while the length of the chain for the highest bridle roll is greater than the length of the chain of the lowest bridle roll.

[0139] The weight of the support structure is considerably reduced with this configuration. The support frames 82 can be connected by two parallel beams 94, each beam 94 being at a respective lateral end of the bridle rolls of the heat exchange apparatus. With reference to Figure 13, preferably along the circuit, considering an advancement direction of the heat-transfer fluid, the following is provided: - a first storage and movement system 36, 37 for the high temperature heattransfer fluid, arranged along a first stretch 70 of the circuit from said cooling section 33 to said preheating section 30;

[0140] - and a second storage and movement system 38, 39 for the low temperature heat-transfer fluid, arranged along a second stretch 71 of the circuit from said preheating section 30 to said cooling section 33.

[0141] In a preferred embodiment, the first storage and movement system 36, 37 comprises a first tank 36 for storing the high temperature heat-transfer fluid and a first pumping unit 37 configured to adjust the flow rate of the heat-transfer fluid towards the preheating section 30.

[0142] Said first tank 36 preferably has insulated walls for minimizing the energy lost into the environment.

[0143] In fact, this tank 36 is a thermal energy storage where the high temperature heattransfer fluid is stored, which will be used to preheat the metal strip 40 at the inlet of the annealing furnace, i.e., at the inlet of the heating section 31.

[0144] Essentially, by decoupling the cooling section 33 from the preheating section 30, whenever the thermal energy removed from strip 40 in the cooling step is different from that required by the strip to be preheated at the inlet of the annealing apparatus, the excess or shortfall is stored or removed from tank 36, respectively. The first tank 36 has no heating means. In particular, no heating means are required inside the first tank to perform the thermal energy storage function.

[0145] Preferably, the flow of the high temperature heat-transfer fluid from the tank 36 is controlled by the pumping unit 37, in which the pump drive motor is a variable speed motor in order to achieve a control or modification mode of the flow rate towards the preheating section 30 through a supply duct 41. The high temperature heat-transfer fluid thus reaches the preheating section 30 through the supply duct 41.

[0146] Likewise, the second storage and movement system 38, 39 comprises a second tank 38 for storing the low temperature heat-transfer fluid and a second pumping unit 39 configured to adjust the flow rate of said heat-transfer fluid towards the cooling section 33. Said second tank 38 preferably has walls which are not insulated. The second tank 38 has no cooling means, in particular no cooling means are arranged inside said second tank, as they are not necessary.

[0147] Preferably, the flow of the low temperature heat-transfer fluid from the tank 38 is controlled by the pumping unit 39, in which the pump drive motor is a variable speed motor in order to achieve a control or modification mode of the flow rate towards the cooling section 33 through a supply duct 42. The low temperature heat-transfer fluid thus reaches the cooling section 33 through the supply duct 42.

[0148] Optionally, a heating device 43 is provided downstream of the first tank 36, preferably between the first tank 36 and the first pumping unit 37, for heating the heat-transfer fluid in the case of cold starting the annealing apparatus, for example after a long maintenance break.

[0149] By way of example, the heating device 43 is provided with at least one heating element, for example an armored electrical resistor immersed in an inner volume of the device 43 crossed by the heat-transfer fluid.

[0150] In a variant of the annealing apparatus of the invention, a further cooling section 44 with gas jets, for preliminarily cooling the strip, is provided between the temperature maintenance section 32 and the cooling section 33.

[0151] After completing the recrystallization cycle in the temperature maintenance section 32, the metal strip 40 thus enters this gas jet cooling section 44, where the strip undergoes a first slow cooling step due to a cold gas, preferably distributed by upper and lower cooling plenums 45, 46. This cooling section 44 is used whenever a slow cooling of the metallurgical recipe is required as a function of the quality of the product to be obtained.

[0152] Optionally, the cooling section 44 can be equipped with further heat recovery systems, in which, once heated having taken heat from the product, the gas flows ejected from the upper and lower cooling plenums 45, 46 are collected by means of a pumping or compression system 47 and sent to a further heat exchanger 48, which cools the hot gas coming from an inlet pipe 49, sending it back to the cooling plenums 45, 46, once cooled, through an outlet pipe 50. Preferably, the cooling speed in this cooling section 44 is in a range from 5 to 15°C / s. After the cooling section 44, the metal strip 40 reaches a temperature from 650 to 900°C and enters the cooling section 33.

[0153] In a further variant of the annealing apparatus of the invention, a post-heating section 51 for heating the metal strip to a lower temperature than the solubilization temperature is provided downstream of the cooling section 33. The function of this post-heating section 51 is purely metallurgical. In fact, since the post-heating takes place at a temperature lower than the solubilization temperature, it allows activating diffusion phenomena which induce a stable, coherent phase formation.

[0154] Preferably, a further gas jet cooling section 52, equal to the cooling section 44, is provided downstream of said post-heating section 51 in order to bring the metal strip 40 to a target temperature for exiting from the apparatus.

[0155] In the example in Figure 13, both the gas jet cooling section 44 and the postheating section 51 followed by the further gas jet cooling section 52 are provided in the annealing apparatus of the invention.

[0156] In some variants of the apparatus, according to the quality of the incoming strip and the desired metallurgical quality, the gas jet cooling section 44 and the postheating section 51 , as well as possibly the gas jet cooling section 52, can be removed.

[0157] Preferred, but not exclusive, variants of the cooling section 33 and the preheating section 30 are described below.

[0158] As described above, the heat-transfer fluid closed circuit crosses in series both the cooling bridle rolls 35, provided in the cooling section 33, and the heating bridle rolls 34, provided in the preheating section 30.

[0159] The cooling bridle rolls 35 are connected in series by means of intermediate pipes 35’ so that the heat-transfer fluid crosses the cooling rolls 35 in countercurrent with respect to the advancement of the metal strip on said cooling rolls 35.

[0160] As illustrated for example in Figure 15, the supply duct 42 supplies the last cooling roll 35 of the cooling section 33 with low temperature heat-transfer fluid; at said cooling roll the metal strip exits after being cooled by the cooling section 33. The supply of the heat-transfer fluid to subsequent rolls 35, upstream of said last roll, occurs by means of respective intermediate pipes 35’ interposed between the cooling rolls 35. A flow of the heat-transfer fluid is thus obtained in countercurrent with respect to the advancement direction of the strip, so that while the metal strip cools down passing from the first to the last roll 35, the heat-transfer fluid instead heats up passing from the last to the first roll 35, beyond which an outlet duct 65 is provided to convey the high temperature heat-transfer fluid, which has removed heat from the strip, from the cooling section 33 towards the first tank 36. The outlet duct 65 is suitably coated with an insulating material in order to minimize energy losses toward the environment.

[0161] Similarly, the different heating bridle rolls 34 are connected in the circuit in series by means of intermediate pipes 34’ so that the heat-transfer fluid crosses in sequence the heating rolls 34 in countercurrent with respect to the advancement of the metal strip on said heating rolls 34.

[0162] As illustrated for example in Figure 16, the supply duct 41 supplies the last heating roll 34 of the preheating section 30 with high temperature heat-transfer fluid, at said heating roll the metal strip exits after being preheated by the preheating section 30. The supply of the heat-transfer fluid to the subsequent rolls 34, upstream of said last roll, occurs by means of respective intermediate pipes 34’ interposed between the heating rolls 34. A flow of the heat-transfer fluid is thus obtained in countercurrent with respect to the advancement direction of the strip, so that while the metal strip is heated passing from the first to the last roll 34, the heat-transfer fluid is instead cooled passing from the last to the first roll 34, beyond which an outlet duct 66 is provided to convey the low temperature heat-transfer fluid, which has transferred heat to the strip, from the preheating section 30 towards the second tank 38.

[0163] In a further preferred variant, for an optimal control of the preheating process in the preheating section 30, the following can be provided:

[0164] - at least one first temperature sensor 67 at the inlet of the preheating section 30 for measuring the strip temperature;

[0165] - at least one second temperature sensor 68 at the outlet of the preheating section 30 for measuring the strip temperature;

[0166] - at least one first flow rate transducer 69 for measuring a first flow rate of the high temperature heat-transfer fluid entering the preheating section 30. It is possible to provide only one first temperature sensor 67, only one second temperature sensor 68, and only one first flow rate transducer 69.

[0167] Advantageously, at least one automatic control unit 72 can be provided, preferably only one automatic control unit, capable of receiving data from said first temperature sensor 67, said second temperature sensor 68 and said first flow rate transducer 69 and thus finely adjusting the flow rate of the heat transfer fluid entering the preheating section 30, preferably by acting on a first proportional valve 73.

[0168] The proportional valve 73 can act in combination with the pumping unit 37. Preferably, the pump drive motor of the pumping unit 37 is a variable speed motor in order to achieve rough control of the flow rate of the heat-transfer fluid towards the preheating section 30, while the proportional valve 73 achieves fine control of said flow rate.

[0169] Similarly, for an optimal control of the cooling process in the cooling section 33, the following can be provided:

[0170] - at least one third temperature sensor 62 at the inlet of the cooling section 33 for measuring the strip temperature;

[0171] - at least one fourth temperature sensor 63 at the outlet of the cooling section 33 for measuring the strip temperature;

[0172] - at least one second flow rate transducer 64 for measuring a second flow rate of the heat-transfer fluid entering the cooling section 33.

[0173] It is possible to provide only one third temperature sensor 62, only one fourth temperature sensor 63, and only one second flow rate transducer 64.

[0174] Said automatic control unit 72 is also adapted to receive data from said third temperature sensor 62, said fourth temperature sensor 63 and said second flow rate transducer 64 and therefore finely adjust the flow rate of the heat transfer fluid entering the cooling section 33, preferably by acting on a second proportional valve 73’.

[0175] The proportional valve 73’ can act in combination with the pumping unit 39. Preferably, the pump drive motor of the pumping unit 39 is a variable speed motor in order to achieve rough control of the flow rate of the heat transfer fluid towards the cooling section 33, while the proportional valve 73’ achieves fine control of said flow rate.

[0176] In all embodiments of the plant of the invention, it is preferable that the preheating section 30 be suitably contained within a metal casing, insulated so as not to disperse heat into the environment, and which can be pressurized with appropriate inert gas or kept in air depending on whether oxidative phenomena are to be avoided or encouraged.

[0177] Similarly, the cooling section 33 can be suitably contained inside a metal casing, insulated so as not to disperse heat into the environment, and which can be pressurized with appropriate inert gas or kept in air depending on whether oxidative phenomena are to be avoided or encouraged.

Claims

CLAIMS1 . Heat exchange apparatus comprising at least one bridle roll for exchanging heat with a metal strip advancing along a plant, said at least one bridle roll comprising- a hollow cylindrical body (1 ) defining a longitudinal rotation axis (X);- an outer shell (2) fastened on the outer lateral surface of said hollow cylindrical body (1 ) and defining an outer cylindrical radial surface of said roll, coaxial to said longitudinal axis (X), for partially winding the metal strip around said outer shell (2) during the advancement thereof;- at least one inner channel (3) obtained by the coupling between the outer lateral surface of said hollow cylindrical body (1 ) and an inner cylindrical radial surface of the outer shell (2); wherein at least one end portion (5) of said hollow cylindrical body (1 ) comprises, in the axial direction, a respective annular gap (6) adapted to contain a heattransfer fluid and to distribute said heat-transfer fluid in said at least one inner channel (3); wherein said annular gap (6) is delimited by at least two parallel walls of said hollow cylindrical body (1 ), orthogonal to the longitudinal axis (X); wherein there is provided a hollow transmission element (7) to which said at least one end portion (5) is connected to receive the transmission of a rotating motion around said longitudinal axis (X), said hollow transmission element (7) comprising an inner duct (8) for feeding said heat-transfer fluid in said annular gap (6); wherein said at least one end portion (5) has a plurality of through holes (11) having a respective axis parallel to the longitudinal axis (X) and defining a respective tubular reinforcing element inside said annular gap (6).

2. Apparatus according to claim 1 , wherein in said at least one bridle roll there are provided- a plurality of first radial holes (9), made in the thickness of said hollow transmission element (7), and connecting said inner duct (8) to said annular gap (6);- and a plurality of second radial holes (10), made in the thickness of a radially peripheral part of said at least one lateral end portion (5), and connecting said annular gap (6) to said at least one inner channel (3).

3. Apparatus according to claim 1 or 2, wherein said through holes (11) are arranged along a circumference coaxial to said longitudinal axis (X).

4. Apparatus according to any one of the preceding claims, wherein said hollow transmission element (7) is a first lateral hub, or a through-axis hub, wherein both end portions (5, 5’) of said hollow cylindrical body (1 ) comprise, in the axial direction, a respective annular gap (6, 6’); wherein a first annular gap (6) of a first end portion (5) is adapted to receive a heat-transfer fluid from the inner duct (8) of said first lateral hub, or of said through-axis hub, and to distribute said heat-transfer fluid in said at least one inner channel (3); and wherein a second annular gap (6’) of a second end portion (5’) is adapted to receive said heat-transfer fluid from said at least one inner channel (3) and to convey said heat-transfer fluid into a further inner duct (8’) of a second lateral hub, or of said through-axis hub, on which said second end portion (5’) is connected.

5. Apparatus according to claim 4, wherein first annular gap (6) and second annular gap (6’) are each delimited by two respective parallel walls, orthogonal to the longitudinal axis (X); wherein both end portions (5, 5’) have a respective plurality of through holes (11) having a respective axis parallel to the longitudinal axis (X) and defining a respective tubular reinforcing element, the plurality of through holes being preferably arranged along a circumference coaxial to said longitudinal axis (X) so that the volume of the respective annular gap (6, 6’) is reduced; preferably, wherein both end portions (5, 5’) are provided with a respective outer covering panel (20); wherein said outer covering panels (20) are held integral to the respective end portion (5, 5’) and held integral to each other by means of a plurality of tie rods (21 ), each tie rod (21 ) passing through a respective through hole (11 ) of each end portion (5, 5’); preferably wherein a further annular gap (74), optionally filled with an insulating material, is provided between each covering panel (20) and the respective end portion (5, 5’).

6. Apparatus according to any one of preceding claims 1 to 3, wherein said hollow transmission element (7) is a first lateral hub;wherein a first lateral end portion (5) of said hollow cylindrical body (1 ) comprises, in the axial direction, a first annular gap (6); wherein said first annular gap (6) is divided into two adjacent and parallel parts (91 , 93), separated by an intermediate wall (92); wherein a first part (91 ) of said annular gap (6) is adapted to receive a heattransfer fluid from the inner duct (8) of said first lateral hub and to distribute said heat-transfer fluid in said at least one inner channel (3); wherein said at least one inner channel (3) is configured to allow the heat-transfer fluid to reach a second annular gap (6’) of a second end portion (5’) of said hollow cylindrical body (1 ) and to return towards the first end portion (5); wherein a second part (93) of said first annular gap (6) is adapted to receive the heat-transfer fluid returning from said at least one inner channel (3) and to convey said heat-transfer fluid into a further inner duct (80) of said hollow transmission element (7), preferably arranged coaxially to, and inside, said inner duct (8).

7. Apparatus according to any one of the preceding claims, wherein said hollow transmission element (7) is a first lateral hub, or a through-axis hub, and wherein there are provided:- a fixed pipe (24) for a passage of heat-transfer fluid;- a hollow drive shaft (15) which is operable by a motor (13), provided therein with a tube (16) integral therewith and coaxial to the longitudinal axis (X), and integrally connected to said first lateral hub or to said through-axis hub (7) so that tube (16) and inner duct (8) define a rotating pipe (16, 8);- a rotating joint (18) connecting said fixed pipe (24) to said rotating pipe (16, 8); preferably wherein the rotating joint (18) comprises a fixed part (25), connected to said fixed pipe (24), and a rotating duct (17) inside said fixed part (25) communicating with said rotating pipe (16, 8); preferably wherein said rotating joint (18) further comprises a flange with conical coupling (26) arranged on said rotating duct (17) and fastened to said hollow drive shaft (15).

8. Apparatus according to claim 7, wherein the tube (16) is provided, in the thickness thereof, with an annular air chamber (16’).

9. Apparatus according to claim 7 or 8, wherein there are provided:- at least one support (19) of the hollow drive shaft (15), with bearings interposed between said support (19) and said hollow drive shaft (15);- and a plurality of cooling fins (22) projecting from said hollow drive shaft (15), arranged between said at least one support (19) and a first end of the hollow drive shaft (15) connected to said first lateral hub or through-axis hub (7).

10. Apparatus according to claim 7 or 8 or 9, wherein there is provided a chain drive (14), preferably with a planetary gear reducer, connecting said motor (13) to a second end of said hollow drive shaft (15) connected to the rotating joint (18); preferably wherein there is provided an adjustment system for adjusting the tension of the chain of said chain drive (14), for example a mechanical or pneumatic or hydraulic actuator.

11. Apparatus according to any one of the preceding claims, wherein said at least one inner channel (3) comprises two or three helical channels, preferably connected in parallel, delimited by a respective helical groove (4) made on the outer lateral surface of said hollow cylindrical body (1 ), and by the cylindrical inner radial surface of the outer shell (2).

12. Apparatus according to any one of the preceding claims, wherein the seal between the hollow cylindrical body (1 ) and the outer shell (2) is obtained at both ends of the bridle roll along the axial direction, preferably exclusively by means of an external welding along a circumferential direction; preferably, wherein there is provided a welding seam at both ends of the bridle roll, considering the axial direction of the roll, in an outer circumferential boundary area (90) between the hollow cylindrical body (1 ) and the outer shell (2).

13. Annealing plant for a metal strip advancing in a direction, said plant comprising in sequence:- at least one preheating section (30);- at least one heating section (31 );- at least one temperature maintaining section (32);- at least one cooling section (33); wherein there is provided a first heat exchange apparatus according to claim 1 in said at least one preheating section (30);wherein there is provided a second heat exchange apparatus according to claim 1 in said at least one cooling section (33); and wherein there is provided a heat-transfer fluid closed circuit configured to cross both said second heat exchange apparatus to subtract thermal energy from the metal strip by conduction, thus obtaining a high temperature heat-transfer fluid, and said first heat exchange apparatus to transfer thermal energy to the metal strip by conduction, thus obtaining a low temperature heat-transfer fluid.

14. Annealing plant according to claim 13, wherein in the first heat exchange apparatus said at least one bridle roll comprises a plurality of heating bridle rolls (34) for the advancement of the metal strip; wherein in the second heat exchange apparatus said at least one bridle roll comprises a plurality of cooling bridle rolls (35) for the advancement of the metal strip; wherein said heat-transfer fluid closed circuit crosses in series both the cooling bridle rolls (35), provided in said at least one cooling section (33), and the heating bridle rolls (34) provided in said at least one preheating section (30).

15. Annealing plant according to claim 13, wherein both the heating bridle rolls (34) and the cooling bridle rolls (35) are arranged in a configuration such that each bridle roll is wound by the metal strip by at least 190°; preferably wherein there are provided, in both said at least one preheating section (30) and said at least one cooling section (33), an even number of bridle rolls (34, 35), preferably six, which are arranged in sequence, in groups of two bridle rolls at different heights from one another, preferably only two different heights, along a conveying direction of the metal strip.

16. Annealing plant according to any one of claims 13 to 15, wherein along said circuit, considering an advancement direction of the heat-transfer fluid, there are provided:- a first storage and movement system (36, 37) for storing and moving the high temperature heat-transfer fluid, acting as a thermal energy storage (TES) and arranged along a first stretch (70) of the circuit from said at least one cooling section (33) to said at least one preheating section (30);- and preferably a second storage and movement system (38, 39) for storing and moving the low temperature heat-transfer fluid, arranged along a second stretch (71 ) of the circuit from said at least one preheating section (30) to said at least one cooling section (33).

17. Annealing plant according to claim 16, wherein the first storage and movement system (36, 37) comprises a first tank (36) for storing the high temperature heattransfer fluid, configured as a thermal energy storage (TES), and a first pumping unit (37) configured to adjust the flow rate of said high temperature heat-transfer fluid towards the at least one preheating section (30); and preferably wherein the second storage and movement system (38, 39) comprises a second tank (38) for storing the low temperature heat-transfer fluid and a second pumping unit (39) configured to adjust the flow rate of said low temperature heat-transfer fluid towards the at least one cooling section (33); preferably wherein the first tank (36) has no heating means and optionally has insulated walls to minimize the energy lost into the environment, and preferably wherein the second tank (38) has no cooling means.

18. Annealing plant according to any one of the preceding claims, wherein there are provided:- at least one first temperature sensor (67) at the inlet of the preheating section (30) for measuring the strip temperature;- at least one second temperature sensor (68) at the outlet of the preheating section (30) for measuring the strip temperature;- at least one first flow rate transducer (69) for measuring a first flow rate of the heat-transfer fluid entering the preheating section (30);- at least one third temperature sensor (62) at the inlet of the cooling section (33) for measuring the strip temperature;- at least one fourth temperature sensor (63) at the outlet of the cooling section (33) for measuring the strip temperature;- at least one second flow rate transducer (64) for measuring a second flow rate of the heat-transfer fluid entering the cooling section (33); and wherein there is provided at least one automatic control unit (72) adapted to receive data from said at least one first temperature sensor (67), said at least onesecond temperature sensor (68) and said at least one first flow rate transducer (69), and consequently adjust said first flow rate, and adapted to receive data from said at least one third temperature sensor (62), said at least one fourth temperature sensor (63), and said at least one second flow rate transducer (64), and consequently adjust said second flow rate.

19. Apparatus according to claim 18, wherein said at least one automatic control unit (72) is adapted to adjust said first flow rate by means of a first proportional valve (73) and to adjust said second flow rate by means of a second proportional valve (73’).

20. Apparatus according to claim 19, wherein said first proportional valve (73) is configured to act in combination with a first pumping unit (37) configured to adjust the first flow rate of said high temperature heat-transfer fluid from a first tank (36), acting as a thermal energy storage (TES) and arranged along a first stretch (70) of the circuit from the at least one cooling section (33) to the at least one preheating section (30), towards said at least one preheating section (30); preferably wherein said second proportional valve (73’) is configured to act in combination with a second pumping unit (39) configured to adjust the second flow rate of said low temperature heat-transfer fluid from a second tank (38), arranged along a second stretch (71 ) of the circuit from the at least one preheating section (30) to the at least one cooling section (33), towards said at least one cooling section (33).

21. Apparatus according to claim 20, wherein both the control motor of said first pumping unit (37) and the control motor of said second pumping unit (39) are a variable speed motor.

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