Annealing apparatus and associated methods

Abstract

An annealing device for a metal strip (2) advancing in the longitudinal direction, said device comprising, in sequence: at least one preheating section (17); at least one heating section (3); at least one temperature maintenance section (4); at least one cooling section (23); wherein said at least one preheating section (17) comprises a plurality of heating rollers (16) for advancing said metal strip (2); wherein said at least one cooling section (23) comprises a plurality of cooling rollers (22) for advancing said metal strip (2), wherein a circuit of heat transfer fluid is provided, said circuit being configured to pass through the cooling rollers (22) of said at least one cooling section (23) in order to extract heat energy from the strip, thus obtaining a high-temperature heat transfer fluid, and through the heating rollers (16) of said at least one preheating section (17) in order to transfer heat energy to the strip, thus obtaining a low-temperature heat transfer fluid.

Description

Technical Field

[0001] This invention relates to the technical field of annealing systems for metal sheets or strips, particularly those made of steel, such as annealing and galvanizing lines known as "hot-dip galvanizing lines" (HDGL) or "continuous annealing production lines" (CAL). The invention also relates to a related annealing method for heating and annealing ferrous or non-ferrous metal strips. Background Technology

[0002] As is well known, cold-rolled steel strip must undergo an annealing cycle to achieve recrystallization of the grains that constitute the product's crystalline structure. In fact, due to the plastic deformation applied during cold rolling, these grains have already been subjected to a crushing effect.

[0003] Annealing furnaces typically consist of the following areas: -Preheating section - Open flame heating section -Radiant heating section -Temperature holding section - Controlled cooling section.

[0004] One possible alternative involves using only radiant tubes. In this case, the furnace is reduced to several zones: -Radiant heating section -Temperature holding section - Controlled cooling section.

[0005] Controlled cooling sections typically include a mixture of industrial gases, such as nitrogen and hydrogen, or hydrogen alone when oxidation of the strip surface in the furnace must be avoided. The controlled cooling section is equipped with a jet cooler.

[0006] Conversely, if strip oxidation is permissible, ambient air is preferred.

[0007] The purpose of airflow is to remove heat from the strip, thereby lowering its temperature and making it suitable for subsequent processing.

[0008] In the case of annealing and galvanizing lines (referred to as "hot-dip galvanizing lines" (HDGL)), the steel strip is cooled from the target temperature of the holding section (650°C–950°C) to the zinc bath temperature (approximately 460°C).

[0009] In the case of a continuous annealing production line (CAL), at the exit of the annealing furnace, the strip is cooled from the target temperature of the holding section to a final temperature below 100°C. The heat removed by the mixture of industrial gas or ambient air is transferred to the equipment's cooling water circuit via a suitable gas / water heat exchanger.

[0010] The cooling mixture of industrial gases is recirculated through a closed loop to the jet cooler in the controlled cooling section to continuously remove heat from the strip.

[0011] Conversely, the heat energy transferred to the cooling water is dissipated / dispersed into the environment through the evaporation tower of the closed cooling water loop.

[0012] This method of operating the annealing apparatus highlights a key issue: - The heat energy transferred to the metal strip for recrystallization is lost; in fact, this unrecovered heat energy is subsequently removed in the controlled cooling section, resulting in the consumption of chemical and electrical energy, which in turn leads to the emission of related carbon dioxide. - The heat removed from the strip in the controlled cooling section is transferred to the cooling water and eventually released into the environment through the evaporation tower, resulting in water consumption; - The energy used for cooling water recirculation involves further carbon dioxide emissions, which is related to the production of electricity consumed.

[0013] In view of the above, it is clear that innovative improvements to the annealing system are needed to eliminate the aforementioned defects while maximizing the recovery and reuse of thermal energy in the heat treatment furnace. Summary of the Invention

[0014] The purpose of this invention is to manufacture an annealing apparatus for metal strip that can fully or partially recover the heat energy extracted from the annealed metal strip during a controlled cooling step, and can reuse the recovered energy by transferring it to the metal strip at the inlet of the apparatus (typically at room temperature) to achieve preheating of the product to be annealed. This has significant advantages for the environment and for reducing furnace operating costs.

[0015] Another object of the present invention is to manufacture an annealing apparatus that allows for high production flexibility while creating a thermal energy storage system that can be used in all cases where the amount of heat energy removed from the product during the cooling step is inconsistent (insufficient or excessive) with the amount of energy required by the product during the preheating step.

[0016] Another objective of this invention is to develop a highly efficient annealing method with minimal environmental impact.

[0017] This innovative solution can be applied to continuous annealing equipment for all ferrous and non-ferrous metal strips.

[0018] Therefore, the present invention aims to achieve the above objective by manufacturing an annealing apparatus for a metal strip that moves longitudinally, the apparatus comprising, in sequence: At least one preheating section; At least one heating section; At least one temperature holding section; At least one cooling section; The at least one preheating section includes a plurality of heating rollers for advancing the metal strip; The at least one cooling section includes a plurality of cooling rollers for advancing the metal strip; The circuit includes a closed loop for heat transfer fluid, which is configured to pass through a cooling roller in the at least one cooling section to conduct heat energy out of the strip to obtain a high-temperature heat transfer fluid, and through a heating roller in the at least one preheating section to conduct heat energy to the metal strip to obtain a low-temperature heat transfer fluid.

[0019] Another aspect of the invention relates to an annealing method for annealing a cold-rolled metal strip advancing longitudinally, the method being performed by the aforementioned apparatus and comprising the following steps: The metal strip is preheated in at least one preheating section; The metal strip is heated in at least one heating section; The temperature of the metal strip is maintained in at least one temperature holding section; The metal strip is cooled in at least one cooling section; The heat transfer fluid in the closed loop passes through the cooling roller of the at least one cooling section and the heating roller of the at least one preheating section. The cooling roller extracts heat energy from the metal strip through conduction and obtains a high-temperature heat transfer fluid, while the heating roller transfers heat energy to the metal strip through conduction and obtains a low-temperature heat transfer fluid.

[0020] Other advantages of some embodiments of the present invention include: - High production flexibility regardless of whether the annealing unit is configured horizontally or vertically; - By significantly saving energy in heating metal strips, production costs are significantly reduced; - Significantly reduces direct and indirect carbon dioxide emissions; -Significant simplification of the cooling water closed loop, while reducing water consumption due to its evaporation losses; - The cooling process is highly flexible, allowing for cooling rates between 10 and 100 °C / s relative to the desired metallurgical quality.

[0021] The dependent claims describe preferred embodiments of the invention. Attached Figure Description

[0022] Further features and advantages of the invention will become more apparent with the aid of the accompanying drawings, and from the detailed description of preferred but non-exclusive embodiments of the device illustrated by non-limiting examples, wherein: Figure 1 A schematic diagram of a first embodiment of an annealing apparatus according to the present invention is depicted; Figure 2 A schematic diagram depicts a preheating section in which heat transfer fluid is supplied parallel to the heating rollers; Figure 3 Another schematic diagram of the preheating section is shown, which continuously supplies heat transfer fluid to the heating roller; Figure 4 A schematic diagram depicts a cooling section in which heat transfer fluid is supplied parallel to the cooling rollers; Figure 5 Another schematic diagram of the cooling section is shown, in which heat transfer fluid is supplied in series to the cooling rollers; Figure 6 A diagram of the components of the device according to the invention is depicted; Figure 7 A schematic diagram depicting other components of the device according to the invention is provided; Figure 8a , 8b Figures 8c and 8c depict three examples of the thermal cycle of the annealing apparatus according to the present invention; Figure 9 A schematic diagram of a second embodiment of the annealing apparatus according to the present invention is depicted; Figure 10 A schematic diagram is depicted relating to the management of a water / heat transfer fluid heat exchanger used for producing hot water; Figure 11 Examples of internal channels in the heating or cooling rollers of the device according to the invention are depicted.

[0023] The same reference numerals in the figure indicate the same elements or parts. Detailed Implementation

[0024] Referring to the accompanying drawings, some exemplary embodiments of an annealing apparatus for metal strip according to the present invention are shown. As is well known, metal strip is a product whose dimensions (i.e., thickness) are significantly smaller than its other two dimensions (i.e., length and width).

[0025] In all embodiments of the present invention, the annealing apparatus for the cold-rolled metal strip 2, preferably advancing longitudinally, comprises in sequence: At least one preheating section 17; At least one heating section 3; At least one temperature holding section 4; At least one cooling section 23.

[0026] Advantageously, at least one preheating section 17 includes a plurality of heating rollers 16 for advancing the metal strip 2; at least one cooling section 23 includes a plurality of cooling rollers 22 for advancing the metal strip 2; and a closed loop of heat transfer fluid is provided, the loop being configured to pass through the cooling rollers 22 and the heating rollers 16, the cooling rollers 22 being used to extract heat energy from the metal strip by conduction to obtain a high-temperature heat transfer fluid, and the heating rollers 16 being used to transfer heat energy to the metal strip by conduction to obtain a low-temperature heat transfer fluid.

[0027] Preferably, only one preheating section 17, one heating section 3, one temperature holding section 4, and one cooling section 23 are provided.

[0028] Therefore, in steady-state operation, the heat transfer fluid allows the heat energy extracted from the annealed metal strip in the cooling section 23 to be fully or partially recovered and reused by transferring it to the metal strip in the preheating section 17 at the inlet of the device, thereby achieving preheating of the product to be annealed. This has significant advantages for the environment and reducing the operating cost of the heating section 3.

[0029] In a preferred variant, both the cooling roller 22 and the heating roller 16 are provided with at least one corresponding internal channel 39, which is configured to allow the low-temperature heat transfer fluid to pass through the cooling roller 22, preferably extending longitudinally therethrough, for cooling the metal strip by conduction, and to allow the high-temperature heat transfer fluid to pass through the heating roller 16, preferably extending longitudinally therethrough, for preheating the metal strip by conduction. The cooling roller 22 and the heating roller 16 are adapted to be in direct contact with the strip during its advance.

[0030] Preferably, considering the direction of the heat transfer fluid (see...) Figure 1 and 10 (as indicated by the arrow in the diagram), along the loop, the following structure is provided: - First storage and movement systems 25, 27, for storing and moving high-temperature heat transfer fluid, are arranged along a first extension 70 of the loop from the cooling section 23 to the preheating section 17; - and a second storage and movement system 19, 20 for storing and moving cryogenic heat transfer fluid, arranged along the second extension 71 of the loop from the preheating section 17 to the cooling section 23.

[0031] In a preferred variant, the first storage and transport systems 25, 27 include a first tank 25 for storing high-temperature heat transfer fluid and a first pumping unit 27 configured to regulate the flow rate of the heat transfer fluid toward the preheating section 17.

[0032] The first tank 25 preferably has an insulating wall 40 to minimize energy loss into the environment. Figure 7 ).

[0033] In fact, the tank 25 forms a thermal energy storage device in which a high-temperature heat transfer fluid is stored. This heat transfer fluid will be used to preheat the metal strip 2 at the inlet of the annealing furnace, that is, at the inlet of the heating section 3.

[0034] Essentially, by separating the cooling section 23 from the preheating section 17, whenever the heat energy extracted from the strip 2 during the cooling step differs from the heat energy required for the strip to be preheated at the inlet of the annealing device, the excess or deficiency is stored in or extracted from the tank 25, respectively.

[0035] The first tank, 25, has no heating device. In particular, it does not require a heating device to perform the thermal energy storage function.

[0036] Preferably, the flow of the high-temperature heat transfer fluid from tank 25 is controlled by pumping unit 27, wherein the pump drive motor is a variable speed motor to achieve a controlled or modified flow pattern toward preheating section 17 via supply conduit 15. The high-temperature heat transfer fluid thus reaches preheating section 17 via supply conduit 15.

[0037] Similarly, the second storage and transport systems 19, 20 include a second tank 19 for storing cryogenic heat transfer fluid and a second pumping unit 20 configured to regulate the flow rate of the heat transfer fluid toward the cooling section 23.

[0038] The second tank 19 preferably has a non-insulated wall 61. Figure 6 The second tank 19 has no cooling device, especially no cooling device arranged inside it, because they are not necessary.

[0039] Preferably, the flow of the cryogenic heat transfer fluid from tank 19 is controlled by pumping unit 20, wherein the pump drive motor is a variable speed motor to achieve control or modification of the flow rate toward cooling section 23 via supply conduit 21. The cryogenic heat transfer fluid thus reaches cooling section 23 via supply conduit 21.

[0040] Optionally, the heating device 26 is located downstream of the first tank 25, preferably between the first tank 25 and the first pumping unit 27, for heating the heat transfer fluid in the event of a cold start of the annealing device (e.g., after a long maintenance interruption).

[0041] For example, the heating device 26 is provided with at least one heating element 47, such as a sheathed resistor immersed in the internal volume of the device 26 through which the heat transfer fluid passes.

[0042] In a variation of the annealing apparatus of the present invention, an additional gas jet cooling section 5 for preliminary cooling of the strip is provided between the temperature holding section 4 and the cooling section 23.

[0043] After the recrystallization cycle is completed in the temperature holding section 4, the metal strip 2 then enters the gas jet cooling section 5, where the metal strip 2 undergoes a first slow cooling step due to the cold gas, which is preferably distributed by the upper and lower cooling pressurization chambers 10 and 11. Figure 1 and 10 Cooling section 5 is used whenever the metallurgical formulation requires slow cooling, depending on the desired product quality.

[0044] Optionally, such as Figure 1 and 10 As shown, the cooling section 5 may be equipped with an additional heat recovery system, wherein the airflow ejected from the upper and lower cooling gas collection chambers 10, 11, once heated by absorbing heat from the product, is drawn by a pumping or compression system 7 and sent to an additional heat exchanger 6, which cools the hot gas from the inlet pipe 8, and once cooled, is sent back to the cooling gas collection chambers 10, 11 through the outlet pipe 9.

[0045] Preferably, the cooling rate in the cooling section 5 is in the range of 5 to 15°C / s.

[0046] After cooling section 5, the metal strip 2 reaches a temperature of 650 to 900°C and enters cooling section 23.

[0047] In another variation of the annealing apparatus of the present invention, a post-heating section 12 is provided downstream of the cooling section 23 for heating the metal strip to a temperature below the solution temperature. The post-heating section 12 functions purely metallurgically. In fact, since the post-heating occurs at a temperature below the solution temperature, it allows for the activation of diffusion phenomena, thereby inducing the formation of stable, coherent phases.

[0048] Preferably, a second gas jet cooling section 13 is provided downstream of the post-heating section 12 for heating the metal strip 2 to a target temperature for exiting the device.

[0049] exist Figure 1 and 10 In the example, the gas jet cooling section 5, the post-heating section 12, and the subsequent gas jet cooling section 13 are all provided in the annealing apparatus of the present invention.

[0050] In some variations of this device, the gas jet cooling section 5 and the post-heating section 12, as well as the possible gas jet cooling section 13, can be removed, taking into account the quality of the introduced strip and the desired metallurgical quality.

[0051] Figure 8a , 8b Figures 8c and 8c show three examples of reference periods. In particular, Figure 8a , 8bThe thermal cycles of the annealing and galvanizing lines (referred to as "hot-dip galvanizing line" (HDGL) and continuous annealing line (CAL)) are shown respectively.

[0052] Figure 8a The thermal cycle of the annealing apparatus is shown. The annealing apparatus is provided in sequence with a preheating section 17 with heating roller 16, a heating section 3, a temperature holding section 4, a gas jet cooling section 5, a cooling section 23 with cooling roller 22, and another gas jet cooling section 13.

[0053] Figure 8b The thermal cycle of the annealing apparatus is shown, which is sequentially provided with a preheating section 17 with heating roller 16, a heating section 3, a temperature holding section 4, a gas jet cooling section 5, a cooling section 23 with cooling roller 22, a post-heating section 12, and an additional gas jet cooling section 13.

[0054] Figure 8c The thermal cycle of the annealing apparatus is shown, which is sequentially provided with a preheating section 17 with heating roller 16, a heating section 3, a temperature holding section 4, and a cooling section 23 with cooling roller 22.

[0055] Preferred, but not unique, variations of the cooling section 23 and the preheating section 17 are described below.

[0056] In a preferred variant, each cooling roller 22 of the cooling section 23 is provided with at least one internal channel 39 communicating with the aforementioned supply conduit 21, so that a low-temperature heat transfer fluid preferably extends longitudinally therethrough and cools the metal strip by conduction.

[0057] For example, the internal channels of different cooling rollers 22 are connected in parallel in the loop; or they are connected in series through intermediate pipes, so that the heat transfer fluid flows in the opposite direction to the advance of the metal strip on the cooling rollers 22.

[0058] In particular, such as Figure 4 As shown, in the parallel connection configuration, a plurality of pipes 35 can exit from the supply conduit 21, the number of which is equal to the number of cooling rollers 22. At the first end of each roller 22, a low-temperature heat transfer fluid is supplied to at least one internal channel. At the second end of each roller 22, at least one internal channel communicates with a corresponding pipe 36. The number of pipes 36 is also preferably equal to the number of cooling rollers 22. The pipes 36 flow into the outlet conduit 24 to convey a high-temperature heat transfer fluid from the cooling section 23 to the first tank 25, which has already carried away heat from the strip.

[0059] The outlet conduit 24 is appropriately coated with insulating material 49. Figure 7 This is to minimize energy loss to the environment.

[0060] Instead, for example,Figure 5 In the illustrated series connection configuration, supply conduit 21 supplies low-temperature heat transfer fluid to at least one internal channel of the last cooling roller 22 of the cooling section 23, from which the metal strip 2 exits after being cooled by the cooling section 23. Supplying heat transfer fluid to at least one internal channel of the subsequent roller 22 upstream of the last roller is achieved via corresponding intermediate pipes 35' inserted between the cooling rollers 22. Therefore, the flow of the heat transfer fluid is counter-current relative to the direction of the strip's movement, such that while the metal strip 2 is cooled from the first roller 22 to the last roller 22, the heat transfer fluid is heated from the last roller 22 to the first roller 22. Outside the first roller 22, an outlet conduit 24 is provided to deliver high-temperature heat transfer fluid from the cooling section 23 to the first tank 25, which has already carried away heat from the strip.

[0061] Similarly, each of the heating rollers 16 in the preheating section 17 is provided with at least one internal channel 39 communicating with the aforementioned supply conduit 15 so that it is preferably extended longitudinally to be traversed by a high-temperature heat transfer fluid and heated by conduction.

[0062] For example, the internal channels of different heating rollers 16 are connected in parallel in the loop; or they are connected in series through intermediate pipes, so that the heat transfer fluid passes through the heating rollers 16 sequentially in a countercurrent manner relative to the advance of the metal strip on the heating rollers 16.

[0063] In particular, such as Figure 2 As shown, in the parallel connection configuration, a plurality of pipes 28 can exit from the supply conduit 15, the number of which is equal to the number of heating rollers 16, each heating roller 16 supplying a high-temperature heat transfer fluid to at least one internal channel at its first end. At the second end of each corresponding roller 16, at least one internal channel communicates with a corresponding pipe 29. The number of pipes 29 is also preferably equal to the number of heating rollers 16. Pipes 29 flow into an outlet conduit 18 to convey a low-temperature heat transfer fluid from the preheating section 17 to the second tank 19, which transfers heat to the strip. The outlet conduit 18 is preferably not insulated.

[0064] Instead, for example, Figure 3In the illustrated series connection configuration, supply conduit 15 supplies high-temperature heat transfer fluid to at least one internal channel of the last heating roller 16 of the preheating section 17, from which the metal strip 2 exits after being preheated by the preheating section 17. Supplying heat transfer fluid to at least one internal channel of the subsequent rollers 16 upstream of the last roller is achieved via corresponding intermediate pipes 28' inserted between the heating rollers 16. Therefore, the flow of the heat transfer fluid is counter-current relative to the direction of the strip's advance, such that as the metal strip 2 is heated from the first roller 16 to the last roller 16, the heat transfer fluid is cooled from the last roller 16 to the first roller 16. Beyond the first roller 16, the outlet conduit 18 is configured to deliver low-temperature heat transfer fluid from the preheating section 17 toward the second tank 19, which transfers heat to the strip.

[0065] In another preferred variation, in order to optimally control the preheating process in preheating section 17, the following structure can be provided: - At least one first temperature sensor 30 is located at the inlet of the preheating section 17 for measuring the strip temperature; - At least one second temperature sensor 31 is located at the outlet of the preheating section 17 for measuring the strip temperature; - At least one first flow sensor 32 is used to measure the first flow rate of the high-temperature heat transfer fluid entering the preheating section 17.

[0066] A single first temperature sensor 30, a single second temperature sensor 31, and a single first flow sensor 32 may be provided.

[0067] Advantageously, at least one automatic control unit 33, preferably a single automatic control unit, can be provided, which is capable of receiving data from the first temperature sensor 30, the second temperature sensor 31 and the first flow sensor 32, and preferably finely adjusting the flow rate of the heat transfer fluid entering the preheating section 17 accordingly by acting on the first proportional valve 34.

[0068] The proportional valve 34 can be used in conjunction with the pumping unit 27. Preferably, the pump drive motor of the pumping unit 27 is a variable speed motor to achieve coarse control of the flow rate of the heat transfer fluid toward the preheating section 17, while the proportional valve 34 achieves fine control of the flow rate.

[0069] Similarly, for optimal control of the cooling process in cooling section 23, the following structure can be configured: - At least one third temperature sensor 62, at the inlet of the cooling section 23, is used to measure the strip temperature; - At least one fourth temperature sensor 63, at the outlet of cooling section 23, is used to measure the strip temperature; - At least one second flow sensor 64 is used to measure the second flow rate of the heat transfer fluid entering the cooling section 23.

[0070] A single third temperature sensor 62, a single fourth temperature sensor 63, and a single second flow sensor 64 can be configured.

[0071] The automatic control unit 33 is also adapted to receive data from the third temperature sensor 62, the fourth temperature sensor 63 and the second flow sensor 64, and therefore preferably to finely regulate the flow rate of the heat transfer fluid entering the cooling section 23 by acting on the second proportional valve 34'.

[0072] The proportional valve 34' can be used in conjunction with the pumping unit 20. Preferably, the pump drive motor of the pumping unit 20 is a variable speed motor to achieve coarse control of the flow rate of the heat transfer fluid toward the cooling section 23, while the proportional valve 34' achieves fine control of the flow rate.

[0073] To further improve the control of the preheating process in preheating section 17, the first tank 25 is equipped with ( Figure 7 A first temperature sensor 45 is provided to measure the temperature of the heat transfer fluid in the first tank, and a first automatic level gauge 46 is provided to detect the level of the heat transfer fluid in the first tank. The automatic control unit 33 is also adapted to receive data from the first temperature sensor 45 and the first automatic level gauge 46 to better regulate the preheating in the preheating section 17.

[0074] An injection device 41 can be provided to inject inert gas in order to pressurize the first tank 25, thereby preventing the heat transfer fluid from degrading due to oxidation.

[0075] Similarly, in order to further improve the control of the cooling process in cooling section 23, the second tank 19 is equipped with ( Figure 6 A second temperature sensor 42 is provided to measure the temperature of the heat transfer fluid in the second tank, and a second automatic level gauge 43 is provided to detect the level of the heat transfer fluid in the second tank. The automatic control unit 33 is also adapted to receive data from the second temperature sensor 42 and the second automatic level gauge 43 to better regulate the cooling in the cooling section 23.

[0076] In the same case, an injection device 41 can be provided to inject inert gas to pressurize the second tank 19, thereby preventing the heat transfer fluid from degrading due to oxidation.

[0077] like Figure 9 and 10As shown, in another variation of the present invention, a first water / heat transfer fluid heat exchanger 50 may be provided along the first extension 70 of the loop, at the outlet of the cooling section 23 and upstream of the first tank 25, for generating hot water to remove the heat energy previously extracted from the metal strip, which is excessive relative to the heat energy required for the strip in the preheating section 17.

[0078] Similarly, along the extension 71 of the loop, at the outlet of the preheating section 17 and upstream of the second tank 19, a second water / heat transfer fluid heat exchanger 50' can be provided to generate hot water in order to minimize the temperature of the heat transfer fluid and promote cooling in the cooling section 23.

[0079] Preferably, both the first heat exchanger 50 and the second heat exchanger 50' are provided with ( Figure 11 ): - Temperature sensors 55 and 57 are used to measure the temperature of water flowing into and out of the heat exchanger; - Flow sensor 56 is used to measure the flow rate of water at the inlet of the heat exchanger; - Additional temperature sensors 52 and 53 are used to measure the temperature of the heat transfer fluid flowing into and out of the heat exchanger; - An additional flow sensor 54 is used to measure the flow rate of the heat transfer fluid at the inlet of the heat exchanger.

[0080] The aforementioned automatic control unit 33 is also adapted to receive data from the temperature sensors 55, 57, the flow sensor 56, the additional temperature sensors 52, 53, and the additional flow sensor 54, thereby adjusting the flow rate of water entering the respective heat exchangers 50, 50' relative to the heat energy to be extracted from the heat transfer fluid in real time, so as to produce hot water with a maximum temperature preferably 80-90°C. Specifically, for example, a proportional valve 60 is disposed along the water supply pipe 58, arranged upstream of the temperature sensor 55 and the flow sensor 56, and controlled by the automatic control unit 33; while the temperature sensor 57 is installed along the pipe 59 from the water flowing out of the exchangers 50', 50.

[0081] Instead, for example, the heat transfer fluid flows into the corresponding heat exchangers 50', 50 along the outlet conduit 18 of the heat transfer fluid from the preheating section 17, or along the outlet conduit 24 of the heat transfer fluid from the cooling section 23, where a flow sensor 54 and a temperature sensor 52 are continuously installed; while a temperature sensor 53 is installed along the conduit 51 of the heat transfer fluid flowing out of the exchangers 50', 50.

[0082] In all embodiments of the device of the present invention ( Figure 1 and 10Preferably, the preheating section 17 is suitably contained within a metal housing 37, which is heat-insulated so as not to dissipate heat into the environment, and the metal housing 37 can be pressurized with a suitable inert gas or kept in air, depending on whether oxidation is to be avoided or promoted.

[0083] Similarly, the cooling section 23 may be suitably contained within a metal casing 38, insulated to prevent heat dissipation into the environment, and may be pressurized with a suitable inert gas or kept in air, depending on whether oxidation is to be avoided or promoted.

[0084] Preferably, the heat transfer fluid that can be used in the annealing apparatus of the present invention is heat transfer oil or another fluid with equivalent function.

[0085] The advantages of using heat transfer oil are as follows: - Excellent performance at high temperatures, including excellent thermal stability and low vapor pressure; -Reliable heat transfer performance over long periods of time; - It provides uniform, reliable, and efficient heat treatment without the need for high pressure; - A high boiling point helps reduce volatility and fluid loss problems associated with other fluids; - It is not corrosive to the metals commonly used in heat transfer system structures.

[0086] Examples of heat transfer oils particularly suitable for the system of the present invention are products commercially known as Therminol, preferably Therminol products from 55 to 75, such as Therminol 66.

[0087] Regarding the heating roller 16 and the cooling roller 22, they can be made of an outer steel or copper sheath. The latter material is preferred to maximize heat exchange through conduction between the strip and the roller.

[0088] The number of rollers 16 and 22 can be defined as a function of the strip speed and its dimensions. Preferably, the number of rollers is in the range of 3 to 6. In the example shown in the figure, the number of rollers 16 and 23 is four.

[0089] Rollers 16 and 22 may have inlets for heat transfer fluid to enter their internal channels and outlets for fluid to flow out of the internal channels, with both inlets and outlets being realized through the roller's own hub.

[0090] The heat exchange capacity is a function of the contact surface between the strip 2 and the rollers 16, 22: optimal results are obtained in a configuration where the rollers are wound around the strip at least 135°. However, if it is necessary to change the heat exchange, for example depending on the product thickness, the wrap angle of the strip around the rollers can be changed, increasing the angle to exchange more heat or decreasing the angle to exchange less heat.

[0091] Preferably, the internal channels of rollers 16 and 22, and more preferably the peripheral internal channels, can define a straight axis substantially parallel to the longitudinal axis of the respective roller, or a spiral axis wound within the longitudinal axis of the respective roller.

[0092] Each roller may have only one internal channel or internal sheath, which may be annular or non-annular; or there may be several internal channels or internal cavities that may be interconnected.

[0093] like Figure 11 As shown, some non-limiting examples of the peripheral inner channel 39 can be seen in the cross-sections of rollers 16 and 22. The inner channel 39 can have any cross-sectional shape, not just a circular cross-section. For example, the cross-section can be polygonal.

[0094] The following describes an annealing method performed using an apparatus according to any of the above variations.

[0095] In all embodiments of the present invention, the method includes the following stages: The metal strip is preheated in preheating section 17; The metal strip is heated in at least one heating section 3; Maintain the temperature of the metal strip in temperature holding section 4; The metal strip is cooled in cooling section 23.

[0096] Advantageously, when the device of the present invention is fully operational, the heat transfer fluid in the closed loop passes through the cooling roller 22 and the heating roller 16. The cooling roller 22 conducts heat energy from the metal strip and obtains a high-temperature heat transfer fluid, while the heating roller 16 conducts heat energy to the metal strip and obtains a low-temperature heat transfer fluid.

[0097] In a preferred variant of the method, the heat transfer fluid in the closed loop passes through at least one corresponding internal channel 39 of the cooling roller 22 and at least one corresponding internal channel 39 of the heating roller 16; the cooling roller 22 and the heating roller 16 are in direct contact with the strip during the strip's advance.

[0098] Preferably, given the direction of travel of the heat transfer fluid in the loop, the high-temperature heat transfer fluid is stored and moved from the cooling section 23 to the preheating section 17 via the first storage and movement systems 25, 27 along the first extension 70 of the loop; while the low-temperature heat transfer fluid is stored and moved from the preheating section 17 to the cooling section 23 via the second storage and movement systems 19, 20 along the second extension 71 of the loop.

[0099] Specifically, for example, the high-temperature heat transfer fluid is stored in the first tank 25, and its flow rate toward the preheating section 17 is regulated by the first pumping unit 27; while the low-temperature heat transfer fluid is stored in the second tank 19, and its flow rate toward the cooling section 23 is regulated by the second pumping unit 20.

[0100] The energy recovery and reuse processes of the cooling section 23 and the preheating section 17, respectively, can exhibit the following energy balance or imbalance states. By using Pc to represent the power subtracted from the strip in the cooling section 23 and Ph to represent the power supplied to the strip in the preheating section 17, we can find that we are in a state of: Pc > Ph, Pc = Ph, or Pc <Ph The case where Pc > Ph can occur under two different operating conditions of the device, namely: (1) Under full operating conditions, the heat energy carried away from the strip is greater than the heat energy supplied to the strip because the temperature difference during the cooling process is greater than that during the preheating process. This effect is mainly due to the fact that during the heating stage, there is a maximum temperature limit that the heat-conducting oil can reach (approximately 350-400°C depending on the type of oil used). Considering that the average temperature of the strip at the outlet of the preheating system is 50°C, the calculated heating temperature difference ΔT does not exceed 250°C (i.e., does not exceed 300°C). However, during the cooling stage, the temperature difference ΔT can be greater than 250°C, reaching up to 490°C for an annealing galvanizing production line (HDGL) furnace and up to 700°C for a continuous annealing production line (CAL) furnace.

[0101] (2) Alternatively, due to transient process conditions, such as changes in the cross-section of the strip to be processed, or changes in the furnace thermal composition when the strip coil is changed, or a combination of both, the power derived from the strip is higher than the power supplied to the strip. This is a transient effect that lasts only for the time it takes for welding to pass between different sections of the strip, and its effect extends from the annealing unit inlet to the cooling section 23. This transient time t can vary from 3 minutes to 20 minutes depending on the furnace geometry and process parameters. This type of phenomenon is appropriately controlled due to the volumes of tanks 25 and 19.

[0102] When Pc = Ph, the energy extracted from the strip is exactly the same as the energy supplied to the strip in the preheating step. Therefore, the flow rate of the cold branch is the same as the flow rate of the hot branch in the loop, and since the process is completely balanced, no thermal energy is stored in the tank.

[0103] Finally, the case of Pc < Ph corresponds to process conditions due to transients, due to changes in the cross-section of the strip to be processed or changes in the thermal recipe of the furnace when the coil changes, or due to the combined effect of these two cases, where the power derived from the strip is lower than the power supplied to the strip. This is a transient effect that persists for the duration of the passage of the different parts of the strip through the welding process, and its range of action extends from the inlet of the annealing device to the cooling section 23. The transient time t can vary between 3 minutes and 20 minutes, depending on the furnace geometry and process parameters. Due to the volume of tanks 25 and 19, this type of phenomenon is properly controlled.

[0104] For case 1) where Pc > Ph, with a continuous difference relative to the power supplied to the strip, it is possible to consider removing this excess thermal energy by generating hot water with the aforementioned heat exchanger 50 located on the extension section 70 of the circuit through which the high-temperature heat transfer fluid flows.

[0105] Preferably, the water / heat transfer fluid heat exchanger 50 can be appropriately sized using the following formula: ΔP = Pc max - Ph min Where: ΔP = the exchange power of the water / heat transfer fluid heat exchanger 50; Pc max = the maximum power derived from the strip in the cooling section 23; Ph min = the minimum power supplied to the strip in the preheating section 17.

[0106] For case 2) where Pc > Ph, in order to appropriately size tanks 25 and 29, it is preferable to use the relationship that relates the mass M of the heat transfer fluid in tank 25 to some process parameters through the following formula: M = - Γ*(1 - r)*t / (ln(T / T1)) Where: Γ = the mass flow rate of the heat transfer fluid, in kilograms per second (kg / s); r = the loss factor %, which is a dimensionless factor calculated as the ratio of the strip cross-section during preheating to the strip cross-section during cooling, with both strip cross-sections expressed in mm 2 represented; t = the instantaneous duration, in seconds (s); T = the initial temperature in tank 25 at t = 0 T1 = the final temperature in tank 25 at t = the instantaneous end time; By dividing the mass M by the density of the heat transfer fluid, the volumes of tanks 25 and 19 for the high-temperature and low-temperature heat transfer fluids are obtained, respectively, in cubic meters (m 3 )

Claims

1. An annealing apparatus for a metal strip (2) traveling in one direction, the apparatus comprising, in sequence: At least one preheating section (17); At least one heating section (3); At least one temperature holding section (4); At least one cooling section (23); The at least one preheating section (17) includes a plurality of heating rollers (16) for advancing the metal strip (2). The at least one cooling section (23) includes a plurality of cooling rollers (22) for advancing the metal strip (2). A closed loop of heat transfer fluid is provided, the loop being configured to pass through the cooling roller (22) of the at least one cooling section (23) to conduct heat energy out of the metal strip to obtain a high-temperature heat transfer fluid, and through the heating roller (16) of the at least one preheating section (17) to conduct heat energy to the metal strip to obtain a low-temperature heat transfer fluid.

2. The apparatus according to claim 1, wherein, Both the cooling roller (22) and the heating roller (16) are provided with at least one corresponding internal channel (39), the internal channel being configured such that the cooling roller (22) allows the low-temperature heat transfer fluid to pass through to cool the metal strip by conduction, and the heating roller (16) allows the high-temperature heat transfer fluid to pass through to preheat the metal strip by conduction, the cooling roller (22) and the heating roller (16) being adapted to be in direct contact with the strip during its advance.

3. The apparatus according to claim 1 or 2, wherein, Along the circuit, considering the direction of the heat transfer fluid, the following is provided: A first storage and movement system (25, 27) for storing and moving the high-temperature heat transfer fluid, acting as a thermal energy storage TES, and arranged along a first extension (70) of the circuit from the at least one cooling section (23) to the at least one preheating section (17); And preferably a second storage and movement system (19, 20) for storing and moving the cryogenic heat transfer fluid, arranged along a second extension (71) of the loop from the at least one preheating section (17) to the at least one cooling section (23).

4. The apparatus according to claim 3, wherein, The first storage and transport system (25, 27) includes a first tank (25) and a first pumping unit (27), the first tank (25) being used to store the high-temperature heat transfer fluid and being configured as a thermal energy storage device (TES), and the first pumping unit (27) being configured to regulate the flow rate of the high-temperature heat transfer fluid toward the at least one preheating section (17). Preferably, the second storage and transport system (19, 20) includes a second tank (19) and a second pumping unit (20), the second tank (19) being used to store the cryogenic heat transfer fluid, and the second pumping unit being configured to regulate the flow rate of the cryogenic heat transfer fluid toward the at least one cooling section (23); Preferably, the first tank (25) has no heating device, and optionally the first tank (25) has an insulating wall (40) to minimize energy loss to the environment. And preferably, the second tank (19) is without a heating device.

5. The apparatus according to claim 4, wherein the heating device (26) is disposed downstream of the first tank (25), preferably between the first tank (25) and the first pumping unit (27), for heating the heat transfer fluid in the event of a cold start of the apparatus.

6. The apparatus according to any one of claims 2 to 5, wherein, A supply conduit (21) is provided along the circuit for supplying the cryogenic heat transfer fluid to the at least one cooling section (23). The at least one internal channel (39) of each of the cooling rollers (22) is in communication with the supply conduit (21); Preferably, the at least one internal channel of the cooling roller (22) is connected in parallel to each other in the circuit; or the at least one internal channel of the cooling roller (22) is connected in series through an intermediate pipe (35'), such that the heat transfer fluid flows in the countercurrent direction to the forward flow of the metal strip on the cooling roller (22).

7. The apparatus according to any one of claims 2 to 6, wherein, A supply conduit (15) is provided along the circuit for supplying the high-temperature heat transfer fluid to the at least one preheating section (17). The at least one internal channel (39) of each of the heating rollers (16) is in communication with the supply conduit (15); Preferably, the at least one internal channel of the heating roller (16) is connected in parallel to each other in the circuit; or the at least one internal channel of the heating roller (16) is connected in series through an intermediate pipe (28'), such that the heat transfer fluid flows sequentially through the heating roller (16) in a countercurrent manner relative to the advance of the metal strip on the heating roller (16).

8. The apparatus according to any one of the preceding claims, wherein, Another gas jet cooling section (5) for preliminary cooling of the strip is provided between the at least one temperature holding section (4) and the at least one cooling section (23).

9. The apparatus according to any one of the preceding claims, wherein, A post-heating section (12) is provided downstream of the at least one cooling section (23) for heating the metal strip to a temperature below the solution temperature; Preferably, a second gas jet cooling section (13) is provided downstream of the post-heating section (12) for heating the metal strip to a target temperature so that it can be discharged from the device.

10. The apparatus according to any one of the preceding claims, wherein, The settings are as follows: At least one first temperature sensor (30) is located at the inlet of the preheating section (17) for measuring the strip temperature; At least one second temperature sensor (31) is located at the outlet of the preheating section (17) for measuring the strip temperature; At least one first flow sensor (32) is used to measure the first flow rate of the heat transfer fluid entering the preheating section (17); At least one third temperature sensor (62) is located at the inlet of the cooling section (23) for measuring the strip temperature; At least one fourth temperature sensor (63) is located at the outlet of the cooling section (23) for measuring the strip temperature; At least one second flow sensor (64) is used to measure the second flow rate of the heat transfer fluid entering the cooling section (23); It is provided with at least one automatic control unit (33), which is adapted to receive data from the at least one first temperature sensor (30), the at least one second temperature sensor (31) and the at least one first flow sensor (32) and thereby adjust the first flow rate, and is adapted to receive data from the at least one third temperature sensor (62), the at least one fourth temperature sensor (63) and the at least one second flow sensor (64) and thereby adjust the second flow rate.

11. The apparatus of claim 10, wherein the at least one automatic control unit (33) is adapted to regulate the first flow rate via a first proportional valve (34) and the second flow rate via a second proportional valve (34').

12. The apparatus of claim 11, wherein the first proportional valve (34) is configured to work in conjunction with a first pumping unit (27), the first pumping unit being configured to regulate the first flow rate of the high-temperature heat transfer fluid from a first tank (25), the first tank (25) serving as a thermal energy storage TES and arranged along a first extension (70) of the circuit from the at least one cooling section (23) to the at least one preheating section (17) toward the at least one preheating section (17); Preferably, the second proportional valve (34') is configured to work in conjunction with a second pumping unit (20), which is configured to regulate the second flow rate of the cryogenic heat transfer fluid from a second tank (19), the second tank (19) being arranged along a second extension (71) of the circuit from the at least one preheating section (17) to the at least one cooling section (23) toward the at least one cooling section (23).

13. The apparatus according to claim 12, wherein the drive motor of the first pumping unit (27) and the drive motor of the second pumping unit (20) are both variable speed motors.

14. The apparatus according to any one of claims 4 to 13, wherein the first tank (25) is provided with a first temperature sensor (45) for measuring the temperature of the heat transfer fluid in the first tank (25) and a first automatic level gauge (46) for detecting the level of the heat transfer fluid in the first tank (25), and wherein at least one automatic control unit (33) is provided, the at least one automatic control unit (33) being adapted to receive data from the first temperature sensor (45) and the first automatic level gauge (46) to better regulate preheating in the preheating section (17); Preferably, the second tank (19) is provided with a second temperature sensor (42) for measuring the temperature of the heat transfer fluid in the second tank (19) and a second automatic level gauge (43) for detecting the level of the heat transfer fluid in the second tank (19), and wherein the at least one automatic control unit (33) is adapted to receive data from the second temperature sensor (42) and the second automatic level gauge (43) to better regulate the cooling in the cooling section (23); Preferably, an injection device (41) for injecting inert gas is provided to pressurize the first canister (25) and / or the second canister (19).

15. The apparatus according to any one of claims 4 to 14, wherein, Along the first extension (70) of the circuit, upstream of the outlet of the cooling section (23) and the first tank (25), a first water / heat transfer fluid heat exchanger (50) for generating hot water is provided to remove excess heat energy from the metal strip that exceeds the heat energy required by the metal strip in the preheating section (17). Preferably, a second water / heat transfer fluid heat exchanger (50') for generating hot water is provided along the second extension (71) of the circuit, upstream of the outlet of the preheating section (17) and the second tank (19), in order to minimize the temperature of the heat transfer fluid and promote cooling in the cooling section (23).

16. The apparatus according to claim 15, wherein, For the first heat exchanger (50) and preferably for the second heat exchanger (50'), the following are provided: Temperature sensors (55, 57) are used to measure the temperature of inflow and outflow water; A flow sensor (56) is used to measure the flow rate of the incoming water; Additional temperature sensors (52, 53) are used to measure the temperature of the heat transfer fluid flowing in and out; An additional flow sensor (54) is used to measure the flow rate of the heat transfer fluid. It is provided with at least one automatic control unit (33) adapted to receive data from the temperature sensor (55, 57), the flow sensor (56), the additional temperature sensor (52, 53) and the additional flow sensor (54), and thus regulate the flow rate of water entering the respective heat exchanger (50, 50').

17. An annealing method performed by the apparatus according to any one of the preceding claims, the method comprising the following stages: The metal strip is preheated in at least one preheating section (17); The metal strip is heated in at least one heating section (3); The temperature of the metal strip is maintained in at least one temperature holding section (4); The metal strip is cooled in at least one cooling section (23); The heat transfer fluid in the closed loop passes through the cooling roller (22) of the at least one cooling section (23) and the heating roller (16) of the at least one preheating section (17). The cooling roller (22) conducts heat energy from the metal strip and obtains a high-temperature heat transfer fluid, while the heating roller (16) conducts heat energy to the metal strip and obtains a low-temperature heat transfer fluid.

18. The method according to claim 17, wherein, The heat transfer fluid of the closed loop passes through at least one corresponding internal channel (39) of the cooling roller (22) and at least one corresponding internal channel (39) of the heating roller (16); the cooling roller (22) and the heating roller (16) are in direct contact with the strip during the advance of the strip.

19. The method according to claim 17 or 18, wherein, Given the direction of travel of the heat transfer fluid in the circuit, the high-temperature heat transfer fluid is stored and moved from the at least one cooling section (23) to the at least one preheating section (17) along the first extension (70) of the circuit via a first storage and movement system (25, 27) that serves as a thermal energy storage TES. Preferably, the cryogenic heat transfer fluid is stored and moved from the at least one preheating section (17) to the at least one cooling section (23) via a second storage and movement system (19, 20) along a second extension (71) of the circuit.

20. The method according to claim 19, wherein, The high-temperature heat transfer fluid is stored in a first tank (25), which serves as a thermal energy storage device (TES), and the flow rate of the first tank (25) toward the at least one preheating section (17) is regulated by a first pumping unit (27). Preferably, the low-temperature heat transfer fluid is stored in a second tank (19), and the flow rate of the second tank (19) toward the at least one cooling section (23) is regulated by a second pumping unit (20).

21. The method according to any one of claims 17 to 20, wherein: At least one first temperature sensor (30) is located at the inlet of the preheating section (17) for measuring the strip temperature; At least one second temperature sensor (31) is located at the outlet of the preheating section (17) for measuring the strip temperature; At least one first flow sensor (32) is used to measure the first flow rate of the heat transfer fluid entering the preheating section (17); At least one third temperature sensor (62) is located at the inlet of the cooling section (23) for measuring the strip temperature; At least one fourth temperature sensor (63) is located at the outlet of the cooling section (23) for measuring the strip temperature; At least one second flow sensor (64) is used to measure the second flow rate of the heat transfer fluid entering the cooling section (23); Furthermore, at least one automatic control unit (33) receives data from at least one first temperature sensor (30), at least one second temperature sensor (31), and at least one first flow sensor (32) to adjust the first flow rate of the heat transfer fluid entering the preheating section (17); and the at least one automatic control unit (33) also receives data from at least one third temperature sensor (62), at least one fourth temperature sensor (63), and at least one second flow sensor (64) to adjust the second flow rate of the heat transfer fluid entering the cooling section (23).

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