METHOD FOR CONTROLLING THE COOLING OF A FLAT METAL PRODUCT

Abstract

The invention relates to a method of cooling a flat metal product having a wide face and a temperature above 400°C, wherein said metal product is brought into contact with a fluidized bed of solid particles, the solid particles having a circulation direction (D) and capturing the heat released by the metal product and transferring said captured heat to a transfer medium wherein: - the metal product is brought into contact with the solid particles so that its wide face is parallel to the circulation direction (D) of the solid particles, - a thermal cooling path of the metal product is defined, considering the product parameters of said metal product, - a gas is injected to fluidize the solid particles in a bubbling regime, the injection flow rate of said gas being controlled to match said defined cooling path of the metal product.

Description

METHOD FOR CONTROLLING THE COOLING OF A FLAT METAL PRODUCT The invention relates to a method for controlling the cooling of a flat metal product. In steel production, and more generally in metal production, there are several plants where hot metal products are manufactured and subsequently cooled. The cooling rate of these products is crucial for achieving the desired microstructure and associated properties. This is even more critical for high-alloy steel grades, where an inadequate cooling rate can lead to product fracture, poor quality, or scrap. This is particularly noticeable for slabs exiting the bar stock or plates exiting the rolling mill. Thus, there is a need for a method that allows the cooling rate of metal products to be controlled. US patent 3,957,111 describes a cooling method in which slabs are placed in a chamber with cooling walls that receive heat radiated from the slabs. Water flows under pressure through channels within the cooling walls, removing heat from them. Controlling the water temperature allows for regulating the slab's cooling rate. A gas, such as steam, fills the space between the slabs and the cooling walls to further control the cooling rate. This method is difficult to control because the gas and water flow rates must be considered. Furthermore, the equipment required is heavy, and the cooling time is lengthy. Document EP 0 960 670 describes a cooling method in which a slab is submerged in a water tank equipped with nozzles to spray water onto the slab. The distance between the nozzles and the slab can be adjusted to control the cooling rate. This method requires a large amount of water, as the tank must be refilled regularly to ensure efficiency. Therefore, there is a need for a method that allows for controlling the cooling rate of flat metal products that overcomes the drawbacks mentioned above. The method according to the invention allows for controlling the cooling rate of the flat metal product without detrimental effects on its quality. For example, it does not cause any harmful chemical effects on the metal product, nor does it have any physical effects on its surface that could create surface defects. This problem is solved by a method according to the invention in which a metal product having a wide face and a temperature above 400°C is brought into contact with a fluidized bed of solid particles, the solid particles having a circulation direction (D) and capturing the heat released by the metal product and transferring said captured heat to a transfer medium in which: The metal product is brought into contact with the solid particles so that its wide face is parallel to the direction (D) of circulation of the solid particles, l Lcnnn / Lznz / E / YiAi A thermal cooling route for the metal product is defined, considering the product parameters of said metal product, a gas is injected to fluidize the solid particles in a bubbling regime, the injection flow rate of said gas is controlled to match said defined cooling route of the metal product. The method of the invention may also comprise the following optional features considered separately or in accordance with all possible technical combinations: The defined cooling path is made up of different portions, each portion has a given cooling rate, and the flow rate of the transfer medium is adjusted to achieve the given cooling rate of the portion. The transfer medium is water; the transfer medium is molten salts; the transfer medium contains nanoparticles; the water is used to produce steam; the method was carried out within a plant that has a steam network and the steam produced is injected into said steam network; the metal product is a slab or plate; the metal product is a steel product; the solid particles have a heat capacity between 500 and 2000 J / kgK; the density of the solid particles in the fluidized bed is between 1400 and 4000 kg / m3; the solid particles are made of alumina, SiC or steel slag; the solid particles have an average size between 30 and 300 pm. The gas is injected at a speed between 5 and 30 cm / s, the gas is air, the metal product is a slab and said slab is placed on a support within the fluidized bed so that its edge is parallel to the floor, the metal product comprises slag particles on its surface, said slag particles are removed by the solid particles and the removed slag particles are regularly extracted from the fluidized bed, the metal product is cooled from 900 to 350 °C in less than 60 minutes. The invention will be better understood by reading the following description, provided with reference to the following accompanying figures: Figure 1 illustrates a plank Figure 2 illustrates one embodiment of the device for performing a supervised cooling method according to the invention. Figure 3 illustrates different fluidization regimes. l Lcnnn / Lznz / E / YiAi Figure 4 illustrates the cooling curves using a method according to the invention. Figure 5 is a curve that simulates the vertical displacement of the surface of a slab using a method in accordance with the invention and the state of the art and its graphical representation. Figure 1 illustrates a slab 3, which is an example of a flat metal product. This slab 3 is rectangular in shape and comprises a top face 3a and a wide bottom face, two small faces 3b, and two edges 3c. The wide faces define the width W and length L of the slab. This width W is typically between 700 and 2500 mm, the length L between 5000 and 15000 mm, and the thickness T of the slab is typically between 150 and 350 mm. More generally, a flat product can be defined as a rectangular prism where the smallest dimension (e.g., the thickness T) is minimal compared to the others (e.g., the length L); for example, the smallest dimension is at least 15 times smaller than the largest dimension. The wide faces of the rectangular prism are the faces that do not include the smallest dimension. Another example of a flat product is a plate or heavy plate. These flat products are typically semi-finished goods, meaning they will undergo further manufacturing steps before being sold. For these subsequent steps, it is crucial that the product is free of defects and, in particular, that its flatness is guaranteed. For example, if a slab has a vertical bend of just a few millimeters, it can cause difficulties during subsequent lamination or even make lamination impossible, which would result in the slab being discarded. Figure 2 illustrates a device 1 for carrying out a cooling method according to the invention. This device 1 comprises the chamber 2 in which a hot, flat metal product, such as a slab 3, is placed. The chamber 2 may be a closed chamber with a closable opening through which hot metal products can be conveyed, but it could also have an open roof or any configuration suitable for conveying hot metal products. The hot metal products 3 can be conveyed into the chamber 2 by a rolling conveyor or placed into the chamber 2 by means of picking, such as cranes or any other suitable picking means. The chamber 2 can preferably receive more than one flat product 3. The chamber 2 contains solid particles and includes a gas injection means 4. The gas is injected to fluidize the solid particles and create a fluidized bed of solid particles 5 in a bubbling regime. The fluidized solid particles circulate along a circulation direction (D). Hot flat metal products 3 are placed in the chamber 2 on support means such that their wide face 3a is parallel to the circulation direction (D) of the fluidized particles. In a preferred embodiment, the direction (D) is vertical, and the slab 3 is placed on the support along its edge 3c so that its wide face is parallel to the vertical direction. This promotes heat transfer efficiency while also preventing product deformation.Hot flat metal products have a temperature above 400SC when placed in chamber 2 and are, for example, slabs or plates and can be made of steel. As illustrated in Figure 3, there are several fluidization regimes. Fluidization is the process by which solid particles are transformed into a fluid state by suspension in a gas or a liquid. Depending on the fluid velocity, the behavior of the particles differs. In gas-solid systems like the one of the invention, with an increase in flow velocity beyond the minimum fluidization, significant instabilities are observed, including bubbling and channeling of gases. At higher velocities, the agitation becomes more violent, and the movement of the solids becomes more vigorous. Furthermore, the bed does not expand much beyond its volume at minimum fluidization. At this stage, the fluidized bed is in the bubbling regime, which is the regime required by the invention to achieve good circulation of the solid particles and a homogeneous temperature within the fluidized bed.The gas velocity to be applied to obtain a certain regime depends on several parameters such as the type of gas used, the size and density of the particles, or the size of chamber 2. This can be easily managed by an expert in the field. The gas can be nitrogen or an inert gas such as argon or helium, and, in a preferred embodiment, air. It is preferably injected at a velocity between 5 and 30 cm / s, which requires low ventilation power and therefore reduced energy consumption. The gas injection flow rate is controlled to match a defined cooling path for the hot metal products. The cooling path to be matched is first defined by considering the product parameters of the metal product to be cooled. In particular, the metal product's chemistry, metallurgical state, or initial and final temperatures may be considered. It can be predetermined according to a nomogram, for example, and / or controlled online by means of temperature measurements taken on the products.This can be advantageous for metal products whose quality is affected by the cooling rate, such as steel, but it can also be advantageous for the plant to regulate production. The solid particles preferably have a specific heat capacity between 500 and 2000 J / kg / K, and a density between 1400 and 4000 kg / m³. They may be ceramic particles such as SiC, alumina, or steel slag. They may also be glass or any other stable solid material up to 1000°C. Preferably, they have a size between 30 and 300 µm. These particles are preferably inert to prevent any reaction with the hot metal product. The device 1 further comprises at least one heat exchanger 6 in which a transfer medium is circulating. The heat exchanger is in contact with the fluidized bed 5. This heat exchanger may be composed, as illustrated in Figure 1, of a first pipe 61 in which a cold transfer medium 10 is circulating for injection into the heat exchanger, a second pipe 62 in which the heated transfer medium 11 is recovered, and a third pipe 63 that connects the first pipe 61 and the second pipe 62 and passes through chamber 2 and the fluidized bed 5, where the cold transfer medium 11 is heated from the first pipe 61. With this device 1, the hot metal products 3 are immersed in the fluidized bed 5 of solid particles. The solid particles capture the heat released by the hot metal products 3.This allows for homogeneous cooling of the metal product, as all parts of the metal product are in contact with the fluidized solid particles. The solid particles are kept in motion by gas injection through injection medium 4 and come into contact with the heat exchanger 6, where they release the captured heat to the circulating transfer medium inside. The flow rate of the medium within the heat exchanger can be regulated to control the cooling rate; in fact, the more medium circulates within the heat exchanger, the more heat is released from the solid particles. This can be particularly advantageous when the cooling path to be matched comprises several parts with different cooling rates. In a preferred embodiment, the heat transfer medium 10 circulating in the heat exchanger is pressurized water which, once heated by the heat released by the fluidized solid particles, is converted into steam 11. The pressurized water can have an absolute pressure of between 100 and 3000 kPa (1 and 30 bar). The pressurized water can then be converted into steam by an expansion drum 7 or any other suitable steam generation equipment. Preferably, the water remains liquid within the heat exchanger. The steam 11 produced can then be reused within the metal production plant by injection into the plant's steam network, for example, for hydrogen production, or for vacuum degassers RH or CO2 gas separation units in the case of a steel plant.Having a steam reuse plant and a metal product manufacturing plant within the same plant network allows for an improvement in the overall energy efficiency of that network. The heat transfer medium 10 circulating in the heat exchanger can also be air or molten salts, preferably having a phase change of between 400 and 800 cS to store the captured heat. The heat transfer medium 10 may include nanoparticles to promote heat transfer. In a further embodiment, the metal product 3 may comprise slag particles on its surfaces. Through chemical or physical interaction with the fluidized solid particles, these slag particles can be removed from the metal product 3 and precipitate to the bottom of the fluidized bed. In such a case, the equipment 1 is provided with a slag removal device, such as a removable metal grid, for the frequent removal of slag particles from the fluidized bed. Using the method according to the invention, metal products can be cooled from 900SC to 350SC in less than 60 minutes. The method according to the invention can be carried out at the exit of a casting plant, in a slab warehouse or at the exit of a rolling or leveling station. The method according to the invention allows for rapid and homogeneous cooling of the metal product while respecting a predetermined cooling path without detrimental effect on the product and, in particular, on its flatness. Furthermore, it allows for the recovery of at least 90% of the heat released by metal products. Additionally, the device according to the invention is quite compact and can be adapted to the available space. Examples A simulation was performed to show how a method according to the invention can be applied. The simulation results are illustrated in Figure 4 with a graph representing the temperature evolution of a slab over time. l Lcnnn / Lznz / E / YiAi The gray curve is a predefined cooling path that must be followed. This cooling path comprises three portions (a, b, c) with different cooling rates. For this simulation, a slab measuring 12 m x 1.5 m x 0.2 m, corresponding to an approximate weight of 28 tons, was considered. The slab, which has an initial temperature of 800°C, is placed in equipment containing solid silicon carbide particles. The fluidized bed temperature was 400°C. For the simulation, a heat exchanger like the one illustrated in Figure 1, using water as the fluid, was used. The gas flow rate injected to fluidize the solid particles was varied among the three sections (a, b, c) so that the heat transfer coefficient (HTC) changed accordingly; an increased flow rate resulted in an increased HTC. The HTC was 750, 1000, and 500 W / m²K for sections a, b, and c, respectively. The black curve illustrates the temperature evolution over time for the slab. As can be seen in Figure 3, by modifying the injected gas flow rate, it is possible to cool the slab according to the predefined cooling path. Effect on the product A simulation was performed to evaluate the effect on the product in terms of deformation of a cooling method according to the state of the art and according to the invention. In both scenario A and scenario B, a slab made of a commercial grade of low carbon steel and having a length L of 10 m, a width W of 1 m and a thickness T of 0.25 m, is placed in equipment comprising solid silicon carbide particles with a density of 320 kg / m3 and a Sauter diameter of 50 pm. These particles are fluidized in a bubbling regime by the injection of air at 5 cm / s and circulate vertically, the bottom of the chamber being in the horizontal direction. For the simulation, a heat exchanger like the one illustrated in Figure 2, which uses water as the fluid, was used. In both scenarios, the initial temperature of the slab is 800°C and it is cooled to 400°C. In scenario A, the slab is placed in the fluidized bed so that one of its wide faces rests on the support media; its wide faces are thus perpendicular to the direction of flow of the fluidized particles. In scenario B, it is placed on one of its edges, so its wide faces are parallel to the direction of flow of the fluidized particles. For both scenarios, the deformation of said slab is simulated and illustrated in Figure 5. Figure 5 first shows the displacement curve in the vertical direction along the length of the product when cooled using a prior art method and a method according to the invention. In the other two images, this displacement is shown directly on the product, and it can be observed that when using a prior art method, there is a clear bending of the product that will not return to its initial flatness. The method according to the invention thus allows control of the cooling path of the flat product without detrimental effect on the product and notably without involving a deformation of said product.

Claims

CLAIMS 1. A method for cooling a flat metal product having a wide face and a temperature above 400 BC, wherein said metal product is brought into contact with a fluidized bed of solid particles, the solid particles having a circulation direction (D) and capturing the heat released by the metal product and transferring said captured heat to a transfer medium, wherein: the metal product is brought into contact with the solid particles so that its wide face is parallel to the circulation direction (D) of the solid particles, a thermal cooling path of the metal product is defined, considering the product parameters of said metal product, a gas is injected to fluidize the solid particles in a bubbling regime, the injection flow rate of said gas is controlled to match said defined cooling path of the metal product.

2. The method according to claim 1, wherein said defined cooling path is composed of different portions, each portion having a given cooling rate, and the flow rate of the transfer medium is adjusted to achieve the given cooling rate of the portion.

3. The method according to claim 1 or 2, wherein the transfer medium is water.

4. The method according to claim 1 or 2, wherein the transfer medium is molten salts.

5. The method according to any of the preceding claims, wherein the transfer medium contains nanoparticles.

6. The method according to claim 3, wherein said water is used to produce steam.

7. The method according to claim 6, wherein the method is performed within a plant having a steam network and the steam produced is injected into said steam network.

8. The method according to any of the preceding claims, wherein the metal product is a slab or plate.

9. The method according to any of the preceding claims, wherein the metal product is a steel product.

10. The method according to any of the preceding claims, wherein the solid particles have a heat capacity between 500 and 2000 J / kg / K.

11. The method according to any of the preceding claims, wherein the density of the solid particles in the fluidized bed is between 1400 and 4000 kg / m3.

12. The method according to any of the preceding claims, wherein the solid particles are made of alumina, SiC or steel slag.

13. The method according to any of the preceding claims, wherein the solid particles have an average size between 30 and 300 pm.

14. The method according to any of the preceding claims, wherein the gas is injected at a speed between 5 and 30 cm / s.

15. The method according to any of the preceding claims, wherein the gas is air.

16. The method according to any of the preceding claims, wherein the flat metal product is a slab and said slab is placed on a support within the fluidized bed so that its edge is parallel to the floor.

17. The method according to any of the preceding claims, wherein the metal product comprises slag particles on its surface, said slag particles are removed by the solid particles and the removed slag particles are regularly extracted from the fluidized bed.

18. The method according to any of the preceding claims, wherein the metal product is cooled from 900 to 350 flC in less than 60 minutes.