DEVICE AND METHOD FOR CONTROLLING A REHEATING OVEN

Description

Designation of the technical field concerned

[0001] The invention relates to a device and method for controlling a reheating furnace for steel products. It is particularly applicable to the reheating of long products, and more specifically to flat products, such as slabs. The device and method according to the invention make it possible to quantify the total loss on ignition associated with reheating a product in the furnace, by determining the quantity of scale that has fallen into the furnace and the quantity that is removed by a descaling machine located downstream of the furnace in the direction of product movement. They also make it possible to optimize furnace operation and reduce this loss on ignition. Technical problems that the invention addresses

[0002] Upstream of hot rolling mills producing semi-finished steel products such as billets, blooms, or slabs, there are reheating furnaces. Inside these furnaces, the metal is heated to a high temperature to facilitate the rolling process. The key criteria for this reheating and rolling process are the quality of the rolled product, the plant's productivity, and its operating costs.

[0003] In these reheating furnaces, numerous burners are traditionally located along the side walls, sometimes also in the vault, to provide heating. Their fuel supply consists primarily of natural gas, LPG, or liquid fuel oil. However, with the rising price of these fuels, it has become common to burn locally sourced fuels, often byproducts of processes carried out on-site. These fuels have a lower calorific value and contain more impurities, but they are much less expensive. This is the case, for example, with COG (Coarse Gas Oil). Coke Oven gas ) or BFG (for English) Blast Furnace GasThe fumes are extracted from the furnace by a suction system, via a heat recovery unit that preheats the combustion air supplying the burners. The hot fumes react with the surface of the product being heated in the furnace, resulting in the formation of surface layers of oxides. These layers are also called scale layers. A distinction is made between primary scale, which includes scale that detaches and falls into the furnace and that removed by the descaling machine located downstream of the furnace, before rolling, and secondary and tertiary scale formed during rolling. Primary scale is also expressed as non-adherent and adherent scale. The non-adherent scale on the underside of the products falls largely into the furnace. The descaling machine removes the non-adherent scale still present on the product, particularly on its upper surface where most of it is present at the descaling machine's inlet, and the adherent scale.Sticky primary scale refers to scale that cannot be removed by the descaling machine and therefore remains attached to the product exiting the machine. The thickness of sticky primary scale is a few tenths of a millimeter, while the thickness of adherent and non-adherent primary scale is expressed in millimeters.

[0004] The composition of the flue gases depends on the type of fuel and the burner settings. It has a direct impact on the proportion of scale formed, as well as its chemical and mechanical properties. For example, according to the article "Scaling of carbon steel in simulated reheat furnace atmospheres," VHJLee, B.Gleesin, DJYoung in 2004 »,The oxidation of carbon steel in hot fumes leads to linear kinetics within a certain range of air / gas ratios, and to parabolic growth at higher air / gas ratios. Furthermore, the material loss resulting from scale formation, known as "loss on ignition," has a considerable economic impact. For example, for a reheating furnace with an annual production capacity of 2.5 million tons, at a carbon steel price of US$400 / ton, a loss on ignition of 0.7 to 1% equates to a revenue loss of US$7 to US$10 million. Moreover, there is also a significant energy and environmental impact when considering the amount of energy consumed and the pollution generated in producing the quantity of steel lost as scale and in recycling the scale recovered by the descaling machine. For this reason, it is important to limit scale formation during preheating before rolling.

[0005] In the industrial world, numerical models can predict loss on ignition for certain steel grades under defined and stable conditions. The thesis by Husein Abuluwefa, "Scale formation in a walking-beam Steel Reheat Furnace," McGill University, 1992, is an example. However, the actual operation of a furnace is never perfectly stable; the product's heating curve changes depending on the furnace's actual production. Similarly, the composition of the flue gases varies according to the fuel quality, the accuracy of the control devices and instruments, and the frequency of their calibration. Furthermore, each steel mill has its own steel recipe to meet specific global market demands. Thus, a model validated under specific conditions will have limitations in its ability to predict loss on ignition under other conditions.

[0006] Despite all the efforts made by various teams around the world, there is still no control system capable of properly: measure and control in real time the formation of primary calamine, reduce loss on ignition. Technical background

[0007] The formation of scale, when steel passes through an industrial reheating furnace before rolling, results from the oxidation of iron (contained in the steel) in contact with oxygen and other oxidizing gases from the combustion products present in the furnace.

[0008] Numerous factors contribute to making this phenomenon complex: Iron essentially exhibits three oxidation states, which are found in scale as FeO, Fe3O4, and Fe2O3. Several intersecting reaction pathways can lead to the formation of these oxides. The chemical and mechanical properties of each layer differ. Furthermore, the scale thickness is not uniform across the entire surface of a product. The kinetics of the different oxidation pathways vary depending on the conditions within the furnace, which are not homogeneous at all points. Oxidation kinetics can also be affected by the chemical composition of the steel, on the one hand, and by the composition of the fumes generated by the burners, on the other. The composition of the fumes depends on both the type of fuel and the burner settings. The residence time of the products in the furnace and their temperature curve, and therefore their exposure to oxidizing conditions, can also vary.

[0009] Technologies exist on the market for determining coating thickness, such as ultrasound or ellipsometry. However, these solutions perform measurements in less constrained environments, including: at room temperature, under a transparent atmosphere, with a smooth coating surface condition, with a coating thickness on the order of a nanometer.

[0010] None of them address all the issues of the subject: high temperature: up to 1280 °C at removal from the kiln, surfaces with coarse roughness exhibiting irregularities, different chemical and mechanical properties for each layer of scale.

[0011] One traditional method for identifying loss on ignition is to place small samples above a product instrumented with thermocouples and heat them in the furnace. After heating, the samples are retrieved using specialized tools for measurements once they have returned to room temperature. This method is complex to implement and presents risks for operators who must retrieve the samples from the furnace while both the product and the samples are at high temperatures.

[0012] Another traditional method is to weigh the product cold, before and after heating, to determine the loss on ignition. This type of measurement also requires significant preparation and resources.

[0013] WO2016125096 of the applicant describes a first solution for the continuous control of the production of scale in a reheating furnace from data measured using laser optical sensors placed at the furnace outlet.

[0014] The device includes at least one optical sensor positioned at the oven outlet that scans the underside of the product, enabling the mapping of its surface as the product moves through the oven. Analysis of this surface map determines the amount of scale that has fallen into the oven. High points on the product's surface correspond to areas where scale is still present. Conversely, low points correspond to areas where scale has detached and fallen into the oven.

[0015] The device also includes two sets of at least two optical sensors, one placed upstream of the descaling machine and the other downstream of it, which allow the height of the product upstream and downstream of the descaling machine to be determined, and by the difference between these heights, the quantity of scale that has fallen into the descaling machine.

[0016] Depending on the amount of scale formed in the oven determined using these sensors, a correction of oven operating parameters is made in order to reduce the amount of scale formed during reheating.

[0017] This solution is not entirely satisfactory because, in practice, several sensors are needed at the oven exit to cover the underside of the products across the entire width of the oven due to the constraints of laser sensor placement on the roller table and their narrow beam width. Complex image processing is required to reconstruct the product map from the images captured by the parallel sensors. Although an inclined screen is positioned above the sensors to protect them, this screen wears quickly due to abrasion caused by falling scale. Furthermore, over time, scale adheres to the inclined screen, partially obscuring the product surface. Regular maintenance of the system is therefore necessary, even though the location is difficult to access and poses risks to operators.

[0018] One aim of the invention is to overcome all or part of the disadvantages of the state of the art, and / or to improve the flexibility and simplicity of controlling a reheating oven while maintaining or improving the robustness and cost of this control, maintenance and / or operation of the means by which this reheating oven is controlled. Summary of the invention

[0019] According to a first aspect of the invention, a method is proposed for controlling a reheating furnace for steel products having an inlet and an outlet along a scroll direction according to claim 1.

[0020] With a control method according to the invention, it becomes possible to control the oven taking into account the respective quantities of non-adherent and adherent scale on the surface of a product, and therefore to adapt one or more control parameters accordingly.

[0021] Although only one face of the product is observed by the camera, the invention makes it possible to correct a determination of the temperature of the unobserved face obtained by calculation, by means of a correction factor determined from a difference between on the one hand the effective temperature of the observed face obtained by the camera and on the other hand a temperature of the observed face obtained by calculation.

[0022] The process includes digital processing to determine a loss on ignition of the product.

[0023] Determining the loss on ignition and knowing the respective quantities of the two types of scale on the upper surface allows us to determine a first approximation of the amount of non-adherent scale from the lower surface that fell into the furnace, which is important information for managing furnace production.

[0024] As a first approximation, we can for example assume that the ratio r between non-adherent and adherent scale is the same on the upper and lower faces, and knowing the loss on ignition pF, we can deduce the mass mCPNS of non-adherent scale that fell into the furnace, which can be written mCPNS = r*pf / 2, if we also consider that the lower mass is equal to the upper mass and that the loss on ignition is homogeneous on both faces.

[0025] The process includes measuring the height of the product by two sensors placed, respectively, upstream and downstream of a descaling machine located downstream of the furnace, and a digital processing to determine the loss on ignition of the product by determining the difference in height of the product between upstream and downstream of said descaling machine.

[0026] This makes it possible to refine the determination of the loss due to fire.

[0027] The sensors are optical sensors, which are well suited to the needs and operating conditions of a steel product heating installation.

[0028] The process includes, when the upper face is imaged by the infrared camera, a determination of the amount of scale from the lower face of the product that fell into the furnace by numerical simulations from the amounts of non-adherent scale and adherent scale on the upper surface of the product obtained from the binarized image, from the determined loss on ignition, and a correlation of these results with furnace operating records and a predictive law of scale formation.

[0029] Correlating the measured results with the oven's operating records allows for refining the oven control strategy.

[0030] According to one possibility, the process includes a step to reduce the loss on ignition and the amount of scale falling into the furnace for a second product, which is reheated after a first product, by modifying the furnace operating parameters according to the loss on ignition of the first product during its passage through the furnace and the amount of scale determined.

[0031] Advantageously, the prediction law for calamine formation can be modified by self-learning.

[0032] The process may include a step of reducing the loss on ignition and the amount of scale that fell in the furnace for a second product which is reheated after that of a first product by modifying the operating parameters of the furnace according to the loss on ignition of the first product when it passes through the furnace and the amount of scale determined.

[0033] According to a second aspect of the invention, a control device for a reheating furnace for steel products is proposed, having an inlet and an outlet along a direction of product flow, according to claim 2.

[0034] According to one embodiment, the furnace can be part of a steelmaking installation comprising a kiln unloading table (also called a discharge table, preferably a roller table) forming the predetermined unloading surface.

[0035] The product moves under the camera, making it possible to reconstruct the complete image of the product.

[0036] The furnace control system includes two sensors positioned upstream and downstream of a descaling unit located downstream of the furnace, and a digital processing module configured to determine the product's loss on ignition by calculating the difference in product height between the upstream and downstream sides of the descaling unit. As mentioned previously, the sensors can be optical sensors.

[0037] According to a third aspect of the invention, an installation is proposed comprising: a steel product reheating furnace, a furnace control device conforming to the second aspect of the invention, or to one or more of its improvements.

[0038] When the installation includes a kiln unloading table, the kiln unloading table can form the predetermined unloading surface.

[0039] When the installation includes a descaling machine, the control device may include the two aforementioned sensors placed, respectively, upstream and downstream of a descaling machine located downstream of the furnace, and the control device may include a digital processing module to determine the loss on ignition of the product by determining the difference in height of the product between upstream and downstream of said descaling machine.

[0040] According to a fourth aspect of the invention, a computer program product is proposed comprising instructions that lead an installation according to the third aspect of the invention, or one or more of its improvements, to execute the steps of the process according to the first aspect of the invention, or one or more of its improvements.

[0041] According to yet another unclaimed aspect of the invention, a computer-readable medium is proposed, on which the computer program product according to the fourth aspect of the invention is recorded.

[0042] The invention comprises both functions for measuring primary scale and functions for predicting and controlling scale formation, all in real time. It combines real-time physical measurements taken by sensors with digital modeling for processing and predicting the collected data. This allows for optimizing the product heating process by reducing primary scale formation.

[0043] The method and device include: A device for acquiring images of a portion of the upper surface of a product exiting an oven in the infrared spectrum using an infrared camera. Optionally, a system for processing multiple images of portions of the upper surface of a product exiting an oven in the infrared spectrum, enabling the reconstruction of an image of the entire surface of said product. A system for determining the area covered by non-adherent scale on the upper surface of a product exiting an oven, based on an infrared image of the product's surface. A system for determining the area covered by non-adherent scale on the lower surface of a product exiting an oven, obtained through numerical simulation from an infrared image of the product's upper surface correlated with oven operating data.A device for measuring the height of scale detached from a product in a descaling machine located downstream of a furnace, using optical sensors positioned upstream and downstream of the descaling machine. A system for determining the loss on ignition of a product based on the height of scale detached from it in a descaling machine located downstream of a furnace. A software application for real-time processing of data from an infrared camera and optical sensors to optimize the reliability and accuracy of the primary scale quantity determined. A module for acquiring and processing the characteristics of each product (material, dimensions, etc.) as well as its thermal path through the furnace. Optionally, a module for acquiring and processing the characteristics of the atmosphere surrounding each product during heating in the furnace.A loss on ignition prediction model built from furnace process measurements and loss on ignition measurements. A module providing guidance to the furnace control system to intelligently heat products in the furnace to minimize scale growth during heating. Optionally, a module to extract information on scale growth and morphology from large and varied furnace data sets, without requiring operator intervention. Optionally, a real-time module combining both furnace operating data and loss on ignition measurements to enhance the reliability of a loss on ignition prediction and control model. Brief description of the figures

[0044] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for which reference should be made to the accompanying drawings in which: [ Fig.1 ] is a schematic side view of a conventional steel product heating installation showing the placement of an infrared camera according to an example of an embodiment of the invention; [ Fig. 2 ] is a right-side view of the figure 1 also showing the installation of an infrared camera and optical sensors according to an example of an embodiment of the invention; [ Fig.3 ] is a schematic view of a cross-section of a product illustrating the scale present on the surface of the product at 4 successive stages; Fig. 4 ] is a schematic side view illustrating the positioning of an infrared camera according to an exemplary embodiment of the invention; [ Fig. 5] is a schematic view illustrating the mapping of primary scale at the furnace outlet of the upper surface of a product obtained by an infrared camera according to the invention; [ Fig. 6 ] is a schematic view illustrating a digital processing of the primary scale mapping at the furnace outlet to determine the ratio between adherent and non-adherent scale according to the invention; [ Fig. 7 ] is a schematic view illustrating a flowchart of the steps of the process according to the invention; [ Fig. 8 ] is a schematic side view illustrating the positioning of an optical sensor according to an exemplary embodiment of the invention; [ Fig. 9A ] is a schematic view of the positioning of an optical sensor according to the figure 8 but viewed from above; Fig. 9B ] is a schematic view of the positioning of an optical sensor according to one embodiment, but in lateral view; [ Fig. 10] is a schematic view of the device for determining loss on fire according to an example embodiment of the invention; [ Fig. 11 ] is a diagram illustrating the accuracy of the optimized law for determining the loss on ignition according to the invention; Detailed description of the invention

[0045] The embodiments described below are not exhaustive; variants of the invention may include only a selection of the described features, hereinafter isolated from the other described features, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one feature, preferably functional, without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0046] In the following description, elements with an identical structure or analogous functions will be designated by the same references.

[0047] THE figures 1 and 2present the principle of a steel product rolling mill. On the figure 1 A roller table 3 brings a product 2 to a steel product reheating furnace 4. Upstream of the roller table 3, in the direction of movement of the product 2, a loading machine 1, for example with fingers, grasps the product 2 and places it in the furnace 4 on transfer beams (not shown).

[0048] During its passage through the furnace, product 2 gradually heats up according to a predetermined heating curve, defining a thermal path, for example to be brought from ambient temperature to a discharge temperature at the furnace outlet typically between 1050 °C and 1300 °C.

[0049] A heated product 5 is removed from the oven 4 by a de-ovening machine 7, for example with fingers, and is placed on another table 6 with rollers which evacuates it to a rolling mill (not shown).

[0050] There figure 2 shows the table 6 with rollers for removing the reheated product 5 after it has come out of the oven 4. This product is moved by the table 6 with rollers towards a descaling machine 8. On the figure 2 The product within the descaling unit 8 is numbered 5'. Product 5' is exposed in the descaling unit 8 to high-pressure water jets 9, 10. The high-pressure water jets are directed respectively onto an upper and a lower part of product 5'. These water jets are arranged to detach the primary scale present on the surface of product 5' and remove it via a circuit 11 to settling tanks (not shown) for recovery.

[0051] After descaling by the descaling machine 8, the product is fed into the inlet of a rolling mill 12. In the rolling mill, the product is designated 5". The 5" product passes through two rolling sections 12a and 12b. The rolling sections 12a and 12b are arranged to obtain a sheet of the desired thickness from the 5" product.

[0052] According to the embodiment shown, the device for determining the loss on ignition of the scale produced by reheating includes sensors placed at the outlet of the furnace 4 and at the descaling machine 8. This device combines physical measurements and the result of numerical models carried out by computer programs.

[0053] It is designed to compare the amount of scale produced to limits set according to the heating method and the type of steel heated in the furnace. This comparison allows for the development of a corrective heating strategy capable of maintaining, or reducing, the scale produced to the desired quantity and quality limits.

[0054] There figure 3 represents a cross-sectional view of a product schematically showing the scale present on the product at different stages of the process: Subfigure A: Product 2 upstream of the reheating furnace. We assume that the surface is not covered with scale (in practice, it may include adherent scale formed during previous stages). Subfigure B: Product 5 exiting the reheating furnace in the theoretical case where no scale has fallen from the underside of the product (in practice, this case B does not occur for a tubular frame furnace). Starting from the center of the product, it is covered on both its upper and lower surfaces with a layer of sticky primary scale (CPCS on the upper surface and CPCI on the lower surface), followed by a layer of adherent primary scale (CPAS on the upper surface and CPAI on the lower surface), and then a layer of non-adherent primary scale (CPNS on the upper surface and CPNI on the lower surface).In theory, after the sticky primary scale layer, it is possible to have only adherent primary scale or only non-adherent primary scale. In practice, this does not occur. Subfigure C: Product 5 exiting the reheating furnace in the case where all the non-adherent scale on the underside of the CPNI product has fallen into the furnace. The fall of the non-adherent scale into the furnace is facilitated by the contact between the product and the product transport mechanism and the translational movement between the furnace inlet and outlet. In practice, some non-adherent scale may still be present on the underside of the product at the furnace outlet and fall from the product between the furnace and the descaling unit. However, since this is in small quantities, it is not taken into account. Subfigure D: Product 5 exiting the descaling unit.All the remaining non-adherent and adherent primary scale present on the product entering the descaling machine has been removed. Only the sticky primary scale (CPCS / CPCI) remains on the product.

[0055] According to the embodiment shown in figures 1, 2 And 4 , an infrared camera 20 is located near the oven, on the side where the products are unloaded.

[0056] The infrared camera 20 is positioned above the heated product 5 when the latter is placed on a predetermined unloading surface.

[0057] In the example shown, the predetermined unloading surface is formed by the roller table 6. Also, the infrared camera is positioned in the vicinity of the roller table 6 which evacuates the products to the descaling machine 8.

[0058] According to one variant of the embodiment shown, the infrared camera could be positioned below the heated product 5.

[0059] The infrared camera's photosensitive sensor utilizes optoelectronic properties, namely the ability to react to changes in light intensity. Advantageously, the camera is selected and positioned at a distance from the roller table so that its P20 field of view covers the entire width of the widest product being heated in the oven.

[0060] Since this type of rolling mill is generally used for long products, such as slabs, the field of view of the infrared camera does not usually allow coverage of the entire length of the products with good measurement accuracy.

[0061] As depicted in figure 5Successive images are taken as the product moves across the roller table at a frequency sufficient to achieve partial overlap of the product between two successive images of a portion 5.1, 5.2, 5.n of the product. Digital processing of the successive images is performed by a computer program called " Image processing This allows for the creation of an image of the entire product. This type of processing can be compared to the construction of a panorama from several photographs with overlapping areas.

[0062] In an alternative embodiment, at least two infrared cameras are used to cover the entire width of the widest product heated in the oven.

[0063] Distinguishing between adherent primary scale (CPAS) and non-adherent primary scale (CPNS) can be achieved by processing an image of the entire product. Since the emissivity of adherent and non-adherent scale is essentially the same, the light intensity emitted by a product surface is directly representative of its temperature. The light intensity emitted by non-adherent scale is significantly lower than that of adherent scale due to its lower temperature. Thus, the image formed by an infrared camera of the product surface covered with non-adherent scale appears dark, while the image formed by an infrared camera of the product surface covered with adherent scale appears bright. This is because non-adherent scale cools more rapidly than adherent scale when the product leaves the furnace, as it does not benefit from, or receives to a lesser extent, heat from the product's core.The image formed by an infrared camera of the product's surface appears mottled, with the proportion of dark areas varying depending on the amount of loose scale. The infrared camera settings are adjusted to clearly distinguish between dark and light areas.

[0064] Digital processing is performed on this image by a computer program, for example implemented within a digital processing module (S2), to map the distribution of non-adherent scale on the upper face of the product and to determine an overall ratio between adherent and non-adherent scale on it.

[0065] The digital processing thus performs a binarization of the infrared image into two classes of pixels, one class of pixels which corresponds to the pixels associated with the presence of adherent scale on the face of the product and the other class of pixels which corresponds to the pixels associated with the presence of non-adherent scale on the face of the product.

[0066] To this end, the binarization of the infrared image can be achieved by thresholding or by one or more image segmentation operations, for example by means of region-based segmentation, contour-based segmentation, segmentation based on classification or thresholding of pixels according to their intensity, possibly adaptive, or on a fusion or cooperation of the first three.

[0067] The S2 module can also be configured to determine the amounts of non-adherent and adherent scale on the product face from the binarized image.

[0068] Il It is therefore possible to modify, by means of a particular module (not shown) one or more oven control parameters based on the determined quantities of non-adherent and adherent scale.

[0069] There figure 6 illustrates the result of the numerical processing to determine the aforementioned ratio for three examples of products with different proportions of non-adherent scale. The proportion of non-adherent scale is highest in the example of the figure 6.1 and is the weakest for the example of the figure 6.3 The right-hand side of each of the subfigures of the figure 6These proportions are illustrated with partial views of the upper surface of these products, with non-adherent scale shown in black. The result of the digital processing performed by the digital processing module (S2) takes the form of a histogram shown on the left side of the figure, with the temperature of the product (according to the light intensity received by the camera pixels) on the x-axis and the number of pixels having this temperature on the y-axis.

[0070] In other words, for each x-coordinate of the histogram, the y-coordinate represents the quantity of surface units of the product at that temperature. On this diagram, a predetermined temperature threshold TL delineates the scale according to its nature. The sum of pixels with a temperature below TL, on the left side of the histogram, corresponds to the surface area of ​​the product's upper surface covered by non-adherent scale. The sum of pixels with a temperature above TL, on the right side of the histogram, corresponds to the surface area of ​​the product's upper surface covered by adherent scale. The temperature TL can be determined from tests on samples. For example, it is 950 °C. This image processing of the product's upper surface obtained by the infrared camera thus allows us to quantify the ratio of non-adherent to adherent scale across the entire upper surface of the product.

[0071] Put another way, the aforementioned ratio can be determined as the ratio of the area between 0 °C and the predetermined temperature TL to the area between the predetermined temperature TL and a predetermined unloading temperature, of the curve representing the quantity of pixels as a function of a pixel intensity.

[0072] Put another way, the aforementioned ratio can be determined as the ratio of the integral between 0 °C and the predetermined temperature TL to the integral between the predetermined temperature TL and a predetermined unloading temperature, of the curve representing the quantity of pixels as a function of a pixel intensity.

[0073] The images obtained by the infrared camera also provide information on the actual temperature of the product as it exits the oven. This makes it possible to determine the temperature profiles across the width and length of the product, as well as the temperature stability of products removed from the oven successively. This information can be used to adjust the oven's operation to achieve a stable temperature and the desired product temperature profile, for example, by adjusting the burner power and / or their operation in long or short flame mode.

[0074] With reference to the figure 7The kiln control system (60) has real-time information on kiln operation, including one or more measurements of the ambient temperature inside the kiln, the flue gas temperature, the oxygen content of the flue gases, the burner operating modes, the burner operating mode when it can change (for example, between a short flame and a long flame mode for the same power output), the product dimensions, and its composition. This information is used for numerical simulations to estimate the evolution of the environment near each point on the product surface during the product's time in the kiln and to simulate scale formation using physicochemical models.

[0075] The data recorded by the oven's control system (system 60), combined with product temperatures measured at the oven exit using an infrared camera, allows for the estimation of the product's temperature profile from its entry into the oven until its removal, using mathematical models. This makes it possible to calculate a curve illustrating the thermal path followed at each point on the product's surface.

[0076] In addition to the infrared camera, the invention also relies on the use of optical sensors for thickness measurements. These sensors are used to quantify the amount of primary scale removed by the descaling machine. Thus, the invention includes at least two optical sensors, one placed upstream of the descaling machine and the other downstream. These sensors allow the product height to be determined upstream and downstream of the descaling machine, and, by subtracting these heights and knowing the product dimensions, the amount of scale removed by the descaling machine to be calculated.

[0077] As depicted in figure 2According to a first example of the optical sensor arrangement according to the invention, a first sensor 30 is placed on the upper surface of the product upstream of the descaling machine, and a second sensor 40 is placed on the same upper surface of the product downstream of the descaling machine. For each point in the area scanned by a sensor, a distance measurement is taken with an accuracy on the order of a micrometer. We will subsequently describe only the first sensor 30, given that its arrangement is identical to that of the second sensor 40. Similarly, we will subsequently describe optical sensors placed directly above a product resting on a roller table, given that the product can rest on any other reference surface.

[0078] As depicted on the figure 8According to the first example of optical sensor placement, the sensor 30, positioned above the product, is vertically aligned with a roller 14 of the descaling machine's roller table over which the products circulate. The sensor is placed on one side of the product so that its measuring field covers at least part of the product's upper surface when a product is present below the sensor, and at least part of the upper generatrix of said roller (or a reference surface). It is positioned at a predetermined distance from the roller, for example, between 250 and 1000 mm. The sensor 30 determines the distance between the upper surface of the product 5 and the upper generatrix of the roller 14, this distance corresponding to the product's height.

[0079] As depicted on the figure 9AThe sensor is advantageously inclined at an angle alpha, in the horizontal plane, relative to the longitudinal axis of the roller, for example, at an angle of 5° to 85°. This inclination ensures that the sensor beam covers the upper generatrix of the roller at at least one point 18. Indeed, if the sensor were positioned with its measuring field parallel to the roller axis, perfect vertical alignment of the sensor with respect to the roller would be necessary so that the sensor 30 sees the upper generatrix of the roller and not a generatrix located on a lower plane.

[0080] The measurements taken from sensors 30 and 40 are divided into two phases. The first phase, called "Baseline measurement," is performed when no product is present. The system continuously scans the surface of the roller table to detect both roller vibration and the distance between the sensor and the top of the roller. These measurements are recorded and processed by a computer program to determine the actual distance between the sensor and the top of the roller. This step can be considered a calibration step without product. The second phase, called "Product measurement," is performed when a product passes over the roller table. Taking into account the measurements taken during the first phase, also called the calibration step, allows the measurements in the second phase to be corrected in order to obtain an accurate measurement of the product height.

[0081] According to another example of an embodiment of the invention illustrated in figure 9BThe optical sensors 30 and 40 are positioned approximately on one side of the product. The sensors are arranged so that their measurement fields cover the side of the product. The product thickness is thus measured directly.

[0082] Alternatively, optical sensors are placed on both sides of the product.

[0083] The device defines an average height over the product's width covered by the sensor's measurement field and over the product's length. As schematically represented in figure 5The non-adherent scale typically covers only part of the product's width, forming islands. Since the scale on the underside of the product fell into the furnace, the underside takes on a hilly surface, with depressions where the non-adherent scale was located. Consequently, at the thickness measurement point at the descaling machine's inlet, the product rests on the rollers only at the level of the scale still present on the product, i.e., the adherent scale. The height measured by sensor 30 thus accurately accounts for the total height of the primary scale formed in the furnace, both adherent and non-adherent, despite the absence of the non-adherent scale that fell upstream of the descaling machine, primarily into the furnace.

[0084] From these measurements of product thickness at the entry and exit of the descaling machine, knowing the width and length of the product, it is easy to calculate the quantity of primary scale, both adherent and non-adherent, formed on the product, and therefore the loss on ignition.

[0085] The infrared and optical sensors used according to the invention are well suited to the needs and operating conditions of a steel product heating installation since they allow: to scan products at very high temperatures, i.e. above 1000-1300 °C, while equipped with a heat protection system; to scan a non-smooth scale surface with a non-uniform thickness; not to be hindered by the significant difference in weight and thickness between the product and the scale: 25,000 kg and 250 mm thick for a slab compared to approximately 200 kg and 2 mm thick for the scale.

[0086] There figure 7 This figure graphically represents a portion of the steps in the process according to the invention. In this figure, a square marker represents physical equipment (hardware), a diamond marker represents a digital processing step by a computer program (software), and a circle marker represents a result. The arrows indicate the direction in which the steps are carried out and / or the direction in which information flows. Step 1: An infrared camera 20 takes successive images of portions of the top face of a moving product and sends them to a computer server 50. Step 2: A computer program implemented in a digital processing module S1 processes these images and delivers as a result R1, a reconstructed image of the entire top surface of the product showing the distribution of adherent and non-adherent scale on the top surface of the product (measurement), and it also delivers as a result R2, the average temperature of the top surface of the product (measurement). Step 3: A computer program implemented in a digital processing module S2 processes the image obtained in R1 and delivers as a result R3, the ratio of overall proportions of adherent and non-adherent scale on the upper face of the product. Step 4: Server 50 receives information about the product (dimensions, material, etc.) from the oven control and command system 60, and data relating to the operation of the oven from measurements taken by sensors (temperatures, pressures, oxygen content in the fumes, etc.), these measurements being able to be taken at several points by oven regulation zones. Step 5: Using data available on server 50 and mathematical models, a computer program implemented in a digital processing module S3 calculates the average unloading temperatures of the product on these two faces, as well as the thermal paths followed by each of these faces. The average temperature calculated on the top surface constitutes the result R4. Step 6: A computer program implemented in a digital processing module S4 compares the average temperature of the top face of the product at unloading from the kiln obtained by simulation (result R4) and that obtained by measurement with the infrared camera 20 (result R2), then delivers to the server 50, in result R5, a factor of difference between the results R2 and R4. Step 7: From the data available in server 50, and by means of mathematical models, a computer program implemented in a digital processing module S5 calculates the difference in thermal paths of the two faces of the product, and of oxygen content in the vicinity of them, during the passage of the product in the oven, and, by means of laws of calamine formation, determines in result R6 a ratio of global proportions of adherent and non-adherent calamine on the upper face of the product and in result R7, a ratio of global proportions of adherent and non-adherent calamine on the lower face. Step 8: A computer program implemented in a digital processing module S6 determines a difference between the ratio of overall proportions of adherent and non-adherent scale on the upper face of the product obtained by simulation (result R6) and that obtained by measurement from the infrared camera (result R3) and, depending on this and the initial value of the ratio of proportions of adherent and non-adherent scale on the lower face (result R7), delivers in result R8, a corrected ratio of overall proportions of adherent and non-adherent scale on the lower face. Step 9: At least one optical sensor 30 measures the thickness of the product entering the descaling machine, and at least one optical sensor 40 measures the thickness of the product exiting the descaling machine. This data is processed by a computer program implemented in a digital processing module S7, which outputs result R9, the total average thickness of the primary scale on both faces of the product. Step 10: From the data available in server 50 on the dimensions of the product and the total average thickness of the primary mill scale on both faces of the product obtained by the optical sensors (result R9), a computer program implemented in a digital processing module S8 delivers in result R10, the measured loss on ignition. Step 11: A computer program implemented in a digital processing module S9 compares the loss on ignition determined by means of optical sensors (result R10) with the ratio of non-adherent scale from the upper face determined from the infrared camera (result R3) and that of the lower face after correction (result R8) and delivers in result R11 the quantity of non-adherent scale that fell into the furnace. Step 12: A computer program implemented in a digital processing module S10 retrieves and processes the process data available in the server 50, the loss on ignition (result R10) and the volume of scale that fell into the furnace during heating (result R11), and delivers in result R12, a process balance which feeds a database 51. Step 13: Using data from database 51, a computer program implemented in a digital processing module S11 regularly delivers by self-learning in result R13, an optimized law for predicting loss on fire. Step 14: A computer program implemented in a digital processing module S12 uses the optimized law for predicting loss on ignition (result R13) and delivers in result R14 an optimal heating strategy (thermal path of the product, oxygen content in the oven, etc.) allowing to minimize the amount of scale formed during the heating of the product which it sends to the oven control and command system 60. Legend for Figure 7

[0087] 20: Infrared camera 30: Optical sensor at the inlet of the decarbonizing machine 40: Optical sensor at the outlet of the decarbonizing machine 50: Scale computer server 51: Process database 60: Oven control and command system S1 to S12: Digital processing modules containing computer programs R1: A reconstructed image of the entire upper surface of the product showing the distribution of adherent and non-adherent scale on the upper surface of the product (measurement). R2: Average temperature of the upper surface of the product (measurement). R3: Ratio of adherent to non-adherent scale on the upper surface of the product (measurement). R4: Average temperature of the upper surface of the product (simulation). R5: Difference factor between the average temperature of the upper surface determined from the infrared camera (result R2) and that obtained by simulation (result R4). R6: Ratio of adherent to non-adherent scale on the upper surface of the product (simulation).R7: Ratio of adherent to non-adherent scale on the underside of the product (simulation). R8: Corrected ratio of adherent to non-adherent scale on the underside of the product. R9: Total average thickness of primary scale at the descaling machine inlet. R9: Surface area of ​​non-adherent scale on the underside of the product. R10: Loss on ignition. R11: Quantity of non-adherent scale from the underside of the product that fell into the furnace. R12: Furnace process data. R13: Prediction law for loss on ignition. R14: Optimal heating strategy to limit loss on ignition.

[0088] As depicted in Figure 10 The control and operation of the oven according to the invention is achieved from: of an L3 system for optimizing the operation of the level 3 furnace based on input data on the products to be reheated (dimensions, weight, steel composition, rolling conditions, etc.) and process data, including target unloading temperatures; of an L2 system for optimizing the regulation of the level 2 furnace based on instructions provided by the L3 furnace operation optimization system, process data (product heating curves and L0 data provided by the furnace instrumentation); of an L2' machine learning computer program improving the L2 level 2 furnace regulation optimization system through self-learning based on R1 results of numerical simulations of the amount of scale and the product temperature, and R2 results of the amount of scale determined by numerical processing D from the data M provided by the infrared camera 20 and the optical sensors 30.40 thickness measurement at the descaling machine, an L1 system for controlling the furnace equipment via level 1 local control loops based on instructions provided by the L2 furnace regulation optimization system and L0 data provided by the furnace instrumentation.

[0089] The furnace control and monitoring system according to the invention takes into account a very large amount of furnace process data and scale measurements (Big Data). The raw data from the instruments is approximately 120 megabytes per product. For a normal production run of a slab reheating furnace producing 360 products per day, this represents approximately 43 gigabytes of data per day. In order to obtain useful information for furnace control from this very large amount of data, algorithms (also known as Data Science) are applied. These algorithms make it possible to extract the essential information from the measurements taken, ensuring their reliability despite the challenging environment of a preheating furnace before rolling.The oven control and piloting system thus uses key information to intelligently heat the products in the oven by controlling the formation of scale during heating, in particular from key process variables, such as: . the thermal path and residence time of the product in critical areas of the furnace, the furnace atmosphere, the composition of the steel.

[0090] There figure 11This diagram shows the tests performed under different operating conditions to verify the performance of the optimized law for predicting loss on ignition (result R13) according to the invention. The x-axis represents the product number and the y-axis the quantity of loss on ignition. In this diagram, the diamonds correspond to the losses on ignition obtained by measurements on samples, and the squares represent the losses on ignition determined using the optimized prediction law. It can be seen that the optimized prediction law gives results very close (within 10% variation on average) to those observed on the samples.

[0091] Of course, the invention is not limited to the examples just described, and many modifications can be made to these examples without departing from the scope of the invention. Furthermore, the various features, forms, variants, and embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive.

Claims

1. Method for controlling a furnace (4) for reheating steel products (5), which furnace has an inlet and an outlet in a direction in which the product is conveyed, comprising the following steps: ∘ using an infrared camera (20) to take successive images of portions of the upper face of a product being conveyed, and sending said images to a computer server (50), ∘ processing these images using a computer program implemented in a digital processing module S1 and outputting as result R1 a reconstructed image of the entire upper face of the product showing the distribution of adherent scale and non-adherent scale on the upper face of the product, and also outputting as result R2 the average temperature of the upper face of the product, ∘ processing the image obtained as R1 using a computer program implemented in a digital processing module S2, and outputting as result R3 the ratio of overall proportions of adherent and non-adherent scale on the upper face of the product, ∘ the server (50) receiving, from the furnace monitoring and control system (60), information relating to the product and data relating to the functioning of the furnace based on sensor measurements, which measurements may be taken at a plurality of points per control zones of the furnace, ∘ calculating, using a computer program implemented in a digital processing module S3, from the data available on the server (50), and by means of mathematical models, the average temperatures of the product on these two faces as said product leaves the furnace, as well as the thermal paths followed by each of these faces, the average temperature calculated on the upper face constituting the result R4, ∘ comparing, using a computer program implemented in a digital processing module S4, the average temperature R4 of the upper face of the product as it leaves the furnace, which average temperature is obtained by simulation, and the average temperature R2 obtained by measurement using the infrared camera (20), then outputting to the server (50), as result R5, a deviation factor between the results R2 and R4, ∘ calculating, using a computer program implemented in a digital processing module S5, from the data available on the server (50), and by means of mathematical models, the difference in thermal paths of the two faces of the product, and the oxygen content in the vicinity thereof, as the product passes through the furnace, and, by means of scale formation laws, determining as result R6 a ratio of overall proportions of adherent and non-adherent scale on the upper face of the product and as result R7 a ratio of overall proportions of adherent and non-adherent scale on the lower face, ∘ determining, using a computer program implemented in a digital processing module S6, a deviation between the ratio R6 of overall proportions of adherent and non-adherent scale on the upper face of the product, which ratio is obtained by simulation, and the ratio R3 obtained by measurement from the infrared camera and, depending thereon and on the initial value R7 of the ratio of proportions of adherent and non-adherent scale on the lower face, outputting as result R8 a corrected ratio of overall proportions of adherent and non-adherent scale on the lower face, ∘ measuring, using at least one optical sensor (30), the thickness of the product as it enters the descaler, and measuring, using at least one optical sensor (40), the thickness of the product as it exits the descaler, and processing these data using a computer program implemented in a digital processing module S7, which program outputs as result R9 the total average thickness of the primary scale on both faces of the product, ∘ outputting, using a computer program implemented in a digital processing module S8, based on the data available on the server (50) on the product dimensions and the total average thickness R9 of the primary scale on both faces of the product, which total average thickness is obtained by the optical sensors, the measured loss on ignition as result R10, ∘ comparing, using a computer program implemented in a digital processing module S9, the loss on ignition R10 determined by means of the optical sensors with the ratio R3 of non-adherent scale of the upper face determined from the infrared camera and the ratio R8 of the lower face after correction, and outputting as result R11 the quantity of non-adherent scale that has fallen into the furnace, ∘ retrieving and processing, using a computer program implemented in a digital processing module S10, the process data available on the server (50), the loss on ignition R10 and the volume of scale R11 that has fallen into the furnace during heating, and outputting as result R12 a process report which supplies a database (51), ∘ outputting regularly by self-learning, using a computer program implemented in a digital processing module S11, based on data in the database (51), an optimized loss on ignition prediction law as result R13, and ∘ using, using a computer program implemented in a digital processing module S12, the optimized law R13 for predicting the loss on ignition and outputting as result R14 an optimal heating strategy enabling the quantity of scale formed during heating of the product to be minimized, and sending said optimal strategy to the furnace monitoring and control system (60).

2. Device (60) for controlling a furnace (4) for reheating steel products (5), which furnace has an inlet and an outlet in a direction in which the product is conveyed, the device comprising: ∘ an infrared camera (20) configured to take successive images of portions of the upper face of a product being conveyed, and send said images to a computer server (50); ∘ a computer program implemented in a digital processing module S1 and configured to process these images and to output as result R1 a reconstructed image of the entire upper face of the product showing the distribution of adherent scale and non-adherent scale on the upper face of the product, and also to output as result R2 the average temperature of the upper face of the product; ∘ a computer program implemented in a digital processing module S2 and configured to process the image obtained as R1 and to output as result R3 the ratio of overall proportions of adherent and non-adherent scale on the upper face of the product; ∘ the server 50 being configured to receive, from the furnace monitoring and control system 60, information relating to the product and data relating to the functioning of the furnace based on sensor measurements; ∘ a computer program implemented in a digital processing module S3 and configured to calculate, from the data available on the server (50), and by means of mathematical models, the average temperatures of the product on these two faces as said product leaves the furnace, as well as the thermal paths followed by each of these faces, the average temperature calculated on the upper face constituting the result R4; ∘ a computer program implemented in a digital processing module S4 and configured to compare the average temperature R4 of the upper face of the product as it leaves the furnace, which average temperature is obtained by simulation, and the average temperature R2 obtained by measurement using the infrared camera (20), then output to the server (50), as result R5, a deviation factor between the results R2 and R4; ∘ a computer program implemented in a digital processing module S5 and configured to calculate, from the data available on the server (50), and by means of mathematical models, the difference in thermal paths of the two faces of the product, and the oxygen content in the vicinity thereof, as the product passes through the furnace, and, by means of scale formation laws, to determine as result R6 a ratio of overall proportions of adherent and non-adherent scale on the upper face of the product and as result R7 a ratio of overall proportions of adherent and non-adherent scale on the lower face; ∘ a computer program implemented in a digital processing module S6 and configured to determine a deviation between the ratio R6 of overall proportions of adherent and non-adherent scale on the upper face of the product, which ratio is obtained by simulation, and the ratio R3 obtained by measurement from the infrared camera and, depending thereon and on the initial value R7 of the ratio of proportions of adherent and non-adherent scale on the lower face, to output as result R8 a corrected ratio of overall proportions of adherent and non-adherent scale on the lower face; ∘ at least one optical sensor (30) configured to measure the thickness of the product as it enters the descaler, and at least one optical sensor (40) configured to measure the thickness of the product as it exits the descaler, and a computer program implemented in a digital processing module S7 and configured to process these data and to output as result R9 the total average thickness of the primary scale on both faces of the product; ∘ a computer program implemented in a digital processing module S8 and configured to output as result R10 the measured loss on ignition, based on the data available on the server (50) on the product dimensions and the total average thickness R9 of the primary scale on both faces of the product, which total average thickness is obtained by the optical sensors; ∘ a computer program implemented in a digital processing module S9 and configured to compare the loss on ignition R10 determined by means of the optical sensors with the ratio R3 of non-adherent scale of the upper face determined from the infrared camera and the ratio R8 of the lower face after correction, and to output as result R11 the quantity of non-adherent scale that has fallen into the furnace; ∘ a computer program implemented in a digital processing module S10 and configured to retrieve and process the process data available on the server (50), the loss on ignition R10 and the volume of scale R11 that has fallen into the furnace during heating, and to output as result R12 a process report which supplies a database (51); ∘ a computer program implemented in a digital processing module S11 and configured to regularly output by self-learning, based on data in the database (51) an optimized loss on ignition prediction law as result R13; ∘ a computer program implemented in a digital processing module S12 and configured to use the optimized law R13 for predicting the loss on ignition and to output as result R14 an optimal heating strategy enabling the quantity of scale formed during heating of the product to be minimized, and to send said optimal strategy to the furnace monitoring and control system.

3. Installation comprising: ∘ a furnace (4) for reheating steel products, ∘ a device for controlling the furnace according to the preceding device claim.

4. Computer program product comprising instructions which cause an installation according to the preceding claim to perform the steps of the method according to claim 1.