DEVICE AND METHOD FOR CONTROLLING A REHEATING FURNACE

Abstract

A method for controlling a furnace for reheating iron and steel products, comprising forming an infrared image, using an infrared camera, of an upper face of a product over the width and at least partially over the length thereof when said product is arranged on a predetermined discharging surface; digital processing comprising binarization of the infrared image into two classes of pixels, one class that corresponds to the pixels associated with the presence of scale that is bonded on the face of the product and one class that corresponds to the pixels associated with the presence of scale that is not bonded on the face of the product; determining the amounts of non-bonded scale and of bonded scale on the upper face of the product on the basis of the binarized image; modifying furnace control parameters on the basis of the determined amounts of non-bonded scale and of bonded scale.

Claims

1. A method for controlling a furnace for reheating iron and steel products having an inlet and an outlet in a reeling-off direction of the product, comprising: forming an infrared image, using an infrared camera, of an upper face of a product over the width and at least partially over the length thereof when said product is arranged on a predetermined discharging surface; digital processing comprising binarization of the infrared image into two classes of pixels, one class of pixels that corresponds to the pixels associated with the presence of scale that is bonded on the face of the product and the other class of pixels that corresponds to the pixels associated with the presence of scale that is not bonded on the upper face of the product; determining the amounts of non-bonded scale and of bonded scale on the upper face of the product on the basis of the binarized image; modifying furnace control parameters on the basis of the determined amounts of non-bonded scale and bonded scale.

2. The control method according to claim 1, further comprising determining a ratio of the amount of bonded scale to the amount of non-bonded scale.

3. The control method according to claim 1, wherein the binarization is carried out by thresholding the light intensity of the pixels.

4. The control method according to claim 1, further comprising digital processing for determining a loss on ignition of the product.

5. The control method according to claim 4, comprising measuring the height of the product using two sensors that are respectively arranged upstream and downstream of a descaling machine located downstream of the furnace, and digital processing for determining the loss on ignition of the product by determining the difference in the height of the product between the upstream side and the downstream side of said descaling machine.

6. The furnace control method according to claim 4, comprising, when the upper face is imaged by the infrared camera, determining the amount of scale on the lower face of the product that has fallen into the furnace using digital simulations on the basis of the amounts of non-bonded scale and of bonded scale on the upper surface of the product obtained on the basis of the binarized image, on the basis of the determined loss on ignition, and of a correlation of these results with operating readings of the furnace and a scale formation prediction law.

7. The method according to claim 6, wherein the scale formation prediction law is modified by self-learning.

8. The method according to claim 5, comprising a step of reducing the loss on ignition and the amount of scale that has fallen into the furnace for a second product, the reheating of which is carried out after that of a first product by modifying operating parameters of the furnace as a function of the loss on ignition of the first product when it passes through the furnace and the determined amount of scale.

9. A device for controlling a furnace for reheating iron and steel products having an inlet and an outlet in a reeling-off direction of the product, comprising: an infrared camera provided to form an infrared image of an upper face of a product (5) over the width and at least partially over the length thereof when said product is arranged on a predetermined discharging surface; a digital processing module arranged to carry out binarization of the infrared image into two classes of pixels, one class of pixels that corresponds to the pixels associated with the presence of scale that is bonded on the face of the product and the other class of pixels that corresponds to the pixels associated with the presence of scale that is not bonded on the face of the product; a module for determining the amounts of non-bonded scale and of bonded scale on the upper face of the product on the basis of the binarized image; a module for modifying furnace control parameters on the basis of the determined amounts of non-bonded scale and of bonded scale.

10. The control device according to claim 9, further comprising two sensors that are respectively arranged upstream and downstream of a descaling machine located downstream of the furnace, and a digital processing module configured for determining the loss on ignition of the product by determining the difference in the height of the product between the upstream side and the downstream side of said descaling machine.

11. A facility comprising: a furnace for reheating iron and steel product; a device for controlling the furnace according to claim 9.

12. A computer program product comprising instructions that causes a facility to execute the steps of the method according to claim 7: wherein the facility comprises a furnace for reheating iron and steel product and a device for controlling the furnace; wherein the device for controlling the furnace has an inlet and an outlet in a reeling-off direction of the product and comprises: an infrared camera provided to form an infrared image of an upper face of a product over the width and at least partially over the length thereof when said product is arranged on a predetermined discharging surface; a digital processing module arranged to carry out binarization of the infrared image into two classes of pixels, one class of pixels that corresponds to the pixels associated with the presence of scale that is bonded on the face of the product and the other class of pixels that corresponds to the pixels associated with the presence of scale that is not bonded on the face of the product; a module for determining the amounts of non-bonded scale and of bonded scale on the upper face of the product on the basis of the binarized image; and a module for modifying furnace control parameters on the basis of the determined amounts of non-bonded scale and of bonded scale.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0083] Further features and advantages of the invention will become apparent from the following detailed description, which can be understood with reference to the accompanying drawings, in which:

[0084] FIG. 1 is a schematic side view of a conventional facility for reheating an iron and steel product showing the layout of an infrared camera according to one embodiment of the invention:

[0085] FIG. 2 is a right-hand view of FIG. 1 also showing the layout of an infrared camera and optical sensors according to one embodiment of the invention;

[0086] FIG. 3 is a schematic view of a section of a product showing the scale present on the surface of the product at 4 successive stages;

[0087] FIG. 4 is a schematic side view showing the positioning of an infrared camera according to one embodiment of the invention;

[0088] FIG. 5 is a schematic view showing the map of the primary scale on the upper face of a product upon exiting the furnace obtained by an infrared camera according to the invention;

[0089] FIG. 6 is a schematic view showing digital processing of the map of the primary scale upon exiting the furnace for determining the ratio between the bonded scale and the non-bonded scale according to the invention;

[0090] FIG. 7 is a schematic view showing a flowchart of the steps of the method according to the invention;

[0091] FIG. 8 is a schematic side view showing the positioning of an optical sensor according to one embodiment of the invention;

[0092] FIG. 9A is a schematic view of the positioning of an optical sensor according to FIG. 8, but as a top view;

[0093] FIG. 9B is a schematic view of the positioning of an optical sensor according to an alternative embodiment, but as a side view;

[0094] FIG. 10 is a schematic view of the device for determining loss on ignition according to one embodiment of the invention;

[0095] FIG. 11 is a diagram showing the accuracy of the optimized law for determining loss on ignition according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0096] Since the embodiments described hereafter are by no means limiting, alternative embodiments of the invention can be particularly considered that comprise only a selection of the features that are described, subsequently isolated from the other described features, provided that this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection comprises at least one preferably functional feature without structural details, or with only some of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0097] Throughout the remainder of the description, elements having an identical structure or similar functions will be designated using the same reference signs.

[0098] FIGS. 1 and 2 show the principle of an iron and steel product rolling facility. In FIG. 1, a roller table 3 conveys a product 2 opposite a furnace 4 for reheating iron and steel products. Upstream of the roller table 3, in the direction of travel 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).

[0099] As it passes through the furnace, the product 2 gradually heats up according to a predetermined heating curve, defining a thermal path, for example, in order to be brought from the ambient temperature to a discharging temperature upon exiting the furnace that typically ranges between 1,050° C. and 1,300° C.

[0100] A reheated product 5 is taken out of the furnace 4 by a discharging machine 7, for example, with fingers, and is placed on another roller table 6 that discharges it to a rolling mill (not shown).

[0101] FIG. 2 shows the roller table 6 for discharging the reheated product 5 after it exits the furnace 4. This product is moved by the roller table 6 to a descaling machine 8. In FIG. 2, the product inside the descaling machine 8 is numbered 5′. The product 5′ is exposed in the descaling machine 8 to high pressure water jets 9, 10. The high pressure water jets are respectively oriented on an upper part and a lower part of the product 5′. These water jets are arranged to detach the primary scale present on the surface of the product 5′ and to discharge said scale along a circuit 11 towards settling tanks (not shown) for the recovery thereof.

[0102] Following descaling by the descaling machine 8, the product is conveyed to the inlet of a rolling machine 12. In the rolling machine, the product is referenced 5″. The product 5″ passes through two rolling sections 12a, 12b. The rolling sections 12a, 12b are arranged to obtain a sheet from the product 5″ that has the desired thickness.

[0103] According to the embodiment that is shown, the device for determining loss on ignition of the scale produced by the reheating comprises sensors arranged at the outlet of the furnace 4 and on the descaling machine 8, This device combines physical measurements and the result of digital modeling carried out by computer programs.

[0104] It is designed to compare the amount of scale that is produced with limits set according to the heating mode and the nature of the steel reheated in the furnace. This comparison allows a corrective heating strategy to be developed that is capable of maintaining, or returning, the scale that is produced within the desired limits in terms of amount and quality.

[0105] FIG. 3 shows a section view of a product schematically showing the scale present on the product at various steps of the process: [0106] sub-figure A: Product 2 upstream of the reheating furnace. It is assumed that the surface is not covered with scale (in practice, it can include bonded scale formed during earlier steps). [0107] sub-figure B: Product 5 exiting the reheating furnace in the theoretical case whereby no scale has fallen from the lower face of the product (in practice, this case B does not occur for a furnace with tubular beams). Starting from the center of the product, this is covered on these two lower and upper faces with a layer of bonded primary scale (CPCS on the upper face and CPCI on the lower face), followed by a layer of bonded primary scale (CPAS on the upper face and CPAI on the lower face), then a layer of non-bonded primary scale (CPNS on the upper face and CPNI on the lower face). In theory, after the layer of bonded primary scale, it is possible to have only bonded primary scale or only non-bonded primary scale. In practice, this does not occur. [0108] sub-figure C: Product 5 exiting the reheating furnace in the case whereby all the non-bonded scale on the lower face of the product CPNI has fallen into the furnace. Non-bonded scale falling into the furnace is facilitated by the contacts between the product and the transport mechanics of the product and the translation movement between the inlet and the outlet of the furnace. In practice, non-bonded scale can still be present on the lower face of the product exiting the furnace and can fall from the product between the furnace and the descaling machine. However, as this is a small amount, it is not taken into account. [0109] sub-figure D: Product 5″ exiting the descaling machine. All non-bonded and bonded primary scale still present on the product entering the descaling machine has been removed. Only the bonded primary scale CPCS, CPCI remains on the product.

[0110] According to the embodiment shown in FIGS. 1, 2 and 4, an infrared camera 20 is located in the vicinity of the furnace, on the product discharge side.

[0111] The infrared camera 20 is positioned above the reheated product 5 when said product is arranged on a predetermined discharging surface.

[0112] In the example shown, the predetermined discharging surface is formed by the roller table 6. Furthermore, the infrared camera is positioned in the vicinity of the roller table 6 for discharging products toward the descaling machine 8.

[0113] According to an alternative embodiment that is shown, the infrared camera could be disposed below the reheated product 5.

[0114] The photosensitive sensor of the infrared camera uses optoelectronic properties, i.e. the ability to react to a variation in light intensity. Advantageously, the camera is selected, and it is positioned at a distance from the roller table, so that its field of vision P20 covers the entire width of the widest product reheated in the furnace.

[0115] With this type of rolling facility generally being used for long products, such as slabs, the field of vision of the infrared camera does not generally allow the entire length of the products to be covered with good measurement accuracy.

[0116] As shown in FIG. 5, successive images are taken when the product moves on the roller table at a sufficient frequency for obtaining a 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 carried out by a computer program, called “Image processing,” allows an image of the whole product to be constituted. This type of processing can be likened to that of constructing a panorama from several photographs having overlapping areas.

[0117] As an alternative embodiment, at least two infrared cameras are used to cover the entire width of the widest product reheated in the furnace.

[0118] The bonded primary scale CPAS and the non-bonded primary scale CPNS can be discriminated based on processing of the image of the entire product. Since the emissivity of bonded and non-bonded scale is substantially the same, the light intensity emitted by a surface of the product directly represents its temperature. The light intensity emitted by non-bonded scale is substantially lower than that of bonded scale due to a lower temperature. Thus, the image formed by an infrared camera of the surface of the product covered with non-bonded scale appears dark and the image formed by an infrared camera of the surface of the product covered with bonded scale appears light. Indeed, the non-bonded scale cools more quickly than the bonded scale when the product leaves the furnace, not benefiting, or to a lesser extent, from calorific intake from the core of the product. The image formed by an infrared camera of the surface of the product thus appears to be spotted, with a greater or lesser proportion of dark zones depending on the amount of non-bonded scale. The setting of the infrared camera is adjusted so that the distinction between dark and light areas is marked.

[0119] This image is digitally processed by a computer program, for example, implemented within a digital processing module (S2), in order to map the distribution of the non-bonded scale on the upper face of the product and to determine an overall ratio between the bonded and non-bonded scale thereon.

[0120] The digital processing thus implements binarization of the infrared image into two classes of pixels, one class of pixels that corresponds to the pixels associated with the presence of scale that is bonded on the face of the product and the other class of pixels that corresponds to the pixels associated with the presence of scale that is not bonded on the face of the product.

[0121] To this end, the binarization of the infrared image can be carried out by thresholding or by one or more image segmentation operations, for example, by means of a segmentation based on the regions, a segmentation based on the contours, a segmentation based on a classification or a thresholding of the pixels as a function of their intensity, possibly adaptive, or on an amalgamation or combination of the first three segmentation operations.

[0122] The module S2 also can be configured to determine the amounts of non-bonded scale and bonded scale on the face of the product on the basis of the binarized image.

[0123] It is thus possible to modify, by means of a particular module (not shown), one or more furnace control parameters on the basis of the determined amounts of non-bonded scale and of bonded scale.

[0124] FIG. 6 shows the result of the digital processing for determining the aforementioned ratio for three examples of products with different proportions of non-bonded scale. The proportion of non-bonded scale is the highest in the example of FIG. 6.1 and is the lowest in the example of FIG. 6.3. The right-hand part of each of the sub-figures of FIG. 6 shows these proportions with partial views of the upper face of these products, with the non-bonded scale being shown in black. The result of the digital processing carried out by the digital processing module (S2) assumes the form of a histogram shown on the left-hand part of the figure, with the product temperature being on the abscissa (according to the light intensity received by the pixels of the camera) and the number of pixels with this temperature being on the ordinate.

[0125] In other words, for each abscissa of the histogram, the ordinate represents the amount of surface units of the product with this temperature. On this diagram, a predetermined temperature threshold TL defines the scale according to its nature. The sum of the pixels with a temperature that is lower than TL, on the left-hand part of the histogram, corresponds to the surface of the upper face of the product covered by non-bonded scale. The sum of the pixels with a temperature that is higher than TL, on the right-hand part of the histogram, corresponds to the surface of the upper face of the product covered by bonded scale. The temperature TL can be determined from tests on samples. It is 950° C., for example. This processing of the image of the upper face of the product that is obtained by the infrared camera thus allows the ratio of proportions of non-bonded and bonded scale on the whole of the upper face of the product to be quantified.

[0126] In other words, the aforementioned ratio can be determined as the ratio of the surface between 0° C. and the predetermined temperature TL to the surface between the predetermined temperature TL and a predetermined discharging temperature of the curve representing the amount of pixels as a function of a pixel intensity.

[0127] In other words, the aforementioned ratio can be determined as the ratio of the integral between 0° C. and the predetermined temperature IL to the integral between the predetermined temperature TL and a predetermined discharging temperature of the curve representing the amount of pixels as a function of a pixel intensity.

[0128] The images obtained by the infrared camera also provide information relating to the actual temperature of the product upon exiting the furnace. It is thus possible to determine the temperature profiles over the width and the length of the product, as well as the stability of the discharging temperature of the products that are successively discharged. This information can be used to adjust the operation of the furnace in order to obtain a stable temperature and the desired product temperature profile, for example, by adjusting the power of the burners and/or their operation in long flame or short flame mode.

[0129] With reference to FIG. 7, the furnace monitoring and control system 60 has real-time information relating to the operation of the furnace, in particular one or more measurements of the ambient temperature inside the furnace, the temperature of the flue gases, the oxygen content of the flue gases, the operating regimes of the burners, the operating mode of the burners when this can change, for example, between a short flame mode and a long flame mode for the same power output, the dimensions of the product and its composition. This information is used for digital simulations in order to estimate the evolution of the environment in the vicinity of each point of the surface of the product while the product remains in the furnace and to simulate the formation of scale by means of physicochemical models.

[0130] The data stored by the furnace monitoring and control system 60, combined with the temperatures of the product measured upon exiting the furnace by means of the infrared camera, allow the evolution of the temperature map of the product to be estimated from the time it enters the furnace until it is discharged from the furnace using mathematical models. It is thus possible to compute a curve showing the thermal path followed at each point of the surface of the product.

[0131] In addition to the infrared camera, the invention is also based on the use of optical sensors for thickness measurements. They are used to quantify the amount of primary scale that is removed by the descaling machine. Thus, the invention comprises at least two optical sensors, one placed upstream of the descaling machine and the other placed downstream thereof. They allow the height of the product upstream and downstream of the descaling machine to be determined, and by virtue of the difference in these heights, knowing the dimensions of the product, they allow the amount of scale removed in the descaling machine to be computed.

[0132] As shown in FIG. 2, according to a first example of the layout of the optical sensors according to the invention, a first sensor 30 is placed on the side of the upper face of the product upstream of the descaling machine and a second sensor 40 is placed on the side of this same upper face of the product downstream of the descaling machine. For each point in the area scanned by a sensor, a distance measurement is carried out with accuracy of the order of a micrometer. Only the first sensor 30 will be described hereafter, given that the arrangement of this sensor is identical to that of the second sensor 40. Similarly, optical sensors will be described hereafter that are placed in line with a product resting on a roller table, given that the product can rest on any other reference surface.

[0133] As shown in FIG. 8, according to the first example of the layout of the optical sensors, the sensor 30 placed above the product is arranged vertically relative to a roller 14 of the roller table of the descaling machine on which the products circulate.

[0134] The sensor is placed on one side of the product so that its field of measurement covers at least part of the upper face of the product, when a product is present under the sensor, and at least part of the upper generatrix of said roller (or a reference surface). It is disposed at a predetermined distance from the roller, for example, ranging between 250 and 1,000 mm. The sensor 30 allows the distance to be determined between the upper face of the product 5 and the upper generatrix of the roller 14, with this distance corresponding to the height of the product.

[0135] As shown in FIG. 9A, the sensor is advantageously inclined by an alpha angle, in the horizontal plane, with respect to the longitudinal axis of said roller, for example, by an angle of 5° to 85°. This incline ensures that the beam of the sensor covers the upper generatrix of the roller on at least one point 18. Indeed, if the sensor was arranged with its field of measurement parallel to the axis of the roller, the sensor would need to be perfectly vertically aligned with respect to the roller so that the sensor 30 sees the upper generatrix of the roller and not a generatrix placed on a lower plane.

[0136] The measurements taken from the sensors 30, 40 separate into two phases. The first phase, called “Baseline measurement,” is carried out in the absence of product. The system continuously scans the roller surface of the roller table to detect both the vibration of the roller and the distance between the sensor and the apex of the roller. The measurements are stored and processed by a computer program in order to define the actual distance between the sensor and the apex of the roller. This step can be likened to a calibration step without product. The second phase, called “Product measurement,” is carried out 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 of the second phase to be corrected so as to obtain an accurate measurement of the height of the product.

[0137] According to another embodiment of the invention shown in FIG. 9B, the optical sensors 30, 40 are substantially placed on one of the sides of the product. The sensors are arranged so that their fields of measurement cover the side of the product. The thickness measurement of the product is thus carried out directly.

[0138] As an alternative embodiment, optical sensors are placed on both sides of the product.

[0139] The device defines an average height over the width of the product covered by the field of measurement of the sensor and over the length of the product. As is schematically shown in FIG. 5, the non-bonded scale generally covers only part of the width of the product, in the form of islands. As the lower face of the product has fallen into the furnace, the lower face of the product assumes the form of an undulating surface, with depressions where the non-bonded scale was located. The result is that, at the thickness measurement point at the inlet of the descaling machine, the product rests on the generatrix of the rollers only in the vicinity of the scale that is still present on the product, i.e. the bonded scale. The height measured by the sensor 30 thus takes into account the total height of the primary scale, bonded and non-bonded, formed in the furnace despite the absence of the non-bonded scale that has fallen upstream of the descaling machine, mainly in the furnace.

[0140] On the basis of these thickness measurements of the product entering and exiting the descaling machine, knowing the width and the length of the product, it is easy to compute the amount of bonded and non-bonded primary scale that is formed on the product, and therefore the loss on ignition.

[0141] The infrared and optical sensors that are used according to the invention are well suited to the requirements and operating conditions of a facility for reheating iron and steel products since they: [0142] allow products to be scanned at very high temperatures, i.e. above 1,000-1,300° C., by being equipped with a heat protection system; [0143] allow a surface of non-smooth scale to be scanned having an inhomogeneous thickness; [0144] are not 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 200 kg and 2 mm thick, approximately, for the scale.

[0145] FIG. 7 graphically shows part of the steps of the method according to the invention. In this figure, a square mark represents physical equipment (hardware), a diamond mark represents a digital processing step by a computer program (software), and a circle mark represents a result. The arrows indicate the direction in which the steps occur and/or the direction in which an information flow circulates. [0146] Step 1: An infrared camera 20 takes successive images of portions of the upper face of a reeled-off product and sends them to a computer server 50. [0147] Step 2: A computer program implemented in a digital processing module S1 processes these images and delivers, as a result R1, a reconstituted image of the entire upper face of the product showing the distribution of bonded scale and of non-bonded scale on the upper face of the product (measurement), and it also delivers, as a result R2, the average temperature of the upper face of the product (measurement). [0148] Step 3: A computer program implemented in a digital processing module S2 processes the image obtained as R1 and delivers, as a result R3, the ratio of overall proportions of bonded and non-bonded scale on the upper face of the product. [0149] Step 4: The server 50 receives information from the furnace monitoring and control system 60 relating to the product (dimensions, material, etc.), data relating to the operation of the furnace on the basis of measurements taken by sensors (temperatures, pressures, oxygen content in the flue gases, etc.), with these measurements being able to be carried out at several points per furnace regulation zone, [0150] Step 5: On the basis of the data available in the server 50, and by means of mathematical models, a computer program implemented in a digital processing module S3 computes the average temperatures for discharging product on these two faces, as well as the thermal paths followed by each of these faces. The average temperature computed on the upper face constitutes the result R4. [0151] Step 6: A computer program implemented in a digital processing module S4 compares the average temperature of the upper face of the product upon discharging that is obtained by simulation (result R4) and that obtained through a measurement with the infrared camera 20 (result R2), then delivers, as a result R5, a factor of the difference between results R2 and R4 to the server 50. [0152] Step 7: On the basis of the data available in the server 50, and by means of mathematical models, a computer program implemented in a digital processing module S5 computes the difference in the 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, determines, as a result R6, a ratio of overall proportions of bonded and non-bonded scale on the upper face of the product and, as a result R7, a ratio of overall proportions of bonded and non-bonded scale on the lower face. [0153] Step 8: A computer program implemented in a digital processing module S6 determines a difference between the ratio of overall proportions of bonded and non-bonded scale on the upper face of the product that is obtained by simulation (result R6) and that obtained by a measurement from the infrared camera (result R3) and, depending on this and the initial value of the ratio of bonded and non-bonded scale proportions on the lower face (result R7), delivers, as a result R8, a corrected ratio of overall proportions of bonded and non-bonded scale on the lower face. [0154] 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. These data are processed by a computer program implemented in a digital processing module S7 that delivers, as a result R9, the total average thickness of the primary scale on the two faces of the product. [0155] Step 10: On the basis of the data available in the server 50 relating to the dimensions of the product and the total average thickness of the primary scale on the two faces of the product obtained by the optical sensors (result R9), a computer program implemented in a digital processing module S8 delivers the measured loss on ignition as a result R10. [0156] Stage 11: A computer program implemented in a digital processing module S9 compares the loss on ignition determined by means of the optical sensors (result R10) with the ratio of non-bonded scale on the upper face determined from the infrared camera (result R3) and that of the lower face after correction (result R8) and delivers, as a result R11, the amount of non-bonded scale that has fallen into the furnace. [0157] Step 12: A computer program implemented in a digital processing module S10 gathers and processes the process data available in the server 50, the loss on ignition (result R10) and the volume of scale that has fallen into the furnace during heating (result R11), and delivers, as a result R12, a process report that feeds a database 51. [0158] Step 13: On the basis of data from the database 51, a computer program implemented in a digital processing module S11 regularly delivers, by self-learning as a result R13, an optimized law for predicting loss on ignition. [0159] 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, as a result R14, an optimal heating strategy (thermal path of the product, oxygen content in the furnace, etc.) for minimizing the amount of scale formed when heating the product that it sends to the furnace monitoring and control system 60.

KEY FOR FIG. 7

[0160] 20: Infrared camera

[0161] 30: Optical sensor at the inlet of the descaling machine

[0162] 40: Optical sensor at the outlet of the descaling machine

[0163] 50: Scale computer server

[0164] 51: Process database

[0165] 60: Furnace monitoring and control system

[0166] S1 to S12: Digital processing modules comprising computer programs

[0167] R1: A reconstituted image of the entire upper face of the product showing the distribution of the bonded scale and of the non-bonded scale on the upper face of the product (measurement).

[0168] R2: Average temperature of the upper face of the product (measurement).

[0169] R3: Proportion ratio of the bonded scale and of the non-bonded scale on the upper face of the product (measurement).

[0170] R4: Average temperature of the upper face of the product (simulation).

[0171] R5: Variance factor between the average temperature of the upper face determined on the basis of the infrared camera (result R2) and that obtained by simulation (result R4).

[0172] R6: Proportion ratio of the bonded scale and of the non-bonded scale on the upper face of the product (simulation).

[0173] R7: Proportion ratio of the bonded scale and of the non-bonded scale on the lower face of the product (simulation).

[0174] R8: Corrected proportion ratio of the bonded scale and of the non-bonded scale on the lower face of the product.

[0175] R9: Total average thickness of the primary scale upon entering the descaling machine.

[0176] R9: Non-bonded scale surface of the lower face of the product.

[0177] R10: Loss on ignition.

[0178] R11: Amount of non-bonded scale from the lower face of the product that has fallen into the furnace.

[0179] R12: Furnace process data

[0180] R13: Loss on ignition prediction law.

[0181] R14: Optimal heating strategy for limiting loss on ignition.

[0182] As shown in FIG. 10, the furnace according to the invention is monitored and controlled from: [0183] a system L3 for optimizing the operation of the level 3 furnace on the basis of input data relating to the products to be reheated (dimensions, weight, steel composition, rolling conditions, etc.) and process data, in particular the target discharging temperatures; [0184] a system L2 for optimizing the regulation of the level 2 furnace on the basis of the instructions provided by the system L3 for optimizing the operation of the furnace, process data (product heating curves and data LO provided by the instrumentation of the furnace); [0185] a “Machine learning” computer program L2′ improving the system L2 for level 2 optimization of furnace regulation by self-learning on the basis of results R1 of digital simulations of the amount of scale and the temperature of the product and of results R2 of the amount of scale determined by digital processing D on the basis of the data M supplied by the infrared camera 20 and the optical sensors 30, 40 for measuring thickness on the descaling machine; [0186] a system L1 for controlling the equipment of the furnace using level 1 local control loops on the basis of the instructions provided by the system L2 for optimizing the regulation of the furnace and data LO provided by the instrumentation of the furnace.

[0187] The furnace monitoring and control 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.

[0188] For normal production of a slab reheating furnace of 360 products per day, this represents approximately 43 gigabytes of data per day. In order to obtain useful information for controlling the furnace from this very large amount of data, algorithms (also called Data Science) are applied. They allow the essential information to be extracted from the measurements that are carried out, while ensuring their reliability despite the difficult environment of a pre-rolling reheating furnace. The furnace monitoring and control system thus uses key information to intelligently heat the products in the furnace by managing the formation of scale during heating, in particular based on key process variables, such as: [0189] the thermal path and the residence time of the product in the critical zones of the furnace; [0190] the atmosphere of the furnace; [0191] the composition of the steel.

[0192] FIG. 11 is a diagram showing the tests carried out for different operating conditions in order to verify the performance of the optimized law for predicting loss on ignition (result R13) according to the invention. The product number is shown on the abscissa and the amount of loss on ignition is shown on the ordinate. On this diagram, the diamonds correspond to the losses on ignition obtained by measurements on samples and the squares represent the losses on ignition determined with the optimized prediction law. It can be seen that the optimized prediction law yields results that are very close (with less than 10% variation on average), to those observed on the samples.

[0193] Of course, the invention is not limited to the examples that have just been described and numerous modifications can be made to these examples without departing from the scope of the invention. In addition, the various features, forms, alternative embodiments, and embodiments of the invention can be grouped together in various combinations as long as they are not incompatible or mutually exclusive.