EP3956482A1

EP3956482A1 - Method to control exhaust fumes aspiration during a steelmaking process

Info

Publication number: EP3956482A1
Application number: EP19726148.0A
Authority: EP
Inventors: Grégory MAES; Jean-François QUENTON; Jean-Baptiste PIOT; Gabriel Vergniez
Original assignee: ArcelorMittal SA
Current assignee: ArcelorMittal SA
Priority date: 2019-04-15
Filing date: 2019-04-15
Publication date: 2022-02-23
Also published as: UA127824C2; ZA202106562B; BR112021018781A2; WO2020212727A1; MX2021012622A; WO2020212782A1; CA3133389A1

Abstract

A method to control exhaust fumes aspiration during a steelmaking process in a steelmaking ladle, the method comprising the following steps: - Capturing at least one image of flames escaping from the top of the steelmaking ladle, - Calculating at least one value representative of the size and/or the intensity of the flame based on the at least one captured flame image, - Measuring a pressure representative of the pressure of the aspired fumes, - Controlling the aspiration of fumes based on said value representative of the flame and on the measured pressure.

Description

Method to control exhaust fumes aspiration during a steelmaking process

[001 ] The invention deals with a method to control exhaust fumes aspiration during a steelmaking process.

[002] In a steelmaking process, such as a converter process, pig iron is poured into a ladle to be turned into steel, notably through decarburization. To do so oxygen is injected into the molten metal so that carbon contained in the pig iron reacts with O2 and form CO and CO2 in gaseous forms. This process thus generates a lot of fumes. A converter is illustrated in figure 1. It usually comprises a ladle 2 containing molten metal and is overtopped by a fumes extraction device 3 to capture those exhaust fumes. This extraction device 3 is movable so as to be removed not to block the ladle 2 tilting when material is charged into the ladle or molten steel is discharged. This extraction device 3 comprises, on its end closest to the ladle, a skirt 4 which is used to reduce the gap 5 between the extraction device 3 and the lip 6 of the ladle, depending on the steelmaking process stage. At the beginning of the steelmaking process, or during scrap charging, a big quantity of CO is formed which is explosive in atmosphere containing more than 6% of oxygen. There is so need for air to get in contact with CO so as to reduce the 0₂ content and let CO be turned in CO2 by reaction with oxygen. During these stages, the skirt 4 of the extraction device is moved away from the lip 6 of the ladle so the gap is large. In the steady state, the skirt 4 is either close to the lip 6 and the gap 5 is for example of 10 cm, or it may be over the lip, so as to extract most of the fumes and avoid their release into the atmosphere. Once captured these fumes are generally cleaned to remove dust particles and their heat is reused in the plant.

[003] The quantity of recovered fumes is notably linked to the aspiration performed by the extraction device. Said aspiration may be controlled by aspiration means such as venturies, fans or shutters integrated into the fumes extraction device. If there is an over-aspiration the pressure inside the extraction device is high and it may damage the extraction device, it also implies that outside air enters the extraction device together with the fumes. This air being colder than the fumes it creates temperature variations which have a thermal impact on the equipment and reduces its lifetime. On the contrary in case of under-aspiration, fumes may escape from the aspiration and be released into the atmosphere which is detrimental for environment and they may damage the surrounding equipment such as cable cranes. Moreover, pressure fluctuations are detrimental to the lifetime of the extraction device and it’s necessary to keep the pressure of the extracted fumes as constant as possible.

[004] Currently, this aspiration control, via the shutters opening for example, is a human controlled device, which presents several disadvantages, such as the delay on shutters opening, security reasons etc. Besides,‘over-aspiration’ and ‘under-aspiration’ happen frequently in a steelmaking process with this human control, as results, both the performance of the process and the quantity of recovered fumes are not optimal. [005] What has been previously explained for a steelmaking process in a converter is also true for an AOD converter or an Electric Arc Furnace.

[006] There is so a need for a method to accurately control the aspiration of fumes which are extracted from a steelmaking process. Another aim of the invention is to decrease the environmental impact of the steelmaking process and to improve the lifetime of the fumes extraction device.

[007] This problem is solved by a method according to the invention which is a method to control exhaust fumes aspiration during a steelmaking process in a steelmaking ladle, the method comprising the following steps:

- Capturing at least one image of flames escaping from the top of the steelmaking ladle,

- Calculating at least one value representative of the size and/or the intensity of the flame based on the at least one captured flame image,

- Measuring a pressure representative of the pressure of the aspired fumes,

- Controlling the aspiration of fumes based on said value representative of the flame and on the measured pressure. The method of the invention may also comprise the following optional characteristics considered separately or according to all possible technical combinations

- the at least one value representative of the flame is at least one value representative of the flame size,

- the at least one value representative of the flame size takes into account the light intensity of the flame,

- the pressure representative of the pressure of the aspired fumes is the difference between the pressure of the aspired fumes and the atmospheric pressure.

[008] The invention is also related to a device to control an exhaust fumes extraction device during a steelmaking process in a steelmaking ladle, said device comprising:

- a camera able to capture at least one image of flames escaping from the top of the steelmaking ladle,

- a processor able to calculate at least one value representative of the flame based on the at least one captured flame image,

- means to measure a pressure representative of the pressure of the aspired fumes,

- a controller able to control the aspiration of the fumes based on said value representative of the flame and on the measured pressure

The device of the invention may also comprise the following optional characteristics considered separately or according to all possible technical combinations the steelmaking ladle is a converter,

- the exhaust fumes extraction device has a skirt and the means to measure the pressure are located on said skirt,

- the steelmaking ladle is an electric arc furnace,

- the means to measure the pressure are located at the gap between the exhaust fumes extraction device and the electric arc furnace,

- the camera is a camera in the visible spectrum,

- the camera is an IR camera. Other characteristics and advantages of the invention will appear at the reading of the following description.

[009] In order to illustrate the invention, trials have been performed and will be described by way of non-limitative examples, notably in reference to figures which represent:

- Figure 1 illustrates a device for a steelmaking process according to an embodiment of the invention

- Figure 2 is an example of a flame captured image

- Figure 3 is curves representing respectively N₂, CO, C0₂ and Fl₂ content of extracted fumes with and without using a method according to the invention

[0010] As previously explained figure 1 illustrates a converter to perform a steelmaking process. A converter is a specific example of a device to perform a steelmaking process but the invention may be applied to any appropriate device to perform a steelmaking process, such as an AOD or an Electric Arc Furnace. The ladle 2 is overtopped by a fumes extraction device 3 comprising a tube 9 through which fumes are aspired and then circulated into a cleaning unit (not represented). Aspiration within the tube 9 is controlled by control means such as shutters 7A, 7B, fan 8 or venturies (not represented). Those control means may indifferently be located upstream, downstream or inside the cleaning unit. The extraction device 3 also comprises a skirt 4 on the side directed to the lip 6 of the converter, i.e. towards the top of the ladle 2. The skirt 4 is movable and forms a gap 5, whose height may vary depending on the process stage, with the ladle lip 6. Flames 10 are formed by the reactions occurring within the ladle and they can either be visible within the gap 5 or escape from this gap, as illustrated in figure 1. In a device according to the invention, at least one camera 1 1 is positioned so as to be able to capture at least one image of said flame. The camera may be a camera in the visible spectrum or an Infrared camera, either near (wavelength 0,75-1 ,4 pm) or long IR (8-15pm). The captured flame image is then sent to a processor 12, which is able to calculate at least one value representative of the flame, based on the at least one captured flame image. This value maybe for example a number of pixels occupied by the flame image within a given frame, a height, a width or an intensity of the flame. In a preferred embodiment this value is the number of pixels in a given frame, expressed in percent, multiplied by the percentage of the captured image which is saturated. An example of captured image is illustrated in figure 2. In this example, the filling rate of the flame in the white frame is of 28% and the saturation rate, which corresponds to the percentage of white flame is of 14.5%, which gives a representative value V_f of the flame of 17.

[001 1 ] This representative value V_f is sent to a controller 14 which combines it with a pressure representative of the pressure of the aspired fumes V_p. This pressure is measured by pressure sensors 13 which may be located for example in the skirt 4. Either directly the measured pressure, or the difference between this measured pressure and the atmospheric pressure, may be used by the controller 14 in combination with the representative V_f value of the flame. This pressure may also be an average value of previous measurement. For example, an average value of the difference between measured pressure at skirt level and the atmospheric pressure has been used in the example of figure 2, which represents a value V_p of 5 Pascal (Pa). Based on those two values, the representative value of the flame V_f, and the representative pressure V_p, the controller is able to detect an over or an under-aspiration and then to control the aspiration means accordingly. This can be done, for example, by comparing those two values or their combination with threshold values. For example, in case of over-aspiration the shutters 7A, 7B may be shut down and/or the fan power reduced. On the opposite, in case of under-aspiration, the shutters may be opened and/or the fan power increased. The controller 14 and the processor 12 may be two distinct devices but could also be one single device able to perform all previously mentioned actions related to those two devices. The processor 12, the camera 1 1 , the controller 14, the aspiration means 7A, 7B, 8 may be either physically connected to one another or signals may be sent wirelessly from one device to another.

[0012] In the example illustrated in figure 2, the value representative of the flame V_f was of 17 and the representative pressure V_p was of 5Pa. Those two values were used in combination according to a predefined formula to give a value representative of the captured signal: V_s = AV_P + BV_f wherein A and B are calibration coefficients which may vary from one installation to another. In considered trial, A is equal to 0.4 and B to 0.6, which gives a signal value V_s of 12eqPa (this unit means equivalent Pascal). The set point of the aspiration control means was set at a pressure of 7Pa and so it means there is an over-aspiration and shutters must be opened to reduce aspiration. In this specific example shutters were used as control means but any other suitable control means could have been used.

Results [0013] Trials were done on a steelmaking process performed with a converter as the one illustrated in figure 1. One camera 1 1 in the visible spectrum was positioned on the roof of the operator desk and turned towards the gap 5 between the ladle and the skirt. The aspiration control was done at the shutters level. The steelmaking process was performed in a classical way, and during this process a 1 ^st part of the aspiration control was performed manually, as in prior art, and a 2^nd part with a method according to the invention.

[0014] Several parameters were measured, the volume of captured fumes, their nitrogen N₂ content and the NCV of the gas after cleaning. The NCV is the Net Calorific Value and represents the quantity of heat released by the combustion of 1 kg of considered product under standardized conditions. Higher the NCV is, more energy is produced by the considered product. Results are illustrated in table 1.

Table 1

[0015] As illustrated in the results, with a method according to the invention, and compared to prior art, more fumes are captured, which means less fumes are released into the atmosphere, which is good for the environment. Moreover, the captured fumes contain less N₂ which means that less air has been captured together with the fumes. The Net Calorific Value is increased, which means more energy may be produced from them which is also good for the environment as less external energy will be needed within the plant.

[0016] For the same trial, figure 3 illustrates the percentage of CO, N₂ and C0₂ within the captured fumes when using a method according to the invention (results in the dotted frame). As can be seen on the curve, N2 percentage is first reduced and then remains stable during a period which corresponds to a process window of high decarburization. It means that the system is more stable and there are less unwilling air entries. This implies less wear of the device and an increased lifetime. [0017] The method and the device according to the invention allow to reduce the environmental impact of the steelmaking process and to increase the lifetime of the fumes extraction device.

Claims

1 ) A method to control exhaust fumes aspiration during a steelmaking process in a steelmaking ladle, the method comprising the following steps:

- Measuring a pressure representative of the pressure of the aspired fumes,

- Controlling the aspiration of fumes based on said value representative of the flame and on the measured pressure.

2) A method according to claim 1 wherein the at least one value representative of the flame is at least one value representative of the flame size.

3) A method according to claim 2 wherein the at least one value representative of the flame size takes into account the light intensity of the flame.

4) A method according to claim 1 to 3 wherein the pressure representative of the pressure of the aspired fumes is the difference between the pressure of the aspired fumes and the atmospheric pressure.

5) A device to control an exhaust fumes extraction device during a steelmaking process in a steelmaking ladle, said device comprising:

a. a camera able to capture at least one image of flames escaping from the top of the steelmaking ladle,

b. a processor able to calculate at least one value representative of the flame based on the at least one captured flame image, c. means to measure a pressure representative of the pressure of the aspired fumes,

d. a controller able to control the aspiration of the fumes based on said value representative of the flame and on the measured pressure

6) A device according to the previous claim wherein the steelmaking ladle is a converter. 7) A device according to the previous claim wherein the exhaust fumes extraction device has a skirt and the means to measure the pressure are located on said skirt.

8) A device according to claim 5 wherein the steelmaking ladle is an electric arc furnace.

9) A device according to claim 8 wherein the means to measure the pressure are located at the gap between the exhaust fumes extraction device and the electric arc furnace.

10)A device according to claims 5 to 9 wherein the camera is a camera in the visible spectrum.

1 1 )A device according to 5 to 9 wherein the camera is an IR camera.