Multi-plug tuyere and use thereof in steel treatment

Abstract

The present invention relates to a constructive arrangement of a multi-plug tuyere with two or more different diameters of the internal gas injection pipes to reduce wear and increase rinsing efficiency in convertors during the combined blowing process for the treatment of steel in steel mills.

Description

[0001] MULTIPLUG TUBE AND ITS USE IN STEEL TREATMENT AMPO DA I NVENÇÃO

[001] The present invention is in the technical field of Metallurgical Engineering and relates to a multi-plug tuyere for converters. The present patent application also relates to the use of said multi-plug tuyere in the treatment of steel. BACKGROUND OF THE INVENTION

[0002] The steelmaking process in BOF (Basic Oxygen Furnace) converters begins with the loading of hot metal, steel scrap, lime, and fluxes. Through the blowing of oxygen, elements such as carbon, silicon, manganese, and iron itself are transformed into oxides that are either released into the slag or incorporated into the gas (CO and CO2). This process, also called primary refining, is the lifeblood of modern steel mills. The steel is then poured into the ladle, which assists in the subsequent treatment of the steel, called secondary refining (Ladle Furnace, Degasser-RH, Bubbling Station, etc.). In this stage, the steel undergoes degassing, desulfurization, decarburization, deoxidation, and heating processes.

[0003] There are three operating methods in the BOF converter: • Top oxygen blowing through a chilled lance, where oxygen, at high pressure and velocity, penetrates the metal bath, promoting the removal of carbon, phosphorus, and other elements; • Bottom oxygen blowing through tuyeres submerged in the metal bath, where oxygen and inert gas are injected. In some practices, lime, coal, and hydrocarbons (oil and / or natural gas) are also injected; • Combined blowing, characterized by top oxygen blowing and additional agitation by bottom inert gas injection through tuyeres.

[004] Top blowing only promotes gentle agitation and the mixing of the metal with the slag is not intense. As a result, the steel produced is more oxidized, with a lower manganese content and higher oxygen and nitrogen contents at the end of blowing, compared to combined blowing.

[0005] The combined blowing process's major advantage was bringing the reactions between slag and metal close to thermodynamic equilibrium, also ensuring better thermal and chemical homogenization of the bath.

[006] Combined blowing in the converter increases bath agitation and reduces stagnation areas in the central region of the bottom, especially at the end of the blowing process, when CO generation falls due to the reduction in the steel's carbon content. The injection of argon through the bottom promotes additional agitation, favoring dephosphorization, increasing manganese yield and reducing the iron content in the slag. With improved refining conditions, there is an increase in metal yield, a reduction in flux consumption, and an increase in refractory life. (LIMA, H. Physical modeling of combined blowing in BOF converters. Master's Dissertation in Metallurgical and Mining Engineering – School of Engineering of UFMG, Federal University of Minas Gerais. Belo Horizonte, pp. 1 and 2. 2011.)

[0007] Argon injection through the bottom of the equipment is performed by special parts, called tuyeres, composed of a refractory block, internally composed of stainless steel tubes (multi-plug), which conduct the gas. The useful life of a tuyere is generally shorter than that of a converter, requiring its interruption to prevent wear on the rest of the converter. Current rates are around 50% of the converter's life, meaning half of the remaining runs operate without the combined blow, compromising steel quality and consequently leading to operational losses.

[0008] During gas injection, fluid dynamic phenomena occur, causing premature wear of the tuyere, forcing its closure over time, interrupting the agitation process and compromising steel quality.

[0009] Gas expansion generates different flow profiles, causing interaction between the argon jet and the refractory.This profile is controlled by the gas flow rate, argon tube diameter, and injection pressure.

[0010] There are three types of gas flow regimes: bubbling regime, transition regime, and back attack regime. Erosion occurs through bubble expansion (cavitation) and back attack, which cyclically causes severe erosion of the tuyere.

[0011] In searching for prior art in scientific and patent literature, the following documents dealing with the subject were found:

[0012] Japanese patent JPH068450 discloses a method for improving the operation of a large top-bottom converter for steel processing. However, this document discloses a refractory block with proportions different from the present invention without evidencing the characteristics of the proportions of the tuyeres contained in a single refractory block, in addition to also guiding a skilled artisan in adjusting the gas flow rate by controlling valves.

[0013] Brazilian patent application BR102020014409-0 discloses a tuyere comprising a concentric inner tube to generate a central jet and an outer gas injection tube to prevent the inner jet from dispersing. However, this type of central jet is very different from a block containing multiple tubes and generates a lower yield in the steel decarburization process due to the smaller surface area of ​​the steel with the gas compared to a block containing several tubes of the present invention.

[0014] Brazilian patent BR112016022757-3 discloses a multi-plug tuyere with a hexagonal spatial arrangement of the tuyere tubes. However, this document does not disclose the proportions of the tuyeres according to that of the present invention.

[0015] The aforementioned master's dissertation (LIMA, H., 2011) defines the general state of the art, but should not be considered of particular relevance to the innovative and inventive characteristics, such as the constructive arrangements and proportions of the tuyeres of the present invention described below.

[0016] Thus, no technologies were found in the state of the art that solved the technical problem of loss of steel quality and, consequently, operational losses in steel treatment, due to premature wear of the tuyeres caused by fluid dynamic phenomena that occur due to the expansion of bubbles (cavitation) and back attack. Such premature erosion forces the tuyere to close over time, interrupting the agitation process and negatively affecting the quality of the steel.

[017] Thus, in order to solve the constant problems of the prior art, the Applicant developed a constructive arrangement of the multiplug tuyere of the present invention that reduces / prevents premature wear of multiplug tuyeres contained in converters during the combined blowing process for steel treatment. BRIEF DESCRIPTION OF THE FIGURES

[018] Figure 1 shows details of the back attack during the injection of a gas into a liquid medium.

[0019] Figure 2 shows the different erosion mechanisms due to bubble expansion and back attack during the injection of gas into a liquid medium.

[020] Figure 3 shows the bubbling profile for different flow rates.

[021] Figure 4 shows the relationship between the increase in gas flow rate in relation to mixing time and wear rate.

[0022] Figure 5 shows the arrangement of the different diameters (A and B) of the stainless steel inner tubes of the tuyere of the present invention.

[023] Figure 6 shows a front perspective view (left view) and a rear perspective view (right view) of the tuyere of the present invention.

[0024] Figure 7 shows a left side view of the tuyere of the present invention.

[025] Figures 8a to 8d show the 2D drawing of the tuyere for simulation in a mathematical model.

[0026] Figure 9 shows a 3D drawing defining the volume occupied by the fluids showing the cylindrical region around the outlet of the tuyere of the present invention, having a diameter of 90 mm and a height of 120 mm in a simulation of the mathematical model.

[0027] Figure 10 shows the side and top views of the mesh for simulation of the mathematical model, with 964,768 nodes and 942,435 elements.

[028] Figures 11 to 14 show a comparison between the gas flow rates (volume fraction of argon) between the standard design (EAR 2428) and the present invention (PROP-4) between the time interval up to the value of 1.2 ms for the flow rate of 150 Nm³ / h.

[029] Figure 15 shows the comparison for different flow rates (volume fraction of argon) for the standard design (EAR2428), which shows the different flow profiles (bubbling, transition and back attack). DETAILED DESCRIPTION OF THE INVENTION

[030] The present invention solves the problems of the prior art through the use of the constructive arrangement of a multi-plug tuyere with two or more different diameters in the internal gas injection tubes to reduce wear and increase rinsing efficiency in converters during the combined blowing process for treating steel in steel mills.

[0031] In a first embodiment, the present patent application relates to a multi-plug tuyere comprising two or more diameters in the internal tubes for gas injection, in which the diameter of the first tube is different from the other diameters of the other internal tubes, respecting a symmetrical distribution of said tubes and in which the diameter of the internal tubes varies between 1 and 3 mm.

[0032] In a preferred embodiment of the tuyere of the invention, the diameter of the tubes further varies between 1.5 and 3 mm, more preferably between 2.0 mm and 2.25 mm.

[0033] In another preferred embodiment, the tuyere comprises more than two tubes that are positioned so that the distance between the tubes is the same; and the tubes are positioned alternatively, in relation to the size of the tube diameter, in which a first tube with a first diameter is horizontally and vertically positioned next to a second tube with a second diameter.

[034] In another preferred embodiment, the tuyere comprises between 1 and 127 internal tubes, preferably between 40 and 100 internal tubes, more preferably 60 internal tubes.

[0035] The internal tubes of the tuyere of the present invention are preferably made of stainless steel.

[036] In a particular embodiment, the tuyere has a refractory block with polygonal shapes, such as trapezoidal, square, rectangular and / or combinations thereof, preferably trapezoidal.

[037] The term “tuyere” is understood herein as special refractory pieces that internally have inert gas passage channels. These channels can be tubular, porous brick or “slit”. The block can be trapezoidal to facilitate the assembly of the refractory lining, but in the center, the assembly can be circular, which internally contains stainless steel tubes.With a fixed internal diameter per tuyere, presenting internal tube diameters that vary between 1 and 3 mm, since diameters smaller than 1 mm would result in difficulty in passing the gas and diameters larger than 3 mm can generate infiltrations.

[0038] For the sake of descriptive sufficiency, the production process of the multi-plug tuyere of the present invention generally comprises the steps of (a) preparing a refractory mixture, based on MgO, graphite and additives; (b) assembling in a template the stainless steel tubes, arranged in the design arrangement, inside the tuyere mold, interspersing tubes of different diameters, preferably, alternating between tubes for each specified diameter; (c) adding the refractory material, filling the mold and between tubes to accommodate the material; (d) isostatic pressing, to ensure the resistance of the multi-plug tuyere; (e) curing the material and (f) final finishing.

[039] In a second embodiment, the present invention provides the use of the multi-plug tuyere in converters in combined blowing methods in steel treatment.

[040] The tubes of the present tuyere inject inert gas, optionally argon or nitrogen gas.

[041] In a preferred embodiment of the use of the tuyere of the present invention, the internal tubes with two or more different diameters modify the kinetic effect on the flow of gases, generating a performance gain for the steel produced and reducing tuyere wear.

[042] The tuyere of the present invention is preferably used at the bottom of converters to treat steel in the combined blowing method.

[0043] The use of the tuyere of the present invention acts on the combination of fluid dynamic phenomena, resulting in wear compensation, avoiding erosion by bubble expansion (cavitation) and back attack, which cyclically causes serious erosion of the tuyere.

[044] As shown in Figure 1, the gas expands and then collapses, triggering a cyclical process of gas impact on the refractory, as can be seen in the details of the back attack during the injection of a gas into a liquid medium.

[045] Increasing the gas flow rate decreases the mixing time, but not as pronounced between flow rates 1 and 2. Where, above 3, there are no improvements, and a negative effect occurs, resulting in an exponential increase in wear, as can be seen in Figure 4.

[0046] The distribution of the internal argon gas injection tubes can be seen in the tuyere of Figure 6 (front perspective view on the left). EXAMPLES

[0047] There is a dimensionless number that correlates the fluid dynamic effects. This dimensionless number is also called the Mass Velocity Dimensionless (NG) which depends on the exit velocity of the gases and their density. The speed depends on the inlet flow rate and the diameter of the gas injection tube. N_G=(ρ.ν) / (ρ^*.ν^* ) where: ρ : gas density at working temperature and pressure; ν : gas velocity at the tuyere; ρ^*: gas density (1 bar, 20ºC); ν^* : speed of sound in air (1 bar, 20ºC). where: N_G < 1.0 – bubbling regime; N_G = 1~2 – transition; N_G > 2.0 – developed jet.

[048] By controlling the NG, for the same operating flow rate, it is possible to minimize the erosion effects caused by fluid dynamic phenomena, that is, a larger inner tube diameter would result in a lower speed and a smaller inner tube diameter at a higher speed.

[049] Therefore, by controlling the flow regimes of the internal tube, regardless of whether the inlet flow rate varies, at the outlet there are three types of regime (bubbling regime, transition regime and back attack regime), being mixed between the tubes, which promotes the interaction of the outlet gases, avoiding erosion, due to the breakdown of this effect.In other words, while one tube generates the bubble-like phenomenon, the other on the side forms the back attack. Because they are close together, the gases interact. Therefore, both tend to shift to the transition regime (equilibrium regime), minimizing the erosive effects of each extreme regime.

[050] The improved technical effects achieved by the tuyere of the present invention are that, through the different diameters of internal tubes in the same multi-plug refractory, the tube flow regimes are controlled, which leads to improved tuyere kinetics and, thus, a more efficient agitation system that increases tuyere performance and life.

[051] In more detail, the operational advantage of this invention is a more efficient agitation system. Initially, during the back attack, part of the agitation energy is used to impact the refractory (return). That is, by reducing the back attack, all the gas kinetic energy will be used to agitate the metal bath.

[0052] Back attack typically occurs at high gas flow rates. This occurs when the operator wants to increase agitation efficiency (improve the steel's chemistry). However, as can be seen in Figure 4, this increase is not linear; that is, there is a limit, above which, increasing the flow rate leads to a higher wear rate.

[0053] Initially, there is a high availability of elements to react, including carbon and silicon. As they are consumed by the oxidation reaction via oxygen blowing from above, the reaction becomes more difficult to occur spontaneously. In this case, combined blowing through tuyeres promotes this interaction more quickly. Preferably, the chemical elements will interact with dissolved oxygen at the inert gas bubble interface; that is, more and smaller bubbles are more effective for combined blowing efficiency.

[0054] In addition to agitating the metal bath, the bubbles also increase the reaction kinetics. Therefore, the combined blowing pattern varies throughout the steel production cycle.

[0055] Treatment time varies from 20 to 40 minutes. Initially, a lower flow rate is used because the reactions occur spontaneously. However, toward the end, around 80% of the treatment time, the gas flow rate from the tuyeres is increased to compensate for this process difficulty.

[0056] Industrial flow rates range from 1 to 5 Nm³ / ht. This rate is specific, that is, it depends on the converter's capacity. Large BOFs require a much larger volume of inert gas than small converters. Working pressures vary depending on the equipment, ranging from 8 to 30 kgf / cm², which modifies the density of the gas injected through the tuyeres.

[0057] The interactions between bottom blowing, tuyere, and steel agitation can be studied using physical and / or mathematical models. The fundamentals of modeling are presented below. E. XEMPLO 1 – M ODELAGEM F ÍSICA

[058] The examples shown here are intended solely to exemplify one of the numerous ways of carrying out the invention, without, however, limiting its scope.

[059] Physical modeling of a 224-ton capacity converter was performed on a 1:8 scale, with the aim of simulating the operational conditions of combined blowing and a new tuyere configuration.

[0060] The aim was to establish the best operational conditions, reducing mixing time and increasing the useful life of the tuyeres, thus providing a series of gains, such as increased metallic yield, better chemical homogenization of the steel, reduced lime consumption and reduced specific refractory consumption. C ONSIDERAÇÕES E APPROACHES MADE NAMODELAGEMGENERAL

[061] In order to comparatively evaluate the present invention, it was decided to perform a mathematical modeling of the proposed system. In this case, the technique of solving differential equations (fluids), via the Finite Volume Method (FVM), is recommended for this type of analysis. For this, specific software is used, which is used to design the proposed system. A discretization of the Control Volume is performed, inserting boundary conditions and properties of the fluids involved. From this tool, it is possible to visualize the fluid dynamics that occur at the gas outlets through the tuyere injecting into the molten steel.

[0062] In this case, some technical considerations were made (incompressible fluid, argon density estimated by the general gas law, isothermal system) so that the simulation represents something close to reality. This tool (Finite Volume Method) is worldwide recognized for simulations of fluid dynamic processes.

[063] In the adopted model, a cylinder cut was highlighted above the tuyere (Control Domain) to represent what happens at this gas outlet.

[064] Two models were compared, a standard one with the same diameter (EAR 2438) and the constructive arrangement of the present invention with alternating tube diameters (PROP-4). In the case of EAR 2438, the diameter was fixed at 2 mm, for 60 tubes and in the case of PRO-4, 30 tubes of 1.9 mm and 30 tubes of 2.1 mm, distributed alternately, symmetrically.

[065] Transient analysis of a small cylindrical region around the tuyere outlet with a diameter of 90 mm and a height of 120 mm, being the control volume for analysis.

[066] From the density of argon estimated by the law of ideal gases considering the bath temperature and an extra pressure of a 2 m steel column, in the dispersed region, the argon forms bubbles of 2 mm in diameter.INITIAL AND BOUNDARY CONDITIONS

[0067] The following conditions were considered: Initial condition: steel at rest inside the entire domain. Injector ducts: uniform flow of 20, 150 or 240 Nm³ / h of argon. Side and bottom of the domain: hydraulically smooth walls. Top of the domain: opening condition that allows. output of all phases and the eventual input of steel. TABLE 1. CONSIDERED PHYSICAL PROPERTIES OF STEEL AND ARGON

[0068] The comparative images between the qualitative results of the simulation of the fluid dynamic effect of the injection of argon gas through the tuyere of the present invention, at a uniform flow rate of 150 Nm 3 / h, during 0 ms to 2.0 ms, can be seen in figure 15. TABLE 2. QUANTITATIVE RESULTS

[069] During the entire simulation, 150nm was defined 3 / h for the standard design (EAR-2438).

[0070] To compare the performance of the PROP-4 and EAR-2438 tuyeres, a time instant close to the initial one (t = 0.2 s) was taken as reference, since, as the two tuyeres have the same height and different diameters, the volume of the simulated domains in each case is different.

[071] Therefore, the tuyeres in the simulations agitate initially different volumes of steel with the same gas flow rate, which vary with time at different relative velocities.

[072] The comparison is facilitated when the steel volume was practically unchanged in each case, which occurs near the beginning of the simulation. TABLE 3. QUANTITATIVE RESULTS

[073] During the entire simulation, 150nm was defined 3 / h for the standard design (PROP-4).

[074] In the value highlighted in Table 3 above, it was observed that the specific surface area was larger for the present invention, which means greater interaction of the metal with the injected gas bubble. In this case, a benefit to facilitate the thermodynamic reactions involved.

[075] The quantitative results presented indicate that the PROP-4 tuyere (present invention), due to its larger diameter, provides less coalescence of the gas jets coming from each hole.

[076] As a consequence, the specific surface area of ​​the gas is larger for the PROP-4 tuyere, even though the volume of stirred steel is also larger.

[077] This indicates that the metal-gas interaction is greater for the PROP-4 tuyere (invention) than for the EAR-2438 tuyere (prior art), which implies higher heat and mass transfer rates between the liquid steel and the injected gas.

[0078] As a way of visualizing the fluid dynamic effects, a comparison between the effect of the argon gas flow at a flow rate of 150 Nm. 3 / h, for 0 ms to 1.2 ms, comparing the standard situation and the present invention, can be seen in figures 11 to 14.

[079] The comparative analysis of the flow rates of 20, 150 and 240 Nm³ / h for the standard (EAR-2428) allows us to conclude that: • For the lowest flow rate, the gas outlet is stable and homogeneous, the gas expands between the tuyere holes tending to cover its surface; • With the progressive increase in the flow rate, the gas jets from each hole become unequal in size and shape; • In addition, transient patterns begin to occur, including the eventual release of bubbles, which may later break. • These transient patterns can lead to refractory wear through the back attack mechanism.

[0080] The quantitative results when compared with the two proposals presented indicate that the two tuyeres have practically the same bath agitation capacity measured by the total momentum (amount of movement) transmitted to the bath, with an advantage for the PROP-4 tuyere (invention).

[081] Nevertheless, the tuyere of the present invention (PROP-4) promotes this agitation with lower speeds in its surroundings, which leads to less wear.

[082] Furthermore, the PROP-4 tuyere has a lower tendency to release bubbles and, consequently, is less subject to the “back-attack” phenomenon.

[0083] The mathematical modeling of the combined blowing allows the understanding of the agitation conditions and chemical and thermal homogeneity of the steel.

[0084] Those skilled in the art will value the knowledge presented herein and will be able to reproduce the invention in the presented modalities and in other variants and alternatives, covered by the scope of the following claims.

Claims

CLAIMS 1. MULTIPLUG TUBE, characterized by comprising two or more different diameters in the internal gas injection tubes; in which the diameter of the first tube is different from the other diameters of the internal tubes, and in which said diameter of the internal tubes varies between 1 to 3 mm.

2. MULTIPLUG TUBE, according to claim 1, characterized by the diameter of the internal tubes varying between 1.5 to 2.25 mm. 3 . VENTANEIRA MULTIPLUGUE, de acordo com qualquer one of claims 1 or 2, characterized in that the two or more tubes are positioned so that the distance between the tubes is the same.

4. MULTIPLUGATE FAN, according to claim 3, characterized in that the two or more tubes are positioned in relation to the size of the tube diameter, in which a first tube with a first diameter is horizontally and vertically positioned next to a second tube with a second diameter. . VENTANEIRA MULTIPLUGUE, de acordo com qualquerone of claims 1 to 4, characterized in that it comprises between 1 to 127 internal tubes.

6. MULTIPLUGATE TUBE, according to claim 5, characterized in that it comprises between 40 to 100 internal tubes. 7 . VENTANEIRA MULTIPLUGUE, de acordo com qualquer one of claims 1 to 6, characterized in that the internal tubes are made of stainless steel.

8. VENTANEIRA MULTIPLUGUE, de acordo com qualquer one of claims 1 to 7, characterized in that it presents a refractory block with polygonal shapes, such as trapezoidal, square, rectangular and / or combinations thereof.

9. MULTIPLUGATE TUBE, according to claim 8, characterized in that the polygonal shape comprises the trapezoidal shape.

0. USO DA VENTANEIRA MULTIPLUGUE, caracterizado for use in converters during the combined blowing process for treating steel in steel mills.

11. USE, according to claim 10, characterized by injecting inert gas.

12. USE, according to either of claims 10 or 11, characterized by being used at the bottom of converters.

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