Converter blowing method

Abstract

To provide a converter blowing method that controls the foaming at a low cost while performing proper desiliconization and dephosphorization during blowing.SOLUTION: In a converter blowing method by dephosphorization blowing in a converter type refining furnace having a top blowing lance, a bottom blowing flow rate is increased by 1.4-1.7 times as well as the top blowing lance is adjusted to a higher position as long as an oxygen jet does not collide with a furnace wall when the dephosphorization is finished, and the FeO concentration in the slag is controlled to 25-35 mass% at the end of the dephosphorization blowing.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a converter blowing method for appropriately controlling forming.

Background Art

[0002] In the converter process, by blowing oxygen into the furnace, the temperature is raised while removing impurities in the molten metal, and the component concentration and temperature of the molten metal after blowing are controlled to fall within a specified range. At this time, oxygen blown from the top lance reacts with carbon in the hot metal to generate CO gas, and due to this CO gas, a phenomenon in which slag foams (hereinafter referred to as forming) occurs. If the expansion amount of the slag due to forming is large, a phenomenon in which slag overflows from the furnace (hereinafter referred to as slopping) will occur. When slopping occurs, it not only causes a decrease in iron yield, but also poses a danger to the operator and causes an operation interruption. Therefore, methods for calming or suppressing the forming of slag have been studied.

[0003] On the other hand, in recent years, the MURC (Multi Refining Converter) method has been proposed, in which a converter is used to sequentially perform hot metal pretreatment (any one or more of desiliconization, dephosphorization, and desulfurization), intermediate slag removal, refining (dephosphorization and decarburization), and tapping in a series of steps. In this MURC method, in slag control during blowing in hot metal pretreatment, a blowing technique is required to form slag to such an extent that a sufficient amount of slag can be removed while suppressing slopping due to excessive forming. Therefore, it is not preferable to completely calm the forming. However, at present, there is a problem that sufficient external oxygen for desiliconization cannot be blown because intermediate slag removal is performed before the forming intensifies, and the P concentration in the hot metal cannot be sufficiently reduced. Therefore, there is a need for a technique for suppressing forming to extend the blowing time rather than a technique for generating forming.

[0004] As a method for calming the formation of slag, generally, a calming material is added to the formed slag. For example, Patent Document 1 discloses a method of adding a carbon material within 3 minutes after the start of acid supply by an upward blowing lance as a method for suppressing the formation of slag.

[0005] In addition to the method of adding a calming material, methods for calming the formation are also known. Patent Document 2 discloses a method for calming the formation of slag in a reaction vessel different from a converter-type refining furnace, in which an opening for gas venting is formed in the slag by inserting and withdrawing a rod from the upper part of the slag. Patent Document 3 discloses a method for calming the formation, in which a jet flow is made to collide with the slag surface, and gas bubble vent holes are formed in the surface layer part of the slag by the collision force generated at that time, and the gas bubbles staying in the slag are vented. Further, Patent Document 4 discloses a method for calming the formation in a standby state where blowing treatment is not performed, in which when forming, gas is blown from an upward blowing lance.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] Compared with the forming during non-blowing, the refining reaction proceeds actively during blowing, and the forming is also intense. Therefore, in order to calm the forming during blowing, a large amount of calming material is required by the method of charging the calming material. Even if the forming is calmed, there is a possibility that the gain from calming cannot be sufficiently obtained from the perspective of cost.

[0009] Also, in the method described in Patent Document 1, since it is a method of preventing slag formation in advance, it cannot cope when forming actually occurs. In the method described in Patent Document 2, when the forming is intense, the opening for gas venting disappears immediately, and a sufficient calming effect cannot be obtained.

[0010] Also, in the method described in Patent Document 3, in addition to the existing top lance, a top lance capable of spraying gas at high pressure must be installed to calm the forming. Therefore, even if the forming is calmed, it is disadvantageous in terms of cost. Furthermore, the method described in Patent Document 4 is a method used in the standby state when the blowing process is not being performed, so it cannot cope with the slag formation that occurs during blowing.

[0011] In view of the above problems, an object of the present invention is to provide a converter blowing method that appropriately performs de-Si and de-P treatments during blowing and controls forming at low cost.

Means for Solving the Problems

[0012] In the refining process of a converter type, when oxygen gas is blown from an upper lance, the oxygen jet penetrates the slag and collides with the molten iron. The inventors of the present invention have noted that since slag is entrained from the side surface of the jet flow and the bubbles in the entrained slag are physically destroyed by the oxygen jet, there is a certain degree of foaming suppression effect by gas blowing from the upper lance. Further, as the flow characteristics of the oxygen jet, it is divided into two regions: an initial region near the nozzle where there is a potential core region (hereinafter referred to as the core region) where the velocity does not decay, and a developed region which is the region downstream thereof. The inventors of the present invention have also noted that it is the developed region where the oxygen jet spreads and entrains the surrounding fluid, and the initial region where the core region exists does not significantly contribute to the entrainment of the fluid.

[0013] Moreover, the higher the upper lance is raised, the larger the side area of the jet flow into which the slag is entrained becomes, and thus it is considered that the foaming suppression effect by the upper lance increases. However, if the upper lance is raised higher than necessary, the jet will collide with the furnace body refractory, leading to a reduction in the life of the furnace body refractory and incurring a large cost for repair. Therefore, the lance height at which the jet flow does not collide with the furnace body refractory and the foaming suppression effect is maximized was geometrically determined.

[0014] In addition, after the completion of desiliconization, a large amount of slag with a low basicity and high viscosity is generated, and the generation of CO gas is also active, so slopping is likely to occur. Therefore, it was speculated that it is necessary to set the lance height as described above after the completion of desiliconization. Here, since slopping is likely to occur after the completion of desiliconization, the timing when the height of slag foaming starts to rise after the start of blowing can be considered as the timing of the completion of desiliconization. As a method for grasping the foaming behavior in the furnace online, for example, a level meter using microwaves that travels straight even in an environment where there are dust, flames, etc. can be mentioned.

[0015] On the other hand, as described above, increasing the height of the top lance results in soft blowing, which increases the FeO concentration in the slag (hereinafter referred to as "(FeO)") and the slag amount. As a result, there is a risk of intense foaming again at the end of the blowing period. In addition, if (FeO) increases excessively, the dephosphorization ability decreases, so it is necessary to appropriately control (FeO). Therefore, the inventors have found that by adjusting the bottom blowing flow rate, it is possible to control foaming while ensuring sufficient dephosphorization ability. Here, foaming control means not only suppressing slopping but also forming foaming to such an extent that smooth intermediate slag removal can be achieved and controlling the foaming height of the slag to a desired height. The desired height is such that when the height from the molten metal surface to the furnace mouth is 100%, the foaming height of the slag is 50% or more and 60% or less.

[0016] The present invention is as follows. (1) A converter-type refining furnace having a top lance using De-phosphorization blowing perform desilication and dephosphorization treatment by A converter blowing method, set the upward oxygen blowing rate in the above dephosphorization blowing to 2.2 Nm 3 / min / t to 2.7 Nm 3 / min / t, At the timing when desiliconization is completed, the height of the top lance is set to a position satisfying the following formula (1), and the bottom blowing flow rate 、(2) is increased to 1.4 to 1.7 times, (Nm 3 / min / t) and at the end of the de-phosphorization blowing, the FeO concentration in the slag is controlled to 25 to 35 mass%. A converter blowing method characterized by this. set the forming height of the slag to be 50% or more and 60% or less of the height from the molten metal surface to the furnace mouth when the height from the molten metal surface to the furnace mouth is taken as 100%, and

Number

Advantages of the Invention

[0017] According to the present invention, during blowing, a converter blowing method can be provided that appropriately performs Si removal and P removal treatments while inexpensively controlling forming.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0019] Hereinafter, a method for controlling the formation of slag during blowing according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the refining furnace 1 has a furnace body 11 and a top blowing lance 2. The furnace body 11 is a refining vessel having an opening 12 formed at the upper part, and the inside is covered with refractory. The top blowing lance 2 is a lance that can be raised and lowered in the vertical direction (the vertical direction in FIG. 1). Oxygen gas is supplied to the top blowing lance 2 from a gas supply path (not shown) connected to the upper end side, and a jet 3 of oxygen gas is jetted from at least one nozzle hole formed at the lower end toward the slag 4 and the molten iron 5.

[0020] At the bottom of the furnace body 11, a plurality of bottom blowing tuyeres 6 are provided, and stirring gas is blown into the furnace body 11 from these bottom blowing tuyeres. The number of tuyeres of the bottom blowing tuyere is not particularly limited, but is, for example, 2 or more and 5 or less. Further, the types of gas used are roughly classified into oxygen gas and inert gas. Examples of the inert gas include nitrogen gas, argon gas, CO 2 etc. Examples of the shape of the bottom blowing tuyere include a single pipe nozzle, a double pipe nozzle, a manifold nozzle, a porous nozzle, etc. When the type of gas used is oxygen, O 2 gas is blown from the inner pipe of the tuyere of the double pipe nozzle, and CO 2 and N 2 , cooling gas such as LPG can be blown in.

[0021] Figure 2 is a schematic diagram showing a detailed structural example of the tip portion of the top blowing lance 2. Figure 2(a) shows a cross-sectional structural example of the tip portion of the top blowing lance 2, and Figure 2(b) shows a structural example of the top blowing lance 2 as viewed from the lower side in the vertical direction. In Figure 2(a), the top blowing lance 2 is composed of a triple pipe of an outer cylinder, a middle pipe, and an inner pipe. Range 21 represents the nozzle outlet diameter, range 22 represents the nozzle inclination angle, range 23 represents the nozzle hole, range 24 represents the central hole, and range 25 represents the PCD (Pitch Circle Diameter). PCD refers to the nut seat pitch diameter, which is the diameter of a circle connecting the center points of the nozzle holes existing along the concentric circumferences. In addition, although Figure 2(a) shows an example of a Laval nozzle, a straight nozzle may also be used, and there is no particular regulation regarding the lance specifications.

[0022] As described above, the jet 3 consists of a core region where the velocity does not decay and a developed region downstream thereof. When the radius of the nozzle hole is r 0 (mm), the length H core of the core region is known to be 10r 0 (see Non-Patent Document 1).

[0023] Next, in this embodiment, a specific method for controlling the formation of slag will be described. Hot metal (molten iron 5) is inserted into the refining furnace 1 shown in Fig. 1, a CaO-based flux is added, an oxygen jet is blown from the top-blown lance 2, and bottom-blown gas is blown into the molten iron, thereby starting the dephosphorization blowing. In the initial stage of dephosphorization blowing, mainly the desiliconization reaction occurs, and the operating conditions at this time may be the same as those in the prior art. Immediately after the completion of desiliconization, the concentration of SiO 2 in the slag is high, and the slag has a low basicity and high viscosity. Also, when shifting from the desiliconization period to the dephosphorization period, the generation of CO gas becomes active, and slopping is likely to occur. Therefore, in order to suppress slopping, after the completion of desiliconization, the height of the top-blown lance is set within the range that satisfies the following equations (1) and (2).

[0024] [Number]

[0025] Here, each parameter will be described with reference to Fig. 4. LH in equation (1) represents the distance (mm) from the static bath surface of the molten iron to the tip of the nozzle of the top-blown lance. H' represents the maximum lance height at which the jet flow does not collide with the furnace wall on the bath surface and is calculated from equation (2). D represents the furnace diameter (mm), and PCD represents the nut seat pitch diameter (mm) as described above. H core represents the length (mm) of the core region where the velocity of the jet does not decay in the vicinity of the nozzle in the region of the oxygen gas jet. Also, θ represents the nozzle inclination angle (deg), and α represents the half angle of jet spread (deg). Also, at the end of desiliconization, it can be judged by calculating the time until all the Si in the hot metal is oxidized theoretically from the Si concentration in the hot metal charged into the refining furnace before the start of blowing, the solid oxygen source such as sinter fines, and the top-blown oxygen supply rate during blowing.

[0026] As described above, in this embodiment, the height of the top lance is adjusted within the range that satisfies formula (2) at the end of desiliconization, but the lance height during the desiliconization period before the end of desiliconization is not particularly limited. However, if soft blowing is performed during the desiliconization period, the desiliconization reaction will be difficult to proceed, and the blowing time will become longer. Therefore, during the desiliconization period, it is preferable to lower the top lance to promote the desiliconization reaction. Specifically, it is preferable that the lance height LH is not less than 0.3H' and less than 0.5H'.

[0027] Regarding the basicity of the slag during dephosphorization blowing, from the viewpoints of slag treatment cost and lime usage cost, 1.0 to 2.0 under low basicity conditions is preferable. However, when the basicity is low, the slag becomes highly viscous, and slopping is likely to occur. Therefore, sufficient desiliconization external oxygen cannot be blown, which affects the dephosphorization reaction. Thus, generally, the viscosity of the slag is reduced by increasing the basicity to avoid slopping. However, in this embodiment, since slopping is suppressed by adjusting the height of the top lance, it is not necessary to increase the basicity. From the cost viewpoint, it is preferable that the basicity is 1.0 to 2.0. More preferably, it is 1.0 to 1.4 from the cost viewpoint. However, when the basicity is greater than 2.0, the slag may not form, and there is a possibility that intermediate slag discharge cannot be achieved.

[0028] Also, the top blowing oxygen feeding rate during blowing is not changed, and basically, oxygen is blown at a constant rate, but the oxygen feeding rate may be decreased at the end of blowing. The range of the top blowing oxygen feeding rate during blowing is based on general blowing conditions. Specifically, it is preferably 2.2 Nm 3 / min / t to 2.7 Nm 3 / min / t.

[0029] Next, the bottom blowing flow rate during blowing will be described. As described above, by raising the top blowing lance, the physical foaming effect by the jet increases, but it becomes a soft blow where the strength of the jet to the molten iron weakens, so the amount of FeO in the slag increases. When the slag amount increases with soft blowing, foaming becomes intense at the end of blowing, and furthermore, since (FeO) is excessively generated, the dephosphorization reaction does not proceed sufficiently.

[0030] Therefore, in this embodiment, by adjusting the bottom blowing flow rate (stirring power density), excessive generation of FeO in the slag is suppressed, the foaming height suitable for intermediate slag removal is controlled, and the dephosphorization reaction is promoted. Accordingly, when (FeO) is 25 to 35 mass% at the end of blowing and the height from the molten metal surface to the furnace mouth is 100%, the bottom blowing flow rate is adjusted so that the foaming height is 50% or more and 60% or less. Specifically, by making the bottom blowing flow rate (stirring power density) 1.4 to 1.7 times at the end of desiliconization, (FeO) is adjusted to 25 to 35 mass% at the end of blowing. Thereby, the foaming height is controlled to 50% or more and 60% or less.

[0031] Here, (FeO) at the end of blowing is calculated using the following formula (3) described in Non-Patent Document 2.

[0032]

Equation

[0033] In formula (3), A represents the reaction interface area (bath surface cross-sectional area) (m 2 ), F O2 represents the top blowing oxygen flow rate (Nm 3 / s / ton-flux). k s represents the mass transfer coefficient (m / s) in the slag, and V s represents the flux volume (m 3 ). t represents the blowing time (s), and (Fe t O) i: represents the initial iron oxide concentration (mass%), and all iron oxides were considered as (FeO). Also, α is a constant representing the oxidation efficiency of iron by upward blowing of oxygen, and it is a fitting parameter.

[0034] Also, regarding the amount of P removed, it shall be calculated and evaluated using the Healy Type phosphorus distribution experimental formula (4) described in Non-Patent Document 3. Here, T represents the molten iron temperature (°C).

[0035]

Equation

[0036] In this embodiment, an example of blowing a jet of oxygen gas from an upward blowing lance has been described. However, in dephosphorization refining and the like, the case of blowing a dephosphorizing agent together with oxygen gas from the upward blowing lance can be similarly applied.

Examples

[0037] Next, examples of the present invention will be described. However, these conditions are an example of the conditions for confirming the feasibility and effects of the present invention, and the present invention is not limited to the description of this example. The present invention can be implemented by various means without departing from the gist of the present invention and achieving the object of the present invention.

[0038] In the experiment, as a refining furnace as shown in FIG. 1, one with a furnace diameter D = 6500 mm and a furnace height of 10000 mm was used. Then, a total of 370 t of hot metal and scrap was charged into the refining furnace, and further a CaO-based flux was added as a dephosphorizing agent, and oxygen gas was blown onto the hot metal from the upward blowing lance at a flow rate of 2.25 Nm 3 / min / t, and further nitrogen gas was bottom-blown as the bottom-blown gas at a flow rate of 0.18 Nm 3 / min / t for dephosphorization blowing. At this time, the basicity of the slag after the de-Si reaction was adjusted to 1.0. The nozzle of the upward blowing lance used at this time had 6 holes, and the radius r of the nozzle hole at the tip 0=69.5 mm, PCD = 265 mm, nozzle tilt angle θ = 20 deg. Also, the half angle α of jet spread was 10 deg. That is, from these conditions, the length H of the core region core = 695 mm, and the maximum lance height H' at which the jet flow did not collide with the furnace wall on the molten metal surface was 5350 mm.

[0039] Also, the lance height was changed according to the sample at the end of de - Si, and further, the bottom - blowing flow rate was increased according to the sample. Also, the slopping situation after the end of de - Si (after the lance height change if the lance height was changed) was also checked. When a large amount of slag overflowed due to slopping, it was evaluated as ×, when slopping occurred slightly but was within an acceptable range, it was evaluated as △, and when no slopping occurred, it was evaluated as ○. Also, regarding the de - Si time, when it significantly hindered the operation cycle, it was evaluated as ×, when it slightly hindered the operation cycle, it was evaluated as △, and when it had no effect on the operation cycle, it was evaluated as ○.

[0040] After the end of de - P blowing, (FeO), the phosphorus distribution ratio, and the forming ratio were evaluated. Note that (FeO) was calculated using the aforementioned formula (3), and the phosphorus distribution ratio was calculated using formula (4). Regarding (FeO), when it was 25 - 35 mass%, it was evaluated that the amount of FeO in the slag could be appropriately controlled. Also, for the phosphorus distribution ratio (%P) / [%P], when it was 200 or more, it was evaluated that the de - P reaction had proceeded sufficiently. Furthermore, regarding the forming ratio, the vertical height of the slag was measured using a microwave level gauge, and the "forming ratio" was calculated as "slag thickness (mm)" ÷ "height from the molten metal surface to the furnace mouth (mm)" × 100%. When the forming ratio was 50% or more and 60% or less, it was evaluated that the forming control was achieved.

[0041] Also, Fig. 3 shows the relationship between the furnace wall and the position of the ignition point on the molten metal surface for four adjusted lance heights LH in this example. Since the maximum lance height H' at which it did not collide with the furnace wall was 5350 mm, in the example where the lance height LH = 7000 mm, as shown in Fig. 3, a part of the jet collided with the furnace wall. The experimental results are shown in Table 1.

[0042]

Table 1

[0043] The underlines in the table indicate that they are outside the conditions of the present invention. For No.1 - 6, there were no problems with either the slopping situation after the end of desiliconization or the refractories. However, for No.1, 3, and 5, excessive FeO was generated in the slag at the end of the blowing process, resulting in a low phosphorus removal distribution ratio and a forming ratio exceeding 60%. On the other hand, for No.2, 4, and 6, after the end of desiliconization, the bottom blowing flow rate was adjusted to 1.6 times, and by controlling (FeO) within an appropriate range, a high phosphorus removal distribution ratio was achieved, and the forming ratio could be controlled between 50% and 60%.

[0044] In No.7, since the lance height was kept at 2000 mm, the forming suppression effect of the top - blowing lance was small, and slopping occurred after the end of desiliconization and at the end of the blowing process. In No.8 - 11, since the height of the top - blowing lance after the end of desiliconization did not meet the range of formula (1), slight slopping occurred after the end of desiliconization. As a result, even by adjusting the bottom blowing flow rate as in No.9 and 11, the forming ratio could not be controlled between 50% and 60%.

[0045] For No.12 - 17, the position of the top - blowing lance after the end of desiliconization was too high, and part of the jet collided with the furnace wall. Among them, in No.12, 14, and 16, due to excessive soft blowing and no change in the bottom blowing flow rate, an excessive amount of FeO was generated in the slag. As a result, the forming ratio exceeded 100% at the end of the blowing process. Also, in No.13, 15, and 17, although the bottom blowing flow rate was increased to 2.6 times to prevent excessive soft blowing, the forming ratio was less than 50%.

Explanation of Symbols

[0046] 1 Refining furnace 2 Top - blowing lance 3 Jet 4 Slag 5 Molten iron 6 Bottom tuyere 11 Furnace body 12 Opening

Claims

1. A converter blowing method for performing desiliconization and dephosphorization treatment by dephosphorization blowing using a converter-type refining furnace having an upper blowing lance, wherein the upper blowing acid supply rate in the dephosphorization blowing is set to 2.2 Nm3 / min / t to 2.7 Nm3 / min / t, at the timing when desiliconization is completed, the height of the upper blowing lance is set to a position satisfying the following formulas (1) and (2), and the bottom blowing flow rate (Nm3 / min / t) is increased to 1.4 to 1.7 times, at the end of the dephosphorization blowing, the forming height of the slag is set to a height of 50% or more and 60% or less when the height from the molten metal surface to the furnace mouth is 100%, and the FeO concentration in the slag is controlled to 25 to 35 mass%, characterized in that it is a converter blowing method. 【Number 1】 Here, H' represents the maximum lance height (mm) at which the jet flow does not collide with the furnace wall on the molten metal surface, D represents the furnace diameter (mm), PCD represents the nut seat pitch diameter (mm) of the circle connecting the center points of the nozzle holes at the tip of the upper blowing lance, LH represents the distance (mm) from the static molten metal surface to the nozzle tip of the upper blowing lance, H core represents the length (mm) of the core region, θ represents the nozzle inclination angle (deg), and α represents the half angle of spread (deg) of the jet from the nozzle of the upper blowing lance.

2. The converter blowing method according to claim 1, wherein in the dephosphorization blowing, before the completion of desiliconization, the distance LH is set to 0.3H' or more and less than 0.5H'.

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