JP2018003132A - Refining method of molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refining method of molten iron, which stably performs decarburization blowing by suppressing a generation amount of dust in decarburization blowing and by suppressing a frequency of exchange of a device or a component.SOLUTION: When decarburization blowing is performed by blowing oxygen to molten iron using a top-blowing lance, by using a top-blowing lance having a nozzle of three holes or more arranged at an equi-distance on the same circumference that has a center axis of the top-blowing lance as a center, blowing is performed such that an index E that is kinetic energy when an oxygen jet collides with the molten iron being>15000, and an index R that represents a ratio of a lance apex and an ignition point that is a bullion source being<6.5 are satisfied.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a hot metal refining method for performing decarburization blowing by blowing oxygen gas to hot metal in a steelmaking converter, for example.

  Conventionally, it is widely known that as a method for efficiently decarburizing and refining molten iron, it is effective to enhance the stirring of molten iron in the converter. Therefore, many decarburization blow smelting in converters currently used are to blow up the oxygen jet (oxygen gas) from the lance installed above the converter and to enhance the stirring of the hot metal. A bottom tuyere is provided at the bottom of the converter, and oxygen, hydrocarbons, inert gas, etc. are blown from the bottom tuyere.

  Factors that deteriorate the yield of charged iron in such a converter blowing process include iron oxide loss in which iron is mixed as iron oxide in slag, contamination of granular iron in slag, and dust generation. Iron loss due to

  The dust generation mechanism includes a mechanism in which fume dust is generated by evaporating iron at a hot point where the oxygen jet blown directly collides with the hot metal and reaches a high temperature of 2000 to 2500 ° C., and decarburization. There is a mechanism in which bubble burst dust is generated when CO gas bubbles burst (bubble burst) in the reaction. Furthermore, spitting occurs when bubble bursts occur or when the hot metal scatters directly from the lip of the cavity formed by the oxygen jet on the bath surface of the hot metal. The particles scattered by this spitting are decarburized (secondary burst) by an oxygen jet during the scattering, and fine hot metal is scattered, which can be a source of dust. The generation of dust reduces the yield of iron in the converter, and is a major cause of cost deterioration.

In view of the generation of such dust, various measures have been taken conventionally. As a method for suppressing fume dust, for example, Patent Document 1 discloses one kind of coolant such as CO ₂ , CaCO ₃ , water vapor, water, Mn ore, iron ore, or the like from a through hole communicating with an upper blowing oxygen nozzle. A method is disclosed in which two or more kinds of mixtures are blown into a hot spot to lower the hot spot temperature so that iron is not evaporated at the hot spot. Patent Document 2 discloses a method for reducing the area of the fire point by changing the shape of the lance nozzle.

  However, since the method disclosed in Patent Document 1 requires a considerable amount of coolant for cooling the hot spot, the cost of the coolant is excessive, and the heat source for blowing is reduced by the blown coolant. Has the disadvantage that the degree of freedom is limited. In addition, the method disclosed in Patent Document 2 has a dust reduction effect, but the effect is insufficient. In the method disclosed in Patent Document 2, the furnace wall is increased as the nozzle inclination angle becomes wider. There is a problem that the melting damage is not solved.

  On the other hand, as a method of suppressing spitting, for example, in Patent Document 3, the ratio L / D between the depth L and the diameter D of the cavity formed on the hot metal bath surface by oxygen jet is controlled to a value larger than 2. Thus, a method for reducing the amount of dust by reducing the proportion of energy contributing to spitting out of the energy given to the hot metal bath surface by the oxygen jet is disclosed.

However, in order to realize the method described in Patent Document 3, it is necessary to set the distance between the lance and the molten metal surface to 1 m or less. In this case, in the less slag blowing with a slag amount of 40 kg or less per 1 ton of molten iron, the surface of the molten iron There is a problem that the tip of the lance is melted by radiant heat from. Patent Document 3 does not clearly define a method for calculating the cavity depth L, and it is described that the relationship between L / D and the lance height does not change depending on the method for calculating the cavity depth L. Actually, it varies greatly, so it is difficult to say that it is generally within a range that can be put into practice. For example, when L is calculated by the equation of Segawa et al. (Equation (3) described later) and the embodiment of Patent Document 3 is implemented, assuming that L ₀ is about 2 m, L / L ₀ > 1 may be obtained. The bath depth refractory is very likely to wear out.

JP 58-193309 A Japanese Patent Laid-Open No. 9-41020 Japanese Patent Laid-Open No. 2-111809

  In view of the above-described problems of the prior art, the present invention provides a hot metal refining method that stably suppresses decarburization while reducing the frequency of lance replacement while suppressing the amount of dust generated in decarburization blowing. For the purpose.

  In order to solve the above-described problems of the prior art, the present inventors have focused on the dust generation mechanism and investigated the relationship between the oxygen blowing condition and the amount of dust in the converter. And as a result of examining the relationship between the top blowing oxygen condition (acid feed rate, lance height and lance shape) and the amount of dust generated, the following was found.

The present invention relates to the depth L (mm) of the hot metal generated when the oxygen jet (oxygen gas) collides with the hot metal, the diameter (fire point diameter) D (mm) of the hot metal, and the collision surface between the oxygen jet and the hot metal. The index E (kg · m ² / s ² ) defined by the formula (1) by the flow velocity V (m / s) of the oxygen jet, the index E, the lance height H (mm), and the nozzle inclination angle θ (deg) This defines the blowing conditions such that the index R defined by the equation (2) satisfies a predetermined range. The nozzle inclination angle θ represents an angle formed by the lance center axis and the nozzle center axis.
E = ρ _g × L / 1000 × (D / 2000) ² × π × V ² (1)
R = (E · cos θ / H) (2)

Here, the index E is an index representative of the kinetic energy of the oxygen jet at the collision interface between the oxygen jet and the steel bath. A dent generated by the collision of the oxygen jet with the molten iron is defined as a cylinder having a height L and a diameter D. This is the kinetic energy when oxygen gas having a mass corresponding to the dent volume collides with the molten iron at a velocity V. When the index E exceeds a certain value, the collision surface between the oxygen jet and the hot metal transitions to an unstable region, the dust generation mechanism changes, and the amount of dust generation decreases. That is, when the oxygen jet deeply enters the gas-liquid collision interface, the position where the bubble burst is generated is pushed deeply into the molten iron, and the generation of droplets during the decarburization reaction is greatly suppressed. Also, the dust decreases as the index E increases. Therefore, the present inventors have clarified the threshold value of the index E through investigation. Regarding the calculation of the index E, the depth L of the hot metal, the diameter of the dent (fire point diameter) D, the linear flow velocity V ₀ (m / s) of the oxygen jet at the nozzle outlet (part where the nozzle cross-sectional area is minimized), and the bath The flow velocity V of the oxygen jet on the surface was calculated using the following equations (3) to (6).
dV ₀ = 0.73 (L + H) L ^0.5 (3)
D = 2 (H / cos θ) × tan α (4)
V ₀ = (Q _O2 / n) / {π (d / 2000) ² } (5)
V = V ₀ × d / D (6)

Here, d represents the diameter (mm) of the portion where the nozzle cross-sectional area is minimized. α represents the half-angle (deg) of the oxygen jet, and since it is experimentally said to be 8 ° to 12 °, it is calculated as α≈10 ° in the present invention. Q _O2 represents the average value (Nm ³ / hr) of the acid feed rate in 10 to 90% of the acid feed period in decarburization blowing, and n represents the number of holes in the lance nozzle. In addition, the lance height H represents the average value of the height of the lance which goes up and down in 10 to 90% of the acid feeding period, where the height of the hot metal bath surface before blowing is 0.

  On the other hand, the index R represents the ratio between the index E and the distance between the tip of the lance and the fire point that is the source of bullion. Considering that the index E, which is the kinetic energy when the oxygen jet collides with the hot metal, is proportional to the scattering distance of the metal, the smaller the index E, the lower the frequency of collision of the metal with the tip of the lance. That is, by keeping the index R small while increasing the index E, it is possible to reduce dust while suppressing the frequency of lance replacement due to adhesion of the metal.

  Thus, since the index E represents the kinetic energy of the oxygen jet at the collision interface, as the index E is increased, the adhesion of bullion to the lance becomes more prominent and the operability is also found during the investigation process. . The present inventor considers that the index E represents the scattering distance of the bullion, and can suppress the adhesion of the bullion by reducing the index R representing the ratio between the index E and the distance between the lance and the fire point. The suitable range of the index R that does not deteriorate the operability is clarified. That is, the idea is that the dust reduction effect can be enjoyed at a level at which stable operation is possible by adjusting the top blowing condition so as to satisfy R <6.5 while increasing the index E as much as possible in the range of E> 15000. It came.

From the above, the present invention can be summarized as follows.
(1) A hot metal refining method for performing decarburization blowing by blowing oxygen gas to hot metal using an upper blowing lance, wherein the upper blowing lance has the same circumference around the central axis of the upper blowing lance An index E and an index R defined by the following formulas (1) to (6) are respectively provided with the following formulas (7) and (8). ) A hot metal refining method characterized in that blowing is performed to satisfy the condition of the formula.
E = ρ _g × L / 1000 × (D / 2000) ² × π × V ² (1)
R = (E · cos θ / H) (2)
dV ₀ = 0.73 (L + H) L ^0.5 (3)
D = 2 (H / cos θ) × tan α (4)
V ₀ = (Q _O2 / n) / {π (d / 2000) ² } (5)
V = V ₀ × d / D (6)
E> 15000 (7)
R <6.5 (8)
Here, [rho _g represents the gas density (kg / m ^3), L represents a recess depth of the molten iron by blowing on (mm). H represents the average value (mm) of the height of the lance that rises and falls in 10 to 90% of the acid feeding period in the blowing, with the height of the hot metal bath surface before blowing being 0, and θ is the nozzle Indicates the tilt angle (deg). D represents the fire spot diameter (mm), and α represents the spreading half angle (deg) of the oxygen jet. Q _O2 represents the average value (Nm ³ / s) of the acid feeding rate in 10 to 90% of the acid feeding period in blowing, and n represents the number of holes in the nozzle of the top blowing lance. d represents the diameter (mm) of the part where the nozzle cross-sectional area is minimum, and V ₀ represents the linear flow velocity (m / s) of oxygen gas at the part where the nozzle cross-sectional area is minimum. V represents the flow rate (m / s) of oxygen gas on the bath surface.

  According to the present invention, it is possible to stably perform decarburization blowing while suppressing the generation amount of dust in decarburization blowing and suppressing the frequency of lance replacement.

It is a figure which shows the relationship between the parameter | index E and a dust index. It is a figure which shows the relationship between the parameter | index R and a lance life index. It is a figure which shows the relationship between the parameter | index E and the parameter | index R. FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

  In the hot metal refining method of the present invention, decarburization blowing is performed by blowing an oxygen jet onto hot metal using an upper blowing lance (hereinafter referred to as lance). At this time, a lance having nozzles having three or more holes at equal intervals on the same circumference around the central axis of the lance is used. This is because when the nozzle has one or two holes, it becomes difficult to adjust the hot spot area as the oxygen flow rate increases. Therefore, the following description will be made on the assumption that the lance has nozzles having three or more holes.

In the decarburization blowing performed in a 300-ton scale converter, the present inventors changed the top blown oxygen flow rate (acid feed rate Q _O2 ), the lance shape, and the lance-metal surface distance (lance height H). The relationship between the index E and the amount of dust generated (dust index) and the relationship between the index R and the amount of metal adhesion (lance life index) were investigated.

First, a hot metal containing, by mass, C: 4.2%, Si: 0.4%, Mn: 0.2%, P: 0.1%, S: 0.001% was loaded into a converter. Type, top-blown oxygen flow rate 4.0~6.0Nm ³ / min / t, the bottom-blown Ar flow rate of 0.25Nm ³ / min / t C: perform blow until more than 0.3%, The amount of dust generated during blowing was investigated. A porous laval lance was used as the lance, and the number of bottom blowing tuyere was four. The distance between the lance and the hot water surface (lance height H) was controlled in the range of 1800 to 4000 mm.

In the calculation of the index E and the index R according to the present invention, the gas density ρ _g is 1.429 kg / m ^3, and the numerical values of the lance height H and the acid feed rate Q _O2 are the acid feed period in each blowing. The average value in 10-90% of was used.

  Here, dust refers to iron particles contained in the converter exhaust gas, and is generally said to be 10 to 30 kg / steel-t of the generated amount. It is said that dust originates from the collision of oxygen jets with hot metal and the granular iron scattered by decarburization and the finer granular iron that evaporates from the hot spot. Therefore, in the following explanation, the dust concentration in the dust collection water is measured, and a value normalized with the dust concentration in the dust collection water under the standard condition as 1 is defined as a dust index. That is, the smaller the dust index, the lower the dust.

  In addition, converter lances usually reach the end of their service life when the number of used charges is about 250 to 350. However, if the wear due to collision, adhesion, peeling, etc. of the metal is large, the service limit is reached with a small number of charges. For example, if the amount and frequency of the adhesion of the bullion to the tip of the lance increase depending on the top blowing condition, the wear rate of the lance is relatively increased and the lance life is shortened. Therefore, in the following description, the value obtained by normalizing the number of charges used for the lance used under the standard condition as 1 is defined as the lance life index. That is, the longer the lance life index is, the longer the life is.

  FIG. 1 is a diagram showing the relationship between the index E and the dust index. The average value of dust generation at E = 5000 to 10000 is defined as the dust index = 1 and the reference value, and the comparison with the reference value is the index. It has become. In addition to the various causes of dust generation, it is difficult to distinguish between dust loss and spattered iron loss due to spitting in actual operations. .

  As shown in FIG. 1, it was confirmed that the dust generation amount started to decrease from the vicinity where E exceeded 12000, and when it exceeded 15000, the dust generation amount was rapidly decreased to 0.85 or less. . This is probably because the interface where the oxygen jet collides with the hot metal transitions to an unstable region, the dust generation mechanism changes, and the amount of dust generation decreases. That is, it is considered that the bubble jet generation position was pushed deeply by the oxygen jet deeply entering the gas-liquid collision interface, and the generation of droplets during the decarburization reaction was greatly suppressed.

  In the region where E> 12000, the amount of dust generated decreased as the index E increased. Further, when E ≦ 10000, there was almost no dust reduction effect even if the index E was increased. This is considered to be because when E ≦ 10000, the interface where the oxygen jet collides with the molten iron was stable, and a large amount of dust was generated near the fire point. From the above, it has been clarified that the condition for greatly reducing converter dust is to increase the index E in the region of E> 12000. Although the upper limit value of the index E is not particularly limited, it is desirable that E ≦ 25000 because the effect of reducing the dust generation amount corresponding to the index E is too high cannot be expected.

  It was found that by increasing the index E and increasing it to a region where E> 15000, the dust decreases rapidly as the index E increases. However, it was discovered that simply increasing the index E would shorten the lance life. On the other hand, it was found that when the index E is constant, the life of the lance is extended by increasing the distance between the tip of the lance and the fire point. The inventor conducted further investigation and increased the ratio (index R) between the index E and the distance between the center of the lance tip and the hot spot (collision position of the hot metal by the oxygen jet) (index R). It was discovered that gold adhesion was suppressed and stable operation was possible. In this investigation, the index E was 5000-22000, the number of nozzle holes n was 3-6, and the nozzle inclination angle θ was 10-30 °. And it has been found that by setting the index R within a predetermined range, it is possible to suppress the decrease in the life of the lance by suppressing the adhesion of the metal to the lance while enjoying the dust reduction effect due to the increase in the index E.

  Since the lance life decreased as the index E increased, the present inventors estimated that the scattering distance of the metal increased with the increase in the inertial force of the oxygen jet. On the other hand, even when the index E was the same, the lance life did not decrease when the nozzle inclination angle θ was large. This is thought to be because the scattering of the bullion is more noticeable just above the fire point, the angle of the oxygen jet is directed by the nozzle inclination angle θ, and the adhesion amount of the bullion is reduced by moving the lance away from just above the fire point. It is done.

  Therefore, the present inventors have conceived that the adhesion of the metal can be suppressed by adjusting the lance height H and the nozzle inclination angle θ, and the distance between the center of the lance tip and the fire point (lance height H), Ecos θ, As a result of investigating the relationship between the ratio (index R) and the lance life, it was found that by setting R <6.5, the index E can be increased without reducing the lance life. FIG. 2 shows the relationship between the index R and the lance life index. Here, the lance life index is a standardized value when the lance life (number of times of blowing) is 1 when blown under the standard top blowing condition.

  As shown in FIG. 2, it was found that when R ≧ 6.5, the lance life index rapidly deteriorates. Note that the lower limit value of the index R is not particularly limited, but naturally has a limit due to the condition of E> 15000. Even if the index R is too low, the lance life reduction effect corresponding to the index R is not expected, but rather the refractory is likely to be worn by the oxygen jet approaching the furnace wall. It is desirable to be.

  From the above, in order to stably operate while enjoying the dust reduction effect due to the increase of the index E, it is necessary to set the index E and the index R to E> 15000 and R <6.5, respectively. I understood that.

  The number of nozzle holes in the lance was investigated from 3 to 10, but no effect on operability was found if blown within a satisfactory range. In the present invention, the number of holes in the nozzle is set to three or more. However, when the outer diameter of the lance is the same, the larger the number of holes, the more difficult it is to secure the cooling water flow path. Conceivable.

  The nozzle inclination angle θ was changed in the range of 6 to 30 ° for investigation, but it did not greatly affect the wear behavior of the refractory. However, considering that the operation of setting the soft blow condition at the initial stage of blowing, which is common in normal operation, is considered, the limit for widening the nozzle inclination angle θ is considered to be about 30 °.

  Next, the present invention will be further described based on examples, but the conditions in the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention. It is not limited to the example conditions. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

In order to confirm the effect of the present invention, an experiment was conducted using a 300 t scale converter. At that time, C: 4.4-6.5%, Si: 0.2-0.5%, Mn: 0.2-0.4%, P: 0.100-0. About 260 tons of hot metal containing 120% and about 20 tons of scrap are charged into the converter, the top blown oxygen flow rate is set to 4.0 Nm ³ / min per 1 ton of hot metal, and the bottom blown CO ₂ flow rate is set to 0.0. It set to 15 Nm < ³ > / min and blown. In the experiment, blowing was performed by changing the shape of the lance and the blowing conditions, and in mass%, C: 0.05 to 0.1%, Si ≦ 0.01%, Mn: 0.1 to 0.2% , P: 0.015 to 0.025% of molten steel was manufactured, and the amount of dust generated and the weight of the metal on the lance were investigated. The dust generation surveyed here also includes iron yield loss due to spitting. The distance between the lance and the molten metal surface (lance height H) is defined as the average distance between the lance and molten metal surface, which varies from 10 to 90% during the blowing process, assuming that the bath surface height of the hot metal before blowing is 0. . Table 1 shows the operating conditions of the examples and comparative examples, and the dust index and lance life index at that time. In Table 1, the diameter of the portion where the nozzle cross-sectional area is minimum is described as the throat diameter.

  The dust index and the lance life index are average values when 250 to 350 ch are used, and normalized values with Comparative Example 1 as 1. The case where the dust index was 0.9 or less and the lance metal adhesion index was 1.0 or more was marked with ◯, and the case where it was not so was marked with ×. The top blow lance has a nozzle of 3 to 6 holes, a porous laval lance having a nozzle inclination angle θ of 10 to 25 °, and the distance between the lance and the molten metal surface (lance height H) is controlled in the range of 2000 to 4000 mm. . FIG. 3 shows the relationship between the index E and the index R for the examples of the present invention and the comparative example. In addition, Comparative Examples 1-3 are conditions adjusted so that it may become the parameter | index E and parameter | index R equivalent to the conventional operation.

  In all of Examples 1 to 5, E> 15000 and R <6.5 were satisfied, and although there was some variation, the larger the index E, the lower the dust index. In particular, when E> 19000, it was confirmed that the dust index could be less than 0.80. This is because the interface where the oxygen jet collides with the hot metal transitions to an unstable region, the dust generation mechanism changes, and the amount of dust generation decreases, that is, the oxygen jet deeply sinks into the gas-liquid collision interface. This is probably because the burst generation position was pushed deeply into the hot metal, and the generation of droplets during the decarburization reaction was greatly suppressed. Further, the lance life index was stable at 1.01 to 1.03, and even when the index E was made high, no decrease in life was observed. This is because the index R is sufficient to suppress the scattering of bullion due to the inertial force of the oxygen jet.

  On the other hand, in Comparative Example 1, a lance having a nozzle having 5 holes and a lance inclination angle θ = 15 ° was used, the lance height H was 3000 mm, the index E was 5294, and the index R was 1.70. In Comparative Example 2, a lance having 6 nozzles and a nozzle inclination angle θ = 18 ° was used, the lance height H was 2000 mm, the index E was 8856, and the index R was 4.21.

  The dust index of Comparative Example 2 was 1.01, and the lance life index was 1.01. In Comparative Example 2, since the value of the index R is small, the lance life index is sufficiently high and there is no problem in operability. However, even if the index E is increased from 5294 to 8856 compared to Comparative Example 1, the dust index hardly changed. This is probably because the interface where the oxygen jet collides with the hot metal is stable and a large amount of dust is generated near the fire point.

  In Comparative Example 3, a lance having four nozzles and a nozzle inclination angle θ = 10 ° was used, the lance height H was 2700 mm, the index E was 19652, and the index R was 7.17. The dust index of Comparative Example 3 was 0.7, and the lance life index was 0.85. Thus, since the index E was increased to an area where E> 15000, the dust index was greatly reduced, but the lance life index was lowered and the operability was greatly deteriorated. This is because the distance between the tip of the lance and the hot spot was small, and the scattering of the metal increased due to the inertial force of the oxygen jet.

  From the above, even when various conditions such as the number of nozzle holes, the nozzle inclination angle, and the distance between the lance and the molten metal surface are different, if the indices E and R can be controlled within a predetermined range, the amount of dust generated is reduced. It was confirmed that the lance life could be reduced. From the above examination, it was confirmed that the ranges of the index E and the index R that can sufficiently enjoy the effects of the present invention are E> 15000 and R <6.5, respectively. In particular, it can be said that the condition of the index E is more preferably E> 19000.

  According to the present invention, in a refining process in which a refining gas is blown onto the hot metal bath surface in a steelmaking converter, iron loss due to dust can be greatly reduced without deteriorating operability. As a result, improvement in the refining yield can be achieved and productivity can be improved, so that it can be said that the industrial value is great.

Claims (1)

A hot metal refining method in which oxygen gas is blown into hot metal using an upper blowing lance to perform decarburization blowing, wherein the upper blowing lance is equal on the same circumference around the central axis of the upper blowing lance. The nozzles having three or more holes arranged at intervals, and the index E and the index R defined by the following formulas (1) to (6) are respectively the following formulas (7) and (8): A method for refining hot metal, which is characterized by performing blowing to satisfy the conditions.
E = ρ _g × L / 1000 × (D / 2000) ² × π × V ² (1)
R = (E · cos θ / H) (2)
dV ₀ = 0.73 (L + H) L ^0.5 (3)
D = 2 (H / cos θ) × tan α (4)
V ₀ = (Q _O2 / n) / {π (d / 2000) ² } (5)
V = V ₀ × d / D (6)
E> 15000 (7)
R <6.5 (8)
Here, [rho _g represents the gas density (kg / m ^3), L represents a dent by blowing on depth (mm). H represents the average value (mm) of the height of the lance that rises and falls in 10 to 90% of the acid feeding period in the blowing, with the height of the hot metal bath surface before blowing being 0, and θ is the nozzle Indicates the tilt angle (deg). D represents the fire spot diameter (mm), and α represents the spreading half angle (deg) of the oxygen jet. Q _O2 represents the average value (Nm ³ / s) of the acid feeding rate in 10 to 90% of the acid feeding period in blowing, and n represents the number of holes in the nozzle of the top blowing lance. d represents the diameter (mm) of the part where the nozzle cross-sectional area is minimum, and V ₀ represents the linear flow velocity (m / s) of oxygen gas at the part where the nozzle cross-sectional area is minimum. V represents the flow rate of oxygen gas on the bath surface.