JP2021147669A - Refining method of melting furnace - Google Patents

Abstract

To provide a refining method of a melting furnace for suppressing foaming during blowing in an inexpensive manner.SOLUTION: When oxidizing gas is blown from a top-blown lance toward molten iron which is charged into a melting furnace, a ratio L/L0 of a depth L (mm) of a recess from a stationary surface of the molten iron by blowing the gas and a depth L0 (mm) of the stationary surface of the molten iron is 0.3-1.0. The top-blown lance performs blowing under the condition that the number of holes of nozzles arranged around the central axis is 7-13 and the lance pre-pressure is 1.0-2.0 MPaG.SELECTED DRAWING: Figure 1

Description

The present invention particularly relates to a refining method for a melting furnace that suppresses forming in desiliconization, dephosphorization, decarburization and the like.

In operation in a melting furnace such as a converter, the temperature is raised while removing impurities in the molten iron by blowing oxygen into the furnace, and the concentration and temperature of the molten iron after blowing are within the specified range. Is controlled. At this time, oxygen blown from the top-blown lance reacts with carbon in the molten iron to generate carbon monoxide gas, and this gas causes slag foaming (hereinafter referred to as forming). If the amount of expansion of the slag is large, the forming will increase, and the phenomenon of slag overflowing from the converter (hereinafter referred to as sloping) will occur. Since sloping not only causes a decrease in iron yield, but also poses a risk to the operator and causes an interruption in operation, methods for calming or suppressing the forming of slag are being studied. As a method for calming the forming of slag, a sedative material is generally added to the formed slag.

Patent Document 1 discloses a method of charging a carbonaceous material from a top-blown lance within 3 minutes after the start of acid feeding as a method of suppressing slag forming. Further, Patent Document 2 discloses a method of forming an opening for venting gas in the slag by inserting and pulling out a rod body from the upper part of the slag as a method of calming the forming of the slag.

Further, in Patent Document 3, as a method of calming the forming, a jet flow is made to collide with the slag surface, a gas bubble vent hole is formed in the slag surface layer portion by the collision force generated at that time, and the gas bubble staying in the slag is removed. The method of care is disclosed. Further, Patent Document 4 discloses a method of blowing gas from a top blowing lance when forming is performed, as a method of calming the forming in a standby state in which the blowing treatment is not performed.

Japanese Patent No. 3888313 Japanese Unexamined Patent Publication No. 10-183217 Japanese Patent No. 6221705 Japanese Unexamined Patent Publication No. 2019-94522

Kiyoshi Segawa: Iron Metallurgical Reaction Engineering p. 94 (1977)

Forming occurs even when the smelting is not performed, but the refining reaction is actively progressing during the smelting, and the forming is also intense. Therefore, in order to add a sedative material to calm the forming during blowing, a large amount of sedative material is required, which costs a lot of money.

Further, the method described in Patent Document 1 is a method of suppressing the forming of slag in advance, but it cannot be dealt with when the forming actually occurs. Further, in the method described in Patent Document 3, in order to calm the forming, an unusual top blowing lance capable of blowing gas at a high pressure must be installed. Therefore, a lot of costs are incurred. Further, since the method described in Patent Document 4 is a method of calming the forming in a state where the blowing treatment is not performed, it cannot cope with the forming generated at the time of blowing.

In view of the above-mentioned problems, it is an object of the present invention to provide a refining method for a melting furnace capable of keeping the forming during blowing inexpensive and low.

The present inventors first investigated the mechanism by which slag forming is suppressed. When gas is blown from the top blown lance in the converter type refining process, the jet penetrates the slag and collides with the molten iron. At this time, the slag is caught from the side surface of the jet flow, and the bubbles in the caught slag are physically destroyed by the jet. Therefore, it is considered that blowing gas from the top blowing lance has a certain forming suppressing effect. Therefore, the present inventors pay attention to the phenomenon that slag is involved in the jet flow, increase the number of nozzle holes at the tip of the top blowing lance, and involve more slag, thereby increasing the forming suppression effect. I focused on the point.

The present inventors further investigated detailed conditions under which forming can be suppressed. As a result, when increasing the number of nozzle holes, it is suitable in relation to the ratio of the depth of the dent formed by blowing gas toward the molten iron surface to the static bath depth of the molten iron, and the prepressure in the top blowing lance. The present invention was reached by finding various conditions.

The present invention is as follows.
(1)
When the oxidizing gas is blown toward the molten iron from the top blowing lance with the molten iron charged in the melting furnace, the blowing of the gas calculated by the following equations (1) and (2) is performed. The ratio L / L ₀ of the depth L (mm) of the depression from the static bath surface of the molten iron to the static bath depth L ₀ (mm) of the molten iron is 0.3 to 1.0, and the top blowing The lance is a melting furnace characterized in that the number of holes of the nozzles arranged around the central axis is 7 to 13, and the lance is blown under the condition that the pre-lance pressure is 1.0 to 2.0 MPaG. Smelting method.
L = L _h × exp (−0.78 × H / L _h ) ・ ・ ・ (1)
L _h = 54.1 × (Q / (n × d)) ^2/3・ ・ ・ (2)
Here, H represents the distance (mm) from the static bath surface of the molten iron to the nozzle tip of the top blowing lance, Q represents the top blowing injection flow rate (Nm ³ / hr), and n is the number of holes in the nozzle. It represents (pieces), and d represents the nozzle outlet diameter (mm).

According to the present invention, the forming during blowing can be kept low at low cost.

It is a figure for demonstrating the state of blowing a gas from a top blowing lance toward molten iron. It is a schematic diagram which shows the detailed structural example of the tip part of the top blowing lance. It is a figure which shows the relationship between the ratio L / L _{0 and the occurrence rate of sloping.} It is a figure which shows the relationship between the number of holes of a nozzle and the occurrence rate of sloping. It is a figure which shows the relationship between the number of holes of a nozzle and the lance front pressure.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram for explaining a state in which gas is blown from a top-blown lance toward molten iron. In FIG. 1, the inside of the furnace body 1 is covered with a refractory material, and a plurality of bottom blowing tuyere (not shown) are provided at the bottom of the furnace body 1. An inert gas for stirring is blown into the furnace body 1 from the bottom blowing tuyere.

The top-blowing lance 2 can move up and down in the vertical direction (vertical direction in FIG. 1) at the opening of the furnace body 1, and the oxidizing gas 3 supplied from a gas supply path (not shown) connected to the upper end side. Is sprayed from the top blowing lance 2 toward the slug 4 and the molten iron 5.

FIG. 2 is a schematic view showing a detailed structural example of the tip portion of the top blowing lance 2. FIG. 2A shows an example of a cross-sectional structure of the tip portion of the top blown lance 2, and FIG. 2B shows a structure example of the top blown lance 2 viewed from below in the vertical direction. In FIG. 2A, the top blowing lance 2 is composed of a triple tube of an outer tube, a middle tube, and an inner tube, and the range 21 represents the nozzle outlet diameter. Although FIG. 2A shows an example of a Laval nozzle, it may be a straight nozzle. In the present embodiment, the nozzle inclination angle 22 is not particularly specified, but if it is too large, the jet will collide with the furnace wall and the refractory will be severely worn. Therefore, the nozzle inclination angle 22 is preferably about 20 ° or less.

Further, as shown in FIG. 2B, it does not have a central hole, and there are a plurality of peripheral holes 23 which are outlets of a plurality of nozzles around the central axis and are arranged concentrically. .. The peripheral holes 23 do not necessarily have to be arranged on the same circumference, and the peripheral holes 23 do not necessarily have to be arranged at equal intervals.

In FIG. 1, the depth L (mm) of the dent from the static bath surface of molten iron by spraying gas is determined by the following equations (1) and (2) based on the calculation method described in Non-Patent Document 1. Defined by. In this embodiment, the L value when the correction term k described in Non-Patent Document 1 is 0.8 (constant value) is used.
L = L _h × exp (−0.78 × H / L _h ) ・ ・ ・ (1)
L _h = 54.1 × (Q / (n × d)) ^2/3・ ・ ・ (2)

Here, H represents the distance (lance height) (mm) from the static bath surface of the molten iron to the nozzle tip of the top blow lance, and Q represents the top blow injection flow rate (Nm ³ / hr). n represents the number of nozzle holes (pieces) of the top blowing lance, and d represents the nozzle outlet diameter (mm).

Next, the conditions for suppressing forming in the embodiment of the present invention will be described. In the present embodiment, the ratio L / L ₀ of the depth L (mm) of the depression and the static bath depth L ₀ (mm) of the molten iron is controlled within an appropriate range. Here, the ratio L / L ₀ is the penetration ratio of the gas (jet) into the molten iron, and is an important parameter for appropriately controlling the reaction in the furnace. The present inventors first conducted an experiment to investigate the relationship between the _{ratio L / L 0 and the occurrence rate of sloping.} In the experiment, the number of nozzle holes n was _{fixed to 5, the nozzle outlet diameter d was fixed to 5.3 mm, the static bath depth L 0} was fixed to 200 mm, and the lance height H and the top blowing injection flow rate were changed to various ratios. The sloping occurrence rate was calculated at L / L _0.

FIG. 3 is a diagram showing the relationship between the ratio L / L ₀ and the occurrence rate of sloping. It was confirmed that when the ratio L / L ₀ was smaller than 0.3, the occurrence rate of sloping increased sharply. Generally, when gas is blown under a condition such as soft blow where the ratio L / L ₀ is small, the amount of FeO in the slag becomes high. Therefore, it is presumed that under the condition that the ratio L / L ₀ is small, the amount of slag increases, the forming becomes intense, and the sloping occurrence rate becomes high. From this experiment, the ratio L / L ₀ is set to 0.3 to 1.0 in order to suppress forming.

Next, the number of nozzle holes at the tip of the top blow lance will be described. When changing to a top blowing lance having a different number of nozzle holes, it is preferable to increase the number of nozzle holes so that _{the above-mentioned ratio L / L 0 becomes a constant value.} The ratio L / L ₀ is considered as an index of refining behavior such as dephosphorization and decarburization reactions in the furnace, and if the value _{of the ratio L / L 0 is different when changing to a top blowing lance with a different number of nozzle holes.} , The operator must adjust by raising or lowering the top blow lance accordingly, which is not preferable for stable operation.

Based on the above points, the present inventors conducted an experiment in which the number of nozzle holes was changed under the condition that the value _{of the ratio L / L 0 was fixed at 0.45.} In the experiment, the static bath depth L ₀ of the molten iron was fixed at 2000 mm, and as can be seen from the above equations (1) and (2), the depth L of the indentation was made the same for each sample. The value of the ratio L / L ₀ was fixed at 0.45. That is, the lance height H is fixed at 2000 mm, the top blowing injection flow rate Q is ^{fixed at 60,000 Nm 3} / hr in the equation (2), and the nozzle outlet diameter d is reduced as the number of nozzle holes n increases. The ropping occurrence rate was calculated. The relationship between the number of nozzle holes n and the nozzle outlet diameter d is shown in Table 1 below.

FIG. 4 is a diagram showing the relationship between the number of nozzle holes and the occurrence rate of sloping. As shown in FIG. 4, it was confirmed that the occurrence rate of sloping was low under the condition that the number of lance holes was 7 or more. From the above results, the number of nozzle holes arranged around the central axis of the top blow lance is set to 7 or more. Further, when the number of nozzle holes is 14 or more, the lance front pressure becomes too large and the nozzle outlet diameter d also becomes small, which will be described in detail later, so that nozzle blockage may occur. Therefore, the number of nozzle holes arranged around the central axis of the top blow lance is set to 7 to 13.

Next, the conditions of the lance prepressure will be described. The lance pre-pressure is the nozzle inlet pressure when the gas branches from the central portion of the top-blown lance to the nozzle. FIG. 5 is a diagram showing the relationship between the number of nozzle holes and the pre-lance pressure. Hereinafter, the lance pre-pressure is indicated by a gauge pressure (MPaG), but when converted to an absolute pressure (MPa), it is a value obtained by adding 0.101 MPa. As described above, when the ratio L / L ₀ is fixed and the number of nozzle holes is increased, the lance outlet diameter (in the case of a Laval nozzle, the throat diameter is further reduced) becomes smaller. Is also on the rise.

Here, the lance front pressure is 1.0 MPaG to 2.0 MPaG. If the lance pre-pressure is less than 1.0 MPaG, soft blow is likely to occur and a sufficient physical defoaming effect cannot be obtained. On the other hand, when the lance front pressure is larger than 2.0 MPaG, the gas is blown too strongly, so that there is a high possibility that the refractory of the furnace wall will be damaged.

As described above, the number of holes of the nozzles arranged around the central axis of the top blowing lance is 7 to 13, but in the example shown in FIG. 5, when the ratio L / L ₀ is 1.0, , The lance pre-pressure exceeds 2.0 MPaG in each case. Therefore, when the gas is blown so that the ratio L / L _{0 becomes 1.0, the ratio L / L 0} is fixed to 1.0 by adjusting the top blowing injection flow rate Q and the lance height H. The lance front pressure can be reduced as it is.

In the examples shown in FIGS. 3 and 4, the occurrence rate of sloping was used as an index, but in order to reduce the occurrence rate of sloping, it is sufficient to consider lowering the slag height due to forming. In the refining process, for example, the height of the slag in the furnace is measured with a slag level meter, and the basicity of the slag (CaO / SiO ₂ ) and the top-blown injection flow rate (acid feeding rate) from the top-blown lance are determined according to the measurement results. The slag operation is performed by adjusting Q, the slag height H of the top blowing slag, etc., and adding a calming material. The slag level meter may be any as long as it can measure the height of the slag in the vertical direction, and for example, a microwave type level meter may be used.

The above-mentioned refining treatment is not limited to a treatment in which desiliconization, dephosphorization and decarburization are performed at the same time. It also includes a refining treatment in which the pretreatment such as desiliconization and dephosphorization treatment and the decarburization treatment are separated.

Next, an example of the present invention will be described. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is described in this one condition example. It is not limited. In the present invention, various conditions can be adopted as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

A converter having a heat size of 280 tons was charged with the maximum capacity of molten iron, and quicklime or the like was charged for dephosphorization. At this time, the static bath depth L ₀ of the molten iron was set to 2000 mm. Then, dephosphorization was performed using the top blowing lance shown in Table 1. In these top-blown lances, a plurality of nozzle holes are arranged at equal intervals around the central axis of the top-blown lance. In the dephosphorization blowing, a gas containing 99.9 vol% or more of oxygen was blown from the top blowing lance toward the molten iron surface, and the injection flow rate (acid feeding rate) Q was set to 40,000 Nm ³ / hr. The lance height H and the ratio L / L ₀ of the top-blown lance were the conditions shown in Table 2.

Then, during the blowing, the height of the slag in the vertical direction was measured using a microwave level meter. "Slag height" in Table 2 is ("Average measured by microwave level meter (average measured at one point at predetermined time intervals) Slag height (m)"-"Still bath depth of molten iron (M) ”) ÷“ Height from the static bath surface of molten iron to the furnace mouth (m) ”× 100 (%), and when it was 60% or less, it was evaluated as having an effect of suppressing forming. The average slag height (m) is the slag height obtained by subtracting the distance between the microwave level gauge and the furnace mouth measured in advance from the measured distance between the microwave level meter and the slag surface. Is average.

As shown in Table 1, No. 1 of Examples. Forming could be suppressed in 1-3. On the other hand, No. In No. 4, the number of nozzle holes was only 4, and the lance front pressure was too low, so that the slag forming could not be suppressed. No. which is a comparative example. In No. 5, the ratio L / L ₀ was too small, so that the amount of FeO in the slag increased due to the soft blow, and as a result, the forming became intense. No. which is a comparative example. Since the number of nozzle holes in No. 6 was only 4, the forming of the slag could not be suppressed.

1 Furnace 2 Top-blown lance 3 Gas 4 Slag 5 Molten iron

Claims (1)

When the oxidizing gas is blown toward the molten iron from the top blowing lance with the molten iron charged in the melting furnace, the blowing of the gas calculated by the following equations (1) and (2) is performed. The ratio L / L ₀ of the depth L (mm) of the depression from the static bath surface of the molten iron to the static bath depth L ₀ (mm) of the molten iron is 0.3 to 1.0, and the top blowing The lance is a melting furnace characterized in that the number of holes of the nozzles arranged around the central axis is 7 to 13, and the lance is blown under the condition that the pre-lance pressure is 1.0 to 2.0 MPaG. Smelting method.
L = L _h × exp (−0.78 × H / L _h ) ・ ・ ・ (1)
L _h = 54.1 × (Q / (n × d)) ^2/3・ ・ ・ (2)
Here, H represents the distance (mm) from the static bath surface of the molten iron to the nozzle tip of the top blowing lance, Q represents the top blowing injection flow rate (Nm ³ / hr), and n is the number of holes in the nozzle. It represents (pieces), and d represents the nozzle outlet diameter (mm).

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