JP2003041312A - Method for removing silicon from molten pig iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for removing silicon from a molten pig iron, while accurately grasping the progress of decarburization in the removal process. SOLUTION: It was found that when the removal step of silicon from the molten pig iron proceeds and a generation rate of a CO gas associated with decarburization reaction exceeds a given value, in a silicon removal step from the molten pig iron, the temperature of a fire point generated on the surface of the molten pig iron bath caused by blown oxygen from a lance for blowing oxygen rises, and that the progress of decarburization of the molten pig iron can be accurately grasped to some extent by catching the temperature rise of the fire point. Thereby, the objective method was completed. The method is characterized by measuring the temperature of the fire point generating on the molten pig iron bath caused by blown oxygen from the lance, with an optical fiber type radiation thermometer which is arranged at the lance for blowing oxygen, and determining a decarburization condition in the molten pig iron, based on the change of the fire point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot metal desiliconizing method which is carried out as a hot metal pretreatment.

[0002]

2. Description of the Related Art In order to efficiently perform dephosphorization and decarburization of hot metal, hot metal desiliconization is performed as a hot metal pretreatment. In the conventional hot metal desiliconization treatment, a method of adding an oxide represented by iron oxide or mill scale to a blast furnace casting floor or a tilt gutter and adding gaseous oxygen as necessary is adopted. Also, oxygen is top-blown from the acid-feeding lance to the hot metal in the container, and if necessary, a solid oxygen source (for example, iron oxide such as sintered powder or mill scale) is added, while a bottom-blown nozzle or immersion is applied. There is also a method in which a stirring gas or a stirring gas and powder (for example, a solvent medium) are blown into the bath through a lance or the like to stir the bath. However, in this hot metal desiliconization treatment, as the silicon concentration in the hot metal decreases due to the progress of desiliconization, the desiliconization oxygen efficiency decreases, and excess oxygen reacts with the carbon in the hot metal (decarburization reaction). The generated CO gas hinders stable operation by forming slag, equipment damage is caused by the high temperature of generated exhaust gas, and the amount of heat supplied to the lower process becomes unstable due to a decrease in carbon concentration in the hot metal. Cause problems.

[0003]

Therefore, in the hot metal desiliconization treatment, it is necessary to suppress the decarburization of the hot metal as the desiliconization progresses. To suppress such decarburization of the hot metal, first, It is necessary to accurately grasp the progress of desiliconization and decarburization during the treatment process. However, there is no known method for accurately grasping the progress of desiliconization and decarburization.

As a conventional technique for suppressing decarburization during hot metal desiliconization, a method of changing the oxygen / inert gas ratio in the gas blown into the hot metal in accordance with the decrease in the silicon concentration in the hot metal. (JP-A 61-15909), a method of controlling decarburization by defining a stirring force (JP-A-7-278).
No. 636), but in this method oxygen /
Since the inertness ratio is large, decarburization proceeds in the low silicon concentration range, and in the method, since the blowing gas contains oxygen gas, the reaction between this oxygen gas and the carbon in the hot metal Is inevitable. Further, since neither method has a method of accurately grasping the progress of desiliconization or decarburization as described above, there is a fundamental problem that it is difficult to perform control at an appropriate timing.

Therefore, it is an object of the present invention to provide a hot metal desiliconizing method capable of performing hot metal desiliconizing while accurately grasping the progress of decarburization during a processing step.
Another object of the present invention is to accurately grasp the progress of decarburization during the treatment process, and based on this, the decarburization reaction is appropriately suppressed especially in the low silicon concentration region where the desiliconization of the hot metal has advanced. It is an object of the present invention to provide a hot metal desiliconizing treatment method capable of performing an efficient hot metal desiliconizing treatment.

[0006]

Means for Solving the Problems The present inventors have proposed a method capable of accurately grasping the progress of decarburization during hot metal desiliconization in order to solve the above-mentioned problems. Based on an accurate grasp of the progress of charcoal, a method that can appropriately suppress the decarburization reaction in the low silicon concentration region was investigated, and the following findings were obtained.

(1) When the silicon removal in the hot metal progresses in the hot metal desiliconization process and the silicon concentration in the hot metal reaches a low silicon concentration region of 0.2 mass% or less, the silicon removal in the bath is rate-determining in the desiliconization reaction. Therefore, the oxygen amount per unit time used for the desiliconization reaction gradually decreases, and the oxygen amount per unit time used for the decarburization reaction increases accordingly. In this way, as the silicon concentration in the hot metal decreases, the amount of decarburization per unit time increases, and when the CO gas generation rate associated with the decarburization reaction exceeds a certain value, the hot metal bath surface is fed by the acid feeding from the acid feeding lance. It was found that the temperature rise of the hot spot that occurred in the above was recognized, and therefore the progress of decarburization of the hot metal can be grasped to some extent accurately by grasping the rise of the hot spot temperature. It was also found that this flash point temperature can be easily detected by an optical fiber type radiation thermometer arranged on the acid feeding lance.

(2) Further, regarding the action for suppressing decarburization based on the understanding of the progress of decarburization, in order to suppress the decarburization of the hot metal, the amount of oxygen other than that consumed for desiliconization is set. Although it is important to reduce the amount, it has been confirmed that for this purpose, it is effective to reduce the rate of oxygen transfer from the oxygen transfer lance (supply rate of gaseous oxygen source or oxygen concentration of gaseous oxygen source). It was also confirmed that under the same acid feeding conditions, by enhancing the stirring of the bath, the moving speed of silicon was increased, which promoted preferential desiliconization, and as a result, the decarburization reaction was suppressed. As a method of increasing the stirring of the bath, no significant difference was observed by increasing the supply rate of the stirring gas, the supply rate of the powder, or the combination of both.

The present invention has been made on the basis of the above findings, and its features are as follows. [1] In the method for performing hot metal pretreatment in a container, in which the hot metal is desiliconized while supplying a gaseous oxygen source from the acid-feeding lance, a lance with an optical fiber type radiation thermometer placed on the acid-feeding lance is used. A hot metal desiliconizing method characterized by measuring the temperature of a hot spot generated on the surface of a hot metal bath due to the feeding of acid from the steel, and determining the decarburization state of the hot metal based on the change in the hot spot temperature. [2] The hot metal desiliconizing method according to the above [1], wherein the stirring gas or the stirring gas and powder are blown into the bath from a bottom blowing nozzle or a dipping lance to stir the bath.

[3] In the hot metal desiliconization method of [1] or [2] above, when an increase in the hot spot temperature is measured, an acid transfer rate by an acid transfer lance, a stirring gas supply rate, a powder At least one of the supply rates of the above is controlled, and the hot metal desiliconization method is characterized. [4] In the hot metal desiliconization treatment method of [3] above, when an increase in the flash point temperature of 50 ° C. or higher is measured for 10 seconds, an acid transfer rate by an acid transfer lance, a stirring gas supply rate, a powder At least one of the supply rates of the above is controlled, The hot metal desiliconization method of description. [5] In the hot metal desiliconization treatment method according to any one of the above [1] to [4], the detection end at the tip of the optical fiber part of the optical fiber type radiation thermometer is provided in the gas injection hole at the tip of the acid-feeding lance or the gas injection hole. A hot metal desiliconization treatment method, characterized in that the hot metal desiliconization treatment is performed in the vicinity of the discharge port.

[6] In the hot metal desiliconization method of the above [5], an oxygen transfer lance having a plurality of gas injection holes having different gas injection flow rates is used, and a gas having the highest gas injection flow rate among the plurality of gas injection holes is used. A hot metal desiliconization treatment method characterized in that a detection end at the tip of an optical fiber portion of an optical fiber type radiation thermometer is arranged in the injection hole or in the vicinity of the discharge port of the gas injection hole. According to the method of the present invention as described above, it is possible to accurately grasp the time when the decarburization reaction occurs due to the decrease in the silicon concentration in the hot metal, which was difficult in the conventional technique, and therefore the decarburization reaction is suppressed for each charge. You can take quick and optimal action.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the method of the present invention, in the hot metal desiliconization treatment carried out as a hot metal pretreatment, an optical fiber type radiation thermometer arranged on an acid feeding lance is used to generate a hot spot on the hot metal bath surface by the acid feeding from the lance. Temperature is measured, and the decarburization status of the hot metal is judged based on this change in the flash point temperature. And
Based on this judgment, take the necessary action to suppress decarburization.

Generally, the hot metal tapped from the blast furnace is poured and stored in a container such as a hot metal ladle via the casting floor, and the desiliconization treatment performed as a hot metal pretreatment is performed in the container such as the hot metal ladle. There are cases where desiliconization treatment is performed only by itself, and cases where desiliconization treatment is performed in the casting bed (cast bed desiliconization) and then further performed in a container such as a hot metal ladle. Can also be applied to. For the desiliconization treatment in the container targeted by the present invention, a ladle such as a hot metal ladle or a charging pot, a toped car (mixed pig car), or another container for desiliconization can be used as the processing container. In the desiliconization treatment, an oxygen source is added as a desiliconizing agent, and if necessary, a CaO source such as calcined lime is added as a solvent to adjust the basicity of the slag. As the oxygen source, at least a gaseous oxygen source is used, and normally this gaseous oxygen source is supplied into the container through an acid feeding lance (upper blowing lance) or the like. In addition, a solid oxygen source (sintered powder, iron oxide such as mill scale) may be added if necessary. The solvent medium and the solid oxygen source are added into the bath by top-up charging from the upper part of the furnace or by blowing into the bath by means such as an immersion lance (injection lance) or a blowing nozzle of the furnace body.

Further, in order to enhance the desiliconization efficiency, it is preferable to blow a stirring gas into the molten pig iron for stirring the bath. Usually, nitrogen gas, argon gas, or the like is used as the stirring gas, and for example, it is blown into the bath through an immersion lance or a blowing nozzle of the furnace body. At this time, the solvent medium and solid oxygen source as described above may be blown together with the stirring gas.

FIG. 1 schematically shows an example of a state of desiliconization treatment using the hot metal ladle 1, in which the acid feeding lance 2 is placed in the hot metal ladle 1.
A gaseous oxygen source is blown in through, and a stirring gas and a solvent are blown into the hot metal through the immersion lance 3.
Further, if necessary, a solid oxygen source (for example, iron oxide such as sintered powder or mill scale) can be placed on top from a raw material feeding device (not shown) above the pot.

In the method of the present invention, an optical fiber type radiation thermometer 4 is arranged on the acid feeding lance 2 and the temperature of the fire point generated on the hot metal bath surface by the acid feeding from the lance is measured. The optical fiber type radiation thermometer 4 is composed of a long optical fiber portion and a thermometer main body. The optical fiber portion is arranged along the longitudinal direction of the lance, and its base end is connected to the thermometer main body.

The mounting position and mounting structure of the optical fiber type radiation thermometer 4 with respect to the acid feeding lance 2 are not particularly limited as long as they are positions and structures capable of measuring the fire point temperature. If the optical fiber part of 4 is arranged along the inside of the lance and the detection end of the optical fiber part is arranged in the gas injection hole (acid feed nozzle) of the lance tip or in the vicinity of the discharge port of the gas injection hole, The temperature of the formed flash point can be detected. In general,
If the gas injection hole of the lance is a single hole, the detection end at the tip of the optical fiber part may be arranged in or near the gas injection hole, and if the gas injection hole is porous, any one of them may be arranged. It may be arranged in the gas injection hole or in the vicinity of the discharge port.

The measurement of the temperature by the optical fiber type radiation thermometer uses the principle of measurement that the absolute temperature can be calculated from the radiation spectrum distribution of the black body if the black body radiation condition is satisfied. Spectral light emitted by the fire point is input from the detection end of the optical fiber tip, and this spectral light propagates in the fiber and is input to the thermometer body. The thermometer main body calculates the temperature by comparing the brightness outputs of two wavelengths, for example.
It consists of a color thermometer and an infrared radiation thermometer that determines the temperature directly from the brightness output of the synchrotron radiation.It calculates the temperature from the input optical spectrum signal according to each measurement method, and the calculated temperature signal is an electrical signal. It is output as a signal and supplied to a recorder.

2 and 3 each show an example of the structure of the tip of the oxygen-sending lance used in the method of the present invention.
(A) and FIG. 3 (A) are front views of the tip of the acid transfer lance, and FIG. 2 (B) and FIG. 3 (B) are respectively FIG. 2 (A).
3 is a cross-sectional view taken along the line BB of FIG. In the figure, 5 is an optical fiber part of the optical fiber type radiation thermometer 4, and 50 is a detection end at the tip thereof.

FIG. 2 is a perforated acid transfer lance 2 having gas injection holes 20a and 20b around the center of the lance tip and around it.
In this embodiment, the detection end 50 at the tip of the optical fiber portion 5 of the optical fiber type radiation thermometer 4 is arranged near the tip in the gas injection hole 20a at the center of the lance tip. FIG. 3 is an embodiment in which a porous oxygen transfer lance 2 having a gas injection hole 20 around the center of the tip of the lance is used, and in this embodiment, any one gas of the plurality of gas injection holes 20 is used. A detection end 50 at the tip of the optical fiber portion 5 of the optical fiber type radiation thermometer 4 is arranged near the tip in the injection hole 20.

When the detection end 50 at the tip of the optical fiber portion 5 of the optical fiber type radiation thermometer 4 is arranged in one gas injection hole among the plurality of gas injection holes 20, 20a, 20b as in the above embodiments, When there is a difference in the gas injection flow rate of each gas injection hole, it is preferable to arrange the detection end of the optical fiber tip 50 in the gas injection hole having the largest gas injection flow rate. This is because the desiliconization rate increases near the fire point where the gas flow rate is large, and the decarburization rate increases from an earlier time, so the progress of decarburization can be detected at the earliest. If the ejection flow rate of each gas injection hole is the same, a large difference does not appear in the brightness of the fire point in any of the gas injection holes. Therefore, the optical fiber tip 50 is placed in any gas injection hole. Good. Further, the above is an example in which the detection end 50 at the tip of the optical fiber portion is arranged in the gas injection hole, but in some cases, a through hole for mounting is provided at the tip of the lance, and the detection end 50 at the tip of the optical fiber portion is provided in this through hole. May be arranged.

In the method of the present invention, during the hot metal desiliconization treatment, the optical fiber type radiation thermometer 4 measures the temperature of the fire point generated by the acid feeding of the acid feeding lance 2, and based on the change in the hot spot temperature. To determine the decarburization status of the hot metal. Specifically, it is determined that the decarburization reaction has progressed rapidly when a rise in the flash point temperature, particularly a rapid rise in temperature, is measured, and the action necessary to suppress decarburization is taken. As described above, when the CO gas generation rate due to the decarburization reaction in the hot metal exceeds a certain value, the hot spot temperature of the acid feeding lance 2 rises. The reason for this is
As the silicon concentration decreases, the amount of decarburization per unit time increases,
This is because the generation rate of CO gas increases, the gas temperature on the surface of the fire point rises, and the temperature is detected by the radiation thermometer. When desiliconization progresses, the flash point temperature rises from a certain point and then becomes a constant value, but the flash point temperature rises as the oxygen transfer rate increases. Therefore, also from this, it is understood that the rise in the fire point temperature is an influence of the generated CO gas.

Further, since the rise of the hot spot temperature due to the rapid progress of the decarburization reaction is relatively rapid, it is usually carried out when the rise of the hot spot temperature of 50 ° C. or more is measured for 10 seconds. It is preferable to determine that the decarburization reaction has proceeded rapidly and take the action necessary to suppress the decarburization. During hot metal desiliconization, the hot spot temperature changes greatly instantaneously because the bath is stirred, but since the rising and falling times can be identified by the moving average before and after,
If you keep following the transition in about 10 seconds, you can easily check the rising point. FIG. 4 shows an example of transition of the flash point temperature measured by an optical fiber type radiation thermometer arranged in the acid feeding lance.

Actions to be taken in order to suppress decarburization include an acid feeding rate from the acid feeding lance 2, a feeding rate of a stirring gas from the immersion lance 3 and the like, and a powder (solvent and solvent) from the immersion lance 3 and the like. It is preferable to control at least one of the supply rates of the powder of solid oxygen source etc.).
In order to suppress the decarburization of the hot metal, it is necessary to reduce the amount of oxygen other than that consumed for desiliconization. For this purpose, the oxygen transfer rate from the oxygen transfer lance 2 (oxygen supply amount per unit time) is reduced. It is effective to let As a method of controlling the acid transfer rate from the acid transfer lance 2, a method of adjusting the supply rate itself of the gas oxygen source supplied from the acid transfer lance 2 and an oxygen concentration of the gas oxygen source supplied from the acid transfer lance 2 are used. Any of the adjusting methods may be used, or the above method may be performed in parallel. However, when the supply rate of the gaseous oxygen source is changed significantly during the process by the method, the oxygen flow rate and the dynamic pressure on the molten metal surface may change, which may adversely affect the oxygen efficiency. In this method, it is possible to change only the oxygen supply amount while keeping the flow rate of oxygen supplied and the dynamic pressure on the molten metal surface constant. From this point of view, the method of It is particularly preferable to control the speed.

Further, if the acid feeding rate is the same, the moving speed of silicon is increased by strengthening the stirring of the bath, and as a result, the desiliconization reaction which takes precedence over the decarburization reaction is promoted and the decarburization is suppressed. It As a method for strengthening the stirring of the bath, the feeding rate of the stirring gas blown into the bath from the immersion lance 3 (or the bottom blowing nozzle) or the like is increased. Similarly, the feeding rate of the powder blown into the bath together with the stirring gas is increased. And increasing the stirring gas and powder supply rates, and any of these methods may be carried out.

[0026]

[Example] 145 t of hot metal tapped from a blast furnace was subjected to desiliconization treatment using a hot metal ladle. The chemical composition of the hot metal before desiliconization is [C]: 4.5 to 4.7 mass%, [Si]: 0.18 to
0.22 mass%, hot metal temperature is 1400 to 1450
It was ℃. In the desiliconization treatment, oxygen gas was supplied from the acid feeding lance to the bath surface in the hot metal ladle, and stirring gas and lime powder were blown into the bath through the injection lance (immersion lance). The lance height of the acid transfer lance is 1100.
It was fixed at mm. The acid transfer rate from the acid transfer lance is 0.1
It was set to 0 to 0.59 Nm ³ / minT. Also, nitrogen is used as the stirring gas blown from the injection lance,
The gas supply rate is 168 to 383 Nm ³ / hr,
The supply rate of lime powder was 28 to 165 kg / min.

The optical fiber portion of the optical fiber type radiation thermometer is mounted inside the acid feeding lance, and the detection end at the tip is arranged near the tip inside the gas injection hole at the center of the lance as shown in FIG. The flash point temperature was measured by this radiation thermometer during the silicidation. As the hot metal desiliconization process progressed, it was confirmed that the hot spot temperature increased from a certain time, but in the present invention example, the decarburization reaction occurred when the hot spot temperature increase of 50 ° C. or higher was measured for 10 seconds. It was determined that the progress was rapid, and at least one of the acid feeding rate from the acid feeding lance, the stirring gas feeding rate, and the powder feeding rate was changed. On the other hand, in the comparative example, the operation was performed under a constant condition regardless of the increase in the fire point temperature.

Table 1 shows each test condition and its result. The term "I" shown in Table 1 means that at least one of the acid feeding rate, the stirring gas supply rate, and the powder supply rate is changed to II.
The term means after changing this. The timing of this change in each example was about 3.4 minutes from the start of acid transfer.
It was 4.7 minutes later. According to Table 1, the example of the present invention in which the rate of oxygen transfer or the stirring power of the bath was controlled at the time when the flash point temperature started to rise rapidly, the desiliconization oxygen efficiency was improved, the oxygen consumption rate was reduced, and The amount of charcoal is small and the processing time can be shortened. Therefore, according to the present invention, it is possible to efficiently desiliconize hot metal to an extremely low silicon concentration while suppressing decarburization, and further, since the processing time can be shortened, productivity is improved and stable operation is possible. I understand.

[0029]

[Table 1]

[0030]

As described above, according to the present invention, it is possible to perform desiliconization while accurately ascertaining the progress of decarburization accompanying a decrease in the silicon concentration in the hot metal during hot metal desiliconization. Therefore, the action required to suppress decarburization can be promptly and appropriately performed. For this reason, it is possible to perform desiliconization treatment in which the decarburization reaction is appropriately suppressed, especially in a low silicon concentration range, and it is possible to improve the efficiency of desiliconization oxygen, reduce the oxygen basic unit, and shorten the treatment time. Therefore, according to the present invention, it is possible to efficiently and stably desilver the hot metal up to an extremely low silicon concentration while suppressing decarburization.
In addition, since hot metal can be desiliconized to an extremely low silicon concentration while suppressing decarburization in this way, the amount of slag generated in the dephosphorization process that is the next step can be reduced, and decarburization of hot metal is suppressed. Therefore, there is an advantage that it is easy to secure a heat margin in the lower step, and similarly, problems of slag forming and equipment damage due to CO gas generated by decarburization of hot metal can be avoided.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing an example of a desiliconization treatment condition using a hot metal ladle.

2A and 2B show an example of the structure of the tip portion of the acid-feeding lance used in the method of the present invention. FIG. 2A is a front view of the tip of the acid-feeding lance, and FIG. Sectional drawing which follows the BB line of A).

3A and 3B show another structural example of the tip portion of the acid feeding lance used in the method of the present invention. FIG. 3A is a front view of the tip of the acid feeding lance, and FIG. Sectional drawing which follows the BB line of (A).

FIG. 4 is a graph showing an example of transition of the fire point temperature measured by an optical fiber type radiation thermometer arranged on the acid sending lance in the method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hot metal pot, 2 ... Acid feeding lance, 3 ... Immersion lance, 4 ... Optical fiber type radiation thermometer, 5 ... Optical fiber part, 20,
20a, 20b ... Gas injection hole, 50 ... Detection end

Continued front page    (72) Inventor Hidetoshi Matsuno             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Yukie Nakai             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Satoshi Kodaira             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Shinichi Akai             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F-term (reference) 4K014 AA01 AC14 AD17

Claims (6)

[Claims] 1. A method for desiliconizing molten pig iron while supplying a gaseous oxygen source from the acid feeding lance into the vessel as a hot metal pretreatment, using a fiber optic radiation thermometer placed on the acid feeding lance. A hot metal desiliconizing method characterized by measuring the temperature of a hot spot generated on a hot metal bath surface by feeding oxygen from a lance and determining the decarburization state of the hot metal based on the change in the hot spot temperature. 2. The hot metal desiliconization treatment method according to claim 1, wherein the stirring gas or the stirring gas and powder are blown into the bath from the bottom blowing nozzle or the immersion lance to stir the bath. 3. When the rise in the flash point temperature is measured, at least one of an acid transfer rate by an acid transfer lance, a stirring gas supply rate, and a powder supply rate is controlled. The hot metal desiliconization treatment method according to claim 1. 4. When at least one increase in the flash point temperature of 50 ° C. is measured in 10 seconds, at least one of an acid transfer rate by an acid transfer lance, a stirring gas supply rate, and a powder supply rate is selected. It controls, The hot metal desiliconization processing method of Claim 3 characterized by the above-mentioned. 5. The detection end at the tip of the optical fiber portion of the optical fiber type radiation thermometer is arranged in the gas injection hole at the tip of the acid feeding lance or in the vicinity of the discharge port of the gas injection hole. 3. The hot metal desiliconization treatment method according to 3 or 4. 6. An oxygen transfer lance having a plurality of gas injection holes having different gas injection flow rates is used, and in the gas injection hole having the largest gas injection flow rate among the plurality of gas injection holes or in the vicinity of the discharge port of the gas injection hole. The hot metal desiliconization treatment method according to claim 5, wherein a detection end at the front end of the optical fiber portion of the optical fiber type radiation thermometer is arranged.