WO2014115526A1

WO2014115526A1 - Preliminary processing method for molten iron

Info

Publication number: WO2014115526A1
Application number: PCT/JP2014/000236
Authority: WO
Inventors: 泰志小笠原; 内田　祐一; 三木　祐司; 伊藤　友彦; 手塚　浩一; 田中　高太郎; 秀光根岸; 川畑　涼; 山本　和人; 奥山　悟郎
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2013-01-24
Filing date: 2014-01-20
Publication date: 2014-07-31
Also published as: BR112015017155B1; TWI576437B; CN104955965A; JP5761459B2; KR20150088889A; CN104955965B; JPWO2014115526A1; KR101751151B1; TW201437377A; BR112015017155A2

Abstract

In the present invention, when using one converter-type smelting furnace to continuously carry out molten iron desiliconization processing and dephosphorization processing with a midway slag discharge step therebetween, in the slag discharge step a sufficient amount of slag is promptly discharged to the outside of the furnace, and sufficient dephosphorization processing in terms of cost and quality is carried out. Provided is a preliminary processing method having the following: a desiliconization step for desiliconizing molten iron (5) by supplying a gaseous oxygen source from a top blowing lance (2) to the molten iron (5) in a converter-type smelting furnace; a slag discharge step for discharging from the converter-type smelting furnace at least a portion of the slag generated by the desiliconization step; a dephosphorization processing step for, after the slag discharge step, dephosphorizing the remaining molten iron by adding a CaO solvent into the converter-type smelting furnace and supplying the gaseous oxygen source from the top blowing lance. During the desiliconization, the slag height in the furnace is measured, and in a state where the measured slag height is in a predetermined range of proportion to a free board in the furnace defined by the distance from the molten iron bath surface to the furnace throat, the desiliconization processing is stopped.

Description

Hot metal pretreatment method

The present invention relates to a hot metal pretreatment method in which a hot metal desiliconization process and a dephosphorization process are continuously performed using a single converter-type refining furnace, with an intermediate exhausting process interposed therebetween.

In recent years, the development of hot metal pretreatment technology using a converter-type refining furnace has progressed, and the following pretreatment methods have been developed. That is, after desiliconizing the molten iron in the converter-type refining furnace, the converter-type refining furnace is tilted to at least slag in the furnace (the slag generated by the desiliconizing process is called “desiliconized slag”). A refining method was developed in which one part was discharged, and then a CaO-based solvent was introduced into the furnace, and the remaining hot metal was dephosphorized (this refining method is called “twice-exhaust method”). (For example, refer to Patent Document 1).

This two-time slagging method is a conventional pretreatment method in a converter-type smelting furnace, that is, a CaO-based solvent is introduced at the start of smelting to perform desiliconization / dephosphorization treatment on the hot metal in the converter-type smelting furnace. Compared with the pretreatment method, there are the following advantages. That is, (1) Since the desiliconization slag is discharged in the middle, it is possible to treat hot metal with a high silicon content, and it is possible to effectively utilize the silicon in the hot metal as a heat source. (2) Desiliconization slag in the middle Is advantageous in that the amount of CaO-based solvent used in the subsequent dephosphorization process can be reduced.

The important point of operation is how to quickly discharge a predetermined amount of desiliconized slag from the furnace in a short time in the exhausting process after the desiliconization process. It becomes. In the case where the amount of desiliconized slag discharged in the evacuation process is small, the above effect cannot be obtained, which is equivalent to the pretreatment method in the conventional converter-type refining furnace described above.

In addition, after the dephosphorization process is completed, the dephosphorized hot metal is discharged from the furnace, but the slag generated by the dephosphorization process (slag generated by the dephosphorization process is referred to as “dephosphorization slag”) is left in the furnace. In addition, a refining method has been developed in which molten iron of the next charge is charged into a converter-type refining furnace in which dephosphorization slag remains, and preliminary treatment is performed on the molten iron according to the above procedure (for example, Patent Documents). 1 and Patent Document 2). This refining method further has the following advantages. (3) By leaving the dephosphorization slag generated in the dephosphorization process in the furnace, reducing the CaO-based solvent during the desiliconization process, utilizing the sensible heat of the dephosphorization slag, the iron content in the dephosphorization slag (4) Reusable dephosphorization slag and effective utilization of silicon in the hot metal as a heat source enables high thermal efficiency and increases the ratio of cold iron source, (5) Basicity ((Mass% CaO) / (mass% SiO ₂ )) is relatively high, suppresses the generation of dephosphorization slag that requires aging treatment, and provides good volume stability even if the aging treatment is omitted. There is an advantage that it can be converted to desiliconized slag that can be obtained.

However, in the method of leaving the dephosphorization slag, if the amount of slag discharged after the desiliconization process is insufficient, a large amount of phosphorus derived from the dephosphorization slag left in the previous charge remains in the furnace. In this dephosphorization treatment, it becomes difficult to reduce the phosphorus concentration of the hot metal to the target level, so it is necessary to secure a sufficient amount of slag discharge in the exhausting step after the desiliconization treatment. On the other hand, if the working time for evacuation becomes longer in order to secure the slag discharge amount, the number of charges that can be carried out for such pretreatment is limited, and the furnace body is increased in order to increase the slag discharge speed. If the inclination angle is too large, the amount of hot metal flowing out together with the slag increases and the iron yield decreases. Therefore, in order to prevent these problems from occurring, it is necessary to efficiently discharge the slag in the discharging process after the desiliconization process.

In addition, steelmaking slag including desiliconized slag and dephosphorized slag contains a large amount of iron oxide, and therefore tends to have a higher density than natural stone sand and blast furnace slag. For this reason, steelmaking slag has not been applied to civil engineering applications where it is feared that steelmaking slag may promote gravitational instability. Furthermore, since the volume per unit mass of steelmaking slag is smaller than that of natural stone sand, etc., an increase in transportation costs is also a drawback as a material for civil engineering work. In order to obtain a material that can be easily used for applications, it is desirable to reduce the bulk specific gravity of the steelmaking slag.

Therefore, the present inventors examined the discharge performance of the desiliconized slag in the discharge process after the desiliconization treatment. As a result, it was found that if the formation of desiliconization slag during desiliconization is small, the flowability of desiliconization slag is low and it is difficult to discharge a sufficient amount of desiliconization slag within a predetermined time. . Accordingly, it has been found that in order to allow a sufficient amount of desiliconized slag to flow out of the furnace quickly in the slagging process, the desiliconized slag must be stably formed during desiliconization blowing. Here, slag forming is a phenomenon in which molten slag contains bubbles and apparently expands in volume.

That is, it was found that it is important to detect the slag level during the desiliconization process and to control the forming of the desiliconization slag. However, excessive forming of desiliconized slag leads to sudden slag outflow during the evacuation process, and it is necessary to take measures to suppress it. On the contrary, the time of the evacuation process is extended, so the forming is controlled appropriately. It was also found that this is important. These findings are not described in Patent Document 1 and Patent Document 2.

Conventionally, as a method for detecting the formation of slag in a converter-type refining furnace, Patent Document 3 discloses that a sublance is measured while applying a constant frequency / amplitude vibration (forced vibration) to the sublance and simultaneously measuring the vibration of the sublance. Has been proposed to detect the forming height of the in-furnace slag based on the amount of damping of the forced vibration. However, this method is based on the premise that the tip of the sublance is buried in the formed slag, and when the forming is small and the tip of the sublance is not buried in the formed slag, it is impossible to detect the forming height. Can not. Further, since the attenuation amount of the forced vibration varies depending on the composition and temperature of the slag to be generated, it is difficult to accurately detect the forming height.

Also, Patent Document 4 and Patent Document 5 propose a method of measuring the slag height during refining using a microwave. However, these technologies are forming detection technology in decarburization and refining of hot metal in the converter, and desiliconization slag in desiliconization in the hot metal pretreatment and converter slag in decarburization and refining in the converter. Since the slag temperature, basicity, and iron oxide concentration differ greatly, the electrical conductivity differs greatly. Therefore, the microwave reflection characteristics differ between desiliconization treatment and decarburization refining. The results cannot be applied to the desiliconization process as it is.

For example, although the principle is unknown in Patent Document 4, the slag level is detected based on the frequency change of the mixed wave of the transmission wave and the reflected wave, or the slag level is detected from the reflectance of the microwave. It is described. However, with desiliconized slag with low electrical conductivity, the reflectivity of the microwave is very small and most of it is transmitted, so the reflected wave from the hot metal bath surface and the multiple reflected waves at the hot metal bath surface and slag surface are also Since it exists, the method of patent document 4 cannot detect a slag level.

Further, in Patent Document 5, a transmission / reception antenna is inserted in the furnace, and in a refining furnace exposed to high-temperature slag or hot metal droplets, these droplets adhere to the antenna even in a short time of use. It is difficult to measure continuously during the refining period.

Japanese Patent Laid-Open No. 11-323420 JP 2001-271113 A JP-A-5-255726 JP 59-41409 A JP-A-3-281717

The present invention has been made in view of the above circumstances, and the object of the present invention is to perform hot metal desiliconization treatment and dephosphorization treatment using a single converter-type refining furnace with an intermediate waste removal step in between. In the continuous hot metal pretreatment method, after the desiliconization process, after the degassing process, the target amount of desiliconized slag can be quickly and quickly removed from the furnace in a short period of time. In the dephosphorization process of the next step, it is possible to provide a hot metal pretreatment method that enables sufficient dephosphorization process in terms of cost and quality. Another object of the present invention is to provide a hot metal pretreatment method capable of obtaining a slag having a relatively small bulk specific gravity suitable for various civil engineering materials.

The gist of the present invention for solving the above problems is as follows.
[1] A desiliconization process for supplying a gaseous oxygen source from an upper blow lance to hot metal in a converter-type refining furnace to desiliconize the hot metal, and at least a part of the slag generated in the desiliconization process Exhaust process discharged from the converter-type refining furnace, and after the exhaust process, a CaO-based solvent was added to the converter-type refining furnace, and a gaseous oxygen source was supplied from the upper blowing lance to remain. A dephosphorization process for dephosphorizing the hot metal, and measuring the slag height in the furnace during the desiliconization process, and the measured slag height is the hot metal in the furnace A hot metal pretreatment method, characterized in that the desiliconization process is terminated in a state where the ratio of the freeboard in the furnace from the bath surface to the furnace opening is in a predetermined range.
[2] The hot metal pretreatment method according to [1], wherein the predetermined range of the ratio is in a range of 0.5 to 0.9.
[3] Based on the measurement result of the slag height, during the desiliconization process, the supply flow rate of the gaseous oxygen source from the top blowing lance, the lance height of the top blowing lance, and the gas for stirring from the bottom blowing tuyere Adjusting at least one selected from the group of supply flow rate, composition of slag in the furnace, and amount of forming sedative material, and controlling the slag height in the furnace during desiliconization by this adjustment The hot metal pretreatment method according to [1] or [2] above.
[4] The slag height in the furnace during the desiliconization process so that the ratio of the slag height to the height of the freeboard in the furnace during the desiliconization process is in the range of 0.5 to 0.9. The hot metal pretreatment method according to [3], wherein the hot metal is controlled.
[5] Using a pseudo-random signal processing radar type microwave rangefinder, a microwave having a frequency of 10 GHz or less is transmitted into the converter-type refining furnace to receive a reflected wave. The distance to the object corresponding to the reflected wave signal is greater than the distance to the furnace port and the distance to the furnace port among the received reflected wave signals with a certain intensity or higher. The signal of the reflected wave closest to is determined as the signal of the reflected wave from the slag surface, the distance to the slag surface is obtained, and the slag height is measured based on the obtained distance to the slag surface. The hot metal pretreatment method according to any one of [1] to [4] above.
[6] Of the reflected wave signals received by the distance meter, the distance to the object corresponding to the reflected wave signal does not change from the start of the desiliconization process, and the reflected waves that exist continuously The hot metal preliminary processing method according to [5], wherein a signal of a reflected wave from the slag surface is determined after removing the signal as noise.
[7] Using a pseudo-random signal processing radar-type microwave rangefinder, a microwave having a frequency of 10 GHz or less is transmitted into the converter-type refining furnace, a reflected wave from the furnace is received, and the reflected wave reciprocates. The distance from the time to the target object is obtained, and the distance to the target object corresponding to the reflected wave signal from the target wave existing in the range from the furnace port to the hot metal bath surface is desiliconized. The reflected wave signal that is continuously present without any change from the beginning is removed as noise, and the reflected wave signal with the highest reflection intensity is removed except for the reflected wave signal corresponding to the hot metal bath surface. [1] to [4], wherein the distance to the slag surface is determined as a signal of a reflected wave from the surface, and the slag height is measured based on the determined distance to the slag surface. The hot metal preparation according to any one of Processing method.
[8] After the completion of the dephosphorization process of the pre-charged hot metal in the converter type refining furnace, the hot metal subjected to the dephosphorization process is discharged, and the converter type is discharged without discharging the slag in the furnace generated by the dephosphorization process. Fresh hot metal left in the smelting furnace is charged into the converter-type smelting furnace, the hot metal is subjected to the desiliconization process, and the basicity of the slag in the furnace is set at the end of the desiliconization process. 0.8 to 1.5 or less, the temperature of the hot metal is 1280 ° C. or more and 1380 ° C. or less, the silicon content of the hot metal is 0.10% by mass or less, and in the exhausting process, 30 More than mass% is discharged out of the furnace, and then the dephosphorization process is performed on the hot metal in the furnace. After the dephosphorization process is completed, the dephosphorized hot metal is discharged and the furnace generated by the dephosphorization process New hot metal is left in the converter-type smelting furnace without being discharged in the converter-type smelting furnace. Charged with, and performs preliminary processing on the molten iron, the above-mentioned [1] to molten iron pretreatment method according to any one of the above [7] to.
[9] The slag height in the furnace is measured during the dephosphorization process after the exhausting process, the supply flow rate of the gaseous oxygen source from the top blowing lance, the lance height of the top blowing lance, and the stirring from the bottom blowing tuyere The above [1] to [8], wherein at least one selected from the group of supply flow rates of the working gas is adjusted, and the slag in the furnace is controlled not to be ejected from the furnace port by this adjustment. The hot metal pretreatment method according to any one of the above.

According to the present invention, in one preliminary treatment of hot metal, which uses a single converter-type smelting furnace, the hot metal desiliconization treatment and the dephosphorization treatment are continuously performed with an intermediate waste removal step interposed therebetween, the desiliconization treatment. At the end of the desiliconization process, the formed desiliconization slag is finished in a state where the height of the formed desiliconization slag is within a predetermined range with respect to the height of the freeboard in the furnace. It is possible to quickly discharge a predetermined amount of desiliconized slag as a target to the outside of the furnace in a short time after suppressing the sudden outflow of slag. As a result, it becomes possible to smoothly carry out the exhausting process without delaying, and in the dephosphorization process of the next process, the phosphorus concentration of the hot metal can be reduced to a low concentration with a small amount of CaO-based solvent used. It becomes possible.

FIG. 1 is a schematic cross-sectional view of a converter-type refining furnace used when carrying out the hot metal pretreatment method according to the present invention. FIG. 2 is a schematic view showing the hot metal pretreatment method according to the present invention in the order of steps. FIG. 3 is a diagram illustrating an example of a reflected wave signal collected using a microwave slag level meter. FIG. 4 is a diagram showing the transition of the slag height in the furnace during the desiliconization process from the measurement result obtained by the microwave slag level meter. FIG. 5 is a diagram showing the relationship between the slag height at the end of the desiliconization process and the intermediate evacuation time. FIG. 6 is a diagram showing the relationship between the slag height at the end of the desiliconization process and the phosphorus concentration in the hot metal after the dephosphorization process. FIG. 7 is a diagram showing the influence of the acid feed rate from the top blowing lance on the slag height. FIG. 8 is a diagram showing the influence of the lance height of the top blowing lance on the slag height. FIG. 9 is a diagram showing the influence of the bottom blowing gas flow rate on the slag height. FIG. 10 is a graph showing the transition of the ratio of the slag height to the height of the free board in the furnace during the desiliconization process in Invention Examples 1 and 2 and Comparative Examples 1 and 2. FIG. 11 is a graph showing the transition of the ratio of the slag height to the height of the free board in the furnace during the dephosphorization process in Invention Example 3 and Comparative Example 2.

Hereinafter, the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of a converter type refining furnace used when carrying out the hot metal pretreatment method according to the present invention, and FIG. 2 is a schematic view showing the hot metal pretreatment method according to the present invention in the order of steps. . FIG. 1 is a diagram showing the desiliconization process of FIG. 2- (B).

In the hot metal pretreatment method according to the present invention, a converter-type refining furnace 1 capable of top bottom blowing as shown in FIG. 1 is used. The top blowing is performed by supplying an oxygen-containing gas toward the hot metal 5 as a gaseous oxygen source from the tip of the top blowing lance 2 via the top blowing lance 2 that can move up and down inside the converter type refining furnace 1. As the oxygen-containing gas, oxygen gas, oxygen-enriched air, air, or a mixed gas of oxygen gas and inert gas can be used. FIG. 1 shows an example in which oxygen gas 8 is used as the oxygen-containing gas. Here, the oxygen gas 8 is industrial pure oxygen. The bottom blowing is performed through a bottom blowing tuyere 3 provided at the bottom of the converter type refining furnace 1. The bottom blowing gas 9 may be a gas containing oxygen gas or only an inert gas such as argon gas or nitrogen gas. Moreover, it has the function of strengthening the stirring of the hot metal 5 by blowing it into the hot metal and accelerating the melting of the cold iron source, and also has the function of blowing the iron making agent into the hot metal together with the conveying gas from the bottom blowing tuyere 3. It may be a thing. Details of FIG. 1 will be described later.

In the present invention, two or more converter-type refining furnaces 1 are used for refining the hot metal 5, and at least one of these converter-type refining furnaces 1 is used for the hot metal pretreatment according to the present invention, and the rest At least one group is used for decarburization refining of the hot metal 5 subjected to the hot metal pretreatment according to the present invention. That is, the pretreatment is performed in the converter type refining furnace 1 for hot metal pretreatment, and then the hot metal 5 subjected to the pretreatment is transferred to the converter type refining furnace 1 for decarburization refining and decarburization treatment is performed. .

In the pretreatment method of the hot metal 5 according to the present invention, as shown in FIG. 2- (A), a charging pot 10 is placed in a converter-type refining furnace 1 in which a cold iron source 7 such as iron scrap is previously charged. Then, the hot metal 5 which has not been subjected to desiliconization and dephosphorization is charged (a hot metal charging step).

Next, a gaseous oxygen source or a gaseous oxygen source and a solid oxygen source such as iron oxide are supplied as an oxygen source to the hot metal 5 in the converter-type refining furnace, and desiliconization treatment is performed as shown in FIG. (Desiliconization process). Silicon contained in the hot metal 5 reacts with oxygen in the oxygen source (Si + 2O → SiO ₂ ), and the desiliconization process proceeds. The hot metal temperature rises due to the oxidation heat of silicon by this desiliconization reaction, and the dissolution of the cold iron source 7 in the hot metal is promoted.

In the present invention, the desiliconization process and the dephosphorization process are performed by using one converter-type refining furnace 1, and when the desiliconization process is performed, the dephosphorization slag generated by the decharge process of the precharge is performed. However, it remains attached to the furnace wall of the converter type refining furnace 1. Therefore, when the basicity ((mass% CaO) / (mass% SiO ₂ )) (hereinafter sometimes simply referred to as “basicity”) of the silica removal slag 6 is not controlled in the silicon removal treatment. The phosphorous oxide (P ₂ O ₅ ) contained in the remaining dephosphorization slag is decomposed, and so-called “rebound” may occur in which the phosphorus concentration in the hot metal 5 increases. If dephosphorization slag is intentionally left in the furnace in order to reduce the amount of CaO-based solvent used during desiliconization, there is a possibility that the phosphorus concentration pick-up due to dephosphorization will become larger. That is, in order to prevent such recovery, it is preferable to adjust the basicity of the desiliconized slag 6 generated by the desiliconization process.

Under normal desiliconization conditions, the hot metal temperature is about 1300 ° C., and the FeO concentration in the desiliconization slag is about 10 to 20% by mass. By setting the basicity to 0.8 or more, the recovery reaction is suppressed.

The basicity ((mass% CaO) / (mass% SiO ₂ )) of the desiliconized slag 6 can be calculated based on the following formula (1).
Basicity = [(Remaining CaO amount in furnace (kg / molten metal-t)) + (Amount of added CaO in desiliconization treatment (kg / molten metal-t))] / [(Remaining SiO ₂ amount in furnace (kg / molten metal) -t)) + (Amount of SiO ₂ produced by desiliconization (kg / molten-t))] ... (1)
Incidentally, furnace residual amount of CaO and furnace residual amount of SiO ₂ is the amount of CaO and SiO ₂ amount contained in the dephosphorization slag before the charge remaining in the furnace, generating SiO ₂ amount of desiliconization treatment Can be calculated from the change in the Si concentration in the hot metal before and after the silicon removal treatment.

As the oxygen source for the desiliconization treatment, only the oxygen gas 8 from the top blowing lance 2 may be used, or the oxygen gas 8 and a solid oxygen source such as iron oxide (not shown) may be used in combination. In order to generate the desiliconized slag 6 having the target basicity during the desiliconization process performed in a short time, it is effective to use iron oxide having a function of promoting the hatching of the CaO-based solvent. is there. However, from the viewpoint of dissolving a large amount of cold iron source 7, which is one of the objects of the present invention, it is not preferable to use a large amount of iron oxide that absorbs heat during heating and decomposition. Is preferably minimized. Moreover, since the converter-type smelting furnace 1 is used as a smelting vessel, the oxygen gas supply rate can be increased, and even if the desiliconization process is performed using only the oxygen gas 8, the CaO-based solvent can be sufficiently used. It is possible to generate the desiliconized slag 6 having the target basicity by promoting the hatching.

After this desiliconization process, as shown in Fig. 2- (C), the converter type refining furnace 1 is tilted to the side opposite to the side where the outlet 4 is installed, and is generated by the desiliconization process. The desiliconized slag 6 containing a large amount of SiO ₂ is discharged through a furnace port of the converter-type refining furnace 1 to a slag pot (not shown) disposed on the lower track (exhaust process). The converter-type refining furnace 1 is tilted within a range in which the molten iron 5 does not flow out of the furnace port, and the desiliconized slag 6 is discharged by the overflow from the furnace port, and the slag surface from the lower end of the tilted furnace body The higher the height is, the more efficiently it can be discharged, but the desiliconized slag 6 cannot be completely discharged, and a part of the desiliconized slag 6 remains in the furnace. Since the removal process of the desiliconization slag 6 is performed between the desiliconization process and the dephosphorization process, it is also referred to as “intermediate waste removal”.

After the slagging step, the hot metal 5 remaining in the converter type refining furnace is supplied with a CaO-based solvent and an oxygen source, and the hot metal 5 is dephosphorized as shown in FIG. Dephosphorization process). In the dephosphorization process, the basicity of the slag in the furnace is adjusted to a range of 1.3 to 3.5. The oxygen source used in this dephosphorization process is mainly composed of the oxygen gas 8 from the top blowing lance 2 as in the desiliconization process, but a part of iron oxide may be used. However, the present invention is intended to dissolve a large amount of cold iron source 7, and as described above, it is possible to avoid using iron oxide that absorbs heat at the time of heating and decomposition as an oxygen source as much as possible. preferable.

As the CaO-based medium solvent used in the dephosphorization treatment, quick lime, calcium carbonate or the like can be used. However, it is not limited to these, What contains 40 mass% or more of CaO, and contains other components, such as a fluorine, an alumina, and an iron oxide as needed, is also used as a CaO type | system | group solvent solvent at the time of a dephosphorization process. be able to. As a method for adding the CaO-based medium solvent, granular and lump-shaped ones can be charged from a hopper on the furnace, and powdery ones can be charged through an upper blowing lance 2 or the like.

Phosphorus in the hot metal is oxidized to oxygen in the supplied oxygen source to become phosphorus oxide (P ₂ O ₅ ), which is produced by the incubation of the CaO-based solvent and functions as a dephosphorizing refining agent. Incorporated into the slag as a stable compound of 3CaO · P ₂ O ₅ , the dephosphorization reaction of the hot metal 5 proceeds. After the dephosphorization treatment, dephosphorization slag containing a phosphorus oxide is generated.

When the phosphorus removal reaction proceeds and the phosphorus concentration in the hot metal is lowered to a predetermined value, the phosphorus removal treatment is terminated. Next, as shown in FIG. 2- (E), the converter-type refining furnace 1 is tilted to the side where the outlet 4 is installed, and the hot metal 5 in the converter-type refining furnace is passed through the outlet 4. Hot water is poured into a hot metal holding container (not shown) (a hot water discharge step).

After discharging the hot water, without discharging the dephosphorization slag in the furnace, the converter type refining furnace 1 may be charged with the cold iron source 7 and the hot metal 5 to start the next charge desiliconization process, In addition, after the dephosphorization slag in the furnace is discharged, the cold iron source 7 and the hot metal 5 may be charged to start the next charge desiliconization process. When all or most of the dephosphorization slag generated in the furnace is left in the furnace and the next charge desiliconization process is started, the heat and iron content of the decharged slag from the previous charge are depleted. It can be recovered in the treatment, and the CaO content in the dephosphorization slag of the previous charge can be used as a CaO source in the desiliconization treatment of the next charge, reducing the amount of CaO-based solvent used during the desiliconization treatment can do.

In the present invention, when performing desiliconization treatment and dephosphorization treatment on the hot metal 5 in this way, the desiliconization slag 6 of a predetermined amount or more is quickly discharged out of the furnace in the exhausting step. The height of the desiliconized slag 6 is measured during the treatment, and the slag height (distance from the hot metal bath surface when stationary in the furnace to the upper end of the desiliconized slag 6) is the target range. Then, the desiliconization slag 6 is formed during the desiliconization process. In addition, since the fluidity of the desiliconization slag 6 is low when the forming of the desiliconization slag 6 is small at the end of the desiliconization process, the present inventors discharge a sufficient amount of the desiliconization slag 6 within a predetermined time. Make sure it is difficult to do. Therefore, in order to allow a sufficient amount of desiliconized slag 6 to flow out of the furnace quickly in the exhausting process, the desiliconized slag 6 is formed so as to be in a predetermined slag height range at the end of the desiliconization process. It is necessary to let Here, slag forming is a phenomenon in which molten slag contains bubbles and apparently expands in volume.

Therefore, the converter type refining furnace 1 used in the present invention is required to have a function of measuring the slag height in the furnace.

In the converter type refining furnace 1 used in the present invention shown in FIG. 1, a hood 12 for recovering exhaust gas generated from the furnace is provided above the furnace port of the converter type refining furnace 1. A flue 11 for introducing exhaust gas into the dust collector is provided at the top of the. The hood 12 is provided with an opening 13 and an opening 14, the upper blowing lance 2 is inserted into the furnace through the opening 13, and the pseudo-random signal processing radar passes through the opening 14. Two waveguides 16 attached to a system microwave distance meter 15 (hereinafter simply referred to as “microwave slag level meter 15”) are installed. A transmitting antenna 17 and a receiving antenna 18 are provided at positions directly below the opening 14 at the ends of the two waveguides 16, respectively. That is, the microwave slag level meter 15 is configured to measure the height of the desiliconized slag 6 in the furnace.

Since the reflectivity of the formed siliconized slag 6 with respect to the microwave is as small as 10 ⁻⁴ or less, in one embodiment of the present invention, the measurement sensitivity is improved by using a signal obtained by modulating the microwave with a pseudo-random signal. Using enhanced radar. As the pseudo-random signal, for example, a pseudo-random signal that repeats the same waveform at a frequency of about 6 MHz that is generated by combining an appropriate logic circuit from a high-frequency clock signal of about 800 MHz can be used. This is an example of a case where the clock signal to generate a pseudo-random signal by 2 ⁷ times (128 times) logic circuit is input to round it.

As a microwave carrier to be used, for example, a microwave having a frequency of about 10 GHz is used, and a microwave that is modulated by multiplying a pseudo-random signal and a transmission antenna 17 installed in the opening 14 of the hood 12 on the furnace is used. And radiates toward the inside of the converter type refining furnace 1.

Here, the wavelength in the air of the electromagnetic wave with a frequency of 10 GHz is about 3.0 cm, and when it is less than 10 GHz, the wavelength is longer than that, which is sufficiently longer than the dust and smoke particles in the converter type refining furnace. Therefore, it is hardly affected by dust and the wavelength is short, which is advantageous for downsizing of the antenna. The transmitting antenna 17 and the receiving antenna 18 are, for example, horn antennas, and the reflected waves from other than the slag surface are made as small as possible by reducing the directivity sharply. The lower the frequency of the microwave, the less susceptible to dust and the like. Accordingly, the microwave used in the present invention has an upper frequency limit of 10 GHz, preferably lower than 10 GHz, and more preferably 8 GHz or lower. . However, if the frequency of the microwave is too low, there is a problem that the resolution of time and distance is lowered, and the size of the antenna is required, which is not preferable for preventing dust from adhering to the antenna. Is preferably 2 GHz or more.

The electromagnetic wave radiated from the transmitting antenna 17 into the converter type refining furnace is reflected on the slag surface and converted into an electric signal through the receiving antenna 18. Naturally, the timing at which the input signal is supplied to the receiver of the microwave slag level meter 15 reciprocates the distance from the timing at which the electromagnetic wave is radiated from the transmitting antenna 17 to the slag level in the converter refining furnace. The electromagnetic wave is delayed by the propagation time of the electromagnetic wave until it reaches the receiving antenna 18. This propagation time can be measured by comparing the phase difference of a pseudo-random signal modulated on a microwave carrier wave between the received wave and the transmitted wave.

At that time, the propagation time can be directly obtained from the time correlation function of the pseudo random signal component modulated into the received wave and the transmitted wave, but the pseudo random signal generated by slightly changing the clock frequency is used. By performing signal processing in this way, it is possible to perform measurement with high resolution by greatly expanding the time axis of the time correlation function.

For example, from a pseudo-random signal that repeats the same waveform at a frequency of about 6 MHz generated from an 800 MHz high-frequency clock signal using an ethical circuit, from a clock signal (for example, 800.004 MHz) whose frequency is changed by 4 kHz. When using pseudo-random signals generated using the same logic circuit, multiplying both pseudo-random signals, if both phases do not match, the multiplication result is only a high-frequency component about the clock frequency, When the two phases coincide with each other, a direct current component or a low frequency component is generated in the multiplication result of two pseudo-random signals having the same waveform. Therefore, when a signal component having a frequency higher than the repetition frequency of the pseudo random signal is further removed by the low-pass filter, a timing at which the phases of the two pseudo random signals coincide with each other at a period of 4 kHz is detected. This is because the pseudo-random signals of the two differ in the reference clock frequency by 4 kHz, so that the phase difference changes little by little and the phases coincide with each other only once in the period of 4 kHz.

In this way, the phase difference within the repetition frequency period of the pseudo random signal of about 6 MHz, that is, the time delay is converted into the time difference within the period of 4 kHz, and the time axis is expanded by about 1500 times, The phase difference between the pseudo-random signal of the received wave and the transmitted wave can be detected.

The received reflected wave includes reflected waves from various paths and objects, and the reflected wave from each object has a pseudo-random signal component corresponding to the reflection intensity and the phase delay corresponding to the propagation time. It is included. For such a reflected wave, signal processing using a pseudo-random signal with the above clock signal frequency changed is performed, and the propagation time is increased by about 1500 times when compared with a signal of a transmission wave that has been similarly processed. It expands and the signal according to the propagation time and intensity | strength of the reflected wave component from each target object is detected.

The signal detected in this way is detected by converting the time delay from the transmission wave into the propagation time, multiplying this by the microwave propagation velocity (3 × 10 ⁸ m / s), and dividing by 2. The distance to the object corresponding to the received signal can be calculated.

FIG. 3 shows the above-described microwave slag level meter when dephosphorization slag generated by the decharge process of the pre-charge is left in the furnace and the desiliconization process is performed after the molten iron 5 of the charge is charged in the furnace. 15 is an example of a reflected wave signal sampled using No. 15. FIG. 3 shows the relationship between the distance from the antenna of the object that is the source of the reflected wave and the intensity of the reflected wave. The horizontal axis of FIG. 3 uses a value obtained by converting the delay time of the detected signal from the transmission wave into the distance from the transmission antenna 17 and the reception antenna 18 to the object. When the signal processing as described above is performed, a detection signal of a reflected wave as shown in FIG. 3 is obtained with a period of 4 kHz, so that further averaging processing is performed to improve the signal / noise ratio, It is possible to continuously measure changes in the slag level.

In FIG. 3, detection signals of reflected waves having peaks at a plurality of positions are shown. With respect to a peak whose intensity is less than a certain value (reflected wave signal), the furnace body refractory and the furnace wall adhesion ground The peak of the reflected wave due to multiple reflection from gold or the top blowing lance 2 was assumed. Among the peak positions having an intensity of a certain value or more, the peak closest to the distance to the furnace mouth with the distance from the antenna larger than the distance to the furnace mouth is the peak of the reflected wave from the slag surface. Peaked.

Specifically, in the detection signal of the reflected wave as shown in FIG. 3, the peak having an intensity of 100 times or more of the background level is larger than the distance to the furnace port and is the most in the distance to the furnace port. A peak corresponding to the surface of the formed desiliconized slag 6 was taken as the peak at the near peak position. In FIG. 3, the distance from the antenna to the position corresponding to the furnace opening is about 9 m, and a large wide peak whose distance from the antenna is about 19 m corresponds to the hot metal bath surface.

In addition, since it can be determined that the peak that has existed without changing the generation position (distance from the antenna) from the start of the desiliconization process does not correspond to the reflected wave from the slag surface, such a peak If the peak corresponding to the slag surface is determined as described above after removing the noise as a noise, a more reliable measurement is possible.

In addition, after removing the peak that does not change position continuously from the start of desiliconization as noise, out of the peaks corresponding to the position in the range from the furnace port to the hot metal bath surface, It is also effective to calculate the distance to the slag surface by determining the peak with the highest intensity as the reflected wave from the slag surface, excluding the corresponding reflected wave peak, enabling highly reliable measurement. .

From the height relative to the reference surface (antenna position) of the slag surface determined by these methods, the height relative to the reference surface (antenna position) of the hot metal bath surface estimated from the sum of the amount of hot metal and iron scrap charged by the charge The absolute value of the difference was defined as the slag height. In FIG. 4, the example which calculated | required transition of the slag height in the furnace during the desiliconization process from the measurement result obtained by the microwave slag level meter 15 is shown. The validity of the obtained slag height was confirmed by collating with the timing of ejection of the formed desiliconized slag 6 from the furnace port (slag slopping).

In addition, the present inventors are concerned with the relationship between the slag height at the end of the desiliconization treatment and the intermediate waste time, and the relationship between the slag height at the end of the desiliconization treatment and the phosphorus concentration in the hot metal after the completion of the dephosphorization treatment. investigated. FIG. 5 shows the results of the investigation of the relationship between the slag height at the end of the desiliconization treatment and the intermediate evacuation time, and the relationship between the slag height at the end of the desiliconization treatment and the phosphorus concentration in the hot metal after the completion of the dephosphorization treatment. The survey results are shown in FIG. The horizontal axis in FIGS. 5 and 6 indicates the height of the free board in the furnace with the slag height (also referred to as “empty part”, the space between the hot metal bath surface and the furnace port when stationary) The distance between the hot metal bath surface and the furnace opening).

If the ratio of the slag height to the height of the freeboard in the furnace exceeds 0.9, the forming of the desiliconized slag 6 will be too intense, and the furnace will be set up once during the evacuation to calm the desiliconized slag 6 It was necessary to take it, and the extension of the intermediate elimination time was invited. On the other hand, when the ratio of the slag height to the height of the freeboard in the furnace is less than 0.5, the discharge performance of the desiliconized slag 6 at the time of intermediate discharge is poor, and in the dephosphorization process of the next step, the silicon removal Since the slag 6 remained excessively, the basicity of the slag decreased, and the phosphorus concentration in the hot metal after the dephosphorization treatment increased.

That is, the slag height of the desiliconized slag 6 is a predetermined range of 0.5 or more and 0.9 or less, preferably a predetermined range of 0.7 or more and 0.9 or less with respect to the height of the free board in the furnace. By completing the desiliconization process in the state of the ratio, it is realized that a sufficient amount of desiliconization slag 6 is quickly discharged out of the furnace in the subsequent exhausting process. In this dephosphorization treatment, it was confirmed that the phosphorus concentration of the hot metal can be reduced to a low concentration with a small amount of CaO-based solvent used. Note that the upper limit value and the lower limit value of the predetermined range are considered to be different from each other depending on differences in the furnace profile and the shape of the furnace port, and therefore, FIG. 5 obtained in accordance with the embodiment in each refining furnace. It is more desirable to adjust the above upper limit value and lower limit value within the above range from the data shown in FIG.

Furthermore, the present inventors conducted experiments to change the top blowing conditions and bottom blowing gas flow rate in the top blowing lance 2 during the desiliconization process, and investigated the influence of these operating factors on the change in slag height. . Fig. 7 shows the results of an investigation on the effect of the change in the slag height due to the change in the oxygen feed rate (oxygen gas supply flow rate) from the top blowing lance 2, and the slag height due to the change in the lance height of the top blowing lance 2 FIG. 8 shows the result of the investigation on the influence on the change speed, and FIG. 9 shows the investigation result on the influence on the change speed of the slag height due to the change in the bottom blowing gas flow rate. Increasing the acid delivery speed from the top blowing lance 2 increases the slag height (FIG. 7). Increasing the lance height of the top blowing lance 2 increases the slag height (FIG. 8). It was found that the slag height was decreased by increasing the stirring gas flow rate from the port 3 (FIG. 9). Here, the lance height of the upper blowing lance 2 is the distance from the lower end of the upper blowing lance 2 to the hot metal bath surface in a stationary state.

In addition, the slag composition has a great influence on the slag height, and the slag height tends to increase as the low basicity, high iron oxide concentration, or high alumina concentration increases. It is also effective to add a slag-forming agent based on the height measurement result. Furthermore, when adjusting to reduce the slag height, it is also effective to use a forming soothing material such as a solid coolant or a gas generating substance.

That is, in the present invention, the height of the desiliconization slag 6 in the furnace is measured during the desiliconization process, and the supply flow rate of the gaseous oxygen source from the upper blowing lance 2 and the upper blowing lance are determined based on the measurement result. At least one selected from the group of the lance height of 2, the supply flow rate of the stirring gas from the bottom blowing tuyere 3, the composition of the slag in the furnace, and the amount of foaming sedative input, and this adjustment It is preferable to control so that the height of the desiliconized slag 6 is within a predetermined range. Thereby, it is possible to easily adjust the ratio of the slag height to the height of the free board in the furnace at the end of the desiliconization process within the predetermined range.

The measurement of the slag height in the furnace is not limited to the desiliconization process, and can be performed in the dephosphorization process as described above. In the dephosphorization process, the dephosphorization slag is controlled so as not to be ejected (slipping) from the furnace port, thereby suppressing the ejection loss of the added CaO-based solvent and performing an efficient dephosphorization process. it can. That is, in the dephosphorization process, the ratio of the slag height to the height of the free board in the furnace may be adjusted to be less than 1.0. Even in the dephosphorization treatment, it is preferable to measure the slag height using the microwave slag level meter 15 described above.

Further, in the present invention, the removal rate of the desiliconization slag 6 in the removal step (removal rate (mass%) = (discharge slag mass) × 100 / [(slag mass generated in the desiliconization treatment step) + (previous The charge residual slag mass)]) is preferably 30% by mass or more. This is because it is necessary to adjust the basicity of the dephosphorization slag to 1.3 to 3.5 in order to proceed with the dephosphorization reaction in the subsequent dephosphorization treatment step, and when the rejection rate is less than 30% by mass, This is because the amount of the CaO-based solvent to be added in the dephosphorization process increases. In addition, if the amount of desiliconization slag remaining is too large, the amount of slag in the dephosphorization process increases, and slag forming during the dephosphorization process cannot be suppressed, and slag is ejected from the furnace port of the converter refining furnace 1. There is also a risk that operational troubles may occur.

Further, in order to increase the removal rate of the desiliconization slag 6, the basicity of the desiliconization slag 6 is set to 0.5 to 1.5 at the end of the desiliconization process, and the hot metal temperature or the desiliconization slag 6 is increased. The temperature is preferably set to 1280 ° C. or higher. When the basicity of the desiliconized slag 6 is less than 0.5, the viscosity increases and the fluidity of the slag decreases, which tends to cause a decrease in the discharge rate and the rejection rate, and the basicity exceeds 1.5. The solid phase slag is generated, so that the slag fluidity is lowered. Moreover, even if the slag temperature falls below 1280 ° C., the decrease in slag fluidity due to the increase in the solid phase slag and the increase in viscosity of the liquid phase slag itself occur. The slag discharge speed and the reduction rate are likely to decrease.

The present inventors have released the desiliconized slag 6 discharged in the slag pot in the above slag pot from the slag pot to the yard and solidified it, and then pulverized it to a particle size of about 30 mm or less. Various characteristics of slag products were investigated. In addition, based on the results of this investigation, we further studied a hot metal pretreatment method capable of obtaining a slag having a relatively low bulk specific gravity suitable for various civil engineering materials.

The unit volume mass of dephosphorized slag in the specified particle size and compacted state is about 2.0 to 2.3 kg / L, which is larger than 1.6 to 1.8 kg / L of natural debris material. Therefore, dephosphorization slag is suitable for applications where higher mass is preferred, for example, due to increased stability against waves, but for civil engineering applications where there is a concern that it may promote gravitational instability. Is difficult to apply, and also has the disadvantages of increased transportation costs due to its large bulk specific gravity.

Therefore, in order to reduce the generation amount of dephosphorization slag having a large bulk specific gravity as much as possible and to convert the dephosphorization slag into the desiliconization slag 6 having a low bulk specific gravity, after the pre-charge dephosphorization process, After the hot water has been discharged, the dephosphorization slag in the furnace is not discharged, but the hot metal is charged with dephosphorization slag remaining in the furnace, and this hot metal is subjected to a desiliconization process. After the treatment, a preliminary treatment method is adopted in which a part of the desiliconization slag 6 is discharged from the smelting furnace by the exhausting process and then the dephosphorization process is performed on the hot metal remaining in the furnace. It is preferable. At that time, at the end of the desiliconization treatment, the basicity of the desiliconization slag 6 is 0.8 or more and 1.5 or less, and the hot metal temperature or the temperature of the desiliconization slag 6 is 1280 ° C or more and 1380 ° C or less. It is preferable to set the content to 0.10% by mass or less and to discharge 30% by mass or more of the desiliconized slag 6 in the exhausting step.

By setting the basicity of the desiliconized slag 6 to 0.8 or more and 1.5 or less and the hot metal temperature or the temperature of the desiliconized slag 6 to 1280 ° C or more and 1380 ° C or less, it is possible to restore the precharge dephosphorization slag to the hot metal. It is possible to efficiently discharge the desiliconized slag 6 in the exhausting process while preventing phosphorus. Here, since the temperature of the desiliconization slag 6 is close to the hot metal temperature at the end of the desiliconization process, either the hot metal temperature or the temperature of the desiliconization slag 6 may be used as an index. The hot metal temperature can be measured by immersing a thermocouple in the hot metal, but instead of the measured value, the temperature and composition of the hot metal before the desiliconization treatment, the amount of various cold iron sources such as iron scrap, and various auxiliary substances such as quick lime The hot metal temperature calculated by calculating the heat balance from the operating conditions such as the amount of raw material used, the amount of various heating agents such as ferrosilicon, and the amount of oxygen gas supplied may be used.

In addition, by setting the silicon content in the hot metal after desiliconization to 0.10% by mass or less, even if the iron oxide concentration in the slag becomes relatively low, CO gas generation due to the decarburization reaction occurs during the desiliconization process. Since it becomes active, forming of the desiliconization slag 6 is promoted, which is advantageous in increasing the slag height at the end of the desiliconization process. Further, in this case, since the forming of the desiliconized slag 6 is maintained even during the discharging process and the slag height is maintained high, it is advantageous in terms of increasing the discharge efficiency of the desiliconized slag 6.

滓 The removal rate of the desiliconized slag 6 in the removal process is preferably 30% by mass or more. As a result, dephosphorizing agents such as quick lime in the dephosphorization treatment process without excessive accumulation of dephosphorization slag of the precharge in the furnace and without causing an excessive decrease in the slag basicity in the dephosphorization treatment process. The amount used can be suppressed and the phosphorus concentration in the hot metal can be lowered.

The slag height in the furnace at the end of the desiliconization process was measured while satisfying the conditions at the end of the desiliconization process as described above, and the measured slag height was 0 with respect to the height of the freeboard in the furnace. The desiliconization slag 6 is discharged from the converter-type refining furnace 1 at a high removal rate in a relatively short time by adjusting the predetermined ratio such as .5 to 0.9 and performing the removal process. It becomes possible to do. The desiliconized slag 6 discharged to the slag pot in this way is further discharged from the slag pot to the yard and solidified, and then pulverized to a particle size of about 30 mm or less. Since microscopic bubbles are included in the particles, the unit volume mass is reduced to about 1.2 kg / L or less. As a result, it is suitable for applications where a low specific gravity is desired, and an effect of reducing the transportation cost per construction volume can be obtained.

In order to stably produce a slag product having a small unit volume mass, the basicity of the desiliconized slag 6 at the end of the desiliconization treatment is 0.8 to 1.25 and the slag temperature is 1360 ° C. or less to increase the viscosity. Reducing the surface tension by setting the phosphoric acid (P ₂ O ₅ ) content in the slag at the end of desiliconization to 2% by mass or more, or using an inclined yard when discharging from the slag pot to the yard It is desirable to disperse the discharged slag over a wide range by increasing the cooling rate of the desiliconized slag 6 by discharging the slag pot while moving it. In addition, in the charge group in which the slag height at the end of the desiliconization process was performed at a ratio of less than 0.5 with respect to the height of the freeboard in the furnace, the average evacuation rate of the desiliconized slag 6 And the average unit volume mass increased to about 1.3 kg / L.

As described above, according to the present invention, using one converter-type refining furnace 1, the hot metal 5 is desiliconized and dephosphorized continuously with an intermediate waste process interposed therebetween. In the preliminary processing, the desiliconization process is completed in a state where the height of the formed desiliconization slag 6 is in a predetermined range with respect to the height of the freeboard in the furnace during the desiliconization process. In the subsequent evacuation process, it is realized that a sufficient amount of desiliconized slag 6 is quickly discharged out of the furnace.

Note that the present invention is not limited to the above description, and various modifications can be made. For example, in the above description, the slag height is measured using the microwave slag level meter 15, but the measurement of the temperature profile in the height direction in the furnace, the measurement value of the top lance or the vibration meter attached to the furnace body. The slag height can also be measured from the detection information of the slag surface based on the measured value of the volume generated from the furnace body.

The slag height is measured by using the converter type refining furnace having a capacity of 330 ton shown in FIG. 1 and measuring the slag height with the hot metal pretreatment (Invention Examples 1 to 3) according to the present invention and the microwave slag level meter. The hot metal preliminary treatment (Comparative Examples 1 and 2) according to the conventional method in which the above control was not performed was performed for 20 charges each. The target value of the phosphorus concentration in the hot metal at the end of the pretreatment was 0.030% by mass.

In Example 1 of the present invention, during the desiliconization process, the slag height during oxygen blowing was measured using a microwave slag level meter, and among the acid feed rate from the top blowing lance, the lance height, and the stirring gas flow rate By adjusting at least one of the above, the ratio of the measured slag height to the freeboard height in the furnace supplies the amount of oxygen necessary for desiliconization obtained by assuming that the desiliconization oxygen efficiency is 50% At the end of the desiliconization treatment, the adjustment was made to be 0.5 to 0.9, intermediate waste was performed, and then the dephosphorization treatment was continued by oxygen blowing.

In Example 2 of the present invention, during the desiliconization process, the slag height during oxygen blowing was measured using a microwave slag level meter, and among the acid feed rate from the top blowing lance, the lance height, and the stirring gas flow rate By adjusting at least one of the above, the ratio of the measured slag height to the freeboard height in the furnace supplies the amount of oxygen necessary for desiliconization obtained by assuming that the desiliconization oxygen efficiency is 50% At the end of the process, an attempt was made to adjust to 0.5 or more, but after the time had elapsed, the ratio of the slag height to the freeboard height in the furnace was less than 0.5. Extend the time, and when the slag height with respect to the height of the freeboard reaches 0.5, finish the desiliconization process and perform intermediate waste removal, and then continue the dephosphorization process by oxygen blowing. It was.

In the present invention example 3, the same control as in the present invention example 1 is performed in the desiliconization process, and then intermediate waste is performed, and then the slag height during oxygen blowing is reduced using a microwave slag level meter during the dephosphorization process. When the ratio of the slag height to the height of the freeboard in the furnace is 0.8 or more, out of the acid feed rate from the top blowing lance, the lance height, and the stirring gas flow rate The dephosphorization treatment was performed by adjusting at least one of these so that the ratio of the slag height to the height of the free board in the furnace was less than 1.0.

In Comparative Example 1 and Comparative Example 2, the desiliconization process is terminated at the time when the amount of oxygen necessary for desiliconization obtained by assuming that the desiliconization oxygen efficiency is 50%, and intermediate waste is performed. Then, the dephosphorization process was continued by oxygen blowing. Here, the hot metal temperature was 1300 ° C. or higher as Comparative Example 1, and the hot metal temperature was lower than 1300 ° C. as Comparative Example 2. The reason for dividing the comparative example into Comparative Example 1 and Comparative Example 2 is that when the hot metal temperature is as high as 1300 ° C. or higher, the slag hatching is promoted, and the slag height changes at a high level. When the hot metal temperature is less than 1300 ° C., the slag height is low.

In each of Invention Examples 1 to 3 and Comparative Examples 1 and 2, the acid feed rate during desiliconization was 30000 Nm ³ / hr, the lance height was 2.5 m, and the bottom blowing gas flow rate was 1200 Nm ³ / hr. . Further, the acid feed rate during the dephosphorization treatment was 25000 Nm ³ / hr, the lance height was 2.1 m, and the bottom blowing gas flow rate was 1200 Nm ³ / hr. As the bottom blowing gas, nitrogen gas was used for both the desiliconization process and the dephosphorization process.

Table 1 shows test results of representative examples of Invention Examples 1 to 3 and Comparative Examples 1 and 2. FIG. 10 shows the transition of the ratio of the slag height to the height of the free board in the furnace during the desiliconization process in each of the representative examples of the present invention examples 1 and 2 and comparative examples 1 and 2. FIG. 11 shows the change in the ratio of the slag height to the height of the free board in the furnace during the dephosphorization process in each of the representative examples of Invention Example 3 and Comparative Example 2. In Table 1, FIG. 10, and FIG. 11, representative examples are shown in Invention Examples 1 to 3 and Comparative Examples 1 and 2, respectively.

In Invention Example 1 shown in Table 1, since the hot metal temperature was high and the hatching rate at the initial stage of the desiliconization process was high, the slag height was high. Therefore, the bottom blowing gas flow rate was increased to 2400 Nm ³ / hr 2 minutes after the start of the desiliconization treatment. As a result, an increase in the slag height is suppressed, and the amount of oxygen necessary for desiliconization obtained by assuming that the desiliconization oxygen efficiency is 50% is supplied to the height of the free board in the furnace. The ratio of slag height was 0.8.

On the other hand, in Comparative Example 1 shown in Table 1 using hot metal having a temperature equivalent to that of Example 1 of the present invention, the slag height is not controlled. The ratio of the slag height to the board height is 1.0, and the slag flow is severe at the time of intermediate evacuation. The furnace once tilted is raised again, the slag height is lowered using a sedative, and then the middle is again I was rejected. This increased the intermediate elimination time.

In Invention Example 2 shown in Table 1, since the hot metal temperature was low and the hatching rate at the initial stage of the desiliconization process was low, the slag height was low. Therefore, the oxygen feeding rate from the top blowing lance was increased to 50000 Nm ³ / hr and the lance height was also increased to 3.5 m after 2 minutes from the start of the desiliconization treatment, and oxygen blowing was performed. However, the ratio of the slag height to the height of the free board in the furnace is less than 0.5 when the supply of the oxygen amount necessary for desiliconization obtained by assuming that the desiliconization oxygen efficiency is 50%. It became. Therefore, the desiliconization process by oxygen blowing was continued, and when the ratio of the slag height to the freeboard height in the furnace reached 0.5, the desiliconization process was terminated, and then intermediate waste was performed. It was. Thereby, the rejection rate in the rejection process became as high as 70%.

On the other hand, in Comparative Example 2 shown in Table 1 using hot metal having the same temperature as Example 2 of the present invention, since the slag height is not controlled, the desiliconization oxygen efficiency is assumed to be 50%. At the time when the oxygen amount necessary for the obtained silicon removal was finished, the slag height with respect to the height of the free board in the furnace was less than 0.5. As a result of performing the intermediate waste in that state, the waste rate was lowered, and the basicity of the subsequent dephosphorization treatment was lowered to cause dephosphorization failure.

In Example 3 of the present invention shown in Table 1, the slag height is controlled during the desiliconization process, and the ratio of the slag height to the freeboard height in the furnace is less than 1.0 during the dephosphorization process. Thus, with respect to the reference value, the acid feed rate is in the range of ± 5000 Nm ³ / hr, the lance height is in the range of ± 0.5 m, and the bottom blowing gas flow rate is in the range of ± 1200 Nm ³ / hr, either one or two More species adjustments were made. As a result, slopping during the dephosphorization process can be prevented, and the CaO-based solvent introduced into the furnace can be prevented from being blown out of the furnace. As a result, the phosphorus concentration in the hot metal at the end of the dephosphorization process Was able to be reduced. On the other hand, in Comparative Example 2, slopping (slag ejection) occurred in the dephosphorization process, and the phosphorus concentration in the hot metal at the end of the dephosphorization process could not achieve the target value.

DESCRIPTION OF SYMBOLS 1 Converter type refining furnace 2 Top blowing lance 3 Bottom blowing tuyere 4 Outlet 5 Hot metal 6 Desiliconization slag 7 Cold iron source 8 Oxygen gas 9 Bottom blowing gas 10 Charging pan 11 Flue 12 Hood 13 Opening 14 Opening 15 Microwave Slag Level Meter 16 Waveguide 17 Transmitting Antenna 18 Receiving Antenna

Claims

A desiliconization process for supplying a gaseous oxygen source to the hot metal in the converter type refining furnace from the top blowing lance to desiliconize the hot metal, and at least part of the slag generated in the desiliconization process is converted into the converter type An exhausting process for discharging from the refining furnace, and after the exhausting process, a CaO-based medium solvent is added into the converter type refining furnace, and a gaseous oxygen source is supplied from the upper blowing lance to remove the remaining hot metal. A hot metal pretreatment method comprising: measuring a slag height in the furnace during the desiliconization process, and measuring the slag height from the hot metal bath surface in the furnace. A hot metal preliminary treatment method, characterized in that the desiliconization process is terminated in a state where the ratio is within a predetermined range with respect to the height of the in-furnace freeboard to the furnace opening.
The hot metal pretreatment method according to claim 1, wherein the predetermined range of the ratio is in the range of 0.5 to 0.9.
Based on the measurement result of the slag height, during the desiliconization process, the supply flow rate of the gaseous oxygen source from the top blowing lance, the lance height of the top blowing lance, the supply flow rate of the stirring gas from the bottom blowing tuyere The composition of the slag in the furnace, adjusting at least one selected from the group of the amount of forming sedative material, the slag height in the furnace during the desiliconization process is controlled by this adjustment, The hot metal pretreatment method according to claim 1 or 2.
The slag height in the furnace during the desiliconization process is controlled so that the ratio of the slag height to the height of the freeboard in the furnace during the desiliconization process is in the range of 0.5 to 0.9. The hot metal pretreatment method according to claim 3, wherein:
Using a pseudo-random signal processing radar-type microwave rangefinder, a microwave with a frequency of 10 GHz or less is transmitted into the converter type refining furnace to receive a reflected wave, and the distance from the round-trip propagation time of the reflected wave to the object Among the received reflected wave signals having a certain intensity or higher, the distance to the object corresponding to the reflected wave signal is larger than the distance to the furnace port and closest to the distance to the furnace port The reflected wave signal is determined as a reflected wave signal from the slag surface, a distance to the slag surface is obtained, and the slag height is measured based on the obtained distance to the slag surface. The hot metal pretreatment method according to any one of claims 1 to 4.
Among the reflected wave signals received by the distance meter, the distance to the object corresponding to the reflected wave signal does not change from the start of the desiliconization process, and the reflected wave signal that exists continuously is noise. The hot metal preliminary processing method according to claim 5, wherein a signal of a reflected wave from the surface of the slag is determined after the removal.
Using a pseudo-random signal processing radar type microwave rangefinder, a microwave with a frequency of 10 GHz or less is transmitted to the converter type refining furnace, a reflected wave from the furnace is received, and the target is determined from the round-trip propagation time of the reflected wave. Find the distance to the object, and among the reflected wave signals from the object existing in the range from the furnace port to the hot metal bath surface, the distance to the object corresponding to the reflected wave signal is The reflected wave signal that is continuously present without any change is removed as noise, and the reflected wave signal with the highest reflection intensity is reflected from the slag surface except for the reflected wave signal corresponding to the hot metal bath surface. The distance to the slag surface is determined by determining the signal as a wave, and the slag height is measured based on the obtained distance to the slag surface. Pretreatment method of hot metal as described in .
After completion of the dephosphorization process of the pre-charged hot metal in the converter type refining furnace, the hot metal that has been dephosphorized is discharged and the slag generated in the dephosphorization process is discharged without discharging the slag in the furnace. In this state, fresh hot metal is charged into the converter type refining furnace, and the hot metal is subjected to the desiliconization process. At the end of the desiliconization process, the basicity of the furnace slag is set to 0.8. 1.5 or less, the hot metal temperature is 1280 ° C. or higher and 1380 ° C. or lower, the silicon content of the hot metal is 0.10% by mass or less, and in the exhausting step, 30% by mass or more of the slag generated in the desiliconization process Then, the dephosphorization process is performed on the hot metal in the furnace, and after the dephosphorization process, the dephosphorized hot metal is discharged, and the slag in the furnace generated by the dephosphorization process is discharged. New hot metal is left in the converter type refining furnace without being discharged and left in the converter type refining furnace. ON is, and performs preliminary processing on the molten pig iron, molten iron pretreatment method according to any one of claims 1 to 7.
The slag height in the furnace was measured during the dephosphorization process after the exhausting process, the supply flow rate of the gaseous oxygen source from the top blowing lance, the lance height of the top blowing lance, and the stirring gas from the bottom blowing tuyere 9. At least one selected from a group of supply flow rates is adjusted, and control is performed so that slag in the furnace is not ejected from the furnace port by this adjustment. The hot metal pretreatment method according to claim 1.