JP5282539B2 - Hot phosphorus dephosphorization method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for dephosphorizing molten iron with which in a converter type dephosphorizing treatment in the molten iron without using halide material, typically fluorite, this method achieves both the production of the molten iron having low phosphor concentration at high efficiency and the reduction of the stuck amounts of the skull and slag in the converter. <P>SOLUTION: Into the molten iron charged in the converter, oxygen gas is supplied within 12 min. and the molten iron is dephosphorized without using the halide material, typically fluorite. In this operation, the dephosphorization is performed by spraying powdery limes having &le;150 &mu;m/ton of the molten iron together with oxygen gas onto the molten iron surface through a top-blowing lance providing 4-12 pieces of tapered nozzles excepting a center nozzle. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a hot metal dephosphorization method, and more specifically, from a throat to a state-of-the-art lance outlet without using a halide typified by fluorite at the time of dephosphorization performed as a hot metal pretreatment. The surface of the hot metal along with oxygen gas using powdered quick lime using an upper blowing lance equipped with a nozzle (hereinafter referred to as “taper nozzle”) having an inner surface shape in which the cross-sectional area of the surface perpendicular to the central axis gradually decreases The present invention relates to a dephosphorization method for hot metal sprayed on a metal.

  In contrast to conventional steel refining methods that used a converter to refin carbon and phosphorus at the same time, recently, a preliminary dephosphorization process in which phosphorus is removed in advance in the hot metal stage has been carried out. A lot of hot metal preliminary dephosphorization is performed.

  In this converter type hot metal dephosphorization, it is effective to increase the iron oxide concentration in the slag in order to stably reduce the phosphorus concentration in the hot metal after dephosphorization without using a halide represented by fluorite. is there. As the iron oxide concentration in the slag increases, the oxygen activity at the slag / metal interface increases, the oxidation reaction of phosphorus proceeds, the melting point of the slag decreases, and the fluidity increases, so the movement of phosphorus in the slag The speed increases and these increase the dephosphorization rate.

  In order to increase the iron oxide concentration in the slag, in Patent Document 1, when dephosphorizing the hot metal in the converter equipment, the lower end portion is provided with nozzle holes in the vertically downward direction and the vertically oblique downward direction, and from the lower end portion. Using a top blow lance with a special structure that has a nozzle hole that opens toward the inner wall surface of the converter at the remote side surface, oxygen gas is supplied from the nozzle hole that opens toward the inner wall surface to the inner wall surface It relates to a method of supplying oxygen gas to the surface of the hot metal from the vertically downward and obliquely downward nozzle holes while dissolving the attached metal or slag to produce iron oxide and supplying this iron oxide to the slag. The invention is disclosed.

However, in the present invention, the added secondary raw material CaO is not yet completely melted, and from the initial stage of the dephosphorization treatment in which the low-basic slag mixed with solid CaO to form SiO ₂ and a compound is mixed. Low basicity slag with poor fluidity due to the rapid increase in the iron oxide concentration and the rapid reaction between the liquid phase iron oxide produced by the dissolution of the metal and the carbon in the hot metal to generate CO gas. This may cause slopping that causes bubbles to flow out of the furnace and hinder the operation.

  Moreover, in this invention, since oxygen is blown directly onto the inner wall of the ingot to form iron oxide, the dissolution of the ingot is fast, and the ingot on the inner wall of the converter is completely dissolved by the processing of several charges. There is also. If this lance is used in the absence of bullion, dephosphorization reaction will not be promoted because the amount of iron oxide produced is not large, and refractory damage due to direct oxygen supply to the converter refractory will be prevented. It will progress rapidly. For this reason, it is difficult to carry out the dephosphorization process using the lance having this special structure continuously for a long period of time.

  Even though it is possible to adjust the oxygen flow rate for melting the metal using the lance function of this special structure, it is actually not easy to properly use that function.

  In order to perform hot metal dephosphorization treatment in a converter type reactor without using fluorite, the present inventors previously blown and melted powdered quick lime into hot metal through a taper nozzle according to Patent Document 2. An invention relating to the phosphorus method has been disclosed.

  This invention is a phenomenon in which hot metal and slag are blown away while using powdered quicklime containing quick lime having a particle diameter exceeding 1 mm and preventing a decrease in dephosphorization efficiency associated with the use of such powdery quicklime. The purpose is to reduce the amount of spitting, which is the main cause of metal adhesion in the upper part of the converter.

Although the present invention achieves both high-efficiency dephosphorization treatment and suppression of the amount of spitting, at the time when the present invention was proposed, there was a demand to produce hot metal having a low phosphorus concentration with high efficiency and stability. But it was not as strong as it is now. For this reason, Patent Document 2 does not disclose the time of dephosphorization treatment or the target of dephosphorization treatment, and does not particularly disclose the timing of using quick lime powder.
JP 2002-285215 A Japanese Patent No. 4069837

  Due to the recent increase in environmental problems, the use of halides typified by fluorite must be avoided as much as possible. Also, since high product cleanliness is required, a reduction in the phosphorus concentration in the product has also been achieved. Must-have. Moreover, in order to maintain a highly efficient and stable operation continuously, it is necessary to achieve both high efficiency and reduction in the amount of metal and slag adhesion in the dephosphorization converter furnace.

  The object of the present invention is to produce a hot metal having a high efficiency and a low phosphorus concentration in a converter hot metal dephosphorization process that does not use a halide typified by fluorite, and to reduce the amount of metal and slag in the converter furnace. An object of the present invention is to provide a hot metal dephosphorization method capable of simultaneously reducing the amount of adhesion.

  The present invention is a method for supplying oxygen gas to the hot metal accommodated in a converter and dephosphorizing the oxygen gas within 12 minutes without using a halide represented by fluorite. The nozzle having an inner surface shape in which the cross-sectional area of the surface perpendicular to the central axis gradually decreases from the throat toward the most advanced lance outlet, through the top blowing lance including 4 to 12 except for the central nozzle, A hot metal dephosphorization method characterized by spraying 5 kg of powdered quicklime having a particle size of 150 μm or less / ton of hot metal together with oxygen gas onto the surface of the hot metal.

  In the hot metal dephosphorization method according to the present invention, 30% by mass or more of the amount of CaO charged into the converter can be sprayed as the powdered quicklime during the second half 50% of the oxygen gas supply time. desirable.

In these hot metal dephosphorization methods according to the present invention, the basicity defined by the mass concentration ratio of CaO and SiO _{2 in} the slag after the dephosphorization treatment is set to 2.2 to 2.7. The Fe concentration is desirably 4% by mass or more.

  According to the present invention, in a converter type hot metal dephosphorization process that does not use a halide typified by fluorite, a high efficiency and low phosphorus concentration hot metal is produced, and the metal in the converter furnace is attached to slag. It is possible to achieve both a reduction in the amount, and an operation capable of obtaining a low phosphorus hot metal in a converter type hot metal dephosphorization process that does not use a halide represented by fluorite. Since it can be performed continuously, the operating efficiency of the dephosphorization furnace can be greatly improved.

  The best mode for carrying out the hot metal dephosphorization method according to the present invention will be described below with reference to the accompanying drawings. In the following description, “%” means “mass%” unless otherwise specified.

  First, the principle of the present invention will be briefly described. In order to solve the problems of the conventional techniques described above, the present inventors diligently studied about optimum processing conditions, and as a result, obtained the knowledge described below.

  First, in hot metal dephosphorization, it is advantageous to dephosphorize the invention described in Patent Document 2, that is, powdery quicklime is blown and melted onto the surface of the hot metal via a taper nozzle. Further, in order to reduce the phosphorus concentration in the hot metal after the dephosphorization process with high efficiency, it is desirable that the particle size of the powdered quicklime is fine. In the present invention, in order to obtain a hot metal dephosphorization rate of 80% or more by dephosphorization within 12 minutes of supplying oxygen gas during the dephosphorization, the particle size of the powdered quicklime is 150 μm or less. In addition, the supply amount of powdered quicklime is set to 5 kg / molten ton or more.

Here, the purpose of the present invention is to obtain a low phosphorus hot metal by dephosphorizing general hot metal, so that the basicity defined by the mass concentration ratio of CaO and SiO _{2 in} the slag after the dephosphorization treatment Is generally 1.5 or more and 3.5 or less. Therefore, the upper limit of the supply amount of powdered quicklime is naturally defined by the upper limit of the basicity of the slag after the treatment.

  Even under this condition, as disclosed in Patent Document 2, using an upper blowing lance equipped with a taper nozzle, the powdered quick lime having a particle size of 150 μm or less is sprayed on the surface of the hot metal together with oxygen gas. When dephosphorization is performed, spitting of hot metal and slag, which cause generation of in-furnace ingots, can be reduced.

  Further, in order to promote the dephosphorization reaction, the oxidation in the slag can be achieved even when using a dephosphorization method in which powdery quick lime having a particle size of 150 μm or less is sprayed on the surface of the hot metal together with the oxygen gas for refining. It is effective to promote the oxidation reaction of phosphorus by increasing the iron concentration and lower the melting point of the slag to increase the fluidity to promote the reaction between the slag and the metal.

  In order to increase the iron oxide concentration, if the metal and slag adhering to the converter inner wall are oxidized and melted, and the molten iron oxide is supplied to the slag and dephosphorized, the dephosphorization reaction will proceed efficiently, and the dephosphorization will proceed. Since the growth of the ingot attached to the inner wall of the converter by the spitting generated in the process becomes more difficult to proceed, a low phosphorus hot metal can be obtained continuously and stably.

  Moreover, if the dissolution of the adherent metal is not allowed to proceed rapidly from the initial stage of the dephosphorization process but gradually proceeds after the middle stage of the dephosphorization process, the iron oxide concentration in the slag can be increased more stably. In the converter-type dephosphorization treatment, iron oxide such as mill scale and iron ore for temperature adjustment is usually added before oxygen is blown from the top blowing lance to the hot metal. Furthermore, in the hot metal dephosphorization method in which powdered quick lime having a particle size of 150 μm or less is sprayed on the surface of the hot metal together with oxygen gas, quick lime is continuously added, so separately such as massive quick lime and ladle slag, etc. Even when a CaO source is used, it is considered that the basicity of the molten slag newly generated at the initial stage of the dephosphorization process changes in a relatively low state.

  Due to these influences, it is considered that there is a period in which the iron oxide concentration in the molten portion in the slag changes at an early stage of the dephosphorization treatment. The dephosphorization process proceeds to some extent and the furnace temperature rises, and when a bulk CaO source or the like is used, they dissolve. Further, even when the bulk CaO source is not used, the reduction reaction of iron oxide in the slag proceeds with the carbon in the hot metal. As a result, the dilution effect of the dissolved CaO source or the continuously supplied powdered quicklime and the effect of reducing the iron oxide are combined to reduce the iron oxide concentration in the molten slag.

  At the stage where the iron oxide concentration in the molten slag decreases, the metal and slag adhering to the inner wall of the converter are melted and iron oxide is supplied to the slag on the hot metal, and the iron oxide concentration in the slag is increased again. Then, it is possible to efficiently perform the dephosphorization process while maintaining the dephosphorization ability of the slag while avoiding the occurrence of slopping due to the temporary increase in the iron oxide concentration in the slag.

  Furthermore, in this embodiment for adjusting the production of iron oxide in the slag, even if a large amount of CaO source is supplied before reaching this stage, the melting and hatching tends to be delayed, so It is considered that the dephosphorization efficiency as a whole of the dephosphorization process is improved by leaving a part of the powdered quicklime to be blown up until the time of dissolution of the adhered metal.

In the present embodiment, secondary combustion of CO gas generated by the dephosphorization process is used in order to achieve dissolution of the adhesion metal on the inner wall surface from the middle of the dephosphorization process.
First, dephosphorization is performed using a lance nozzle that promotes secondary combustion of CO gas. As the dephosphorization process progresses, the oxidation of CO gas, that is, the secondary combustion reaction progresses, the temperature near the furnace mouth of the converter gradually rises, and the metal and slag adhering to the inner wall surface starts to melt and melt. Since iron oxide is supplied to the slag on the hot metal, the iron oxide concentration in the slag increases.

  In order to promote secondary combustion, a porous lance nozzle is used as the lance nozzle for blowing oxygen. In addition, in order to increase the amount of iron oxide produced per unit time due to the reaction between top blowing oxygen and hot metal, it is also possible to use a taper nozzle in which the reaction area (fire point) between oxygen and hot metal is wider than that of the Laval nozzle. Favorable for promoting secondary combustion.

  In addition, unlike the method in which oxygen is directly blown onto the bare metal, this method of dissolving the attached bare metal does not involve rapid dissolution of the bare metal. it can.

  From this point of view, in this embodiment, it is desirable to spray 30% or more of the amount of CaO charged into the converter as powdered quicklime during the latter half 50% of the oxygen gas supply time. .

  Next, the best mode for carrying out the present invention will be described with reference to the accompanying drawings. A converter having an upper bottom blowing function is used as a reaction vessel for hot metal preliminary dephosphorization treatment. It is desirable to use an upper blowing lance in which an oxygen line and a line for spraying powdered quicklime used as a dephosphorizing material on the hot metal join at the upper portion of the lance. The carrier gas used for spraying powdered quicklime may be any of oxygen gas, air, nitrogen gas, carbon dioxide gas and argon, but nitrogen gas is preferably used from the viewpoint of safety. .

  This top blow lance nozzle has an inner surface shape in which the cross-sectional area of the surface perpendicular to the central axis gradually decreases from the throat toward the most advanced lance outlet, except for the central nozzle provided at the center of the lance shaft. Use a taper nozzle. The number of tapered nozzles may be four or more, but is preferably eight or more from the viewpoint of increasing the secondary combustion rate. However, in practice, about 12 is the limit due to the strength and durability of the lance tip.

  In order to prevent spitting, the inclination angle θ of the inner wall surface from the throat to the outlet of the taper nozzle with respect to the central axis is in the range of 1 ° to 12 ° as disclosed in Patent Document 2. Therefore, an inclination angle θ that can be manufactured in this range may be set.

  Note that the center nozzle of the upper blowing lance need not be provided. When the center nozzle is provided, the center nozzle may be a straight type or a tapered type taper.

  In the present embodiment, using the converter having the upper bottom blowing function, dephosphorization treatment for hot metal that has been subjected to desulfurization treatment or desiliconization treatment in advance, or hot metal that has not been subjected to preliminary treatment in advance. I do.

  First, iron scrap used as a coolant is charged into a converter. If this blending ratio is 30% or less of the entire main raw material, there will be no hindrance to the dephosphorization treatment. Moreover, you may throw in the auxiliary material used as a dephosphorization material with iron scrap.

  Thereafter, the above hot metal is charged into the converter. The temperature of the hot metal is 1250 ° C. or higher and 1400 ° C. or lower, and the main components are C: 4.0% or higher and 5.0% or lower, Si: 0.01% or higher and 1.00% or lower, Mn: 0.00%. 1% or more and 0.5% or less, S: 0.1% or less, P: 0.05% or more and 0.20% or less.

Before and after the hot metal and iron scrap are charged, auxiliary lime, etc., as a dephosphorizing raw material is introduced into the furnace as necessary. Halides such as fluorite are not used as auxiliary materials.
Thereafter, oxygen is started to be blown onto the hot metal from an upper blowing lance provided with a taper nozzle 4 or more and 12 or less excluding the central nozzle, and at the same time or a little later, spraying of powdered quicklime is also started and dephosphorization is performed. . Any of nitrogen gas, carbon dioxide gas, and argon gas may be used as the bottom blowing gas during the dephosphorization treatment, but it is desirable to use nitrogen gas from the viewpoint of cost.

  After the dephosphorization process is started, secondary combustion of CO gas is promoted by the four or more tapered nozzles of the upper blowing lance, and the temperature in the upper part of the furnace rises. Due to this temperature rise, in the middle and later stages of the dephosphorization treatment, the bullion attached to the inner wall of the converter (attached to the inner wall of the furnace due to spitting during the dephosphorization treatment) is melted and becomes iron oxide on the hot metal. The slag is increased in iron oxide concentration (T.Fe), and the slag dephosphorization ability is increased. Since the dephosphorization process using the slag having a high dephosphorization performance is performed, it becomes possible to stably produce the low phosphorus hot metal.

Moreover, since the metal on the inner wall of the furnace is melted during the dephosphorization process, an increase in the amount of attached metal is also suppressed.
As described above, according to the present embodiment, in the converter type hot metal dephosphorization treatment that does not use a halide represented by fluorite, a high efficiency and low phosphorus concentration hot metal is produced, and the converter furnace It is possible to reduce both the amount of bullion and slag adhesion. For this reason, an operation capable of obtaining low phosphorus hot metal in a converter type hot metal dephosphorization process that does not use a halide typified by fluorite can be performed efficiently, stably and continuously. The operational efficiency of can be greatly improved.

The present invention will be described more specifically with reference to examples.
The hot metal component before dephosphorization is [C] = 4.4 to 4.95%, [Si]: 0.14 to 0.37%, and [P]: 0.080 to 0.120%. 250 to 270 tons of hot metal having a temperature before dephosphorization treatment of 1296 to 1414 ° C. and 23 to 29 tons of scrap are charged into an upper bottom blowing converter (capacity 300 t), and nitrogen is used as a bottom blowing gas in an amount of hot metal mass tons. 1 using a Laval nozzle 6-hole lance 1 having a tip shape shown in FIG. 1, and a tapered nozzle 8-hole lance 2 having a longitudinal section shape shown in FIG. 2 while blowing at a rate of 0.27 Nm ³ / min. , Top blown oxygen at 1.25 Nm ³ / min. As sprayed.

In addition to ladle slag (CaO content: 40 to 50%) 3 kg / molten iron to be added as an auxiliary material just before the start of supply of top blown oxygen, massive quicklime (particle size 10 to 25 mm, CaO content: 92) %, Remaining: CO ₂ etc.) before and after the start of supply of top-blown oxygen, 5 to 15 kg / ton of hot metal are added, and powdered quicklime (particle size ≦ 150 μm, CaO content: 92%, remaining: CO ₂ etc. ) Was sprayed over 5 to 15 kg / ton of hot metal.

  Powdered quicklime is 300 to 450 kg / min. Sprayed on the hot metal at a speed of. With respect to one dephosphorization process in the converter, the total CaO charging time is 50 to 80% in the first 50% period of the supply time of the top blown oxygen and 20 to 50 in the second 50% period. %.

The distance between the tips of the lances 1 and 2 and the surface of the hot water surface during the dephosphorization treatment is 3.2 to 3.4 m during the spraying of powdered quicklime and 3.5 to 3.3 before or after the spraying is completed. 7 m.
After completion of the dephosphorization process, the hot metal was transferred to the hot metal ladle, and the slag remaining in the furnace was collected, and the basicity and total iron content T.I. Analysis with Fe was performed. The phosphorus concentration in the hot metal was determined by analyzing a metal sample taken from the hot metal after being transferred to the hot metal hot pot.

  Table 1 shows the operating conditions of the dephosphorization treatment.

  Table 2 summarizes the dephosphorization treatment using the tapered nozzle 8-hole lance 2 as an example of the present invention and the dephosphorization treatment of the Laval nozzle 6-hole lance 1 as a comparative example. It should be noted that the total CaO charging time in the investigation of Table 2 was 50 to 80% in the first half 50% of the oxygen supply time from the top blowing lance and 20 to 50% in the second half 50% in both the inventive example and the comparative example. .

FIG. 3 is a graph showing the transition of the secondary combustion rate {secondary combustion rate = exhaust gas CO ₂ (%) / (exhaust gas CO (%) + exhaust gas CO ₂ (%))} over time during the dephosphorization process. It is.

The value of the exhaust gas component used for calculating the secondary combustion rate is a numerical value obtained by sampling the exhaust gas in the exhaust gas hood after the secondary combustion and analyzing it. In this gas sampling in the exhaust gas hood, it is not possible to distinguish between secondary combustion by oxygen gas supplied from the tip of the top blowing lance and secondary combustion by air entering the furnace or the hood from the furnace port. Here, as in the present invention, the influence of oxygen gas supplied from the tip of the top blowing lance is large even when the purpose is to dissolve the deposited metal by secondary combustion from the upper part of the furnace to the furnace port. Of course, since combustion by the atmosphere from the furnace opening also affects, this time, the pressure in the converter is 0 to 3 mmH ₂ O under the common condition, and the metal as the whole secondary combustion without distinguishing both The effect on dissolution was investigated.

  As shown in the graph of FIG. 3, it can be seen that the example of the present invention using the tapered nozzle 8-hole lance 2 has a higher secondary combustion rate during the dephosphorization process than the comparative example using the Laval nozzle 6-hole lance 1. .

  FIG. 4 is a graph showing T.D. in the slag after dephosphorization for each of the present invention example using the tapered nozzle 8-hole lance 2 and the comparative example using the Laval nozzle 6-hole lance 1. FIG. 5 is a graph showing the relationship between Fe concentration and slag basicity, and FIG. 5 is a graph showing the relationship between [P] after dephosphorization and slag basicity.

  As shown in the graphs of FIGS. 4 and 5, when compared with the same slag basicity, the example of the present invention has a higher T.S. It was found that the Fe concentration was higher, and [P] was also lower after dephosphorization.

  In particular, an upper blowing lance having a taper nozzle 2 is used. Fe% is increased, the basicity at the end of the treatment is 2.2 to 2.7, and T.I. By making the Fe% 4% or more, [P] ≦ 0.020% (dephosphorization rate ≧ 80%) can be stably obtained after the dephosphorization treatment even if the oxygen supply time is within 12 minutes. I knew it was possible.

  Here, the T.O. As a result of Fe%, it was obtained up to about 10%, but this concentration is sufficient for actual operation. More than this This is because even if the Fe% is increased, the degree of non-equilibrium between the slag and the molten iron is further increased, so that the dephosphorization improving effect is diminished. Moreover, since the slag forming after the treatment increases, there may be a case where the dephosphorized hot metal after the dephosphorization treatment is hindered from being discharged from the converter.

  In this test using the taper nozzle 2, spitting and slopping will not be a problem even if a predetermined dephosphorization process is performed for 12 minutes or less, and the amount of metal in the furnace and the furnace mouth is attached. It was also stable and no special bullion removal treatment was required.

  On the other hand, in the comparative test using the Laval nozzle 1, the adhesion of the metal in the furnace and the furnace port gradually increased, and it was sometimes necessary to remove the metal.

It is explanatory drawing which shows the front-end | tip shape of the Laval nozzle 6 hole lance of a comparative example, and each taper nozzle 8 hole lance of the example of this invention. It is explanatory drawing which shows the longitudinal cross-sectional shape of the taper nozzle 8 hole lance of the example of this invention. It is a graph which shows transition of the secondary combustion rate during dephosphorization processing with time. In each of the present invention example using the taper nozzle 8-hole lance and the comparative example using the Laval nozzle 6-hole lance, T.O. It is a graph which shows the relationship between Fe density | concentration and slag basicity. It is a graph which shows the relationship between [P] after a dephosphorization process, and slag basicity.

Explanation of symbols

1 Comparative Example Laval Nozzle 6 Hole Lance 2 Inventive Example Taper Nozzle 8 Hole Lance

Claims (3)

A method of supplying oxygen gas to hot metal accommodated in a converter and dephosphorizing the oxygen gas supply time within 12 minutes without using a halide represented by fluorite,
Through an upper blowing lance having an inner surface shape in which the cross-sectional area of the surface perpendicular to the central axis gradually decreases from the throat toward the most advanced lance outlet, with 4 to 12 except for the central nozzle. A method for dephosphorizing hot metal, which comprises spraying 5 kg of powdered quicklime having a diameter of 150 μm or less / ton of hot metal to the hot metal surface together with the oxygen gas.   The hot metal desorption according to claim 1, wherein 30% by mass or more of the amount of CaO charged into the converter is sprayed as the powdered quicklime during the latter half 50% of the supply time of the oxygen gas. Phosphorus method. The basicity defined by the mass concentration ratio of CaO and SiO _{2 in} the slag after the dephosphorization treatment is set to 2.2 to 2.7, and The hot metal dephosphorization method according to claim 1 or 2, wherein the Fe concentration is 4% by mass or more.

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