JPS642644B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a hot metal pretreatment method that sequentially performs desiliconization and dephosphorization of hot metal, and in particular, it provides excellent desiliconization and dephosphorization while minimizing wear and tear on desiliconization flux injection lances. The present invention relates to a pretreatment method capable of obtaining a phosphorous effect. [Prior art] Pre-treatment of hot metal is carried out with the main purpose of dephosphorization and desulfurization, and by performing such pre-treatment, Si, which reduces the dephosphorization and desulfurization efficiency, is removed before charging into the converter. A system is being perfected in which the main impurities such as phosphorus and sulfur are removed, and the converter is used exclusively for decarburization and temperature raising. The applicant has been conducting basic research and research into practical operation of hot metal pretreatment technology for some time.
For example, the technique disclosed in Japanese Unexamined Patent Publication No. 16006/1983 is disclosed. According to the disclosed method, a flux powder consisting of CaO, iron oxide, and a solvent (and if necessary, a reaction accelerator) is injected into the deep part of the hot metal using a carrier gas (hereinafter simply referred to as injection).
Oxygen top blowing is also used to promote desiliconization and phosphorus removal. This method has been shown to be working smoothly on an actual machine level, and has been successful in producing low-silicon and low-phosphorus hot metal. [Problems to be Solved by the Invention] The present inventors have been conducting research in the direction of further improving the above method, and have found that even if the amount of flux used is reduced, desiliconization to the same level or greater than the above method can be achieved.・We aim to establish a pretreatment method that can achieve high dephosphorization efficiency and also have various advantages from an operational perspective. That is, all the fluxes used in the method disclosed in the above publication are in powder form, and all of them are supplied by the injection method.
Not only does the manufacturing cost of flux become expensive,
When there is a large amount of Si in the hot metal, it is necessary to adjust the basicity of the slag, and a considerable amount of flux must be input, which raises the problem of increasing costs. Furthermore, if a large amount of flux is to be injected, it is theoretically difficult to avoid increasing the total processing time, and as a result, decarburization in the hot metal progresses more than planned, reducing the heat-raising effect in converter operation. A new problem arises in that heat compensation in the converter must be taken care of. The inventors of the present invention have focused on the above-mentioned circumstances, conducted research in the direction of improving these problems, and have
Even if the amount of Si is slightly large, the above-mentioned disadvantages do not occur, and the total amount of flux used can be reduced, contributing to cost reduction, as well as shortening the total processing time and suppressing decarburization. Established a new preliminary treatment method and filed a patent application (patent application filed in 1980-
No. 41542 (Special Publication No. 63-6606) and No. 60-249672
No. (Japanese Patent Publication No. 109916/1983). That is, in the method of the above-mentioned prior invention, a top-mounted flux is spread on top of the hot metal in the hot metal pretreatment vessel, and the dephosphorization reaction mainly proceeds at the interface between the hot metal and the flux, and an injection lance is used. In this method, flux powder is injected into hot metal to mainly proceed with the desiliconization reaction, thereby allowing the dephosphorization and desiliconization reactions to proceed efficiently. In this method, in order to efficiently advance the dephosphorization reaction at the interface between the hot metal and the flux placed on the top, it is necessary to increase the oxygen potential of the flux placed on the top. The supply of solid oxygen sources such as iron and Mn ore will be carried out in parallel. By the way, when desiliconization and dephosphorization of hot metal as described above is performed, it is known that the dephosphorization reaction starts to proceed rapidly from the time when the desiliconization reaction is almost completed. In addition, the desiliconization reaction proceeds efficiently by the injection of the desiliconizing flux, while the dephosphorization reaction does not require the injection of the flux under the condition that an effective dephosphorizing flux exists at the hot water surface. The most important point in increasing the dephosphorization efficiency is how efficiently the P component in the deep part can be brought into contact with the dephosphorizing flux at the surface of the hot metal by stirring the hot metal. For this reason, in carrying out the invention of the prior application, in the initial desiliconization step, the desiliconization reaction is carried out by injecting the desiliconization flux into the hot metal using a carrier gas using an injection lance. In the subsequent dephosphorization process, inert gas is injected into the hot metal using the injection lance, and the stirring force from gas bubbling is used to stir the hot metal to promote the dephosphorization reaction. It's on. However, as we proceeded with practical-scale operational experiments using the above pretreatment method, it became clear that the following problems occurred. That is, in the above method, the injection lance refractories are subject to severe melting and have a very short lifespan, which increases the cost of the lance and also causes a decrease in productivity due to lance replacement work, which cannot be ignored. When we investigated the main cause of lance erosion, the following facts were confirmed. That is, in the method described above, the lance for flux injection for desiliconization is used as is for blowing bubbling gas during dephosphorization, but wear and slag due to hot metal flow increase in proportion to injection time. The amount of erosion of the lance refractory due to chemical reactions and other causes increases, and the life of the lance decreases. In addition, the nozzle diameter of the flux injection lance is designed to be thick for stable injection of powder and granular materials, so if you are trying to inject only inert gas through this nozzle, the injection at the tip of the nozzle will The kinetic energy of the gas volume cannot be sufficiently large, and hot metal tends to enter the nozzle and solidify, clogging the nozzle and making it unusable. The present invention focuses on these circumstances and attempts to provide a means that can solve the problem of lance wear and tear. [Means for Solving the Problems] The configuration of the present invention that has achieved the above-mentioned object is that in a hot metal pretreatment method that sequentially performs desiliconization and dephosphorization of hot metal, hot metal is introduced into a hot metal pretreatment furnace. The surface of the hot metal is coated with a flux made of CaO as the main component and a slag slag improvement material from the initial stage of hot metal pretreatment. In the subsequent dephosphorization process, flux powder containing iron oxide as the main component is injected into the hot metal using a carrier gas while blowing gas into the hot metal using a carrier gas. Either pull up the flux injection special lance and supply an oxygen source to the surface of the hot metal while continuing to stir the hot metal by blowing bubbling gas, or use the flux injection special lance in the desiliconization process. Flux powder containing iron oxide as a main component is injected into the hot metal using a carrier gas, and in the subsequent dephosphorization process, the above-mentioned flux injection lance is pulled up and a nozzle dedicated to bubbling gas injection is used. The gist of this method is to supply an oxygen source to the surface of the hot metal while stirring the hot metal by blowing gas. [Function] The present invention is based on the aforementioned earlier inventions (Japanese Patent Application No. 60-41542 (Japanese Patent Publication No. 63-6606) and Patent Application No. 63-6606) in its main parts.
-249672 (Japanese Unexamined Patent Publication No. 62-109916), it has the same configuration as that of No. 249672 (Japanese Unexamined Patent Publication No. 62-109916), that is, instead of performing flux injection alone, the flux injected onto the top of the hot metal is sprinkled on top of the hot metal in advance. The surface is coated, and in the initial desiliconization process, the desiliconization reaction is advanced by blowing the desiliconization flux into the hot metal along with a carrier gas.After that, the injection of the desiliconization flux is stopped and the hot metal is bubbled with gas. The dephosphorization reaction is advanced by supplying a gaseous oxygen source (oxygen gas, etc.) or solid oxygen source (scale, Mn ore, etc.) to the surface of the hot metal while stirring it by increasing the oxygen potential of the upper flux. The top-mounted flux used in the present invention has CaO as its main component, and CaO can be of high purity (about 98%, such as lump coal) or of low purity (such as that of 98% slag from converter slag). 50%, etc.) can be used. The latter converter slag is 1/3 to 1/4
Although it has the disadvantage that the amount used is a little large because it contains a certain amount of SiO ₂ , it is advantageous because it has the effect of lowering costs and increasing the dephosphorization efficiency by increasing T and Fe in the slag. This CaO fixes SiO ₂ produced by the desiliconization reaction and is the main material for dephosphorization.Moreover, since CaO also has a desulfurization effect, it also contributes to the promotion of desulfurization. However, since CaO has a high melting point and lacks sludge-forming properties, the present invention uses a sludge-forming property improving material in combination. As a material that improves sludge formation
Low melting point components such as Mn ore and calcium fluoride are used. That is, the top-placed flux used in the present invention contains CaO and a slagging property improving material as essential components, and the cooperative action of these forms a highly fluid slag, which improves the slag-metal interface. Various reactions such as dephosphorization can proceed efficiently. Desiliconization and dephosphorization reactions in hot metal pretreatment, especially desiliconization reactions, proceed from the beginning of the entire treatment process, so it is best to place the above-mentioned upper flux on the hot metal surface from the early stage of pretreatment. The initial stage mentioned above can be considered to be within 3 minutes from the start of the preliminary processing. However, as mentioned above, the dephosphorization reaction starts to proceed rapidly after the desiliconization reaction has progressed to a certain extent, so in order to make the dephosphorization reaction proceed efficiently, it is necessary to carry out the desiliconization reaction promptly at the early stage of the pretreatment. It has to proceed. Therefore, in the present invention, a desiliconizing flux is injected into the hot metal at an early stage to preferentially advance the desiliconizing reaction. As the flux for desiliconization, powdered products such as mill scale, iron ore (iron oxide), and Mn ore (MnO ₂ ) are recommended. In addition, when injecting the above-mentioned iron oxide etc. alone as a flux for desiliconization, it is not necessary to use a slag-improving material such as CaF ₂ together, but it is possible to mix CaO into the flux for dephosphorization to facilitate the dephosphorization reaction. If a contribution is expected, it is advisable to mix in some sludge-promoting material. When the desiliconization reaction is carried out as described above and the amount of silicon in the hot metal is reduced to about 0.10 to 0.15% (usually about 3 minutes from the start of the process), the dephosphorization reaction begins to proceed rapidly. In this case, even if more flux is injected for desiliconization, it will have almost no positive effect on the dephosphorization reaction, and the stirring efficiency of the hot metal and the oxygen potential of the slag existing at the hot metal surface will be the controlling factors for the dephosphorization rate. Become. Therefore, in the present invention, in order to prevent the decarburization reaction and wasteful consumption of flux, injection of the desiliconizing flux is stopped and only stirring is performed by gas bubbling, and at the same time, the dephosphorization reaction at the slag-metal interface on the surface of the hot metal is stopped. In order to proceed efficiently, the slag is treated to improve its oxygen potential. Specific examples of this improvement treatment include a method in which a gaseous oxygen source such as oxygen gas is sprayed from above, and a method in which scale (iron oxide), Mn
Examples include a method of supplying a solid oxygen source such as ore (MnO ₂ ), iron-Mn ore (FeO-Mn ₂ O ₃ ), etc. In the case of this method, the preferred amount of gaseous oxygen source sprayed is 0.20 to 0.80 Nm in terms of oxygen. ³ /min・t, the preferred solid oxygen source supply amount in the case of the method is
It is of the order of 0.2 Kg/min·t or more, and it is of course possible to use the above method in combination. In the above series of preliminary treatment steps, injection of desiliconization flux is carried out in the desiliconization step, and gas injection for gas bubbling is carried out in the dephosphorization step, but these are carried out using a common injection lance. If this is done, as mentioned above, the lance nozzle is subject to severe wear, especially when blowing the bubbling gas, and the lance must be replaced frequently. In order to solve these problems, the present invention uses a pretreatment furnace equipped with a bottom-blowing nozzle dedicated to blowing bubbling gas, or separately provides a lance dedicated to bubbling agitation, so that the desiliconization flux can be used in the desiliconization process. A special injection lance for blowing is inserted into the hot metal to inject desiliconization flux, and when the dephosphorization period begins, the injection lance is pulled up and replaced with a bottom blowing nozzle [or an injection lance]. The dephosphorization reaction is promoted by blowing bubbling gas into the hot metal using a bubbling gas injection lance (with a small nozzle diameter) that is inserted into the hot metal and stirring the hot metal. There is. Therefore, wear and tear on the lance nozzle that occurs when the injection lance is used for blowing bubbling gas is prevented, and the life of the injection lance can be significantly extended. As a result, not only the economic burden required to replace the injection lance is reduced, but also the labor burden is reduced by reducing the frequency of replacement, and work efficiency can also be improved. Porous plugs or tuyere nozzles are used as bottom-blowing nozzles exclusively for bubbling gas injection, but if hot metal enters these nozzles and solidifies, the nozzles will become clogged. It is necessary to blow gas from the beginning, and by doing so, the effect of stirring the hot metal can be improved and the time required for desiliconization can be shortened. In this case, it is of course effective to add measures such as controlling the flow rate of the bottom blowing gas so that the reaction efficiency is maximized in each of the desiliconization period and the dephosphorization period. However, when a bottom-blowing nozzle is used for gas bubbling, gas must be constantly blown to prevent the nozzle from clogging as described above, so there is a problem that the amount of bubbling gas consumed increases. On the other hand, when using a lance exclusively for bubbling gas injection, the lance can be pushed into the molten iron only when gas bubbling is necessary (especially during the dephosphorization period), and can be pulled upward when not needed. Although there is an advantage that there is no need to blow gas to prevent nozzle clogging as mentioned above, using a bubbling gas injection lance requires multiple lance lifting devices and auxiliary equipment (gas A more practical method is to use a bottom-blowing nozzle, as this increases the burden on equipment and tends to reduce maintenance. By the way, regarding the basicity of the total slag when carrying out the present invention, since in the present invention a top-loaded flux is introduced onto the surface of the hot metal, a considerable amount of slag is present from the initial stage of the pretreatment. Since the dephosphorization reaction must proceed under such conditions, it is desirable that the slag exhibits sufficient fluidity. That is, if the fluidity of the slag is low, not only will the progress of the slag-metal interface reaction be inhibited as described above, but also forming will occur due to the rise of inert gas bubbles blown in by injection or bottom blowing. is,
Operational safety is compromised. From this point of view, the amount of CaO added is set to be large, taking into consideration the amount of SiO ₂ mixed in during the desiliconization process, and the basicity (CaO/SiO ₂ ) is increased.
The amount added is preferably set so that the basicity is 1.0 or more, preferably 1.5 or more, and a high level of dephosphorization efficiency is guaranteed under such basicity. However, the basicity
If it exceeds 4.5, there is a risk of poor slag formation due to an increase in the melting point, a risk of slopping due to an increase in the amount of slag, or CaO
Problems such as increased costs will arise as unit consumption increases. [Example] Using a pretreatment furnace equipped with four bottom blowing nozzles at the bottom, desiliconization and dephosphorization treatments were carried out under the following conditions. (Pre-treatment conditions) Amount of hot metal: 90 tons Flux placed above: Massive quicklime introduced immediately after the start of pre-treatment...10.0Kg/ton scale...8.1Kg/tonMn ore...5.9Kg/ton Desiliconization period: 0 to 3 minutes; Desiliconizing agent using dedicated injection lance (Fe ₂ O ₃ : 100%)…7.8Kg/ton Supply rate…2.6Kg/ton・min Carrier gas… _N2 gas, 2.1Nm ³ /hr・t (3
0.11Nm ³ /t for 3 minutes) Injection depth: 1500mm below the hot water surface Bottom blowing gas: N ₂ gas, 2.0Nm ³ /hr・t (0.10Nm ³ /t for 3 minutes) x 4 holes Dephosphorization period: 3~ 10 minutes Bottom blowing gas... _N2 gas, 2.0Nm ³ /hr・t (0.23Nm ³ /t for 7 minutes) x 4 holes Additionally, 5.8Nm ³ /t oxygen gas was top blown throughout the entire period of preliminary treatment. For comparison, a pretreatment furnace without a bottom blowing nozzle was used to perform desiliconization and dephosphorization under the following conditions. (Pretreatment conditions) Amount of hot metal: 90 tons Flux placed on top: Massive quicklime introduced immediately after the start of pretreatment...10.0Kg/ton scale...8.1Kg/tonMn ore...5.9Kg/ton Desiliconization period: 0 to 3 minutes; Desiliconizing agent using special injection lance (Fe ₂ O ₃ : 100%)…7.8Kg/ton Supply rate…2.6Kg/ton・min Carrier gas… _N2 gas, 2.1Nm ³ /hr・t (3
min. 0.11Nm ³ /t) Injection depth: 1500mm below the hot water surface Dephosphorization period: 3 to 10 minutes, using injection lance Bubbling gas...N ₂ gas, 2.1Nm ³ /hr・t
(0.25 Nm ³ /t for 7 minutes) The pretreatment effects (chemical composition and hot metal temperature before and after pretreatment) and the life of the injection lance obtained in the above experiment are summarized in Table 1.

[Table] As is clear from Table 1, by employing the method of the present invention, the life of the injection lance is extended to more than twice that of the comparative method. Moreover, in the method of the present invention, the stirring efficiency of the hot metal is increased by the combined use of bottom-blown gas, so that lower phosphorus is achieved than in the comparative method, and the drop in the hot metal temperature is also suppressed. [Effects of the Invention] The present invention is constructed as described above, but the main point is that it is based on the inventions of earlier applications (Japanese Patent Application No. 60-41542 (Japanese Patent Publication No. 63-6606) and Patent Application No. 60-249672 (Japanese Patent Application Laid-open No. 60-249672). 109916), a special injection lance is used to inject the desiliconizing flux, and at least during the dephosphorization stage, the hot metal is stirred by injecting gas from a bottom blowing nozzle or a bubbling gas injection lance. As a result, the nozzle wear of the injection lance is suppressed and its lifespan can be significantly extended.As a result, not only the cost required for the lance is reduced, but also the frequency of lance replacement is reduced. As a result of the reduction in labor costs, the company can enjoy benefits such as a reduction in labor burden and an improvement in productivity.
Furthermore, as the hot metal stirring efficiency is improved by gas bubbling, the desiliconization and dephosphorization effects themselves are also enhanced, and effects such as suppressing the temperature drop of the hot metal can also be obtained.

Claims (1)

[Scope of Claims] 1. A hot metal pretreatment method that sequentially performs desiliconization and phosphorization of the hot metal, in which hot metal is charged into a hot metal pretreatment vessel, and contains CaO as a main component and a slag slag-improving material. The surface of the hot metal is coated with flux from the initial stage of hot metal pretreatment, and in the desiliconization process, gas is blown into the hot metal using a nozzle dedicated to bubbling gas injection, and a lance dedicated to flux injection is used to inject gas into the hot metal. Flux powder containing iron oxide as a main component is injected into the hot metal using a carrier gas, and in the subsequent dephosphorization process, the flux injection lance is pulled up,
A hot metal pretreatment method characterized by supplying an oxygen source to the surface of the hot metal while continuing to stir the hot metal by blowing bubbling gas. 2. In a hot metal pretreatment method that sequentially performs desiliconization and dephosphorization of hot metal, hot metal is charged into a hot metal pretreatment vessel, and a flux made of CaO as a main component and a slag slag improving material is added to the hot metal pretreatment method. The surface of the hot metal is coated from the initial stage of the treatment, and in the desiliconization process, a flux injection lance is used to inject flux powder whose main component is iron oxide into the hot metal using a carrier gas. In the dephosphorization process to be carried out, the lance dedicated to flux injection is pulled up and the hot metal is stirred by gas injection using a nozzle dedicated to bubbling gas injection, while an oxygen source is supplied to the surface of the hot metal. Pretreatment method for hot metal.