JP2001294924A - Method for desiliconizing and desulfurizing molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover valuable components in a secondary refining slag or con verter slag, to perform a desiliconization and desulfurization in one furnace and to simplify a process by solving such problems the elution of a halogen from the discharged slag without using a fluorspar, etc. SOLUTION: The secondary slag or converter slag is added into molten iron with CaO in stead of a halogenide such as the fluorspar. The desiliconizing and desulfurizing treatments are continuously performed, and FeO and MnO as the valuable components in these slags are reduced are recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an efficient method for desiliconization and desulfurization of hot metal, and is widely used in a refining process of steel using pig iron as a raw material.

[0002]

2. Description of the Related Art Along with the stricter use environment of steel materials, demands for reduction of impurity elements in steel represented by phosphorus and sulfur are severe. On the other hand, steel materials are basic materials that are used in large quantities, and it is important that they are inexpensive as well as quality.Technological developments have been made in pursuit of more efficient manufacturing processes to balance quality and cost. I have. Under these circumstances,
A so-called hot metal pretreatment technology for obtaining steel by converter blowing of pig iron from which silicon, phosphorus and sulfur have been removed in advance has been developed.

[0003] In recent years, with increasing public interest in environmental issues, problems have been raised with respect to methods for treating various by-products generated in the steel refining process. In particular, blast furnace slag generated in the iron making process among slag that is a by-product of iron manufacturing has been proven to be effective in ensuring the strength of cement, and is used as a material for cement, but it is generated in the steel making process Hot metal dephosphorization slag is basically (CaO wt%) /
(SiO ₂ wt%) (hereinafter abbreviated as basicity)
Because it contains a large amount of, expansion and weatherability are considered to be a problem, and there are few effective reuse destinations for building and civil engineering materials. Therefore, aging treatment is performed for a long time so that the problem of weathering / expansion does not occur. However, it is difficult to completely suppress the problem of weathering / expansion, and the present situation is that landfilling and other treatments are inevitable. Further, the fluorine contained in the slag has a problem of elution into the environment, and it is not desirable to add a halide such as fluorite in the steel making process. The method has not been established yet.

[0004] From such a point, it is important to establish a process that does not use halides such as fluorides and generates a small amount of slag itself, in addition to making use of slag. From such a viewpoint, various attempts have been made to reuse the slag in each of the divided refining processes. For example, JP-A-57-140808 discloses that converter slag is added to iron oxide, lime, fluorite and other auxiliaries, cooled, and then pulverized to be used in hot metal desulfurization or dephosphorization. There is a description. Japanese Patent Application Laid-Open No. 57-145916 also describes that slag generated in a converter is returned to a preliminary dephosphorization and desulfurization step of hot metal and used. Furthermore, Japanese Patent Application Laid-Open No. 61-44115 discloses that by using converter slag with Mn ore added in a converter and having a MnO concentration of 6% or more returned to the desiliconization, dephosphorization and desulfurization steps, Increase Mn concentration in hot metal, and
It describes a method for increasing the utilization efficiency of a computer.

[0005]

The above cited technologies are all attempts to reduce the total amount of slag produced by reusing converter slag. However, in the steel refining process, there is slag generated in the secondary refining process after the converter, and this amount cannot be ignored. Here, the secondary smelting slag is derived from deoxidation products generated in the secondary smelting process or fluxes that have flowed out to the steel ladle during the tapping of the converter and from the molten steel ladle during the casting process. Refers to slag remaining after being discharged. Conventionally, a method for effectively reusing slag generated in the secondary refining process has not been proposed.
In the secondary refining process, in many cases, deoxidation is performed by adding aluminum, and therefore, it is characterized in that the product, Al ₂ O ₃ , is contained at a considerably high concentration. The slag contains CaO, and further contains about 10% of FeO and MnO. Therefore, a method of reusing the secondary smelting slag by returning it to the hot metal desiliconization / desulfurization step can be considered. However, when secondary refining slag is used when performing desiliconization treatment in a small reaction vessel such as a torpedo car or a pan, the bubbling of the slag is remarkably promoted by the influence of Al ₂ O ₃ contained therein, and the hot metal is reduced. This causes problems such as protruding out of the container, making the operation impossible, and increasing iron loss. Therefore, the acid feeding rate is remarkably reduced, so that refining is required for a long time, and as a result, the productivity is remarkably reduced. In addition, there is a problem in that even if used after returning to the oxidizing and refining period such as desiliconization and dephosphorization, reduction of FeO and MnO does not proceed so much, and effective recovery of iron and manganese cannot be expected.

[0006] Further, converter slag contains useful components such as MnO, FeO and CaO that can be recovered, but the CaO content can be effectively used by returning to hot metal dephosphorization treatment, which is basically oxidative refining. Even if it is, the reduction of FeO and MnO is insufficient.
Further, Japanese Patent Application Laid-Open No. 57-140808 describes that auxiliaries such as iron oxide, lime and fluorite are added to converter slag, cooled, and then pulverized and used in a hot metal desulfurization step. However, it is necessary to use a reducing atmosphere to promote the desulfurization reaction, and if the converter slag with high oxidizing power is returned to the desulfurization step, the efficiency of the desulfurization reaction itself will increase even if the reduction of FeO and MnO is promoted. , The amount of desulfurizing agent used increases, the amount of slag not only does not decrease, but also the heat loss increases, the amount of slag generated increases, and iron loss due to waste and prolonged time occur.

[0007]

Means for Solving the Problems The present invention made to solve the above problems is as follows. (1) Using a converter-type reaction vessel, adding a CaO source and an oxidizing source to desiliconize and refine hot metal, and a second step of blowing a desulfurizing agent into hot metal to perform desulfurization In the desiliconization / desulfurization method, a method for desiliconization / desulfurization of hot metal characterized by adding secondary refining slag in the first step. (2) Using a converter type reaction vessel, a CaO source and oxidation De-siliconization of hot metal consisting of a first step in which hot metal is desiliconized and refined by adding a source, and a second step in which a desulfurizing agent is blown into the hot metal to perform desulfurization.
In the desulfurization method, converter slag generated in the converter step in the first step is added, and
This is a desulfurization treatment method.

First of all, when a converter type reaction vessel is used, forming slag generated in the secondary refining process is re-used, and there is a problem of promoting forming due to Al ₂ O ₃ and overflow from the furnace. Can be avoided. Further, in the case of a converter type reaction vessel, a method of dropping a massive refining agent having a particle diameter of usually about 25 mm from the furnace hopper is a convenient, fast and convenient method for adding the auxiliary material, but at the hot metal processing temperature, When a halide such as fluorite, which is a chemical accelerator, is not used, there is a problem in that quicklime does not turn into slag, does not generate basic slag, and lowers reaction efficiency. On the other hand, Al ₂ O ₃ in the secondary smelting slag has the effect of remarkably lowering the melting point of CaO, so that it can promote slagification of massive quicklime and does not require the use of halides such as fluorite. The reaction efficiency can be increased, the weathering and expansion of the discharged slag can be reduced, and the problem of elution of fluorine from the generated slag can be solved. Further, when the oxygen supply is stopped and the desulfurization treatment, which is a reduction reaction, is performed as the second step, FeO and MnO contained in the slag are reduced, and the iron yield and the Mn reduction recovery rate are improved.

[0009] When the converter slag is reused, compared to the case of simply returning to the conventional hot metal dephosphorization step, Fe desiliconization is performed.
The reduction of O 2 and MnO 2 proceeds to some extent, and further reduction occurs without reducing the desulfurization efficiency so much during the subsequent desulfurization, and these can be effectively used.

Generally, when desulfurization treatment is performed using a torpedo car or a hot metal pot as a reaction vessel, it is difficult to completely separate the desulfurized slag from the hot metal, and it takes a long time to completely separate it. The remaining desulfurized slag causes resulfurization in the subsequent process, causing problems such as the inability to produce ultra-low sulfur steel.However, if a converter is used, it is possible to efficiently separate the slag from hot metal at the time of tapping. I can do it. Furthermore, when secondary refining slag or converter slag is used, the final amount of slag increases compared to when it is not used, but in this case the sulfur concentration in the slag after desulfurization is low, Even if it comes out at the same time, there is little resulfurization in the post-process, so ultra-low sulfur steel can be easily manufactured, or it is necessary to carry out over-desulfurization using an extra desulfurizing agent in anticipation of the resulfurized component. Is also reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a processing furnace for hot metal, in which 1 is a converter type refining vessel and 2 is hot metal charged therein. Reference numeral 3 denotes an oxygen gas upper blowing lance provided for blowing oxygen gas to the hot metal 2 in the refining vessel 1, reference numerals 4 and 5 denote blow tanks for blowing calcium carbonate or a desulfurizing agent, and reference numeral 6 denotes powder together with the gas. The tuyere 7 for blowing is a nitrogen gas holder. Reference numeral 9 denotes a hopper for adding auxiliary materials such as quicklime and a solid oxygen source from above. When calcium carbonate is blown into the hot metal during the desiliconization period, a large amount of CO ₂ gas is generated by the following reaction, and an inexpensive stirring method can be obtained.

## EQU1 ## CaCO ₃ = CaO + CO ₂ (C)

A scrap chute together with the scrap 10
At 11, secondary refining slag or converter slag 12 is charged, and further hot metal 2 is charged. A refining agent such as quicklime or iron ore is added upward from a furnace hopper, and desiliconization is performed while stirring the hot metal by the above method. Further, in order to perform the desulfurization treatment, the top-blown oxygen gas is stopped, and a desulfurizing agent is blown with nitrogen gas from the blowing tuyere 6 to perform the desulfurization treatment. Even if secondary refining slag is used because it is a converter type reaction vessel, the problem of promoting slag forming by Al ₂ O ₃ can be avoided. In addition, it is possible to reduce and recover FeO and MnO contained in the secondary smelting slag.When converter slag is used, the converter slag is also melted and melted by the melting and slagging of SiO ₂ generated by the desiliconization reaction.
The slag is formed, and the contained FeO and MnO are sufficiently reduced.
In this method, these reductions and recovery proceed further during desulfurization treatment,
In general, refining in one furnace enables desiliconization and desulfurization, and recovery of useful components in slag generated in these subsequent processes.

On the other hand, during the desulfurization treatment, by blowing a desulfurizing agent which is a fine powder, the desulfurization reaction of the hot metal is sufficiently performed while the desulfurizing agent floats in the hot metal. Without this, efficient desulfurization treatment becomes possible. In addition, since the secondary refining slag or converter slag is added, the basicity of the slag can be secured to some extent, so that the solid phase ratio of the slag is high, and CaS contained in the desulfurizing agent after floating is mixed with the top slag. The so-called resulfurization reaction, which is melted and returned to the hot metal side, is slight. Also, when entering the desulfurization period, oxygen gas is stopped, so FeO,
The MnO concentration decreases, the solid fraction of slag increases rapidly, and the desulfurization efficiency does not decrease. Desirably, the basicity of the slag after the desiliconization treatment should be maintained at 1.0 or more from the viewpoint of securing the solid fraction of the slag.In this method, secondary refining slag or converter slag is used as the CaO component. Be able to
FeO and MnO can also be recovered.

[0014]

Embodiments of the present invention will be described below. (Example 1) In a converter type refining furnace, desiliconization was performed while blowing 265 tons of hot metal together with 7.2 tons of secondary refining slag with oxygen gas. At this time, limestone powder was blown in with nitrogen gas from a tuyere provided at the furnace bottom to perform stirring. Next, the oxygen gas was stopped, and a desulfurizing agent was blown from a tuyere provided at the furnace bottom to perform a desulfurization treatment. No new quicklime was added, but the basicity of the slag was 1.4 after desiliconization. Also, during refining,
The manganese concentration in the hot metal increased. Halides such as fluorite were not used. Thereafter, hot metal dephosphorization and converter decarburization were performed, but no resulfurization was observed.

(Example 2) In a converter type refining furnace, 298 tons of hot metal was subjected to desiliconization while blowing oxygen gas upward with 2.0 tons of converter slag and 1.0 ton of quicklime. At this time, limestone powder was blown in with nitrogen gas from a tuyere provided at the furnace bottom to perform stirring. Next, the oxygen gas was stopped, and a desulfurizing agent was blown from a tuyere provided at the furnace bottom to perform a desulfurization treatment. No new quicklime was added, but the basicity of the slag after desiliconization was 1.3. During refining, the manganese concentration in the hot metal increased. Halides such as fluorite were not used. afterwards,
After hot metal dephosphorization and converter decarburization process, only 0.001% resulfurization
Fit in.

Comparative Example A comparative example was an example in which no secondary smelting slag was used. Desiliconization and desulfurization proceeded, but the manganese concentration decreased before and after the treatment. Also, during the desiliconization period, massive quicklime with a particle size of 25 mm inside and outside was added from the furnace hopper,
Since no slagging accelerator such as fluorite was added, slagging during the desiliconization period was poor, and the basicity was only 0.7. Therefore, oxidation loss of manganese was observed, the efficiency of the desulfurizing agent in the subsequent desulfurization treatment was low, and a large amount of desulfurizing agent was required. Also, resulfurization in the post-process was large.

[0017]

[Table 1]

[0018]

According to the present invention, desiliconization and desulfurization can be performed without using a halide such as fluorite, and the secondary smelting slag can be effectively used, that is, iron and manganese can be recovered and Ca can be removed.
Utilization of O 2 is reduced, reducing resulfurization in the post-process and reducing the amount of slag generated in the steel-making process as a whole.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a converter type reactor suitable for carrying out the present invention.

[Description of Signs] 1 Converter 2 Hot metal 3 Oxygen gas upper blowing lance 4 Blow tank 5 Blow tank 6 Blow tuyere 7 Nitrogen gas holder 8 Oxygen gas holder 9 Furnace hopper 10 Scrap 11 Scrap chute 12 Secondary refining slag, Or converter slag

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Chiaki Tazaki 5-3 Tokai-cho, Tokai City, Aichi Prefecture Inside Nippon Steel Corporation Nagoya Works (72) Inventor Takuo Mito 5-Tokai-cho, Tokai City, Aichi Prefecture 3 F-term in Nippon Steel Corporation Nagoya Works (reference) 4K014 AA01 AA02 AB02 AB03 AB04 AB12 AB13 AC03 AC08 AC11 AC14 AC16 AC17 AD00 AD27

Claims (2)

[Claims] 1. A first step of performing desiliconization and refining of hot metal by adding a CaO source and an oxidation source using a converter type reaction vessel, and a second step of performing desulfurization by blowing a desulfurizing agent into the hot metal. A method for desiliconizing and desulfurizing hot metal, comprising adding a secondary refining slag in a first step in a method for desiliconizing and desulfurizing hot metal. 2. A first step in which a CaO source and an oxidizing source are added to perform desiliconization refining of hot metal using a converter type reaction vessel, and a second step in which a desulfurizing agent is blown into the hot metal to perform desulfurization. A method for desiliconizing and desulfurizing hot metal, comprising adding converter slag generated in a converter step in a first step in a method for desiliconizing and desulfurizing hot metal.