JP5163012B2 - Hot metal desulfurization treatment method - Google Patents

Description

  The present invention relates to a steelmaking facility in which a process for producing hot metal using iron-based scrap as a main raw material and coke as a main heat source, and a process for producing hot metal using iron ore as a main raw material and coke as a main heat source, The present invention relates to a method for efficiently desulfurizing slag.

  With the increasing demand for steel, an integrated steelworks that produces hot metal in a blast furnace is also considering a production method that effectively uses iron scrap (iron scrap) that is available in the city to increase the production elasticity of hot metal. Has been. Iron-based scrap is generally melted by an electric furnace method using electricity as a heat source to produce molten steel. However, at integrated steelworks, the liquidus temperature is low even if the temperature is lowered. Since it is blown in the converter of the next process, there is an advantage that high quality such as low nitrogen is obtained, so there are cases where hot metal production from iron-based scrap is desired. In that case, since a process capable of directly producing hot metal is efficient, it is effective to use a shaft-type cupola (scrap melting furnace) using coke as a heat source.

Cupola has a lower slag ratio than blast furnaces due to the difference in raw materials, and generally uses cast coke as a heat source, so the oxygen partial pressure in the atmosphere in contact with the hot metal is high, and so on. The concentration is higher than that of blast furnace hot metal. In general cupola, cast iron and cast steel are basically manufactured. Therefore, the standard of S is higher than steel materials such as thick plate, thin plate and steel pipe, and S ≦ 0.003mass% required by integrated steelworks. Low sulfidation is not required. Therefore, (i) Mg treatment that also serves as inoculation by receiving the hot metal taken out from the ladle is performed (for example, Non-Patent Document 1), (ii) A desulfurizing agent is blown into the hot metal in the middle of the production (for example, In general, desulfurization treatment such as Patent Document 1) is performed.
Kurimoto Technical Report, No. 41 (19999.9), p.70-73. JP-A-2-250912

In these methods, Mg is used, so that low sulfidation is difficult on thermodynamic equilibrium (method (i) above), and it is difficult to lengthen the reaction treatment time because it is a continuous treatment (above ( For reasons such as method ii), it is difficult to stably treat cupola hot metal up to S ≦ 0.003 mass%.
Accordingly, an object of the present invention is to provide an iron making facility in which a process of producing hot metal using iron-based scrap as a main raw material and coke as a main heat source and a process of producing hot metal using iron ore as a main raw material and coke as a main heat source Is to provide a hot metal desulfurization treatment method capable of efficiently desulfurizing hot metal with a small amount of lime basic unit.

  The present inventors conducted an experiment using a mechanical stirring type desulfurization apparatus using an impeller using a hot metal ladle and a top blowing type desulfurization apparatus installed between a cupola casting bed and a tilting pouring pad, and discharged from the cupola. When the molten iron (cupola hot metal) and the hot metal discharged from the blast furnace (blast furnace hot metal) coexist, a method for efficiently desulfurizing the hot metal was investigated. As a result, cupola hot metal has a higher S concentration in the hot metal than blast furnace hot metal, so if the S concentration after the treatment is about 0.01 mass% or less, the desulfurized lime efficiency is high due to the effect of the initial S concentration being high. It has been found that when the sulfur concentration after treatment is desulfurized to a low concentration of 0.003 mass% or less, the desulfurized lime efficiency becomes very low. On the other hand, when cupola hot metal is combined with blast furnace hot metal without desulfurization, and the combined hot metal is desulfurized, the cupola hot metal itself is used in an iron manufacturing facility where blast furnace hot metal and cupola hot metal coexist. It was found that the total amount of lime (desulfurization agent) used can be reduced as compared with the case of having a desulfurization process.

The present invention has been made on the basis of such knowledge and has the following gist.
[1] The process of producing hot metal (A) using iron-based scrap as the main raw material and coke as the main heat source and the process of producing hot metal (B) using iron ore as the main raw material and coke as the main heat source coexist. In a steelmaking facility, hot metal (A) is combined with hot metal (B) without desulfurization treatment, and then the hot metal combined with the hot water is desulfurized to a concentration of 0.003 mass% or less after treatment. Hot metal desulfurization treatment method.
[2] The desulfurization treatment method according to [1], wherein the mass a of the hot metal (A) and the mass b of the hot metal (B) to be combined together satisfy the following formula (1): .
0 <a / (a + b) ≦ 0.5 (1)
[3] In the desulfurization treatment method of [1] or [2] above, the step of producing hot metal (A) using iron-based scrap as a main raw material and coke as a main heat source is performed using a shaft-type cupola. A hot metal desulfurization process characterized by the above.

  According to the hot metal desulfurization processing method of the present invention, a process of producing hot metal (A) using iron-based scrap as a main raw material and coke as a main heat source, and a hot metal (B) using iron ore as a main raw material and coke as a main heat source ) In the steelmaking facility where the manufacturing process is combined, the hot metal (A) is combined with the hot metal (B) without desulfurizing, and the hot metal combined with the hot metal is desulfurized to reduce the amount of lime. Can be efficiently desulfurized.

The present invention uses iron-based scrap as the main raw material, coke as the main heat source, and a process for producing hot metal A (= Cupola hot metal A), hereinafter referred to as “cupola hot metal A” for convenience, and iron ore as the main raw material. In a steelmaking facility where coke is used as a main heat source and a process for producing hot metal B (= represented by “blast furnace hot metal B” for the sake of convenience below) is used as a main heat source, blast furnace hot metal without desulfurizing cupola hot metal A The hot water combined with B is desulfurized.
In the following explanation, “cupola” refers to charging iron-based scrap and coke from the top of the furnace, blowing hot air from multiple tuyere at the bottom of the furnace, and melting iron-based scrap with the combustion heat of the coke. And a vertical melting furnace for producing hot metal.

Here, the operation of cupola is as follows: (i) the amount of slag is as low as about 1/5 compared to blast furnace operation due to the difference in raw materials; (ii) the degree of oxidation in the furnace is high and the iron oxide concentration in the slag is high. Since the basicity of slag is low, desulfurization to the slag side is difficult to be performed, and the sulfur content is distributed to the hot metal side, so that the S concentration in the hot metal becomes high.
In the present invention, the S concentration after the desulfurization treatment of the molten hot metal (cupola hot metal A + blast furnace hot metal B) is not particularly limited, but is generally 0.003 mass% or less.

  FIG. 1 schematically shows a cupola for producing hot metal A and its basic operation mode. In the figure, 1 is a raw material charging portion provided at the top of the furnace, 2 is a plurality of tuyere (blower tuyere) provided at appropriate intervals in the circumferential direction of the lower part of the furnace, and 3 is supplying hot air to the tuyere 2 A hot air pipe, 4 is an exhaust gas outlet, and 5 is an outlet. Although there is no essential limitation on the size of the cupola, the furnace inner diameter at the tuyere position is usually about 2 to 4 m, and the furnace height is 6 to 10 m. Degree.

In such a cupola, iron scrap and coke are charged from the raw material charging section 1 at the top of the furnace, hot air is blown from a plurality of tuyere 2 and the iron scrap is melted by the heat of the coke combustion gas. Let's use hot metal. The produced hot metal is taken out of the furnace through the outlet 5 at the bottom of the furnace.
The raw iron scrap and coke may be charged into the furnace at the same time or alternately. The main furnace charge materials are iron scrap and coke, but other than that, for example, pig iron, reduced iron, agglomerates of dust and sludge, iron sources such as iron ore, limestone, charcoal and anthracite Charcoal materials may be charged.

In the hot metal desulfurization reaction, S in the hot metal is taken into the slag in the form of CaS by the reaction of the following formula (2). The desulfurization ability of slag at this time is generally expressed by the following formula (3) (apparent equilibrium formula) The distribution ratio Ls shown in FIG.
CaO + S = CaS + O (2)
Ls = (S) / [S] = ([S] _i / [S] _f −1) / w _s (3)
Ls: distribution ratio (-)
(S): Sulfur concentration in slag (mass%)
[S]: Sulfur concentration in hot metal (mass%)
[S] _i : Sulfur concentration (mass%) in hot metal before treatment
[S] _f : Sulfur concentration (mass%) in the hot metal after the treatment
w _s : Slag ratio (-)

As described above, the distribution ratio Ls is the desulfurization ability of slag. If the slag composition is constant, the [S] _f concentration corresponding to the [S] _i concentration is determined. Therefore, as the [S] _i concentration increases, the [S] _f concentration also increases. Therefore, in order to lower the [S] _f concentration, it is necessary to increase the slag ratio (lime basic unit).
Generally, cupola hot metal A has an S concentration several times higher than that of blast furnace hot metal B. Therefore, in order to reduce the concentration of cupola hot metal A to S ≦ 0.003 mass% in a single process, the slag ratio must be increased. The desulfurized lime efficiency becomes very low as described above. On the other hand, when the cupola hot metal A is combined with the blast furnace hot metal B and then desulfurized, the S concentration of the cupola hot metal A is diluted with the blast furnace hot metal B, so that the desulfurized lime efficiency does not deteriorate. .

In addition, when cupola hot metal A is combined with blast furnace hot metal B, the slag ratio increases as the initial S concentration increases. However, if the slag ratio is too high, there is not enough free board in the processing vessel (usually hot metal ladle). It has also been found that slag and hot metal may overflow from the processing vessel, and the processing may not be performed substantially. It was also found that the limit was [a / (a + b)] ≦ 0.5 as the mass ratio of cupola hot metal A (mass a) and blast furnace hot metal B (mass b) to be combined. Therefore, in the present invention, it is preferable to combine the cupola hot metal A and the blast furnace hot metal B so as to satisfy the following expression (1).
0 <a / (a + b) ≦ 0.5 (1)
By performing the desulfurization treatment of the hot metal as described above, the S concentration of the hot metal can be reduced to the target value with a small amount of lime basic unit as a whole in the iron making facility in which the cupola hot metal A and the blast furnace hot metal B coexist.

  As an example of the present invention, the following desulfurization treatment was performed. Blast furnace hot metal B (average S concentration: 0.03 mass%) extracted from the blast furnace is received in the hot metal ladle, the hot metal ladle is moved to the cupola center by rail, and cupola hot metal A (average S) discharged from the cupola is obtained. Concentration: 0.08 mass%) and then the hot metal ladle is moved to the desulfurization center, and the hot metal in the hot metal ladle is converted to S concentration: 0 using a mechanical stirring type desulfurization apparatus with an impeller as shown in FIG. It was desulfurized to 0.002 mass%. In this desulfurization treatment, the desulfurization agent 13 was added from the shooter 8 to the hot metal 11 in the hot metal pan 6, and the hot metal 11 and the slag 12 were stirred using the impeller 7. In addition, in drawing, 9 is the trolley | bogie which holds the hot metal ladle 1, and 10 is the hopper 5 for desulfurization agents. The amount of hot metal treated was 230 to 240 t / ch, and the hot metal temperature before treatment was 1400 to 1410 ° C. Lime having a particle size of 30 mm or less was used as a desulfurization agent, the impeller rotation speed was 120 to 130 rpm, and the desulfurization treatment time was 8 to 10 min.

  Further, as a comparative example, the following desulfurization treatment was performed. The cupola hot metal A (average S concentration: 0.08 mass%) extracted from the cupola was used with a top blowing type desulfurization apparatus installed between the cupola casting bed and the tilting iron as shown in FIG. The desulfurization treatment was performed to 0.002 mass%. In this desulfurization process, a desulfurizing agent is added to the hot metal 11 flowing in the hot metal 14 from an upper blowing lance 15 installed above the hot metal 14, and the desulfurized hot metal 11 falls into the hot metal pan through the tilting iron. And it was received in hot metal hot pot. The average passing amount of the cupola molten iron A was 1.5 t / min, the average temperature of the hot iron was 1530 ° C., and lime of 3 mm or less was used as a desulfurizing agent for top blowing.

  The hot metal ladle is charged with a specified amount of blast furnace hot metal B (average S concentration: 0.002 mass%) that has been desulfurized in advance, and cupola hot metal A that has been subjected to desulfurization treatment as described above. At the time of receiving, the blast furnace hot metal B was put together. In the desulphurization treatment method for blast furnace hot metal B, the hot metal ladle receiving the blast furnace hot metal B is moved to the desulfurization center, and the mechanical stirring type desulfurization apparatus (Fig. 2) using the impeller is used as in the present invention example. The hot metal was desulfurized to an S concentration of 0.002 mass%. The amount of hot metal treated was 230 to 240 t / ch, and the hot metal temperature before treatment was 1400 to 1410 ° C. Lime having a particle size of 30 mm or less was used as a desulfurization agent, the impeller rotation speed was 120 to 130 rpm, and the desulfurization treatment time was 8 to 10 min.

As described above, in the example of the present invention, the cupola hot metal A was combined with the blast furnace hot metal B without desulfurization, and then desulfurized with a mechanical stirring type desulfurization apparatus using an impeller. On the other hand, in the comparative example, cupola hot metal A was desulfurized and then combined with blast furnace hot metal B that had already been desulfurized.
FIG. 4 shows the relationship between the mass ratio [a / (a + b)] and the total lime unit for cupola hot metal A (mass a) and blast furnace hot metal B (mass b) to be combined. Here, the total lime unit in the comparative example is the total of lime that desulfurizes cupola hot metal A and lime that desulfurizes blast furnace hot metal B. According to FIG. 4, it can be seen that, regardless of the mass ratio [a / (a + b)], the inventive example has less total lime basic unit than the comparative example, and an efficient treatment is performed. . In the present invention example, if the mass ratio [a / (a + b)] exceeds 0.5, the amount of the desulfurizing agent increases too much, so that slag and hot metal overflow from the hot metal pan, and stable treatment may not be possible. there were.

Explanatory diagram schematically showing the cupola and its basic operating mode Explanatory drawing which shows the implementation status of the desulfurization process using the mechanical stirring type desulfurization apparatus by the impeller Explanatory drawing which shows the implementation status of the desulfurization process using the top blowing type desulfurization device installed between the cupola cast floor and the tilting iron In an Example, the graph which shows the relationship between mass ratio [a / (a + b)] and a total lime basic unit about cupola hot metal A (mass a) and blast furnace hot metal B (mass b) to join together.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw material charging part 2 Tuyere 3 Hot air pipe 4 Exhaust gas outlet 5 Outlet 6 Hot metal ladle 7 Impeller 8 Shooter 9 Bogie 10 Hopper 11 Hot metal 12 Slag 13 Desulfurizing agent 14 Hot metal 15 Top blowing lance

Claims (3)

In steelmaking facilities where iron scrap is the main raw material and the process of producing hot metal (A) using coke as the main heat source and the process of producing hot metal (B) using iron ore as the main raw material and coke as the main heat source The hot metal (A) is combined with the hot metal (B) without desulfurization treatment, and then the hot metal combined with the hot water is subjected to desulfurization treatment so that the S concentration after the treatment is 0.003 mass% or less. Processing method. 2. The hot metal desulfurization method according to claim 1, wherein the mass a of the hot metal (A) and the mass b of the hot metal (B) satisfying the following formula (1):
0 <a / (a + b) ≦ 0.5 (1) The hot metal desulfurization treatment according to claim 1 or 2, wherein the step of producing hot metal (A) using iron-based scrap as a main raw material and coke as a main heat source is performed using a shaft-type cupola. Method.

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