JP2556077B2 - Cr smelting reduction method for raw ore - Google Patents

Description

The present invention relates to a method for smelting and reducing Cr ore.

[Conventional technology and its problems]

Hitherto, high Cr steel such as stainless steel has been melted using ferrochrome produced from Cr ore as a raw material. In contrast to such a conventional method, a so-called smelting reduction method, which directly obtains high Cr hot metal from Cr ore, has recently attracted attention from the viewpoint of energy saving and low manufacturing cost. Generally, in this method, Cr ore, carbonaceous material, etc. are charged into a converter-type reduction furnace, and Cr is reduced to directly obtain high Cr hot metal.

As the smelting reduction method, some conventional methods have been proposed, as one of them, O ₂ top-blown with from the lance, the bottom tuyeres O _2, from the side tuyeres N _2, respectively method of blowing, or O ₂ top blowing with from the lance, O ₂ from the bottom tuyeres, a method of blowing from the side blowing tuyeres O ₂ and N _2, respectively are known. For example, JP-A-61-279608 is an example of the latter.

However, each of these conventional methods has a serious problem that the reduction rate of Cr is low and the processing takes time.
This can be explained by the following points.

Conventionally, the reduction of Cr ore in the furnace proceeds by the action of C of carbonaceous material after the dissolution of Cr ore in the slag, and the melting of Cr ore is considered to be the rate-determining factor of Cr reduction. Therefore, the main technical interest for shortening the processing time has been directed to the identification of the slag composition. However, Cr ore is basically infusible, and there is a limit to promoting the melting of Cr ore and increasing the reduction rate.

In order to increase the melting rate of Cr ore slag and improve the reduction treatment of Cr ore, a method of secondary combustion of CO gas in the furnace and utilizing the heat can be considered. The method of blowing in O ₂ is used. However, conventionally, although the exhaust gas temperature rises when the secondary combustion ratio is increased, there is no technology to efficiently transfer the sensible heat of the exhaust gas to the molten metal, and as a result, the heat deposition efficiency is lowered and the hot lung gas must be discharged. Absent. And, it is a general idea that such high-temperature exhaust gas has a big problem that the refractory material on the inner wall of the furnace and the refractory material of the exhaust gas hood are severely worn, and therefore the secondary combustion ratio cannot be raised so much.

Also, Cr ore has a very fine grain size, usually 1 mm.
About 90% of the following particles are included. Therefore, when such powdered Cr raw ore is dropped into a converter-type reduction furnace from above, the ore scatters outside the furnace, and the scattering loss reaches 30%.

In order to prevent such scattering loss, charging by injection may be considered, but this method requires special equipment for that, and since Cr ore has a considerably high hardness, the transport pipe will be worn quickly. There is a problem,
Not actually adopted.

For this reason, under the present circumstances, Cr raw ore must be used in the form of pellets or briquettes, which increases the manufacturing cost. In addition, if the ore is made agglomerate in this way, the specific surface area of the ore becomes small and the preheating time becomes long, so that the reduction rate decreases and the processing time becomes long.

[Means for solving problems]

With respect to such conventional recognitions and problems, the present inventors have repeatedly studied the mechanism of smelting reduction and specific means corresponding thereto, and as a result, have found the following facts. .

As described above, it is conventionally thought that the Cr ore is dissolved in the slag and then reduced by the carbonaceous material in the slag. Was found to be acting. Therefore, the rate of reduction is controlled by the contact of the molten metal with Cr ore heated to a high temperature, not by the dissolution of Cr ore into the slag, and the reduction rate is effectively increased by positively contacting the molten metal with the ore. Can be increased.

As mentioned above, the basic idea is that the secondary combustion ratio cannot be increased significantly in terms of the technical limit for improvement of heat transfer efficiency and the wear of refractory materials, but secondary combustion is mainly used in slag. By injecting C ₂ so as to generate and strongly stirring the slag, it is possible to effectively enhance the heat deposition efficiency while ensuring high secondary combustion. Due to such high secondary combustion and high heat deposition efficiency, the temperature of the slag and the Cr ore in the slag increases, and the reduction rate of Cr ore by C ( C in molten metal) represented by Cr ₂ O ₃ +3 C = 2Cr + 3CO is effective. Can be increased.

In the conventional method, there is an example in which bottom blowing of O ₂ is performed for one period or the entire reduction treatment, but such bottom blowing of O ₂ is harmful to secondary combustion. That is, when O ₂ is blown from the bottom, a large amount of CO gas is generated in the molten metal, and the molten metal is strongly stirred,
As a result, the molten metal splash reaches the secondary combustion zone, and C in the molten metal reacts with O ₂ and CO ₂ gas to generate CO gas, which hinders secondary combustion. Therefore, it is absolutely necessary to avoid bottom-blowing of O ₂ during part or all of the reduction period.

As described above, the drop charging of Cr raw ore has a problem of large scattering loss. However, by increasing the feeding speed, the probability that individual Cr raw ore particles are exposed to the rising gas flow is reduced, and the scattering loss is reduced.In particular, the Cr raw ore feeding rate is 4 kg / min per Cr net content.・ We have found that scattering loss can be significantly reduced by setting the melt ton or higher.

The present invention defines the following conditions based on such knowledge, and thereby enables reduction treatment at a high treatment speed while preventing scattering loss of Cr raw ore.

(B) By combining bottom blowing and side blowing of stirring gas,
The molten metal is positively diffused in the area where Cr ore is present in the slag, and the reducing action of Cr ore by C in the molten metal is promoted.

(B) In order to obtain a secondary combustion ratio above a certain level,
The decarburization for O ₂ performs separately blowing secondary combustion O _2. Then, the secondary combustion O ₂ is blown into the slag from the upper blowing lance to form a secondary combustion region in the slag, and the slag is vigorously stirred by the side-blown gas, and the heat generated by the secondary combustion is converted into Cr. Heat the ore.

(C) Reduction of Cr ore by C in molten metal and top-blown O ₂
In order to prevent the secondary combustion from being disturbed, the side blown gas and bottom blown gas are CO or inert gas, and O ₂ is not used.

(D) Cr Cr in the raw ore Cr is used to suppress the loss of the original ore.
The feed rate converted to pure content should be 4 kg / min.

That is, the present invention uses a smelting reduction furnace equipped with a bottom blowing tuyere, a side blowing tuyere, and a top blowing lance to obtain a high Cr hot metal by reducing Cr raw ore with a carbon source of carbonaceous material. In the middle, the following (a) to (c) gas is blown, (a) CO or / and an inert gas is blown from the bottom blowing tuyere, (b) At least a part of the gas flow is melted by the bottom blowing gas. as striking the ridges, lateral tuyeres blowing CO and / or inert gas from a lance above (c), into the melt with blowing decarburization for O _2, the secondary combustion O ₂ into the slag The basic feature is that the Cr raw ore is reduced while it is blown in and the feed rate of the pure Cr content (the feed rate of the raw Cr ore converted to the pure Cr amount) is 4 kg / min. And

 Hereinafter, the details of the present invention will be described.

1 and 2 schematically show the present invention.

In the present invention, mainly a converter type smelting reduction furnace is used to reduce Cr raw materials such as Cr ore and Cr pellets. Specifically, bottom blowing tuyere 1, side blowing tuyere 2 and Top blowing lance 3
A furnace equipped with is used.

According to the method of the present invention, a Cr raw material (hereinafter, Cr ore will be described as an example), carbonaceous material and flux are charged into the metal bath in the smelting reduction furnace, and reduction treatment is performed under the following conditions. Be seen.

First, during the reduction process, gas is blown from the bottom blowing tuyere 1, side blowing tuyere 2 and top blowing lance 3 from the initial stage to the final stage.

The gas injection from the bottom blowing tuyere 1 and the side blowing tuyere 2 causes the molten metal to diffuse into the slag by the cooperation of the two.
It has the effect of dramatically increasing the reduction rate.

As described above, the present inventors have clarified the fact that the reduction of Cr ore in the slag mostly proceeds by using C in the molten metal as a reducing substance, and based on this, the molten metal is strongly stirred and the slag (Cr ore (A region in which is suspended) is positively diffused to increase the reduction rate. Therefore, according to the present invention, the stirring gas is supplied from the bottom blowing tuyere 1 to form the raised portion A on the molten metal surface, and at the same time, at least a part of the gas flow from the side blowing tuyere 2 hits the molten metal raised portion A. The agitating gas is supplied as described above, and the molten metal in the molten metal swelling portion A is scattered into the slag by this laterally blown gas. The apparent specific gravity of slag is usually 0.3 to 0.5, while the bulk specific gravity of Cr ore is around 3.0. Therefore, the Cr ore in the slag is mostly concentrated in the lower slag region and floats as shown in Fig. 2. are doing. As described above, when the molten metal swelling portion is scattered by the side-blown gas, this scattered molten metal diffuses into the slag lower region where Cr ore is present, and C in this diffused molten metal is Cr ₂ O ₃ is reduced and a high reduction rate is obtained.

In order to obtain such an action, it is preferable that the side-blown gas strikes the molten metal ridge A as accurately as possible in the vertical and horizontal directions of the furnace. For example, in the horizontal direction, FIG. It is preferable to provide the bottom blown tuyere 1 and the side blown tuyere 2 in a positional relationship as shown in FIGS.

The side-blown gas has a function of stirring the slag in which the secondary combustion region is formed, in addition to the function of diffusing the scattered molten metal as described above, which will be described later.

The side-blown gas and the bottom-blown gas used in the present invention are limited to CO and an inert gas (N ₂ , Ar, etc.), and O ₂ is not used. This is for the following reasons.

First, when O ₂ is used as the side-blown gas, C in the molten metal scattered for the reduction of Cr ore reacts with this O _2, and C 2
There is a fundamental problem that the reduction action of Cr ore by Cr is inhibited. In addition, when O ₂ is used, the temperature of the refractory rises, causing a problem of wear of the refractory.

Also, when O ₂ is used as the bottom blown gas, a large amount of CO gas is generated in the molten metal as described above, and the molten metal is excessively stirred,
As a result, the splash of the molten metal reaches the secondary combustion region (see FIG. 2), and the C in the molten metal reacts with O ₂ for secondary combustion described later to hinder the secondary combustion. In addition, when O ₂ is used, the temperature of the refractory such as the bottom blowing tuyere rises too much, so it is necessary to add a cooling gas (C ₃ H ₈ etc.), which also increases the bottom blowing gas amount and vigorous stirring → It will excessively promote the generation of molten metal splash. Figure 4 is a present invention method in which the blowing N ₂ bottom, the comparative example in which the blowing O ₂ bottom instead of N _2, setting the secondary combustion ratio [PcO ₂ / (DCO ₂ + ore O _2)] It shows the result of actually inspecting the secondary combustion ratio (actual measurement) with respect to, and it is shown that the secondary combustion is obstructed by the O ₂ bottom blowing.

In addition, an inert gas such as CO, N ₂ , or Ar serving as a stirring gas can be used alone or as a mixture.

Next, O ₂ for decarburization is blown into the molten metal from the upper blowing lance 3 and O ₂ for secondary combustion is blown into the slag. The upper blowing lance 3 is provided with a decarburizing O ₂ nozzle hole and a secondary combustion O ₂ nozzle hole. The secondary combustion O ₂ is supplied from the decarburizing O ₂ through the supply nozzle hole. Is also supplied obliquely downward to the outside.

In the present invention, high secondary combustion is realized while forming the secondary combustion region mainly in the slag, and thus the secondary combustion region is formed in the slag and the slag is strongly stirred by the side-blown gas. As a result, it is possible to obtain high secondary combustion while ensuring high secondary combustion. Therefore,
The secondary combustion O ₂ needs to be mainly blown into the slag so that a secondary combustion region is formed in the slag. In particular, in the present invention, a high Cr raw ore charging speed is adopted to prevent the loss of Cr ore scattering, and in order to maintain such a charging speed without lowering the molten metal temperature, high secondary combustion is performed. It is necessary to secure a high heat-transfer efficiency while ensuring the same.

Specifically, the height of the upper blowing lance needs to be set to an appropriate level with respect to the slag and molten metal levels.
That is, although the nozzle hole height of the upper blowing lance 3 can be set above the slag surface or below the slag surface, if the height is too high, the secondary combustion region is not formed in the slag, and the heat deposition efficiency decreases. If the lance height is too low, secondary combustion O ₂ will be blown into the Cr ore floating region in the slag (see Fig. 2), and the secondary combustion region will not be formed properly. .

Fig. 5 shows the relationship between the height of the tip of the lance from the slag surface (forming level) and the heat transfer efficiency. It shows that good heat transfer efficiency cannot be obtained if the lance height is too high with respect to the slag surface. Has been done. Further, FIG. 6 shows the relationship between the amount of laterally blown gas and the heat transfer efficiency, and it can be seen that good heat transfer efficiency can be obtained by injecting a large amount of horizontally blown gas and strongly stirring the slag layer.

The secondary combustion ratio is (CO ₂ + H) of the gas component in the exhaust gas.
It is defined by O ₂ ) / (CO + CO ₂ + H ₂ + H ₂ O), but in the present invention, it is preferable to perform the above-mentioned reduction treatment by setting the secondary combustion ratio to 0.3 or more. In the present invention, since high heat transfer efficiency can be obtained, high reduction processability (reduction rate) can be obtained by increasing the secondary combustion ratio as described above. In addition to this, it is necessary to increase the secondary combustion ratio. The amount of carbonaceous material (mainly coke) can be kept low by this, and as a result,
It is possible to reduce the carbonaceous material unit and to reduce the P content in the molten metal because most of the P component in the molten metal is brought in by the carbonaceous material. Also, when the secondary combustion ratio increases, the vaporization desulfurization phenomenon becomes active, and S in the molten metal also decreases. From such a viewpoint, the present invention sets the secondary combustion ratio to 0.3 or more. FIG. 7 shows the secondary combustion ratio in the furnace, the coke consumption rate, and the P in the molten metal in the smelting reduction of the method of the present invention.
It shows the relationship between the S and S components.
By setting the ratio to 0.3 or more, the coke basic unit is suppressed, and P and S in the molten metal are appropriately reduced.

The above is the detailed contents of the present invention. When the present invention is actually carried out, usually, the steps are charging, slag making, heat-up, and smelting reduction of Cr ore.

Further, in the present invention, in the smelting reduction treatment as described above, the treatment is performed while keeping the charging rate of the pure Cr content (the charging rate of the Cr raw ore converted into the pure Cr amount) at 4 Kg / min.mol. By controlling the feeding rate of pure Cr as described above, the probability that individual Cr ore particles are exposed to the rising gas flow is reduced, and the ore scattering loss is significantly reduced.

Here, the charging step means charging a Fe source such as hot metal and forming a metal bath in the furnace. In the slag / heating process, acid is fed into the bath and carbonaceous material, flux, etc. are charged to form slag, which is a reduction region of Cr ore, and the bath temperature is raised to the temperature required for reduction. In the Cr ore smelting reduction process, Cr ore, carbonaceous material, and flux are sequentially charged into the smelting reduction furnace. At the end of this process, finish reduction is performed without adding Cr ore, and the reduction treatment is completed when the Cr concentration in the molten metal reaches the target value.

〔Example〕

Example 1. Using a converter type smelting reduction furnace (5Ton), 3.7Ton of hot metal was charged, then Cr ore, coke, and flux were charged to perform smelting reduction, and 5.5Ton of 18% Cr hot metal was added. Obtained. Figure 8 shows the Cr and C concentrations in the hot metal, bath temperature, and secondary combustion ratio OD at that time.
And the like, the amount of acid fed by the lance, the amount of gas for bottom blowing and the amount of gas for side blowing, and the amount of raw material charged.

FIG. 9 shows the processing time (the time from the start of reduction to the end) of this embodiment in comparison with the processing time of the conventional method shown in FIGS. 10 (a) and 10 (b). In the conventional method (1), pulverized coal and O ₂ are blown up from the top blow lance,
A method of blowing stirring gas from the bottom tuyere, conventional method (2)
Blows O ₂ from the top blowing lance onto the slag,
This is a method of blowing N ₂ from the bottom-blowing tuyere and N ₂ and O ₂ from the side-blowing tuyere, respectively, and the specific operating conditions are as follows.

Blowing the conventional method (1) the top-blown O ₂ 1700Nm ³ / Hr bottom blowing N ₂ 350 Nm ³ / Hr molten iron 5 ton Cr ore 4600kg carbonaceous material 6700Kg (injection from lance) conventional method (2) top-blown O ₂ 1000 Nm ³ / Hr bottom N ₂ 120Nm ³ / Hr lateral blowing N ₂ (placed on) 350 Nm ³ / Hr lateral blowing O ₂ 800Nm ³ / Hr molten iron 5 ton Cr ore (iron ore fines) 5000 kg (placed on) the carbonaceous material 3200kg According to FIG. 9, In the conventional method (2), the Cr concentration is only about 6 to 7%, and in the conventional method (1), the Cr concentration is the target.
Although it is 18%, it takes 110 minutes to process. On the other hand, according to the present invention, about 50% of the processing time of 50% is 18%
It has reached Cr, which shows the extremely excellent processing performance of the present invention.

Example 2. Using the same converter-type smelting reduction furnace as in Example 1, the charge rate of the powdery Cr raw ore was changed variously to carry out smelting reduction.
In this smelting reduction, molten iron was charged into the furnace, then Cr ore, coke and flux were charged and smelting reduction was performed under the following conditions to obtain 5 Ton of 18% Cr molten iron.

Upper吹脱charcoal for O _2: 1500Nm ³ / Hr on blowing secondary combustion O _2: 1100Nm ³ / Hr Soko吹gas volume ^{_{(N 2): 700Nm 3 /}} Hr Yokobuki gas volume ^{_{(N 2): 300Nm 3 /}} Hr The particle size distribution of the charged Cr ore was as follows.

Moreover, T.Cr contained in Cr raw ore was 30%.

FIG. 11 shows the relationship between the feed rate of Cr raw ore (Cr feed rate) and the ore scattering loss in this example.
It can be seen that the dispersion loss is remarkably reduced by using the Cr raw ore (Cr pure content) feeding rate of 4 kg / min and the molten metal Ton.

In addition, Fig. 12 shows the Cr pure feed rate (Cr converted to pure Cr amount).
The rate of increase of Cr with respect to the ore input rate) was investigated.
It can be seen that a higher Cr ascent rate is obtained compared to the conventional method. In addition, when the pure Cr content input rate is 4 kg / min and the molten metal Ton is C
r The loss of ore scattering is reduced, and the Cr ore has a higher Cr ascent rate than the Cr ore pellets. This is because when Cr ore is lumped, the specific surface area of Cr ore becomes small and the temperature increase rate of Cr ore becomes small, so that the Cr reduction rate decreases.

〔The invention's effect〕

According to the present invention described above, since the reduction action of Cr ore by C in the molten metal is positively promoted and the treatment is performed while ensuring a high secondary combustion ratio and heat-transfer efficiency, the reduction rate of Cr ore is at the conventional level. As compared with the above, the smelting reduction treatment can be efficiently performed in a short time.
In addition, since the secondary combustion ratio is high, the carbonaceous material unit can be reduced and the amounts of P and S components in the obtained hot metal can be suppressed to be low. In addition, it is possible to significantly reduce the scattering loss of the Cr raw ore, and to perform the smelting reduction using the Cr raw ore as a raw material at low cost.

[Brief description of drawings]

1 and 2 are explanatory diagrams schematically showing the principle of smelting reduction in the present invention. FIGS. 3 (a) and 3 (b) are explanatory views showing a preferred side-blown gas injection direction for the bottom-blow tuyere. FIG. 4 shows the measured secondary combustion ratio with respect to the set secondary combustion ratio for the method of the present invention and the comparative method of performing O ₂ bottom blowing. FIG. 5 shows the relationship between the height of the upper blowing lance and the heat transfer efficiency. FIG. 6 shows the relationship between the laterally blown gas amount and the heat deposition efficiency. FIG. 7 shows the relationship between the in-furnace secondary combustion ratio and the amounts of S and P in the molten metal and the basic unit of coke. FIG. 8 shows Cr, C in the molten metal in the example.
It shows changes with time of concentration, bath temperature, secondary combustion ratio, lance acid supply amount, raw material supply amount and the like. FIG. 9 shows the reduction treatment time of the example of the present invention in comparison with the conventional method. First
10 (a) and 10 (b) are explanatory views showing the processing methods of the conventional methods (1) and (2) shown in FIG. Fig. 11 shows the effect of the feed rate of Cr raw ore on the scattering loss of powdered Cr raw ore. FIG. 12 shows the relationship between the Cr pure addition rate and the Cr increase rate in the example of the present invention in comparison with the conventional method. In the figure, 1 is a bottom blowing tuyere, 2 is a lateral blowing tuyere, 3 is a top blowing lance, and A is a molten metal ridge.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiro Iwasaki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Co., Ltd. (72) Inventor Shigeru Inoue 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Within the corporation (56) Reference JP-A 64-83606 (JP, A) JP-A 1-96313 (JP, A) JP-A 62-214116 (JP, A) JP-A 64-68415 (JP, A) JP-A-63-86807 (JP, A) JP-A-61-279608 (JP, A)

Claims (2)

(57) [Claims] 1. A method for obtaining high Cr hot metal by using a smelting reduction furnace equipped with a bottom blowing tuyere, side blowing tuyere, and top blowing lance to reduce Cr raw ore with a carbon source of carbonaceous material to obtain high Cr hot metal. During,
The following (a) to (c) gas is blown, (a) CO or / and an inert gas is blown from the bottom blowing tuyere, (b) At least a part of the gas flow is a molten metal raised part due to the bottom blown gas. CO or / and an inert gas is blown from the side blowing tuyere, so that (2) O ₂ for decarburization is blown into the molten metal from the top blowing lance, and O ₂ for secondary combustion is blown into the slag. In addition, the method for smelting and reducing Cr raw ore is characterized by performing the reduction treatment while maintaining the input rate of pure Cr content (the input rate of Cr raw ore converted into pure Cr amount) at 4 kg / min. . 2. O ₂ for decarburization and secondary combustion by a lance whose tip is located near the slag surface during operation or below the slag surface.
The method for smelting and reducing Cr ore according to claim (1), characterized in that the reduction treatment is performed while blowing O ₂ and maintaining the secondary combustion ratio at 0.3 or more.