JP2595597B2 - Melt reduction method of Cr raw material - Google Patents

Description

The present invention relates to the direction of smelting reduction of Cr raw materials such as Cr ore and Cr ore pellets.

[Conventional technology and its problems]

Conventionally, high Cr steels such as stainless ores have been produced by melting ferrochrome produced from Cr ore as a raw material. In contrast to such conventional methods, recently, from the viewpoint of energy saving and low production cost, Cr ore, a Cr raw material such as a Cr ore pellet (hereinafter, Cr ore is described as an example), and a high Cr hot metal is directly obtained.
The so-called smelting reduction method has attracted attention. In this smelting reduction method, Cr ore, carbonaceous material and the like are charged into a reduction furnace, and Cr is reduced to directly obtain high Cr hot metal.

As the smelting reduction method, which some conventional methods have been proposed, as one of them, O ₂ top-blown with from lance blown O ₂ from the bottom tuyeres, from the side tuyeres N _2, respectively method, or O ₂ top blowing with from the lance, O ₂ from the bottom tuyeres, a method of blowing O ₂ and N _2, respectively are known from the side tuyeres.

In addition, the present inventors also blow inert gas (or / and CO) from the bottom blow tuyere, and inject the inert gas from the side blow tuyere so that at least a part of the gas flow hits the molten metal ridge due to the bottom blow gas. Activated gas (or / and CO) is blown, and from the top blowing lance for decarburization into the molten metal
With blowing O _2, into the slag as blowing secondary combustion O _2, the secondary combustion ratio in the furnace to propose a new smelting reduction method characterized by performing the processing while maintaining less than 0.3 ing.

By the way, in this type of smelting reduction, it is required to accurately grasp the progress of the smelting reduction and complete the process from the viewpoint of stabilizing the operation, securing reservation, and the like. In particular, if the blowing is continued after the completion of the reduction of the Cr ore (completion), the temperature of the molten metal becomes 10 to 50 ° C / m due to the re-melting allowance of Cr and the decarburization reaction of [C] in the molten metal.
in also rises, significantly increasing refractory wear. Therefore, it is indispensable for economical operation to know the completion of the reduction accurately and immediately end the blowing. Conventionally, the time required for the reduction process is predicted from the amount of input of the Cr raw material, etc., and the process is terminated when a certain period of time has elapsed after the start of the process.
In order to perform a stable and economical operation, such as the end of the treatment is too early or too late, unreduced Cr remains in the slag in a large amount, or the temperature of the molten metal is unnecessarily increased. Had a problem.

The present invention has been made in view of such conventional problems, and has as its object to provide a method capable of accurately grasping the progress of smelting reduction and appropriately and promptly terminating blowing.

[Means for solving the problem]

Therefore the present invention is determined by focusing on the relationship that the amount of O ₂ source in the exhaust gas is reduced, based on a difference reduction completion time of the O ₂ source and the blowing O ₂ in the exhaust gas with decreasing reduction It is something to do.

That is, the present invention measures the flow rate of the exhaust gas and the CO and CO ₂ concentrations in the exhaust gas during the smelting reduction treatment, obtains the Cr raw material reduction rate R from the measured values based on the following equation, and performs the smelting reduction based on the Cr raw material reduction rate R. It is characterized in that the processing completion timing is determined and the return processing is terminated.

However, Wore: Cr raw material input amount [Ton] Oore: Cr raw material containing O ₂ amount [Nm ³ / Ton] Q _E : Exhaust gas flow rate [Nm ³ / min] [% CO]: CO concentration in exhaust gas [%] [ % CO ₂ ]: CO ₂ concentration in exhaust gas [%] Fo ₂ : Injection O ₂ flow rate [Nm ³ / min] Hereinafter, the present invention will be described in detail.

Conventionally, it was thought that the Cr ore was dissolved in the slag and then reduced by the carbonaceous material in the slag. However, the present inventors have found that most of the actual reduction reaction actually It was found out that it was caused by acting as a reducing substance.

In such smelting reduction of Cr ore, reduction proceeds as a whole by the following reaction.

Therefore, the more the reduction reaction is active, the larger the amount of CO generated.The measurement of the O ₂ source contained in the CO and CO ₂ in the exhaust gas and the difference between this and the amount of the injected O ₂ indicate the reduction reaction. You can know the degree of progress.

The amount of O ₂ contained in the exhaust gas is determined by the following equation (1).

However, Q _E : Exhaust gas flow rate [Nm ³ / min] [% CO]: CO concentration in exhaust gas [%] [% CO ₂ ]: CO ₂ concentration in exhaust gas [%] as described above, obtains a difference between the O ₂ blown into this way determined value and the furnace, by obtaining the ratio of Cr raw material containing O ₂ of this value, the degree of reduction of Cr raw material, i.e., Cr raw material reduction rate R
Can be requested.

However, Wore: Cr raw material input amount [Ton] Oore: Cr raw material containing O ₂ amount [Nm ³ / Ton] Fo ₂ : Injection O ₂ flow rate [Nm ³ / min] In the present invention, the exhaust gas flow rate and the CO in the exhaust gas , CO ₂ concentration, and based on the above equation (2), the reduction process is terminated when the value of the Cr raw material reduction rate R reaches a predetermined target value.

Specifically, when the R value is in the range of 0.01 (min ^-1 ) or less, Cr
It can be seen that the reduction of the ore is almost completed, and it is therefore preferable to terminate the blowing when R becomes 0.005 (min ^-1 ) or less. Further, by observing such R value, the reaction rate of the Cr ore can be grasped. For example, when it is determined that the reaction rate is small and the reduction is delayed, the stirring gas flow is increased. And other actions can be taken. Further, the molten metal temperature can be estimated from the R value, and an action for securing the molten metal temperature can be taken until the blowing is completed.

〔Example〕

Using a converter-type smelting reduction furnace (5Ton), after charging 2.7Ton hot metal, Cr ore, coke and flux were charged and smelting reduction was performed to obtain 5.5Ton 18% Cr hot metal. In this smelting reduction, the gas blowing conditions in the finish reduction period are as follows.

Lance oxygen-flow amount FO _2: 1500Nm ³ / hr Soko吹gas volume ^{_{(N 2): 750Nm 3 /}} hr Yokobuki gas volume ^{_{(N 2): 360Nm 3 /}} hr in such reduction treatment, finished with the following criteria The reduction process was terminated.

(1) The method of the present invention: the process is terminated when the R value becomes 0.005 (min ^-1 ) or less.

(2) Comparative method: The finish reduction treatment time was fixed at 15 minutes.

Fig. 2 shows an example of finish reduction by the comparative method. Finish reduction is completed at the time of 13 minutes. However, since the blowing is performed for 15 minutes, the temperature of the molten metal rises rapidly. It can be seen that once reduced Cr is reoxidized and the temperature rises sharply.

FIG. 3 is a diagram showing the relationship between the R value and the Cr content in the slag at that time. If the R value is 0.01 or less, it can be seen that the Cr content in the slag is 1% or less.

FIGS. 4 and 5 show the Cr concentration in the slag at the end of reduction and the molten metal temperature at the time of blow-off in the method of the present invention and the comparative method. According to the method of the present invention, Cr in the slag is effective. And the temperature of the molten metal at the time of blowing is also substantially at the target level. Therefore, it can be seen that in the present invention, the completion of the reduction is accurately detected, and the blowing is quickly terminated.

On the other hand, in the comparative method, there is considerable variation in the chromium concentration in the slag and the molten metal temperature at the time of blowing, and the blowing is completed too late or, conversely, too early. It can be seen that a decrease has occurred.

〔The invention's effect〕

As described above, according to the present invention, it is possible to accurately capture the completion timing of the smelting reduction and terminate the blowing, thereby stably performing the smelting reduction operation while securing a yield. Can be.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a blowing situation in the embodiment.
FIG. 2 shows the time change of the molten metal temperature and the Cr concentration in the slag in the embodiment. FIG. 3 shows R in the embodiment.
It shows the relationship between the value and the Cr concentration in the slag. 4th
The figure shows the Cr concentration in the slag at the end of the reduction in the example. FIG. 5 shows the molten metal temperature at the time of blowing.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Katsuhiro Iwasaki, Inventor Katsuhiro Iwasaki, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Shigeru Inoue 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Inside the corporation

Claims (1)

(57) [Claims] (1) During the smelting reduction treatment, the flow rate of exhaust gas and the amount of
Measure the CO and CO ₂ concentrations and calculate the Cr
A smelting reduction method for a Cr raw material, wherein a raw material reduction rate R is determined, a completion timing of the smelting reduction processing is determined based on the Cr raw material reduction rate R, and the reduction processing is terminated. However, Wore: Cr raw material input amount [Ton] Oore: Cr raw material containing O ₂ amount [Nm ³ / Ton] Q _E : Exhaust gas flow rate [Nm ³ / min] [% CO]: CO concentration in exhaust gas [%] [ % CO ₂ ]: CO ₂ concentration in exhaust gas [%] Fo ₂ : Blow-in O ₂ flow rate [Nm ³ / min]