JP6471526B2 - A method for melting auxiliary materials in an arc bottom-blown electric furnace. - Google Patents

Description

  The present invention relates to a method for melting an auxiliary material to be charged in an arc type bottom blowing electric furnace.

  When melting molten metal by melting scrap or the like in an arc electric furnace, generally, for example, lime or quick lime is charged as an auxiliary material. The auxiliary material generally has poor electrical conductivity and is heated and melted by receiving heat from a molten metal (hereinafter also referred to as “molten metal”). Therefore, the melting process of the auxiliary material charged in the arc electric furnace requires a certain time, and in order to increase the production efficiency, it is necessary to quickly heat and dissolve the auxiliary material. In recent years, as a secondary raw material, for example, those containing a large amount of CaO, such as converter decarburized slag, have been used as a substitute for quicklime, and oxides and hydroxides containing valuable metals have been increasingly used for recycling purposes. Therefore, the need to quickly heat and dissolve the auxiliary material has become apparent.

For example, claim 1 of Patent Document 1 discloses a technique for recovering valuable metals such as Ni and Cr by melting and reducing oxides in an electric smelting furnace (arc electric furnace). In the technique described in Patent Document 1, the power load is adjusted so that the tip position of the electrode is equal to or less than 0.75 × furnace depth during energization, and the tip position of the electrode is equal to or less than 0.75 × furnace depth. In this case, heating of the oxide is promoted by adjusting the electric power load so that the difference S between the electrode tip positions at the start of energization and at the end of energization is 0.35 × the depth of the furnace or less.
Patent Document 2 describes the use of a slag adjusting agent containing oxide as one of main components and chromium ore containing chromium oxide in electric furnace refining (page 4 of Patent Document 2). reference). In the technique described in Patent Document 2, in order to uniformly disperse auxiliary materials such as slag adjusting agents and chrome ore in the electric furnace, three gas injection nozzles (plugs) are arranged at the furnace bottom, and the electric furnace is started from the gas injection nozzle. Gas is blown into the molten metal inside and the molten metal is stirred. The gas flow rate of the bottom blowing agitation is 70 L / min (4.2 Nm ³ / Hr) per gas blowing nozzle.

JP-A-8-260014 JP-A-1-294815

  However, the method described in Patent Document 1 not only requires excessive input power, but also presupposes a long-time treatment exceeding 3 hours, thereby realizing efficient heating and melting of auxiliary materials such as oxides. Can not do it.

  In addition, when the particle size of the auxiliary material is large (for example, over 25 mm), according to the knowledge of the present inventors, rapid stirring of the auxiliary material can be achieved with stirring that is about equalizing the components of the molten metal described in Patent Document 2. It is not possible to realize this, and it is known that a long time treatment is required to complete the dissolution of the auxiliary material because the auxiliary material is not dissolved in a short time treatment. Incidentally, Patent Document 2 describes that the shape (diameter) of the slag adjusting agent is 3 mm or less, and the substantial particle size of the chromium ore is less than 1 mm.

The present invention has been made in view of such circumstances, and even when the particle size of the auxiliary material charged into the arc electric furnace is large (for example, over 25 mm), the auxiliary material is rapidly heated and melted for refining. It is an object to provide a method capable of suppressing the shortage.
In addition, this subject is a subject resulting from a low electrical conductivity, especially a low heat conductivity compared with a metal raw material.

In order to achieve the above object, the present invention is a method for melting an auxiliary material that is charged in an arc-type bottom-blown electric furnace and is one or more of oxide, carbonate, and hydroxide ,
The auxiliary material having a sieve mesh over 25 mm is 5-30% by mass of the furnace interior,
The auxiliary material having a mesh size of 3.15 mm or less is 3% by mass or more of the furnace interior and the basicity is 2.5 or less.

Here, the oxide is quick lime, quartzite, metal oxide such as magnesia or alumina, waste furnace material, slag, etc., the carbonate is limestone, dolomite, etc., and the hydroxide is metal hydroxide or the like.
The auxiliary material with a mesh size over 25 mm is a secondary material remaining on the sieve of a plate sieve with a nominal opening of 25 mm of JIS Z8801-2: 2000, and the auxiliary material with a mesh size under 3.15 mm is 3.15 mm with a nominal opening of JIS This refers to the auxiliary material under the sieve of the plate sieve.
The basicity of the auxiliary material with a mesh size of 3.15 mm under is a value calculated by mass% CaO / mass% SiO ₂ .

The mass ratio of the auxiliary material having a mesh size over 25 mm (hereinafter sometimes referred to as “bulk auxiliary material”) is defined as the auxiliary material which is difficult to heat and thus difficult to dissolve.
Assuming the use of a lump of converter decarburization slag, which is a substitute for quick lime, as an auxiliary material, the mass auxiliary material is 5 to 30% by mass of the furnace interior.

The auxiliary raw material having a mesh size of 3.15 mm or less (hereinafter sometimes referred to as “fine powder auxiliary raw material”) is easily dissolved by contact with the molten metal, and therefore is not likely to be a significant problem in terms of heating time. In the present invention, dissolution of the bulk auxiliary material is promoted using the dissolved fine powder auxiliary material. If the fine powder auxiliary material is 3% by mass or more, the dissolved fine powder auxiliary material is present around the massive auxiliary material, and contributes to the heating and dissolution of the massive auxiliary material including the action of the stirring gas described later. .
The upper limit of the fine powder auxiliary material is not particularly defined, but if the bulk auxiliary material is 5 to 30% by mass, it may be about 25% by mass for securing the amount of molten metal to be produced.

If the fine powder auxiliary material after melting has a certain fluidity, it contributes to the heating promotion of the bulk auxiliary material together with the molten metal. The present inventors have found that if the basicity of the fine powder auxiliary material is 2.5 or less, the fine powder auxiliary material after dissolution has a certain fluidity and contributes to heat transfer to the bulk auxiliary material.
The lower limit value of the basicity of the fine powder auxiliary material is not particularly defined, but is assumed to be about 0.6 when an auxiliary material charged in a normal arc type bottom blowing electric furnace is assumed.

Moreover, in the melting method of the auxiliary material in the arc type bottom blowing electric furnace according to the present invention, 0.12 or more stirring gas blowing plugs per 1 m ² of the molten metal surface area are arranged on the bottom of the arc type bottom blowing electric furnace. Further, it is preferable that a stirring gas of 10 Nm ³ / Hr or more per plug is blown into the furnace from the stirring gas blowing plug.
Here, the molten metal surface area is an area of the molten metal surface when the arc type bottom blowing electric furnace is viewed from above.

  In this configuration, the sub-material layer floated on the upper layer of the molten metal is brought into contact with the molten metal melted by stirring, thereby defining conditions for realizing more effective heating. Specifically, the conditions that allow the stirring gas blown into the furnace from the stirring gas blowing plug to act as widely as possible on the surface of the molten metal bath (hot water surface) to efficiently stir the auxiliary material layer on the upper surface of the hot water surface are specified. To do.

The auxiliary material layer includes an auxiliary material dissolved layer that has been heated and dissolved and an auxiliary material undissolved layer that is not dissolved. The auxiliary material layer may be both in the case where the auxiliary material undissolved layer is present above the auxiliary material dissolved layer and in the case where both are mixed. By setting the flow rate of the stirring gas around the stirring gas blowing plug to 10 Nm ³ / Hr or more per plug, the contact of the auxiliary raw material undissolved layer, the auxiliary raw material dissolved layer, and the molten metal layer can be further promoted. The heating of the undissolved auxiliary material and the dissolved auxiliary material can be promoted, and the heating of the undissolved auxiliary material by the dissolved auxiliary material can be promoted.
If the flow rate of the stirring gas is too large, the stirring gas that blows through the molten metal layer and the auxiliary material layer becomes significant, and a part of the blown stirring gas cannot be used for stirring. Therefore, the upper limit value of the stirring gas flow rate is preferably set to 100 Nm ³ / Hr per plug.

By regulating the flow rate of the stirring gas blown into the furnace from the stirring gas blowing plug, it becomes possible to accelerate the heating of the auxiliary material, but it has been found that there is room for further improvement in the heating promotion of the auxiliary material.
The present inventors have found that the auxiliary raw material undissolved layer floating in the upper layer is difficult to move in the direction parallel to the molten metal surface, that is, in the horizontal direction. As a cause of this, it was considered that the bulk auxiliary material consisting of the solid being heated floated on almost the entire surface of the molten bath, and it was difficult to ensure the fluidity of the bulk auxiliary material in the direction parallel to the molten metal surface. This is because the bulk auxiliary material stirred and heated immediately above and around the stirring gas blowing plug does not easily move to the outside of the stirring region, and is present in the bulk auxiliary material existing in the stirring region and the weak stirring region around the stirring region. It means that the bulk auxiliary material is difficult to be replaced.
In addition, since the thermal conductivity of the bulk auxiliary material is generally low (the thermal conductivity of 20% chromium molten steel is 22 W / mK, for example, the thermal conductivity of oxide is about 0.9 W / mK), the stirring region It was also considered that the heated bulk auxiliary material present in the column hardly contributes to the heating of the bulk auxiliary material present in the adjacent weak stirring region.

Based on the above knowledge, the present inventors have conceived that the number of stirring gas blowing plugs per 1 m ² of the molten metal surface area should be within a predetermined range in order to promote heating of the auxiliary material layer. By setting the number of stirring gas blowing plugs within a predetermined range, a predetermined amount of stirring region in which the molten metal is exposed above the bulk auxiliary material is secured by blowing the stirring gas. As a result, a predetermined amount of arc energized portions are secured, and heating of the bulk auxiliary material over the entire molten metal surface is promoted. Specifically, by increasing the number of plugs installed by setting the number of stirring gas blowing plugs to be 0.12 or more per 1 m ^{2 of} the hot water surface area, the area of the weak stirring region is reduced, and the auxiliary material heating of the entire hot water surface is reduced. Can promote.
Note that there is a physical upper limit (installation location) for the number of plugs installed, and it is generally considered to be about 0.5 per 1 m ² of the molten metal surface area.

According to the present invention according to claims 1 and 2, even if a large amount of the bulk auxiliary material is blended, the molten fine raw material can be heated and melted by the dissolved fine powder auxiliary material, and the bulk in the arc-type bottom blowing electric furnace It is possible to suppress insufficient heating of the auxiliary raw materials and insufficient refining due to dissolution residue.
In particular, according to the second aspect of the present invention, heating and melting of the bulk auxiliary material can be further promoted, so that refining in an arc type bottom blowing electric furnace is promoted and further stabilized.

It is a longitudinal cross-sectional view of the arc type bottom blowing electric furnace used with the melting | dissolving method of the auxiliary material which concerns on one embodiment of this invention. It is a schematic diagram which shows arrangement | positioning of the stirring gas blowing plug installed in the furnace bottom of the arc type bottom blowing electric furnace, (A) is the number of stirring gas blowing plugs, (B) is the stirring gas blowing plug When the number is four, (C) shows the case where the number of the stirring gas blowing plugs is five.

  Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention.

The present invention is directed to an arc-type bottom blowing electric furnace capable of melting 5 to 150 ton of molten metal. In addition, the minimum of the preferable furnace capacity of the arc type bottom blowing electric furnace which this invention makes object is 10 tons, More preferably, it is 30 tons, The upper limit of a preferable furnace capacity is 100 tons.
FIG. 1 shows a longitudinal sectional view of an arc-type bottom blowing electric furnace 10 used in the auxiliary material melting method according to the embodiment of the present invention.
The furnace body 11 of the arc type bottom blowing electric furnace 10 has a bottomed cylindrical shape, and around the central axis, three electrodes 15 are arranged in a regular triangle shape in plan view (see FIG. 2). The furnace bottom 12 holding the molten metal 16 is formed in a bowl shape with a refractory, and a water cooling panel 14 is disposed on the side wall of the furnace body.

In the furnace bottom 12, a plurality of stirring gas blowing plugs 13 such as a thin tube assembly type plug in which thin tubes are bundled and a porous plug made of a porous refractory are embedded. Stirring gas such as nitrogen gas or argon gas is blown into the molten metal 16 from the stirring gas blowing plug 13 to stir the molten metal 16.
The number of the stirring gas blowing plugs 13 is 0.12 or more per 1 m ² of the hot water surface area. An arrangement example of the stirring gas blowing plug 13 is shown in FIG. In this example, assuming a regular hexagon surrounding the three electrodes 15 when looking at the furnace bottom 12 from above, a case where the stirring gas blowing plugs 13 are arranged at the apexes of every other regular hexagon ( FIG. 2A shows a case in which every two vertices are removed from the regular hexagon and the stirring gas blowing plugs 13 are arranged at the remaining vertices (the stirring gas blowing plug 13 has three stirring gas blowing plugs 13). 4 (B), FIG. 2 (B) shows a case where one vertex is deleted from the regular hexagon, and the stirring gas blowing plug 13 is arranged at the remaining vertex (five stirring gas blowing plugs 13). ) Respectively.

Next, a method for melting the auxiliary material using the arc type bottom blowing electric furnace 10 will be described.
A metal raw material such as scrap, alloy iron, cast iron, and granular iron is charged in the arc-type bottom-blown electric furnace 10 in advance, and melting of the metal raw material is started by starting energization. A part of the metal raw material may be charged after the start of energization.

The charging of the auxiliary raw material into the furnace may be performed before the start of energization of the metal raw material or after the completion of the melting of the metal raw material.
The auxiliary raw material is one or more of oxide, carbonate, and hydroxide, and the bulk auxiliary raw material with a mesh size over 25 mm is 5 to 30% by mass of the furnace interior, and the mesh size is under 3.15 mm. The fine powder auxiliary material is 3 mass% or more, preferably 25 mass% or less of the furnace interior. The basicity of the fine powder auxiliary material is 2.5 or less.
When the bulk auxiliary material is 5 to 30% by mass of the furnace interior input and the fine powder auxiliary material is 3% to 25% by mass of the furnace interior input, the metal raw material is 45 to 92% by mass of the furnace interior input. Become.

The stirring gas may be blown by the stirring gas blowing plug 13 from the beginning of the melting of the metal raw material and the auxiliary raw material. However, in order to prevent plug clogging, the stirring gas is blown into the furnace before the material is charged. And even better.
The flow rate of the stirring gas is set to 10 Nm ³ / Hr or more per plug.

  The metal raw material charged in the arc type bottom blowing electric furnace 10 is heated and melted by the electric current flowing between the electrode 15 and the metal raw material. As melting of the metal raw material proceeds, a molten metal layer is formed in the furnace, and an auxiliary raw material layer floating according to the specific gravity is formed on the molten metal layer.

  Arc energization mainly occurs between the metal raw material and the molten metal 16 after melting. The sub-material is not substantially energized by arc, and the sub-material is heated and melted by receiving heat from the metal material and the molten metal 16 after melting. In the present embodiment, in addition to the heat received from the metal raw material and the molten metal 16 after melting, the dissolved fine powder auxiliary material is present around the massive auxiliary material, and promotes melting of the massive auxiliary material by heating.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and is within the scope of matters described in the claims. Other possible embodiments and modifications are also included. For example, in the above embodiment, the number of electrodes is three, but the number of electrodes is not limited to this, and may be one, two, or four or more.

A verification test carried out to verify the effects of the present invention will be described.
As the arc type bottom blowing electric furnace, a furnace capable of melting a 100 ton melt was used. The electrodes were 3 x 24 inch diameter, the total input power was 40 MW except for one case, and the energization time for each case was 60 minutes.

The furnace interior contents used are as follows.
a) Metal raw materials: Total of 55 tons of scrap, alloy iron, cast iron (solidified blast furnace hot metal) (55% by mass of furnace interior contents)
b) Auxiliary raw materials / bulk auxiliary raw materials: 25 tons of converter decarburized slag 30 tons (30% by mass of furnace interior contents)
・ Powder auxiliary material: 3.15mm under converter decarburization slag 3ton (3% by mass of furnace interior)
・ Other auxiliary materials: 3.15 mm over to 25 mm under converter decarburization slag 10 tons (10 mass% of furnace interior contents)
In addition, the fine powder auxiliary material contained 3.15 mm under silica and quicklime, and the basicity of the fine powder auxiliary material was set at three levels of 2.0, 2.5, and 3.0.

Gas flow blown from the stirring gas blowing plug in the melt was set to 2 conditions 10Nm ³ /Hr,4.2Nm ³ / Hr per plug. Note that 4.2 Nm ³ / Hr is a gas flow rate described in Patent Document 2.
The number of stirring gas blowing plugs arranged at the furnace bottom is three (see FIG. 2 (A)), four (see FIG. 2 (B)), and five (see FIG. 2 (C)). It was. The number of plugs per 1 m ^{2 of the} molten metal surface area is 0.11 when the number of plugs is 3, 0.14 when the number of plugs is 4, and 0.18 when the number of plugs is 5. The number of plugs of 3 is the condition described in Patent Document 2.

After the energization treatment, the molten metal and slag were discharged from the furnace body to the pan. Observe the outlet at the time of discharge, the residue of auxiliary materials is not observed, the sulfur concentration as a result of desulfurization treatment is stable and low, ◎, the residue of dissolution is not observed, sulfur as a result of desulfurization treatment ○ If the concentration variation is slightly observed (adopted for actual operation), no dissolution residue is observed, and if the sulfur concentration is slightly higher (applicable for actual operation), Δ, dissolution residue is observed In the case where it was judged that it could not be adopted as an actual operation due to insufficient desulfurization.
Table 1 shows a list of test results.

The results of the verification test revealed the following.
As shown in Comparative Examples 1 and 2, under the conditions of Patent Document 2 (gas flow rate per plug: 4.2 Nm ³ / Hr, number of plugs: 3), heating of the bulk auxiliary material was insufficient. As shown in Examples 1 and 5, improvement is possible by making the fine powder auxiliary material 3 mass% and the basicity 2.5 or less.
Further improvement is possible by increasing the number of plugs per 1 m ^{2 of} hot water surface area and the amount of stirring gas blowing (see Examples 2, 3, 4 for Example 1 and Example 6 for Example 5).
Further improvements are possible by reducing the basicity of the fine powdered auxiliary material (see Example 6 relative to Example 2).

  In addition, although the melting result of Example 4 is further improved as compared with Example 2, in Examples 2 and 4, the arc energization area is expanded as compared with Example 1 due to the increase in the number of plugs and the amount of stirring gas blown. Therefore, in Example 4 where the input power is increased, it is considered that the effect appears.

10: arc type bottom blowing electric furnace, 11: furnace body, 12: furnace bottom, 13: stirring gas blowing plug, 14: water cooling panel, 15: electrode, 16: molten metal

Claims (2)

A method for melting an auxiliary material that is charged in an arc-type bottom-blown electric furnace and is one or more of oxide, carbonate, and hydroxide ,
The auxiliary material having a sieve mesh over 25 mm is 5-30% by mass of the furnace interior,
A method for melting an auxiliary material in an arc-type bottom-blown electric furnace, characterized in that the auxiliary material having a mesh size of 3.15 mm or less is 3% by mass or more of the furnace interior and the basicity is 2.5 or less. 2. The method for melting auxiliary raw materials in an arc-type bottom-blown electric furnace according to claim 1, wherein at least 0.12 stirring gas blowing plugs per 1 m ² of the molten metal surface area are disposed on the bottom of the arc-type bottom-blown electric furnace. A method of melting an auxiliary material in an arc type bottom blowing electric furnace, wherein a stirring gas of 10 Nm ³ / Hr or more per plug is blown into the furnace from the stirring gas blowing plug.

Images