JP6620781B2 - Dust smelting reduction method and reuse method - Google Patents

Description

  The present invention relates to a dust smelting reduction method and a reuse method.

  When steel containing a large amount of chromium such as stainless steel is blown in a converter or the like, dust containing a large amount of chromium (Cr) in addition to iron (Fe) is generated together with exhaust gas. Since this dust is wet-collected, it is recovered as a slurry containing a large amount of moisture. The recovered slurry-like dust is solidified and then melted in a converter-type smelting reduction furnace and subjected to reduction treatment, thereby being used as an iron source and a chromium source (for example, Patent Document 1). ).

Japanese Patent Laying-Open No. 2015-193928

  By the way, the above smelting reduction treatment of dust is generally performed in a converter type smelting reduction furnace, but a large amount of carbonaceous material such as graphite containing carbon (C) as a heat source or a reducing agent is used. Since it is necessary, picking up phosphorus (P) in the carbonaceous material becomes a problem. Further, when there is no smelting reduction furnace, it is necessary to newly introduce a smelting reduction furnace. Furthermore, when a lot of dust is generated exceeding the processing capacity of the smelting reduction furnace, there is a problem that all the generated dust cannot be reused.

In order to deal with these problems, a method of performing smelting reduction treatment of dust using an electric furnace as a refining facility other than the smelting reduction furnace can be considered. However, when an electric furnace is used, it is necessary to reduce the moisture as much as possible by subjecting the dust to be used to a special treatment such as a drying treatment because of the danger of steam explosion. For this reason, the smelting reduction process of the dust by an electric furnace has not been a practical method from the viewpoint of manufacturing cost.
Then, this invention is made paying attention to said subject, and provides the smelting reduction | restoration processing method of a dust, and the reuse method which can melt | dissolve and reduce the dust containing a water | moisture content with an electric furnace. It is an object.

According to one aspect of the present invention, scrap generated in an electric furnace is melted by arc heating, and after the scrap melting step, dust generated from the chromium-containing steel melting step is transferred. A granulation product produced by dynamic granulation and a reducing agent are charged into the electric furnace, and the granulation product is melted and a reduction treatment step for reduction treatment is performed. A dust smelting reduction method is provided, wherein the granulated product is charged into the electric furnace in a state of containing 10% by mass or more and 18% by mass or less of moisture.
According to one aspect of the present invention, using the dust smelting reduction method described above, the dust generated in the converter is melted and reduced including chromium oxide and 10% by mass or more and 18% by mass or less of moisture, Thereafter, a method for reusing dust is provided, wherein the manufactured molten iron or cast iron obtained by solidifying the molten iron is used as an iron source and a chromium source of high chromium steel.

  According to one embodiment of the present invention, there is provided a dust smelting reduction method and a reuse method capable of melting and reducing moisture-containing dust in an electric furnace.

It is a schematic diagram which shows an electric furnace. It is a schematic diagram explaining the injection | throwing-in position of a granulated material, The upper side is sectional drawing of the furnace shell of an electric furnace, and the lower side is a top view of a furnace shell. It is explanatory drawing which shows the process pattern in an Example.

  In the following detailed description, numerous specific details are set forth, illustrating embodiments of the present invention, in order to provide a thorough understanding of the present invention. However, it will be apparent that one or more embodiments may be practiced without such specific details. In the drawings, well-known structures and devices are schematically shown for simplicity.

<Dust smelting reduction method>
With reference to the drawings, a dust smelting reduction method according to an embodiment of the present invention will be described. In this embodiment, the dust generated by the blowing process of stainless steel in the converter is melted and reduced using the electric furnace 1.
The electric furnace 1 is a conventional three-phase AC type AC arc furnace having a processing capacity of 50 t, and includes a furnace shell 10, a furnace lid 11, three electrodes 12, a burner 13, and a charging chute 14. Have. The furnace shell 10 is a container having an opening at the upper end, and a refractory is provided inside. The bottom portion of the furnace shell 10 has a shape in which the central portion is recessed downward with respect to the end portion, that is, a shape that is recessed downward in an arch shape in the cross-sectional view shown in FIGS. 1 and 2. In addition, a plurality of bottom blowing nozzles 100 for blowing a stirring gas such as argon are provided at the bottom of the furnace shell 10. The furnace lid 11 is provided so as to cover the opening of the furnace shell 10 and is configured to be movable or rotatable so as to open and close the opening of the furnace shell 10. The three electrodes 12 are graphite electrodes, and are provided so as to be movable in the vertical direction (vertical direction in FIG. 1). The three electrodes 12 are connected to a power source (not shown), and generate an arc between the raw materials in the furnace shell 10 by three-phase AC power supplied from the power source. The burner 13 is an auxiliary combustion device, and is used for the purpose of accelerating melting of the raw material in the furnace shell 10 by injecting combustible gas, raw material, oxygen gas or the like into the furnace shell 10 to form a flame. It is done. The input chute 14 is connected to an unillustrated auxiliary material hopper for storing auxiliary materials such as a medium solvent, a reducing agent, and a granulated material to be described later, and inputs the auxiliary material cut out from the auxiliary material hopper into the furnace shell 10. Further, the charging chute 14 is configured such that the tip in the furnace shell 10 is movable so that the charging position of the auxiliary raw material can be adjusted.

  The dust used in the smelting reduction process is a pellet-shaped granulated product. This granulated material wet-collects dust generated from the melting process in a converter of chromium-containing steel, more preferably high-chromium steel such as stainless steel (a steel type having a chromium content of 9% by mass or more). Then, it is manufactured by rolling granulation. In addition, when manufacturing a granulated material, you may add a binder to dust. The granulated product contains chromium oxide and preferably has a chromium concentration of 7% by mass or more. Moreover, the water | moisture content of a granulated material is 10 mass% or more, and it is preferable that it is 18 mass% or less. If the water content of the granulated product is less than 10% by mass, it is necessary to perform a drying treatment before or after rolling granulation, which is not preferable because the production cost of the granulated product increases. On the other hand, when the water content of the granulated product exceeds 18% by mass, the water vapor may exceed 18% by mass at the time of charging into the furnace shell 10, so that a steam explosion may occur. Furthermore, it is preferable that the granulated material contains 90% by mass or more of particles having a particle size of 10 mm or less (the ratio under 10 mm sieve is 90% by mass or more). By setting the particle size of the granulated product within this range, the granulated product can be input more safely.

  In the dust smelting reduction method according to the present embodiment, first, scrap as an iron source is charged into the furnace shell 10 of the electric furnace 1. The amount of scrap charged is set so that the molten iron melted by the scrap is 2 t or more and 4 t or less per 10 t of the scheduled addition amount of the granulated material added in the smelting reduction process described later. For the purpose of securing a heat source in the initial stage of melting, a carbonaceous material such as graphite may be charged into the furnace shell 10 together with scrap. In this case, it is necessary that the amount of carbon material added is such that the pickup of P in the carbon material (increase in the P concentration of molten iron due to P in the carbon material) does not cause a problem in quality. In order to increase the amount of dust used as much as possible, the granulated material may be charged into the furnace shell 10 together with scrap. In this case, it is preferable that the amount of the granulated material charged together with the scrap is 0.2 t or less with respect to 1 t of the scrap. When the charged amount of the granulated product exceeds 0.2 t with respect to 1 t of scrap, the granulated product cannot be sufficiently dried at the initial stage of melting, and the molten iron and moisture in the granulated product can react. There is sex.

  Next, a scrap melting step for melting the scrap in the furnace shell 10 is performed. In the scrap melting step, an arc is generated between the three electrodes 12 and a raw material such as scrap by three-phase alternating current, whereby the scrap is arc-heated and melted. At this time, heating by the burner 13 may be performed in parallel with the arc heating. The scrap melting step is preferably performed until the area ratio, which is the ratio of the area of the molten iron bath surface where the scrap is melted, to the area of the opening of the furnace shell 10 is about 30%.

Further, after the scrap melting step, a melting reduction step is performed in which the remaining undissolved scrap is melted, the newly added granulated material is melted, and the molten chromium oxide is reduced.
In the smelting reduction process, first, the granulated material is charged from the charging chute 14 while continuing the arc heating. At this time, the water content of the granulated product is 10 mass% or more and 18 mass% or less. In the smelting reduction step, a predetermined amount of granulated material is continuously charged at a charging speed of 5 t / h or more and 10 t / h or less. Furthermore, it is preferable that the granulated material is not directly charged into the bath surface of the molten iron 2 from the charging chute 14 until the slag layer 3 is formed on the bath surface of the molten iron 2. Furthermore, as shown in FIG. 2, until the slag layer 3 is formed on the bath surface 2a of the molten iron 2, the bath surface with respect to the area of the opening 10a of the electric furnace (area in plan view on the lower side of FIG. 2). It is preferable that the area ratio, which is the ratio of the area 2a (area in plan view on the lower side in FIG. 2), is 30% or more and 64% or less. That is, before the slag layer 3 is formed on the bath surface 2a of the molten iron 2, the charging position by the charging chute 14 is adjusted, and the granulated material is charged into the region outside the bath surface 2a inside the furnace shell 10. It is preferable. Thereby, the rate of temperature rise of the granulated product can be reduced, and the granulated product can be added to the molten iron 2 more safely. Furthermore, after the slag layer 3 is formed with a thickness of about 50 mm, the granulated material may be charged using the charging position as the region of the bath surface 2a. In the state in which the slag layer 3 is formed, the granulated material is not directly charged into the bath surface 2a, but is charged into the slag layer 3 formed on the bath surface 2a. Is suppressed. In this case as well, the rate of adding the granulated product is 5 t / h or more and 10 t / h or less.

  In the present embodiment, the granulated product can be efficiently and safely added by setting the input rate of the granulated product to 5 t / h or more and 10 t / h or less. When the addition rate of the granulated product is less than 5 t / h, the input rate becomes too slow, and the production efficiency is lowered. On the other hand, when the addition rate of the granulated product exceeds 10 t / h, a large amount of the granulated product containing moisture is added to the molten iron 2, which may cause a steam explosion. Further, until the slag layer 3 is sufficiently formed, the area ratio of the bath surface is set to 30% or more and 64% or less so that the granulated material is not directly charged from the charging chute 14 to the bath surface, thereby further safety. A granulated product can be added to.

  Next, after the granulated material is completely charged, the reducing agent is charged from the charging chute 14 while continuing the arc heating. As the reducing agent, ferrosilicon (FeSi) containing Si, Al dross containing aluminum (Al), or the like can be used. Note that a carbon material may be used as a part of the reducing agent as long as the pickup of P does not cause a problem in quality. The reducing agent is added in an amount at least necessary for the reduction reaction of chromium oxide according to the amount of granulated material added. In addition, when introducing the reducing agent, the molten iron 2 is agitated by blowing a stirring gas from the plurality of bottom blowing nozzles 100 into the molten iron 2. Furthermore, after the addition of the reducing agent is completed, the smelting reduction process is completed by stirring and arc heating until a predetermined temperature and components are obtained.

The granulated material added in the furnace shell 10 is heated to form a slag layer 3 containing a large amount of chromium oxide on the bath surface of the molten iron 2. Then, the added reducing agent is melted by being heated and reduces chromium oxide in the slag layer 3. By such a reduction reaction, the chromium concentration of the molten iron 2 increases, and the molten iron 2 having a high chromium concentration is produced.
After the smelting reduction process, the molten iron 2 having a high chromium concentration is reused as an iron source and a chromium source when melting high chromium steel such as stainless steel. As this reuse method, for example, the molten iron 2 may be reused by transferring it in a molten state to a refining apparatus such as a converter where high chromium steel is melted. Further, the molten iron 2 that has been melted may be solidified as cast iron, and reused by adding this cast iron to a refining apparatus such as a converter in which high chromium steel is melted. In this case, the steel ingot in which the molten iron 2 is solidified with a large mold may be cut and used, or the molten iron 2 is solidified in a facility that continuously casts with a plurality of molds such as a casting machine. May be.

<Modification>
Although the present invention has been described above with reference to specific embodiments, it is not intended that the present invention be limited by these descriptions. By referring to the description of the present invention, other embodiments of the present invention will be apparent to those skilled in the art, including various modifications along with the disclosed embodiments. Therefore, it should be understood that the embodiments of the present invention described in the claims also include embodiments including these modifications described in the present specification alone or in combination.

  For example, in the above embodiment, the reducing agent is added after the granulated product is added in the melt reduction step, but the present invention is not limited to such an example. For example, the reducing agent may be added simultaneously with the addition of the granulated product. By doing in this way, since the melted granulated material is sequentially reduced by the reducing agent, the granulated material can be melted and reduced in parallel, and the time required for the melt reduction treatment can be shortened. it can.

Moreover, in the said embodiment, although the molten iron 2 was stirred with the gas for stirring after adding a granulated material in a melt reduction process, this invention is not limited to this example. For example, the molten iron 2 may be stirred from the initial stage of the smelting reduction process in which the granulated product is added.
Furthermore, in the said embodiment, although the dust used for a smelting reduction process shall generate | occur | produce when melting chromium containing steel, this invention is not limited to this example. The dust should just contain what was generated when smelting chromium-containing steel with refining equipment such as a converter, and it contains dust generated when smelting other steel types such as general steel types. Also good.

Furthermore, in the above-described embodiment, it is assumed that a predetermined amount of granulated material is continuously charged in the smelting reduction step, but the present invention is not limited to such an example. For example, a predetermined amount of granulated material may be divided into a plurality of times.
Furthermore, all scraps may be melted in the scrap melting step. In this case, it is preferable that the area ratio of the bath surface of the molten iron 2 after dissolution is 30% or more and 64% or less.
Further, in the smelting reduction process, a solvent containing CaO may be introduced into the furnace shell 10. However, since the amount of slag increases and chromium to be reduced decreases when the solvent is added, it is preferable to reduce the amount of solvent input as much as possible.

Furthermore, in the said embodiment, although the injection | throwing-in speed | rate of granulated material shall be 5 t / h or more and 10 t / h or less in the melt reduction process, this invention is not limited to this example. In the electric furnace 1 having a processing capacity of about 20 t to 100 t, it is preferable that the input rate of the granulated product is 5 t / h or more and 10 t / h or less. On the other hand, in the electric furnace 1 whose processing capacity is different from the above range, it is preferable to increase or decrease the charging speed according to the processing capacity. In this case, in the electric furnace 1 with a small processing capacity, the charging speed may be lower than in the above embodiment, and in the electric furnace 1 with a large processing capacity, the charging speed may be higher than in the above embodiment.
Furthermore, in the above embodiment, ferrosilicon or Al dross is used as the reducing agent, but the present invention is not limited to such an example. For example, as a reducing agent containing Si or Al, an alloy containing Al or Si, metallic aluminum, or the like may be used.

<Effect of embodiment>
(1) The dust smelting reduction method according to one aspect of the present invention includes a scrap melting step in which scrap charged in the electric furnace 1 is melted by arc heating, a melting step of the chromium-containing steel after the scrap melting step. Smelting reduction in which a granulated product and a reducing agent produced by rolling granulation of dust generated from the production process are put into the electric furnace 1 (furnace shell 10), the granulated product is melted, and reduction treatment is performed. In the smelting reduction step, the granulated product is charged into the electric furnace 1 in a state containing 10% by mass or more and 18% by mass or less of moisture.

  According to the configuration of the above (1), by setting the moisture of the granulated product within the above range, the dust can be melted and reduced without performing a special treatment such as a drying treatment. Moreover, a granulated material can be efficiently and safely fuse | melted by the water | moisture content of a granulated material being 18 mass% or less. Furthermore, by making the water content of the granulated product 10% by mass or more, there is no need to perform a drying process or a compression molding process to reduce the moisture content of the dust, thus reducing the cost of manufacturing the granulated material. can do. For this reason, the dust containing chromium can be reused efficiently and safely. Moreover, in the structure of said (1), if it is a conventional electric furnace, it can be applied, and such an electric furnace becomes equipment often used in the factory which manufactures stainless steel. For this reason, the dust containing chromium oxide can be reused without newly providing special equipment such as a smelting reduction furnace. Furthermore, even in factories with smelting reduction furnaces, it becomes possible to perform smelting reduction processing of dust in an electric furnace in addition to smelting reduction furnaces, so even when the amount of dust generated is large, the amount of dust reuse is improved. be able to. Furthermore, according to the structure of said (1), since it heats with the electric furnace 1, it is not necessary to use heat sources, such as a carbonaceous material. For this reason, since the usage-amount of the heat source containing P can be reduced compared with the case where it processes with a smelting reduction furnace, the content of P is low and the molten iron 2 with versatility can be manufactured.

(2) In the configuration of (1) above, in the smelting reduction step, the granulated product is added at a charging rate of 5 t / h or more and 10 t / h or less.
According to the configuration of (2) above, in a general electric furnace 1 having a processing capacity of about 20 to 100 t, the granulated product can be charged more efficiently and safely.
(3) In the configuration of (1) or (2), the granulated product contains 90% by mass or more of particles having a particle size of 10 mm or less.
According to the configuration of (3) above, the granulated product can be added more safely.

(4) In any configuration of the above (1) to (3), before the scrap melting step, a granulated material is charged in advance into the electric furnace 1 in addition to the scrap.
According to the configuration of the above (3), the granulated material charged in advance is heated in accordance with the heating of the scrap and dried or melted. For this reason, the amount of dust to be melted and reduced can be increased. Moreover, since the slag layer 3 is formed earlier because the granulated material charged in advance is melted, it is easy to adjust the input position of the granulated material in the smelting reduction process.

(5) In any one of the constitutions (1) to (4), in the smelting reduction step, a stirring gas is blown from the bottom of the electric furnace 1 and the reduction treatment is performed while stirring the molten iron 2.
According to the configuration of (4) above, the time required for the reduction process can be shortened.
(6) In the configuration of any one of (1) to (5) above, in the smelting reduction step, the area of the opening 10a of the electric furnace 1 until the slag layer 3 is formed on the bath surface 2a of the molten iron 2 The area ratio, which is the ratio of the area of the bath surface 2a to 30% or less, is set to 30% or more and 64% or less, and the granulated material is charged outside the bath surface 2a.
According to the configuration of (6) above, since the granulated material is not directly charged into the molten iron 2 from the charging chute 14 until the slag layer 3 is formed, the temperature rise of the granulated material is alleviated, and more The granulated material can be thrown in safely.
(7) In the configuration of any of (1) to (6) above, an AC arc furnace is used as the electric furnace.
According to the configuration of (7) above, since a general-purpose AC arc furnace is used, there is no need for modification of equipment and the like, and dust can be melted and reduced at low cost.

(8) A method for reusing dust according to one embodiment of the present invention is the method of using the dust smelting reduction method according to any one of (1) to (7) above. Dust containing 10% by mass or more and 18% by mass or less of moisture is melted and reduced, and then the manufactured molten iron 2 or cast iron obtained by solidifying the molten iron 2 is used as an iron source and a chromium source of high chromium steel.
According to the configuration of (6) above, dust can be melted and reduced efficiently and safely, so that high chromium steel can be produced at low cost.

Next, examples performed by the present inventors will be described. In the example, similarly to the above-described embodiment, the granulated product obtained by rolling and granulating dust generated in the high-chromium steel blowing process in the converter is melt-reduced in the electric furnace 1 of 50 t to have a high chromium concentration. Molten iron was melted. FIG. 3 shows a pattern of processing performed in the example.
In the example, 10 t of mild steel scrap, 1.2 t of granulated material, and 0.45 t of graphite (carbon material) were charged in the furnace shell 10 in advance. The component composition (mass%) and moisture (mass%) of the granulated product are shown in Table 1. In Table 1, T.W. Fe represents the total content of Fe including oxidized Fe, and T.Cr represents the total content of Cr including oxidized Cr.

In the examples, first, the scrap melting step was performed for 56 minutes. In the scrap melting step, the scrap was melted by arc heating the raw material at a tap voltage of 340V.
Subsequently, the smelting reduction process was performed over 497 minutes. In the smelting reduction step, first, the 23 t granulated product was added to the molten iron 2 in a plurality of times. At this time, adjustment is made so that the charging speed at the time of addition is 5 t / h or more and 10 t / h or less, and before the slag layer 3 is sufficiently formed, the granulated material is directly applied to the bath surface from the charging chute 14. I did not throw it in. Moreover, when adding the granulated product, 700 kg of ferrosilicon was added in two portions. After the addition of the granulated material was completed, 750 kg of Al dross was added in two portions while stirring the molten iron 2, and an additional 500 kg of ferrosilicon was added. Thereafter, the molten iron 2 was further stirred to complete the treatment.

  Furthermore, in the Example, after completion | finish of injection | pouring of a granulated material, sampling of slag and molten iron 2 (metal) was performed 5 times at predetermined time intervals. As shown in FIG. 3, the first sampling timing is between the timings of the second Al dross input, and the second sampling timing is the timing between the second Al dross input timing and the last ferrosilicon input timing. Between. Table 2 shows the analysis results of the component composition of the metal sample and the slag sample sampled at each timing of the first to fifth times (s1 to s5).

  As shown in Table 2, after introducing the reducing agent, by performing the treatment while stirring, the Cr component in the slag layer 3 is reduced, the Cr concentration of the molten iron 2 is increased, and the reduction treatment is performed. It could be confirmed. Moreover, in the Example, even if it added the granulated material containing a water | moisture content in the furnace shell 10 in which the molten iron 2 was accommodated, it has confirmed that there was no problem of a steam explosion etc. and it can process safely.

DESCRIPTION OF SYMBOLS 1 Electric furnace 10 Furnace shell 100 Bottom blowing nozzle 11 Furnace lid 12 Electrode 13 Burner 14 Input chute 2 Molten iron 3 Slag layer

Claims (6)

A scrap melting process for melting the scrap charged in the electric furnace by arc heating;
After the scrap melting step, a granulated product produced by rolling granulation of dust generated from the melting step of the chromium-containing steel and a reducing agent are put into the electric furnace to melt the granulated product. A smelting reduction process for performing reduction treatment,
With
In the smelting reduction step, the granulated product is charged into the electric furnace in a state containing moisture of 10% by mass or more and 18% by mass or less ,
In the smelting reduction process,
The granulated product is added at a charging speed of 5 t / h or more and 10 t / h or less,
Until the slag layer is formed on the bath surface of the molten iron, the area ratio, which is the ratio of the area of the bath surface to the area of the opening of the electric furnace, is 30% to 64%, and the outside of the bath surface A method for smelting and reducing dust , wherein the granulated product is charged into the product . 2. The dust smelting reduction method according to claim 1, wherein the granulated material contains 90% by mass or more of particles having a particle size of 10 mm or less. The dust smelting reduction method according to claim 1 or 2 , wherein the granulated material is charged in advance into the electric furnace in addition to the scrap before the scrap melting step. In the melt reduction step, blowing stirring gas from the bottom of the electric furnace, smelting reduction method of dust according to any one of claims 1 to 3, characterized in that performing the reduction treatment while stirring the molten iron. Wherein as an electric furnace, smelting reduction method of dust according to any one of claims 1-4, characterized by using an alternating current arc furnace. A method for melting and reducing dust generated in a converter and containing chromium oxide and 10% by mass or more and 18% by mass or less of moisture using the method for melting and reducing dust according to any one of claims 1 to 5. And
Thereafter, the manufactured molten iron or cast iron obtained by solidifying the molten iron is used as an iron source and a chromium source of high chromium steel, and a method for reusing dust.

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