JP2008050659A - Desulfurizing agent for molten iron and method for desulfurization treatment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a CaO based desulfurizing agent which has the desulfurizing ability equal to that of the conventional CaO-CaF<SB>2</SB>based desulfurizing agent when desulfurizing molten iron with a mechanical stirring type desulfurizing device, even if fluorine-containing material is not used as a slag-formation promotor and Na<SB>2</SB>O increasing the erosion of a refractory is not used. <P>SOLUTION: The above problems are solved with the desulfurizing agent, in which to 100 mass parts of CaO powder having ≥90 mass% fine powder of ≤150 μm grain diameter, an alumina-metallic Al mixed material containing ≤50 mass% Al<SB>2</SB>O<SB>3</SB>is added at 5-20 mass parts. This desulfurizing agent 7 is added by top-blowing together with a gas for conveying through a top-blown lance 5 on the surface of the molten iron 3 stirred with the stirring blades 4 and in this way, the desulfurizing treatment can effectively be performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a desulfurization agent and a desulfurization treatment method capable of efficiently desulfurizing hot metal in a mechanical stirring desulfurization apparatus, and more particularly, to efficiently desulfurize without using a fluorine-containing substance as a hatching accelerator. The present invention relates to a desulfurization agent and a desulfurization treatment method that can be used.

  The hot metal discharged from the blast furnace usually contains a high concentration of sulfur (S), which adversely affects the quality of the steel, and various hot metal desulfurization and molten steel desulfurization can be performed depending on the required quality of the steel. Has been done. Among these, for desulfurization of hot metal, inexpensive desulfurization agents mainly composed of CaO (lime) are widely used. In this case, the desulfurization reaction proceeds based on the reaction formula shown by “CaO + S → CaS + O”. To do.

In this desulfurization treatment, a fluorite (CaF ₂ ) -based solvent has been conventionally used as a CaO hatching accelerator. For example, CaO- in which about 5% by mass of fluorite is mixed with quick lime as a CaO source. CaF ₂ -based desulfurization agents have been widely used. However, the fluorite-based solvent is expensive, and the addition of the fluorite-based solvent leads to an increase in the cost of the desulfurizing agent, and in recent years, there is a concern about the outflow of fluorine (F) to the environment from the viewpoint of global environmental conservation. Therefore, it is desired to avoid using a fluorine-containing material as a solvent.

As an example of a desulfurizing agent that does not use fluorite, a calcium carbide desulfurizing agent and a soda desulfurizing agent have been put into practical use, both of which have advantages and disadvantages. Calcium carbide-based desulfurization agents have a strong desulfurization ability, but there are safety problems such as the generation of acetylene gas in the post-treatment of the desulfurization slag after the desulfurization treatment. Moreover, since it is expensive and dangerous, it is extremely difficult to handle. A soda-based desulfurization agent is relatively inexpensive, but has a strong alkalinity, and thus has a great influence on the refractories of the processing furnace and the processing vessel. Further, since Na is contained in the exhaust gas, it is necessary to remove it. Furthermore, since the content of Na ₂ O in the slag becomes high, there are restrictions on the reuse to cement and the like, which is undesirable from the influence on the environment.

Considering these, a desulfurization agent mainly composed of CaO is inexpensive and easy to handle. Therefore, even a desulfurization agent mainly composed of CaO does not use a fluorine-containing substance as a hatching accelerator. Agents have been proposed. For example, Patent Document 1 discloses a desulfurization agent in which 0.02 to 0.05 parts by mass of Na ₂ O and 0.05 to 0.20 parts by mass of Al ₂ O ₃ are added to 1 part by mass of CaO. Proposed. According to Patent Document 1, the addition of Al ₂ O ₃ promotes the hatching of CaO, and the decrease in the desulfurization capacity due to the addition of Al ₂ O ₃ can be compensated by Na ₂ O, so that desulfurization can be performed with high efficiency. Yes.
JP 2001-335820 A

However, Na ₂ O used in Patent Document 1 significantly increases the refractory erosion resistance of the generated slag. For this reason, when the desulfurization agent proposed in Patent Document 1 is used, the refractory in the processing container is significantly melted and the life of the processing container is shortened. Therefore, the desulfurization agent proposed in Patent Document 1 is practically used. There is a problem that it cannot be provided.

The present invention has been made in view of the above circumstances. The object of the present invention is to use no fluorine-containing substance as a hatching accelerator when desulfurizing hot metal in a mechanical stirring desulfurization apparatus, and A desulfurization treatment method capable of efficiently desulfurizing at the same time as providing a CaO-based desulfurization agent having a desulfurization ability equivalent to that of a conventional CaO-CaF ₂ desulfurization agent without using Na ₂ O that increases erosion Is to provide.

The hot metal desulfurization agent according to the first aspect of the present invention for solving the above-mentioned problems is that 50% by mass of Al ₂ O ₃ with respect to 100 parts by mass of CaO powder having a fine particle diameter of 150 μm or less of 90% by mass or more. 5-20 mass parts of alumina-metal Al mixtures contained below are added.

  The hot metal desulfurization treatment method according to the second invention is characterized in that the hot metal desulfurization agent according to the first invention is added to the bath surface of the hot metal being stirred by the stirring blade to desulfurize the hot metal. .

  The hot metal desulfurization treatment method according to the third invention is characterized in that, in the second invention, the desulfurizing agent is added by top blowing to the bath surface of the hot metal together with the conveying gas through the top blowing lance.

According to the present invention, CaO, which is a desulfurizing agent, is a powder having a fine particle size of 150 μm or less of 90% by mass or more, so that the reaction interface area is increased, the desulfurization reaction is promoted, and the desulfurization rate is improved. Can do. In addition, the hatching of CaO is promoted by Al ₂ O ₃ added at the same time, and the desulfurization reaction is promoted. Thereby, it is also possible to efficiently desulfurize without using a fluorine-containing substance such as fluorite as a hatching accelerator. When CaO is made into fine powder, it becomes easy to agglomerate, but the alumina-metal Al mixture added at the same time prevents the aggregation of CaO and provides high desulfurization efficiency. That is, desulfurization efficiency equivalent to that of a conventional CaO—CaF ₂ -based desulfurization agent can be obtained without using a fluorine-containing substance as a hatching accelerator and without increasing the melting loss of the processing vessel.

  Hereinafter, the present invention will be specifically described.

CaO-Al ₂ O ₃ -based desulfurization agent in a mechanically stirred desulfurization apparatus without using fluorine-containing materials such as fluorite as hatching accelerators and without using Na ₂ O which increases erosion of refractories We studied and studied the method of obtaining a high desulfurization rate by using NO. The results of the examination and research are explained below.

  In a desulfurization treatment method using a mechanical stirring desulfurization apparatus equipped with a stirring blade (also referred to as an “impeller”), the desulfurizing agent is generally placed on the hot metal in a state of being vigorously stirred by the stirring blade, above the processing vessel. Continuously added. In this case, in order to promote the desulfurization reaction, the larger the reaction interface area, the more advantageous. Therefore, it was examined to pulverize CaO as a desulfurization agent.

However, when actually tested, finely powdered CaO aggregated, and the effect of increasing the reaction interface area was not obtained. In order to investigate this cause, the generated slag was investigated in detail. As a result, the aggregation of CaO is caused by the formation of a CaO-Al ₂ O ₃ -based low melting point compound by Al ₂ O ₃ added as a hatching accelerator, which acts as a binder to aggregate CaO particles together. It became clear.

Therefore, it was found that when an alumina-metal Al mixture having an Al ₂ O ₃ content of 50% by mass or less was used as the Al ₂ O ₃ source, aggregation was prevented and a high desulfurization rate was obtained. As this alumina-metal Al mixture, aluminum dross (also referred to as “Al ash”) is optimal. Almidros is a mixture of metal Al containing 30 to 50% by mass of metal Al and Al ₂ O _3, and also contains other components. The reason why aggregation was prevented by the addition of the alumina-metal Al mixture is considered to be because the formation of the low melting point compound was suppressed by components other than Al ₂ O ₃ contained in the alumina-metal Al mixture.

  When the desulfurizing agent is pulverized, in the case of top addition, the amount of scattering at the time of addition increases and the yield deteriorates. In order to prevent this decrease in yield, it has been found that a fine desulfurization agent can be solved by adding the carrier gas to the hot metal surface by blowing it upward. Moreover, CaO, which is a desulfurizing agent, has poor wettability with hot metal and is difficult to be caught in hot metal, and the desulfurizing agent added to the bath is agglomerated in the bath surface of the hot metal being strongly stirred or in the bath. However, it has been found that the reaction interface area tends to decrease, but this can also be eliminated by adding it by top blowing. In other words, it was found that the desulfurization reaction interfacial area can be increased without lowering the yield of the desulfurizing agent by adding the top blowing.

  In this case, the carrier gas is preferably a gas not containing oxygen, for example, nitrogen gas, because the desulfurization reaction is a reduction reaction. In addition, if the desulfurizing agent sprayed onto the hot metal bath surface by top blowing enters the hot metal, it is easy to get caught in the hot metal, which is desirable for the desulfurization reaction. It is preferable to adjust the gas flow rate.

The hot metal desulfurization agent and the desulfurization processing method according to the present invention are based on the results of the above examination and research. That is, the hot metal desulfurization agent according to the present invention is an alumina-metal Al mixture containing 50% by mass or less of Al ₂ O ₃ with respect to 100 parts by mass of CaO powder having a fine particle size of 150 μm or less of 90% by mass or more. It is characterized by adding 5 to 20 parts by mass of the body.

The CaO particle size distribution conditions in this case are based on the examples described later. Further, when the addition amount of the alumina-metal Al mixture is less than 5 parts by mass, the effect of promoting the hatching by Al ₂ O ₃ cannot be obtained, while the addition amount of the alumina-metal Al mixture is 20 parts by mass. This is because the CaO concentration decreases and the desulfurization efficiency decreases. Here, the particle size of 150 μm or less is defined by the sieve size of the sieving device. Even if the major axis exceeds 150 μm, the particle size is defined as 150 μm or less as long as it passes through the sieving machine having a size of 150 μm To do.

  Next, the hot metal desulfurization method according to the present invention will be described with reference to the drawings. Naturally, in the hot metal desulfurization treatment method according to the present invention, the desulfurization agent according to the present invention is used as the desulfurization agent.

  FIG. 1 is a schematic side view showing an example of the desulfurization processing method according to the present invention, and FIG. 1 shows an example in which a ladle type hot metal ladle is used as a processing container for containing hot metal. As for the shape of the processing container, a ladle-type processing container is optimal as shown in FIG. 1 because desulfurization is performed by a mechanical stirring type desulfurization apparatus, but it can also be used in a torpedo car. Hereinafter, an example in which a hot metal ladle is used as the processing container will be described.

  The hot metal 3 discharged from the blast furnace is received by the hot metal ladle 2 or the torpedo car mounted on the carriage 1, and the received hot metal 3 is conveyed to a mechanical stirring desulfurization apparatus. When it is received by a torpedo car, it is desirable to transfer to a ladle type processing container prior to the desulfurization process. The hot metal 3 to be subjected to the desulfurization treatment according to the present invention may be any component, and for example, desiliconization treatment or dephosphorization treatment may be performed in advance. The desiliconization treatment is a treatment for mainly removing Si in the hot metal by adding an oxygen source such as oxygen gas or iron ore to the molten iron 3 prior to the dephosphorization treatment in order to efficiently perform the dephosphorization treatment.

  The mechanical stirring-type desulfurization apparatus includes a refractory stirring blade 4 that is immersed and buried in a hot metal 3 accommodated in a hot metal ladle 2 and swirls to stir the hot metal 3. It is moved up and down in a substantially vertical direction by an elevating device (not shown), and is turned around a shaft 4a as a rotating shaft by a rotating device (not shown). The mechanical stirring type desulfurization apparatus is provided with an upper blowing lance 5 for adding the desulfurizing agent 7 according to the present invention by blowing upward toward the hot metal 3 accommodated in the hot metal ladle 2. Moreover, the inlet 6 for adding the desulfurization agent 7 which concerns on this invention on the bath surface of the hot metal 3 accommodated in the hot metal ladle 2 is also installed. That is, the desulfurizing agent 7 can be added by spraying from the top blowing lance 5 or can be added on top. Further, an exhaust duct port (not shown) connected to a dust collector (not shown) is provided at an upper position of the hot metal ladle 2, and gas and dust generated during the desulfurization process are discharged. . The desulfurizing agent 7 is prepared by previously mixing CaO powder and an alumina-metal Al mixture at a predetermined mixing ratio.

  The top blowing lance 5 is connected to a supply device including a hopper 8 that contains the powdery desulfurizing agent 7 and a cutting device 9 for quantitatively cutting out from the hopper 8. The powdery desulfurizing agent 7 can be supplied at an arbitrary timing. Of course, it has a structure in which only the carrier gas can be blown up.

  In this case, the top blowing lance 5 may be a single hole or may be made porous for the purpose of increasing the spraying area on the surface of the molten metal. Further, the spray angle of the top blowing lance 5, that is, the angle at which the desulfurizing agent 7 is sprayed from the top blowing lance 5 onto the hot metal bath surface is not limited to the vertical direction, and the hot metal surface during stirring (swells and vortices are formed). Therefore, it is possible to supply perpendicularly with respect to the horizontal plane), and to add up at an arbitrary angle between the vertical direction and the direction perpendicular to the molten metal surface Can be done.

  The input port 6 is connected to a supply device including a hopper 10 containing the powdered desulfurizing agent 7 and a rotary feeder 11 for quantitatively cutting out from the hopper 10, and the desulfurizing agent 7 is optionally supplied from the input port 6. It has a structure that can be supplied at the timing.

  The position of the carriage 1 on which the hot metal ladle 2 is mounted is adjusted so that the position of the stirring blade 4 is substantially at the center of the hot metal ladle 2, and then the stirring blade 4 is lowered and immersed in the hot metal 3. If the stirring blade 4 is immersed in the hot metal 3, the stirring blade 4 starts to turn and the speed is increased to a predetermined rotational speed. When the rotational speed of the stirring blade 4 reaches a predetermined rotational speed, the cutting device 9 is started and the desulfurizing agent 7 accommodated in the hopper 8 is blown upward toward the bath surface of the hot metal 3 together with the conveying gas. Spray from lance 5 and add. As the carrier gas, a reducing gas, an inert gas, or a non-oxidizing gas is used. Instead of adding the desulfurizing agent 7 by spraying from the top blowing lance 5, it is possible to add the desulfurizing agent 7 from the inlet 6, but as described above, the yield of the desulfurizing agent 7 is high and the desulfurization reaction interfacial area is increased. It is preferable to add by spraying from the top blowing lance 5 from the advantage that it can be made.

  When the addition of a predetermined amount of the desulfurizing agent 7 is completed and stirring is performed for a predetermined time, the rotational speed of the stirring blade 4 is decreased and stopped. When the swirling of the stirring blade 4 is stopped, the stirring blade 4 is lifted and waited above the hot metal pan 2. The generated slag floats to cover the hot metal surface, and the desulfurization process of the hot metal 3 is completed in a stationary state. After the desulfurization treatment, the generated slag is discharged from the hot metal ladle 2 and conveyed to the next refining process.

As described above, according to the present invention, CaO, which is a desulfurizing agent, is a fine particle having a particle size of 150 μm or less and a powder having a mass of 90% by mass or more. The desulfurization rate can be improved. In addition, the hatching of CaO is promoted by Al ₂ O ₃ added at the same time, and the desulfurization reaction is promoted. That is, desulfurization efficiency equivalent to that of a conventional CaO—CaF ₂ -based desulfurization agent can be obtained without using a fluorine-containing substance as a hatching accelerator and without increasing the melting loss of the processing vessel.

  A description will be given of an example in which about 300 tons of hot metal in the hot metal ladle is desulfurized using the mechanical stirring type desulfurization apparatus shown in FIG.

  The hot metal to be treated was one that was removed from the blast furnace and then desiliconized on the blast furnace casting floor. The hot metal composition was C: 4.1 to 4.5% by mass, Si: 0.13 to 0.20% by mass, Mn: 0.15 to 0.25% by mass, P: 0 by prior desiliconization treatment. It was 0.9-1.3 mass%, S: 0.02-0.03 mass%. The hot metal temperature was 1300 to 1350 ° C.

The desulfurization agent used is aluminum dross containing 40% by mass of Al ₂ O ₃ with respect to 100 parts by mass of CaO powder prepared by pulverizing quick lime (CaO) so that the particle size is 150 μm or less. 10 parts by mass of added and mixed was used. This desulfurizing agent was desulfurized by spraying nitrogen gas from the top blowing lance onto the hot metal bath surface as a carrier gas. As a result, it was possible to stably obtain hot metal having an S concentration of 0.002 to 0.005% by mass and a temperature of 1280 to 1330 ° C. after the treatment.

It is a side surface schematic diagram showing an example of a desulfurization processing method concerning the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bogie 2 Hot metal ladle 3 Hot metal 4 Stirrer blade 5 Top blowing lance 6 Loading port 7 Desulfurizing agent 8 Hopper 9 Cutting device 10 Hopper 11 Rotary feeder

Claims (3)

5 to 20 parts by mass of an alumina-metal Al mixture containing 50% by mass or less of Al ₂ O ₃ is added to 100 parts by mass of CaO powder having a fine particle size of 150 μm or less of 90% by mass or more. A hot metal desulfurization agent.   A hot metal desulfurization method according to claim 1, wherein the hot metal desulfurization agent according to claim 1 is added to the bath surface of the hot metal being stirred by a stirring blade to desulfurize the hot metal.   3. The hot metal desulfurization processing method according to claim 2, wherein the desulfurization agent is added to the hot metal bath surface together with a carrier gas through an upper blow lance.

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