JP5668641B2 - Hot metal desulfurization method - Google Patents

Description

  The present invention relates to a hot metal desulfurization method using a mechanically stirred hot metal desulfurization apparatus, and particularly to improve the productivity of the desulfurization treatment.

Since the hot metal discharged from the blast furnace contains impurities such as phosphorus (P) and sulfur (S) that adversely affect the quality of the steel, they must be removed. In today's refining process, prior to decarburization refining in a converter, a treatment for removing P and S contained in the hot metal, that is, a pretreatment of the hot metal is generally performed.
Among these, in the hot metal desulfurization treatment, the hot metal is held in the hot metal pan, a desulfurizing agent is added onto the hot metal, a rotor called impeller having blades is immersed in the hot metal and rotated, and the hot metal is stirred. A method of accelerating the desulfurization reaction by using a mechanical stirring type hot metal desulfurization method is known. Examples of the desulfurizing agent used here include a desulfurizing agent mainly composed of lime (CaO) powder and calcium carbide (CaC ₂ ). However, many desulfurizing agents mainly composed of CaO powder are used from the viewpoint of processing cost. Has been used.

This desulfurization reaction by CaO is generally represented by the following formula.
[S] + CaO = (CaS) + [O]
Here, [S] indicates sulfur in hot metal, (CaS) indicates CaS in slag, and [O] indicates oxygen in hot metal.
In the mechanical stirring type hot metal desulfurization method, as one of the methods for realizing the dispersion of the desulfurizing agent in the hot metal and promoting the desulfurization reaction, for example, in Patent Document 1, a desulfurizing agent is added to the hot metal stored in the hot metal pan. Rotating and stirring with an impeller and causing the stirring flow to collide with the rectifier provided on the inner wall surface of the pan or in the vicinity of the inner wall surface of the pan, and desulfurizing by desulfurizing agent in the hot metal flow descending the inner wall surface of the pan A hot metal desulfurization method is described.

However, in the technique described in Patent Document 1, since the rotational stirring force by the impeller is very strong, it is necessary to use a tough material as the rectifier and to firmly install it on the inner wall of the pan. Therefore, there is a disadvantage that a lot of labor and cost are required for the production and maintenance of the rectifier.
In Patent Document 2, a desulfurizing agent is added separately, a part of the desulfurizing agent is added on the hot metal bath surface, and the rest is added on the hot metal bath surface being stirred by the stirring blade. A hot metal desulfurization method is described in which top blowing is added together with a carrier gas via a blowing lance. According to the technique described in Patent Document 2, the desulfurization reaction can be accelerated even by using a desulfurization agent that does not use fluorine.

  In the technique described in Patent Document 2, the desulfurization agent added on the hot metal bath surface for promoting the desulfurization reaction is a lime (CaO) -containing substance that is produced as a secondary product in the iron making process, or a machine. It is preferable to use desulfurization slag (recycled desulfurization slag) generated by stirring-type hot metal desulfurization treatment. According to this technology, when the reused desulfurized slag is charged and when stirring is started, the granular slag is partially cut off, and the gangue is mixed in the hot metal in a fine state, and finely added CaO added by top blowing. Grains are combined with gangue from recycled desulfurized slag in the bath, and a part of CaO grains melt into gangue grains, thereby forming a molten slag phase with relatively high desulfurization ability around CaO grains. The desulfurization reaction is promoted.

JP-A-51-112416 JP 2009-79261 A

  However, in the technique described in Patent Document 2, the reuse desulfurization slag to be added on top and the lime (CaO) -containing substance to be added on top are added separately, both of which are added after the start of stirring. Therefore, mixing and stirring with CaO grains before the temperature of the reused desulfurized slag is not sufficiently increased, the effect of mixing the granular granulated slag into the molten iron in a fine state is relatively small, and the desulfurization reaction proceeds sufficiently In some cases, further acceleration of desulfurization reaction and improvement of productivity have been demanded.

  The present invention has been made to solve such a problem of the prior art, and when performing hot metal desulfurization using a mechanical stirring type hot metal desulfurization apparatus, it is possible to increase the desulfurization speed and further improve productivity. It is an object of the present invention to provide a hot metal desulfurization method.

In order to solve the above-mentioned problems, the inventors diligently observed the state of desulfurization treatment of the hot metal held in the hot metal ladle. As a result, there are many cases where the hot metal ladle to be desulfurized next comes to the standby position while the internal hot metal is being stirred and desulfurized in one hot metal ladle. I came up with it.
The inventors added CaO-based reused desulfurized slag (desulfurized slag) in advance during this waiting time, thereby increasing the temperature of the desulfurized slag before stirring. It was conceived that the desulfurization slag at the time was helped to be refined and the reaction rate was substantially improved, and further productivity was improved, and the present invention was made.

That is, the present invention is as follows.
(1) In the hot metal desulfurization method in which lime and desulfurization slag are added to the hot metal held in the hot metal ladle to perform desulfurization treatment, the desulfurization slag is placed on the hot metal of the hot metal ladle while the hot metal ladle is waiting. After waiting for 10 minutes or more after the addition, the temperature of the desulfurization slag is preliminarily increased , and then mechanical stirring of the hot metal is started. The hot metal desulfurization method characterized by performing.
(2) Instead of performing the desulfurization treatment by adding the lime to the hot metal, the desulfurization treatment is performed by adding the lime by both the upper blowing and the upper placement methods ( The method for desulfurizing hot metal as described in 1).

  ADVANTAGE OF THE INVENTION According to this invention, when performing hot metal desulfurization using a mechanical stirring type hot metal desulfurization apparatus, a desulfurization speed | rate can be raised and productivity can be improved further and there exists a remarkable effect on an industry. Further, there is an effect that the ratio of the reused desulfurized slag can be improved and the basic unit of the desulfurizing agent can be reduced.

It is explanatory drawing which shows typically an example of the desulfurization method of the hot metal of this invention. It is explanatory drawing which shows typically the example of the desulfurization method of the other hot metal of this invention.

  In the present invention, desulfurization slag and lime are added to the hot metal held in the hot metal ladle to desulfurize the hot metal. In the present invention, as shown in FIG. 1, while the hot metal ladle 1 is waiting, desulfurization slag 9 is added from the hopper 10 through the charging chute 6 to the hot metal 8 held in the hot metal ladle 1 in advance. A temperature rise process of desulfurization slag is performed. Thereafter, the impeller blades 3 attached to the rotary shaft 4 are immersed and rotated in the hot metal 8 that has been subjected to the temperature raising treatment of the desulfurized slag 9 in advance, and mechanical stirring of the hot metal 8 is started. 8 and desulfurization treatment is performed by adding the lime 11 through the top blowing lance 7 together with the carrier gas.

Accordingly, when the temperature of the desulfurized slag 9 is increased during the standby time, the refinement of the desulfurized slag at the time of stirring is helped, so that the desulfurization productivity can be improved. Moreover, it is considered that there is an effect of pre-desulfurization by the time of mechanical stirring by adding desulfurization slag 9 on the hot metal during the waiting time.
The desulfurization slag 9 to be added on top has CaO / SiO ₂ in a mass ratio of 2 or more, CaO content of 40% by mass or more, Al ₂ O ₃ content of 10% by mass or less, and S content of 5.0% by mass or less. Preferably there is. The lime 11 to be added by top blowing preferably contains 50% by mass or more of CaO. It goes without saying that hatching accelerators such as Al ₂ O ₃ and MgO may be contained as other components as required.

The desulfurization slag 9 added on top is preferably 2.0 kg / t or more in terms of CaO per mass of molten iron because an improvement in desulfurization rate is clearly recognized. The upper limit is not particularly limited, but it is preferably 3.5 kg / t or less because the effect of improving the desulfurization rate is saturated even if added over 3.5 kg / t.
The particle size of the desulfurized slag 9 is preferably 10 mm below the sieve. Furthermore, the particle size of the lime 11 to be added by top blowing is preferably 1 mm below the sieve.

The molten iron 8 subjected to the temperature raising process of the desulfurized slag 9 performed during the standby time is mechanically stirred, and lime 11 is added to the molten iron 8 from the top blowing lance 7 by top blowing. The top blowing lance 7 may not be immersed in the hot metal.
The lime 11 to be added by top blowing is preferably the sum of the desulfurized slag 9 to be added by top addition and 5.0 kg / t or more in terms of CaO per unit molten iron mass, since an improvement in the desulfurization rate is clearly recognized. The upper limit is not particularly limited, but it is preferably 12.0 kg / t or less because the effect of improving the desulfurization rate is saturated even if it is added in excess of 12.0 kg / t.

The carrier gas used when the lime 11 is added by top blowing from the top blowing lance 7 can be at least one of an inert gas, a non-oxidizing gas and a reducing gas, and N ₂ gas or the like is used. it can. However, oxidizing gas is not suitable because it raises the oxygen potential in the hot metal and is disadvantageous for desulfurization. However, as long as the increase in oxygen potential in the hot metal is below the allowable limit, it may be contained in a trace amount in the inert gas, non-oxidizing gas, and reducing gas.

In the present invention, instead of performing the desulfurization treatment by adding the lime to the hot metal, the desulfurization treatment may be performed by adding the lime by both the method of top blowing and placing the lime.
In FIG. 2, as a desulfurization agent charging facility, a hopper 10 for adding lime 12 on top and a charging chute 6 are additionally provided. That is, by impregnating and rotating the impeller blade 3 attached to the rotating shaft 4 in the hot metal 8, the hot metal 8 is mechanically stirred, and the lime 11 is added to the hot metal 8 through the upper blowing lance 7. In addition, lime 12 is added to hot metal 8 from hopper 10 through charging chute 6.

In addition to the method in which the lime 11 is added through the top blowing lance 7, the productivity is improved by adding the lime 12 from the hopper 10 through the charging chute 6.
In addition, it is preferable that the particle size of the lime 12 added on top is 10 mm below the sieve.
Depending on the difference between the S content in the hot metal discharged from the blast furnace and the target S content after desulfurization, the addition of CaO This is preferable because the amount can be increased.

  The lime 11 to be added on top and the lime 12 to be added on top are preferably the sum of the desulfurized slag 9 to be added on top and from 5.0 kg / t to 12.0 kg / t in terms of CaO per unit hot metal mass. . This is also due to the same reason as the case where only lime is added by top blowing.

Example 1
The hot metal ladle 1 contains, by mass%, C: 4.2 to 4.6%, Si: 0.1 to 0.4%, S: 0.008 to 0.013%, and the remaining hot metal 275 to 1250 to 1350 ° C composed of Fe and inevitable impurities. 315t was prepared, and the amount of desulfurization slag 9 and lime 11 was changed in various ways, and the change in the desulfurization rate was investigated. At that time, mechanical stirring was started 10 minutes after the desulfurization slag 9 was added from the hopper 10 through the charging chute 6, and lime 11 was added through the top blowing lance 7. Here, the total of the desulfurization slag 9 and the lime 11 as the desulfurization agent was adjusted to be 6.8 kg / t in terms of CaO per unit molten iron mass. Further , when the present invention is applied, it is more effective when there is a waiting time of 10 minutes or more .

The stirring time T for mechanical stirring is
T (min) = total amount of desulfurizing agent added (CaO equivalent) / 400 + 13 (1)
It was. In actuality, S in the hot metal discharged from the blast furnace fluctuates in the range of 0.008 to 0.100% in mass%, so the total addition amount of CaO is set according to the difference from the target S content after desulfurization. It is sufficient to increase the stirring time.

The top blow lance 7 has a nozzle diameter of 80 mm, the height from the hot metal surface at the nozzle tip is 1000 mm, and lime 11 is blown together with N ₂ . The hot metal ladle 1 used had a capacity of 300 tons as the weight of the hot metal to be filled, and was stirred using a four-blade impeller. The results are shown in Table 1.

In Table 1, the desulfurization speed V is
V (1 / min) = ln (before desulfurization [S] / after desulfurization [S]) ÷ T (min) (2)
As calculated.
From Table 1, compared to Case No. 1 where desulfurized slag 9 was not added on top and Case No. 2 where desulfurized slag 9 and lime 11 were added simultaneously, Case No. where desulfurized slag 9 was added on top in advance. In 3-6, it turns out that the desulfurization rate is improving.

(Example 2)
The hot metal ladle 1 contains, by mass%, C: 4.2 to 4.6%, Si: 0.1 to 0.4%, S: 0.016 to 0.034%, and the remainder of Fe and unavoidable impurities. Prepare 315 tons, add desulfurized slag 9 in the range of 3.1 to 3.3 kg / t in terms of CaO, and then add various amounts of lime 11 to be added by top blowing and lime 12 to be added by addition. The desulfurization rate was measured. At that time, the sum of the desulfurization slag 9 as a desulfurization agent, the lime 11 to be added by top blowing, and the lime 12 to be added on top increases the total addition amount of CaO depending on the difference from the target S content after desulfurization. Thus, the stirring time was increased, and the other conditions were the same as in Example 1. The results are shown in Table 2.

From Table 2, compared with No.7-9 which did not add desulfurization slag 9 beforehand, No.10-17 which added desulfurization slag9 beforehand added that desulfurization speed is improving. Recognize.
When the S content in the hot metal before desulfurization is relatively high, the total amount of CaO required to be added increases as described above, but by adding a part of the lime to be added as lime 12, the lime is added. The desulfurization can be performed without increasing the desulfurization time due to the increase in the top blowing time.

1 container (hot metal hot pot)
3 Impeller blades 4 Rotating shaft 6 Charging chute 7 Top blowing lance 8 Hot metal 9 CaO-based reuse desulfurization slag (desulfurization slag)
10 Hopper 11 Lime added on top 12 Lime added on top

Claims (2)

In the hot metal desulfurization method in which lime and desulfurization slag are added to the hot metal held in the hot metal ladle to perform desulfurization treatment,
While the hot metal ladle is waiting, after the desulfurization slag is added to the hot metal in the hot metal ladle for 10 minutes or more, and after the desulfurization slag is heated in advance, mechanical stirring of the hot metal The hot metal desulfurization method is characterized in that the desulfurization treatment is performed by adding the above-mentioned lime to the hot metal and then performing desulfurization treatment.   2. The desulfurization treatment is performed by adding the lime to the hot metal in both of the top blowing and top-positioning methods instead of performing the desulfurization treatment by adding the lime to the top blowing. The hot metal desulfurization method as described.

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