JPH0459909A - Method for desulfurizing molten iron - Google Patents

Abstract

PURPOSE:To execute stable desulfurization to molten iron in the limited space by arranging a reacting vessel at downstream of a skimmer, using different kind of plural CaO-based desulfurizing agents having different m.p. according to the variation of desulfurizing performance or molten iron temp. or the combination of them. CONSTITUTION:In the desulfurizing method for molten iron by arranging the pre-treated reacting vessel 16 at downstream of the skimmer 6 on casting floor in a blast furnace and adding the CaO-based desulfurizing agent, according to the variation of molten iron temp. and desulfurizing performance, the different kinds of plural CaO-based desulfurizing agents having different m.p. and CaF2 contents, are separately used to execute a stable desulfurization. Into the molten iron 2 in the reacting vessel 16, the CaO-based desulfurizing agent fed with an inert gas from a lance 18 is blown to execute the desulfurization, and slag 4 is floated upward and piled and the molten iron 2 is desulfurized.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for desulfurizing hot metal, and in particular to a method for desulfurizing high-temperature hot metal immediately after being tapped from a blast furnace with excellent efficiency in a simple manner. Widely used in the field of processing.

[Conventional technology]

Desulfurization of hot metal is generally carried out in a mixer furnace or ladle, and the desulfurization agent is CaCO2 or CaO.

In addition to CaO-based desulfurization agents such as CaC2, there is a method in which Na2Co is injected into the hot metal through a lance while stirring, using an inert gas as a carrier gas. However, since the desulfurization reaction is a reduction method and an endothermic reaction, even if a desulfurization agent such as soda ash or lime is injected into the pig iron mixer, the temperature of the hot metal is low and the desulfurization reaction is difficult to proceed.
There are limits to the desulfurization treatment in pig iron mixed cars.

For the above reasons, it goes without saying that it is most desirable to desulfurize during the process of flowing down the tap culvert, which is the period of highest temperature immediately after tapping from the blast furnace.

From this point of view, many conventional techniques have been disclosed in which desulfurization treatment is performed immediately after the iron is tapped into the cast bed of a blast furnace. For example, JP-A-51
-105913, JP-A-52-42411, JP-A-59
-143010, Special Publication No. 62-42010, etc. An overview of these conventional techniques will be explained.

(a) JP-A No. 51-1059i3 This invention provides continuous eyebrows that are provided with an inlet at one end and an outlet at the other end, and which have a circular horizontal cross section and are arranged in a row with a slight overlap. A rotating shaft is provided at the center of each single circular portion of the shaped processing tank, and a stirring mechanism having a plurality of stirring rods fixed to the rotating shaft via an arm is provided, and the direction of rotation of each of the rotating shafts is controlled. This is a continuous desulfurization method for molten metal in which desulfurization is performed in the same direction and with the upper end of the stirring rod always positioned below the static surface of the molten metal in a processing tank.

Although this invention seems to have a stirring effect, it is thought that running costs are relatively high due to wear and tear of the contents.

(b) JP-A-52-42411 The present invention is a method of continuously pouring hot metal from a tap runner or a hot metal ladle into a desulfurization tank having a gas-injected porous plug for stirring hot metal at the bottom and a heating electrode. This continuous desulfurization method for hot metal is characterized by performing electric arc heating while stirring and using a mixture of blast furnace slag and fluorite or CaO-based synthetic slag as a desulfurization agent.

In this method, the molten pig iron is heated with a heating electrode, and inert gas is injected through a porous plug at the bottom for stirring, so the reaction efficiency is expected to increase, but the equipment cost is high and the There are problems with space, etc., and it is thought that the cost will be high.

(c) JP-A-59-143010 This invention divides the hot metal that is continuously flowing down in the hot metal gutter in the middle of the flow system of the hot metal, and creates a distributed flow with a head difference in the downstream flow system. A granular additive powder for pre-treatment of the hot metal is added to the entrained flow region generated on the surface of the hot metal in the downstream flow system along with this dispersed fall flow, using a high-speed air flow as a conveying means. This is a method for continuous preliminary treatment of hot metal, which consists of accelerating the injection of hot metal by projecting the iron into the hot metal.

This invention also seems to be able to desulfurize at a relatively low cost because the hot metal is divided into streams and the hot metal is stirred using a head, and the pneumatic desulfurization agent is jetted into this stirring flow, but it is not suitable for blast furnace casthouses. There is a problem in that a large space is required for dividing the flow.

(d) Japanese Patent Publication No. 62-42010 This invention is a hot metal sluice refining method in which a wide slag channel is formed in the molten metal sluice, and an injection lance is inserted into the molten metal channel to inject a refining agent together with a carrier gas.

In this invention, when a desiliconizing agent has a low melting point and turns into slag, the desulfurization efficiency is good, but with a solid desulfurizing agent flux such as CaO, desulfurization does not proceed due to the rate-limiting reaction at the solid-liquid reaction interface. If CaF2 is added to make liquefied slag, desulfurization will proceed, but if CaO-based frances are used instead of low-melting-point slag such as CaF2 during refining by injection in hot metal slugs in a flow system, slag will stagnate in the molten metal slugs. However, there is a problem that the reaction does not proceed.

As mentioned above, conventional methods for continuous desulfurization treatment in blast furnace casthouses include methods such as injection in the flow or projection blasting from the surface of the hot metal, but both require a large space. Otherwise, there are problems such as requiring expensive equipment.

Furthermore, regarding desulfurization agents, in addition to a mixture of CaO-based synthetic slag and fluorite, soda ash (Na2C○, ), and other BaC
Some contain halogen compounds such as Q2, but other than CaO-based desulfurization agents, they are not suitable for use as cement or roadbed materials in terms of quality, and have to be disposed of as industrial waste at great expense.

CaO-based desulfurization agents can be reused as sintering raw materials in steel plants, but in this case, N
Slabs containing a, Ba, F, etc. cannot be reused.

Therefore, as a desulfurization agent that can be reused as a sintering raw material, C
Although only aO is used, the use of CaO-based desulfurization agents has the following problems.

In other words, the reaction when desulfurizing continuously with a CaO-based desulfurizing agent is Ca○+S-+CaS+0, but this reaction is rate-limiting by the S diffusion of solid CaO.
Since CaO alone has poor wettability, it is not sufficiently dispersed in a shallow reaction tank with a hot metal bath.

Therefore, there is a problem that the desulfurization reaction does not proceed. Providing a deep reaction tank such as a pig iron mixer in a blast furnace casthouse requires a considerable amount of capital in terms of equipment and also requires a large space.

In addition, when we examine the reaction progress of hot metal pretreatment in detail, we find that the reaction situation changes depending on changes in slag formation in the reaction tank, hot metal temperature, etc., as described later, and the desulfurization agent performs the optimal reaction according to these changes. The current situation is such that it is difficult to say that this is the case.

[Problem to be solved by the invention]

An object of the present invention is to solve the above-mentioned problems of the prior art in the pretreatment of hot metal using a CaO-based desulfurization agent in a blast furnace casthouse by using different CaO-based desulfurization agents.

To provide a method for desulfurizing hot metal that can efficiently and stably desulfurize at low cost.

[Means and effects for solving the problems] The above objects of the present invention are achieved by the following three inventions.

The gist of the first invention is as follows.

A pretreatment reaction tank is installed downstream of the skimmer in the blast furnace casthouse.
A hot metal desulfurization method for desulfurizing hot metal by adding an aO-based desulfurization agent, characterized in that desulfurization is carried out by selectively using a plurality of CaO-based desulfurization agents having different melting points or CaF2 contents according to changes in desulfurization ability. It's a method.

The gist of the second invention is that, in a desulfurization reaction in a pretreatment reaction tank similar to the first invention, a plurality of Ca
This is a hot metal desulfurization method characterized by desulfurization using different O-based desulfurization agents.

The gist of the third invention is that, in the desulfurization reaction in a pretreatment reaction tank similar to the first invention, a plurality of the CaO-based desulfurization agents having different melting points or CaF2 contents are used according to changes in hot metal temperature and desulfurization capacity. This is a hot metal desulfurization method characterized by desulfurization using different methods.

First, an outline of the desulfurization method for the pretreatment reaction tank will be explained with reference to FIG.

Hot metal 2 tapped from the blast furnace flows down the tap trough together with slag 4 and reaches the skinmer 6, and the slag 4 that is blocked by the skinmer damper 8 and floats on the surface is separated into the slag trough 10 and undergoes a separate slag treatment process. sent to. The hot metal 2 that has passed through the lower end of the skinmer damper 8 is temporarily stored by a weir 12 on the outlet side of the skinmer 6, and is guided to the hot metal @14 provided on the weir 12 and introduced into the reaction tank 16.

The hot metal 2 in the reaction tank 16 is desulfurized by injecting a CaO-based desulfurization agent pneumatically with an inert gas from the lance 18, and the slag 2 is floated upward and deposited, and the hot metal 2 is desulfurized.First, the first invention will be explained. do. In the conventional preliminary treatment using a CaO-based desulfurization agent, since a single CaO-based desulfurization agent is used, desulfurization slag floats up and accumulates in the reaction tank over the course of an hour, obstructing the flow of hot metal, and causing problems over time. Along with this, the desulfurization ability decreases.

Desulfurization ability is expressed as the ratio (S)/(S) of the amount of S (S) in hot metal after treatment to the amount of S (S) in slag after treatment.

In the desulfurization treatment immediately after tapping in the blast furnace casthouse, the desulfurization ability (S) / [5) = equivalent to that in the pig iron mixer car or ladle
In order to ensure a value of 100 or more, it is necessary to remove the desulfurization slag during the process, and therefore the desulfurization process in which the desulfurization agent is injected is interrupted, reducing the effectiveness.

The first invention first uses a desulfurizing agent with a high melting point in the CaO-CaCO system, and when the desulfurization ability becomes less than 100, CaF2
The desulfurization process is continued by switching to a desulfurization agent with a low melting point containing CaO-
Desulfurization is performed using a CaC0, based desulfurization agent. According to the present invention, CaO-based desulfurization agents having different melting points or CaF2 contents are used depending on the change in desulfurization ability, and desulfurization can be carried out efficiently without interruption due to slag removal.

The details of the first invention will be explained using examples and comparing with the conventional example. That is, as shown in Table 1, the same hot metal was desulfurized by the method of the present invention and the conventional method by blowing a desulfurizing agent into the pretreatment reactor at the same blowing rate of 100 kg/min. In addition, in FIGS. 2(A) and (B), the first
The changes over time in the desulfurization ability in the desulfurization of the invention example and the conventional example are shown. Additionally, Table 1 also shows the desulfurization results for comparison.

As is clear from Table 1, Table 2, and Figure 2, the first invention method uses a desulfurizing agent with a low melting point when the desulfurization ability becomes less than 100,
When desulfurization ability is restored, a desulfurization agent with a high melting point is used, and by using different desulfurization agents according to changes in desulfurization ability, stable desulfurization can be achieved without removing slag during the process compared to conventional methods.

Next, the second invention will be explained. When desulfurizing hot metal, the temperature of the hot metal is generally low for about one hour after the start of tapping, and the desulfurization slag tends to harden and desulfurization may not be possible. When the hot metal temperature is low (desulfurization is not possible using conventional methods), a desulfurization agent with a low melting point is used to facilitate the removal of the generated slag, and as the hot metal temperature rises, the use of a desulfurization agent with a high melting point is switched to. This method performs stable desulfurization by using different desulfurizing agents depending on changes in hot metal temperature.

Details of the second invention will be explained using examples and comparison with a conventional example. That is, when the temperature of hot metal at the start of tapping is relatively low, as shown in Table 3, in both the method of the present invention and the conventional method, the bath depth is 500 m in the pretreatment reaction tank, and the temperature is Desulfurization was carried out by blowing a desulfurizing agent at a rate of 150 kg/min. Moreover, in FIGS. 3(A) and 3(B), changes over time in the desulfurization ability of the second invention example and the conventional example are shown. Table 3 also shows the desulfurization results for each.

As is clear from Table 3, the second invention uses different CaO-based desulfurization agents with different melting points depending on the tapping temperature, thereby eliminating the need to interrupt desulfurization due to slag removal, and without being affected by the tapping temperature. Desulfurization was possible with stable and high desulfurization ability. On the other hand, in the conventional example, due to the low tapping temperature, desulfurization could not be performed at first due to agglomeration of the slag, making it difficult to perform desulfurization continuously. Therefore, while the amount of desulfurized hot metal is 1000 tons in the second invention example,
The conventional example is 500 t, which is half the amount, and the average desulfurization capacity is 145 in the example, whereas the conventional example is as low as 130.

Next, the third invention will be explained. The third invention is a combination of the first invention and the second invention, and stabilizes the hot metal by selectively using a plurality of CaO-based desulfurization agents with different melting points or CaF2 contents according to changes in both the temperature and desulfurization ability of the hot metal. This method performs desulfurization.

〔Effect of the invention〕

As is clear from the above embodiments, the present invention provides a reaction tank downstream of the skinmer of a blast furnace casthouse, and a plurality of CaO-based desulfurizers having different melting points in response to changes in desulfurization capacity, hot metal temperature, or a combination thereof. By using different agents for desulfurization, we were able to stably desulfurize hot metal in the limited space of a blast furnace.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a hot metal desulfurization equipment implementing the present invention;
Figures (A) and (B) are diagrams showing changes in desulfurization ability during desulfurization. (A) is the first embodiment of the invention, (B) is the conventional example, and Figures 3 (A) and (B) are Both are drawings showing changes in desulfurization ability during desulfurization, where (A) is the second invention example and (B) is the conventional example. 2... Hot metal 4... Slag 6... Skinmer 8... Skinmer damper 1o... Slag gutter 12... Weir 14... Hot metal gutter 1
6... Reaction tank 18... Lance

Claims (3)

[Claims] (1) In a hot metal desulfurization method in which a pretreatment reaction tank is provided downstream of the skinmer of a blast furnace casthouse and a CaO-based desulfurization agent is added to desulfurize the hot metal, the melting point or CaF_
2. A method for desulfurizing hot metal, characterized in that desulfurization is carried out by selectively using a plurality of the CaO-based desulfurization agents having different contents. (2) In a hot metal desulfurization method in which a pretreatment reaction tank is provided downstream of the skinmer of a blast furnace casthouse and a CaO-based desulfurization agent is added to desulfurize the hot metal, the melting point or CaF
A method for desulfurizing hot metal, characterized in that desulfurization is carried out by selectively using a plurality of the CaO-based desulfurization agents having different _2 contents. (3) In a hot metal desulfurization method in which a pretreatment reaction tank is installed downstream of the skinmer of a blast furnace casthouse and a CaO-based desulfurization agent is added to desulfurize the hot metal, the melting point or CaF_2 content is A method for desulfurizing hot metal, characterized in that desulfurization is carried out by selectively using a plurality of different CaO-based desulfurization agents.