JPH0387309A - Method for desulfurizing molten iron - Google Patents

Abstract

PURPOSE:To effectively execute desulfurization at a low cost by adding desulfurizing agent so that the desulfurized slag in a reaction vessel becomes the specific basicity at the time of continuously desulfurizing molten iron in a pre- treating reaction vessel arranged at downstream side of a skimmer and reusing the desulfurized slag as sintering raw material. CONSTITUTION:The molten iron 2 tapped from a blast furnace is guided to the skimmer 6 together with slag 4, and the slag 4 is separated into a slag vessel 10 with a skimmer damper 8 and the molten iron 2 is allowed to flow into pre-treating reaction vessel 18 through a molten iron tough 14 on a weir 12. At the time of blowing the desulfurizing agent 22 in a storing vessel 24 to the flowing molten iron pool 2A with inert gas through a lance in a desulfurizing agent blowing device 20, the CaO-SiO2 series desulfurizing agent with the component pre-adjusted is blown so that the basicity CaO/SiO2 becomes 1.2-1.5, and the pre-treated slag 22A after desulfurizing is reused as the sintering raw material.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for desulfurizing hot metal, and in particular, it desulfurizes high-temperature hot metal immediately after being tapped from a blast furnace by a simple method, and recycles the desulfurization slag as a sintering raw material. Regarding available desulfurization methods, they are widely used in the field of hot metal pretreatment.

[Conventional technology]

Desulfurization of hot metal is generally carried out in a mixer furnace or ladle, and CaC0, CaO is used as the desulfurization agent.

In addition to Ca2O-based desulfurization agents such as CaC, there are methods 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 both a reduction reaction and an endothermic reaction, even if a desulfurization agent such as soda ash or lime is injected into the pig iron mixer car, the temperature of the hot metal is low and the desulfurization reaction does not proceed easily. There are limits to desulfurization treatment. For the reasons mentioned above, it goes without saying that it is most desirable to perform the desulfurization treatment during the process of flowing down the tap hole, which is the highest temperature period immediately after the iron is tapped 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 etc.

An overview of these conventional techniques will be explained.

(a) JP-A-51-105913 This invention provides a continuous eyebrow that has an inlet at one end and an outlet at the other end, and has a circular horizontal cross-sectional shape that is continuous 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.

This invention seems to have a stirring effect, but running costs are thought to be relatively high due to wear and tear on the refractories.

(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. Electric arc heating is performed while stirring, and a mixture of blast furnace slag and fluorite or CaO-based combined slag is used as a desulfurization agent.
This is a unique continuous desulfurization method for hot metal.

In this method, hot metal is heated using a heating electrode.

Moreover, since inert gas is injected and stirred through the porous plug at the bottom, the reaction efficiency is expected to increase, but the equipment costs are high and there are r1□ problems such as space in the blast furnace casting bed, which results in high costs. it is conceivable that.

(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 means for conveying pre-treated coarse powder and granular additives of the hot metal into an entrained flow area generated on the surface of the hot metal in the downstream flow system by means of conveying high-speed airflow to the flow area generated on the surface of the hot metal in the downstream flow system accompanying this dispersed fall flow. This is a method for continuous preliminary treatment of hot metal, which consists of charging the hot metal at an accelerated rate by means of a jet.

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.

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. Alternatively, there are problems such as requiring expensive equipment.

Furthermore, regarding desulfurization agents, in addition to CaO-based combined slag and fluorite mixtures, soda ash (Na, Go, etc.), and other Ba
Some contain halogen compounds such as CQ, but CaO
There is a problem in that products other than desulfurization agents are not suitable for use as cement or roadbed materials in terms of quality, and must be disposed of as industrial waste at great expense.

Regarding the CaO-based desulfurization agent, it is possible to reuse it as a sintering raw material in the I2# plant, but in this case as well, N
Slag containing a, Ba, F, etc. cannot be reused.

Therefore, Ca is used as a desulfurization material that can be reused as a sintering raw material.
Although only O-based desulfurization agents are used, the following problems arise when using CaO-based desulfurization agents.

In other words, the reaction when desulfurizing continuously with a CaO-based desulfurizing agent is CaO+S-+CaS+0, but in addition to being rate-limited by the S diffusion of solid CaO, this reaction
Since Ca01 has poor wettability, it is insufficiently dispersed in a shallow reaction tank of a hot metal bath, and therefore the desulfurization reaction does not proceed. Providing a deep bath reaction tank such as a pig iron mixer in a blast furnace casthouse requires a huge amount of capital in terms of equipment and also requires a large space.

[Problem to be solved by the invention]

The purpose of the present invention is to solve the above-mentioned problems of the prior art in the desulfurization operation as a pretreatment of hot metal in a blast furnace casthouse, and to take into account the reactivity of the CaO-based desulfurization agent. is continuously processed while flowing down the outflow gutter.

(b) Is there enough space in the reaction tank for processing in the blast furnace casthouse? ?
j I can't get deep.

(c) Because of continuous processing, the residence time of hot metal cannot be kept long.

(2) The generated desulfurization slag is reused as a sintering raw material.

It is an object of the present invention to provide an effective desulfurization method that can desulfurize at low cost under such conditions and restrictions.

[Means to solve the problem]

The gist of the present invention is as follows.

That is, in a hot metal desulfurization method in which a pretreatment reaction tank is provided downstream of a skinmer in a blast furnace casthouse and a desulfurization agent is added to continuously desulfurize the hot metal, the basicity of the desulfurization slag Cab/Si is added to the hot metal introduced into the reaction tank. The process includes a step of injecting a CaO-8in desulfurization agent whose composition has been adjusted in advance so that the composition is 1.2 to 1.5 through a lance, and the pretreated slag after desulfurization is used as a sintering raw material. This is a method for desulfurizing hot metal, which is characterized by reusing it as a hot metal.

An embodiment of the present invention will be described 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 a hot metal trough 14 provided above the salt 12 and introduced into a reaction tank 18.

A storage tank 24 containing a desulfurizing agent 22 is provided in the vicinity of the reaction tank 18, and the desulfurizing agent 22 is pneumatically supplied with an inert gas such as N2 through the lance of the desulfurizing agent blowing device 2o, and the desulfurizing agent 22 is pumped into the hot metal pool at the bottom of the reaction tank 18. It is blown into 2A.

The desulfurization agent used in the present invention is not only inexpensive, but also because the desulfurization slab is intended to be reused as a sintering raw material, so it should be limited to an inexpensive CaO-based desulfurization agent that does not contain Na, F2, etc. . For example, quicklime CaO - limestone Ca
A mixture of C0,-calcium carbide CaC2 or a mixture of CaO-8in2 is preferable. The desulfurized slag 22A after desulfurization is reused as a sintering raw material.

[Effect]

As described above, the continuous desulfurization reaction using the CaO-based desulfurization agent results in CaO+S-+CaS+0, but this reaction is rate-determined by the S diffusion of solid CaO. Moreover, since CaO alone has poor wettability, the following comparative test by the present inventors revealed that the CaO-5in2 desulfurization agent is preferable.

That is, an injection test was conducted in the reaction tank 18 using the five types of desulfurization agents shown in Table 1, and the desulfurization rate of hot metal and the (
The results of measuring S)/(S) are shown in Table 1. As is clear from Table 1, CaO: 55%, S
It was found that sample material No. 004 with in.:45% was the best.

The basic unit of desulfurizing agent in the tests shown in Table 1 is Ca basic unit of 5 kg/t of hot metal for the hot metal iron machine, but the reactivity of the sample material Not, 2.3 which does not contain Sio2 is poor, and therefore the desulfurization rate is low. CaO-5io2 desulfurization agent has good reactivity, but
The desulfurization rate changes depending on the basicity Cab/5in2.

Figure 2 shows (S)/(S) with changes in CaO/SiO2.
) are the experimental results of the present inventors showing the influence on

As is clear from Figure 2, Ca O/5 in the desulfurization slag
When iO2=1.2 to 1.5, (S)/(S)≧
30, indicating the maximum desulfurization rate. However, CaO/Si
When o is >1.5, (S)/(S) decreases. The reason for this is that CaO/5iO2=1.5 and the melting point of slag is 15.
Since the temperature exceeds 50°C, CaO-3in and system slag become solid in the hot metal or on the surface of the hot metal below this temperature, and S diffusion in the solid becomes rate-determining.

〔Example〕

Blast furnace tapping speed 5t/min 1500-1510'
[S] of hot metal C before pretreatment was 0.034%.

For this hot metal, Cab: 37.3%CaC
○,: 22.7% 5in2: 40% synthetic desulfurization agent with Ca basic unit of 5kg/t hot metal table,
50 kg using the apparatus having the reaction tank shown in Figure 1.
/ I blew a win. In this case, N2 was used as the carrier gas. [S] after desulfurization was 0.012%, and the desulfurization rate was 65%.

The basicity of desulfurization slag in this case, CaO/Sio2, is
25, which was within the appropriate range as a sintering raw material, so it could be used effectively as it is at a blending ratio of 1% in the sintering raw material.

〔Effect of the invention〕

The present invention provides a reaction tank downstream of the skimmer of the blast furnace casthouse,
A CaO-5in2 desulfurization agent was gas-transported with N2 or the like through a lance immersed in the reaction tank.

Basicity of desulfurization slag CaO/5iO2=1.2-1.5
In this case, even if the contact time between the desulfurization agent and the hot metal is short, the reaction rate is fast due to the S diffusion rate of CaO solid We were able to respond effectively and achieve the following effects.

(a) Since the present invention desulfurizes high-temperature hot metal immediately after being tapped from a blast furnace, even if the bath depth of the reaction tank is not as deep as the pig iron mixer car or ladle, the desulfurization rate is comparable to that of these. I was able to list.

(b) Since the reaction tank used in the present invention is in the shape of a tap trough,
It can be installed even in the limited space of a blast furnace casthouse, and the installation cost is low.

(c) The desulfurization slag after pretreatment is CaO-3in2 slag that does not contain Na, F2, etc., so it can be recycled as it is as part of the sintering raw material.
It is also effective in terms of in2 resource utilization.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a hot metal desulfurization equipment used in carrying out the present invention, and FIG. 2 is a diagram showing changes in the basicity (S)/(S)/(
It is a diagram showing the influence on S). 2... Hot metal, 4... Slag 6...
・Skinmer 8...Skinmer damper 4...Hot metal gutter, 18...Reaction tank 20...
...Desulfurizing agent injection device. 22...Desulfurization agent 22A...Desulfurization slag

Claims (1)

[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 desulfurization agent is added to continuously desulfurize the hot metal, the basicity of desulfurization slag CaO/ It consists of a step of injecting a CaO-SiO_2 desulfurization agent whose composition has been adjusted in advance so that SiO_2 = 1.2 to 1.5 through a lance, and the pretreated slag after the desulfurization is recycled as a sintering raw material. A method for desulfurizing hot metal characterized by using