JPH0525526A - Desulfurizing method of molten iron - Google Patents

Abstract

PURPOSE:To decrease the evaporation loss of a main desulfurizing agent consisting of Na2CO3 or metallic Mg and to execute desulfurization with high reaction efficiency by compounding a specific ratio of a desulfurization assistant essentially consisting of CaO or CaC2 with the main desulfurizing agent and blowing the mixture into the molten iron in a vessel kept under a specific pressure. CONSTITUTION:The molten iron in the vessel is subjected to a desulfurization treatment by blowing the desulfurizing agent via a carrier gas into the molten iron. The above-mentioned desulfurizing agent is constituted by compounding 30 to 90% desulfurization assistant essentially consisting of the CaO or CaC2 with the main desulfurizing agent consisting of the CaCO3 or metallic Mg of 10 to 70wt.% pure component. Further, the blowing of this desulfurizing agent is executed in the pressurized atmosphere of 1.2 to 9.9atm pressure. The loss by the evaporation of the main desulfurizing agent is suppressed and the reaction efficiency thereof is easily improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of desulfurizing hot metal by injecting powder under pressure, which is excellent in powder utilization efficiency.

[0002]

2. Description of the Related Art Hot metal pretreatment (dephosphorization, desulfurization) is widely used in integrated steelworks as an essential process for economically producing clean steel. Recently, there are strong demands for high-purity steel to be melted, and in many cases P ≦ 0.020% and S ≦ 0.003% in the hot metal are required, and sometimes S ≦ 0.001%. Desulfurization is difficult in subsequent converter refining, and it is not economical to perform desulfurization in secondary refining.
The level needs to be low.

As a method for effectively desulfurizing hot metal and increasing the utilization efficiency of a desulfurizing agent, for example, the method disclosed in Japanese Patent Laid-Open No. 2-10095 has been proposed. This method is effective in increasing the chance of contact between the sodium carbonate (soda ash) blown into the hot metal and the hot metal, but since the treatment is performed under atmospheric pressure, the reaction of the following equation (1) It is difficult to suppress the loss of Na caused by. For this reason, there is a large loss of sodium carbonate due to dust generation (20 to 30% of the blowing amount), which is a disadvantage.

Na ₂ CO ₃ (l) +2 C = 2 Na (g) +3 CO (g) (1) Iron and steel, 64 (1978) 9, P. As shown in 1323 to 1332, metallic magnesium also has a strong chemical affinity with S in the hot metal, and metallic magnesium alone or CaO or
It is used in the form of a mixture with CaC ₂ . However,
Since metal magnesium also has a high vapor pressure, it has a drawback that its utilization efficiency for desulfurization reaction is low under atmospheric pressure.

[0005]

DISCLOSURE OF THE INVENTION In order to solve the above-mentioned problems of the prior art, the present invention makes effective the desulfurization ability of a desulfurization agent composed of sodium carbonate or metallic magnesium and a desulfurization aid. It is an object of the present invention to provide a method for desulfurizing hot metal that can be blown into the hot metal together with a carrier gas while suppressing the loss due to evaporation.

[0006]

Means for Solving the Problems The present invention for achieving the above-mentioned object is to provide a molten metal in a container under a pressure atmosphere of 1.2 atm or more and 9.9 atm or less under pressure of sodium carbonate or a pure content of 10%. the desulfurization main agent consisting of 70 wt% of the metal magnesium, the desulfurizing aids mainly comprising CaO or CaC ₂ 30 to 90
It is a desulfurization method for hot metal, characterized in that a desulfurizing agent mixed in a range of wt% is blown together with a carrier gas.

[0007]

[Operation] By increasing the pressure in the container to 1.2 atm or more, the generation of soda ash dust was suppressed and the effect of improving the desulfurization reaction efficiency of soda ash was observed. This phenomenon was the same when a desulfurizing agent containing metallic magnesium was used. The higher the pressure is, the more the effect is improved. However, as shown in the amount of soda ash dust generation shown in FIG. Therefore, 1.2 atm or more and 9.9 atm
The following pressurized atmosphere is good, and 1.2 atm or more and 5 atm or less is practically sufficient considering the cost of equipment and maintainability.

The desulfurizing agent is limited to those containing sodium carbonate or metallic magnesium, because a remarkable improvement effect can be obtained by applying pressure when using these desulfurizing agents. Next, in the desulfurizing agent using metallic magnesium, it is not sufficient to limit the composition ratio of magnesium if the amount of metallic magnesium is less than 10%, although an improvement effect by pressurization can be obtained. Of course, even if the content of metallic magnesium exceeds 70%, the pressurizing effect is recognized, but the effect of improving the reaction efficiency per pure metal magnesium is rather lowered, so 70% or less is economically sufficient. The reason why the improvement of the reaction efficiency declines by more than 70% is that the generated MgS reacts with FeO and MnO in the slag without being absorbed by the slag on the surface of the molten metal, and returns to S in the hot metal again. The use of CaO or CaC ₂ as a desulfurization aid prevents the reaction of oxygen in the atmosphere or slag to cause re-sulfurization by the following formula (2) MgS + (O) → MgO + S … (2) Therefore, it is absorbed in the slag as more stable CaS. The amount of desulfurization aid was 30-90%, which was determined by experimentally examining the desulfurization effect of metallic magnesium. When desulfurizing with magnesium metal, the contact area between magnesium and hot metal is increased, the chance of particle collision is increased to agglomerate the generated MgS, and the sulfide generated as CaS described above is stably immobilized. The addition of CaO or CaC ₂ is essential.

[0009]

EXAMPLE FIG. 1 shows 300 g of hot metal contained in a container and 200 g of soda ash at 1320 ± 30 ° C. while adjusting the pressure in the container.
The amount of dust generated (g / kg hot metal) when air is blown at 50 Nl / min as a carrier gas for 5 min / min is indexed as 1 under normal atmospheric pressure.

FIG. 2 shows Mg 20% -CaO 75% -COKe 5%.
-1mm of desulfurizing agent at 100g / min for 5min for 1320 ~ 13
Blow with 50 kg of hot metal at 60 ° C using carrier gas N ₂ 60Nl / min and then for another 5 minutes with the blowing stopped.
The desulfurization curve when held for a while is shown by comparison between atmospheric pressure and a state of 2.5 atm or less. It can be seen from Fig. 1 that the amount of soda ash dust generated sharply decreases when the pressure inside the container exceeds 1.2 atm. Further, it can be seen from FIG. 2 that the S concentration in the hot metal at 2.5 atm is significantly reduced compared to that at atmospheric pressure.

[0011]

As described above, according to the present invention, the loss due to the evaporation of sodium carbonate or magnesium metal, which is the main component of the desulfurization agent, can be suppressed and blown by making the hot metal in the container a pressurized atmosphere. Therefore, the reaction efficiency of the desulfurizing agent can be easily improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a container internal pressure and a soda ash dust generation amount.

FIG. 2 is a diagram showing changes in the atmospheric pressure in a container and the hot metal S due to hot metal desulfurization.

Claims (1)

[Claims] [Claim 1] The molten pig iron in the container has a pressure of 1.2 atm or more, 9.9
Under a pressure atmosphere of atmospheric pressure or less, a desulfurization main agent composed of sodium carbonate or a magnesium content of 10 to 70% by weight of metallic magnesium in the hot metal, a desulfurization auxiliary agent containing CaO or CaC ₂ as a main component is 30 to
A method for desulfurizing hot metal, characterized in that a desulfurizing agent mixed in a range of 90% by weight is blown together with a carrier gas.