JPH01165709A - Method for refining molten iron - Google Patents

Abstract

PURPOSE:To enable refining in single furnace under good efficiency by adding refining agent into molten iron, blowing gas adjusting equilibrium oxygen partial pressure on slag surface, desulfurizing and successively, executing desiliconizing and dephosphorizing treatments without slag off. CONSTITUTION:Refining agent of lime, etc., and slagging promoting agent fluorite, etc., are added on the molten metal in the converter, etc., and oxidizing gas controlling the equilibrium oxygen partial pressure to 0.2-0.8atm. is blown on the slag surface. Gasified desulfurizing reaction between gas and slag is promoted and sulfur is removed from the slag and successively, the desiliconization and dephosphorization are executed without slag off. Then, at the time of gradually increasing oxygen potential in the blowing gas, the desulfurizing reaction from the molten iron into the slag is mainly developed at the initial stage of the refining and the desulfurizing reaction from the slag into the gas is mainly developed after middle stage and as the whole, the desiliconizing and dephosphorizing reactions are promoted at the same time of desulfurizing reaction.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention is useful for efficiently producing hot metal or steel.
It also relates to an economical method of refining.

Conventional technology Conventionally, when producing steel from hot metal, desiliconization, dephosphorization, and decarburization are performed using solid oxides such as iron ore or oxidation with oxygen gas, as seen in the example of a pure oxygen top-bottom blowing converter. , methods have been adopted to remove it. Furthermore, in recent years, with the stricter requirements for steel properties, a split refining method has been developed in which after desiliconization, slag is removed, dephosphorization is performed using low-temperature hot metal, and only decarburization is performed in a converter ( For example, JP-A-57-188
No. 810), by reducing silicon, phosphorus, and sulfur at the hot metal stage, the phosphorus distribution ratio between slag and hot metal can be maintained high, and in converter steelmaking, refining agents such as quicklime can be used. The amount of slag used can be reduced, and as a result, the total amount of slag generated can be reduced, and since converter steelmaking is performed with a small amount of slag, the productivity of the converter improves and the temperature can be maintained. This is because there is.

However, the slag after dephosphorization must be slaged off, and there is a problem of iron loss and heat loss in the slag.

In addition, we also provide equipment for desiliconization, dephosphorization, and decarburization, and after desiliconization,
Additionally, equipment for discharging the sludge after de-9ing is required, resulting in a problem that the equipment becomes oversized. Additionally, since refining takes a long time, there is a problem of large heat loss.

In addition, generally, when desiliconization, dephosphorization, and decarburization reactions are to be carried out efficiently, an oxidation refining method is adopted, in which a spirit agent such as quicklime 8 is used together with oxygen gas or a solid oxygen source such as iron ore. A method of adding CaO to oxidize and remove phosphorus and fixing it in the slag with CaO has been adopted.

On the other hand, since the desulfurization reaction tends to proceed in a reducing atmosphere, simultaneous desulfurization reaction during dephosphorization using quicklime is not very promising. However, there is also a new method of adding a desulfurizing agent made of quicklime, calcium carbide, fluorite, etc. (for example, JP-A-53-70020).

However, in this method, the temperature of the hot metal is further reduced,
There is an increase in costs due to an increase in flux intensity, and
There were problems such as the need for desulfurization equipment. Furthermore, when the dephosphorization slag is not discharged, a method of adding soda ash has been developed.

However, even in this method, there is a cost problem since expensive refining flux is used, and the refractory material suffers from large amounts of erosion, which further increases the refining cost.

Means for Solving the Problems In view of these points, the present inventors invented a method for simultaneous desiliconization, dephosphorization, and decarburization in a single furnace, with the aim of significantly reducing refining costs.

The gist of this is that after adding appropriate amounts of refining agents such as quicklime and slag accelerators such as fluorite, sulfur is removed from the slag by blowing acetylating gas with an appropriately controlled oxygen potential. This is a method of removing silicon and further performing desilicification and dephosphorization to produce hot metal with a low silicon concentration, low phosphorus concentration, and low sulfur concentration. In order to control the oxygen potential of the blown gas, an oxidizing gas such as oxygen may be diluted with a gas such as nitrogen, a mixed gas of CO and CO2 may be used, or the atmosphere may be reduced in pressure. You can also place it below.

Generally, the desulfurization reaction in the slag-hot metal reaction using CaO proceeds by the following reaction.

C+ ((:aO) +S +(CaS) +ll:
0 -611 (1) Here, q: Carbon in hot metal (Cab) Calcium oxide in varnish slag CO: Carbon monoxide in gas Sulfur in mini hot metal (CaS) Represents calcium sulfide in varnish slag.

The reaction of formula (1) progresses more easily as the oxygen potential P (12) between the slag and hot metal is lower.

However, in general, when oxidative desiliconization and dephosphorization reactions occur in carbon-saturated molten iron, the oxygen potential Pψ at the slag-hot metal interface is approximately 1 G-12 to 1 g-14 atm. ) reaction does not proceed much, and when obtaining hot metal with low silicon concentration, low phosphorus concentration, and low sulfur concentration, when desulfurization is performed at the same time as desiliconization and dephosphorization, soda, which has a high flux cost, is used. The methods used were to use ash or to further separate desiliconization/dephosphorization and desulfurization refining.

Here, the present inventors focused on the vaporization reaction between gas and slag, and conducted a small-scale experiment using an electric furnace. By optimizing the oxygen potential in the blown gas, (2) It was discovered that the sulfur vaporization reaction shown by the formula occurs.

((:aS) +%(x+1)02-+(CaO)
+SOX Fist Fist ・ (1) Here, (Gas)
Calcium sulfide (Cab) in Nisslag Calcium oxide in Nisslag 02: Oxygen gas SOX: Represents sulfur oxide in gas.

In order to promote the reaction in equation (2), the higher the oxygen potential between the gas and slag, the faster the reaction progresses, so it is better to increase the oxygen potential in the blown gas, but on the other hand, the reaction in equation (1) progresses. To avoid this, first, refining flux is added to cause the reaction of formula (1) in which the metal in the hot metal transfers to slag, and then oxidizing gas is blown to promote the reaction of formula (2). I thought about that. In this experiment, an example of the experimental results is shown in Figure 1.
The amount of slag was 10 kg/l-p per unit amount of hot metal. Moreover, the amount of hot metal was 400g. The initial composition of the flux shown in Table 1 was used. The temperature is 1
The temperature was 400°C. In this case, it was confirmed that by initially using Ar as the blown gas and gradually increasing the oxygen concentration in the blown gas, desiliconization and dephosphorization could proceed without causing resulfurization. .

Table 1 Experimental conditions At Honbo, the oxygen potential at the gas-slag interface was kept higher than that at the slag-hot metal interface, and at the slag-hot metal interface,
The reaction of formula (1) progresses, while the reaction of formula (2) progresses at the gas-slag interface, so that desulfurization can proceed simultaneously with desiliconization and dephosphorization. In addition, by gradually increasing the oxygen potential of the blown gas,
In the early stage of refining, (i) the desulfurization reaction from hot metal to slag mainly occurs, and from the middle stage onward (Ill) the desulfurization reaction from slag to gas mainly occurs, and as a whole, the desulfurization reaction can be promoted at the same time as desiliconization and dephosphorization. .

In carrying out the present invention, it is possible to simply install gas blowing equipment by using a converter, hot metal pot, etc., without significantly modifying conventional equipment or installing new large equipment. It only needs to be modified, so it has the advantage of being able to easily produce high-purity hot metal at low cost. Furthermore, it is possible to produce high-purity hot metal without undesirable operational disadvantages such as temperature drop.

Furthermore, as shown in FIG. 2, the single method includes an inert gas flow path 5 and a gas supply source 6 in the oxygen flow path 7 for supplying inert gas to the top blowing lance 4 of the converter 3. It is possible to implement it by installing . Here, l is hot metal and 2 is a refining agent.

Also, as shown in FIG. 3, when using the hot metal ladle 8, a lance 4 for blowing gas and a gas supply source 6 are installed, and the oxidizing gas is poured over the refining agent 2 floating on the hot metal 1. This can be carried out by attaching an inert gas flow path 5 and an inert gas source 6 to the lance 4 for spraying and the oxygen flow path 7.

Furthermore, as shown in FIG. 4, it is also possible to use a torpedo car 9. Further, as the oxidizing gas, a mixed gas of oxygen 7 and inert gas 5 may be used, or a mixture of CO2 and CO2 may be used.
A mixture of gases may be used, or the atmosphere may be under reduced pressure.

EXAMPLES Next, examples of the present invention will be described in Table 2 and compared with the conventional method.

Example 1 shows the results of a test in which hot metal tsot was refined in a converter.
A gas containing 0% was blown, and after 10 minutes, the oxygen concentration in the gas was increased to 100% to promote desiliconization and dephosphorization, and the refining was completed in 20 minutes. As a result, the silicon concentration was 0.012%,
It was possible to obtain low-phosphorus hot metal with a manganese concentration of 0.04%, a phosphorus concentration of o, ots%, and a sulfur concentration of 0.004%.

Example 2 shows the results of a test in which 180 tons of hot metal was refined in a converter. In this case, in the early stage of refining, after adding refining flux, stirring was performed using bottom-blown gas, and after 3 minutes, 20% oxygen was added. This is a case in which the oxygen concentration in the blown gas is gradually increased so that the oxidizing gas containing the oxidizing gas is started to be blown and the oxygen concentration in the blown gas reaches 100% at the end of the 20-minute refining time. As a result, silicon concentration was 0.01%, manganese concentration was 0.06%, and phosphorus concentration was 0.0%.
High purity hot metal with a sulfur concentration of 0.08% and a sulfur concentration of 0.003% was produced.

Example 3 shows the results of a test in which 180 tons of hot metal was refined in a converter. In this case, in the early stage of refining, quicklime,
In addition to the refining flux made of fluorite, 5 kg/l-p of ferromanganese ore was added after 10 minutes from the start of refining.
An example will be shown in which Mn ore is reduced at the same time as desiliconization, dephosphorization, and desulfurization.

In this case as well, high-purity hot metal with a silicon concentration of 0.01%, a manganese concentration of 0.15%, a phosphorus concentration of 0.010%, and a sulfur concentration of 0.004% after refining was produced.

Example 4 is an example in which the final method is applied to a torpedo car. Refining flux consisting of quicklime and fluorite was added to 270 tons of hot metal in a torpedo car, and gas was blown onto the bath surface from a top blowing lance. To start with.

Spray at 20% oxygen concentration in the gas, after 5 minutes.
During the spraying, the oxygen concentration in the gas was gradually changed so that the oxygen concentration in the gas was 80%. Furthermore, quicklime and oxygen gas were blown in using a gas blowing lance to perform desiliconization and dephosphorization treatments.

Comparative Example 1 shows an example of refining using a conventional hot metal pretreatment method. Desiliconization is performed in a torpedo car, and after slag is removed, dephosphorization is performed in a separate station. There is iron loss, heat loss, temperature drop due to long processing time, melting of refractories, and desulfurization does not progress very much. Therefore, subsequent desulfurization of hot metal or desulfurization treatment at the molten steel stage was required.

Comparative Example 2 shows an example in which 160 tons of hot metal was refined in a converter. In this case, after adding a refining flux consisting of quicklime and fluorite at the initial stage of refining, pure oxygen gas was blown to perform refining. Therefore, desiliconization and dephosphorization were promoted, but since the oxygen potential at the slag-hot metal interface was increased from the early stage of refining, the desulfurization reaction hardly progressed.

Comparative Example 3 shows an example in which 180 tons of hot metal was refined in a converter. In this case, after adding refining flux consisting of quicklime and fluorite at the initial stage of refining, a mixture of oxygen and nitrogen containing 30% oxygen was added. This is the case when gas is blown, and the desiliconization and
Although dephosphorization is promoted, the desulfurization rate is low and the refining time is 4
It took a long time, 0 minutes.

(Margin below) Effect of the invention According to the present invention, refining can be performed efficiently.

[Brief explanation of the drawing]

Figure 1 shows an example of experimental results for verifying the present invention, and shows the transition of hot metal components. Figure 2 shows an outline of equipment when applying the present invention to a method for refining hot metal using a converter. An elevational view showing an example, FIG. 3, shows a setup for applying the present invention to a hot metal refining method using a hot metal pot! Elevation showing an example of 1.
The figure is an elevational view showing an outline of equipment when the present invention is applied to a method for refining hot metal using a torpedo car. i--Hot metal, 2-φφ refining 7 racks, 3a-Converter, 4-Gas blowing lance, 5-Inert gas,
6...Inert gas holder, 7...11 Oxygen gas, 8
...hot metal pot, 9...torpedo car.

Claims (1)

[Claims] When refining hot metal, a refining agent is added and a gas whose equilibrium oxygen partial pressure is controlled at 0.2 to 0.8 atmospheres is blown onto the slag surface to promote the vaporization desulfurization reaction between the gas and the slag. A hot metal refining method characterized by obtaining high-purity hot metal with low sulfur concentration, low phosphorus concentration, and low silicon concentration by performing desiliconization and dephosphorization treatment without discharging slag.