JPS58221210A - Preliminary treatment of molten iron - Google Patents

Abstract

PURPOSE:To compensate the decrease in the carbon content in molten iron by immersing a lance of double-pipe construction into the molten iron, blowing a treating agent for molten iron through the inside pipe and blowing gaseous hydrocarbon through the flow passage between the inside and outside pipes thereby preventing the erosion at the forward end of the lance. CONSTITUTION:A lance 8 of the double-pipe construction consisting of an inside pipe 1 and an outside pipe 2 is immersed in the molten iron 10 in a preliminary treatment vessel 9. A treating agent 11 for molten iron is supplied into the flow passage 3 of the inside pipe 1 of the lance 8 by using a carrier gas 12 and is blown into the iron 10 through an inside blow port 5. At the same instant, gaseous hydrocarbon 13 is supplied into the outside flow passage 4 formed between the pipe 1 and the pipe 2 of the lance 8 and is blown into the iron 10 through an outside blow port 6, whereby the molten iron is subjected to preliminary treatments such as desiliconization, dephosphorization and desulfurization. The erosion at the forward end of the lance 8 is prevented by the above-mentioned method; in addition, the content of the carbon in the molten iron decreased in the decarburization treatment is compensated and the heat source for refining in a converter, etc. is assured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot metal pretreatment method that is carried out for desiliconization, dephosphorization, and desulfurization of hot metal prior to decarburization refining in a converter, etc. The present invention relates to a hot metal pretreatment method using a so-called in-die injection method in which a pretreatment agent is blown into the hot metal.

As is well-known, hot metal pretreatment involves desiliconization, dephosphorization, and desulfurization prior to refining in a converter, etc., which reduces the load on subsequent refining in a converter, etc., and improves the efficiency of the steelmaking process and improves iron yield. The aim is to improve the production efficiency and reduce the basic unit of steelmaking auxiliary raw materials.

The processing agents used for hot metal pretreatment are soda carbonate (Na2co3) and quicklime (CaO).
In order to improve treatment efficiency, especially dephosphorization efficiency, for any type of treatment agent, it is necessary to effectively utilize the process in which the powder of the treatment agent floats through the hot metal. Therefore, recently, various so-called injection methods, in which processing agent powder is injected into hot metal, have been developed and put into practical use.

However, the hot metal pretreatment using the injection method as described above has the following various problems. That is, in hot metal pretreatment by the injection method, a lance is immersed in the hot metal, and a pretreatment agent is injected into the hot metal through the lance using nitrogen gas, oxygen gas, or a mixture of both as a carrier gas. Normal.

Here, since the dephosphorization reaction is an oxidation reaction, it is considered desirable to use a mixed gas with a high oxygen gas mixing ratio or pure oxygen gas as the carrier gas in order to improve the dephosphorization efficiency. However, when the oxygen gas mixing ratio is increased or when pure oxygen gas is used, the area around the lance tip becomes high temperature due to the exothermic reaction between these oxidizing gases and various components in the hot metal, leading to melting of the lance tip. As a result, it is often necessary to interrupt the injection of the processing agent powder in the middle of the pretreatment. Furthermore, when a mixed gas with a high oxygen gas mixing ratio or pure oxygen gas is used as a carrier gas, not only phosphorus, silicon, and sulfur in the hot metal but also a considerable amount of carbon are oxidized and removed, resulting in a decrease in the hot metal carbon concentration. 3. Carbon in the hot metal is a heat source in the subsequent converter blowing, so if the carbon concentration in the hot metal decreases in the hot metal pretreatment as described above, there will be a shortage of heat source in the converter blowing process, A problem arises in that it is difficult to maintain the steel bath temperature at a predetermined target temperature. Furthermore, in the desulfurization reaction of hot metal, it is known that a lower oxygen partial pressure P02 is more advantageous; however, as mentioned above, if a mixed gas with a high oxygen mixing ratio or pure oxygen gas is used, the P02 will be higher. There is a problem that this becomes extremely disadvantageous for the desulfurization reaction and the desulfurization rate decreases.

As mentioned above, in hot metal pretreatment using the conventional Indie Excine method, when a mixed gas with a high oxygen gas mixing ratio or pure oxygen gas is used as the carrier gas in order to increase the dephosphorization efficiency, (1) the lance There were drawbacks such as melting loss, (2) difficulty in converter blowing due to a decrease in carbon concentration in hot metal, and (3) decrease in desulfurization rate.

This invention was made in view of the above circumstances, and even when a mixed gas with a high oxygen gas mixing ratio or pure oxygen gas is used as the carrier gas for the hot metal treatment agent, it is possible to prevent lance erosion as much as possible. The purpose of this invention is to compensate for the decrease in carbon in hot metal, which is a heat source during converter blowing, and to prevent a decrease in the desulfurization rate.

That is, in the hot metal pretreatment method of the present invention, the lance for injecting the hot metal treatment agent has a double tube structure, and at the same time, the treatment agent is injected from the inner tube and from the flow path between the inner tube and the outer tube. It is characterized by blowing in hydrocarbon gas.

The hot metal pretreatment method of the present invention will be explained in more detail below.

In the method of this invention, as described above, a double-pipe lance is used as the lance that is immersed in the hot metal and into which the hot metal treatment agent is blown. Specifically, as shown in FIG. 1, for example, the outside of a straight inner tube 1 made of stainless steel, ordinary steel, etc. is surrounded by outer tubes 2 made of the same material concentrically at intervals, and the inner tube 1 and the flow path 4 between the inner tube 1 and the outer tube 2. A lance having an inner outlet 5 and an outer outlet 6 and a refractory 7 provided on the outer circumferential surface of the outer tube 2 may be used. Alternatively, as shown in FIG. 2 or 3, the lower end of the inner tube 1 is branched into an inverted T-shape or an inverted T-shape to form a left and right pair of inner air outlet 5 and outer air outlet 6 (5). You may also use a shiku lance.

In the hot metal pretreatment method of this invention, the above-mentioned two
The lower part of the lance 8 having a heavy pipe structure is immersed in hot metal 10 in a pre-treatment container 9 such as a hot metal charging pot or a pig iron mixing car, and a hot metal treatment agent 11 is introduced into the flow path in the inner pipe 1 of the lance 8 using nitrogen gas. ,
Alternatively, oxygen gas is supplied using a carrier gas 12 made of a mixture of these gases, and the hot metal treatment agent 11 is blown into the hot metal together with the carrier gas 12 from the inner blowing port at the tip, and at the same time the outer side of the lance 8 is Hydrocarbon gas (C
nHm) 13 is supplied, and the hydrocarbon gas 13 is blown into the hot metal from the outside blowing point at the tip.

As the hot metal treatment agent, a conventionally known quicklime-based flux or soda carbonate-based flux may be used. In other words, quicklime-based 7-luxes include fluxes whose main component is quicklime (CaO) mixed with iron oxides such as iron ore and mill scale, or fluxes containing fluorides such as CaF2 and CaC-9 as solvents.
The flux used is one (6) selected from chlorides such as No. 2, carbonates of alkali metals such as Na2CO3, or a mixture of two or more of them. As the soda carbonate flux, a flux containing soda carbonate (Na2C03) as a main component and iron oxide such as iron ore added thereto as necessary is used. In addition, as the carrier gas for blowing the hot metal treatment agent, K is an oxygen-nitrogen mixed gas with a high oxygen gas mixing ratio (for example, 0.260% or more) in order to increase the dephosphorization efficiency, as described above.
Alternatively, it is preferable to use pure oxygen gas, and in that case, the effects of the present invention can be expected most, but it is not necessarily limited to this, and can also be applied when a mixed gas with a low oxygen gas mixing ratio or nitrogen gas is used as the carrier gas. It is possible.

On the other hand, the hydrocarbon gas flowing into the outer flow path is propylene gas.
(C3HB) and butane (C4H10) are typical, and natural gas can also be used.

As mentioned above, the hydrocarbon gas flowing through the outer flow path of the lance is blown into the hot metal and decomposed at high temperature, but since the decomposition reaction is an endothermic reaction, it takes away the heat near the tip of the lance. Therefore, even if the carrier gas for the hot metal treatment agent blown in from the inner tube is oxygen gas or a mixed gas with a high oxygen concentration, melting damage due to heat generation at the tip of the lance can be effectively prevented.

In addition, when 1 mole of hydrocarbon gas (CH) is decomposed, n moles of carbon (C) are generated and dissolved in the hot metal, so the amount of carbon required for converter blowing following hot metal pretreatment is eliminated. The shortage of charcoal can be compensated for, and as a result, it becomes possible to secure the target temperature during converter blowing without any problem.

Furthermore, 1 mol of hydrogen gas is generated by decomposing 1 mol of hydrocarbon gas (CnHm). Usually the value of m is 8
Because of the above, hydrogen gas of about 4 moles or more is generated,
Therefore, the atmospheric carbon monoxide partial pressure PCO decreases, and the oxygen partial pressure P also decreases. Since the desulfurization efficiency also decreases, the desulfurization efficiency also improves.

Next, examples of the present invention and comparative examples using a conventional method will be described.

EXAMPLE A blowing experiment was carried out on 100 tons of hot metal in a hot metal charging pot or a hot metal mixing car using a double pipe lance. The material of the inner and outer tubes of the lance was ordinary steel, the inner diameter of the inner tube was 3Q+am, and the gap between the inner tube and the outer tube was 1 m. As a hot metal treatment agent, known CaO-based flux (Ca030
%, iron ore 60%, Ca F 210%), this was injected at 381 rt from the inner tube with a mixed gas of nitrogen gas and oxygen gas at a mixing ratio of 1:4, and at the same time the gap between the outer tube and the inner tube was Propane gas was blown in.

However, the mixed gas flow rate in the inner tube was 5 N771%in, and the propane gas flow rate in the outer tube was 0.25 Nmymin.

Comparative Example As in the previous example, a blowing experiment was carried out on 100 tons of hot metal using a single tube lance.

The pipe material of the lance was ordinary steel, its inner diameter was 3o-, and the same CaO-based flux as above was used as the hot metal treatment agent, and approximately the same amount of the same mixed gas as above was injected as the carrier gas.◎ In Examples and Comparative Examples, the components of hot metal before and after treatment, the temperature, and the amount of decrease in the amount of carbon in hot metal during treatment (ΔC
), and the number of heats the lance can withstand are shown in Table 1.

(9) As is clear from Table 1, in the comparative example using the conventional method using a lance with a single tube structure, the durability of one lance was 3 to 4 times, whereas in the example of the present invention Because there was less erosion at the tip of the lance, the service life was approximately twice as long. In addition, in the comparative example using the conventional method, decarburization (reduction in the amount of carbon in the hot metal) of about 0.5% was observed, making it difficult to maintain the target temperature in the subsequent converter blowing, whereas the example of the present invention In this case, the amount of carbon reduction in the hot metal was suppressed to within 0.1 inch, and as a result, it became easy to secure the target temperature in the subsequent converter blowing. Furthermore, it was confirmed that the desulfurization rate was better in the examples of the present invention than in the comparative examples using the conventional method.

As described above, according to the hot metal pretreatment method of the present invention, it is possible to prevent the melting loss of the tip of the lance, and also compensate for the decrease in the amount of carbon in the hot metal due to decarburization during treatment, so that the subsequent converter etc. By securing a heat source for the refining process, it is possible to easily maintain the target temperature of the steel bath, and furthermore, a variety of effects can be obtained, such as being able to prevent a decrease in the desulfurization rate.

(II) (10)

[Brief explanation of the drawing]

Figures 1 to 3 are cross-sectional views showing an example of a double-pipe structure lance used in the hot metal pretreatment method of the present invention, and Figure 4 shows a diagram in which the hot metal pretreatment method of the present invention is implemented. It is a schematic diagram showing an example of the situation. DESCRIPTION OF SYMBOLS 1... Inner tube, 3... Outer tube, 4... Channel between inner tube and outer tube, 7... Refractory, 8... Lance, 10...
-Hot metal, 11...Hot metal treatment agent, 12...Carrier gas consisting of nitrogen gas and/or oxygen gas, 13...Hydrocarbon gas. Applicant: Kawasaki Steel Corporation (12) Figure 1 Figure 2 Figure 3 Figure 4 53-

Claims (1)

[Scope of Claims] A method of pre-treating hot metal by immersing a waste in hot metal and injecting a hot metal treatment agent into the hot metal through the lance, prior to decarburization refining in a converter or the like, comprising: The lance has a double pipe structure, and the hot metal treatment agent is blown into the hot metal from the inner pipe of the lance using nitrogen gas and/or oxygen gas as a carrier gas, and at the same time, hydrocarbons are injected from the flow path between the inner pipe and the outer pipe. A hot metal pretreatment method characterized by blowing system gas into hot metal.