JPH0660343B2 - Method of protecting bottom blown tuyere in refining vessel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a converter in which a part or all of oxygen gas for blowing is bottom-blown through a tuyere located below the bath surface of a molten metal bath. In the steelmaking method, it is intended to effectively extend the life of the tuyere without hindering the blowing work.

(Prior Art) In a converter for refining molten metal such as hot metal, a so-called bottom blowing method is used, in which oxygen gas for refining is blown from the tuyere provided at the bottom of the converter to stir the molten metal. In the converter, melting and the like of the tuyere were unavoidable, and there was a problem in durability. Therefore, conventionally, the tuyere is a concentric double tube, oxygen gas is blown from the inner tube, while hydrocarbon such as propane gas is flown between the inner tube and the outer tube to thermally decompose the hydrocarbon. It was common to cool the tuyere by utilizing the heat of endothermic reaction.

The above method is an excellent method that allows stable blowing of pure oxygen gas into the molten bath through the tuyere provided at the bottom of the converter. Has adopted this method. However, in order to reduce the cost of the refractory of the converter, especially the cost of the bottom refractory, it is strongly desired to improve the life of the tuyere that determines the life of the bottom refractory. Rarely, the conventional technology has not reached a satisfactory level in this respect.

In an attempt to extend the life of the tuyere, the present inventors have previously proposed that oxygen or a gas containing oxygen be at least 30% at the tuyere inlet.
A method of blowing gas under a high pressure of kgf / cm ² has been proposed (see Japanese Patent Laid-Open No. 61-87810).

(Problems to be Solved by the Invention) By the way, the technique disclosed in the above publication is a system in which the gas to be blown into the molten metal is maintained at a high pressure over the entire blowing period, so the equipment cost for pressurization increases. Moreover, the large amount of energy consumption is advantageous for extending the life of the tuyere, but there is a problem in economic efficiency.

It is possible to solve the above-mentioned conventional problems and to improve the durability of tuyere provided at the bottom of the refining vessel, and to provide an effective method that also gives good results on the refining effect of molten metal. It is the object of the invention to propose.

(Means for Solving Problems) The inventors have conducted various experiments to improve the durability of tuyere at the bottom of a refining vessel such as a converter without increasing equipment costs and energy consumption. As a result of repeated studies, it was found that it is extremely effective to adjust the supply gas pressure at the tuyere to an appropriate range during blowing.

That is, the present invention is a refining method of bottom blowing a refining gas into a molten metal bath in a refining vessel from a tuyere provided at the bottom of the vessel, when the temperature of the molten metal at the latter stage of blowing reaches at least 1500 ° C. A method for protecting a bottom-blown tuyere in a refining vessel (first invention), characterized in that oxygen gas having an absolute pressure of 30 atm or more is supplied from the tuyere at an absolute pressure. In the refining method in which the refining gas is bottom-blown into the molten metal bath in the refining vessel from the tuyere provided at the bottom of the vessel, the inert gas is supplied from the tuyere in the first period of blowing, and then the molten metal is blown in the latter stage of blowing. At a temperature of at least 1500 ° C., oxygen gas having an absolute pressure of 30 atm or more at the inlet is supplied from the tuyere to protect the bottom-blown tuyere in the refining vessel (second invention) Is.

Factors that determine the durability of the tuyere include the temperature of the molten metal, the size of the tuyere, the flow ratio of oxygen gas to hydrocarbon gas, the pressure of oxygen gas, and the flow rate. It was revealed from the experiments described below that the gas injection pressure has a great influence on the tuyere life. Of course, the temperature of the molten metal during blowing is the most important factor that determines the durability of the tuyere, but since the temperature of the molten metal is determined by the entire refining and casting process, it improves the durability of the tuyere. The temperature cannot be lowered just because of this. Further, the oxygen gas flow rate is determined from the viewpoint of performing desired stirring in order to improve refining reaction characteristics, and is not uniquely determined in terms of the tuyere durability as described above.

Therefore, in the present invention, first, using a 5 ton scale test converter in which various sizes of tuyere are attached to the bottom of the container, the representative components are C: 4.3%, Si: 0.23%, Mn: 0.32.
%, P: 0.11%, S: 0.021%, blast furnace hot metal with a carbon concentration of 0.08% or less and a temperature of 1670 to 1780 ℃ is continuously smelted at a relatively high temperature for 25 charges. After the completion, the tuyere was collected, the remaining length was measured, and the average amount of 25 charges was used to investigate the amount of wear of the tuyere per charge. Also, although the same blowing as this, when the molten steel temperature rises in the latter stage of blowing, scrap is put in from above the converter,
The amount of tuyere wear when blowing is carried out continuously for 25 charges at a relatively low temperature, with the temperature of the molten steel at the end of blowing being 1580 to 1610 ° C, while preventing the temperature from rising excessively. Was also investigated.

The tuyeres used in the experiments were all concentric double-tube tuyeres. Oxygen gas flowed from the inner tube and the oxygen gas flow rate between the outer tube and the inner tube was to protect the tuyere. Propane gas of 5% was flowed.

The results are shown in table with tuyere size and oxygen gas pressure.
Shown in 1.

Figure 1 shows the data obtained in the experiment as a graph. From the figure, it can be seen that in high temperature blowing, when the oxygen gas flow rate per tuyere is constant (1.5 Nm ³ / min). However, increasing the gas pressure by reducing the diameter of the tuyere is advantageous for improving the durability of the tuyere, especially when the supply pressure is 30 atm or more, compared with the normal blowing method of less than 10 atm. It was found that the tuyere loss amount was about 50% or less, and in low temperature blowing where the molten steel temperature was adjusted to 1580 ℃ to 1610 ℃, the wear amount was 0.65 in the supply pressure range of 3.8 to 45 atmospheres.
It was found to be ~ 0.40, and the dependence of gas pressure on the tuyere wear amount was small.

Therefore, it is extremely effective to use oxygen gas having a high atmospheric pressure for blowing in which the temperature of the molten metal rises.

(Operation) In the present invention, the temperature of the molten metal rises, and oxygen gas which has a predetermined atmospheric pressure (30 atm) or higher only in the latter stage of blowing, which has a great effect on the life of the tuyere, In the relatively low temperature section from the first half to the middle term of blowing, where the influence is relatively small, the oxygen gas that becomes the normal pressure or the inert gas instead of this is supplied, so that the intended purpose can be achieved advantageously. Of.

Suction of high-pressure oxygen gas into the molten metal when the temperature of the molten metal reaches at least 1500 ° C in the latter half of the blowing is that the carbon temperature of the molten metal is reduced to 0.5% or less, and the addition of iron It is the time when the oxidation reaction becomes active and the temperature of the molten metal rises sharply, which prevents damage to the tuyere etc. and also enhances the stirring effect to give good results for refining the molten metal. Because it is advantageous to.

Further, in the present invention, the inert gas is used in place of the oxygen gas that reaches a normal atmospheric pressure until the latter half of the blowing, because the amount of wear of the tuyere is as shown in Examples described later. It is the smallest and has the advantage that the amount of iron oxide in the slag is also small. However, in this case, since an inert gas that does not have a direct refining action as compared with oxygen gas is used, the cost of the inert gas is required.

(Example) Four concentric double tube tuyere which has an oxygen gas passage with an inner diameter of 6.5 mm at the bottom of the furnace and is a mechanism for flowing propane gas for tuyere protection at a flow rate of 5% of the oxygen flow rate 5 to 8 tons of scrap and 95 to 9 of hot metal from the blast furnace in a 100 ton top and bottom blowing converter.
After charging 8 tons, normal decarburization refining was performed under the conditions described below, and the amount of tuyere wear was investigated after the completion of blowing. The blowing temperature of molten pig iron in the refining is 1230 to 1260 ° C, the molten steel temperature at the end of blowing is 1650 to 1710 ° C, the carbon concentration of the molten steel is 0.02 to 0.05%, and the oxygen gas from the upper blowing lance is further. The flow rate was 200 Nm ³ / min up to 0.5% C, and 150 Nm ³ / min below 0.5% C. First, as treatment No. 1, the oxygen gas pressure at the tuyere inlet was 3 to 7 atm, and the flow rate per tuyere was 1.5 to 2.1 in the section from the start of blowing, where the hot metal temperature was relatively low, to the middle stage of blowing. Set in the range of Nm ³ / min, and the carbon concentration of the hot metal is 0.5% or less, the temperature is 1500
When the temperature is expected to rise above ℃, increase the gas pressure to 35-41
The atmospheric pressure and the oxygen flow rate per tuyere were set to 11 to 12 Nm ³ / min. The tuyere length was measured after continuous blowing of 250 charges at which the blowing rate was 93%, and the amount of wear of the tuyere per charge was 0.65 mm.

Next, as the treatment No. 2, under the same conditions as the treatment No. 1, the pressure at the tuyere inlet was 3 to 7 atm and the oxygen flow rate per tuyere was 1.5 to 2.1 Nm over the entire blowing period. ^In blowing with the setting of ³ / min, the average loss of 250 charges is 0.93 m
It was m / charge.

From the above results, it was confirmed that according to the present invention, the tuyere protection effect is high when the oxygen gas pressure at the tuyere inlet is increased in the latter stage of blowing, particularly the last stage, when the molten steel temperature becomes high. Next, as treatment No. 3, the oxygen gas pressure at the tuyere inlet was 35 to 41 atm, and the oxygen flow rate per tuyere was changed over the entire blowing period.
When set to 11 to 12 Nm ³ / min, the tuyere loss amount after continuous blowing of 250 charges was 0.59 mm / charge.
When treatment No. 3 is applied, the effect of improving tuyere wear amount is smaller than that of treatment No. 1, despite the large amount of high-pressure oxygen gas that consumes energy required for pressurization. Is clear.

Furthermore, as treatment No. 4, the hot metal temperature is 150 after the start of blowing.
By the time the temperature reaches 0 ° C, nitrogen gas with the tuyere inlet pressure of 6-9 atm and the flow rate per tuyere of 1.5-2.1 Nm ³ / min was used, and then the nitrogen gas was 35-41 atm. Also, when the oxygen flow rate was changed to 11 to 12 Nm ³ / min per tuyere, the average wear amount of 250 charges was also investigated and found to be 0.51 mm / charge. In treatment No. 4, while blowing the nitrogen gas, the propane gas for cooling the tuyere was replaced with the nitrogen gas equivalent to 5 to 10% of the inner pipe flow rate.

It was confirmed that the treatment No. 4 was the smallest method in which the amount of wear on the tuyere was the smallest as compared with the above Nos. This is because the blowing time of the inert gas is long, so that the tuyere is less likely to be melted and damaged, and at the time of high temperature blowing, the oxygen gas pressure is high, so that the tuyere is prevented from being worn.

It should be noted that in Treatment Nos. 1 to 4, since the oxygen flow rates of bottom blowing are different, the stirring force of the steel bath is different as a natural result, and the metallurgical reaction effect is also different. As a representative characteristic value of the metallurgical reaction effect, when comparing the iron concentration (% T.Fe) as iron oxide in the slag at the end of blowing, No. 1 was 16.7% and No. 2 was
19.5%, No. 3 was 15.9%, and No. 4 was 16.1%.

The above results are summarized in Table 2 for easy understanding.

The iron concentration in the slag corresponds to the flow rate of the bottom-blown gas in each treatment No., but in treatment Nos. 1 and 4, the amount of high-pressure oxygen gas used is relatively small, but the tuyere Although it is superior to No. 2 in the protection effect of No. 2 and the effect of suppressing the production of iron oxide, and the amount of high-pressure oxygen gas used is large, it can be seen that it is very close to No. 3, which gives relatively good results. In practicing the present invention, the diameter and number of tuyere are appropriately selected so that the required flow rate of the bottom-blown gas can be obtained from the viewpoint of the effect of improving the metallurgical reaction. It is essential to obtain

Further, in the present invention, as the second invention, an inert gas is used in most of the period of blowing using a low-pressure gas, but the cost depends on whether oxygen gas or inert gas is used in this period. And the effect of extending tuyere life should be taken into consideration. That is, since oxygen gas is used as a gas for decarburizing molten steel, there is no increase in cost as a gas for stirring, but inert gas such as nitrogen gas does not react with the steel bath, so there is no cost as a gas for stirring. Because it will be necessary.

In addition, change to high pressure oxygen gas used in the latter stage of blowing,
Although it is possible to use an inert gas, in such a method, the amount of the inert gas used increases because the gas to be blown requires a large flow rate at the latter stage of blowing, especially at the latter stage. Further, when nitrogen gas which is relatively inexpensive is used, it is necessary to use expensive argon gas from the fear that the nitrogen concentration of the molten steel will increase, which is a problem in terms of economy.

(Effects of the Invention) Thus, according to the present invention, the durability of the bottom blown tuyere can be advantageously increased without significantly increasing the equipment cost and energy cost for increasing the pressure of the gas blown into the molten metal. be able to. Moreover, according to the present invention, the effect of suppressing the production of iron oxide is extremely high in the refining of molten metal.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the gas pressure at the tuyere inlet and the tuyere wear amount.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Kishimoto 1 Kawasaki-cho, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Yukio Takahashi 1 Kawasaki-cho, Chiba City Chiba Prefecture Kawasaki Steel Co., Ltd. Research headquarters

Claims (2)

[Claims] 1. A refining method in which a refining gas is bottom-blown from a tuyere provided at the bottom of a container into a molten metal bath in a refining container, and the temperature of the molten metal in the latter stage of blowing is at least 15
A method for protecting a bottom-blown tuyere in a refining vessel, which comprises supplying oxygen gas having an absolute pressure of 30 atm or more from the tuyere at the time of reaching 00 ° C. 2. A refining method in which a refining gas is bottom-blown into a molten metal bath in a refining vessel from a tuyere provided at the bottom of the vessel, wherein an inert gas is supplied from the tuyere in the first half of blowing and then blown. At the time when the temperature of the molten metal reaches at least 1500 ° C in the latter stage of smelting, oxygen gas whose atmospheric pressure at the inlet is 30 atm or more in absolute pressure is supplied from the tuyere. How to protect.