JPH01149914A - Method for protecting bottom blowing tuyere in refining vessel - Google Patents

Abstract

PURPOSE:To improve the durability of a tuyere and to give good refining effect by supplying oxygen gas from the bottom blowing tuyere at more than the specific pressure when molten metal reaches to the specific temp. at the latter period of blowing. CONSTITUTION:At the time of executing refining by bottom-blowing refining gas into the molten metal from the tuyere arranged at the bottom part of the vessel, when the temp. of the molten metal becomes at least 1,500 deg.C at the latter period of blowing, the oxygen gas is supplied from the bottom blowing tuyere at >=30atm. of the absolute pressure in the atm. at the inlet thereof. By this method, the durability of the tuyere is improved and the restraint effect for generating iron oxide is increased without causing to increase cost of the equipment and consumption of the energy.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a converter in which a part or all of oxygen gas for blowing is bottom-blown through tuyeres located below the bath surface of a molten metal bath. The objective is to effectively extend the life of the tuyere in the steel manufacturing process without interfering with the blowing operation.

(Prior art) In a converter for refining molten metal such as hot metal, oxygen gas for refining is blown into the tuyere provided at the bottom of the converter to stir the molten metal, which is the so-called bottom-blowing type. In the converter, melting and damage of the tuyeres is unavoidable, and there is a problem in durability. Therefore, in the past, the tuyeres were made of concentric double tubes, oxygen gas was blown into the inner tube, and hydrocarbons such as prospane gas were flowed between the one-way tube and the outer tube, and the hydrocarbons were thermally decomposed. It was common practice to cool the tuyere using the endothermic reaction heat generated by the tuyere.

The above method is an excellent method that makes it possible to stably blow pure oxygen gas into the molten bath through the tuyeres installed at the bottom of the converter. has adopted this method. However, in order to reduce the cost of converter refractories, especially the cost of large hearth refractories, it is strongly desirable to improve the life of the tuyere, which determines the life of the large hearth refractories. Currently, conventional techniques have not reached a satisfactory level in this regard.

In an attempt to extend the life of the tuyere, the inventors previously introduced at least 30% of oxygen or oxygen-containing gas at the tuyere inlet.
A method of blowing gas under high pressure of 0 kgf/cm" was proposed (see Japanese Patent Application Laid-open No. 87810/1983).

(Problems to be Solved by the Invention) By the way, the technique disclosed in the above publication is a method in which the gas to be blown into the molten metal is maintained at a high pressure throughout the period of blowing, so the equipment cost for pressurization increases. Although this method is advantageous in extending the life of the tuyere, it still poses a problem in terms of economic efficiency.

We have developed an effective method that solves the conventional problems mentioned above, improves the durability of the tuyeres provided at the bottom of the refining vessel, and also provides good results for refining molten metal. It is the purpose of this invention to propose.

(Means for Solving the Problems) The inventors conducted various experiments in order to improve the durability of the tuyere at the bottom of a refining vessel such as a converter without increasing equipment costs or 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, this invention provides a refining method in which refining gas is bottom-blown into a molten metal bath in a refining container from a tuyere provided at the bottom of the refining container. A method for protecting a bottom blowing tuyere in a refining vessel (first invention), characterized in that oxygen gas having an absolute pressure of 30 atmospheres or more at the inlet is supplied from the tuyere, and the present invention In addition to the refining method in which refining gas is bottom-blown into the molten metal bath in the refining container from a tuyere provided at the bottom of the container, inert gas is supplied from the tuyere during the first stage of blowing, and then during the latter stage of blowing. When the temperature of the molten metal is at least 1500℃
A method for protecting a bottom blowing tuyere in a refining vessel (second invention), characterized by supplying oxygen gas from the tuyere to the inlet at an absolute pressure of 30 atm or more when the temperature reaches ℃. .

The factors that determine the durability of the tuyeres include the temperature of the molten metal, the dimensions of the tuyeres, the flow rate ratio of oxygen gas and hydrocarbon gas, or the pressure and flow rate of oxygen gas, among others, the dimensions of the tuyeres and the oxygen The experiments described below have revealed that the gas blowing pressure has a significant effect on the tuyere life. Of course, the temperature of the molten metal during blowing is the biggest factor determining the durability of the tuyere, but the temperature of the molten metal is determined by the entire smelting and casting process, so it improves the durability of the tuyere. It is not possible to lower the temperature just for the sake of this. Further, the oxygen gas flow rate is determined from the viewpoint of performing the desired stirring to improve the refining reaction characteristics, and is not determined primarily from the viewpoint of the durability of the tuyere, as described above.

Therefore, in this invention, we first used a 5-ton scale test converter with various tuyeres of different sizes attached to the bottom of the container, and found that the typical components were C: 4.3%, S! 20.23%,
Mn: 0.32%, P: 0.11%, S: 0.021%
Blast furnace hot metal is continuously refined at a relatively high temperature for 25 charges to make it into molten steel with a carbon concentration of 0.08% or less and a temperature of 1,670 to 1,780°C. After refining, the tuyeres are collected and the The remaining length was measured and averaged over 25 charges, and the amount of wear on the tuyere per charge was investigated. In addition, in a similar blowing process, scrap is introduced from above the converter during the latter stage of blowing when the temperature of the molten steel rises, and the blowing process is carried out while preventing the temperature from rising excessively. The amount of tuyere wear was also investigated when blowing was performed continuously for 25 charges at a relatively low temperature of 1,580 to 1,610° C. at the end of blowing.

The tuyeres used in the experiment were all concentric double-tube tuyeres, with oxygen gas flowing from the inner tube and oxygen gas flowing between the outer tube and the inner tube to protect the tuyere. Propane gas was supplied at a concentration of 5%.

The results are shown along with the 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'/m
For 1n), it is advantageous to increase the gas pressure by reducing the diameter of the tuyere, etc., to improve the durability of the tuyere.
In particular, it was found that when the supply pressure is 30 atm or more, the amount of tuyere wear is about 50% or less compared to the normal blowing method at less than 10 atm.
In low-temperature blowing adjusted to 10℃, the supply pressure is 3.8-45
It was found that the loss amount was 0.65 to 0.40 in the atmospheric pressure range, indicating that the dependence of gas pressure on the tuyere loss amount was small.

Therefore, it is extremely effective to use high-pressure oxygen gas for blowing, which increases the temperature of the molten metal.

(Function) In this invention, the temperature of the molten metal rises, and the oxygen gas reaches a predetermined 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 early to middle stages of blowing, where the influence on the temperature is relatively small, oxygen gas at normal atmospheric pressure or an inert gas instead is supplied, so that the intended purpose can be advantageously achieved. You get it.

The reason why high-pressure oxygen gas is inhaled in the late stage of blowing when the temperature of the molten metal reaches at least 1500°C is to reduce the carbon concentration of the molten metal to 0.5% or less, and in addition to the carbon oxidation reaction. This is the period when the oxidation reaction of iron becomes active and the temperature of the molten metal rises rapidly, which not only prevents wear and tear on the tuyere, but also improves the stirring effect and improves the refining of the molten metal. This is because it is advantageous to give.

In addition, in this invention, an inert gas is used instead of oxygen gas, which reaches normal pressure until the latter stage of blowing.The reason for this is that the amount of wear on the tuyere is reduced, as shown in the examples below. It has the advantage of being the least susceptible to slag, and the amount of iron oxide in the slag is also small. However, in this case, an inert gas that does not have a direct refining effect compared to oxygen gas is used, so the cost of the inert gas is increased.

(Example) Four concentric double-tube tuyeres each have an oxygen gas flow path with an inner diameter of 5.5 mm at the bottom of the furnace and allow propane gas for tuyere protection to flow at a flow rate of 5% of the oxygen flow rate. 5 to 8 tons of scrap and 95 to 9 g of hot metal from the blast furnace are charged into a top-bottom blowing converter with a capacity of 100 tons, and normal decarburization and refining is performed under the conditions described below. The amount of wear and tear was investigated. In addition, the starting temperature of hot metal blowing in the above refining is 1230 to 1260°C, and the molten metal temperature at the end of blowing is 16
50~1710℃, and the carbon concentration of molten steel is 0.02~0
．． 05%, and the oxygen gas flow rate from the top blowing lance is 20ONm'/min until 0.5%C, and 0.5%
Below C, the speed was set to 15ONm3/min.

First, as treatment No. 1, in the section from the start of blowing to the middle stage of blowing, where the hot metal temperature is relatively low, the oxygen gas pressure at the tuyere crater was set at 3 to 7 atmospheres, and the flow rate per tuyere was set at 1.
5-2. 'lNm3/min, and the carbon concentration of the hot metal is 0.5% or less and the temperature is 150%.
When the temperature is expected to rise above 0°C, the above gas pressure is increased to 35°C.
~41 atm, oxygen flow rate per tuyere 11-12 Nm
'/min. The implementation rate of such blowing training is 93
After 250 charges of continuous blowing, the length of the tuyere was measured and the amount of wear of the tuyere per charge was 0.65 mff1.

Next, as Process No. 2, under the same conditions as the above Process No. 011, the pressure at the tuyere crater was increased to 3.
~7 atm, oxygen flow rate per tuyere 1.5~2. lN
In blowing when the setting was m37m1n, the average loss amount for 250 charges was 0.93 mm/charge.

From the above results, it was confirmed that according to the present invention, increasing the oxygen gas pressure at the tuyere inlet at the late stage of blowing, particularly at the final stage, when the molten steel temperature becomes high, provides a high tuyere protection effect. Next, as treatment No. 3, when the oxygen gas pressure at the tuyere inlet was set to 35 to 41 atm and the oxygen flow rate per tuyere was set to 11 to 12 Nm'/min throughout the blowing period, a charge of 250 After continuous blowing, the amount of wear and tear on the feathers is reduced,
It was 59mm/charge.

It is clear that when treatment Nα3 is applied, the effect of improving the amount of tuyere wear is smaller than that of treatment Nα1, despite using a large amount of high-pressure oxygen gas that consumes energy required for pressurization. .

Furthermore, as treatment Nα4, the temperature of hot metal is 1 from the start of blowing.
Until the temperature reaches 500°C, the tuyere inlet pressure is set to 6 to 9 atm, and the flow rate per tuyere is set to 1.5 to 2.0 atm. lNm3/mi
Using nitrogen gas set to n, then nitrogen gas at 35~
41 atm, flow rate per tuyere 11-12Nm37m
The same <25 when changing to oxygen gas that becomes in
When we investigated the average amount of wear at 0 charge, it was 0.51mm.
/ It was a charge. In Process No. 4, during the blowing of nitrogen gas, propane gas was used for cooling the tuyeres, and nitrogen gas equivalent to 5 to 10% of the flow rate of the inner pipe was flowed.

It was confirmed that treatment No. 4 was an excellent method in that the amount of wear on the tuyere was the smallest compared to Nos. 011 to 3 above. This is because the inert gas blowing period is long, so there is little melting loss of the tuyere, and during high-temperature blowing, the oxygen gas pressure is high, so wear and tear on the tuyere is prevented.

In Process Nos. 1 to 4, since the bottom-blown oxygen flow rate was different, the stirring power of the steel bath was naturally different, and the metallurgical reaction effect was also different. Comparing the iron concentration (%T, Fe) as iron oxide in the slag at the end of blowing as a typical characteristic value of the metallurgical reaction effect, it is 16.7 for Nα1.
%, 19.5% for Nα2, 15.9% for Nα3, N
For α4, it 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 bottom blowing gas in each treatment No., but treatments No. 1 and 4 protect the tuyeres even though the amount of high-pressure oxygen gas used is relatively small. No. 2 in terms of effectiveness and iron oxide production suppression effect.
Better than 1. It can be seen that although the amount of high-pressure oxygen gas used is large, it is very close to No. 3, which yields relatively good results. In carrying out the present invention, the diameter and number of tuyeres must be appropriately selected to obtain the necessary flow rate of bottom-blown gas from the viewpoint of improving the metallurgical reaction. It is important to ensure that the following can be obtained.

In addition, in this invention, as a second invention, inert gas is used during most of the period of blowing using low pressure gas, but the cost of using oxygen gas or inert gas during this period is determined. It should be determined by taking into consideration the effect of extending the life of the tuyere. In other words, oxygen gas is used as a gas for decarburizing molten steel, so there is no cost increase as a stirring gas, but inert gases such as nitrogen gas do not react with the steel bath, so there is no cost increase as a stirring gas. This is because it would require the following.

In addition, instead of the high pressure oxygen gas used in the latter stage of blowing,
It is also possible to use an inert gas, but with this method, the amount of inert gas used increases because the gas to be blown requires a large flow rate in the latter stages of blowing, especially at the end. Furthermore, if relatively inexpensive nitrogen gas is used, there is a concern that the nitrogen concentration in the molten steel will increase, so it is necessary to use expensive argon gas, which poses a problem in terms of economy.

(Effects of the Invention) Thus, according to the present invention, the durability of the bottom blowing tuyere can be advantageously increased without significantly increasing the equipment and energy costs 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 in refining molten metal is extremely high.

[Brief explanation of the drawing]

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

Claims (1)

[Claims] 1. In a refining method in which refining gas is bottom-blown into a molten metal bath in a refining container from a tuyere provided at the bottom of the container, the temperature of the molten metal in the latter stage of blowing is at least 1500°C. A method for protecting a bottom-blowing tuyere in a refining vessel, characterized by supplying oxygen gas having an absolute pressure of 30 atm or more at the inlet from the tuyere at the time when the bottom blowing tuyere is blown. 2. In a refining method in which refining gas is bottom-blown into the molten metal bath in the refining container from a tuyere provided at the bottom of the container, inert gas is supplied from the tuyere during the early stage of blowing, and then during the latter stage of blowing. A method for protecting a bottom blowing tuyere in a refining vessel, characterized in that when the temperature of molten metal reaches at least 1500° C., oxygen gas having an absolute pressure of 30 atmospheres or more at the inlet of the tuyere is supplied from the tuyere.