JP3496490B2 - Method of blowing hydrocarbon gas into molten metal - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for blowing hydrocarbon gas into a molten metal using a double pipe. It is widely known that it is effective to enhance the stirring of molten steel in order to efficiently advance decarburization refining in a converter. For this reason, current converters are equipped with a bottom blowing tuyere for the purpose of stirring molten steel in addition to the top blowing lance, which is the main oxygen supply source, and pass oxygen, hydrocarbon gas and inert gas through the bottom blowing tuyere. Injecting into molten steel. The inventors have previously proposed a tuyere having a triple tube structure in Japanese Patent Application Laid-Open No. Hei 5-214420, and degassing the tuyere by blowing hydrocarbon gas into the inner and outer tubes and oxygen into the middle tube. Although it has been shown that a large amount of inexpensive hydrocarbon gas can be blown in place of expensive inert gas as a means of increasing the stirring of molten steel during coal, there are the following problems. (1) There are three gas flow control systems per tuyere
The system is required and the equipment cost is high. (2) Even in the initial and middle stages of blowing, which has a large gas passage area and does not require a large amount of gas, the amount of gas required to prevent tuyere smelting (by applying gas pressure to prevent metal from entering) is simple. More than in the case of tube and double tube tuyere, gas cost rises. SUMMARY OF THE INVENTION An object of the present invention is to use a double tube tuyere to inject a large amount of hydrocarbon gas to stir molten metal and to obtain an effect equal to or greater than that of a triple tube tuyere. To provide a method for obtaining [0006] blowing year SUMMARY OF THE INVENTION performs blowing all tubes Ar triple tube, using LPG as the hydrocarbon gas blowing late, the inner tube LPG- middle tube O ₂ - outside The temperature change after switching to the tube LPG was investigated. [0007] The temperature transition was determined by embedding a thermocouple in the inner portion of the inner tube 50 mm in front of the surface in contact with the hot metal of the triple tube and measuring the temperature. The following findings (A) and ideas (B) were obtained from the results of the investigation of the temperature transition. (A) The LPG of the inner tube is
Double insulation by O ₂ and LPG in outer tube, LPG in inner tube has not reached the decomposition temperature. (B) Even if there is no double insulation as in the case of a triple tube, if the hydrocarbon gas in the inner tube can be kept at a decomposition temperature or lower by single insulation (single layer), the double tube is used. Also, similar hydrocarbon gas blowing is possible. As a means for realizing the idea of (B), a critical condition under which the hydrocarbon gas in the inner tube is not decomposed in the tuyere has been found as follows, and the present invention has been completed. That is, the present invention provides a method for blowing a hydrocarbon gas into a molten metal using a double tube tuyere comprising an inner tube and an outer tube.
Insulating gas is blown , and the ratio Q / Q ₀ of the hydrocarbon gas flow rate Q ₀ of the inner pipe to the insulating gas flow rate Q of the outer pipe is in the range of 0.05 to 1.0. Is the way. The preferred embodiments of the present invention include:
Injection of hydrocarbon gas from the bottom of the furnace at the time of bottom blowing refining is exemplified. FIG. 1 shows an example of a double-tube tuyere for blowing the bottom of a converter. The inner tube 1 and the outer tube 2 are installed at the bottom of the converter.
It consists of two pipes (made of stainless steel). In the present invention, the inner pipe is provided with a hydrocarbon gas 3,
An insulating gas 4 or a mixed gas of an insulating gas and a hydrocarbon gas is introduced into the outer tube. It is desirable to control the flow rate of each gas independently for each channel and gas type. The hydrocarbon gas is CH ₄ , C ₂ H ₆ , C ₃ H ₈ , C ₄ H
₁₀ or the like is used alone or as a mixed gas. The heat insulating gas includes an inert gas such as Ar or N ₂ , but CO, CO _2, etc., which are expected to have the heat insulating effect aimed at by the present invention, can be used alone or as a mixed gas. Inner tube (LPG = 3 to 12 Nm ³ / min) Outer tube (Ar = 0.1
FIG. 2 shows test results obtained by changing the flow rate (to 15 Nm ³ / min) (hereinafter, all flow rates indicate the flow rate per tuyere). As shown in FIG. 2, the flow rate of hydrocarbon gas (LPG) in the inner pipe is Qo (Nm ³ / min), and the heat insulating gas (Ar) in the outer pipe is
Let Q (Nm ³ / min) be the flow rate and organize Q / Qo by the flow rate ratio Q / Qo.
By controlling to 0.05 to 1.0, the tuyere wear rate can be kept low and stable operation is possible. The "pre-tuyere pressure" shown in FIG. 2 indicates the value of the gas pressure just before the tuyere, and is an index indicating the tuyere blocking condition. The lower the value, the smaller the pressure loss and the lower the gas source. Pressure 10kg / c
closer to m ² indicate that a blockage situation has deteriorated. Usually of "feather preoral pressure" no blockage is about 6kg / cm ^2. When the flow ratio Q / Qo is less than 0.05, the heat insulation effect of the outer pipe gas is significantly reduced, the temperature of the hydrocarbon gas (LPG) in the inner pipe rises above the decomposition temperature, and the hydrocarbon gas ( LPG) causes a decomposition reaction, and this endothermic reaction overlaps with the small outer tube heat insulation effect, lowering the temperature of the outer metal fittings, lowering the temperature of the refractory in contact with the outer metal fittings, and removing the refractory due to heat spall And the tuyere life is remarkably deteriorated. Further, mushrooms formed by solidification of molten iron due to supercooling grow excessively, the pressure in front of the tuyere increases, and stable operation becomes impossible. When the flow ratio Q / Qo exceeds 1.0, the amount of scattered particles of hot metal adhering to the converter furnace mouth increases, and the scattered particles reach the exhaust system, and the Fe concentration in the dust collection water rapidly increases. Increase.
If the amount of ingots attached to the furnace mouth of the converter increases, it becomes difficult to pour the hot metal into the converter. This necessitates the reduction of converter productivity. Further, when the amount of the scattered particles reaching the exhaust system increases, there arises a problem that the yield of molten iron decreases and the production cost increases. The flow ratio Q / Qo is preferably 0.1 to 0.5
It is. Also, during this time, there is almost no difference between the effects, so that there is no particular problem even if the blowing amount of the insulating gas is reduced. Therefore, from the viewpoint of gas cost reduction, the flow ratio is Q /
A place close to Qo0.1 is economical. The "iron yield" shown in FIG. 2 was compared with the increase / decrease% based on the average tapping yield in a triple pipe. CH ₄ , C ₂ H ₆ ,
A single or mixed gas of C ₃ H ₈ and C ₄ H ₁₀ is used, and a single or mixed gas of Ar, N ₂ , CO, and CO ₂ is used as the adiabatic gas type, but the upper and lower limits of the above Q / Qo are used. Has no effect. EXAMPLES Example 1 250 tons of hot metal (temperature 1200-1300 ° C.,
Components charged are shown in Table 1) to the converter, 850 nm ³ oxygen gas
/ lance (6 holes, inclination angle 15 degrees, throat diameter 48
mm, lance height 2.5m). [Table 1] In the first and middle stages of blowing, CO ₂ is passed through the inner and outer tubes from the four double tube tuyeres provided at the bottom of the converter, and the latter stage of blowing ([C] = 0.5% or less) ), LPG in the inner tube and CO _{2 in the} outer tube
And blown until [C] = 0.05%. Table 2 summarizes the results. A test incorporating the triple tube shown in Comparative Example 1 was conducted and compared with the present invention. Also, the running cost with the triple tube tuyere,
A comparison of equipment costs was made, but the value for a single pipe was used as a reference (1.
0). [Table 2] Invention Example 1 (Q / Qo = 0.06) to Invention Example 4
(Q / Qo = 0.9), the tuyere wear rate was 0.17 to 0.20 mm / ch, which was comparable to that of a triple pipe (the tuyere wear rate of Comparative Example 1 was 0.3 mm / ch). Further, as shown in Inventive Examples 5 to 7, under the condition that Q / Qo = 0.2 is constant, the tuyere wear rate is 0.17 mm / ch even when the type of the insulating gas is changed. It was constant. Comparative Example 2 (Q / Qo = 0.04), Comparative Example 3 (Q / Qo
= 1.2), the tuyere wear rates are 1.0 and 1.1 mm / ch, respectively.
And sooner. The gas cost of the double tube tuyere was about half that of the triple tube, and the equipment cost was as small as about 1/3. According to the present invention, the running cost and equipment cost can be reduced as compared with the conventional triple pipe, and hydrocarbon gas can be blown in at the same level as the triple pipe.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual diagram showing a structure of a tuyere of a double pipe and a method of using the tuyere. FIG. 2 is a graph showing a relationship between Q / Q ₀ , an iron yield index, and a tuyere pre-pressure. [Description of Signs] 1: Inner pipe, 2: Outer pipe, 3: Hydrocarbon gas, 4: Insulating gas

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C21C 5/48 C21C 7/072

Claims (1)

(57) [Claim 1] In a method of blowing a hydrocarbon gas into a molten metal using a double tube tuyere comprising an inner tube and an outer tube ,
Hydrocarbon gas from the pipe, heat insulating gas from the outer pipe
Blowing method blowing a hydrocarbon gas, wherein the hydrocarbon gas flow rate Q ₀ and the ratio Q / Q ₀ of the insulating gas flow rate Q of the outer tube of the inner tube is in the range of 0.05 to 1.0.