JP2877026B2 - How to protect the refining tuyere - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention, N ₂ of the molten metal container refining furnace for the purpose of agitation of the molten iron and molten steel, CO _2,
The present invention relates to a method for protecting a tuyere that blows Ar gas or the like.

[0002]

2. Description of the Related Art There are various types of containers for storing molten metal for the purpose of refining, keeping heat, storing, transporting, and the like. For example, as refining furnaces, in addition to LD converters, LF
Furnace, VAD furnace, AOD furnace, STB furnace, RH vacuum equipment, K
R vacuum devices and the like are known. Ladles, mixed iron furnaces, mixed iron wheels, tundishes and the like are known as containers other than smelting furnaces. These containers sometimes or occasionally need to be stirred, and a mechanical stirring method or a gas stirring method is employed. Among them, when the gas stirring method is adopted, generally, a single tube, a double tube and an SA (Sin
A method using a metal pipe such as a tuyere (gle Annular) tuyere, MHP (Multi Hole Drug),
It is classified into a method using a refractory such as PE (Permable Element) and a perforated nozzle (from the Iron and Steel Institute of Japan, 100th and 101st Nishiyama Memorial Technical Lecture: "Recent trends in steelmaking technology using agitation").

[0003] In the gas stirring by blowing inert gas from the bottom tuyere of the above molten metal vessel, as shown in FIG. The metal is solidified at the upper part of the tuyere 3 by the cooling action, and forms a metal lump called mushroom 5. And inside the mushroom 5, there is a thin venting path 6
Is formed, and the blown gas 4 is ejected into the molten metal 2 through the gas vent path 6, and rises as bubbles. However, depending on the state of the mushroom 5, the gas vent path 6 may not be formed sufficiently, and may be blocked at a considerable frequency, so that stable gas blowing may not be achieved. Also, in the gas stirring of the molten metal container,
In addition to the problems described above, the behavior of the gas jet injected into the molten metal, particularly the bottom strike (back attack) due to the downward flow immediately after the injection, is large, and as shown in FIG. There is a problem that the furnace bottom refractory 1 is severely melted or cracked.

[0004] As a method of preventing the gas stirring tuyere of the molten metal vessel from being melted, a tuyere provided to blow a fluid for refining or stirring into the molten metal is provided as follows.
A tuyere (JP-B-56-52100) in which the ratio of the inner peripheral length of the cross section to the circumference of a circle having an area equal to the inner peripheral cross-sectional area is 1.07 or more. A gas injection nozzle provided on a side wall, wherein an outer tube is fitted and fixed at an appropriate interval between the core body and the outside of a core body located at a central portion, thereby forming a ring-shaped gas discharge flow. A nozzle having a passage formed therein (Japanese Patent Laid-Open No. 57-114623) has been proposed.

[0005]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Publication No. Sho 56-52.
The tuyere disclosed in Japanese Patent Publication No. 100 is intended to prevent the erosion of the tuyere by reducing the impact by suppressing the occurrence of the back attack, and to extend the life of the tuyere and the refractory in the vicinity of the tuyere by forming a mushroom. Absent. Further, the nozzle disclosed in Japanese Patent Application Laid-Open No. 57-114623 has an outer tube fitted and fixed to the outside of a core located at a central portion thereof with an appropriate gap between the core and the core. The mushroom is made porous by forming a gas discharge flow path of
Although it is intended to reduce the pressure loss in the mushroom and suppress the occurrence of back attack, the interval between the outer tube and the core is not specified, and slightly in the embodiment, the back pressure of the nozzle and the outer tube Only the relationship between the spacing between the core and the nozzle blockage during blowing is shown.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks of the prior art and to form an appropriate mushroom in a tuyere portion in an operable gas injection pressure range, so that the tuyere and a refractory in the vicinity of the tuyere can be formed. It is an object of the present invention to provide a method for protecting a bottom blowing tuyere for refining, which can extend the life of the bottom.

[0007]

Means for Solving the Problems The present inventors have conducted various tests and studies on the quantification of the shape of the bottom blowing tuyere for refining and the state of mushroom formation in order to achieve the above object. As a result, cooling with the bottom blown gas is necessary to prevent melting of the tuyere, but thermal stress in the bottom refractory generated by cooling the bottom blown gas is harmful to spalling suppression. In addition, since the bottom blown gas amount is originally determined by the refining characteristics, it is necessary to match factors that are inconsistent with the life extension of the tuyere and the refractory near the tuyere. Also, the formation of mushrooms in the tuyere part of the bottom blow, the larger the amount of mushrooms formed, the greater the pressure loss in the mushrooms,
Although the blowable gas flow rate area is narrowed, the effect of suppressing tuyere erosion is increased. On the other hand, if the formation amount of the mushroom is small, the pressure loss amount in the mushroom is small, and the blowable gas flow rate region is wide, but the tuyere erosion suppression effect is small.

[0008] That is, it is considered that the larger the amount of mushrooms formed, the more effective the tuyere protection effect is. However, the increase in pressure loss due to the mushrooms restricts the flow rate of the blown gas, so that the mushrooms must be formed within an operable range. There is. Furthermore, as a result of further study, it was found that the amount of mushrooms produced can be controlled by the heat balance of the tuyere shape, and the present invention has been achieved.

That is, according to the present invention, an outer tube is fitted and fixed to an outer inner tube of a core located at a central portion with an appropriate gap provided between the inner tube and the outer tube, thereby forming a ring-shaped gas discharge passage. In the method for protecting a bottom blowing tuyere for refining having a formed gas blowing nozzle, the following (1)
The inner and outer diameters of the inner tube and the outer tube having a value obtained by dividing the heat receiving rate determined by the following equation (2) by the heat removal rate determined by the following equation (3) is 20 to 40. And a method for protecting a bottom blowing tuyere for refining. Heat index = heat rate / heat extraction rate (1) heat rate ^{_{= D 0 2 - (D 1}} 2 -d 0 2) (2) Equation heat extraction rate _{= (0.13 × D 1 × V} 0.8) / ( ^{_{D 1 2 -d 0 2) 2}} (3) equation However, D _0: the outside diameter of the outer tube (mm), D _1: inside diameter of the outer tube (mm), d _0: the outside diameter of the inner tube (mm), d ₁ : inner diameter of inner tube (mm), V: gas flow rate (Nm ³ / hr)

[0010]

[Function] The mushrooms are generated by the tuyere heat balance,
That is, the heat receiving index by the above equation (1), that is, the heat receiving index by the above equation (2), is used to quantify the change in the heat balance due to the tuyere shape because it is affected by the heat received from the molten steel and the cooling by the blown gas. The value obtained by dividing the obtained heat receiving rate by the heat removal rate obtained by the equation (3) was used as an index of mushroom formation. The heat receiving speed was the tuyere cross-sectional area excluding the slit portion, and the heat removal speed was the convection heat removal speed by gas. Then, as a result of arranging the mushroom pressure loss amount by the heat receiving index, as shown in FIG. 1, it was found that the mushroom formation amount could be controlled by the heat balance by the tuyere shape. When the heat receiving index is less than 20, the pressure loss (kg / cm ² ) of the mushroom becomes too large, and sufficient molten steel stirring is impossible. Therefore, if the heat receiving index is lowered within the operable mushroom pressure loss range and an appropriate mushroom is formed, the tuyere metal can be blown without direct contact with the molten steel, and the tuyere can be melted. Can be suppressed.

In the present invention, based on the flow rate of the bottom blown gas, the heat receiving index obtained by the above equation (1), that is, the heat receiving rate obtained by the above equation (2) is calculated by the heat removal rate obtained by the above equation (3). By selecting the inner and outer diameters of the inner and outer pipes, the value of which is obtained by dividing by 20 to 40, an appropriate mushroom is formed, and the tuyere fitting can blow gas without directly contacting the molten steel Thus, it is possible to suppress erosion of the tuyere hardware.

[0012]

【Example】

Example 1 150 Ton / charge, 19 charges / day, blowing time 25 minutes, tapping temperature 1675 ° C., four bottom-blowing tuyere type box-type four top-bottom-blowing converters, and a heat receiving index of 21, 33, 46 A test wing formed by inserting and fixing an outer tube to an outer inner tube of a core body located at a central portion with an appropriate gap between the inner tube and the inner tube, and forming a ring-shaped gas discharge channel at a bottom portion. The amount of N ₂ and CO ₂ blown from the four bottom-blown test tuyeres was
ax350Nm ³ / hr, the non-blowing in 50 Nm ³ / hr, top-blown oxygen amount is blow early 5 to 10 nm ³ / Ton, blowing metaphase 20-25 nm ³ / Ton, the blow end 40
When refined by blowing at 45 Nm ³ / Ton,
The mushroom resistance was measured at the beginning of blowing, during the middle of blowing, at the end of blowing, and during the tailing phase. The result is shown in FIG. The amount of N ₂ and CO ₂ blown from the four test tuyeres was Max 350 Nm ³ / hr during blowing and 50 during non-blowing.
Nm ³ / hr was constant.

As shown in FIG. 2, it was estimated that the smaller the heat receiving index was, the higher the gas resistance due to the mushroom was, and that a large mushroom was formed. The mushrooms formed in each tuyere grow from the early stage of blowing to the last stage of blowing, dissolve at the last stage and become the lowest at the tailing stage. The relationship between the mushroom pressure loss during the slag period based on the heat receiving index of each tuyere and the gas flow rate at each tuyere was investigated. The result is shown in FIG. As shown in FIG. 3, as compared with the tuyere with the heat receiving index 46, the mushroom pressure loss amount increases about 1.5 times in the tuyere with the heat receiving index 33 and about 4 times in the tuyere with the heat receiving index 21. Further, with respect to the tuyere mushrooms collected during the converter repair, it was visually confirmed that the smaller the heat receiving index, the larger the amount of mushrooms formed.

Example 2 The converter of Example 1 was used, and heat receiving indices 21, 33, and 46 were used.
The outer tube is inserted and fixed in the outer inner tube of the core located at the center of the and 105 with an appropriate gap between the inner tube and the outer tube.
Using a test tuyere formed with a ring-shaped gas discharge channel at the bottom, refining was performed under the same conditions as in Example 1, and the state of erosion of the tuyere by a laser method in the converter was measured. FIG. 4 shows the results. In addition, FIG. 4 shows the erosion rate index at the bottom of the furnace without the influence of the tuyere as A. As shown in FIG. 4, it is shown that the use of tuyeres having heat receiving indices of 20 to 40 can suppress the melting loss rate index to be substantially the same as the melting rate index A at the furnace bottom without tuyere influence.

[0015]

As described above, according to the method of the present invention, the amount of mushrooms formed in the tuyere is determined by the heat balance by the tuyere shape, that is, the value obtained by dividing the heat receiving speed by the heat removal speed, ie, the heat receiving index. By controlling, a proper mushroom can be formed, and without limiting the gas flow rate range from the tuyere, it is possible to suppress the melting loss of the tuyere and extend the life.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a heat receiving index and a pressure loss amount of a mushroom.

FIG. 2 is a graph showing changes in the heat receiving index of the tuyere and the resistance of the mushroom at the beginning of blowing, during the middle of blowing, at the end of blowing, and at the tailing stage.

FIG. 3 is a graph showing a relationship among a tuyere heat receiving index, a gas flow rate, and a mushroom pressure loss amount.

FIG. 4 is a graph showing a relationship between a heat receiving index of a tuyere and a erosion rate.

FIG. 5 is a schematic sectional view showing a mushroom formed in a tuyere.

FIG. 6 is a schematic sectional view showing the state of erosion of the tuyere and the refractory near the tuyere.

[Explanation of symbols]

 1 Furnace refractory 2 Molten metal 3 Tuyere 4 Gas 5 Mushroom 6 Degassing path

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C21C 5/48 C21C 5/34 C21C 7/072 F27B 1/16 F27D 3/16

Claims (1)

(57) [Claims] 1. An outer tube is fitted and fixed to an outer inner tube of a core body located at a central portion with an appropriate gap between the inner tube and the outer tube.
In the method for protecting a bottom blowing tuyere for refining having a gas injection nozzle formed with a ring-shaped gas discharge flow path, a heat receiving index according to the following equation (1) based on the bottom blowing gas flow rate;
That is, the value obtained by dividing the heat receiving rate determined by the following equation (2) by the heat removal rate determined by the following equation (3) is 20.
A method for protecting a bottom blowing tuyere for refining, comprising selecting inner and outer diameters of an inner pipe and an outer pipe of up to 40. Heat index = heat rate / heat extraction rate (1) heat rate ^{_{= D 0 2 - (D 1}} 2 -d 0 2) (2) Equation heat extraction rate _{= (0.13 × D 1 × V} 0.8) / ( ^{_{D 1 2 -d 0 2) 2}} (3) equation However, D _0: the outside diameter of the outer tube (mm), D _1: inside diameter of the outer tube (mm), d _0: the outside diameter of the inner tube (mm), d ₁ : inner diameter of inner tube (mm), V: gas flow rate (Nm ³ / hr)