JP5463623B2 - Brick structure of converter bottom blowing tuyere - Google Patents

Description

  The present invention has a gas injection pipe for refining gas, and is composed of a tuyere brick made of magnesia carbon brick and a tuyere surrounding brick made of magnesia carbon brick surrounding the tuyere brick, It is related with the brick structure of the bottom blowing tuyere installed in the bottom part.

  In a converter that performs hot metal decarburization and dephosphorization, and further iron smelting reduction refining, a bottom blowing tuyere for blowing a gas for refining is installed at the bottom. The tuyere is usually composed of tuyere bricks having a metal gas blowing pipe inside and tuyere surrounding bricks surrounding the tuyere bricks. From the gas blowing tube, Ar gas, nitrogen gas or the like is blown as a stirring gas, or oxygen gas is blown as a decarburization reaction gas. The tuyere brick and the tuyere surrounding brick are generally made of magnesia carbon brick because they are excellent in erosion resistance and wear resistance. In the present invention, all gases used in refining or refining, such as stirring gas and decarburization reaction gas, are defined as refining gas.

  In the bottom blowing tuyere of this structure, room temperature, that is, low-temperature gas is blown from the gas blowing pipe, so that the tuyere brick and the tuyere surrounding brick are cooled by the gas passing through the gas blowing pipe. In particular, the cooling of the tuyere bricks is remarkable, and a temperature difference occurs in the tuyere bricks themselves, and a large temperature difference tends to occur between the tuyere bricks. Due to the thermal stress due to this temperature difference, cracks and the like occur in the tuyere brick, and damage to the tuyere brick proceeds. In addition, gas back-attack is also generated, so that damage to the tuyere bricks is promoted, resulting in reduced durability of the bottom-blown tuyere. Many proposals have been made to solve this problem.

  For example, in Patent Document 1, “in a bottom blowing tuyere composed of a gas blowing pipe and a tuyere brick surrounding the gas blowing pipe, the gas blowing pipe includes a graphite pipe and a metal pipe inserted therein. A bottom blow tuyere having a three-layer structure composed of a long fiber reinforced heat insulating layer provided on the outer surface side of the graphite pipe is disclosed. According to Patent Document 1, it is described that abnormal melting loss of the gas blowing pipe is eliminated, cooling of the tuyere bricks is suppressed, the wear rate of the tuyere can be reduced, and the lifetime of the refining furnace can be extended. ing.

Patent Document 2 states that, in a bottom-blown tuyere composed of a carbon-containing tuyere brick and a carbon-containing tuyere surrounding brick, the carbon content of the tuyere brick and the tuyere surrounding brick is set to Ct and When expressed as Cb, 100 mass%>Ct> 0 mass% and 100 mass%>Cb> 0 mass%, and [ΔL = −225.921 + 15.951 Ct + 0.905 Cb−0.304 Ct ² +0.189 Cb ² ] A “brick structure that is a combination of Ct and Cb with which ΔL determined by the equation is 60 or less” is disclosed. Specifically, for example, when the carbon amount (Cb) of the tuyere surrounding brick is set to 20% by mass, the carbon amount (Ct) of the tuyere brick is about 18.7% by mass or less or about 34% by mass or more. Is reasonable. According to Patent Document 2, by setting the above-described carbon content, the gap between the tuyere brick and the tuyere surrounding brick can be set small. It is described that the polling damage does not occur and the durability of the tuyere brick can be greatly improved.
JP-A-10-280027 JP 2003-261374 A

  Despite the above proposals, the actual situation is that the tuyere bricks are still not damaged and the durability of the bottom-blown tuyere is not improved.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tuyere brick made of magnesia-carbon brick having a gas blowing pipe for refining gas, and surrounding the tuyere brick, magnesia・ Provides a brick structure for converter bottom-blown tuyere that suppresses damage to tuyere bricks and can withstand long-term use in bottom-blown tuyers composed of carbon bricks. It is to be.

  A brick structure of a converter bottom blowing tuyere according to the first invention for solving the above-mentioned problem has a gas blowing pipe for blowing a refining gas, and a tuyere brick made of magnesia carbon brick, A bottom-blown tuyere brick structure that is installed at the bottom of a converter and surrounds the tuyere brick, and has a carbon content of the tuyere brick. Lower than the carbon content of the perimeter of the brick, so that the thermal expansion coefficient of the tuyere brick is relatively large compared to the thermal expansion coefficient of the perimeter of the tuyere and the thermal conductivity of the tuyere brick is lower. It is characterized by being relatively small compared to the thermal conductivity of the brick around the mouth.

  In the brick structure of a converter bottom blow tuyere according to the second invention, the difference between the carbon content of the tuyere brick and the carbon content of the bricks around the tuyere is 5% by mass or more. It is characterized by being.

  According to the present invention, in a bottom-blown tuyere composed of a tuyere brick made of magnesia carbon brick and a tuyere surrounding brick made of magnesia carbon brick surrounding the tuyere brick, The thermal expansion coefficient is larger than the thermal expansion coefficient of the bricks around the tuyere and the thermal conductivity of the tuyere bricks is smaller than the thermal conductivity of the bricks around the tuyere, so the tuyere bricks are compared with the bricks around the tuyere Even though the temperature is low, the thermal expansion of the tuyere bricks is larger than that of the bricks around the tuyere, and the tuyere bricks are located at the boundary between the tuyere bricks and the bricks around the tuyere. Constrained by the surrounding bricks, thereby a compressive force acts on the tuyere bricks, the thermal stress generated by the temperature difference of the tuyere bricks is canceled by the compressive force, and the occurrence of cracks in the tuyere bricks is suppressed, The durability of the bottom blowing tuyere is improved.

  Hereinafter, the present invention will be specifically described.

  The inventors of the present invention have a bottom blowing feather having a gas blowing pipe, and a tuyere brick made of magnesia / carbon brick and a tuyere surrounding brick made of magnesia / carbon brick surrounding the tuyere brick In order to improve the endurance of the mouth, the damage situation of tuyere bricks in an actual furnace was examined and analyzed in detail. As a result, the main cause of damage of tuyere bricks is the occurrence of cracks due to thermal stress in tuyere bricks, and the occurrence of cracks causes damage within a range exceeding several tens of millimeters from the operating surface side at once. I understood that.

  Therefore, the cause of this crack was investigated. FIG. 1 shows a schematic view of a part of a converter in which a bottom blowing tuyere is arranged at the bottom, and FIG. 2 shows a schematic view taken along line X-X ′ of FIG. 1. In FIG. 2, the work bricks around the bottom blowing tuyere are not shown and are omitted.

  As shown in FIGS. 1 and 2, the converter includes an iron shell 6 that forms an outer shell, a permanent brick 10 that is lined on a portion that contacts the iron shell 6 inside the iron shell 6, and an inner side of the permanent brick 10. And a work brick 9 as a consumable member that is lined inside. In the figure, the work brick 9 and the permanent brick 10 are one-layered, but may be two-layered or more. A bottom blowing tuyere 1 is provided at the bottom of the converter through the work brick 9 and the permanent brick 10 and fitted to the work brick 9 and the permanent brick 10. Stirring gas such as Ar gas, nitrogen gas, carbon dioxide gas, and oxygen gas for decarburization reaction is blown into the iron bath in the furnace as a refining gas, and the iron bath is stirred or refined. Yes. In FIG. 1, only one bottom blowing tuyere 1 is shown, but a plurality of bottom blowing tuyere 1 is provided at the bottom of the converter.

  The bottom blowing tuyere 1 includes a gas blowing pipe 2, a tuyere brick 3 provided so as to surround the gas blowing pipe 2, a tuyere surrounding brick 4 surrounding the tuyere brick 3, and the above-described stirring gas or And a gas introduction pipe 5 for supplying a gas for refining. The stirring gas or the refining gas introduced through the gas introduction pipe 5 is blown into the iron bath from the gas blowing pipe 2.

  The iron skin 6 is provided with a flange 7, and the bottom blowing tuyere 1 is inserted into the converter through the opening of the flange 7 and held by the tuyere presser cover 8. The tuyere brick 3 and the tuyere surrounding brick 4 are made of magnesia carbon brick. When the bottom blow tuyere 1 is molded, first, the gas blowing pipe 2 and the tuyere brick 3 are compression molded, and then the tuyere surrounding brick 4 is compression molded around the molded tuyere brick 3. Thus, the whole is integrally formed.

  The bottom blowing tuyere 1 shown in the figure has one gas blowing pipe 2, but the bottom blowing tuyere 1 is limited to such a structure (referred to as “single tube tuyere”). What is necessary is just to select suitably according to the objective. For example, the gas blowing tube 2 may be a single multiple tube (referred to as “multiple tube tuyere”) or a structure having a plurality of gas blowing tubes 2 (referred to as “porous tuyere”). .

  In the bottom blowing tuyere 1 having such a configuration, when normal temperature refining gas is blown from the gas blowing pipe 2 in a state where the molten iron or molten steel is accommodated in the converter, the gas blowing pipe 2 is cooled by the refining gas, Accordingly, the tuyere brick 3 around the gas blowing tube 2 is also cooled, and the tuyere brick 3 becomes cooler than the tuyere brick 4.

  Considering the transfer of heat in the length of the brick (lining depth) to the tuyere brick 3 in use, the heat of the iron bath in the furnace is supplied from the working surface (exposed surface inside the furnace). However, since heat transfer does not reach a steady state within the refining treatment time, a temperature difference occurs in the depth direction of the tuyere brick 3. As a result, the amount of thermal expansion is relatively small in the low temperature interior compared to the amount of thermal expansion of the brick on the working surface side where the temperature is high. It is done.

  FIG. 3 shows the relationship between the temperature and the coefficient of thermal expansion in magnesia / carbon brick. As shown in FIG. 3, the coefficient of thermal expansion increases in proportion to the increase in temperature, and the coefficient of thermal expansion increases as the carbon content decreases. FIG. 3 also shows the thermal expansion coefficient of magnesia brick.

  The direction of thermal expansion in the bottom blowing tuyere 1 is the direction from the center position in the longitudinal direction of the bottom blowing tuyere 1 toward the outside, that is, the direction toward the work brick 9 and the permanent brick 10 around the bottom blowing tuyere 1. It is. Therefore, when the tuyere brick 3 and the tuyere brick 4 are made of the same material, or when the carbon content of the tuyere brick 3 is higher than the carbon content of the tuyere brick 4, the tuyere brick 3 has a lower temperature, the amount of thermal expansion of the tuyere brick 3 is less than that of the tuyere brick 4, and the binding force of the tuyere brick 3 by the tuyere brick 4 is reduced.

  As the binding force becomes weaker, it is concluded that cracks occur due to thermal stress or the like in the portion where the temperature inside the tuyere brick 3 is 1000 ° C. or less, and damage to the tuyere brick 3 progresses. It was. That is, it has been found that the main cause of the crack in the tuyere brick 3 is a decrease in the binding force of the tuyere brick 3 due to the tuyere surrounding brick 4 resulting from the difference in thermal expansion.

  From these examination results, in order to suppress the occurrence of cracks in the tuyere brick 3, it is to make the thermal expansion amount of the tuyere brick 3 larger than the thermal expansion amount of the tuyere surrounding brick 4, and for that purpose, At least the thermal expansion coefficient of the tuyere brick 3 needs to be higher than the thermal expansion coefficient of the tuyere brick 4, and in order to suppress the temperature drop of the tuyere brick 3, the heat conduction of the tuyere brick 3 It was found that lowering the rate is also effective. As a result, the thermal expansion of the tuyere brick 3 is larger than that of the tuyere surrounding brick 4.

  Increasing the thermal expansion coefficient and lowering the thermal conductivity of the tuyere brick 3 means that the carbon content of the magnesia carbon brick constituting the tuyere brick 3 is the same as the magnesia carbon brick constituting the tuyere brick 4. This is achieved by lowering the carbon content. Therefore, the tuyere brick 3 was composed of magnesia / carbon brick having a carbon content of 15% by mass, and the tuyere surrounding brick 4 was composed of magnesia / carbon brick having a carbon content of 20% by mass, and an actual test was performed.

  As a result, the tuyere brick 3 is a magnesia carbon brick having a carbon content of 15% by mass, and the perimeter of the tuyere 4 is a magnesia carbon brick having a carbon content of 20% by mass. It was confirmed that the wear rate was reduced as compared with the case where the tuyere brick 3 and the tuyere surrounding brick 4 were both magnesia carbon bricks having a carbon content of 20% by mass.

  The present invention was made on the basis of the above test results, and has a gas blowing pipe 2 for blowing a refining gas, a tuyere brick 3 made of magnesia carbon brick, and surrounding the tuyere brick 3, In the brick structure of the bottom-blown tuyere 1 composed of carbon bricks and around the tuyere 4 and installed at the bottom of the converter, the carbon content of the tuyere brick 3 is the carbon content of the bricks around the tuyere 4 The thermal expansion coefficient of the tuyere brick 3 is relatively larger than the thermal expansion coefficient of the tuyere surrounding brick 4, and the thermal conductivity of the tuyere brick 3 is lower than the quantity. 4 is relatively small compared to the thermal conductivity of 4.

  When the present invention is applied, it is sufficient that the difference in carbon content between the tuyere brick 3 and the tuyere surrounding brick 4 is 5% by mass or more. However, in the present invention, the thermal expansion amount of the tuyere brick 3 needs to be larger than the thermal expansion amount of the tuyere surrounding brick 4, and the temperature difference between the tuyere brick 3 and the tuyere surrounding brick 4 is large. If it is small, the thermal expansion amount of the tuyere brick 3 can be made larger than the thermal expansion amount of the tuyere surrounding brick 4 even if the difference in carbon content is less than 5% by mass. In view of the above, the carbon content may be made different. Conversely, when the temperature difference between the tuyere brick 3 and the tuyere surrounding brick 4 is large, the difference in carbon content must be increased, but a difference in carbon content of 25% by mass is sufficient. is there.

  According to the present invention, the thermal expansion amount of the tuyere brick 3 is larger than the thermal expansion amount of the tuyere brick 4 although the temperature of the tuyere brick 3 is lower than that of the tuyere brick 4. The tuyere brick 3 is constrained by the tuyere surrounding brick 4, whereby a compressive force acts on the tuyere brick 3, and the thermal stress generated by the temperature difference of the tuyere brick 3 is canceled by the compressive force, The occurrence of cracks in tuyere brick 3 is suppressed, and the durability of bottom-blown tuyere 1 is improved.

  In the bottom-blown tuyere shown in FIG. 1, the tuyere brick is composed of magnesia carbon brick with a carbon content of 15% by mass, and the brick around the tuyere is composed of magnesia carbon brick with a carbon content of 20% by mass, An actual machine test (test level 1) was conducted. For comparison, an actual machine test (test level 2) in which both the tuyere brick and the tuyere brick were made of magnesia carbon brick having a carbon content of 20% by mass was also conducted. Table 1 shows the quality characteristics of the magnesia carbon bricks used.

  Evaluation of wear suppression of tuyere bricks was carried out by periodically measuring with a laser profile meter and using the wear rate determined from the numerical change between measurements. Comparing the wear rate at the test level 1 and the test level 2, as shown in FIG. 4, the test level 1 improved the wear rate by about 8% compared to the test level 2.

  Thus, it was confirmed that the durability of the bottom blowing tuyere was improved by applying the present invention.

It is the schematic which shows a part of converter with the bottom blowing tuyere arrange | positioned at the bottom part. It is the schematic by the X-X 'arrow of FIG. It is a figure which shows the relationship between the temperature in a magnesia carbon brick, and a thermal expansion coefficient. It is a figure which compares and shows the wear rate in the test level 1 and the test level 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bottom blowing tuyere 2 Gas blowing pipe 3 Tubular brick 4 Brick around bricks 5 Gas introduction pipe 6 Iron skin 7 Flange 8 Tuyere presser cover 9 Work brick 10 Permanent brick

Claims (1)

To have the gas blowing tube for blowing the refining gas into the tuyere bricks made of magnesia-carbon bricks, a member surrounding the該羽port bricks directly, and tuyere surrounding bricks made of magnesia-carbon bricks, a bottom-blown tuyeres that consists from the can and the tuyere brick and the gas blowing tube compression molded, then the tuyere surrounding bricks is compression molded around the tuyere bricks molded, In the brick structure of a bottom blow tuyere installed at the bottom of a converter in which the tuyere brick and the brick around the tuyere are integrally formed, the carbon content of the tuyere brick is the brick around the tuyere 5 wt% or more lower than the carbon content, by this, relatively large compared coefficient of thermal expansion of the tuyere bricks to the coefficient of thermal expansion of the tuyere surrounding bricks and, thermal conductivity of the tuyere brick Relative to the thermal conductivity of bricks around tuyere Characterized in that again, brick structure of the converter bottom tuyeres.

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