JP2003313609A - Method for disposing refractory material in regenerator of hot stove - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for disposing high-alumina bricks for preventing the occurrence of cracks in checker bricks in lower parts of a regenerator of a hot stove. <P>SOLUTION: In the method for disposing the refractory material in the regenerator of the hot stove for heating air blasted into the blast furnace, the high- alumina bricks having a cristobalite content of ≤10 mass% are placed at parts where the working temperature is ≤300°C. Preferably, high-alumina bricks having cristobalite in the above content and mullite in a content of ≥10 mass% are placed. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractory material distribution method for preventing brittleness of a brick installed in a hot-air stove thermal storage chamber for heating air blown to a blast furnace.

[0002]

2. Description of the Related Art A hot-blast stove uses a large amount of refractory material for a checker brick, which is a heat storage medium, along with its furnace wall, dome, burner, and the like. In recent blast furnaces, an external combustion hot-air stove, in which a combustion chamber and a heat storage chamber are separated, has become the mainstream.

FIG. 1 is a schematic view of a vertical section of an external combustion hot stove. A burner 2 constructed of a refractory is installed at the base of the combustion chamber 1. Further, checker bricks, which are heat exchange media, are stacked in the heat storage chamber 3. In the external combustion hot stove, combustible gas is burned in the combustion chamber, the generated high temperature gas is introduced into the heat storage chamber through the connecting pipe 4, and the checker brick in the heat storage chamber is heated to store heat. Then, the air 5 is sent to the heat storage chamber at the timing of blowing air to the blast furnace, and this is heated by the heat stored in the checker bricks to become high-temperature air, which is sent as hot air 6 to the blast furnace.

The hot gas that heats the checker brick is
Since it is guided to the heat storage chamber through a connecting pipe that connects the upper part of the combustion chamber and the upper part of the heat storage chamber, temperature distribution occurs in the checker bricks piled in the heat storage chamber, and the temperature becomes higher at the upper part of the heat storage chamber, that is, the higher the checkered stack. In addition, the temperature of the checker bricks at the same position changes depending on the operation time. That is, when the checker brick is heated (combustion period),
Comparing the time when the air is blown to the blast furnace (air blowing period), the temperature of the checker brick is lower than that during the combustion period because heat is transferred to the air that is blown during the air blowing period. Since the combustion period and the blast period are alternately repeated, the temperature of the checker brick repeatedly repeats increasing and decreasing.

The temperature of the checker brick also changes depending on the temperature of the air blown into the blast furnace. For example, when the temperature of air blown to the blast furnace is high, that is, when hot air is blown, it is necessary to increase the heat storage amount of the checker bricks, and therefore the temperature distribution of the checker bricks generally shifts to the high temperature side.
On the other hand, in the case of low temperature air blowing, the temperature distribution of the checker brick shifts to the low temperature side. For these reasons, when the temperatures of the checker bricks in the same part are compared, it becomes the highest in the combustion period of high temperature blast and the lowest in the blast period of low temperature blast.

By the way, the checker bricks in the heat storage chamber are
Since it is always under high temperature and is piled up, compressive stress acts due to the load of bricks,
Creep is likely to occur. It should be noted that creep is a time-dependent plastic deformation and is a phenomenon in which the amount of deformation increases with the passage of time.

The creep phenomenon is one of the causes of damage to the checker brick because the checker brick is destroyed when the amount of deformation increases. As a measure against this,
A method is adopted in which the material of the brick is selected in consideration of creep resistance and the material is distributed. Bricks distributed as checker bricks include types such as silica bricks, high-alumina bricks, and clay bricks.

Among these types of bricks, silica bricks have the highest creep resistance and are therefore used for the upper checker bricks in the highest temperature range. Next, the creep resistance of the high-alumina bricks decreases in the order of the clay bricks. Among these bricks, the clay brick has the poorest creep resistance, but it is cheap and economical, so that it is used for the checker brick in the low temperature region where creep hardly occurs as described later.

The characteristics of silica bricks are their excellent creep resistance at high temperatures and their expansion characteristics. Since the variation of the expansion coefficient of silica brick in the temperature range of 600 ° C or higher is extremely small, even if a rapid temperature change is applied at 600 ° C or higher, it is less likely to be broken by thermal shock. But 60
If the temperature is less than 0 ° C, the expansion coefficient changes greatly and is easily broken by thermal shock.
Limited to a range of 0 ° C or higher.

As described above, the temperature distribution of the checkered bricks changes depending on the operation time and the temperature of the air blown to the blast furnace, and the temperature is the lowest during the air blow period of low temperature air blow. Silica bricks can be used in the part in the heat storage chamber where the temperature is 600 ° C. or higher even in the blowing period of this low-temperature air blowing, but in the parts below 600 ° C., destruction due to thermal shock occurs, and silica brick cannot be used. Even in the area where this silica brick cannot be used, the temperature rises to 1000 ° C. or higher during the high temperature air blowing period, and the risk of creeping increases. Therefore, as the checker brick at such a position, a high-alumina brick having creep resistance is often used next to silica brick. The change in the expansion coefficient of high-alumina bricks is not as rapid as that of silica bricks, and is less likely to be destroyed by thermal shock. The operating temperature range of high alumina bricks is approximately 1100 to 1400 ° C.
Clay brick is used below ℃.

Clay brick 110 having poor creep resistance
The reason why it can be used in a temperature range of 0 ° C. or less is that even clayey bricks hardly cause creep in this temperature range. However, the clay brick may include cristobalite, which is one of the SiO ₂ crystals.

Cristobalite causes an α-β type transition accompanied by a large volume change in a low temperature range. This transition temperature has a range and is generally set to 200 to 210 ° C, but it is set to 180 to 270 ° C depending on the literature. Shinagawa Technical Report, vol. 17 (1971), P23, it is reported that the brick becomes brittle when the clay brick containing cristobalite is repeatedly heated and cooled at about 200 ° C. In this report, when seven types of clay bricks including cristobalite were subjected to a thermal cycle of 140 to 380 ° C., there was no apparent change in appearance,
It is described that the brick became brittle because the air permeability, elastic modulus and bending strength changed, and the volume of cristobalite changed.

Also, in the third and fourth Shiraishi Memorial Lectures (1983) edited by the Iron and Steel Institute of Japan, P80 uses checker bricks in the lower end region of the heat storage chamber with high-alumina bricks to prevent brittleness of the bricks. It has been reported that the life of the hot stove has been significantly improved.

However, if a high-alumina brick is simply used as the checker brick in the lower end region of the heat storage chamber, there is a problem that it is difficult to stably prevent cracking of the brick.

[0015]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above problems and to prevent cracking of bricks stably when using high alumina bricks as checker bricks in the lower region of the heat storage chamber. It is intended to provide a method for distributing a refractory material for a hot-blast stove heat storage chamber.

[0016]

Means for Solving the Problems In order to achieve the above-mentioned objects, the present inventors have studied the problems of the prior art and have obtained the following findings.

A) When the cristobalite content in the high-alumina brick is 10 mass% or less, brittle brittleness due to the transition of cristobalite can be prevented even under heating / cooling conditions in a temperature range of 300 ° C. or less. . b) When the cristobalite content in the high-alumina brick is 10 mass% or less, the mullite content is 10 mass% or more, whereby the embrittlement resistance of the brick is further improved. The present invention has been completed based on the above findings, and the gist thereof is a method for distributing a refractory material shown below.

(1) A refractory material distribution method for a hot-blast stove heat storage chamber for heating blast air to a blast furnace, wherein a high-alumina brick with a cristobalite content of 10% by mass or less is applied to a site at a working temperature of 300 ° C or less. A method for distributing refractory materials in a hot-air stove thermal storage room.

(2) A refractory material distribution method for a hot-blast stove heat storage chamber for heating blown air to a blast furnace, wherein a high-alumina brick having a cristobalite content of 10% by mass or less is provided from the bottom of the hot-blast furnace. A refractory material distribution method for a hot-blast stove heat storage chamber, which is arranged within 10 m.

(3) The above-mentioned (1) or (2) in which a high-alumina brick containing 10% by mass or more of mullite is arranged.
The method for distributing a refractory material in a hot stove heat storage chamber according to any one of 1.

In the present invention, the term "air" means not only normal air having an oxygen concentration of 21% by volume, but also air having a higher oxygen content, air having a higher nitrogen content, Moisture-adjusted air and pure oxygen are collectively referred to.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The refractory material distribution method of the present invention will be described in detail below. (1) Confirmation of cristobalite and mullite The inventors of the present invention conducted X-ray diffraction analysis on a plurality of high-alumina bricks and clay bricks to investigate the intrinsic mineral phase. Cristobalite was present in some of the bricks. Mullite was present in all high-alumina bricks.

In order to investigate the effect of this cristobalite on the properties of bricks, the coefficient of linear thermal expansion of these brick materials was measured. As a result, the clay bricks
An abnormal increase in expansion coefficient due to the transition of cristobalite was observed near 200 ° C.

The high-alumina brick in which the presence of cristobalite was found to have an abnormal increase in expansion coefficient similar to that of clay brick, and as described later, there was a difference between the abnormal increase in expansion coefficient and the amount of cristobalite. Was found to be correlated.

On the other hand, no abnormal increase in expansion coefficient was observed in the high-alumina brick in which cristobalite was not present.

From the above facts, even in the case of high-alumina bricks, if there is a brick material in which cristobalite is present and a temperature change is given at around 200 ° C., cristobalite causes a volume change as in the case of clay brick. I got the idea that it may cause brittleness of the brick.

Next, the influence of mullite was investigated.

Mullite is a complex oxide having a chemical composition of 3Al ₂ O ₃ .2SiO ₂ , and its coefficient of linear thermal expansion is smaller than that of alumina. Although mullite was present in all high-alumina bricks, the mullite content in the bricks showed a correlation with the expansion coefficient, and the expansion coefficient decreased with the increase of the mullite content.

As described above, the checker brick material in the hot stove heat storage chamber is periodically heated and cooled. At this time, a difference occurs in the expansion amount between the surface and the inside of the checker brick, and when the stress (thermal stress) generated by the difference in the expansion amount is equal to or higher than the fracture stress of the brick, cracks occur. In order to reduce this thermal stress, it is desirable that the expansion coefficient of the brick is low, which suggests that the high-alumina brick having a high mullite content has high resistance to thermal shock.

Therefore, the cause of the presence of cristobalite in the high-alumina brick was examined from the viewpoint of raw materials used and manufacturing process.

The high alumina bricks and the clay bricks are both refractory materials using Al ₂ O ₃ —SiO ₂ type raw materials. High-alumina bricks use artificial raw materials such as sintered alumina, fused alumina, and sintered mullite, or natural raw materials with high alumina content such as bauxite, shale shale, and pyrophyllite, either alone or mixed together. .
Although artificial raw materials have high alumina purity, they are expensive, so cheap natural raw materials are often used in the manufacture of brick materials.

Further, natural raw materials such as bauxite, shale shale and pyrophyllite contain SiO ₂ as an impurity. This SiO ₂ often reacts with Al ₂ O ₃ during calcination of the raw material or firing of the brick material to form a stable complex oxide such as andalusite or mullite. Mullite found in high-alumina bricks is presumed to have arisen in this way. However, depending on the chemical composition of the raw material, the firing temperature, etc., Si that was not consumed in the formation of this composite oxide
It is estimated that O ₂ remains as cristobalite.

In the present invention, the term "high-alumina brick" refers to a high-alumina refractory brick according to JIS R2305, which contains 45 mass% of alumina as a chemical component.
Percentage of more than%.

"Clay brick" means Al ₂ O _3-
This refers to refractory clay, which is a SiO ₂ -based material, and brick made from chamotte, which is obtained by calcining this. It is presumed that the refractory clay decomposes during firing and unreacted SiO ₂ is produced as cristobalite. (2) Effect of bricks on embrittlement Based on the above results, we investigated the relationship between the cristobalite content in high-alumina bricks and the embrittlement due to the volume change of cristobalite, and found the mullite in high-alumina bricks. The relationship between the content and the brittleness of bricks due to thermal shock was also investigated.

The method for investigating the embrittlement by cristobalite is as follows. A brick heated at 300 ° C. for 20 minutes is immersed in hot water at 100 ° C. for 10 minutes to rapidly cool it, and heat is applied so that cristobalite causes a volume change around 200 ° C. It was done by applying a shock. Then, the heating and the rapid cooling were set as one cycle, a total of 10 cycles of thermal shock were applied, and after drying, the bending strength of the brick was measured. At the same time, the bending strength without thermal shock was also measured, and according to the following equation (1),
The rate of change in bending strength due to thermal shock was determined.

Bending strength change rate (%) = ((strength after thermal shock-strength before thermal shock) / strength before thermal shock) × 100 (1) In addition, the brick material at this time The amount of mullite is approximately 30% by mass
Then, brick materials with different cristobalite contents were selected. The contents of cristobalite and mullite were determined by the internal standard method of X-ray diffraction analysis.

FIG. 2 shows the relationship between the cristobalite content of high alumina bricks and the rate of change in bending strength due to thermal shock. According to the results of the figure, there is a correlation between the cristobalite content and the bending strength change rate due to thermal shock, and the bending strength change rate decreases as the cristobalite content increases.

Therefore, the high-alumina brick material may contain cristobalite as well as the clay brick, and the high-alumina brick is simply used instead of the clay brick in the lower end region of the heat storage chamber of the hot stove. However, it was found that it is impossible to completely prevent brittle brittleness caused by cristobalite.

Next, the limit value of the cristobalite content in high alumina bricks was examined. The checker brick installed in the hot-blast stove is always in a state of being subjected to compressive stress, and the checker brick in the lower end region of the heat storage chamber, which is the lowest layer of the checker stack, is subjected to the greatest compressive stress.

A compressive stress of 1.0 MPa was continuously applied to the brick material subjected to the thermal shock by the above method at room temperature for 50 hours, and after the stress was removed, the rate of change in height was calculated by the following formula (2). The added compressive stress of 1.0 MPa corresponds to the compressive stress in the lower end region of the checker brick stack having a height of about 40 m.

Height change rate (%) = ((height of brick after test−height of brick before test) / height of brick before test) × 100 ... (2) FIG. 3 shows the relationship between the cristobalite content in high-alumina bricks subjected to thermal shock and the rate of change in brick height. It can be seen that as the cristobalite content increases, the height change rate of the brick decreases, and when the content exceeds 10 mass%, the height change rate decreases to -0.5% or less and further deteriorates. .

The height of the checker brick itself is 200 mm.
A degree of shrinkage of 0.5% corresponds to a shrinkage amount of about 1 mm. The checker bricks piled at the lower end of the heat storage room, which is subject to a temperature change of around 200 ° C, are several meters in height, so the total amount of shrinkage of the checker brick piles is 20 meters.
It becomes ~ 30 mm. Then, when the step difference generated in the checker brick stack due to the contraction reaches 20 to 30 mm, the checker brick stack may be collapsed.

The cristobalite content is 10 mass.
In the case of a high-alumina brick having a content of more than 10%, the occurrence of cracks was observed after the test, whereas in the case of a brick having a content of 10% by mass or less, no crack was observed.

From these results, it was clarified that the brittleness of the brick due to the transition of cristobalite does not occur and the problem can be solved if the high-alumina brick with the cristobalite content of 10% by mass or less.

Next, the influence of mullite in high alumina bricks was investigated. Investigations were conducted for high-alumina bricks with a cristobalite content of 10 mass% or less and a different mullite content, and for a brick material with a cristobalite content of more than 10 mass% and a different mullite content. It was carried out in two cases. In each case, the variation in cristobalite content was 2 mass.
Brick material was selected to be within%.

As in the case of investigating the effect of the cristobalite content, the operation of giving a thermal shock by rapidly cooling a brick heated to 300 ° C. to 100 ° C. was carried out.
The bending strength before and after applying thermal shock is measured,
The rate of change in bending strength was calculated from the equation (1).

FIG. 4 shows the relationship between the mullite content and the bending strength change rate in high alumina bricks. The symbol □ in the figure represents the case of high-alumina brick with a cristobalite content of 10 mass% or less, and the symbol ○ in the figure represents the high-alumina brick with a cristobalite content of more than 10 mass%. Represents the case.

It is clear that when the cristobalite content is 10% by mass or less, the flexural strength change rate increases with the increase of the mullite content, and the flexural strength is less likely to decrease. On the other hand, when the cristobalite content exceeds 10% by mass, no clear relationship was observed between the mullite content and the bending strength change rate.

From these results, when the cristobalite content of the high-alumina brick is 10% by mass or less, the influence of the mullite content in the brick becomes obvious, while the cristobalite content is 10% by mass. It has been found that, when it exceeds, the effect of the cristobalite content appears rather than the effect of the mullite content.

Further, the upper limit of the mullite content in the high alumina brick was investigated. The investigation was performed on a high-alumina brick having a cristobalite content of 10% by mass or less, by applying stress after applying thermal shock, and measuring the rate of height change of the brick at that time.

FIG. 5 shows the relationship between the mullite content and the height change rate of the brick in the high-alumina brick with the cristobalite content of 10% by mass or less. The height change rate of all bricks exceeded -0.5%, but the height change rate of the bricks increased with the increase of the mullite content, and increased when the mullite content was 10 mass% or more. The rate of change is
It became larger than 0.4%.

From the above test results, the inventors of the present invention made brittle brittle by setting the content of mullite to be 10% by mass or more when the cristobalite amount is 10% by mass or less in the high alumina brick. We have found that it can be further suppressed. (3) Reasons for limiting numerical values in the present invention Cristobalite content: 10% by mass or less Cristobalite content in high alumina refractory is 10
If it is at most% by mass, cracks will not occur even if heating and cooling are repeated at around 200 ° C., which is the transition temperature of cristobalite, and the height change rate caused by applying compressive stress is also at least −0.5%. . Therefore, the cristobalite content is set to 10% by mass or less.

Mullite content: 10% by mass or more Cristobalite content in high alumina refractory is 10
When the content of the mullite is 10% by mass or less and the mullite content is 10% by mass or more, the resistance to embrittlement is further increased. Therefore, the mullite content is set to 10% by mass or more.
On the other hand, there is no particular deterioration in the physical properties of the brick due to the increase in the mullite content, but Al ₂ O ₃
The SiO ₂ -based raw material is relatively expensive, and the use of a large amount of this leads to an increase in the price of the brick. Therefore, the mullite content in the brick is preferably 70% by mass or less.

Operating temperature: 300 ° C. or less When the minimum operating temperature is higher than 300 ° C., no cristobalite transition occurs, and thus no cracking of bricks occurs due to the transition. Therefore, the operating temperature is set to 300 ° C. or lower.

Further, in the case of a large hot stove, the above temperature range corresponds to a range within 10 m in height from the bottom surface of the heat storage chamber. Therefore, the distribution position of high-alumina bricks is 10m.
The range was as follows.

[0056]

Example The brick material used in the above evaluation was placed in the lower region of the hot-air stove thermal storage chamber for 6 months, and a test was conducted to investigate the brittleness of the brick. [Test target hot blast stove] The heat storage chamber of the hot blast stove used in the test has the following types and specifications.

-Type: external combustion hot air stove-Checker receiving material: from the ground to a height of 5 m-Checker brick loading: Height above ground 5-35 m [Brick material dimensions and installation position] -Brick material shape: Cylinder with an outer diameter of 50 mm and a height of 50 mm ・ Types of high-alumina bricks: 10 types (change in mineral content) ・ Brick installation position: 5 m above ground level (= receiving surface)
7.5m, 10.0m and 12.5m at 4 places ・ Install a thermocouple with a brick at each installation position, measure the temperature change, collect the brick after the test, and collect the following items. went. [Crack occurrence status] -By visual inspection-Crack evaluation: Large crack occurrence: When a crack with a width of 0.4 mm or more is recognized, With crack occurrence: When a crack with a width of less than 0.4 mm is recognized, no crack occurs : When there is no visible crack. [Compression test] ・ Test temperature: normal temperature ・ Compressive stress: 1.0 MPa ・ Stress load time: 50 hours ・ After stress removal, the height change rate of the brick material is measured, and the height from the ground is 12.5 m In the position of, the minimum temperature is 3
The temperature was 10 ° C., no crack was observed in any of the brick materials, and no shrinkage occurred.

On the other hand, at a position where the height from the ground is 10 m or less, the maximum temperature is 300 ° C. or less, and cracks are observed in the brick material in which the cristobalite content in the brick exceeds 10% by mass. Was given. Further, the rate of change in height was −0.5% or less. On the other hand, in the case of the brick material having the cristobalite content of 10% by mass or less, the height change rate was more than -0.5%, and no crack was observed.

Among the above-mentioned brick materials having a cristobalite content of 10% by mass or less, those having a mullite content of 10% by mass or more have a height change rate of more than -0.4% and a mullite content of 10%. Those having a mass% or less had a height change rate of −0.4 to −0.5%. That is, when the mullite content was 10% by mass or more, the rate of change in height was large and good results were obtained, as compared with the mullite content of 10% by mass or less.

Table 1 shows the types of bricks installed at a height of 7.5 m above the ground, the occurrence of cracks, and the results of compression tests.

[0061]

[Table 1]

Test Nos. 1 to 6 are tests according to the present invention, using high alumina bricks having a cristobalite content of 10% by mass or less. Also, test number 7
Nos. 10 to 10 are tests of comparative examples, which are tests using high alumina bricks having a cristobalite content of more than 10% by mass.

In Test Nos. 1 to 6, which are examples of the present invention, no cracks were observed and the rate of change in height was -0.5%.
, And good results were obtained. Among them, the test numbers 1 to 3 in which the mullite content in the brick is 10% by mass or more has a larger height change rate than the cases in the test numbers 4 to 6 in which the mullite content is less than 10% by mass. The result was even better.

On the other hand, test numbers 7 to 7 which are comparative examples
In No. 10, cracks were generated, and the height change rate was −0.5% or less, which was inferior to the cases of Test Nos. 1 to 6. Test numbers 7 and 8 are for a brick material having a mullite content of 10% by mass or more, and test numbers 9 and 10 having a mullite content of less than 10% by mass.
Although the cracks were slightly generated, the rate of change in height was smaller than -0.5%, and the embrittlement was more advanced than in the case of Test Nos. 1 to 6 which are examples of the present invention. In the test numbers 9 and 10 in which the cristobalite content exceeds 10% by mass and the mullite content is less than 10% by mass, large cracks are generated, and the height change rate is -1, respectively. The results were inferior and were 0.2% and -0.8.

[0065]

EFFECTS OF THE INVENTION According to the method for distributing a high-alumina refractory material of the present invention, it is possible to prevent brittle brittleness due to the transfer of cristobalite in the lower region of the hot-air stove storage chamber, and to extend the life of the hot-air stove. Has a great effect on.

[Brief description of drawings]

FIG. 1 is a schematic view of a vertical section of an external combustion hot stove.

FIG. 2 is a graph showing the relationship between the cristobalite content of high-alumina bricks and the bending strength change rate due to thermal shock.

FIG. 3 is a diagram showing the relationship between the cristobalite content of high alumina bricks subjected to thermal shock and the height change rate of bricks.

FIG. 4 is a diagram showing a relationship between a mullite content and a bending strength change rate in a high alumina brick.

FIG. 5 is a graph showing the relationship between the mullite content and the height change rate of bricks in a high-alumina brick having a cristobalite content of 10% by mass or less.

[Explanation of symbols]

1: combustion chamber, 2: Burner, 3: heat storage room, 4: Connection pipe, 5: Air, 6: hot air, 7: mixing chamber, 8: Hot air valve, 9: Gas valve, 10: Air valve, 11: blower valve, 12: Flue valve.

Claims (3)

[Claims] 1. A refractory material distribution method for a hot-blast stove heat storage chamber for heating air blown to a blast furnace, which comprises using a high-alumina brick having a cristobalite content of 10% by mass or less at a working temperature of 30.
A refractory material distribution method for a hot-blast stove heat storage chamber, characterized in that the refractory material is placed at a temperature of 0 ° C or lower. 2. A refractory material distribution method for a hot stove heat storage chamber for heating air blown to a blast furnace, wherein a high alumina brick having a cristobalite content of 10% by mass or less is 10 m high from the bottom surface of the hot stove. A refractory material distribution method for a hot-blast stove thermal storage chamber, characterized in that the refractory material is placed inside 3. The method for distributing a refractory material in a hot stove thermal storage chamber according to claim 1, wherein a high alumina brick containing 10% by mass or more of mullite is arranged.