JP3958812B2 - Basic brick for cement kiln - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to basic bricks suitable as lining bricks for cement fired kilns, and in particular, basics for cement fired kilns that have excellent cement coating properties that can be used as substitutes for machrome bricks that have been used mainly in fired zones. Regarding bricks.
[0002]
[Prior art]
Conventionally, high-temperature or ultra-high-temperature fired magchromic bricks or magnesia-spinel bricks have been used in the firing zone of cement rotary kilns, but cement rotary kilns are operating at high operating rates and long-term operations. Operating conditions have become increasingly severe due to the variety of varieties. On the other hand, as environmental problems become severe, chromium, which is a harmful substance contained in magchromic bricks, has been regarded as a problem, and its use will be greatly restricted in the future.
[0003]
In such a flow, application of magnesia-spinel brick to a fired zone in which magchromic brick has been used has been studied. However, since the conventional magnesia-spinel brick uses a high-purity raw material and the total flux amount is suppressed to 1% by weight or less, the coating property of cement to the obtained brick is insufficient, and as a result, The bricks were directly exposed to the frames and raw materials, and their lifetime was greatly limited.
[0004]
In order to solve such problems, improvement of magnesia-spinel bricks is being studied. For example, Japanese Patent Publication No. 60-34513 discloses that 0.4 to 4.6% by weight of iron oxide is added to magnesia-spinel brick in terms of Fe ₂ O ₃ to improve cement coating properties. JP-B-7-108803 discloses that it is more effective to add 0.5 to 5% by weight of iron oxide in terms of Fe ₂ O ₃ and 0.5 to 5% by weight of titania. Yes. Further, in JP-A-4-310561, the use of electrofused magnesia containing 1 to 3% by weight of lime and silica, respectively, and the addition of 0.5 to 10% by weight of zirconia to the matrix part improves cement coating properties. It is disclosed that it is effective in suppressing penetration of cement components. Further, JP-A-5-58713 discloses that cement coating properties are improved by adding 0.3 to 5% by weight of silica in the form of a raw material containing 20% by weight or more of silica. Further, it is shown in refractory 38, 398-401 (1986-No. 6) that dolomite brick can be applied.
[0005]
[Problems to be solved by the invention]
When magnesia-spinel brick containing iron oxide is used for a long time, iron oxide in the brick repeats redox of Fe ₂ O ₃ ⇔FeO due to changes in furnace atmosphere and temperature, resulting in the structure due to brittleness of the brick structure Causes deterioration. In addition, when zirconia is added to the matrix portion, deterioration proceeds due to repeated crystal transformation accompanying the temperature change in the furnace of zirconia as in the case where the structure is added with iron oxide. These additive components exhibit their characteristics when added to the matrix portion.
[0006]
By the way, in long-term operation in an actual furnace, the wear tends to proceed from the matrix portion of the brick where the penetration of cement components easily occurs. In other words, it is not preferable to add a low-melting component to a site where melting loss is most likely to proceed or to add a component that causes tissue deterioration.
[0007]
Dolomite bricks have no problems with the formation of stable coating or corrosion resistance during operation, but tissue degradation rapidly proceeds due to digestion of the lime component at rest. Therefore, it cannot be used in operating conditions where there are many rests.
[0008]
The present invention provides a basic brick for a cement fired kiln comprising a magnesia-spinel basic brick capable of solving the above problems and improving the service life excellent in coating property, corrosion resistance and spalling resistance. It is to provide.
[0009]
[Means for Solving the Problems]
The basic brick for a cement fired kiln of the present invention contains 0.5-2% by weight of lime, 0.58-2% by weight of silica, and 0.2-1% by weight of iron oxide in terms of Fe ₂ O _3. 5 to 95% by weight of magnesia aggregate having a particle size of 0.5 mm or more is used, and the raw material of less than 0.5 mm is composed of less than 0.6% by weight of lime, less than 0.3% by weight of silica, and iron oxide. It is characterized by using a magnesia raw material and a spinel raw material that are less than 0.4% by weight in terms of Fe ₂ O ₃ and having a magnesia component of 50 to 90% by weight .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is highly reactive with cement components, and by defining the locations and types and amounts of components that contribute to coating formation, the coating properties and the ability to maintain the coating are greatly improved, and the life of the brick is prolonged. The present invention has been completed by obtaining new knowledge that it has a great influence.
[0013]
In the present invention, aggregate refers to a raw material having a raw material particle size of 0.5 mm or more, fine powder refers to a raw material having a raw material particle size of less than 0.5 mm, and a portion composed of the fine powder is referred to as a matrix.
[0014]
The magnesia aggregate is not limited by its production method, and a magnesia aggregate produced by natural, sintering, or electrofusion methods can be used. The magnesia aggregate, lime 0.5-2 wt%, silica 0.58 to 2%, of iron oxide is contained 0.2 to 1% by weight calculated as Fe ₂ O _3. In addition to the single magnesia raw material that falls within the content range defined in the present invention, it is sufficient that one or two or more magnesia raw materials that fall outside the content range are within the content range. Since iron oxide includes compounds in different oxidation states such as FeO, Fe ₃ O ₄ , and Fe ₂ O ₃ , in the present invention, all iron oxides are shown as amounts converted to Fe ₂ O ₃ . If the amount of each of lime, silica and iron oxide is greater than the upper limit of the content range, the cement coating property is improved, but this is not preferable because the amount of low-melted material is increased and the corrosion resistance of the aggregate is lowered. In addition, when the content is less than the lower limit of the content range, the amount of low melt produced is reduced and the corrosion resistance of the aggregate is improved, but the target cement coating property is lowered, which is not preferable.
[0015]
Further, magnesia aggregate is contained in the basic brick in an amount of 5 to 95% by weight. When it is less than 5% by weight, the cement coating property is lowered, and when it exceeds 95% by weight, the corrosion resistance and the spalling resistance are lowered. To do. The use of electromelting materials as aggregates slightly reduces the thermal shock resistance of bricks compared to sintered materials, but other properties such as hot strength and corrosion resistance are greatly improved and the total performance is improved. The use of a melt raw material is more preferable.
[0016]
Magnesia raw materials including lime, silica, and iron oxide can be used in all particle sizes of aggregate and fine powder. However, when the amount of lime, silica and iron oxide in the matrix increases, the strength at a high temperature range of 1200 ° C. or more tends to decrease. Therefore, it is more preferable to use a raw material having a higher purity than the aggregate of the present invention for the fine powder. The high-purity magnesia material is less than 0.6% by weight of lime, less than 0.3% by weight of silica, and less than 0.4% by weight of iron oxide in terms of Fe ₂ O ₃ , more preferably 0.2% by weight. Is less than. Even if it is the magnesia raw material of the 1 type or 2 or more types component which remove | deviates this content, what was combined with the high purity magnesia raw material should just be in a limited range. In addition, the use of low-purity raw materials in which lime is 2% by weight or more, silica is 2% by weight or more, and iron oxide is 1% by weight or more in terms of Fe ₂ O ₃ is used as fine powder. Since it lowers, it is not preferable.
[0017]
As the spinel material used for the aggregate and matrix, in addition to the spinel material having the theoretical composition, a spinel material having an alumina component in the range of 40 to 90% by weight can be used. Can be used and is not particularly limited. When used as an aggregate, it is preferable that lime is 2% by weight or less, silica is 2% by weight or less, and iron oxide is 1% by weight or less in terms of Fe ₂ O ₃ . When it exceeds this range and contains many components, such as a lime, a silica, and an iron oxide, since the intensity | strength in high temperature is reduced, it is unpreferable. When a spinel raw material is used for the matrix, lime is less than 0.6% by weight, silica is less than 0.3% by weight, and iron oxide is less than 0.4% by weight in terms of Fe ₂ O ₃ , more preferably 0. Used under the condition of less than 2% by weight.
[0018]
In addition, it can replace with a spinel raw material, an alumina raw material can be added, and it can also be set as a spinel in a brick by reaction with the magnesia component in a brick by baking, and in this case, it uses for a matrix by the component conditions of the above-mentioned matrix.
[0019]
The compound having a mineral spinel structure includes a combination of various elements, but unless otherwise specified, the spinel referred to in the present invention is a magnesia-alumina spinel composed mainly of magnesia and an alumina component. (MgO—Al ₂ O ₃ ) is shown.
[0020]
In the present invention, magnesia and spinel raw materials are blended so that the amount of magnesia component in the brick is 50 to 90% by weight. When the amount of magnesia component exceeds 90% by weight, the amount of spinel in the brick decreases, and as a result, the thermal shock resistance decreases. If the amount of magnesia component is less than 50% by weight, the amount of alumina component in the brick increases and the corrosion resistance decreases.
[0021]
In the examples of the present invention, titania as an impurity component other than magnesia, alumina, lime, silica, and iron oxide is less than 0.5% by weight as a component amount in the brick in order to reduce the coating property of cement, and zirconia is In order to avoid structural deterioration, the amount of components in the brick is preferably less than 0.5% by weight.
[0022]
The basic brick of the present invention is manufactured by a method known to those skilled in the art, and the manufacturing method is not particularly limited.
[0023]
FIG. 1 is a schematic diagram showing the location of iron oxide in a basic brick of the present invention, FIG. 2 is a schematic diagram of the location of iron oxide in a conventional basic brick, and in order to improve the coating properties of cement, As shown in FIG. 1, it is important that the components 1 of lime 2, silica 3 and iron oxide 4 are simultaneously present in the aggregate 1. If an attempt is made to improve the coating properties of the cement by adding only the iron oxide component, the amount added must be several times that of the present invention, and as described above, the structure caused by repeated changes in Fe ₂ O ₃ ⇔FeO The effects of deterioration cannot be avoided. Further, as shown in the conventional example of FIG. 2, these harmful effects of iron oxide are manifested because iron oxide is present in the matrix 5, so that the iron oxide 4 is present in the aggregate 1 as in the present invention. If you do, it will not be a problem. On the other hand, if it is going to acquire the same effect only with lime and a silica, the required amount will increase and as a result, corrosion resistance will fall significantly. However, in the present invention, the three components of lime 2, silica 3 and iron oxide 4 coexist in the aggregate 1, and due to their synergistic effect, sufficient cement coating properties can be obtained even if the amount of each component is small. Can be obtained.
[0024]
By increasing the abundance of lime, silica, and iron oxide in the aggregate instead of the matrix, the coating of the cement component proceeds preferentially in the brick aggregate, and the corrosion resistance of the aggregate is superior to that of the matrix. Compared to the case where the cement coating property is improved by adding a component that improves the cement coating property to the matrix, the previous erosion of the matrix due to the reaction with the cement component is greatly suppressed. Further, since the area of the exposed brick surface of the aggregate on the brick surface is larger than that of the matrix, components that promote cement coating are distributed over a wide range. As a result, the formation of the coating is promoted and the brick life is extended.
[0025]
In FIG. 1, the lime 2, silica 3 and iron oxide 4 are shown to be present only in the aggregate 1, but the lime, silica and iron oxide are limited in the matrix as the above-mentioned impurities. If it is less than 1, the mechanical strength does not decrease at a high temperature of 1000 ° C or higher.
[0026]
【Example】
Table 1 shows the respective contents and production methods of lime, silica and iron oxide as magnesia starting materials. Raw materials A to E in Table 1 are raw materials used in the present invention.
[0027]
[Table 1]
Table 2 shows the contents and production methods of alumina, lime, silica, and iron oxide, which are magnesia starting materials used in the present invention.
[0028]
[Table 2]
Tables 3 and 4 show the compositions of Examples and Comparative Examples of the present invention.
[0029]
[Table 3]
[Table 4]
The compositions of Examples 1 to 16 blended at the ratios shown in Table 3 and Table 4 were kneaded at room temperature using a magnesium chloride aqueous solution as a binder. Thereafter, a shape of 230 × 110 × 100 mm was molded at a molding pressure of 200 MPa and fired at a firing temperature of 1750 ° C.
[0030]
In Examples 17 and 18 , the compacts obtained under the same conditions were fired at 1600 ° C.
[0031]
In Example 13, magnesia raw materials D and G, and in Examples 14, 15, 17 , and 18 , magnesia raw materials D and H were used as magnesia aggregates in a ratio of 1: 1.
[0032]
Further, Examples 15 and 18 used spinel raw materials J and K in a ratio of 1: 1, respectively.
[0033]
As Comparative Examples 1 to 3, bricks having the same composition using raw materials G to I were molded under the same conditions, and fired at 1750 ° C. to produce. Comparative Example 4 was obtained using a composition in which 1.3% by weight of Bengala was externally added to the composition of Comparative Example 2.
[0034]
In the examples of the present invention, the abundances of titania and zirconia existing as raw material impurities as components other than magnesia, alumina, lime, silica and iron oxide are 0.13% by weight or less and 0.05% by weight or less, respectively, as bricks. It was hot.
[0035]
Tables 5 and 6 show the evaluation results of the examples of the present invention and the comparative examples.
[0036]
[Table 5]
[Table 6]
The physical properties of the obtained bricks were measured, and the coating properties, thermal shock resistance, and corrosion resistance of the cement composition were investigated. The cement coating test was conducted at 1550 ° C. by a rotating drum method using a mixture of 65% by weight of Portland cement, 30% by weight of potassium sulfate and 5% by weight of fly ash. Evaluation was made by direct observation of the coating state of the cement in the heated state and the coating formation thickness after cooling. The thermal shock resistance was evaluated by inserting and heating a 50 × 50 × 50 mm square sample in an electric furnace heated to 1400 ° C., cooling with water, and evaluating the number of dropouts by this repetition. Corrosion resistance was measured by the rotating drum method at 1750 ° C. using the same cement composition as in the cement coating test. Evaluation was based on the amount of reduction after the test.
[0037]
The brick of the present invention using the magnesia raw material containing lime, silica, and iron oxide in the specific range in the aggregate has no problem in bending strength under high-temperature heating conditions, and has good cement coating and corrosion resistance. (Examples 1-12, 16).
[0038]
Even if spinel raw materials (raw materials J and L) having different magnesia ratios are used, no significant difference is observed in characteristics. Even when the magnesia raw material was replaced with ordinary high-purity products G and H up to about 50%, no significant decrease in cement coating property was observed (Examples 13 to 15).
[0039]
Even if a part or all of the spinel raw material is replaced from a sintered product to an electrofused product, no deterioration in general physical properties or cement coating properties is observed (Examples 5 and 15).
[0040]
When the firing temperature is 1600 ° C. (Examples 17 and 18 ), the hot strength at 1400 ° C. tends to be slightly lowered, but conversely, the thermal shock resistance is improved and there is no problem in cement coating properties and corrosion resistance.
[0041]
In Comparative Examples 1 and 2 in which the amounts of lime, silica, and iron oxide in the magnesia aggregate are less than the scope of the present invention, the general physical properties and corrosion resistance or thermal shock resistance are good, but no cement coating is observed. There is a problem with the use of alternatives to mugaceous bricks. Conversely, in Comparative Example 3 where the amounts of lime, silica, and iron oxide are greater than the scope of the present invention, there is no problem with the coating properties of the cement, but this is not preferable because the strength at high temperatures is low and the corrosion resistance is greatly reduced. . In Comparative Example 4 in which iron oxide was added as an outer coating, that is, a large amount of iron oxide was present in the matrix, although the coating property of the cement had no problem, the corrosion resistance was greatly reduced.
[0042]
The characteristics of the bricks of Examples 4, 14 , 15, and 17 of the present invention were confirmed by using the bricks for the firing zone of the rotary kiln for cement firing. It was confirmed that sufficient cement coating was produced over the course of one year and sufficient durability was obtained. In addition, it was found that there was no problem in actual operation because there were no problems caused by brick spalling or chemical erosion due to thermal spalls even when using a desorption zone or cooling zone.
[0043]
【The invention's effect】
The basic brick for a cement firing kiln of the present invention has good coating properties, excellent mechanical properties, corrosion resistance, and thermal shock resistance, and can improve the useful life of the cement firing kiln.
[0044]
A basic brick for cement-fired kilns having excellent cement coating properties can be obtained as an alternative to magchromic bricks containing chromium, which is a harmful substance that causes environmental problems.
[0045]
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the location of iron oxide in a basic brick of the present invention.
FIG. 2 is a schematic view showing the location of iron oxide in a conventional basic brick.
[Explanation of symbols]
1 Aggregate 2 Lime 3 Silica 4 Iron oxide 5 Matrix

Claims (1)

A magnesia aggregate containing 0.5 to 2% by weight of lime, 0.58 to 2% by weight of silica, and 0.2 to 1% by weight of iron oxide in terms of Fe ₂ O ₃ and having a particle size of 0.5 mm or more. 5 to 95% by weight, and less than 0.5 mm of raw material is less than 0.6% by weight of lime, less than 0.3% by weight of silica and less than 0.4% by weight of iron oxide in terms of Fe ₂ O ₃ A basic brick for cement-fired kilns comprising a magnesia raw material and a spinel raw material, wherein the magnesia component is 50 to 90% by weight.