JP2011057536A - Spinel refractory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spinel refractory which suppresses reaction with foreign components such as sulfur, boron and vanadium even when used in the transition zone of a cement kiln and in a glass kiln regenerator. <P>SOLUTION: Provided is the spinel refractory which consists essentially of MgO and Al<SB>2</SB>O<SB>3</SB>, and, as chemical components, contain 20 to 40 mass% MgO and 60 to 80 mass% the Al<SB>2</SB>O<SB>3</SB>, wherein the main mineral phase is spinel, and also, the whole quantity or the most of the spinel composing the refractory uses a molten spinel raw material produced by a melting method. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a refractory for lining of a rotary kiln such as a kiln for cement firing and a kiln for lime firing, and a refractory for a heat storage chamber of a glass kiln. In particular, the present invention relates to a refractory material used for a portion called a “transition zone” of a cement kiln and a middle stage region of a glass kiln heat storage chamber.

  Conventionally, magnesia-chromium bricks or magnesia-spinel bricks are used as refractories used for the lining of rotary kilns for cement firing. In recent years, the importance of refractories that do not contain chromium has been increasing from the environmental aspect, and magnesia-spinel brick has been widely used.

  Cement rotary kiln lining refractories usually have a large damage to the part called “firing zone” with the highest heat load and often limit the life of the kiln, but in the transition zone where the heat load is relatively light In many cases, however, the infiltration of exogenous components such as sulfur and chlorine and the embrittlement damage due to the reaction with the exogenous components progress, causing the sudden stoppage of the kiln.

  As for the fired zone, the remaining size of the brick becomes thinner as the damage progresses, and it is relatively easy to determine the degree of damage from the appearance at the time of inspection in the furnace after the kiln is stopped. The resulting brittle damage has a problem that it is difficult to determine the degree of damage because the remaining thickness of the brick is often sufficient in terms of the appearance of the brick.

  In recent years, the amount of waste plastic, sludge, industrial waste, and the like has increased remarkably, and along with this, the damage to bricks used in transition zones has also been increasing. Prevention of brick damage in the transition zone is one of the major solutions for improving the life of cement kilns.

  On the other hand, glass kilns often last for more than 10 years, but especially checker bricks used in heat storage rooms are strongly influenced by sulfur, boron, vanadium, etc. derived from glass raw materials and fuels. The degree of damage often determines the life of the glass kiln. In recent years, low-purity heavy oil is often used to reduce costs, and the use of recycled glass is also increasing, and the influence of these extraneous components has become larger, and checker bricks have collapsed. Cases have also been reported.

  By the way, conventionally, the improvement of the refractory for cement kiln has been mainly the improvement of the brick used in the fired zone, and the main focus has been on the improvement of the adhesion of the coating. This is due to the problem that the adhesiveness of the coating decreases with the transition from the magnesia-chromic brick to the magnesia-spinel brick, resulting in increased brick damage and reduced durability.

  In order to solve this problem, for example, in JP-A-4-310561 (Patent Document 1) and JP-A-2000-72528 (Patent Document 2), 5 to 30 wt% of magnesia-alumina spinel clinker, 10 A magnesia-spinel refractory containing ˜50 wt% electrofused magnesia clinker and containing 0.5 to 10 wt% partially stabilized zirconia in the joint is disclosed. The means of the present invention is considered to be effective for the coating adhesion, but when the brick according to the present invention is used in the transition zone, it is sufficient for suppressing the reaction with a foreign component such as sulfur. There is a drawback that the effect cannot be obtained.

For example, in Japanese Patent Laid-Open No. 5-58713 (Patent Document 3), a powder containing 20% by weight or more of SiO ₂ component in a blend consisting of 5 to 40% by weight of magnesia-alumina-based spinel powder and the balance being substantially magnesia powder. Discloses a refractory material in which is added so that the SiO ₂ content is 0.3 to 5% by weight. However, although this technique is considered to be effective for improving the coating adhesion, it is not possible to obtain a sufficient effect for suppressing embrittlement damage in the transition zone.

Also, for example, in Japanese Patent Laid-Open No. 7-291715 (Patent Document 4), MgO and Al ₂ O ₃ are included as main constituent components, or MgO, Al ₂ O ₃ and SiO ₂ are included as main constituent components. In addition, a spinel mainly composed of a magnesia clinker in which a spinel phase or a spinel phase and a forsterite phase are present at the grain boundaries of the magnesia particles and a spinel clinker whose main component is spinel as a main component. Quality refractory bricks are disclosed. In the present invention, it is necessary to prepare a special clinker in which the intended grain boundary phase is formed in advance, which inevitably increases the cost.

  JP-A-4-198058 (Patent Document 5) discloses a magnesia clinker having a mineral composition mainly composed of periclase and cubic zirconia and forsterite as auxiliary components. Although the refractory manufactured using the magnesia clinker according to the present invention technology is considered to be effective in terms of corrosion resistance, it is necessary to prepare a special clinker intended in advance as in JP-A-7-291715 (Patent Document 4). There is a problem in terms of cost.

  JP 2002-308667 (Patent Document 6) discloses a method for producing a magnesia-spinel basic refractory containing an alumina-magnesia spinel clinker and a high-purity magnesia clinker. The present technology is characterized in that a spinel bond is formed in a matrix portion between spinel and magnesia aggregate, and a cement kiln brick having excellent coating adhesion, high hot strength and high corrosion resistance is provided. Although the basic refractory of the present technology is considered to be effective for use in the calcined zone, there is a disadvantage that the durability is poor under the condition of the transition zone.

  On the other hand, Japanese Patent Laid-Open No. 10-226522 (Patent Document 7) discloses a spinel brick for a glass kiln heat storage chamber made of alumina-magnesia spinel. This technology utilizes spinel's sulfur resistance, but it cannot be said that it has sufficient durability against foreign components such as boron and vanadium including sulfur.

  Japanese Utility Model Laid-Open No. 58-92336 (Patent Document 8) also discloses a checker structure for a glass kiln heat storage chamber made of alumina-magnesia spinel. In this technology, it is described that the spinel to be used is preferably a sintered spinel. However, the sintered spinel is a sintered crystal composed of polycrystals by reacting foreign components such as sulfur, boron, vanadium and the grain boundary phase in the spinel particles. There is a problem that the structure change of the spinel particles occurs.

  Furthermore, Japanese Patent Laid-Open No. 48-28008 (Patent Document 9) discloses a magnesia fired refractory characterized by using a raw material composed of mixed particles of periclase and spinel. Since the refractory according to the present invention contains 85% by weight or more of MgO as a chemical component, there is a problem that the tissue change accompanying the reaction between periclase and sulfur is large in a sulfur atmosphere.

JP-A-4-310561 JP 2000-72528 A JP-A-5-58713 JP-A-7-291715 JP-A-4-198058 JP 2002-308667 A Japanese Patent Laid-Open No. 10-226522 Japanese Utility Model Publication No. 58-92336 JP-A-48-28008

Problems to be solved by the invention

  The present invention reduces the embrittlement damage of the refractory by suppressing the reaction with foreign components such as sulfur, boron, vanadium even when used in the transition zone of a cement kiln or a glass kiln heat storage chamber, The object is to provide a refractory that can achieve a long life.

Means to solve the problem

  The refractory for a cement firing kiln and the refractory for a heat storage chamber of a glass kiln according to the present invention, the refractory whose main constituent phase is spinel, the use of a molten spinel raw material as a spinel constituting the refractory, the above problem This is a solution to the problem.

The invention's effect

According to the present invention, there is provided a spinel refractory made of a fused spinel, which can be suitably used as a material for a cement kiln transition zone or a checker brick in a glass kiln heat storage chamber.
The spinel refractory of the present invention has a feature that hardly reacts with foreign components such as sulfur, boron and vanadium even when used for a long time, and it becomes possible to greatly reduce damage to the refractory. .

  Hereinafter, embodiments of the refractory for a cement kiln or a glass kiln heat storage chamber according to the present invention will be described in detail. In addition, the melt spinel raw material said here shows the spinel raw material manufactured by melt | dissolution methods, such as an electric melting method, and if it is manufactured by the melt method, the heating method will not be limited.

  Since the melted spinel raw material is generally manufactured by an electric melting method, it is hereinafter expressed as “electrofused spinel” in the present invention.

  When the main mineral phase is a refractory composed of spinel, and the spinel constituting the refractory is a fused spinel, the reaction between the refractory and a foreign component such as sulfur is suppressed. And found that the damage was greatly reduced.

  Spinel used for the production of magnesia-spinel refractories and spinel refractories is generally divided into two types: sintered spinel in which a large number of spinel crystals are combined and fused spinel produced by the melting method. Separated.

In sintered spinel, individual spinel crystal particles may be bonded directly, but usually there is a grain boundary phase between the crystal particles and it is generally bonded via the grain boundary phase. It is. In this grain boundary phase, a CaO component is usually the main constituent, and other components include SiO ₂ , MgO, Al ₂ O _{3 and the} like.

  On the other hand, magnesia used for the production of magnesia-spinel refractories is roughly classified into sintered magnesia formed by combining a large number of periclase crystals and electrofused magnesia produced by a melting method. In sintered magnesia, a grain boundary phase mainly composed of a CaO component is generally present between the individual periclase crystal particles as in the sintered spinel.

  Cement kiln lining bricks or checker bricks used in heat storage chambers of glass kilns cause refractory embrittlement damage that may be due to the influence of foreign components such as sulfur, boron and vanadium caused by fuel and raw materials. There is a problem of doing. In particular, embrittlement damage is significant in checker bricks used in the transition zone of cement kilns and in the middle stage of glass kiln heat storage chambers.

  When the brick after use in which such embrittlement damage occurs is investigated, it can be confirmed that the CaO content in the brick is greatly reduced in many cases. Usually, since the CaO-containing phase is contained as a grain boundary phase in magnesia or spinel, a decrease in the CaO component indicates that the grain boundary phase has disappeared. As a result, the connective structure of spinel crystals and the connective structure of spinel crystal grains are weakened, resulting in brittle damage to the refractory.

  When observing the structure of magnesia-spinel brick used in the transition zone of cement kiln, the grain boundary phase part in the magnesia and spinel particles made of polycrystals disappears, and the structure that is hollow is remarkably confirmed. Although this can be done, this directly indicates that the CaO-containing grain boundary phase has disappeared.

  Further, when the magnesia-spinel brick used in the transition zone of the cement kiln is observed, the following characteristic structure is observed.

  It can be confirmed that the magnesia crystal particles (periclase) constituting the magnesia particles themselves disappear and a hollow structure is formed on the working surface side of the brick where the embrittlement damage has progressed. Periclase crystals are thought to have disappeared due to the reaction with sulfur, and it is also considered to be one of the main causes of embrittlement damage of magnesia-spinel bricks.

  On the other hand, electrofused spinel is derived from the manufacturing method and has a feature that it has almost no grain boundary phase. The inventors of the present invention have made extensive studies focusing on this point and found that an electrofusion spinel is suitable as a spinel constituting a refractory. It has been found that since an electrofused spinel has almost no grain boundary phase, it hardly reacts with foreign components such as sulfur, boron, vanadium, and the like, and damage to the refractory can be greatly suppressed.

  In the prior art, there is a description that it is possible to use a fused spinel, but there is no mention of the characteristics of the fused spinel having no or almost no grain boundary phase. It should be noted in advance that the significance of the inventive technique is not impaired at all.

The spinel is a crystal structure represented by the general formula XY ₂ O ₄ in a narrow sense, and a spinel represented by MgAl ₂ O ₄ is representative. And it has the remarkable feature that it has a wide solid solubility between Al ₂ O ₃ and MgO.

  Spinel used as a refractory material is usually a spinel having a theoretical composition, but magnesia-rich or alumina-rich spinel is also widely used. When magnesia-rich spinel is out of the solid solution range, it becomes a structure in which free periclase coexists. Free periclase reacts with sulfur to form a sulfide phase, causing a structural change and causing embrittlement damage. Therefore, it is not preferable that excessive MgO is present. On the other hand, alumina-rich spinel also has a problem that it reacts with a foreign component as the alumina content increases, and a reaction phase is easily generated.

For these reasons, the chemical composition of the spinel refractory in the present invention is preferably in the range of MgO: 20 to 40% by mass and Al ₂ O ₃ : 60 to 80% by mass.

  In the present invention, in the above composition range, it is also possible to use a magnesia raw material in addition to the spinel raw material as a starting raw material at the time of production. In the case of the spinel single phase, there is a feature that the degree of densification in the baking process at the time of brick production is large, and by adding a small amount of magnesia raw material, densification can be suppressed and an appropriate structure can be obtained.

  In particular, in cement kilns, there is a concern about spalling damage due to thermal fluctuations in the kiln, so an excessively densified structure is not preferable in terms of heat-resistant spalling properties. In the present invention, by adding a small amount of magnesia raw material, fine microcracks can be formed in the structure, and the heat resistant spalling property can be improved.

  On the other hand, since the heat storage chamber of the glass kiln does not change as much as in the cement kiln, it is preferable to use a densified spinel single phase to suppress reaction with foreign components.

  By the way, when a magnesia raw material is used in the manufacturing process, the case where periclase as a mineral phase is contained in the refractory finally obtained is considered. However, in the present invention, as long as the chemical composition of the entire refractory is in the range of MgO: 20 to 40% by mass, there is no problem even if periclase is present as the mineral phase.

  In the present invention, it is preferable that the total amount of the spinel constituting the refractory is composed of a fused spinel, but a sintered spinel can be used as long as it is within an appropriate range. In some cases, sintered spinel is used in terms of securing formability at the time of manufacturing, and can be suitably used within a range of less than 20% by mass with respect to the total amount of spinel. If it exceeds 20% by mass, the influence of embrittlement damage associated with the reaction between the sintered spinel and foreign components such as sulfur is increased, which is not preferable.

  By the way, about 0.3-1.5 mass% of CaO components are usually contained in the electrofused spinel, sintered spinel, electrofused magnesia, and sintered magnesia used in the present invention. And most of this CaO component exists in a grain boundary as a CaO containing compound. The CaO-containing phase present in the grain boundary forms a reaction phase by reacting with a foreign component such as sulfur, and finally disappears from the spinel particles and magnesia particles. As a result, the connective structure between the particles We believe that brick is weakening the organization.

  In the present invention, the CaO content contained in the refractory is preferably 0.6% by mass or less, and more preferably CaO: 0.5% by mass or less. When the CaO content in the refractory exceeds 0.6% by mass, the resistance to embrittlement damage is lowered, which is not preferable.

  It does not specifically limit about the manufacturing method of the spinel refractory of this invention, It can manufacture using the manufacturing method of a well-known refractory. The particle size composition of the fused spinel raw material, sintered spinel raw material, sintered magnesia raw material or fused magnesia raw material to be used is not particularly limited, and any particle size constitution can be used as long as the shape of the brick can be maintained after molding and firing. It is possible to apply. Moreover, it is possible to use a small amount of additives except inevitable impurities as long as the effects of the present invention are not impaired.

  In order to confirm the effect of the present invention, the present inventors conducted a heating test of the sample according to the present invention at a high temperature using a compound containing sulfur, boron, vanadium or the like as an erodant. Then, after the test, the appearance structure and the fine structure were observed, the analysis with an electron beam microanalyzer, the measurement of the compressive strength, the chemical analysis, etc. were conducted, and the influence of these erodants was investigated.

  Hereinafter, examples of the present invention will be described together with comparative examples to specifically describe the present invention, but the present invention is not limited to the scope of the following examples.

Example 1
Using a spinel raw material and a magnesia raw material having the chemical composition shown in Table 1, a preparation having the raw material mixing ratio shown in Table 2 is prepared, and a small amount of magnesium lignin sulfonate is added to the mixture as a high speed. Kneading was performed with a mixer. The obtained kneaded product was formed into a JIS parallel shape (230 mm × 114 mm × 65 mm) by an oil press, dried, and fired at 1700 ° C. in a tunnel kiln, which is shown in the spinel refractory of the present invention or a comparative example. A spinel refractory was obtained.

In Table 2, no. 1-5 are examples of the present invention, No. 6 to 9 are comparative examples.
About the obtained sample, while performing a chemical analysis, the mineral phase was identified with the X-ray-diffraction apparatus. The results are also shown in Table 2.

Next, one sample each having a width of 15 mm, a thickness of 15 mm, and a length of 150 mm was cut out from the parallel samples of Examples and Comparative Examples, and used as a sample for a heating test. This sample was placed in an alumina tubular tube closed on one side, filled with 10 g and 3 g of K ₂ SO ₄ and carbon black respectively at the bottom, covered, set in an electric furnace, and heated at 1300 ° C. for 2 Heating for hours was performed.
After the test, the sample was cut in parallel to the length direction of the sample and observed for external appearance, and the sample for preparing the mirror-polished piece was cut out from the bottom of the sample, and the mirror-polished piece was prepared and observed for the microstructure using an electron microscope. It was.

  Table 2 also shows the results of observation of the appearance structure and the results of observation of the fine structure by an electron microscope. As is clear from Table 2, it can be seen that the samples of the examples maintain a healthy structure even after the heating test. Also in the observation of the cut surface, the phenomenon of particle dropout is slight and the connective tissue is maintained.

  As a result of observation of the fine structure by an electron microscope, it was found that the structure change of the electrofused spinel particles was slight and the structure before the heat treatment was maintained.

  On the other hand, in Comparative Example 6 and Comparative Example 7, it was revealed that the drop-off phenomenon of the particles at the cut surface was conspicuous, and the embrittlement damage was progressing. In the observation of the structure with an electron microscope, the structure change of sintered magnesia particles and sintered spinel particles is large, and the phenomenon that the individual crystal particles constituting these particles separate from the grain boundary part is noticeable. It was.

  In Comparative Example 8 and Comparative Example 9, the structural change in appearance was slight. However, when the fine structure was observed, in Comparative Example 8, the formation of a reaction phase considered to be a glass phase was remarkably observed between the spinel particles. It was. In Comparative Example 9, the disappearance of the CaO-containing grain boundary phase in the sintered magnesia particles is remarkable, a large number of cavities are formed in the particles, and the collapse phenomenon associated with the separation of the periclase crystal particles from the grain boundary part is also conspicuous. It was.

Example 2
Two samples each having a size of 30 mm × 30 mm × 30 mm were prepared from the parallel-shaped sample prepared in Example 1 and used as samples for compressive strength measurement.

Each one of the samples is filled in a magnesia crucible having an inner size of width 70 mm × length 150 mm × height 60 mm, and mixed with a mixed powder of K ₂ SO ₄ and carbon black around half the height of the sample. And then the lid was adhered with mortar. Then, the magnesia crucible containing the sample was set in an electric furnace, and heat treatment was performed at 1200 ° C. for 50 hours in an air atmosphere. Here, the mixing ratio of K ₂ SO ₄ and carbon black was set to be K ₂ SO ₄ : carbon black = 10: 3 in the weight ratio as in Example 1.

  After the completion of the heating test, samples were taken out from the crucible, and the samples were further heat-treated at 1200 ° C. for 10 hours in the air. The reason why the heat treatment is performed in the atmosphere is to remove a low melting point reaction product that may be contained in the sample.

  Thereafter, the compressive strength was measured for each sample. For comparison, the compressive strength was also measured for a raw brick sample that was not heat-treated. The results are shown in Table 2.

In the example of the present invention, it was found that almost no decrease in compressive strength due to heat treatment in a K ₂ SO ₄ + carbon black atmosphere was observed, and the strength of the original brick was maintained. On the other hand, in Comparative Example 6, Comparative Example 7, and Comparative Example 9, it can be seen that the rate of decrease in compressive strength is large, and embrittlement damage is advanced. In Comparative Example 8, no decrease in compressive strength was observed, but this was presumed to be because a reaction phase considered to be a glass phase was formed in the structure as confirmed in Example 1 of the present invention. However, the formation of a reaction phase is not preferable because it deteriorates characteristics at high temperatures.

Example 3
Using a spinel raw material and a magnesia raw material having the chemical composition shown in Table 1, prepare a blend having the raw material blending ratio shown in Table 3, adding a small amount of phenol resin as a binder to the blend, and using a high speed mixer. Kneaded. The obtained kneaded material was formed into a JIS parallel shape by an oil press, dried, and then fired at 1700 ° C. in a tunnel kiln to obtain the spinel refractory of the present invention or the spinel refractory shown in the comparative example. .

Two samples each having a width of 60 mm, a thickness of 60 mm, and a height of 65 mm were cut out from the obtained parallel sample, and a hole with a diameter of 30 mm and a depth of 40 mm was formed in the center.
One of each of the two prepared samples was filled with a mixture of Na ₂ SO ₄ and B ₂ O ₃ and the other with a mixture of Na ₂ SO ₄ and V ₂ O ₅ to a depth of 30 mm. Covered with a lid made in Here, the mixing ratio of Na ₂ SO ₄ to B ₂ O ₃ and V ₂ O ₅ was set to be Na ₂ SO ₄ : B ₂ O ₃ (V ₂ O ₅ ) = 4: 1 by weight.

  Next, this crucible was set in an electric furnace, and heat treatment was performed at 1200 ° C. for 50 hours in an air atmosphere. After the test, the sample was cut in the longitudinal direction at a position including a hole formed in the central portion, a mirror-polished piece was prepared, and the surface in contact with the erodant was observed with an electron microscope.

  Table 3 also shows the results of the tissue observation.

  As a result of the structure observation, it was found that in Examples 10 to 13 of the present invention, the change in the structure of the electrofused spinel was slight, and the structure of the original brick was maintained. On the other hand, in Comparative Examples 14 to 16, under the conditions using any of the erodants, the structural change of the sintered spinel is very large, and the sintered spinel particles are separated from the grain boundary portion, The phenomenon of disintegrating into spinel crystal particles was noticeable. In Comparative Example 16, the structural change of the fused spinel was slight, but the formation of a reaction phase considered to be a glass phase between the fused spinel particles was remarkably recognized.

These reaction phases are not preferred because they are thought to reduce the hot properties of the brick. From the examples of the present invention and the comparative examples, it was found that B ₂ O ₃ and V ₂ O ₅ have a very large influence on the structural change of the sintered spinel.

  The present invention can provide a refractory that hardly reacts to foreign components (sulfur component, vanadium component, boron component, etc.), a transition kiln of a rotary kiln such as a kiln for cement firing, a kiln for lime firing, or a glass kiln. The durability of these kilns can be extended more than before by using them as lining refractories for heat storage chambers.

Claims (4)

In a refractory material having MgO and Al ₂ O ₃ as main constituent components, MgO content of 20 to 40% by mass and Al ₂ O ₃ content of 60 to 80% by mass as chemical components, the main mineral phase A spinel refractory characterized in that is a spinel, and the total amount or most of the spinel constituting the refractory is made of a molten spinel raw material produced by a melting method.   The spinel refractory according to claim 1, wherein a blending ratio of the molten spinel raw material at the time of blending the spinel raw material during refractory production is 80% by mass or more based on the total amount of the molten spinel raw material and the sintered spinel raw material. .   The spinel refractory according to claim 1 or 2, wherein the mineral phase constituting the refractory is substantially composed of spinel or spinel and periclase.   The spinel refractory according to claim 1, wherein the CaO content in the refractory is 0.6 mass% or less.