High alumina castables and waste treatment furnaces

Abstract

To provide a castable that can be used as a refractory material for furnace and has excellent acid resistance, alkali resistance, and corrosion resistance, and to provide a furnace using the same.SOLUTION: A high alumina castable of the present invention is a high alumina castable composed of an aggregate, a powder and a binder, and does not contain cement, and in which, characterized, setting the total as 100 mass%, alumina is contained by 50 to 95 mass%, silica is contained by 4.5 to 49.5 mass%, and calcia is contained by less than 0.5 mass%. The waste processing furnace of the present invention is characterized in that the high alumina castable is used in the furnace wall.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a high-alumina castable containing alumina as a main component, and a waste treatment furnace using the same. [Background technology]

[0002] Castables (unshaped refractories) are widely used as refractories (also called fireproofing materials) for various furnaces such as melting furnaces and incinerators due to their ease of construction, cost, and the high degree of freedom in being able to select materials according to the conditions of use.

[0003] Conventionally, cement castables containing a large amount of alumina cement have been used as castables. In cement castables, the main component of cement, calcia (CaO), reacts during use to form anorthite (CaO·Al 2 O 3 2SiO 2 ), which produces low-melting point compounds. The anorthite produced causes erosion of the cement castable by slag, etc. Furthermore, in the cement castable of the furnace, the calcia reacts with acidic components present in the furnace (for example, acidic components contained in the material to be treated, the atmosphere in the furnace, and the exhaust gas), causing embrittlement and dissolution of the structure. In conventional cement castables, the presence of calcia reduces hot strength in high temperature ranges and significantly increases the erosiveness of slag. To address this issue, low-cement castables, which use a reduced amount of alumina cement, and ultra-low-cement castables, which use ultra-fine silica and alumina powder, have been put into practical use.

[0004] In recent years, non-cement castables have been developed that use hydraulic alumina or colloidal silica as a binder and do not contain any alumina cement at all. Applications of non-cement castables as materials for storage vessels for molten metal and as lining castables for melting furnaces are being considered.

[0005] On the other hand, the influence of diversification of waste is becoming prominent in melting furnaces in which castables are used, especially in industrial waste incinerators. Specifically, there is a problem that reactive components such as acidic and alkaline components from the waste react with castables, damaging the furnace. Furthermore, if the waste material and processing temperature are different, the reactivity of the reactive components (e.g., acidity and alkalinity) also differs. Thus, the refractory material of the furnace is required to be able to handle reactive components with a wide range of acidity (or alkalinity). Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a castable that can be used as a refractory material for a furnace and has excellent acid resistance, alkali resistance, and corrosion resistance, and a furnace using the same. [Means for solving the problem]

[0007] The high alumina castable of the present invention, which solves the above problems, is a high alumina castable that is composed of aggregate, powder, and binder and does not contain cement, and is characterized in that, when the whole is taken as 100 mass%, it contains 50 to 95 mass% alumina, 4.5 to 49.5 mass% silica, and less than 0.5 mass% calcia. The high alumina castable of the present invention has a low calcia content and contains silica, which makes it a castable excellent in acid resistance and alkali resistance. Furthermore, the generation of low melting point components is suppressed, and the castable has excellent corrosion resistance and resistance to melting damage by slag, etc.

[0008] The waste treatment furnace of the present invention, which solves the above problems, is characterized in that the above-mentioned high alumina castable is used for the furnace wall. The waste treatment furnace of the present invention uses the high alumina castable as the furnace wall and has a furnace wall with excellent corrosion resistance. That is, the waste treatment furnace of the present invention is a furnace that is suppressed from being damaged by corrosion caused by acids and alkalis. [Brief description of the drawings]

[0009] [Figure 1] 1 is a photograph showing the top, side and cross-section of Samples 1 to 4 after alkali resistance test A was performed. [Diagram 2] 6 is a photograph showing the top, side and cross-section of Samples 1 to 3 after alkali resistance test B. [Diagram 3] 6 is a photograph showing the top, side and cross-section of Samples 1 to 3 after alkali resistance test C. [Figure 4] Photographs showing the top surfaces of Samples 1 to 6 before and after an acid resistance test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described below using embodiments. [Embodiment] (High alumina castable) The high alumina castable (hereinafter, castable) of this embodiment is a high alumina castable that is composed of aggregate, powder, and binder and does not contain cement. When the whole is taken as 100 mass%, it contains 50 to 95 mass% alumina, 4.5 to 49.5 mass% silica, and less than 0.5 mass% calcia.

[0011] The castable refractory of this embodiment is made by binding aggregate and powder with a binder, similar to conventional castable refractories. The castable refractory of this embodiment does not contain cement as a binder. Here, cement is a material whose main component is calcia (CaO), and the castable refractory of this embodiment does not contain calcia (CaO) as a binder. The castable of the present embodiment is a high alumina castable, and contains alumina as the most abundant component. By containing alumina as the most abundant component, the content ratio of components with low corrosion resistance is reduced.

[0012] The castable of this embodiment contains 50 to 95 mass% alumina when the whole is 100 mass%. By containing alumina at this ratio, the castable of this embodiment can suppress the decrease in corrosion resistance against slag or heat resistance. By containing 50 mass% or more alumina is contained as the most abundant component. By containing 95 mass% or less alumina, the function of the castable can be exerted. In other words, if an excessive amount of alumina is contained, the content ratio of other components (for example, binder) is relatively decreased. The preferred content ratio of alumina is 70 to 90 mass%.

[0013] The castable of this embodiment contains silica at 4.5 to 49.5 mass% when the whole is taken as 100 mass%. When the castable of this embodiment is exposed to high temperatures, silica is vitrified to form a glassy coating on the surface of the entire refractory material made of castable and on the surfaces of particles such as aggregate and powder that form the castable. The glassy coating suppresses the penetration of alkaline components. That is, silica increases the alkali resistance of the castable. If the content of silica is too low, the effect of containing silica is not exhibited. Specifically, when the castable (refractory) is exposed to high temperatures in the presence of alkaline components, if the amount of silica is too low (a glassy coating is not formed), β-alumina is generated. β-alumina causes volume expansion in the generation reaction. When volume expansion occurs, cracks are generated in the castable (refractory), and the expanded cracks cause the castable (refractory) to collapse. Moreover, if the silica content is excessive, the alumina content becomes relatively small, and the heat resistance of the castable deteriorates.The preferred silica content is 9 to 29.5 mass%.

[0014] The castable of this embodiment contains less than 0.5 mass% of calcia when the whole is taken as 100 mass%. Calcia is a component that reduces the acid resistance of the castable. By making the calcia content of the castable of this embodiment small, less than 0.5 mass%, the decrease in acid resistance is suppressed. Calcia also generates low melting point compounds such as anorthite. By reducing the amount of calcia, the generation of these low melting point compounds is suppressed. As a result, the occurrence of the above-mentioned problems caused by the low melting point compounds is suppressed. In other words, the castable of this embodiment suppresses the decrease in hot strength in the high temperature range and the erosion of slag. The content of calcia is preferably small. Specifically, it is preferably less than 0.3 mass%, more preferably less than 0.2 mass%, and even more preferably less than 0.1 mass%. In the castable refractory of this embodiment, it is preferable that calcia is not contained as much as possible. It is most preferable that no calcia is contained (i.e., the content of calcia is 0 mass%).

[0015] In the castable refractory of this embodiment, when calcia is contained, it is preferably contained in aggregate or powder. In other words, it is preferable not to contain calcia as a binder. Calcia contained in aggregate or powder is less reactive than when it is contained in a binder. In other words, castables containing calcia in aggregate or powder have less deterioration in corrosion resistance than castables containing calcia in a binder.

[0016] The castable refractory of this embodiment is composed of aggregate, powder, and binder, and the aggregate, powder, and binder are appropriately selected so as to obtain the above-mentioned content ratio. In other words, the specific compositions of the aggregate, powder, and binder are not limited, and are appropriately selected from conventionally known aggregates, powders, binders, etc.

[0017] The castable of this embodiment preferably contains amorphous silica in the binder. Amorphous silica is a substance containing silica that does not have a crystal structure. An example of amorphous silica is wet silica (colloidal silica). By containing amorphous silica in the binder, the above-mentioned glassy coating can be easily formed. That is, amorphous silica can easily form a glassy coating compared to silicon contained in aggregate or powder.

[0018] When at least one of the aggregate and the powder and the binder contain silica, the mass of silica contained in the binder is preferably smaller than the mass of silica contained in at least one of the aggregate and the powder. Even if the mass of silica contained in the binder is smaller than the mass of silica contained in at least one of the aggregate and the powder, the effect of containing silica in the binder can be exhibited. Here, the silica contained in at least one of the aggregate and the powder can be exemplified by a compound having a structure in which at least one of the aggregate and the powder has a structure in which a part of the silicon atoms in a silicate is replaced with an element such as aluminum. For example, aluminosilicate such as mullite, sillimanite, and andalusite can be exemplified. The castable refractory of the present embodiment may contain other components and additives within a range that does not impair the above-mentioned configuration and effects. For example, it may contain compounds such as binder solvents and stabilizers, and inevitable impurities.

[0019] The castable of this embodiment has excellent acid resistance and alkali resistance. Therefore, it is effective when applied to applications requiring acid resistance and alkali resistance. In addition, it has high heat resistance as a castable, and is preferably applied to applications such as heat treatment furnaces. Furthermore, it is preferably used for furnace walls of various furnaces such as melting furnaces and incinerators, which require not only acid resistance and alkali resistance but also corrosion resistance against slag.

[0020] (Waste treatment furnace) The waste treatment furnace of this embodiment uses the castable of this embodiment for the furnace wall. As described above, the castable of this embodiment has excellent corrosion resistance against slag as well as acid and alkali resistance. Therefore, even if the furnace wall comes into contact with the material to be treated that contains acids, alkalis, salts, etc. contained in the waste or gas containing acidic or alkaline components volatilized from the material to be treated, the occurrence of melting damage is suppressed. In other words, the castable of this embodiment is prevented from reacting and damaging the furnace wall. As a result, the waste treatment furnace of this embodiment is prevented from reducing the lifespan of the furnace wall due to damage. In the waste treatment furnace of this embodiment, the furnace wall is a member forming the inner circumferential surface of the treatment furnace that comes into contact with the material to be treated and the exhaust gas. That is, the furnace wall includes not only the inner surface of the treatment furnace, but also the bottom surface, the top surface, the inner circumferential surface of the exhaust flow path, etc. Furthermore, the furnace wall includes a member forming the surface of the storage container that stores and holds the material to be treated before and after treatment. In the waste treatment furnace of this embodiment, the specific properties of the furnace wall formed by the castable of this embodiment can be the properties required for the treatment furnace. For example, the porosity, bulk density, and strength (compressive strength) can be set arbitrarily. These properties can be measured by the method described in the examples below.

[0021] In the waste treatment furnace of the present embodiment, the porosity of the furnace wall formed from the castable of the present embodiment is preferably 10% or more, more preferably 10 to 20%, and even more preferably 10 to 15%. When the porosity is 10% or more, the furnace wall has sufficient spalling resistance.

[0022] In the waste treatment furnace of the present embodiment, the bulk density of the furnace wall formed by the castable of the present embodiment is preferably 2.5 or more, more preferably 2.5 to 3.5, and even more preferably 2.5 to 3.2. By making the specific gravity 2.5 or more, the furnace wall has sufficient strength. In the waste treatment furnace of this embodiment, the strength of the furnace wall formed by the castable of this embodiment is preferably 20 (MPa) or more. When the strength is 20 (MPa) or more, the furnace wall has sufficient strength.

[0023] The waste treatment furnace of this embodiment is not limited in the configuration of the treatment furnace itself, and may have the same configuration as a conventional waste treatment furnace. That is, the waste treatment furnace of this embodiment is preferably a conventional waste treatment furnace with a furnace wall formed from the castable refractory of this embodiment. EXAMPLES

[0024] The present invention will now be described with reference to specific examples.

[0025] Examples and Comparative Examples As examples and comparative examples, castables having the chemical compositions shown in Table 1 were prepared from aggregate, powder, and binder, and test pieces (samples 1 to 6) were molded. Specifically, castables for samples 1 to 6 were prepared, a specified amount of water was added, and the mixture was kneaded in a mortar mixer, poured into a specified formwork on a vibration table, naturally cured for 48 hours, removed from the formwork, and dried at 110°C for 24 hours. As a result, test pieces measuring 40 x 40 x 160 (mm) were manufactured. The binder was added at a ratio of 1 to 10 mass%, and colloidal silica was included in the binders of samples 1, 2, 3, and 6. Colloidal silica was not included in the binders of samples 4 and 5. In addition, materials such as fused alumina, sintered alumina, mullite, sillimanite, andalusite, bauxite, chamotte, and ash were used as aggregates and powders.

[0026] [Table 1]

[0027] The porosity and bulk density shown in Table 1 were measured by a method conforming to JIS R 2205. The compressive strength was measured by a method conforming to JIS R 2553.

[0028] (evaluation) To evaluate the castables of Samples 1 to 6, an alkali resistance test and an acid resistance test were carried out.

[0029] (Alkaline resistance test) A crucible erosion test was conducted as an alkali resistance test. The crucible was formed by drilling a hole of φ30×35 mm in a prismatic test piece of 70×70×65 mm. 20 g of sodium carbonate (commercially available) was placed in the hole of the crucible, and heat treatment was performed at 1200°C for 12 hours. After heat treatment, the crucible was allowed to cool (naturally cooled) to room temperature, and the appearance was observed. After that, the crucible was cut in the center (cross section in the axial direction of the hole), and the cut surface was observed (alkali resistance test A).

[0030] For the castables of Samples 1 to 3, crucibles of the same shape were formed, 25 g of sodium hydroxide was placed in them, and they were subjected to a heat treatment at 900° C. for 12 hours. Thereafter, the appearance and the cut surface were observed in the same manner (alkali resistance test B).

[0031] For the castables of Samples 1 to 3, crucibles of the same shape were formed, 25 g of sodium hydroxide was placed in them, and they were subjected to a heat treatment at 1200° C. for 12 hours, after which the appearance and the cut surface were similarly observed (alkali resistance test C). In all of the above tests, the hole was covered with a lid made of the same material as the crucible.

[0032] The observation results after these evaluation tests are shown in Figures 1 to 3. Figure 1 shows top, side and cross-sectional photographs of Samples 1 to 4 after alkali resistance test A. Figure 2 shows top, side and cross-sectional photographs of Samples 1 to 3 after alkali resistance test B. Figure 3 shows top, side and cross-sectional photographs of Samples 1 to 3 after alkali resistance test C.

[0033] As shown in Figure 1, no cracks were observed in the castables of samples 1 to 3, which had a calcia content of less than 0.5 mass%. Molten reagent (sodium carbonate) was observed at the top of the hole in the test piece. Furthermore, it was confirmed that the crucible was attached to the lid, which indicates that the penetration of alkaline components into the refractory structure was suppressed. In contrast, it can be seen that the castable of Sample 4 containing 0.7 mass% calcia has large cracks due to structural deterioration and volume expansion.

[0034] Furthermore, the amount of Na component permeated (depth of penetration from the surface) from the inner circumferential surface of the hole in the crucible was measured for the cross sections of the test pieces of Sample 2 and Sample 4 that had been subjected to Alkaline Test A. In Sample 2, Na penetration of about 1 mm was confirmed. In contrast, in Sample 4, penetration of 2 to 5 mm was confirmed. From this point of view, it can be confirmed that the castables of Samples 1 to 3, which contain less than 0.5 mass % of calcia, are more excellent in alkali resistance than the castable of Sample 4, which contains calcia.

[0035] Furthermore, as shown in Figures 2 to 3, traces of reagent corrosion can be confirmed on the surface of the test pieces of Samples 1 to 3. Alkaline tests B to C use more corrosive reagents than alkaline test A. For this reason, even in Samples 1 to 3 where no corrosion was confirmed in the case of sodium carbonate, slight corrosion occurred.

[0036] However, in the test pieces of samples 1 to 3, regardless of the test temperature, no large cracks were generated due to structural deterioration or volume expansion. The internal structure was sound. In other words, even when treated at a high temperature of 1200°C, high alkali resistance was exhibited.

[0037] The amount of sodium penetration was then measured after alkaline tests B and C. In both alkaline tests B and C, the amount of penetration decreased as the alumina content increased. Also, when comparing the samples after alkaline test B with the samples after alkaline test C, the amount of sodium penetration was smaller in the samples after alkaline test B, which was tested at a lower temperature. As described above, it was confirmed that the castable test pieces of Samples 1 to 3 corresponding to the examples of the present invention exhibited high alkali resistance.

[0038] (Acid resistance test) A hydrochloric acid corrosion test was conducted as an acid resistance test. A cubic test piece measuring 40×40×40 (mm) was cut out from each of the castables of Samples 1 to 6, and dried at 110° C. for 24 hours to produce the test piece. The test piece was then immersed in a 20% hydrochloric acid solution for 8 days. After the immersion, the specimens were dried and the appearance was observed. The masses of the specimens after drying were measured, and the rate of change in mass (%) before and after the acid treatment was measured. The test results are shown in Figure 4. Figure 4 shows photographs of the appearance of the specimens before and after the acid resistance test.

[0039] As shown in Fig. 4, the castable test pieces of Samples 1 to 3, which contain less than 0.5 mass% of calcia, did not show any cracks or embrittlement even after treatment with the acid solution. In addition, the mass change was almost 1% or less.

[0040] In contrast, in the castable test pieces of Samples 4 to 5, which contained 0.5 mass% or more of calcia, tissue embrittlement and collapse were confirmed on the outer surface. This is believed to be due to the calcia in the castable reacting with hydrochloric acid to produce calcium chloride. When calcium chloride is produced, the bonding strength decreases. As a result, tissue embrittlement led to collapse. This was confirmed more significantly in the castables of Samples 4 to 5, as the calcia content increased.

[0041] The castable of sample 6 contains fine silica powder, and this silica makes it more acid resistant than the castables of samples 4 and 5. However, the castable of sample 6 has a low alumina content, and its heat resistance is reduced.

[0042] As described above, it was confirmed that the castable test pieces of Samples 1 to 3 corresponding to the examples of the present invention exhibited high acid resistance.

[0043] (summary) From the results of the above-mentioned alkali resistance test and acid resistance test, it was confirmed that the castable test pieces of Samples 1 to 3 corresponding to the examples of the present invention had alkali resistance and acid resistance.

Claims

1. A high alumina castable for pouring construction, which is composed of aggregate, powder, and binder and does not contain calcia (CaO) as a binder, When the whole is 100 mass%, the alumina is 70 to 90 mass%, the silica is 9 to 29.5 mass%, and the calcia is 0.1 mass% or more and less than 0.5 mass%, The high alumina castable is characterized in that the binder contains amorphous silica.

2. A high alumina castable for pouring construction, which is composed of aggregate, powder, and binder and does not contain calcia (CaO) as a binder, A high alumina castable characterized in that, when the whole is taken as 100 mass%, it contains 50 to 95 mass% of alumina, 4.5 to 49.5 mass% of silica, and 0.1 mass% or more but less than 0.5 mass% of calcia (excluding cases where any of the following (1) to (4) is satisfied): (1) The aggregate and the powder contain 15 to 60 mass% spinel particles, where the spinel particles are MgAl ２ O ４ The particles contain 5 to 28 mass % of MgO and Al. ２ O ３ The total amount of the components is 95% by mass or more. (2) A compound of Mg or Ca having a particle size of 1 mm or less is added as a hardener in an amount of 0.05 to 1.0 mass %, and a metal sulfate or metal halide salt is added as a flocculating agent in an amount of 0.01 to 1.0 mass %, (3) A lignin-based dispersant is added, and the ratio of the weight of the aggregate and the powder to the weight of the lignin-based dispersant is 1:0.001 to 0.02; Further, an alkali salt is added, and the ratio of the weight of the aggregate and the powder to the weight of the alkali salt is 1:0.0005 to 0.02; (4) Magnesia fine powder having a particle size of 0.10 mm or less is added as a hardening agent in an amount of 0.05 to 1.0 mass %, and condensed phosphate is added as a hardening regulator in an amount of 0.01 to 0.2 mass %.

3. 3. The high alumina castable according to claim 2, wherein the alumina accounts for 70 to 90 mass% of the total mass being 100 mass%.

4. The high alumina castable according to any one of claims 2 to 3, wherein the binder contains amorphous silica.

5. The high alumina castable according to any one of claims 1 to 4, wherein when at least one of the aggregate and the powder, and the binder contain silica, the mass of silica contained in the binder is smaller than the mass of silica contained in at least one of the aggregate and the powder.

6. The high alumina castable according to any one of claims 1 to 5, wherein the calcia is contained in the aggregate.

7. A waste treatment furnace, characterized in that the high alumina castable according to any one of claims 1 to 6 is used for a furnace wall.

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