Poured materials for kilns

Abstract

The invention proposes a castable material for a furnace that allows for the elimination of post-casting drying and limits corrosion by alkali and mechanical stress from materials in the furnace. The castable material under the invention comprises: a refractory mixture containing: a total of 75% by mass or more of one or more selected materials from the group comprising aluminum oxide, aluminum oxide silicon oxide, and silicon carbide materials; and 1% by mass to 15% by mass silica powder, with remainders in which the proportion of CaO content derived from aluminum oxide cement is equal to or less than 0.5% by mass (including 0%); and colloidal silica added to this refractory mixture in the proportion of addition ranging from 0.5% by mass to 5% by mass based on its SiO2 content.

Description

Casting material for firing furnaces

[0001] The present invention relates to a pourable material for calcination furnaces such as incinerators, fluidized bed furnaces, industrial waste kiln treatment furnaces, circulating fluidized bed (CFB) boiler furnaces, cement manufacturing facility furnaces, gasification melting furnaces, and stoker furnaces.

[0002] Castable refractories are a general term for monolithic refractories that can be poured, and are also called castable refractories or castables. Such castable refractories generally use cement (alumina cement, Portland cement, magnesia cement, etc.) as a binder. However, when cement is used as a binder, a hydration reaction occurs at room temperature, increasing the strength of the castable material, making it difficult to dehydrate, and there is a risk of explosion if the temperature inside the furnace rises. Therefore, a drying process is required after pouring, which is costly and requires long periods of shutdown.

[0003] On the other hand, castable materials using silica sol, i.e., colloidal silica, as a binder are also known (e.g., Patent Documents 1 to 4). However, in a calciner that heat-treats (calcines or incinerates) materials inside the furnace, such as an incinerator, the castable material that forms the furnace wall has a problem in that it is susceptible to physical impacts and erosion reactions from the materials flowing inside the furnace.

[0004] JP 2015-168596 A JP 2018-111612 A JP 2019-119653 A JP 2019-142727 A

[0005] The inventors of the present invention have conducted a detailed investigation into the corrosion reaction that occurs in the firing furnace, and have found that the corrosion reaction occurs when an alkaline component (Na ２ O.K. ２ It has been found that corrosion by alkalis (e.g., O, CaO), known as alkali attack, is a major factor in the corrosion reaction. In other words, in the kiln, alkali attack reduces the viscosity of the working surface (surface of the workpiece), allowing alkali to easily penetrate into the workpiece. As a result, the difference in expansion between the alkali-permeated layer and the non-permeated layer causes peeling, and corrosion progresses.

[0006] In view of the above, the problem that the present invention aims to solve is to provide a pourable material for a firing furnace that does not require a drying process after pouring, can suppress physical impacts from objects inside the furnace, and can suppress alkali attack.

[0007] The present inventors have conducted extensive testing and research to find a means for suppressing alkali penetration due to alkali attack in a pourable material using colloidal silica as a binder, and have found that it is effective to generate high viscosity glass on the surface (working surface) of the applied body. To achieve this, it is important to control the amount of silicate bond in the matrix of the applied body. Specifically, the refractory raw material mixture of the pourable material contains silica flour in a specific range of content and the SiO of colloidal silica is ２ It has been found that it is important to set the addition rate of the component within a specific range.

[0008] The present invention has been conceived based on these findings and technical ideas, and in one aspect thereof, provides the following pourable material for a firing furnace: A refractory raw material blend containing at least 75 mass% of alumina raw materials excluding calcined alumina and at least one of alumina-silica raw materials, 1 mass% to 15 mass% of silica flour, and 4 mass% to 10 mass% of calcined alumina, and having a CaO content of 0.5 mass% or less (including zero) derived from alumina cement, and further comprising: adding colloidal silica to a refractory raw material blend containing at least one of alumina raw materials excluding calcined alumina and alumina-silica raw materials in a total amount of at least 75 mass%; ２ According to another aspect of the present invention, there is provided the following pourable material for a firing furnace: A refractory raw material mixture containing 75% by mass or more of a silicon carbide raw material and 1% by mass or more and 15% by mass or less of silica flour, and having a CaO content of 0.5% by mass or less (including zero), wherein colloidal silica is added to a refractory raw material mixture containing SiO ２ A pourable material for a firing furnace, which is added as a component at an addition rate of 0.5 mass % or more and 5 mass % or less.

[0009] According to the present invention, a drying process is not required after pouring, and physical impacts from objects inside the furnace can be suppressed, as well as alkali attack.

[0010] The pourable material for a firing furnace according to the present invention (hereinafter simply referred to as "the pourable material of the present invention") is a refractory raw material blend containing at least one of an alumina raw material, an alumina-silica raw material, and a silicon carbide raw material in a total amount of 75 mass% or more, and 1 mass% to 15 mass% of silica flour, and having a content of CaO component derived from alumina cement of 0.5 mass% or less (including zero), and further comprising colloidal silica and SiO ２ The component is added at a rate of 0.5% by mass or more and 5% by mass or less.

[0011] Thus, in the pourable material of the present invention, the refractory raw material composition is characterized by having one or more of an alumina raw material, an alumina silica raw material, and a silicon carbide raw material as the main material, containing 1% by mass or more and 15% by mass or less of silica flour, and having a content of the CaO component derived from alumina cement of 0.5% by mass or less (including zero).

[0012] If the silica flour content is less than 1% by mass, sufficient silicate bonds are not formed in the matrix of the construction. Therefore, the effects of inhibiting alkali penetration and suppressing physical impacts from objects inside the furnace cannot be obtained. On the other hand, if the silica flour content exceeds 15% by mass, the construction becomes excessively dense because the silica flour is a fine powder. Therefore, there is a risk of explosion when the temperature inside the furnace rises. Furthermore, the particle size structure of the refractory raw material composition becomes excessively fine, resulting in a relative decrease in the aggregate content, which reduces the compressive strength of the construction and reduces the effect of suppressing physical impacts from objects inside the furnace. The silica flour content is preferably 3% by mass or more and 10% by mass or less.

[0013] Furthermore, in the present invention, the content of the CaO component derived from alumina cement in the refractory raw material blend is limited to 0.5 mass% or less (including zero). This is because the CaO component derived from alumina cement promotes alkali penetration due to alkali attack. Furthermore, as mentioned above, the CaO component derived from alumina cement causes spalling, making a drying process necessary after pouring. From these perspectives, the lower the content of the CaO component derived from alumina cement, the better, and zero is most preferable.

[0014] In the pourable material of the present invention, the refractory raw material composition preferably contains 4% by mass or more and 10% by mass or less of calcined alumina. By including calcined alumina in this range, the cast body is appropriately densified, improving the effects of suppressing alkali penetration and suppressing physical impacts from objects inside the furnace. Note that, in the present invention, calcined alumina does not fall under the category of the alumina raw material, which is one of the main components of the refractory raw material composition. In other words, the content of the alumina raw material in the present invention does not include the content of calcined alumina.

[0015] As described above, in the present invention, colloidal silica is used as a binder, and its addition rate is SiO ２ The content of the colloidal silica component is 0.5% by mass or more and 5% by mass or less. ２ This refers to the addition rate of the colloidal silica component. The same applies hereinafter. If the addition rate of colloidal silica is less than 0.5% by mass, sufficient silicate bonds are not formed in the matrix of the applied body. As a result, the effects of suppressing alkali penetration and suppressing physical impacts from objects inside the furnace are insufficient. On the other hand, if the addition rate of colloidal silica exceeds 5% by mass, the porosity of the applied body increases, and the density of the applied body also decreases, resulting in a decrease in the compressive strength of the applied body. As a result, the effects of suppressing alkali penetration and suppressing physical impacts from objects inside the furnace are reduced. The addition rate of colloidal silica is preferably 1.5% by mass or more and 5% by mass or less.

[0016] In the present invention, colloidal silica is added as a binder to the refractory raw material composition described above. In addition, various additives such as dispersants, set modifiers, and anti-splintering agents may also be added as appropriate. Dispersants impart fluidity during application, and specific examples include inorganic salts such as sodium tripolyphosphate, sodium hexametaphosphate, sodium ultrapolyphosphate, acidic sodium hexametaphosphate, sodium borate, sodium carbonate, and polymetaphosphates, as well as sodium citrate, sodium tartrate, sodium polyacrylate, sodium sulfonate, polycarboxylates, β-naphthalenesulfonates, and naphthalenesulfonic acid. Set modifiers include set accelerators and set retarders. Specific examples of set accelerators include slaked lime, calcium chloride, gypsum, magnesia, sodium aluminate, and lithium carbonate. Specific examples of set retarders include boric acid, oxalic acid, citric acid, gluconic acid, sodium carbonate, and sugar. Specific examples of anti-splitters include organic fibers, organic foaming agents, basic aluminum lactate, metallic aluminum, etc. Specific examples of organic fibers include polymeric organic fibers such as vinylon (including polyvinyl alcohol), rayon, polyester, nylon, polypropylene, and polyethylene. These additives, like colloidal silica as a binder, are added in proportions based on 100% by mass of the refractory raw material blend. The addition rate may be the same as that of general pouring materials.

[0017] In addition to the refractory raw material mixture, binder, and additives described above, the castable material of the present invention can also contain large coarse particles having a particle size of 8 mm or more. These large coarse particles serve to prevent the propagation of cracks that have occurred in the refractory structure, and as the material for these particles, one or more of alumina, alumina silica, and silicon carbide can be used, as in the main materials of the refractory raw material mixture. However, in the castable material of the present invention, the large coarse particles are not included in the refractory raw material mixture. In other words, in the castable material of the present invention, the large coarse particles are added in an amount equivalent to an outer percentage of 100% by mass of the refractory raw material mixture. In other words, the refractory raw material mixture in the castable material of the present invention is a mixture of refractory raw materials having a particle size of less than 8 mm.

[0018] The raw material compositions and evaluation results of the examples and comparative examples of the present invention are shown in Table 1. The evaluation items and evaluation methods in the examples and comparative examples are as follows.

[0019] <Alkali Penetration Resistance> A predetermined amount of water was added to each raw material blend and kneaded. A 70 x 70 x 65 mm prismatic test piece was prepared by drilling a φ30 x 35 mm hole in the crucible test piece. 20 g of sodium carbonate (commercially available) was placed in the hole of the crucible test piece, and the crucible test piece was subjected to a heat treatment at 1200°C for 12 hours. After the heat treatment, the crucible test piece was allowed to cool to room temperature (natural cooling). Thereafter, the crucible test piece was cut at the center (cross section in the axial direction of the hole), and the cut surface was observed. In observing the cut surface, the remaining thickness of the most corroded area was measured, and the remaining ratio relative to the thickness before the test was calculated. The alkali penetration resistance was evaluated using an erosion index, where the remaining ratio of Comparative Example 1 was set to 100. The smaller the corrosion index, the better the resistance to alkali penetration, i.e., the greater the effect of suppressing alkali penetration due to alkali attack. The corrosion index was evaluated as follows: ⊚ (good); 80 or more but less than 90; ◯ (passable); 90 or more but less than 100; and × (poor); and 100 or more.

[0020] <Explosion Resistance> A predetermined amount of water was added to each raw material blend and kneaded. The mixture was then poured into a 100 mm diameter x 100 mm height cylindrical mold, cured for 24 hours, and removed from the mold to obtain two cylindrical test pieces. Each test piece was placed in an electric furnace at 900°C, heated, and held for 30 minutes before being removed. Each test piece was inspected for the presence or absence of explosion and cracking. Evaluation was performed on two test pieces, with the following criteria: ◎ (good) for no cracking, ○ (passable) for minor cracking, △ (fail) for partial surface fracture, and × (poor) for fracture or 50% or more damage. The inventors confirmed that if the explosion resistance was evaluated as ◎ (good) or ○ (passable), a drying process was not required after casting in an actual furnace.

[0021] <Abrasion Resistance> A predetermined amount of water was added to the raw material composition of each example, and the mixture was kneaded. The mixture was poured into a 115 x 115 x 65 mm mold, cured for 24 hours, removed from the mold, and dried to obtain a test specimen, which was then heat-treated at 800 °C for 5 hours. The test specimens were measured in accordance with ASTM C704 (Abrasion Resistance of Refractory Materials at Room Temperature). Specifically, the 115 x 115 mm surface was set at a 45° angle relative to the direction of the abrasive material discharge. Then, while rotating the test specimen at 15 revolutions per minute around the vertical centerline of the 115 x 115 mm surface, 1 kg of abrasive material was continuously sprayed onto the 115 x 115 mm surface. Silicon carbide particles with a particle size adjusted to 1 to 0.3 mm were used as the abrasive material. The spray air pressure was 0.4 MPa. The mass of the test specimen was measured before and after the test, and the abrasion volume was calculated from the change in mass and the bulk specific gravity of the test specimen. The abrasion resistance was evaluated by an abrasion index when the abrasion volume of Comparative Example 1 was set to 100. The smaller the abrasion index, the better the abrasion resistance, i.e., the greater the effect of suppressing physical impact from objects inside the furnace. The abrasion index was evaluated as follows: ⊚ (good); 80 or more but less than 90; ◯ (passable); 90 or more but less than 100; △ (unacceptable); and × (poor); 100 or more.

[0022] <Overall evaluation> When the evaluations of alkali penetration resistance, explosion resistance, and abrasion resistance were all rated as ◎ (good), when at least one of these evaluations was ◯ (passable), when at least one of these evaluations was △ (fail), and when at least one of these evaluations was × (poor). That is, the overall evaluation was ranked in the order of ◎, ○, △, ×, with the overall evaluations of ◎ and ◯ being pass, and △ and × being fail.

[0023]

[0024] Examples 1 to 6 are examples in which the main component of the refractory raw material composition was an alumina raw material, and the silica flour content was varied within the range of the present invention. The overall evaluation was ⊚ or ◯, and good results were obtained. Among these, Examples 2 to 4 and 6, in which the silica flour content was within the preferred range of 3% by mass or more and 10% by mass or less, were overall evaluated as ⊚, and particularly good results were obtained. In contrast, Comparative Example 1 is an example in which the silica flour content was below the lower limit of the present invention, and the alkali penetration resistance and abrasion resistance were significantly reduced. Furthermore, Comparative Example 2 is an example in which the silica flour content exceeded the upper limit of the present invention, and the explosion resistance was significantly reduced and the abrasion resistance was also insufficient.

[0025] Example 7 is an example containing 0.5% by mass of the CaO component derived from alumina cement. Compared with Example 6, which does not contain the CaO component derived from alumina cement, the alkali penetration resistance and explosion resistance were slightly reduced but still at an acceptable level. In contrast, Comparative Example 3 is an example in which the content of the CaO component derived from alumina cement was 1% by mass, which exceeds the upper limit value of the present invention, and the alkali penetration resistance and explosion resistance were significantly reduced.

[0026] Reference Example 8 is an example that does not contain calcined alumina. Compared with Example 6 that contains calcined alumina, the alkali penetration resistance and abrasion resistance were slightly lower but still at an acceptable level. Examples 9 and 10 are examples in which the content of calcined alumina was changed, but like Example 6, the overall evaluation was ⊚, and good results were obtained.

[0027] Although the main component of the refractory raw material blend was changed in Examples 11 to 13, all of the results were within the scope of the present invention and were satisfactory. Furthermore, a comparison between Examples 12 and 13 revealed that when the main component of the refractory raw material blend was a silicon carbide raw material, satisfactory results could be obtained even without the inclusion of calcined alumina.

[0028] Examples 14 to 16 are examples in which the main component of the refractory raw material formulation was an alumina raw material, and the colloidal silica addition rate was varied within the range of the present invention. The overall evaluation was ⊚ or ◯, and good results were obtained. Among these, Examples 15 and 16, in which the colloidal silica addition rate was 1.5 mass% or more and 5 mass% or less, which was within the preferred range, were overall evaluated as ⊚, and particularly good results were obtained. In contrast, Comparative Example 4 is an example in which the colloidal silica addition rate was below the lower limit of the present invention, and the abrasion resistance was significantly reduced, and the alkali penetration resistance was also insufficient. Furthermore, Comparative Example 5 is an example in which the colloidal silica addition rate exceeded the upper limit of the present invention, and the alkali penetration resistance and abrasion resistance were significantly reduced.

Claims

1. A refractory raw material mixture containing at least one of alumina raw materials other than calcined alumina and alumina silica raw materials in a total amount of 75% or more, silica flour in an amount of 1% by mass to 15% by mass, calcined alumina in an amount of 4% by mass to 10% by mass, and a content of CaO component derived from alumina cement of 0.5% by mass or less (including zero) is added with colloidal silica in the amount of SiO ２ A pouring material for a firing furnace, comprising a component added at an addition rate of 0.5 mass% or more and 5 mass% or less.

2. A refractory raw material mixture containing 75% by mass or more of silicon carbide raw material, 1% by mass or more and 15% by mass or less of silica flour, and a content of CaO component derived from alumina cement of 0.5% by mass or less (including zero) is added to the refractory raw material mixture. ２ A pouring material for a firing furnace, comprising a component added at an addition rate of 0.5 mass% or more and 5 mass% or less.

3. A pourable material for incinerators as described in claim 1 or 2, in which the silica flour content is 3% by mass or more and 10% by mass or less.

4. The colloidal silica addition rate is SiO ２ The incinerator pourable material according to claim 1 or 2, wherein the component is 1.5% by mass or more and 5% by mass or less.