Precast block for coke oven and method for manufacturing the same

Abstract

To provide a precast block for coke ovens, capable of suppressing shrinkage under load at high temperatures, and capable of being removed from a mold only after curing at room temperature, and to provide a method for manufacturing the same.SOLUTION: A refractory raw material mixture containing at least 65 mass% or more of fused silica, at least 0.5 mass% or more and 15 mass% or less of silica flour, at least 0.5 mass% or more and 3.5 mass% or less of Portland cement, and at least 0.5 mass% or more and 1.5 mass% or less of sodium phosphate glass is kneaded, poured into a mold, cured at room temperature, removed from the mold, and then dried.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a precast block suitable for use in a coke oven and a method for manufacturing the same. [Background technology]

[0002] Traditionally, coke ovens have been lined with silica bricks. However, when using silica bricks, a large number of bricks must be laid, which is problematic as it takes a long time to lay them. Therefore, in recent years, especially in hot repair work, construction using silica precast blocks, which are easier to make larger than silica bricks, has become common.

[0003] Such precast blocks are required to have hot properties as structures. In particular, in coke ovens, in addition to hot strength, the stability of the expansion and contraction behavior under load at high temperatures (hereinafter collectively referred to as the expansion and contraction behavior under load) is required. If the expansion and contraction behavior under load at high temperatures is unstable (if the deformation due to the expansion and contraction under load at high temperatures is large), the resistance increases when pushing out the coke, hindering operation and the precast block itself may be damaged.

[0004] Patent Document 1 describes a technology that uses fused quartz as the main raw material and Portland cement as the binder. However, when Portland cement is used as the binder, the CaO component in the Portland cement makes the fused quartz more likely to sinter, which causes a problem of significant shrinkage under load at high temperatures.

[0005] Patent Document 2 discloses a method for manufacturing a precast block for a coke oven, which comprises blending a siliceous raw material (a source of a SiO2 component) with sodium phosphate as a binder (a source of a P2O5 component), adding an appropriate amount (for example, 5% by mass to 7% by mass) of construction water to the resulting refractory raw material blend, and then kneading, forming, curing, demolding, and drying. It is said that by using a P2O5 component as a binder component, rather than using a large amount of cement as a binder or using colloidal silica and sodium silicate as binders, it is possible to stably control the expansion and contraction behavior under load at high temperatures while maintaining high hot strength.

[0006] However, when a P2O5 component such as sodium phosphate is used as a binder, the curing strength at room temperature is insufficient, so the form cannot be removed by room temperature curing alone, and the form must be removed after about 12 hours of heat curing (steam curing). This means that the precast blocks tend to stick to the formwork due to heating, making the form removal process time-consuming, and the surface of the precast blocks becomes rough after removal from the form, resulting in a problem of reduced yield.

[0007] Furthermore, in the examples of Patent Document 3, a precast block for a coke oven is disclosed in which fused silica raw material and silica fume are used, and magnesia fine powder with a particle size of 75 μm or less is added as a hardener, condensed phosphate as a dispersant, and phosphate (phosphate glass) as a sintering aid in amounts of 0.4 mass%, 0.2 mass%, and 1 mass%, respectively, relative to 100 mass% of the refractory raw material mixture. However, because this example does not contain cement, there is a problem, similar to Patent Document 2, in that heat curing is required to manufacture a large block. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 56-78476 [Patent Document 2] Patent No. 6823042 [Patent Document 3] Patent No. 6964787 Summary of the Invention [Problem to be solved by the invention]

[0009] The problem that the present invention aims to solve is to provide a precast block for a coke oven that suppresses shrinkage under load at high temperatures and can be removed from the formwork simply by curing at room temperature, and a method for manufacturing the same. [Means for solving the problem]

[0010] The inventors conducted various studies to suppress shrinkage under load at high temperatures of precast coke oven blocks that use Portland cement as a binder, and discovered that shrinkage under load at high temperatures can be suppressed by adding sodium phosphate glass.

[0011] That is, the manufacturing method of the precast block for coke oven of the present invention is characterized in that a refractory raw material composition containing 65 mass% or more of fused silica, 0.5 mass% to 15 mass% of silica flour, 0.5 mass% to 3.5 mass% of Portland cement, and 0.5 mass% to 1.5 mass% of sodium phosphate glass is mixed and cast, cured at room temperature, and dried after removal from the frame. The precast block for a coke oven of the present invention is characterized in that it is made using a refractory raw material composition containing 65% by mass or more of fused silica, 0.5% by mass to 15% by mass of silica flour, 0.5% by mass to 3.5% by mass of Portland cement, and 0.5% by mass to 1.5% by mass of sodium phosphate glass. Effect of the Invention

[0012] According to the present invention, the precast blocks can be removed from the frames after curing at room temperature, which simplifies the removal work and improves the work efficiency, and the surface roughness of the precast blocks after removal from the frames is prevented, which improves the yield. Furthermore, the shrinkage under load at high temperatures can be suppressed, which prevents the precast blocks from protruding into the coke chamber, stabilizing the operation of the coke oven and preventing damage to the precast blocks. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In the present invention, Portland cement is used as a binder, and since it hardens at room temperature and has sufficient strength, it has the effect of preventing the surface of the precast block from becoming rough after removal from the form. If the Portland cement content is less than 0.5% by mass, the surface of the precast block becomes rough after removal from the form, and if it exceeds 3.5% by mass, shrinkage under load at high temperatures tends to increase.

[0014] The Portland cement that can be used in the present invention can be one or more of ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, sulfate-resistant Portland cement, and the like.

[0015] In the present invention, the sodium phosphate glass reacts with CaO due to heat received during use faster than the reaction between fused silica and CaO in Portland cement. Therefore, the reaction between fused silica and CaO can be suppressed, and shrinkage under load at high temperatures can be suppressed. If the sodium phosphate glass is less than 0.5% by mass, the shrinkage suppression effect under load is insufficient, and if it exceeds 1.5% by mass, the sodium content becomes too high and the shrinkage suppression effect under load is insufficient. In the present invention, the sodium phosphate glass is preferably used as a fine powder in order to disperse uniformly in the structure and to increase reactivity, and specifically, a particle size of less than 0.1 mm can be used. Here, the "particle size" refers to the sieve mesh, and a particle size of less than 0.1 mm refers to one that passes through a sieve mesh of 0.1 mm.

[0016] The sodium phosphate glass used in the present invention is a glass powder that is poorly soluble in water at room temperature, unlike phosphates used as dispersants for refractories, and can be one that is generally commercially available as a binder for refractories. More specifically, one with a melting point of 300°C to 500°C and chemical components of 60 to 70 mass% P2O5, 15 to 30 mass% Na2O, and 3 to 10 mass% Al2O3 can be used. Here, poorly soluble in water means that the amount of dissolution in 100 g of water at 20°C is 20 g or less.

[0017] In the present invention, by using sodium phosphate glass which is poorly soluble in water, the sodium phosphate glass is not affected by the movement of moisture (bond migration) during drying of the molded body and is uniformly dispersed in the refractory structure, so that the above-mentioned sintering suppression effect can be further enhanced, and since the phosphoric acid component does not dissolve at room temperature, an increase in viscosity is suppressed and good workability can be obtained during pouring.

[0018] In the present invention, 65% by mass or more of fused silica is used in the refractory raw material blend because it contains few impurities, has excellent heat resistance, has a small thermal expansion coefficient, and is excellent in volume stability and thermal shock resistance. The content of fused silica is preferably 82% by mass or more. The upper limit of the content of fused silica can be 98% by mass.

[0019] Silica flour is used to maintain strength when hot; if it is less than 0.5% by mass, the strength will be insufficient, and if it exceeds 15% by mass, the viscosity will increase during mixing, making workability difficult and causing the surface of the precast block to become rough after removal from the form.

[0020] Silica flour as used in this invention refers to fine silica particles with an average primary particle size of 10 μm or less, and generally refers to silica fume, fumed silica, and white carbon. Silica fume is a by-product obtained by collecting exhaust gas generated during the refining process of ferrosilicon, metallic silicon, electrofused zirconia, etc., and is relatively inexpensive to obtain. Fumed silica is produced by hydrolyzing silicon tetrachloride and other silicon compounds in a flame of oxygen and hydrogen. White carbon is obtained by decomposing sodium silicate using an acid or alkali. The term "average particle size" as used herein refers to the volume average particle size corresponding to the median cumulative value (D50) of a cumulative curve measured using a laser diffraction / scattering particle size distribution analyzer.

[0021] In the present invention, in addition to the above refractory raw materials, siliceous raw materials such as silica stone and silica brick chips can be used at 20% by mass or less since they have no adverse effect. Also, dispersants, hardening regulators, defoamers, fibers, etc., which are generally used in monolithic refractories, can be used at 2% by mass or less each.

[0022] In the present invention, the above-mentioned refractory raw material mixture is mixed with an appropriate amount of water, poured into a formwork, cured at room temperature, removed from the formwork, and dried to obtain the desired precast block for a coke oven. The curing time can be, for example, 12 hours to 24 hours. Drying is performed to remove moisture, but it is not necessary to remove all moisture. The drying temperature can be, for example, 50°C to 400°C. EXAMPLES

[0023] The raw materials were mixed according to the raw material composition in Table 1, 6.5 mass% of construction water was added, and the mixture was kneaded and poured into a formwork. It was then cured at 20°C for 12 hours. After removal from the formwork, it was dried at 110°C for 12 hours to obtain a test piece (200 x 200 x 200 mm) of a precast block for a coke oven. The expansion and contraction behavior under load, hot bending strength, ease of removal from the formwork, and surface condition of the molded body after removal from the formwork were evaluated using the test piece.

[0024] The particle sizes of the fused silica and the calcined silica were mixed in a ratio of 6:4, with particles between 1 mm and 5 mm and particles less than 1 mm. Fumed silica was used as the silica fuller, with an average particle size of 0.5 μm. The chemical components of the refractory raw materials were as follows: fused silica 99.7% by mass SiO2, calcined silica 99.5% by mass SiO2, fumed silica 96% by mass SiO2 and 0.2% by mass Na2O, sodium phosphate glass 65% by mass P2O5, 7% by mass Al2O3 and 23% by mass Na2O, sodium phosphate (soluble) 69% by mass P2O5 and 21% by mass Na2O, and portland cement 24% by mass SiO2 and 67% by mass CaO. A polycarboxylic acid type surfactant was used as the dispersant. The sodium phosphate glass used had a dissolution rate of about 1 g in 100 g of water at 20° C., and the sodium phosphate (soluble) used had a dissolution rate of 97 g in 100 g of water at 20° C. The particle sizes of the sodium phosphate glass and the sodium phosphate (soluble) were each less than 74 μm.

[0025] The expansion / contraction rate under load (%) was measured in accordance with JIS R 2207-2 under a load of 0.2 MPa in the temperature range from room temperature to 1300° C. In either case, the change in expansion / contraction was large between 1000° C. and 1100° C., so the maximum value of this expansion / contraction rate is shown in Table 1. The hot bending strength was measured at 1000° C. in accordance with JIS R 2213. The test piece was kept in a furnace for 1 hour to reach the measurement temperature, and the hot bending strength was measured. The ease of removal from the mold was evaluated as ◯ (good) when there was no adhesion between the mold and the shaped body and they could be easily separated, and evaluated as × (bad) when there was adhesion between the mold and the shaped body and separation was difficult. The surface condition of the molded body after removal from the frame was evaluated as × (bad) when it was stuck to the metal frame and a dent was generated on the surface of the molded body, and ◯ (good) when no dent was generated on the surface of the molded body. Note that pores on the surface of the molded body were not considered to be dents. The overall evaluation was based on the criteria in Table 2, with ◎ (excellent) and 〇 (good) being considered passing. The evaluation results are shown in Table 1.

[0026] [Table 1]

[0027] [Table 2]

[0028] Examples 1 to 3 have different Portland cement contents, but are within the range of the present invention, and the expansion and contraction rate under load is small, the hot strength is sufficient, and the surface condition of the molded body after removal from the form is also good. In contrast, Comparative Example 1 has a Portland cement content below the lower limit of the present invention, and the formwork does not peel off well from the surface of the molded body due to insufficient hardening of the castable, causing the surface of the molded body to become rough. On the other hand, Comparative Example 2 has a Portland cement content above the upper limit of the present invention, and the shrinkage under load is large.

[0029] Although the contents of sodium phosphate glass were different in Examples 4 to 6, they were within the range of the present invention and gave good results. In contrast, Comparative Example 3 was a case in which the amount of sodium phosphate glass added was below the lower limit of the present invention, and shrinkage under load was large. Comparative Example 4 was a case in which the content of sodium phosphate glass exceeded the upper limit of the present invention, and shrinkage under load was large. Comparative Example 5 was a case in which soluble sodium phosphate was used, and surface roughness occurred due to adhesion between the molded body and the form when the form was removed.

[0030] Although the contents of fumed silica in Examples 7 and 8 were different, they were within the range of the present invention and gave good results. In contrast, Comparative Example 6 was a case in which the content of fumed silica was below the lower limit of the present invention, resulting in low strength. Comparative Example 7 was a case in which the content of fumed silica was above the upper limit of the present invention, resulting in high viscosity during kneading and surface roughness due to adhesion between the molded body and the formwork during removal from the formwork.

[0031] Example 9 is a case where calcined silica was used, and Example 10 is a case where the content of fused silica was high, but both were within the range of the present invention and provided good results.

Claims

1. The method for producing a precast block for a coke oven comprises kneading a refractory raw material mixture containing 65% by mass or more of fused silica, 0.5% by mass to 15% by mass of silica flour, 0.5% by mass to 3.5% by mass of Portland cement, and 0.5% by mass to 1.5% by mass of sodium phosphate glass, pouring the mixture into a mold, curing the mold at room temperature, and drying the mold after removing the mold.

2. 2. The method for producing a precast block for a coke oven according to claim 1, wherein the content of Portland cement in the refractory raw material mixture is 0.5% by mass or more and 2.5% by mass or less.

3. A precast block for a coke oven is made using a refractory raw material blend containing 65% by mass or more of fused silica, 0.5% by mass or more and 15% by mass or less of silica flour, 0.5% by mass or more and 3.5% by mass or less of Portland cement, and 0.5% by mass or more and 1.5% by mass or less of sodium phosphate glass.

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