Method for sorting silica brick, silica brick, and coke oven

Abstract

To construct a sound coke oven by using silica bricks which are hardly chipped and have damage resistance.SOLUTION: Provided is a method for sorting silica bricks for constructing a coke oven, the method comprising sorting silica bricks that satisfy all of the following conditions i) to iii): i) a bending strength of 7MPa or more and 15MPa or less, ii) a shape parameter m in a Weibull distribution of the bending strength of 5 or more, and iii) a ratio of a dynamic modulus of elasticity to a square of the bending strength of 80 or more SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for selecting silica bricks, silica bricks, and coke ovens. [Background technology]

[0002] A coke oven is a facility for carbonizing coal, with alternating arrangements of coke chambers into which raw coal is inserted and combustion chambers in which gas is burned to maintain high temperatures. Coke ovens are constructed using various types of bricks, but silica bricks, which have excellent hot strength and hot volume stability, are used for the structural components of the coke chambers and combustion chambers. Technology related to silica bricks is described in Patent Documents 1 and 2, for example.

[0003] In constructing a coke oven like the one described above, the bricks must be stacked without misalignment in the vertical and depth directions, so high precision is required for brick positioning. However, silica bricks can have chips along their ridges in the longitudinal direction, which reduces the precision of positioning using strings or other methods. Therefore, silica bricks used to construct coke ovens must be chip-resistant. Furthermore, because coke ovens reach high temperatures during operation, especially in the carbonization chamber and combustion chamber, silica bricks must also be resistant to damage caused by temperature fluctuations. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-4864 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-327408 Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, an object of the present invention is to provide a method for selecting silica bricks, silica bricks, and coke ovens that enable the construction of sound coke ovens by using silica bricks that are less likely to chip and are resistant to damage. [Means for solving the problem]

[0006] [1] A method for selecting silica bricks for constructing a coke oven, comprising the steps of: A method for selecting silica bricks, which selects silica bricks that satisfy all of the following conditions i) to iii): i) The bending strength measured by the three-point bending test method at room temperature is 7 MPa or more and 15 MPa or less ii) The shape parameter m in the Weibull distribution of the bending strength is 5 or more. iii) The ratio of the dynamic modulus of elasticity to the square of the bending strength is 80 or more. [2] The method for selecting silica bricks according to [1], wherein the silica bricks contain particles with a particle size of 1 mm or more and 5 mm or less in an amount of 10% by volume to 30% by volume. [3] The method for selecting silica bricks according to [1] or [2], wherein the silica bricks contain 10% by mass or more and 30% by mass or less of cristobalite. [4] Silica bricks for constructing coke ovens, Silica bricks that meet all of the following conditions i) to iii) in the test. i) The bending strength measured by the three-point bending test method at room temperature is 7 MPa or more and 15 MPa or less ii) The shape parameter m in the Weibull distribution of the bending strength is 5 or more. iii) The ratio of the dynamic modulus of elasticity to the square of the bending strength is 80 or more. [5] The silica brick according to [4], containing particles with a particle size of 1 mm or more and 5 mm or less at 10% by volume or more and 30% by volume or less. [6] A silica brick according to [4] or [5], containing 10% by mass or more and 30% by mass or less of cristobalite. [7] A coke oven constructed at least in part using the silica bricks described in any one of [4] to [6]. [Effects of the Invention]

[0007] According to the above-mentioned configuration, a coke oven can be constructed using silica bricks that are chip-resistant and have resistance to damage. Because they are chip-resistant, they can be positioned with high precision during construction, and by using silica bricks with sufficient resistance to damage, a sound coke oven can be constructed. DETAILED DESCRIPTION OF THE INVENTION

[0008] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0009] In an embodiment of the present invention, silica bricks that satisfy all of the following conditions i) to iii) in a test are selected as silica bricks for constructing a coke oven. Note that in this specification, constructing a coke oven means building a coke oven. i) The bending strength measured by the three-point bending test method at room temperature is 7 MPa or more and 15 MPa or less ii) The shape parameter m in the Weibull distribution of bending strength in i) is 5 or more iii) The ratio of the dynamic modulus of elasticity to the square of the bending strength of i) is 80 or more

[0010] Note that, because the bricks are deformed or destroyed by the test for measuring bending strength in i), the bricks used in the test and the bricks used in constructing coke ovens are not the same individual bricks, even if they have the same components and are manufactured by the same method. On the other hand, for already selected silica bricks, if the bricks used in constructing coke ovens are extracted and further subjected to the tests and analysis in i) to iii), it can be determined whether or not they are silica bricks according to the embodiment of the present invention.

[0011] In i), the bending strength is measured at room temperature using a three-point bending test method in accordance with JIS R2213-1995, "Testing Method for Bending Strength of Refractory Bricks." Note that room temperature is between 5°C and 35°C, and the bending strength is determined by averaging the measurements from 20 test pieces and rounding to the nearest integer. In ii), the shape parameter m (Weibull coefficient) in the Weibull distribution is calculated from the bending strength test data from 20 test pieces in accordance with JIS R1625:2010, "Weibull Statistical Analysis Method for Strength Data of Fine Ceramics." In iii), the dynamic modulus of elasticity is measured using the ultrasonic pulse method in accordance with JIS R1602-1995, "Testing Method for Elastic Modulus of Fine Ceramics."

[0012] As will be shown in the examples described later, chipping along the ridgelines of silica bricks can be effectively prevented when the bending strength (i) is 7 MPa or greater and the shape parameter m in the Weibull distribution (ii) is 5 or greater. On the other hand, when the bending strength is less than 7 MPa or the shape parameter m in the Weibull distribution is less than 5, the structure of the silica brick is weak, making chipping more likely to occur along the ridgelines.

[0013] Furthermore, if the bending strength (i) is 15 MPa or less and the ratio of the dynamic modulus of elasticity to the square of the bending strength (iii) is 80 or more, the strain energy accumulated in the silica bricks will not become excessive even if temperature fluctuations occur inside the coke oven during operation, and even if damage occurs, it will be minor. On the other hand, if the bending strength exceeds 15 MPa or the ratio of the dynamic modulus of elasticity to the square of the bending strength is less than 80, the strain energy accumulated in the silica bricks will become excessive when temperature fluctuations occur inside the coke oven during operation, and once damage occurs, it may become severe.

[0014] The inventors have found that conditions i) to iii) of the above-mentioned selection method are likely to be met when the silica brick contains 10 to 30 volume % of particles with a particle size of 1 to 5 mm and 10 to 30 mass % of cristobalite. The volume fraction of each particle size in the silica brick can be calculated by analyzing X-ray CT images of the fired silica brick to extract particles of a predetermined particle size (1 to 5 mm). The particle size in this case is the spherical equivalent diameter. The cristobalite content can be measured by crushing the fired silica brick and using an internal standard method using powder X-ray diffraction. The particle size and cristobalite content are considered to be within the ranges that do not weaken the structure of the silica brick and do not excessively densify it. Even if the particle size and cristobalite content are not within the above-mentioned ranges, a silica brick that is chip-resistant and damage-resistant can be obtained if conditions i) to iii) of the selection method are met.

[0015] A non-limiting example of a silica brick according to an embodiment of the present invention is a silica brick obtained by crushing and magnetically separating a silica raw material, followed by particle size adjustment, to obtain raw material particles with a particle size of less than 1 mm. The surfaces of the resulting particles are coated with Ca(OH)2 or Ca(CO)3 particles, and raw material particles with a particle size of 1 mm to 5 mm are then added to the resulting mixture, followed by a binder. The resulting mixture is then molded by uniaxial pressing, and the resulting molded body is dried and then fired in air at a temperature of more than 1400°C and less than 1500°C for at least 6 hours. The raw material particles with a particle size of 1 mm to 5 mm may be naturally occurring silica raw material, or may be crushed used or defective silica bricks (hereinafter also referred to as recycled silica bricks).

[0016] The particles in silica bricks with a particle size of 1 mm to 5 mm can be derived from raw material particles with a particle size of 1 mm to 5 mm in the manufacturing process described above. Therefore, silica bricks that contain 10% to 30% by volume of particles with a particle size of 1 mm to 5 mm after firing can be produced by mixing the same amount of raw material particles with a particle size of 1 mm to 5 mm during manufacturing. For example, when using recycled silica bricks as a raw material, the inclusion of relatively large particles with a particle size of 1 mm or more is advantageous because it simplifies the crushing process as a pretreatment for reuse. [Example]

[0017] Next, examples of the present invention will be described. Table 1 shows examples of the present invention and comparative examples. Examples 1 to 4 satisfy the above conditions i) to iii) in the test, that is, the bending strength S is 7 MPa or more and 15 MPa or less, the shape parameter m in the Weibull distribution of the bending strength S is 5 or more, and the ratio E / S of the dynamic modulus of elasticity E to the square of the bending strength S is 0. 2 These are examples of test coke ovens constructed using silica bricks with the same composition and manufacturing method as over 80 silica bricks. In these examples, there was almost no chipping of the ridges of the silica bricks, so the coke ovens could be constructed by stacking the bricks without any misalignment, and no major damage occurred during the operation of the coke ovens.

[0018] On the other hand, in Comparative Examples 1 to 3, many edge chips occurred in the silica bricks, making it difficult to position the bricks and preventing the construction of coke ovens. Edge chips occurred in Comparative Example 1, where the bending strength S was less than 7 MPa and the shape parameter m was less than 5, Comparative Example 2, where the bending strength S was 7 MPa or more but the shape parameter m was less than 5, and Comparative Example 3, where the shape parameter m was 5 or more but the bending strength S was less than 7 MPa. This shows that in order to effectively prevent edge chips in silica bricks, it is necessary to satisfy both the conditions of a bending strength of 7 MPa or more and a shape parameter m of 5 or more, as in Examples 1 to 4.

[0019] In Comparative Example 4, the coke oven could be constructed because almost no chipping occurred on the ridge lines of the silica bricks, but significant damage occurred due to temperature fluctuations during operation of the test oven. In Comparative Example 4, the bending strength S exceeded 15 MPa, and the ratio E / S of the dynamic elastic modulus E to the square of the bending strength S was 2 From this result, in order to have sufficient damage resistance to temperature fluctuations during operation in a coke oven, the bending strength must be 15 MPa or less, and the ratio of the dynamic modulus of elasticity E to the square of the bending strength S, E / S, as in Examples 1 to 4, must be 15 MPa or less. 2 It can be seen that both conditions must be met:

[0020] [Table 1]

Claims

1. A method for selecting silica bricks for constructing a coke oven, comprising the steps of: A method for selecting silica bricks, which selects silica bricks that satisfy all of the following conditions i) to iii) in a test. i) A bending strength measured by a three-point bending test at room temperature of 7 MPa or more and 15 MPa or less ii) The shape parameter m in the Weibull distribution of the bending strength is 5 or more iii) The ratio of the dynamic modulus of elasticity to the square of the bending strength is 80 or more.

2. 2. The method for selecting silica bricks according to claim 1, wherein the silica bricks contain particles having a particle size of 1 mm or more and 5 mm or less in an amount of 10% by volume to 30% by volume.

3. 2. The method for selecting silica bricks according to claim 1, wherein the silica bricks contain 10% by mass or more and 30% by mass or less of cristobalite.

4. Silica bricks for constructing coke ovens, Silica bricks that meet all of the following conditions i) to iii) in the test. i) A bending strength measured by a three-point bending test at room temperature of 7 MPa or more and 15 MPa or less ii) The shape parameter m in the Weibull distribution of the bending strength is 5 or more iii) The ratio of the dynamic modulus of elasticity to the square of the bending strength is 80 or more.

5. 5. The silica brick according to claim 4, containing particles having a particle size of 1 mm or more and 5 mm or less in an amount of 10% by volume to 30% by volume.

6. 5. The silica brick according to claim 4, containing 10% by mass or more and 30% by mass or less of cristobalite.

7. A coke oven constructed at least in part from the silica bricks according to any one of claims 4 to 6.

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