A method for estimating the bulk fracture strength of coke.

Abstract

To provide a method for highly accurate and rapid estimation of volume destruction strength DI1506-15, irrespective of a mixing condition of mixed coal, and so on.SOLUTION: An estimation method of volume destruction strength of coke comprises: a first step of carrying out image-capturing processing of the coke obtained by destructive distillation of coal in a test coke oven with X-ray CT to acquire information on a crack shape of the coke; a second step of carrying out image analysis of the information on the crack shape to calculate an area of crack surfaces having a crack width of a threshold value or less; a third step of, for a plurality of pieces of coal differing in a property from each other, carrying out the first step and the second step to calculate the area of the crack surfaces having the crack width of the threshold value or less of each of pieces of coke and constructing an estimation formula of the volume destruction strength on the basis of the area of each of the crack surfaces and the volume destruction strength actually measured for each of the pieces of coke; and a fourth step of, using pieces of coal scheduled to be used in a blast furnace, estimating the volume destruction strength from the area of the crack surfaces of the pieces of coke obtained by carrying out the first step and the second step and the estimation formula obtained at the third step.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for estimating the volumetric breaking strength of coke. [Background technology]

[0002] Coke drum strength is known as an important control index for blast furnace operation, and is generally known as the drum strength DI 150 15 is defined as the mass fraction of particles 15 mm or larger after a sample of coke is rotated 150 times in a drum test machine. Powders 15 mm or smaller are generated by surface or volumetric destruction, and it is known that such destruction is caused by cracks, poor adhesion of non-melted components, flat pores, etc. (see Non-Patent Document 1). It is also known that surface destruction and volumetric destruction correspond to powders 6 mm or smaller and 15-6 mm, respectively (see Non-Patent Document 2). Therefore, the drum strength DI of coke is 150 15 is the surface destruction strength DI for powders of 6 mm or less 150 6 and the volumetric fracture strength DI for powders in the 6-15 mm range 150 6-15 It is defined as the sum of

[0003] Patent Document 1 describes a method for estimating the amount of fine coke generated by volumetric destruction of coke from the relationship between the resolidification temperature of a coal blend and the amount of fine coke generated having a size of more than 6 mm and less than 15 mm after a coke strength test. Patent Document 2 describes a method for blending high-rank coal and low-rank coal and estimating the amount of volume-destroyed coke fines based on coal properties measured before carbonization for each blended coal, using the average reflectance of the coal blend, the blending ratio of low-rank coal, the bulk density of the coal blend, and the temperature of the coke oven.

[0004] In Patent Document 3, the volatile matter (VM) and volumetric fracture strength (DI) of coal are 150 6-15 Based on the linear equation that defines the correlation with 1506-15 A method for estimating is described. Patent Document 4 describes the relationship between the shrinkage rate of a measured blended coal and the volumetric fracture strength DI of coke obtained from the blended coal. 150 6-15 Based on the relationship (α2), the volumetric fracture strength DI 150 6-15 A method for estimating is described. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-263764 [Patent Document 2] JP 2005-194358 A [Patent Document 3] JP 2007-291262 A [Patent Document 4] JP 2020-094200 A [Non-patent literature]

[0006] [Non-Patent Document 1] Peirce, TJ, et al. (1980). "Coke breakage behavior in relation to its structure." Journal of Physics D: Applied Physics 13(6): 953. [Non-Patent Document 2] Arima, T., et al. (1992). "Mechanism of Coke Size Degradation by Mechanical Impact." Tetsu-to-Hagane 78(7): 1101-1108. Summary of the Invention [Problem to be solved by the invention]

[0007] However, the estimation methods of Patent Documents 1 to 4 above can simply and accurately estimate the volumetric fracture strength DI within the range of conditions that are the basis for the estimation (e.g., blending conditions, bulk density, furnace temperature). 150 6-15 However, for coke that does not meet the conditions, the accuracy of the estimation decreases, so it was necessary to derive a new estimation formula based on the changed conditions. Since it is necessary to conduct new experiments, etc. when reconstructing the estimation formula, the volumetric fracture strength DI 150 6-15 In some cases, it was not possible to quickly estimate

[0008] Therefore, the present invention aims to improve the volumetric fracture strength DI regardless of the blending conditions of the blended coal. 150 6-15 The object of the present invention is to provide a method for quickly and accurately estimating [Means for solving the problem]

[0009] In order to solve the above problems, the method for producing coke according to the present invention includes: (1) a first step of performing an imaging process using X-ray CT on coke obtained by carbonizing coal in a test coke oven to obtain information about the crack shape of the coke; a second step of calculating the area of ​​crack surfaces whose crack width is equal to or less than a threshold value by performing image analysis on the obtained information about the crack shape; a third step of performing the first and second steps for a plurality of coals having different properties to calculate the area of ​​crack surfaces whose crack width is equal to or less than a threshold value for each coke, and then constructing an estimation equation for estimating the volumetric fracture strength based on the calculated area of ​​each crack surface and the volumetric fracture strength actually measured for each coke; and a fourth step of estimating the volumetric fracture strength from the area of ​​the crack surfaces of the coke obtained by performing the first and second steps using coal for producing coke to be used in a blast furnace and the estimation equation obtained in the third step.

[0010] (2) A method for estimating the volumetric fracture strength of coke described above in (1), characterized in that the threshold value is set so that the correlation coefficient between the actual measured value of the volumetric fracture strength and the estimated value by the estimation equation constructed in the third step satisfies 0.85 or more. Effect of the Invention

[0011] According to the present invention, the volumetric fracture strength DI can be calculated simply by obtaining information on the crack shape of the coke cake using X-ray CT. 150 6-15 can be estimated quickly and with high accuracy. [Brief description of the drawings]

[0012] [Figure 1] FIG. 11 is a transition diagram illustrating a method of image processing. [Diagram 2] FIG. 13 is a diagram for explaining estimation of the volumetric fracture strength DI150 6-15 using the area of ​​a crack surface with a small crack width. [Diagram 3] 13 is a graph showing the degree of correlation between the estimation results and the test results of the drum test (Example). [Figure 4] 13 is a graph showing the degree of correlation between the estimation result and the test result of the drum test (comparison example). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] As mentioned above, the drum strength of coke DI 150 15 is the surface destruction strength DI 150 6 and volumetric fracture strength DI 150 6-15 In this embodiment, the volumetric fracture strength DI 150 6-15 This paper proposes a method for estimating the volumetric fracture strength DI 150 6-15 The estimation method will be explained in detail below by dividing it into steps S1 to S4.

[0014] (Step S1) The coke cake obtained by carbonizing coal in the test coke oven is imaged, for example, by a 3D medical X-ray CT before being broken into coke blocks (i.e., while still in the carbonization vessel). By imaging with a 3D medical X-ray CT, information regarding the crack shape in the coke cake can be obtained in three dimensions. A microfocus X-ray CT can also be used instead of a 3D medical X-ray CT. However, since a 3D medical X-ray CT can obtain the crack shape earlier than a microfocus X-ray CT, it is preferable to use a 3D medical X-ray CT.

[0015] Also, the coke cake can be imaged using a two-dimensional X-ray CT. In this case, by increasing the number of images captured, the crack shape of the entire coke cake can be grasped. Although a method of grasping the crack shape by observation with a microscope is also conceivable, this method requires work such as resin filling and polishing, and is therefore outside the scope of the present invention, since it takes time for processing.

[0016] (Step S2) Next, the information on the crack shape acquired in step S1 is subjected to image analysis to acquire the crack surface, and the area and width of the crack surface are calculated. For the image analysis, known software (for example, Avizo, known as three-dimensional image analysis software) can be used. Specifically, the image analysis can be performed according to the procedure shown in the following steps S2-1 to 2-4. In this embodiment, a three-dimensional medical X-ray CT with a resolution of about 1 mm can be used.

[0017] (Regarding step S2-1) In step S2-1, the captured image is subjected to image processing (for example, binarization processing based on the difference in brightness value) to separate the coke portion from the crack (space) portion. By the binarization processing, for example, the coke portion can be separated into black and the crack portion into white. However, the color-coding method is not limited to this, and other colors can be used. Although (a) of FIG. 1 is a two-dimensional schematic representation of the coke and cracks after separation, in reality, three-dimensional image data is obtained. Note that (b) to (d) of FIG. 1, which are cited in the following description, are also two-dimensional schematic diagrams, but in reality, three-dimensional image data is obtained.

[0018] (Regarding step S2-2) In step S2-2, a separation process is performed to further separate the coke portion into chunks. Here, as shown in FIG. 1(b), the coke block A appears to be one block at first glance, but has a crack x inside, and when an impact is applied, it splits into two starting from the crack x. Therefore, even if a coke block appears to be one block at first glance, if it has a crack x, it is considered to split when it receives an impact, and is determined to be a different block. For the separation process in this step, a Watershed algorithm (see non-patent document: Beucher and Meyer. The morphological approach to segmentation: the watershed transformation. Mathematical morphology in image processing; 34, 433-81 (1993)) that performs processing to identify each particle in an image as a separate entity can be used.

[0019] Here, if the width of the crack x is extremely small, the coke lump will not break even if it is subjected to an impact. Therefore, in order to consider only cracks that affect the breakup when it is subjected to an impact, cracks with a predetermined width or less that do not contribute to the breakup when it is subjected to an impact are filled by image processing. This predetermined width can be obtained by an experiment or the like. For example, a coke that has actually been subjected to a rotational impact is observed by X-ray CT or a microscope to identify multiple coke cracks remaining in the coke lump. Then, the crack with the largest crack width is identified from among these cracks, and the width of this identified largest crack can be set as the predetermined width. Here, as an example, the width that does not contribute to the breakup when it is subjected to a rotational impact can be set to 0.1 mm. The rotational impact can be applied by, for example, a rotating drum, and the volumetric fracture strength DI can be determined by setting the rotation speed to 150 revolutions. 150 6-15 It can be evaluated as follows.

[0020] (Step S2-3) The expansion process is performed uniformly for each separated coke lump, and image processing is performed to fill in the cracks, thereby extracting the boundaries between the separated coke lumps in step S2-2 (see Fig. 1(c)).

[0021] (Step S2-4) The boundary extracted in step S2-3 is compared with the location of the crack in step S2-1, and the surface that is the boundary and located at the location of the crack is extracted as a crack surface CF, and the crack width P is calculated (see Fig. 1(d)). Here, the crack surface CF is the surface that extends along the crack toward the paper surface side of Fig. 1(d), and the crack width P is the distance between the coke lumps facing each other across the crack surface CF. As shown in Fig. 2(a), when each crack surface CF is defined as crack surfaces CF1 to CF4, in this embodiment, the crack surface CF is divided into two sections according to the size of the crack width P. Fig. 2(b) is a diagram after the division, in which the crack surfaces CF1 to CF3 with a relatively large crack width P are shown by solid lines, and the crack surface CF4 with a relatively small crack width P is shown by a dashed line.

[0022] In this manner, in this embodiment, the crack surface CF is divided into two sections according to the size of the crack width P, and the volumetric fracture strength DI is calculated based on the area of ​​the crack surface CF where the crack width P is relatively small, as described later. 150 6-15 The reason for focusing on the area of ​​the crack surface CF where the crack width P is relatively small is as follows.

[0023] It is known that among the cracks formed in the coke, those with a relatively large crack width are related to the grain size of the coke, while those with a relatively small crack width are related to the destruction of the coke. Therefore, it is presumed that only cracks with a small crack width need to be considered for the volume destruction of the coke. The inventors of the present invention presumed that cracks with a width of a threshold value (Xmm) or less affect the volume destruction based on the prior art (Sakimoto et al. ISIJ International; 56(11), 1948-55 (2016)). Here, the threshold value (Xmm) depends on the resolution of the X-ray CT, but since the example described below was 2.5mm, it is presumed to be approximately several mm. Specifically, the threshold value (Xmm) is set to a value that satisfies the estimation accuracy required in the linear equation described below. The required estimation accuracy is not particularly limited, but may be set to a value that satisfies the correlation coefficient (R 2 ), the correlation coefficient is preferably 0.85 or more. In other words, it is desirable to set the threshold value (X mm) so that the correlation coefficient between the estimated value by the linear expression and the actual measured value is 0.85 or more.

[0024] As described above, the resolution of the three-dimensional medical X-ray CT used in this embodiment is about 1 mm. However, if a three-dimensional medical X-ray CT with a higher resolution is available, the crack width below the threshold (X mm) can be further divided into multiple sections, and a weighting process is performed taking into account the influence of the crack width of each section to calculate the volumetric fracture strength DI 150 6-15 may be estimated.

[0025] For the evaluation of three-dimensional crack width, the evaluation method shown in the non-patent literature (Hildebrand and Ruegsegger. A new method for the model-independent assessment of thickness in three-dimensional images. Journal of Microscopy; 185(1), 67-75 (1997)) can be used. Specifically, a method can be used in which the largest sphere that touches the boundary between a target three-dimensional region and an outside region is placed in the target region, and the width of the target object can be measured from the diameter of the placed sphere. In the case of two dimensions, the two-dimensional crack width can be evaluated by placing a circle instead of a sphere in three dimensions, but in the case of two dimensions, the width may change even at the same site depending on the direction of the cross section, so three-dimensional evaluation is desirable.

[0026] (Step S2-5) The area of ​​the crack surface with a crack width below the threshold (X mm) extracted in step S2-4 is normalized by the volume of the entire analysis domain, which is the sum of the coke part and the crack part, to obtain S -Xmm Calculate.

[0027] (Step S3) The above-mentioned steps S1 and S2 are carried out for each of a plurality of coals having different properties, and S -Xmm Here, from the viewpoint of constructing the estimation equation, the volumetric fracture strength DI 150 6-15 It is preferable that the values ​​of DI are more dispersed. Therefore, it is desirable that the blending conditions (coal brand, blending ratio, bulk density, addition of coke powder, etc.) and heating conditions (heating rate, ultimate temperature, heating time) of the coal blends used in each coke production are different from each other. In addition, by performing drum tests on each coke, the volumetric fracture strength DI 150 6-15 The following is required in advance. By the above process, S -Xmm and the actual measured value of volumetric fracture strength DI150 6-15 A set of data consisting of the above is obtained the number of times that steps S1 and S2 are performed using a plurality of coals having different properties, and these data are fitted to a linear function based on the least squares method to construct the following linear equation (1) as an estimation equation.

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[0028] (Step S4) The S of the coke (coke obtained by carbonization in a test coke oven using coal for coke production to be used in a blast furnace) measured by carrying out steps S1 to S3 -Xmm By substituting into the linear equation (1), the volumetric fracture strength DI 150 6-15 Estimate.

[0029] According to the method of this embodiment, by simply acquiring information about cracks in the coke cake and calculating the area of ​​the crack surface whose crack width is equal to or less than the threshold value (X mm), the volumetric fracture strength DI 150 6-15 Even if the coal blending conditions, the presence or absence of coke fines, or other conditions are changed, there is no need to reconstruct the estimation equation (1), so the volumetric fracture strength DI can be estimated quickly and simply. 150 6-15 Furthermore, after constructing the estimation formula (1), the volumetric fracture strength DI 150 6-15 Since drum testing to obtain the above is not necessary, the labor and time required for drum testing can be reduced. EXAMPLES

[0030] Next, the present invention will be specifically described with reference to examples. Coals C1 to C25 were produced by carbonizing a coal blend having the properties shown in Table 1 in a test coke oven. In Table 1, ΣTD (%) is the weighted average value of the total expansion coefficient TD of each single coal contained in the coal blend, and ΣVM (mass%) is the weighted average value of the volatile matter of each single coal contained in the coal blend. The dimensions of the carbonization vessel of the test coke oven were oven width (W): 400 mm, oven length (L): 600 mm, and oven height (H): 420 mm. The charged bulk density (BD) of the coal was 850 (kg / m) on a dry basis. 3 ), or 900 (kg / m 3 ) The final temperature of the test coke oven was set to 950°C, 1050°C, or 1150°C, and the carbonization time was set to 18.5 hours for each. The average particle size of coke fines C16 and C18 is expressed by the last digit, while the average particle size of other coke fines is expressed by the last two digits because the accuracy of the sieve mesh used to calculate the average particle size is different. The addition rate of coke fines (mass%) is expressed as an additional number. [Table 1]

[0031] As a process corresponding to step S1 described above, after carbonization, each coke was placed in a carbonization vessel and a three-dimensional image was obtained using a three-dimensional medical X-ray CT. After the image was captured, a drum test was performed to measure the volumetric fracture strength DI 150 6-15 was measured.

[0032] The imaging conditions for the X-ray CT were a tube voltage of 120 kV, a tube current of 350 mA, and a slice pitch of 0.5 mm. The image size was 512 × 512 pixels. The image resolution was 1.132 mm / pixel. For the segmentation process (corresponding to step S2), the segmentation module provided by Avizo was used.

[0033] That is, in the process corresponding to step S2-1, the coke portion and the crack (space) were separated by binarization. In the process corresponding to step S2-2, the coke portion was further separated into chunks using a watershed algorithm. In this case, a parameter (marker extent) that determines the strength of the separation process was set to 1, which indicates strong separation, and coke chunks having cracks with a width of more than 0.1 mm were separated. In the process corresponding to step S2-3, an expansion process was performed on each separated coke chunk, and image processing was performed to fill the cracks. In the process corresponding to step S2-4, the boundary portion extracted in step S2-3 was compared with the crack portion in step S2-1, and a surface that was the boundary portion and located at the crack portion was extracted as a crack surface, and the crack width was calculated.

[0034] As a process corresponding to step S2-5, the crack width is set to 2.5 mm as a threshold, and for cracks with a width of 2.5 mm or less, the area of ​​the crack surface is normalized by the volume of the entire analysis domain, which is the sum of the coke portion and the crack portion (however, the area of ​​the void between the coke and the carbonization vessel is excluded from the normalized volume), to obtain S -2.5mm was calculated. The threshold value of the crack width may change depending on the resolution of the three-dimensional medical X-ray CT or the value of the correlation coefficient to be obtained. Therefore, the threshold value of the crack width in the present invention is not limited to 2.5 mm.

[0035] The above-mentioned process was carried out for each coke (corresponding to step S3). In this embodiment, for comparison, the area of ​​the crack surface (regardless of the crack width) was normalized by the volume of the entire analysis area obtained by adding up the coke part and the crack part (however, the area of ​​the void between the coke and the carbonization vessel was excluded from the normalized volume) to obtain S all was also calculated.

[0036] Volumetric fracture strength DI, which is the result of the drum test 150 6-15 and S calculated using the above method -2.5mmThe volumetric fracture strength DI, which is the result of the drum test, was calculated as follows: 150 6-15 and S calculated using the above method all and were fitted to a linear function based on the least squares method, and the following equation (3) was calculated as an estimated equation (corresponding to a comparative example).

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[0037] Fig. 3 is a graph showing the degree of correlation between the estimation result based on formula (2) and the test result of the drum test, where the horizontal axis is the estimated value and the vertical axis is the test result of the drum test (actual value). Fig. 4 is a graph showing the degree of correlation between the estimation result based on formula (3) and the test result of the drum test, where the horizontal axis is the estimated value and the vertical axis is the test result of the drum test (actual value).

[0038] 3 and 4, the estimation method of this embodiment uses a correlation coefficient R 2 The correlation coefficient of the estimation method of the comparative example was 0.860, and the correlation coefficient of the estimation method of the comparative example was 0.246. Therefore, for the coke cake carbonized in the test coke oven, the area of ​​the crack surface with a crack width of 2.5 mm or less was obtained, and the volumetric fracture strength DI 150 6-15 It was found that it is possible to estimate with high accuracy. 2 is less than 0.850, the correlation coefficient R 2 If an estimation accuracy of 0.850 or more is required, the threshold value of the crack width may be changed and set so as to satisfy the estimation accuracy.

[0039] In addition, for the coke cake obtained in the test coke oven, a conventional drum test required about 1.5 hours per level, but in this embodiment, this could be shortened to about 10 minutes per level.

Claims

[Claim 1] A first step of acquiring information about the shape of cracks in a coke by performing imaging processing using an X-ray CT on the coke obtained by carbonizing coal in a test coke oven; A second step of calculating an area of ​​a crack surface having a crack width equal to or smaller than a threshold value by performing image analysis on the acquired information on the crack shape; a third step of calculating an area of ​​a crack surface of each coke having a crack width equal to or smaller than a threshold value by performing the first step and the second step for a plurality of coals having different properties, and then constructing an estimation equation for estimating the volumetric fracture strength based on the calculated area of ​​each crack surface and the volumetric fracture strength actually measured for each coke; A fourth step of estimating a volumetric fracture strength from the crack surface area of ​​the coke obtained by performing the first step and the second step using coal for producing coke to be used in a blast furnace and the estimation formula obtained in the third step; having A method for estimating the volumetric fracture strength of coke, characterized in that the threshold value is set so that the correlation coefficient between the actual measured value of the volumetric fracture strength and the estimated value using the estimation equation constructed in the third step is 0.85 or more.

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