Coke manufacturing method

Abstract

To provide an analysis method of an amount of voids around briquette coal, capable of highly accurately analyzing the amount of voids around the briquette coal generated when a container is filled with blended coal containing the briquette coal and powdered coal, regardless of the properties of the blended coal, an estimation method of the amount of voids around the briquette coal using the analysis method, and a manufacturing method of high-strength coke using the analysis method or the estimation method.SOLUTION: An analysis method of an amount of voids around briquette coal generated when a container is filled with blended coal containing the briquette coal and powdered coal, comprises: in 3D analysis of an X-ray CT cross-sectional image, executing expansion processing for expanding one unit volume of briquette coal similar in shape with a briquette coal part per time from a periphery of the briquette coal part; multiplying a volume of an area whose volume has increased in each expansion processing by a difference value between an average density of a powdered coal part and an average density of a void part to calculate a filling reduction amount; integrating the filling reduction amount by the total number of expansion processing to calculate an integrated filling reduction amount; and using the integrated filling reduction amount as an index of the amount of voids around the briquette coal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for producing coke. [Background technology]

[0002] Conventionally, in the production of coke used in blast furnace operations, various methods have been considered to maintain good coke strength while increasing the proportion of inferior coal, such as non-coking coal, in the blended coal composed of molded coal and pulverized coal, in order to address the depletion of resources of high-quality, strongly coking coal. In order to obtain the desired coke strength using blended coal containing inferior coal, a coal pretreatment process may be useful. For example, known coal drying processes include the Coal Moisture Coal (CMC) method and the Dry-cleaned and Agglomerated Pre-compaction System (DAPS), while processes for blending molded materials such as molded coal include the Dry-cleaned and Agglomerated Precompaction System (DAPS), molded coal blending methods, and other methods for adjusting the particle size of crushed coal. These are combined as appropriate.

[0003] By appropriately utilizing the coal pretreatment processes described above to adjust the particle size composition and moisture content of pulverized coal, it becomes possible to reduce residual voids in the coke and obtain good coke strength, even when the expansion properties of the pulverized coal are relatively low. However, when molded coal is blended, voids may form around the molded coal, and these voids may remain even after carbonization. Since these residual voids around the molded coal cause a decrease in coke strength, it is important to produce molded coal with sufficient expansion properties to fill these voids during carbonization. In order to understand the expansion properties of the molded coal necessary to fill these voids and to determine the coal blend composition, it is important to accurately estimate the amount of voids around the molded coal in the blended coal charged into the coke oven.

[0004] In the method for producing coke in which a blended coal obtained by blending formed coal and pulverized coal obtained by pulverizing coal is charged into a coke oven and carbonized, a test apparatus is used to fill a container with the blended coal obtained by blending formed coal and pulverized coal obtained by pulverizing coal by natural dropping, an X-ray CT is used to image a cross-sectional image inside the container, and from the obtained cross-sectional image, the maximum width W of the voids formed around the formed coal is quantified. Further, using a test apparatus, the maximum expansion volume during carbonization of the formed coal is measured, and the expansion amount of the formed coal is determined as the change amount Δr (mm) of the equivalent circle diameter before and after expansion. When the obtained change amount Δr is less than 40% of the maximum width W (mm), the coal blend constituting the formed coal is changed, and a coal blend in which the change amount Δr is 40% or more of the maximum width W is obtained, and a method for producing coke is provided, characterized in that formed coal produced based on this blend is used.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the method described in Patent Document 1, the voids around the formed coal in the blended coal containing formed coal and pulverized coal are evaluated as the width by two-dimensional image analysis. However, this method still has room for improvement in terms of the accuracy of evaluation when the voids around the formed coal are too small, when pulverized coal containing lump coal is used, etc.

[0007] In addition, in the production of coke, by using the value of the void volume around the formed coal obtained by the method described in Patent Document 1 and calculating the expansibility value (specifically, SV (specific volume)) of the formed coal required to obtain the target coke strength, the coal blend constituting the blended coal can be determined. However, when changing the particle size composition of the pulverized coal used, there is a problem that the correspondence between the SV of the formed coal part required to obtain the target coke strength obtained by the method described in Patent Document 1 and the target coke strength may not match the correspondence between the actually measured value of the SV of the formed coal part and the actually measured value of the coke strength.

[0008] As described above, in the method described in Patent Document 1, there is still room for improvement in order to analyze the void volume around the formed coal with high accuracy regardless of the pulverized coal particle size composition.

[0009] One aspect of the present invention is to solve the above problems, and to provide an analytical method for the void volume around the formed coal that can accurately analyze the voids around the formed coal generated when a blended coal containing the formed coal and pulverized coal is filled into a container regardless of the particle size composition of the pulverized coal, an estimation method for the void volume around the formed coal using the analytical method, and a method for producing high-strength coke using the analytical method or the estimation method.

Means for Solving the Problems

[0010] The gist of the present invention is as follows. [1] An analytical method for the void volume around the formed coal generated when a blended coal containing the formed coal and pulverized coal is filled into a container, comprising: filling the formed coal and pulverized coal into a test container by natural fall using a test device, imaging a cross-sectional image in the test container by X-ray CT, obtaining the void volume around the formed coal by 3D analysis of the obtained cross-sectional image, In the 3D analysis, defining a high-density part with a density exceeding a predetermined value and a low-density part with a density not exceeding the predetermined value, respectively, filtering the high-density part with a predetermined shape parameter to define the formed coal part, Optionally, within the high-density portion, any region other than the molded charcoal portion and whose volume exceeds a predetermined value is defined as the agglomerated charcoal portion, and this agglomerated charcoal portion is excluded from the analysis by being treated as having no pixel data. An expansion process is performed (n+1) or more times, starting from the periphery of the molded charcoal portion and expanding by 1 unit volume each time in a shape similar to the molded charcoal portion, where n is a natural number. The (n+1) mentioned above is the number at which the average density of the region whose volume increased in the (n+1)th expansion process is approximately the same as the average density of the region whose volume increased in the nth expansion process. The average density of the region whose volume increased in the nth and subsequent expansion processes is used as the threshold. In each expansion treatment, the region whose volume increases is defined as follows: the region whose density exceeds the threshold is defined as the pulverized coal portion, and the region whose density is below the threshold is defined as the void portion. For each expansion treatment, the difference between the average density of the pulverized coal portion and the average density of the void portion is calculated for the region whose volume has increased. The amount of filling reduction is calculated by multiplying the volume of the region that has increased in volume during each expansion process by the difference value. The cumulative amount of filling loss is calculated by accumulating the amount of filling loss over the total number of expansion treatments, and this cumulative amount of filling loss is used as an indicator of the amount of voids around the molded coal. Method for analyzing the amount of voids around molded coal. [2] A method for estimating the amount of voids around molded coal when a blend of charcoal containing molded coal and powdered coal is filled into a container, Multiple types of blended coal samples are prepared by combining each of several types of powdered coal samples, selected to include different levels of particle size composition and different levels of moisture content, with an arbitrarily selected molded coal sample. For each blended coal sample, the cumulative sample packing reduction was determined according to the method for analyzing the amount of voids around the molded coal described in [1] above. Based on the relationship between the particle size composition and moisture content of the pulverized coal sample and the cumulative filling loss of the sample, we obtained equation (I) relating the particle size composition and moisture content of the pulverized coal to the cumulative filling loss. For blended coal, which is a combination of pulverized coal intended for use in coke production and arbitrarily selected molded coal for analysis, the particle size composition and moisture content of the pulverized coal intended for use are substituted into the above relational equation (I) to calculate an estimated cumulative filling loss, and this estimated cumulative filling loss is used as an indicator of the amount of voids around the molded coal. A method for estimating the amount of voids around molded charcoal. [3] A method for producing coke using a blend of coals including molded coal and powdered coal, For the selected coal blend sample for testing, a relationship equation (II) is predetermined between the cumulative packing reduction calculated by the analysis method for the amount of voids around the molded coal described in [1] above, and the lower limit of the molded coal SV range, which is the lower limit of the molded coal SV range in which the coke strength remains constant even when the molded coal SV is changed. For blended coal, which is a combination of pulverized coal intended for use in coke production and arbitrarily selected molded coal for analysis, the cumulative packing reduction is determined according to the analysis method for the amount of voids around the molded coal described in [1] above, or the estimated value of the cumulative packing reduction is determined according to the estimation method for the amount of voids around the molded coal described in [2] above. Substitute the cumulative filling loss or the estimated cumulative filling loss into relational equation (II) to determine the lower limit of SV in the molded coal section. A molded charcoal is manufactured in which the measured SV value is equal to or greater than the lower limit of the SV value of the molded charcoal portion. The blended coal, consisting of the aforementioned pulverized coal intended for use and the manufactured molded coal, is used for coke production. A method for producing coke. [Effects of the Invention]

[0011] According to one aspect of the present invention, a method for analyzing the amount of voids around molded coal, which can analyze with high accuracy the voids around molded coal that occur when a blend of coal containing molded coal and powdered coal is filled into a container, regardless of the particle size composition of the powdered coal; a method for estimating the amount of voids around molded coal using the analysis method; and a method for producing high-strength coke using the analysis method or the estimation method can be provided. [Brief explanation of the drawing]

[0012] [Figure 1]This is a schematic diagram illustrating an image processing flow according to one aspect of the present invention. [Figure 2] This is a schematic diagram illustrating the amount of filling loss. [Figure 3] This figure shows the particle size distribution of the pulverized coal used in the examples and conventional examples. [Figure 4] This figure shows the X-ray CT image in Example 1. [Figure 5] This figure shows the relationship between the number of expansion treatments and the amount of filling loss when using crushed charcoal (moisture content 4% by mass) in Example 1. [Figure 6] This figure shows the relationship between the number of expansion treatments and the amount of filling loss when using crushed charcoal (moisture content 10% by mass) in Example 1. [Figure 7] This figure shows the relationship between the number of expansion treatments and the amount of filling reduction when using sized charcoal in Example 1. [Figure 8] This figure shows the relationship between the number of expansion treatments and the amount of filling loss when using a combination of coarse-grained charcoal and agglomerated charcoal in Example 1. [Figure 9] This figure shows the relationship between the distance from molded charcoal and the change in bulk density when using crushed charcoal (moisture content 4% by mass) in Conventional Example 1. [Figure 10] This figure shows the relationship between the distance from molded charcoal and the change in bulk density when using crushed charcoal (moisture content 10% by mass) in Conventional Example 1. [Figure 11] This figure shows the relationship between the distance from molded coal and the change in bulk density when using whole-grain coal in Conventional Example 1. [Figure 12] This figure shows the relationship between the distance from molded coal and the change in bulk density when using a combination of coarse-grained coal and agglomerated coal in Conventional Example 1. [Figure 13] This figure shows the relationship between the mass percentage of pulverized coal on a 3mm sieve and the cumulative filling loss in Example 2. [Figure 14] This figure shows the relationship between the mass percentage of pulverized coal on a 6mm sieve and the cumulative filling loss in Example 2. [Figure 15]This figure shows the relationship between the mass-average diameter of pulverized coal and the cumulative filling loss in Example 2. [Figure 16] This figure shows the relationship between the moisture content of pulverized coal and the cumulative filling loss in Example 2. [Figure 17] This figure shows the relationship between the cumulative filling loss estimated from the mass percentage and moisture content of the 3mm sieved coal powder in Example 2-1 and the cumulative filling loss obtained using the procedure in Example 1. [Figure 18] This figure shows the relationship between the cumulative filling loss estimated from the mass percentage and moisture content of the 6mm sieved coal in Example 2-2 and the cumulative filling loss obtained using the procedure in Example 1. [Figure 19] This figure shows the relationship between the cumulative filling loss estimated from the mass-average diameter and moisture content of the pulverized coal in Examples 2-3 and the cumulative filling loss obtained using the procedure in Example 1. [Figure 20] This figure shows the relationship between the cumulative filling loss estimated from the mass percentage of pulverized coal on a 3mm sieve in Reference Example 1 and the cumulative filling loss obtained using the procedure in Example 1. [Figure 21] This figure shows the relationship between the cumulative filling loss estimated from the mass percentage of pulverized coal on a 6mm sieve in Reference Example 2 and the cumulative filling loss obtained using the procedure in Example 1. [Figure 22] This figure shows the relationship between the cumulative filling loss estimated from the mass-average diameter of the pulverized coal in Reference Example 3 and the cumulative filling loss obtained using the procedure in Example 1. [Figure 23] This figure shows the relationship between the cumulative filling loss estimated from the moisture content of the pulverized coal in Reference Example 4 and the cumulative filling loss obtained using the procedure in Example 1. [Figure 24] This figure shows the relationship between the cumulative filling loss estimated from the mass percentage and moisture content of the 3mm sieved coal in Examples 2-4 and the cumulative filling loss obtained using the procedure in Example 1. [Figure 25] This figure shows the relationship between the cumulative filling loss estimated from the mass percentage and moisture content of the 6mm sieved coal in Examples 2-5 and the cumulative filling loss obtained using the procedure in Example 1. [Figure 26]This figure shows the relationship between the cumulative filling loss estimated from the mass-average diameter and moisture content of the pulverized coal in Example 2-6 and the cumulative filling loss obtained using the procedure in Example 1. [Figure 27] This figure shows the relationship between the molded coal portion SV and the coke strength DI150 6 when using whole-grain coal in Evaluation Example 1. [Figure 28] This figure shows the relationship between the molded coal portion SV and the coke strength DI150 15 when using whole-grain coal in Evaluation Example 1. [Figure 29] This figure shows the relationship between the molded coal portion SV and the coke strength DI150 6 when using crushed coal (moisture content 4% by mass) in Evaluation Example 1. [Figure 30] This figure shows the relationship between the molded coal portion SV and the coke strength DI150 6 when using crushed coal (moisture content 10% by mass) in Evaluation Example 1. [Figure 31] This figure shows the relationship between the value based on Comparative Evaluation Example 1 and the value based on the carbonization test for the lower limit of the molded coal SV value, which is the limit at which the coke strength DI150 15 is maintained at a constant level. [Figure 32] This figure shows the relationship between the cumulative filling loss in Example 1 and the lower limit of the molded coal portion SV, which is the limit at which the coke strength DI150 6 is maintained at a constant level, in Evaluation Example 1. [Figure 33] This figure shows the relationship between the cumulative filling loss in Example 1 and the lower limit of the molded coal portion SV, which is the limit at which the coke strength DI150 15 is maintained at a constant level, in Evaluation Example 1. [Figure 34] This figure shows the relationship between the cumulative filling loss in Example 2-5 and the lower limit of the molded coal portion SV, which is the limit at which the coke strength DI150 6 is maintained at a constant level, in Evaluation Example 1. [Modes for carrying out the invention]

[0013] The following describes exemplary embodiments of the present invention (which may also be referred to as these embodiments in this disclosure), but the present invention is not limited to these embodiments.

[0014] [Method for analyzing the amount of voids around molded coal] One aspect of the present invention provides a method for analyzing the amount of voids around molded coal in a blended coal mixture composed of pulverized coal and molded coal. In this disclosure, pulverized coal refers to crushed coal, and includes coal that has been further size-adjusted after crushing, and agglomerated coal if it is present. In this disclosure, agglomerated coal refers to coal with an equivalent spherical radius of less than 6 mm obtained by adding a binding filler to pulverized coal (in one aspect, pulverized coal below a 0.3 mm sieve) and press-molding. In this disclosure, molded coal refers to coal with an equivalent spherical radius of 6 mm or more obtained by adding a binding filler to pulverized coal (in one aspect, pulverized coal below a 0.3 mm sieve) and press-molding.

[0015] In the method for analyzing the amount of voids around molded coal according to this embodiment, a 3D analysis of a cross-sectional image of the blended coal obtained using X-ray CT (Computed Tomography) is performed. When attempting to evaluate the voids around molded coal by 3D analysis of a cross-sectional image, the evaluation results vary depending on which area is considered a void, because the void is a region with low packing density, but the density is not completely zero. In the method described in Patent Document 1 mentioned above, the void is evaluated by the width from the periphery of the molded coal using 2D analysis of the cross-sectional image, making it difficult to determine the region to be considered a void when the void is small. In particular, when agglomerated coal and molded coal are mixed, it is difficult to clearly distinguish between them, resulting in low accuracy in identifying molded coal and making it difficult to accurately evaluate the amount of voids around molded coal.

[0016] Therefore, the inventors conceived the idea of ​​evaluating the voids around molded charcoal by 3D analysis of cross-sectional images, and at that time, adopting an index called the packing reduction amount, which takes into account the weight of volume by multiplying the density by the volume in the areas considered to be voids.

[0017] One aspect of the present invention is, A method for analyzing the amount of voids around molded coal when a blend of coal containing molded coal and powdered coal is filled into a container, Using a test apparatus, molded coal and powdered coal are filled into a test container by gravity. Cross-sectional images of the inside of the test container were acquired using X-ray CT. The amount of voids around the molded coal was determined by 3D analysis of the obtained cross-sectional images. In the aforementioned 3D analysis, A high-density section where the density exceeds a predetermined value and a low-density section where the density is less than or equal to the predetermined value are defined, The aforementioned high-density portion is filtered using a predetermined shape parameter and defined as a molded char portion. Optionally, within the high-density portion, any region other than the molded charcoal portion and whose volume exceeds a predetermined value is defined as the agglomerated charcoal portion, and this agglomerated charcoal portion is excluded from the analysis by being treated as having no pixel data. An expansion process is performed (n+1) or more times, starting from the periphery of the molded charcoal portion and expanding by 1 unit volume each time in a shape similar to the molded charcoal portion, where n is a natural number. The (n+1) mentioned above is the number at which the average density of the region whose volume increased in the (n+1)th expansion process is approximately the same as the average density of the region whose volume increased in the nth expansion process. The average density of the region whose volume increased in the nth and subsequent expansion processes is used as the threshold. In each expansion treatment, the region whose volume increases is defined as follows: the region whose density exceeds the threshold is defined as the pulverized coal portion, and the region whose density is below the threshold is defined as the void portion. For each expansion treatment, the difference between the average density of the pulverized coal portion and the average density of the void portion is calculated for the region whose volume has increased. The amount of filling reduction is calculated by multiplying the volume of the region that has increased in volume during each expansion process by the difference value. The cumulative amount of filling loss is calculated by accumulating the amount of filling loss over the total number of expansion treatments, and this cumulative amount of filling loss is used as an indicator of the amount of voids around the molded coal. This invention provides a method for analyzing the amount of voids surrounding molded coal. Evaluation using the amount of filling reduction allows for highly accurate quantitative evaluation of the amount of voids without being constrained by the size and shape of the voids around the molded coal.

[0018] In this disclosure, the expansion process refers to a process in which one voxel (unit volume) (central voxel) and 26 adjacent voxels (peripheral voxels) are considered, the maximum value of the peripheral voxels is calculated, and if it is greater than the value of the central voxel, the value of the central voxel is replaced with the maximum value. In the cross-sectional image, the molded coal is denser than its surroundings (i.e., has a larger X-ray CT value), so by performing this expansion process on the periphery of the molded coal, the molded coal expands in a similar shape at a rate of 1 voxel per process.

[0019] Figure 1 is a schematic diagram illustrating the image processing flow in one embodiment of the present invention. In the method of this embodiment, the voids around the molded coal are analyzed by performing 3D analysis in steps S12 to S18 on the X-ray CT cross-sectional image acquired in step S11. Below, an example of the procedure for analyzing the amount of voids around molded coal according to this embodiment will be described with reference to Figure 1.

[0020] (Step S11) In this step, molded coal and pulverized coal are filled into a test container by gravity using a test apparatus, and a cross-sectional image of the inside of the test container is captured by X-ray CT. The coal constituting each of the molded coal and pulverized coal may be one type or a combination of two or more types. The pulverized coal may include agglomerated coal in one embodiment, or it may not include agglomerated coal in another embodiment. The test apparatus and X-ray CT apparatus may be commercially available devices, and the measurement conditions of the X-ray CT may be set as desired. The voxel size is preferably small and is not particularly limited from the viewpoint of obtaining good analytical accuracy. In one embodiment of the present invention, the size was set to 0.488 mm × 0.488 mm × 0.488 mm.

[0021] (Step S12) In steps S12 to S18, the software attached to the X-ray CT scanner may be used for 3D analysis. In step S12, the analysis area (hereinafter also referred to as ROI) within the cross-sectional image (hereinafter also referred to as the original image) acquired in step S11 is binarized by density, and high-density areas where the density exceeds a predetermined value and low-density areas where the density is below a predetermined value are defined. The above default value may be set appropriately so that molded coal and agglomerated coal, if present, are classified as high-density areas, and pulverized coal other than agglomerated coal are classified as low-density areas, for example, 1.0 g / cm³. 3 That is acceptable.

[0022] (Step S13) In this step, the high-density portion described above is filtered using predetermined shape parameters to define the molded char portion. The molded char portion may be defined using the following procedure. a) For the high-density section defined in step S12, small particles (in one embodiment, small particles of 100 voxels or less) are removed to reduce noise. b) Separate the particles in the high-density portion after the processing in a) above so that each particle can be distinguished. Separation may be performed by labeling. c) From the high-density portion after the processing in b) above, the region corresponding to molded coal is extracted by filtering using predetermined shape parameters. The predetermined shape parameters are set so as to accurately define the molded coal portion, and in one embodiment, they may be one or more of the following: Anisotropy, Flatness, Elongation, Volume, etc. A combination of Anisotropy, Flatness, and Elongation is preferred because it allows for easy implementation of the desired filtering regardless of the size of the molded coal. For example, filtering may be performed using Anisotropy < 0.9, Flatness < 0.4, and Elongation > 0.4. d) In the region extracted in c) above, detect and remove any constrictions. Generally, molded charcoal often has constrictions in the burr area. Constrictions may be detected using the watershed method. e) The area after processing d) above is subjected to one shrink (i.e., one voxel shrink), small particle removal using the same procedure as a) above, one expansion (i.e., one voxel expansion), and smoothing in that order, and the remaining area is defined as the molded charcoal portion.

[0023] (Step S14) This step may only be performed if the pulverized coal contains agglomerated coal. In this step, the agglomerated coal region is defined as the area of ​​the high-density region defined in step S12 that is not the molded coal region defined in step S13 and whose volume exceeds a predetermined value. The agglomerated coal region is treated as having no pixel data. When pulverized coal contains agglomerated coal, the agglomerated coal has an equivalent sphere radius of less than 6 mm, but its density is as high as that of molded coal. If such agglomerated coal is included in the expansion treatment area in addition to molded coal, there is a risk that the voids will not be accurately evaluated. Therefore, if the blended coal contains agglomerated coal, the agglomerated coal is excluded from the analysis.

[0024] Specifically, the molded char portion defined in step S13 is subtracted from the high-density portion defined in step S12, and the remaining area is labeled. From this labeled area, volume filtering is performed (in one embodiment, Volume > 15 mm). 3 The aggregated charcoal portion is extracted by selecting only the region that satisfies the volume parameter.

[0025] Furthermore, if the blended coal contains agglomerate, voids are formed not only around the molded coal but also around the agglomerate. When agglomerate is present around the molded coal, it is conceivable that the amount of packing loss around the agglomerate should be included in the packing loss around the molded coal. Therefore, it is conceivable to determine the packing loss around the agglomerate and subtract it from the packing loss around the molded coal. However, according to the inventors' studies, the proportion of the packing loss around the agglomerate included in the packing loss around the molded coal is negligible, and the influence of the presence of voids around the agglomerate on coke strength is negligible. Therefore, in the evaluation of packing loss in this embodiment, the packing loss around the agglomerate does not need to be considered. Specifically, in the 3D analysis of this embodiment, the area corresponding to the agglomerate is excluded from the analysis of this embodiment by being treated as an area without pixel data. In the present invention, cumulative packing loss refers to the packing loss around the molded coal.

[0026] (Step S15) In this step, within the ROI of the original image, the molded charcoal portion defined in step S13 above is subjected to an expansion process of 1 unit volume (i.e., 1 voxel) at a time, starting from the periphery of the molded charcoal portion and expanding in a similar shape to the molded charcoal portion, at least (n+1) times, where n is a natural number. (n+1) is the number at which the average density of the region whose volume increased in the (n+1)th expansion process is approximately the same as the average density of the region whose volume increased in the nth expansion process. Here, "approximately the same" means, in one embodiment, that the average density of the region whose volume increased in the (n+1)th expansion process is within ±0.3% of the average density of the region whose volume increased in the nth expansion process. Here, ±0.3% corresponds to measurement variability and is not limited to this value.

[0027] After each expansion process is completed, the volume of the region increased by that expansion process (i.e., the volume increase due to that expansion process) and the average density are calculated. The volume corresponds to the number of voxels in the region whose volume increased. The average density is calculated by taking the number average of the CT values ​​of each voxel in the region whose volume increased by the number of voxels in that region. The expansion process is carried out at least until the average density of the region increased by one expansion process becomes approximately the same even if the number of expansion processes is increased. The total number of expansion processes may be (n+1), or it may be more than (n+1), for example, 10 or more, or 20 or more. In one embodiment, the total number of expansion processes may be 30 to 50, for example, 30.

[0028] (Step S16) In this step, the average density of the region whose volume increased in the nth expansion treatment is used as a threshold. For each expansion treatment, the region whose density exceeds the threshold is defined as the pulverized coal portion, and the region whose density is below the threshold is defined as the void portion.

[0029] (Step S17) Next, for the region whose volume increased in each expansion treatment, the difference between the average density of the pulverized coal portion and the average density of the void portion is calculated. The average density of the pulverized coal portion is the number average of the CT values ​​of each voxel contained in the pulverized coal portion, multiplied by the total number of voxels in the pulverized coal portion. The average density of the void portion is the number average of the CT values ​​of each voxel contained in the void portion, multiplied by the total number of voxels in the void portion. Next, the amount of filling reduction is calculated by multiplying the volume of the region whose volume increased in each expansion treatment by the above difference value.

[0030] (Step S18) In this step, the packing reduction amount calculated in step S17 is accumulated over the total number of expansion treatments to calculate the cumulative packing reduction amount. This cumulative packing reduction amount can be used as an indicator of the amount of voids around the molded coal. Figure 2 is a schematic diagram illustrating the packing reduction amount of this disclosure. The packing reduction amount calculated as described above in this step changes due to the presence of voids up to a certain number of expansion treatments (n times in one embodiment), but beyond that number (more than (n+1) times in one embodiment), it becomes almost constant because there are no longer any voids in the region increased by the expansion treatment. For example, in Figure 2, the packing reduction amount in the region increased by one expansion treatment changes up to the 8th expansion treatment, but from the 9th expansion treatment onward, the packing reduction amount becomes almost constant from the value after the 8th expansion treatment. The cumulative value of the packing reduction amount over the number of expansion treatments until the packing reduction amount becomes almost constant reflects the total amount of voids present around the molded coal. From the above perspective, in one embodiment, the cumulative amount of filling reduction obtained by summing the filling reduction amounts over the total number of expansion treatments, which is (n+1) or more times, is useful as an indicator of the amount of voids around the molded coal.

[0031] [Method for estimating the amount of voids around molded coal] One aspect of the present invention also provides a method for estimating the amount of voids around molded coal in a blended coal mixture composed of pulverized coal and molded coal.

[0032] For example, in the method described in Patent Document 1 mentioned above, when using various types of pulverized coal with different properties such as particle size composition and moisture content, it was necessary to perform cross-sectional image analysis each time. On the other hand, by using the method for analyzing the amount of voids around molded coal according to this embodiment, it is possible to estimate the amount of stacking fill reduction for pulverized coal with various properties without actual image analysis, by pre-determining the relationship between the properties such as particle size composition and moisture content of the pulverized coal and the amount of stacking fill reduction.

[0033] Factors influencing the cumulative filling loss include the particle size composition of the pulverized coal, the moisture content of the pulverized coal, and other factors. However, based on the inventors' examination of the cumulative filling loss obtained using the analysis method for voids around the molded coal according to this embodiment, it is considered that the particle size composition and moisture content of the pulverized coal have a particularly significant influence on the amount of voids around the molded coal. Furthermore, among the particle size composition, the mass ratio of coarse particles contained in the pulverized coal is considered to have a particularly significant influence. In addition, the moisture content of the pulverized coal is thought to affect the amount of voids around the molded coal by affecting the fluidity of the pulverized coal.

[0034] Therefore, we conceived of a method to estimate the voids around molded coal by using the particle size composition of the pulverized coal, preferably the mass ratio of coarse particles in the pulverized coal, and determining the relationship between the combination of the particle size composition and the moisture content of the pulverized coal and the cumulative filling reduction.

[0035] One aspect of the present invention is, A method for estimating the amount of voids around molded coal when a blend of coal containing molded coal and powdered coal is filled into a container, Multiple types of blended coal samples are prepared by combining each of several types of powdered coal samples, selected to include different levels of particle size composition and different levels of moisture content, with an arbitrarily selected molded coal sample. For each blended coal sample, the cumulative sample packing reduction was determined according to the method for analyzing the amount of voids around the molded coal in this embodiment. Based on the relationship between the particle size composition and moisture content of the pulverized coal sample and the cumulative filling loss of the sample, we obtained equation (I) relating the particle size composition and moisture content of the pulverized coal to the cumulative filling loss. For blended coal, which is a combination of pulverized coal intended for use in coke production and arbitrarily selected molded coal for analysis, the particle size composition and moisture content of the pulverized coal intended for use are substituted into the above relational equation (I) to calculate an estimated cumulative filling loss, and this estimated cumulative filling loss is used as an indicator of the amount of voids around the molded coal. This invention provides a method for estimating the amount of voids surrounding molded coal.

[0036] <Selection of charcoal powder samples> The pulverized coal samples used in the estimation method of this embodiment are selected to include levels with different particle size configurations and levels with different moisture content. The pulverized coal samples may also include levels with the same particle size configuration or moisture content. In one embodiment, the pulverized coal samples consist of groups of levels having two or more, preferably three or more, different values ​​for each of the particle size configuration and moisture content. From the viewpoint of estimation accuracy, a larger number of different values ​​is advantageous, but from the viewpoint of work efficiency, the number of different values ​​may be 10 or less, or 8 or less, in one embodiment.

[0037] The particle size composition value used for estimation is, in one embodiment, the value of the mass percentage of coarse particles, and preferably, one value selected from the group consisting of the sieve mass percentage and particle size. The size of the molded coal is usually assumed to be 30cc to 120cc. The sieve size for the sieve mass percentage, which is an indicator of the mass percentage of coarse particles in the pulverized coal, more specifically, the mesh opening size in accordance with JIS Z 8801-1, is typically 2mm or larger, preferably 2.8mm or larger, or 5.6mm or larger. From the viewpoint of more accurately estimating the influence of coarse particles in the pulverized coal on the amount of voids around the molded coal, the sieve size may be 8mm or smaller, or 6.7mm or smaller, in one embodiment. As for the particle size, the mass-average diameter, which is an indicator in which the presence of coarse particles contributes greatly to the value, is preferred, but other average particle diameters, or parameters obtained by the functional representation of the particle size distribution (e.g., 50% diameter), may also be adopted.

[0038] <Derivation of relation (I)> For each blended coal sample, the cumulative sample filling loss is determined according to the method for analyzing the amount of voids around molded coal according to one aspect of the present invention described above. Then, based on the relationship between the particle size composition and moisture content of the pulverized coal sample and the cumulative sample filling loss, a relational equation (I) between the particle size composition and moisture content of the pulverized coal and the cumulative filling loss is derived. In one embodiment, relational equation (I) is expressed as shown in relational equation (I-1) below. Cumulative filling loss = a × [value of particle size composition of pulverized coal] + b × [value of moisture content of pulverized coal] + c (I-1) (In the formula, a and b are coefficients derived from the relationship between the particle size composition and moisture content of the pulverized coal sample and the cumulative sample filling loss, and c is a constant term derived from the relationship between the particle size composition and moisture content of the pulverized coal sample and the cumulative sample filling loss.) The method for deriving relational equation (I) from the relationship between the particle size composition and moisture content of the pulverized coal sample and the cumulative sample filling loss is not limited to this, but may include multivariate analysis such as simple regression analysis or multiple regression analysis. The analytical procedures for each of these examples will be described below.

[0039] (Simple linear regression analysis) In one embodiment of simple regression analysis, particle size composition and moisture content are used as variables, and the relationship between each of these and the cumulative sample filling loss may be determined by linear regression or polynomial regression, typically linear regression. Specifically, the values ​​of particle size composition and moisture content are plotted on the x-axis, and the value of the cumulative filling loss is plotted on the y-axis, and from this plot, a simple regression equation may be obtained, for example, by linear regression using the least squares method.

[0040] Next, the value of the regression coefficient (in one embodiment, the slope of the linear regression equation) obtained from a simple regression equation showing the relationship between particle size composition and cumulative filling loss is set as coefficient a of the above relational equation (I-1), and the value of the regression coefficient (in one embodiment, the slope of the linear regression equation) obtained from a simple regression equation showing the relationship between moisture content and cumulative filling loss is set as coefficient b of relational equation (I-1). Coefficient c may be, for example, 0, or non-zero. In this way, relational equation (I-1) can be obtained as relational equation (I) between the particle size composition and moisture content of pulverized coal and cumulative filling loss.

[0041] (Multiple regression analysis) In one embodiment of the multiple regression analysis, both particle size composition and moisture content are used as variables, and the relationship between these variables and the cumulative sample filling loss may be examined using linear regression or polynomial regression, typically linear regression. Specifically, a multiple regression analysis may be performed with particle size composition and moisture content as explanatory variables and cumulative filling loss as the dependent variable. According to the inventors' studies, there is no strong correlation between particle size composition and moisture content, so using them as explanatory variables may be advantageous in performing a significant multiple regression analysis. The regression may be performed, for example, by the least squares method, although this is not limited to this.

[0042] Next, the regression coefficients obtained from the multiple regression equation showing the relationship between particle size composition, moisture content, and cumulative filling loss are used as coefficients a and b of the above relation (I-1), and the value of the intercept of the said multiple regression equation is used as coefficient c. In this way, the above relation (I-1) can be obtained as relation (I) between the particle size composition and moisture content of pulverized coal and cumulative filling loss. In the multiple regression analysis, relation (I-1) with an intercept c (i.e., constant term) of 0 may be obtained by standardization, but standardization may also be omitted.

[0043] There are no particular limitations on how to confirm whether the multiple regression analysis was performed effectively, and the test may be performed using standard methods. The significance level may be selected as desired, for example, 5% or 1%. If the regression results do not meet the significance level, the operation of changing the parameters selected as the granularity composition and performing the multiple regression analysis again may be repeated until the significance level is met. When using sieve mass ratio as the granularity composition, if the multiple regression analysis using sieve mass ratio at a certain sieve size does not meet the significance level, the sieve size may be changed to a larger one and the multiple regression analysis may be performed again. Increasing the sieve size of the sieve mass ratio used as the variable tends to decrease the significance F, which is a desirable trend.

[0044] In the above, we have described the case in which the particle size composition and moisture content of pulverized coal are used as variables in estimating the amount of voids around molded coal. However, if there are other factors that significantly affect the amount of reduction in stacking capacity, it is possible to use those other factors instead of, or in addition to, the particle size composition and moisture content. For example, the above example shows a case where there are two explanatory variables in the multiple regression analysis, but it is also possible to use three or more explanatory variables.

[0045] <Calculation of estimated cumulative filling loss> By using the relational equation (I) derived using the procedure exemplified above, an estimated cumulative fill loss of the blended coal can be calculated. In one embodiment, for a blended coal which is a combination of pulverized coal intended for use in coke production and arbitrarily selected molten coal for analysis, the particle size composition and moisture content of the pulverized coal intended for use are substituted into relational equation (I) above to calculate the estimated cumulative fill loss. This estimated cumulative fill loss can be used as an indicator of the amount of voids around the molten coal.

[0046] [Method of producing coke] One aspect of the present invention also provides a method for producing coke using a blended coal mixture containing molded coal and pulverized coal. The inventors have found that by using the packing loss amount, an index of this embodiment, to analyze the amount of voids around the molded coal with high precision, it is possible to produce high-strength coke while using a large amount of inferior coal. According to the inventors' studies, the coke strength of a blended coal mixture containing molded coal and pulverized coal is almost constant when the SV of the molded coal portion is above a predetermined value, but when it falls below that predetermined value, it tends to decrease as the SV of the molded coal portion decreases. This tendency is observed similarly regardless of the expandability, moisture content, and particle size composition of the pulverized coal, and the above predetermined value differs depending on the cumulative packing loss amount. Molded coal with a low SV can be inexpensive because it is of inferior quality. Therefore, determining the predetermined value of the SV of the molded coal section, that is, the lower limit of the molded coal section SV which is the limit value at which a decrease in the molded coal section SV does not occur, and selecting and using molded coal that exhibits this lower limit of the molded coal section SV is advantageous in that high-strength coke can be obtained inexpensively. The relationship equation (II) between the cumulative filling loss and the lower limit of the molded coal section SV can be determined in advance, the cumulative filling loss for the blended coal including the pulverized coal to be used can be determined, and this can be substituted into the above relationship equation (II) to calculate the lower limit of the molded coal section SV. Then, molded coal whose SV is equal to or greater than this lower limit of the molded coal section SV can be blended with the pulverized coal to be used. Furthermore, in order to construct a blended coal that can form high-strength coke while using a large amount of inferior coal, it is preferable that the value is as close as possible to the lower limit of the molded coal section SV. Specifically, the variation in the molded coal section SV during actual operation is typically ±0.1 cm. 3 Considering that it is approximately / g, the SV lower limit of the molded charcoal portion is +0.1cm. 3 It is preferable to blend molded charcoal having an SV value of / g with the charcoal powder intended for use as described above.

[0047] In the coke manufacturing method of this embodiment, A) For the coal blend selected for testing, a relationship equation (II) is determined in advance between the cumulative packing reduction calculated by the analysis method for the amount of voids around the molded coal in this embodiment and the lower limit of the molded coal SV range, which is the lower limit of the molded coal SV range in which the coke strength remains constant even when the molded coal SV is changed. B) For combinations of pulverized coal intended for use in coke production and arbitrarily selected molded coal for analysis, B1) the cumulative packing reduction is determined using the analysis method for the amount of voids around the molded coal of this embodiment, or B2) the estimated value of the cumulative packing reduction is determined using the estimation method for the amount of voids around the molded coal of this embodiment. C) Substitute the cumulative filling loss obtained in B1) or the estimated cumulative filling loss obtained in B2) into the above relational equation (II) to determine the lower limit of SV for the molded coal section. D) Manufacture molded coal in which the measured SV value is equal to or greater than the lower limit of the SV value of the molded coal portion, and use the blended coal, which consists of the pulverized coal to be used and the manufactured molded coal, for coke production. The following provides a more detailed explanation.

[0048] (Derivation of the relationship between cumulative filling loss and the lower limit of SV in the molded coal section (II)) In A) above, for the blended coal selected for testing, a relationship formula (II) is predetermined between the cumulative packing reduction calculated by the analysis method for the amount of voids around the molded coal in this embodiment and the lower limit of the molded coal SV, which is the limit value at which a decrease in coke strength does not occur when the SV of the molded coal is reduced. In one embodiment, multiple levels of pulverized coal with different moisture content and / or particle size composition, and multiple levels of molded coal with different SV are selected. For the test blended coal, which is a combination of each level of pulverized coal and one level of molded coal arbitrarily selected, the cumulative packing reduction is calculated using the method of this embodiment. For example, if three levels of pulverized coal and ten levels of molded coal are selected, the cumulative packing reduction is calculated for a total of three types of test blended coal. As the molded coal to be used to calculate the cumulative packing reduction, one without defects, etc., is selected from the above multiple levels.

[0049] The lower limit of the molded coal SV, which is the limit at which a decrease in the molded coal SV does not occur and thus does not result in a decrease in coke strength, is determined as follows. a) For each level of molded coal selected for testing, the SV (Superficial Value) will be measured by carbonization test using a dilartometer in accordance with JIS M8801. b) For each of the cokes obtained from the test blend coals, in accordance with JIS K 2151, the coke strength is actually measured by a drum test. The coke strength may be, in one aspect, DI 150 15 or DI 150 6. DI 150 15 is the ratio of the material remaining on a 15 mm sieve after 150 rotations in the drum test and is an index mainly representing the volume fracture strength of the coke, and DI 150 6 is the ratio of the material passing through a 6 mm sieve after 150 rotations in the drum test and is an index mainly representing the surface fracture strength of the coke. c) For all the test blend coals, for each level of pulverized coal, plot the relationship between the molded coal part SV (x-axis) and the coke strength (y-axis) obtained from the test blend coal. For example, when selecting 3 levels of pulverized coal and 10 levels of molded coal, the first plot for the test blend coal related to the combination of the first level of pulverized coal and each of the first to tenth levels of molded coal, the second plot for the test blend coal related to the combination of the second level of pulverized coal and each of the first to tenth levels of molded coal, and the third plot for the test blend coal related to the combination of the third level of pulverized coal and each of the first to tenth levels of molded coal are created. For each plot, the minimum value of the molded coal part SV in the region where the coke strength is maintained constant regardless of the value of the molded coal part SV is defined as the molded coal part SV lower limit value. The region where the coke strength is maintained constant regardless of the value of the molded coal part SV means the region where the value of the coke strength falls within the standard deviation in each plot. For example, when the standard deviation of each plot is 0.4, the region where the coke strength is maintained constant regardless of the value of the molded coal part SV is the region where the coke strength falls within the range of ±0.4. In this way, the molded coal part SV lower limit value for each level of pulverized coal is obtained. In addition, if the degree of increase in the coke strength obtained from the test blend coal clearly changes and is maintained at almost the same value with respect to the increase in the molded coal part SV (x-axis), it can be regarded as a region where it is maintained constant, and the judgment is not limited to the standard deviation. d) The cumulative filling loss for each level of pulverized coal calculated above is plotted on the x-axis, and the lower limit of SV of the molded coal portion for each level of pulverized coal, as defined above, is plotted on the y-axis. Then, for example, by linear approximation, equation (II) relating the cumulative filling loss and the lower limit of SV of the molded coal portion is derived.

[0050] (Selection of coal candidates for use in coke production) In B1) above, the cumulative packing reduction is determined using the void volume analysis method around the molten coal of this embodiment for combinations of pulverized coal intended for use in coke production and arbitrarily selected molten coal for analysis. Molten coal without defects may be selected.

[0051] Alternatively, in B2) above, for a combination of pulverized coal intended for use in coke production and arbitrarily selected molded coal for analysis, the estimated cumulative packing reduction is obtained using the method for estimating the void volume around the molded coal of this embodiment.

[0052] In C) above, the cumulative filling loss obtained in B1) or the estimated cumulative filling loss obtained in B2) is substituted into relational equation (II) obtained in A) above to determine the lower limit of SV for the molded coal portion. This lower limit of SV for the molded coal portion indicates the limit to which the SV for the molded coal portion can be reduced (i.e., to utilize lower quality molded coal) without causing a decrease in coke strength due to the molded coal (more specifically, due to voids remaining in the coke caused by insufficient expansion of the molded coal portion during coking) in the blended coal containing the pulverized coal to be used.

[0053] In step D) above, molded coal is produced in which the measured SV value is equal to or greater than the lower limit of the molded coal portion SV value determined above. It is preferable that the measured SV value of the manufactured molded coal is as close as possible to the lower limit of the molded coal portion SV value, but the variation in the molded coal portion SV during actual operation is usually ±0.1 cm. 3 Considering that it is approximately / g, for example, the lower limit of SV for molded charcoal + 0.1cm 3A value of / g is preferred. Such molded coal may be of the lowest quality to the extent that it does not cause a decrease in coke strength due to the molded coal. The measured SV value of the molded coal can be adjusted to the desired value by, for example, adjusting the type and / or amount of coal and / or binding filler used in the production of the molded coal. By using the molded coal produced as described above in the production of coke, it becomes possible to produce coke that is inexpensive while maintaining the desired coke strength. [Examples]

[0054] The following describes exemplary embodiments of the present invention with reference to examples, but the present invention is not limited to these embodiments.

[0055] [Example 1] <Analysis of void volume around molded coal> (Coal used) For the analysis, we used pulverized coal of levels 1 to 4 shown in Table 1, and molded coal without defects. "Pulverized coal" refers to the coal itself obtained by pulverization; "coarse-grained coal" refers to coal from which fine particles smaller than 0.3 mm have been removed; and "smooth-grained coal" refers to coal with a particle size of 0.3 mm to 3 mm. Figure 3 shows the particle size distribution of each type of pulverized coal. For molded coal, a pillow-type mold with a particle size of approximately 40 mm was used.

[0056] The voids around the molded coal were analyzed by the amount of filling reduction using the following procedure.

[0057] (Step S11) Using a test apparatus, molded coal and pulverized coal were filled into a test container by gravity, and cross-sectional images of the inside of the test container were captured using X-ray CT.

[0058] As the test apparatus, a Mini ASTM apparatus (drop height 1m) was used, which is a 1 / 2 scale version of the ASTM improved bulk density measuring apparatus (Qingtang et al., Coke Circular, 30(11), 13-5(1981)), which is an improved version of the bulk density test in accordance with ASTM D 291-86, with the following conditions improved.

[0059] In the Mini ASTM apparatus test container (150 × 150 × 150 mm), 1.5 kg of pulverized coal of each level was dropped, followed by molded coal (cup size 30 cc, spherical particle size 39 mm), and finally the remaining 2.75 kg of pulverized coal of each level was dropped to fill the container with coal. The sample container filled with coal was imaged using an X-ray CT diagnostic device (TSX-201 (Aquilion LB) manufactured by Toshiba Medical Systems Corporation). The X-ray CT imaging conditions were as follows. Under the following imaging conditions, a resolution of 0.488 mm per pixel was obtained. Scan Mode: Helical Tube voltage: 120kV Tube current: 400mA FOV (Field of View): 440mm Image slice thickness: 0.5mm

[0060] The obtained cross-sectional images were processed using the image analysis software Avizo. All analyses were performed in 3D. The region of interest (ROI) was defined as the central 120mm rectangular area (i.e., the central part (120×120×120mm) within the container dimensions (150×150×150mm)) to exclude wall effects.

[0061] (Step S12) Based on the X-ray CT value of each pixel within the ROI, the density (BD) is expressed by the following relationship: BD(t / m 3 ) = 0.001 × (X-ray CT value) + 1 The calculation was performed according to the following formula. Density is 1.0 g / cm³. 3 Areas exceeding 1.0 g / cm³ are high-density areas. 3 The following regions were defined as low-density areas.

[0062] (Step S13) a) Small particles of 100 voxels or less were removed from the high-density region defined in step S12. b) The high-density portion after the processing in a) above was subjected to a labeling process so that the particles could be separated and distinguished one by one. c) From the high-density region after the processing described in b) above, only those particles satisfying the shape parameters of Anisotropy < 0.9, Flatness < 0.4, and Elongation > 0.4 were selected as heteromorphic particles. d) The irregularly shaped particles extracted in c) above were subjected to the watershed method to detect and remove constrictions. e) The irregularly shaped particles after the process in d) above were processed in the following order: 1 voxel shrinkage, removal of small particles using the same procedure as in a), 1 voxel expansion, and smoothing. The remaining area was defined as the molded carbon portion. All expansion and shrinkage processes were performed in a spherical shape (ball dilation / ball erosion).

[0063] (Step S14) This step was performed only at levels containing agglomerated charcoal. The molded charcoal portion defined in step S13 was subtracted from the high-density portion defined in step S12, and the remaining area was labeled. From this labeled area, Volume > 15 mm 3 Only the region satisfying the volume parameter was selected as the agglomerate carbon region. This region was excluded from the analysis by masking it.

[0064] (Step S15) Within the ROI of the original image, the molded char portion defined in step S13 above was subjected to an expansion process 30 times, in which one voxel was expanded each time from the periphery of the molded char portion in a shape similar to the molded char portion.

[0065] (Step S16) After each expansion treatment was completed, the volume of the area increased by that treatment (i.e., the volume increase due to one expansion treatment) and the average density were calculated. After more than 21 expansion treatments, the average density remained almost unchanged, so the average density after 21 expansion treatments was defined as the average density of the pulverized coal portion. This average density was used as a threshold, and the area exceeding this threshold was defined as the pulverized coal portion, while the area below this threshold was defined as the void portion.

[0066] (Step S17) The average density of the coal pulverized portion was calculated by taking the number average of the densities of each voxel corresponding to the coal pulverized portion, and the average density of the void portion was calculated by taking the number average of the densities of each voxel corresponding to the void portion, and the difference between the average density of the coal pulverized portion and the average density of the void portion was calculated. For each expansion treatment cycle, the amount of filling reduction was calculated according to the following formula. Filling reduction amount = [Volume of the region that increased in volume during each expansion treatment] × [Difference between the average density of the pulverized coal portion and the average density of the void portion]

[0067] (Step S18) The cumulative filling loss was calculated by accumulating the above-mentioned filling loss over the number of expansion treatments. Figure 2 shows the cumulative filling loss when using powdered coal made from coarse-grained coal + agglomerated coal (4% moisture content). The hatched area in Figure 2 corresponds to the cumulative filling loss. This cumulative filling loss was used as an indicator of the amount of void around the molded coal.

[0068] As shown in Figure 2, in void evaluation using cumulative filling loss as an indicator, once the expansion treatment exceeds a predetermined number of times (8 times in Figure 2), the variation in filling loss due to the number of expansion treatments almost disappears. Therefore, it can be seen that good evaluation results can be obtained if the number of expansion treatments is set to a predetermined number or more.

[0069] Figure 4 shows X-ray CT images of examples using each of the four levels of pulverized coal. Comparing the CT images of Level 1 and Level 2, which have different moisture content, it was found that the voids were smaller in Level 1, which has less moisture, than in Level 2, which has more moisture. Furthermore, comparing the CT images of Levels 1, 3, and 4, which have different particle size compositions, it was found that the voids were smaller in whole-grain coal (Level 3) compared to crushed coal (Level 1), coarse-grained coal, and agglomerated coal (Level 4).

[0070] Figures 5-8 show the relationship between the number of expansion treatments and the cumulative filling loss in Example 1, using each of the pulverized coal levels 1-4.

[0071] [Conventional Example 1] Using the same coal blend as in Example 1, the width of the voids around the molded coal was evaluated according to the method described in Patent Document 1 (particularly paragraphs 0020 to 0026) using the following procedure. The molded coal portion extracted by binarization was selected as the region, and the molded coal portion was expanded n times with a unit width a (mm) = 0.488 mm. The density BDp,n of the pulverized coal portion in the area excluding the region separated by a width Xn (= a × n) (mm) from the periphery of the molded coal was determined, and the width of the void around the molded coal was defined as Xn when the change in BDp,n + 1 - BDp,n with respect to Xn converged to a predetermined range.

[0072] Figures 9-12 show the relationship between the distance X from the molded coal using each of the pulverized coal levels 1-4 in Conventional Example 1 and the change in bulk density during each expansion treatment.

[0073] Table 1 shows the analysis results of the cumulative packing reduction around the molded coal (Example 1) and the analysis results of the maximum width of the void around the molded coal (Conventional Example 1), obtained from the results shown in Figures 5 to 12.

[0074] In the evaluation based on the maximum void width in Conventional Example 1, the void width was smaller for crushed coal (level 1) compared to whole-grain coal (level 3). In contrast, in the evaluation based on cumulative filling loss in Example 1, the void value was larger for crushed coal (level 1) compared to whole-grain coal (level 3), resulting in the opposite outcome to Conventional Example 1. It is thought that the method in Conventional Example 1 could not correctly distinguish between the pulverized coal and the voids. The analysis results based on cumulative filling loss in Example 1 also showed good agreement with the CT image shown in Figure 4, and the cumulative filling loss was smallest under the whole-grain coal condition (level 3) among levels 1 to 4. From the above, it can be seen that the analysis method in Example 1 is superior to the analysis method in Conventional Example 1.

[0075] We investigated whether the cumulative fill loss around molded charcoal changes when multiple molded charcoal pieces are used. As part of this investigation, a blended charcoal mixture consisting of 70% by mass of level 2 crushed charcoal and 30% by mass of molded charcoal was prepared and thoroughly mixed beforehand. The mixed charcoal mixture was filled into a test container by gravity using a test apparatus, and cross-sectional images of the inside of the test container were acquired by X-ray CT. Steps S12 to S18 described above were performed for the analysis of the acquired cross-sectional images. The number of molded charcoal pieces in the analysis area was determined by dividing the volume of the molded charcoal area by the volume of one molded charcoal piece, and it was found to be approximately 11.2 pieces. The absolute value of the cumulative fill loss when multiple molded charcoal pieces were used was 6.83g (equivalent to 0.61g per molded charcoal piece), which was found to be close to the cumulative fill loss of level 2 of 0.68g shown in Table 1 for Example 1.

[0076] [Example 2] <Estimation of void volume around molded coal> In Example 2, a method was investigated to estimate the amount of voids around molten coal using factors that affect the voids around the molten coal, without image analysis. As shown in Figure 4 and Table 1, the size of the voids around the molten coal is influenced by the particle size composition of the pulverized coal (more specifically, the proportion of coarse particles) and the moisture content of the pulverized coal. In this example, the particle size composition of the pulverized coal was considered to be the mass percentage on a 3mm sieve, the mass percentage on a 6mm sieve, and the mass-average diameter. All of these are indicators of the proportion of coarse particles in the pulverized coal. Furthermore, the moisture content of the pulverized coal is thought to affect the fluidity of the pulverized coal and therefore the cumulative filling loss. It should be noted that the factors that affect the cumulative filling loss are not limited to the particle size composition and moisture content of the pulverized coal, but in this example, the estimation was performed by focusing on the particle size composition and moisture content, which are the main factors that have a large influence on the cumulative filling loss. For convenience, in the examples and reference examples, sieves with mesh openings of 2.8 mm and 5.6 mm in accordance with JIS Z 8801-1 are referred to as 3 mm sieves and 6 mm sieves, respectively.

[0077] (1) Examples 2-1 to 2-3: Combinations of simple linear regression analysis In this example, a simple regression analysis was performed with the particle size composition and moisture content of pulverized coal as independent explanatory variables and the cumulative fill loss as the dependent variable. Using the obtained regression coefficients, a relationship between particle size composition, moisture content, and cumulative fill loss was determined. For the particle size composition, one was selected from the mass percentage of pulverized coal sieved through a 3 mm sieve, the mass percentage of pulverized coal sieved through a 6 mm sieve, and the mass-average diameter of the pulverized coal.

[0078] (Coal used) For estimation, we used pulverized coal of levels 1 to 4 and molded coal without defects, as shown in Table 1, similar to those used in Example 1.

[0079] (Estimated procedure) For each of the above pulverized coals and the above molded coal combinations, the cumulative packing loss was determined using the same procedure as in Example 1, and plotted as shown in Figures 13 to 16. Figure 13 shows the relationship between the mass percentage on a 3 mm sieve and the cumulative packing loss, Figure 14 shows the relationship between the mass percentage on a 6 mm sieve and the cumulative packing loss, Figure 15 shows the relationship between the average mass diameter and the cumulative packing loss, and Figure 16 shows the relationship between the moisture content and the cumulative packing loss. As shown in Figures 13 to 16, simple linear regression was performed using the least squares method from the plotted values ​​to obtain regression equations. Using the regression coefficients, which are the slopes of each regression equation, the relationship equation (I) between the particle size composition and moisture content and the cumulative packing loss was derived.

[0080] (Example 2-1) Using the mass percentage on the 3mm sieve and the moisture content as explanatory variables, and the cumulative fill-down as the objective function, we obtained the following relation (2-1) as relation (I) using the regression coefficients of the simple regression equation shown in Figure 13 (=0.0222) and the simple regression equation shown in Figure 16 (=0.0539). Cumulative filling loss = [Percentage of pulverized coal on a 3mm sieve (mass%)] × 0.0222 + [Moisture content of pulverized coal (mass%)] × 0.0539 (2-1) Figure 17 shows the relationship between the estimated cumulative filling loss calculated by substituting the 3mm sieve mass percentage and moisture content values ​​of each pulverized coal into the above formula, and the cumulative filling loss obtained for each pulverized coal using the procedure of Example 1.

[0081] (Example 2-2) Using the mass percentage on the 6mm sieve and the moisture content as explanatory variables, and the cumulative fill-down as the objective function, we obtained the following relation (2-2) as relation (I) using the regression coefficients of the simple regression equation shown in Figure 14 (=0.0395) and the simple regression equation shown in Figure 16 (=0.0539). Cumulative filling loss = [Percentage of pulverized coal sieved in 6mm (mass%)] × 0.0395 + [Moisture content of pulverized coal (mass%)] × 0.0539 (2-2) Figure 18 shows the relationship between the estimated cumulative filling loss calculated by substituting the 6mm sieve mass percentage and moisture content values ​​of each pulverized coal into the above formula, and the cumulative filling loss obtained for each pulverized coal using the procedure of Example 1.

[0082] (Examples 2-3) Using the average mass diameter and moisture content as explanatory variables, and the cumulative fill-down as the objective function, the regression coefficients of the simple regression equation shown in Figure 15 (=0.3347) and the simple regression equation shown in Figure 16 (=0.0539) were used to obtain the following relation (2-3) as relation (I). Cumulative filling loss = [average diameter of pulverized coal (mm)] × 0.3347 + [moisture content of pulverized coal (mass%)] × 0.0539 (2-3) Figure 19 shows the relationship between the estimated cumulative filling loss calculated by substituting the mass-average diameter and moisture content values ​​of each pulverized coal into the above formula, and the cumulative filling loss obtained for each pulverized coal using the procedure of Example 1.

[0083] The results shown in Figures 17-19 demonstrate that the cumulative filling loss can be estimated using any of the methods described in Examples 2-1 to 2-3 above. Specifically, for blended coal, which is a combination of pulverized coal intended for use in coke production and arbitrarily selected molded coal for analysis, the particle size composition and moisture content of the pulverized coal intended for use can be substituted into any of the above relational equations (2-1) to (2-3) as relational equation (I) of this disclosure to calculate an estimated cumulative filling loss. By using this estimated cumulative filling loss as an indicator of the void amount around the molded coal, it is possible to accurately estimate the void amount around the molded coal of the blended coal.

[0084] [Reference example 1] Using only the mass percentage on the 3mm sieve as the variable, the cumulative fill-down was calculated according to the following relationship (A), using the regression coefficient (=0.0222) of the simple regression equation shown in Figure 13. Cumulative filling loss = [Percentage of pulverized coal on a 3mm sieve (mass%)] × 0.0222 (A) Figure 20 shows the relationship between the estimated cumulative filling loss calculated by substituting the mass percentage of each pulverized coal on a 3mm sieve into the above formula, and the cumulative filling loss obtained for each pulverized coal using the procedure of Example 1.

[0085] [Reference example 2] Using only the mass percentage on the 6mm sieve as the variable, the cumulative fill-down was calculated according to the following relationship (B) using the regression coefficient (=0.0395) of the simple regression equation shown in Figure 14. Cumulative filling loss = [Percentage of pulverized coal on a 6mm sieve (mass%)] × 0.0395 (B) Figure 21 shows the relationship between the estimated cumulative filling loss calculated by substituting the mass percentage of each pulverized coal on a 6mm sieve into the above formula, and the cumulative filling loss obtained for each pulverized coal using the procedure of Example 1.

[0086] [Reference example 3] Using only the average mass diameter as the variable, the cumulative fill-down was calculated according to the following relationship (C) using the regression coefficient (=0.3347) of the simple regression equation shown in Figure 15. Cumulative filling loss = [average diameter of pulverized coal (mm)] × 0.3347 (C) Figure 22 shows the relationship between the estimated cumulative filling loss calculated by substituting the mass-average diameter value of each pulverized coal into the above formula, and the cumulative filling loss obtained for each pulverized coal using the procedure of Example 1.

[0087] [Reference example 4] Using only the moisture content as the variable, the cumulative fill loss was calculated according to the following relationship (D) using the regression coefficient (=0.0539) of the simple regression equation shown in Figure 16. Cumulative filling loss = [Moisture content of pulverized coal (mass%)] × 0.0539 (D) Figure 23 shows the relationship between the estimated cumulative filling loss calculated by substituting the moisture content values ​​of each type of coal powder into the above formula, and the cumulative filling loss obtained for each type of coal powder using the procedure in Example 1.

[0088] The results shown in Figures 20-23 indicate that in Reference Examples 1-4, there is a large discrepancy between the cumulative fill-down amount obtained using relational equations (A)-(D) and the cumulative fill-down amount obtained using the procedure in Example 1. In other words, when only one variable selected from particle size composition and moisture content is used, the cumulative fill-down amount cannot be estimated with high accuracy.

[0089] (2) Examples 2-4 to 2-6: Multiple regression analysis In this example, multiple regression analysis was performed using linear regression by least squares, with the particle size composition and moisture content of pulverized coal as explanatory variables and the cumulative packing loss as the dependent variable. Using the regression coefficient, which is the slope of the obtained regression equation, equation (I) relating the particle size composition and moisture content to the cumulative packing loss was derived. For the particle size composition, one was selected from the mass percentage of pulverized coal sieved through a 3 mm sieve, the mass percentage of pulverized coal sieved through a 6 mm sieve, and the mass-average diameter of the pulverized coal.

[0090] Furthermore, the lack of a strong correlation between the particle size composition and moisture content, which were used as explanatory variables, was confirmed in advance using the following method. In the figure showing the relationship between particle size composition and moisture content, a simple linear regression was performed using the least squares method from the plotted values, and the coefficient of determination (R-squared value) of the regression equation was obtained, confirming that the tolerance (=1-R-squared value) was greater than 0.1.

[0091] (Coal used) For estimation, we used pulverized coal of levels 1 to 7 shown in Table 2, and molded coal, the same as in Example 1. The pulverized coal of levels 1 to 4 shown in Table 2 are the same as the pulverized coal of levels 1 to 4 shown in Table 1. In this example, in addition to levels 1 to 4, we used coarse-grained coal (level 5) with fine particles smaller than 0.3 mm removed, crushed coal with a 3 mm sieve mass ratio of 100% (level 6), and whole-grained coal + agglomerated coal (level 7) which is whole-grained coal of level 3 blended with agglomerated coal. In other words, by using seven types of pulverized coal related to levels 1 to 7, we secured a sufficient sample size to perform multiple regression analysis appropriately.

[0092] (Estimated procedure) For each of the above pulverized coals and the above molded coal combinations, the cumulative filling loss was determined by cross-sectional image analysis using the same procedure as in Example 1. Table 2 shows the cumulative filling loss for each condition. Based on the results for levels 1 to 7, multiple regression analysis was performed with the cumulative filling loss as the dependent variable, using the combination of the 3mm sieve mass percentage and moisture content of the pulverized coal (for Example 2-4), the 6mm sieve mass percentage and moisture content of the pulverized coal (for Example 2-5), or the mass-average diameter and moisture content of the pulverized coal (for Example 2-6) as explanatory variables. At this time, a significance level of 5%, which is common in multiple regression analysis, was adopted.

[0093] (Examples 2-4) Multiple regression analysis was performed using the mass percentage on a 3mm sieve and the moisture content as explanatory variables. Using the regression coefficients (=0.01956, 0.03984) of the obtained regression equation, the following relation (2-4) was obtained as relation (I). Cumulative filling loss = [Percentage of pulverized coal on a 3mm sieve (mass%)] × 0.01956 + [Moisture content of pulverized coal (mass%)] × 0.03984 (2-4) In this example, when multiple regression analysis was performed with the intercept significantly different from 0, the p-value for the intercept exceeded the significance level. Therefore, the multiple regression analysis was performed again with the intercept not significantly different from 0 (i.e., intercept = 0), and the results obtained were adopted. Figure 24 shows the relationship between the estimated cumulative filling loss calculated by substituting the 3mm sieve mass percentage and moisture content values ​​of each pulverized coal into the above formula, and the cumulative filling loss obtained for each pulverized coal using the procedure of Example 1.

[0094] The above multiple regression analysis showed that the upper tail probability (significance F) of the ratio of variances between the two groups—the cumulative filling reduction calculated according to relational equation (2-4) and the cumulative filling reduction obtained by the procedure in Example 1 (i.e., the measured value)—was 0.00030, which is less than 0.05, thus the regression analysis was deemed meaningful. Furthermore, the p-values, which represent the probability that the regression coefficients for the mass percentage of pulverized coal on a 3mm sieve and the moisture content of pulverized coal are at extreme values, were 0.00124 and 0.00788, respectively, and both were less than 0.05, so each regression coefficient was deemed significant.

[0095] (Examples 2-5) Multiple regression analysis was performed using the mass percentage on a 6mm sieve and the moisture content as explanatory variables. Using the regression coefficients (=0.03366, 0.05159) of the obtained regression equation, the following relation (2-5) was obtained as relation (I). Cumulative filling loss = [Percentage of pulverized coal on a 6mm sieve (mass%)] × 0.03366 + [Moisture content of pulverized coal (mass%)] × 0.05159 (2-5) In this example, when multiple regression analysis was performed with the intercept significantly different from 0, the p-value for the intercept exceeded the significance level. Therefore, the multiple regression analysis was performed again with the intercept not significantly different from 0 (i.e., intercept = 0), and the results obtained were adopted. Figure 25 shows the relationship between the estimated cumulative filling loss calculated by substituting the 6mm sieve mass percentage and moisture content values ​​of each pulverized coal into the above formula, and the cumulative filling loss obtained for each pulverized coal using the procedure of Example 1.

[0096] The above multiple regression analysis was deemed meaningful because the significance level F in the analysis of variance was 0.00023, which is less than 0.05. Furthermore, the P-values ​​for the mass percentage of 6mm sieved coal and the moisture content of pulverized coal were 0.00093 and 0.00107, respectively, both of which are less than 0.05, indicating that each regression coefficient is significant.

[0097] (Examples 2-6) Multiple regression analysis was performed using the mass-average diameter and moisture content as explanatory variables. Using the regression coefficients (=0.02924, 0.06227) and constant term (=-0.3472) of the obtained regression equation, the following relation (2-6) was obtained as relation (I). Cumulative filling loss = [average diameter of pulverized coal (mm)] × 0.02924 + [moisture content of pulverized coal (mass%)] × 0.06227 - 0.3472 (2-6) In this example, since the p-value of the intercept in the multiple regression analysis, which was performed with the intercept significantly different from 0, did not exceed the significance level, the results of that multiple regression analysis were used as is. Figure 26 shows the relationship between the estimated cumulative filling loss calculated by substituting the mass-average diameter and moisture content values ​​of each pulverized coal into the above formula, and the cumulative filling loss obtained for each pulverized coal using the procedure of Example 1.

[0098] The above multiple regression analysis was deemed meaningful because the significance level F in the analysis of variance was 0.00456, which is less than 0.05. Furthermore, the P-values ​​for the mass-average diameter of the pulverized coal, the moisture content of the pulverized coal, and the intercept were 0.00256, 0.01276, and 0.03849, respectively, all of which are less than 0.05, thus indicating that each regression coefficient is significant.

[0099] It has been shown that the cumulative filling loss can be estimated using any of the methods described in (Examples 2-4) to (Examples 2-6) above, and that the moisture content of the pulverized coal can be used as an indicator of the fluidity of the pulverized coal. In other words, for a blended coal which is a combination of pulverized coal intended for use in coke production and arbitrarily selected molten coal for analysis, the particle size composition and moisture content values ​​of the pulverized coal intended for use can be substituted into any of the above relational equations (2-4) to (2-6) as relational equation (I) of this disclosure to calculate an estimated cumulative filling loss, and if this estimated cumulative filling loss is used as an indicator of the amount of voids around the molten coal, it is possible to accurately estimate the amount of voids around the molten coal of the blended coal.

[0100] [Evaluation Example 1] <Evaluation of the lower limit of SV of molded coal by carbonization test using a test coke oven> (Coal used) Next, for blended coal prepared by mixing powdered coal with molded coal at a moisture content of 4% or 10% by mass, the lower limit of the SV value of the molded coal portion was evaluated by carbonization tests using a test coke oven.

[0101] Table 3 shows the properties of each coal, and Tables 4 and 5 show the blending conditions for the pulverized coal portion in the blended coal using the coals in Table 3. Blending condition 1 was whole-grain coal with a particle size of 0.3 to 3 mm (moisture content 4% by mass), blending condition 2 was crushed coal with an 85% sieve-down ratio of 3 mm (moisture content 4% by mass), and blending condition 3 was crushed coal with an 85% sieve-down ratio of 3 mm (moisture content 10% by mass). The 3 mm sieve-down ratio as the crushed particle size was 92.5%, 85%, and 85% for blending conditions 1, 2, and 3, respectively. A tar-based binder was used as the liquid binder, and asphalt pitch (ASP) was used as the solid binder.

[0102] Table 6 shows the formulations for the molded coal portion. Molded coal was produced by molding powdered coal with a particle size of 3 mm and a sieve mass ratio of 90% using a molding machine (BMS II manufactured by Shinto Kogyo Co., Ltd.) according to formulations 1 to 23. The molded coal was in the shape of a pillow block with a particle size of approximately 40 mm. A tar-based binder was used as the liquid binder, and asphalt pitch (ASP) was used as the solid binder. Of the three series of formulations (1-8, 9-15, and 16-23), formulations 1-8 and 9-15 were made to have nearly the same ΣVM value while varying the molded coal portion SV in order to evaluate the effect of the molded coal portion SV. The whole-grain coal used in levels 1-8 had a powdered coal portion SV × BD = 1.13. SV × BD is called the void filling degree and represents the proportion of space that can be filled by expanded coal in a unit volume.

[0103] (Measurement of SV of molded charcoal by carbonization test using a dilartometer) A carbonization test was conducted using a dilartometer. Molded charcoal under each of the blending conditions shown in Table 6 was crushed and the particle size was adjusted to 100% of the mass below a 3 mm sieve. Then, using a molding machine for the dilartometer, the bulk density was determined to be 1.10 g / cm³. 3 (Dry basis) A molded product with a height of 60 mm was placed in a reaction tube and heated at a heating rate of 3°C / min to perform a carbonization test, and the SV of the molded carbon was measured. The results are shown in Table 6.

[0104] (Measurement of coke strength by drum test) Blended coal, consisting of pulverized coal and molded coal, was prepared under the conditions of levels 1 to 23 shown in Table 7. The resulting coke was then carbonized in a test coke oven, and drum tests were conducted at rotation speeds of 30 and 150 revolutions per minute, with N=3. The results are shown in Table 7. Furthermore, for levels 1 to 8, the molded coal portion's SV and DI were analyzed. 150 The relationship with 6 is shown in Figure 27, and the molded charcoal section SV and DI 150 15 The relationship is shown in Figure 28.

[0105] The lower limit of the molded coal SV, which is the limit at which the coke strength remains constant, was determined from the values ​​of the molded coal SV measured in the carbonization test using a dilartometer and the coke strength measured in the drum test. As shown in Figure 27, the molded coal SV is 1.0 cm. 3 In the range higher than / g, the coke strength DI of the entire coal blend is 1. 150 6 is almost identical, but the molded charcoal portion SV is 0.93 cm 3 / g, plus 0.9cm 3 When the / g decreases, the coke strength DI 150 It can be seen that 6 has decreased significantly. The molded charcoal portion SV is 0.9 cm 3 / g and 0.93cm 3 The straight line connecting the plots that represent / g and the DI of the other plots 150 The intersection point with the line representing the average value of 6 was determined as the lower limit of the molded charcoal SV, which was 0.97 cm. 3 The values ​​were / g. Figure 28 shows the SV and DI of the molded charcoal portion. 150 15 Similarly, when the lower limit of SV in the molded charcoal portion was determined in relation to the same method, it was found to be 0.95 cm. 3 / g is DI 150 The value obtained for 6 was close to the lower limit of SV in the molded charcoal portion.

[0106] Similarly, for levels 9-15 (i.e., blended with crushed charcoal with a moisture content of 4% by mass, which is blending condition 2), the SV and DI of the molded charcoal portion are as follows: 150 The lower limit of SV in the molded charcoal portion, as determined from Figure 29 which shows the relationship with 6, is 1.10 cm. 3The values ​​are / g, and the molded charcoal portion SV and DI for levels 16-23 (i.e., blended with crushed charcoal with a moisture content of 10% by mass, which is blending condition 3). 150 The lower limit of SV in the molded charcoal portion, as determined from Figure 30 which shows the relationship with 6, is 1.50 cm. 3 The value was / g, and in the case of blended charcoal using crushed charcoal, the lower limit of SV in the molded charcoal portion was higher than in the case of blended charcoal using whole-grain charcoal.

[0107] [Comparative Evaluation Example 1] From the maximum width of the void around the molded char obtained by the method according to Conventional Example 1, the following formula (1) described in Patent Document 1 (Japanese Patent Publication No. 2014-224242): Δr = r{(SV × ρ)} 1 / 3 -1} (1) (Here, r: equivalent radius of the circle before expansion (mm), SV: specific volume of expansion of molded coal (cm³) 3 ( / g), ρ: density of molded charcoal (g / cm³) 3 ) is. ) Using the coke strength DI, 150 15 The lower limit of SV in the molded charcoal portion, which is the limit at which the coefficient of SV remains constant, was determined. The following process was performed to determine this lower limit.

[0108] The maximum width of the void around the molded coal in Conventional Example 1, shown in Table 1, is the maximum width of the void that occurs around a single molded coal, and differs from the maximum width of the void around multiple molded coals as described in Patent Document 1. When the number of molded coals increases, if the distance between molded coals is close, low-density regions will combine, so it is thought that the maximum width of the void around the molded coal will be calculated as a larger value when there are multiple molded coals compared to when there is one molded coal. Therefore, when determining the molded coal portion SV, a correction was made by multiplying the value of the maximum width of the void around the molded coal obtained in Conventional Example 1 shown in Table 1 by approximately 3.1, so that the value of the maximum width of the void around the molded coal in the example using level 2 powdered coal shown in Table 1 matches the value of 5.37 mm described in paragraph 0044 of the example in Patent Document 1.

[0109] Furthermore, Patent Document 1 describes the coke strength DI of the entire blended coal. 150 15The range of SV in the molded coal portion that is maintained at a constant level is being investigated under blending conditions in which both SV and ΣVM are changed, therefore, the coke strength DI 150 The molded coal section SV, where 6 is maintained at a constant level, has a coke strength DI. 150 15 Unlike the molded char section SV, where the DI is maintained at a constant level, Patent Document 1 describes DI 150 The evaluation conditions for determining the range of SV in the molded charcoal section where 6 is consistently maintained are not described.

[0110] Therefore, in this comparative evaluation example, when the maximum width of the void around the molded char at level 2 in Table 1 is set to 5.37 mm, the lower limit of the molded char portion SV obtained from the above formula (1) described in Patent Document 1 is 1.50 cm. 3 To achieve a value of / g, the change in the equivalent spherical radius Δr before and after expansion of the molded coal was calculated using the formula Δr = w × 0.75 (where w is the maximum width of the void around the molded coal).

[0111] [Evaluation Results] The relationship between the lower limit of SV of the molded coal portion calculated in Comparative Evaluation Example 1 and the lower limit of SV of the molded coal portion calculated based on the SV of the molded coal portion obtained in the carbonization test is shown in Table 8 and Figure 31. In particular, at level 3 (whole-grain coal conditions), the lower limit of SV of the molded coal portion based on Comparative Evaluation Example 1 is 1.40 cm. 3 / g and the lower limit of SV of the molded charcoal based on the carbonization test is 0.97 cm. 3 The value differed significantly from the value per g. This is thought to be because the conventional method for analyzing the amount of voids around molded coal based on the maximum width of the voids, as described in Example 1, could not correctly distinguish between the pulverized coal portion and the voids under the conditions of whole-grain coal, where the particle size composition of the pulverized coal portion differed from conventional methods.

[0112] On the other hand, the cumulative filling loss around the molded coal shown in Table 1 and the coke strength DI obtained as shown in Figures 27, 29, and 30 are used. 150 When the relationship with the lower limit of SV in the molded coal section, which is the limit at which 6 is maintained at a constant value, was analyzed (Figure 32), a strong correlation was obtained. Using the correlation equation obtained from Figure 32 as relational equation (II) of this disclosure, the coke strength DI was obtained. 150The lower limit of SV in the molded charcoal portion, which is the limit at which 6 is maintained at a constant level, was found to be 0.95 cm under blending condition 1 (whole granule charcoal condition). 3 / g, under blending condition 2 (crushed charcoal conditions, moisture content 4% by mass), 1.12cm 3 / g, under blending condition 3 (crushed charcoal conditions, moisture content 10% by mass), 1.49cm 3 The value was / g. In particular, the lower limit of SV for the molded coal portion under whole-grain coal conditions was 0.97 cm, which is higher than the value for whole-grain coal conditions in the carbonization test compared to comparative evaluation example 1. 3 The value was close to / g, which indicates that the method for analyzing the amount of voids around molded charcoal based on the cumulative filling reduction amount in Example 1 has higher analytical accuracy than the analytical method in Conventional Example 1. Similarly, the cumulative filling loss around the molded coal and the coke strength DI 150 15 A strong correlation was also obtained in relation to the lower limit of SV in the molded coal portion, which is the limit at which the coke strength is maintained at a constant level (Figure 33). Therefore, based on the relationship between the cumulative packing loss around the molded coal and the lower limit of SV in the molded coal portion, which is the limit at which the coke strength is maintained at a constant level, the lower limit of SV in the molded coal portion of the blended coal can be predicted with high accuracy. By producing molded coal with a low SV at a level that does not fall below such a lower limit of SV in the molded coal portion, and using it in coke production, it becomes possible to produce inexpensive and high-strength coke.

[0113] Furthermore, the estimated cumulative filling loss (x axis) calculated according to relational equation (2-5) in Example 2-5, and the coke strength DI 150 When we organize the relationship with the lower limit of SV in the molded charcoal section (y-axis), which is the limit at which 6 is maintained at a constant level (Figure 34), we can confirm that a strong correlation is obtained, similar to Figure 32, where the cumulative filling reduction obtained in the procedure of Example 1 is on the x-axis.

[0114] [Table 1]

[0115] [Table 2]

[0116] Table 3

[0117] Table 4

[0118] Table 5

[0119] Table 6

[0120] Table 7

[0121] Table 8

Claims

1. A method for analyzing the amount of voids around molded coal when a blend of coal containing molded coal and powdered coal is filled into a container, Using a test apparatus, molded coal and powdered coal are filled into a test container by gravity. Cross-sectional images of the inside of the test container were acquired using X-ray CT. The amount of voids around the molded coal was determined by 3D analysis of the obtained cross-sectional images. In the aforementioned 3D analysis, A high-density section where the density exceeds a predetermined value and a low-density section where the density is less than or equal to the predetermined value are defined, The high-density portion is filtered using a predetermined shape parameter to define the molded char portion. Optionally, within the high-density portion, any region other than the molded charcoal portion and whose volume exceeds a predetermined value is defined as the agglomerated charcoal portion, and this agglomerated charcoal portion is excluded from the analysis by being treated as having no pixel data. An expansion process is performed (n+1) or more times, starting from the periphery of the molded charcoal portion and expanding by one unit volume each time in a shape similar to the molded charcoal portion, where n is a natural number. The (n+1) is the number at which the average density of the region whose volume increased in the (n+1)th expansion process is approximately the same as the average density of the region whose volume increased in the nth expansion process. The average density of the region whose volume increased in the nth and subsequent expansion processes is used as the threshold. In each expansion treatment, the region whose volume increases is defined as follows: the region where the density exceeds the threshold is defined as the pulverized coal portion, and the region where the density is below the threshold is defined as the void portion. For each expansion treatment, the difference between the average density of the pulverized coal portion and the average density of the void portion is calculated for the region whose volume has increased. The amount of filling reduction is calculated by multiplying the volume of the region that has increased in volume during each expansion process by the difference value. The cumulative amount of filling loss is calculated by accumulating the amount of filling loss over the total number of expansion treatments, and this cumulative amount of filling loss is used as an indicator of the amount of voids around the molded coal. Method for analyzing the amount of voids around molded coal.

2. A method for estimating the amount of voids around molded coal when a blend of coal containing molded coal and powdered coal is filled into a container, Multiple types of blended coal samples are prepared by combining each of several types of powdered coal samples, selected to include different levels of particle size composition and different levels of moisture content, with an arbitrarily selected molded coal sample. For each blended coal sample, the cumulative sample filling reduction is determined according to the method for analyzing the amount of voids around molded coal described in claim 1. Based on the relationship between the particle size composition and moisture content of the pulverized coal sample and the cumulative filling loss of the sample, equation (I) relating the particle size composition and moisture content of the pulverized coal and the cumulative filling loss was obtained. For blended coal, which is a combination of pulverized coal intended for use in coke production and arbitrarily selected molded coal for analysis, the particle size composition and moisture content of the pulverized coal intended for use are substituted into the above relational formula (I) to calculate an estimated cumulative filling loss, and this estimated cumulative filling loss is used as an indicator of the amount of voids around the molded coal. A method for estimating the amount of voids around molded coal.

3. A method for producing coke using a blend of coal containing molded coal and powdered coal, For the selected coal blend sample for testing, a relationship equation (II) is predetermined between the cumulative packing reduction calculated by the method for analyzing the amount of voids around the molded coal described in claim 1, and the lower limit of the molded coal SV range, which is the lower limit of the molded coal SV range in which the coke strength remains constant even when the molded coal SV is changed. For blended coal, which is a combination of pulverized coal intended for use in coke production and arbitrarily selected molded coal for analysis, the cumulative filling reduction is determined according to the method for analyzing the amount of voids around the molded coal described in claim 1, or the estimated cumulative filling reduction is determined according to the method for estimating the amount of voids around the molded coal described in claim 2. Substitute the cumulative filling loss or the estimated cumulative filling loss into the relational formula (II) to determine the lower limit of the molded coal portion SV. Molded coal is manufactured in which the measured SV value is equal to or greater than the lower limit of the SV value of the molded coal section. The blended coal, consisting of the aforementioned pulverized coal intended for use and the manufactured molded coal, is used for coke production. A method for producing coke.

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