JP2022149760A - Estimation method of volume destruction strength of coke - Google Patents

Abstract

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

Description

The present invention relates to an estimation method for estimating the volumetric breaking strength of coke.

Drum strength of coke is known as an important control index of blast furnace operation, and drum strength DI ¹⁵⁰ ₁₅ is generally defined as a mass fraction of 15 mm or more after rotating the sampled coke 150 times with a drum tester. . Powder of 15 mm or less is generated by surface destruction or volume destruction, and these destructions are known to be caused by cracks, poor adhesion sites of non-melting components, flat-shaped pores, etc. (See Non-Patent Document 1. ). It is also known that surface fracture and volume fracture correspond to powders of 6 mm or less and 15-6 mm, respectively (see Non-Patent Document 2). The drum strength DI ¹⁵⁰ ₁₅ of coke is therefore defined by the sum of the surface breaking strength DI ¹⁵⁰ ₆ corresponding to powders up to 6 mm and the volume breaking strength DI ¹⁵⁰ _6-15 corresponding to powders in the range 6-15 mm.

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

Patent Literature 3 describes a method for estimating the volume breaking strength DI ¹⁵⁰ _6-15 based on a linear expression that defines the correlation between the volatile matter VM of coal and the volume breaking strength DI ¹⁵⁰ _6-15 .
Patent Document 4 describes a method for estimating the volume breaking strength DI ¹⁵⁰ _6-15 based on the relationship (α2) between the measured shrinkage ratio of the coal blend and the volume breaking strength DI ¹⁵⁰ _6-15 of coke obtained from the coal blend. is described.

JP-A-9-263764 JP-A-2005-194358 JP 2007-291262 A Japanese Patent Application Laid-Open No. 2020-094200

Peirce, T. J., et al. (1980). "Coke breakage behavior in relation to its structure." Journal of Physics D: Applied Physics 13(6): 953. Arima, T., et al. (1992). "Mechanism of Coke Size Degradation by Mechanical Impact." Tetsu-to-Hagane 78(7): 1101-1108.

However, the estimation methods of Patent Documents 1 to 4 can easily and accurately determine the volume breaking strength DI ¹⁵⁰ _6-15 within the range of the conditions that form the basis of estimation (for example, blending conditions, bulk density and furnace temperature). However, for coke outside the conditions, the accuracy of the estimation decreases, so it was necessary to calculate the estimation formula again based on the changed conditions. When reconstructing the estimation formula, it was necessary to conduct experiments and the like again, so there were cases where the volume breaking strength DI ¹⁵⁰ _6-15 could not be estimated quickly.

Therefore, the object of the present invention is to provide a method for estimating the volume breaking strength DI ¹⁵⁰ _6-15 with high accuracy and speed regardless of the blending conditions of blended coal.

In order to solve the above problems, the method for producing coke according to the present invention is as follows: (1) Coke obtained by carbonizing coal in a test coke oven is subjected to imaging processing by X-ray CT, The first step of obtaining information about the crack shape of the above, and the second step of calculating the area of the crack surface whose crack width is less than the threshold value by image analysis of the obtained information about the crack shape, and the properties are different from each other. By performing the first step and the second step for a plurality of coals, after calculating the area of the crack surface whose crack width is equal to or less than the threshold value of each coke, the calculated area of each crack surface and each coke A third step of constructing an estimation formula for estimating the volumetric fracture strength based on the measured volumetric fracture strength and using coal for coke production scheduled to be used in a blast furnace, the first step and the second step and a fourth step of estimating the volumetric fracture strength from the estimation formula obtained in the third step.

(2) The threshold value is set so that the correlation coefficient between the measured value of the volume breaking strength and the estimated value by the estimation formula constructed in the third step satisfies 0.85 or more. ) method for estimating the volume breaking strength of coke described in ).

According to the present invention, the volume breaking strength DI ¹⁵⁰ _6-15 can be estimated with high accuracy and speed only by obtaining information on the crack shape of the coke cake using X-ray CT.

FIG. 4 is a transition diagram schematically showing an image processing method; FIG. 4 is a diagram for explaining estimation of volume fracture strength DI ¹⁵⁰ _6-15 using the area of a crack face with a small crack width. 7 is a graph showing the degree of correlation between the estimated result and the test result of the drum test (Example) 7 is a graph showing the degree of correlation between the estimated result and the test result of the drum test (comparative example)

As mentioned above, the coke drum strength DI ¹⁵⁰ ₁₅ can be defined by the sum of the surface breaking strength DI ¹⁵⁰ ₆ and the volume breaking strength DI ¹⁵⁰ _6-15 . This embodiment proposes a method for estimating the volume breaking strength DI ¹⁵⁰ _6-15 with high accuracy and speed. Hereinafter, the method for estimating the volume breaking strength DI ¹⁵⁰ _6-15 according to the present embodiment will be described in detail by dividing into steps S1 to S4 below.

(Step S1)
A coke cake obtained by carbonizing coal in a test coke oven is imaged by, for example, three-dimensional medical X-ray CT before being cut into coke lumps (that is, in a state of being placed in a carbonization container). By imaging with a three-dimensional medical X-ray CT, it is possible to three-dimensionally acquire information about the crack shape of the coke cake. Microfocus X-ray CT can also be used instead of three-dimensional medical X-ray CT. However, it is desirable to use three-dimensional medical X-ray CT because three-dimensional medical X-ray CT can acquire the shape of cracks earlier than microfocus X-ray CT.

Also, coke cake can be imaged using two-dimensional X-ray CT. In this case, the crack shape of the entire coke cake can be grasped by increasing the number of images. A method of grasping the shape of the crack by microscopic observation is also conceivable, but it is out of the scope of the present invention because it requires work such as resin embedding polishing and takes time for processing.

(Step S2)
Next, by image-analyzing the information about the crack shape acquired at step S1, a crack surface is acquired and the area and crack width of a crack surface are calculated. Known software (for example, Avizo known as three-dimensional image analysis software) can be used for image analysis. Specifically, image analysis can be performed according to the procedure shown in steps S2-1 to 2-4 below. In addition, in this embodiment, a three-dimensional medical X-ray CT having a resolution of about 1 mm can be used.

(About step S2-1)
In step S2-1, the captured image is subjected to image processing (for example, binarization processing based on the difference in luminance values) to separate the coke portion and the crack (space) portion. By the binarization process, for example, the coke portion can be separated into black and the crack portion into white. However, the method of color coding is not limited to this, and other colors can also be used. Although (a) of FIG. 1 schematically shows the separated coke and cracks in two dimensions, three-dimensional image data is actually obtained. Although FIGS. 1(b) to 1(d) cited in the following description are also two-dimensional schematic diagrams, three-dimensional image data can actually be obtained.

(About step S2-2)
In step S2-2, separation processing is performed to further separate the coke portion into lumps. Here, as illustrated in FIG. 1(b), the coke mass A looks like one mass at first glance, but has a crack x inside, and when an impact is applied, it splits into two cracks starting from the crack x. divided into two. Therefore, even coke lumps that seem to be one lump at first glance, but have cracks x, are considered to be separated when subjected to an impact, and are discriminated as different lumps. The separation processing in this step includes the Watershed algorithm (Non-Patent Document: Beucher and Meyer. The morphological approach to segmentation: the watershed transformation. Mathematical morphology in image processing; 34, 433-81 (1993).) can be used.

Here, if the width of the crack x is extremely small, the lump of coke will not split even if it receives an impact. Therefore, in order to consider only the cracks that affect the splitting when receiving an impact, the cracks with a width of less than a predetermined width that do not contribute to the splitting when receiving an impact are filled by image processing. This predetermined width can be determined by experiments or the like. For example, multiple coke cracks remaining in the coke mass can be identified by observing coke that has actually been subjected to rotational impact with X-ray CT or a microscope. Then, a crack having the largest crack width is specified from among these cracks, and the specified width of the largest crack can be set as the predetermined width. Here, as an example, the width that does not contribute to division at the time of rotational impact can be set to 0.1 mm. Rotational impact can be applied, for example, by a rotating drum, and the number of rotations is 150 so that the volume breaking strength DI ¹⁵⁰ _6-15 can be evaluated.

(Step S2-3)
Each separated coke mass is uniformly subjected to expansion processing, and image processing is performed to fill the cracks. As a result, boundaries between coke lumps separated in step S2-2 are extracted (see FIG. 1(c)).

(Step S2-4)
The boundary extracted in step S2-3 is compared with the crack site in step S2-1, and the surface that is the boundary and is located in the crack site is extracted as the crack plane CF, and the crack width P is Calculate (see (d) in FIG. 1). Here, the crack surface CF is a surface extending along the crack in the paper surface direction of FIG. It's about.
As shown in FIG. 2(a), when each crack plane CF is defined as crack planes CF1 to CF4, in this embodiment, the crack plane CF is divided into two sections according to the size of the crack width P. FIG. 2(b) is a diagram after division, in which crack faces CF1 to CF3 with a relatively large crack width P are indicated by a solid line, and crack face CF4 with a relatively small crack width P is indicated by a broken line.

Thus, in the present embodiment, the crack face CF is divided into two sections according to the size of the crack width P, and the volume fracture strength is determined based on the area of the crack face CF having a relatively small crack width P as described later. Estimate DI ¹⁵⁰ _6-15 . The reason why attention is focused on the area of the crack face CF where the crack width P is relatively small is as follows.

It is known that among cracks formed in coke, cracks with relatively large crack widths are related to coke grain size, and cracks with relatively small crack widths are related to coke fracture. Therefore, it is inferred that only cracks with a small crack width should be considered for coke volume fracture. The present inventors presumed from the prior art (Sakimoto et al. ISIJ International; 56(11), 1948-55 (2016)) that cracks with a crack width equal to or less than the threshold value (X mm) affect volumetric fracture. Here, the threshold value (X mm) depends on the resolution of the X-ray CT, but since it was 2.5 mm in the example described later, it is estimated to be approximately several mm. Specifically, the threshold value (Xmm) is set to a value that satisfies the estimation accuracy required in a linear expression to be described later. The required estimation accuracy is not particularly limited, but is preferably 0.85 or more when represented by a correlation coefficient (R ² ), which will be described later. In other words, it is desirable to set the threshold value (Xmm) such that the correlation coefficient between the estimated value and the measured value by the linear expression is 0.85 or more.

The resolution of the three-dimensional medical X-ray CT used in this embodiment is about 1 mm as described above, but if a higher-resolution three-dimensional medical X-ray CT can be prepared, the threshold value (X mm) or less The crack width of is further divided into a plurality of divisions, and a weighting process considering the influence of the crack width of each division may be performed to estimate the volume fracture strength DI ¹⁵⁰ _6-15 .

Non-patent literature (Hildebrand and Ruegsegger. A new method for the model-independent assessment of thickness in three-dimensional images. Journal of Microscopy; 185(1), 67- 75 (1997)) can be used. Specifically, a method can be used in which the largest sphere that touches the boundary between the target three-dimensional region and the outer region is placed. can be measured. In the two-dimensional case, the two-dimensional crack width can be evaluated by arranging a circle instead of the three-dimensional sphere. A three-dimensional evaluation is preferable as it may change.

(Step S2-5)
The area of the crack surface where the crack width is equal to or less than the threshold value (X mm) extracted in step S2-4 is normalized by the volume of the entire analysis region, which is the sum of the coke portion and the crack portion, to calculate S _{-X mm} . .

(Step S3)
The above-described steps S1 and S2 are executed for each of a plurality of coals having different properties, and S _{1 −Xmm} is calculated for each coke. Here, from the viewpoint of constructing an estimation formula, it is preferable that the values of the volume breaking strength DI ¹⁵⁰ _6-15 of each coke are more dispersed. Therefore, the blending conditions (coal brand, blending ratio, bulk density, addition or non-addition of fine coke, etc.) and heating conditions (heating rate, ultimate temperature, heating time) used for each coke production are different from each other. is desirable. Also, the volume breaking strength DI ¹⁵⁰ _6-15 is obtained in advance by performing a drum test on each coke.
Through the above-described processing, a set of data consisting of S _{−X mm} and the measured value of volumetric breaking strength DI ¹⁵⁰ _6-15 is obtained for the number of times the above steps S1 and S2 are performed using a plurality of coals with different properties. By fitting these data to a linear function based on the method of least squares, the following linear equation (1) is constructed as an estimation equation.

(Step S4)
S _-Xmm of coke (coke obtained by dry distillation in a test coke oven using coal for coke production scheduled to be used in a blast furnace) measured by newly performing steps S1 to S3 is expressed by a primary expression ( Estimate the volume breaking strength DI ¹⁵⁰ _6-15 by substituting in 1).

According to the method of the present embodiment, the volume fracture strength DI ¹⁵⁰ _6-15 is estimated simply by obtaining information about cracks in the coke cake and calculating the area of the crack surface where the crack width is equal to or less than the threshold value (X mm). be able to. Even if conditions such as coal blending conditions and the presence or absence of ^coke _fine are changed, there is no need to reconstruct the estimation formula (1). be able to. Furthermore, after constructing the estimation formula (1), the drum test for obtaining the volume breaking strength DI ¹⁵⁰ _6-15 is no longer necessary, so the labor and time required for the drum test can be reduced.

EXAMPLES Next, the present invention will be described in detail with reference to examples. Coal blends having properties shown in Table 1 were carbonized in a test coke oven to produce cokes C1 to C25. In Table 1, ΣTD (%) is the weighted average value of the total expansion rate TD of each single coal contained in the blended coal, and ΣVM (mass%) is the weighted volatile content of each single coal contained in the blended coal. Average value. The size of the carbonization vessel of the test coke oven was oven width (W): 400 mm, oven length (L): 600 mm, and oven height (H): 420 mm. The charged bulk density (BD) of coal was 850 (kg/m ³ ) or 900 (kg/m ³ ) on a dry basis. The ultimate temperature of the test coke oven was set to 950°C, 1050°C, or 1150°C, and the carbonization time was set to 18.5 (hours). The reason why the average particle size of coke breeze C16 and C18 is indicated by the last one digit and the average particle size of other coke breeze is indicated by the last two digits is because the accuracy of the sieve mesh used when obtaining the average particle size is different. The addition rate (% by mass) of coke breeze was expressed as an external number.

As a process corresponding to step S1 described above, a three-dimensional image was acquired using a three-dimensional medical X-ray CT while each coke was placed in a dry distillation container after the dry distillation. After imaging, a drum test was performed to measure the volume breaking strength DI ¹⁵⁰ _6-15 .

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

That is, as a process corresponding to step S2-1, the coke portion and the crack (space) were separated by binarization. As a process corresponding to step S2-2, the coke portion was further separated into chunks using the Watershed algorithm. At this time, the parameter (marker extent) that determines the strength of the separation process was set to 1, which is strongly separated, to separate coke lumps having cracks with a width of more than 0.1 mm. As a process corresponding to step S2-3, an expansion process was performed for each separated coke mass and an image process for filling cracks was performed. As a process corresponding to step S2-4, the boundary part extracted in step S2-3 is compared with the crack part in step S2-1, and the boundary part and the crack part are located. The crack surface was extracted and the crack width was calculated.

As a process corresponding to step S2-5, the crack width is 2.5 mm as a threshold, and for cracks with a crack width of 2.5 mm or less, the area of the crack surface is calculated by adding the coke part and the crack part. S _{−2.5 mm} was calculated by normalizing by the volume of the analysis region (however, the void region between the coke and the carbonization vessel was excluded from the volume to be normalized).
Note that the threshold value of the crack width may change when the resolution of the three-dimensional medical X-ray CT changes or depending on the value of the correlation coefficient to be obtained. Therefore, the crack width threshold of the present invention is not limited to 2.5 mm.

The above process was performed for each coke (corresponding to step S3). In this example, for comparison, the area of the crack surface (regardless of the crack width) is the volume of the entire analysis area that is the sum of the coke part and the crack part (however, the space between the coke and the carbonization vessel The void area was excluded from the volume to be normalized), and the normalized S _all was also calculated.

The volume breaking strength DI ¹⁵⁰ _6-15 , which is the test result of the drum test, and S _{-2.5 mm} calculated by the above method are fitted to a linear function based on the least squares method, and the following equation (2) is used as an estimation equation. calculated (corresponding to Example). In addition, the volume breaking strength DI ¹⁵⁰ _6-15 , which is the test result of the drum test, and S _all calculated by the above method are fitted to a linear function based on the least squares method, and the following formula (3) is calculated as an estimation formula. (corresponding to Comparative Example).

FIG. 3 is a graph showing the degree of correlation between the estimated result based on Equation (2) and the test result of the drum test, where the horizontal axis is the estimated value and the vertical axis is the test result (actual value) of the drum test. FIG. 4 is a graph showing the degree of correlation between the estimated result based on Equation (3) and the test result of the drum test, where the horizontal axis is the estimated value and the vertical axis is the test result (actual value) of the drum test.

3 and 4, the estimation method of the present example had a correlation coefficient ^R2 of 0.860, and the estimation method of the comparative example had a correlation coefficient of 0.246. Therefore, for the coke cake carbonized in the test coke oven, the area of the crack surface with a crack width of 2.5 mm or less is obtained, and by substituting the obtained crack surface area into Equation (2), the volume fracture It was found that the intensity DI ¹⁵⁰ _6-15 can be estimated with good accuracy. In addition, when the correlation coefficient R ² is less than 0.850 and an estimation accuracy of 0.850 or more is required as the correlation coefficient R ² , the crack width should be set by changing the threshold of .

Also, for the coke cake obtained in the test coke oven, the conventional drum test required about 1.5 hours per level, but in this example, it was possible to shorten it to about 10 minutes per level.

Claims (2)

A first step of obtaining information on the crack shape of coke by performing imaging processing by X-ray CT on coke obtained by carbonizing coal in a test coke oven;
A second step of calculating the area of the crack surface whose crack width is equal to or less than the threshold value by image analysis of the acquired information about the crack shape;
By performing the first step and the second step for a plurality of coals having different properties, the crack width of each coke is less than the threshold value. After calculating the area of the crack surface, the calculated area of each crack surface and a third step of constructing an estimation formula for estimating the volumetric fracture strength based on the volumetric fracture strength actually measured for each coke;
The area of the crack surface of the coke obtained by performing the first step and the second step using coal for coke production scheduled to be used in the blast furnace, and the estimation formula obtained in the third step a fourth step of estimating the volumetric breaking strength from
A method for estimating the volume fracture strength of coke, characterized by having 2. The threshold value according to claim 1, wherein the threshold value is set so that the correlation coefficient between the measured value of the volumetric breaking strength and the estimated value by the estimation formula constructed in the third step satisfies 0.85 or more. A method for estimating the volumetric breaking strength of coke.

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