Method for estimating coke strength

Abstract

To provide a technique for estimating the strength of a targeted coke sample by a method that is simpler and quicker compared to conventional methods.SOLUTION: An estimation method for coke strength comprises: measuring the proportion of fine particles with a particle diameter smaller than that of coarse powder, with a particle diameter of 15 mm or smaller, among powder generated as a result of coke fracture, and estimating the coke strength based on a predetermined relation between coke strength and the proportion of fine particles, or measuring the average particle diameter of coke powder, with a particle diameter of 10 mm or smaller, among the powder generated as a result of coke fracture, and estimating the coke strength based on a predetermined relation between coke strength and the average particle diameter of the coke powder.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for estimating coke strength, which is the most important quality of coke. [Background technology]

[0002] Generally, coke for steelmaking is produced by carbonizing coal in a coke oven to temperatures above 900°C and is primarily used in blast furnaces. The coke charged into the blast furnace is required to function as a reducing agent, reducing iron ore, the main raw material in the ironmaking process. A blast furnace is a countercurrent reactor between solids, liquids, and gases, and coke also functions as a spacer to ensure gas permeability and liquid permeability. This spacer function is particularly important for smooth blast furnace operation. If this function is impaired, gas permeability within the blast furnace will be reduced, hindering the flow of reducing gas and the dripping of molten pig iron and slag. To maintain its function as a spacer, high coke strength is required. If coke strength is low, it will break down in the blast furnace, and the resulting powder will accumulate between the coke lumps, impairing gas permeability and liquid permeability.

[0003] For example, the drum strength index, particularly the drum index (DI(150 / 15)) specified in JIS K 2151, is known as an evaluation method for coke strength. This DI(150 / 15) value is also widely used as a control index for coke strength in coke plants. Therefore, the coke produced each day is sampled multiple times and the DI(150 / 15) value is determined by drum strength tests.

[0004] In this drum strength test, coke is sampled and divided to prepare 10 kg or more of coke with particle sizes of 50 mm or larger or 25 mm or larger. The sample (coke) is then subjected to 150 impact revolutions in a cylindrical drum with an inner diameter and depth of 1500 mm, a height of 250 mm, and six blades. The collected coke is then sieved, and the weight ratio of coke 15 mm or larger (x 100) is calculated as the DI (150 / 15) index.

[0005] This drum strength test is extremely time-consuming, and there is a limit to the frequency of measurements per day. However, if the strength of the coke supplied to the blast furnace can be measured quickly and the results can be fed forward quickly to blast furnace operation, it can contribute to stable blast furnace operation. Furthermore, if the temporal fluctuations in coke strength can be grasped at shorter intervals, feedback can be provided to coke operation, and coke strength can be stabilized, it can also contribute to stable blast furnace operation. As a result, there is a demand for rapid and frequent measurement of these drum strength indices in order to save energy and reduce CO2 emissions.

[0006] Therefore, attempts have been made to measure or estimate coke strength using simpler methods. For example, Patent Document 1 proposes a method in which the fineness and particle size of the coke are measured at at least two or more arbitrary positions during the conveyance process, and the drum strength of the coke is estimated from the mechanical impact force received during the conveyance process and the change in particle size distribution of the coke refined by the impact force. Patent Document 2 discloses a method for estimating drum strength from the amount of coke powder recovered from circulating gas using a dust collector, which generates coke powder when quenched coke is destroyed in a coke dry quenching system (CDQ). This method utilizes the correlation between the proportion of collected dust and coke strength for quenched coke, and creates a calibration curve in advance between the fine yield generated in CDQ (the proportion of collected dust per processing amount) and drum strength, and estimates drum strength from the measured fine yield. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 4-23736 [Patent Document 2] Japanese Patent Application Publication No. 2-216455 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, conventionally, the drum strength index of coke has been evaluated by a labor-saving method of the complicated drum strength test, but these conventional techniques have the following problems.

[0009] First, the method for estimating drum strength based on particle size measurement proposed in Patent Document 1 can provide a relatively quick and easy estimation. However, measuring coke with large particle sizes requires a large amount of sampling, resulting in a large-scale device. Furthermore, there are problems with the measurement work and the disposal of remaining samples, which are time-consuming. Statistically, for coke with a maximum particle size of 63 mm, a minimum of 250 kg of sample is required to perform a representative particle size measurement. Patent Document 1 also mentions the possibility of determining the particle size distribution of coke from images of the coke. However, determining the particle size from images of coke is problematic in that, while large chunks can be analyzed, analyzing powdered coke is difficult, resulting in insufficient accuracy. As a result, Patent Document 1 requires collecting a large amount of coke sample, sieving it, and measuring the particle size distribution. This method merely omits the drum rotation step in drum strength measurement.

[0010] The method described in Patent Document 2, which estimates drum strength by measuring the fines yield from the fines collected by CDQ, has the advantage of being relatively quick and easy to estimate and does not require the addition of special auxiliary equipment. However, it is known that the amounts of fines generated and recovered are affected not only by the coke drum strength but also by CDQ operating conditions, such as the coke throughput and reflux inert gas flow rate. Therefore, when operating conditions change, the amounts of fines generated and recovered vary depending on the CDQ operating conditions, reducing the accuracy of coke strength estimation. Furthermore, the amount of fines recovered cannot be accurately determined unless the fines are collected over a certain period of time and the weight of the collected fines is measured. Therefore, Patent Document 2 has the disadvantages of making it difficult to increase the frequency of coke strength estimation and of being unable to accurately calculate the fines yield unless the coke throughput during the fine collection period is accurately known.

[0011] The present invention has been made in consideration of the above-mentioned problems of the conventional techniques, and an object of the present invention is to provide a technique for estimating the strength of a target coke sample in a simpler and faster manner than conventional techniques. [Means for solving the problem]

[0012] The method for estimating coke strength according to the present invention, which advantageously solves the above-mentioned problems, is characterized in that it measures the proportion of fine particles smaller than the particle size of coarse particles having a particle size of 15 mm or less among the broken particles generated by the breakdown of coke, and estimates the coke strength based on a previously determined relationship between the coke strength and the proportion of fine particles.

[0013] The method for measuring coke strength according to the present invention is characterized in that it measures the average particle size of coke powder, which is generated by the destruction of coke and has a particle size of 10 mm or less, and estimates the coke strength based on a relationship between the coke strength obtained in advance and the average particle size of the coke powder.

[0014] The method for measuring coke strength according to the present invention is as follows: (1) The particle size of the coarse powder is equal to or smaller than 10 mm, and the particle size of the fine powder is equal to or smaller than 0.7 times the maximum particle size of the coarse powder and equal to or smaller than 1 mm; (2) The particle size of the coke powder is 6 mm or less; (3) The broken powder is powder recovered from the circulating gas of a coke dry quenching system; (4) determining the particle size distribution of the broken powder by a laser diffraction method, and determining the proportion of the fine powder, which is smaller than the coarse powder, in the coarse powder from the particle size distribution obtained; (5) determining the particle size distribution of the broken powder by a laser diffraction method, and determining the average particle size of the coke powder having a particle size of 10 mm or less from the obtained particle size distribution; This is thought to be a more preferable solution. [Effects of the Invention]

[0015] According to the present invention having the above configuration, coke strength can be estimated from the particle size analysis results of the broken powder generated by the coke breakdown, eliminating the need to analyze a large amount of coke, and allowing for simpler and faster estimation than conventional methods. Moreover, it becomes possible to measure coke strength more frequently than conventional methods. Furthermore, according to the present invention, the frequency of control based on operating conditions based on coke strength can be increased, contributing to the stabilization of coke strength, which is expected to lead to the stabilization of the coke production process and blast furnace operation, thereby enabling cost reduction. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a graph showing the relationship between the proportion of fine particles with a particle size of 0.5 mm or less among coarse particles with a particle size of 1 mm or less and coke strength. [Figure 2] FIG. 1 is a graph showing the relationship between the proportion of fine particles with particle diameters of 0.5 mm or less or 1 mm or less among coarse particles with particle diameters of 3 mm or less and the strength of coke. [Figure 3]FIG. 1 is a graph showing the relationship between the proportion of fine particles with particle sizes of 0.5 mm or less, 1 mm or less, or 3 mm or less among coarse particles with particle sizes of 6 mm or less, and coke strength. [Figure 4] FIG. 1 is a graph showing the relationship between the proportion of fine particles with particle sizes of 0.5 mm or less, 1 mm or less, 3 mm or less, or 6 mm or less among coarse particles with particle sizes of 15 mm or less, and coke strength. [Figure 5] This is a graph showing the relationship between the proportion of fine particles with particle sizes of 0.5 mm or less, 1 mm or less, 3 mm or less, 6 mm or less, or 15 mm or less among coarse particles with particle sizes of 25 mm or less, and coke strength. [Figure 6] FIG. 10 is a diagram showing the relationship between the first particle size and the coefficient of determination when the second particle size is 0.5 mm. [Figure 7] FIG. 1 is a graph showing the relationship between the average particle size of coke breeze having a particle size of 1 mm or less, 3 mm or less, 6 mm or less, 15 mm or less, or 25 mm or less, and coke strength. [Figure 8] This figure shows the relationship between the proportion of fine powder with a particle size of 0.5 mm or less among the coarse powder with a particle size of 6 mm or less among the broken powder recovered from an actual coke oven, and the drum strength index DI (150 / 15). [Figure 9] This figure shows the relationship between the drum strength index: estimated DI (150 / 15) estimated by the method of the present invention and the actual DI (150 / 15) based on the relationship between the drum strength index: actual DI (150 / 15) shown in Figure 8 and the proportion of fine powder with a particle size of 0.5 mm or less among coarse powder with a particle size of 6 mm or less among the broken powder. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail. The method for estimating coke strength according to the present invention is characterized by focusing on the particle size distribution of broken powder generated by the destruction of coke. Conventional methods for measuring coke strength focus on the amount of remaining coke lump or the amount of broken powder generated after applying an impact force to the coke using a drum testing machine or the like, but do not pay any attention to the particle size distribution of the broken powder generated. Therefore, the inventors subjected coke to a force such as an impact force to destroy it, and conducted a detailed study on the particle size distribution of the broken powder generated during the process. As a result, they applied the same impact to cokes with different strengths, and found that there is an extremely strong correlation between the particle size information of the broken powder generated by the destruction of the coke and the drum strength index of the coke, which led to the development of the present invention.

[0018] [Relationship between coke strength and particle size distribution of broken powder] First, the inventors subjected cokes of different strengths to the same impact and conducted a detailed study of the particle size of the broken powder generated by the destruction of the coke. As a result, they found that when the broken powder exhibits a specific particle size ratio or a specific average particle size, it shows a strong correlation with the coke strength, and developed the present invention. The details of this study are described below.

[0019] The results of the experiments conducted to collect basic data are described below. The coke used in the tests was prepared as follows: Single coal and blended coal raw materials with an average maximum vitrinite reflectance (Ro), an index of coal rank, of 0.65 to 1.59% were adjusted so that the proportion of particles with a particle size of 3 mm or less was 65 to 100 mass%. The raw materials were carbonized in a small carbonization furnace with a furnace wall temperature of 1,050°C for 6 hours, and then cooled in a nitrogen gas atmosphere to produce coke (39 levels in total).

[0020] The cokes thus obtained were loaded into a drum strength testing device, and the drum was rotated 150 times to apply the same impact to each coke. The broken powder generated during this process was collected and its particle size distribution was measured. Specifically, the relationship between the drum strength index (DI) (150 / 15), calculated from the ratio of coke lumps with a particle size of 15 mm or more to the charged amount after 150 rotations, and the particle size distribution of the recovered broken powder was investigated. As a result, it was found that the proportion of fine powder in the broken powder increases with increasing coke strength. However, since the total amount of broken powder generated from a high-strength coke is small, the amount of fine powder generated alone cannot be used as an indicator of the correlation with coke strength.

[0021] Therefore, to consider the particle size distribution of the broken powder generated by the destruction of coke, the proportion of broken powder defined by two particle sizes was used as an index. Specifically, the proportion of fine particles with a particle size smaller than a predetermined particle size (hereinafter referred to as the "second particle size") in the coarse particles with a particle size equal to or smaller than the coarse particles was measured, and the correlation between the proportion of fine particles and coke strength was investigated. Here, the fact that the fine particles with a particle size equal to or smaller than the second particle size is smaller than the coarse particles with a particle size equal to or smaller than the first particle size means that the particle with the largest particle size in the fine particles is smaller (smaller particle size) than the particle with the largest particle size in the coarse particles. As a result, the inventors discovered that by using the ratio of fine powder to coarse powder as one of the indicators, coke strength can be accurately estimated without being affected by the total amount of broken powder.

[0022] In the present invention, particle size is defined as the size of the smallest sieve opening that a particle can pass through. The particle size may be determined using a measuring instrument such as a laser diffraction analyzer. Furthermore, since there is no significant difference between the major and minor diameters of the particles in the crushed coke powder, the definition of particle size does not significantly affect the results of particle size distribution measurements.

[0023] For example, if the first particle size is 1 mm and the second particle size is 0.5 mm, the amount of coarse particles (including relatively coarse particles) equal to or smaller than the first particle size and the amount of fine particles equal to or smaller than the second particle size are calculated, and the ratio of the amount of fine particles equal to or smaller than the second particle size to the amount of coarse particles equal to or smaller than the first particle size is calculated. The relationship between the ratio of fine particles to coarse particles calculated in this way ((amount of fine particles equal to or smaller than 0.5 mm) / (amount of coarse particles equal to or smaller than 1 mm)×100 (mass%)) and coke strength DI (150 / 15) is shown in Figure 1.

[0024] Figure 1 also shows a linear regression equation that shows the relationship between the amount of fine particles (those with a particle size of less than the second particle size) in the coarse particles (those with a particle size of less than the first particle size) and the coke strength DI (150 / 15). As a result, the coefficient of determination R 2 The value was 0.789, which indicates that the coke strength can be estimated with a fairly high degree of accuracy from the fine powder fraction.

[0025] However, it was also found that the accuracy of estimating coke strength varies depending on how the first and second particle sizes are selected. Therefore, the first and second particle sizes were varied to determine the proportion of fine particles with a particle size of the second particle size or smaller among the coarse particles with a particle size of the first particle size or smaller, and the relationship between this proportion and coke strength was investigated.

[0026] Figure 2 shows the relationship between the ratio of fine particles with a particle size of 3 mm or less to the coarse particles with a particle size of 0.5 mm or 1 mm and the coke strength when the first particle size is 3 mm and the second particle size is 0.5 mm or 1 mm. As shown in Figure 2, a relatively good correlation was observed in this example as well.

[0027] FIG. 3 is a graph showing the relationship between the proportion of fine particles having a second particle size or smaller in the coarse particles having a first particle size or smaller and the coke strength when the first particle size is 6 mm and the second particle size is 0.5 mm, 1 mm, or 3 mm.

[0028] In the example shown in Fig. 3, it is also possible to predict coke strength from the proportion of fine particles. However, when the second particle size was set to 3 mm, the correlation became slightly poorer, and the correlation tended to worsen as the second particle size increased.

[0029] FIG. 4 is a graph showing the relationship between the proportion of fine particles having a second particle size or smaller in the coarse particles having a first particle size or smaller and the coke strength when the first particle size is 15 mm and the second particle size is 0.5 mm, 1 mm, 3 mm, or 6 mm.

[0030] In the example shown in Figure 4, it is also possible to predict coke strength from the proportion of fine particles equal to or smaller than the second particle size. However, as in the case of Figure 3, the correlation tends to worsen as the second particle size increases.

[0031] Figure 5 shows the relationship between the proportion of fine particles with a second particle size or smaller in the coarse particles with a first particle size or smaller and coke strength when the first particle size is 25 mm and the second particle size is 0.5 mm, 1 mm, 3 mm, 6 mm, or 15 mm. In all of the examples in Figure 5, the correlation is poor, and in some cases ((2) to (5) in Figure 5) the correlation was the opposite of that observed in the examples in Figures 1 to 4. Therefore, it was found that when the first particle size is 25 mm, coke strength cannot be estimated well.

[0032] From the above results, we have obtained a guideline for how to select the first and second particle sizes in order to estimate coke strength. Table 1 shows the first and second particle sizes and the coefficient of determination R obtained under each condition for each correlation shown in Figures 1 to 5. 2 The coefficient of determination R 2 is rounded to the third decimal place.

[0033] [Table 1]

[0034] From Table 1, for the first particle size, the smaller the particle size, the lower the coefficient of determination R 2The coefficient of determination is large and a high correlation is observed. When the first particle size is 15 mm, if the second particle size is 0.5 mm, the coefficient of determination is sufficiently high, and it is preferable that the first particle size is 15 mm or less. Figure 6 shows the relationship between the first particle size and the coefficient of determination R when the second particle size is 0.5 mm. 2 From Figure 6, when the first particle size is 10 mm or less, the coefficient of determination R 2 Since it is estimated that the correlation coefficient will be 0.75 or more, a more preferable first particle size is 10 mm or less. An even more preferable first particle size is 6 mm or less. Furthermore, the smaller the particle size of the second particle size, the higher the correlation, so it is preferably 1 mm or less, and more preferably 0.5 mm or less. From these results, it was found that when the first particle size is 15 mm or less and the second particle size is 1 mm or less, there is a high correlation between the ratio of fine particles of the second particle size in coarse particles of the first particle size or less and coke strength.

[0035] The average particle size of coke breeze below a predetermined particle size (hereinafter referred to as the "third particle size") can also be used as a numerical value representing the particle size of the broken powder. The third particle size of the broken powder is set to 1 mm, 3 mm, 6 mm, 15 mm, or 25 mm. Figure 7 shows the relationship between the average particle size of coke breeze below the third particle size and the coke strength (DI(150 / 15)). The average particle size on the horizontal axis is logarithmic. The average particle size here is the arithmetic mean particle size calculated from the mass fraction of coke breeze within each particle size range.

[0036] From Figure 7, when the third particle size is 1 mm, 3 mm, or 6 mm, it was found that the smaller the average particle size, the higher the coke strength. This is consistent with the tendency shown in Figures 1 to 5 that the higher the proportion of fine particles of the second particle size or smaller in the coarse particles of the first particle size or smaller, the higher the coke strength. Note that the coefficient of determination R of the correlation between the average particle size of coke breeze particles of the third particle size or smaller and coke strength when the third particle size is 6 mm (Figure 7 (3)), 3 mm (Figure 7 (2)), or 1 mm (Figure 7 (1)) 2The coefficient of determination R was 0.57 or higher in all cases, indicating a good correlation. On the other hand, when the third particle size was set to 15 mm (Fig. 7 (4)) and 25 mm (Fig. 7 (5)), the coefficient of determination R 2 was found to be small and the correlation was low.

[0037] From the above results, it was found that by setting the third particle size to 10 mm, it is possible to predict the coke strength from the average particle size of the coke breeze that is equal to or smaller than the third particle size. A more preferable value for the third particle size is 1 mm to 6 mm.

[0038] According to conventional knowledge, broken powder with a particle size of 0.5 mm or less is mainly generated by compression fracture, while broken powder with a particle size of 6 mm or more is mainly generated by volumetric fracture. Broken powder with a particle size of 0.5 mm to 6 mm is considered to be intermediate between the two types of broken powder. The relationship between coke strength and the size of broken powder generated by coke fracture had not been elucidated until now. However, experiments conducted by the present inventors have revealed for the first time that the higher the drum strength index DI (150 / 15) of coke, the higher the proportion of fine powder due to compression fracture in the broken powder. A high proportion of fine powder in the broken powder generated by coke fracture tends to reduce the weight loss of the coke lump, which is thought to result in a higher lump yield after impact.

[0039] Based on the above findings, the inventors discovered that if the proportion of fine particles of a second particle size or smaller among coarse particles of a first particle size or smaller, or the particle size of the broken particles, such as the average particle size, is known, the drum strength of the coke can be estimated using these as an index. For example, as shown in Patent Document 1, a method for estimating coke strength using the particle size distribution of coke has been known. However, in the present invention, coke strength can be estimated by determining the particle size distribution of a portion of the broken particles generated by the coke breaking. This has the advantage of enabling coke strength to be estimated with a small sample. For example, if the broken particles have a maximum particle size of 6 mm, a sample of several kilograms is sufficient to estimate coke strength. Therefore, the technology of the present invention reduces the amount of sample to be sampled, measured, and post-processed compared to prior art, thereby enabling the miniaturization of equipment and the simplification and speed of operations.

[0040] [Method for estimating coke strength] A method for estimating coke strength based on the above findings will be described below. In the above-described verification of the principles of the present invention, coke was broken using a drum test machine. However, coke can be broken by various forces, such as impact and compression. For example, coke can be broken by impacts received during the coke production and transportation process (e.g., impacts received during charging and unloading into a coke dry quenching (CDQ) system, impacts received when transferring between conveyor belts, and impacts received during charging and unloading when storing in a hopper). Therefore, in the present invention, the broken powder generated by the impacts can be collected and used. Alternatively, a dedicated impact mechanism can be installed and broken powder obtained from coke sampled by the mechanism. In particular, the impacts in a CDQ system are closer in principle to the impacts received in a blast furnace than conventional rotation tests. Therefore, by utilizing information on the broken powder generated by the impacts, coke strength in blast furnace operation can be estimated more accurately than conventional rotation strength indices. Furthermore, CDQ systems are cost-effective because they do not require additional special equipment, making them a particularly effective method.

[0041] The location for sampling the broken powder may be any location in the transportation process from the coke oven to the blast furnace, but it is preferable to sample the broken powder in a state where it has been subjected to a certain amount of impact and a large amount of broken powder has been generated, because this makes it easier to collect the broken powder. For example, inside the CDQ facility or its outlet, on the belt conveyor, at the junction of the belt conveyor, inside the debris storage tank or its outlet, or in a sieving device.

[0042] When dealing with the broken fines generated in CDQ facilities, the recovery rate of the broken fines is thought to depend not only on the strength of the coke drum but also on the operating conditions of the CDQ facility. For example, if the amount of broken fines generated and the flow rate of reflux gas change with an increase or decrease in the coke throughput, the dust collection efficiency of the dust collector is expected to change. Therefore, in the method of estimating drum strength from the total amount of dust collected by dust collection equipment as in Patent Document 2, there is a concern that the estimation accuracy may be reduced due to the influence of operating conditions.

[0043] On the other hand, in the estimation method of the present invention, the impacts experienced within the CDQ equipment are mainly due to the drop when the coke is loaded into the pre-chamber at the top of the equipment and the abrasion (between the coke lumps and between the coke and the equipment inner wall) when the load is lowered within the equipment. Both of these are equipment-specific and are considered to be less affected by the operating conditions of the CDQ equipment. Therefore, the present invention makes it possible to stably estimate the drum strength. In addition, although it is necessary to obtain information on a specific particle size of the generated broken powder, it is not necessarily necessary to obtain information on the total amount of broken powder. Therefore, it can be said that the present invention is a simpler and more advantageous method.

[0044] Note that the value representing the particle size distribution itself may change depending on the generation conditions of the broken powder, the method of recovering the broken powder, etc. Therefore, it is necessary to collect information on the particle size of the actually recovered broken powder and to determine in advance the correlation between the index value relating to the particle size distribution of the broken powder and the coke strength. This correlation can be determined in the same manner as the method for obtaining the relationship between the broken powder and the coke strength using the drum tester described above. In this way, in the present invention, by determining in advance the correlation between the particle size of the broken powder and the coke strength, it is possible to estimate the coke strength based on the correlation from the particle size distribution of the recovered broken powder.

[0045] The coke strength to be estimated is not limited to the DI (150 / 15) specified in JIS. The drum rotation speed may be changed, or the sieve size measured after the drum rotation may be different. For example, the ASTM and Micam tests use rotating drums similar to those specified in JIS, so the estimation method of the present invention can be suitably applied. The estimation method of the present invention can also be used as a strength index that represents the pulverization characteristics due to the impact of dropping an I-type drum or the pulverization characteristics due to abrasion. In the present invention, the correlation between coke strength and the index representing the particle size distribution of the broken powder exemplified in the present invention is determined in advance, so the present invention can be suitably applied to any strength index that provides a good correlation.

[0046] The first particle size for obtaining information about the particle size of the broken powder is preferably 15 mm or less, more preferably 10 mm or less, as revealed by the above-mentioned drum strength test of broken powder. The second particle size is smaller than the first particle size. If the second particle size and the first particle size are close to each other, the proportion of fine powder equal to or less than the second particle size approaches 100%, which may reduce the detection sensitivity when measuring the proportion of particles equal to or less than the second particle size. Therefore, the second particle size is preferably 0.7 times the first particle size or less, more preferably 0.5 times the first particle size or less, and specifically, it is preferably 1 mm or less, more preferably 0.5 mm or less. The same applies to the third particle size. As revealed by the above-mentioned drum strength test of broken powder, the third particle size may be 10 mm or less, more preferably 6 mm or less. In practice, when determining the correlation between coke strength and the particle size of broken powder in advance, the first, second, and third particle sizes can be determined so that the correlation is highly expressed. As for the average particle size, various representative values ​​of particle size distribution such as arithmetic mean diameter, harmonic mean diameter, median value, mode value, etc. may also be used.

[0047] There are no particular restrictions on the method for sampling broken powder, as long as the representativeness of the sample can be ensured. For example, broken powder generated in CDQ equipment can be sampled using the following method. In CDQ equipment, an inert gas (nitrogen) is circulated to quench the coke and recover heat, and broken powder is entrained in the circulating gas. Therefore, one method is to sample the broken powder entrained in the circulating gas by aspirating it. As mentioned above, the broken powder is generally collected using a dust collector installed in the circulating gas flow path of the CDQ equipment. Another method is to sample the recovered broken powder using an appropriate sampler. Other suitable methods include sampling from the rear of the sieving device or from the broken powder that falls below the sieve.

[0048] The method for measuring the particle size of the broken powder is not particularly limited, as long as it can accurately measure a specific particle size distribution range (particularly particle size distribution of 15 mm or less in the present invention). For example, the broken powder may be sieved to determine the mass proportion of each particle size, and examples of quick and simple measurement methods include the use of an automatic sieving device, measurement by image processing, and measurement by laser diffraction. In particular, particle size measurement by laser diffraction is particularly preferred because it can be performed in a short time of less than one minute, and is simple and accurate.

[0049] Laser diffraction is particularly advantageous because it can measure the particle size of broken powders accompanying the return gas of a CDQ system inline, allowing for real-time measurement of the particle size distribution of broken powders. However, because the return gas can reach high temperatures exceeding 900°C in some locations, it is necessary to provide particle size distribution measurement equipment with appropriate heat resistance. Furthermore, because fine powders tend to agglomerate, accurate particle size distribution measurements require that the fine powders be properly de-agglomerated. Therefore, prior to particle size distribution measurement, it is advisable to dry the sample and perform pre-treatment such as crushing or dispersing pseudo-particles to de-agglomerate the particles.

[0050] <Example> This example shows an example of estimating the drum strength of coke from the particle size distribution of broken fines intermittently collected in a CDQ system. Approximately 125 t of coke (equivalent to about five coke chambers) was treated as the same lot when it was being charged to the CDQ system. While the coke from that lot was being cooled, broken fines were collected from the circulating gas flow path, and the coke was sampled at the outlet of the CDQ system. The drum strength of the cooled coke was investigated. Note that conditions such as the coke charging rate into the CDQ system and the circulating gas flow rate were kept constant.

[0051] To sample the broken powder and measure its particle size, the piping for the circulating gas of the CDQ equipment was partially branched off, and some of the circulating gas was introduced into the branched piping and cooled. After cooling, the particle size of the broken powder accompanying the circulating gas was measured by laser diffraction. The broken powder accompanying the circulating gas of the CDQ equipment contained a small amount of powder with a particle size of about 5 mm, but the total particle size was 6 mm or less. Furthermore, because the powder was in a dry state, there was no need to eliminate the agglomeration.

[0052] The lump coke samples for measuring drum strength were collected in five increments (samples) for each lot using an automatic sampler installed on the belt conveyor at the outlet of the CDQ facility. Approximately 250 kg was collected per increment. These samples were then divided into samples for the drum test using an automatic dividing machine conforming to JIS. These samples were then subjected to the drum test.

[0053] First, for 10 lots, the correlation between the ratio (mass%) of fine particles with a particle size of 0.5 mm or less to the coarse particles with a particle size of 6 mm or less and the drum strength index DI (150 / 15) was determined using the same method as described above using the drum tester. The results are shown in Figure 8.

[0054] As shown in Figure 8, a high positive correlation was confirmed between the proportion (mass%) of fine powder with a particle size of 0.5 mm or less among coarse powder with a particle size of 6 mm or less and the drum strength index DI (150 / 15). The regression equation obtained from this relationship is shown below in equation (1). Estimated DI (150 / 15) = (proportion (mass%) of fine powder with a particle size of 0.5 mm or less of coarse powder with a particle size of 6 mm or less) × 0.1192 + 78.162 (1) This correlation differs from the correlation shown in Figure 3, which is thought to be due to differences in the coke used in the test, the fracture morphology, and the method for recovering the fractured powder.

[0055] Next, for another batch of coke, the broken powder was collected while the coke was cooling, and the proportion (mass%) of fine powder with a particle size of 0.5 mm or less among the coarse powder with a particle size of 6 mm or less was measured. Furthermore, the coke strength DI (150 / 15) of the cooled and collected lump coke was measured (measured DI) in the same manner as when the correlation was calculated.

[0056] Based on the correlation shown in Fig. 8, coke strength was estimated (estimated DI) from the proportion of fine particles with a particle size of 0.5 mm or less among coarse particles with a particle size of 6 mm or less, and the relationship between the estimated DI and the measured DI was plotted and shown in Fig. 9. The results in Fig. 9 confirmed a good correlation between the estimated DI and the measured DI, confirming that the method of the present invention can estimate the drum strength index from information on the particle size of broken powder.

Claims

1. A method for estimating coke strength includes measuring a proportion of fine particles having a second particle size smaller than a first particle size among coarse particles having particle sizes equal to or smaller than a first particle size among broken particles generated by the breakdown of coke, and estimating coke strength based on a previously determined relationship between coke strength and the proportion of fine particles having the second particle size among coarse particles having the first particle size or smaller, the method comprising: A method for estimating coke strength, characterized in that the first particle size is 1 mm or more and 15 mm or less, and the second particle size is 0.7 times or less the first particle size and 1 mm or less.

2. A method for estimating coke strength, comprising measuring an average particle size of coke powder having a particle size of a third particle size or less among the broken powder generated by the destruction of coke, and estimating coke strength based on a relationship between a previously determined coke strength and the average particle size of the coke powder having a particle size of the third particle size or less, wherein the third particle size is 10 mm or less.

3. The method for estimating coke strength according to claim 2, wherein the third particle size is 1 mm or more and 6 mm or less.

4. 4. The method for estimating coke strength according to claim 1, wherein the broken powder is powder recovered from circulating gas in a coke dry quenching facility.

5. 2. The method for estimating coke strength according to claim 1, wherein the particle size distribution of the broken powder is determined by a laser diffraction method, and the proportion of fine powder having the second particle size smaller than the first particle size in coarse powder having the first particle size or smaller is determined from the obtained particle size distribution.

6. 4. The method for estimating coke strength according to claim 2 or 3, wherein the particle size distribution of the broken powder is determined by a laser diffraction method, and the average particle size of the coke powder having a particle size equal to or smaller than the third particle size is determined from the particle size distribution thus obtained.

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