Method for evaluating weathering degree of coal, method for predicting coke strength, and method for producing coke

Abstract

To provide a method for evaluating the weathering degree of coal capable of simply predicting the weathering degree of coal.SOLUTION: A method for evaluating a degree of weathering of coal, the method comprising: acquiring a quantity related to an affinity of the coal for a solvent; and evaluating the degree of weathering of the coal using the acquired quantity related to the affinity for the solvent, wherein the quantity related to the affinity for the solvent is at least one of a permeation time when the solvent is permeated into the coal and a quantity based on a dispersion state when the coal is dispersed in the solvent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the weathering degree of coal. [Background technology]

[0002] Coke used in blast furnaces requires strength to maintain permeability within the furnace. Coke strength is highly dependent on the average vitrinite reflectance (hereinafter referred to as Ro) and maximum fluidity (hereinafter referred to as MF) of the coal used to produce the coke. For example, if coke is produced using coal with a low MF, the coke strength, as measured by the drum index, will be low, and lumpy coke will not be obtained. Furthermore, the use of such coke can lead to blockages in the blast furnace. Therefore, when producing coke, it is common to blend multiple coal brands and determine the coal blend so that the weighted average logarithm of MF (LogMF) falls within a certain range.

[0003] However, the MF of coal is often measured upon arrival at the yard. Therefore, it has been reported that the MF of coal decreases due to weathering during storage in the yard, resulting in a lower than expected MF of the coal after blending (Non-Patent Document 1). As such, it has been known that predicted values ​​of coke strength using Ro or MF often deviate from the actual coke strength due to coal weathering.

[0004] Therefore, in order to accurately predict coke properties such as coke strength, studies are being conducted to use the degree of coal weathering as an index in addition to MF. For example, Non-Patent Document 2 reports that the degree of coal weathering can be measured by the surface tension of unheated coal measured by the film flotation method, taking advantage of the fact that the surface tension of coal increases as weathering progresses. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Coke Circular, Vol. 37 (1988), p. 209 [Non-patent document 2] DWFuerstenau, Jianli Diao: Coal Preparation, Vol. 10 (1992), p1-17. Summary of the Invention [Problem to be solved by the invention]

[0006] However, the film flotation method had the problem of being difficult to operate experimentally.

[0007] The present invention has been made in view of the above points, and an object of the present invention is to provide a method for evaluating the degree of coal weathering that can easily predict the degree of coal weathering. [Means for solving the problem]

[0008] The gist of the present invention for solving the above problems is as follows.

[0009] 1. Obtaining a quantity related to the affinity of coal with a solvent; and evaluating the weathering degree of the coal using the obtained amount related to affinity with the solvent, a method for evaluating the degree of coal weathering, wherein the quantity related to the affinity with the solvent is at least one of a permeation time when the solvent is permeated into the coal and a quantity based on a dispersion state when the coal is dispersed in the solvent.

[0010] 2. A method for evaluating the degree of coal weathering according to claim 1, wherein the evaluation of the degree of coal weathering is carried out using a regression equation in which the explanatory variables include quantities related to the affinity with the solvent and the objective variable is information representing the degree of weathering.

[0011] 3. The method for evaluating the degree of weathering of coal according to 2 above, wherein the information representing the degree of weathering is information based on the change in weight before and after weathering.

[0012] 4. A method for predicting coke strength, comprising predicting the strength of coke containing the coal as a raw material based on the degree of coal weathering evaluated using the method for evaluating the degree of coal weathering described in any one of 1 to 3 above.

[0013] 5. A method for producing coke, which comprises changing coke production conditions based on the coke strength predicted by the method for predicting coke strength described in 4 above.

[0014] 6. The method for producing coke according to 5 above, wherein the change in the production conditions is a change in the blending ratio of the coal. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a method for evaluating the weathering degree of coal, which allows the weathering degree of coal to be easily predicted. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a graph plotting the relationship between the solvent penetration time and the weight gain rate when methanol is used as the solvent for Sample A. [Figure 2] FIG. 2 is a graph with the δH of the solvent on the horizontal axis and the coefficient of determination on the vertical axis. [Figure 3] FIG. 3 is a graph with the δtot of the solvent on the horizontal axis and the coefficient of determination on the vertical axis. [Figure 4] FIG. 4 is a graph plotting the relationship between the time at which precipitation begins and the rate of weight increase when methanol or ethanol is used as the solvent. [Figure 5] FIG. 5 is a graph plotting the relationship between ΔD and the weight gain rate of coal. DETAILED DESCRIPTION OF THE INVENTION

[0017] First, the findings of the present inventors will be described.

[0018] First, coal thermoplasticity is thought to occur through the following mechanism. Coal generally has a high-order structure that includes cross-linked polymers. When coal is heated, bonds within the coal molecules are broken, generating radicals. If sufficient hydrogen is present in the coal, the radicals are stabilized by the hydrogen in the coal, generating molecules with relatively low molecular weights. This leads to the thermoplasticity of the coal as the molecular weight of the coal decreases and the cross-link density decreases. On the other hand, if there is insufficient hydrogen in the coal, instead of stabilization by hydrogen, the recombination of radicals progresses, preventing the development of a low-molecular structure and suppressing thermoplasticity.

[0019] It is believed that the oxidation of molecules in coal progresses as coal weathers, and that the decrease in MF in weathered coal is caused by the increased oxygen in the coal reacting with hydrogen, resulting in a decrease in the hydrogen that contributes to stabilizing radicals.

[0020] The inventors therefore conducted extensive research into methods for evaluating the degree of coal weathering and came to the conclusion that an increase in the number of oxygen-containing functional groups in coal molecules due to weathering changes the affinity of coal with solvents. Further research led to the discovery that, when coals with different degrees of weathering were molded into pellets and various solvents were dropped onto them, the time it took for the solvent to penetrate the pellets varied depending on the degree of coal weathering. Furthermore, the inventors discovered that the state of dispersion of coal in a solvent varied depending on the degree of coal weathering. Based on these findings, the inventors conducted various research and completed the present invention.

[0021] [Obtaining quantities related to solvent affinity] A method for evaluating the degree of coal weathering in one embodiment of the present invention includes obtaining a quantity related to the affinity of coal with a solvent. That is, in the method for evaluating the degree of coal weathering in one embodiment of the present invention, a quantity related to the affinity of coal with a solvent is obtained for the coal to be evaluated for its degree of weathering.

[0022] [coal] The type of coal to be evaluated for weathering degree is not limited, and the weathering degree can be evaluated for any coal. However, lignite, subbituminous coal, or anthracite is preferred. Lignite and subbituminous coal have a relatively high oxygen content, while anthracite has a relatively low hydrogen content. Therefore, lignite, subbituminous coal, and anthracite may have a low MF or below the lower limit of MF measurement even when not weathered, and the MF may not change or change very little before and after weathering. The technical significance of evaluating the weathering degree of lignite, subbituminous coal, or anthracite using the method of the present invention is particularly great, as it allows the degree of weathering to be evaluated even in such cases. Furthermore, from the viewpoint of practical ease of use as a coke raw material, subbituminous coal or anthracite is more preferred, and anthracite is even more preferred. Note that lignite, subbituminous coal, and anthracite are classified in accordance with JIS M 1002.

[0023] [Quantity related to affinity with solvent] In the present invention, the quantity relating to the affinity for a solvent is at least one of the penetration time when the solvent is penetrated into coal and the quantity based on the dispersion state when the coal is dispersed in the solvent. Both the penetration time and the quantity based on the dispersion state can be measured by a simple method. Therefore, by obtaining at least one of the penetration time and the dispersion state for the coal to be evaluated for weathering and using this to evaluate the weathering of the coal, a simple evaluation of the weathering degree is possible.

[0024] [Seep Time] The permeation time refers to the time from when the solvent contacts the coal to when permeation is complete. For example, permeation can be considered complete when the solvent disappears from the coal surface. Generally, the shorter the permeation time, the higher the affinity of the coal with the solvent.

[0025] The permeation time can be obtained by permeating the coal with a solvent and measuring the permeation time.

[0026] The penetration time can be measured by dripping a predetermined amount of solvent onto coal. It is preferable to use pellets made by compressing coal. Compared to powder samples, pellets have uniform irregularities, which prevents the contact area between the solvent and coal from changing depending on the location of the solvent penetration. The amount of solvent dripped is not particularly limited. When using pellets, the amount should be such that the solvent does not spill from the pellet surface. For example, for a 32 mm diameter pellet, 2 μL should be dripped. The method for determining the end of the penetration time is not particularly limited, but for example, an operator can visually determine the moment when the droplet disappears from the pellet surface. At the moment of dripping, the droplet is shiny because it reflects the surrounding light. However, as the droplet penetrates, the area where the gloss is visible gradually decreases. Therefore, the point at which the gloss disappears can be determined as the end of the penetration time.

[0027] In addition, in obtaining the permeation time, it is preferable to perform the following treatments (1) to (3) on the coal before measuring the permeation time. (1) Air-dry the coal to be measured for permeation time. (2) The air-dried coal is classified into particles of a predetermined size or less. (3) A predetermined amount is collected from the classified coal.

[0028] (1) Air drying Air-drying coal removes moisture from the coal, preventing coal particles from agglomerating and forming secondary particles, and facilitating subsequent coal classification. Residual moisture may also affect the coal's affinity with the solvent. Therefore, air-drying the coal to be measured is preferable. Specifically, air-drying can be achieved by blowing gas onto the coal to evaporate the moisture. Because using air as the gas may accelerate weathering, it is preferable to use a gas that does not contain O2, and more preferably, an inert gas. Examples of inert gases include nitrogen, argon, and helium. To remove as much moisture as possible, air-drying is preferably performed under heating, and more preferably in an inert gas atmosphere. The time and temperature of air-drying are not limited. For example, when air-drying 10 g of a sample with 10% moisture, it is preferable to air-dry it for 24 hours at 120°C.

[0029] (2) Classification The air-dried coal is preferably classified into particle sizes below a predetermined value, for example, 125 μm or less. Even for coals with the same degree of weathering, coals with larger particle sizes have non-uniform surface properties (particularly the surface properties when molded into pellets). Therefore, when measuring the penetration time, for example, dropping a solvent can cause large variations in the measured values. Therefore, it is preferable to classify the coal into particle sizes below a predetermined value. The classification method is not particularly limited, but using a sieve is common and preferred. The coal may also be crushed prior to classification.

[0030] (3) Collection A predetermined amount of coal is sampled from the classified coal. The amount sampled is not limited, but may be determined according to the amount to be measured (the size of the pellets if the coal is molded into pellets). For example, to prepare pellets with a diameter of 32 mm, approximately 2 g of coal may be sampled. The coal to be evaluated for weathering degree may be measured using the sampled coal according to the method described above.

[0031] [Quantity based on dispersion state] The dispersion state refers to the liquid state of coal after it is dispersed in a solvent. When coal is dispersed in a solvent, it may remain suspended, or the coal powder may completely settle or float, separating the coal from the solvent. Generally, the easier it is to suspend coal in a solvent, the higher the coal's affinity with the solvent.

[0032] The amount based on the dispersion state includes the presence or absence of suspension, absorbance, turbidity, and changes in these with time.

[0033] The amount based on the dispersion state can be obtained by measuring the amount based on the dispersion state for the liquid after dispersing the coal in the solvent. The amount based on the dispersion state can be measured, for example, as follows. First, the coal is dispersed in the solvent. Specifically, the coal and the solvent may be placed in a sealed container and stirred manually, for example by shaking by hand. Alternatively, the mixture may be stirred automatically using a device such as a stirrer. Next, the amount based on the dispersion state in the liquid is measured. For example, the presence or absence of suspension can be confirmed visually, or it can also be measured using a measuring device. The absorbance can be measured with an absorbance meter. The turbidity can be measured with a turbidity meter (for example, a laser turbidity meter). Furthermore, before measuring the amount based on the dispersion state, it is preferable to subject the coal to the above-mentioned treatments (1) to (3).

[0034] [solvent] The solvent is not limited when obtaining the quantity related to the affinity with the solvent. However, it is preferable to use a solvent that has a stronger correlation between the degree of weathering and the affinity. The inventors investigated suitable solvents using coals with different degrees of weathering and found that the degree of correlation between the degree of weathering and the affinity is influenced by the Hansen solubility parameter of the solvent. The Hansen solubility parameter is a physical property expressed by the hydrogen bond term δH, the polarization term δP, and the dispersion term δD. δH has the greatest influence on the correlation. Therefore, when δH is 10.0 MPa, 1 / 2It is preferable to use the above solvents. This will result in a stronger correlation between the degree of weathering and the affinity. In addition, although the influence of δP and δD on the correlation is also observed, δD has a large negative influence on the correlation. Therefore, when δtot expressed by the following formula is 12.0 MPa, 1 / 2 It is preferable to use the above solvents, as this provides a stronger correlation between the degree of weathering and the affinity. δtot=-2×δD+δP+4×δH

[0035] It is also preferable to use an alcoholic solvent as the solvent, such as methanol, ethanol, 1-propanol, 1-butanol, and 2-phenylethanol.

[0036] [Evaluation of the degree of weathering of coal] In one embodiment of the present invention, a method for evaluating the degree of coal weathering includes evaluating the degree of coal weathering using the obtained quantity related to affinity with the solvent. As coal weathering progresses, its affinity with the solvent changes. Therefore, the degree of coal weathering can be evaluated using the affinity with the solvent.

[0037] In a preferred embodiment of the present invention, the evaluation of the degree of coal weathering is performed using a regression equation in which the explanatory variables include quantities related to the affinity with the solvent and the response variable is information representing the degree of weathering. For example, by substituting the quantities related to the affinity with the solvent obtained for the coal to be evaluated into the regression equation, information representing the degree of weathering of the coal can be obtained. In another embodiment of the present invention, the evaluation of the degree of coal weathering can also be performed using a regression equation in which the explanatory variables include other parameters calculated from the quantities related to the affinity with the solvent and the response variable is information representing the degree of weathering. For example, by obtaining the quantities related to the affinity with the solvent for the coal to be evaluated, calculating the parameters from the obtained results, and substituting the calculated results into the regression equation, information representing the degree of weathering of the coal can be obtained.

[0038] First, a case will be described in which a regression equation is used in which the explanatory variables include quantities related to the affinity with the solvent and the response variable is information representing the degree of weathering.

[0039] [Regression equation] The type of the regression equation is not limited, but is typically a linear regression equation. The explanatory variables of the regression equation include quantities related to the affinity with the solvent. The response variable of the regression equation is information representing the weathering degree of the coal.

[0040] The regression equation may be derived from the explanatory variables and the response variables obtained for a plurality of coals with different degrees of weathering. The coefficient of determination of the regression equation is not particularly limited, but is preferably 0.80 or greater to obtain even higher evaluation accuracy. The upper limit of the coefficient of determination is not particularly limited, and may be 1.

[0041] The plurality of coals is not particularly limited and any coal can be used, but it is preferable that all of them are the same brand as the coal whose weathering degree is to be evaluated. The number of the plurality of coals may be two. For example, a coal (coal 1) of the same brand as the coal whose weathering degree is to be evaluated and that is in a relatively unweathered state, and coal 2, which is a weathered version of coal 1, may be used. The greater the number of coals, the higher the accuracy, so three or more is preferable. For example, in addition to coal 1, two or more coals (coal 2, coal 3, ...) with different weathering degrees of coal 1 may be used. On the other hand, using too many coals increases the working time, so the number of coals is preferably six or less. In other words, the number of coals with different weathering degrees of coal 1 is preferably five or less.

[0042] [Amount based on penetration time and dispersion state] The permeation time as the explanatory variable may be obtained by permeating the coal with a solvent and measuring the permeation time for the plurality of coals. Furthermore, the quantity based on the dispersion state as the explanatory variable may be obtained by dispersing the coal in the solvent and measuring the quantity based on the dispersion state for the liquid. The permeation time and the quantity based on the dispersion state for the plurality of coals may be measured using the same method as for the coal whose weathering degree is to be evaluated.

[0043] The treatment prior to measuring the amount based on the penetration time or dispersion state can be carried out in the same manner as for the coal to be evaluated for weathering degree. However, when collecting a predetermined amount of coal, it is preferable to collect multiple sets of coals with the same degree of weathering and then produce multiple coals with different degrees of weathering from the multiple sets. Specifically, it is preferable to carry out the following weathering treatment. Here, although it is possible to carry out the weathering treatment under different conditions for all the sets, it is preferable to select one set that is not weathered and weather the other sets under different conditions.

[0044] [Weathering treatment] Weathering conditions, such as the weathering time, weathering temperature, and atmospheric gas composition, are not particularly limited. However, because coal weathering proceeds primarily through oxidation reactions, heat treatment is preferred for weathering in order to promote the oxidation reaction and produce weathered coal in a short period of time. Weathering may be performed, for example, at a temperature of 80°C to 150°C for a period of at least one hour. If the weathering temperature exceeds 150°C, volatile substances in the coal may evaporate, potentially causing changes in functional groups in the coal for reasons other than weathering. Therefore, the weathering temperature is preferably 150°C or less. Furthermore, if the weathering temperature is less than 80°C, the weathering process takes a long time and is inefficient, so the weathering temperature is preferably 80°C or higher. If the weathering time is less than one hour, the progress of weathering may be insufficient, potentially making it difficult to accurately evaluate differences in the degree of weathering. Therefore, the weathering time is preferably at least one hour. Furthermore, air is preferred as the atmospheric gas from the standpoints of ease and safety of weathering. However, from the viewpoint of accelerating the oxidation reaction of coal and enabling treatment in a short period of time, it is preferable to carry out the weathering treatment in a gas atmosphere with an oxygen concentration higher than that of the atmosphere.

[0045] [Information showing the degree of weathering] The method of acquiring the information representing the degree of weathering as the objective variable is not particularly limited. However, it is sufficient to acquire at least one of information based on the weathering treatment conditions and information based on changes in coal due to weathering as the information representing the degree of weathering. In other words, the information representing the degree of weathering may be at least one of information based on the weathering treatment conditions and information based on changes in coal before and after weathering.

[0046] Weathering conditions that can be used as response variables include weathering time, weathering temperature, oxygen concentration in the atmospheric gas, etc. When weathering conditions are used as response variables, it is preferable to fix weathering conditions other than those used as response variables.

[0047] Examples of information based on changes in coal before and after weathering include information based on weight changes before and after weathering, such as the rate of weight gain or the amount of weight gain. The inventors conducted research focusing on the fact that coal weathering proceeds primarily through oxidation reactions, and discovered that the weight of coal changes depending on the degree of coal weathering. By using information based on weight change as information representing the degree of weathering, it is possible to express the degree of weathering with a single index, even when, for example, both the time and temperature of the weathering treatment are changed. Because this allows for relaxation of constraints on the weathering treatment conditions, it is preferable to use information based on weight change as information representing the degree of weathering.

[0048] When information based on the change in weight before and after weathering is used as information representing the degree of weathering, the change in weight can be determined by measuring the weight of the coal before and after the weathering treatment.

[0049] As explained above, because there is a correlation between the degree of weathering and the affinity for the solvent, the regression equation can be used to obtain information representing the degree of weathering of the coal to be evaluated with high accuracy. Furthermore, using at least one of the penetration time and the dispersion state as explanatory variables enables simple evaluation of the degree of weathering. Here, when the objective variable is the weathering conditions, the conditions obtained do not necessarily reflect the actual weathering conditions of the coal to be evaluated. Instead, it is possible to obtain the weathering conditions that would result if coal with an equivalent degree of weathering were produced by the weathering treatment. For example, suppose a regression equation with heating time as the explanatory variable is derived from weathering treatments in air at 150°C with varying heating times. An evaluation using this regression equation yields "heating time: 1 hour" as information representing the degree of weathering of the coal to be evaluated. In this case, the information representing the degree of weathering does not mean that the coal to be evaluated was actually heated for 1 hour and weathered, but rather that the weathering of the coal to be evaluated is equivalent to that obtained when the coal is weathered in air at 150°C for 1 hour.

[0050] Next, we will explain the case where a regression equation is used in which the explanatory variables include other parameters calculated from the amount related to the affinity with the solvent, and the objective variable is information representing the degree of weathering. The method for obtaining the amount related to the affinity with the solvent and the method for obtaining the information representing the degree of weathering can be the same as when a regression equation is used in which the explanatory variables include the amount related to the affinity with the solvent.

[0051] The parameter may be, for example, the solubility parameter of coal, such as the Hansen solubility parameter.

[0052] To calculate the solubility parameter of coal from the amount related to its affinity with a solvent, it is sufficient to obtain the amount related to the affinity of coal with a solvent for multiple solvents. Then, calculations can be made appropriately so that the distance between the solubility parameter of a solvent with high affinity is small and the distance between the solubility parameter of a solvent with low affinity is large. For example, the Hansen solubility parameter of coal can be calculated using the dissolving sphere method with a data set of the amount related to the affinity with a solvent and the Hansen solubility parameters of the solvents. Also, known software for deriving solubility parameters may be used.

[0053] [Method for predicting coke strength and method for producing coke] A method for predicting coke strength according to one embodiment of the present invention is a method for predicting the strength of coke containing a coal as a raw material based on the degree of coal weathering evaluated using a method for evaluating the degree of coal weathering. By using the degree of coal weathering evaluated using the above-described method, the physical properties of the coke, particularly coke strength, can be predicted simply and accurately. Specifically, the relationship between the degree of coal weathering and the strength of coke containing the coal as a raw material is determined in advance, and the degree of coal weathering evaluated using the method for evaluating the degree of coal weathering is applied to this relationship, thereby predicting coke strength. Coke strength can be expressed, for example, using the drum index.

[0054] The coal used as a raw material for the coke whose strength is to be predicted may include coal whose weathering degree has been evaluated by the evaluation method. For example, when the coal used as a raw material for the coke is composed of multiple types of coal, it is sufficient that the weathering degree of at least one type of coal has been evaluated by the evaluation method. However, from the viewpoint of further improving the prediction accuracy, it is preferable that the coal used as the raw material consists of coal whose weathering degree has been evaluated by the evaluation method. In other words, it is preferable that the weathering degree of all types of coal contained in the raw material has been evaluated by the evaluation method.

[0055] Furthermore, a coke production method according to one embodiment of the present invention is a method of changing coke production conditions based on the coke strength predicted by the coke strength prediction method. In other words, the coke production method of the present invention includes a step of changing the coke production conditions based on the coke strength predicted by the coke strength prediction method. This makes it possible to produce coke having a desired strength.

[0056] Although the production conditions to be changed are not particularly limited, it is preferable to change the blending ratio of coal. That is, the change in the production conditions is preferably a change in the blending ratio of coal. For example, if the predicted coke strength is low, the strength of the produced coke can be increased by decreasing the blending ratio of coal with advanced weathering.

[0057] In the coke strength prediction method and coke manufacturing method, Ro and MF can be used as indicators for predicting coke strength in addition to the coal weathering degree. For example, if coal with an MF below the detection limit is weathered, using the weathered coal as a raw material may result in a decrease in the amount of hydrogen required to stabilize radicals, causing the actual MF of the blended coal to be significantly lower than the value predicted from the MF of the unblended coal. It is believed that using the coal weathering degree makes it possible to accurately predict the physical properties of coke even in such cases. [Example]

[0058] Hereinafter, an application method of the present invention will be described based on the following embodiment, but the present invention is not limited to this embodiment.

[0059] Three different brands of coal were used (Sample A, Sample B, and Sample C). Table 1 shows the coal properties (Ro according to JIS M 8816 and LogMF calculated from MF according to JIS M 8801-10).

[0060] [Table 1]

[0061] Example 1 In Example 1, a regression analysis was performed using the penetration time, which is a quantity related to the affinity with the solvent, as the explanatory variable and the weight increase rate before and after weathering as the response variable.

[0062] First, Sample A was packed into a gas bag and stored under nitrogen gas flow for one day for air-drying. Next, the air-dried coal was crushed in an agate mortar and classified using a sieve to particles of 125 μm or less. Next, a predetermined amount of four sets of coals 1 to 4 were collected from the classified coal, and the weights of each were measured. Subsequently, Coal 1 was not subjected to weathering treatment (Condition 1), and Coals 2 to 4 were weathered under the following conditions 2 to 4, respectively, and the weights of each were measured after treatment. <Weathering treatment conditions> Condition 2: Heat in air at 150°C for 1 hour. Condition 3: Heat in air at 150°C for 5 hours. Condition 4: Heated in air at 150°C for 24 hours. An increase in weight was observed due to weathering treatment. Therefore, the weight increase rate of coals 1 to 4 before and after weathering treatment was calculated using the following formula. Weight increase rate [wt%]=(m oxi -m initial ) / m initial ×100 where m oxi :Weathered mass [g], m initial : Mass before weathering [g].

[0063] 3.5 g of each of Coals 1 to 4 was placed in a 13 mm diameter mold and pressed at a surface pressure of 15 tons for 3 minutes to form pellets. 2 μl of the solvent shown in Table 2 was added dropwise to the pelletized Coals 1 to 4, and the penetration time was measured. The end point of the penetration time was defined as the time when the droplet disappeared.

[0064] Sample B was also similarly air-dried, crushed, classified, collected, and weathered, and the penetration time was measured.

[0065] For each of the coals 1 to 4 under different conditions, regression analysis was performed for each solvent, using the solvent permeation time as the explanatory variable and the weight gain rate as the response variable, and the coefficient of determination was calculated. For example, Figure 1 is a graph plotting the relationship between permeation time and weight gain rate for sample A when methanol was used as the solvent. The permeation time is expressed with the measured permeation time for coal 1 set at 100%. Regression analysis using the plot shown in Figure 1 yielded a coefficient of determination of 0.92. Regression analysis was performed in this way for each coal and each solvent, and the calculated coefficients of determination are shown in Table 2.

[0066] [Table 2]

[0067] Figure 2 is a graph with δH on the horizontal axis and the coefficient of determination on the vertical axis, and Figure 3 is a graph with δtot on the horizontal axis and the coefficient of determination on the vertical axis. As shown in Figure 2, 1 / 2 When the above solvents were used, the coefficient of determination was 0.80 or more, and a stronger correlation was observed. 1 / 2 When these solvents were used, the coefficient of determination was 0.80 or higher, indicating a stronger correlation.

[0068] As described above, a correlation was observed between the weight gain rate and the permeation time. Therefore, by determining the permeation time of the coal to be evaluated and substituting it into the regression equation derived from the regression analysis described above, the weight gain rate, which represents the degree of weathering of the coal to be evaluated, can be obtained easily and with high accuracy.

[0069] Example 2 In Example 2, a regression analysis was performed using the amount based on the dispersion state, which is a quantity related to the affinity with the solvent, as the explanatory variable and the weight increase rate before and after weathering as the response variable.

[0070] Coals 1 to 4 were produced from sample C by carrying out the air drying, pulverization, classification, collection, and weathering treatment described above in the same manner as in Example 1. The weight gain rates of the obtained coals 1 to 4 before and after the weathering treatment were also calculated.

[0071] Next, 0.5 g of each of the obtained coals 1 to 4 was sampled. Four test containers containing 10 ml of methanol were also prepared. The test containers were transparent containers marked with black numbers and a scale.

[0072] First, coals 1 to 4 were each placed in the test vessel containing the solvent, and the coal was dispersed. The amount of coal dispersed in the solvent was then measured visually to determine the time it took for the coal to begin settling (settling start time). Specifically, the settling start time was measured as follows. When the coal was completely dispersed, the marker was not visible due to the black color of the coal. However, once the coal began to settle, the concentration of coal near the solvent surface decreased and the transparency increased, allowing the marker near the solvent surface to be clearly visible. Therefore, the elapsed time was measured when the marker near the solvent surface was clearly visible by visual inspection.

[0073] A similar test was also carried out using ethanol as the solvent.

[0074] Figure 4 is a graph plotting the relationship between the settling start time and the weight gain rate when methanol or ethanol was used as the solvent. Regression analysis using the plot shown in Figure 4 yielded a coefficient of determination of 0.93 when methanol was used and 0.91 when ethanol was used, indicating a strong correlation between the settling start time and the weight gain rate.

[0075] As described above, a correlation was observed between the weight gain rate and the settling start time, which is a quantity based on the dispersion state of coal when dispersed in a solvent. Therefore, by determining the settling start time when the target coal is dispersed in a solvent and substituting this into the regression equation derived from the regression analysis, the weight gain rate, which represents the degree of weathering of the target coal, can be obtained simply and with high accuracy.

[0076] Example 3 In Example 3, the ΔD of the coal was calculated from the amount based on the dispersion state, which is a quantity related to the affinity with the solvent, and a regression analysis was performed using the calculated ΔD as the explanatory variable and the weight increase rate before and after weathering as the response variable.

[0077] In Example 3, Coals 1 to 4 obtained from Sample C were used, as in Example 2. 0.5 g of each of the obtained Coals 1 to 4 was collected. Four test vessels containing 10 ml of the solvents listed in Table 2 were prepared for each solvent.

[0078] First, Coals 1 to 4 were each placed in the test vessel containing the solvent and dispersed. After 30 minutes, the state of dispersion of the coal was visually evaluated on a two-level scale. Score 1: Coal is dispersed throughout the solvent Score 0: More than 10% of the solvent is transparent The above evaluation was carried out for each coal using all the solvents listed in Table 2.

[0079] Next, for each coal, the dispersion state score (quantity based on the dispersion state) for each solvent and the Hansen solubility parameters of the solvent were entered as a data set into HSPiP software (5th Edition 5.4.08), and the Hansen solubility parameters of the coal (δH, δP, δD) were calculated.

[0080] Figure 5 is a graph plotting the relationship between δD and the weight gain rate of coal. A regression analysis using the plot shown in Figure 5 calculated the coefficient of determination to be 0.85, indicating a strong correlation between δD and the weight gain rate of coal.

[0081] As described above, a correlation was observed between the weight gain rate and the δD of coal. Therefore, by determining the δD of the coal to be evaluated and substituting it into the regression equation derived from the regression analysis described above, the weight gain rate, which serves as information indicating the degree of weathering of the coal to be evaluated, can be obtained simply and with high accuracy.

Claims

1. Obtaining a quantity related to the affinity of the coal for the solvent; and evaluating the weathering degree of the coal using the obtained amount related to affinity with the solvent, a method for evaluating the degree of coal weathering, wherein the quantity related to the affinity with the solvent is at least one of a permeation time when the solvent is permeated into the coal and a quantity based on a dispersion state when the coal is dispersed in the solvent.

2. 2. The method for evaluating the degree of coal weathering according to claim 1, wherein the evaluation of the degree of coal weathering is performed using a regression equation in which an explanatory variable includes an amount related to affinity with the solvent and a response variable is information representing the degree of coal weathering.

3. The method for evaluating the degree of weathering of coal according to claim 2 , wherein the information representing the degree of weathering is information based on a change in weight before and after weathering.

4. A method for predicting coke strength, comprising predicting the strength of coke containing coal as a raw material, based on the degree of coal weathering evaluated using the method for evaluating the degree of coal weathering according to any one of claims 1 to 3.

5. A method for producing coke, comprising changing coke production conditions based on the coke strength predicted by the method for predicting coke strength according to claim 4.

6. The method for producing coke according to claim 5 , wherein the change in the production conditions is a change in the blending ratio of the coals.

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