RU2782524C1 - Method for assessing the quality of coal, methods for preparing a coal mix and method for producing coke - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: group of inventions relates to a method for assessing the quality of coal used as a raw material for metallurgical coke, and to methods for preparing a coal mix using the values measured in the method for assessing the quality of coal, and also relates to a method for producing coke from the coal mix produced by the above method for preparing a coal mix. Method for assessing the quality of coal includes the following stages: preparing coal samples with different amounts of an inert component by grinding a single grade of coal; measuring the amount of the inert component of the corresponding coal samples and measuring the surface tension of the semi-coke produced by heat treatment of the corresponding coal samples; determining the surface tension γ₁₀₀ corresponding to the 100% amount of the inert component, and the surface tension γ₀ corresponding to the 0% amount of the inert component, using a regression line based on said amounts of the inert component and said surface tensions; and calculating the absolute value of the difference between the surface tension γ₁₀₀ and the surface tension γ₀; wherein the coal with an absolute difference value between γ₁₀₀ and γ₀ of 6 mN/m or more is not suitable as a raw material for coke, and coal with an absolute difference value between γ₁₀₀ and γ₀ of less than 6 mN/m is suitable as a raw material for coke. Method for preparing a coal mix containing at least two coal grades includes the following stages: determining the surface tension γ₁₀₀ and the surface tension γ₀ of each coal grade in the coal mix from the regression line determined by the above method for assessing the quality of coal, wherein the surface tension γ₁₀₀ corresponds to the 100% amount of the inert component, the surface tension γ₀ corresponds to the 0% amount of the inert component; determining the interphase tension of the coal mix based on said surface tension γ₁₀₀, said surface tension γ₀, the mixing ratio of each coal grade in the coal mix, and the mass fraction of the inert component and the mass fraction of the reactive component in each coal grade; determining the correlation between said interphase tension and the strength of coke produced from the coal mix; determining the interphase tension corresponding to the sought strength of coke based on said correlation; determining the mass fractions of said at least two coal grades so as to achieve the interphase tension corresponding to the sought strength of coke or a lower interphase tension; and preparing a coal mix by mixing said at least two coal grades in the above mass fractions.

EFFECT: development of methods for preparing a coal mix used to produce coke of the sought strength, and accurate determining of the mass fractions of these types of coal.

5 cl, 4 dwg, 5 tbl, 2 ex

Description

The field of technology to which the invention belongs

The present invention relates to a method for evaluating the quality of coal that serves as a raw material for metallurgical coke, and methods for preparing a coal mixture that use the measured values obtained in the method for evaluating the quality of coal. The present invention also relates to a method for producing coke from a coal mixture obtained by said method for preparing a coal mixture.

State of the art

Preferably, the metallurgical coke, which is used as a blast furnace feedstock for iron production in a blast furnace, has high strength. If the coke has low strength, the coke breaks down in the blast furnace, and the broken coke deteriorates the permeability of the blast furnace; consequently, the stability of pig iron production deteriorates.

Usually, coke is produced by coking a coal mixture, which is obtained by mixing two or more types of coal, in a coke oven. There are various ways of mixing coal to obtain coke having the desired strength.

Patent Literature 1 discloses a coal mixing method, which is a method in which coal compatibility is taken into account. In this method, using as an indicator the value of interfacial tension calculated on the basis of the surface tension of semi-coke, which is obtained by heat treatment of each of the coal grades that make up the coal mixture, and the mixing ratio (mass fraction) of each of the coal grades in the coal mixture, the mixing ratio is adjusted coal mixture. Used in the description, the term "coal compatibility" refers to the property in which several grades of coal in the coal mixture interact with each other. It is known that in some cases, depending on the compatibility of the coal, the additivity property is not valid for the strengths of the cokes obtained from the respective types of coal of the coal mixture, and the strength of the coke obtained from the coal mixture.

List of sources cited

Patent Literature

PTL 1: International Publication No. 2013/145680

Non-Patent Literature

NPL 1: D.W. Fuerstenau: International Journal of Mineral Processing, 20 (1987), 153

Disclosure of invention

Technical problem

In recent years, in terms of ensuring the optimal procurement of coal resources and reducing the cost of raw materials, it has become increasingly necessary to purchase coal mined from more than one location and use several grades of coal with different properties as raw materials for coal mixture. In cases where several types of coal having different properties are to be used in the coal mixture, the method disclosed in Patent Literature 1 can be used to prepare a coal mixture from which coke having the desired strength is expected to be obtained. However, with regard to some types of coal, there have been cases where coke not having the desired strength was obtained even in the case where the coal mixture was prepared by mixing together several grades of coal in mass fractions determined by the method described in Patent Literature 1.

The present invention has been made in view of the cases described above. By carrying out the method of the present invention for preparing a coal mixture, the types of coal that should constitute a coal mixture from which coke having the desired strength can be obtained, and the mass fractions of these types of coal can be accurately determined compared to prior art methods. The purpose of the present invention is to provide such methods for the preparation of a coal mixture. In addition to methods for preparing coal mixture, the present invention also provides a method for producing coke using such a method for preparing coal, and a method for evaluating the quality of coal that serves as a raw material for metallurgical coke.

Solution

The inventors of the present invention found the following phenomenon: in cases where the amount of the inert component in the coal was varied, the variation in the surface tension of the char which was obtained by heat treatment of this coal, relative to the amount by which the amount of the inert component was varied (variation), varied between different grades of coal. The present inventors have studied this phenomenon and first developed a method for judging the quality of coal based on the content of the inert component of the coal and the surface tension of the char.

For example, in the prior art method described in Patent Literature 1, the surface tension of char obtained by heat treatment of one grade of coal is given as an average value in the distribution of measured values of surface tension. In the understanding of the prior art, it has simply been assumed that the reason that surface tension distribution occurs is the inhomogeneity of the coal, and the details have not been elucidated. The inventors of the present invention have made more detailed investigations into the reasons for the variation in the surface tension values of the char associated with coal components. The components of coal that particularly affect the strength of the coke are a component that softens and melts when heated (hereinafter, the component may be referred to as "reactive"), and a component that does not soften or melt even when heated (the component hereinafter may be referred to as "inert"). Based on this fact, the inventors of the present invention conducted research to develop a method for estimating the surface tension values of the char obtained by heat treatment of the respective two components.

With respect to coal components, no methods are known to accurately separate a component that softens and melts when heated from a component that does not soften or melt when heated; however, it is known that the inert component, which can be identified by observing the coal under a microscope, usually corresponds to the component in the coal that does not soften or melt. The method for analyzing the content of the inert component is specified in JIS M 8816. The inventors of the present invention used the total content of the inert component (TI) specified in JIS M 8816 as the content of the component that does not soften or melt when heated.

It is difficult to separate the coal component that softens and melts from the coal component that does not soften and melt. As an alternative means for evaluating the surface tension of the char made from the respective components, the inventors of the present invention have focused on the inert components. The inventors of the present invention made the following attempt: to separate the coal into a portion with a high content of the inert component and a portion with a low content of the inert component (the content of the inert component hereinafter may be referred to as the "amount of the inert component"); carry out heat treatment of the relevant parts to form semi-coke; and, based on the surface tension values of the char, estimate the surface tension values of coal having an inert component content of 100% and the surface tension values of coal having an inert component content of 0%.

The inert component of coal is harder than the reactive component. This fact is used to separate the coal into a portion with a high amount of the inert component and a portion with a low amount of the inert component. Since the inert component is harder than the reactive component, the inert component tends to be concentrated in coarse coal particles when grinding coal. Using this trend, samples with different amounts of the inert component can be prepared from the same grade of coal by grinding and screening. Semi-coke was obtained by heat treatment of such samples and its surface tension was measured. As a result, the present inventors have found that the variation in surface tensions relative to the variation in the amounts of the inert component varies between different grades of coal; and in the case where the samples were obtained by separating the coal into a part having a high amount of an inert component and a part having a low amount of an inert component, there is usually a linear relationship between the amounts of the inert component of the samples and the surface tensions of the char obtained by heat treatment of these samples. In addition, the present inventors have found that since the relationship between varying the amounts of the inert component and varying the surface tension affects the strength of the coke obtained from the coal mixture that includes this coal grade, assessing whether this coal grade is suitable as a feedstock for coke can be obtained depending on the relationship between these variations.

The authors of the present invention have created methods for preparing a coal mixture using the parameters identified in the evaluation described above. In the methods for preparing the coal mixture of the present invention, it is assumed that each of the grades (one grade) of coal in the coal mixture consists of an inert component in which the proportion of the inert component is 100%, and a reactive component in which the proportion of the inert component is 0%; using a regression line that is based on the amounts of the inert component of the coal and the surface tensions of the char obtained by heat treatment of these samples, as determined using the evaluation method described above, determine the surface tension γ ₁₀₀ , which corresponds to the content of the inert component of 100%, and the surface tension γ ₀ , which corresponds to the content of the inert component 0%; and it is assumed that the surface tension of the char obtained from the inert component is γ ₁₀₀ and the surface tension of the char obtained from the reactive component is γ ₀ . In the methods for preparing the coal mixture of the present invention, based on this assumption, the interfacial tension is calculated from the mixing ratio, the mass fraction of the inert component, the mass fraction of the reactive component, the surface tension γ ₁₀₀ and the surface stress γ ₀ of each of the coal grades of the coal mixture; and based on the relationship between the interfacial tension and the strength of the coke obtained from the coal mixture, the mass fractions of the respective grades are determined. In addition, it is possible to determine the mass fractions of the respective grades in the coal mixture so that the proportion of coal in the coal mixture having a high ratio of variation in the surface tension of the char to the variation in the amount of the inert component is limited.

In particular, the essence of the present invention is as follows.

(1) A method for assessing the quality of coal, including preparing samples of coal having different amounts of an inert component by grinding one grade of coal; measuring the amount of the inert component of the respective coal samples and measuring the surface tension of the char obtained by heat treatment of the respective coal samples; and determining a regression line that is based on said amounts of inert component and said surface tensions, and evaluating coal quality using the ratio of variation in surface tension to variation in amounts of inert component determined from said regression line as an indicator.

(2) A method for preparing a coal mixture, said method being a method for preparing a coal mixture containing at least two grades of coal, the method including determining the surface tension γ ₁₀₀ and the surface tension γ ₀ of each of the coal grades of the coal mixture according to regression line determined by the method of assessing the quality of coal according to (1), while the surface tension γ ₁₀₀ corresponds to the amount of the inert component 100%, the surface tension γ ₀ corresponds to the amount of the inert component 0%; determination of the interfacial tension of the coal mixture according to the specified surface tension γ ₁₀₀ , the specified surface tension γ ₀ , the mixing ratio of each of the coal grades of the coal mixture, as well as the mass fraction of the inert component and the mass fraction of the reactive component in each of the coal grades; determining the correlation between said interfacial tension and the strength of the coke produced from said coal mixture; on the basis of said correlation, determining the interfacial tension corresponding to the desired strength of the coke; determining the mass fractions of said at least two grades of coal so that an interfacial tension corresponding to the desired coke strength or a lower interfacial tension is achieved; and preparing a coal mixture by mixing said at least two grades of coal in said mass fractions.

(3) A method for preparing a coal mixture, which method is a method for preparing a coal mixture containing at least two grades of coal, the method including determining the surface tension γ ₁₀₀ and the surface tension γ ₀ of each of the coal grades of the coal mixture along the regression line determined by the method for assessing the quality of coal according to (1), while the surface tension γ ₁₀₀ corresponds to the amount of the inert component 100%, the surface tension γ ₀ corresponds to the amount of the inert component 0%; determining the mass fractions of said at least two grades of coal so that an interfacial tension of 0.26 mN/m or less is achieved, calculated from the specified surface tension γ ₁₀₀ , the specified surface tension γ ₀ , the mixing ratio of each of the coal grades of the coal mixture, and also the mass fraction of the inert component and the mass fraction of the reactive component in each of the coal grades; and preparing a coal mixture by mixing said at least two grades of coal in said mass fractions.

(4) A method for preparing a coal mixture, wherein said method is a method for preparing a coal mixture containing at least two grades of coal, the method including determining the surface tension γ ₁₀₀ and the surface tension γ ₀ of each of the coal grades of the coal mixture according to regression line determined by the method of assessing the quality of coal according to (1), while the surface tension γ ₁₀₀ corresponds to the amount of the inert component 100%, the surface tension γ ₀ corresponds to the amount of the inert component 0%; and preparing a coal mixture by mixing said at least two grades of coal so that the mass fraction of coal having an absolute value of the difference between surface tension γ ₁₀₀ and surface tension γ ₀ equal to 6 mN/m or more is less than or equal to 45 wt. % coal mixture.

(5) A method for producing coke, including preparing a coal mixture using the method for preparing a coal mixture according to any one of paragraphs (2) - (4); and obtaining coke by carbonizing said coal mixture.

Beneficial Effects of the Invention

With the present invention, the types of coal that should constitute a coal mixture from which coke having the desired strength can be obtained, and the mass fractions of these types of coal can be accurately determined in comparison with prior art methods. Accordingly, it is possible to prepare a coal mixture from which coke having the desired strength can be obtained. In addition, the quality of coal, which serves as a raw material for metallurgical coke, can be assessed using the present invention.

Brief description of the drawings

Fig. 1 is a graph illustrating the relationship between interfacial tension, which was calculated by the method described in Patent Literature 1, and coke strength.

Fig. 2 is a graph illustrating the relationship between the amount of the inert component in the coal samples and the surface tension of the char obtained by heat treatment of these coal samples.

Fig. 3 is a graph illustrating the relationship between interfacial tension, which was calculated by the method of the present invention, and coke strength.

Fig. 4 is a graph illustrating the relationship between coke strength and low value coal mixing ratio.

Implementation of the invention

The present invention relates to a method for assessing the quality of coal, and this method uses the surface tension of char obtained by heat treatment of coal. The present invention also relates to methods for preparing a coal mixture that contains at least two grades of coal, and the methods use the parameters identified by this evaluation method. The method for evaluating coal quality according to the present embodiment uses the surface tension of the char and the interfacial tension calculated from the surface tension values. Accordingly, the char preparation method, the method for measuring the surface tension of the char, and the method for calculating the interfacial tension will be described first.

Method for obtaining semi-coke

Semi-coke is a thermally processed product obtained by thermal treatment of coal. Adhesion phenomena in coals affect the compatibility between different types of coal and affect the strength of the coke. Accordingly, in cases where it is necessary to study adhesion phenomena in coals, it is preferable to determine the properties of the coal melt at a temperature of 350 to 800°C, at which the coal is heated, the coal actually begins to soften and melt, and the coal sticks together and solidifies when coking is completed. However, methods for measuring the properties of coal melt in such a high temperature range are not known. In cases where the measured property is surface tension, the value of the surface tension of coal in the plastic state can be estimated, as described in Patent Literature 1, by measuring the surface tension of char, which is obtained by carbonizing coal by heating coal to a temperature at which the coal softens and melts, and subsequent cooling.

With regard to the heating temperature of the coal, heating should be carried out at a temperature greater than or equal to 350°C, at which the coal begins to soften and melt, up to 800°C, at which coking is completed as described above. This is justified from the point of view that surface tension affects the adhesion between coal particles. At heating temperatures of 350 to 800°C, temperatures that are particularly conducive to adhesion are temperatures of 350 to 550°C, which are temperatures at which softening and melting occurs, and it is believed that the adhesion structure is determined at about 500°C. Accordingly, it is preferable that the heating temperature is 480 to 520°C, about 500°C. Preferably, the heating is carried out in an atmosphere of inert gas (eg, nitrogen, argon, helium, etc.), which does not react with coal.

Preferably, cooling is carried out in an atmosphere of inert gas, which does not react with coal. In addition, it is preferable that the carbonized coal is subjected to rapid cooling (quenching) at a rate of 10°C/second or higher. The reason for the quenching is to keep the molecular structure achieved in the plastic state, and therefore it is preferable that the cooling be carried out at a cooling rate of 10° C./second or higher, at which the molecular structure is considered not to change. Extinguishing methods include methods using liquid nitrogen, ice water, water, or an inert gas such as nitrogen gas. Preferably, the extinguishing is carried out using liquid nitrogen. Gas cooling is not preferred because, in such cooling, the cooling of the interior of the coal takes time and the variation in the cooling rate is significant. Cooling with ice water or water is not preferred because moisture deposition during such cooling affects the measurement of surface tension.

In the present invention, examples of heat treatment operations performed on coal are described in (a) to (c) below.

(a) Coal is pulverized. With regard to the size of the pulverized coal particles, in terms of preparing a homogeneous sample from the coal which is inhomogeneous in terms of components, properties, and the like, it is preferable that the coal be pulverized to a particle size of less than or equal to 250 µm, which is the particle size for the technical analysis of coal described in JIS M 8812. More preferably, the coal is crushed to a smaller particle size less than or equal to 200 µm.

(b) The coal pulverized in process (a) is heated at an appropriate heating rate in an airless state or in an inert gas atmosphere. It is sufficient to heat the coal to a temperature in the above range of 350 - 800°C. Preferably, the heating rate is a rate in accordance with the heating rate used in the production of coke in a coke oven.

(c) The coal heated during operation (b) is cooled. Preferably, the cooling is carried out in the manner described above.

Method for measuring the surface tension of semi-coke

Known methods for measuring the surface tension of ordinary matter include the sessile drop method, capillary liquid rising method, gas bubble maximum slip pressure methods, drop weighing methods, hanging drop method, ring tear method, plate wetting methods (Wilhelmy), inflow/outflow angle methods , oscillating plate method, etc. Since coal is composed of various molecular structures and its surface tension is not uniform, the measurement of coal surface tension can be performed using a method that can estimate the surface tension distribution, and an example of the method is the film flotation method described in non-patent literature 1. This method can be used as for coal, and for semi-coke produced from coal, in a similar way, and the distribution of surface tensions of coal can be determined using a finely divided sample of coal. The average value in the obtained distribution of surface tensions is designated as a representative value of the surface tensions of the coal sample. In cases where char is used as a sample, it is preferable that the heat treatment temperature for heat treatment of coal is in the range of coal thermoplasticity temperatures. Details of the measurement method are described in Patent Literature 1.

Method for calculating interfacial tension

The method for calculating interfacial tension is as follows. Since attention is focused on two grades of coal from a number of grades of coal included in the coal mixture, the method includes the step of determining the interfacial tension γ _ij , which is the interfacial tension between two types of semi-coke obtained from the corresponding two grades of coal, and the step of calculating the interfacial tension γ of the _mixture , which is the interfacial tension of the coal mixture, based on the interfacial tension γ _ij and the mass fraction of each of the coal grades in the coal mixture. Since the interfacial tension γ of the _{mixture of} coal mixture is calculated based on the interfacial tension between different types of char, the interfacial tension γ of the _mixture can be considered as the value corresponding to the interfacial tension of the char obtained from the coal mixture; however, in the present invention, the interfacial tension determined by the described method is called the interfacial tension γ of the coal _mixture mixture.

The step of determining the interfacial tension γ _ij between two grades of char will now be described. For two types of ordinary substances, their interfacial tension can be measured directly, or the interfacial tension value can be determined from the surface tension of the respective substances. For example, considering different substances i and j, the interfacial tension γ _ij between substance i and substance j can be determined from the surface tension γ _i of substance i and the surface tension γ _j of substance j. The interfacial tension γ _ij between substance i and substance j can be represented by the equation [1] below, which is the Girifalco-Goode equation.

In equation [1], ϕ is the interaction parameter; the interaction parameter ϕ can be determined experimentally and, as is known, varies depending on substances i and j. In addition, D. Li and AW Neumann et al. assumed that the value of the interaction parameter ϕ increases with increasing difference between the surface tension value γ _i of substance i and the surface tension value γ _j of substance j, and accordingly, equation [2] below is proposed, which is an equation derived from equation [1].

In equation [2], β represents a constant obtained experimentally. D. Li and A. W. Neumann et al. performed calculations and found that β is 0.0001247 (m ² /mJ) ² . Assuming that substance i is char i made from coal i and substance j is char j made from coal j, the interfacial tension γij between char i and char j can be calculated from the formula by measuring the surface tension γi of char i and the surface tension γj of char j and substituting the surface tension values into equation [1] or equation [2]. In cases where equation [1] is used, the value of the interaction parameter ϕ must be determined experimentally. Accordingly, from the point of view of simplifying the calculation of interfacial tension, it is preferable to use the equation [2], which uses the calculated value of the interaction parameter.

Now, the stage of calculating the interfacial tension γ _{of a mixture of} coal mixture will be described. In cases where the grades of coal in the coal mixture and their mass fractions are known, it is possible to calculate the interfacial tension of semi-coke obtained from the coal mixture. Assuming that in the case when n grades of coal are present in the coal mixture, their mass fractions are denoted as w _i (which represents the mass fractions of the 1st, 2nd, ... i-th, ... and n-th coal ), the probability of having interfaces ij formed between the char produced from coal i and the char produced from coal j can be represented as the product of w _i and w _j . When the interfacial tension at the interfaces of the char is denoted as γij, it is possible to determine the interfacial tension γ of the _mixture , which is the interfacial tension of the char obtained from a coal mixture in which n grades of coal are mixed, expressed by the following equation [3].

In fact, in equation [3], it is preferable that each w _i and w _j be expressed as the mass fraction of char in the char mixture obtained from the coal mixture. However, the relative content of char types that are derived from the respective coal types in the char mixture does not differ significantly from the relative content of the respective coal types in the coal mixture. Accordingly, each w _i and wj is expressed as the mass fraction of coal in the coal mixture.

In the present invention, it is assumed that several types of char produced from respective types of coal and its constituents forming a coal mixture are mixed and the interfacial tension γ of the _mixture corresponds to the interfacial tension of the char mixture, which is supposed to be the result of mixing. That is, the present invention is not based on the actual preparation of the char mixture, and the interfacial tension of the present invention is an indicator (value) determined from the surface tensions of the char and the mass fractions of coal from which the char is obtained in the coal mixture.

Now, a comparative experiment will be described which was carried out to determine the relationship between the interfacial tension γ of the _mixture and the strength of coke DI150/15 obtained from a coal mixture prepared by mixing several grades of coal; the interfacial tension γ of the _mixture was calculated using the method disclosed in Patent Literature 1 for comparison with the present invention.

Comparative experiment

Several coal mixtures were prepared, each of which was formed from several grades of coal, and the coal mixtures were carbonized using an electric furnace that can simulate the carbonization conditions of a coke oven. Accordingly, coke was obtained.

The surface tension of the char obtained by heat treatment at 500° C. of each of the coal grades constituting the coal mixture was measured, and the interfacial tension γ of the _mixture was calculated using Equation [2] and Equation [3]. In addition, the drum strength DI (150/15) was used as the strength of the coke. Specifically, according to the JIS K 2151 coke drum strength test method, a drum testing machine loaded with a predetermined amount of coke was rotated at 15 rpm 150 times, and then the mass fraction of coke having a particle diameter of 15 mm or more. The drum strength DI (150/15) represents the mass ratio of the specified mass fraction to the mass fraction before rotation.

The carbon used in the comparative experiment and its properties are shown in Table 1.

Table 1

Coal log MF (log/ddpm) Ro(%) TI (%) Volatile substances (by dry weight) Ash (by dry weight) Surface tension γ (mN/m) A 0.90 1.59 23.6 17.5 9.3 40.3 B 1.23 1.49 18.7 18.1 8.6 40.1 C 0.48 1.56 21.0 17.1 10.8 39.1 R 2.97 1.20 20.4 24.2 10.8 40.5

In a comparative experiment, coals A - C and R were prepared as shown in Table 1, and coals A - C and R were mixed in the mass fractions shown in Table 2. Charcoal mixtures 1 - 4 were prepared accordingly.

table 2

Coal mixture 1 Charcoal mix 2 Coal mix 3 Charcoal mix 4 Mass fraction (%) of coal A fifty - - thirty Mass fraction (%) of coal B - fifty - twenty Mass fraction (%) of coal C - fifty - Mass fraction (%) of coal R fifty fifty fifty fifty log MF (log/ddpm) 1.94 2.10 1.72 2.00 Ro(%) 1.39 1.34 1.38 1.37 TI (%) 22.0 19.5 20.7 21.0 γ _mixture (mN/m) 0.0003 0.0013 0.0159 0.0008 DI150/15 (-) 82.0 82.6 81.0 82.5

In Table 1, "Surface Tension (mN/m)" represents the surface tension of the char obtained by heat treatment of each of coals A - C and R, and is the average value of the surface tension distribution measured by the film flotation method. In Table 1 and Table 2, "Ro (%)" represents the average maximum reflectance of coal vitrinite (charcoal mixture) according to JISM 8816, and "TI (%)" represents the amount of inert component (vol.%) for the analysis of coal macerals, calculated using the JISM 8816 method for determining macerals of coal (coal mixture) and the equation [4] below, which is based on the Parr equation described in the explanation of the method.

Amount of inert component (vol.%) = fusinite (vol.%) + micrinite (vol.%) + (2/3) semifusinite (vol.%) + mineral substance (vol.%) ... [4]

In Tables 1 and 2, "logMF" is the logarithm of the maximum flowability (MF) of the coal or coal mixture, as measured by the Gieseler plastometer method described in JISM 8801. . In "Ash (by dry weight)" and "Volatile matter (by dry weight)" in Table 1, the values are the measured values by dry weight of the sample, determined by the rapid analysis method described in JISM 8812.

In Table 2, _mixture γ represents the interfacial tension of coal mixtures 1 to 4, calculated from the surface tension value γ shown in Table 1 and the mass fractions shown in Table 2 according to Equation [2] and Equation [3]. "DI150/15 (-)" represents the strength of coke obtained by carbonization of coal mixtures 1 to 4.

Fig. 1 is a graph illustrating the relationship between the interfacial tension γ of the _mixture , which was calculated by the method described in Patent Literature 1, and the coke strength DI150/15 (-). As can be seen from FIG. 1, in coal mixtures 1, 2 and 4, the values of interfacial tension γ of the _mixture were close to 0, but there were variations in the coke strength DI150/15. In coal mixture 3, the values of interfacial tension γ of the _mixture and coke strength DI150/15 showed a trend different from that for coal mixtures 1, 2, and 4.

Patent Literature 1 states that a high correlation relationship is maintained between the interfacial tension γ of the _mixture and the strength DI150/15. In some cases, there is a tendency for a high correlation relationship between the interfacial tension of the mixture and the strength of DI150/15, while in other cases, as shown in Fig. 1, the relationship is not preserved.

Now, embodiments of the present invention will be described. First, the coal quality evaluation method according to the present embodiment will be described.

Coal quality assessment method

In the coal quality evaluation method according to the present embodiment, coal samples having different amounts of inert components are prepared by grinding one grade of coal, and the content of inert components in the respective coal samples is determined. In addition, the surface tension of the char obtained by heat treatment of the respective prepared coal samples is measured. The ratio of surface tension variation to inert content variation is determined from a regression line that is based on reported inert content and reported surface tension values. Using this ratio as an indicator, the quality of the coal to be used as a raw material for metallurgical coke is evaluated.

Evaluation of the surface tension of the char obtained from the inert component, in which the proportion of the inert component is 100%, and the surface tension of the char obtained from the reactive component, in which the proportion of the inert component is 0%

It is assumed that each of the grades of coal constituting the coal mixture consists of an inert component, in which the proportion of the inert component is 100%, and a reactive component, in which the proportion of the inert component is 0%. Coal samples with different amounts of an inert component are prepared by grinding coal of the same brand. The quantities of the inert component of the coal samples are measured and the surface tensions of the char obtained by heat treatment of the respective coal samples are measured. A regression line is determined based on the specified inert content and surface tension values. The regression line determines the surface tension γ ₁₀₀ and the surface tension γ ₀ . The surface tension γ ₁₀₀ represents the surface tension of the inert component in which the proportion of the inert component is 100%, and the surface tension γ ₀ represents the surface tension of the reactive component in which the proportion of the inert component is 0%. γ ₁₀₀ defined in this way can be considered as corresponding to the surface tension of the inert component of the coal converted to char; however, in the present implementation, γ ₁₀₀ refers to "surface tension γ ₁₀₀ of the inert component". Similarly, γ ₀ can be considered as the corresponding surface tension of the reactive component of coal converted to char; however, in the present implementation, γ ₀ refers to the "surface tension of the reactive component".

The method for determining the regression line will now be described. First, samples of coal obtained by grinding one brand of coal are sieved. When coal is crushed, a large amount of the inert component is in large particles. Accordingly, the mass fraction of the inert component in the crushed coal varies as a result of grinding and screening. Experiment 1, described below, was carried out to demonstrate that the mass fraction of the inert component can vary and a regression line can be determined. Experiment 1 used coals A - C and R, which were prepared in a comparative experiment.

Experiment 1

Coals A - C and R were crushed and sieved. Accordingly, coal samples containing a large amount of a reactive component that is a component other than an inert component and coal samples containing a large amount of an inert component were prepared. These coal samples were subjected to the measurement of constituent fractions, which was carried out using the method of point counting using an optical microscope in accordance with JIS M 8816. Accordingly, the total content of the inert component TI was measured. In addition, the char was obtained by heat treatment of the respective coal samples at 500°C, and the surface tension γ of the respective types of char was measured using the film flotation method. The surface tension γ of the char represents the average value in the surface tension distribution determined by the film flotation method. Additionally, standard samples of coals A - C and R were prepared, which were prepared without grinding or sifting, the total content of the inert component TI of each of the standard samples of coal and the surface tension of semi-coke, which was obtained by heat treatment of the corresponding samples at 500°C, were measured.

Fig. 2 is a graph illustrating a curve that shows the relationship between the content of the inert component TI of the coal samples and the surface tension γ of the char obtained by heat treatment of these coal samples, and illustrating the regression lines in the graph. Each of the regression lines shown in Fig. 2 is a simple least squares regression line, so that the error on the three curves showing the relationship between the total inert component TI and surface tension γ can be minimized. The surface tension γ ₀ , which corresponds to the amount of the inert component TI equal to 0%, and the surface tension γ ₁₀₀ , which corresponds to the amount of the inert component TI equal to 100%, can be calculated using a regression line. As an example, surface tension γ ₀ and surface tension γ ₁₀₀ of coal samples from coal A are shown in FIG. 2. From FIG. 2 shows that the mass fraction of the inert component can be changed by grinding and sieving and a linear regression equation can be obtained with a high correlation between the surface tension γ and the amount of the inert component TI.

The total content of the inert component TI (%) of each of the standard samples of coals A - C and R represents the volume fraction of the inert component of the coal; however, since the specific gravity of the inert component is essentially equal to the specific gravity of the reactive component, the volume fraction was considered to be approximately equivalent to the mass fraction. The mass fractions (%) of the reactive components of standard coal samples were calculated by subtracting the value of the amount of the inert component TI from the total mass fraction (100%). The mass fractions (%) of the inert and reactive components of coals A - C and R, as well as their surface tension γ ₁₀₀ and surface tension γ ₀ are shown in Table 3. As described in the present implementation, the mass fraction of the inert component may be the amount of the inert component (volume percentage) determined by the method of JIS M 8816 and the equation [4], and the mass fraction of the reactive component can be the value obtained by subtracting the amount of the inert component (volume fraction) from 1.

Table 3

Coal Component Mass fraction (%) Surface tension γ ₁₀₀ (mN/m) Surface tension γ ₀ (mN/m) A Inert 23.6 37.0 - reactive 76.4 - 41.3 B Inert 18.7 41.2 - reactive 81.3 - 39.8 C Inert 21.0 35.5 - reactive 79.0 - 40.0 R Inert 20.4 40.8 - reactive 79.6 - 40.3

Assessment of coal quality, which uses as an indicator the variation in surface tension in relation to the variation in the amounts of an inert component

The inventors of the present invention found a phenomenon in which, in cases where the content of the inert component of coal varied, the variation in the surface tension of the char which was obtained by heat treatment of coal, compared with the variation in the amounts of the inert component, varied between different grades of coal. For example, in FIG. 2, considering coals A and C, their regression lines had a large slope in absolute value, indicating that the variation in the surface tension of the char compared to the variation in the amounts of the inert component was large. For coal B and coal R, their regression lines had a slight slope in absolute value, indicating that the variation in the surface tension of the char relative to the variation in the amounts of the inert component was small.

In particular, in the case where the content of the inert component changes from 0% to 100%, the variation in surface tension is equal to the difference between γ ₁₀₀ and γ ₀ , that is, γ ₁₀₀ - γ ₀ . γ ₁₀₀ - γ ₀ coal A is -4.3 mN/m. γ ₁₀₀ - γ ₀ coal C is -4.5 mN/m. On the other hand, γ ₁₀₀ - γ ₀ of coal B is 1.4 mN/m, and γ ₁₀₀ - γ ₀ of coal R is 0.5 mN/m. Since the variation in surface tension is expressed as an absolute value of γ ₁₀₀ - γ ₀ , coal A and coal C are coals having a high ratio of char surface tension variation to inert component variation, compared to coal B and coal R.

As shown in Table 2, in the experimental examples of coal mixtures 1 - 3, coal R was included in the amount of 50 wt.%, and coals A - C were added to it, respectively, in the amount of 50 wt.%. Note that coal blend 2 has the highest coke strength. Coal B, which was added to the coal mixture 2, is a coal having little variation in the surface tension of the char as compared to the variation in the amounts of the inert component. On the contrary, coal mixture 1 and coal mixture 3, which have low coke strength, are coal mixtures in which coal A or coal C is mixed, which has a large variation in the surface tension of the char compared to the variation in the amounts of the inert component. That is, in the case of adding coal having a large variation in the surface tension of the char as compared to varying the amounts of the inert component, as a result, the strength of the coke decreased.

Coal mixture 1 and coal mixture 4 are compared. In coal mixture 4, the amount of coal A was reduced by 20% compared to coal mixture 1, and coal B was added accordingly. the inert component replaced the portion corresponding to 20 wt.% of coal A, which has a large variation in the surface tension of the char with respect to the variation in the amounts of the inert component. Since the coke strength of the coal mixture 4 is higher than that of the coal mixture coke 1, it is clear that coal having little variation in the surface tension of the char compared with the variation in the amounts of the inert component is a favorable coal as a raw material for coke, increasing coke strength.

The results described above show that in cases where the variation in the surface tension of the char compared to the variation in the amounts of the inert component is used as an indicator, it can be determined that coal having little variation in the surface tension of the char is suitable as a coke feedstock. The results are believed to be based on the effect of interfacial tension on coke strength. That is, coal having a large variation in the surface tension of the char compared to the variation in the amounts of the inert component has a large difference between the value of γ ₁₀₀ and the value of γ ₀ . The difference means that, assuming that the coal is composed of a component that softens and melts and a component that does not soften or melt, the surface tensions of the char produced from the respective two components are significantly different. When it is assumed that one grade of coal consists of a component that softens and melts and a component that does not soften or melts and is not homogeneous, in the case where the raw material for coke is formed by mixing coal, the raw material includes components having significantly different surface char tension. As the difference in surface tension increases, the interfacial tension increases, and therefore, the interfacial tension γ of the _{mixture of} the coal mixture including components having significantly different surface tension of the char is high, which reduces the adhesiveness at the interfaces. As a result, presumably, the strength of the coke deteriorates.

Now will be described the implementation of the method of preparing coal mixture. There are three options for the preparation of coal mixture. In the coal mixture preparation method of the first embodiment, the interfacial tension is calculated and the correlation between the interfacial tension and coke strength is determined; from this correlation, the interfacial tension corresponding to the desired coke strength is determined; and the coal mixture is obtained by mixing coal in such mass fractions that the specified interfacial tension or a lower interfacial tension is achieved. In the method for preparing a coal mixture according to the second implementation, the coal mixture is prepared by mixing coal in such mass fractions that a calculated interfacial tension of 0.26 mN/m or less is achieved. In the charcoal mixture preparation method of the third embodiment, the charcoal mixture is prepared such that the proportion of unfavorable coal in the mixture as judged by the coal quality evaluation method described above is limited. First, the method for preparing the coal mixture of the first embodiment will be described.

The method of preparing the coal mixture of the first implementation

The method for preparing the coal mixture according to the first implementation includes stages 1 to 3, as described below.

Stage 1

At stage 1, it is assumed that each of the coal grades that make up the coal mixture consists of an inert part, in which the proportion of the inert component is 100%, and a reactive part, in which the proportion of the inert component is 0%. Coal samples having different amounts of the inert component are prepared by grinding one grade of coal, and the amount of the inert component in the respective coal samples is measured. In addition, the surface tension of the char obtained by heat treatment of the respective coal samples is measured, a regression line is determined based on the indicated amounts of the inert component and the indicated surface tensions, and, based on the regression line, the surface tension γ ₁₀₀ is determined, which corresponds to the content of the inert component of 100% , and surface tension γ ₀ , which corresponds to the content of the inert component of 0%.

Stage 2

In step 2, following step 1, it is assumed that the surface tension of the char obtained from the inert component is equal to the surface tension γ ₁₀₀ , and the surface tension of the char obtained from the melt and the reactive component is equal to the surface tension γ ₀ , and the interfacial tension γ the _mixture is calculated from the mass fraction of the inert component, the mass fraction of the reactive component, surface tension γ ₁₀₀ and surface tension γ ₀ of each brand using equation [1] or equation [2] and equation [3].

In the present embodiment, it is assumed that one grade of coal is formed from two types of coal, namely, coal formed from an inert component in which the proportion of the inert component is 100%, and coal formed from a reactive component in which the proportion of the inert component is 0%. , and it is assumed that the surface tension of the char obtained from the coal formed from the inert component is equal to the surface tension γ ₁₀₀ , and the surface tension of the char obtained from the coal formed from the reactive component is equal to the surface tension γ ₀ . In the present implementation, based on these assumptions, the interfacial tension γ of the _mixture is calculated using equation [1] or [2] and equation [3].

That is, in the present implementation, in the case where n coal grades are actually present in the coal mixture, the following assumptions are made: 2 (types) × n (number of grades) types of coal are present, and out of two, one coal is formed by an inert component, and one coal formed by the reactive component; and the mass fractions of the coal formed by the inert component and the coal formed by the reactive component are denoted as w _i (which represents the mass fractions of the 1st, 2nd, ... i-th, ... and 2×n-th coal ). By substituting the surface tension γ ₁₀₀ and the surface tension γ ₀ of these types of coal that are assumed to be present for γ _i and γ _j in equation [1] or [2], one can calculate the interfacial tension γ _ij , which is the interfacial tension between two types of semi-coke obtained from two grades of coal. The interfacial tension γ of the _mixture can be calculated from the interfacial tension γ _ij using the equation [3]. With regard to equation [3], the mass fractions w _i and w _j of coal formed by the inert component and coal formed by the reactive component in the coal mixture can be calculated by multiplying the mass fraction of one grade of coal in the coal mixture by each of the mass fractions of inert and reactive components in a sample of standard coal (see, for example, table 3).

Experiment 2 was carried out as follows. With regard to the coal mixtures 5 to 14, each of which is formed from two or more coals D to N listed in Table 4, assuming that there are two types of coal, namely the coal formed by the inert component and the coal formed by the reactive component, as described above, the interfacial tension γ of the _mixture is calculated, and the relationship between the interfacial tension γ of the _mixture and the coke strength DI150/15 (-) is determined. The analysis results shown in Table 4 are measured by the same method as described in the description of Table 1. Surface tension represents the average value in the surface tension distribution obtained by measuring, using the film flotation method, the surface tension of char obtained by heat treatment of the respective types coal at 500°C. The surface tension of the inert component, in which the proportion of the inert component is 100%, and the surface tension of the reactive component, in which the proportion of the inert component is 0%, are the values γ ₁₀₀ and γ _0, respectively, calculated by the method described in experiment 1.

Table 4

brand log MF (log/ddpm) Ro(%) TI (%) Volatiles
(wt.% dry weight) Ash
(wt.% dry weight) Surface tension (mN/m) Surface tension of the inert component (mN/m) Surface tension of the reactive component (mN/m) D 2.95 1.10 37.8 25.7 9.3 40.1 43.1 38.3 E 2.48 1.24 38.4 23.3 8.4 39.3 41.2 38.1 F 1.04 1.23 45.6 21.6 8.0 40.2 41.2 39.3 G 2.77 0.97 43.4 27.0 9.2 40.9 44.9 37.9 H 2.58 0.98 33.8 27.1 8.3 41.1 44.8 39.2 I 0.48 0.99 46.6 25.7 9.8 41.3 44.7 38.4 J 1.79 0.97 32.4 29.0 8.7 40.2 44.9 37.9 K 0.85 1.54 21.4 18.6 10.7 38.7 37.1 39.1 L 3.47 0.64 21.8 42.1 6.8 41.6 49.4 39.4 M 2.85 1.18 30.8 23.3 10.4 39.8 42.0 38.8 N 2.65 1.17 29.2 22.8 10.2 39.8 42.1 38.8

Experiment 2

The mixing ratio of each of the grades, the quality of the coal mixtures and the strength DI(150/15) of the coke obtained by carbonization of the respective coal mixtures are shown in Table 5. The values of logMF, Ro, TI, ash and volatiles are weighted average, according to the mixing ratio, the values of the analysis results for the types of coal included in the coal mixture. "γ _mixture " is a value calculated by the same method as the method described in Step 2. In this example, low-value coal was defined as coal having an absolute value of γ ₁₀₀ - γ ₀ equal to 6 mN/m or more; γ ₁₀₀ - γ ₀ represents the variation in the surface tension of the char relative to the variation in the content of the inert component. Accordingly, the proportion of low-value coal is the sum of the proportions of coal in the mixture having an absolute value of γ ₁₀₀ - γ ₀ equal to 6 mN/m or more.

In the mixing examples in Table 5, the coal was mixed such that the Ro of the coal mixture was about 1.03%. In the blending examples shown in Table 2, coal having a Ro of 1.20 to 1.59% was used, and the Ro of the coal mixtures ranged from 1.30 to 1.40%. However, with regard to the coal mixture for coke production, it is common to mix a large number of coal grades (5 to 20 grades) having different coal properties, and limiting the blending of a small number of coal grades is not preferable, because in such a case, operation flexibility is limited as a result. restrictions on the coal to be blended. Because high Ro coals tend to be expensive, experiment 2 used coal blends having a lower Ro than the mixing examples in Table 2 because experiment 2 was designed to use real operating conditions.

In the present implementation, the qualities of the coal mixtures are not limited to the examples shown in Table 5. With regard to the average quality of the coal mixture, the following ranges can be used so that the present invention can be suitably used: Ro, 0.9 - 1.4%; log MF 1.7 - 3.0 (logddpm); and TI 15 - 40%. The following ranges are particularly preferred: Ro 0.9-1.3%; log MF, 2.0 - 3.0 (logddpm); and TI 20 - 40%. With regard to the quality of individual grades of coal, the coal may be as follows, so that the present invention can be suitably used: Ro 0.6 - 1.7 (%); MF, 0 - 60000dpm; TI 3 - 45 (%); volatile substances 3 - 45%; ash 1 - 20%; and surface tension (average value in distribution) 36 - 46 mN/m.

Table 5

Coal Coal mixture 5 Coal mixture 6 Coal mixture 7 Coal mixture 8 Coal mixture 9 Coal mixture 10 Coal mixture 11 Coal mixture 12 Coal mixture 13 Coal mixture 14 D 30.0 30.0 30.0 E 30.0 30.0 30.0 F 30.0 30.0 G 30.0 30.0 H 7.0 25.0 I 18.6 18.0 8.0 16.0 15.8 17.6 13.0 17.3 0.0 11.0 J 25.1 25.0 10.5 23.0 24.1 16.0 23.0 7.9 0.0 17.0 K 4.9 1.1 1.0 4.7 2.5 0.7 0.0 0.0 0.0 0.0 L 9.6 14.9 21.6 4.0 9.4 18.5 9.2 21.4 21.4 5.0 M 0.0 0.0 18.4 8.0 8.4 10.4 16.8 20.4 23.6 19.0 N 11.8 11.0 3.5 14.3 9.9 6.8 8.0 3.0 0.0 18.0 log MF
(log/ddpm) 2.11 2.10 2.09 2.11 2.24 2.24 2.37 2.37 2.37 2.38 Ro(%) 1.033 1.034 1.030 1.032 1.033 1.033 1.033 1.033 1.029 1.032 TI (%) 34.7 34.7 34.8 36.4 34.5 34.3 34.4 34.0 34.1 35.9 Ash (wt.%
dry
mass) 9.2 8.7 8.5 9.4 9.2 8.7 9.3 8.8 8.4 9.5 Volatile substances (wt.% by
dry weight) 27.4 27.9 27.8 26.6 27.4 28 27.3 28.2 27.8 26.5 γ _mixtures 0.28 0.29 0.24 0.31 0.27 0.28 0.26 0.27 0.22 0.28 Share of low-value coal (%) 53.3 57.9 40.1 73.0 49.3 52.1 45.2 46.6 21.4 63.0 DI150/15 (-) 78.7 79.4 80.3 78.6 79.1 79.7 80.5 80.0 80.6 79.3

With respect to Table 5, the γ of the _mixture was calculated as follows. For example, in the case of coal D in coal mixture 5 of Table 5, the proportion of coal D in the mixture is 30%. For coal mixture 5, it was assumed that coal D is formed from two types of coal, namely, coal formed by an inert component and coal formed by a reactive component. The proportion in the mixture of coal formed from the inert component of coal D was determined to be 11.3%; which was obtained by multiplying the proportion in the mixture of coal D, which is 30%, by the proportion of the inert component of coal D, which was 37.8%. The proportion in the mixture of coal formed by the reactive component of coal D was determined to be 18.7%; which was obtained by multiplying the proportion in the mixture of coal D, which is 30%, by the proportion of the reactive component in coal D, which is 62.2%. Thus, for each of the types of coal, the coal formed from the inert component and the coal formed from the reactive component of the coal were each treated as if the coal were the same grade of coal, and the γ of the _mixture was calculated using the equation [3].

Fig. 3 is a graph illustrating the relationship between the interfacial tension γ of the _mixture , which was calculated by the method of the present invention, and the coke strength DI150/15 (-). As shown by the dash-dotted curve in FIG. 3, it is obvious that there is a correlation between the interfacial tension γ of the _mixture and the coke strength DI150/15 (-); that is, when the interfacial tension γ of the _mixture increases, the coke strength DI150/15 (-) decreases. The curve can be obtained by plotting a correlation curve using the least squares method or by hand on a graph such as in FIG. 3.

Stage 3

At stage 3, the interfacial tension γ of the _mixture , corresponding to the desired strength, is determined from the correlation determined at stage 2. Since with an increase in the interfacial tension γ of the _mixture , the adhesion between coal particles decreases, the coal mixture must be prepared by mixing coal grades in such mass fractions at which the specified defined interfacial tension γ of the _mixture or a lower interfacial tension is achieved. In the case when the interfacial tension is calculated from the surface tension of semi-coke obtained from coal, which is part of the coal mixture, and mass fractions of coal, and the calculated interfacial tension is equal to or less than the interfacial tension corresponding to the desired coke strength, the coal mixture must be prepared by mixing several grades of coal in the specified mass fractions. It can be expected that the coke obtained by carbonizing the coal mixture prepared in this way will have the desired or greater strength.

The coal that will be used in the preparation of the coal mixture in stage 3 may differ from the coal used in experiment 2 with respect to stage 2. Stage 2 is implemented to determine the correlation between γ of the _{mixture of} coal mixture and coke strength by conducting, previously, a coke test with using a specific coal mixture. In step 3, based on the correlation predetermined in step 2, the coal can be freely selected so that a γ of the _mixture is achieved equal to or less than the value at which the desired strength is achieved. In this case, it is preferable to ensure that the average properties of the coal mixture used in the test for coke production, which is previously carried out in stage 2, have values close to the average properties of the coal mixture prepared in stage 3. In this case, the strength of the coke obtained from the coal the mixture prepared in step 3 can be predicted more accurately. For example, it is more preferable to provide the following differences between the average characteristics of the carbon mixture used in stage 2 and the average characteristics of the coal mixture prepared in stage 3: the difference in average reflectance is less than or equal to 0.2%; and a difference in log MF less than or equal to 1.0 (logddpm). More preferably, the stage 2 test is carried out using half or more of the types of coal used in stage 3. However, regardless of the properties of the coal mixture, provided that the γ of the _{mixture of} the coal mixture is equal to or less than the value of γ of the _mixture , which provides the desired strength coke, one can expect to obtain a coke having a higher strength than in the case of a coal mixture having a _mixture γ value greater than or equal to the indicated _mixture γ value.

In the examples presented in Table 5 and in FIG. 3, coke with a preferred coke strength of 78.5-80.5 can be produced. If necessary, higher coke strength can be achieved by changing the type of coal used and/or preparing the quality of the coal mixture. In particular, since the strength of the coke increases with increasing Ro of the coal mixture, a coke production test using a higher Ro of the coal mixture than Ro in the examples of Table 5 can be carried out to change the γ value of the _mixture , and under mixing conditions can be determined the ratio between γ of the _mixture and coke strength; on the basis of this ratio, it is possible to determine the γ of the _mixture for the production of coke having the desired strength.

In the coal mixture preparation method of the first embodiment, the performer performing steps 1 and 2 may be different from the performer performing step 3. Step 1 and step 2 may be performed in advance, and in step 3, the interfacial tension γ of the _mixture may be determined based on a predetermined correlation . That is, even when the performer performing steps 1 and 2 is different from the performer performing step 3, the charcoal mixture preparation method of the first embodiment can be implemented. Similarly, the performer performing stage 1 may be different from the performer performing stage 2 and stage 3. That is, the correlation between coke strength and γ of the _mixture can be determined based on predetermined surface tensions γ ₁₀₀ and γ ₀ . Now, the method for preparing the coal mixture of the second embodiment will be described.

The method of preparing the coal mixture of the second implementation

The method for preparing the coal mixture of the second implementation includes stages α and β, as described below.

Stage α

In step α, it is assumed that each of the coal grades that make up the coal mixture is formed from an inert component in which the proportion of the inert component is 100%, and a reactive component in which the proportion of the inert component is 0%. Thereafter, coal samples having different amounts of the inert component are prepared by grinding one grade of coal, and the amounts of the inert component of the respective coal samples are measured. In addition, the surface tension of the char obtained by heat treatment of the respective coal samples is measured, a regression line is determined based on the indicated amounts of the inert component and the indicated surface tensions, and, based on the regression line, the surface tension γ ₁₀₀ is determined, which corresponds to the content of the inert component of 100%, and surface tension γ ₀ , which corresponds to the content of the inert component of 0%. Step α is the same as Step 1 of the charcoal preparation method of the first embodiment, and therefore redundant descriptions are omitted.

Stage β

In step β, it is assumed that the surface tension of the char obtained from the inert component is equal to the surface tension γ ₁₀₀ and that the surface tension of the char obtained from the reactive component is equal to the surface tension γ ₀ . After that, the interfacial tension γ of the _mixture is calculated based on the mixing ratio of each of the brands, the mass fractions of the inert component and the reactive component, the surface tension γ ₁₀₀ and the surface tension γ ₀ using the equation [3]. This step, which is for determining the interfacial tension, is the same as Step 2 of the charcoal preparation method of the first embodiment, and therefore redundant descriptions are omitted.

At stage β, the mass fraction of each of the coal grades that make up the coal mixture is set so that a design interfacial tension of 0.26 mN/m or less is achieved. As shown by the dash-dotted curve in FIG. 3, in cases where the coal mixture is prepared by mixing several grades of coal in certain mass fractions, so that the calculated interfacial tension γ of the _mixture is 0.26 mN/m or less, the decrease in the strength of the coke obtained by carbonizing this coal mixture can be prevented. , and hence coke having high strength can be expected. The results in FIG. 3 are based on the results of the preparation of semi-coke, carried out by heat treatment of coal at 500°C. Accordingly, it is preferable to use the value of the surface tension of the char produced at 500°C. However, the value of interfacial tension does not change significantly with a change in the temperature of preparation of semi-coke. Accordingly, even in cases where the char is produced at a different temperature, the preparation of a coke having high strength can be realized by ensuring that the coal mixture has an interfacial tension value of 0.26 mN/m or less.

In the coal mixture preparation method of the second embodiment, the α step can be implemented in advance to determine the surface tension γ ₁₀₀ and the surface tension γ ₀ of the coal, and the β step can be implemented using the predetermined surface tension γ ₁₀₀ and the surface tension γ ₀ . That is, even when the performer performing step α is different from the performer performing step β, the charcoal mixture preparation method of the second embodiment can be implemented. The method for preparing the coal mixture of the third embodiment will now be described.

The method of preparing coal mixture of the third implementation

The method for preparing the coal mixture of the third implementation includes stages A and B, as described below. In a third embodiment, the variation in surface tension relative to the variation in inert component contents is used as an indicator. As shown in Table 2, coal having a small variation in char surface tension compared to variation in inert component contents is judged to be suitable as a coke feedstock, and coal having a large variation in char surface tension compared to variation in inert component contents is judged unsuitable. as raw material for coke. In Table 2, the number of coal types used is small and limited, and the Ro values of coal mixtures are larger than those of commonly used coal mixtures. Accordingly, based on the results of Table 5, which were obtained under mixing conditions closer to real mixing conditions, studies were carried out on the criteria for varying the surface tension of char compared to varying the contents of the inert component, which is used to evaluate coal.

Stage A

In step A of the third implementation, it is assumed that each of the grades of coal constituting the coal mixture is formed from an inert component in which the proportion of the inert component is 100%, and a reactive component in which the proportion of the inert component is 0%. Thereafter, coal samples having different amounts of the inert component are prepared by grinding one grade of coal, and the amounts of the inert component of the respective coal samples are measured. In addition, the surface tension of the char obtained by heat treatment of the respective samples of coal is measured, a regression line is determined based on the indicated contents of the inert component and the indicated surface tensions, and, based on the regression line, the surface tension γ ₁₀₀ is determined, which corresponds to the content of the inert component of 100% , and surface tension γ ₀ , which corresponds to the content of the inert component of 0%. Step A is the same as Step 1 of the charcoal preparation method of the first embodiment and Step α of the charcoal preparation method of the second embodiment, and therefore redundant descriptions are omitted.

Stage B

In step B, it is assumed that the surface tension of the char obtained from the inert component is equal to the surface tension γ ₁₀₀ and the surface tension of the char obtained from the reactive component is equal to the surface tension γ ₀ . Thereafter, coal unfavorable as a raw material for coke is determined based on the absolute value of the difference between γ ₁₀₀ and γ ₀ , and the coal mixture is prepared so that the proportion of unfavorable coal in the mixture is low. Of the coals from D to N listed in Table 4, the coal having a difference between γ ₁₀₀ and γ ₀ 6 mN/m or more was classified as low value coal, which is not suitable as a raw material for coke, and the coal having a difference between γ ₁₀₀ and γ ₀ less than 6 mN/m were classified as valuable coal, which is suitable as a raw material for coke. The relationship between the proportion of low-value coals in the mixture and the strength of the coke was investigated.

4 is a graph illustrating the relationship between coke strength and low value coal blend ratio. As shown in FIG. 4, it is clear that there is a high correlation between the strength of the coke and the mixture ratio of low-value coals having a difference between γ ₁₀₀ and γ ₀ of 6 mN/m or more. That is, coal having an absolute value of γ ₁₀₀ - γ ₀ equal to 6 mN/m or more refers to low-value coal, not suitable as a raw material for coke. Accordingly, the coal mixture should be prepared by mixing coal in such a way that the proportion of low-value coals in the mixture is less than or equal to 45 wt.%. In cases where the coal mixture is prepared in this way, the obtained coal mixture is a coal mixture from which coke having high strength is expected to be obtained. This result is also based on the surface tension of the char produced at 500°C. However, a value for char produced at a different temperature may be used, in which case a similar estimate may also be made. Coal having an absolute value of γ ₁₀₀ - γ ₀ 6 mN/m or more can be classified as low-value coal, not suitable as a raw material for coke, and therefore it is preferable that the proportion in the mixture of such coal is as low as possible. That is, it is preferable that the lower limit of the proportion in the mixture of coal having an absolute value of γ ₁₀₀ - γ ₀ equal to 6 mN/m or more is 0%.

In the coal mixture preparation method of the third embodiment, step A may be implemented in advance to determine the surface tension γ ₁₀₀ and surface tension γ ₀ of coal, and step B can be implemented using a predetermined surface tension γ ₁₀₀ and surface tension γ ₀ . That is, even when the performer performing step A is different from the performer performing step B, the charcoal mixture preparation method of the third embodiment can be implemented.

According to the description, with the help of the present invention it is possible to evaluate whether the grade of coal is suitable as a raw material for metallurgical coke. In addition, the types of coal that should constitute a coal mixture from which coke having the desired strength can be obtained, and the mass fractions of coal types can be accurately determined by comparison with prior art methods. As a result, the production of coke having the desired strength can be realized.

Claims (23)

1. A method for assessing the quality of coal, and this method includes: preparation of coal samples having different amounts of an inert component by grinding one brand of coal; measuring the amount of the inert component of the respective coal samples and measuring the surface tension of the char obtained by heat treatment of the respective coal samples; determining the surface tension γ ₁₀₀ corresponding to the amount of the inert component of 100%, and the surface tension γ ₀ corresponding to the amount of the inert component 0%, using a regression line based on the indicated amounts of the inert component and the indicated surface tensions; and calculating the absolute value of the difference between the surface tension γ ₁₀₀ and the surface tension γ ₀ ; wherein the coal having an absolute value of the difference between γ ₁₀₀ and γ ₀ of 6 mN/m or more is not suitable as a raw material for coke, and the coal having an absolute value of the difference between γ ₁₀₀ and γ ₀ of less than 6 mN/m is suitable as raw material for coke. 2. A method for preparing a coal mixture, moreover, this method is a method for preparing a coal mixture containing at least two grades of coal, and the method includes: determination of surface tension γ ₁₀₀ and surface tension γ ₀ of each of the coal grades of the coal mixture along the regression line determined by the method for assessing the quality of coal according to clause 1, while the surface tension γ ₁₀₀ corresponds to the amount of the inert component 100%, the surface tension γ ₀ corresponds to the amount of the inert component 0%; determination of the interfacial tension of the coal mixture according to the specified surface tension γ ₁₀₀ , the specified surface tension γ ₀ , the mixing ratio of each of the coal grades of the coal mixture, as well as the mass fraction of the inert component and the mass fraction of the reactive component in each of the coal grades; determining the correlation between said interfacial tension and the strength of the coke produced from said coal mixture; on the basis of said correlation, determining the interfacial tension corresponding to the desired strength of the coke; determining the mass fractions of said at least two grades of coal so that an interfacial tension corresponding to the desired coke strength or a lower interfacial tension is achieved; and preparation of a coal mixture by mixing said at least two grades of coal in the specified mass fractions. 3. A method for preparing a coal mixture, moreover, this method is a method for preparing a coal mixture containing at least two grades of coal, and the method includes: determination of surface tension γ ₁₀₀ and surface tension γ ₀ of each of the coal grades of the coal mixture along the regression line determined by the method for assessing the quality of coal according to clause 1, while the surface tension γ ₁₀₀ corresponds to the amount of the inert component 100%, the surface tension γ ₀ corresponds to the amount of the inert component 0%; determining the mass fractions of said at least two grades of coal so that an interfacial tension of 0.26 mN/m or less is achieved, calculated from the specified surface tension γ ₁₀₀ , the specified surface tension γ ₀ , the mixing ratio of each of the coal grades of the coal mixture, and also the mass fraction of the inert component and the mass fraction of the reactive component in each of the coal grades; and preparation of a coal mixture by mixing said at least two grades of coal in the specified mass fractions. 4. A method for preparing a coal mixture, moreover, this method is a method for preparing a coal mixture containing at least two grades of coal, and the method includes: determination of surface tension γ ₁₀₀ and surface tension γ ₀ of each of the coal grades of the coal mixture along the regression line determined by the method for assessing the quality of coal according to clause 1, while the surface tension γ ₁₀₀ corresponds to the amount of the inert component 100%, the surface tension γ ₀ corresponds to the amount of the inert component 0%; and preparation of a coal mixture by mixing said at least two grades of coal so that the mass fraction of coal having an absolute value of the difference between surface tension γ ₁₀₀ and surface tension γ ₀ equal to 6 mN/m or more is less than or equal to 45 wt. % coal mixture. 5. A method for producing coke, including: preparation of a coal mixture using the method of preparing a coal mixture according to any one of paragraphs. 2-4; and obtaining coke by carbonization of said coal mixture.

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