JP2010138254A - Method of manufacturing coke for blast furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing coke which has extremely high strength without increasing pulverized coal having the particle size of ≤0.3 mm and reducing the bulk density of blended coal. <P>SOLUTION: In the method of manufacturing coke for blast furnace by pulverizing a plurality of brands of coking coals by brands, and charging the blended coal blended to be the target coke strength DI<SP>150</SP><SB>15</SB>into a coke furnace, an inert tissue having a length size of ≥0.6 mm is divided into a size division i (=1 to m[natural number]) in length size, the degree of influence Ai(-/volume%) to coke surface breakage powder ratio DI<SP>150</SP><SB>-6</SB>of the inert tissue and/or the degree of influence Bi(-/volume%) to coke volume breakage powder ratio DI<SP>150</SP><SB>6-15</SB>of the inert tissue are predetermined by size divisions i, and the coking coals constituting the blended coal are effectively pulverized, then are blended so as to obtain the target coke strength in consideration of the difference between the degrees of influence Ai and Bi. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing coke for blast furnace using a blended coal containing non-slightly caking coal and caking coal, and in particular, in various brands of coking coal regardless of non-slightly caking coal and caking coal. The present invention relates to a method for producing coke for a blast furnace for suppressing a reduction in coke strength due to an inert (inert) structure present in the steel.

  In general, the reducing material in the iron making process and the blast furnace coke used as a heat source are obtained by pulverizing a plurality of brand raw coals, respectively, blending them at a predetermined ratio, and forming a blended coal having a predetermined particle size. It is manufactured by charging in a coke oven and dry distillation for a predetermined time.

At this time, the coke strength DI ¹⁵⁰ ₁₅ is affected by the properties of a plurality of brand raw coals constituting the blended coal and the particle size of the blended coal. Here, DI ¹⁵⁰ ₁₅ is a ratio (−) on a 15 mm sieve after 150 rotations by a drum tester stipulated in JIS K 2151, and is an index representing coke strength (also referred to as drum strength). is there.

Examples of the properties of coal that affect the coke strength DI ¹⁵⁰ ₁₅ include coal caking properties. The cohesiveness of coal can be determined from the maximum fluidity measured by a fluidity test using a JIS M 8801 Gisela plastometer and the total expansion coefficient measured by an expansion test using a dilatometer of JIS M 8801. The higher these measured values, the higher the fluidity and expansibility of the coal during softening and melting.

  Coking coal is classified into caking coal with high caking properties and non-slightly caking coal with low caking properties based on the caking properties of coal. Since caking coal has high fluidity and expansibility during softening and melting, it has an effect of facilitating adhesion between coal particles and increasing coke strength. On the other hand, non-slightly caking coal has low fluidity and expansibility during softening and melting of caking coal, so the adhesion between coal particles becomes insufficient. descend.

In addition, as a property of coal affecting coke strength DI ¹⁵⁰ ₁₅ , regardless of caking coal or non-slightly caking coal, it is a structure composed of an inert component that is present in coal and does not soften and melt when the coal is heated (hereinafter, “ "Inert organization").

  The inert structure in coal does not expand during softening and melting of coal and is difficult to contract during re-solidification of coal, thus preventing adhesion between coal particles due to expansion of coal and generating cracks during contraction of coal. Cause coke strength to decrease.

  On the other hand, the particle size of the blended coal affects the bulk density when the coke oven is charged. When the blended coal has a coarse particle size, the filling structure in the furnace approaches a close-packed structure, the bulk density when charging the coke oven is improved, and the coal particles are easily bonded and melted during softening and melting of the coal. However, if coarse coal particles are present in the blended coal, cracks are induced from the particle interface, and the fracture strength of coke is reduced.

  On the other hand, if the particle size of the blended coal is too small, the bulk density when charged in the coke oven is reduced, and the voids between the coal particles are increased, resulting in insufficient adhesion between the coal particles during softening and expansion. Coke strength decreases.

  For this reason, in general, in order to make the properties of coal uniform and maintain the bulk density at the time of coke charging at a predetermined level to increase the coke strength, the particle size of the entire blended coal is accumulated to a particle size of 3 mm or less. % Is adjusted to be 70 to 85% by mass.

  In recent years, along with the depletion of coal resources, it is possible to produce high-strength coke by using a large amount of non-slightly caking coal and using caking coal and non-slightly caking coal containing a large amount of inert tissue. It is requested.

  Using non-slightly caking coal that causes a decrease in coke strength and / or coal containing a large amount of inert structure, and ensuring a certain level of coke strength, The particle size adjustment by pulverization is important. Therefore, conventionally, several methods for pulverizing coal according to the properties and brands of coal and methods for producing high-strength coke using the same have been proposed (see Patent Documents 1 to 3).

  For example, in Patent Document 1, a plurality of brands of coal, non-slightly caking coal having an average reflectance of 0.9% by volume or less, an average reflectance of more than 0.9%, and a total inert amount of 35% are used. It is divided into high inert charcoal with volume% or more, and low inert with average reflectivity exceeding 0.9% and total inert amount less than 35 vol%, and the particle size of non-finely caking coal is 3mm or less. The mass ratio is higher than the mass ratio of 3 mm or less of the blended coal and the mass ratio of 3 mm or less of the high inert coal is less than or equal to the mass ratio of 3 mm or less of the non-slightly caking coal. A method characterized by pulverizing so that the mass ratio of the particle diameter of 3 mm or less is less than the mass ratio of the high inert coal particle diameter of 3 mm or less, mixing all the pulverized coal, and dry-distilling in a coke oven. It is disclosed.

However, even with the method described in Patent Document 1, the coke strength is DI ¹⁵⁰ ₁₅ and is about 78, and the desired coke strength may not be obtained.

  Patent Document 2 classifies coal with high hardness or coal with a large amount of inert into coal with a large particle size and coal with a small particle size, and pulverizes the coal with a large particle size (first pulverization). Step), after blending the coal treated in the first pulverization step and the small particle size coal, the blended coal is further pulverized (second pulverization step), and the remaining coal is blended and then pulverized. (Third pulverization step), and a method characterized in that it is blended with the coal treated in the second pulverization step and charged into a coke oven.

However, even with the method described in Patent Document 2, the coke strength is DI ³⁰ ₁₅ and is a maximum of 94.3 (corresponding to about 84 for DI ¹⁵⁰ ₁₅ ), and the desired coke strength may not be obtained.

As described above, the methods proposed in Patent Documents 1 and 2 mainly pulverize coal for each brand such as average reflectance of coal, properties such as inert structure, non-coking coal, and the like. The coke strength is improved by homogenizing and adjusting the particle size distribution of the entire blended coal, but in any case, the coke strength may not reach the expected DI ¹⁵⁰ ₁₅ in some cases.

  Further, according to the examination results of the present inventors, it has been confirmed that the coke strength is dominated by a coarse inert structure having a specific size or more, not the total amount of the inert structure. Coal crushing based on the total amount of inert structure in coal in the disclosed method may not sufficiently improve coke strength.

  The present applicant has recognized that there is a limit to the improvement of coke strength in the adjustment of the particle size of the coal by these methods, and the cumulative volume of the coarse inert structure having a maximum length of 1.5 mm or more in the blended coal. By investigating the relationship between the ratio and the pulverized particle size, Patent Literature 3 proposed a method for adjusting the particle size of blended coal that can produce high-strength coke.

According to the method of adjusting the particle size of the blended coal proposed in Patent Document 3, even if a large amount of low-grade non-slightly caking coal that causes a decrease in altitude is used, the strength of about 86 to 87 is obtained with DI ¹⁵⁰ ₁₅ The coke which has can be manufactured regularly.

However, in this method, when a high strength of 87 or more is required for DI ¹⁵⁰ ₁₅ , in order to reduce the cumulative volume ratio of the coarse inert structure, it is necessary to pulverize the coal with an increased pulverization strength. When the pulverization strength is increased, pulverized coal having a particle size of 0.3 mm or less is increased, and the bulk density of the entire blended coal is also decreased. Therefore, a target coke strength of 87 or more may not be achieved with DI ¹⁵⁰ ₁₅ in some cases.

  In addition, an increase in pulverized coal with a particle size of 0.3 mm or less leads to a problem of dust generation during the coal transport process and charging into the coke oven, and further, coke extrusion due to an increase in the amount of carbon adhering to the furnace wall in the coke oven. It causes an increase in load and a decrease in tar quality, which is not preferable.

Therefore, it is stable and effective while suppressing an increase in pulverized coal having a particle size of 0.3 mm or less and a decrease in bulk density (t / m ³ ) of the entire blended coal accompanying strong pulverization of coal containing a coarse inert structure. In particular, there is a need for a particle size adjustment method that can increase coke strength.

JP 2006-27384 A JP 2006-348309 A JP 2004-339503 A

  In view of the above situation of the prior art, the present invention effectively pulverizes coal containing a coarse inert structure having a maximum length of 1.5 mm or more, which causes a decrease in strength, and is associated with coal pulverization. An object of the present invention is to provide a method for producing blast furnace coke that can stably and effectively increase coke strength by suppressing an increase in pulverized coal of 0.3 mm or less and a decrease in bulk density of the entire blended coal. And

  The present inventors have intensively studied on coal pulverization, particle size adjustment, and blending that solve the above problems.

As a result, the inert structure is divided into length size and size classification i (= 1 to m [natural number]), and the influence of the inert structure on the coke surface fracture powder rate (DI ¹⁵⁰ _-6 ) for each size classification i. If the degree of influence on the coke volume fracture powder ratio (DI ¹⁵⁰ _6-15 ) of the inertness structure and / or the inert structure is determined in advance, and the pulverization and blending of the raw coal is adjusted in consideration of the difference in the degree of influence, It was found that the coke strength can be obtained.

  This invention was made | formed based on the said knowledge, The summary is as follows.

(1) In a method of producing coke for a blast furnace by pulverizing multiple brands of coking coal according to brands and charging the blended coal blended to a target coke strength DI ¹⁵⁰ ₁₅ into a coke oven,
(A) (A1) An inert structure having a maximum length of 0.6 mm or more is divided into size categories i (= 1 to m [natural number]) by length size,
(A2) Coke surface destruction of coke obtained by dry distillation of coal containing inert structures with different volume fractions (volume%) according to size category i (= 1 to m) under conditions with different average shrinkage of blended coal based on Konaritsu DI ^0.99 _-6, size levels i separately, influence a _i to the coke surface fracture powder ratio DI ^0.99 _-6 of inert tissues (- / vol%) predetermining,
(B) (B1) Containment of coarse inert structure having maximum length of 1.5 mm or more with respect to coking coal of brand j (= 1 to n [natural number]) having a cumulative particle size of 3 mm or less and 70 to 85 mass% Measure the amount (volume%) and the content Ib _{i, j} (volume%) of the inert tissue for each size category i,
(B2) Based on the measured value of the content (volume%) of the coarse inert structure, a boundary value for classifying the raw material coal of the brand j is determined within a range of 5 to 7 volume%,
(C) (C1) The raw material coal of brand j is composed of a high inert-containing coal in which the content of the coarse inert structure is equal to or higher than the boundary value, and a low inert-containing coal in which the content of the coarse inert structure is less than the boundary value. Divided into two types
(C2) Brand j ', which is classified as low-inert coal, is crushed so that the cumulative percentage of particle size 3mm or less is 70 to 85% by mass, and is classified as high-inert coal The raw coal is pulverized so that the cumulative percentage with a particle size of 3 mm or less is larger than the cumulative percentage with a particle size of 3 mm or less of the low-inert coal.
(C3) Measure the content Ia _{i, j} (volume%) of the inert structure by size category i in the coking coal by brand j after grinding,
(D) A method for producing coke for blast furnace, characterized by blending the raw material coal of brand j after pulverization so as to satisfy the following formula (1).
Target DI ¹⁵⁰ _{-6 -reference} DI ¹⁵⁰ _-6 = Σj _{= 1 to n} {Σi _{= 1 to m} A _i × (Ib _{i, j} −I a _{i, j} )}
× X _j (1)
However,
Target DI ¹⁵⁰ _-6 : Target coke strength (-)
Criteria DI ¹⁵⁰ _-6 : Coke strength of coke produced by blended coal prepared by crushing and blending all the raw material coal of brand j so that the cumulative percentage of particle size of 3 mm or less is 70 to 85 mass% (−)
X _j : Mixing ratio (mass%) of the raw material coal of brand j constituting the blended coal

(2) In a method for producing coke for a blast furnace by pulverizing multiple brands of coking coal according to brands and charging the blended coal blended to a target coke strength DI ¹⁵⁰ ₁₅ into a coke oven,
(A) (A1) An inert structure having a maximum length of 0.6 mm or more is divided into size categories i (= 1 to m [natural number]) by length size,
(A2) Coke surface destruction of coke obtained by dry distillation of coal containing inert structures with different volume fractions (volume%) according to size category i (= 1 to m) under conditions with different average shrinkage of blended coal Based on the powder rate DI ¹⁵⁰ _-6 and the coke volume fracture powder rate DI ¹⁵⁰ _6-15 , the influence degree A _i (− / volume%) of the inert structure on the coke surface fracture powder rate DI ¹⁵⁰ _-6 for each size category i And the influence degree B _i (− / volume%) of the coke volume fracture powder ratio DI ¹⁵⁰ _{6-15 of} the inert structure is determined in advance,
(B) (B1) Containment of coarse inert structure having maximum length of 1.5 mm or more with respect to coking coal of brand j (= 1 to n [natural number]) having a cumulative particle size of 3 mm or less and 70 to 85 mass% the amount (% by volume), and the content of the size classification i another inert tissue Ib _{i, j} (volume%) was measured,
(B2) Based on the measured value of the coarse inert structure content (% by volume), a boundary value for classifying the raw material coal of the brand j is determined within a range of 5 to 7% by volume,
(C) (C1) The raw material coal of brand j is composed of a high inert-containing coal in which the content of the coarse inert structure is equal to or higher than the boundary value, and a low inert-containing coal in which the content of the coarse inert structure is less than the boundary value. Divided into two types
(C2) Brand j ', which is classified as low-inert coal, is crushed so that the cumulative percentage of particle size 3mm or less is 70 to 85% by mass, and is classified as high-inert coal The raw coal is pulverized so that the cumulative percentage with a particle size of 3 mm or less is larger than the cumulative percentage with a particle size of 3 mm or less of the low-inert coal.
(C3) Measure the content Ia _{i, j} (volume%) of the inert structure by size category i in the coking coal by brand j after grinding,
(D) A method for producing coke for blast furnace, characterized by blending the raw material coal of brand j after pulverization so as to satisfy the following formula (1).
Target DI ¹⁵⁰ ₁₅ -reference DI ¹⁵⁰ ₁₅ = Σ _{j = 1 to n} {Σ _{i = 1 to m} A _i × (I b _{i, j} −I a _{i, j} )
+ Σ _{i = 1 to m} B _i × (Ib _{i, j} −I a _{i, j} )} × X _j (1)
However,
Target DI ¹⁵⁰ ₁₅ : Target coke strength (-)
Criteria DI ¹⁵⁰ ₁₅ : Coke strength of coke produced by blended coal obtained by pulverizing and blending all the raw material coals of brand j so that the cumulative percentage of particle size of 3 mm or less is 70 to 85% by mass (−)
X _j : blending ratio (mass%) of the raw material coal of brand j constituting the blended coal

  (3) When the size classification is m = 5, i = 1 (size classification 1: less than 0.6 to 1.5 mm), i = 2 (size classification 2: less than 1.5 to 3 mm), i = 3 (Size division 3: less than 3-5 mm), i = 4 (size division 4: less than 5-10 mm), and i = 5 (size division 5: 10 mm or more) 2. A method for producing coke for blast furnace according to 2.

  According to the present invention, an inert structure having a maximum length of 0.6 mm or more that causes reduction in coke strength is classified by length size, and the degree of influence on the coke strength according to the size of the inert structure is determined in advance. In consideration of the difference of the above, by effectively pulverizing and blending coal, it has extremely high strength without causing an increase in pulverized coal with a particle size of 0.3 mm or less and a decrease in bulk density of the blended coal Coke can be produced.

  In addition, even if the use ratio of low-cost non-slightly caking coal is increased, multiple brands of coking coal are grouped by the cumulative volume ratio of the inert structure, and the influence on the coke strength by the size of the inert structure The coke is pulverized and blended in consideration of the degree, and the blended coal is dry-distilled with a high degree of void filling, so that high strength and homogeneous coke can be produced.

  In general, the coke strength is governed by physical properties such as Young's modulus and defects. However, the physical properties of the coking coal used in the normal blast furnace coke production process, the blending ratio, and the Young's modulus of the coke substrate produced under the conditions of normal carbonization temperature do not change significantly. The coke strength is believed to be dominated by defects in the coke.

  There are two main types of defects in coke that control the strength of coke: structurally, poor adhesion between coal particles and coarse pores that occur during softening and expansion of coal, and other types of cracks that occur mainly during shrinkage after resolidification. Divided.

  Ordinary coke for coke production begins to soften and expand at a temperature of about 400 ° C. in a coke oven, resolidifies at a temperature of about 500 ° C., and cokes.

  During the softening and expansion of the coal, the softened and melted coal enters the gaps between the coal particles, and the coal particles adhere to each other. Thereafter, the soft and molten coal particles are re-solidified and coke, but in this process, the coal particles shrink.

  In the shrinking process after re-solidification of coal particles, if there are structures with different shrinkage rates in the coal particles, a shrinkage difference occurs between these structures, and cracks are generated in the coal particles. The cracks in the coal particles serve as a starting point for the destruction of the coke and cause a reduction in the coke strength.

  The inert structure present in coal is a structure that has less volatile content, hardly expands during softening / expansion of coal, and has a low shrinkage rate after resolidification, compared to vitrinite and exignite structures that soften and melt when heated. is there.

  Cracks that occur during shrinkage after coal resolidification are caused by stress at the interface of the inert structure due to the difference in shrinkage rate between the inert structure and the softened molten structure such as vitrinite structure and exitnite structure. It is considered that the main cause is the occurrence of cracks.

  According to the results of our investigation on coking coal for coke, the shrinkage rate of softened molten structures such as vitrinite structure and exitnite structure contained in the coal has a range of 12 to 16%. The shrinkage rate of the inert structure was constant at about 10% regardless of the coal brand.

  Therefore, the decrease in coke strength due to the occurrence of cracks occurring at the time of shrinkage after resolidification of coal depends on the difference between the shrinkage rate of the inert structure and the shrinkage rate of the softened molten structure such as the vitrinite structure and the exitnite structure, This difference in shrinkage rate is considered to be determined by the average shrinkage rate of the blended coal because the shrinkage rate of the inert structure is almost constant.

  In addition, the shrinkage rate of the inert structure | tissue in coal can be measured with the following method.

  Since the inert structure in coal has a larger specific gravity than other softened and melted structures such as a vitrinite structure and an exitnite structure, it can be separated by a specific gravity difference using a heavy liquid.

Specifically, coal is finely pulverized to a particle size of 75 μm or less, suspended in a specific gravity solution of a zinc chloride aqueous solution having a specific gravity of 1.5 to 1.7 g / cm ³ , and then subjected to centrifugal sedimentation. Concentrate the inert. About this inert concentrate, while measuring inert purity by the structure | tissue analysis using a microscope, according to the measuring method of the shrinkage rate of coal disclosed by Unexamined-Japanese-Patent No. 2005-232349 etc., the shrinkage rate of an inert concentrate Measure.

  Specifically, the inert concentrate (sample) is charged into a container, and the coal is heated from normal temperature to a temperature T higher than the resolidification temperature (for example, T = 1000 ° C.) (° C.) in an electric furnace, A value obtained by dividing the volume difference or length difference of the contents at the resolidification temperature and the temperature T by the volume or length at the resolidification temperature is defined as a shrinkage rate of the inert concentrate (sample).

Volume of inert concentrate (sample) at resolidification temperature: V _R and length: L _R , Volume of inert concentrate (sample) at temperature T: V _T and length: L _T The coke shrinkage ratio R (−) can be defined by the following equation (a) or (b).
R = (V _R −V _T ) / V _R (a)
R = (L _R −L _T ) / L _R (b)

  In addition, when an inert tissue having a purity of 100% cannot be obtained by the above-described inert tissue separation method, the shrinkage rate of separated inert concentrates (samples) with different purity is measured, and extrapolation is performed based on these. Thus, the shrinkage rate of 100% pure inert tissue can be obtained.

  The shrinkage rate of the softened molten structure such as vitrinite structure or exitnite structure in coal is also measured by the above method.

  FIG. 1 shows an example of an inert structure existing in coke and surrounding structures. Since the inert structure does not soften and melt by heating and remains in the coke, the size can be measured by observing the cross-sectional structure of coke or coal as shown in FIG. 1 with a microscope. In addition, in this invention, the size of the inert structure | tissue in coal shall mean the maximum length (mm).

  The size (maximum length) of the inert structure in FIG. 1 is a little less than 3 mm, but the inert structure usually exists in a wide range of sizes (maximum length) of 0.1 μm to 10 mm in coal.

  As a result of the study by the present inventors, cracks in coke that cause a significant decrease in coke strength are generated in or around a coarse inert structure having a size (maximum length) of the order of mm (1.0 mm or more). It is confirmed that the crack is a large crack on the order of mm (1.0 mm or more) (see FIG. 1. Cracks are generated around the inert structure).

  In other words, according to Griffith's fracture condition formula (see, for example, “J.F. Knott (translated by Hiroshi Miyamoto),“ Fundamental Mechanics ”, p. 107) [issued by Baifukan (1977)]), a large crack is Since the crack grows and expands with a lower stress than a small crack, a large crack in the order of mm generated in or around a coarse inert structure acts as a starting point (defect) for brittle fracture when coke is impacted.

  Therefore, coke containing a large number of large cracks on the order of mm (1.0 mm or more) is extremely low in strength and easily pulverizes.

  Based on the above knowledge, the present applicant, based on the relationship between the cumulative volume ratio of the coarse inert structure having a maximum length of 1.5 mm or more and the pulverized particle size in the coal constituting the coal blend, Patent Document 3 proposed a particle size adjustment method for increasing coke strength by pulverization.

According to the method for adjusting the particle size of the blended coal proposed in Patent Document 3, even if a large amount of low-grade non-slightly caking coal that causes a decrease in strength is used, the strength of about 86 to 87 is obtained with DI ¹⁵⁰ ₁₅ The coke which has can be manufactured regularly.

However, when trying to achieve a high coke strength of DI ¹⁵⁰ ₁₅ 87 or higher by the above method, it is necessary to increase the pulverization strength of coal in order to reduce the cumulative volume ratio of the coarse inert structure. Then, pulverized coal with a particle size of 0.3 mm or less increases, the bulk density of the entire blended coal also decreases, and a coke strength of 87 or more may not be achieved with the target DI ¹⁵⁰ ₁₅ .

  In addition, an increase in pulverized coal having a particle size of 0.3 mm or less leads to a problem of dust generation during the coal transportation process and charging into the coke oven, and further, an increase in coke extrusion load due to the generation of precarbon in the coke oven. In addition, the tar quality is deteriorated, which is not preferable.

  Therefore, the present inventors classify the coarse inert structure by the length size, predetermine the degree of influence on the coke strength by the size of the structure, considering the difference in the degree of influence, the particle size of 0.3 mm or less An effective pulverization and blending method for producing coke having extremely high strength without causing an increase in pulverized coal and a decrease in bulk density of the blended coal was further studied.

Specifically, as will be described below, coal containing an inert structure having different volume fractions (volume%) by size category is subjected to dry distillation for each condition in which the average shrinkage ratio of the blended coal differs, and the coke strength DI ^{150 is set.} ₁₅ was measured, and the influence on the strength DI ¹⁵⁰ ₁₅ of the coke of the inert structure was examined according to the size classification of the inert structure.

  As a coal, a single brand of coal (a brand of coal containing almost no inert structure), No. 1: Less than 0.1-0.3 mm, No. 2: Less than 0.3-0.6 mm, No. 3: Less than 0.6 to 1.5 mm. 4: 1.5-3.0 mm, no. 5: 3.0 to less than 5.0 mm, No. 5 6: 5.0 to less than 10.0 mm, and 7: Charcoal blended with 10% each of inert structures of different sizes adjusted by sieving into 7 grades of particle size fraction of less than 10-15mm, and preparing these 7 types (Nos. 1-7) Coke was carbonized in a carbonization furnace under the three conditions of 16%, 14%, and 12% of the average shrinkage of the blended coal to produce coke.

  And the size (maximum length) of the inert structure | tissue in coal and the volume ratio of the inert structure | tissue according to size classification were measured with the following method.

  The measurement of the size (maximum length) of the inert structure in coal and the volume ratio of the inert structure for each size category can be performed, for example, by the measurement method described in JP-A-2004-339503.

  In other words, resin was embedded in the cut surface of the obtained coke, the cut surface was photographed with a microscope, and the inert tissue was marked in the photograph of the cut surface, and the size of the inert tissue ( The maximum length) and the area ratio (area%) are measured, and the volume ratio (volume%) of the inert tissue can be obtained for each size classification of the inert structure from these measured values.

  In FIG. 2, the size distribution of the inert structure | tissue which exists in seven types of combination charcoal (No. 1-7) is shown. In addition, the size of the inert structure | tissue shown on the horizontal axis | shaft of FIG. 2 shows the maximum length (mm) of the inert structure | tissue measured by the said method. The vertical axis represents the cumulative volume fraction (volume%) of the inert tissue measured for each size category.

3 (a) to 3 (c), the average shrinkage of the seven types of blended coals (No. 1 to 7) is 16%, 14%, and 12% under three conditions. .1-7) shows the coke surface breaking powder ratio DI ¹⁵⁰ _-6 of coke obtained by dry distillation. Similarly, FIGS. 4A to 4C show the coke volume breaking powder ratio DI ¹⁵⁰ _6-15 when the average shrinkage is 16%, 14%, and 12%.

Here, the coke surface breaking powder ratio DI ¹⁵⁰ _-6 indicates a ratio (powder ratio) (−) under 6 mm sieve after 150 rotations by a drum tester defined in JIS K 2151, and the coke volume breaking powder ratio. DI ¹⁵⁰ _6-15 indicates a ratio (powder ratio) (−) on a 6 mm sieve after 150 rotations and a 15 mm sieve under the drum tester specified in JIS K 2151.

The relationship between the coke strength DI ¹⁵⁰ ₁₅ that is used as a normal control index for coke strength, the coke surface fracture powder rate DI ¹⁵⁰ _-6 , and the coke volume fracture powder rate DI ¹⁵⁰ _6-15 is expressed by the following equation (2). be able to.
DI ¹⁵⁰ ₁₅ = 100- (DI ¹⁵⁰ _-6 + DI ¹⁵⁰ _6-15 ) (2)

The coke surface breaking powder ratio DI ¹⁵⁰ _-6 is a powder ratio caused by a small defect caused by a local adhesion failure portion between coal particles, a minute size pore, and an inert structure because the fracture unit is small. Coke volume fracture powder ratio DI ¹⁵⁰ _6-15 has a larger fracture unit than DI ¹⁵⁰ _-6 , so it is a powder ratio caused by coarse defects such as connected pores and coarse size pore structure and coarse structure. is there.

FIG. 3 (a) shows that when the average shrinkage of the blended coal is 16%, the length of the inert structure existing in the blended coal (maximum length) is less than 0.6 mm (the inert structure of the sieving maximum size, Nanba1～2 coal blend of less than 0.6 mm), the coke surface-breaking dust index DI ^0.99 _-6 low as about 12.9, the influence of the coke surface fracture powder ratio DI ^0.99 _-6 is small.

Moreover, when the size of the inert structure | tissue which exists in coal is 0.6 mm or more and less than 3.0 mm (the length size of the inert structure | tissue by sieving is No. 3-4 less than 0.6-3.0 mm) In the case of the blended coal), the coke surface breaking powder ratio DI ¹⁵⁰ _-6 increases as the size of the inert structure increases.

Furthermore, when the length size of the inert structure | tissue which exists in coal becomes 3 mm or more (The length size of the inert structure | tissue by sieving is No. 5-7 coal blend which is less than 3.0-15mm), coke surface The breaking powder ratio DI ¹⁵⁰ _-6 is constant at about 15.5 (−).

As shown in FIG. 3B, when the average shrinkage of the blended coal is 14%, the length of the inert structure existing in the blended coal (maximum length) is less than 1.5 mm (the inert structure by sieving). No. 1 to 3 in which the length size of the coke is less than 1.5 mm), the coke surface breaking powder rate DI ¹⁵⁰ _-6 is as low as about 12.2, and the coke surface breaking powder rate DI ¹⁵⁰ _-6 The impact on is estimated to be small.

Moreover, when the length size of the inert structure | tissue which exists in coal is 1.5 mm or more and less than 5 mm (The length size of the inert structure | tissue by sieving is mixing No. 4-5 less than 1.5-5 mm) In the case of charcoal, the coke surface breaking powder ratio DI ¹⁵⁰ _-6 increases as the length of the inert structure increases.

Further, when the length of the inert structure present in the coal is 5 mm or more (the blended coal of No. 6 to 7 whose length of the inert structure by sieving is less than 5 to 15 mm), the coke surface breaking powder The rate DI ¹⁵⁰ _-6 is constant at about 14.2 (−).

From FIG. 3 (c), when the average shrinkage of the blended coal is 12%, the length of the inert structure (maximum length) present in the blended coal is less than 1.5 mm (the inert structure by sieving). the length size of less than 1.5mm coal blend of Nanba1～3) is coke surface-breaking dust index DI ^0.99 _-6 as low as about 11.8, coke surface-breaking dust index DI ^0.99 _-6 The impact on is estimated to be small.

Moreover, when the length size of the inert structure | tissue which exists in coal will be 3 mm or more (the length size of the inert structure | tissue by sieving is No. 5-7 coal mix of less than 3.0-15mm), an inert structure | tissue As the size of the coke increases, the coke surface breaking powder ratio DI ¹⁵⁰ _-6 increases.

From the other experimental results of the present inventors, in FIG. 3 (c), the coke volume breaking powder ratio DI ¹⁵⁰ _{-6 in} the case where the size of the inert structure present in the blended coal is 15 mm or more is No. It was confirmed that the same DI ¹⁵⁰ _-6 (= 13.7 (−)) as in the case of using the 7 coal blend was constant.

As described above, from FIGS. 3A to 3C, the length size of the inert structure that is present in the blended coal and has an effect on the coke surface breaking powder ratio DI ¹⁵⁰ _-6 as the average shrinkage of the blended coal increases. (Maximum length) is shifted to the fine-grained side, and the blended coal with a high average shrinkage of the blended coal (a) is compared with the blended coal with a low average shrinkage of the blended coal (c). It can be seen that the increase rate of the coke surface breaking powder ratio DI ¹⁵⁰ _-6 for the inert structure of the same length size is large.

  The reason is considered as follows.

  The size of a crack (crack) generated around an inert structure when coke breaks is proportional to the size of the inert structure. Regarding the strength of a brittle body such as coke, the fracture toughness value K in the plane tensile stress state when a crack having a length of 2c exists is expressed by the following equation (3) (Gillifis fracture condition equation).

K = σ√πc (3)
K [Pa · m ^1/2] of fracture toughness value, sigma [Pa] of tensile stress, c [m] is the crack half length.

  The above equation (3) is an equation for predicting the critical value of the size at which the crack starts to progress, and the crack progresses when σ√πc on the right side reaches the value of K on the left side.

  Even if the average shrinkage of blended coal increases, the shrinkage of the inert structure is constant at around 10%, so there is a large difference in shrinkage between the inert structure and the softened molten structure such as the vitrinite and surrounding structures. Become. Due to the increase in the difference in shrinkage rate, the strain near the interface between the inert structure and the surrounding softened molten structure increases, and the tensile stress σ on the right side of the equation (3) increases.

For this reason, even when the crack half length c on the right side of the above equation (3) is small, it becomes easy to reach the fracture toughness value K. For this reason, as shown in FIG. With this, it is considered that the change area of the influence degree A _i on the surface breaking powder ratio DI ¹⁵⁰ _-6 shifts the length size of the inert structure to the fine grain side.

From these findings, for coal containing an inert structure with a maximum length of 0.6 mm or more, the coke surface fracture powder ratio DI ¹⁵⁰ _-6 of the inert structure by size classification is 0.6 mm or more. When determining the influence degree A _i (− / volume%), the inert tissue is classified into five size categories (for example, less than 0.6 to 1.5 mm, and less than 0.6 to 15 mm). It is understood that it is necessary to determine the degree of influence A _i for each size category by dividing it into less than 5 to 3 mm, less than 3 to 5 mm, less than 5 to 10 mm, and 10 m or more.

  In the experiment which acquired the said knowledge, the inert structure | tissue whose length size is 0.6 mm or more was divided into five size classifications, but it is not necessary to restrict to five size classifications. According to the length of the maximum length of the inert structure, the interval may be appropriately determined and divided into an appropriate number (i = 1 to m [natural number]) size categories.

On the other hand, as shown in FIGS. 4A to 4C, the coke volume breaking powder ratio DI ¹⁵⁰ _6-15 is the length size of the inert structure present in the blended coal regardless of the average shrinkage of the blended coal. When the (maximum length) is less than 5.0 mm (the blended charcoal of No. 1 to No. 5 in which the length of the inert structure by sieving is less than 5.0 mm) is as low as about 1.2 (−). The effect on the coke volume breaking powder ratio DI ¹⁵⁰ _6-15 is small.

In addition, when the length of the inert structure existing in the blended coal is 5 mm or more (the blended coals of No. 6 to 7 in which the length of the inert structure by sieving is less than 5.0 mm), the inert The coke volume breaking powder ratio DI ¹⁵⁰ _6-15 increases with the length size of the tissue.

In addition, from other experimental results of the present inventors, in FIGS. 4A to 4C, the coke volume breaking powder ratio DI ¹⁵⁰ _{6 in} the case where the length size of the inert structure present in the blended coal is 15 mm or more. _-15 is No. It was confirmed that the same DI ¹⁵⁰ _6-15 (= 2.2 (−)) as in the case of using the 7 coal mixture was constant.

As shown in FIGS. 4A to 4C, the increase in the coke volume breaking powder ratio DI ¹⁵⁰ _6-15 does not change depending on the average shrinkage ratio of the blended coal. This is because a large-sized crack (crack) that affects the coke volume fracture powder ratio DI ¹⁵⁰ _6-15 develops regardless of the fracture toughness value K of the matrix portion around the inert structure.

From these findings, for coal containing an inert structure with a length of 0.6 mm or more, the influence of the coarse inert structure by size classification on the coke volume fracture powder ratio DI ¹⁵⁰ _6-15 at 0.6 mm or more When determining the degree B _i (− / volume%), the inert tissue size category is 0.6 to less than 5 mm, at least one size category, and 5 mm or more and at least two size categories (for example, 5 and less to 10 mm, 10 mm or more) and, in total, divided into three size levels, size levels separately, it is understood that it is necessary to determine the degree of influence B _i.

As in the case of determining the degree of influence A _i , the number of size categories is determined appropriately according to the length of the maximum length of the inert tissue, and an appropriate number (i = 1 to m [natural number]). ).

Based on the results of FIG. 3 and FIG. 4, in FIGS. 5A to 5C, the length existing in the coal under the conditions where the average shrinkage of the blended coal is 16%, 14%, and 12%. Coarse inert structures with a size of 1.5 mm or more are classified by length, and the coke surface breaking powder ratio DI ¹⁵⁰ _-6 and the coke volume breaking powder ratio DI ¹⁵⁰ _6-15 are measured for each size classification, and i = 1 (Size category 1: 0.6 to less than 1.5 mm), i = 2 (Size category 2: less than 1.5 to 3 mm), i = 3 (Size category 3: less than 3 to 5 mm), i = 4 (Size) Category 4: Less than 5 to 10 mm) and size category i of i = 5 (size category 5: 10 mm or more), the influence degree A _i (− / volume) of the inert structure on the coke surface fracture powder ratio DI ¹⁵⁰ _-6 %), and, the degree of influence on the coke volume breakdown powder ratio DI ¹⁵⁰ _6-15 B _i (- / vol%) constant Indicating the example.

In the present invention, the influence degree A _i (− / volume%) of the inert structure by size category i on the coke surface breaking powder rate DI ¹⁵⁰ _-6 and the degree of influence on the coke volume breaking powder rate DI ¹⁵⁰ _6-15 B _i (− / volume%) is the coke surface breaking powder ratio DI ¹⁵⁰ ₋₆ per 1% volume ratio of the inert structure existing in the size category i in coke co-distilled under different conditions of the average shrinkage of the blended coal, and The degree of influence of the coke volume breaking powder ratio DI ¹⁵⁰ _6-15 is shown respectively.

Specifically, the degree of influence A _i (− / volume%) on the coke surface fracture powder rate DI ¹⁵⁰ _-6 for each size category i (= 1 to m) of the inert structure and the coke volume fracture powder rate DI ¹⁵⁰ _{6 -15} influence level B _i (− / volume%) can be obtained by regression analysis by the least square method of the following formulas (4) and (5).

DI ¹⁵⁰ ₋₆ (−) − reference DI ¹⁵⁰ ₋₆ = Σ _{i = 1 to m} A _i × Ib _{i, j} (4)
DI ¹⁵⁰ _6-15 (-) - reference _{^{DI 150 6-15 = Σ i = 1}} ~ m B i × Ib i, j ··· (5)
Here, Ib _{i, j} is the content (volume%) of the inert structure of size category i (= 1 to _m ).

j is a brand of raw coal constituting the blended coal. DI ¹⁵⁰ _-6 and DI ¹⁵⁰ _6-15 have an inert structure with a length size of 0.6 mm or more that has a large effect on coke surface fracture strength (-) and coke volume fracture strength (-). Coke surface fracture strength (-) and coke volume fracture strength (-) of coke produced using coal pulverized to satisfy i (= 1 to m).

The standard DI ¹⁵⁰ _-6 and the standard DI ¹⁵⁰ _6-15 have zero length of the inert structure (maximum length) that has no effect on the coke surface fracture strength (-) and the coke volume fracture strength (-), respectively. The coke surface fracture strength (-) and coke volume fracture strength (-) of coke produced using coal pulverized to be less than 6 mm are shown.

In the case of m = 5, it can obtain | require by the regression analysis by the least square method of following formula (4 ') and (5').
DI ¹⁵⁰ ₋₆ (−) − reference DI ¹⁵⁰ ₋₆ = Σ _{i = 1 to 5} A _i × Ib _{i, j} (4 ′)
DI ¹⁵⁰ _6-15 (−) − reference DI ¹⁵⁰ _6-15 = Σ _{i = 1 to 5} B _i × Ib _{i, j} (5 ′)

Here, Ib _{i, j} is, for example, i = 1 (size category 1: less than 0.6 to 1.5 mm), i = 2 (size category 2: less than 1.5 to 3 mm), i = 3 (size) Category 3: Less than 3 to 5 mm), i = 4 (Size category 4: Less than 5 to 10 mm), and i = 5 (Size category 5: 10 mm or more) The content of inert tissue by size category i (volume%) ).

For example, when m = 5, the reference DI ¹⁵⁰ _-6 and the reference DI ¹⁵⁰ _6-15 have an average shrinkage of the blended coal of 14 as shown in FIGS. 3 (b) and 4 (b). when percent, respectively, 12.2 (DI ^0.99 _-6 coal Nanba1～3), and a 1.2 (DI ^0.99 _6-15 of coal No.1~4).

In addition, the influence degree A _i (− / volume%) of the inert structure for each size category i on the coke surface fracture powder ratio DI ¹⁵⁰ _-6 and the influence degree B on the coke volume fracture powder ratio DI ¹⁵⁰ _6-15 It has been confirmed that additivity is established between _i (− / volume%) and the content Ib _{i, j} (volume%) of the inert structure for each size category i.

Further, the influence degree A _i (− / volume%) and the influence degree B _i (− / volume%) are less affected by the difference in the coal brand j (= 1 to n [natural number]), and the coal brand j Regardless of whether or not

Therefore, the change [Delta] Di ^0.99 _-6 coke surface fracture powder ratio DI ^0.99 _-6 by milled particle size changes in the raw material coal grade j and the change [Delta] Di ^0.99 _6-15 coke volume breakdown powder ratio DI ^0.99 _6-15 is stocks Change in the content of the inert structure of size category i due to the change in the pulverized particle size of the raw coal of _j. Effect of the measured value of Ib _{i, j} (volume%) on the coke surface fracture powder ratio DI ¹⁵⁰ _-6 Based on the degree A _i (− / volume%) and the influence degree B _i (− / volume%) on the coke volume fracture powder ratio DI ¹⁵⁰ _6-15 , the following formulas (6) and (7) are used. be able to.

ΔDI ¹⁵⁰ ₋₆ (−) = Σ _{i = 1 to m} A _i × ΔIb _{i, j} (6)
ΔDI ¹⁵⁰ _6-15 (−) = Σ _{i =} 1˜m B _i × ΔIb _{i, j} (7)

Furthermore, from the above equation (2), the coke strength change ΔDI ¹⁵⁰ ₁₅ when the raw material coal of brand j (= 1 to n) is pulverized under predetermined conditions can be expressed by the following equation (8).
_{^{ΔDI 150 15 (-) = Σ}} i = 1 ~ m A i × ΔIb i, j + Σ i = 1 ~ m B i × ΔIb i, j ··· (8)

Above (8), the stock j when the milled particle size of the raw coal was changed in (= 1 to n), from an expression showing changes in coke strength DI ^0.99 _15, coke surface-breaking dust index DI ^0.99 _- influence a _i to _6, and / or, as the content of inert tissue influence B _i to coke volume breakdown powder ratio DI ^0.99 _6-15 corresponds to a larger size levels i (vol%) is reduced This suggests that the coke strength DI ¹⁵⁰ ₁₅ can be effectively increased by pulverizing the raw coal.

The present invention pulverizes and blends multiple brands of coking coal according to brand, forms blended coal so as to have a target coke strength DI ¹⁵⁰ _15, and then charges the blended coal into a coke oven and dry-distills it for blast furnace. In the method for producing coke, an inert structure having a length size of 0.6 mm or more is classified according to the length size, resulting in a decrease in coke strength, with respect to coke that has been carbonized under conditions in which the average shrinkage ratio of the blended coal differs. Increase in the number of pulverized coal with a particle size of 0.3 mm or less by effectively crushing coking coal in consideration of the difference in the degree of influence on coke strength (influence degree A _i and influence degree B _i ) by size category In addition, the basic technical idea is to produce coke having extremely high strength without causing a decrease in the bulk density of the blended coal.

For this reason, in the present invention, the coke strength DI ¹⁵⁰ ₁₅ used as the reference is that the pulverization condition of the blended coal is all the raw material coal of the brand j constituting the blended coal, and the cumulative percentage with a particle size of 3 mm or less is 70 to 85. The coke strength (−) of the blended coal pulverized so as to have a particle size of mass% (control standard particle size in normal coke operation).

  Then, the coarse coal texture of the brand j constituting the blended coal is defined with the content of the coarse inert structure having a length size of 1.5 mm or more existing in the raw coal as “5-7% by volume” as a boundary value. Coal coal of brand j ', which is classified into two types: high inert coal with a content of not less than the boundary value and low inert coal with a content of the above inert structure less than the boundary value. The raw material coal of grade j "classified as high-inert coal is low in the cumulative% of particle size of 3 mm or less, and the cumulative% of particle size of 3 mm or less is reduced to a particle size of 70 to 85% by mass. It grind | pulverizes so that it may become larger than accumulation% with a particle size of 3 mm or less of an inert containing charcoal.

The reason why the pulverization condition of the blended coal having the standard coke strength DI ¹⁵⁰ ₁₅ is 70% or more of the cumulative percentage of the particle size 3 mm or less of all the brand j coals constituting the blended coal is as follows. It is.

  6 and 7, the pulverized particle size (cumulative ratio (mass%) of particle size of 3 mm or less) of the high inert content coal (A charcoal) and the low inert content coal (B charcoal) and the inert structure of each size or more. Shows the relationship with the cumulative volume ratio (volume%).

  From these figures, when the cumulative percentage of 3 mm or less is less than 70%, not only high inert coal (A charcoal) but also low inert coal (B charcoal) is very coarse of 10 mm or more and 5 mm or more. It can be seen that the cumulative volume ratio of the inert structure increases significantly.

These coarse inert structures induce cracking from the particle interface and significantly reduce the fracture strength of the coke. Therefore, under the pulverization conditions of the blended coal having the standard coke strength DI ¹⁵⁰ ₁₅ , all of the brand j raw coal is pulverized so that the cumulative percentage with a particle size of 3 mm or less becomes 70% or more.

The reason for setting the pulverization conditions of the blended coal to be the standard coke strength DI ¹⁵⁰ ₁₅ to be 85% or less of the cumulative percentage with the particle size of 3 mm or less for all of the brand j raw coals constituting the blended coal is as follows. It is.

If the particle size of the blended coal is too small, the bulk density when charged in the coke oven will decrease, and the voids between the coal particles will increase, so the coal particles will have insufficient adhesion during softening and expansion of the coal, Coke strength decreases. Therefore, in the pulverization of the blended coal having the standard coke strength DI ¹⁵⁰ ₁₅ , all of the brand j raw coal is pulverized so that the cumulative percentage with a particle size of 3 mm or less is 85% or less.

  On the other hand, the reason why the boundary value for classifying the high inert content coal and the low inert content coal is set within the range of 5 to 7% by volume of the inert structure is as follows.

  When the content of the inert structure is divided into volume percentages of less than 5% by volume, brands of coal having a relatively low content of the inert structure are also subject to strong pulverization. As shown in FIG. 7, the coal type with a small content of the inert structure increases even if the cumulative percentage of 3 mm or less exceeds the normal pulverized particle size (cumulative percentage of 3 mm or less is 70 to 85 mass%). That is, even if pulverized strongly, the margin of decrease in the cumulative volume ratio of the inert structure is small.

  Therefore, strong pulverization does not contribute to the improvement of coke strength, and strong pulverization causes only an increase in pulverized coal having a particle size of 0.3 mm or less and a decrease in bulk density of the blended coal.

  When the content of the inert structure is classified by volume% exceeding 7% by volume, a large amount of inert remains in the raw coal having a relatively high content of the inert structure that is not subject to strong pulverization. Therefore, the coke strength cannot be sufficiently increased.

  The raw coal of grade j ″ classified as high inert coal is pulverized so that the cumulative percentage with a particle size of 3 mm or less is larger than the pulverized particle size of low inert coal. Compared to strong crushing.

At this time, the influence degree A _{i of} the inert structure existing in the coking coal of the grade j ″ classified as the high inert content coal on the coke surface fracture powder rate DI ¹⁵⁰ _-6 and the coke volume fracture powder rate DI ¹⁵⁰ ₆₋ Based on the degree of influence B _i on ₁₅ , the raw coal is pulverized so that the content (volume%) of the inert structure corresponding to the size category i having a large degree of influence is intensively reduced.

  In this way, the raw coals of each brand constituting the blended coal are divided into two types: high inert content coal with an inert structure content equal to or higher than the boundary value, and low inert content coal with an inert structure content less than the boundary value. By classifying and pulverizing under each pulverization condition, it is possible to produce coke with extremely high strength without causing an increase in pulverized coal with a particle size of 0.3 mm or less and a decrease in the bulk density of the blended coal. It becomes.

  In the present invention, when the raw material coal of the brand j corresponding to the high inert content coal and the low inert content coal is pulverized to the respective pulverized particle sizes and blended, the brand j raw coal constituting the blended coal is expressed by the following (1x ) Formula or (1y) Formula is satisfied. This point is also a feature of the present invention.

Target DI ¹⁵⁰ _{-6 -reference} DI ¹⁵⁰ _-6 = Σj _{= 1 to n} {Σi _{= 1 to m} A _i × (Ib _{i, j} −I a _{i, j} )}
× X _j (1x)
Target DI ¹⁵⁰ ₁₅ -reference DI ¹⁵⁰ ₁₅ = Σ _{j = 1 to n} {Σ _{i = 1 to m} A _i × (I b _{i, j} −I a _{i, j} )
+ Σ _{i = 1 to m} B _i × (Ib _{i, j} −I a _{i, j} )} × X _j (1y)

However,
Target DI ¹⁵⁰ ₁₅ , Target DI ¹⁵⁰ _-6 : Target coke strength (-)
Standard DI ¹⁵⁰ ₁₅ , Standard DI ¹⁵⁰ _-6 : Coke strength (−) of blended coal obtained by pulverizing all the raw material coals of brand j so that the cumulative percentage with a particle size of 3 mm or less is 70 to 85 mass%.
i (= 1 to m [natural number]): size of inert tissue having a maximum length of 0.6 mm or more (size is measured by the maximum length (mm))
j (= 1 to n [natural number]): Brand of coking coal constituting blended coal A _i : Coke surface of inert structure by size category i obtained by dry distillation of blended coal under conditions with different average shrinkage ratios Degree of influence on breaking powder ratio DI ¹⁵⁰ _-6 (-/ vol%)
B _i : The degree of influence (− / volume%) on the coke volume fracture powder ratio DI ¹⁵⁰ _6-15 of the inert structure by size category i obtained by dry distillation of blended coal under conditions with different average shrinkage rates
Ib _{i, j} : Content of inert structure by volume category (volume%) in coking coal of grade j having a cumulative particle size of 3 mm or less and 70 to 85 mass%
Ia i, _j: the low inert-containing coal, ground to a particle size less than 3mm cumulative% is 70 to 85 wt%, a high inert-containing coal, cumulative% of particle size less than 3mm, low inert-containing coal The content of the inert structure by volume category (volume%) in the raw coal by brand j after pulverization to be larger than the cumulative percentage of 3 mm or less of particle size
X _j : blending ratio (mass%) of the raw material coal of brand j constituting the blended coal

The inert tissue size category i (= 1 to m [natural number]) is assumed to be m = 5.
Size category 1: 0.6 to less than 1.5 mm, Size category 2: less than 1.5 to 3 mm, Size category 3: less than 3 to 5 mm, Size category 3: less than 5 to 10 mm, and Size category 5: 10 mm or more ).

First, the above equation (1y) will be described. Above (1y) expression (7) above proportion X _j coking coal of Formula stocks j is applied to (mass%), coke strength of coke strength (DI ^0.99 ₁₅₎ and reference (reference DI ^0.99 ₁₅₎ On the other hand, in order to improve to the target coke strength (target DI ¹⁵⁰ ₁₅ ), the inclusion of the inert structure by size category i in the stock coal of brand j having a cumulative percentage of particle size of 3 mm or less of 70 to 85% by mass the amount Ib _i, with respect to _j, in the raw material coal in stock j after grinding, determines the milling conditions of whether content Ia i of size level i another inert _{tissue, j,} it is only necessary to what extent changes in formula It is.

In addition, in the blended coal in which the brand j coking coal is blended at a predetermined blending ratio X _j (mass%), as shown in the above formula (1y), the coke strength DI ¹⁵⁰ of the brand j coking coal is ^150. _15, with the mixing ratio X _j coking coal stocks j, formed of pressure is known to be established.

In the above equation (1y), the target coke strength (target DI ¹⁵⁰ ₁₅ ) is set according to the demands of coke oven productivity and blast furnace coke quality. (Standard DI ¹⁵⁰ ₁₅ ) is, as described above, the coke strength (−) of the coal blend obtained by pulverizing all the raw material coal of the brand j so that the cumulative percentage of the particle size of 3 mm or less is 70 to 85 mass%. To do.

In the present invention, the target coke strength (target DI ¹⁵⁰ ₁₅ ) is not particularly limited. In the present invention, for example, when the target coke strength (target DI ¹⁵⁰ ₁₅ ) is 86 or more, and further 87 or more, the particle size is 0.3 mm or less accompanying the strong pulverization of coal containing a nart structure. The coke strength can be increased stably and effectively by suppressing an increase in pulverized coal and a decrease in the bulk density of the blended coal as a whole.

Next, the formula (1x) will be described. As shown in FIG. 5, the size classification i another inert tissue coke volume impact B _i to destruction powder ratio DI ¹⁵⁰ _6-15 (- / vol%) variation of) the Alternative size level i of inert tissue Since the change in the influence degree A _i (− / volume%) on the coke surface breaking powder ratio DI ¹⁵⁰ _-6 is small, the change in the influence degree B _i (− / volume%) is approximately zero. can do.

Since the change in B _i is small in the above expression (1x), in the above expression (1y), (i) Σ _{i = 1 to m} B _i × (Ib _{i, j} −Ia _{i, j} ) = 0, coke strength and (ii) the target and reference, DI ¹⁵⁰ _-6 (target DI ^0.99 _-6, reference DI ^0.99 _-6) and was an expression.

  Using a test coke oven capable of simulating an actual coke oven, four types of coal shown in Table 1 (A1 coal to D1 coal) were used, and a coal dry distillation test and coke -An evaluation test was conducted.

  In addition, the shrinkage | contraction rate of the inert structure | tissue of coal was measured with the following method.

The coal is finely pulverized to a particle size of 75 μm or less, and this is suspended in a specific gravity solution of a zinc chloride aqueous solution having a specific gravity of 1.5 to 1.7 g / cm ^3. Concentrated. About this inert concentrate, while measuring inert purity by the structure | tissue analysis using a microscope, according to the measuring method of the shrinkage rate of coal disclosed by Unexamined-Japanese-Patent No. 2005-232349 etc., the shrinkage rate of an inert concentrate Based on these measured values, the shrinkage rate of an inert tissue having a purity of 100% was determined.

The shrinkage rate of the inert concentrate is measured by charging the above-described inert concentrate (sample) into a container and heating the coal from room temperature to a temperature T = 1000 ° C. (° C.) above the resolidification temperature in an electric furnace. Based on the measured value of the content length L _R at the re-solidification temperature and the content length L _{T at} the temperature T, the inert concentrate (sample) at the temperature T using the following equation (b) The shrinkage ratio R was determined.
R = (L _R −L _T ) / L _R (b)

  The average shrinkage of coal was also measured by the above method.

  Coarse inert tissue content (volume%) TI with a maximum length of 1.5 mm or more is embedded in resin in the cut surface of coke obtained by dry distillation of the coal to be measured, and the cut surface is photographed with a microscope After that, the inert structure in the cut surface photograph is marked, and the size (maximum length) of the inert structure and the area ratio (area%) are measured using image analysis software. From these measured values, the inert structure of the inert structure is measured. The volume ratio (volume%) of the inert structure is obtained for each size category, and the cumulative percentage of coarse inert structures having a maximum length of 1.5 mm or more can be calculated (for example, JP-A-2004-339503, reference).

  First, A1 charcoal to D1 charcoal shown in Table 1 are pulverized so that the cumulative percentage with a particle size of 3 mm or less is 83 mass%, and size classification with the maximum length included in each of A1 charcoal to D1 charcoal is 1: It belongs to each size category of 0.6 to less than 1.5 mm, size category 2: less than 1.5 to 3 mm, size category 3: less than 3 to 5 mm, size category 4: less than 5 to 10 mm, and size category 5: 10 mm or more. The content Ib (volume%) of the inert structure was measured, and the content (volume%) of a coarse inert structure having a maximum length of 1.5 mm or more was measured. The results are shown in Table 2.

  Next, A1 charcoal to D1 charcoal obtained by pulverizing a cumulative particle size of 3 mm or less to 83% by mass shown in Table 2 are shown in Table 3 (A1 charcoal: B1 charcoal: C1 charcoal: D1 charcoal = 25). %: 25%: 25%: 25%), charged in a coke oven, and dry-distilled to produce coke.

The influence A _i (− / volume%) of the inert structure by the size category i on the coke surface fracture powder rate DI ¹⁵⁰ _-6 and the coke volume fracture powder rate DI ¹⁵⁰ , which are used as indexes when pulverizing the blended coal, The influence degree B _i (− / volume%) on _6-15 is the coke surface fracture powder ratio DI ¹⁵⁰ _-6 obtained by dry distillation under the conditions of the average shrinkage of coal shown in Table 1, and the coke volume fracture. Based on the powder ratio DI ¹⁵⁰ _6-15 , settings were made in advance as shown in Table 4.

In invention example 1, the target of coke strength is set to the target DI ¹⁵⁰ ₁₅ = 86.5 shown in Table 3, and the length size for separating high inert coal and low inert coal is 1.5 mm or more. The boundary value of the content (volume%) of the coarse inert structure was set to 6%.

D1 charcoal, which is a low inert content charcoal, whose content (volume%) of the inert structure is lower than the boundary value of the content (volume%) of the coarse inert structure having a length size of 1.5 mm or more: The influence degree A _i (− / volume%) on the coke surface fracture powder ratio DI ¹⁵⁰ _-6 of the inert structure of size categories 1 to 5 is pulverized to a particle size containing 78% of a particle size of 3 mm or less, And, based on the degree of influence B _i (− / volume%) on the coke volume breaking powder ratio DI ¹⁵⁰ _6-15 , it was blended so as to satisfy the formula (1y).

Further, the content (volume%) of the inert structure is a boundary value of the content (volume%) of the coarse inert structure having a maximum length of 1.5 mm or more: A1 to C1 charcoal that is a high inert charcoal of 6% or more, The degree of influence on the coke surface fracture powder ratio DI ¹⁵⁰ _-6 of the inert structure of size categories 1 to 5 pulverized to a particle size containing 93%, 88%, and 85% of the particle size of 3 mm or less shown in Table 3, respectively. Based on A _i (− / volume%) and the degree of influence B _i (− / volume%) on the coke volume breaking powder ratio DI ¹⁵⁰ _6-15 , the above-mentioned formula (1y) was satisfied.

In Invention Example 1, since the blended coal was pulverized and blended according to the present invention, the content of fine powder of 0.3 mm or less causing dust generation was not increased in the blended coal, and the coke oven was charged. A target coke strength DI ¹⁵⁰ ₁₅ of 86.5 or more could be achieved without reducing the bulk density at the time.

  In Comparative Example 1, A1 to B1 were all pulverized to a particle size of 85% by mass of 3 mm or less, but DI was low. In Comparative Example 2, A1 to C1 charcoal, which is high inert charcoal, was pulverized so that particle size of 3 mm or less, 88%, and D1 charcoal, which is low inert charcoal, was 78%, but DI was low.

  According to the present invention, coke is effectively pulverized to produce coke having extremely high strength without causing an increase in pulverized coal having a particle size of 0.3 mm or less and a reduction in bulk density of the blended coal. be able to. Further, according to the present invention, even if the use ratio of low-grade non-slightly caking coal is increased, high strength and homogeneous coke can be produced. Therefore, the present invention has high applicability in the coke manufacturing industry.

It is a figure which shows the inert structure | tissue which exists in coke, and the structure | tissue of the circumference | surroundings. It is a figure which shows the size distribution of the inert structure | tissue of coal (No.1-No.7) containing the inert structure | tissue from which the volume ratio (volume%) according to size classification differs. No. 1-No. The coke surface breakage rate DI ¹⁵⁰ _-6 of coke obtained by carbonizing coal containing seven different sized inert structures under three conditions of average shrinkage of coal of 16%, 14%, and 12% FIG. (A) shows the case where the average shrinkage of coal is 16%, (b) shows the case where the average shrinkage of coal is 14%, and (c) shows that the average shrinkage of coal is 12%. Show the case. No. 1-No. Coke coke volume breaking powder ratio DI ¹⁵⁰ _6-15 obtained by carbonizing coal containing seven different sized inert structures under three conditions of average shrinkage of coal: 16%, 14%, and 12% FIG. (A) shows the case where the average shrinkage of coal is 16%, (b) shows the case where the average shrinkage of coal is 14%, and (c) shows that the average shrinkage of coal is 12%. Show the case. Coke obtained by carbonizing coal containing an inert structure by size category under the three conditions of average shrinkage of coal of 16%, 14%, and 12% to coke surface fracture powder ratio DI ¹⁵⁰ _-6 influence, and is a diagram showing the influence of the coke volume breakdown powder ratio DI ^0.99 _6-15. (A) shows the case where the average shrinkage of coal is 16%, (b) shows the case where the average shrinkage of coal is 14%, and (c) shows that the average shrinkage of coal is 12%. Show the case. It is a figure which shows the relationship between the grinding | pulverization particle size (accumulation ratio of particle size of 3 mm or less) of high inert content charcoal (A charcoal), and the accumulation volume ratio of the inert structure | tissue of each size or more. It is a figure which shows the relationship between the grinding | pulverization particle size (accumulation ratio of particle size of 3 mm or less) of low inert content charcoal (B charcoal), and the accumulation volume ratio of the inert structure | tissue of each size or more.

Claims (3)

By crushing raw coals multiple brands by brand, in the method of the coal blend obtained by blending such that the target coke strength DI ^0.99 ₁₅ was charged into a coke oven to produce a blast furnace coke,
(A) (A1) An inert structure having a maximum length of 0.6 mm or more is divided into size categories i (= 1 to m [natural number]) by length size,
(A2) Coke surface destruction of coke obtained by dry distillation of coal containing inert structures with different volume fractions (volume%) according to size category i (= 1 to m) under conditions with different average shrinkage of blended coal based on Konaritsu DI ^0.99 _-6, size levels i separately, influence a _i to the coke surface fracture powder ratio DI ^0.99 _-6 of inert tissues (- / vol%) predetermining,
(B) (B1) Containment of coarse inert structure having maximum length of 1.5 mm or more with respect to coking coal of brand j (= 1 to n [natural number]) having a cumulative particle size of 3 mm or less and 70 to 85 mass% Measure the amount (volume%) and the content Ib _{i, j} (volume%) of the inert tissue for each size category i,
(B2) Based on the measured value of the coarse inert structure content (% by volume), a boundary value for classifying the raw material coal of the brand j is determined within a range of 5 to 7% by volume,
(C) (C1) The raw material coal of brand j is composed of a high inert-containing coal in which the content of the coarse inert structure is equal to or higher than the boundary value, and a low inert-containing coal in which the content of the coarse inert structure is less than the boundary value. Divided into two types
(C2) Brand j ', which is classified as low-inert coal, is crushed so that the cumulative percentage of particle size 3mm or less is 70 to 85% by mass, and is classified as high-inert coal The raw coal is pulverized so that the cumulative percentage with a particle size of 3 mm or less is larger than the cumulative percentage with a particle size of 3 mm or less of the low-inert coal.
(C3) Measure the content Ia _{i, j} (volume%) of the inert structure by size category i in the coking coal by brand j after grinding,
(D) A method for producing coke for blast furnace, characterized by blending the raw material coal of brand j after pulverization so as to satisfy the following formula (1x).
Target DI ^0.99 _-6 - reference _{^{DI 150 -6 = Σ j = 1}} ~ n {Σ i = 1 ~ m A i × (Ib i, j -Ia i, j)}
× X _j (1x)
However,
Target DI ¹⁵⁰ _-6 : Target coke strength (-)
Criteria DI ¹⁵⁰ _-6 : Coke strength of coke produced by blended coal prepared by crushing and blending all the raw material coal of brand j so that the cumulative percentage of particle size of 3 mm or less is 70 to 85 mass% (−)
X _j : blending ratio (mass%) of the raw material coal of brand j constituting the blended coal In a method for producing coke for blast furnace by pulverizing multiple brands of coking coal by brand and charging the blended coal blended to a target coke strength DI ¹⁵⁰ ₁₅ into a coke oven,
(A) (A1) An inert structure having a maximum length of 0.6 mm or more is divided into size categories i (= 1 to m [natural number]) by length size,
(A2) Coke surface destruction of coke obtained by dry distillation of coal containing inert structures with different volume fractions (volume%) according to size category i (= 1 to m) under conditions with different average shrinkage of blended coal Konaritsu DI ^0.99 _-6 and based on coke volume fracture powder ratio DI ^0.99 _6-15, size levels i separately, influence a _i to the coke surface fracture powder ratio DI ^0.99 _-6 of inert tissues (- / vol%) And the influence degree B _i (− / volume%) of the coke volume fracture powder ratio DI ¹⁵⁰ _{6-15 of} the inert structure is determined in advance,
(B) (B1) Containment of coarse inert structure having maximum length of 1.5 mm or more with respect to coking coal of brand j (= 1 to n [natural number]) having a cumulative particle size of 3 mm or less and 70 to 85 mass% Measure the amount (volume%) and the content Ib _{i, j} (volume%) of the inert tissue for each size category i,
(B2) Based on the measured value of the coarse inert structure content (% by volume), a boundary value for classifying the raw material coal of the brand j is determined within a range of 5 to 7% by volume,
(C) (C1) The raw material coal of brand j is composed of a high inert-containing coal in which the content of the coarse inert structure is equal to or higher than the boundary value, and a low inert-containing coal in which the content of the coarse inert structure is less than the boundary value. Divided into two types
(C2) Brand j ', which is classified as low-inert coal, is crushed so that the cumulative percentage of particle size 3mm or less is 70 to 85% by mass, and is classified as high-inert coal The raw coal is pulverized so that the cumulative percentage with a particle size of 3 mm or less is larger than the cumulative percentage with a particle size of 3 mm or less of the low-inert coal.
(C3) Measure the content Ia _{i, j} (volume%) of the inert structure by size category i in the coking coal by brand j after grinding,
(D) A method for producing coke for blast furnace, characterized by blending the raw material coal of brand j after pulverization so as to satisfy the following formula (1y).
Target DI ¹⁵⁰ ₁₅ -reference DI ¹⁵⁰ ₁₅ = Σ _{j = 1 to n} {Σ _{i = 1 to m} A _i × (I b _{i, j} −I a _{i, j} )
+ Σ _{i = 1 to m} B _i × (Ib _{i, j} −I a _{i, j} )} × X _j (1y)
However,
Target DI ¹⁵⁰ ₁₅ : Target coke strength (-)
Criteria DI ¹⁵⁰ ₁₅ : Coke strength of coke produced by blended coal obtained by pulverizing and blending all the raw material coals of brand j so that the cumulative percentage of particle size of 3 mm or less is 70 to 85% by mass (−)
X _j : blending ratio (mass%) of the raw material coal of brand j constituting the blended coal   Assuming that the size classification is m = 5, i = 1 (size classification 1: less than 0.6 to 1.5 mm), i = 2 (size classification 2: less than 1.5 to 3 mm), i = 3 (size classification) 3: less than 3-5 mm), i = 4 (size division 4: less than 5-10 mm), and i = 5 (size division 5: 10 mm or more) Of blast furnace coke.