Method for producing metallurgical coke

Abstract

To provide a method in which a clearance can be secured to avoid push clogging even when an amount of used non- or slightly-caking coal is increased, enabling metallurgical coke to be stably produced.SOLUTION: A metallurgical coke production method includes carbonizing mixed coal including shaped coal 3 produced by shaping a part of raw material coal and a fine coal part 2 composed of powdery fine coal of the raw material coal to produce metallurgical coke. At least one of formulation of the raw material coal used for the shaped coal 3 and formulation of the raw material coal used for the fine coal part 2 is regulated so that a first standard deviation σRo1 of a reflectance of vitrinite in the shaped coal 3 is larger than a second standard deviation σRo2 of a reflectance of the vitrinite in the fine coal part 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing metallurgical coke, and more particularly to a method for producing metallurgical coke by carbonizing molded coal, which is made by mechanically compressing a portion of coal that is a raw material for metallurgical coke, together with unmolded powdered coal. [Background technology]

[0002] In recent years, the global demand for steel has increased, leading to a tight coal supply and demand situation, and coal prices have soared. In general, high-quality coal with high caking properties (the property of coal melting and solidifying when carbonized) is more effective for producing high-strength coke suitable for use in blast furnaces than coal with low caking properties (called non- or slightly caking coal). However, the price of such coal tends to be high. In addition, the reserves of high-quality coal resources are limited, and there are concerns that they may be depleted in the future. Therefore, in order to reduce raw material costs and expand the range of usable coal resources to ensure stable coal resources, it is highly desirable to develop a technology that actively uses non- or slightly caking coal as a coke raw material while maintaining coke strength.

[0003] As a method for increasing the amount of non- or slightly caking coal used, there is a technology for increasing the bulk density of non- or slightly caking coal when it is charged into a coke oven. By increasing the bulk density, the distance between the particles of the raw coal, i.e., non- or slightly caking coal, can be shortened, and even if the coal has poor caking properties, the adhesion between the non- or slightly caking coals is promoted, and the coke strength is improved. Therefore, the amount of non- or slightly caking coal used can be increased while maintaining the coke strength. Various technologies for increasing bulk density have been developed and put into practical use. One of them is a method in which a binder is mixed with a part of the raw coal, kneaded, and then mechanically compressed to form molded coal. The method in which this molded coal is mixed with unmolded powder coal to form a blended coal, which is then charged into a coke oven and carbonized is called the molded coal blending method (sometimes called the molded coal partial charging method). There are two types of coal-briquette blending methods: the uniform blending method, in which the same coal is blended into the powdered coal and the molded coal, and the concentrated blending method, in which the type and blending ratio of coal is different between the molded coal and the powdered coal. The concentrated blending method is said to have the characteristic that it can increase the amount of non- or slightly caking coal used compared to the uniform blending method (for example, Non-Patent Document 1), and therefore is said to be effective in reducing raw material costs.

[0004] On the other hand, for stable coke production, it is necessary to smoothly discharge the coke cake generated by carbonization from the carbonization chamber of the coke oven. To achieve this, it is necessary to secure a sufficient clearance between the oven wall of the carbonization chamber and the outer surface of the coke cake facing it. The coke cake is formed by heating the blended coal charged into the carbonization chamber of the coke oven by heat transmitted from the combustion chamber adjacent to the carbonization chamber and carbonizing it in sequence from the oven wall side. After carbonization, it is pushed out of the carbonization chamber by a dedicated pusher. However, if the above-mentioned clearance is insufficient, a problem called clogging may occur, in which the coke cake cannot be discharged outside the oven. When clogging occurs, it is recognized as an extremely serious problem because it is necessary to change the coke production schedule to resolve it, it leads to a decrease in coke production, and it even leads to damage to the oven body, shortening the oven life. Therefore, in the operation of a coke oven, it is as important to manage the above-mentioned clearance and to secure it as necessary and sufficient as managing the coke strength.

[0005] The clearance occurs when the coal (coal blend) charged in the carbonization chamber softens and melts to become lumpy semi-coke during the carbonization process, and then the lumps shrink due to heat. It has been revealed that the clearance is affected by the quality of the raw coal, such as the coalification degree, the fluidity of the coal, and the standard deviation of the distribution of the coalification degree, the influence of pre-treatment such as the particle size and bulk density, and the influence of the carbonization conditions. Of these factors that affect the clearance, it has been confirmed that the higher the bulk density, the smaller the clearance. It is also known that the larger the distribution of the coalification degree of the coal blend, the smaller the clearance (Patent Document 1), and that many macrocracks (cracks of several centimeters to several tens of centimeters that divide the coke cake and determine the size of the coke lump) are generated in the coke cake, which deteriorates the extrusion property of the coke cake from the carbonization chamber (Patent Document 2). The reason for this is believed to be that the greater the distribution of coal rank in a coal blend, the greater the difference in the thermoplastic melting temperature ranges (generally between 400°C and 500°C) between the constituent coals, which leads to poor fusion and makes it easier for cracks to develop. In addition, it is believed that the greater difference in the amount of shrinkage of semi-coke after resolidification (below approximately 500°C) increases, which in turn increases the thermal stress generated between fused particles, which also works to promote crack formation. Note that the above-mentioned constituent coal refers to the multiple types of coal used in the coal blend that is the raw material for producing coke, i.e., raw coal. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4899326 [Patent Document 2] Patent No. 5011839 [Non-patent literature]

[0007] [Non-Patent Document 1] Toshio Abe and 2 others, "Coke production by molded coal blending method - inferior coal concentrated blending method -", Coke Circular, 1981, Vol. 30, No. 1, pp. 36-40 Summary of the Invention [Problem to be solved by the invention]

[0008] Briquetting is considered to be an effective method for the effective use of non- or slightly caking coal. However, since the briquetting method is an operation to increase the bulk density of coal, the shrinkage during heating is smaller than that of conventional coke production using only powder coal, and the clearance is smaller. In addition, the more non- or slightly caking coal is blended into the coal blend, the wider the distribution of coal rank becomes, which may result in a decrease in the clearance.

[0009] In light of this, it is desirable to establish a technology that can increase the amount of non- or slightly caking coal used by using a coal blend with a wide coal rank distribution while ensuring clearance to ensure extrusion performance.

[0010] Non-Patent Document 1 does not discuss the clearance problem and is therefore not sufficient for practical use. On the other hand, Patent Documents 1 and 2 are also insufficient in that they do not take into account the use of non- or slightly caking coal.

[0011] In other words, there is still room for improvement in order to prepare a coal blend with a wide distribution of coal rank using molded coal technology, and to use this coal blend to increase the amount of non- or slightly caking coal used while ensuring a clearance that can improve the pushability of the coke.

[0012] The present invention has been made to solve the above-mentioned problems, and aims to provide a method for stably producing metallurgical coke by ensuring the above-mentioned clearance and avoiding clogging, even when the amount of non- or slightly caking coal used is increased. [Means for solving the problem]

[0013] In order to achieve the above object, the present invention provides [1] A method for producing metallurgical coke by carbonizing a coal blend having molded coal produced by molding a portion of raw coal and a powdered coal portion consisting of powdered coal of the raw coal, wherein at least one of the blending of raw coal used in the molded coal and the blending of raw coal used in the powdered coal portion is adjusted so that a first standard deviation of vitrinite reflectance in the molded coal is greater than a second standard deviation of vitrinite reflectance in the powdered coal portion. [2] The method for producing metallurgical coke described in [1] above, wherein at least one of the blending of raw coal used in the molded coal and the blending of raw coal used in the powder coal portion is adjusted so that each of the first standard deviation, the second standard deviation, and a third standard deviation of the vitrinite reflectance in the entire coal blend satisfies the following formula (1): 2nd standard deviation < 3rd standard deviation < 1st standard deviation (1) [3] A method for producing metallurgical coke described in [1] or [2] above, wherein at least one of the blending of raw coal used in the molded coal and the blending of raw coal used in the powdered coal portion is adjusted so that the difference between the first standard deviation and the second standard deviation is 0.130% or more. [4] The method for producing metallurgical coke described in [1] above, further comprising adjusting at least one of the blending of raw coal used in the molded coal and the blending of raw coal used in the powder coal portion so that the second standard deviation is 0.230% or less and the third standard deviation of the vitrinite reflectance in the entire blended coal exceeds 0.245%. [5] The method for producing metallurgical coke described in [2] above, wherein at least one of the blend of raw coal used in the molded coal and the blend of raw coal used in the powdered coal portion is adjusted so that the second standard deviation is 0.230% or less and the third standard deviation exceeds 0.245%. [6] A method for producing metallurgical coke described in [3] which cites [2] above, comprising adjusting at least one of the blending of raw coal used in the molded coal and the blending of raw coal used in the powdered coal portion so that the second standard deviation is 0.230% or less and the third standard deviation exceeds 0.245%. [7] The raw coal comprises non- or slightly caking coal; The method for producing metallurgical coke according to the above item [1], wherein the non- or slightly-caking coal is blended with the molded coal so that the first standard deviation is larger than the second standard deviation. Effect of the Invention

[0014] According to the present invention, even if the amount of non- or slightly caking coal used is increased, which is cheaper than caking coal, and the distribution of the coalification rank of the blended coal becomes wider, the reduction in clearance, which is a problem when producing coke by the molded coal blending method, can be suppressed without requiring any special additional cost. Therefore, even if the amount of non- or slightly caking coal used is increased more than before in the molded coal blending method, the effect of enabling stable coke production while avoiding the problem of clogging is exhibited. Note that non- or slightly caking coal means coal that has a lower fluidity than caking coal and has a coalification rank near both ends of the range of general raw coal or outside that range. The range of general raw coal rank means that the average maximum reflectance of vitrinite is approximately 0.6% or more and 1.7% or less. Therefore, the typical properties of non- or slightly caking coal are that the average maximum reflectance of vitrinite is 0.9% or less or 1.5% or more, and the maximum Gieseler fluidity is 300 ddpm or less. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing an example of a retort for carbonizing a coal blend, in which (A) in FIG. 1 shows a state in which the coal blend filled in the retort is being carbonized, and (B) in FIG. 1 shows a clearance generated between a coke cake obtained by carbonizing the coal blend and a furnace wall of the retort. [Diagram 2]FIG. 1 is a scatter diagram showing the relationship between the standard deviation of vitrinite reflectance and clearance for an entire coal blend consisting of 80 wt% fine coal and 20 wt% briquettes. [Diagram 3] FIG. 1 is a scatter diagram showing the relationship between the standard deviation of vitrinite reflectance of powder coal and the clearance in a coal blend consisting of 80 wt% powder coal and 20 wt% molded coal. [Figure 4] FIG. 1 is a scatter diagram showing the relationship between the standard deviation of the reflectance of vitrinite in the briquettes and the clearance in a coal blend consisting of 80 wt% fine coal and 20 wt% briquettes. [Diagram 5] FIG. 1 is a scatter diagram showing the relationship between the difference between the standard deviation of the vitrinite reflectance of the molded coal and the standard deviation of the vitrinite reflectance of the powdered coal in a coal blend consisting of 80 wt% powdered coal and 20 wt% molded coal, and the clearance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In order to achieve the above object, the present inventors have conducted extensive research into the influence of the coalification distribution of the briquettes (hereinafter simply referred to as briquettes) of a coal blend and the coalification distribution of the powder coal part (hereinafter simply referred to as the powder coal part) of a coal blend, which is made of powdered powder coal, on the clearance generated between the furnace wall and the coke cake after carbonization of the coal blend. As a result, it was found that the coalification distribution of the powder coal part is the main controlling factor that greatly affects the clearance, whereas the coalification distribution of the briquettes is unlikely to affect the clearance and can be almost ignored. The present invention has been made based on this finding, and the following will specifically describe how to adjust the blending of multiple coals in the briquettes and the blending of multiple coals in the powder coal part.

[0017] A coal blend is made up of multiple types of coal (sometimes called raw coal), and each of these coals refers to a single brand of coal or a coal group in which multiple brands of coal are mixed and managed as coal of approximately uniform quality. In other words, the above-mentioned coal blend is a mixture of coals of different brands and qualities, and the quality of the briquettes, the quality of the powder coal portion, or the quality of the entire coal blend can be changed by changing the brand and quality of the coal blended, the blending ratio, etc.

[0018] (Conditions for blending raw coal for powdered coal and molded coal) This is the most important point of the present invention. The method for producing metallurgical coke according to the present invention is one form of concentrated blending among briquette blending methods, and at least one of the blending of raw coal in the powder coal part and the blending of raw coal in the briquette is adjusted. By doing so, the standard deviation (hereinafter referred to as the first standard deviation) σRo1 of the distribution of the reflectance (Ro) of vitrinite in the briquette and the standard deviation (hereinafter referred to as the second standard deviation) σRo2 of the reflectance (Ro) of vitrinite in the powder coal part are independently controlled. Each of the standard deviations σRo1 and σRo2 is an index representing the distribution of the coal rank, and is also used in the above-mentioned Patent Document 1 and Patent Document 2. The method for obtaining each of the standard deviations σRo1 and σRo2 will be described below.

[0019] First, the distribution of the reflectance of the vitrinite of each coal contained in the coal blend (coal mixture) is obtained. Vitrinite is a type of coal structure, and its reflectance (Ro) can be obtained by the method described in JIS M8816 "Method of measuring microstructure components and reflectance of coal". Since coal is a heterogeneous material, even vitrinite in the same coal has different reflectances at different measurement points, that is, it is not constant and has a distribution. Therefore, the reflectance is measured at each different point of the vitrinite in the coal sample to be measured. Then, based on these measured reflectances, the distribution of the presence ratio of components with different reflectances is obtained as a reflectance distribution. Based on the reflectance distribution of each brand of coal contained in the coal blend and the content of that brand, that is, the blending ratio of each brand of coal in the coal blend, the reflectance distribution of the vitrinite in the coal mixture, i.e., the entire coal blend, is obtained. Then, the standard deviation of the distribution, i.e., the standard deviation of the reflectance (Ro) of the vitrinite in the entire coal blend (hereinafter referred to as the third standard deviation) σRo3 is obtained.

[0020] Similarly, the first standard deviation σRo1 of the briquettes and the second standard deviation σRo2 of the powder coal are calculated. In the embodiment of the present invention, the first standard deviation σRo1 and the second standard deviation σRo2 are set to specific conditions (numerical ranges) described below, so that the briquettes blending method can increase the above-mentioned clearance more than in the past.

[0021] As described above, the clearance usually decreases with an increase in the third standard deviation σRo3 of the entire coal blend. However, in the briquette blending method, the second standard deviation σRo2 of the powder coal part is the main factor affecting the clearance, and the clearance decreases with an increase in the second standard deviation σRo2 of the powder coal part. On the other hand, the inventors have found that the first standard deviation σRo1 of the briquette does not affect the clearance as much as the second standard deviation σRo2 of the powder coal part. Therefore, when the third standard deviation σRo3 of the entire coal blend is constant, it is desirable to decrease the second standard deviation σRo2 of the powder coal part and, conversely, increase the first standard deviation σRo1 of the briquette in order to expand the clearance. Specifically, the multiple coals constituting the briquettes and the powder coal part are blended so that the first standard deviation σRo1 of the briquettes is greater than the second standard deviation σRo2 of the powder coal part (σRo1>σRo2), or the value obtained by subtracting the second standard deviation σRo2 of the powder coal part from the first standard deviation σRo1 of the briquettes is greater than "0 (zero)" (σRo1-σRo2>0). This allows the clearance to be expanded compared to when the briquettes and the powder coal part are blended in the same way.

[0022] Furthermore, the standard deviations of all the coals that are the raw materials of the coal blend, including the briquettes and the powder coal, i.e., the third standard deviation σRo3 of the entire coal blend, can be included in the clearance setting conditions. In that case, it is preferable that the third standard deviation σRo3 of the entire coal blend is set to a value larger than the second standard deviation σRo2 of the powder coal part and smaller than the first standard deviation σRo1 of the briquettes (σRo2<σRo3<σRo1).

[0023] As a specific operation of blending coals, among the multiple coals constituting the coal blend, coals whose coalification rank is near both ends of the range of general raw coal or outside the range are blended as much as possible in the briquettes, rather than blended in the powder coal portion. That is, the first standard deviation σRo1 of the briquettes is increased, and the third standard deviation σRo3 of the entire coal blend increases accordingly, but the second standard deviation σRo2 of the powder coal portion is blended so that it is almost constant. The range of the general coalification rank of raw coal means that the average maximum reflectance of vitrinite is in the range of approximately 0.6 to 1.7. In addition, during this blending operation, the average quality of the coal blend (average reflectance: Ro, maximum fluidity: logMF, total inert amount: TI, etc.) may be adjusted to the required target range at the same time in order to achieve the target value of coke strength that is generally managed.

[0024] Furthermore, as shown in the examples below, the difference ΔσRo between the first standard deviation σRo1 of the briquettes and the second standard deviation σRo2 of the powder coal portion is particularly preferable when it is 0.130% or more, since the effect of increasing the clearance is remarkable. In addition, since the clearance increases with an increase in the difference ΔσRo, by utilizing this relationship, it becomes possible to increase the third standard deviation σRo3 of the entire coal blend while maintaining the clearance constant, as opposed to increasing the clearance while keeping the third standard deviation σRo3 of the entire coal blend constant. That is, a raw coal blend is performed that increases the first standard deviation σRo1 of the briquettes and the second standard deviation σRo2 of the powder coal portion while maintaining the difference ΔσRo at 0.130% or more. This makes it possible to increase the amount of coal whose coalification rank is near both ends of the range of general raw coal, or outside the range, that is, so-called non-slightly caking coal, which is cheaper than caking coal. Typical properties of non- or slightly caking coal are that the average maximum reflectance of vitrinite is 0.9% or less or 1.5% or more, and the maximum Gieseler fluidity is 300 ddpm or less.

[0025] In general, when the third standard deviation σRo3 of the entire coal blend including the molded coal and the powder coal portion exceeds 0.245%, the clearance exceeds a suitable value, that is, the clearance becomes small, and the possibility of clogging tends to increase. However, even in such a case, by adjusting the blending of the multiple coals constituting the powder coal portion so that the second standard deviation σRo2 of the powder coal portion is 0.230% or less, the clearance can be expanded to ensure a sufficient clearance for good extrudability. Therefore, stable production of coke is possible.

[0026] Here, the reason why the first standard deviation σRo1 of the molded coal does not affect the clearance or has a smaller effect on the clearance than the second standard deviation σRo2 of the powdered coal part will be explained. The molded coal itself has a higher packed bulk density than the powdered coal. Therefore, even if the distance between the coal particles constituting the molded coal is closer than the distance between the powdered coal particles, and the first standard deviation σRo1 is larger than the second standard deviation σRo2, fusion in the thermoplastic melting temperature range proceeds sufficiently. Therefore, the strength of that part, that is, the part of the molded coal where fusion has progressed, becomes high. As a result, in the molded coal, cracks are less likely to develop when the semi-coke shrinks compared to the powdered coal part, and it is considered that the decrease in the clearance due to crack generation can be suppressed.

[0027] (Ratio of molded coal to total raw material (coal blend)) In an embodiment of the present invention, the briquettes are mixed with powdered coal and charged into the carbonization chamber of the coke oven. Here, the powdered coal is produced by pulverizing raw coal by a normal operation. Specifically, the content of coal particles (powdered coal) having a particle size of 3 mm or less in the powdered coal portion is about 70% by mass or more and 90% by mass or less, and the raw coal is pulverized so as to obtain such a particle size distribution. The pulverization of the raw coal may be performed by a conventional operation or method known as a normal operation.

[0028] Although there is no particular restriction on the blending ratio (blending ratio) of the molded coal to the total blended coal, there is a suitable range, and the range of 5% by mass or more and 50% by mass or less is desirable. If the blending ratio of the molded coal is too small, that is, less than 5% by mass, there is a possibility that the merits of the improvement of the coke strength by the molded coal blending method and the increase in the use ratio of the non-slightly caking coal may not be effectively enjoyed. Therefore, it is preferable to blend at least 5% by mass of molded coal in the blended coal. On the other hand, if the blending ratio of the molded coal is too high, that is, more than 50% by mass, the bulk becomes large as a whole and the bulk density becomes small. Therefore, there is a possibility that the effect of improving the coke strength may not be effectively obtained. Therefore, the blending ratio of the molded coal is preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 35% by mass or less.

[0029] (Shape of briquettes) The shape of the molded charcoal is not particularly limited, and may be, for example, spherical, pillow-shaped, egg-shaped, Masek-shaped, or lens-shaped.

[0030] (Bulk coal size) There is no particular restriction on the size of each briquette. For example, the volume of each briquette is 6 cm. 3 More than 120cm 3 Considering production volume and strength of molded coal, 25cm or less is preferable. 3 More than 80cm 3 The following ranges are particularly preferred:

[0031] (Bulk density of briquettes) In order to obtain the effects of the coal briquetting method, i.e., to obtain the effects of improving the coke strength and increasing the proportion of non- or slightly caking coal used, it is desirable for the bulk density of the coal briquette to be higher than a certain level. Specifically, the bulk density of the briquette should be 0.90 g / cm3 based on the dry coal standard. 3 More preferably, it is 1.1 g / cm 3 The bulk density of pulverized coal varies depending on the particle size, moisture, and coal loading method of the coal, but in the case of a typical coke manufacturing process using a chamber-type coke oven, the bulk density is approximately 0.70 g / cm in a dry state. 3 More than 0.80g / cm3 The following is the result.

[0032] (Manufacturing method of molded charcoal) The method for producing the molded coal is not particularly limited, and may be a conventionally known method, such as a double roll method, a punching method, an extrusion method, or a pelletizing method.

[0033] (Method of carbonizing blended coal) There are no particular restrictions on the method of carbonizing the coal blend, and the coal (coal blend) may be carbonized in a general chamber-type coke oven under conditions in which the temperature of the coal (coal blend) is about 900°C or higher and 1300°C or lower.

[0034] (Coal for blending coal and powdered coal) There are no particular restrictions on the raw coal used in the blending of either powdered coal or molded coal. In addition to raw coal commonly used in coke production, anthracite, semi-anthracite, bituminous coal, subbituminous coal, lignite, etc., which have no or poor caking properties, can be used. In addition, molded coal may be molded by adding a binder to the raw coal to improve moldability. The binder may be water, a coal-based binder, a petroleum-based binder, an organic binder, etc. Examples of the coal-based binder include coal tar pitch, solvent refined coal, solvent extracted coal, tar, and tar slag, and examples of the petroleum-based binder include asphalt, asphalt pitch, and propane deasphalted asphalt, and examples of the organic binder include starch, molasses, and resin. In addition, powdered coke, oil coke, plastic, and binders (pitches, solvent refined coal, etc.) may be used as part of the binder.

[0035] (Method and conditions for preparing raw coal) The preparation methods and conditions generally used in coke production can be applied. The preparation process may include some or all of the steps of crushing, classifying, mixing, kneading, drying, hydration, preheating, etc. By these processes, raw coal having any coal particle size, moisture, temperature, and mixture state can be prepared. EXAMPLES

[0036] Examples of the present invention are shown below. The raw coal used for blending the powdered coal and molded coal was selected from 6 to 12 brands of raw coal having an average maximum vitrinite reflectance (Ro) of 0.6% to 1.7% and a maximum Gieseler fluidity MF of 0 ddpm to 15,000 ddpm.

[0037] By changing the brand and blending ratio of raw coal to be mixed with the briquettes and powder coal, several briquettes and powder coals with different standard deviations of vitrinite reflectance were prepared, and the influence on the above-mentioned clearance was investigated. The standard deviations of vitrinite reflectance of the briquettes, powder coal, and the entire blend consisting of briquettes and powder coal used in the investigation are summarized in Table 1.

[0038] [Table 1]

[0039] As shown in Table 1, the third standard deviation σRo3 of the entire coal blend was changed in the range of 0.210% to 0.271%, the second standard deviation σRo2 of the powder coal part was changed in the range of 0.167% to 0.250%, and the first standard deviation σRo1 of the briquettes was changed in the range of 0.210% to 0.422%. The average quality, which was calculated by weighting the mass blending ratio of the constituent coals of the briquettes and powder coal part, i.e., the raw coal, was adjusted to 1.01% to 1.03% as the weighted average of the average maximum reflectance of vitrinite of each coal, Gieseler maximum fluidity logMF (ddpm / log) was adjusted to 2.5 to 2.6, and total inert TI (vol%) was adjusted to 29% to 32%. Here, the average maximum reflectance of vitrinite of coal is the average maximum reflectance of vitrinite measured according to the method described in JIS M8816, and the total inert amount (TI) of raw coal is the total inert amount calculated based on the method described in JIS M8816 and Parr's formula described in the explanation thereof as follows: Total inert amount (volume%) = fusinite (volume%) + micrinite (volume%) + (2 / 3) × semifusinite (volume%) + mineral matter (volume%). It has been confirmed that the drum strength of the coke after carbonization under either condition is in the range of 82.5 to 83.1 in I-type drum strength, which is about the same.

[0040] Of the blended coal, the powder coal portion was prepared by adjusting the particle size of each of the air-dried raw coals (100% by mass) to a particle size of 3 mm or less, and then blending them to a predetermined blending ratio. The molded coal was produced as follows. Each of the raw coals (100% by mass) was adjusted to a particle size of 3 mm or less, and then blended to a predetermined blending ratio, and a binder was added thereto. Specifically, 4 parts by mass of medium coal tar pitch and 6 parts by mass of soft pitch were added as binders to 100 parts by mass of dried raw coal. Then, the mixture was thoroughly kneaded while being heated to about 80°C in a kneader. After that, the mixture was molded in a double roll molding machine, which is a Masek type with a cup shape of the rolls of 44 mm square, to produce molded coal.

[0041] The clearance was measured according to the following procedure. A small mock retort for clearance measurement (hereinafter simply referred to as a retort) 1 shown in (A) and (B) of FIG. 1 was filled with 1000g of ... 3 ), and the blending ratio of the powdered coal part 2 and the molded coal 3 was "8" by mass to "2" by mass (powdered coal part: molded coal = 8:2). The retort 1 was placed in an electric furnace (not shown) and carbonized at a carbonization temperature (the furnace wall temperature of the retort 1) of 1050 (℃) for 4 hours and 20 minutes. Thereafter, the retort 1 was taken out of the electric furnace and cooled with nitrogen to obtain a coke cake 4. In the width direction of the retort 1 (the direction indicated by the symbol "W" in FIG. 1), the distance D between one of the two furnace walls 5 of the retort 1 and the outer surface of the coke cake 4 facing the one furnace wall 5 was measured at multiple points by a laser distance meter, and the arithmetic average value was calculated. Similarly, the distance D between the other of the two oven walls of the retort 1, 6 and the outer surface of the coke cake 4 facing the other oven wall 6, was measured at a plurality of points in the width direction by a laser distance meter, and the arithmetic average value was calculated. The sum of the arithmetic average value of the distance D on the one oven wall 5 side and the arithmetic average value of the distance D on the other oven wall 6 side was defined as the above-mentioned clearance.

[0042] The retort 1 shown in (A) and (B) of FIG. 1 includes a bottom plate 7 formed of bricks, the pair of furnace walls 5, 6 made of carbon plates erected on the bottom plate 7, and a top plate 8 formed of bricks arranged on the pair of furnace walls 5, 6. As shown in (A) of FIG. 1, blended coal is filled into the space of the retort 1 and carbonized. As shown in (B) of FIG. 1, a distance D between the coke cake 4 obtained by carbonization and the pair of furnace walls 5, 6 is measured using a laser distance meter. In this embodiment, the blended coal filled in the retort has dimensions of length L: 114 mm x width W: 190 (mm) x height H: 120 (mm).

[0043] Table 1 shows the measurement results of the clearance. FIG. 2 shows the relationship between the third standard deviation σRo3 and the clearance of all the coal blends used in the clearance investigation. As shown in FIG. 2, the correlation between the third standard deviation σRo3 and the clearance of each coal blend is low, but a weak correlation was observed in which the clearance decreases when the third standard deviation σRo3 is large. Each of the symbols shown in white squares in FIG. 2 indicates Comparative Examples 1 to 3, and in these Comparative Examples 1 to 3, the blending of raw coal is the same for powder coal and briquettes. That is, in each of Comparative Examples 1 to 3, the first standard deviation σRo1 of the reflectance of vitrinite in the briquettes is equal to the second standard deviation σRo2 of the reflectance of vitrinite in the powder coal part. In addition, in each of Comparative Examples 1 to 3, the third standard deviation σRo3 of the reflectance of vitrinite in the entire raw coal is different from each other. From the symbols of Comparative Examples 1 to 3 shown in Fig. 2, a correlation was observed in which the clearance decreased as the third standard deviation σRo3 of the overall vitrinite reflectance increased. However, when the blending ratio of raw coal was changed between molded coal and pulverized coal, that is, in Examples 1 to 9, each clearance varied greatly, and it was found that the clearance could not be controlled only by the third standard deviation σRo3 of the entire raw coal.

[0044] On the other hand, as shown in FIG. 3, a clear negative correlation was observed between the second standard deviation σRo2 of the powder coal portion and the clearance in each of Examples 1 to 9. The correlation observed in FIG. 3 is similar to the tendency reported in the method using blended coal containing no molded coal as the raw material disclosed in Patent Document 1 and the like. Here, the symbols shown in white squares in FIG. 3 indicate Comparative Examples 1 to 3 in which the blending of raw coal was the same for powder coal and molded coal, respectively. Therefore, in each of Comparative Examples 1 to 3, the first standard deviation σRo1 of the reflectance of vitrinite in the molded coal is equal to the second standard deviation σRo2 of the reflectance of vitrinite in the powder coal portion. There was no significant difference in the tendency for the above-mentioned negative correlation to occur between the case where the raw coal blend in the molded coal was the same as the raw coal blend in the powdered coal, i.e., each of Comparative Examples 1 to 3, and the case where the raw coal blend in the molded coal was different from the raw coal blend in the powdered coal, i.e., each of Examples 1 to 9, and it became clear that in both cases, the second standard deviation σRo2 of the powdered coal portion has a significant effect on clearance.

[0045] On the other hand, the relationship between the first standard deviation σRo1 of the briquettes and the clearance shows the tendency shown in Figure 4. According to the results in Figure 4, the clearance does not become particularly small even if the first standard deviation σRo1 of the briquettes becomes large. On the contrary, the clearance tends to become large when the first standard deviation σRo1 of the briquettes is large. However, in this experiment, when the first standard deviation σRo1 of the briquettes is large, the second standard deviation σRo2 of the powdered coal becomes small. Therefore, it is considered that the clearance increases due to the second standard deviation σRo2 of the powdered coal becoming small. From this result, it can be seen that the effect of the first standard deviation σRo1 of the briquettes on the clearance is small in the briquettes blending method.

[0046] Therefore, in the coal briquetting method, even if the first standard deviation σRo1 of the coal briquette increases, it is effective to reduce the second standard deviation σRo2 of the powder coal to increase the clearance. That is, by making the blending of raw coal in the coal briquette and the blending of raw coal in the powder coal part different from each other and blending raw coal, i.e., non- or slightly caking coal, which causes an increase in the third standard deviation σRo3 of the entire coal blend, into the coal briquette, the reduction in the clearance can be suppressed. As a result, in the coal briquetting method, even if the amount of non- or slightly caking coal used is increased compared to the conventional method, the effect of enabling stable coke production while avoiding the clogging problem can be obtained.

[0047] In the examples shown in Table 1, in all of Examples 1 to 9, the first standard deviation σRo1 of the briquettes is greater than the second standard deviation σRo2 of the pulverized coal (σRo1>σRo2). The first standard deviation σRo1 of the briquettes is greater than the third standard deviation σRo3 of the entire coal blend, and the third standard deviation σRo3 of the entire coal blend is greater than the second standard deviation σRo2 of the pulverized coal (σRo1>σRo3>σRo2). Therefore, it is preferable to adjust the blending ratio of the multiple raw coals constituting the coal blend to satisfy these conditions.

[0048] In order to clarify the more preferable blending conditions of raw coal that can increase the amount of non- or slightly caking coal used and increase the clearance, the difference ΔσRo between the first standard deviation σRo1 of the briquettes and the second standard deviation σRo2 of the powder coal was calculated as an index, and the correlation between the difference ΔσRo and the clearance was organized. The results are shown in Figure 5. In addition, the third standard deviation σRo3 of the entire coal blend was stratified into a case where it is 0.245% or less (σRo3≦0.245%) and a case where it is greater than 0.245% (σRo3>0.245%). In Figure 5, the difference ΔσRo when the third standard deviation σRo3 of the entire coal blend is 0.245% or less is shown by a white diamond symbol, and the difference ΔσRo when the third standard deviation σRo3 is greater than 0.245% is shown by a black square symbol. The value used as the criterion for the above-mentioned stratification (hereinafter referred to as threshold value α, 0.245%) was set based on the fact that, in FIG. 2, when the third standard deviation σRo3 exceeds 0.245%, the clearance becomes smaller at around 12 mm compared to when the third standard deviation σRo3 is 0.245% or less, and the number of cases in which problems with the pushability of the coke are easily encountered increases significantly.

[0049] As shown in Fig. 5, when the first standard deviation σRo1 of the molded coal and the second standard deviation σRo2 of the powdered coal are almost the same, that is, when the difference ΔσRo is almost "0", the clearance when the third standard deviation σRo3 is larger than the threshold value α is smaller than the clearance when the third standard deviation σRo3 is equal to or smaller than the threshold value α. Furthermore, it was also recognized that the clearance tends to be smaller when the third standard deviation σRo3 is large regardless of the value of the difference ΔσRo. It was also recognized that the clearance increases with the increase in the difference ΔσRo, and in particular, when the difference ΔσRo is "0.130%" or more, the effect of increasing the clearance is greater than when it is not.

[0050] The pushability of the coke cake is also affected by the state of the coke chamber in the coke oven. For example, when the coke oven is aged and the unevenness of the oven wall of the coke chamber is large, or when the temperature distribution in the coke chamber is disturbed, the pushability changes even if the same blended coal is used. The pushability also changes depending on the operating rate of the coke oven. Therefore, in the operation of the coke oven as described above, it is preferable to appropriately set the clearance that does not cause problems in pushability or is unlikely to cause problems by taking into account the state of the coke oven. However, in the operation of a normal coke oven without taking into account the state of the coke oven in particular, it is preferable to adjust the blending of the blended coal so that the difference ΔσRo is 0.130% or more with reference to FIG. 5. This is because, as described above, if the difference ΔσRo is 0.130% or more, the effect of expanding the clearance is more noticeable than when it is not.

[0051] Among raw coals that can be used as coke raw materials, the average maximum vitrinite reflectance of non- or slightly caking coals, which have inferior caking properties compared to so-called caking coals, is often on either side of the range of general raw coals, or outside the range. The range of general raw coals is generally a range in which the average maximum vitrinite reflectance is between 0.6% and 1.7%. Therefore, if the amount of non- or slightly caking coal used in the entire coal blend (blending amount) is increased, that is, if the amount of non- or slightly caking coal used in both the molded coal and the pulverized coal part is increased, the third standard deviation σRo3 of the entire coal blend becomes large. In addition, if the third standard deviation σRo3 of the entire coal blend exceeds 0.245%, the clearance becomes low, and there is a concern that the extrusion property will deteriorate.

[0052] However, according to the method of the present invention, even if the third standard deviation σRo3 of the entire coal blend exceeds 0.245%, for example, the clearance can be increased by enlarging the difference ΔσRo and reducing the second standard deviation σRo2 of the powder coal portion. Specifically, the amount of coal used, which is a coal whose coalification rank is at both ends of the range of general raw coal or outside the range, i.e., non-slightly caking coal that is cheaper than caking coal, can be increased more than before, and the clearance can be maintained. Therefore, by maintaining good pushability, it is possible to contribute to stable production of coke. More specifically, as shown in FIG. 3 and Table 1, if the second standard deviation σRo2 of the powder coal portion is set to 0.230% or less, it is expected that the clearance will be 12.3 mm or more, and the pushability can be improved. Therefore, when the third standard deviation σRo3 of the entire coal blend exceeds 0.245%, it is particularly preferable to adjust the blending ratio of each raw coal constituting the coal blend so that the second standard deviation σRo2 of the powder coal portion is 0.230% or less.

[0053] In the above test, the blending ratio of powdered coal to briquettes in the coal blend was 8:2 by mass, but even if the blending ratio of briquettes was changed, the influence of each standard deviation σRo1, σRo2, σRo3 on the clearance was the same, and the influence of the second standard deviation σRo2 of the powdered coal part on the clearance was particularly large. When the blending ratio of briquettes in the coal blend increases, the bulk density of the entire coal blend increases and the clearance tends to become smaller, but since the blending ratio of powdered coal, which has a large effect on the clearance, decreases, the effects of the two cancel each other out, and the clearance does not change significantly overall. For example, although not shown in detail, in the blending of Example 1 in Table 1, in an example in which powdered coal and briquette coal were blended in a mass ratio of "7" powdered coal to "3" briquette coal (powdered coal:briquette coal = 7:3), the clearance was 12.8 mm when a test similar to the above test was performed. Thus, even when the blending ratio of briquette coal in the coal blend was changed, the clearance was almost unchanged. [Explanation of symbols]

[0054] 1 Retort 2. Powder Coal Section 3 Molded coal 4. Coke Cake 5 One side of the furnace wall 6. The other furnace wall 7 Bottom plate 8. Top plate

Claims

1. A method for producing metallurgical coke by carbonizing a coal blend having a coal briquette produced by briquetting a part of raw coal and a powder coal portion made of powdered coal of the raw coal, comprising: The raw coal comprises non- or slightly caking coal, A method for producing metallurgical coke, comprising blending the non- or slightly caking coal with the molded coal such that a first standard deviation of vitrinite reflectance in the molded coal is greater than a second standard deviation of vitrinite reflectance in the powder coal portion, the second standard deviation is 0.230% or less, and a third standard deviation of vitrinite reflectance in the entire blended coal exceeds 0.245%.

2. 2. The method for producing metallurgical coke according to claim 1, wherein at least one of a blend of raw coal used in the molded coal and a blend of raw coal used in the powder coal portion is adjusted so that each of the first standard deviation, the second standard deviation, and a third standard deviation of the vitrinite reflectance in the entire coal blend satisfies the following formula (1): 2nd standard deviation < 3rd standard deviation < 1st standard deviation ... (1)

3. A method for producing metallurgical coke as described in claim 1 or 2, wherein at least one of the blending of raw coal used in the molded coal and the blending of raw coal used in the powdered coal portion is adjusted so that the difference between the first standard deviation and the second standard deviation is 0.130% or more.

Images