JP2015203045A - Method for producing coke - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a coke, when a non-fine-caking coal is used as a part of a coal blend, capable of easily obtaining a coke having higher strength.SOLUTION: Provided is a method for producing a coke, when a coke is produced as a part of a coal blend by pulverizing a non-fine-caking coal in which a volatile matter content is 30 mass% or higher, the total expansion ratio by dilatometer measurement is 40% or lower, and the logarithm value of Gieseler fluidity (ddpm) is 1.5 or lower, the pulverization particle diameter of the non-fine-caking coal is decided in such a manner that an expandable obstruction variability rate reaches a prescribed value or lower.

Description

  The present invention relates to a method for producing coke.

In the production of coke, it is desired to use a large amount of non-slightly caking coal that is an inexpensive raw material. Since non-slightly caking coal has a high volatile content, the (semi) coke shrinkage after softening and melting and resolidification is high. As a result of the high shrinkage of the non-slightly caking coal, cracks are generated in the coke mass. The generated crack becomes a factor of reducing the coke strength.
The coke strength is improved by pulverizing non-slightly caking coal for the above problem. Specifically, the non-slightly caking coal is pulverized to reduce the particle size of the non-slightly caking coal. Thereby, since the crack size in the coke lump produced | generated by the high shrinkage | contraction of a non-slightly caking coal falls, as a result, the fall of the coke intensity | strength resulting from a crack production | generation can be suppressed.

On the other hand, it is known that the non-slightly caking coal is excessively pulverized and the expansibility is lowered when the particle size is reduced.
As described above, when the non-coking coal is pulverized into fine particles, the coke strength is improved. However, when the pulverized coal is excessively pulverized, the expansibility is lowered, and on the contrary, the coke strength is considered to be decreased.
Therefore, it is desired to enjoy the effect of pulverization without causing a decrease in coke strength due to a decrease in expansibility.

The following is disclosed as a method for defining the pulverized particle size of non-slightly caking coal.
A method is disclosed in which weakly caking coal having an average reflectance of 0.6% to 1.1% and an expansion rate of -10% or more is pulverized to a particle size of 2 mm or less and 90% by mass or more (Patent Document 1). By pulverizing finer than the conventional technical range (3 mm or less, 60 mass% to 90 mass%), the crack suppression effect is great and the coke strength is improved.
Regardless of caking coal or non-caking coal, coarse inert structures having a maximum length of 0.6 mm or more are sectioned, pulverized into sections, and pulverized coal having a particle size of 0.3 mm or less accompanying coal pulverization. A method for producing coke for blast furnace that increases the coke strength stably and effectively by suppressing the decrease in the bulk density of the entire blended coal due to the increase in the amount of coal is disclosed (Patent Document 2).
Furthermore, since the expansibility of coal decreases due to over-pulverization, the specific volume of coal is crushed using the specific volume, which is an index of the expansibility of coal, as an index for determining the optimum particle size of non-slightly caking coal. A method of adjusting the particle size of coal according to the degree is disclosed (Patent Document 3).

JP 2002-121567 A Japanese Patent No. 4551494 Japanese Patent No. 4102015

Patent Document 1 pulverizes weakly caking coal to a particle size of 2 mm or less and 90% by mass or more, but there is no description regarding the influence on the expansibility of fine powder and blended coal generated by pulverization.
Patent Document 2 proposes a pulverization method corresponding to the properties of coal, and focuses on the coarse inert structure and pulverizes according to the characteristics. However, as with Patent Document 1, there is no description of the change in expansibility associated with the pulverization of non-slightly caking coal.
In Patent Document 3, attention is paid to a change in expansibility when non-slightly caking coal is pulverized. However, the specific volume when the non-slightly caking coal is pulverized to 2 to 3 mm and an average particle size of 2.5 mm is a standard, and it is difficult to pulverize the non-slightly caking coal to such a particle size distribution. Moreover, the particle size distribution of the non-slightly caking coal obtained by actual operation is not narrow as mentioned above, and cannot be said to be a realistic method.

  In view of such circumstances, the object of the present invention is to provide a method for producing coke that can easily obtain higher-strength coke when using non-slightly caking coal as part of the blended coal. That is.

  The present inventors pay attention to the expansion characteristics for each particle size of the non-slightly caking coal, and by determining the pulverized particle size of the non-slightly caking coal so that the rate of change that inhibits the expandability is a predetermined value or less. The present inventors have found that coke with higher strength can be easily produced.

The gist of the present invention is as follows.
(1) Non-slightly caking coal with a volatile content of 30% by mass or more, a total expansion rate of 40% or less as measured by dilatometer, and a logarithmic value of Gieseller fluidity (ddpm) of 1.5 or less is pulverized. In producing coke as a part, a method for producing coke is characterized in that the pulverized particle size of the non-coking coal is determined so that the expansion inhibition fluctuation rate is a predetermined value or less.
Here, the expansion inhibiting fluctuation rate is obtained by the following method. That is, the expansion inhibition index (IFC ₀ ) of coal having a particle size of 1 mm to 3 mm when the non-finely caking coal is pulverized to a ratio of 65% by mass to 85% by mass of a 3 mm sieving ratio is obtained. Next, an increase coefficient (ΔIFC _i ) from the IFC ₀ is calculated by calculating an expansion inhibition index (IFC _i ) of the coal for each particle size i for the particle size i generated by pulverizing the coal having a particle size of 1 mm to 3 mm. Calculate it. Next, the mass ratio increment (ΔFC _i ) of the particle size i is obtained for each particle size classification under a 1 mm sieve when the IFC _{0 of the} non-slightly caking coal is crushed to the calculated pulverized particle size or more. Incidentally, the? Fc _i is the mass ratio increment in the particle size i the total amount of the non- or slightly caking coal. The ΔIFC _i and the ΔFC _i are multiplied and totaled for each granularity i to calculate Σ (ΔIFC _i × ΔFC _i ). Finally, the calculated Σ (ΔIFC _i × ΔFC _i ) is multiplied by the blending ratio α of the non-slightly caking coal in the blended coal to be subjected to the dry distillation test to obtain an expansion inhibition variation rate.
(2) The method for producing coke according to (1), wherein the pulverized particle size of the non-slightly caking coal is determined so that the expansion inhibition fluctuation rate is 0.02 or less.

  According to the present invention, when using non-slightly caking coal as a part of blended coal, it is possible to easily obtain higher strength coke by determining the pulverized particle size of non-slightly caking coal.

The figure which shows the relationship between the particle size of non-caking coal, I type intensity | strength, and the expansion specific volume of a combination coal. The figure which shows the relationship between the particle size of non-coking coal, and an expansibility inhibition index (IFC). The figure which shows the particle size distribution of the non-slightly caking coal in Example 1. FIG. The figure which shows the change of the expansibility inhibition index (IFC) by the particle size fall of the non-slightly caking coal in Example 1. FIG. The figure which shows the change of the particle size distribution by the grinding | pulverization reinforcement | strengthening of the non-slightly caking coal C in Example 1. FIG. The figure which shows the relationship between the particle size of non-slightly caking coal and drum strength in Example 1. FIG. It is a figure regarding the expansion | swelling inhibition fluctuation rate in Example 1, (A) is a figure which shows the relationship between expansion | swelling inhibition fluctuation | variation rate and drum strength, (B) is a figure which shows the relationship between expansion | swelling inhibition fluctuation | variation rate and a grinding | pulverization level. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In the present embodiment, the non-slightly caking coal to be pulverized has a volatile content of 30% by mass or more, a total expansion rate by dilatometer measurement of 40% or less, and a logarithmic value of Gieseller fluidity (ddpm) of 1.5 or less. Means things.
First, the coke strength for each particle size of the non-slightly caking coal and the expansibility of the blended coal were investigated.
The properties of the non-slightly caking coal and caking coal used in this investigation are shown in Table 1 below.

The non-slightly caking coal was pulverized so that the 3 mm sieving ratio was 75% by mass. Then, the pulverized product was sieved into 7 particle size categories with 7 mm, 5 mm, 3 mm, 1 mm, 0.6 mm, 0.3 mm, and 0.1 mm sieves.
Next, non-finely caking coal of each particle size after sieving and caking coal having a 1 mm sieving ratio of 100% by mass were mixed to prepare blended coal for each particle size. The proportions of the blended charcoal were 30 dry mass% non-caking coal and 70 dry mass caking coal.
Next, 100 g of the blended coal was charged into a test coke oven, heated to 1000 ° C. at a rate of 3 ° C./min, held at 1000 ° C. for 30 minutes, and the coal blend was dry-distilled to produce coke. did. The test coke oven used a small dry distillation apparatus with a coal loading capacity of 144 cm ³ (W 40 mm, L 60 mm, H 60 mm).

The strength of the obtained coke was measured by a type I strength test.
In the I-type strength test, a sample is put in a cylindrical container, and the cylindrical container is rotated at a predetermined speed, and an impact is applied. Then, the residual rate of the sample on a 9.52 mm sieve is obtained. The rotation of the cylindrical container was performed by providing a rotation axis at the center of the length of the cylindrical container and rotating the rotation at a rotation speed of 20 times per minute around the rotation axis for a total of 600 rotations.
In this test, a cylindrical container having an inner diameter of 132 mm and a length of 600 mm was used, and about 72 cm ³ and about 40 g of coke obtained above were used as samples.

Moreover, the expansion specific volume was calculated | required based on the following method as an expansion | swelling parameter | index about the combination charcoal before coke preparation. The expansion specific volume is the volume after the coal expansion relative to the coal mass.
First, the blended charcoal was charged as powder into a thin tube defined in JIS M8801 at a predetermined charging density (0.85 [dry, g / cm ³ ]) to a height of 60 mm. Next, the piston is charged on the blended coal in the narrow tube, and the thin tube is heated from 300 ° C. to 600 ° C. at a temperature increase rate of 3.0 ± 0.1 ° C./min with the piston loaded. The height of the blended coal after completion of heating was measured. In this investigation, the load that the piston exerts on the blended coal was about 110 g. The height of the blended coal after the heating was set to L [mm]. And expansion specific volume [cm < ³ > / g] was calculated | required from the following formula | equation (1).
Expansion specific volume = L / (60 × 0.85) (1)

FIG. 1 shows the relationship between the particle size of non-caking coal, type I strength, and expansion specific volume of blended coal.
As shown in FIG. 1, when the non-slightly caking coal had a particle size of 1 mm to 3 mm, a result that the coke strength was maximized was obtained. Therefore, coarse non-coking coal particles can be reduced to a crack size due to the difference in shrinkage of semi-coke by pulverizing to a particle size of about 1 to 3 mm, resulting in improved coke strength. I think that.
On the other hand, at a particle size of 1 mm or less, the coke strength was significantly reduced. From this, it is considered that even if the particle size is smaller than 1 mm, the effect of improving the coke strength due to the decrease in crack size is small. Further, the decrease in coke strength with a particle size of 1 mm or less is considered to be caused by a decrease in the expansion specific volume.
From the above results, in order to obtain the effect of improving the coke strength by pulverization, it is desirable to pulverize the non-slightly caking coal to be in the range of 1 mm to 3 mm. However, in an actual pulverization operation, fine powder smaller than 1 mm is inevitably generated. And it is guessed that the influence with respect to the coke strength which the fine powder with a particle size of 1 mm or less exerts is very large.

Then, the influence on the expansibility which fine powder with a particle size of 1 mm or less exerts was evaluated.
The properties of the non-slightly caking coal and caking coal used in this investigation are shown in Table 2 below.

The non-slightly caking coals of different brands were calculated to have an expansion inhibition index (IFC) in a particle size number category of 3 mm or less when pulverized to a 75% by mass ratio of 3 mm under sieve.
Here, the expansivity inhibition index (IFC) refers to a constant f when calculating an inert factor IF shown in the following formula (2), which is disclosed in, for example, Japanese Patent No. 5402369.
Inert factor IF = −f × x + 1.00 (2)
In the above formula, x is a low coal content ratio.
In the expansibility inhibition index (IFC), it can be seen how much non-slightly caking coal inhibits expansibility by particle size classification.

In the method for calculating the expansion inhibition index (IFC), first, the specific expansion volumes of non-slightly caking coal, caking coal, and coal blended with non-slightly caking coal and caking coal were respectively calculated. . In addition, the expansion specific volume was computed from Formula (1) using the above-mentioned method. Next, the expansion specific volume of the blended coal by the weighted average value based on the blending ratio of the non-slightly caking coal and the caking coal was determined. And it calculated | required by dividing the difference of the expansion specific volume by a weighted average, and the actual mixing coal expansion specific volume by the percentage of the non-slightly caking coal added to the mixing coal.
That is, the expansibility inhibition index (IFC) is represented by the following formula (3).

非微粘結炭の粒度と膨張性阻害指数（ＩＦＣ）との関係を図２に示す。
図２に示すように、非微粘結炭の粒度が低下するに従ってＩＦＣは高くなる傾向にあり、粒度が１ｍｍ以下の微粉が膨張性に影響を与えていることを明らかとした。なお、ＩＦＣの増加度合いは非微粘結炭の銘柄によって異なっており、全膨張率が４０％と高い非微粘結炭ＡのＩＦＣの増加度合いは低く、全膨張率が０％のほとんど膨張しない非微粘結炭Ｄの増加度合いが高い結果が得られた。

FIG. 2 shows the relationship between the particle size of non-coking coal and the expansibility inhibition index (IFC).
As shown in FIG. 2, the IFC tends to increase as the particle size of the non-slightly caking coal decreases, and it has been clarified that fine powder having a particle size of 1 mm or less has an effect on expansibility. The degree of increase in IFC differs depending on the brand of non-slightly caking coal, and the rate of increase in IFC for non-slightly caking coal A, which is as high as 40%, is low, and the expansion rate is almost 0%. The result which the increase degree of the non-slightly caking coal D which does not do was high was obtained.

Therefore, an increase coefficient (ΔIFC _i ) from IFC ₀ was determined when non-slightly caking coal of 1 mm to 3 mm particles was pulverized to reduce the particle size to a particle size i of 1 mm or less. In addition, the expansion | swelling inhibition index of 1 mm-3 mm particle | grains with a small difference of the expansion | swelling inhibition index (IFC) by a brand was made into the reference | standard. The expansion inhibition index of ₁ mm to 3 mm particles based on this standard is defined as IFC ₀ .
ΔIFC _i is calculated based on the difference between the expansion inhibition index (IFC _i ) calculated for each particle size i and IFC ₀ for the particle size i generated by pulverizing 1 to 3 mm non-coking coal (ΔIFC _i = IFC _i -IFC ₀ ).
That is, the increase coefficient (ΔIFC _i ) from IFC ₀ is expressed by the following equation (4).

ΔＩＦＣ_ｉは、増分が大きいほど、非微粘結炭の粉砕強化によって、配合炭の膨張性をより低下させることを意味している。このため、銘柄毎のΔＩＦＣ_ｉの違いによって、どの程度にまで粉砕強化することが可能かの指標になるといえる。

ΔIFC _i means that the larger the increment, the lower the expansibility of the blended coal by pulverizing and strengthening the non-slightly caking coal. For this reason, it can be said that it is an index of how much crushing and strengthening can be performed by the difference in ΔIFC _i for each brand.

In addition, if an expansibility inhibition index is calculated for each brand, the blended coal used for coke production can save time and effort for evaluating the expansibility each time. The grinding particle size can be determined.
In addition, when calculating the expansion inhibition index (IFC), when measuring the expansion specific volume, when the expansion specific volume is measured, sufficient expansion is required for the caking coal blended with the blended coal. It is desirable to have it.

On the other hand, it was evaluated how the fine powder having a particle size of 1 mm or less increases by pulverization strengthening.
Here, the particle size distribution was measured when the non-finely caking coal was pulverized and strengthened from a 3 mm sieving ratio of 75% by mass. Then, the 1 mm sieve was divided into several particle sizes i, and the mass ratio increment (ΔFC _i ) of the particle size i was calculated for each particle size category. From this ΔFC _i , it can be understood which particle size occupies with what mass with respect to the total amount of non-slightly caking coal by pulverization strengthening. Incidentally,? Fc _i is the mass ratio increment in the particle size i the total amount of non- or slightly caking coal.
Then, ΔIFC _i and ΔFC _i were multiplied and this ΔIFC _i × ΔFC _i was summed for each particle size i to calculate Σ (ΔIFC _i × ΔFC _i ).
By ΔIFC _i × ΔFC _i , it is understood how much the non-slightly caking coal of particle size i inhibits the expandability with respect to the total amount of the non-slightly caking coal. It is possible to index how much the lower fine powder inhibits the expansibility with respect to the total amount of non-slightly caking coal.

Furthermore, Σ (ΔIFC _i × ΔFC _i ) × α, which is obtained by multiplying the calculated Σ (ΔIFC _i × ΔFC _i ) by the blending ratio α of non-slightly caking coal in the blended coal used in the dry distillation test, It was set as the swelling inhibition variation rate.
By obtaining the expansion inhibition variation rate, it is possible to predict the degree of decrease in the expansion of the blended coal when non-slightly caking coal is pulverized and strengthened. That is, the smaller the expansion inhibition variation rate, the smaller the decrease in expansibility of the blended coal even if the non-slightly caking coal is pulverized, that is, the pulverization of the non-slightly caking coal can be strengthened.

Crushing the non-slightly caking coal reduces the crack size in the coke mass and improves the coke strength. However, over-pulverization increases the degree of expansion inhibition and reduces the coke strength.
Here, expansibility inhibition is a factor which inhibits expansion of other coal (mainly caking coal).
The influence of coke strength due to the pulverization of non-slightly caking coal is also complicated by the reduction of coarse coal (over 3 mm) and the expansion specific volume of non-slightly caking coal itself due to pulverization. is there.
In the coke production method of the present embodiment, attention is paid to the fact that the effect of the expansion inhibiting factor of the non-slightly caking coal is large, and the non-slightly caking coal is set so that the expansion inhibiting fluctuation rate is not more than a predetermined value. Was determined. Specifically, the pulverized particle size of the non-slightly caking coal was determined to be 0.02 or less. Then, the non-coking coal is pulverized with the determined pulverized particle size to produce coke as part of the blended coal.
In this way, considering the influence of the expansion of the particle size of 1 mm or less, and pulverizing so as to minimize this influence, the reduction of the coke strength due to the decrease of the expansion can be suppressed.
Moreover, the reduction | decrease of the coke intensity | strength resulting from a crack production | generation can be suppressed by grind | pulverizing non-slightly caking coal and making the particle size of non-slightly caking coal small.
In addition, although it is necessary to consider the decrease in the expandability of the non-slightly caking coal itself after pulverization by pulverization, if it is a non-slightly caking coal to be pulverized in this embodiment, the non-slightly caking after pulverization The reduction in the expansion of the charcoal itself can be almost ignored.
As a result, according to the coke production method of the present embodiment, coke having a higher strength can be easily obtained.
In this embodiment, the expansion inhibition index of coal having a particle size of 1 mm to 3 mm when pulverized to a 3 mm sieving ratio of 75% by mass is IFC ₀ , but IFC ₀ has a 3 mm sieving ratio of 65% by mass or more. It can be calculated from coal having a particle size of 1 mm to 3 mm when pulverized within the range of 85% by mass or less. If the 3 mm sieving ratio is within the above range, the difference in expansibility inhibition index (IFC) depending on the brand is small, so that it can be used as a reference for calculating ΔIFC _i .

  Next, the present invention will be described in more detail with reference to examples. In addition, this invention is not restrict | limited to the description content of these Examples at all.

<Example 1>
The properties of non-coking coals A, B, C and D are shown in Table 3 below, and the particle size distribution is shown in Table 4 below and FIG.

First, each of the non-slightly caking coals A, B, C, and D was pulverized so that the 3 mm sieving ratio was 75% by mass. Particles having a particle size of 1 mm to 3 mm were collected from the pulverized particles, and the expansion specific volume was calculated from the above formula (1) using the method described above.
Further, the particles having a particle size of 1 to 3 mm are added to caking coal (1 mm sieving ratio is 100% by mass) whose expansion specific volume is known in advance at a rate of 30% by mass. By measuring the expansion specific volume, the expansion inhibition index (IFC ₀ ) was calculated. The total expansion rate of this caking coal is 79%.
Furthermore, the above-mentioned particles having a particle size of 1 to 3 mm were pulverized by hand to 0.3 to 0.6 mm or 0.1 mm or less. The pulverized particles were added to caking coal in the same manner as described above, and the expansion specific volume of the blended coal was measured. From this expansion specific volume, the expansibility inhibition index for each particle size was calculated. FIG. 4 shows the change in the expansion inhibition index (IFC) due to the particle size reduction of the non-slightly caking coal.
As shown in FIG. 4, IFC tends to increase as the particle size of non-slightly caking coal decreases, and it can be confirmed that the degree of increase differs depending on the brand of non-slightly caking coal.

Moreover, the non-slightly caking coal was grind | pulverized so that a 3 mm sieving ratio might be 75 mass%, 85 mass%, and 95 mass%, respectively, and the particle size distribution of the obtained ground material was measured by sieving. As an example, FIG. 5 shows a change in particle size distribution due to pulverization and strengthening of non-slightly caking coal C.
As shown in FIG. 5, there is a tendency for fine powder having a particle size of 1 mm or less to increase by crushing and strengthening the 3 mm sieving ratio of non-slightly caking coal from 75 mass% to 85 mass% and 95 mass%. It is done.

Next, among the pulverized product obtained by pulverization, fine particles of 1 mm or less are divided into four particle sizes (1 mm to 0.6 mm, 0.6 mm to 0.3 mm, 0.3 mm to 0.1 mm, 0.1 mm). The mass ratio increment (ΔFC _i ) was calculated for each particle size category.
Also, ΔIFC _i (ΔIFC _i = IFC _i -IFC ₀ ) at the median value of the four granularity sections was estimated based on the lines connecting adjacent plots with straight lines shown in FIG.
Next, ΔIFC _i obtained above and ΔFC _i were multiplied and totaled for each particle size i to calculate Σ (ΔIFC _i × ΔFC _i ).

Moreover, about 80 kg of blended coal containing 25% by mass of non-slightly caking coal was prepared. Then, the coal blend was charged at a bulk density of 0.87 t / m ³ into a test coke oven having a carbonization chamber size of W450 mm × L500 mm × H500 mm, and subjected to dry distillation at a dry distillation temperature of 1000 ° C. for 21 hours.
The discharged coke was cooled under nitrogen flow, and then subjected to a drum strength (DI ¹⁵⁰ ₁₅ ) measurement test specified in JIS-K2151. FIG. 6 shows the result of the drum strength test.
As shown in FIG. 6, there are examples in which the drum strength is improved or decreased by pulverization strengthening, and the results are greatly different depending on the brand.
4 and 6, it can be seen that the degree of influence (expansion inhibition index; IFC) of particles having a particle size of 1 mm or less greatly varies depending on the brand and the particle size classification of particles having a particle size of 1 mm or less. .

Next, by multiplying the calculated Σ (ΔIFC _i × ΔFC _i ) by the blending ratio (α = 25) of non-slightly caking coal in the blended coal of the coke produced above, the expansion inhibition fluctuation rate Σ ( ΔIFC _i × ΔFC _i ) × α was determined.
FIG. 7A shows the relationship between the expansion inhibition fluctuation rate and the drum strength, and FIG. 7B shows the relationship between the expansion inhibition fluctuation rate and the grinding level. FIG. 7 (A) shows the change of DI ¹⁵⁰ ₁₅ when non-slightly caking coal is pulverized and strengthened as ΔDI, based on DI ¹⁵⁰ ₁₅ when the particle size of non-slightly caking coal is 75% by mass under a 3 mm sieve. FIG. 6 is a diagram in which ΔDI is plotted against the rate of expansion inhibition fluctuation.
As shown in FIG. 7 (A), it can be seen that ΔDI is negative when the expansion inhibition fluctuation rate is greater than 0.02. That is, it can be said that the influence of expansion | swelling inhibition became large and DI fell by strengthening a grinding | pulverization. Moreover, from FIG. 7 (A) and FIG. 7 (B), the non-slightly caking coal with a large expansion | swelling inhibition fluctuation | variation rate can see the tendency for drum strength to fall as a grinding | pulverization level is strengthened.

  It can be used for the production of coke when a large amount of non-coking coal is used as part of the blended coal.

Claims (2)

Non-slightly caking coal with a volatile content of 30% by mass or more, a dilatometer measurement with a total expansion rate of 40% or less, and a logarithmic value of Gieseller fluidity (ddpm) of 1.5 or less is used as part of the blended coal In making coke,
A method for producing coke, wherein the pulverized particle size of the non-slightly caking coal is determined so that the expansion inhibition fluctuation rate is a predetermined value or less.
Here, the expansion inhibiting fluctuation rate is obtained by the following method. That is,
The expansion inhibition index (IFC ₀ ) of coal having a particle size of 1 mm to 3 mm when the non-slightly caking coal is pulverized to a ratio of 65% by mass to 85% by mass of the 3 mm sieving ratio is obtained.
Next, an increase coefficient (ΔIFC _i ) from the IFC ₀ is calculated by calculating an expansion inhibition index (IFC _i ) of the coal for each particle size i for the particle size i generated by pulverizing the coal having a particle size of 1 mm to 3 mm. Calculate it.
Next, the mass ratio increment (ΔFC _i ) of the particle size i is obtained for each particle size classification under a 1 mm sieve when the IFC _{0 of the} non-slightly caking coal is crushed to the calculated pulverized particle size or more. Incidentally, the? Fc _i is the mass ratio increment in the particle size i the total amount of the non- or slightly caking coal.
The ΔIFC _i and the ΔFC _i are multiplied and totaled for each granularity i to calculate Σ (ΔIFC _i × ΔFC _i ).
Finally, the calculated Σ (ΔIFC _i × ΔFC _i ) is multiplied by the blending ratio α of the non-slightly caking coal in the blended coal to be subjected to the dry distillation test to obtain an expansion inhibition variation rate.   The method for producing coke according to claim 1, wherein the pulverized particle size of the non-slightly caking coal is determined so that the expansion inhibition fluctuation rate is 0.02 or less.

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