WO2018008339A1 - Method for refining low-rank coal, method for producing coke, and method for producing pig iron - Google Patents

Abstract

The key feature of this method for refining low-rank coal is the feature of subjecting low-rank coal to a chemical reduction treatment. The key feature of this method for producing coke is the feature of producing refined coal using the method for refining low-rank coal and then carbonizing the refined coal. The key feature of this method for producing pig iron is the feature of producing coke using the method for producing coke, introducing the obtained coke into a blast furnace together with limestone and iron ore, and chemically reducing the iron ore. According to the present invention, it is possible to provide a method for refining low-rank coal, a method for producing coke and a method for producing pig iron which are useful for producing high strength coke at low cost.

Description

Method for reforming inferior coal, method for producing coke, and method for producing pig iron

The present invention relates to a method for reforming inferior coal, a method for producing coke using the modified coal obtained by the reforming method, and a method for producing pig iron using the coke.

As a coke raw material, blended coals that are a mixture of high-grade caking coal (hereinafter sometimes referred to as “high-grade coal”) and inferior coals such as lignite and sub-bituminous coal with a low caking component are widely used. . However, the price has soared due to the low reserves of high-grade coal and the decrease in the number of harvestable years. For this reason, there is a demand for the production of coke with an increased amount of inferior coal. However, since the coke strength tends to decrease as the blending amount of the inferior coal increases, sufficient coke strength cannot be obtained, and the coke is easily pulverized in the blast furnace. As a result, there has been a problem that the air permeability in the blast furnace is hindered and the progress of proper iron ore reduction is hindered. In view of these circumstances, in recent years, research has been conducted on increasing the strength of coke containing inferior quality coal.

For example, in Patent Document 1, in a method of heating raw coal to be charged into a chamber coke oven with a coal heater in advance, an air dryer with a classification function is used before and / or after charging coal with the coal heater. A rapid heating method of coal that separates and removes pulverized coal of 0.1 mm or less contained in charging coal is disclosed. According to Patent Document 1, it is described that non-slightly caking coal can be mixed and used for 40-60% charging coal by preheating treatment of non-slightly caking coal, and coke strength can be improved. .

Japanese Unexamined Patent Publication No. 7-109465

However, in Patent Document 1, there is a problem that a manufacturing cost becomes high in consideration of equipment introduction costs, maintenance costs, and the like, such as a facility for rapid heating.

The present invention has been made paying attention to the circumstances as described above, and the object thereof is a method for reforming inferior coal useful for producing coke having high strength at low cost, a method for producing coke, and It is to provide a method for producing pig iron.

The present invention that has solved the above problems has a gist in reducing the inferior quality coal.

The reduction treatment is preferably performed in the presence of a reducing agent, and the reducing agent is preferably in the form of a gas or liquid.

In addition, the reduction treatment is preferably performed in a temperature range of room temperature to 65 ° C. for 10 minutes to 6 hours. In the present invention, the reducing agent is preferably at least one selected from the group consisting of formic acid and oxalic acid.

The present invention also includes a coke production method in which reformed coal is produced by the above-described reforming method of inferior coal, and this reformed coal is carbonized.

The present invention also includes a method for producing pig iron in which coke is produced by the above production method, and the obtained coke is introduced into a blast furnace together with limestone and iron ore to reduce the iron ore.

According to the present invention, a modified coal having an effect of improving coke strength is obtained. Further, high strength coke can be produced by using the modified coal of the present invention. Moreover, according to the production method of the present invention, since conventional coke production equipment can be used as it is, high strength coke can be produced at low cost. Furthermore, since the coke of the present invention has sufficient strength and can prevent crushing, pulverization, etc. in a blast furnace, it is suitable as coke for producing pig iron.

FIG. 1 is a graph showing the results of measurement of softening and melting properties of coke of the present invention produced in Examples and coke produced by a conventional method. FIG. 2 is a graph showing the results of measurement of softening and melting properties of the coke of the present invention produced in the example and the coke produced by the conventional method. FIG. 3 is a graph showing the results of measurement of softening and melting properties of the coke of the present invention produced in the example and the coke produced by the conventional method. FIG. 4 is a graph showing the strength measurement results of the coke of the present invention produced in the example and the coke produced by the conventional method. FIG. 5 is a graph showing the strength measurement results of the coke of the present invention produced in the example and the coke produced by the conventional method.

Inferior coal contains many oxygen-containing functional groups. When heated, pyrolytic radicals are likely to be generated at a relatively low temperature, and the radicals are bonded to each other to form a crosslinked structure. Therefore, even when heated to a softening and melting temperature range of about 400 to 500 ° C., the movement of coal molecules is hindered, the coal fluidity becomes insufficient, the caking property is suppressed, and the strength of coke is considered to decrease. ing.

As a result of diligent research by the present inventors, it was found that if poor quality coal previously subjected to reduction treatment is used as a coke raw material, fluidity in the softening and melting temperature range can be improved, and high strength coke can be obtained. The present invention has been reached.

The background to the present invention is as follows. That is, as a result of the study by the present inventors, inferior coal has unstable radicals having high reactivity even in a temperature range from room temperature to about 65 ° C., and these radicals are softened and melted by stabilizing them. It was found that the crosslinking reaction and polymerization reaction caused by the radical can be suppressed even when heated to a temperature range. Specifically, it has been found that the radical can be made stable by subjecting the inferior coal to a reduction treatment. When coking with reduced quality inferior coal (hereinafter sometimes referred to as “modified coal”), the formation of the cross-linked structure is suppressed even when the softening and melting temperature range is reached, and the fluidity of the coal is improved. At the same time, since the orientation of coal molecules is improved and the crystallinity is increased, a strong coke structure is obtained above the resolidification temperature, and as a result, high strength coke is considered to be obtained. Hereinafter, the reforming method for inferior coal and the method for producing coke of the present invention will be described.

The modification target of the present invention is poor quality coal. Inferior coal means coal having a calorific value of 5700 kcal / kg or less and a volatile content of 31% or more. Examples of such inferior coals include brown coals such as Victoria coal, North Dagota coal, and Berga coal; and sub-bituminous coals such as West Banco coal, Vinungan coal, and Samarangau coal. The inferior charcoal of the present invention is not limited to the above examples, and the vitrinite average reflectance Ro is 0.85% or more, and the Gieseler maximum fluidity logMF is 10 ddpm or less, or the vitrinite average reflectance Ro is 0.85% or less. Moreover, non-slightly caking coal having a Gieseler maximum fluidity log MF of 50 ddpm or less is also included.

In order to improve the reduction treatment efficiency, the inferior coal is preferably pulverized to a diameter of 5 mm or less, more preferably 3 mm or less.

In the present invention, the inferior coal is reduced to reduce the inferior coal. However, the reduction treatment method is not particularly limited as long as the radical in the inferior coal is stabilized by the reduction treatment. That is, it is only necessary that the radical amount of the poor quality coal after the reduction treatment is reduced. Although it is difficult to directly measure the amount of radicals before and after the reduction treatment, for example, when the reduction treatment is performed as shown in the examples of the present invention, the flow in the softening and melting temperature range is less than when the reduction treatment is not performed. If the property is improved or the coke strength is improved, it can be determined that the amount of radicals has been reduced by the reduction treatment, and the inferior coal has been modified.

It is desirable to use a reducing agent in the reduction treatment of the present invention. By using a reducing agent, the poor quality coal can be modified efficiently. In particular, when used as coke for pig iron production, it is preferable that the reducing agent is carbon dioxide by reduction treatment because it can prevent the mixing of components unnecessary for pig iron production. Therefore, the reducing agent is preferably an organic reducing agent. Of the organic reducing agents, lower alcohols, aldehydes, and carboxylic acids that can be vapors in the temperature range from room temperature to 65 ° C. are desirable. Examples of such alcohols include methanol and 2-propanol. Examples of aldehydes include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, and the like. Examples of carboxylic acids include formic acid and oxalic acid. Of these, carboxylic acids are more preferable, and formic acid and oxalic acid are particularly preferable. The inferior coal obtained by reduction using such a reducing agent has been modified as described above.

When formic acid is used as the reducing agent, hydrogen and electrons are donated to the poor coal by the reaction shown in the following formula, and radicals in the poor coal can be stabilized.
HCOOH → CO ₂ + 2H ⁺ + 2e ⁻

When oxalic acid is used as the reducing agent, hydrogen and electrons are donated to the poor coal by the reaction shown in the following formula, and radicals in the poor coal can be stabilized.
(COOH) ₂ → 2CO ₂ + 2H ⁺ + 2e ⁻

As a result of donating hydrogen and electrons to the inferior coal by the reducing agent, the radicals contained in the inferior coal are stabilized. Therefore, when the reformed coal obtained as described above is heated to the softening and melting temperature range, The fluidity is improved and high strength coke is obtained. When a reducing agent is used, it is preferable to increase the contact efficiency by stirring or the like because the reduction treatment can be performed efficiently.

The reducing agent may be gaseous or liquid. When the reducing agent is used in a gaseous state, for example, steam obtained by heating the reducing agent may be brought into contact with inferior coal. In the case where the reducing agent is used in a liquid state, for example, an aqueous solution containing the reducing agent (hereinafter sometimes referred to as “reducing agent-containing aqueous solution”) may be brought into contact with inferior coal to perform the reduction treatment. As a contact method, inferior charcoal may be immersed in the reducing agent-containing aqueous solution, or the reducing agent-containing aqueous solution may be sprayed on the inferior coal. When the reducing agent is used in a gaseous state, for example, the reducing agent is heated and vaporized in a sealed space containing inferior coal, or steam obtained by heating the reducing agent externally is supplied to the sealed space. May be.

The amount of reducing agent consumed in the reduction treatment is estimated to be about 0.2 mmol / g-coal as an electron donating amount, although it depends on the kind of poor coal used, and based on this, In the case of formic acid, it is 0.45 mass% (based on dry coal), and in the case of oxalic acid, it is 0.9 mass% (based on dry coal). Since the reducing agent that does not participate in the reduction reaction maintains the original molecular state and maintains the reducing ability, it is desirable to recover and recycle the unreacted reducing agent after the reduction treatment.

The reaction temperature during the reduction treatment is not particularly limited. When the reaction temperature is raised, the reducing agent is easily diffused on the surface of the inferior coal, the reduction reaction is promoted, and the production efficiency is improved. Therefore, the temperature during the reduction reaction is preferably normal temperature or higher, more preferably 40 ° C. or higher. On the other hand, the upper limit of the reaction temperature is not limited as long as it is lower than the softening and melting temperature of coal, but it is preferably 65 ° C. or less, more preferably 60 ° C. or less in consideration of heating costs, diffusion on the coal surface and inside the coal substrate, and the like. is there. The reaction temperature may be adjusted by heating by any means.

The time for the reduction treatment is not limited as long as sufficient reduction is performed, but is preferably 10 minutes or more, more preferably 30 minutes or more, preferably 6 hours or less, more preferably 2 hours or less.

After the reduction treatment, the modified coal obtained by performing the reduction treatment is subjected to a cooling treatment as necessary, a washing treatment for removing the reducing agent with water or the like, and a drying treatment for drying the reduced treatment coal after the washing treatment. Also good.

Even if a reducing agent is used for reforming inferior coal, the reformed coal contains no components other than C, H, and O derived from the reducing agent, and unnecessary components derived from the coke are present in the production process of pig iron. Since it is not contained, it is suitable as a raw coal for coke for pig iron production.

The reduction treatment of the inferior coal is not limited as long as it is performed at any timing before the coking treatment, preferably before heating to the softening and melting temperature. For example, the inferior quality coal stored in a yard or the like may be subjected to a reduction process, or may be subjected to a reduction process during coal transportation. By reducing the inferior coal before the coking process, high strength coke can be produced without increasing the lead time for coke production and without any new changes or additions to the existing coke production facility. Since it can manufacture, it is desirable also from a viewpoint of production cost.

Hereinafter, a method for producing coke using the modified coal obtained by the above reduction treatment as a coke raw material will be described, but the method for producing coke is not particularly limited, and a conventional coke production method can be adopted. Therefore, the method for producing coke is not limited to the following examples, and can be appropriately changed. The manufacturing method of the coke of this invention has a mixing process and a dry distillation process.

<Mixing process>
First, a mixture is produced using the above-mentioned modified coal as a coke raw material. The mixing step is a step of obtaining a mixture by mixing the reformed coal with other coal or caking additive added as necessary. The mixing method of the modified coal and the binder is not particularly limited as long as a uniform mixture is obtained. For mixing, a known means such as a mixer, a kneader, or a mixer may be used.

In the present invention, the modified coal may be used alone as a coke raw material, but other coal may be blended and used together with the modified coal (hereinafter sometimes referred to as “coking coal”). The kind of other coal to be used is not particularly limited, and it is desirable to use at least one selected from the group consisting of strongly caking coal, semi-caking coal, slightly caking coal, and non-caking coal. In the present invention, the strongly caking coal is a coal having a vitrinite average reflectance Ro of more than 1.1 to 1.5% and a Gieseler maximum fluidity log MF of 0.5 to 3.5 ddpm, and a semi-caking coal is vitrinite. Coal and fine caking coal having an average reflectance Ro of 0.7 to 1.1% and a Gieseler maximum fluidity log MF of more than 2.5 to 3.5 ddpm have a vitrinite average reflectance Ro of 0.7 to 1. 1%, coal with a highest Guessar flow rate log MF of 0.5 to 2.5 ddpm. The vitrinite average reflectance Ro is the maximum fluidity based on the Gieseler plastometer method defined in JIS M8816 and the Gieseler maximum fluidity log MF.

The reformed coal of the present invention uses inferior quality coal as a raw material, but as described above, the reformed coal contributes to increasing the strength of coke. For this reason, high-strength coke can be obtained even when reformed coal is used alone as raw coal. However, when blended coal is used in combination with reformed coal and other coals, increasing the amount of reformed coal improves coke strength. To do. Therefore, if the blending amount of the modified coal is increased, a high strength coke can be obtained even if the blending ratio of the strong caking coal is reduced as compared with the conventional one.

Further, strong caking coal, semi-caking caking coal, slightly caking coal, and non-caking coal can be used in combination of plural kinds, and may be appropriately combined according to the required coke characteristics. Increasing the amount of strong caking coal improves the strength of coke. Moreover, since semi-strongly caking coal has the viscosity next to strongly caking coal and has the characteristics of high fluidity and high expansibility, the properties of blended coal can be controlled by appropriately combining these coals. Moreover, when the compounding quantity of a slightly caking coal and a non-caking coal is increased, the intensity | strength of coke will fall.

In order to improve the strength of the coke, the particle size of the raw coal may be determined as appropriate in consideration of the industrially possible pulverized particle size range and dust, and is not limited. For example, the raw coal preferably has a particle size of 80% by mass or more, more preferably 85% by mass or more, and still more preferably 90% by mass or more, of 3 mm or less. In the present invention, the “particle size” is a value determined by a particle size test method described in JIS M8801.

In the present invention, a binder may be used as necessary. As the binder, various known binders such as petroleum pitch, coal pitch, and solvent extracted coal can be used. The mixing ratio of raw coal and caking additive is not particularly limited. In the present invention, from the viewpoint of improving the coke strength, it is desirable to adjust the fluidity after blending the binder. For example, the coke strength can be improved by adjusting the fluidity to, for example, 1.5 to 3.5 ddpm, more preferably 2.0 to 3.0 ddpm, in terms of the Gieseler maximum fluidity logMF. Moreover, what is necessary is just to determine a mixing ratio suitably according to properties, such as coke reactivity requested | required and the fluidity | liquidity of the coking coal to be used, and reactivity.

In the production of the mixture, known additives and the like may be included as necessary.

In the present invention, a desired ratio of iron ore may be mixed with the above mixture. The mixture may be formed into a desired shape. The molding method is not particularly limited, and for example, any of a double roll type molding machine using a flat roll, a double roll type molding machine having an almond type pocket, a uniaxial press or roller type molding machine, an extrusion molding machine, and the like can be adopted.

Molding may be either cold molding performed at around room temperature or hot molding performed by heating. The hot forming is preferably performed at a thermal decomposition temperature of coal exceeding room temperature, for example, less than 400 ° C., more preferably 250 to 350 ° C. When the temperature exceeds 400 ° C., coal is thermally decomposed and tar may be generated to lose the coal component. The molding pressure is not particularly limited, and known conditions may be adopted.

The size of the molded body obtained through the molding as described above is about 10 to 30 mm, although it varies depending on the type of raw iron ore and coal, production conditions, and operating conditions in the blast furnace.

<Dry distillation process>
The dry distillation step is a step of dry distillation of the mixture obtained in the mixing step. By coking, the coal portion can be coke to produce coke.

The carbonization process can be performed using an existing coke oven. The shape of the furnace used for dry distillation is not particularly limited, and batch distillation may be performed using a chamber furnace, or continuous distillation may be performed using a vertical shaft furnace. When a vertical shaft furnace is used, the molded body is charged from above the furnace, and is dry-distilled while moving in the furnace from top to bottom, and is dry-distilled from below the furnace and discharged. The mixture may be preheated as necessary.

Known conditions can be adopted as the carbonization conditions such as the carbonization temperature and the carbonization time. The carbonization temperature is preferably 650 ° C. or higher, more preferably 700 ° C. or higher, preferably 1200 ° C. or lower, more preferably 1110 ° C. or lower. . The dry distillation time is preferably 5 minutes or longer, more preferably 10 minutes or longer, preferably 24 hours or shorter, more preferably 12 hours or shorter. The dry distillation atmosphere is preferably a non-oxidizing gas atmosphere from the viewpoint of preventing oxidation of coal.

In the above coke manufacturing method, a new process may be provided between or before and after each process within a range that does not adversely affect each process. For example, a coal pulverization step for pulverizing raw coal, a step for adjusting softening and melting properties by heat treatment, a removal step for removing unnecessary substances such as dust, and the like may be performed.

The obtained coke of the present invention has higher strength than coke using conventional inferior coal as the raw coal. Specifically, the strength of the coke of the present invention is 0.4 MPa or more, preferably 0.5 MPa. As described above, it has a sufficient strength of 1.0 MPa or more.

Since the coke obtained by the production method of the present invention is excellent in strength, it can be suitably used for producing pig iron in a blast furnace. That is, since the coke obtained by the production method of the present invention has a sufficient strength that does not crush, it is effective in improving gas permeability when producing pig iron in a blast furnace.

As a method for producing pig iron in a blast furnace, a known method may be adopted.For example, limestone, iron ore and coke are alternately laminated in a blast furnace in layers, and hot air from the lower part of the blast furnace, and if necessary, pulverized coal. The method of blowing can be mentioned.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Coke raw materials were produced based on the following (1) to (3) using the inferior coal shown in Table 1. In addition, the analysis method of inferior quality coal is as follows.
Elemental content (dry ash free): Elemental content (% by mass) of organic matter (C, H, O, N) excluding coal moisture and ash as measured by JIS M8801
Ash content and volatile content: JIS M8812

(1) Coal reduction treatment A
10 g of F charcoal or 10 g of G charcoal and 250 mL of 0.5 mol / L formic acid aqueous solution were placed in a 500 mL Erlenmeyer flask and shaken for 6 hours while maintaining the temperature at 65 ° C. to carry out a reduction reaction. After the reduction reaction, the coal was taken out, washed with water, and dried to obtain reduced coal. Reduced coal using F charcoal was reduced to AF coal, and reduced coal using G coal was reduced to AG coal.

(2) Coal reduction treatment B
After filling 10 g of F charcoal or 10 g of G charcoal into a sealed container with an inner volume of 250 mL, a beaker having a diameter of 2 cm and a height of 4 cm containing 3 mL of 99% formic acid was left in the sealed container to seal the container. . The temperature of the sealed container was maintained at 60 ° C. for 2 hours or 6 hours to carry out the reduction reaction. After the reduction reaction, the coal was taken out and cooled to room temperature to obtain reduced coal. Reduced coal maintained for 2 hours using F charcoal is reduced B2-F charcoal, reduced coal maintained for 2 hours using G charcoal is reduced B2-G charcoal, reduced coal maintained for 6 hours using G charcoal B6 -G charcoal.

(3) Coke production method 2 g of untreated F charcoal or 2 g of untreated G charcoal in a stainless steel mold having an inner diameter of 1.7 cm and a height of 1.4 cm, or F charcoal subjected to reduction treatment under the above conditions or 2 g of G charcoal was charged, and a stainless steel lid was placed on the upper part of the coal bed so that a load of 34.8 gf was applied to the coal. The mold was placed inside a container in a vertical heating furnace. The inside of the container was heated to 900 ° C. at a rate of temperature increase of 10 ° C./min under a nitrogen flow rate of 0.1 NL / min, and kept at this temperature for 30 minutes to perform a coking reaction to obtain each coke sample. .

Using untreated coal and reduced coal, the softening meltability is evaluated by the following softening melt measurement test, and using the coke samples produced from untreated coal and reduced coal, the coke strength is evaluated by the following strength measurement test. did.

Softening and meltability measurement test The softening and melting properties of each untreated coal and each reduced coal were evaluated using thermomechanical analysis (manufactured by Shimadzu Corporation: TMA-50). An untreated coal or reduced coal is filled in a cell having an inner diameter of 5.2 mm and a height of 6.0 mm to a thickness of about 1 mmL, and a 10 gf load is applied to the cylindrical quartz rod having a diameter of 4.3 mm. The sample was heated to 900 ° C. at 10 ° C./min in a nitrogen atmosphere, and the change in the position of the rod when the sample was softened and melted and the rod was pushed into the sample layer was continuously measured. In this measurement, the higher the softening and melting property, the greater the change in position of the rod.

Strength measurement test Each coke sample was directly subjected to strength measurement. The strength of the coke was evaluated by conducting a crushing strength test of the coke using a precision universal testing machine (Autograph AGS-10kNJ, manufactured by Shimadzu Corporation).

Fig. 1 shows the results of measurement of softening and melting properties of untreated F coal and reduction-treated A-F coal. From FIG. 1 and FIG. 2, the softening and melting properties were improved by reducing the inferior coal with a formic acid aqueous solution.

Fig. 3 shows the results of measurement of softening and melting properties of untreated G charcoal, reduced B2-G charcoal, and reduced B6-G charcoal. From FIG. 3, it can be seen that the softening and melting property is also improved by performing the reduction treatment with formic acid vapor.

FIG. 4 shows the strength measurement results for each coke produced from untreated F charcoal, reduced treated AF charcoal, untreated G charcoal, and reduced treated AG charcoal. As shown in FIG. 4, coke produced from reduced coal was about 3-6 times stronger in coke strength than coke produced from untreated coal.

FIG. 5 shows the strength measurement results of each coke produced from untreated F charcoal, reduced B2-F charcoal, untreated G charcoal, reduced B2-G charcoal, and reduced B6-G charcoal. As shown in FIG. 5, coke produced from reduced coal had a coke strength of about 2-5 times higher than coke produced from untreated coal. In addition, coke produced from reduction-treated B6-G charcoal with a reduction time of 6 hours has a further increase in coke strength, and is about 2.5 times that of coke produced from reduction-treated B2-G coal. The strength was improved about 5 times compared to the coke produced from

1, 2, and 3, it was found that softening and melting properties can be improved by reducing the inferior coal. This is considered to be because the crosslinking reaction in the softening and melting temperature region was suppressed by stabilizing the radicals present in the poor quality coal by performing the reduction treatment. Moreover, it turned out that coke intensity | strength can be improved from FIG. 4, FIG. 5 if the modified coal which reduced the poor quality coal was used. Further, when the reduction treatment time was lengthened, the strength tended to be further improved. This is because the reduction treatment time was increased and sufficient reduction treatment was performed, resulting in a decrease in the amount of unstable radicals present in inferior coal and an improvement in softening and melting performance, resulting in the formation of a stronger coke structure. It is thought that.

Although the invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application filed on July 5, 2016 (Japanese Patent Application No. 2016-133282), which is incorporated by reference in its entirety.

Claims (10)

A method for reforming inferior coal, which is to reduce inferior coal. The method for reforming inferior coal according to claim 1, wherein the reduction treatment is performed in the presence of a reducing agent. The method for reforming inferior coal according to claim 2, wherein the reducing agent is gaseous or liquid. The method for reforming inferior coal according to claim 2 or 3, wherein the reduction treatment is carried out in a temperature range of room temperature to 65 ° C for 10 minutes to 6 hours. The method for reforming poor coal according to claim 2 or 3, wherein the reducing agent is at least one selected from the group consisting of formic acid and oxalic acid. The method for reforming inferior coal according to claim 4, wherein the reducing agent is at least one selected from the group consisting of formic acid and oxalic acid. A method for producing coke in which reformed coal is produced by the method for reforming inferior coal according to any one of claims 1 to 3, and the reformed coal is dry-distilled. A method for producing coke in which reformed coal is produced by the method for reforming inferior coal according to claim 4 and the reformed coal is carbonized. A method for producing coke in which reformed coal is produced by the method for reforming inferior coal according to claim 5, and the reformed coal is dry-distilled. A method for producing pig iron, wherein coke is produced by the production method according to claim 7 and the obtained coke is introduced into a blast furnace together with limestone and iron ore to reduce the iron ore.

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