AU2018378746B2

AU2018378746B2 - Method for producing reformed coal

Info

Publication number: AU2018378746B2
Application number: AU2018378746A
Authority: AU
Inventors: Akinobu IMAMURA; Katsushi Kosuge; Hiroyuki Kozuru; Wataru Tanioku
Original assignee: Nippon Steel Corp; Nippon Steel Engineering Co Ltd
Current assignee: Nippon Steel Corp; Nippon Steel Engineering Co Ltd
Priority date: 2017-12-08
Filing date: 2018-10-16
Publication date: 2021-02-25
Anticipated expiration: 2038-10-16
Also published as: CN111433330A; AU2018378746A1; JP6402235B1; JP2019099777A; WO2019111540A1

Abstract

Provided is a method for producing reformed coal, the method having a dry distillation step for dry-distilling coal at 300-650°C to obtain dry-distilled coal, and an oxidation treatment step in which the dry-distilled coal is subjected to oxidation treatment for 10-60 minutes in a temperature range from more than 200°C to no more than 240°C.

Description

DESCRIPTION Title METHOD FOR PRODUCING REFORMED COAL Technical Field

[0001] The present disclosure relates to a method for producing reformed coal. Background Art

[0002] There is a known technique for drying and carbonizing low grade coal to reform such low grade coal such as lignite or subbituminous coal. However, it is known that, in a case where coal is reformed by such a technique, a surface thereof is activated, and coal spontaneously ignites due to heat of reaction with oxygen in the air. As a technique for preventing such spontaneous ignition, a technique for deactivating coal within a temperature range of 40°C and 95°C using a processing gas containing oxygen is proposed (refer to Patent Literature 1). Citation List Patent Literature

[0003]

[Patent Literature 1] Japanese Unexamined Patent Publication No. 2013-139537 Summary Technical Problem

[0004] It is considered that carbonized coal can be deactivated to some extent by performing a deactivation treatment of the related art as disclosed in Patent Literature 1. However, according to the examination of the inventors of the present disclosure, it has been found that pyrophoricity is not sufficiently reduced even by performing such deactivation treatment of the related art. Meanwhile, in a case where the deactivation treatment is performed excessively to reduce , a content of volatile matter is decreased, and coal cannot be effectively utilized as fuel. The present disclosure provides a method for producing reformed coal which can produce, at a high yield, the reformed coal with sufficiently inhibited pyrophoricity.

[0004A]Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.

[0004B] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Solution to Problem

[0005] The present disclosure provides a method for producing reformed coal, the method including a carbonization step of carbonizing coal at 300°C to 650°C to obtain carbonized coal; and an oxidation treatment step of oxidizing the carbonized coal within a temperature range of higher than 200°C and equal to or lower than

240°C for 10 to 60 minutes.

[0006] In this production method, an oxidation treatment of raw material coal is performed within a temperature range of higher than 200°C and lower than 240°C for 10 to 60 minutes. It is considered that, in a case where the oxidation treatment is performed under such conditions, surface components of the raw material coal are oxidized, and a surface state thereof is stabilized, and thereby self-heating properties are reduced, and pyrophoricity is inhibited. In addition, loss due to self-combustion is inhibited, and thereby a yield can be increased.

[0007] The production method includes the carbonization step of carbonizing coal to obtain carbonized coal prior to the oxidation

2A treatment step. Carbonization of coal is effective as a means of upgrading coal. Performing carbonization of coal at 650°C or lower tends to increase pyrophoricity, while yield during carbonization increases. In the production method, self-heating properties can be reduced by the oxidation treatment step. For this reason, pyrophoricity can be inhibited even in a case where a carbonization temperature in the carbonization step is 650°C or lower. Accordingly, it is possible to produce, at a high yield, a high grade reformed coal with sufficiently inhibited pyrophoricity.

[0008] The production method may include a drying step of drying the coal at 150°C or lower prior to the oxidation treatment step. Thereby, moisture of the coal is reduced, and therefore higher grade reformed coal can be obtained by the oxidation treatment step, or the carbonization step and the oxidation treatment step.

[0009] The production method may include a combustion step of combusting, in a combustion furnace, a gas containing volatile matter generated by carbonization of the coal. In this case, in the oxidation treatment step, the carbonized coal is preferably oxidized by exhaust gas that contains oxygen and is from the combustion furnace. Thereby, efficiency and safety of the oxidation treatment can be improved while reducing production cost of reformed coal. Advantageous Effects of Invention

[0010] The present invention can provide a method for producing reformed coal which can produce, at a high yield, a high grade reformed coal with sufficiently inhibited pyrophoricity. Brief Description of Drawings

[0011] Fig. 1 is a flowchart showing an example of a method for producing reformed coal. Fig. 2 is a graph showing results of tests for evaluating pyrophoricity in Examples 1 and 2, Reference Examples 1 and 2, and Comparative Examples 1 to 4. Fig. 3 is a graph showing time-dependent changes in calorific value of carbonized coals of Comparative Examples 5 to 8 respectively having different degrees of carbonization. Fig. 4 is a graph showing time-dependent changes in calorific value of reformed coals of Example 3, Reference Example 4, and Comparative Examples 9 and 10, and a carbonized coal of Comparative Example 6 respectively having different oxidation treatment temperatures. Fig. 5 is a graph showing concentrations of carbon monoxide and carbon dioxide in an exhaust gas at the time of an oxidation treatment in Examples 5 and 6, Reference Example 7, and Comparative Examples 11 to 13. Fig. 6 is a diagram showing results of infrared spectroscopic analysis in Comparative Example 6, Comparative Example 14, and Comparative Example 15. Fig. 7 is a graph showing results of thermogravimetric analysis in Comparative Examples 16 to 19, Examples 8 and 9, and Reference Example 10 in which oxidation treatment temperatures are different. Fig. 8 is a graph showing results of differential thermal analysis in Comparative Examples 16 to 19, Examples 8 and 9, and Reference Example 10 in which oxidation treatment temperatures are different.

Fig. 9 is a graph showing a relationship between a maximum peak height and an oxidation treatment temperature in results of differential thermal analysis in Comparative Examples 16 to 19, Examples 8 and 9, and Reference Example 10 in which oxidation treatment temperatures are different. Fig. 10 is a graph showing results of a test for evaluating pyrophoricity. Description of Embodiments

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings in some cases. However, the following embodiments are exemplifications for describing the present invention, and are not intended to limit the present invention to the following contents.

[0013] A method for producing reformed coal according to the present embodiment includes a carbonization step of carbonizing coal at 300°C to 650°C to obtain carbonized coal, and an oxidation treatment step of oxidizing the carbonized coal within a temperature range of higher than 200°C and equal to or lower than 240°C. In general, there is a tendency of carbonized coal to spontaneously ignite more easily than dried coal of coal. In the present embodiment, it is possible to obtain reformed coal with sufficiently inhibited pyrophoricity from carbonized coal by subjecting the carbonized coal having a surface condition different from a surface condition of coal and dried coal thereof to an oxidation treatment step under predetermined conditions.

[0014] The carbonization step is a step of carbonizing coal at 3000 C to 650 0C to obtain carbonized coal. The carbonization step may be performed first without performing a drying step to be described later. In this case, moisture of coal is reduced at an initial stage of the carbonization step. The carbonization step is preferably performed within a temperature range of 300°C and 600°C. Accordingly, a yield can be maintained high while carbonization of coal sufficiently proceeds. The carbonization step can be performed using a general carbonization furnace such as a vertical shaft furnace, a coke furnace, or a tunnel kiln furnace.

[0015] A volatile-matter content (VM) of carbonized coal to be obtained in the carbonization step is preferably 10% to 30% by mass. Such carbonized coal generally increases pyrophoricity, but in the present embodiment, it is possible to inhibit pyrophoricity by performing the oxidation treatment step after the carbonization step. Thereby, a high yield can be realized.

[0016] The coal may include low grade coal or high grade coal. In a case where low grade coal is included, it is preferable to perform a drying step to be described later prior to the oxidation treatment step. However, performing the drying step is not always essential. A particle diameter of raw material coal may be, for example, 50 mm or less, 30 mm or less, or 10 mm or less.

[0017] In the oxidation treatment step, by setting a temperature at which carbonized coal is oxidized (an oxidation treatment temperature) within a range higher than 200°C, a surface of the carbonized coal is sufficiently reformed, and thereby it is possible to obtain reformed coal with sufficiently inhibited pyrophoricity. By setting an oxidation treatment temperature to 240°C or lower, a decrease in volatile-matter content in the oxidation treatment step is inhibited, and thereby reformed coal can be produced at a high yield.

[0018] An oxidation treatment temperature is preferably 210°C to 240°C and more preferably 220°C to 240°C from the viewpoint of allowing both inhibition of pyrophoricity and further improvement of yield to be compatible in a higher standard. The oxidation treatment step may not be performed at a constant oxidation treatment temperature, and an oxidation treatment temperature may vary within the above-described range. A time of the oxidation treatment step is to 60 minutes from the viewpoint of producing reformed coal at a high yield. A time of the oxidation treatment step may be 15 to 60 minutes from the viewpoint of sufficiently inhibiting spontaneous ignition properties.

[0019] An atmosphere in the oxidation treatment step is not particularly limited as long as the atmosphere contains oxygen, and may be air or may be a mixed atmosphere of an inert gas such as nitrogen and oxygen. In addition, the atmosphere may contain an exhaust gas from a combustion furnace. A concentration of oxygen may be, for example, 2% to 13% by volume or may be 3% to 10% by volume from the viewpoint of safety and efficiency of the oxidation treatment. The term "% by volume" refers to a volume ratio under conditions of a standard state (25°C, 100 kPa).

[0020] In the oxidation treatment step, functional groups on a surface of raw material coal are oxidized. Accordingly, self-heating properties due to oxidation are reduced, and thereby it is possible to produce reformed coal with sufficiently inhibited pyrophoricity. A volatile-matter content (VM) of reformed coal may be 5% by mass or more or may be 10% by mass or more from the viewpoint of increasing usefulness of reformed coal as a fuel. Meanwhile, a volatile-matter content (VM) of reformed coal may be 30% by mass or less or may be % by mass or less from the viewpoint of further reducing pyrophoricity. A volatile-matter content in the present specification is a value on a dry basis measured in accordance with a "Square Electric Furnace Method" of JIS M 8812:2006.

[0021] According to the production method of the present embodiment, it is possible to produce, at a high yield, reformed coal with sufficiently inhibited pyrophoricity. Such reformed coal can contain a certain volatile-matter content, and thus it can be effectively utilized as fuel. As described above, the reformed coal is highly useful as fuel, and furthermore, it is possible to safely perform coal storage in the yard, and land and sea transportation from coal mining areas.

[0022] A method for producing reformed coal according to another embodiment includes a drying step of drying coal at 150°C or lower prior to the above-described carbonization step. It is preferable to perform the drying step as in the case of the present embodiment in a case of using low grade coal having a high moisture content (for example, lignite or subbituminous coal having a moisture content of % by mass or more).

[0023] In the drying step, coal is heated and dried within a temperature range of, for example, 40°C and 150°C. The drying step may be performed in the air or may be performed in an inert gas atmosphere. In addition, the drying step may be performed in an exhaust gas from a combustion furnace. In the drying step, a moisture content of coal is reduced to, for example, 20% by mass or less. By performing such a drying step, it is possible to sufficiently obtain reforming effects of a carbonization or oxidation treatment.

[0024] The drying step may be performed using a general electric furnace or the like, or may be performed using an indirect heater or an air fluidized bed dryer. A time of the drying step is not particularly limited, and can be adjusted depending on a moisture content of coal, a particle diameter of coal, and the like.

[0025] According to the production method of the present embodiment, even in a case where low grade coal is used, it is possible to produce, at a high yield, reformed coal with sufficiently inhibited pyrophoricity. A particle diameter of reformed coal may be, for example, 50 mm or less or 10 mm or less.

[0026] Reformed coal to be obtained by the above-described production method may be classified and divided into granular reformed coal (for example, a grain having a particle diameter of 3 mm or more) and powdery reformed coal (for example, a powder having a particle diameter of less than 3 mm). The powdery reformed coal (powder) obtained by the classification may be molded using a binder or without using a binder, and mixed with the granular reformed coal (grain) obtained by the classification. In a case where an average particle diameter of the reformed coal is increased in this manner, generation of powdery dust during transportation and storage of coal is further reduced, and thereby handleability of reformed coal can be further improved.

[0027] Fig. 1 is a diagram showing an example of an apparatus configuration for performing a method for producing reformed coal of one embodiment. In the example of Fig. 1, a drying step is performed in a drying apparatus 10, a carbonization step is performed in a carbonization apparatus 20, and an oxidation treatment step is performed in an oxidation treatment apparatus 30. A gas containing volatile matter generated from the carbonization apparatus 20 is consumed as a fuel gas by a combustion furnace 40 (a combustion step). Examples of the drying apparatus 10 include a general dryer. Examples of the oxidation treatment apparatus 30 include a general electric furnace.

[0028] An exhaust gas generated by combusting a fuel gas containing volatile matter in the combustion furnace 40 generally contains about % to 10% by volume of oxygen. By utilizing such exhaust gas in the oxidation treatment apparatus 30, it is possible to sufficiently increase efficiency and safety of the oxidation treatment in the oxidation treatment step. In addition, because a temperature of the exhaust gas can be effectively utilized, energy can be reduced. The exhaust gas generated in the combustion furnace 40 may be used as a gas for heating in the drying apparatus 10. It is possible to reduce production cost of reformed coal by effectively utilizing heat generated in the carbonization step.

[0029] Hereinbefore, the embodiments of the present invention have been described, but the present invention is not limited to the above-describedembodiments. Examples

[0030] The content of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0031] (Example 1)

[Production of reformed coal] A subbituminous coal (an Adaro coal produced in Indonesia), which is a commercially available coal for boilers, was dried in the air using a dryer, and thereby a dried coal was obtained (a drying step). A heating temperature in the drying step was 150°C, and a heating time was 30 minutes. A volatile-matter content (VM) of the obtained dried coal was 50% by mass, and a moisture content was 10% by mass or less. The obtained dried coal was carbonized using a carbonization furnace, and thereby a carbonized coal was obtained (a carbonization step). A heating temperature in the carbonization step was 430°C, and a heating time was 40 minutes. A volatile-matter content (VM) of the carbonized coal was 25% by mass.

[0032] Subsequently, the obtained carbonized coal was oxidized using an electric furnace, and thereby a granular reformed coal (a particle diameter: about 1 to 3 mm) was produced (an oxidation treatment step). Conditions for the oxidation treatment were as follows: a mixed gas atmosphere of nitrogen gas and oxygen gas (a concentration of oxygen: 8% by volume), a heating temperature of 240°C, and a heating time of minutes.

[0033] [Evaluation of pyrophoricity (Fig. 2)] A test for evaluating pyrophoricity of the obtained reformed coal was performed by a method according to the United Nations

Transport Recommendations for Dangerous Goods Test [Class 4, Category 4.2 (Pyrophoric substances /Self-heating substances)]. Specifically, the reformed coal was put in a container which had a cubic shape with one side of 10 cm was formed of a wire mesh, the container was stored in air at 140°C, and time-dependent changes in heat generation temperature were examined. The results were as shown by Curve Al (the reformed coal) in Fig. 2.

[0034] (Example 2) A reformed coal was produced in the same manner as in Example 1 except that a heating temperature in the oxidation treatment step was changed to 210°C. Then, a test for evaluating pyrophoricity was performed in the same manner as in Example 1. The results were as shown by Curve A2 in Fig. 2.

[0035] (Reference Example 1) A test for evaluating pyrophoricity of the subbituminous coal (an Adaro coal produced in Indonesia) used in Example 1 was performed in the same manner as in Example 1. The results were as shown by Curve C1 in Fig. 2.

[0036] (Reference Example 2) A test for evaluating pyrophoricity of a bituminous coal (a Mount Arthur coal produced in Australia), which is a commercially available coal for boilers, was performed in the same manner as in Example 1. The results were as shown by Curve C2 in Fig. 2.

[0037] (Comparative Example 1) Comparative Example 1 was performed in the same manner as in Example 1 except that the oxidation treatment step was not performed. That is, a test for evaluating pyrophoricity of carbonized coal obtained in a carbonization step was performed. The results were as shown by Curve El in Fig. 2.

[0038] (Comparative Example 2) A reformed coal was produced in the same manner as in Example 1 except that a heating temperature in the oxidation treatment step was changed to 200°C. Then, a test for evaluating pyrophoricity was performed in the same manner as in Example 1. The results were as shown by Curve B1 in Fig. 2.

[0039] (Comparative Example 3) A reformed coal was produced in the same manner as in Example 1 except that a heating temperature in the oxidation treatment step was changed to 290°C. Then, a test for evaluating pyrophoricity was performed in the same manner as in Example 1. The results were as shown by Curve B2 in Fig. 2.

[0040] (Comparative Example 4) A dried coal was obtained in the same manner as in Example 1. A volatile-matter content (VM) of the dried coal was 50% by mass, and a moisture content thereof was 10% by mass or less. A test for evaluating pyrophoricity of the obtained dried coal was performed. The results were as shown by Curve D1 in Fig. 2.

[0041] As shown in Fig. 2, the carbonized coal (Curve El) of Comparative Example 1 in which the oxidation treatment step was not performed generated heat at 250°C or higher within about 1 hour. That is, the reformed coal had the highest pyrophoricity. On the other hand, the dried coal of Comparative Example 4 (Curve Dl) had lower pyrophoricity than the carbonized coal of Comparative Example 1 (Curve El).

[0042] The reformed coal of Comparative Example 2 (Curve B1) and the reformed coal of Comparative Example 3 (Curve B2), which were respectively subjected to the oxidation treatment at 200°C and 290°C, had lower pyrophoricity than in Comparative Example 1. In addition, the reformed coal of Example 2 (Curve A2) and the reformed coal of Example 1 (Curve Al), which were respectively subjected to the oxidation treatment at temperatures of 210°C and 240°C, had even lower pyrophoricity than in Comparative Example 2 and Comparative Example 3.

[0043] Pyrophoricity of the reformed coal of Example 2 was lower than that of the commercial subbituminous coal, and pyrophoricity of the reformed coal of Example 1 was lower than that of the commercial bituminous coal. As described above, it was confirmed that, even though the reformed coals of Example 1 and Example 2 were carbonized, pyrophoricity thereof were sufficiently inhibited.

[0044] [Influence of degree of carbonization on calorific value (Fig.

3)] (Comparative Example 5) A subbituminous coal (an Adaro coal produced in Indonesia), which is a commercially available coal for boilers, was dried in the air using a dryer, and thereby a granular dried coal (a particle diameter: 0.5 mm or less) was obtained (a drying step). A heating temperature in the drying step was 150°C, and a heating time was 30 minutes. A volatile-matter content (VM) of the dried coal was 50% by mass, and a moisture content thereof was 10% by mass or less.

[0045] Differential scanning calorimetry (DSC measurement) was performed on the prepared dried coal using a commercially available measuring device. Specifically, the dried coal and a reference substance were each heated by a heater in a nitrogen atmosphere to raise temperatures thereof to 107°C. Thereafter, the nitrogen atmosphere was switched to air, and a calorific value when air oxidation was performed at a constant temperature (107°C) was measured. The results were as shown by Curve D2 in Fig. 3.

[0046] (Comparative Example 6) The carbonization step was performed using the dried coal of Comparative Example 5, and thereby a carbonized coal was prepared. A heating temperature in the carbonization step was 430°C, and a heating time was 40 minutes. A volatile-matter content (VM) of the carbonized coal was 25% by mass. DSC measurement of the carbonized coal was performed in the same manner as in Comparative Example 5. The results were as shown by Curve E2 in Fig. 3.

[0047] (Comparative Example 7) A carbonized coal was prepared in the same manner as in Comparative Example 6 except that the heating temperature in the carbonization step was changed to 550°C. A volatile-matter content (VM) of the carbonized coal was 12% by mass. DSC measurement of the carbonized coal was performed in the same manner as in Comparative Example 5. The results were as shown by Curve E3 in Fig. 3.

[0048] (Comparative Example 8)

A carbonized coal was prepared in the same manner as in Comparative Example 6 except that the heating temperature in the carbonization step was changed to 1000°C. A volatile-matter content (VM) of the carbonized coal was 0% by mass. DSC measurement of the carbonized coal was performed in the same manner as in Comparative Example 5. The results were as shown by Curve E4 in Fig. 3.

[0049] Based on the results of Comparative Examples 6 to 8, it was found that the lower the carbonization temperature (a degree of carbonization), the higher the volatile-matter content remaining in the carbonized coal, and therefore a yield was higher. However, as shown in Fig. 3, it was confirmed that a calorific value due to oxidation was increased in a case where a carbonization temperature was decreased. The reason for this is considered as follows: as a carbonization temperature is decreased, a remaining content of volatile matter is increased, and as a result, an amount of generation of highly active radicals on a surface of the carbonized coal is increased. A calorific value of the carbonized coal of Comparative Example 6 (Curve E2) in which the carbonization temperature was 430°C was significantly higher than a calorific value of the dried coal of Comparative Example 5 (Curve D2). Based on these results, it was confirmed that a yield and self-heating properties of the carbonized coal are in a trade-off relationship with each other, and therefore, in a state of the carbonized coal, it is difficult to allow both a high yield and inhibition of pyrophoricity to be compatible.

[0050] As shown in Fig. 3, a calorific value of the dried coal of

Comparative Example 5 (Curve D2) was lower than a calorific value of the carbonized coal of Comparative Example 6 (Curve E2). Fig. 2 also shows that pyrophoricity of the dried coal (Curve D1) was lower than pyrophoricity of the carbonized coal (Curve E). Based on these tendencies, it can be said that, pyrophoricity can also be inhibited in a case where an oxidation treatment is performed on a dried coal, as in the case where it is performed on a carbonized coal. That is, the oxidation treatment is effective for a dried coal as well as for a carbonized coal.

[0051] [Influence of oxidation treatment temperature (Fig. 4)] (Example 3) The oxidation treatment step was performed using the carbonized coal of Comparative Example 6, and thereby a reformed coal was produced. Conditions for the oxidation treatment were as follows: a mixed gas atmosphere of nitrogen gas and oxygen gas (a concentration of oxygen: 10% by volume), a heating temperature of 240°C, and a heating time of 40 minutes. DSC measurement of the produced reformed coal was performed in the same manner as in Comparative Example 5. The results were as shown by Curve A3 in Fig. 4.

[0052] (Reference Example 4) The oxidation treatment step was performed using the carbonized coal of Comparative Example 6, and thereby a reformed coal was produced. Conditions for the oxidation treatment were as follows: a mixed gas atmosphere of nitrogen gas and oxygen gas (a concentration of oxygen: 10% by volume), a heating temperature of 260°C, and a heating time of 40 minutes. DSC measurement of the produced reformed coal was performed in the same manner as in Comparative Example 5. The results were as shown by Curve A4 in Fig. 4.

[0053] (Comparative Example 9) The oxidation treatment step was performed using the carbonized coal of Comparative Example 6, and thereby a reformed coal was produced. Conditions for the oxidation treatment were as follows: a mixed gas atmosphere of nitrogen gas and oxygen gas (a concentration of oxygen: 10% by volume), a heating temperature of 200°C, and a heating time of 40 minutes. DSC measurement of the produced reformed coal was performed in the same manner as in Comparative Example 5. The results were as shown by Curve B3 in Fig. 4.

[0054] (Comparative Example 10) The oxidation treatment step was performed using the carbonized coal of Comparative Example 6, and thereby a reformed coal was produced. Conditions for the oxidation treatment were as follows: a mixed gas atmosphere of nitrogen gas and oxygen gas (a concentration of oxygen: 10% by volume), a heating temperature of 300°C, and a heating time of 40 minutes. DSC measurement of the produced reformed coal was performed in the same manner as in Comparative Example 5. The results were as shown by Curve B4 in Fig. 4.

[0055] Fig. 4 shows the results of Comparative Example 6 in combination for easy comparison. A calorific value of each of the reformed coals of Example 3 and Reference Example 4 (Curves A3 and

A4) was significantly reduced as compared with that of the carbonized coal of Comparative Example 6 (Curve E2). A calorific value of each of the reformed coals of Example 3 and Reference Example 4 was lower than a calorific value of each of the reformed coals of Comparative Example 9 and Comparative Example 10. Based on this description, it was confirmed that self-heating properties of the reformed coals of Example 3 and Reference Example 4 could be reduced as compared with those of Comparative Examples 6, 9, and 10.

[0056] [Changes in amount of generated gas depending on oxidation treatment temperatures (Fig. 5)] (Comparative Example 11) The carbonized coal of Comparative Example 6 was heated to 140°C in a nitrogen gas atmosphere using an electric furnace. After raising the temperature, an oxidation treatment step was performed to produce a reformed coal. Conditions for the oxidation treatment were as follows: a mixed gas atmosphere of nitrogen gas and oxygen gas (a concentration of oxygen: 10% by volume), an oxidation treatment temperature of 140°C, and an oxidation treatment time of 20 minutes. All exhaust gases from the oxidation treatment step were sampled and averaged, and concentrations of CO2 and CO in the averaged gas were measured using a gas chromatograph method.

[0057] (Comparative Example 12) A reformed coal was produced in the same manner as in Comparative Example 11 except that an oxidation treatment temperature in the oxidation treatment step was changed to 200°C. In the same manner as in Comparative Example 11, concentrations of CO2 and CO in the exhaust gas from the oxidation treatment step were analyzed.

[0058] (Example 5) A reformed coal was produced in the same manner as in Comparative Example 11 except that an oxidation treatment temperature in the oxidation treatment step was changed to 220°C. In the same manner as in Comparative Example 11, concentrations of CO2 and CO in the exhaust gas from the oxidation treatment step were analyzed.

[0059] (Example 6) A reformed coal was produced in the same manner as in Comparative Example 11 except that an oxidation treatment temperature in the oxidation treatment step was changed to 240°C. In the same manner as in Comparative Example 11, concentrations of CO2 and CO in the exhaust gas from the oxidation treatment step were analyzed.

[0060] (Reference Example 7) A reformed coal was produced in the same manner as in Comparative Example 11 except that an oxidation treatment temperature in the oxidation treatment step was changed to 260°C. In the same manner as in Comparative Example 11, concentrations of CO2 and CO in the exhaust gas from the oxidation treatment step were analyzed.

[0061] (Comparative Example 13) A reformed coal was produced in the same manner as in Comparative Example 11 except that an oxidation treatment temperature in the oxidation treatment step was changed to 300°C. In the same manner as in Comparative Example 11, concentrations of CO2 and CO in the exhaust gas from the oxidation treatment step were analyzed.

[0062] Fig. 5 is a graph in which the concentrations of CO2 and CO in the exhaust gas which were obtained in Examples 5 and 6, Reference Example 7, and Comparative Examples 11 to 13 are plotted. As shown in Fig. 5, it was confirmed that an amount of generated CO2 and CO was increased when an oxidation treatment temperature was higher than 200°C. Based on this description, it can be said that a surface of the reformed coal can be sufficiently reformed by setting an oxidation treatment temperature within a range higher than 200°C.

[0063] [Analysis of surface condition of carbonized coal and reformed coal (Fig. 6)] (Comparative Example 14) A reformed coal (an oxidation treatment temperature: 200°C) was produced in the same manner as in Comparative Example 12 except that a concentration of oxygen in the mixed gas atmosphere in the oxidation treatment step was changed to 8% by volume. Infrared spectroscopic analysis (IR analysis) was performed on the produced reformed coal using a commercially available infrared spectrometer. The analysis results were as shown by Curve B5 in Fig. 6.

[0064] (Comparative Example 15) A reformed coal (an oxidation treatment temperature: 300°C) was produced in the same manner as in Comparative Example 13 except that a concentration of oxygen in the mixed gas atmosphere in the oxidation treatment step was changed to 8% by volume. Then, infrared spectroscopic analysis was performed on the produced reformed coal in the same manner as in Comparative Example 14. The analysis results were as shown by Curve B6 in Fig. 6.

[0065] Fig. 6 shows an enlarged portion at 2800 to 3000 cm-1 where a peak derived from an aliphatic hydrocarbon group is observed among measurement charts of the infrared spectroscopic analysis of Comparative Example 14 and Comparative Example 15. In addition, for comparison, Fig. 6 also shows results of infrared spectroscopic analysis of the carbonized coal prepared in Comparative Example 6 (Curve E2). As shown in Fig. 6, it was confirmed that a surface composition of the carbonized coal was changed by oxidizing the carbonized coal. Furthermore, it was confirmed that when an oxidation treatment temperature was changed within the temperature range of 200°C and 300°C, a surface composition of the obtained reformed coal was significantly changed.

[0066] [Thermogravimetric and differential thermal analysis in oxidation treatment step (Figs. 7 and 8)] (Comparative Example 16) The oxidation treatment step was performed using the carbonized coal of Comparative Example 6. A weight and a differential heat during the oxidation treatment step were measured using a commercially available analyzer for simultaneous thermogravimetric and differential thermal analysis. Specifically, the carbonized coal was installed in the analyzer, and a temperature was raised to 140°C at a rate of10°C/min in a nitrogen atmosphere.

Thereafter, the atmosphere was switched to a mixed atmosphere of nitrogen and oxygen (a concentration of oxygen: 10% by volume), and an oxidation treatment was started. The simultaneous thermogravimetric and differential thermal analysis was performed based on the time of this switching. The results of the thermogravimetric analysis were as shown by Curve B7 in Fig. 7, and the results of the differential thermal analysis were as shown by Curve B7 in Fig. 8.

[0067] (Comparative Example 17) Simultaneous thermogravimetric and differential thermal analysis was performed in the same manner as in Comparative Example 16 except that the oxidation treatment temperature (a temperature for switching to the mixed atmosphere) in the oxidation treatment step was changed to 180°C. The results of the thermogravimetric analysis were as shown by Curve B8 in Fig. 7, and the results of the differential thermal analysis were as shown by Curve B8 in Fig. 8.

[0068] (Comparative Example 18) Simultaneous thermogravimetric and differential thermal analysis was performed in the same manner as in Comparative Example 16 except that the oxidation treatment temperature (a temperature for switching to the mixed atmosphere) in the oxidation treatment step was changed to 200°C. The results of the thermogravimetric analysis were as shown by Curve B9 in Fig. 7, and the results of the differential thermal analysis were as shown by Curve B9 in Fig. 8.

[0069] (Example 8) Simultaneous thermogravimetric and differential thermal analysis was performed in the same manner as in Comparative Example 16 except that the oxidation treatment temperature (a temperature for switching to the mixed atmosphere) in the oxidation treatment step was changed to 220°C. The results of the thermogravimetric analysis were as shown by Curve A5 in Fig. 7, and the results of the differential thermal analysis were as shown by Curve A5 in Fig. 8.

[0070] (Example 9) Simultaneous thermogravimetric and differential thermal analysis was performed in the same manner as in Comparative Example 16 except that the oxidation treatment temperature (a temperature for switching to the mixed atmosphere) in the oxidation treatment step was changed to 240°C. The results of the thermogravimetric analysis were as shown by Curve A6 in Fig. 7, and the results of the differential thermal analysis were as shown by Curve A6 in Fig. 8.

[0071] (Reference Example 10) Simultaneous thermogravimetric and differential thermal analysis was performed in the same manner as in Comparative Example 16 except that the oxidation treatment temperature (a temperature for switching to the mixed atmosphere) in the oxidation treatment step was changed to 260°C. The results of the thermogravimetric analysis were as shown by Curve A7 in Fig. 7, and the results of the differential thermal analysis were as shown by Curve A7 in Fig. 8.

[0072] (Comparative Example 19) Simultaneous thermogravimetric and differential thermal analysis was performed in the same manner as in Comparative Example 16 except that the oxidation treatment temperature (a temperature for switching to the mixed atmosphere) in the oxidation treatment step was changed to 300°C. The results of the thermogravimetric analysis were as shown by Curve B10 in Fig. 7, and the results of the differential thermal analysis were as shown by Curve B10 in Fig. 8.

[0073] Fig. 9 is a graph showing a relationship between a maximum peak (the highest peak) height and an oxidation treatment temperature in the DTA analysis results (the results of the differential thermal analysis) in each of the examples and comparative examples shown in Fig. 8. As shown in Fig. 9, an oxidation reaction (an exothermic reaction) did not proceed very actively when an oxidation treatment temperature was 200°C or lower (Comparative Examples 16, 17, and 18). On the other hand, an oxidation reaction rapidly proceeded when an oxidation treatment temperature was higher than 200°C. Accordingly, it can be said that an oxidation treatment temperature needs to be within a range higher than 200°C to allow oxidation of a surface of the reformed coal to proceed to some extent.

[0074] However, as shown in Figs. 7 to 9, when the oxidation treatment temperature exceeds 240°C, an exothermic reaction tends to become active and a weight loss tends to increase. In addition, when the oxidation treatment temperature was 300°C, the reformed coal disappeared by spontaneous ignition in about 3 to 4 hours after the start of an oxidation treatment. Based on this description, it can be said that the oxidation treatment temperature needs to be 240°C or lower to increase a yield of the reformed coal in the oxidation treatment step.

[0075] <Mechanism of inhibiting pyrophoricity> Elemental analysis was performed on the carbonized coal of

Comparative Example 6, and the reformed coals of Comparative Example 9, Example 3, and Comparative Example 10. The results are shown in Table 1.

[0076] [Table 1] Oxidation treatment Elemental analysis step Treatment C H N 0 S temperature [daf wt%] [daf wt%]

Comparative

[0C] Not performed I [daf wt%] [daf wt%] [daf wt%]

79.6 3.7 0.8 15.5 0.3 Example 6 Comparative 200 76.9 3.3 0.8 18.7 0.3 Example 9 Example 3 240 76.2 3.4 0.8 19.2 0.3 Comparative 300 74.7 3.0 0.8 21.1 0.3 Example 10 1________ 1_____ _____ _____ _____

[0077] As shown in Table 1, it was confirmed that a concentration of oxygen was increased by oxidizing the carbonized coal at 200°C to 300°C. That is, the oxidation treatment step has an action of oxidizing functional groups, thereby increasing a content of oxygen. It is considered that pyrophoricity is inhibited by such an action.

[0078] <Comparison of pyrophoricity> The dried coal of Example 1 obtained by performing the drying step was heated at 660°C for 40 minutes, and thereby a carbonized coal was prepared. The same test for evaluating pyrophoricity as in Example 1 was performed, and pyrophoricity of the prepared carbonized coal were evaluated. The results are shown by Curve F1 in Fig. 10. In addition, for comparison, Fig. 10 also shows Curve El (the carbonized coal, a carbonization temperature: 430°C) shown in Fig. 2.

[0079] As shown in Fig. 10, when a carbonization temperature is higher than 650°C, pyrophoricity are significantly reduced. However, when a carbonization temperature is within a range higher than 650°C, a yield of the reformed coal obtained through the oxidation treatment step decreases. Accordingly, by performing an oxidation treatment of carbonized coal, which is obtained by carbonizing a coal at 3000 C to 650 0C, within a temperature range of higher than 200 0C and equal to or lower than 240 0C, it is possible to produce, at a high yield, a high grade reformed coal with sufficiently inhibited pyrophoricity. Industrial Applicability

[0080] According to the present disclosure, there is provided a method for producing reformed coal which can produce, at a high yield, a high grade reformed coal with sufficiently inhibited pyrophoricity. Reference Signs List

[0081] 10 Drying apparatus 20 Carbonization apparatus 30 Oxidation treatment apparatus 40 Combustion furnace

Claims

CLAIMS 1. A method for producing reformed coal, the method comprising: a carbonization step of carbonizing coal at 3000 C to 6500 C to obtain carbonized coal; and an oxidation treatment step of oxidizing the carbonized coal within a temperature range of higher than 200 0C and equal to or lower than 240 0C for 10 to 60 minutes.

2. The method for producing reformed coal according to claim 1, further comprising: a drying step of drying the coal at 1500 C or lower prior to the carbonization step, wherein, in the carbonization step, the coal dried in the drying step is carbonized.

3. The method for producing reformed coal according to claim 1 or 2, wherein a moisture content of the coal is 50% by mass or more.

4. The method for producing reformed coal according to any one of claims 1 to 3, wherein a volatile-matter content of the carbonized coal obtained in the carbonization step is 10% to 30% by mass.

5. The method for producing reformed coal according to any one of claims 1 to 4, wherein a volatile-matter content of the reformed coal obtained in the oxidation treatment step is 5% to 30% by mass.

6. The method for producing reformed coal according to any one of claims 1 to 5, further comprising: a combustion step of combusting, in a combustion furnace, a gas containing volatile matter generated by carbonization of the coal, wherein, in the oxidation treatment step, the carbonized coal is oxidized by exhaust gas that contains oxygen and is from the combustion furnace.

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