CN111433330A

CN111433330A - Method for producing modified coal

Info

Publication number: CN111433330A
Application number: CN201880077972.7A
Authority: CN
Inventors: 今村彰伸; 小菅克志; 小水流广行; 谷奥亘
Original assignee: Nippon Steel and Sumitomo Metal Corp; Nippon Steel and Sumikin 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: 2020-07-17
Also published as: JP6402235B1; AU2018378746B2; AU2018378746A1; WO2019111540A1; JP2019099777A

Abstract

Provided is a method for producing modified coal, which comprises: a carbonization step of carbonizing coal at 300 to 650 ℃ to obtain carbonized coal; and an oxidation treatment step of subjecting the carbonized coal to oxidation treatment at a temperature of more than 200 ℃ and 240 ℃ or less for 10 to 60 minutes.

Description

Method for producing modified coal

Technical Field

The present invention relates to a method for producing modified coal.

Background

In order to modify low-quality coal such as lignite or subbituminous coal, a technique of drying and carbonizing the low-quality coal is known. However, it is known that when coal is modified by this technique, the surface thereof is activated and spontaneously ignited by the heat of reaction with oxygen in the air. As a technique for preventing spontaneous combustion, there has been proposed a technique for deactivating coal at a temperature in the range of 40 to 95 ℃ using a treatment gas containing oxygen (see patent document 1).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-139537

Disclosure of Invention

Problems to be solved by the invention

It is considered that the carbonized coal can be deactivated to some extent by performing the conventional deactivation treatment as described in patent document 1. However, according to the studies of the present inventors, it has been found that the spontaneous combustibility cannot be sufficiently reduced even by performing the conventional deactivation treatment. On the other hand, if the deactivation treatment is excessively performed to reduce the spontaneous combustibility, the volatile matter is reduced, and the fuel cannot be effectively used. Accordingly, an object of the present invention is to provide a method for producing a modified coal, which can produce a modified coal having a sufficiently suppressed spontaneous combustibility at a high yield.

Means for solving the problems

The present invention provides a method for producing modified coal, comprising: a carbonization step of carbonizing coal at 300 to 650 ℃ to obtain carbonized coal; and an oxidation treatment step of subjecting the carbonized coal to oxidation treatment at a temperature of more than 200 ℃ and 240 ℃ or less for 10 to 60 minutes.

The method comprises oxidizing raw material coal at a temperature of more than 200 ℃ and less than 240 ℃ for 10 to 60 minutes. When the oxidation treatment is performed under such conditions, it is considered that the self-heat property is reduced and the self-combustion property is suppressed because the surface components of the raw material coal are oxidized and the surface state is stabilized. Further, the disappearance by spontaneous combustion can be suppressed, and the yield can be improved.

The above production method has a carbonization step of carbonizing coal to obtain carbonized coal before the oxidation treatment step. Dry distillation of coal is effective as a means for improving the quality of coal. Here, when coal is dry distilled at 650 ℃ or lower, the yield during dry distillation is improved, while spontaneous combustibility tends to be improved. In the above-described manufacturing method, the self-heating property can be reduced by the oxidation treatment step. Therefore, pyrophoricity can be suppressed even when the carbonization temperature in the carbonization step is 650 ℃ or lower. Therefore, it is possible to produce a modified coal having a high quality and sufficiently suppressed spontaneous combustibility at a high yield.

The above-mentioned production method may further comprise a drying step of drying the coal at 150 ℃ or lower before the oxidation treatment step. Since the moisture content of the coal can be reduced, a modified coal of higher quality can be obtained by the oxidation treatment step or the carbonization step and the oxidation treatment step.

The above production method may further include a combustion step of combusting a gas containing volatile components generated by carbonization of coal in a combustion furnace. In this case, in the oxidation treatment step, the carbonized coal is preferably subjected to oxidation treatment by using an oxygen-containing off gas from a combustion furnace. This can reduce the production cost of the modified coal and improve the efficiency and safety of the oxidation treatment.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention can provide a method for producing modified coal, which can produce modified coal having sufficiently suppressed spontaneous combustibility at a high yield.

Drawings

Fig. 1 is a flowchart showing an example of a method for producing modified coal.

FIG. 2 is a graph showing the results of the spontaneous combustibility evaluation tests of examples 1 and 2, reference examples 1 and 2, and comparative examples 1 to 4.

FIG. 3 is a graph showing the change with time in the calorific value of the carbonized coal in comparative examples 5 to 8 having different carbonization degrees.

FIG. 4 is a graph showing the change with time in the calorific values of the modified coals of example 3, reference example 4 and comparative examples 9 and 10 and the carbonized coal of comparative example 6, which have different oxidation treatment temperatures.

FIG. 5 is a graph showing the concentrations of carbon monoxide and carbon dioxide in the exhaust gas during the oxidation treatment in examples 5 and 6, reference example 7, and comparative examples 11 to 13.

Fig. 6 is a graph showing the results of infrared spectroscopic analysis of comparative example 6, comparative example 14, and comparative example 15.

FIG. 7 is a graph showing the results of thermogravimetric analysis of comparative examples 16 to 19, examples 8 and 9, and reference example 10, in which the oxidation treatment temperature was different.

FIG. 8 is a graph showing the results of differential thermal analysis of comparative examples 16 to 19, examples 8 and 9, and reference example 10, in which the oxidation treatment temperature was different.

FIG. 9 is a graph showing the relationship between the oxidation treatment temperature and the height of the maximum peak in the results of differential thermal analysis of comparative examples 16 to 19, examples 8 and 9, and reference example 10, in which the oxidation treatment temperatures are different.

Fig. 10 is a graph showing the results of the spontaneous combustibility evaluation test.

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings. However, the following embodiments are examples for illustrating the present invention, and the present invention is not intended to be limited to the following.

The method for producing modified coal of the present embodiment includes: a carbonization step of carbonizing coal at 300 to 650 ℃ to obtain carbonized coal; and an oxidation treatment step of oxidizing the carbonized coal at a temperature in a range of more than 200 ℃ and 240 ℃ or less. Generally, there is a tendency for retorted coal to be more pyrophoric than dried coal of coal. In the present embodiment, the carbonized coal having a different surface state from the coal and the dried coal thereof can be subjected to an oxidation treatment step under predetermined conditions, whereby a modified coal having sufficiently suppressed spontaneous combustibility can be obtained from the carbonized coal.

The carbonization step is a step of carbonizing the coal at 300 to 650 ℃ to obtain carbonized coal. The carbonization step may be performed without performing a drying step described later. At this time, the moisture content of the coal decreases in the initial stage of the carbonization step. The dry distillation step is preferably carried out at a temperature of 300 to 600 ℃. Thereby, the coal can be sufficiently carbonized and the high yield can be maintained. The carbonization step can be performed by using a general carbonization furnace such as a vertical blast furnace, a coke oven, or a tunnel kiln.

The Volatile Matter (VM) of the carbonized coal obtained in the carbonization step is preferably 10 to 30 mass%. The carbonized coal generally has high spontaneous combustibility, but in the present embodiment, spontaneous combustibility can be suppressed by performing the oxidation treatment step after the carbonization step. Therefore, high yield can be achieved.

The coal may comprise low quality coal or high quality coal. When low-quality coal is contained, a drying step described later is preferably performed before the oxidation treatment step. However, the drying step is not necessarily required. The particle size of the raw coal may be, for example, 50mm or less, 30mm or less, or 10mm or less.

In the oxidation treatment step, the surface of the carbonized coal can be sufficiently modified by setting the temperature at which the carbonization treatment of the carbonized coal is performed (oxidation treatment temperature) to a range of more than 200 ℃. By setting the oxidation treatment temperature to 240 ℃ or lower, the reduction of volatile components in the oxidation treatment step can be suppressed, and the modified coal can be produced with a high yield.

The oxidation treatment temperature is preferably 210 to 240 ℃, and more preferably 220 to 240 ℃ from the viewpoint of achieving both suppression of spontaneous combustibility and improvement of yield at a higher level. The oxidation treatment step may not be performed at a fixed oxidation treatment temperature, and the oxidation treatment temperature may be varied within the above range. The time for the oxidation treatment step is 10 to 60 minutes from the viewpoint of producing the modified coal at a high yield. The time for the oxidation treatment step may be 15 to 60 minutes from the viewpoint of sufficiently suppressing spontaneous combustibility.

The atmosphere in the oxidation treatment step is not particularly limited as long as it is an atmosphere containing oxygen, and may be air or a mixed atmosphere of an inert gas such as nitrogen and oxygen. Further, the exhaust gas may be an exhaust gas from a combustion furnace. The oxygen concentration may be, for example, 2 to 13 vol%, or 3 to 10 vol%, from the viewpoint of safety and efficiency of oxidation treatment. The "volume%" is a volume fraction under the conditions of the standard state (25 ℃, 100 kPa).

In the oxidation treatment step, the functional groups on the surface of the raw material coal are oxidized. Thus, a modified coal in which the spontaneous heat caused by oxidation is reduced and the spontaneous combustion is sufficiently suppressed can be produced. From the viewpoint of improving the usefulness as a fuel, the Volatile Matter (VM) of the modified coal may be 5 mass% or more, or may be 10 mass% or more. On the other hand, from the viewpoint of further reducing the spontaneous combustibility, the Volatile Matter (VM) of the modified coal may be 30% by mass or less, or may be 25% by mass or less. In the present specification, the volatile component is a volatile component based on JIS M8812: value of dry basis measured by "Square electric furnace method" of 2006.

According to the production method of the present embodiment, the modified coal having sufficiently suppressed spontaneous combustibility can be produced at a high yield. The modified coal may also contain volatile components to some extent and thus can be effectively used as a fuel. It is clear that the coal can be safely stored in the open air and safely transported on land or on the sea from a coal production site, while having high usefulness as a fuel.

The method for producing modified coal according to another embodiment includes a drying step of drying coal at 150 ℃ or lower before the carbonization step. When low-quality coal having a high moisture content (for example, lignite or subbituminous coal having a moisture content of 50 mass% or more) is used, it is preferable to have a drying step as in the present embodiment.

In the drying step, the coal is heated to a temperature in the range of, for example, 40 to 150 ℃ to be dried. The drying step may be performed in air or in an inert gas atmosphere. Alternatively, the reaction may be carried out in the exhaust gas of a combustion furnace. In the drying step, the moisture content of the coal is reduced to, for example, 20 mass% or less. By performing this drying step, the modification effect by the dry distillation or oxidation treatment can be sufficiently obtained.

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. The time of the drying step is not particularly limited, and may be adjusted according to the moisture content of the coal, the particle size of the coal, and the like.

According to the production method of the present embodiment, even when low-quality coal is used, modified coal having sufficiently suppressed spontaneous combustibility can be produced at a high yield. The particle diameter of the modified coal may be, for example, 50mm or less, or 10mm or less.

The modified coal obtained by the above-mentioned production method may be classified into modified coal in a granular form (for example, particles having a particle diameter of 3mm or more) and modified coal in a powdery form (for example, powder having a particle diameter of less than 3 mm). The pulverized modified coal (powder) obtained by classification may be formed with or without a binder, and mixed with granular modified coal (particles) obtained by classification as well. By increasing the average particle size of the reformed coal in this manner, the generation of dust during transportation and storage of the coal can be further reduced, and the operability of the reformed coal can be further improved.

Fig. 1 is a diagram showing an example of an apparatus configuration for carrying out the method for producing reformed coal according to the embodiment. In the example of fig. 1, the drying step is performed in the drying device 10, the dry distillation step is performed in the dry distillation device 20, and the oxidation treatment step is performed in the oxidation treatment device 30. The volatile component-containing gas generated by the retort 20 is consumed as a fuel gas in the combustion furnace 40 (combustion step). The drying device 10 may be, for example, a general dryer. The oxidation treatment apparatus 30 may be, for example, a normal electric furnace.

The exhaust gas generated by burning the fuel gas containing volatile components in the combustion furnace 40 usually contains about 5 to 10 vol% of oxygen. By utilizing the exhaust gas in the oxidation treatment device 30, the efficiency and safety of the oxidation treatment in the oxidation treatment step can be sufficiently improved. In addition, since the 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 heating gas in the drying apparatus 10. By effectively utilizing the heat generated in the carbonization step in this manner, the production cost of the modified coal can be reduced.

While the present invention has been described with reference to the embodiments, the present invention is not limited to the embodiments.

Examples

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.

(example 1)

[ production of modified coal ]

Sub-bituminous coal (adapalene produced in indonesia) which is commercially available boiler coal was dried in air using a dryer to obtain dry coal (drying step). The heating temperature in the drying step was 150 ℃ and the heating time was 30 minutes. The Volatile Matter (VM) of the obtained dry coal was 50 mass%, and the water content was 10 mass% or less. The obtained dry coal is carbonized in a carbonization furnace to obtain carbonized coal (carbonization step). The heating temperature in the dry distillation step was 430 ℃ and the heating time was 40 minutes. The Volatile Matter (VM) of the carbonized coal was 25% by mass.

Next, the carbonized coal obtained is oxidized in an electric furnace to produce granular modified coal (particle diameter: about 1 to 3mm) (oxidation step). The conditions of the oxidation treatment were a mixed gas atmosphere of nitrogen and oxygen (oxygen concentration: 8 vol%), a heating temperature of 240 ℃ and a heating time of 40 minutes.

[ evaluation of spontaneous combustibility (FIG. 2) ]

The modified coal obtained was subjected to an spontaneous combustibility evaluation test in accordance with the method of the Association's recommendation test for transportation of dangerous goods [ class 4, 4.2 (pyrophoric substance/self-heating substance) ]. Specifically, modified coal was put into a container formed of a metal mesh and having a cubic shape with a side length of 10cm, and stored in air at 140 ℃ to examine a change with time of an exothermic temperature. The results are shown in FIG. 2, curve A1 (modified coal).

(example 2)

Modified coal was produced in the same manner as in example 1, except that the heating temperature in the oxidation treatment step was 210 ℃. Then, the spontaneous combustibility evaluation test was performed in the same manner as in example 1. The result is shown in curve a2 of fig. 2.

(reference example 1)

The spontaneous combustibility evaluation test of the sub-bituminous coal (adapalo coal produced in indonesia) used in example 1 was carried out in the same manner as in example 1. The result is shown in curve C1 of fig. 2.

(reference example 2)

An spontaneous combustibility evaluation test of bituminous coal (taiyase coal produced in australia) as a commercially available boiler coal was performed in the same manner as in example 1. The result is shown in curve C2 of fig. 2.

Comparative example 1

The procedure was as in example 1 except that the oxidation treatment step was not performed. That is, the spontaneous combustibility evaluation test of the carbonized coal obtained in the carbonization step was carried out. The result is shown in curve E1 of fig. 2.

Comparative example 2

Modified coal was produced in the same manner as in example 1, except that the heating temperature in the oxidation treatment step was set to 200 ℃. Then, the spontaneous combustibility evaluation test was performed in the same manner as in example 1. The result is shown in curve B1 of fig. 2.

Comparative example 3

Modified coal was produced in the same manner as in example 1, except that the heating temperature in the oxidation treatment step was 290 ℃. Then, the spontaneous combustibility evaluation test was performed in the same manner as in example 1. The result is shown in curve B2 of fig. 2.

Comparative example 4

Dried coal was obtained in the same manner as in example 1. The Volatile Matter (VM) of the dried coal was 50 mass%, and the water content was 10 mass% or less. The spontaneous combustibility of the resulting dried coal was evaluated. The result is shown in the curve D1 of fig. 2.

As shown in FIG. 2, the carbonized coal (curve E1) of comparative example 1, which was not subjected to the oxidation treatment step, generated heat to 250 ℃ or higher in about 1 hour. Namely, the modified coal has the highest spontaneous combustibility. On the other hand, the spontaneous combustibility of the dried coal of comparative example 4 (curve D1) was lower than that of the carbonized coal of comparative example 1 (curve E1).

The modified coal of comparative example 2 (curve B1) and the modified coal of comparative example 3 (curve B2), which were subjected to oxidation treatment at 200 ℃ and 290 ℃ respectively, had lower spontaneous combustibility than comparative example 1. The modified coal of example 2 (curve a2) and the modified coal of example 1 (curve a1) that were oxidized at 210 ℃ and 240 ℃ respectively had a further reduced spontaneous combustibility as compared with comparative examples 2 and 3.

The modified coal of example 2 had lower spontaneous combustibility than commercial sub-bituminous coal, and the modified coal of example 1 had lower spontaneous combustibility than commercial bituminous coal. It was found that although the carbonization was performed, the spontaneous combustibility of the modified coals of examples 1 and 2 was sufficiently suppressed.

[ Effect of Dry distillation degree on Heat Generation amount (FIG. 3) ]

Comparative example 5

Sub-bituminous coal (adapalene produced in indonesia) which is commercially available boiler coal was dried in air using a dryer to obtain granular dry coal (particle size: 0.5mm or less) (drying step). The heating temperature in the drying step was 150 ℃ and the heating time was 30 minutes. The Volatile Matter (VM) of the dried coal was 50 mass%, and the water content was 10 mass% or less.

Differential scanning calorimetry (DSC measurement) of the prepared dry coal was performed using a commercially available measuring apparatus. Specifically, the dried coal and the reference material were heated by a heater in a nitrogen atmosphere, and the temperature was raised to 107 ℃. Then, the nitrogen atmosphere was changed to air, and the amount of heat generated when air oxidation was performed at a fixed temperature (107 ℃ C.) was measured. The result is shown in the curve D2 of fig. 3.

Comparative example 6

The dry coal of comparative example 5 was used to perform a dry distillation step to prepare dry distilled coal. The heating temperature in the dry distillation step was 430 ℃ and the heating time was 40 minutes. The Volatile Matter (VM) of the carbonized coal was 25% by mass. The DSC measurement of the carbonized coal was performed in the same manner as in comparative example 5. The result is shown in curve E2 of fig. 3.

Comparative example 7

Carbonized coal was produced in the same manner as in comparative example 6, except that the heating temperature in the carbonization step was 550 ℃. The Volatile Matter (VM) of the carbonized coal was 12% by mass. The DSC measurement of the carbonized coal was performed in the same manner as in comparative example 5. The result is shown in curve E3 of fig. 3.

Comparative example 8

Carbonized coal was produced in the same manner as in comparative example 6, except that the heating temperature in the carbonization step was 1000 ℃. Volatile Matter (VM) of the carbonized coal was 0 mass%. The DSC measurement of the carbonized coal was performed in the same manner as in comparative example 5. The result is shown in curve E4 of fig. 3.

According to the results of comparative examples 6 to 8, when the carbonization temperature (carbonization degree) is low, the volatile matter remaining in the carbonized coal increases, and thus the yield is high. However, as shown in FIG. 3, it was confirmed that if the carbonization temperature is lowered, the amount of heat generated by oxidation increases. This is considered to be caused by the fact that the amount of volatile components remaining increases as the carbonization temperature decreases, and as a result, the amount of highly active radicals generated on the surface of the carbonized coal increases. The calorific value of the carbonized coal of comparative example 6 (curve E2) having a carbonization temperature of 430 ℃ was significantly higher than that of the dried coal of comparative example 5 (curve D2). From these results, it was confirmed that the yield and the self-heat of the carbonized coal are in a trade-off relationship with each other, and it is difficult to achieve both a high yield and suppression of the self-heat property in the carbonized coal state.

As shown in fig. 3, the calorific value of the dried coal of comparative example 5 (curve D2) was lower than that of the carbonized coal of comparative example 6 (E2). It is also shown in FIG. 2 that the self-ignition property of the dried coal (curve D1) is lower than that of the carbonized coal (E1). From these tendencies, it is considered that when the dry coal is subjected to the oxidation treatment, the spontaneous combustibility can be suppressed as in the case of the carbonized coal. That is, the oxidation treatment is effective for drying coal as in the case of the carbonized coal.

[ Effect of Oxidation treatment temperature (FIG. 4) ]

(example 3)

Modified coal was produced by performing an oxidation treatment step using the carbonized coal of comparative example 6. The conditions of the oxidation treatment were a mixed gas atmosphere of nitrogen and oxygen (oxygen concentration: 10 vol%), a heating temperature of 240 ℃ and a heating time of 40 minutes. DSC measurement of the produced modified coal was performed in the same manner as in comparative example 5. The result is shown in curve a3 of fig. 4.

(reference example 4)

Modified coal was produced by performing an oxidation treatment step using the carbonized coal of comparative example 6. The conditions of the oxidation treatment were a mixed gas atmosphere of nitrogen and oxygen (oxygen concentration: 10 vol%), a heating temperature of 260 ℃ and a heating time of 40 minutes. DSC measurement of the produced modified coal was performed in the same manner as in comparative example 5. The result is shown in curve a4 of fig. 4.

Comparative example 9

Modified coal was produced by performing an oxidation treatment step using the carbonized coal of comparative example 6. The conditions of the oxidation treatment were a mixed gas atmosphere of nitrogen and oxygen (oxygen concentration: 10 vol%), a heating temperature of 200 ℃ and a heating time of 40 minutes. DSC measurement of the produced modified coal was performed in the same manner as in comparative example 5. The result is shown in curve B3 of fig. 4.

Comparative example 10

Modified coal was produced by performing an oxidation treatment step using the carbonized coal of comparative example 6. The conditions of the oxidation treatment were a mixed gas atmosphere of nitrogen and oxygen (oxygen concentration: 10 vol%), a heating temperature of 300 ℃ and a heating time of 40 minutes. DSC measurement of the produced modified coal was performed in the same manner as in comparative example 5. The result is shown in curve B4 of fig. 4.

For ease of comparison, fig. 4 also shows the results of comparative example 6. The modified coals of example 3 and reference example 4 (curves A3 and a4) can significantly reduce the calorific value as compared with the carbonized coal of comparative example 6 (curve E2). The calorific values of the modified coals of example 3 and reference example 4 were lower than those of the modified coals of comparative examples 9 and 10. From this, it was confirmed that the modified coals according to examples 3 and 4 can reduce the self-heating property as compared with comparative examples 6, 9 and 10.

[ Change in gas Generation amount due to Oxidation treatment temperature (FIG. 5) ]

Comparative example 11

The carbonized coal of comparative example 6 was heated to 140 ℃ in a nitrogen atmosphere using an electric furnace. After the temperature is raised, an oxidation treatment step is performed to produce modified coal. The oxidation treatment was carried out under a mixed gas atmosphere of nitrogen and oxygen (oxygen concentration: 10 vol%), at an oxidation treatment temperature of 140 ℃ and for an oxidation treatment time of 20 minutes. The waste gas generated in the oxidation treatment process is treatedPartial sampling and averaging, and measuring CO in the averaged gas by gas chromatography₂And the concentration of CO.

Comparative example 12

Modified coal was produced in the same manner as in comparative example 11, except that the oxidation treatment temperature in the oxidation treatment step was set to 200 ℃. CO in the exhaust gas in the oxidation treatment step was analyzed in the same manner as in comparative example 11₂And the concentration of CO.

(example 5)

Modified coal was produced in the same manner as in comparative example 11, except that the oxidation treatment temperature in the oxidation treatment step was set to 220 ℃. CO in the exhaust gas in the oxidation treatment step was analyzed in the same manner as in comparative example 11₂And the concentration of CO.

(example 6)

Modified coal was produced in the same manner as in comparative example 11, except that the oxidation treatment temperature in the oxidation treatment step was 240 ℃. CO in the exhaust gas in the oxidation treatment step was analyzed in the same manner as in comparative example 11₂And the concentration of CO.

(reference example 7)

Modified coal was produced in the same manner as in comparative example 11, except that the oxidation treatment temperature in the oxidation treatment step was 260 ℃. CO in the exhaust gas in the oxidation treatment step was analyzed in the same manner as in comparative example 11₂And the concentration of CO.

Comparative example 13

Modified coal was produced in the same manner as in comparative example 11, except that the oxidation treatment temperature in the oxidation treatment step was set to 300 ℃. CO in the exhaust gas in the oxidation treatment step was analyzed in the same manner as in comparative example 11₂And the concentration of CO.

FIG. 5 is a graph showing the CO content in exhaust gas obtained in examples 5 and 6, reference example 7, and comparative examples 11 to 13₂And CO concentration. As shown in FIG. 5, it was confirmed that CO was present at an oxidation treatment temperature of more than 200 ℃₂And the amount of CO produced increases. From this, it is considered that the surface of the modified coal can be sufficiently modified by setting the oxidation treatment temperature to be in the range of more than 200 ℃.

[ analysis of surface states of Dry coal and modified coal (FIG. 6) ]

Comparative example 14

Modified coal was produced in the same manner as in comparative example 12 (oxidation temperature: 200 ℃ C.) except that the oxygen concentration of the mixed gas atmosphere in the oxidation treatment step was adjusted to 8 vol%. Infrared spectroscopic analysis (IR analysis) of the produced modified coal was performed using a commercially available infrared spectrometer. The analysis results are shown in fig. 6 as curve B5.

Comparative example 15

Modified coal was produced in the same manner as in comparative example 13 except that the oxygen concentration of the mixed gas atmosphere in the oxidation treatment step was changed to 8 vol% (oxidation treatment temperature: 300 ℃). Then, infrared spectroscopic analysis of the produced modified coal was performed in the same manner as in comparative example 14. The analysis results are shown in fig. 6 as curve B6.

In FIG. 6, 2800 to 3000cm of a peak derived from an aliphatic hydrocarbon group is observed in the measurement chart of the infrared spectroscopic analysis of comparative example 14 and comparative example 15^-1The portion of (a) is shown enlarged. For comparison, fig. 6 also shows the 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 the surface composition of the carbonized coal was changed by subjecting the carbonized coal to oxidation treatment. Further, it was confirmed that when the oxidation treatment temperature was changed in a temperature range of 200 to 300 ℃, the surface composition of the obtained modified coal was largely changed.

[ thermogravimetric and differential thermal analysis in the Oxidation treatment step (FIGS. 7 and 8) ]

Comparative example 16

The oxidation treatment step was carried out using the carbonized coal of comparative example 6. The weight and differential heat in the oxidation treatment step were measured using a commercially available thermogravimetric and differential heat simultaneous analyzer. Specifically, the carbonized coal was placed in an analyzer, and the temperature was raised to 140 ℃ at a rate of 10 ℃ per minute in a nitrogen atmosphere. Then, the atmosphere was switched to a mixed atmosphere of nitrogen and oxygen (oxygen concentration: 10 vol%), and the oxidation treatment was started. The thermogravimetric and differential thermal analyses were performed simultaneously based on the switching times. The results of the thermogravimetric analysis are shown in curve B7 of fig. 7, and the results of the differential thermal analysis are shown in curve B7 of fig. 8.

Comparative example 17

Thermogravimetry and differential thermal analysis were performed simultaneously in the same manner as in comparative example 16, except that the oxidation temperature (temperature for switching to the mixed atmosphere) in the oxidation treatment step was set to 180 ℃. The results of the thermogravimetric analysis are shown in curve B8 of fig. 7, and the results of the differential thermal analysis are shown in curve B8 of fig. 8.

Comparative example 18

Thermogravimetry and differential thermal analysis were performed simultaneously in the same manner as in comparative example 16, except that the oxidation temperature (temperature for switching to the mixed atmosphere) in the oxidation treatment step was set to 200 ℃. The results of the thermogravimetric analysis are shown in curve B9 of fig. 7, and the results of the differential thermal analysis are shown in curve B9 of fig. 8.

(example 8)

Thermogravimetry and differential thermal analysis were performed simultaneously in the same manner as in comparative example 16, except that the oxidation temperature (temperature for switching to the mixed atmosphere) in the oxidation treatment step was 220 ℃. The results of the thermogravimetric analysis are shown in curve a5 of fig. 7, and the results of the differential thermal analysis are shown in curve a5 of fig. 8.

(example 9)

Thermogravimetry and differential thermal analysis were performed simultaneously in the same manner as in comparative example 16, except that the oxidation temperature (temperature for switching to the mixed atmosphere) in the oxidation treatment step was 240 ℃. The results of the thermogravimetric analysis are shown in curve a6 of fig. 7, and the results of the differential thermal analysis are shown in curve a6 of fig. 8.

(reference example 10)

Thermogravimetry and differential thermal analysis were performed simultaneously in the same manner as in comparative example 16, except that the oxidation temperature (temperature for switching to the mixed atmosphere) in the oxidation step was 260 ℃. The results of the thermogravimetric analysis are shown in curve a7 of fig. 7, and the results of the differential thermal analysis are shown in curve a7 of fig. 8.

Comparative example 19

Thermogravimetry and differential thermal analysis were performed simultaneously in the same manner as in comparative example 16, except that the oxidation temperature (temperature for switching to the mixed atmosphere) in the oxidation step was set to 300 ℃. The results of the thermogravimetric analysis are shown in curve B10 of fig. 7, and the results of the differential thermal analysis are shown in curve B10 of fig. 8.

Fig. 9 is a graph showing the relationship between the height of the maximum peak (peak top) in the DTA analysis results (differential thermal analysis results) of each example and each comparative example shown in fig. 8 and the oxidation treatment temperature. As shown in fig. 9, when the oxidation treatment temperature was 200 ℃ or lower (comparative examples 16, 17, and 18), the oxidation reaction (exothermic reaction) proceeded inefficiently. On the other hand, when the oxidation treatment temperature is more than 200 ℃, the oxidation reaction rapidly proceeds. Therefore, it is considered that the oxidation treatment temperature must be set to a range of more than 200 ℃ in order to oxidize the surface of the modified coal to some extent.

However, as shown in fig. 7 to 9, if the heat treatment temperature is higher than 240 ℃, the exothermic reaction tends to become active and the weight loss tends to become large. Further, when the heat treatment temperature is 300 ℃, the modified coal disappears by spontaneous combustion about 3 to 4 hours after the start of the heat treatment. From this, it is considered that the heat treatment temperature needs to be 240 ℃ or lower in order to improve the yield of the modified coal in the oxidation treatment step.

< mechanism for suppressing spontaneous Combustion >

Elemental analyses were performed on the carbonized coal of comparative example 6 and the modified coals of comparative examples 9, 3 and 10. The results are shown in table 1.

[ Table 1]

As shown in Table 1, it was confirmed that the oxygen concentration was increased by oxidizing the carbonized coal at 200 to 300 ℃. That is, the oxidation treatment step has an effect of oxidizing the functional group to increase the oxygen content. It is considered that the spontaneous combustibility is suppressed by this action.

< comparison of spontaneous combustibility >

The dry coal obtained by the drying step of example 1 was heated at 660 ℃ for 40 minutes to prepare a carbonized coal. The same spontaneous combustibility evaluation test as in example 1 was conducted to evaluate the spontaneous combustibility of the produced carbonized coal. The result is shown in a curve F1 in fig. 10. For comparison, FIG. 10 also shows a curve E1 (carbonization temperature: 430 ℃ C.) shown in FIG. 2.

As shown in FIG. 10, when the dry distillation temperature was higher than 650 ℃, the spontaneous combustibility was greatly reduced. However, when the carbonization temperature is set to a range of more than 650 ℃, the yield of the modified coal obtained through the oxidation treatment step is lowered. Therefore, by subjecting the carbonized coal obtained by carbonizing coal at 300 to 650 ℃ in a temperature range of more than 200 ℃ and 240 ℃ or less to an oxidation treatment, it is possible to produce a modified coal having a high quality and sufficiently reduced spontaneous combustibility at a high yield.

Industrial applicability

According to the present invention, it is possible to provide a method for producing a modified coal in which spontaneous combustibility is sufficiently suppressed, with a high yield.

Description of the reference numerals

10 … drying device, 20 … dry distillation device, 30 … oxidation treatment device and 40 … combustion furnace.

Claims

1. A method for producing modified coal, comprising:

a carbonization step of carbonizing coal at 300 to 650 ℃ to obtain carbonized coal; and the number of the first and second groups,

and an oxidation treatment step of subjecting the carbonized coal to oxidation treatment at a temperature of more than 200 ℃ and 240 ℃ or less for 10 to 60 minutes.

2. The method for producing modified coal according to claim 1, comprising a drying step of drying coal at 150 ℃ or lower before the carbonization step,

in the dry distillation step, the coal dried in the drying step is dry distilled.

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

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

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

6. The method for producing modified coal according to any one of claims 1 to 5, comprising a combustion step of combusting a gas containing volatile components generated by carbonization of the coal in a combustion furnace,

in the oxidation treatment step, the carbonized coal is subjected to oxidation treatment using oxygen-containing exhaust gas from the combustion furnace.