COAL STORAGE SYSTEM AND METHOD FOR STORING COAL
Technical Field [0001]
The present invention relates to a coal storage system and a method for storing coal.
Background Art [0002]
Conventionally, since coal easily oxidizes and generates heat, it is common to control the temperature by spraying water or the like when storing coal. As such a technique, Patent Literature 1 discloses suppressing a self-heating of the coal by storing the coal soaked in water at least 50% of its total height, taking out the stored coal in a wet state and heating and drying the coal with extracted steam from power plant.
Citation List
Patent Literature
[0005]
Patent Literature V Japanese Patent Laid-Open No. 2015-055375
Summary of Invention Technical Problem [0004]
However, in the technique disclosed in Patent Literature 1, the moisture content of the coal has increased significantly by soaking the coal. Since such coal with increased moisture content is dried with extracted steam, there was a problem that a process of treating the stored coal to a usable state is complicated and the cost of the coal may be increased. In addition, since the extracted steam from the power plant is used to dry the coal, there was also a problem that a coal storage location is restricted to a place adjacent to the power plant. [0005]

The present invention has been made to solve the above problems, and it is an object of the present invention to provide a coal storage system and a method for storing coal that realizes appropriate temperature control with low cost.
Solution to Problem [0006]
The coal storage system of the present invention comprises a yard for storing coal,
a coal stockpile having a frustum shape with a ceiling surface and a side surface formed by piling up the coal on the yard;
a pressing equipment for pressing the coal stockpile;
a sprinkler for watering to the coal stockpile; and
wherein pressing on at least outer circumference portion of the ceiling surface of the coal stockpile is performed by the pressing equipment, and watering to the side surface of the coal stockpile is performed by the sprinkler.
[0007]
The present invention also provides a method for storing coal and the method, the method comprises the steps of:
forming a coal stockpile having a frustum shape with a ceiling surface and a side surface by piling up coal on a yard;
pressing at least outer circumference portion of the ceiling surface of the coal stockpile; and
watering on the side surface of the coal stockpile which is pressed.
[0008] (Definition of terms)
In the present invention, "pressing" means pressurizing and compacting to the surface of the coal stockpile during or after formation to reduce the stockpile porosity. [0009]

"Pressing equipment" refers to general equipment used for pressing the coal stockpile. "Heavy machine" can be conveniently used as "pressing equipment". Another usable "pressing equipment" includes a combination of a weight having a flat bottom surface and a vertically moving device for vertical moving the weight such that the surface of the coal stockpile can be pressurized as "pressing equipment". "Heavy machine" is a generic term for construction machines, and "construction vehicle", among "heavy machine", can perform "pressing" with utilizing its own weight by merely running on the surface of the coal stockpile. In case of using a power shovel as a "heavy machine", it is possible to perform "pressing" by pushing or striking a bucket or a backhoe of the power shovel on the surface of the coal stockpile. This is effective when "pressing" a place where "heavy machine" cannot run. Furthermore, "compaction apparatus" which is a type of "heavy machine" can be used for pressing. [0010]
Also, in the present invention, the pressing which specifies a part of the coal stockpile among "pressing" is defined as follows. [0011]
"Outer circumference pressing" means pressing only an area of 3-5 m inside from the position of 1-2 m from the outer circumferential edge of the ceiling surface in the ceiling surface of the coal stockpile. [0012]
"Surface pressing" refers to pressing the entire ceiling surface of the coal stockpile. Therefore, in the "surface pressing", in addition to the area to be pressed by "outer circumference pressing", inner and outer areas thereof are pressed. In addition, in "surface pressing", the outer edge portion (corresponding to "top of slope" in civil engineering term) of the ceiling surface of the coal stockpile is formed to be roughly round. [0013]
"Corner portion pressing" means pressing the corner portion (the portion corresponding to the side ridge of the truncated pyramid) on the side surface of the coal stockpile. In this case, it is preferable to press such that corner portions are formed to be roughly round.

When "corner portion pressing" is carried out with a heavy machine, heavy machine cannot run on the side surface of the coal stockpile. However, it is possible to perform pressing the corner portion by pushing or striking the bucket or the backhoe described above against the corner portion.
Advantageous Effects of Invention [0014]
According to the present invention, it is possible to provide a coal storage system and a coal storing method that controls the stockpile temperatures appropriately with low cost.
Brief Description of Drawings
[0015]
[FIG. l] FIG. 1 is a top view of a coal stockpile according to an embodiment of
the present invention.
[FIG. 2] FIG. 2 is a side view of the coal stockpile shown in FIG. 1.
[FIG. 3] FIG. 3 is a view showing the surface corner portion pressing of the
coal stockpile shown in FIG. 1.
[FIG. 4] FIG. 4 is a schematic top view of a coal stockpile in Example 1.
[FIG. 5] FIG. 5 is a graph showing the correlation between the temperature
of coal stockpile and watering in Example 1.
[FIG. 6] FIG. 6 is a graph showing a correlation between moisture content
and watering of coal stockpile in Example 1 of the present invention.
[FIG. 7] FIG.7 is a schematic top view of a coal stockpile in Example 2.
[FIG. 8] FIG. 8 is a graph showing the correlation between the temperature
and watering of the coal stockpile in Example 2.
[FIG. 9] FIG. 9 is a graph showing a correlation between moisture content
and watering of the coal stockpile in Example 2.
[FIG. 10A] FIG. 10A is a graph showing a transition in average temperature
and moisture content of the coal stockpile in Example 3.
[FIG. 10B] FIG. 10B is a graph showing a transition of maximum
temperature and moisture content of coal stockpile in Example 3.
[FIG. 11] FIG. 11 is a schematic top view of a coal stockpile in Comparative
Example 1.

[FIG. 12] FIG. 12 is a graph showing a temperature transition of the coal
stockpile in Comparative Example 1.
[FIG. 13] FIG. 13 is a schematic top view of a coal stockpile in Comparative
Example 2.
[FIG. 14] FIG. 14 is a graph showing transitions of average temperature and
maximum temperature of the coal stockpile in Comparative Example 2.
[FIG. 15] FIG. 15 is a schematic top view of a coal stockpile in Comparative
Example 3.
[FIG. 16] FIG. 16 is a graph showing a transition of the maximum
temperature of the coal stockpile in Comparative Example 3.
Description of Embodiments [0016]
Referring to FIG. 1 and FIG. 2, a top view and a side view of a coal stockpile 1 constituting a part of a coal storage system according to an embodiment of the present invention are shown. The coal stockpile 1 is formed by piling up coal on a coal yard 2 and usually has a ceiling surface 11 which is a substantially horizontal surface and an side surface 12 which is continuous from the edge of the ceiling surface and extends to incline toward to the bottom, such that the coal stockpile has a frustum shape in which the cross section in the vertical direction is roughly trapezoidal as a whole. Pressing and watering are performed on the coal stockpile 1 to suppress self-heating. Pressing equipment such as a heavy machine is used for pressing of the coal stockpile 1, and sprinkler is used for watering. Therefore, the coal storage system includes the pressing machine and the sprinkler in addition to the coal stockpile 1. [0017]
These configurations for pressing, watering and others will be described below. [0018] [Pressing]
The coal stockpile 1 can be formed by shaping the surface of the coal piled up by the stacker with pressing equipment such as a heavy machine. In the piled and shaped coal stockpile 1, the stockpile pores are reduced by

pressing and oxidation and heat generation of the coal is suppressed. The coal stockpile 1 can be formed, for example, by repeating the steps of piling the coal with a height of about 2m and pressing, further piling the coal with a height of 2m and pressing. Pressing can be performed by loading the heavy machine on the ceiling surface 11 which is the upper surface of the coal stockpile 1. The coal stockpile having a desired size can be formed by piling up more coal on the pressed ceiling surface 11 and further pressing the piled coal. [0019]
When pressing is performed, pressing entire of the ceiling surface 11 (surface pressing) may be performed or pressing only outer circumference portion 13 of the ceiling surface (outer circumference pressing) may be performed. However, pressing of the outer circumference portion 13 of the ceiling surface is essential. The reason for this is that the oxidation and the heat generation proceed by air flowing into the coal stockpile 1 from the side surface 12, and pressing the outer circumference portion 13 of the ceiling surface increases the density of the coal, whereby the inflow of air from the side surface 12 is difficult. In pressing the outer circumference portion 13 of the ceiling surface, if the heavy machine is too close to the end portion 15 of the ceiling surface, there is a possibility that the heavy machine falls from the coal stockpile 1. Therefore, a passage of the heavy machine is secured by providing the outer circumference portion 13 of the ceiling surface where pressing is performed to an inner circumference portion of the end portion 15. [0020]
The coal stockpile 1 can have a vehicle path 14 on a part of the side surface 12, which serves as a path for the heavy machine traveling between the coal yard 2 and the ceiling surface 11 of the coal stockpile 1. The shape and position of the vehicle path 14, that is the path of the heavy machine, can be arbitrary. For example, the vehicle path 14 can be provided on a diagonal line of the coal stockpile 1 as shown in FIG. 1 or out of the diagonal line of the coal stockpile 1 as shown in FIG. 4 when the coal stockpile 1 is viewed from above. [0021]

The side surface 12 of the coal stockpile 1 is formed by the coal which is piled up and flowed down to the surroundings. Since it is difficult for the heavy machine to run steadily on the side surface 12 except for the vehicle path 14, pressing to the side surface 12 is not usually performed. [0022] [Watering]
Since coals, especially subbituminous coals and brown coals (including upgraded brown coals), tend to oxidize and generate heat in many cases, watering to the coal stockpile 1 is performed by sprinkler 3 (see FIG. l) during storing the coal. In the coal stockpile 1, since air flows in from the side surface 12, the vicinity of the side surface 12 is most liable to oxidize and generate heat. Therefore, self-heating can be suppressed efficiently by watering at least the side face 12. [0023]
Oxidation and heat generation of the coal stockpile 1 can be suppressed even with watering only on the side surface 12, and in this case, increase in the coal moisture content and increase in the amount of watering can be suppressed as compared with the case of watering over the entire coal stockpile 1. The installation position and the number of the sprinkler 3 may be arbitrary, such as the position and the number shown in FIG. 1, as long as watering can be performed in a desired area on the side surface 12. [0024]
Watering is not required to be performed continuously, it is sufficient to perform periodic watering such as few hours per day. By combining pressing and watering, it is possible to sufficiently suppress the self-heating and the increase in moisture content of coal. Regarding the frequency of watering, it is also possible to reduce, for example, the subsequent frequency of watering to half relative to that during the period from the start of storing the coal to the 10th - 14th day, whereby the increase in moisture content is further suppressed. Furthermore, it is also possible to suppress the self-heating of coal even if watering is stopped after about l-2month from the start of storing the coal. [0025] [Corner portion pressing]

FIG. 3 shows an example of pressing on the surface corner portion of the coal stockpile 1. For simplifying the explanation, the vehicle path 14 is omitted in FIG. 3. Since the coal stockpile 1 is formed by piling up bulk coal, air is easy to flow into the vicinity of the corner portion 16 and the coal is easily oxidized. In particular, the amount of air flowing into the corner portion 16 of the coal stockpile 1 (in the example shown in FIG. 2, since the coal stockpile 1 is a substantially truncated pyramidal shape, the corner portion 16 corresponds to the vicinity of the circumference 4 sides) is increased by the wind. Therefore, oxidation of coal is suppressed by pressing the corner portion 16 of the coal stockpile 1 with the heavy machine to reduce the amount of air flowing by the wind. [0026] [Other configuration]
The coal stockpile 1 may be sprayed with a chemical agent as necessary. Spraying the chemical agent may be performed to the entire surface of the coal stockpile 1 after the coal stockpile 1 is formed or to the coal before constituting the coal stockpile 1. Examples of the agent include a surfactant for imparting hydrophilicity to coal and a coating agent for maintaining the shape of the coal stockpile 1. In the case of spraying the surfactant, it is preferable to spray it on the coal before forming the coal stockpile 1 so as to impart hydrophilicity also inside the coal stockpile 1. On the other hand, in the case of spraying the coating agent, since it is sufficient for the surface of the coal stockpile 1 to be coated with the coating agent, it is preferable to spray after forming the coal stockpile 1. [0027]
When the chemical agent is sprayed in this manner, the coal storage system may further include appropriate chemical agent spraying equipment suitable for the chemical agent to be sprayed.
Examples [0028]
The effect of suppressing the self-heating of the coal stockpile 1 was evaluated in Examples 1-3 and Comparative Examples 1-3. Table 1 shows the properties of coal used in these examples and comparative examples.


(Example l)
FIG. 4 shows a schematic top view of the coal stockpile 1 in Example 1. The coal stockpile 1 was formed by repeating steps of piling up coal with a stacker and pressing to shape the surface of the piled coal with a heavy machine. In FIG. 4, the outer circumference portion 13 of the ceiling surface is omitted. [0031]
In Example 1, the hydrophilicity was improved by spraying a surfactant on the coal stockpile 1 (coal storage amount: about 30,000 tons) formed on the coal yard 2. The surfactant was sprayed on the coal by means of chemical agent spraying equipment installed in a discharging feeder of an unloader before the coal was piled. As the surfactant, a known one (Das Seal F-10, manufactured by NOF CORPORATION) was used. [0032]
After forming the coal stockpile 1, pressing only the outer circumference portion 13 in the ceiling portion 11 was performed by treading down with a heavy machine. Further, with respect to the corner portion 16, pressing its surface was performed by striking the surface and shaping round

with a heavy machine (a bucket or a back hoe of a power shovel). Watering was made only on the side surface 12. Thermocouples were installed as temperature measuring devices at positions on the side surface 12 indicated by circled numerals 1-16 in FIG. 4. And then, the temperature at each position was measured and the average value of the measured temperatures was given as the temperature of the coal stockpile 1. Specifically, each of thermocouples was inserted in protective tubes and they were inserted into the coal stockpile 1 at positions where the height of the surface of the coal stockpile 1 is 3m from the ground (coal yard 2). The depth of insertion of the thermocouples into the coal stockpile 1 was 1.5m, and the distance between the thermocouples in the horizontal direction was 10m.
[0033]
The correlation between the temperature of the coal stockpile 1 and watering in Example 1 is shown in the graph of FIG. 5. In the graph of FIG. 5, one scale on the horizontal axis indicates 10 days. In Example 1, watering was performed almost evenly to the side surface 12. The amount of watering in Example 1 is shown in Table 2 below.


[0035]
The above "Elapsed days" is the days from the start of coal storing. This also applies to the following Examples and Comparative Examples. As shown in FIG. 5, the temperature of the coal stockpile 1 in Example 1 is constantly below 60 °C, which is the upper limit of the control temperature during storing the coal. It was shown that self-heating of the coal stockpile 1 is suppressed by watering only on the side surface 12. [0036]
In addition, in Example 1, moisture content of outer circumference portion of the coal stockpile 1 was measured in order to confirm the transition of moisture content in the coal stockpile 1 due to watering and

rainfall. The measurement of the outer circumference moisture content was carried out as follows. Each of 4 side faces 12 of the coal stockpile 1 was divided into 2 areas, that is 8 areas in total, in the horizontal direction and 3 samples per area were collected from positions of a height of 40cm from the ground surface and a depth of 30cm from the side surface 12. The collected samples were mixed, and the moisture content measured in the mixed sample was used as an outer circumference moisture content of the coal stockpile 1. [0037]
The correlation between the moisture content and watering of the coal stockpile 1 in Example 1 is shown in FIG.6. In FIG. 6, one scale on the horizontal axis also indicates 10 days as in the case of FIG. 5. The vertical axis also shows rainfall. In Example 1, since watering was performed only to the side surface 12, the increase in moisture content was only a few% from the moisture content at the start of the coal storage despite some rainfall. Thus, the self-heating was suppressed without unnecessarily increasing the moisture content of the coal in Example 1. [0038]
Although not used in Example 1, a known coating agent may be sprayed in order to maintain the shape of the coal stockpile 1. In addition to the dust suppressing effect (see, for example, JP-A-7-117823 and JP-A-2000-80356), oxidation and heat generation of the coal stockpile 1 can be further suppressed by spraying the coating agent. In Example 1, a sufficient temperature suppressing effect was obtained without spraying a coating agent. [0039] (Example 2)
FIG. 7 shows a schematic top view of the coal stockpile 1 in Example 2. In Example 2, although the shape of the coal stockpile 1 is almost the same as in Example 1, the amount of coal to be stored was about 26,770 tons. As in the case of Example 1, a surfactant was sprayed on the coal stockpile 1 and no coating agent was sprayed. As for pressing, as in the case of Example 1, pressing to the ceiling 11 was performed on only the outer circumference portion 13 of the ceiling surface as to the ceiling surface 11,

and further pressing on the corner portion 16 was performed. Regarding watering, watering only to the side surface 12 was performed with the continuous watering and the subsequent periodic watering as in the case of Example 1. The amount of watering in Example 2 is shown in Table 3 below. After the periodic watering, watering was not performed until 49th day. The temperature and the moisture content were measured during this 49 days and the effect of the coal stockpile 1 in Example 2 was verified.


[0041]
The temperatures were measured by means of thermocouples installed in the same manner as in Example 1 at positions indicated by circled numbers 1-16 in FIG. 4 and the transition of the outer circumferential temperature of the coal stockpile 1 which is the average value of the

measured temperatures was measured. In Example 2, the transitions of the internal temperatures of the coal stockpile 1 were also measured. In the measuring the internal temperature, the ceiling surface 11 of the coal stockpile 1 was bored at positions indicated by A, B, C in FIG. 7 after the initial watering, and 5 thermocouples were buried at intervals of 1.5m such that the lowest thermocouple was located at a height of 1.5m from the ground (coal yard 2). The internal temperature was determined by the average value of the temperatures measured with 3rows x 5 thermocouples. [0042]
FIG. 8 shows the transition of the outer circumferential temperatures and the internal temperatures of the coal stockpile 1. From FIG. 8, it is understood that the self-heating of the coal stockpile 1 is suppressed by the effect of watering, and both the outer circumferential temperature and the inner temperature was controlled at 40 °C or less throughout the coal storage period. [0043]
Regarding the moisture content, outer circumference moisture content and internal moisture content were measured. Since the measurement of the outer circumference moisture content is the same as that in Example 1, its explanation is omitted here. Samples were collected from the inside of the coal stockpile 1 when boring to install thermocouples for measuring the internal temperature of the coal stockpile 1 and dismantling the coal stockpile 1, and the moisture contents of the samples were measured as the internal moisture content. [0044]
FIG. 9 shows the transition of the moisture content of the coal stockpile 1. From FIG. 9, it was confirmed that although the outer circumference moisture content increased about 1-3 % against the moisture content at the start of the coal storage, the increase in the internal moisture content was within 1% against the moisture content at the start of the coal storage when measuring the internal moisture content at the time of dismantling the coal stockpile 1. From the above, the self-heating is suppressed without unnecessarily increasing the moisture content of the coal in Example 2. [0045]

(Example 3)
In Example 3, a coal stockpile was formed in the same shape as in Example 1 except that the amount of coal to be stored was about 19,664 tons, and the transition of the outer circumferential temperature of the coal stockpile and the transition of the outer circumference moisture content were confirmed in the same manner as in Example 1. Regarding the outer circumferential temperature of the coal stockpile, the transition of the maximum temperature was also determined in addition to the average temperature obtained in the same manner as in Example 1. With respect to pressing, as in the case of Example 1, pressing was performed on the outer circumference portion of the ceiling surface as to the ceiling surface and further performed on the corner portion. [0046]
However, in Example 3, the spraying of the surfactant and the coating agent to the coal stockpile were not carried out. Watering was performed for 8 hours per day (the amount of watering in 8 hours is 176 tons) as the initial watering from the 3rd day to the 16th day from the start of the coal storing and the periodic watering was performed from the 17th day. The periodic watering was divided into three periods. The first period was the period from the 17th day to the 28th day from the start of the coal storing, and watering was performed for 8hours per day (the amount of watering in 8 hours was 176 tons). The second period was the period from the 31st day to the 34th day from the start of the coal storing, and the watering was performed twice for 8 hours per week (the amount of watering in 8 hours was 176 tons). The third period was the period from the 38th day to the 45th day from the start of coal storing, and watering was performed for 8 hours per week (the amount of watering in 8 hours was 176 tons). The amount of watering in Example 3 is shown in Table 4 below.


FIG. 10A shows an average temperature transition (outer circumferential temperature) of coal stockpile of Example 3. In addition, FIG. 10B shows a maximum temperature transition (outer circumferential temperature) of the coal stockpile of Example 3. Further, FIG. 10A and FIG. 10B also show the moisture content at the start of the coal storage and the outer circumference moisture content of the coal stockpile on the 2nd day and the 16th day from the start of coal storing of Example 3. From FIG. 10A, it is understood that the self-heating of coal stockpile is suppressed by the effect of watering and the average temperature is controlled at 40 °C or less throughout the coal storage period. Also, from FIG. 10B, it is understood that the maximum temperature is controlled at 50 °C or less, which is sufficiently lower than 60 °C that is the upper limit of the control temperature in the coal storage. Although the moisture content increases greatly against the moisture content at the start of the coal storage as compared with Example 1 and 2, it is only an increase of several%. This means that the self-heating is suppressed without unnecessarily increasing the moisture content of coal. [0049] (Comparative Example l)
FIG. 11 shows a schematic top view of the coal stockpile 1 in Comparative Example 1. In Comparative Example 1, although the shape of the coal stockpile 1 is almost the same as in Example 1, the amount of coal to be stored was about 18,000 tons. As in the case of Example 1, a surfactant was sprayed on the coal stockpile 1. However, in Comparative Example 1, no

watering was performed on the coal stockpile 1, and a coating agent was sprayed on the coal stockpile 1 in order to suppress the coal particles breakdown in the coal stockpile 1, unlike Example 1. As a coating agent, Rikabond ET-39 manufactured by MC Ebatech Corporation was used. Spraying of the coating agent was performed by means of a portable power pump after installing a thermocouple for temperature measurement. [0050]
For the measurement of the temperatures, thermocouples were installed at the position indicated by the circled numerals 1-42 in FIG. 11 on the side surface 12 (a position at a height of 3 m from the ground, an interval of 5 m in the horizontal direction, a depth of 1.5 m). The temperature at each position was measured and the temperature of coal stockpile 1 was given by the average value. Pressing was performed on the entire of the ceiling surface 11 unlike Example 1. [0051]
FIG. 12 shows a temperature transition of the coal stockpile 1 in Comparative Example 1. In Comparative Example 1, the temperature of the coal stockpile 1 continued to rise from the 5th day from start of the coal storing and reached 60 °C which is the upper limit of the control temperature in the coal storage around 22th day. Thus, the subsequent temperature measurement was stopped. In Comparative Example 1, since watering is not performed, it can be understood that an increase in temperature cannot be suppressed even by pressing and spraying the coating agent. [0052] (Comparative Example 2)
FIG. 13 shows a schematic top view of the coal stockpile 1 in Comparative Example 2. In Comparative Example 2, the shape of the coal stockpile 1 was substantially square truncated pyramidal shape, and its amount of coal was about 72,900 tons. The surfactant was sprayed but the coating agent was not sprayed as in the case of Example 1. [0053]
In Comparative Example 2, unlike Comparative Example 1, pressing was not performed, and only watering to the side surface 12 was performed. Watering was started on the 4th day from the start of coal storing. However,

since part of the coal slid down in 3 hours from the start of watering, it was switched to 7 hours per day from the 12th day from the start of coal storing after seeing the situation for a while (initial watering).
The initial watering was continued until the 18th day from the start of coal storing and watering was switched to periodic watering for 7 hours per 2 days from the 19th day. However, since the temperature tended to rise during the periodical watering, periodic watering for 7 hours per day was performed from the 25th day. And further, since self-heating from other than the temperature measuring portion was observed on the 38th day, periodic watering was changed to continuous watering for 24 hours per day from the 38th day. The amount of watering in Comparative Example 2 is shown in Table 5 below.

[0055]
FIG. 14 shows the transition of the average temperature and the maximum temperature of the coal stockpile 1 in Comparative Example 2. The temperature of the coal stockpile was measured in the same manner as in Example 1. From FIG. 14, it was confirmed that even though the average temperature rose to about 50 °C around 14th day from the start of coal storing and thereafter tended to descend, the maximum temperature exceeded 60 °C, which is control temperature, between 10th and 17th day. As described above, despite the watering, the effect of suppression of self-heating as in Examples 1 and 2 was not observed in Comparative Example 2. [0056] (Comparative Example 3)
FIG. 15 shows a schematic top view of the coal stockpile 1 in Comparative Example 3. In Comparative Example 3, the shape of the coal stockpile 1 was substantially square truncated pyramidal shape as in the case of Comparative Example 2, and its coal amount was about 32,690 tons. Neither surfactant nor coating agent was sprayed. [0057]
In Comparative Example 3, thermocouples were installed at positions indicated by circled numerals 1-4 in FIG. 15 and the temperatures of the coal stockpile 1 were measured. The method for installing the thermocouples was the same as in Example 1. In addition, in Comparative Example 3, watering was performed to the entire surface of the coal stockpile 1 without pressing. Watering apparatuses (sprinklers) were installed at positions indicated by circle in FIG. 15, and watering was performed from the 13th day from the start of coal storing. Basically, watering was performed constantly (24 hours), but there were only 9 days, on which either watering was not performed or performed for about 6-7 hours per day depending on the temperature condition etc. of coal during the coal storage perio d (70 days). In addition, sprinklers were added or removed according to shipping conditions of coal from coal stockpile 1 and temperature condition of coal stockpile 1. The shipment of coal from the coal stockpile 1 was carried out sequentially from the upper left corner and the lower left corner shown in


Luuoyj
FIG. 16 shows the transition of the maximum temperature of coal in Comparative Example 3. Since the maximum temperature of the coal exceeded the control temperature of 60 °C due to not watering until the 12th day from the start of the coal storing, watering was performed from the 13th day, but the rise in the temperature continued until the 14th day and the temperature reached 79 °C. The temperature decreased from the 15th day

(*l) In Comparative Example 1, there is no data on the amount of the coal per lm3 of the amount of watering when watering at the maximum amount (the entirety of the stockpile and the side surface of the stockpile), since watering was not performed. In addition, the amount of the coal in non-watering area is the amount of the coal in the entirety of the stockpile.
(*2) In comparative Example 3, the amount of the coal in watering area is the amount of coal in the entirety of the stockpile and there is no data on the amount of the coal in non-watering area, since watering was performed to the entirety of the stockpile. In addition, since the amount of the coal was changed during the experiment, data on the amount of the coal per lm3 of the amount of watering at maximum watering was omitted.
[0064]
The amount of coal per lm3 of the amount of watering at the maximum watering shown in Table 8 can be regarded as one index representing the magnitude of the self-heating suppression effect of coal by watering. That is, it shows that as the amount of coal per unit amount of watering increases, it is possible to suppress the self-heating of a larger amount of coal with less amount of watering, or in other words, the watering efficiency is excellent. Referring to Table 8 from this point of view, it can be understood that the watering efficiency of Examples 1-3 is better than that of Comparative Example 2. [0065] (Summary)
From the above examples and comparative examples, the following can be said.
(1) It was observed that by performing initial watering, self-heating of
coal at the beginning of coal storage can be suppressed and coal can be stored
for a long time.
(2) It was observed the possibility of control without watering in about
1 to 2 months after shifting from initial watering to periodic watering.
(3) It was observed that it is possible to suppress self-heating without a
coating agent and to control moisture content.

(4) It was observed that it is possible to control the temperature of the entirety of coal stockpile even with watering only on the side surface.
Explanation of Symbols [0066]
1 Coal stockpile
2 Coal yard
11 Ceiling surface
12 Side surface
13 Outer circumference portion of ceiling surface
14 Road
15 End
16 Corner

1. A coal storage system comprising:
a yard for storing coal;
a coal stockpile having a frustum shape with a ceiling surface and a side surface formed by piling up the coal on the yard;
a pressing equipment for pressing the coal stockpile;
a sprinkler for watering to the coal stockpile; and
wherein pressing on at least outer circumference portion of the ceiling surface of the coal stockpile is performed by the pressing equipment, and watering to the side surface of the coal stockpile is performed by the sprinkler.
2. The coal storage system according to claim 1, wherein the coal stockpile
is pressed at a corner portion in the side surface.
3. The coal storage system according to claim 1 or 2, further comprising at
least one chemical agent spraying equipment for spraying a chemical agent
on a surface of the coal or the coal stockpile.
4. The coal storage system according to any one of claims 1 to 3, wherein
the pressing equipment is a heavy machine.
5. A method for storing coal, comprising the steps of:
forming a coal stockpile having a frustum shape with a ceiling surface and a side surface by piling up coal on a yard;
pressing at least outer circumference portion of the ceiling surface of the coal stockpile; and
watering on the side surface of the coal stockpile which is pressed.
6. The method for storing coal according to claim 5, wherein the step of
pressing the coal stockpile includes pressing a corner portion in the side
surface.

7. The method for storing coal according to claim 5 or 6, wherein a
watering time per day in the step of watering on the coal stockpile is
determined such that a watering frequency after 10th - 14th day from the
start of coal storage becomes half of the watering frequency during the period
from the start to 10th - 14th day.
8. The method for storing coal according to any one of claims 5 to 7,
further comprising at least one step of spraying a chemical agent on the
surface of the coal or the coal stockpile.
9. The method for storing coal according to claim 8, wherein the step of
spraying the chemical agent includes spraying a surfactant as the chemical
agent on the coal before forming the coal stockpile.
10. The method for storing coal according to claim 8 or 9, wherein the step
of spraying the chemical agent includes spraying a coating agent for
maintaining the shape of the coal stockpile as the chemical agent on the coal
stockpile.