Methane fermentation tank, and method for operating methane fermentation tank

Abstract

To make it possible to release heat in the case where a temperature of methane fermentation liquid rises too high without causing a problem of deterioration due to sunlight, and appropriately perform methane fermentation treatment.SOLUTION: A methane fermentation tank that produces biogas by performing methane fermentation treatment to organic waste is provided with a tank body 11 storing methane fermentation liquid 4, and a covering material 5 covering external surfaces 13, 14 other than a bottom 12 of the tank body 11, wherein the covering material 5 has light shielding properties, and is disposed in a state of forming a space 6 between the tank body 11 and the material, and at least a part of the space 6 includes a non-heat-insulated material space 61 where a heat insulation material 7 is not disposed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a methane fermenter that produces biogas by subjecting organic waste to methane fermentation treatment, and a method for operating the methane fermenter. [Background technology]

[0002] For example, methane fermentation (anaerobic fermentation) is widely used to reduce the volume of organic waste such as sludge and biomass generated during wastewater treatment and to convert it into energy. Methane fermentation is a technology in which organic waste is stored for a certain period of time under anaerobic conditions, whereby the organic waste is decomposed by the action of anaerobic microorganisms to produce biogas such as methane gas and carbon dioxide, and is widely used in wastewater treatment facilities and wastewater treatment facilities in Japan.

[0003] A methane fermentation facility that performs methane fermentation is primarily equipped with a methane fermentation tank in which organic waste is stored and methane fermented, an agitator that agitates the methane fermentation liquid in the methane fermentation tank, and a heating device that heats the methane fermentation liquid.

[0004] In order to smoothly carry out methane fermentation, it is necessary to maintain the temperature in the methane fermentation tank within a certain range. When performing methane fermentation at a medium temperature, the temperature is maintained within a range of, for example, 30°C to 45°C, and when performing methane fermentation at a high temperature, the temperature is maintained within a range of, for example, 50°C to 60°C.

[0005] Conventionally, a heating device has been provided to heat the methane fermentation liquid in the methane fermentation tank. However, simply heating the tank using the heating device causes heat to be dissipated from the surface of the methane fermentation tank, and so it is common to install a heat insulating material on the outer surface of the methane fermentation tank (see, for example, Patent Documents 1 and 2 and Non-Patent Document 1).

[0006] In Patent Document 1, the methane fermentation tank is configured as a double cylindrical body having an inner wall and an outer wall, and a space between the inner wall and the outer wall is divided by a partition plate to form a plurality of compartment spaces. The plurality of compartment spaces can be freely switched between a state in which the insulation material is filled and a state in which the insulation material is emptied.

[0007] In Patent Document 2, a surrounding wall is provided around the methane fermentation tank, and agricultural and forestry by-products are filled between the surrounding wall and the outer wall surface of the methane fermentation tank to form an insulation layer. In Non-Patent Document 1, polystyrene foam is placed on the outer surface of the methane fermentation tank as a heat insulating material. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 57-1989 [Patent Document 2] JP 2002-192192 A [Non-patent literature]

[0009] [Non-Patent Document 1] Steel Plate Digestion Tank Technical Manual - March 2013 - Published on March 31, 2013 by the Sewerage Technology Promotion Organization Summary of the Invention [Problem to be solved by the invention]

[0010] In Patent Document 2 and Non-Patent Document 1, the entire side of the methane fermentation tank is covered with a heat-insulating material, so that a decrease in the temperature of the methane fermentation liquid in the methane fermentation tank can be suppressed. However, if the temperature of the methane fermentation liquid in the methane fermentation tank rises too much, the temperature of the methane fermentation liquid does not decrease easily, and the activity of the microorganisms performing methane fermentation decreases, which may prevent the methane fermentation process from being performed properly.

[0011] In this regard, in Patent Document 1, some of the compartment spaces are switched to an empty state without supplying insulation material, so that there can be a portion on the side of the methane fermentation tank that is not covered with insulation material. However, in Patent Document 1, the heat of sunlight or the outside air is transmitted through the outer wall, and the heat of the sun or the outside air is taken into the compartment space where the insulation material is switched to an empty state, thereby obtaining a heating effect of heating the methane fermentation liquid. Therefore, it is not considered to dissipate heat from the compartment space where the insulation material is switched to an empty state, and if the temperature of the methane fermentation liquid in the methane fermentation tank rises too much, the temperature of the methane fermentation liquid does not decrease easily, as in Patent Document 2 and Non-Patent Document 1, and the activity of the microorganisms performing methane fermentation decreases, which may prevent the methane fermentation process from being performed properly.

[0012] Moreover, in Patent Document 1, a highly translucent exterior wall is used to allow sunlight to pass through, so in the compartmented space where the state is switched to filling with insulation material, sunlight directly hits the insulation material, which may cause deterioration of the insulation material. Also, sunlight that has passed through the exterior wall may hit the inner wall of the methane fermentation tank, causing deterioration due to ultraviolet rays in areas where packing or caulking agents are used.

[0013] In view of this situation, the main object of the present invention is to provide a methane fermentation tank and an operating method for a methane fermentation tank that can dissipate heat when the temperature of the methane fermentation liquid becomes too high, and can properly carry out methane fermentation processing, without causing problems of deterioration due to sunlight. [Means for solving the problem]

[0014] The first characteristic configuration of the present invention is a methane fermentation tank for producing biogas by methane fermentation of organic waste, A tank body for storing a methane fermentation liquid; An exterior material that covers the outer surface of the tank body other than the bottom portion is provided, The exterior material has a light-shielding property and is disposed in a state in which a space is formed between the exterior material and the tank body, The space includes at least a portion of a non-insulating space in which no insulating material is provided.

[0015] According to this configuration, the exterior material covering the outer surface of the tank body other than the bottom has a light-shielding property, so that it is possible to suppress the transmission of sunlight through the exterior material, and the occurrence of the problem of deterioration due to sunlight can be prevented. Moreover, since the space formed between the tank body and the exterior material includes at least a non-insulated space, if the temperature of the methane fermentation liquid rises too much, heat can be released from the non-insulated space. Therefore, it is possible to suppress the temperature of the methane fermentation liquid from rising to a temperature at which the activity of the microorganisms performing methane fermentation decreases, and the methane fermentation process can be carried out appropriately.

[0016] A second characteristic configuration of the present invention is that the space includes at least a portion of an insulating material space in which a thermal insulating material is disposed.

[0017] For example, if the entire space formed between the tank body and the exterior material were made a non-insulated space, heat would be radiated from the entire outer surface of the tank body except for the bottom, which could result in the temperature of the methane fermentation liquid dropping too much.

[0018] Therefore, according to the present configuration, the space formed between the tank body and the exterior material includes at least a part of the thermal insulation space. As a result, the presence of not only a non-insulated space but also a thermal insulation space makes it possible to prevent the temperature of the methane fermentation liquid from rising too high or falling too low, making it easier to maintain the temperature of the methane fermentation liquid at a temperature suitable for methane fermentation treatment.

[0019] A third characteristic configuration of the present invention is that the non-insulating space is disposed above the tank body, The insulating space is disposed below the tank body.

[0020] According to this configuration, since the non-insulated space is disposed on the upper side of the tank body, if the temperature of the methane fermentation liquid becomes too high, the heat rises to the upper side of the tank body where the non-insulated space is located, and therefore the heat can be efficiently dissipated from the non-insulated space.

[0021] Furthermore, since the insulation space is arranged on the lower side of the tank body, there is no need to work at high altitudes to install insulation on the upper side of the tank body, and the temperature drop of the methane fermentation liquid can be suppressed while simplifying the insulation installation work.

[0022] A fourth characteristic configuration of the present invention is that the exterior material is provided with an opening that communicates the non-insulated space with the outside.

[0023] According to this configuration, since the exterior material has an opening, heat can be dissipated from the non-insulated space to the outside through the opening in the exterior material, and heat can be dissipated efficiently. Moreover, outside air can be introduced into the non-insulated space from the outside of the exterior material through the opening, and this inflow of outside air can also promote heat dissipation.

[0024] A fifth characteristic feature of the present invention is that a plurality of the openings are provided.

[0025] According to this configuration, since heat can be dissipated through each of the multiple openings, heat dissipation can be performed more efficiently. For example, an air flow can be formed in which outside air flows in from one opening, flows through the non-insulated space, and flows out to the outside of the exterior material from another opening, so that the air flow can efficiently dissipate heat from the non-insulated space.

[0026] A sixth characteristic feature of the present invention is that a blower is provided at the opening.

[0027] According to this configuration, since the opening is provided with a blower, the blower can create an air flow, and the air flow can efficiently dissipate heat. Moreover, when it is desired to suppress a decrease in temperature of the methane fermentation liquid, the operation of the blower can be stopped to prevent heat dissipation associated with the air flow, and the decrease in temperature of the methane fermentation liquid can be appropriately suppressed.

[0028] A seventh characteristic configuration of the present invention is a method for operating a methane fermentation tank for producing biogas by methane fermentation of organic waste, comprising: A tank body for storing a methane fermentation liquid; An exterior material that covers the outer surface of the tank body other than the bottom portion is provided, The exterior material has a light-shielding property and is disposed in a state in which a space is formed between the exterior material and the tank body, The exterior material is provided with an opening / closing part that can be switched between an open state in which the space communicates with the outside and a closed state in which the space is blocked from the outside, When the temperature of the methane fermentation liquid in the tank body or the temperature of the space becomes equal to or higher than a first set temperature, an opening / closing switching process is performed in which the opening / closing part is switched to an open state, and when the temperature of the methane fermentation liquid in the tank body or the temperature of the space becomes equal to or lower than a second set temperature, the opening / closing part is switched to a closed state.

[0029] According to this configuration, the exterior material covering the outer surface of the tank body other than the bottom has a light-shielding property, so that it is possible to suppress the transmission of sunlight through the exterior material, and to prevent the occurrence of problems of deterioration due to sunlight. Moreover, in the opening / closing switching process, the opening / closing part is switched to an open state or a closed state according to the temperature of the methane fermentation liquid in the tank body or the temperature of the space formed between the exterior material and the tank body. As a result, when the temperature of the methane fermentation liquid or the temperature of the space becomes equal to or higher than the first set temperature, the opening / closing part is switched to an open state, so that heat can be dissipated from the space through the opening / closing part to the outside of the exterior material. Therefore, when the temperature of the methane fermentation liquid rises too much, the heat can be dissipated to suppress the temperature of the methane fermentation liquid from rising to a temperature at which the activity of the microorganisms performing methane fermentation decreases, and the methane fermentation process can be performed appropriately. Conversely, when the temperature of the methane fermentation liquid or the temperature of the space falls below the second set temperature, the opening / closing section is switched to a closed state to prevent heat from being dissipated from the space to the outside of the exterior material through the opening / closing section. This suppresses a decrease in the temperature of the methane fermentation liquid, prevents the temperature of the methane fermentation liquid from dropping too low, and allows the methane fermentation process to be carried out appropriately. [Brief description of the drawings]

[0030] [Figure 1] 1 shows a methane fermentation tank of the first embodiment, where (A) is a longitudinal side view of the methane fermentation tank, (B) is a cross-sectional view of the lower part of the methane fermentation tank, and (C) is a cross-sectional view of the upper part of the methane fermentation tank. [Diagram 2] FIG. 1 shows a methane fermentation tank according to a second embodiment, where (A) is a longitudinal sectional side view of the methane fermentation tank, and (B) is a transverse sectional view of the methane fermentation tank. [Diagram 3] FIG. 11 is a vertical sectional side view of a methane fermentation tank according to a third embodiment. [Figure 4] 13A and 13B show a main part of a methane fermentation tank according to a fourth embodiment, in which (A) is a side view of the methane fermentation tank, and (B) is a longitudinal sectional side view of the methane fermentation tank. [Diagram 5] 13 shows an opening / closing section in a fourth embodiment, where (A) shows the opening / closing section in an open state and (B) shows the opening / closing section in a closed state. [Figure 6] FIG. 13 is a vertical sectional side view of a methane fermentation tank according to a fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A methane fermenter and a method for operating a methane fermenter according to an embodiment of the present invention will be described with reference to the drawings. [First embodiment] As shown in Fig. 1, the methane fermentation tank 1 is used to subject organic waste such as sewage sludge and food waste to methane fermentation treatment (anaerobic fermentation treatment). In the methane fermentation tank 1, the temperature of the methane fermentation liquid is maintained within a predetermined range and methane fermentation treatment is performed to produce biogas such as methane gas. The produced biogas is extracted from an extraction section (not shown) disposed, for example, on the top of the methane fermentation tank 1, and can be supplied to a biogas utilization facility that utilizes the biogas.

[0032] Regarding the specified range of optimum temperatures in methane fermentation processing, when methane fermentation processing is performed at medium temperatures, the specified range of optimum temperatures can be set, for example, to a temperature range of 30°C to 45°C, and when methane fermentation processing is performed at high temperatures, the specified range of optimum temperatures can be set, for example, to a temperature range of 50°C to 60°C.

[0033] As shown in FIG. 1(A), the methane fermentation tank 1 is equipped with a supply device (not shown) for supplying organic waste into the methane fermentation tank 1, an agitator 2 for agitating the methane fermentation liquid 4 in the methane fermentation tank 1, a heating device 3 for heating the methane fermentation liquid 4 in the methane fermentation tank 1, and a discharge device (not shown) for discharging sediments and the like accumulated in the methane fermentation tank 1.

[0034] As shown in Fig. 1(A), the agitator 2 is disposed in the center of the methane fermentation tank 1 in plan view. The agitator 2 is equipped with a blade 21 that can freely rotate about a vertical axis, and a rotation drive device 22 such as a motor M that drives and rotates the blade 21. Incidentally, the agitator 2 shown in Fig. 1(A) is merely an example, and various other types of agitator 2 can be applied.

[0035] 1(A), the heating device 3 is equipped with a circulation path 31 that takes the methane fermentation liquid in the methane fermenter 1 to the outside and circulates it, a circulation pump 32 that circulates the methane fermentation liquid in the circulation path 31, and a heat exchanger 33 that exchanges heat between the methane fermentation liquid in the circulation path 31 and a heating medium. By operating the circulation pump 32, the heating device 3 circulates the methane fermentation liquid through the circulation path 31 in a form in which the methane fermentation liquid is heated in the heat exchanger 33, thereby heating the methane fermentation liquid.

[0036] In the methane fermentation tank 1, since it is considered that the temperature of the methane fermentation liquid will normally drop due to heat radiation, etc., the temperature of the methane fermentation liquid is maintained within a predetermined temperature range suitable for methane fermentation by heating the methane fermentation liquid with the heating device 3. The heating device 3 may be operated at all times, but may also be operated as necessary to heat the methane fermentation liquid only when the temperature of the methane fermentation liquid drops below the predetermined suitable temperature range.

[0037] In order to suppress a decrease in the temperature of the methane fermentation liquid, it is possible to provide a heat insulating material on the outer wall of the methane fermentation tank 1. However, depending on various circumstances, the temperature of the methane fermentation liquid may rise too high. Therefore, simply providing a heat insulating material to cover the entire side of the methane fermentation tank 1 may make it difficult for the temperature of the methane fermentation liquid to decrease, which may reduce the activity of the microorganisms that perform methane fermentation, making it impossible to perform the methane fermentation process appropriately.

[0038] Therefore, in this embodiment, a heat dissipation structure that can actively dissipate heat is adopted, and if the temperature of the methane fermentation liquid rises too high, the heat dissipation structure prevents the temperature of the methane fermentation liquid from rising to a temperature at which the activity of the microorganisms performing methane fermentation decreases.

[0039] The heat dissipation structure employed in this embodiment will now be described. As shown in Fig. 1(A), the methane fermentation tank 1 is provided with a hollow tank body 11 made of steel plate having a bottom 12, a side portion 13, and an upper portion 14, and a methane fermentation liquid 4 is stored inside the tank body 11. Regarding the shape of the tank body 11 in the methane fermentation tank 1, Fig. 1 shows an example in which the tank body 11 is formed into a cylindrical shape with a circular cross section, but it can also be formed into a cylindrical shape with a polygonal cross section, and various shapes can be applied.

[0040] As shown in Fig. 1, the side portion 13, the top portion 14, etc. of the tank body 11 are not exposed to the outside, and the outer surface including the side portion 13 and the top portion 14 except for the bottom portion 12 is covered with an exterior material 5. The exterior material 5 is made of, for example, a steel plate and has a light-shielding property. The material from which the exterior material 5 is made can be changed as appropriate, but it is sufficient that the material has a light-shielding property.

[0041] 1, the exterior material 5 is disposed so as to cover the side parts 13 and the upper part 14 of the tank body 11, which form the outer surface. The exterior material 5 is disposed at a predetermined distance outward from the side parts 13 and the upper part 14 of the tank body 11, and is disposed in a state in which a space 6 is formed between the side parts 13 and the upper part 14.

[0042] 1(A) and (C), the space 6 formed between the tank body 11 and the exterior material 5 includes at least a portion of a non-insulated space 61 in which no insulating material 7 is disposed. This allows heat to be dissipated from the non-insulated space 61 to the outside of the exterior material 5.

[0043] 1(A) and (B), the space 6 formed between the tank body 11 and the exterior material 5 includes not only a non-insulated space 61 but also at least an insulating space 62 in which an insulating material 7 is disposed. The insulating material 7 may be any material capable of providing thermal insulation, and various materials may be used.

[0044] As shown in Figure 1 (A), the non-insulated space 61 is arranged on the upper side of the tank body 11, and the insulating space 62 is arranged on the lower side of the tank body 11, with the non-insulated space 61 and the insulating space 62 being arranged separately in the vertical direction.

[0045] As shown in FIG. 1(A), the insulating space 62 is set at a position up to a predetermined height from the bottom 12 of the tank body 11, and the portion above the insulating space 62 is set as the non-insulating space 61. In this case, the predetermined height can be appropriately changed. If it is desired to make the non-insulating space 61 larger, the predetermined height can be reduced, and thus the ratio between the size of the non-insulating space 61 and the size of the insulating space 62 can be adjusted by adjusting the predetermined height. For example, when the height of the tank body 11 is H, the predetermined height from the bottom 12 of the tank body 11 can be set in the range of H / 2 to H / 10, preferably H / 2 to H / 5.

[0046] As shown in Figures 1(A) and (C), the exterior material 5 is provided with openings 8 that communicate between the non-insulated space 61 and the outside in order to promote heat dissipation. A plurality of openings 8 are provided, and a blower 9 such as a fan is disposed in some of the plurality of openings 8. In Figure 1, a total of two openings 8 are provided, one each on the left and right sides of the exterior material 5, and a blower 9 is disposed in the opening 8 on the right side.

[0047] The locations of the openings 8 can be changed as appropriate, for example, by arranging a plurality of openings 8 at the same position in the circumferential direction of the exterior material 5 (tank body 11) so as to be lined up at intervals in the vertical direction, or by arranging a plurality of openings 8 at intervals in the circumferential direction of the exterior material 5. In FIG. 1, the openings 8 are arranged on the side 13 of the tank body 11, but the openings 8 can also be arranged on the upper part 14 of the tank body 11, or the openings 8 can be arranged only on the upper part 14 of the tank body 11. The number of openings 8 provided can also be changed as appropriate.

[0048] As shown in FIG. 1(C), a plurality of openings 8 are provided in a state in which they communicate with each other via the non-insulated space 61, and a blower 9 is disposed at the openings 8, so that outside air flowing in from the opening 8 on the left side flows through the non-insulated space 61 and flows out from the opening 8 on the right side to the outside of the exterior material 5. This forms an air flow, and allows efficient heat dissipation from the non-insulated space 61. Therefore, for example, in a situation where active heat dissipation is desired, such as when the temperature of the methane fermentation liquid becomes too high, the blower 9 can be operated to actively dissipate heat, and in a situation where active heat dissipation is not desired, the blower 9 can be stopped.

[0049] When multiple openings 8 are provided at intervals in the circumferential direction of the exterior material 5, for example, if there are windward and leeward locations in the circumferential direction of the exterior material 5 depending on the annual wind direction, the surrounding environment, etc., openings 8 can be provided at each of the windward and leeward locations. When arranged in this manner, outside air flows in from the openings 8 at the windward locations, flows through the non-insulated space 61, and flows out to the outside of the exterior material 5 from the openings 8 at the leeward locations. Thus, an air flow can be formed, and for example, the blower 9 provided at the openings 8 can be omitted.

[0050] Second Embodiment The second embodiment is an embodiment different from the first embodiment in terms of the locations of the non-insulated space 61 and the insulating space 62. Other configurations are the same as those of the first embodiment, so the same reference numerals are used and the description thereof is omitted. The description will be centered on the locations of the non-insulated space 61 and the insulating space 62 with reference to FIG. 2.

[0051] In the second embodiment, as shown in Fig. 2, the non-insulated space 61 is disposed in the right region in Fig. 2, and the insulating space 62 is disposed in the left region in Fig. 2, with the non-insulated space 61 and the insulating space 62 being disposed separately on the left and right sides in the circumferential direction of the tank body 11. In Fig. 2, the non-insulated space 61 and the insulating space 62 are divided into halves in the circumferential direction of the tank body 11, but the ratio between the size of the non-insulated space 61 and the size of the insulating space 62 can be changed as appropriate, for example, by making the non-insulated space 61 larger than the insulating space 62.

[0052] The location of the non-insulated space 61 in the circumferential direction of the tank body 11 can also be changed as appropriate. For example, depending on the direction and surrounding conditions, the non-insulated space 61 can be disposed in a location that is less exposed to sunlight, and the insulating space 62 can be disposed in a location that is more exposed to sunlight, and the locations of the non-insulated space 61 and the insulating space 62 can be adjusted in relation to the sunlight.

[0053] As in the first embodiment, the exterior material 5 is provided with a plurality of openings 8 that communicate between the non-insulating material space 61 and the outside, as shown in Fig. 2. A plurality of openings 8 are provided, and a blower 9 such as a fan is disposed in some of the openings 8.

[0054] In FIG. 2, two openings 8 are provided at the same position in the circumferential direction of the tank body 11, and are arranged at an interval in the vertical direction, for a total of four openings 8. A blower 9 is provided in one of the four openings 8 arranged on the upper side. The openings 8 are provided in a state in which they communicate with each other via a non-insulating material space 61. Therefore, outside air flowing in from a plurality of openings 8 where no blower 9 is provided flows through the non-insulating material space 61 and flows out from the opening 8 where the blower 9 is provided to the outside of the exterior material 5, forming an air flow and allowing efficient heat dissipation.

[0055] Third Embodiment Like the second embodiment, the third embodiment is an embodiment different from the first embodiment in terms of the locations of the non-insulated space 61 and the insulating space 62. Other configurations are the same as those of the first embodiment, so the same reference numerals are used and the description thereof is omitted. The description will be centered on the locations of the non-insulated space 61 and the insulating space 62 with reference to FIG. 3.

[0056] In the third embodiment, as shown in FIG. 3, non-insulated spaces 61 are provided in the lower and upper portions of the tank body 11 in the vertical direction, and an insulating space 62 is provided in the middle portion.

[0057] The non-insulating space 61 in the lower portion is set in an area from the bottom 12 of the tank body 11 to a predetermined height, but the predetermined height can be changed as appropriate.

[0058] In the third embodiment, the exterior material 5 can also be provided with openings 8, but the number and locations of the openings can be changed as appropriate, as in the first embodiment, so they are not shown in Figure 3 and the description thereof is also omitted.

[0059] [Fourth embodiment] In the fourth embodiment, as shown in Fig. 4 and Fig. 5 in the first embodiment, an opening / closing unit 53 is provided that can be switched between an open state in which the space 6 formed between the tank body 11 and the exterior material 5 is opened to the outside of the exterior material 5 and a closed state. Other configurations are the same as those in the first embodiment, so the same reference numerals are used and the description thereof is omitted. The opening / closing unit 53 will be mainly described with reference to Fig. 4 and Fig. 5.

[0060] As shown in Fig. 4, a plurality of steel panel bodies 15 are provided, and the tank body 11 is constructed by combining the plurality of panel bodies 15. Fig. 4(A) shows a part of the side portion 13 of the tank body 11, with the front side of the paper being the outer side of the tank body 11 and the rear side of the paper being the inner side of the tank body 11. Fig. 4(B) also shows a part of the side portion 13 of the tank body 11, with the left side being the outer side of the tank body 11 and the right side being the inner side of the tank body 11.

[0061] The panel bodies 15 are formed, for example, in a rectangular shape, and as shown in Fig. 4, the ends of the panel bodies 15 are overlapped and fastened with fasteners 71 such as bolts and nuts to connect the multiple panel bodies 15 and form the side portion 13 of the tank body 11, etc. The fastening points by the fasteners 71 can be changed as appropriate in the direction in which the panel bodies 15 are overlapped, such as to have one or multiple fastening points. Although not shown in the figures, the upper portion 14 of the tank body 11 is also formed by connecting multiple panel bodies 15.

[0062] As shown in Fig. 4, a first mounting bracket 72 and a second mounting bracket 73 are provided to attach the exterior material 5 to the panel body 15, and the exterior material 5 is disposed at a distance from the outer surface of the panel body 15 using the first mounting bracket 72 and the second mounting bracket 73. The first mounting brackets 72 are attached to the outer surface of the panel body 15, and second mounting brackets 73 are attached to a number of the first mounting brackets 72, and the exterior material 5 (see the dashed line in Fig. 4(A)) is attached to the second mounting brackets 73.

[0063] As shown in Fig. 4(A), the first mounting fittings 72 are arranged in a plurality of rows spaced apart in the vertical direction, with one row being spaced apart in the circumferential direction (left-right direction in Fig. 4(A)) of the side portion 13 of the tank body 11. The second mounting fittings 73 are formed in an elongated shape extending in the circumferential direction (horizontal direction) of the side portion 13 of the tank body 11, and are arranged across the plurality of first mounting fittings 72 arranged in a row in the vertical direction. The exterior material 5 (see dashed line in Fig. 4(A)) is arranged across the plurality of second mounting fittings 73 spaced apart in the vertical direction.

[0064] As shown in Fig. 4(B), the first mounting bracket 72 and the second mounting bracket 73 are used to arrange the exterior material 5 at a distance from the outer surface of the panel body 15, thereby forming a space 6 between the panel body 15 and the exterior material 5. By not arranging a thermal insulating material in this space 6, the space 6 is made into a non-insulating material space 61.

[0065] As shown in Fig. 4(B), a part of the exterior material 5 (panel body 15) is provided with a porous body 52 having a large number of holes 51, and a plate-shaped opening / closing part 53 is provided on the outer side of the porous body 52. ​​As shown in Figs. 4(B) and 5(A), the opening / closing part 53 can be switched to an open state in which the non-insulating material space 61 communicates with the outer side of the exterior material 5 by opening the holes 51 of the porous body 52. ​​When the opening / closing part 53 is switched to the open state, air in the non-insulating material space 61 can be discharged to the outer side of the exterior material 5 through the multiple holes 51, thereby effectively dissipating heat.

[0066] 4(B) and 5(B), the opening / closing part 53 closes the holes 51 of the porous body 52, and is thereby switched to a closed state in which the non-insulating material space 61 and the outer side of the exterior material 5 are closed. When the opening / closing part 53 is switched to the closed state, the multiple holes 51 are closed, so that the air in the non-insulating material space 61 is prevented from being discharged to the outer side of the exterior material 5 through the multiple holes 51, thereby suppressing heat dissipation.

[0067] The opening / closing section 53 is provided so as to be freely slidable in the horizontal direction. As shown in Fig. 5, the opening / closing section 53 is configured to be slidable to switch between an open state in which the hole 51 is opened (see Fig. 5(A)) and a closed state in which the hole 51 is closed (see Fig. 5(B)). In this way, a porous body 52 is provided in a part of the exterior material 5, and the hole 51 of the porous body 52 is opened and closed by the opening / closing section 53, so that the non-insulating material space 61 communicates with the outside of the exterior material 5 without forming an opening with a large opening area, thereby suppressing the intrusion of foreign matter into the non-insulating material space 61 and excessive heat dissipation, and suitable heat dissipation can be achieved.

[0068] The tank body 11 is constructed by connecting the panel bodies 15 with fasteners 71, etc., and the locations where the fasteners 71, etc. are installed are locations where packing and caulking agents are used. If the locations where packing and caulking agents are used are exposed to direct sunlight, degradation due to ultraviolet rays may occur.

[0069] 4(B) and 5, the exterior material 5 is provided with a porous body 52 having a plurality of holes 51, but the porous body 52 is disposed at a position away from the location of the fasteners 71, etc. (where packing or caulking agent is used) in the panel body 15, as shown in FIG. 5(A). In the inside-outside direction of the tank body 11, the panel body 15 is disposed on the inside side, and the exterior material 5 is disposed on the outside side. In FIG. 5, the locations of the fasteners 71, etc. that fasten the panel bodies 15 located on the inside side are shown by dotted lines, so that the positional relationship between the location of the porous body 52 in the exterior material 5 and the locations of the fasteners 71, etc. in the panel body 15 can be easily understood. FIG. 5 also illustrates a case where the panel bodies 15 are connected with the fastening points of the fasteners 71 lined up two by two.

[0070] 5(A), when the opening / closing part 53 is switched to the open state, even if sunlight passes through the multiple holes 51 in the porous body 52, it does not directly strike the locations where the fasteners 71 and the like are disposed, and deterioration due to ultraviolet rays can be prevented. Therefore, by switching the opening / closing part 53 to the open state, heat can be dissipated to the outside of the exterior material 5 through the multiple holes 51, while preventing the problem of deterioration due to sunlight from occurring in the first place.

[0071] 4 and 5 show an example in which a sliding structure is adopted as the structure of the opening / closing part 53, in which the plate-shaped opening / closing part 53 is slid horizontally to open and close the hole 51 of the porous body 52. ​​The structure of the opening / closing part 53 is not limited to the sliding structure, and for example, a blind structure in which a plurality of wing parts are arranged adjacent to each other and are opened and closed by rotating the plurality of wing parts in response to the operation of the operating part, etc., can also be adopted, and various other structures can also be adopted.

[0072] Since the opening / closing unit 53 can be freely switched between an open state and a closed state, this embodiment employs an operating method of the methane fermenter 1 in which the opening / closing unit 53 is switched between an open state and a closed state.

[0073] In this method of operating the methane fermentation tank 1, an opening / closing switching process is performed in which, when the temperature of the methane fermentation liquid 4 in the tank body 11 or the temperature of the non-insulated space 61 (space 6) becomes equal to or higher than a first set temperature, the opening / closing section 53 is switched to an open state, and, when the temperature of the methane fermentation liquid 4 in the tank body 11 or the temperature of the non-insulated space 61 (space 6) becomes equal to or lower than a second set temperature, the opening / closing section 53 is switched to a closed state.

[0074] The first and second set temperatures may be set only to the temperature of the methane fermentation liquid 4 in the tank body 11, only to the temperature of the non-insulated space 61 (space 6), or to both the temperature of the methane fermentation liquid 4 in the tank body 11 and the temperature of the non-insulated space 61 (space 6). When both are set, the first set temperature of the temperature of the methane fermentation liquid 4 in the tank body 11 and the first set temperature of the temperature of the non-insulated space 61 (space 6) may be the same or different. The same applies to the second set temperature. When both are set, it is preferable to open and close the opening / closing part 53 by giving priority to the temperature of the methane fermentation liquid 4 for both the first and second set temperatures.

[0075] Although not shown in the figures, the temperature of the methane fermentation liquid 4 can be obtained, for example, by providing a temperature sensor or the like inside the tank body 11. Although not shown in the figures, the temperature of the non-insulated space 61 (space 6) can also be obtained, by providing a temperature sensor or the like inside the non-insulated space 61 (space 6).

[0076] The opening / closing unit 53 can be switched between the open state and the closed state, for example, by manually sliding the opening / closing unit 53 by an operator or the like. Also, the opening / closing unit 53 can be automatically switched between the open state and the closed state by including a drive unit that slides the opening / closing unit 53 using a driving force such as a motor, and a control unit or the like controlling the operation of the drive unit based on temperature conditions such as the first set temperature and the second set temperature.

[0077] Fifth embodiment The fifth embodiment is an embodiment different from the first embodiment in terms of the location of the non-insulating space 61. Other configurations are the same as those of the first embodiment, so the same reference numerals are used and the description thereof is omitted. The description will be centered on the location of the non-insulating space 61 with reference to FIG. 6.

[0078] In the first embodiment, as shown in Fig. 1, the space 6 formed between the tank body 11 and the exterior material 5 includes a non-insulated space 61 and an insulating space 62. In contrast, in the fifth embodiment, as shown in Fig. 6, the space 6 formed between the tank body 11 and the exterior material 5 includes only a non-insulated space 61, and no insulating space 62 exists.

[0079] In the fifth embodiment, as shown in FIG. 6, no insulation material 7 is provided in the entire space 6 formed between the tank body 11 and the exterior material 5, and the entire space 6 is a non-insulated space 61.

[0080] In the fifth embodiment, the exterior material 5 can also be provided with openings 8, but the number and locations of the openings can be changed as appropriate, as in the first embodiment, so they are not shown in Figure 6 and the description thereof is also omitted.

[0081] [Another embodiment] Other embodiments of the present invention will be described below. Note that the configurations of the embodiments described below are not limited to being applied alone, but may also be applied in combination with the configurations of other embodiments.

[0082] (1) In the above first and second embodiments, an opening 8 is provided that connects the non-insulated space 61 to the outer side of the exterior material 5, and the opening 8 is always connected to the outer side of the exterior material 5. However, for example, as in the fourth embodiment, it is also possible to provide an opening / closing part that can be freely switched between an open state that opens the opening 8 and a closed state that closes the opening 8.

[0083] In this case, by switching the opening / closing part to the open state, the opening 8 is opened, the non-insulating material space 61 is communicated with the outer side of the exterior material 5, and heat can be dissipated through the opening 8. Conversely, by switching the opening / closing part to the closed state, the opening 8 is closed, the gap between the non-insulating material space 61 and the outer side of the exterior material 5 is blocked, and heat dissipation through the opening 8 is prevented.

[0084] In this way, when an opening / closing section is provided, as described in the fourth embodiment, an operating method of the methane fermentation tank 1 can be adopted in which an opening / closing switching process is performed in which the opening / closing section is switched to an open state when the temperature of the methane fermentation liquid 4 in the tank body 11 or the temperature of the non-insulated space 61 (space 6) becomes equal to or higher than a first set temperature, and the opening / closing section is switched to a closed state when the temperature of the methane fermentation liquid 4 in the tank body 11 or the temperature of the non-insulated space 61 (space 6) becomes equal to or lower than a second set temperature.

[0085] (2) In the above first and second embodiments, the opening 8 that communicates the non-insulating material space 61 with the outer side of the exterior material 5 is provided, but the embodiment may be implemented without providing the opening 8. In addition, the number of openings 8 is not limited to a plurality of openings, and only one opening may be provided.

[0086] (3) In the first and second embodiments described above, a blower device 9 is provided at some of the multiple openings 8. However, as described in the first embodiment, the blower device 9 can be omitted, not only in cases where an opening 8 is provided at each of the upwind and downwind locations.

[0087] (4) In the above embodiment, the exterior material 5 is arranged to cover not only the side 13 of the tank body 11 but also the upper part 14 of the tank body 11. However, for example, the exterior material 5 can be arranged to cover only the side 13 of the tank body 11, and the location of the exterior material 5 on the outer surface of the tank body 11 can be changed as appropriate. [Explanation of symbols]

[0088] 1. Methane fermentation tank 4. Methane fermentation liquid 5 Exterior materials 6 Space 7. Insulation 8 Openings 9. Blower 11 Tank body 53 Opening and closing section 61 Non-insulated space 62 Insulation Space

Claims

1. In a methane fermentation tank that produces biogas by methane fermentation of organic waste, A tank body for storing a methane fermentation liquid; An exterior material that covers the outer surface of the tank body other than the bottom portion is provided, The exterior material has a light-shielding property and is disposed in a state in which a space is formed between the exterior material and the tank body, The space in the methane fermentation tank includes at least a portion of an uninsulated space in which no insulating material is provided.

2. 2. The methane fermentation tank according to claim 1, wherein the space at least partially includes an insulation space in which a heat insulating material is disposed.

3. The non-insulating space is disposed above the tank body, 3. The methane fermentation tank according to claim 2, wherein the heat insulating material space is disposed below the tank body.

4. 2. The methane fermentation tank according to claim 1, wherein the exterior material is provided with an opening that connects the non-insulated space to the outside.

5. The methane fermentation tank according to claim 4 , wherein a plurality of the openings are provided.

6. 6. The methane fermentation tank according to claim 4, wherein a blower is provided at the opening.

7. A method for operating a methane fermentation tank for producing biogas by methane fermentation of organic waste, comprising the steps of: A tank body for storing a methane fermentation liquid; An exterior material that covers the outer surface of the tank body other than the bottom portion is provided, The exterior material has a light-shielding property and is disposed in a state in which a space is formed between the exterior material and the tank body, The exterior material is provided with an opening / closing part that can be switched between an open state in which the space communicates with the outside and a closed state in which the space is blocked from the outside, A method for operating a methane fermentation tank, comprising: an opening / closing switching step for switching the opening / closing section to an open state when the temperature of the methane fermentation liquid in the tank body or the temperature of the space in the tank body becomes equal to or higher than a first set temperature; and switching the opening / closing section to a closed state when the temperature of the methane fermentation liquid in the tank body or the temperature of the space in the tank body becomes equal to or lower than a second set temperature.

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