Methane fermentation tank and method for operating the same

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, 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 generated in wastewater treatment, such as sludge and biomass, and to convert it into energy. Methane fermentation is a technology in which organic waste is stored under anaerobic conditions for a certain period of time, whereby the organic waste is decomposed by anaerobic microorganisms to produce biogas such as methane gas and carbon dioxide. This technology is widely used in waste 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 that stores organic waste and performs methane fermentation, an agitator that agitates the methane fermentation liquid in the methane fermentation tank, and a heating device that heats the methane fermentation liquid.

[0004] To ensure smooth methane fermentation, it is necessary to maintain the temperature in the methane fermenter 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 methane fermentation tank with the heating device results in heat being dissipated from the surface of the methane fermentation tank, so it is common to install 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-walled cylindrical body having an inner wall and an outer wall, and the space between the inner wall and the outer wall is divided by partition plates to form multiple compartment spaces. The multiple compartment spaces can be freely switched between a state where they are filled with insulation material and a state where they are emptied of insulation material.

[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 a heat-insulating 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] Japanese Patent Application Laid-Open No. 2002-192192 [Non-patent literature]

[0009] [Non-Patent Document 1] Steel Plate Digestion Tank Technical Manual - March 2013 - Published on March 31, 2013 Published 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 surface of the methane fermentation tank is covered with a heat insulating material, which makes it possible to suppress a decrease in the temperature of the methane fermentation liquid in the methane fermentation tank. 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, which reduces the activity of the microorganisms that perform methane fermentation, and there is a possibility that the methane fermentation process cannot be carried out properly.

[0011] In this regard, in Patent Document 1, some of the compartments among the multiple compartments are switched to an emptying state without supplying insulation, so that there can be portions of the side of the methane fermentation tank that are not covered with insulation. However, in Patent Document 1, heat from sunlight or the outside air is transmitted through the exterior wall, and solar energy or the heat from the outside air is taken into the compartments where the insulation is switched to an emptying state, thereby achieving a heating effect that heats the methane fermentation liquid. Therefore, no consideration is given to dissipating heat from the compartments where the insulation is switched to an emptying state. If the temperature of the methane fermentation liquid in the methane fermentation tank rises too high, as in Patent Document 2 and Non-Patent Document 1, the temperature of the methane fermentation liquid will not decrease easily, which may reduce the activity of the microorganisms that perform methane fermentation and 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 insulation is being filled, sunlight directly hits the insulation, which could lead to deterioration of the insulation. Also, sunlight that has passed through the exterior wall could 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 a method for operating a methane fermentation tank that can dissipate heat when the temperature of the methane fermentation liquid becomes too high and can perform methane fermentation treatment appropriately without causing the problem of deterioration due to sunlight. [Means for solving the problem]

[0014] A 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 covering the outer surface of the tank body other than the bottom, The exterior material has a light-blocking property and is disposed so as to form a space between the exterior material and the tank body, The space includes at least a portion of a non-insulating space where 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 light-blocking properties, which prevents sunlight from passing through the exterior material and prevents deterioration caused by sunlight. Moreover, the space formed between the tank body and the exterior material includes at least a non-insulated space, so that if the temperature of the methane fermentation liquid rises too high, heat can be released from the non-insulated space. Therefore, the temperature of the methane fermentation liquid can be prevented 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 feature of the present invention is that the space at least partially includes a heat insulating space in which a heat insulating material is disposed.

[0017] For example, if the entire space formed between the tank body and the exterior material were made into 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 this configuration, the space formed between the tank body and the exterior material includes at least a part of an insulated space. As a result, the presence of not only a non-insulated space but also an insulated 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-insulated space is arranged above the tank body, The heat insulating space is disposed below the tank body.

[0020] According to this configuration, since the non-insulated space is disposed above the tank body, if the temperature of the methane fermentation liquid rises too high, the heat rises above the tank body where the non-insulated space is located, and thus 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 perform high-altitude work 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 feature of the present invention is that the exterior material is provided with an opening that connects the non-insulated space to 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, allowing for efficient heat dissipation. Moreover, outside air can be introduced into the non-insulated space from outside the exterior material through the opening, which also promotes heat dissipation.

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

[0025] With this configuration, heat can be dissipated through each of the multiple openings, resulting in more efficient heat dissipation. For example, an air flow can be formed in which outside air flows in through one opening, flows through the non-insulated space, and flows out to the outside of the exterior material through another opening, thereby efficiently dissipating heat from the non-insulated space.

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

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

[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 covering the outer surface of the tank body other than the bottom, The exterior material has a light-blocking property and is disposed so as to form a space 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 an outside side and a closed state in which the space is closed off from the outside side, 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 open / close switching step is performed to switch the opening / closing part 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, an open / close switching step is performed to switch the opening / closing part 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 light-blocking properties, which prevents sunlight from passing through the exterior material, thereby preventing the occurrence of problems with deterioration due to sunlight. Moreover, in the open / close switching process, the open / close unit is switched between an open state and a closed state depending on 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 reaches or exceeds a first set temperature, the open / close unit is switched to an open state, allowing heat to be dissipated from the space through the open / close unit to the outside of the exterior material. Therefore, when the temperature of the methane fermentation liquid rises too high, heat dissipation can prevent the temperature of the methane fermentation liquid from rising to a temperature at which the activity of the microorganisms performing methane fermentation decreases, allowing the methane fermentation process to be carried out appropriately. Conversely, when the temperature of the methane fermentation liquid or the temperature of the space drops below the second set temperature, the opening / closing unit is switched to the closed state, thereby preventing heat from being dissipated from the space to the outside of the exterior packaging material through the opening / closing unit. This suppresses a decrease in the temperature of the methane fermentation liquid, preventing the temperature of the methane fermentation liquid from dropping too low, and allowing the methane fermentation process to be carried out appropriately. [Brief explanation 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. [Figure 2] 1 shows a methane fermentation tank according to a second embodiment, where (A) is a longitudinal side view of the methane fermentation tank, and (B) is a transverse cross-sectional view of the methane fermentation tank. [Figure 3] FIG. 10 is a longitudinal sectional side view of a methane fermentation tank according to a third embodiment. [Figure 4] 10A and 10B show the main parts 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. [Figure 5] 10A and 10B show an opening / closing section in a fourth embodiment, in which FIG. 10A shows the opening / closing section in an open state, and FIG. 10B shows the opening / closing section in a closed state. [Figure 6] FIG. 10 is a longitudinal sectional side view of a methane fermentation tank according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[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 (anaerobic fermentation). In the methane fermentation tank 1, the temperature of the methane fermentation liquid is maintained within a predetermined range and methane fermentation is carried out to produce biogas such as methane gas. The produced biogas is extracted from an extraction section (not shown) disposed, for example, at the top of the methane fermentation tank 1, and can be supplied to a biogas utilization facility that utilizes the biogas.

[0032] Regarding the predetermined range of optimum temperatures in methane fermentation treatment, when methane fermentation treatment is performed at a medium temperature, the predetermined range of optimum temperatures can be set to, for example, a temperature range of 30°C to 45°C, and when methane fermentation treatment is performed at a high temperature, the predetermined range of optimum temperatures can be set to, for example, 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) that supplies organic waste into the methane fermentation tank 1, an agitator 2 that agitates the methane fermentation liquid 4 in the methane fermentation tank 1, a heating device 3 that heats the methane fermentation liquid 4 in the methane fermentation tank 1, and a discharge device (not shown) that discharges sediments and the like that accumulate 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 provided with blades 21 that are rotatable about vertical axes, and a rotary drive device 22 such as a motor M that drives the blades 21 to rotate. The agitator 2 shown in Fig. 1(A) is merely an example, and various other agitators 2 can be applied.

[0035] 1(A), the heating device 3 is equipped with a circulation path 31 that extracts the methane fermentation liquid in the methane fermentation tank 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 that heats the methane fermentation liquid in the heat exchanger 33, thereby heating the methane fermentation liquid.

[0036] In the methane fermentation tank 1, it is generally expected that the temperature of the methane fermentation liquid will drop due to heat radiation, etc., so the temperature of the methane fermentation liquid is maintained within a predetermined temperature range appropriate for methane fermentation by heating the methane fermentation liquid with the heating device 3. The heating device 3 may be operated all the time, but may also be operated as needed to heat the methane fermentation liquid only when the temperature of the methane fermentation liquid drops below the predetermined temperature range appropriate for methane fermentation.

[0037] In order to prevent the temperature of the methane fermentation liquid from decreasing, it is conceivable 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 much. Therefore, simply providing a heat insulating material to cover the entire side surface 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 carry out the methane fermentation process properly.

[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 much, the heat dissipation by the heat dissipation structure prevents the temperature of the methane fermentation liquid from rising to a temperature that would reduce the activity of the microorganisms that perform methane fermentation.

[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 13, and an upper part 14, and a methane fermentation liquid 4 is stored inside the tank body 11. Regarding the shape of the tank body 11 of 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 may also be formed into a cylindrical shape with a polygonal cross section, and various other shapes are applicable.

[0040] As shown in Fig. 1, the tank body 11 does not have sides 13, an upper part 14, etc. exposed to the outside, and the outer surface including the sides 13 and the upper part 14 except for the bottom part 12 is covered with an exterior material 5. The exterior material 5 is made of, for example, a steel plate and has light-blocking properties. The material from which the exterior material 5 is made can be changed as appropriate, but it should be any material that has light-blocking properties.

[0041] As shown in Fig. 1, the exterior material 5 is disposed so as to cover the side portions 13 and upper portion 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 portions 13 and upper portion 14 of the tank body 11, and is disposed so as to form a space 6 between the side portions 13 and upper portion 14.

[0042] As shown in Figures 1(A) and 1(C), the space 6 formed between the tank body 11 and the exterior material 5 includes at least 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] As shown in Figures 1(A) and 1(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. Any insulating material can be used for the insulating material 7 as long as it can provide thermal insulation.

[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 located at a predetermined height from the bottom 12 of the tank body 11, and the portion above the insulating space 62 is defined as the non-insulating space 61. The predetermined height can be changed as needed. If the non-insulating space 61 is desired to be larger, the predetermined height can be reduced. Therefore, by adjusting the predetermined height, the ratio between the size of the non-insulating space 61 and the size of the insulating space 62 can be adjusted. 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 1(C), the exterior packaging material 5 is provided with openings 8 that connect the non-insulated space 61 with 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 openings 8. In Figure 1, a total of two openings 8 are provided, one on each of the left and right sides of the exterior packaging 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 multiple openings 8 at the same position in the circumferential direction of the exterior material 5 (tank body 11) and spaced apart from each other in the vertical direction, or by arranging multiple 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 openings 8 can also be arranged on the top 14 of the tank body 11, or openings 8 can be arranged only on the top 14 of the tank body 11. The number of openings 8 can also be changed as appropriate.

[0048] As shown in FIG. 1(C), the 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 in 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 creates an air flow that allows efficient heat dissipation from the non-insulated space 61. Therefore, for example, in situations 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 situations 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 cladding 5, for example, if there are upwind and downwind locations in the circumferential direction of the exterior cladding 5 depending on the annual wind direction, the surrounding environment, etc., openings 8 can be provided at each of the upwind and downwind locations. When arranged in this manner, outside air flows in through the openings 8 at the windward locations, flows through the non-insulated space 61, and flows out to the outside of the exterior cladding 5 through the openings 8 at the downwind locations. This allows an air flow to be created, and for example, the air blower 9 provided at the openings 8 can be omitted.

[0050] Second Embodiment This 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. Since other configurations are the same as those of the first embodiment, the same reference numerals are used and the description thereof will be 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 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 position of the non-insulated space 61 can also be changed as appropriate in the circumferential direction of the tank body 11. 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 sunlight.

[0053] As in the first embodiment, the exterior packaging material 5 is provided with a plurality of openings 8 that connect the non-insulated space 61 with 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 circumferential position of the tank body 11, lined up and down with a gap between them, for a total of four openings 8. A blower 9 is provided in one of the four openings 8, which is located at the top. The openings 8 are provided in a state where they communicate with each other via a non-insulated space 61. Therefore, outside air that flows in through multiple openings 8 where no blower 9 is provided flows through the non-insulated 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 that enables 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. Since the other configurations are the same as those of the first embodiment, the same reference numerals are used and the description thereof will be 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 arranged in the lower and upper portions of the tank body 11 in the vertical direction, and an insulating space 62 is arranged in the middle portion.

[0057] The non-insulated 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 height at which this predetermined height is set can be changed as appropriate.

[0058] In the third embodiment, openings 8 can also be provided in the exterior material 5, 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 their description is also omitted.

[0059] [Fourth embodiment] In this fourth embodiment, as shown in Figures 4 and 5, the first embodiment is provided with an opening / closing unit 53 that can be switched between an open state in which the space 6 formed between the tank body 11 and the outer packaging material 5 is opened to the outside of the outer packaging material 5 and a closed state. Since other configurations are the same as those in the first embodiment, the same reference numerals are used and the description thereof will be omitted. The following description will focus on the opening / closing unit 53, with reference to Figures 4 and 5.

[0060] As shown in Figure 4, a plurality of steel panel bodies 15 are provided, and the tank body 11 is constructed by combining these plurality of panel bodies 15. Figure 4(A) shows a portion of the side 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. Figure 4(B) also shows a portion of the side 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 portions 13 of the tank body 11. The fastening points using 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 fasteners. 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 Figure 4, first mounting brackets 72 and second mounting brackets 73 are provided to attach the exterior material 5 to the panel body 15, and the first mounting brackets 72 and second mounting brackets 73 are used to arrange the exterior material 5 at a distance from the outer surface of the panel body 15. The first mounting brackets 72 are attached to the outer surface of the panel body 15, and second mounting brackets 73 are attached to multiple first mounting brackets 72, and the exterior material 5 (see dashed line in Figure 4(A)) is attached to the second mounting brackets 73.

[0063] As shown in Figure 4(A), the first mounting brackets 72 are arranged in multiple rows spaced apart in the vertical direction, with one row being spaced apart in the circumferential direction of the side portion 13 of the tank body 11 (left and right in Figure 4(A)). The second mounting brackets 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 so as to span the multiple first mounting brackets 72 lined up in a row in the vertical direction. The exterior material 5 (see the dashed dotted line in Figure 4(A)) is arranged so as to span the multiple second mounting brackets 73 spaced apart in the vertical direction.

[0064] As shown in Figure 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 heat 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 porous body 52 having a large number of holes 51 is provided in a portion of the exterior packaging material 5 (panel body 15), 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 packaging material 5 by opening the holes 51 in the porous body 52. ​​When the opening / closing part 53 is switched to the open state, air in the non-insulating material space 61 is discharged to the outer side of the exterior packaging material 5 through the multiple holes 51, thereby enabling effective heat dissipation.

[0066] 4(B) and 5(B), the opening / closing unit 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 is closed from the outer side of the exterior packaging material 5. When the opening / closing unit 53 is switched to the closed state, the multiple holes 51 are closed, and therefore the air in the non-insulating material space 61 is prevented from being discharged to the outer side of the exterior packaging material 5 through the multiple holes 51, thereby suppressing heat radiation.

[0067] The opening / closing unit 53 is provided so as to be slidable in the horizontal direction. As shown in Fig. 5, by sliding the opening / closing unit 53, it is possible 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 packaging material 5, and by opening and closing the hole 51 of the porous body 52 with the opening / closing unit 53, the non-insulating material space 61 is communicated with the outside of the exterior packaging material 5 without forming an opening with a large opening area, thereby enabling suitable heat dissipation while suppressing the intrusion of foreign matter into the non-insulating material space 61 and excessive heat dissipation.

[0068] The tank body 11 is constructed by connecting the panel bodies 15 with fasteners 71, etc., so 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, there is a possibility that they will deteriorate due to ultraviolet rays.

[0069] 4(B) and 5, the exterior material 5 is provided with a porous body 52 having a plurality of holes 51. However, as shown in FIG. 5(A), the porous body 52 is disposed at a position away from the positions of fasteners 71 and the like (positions where packing or caulking agent is used) on the panel body 15. In the inward / outward direction of the tank body 11, the panel body 15 is disposed on the inner side, and the exterior material 5 is disposed on the outer side. Therefore, in FIG. 5, the positions of fasteners 71 and the like that fasten the panel bodies 15 located on the inner side are shown with dotted lines to make it easier to understand the positional relationship between the positions of the porous body 52 on the exterior material 5 and the positions of the fasteners 71 and the like on the panel body 15. Furthermore, FIG. 5 illustrates a case where the panel bodies 15 are connected with the fastening positions of the fasteners 71 lined up two by two.

[0070] 5(A), when the opening / closing unit 53 is switched to the open state, even if sunlight passes through the plurality of holes 51 in the porous body 52, it does not directly hit 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 unit 53 to the open state, heat can be dissipated to the outside of the exterior packaging material 5 through the plurality of 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 unit 53, in which the plate-shaped opening / closing unit 53 is slid horizontally to open and close the holes 51 of the porous body 52. ​​The structure of the opening / closing unit 53 is not limited to the sliding structure, and for example, a blind structure in which multiple blades are arranged adjacent to each other and are rotated in response to the operation of an operating unit, etc., to open and close the opening / closing unit 53, or any other structure can be adopted.

[0072] Since the opening / closing unit 53 can be freely switched between an open state and a closed state, this embodiment employs a method of operating the methane fermentation tank 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 for the temperature of the methane fermentation liquid 4 in the tank body 11, only for the temperature of the non-insulated space 61 (space 6), or for 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 for the temperature of the methane fermentation liquid 4 in the tank body 11 and the first set temperature for 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 disposing 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 disposing 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. Alternatively, 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. Since other configurations are the same as those of the first embodiment, the same reference numerals are used and the description thereof will be 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 insulating 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-insulating material space 61.

[0080] In the fifth embodiment, openings 8 can also be provided in the exterior material 5, 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 their description 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 independently, but can 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, as in the fourth embodiment, for example, an opening / closing part can be provided that can be 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 unit to the open state, the opening 8 is opened, the non-insulating material space 61 is connected to the outside of the exterior packaging material 5, and heat can be dissipated through the opening 8. Conversely, by switching the opening / closing unit to the closed state, the opening 8 is closed, the gap between the non-insulating material space 61 and the outside of the exterior packaging 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 first and second embodiments, the opening 8 is provided to connect the non-insulating material space 61 to the outside of the exterior packaging material 5, 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 it may be just one opening.

[0086] (3) In the first and second embodiments, a blower 9 is provided at some of the openings 8. However, as described in the first embodiment, the blower 9 can be omitted, not only when openings 8 are provided at both 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 top 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 on the outer surface of the tank body 11 where the exterior material 5 is arranged 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 covering the outer surface of the tank body other than the bottom, The exterior material has a light-blocking property and is disposed so as to form a space between the exterior material and the tank body, The space includes at least a portion of a non-insulated space in which no insulating material is disposed, The space includes at least a portion of an insulation space in which an insulation material is disposed, A methane fermentation tank in which the non-insulated space is an air layer.

2. 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 covering the outer surface of the tank body other than the bottom, The exterior material has a light-blocking property and is disposed so as to form a space between the exterior material and the tank body, The space includes at least a portion of a non-insulated space in which no insulating material is disposed, The methane fermentation tank has an opening in the exterior material that connects the non-insulated space to the outside.

3. 3. The methane fermentation tank according to claim 2, wherein the space includes at least a portion of an insulating space in which a thermal insulating material is disposed.

4. The non-insulated space is disposed above the tank body, 4. The methane fermentation tank according to claim 1, wherein the heat insulating material space is disposed below the tank body.

5. 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.

6. The methane fermentation tank according to claim 2 or 5, wherein a plurality of the openings are provided.

7. 6. The methane fermentation tank according to claim 2 or 5, wherein a blower is provided at the opening.

8. 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 covering the outer surface of the tank body other than the bottom, The exterior material has a light-blocking property and is disposed so as to form a space between the exterior material and the tank body, In the method for operating a methane fermentation tank, at least a portion of the space includes an uninsulated space in which no insulating material is provided, The exterior material is provided with an opening / closing part that can be switched between an open state in which the space communicates with an outside side and a closed state in which the space is closed off from the outside side, A method for operating a methane fermentation tank, comprising: an opening / closing switching step of switching the opening / closing unit to an open state 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; and switching the opening / closing unit to a closed state 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.

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