Digestion tank and method for keeping digestion tank warm

Abstract

To provide a digester excellent in a heat retaining property, and a method for keeping the warmth of the digester.SOLUTION: There is provided a digester including: a foundation formed of concrete; and a digester main body installed on the foundation. The foundation has: an installation surface on which the digester main body is installed; and an outer surface that is a surface other than the installation surface. At least a part of the outer surface is covered with a heat retaining member.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a digester and a method for keeping a digester warm. [Background technology]

[0002] Conventionally, digesters are used to treat organic waste such as sewage sludge. Typically, digesters are provided with a foundation made of concrete and a digester body that is installed on the foundation and treats organic waste with anaerobic bacteria. The temperature inside the digester body (internal temperature) is, for example, 35 to 60°C, more specifically, 35 to 40°C for mesophilic digestion and 50 to 60°C for thermophilic digestion. As a result, the organic matter in the sludge is decomposed by the anaerobic bacteria, and biogas consisting of methane and carbon dioxide is generated. Since the biogas contains methane, it can be used as fuel.

[0003] Also, in order to maintain the internal temperature of the digester body in a stable state, attempts have been made to improve the heat retention of the digester body. For example, the digester described in Patent Document 1 has a heat retention member (polystyrene foam) provided at the bottom of the digester body. Specifically, the digester in Patent Document 1 has an internal space of the digester body divided vertically by a partition plate, and is configured so that sludge is introduced into the upper space, and a heat insulating structure is provided in the lower space. The heat insulating structure has a plurality of short pipes extending between the bottom of the digester body and the partition plate, and the heat insulating member is provided between each of the short pipes. The partition plate and the short pipes are made of steel. In such a heat insulating structure, the short pipes prevent the heat insulating member from being crushed by the load of the sludge. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5806747 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the digester tank of Patent Document 1, the short pipes in the thermal insulation structure are made of steel, so there is a risk of heat radiation from the digester tank body via the short pipes and the foundation. In other words, the digester tank of Patent Document 1 has room for improvement in terms of heat retention of the digester tank body.

[0006] In addition, although Patent Document 1 does not pay attention to the heat retention of the foundation, if the heat retention of the foundation is insufficient, the temperature of the foundation will be easily changed by the external environment, causing thermal stress in the foundation. In order to suppress the effects of thermal stress, it will be necessary to install additional reinforcement in the foundation, which will increase the work and cost of construction.

[0007] In view of the above problems, an object of the present invention is to provide a digester tank having excellent heat retention properties and a method for keeping the digester tank warm. [Means for solving the problem]

[0008] The digester according to the present invention comprises: The digester tank comprises a foundation made of concrete and a digester tank body installed on the foundation, The foundation portion has an installation surface on which the digester tank body is installed and an outer surface other than the installation surface, At least a portion of the outer surface is covered with a heat retaining material.

[0009] According to this configuration, at least a part of the outer surface of the foundation is covered with a heat-insulating material, which suppresses heat dissipation through the foundation, resulting in excellent heat retention not only in the digester tank body but also in the foundation, which in turn makes it possible to reduce the amount of reinforcement in the foundation to suppress the effects of thermal stress.

[0010] In addition, the digester according to the present invention comprises: The outer surface has a lower surface and a side surface, At least a portion of the lower surface and the side surfaces may be covered with the heat-insulating member.

[0011] According to this configuration, at least a portion of the bottom surface and side surfaces of the foundation are covered with the heat-insulating material, thereby further suppressing heat dissipation through the foundation.

[0012] The digester according to the present invention further comprises: The outer surface has an upper surface; At least a portion of the upper surface may be covered with the heat retaining member.

[0013] According to this configuration, at least a portion of the upper surface of the foundation is covered with the heat-insulating member, so that heat dissipation through the foundation is further suppressed.

[0014] The digester according to the present invention further comprises: The heat retaining member covering the upper surface may be covered with a protective layer.

[0015] According to this configuration, since the heat retaining member covering the upper surface is covered with the protective layer, deterioration of the heat retaining member is suppressed, and as a result, heat retention can be maintained for a long period of time.

[0016] In the method for insulating a digester tank according to the present invention, at least a portion of the outer surface is covered with a heat-insulating material.

[0017] With this configuration, at least a portion of the outer surface of the foundation is covered with a heat-insulating material, making it possible to construct a digester with excellent heat retention not only in the digester body but also in the foundation. Effect of the Invention

[0018] As described above, according to the present invention, a digester tank with excellent heat retention properties and a method for keeping a digester tank warm can be provided. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram of a digester according to one embodiment. [Diagram 2] FIG. 2 is a top view of the digester tank in FIG. 1. [Diagram 3]FIG. 13 is a diagram showing a modified example of a waterway. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, a digester according to one embodiment of the present invention will be described with reference to the drawings.

[0021] As shown in Figure 1, the digester tank 1 of this embodiment includes a digester tank body 10 that treats organic waste such as sewage sludge, a heating section 20 that heats the sludge in the digester tank body 10, an agitation section 30 that agitates the sludge in the digester tank body 10, and an extraction device 40 that serves as a discharge section that discharges the digested sludge from the digester tank body 10. The digester tank 1 of this embodiment also includes a base section 50 for installing the digester tank body 10, and a heat-retaining member 60 that covers the base section 50.

[0022] The digester tank 1 of this embodiment is provided in a recess G formed in the natural ground. The recess G includes a flat portion G1 formed to support the foundation portion 50 from below, and a peripheral wall portion G2 formed to surround the foundation portion 50. Note that the recess does not necessarily have to include the peripheral wall portion G2.

[0023] The digestion tank body 10 of this embodiment is made of steel plates. The digestion tank body 10 is formed in a cylindrical shape and has a bottom 11 grounded on a foundation 50, a side wall 12 rising from the bottom 11, and an upper wall 13 facing the bottom 11 and closing the upper end of the side wall 12. Inside the digestion tank body 10, a cylindrical sludge storage space V is formed, which is defined by the bottom 11, the side wall 12, and the upper wall 13. The digestion tank body may be formed in a cylindrical shape or, for example, a rectangular tube shape. The digestion tank body may be made of concrete. Asphalt sand may be laid between the outer surface of the bottom 11 and the foundation 50 to prevent corrosion of the bottom 11.

[0024] The heating section 20 of this embodiment is provided to maintain the temperature of the sludge in the digestion tank body 10 at a temperature suitable for digestion, for example, 35 to 60°C, more specifically, 35 to 40°C for mesophilic digestion and 50 to 60°C for high-temperature digestion. The heating section 20 of this embodiment has a heat exchange section 23 provided outside the digestion tank body 10, and is configured to take out a portion of the sludge from the digestion tank body 10, heat it in the heat exchange section 23, and return the heated portion of the sludge to the digestion tank body 10. More specifically, the heating section 20 has a first piping section 21 for discharging a portion of the sludge from the digestion tank body 10 and transferring it to the heat exchange section 23, and a second piping section 22 for transferring the heated portion of the sludge from the heat exchange section 23 to the digestion tank body 10. The heating section 20 also has a circulation pump 24 for moving the sludge from the first piping section 21 to the second piping section 22.

[0025] The agitator 30 of this embodiment functions to mix the anaerobic microorganisms and organic waste in the sludge uniformly and promote the conduction of heat in the sludge. The agitator 30 has a shaft 31 having a rotation shaft extending in the vertical direction, a drive unit 32 that rotates the shaft 31 around the rotation shaft, and a blade 33 that is fixed to the shaft 31 and rotates with the rotation of the shaft 31.

[0026] In the agitation unit 30 of this embodiment, the shaft 31 is disposed above the center of the bottom 11. The blade 33 is composed of a first blade 33a and a second blade 33b that are disposed at an interval in the vertical direction. That is, the blade 33 is configured by arranging the first blade 33a and the second blade 33b in two stages. The blade 33 is configured to move the sludge from above to below on the rotation surface when it rotates. That is, the agitation unit 30 can generate a flow of sludge toward the bottom 11 of the digestion tank body 10 at the radial center of the sludge storage space V. Then, the sludge that reaches the bottom 11 flows along the extension direction of the bottom 11 to reach the side wall 12, and further flows upward along the side wall 12. This causes the sludge to circulate in the sludge storage space V. The blade is not limited to being disposed in two stages, and may be, for example, only one stage or multiple stages.

[0027] The extraction device 40 of this embodiment is provided to discharge digested sludge from the bottom 11 of the digestion tank body 10 to the outside of the tank. The extraction device 40 of this embodiment is composed of an extraction pump 42 for discharging the digested sludge and a third piping section 41 connected to the extraction pump 42.

[0028] The foundation portion 50 of this embodiment is formed by pouring concrete into the recess G. The foundation portion 50 is formed of reinforced concrete, that is, the foundation portion 50 has concrete and a plurality of reinforcing bars embedded in the concrete. A plurality of piles P that support the foundation portion 50 from below are embedded below the recess G. The tip of each pile P protrudes upward from the flat portion G1 and is embedded in the foundation portion 50. As a result, the foundation portion 50 has a plurality of support surfaces 521 supported by the piles P.

[0029] The base portion 50 has an installation surface 51a on which the digester body 10 is installed, and an outer surface 52 that is outside the installation surface 51a.

[0030] The installation surface 51a is included in a foundation surface 51 formed horizontally for installing the digester body 10.

[0031] The outer surface 52 has a support surface 521 supported by the pile P, a lower surface 522 supported by the flat surface G1 of the recess G, a side surface 523 supported by the peripheral wall G2 of the recess G, and an upper surface 524 located outside the installation surface 51a on the foundation surface 51. The side surface 523 has a non-exposed surface 523a that is not exposed by being directly supported by the peripheral wall G2, and an exposed surface 523b that is exposed. At least a part of the outer surface 52 except for the support surface 521 is covered with a heat retaining member 60. Since the pile P functions to reinforce the foundation 50 by being integrated with the foundation 50, the support surface 521 that is the boundary surface between the pile P and the foundation 50 is usually not covered with the heat retaining member 60.

[0032] The digester 1 of this embodiment is equipped with heat insulation members 60, which include a bottom heat insulation member 61 covering the lower surface 522 of the foundation 50, a side heat insulation member 62 covering the side surface 523, and an upper heat insulation member 63 covering the upper surface 524.

[0033] The bottom heat-insulating member 61 is provided so as to form a heat-insulating layer between the flat portion G1 of the recess G and the lower surface 522 of the base portion 50. Moreover, the bottom heat-insulating member 61 is provided so as to entirely cover the lower surface 522. In this manner, the bottom heat-insulating member 61 preferably covers 70% or more of the lower surface 522, more preferably covers 80% or more, and further preferably covers 90% or more.

[0034] The side heat-insulating members 62 are provided so as to form a heat-insulating layer between the peripheral wall portion G2 of the recess G and the side surface 523 of the base portion 50. In this embodiment, the side heat-insulating members 62 are provided so as to cover the side surface 523, and preferably cover 70% or more of the side surface 523, more preferably cover 80% or more, and even more preferably cover 90% or more.

[0035] Upper heat-insulating member 63 is provided so as to form an insulation layer on upper surface 524. When digester 1 is viewed from above, upper heat-insulating member 63 is provided so as to surround digester body 10. Upper heat-insulating member 63 preferably covers 70% or more of upper surface 524, more preferably covers 80% or more, and even more preferably covers 90% or more.

[0036] The thickness of each thermal insulation layer is not particularly limited, but is preferably 20 mm or more. Since the thermal conductivity of soil is greater than that of air, it is preferable that the thermal insulation layers formed by the bottom thermal insulation member 61 and the side thermal insulation member 62 have a greater thickness than the thermal insulation layer formed by the upper thermal insulation member 63. In this manner, the thickness of each thermal insulation layer may be changed according to the external environment. For example, when the side thermal insulation member 62 is exposed, the thickness of the thermal insulation layer of the side thermal insulation member 62 may be smaller than the thickness of the bottom thermal insulation member 61. The thicknesses of each thermal insulation layer may all be the same.

[0037] The material constituting the heat retaining member 60 is preferably a material having a thermal conductivity lower than that of concrete. Since the thermal conductivity of concrete is usually 1.2 to 1.6 W / m·K, the material of the heat retaining member 60 preferably has a thermal conductivity lower than 1.2 W / m·K, and more preferably lower than 0.5 W / m·K. The material of the heat retaining member 60 is preferably polystyrene foam or polyurethane foam having a thermal conductivity of 0.02 to 0.03 W / m·K. Other materials for the heat retaining member 60 may include glass wool, perlite, perlite mortar, aggregate (gravel), etc.

[0038] The heat retaining member 60 may be made of a single material. The heat retaining member 60 may also be made of a combination of a plurality of materials. For example, the heat retaining member 60 is preferably made of a combination of aggregate and perlite or perlite mortar.

[0039] The digester 1 of this embodiment further includes a protective layer 70 for protecting the heat-insulating member 60. Specifically, in the digester 1, the protective layer 70 for protecting the upper heat-insulating member 63 is a concrete layer, and the concrete layer is formed so as to cover the upper heat-insulating member 63 from above. The concrete forming the concrete layer is unreinforced concrete. The thickness of the concrete layer is not particularly limited, but is preferably 80 mm or more. This prevents deterioration of the upper heat-insulating member 63 due to the influence of the external environment, and ultimately maintains the heat-insulating properties of the digester 1. The protective layer 70 also functions as a fixing member (weight) for preventing the upper heat-insulating member 63 from shifting out of position. That is, the digester 1 of this embodiment includes a protective layer 70 for fixing the upper heat-insulating member 63 to the upper surface 524. The protective layer 70 is not limited to concrete, and may be made of other materials such as mortar.

[0040] In the digester tank 1 of this embodiment, the base 50 is covered with the heat-retaining material 60, which suppresses heat radiation from the digester tank body 10 via the base 50. This reduces the energy consumption of the heating section 20. In addition, since less heat is dissipated from the base 50, it is easier to maintain a stable temperature of the sludge throughout the digester tank 1. This reduces the amount of sludge circulated for heating, and therefore the power required for the circulation pump 24.

[0041] In addition, since the foundation portion 50 is kept warm by the heat-insulating member 60, the temperature in the foundation portion 50 can be maintained at a stable state. This reduces the generation of thermal stress in the foundation portion 50 and enables a reduction in the amount of reinforcing bars (amount of reinforcing bars) in the foundation portion 50, which leads to a reduction in the work, costs, and materials required for construction.

[0042] As shown in FIG. 1, the foundation 50 of this embodiment has a foundation main body 501 forming a foundation surface 51, and a foundation peripheral wall 502 rising from the outer periphery of the foundation main body 501. The foundation peripheral wall 502 is provided to surround the digester body 10, and has a pair of wall surfaces extending in the vertical direction. More specifically, as shown in FIG. 2, the foundation peripheral wall 502 has an outer wall surface 502a (a surface forming a part of the side surface 523) facing the peripheral wall G2 of the recess G, and an inner wall surface 502b facing the side wall 12 of the digester body 10. In the digester 1 of this embodiment, the upper heat-insulating member 63 is provided so as to contact the inner wall surface 502b of the foundation peripheral wall 502. This prevents the upper heat-insulating member 63 from shifting out of position, thereby preventing heat leakage due to the shifting. The foundation does not have to have the foundation peripheral wall.

[0043] Furthermore, in the digester 1 of this embodiment, a gap 80 is provided between the side wall 12 of the digester body 10 and the upper heat-insulating member 63. The presence of such gap 80 ensures space for maintenance such as replacing the upper heat-insulating member 63 or replacing the heat-insulating member near the side wall 12 of the digester body 10, improving workability. Note that it is sufficient that the gap 80 is formed so as to surround a portion of the side wall 12 when the digester 1 is viewed from above. In other words, a portion of the upper heat-insulating member 63 may be provided so as to be in contact with the side wall 12.

[0044] Furthermore, as shown in FIG. 2, when the gap 80 is provided, a water channel 90 may be provided to drain water accumulated in the gap 80 due to rainfall or the like from the digestion tank 1. In the digestion tank 1 of this embodiment, an open portion 91 is provided in the base peripheral wall portion 502 in the circumferential direction to form the water channel 90, and the upper heat-retaining member 63 and the protective layer 70 are laid so that the open portion 91 communicates with the gap 80. That is, the upper heat-retaining member 63 and the protective layer 70 are also provided with an open portion 92 in the circumferential direction, similar to the base peripheral wall portion 502. When the water channel 90 is provided, it is preferable that the upper surface 524 of the gap 80 is formed so as to be inclined downward toward the water channel 90. In addition, as shown in FIG. 3, the water channel 90 may be formed as a through hole (a through hole penetrating the base portion 50) that opens at the upper surface 524 of the gap 80 and opens at a position lower than the upper surface 524 of the side heat-retaining member 62. Such a gap or water channel does not have to be provided.

[0045] Next, a method for keeping a digester warm according to one embodiment of the present invention will be described.

[0046] The method for insulating a digester tank in this embodiment includes a first insulation step of forming a foundation portion 50 in the recess G and covering the foundation portion 50 with an insulation material, an installation step of installing the digester tank main body 10 on the foundation portion 50, a second insulation step of covering the upper surface 524 with an insulation material, and a protective layer formation step of forming a protective layer 70 to cover the insulation material covering the upper surface 524.

[0047] In the first insulation step, reinforcing bars for forming the foundation portion 50 and a formwork for pouring concrete are placed in the recess G. Next, in the first insulation step, an insulation layer is formed by the insulation member 60 so as to cover the surface of the flat portion G1, and an insulation layer is also formed by the insulation member 60 so as to cover the inner peripheral surface of the formwork. Then, in the first insulation step, concrete is poured into the formwork to form the foundation portion 50 having a lower surface 522 and side surfaces 523 covered with the insulation member 60 (insulation layer).

[0048] In the second insulation step, an insulation layer is formed on the upper surface 524 of the foundation portion 50 using a heat-insulating material, and then in the protective layer forming step, for example, concrete is poured to cover the insulation layer, thereby forming the protective layer 70.

[0049] According to the method for insulating a digester of this embodiment, heat radiation through the foundation 50 is suppressed, making it possible to construct a digester with excellent heat retention properties.

[0050] The digester tank and the method for keeping a digester tank warm according to the present invention are not limited to the above-mentioned embodiment. Furthermore, the digester tank and the method for keeping a digester tank warm according to the present invention are not limited by the above-mentioned effects. The digester tank and the method for keeping a digester tank warm according to the present invention can be modified in various ways without departing from the gist of the present invention.

[0051] For example, the digester tank 1 in the above embodiment is provided with an upper heat-insulating member 63, but the desired effect can be achieved even if the digester tank 1 does not have an upper heat-insulating member. On the other hand, it is preferable to provide a heat-insulating member between the digester tank 1 and the external environment (e.g., the atmosphere in cold seasons) that may become as low as 10°C or lower. From this perspective, it is preferable to provide the upper heat-insulating member.

[0052] The digester of the present invention may further include a protective layer for protecting the bottom heat-insulating member, and may further include a protective layer for protecting the side heat-insulating member. The protective layer for protecting the bottom heat-insulating member and the side heat-insulating member is preferably made of a steel plate. As the steel plate, Galvalume steel plate (registered trademark) is preferable. [Explanation of symbols]

[0053] 1: digestion tank, 10: digestion tank body, 11: bottom, 12: side wall, 13: upper wall, V: sludge storage space, 20: heating section, 21: first piping section, 22: second piping section, 23: heat exchange section, 24: circulation pump, 30: mixing section, 31: shaft section, 32: drive section, 33: blade section, 33a: first blade section, 33b: second blade section, 40: extraction device, 41: third piping section, 42: extraction pump, 50: foundation section, 501: foundation section body, 502: foundation section peripheral wall part, 502a: outer wall surface, 502b: inner wall surface, 51: foundation surface, 51a: installation surface, 52: outer surface, 521: support surface, 522: lower surface, 523: side surface, 523a: non-exposed surface, 523b: exposed surface, 524: upper surface, 60: heat insulation member, 61: bottom heat insulation member, 62: side heat insulation member, 63: upper heat insulation member, 70: protective layer, 80: gap, 90: water channel, 91: open portion, 92: open portion, G: recess, G1: flat portion, G2: peripheral wall portion, P: pile

Claims

1. The digester tank comprises a foundation made of concrete and a digester tank body installed on the foundation, The foundation portion has an installation surface on which the digester tank body is installed and an outer surface other than the installation surface, A digester tank, wherein at least a portion of the outer surface is covered with a thermal insulation material.

2. The outer surface has a lower surface and a side surface, The digestion tank according to claim 1 , wherein at least a portion of the lower surface and the side surfaces are covered with the thermal insulation material.

3. The outer surface has an upper surface; The digestion tank according to claim 1 or 2, wherein at least a portion of the upper surface is covered with the heat-insulating material.

4. The digester tank according to claim 3 , wherein the heat-insulating material covering the upper surface is covered with a protective layer.

5. A method for keeping a digester warm, comprising the steps of: The digestion tank includes a foundation formed of concrete and a digestion tank body installed on the foundation, The foundation portion has an installation surface on which the digester tank body is installed and an outer surface other than the installation surface, A method for insulating a digester tank, comprising covering at least a portion of the outer surface with an insulating material.

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