Digester and Method for Insulating the Digester

Abstract

To provide a digestion tank capable of curbing fixation of sediment in a digestion tank body, and a method of retaining the temperature of the digestion tank.SOLUTION: A digestion tank includes a digestion tank body that processes organic waste fed thereinto and a temperature retaining material that covers at least a part of the bottom of the digestion tank body from its inside.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a digester and a method for insulating the digester.

Background Art

[0002] Conventionally, digesters have been used to treat organic waste such as sewage sludge. Usually, a digester includes a base portion formed of concrete and a digester main body installed on the base portion for treating organic waste by anaerobic bacteria. The internal temperature (inner temperature) of the digester main body is, for example, 35 to 60°C, more specifically 35 to 40°C for medium-temperature digestion and 50 to 60°C for high-temperature digestion. Thereby, the organic matter in the sludge is decomposed by anaerobic bacteria, and biogas composed of methane and carbon dioxide is generated. Since biogas contains methane, it can be utilized as fuel.

[0003] In addition, in order to maintain the inner temperature of the digester main body in a stable state, attempts have been made to enhance the heat insulation property of the digester main body. For example, in the digester described in Patent Document 1, a heat insulation structure is provided in the concrete foundation cast under the digester main body. The heat insulation structure has a plurality of short pipes and the heat insulation member disposed between the respective short pipes. Further, the short pipes are made of steel material. In such a heat insulation structure, the heat insulation member is prevented from being crushed by the load of the sludge by the short pipes.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in a digester, deposits derived from sludge may occur at the bottom of the digester body. Such deposits adhere to the bottom of the digester body or the like, and due to the adhesion, the effective volume of the digester decreases, which may cause a decrease in the amount of biogas generated.

[0006] In view of the above circumstances, an object of the present invention is to provide a digester and a heat insulation method for a digester that can suppress the adhesion of deposits in the digester body.

Means for Solving the Problems

[0007] The digester according to the present invention includes a digester body that treats organic waste introduced therein, and has a heat insulation member that covers at least a part of the bottom of the digester body from the inside.

[0008] According to such a configuration, since at least a part of the bottom of the digester body is covered with the heat insulation member from the inside, the heat insulation member is disposed between the contact surface of the organic waste and the treated sludge in the digester body and the bottom. And at such a contact surface, since the temperature decrease is suppressed by the heat insulation member, the adhesion of deposits is suppressed.

[0009] Further, the digester according to the present invention is provided with a drawout port for discharging digested sludge inside the digester body, and the upper surface of the heat insulation member may be inclined downward so that the height decreases toward the drawout port.

[0010] According to such a configuration, since the upper surface of the heat insulation member is inclined downward so that the height decreases toward the drawout port, the deposits are likely to move toward the drawout port, and the deposits can be easily discharged from the drawout port. Further, since the deposits are likely to move (flow) as described above, the adhesion of the deposits on the contact surface is further suppressed.

[0011] Further, the digester according to the present invention has a side wall portion rising from the bottom, The outer peripheral edge of the heat insulating member may be arranged to contact the side wall portion.

[0012] According to such a configuration, the heat insulation property in the outer peripheral region of the contact surface is enhanced. And since deposits are likely to occur in the outer peripheral region of the contact surface, according to the above configuration, the adhesion of deposits in the outer peripheral region of the contact surface is suppressed.

[0013] Further, the digestion tank according to the present invention The heat insulating member may be configured such that the thickness in the height direction increases as it approaches the side wall portion.

[0014] According to such a configuration, the thickness of the heat insulating member is configured to be larger in the outer peripheral region of the bottom, that is, the heat insulation property in the outer peripheral region of the contact surface is further enhanced. Therefore, according to the above configuration, the adhesion of deposits in the outer peripheral region of the contact surface is suppressed.

[0015] In the heat insulation method of the digestion tank according to the present invention, at least a part of the bottom of the digestion tank body is covered with a heat insulating member from the inside.

[0016] According to such a configuration, a digestion tank can be constructed in which the adhesion of deposits on the contact surface is suppressed. Further, the heat insulation method having the above configuration is also applicable to an already installed digestion tank, and it is possible to improve the heat insulation property of the digestion tank and suppress the adhesion of deposits in the digestion tank without newly constructing the digestion tank or modifying the tank shape.

Advantages of the Invention

[0017] As described above, according to the present invention, it is possible to provide a digestion tank and a heat insulation method for the digestion tank that can suppress the adhesion of deposits in the digestion tank body.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0019] As shown in FIG. 1, the digester 1x according to the present embodiment includes a base portion 10 formed of concrete, a digester main body 20 installed on the base portion 10 for treating organic waste such as sewage sludge, a drawing device 30 as a discharge portion for discharging digested sludge from the digester main body 20, a heat insulating member 40 covering the bottom portion 21 of the digester main body 20 from the inside, a stirring portion 50 for stirring the sludge in the digester main body 20, and a heating portion 60 for heating the sludge in the digester main body 20.

[0020] The digester 1x of the present embodiment is provided in a recess G formed in the natural ground. The recess G includes a flat portion G1 formed to support the base portion 10 from below and a peripheral wall portion G2 formed to surround the base portion 10. Note that the recess may not include the peripheral wall portion G2.

[0021] The base portion 10 of the present embodiment is formed by placing concrete in the recess G. The base portion 10 is formed of reinforced concrete, that is, it has concrete and a plurality of reinforcing bars embedded in the concrete. A plurality of piles P for supporting the base portion 10 from below are embedded below the recess G. Each pile P is composed of concrete and a plurality of reinforcing bars extending in the length direction embedded in the concrete. The tip portion of each pile P protrudes upward from the flat portion G1 and is embedded in the base portion 10. That is, the tip portion of the pile P is integrated with the concrete of the base portion 10.

[0022] The digester body 20 of this embodiment is made of steel plate. The digester body 20 is formed in a cylindrical shape and has a bottom portion 21 grounded on the foundation portion 10, a side wall portion 22 rising from the bottom portion 21, and an upper wall portion 23 facing the bottom portion 21 and closing the upper end of the side wall portion 22. Inside the digester body 20, a cylindrical internal space defined by the bottom portion 21, the side wall portion 22, and the upper wall portion 23 is formed. Note that the digester body may be formed not only in a cylindrical shape but also, for example, in a rectangular tube shape. Further, the digester body may be formed of concrete. Also, asphalt sand for preventing corrosion of the bottom portion 21 may be laid between the outer surface of the bottom portion 21 and the foundation portion 10.

[0023] The extraction device 30 of this embodiment functions to discharge digested sludge from the digester body 20 to the outside of the tank. The extraction device 30 of this embodiment is composed of an extraction pump 31 for discharging digested sludge from the digester body 20 and a first piping portion 32 connected to the extraction pump 31. The first piping portion 32 extends from the inside of the digester body 20 to the outside of the digester body 20 and has an extraction port 321 for sucking in digested sludge at the inner end portion. The first piping portion 32 of this embodiment is provided such that the extraction port 321 faces the central portion of the bottom portion 21 in the digester body 20. More specifically, the extraction port 321 is provided such that its opening surface is parallel to the bottom surface 211.

[0024] The heat insulation member 40 is disposed in the internal space of the digester body 20. The heat insulation member 40 of this embodiment is disposed over the bottom surface 211 and forms a heat insulation layer 40L that covers the bottom portion 21 of the digester body 20 from the inside. Also, the heat insulation member 40 forms a contact surface that comes into contact with the sludge introduced into the digester body 20. That is, the heat insulation layer 40L has an upper surface 41 that forms the contact surface with the sludge. As a result, the digester body 20 of this embodiment has a sludge storage space V defined by the upper surface 41 of the heat insulation layer 40L, the side wall portion 22, and the upper wall portion 23.

[0025] In this embodiment, the heat-insulating member 40 is arranged such that its outer peripheral edge is in contact with the side wall portion 22. Here, on the bottom surface 211, when the region including the connection edge with the side wall portion 22 and closer to the side wall portion 22 is defined as the outer region, and the region inside the outer region is defined as the inner region, it is preferable that the heat-insulating member 40 is arranged to cover at least the outer region. The outer region is preferably 25% or more of the total area of the bottom surface 211, and more preferably 50% or more.

[0026] Here, FIG. 1 shows a cross-section of the digestion tank body 20, and more specifically, a cross-section with a vertical plane passing through the center of the bottom surface 211 as the cutting plane. As shown in the cross-sectional view in FIG. 1, the heat-insulating layer 40L is formed such that its thickness (thickness in the vertical direction) increases as it goes from the extraction port 321 toward the side wall portion 22. Further, the heat-insulating layer 40L is formed such that it has the largest thickness at the portion covering the connection edge with the side wall portion 22 of the bottom surface 211 and the smallest thickness at the portion covering the center of the bottom surface 211.

[0027] As a result, the heat-insulating layer 40L has an upper surface 41 that slopes downward so that the height decreases from the side wall portion 22 toward the extraction port 321. The upper surface 41 has a central region 41a including the center located at the lowest position and an outer peripheral region 41b including the outer peripheral edge located at the highest position. The upper surface 41 is formed such that the inclination angle at the outer peripheral edge is the largest. Further, the upper surface 41 is formed such that the inclination angle decreases as it goes from the outer peripheral edge toward the center. The inclination angle at the outer peripheral edge of the upper surface 41 is preferably 5 to 45°, and more preferably 15 to 30°. The upper surface 41 of this embodiment is curved. Further, in the cross-section, the upper surface 41 is formed such that the inclination angle of the tangent line with respect to the horizontal plane decreases as it goes from the outer peripheral edge toward the center.

[0028] In addition, the heat-insulating member 40 of the present embodiment is provided so as to partially cover the first pipe portion 32. As a result, a part of the first pipe portion 32 is arranged to pass through the heat-insulating layer 40L. Specifically, the heat-insulating member 40 of the present embodiment is provided so as to at least cover the base end portion of the first pipe portion 32 in the digestion tank body 20. This eliminates the sticking of deposits at the base end portion, which is easily affected by the temperature of the external environment. Note that the heat-insulating member may be provided below the first pipe portion.

[0029] As the material constituting the heat-insulating member 40, it is only necessary that the thermal conductivity is smaller than the material constituting the digestion tank body 20 (steel plate in the present embodiment), and it is preferable that the thermal conductivity is smaller than that of the concrete in the base portion 10. Specifically, the thermal conductivity of the material constituting the heat-insulating member 40 is preferably less than 1.2 W / m·K, and more preferably less than 0.5 W / m·K. As the material of the heat-insulating member 40, polystyrene foam or polyurethane foam having a thermal conductivity of 0.02 to 0.03 W / m·K is preferable. In addition, the material of the heat-insulating member 40 may be glass wool, perlite, perlite mortar, aggregate (gravel), or the like.

[0030] The heat-insulating member 40 may be composed of a single material. Also, the heat-insulating member 40 may be composed of a combination of a plurality of materials. For example, the heat-insulating member 40 is preferably composed of a combination of aggregate and perlite or perlite mortar.

[0031] The digestion tank 1x of the present embodiment includes a fixing member for preventing the floating and displacement of the heat-insulating member 40 in the sludge. Examples of the fixing member include metal fittings such as anchor bolts embedded in the bottom portion 21 or the side wall portion 22 from the heat-insulating member 40, and adhesives for adhering the heat-insulating member 40 to the bottom portion 21 or the side wall portion 22.

[0032] The stirring unit 50 of this embodiment functions to mix the anaerobic microorganisms and organic waste in the sludge to make them uniform and to promote the heat conduction in the sludge. The stirring unit 50 includes a shaft portion 51 having a rotating shaft extending in the vertical direction, a driving unit 52 that rotates the shaft portion 51 around the rotating shaft, and blade portions 53 fixed to the shaft portion 51 and rotating along with the rotation of the shaft portion 51.

[0033] In the stirring unit 50 of this embodiment, the shaft portion 51 is arranged above the central portion of the bottom 21. The blade portions 53 are composed of a first blade portion 53a and a second blade portion 53b that are spaced apart in the vertical direction. That is, the blade portions 53 are configured by arranging the first blade portion 53a and the second blade portion 53b in two stages. When the blade portions 53 rotate, they are configured to move the sludge from above to below on the rotation plane. That is, the stirring unit 50 can generate a flow of sludge toward the upper surface 41 of the heat insulation layer 40L at the radial center of the sludge storage space V. Then, the sludge that reaches the upper surface 41 flows along the extending direction of the upper surface 41 and reaches the side wall portion 22, and further flows upward along the side wall portion 22. As a result, the sludge in the sludge storage space V circulates. Note that the blade portions are not limited to the two-stage arrangement, and for example, there may be only one stage, or there may be multiple stages.

[0034] The heating unit 60 of this embodiment is provided to maintain the temperature of the sludge in the digestion tank body 20 at a temperature suitable for digestion, for example, 35 to 60 °C, and more specifically, 35 to 40 °C for mesophilic digestion and 50 to 60 °C for thermophilic digestion. The heating unit 60 of this embodiment has a heat exchange unit 61 provided outside the digestion tank body 20, and is configured to take out a part of the sludge from the digestion tank body 20, heat it in the heat exchange unit 61, and return the heated part of the sludge to the digestion tank body 20. More specifically, the heating unit 60 includes a second piping unit 62 for discharging a part of the sludge from the digestion tank body 20 and transferring it to the heat exchange unit 61, and a third piping unit 63 for transferring the heated part of the sludge from the heat exchange unit 61 to the digestion tank body 20. Further, the heating unit 60 has a circulation pump 64 for moving the sludge from the second piping unit 62 to the third piping unit 63.

[0035] According to the digester 1x of the present embodiment, the heat insulation layer 40L is arranged so as to cover the bottom 21 of the digester main body 20 from the inside, and since the heat insulation layer 40L forms the upper surface 41 which is the contact surface of the sludge, the decrease in temperature at the contact surface is suppressed, so that the adhesion of deposits to the contact surface is suppressed.

[0036] In addition, since the upper surface 41 of the heat insulation layer 40L is inclined downward so that the height decreases from the side wall portion 22 toward the extraction port 321, the deposits are likely to move toward the extraction port 321, and the deposits can be easily discharged from the extraction port 321. Further, since the deposits are likely to move downward on the upper surface 41, the adhesion of the deposits on the upper surface 41 is suppressed.

[0037] In addition, the heat insulation layer 40L has the largest thickness in the portion covering the outer peripheral edge of the bottom surface 211, that is, in the heat insulation layer 40L, the heat insulation property is enhanced most in the outer peripheral region 41b. As a result, in the digester main body 20 where the sludge circulates as described above, the adhesion of deposits at the connection portion (corner portion) between the upper surface 41 and the side wall portion 22 where sludge is likely to stagnate is suppressed.

[0038] In addition, since the heat insulation layer 40L is formed so as to cover the bottom surface 211, the heat dissipation from the digester main body 20 to the base portion 10 is suppressed. That is, the base portion 10 is less likely to be affected by temperature changes due to at least the heat from the digester main body 20, and can be maintained in a relatively stable temperature state. As a result, the generation of thermal stress in the base portion 10 is reduced, and it becomes possible to reduce the amount of reinforcing bars (amount of reinforcement) in the base portion 10, leading to a reduction in construction labor, cost, and members.

[0039] Next, a heat insulation method for a digester according to an embodiment of the present invention will be described. In the present embodiment, a heat insulation method for insulating an existing digester main body will be exemplified.

[0040] The heat insulation method for a digester of the present embodiment includes a heat insulation step of covering the bottom of the digester main body with a heat insulation member from the inside.

[0041] In the heat insulation process, a heat insulation layer made of a heat insulation member is formed on the bottom surface at the bottom part.

[0042] According to the heat insulation method of the digestion tank of the present embodiment, not only the newly constructed digestion tank body but also the existing digestion tank body can be provided with the above functions (the same functions as those of the digestion tank 1x provided with the heat insulation member 40).

[0043] Note that the digestion tank and the heat insulation method of the digestion tank according to the present invention are not limited to the above embodiment. Also, the digestion tank and the heat insulation method of the digestion tank according to the present invention are not limited by the above effects. The digestion tank and the heat insulation method of the digestion tank according to the present invention can be variously modified without departing from the gist of the present invention.

[0044] For example, in the above embodiment, the upper surface 41 is formed in a curved shape, but the present invention is not limited thereto, and the upper surface may be formed in a straight line shape.

[0045] Also, in the above embodiment, the extraction port 321 is arranged to face the central part of the bottom part 21, but the present invention is not limited thereto, and for example, the modified examples shown in FIGS. 2 to 4 may be used. In each modified example, the same components as those of the digestion tank 1x in FIG. 1 are denoted by the same reference numerals and their descriptions are omitted.

[0046] In the modified example of FIG. 2, the extraction port 321 is arranged to face the outer peripheral part of the bottom part 21. In this case, it is preferable that the heat insulation layer 40L is formed to have the largest thickness at the position farthest from the extraction port 321 on the bottom surface 211 and to have the smallest thickness at the position facing the extraction port 321 on the bottom surface 211. Also, it is preferable that the upper surface 41 of the heat insulation layer 40L is formed to slope downward so that the height decreases toward the extraction port 321.

[0047] In the modification of FIG. 3, similar to FIG. 2, the extraction port 321 is arranged to face the outer peripheral portion of the bottom portion 21. In this case, the heat insulation layer 40L may be formed such that the thickness is the largest at the central portion of the bottom surface 211 and the thickness is the smallest at the position facing the extraction port 321 on the bottom surface 211. Further, it is preferable that the upper surface 41 of the heat insulation layer 40L is inclined downward so that the height decreases toward the extraction port 321 (from the central portion of the bottom surface 211 toward the outer peripheral portion).

[0048] In the modification of FIG. 4, in the digester body 20, the first piping portion 32 in the extraction device 30 is arranged closer to the bottom surface 211 compared to the digester 1x. Specifically, in the digester body 20 of FIG. 4, the first piping portion 32 is arranged such that the distance between its lower end and the bottom surface 211 is about 50 cm. Further, the first piping portion 32 is arranged such that the opening surface of the extraction port 321 faces downward or horizontally, and the inner end portion of the digester body 20 expands in diameter toward the tip. In this case, it is preferable that the heat insulation member 40 is provided so as to cover 50% or more of the length from its base end portion in the portion of the first piping portion 32 located inside the digester body 20. Thereby, the portion that can become an obstacle to sludge circulation in the first piping portion 32 can be reduced.

[0049] Further, the digester of the present invention may be the digester 1y shown in FIG. 5. In the digester 1y, the same components as those of the digester 1x in FIG. 1 are denoted by the same reference numerals and the description thereof is omitted.

[0050] In the digester 1y of FIG. 5, it includes a digester body 20 having a flat bottom surface 211 and a heat insulation member 40 that partially covers the bottom surface 211. The bottom surface 211 has a covered surface 211a covered by the heat insulation member 40 and an exposed surface 211b not covered by the heat insulation member 40. The exposed surface 211b is the contact surface with the sludge.

[0051] The heat insulation member 40 is arranged to form a heat insulation layer 40L at least in the outer region of the bottom surface 211. The inner peripheral portion of the heat insulation layer 40L is formed to be arranged radially outward of the blade portion 53 of the stirring portion 50. The upper surface 41 of the heat insulation layer 40L is inclined downward so that the height decreases from the side wall portion 22 toward the extraction port 321. The upper surface 41 serves as the contact surface for the sludge.

[0052] With the above configuration, the digestion tank 1y has enhanced heat insulation in the outer peripheral region of the contact surface of the sludge, and the adhesion of deposits is sufficiently suppressed. More specifically, the adhesion of deposits at the connection portion between the upper surface 41 of the heat insulation layer 40L and the side wall portion 22 is suppressed.

[0053] Also, since the contact surface of the sludge is flat below the blade portion 53, the sludge is likely to move from the central portion to the outer peripheral portion on the contact surface by the stirring by the blade portion 53 during rotation. From this perspective, the upper surface of the heat insulation layer may be composed of a flat region (contact surface of the sludge) formed along a horizontal plane in the inner region and an inclined region inclined upward toward the side wall portion in the outer region. Further, the heat insulation layer may have a flat portion that covers the lower part (opposing position of the blade portion 53) of the blade portion 53 on the bottom surface 211 and is formed in a flat shape with a constant thickness in the height direction, and an inclined portion that extends from the flat portion toward the side wall portion and is formed such that the thickness in the height direction increases toward the side wall portion.

Explanation of Reference Numerals

[0054] 1x, 1y: Digestion tank, 10: Foundation portion, G: Recess, G1: Flat portion, G2: Peripheral wall portion, P: Pile, 20: Digestion tank body, 21: Bottom, 211: Bottom surface, 211a: Covered surface, 211b: Exposed surface, 22: Side wall portion, 23: Upper wall portion, V: Sludge accommodation space, 30: Extraction device, 31: Extraction pump, 32: First piping portion, 321: Extraction port, 40: Heat insulation member, 40L: Heat insulation layer, 41: Upper surface, 41a: Central region, 41b: Outer peripheral region, 50: Stirring portion, 51: Shaft portion, 52: Driving portion, 53: Blade portion, 53a: First blade portion, 53b: Second blade portion, 60: Heating portion, 61: Heat exchange portion, 62: Second piping portion, 63: Third piping portion, 64: Circulation pump

Claims

1. A digester comprising a digester body for treating organic waste introduced therein, having a heat-insulating member covering at least a part of the bottom surface of the digester body from the inside, wherein the digester body has a side wall rising from the bottom surface, the heat-insulating member includes an outer peripheral region including an outer peripheral edge in contact with the side wall, and in at least one vertical cross-section of the digester body passing through the center of the bottom surface, the heat-insulating member is formed such that the thickness in the vertical direction increases as it goes toward the outer peripheral edge on at least one side in the horizontal direction, and forms a contact surface with at least one of the organic waste and the digested sludge in the outer peripheral region.

2. A draw-out port for discharging digested sludge is provided inside the digester body, and the upper surface of the heat-insulating member is inclined downward so that the height decreases toward the draw-out port. The digester according to claim 1.

3. A method for heat-insulating a digester, wherein the digester comprises a digester body for treating organic waste introduced therein, the digester body has a heat-insulating member covering at least a part of the bottom surface of the digester body from the inside and a side wall rising from the bottom surface, the heat-insulating member includes an outer peripheral region including an outer peripheral edge in contact with the side wall, and in at least one vertical cross-section of the digester body passing through the center of the bottom surface, the heat-insulating member is formed such that the thickness in the vertical direction increases as it goes toward the outer peripheral edge on at least one side in the horizontal direction, and the outer peripheral region forms a contact surface with at least one of the organic waste and the digested sludge. A method for heat-insulating a digester.

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