Decomposed gas recovery system

Abstract

To suppress discharge of gas generated in a landfill of an organic waste into the atmosphere.SOLUTION: A system for recovering decomposed gas includes a ventilation pipe, and a gas recovery structure. The ventilation pipe is provided in substantially a vertical direction to a bottom surface of a landfill disposal site formed in the ground. The ventilation pipe discharges decomposed gas generated by decomposition of an organic waste landfilled in the landfill disposal site to the upper side of a landfill surface. The gas recovery structure is provided on a discharge route of the decomposed gas passing through the ventilation pipe. The gas recovery structure recovers at least one of CO2 gas and CH4 gas from the decomposed gas.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a system for recovering decomposition gas generated by the decomposition of organic waste in a landfill site. [Background technology]

[0002] Patent Document 1 discloses the structure of a semi-aerobic waste disposal site. This conventional structure includes a landfill formed in the ground, a leachate collection pit formed adjacent to the landfill, and a leachate collection and drainage pipe arranged on the bottom of the landfill. The leachate collection and drainage pipe is a perforated pipe. The leachate collection and drainage pipe collects leachate from the landfill through the holes and sends it to the collection pit. The collection pit sends the leachate sent from the leachate collection and drainage pipe to an external disposal facility.

[0003] The conventional structure also includes an air pipe and a vent pipe. One end of the air pipe is connected to the leachate collection drainage pipe, and the other end is open to the ground. A blower is provided at the open end on the ground side of the air pipe, and by operating this blower, outside air is sent to the leachate collection drainage pipe via the air pipe, or gas within the leachate collection drainage pipe is exhausted to the outside via the air pipe. The vent pipe is a perforated pipe, one end of which is connected to the leachate collection drainage pipe, and the other end is open to the ground. The vent pipe exhausts gas generated in the landfill to the outside through this hole. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-634 A Summary of the Invention [Problem to be solved by the invention]

[0005] In organic waste landfills, the decomposition of organic waste by microorganisms progresses. As this decomposition progresses, gases such as CH4 gas and CO2 gas are generated. The generated gases are called "decomposition gas" or "landfill gas." In anaerobic landfills, the proportion of CH4 gas in the decomposition gas is high. On the other hand, in semi-aerobic landfills, the proportion of CH4 gas in the decomposition gas is low and the proportion of CO2 gas is high. In Japan, many semi-aerobic landfills have been installed, which are able to reduce CH4 gas emissions.

[0006] The CH4 gas and CO2 gas contained in the decomposition gas are also greenhouse gases. Therefore, it is desirable to prevent these gases generated in the landfill from being discharged from the ground into the atmosphere. In this respect, the structure of Patent Document 1 actively discharges the decomposition gas generated in the landfill into the atmosphere, so there is room for improvement.

[0007] One object of the present invention is to provide a technique for reducing the emission of gases generated in organic waste landfills into the atmosphere. [Means for solving the problem]

[0008] The present invention is a system for recovering cracked gas and has the following features. The system includes a vent pipe and a gas collection structure. The vent pipe is disposed in a direction substantially perpendicular to the bottom surface of the landfill site formed underground, and discharges decomposition gas generated by the decomposition of organic waste buried in the landfill site above the landfill surface through the vent pipe. The gas recovery structure is provided in a discharge path of the decomposition gas passing through the vent pipe. The gas recovery structure recovers at least one of CO2 gas and CH4 gas from the decomposition gas.

[0009] In the present invention, the vent pipe may include a first vent pipe and a second vent pipe. The second vent pipe is provided inside the first vent pipe. The second vent pipe has a smaller diameter than the first vent pipe. The first and second vent pipes each have a plurality of ventilation holes formed on an outer circumferential surface. In the present invention, the gas recovery structure may include a gas recovery material located inside the first vent pipe and outside the second vent pipe, and configured to recover at least one of CO2 gas and CH4 gas.

[0010] In the present invention, the vent pipe may have an opening located above the landfill surface. In the present invention, the gas recovery structure includes a ventilator detachably attached to the opening, and a gas recovery material incorporated in the ventilator for recovering at least one of CO2 gas and CH4 gas. Effect of the Invention

[0011] According to the present invention, since the gas recovery structure is provided in the exhaust path of the decomposition gas passing through the vent pipe, at least one of CO2 gas and CH4 gas can be recovered from the decomposition gas by the gas recovery structure. Therefore, it is possible to prevent the CO2 gas or CH4 gas contained in the decomposition gas from being exhausted into the atmosphere via the vent pipe. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing an example of the configuration of a landfill site to which a decomposition gas recovery system according to an embodiment is applied; [Diagram 2] FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. [Diagram 3] FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. [Figure 4] FIG. 2 is a diagram illustrating the discharge paths of gas and liquid at a landfill site. [Diagram 5] 1A to 1C are diagrams illustrating a first example of a gas recovery structure. [Figure 6]11A to 11C are diagrams illustrating a second example of the gas recovery structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In addition, elements common to each drawing are given the same reference numerals and duplicated explanations are omitted. In addition, the present invention is not limited to the following embodiment.

[0014] 1. Example of landfill site configuration FIG. 1 is a diagram showing an example of the configuration of a waste landfill site to which a decomposition gas recovery system according to an embodiment is applied. FIG. 1 shows a plan view of a waste landfill site 10. The XY plane in FIG. 1 is approximately parallel to the ground, and the landfill site 10 is provided underground. The bottom surface 11 of the landfill site 10, side surfaces 12 and 13 in the X-axis direction (longitudinal direction), and side surface 14 in the Y-axis direction are made of, for example, concrete plates. At least one protective mat and one waterproof sheet are laid on the bottom surface 11. Protective mats and waterproof sheets may also be laid on the side surfaces 12, 13, and 14.

[0015] A leachate collection drainage pipe is also laid on the bottom surface 11. The leachate collection drainage pipe collects leachate within the disposal space partitioned by the bottom surface 11 and the sides 12, 13, 14, etc., and discharges the collected leachate to the outside of the disposal space. In the example shown in FIG. 1, the leachate collection drainage pipe includes a main line 21 and branch lines 22-29. The main line 21 and the branch lines 22-29 are formed, for example, from a synthetic resin. A plurality of water passage holes are formed on the outer circumferential surface of each of the main line 21 and the branch lines 22-29. Water (leachate) present around each pipe moves to the inside of each pipe through these water passage holes.

[0016] The main line 21 extends in a straight line in the X-axis direction. Each of the branches 22-25 has one end located on the side surface 12 side and the other end connected to the main line 21. Each of the branches 26-29 has one end located on the side surface 13 side and the other end connected to the main line 21. Therefore, the leachate collected by the branches 22-29 moves to the main line 21. A leachate collection pit 31 is connected to the end of the main line 21. The leachate collection pit 31 is equipped with a drainage pump. When the drainage pump is driven, the leachate collected in the main line 21 is discharged outside the disposal space.

[0017] Vent pipes 32 and 33 are provided in the longitudinal direction of the trunk line 21. The vent pipes 32 and 33 are provided mainly for the purpose of supplying outside air (air) into the disposal space or discharging gas within the disposal space to the outside. The vent pipes 32 and 33 are provided in a direction substantially perpendicular to the bottom surface 11. The vent pipes 32 and 33 are formed, for example, from a synthetic resin. In addition, a plurality of vent holes are formed on the outer circumferential surface of each of the vent pipes 32 and 33. Therefore, not only outside air and gas but also leachate flows through the vent pipes 32 and 33. For the vent pipes 32 and 33, a pipe (for example, a presto pipe) that can be extended according to the progress of the landfill is used.

[0018] FIG. 2 is a diagram showing a cross section taken along line 2-2 in FIG. 1. FIG. 2 is also a cross section taken along the axial direction of the vent pipe 32 shown in FIG. 1. The positive Z-axis direction in FIG. 2 coincides with the vertically upward direction and also coincides with the direction substantially perpendicular to the bottom surface 11. The cross section taken along the axial direction of the vent pipe 33 shown in FIG. 1 is basically the same as that of the vent pipe 32 described below. As shown in FIG. 2, the vent pipe 32 includes a first vent pipe 32a and a second vent pipe 32b. The second vent pipe 32b has a smaller diameter than the first vent pipe 32a and is inserted inside the first vent pipe 32a.

[0019] The base end (open end) of the first vent pipe 32a is connected to a cut stone base 34 that covers the entire trunk line 21. The tip (open end) of the first vent pipe 32a is covered by a cover member 35. A hole is formed in the center of the cover member 35 through which the second vent pipe 32b passes. The base end (open end) of the second vent pipe 32b is connected to the trunk line 21, and the tip (open end) of the second vent pipe 32b is open. A cut stone group 36 is arranged in the space inside the first vent pipe 32a and outside the second vent pipe 32b. In the example shown in FIG. 2, the cut stone group 36 is drawn in a part of the space inside the first vent pipe 32a and outside the second vent pipe 32b, but in reality, the cut stone group 36 is evenly arranged throughout the entire space.

[0020] The cut stones that make up the cut stone base 34 are the same as the cut stones that make up the cut stone group 36. The main purpose of arranging the cut stone base 34 is to ensure good ventilation and water permeability around the main line 21 and branch lines 22-29. The main purpose of arranging the cut stone group 36 is to maintain the upright position of the vent pipe 32 and to ensure good ventilation and water permeability around the second vent pipe 32b. The cut stone group 36 forms part of a first example of a gas recovery structure which will be described later.

[0021] Figure 3 is a diagram showing a cross section taken along line 3-3 in Figure 1. While Figure 2 shows a cross section of the main line 21, Figure 3 shows a cross section of the branch line 24. As shown in Figure 3, the entire branch line 24 is covered by a cut stone base 34. Soil 37 is laid on the left and right sides of the cut stone base 34.

[0022] An example of the state in which organic waste has been buried in the landfill site 10 will be described with reference to FIG. 4. The position of the cross section depicted in FIG. 4 is the same as the position of the cross section described in FIG. 2. The organic waste WS disposed in the disposal space is piled up facing upward along the Z axis. Each time organic waste WS is disposed of, soil 38 is laid down to cover the exposed surface of the organic waste WS. Two sets of organic waste WS and soil 38 are depicted in FIG. 4. The first set is the older set, and the second set is the newer set. The surface of the soil 38 that constitutes the second set constitutes the "landfill surface."

[0023] The tips of the first vent pipe 32a and the second vent pipe 32b are located above the landfill surface. In the example shown in Fig. 4, when further filling the organic waste WS, additional pipes are connected to the tips of the first vent pipe 32a and the second vent pipe 32b. This keeps the tips of the first vent pipe 32a and the second vent pipe 32b above the landfill surface. When connecting an additional pipe to the first vent pipe 32a, the cover member 35 is temporarily removed before the connection, and the cover member 35 is attached to the tip of the additional pipe after the connection.

[0024] 2. Discharge route of decomposition gas When the organic waste WS is decomposed by the action of microorganisms, decomposition gas GAS containing CH4 gas and CO2 gas is generated. This decomposition gas GAS moves through the layer of the organic waste WS and moves to the vicinity of the first vent pipe 32a. The decomposition gas GAS near the first vent pipe 32a passes through the vent hole of the first vent pipe 32a and enters the inside of the first vent pipe 32a, and moves further through the gaps in the ashlar group 36 to the vicinity of the second vent pipe 32b. The decomposition gas GAS near the second vent pipe 32b passes through the vent hole of the second vent pipe 32b and enters the inside of the second vent pipe 32b. Then, it moves inside the second vent pipe 32b upward in the Z axis direction (upward) and is discharged to the outside from the tip of the second vent pipe 32b.

[0025] In this embodiment, CH4 gas and CO2 gas are collected in a series of exhaust paths of the decomposition gas GAS from the layer of organic waste WS to the tip of the second vent pipe 32b. An example of a gas collection mechanism for collecting this CH4 gas and CO2 gas will be described below.

[0026] 3.Gas recovery mechanism 3-1. First Example Fig. 5 is a diagram illustrating a first example of the gas recovery mechanism. Fig. 5 shows an enlarged schematic diagram of a quarry stone group 36. In Fig. 5, the quarry stone group 36 includes a quarry stone 41 and a gas recovery material 42 arranged in the vicinity of the quarry stone 41. The gas recovery material 42 includes a material that mainly recovers CO2 gas and a material that mainly recovers CH4 gas.

[0027] Examples of the gas capture material 42 that captures CO2 gas include inorganic CO2 adsorbents such as sodium salts, calcium salts, and magnesium salts, and amine-based CO2 adsorbents. Examples of the gas capture material 42 include slag containing a large amount of the chemical substances exemplified as inorganic CO2 adsorbents, and incineration ash into which excess slaked lime is injected to immobilize harmful substances in fly ash in a waste incineration process. Examples of the gas capture material 42 that captures CH4 gas include carbon-based adsorbents such as activated carbon with adjusted specific surface area and pore size, carbon nanotubes, and carbon nanohorns.

[0028] By arranging the gas recovery material 42 near the cut stone 41, it becomes possible to separate and recover at least one of CO2 gas and CH4 gas from the decomposition gas GAS that passes further through the gaps in the cut stone group 36 and moves to the vicinity of the second vent pipe 32b.

[0029] 3-2. Second Example FIG. 6 is a diagram for explaining a second example of the gas recovery mechanism. The position of the cross section depicted in FIG. 6 is the same as the position of the cross section described in FIG. 2. FIG. 6 also depicts a set of organic waste WS and soil 38 described in FIG. 4. In the example shown in FIG. 6, a ventilator 43 is detachably attached to the tip of the second vent pipe 32b. The ventilator 43 is detachably attached for the purpose of periodic inspection and replacement. The ventilator 43 discharges the decomposition gas GAS in the second vent pipe 32b to the outside by the suction action of the wind flowing above the landfill surface.

[0030] In the second example, the gas recovery material 42 described in the first example is incorporated into the ventilator 43. As an example of incorporating the gas recovery material 42, a unit containing the gas recovery material 42 is attached to the middle of the air passage in the ventilator 43.

[0031] 4.Effects According to the embodiment described above, since the gas recovery structure is provided in the exhaust path of the decomposition gas GAS passing through the ventilation pipes 32 and 33, at least one of the CO2 gas and the CH4 gas can be recovered from the decomposition gas GAS by the gas recovery structure. Therefore, it is possible to prevent the CO2 gas or the CH4 gas contained in the decomposition gas GAS from being exhausted into the atmosphere through the ventilation pipes 32 or 33. [Explanation of symbols]

[0032] 10...landfill site, 11...bottom, 12,13,14...side, 21...main line, 22,23,24,25,26,27,28,29...branch line, 31...leachate collection pit, 32,33...ventilation pipe, 32a...first ventilation pipe, 32b...second ventilation pipe, 34...cut stone base, 35...cover member, 36...cut stone group, 37,38...soil, 41...cut stone, 42...gas recovery material, 43...ventilator, WS...organic waste, GAS...decomposition gas

Claims

1. a vent pipe that is provided in a direction substantially perpendicular to the bottom surface of the landfill site formed underground and that discharges decomposition gas generated by decomposition of the organic waste buried in the landfill site above the landfill surface; The exhaust pipe is provided in a discharge path of the decomposition gas passing through the exhaust pipe, and the exhaust pipe is adapted to extract CO from the decomposition gas. ２ Gas and CH ４ a gas recovery structure for recovering at least one of the gases; A decomposition gas recovery system comprising:

2. The ventilation pipe includes a first ventilation pipe and a second ventilation pipe provided inside the first ventilation pipe and having a smaller diameter than the first ventilation pipe, The first and second vent pipes each have a plurality of vent holes formed on an outer circumferential surface, The gas recovery structure is located inside the first vent pipe and outside the second vent pipe, ２ Gas and CH ４ A gas recovery material is included to recover at least one of the gases.

2. The decomposition gas recovery system according to claim 1 .

3. the vent pipe has an opening located above the landfill surface; The gas recovery structure includes a ventilator detachably attached to the opening, and a CO ２ Gas and CH ４ and a gas recovery material for recovering at least one of the gases.

3. The decomposition gas recovery system according to claim 1 or 2.

Images