Methane production method and methanation system
By recovering and reacting methane and carbon dioxide from wastewater treatment with ammonia, the method addresses the issue of carbon dioxide discharge, achieving efficient methane production with reduced emissions and costs.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- METAWATER CO LTD
- Filing Date
- 2022-08-31
- Publication Date
- 2026-07-29
AI Technical Summary
Existing methanation processes discharge significant amounts of carbon dioxide into the atmosphere, and there is a need to reduce these emissions.
A method that recovers methane and carbon dioxide generated during wastewater treatment and reacts them with ammonia to produce methane, utilizing a methanation system that includes a methanation device, pretreatment device, and nitrogen separation unit to simplify the process and reduce emissions.
The method effectively suppresses atmospheric carbon dioxide discharge by utilizing wastewater-generated carbon dioxide, reducing the need for cooling systems and separation devices, thereby lowering costs and emissions.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for producing methane and methanation system and pertains to it.
Background Art
[0002] In recent years, methanation that produces methane by reacting carbon dioxide with hydrogen has been carried out (see Patent Document 1).
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] In the methanation as described above, for example, it is desired to suppress the amount of carbon dioxide discharged into the atmosphere by utilizing the carbon dioxide generated in other facilities.
Means for Solving the Problems
[0005] In order to suppress the amount of carbon dioxide discharged into the atmosphere as described above, the methane production method in the present invention includes a step of recovering methane and carbon dioxide generated along with the treatment of wastewater in a wastewater treatment facility, and a step of reacting a first gas containing the recovered methane and carbon dioxide with a second gas containing ammonia to produce methane.
Effects of the Invention
[0006] According to the methane production method in the present invention and methanation system it becomes possible to suppress the amount of carbon dioxide discharged into the atmosphere.
Brief Description of the Drawings
[0007] [Figure 1] Figure 1 is a diagram illustrating the configuration of the wastewater treatment facility 1000 in the first embodiment. [Figure 2] Figure 2 is a diagram illustrating the configuration of the methanation equipment 100 in the first embodiment. [Figure 3] Figure 3 is a flowchart illustrating the methane production method in the first embodiment. [Figure 4] Figure 4 is a diagram illustrating the configuration of the methanation equipment 200 in the second embodiment. [Figure 5] Figure 5 is a flowchart illustrating the methane production method in the second embodiment. [Modes for carrying out the invention]
[0008] Embodiments of the present invention will be described below with reference to the drawings. However, these embodiments do not limit the technical scope of the present invention.
[0009] [Wastewater treatment equipment 1000 in the first embodiment] First, we will describe the wastewater treatment equipment 1000 in the first embodiment. Figure 1 is a diagram illustrating the configuration of the wastewater treatment equipment 1000 in the first embodiment.
[0010] As shown in Figure 1, the wastewater treatment facility 1000 in this embodiment includes, for example, a methanation facility 100, a primary sedimentation tank 110, a reaction tank 120, a final sedimentation tank 130, a digester 140, a dewatering machine 150, and an ammonia recovery device 160.
[0011] The primary sedimentation tank 110 separates organic matter and suspended solids (hereinafter collectively referred to as pollutants) contained in wastewater (e.g., sewage wastewater) discharged via line L11 by sedimentation. Line L11 is, for example, a pipe connecting the wastewater supply source and the primary sedimentation tank 110. The primary sedimentation tank 110 then discharges the separated pollutants as primary sludge to the digestion tank 140 via line L15. Line L15 is, for example, a pipe connecting the primary sedimentation tank 110 and the digestion tank 140. The primary sedimentation tank 110 also discharges the wastewater from which the pollutants have been separated to the reaction tank 120 via line L12. Line L12 is, for example, a pipe connecting the primary sedimentation tank 110 and the reaction tank 120.
[0012] Line L15 may, for example, be a pipe connecting the primary sedimentation tank 110 and a thickening tank (not shown), and further connecting the thickening tank and the digestion tank 140. In this case, the thickening tank may, for example, concentrate the primary sediment sludge discharged from the primary sedimentation tank 110 and supply it to the digestion tank 140.
[0013] The reaction tank 120 treats wastewater supplied from the primary sedimentation tank 110 via line L12 by biological treatment using activated sludge (for example, biological treatment by the standard activated sludge method or the circulating nitrification-denitrification method). The reaction tank 120 then discharges the wastewater, after biological treatment, to the final sedimentation tank 130 via line L13. Line L13 is, for example, a pipe connecting the reaction tank 120 and the final sedimentation tank 130.
[0014] The final sedimentation tank 130 separates the sludge contained in the wastewater discharged from the reaction tank 120 via line L13. The final sedimentation tank 130 then returns a portion of the separated sludge as return sludge to the reaction tank 120 via line L21. Line L21 is, for example, a pipe that directly connects the final sedimentation tank 130 and the reaction tank 120, or a pipe that connects line L16 and the reaction tank 120. Furthermore, the final sedimentation tank 130 discharges the sludge other than the return sludge as excess sludge to the digestion tank 140 via line L16. Line L16 is, for example, a pipe that directly connects the final sedimentation tank 130 and the digestion tank 140, or a pipe that connects the final sedimentation tank 130 and line L15.
[0015] Line L16 may, for example, be piping connecting the final sedimentation tank 130 and a concentration device (not shown), and further connecting the concentration device and the digester 140. The concentration device may, for example, concentrate the excess sludge discharged from the final sedimentation tank 130 and supply it to the digester 140.
[0016] Furthermore, the final sedimentation tank 130 discharges, for example, the wastewater (supernatant) from which sludge has been separated through line L14 to a downstream sterilization treatment device (not shown). The sterilization treatment device (not shown) then sterilizes the wastewater discharged from the final sedimentation tank 130 via line L14 and discharges the sterilized treated water. Line L14 is, for example, a pipe connecting the final sedimentation tank 130 and the sterilization treatment device.
[0017] The digester 140, for example, uses anaerobic bacteria within the digester 140 to digest (decompose) the organic matter contained in the primary sludge supplied via line L15 and the excess sludge supplied via line L16, thereby producing digested sludge. In this case, the anaerobic bacteria in the digester 140 produce digester gas (hereinafter also simply referred to as digester gas) containing methane gas and carbon dioxide during the process of digesting organic matter.
[0018] The dehydrator 150 separates the digested sludge supplied from the digester 140 via line L17 into solids and a separated liquid (hereinafter also simply referred to as the separated liquid). Line L17 is, for example, a pipe that connects the digester 140 and the dehydrator 150. Then, the dehydrator 150 supplies the separated liquid from line L18 to the ammonia recovery device 160. Line L18 is, for example, a pipe that connects the dehydrator 150 and the ammonia recovery device 160. Also, the dehydrator 150 supplies the digested sludge (solids) from which the separated liquid has been separated to subsequent equipment (not shown) such as an incinerator via line L20. Line L20 is, for example, a pipe that connects the dehydrator 150 and subsequent equipment such as an incinerator.
[0019] The ammonia recovery device 160 recovers the ammonia contained in the separated liquid supplied from the dehydrator 150 via line L18. Specifically, the ammonia recovery device 160 performs ammonia recovery, for example, by stripping, zeolite adsorption / desorption, etc. Then, the ammonia recovery device 160 supplies the recovered ammonia to the methanation device 10 via line L3. Line L3 is, for example, a pipe that connects the ammonia recovery device 160 and the methanation device 10.
[0020] Also, the ammonia recovery device 160 supplies the separated liquid after ammonia recovery to the primary sedimentation tank 110 via line L19. Line L19 is, for example, a pipe that directly connects the ammonia recovery device 160 and the primary sedimentation tank 110, or a pipe that connects the ammonia recovery device 160 and line L11.
[0021] As shown in FIG. 1, the methanation facility 100 has, for example, a methanation device 10 that performs methanation.
[0022] Specifically, the methanation device 10 recovers, for example, the digested gas generated in the digester 140. Then, the methanation device 10 performs methanation by reacting, for example, the carbon dioxide and methane contained in the recovered digested gas with the ammonia recovered in the ammonia recovery device 160.
[0023] In other words, in the methanation equipment 100 of this embodiment, methane is produced by using (reusing) carbon dioxide generated as a result of wastewater treatment in the wastewater treatment equipment 1000 (digestion tank 140).
[0024] As a result, the methanation equipment 100 in this embodiment can effectively utilize carbon dioxide generated in, for example, the wastewater treatment equipment 1000. Therefore, the methanation equipment 100 can, for example, reduce the amount of carbon dioxide emitted from the wastewater treatment equipment 1000.
[0025] The following description will focus on the case where methane is produced using ammonia recovered in the ammonia recovery device 160, but is not limited to this. The methanation equipment 100 in this embodiment may, for example, produce methane using ammonia other than the ammonia recovered in the ammonia recovery device 160 (for example, commercially available ammonia).
[0026] [Details of the methanation equipment 100 in the first embodiment] Next, we will describe the details of the methanation equipment 100 in the first embodiment. Figure 2 is a diagram illustrating the configuration of the methanation equipment 100 in the first embodiment.
[0027] In this embodiment, the methanation equipment 100 includes, in addition to the methanation device 10, a pretreatment device 20 and a nitrogen separation device 30.
[0028] The pretreatment device 20 removes harmful substances contained in the digester gas supplied from the digester tank 140 via line L1. Specifically, the pretreatment device 20 removes, for example, sulfur compounds including hydrogen sulfide and siloxanes from the digester gas. Line L1 is, for example, piping connecting the digester tank 140 and the pretreatment device 20. The pretreatment device 20 then supplies the digester gas from which harmful substances have been removed to the methanation device 10 via line L4. Line L4 is, for example, piping connecting the pretreatment device 20 and the methanation device 10.
[0029] The pretreatment device 20 may also include, for example, a removal device (not shown) for removing hydrogen sulfide and other substances contained in the digester gas, and a removal device (not shown) for removing other sulfur compounds and siloxanes contained in the digester gas.
[0030] The methanation device 10 generates methane by reacting, for example, carbon dioxide and methane contained in the digester gas supplied from the pretreatment device 20 via line L4 with ammonia supplied from the ammonia recovery device 160 via line L3.
[0031] Specifically, the methanation apparatus 10 uses, for example, a Ni-based catalyst or a Ru-based catalyst to carry out the reaction as shown in Equation 1 below.
[0032]
number
[0033] Thus, in the methanation equipment 100 of this embodiment, methane is produced, for example, by reacting carbon dioxide contained in the digester gas with ammonia.
[0034] As a result, the methanation equipment 100 in this embodiment can suppress, for example, the amount of heat generated during the catalytic reaction of methanation. Therefore, the methanation equipment 100 can suppress, for example, the generation of localized high temperatures during the catalytic reaction of methanation, eliminating the need to use a methanation device 10 equipped with a localized cooling function.
[0035] Furthermore, in the methanation equipment 100 of this embodiment, for example, methanation is performed using digester gas containing methane and carbon dioxide without separating the methane and carbon dioxide contained in the digester gas generated in the digester tank 140.
[0036] As a result, in the methanation equipment 100 of this embodiment, the rate of heat generation can be mitigated by, for example, the presence of pre-contained methane that does not contribute to the catalytic reaction of methanation. Therefore, in the methanation equipment 100, as in the case described above, it becomes possible to suppress the generation of localized high temperatures during the catalytic reaction of methanation, eliminating the need to use a methanation device 10 equipped with a localized cooling function. Furthermore, in the methanation equipment 100, for example, it becomes unnecessary to use a device (for example, a carbon dioxide separation device or recovery device) to separate methane and carbon dioxide contained in the digester gas generated in the digester tank 140.
[0037] Therefore, in the methanation equipment 100, for example, it becomes possible to simplify the structure of the methanation device 10, and thus reduce the costs associated with methane production.
[0038] In the methanation process performed in the methanation device 10, nitrogen and water are produced in addition to methane, as shown in Equation 1 above. Therefore, as shown in Figure 2, the methanation device 10 discharges water (condensed water) to the outside via line L7, for example. Line L7 is, for example, a pipe connecting the methanation device 10 to the outside of the building (not shown) in which the methanation device 10 is installed. Furthermore, as shown in Figure 2, the methanation device 10 supplies a gas containing methane and nitrogen (hereinafter also referred to as mixed gas) to the nitrogen separation device 30 via line L5, for example. Line L5 is, for example, a pipe connecting the methanation device 10 and the nitrogen separation device 30.
[0039] The nitrogen separation unit 30 separates methane and nitrogen contained in the mixed gas supplied from the methanation unit 10 via line L5. The nitrogen separation unit 30 then discharges the nitrogen to the outside via line L6. Line L6 is, for example, a pipe connecting the nitrogen separation unit 30 to the outside of the building (not shown) in which the nitrogen separation unit 30 is installed. The nitrogen separation unit 30 also supplies methane to other devices such as power generators and boilers (hereinafter simply referred to as "other devices") via line L2. Line L2 is, for example, a pipe connecting the nitrogen separation unit 30 to the other devices. In other words, the nitrogen separation unit 30 supplies methane to other devices that use methane as fuel, for example.
[0040] In the above example, we have described a case where the methanation device 10 supplies the mixed gas to the nitrogen separation device 30, but the explanation is not limited to this. The methanation device 10 may, for example, directly supply the mixed gas to other devices.
[0041] [Method for producing methane in the first embodiment] Next, the methane production method in the first embodiment will be described. Figure 3 is a flowchart illustrating the methane production method in the first embodiment.
[0042] The digester 140 generates digester gas containing methane and carbon dioxide by digesting (decomposing) organic matter contained in, for example, the primary sludge supplied from the primary sedimentation tank 110 and the excess sludge supplied from the final sedimentation tank 130. The methanation equipment 100 then recovers the digester gas generated in the digester 140 (step S1 in Figure 3).
[0043] Furthermore, the ammonia recovery device 160 recovers ammonia contained in the separated liquid supplied from the dewatering machine 150, for example (step S2 in Figure 3).
[0044] Subsequently, the methanation equipment 100 generates methane by reacting, for example, the methane and carbon dioxide contained in the digester gas recovered in step S1 with the ammonia recovered by the ammonia recovery device 160 in step S2 (step S3 in Figure 3).
[0045] Thus, the methanation equipment 100 in this embodiment recovers methane and carbon dioxide generated during the treatment of wastewater in the wastewater treatment equipment 1000, and generates methane by reacting the recovered gas containing methane and carbon dioxide (hereinafter also referred to as the first gas) with a gas containing ammonia (hereinafter also referred to as the second gas).
[0046] Specifically, the wastewater treatment facility 1000 includes, for example, a digester 140 that digests organic matter contained in sludge separated from the wastewater. The methanation facility 100 then recovers the digester gas generated during the digestion of sludge in the digester 140. In this case, the methanation facility 100 also removes, for example, at least one of sulfur compounds (e.g., hydrogen sulfide) and siloxanes contained in the recovered digester gas.
[0047] Furthermore, the ammonia recovery device 160 in this embodiment recovers ammonia generated during the treatment of wastewater in the wastewater treatment facility 1000, for example. Specifically, the ammonia recovery device 160 recovers ammonia from sludge discharged from the digester 140, for example. The methanation facility 100 then generates methane, for example, by using the ammonia recovered by the ammonia recovery device 160.
[0048] As a result, the methanation equipment 100 in this embodiment can effectively utilize the carbon dioxide generated in the digester 140, for example. Therefore, the methanation equipment 100 can suppress the amount of carbon dioxide emitted from the wastewater treatment equipment 1000, for example. In other words, the methanation equipment 100 can achieve negative emissions by generating methane from the carbon dioxide generated in the digester 140, for example.
[0049] Furthermore, in the methanation equipment 100 of this embodiment, by performing methanation using ammonia contained in the separated liquid separated from digested sludge, for example, it becomes possible to suppress the amount of ammonia contained in the separated liquid supplied to the primary sedimentation tank 110 (the separated liquid supplied to the primary sedimentation tank 110 via line L19). As a result, the methanation equipment 100 can suppress the amount of ammonia supplied to the reaction tank 120, for example, and suppress the amount of oxygen required for the denitrification of the nitrogen components contained in ammonia. Consequently, the methanation equipment 100 can suppress the amount of oxygen that needs to be supplied into the reaction tank 120 (i.e., aeration costs).
[0050] In the above example, we described a case where methane is produced by reacting carbon dioxide contained in the digester gas generated in the digester tank 140 with ammonia, but hydrogen may be used instead of ammonia. Specifically, in the methanation equipment 100, methane may be produced by reacting carbon dioxide contained in the digester gas with hydrogen produced from renewable energy or commercially available hydrogen.
[0051] [Methanation equipment 200 in the second embodiment] Next, we will describe the methanation equipment 200 in the second embodiment. Figure 4 is a diagram illustrating the configuration of the methanation equipment 200 in the second embodiment. Below, we will explain the differences from the methanation equipment 100 in the first embodiment.
[0052] The methanation equipment 200, like the methanation equipment 100, is equipment that generates methane by performing methanation, and can be used, for example, in place of the methanation equipment 100 in a wastewater treatment facility 1000.
[0053] Specifically, the methanation facility 200, like the methanation facility 100, includes, for example, a methanation device 10 and a pretreatment device 20. However, unlike the methanation facility 100, the methanation facility 200 also includes, for example, an ammonia generator 40.
[0054] The ammonia generator 40 produces ammonia by reacting nitrogen contained in the mixed gas supplied from the methanation device 10 via line L31 with hydrogen supplied from an external source via line L32. Line L31 is, for example, a pipe connecting the methanation device 10 and the ammonia generator 40. Line L32 is, for example, a pipe connecting the hydrogen supply source and the ammonia generator 40. The hydrogen supplied to the ammonia generator 40 may be, for example, hydrogen produced from renewable energy or commercially available hydrogen.
[0055] Specifically, the ammonia generator 40 is carried out by a reaction as shown in Equation 2 below, for example, by using an iron-based catalyst.
[0056]
number
[0057] The ammonia generator 40 then supplies the generated ammonia to the methanation device 10 via line L33. Line L33 is, for example, a pipe that directly connects the ammonia generator 40 and the methanation device 10, or a pipe that connects the ammonia generator 40 and line L3.
[0058] In other words, the ammonia generator 40 in this embodiment generates ammonia by using nitrogen generated in the methanation device 10, for example, and supplies the generated ammonia to the methanation device 10.
[0059] As a result, in the methanation equipment 200 of this embodiment, methanation can be performed by using, for example, the ammonia recovered in the ammonia recovery device 160 as well as the ammonia generated in the ammonia generation device 40.
[0060] The ammonia generator 40 supplies methane contained in the mixed gas supplied from the methanation device 10 to other devices (such as power generators and boilers) via line L34. Line L34 is, for example, piping that connects the ammonia generator 40 to other devices. The ammonia generator 40 also supplies water (condensed water) formed by the condensation of water vapor contained in the mixed gas supplied from the methanation device 10 to the outside via line L35. Line L35 is, for example, piping that connects the ammonia generator 40 to the outside of the building (not shown) in which the ammonia generator 40 is installed.
[0061] Alternatively, a device for removing water vapor from the mixed gas containing methane, nitrogen, and water vapor generated in the methanation device 10 (in other words, a device that condenses the water vapor from this mixed gas and removes it as condensed water) may be installed between the methanation device 10 and the ammonia generator 40, and the gas with a reduced water vapor content may be supplied to the ammonia generator 40.
[0062] [Methane production method in the second embodiment] Next, the methane production method in the second embodiment will be described. Figure 5 is a flowchart illustrating the methane production method in the second embodiment.
[0063] The digester 140 generates digester gas containing methane and carbon dioxide by digesting (decomposing) organic matter contained in, for example, the primary sludge supplied from the primary sedimentation tank 110 and the excess sludge supplied from the final sedimentation tank 130. The methanation equipment 100 then recovers the digester gas generated in the digester 140 (step S11 in Figure 5).
[0064] Furthermore, the ammonia recovery device 160 recovers, for example, the ammonia contained in the separated liquid supplied from the dewatering machine 150 and the ammonia generated in step S14, which will be described later (step S12 in Figure 5).
[0065] Subsequently, the methanation equipment 100 generates methane by reacting, for example, the methane and carbon dioxide contained in the digester gas recovered in step S11 with the ammonia recovered in step S12 (step S13 in Figure 5).
[0066] Furthermore, the ammonia generator 40 generates ammonia by reacting the nitrogen produced together with methane in step S13 with hydrogen supplied from a hydrogen source (step S14 in Figure 5).
[0067] Thus, the methanation equipment 100 in this embodiment produces methane and nitrogen by reacting a first gas and a second gas, for example. The methanation equipment 100 then includes a step of producing ammonia by reacting the nitrogen-containing gas with a hydrogen-containing gas, and further producing methane by reacting the produced ammonia with the first gas.
[0068] As a result, in the methanation equipment 200 of this embodiment, methanation can be performed by using, for example, the ammonia produced in the ammonia generator 40. Therefore, in the methanation equipment 200, for example, the amount of commercially available ammonia required can be reduced, and the cost required for methane production can be further reduced. [Explanation of Symbols]
[0069] 10: Methanation device 20: Pretreatment device 30: Nitrogen separation unit 40: Ammonia generation unit 100: Methanation equipment 110: Primary sedimentation tank 120: Reaction tank 130: Final sedimentation tank 140: Digestion tank 150: Dehydrator 160: Ammonia recovery equipment 200: Methanation equipment 1000: Wastewater treatment equipment L1: Line L2: Line L3: Line L4: Line L5: Line L6: Line L7: Line L11: Line L12: Line L13: Line L14: Line L15: Line L16: Line L17: Line L18: Line L19: Line L20: Line L31: Line L32: Line L33: Line L34: Line L35: Line
Claims
1. A process for recovering methane and carbon dioxide generated during wastewater treatment at a wastewater treatment facility, A step of producing methane and nitrogen by reacting the recovered methane and carbon dioxide-containing first gas with ammonia-containing second gas, A step of producing ammonia by reacting the generated nitrogen-containing gas with a hydrogen-containing gas, A method for producing methane, comprising the step of further producing methane by reacting the generated ammonia with the first gas.
2. A methanation device that recovers methane and carbon dioxide generated during wastewater treatment in a wastewater treatment facility, and generates methane and nitrogen by reacting a first gas containing the recovered methane and carbon dioxide with a second gas containing ammonia, The apparatus includes an ammonia generator that produces ammonia by reacting the generated nitrogen-containing gas with a hydrogen-containing gas, The methanation apparatus further comprises a methanation system that generates methane by reacting the generated ammonia with the first gas.
3. The wastewater treatment facility includes a digester tank for digesting organic matter contained in the sludge separated from the wastewater, The methanation system according to claim 2, wherein the methanation device recovers the digester gas generated in the digester tank during the digestion of the sludge.
4. Furthermore, the methanation system according to claim 2 or 3, further comprising an ammonia recovery device for recovering the ammonia generated in connection with the treatment of the wastewater in the wastewater treatment facility.
5. The wastewater treatment facility includes a digester tank for digesting organic matter contained in the sludge separated from the wastewater, The methanation system according to claim 4, wherein the ammonia recovery device recovers the ammonia from the sludge discharged from the digester.