Methane generation system and methane generation method

Abstract

This methane generation system includes: a methane generation device that generates methane from a first gas containing methane and carbon dioxide generated during the treatment of wastewater in a wastewater treatment facility, and that discharges a second gas containing the generated methane; and a control device that controls the generation of methane by the methane generation device. The control device controls the generation of methane by the methane generation device based on the amount of carbon dioxide included in the first gas, and at least one of the concentration of carbon dioxide in the second gas, the concentration of hydrogen in the second gas, and the concentration of carbon monoxide in the second gas.

Description

Methane generation system and methane generation method

[0001] The present disclosure relates to a methanation system and method.

[0002] In recent years, methanation has been practiced in which methane is produced by reacting carbon dioxide with hydrogen (see Patent Document 1).

[0003] JP 2013-095681 A

[0004] In the above-described methanation, for example, when carbon dioxide generated in association with the treatment of wastewater (hereinafter also referred to as water to be treated) in a wastewater treatment facility is used, the amount and concentration of carbon dioxide supplied to the system in which methanation is performed (hereinafter also referred to as methanation facility) may fluctuate, and methane production may not be stable. Therefore, in the above-described methanation, for example, a method that enables stable methane production is desired.

[0005] A methane generation system in one aspect of the present disclosure includes a methane generation device that generates methane from a first gas containing methane and carbon dioxide that is generated during the treatment of wastewater in a wastewater treatment facility and discharges a second gas containing the generated methane, and a control device that controls the generation of methane by the methane generation device, wherein the control device controls the generation of methane by the methane generation device in accordance with at least one of the concentration of carbon dioxide in the second gas, the concentration of hydrogen in the second gas, and the concentration of carbon monoxide in the second gas, and the amount of carbon dioxide contained in the first gas.

[0006] According to the methane generation system and methane generation method in one aspect of the present disclosure, it is possible to stably generate methane.

[0007] FIG. 1 is a diagram illustrating the configuration of a wastewater treatment facility 1000 in a first embodiment. FIG. 2 is a diagram illustrating the configuration of a methanation facility 100 in a first embodiment. FIG. 3 is a diagram illustrating the configuration of a methanation facility 100 in a first embodiment. FIG. 4 is a diagram illustrating the configuration of a methanation facility 100 in a first embodiment. FIG. 5 is a diagram illustrating the configuration of a methanation facility 100 in a first embodiment. FIG. 6 is a flowchart illustrating a first generation control process in a first embodiment. FIG. 7 is a diagram illustrating the configuration of a wastewater treatment facility 2000 in a second embodiment. FIG. 8 is a diagram illustrating the configuration of a methanation facility 200 in a second embodiment.

[0008] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, such description should not be interpreted in a limiting sense, and does not limit the subject matter described in the claims. Furthermore, various changes, substitutions, and modifications can be made without departing from the spirit and scope of the present disclosure. Furthermore, different embodiments can be combined as appropriate.

[0009] [Wastewater treatment facility 1000 according to a first embodiment] First, the wastewater treatment facility 1000 according to a first embodiment will be described. Fig. 1 is a diagram illustrating the configuration of the wastewater treatment facility 1000 according to the first embodiment. Note that the configuration examples of each line shown below are merely examples and are not intended to be limiting.

[0010] As shown in FIG. 1 , the wastewater treatment facility 1000 in this embodiment includes, for example, a methanation facility 100 (hereinafter also referred to as a methane generation system 100), a primary sedimentation tank 110, a reaction tank 120, a final sedimentation tank 130, a digester 140, and a dehydrator 150.

[0011] The primary sedimentation tank 110, for example, separates and settles organic matter and suspended solids (hereinafter collectively referred to as pollutants) contained in wastewater (e.g., wastewater such as sewage) discharged via line L11. Line L11 is, for example, a pipe connecting a wastewater supply source to the primary sedimentation tank 110. The primary sedimentation tank 110 then discharges the separated pollutants as primary sludge via line L15 to the digestion tank 140. Line L15 is, for example, a pipe connecting the primary sedimentation tank 110 and the digestion tank 140. The primary sedimentation tank 110 then discharges the wastewater from which pollutants have been separated via line L12 to the reaction tank 120. Line L12 is, for example, a pipe connecting the primary sedimentation tank 110 and the reaction tank 120.

[0012] The line L15 may be, for example, a pipe that connects the primary sedimentation tank 110 to a thickening tank (not shown) and further connects the thickening tank to the digestion tank 140. In this case, the thickening tank may thicken the primary sludge discharged from the primary sedimentation tank 110 and supply the thickened sludge to the digestion tank 140.

[0013] The reaction tank 120 treats the wastewater supplied from the primary sedimentation tank 110 via line L12, for example, by biological treatment using activated sludge (for example, biological treatment using a standard activated sludge process or a circulating nitrification-denitrification process). The reaction tank 120 then discharges the wastewater after biological treatment via line L13 to the final sedimentation tank 130. The line L13 is, for example, a pipe connecting the reaction tank 120 and the final sedimentation tank 130.

[0014] The final settling tank 130, for example, settles and separates sludge contained in the wastewater discharged from the reaction tank 120 via line L13. The final settling tank 130 then returns, for example, a portion of the settled and separated sludge to the reaction tank 120 via lines L16 and L20 as returned sludge. Line L16 is, for example, a pipe connecting the final settling tank 130 to line L15. Line L20 is, for example, a pipe connecting line L16 to the reaction tank 120. The final settling tank 130 then discharges, for example, the settled and separated sludge other than the returned sludge to the digestion tank 140 via lines L16 and L15 as excess sludge.

[0015] The line L16 may be, for example, a pipe that connects the final settling tank 130 to a thickener (not shown) and further connects the thickener to the line L15. The thickener may be, for example, a pipe that thickens excess sludge discharged from the final settling tank 130 and supplies the sludge to the digester 140.

[0016] The final settling tank 130 also discharges wastewater (supernatant) from which sludge has been separated, via line L14, to a downstream sterilization treatment device (not shown). Line L14 is, for example, a pipe connecting the final settling tank 130 to the sterilization treatment device. The sterilization treatment device (not shown) then sterilizes the wastewater discharged from the final settling tank 130 via line L14, and discharges the sterilized treated water.

[0017] The digestion tank 140 produces digested sludge by, for example, using anaerobic bacteria in the digestion tank 140 to digest (decompose) organic matter contained in the primary sludge supplied via line L15 and the excess sludge supplied via lines L16 and L15. Specifically, the anaerobic bacteria in the digestion tank 140 produce, for example, a digestion gas (hereinafter also simply referred to as a first gas) containing methane and carbon dioxide during the process of digesting the organic matter.

[0018] The dehydrator 150 separates the digested sludge supplied from the digester 140 via, for example, line L17 into solids and a separation liquid (hereinafter also simply referred to as separation liquid). Line L17 is, for example, a pipe connecting the digester 140 and the dehydrator 150. The dehydrator 150 then supplies, for example, the separation liquid to the primary sedimentation tank 110 via line L18. Line L18 is, for example, a pipe connecting the dehydrator 150 and line L11. The dehydrator 150 then supplies, for example, the digested sludge (solids) from which the separation liquid has been separated to downstream equipment (not shown), such as an incinerator, via line L19. Line L19 is, for example, a pipe connecting the dehydrator 150 and downstream equipment, such as an incinerator.

[0019] As shown in FIG. 1, the methanation facility 100 includes, for example, a methanation device 10 (hereinafter also referred to as a methane generation device 10) that performs methanation.

[0020] Specifically, the methanation device 10 recovers, for example, a first gas generated in the digestion tank 140. The methanation device 10 then performs methanation by, for example, reacting carbon dioxide and methane contained in the recovered first gas with hydrogen contained in a gas (hereinafter also referred to as a third gas) supplied from a hydrogen supply device (not shown) that supplies (stores) hydrogen. The hydrogen supplied to the methanation device 10 may be, for example, hydrogen produced by electrolysis of water using renewable energy, or commercially available hydrogen.

[0021] That is, in the methanation facility 100 of this embodiment, methane is produced by using (reusing) carbon dioxide generated in conjunction with the treatment of wastewater in the wastewater treatment facility 1000 (digestion tank 140).

[0022] This allows the methanation facility 100 in this embodiment to effectively utilize, for example, carbon dioxide generated in the wastewater treatment facility 1000. Therefore, the methanation facility 100 can suppress, for example, the amount of carbon dioxide emitted from the wastewater treatment facility 1000.

[0023] [Details of the methanation facility 100 in the first embodiment] Next, details of the methanation facility 100 in the first embodiment will be described. Figures 2 to 5 are diagrams illustrating the configuration of the methanation facility 100 in the first embodiment.

[0024] As shown in FIG. 2 , the methanation facility 100 in this embodiment includes, for example, a pretreatment device 20 in addition to the methanation device 10 .

[0025] As shown in Fig. 2, the pretreatment device 20 removes harmful substances contained in the first gas supplied from the digestion tank 140 via, for example, line L1. Specifically, the pretreatment device 20 removes, for example, sulfur compounds including hydrogen sulfide, siloxanes, and the like from the first gas. Line L1 is, for example, a pipe connecting the digestion tank 140 and the pretreatment device 20. The pretreatment device 20 then supplies the first gas from which the harmful substances have been removed to the methanation device 10 via line L4. Line L4 is, for example, a pipe connecting the pretreatment device 20 and the methanation device 10.

[0026] The pretreatment device 20 may include, for example, a removal device (not shown) for removing hydrogen sulfide and the like contained in the first gas, and a removal device (not shown) for removing other sulfur compounds, siloxanes, and the like contained in the first gas.

[0027] The methanation device 10 generates methane by, for example, reacting carbon dioxide and methane contained in the first gas supplied from the pretreatment device 20 via line L4 with hydrogen supplied from a hydrogen supply device via line L3. Line L3 is, for example, a pipe connecting the hydrogen supply device and the methanation device 10. The methanation device 10 then supplies the generated methane-containing gas (hereinafter also referred to as the second gas) via line L2 to another device (hereinafter simply referred to as the other device), such as a power generation device or a boiler. Line L2 is, for example, a pipe connecting the methanation device 10 to the other device. That is, the methanation device 10 supplies methane to, for example, another device that uses methane as fuel. The methanation device 10 also supplies the second gas to, for example, an existing gas pipe (not shown).

[0028] Specifically, the methanation device 10 uses, for example, a Ni-based catalyst or a Ru-based catalyst to cause a reaction as shown in the following formula 1.

[0029]

[0030] In this way, in the methanation facility 100 of this embodiment, methanation is performed using the first gas that contains methane, for example, without separating the methane and carbon dioxide contained in the first gas generated in the digestion tank 140.

[0031] As a result, in the methanation system 100 of this embodiment, for example, the presence of methane already present in the system that does not contribute to the methanation catalytic reaction can slow the rate of heat generation. Therefore, in the methanation system 100, similar to the above case, for example, it is possible to suppress the generation of localized high temperatures during the methanation catalytic reaction, thereby reducing the need for localized cooling. Furthermore, in the methanation system 100, for example, there is no need to use a device (for example, a carbon dioxide separation device or recovery device) that separates the methane and carbon dioxide contained in the first gas generated in the digester 140.

[0032] Therefore, in the methanation facility 100, for example, it is possible to simplify the structure of the methanation device 10, and to reduce the costs associated with the production of methane.

[0033] Note that in the methanation performed in the methanation device 10, water is produced in addition to methane, for example, as shown in the above formula 1. Therefore, the methanation device 10 discharges water (condensed water) to the outside, for example, via line L7, as shown in Fig. 2. Line L7 is, for example, a pipe connecting the methanation device 10 to the outside of a building (not shown) in which the methanation device 10 is installed.

[0034] As shown in FIG. 3, the methanation facility 100 in this embodiment also includes a control device 40 that can communicate with the methanation device 10 via a network NW such as the Internet.

[0035] The control device 40 is, for example, an electronic device having an electronic circuit. Specifically, as shown in FIG. 4 , the control device 40 is, for example, a computer device having a CPU (Central Computing Unit) 401, which is a processor, a memory 402, a communication device 403, and a storage medium 404. The various components are connected to each other, for example, via a bus 405. The control device 40 then performs, for example, a process for controlling the generation of methane in the methanation device 10 (hereinafter also referred to as a first generation control process).

[0036] The storage medium 404 has, for example, a program storage area (not shown) that stores a program 410 for performing the first generation control process. The storage medium 404 also has, for example, a storage unit 430 (hereinafter also referred to as information storage area 430) that stores various information required to perform the first generation control process. Specifically, the storage medium 404 may be, for example, a hard disk drive (HDD) or a solid state drive (SSD).

[0037] The CPU 401 performs the first generation control process by executing, for example, a program 410 loaded from the storage medium 404 into the memory 402 .

[0038] The communication device 403 communicates with, for example, the methanation device 10. The communication device 403 also communicates with, for example, an operation terminal (hereinafter simply referred to as the operation terminal) through which an administrator of the methanation facility 100 (hereinafter simply referred to as the administrator) inputs necessary information.

[0039] The electronic circuit of the control device 40 may be, for example, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). In this case, the first generation control process may be executed in, for example, the FPGA or the ASIC.

[0040] The control device 40 then performs the first generation control process by using values ​​measured by the respective measuring devices attached to the methanation device 10, for example.

[0041] Specifically, as shown in FIG. 5 , the control device 40 performs the first generation control process by using values ​​measured by, for example, a flow meter Q1, a concentration meter C1, and a thermometer T1 attached to line L4; a flow meter Q2, a concentration meter C2, and a thermometer T2 attached to line L2; a flow meter Q3 and a thermometer T3 attached to line L3; and a flow meter Q4 and a thermometer T4 attached to line L8. Line L8 is, for example, a piping (annular piping) connecting the methanation device 10 to a cooling water circulation device (not shown) that circulates cooling water. The flow meter Q1, the concentration meter C1, and the thermometer T1 are measuring devices that measure, for example, the flow rate, concentration, and temperature of the first gas supplied from the digester 140 (pretreatment device 20) to the methanation device 10. The flow meter Q2, the concentration meter C2, and the thermometer T2 are measuring devices that measure, for example, the flow rate, concentration, and temperature of the second gas containing methane generated in the methanation device 10. Furthermore, the flow meter Q3 and the thermometer T3 are measuring devices that measure, for example, the flow rate and temperature of the third gas supplied from the hydrogen supply device to the methanation device 10. Furthermore, the flow meter Q4 and the thermometer T4 are measuring devices that measure, for example, the flow rate and temperature of the cooling water supplied from the cooling water circulation device to the methanation device 10.

[0042] That is, the control device 40 in this embodiment controls the flow rates of the first gas (gas containing carbon dioxide and methane) and the third gas (gas containing hydrogen) supplied to the methanation device 10, for example, so as to suppress the concentrations of gases other than methane in the second gas produced in the methanation device 10. Specifically, the control device 40 controls the flow rates of the first gas and the third gas supplied to the methanation device 10, for example, so as to suppress the generation of carbon dioxide and hydrogen that are not used in the production of methane in the methanation device 10. Furthermore, the control device 40 controls the flow rates of the first gas and the cooling water supplied to the methanation device 10, for example, so as to suppress the generation of carbon monoxide associated with the production of methane in the methanation device 10.

[0043] As a result, the methanation facility 100 of this embodiment can produce, for example, high-purity methane. Therefore, the methanation facility 100 can produce methane that meets the standards required by the supply destination, for example.

[0044] The concentration meter C1 may measure, for example, the concentration of carbon dioxide in the first gas, and the concentration meter C2 may measure, for example, at least one of the concentrations of carbon dioxide, carbon monoxide, and hydrogen in the second gas.

[0045] Furthermore, the control device 40 may, for example, obtain measurement values ​​from each of the flow meter Q1, concentration meter C1, thermometer T1, flow meter Q2, concentration meter C2, thermometer T2, flow meter Q3, thermometer T3, flow meter Q4 and thermometer T4 (hereinafter collectively referred to as simply flow meter Q1, etc.) at predetermined intervals such as one minute.

[0046] [First Generation Control Process in First Embodiment] Next, the first generation control process in the first embodiment will be described with reference to Fig. 6, which is a flowchart illustrating the first generation control process in the first embodiment.

[0047] The control device 40 measures, for example, the flow rate of carbon dioxide contained in the first gas supplied from the digestion tank 140 to the methanation device 10 (step S1 in FIG. 6).

[0048] Specifically, the control device 40 measures, for example, the flow rate of the first gas measured by a flow meter Q1 attached to line L4 and the concentration of carbon dioxide in the first gas measured by a concentration meter C1 attached to line L4. Then, the control device 40 calculates the flow rate of carbon dioxide contained in the first gas by, for example, multiplying the measured flow rate of the first gas by the measured concentration of carbon dioxide in the first gas.

[0049] Furthermore, the control device 40 measures, for example, the concentration of at least one of carbon dioxide, hydrogen, and carbon monoxide in the second gas supplied from the methanation device 10 (step S2 in FIG. 6).

[0050] Specifically, the control device 40 measures the concentration of at least one of carbon dioxide, hydrogen, and carbon monoxide in the second gas, for example, using a concentration meter C2 attached to the line L2.

[0051] Then, the control device 40 controls the methanation device 10 in accordance with the measurement results in steps S1 and S2 (step S3 in FIG. 6), for example.

[0052] Specifically, the control device 40 controls the amount of hydrogen contained in the third gas supplied from the hydrogen supply device to the methanation device 10, for example, in accordance with the flow rate of carbon dioxide measured in step S1.

[0053] More specifically, the control device 40 calculates the amount of hydrogen (hereinafter also referred to as the first amount) required to produce methane using carbon dioxide at the flow rate measured in step S1, for example, by following the above-mentioned formula 1. Then, the control device 40 controls, for example, the amount of hydrogen supplied from the hydrogen supply device to the methanation device 10 (the amount of hydrogen contained in the third gas) so that it becomes the first amount.

[0054] In addition, the control device 40 controls at least one of the amount of carbon dioxide contained in the first gas and the amount of hydrogen contained in the third gas, for example, depending on the concentration of carbon dioxide measured in step S2.

[0055] Specifically, for example, when the carbon dioxide concentration measured in step S2 is equal to or greater than a predetermined threshold value (hereinafter also referred to as the first threshold value), the control device 40 performs at least one of control to reduce the amount of carbon dioxide supplied to the methanation device 10 and control to increase the amount of hydrogen supplied to the methanation device 10.

[0056] That is, the above formula 1 indicates, for example, that new carbon dioxide is not produced in conjunction with the production of methane. Therefore, a case in which the concentration of carbon dioxide measured in step S2 is high can be determined, for example, as a case in which the proportion of carbon dioxide that is not used in the production of methane out of the carbon dioxide supplied to the methanation device 10 is high. In other words, a case in which the concentration of carbon dioxide measured in step S2 is high can be determined, for example, as a case in which the carbon dioxide supplied to the methanation device 10 is in excess in the methanation device 10.

[0057] Therefore, in this case, the control device 40 reduces the amount of carbon dioxide that is not used in the production of methane in the methanation device 10, for example, by reducing the amount of carbon dioxide supplied to the methanation device 10.

[0058] Furthermore, when the concentration of carbon dioxide measured in step S2 is high, it can also be determined that the amount of hydrogen supplied to the methanation device 10 is insufficient in the methanation device 10, for example.

[0059] Therefore, in this case, the control device 40 may increase the amount of methane produced in the methanation device 10, for example, by increasing the amount of hydrogen supplied to the methanation device 10, thereby suppressing the generation of carbon dioxide that is not used in the production of methane.

[0060] This enables the control device 40 to, for example, reduce the concentration of carbon dioxide in the second gas.

[0061] In step S2, the control device 40 may measure, for example, the concentration of carbon dioxide in the second gas measured by a concentration meter C2 attached to line L2 and the flow rate of the second gas measured by a flow meter Q2 attached to line L2. Then, when the product of the concentration and flow rate measured in step S2 (i.e., the amount of carbon dioxide contained in the second gas) is equal to or greater than a predetermined threshold, the control device 40 may perform at least one of control to decrease the amount of carbon dioxide supplied to the methanation device 10 and control to increase the amount of hydrogen supplied to the methanation device 10.

[0062] In addition, the control device 40 controls at least one of the amount of cooling water supplied to the methanation device 10 and the amount of carbon dioxide contained in the first gas, for example, depending on the concentration of carbon monoxide measured in step S2.

[0063] Specifically, for example, when the carbon monoxide concentration measured in step S2 is equal to or greater than a predetermined threshold value (hereinafter also referred to as the second threshold value), the control device 40 performs at least one of control to increase the amount of cooling water supplied to the methanation device 10 and control to decrease the amount of carbon dioxide supplied to the methanation device 10.

[0064] That is, the above formula 1 indicates that, for example, carbon monoxide is not produced in conjunction with the production of methane. Therefore, when the carbon monoxide concentration measured in step S2 is high, it can be determined that, for example, the methane production reaction in the methanation device 10 is actively carried out, resulting in a rise in the temperature inside the methanation device 10 due to the heat of reaction of methane, and carbon monoxide is produced along with the production of methane.

[0065] Therefore, in this case, the control device 40 reduces the temperature inside the methanation device 10 and suppresses the generation of carbon monoxide, for example, by increasing the amount of cooling water supplied to the methanation device 10. In addition, in this case, the control device 40 reduces the amount of carbon dioxide supplied to the methanation device 10, for example, to suppress the amount of methane produced in the methanation device 10, thereby lowering the temperature inside the methanation device 10 and suppressing the generation of carbon monoxide.

[0066] This enables the control device 40 to reduce the concentration of carbon monoxide in the second gas, for example.

[0067] The control device 40 may, for example, measure the temperature of the second gas supplied from the methanation device 10. Specifically, the control device 40 may, for example, measure the temperature of the second gas using a thermometer T2 attached to the line L2. When the temperature of the second gas is equal to or higher than a predetermined threshold, the control device 40 may, for example, reduce the concentration of carbon monoxide in the second gas by performing at least one of control to increase the amount of cooling water supplied to the methanation device 10 and control to decrease the amount of carbon dioxide supplied to the methanation device 10.

[0068] In step S2, the control device 40 may measure, for example, the concentration of carbon monoxide in the second gas measured by a concentration meter C2 attached to line L2 and the flow rate of the second gas measured by a flow meter Q2 attached to line L2. Then, for example, when the product of the concentration and flow rate measured in step S2 (i.e., the amount of carbon monoxide contained in the second gas) is equal to or greater than a predetermined threshold, the control device 40 may perform at least one of control to increase the amount of cooling water supplied to the methanation device 10 and control to decrease the amount of carbon dioxide supplied to the methanation device 10.

[0069] Furthermore, the control device 40 controls at least one of the amount of hydrogen contained in the third gas and the amount of carbon dioxide contained in the first gas, for example, depending on the concentration of hydrogen measured in step S2.

[0070] Specifically, for example, when the hydrogen concentration measured in step S2 is equal to or greater than a predetermined threshold value (hereinafter also referred to as the third threshold value), the control device 40 performs at least one of control to reduce the amount of hydrogen supplied to the methanation device 10 and control to increase the amount of carbon dioxide supplied to the methanation device 10.

[0071] That is, the above formula 1 indicates, for example, that hydrogen is not produced in conjunction with the production of methane. Therefore, a case in which the hydrogen concentration measured in step S2 is high can be determined, for example, as a case in which the proportion of hydrogen that is not used in the production of methane out of the hydrogen supplied to the methanation device 10 is high. In other words, a case in which the hydrogen concentration measured in step S2 is high can be determined, for example, as a case in which the hydrogen supplied to the methanation device 10 is in excess in the methanation device 10.

[0072] Therefore, in this case, the control device 40 reduces the amount of hydrogen that is not used in the production of methane in the methanation device 10, for example, by reducing the amount of hydrogen supplied to the methanation device 10.

[0073] Furthermore, when the hydrogen concentration measured in step S2 is high, it can also be determined that the carbon dioxide supplied to the methanation device 10 is insufficient in the methanation device 10, for example.

[0074] Therefore, in this case, the control device 40 may increase the amount of methane produced in the methanation device 10, for example, by increasing the amount of carbon dioxide supplied to the methanation device 10, thereby suppressing the generation of hydrogen that is not used to produce methane.

[0075] This allows the control device 40 to, for example, reduce the concentration of hydrogen in the second gas.

[0076] In step S2, the control device 40 may measure, for example, the concentration of hydrogen in the second gas measured by a concentration meter C2 attached to line L2 and the flow rate of the second gas measured by a flow meter Q2 attached to line L2. Then, when the product of the concentration and flow rate measured in step S2 (i.e., the amount of hydrogen in the second gas) is equal to or greater than a predetermined threshold, the control device 40 may perform at least one of control to decrease the amount of hydrogen supplied to the methanation device 10 and control to increase the amount of carbon dioxide supplied to the methanation device 10.

[0077] As described above, the methanation facility 100 in this embodiment includes, for example, a methanation device 10 that generates methane from a first gas containing methane and carbon dioxide that is generated during wastewater treatment in the wastewater treatment facility 1000, and discharges the generated second gas containing methane. The methanation facility 100 also includes, for example, a control device 40 that controls the generation of methane by the methanation device 10. The control device 40 controls the generation of methane by the methanation device 10 in accordance with, for example, at least one of the concentration of carbon dioxide in the second gas, the concentration of hydrogen in the second gas, and the concentration of carbon monoxide in the second gas, and the amount of carbon dioxide contained in the first gas.

[0078] Specifically, the methanation device 10 generates methane by, for example, reacting a first gas with a third gas containing hydrogen.

[0079] The control device 40 then controls the amount of hydrogen contained in the third gas in accordance with the amount of carbon dioxide contained in the first gas, for example.

[0080] Furthermore, the control device 40 controls at least one of the amount of carbon dioxide contained in the first gas and the amount of hydrogen contained in the third gas, for example, in accordance with the concentration of carbon dioxide in the second gas.

[0081] Furthermore, the control device 40 controls at least one of the amount of cooling water supplied to the methanation device and the amount of carbon dioxide contained in the first gas, for example, depending on the concentration of carbon monoxide in the second gas.

[0082] Furthermore, the control device 40 controls at least one of the amount of hydrogen contained in the third gas and the amount of carbon dioxide contained in the first gas, for example, in accordance with the concentration of hydrogen in the second gas.

[0083] This enables the control device 40 in the present embodiment to suppress, for example, the concentrations of gases other than methane in the second gas. Specifically, for example, the control device 40 can stably suppress the concentrations of gases other than methane in the second gas even when the concentrations (amounts) of gases contained in the first gas fluctuate due to the properties of sludge, etc., as in the case where the first gas is digester gas, and the concentrations (amounts) of gases in the second gas fluctuate. Furthermore, the control device 40 can stably suppress the concentrations of gases other than methane in the second gas even when the concentrations (amounts) of gases in the second gas fluctuate due to changes in reaction conditions, such as temperature changes in the methanation equipment 100 accompanying methane production or deterioration over time of a catalyst used for methane production.

[0084] Therefore, the methanation facility 100 of this embodiment can stably produce, for example, high-purity methane. Therefore, the methanation facility 100 can produce methane that meets the standards required by the supply destination, for example.

[0085] In the above example, the methanation facility 100 includes one methanation device 10, but the present invention is not limited to this. Specifically, the methanation facility 100 may include, for example, a plurality of methanation devices 10 arranged in series. The control device 40 may control the generation of methane in each of the plurality of methanation devices 10 by using, for example, measurement results of the gas (first gas) supplied to each methanation device 10 and measurement results of the gas (second gas) supplied from each methanation device 10.

[0086] Furthermore, the control device 40 may determine whether the measurement value of each measuring device, such as the flowmeter Q1, is within a predetermined normal range for that measuring device. If the control device 40 detects the presence of a measuring device whose measurement value is outside the normal range, the control device 40 may output information indicating the detected measuring device to the operation terminal.

[0087] The control device 40 may adjust the amount of carbon dioxide supplied to the methanation device 10 (the amount of carbon dioxide contained in the first gas) by, for example, adjusting the aperture of a valve (not shown) installed in a fan, blower, or compressor (not shown) that supplies the first gas from the digester 140 to the methanation device 10. The control device 40 may adjust the amount of hydrogen supplied to the methanation device 10 (the amount of hydrogen contained in the third gas) by, for example, adjusting the aperture of a valve installed in a fan, blower, or compressor that supplies the third gas from a hydrogen supply device to the methanation device 10. The control device 40 may adjust the amount of cooling water supplied to the methanation device 10 from a cooling water circulation device by, for example, adjusting the aperture of a valve (not shown) installed in a pump (not shown) that supplies cooling water from the cooling water circulation device to the methanation device 10.

[0088] Furthermore, the control device 40 may control the methanation device 10 based on the measurement results in steps S1 and S2, for example, by using a model predictive control technique that performs feedforward. Specifically, the control device 40 may, for example, appropriately adjust the amount of carbon dioxide supplied to the methanation device 10 (the amount of carbon dioxide contained in the first gas) so that the carbon dioxide concentration in the second gas discharged from the methanation device 10 is equal to or less than a first threshold value.

[0089] Furthermore, the control device 40 may control the methanation device 10 based on the measurement results in steps S1 and S2, for example, by using a learning model generated by machine learning. Specifically, the control device 40 may perform control such that the amount of carbon dioxide output from the learning model in response to an input of the carbon dioxide concentration in the second gas is used as the amount of carbon dioxide supplied to the methanation device 10 (the amount of carbon dioxide contained in the first gas).

[0090] Furthermore, the control device 40 may control the pressure inside the methanation device 10 so that methane is produced under a predetermined pressure, for example.

[0091] [Wastewater Treatment Facility 2000 in Second Embodiment] Next, a description will be given of the wastewater treatment facility 2000 in the second embodiment. Fig. 7 is a diagram illustrating the configuration of the wastewater treatment facility 2000 in the second embodiment.

[0092] As shown in FIG. 7 , the wastewater treatment facility 2000 in this embodiment includes, for example, a primary sedimentation tank 110, a reaction tank 120, a final sedimentation tank 130, a digestion tank 140, a dehydrator 150, an ammonia recovery unit 160, and a methanation facility 200.

[0093] The dehydrator 150 separates the digested sludge supplied from the digester 140 via line L17 into solids and a separated liquid, similar to the wastewater treatment equipment 1000 in the first embodiment, for example. Unlike the wastewater treatment equipment 1000 in the first embodiment, the dehydrator 150 supplies the separated liquid to the ammonia recovery unit 160 via line L21. The line L21 is, for example, a pipe connecting the dehydrator 150 and the ammonia recovery unit 160. Similarly to the wastewater treatment equipment 1000 in the first embodiment, the dehydrator 150 supplies the digested sludge (solids) from which the separated liquid has been separated via line L19 to downstream equipment (not shown), such as an incinerator.

[0094] The ammonia recovery unit 160 recovers ammonia contained in the separated liquid supplied from the dehydrator 150 via, for example, a line L21. Specifically, the ammonia recovery unit 160 recovers the ammonia by, for example, stripping or zeolite adsorption / desorption. The ammonia recovery unit 160 then supplies the recovered ammonia via, for example, a line L22 to a methanation unit 50 (described later). The line L22 is, for example, a pipe connecting the ammonia recovery unit 160 and the methanation unit 50.

[0095] Furthermore, the ammonia recovery apparatus 160 supplies, for example, a separated liquid obtained after recovering ammonia from a line L23 to the primary sedimentation tank 110. The line L23 is, for example, a pipe that directly connects the ammonia recovery apparatus 160 and the primary sedimentation tank 110, or a pipe that connects the ammonia recovery apparatus 160 and the line L11.

[0096] As shown in FIG. 7, the methanation facility 200 includes, for example, a methanation device 50 that performs methanation.

[0097] Specifically, the methanation device 50 recovers, for example, a first gas (digestion gas) generated in the digestion tank 140. Then, the methanation device 50 performs methanation by, for example, reacting carbon dioxide and methane contained in the recovered first gas with ammonia contained in gas recovered in the ammonia recovery device 160 (hereinafter also referred to as a fourth gas).

[0098] That is, in the methanation facility 200 of this embodiment, similarly to the wastewater treatment facility 1000 of the first embodiment, methane is produced by using (reusing) carbon dioxide generated in the treatment of wastewater in the wastewater treatment facility 1000 (digestion tank 140).

[0099] As a result, the methanation facility 200 of this embodiment can effectively utilize the carbon dioxide generated in the wastewater treatment facility 1000, similar to the wastewater treatment facility 1000 of the first embodiment, for example. Therefore, the methanation facility 100 can suppress the amount of carbon dioxide emitted from the wastewater treatment facility 2000, for example.

[0100] The following description will be given of a case where methane is produced by using ammonia recovered in the ammonia recovery unit 160, but the present invention is not limited to this. Specifically, the methanation facility 200 in this embodiment may produce methane by using, for example, commercially available ammonia.

[0101] [Details of the methanation facility 200 in the second embodiment] Next, details of the methanation facility 200 in the second embodiment will be described. Fig. 8 is a diagram illustrating the configuration of the methanation facility 200 in the second embodiment.

[0102] As shown in FIG. 8, the methanation facility 200 in this embodiment includes a pretreatment device 20, a nitrogen separation device 30, and a methanation device 50.

[0103] The methanation device 50 produces methane, for example, by reacting 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 L22.

[0104] Specifically, the methanation device 50 uses, for example, a Ni-based catalyst or a Ru-based catalyst to cause a reaction as shown in the following formula 2.

[0105]

[0106] Note that in the methanation performed in the methanation device 50, nitrogen and water are produced in addition to methane, for example, as shown in the above formula 2. Therefore, as shown in Fig. 8, the methanation device 50 discharges water (condensed water) to the outside, for example, via line L7. Also, as shown in Fig. 8, the methanation device 50 supplies gas containing methane and nitrogen to the nitrogen separation device 30, for example, via line L5. Line L5 is, for example, a pipe connecting the methanation device 50 and the nitrogen separation device 30.

[0107] The nitrogen separation device 30 separates methane and nitrogen contained in the gas supplied from the methanation device 50, for example, via line L5. The nitrogen separation device 30 then discharges the nitrogen to the outside, for example, via line L6. The line L6 is, for example, a pipe connecting the nitrogen separation device 30 to the outside of a building (not shown) in which the nitrogen separation device 30 is installed. The nitrogen separation device 30 also supplies the methane to other devices, such as a power generation device or a boiler, via line L2, for example.

[0108] Furthermore, the methanation equipment 200 in this embodiment has a control device 40 capable of communicating with the methanation device 50 via a network NW such as the Internet, similar to the wastewater treatment equipment 1000 in the first embodiment, for example.

[0109] The control device 40 performs, for example, a process (hereinafter also referred to as a second production control process) to control the production of methane in the methanation device 50. That is, the second production control process is a process to control the production of methane using ammonia, for example.

[0110] Specifically, unlike the first production control process, the control device 40 controls the amount of ammonia contained in the fourth gas in accordance with the flow rate of carbon dioxide contained in the first gas.

[0111] More specifically, the control device 40 calculates the amount of ammonia (hereinafter also referred to as the second amount) required to produce methane using the carbon dioxide contained in the first gas at a flow rate, for example, by using the above-described formula 2. Then, the control device 40 controls the amount of ammonia supplied from an ammonia supply device (not shown) to the methanation device 50 (the amount of ammonia contained in the fourth gas) to be the second amount.

[0112] In addition, unlike in the first generation control process, the control device 40 controls at least one of the amount of carbon dioxide contained in the first gas and the amount of ammonia contained in the fourth gas depending on the concentration of carbon dioxide in the second gas.

[0113] Specifically, for example, when the concentration of carbon dioxide in the second gas is equal to or greater than a predetermined threshold, the control device 40 performs at least one of control to reduce the amount of carbon dioxide supplied to the methanation device 50 and control to increase the amount of ammonia supplied to the methanation device 50.

[0114] In addition, the control device 40 controls at least one of the amount of cooling water supplied to the methanation device 50 and the amount of carbon dioxide contained in the first gas, depending on the concentration of carbon monoxide in the second gas, as in the first generation control process, for example.

[0115] Specifically, for example, when the concentration of carbon monoxide in the second gas is equal to or greater than a predetermined threshold, the control device 40 performs at least one of control to increase the amount of cooling water supplied to the methanation device 50 and control to decrease the amount of carbon dioxide supplied to the methanation device 50.

[0116] In addition, unlike in the first generation control process, the control device 40 controls at least one of the amount of ammonia contained in the fourth gas and the amount of carbon dioxide contained in the first gas depending on the concentration of hydrogen in the second gas.

[0117] Specifically, for example, when the concentration of hydrogen in the second gas is equal to or greater than a predetermined threshold, the control device 40 performs at least one of control to reduce the amount of ammonia supplied to the methanation device 50 and control to increase the amount of carbon dioxide supplied to the methanation device 50.

[0118] In this way, in the methanation facility 200 of this embodiment, similar to the methanation facility 100 of the first embodiment, for example, methanation is performed using the digestion gas generated in the digestion tank 140 in a state where it still contains methane and carbon dioxide, without separating the methane and carbon dioxide contained in the digestion gas.

[0119] As a result, in the methanation system 200 of this embodiment, similar to the methanation system 100 of the first embodiment, for example, the presence of methane already present in the system that does not contribute to the methanation catalytic reaction makes it possible to slow the rate of heat generation. Therefore, in the methanation system 200, for example, it is possible to suppress the generation of localized high temperatures during the methanation catalytic reaction, thereby reducing the need for localized cooling. Furthermore, in the methanation system 200, for example, there is no need to use a device (for example, a carbon dioxide separation device or recovery device) that separates the methane and carbon dioxide contained in the digestion gas generated in the digester tank 140.

[0120] Therefore, in the methanation facility 200, for example, similar to the methanation facility 100 in the first embodiment, it is possible to simplify the structure of the methanation device 50, and it is possible to reduce the costs associated with methane production.

[0121] Furthermore, the control device 40 in this embodiment can suppress the concentration of gases other than methane in the second gas, for example, similar to the control device 40 in the first embodiment. Therefore, the methanation facility 200 in this embodiment can stably produce, for example, high-purity methane. Therefore, the methanation facility 200 can produce methane that meets the standards required by the supply destination, for example.

[0122] 10: Methanation device 20: Pretreatment device 30: Nitrogen separation device 40: Control device 50: Methanation device 100: Methanation equipment 110: Primary sedimentation tank 120: Reaction tank 130: Final sedimentation tank 140: Digestion tank 150: Dehydrator 160: Ammonia recovery device 200: Methanation equipment 401: CPU 402: Memory 403: Communication device 404: Storage medium 405: Bus 410: Program 430: Information storage area 1000: Wastewater treatment equipment 2000: 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 L21: Line L22: Line L23: Line

Claims

1. A methane generation system comprising: a methane generation device that generates methane from a first gas containing methane and carbon dioxide generated during the treatment of wastewater in a wastewater treatment facility, and discharges a second gas containing the generated methane; and a control device that controls the generation of the methane by the methane generation device, wherein the control device controls the generation of the methane by the methane generation device in accordance with at least one of the concentration of carbon dioxide in the second gas, the concentration of hydrogen in the second gas, and the concentration of carbon monoxide in the second gas, and the amount of the carbon dioxide contained in the first gas.

2. The methane generation system of claim 1, wherein the methane generation device generates the methane by reacting the first gas with a third gas containing hydrogen, and the control device controls at least one of the amount of carbon dioxide contained in the first gas and the amount of hydrogen contained in the third gas depending on the concentration of carbon dioxide in the second gas.

3. The methane generation system of claim 1, wherein the methane generation device generates the methane by reacting the first gas with a third gas containing hydrogen, and the control device controls at least one of the amount of cooling water supplied to the methane generation device and the amount of carbon dioxide contained in the first gas depending on the concentration of carbon monoxide in the second gas.

4. The methane generation system of claim 1, wherein the methane generation device generates the methane by reacting the first gas with a third gas containing hydrogen, and the control device controls at least one of the amount of hydrogen contained in the third gas and the amount of carbon dioxide contained in the first gas depending on the concentration of the hydrogen in the second gas.

5. The methane generation system described in claim 1, wherein the methane generation device generates the methane by reacting the first gas with a fourth gas containing ammonia, and the control device controls at least one of the amount of carbon dioxide contained in the first gas and the amount of ammonia contained in the fourth gas depending on the concentration of carbon dioxide in the second gas.

6. A methane generation method in a methane generation system having a methane generation device that generates methane from a first gas containing methane and carbon dioxide generated during wastewater treatment in a wastewater treatment facility and discharges a second gas containing the generated methane, and a control device that controls the generation of the methane by the methane generation device, wherein the control device controls the generation of the methane by the methane generation device depending on at least one of the concentration of carbon dioxide in the second gas, the concentration of hydrogen in the second gas, and the concentration of carbon monoxide in the second gas, and the amount of the carbon dioxide contained in the first gas.

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