Methane manufacturing system

Abstract

To provide a methane manufacturing system that can reduce energy loss.SOLUTION: A system comprises a steam generating device 11 that generates steam, an electrolysis methanation device 12 that introduces a first gas mainly composed of carbon dioxide through a first pipe P1 and also introduces the steam generated in the steam generating device 11 through a second piping P2, causing electrolysis of the steam and the Sabatier reaction to produce a second gas mainly composed of methane and oxygen-containing steam that is steam containing oxygen, and sending the second gas to a third pipe P3 and the oxygen-containing steam to a fourth pipe P4. and a return pipe P5 that supplies the oxygen-containing steam sent to the fourth pipe P4 to at least one of the steam generating device 11 and the second pipe P2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a methane production system. [Background technology]

[0002] In recent years, incineration plants are sometimes equipped with equipment that produces methane using organic matter contained in waste before incineration. For example, Patent Document 1 describes that an incineration plant is equipped with a methane fermentation device, and that materials unsuitable for fermentation are removed from the waste and used as raw material for the methane fermentation device. In the case of Patent Document 1, the biogas produced in the methane fermentation device is separated into methane and carbon dioxide. Furthermore, the separated carbon dioxide and hydrogen produced in the water electrolysis device are supplied to a methanation device, where methane and water are synthesized. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6940713 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, Patent Document 1 describes a methanation device that generates methane by introducing carbon dioxide and hydrogen. Meanwhile, an electrolytic methanation device is known that generates methane by introducing carbon dioxide and water vapor. In this electrolytic methanation device, electrolysis of water vapor and the Sabatier reaction are caused to occur, and a gas mainly composed of methane is extracted, and oxygen-containing water vapor, which is water vapor containing oxygen, is extracted as a by-product. The water vapor contained in this oxygen-containing water vapor is surplus water vapor that was not used in the reaction. This oxygen-containing water vapor has a very high temperature compared to the atmosphere, and releasing it into the atmosphere would result in energy loss.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a methane production system that can reduce energy loss. [Means for solving the problem]

[0006] In order to achieve the above object, a methane production system according to an embodiment of the present disclosure includes a steam generator that generates steam, an electrolytic methanation device that introduces a first gas mainly composed of carbon dioxide through a first pipe and introduces the steam generated by the steam generator through a second pipe, electrolyzes the steam and causes a Sabatier reaction to generate a second gas mainly composed of methane and oxygen-containing steam, which is steam containing oxygen, and delivers the second gas to a third pipe and the oxygen-containing steam to a fourth pipe, and a return pipe that supplies the oxygen-containing steam delivered to the fourth pipe to at least one of the steam generator and the second pipe. Effect of the Invention

[0007] The present disclosure has an effect of providing a methane production system having the configuration described above and capable of reducing energy loss. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram illustrating an example of a methane production system according to the first embodiment. [Diagram 2] FIG. 2 is a diagram showing an outline of the structure of a cell used in the electrolytic methanation device. [Diagram 3] FIG. 3 is a block diagram illustrating an example of a methane production system according to the second embodiment. [Figure 4] FIG. 4 is a block diagram illustrating an example of a methane production system according to the third embodiment. [Diagram 5] FIG. 5 is a block diagram showing an example of a methane production system according to the fourth embodiment. [Figure 6]FIG. 6 is a block diagram illustrating an example of a methane production system according to the sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, preferred embodiments of the present disclosure will be described with reference to the drawings. In the following, the same or corresponding elements are denoted by the same reference numerals throughout the drawings, and duplicated descriptions thereof may be omitted. In addition, the drawings are schematic illustrations of the respective components for ease of understanding, and shapes, dimensional ratios, and the like may not be accurately depicted.

[0010] (First embodiment) Fig. 1 is a block diagram showing an example of a methane production system according to Embodiment 1. The methane production system 10A shown in Fig. 1 includes a water vapor generator 11, an electrolytic methanation device 12, flow control valves 13 and 14, first to fourth pipes P1 to P4, a return pipe P5, a control device 20, etc.

[0011] This methane production system 10A is installed in an incineration plant. The incineration plant is equipped with, for example, a waste incinerator, an exhaust gas treatment device that separates soot from the exhaust gas discharged from the incinerator, and a chimney that releases the exhaust gas from which the soot has been separated in the exhaust gas treatment device into the atmosphere. Furthermore, the incineration plant may be equipped with a boiler that recovers exhaust heat from the incinerator, and a steam turbine generator that generates power using steam generated in the boiler. In addition, the incineration plant may be equipped with a carbon dioxide separation and capture device that separates and captures carbon dioxide from the exhaust gas from which the soot has been separated in the exhaust gas treatment device.

[0012] In addition, incineration plants may also be equipped with a methane fermentation device that performs methane fermentation on food waste selected from waste that is not fed into the incinerator, and a gas purification device that extracts carbon dioxide and methane from the biogas produced in the methane fermentation device.

[0013] In this embodiment, the first gas introduced into the electrolytic methanation device 12 can be a gas mainly composed of carbon dioxide separated and recovered from the carbon dioxide separation and recovery device, or a gas mainly composed of carbon dioxide extracted by a gas purification device.

[0014] The water vapor generator 11 heats water to generate water vapor, and heats the generated water vapor to a predetermined temperature suitable for the reaction in the electrolytic methanation device 12 and sends it to the second piping P2. The water vapor generator 11 is capable of adjusting the flow rate of water vapor sent to the second piping P2.

[0015] The electrolytic methanation device 12 introduces the first gas through the first pipe P1, and also introduces the water vapor generated in the water vapor generator 11 through the second pipe P2. As described above, the first gas is a gas mainly composed of carbon dioxide supplied from a carbon dioxide separation and capture device or a gas purification device.

[0016] The electrolytic methanation device 12 uses carbon dioxide and water vapor contained in the first gas as raw materials to produce methane, water (water vapor), and oxygen through electrolysis of the water vapor and the Sabatier reaction. Thus, the electrolytic methanation device 12 is a methane production device.

[0017] 2 is a diagram showing an outline of the structure of a cell used in the electrolytic methanation device 12. In the cell of the electrolytic methanation device 12, an electrolyte layer 122 is sandwiched between a positive electrode 121 and a negative electrode 123, and a catalyst layer 124 is formed on the outer surface of the negative electrode 123. Water vapor (H2O) is electrolyzed at the positive electrode 121 to generate oxygen (O2) and hydrogen ions (H + ) and hydrogen ions (H + ) moves through the electrolyte layer 122 to the negative electrode 123, and converts into hydrogen ions (H + The Sabatier reaction between argon and carbon dioxide (CO2) produces water vapor (H2O) and methane (CH4).

[0018] As a result, the following reaction occurs in the electrolytic methanation device 12: CO2+4H2O→CH4+2H2O+2O2 The electrolytic methanation device 12 is provided with one or more cells as shown in FIG. 2. The electrolytic methanation device 12 is provided with a first gas outlet from which the second gas containing the generated water vapor and mainly composed of methane is discharged, and a second gas outlet from which oxygen-containing water vapor, which is a mixture of the generated oxygen and the excess water vapor that was introduced and not electrolyzed, is discharged. A third pipe P3 is connected to the first gas outlet, and the second gas discharged to the third pipe P3 is a gas having a temperature of about 180°C to 500°C, which is higher than the atmosphere, and the methane in the second gas can be used as fuel or the like. A fourth pipe P4 is connected to the second gas outlet, and the oxygen-containing water vapor discharged to the fourth pipe P4 is a gas having a temperature of about 180°C to 300°C, which is higher than the atmosphere.

[0019] The upstream end of the return pipe P5 is connected to the fourth pipe P4. The downstream side of the return pipe P5 is branched into two pipes P51 and P52, the pipe P51 is connected to the middle of the second pipe P2, and the other pipe P52 is connected to the steam generator 11. Therefore, the oxygen-containing steam sent to the fourth pipe P4 is supplied to the second pipe P2 through the return pipes P5 and P51, and is also supplied to the steam generator 11 through the return pipes P5 and P52. The return pipe P5 may be provided with a fan for drawing in the oxygen-containing steam passing through the fourth pipe P4 and sending it to the pipes P51 and P52. Also, the return pipe P5 may have a portion for temporarily retaining the oxygen-containing steam in the middle.

[0020] A flow control valve 13 for adjusting the gas flow rate is provided on the fourth pipe P4 downstream of the connection portion of the return pipe P5. The oxygen-containing steam that has passed through the flow control valve 13 is released, for example, into the atmosphere. In addition, a flow control valve 14 for adjusting the gas flow rate is provided on the return pipe P5. By adjusting the opening of the flow control valves 13 and 14, the flow rate of the oxygen-containing steam released into the atmosphere and the flow rate of the oxygen-containing steam sent to the return pipe P5 can be adjusted.

[0021] In addition, an oxygen concentration sensor 31 is installed in the fourth pipe P4 upstream of the connection portion with the return pipe P5. The oxygen concentration sensor 31 measures the oxygen concentration of the oxygen-containing steam sent from the electrolytic methanation device 12 to the fourth pipe P4. The measurement value of the oxygen concentration sensor 31 is output to the control device 20.

[0022] The return pipe P5 including the pipes P51 and P52 and the flow rate control valve 14 constitute a return device 18. Thus, the return device 18 can supply the oxygen-containing steam sent to the fourth pipe P4 to the steam generator 11 and the second pipe P2 and adjust the flow rate of the supply.

[0023] The control device 20 is configured to include, for example, a CPU, a memory, etc., and the CPU executes a control program stored in the memory to perform various calculations and control the overall operation of the methane production system 10A. For example, the control device 20 includes a function as a flow rate controller 21 that controls the flow rate regulating valves 13, 14, etc. The control device 20 may be configured as a single control device that performs centralized control, or may be configured as a plurality of control devices that cooperate with each other to perform distributed control.

[0024] It should be noted that the functions of the control device 20 disclosed herein can be performed using circuits or processing circuits including general purpose processors, special purpose processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, or combinations thereof configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuits. In this specification, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed in this specification or other known hardware that is programmed or configured to perform the recited functions. If the hardware is a processor, which is considered a type of circuit, the circuit, unit, or means is a combination of hardware and software, and the software is used to configure the hardware or processor.

[0025] At the start of operation of this methane production system 10A, the flow rate control valves 13, 14 are controlled by the flow rate controller 21 so as to have predetermined openings. Also, at the start of operation, the flow rate of water vapor to be sent to the second pipe P2 by the water vapor generator 11 is predetermined according to the flow rate of the first gas introduced into the electrolytic methanation device 12. Then, the operation of the water vapor generator 11 and the electrolytic methanation device 12 is started under the control of the control device 20, and the operation of the methane production system 10A is started.

[0026] When the operation is started, the steam generator 11 generates steam heated to a predetermined target gas temperature and sends the steam to the second pipe P2 at a predetermined flow rate. The electrolytic methanation device 12 introduces the first gas from the first pipe P1 and introduces steam from the second pipe P2. The electrolytic methanation device 12 then sends out the second gas from the third pipe P3 and sends out the oxygen-containing steam from the fourth pipe P4. A part of the sent out oxygen-containing steam is supplied to the second pipe P2 and the steam generator 11 through the return pipe 5. During operation, the oxygen concentration sensor 31 repeatedly measures the oxygen concentration of the oxygen-containing steam at a predetermined time interval and transmits the measured oxygen concentration, which is a measured value, to the control device 20 each time the measurement is performed.

[0027] In this embodiment, for example, a target oxygen concentration of the oxygen-containing steam sent from the electrolytic methanation device 12 to the fourth pipe P4 is determined in advance and stored in the memory of the control device 20.

[0028] The flow rate controller 21 of the control device 20 compares the oxygen concentration measured by the oxygen concentration sensor 31 with the target oxygen concentration, and when the measured oxygen concentration exceeds the target oxygen concentration, reduces the opening of the flow rate control valve 14 by a predetermined amount so that the flow rate of the oxygen-containing steam flowing through the return pipe P5 is reduced by a predetermined amount, and increases the flow rate of the steam sent out from the steam generator 11 by a predetermined amount. In other words, when the oxygen concentration of the oxygen-containing steam is higher than the target oxygen concentration, the flow rate of the steam contained in the oxygen-containing steam returned through the return pipe P5 is low, and there is a possibility that the steam required for the reaction in the electrolytic methanation device 12 will be insufficient. Therefore, by decreasing the flow rate of the oxygen-containing steam returned through the return pipe P5 and increasing the flow rate of the steam from the steam generator 11, a sufficient amount of steam for the reaction can be supplied to the electrolytic methanation device 12.

[0029] Further, when the measured oxygen concentration by the oxygen concentration sensor 31 becomes less than the target oxygen concentration, the flow controller 21 may increase the opening degree of the flow control valve 14 by a predetermined amount so that the flow rate of the oxygen-containing water vapor flowing through the return pipe P5 increases by a predetermined amount, and may decrease the flow rate of the water vapor sent from the water vapor generator 11 by a predetermined amount. Thereby, the energy consumed for heating water to generate water vapor in the water vapor generator 11 can be reduced.

[0030] In the above, the flow controller 21 controls the opening degree of the flow control valve 14 and the flow rate sent from the water vapor generator 11 so that the gas flow rate introduced from the second pipe P2 into the electrolytic methanation device 12 becomes a predetermined target flow rate.

[0031] In the above, the measured oxygen concentration is compared with the target oxygen concentration. However, an allowable range with respect to the target oxygen concentration may be determined in advance, and the measured oxygen concentration may be compared with the allowable range. For example, let the lower limit value of the allowable range be At1 and the upper limit value of the allowable range be At2. And if the measured oxygen concentration is Am, when Am > At2, the flow controller 21 may decrease the opening degree of the flow control valve 14 by a predetermined amount and increase the flow rate of the water vapor sent from the water vapor generator 11 by a predetermined amount. And when Am < At1, the flow controller 21 may increase the opening degree of the flow control valve 14 by a predetermined amount and decrease the flow rate of the water vapor sent from the water vapor generator 11 by a predetermined amount. Also, when At1 ≤ Am ≤ At2, the opening degree of the flow control valve 14 is not changed, and the flow rate of the water vapor sent from the water vapor generator 11 is not changed either.

[0032] In the above, when the aperture of the flow rate regulating valve 14 is reduced, the aperture may be set to 0. That is, the flow rate regulating valve 14 may be fully closed. In addition, in the above, the flow rate controller 21 also changes the aperture of the flow rate regulating valve 13 in response to the change in the aperture of the flow rate regulating valve 14. That is, the apertures of the flow rate regulating valves 13, 14 are controlled so that the sum of the flow rate of the oxygen-containing steam passing through the flow rate regulating valve 14 and the flow rate of the oxygen-containing steam passing through the flow rate regulating valve 13 becomes the flow rate of the oxygen-containing steam sent from the electrolytic methanation device 12 to the fourth pipe P4. Therefore, when the aperture of the flow rate regulating valve 14 is reduced, the aperture of the flow rate regulating valve 13 is increased, and when the aperture of the flow rate regulating valve 14 is increased, the aperture of the flow rate regulating valve 13 is reduced.

[0033] In this embodiment, oxygen-containing steam, which is generated as a by-product by the electrolytic methanation device 12 and has a higher temperature than the air, is supplied to the steam generator 11 and the second pipe P2 through the return pipe P5. This allows the oxygen-containing steam to be introduced into the electrolytic methanation device 12 together with the steam generated by the steam generator 11 for use, thereby reducing energy loss. In addition, the amount of steam generated in the steam generator 11 can be reduced, thereby reducing the energy consumption in the steam generator 11.

[0034] In the first embodiment, the oxygen-containing steam flowing through the return pipe P5 is supplied to both the second pipe P2 and the steam generator 11, but it may be configured to be supplied to either the second pipe P2 or the steam generator 11. That is, the pipe P52 may be omitted and the oxygen-containing steam may be supplied only to the second pipe P2, or the pipe P51 may be omitted and the oxygen-containing steam may be supplied only to the steam generator 11.

[0035] Second embodiment Fig. 3 is a block diagram showing an example of a methane production system according to the second embodiment. The methane production system 10B shown in Fig. 3 is different from the methane production system 10A shown in Fig. 1 in the method of controlling the flow rate control valve 14 and does not include an oxygen concentration sensor 31.

[0036] In this methane production system 10B, a carbon dioxide measuring instrument 32 is installed in the first pipe P1, and a methane measuring instrument 33 is installed in the third pipe P3. The carbon dioxide measuring instrument 32 measures the flow rate of carbon dioxide in the first gas introduced into the electrolytic methanation device 12. This carbon dioxide measuring instrument 32 can be configured using a flow sensor S1 that measures the flow rate of the first gas, and a carbon dioxide concentration sensor S2 that measures the carbon dioxide concentration in the first gas. In other words, the flow rate of carbon dioxide introduced into the electrolytic methanation device 12 can be calculated by multiplying the flow rate measured by the flow sensor S1 by the carbon dioxide concentration measured by the carbon dioxide concentration sensor S2.

[0037] Furthermore, the methane meter 33 measures the flow rate of methane in the second gas sent from the electrolytic methanation device 12 to the third pipe P3. This methane meter 33 can be configured using a flow rate sensor S3 that measures the flow rate of the second gas, and a methane concentration sensor S4 that measures the methane concentration in the second gas. That is, the flow rate of methane sent from the electrolytic methanation device 12 can be calculated by multiplying the flow rate measured by the flow rate sensor S3 by the methane concentration measured by the methane concentration sensor S4.

[0038] In the second embodiment, operation is started in the same manner as in the first embodiment. During operation, the carbon dioxide measuring instrument 32 repeatedly measures the flow rate of carbon dioxide in the first gas at predetermined time intervals, and transmits the measured flow rate of carbon dioxide to the control device 20 each time the measurement is performed. The methane measuring instrument 33 repeatedly measures the flow rate of methane in the second gas at predetermined time intervals, and transmits the measured flow rate of methane to the control device 20 each time the measurement is performed.

[0039] The control device 20 calculates the reaction rate of carbon dioxide in the electrolytic methanation device 12 based on the flow rate of carbon dioxide measured by the carbon dioxide measuring device 32 and the flow rate of methane measured by the methane measuring device 33. This reaction rate can be calculated by dividing the flow rate of methane measured by the methane measuring device 33 by the flow rate of carbon dioxide measured by the carbon dioxide measuring device 32. In this case, it is preferable to use, as the measurement value of the carbon dioxide measuring device 32, a measurement value measured at a time a predetermined reaction time before the measurement time of the measurement value of the methane measuring device 33. The predetermined reaction time is a time that is preset as the time required for the reaction in the electrolytic methanation device 12.

[0040] In this embodiment, for example, a target reaction rate of carbon dioxide in the electrolytic methanation device 12 is determined in advance and stored in the memory within the control device 20.

[0041] The flow rate controller 21 of the control device 20 compares the calculated reaction rate, which is the calculated reaction rate of carbon dioxide, with the target reaction rate, and when the calculated reaction rate is less than the target reaction rate, the opening of the flow rate control valve 14 is reduced by a predetermined amount so that the flow rate of the oxygen-containing steam flowing through the return pipe P5 is reduced by a predetermined amount, and the flow rate of the steam sent out from the steam generator 11 is increased by a predetermined amount. In other words, when the calculated reaction rate is lower than the target reaction rate, it is considered that the amount of steam required for the reaction in the electrolytic methanation device 12 is insufficient. Therefore, by reducing the flow rate of the oxygen-containing steam returned through the return pipe P5 and increasing the flow rate of the steam from the steam generator 11, a sufficient amount of steam for the reaction can be supplied to the electrolytic methanation device 12.

[0042] Furthermore, when the calculated reaction rate exceeds the target reaction rate, the flow rate controller 21 may increase the opening of the flow rate control valve 14 by a predetermined amount so that the flow rate of the oxygen-containing steam flowing through the return pipe P5 increases by a predetermined amount, thereby decreasing the flow rate of the steam sent out from the steam generator 11 by a predetermined amount. This makes it possible to reduce the energy consumed to heat water in the steam generator 11 to generate steam.

[0043] In the above description, the calculated reaction rate is compared with the target reaction rate. However, an allowable range for the target reaction rate may be determined in advance, and the calculated reaction rate may be compared with the allowable range. For example, let the lower limit value of the allowable range be Bt1 and the upper limit value of the allowable range be Bt2. And if the calculated reaction rate is Bm, the flow controller 21 may reduce the opening degree of the flow control valve 14 by a predetermined amount and increase the flow rate of the steam sent from the steam generator 11 by a predetermined amount when Bm < Bt1. And when Bm > Bt2, the opening degree of the flow control valve 14 may be increased by a predetermined amount and the flow rate of the steam sent from the steam generator 11 may be decreased by a predetermined amount. Also, when Bt1 ≤ Bm ≤ Bt2, the opening degree of the flow control valve 14 is not changed and the flow rate of the steam sent from the steam generator 11 is not changed either.

[0044] In addition, in the above, when reducing the opening degree of the flow control valve 14, the opening degree may be set to 0. Also in this embodiment, similar to the first embodiment, the flow controller 21 controls the opening degree of the flow control valve 14 and the delivery flow rate of the steam generator 11 so that the gas flow rate introduced from the second pipe P2 into the electrolytic methanation device 12 becomes a predetermined target flow rate. Also, similar to the first embodiment, the flow controller 21 changes the opening degree of the flow control valve 13 in response to the change in the opening degree of the flow control valve 14.

[0045] Also in this embodiment, oxygen-containing steam at a temperature higher than that of the atmosphere generated as a by-product by the electrolytic methanation device 12 is supplied to the steam generator 11 and the second pipe P2 through the return pipe P5, and the same effects as in the first embodiment can be obtained.

[0046] In the above second embodiment, the oxygen-containing steam flowing through the return pipe P5 is supplied to both the second pipe P2 and the steam generator 11. However, it may be configured to be supplied to either the second pipe P2 or the steam generator 11.

[0047] (Third Embodiment) Fig. 4 is a block diagram showing an example of a methane production system according to the third embodiment. The methane production system 10C shown in Fig. 4 is different from the methane production system 10A shown in Fig. 1 in the method of controlling the flow rate control valve 14 and does not include an oxygen concentration sensor 31.

[0048] In this methane production system 10C, a temperature sensor 34 is installed in the second pipe P2 to measure the temperature of the gas introduced into the electrolytic methanation device 12 through the second pipe P2. The gas introduced into the electrolytic methanation device 12 through the second pipe P2 is a mixture of water vapor generated in the water vapor generator 11 and oxygen-containing water vapor returned through the return pipe P5.

[0049] In the case of the third embodiment, operation is started in the same manner as in the case of the first embodiment. During operation, the temperature sensor 34 repeatedly measures the temperature of the gas introduced into the electrolytic methanation device 12 at a predetermined time interval, and transmits the measured gas temperature, which is the measured value, to the control device 20 each time a measurement is taken. Note that the target gas temperature, which is the target value for the temperature of the gas introduced into the electrolytic methanation device 12, is determined in advance and stored in the memory of the control device 20.

[0050] The flow rate controller 21 of the control device 20 compares the measured gas temperature detected by the temperature sensor 34 with the target gas temperature, and when the measured gas temperature falls below the target gas temperature, reduces the opening of the flow rate control valve 14 by a predetermined amount so that the flow rate of oxygen-containing steam flowing through the return pipe P5 decreases by a predetermined amount, and increases the flow rate of water steam sent out from the water vapor generator 11 by a predetermined amount.

[0051] In other words, when the gas temperature measured by the temperature sensor 34 falls below the target gas temperature, it is considered that the temperature of the oxygen-containing steam returned through the return pipe P5 has dropped, which may deteriorate the reaction in the electrolytic methanation device 12. Therefore, by decreasing the flow rate of the oxygen-containing steam returned through the return pipe P5 and increasing the flow rate of steam from the steam generator 11, it is possible to supply steam at a temperature at which a good reaction can be obtained to the electrolytic methanation device 12.

[0052] On the other hand, when the measured gas temperature by the temperature sensor 34 rises above the target gas temperature, the control device 20 may increase the opening degree of the flow rate adjustment valve 14 by a predetermined amount so that the flow rate of the oxygen-containing water vapor flowing through the return pipe P5 increases by a predetermined amount, and may decrease the flow rate of the water vapor sent from the water vapor generator 11 by a predetermined amount. Thereby, the energy consumed for heating water to generate water vapor in the water vapor generator 11 can be reduced.

[0053] In the above, the measured gas temperature is compared with the target gas temperature. However, an allowable range with respect to the target gas temperature may be determined in advance, and the measured gas temperature may be compared with the above allowable range. For example, let the lower limit value of the above allowable range be Ct1 and the upper limit value of the above allowable range be Ct2. And if the measured gas temperature is Cm, the control device 20 may decrease the opening degree of the flow rate adjustment valve 14 by a predetermined amount and increase the flow rate of the water vapor sent from the water vapor generator 11 by a predetermined amount when Cm < Ct1. And when Cm > Ct2, the opening degree of the flow rate adjustment valve 14 may be increased by a predetermined amount, and the flow rate of the water vapor sent from the water vapor generator 11 may be decreased by a predetermined amount. Also, when Ct1 ≤ Cm ≤ Ct2, the opening degree of the flow rate adjustment valve 14 is not changed, and the flow rate of the water vapor sent from the water vapor generator 11 is also not changed.

[0054] In the above, when reducing the opening degree of the flow rate adjustment valve 14, the opening degree may be set to 0. Also in this embodiment, similar to the first embodiment, the flow rate controller 21 controls the opening degree of the flow rate adjustment valve 14 and the delivery flow rate of the water vapor generator 11 so that the gas flow rate introduced from the second pipe P2 into the electrolytic methanation device 12 becomes a predetermined target flow rate. Also, similar to the first embodiment, the flow rate controller 21 changes the opening degree of the flow rate adjustment valve 13 in response to the change in the opening degree of the flow rate adjustment valve 14.

[0055] Also in this embodiment, the oxygen-containing water vapor at a temperature higher than that of the atmosphere generated as a by-product by the electrolytic methanation device 12 is supplied to the water vapor generator 11 and the second pipe P2 through the return pipe P5, and the same effects as in the first embodiment can be obtained.

[0056] In the third embodiment, the oxygen-containing steam flowing through the return pipe P5 is supplied to both the second pipe P2 and the steam generator 11, but may be supplied to either the second pipe P2 or the steam generator 11. In this example, when the steam generator 11 is configured to make the temperature of the gas sent to the second pipe P2 approximately equal to the target gas temperature, if all of the oxygen-containing steam flowing through the return pipe P5 is supplied to the steam generator 11, there is almost no fluctuation in the measured gas temperature measured by the temperature sensor 34. Therefore, in this example, the oxygen-containing steam flowing through the return pipe P5 may be supplied to at least the second pipe P2 of the second pipe P2 and the steam generator 11. On the other hand, when the water vapor generator 11 is configured to generate water vapor, for example, by utilizing some kind of waste heat, and the temperature of the gas discharged from the water vapor generator 11 is prone to fluctuate to some extent, the oxygen-containing water vapor flowing through the return pipe P5 may be configured to be supplied to either the second pipe P2 or the water vapor generator 11, or to both.

[0057] (Fourth embodiment) Fig. 5 is a block diagram showing an example of a methane production system according to the fourth embodiment. The methane production system 10D shown in Fig. 5 is different from the methane production system 10A shown in Fig. 1 in the method of controlling the flow rate control valve 14 and does not include an oxygen concentration sensor 31.

[0058] In this methane production system 10D, a temperature sensor 34 is installed in the second pipe P2 to measure the temperature of the gas introduced into the electrolytic methanation device 12 through the second pipe P2. In addition, a heating device 15 is installed in the return pipe P5 to heat the oxygen-containing steam flowing through the return pipe P5 and to adjust the heating temperature. The heating device 15 may be a device that heats the return pipe P5, or may be a heat exchanger. The control device 20 also includes a function as a heating controller 22 that controls the heating device 15.

[0059] In the case of the fourth embodiment, operation is started in the same manner as in the case of the first embodiment. At this time, the heating device 15 starts operating at a predetermined heating temperature. During operation, the temperature sensor 34 repeatedly measures the temperature of the gas introduced into the electrolytic methanation device 12 at predetermined time intervals, and transmits the measured gas temperature, which is the measured value, to the control device 20 each time the temperature sensor 34 measures the temperature of the gas.

[0060] The heating controller 22 of the control device 20 compares the measured gas temperature by the temperature sensor 34 with a predetermined temperature range including the above-mentioned target gas temperature, and controls the heating temperature of the heating device 15 so that the measured gas temperature is within the predetermined temperature range. For example, when the measured gas temperature by the temperature sensor 34 falls below the lower limit temperature of the predetermined temperature range, the heating controller 22 increases the heating temperature of the heating device 15 by a predetermined value. Also, when the measured gas temperature by the temperature sensor 34 exceeds the upper limit temperature of the predetermined temperature range, the heating controller 22 decreases the heating temperature of the heating device 15 by a predetermined value. This allows the reaction in the electrolytic methanation device 12 to proceed smoothly.

[0061] In the above, the heating controller 22 is configured to compare the measured gas temperature detected by the temperature sensor 34 with a predetermined temperature range, but it may also be configured to compare the measured gas temperature with a target gas temperature and control the heating temperature of the heating device 15 so that the measured gas temperature becomes the target gas temperature.

[0062] In this embodiment, oxygen-containing steam having a higher temperature than the air generated as a by-product by the electrolytic methanation device 12 is supplied to the steam generator 11 and the second pipe P2 via the return pipe P5, thereby obtaining the same effects as in the first embodiment.

[0063] In the above-described fourth embodiment, the oxygen-containing steam flowing through the return pipe P5 is supplied to both the second pipe P2 and the steam generator 11. However, as in the case of the third embodiment shown in FIG. 4, the oxygen-containing steam may be supplied to either the second pipe P2 or the steam generator 11.

[0064] Fifth embodiment Although not shown, the fifth embodiment has a configuration in which the heating device 15, the heating controller 22, and the temperature sensor 34 of the fourth embodiment are applied to the first or second embodiment.

[0065] 1 and 3, a temperature sensor 34 is installed in the second pipe P2, and a heating device 15 is installed in the return pipe P5, and similarly to the fourth embodiment, the heating controller 22 controls the heating temperature of the heating device 15 based on the gas temperature measured by the temperature sensor 34. In the fifth embodiment, the same effects as in the first embodiment can be obtained.

[0066] In the case of the fifth embodiment, similarly to the case of the fourth embodiment, the oxygen-containing steam flowing through the return pipe P5 can be configured to be supplied to both or either one of the second pipe P2 and the steam generator 11.

[0067] Sixth embodiment Fig. 6 is a block diagram showing an example of a methane production system according to a sixth embodiment. A methane production system 10E shown in Fig. 6 is different from the methane production system 10A shown in Fig. 1 in the method of controlling the flow control valve 14, and includes, in addition to the oxygen concentration sensor 31, a carbon dioxide measuring instrument 32 and a methane measuring instrument 33 similar to those in Fig. 3, and a temperature sensor 34 similar to those in Fig. 4.

[0068] In the case of the sixth embodiment, operation is started in the same manner as in the case of the first embodiment. During operation, the oxygen concentration measured by the oxygen concentration sensor 31, the values ​​measured by the carbon dioxide measuring instrument 32 and the methane measuring instrument 33, and the gas temperature measured by the temperature sensor 34 are repeatedly measured at predetermined time intervals, and each time a measurement is made, the values ​​are transmitted to the control device 20. Then, the flow rate controller 21 of the control device 20 calculates the reaction rate of carbon dioxide in the electrolytic methanation device 12 based on the flow rate of carbon dioxide measured by the carbon dioxide measuring instrument 32 and the flow rate of methane measured by the methane measuring instrument 33, in the same manner as in the case of the second embodiment shown in FIG. 3.

[0069] In this embodiment, the target oxygen concentration of the oxygen-containing water vapor sent from the electrolytic methanation apparatus 12 to the fourth pipe P4, the target reaction rate of carbon dioxide in the electrolytic methanation apparatus 12, and the target gas temperature introduced from the second pipe P2 into the electrolytic methanation apparatus 12 are predetermined and stored in the memory in the control device 20.

[0070] Based on the measured oxygen concentration by the oxygen concentration sensor 31, the calculated reaction rate of carbon dioxide which is the reaction rate calculated from the measured values of the carbon dioxide measuring device 32 and the methane measuring device 33, and the measured gas temperature by the temperature sensor 34 at the same time, the control device 20 controls the flow rate adjustment valve 14. This will be described in detail below.

[0071] The flow rate controller 21 of the control device 20 sets the measured oxygen concentration as Am, the target oxygen concentration as At, the calculated reaction rate as Bm, the target reaction rate as Bt, the measured gas temperature as Cm, and the target gas temperature as Ct, and calculates the following value D. D = a(Am - At) + b(Bm - Bt) + c(Cm - Ct) In the above formula, a, b, and c are predetermined coefficients. Here, a is a positive value, and b and c are negative values. The calculated value D is a value obtained by weighted addition of the difference between the measured oxygen concentration Am and the target oxygen concentration At, the difference between the calculated reaction rate Bm and the target reaction rate Bt, and the difference between the measured gas temperature Cm and the target gas temperature Ct.

[0072] The control device 20 compares the calculated value D with a predetermined reference value E. When D > E, the opening degree of the flow rate adjustment valve 14 is reduced by a predetermined amount, and the flow rate of the water vapor sent from the water vapor generator 11 is increased by a predetermined amount. When D < E, the opening degree of the flow rate adjustment valve 14 is increased by a predetermined amount, and the flow rate of the water vapor sent from the water vapor generator 11 is decreased by a predetermined amount.

[0073] Note that in the above description, the calculated value D is compared with the reference value E. However, an allowable range with respect to the reference value E may be determined in advance, and the calculated value D may be compared with the above allowable range. For example, let the lower limit value of the above allowable range be the lower reference value E1, and the upper limit value of the above allowable range be the upper reference value E2. Then, when D > E2, the control device 20 may reduce the opening degree of the flow rate adjustment valve 14 by a predetermined amount and increase the flow rate of the water vapor sent from the water vapor generation device 11 by a predetermined amount. And when D < E1, the control device 20 may increase the opening degree of the flow rate adjustment valve 14 by a predetermined amount and decrease the flow rate of the water vapor sent from the water vapor generation device 11 by a predetermined amount. Also, when E1 ≤ D ≤ E2, the opening degree of the flow rate adjustment valve 14 is not changed.

[0074] Note that in the above, when reducing the opening degree of the flow rate adjustment valve 14, the opening degree may be set to 0. Also in this embodiment, similar to the first embodiment, the flow rate controller 21 controls the opening degree of the flow rate adjustment valve 14 and the flow rate sent from the water vapor generation device 11 so that the gas flow rate introduced from the second pipe P2 into the electrolytic methanation device 12 becomes a predetermined target flow rate. Also, similar to the first embodiment, the flow rate controller 21 changes the opening degree of the flow rate adjustment valve 13 in response to the change in the opening degree of the flow rate adjustment valve 14.

[0075] Also in this embodiment, oxygen-containing water vapor at a temperature higher than that of the atmosphere generated as a by-product by the electrolytic methanation device 12 is supplied to the water vapor generation device 11 and the second pipe P2 by the return pipe P5, and the same effect as in the first embodiment can be obtained.

[0076] In the above sixth embodiment, the oxygen-containing water vapor flowing through the return pipe P5 is supplied to both the second pipe P2 and the water vapor generation device 11. However, it may be configured to be supplied to either the second pipe P2 or the water vapor generation device 11.

[0077] In the sixth embodiment, the flow rate control valve 14 is controlled based on three values, namely, the measured oxygen concentration, the calculated reaction rate, and the measured gas temperature, but the flow rate control valve 14 may be controlled in a similar manner based on any two values ​​of the measured oxygen concentration, the calculated reaction rate, and the measured gas temperature. In this case, too, the oxygen-containing water vapor flowing through the return pipe P5 can be configured to be supplied to at least one of the second pipe P2 and the water vapor generator 11.

[0078] 6, the heating device 15 of FIG. 5 may be added, and the control device 20 may control the heating device 15 based on the measured gas temperature by the temperature sensor 34, in the same manner as in FIG. 5. In this case, the control device 20 controls the flow rate control valve 14 based on two values, the measured oxygen concentration and the calculated reaction rate. In this case, too, the oxygen-containing steam flowing through the return pipe P5 can be configured to be supplied to at least one of the second pipe P2 and the steam generator 11.

[0079] In the embodiment described above, the oxygen-containing steam delivered from the fourth pipe P4 may be mixed with the combustion air supplied to the incinerator in the incineration plant.

[0080] In the above-described embodiment, the heat exchanger 16, 17 may be installed in at least one of the third pipe P3 from which the second gas at about 180°C to 500°C is sent out and the fourth pipe P4 from which the oxygen-containing gas at about 180°C to 300°C is sent out, so as to supply heat to the equipment in the incineration plant. For example, it may be used as a heat source for preheating the combustion air to be supplied to the incinerator in the incineration plant. It may also be used as a heat source for regenerating a carbon dioxide absorbent such as an amine used in a carbon dioxide separation and capture device in the incineration plant. It may also be used as a heat source for heating water in a methane fermentation tank in a methane fermentation device.

[0081] From the above description, many improvements and other embodiments of the present disclosure will be apparent to those skilled in the art. Therefore, the above description should be construed as merely illustrative and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present disclosure. Details of the structure and / or function thereof may be substantially changed without departing from the spirit of the present disclosure.

[0082] Summary of the Disclosure A methane production system according to a first aspect of the present disclosure includes a water vapor generation device that generates water vapor, an electrolytic methanation device that introduces a first gas mainly composed of carbon dioxide through a first pipe and introduces the water vapor generated by the water vapor generation device through a second pipe, electrolyzes the water vapor and causes a Sabatier reaction to generate a second gas mainly composed of methane and oxygen-containing water vapor, which is water vapor containing oxygen, and delivers the second gas to a third pipe and delivers the oxygen-containing water vapor to a fourth pipe, and a return pipe that supplies the oxygen-containing water vapor delivered to the fourth pipe to at least one of the water vapor generation device and the second pipe.

[0083] According to this configuration, oxygen-containing steam, which is generated as a by-product by the electrolytic methanation device and has a higher temperature than the air, is supplied to at least one of the steam generator and the second pipe through the return pipe. This allows the oxygen-containing steam to be introduced into the electrolytic methanation device together with the steam generated by the steam generator for use, thereby reducing energy loss. Also, the amount of steam generated by the steam generator can be reduced.

[0084] A methane production system according to a second aspect of the present disclosure is the methane production system according to the first aspect, further comprising a flow control valve installed in the return piping for adjusting a flow rate of the oxygen-containing steam, and a flow controller for controlling the flow control valve.

[0085] According to this configuration, the flow rate of the oxygen-containing steam returned by the return pipe can be adjusted.

[0086] A methane production system according to a third aspect of the present disclosure is the methane production system according to the second aspect, wherein the flow rate controller controls the flow control valve based on at least one of the oxygen concentration of the oxygen-containing steam delivered from the electrolytic methanation device to the fourth piping, and a reaction rate of carbon dioxide calculated based on the flow rate of carbon dioxide in the first gas introduced into the electrolytic methanation device and the flow rate of methane in the second gas delivered from the electrolytic methanation device to the third piping.

[0087] According to this configuration, the flow rate of the oxygen-containing steam returned through the return pipe is adjusted by controlling the flow control valve based on at least one of the oxygen concentration of the oxygen-containing steam and the reaction rate of carbon dioxide in the electrolytic methanation device, thereby making it possible to suppress a decrease in the methane production efficiency in the electrolytic methanation device caused by the introduction of oxygen-containing steam into the electrolytic methanation device.

[0088] A methane production system according to a fourth aspect of the present disclosure is the methane production system according to the second aspect, wherein the flow rate controller controls the flow control valve based on at least one of: the oxygen concentration of the oxygen-containing steam delivered from the electrolytic methanation device to the fourth piping; a reaction rate of carbon dioxide calculated based on the flow rate of carbon dioxide in the first gas introduced into the electrolytic methanation device and the flow rate of methane in the second gas delivered from the electrolytic methanation device to the third piping; and a temperature of the gas introduced into the electrolytic methanation device through the second piping.

[0089] According to this configuration, the flow rate of the oxygen-containing steam returned through the return pipe is adjusted by controlling the flow control valve based on at least one of the oxygen concentration of the oxygen-containing steam, the reaction rate of the carbon dioxide, and the temperature of the gas. This makes it possible to suppress a decrease in the methane production efficiency in the electrolytic methanation device caused by the introduction of the oxygen-containing steam into the electrolytic methanation device.

[0090] A methane production system according to a fifth aspect of the present disclosure is the methane production system according to the first aspect, further comprising a temperature sensor that measures a temperature of the gas introduced into the electrolytic methanation apparatus through the second piping, a heating device that heats the oxygen-containing steam flowing through the return piping and is capable of adjusting the heating temperature, and a heating controller that controls the heating device, wherein the heating controller controls the heating device so that the gas temperature measured by the temperature sensor is maintained within a predetermined range.

[0091] According to this configuration, the heating device is controlled so that the temperature of the gas introduced into the electrolytic methanation device through the second pipe is maintained within a predetermined range, thereby making it possible to maintain the temperature of the mixed gas of water vapor and oxygen-containing water vapor introduced into the electrolytic methanation device at a temperature suitable for the reaction in the electrolytic methanation device, and to suppress a decrease in the efficiency of methane production in the electrolytic methanation device.

[0092] A methane production system according to a sixth aspect of the present disclosure is the methane production system according to the fifth aspect, further comprising a flow control valve installed in the return piping to adjust the flow rate of the oxygen-containing steam, and a flow controller controlling the flow control valve, wherein the flow controller controls the flow control valve based on at least one of the oxygen concentration of the oxygen-containing steam sent from the electrolytic methanation device to the fourth piping, and a reaction rate of carbon dioxide calculated based on the flow rate of carbon dioxide in the first gas introduced into the electrolytic methanation device and the flow rate of methane in the second gas sent from the electrolytic methanation device to the third piping.

[0093] According to this configuration, the flow rate of the oxygen-containing steam returned through the return pipe is adjusted by controlling the flow control valve based on at least one of the oxygen concentration of the oxygen-containing steam and the reaction rate of the carbon dioxide, thereby making it possible to suppress a decrease in the methane production efficiency in the electrolytic methanation device caused by the introduction of the oxygen-containing steam into the electrolytic methanation device. [Explanation of symbols]

[0094] 10A~10E Methane production system 11 Steam generator 12 Electrolytic methanation equipment 21 Flow Controller 22 Heating Controller 14 Flow control valve 15 Heating device 31 Oxygen concentration sensor 32 Carbon dioxide measuring device 33 Methane Meter 34 Temperature Sensor P1 First pipe P2 Second piping P3 3rd piping P4 4th pipe P5 Return piping

Claims

1. A water vapor generator for generating water vapor; an electrolytic methanation device that introduces a first gas containing carbon dioxide as a main component through a first pipe, introduces water vapor generated by the water vapor generator through a second pipe, electrolyzes the water vapor and causes a Sabatier reaction to generate a second gas containing methane as a main component and oxygen-containing water vapor, and delivers the second gas to a third pipe and the oxygen-containing water vapor to a fourth pipe; a return pipe that supplies the oxygen-containing steam sent to the fourth pipe to at least one of the steam generator and the second pipe; A methane production system equipped with

2. a flow rate control valve installed in the return pipe for controlling the flow rate of the oxygen-containing steam; A flow controller for controlling the flow rate regulating valve; The methane production system according to claim 1 .

3. The flow rate controller includes: the oxygen concentration of the oxygen-containing steam sent from the electrolytic methanation device to the fourth pipe; and A reaction rate of carbon dioxide calculated based on a flow rate of carbon dioxide in the first gas introduced into the electrolytic methanation device and a flow rate of methane in the second gas sent from the electrolytic methanation device to the third pipe; The flow rate regulating valve is controlled based on at least one of the following: The methane production system according to claim 2 .

4. The flow rate controller includes: the oxygen concentration of the oxygen-containing steam sent from the electrolytic methanation device to the fourth pipe; and A reaction rate of carbon dioxide calculated based on a flow rate of carbon dioxide in the first gas introduced into the electrolytic methanation device and a flow rate of methane in the second gas sent from the electrolytic methanation device to the third pipe; The temperature of the gas introduced into the electrolytic methanation device through the second pipe; and The flow rate regulating valve is controlled based on at least one of the following: The methane production system according to claim 2 .

5. a temperature sensor for measuring a temperature of the gas introduced into the electrolytic methanation device through the second pipe; A heating device capable of heating the oxygen-containing steam flowing through the return pipe and adjusting the heating temperature; A heating controller for controlling the heating device, The heating controller includes: controlling the heating device so as to maintain the temperature of the gas measured by the temperature sensor within a predetermined range; The methane production system according to claim 1 .

6. a flow rate control valve installed in the return pipe for controlling the flow rate of the oxygen-containing steam; A flow rate controller that controls the flow rate adjustment valve, The flow rate controller includes: the oxygen concentration of the oxygen-containing steam sent from the electrolytic methanation device to the fourth pipe; and A reaction rate of carbon dioxide calculated based on a flow rate of carbon dioxide in the first gas introduced into the electrolytic methanation device and a flow rate of methane in the second gas sent from the electrolytic methanation device to the third pipe; The flow rate regulating valve is controlled based on at least one of the following: The methane production system according to claim 5 .

Images