Thermal energy generation system and thermal energy generation method

Abstract

The present invention provides a thermal energy generation system and method that can reduce the difficulty of separating carbon dioxide and impurities from exhaust gas after a combustion reaction, while making maximum use of existing combustion equipment. [Solution] The thermal energy generation system 10 comprises a water electrolysis device 20, a methanation device 30 that generates methane and water by reacting carbon dioxide with hydrogen produced in the water electrolysis device 20, a combustion device 40 that burns the methane discharged from the methanation device 30 using a combustion gas containing oxygen discharged from the water electrolysis device 20, and a CO2 distribution unit 55 that distributes and supplies the carbon dioxide discharged from the combustion device 40 to the methanation device 30 and the combustion device 40, respectively. The methanation device 30 carries out the methanation reaction using carbon dioxide from the CO2 distribution unit 55. The combustion device 40 carries out the combustion reaction by incorporating carbon dioxide from the CO2 distribution unit 55 into the combustion gas.

Description

Technical Field

[0001] The present invention relates to a heat energy generation system and a heat energy generation method.

Background Art

[0002] Conventionally, in order to reduce carbon dioxide generated during the combustion of fuels derived from fossil resources, a heat energy generation system is known that recovers carbon dioxide generated during combustion, reacts it with hydrogen to convert it into methane, and uses the converted methane as a fuel during combustion.

[0003] For example, Patent Document 1 discloses an example of using the heat energy generation system in a power generation system. This power generation system includes a generator that generates heat energy by a combustion reaction and converts it into electric power, a dehydrogenation reactor that generates hydrogen from a hydrogenated aromatic by a dehydrogenation reaction, a separator that separates carbon dioxide from the exhaust gas generated by the combustion reaction, and a methanation reactor that generates methane and water by reacting the carbon dioxide separated by the separator with the hydrogen generated by the dehydrogenation reactor. The generator generates heat energy by burning the methane generated in the methanation reactor together with fossil fuel.

[0004] In Patent Document 1, air in the atmosphere is used for the combustion of fuel in the generator. However, for example, as shown in Patent Document 2, there may be a case where a combustion reaction is performed by pure oxygen combustion using oxygen generated by an electrolysis reaction of water.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the thermal energy generation system shown in Patent Document 1 utilizes oxygen from the air taken in from the outside when burning fuel. As a result, the exhaust gas (product gas) after combustion contains impurities such as nitrogen in addition to carbon dioxide. In such cases, it is necessary to separate the carbon dioxide used for the methanation reaction from the nitrogen and other impurities in the exhaust gas. However, when the carbon dioxide concentration is low, the energy required for separation becomes large, making separation difficult. As a result, the separation device has to be made larger.

[0007] In contrast, the thermal energy generation system shown in Patent Document 2 uses pure oxygen combustion for the combustion reaction, thereby suppressing the mixing of impurities such as nitrogen into the exhaust gas. However, in this case, the equipment constituting the combustion device (e.g., burners) must be equipped to handle pure oxygen combustion. Therefore, existing equipment that relies on the use of air from the atmosphere cannot cope, leading to the problem of increased costs due to equipment modifications, etc.

[0008] The present invention was made to solve the aforementioned problems, and aims to provide a thermal energy generation system and thermal energy generation method that can reduce the difficulty of separating carbon dioxide and impurities in the exhaust gas after the combustion reaction, while making use of existing combustion equipment as much as possible. [Means for solving the problem]

[0009] The thermal energy generation system according to the first invention comprises a water electrolysis device that generates and discharges hydrogen and oxygen by electrolyzing water; a methanation device that generates and discharges methane and water by a methanation reaction between carbon dioxide and hydrogen generated in the water electrolysis device; a combustion device that generates thermal energy by carrying out a combustion reaction using methane discharged from the methanation device and a combustion gas containing oxygen discharged from the water electrolysis device, and discharges carbon dioxide as a reaction product of the combustion reaction; and a CO2 distribution unit that distributes and supplies carbon dioxide discharged from the combustion device to the methanation device and the combustion device, respectively. The methanation device is configured to carry out the methanation reaction using carbon dioxide supplied from the CO2 distribution unit, and the combustion device is configured to carry out the combustion reaction by incorporating carbon dioxide supplied from the CO2 distribution unit into the combustion gas.

[0010] This configuration allows carbon dioxide generated in the combustion device to be supplied to the combustion device via a CO2 distribution unit and used as part of the combustion gas during the combustion reaction. This reduces the oxygen concentration in the combustion gas compared to pure oxygen combustion. Therefore, existing combustion devices can be used as much as possible without the need for dedicated burners or other equipment designed for pure oxygen combustion. Furthermore, by adjusting the oxygen concentration with carbon dioxide instead of atmospheric air, the energy required to increase the carbon dioxide concentration in the exhaust gas and separate the carbon dioxide from impurities can be reduced. Thus, the difficulty of separating carbon dioxide from impurities can be avoided, simplifying the system configuration. Consequently, the entire system can be constructed at a low cost.

[0011] In the second invention, it is preferable that the first invention further includes a first flow rate adjustment unit that adjusts the flow rate of carbon dioxide supplied to the combustion device so that the concentration of oxygen in the combustion gas is equivalent to the concentration of oxygen in the atmosphere.

[0012] With this configuration, the oxygen concentration of the combustion gas used in the combustion reaction becomes equivalent to the oxygen concentration in the atmosphere, so a general combustion device that uses air from the atmosphere for the combustion reaction can be used. Therefore, it becomes easier to use existing combustion devices.

[0013] In the third invention, it is preferable that the first or second invention further includes a second flow rate adjustment unit that adjusts the flow rate of methane supplied to the combustion device and the flow rate of oxygen supplied to the combustion device so that the combustion reaction of methane in the combustion device is carried out in an oxygen-rich state in which there is more oxygen than the theoretical air ratio.

[0014] With this configuration, the combustion reaction of methane in the combustion device is carried out in an oxygen-rich state, thus preventing incomplete combustion of methane. Therefore, sufficient thermal energy can be generated. In this invention, since atmospheric air is not used in the combustion reaction in the combustion device, the term "air ratio" is defined as the ratio of oxygen amounts, not the ratio of air amounts. That is, the "air ratio" is defined as the value obtained by dividing the actual amount of oxygen used for methane combustion by the theoretical amount of oxygen required for methane combustion. Therefore, if the air ratio is greater than 1, it means that the combustion gas is oxygen-rich, and if the air ratio is less than 1, it means that the combustion gas is oxygen-lean.

[0015] In the fourth invention, it is preferable that, in the third invention, the combustion apparatus is configured to discharge combustion exhaust gas containing carbon dioxide and oxygen by performing the combustion reaction in the oxygen-rich state, and the CO2 distribution unit has a separator that separates high-purity CO2 gas having a predetermined carbon dioxide concentration from the combustion exhaust gas discharged from the combustion apparatus, and supplies the high-purity CO2 gas separated by the separator to the methanation device, and supplies the low-purity CO2 gas, which contains carbon dioxide and oxygen and has a carbon dioxide concentration lower than the predetermined concentration, that remains after the high-purity CO2 gas has been separated from the combustion exhaust gas, to the combustion apparatus.

[0016] This configuration allows for the separation of high-purity CO2 gas from the combustion exhaust gas, and the remaining exhaust gas (low-purity CO2 gas) is supplied to the combustion device to reduce the oxygen concentration in the combustion gas. This prevents the release of unseparated carbon dioxide into the atmosphere. As a result, a thermal energy generation system that satisfies the requirements of carbon neutrality is provided.

[0017] In the fifth invention, it is preferable that, in the fourth invention, the CO2 distribution unit further comprises a combustion exhaust gas distribution unit that supplies a portion of the combustion exhaust gas discharged from the combustion device to the separator and supplies the remaining combustion exhaust gas to the combustion device, and the separator is configured to separate high-purity CO2 gas from the combustion exhaust gas supplied from the combustion exhaust gas distribution unit.

[0018] This configuration allows for a smaller separator to be used to separate high-purity CO2 gas from combustion exhaust gas, thereby suppressing the increase in equipment costs and operating costs that would otherwise be incurred due to the larger size of the separator.

[0019] In other words, if all of the combustion exhaust gas discharged from the combustion device is supplied to the separator, the separator needs to process a large amount of combustion exhaust gas to separate high-purity CO2 gas. To increase the separation efficiency of high-purity CO2 gas, it is preferable to reduce the linear velocity (flow rate) of the combustion exhaust gas within the separator as much as possible. However, reducing the linear velocity of the combustion exhaust gas requires increasing the cross-sectional area of ​​the flow path of the combustion exhaust gas within the CO2 separator, which results in the overall size of the separator becoming larger.

[0020] In contrast, in the above configuration, instead of supplying all of the combustion exhaust gas discharged from the combustion device to the separator, a portion of the combustion exhaust gas is supplied (distributed) to the separator by a combustion exhaust gas distribution unit. This reduces the flow rate of combustion exhaust gas to be processed in the separator, and consequently, allows for miniaturization of the separator. Therefore, it is possible to suppress the increase in equipment costs that would otherwise be caused by an enlarged separator. Furthermore, by miniaturizing the separator, the power consumption of the separator can be reduced, thereby suppressing the increase in operating costs. In addition, by reducing power consumption, the amount of carbon dioxide emitted outside the system (carbon dioxide emitted outside the system during the power generation stage) can be reduced.

[0021] In the sixth invention, it is preferable that the first or second invention further includes a third flow rate adjustment unit that adjusts the flow rate of methane supplied to the combustion device and the flow rate of oxygen supplied to the combustion device so that the combustion reaction of methane in the combustion device is carried out at a stoichiometric air ratio.

[0022] With this configuration, the combustion reaction in the combustion device is carried out at a stoichiometric air ratio (air ratio = 1), so the oxygen in the combustion gas is used without excess or deficiency in the combustion reaction. As a result, the combustion exhaust gas consists only of carbon dioxide, and no oxygen is mixed in the combustion exhaust gas. Therefore, the carbon dioxide emitted from the combustion device can be supplied directly to the methanation device without passing through an oxygen separator. Thus, the configuration of the thermal energy generation system can be simplified, and the system can be provided at a low cost.

[0023] In the seventh invention, it is preferable that the first invention further includes a fourth flow rate adjustment unit that adjusts the flow rate of hydrogen and the flow rate of carbon dioxide supplied to the methanation apparatus so that the ratio of hydrogen to carbon dioxide used in the methanation reaction in the methanation apparatus becomes a predetermined ratio in which there is more hydrogen than the stoichiometric ratio.

[0024] With this configuration, the conversion rate from carbon dioxide to methane in the methanation device can be improved by increasing the flow rate of hydrogen supplied to the methanation device to a rate greater than that determined by the stoichiometric ratio.

[0025] The thermal energy generation method according to the eighth invention comprises a water electrolysis step of generating hydrogen and oxygen by electrolyzing water; a methanation step of generating methane and water by a methanation reaction between carbon dioxide and the hydrogen generated in the water electrolysis step; a combustion step of generating thermal energy by carrying out a combustion reaction of methane generated in the methanation step using a combustion gas containing oxygen generated in the water electrolysis step, and emitting carbon dioxide as a reaction product of the combustion reaction; and a distribution step of separating the carbon dioxide generated in the combustion step into carbon dioxide for the methanation step and carbon dioxide for the combustion step, wherein in the methanation step, the methanation reaction is carried out using the carbon dioxide for the methanation step, and in the combustion step, the carbon dioxide for the combustion step is included in the combustion gas and the combustion reaction is carried out.

[0026] This method allows us to obtain the same effects and benefits as the thermal energy generation system according to the first invention. [Effects of the Invention]

[0027] According to the present invention, a thermal energy generation system and a thermal energy generation method are provided that can reduce the difficulty of separating carbon dioxide and impurities in the exhaust gas after a combustion reaction, while making use of existing combustion equipment as much as possible. [Brief explanation of the drawing]

[0028] [Figure 1] Figure 1 is a schematic diagram showing the general configuration of the thermal energy generation system of this embodiment. [Figure 2] Figure 2 is a schematic diagram showing the flow rates of each working fluid in Example 1-1. [Figure 3] Figure 3 is a diagram corresponding to Figure 2, showing Example 1-2. [Figure 4] Figure 4 is a diagram corresponding to Figure 1, showing Embodiment 2. [Figure 5] Figure 5 is a schematic diagram showing the flow rates of each working fluid in Example 2-1. [Figure 6] Figure 6 is a diagram corresponding to Figure 5, showing Example 2-2. [Figure 7] Figure 7 is a diagram corresponding to Figure 1, showing Embodiment 3. [Figure 8] Figure 8 is a schematic diagram showing the flow rates of each working fluid in Example 3-1. [Figure 9] Figure 9 is a diagram corresponding to Figure 8, showing Example 3-2. [Modes for carrying out the invention]

[0029] Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the drawings.

[0030] (Embodiment 1) Figure 1 is a schematic diagram showing the general configuration of the thermal energy generation system 10 of this embodiment. This thermal energy generation system 10 converts carbon dioxide emitted by a combustion reaction into methane, and generates thermal energy by using the methane as fuel to carry out the combustion reaction. The thermal energy generated by the thermal energy generation system 10 can be used, for example, for power generation, metal melting and processing, glass manufacturing, or ceramic firing.

[0031] Specifically, the thermal energy generation system 10 includes a water electrolysis device 20, a methanation device 30, a combustion device 40, and a high-purity CO2 separator 50.

[0032] The water electrolysis device 20 is a device that uses electrical energy to decompose water supplied from an external source into hydrogen and oxygen. The reaction equation for the water electrolysis reaction in the water electrolysis device 20 is as follows (1).

[0033] H2O→H2+(1 / 2)O2………(1) The oxygen generated by this water electrolysis reaction is supplied to the combustion device 40 via the flow path 61 and the combustion gas supply flow path 62. Meanwhile, the hydrogen generated by the water electrolysis reaction is supplied to the methanation device 30 via the flow path 63.

[0034] The methanation device 30 produces methane and water (more precisely, water vapor) by reacting hydrogen supplied from the water electrolysis device 20 with carbon dioxide (high-purity CO2 gas) supplied from the high-purity CO2 separator 50. The reaction equation for this reaction (hereinafter referred to as the methanation reaction) is shown in equation (2) below.

[0035] CO2+4H2→CH4+2H2O…………(2) The mixture of methane and water produced by the methanation device 30 is supplied to the water separator 11 via the flow path 64.

[0036] The water separator 11 is a so-called condenser, which separates the water supplied from the methanation device 30 by liquefying it through condensation. The methane, from which the water has been separated, is supplied to the combustion device 40 via the flow path 65. More specifically, the methane from which the water has been separated in the water separator 11 is supplied to the CH4 tank 31 via the flow path 65a for temporary storage, and then supplied to the combustion device 40 via the flow path 65b.

[0037] The combustion device 40 is a device that burns methane supplied from the methanation device 30 via the water separator 11. Specifically, the combustion device 40 supplies the methane fuel and combustion gas to the combustion furnace and ignites the combustion gas using a burner or the like to produce the combustion reaction shown in equation (3) below. In this way, the combustion device 40 burns the methane through this combustion reaction and generates thermal energy.

[0038] CH4+2O2→CO2+2H2O………(3) In this embodiment, the combustion reaction takes place in an oxygen-rich state where the air ratio λ is greater than 1 (i.e., a state in which the actual amount of oxygen in the combustion gas is greater than the theoretical amount of oxygen required to burn methane based on reaction equation (3)).

[0039] Since the combustion reaction in reaction equation (3) takes place in an oxygen-rich state, the post-combustion products after the combustion reaction are a mixture of carbon dioxide, water (more precisely, water vapor), and oxygen. This mixture is supplied to the water separator 12 via the flow path 66.

[0040] The water separator 12 is a so-called condenser, which separates water from the combustion exhaust gas supplied from the combustion device 40 by liquefying it through condensation. The combustion exhaust gas from which the water has been separated becomes a mixed gas containing only carbon dioxide and oxygen, and is supplied to the high-purity CO2 separator 50 via the flow path 67.

[0041] In the high-purity CO2 separator 50, the mixed gas containing carbon dioxide and oxygen is separated into high-purity CO2 gas consisting of carbon dioxide at a predetermined concentration close to 100% purity, and low-purity CO2 gas containing oxygen in addition to carbon dioxide, with a lower carbon dioxide concentration than the high-purity CO2 gas. Various methods can be used for separating carbon dioxide in this high-purity CO2 separator 50, such as low-temperature separation, membrane separation, absorption, and adsorption. The predetermined concentration is set to a concentration close to 100% (for example, 95% or higher), but this does not exclude 100%, and it may be 100%.

[0042] The high-purity CO2 separated in the high-purity CO2 separator 50 is supplied to the high-purity CO2 tank 51 via the flow path 68, where it is temporarily stored, and then supplied to the methanation device 30 via the flow path 69.

[0043] Meanwhile, the low-purity CO2 gas separated in the high-purity CO2 separator 50 is supplied to the low-purity CO2 tank 52 via the flow path 70 for temporary storage, and then merges with the combustion gas supply flow path 62 via the flow path 71 and is supplied to the combustion device 40. In the combustion device 40, this carbon dioxide is supplied into the combustion furnace and incorporated (mixed) into the combustion gas for burning the fuel, methane. As a result, the combustion gas contains carbon dioxide supplied from the high-purity CO2 separator 50 in addition to the oxygen supplied from the water electrolysis device 20. The flow rates of oxygen and carbon dioxide supplied to the combustion device 40 are controlled by the flow rate control device 100, which will be described later.

[0044] In this embodiment, the high-purity CO2 separator 50, the high-purity CO2 tank 51, the low-purity CO2 tank 52, the flow paths 68-71, and the combustion gas supply flow path 62 function as a CO2 distribution unit 55 that distributes and supplies carbon dioxide emitted from the combustion device 40 to the methanation device 30 and the combustion device 40, respectively.

[0045] [Configuration of flow control device] The thermal energy generation system 10 further includes a flow control device 100 (corresponding to the first to fourth flow adjustment units) for controlling the flow rate of the working fluid (oxygen, carbon dioxide, methane, etc.).

[0046] Specifically, the flow control device 100 includes a controller 101, a first flow control valve 102, a second flow control valve 103, a third flow control valve 104, a fourth flow control valve 105, a fifth flow control valve 112, and an oxygen concentration detection sensor 106. The first flow control valve 102 is located in a flow path 69 for supplying carbon dioxide from a high-purity CO2 tank 51 to a methanation device 30. The second flow control valve 103 is located in a flow path 63 from a water electrolysis device 20 to a methanation device 30. The third flow control valve 104 is located in a flow path 61 for supplying oxygen from a water electrolysis device 20 to a combustion device 40. The fourth flow control valve 105 is located in a flow path 71 for supplying low-purity CO2 gas (a gas containing oxygen in addition to carbon dioxide) from a low-purity CO2 tank 52 to a combustion device 40. The fifth flow control valve 112 is located in a flow path 65b for supplying methane from a CH4 tank 31 to a combustion device 40. In Figure 1, reference numeral 61a indicates a branch channel for discharging excess oxygen discharged from the water electrolysis device 20, and channel 63a indicates a branch channel for discharging excess hydrogen discharged from the water electrolysis device 20.

[0047] The oxygen concentration detection sensor 106 detects the oxygen concentration in the low-purity CO2 gas stored in the low-purity CO2 tank 52 and transmits the detection signal to the controller 101. The controller 101 is composed of a computer having a CPU, ROM, and RAM, and controls the opening degree of each flow control valve 102 to 105.

[0048] The flow rate control process performed by the controller 101 controls the flow rate Q of hydrogen supplied to the methanation device 30. H2 and the flow rate of carbon dioxide Q CO2 A first control process that controls the flow rate Q of oxygen supplied to the combustion device 40. O2,com and the flow rate of carbon dioxide Q CO2,com And, the flow rate of methane Q CH4,com It can be broadly divided into two parts: a first control process and a second control process that controls the second control process.

[0049] In the first control process, the controller 101 controls the opening degree of the first flow rate adjustment valve 102 so that the flow rate Q of carbon dioxide supplied from the high-purity CO2 tank 51 to the methanation device 30 becomes the preset target flow rate. This target flow rate is set by calculation based on, for example, the methane consumption by the combustion device 40 and the pressure of the CH4 tank 31. The opening degree control of the first flow rate adjustment valve 102 is executed by feedback control based on the flow rate of carbon dioxide measured by the flow meter 107 connected to the flow path 69. Note that a flow indicator controller (hereinafter referred to as FIC) in which the first flow rate adjustment valve 102, the flow meter 107, and the controller are unitized may be used to transmit the target flow rate from the controller 101 to the FIC, and the FIC may control the flow rate Q of carbon dioxide to the target flow rate. CO2 In the first control process, the controller 101 controls the opening degree of the first flow rate adjustment valve 102 so that the flow rate Q of carbon dioxide supplied from the high-purity CO2 tank 51 to the methanation device 30 becomes the preset target flow rate. This target flow rate is set by calculation based on, for example, the methane consumption by the combustion device 40 and the pressure of the CH4 tank 31. The opening degree control of the first flow rate adjustment valve 102 is executed by feedback control based on the flow rate of carbon dioxide measured by the flow meter 107 connected to the flow path 69. Note that a flow indicator controller (hereinafter referred to as FIC) in which the first flow rate adjustment valve 102, the flow meter 107, and the controller are unitized may be used to transmit the target flow rate from the controller 101 to the FIC, and the FIC may control the flow rate Q of carbon dioxide to the target flow rate. CO2 may be controlled to the target flow rate.

[0050] Furthermore, in the first control process, the controller 101 calculates the target flow rate of hydrogen to be supplied to the methanation device 30 based on the stoichiometric ratio determined from the reaction formula (2) based on the target flow rate Q of the carbon dioxide. Then, the controller 101 controls the opening degree of the second flow rate adjustment valve 103 so that the flow rate Q of hydrogen supplied from the water electrolysis device 20 to the methanation device 30 via the flow path 63 becomes the calculated target flow rate. This opening degree control is executed by feedback control based on the flow rate of oxygen measured by the flow meter 108 connected to the flow path 63. Note that this opening degree control may also be performed using the above-mentioned FIC. CO2 Furthermore, in the first control process, the controller 101 calculates the target flow rate of hydrogen to be supplied to the methanation device 30 based on the stoichiometric ratio determined from the reaction formula (2) based on the target flow rate Q of the carbon dioxide. Then, the controller 101 controls the opening degree of the second flow rate adjustment valve 103 so that the flow rate Q of hydrogen supplied from the water electrolysis device 20 to the methanation device 30 via the flow path 63 becomes the calculated target flow rate. This opening degree control is executed by feedback control based on the flow rate of oxygen measured by the flow meter 108 connected to the flow path 63. Note that this opening degree control may also be performed using the above-mentioned FIC. H2 Furthermore, in the first control process, the controller 101 calculates the target flow rate of hydrogen to be supplied to the methanation device 30 based on the stoichiometric ratio determined from the reaction formula (2) based on the target flow rate Q of the carbon dioxide. Then, the controller 101 controls the opening degree of the second flow rate adjustment valve 103 so that the flow rate Q of hydrogen supplied from the water electrolysis device 20 to the methanation device 30 via the flow path 63 becomes the calculated target flow rate. This opening degree control is executed by feedback control based on the flow rate of oxygen measured by the flow meter 108 connected to the flow path 63. Note that this opening degree control may also be performed using the above-mentioned FIC.

[0051] In the second control process, the controller 101 first determines the methane flow rate Q supplied from the CH4 tank 31 to the combustion device 40 CH4The opening degree of the fifth flow control valve 112 is controlled so that the flow rate becomes a preset target flow rate. This target flow rate is set by calculation based on, for example, the amount of heat required by the thermal energy generation system 10 (the amount of heat determined from the system design requirements). The opening degree control of the fifth flow control valve 112 is performed by feedback control based on the flow rate of methane measured by the flow meter 111 connected to the flow path 65b. Furthermore, in the second control process, the flow rate Q of methane supplied to the combustion device 40 is controlled. CH4 Therefore, the theoretical oxygen flow rate Q required for the complete combustion of methane (or methane and hydrogen if there is an excess of hydrogen) contained in the gas is... O2,th The controller 101 then calculates the theoretical oxygen flow rate Q. O2,th The target air ratio λ during the combustion reaction in the combustion device 40, and the oxygen concentration A in the low-purity CO2 gas detected by the oxygen concentration detection sensor 106. CO2,L And the target oxygen concentration A during the combustion reaction in the combustion device 40. O2 Based on this, the target flow rate of low-purity CO2 gas to be supplied from the low-purity CO2 tank 52 to the combustion device 40, and the target flow rate of oxygen to be supplied from the water electrolysis device 20 to the combustion device 40 are calculated.

[0052] Here, the target air ratio λ and the target oxygen concentration A are as follows: O2 This is pre-stored in a memory unit such as a ROM provided in the controller 101. In this embodiment, the target air ratio λ is set to a value greater than 1. Target oxygen concentration A O2 This value is set to be equivalent to the oxygen concentration in the atmosphere, which is 21%. Here, "equivalent" does not mean that it must be exactly the same as the oxygen concentration in the atmosphere; it may be within a range that includes an error of, for example, about 1% (for example, between 20% and 22%).

[0053] The controller 101 then controls the flow rate Q of the low-purity CO2 gas supplied from the low-purity CO2 tank 52 to the combustion device 40 via the flow path 71 (and the combustion gas supply flow path 62). CO2,L The opening degree of the fourth flow control valve 105 is controlled so that the flow rate Q of the low-purity CO2 gas is measured by the flow meter 109 connected to the flow path 71. CO2,LThis is executed by feedback control based on the above. Alternatively, this opening degree control may be performed using the FIC described above.

[0054] Furthermore, the controller 101 controls the flow rate Q of oxygen supplied from the water electrolyzer 20 to the combustion device 40 via the flow path 61 (and the combustion gas supply flow path 62). O2 The opening degree of the third flow control valve 104 is controlled so that the flow rate Q is the target flow rate calculated above. This opening degree control is controlled by the oxygen flow rate Q measured by the flow meter 110 connected to the flow path 61. O2 This is executed by feedback control based on the above. Alternatively, this opening degree control may be performed using the FIC described above.

[0055] [Effects and Effects] As described above, the thermal energy generation system 10 of this embodiment includes a water electrolysis device 20 that generates and discharges hydrogen and oxygen by electrolyzing water; a methanation device 30 that generates and discharges methane and water by a methanation reaction between carbon dioxide and hydrogen generated in the water electrolysis device 20; a combustion device 40 that generates thermal energy by carrying out a combustion reaction using methane discharged from the methanation device 30 and a combustion gas containing oxygen discharged from the water electrolysis device 20, and discharges carbon dioxide as a reaction product of the combustion reaction; and a CO2 distribution unit 55 that distributes and supplies carbon dioxide discharged from the combustion device 40 to the methanation device 30 and the combustion device 40, respectively. The methanation device 30 is configured to carry out the methanation reaction using carbon dioxide supplied from the CO2 distribution unit 55, and the combustion device 40 is configured to carry out the combustion reaction by incorporating carbon dioxide supplied from the CO2 distribution unit 55 into the combustion gas.

[0056] With this configuration, carbon dioxide generated in the combustion device 40 is supplied to the combustion device 40 via the CO2 distribution unit 55 and used as part of the combustion gas during the combustion reaction. This allows for a reduction in the oxygen concentration in the combustion gas compared to pure oxygen combustion. Therefore, existing combustion devices 40 can be used as much as possible without the need for dedicated burners or other equipment designed for pure oxygen combustion. Furthermore, by adjusting the oxygen concentration with carbon dioxide instead of atmospheric air, the carbon dioxide concentration in the combustion exhaust gas can be increased. This reduces the difficulty of separating impurities from the exhaust gas and simplifies the system configuration. Consequently, the entire system can be constructed at a low cost.

[0057] Furthermore, the thermal energy generation system 10 of this embodiment is equipped with a flow rate control device 100. The flow rate control device 100 controls the concentration of oxygen in the combustion gas to be equal to the concentration of oxygen in the atmosphere. The flow rate of carbon dioxide supplied to the combustion device 40 is adjusted so that the following conditions are met.

[0058] With this configuration, the oxygen concentration of the combustion gas used in the combustion reaction becomes equivalent to the oxygen concentration in the atmosphere, so a general combustion device 40 that uses air from the atmosphere for the combustion reaction can be used. Therefore, it becomes easier to use existing combustion devices 40.

[0059] Furthermore, in this embodiment, the flow rate control device 100 adjusts the flow rate of methane supplied to the combustion device 40 and the flow rate of oxygen supplied to the combustion device 40 so that the methane combustion reaction in the combustion device 40 is carried out in an oxygen-rich state where there is more oxygen than the theoretical air ratio.

[0060] With this configuration, the methane combustion reaction in the combustion device 40 is carried out in an oxygen-rich state, thus preventing incomplete combustion of methane. Therefore, the necessary thermal energy can be reliably generated.

[0061] Furthermore, in this embodiment, the combustion device 40 is configured to discharge combustion exhaust gas containing carbon dioxide and oxygen by performing a combustion reaction in an oxygen-rich state. The CO2 distribution unit 55 has a high-purity CO2 separator 50 that separates high-purity CO2 gas (an example of high-purity CO2 gas with a predetermined carbon dioxide concentration) with a carbon dioxide concentration close to 100% from the combustion exhaust gas discharged from the combustion device 40. The high-purity CO2 gas separated by the separator 50 is supplied to the methanation device 30, and the low-purity CO2 gas containing carbon dioxide and oxygen that remains after the high-purity CO2 gas has been separated from the combustion exhaust gas is supplied to the combustion device 40.

[0062] With this configuration, after separating high-purity CO2 gas from the combustion exhaust gas, the remaining combustion exhaust gas (low-purity CO2 gas) is supplied to the combustion device 40 and used to reduce the oxygen concentration in the combustion gas. This prevents the unseparated carbon dioxide from being released into the atmosphere. As a result, a thermal energy generation system 10 that satisfies the requirements of carbon neutrality is provided.

[0063] In this embodiment, the second control process may be performed based on the gas composition in the CH4 tank detected by a gas composition detection instrument 113 provided in the CH4 tank 31. In this case, the controller 101 first calculates the fuel gas supply flow rate Q (hereinafter referred to as the fuel gas supply flow rate) of the fuel gas containing methane CH4 to be supplied to the combustion device 40, based on the gas composition detected by the instrument 113 located in the CH4 tank 31 and the target heat load in the combustion device 40 (information on the target heat load received from the combustion device 40 via a signal line, etc.). The instrument 113 can be configured, for example, as a gas analyzer or a calorimeter. The controller 101 controls the fifth flow control valve 112 so that the flow rate detected by the flow meter 111 becomes the calculated fuel gas supply flow rate Q. Furthermore, based on the calculated fuel gas supply flow rate Q, the controller 101 calculates the theoretical oxygen flow rate Q required for the complete combustion of methane (or methane and hydrogen if there is an excess of hydrogen) contained in the fuel gas. O2,thThe controller 101 then calculates the theoretical oxygen flow rate Q. O2,th The target air ratio λ during the combustion reaction in the combustion device 40, and the oxygen concentration A in the low-purity CO2 gas detected by the oxygen concentration detection sensor 106. CO2,L And the target oxygen concentration A during the combustion reaction in the combustion device 40. O2 Based on this, the target flow rate of low-purity CO2 gas to be supplied from the low-purity CO2 tank 52 to the combustion device 40, and the target flow rate of oxygen to be supplied from the water electrolysis device 20 to the combustion device 40 are calculated.

[0064] (Example 1-1) Next, we will describe Example 1-1, a specific example of Embodiment 1, with reference to Figure 2.

[0065] Figure 2 is a schematic diagram showing the flow rates of each working fluid in Example 1-1. In Figure 2, the flow control device 100 is omitted for clarity.

[0066] In this embodiment, the target air ratio λ is set to 1.4, and the target oxygen concentration A in the combustion device 40 is set to 1.4. O2 It is set to 20%.

[0067] When the thermal energy generation system 10 is in operation, first, the electrolysis reaction of water in the water electrolyzer 20 generates 100 Nm³ in terms of volumetric flow rate. 3 Hydrogen and 50 Nm 3 Oxygen is produced at a rate of / h. The generated hydrogen is supplied to the methanation device 30.

[0068] In the methanation device 30, this 100 Nm 3 Hydrogen at / h and 25Nm³ supplied from high-purity CO2 separator 50. 3 The methanation reaction with carbon dioxide at / h (see reaction equation (2) above) produces 25 Nm³ 3 methane and 50 Nm³ / h 3 Water (more precisely, water vapor) is generated per hour. Of this, the water is separated in the water separator 11, and only methane is supplied to the combustion device 40.

[0069] The combustion device 40 is supplied with 50 Nm³ of water from the water electrolysis device 20 via the flow path 61. 3 The system supplies oxygen at a rate of / h and low-purity CO2 gas supplied from the high-purity CO2 separator 50 via the flow path 71. The low-purity CO2 gas is 280 Nm³. 3 / h carbon dioxide and 20 Nm 3 Since it is composed of oxygen at a rate of / h, as a result, the combustion device 40 receives 70 (=50+20) Nm of combustion gas via the combustion gas supply passage 62. 3 Oxygen at / h and 280Nm 3 A supply of carbon dioxide is provided at a rate of 1 / h. Then, in the combustion device 40, methane is burned using this combustion gas consisting of oxygen and carbon dioxide.

[0070] Here, as shown in the reaction equation (3) above, only oxygen in the combustion gas contributes to the actual combustion reaction. However, by including carbon dioxide in the combustion gas, the oxygen concentration in the combustion gas is controlled to 20%, which is equivalent to the oxygen concentration in the atmosphere. As a result, the combustion reaction in the combustion device 40 is no longer pure oxygen combustion, and existing combustion devices can be used without modification. In addition, in this embodiment, the combustion device 40 contains 25 Nm 3 The theoretical amount of oxygen required to burn methane at a rate of 50 Nm³ / h 3 70Nm, which is more than / h 3 Since oxygen is supplied at a rate of / h, incomplete combustion of the fuel, methane, can be prevented.

[0071] Then, the combustion reaction in the combustion device 40 generates 305 Nm³ 3 / h carbon dioxide and 50 Nm 3 / h of water (strictly speaking, water vapor) and 20Nm 3 Combustion exhaust gas containing oxygen at a rate of 1 / h is generated. This combustion exhaust gas passes through the water separator 12 and is then supplied to the high-purity CO2 separator 50. The combustion exhaust gas supplied to the high-purity CO2 separator 50 is separated into high-purity CO2 gas and low-purity CO2 gas. The high-purity CO2 gas is supplied to the methanation device 30 via flow paths 68 and 69, and the low-purity CO2 gas is supplied to the combustion device 40 via flow paths 70 and 71.

[0072] (Examples 1-2) Next, Example 1-2, which is an embodiment of Embodiment 1, will be described with reference to Figure 3.

[0073] Figure 3 is a diagram corresponding to Figure 2, showing Example 1-2.

[0074] In this embodiment, the target air ratio λ is set to 1.4, and the target oxygen concentration A in the combustion device 40 is set to 1.4. O2 The setting of 20% is the same as in Example 1, but the difference from Example 1-1 is that the flow rate of hydrogen supplied from the water electrolysis device 20 to the methanation device 30 is set to be greater than the flow rate of hydrogen based on the stoichiometric ratio (1:4) of the reaction equation (2).

[0075] In other words, in the above example 1-1, 100 Nm 3 While hydrogen at 106.25 Nm³ / h is supplied to the methanation device 30, in this embodiment, 106.25 Nm³ 3 6.25N of hydrogen per hour is supplied to the methanation unit 30. As a result, the methanation unit 30 supplies the excess hydrogen. m3 / h is discharged, and 25 Nm³ is obtained by the methanation reaction. 3 It is supplied to the combustion device 40 along with methane at a rate of / h. The water is removed by the water separator 11, as in Example 1-1. In the combustion device 40, this excess supplied 6.25 Nm³ 3 Hydrogen and 25 Nm³ / h 3 To burn methane at an air ratio of 1.4, 74.375 Nm³ 3 Oxygen at a rate of / h (=(6.25*1 / 2+25*2)*1.4) is used, and the controller 101 controls the opening of the third flow control valve 104 and the fourth flow control valve 105 (see Figure 1) to ensure this amount of oxygen is available.

[0076] Thus, according to this embodiment, in addition to the same effects as in Example 1-1, the following effects can be obtained. That is, according to this embodiment, the flow rate control device 100 controls the flow rates of hydrogen and carbon dioxide supplied to the methanation device 30 so that the ratio of hydrogen to carbon dioxide used in the methanation reaction in the methanation device 30 becomes a predetermined ratio in which there is more hydrogen than the stoichiometric ratio.

[0077] With this configuration, the conversion rate from carbon dioxide to methane in the methanation device 30 can be improved by increasing the flow rate of hydrogen supplied to the methanation device 30 to a rate determined by the stoichiometric ratio. Furthermore, any excess hydrogen supplied reacts with oxygen in the combustion device 40 to form water, so hydrogen does not mix with the carbon dioxide emitted from the combustion device 40. Therefore, there is no need to provide a separate separation device to separate carbon dioxide and hydrogen.

[0078] (Embodiment 2) Figure 4 is a diagram corresponding to Figure 1, showing Embodiment 2. This embodiment differs from Embodiment 1 in that the target air ratio λ during the combustion reaction in the combustion device 40 is set to 1, and that it does not have a high-purity CO2 separator 50. In the following description, the same reference numerals are used for components that are the same as in Embodiment 1, and their detailed descriptions are omitted.

[0079] In other words, in this embodiment, since the target air ratio λ during the combustion reaction in the combustion device 40 is set to 1, all the oxygen in the combustion gas is burned by the combustion reaction in the combustion device 40. Therefore, the combustion exhaust gas discharged from the combustion device 40 consists only of carbon dioxide and does not become a mixed gas of carbon dioxide and oxygen as in Embodiment 1.

[0080] Therefore, in this embodiment, instead of providing a high-purity CO2 separator 50 as in Embodiment 1, the flow path 67 downstream of the combustion device 40 is connected to the branching section 72. The branching section 72 distributes the carbon dioxide that has passed through the flow path 67 to the methanation device 30 and the combustion device 40 by branching it into a flow path 68 for supplying it to the methanation device 30 and a flow path 70 for supplying it to the combustion device 40. This branching section 72 is composed of a three-way joint such as a T-pipe. A flow control valve may also be provided in the branching section 72.

[0081] In this embodiment, unlike Embodiment 1, there is no distinction between the high-purity CO2 tank 51 and the low-purity CO2 tank 52. As shown in Figure 4, the high-purity CO2 tank 51 and the low-purity CO2 tank 52 of Embodiment 1 are replaced by the first CO2 tank 53 and the second CO2 tank 54, respectively. 100% pure carbon dioxide discharged from the combustion device 40 flows into and is stored in the first CO2 tank 53 and the second CO2 tank 54 via the flow paths 68 and 70, respectively.

[0082] (Effects and Benefits) The thermal energy generation system 10 configured as described above provides the same effects as in Embodiment 1, in addition to the following effects.

[0083] In other words, in this embodiment, the flow rate control device 100 is configured to adjust the flow rate of methane supplied to the combustion device 40 and the flow rate of oxygen supplied to the combustion device 40 so that the combustion reaction of methane in the combustion device 40 is carried out at the theoretical air ratio (λ=1).

[0084] With this configuration, the combustion reaction in the combustion device 40 is carried out at a stoichiometric air ratio (air ratio = 1), so the oxygen in the combustion gas is used in the combustion reaction without excess or deficiency, and the combustion exhaust gas consists only of carbon dioxide, with no oxygen mixed in the combustion exhaust gas. Therefore, the carbon dioxide emitted from the combustion device 40 can be supplied directly to the methanation device 30 without going through an oxygen separator. Thus, the configuration of the thermal energy generation system 10 can be simplified, and the system can be provided at a low cost.

[0085] (Example 2-1) Next, we will describe Example 2-1, a specific example of Embodiment 2, with reference to Figure 5. Figure 5 is a schematic diagram showing the flow rates of each working fluid in Example 2-1. In the following, we will mainly describe the differences from Example 1-1 (see Figure 2), and will omit explanations as appropriate.

[0086] In other words, this embodiment differs from Embodiment 1-1 in that the air ratio λ is set to 1.

[0087] Here, the processing in the water electrolysis device 20 and the methanation device 30 is the same as in Example 1-1, so the explanation is omitted. In the combustion device 40, in order to achieve an air ratio of 1, 25 Nm 3 50 Nm³ per hour of methane 3 Oxygen is used at a rate of / h. In addition, in the combustion device 40, this 50Nm 3 Based on an oxygen flow rate of 1 / h, 200 Nm³ is added to the combustion gas so that the oxygen concentration reaches the target oxygen concentration of 20%. 3 A certain amount of carbon dioxide per hour is supplied.

[0088] Then, in the combustion device 40, the methane combustion reaction takes place with an air ratio of 1, so 225 Nm³ is released from the combustion device 40. 3 / h carbon dioxide and 50 Nm 3 Only water (strictly speaking, water vapor) per hour is discharged, and no excess oxygen is discharged as in Example 1-1. This water is separated by the water separator 12, leaving 225 Nm³. 3 200 Nm³ of carbon dioxide per hour3 / h is supplied to the combustion device 40, and 25Nm 3 / h is supplied to the methanation device 30.

[0089] According to this embodiment, the oxygen concentration in the combustion gas is controlled to 20%, which is equivalent to the oxygen concentration in the atmosphere (21%). Therefore, the combustion reaction in the combustion device 40 can be carried out under conditions equivalent to the oxygen concentration in the atmosphere, rather than pure oxygen combustion. Thus, existing combustion devices can be used without modification for pure oxygen combustion.

[0090] Furthermore, according to this embodiment, since the air ratio is set to 1, oxygen does not mix with the carbon dioxide emitted from the combustion device 40. Therefore, there is no need to provide a high-purity CO2 separator 50 as in Examples 1-1 and 1-2, which simplifies the configuration of the thermal energy generation system 10 and reduces costs.

[0091] (Example 2-2) Next, we will describe Example 2-2, another embodiment of Embodiment 2, with reference to Figure 6. Figure 6 is a diagram corresponding to Figure 5, showing Example 2-2. Below, we will mainly describe only the differences from Example 2-1.

[0092] In other words, in this embodiment, the target air ratio λ is set to 1, and the target oxygen concentration A in the combustion device 40 is set. O2 The fact that the ratio is set to 20% is the same as in Example 2-1, but the difference from Example 2-1 is that the flow rate of hydrogen supplied from the water electrolysis device 20 to the methanation device 30 is set to be greater than the flow rate of hydrogen based on the stoichiometric ratio (1:4) of the reaction equation (2).

[0093] In other words, in the above example 2-1, 100 Nm 3 While hydrogen at 106.25 Nm³ / h is supplied to the methanation device 30, in this embodiment, 106.25 Nm³ 3 6.25 Nm³ of hydrogen per hour is supplied to the methanation unit 30. As a result, the methanation unit 30 supplies the excess hydrogen. 3 / h is discharged, and 25Nm³ is obtained by the methanation reaction. 3 It is supplied to the combustion device 40 along with methane at a rate of / h. The water is removed by the water separator 11, as in Example 2-1. In the combustion device 40, this excess 6.25 Nm³ is then used. 3 Hydrogen and 25 Nm³ / h 3 To burn methane at a ratio of 1 / h to 1 / h of air, 74.375 Nm 3 Oxygen at a rate of / h (=(6.25*1 / 2+25*2)*1.0) is used, and the controller 101 controls the opening of the third flow control valve 104 and the fourth flow control valve 105 to ensure this amount of oxygen is maintained.

[0094] Thus, according to this embodiment, in addition to the effects and advantages similar to those of Embodiment 2-1, the following effects and advantages can be obtained. Specifically, according to this embodiment, by increasing the flow rate of hydrogen supplied to the methanation device 30 to a level greater than the stoichiometric ratio, the conversion rate from carbon dioxide to methane in the methanation device 30 can be improved. Furthermore, since the excess hydrogen supplied reacts with oxygen in the combustion device 40 to form water, hydrogen does not mix with the carbon dioxide emitted from the combustion device 40. Therefore, there is no need to provide a separate separation device for separating carbon dioxide and hydrogen.

[0095] (Embodiment 3) Figure 7 is a diagram corresponding to Figure 1, showing Embodiment 3. In this embodiment, the CO2 distribution unit 55 differs from Embodiment 1 in that it has a combustion exhaust gas distribution unit 73 that supplies a portion of the combustion exhaust gas discharged from the combustion device 40 to the high-purity CO2 separator 50 and supplies the remaining combustion exhaust gas to the combustion device 40. In the following description, the same reference numerals are used for components that are the same as in Embodiment 1, and their detailed descriptions are omitted.

[0096] In other words, in this embodiment, the CO2 distribution unit 55 further includes a combustion exhaust gas distribution unit 73 provided in the middle of the flow path 67 downstream of the combustion device 40, and a branch flow path 74 connected to the combustion exhaust gas distribution unit 73.

[0097] The flow path 67 has an upstream flow path section 67a and a downstream flow path section 67b, located upstream of the combustion exhaust gas distribution section 73. The upstream flow path section 67a is connected to the combustion device 40 via the water separator 12 and the flow path 66. The downstream flow path section 67b is connected to the high-purity CO2 separator 50.

[0098] The combustion exhaust gas distribution section 73 is configured by a three-way joint, such as a T-shaped pipe. The combustion exhaust gas distribution section 73 has a first port 73a connected to the upstream flow path section 67a, a second port 73b connected to the downstream flow path section 67b, and a third port 73c connected to the branch flow path 74.

[0099] The branch channel 74 has an upstream end connected to the third port 73c and a downstream end connected to the middle section of the channel 71 downstream of the low-purity CO2 tank 52. The downstream end of the branch channel 74 is connected to the channel 71 via a junction 75. The junction 75 is made up of a three-way joint, such as a T-shaped pipe.

[0100] The combustion exhaust gas distribution unit 73 discharges the combustion exhaust gas that flows from the combustion device 40 to the first port 73a via the upstream flow path 67a through the second port 73b and the third port 73c. ​​As described above, the second port 73b is connected to the high-purity CO2 separator 50 via the downstream flow path 67b of the flow path 67, and the third port 73c is connected to the combustion device 40 via the combustion exhaust gas distribution unit 73 and the flow path 71. Therefore, the combustion exhaust gas distribution unit 73 is configured to distribute the combustion exhaust gas that flows in from the first port 73a to the high-purity CO2 separator 50 and the combustion device 40 via the second port 73b and the third port 73c.

[0101] In this embodiment, when the distribution flow rate of combustion exhaust gas to the high-purity CO2 separator 50 is A and the distribution flow rate to the combustion device 40 is B, the distribution ratio R of combustion exhaust gas to the high-purity CO2 separator 50 is defined as R = A / (A + B). The ratio of the flow path cross-sectional areas of the second port 73b and the third port 73c of the combustion exhaust gas distribution unit 73 is set so that this distribution ratio R becomes the target distribution ratio Rt.

[0102] The target distribution ratio Rt is set to satisfy the condition that the flow rate of carbon dioxide in the combustion exhaust gas distributed to the high-purity CO2 separator 50 by the combustion exhaust gas distribution unit 73 is equal to or greater than the flow rate of carbon dioxide required by the methanation device 30. Within the range that satisfies this condition, it is preferable to set the target distribution ratio so that the flow rate of combustion exhaust gas distributed to the high-purity CO2 separator 50 is as low as possible.

[0103] [Operation Description] In the thermal energy generation system 10 configured as described above, the combustion exhaust gas discharged from the combustion device 40 flows into the combustion exhaust gas distribution unit 73. The combustion exhaust gas distribution unit 73 supplies a portion of the combustion exhaust gas to the high-purity CO2 separator 50, and the remaining combustion exhaust gas is supplied into the branched flow path 74.

[0104] The combustion exhaust gas supplied from the combustion exhaust gas distribution unit 73 to the high-purity CO2 separator 50 is separated into high-purity CO2 gas and low-purity CO2 gas, and the high-purity CO2 gas is supplied to the methanation device 30 via flow paths 68 and 69. On the other hand, the low-purity CO2 gas (gas containing carbon dioxide and oxygen) flows into the flow path 71 via the low-purity CO2 tank 52, and at the confluence section 75 provided in the middle of the flow path 71, it is combined with the combustion exhaust gas flowing in from the branch flow path 74 (strictly speaking, the combustion exhaust gas that has passed through the water separator 12 and is low-purity CO2 gas containing carbon dioxide and oxygen) and then supplied to the combustion device 40.

[0105] [Effects and Effects] The thermal energy generation system 10 configured as described above provides the same effects as in Embodiment 1, in addition to the following effects.

[0106] In other words, in this embodiment, the CO2 distribution unit 55 further includes a combustion exhaust gas distribution unit 73 that supplies a portion of the combustion exhaust gas discharged from the combustion device 40 to a high-purity CO2 separator 50 and supplies the remaining combustion exhaust gas to the combustion device 40. The high-purity CO2 separator 50 is configured to separate high-purity CO2 gas from the combustion exhaust gas supplied by the combustion exhaust gas distribution unit 73.

[0107] This configuration allows for miniaturization of the high-purity CO2 separator 50, which separates high-purity CO2 gas from the combustion exhaust gas. This suppresses the increase in equipment costs and operating costs that would result from the increased size of the high-purity CO2 separator 50.

[0108] In other words, if all of the combustion exhaust gas discharged from the combustion device 40 is supplied to the high-purity CO2 separator 50, the high-purity CO2 separator 50 needs to process a large amount of combustion exhaust gas and separate high-purity CO2 gas. Here, in order to increase the separation efficiency of high-purity CO2 gas, it is preferable to reduce the linear velocity (flow rate) of the combustion exhaust gas within the high-purity CO2 separator 50 as much as possible. However, in order to reduce the linear velocity of the combustion exhaust gas, it is necessary to increase the cross-sectional area of ​​the flow path of the combustion exhaust gas within the high-purity CO2 separator 50 (for example, the cross-sectional area of ​​the piping), which results in the problem of the entire high-purity CO2 separator 50 becoming larger.

[0109] In contrast, in the above configuration, instead of supplying all of the combustion exhaust gas discharged from the combustion device 40 to the high-purity CO2 separator 50, a portion of the combustion exhaust gas distributed from the combustion exhaust gas distribution unit 73 is supplied to the high-purity CO2 separator 50. This reduces the flow rate of combustion exhaust gas to be processed in the high-purity CO2 separator 50, and consequently, allows for miniaturization of the high-purity CO2 separator 50. Therefore, the increase in equipment costs due to the enlargement of the high-purity CO2 separator 50 can be suppressed. Furthermore, by miniaturizing the high-purity CO2 separator 50, the power consumption of the high-purity CO2 separator 50 can be suppressed, thereby reducing operating costs. In addition, by suppressing power consumption, the amount of carbon dioxide emitted outside the system (carbon dioxide emitted outside the system during the power generation stage) can be suppressed.

[0110] (Example 3-1) Next, we will describe Example 3-1, a specific example of Embodiment 3, with reference to Figure 8.

[0111] Figure 8 is a schematic diagram showing the flow rates of each working fluid in Example 3-1. In the following, we will mainly explain the differences from Example 1-1 (see Figure 2), and will omit explanations where appropriate.

[0112] In this embodiment, similar to Example 1-1, the target air ratio λ is set to 1.4, and the target oxygen concentration A in the combustion device 40 is set. O2 The ratio is set to 20%, and the processing in the water electrolysis device 20 and the methanation device 30 is the same as in Example 1-1. Finally, the flow rate of methane, the flow rate of oxygen, and the flow rate of carbon dioxide supplied to the combustion device 40, as well as the composition of the combustion exhaust gas (gas containing carbon dioxide, water, and oxygen) discharged from the combustion device 40 and the flow rates of each component are the same as in Example 1-1, however, the flow path of the combustion exhaust gas discharged from the combustion device 40 is different from that of Example 1-1.

[0113] In other words, in this embodiment, 305 Nm³ was discharged from the combustion device 40. 3 / h carbon dioxide and 50 Nm 3 / h of water (strictly speaking, water vapor) and 20Nm 3 The combustion exhaust gas containing oxygen at a rate of / h passes through the water separator 12 to separate the water, and then first flows into the combustion exhaust gas distribution section 73.

[0114] In the combustion exhaust gas distribution unit 73, 10% of the combustion exhaust gas after water separation is supplied to the high-purity CO2 separator 50, and the remaining 90% of the combustion exhaust gas is supplied to the combustion device 40 via the branched flow path 74. In other words, the combustion exhaust gas distribution unit 73 supplies the combustion exhaust gas to the high-purity CO2 separator 50 and the branched flow path 74 respectively so that the distribution ratio R of the combustion exhaust gas to the high-purity CO2 separator 50 is a predetermined target distribution ratio Rt (in this example, Rt = 10 / (10 + 90)). In the example shown in Figure 8, the flow rate of carbon dioxide in the combustion exhaust gas discharged from the combustion device 40 is 305 Nm³ 3 The oxygen flow rate is 20 Nm³ / h. 3 Since it is / h, 10% of each component is 30.5Nm 3 / h carbon dioxide and 2Nm 360% of oxygen and 274.5 Nm³ are supplied to the high-purity CO2 separator 50, and the remaining 90% is 274.5 Nm³. 3 / h carbon dioxide and 18Nm 3 Oxygen is supplied to the branch channel 74.

[0115] Ten percent of the combustion exhaust gas supplied to the high-purity CO2 separator 50 is separated into high-purity CO2 gas and low-purity CO2 gas. The high-purity CO2 gas is supplied to the methanation device 30 via flow paths 68 and 69.

[0116] Meanwhile, the low-purity CO2 gas flows into channels 70 and 71, and at the confluence 75 of channel 71, it merges with 90% of the combustion exhaust gas flowing in from the branch channel 74. This merged gas is equivalent to the gas obtained by removing the necessary carbon dioxide from the combustion exhaust gas after it has been discharged from the combustion device 40 and the water has been separated, in the methanation device 30. Therefore, its composition and flow rate are 280 Nm³ of carbon dioxide. 3 / h, oxygen 20Nm 3 The combined gas is 50 Nm³ of oxygen supplied from the water electrolysis device 20 via the flow path 61. 3 After further merging with / h, it is supplied to the combustion device 40 as combustion gas. Consequently, the combustion device 40 receives 70 (=50+20) Nm of combustion gas via the combustion gas supply channel 62, similar to Example 1-1. 3 Oxygen at / h and 280Nm 3 A supply of carbon dioxide is provided at a rate of 1 / h. Then, in the combustion device 40, methane is burned using this combustion gas consisting of oxygen and carbon dioxide.

[0117] Thus, according to this embodiment, by including carbon dioxide in the combustion gas in the combustion device 40, similar to Example 1-1, the same effects and advantages as in Example 1-1 can be obtained.

[0118] Furthermore, according to this embodiment, 10% of the combustion exhaust gas discharged from the combustion device 40 is distributed to the high-purity CO2 separator 50, and the remaining 90% is supplied to the combustion device 40 via the branched flow path 74. This reduces the flow rate of combustion exhaust gas to be processed in the high-purity CO2 separator 50, and consequently, allows for miniaturization of the high-purity CO2 separator 50. Thus, equipment costs and operating costs can be suppressed, as well as the emission of carbon dioxide outside the system due to increased power consumption (for example, carbon dioxide emissions outside the system during the power generation stage).

[0119] (Example 3-2) Next, we will describe Example 3-2, another embodiment of Embodiment 3, with reference to Figure 9. Figure 9 is the equivalent of Figure 8, showing Example 3-2. Below, we will mainly describe only the differences from Example 3-1.

[0120] In this embodiment, the flow rate of hydrogen supplied from the water electrolysis device 20 to the methanation device 30 is set to be greater than the flow rate of hydrogen based on the stoichiometric ratio (1:4) of the reaction equation (2), which is the difference from Example 3-1. This configuration of supplying hydrogen in excess of the stoichiometric ratio is the same as in Example 1-2 (see Figure 3), and in the combustion device 40, this surplus 6.25 Nm³ is used. 3 Hydrogen and 25 Nm³ / h 3 To burn methane at an air ratio of 1.4, 74.375 Nm³ 3 / h (=(6.25*1 / 2+25*2)*1.4) of oxygen is used, and as a result, 322.5 Nm³ is released from the combustion device 40. 3 Carbon dioxide at 1 / h and 21.25 Nm³ 3 Oxygen at / h and 56.25 Nm 3 Combustion exhaust gas containing water (more precisely, water vapor) is emitted.

[0121] The combustion exhaust gas discharged from the combustion device 40 passes through the water separator 12 to separate the water, and then flows into the combustion exhaust gas distribution unit 73.

[0122] The combustion exhaust gas distribution unit 73 supplies a part of the combustion exhaust gas to the high-purity CO2 separator 50 and supplies the remaining combustion exhaust gas to the combustion device 40 via the branch flow path 74. In the example of FIG. 9, the combustion exhaust gas distribution unit 73 supplies the combustion exhaust gas to the high-purity CO2 separator 50 and the branch flow path 74 such that the distribution ratio R of the combustion exhaust gas supplied to the high-purity CO2 separator 50 is 10.9% (an example of the target distribution ratio Rt).

[0123] In the example of FIG. 9, the flow rate of carbon dioxide in the combustion exhaust gas discharged from the combustion device 40 is 322.5 Nm 3 / h, and the flow rate of oxygen is 21.25 Nm 3 / h. Therefore, 35 Nm 3 / h of carbon dioxide, which is 10.9% thereof, and 2.31 Nm 3 / h of oxygen are supplied to the high-purity CO2 separator 50, and 287.5 Nm 3 / h of carbon dioxide, which is 89.1% of the remainder, and 18.94 Nm 3 / of oxygen are supplied to the branch flow path 74.

[0124] According to the present embodiment, by making the flow rate of hydrogen supplied to the methanation device 30 larger than the stoichiometric ratio, the conversion rate of carbon dioxide to methane in the methanation device 30 can be improved, and the same operational effects as those in Example 3-1 can be obtained.

[0125] (Other Embodiments) As described above, the embodiments and examples of the present invention have been described. However, the present invention is not limited thereto, and for example, the following embodiments can be adopted.

[0126] (1) [Target Oxygen Concentration] In each of the above embodiments and examples, the target oxygen concentration in the combustion device 40 is set to be equal to the oxygen concentration contained in the air in the atmosphere. However, the present invention is not limited thereto, and the target oxygen concentration may be, for example, higher or lower than the oxygen concentration in the atmosphere.

[0127] (2) [Reuse of Water] In the above embodiments and examples, the water generated during the methanation reaction and combustion is separated and discarded by water separators 11 and 12, respectively. However, the invention is not limited to this, and the separated water may be recovered and used as water for electrolysis in the water electrolysis device 20.

[0128] (3) [Combustion exhaust gas distribution section] In the above embodiment 3, the combustion exhaust gas distribution unit 73 is configured to set the distribution ratio R of the combustion exhaust gas supplied to the high-purity CO2 separator 50 to a target distribution ratio Rt by appropriately setting the ratio of the flow path cross-sectional areas of the second port 73b and the third port 73c, but it is not limited to this. That is, the combustion exhaust gas distribution unit 73 may have a flow rate adjustment mechanism for controlling the distribution ratio R. The flow rate adjustment mechanism may include, for example, a flow rate adjustment valve.

[0129] Here, the flow control valve can be provided in at least one of the downstream flow path section 67b and the branch flow path 74, for example. However, from the viewpoint of reducing pressure loss when the combustion exhaust gas passes through the flow control valve, it is preferable to provide the flow control valve in the flow path with a smaller flow rate of combustion exhaust gas (in Examples 3-1 and 3-2, the downstream flow path section 67b).

[0130] Furthermore, the flow control valve may be a so-called uncontrolled valve that is not controlled by the controller 101, or it may be a controlled valve that is controlled by the controller 101. In this case, if a controlled valve is used as the flow control valve, for example, flow meters may be provided in the downstream flow path section 67b and the branch flow path 74, and the controller 101 may control the flow control valve based on the flow rate of the combustion exhaust gas measured by each flow meter so that the distribution ratio R of the combustion exhaust gas to the high-purity CO2 separator 50 becomes the target flow rate. Alternatively, a flow indicator that integrates the flow control valve and the flow meter may be used.

[0131] (4) In the embodiment 3 described above, the downstream end of the branched channel 74 is connected to the channel 71 downstream of the low-purity CO2 tank 52, but it is not limited to this. The downstream end of the branched channel 74 may be connected to the low-purity CO2 tank 52, for example, or to the channel 70 upstream of the low-purity CO2 tank 52. This allows for a stable supply of carbon dioxide to the combustion device 40 through the fourth flow control valve 105 by using the low-purity CO2 tank 52 as a buffer. When the downstream end of the branched channel 74 is connected to the channel 71, the connection position is not limited to the middle of the channel 71, but may also be at the upstream or downstream end. The same applies when the downstream end of the branched channel 74 is connected to the channel 70. [Explanation of symbols]

[0132] λ: Air ratio 10: Thermal energy generation system 20: Water electrolysis device 30: Methanation device 40: Combustion device 50: High purity CO2 separator (CO2 distribution section) 55:CO2 distribution section 73: Combustion exhaust gas distribution section (CO2 distribution section) 100: Flow control device (1st to 4th flow adjustment section)

Claims

1. A water electrolysis device that generates and discharges hydrogen and oxygen by electrolyzing water, A methanation device that produces and discharges methane and water through a methanation reaction between carbon dioxide and hydrogen produced in the water electrolysis device, A combustion device that generates thermal energy by carrying out a combustion reaction between methane discharged from the methanation device and a combustion gas containing oxygen discharged from the water electrolysis device, and discharges carbon dioxide as a reaction product of the combustion reaction, CO2 is supplied by distributing the carbon dioxide emitted from the combustion device to the methanation device and the combustion device, respectively. ２ It includes a distribution unit, The aforementioned methanation device is the CO ２ It is configured to carry out the methanation reaction using carbon dioxide supplied from the distribution unit, The combustion device, ２ A thermal energy generation system configured to incorporate carbon dioxide supplied from a distribution unit into the combustion gas to carry out the combustion reaction.

2. In the thermal energy generation system according to claim 1, A thermal energy generation system further comprising a first flow rate adjustment unit that adjusts the flow rate of carbon dioxide supplied to the combustion device so that the concentration of oxygen in the combustion gas is equivalent to the concentration of oxygen in the atmosphere.

3. In the thermal energy generation system according to claim 1 or 2, A thermal energy generation system further comprising a second flow rate adjustment unit that adjusts the flow rate of methane and the flow rate of oxygen supplied to the combustion device so that the combustion reaction of methane in the combustion device is carried out in an oxygen-rich state where there is more oxygen than the theoretical air ratio.

4. In the thermal energy generation system according to claim 3, The combustion apparatus is configured to discharge combustion exhaust gas containing carbon dioxide and oxygen by performing the combustion reaction in the oxygen-rich state. The aforementioned CO ２ The distribution unit extracts high-purity CO2 with a predetermined concentration from the combustion exhaust gas discharged from the combustion device. ２ It has a separator for separating gases, and high-purity CO separated by the separator ２ The gas is supplied to the methanation device, and the high-purity CO2 is obtained from the combustion exhaust gas. ２ Low-purity CO2, which remains after gas separation, contains carbon dioxide and oxygen, and has a carbon dioxide concentration lower than the predetermined concentration. ２ A thermal energy generation system configured to supply gas to the combustion device.

5. In the thermal energy generation system according to claim 4, the CO ２ The distribution unit further has a combustion exhaust gas distribution unit that supplies a part of the combustion exhaust gas discharged from the combustion device to the separator and supplies the remaining combustion exhaust gas to the combustion device. The separator filters high-purity CO2 from the combustion exhaust gas supplied from the combustion exhaust gas distribution unit. ２ A thermal energy generation system configured to separate gases.

6. In the thermal energy generation system according to claim 1 or 2, A thermal energy generation system further comprising a third flow rate adjustment unit that adjusts the flow rate of methane supplied to the combustion device and the flow rate of oxygen supplied to the combustion device so that the combustion reaction of methane in the combustion device is carried out at a stoichiometric air ratio.

7. In the thermal energy generation system according to claim 1, A thermal energy generation system further comprising a fourth flow rate adjustment unit that adjusts the flow rate of hydrogen and the flow rate of carbon dioxide supplied to the methanation apparatus so that the ratio of hydrogen to carbon dioxide used in the methanation reaction in the methanation apparatus becomes a predetermined ratio in which hydrogen is more abundant than the stoichiometric ratio.

8. A method for generating thermal energy, A water electrolysis process that generates hydrogen and oxygen by electrolyzing water, The methanation reaction between carbon dioxide and hydrogen produced in the water electrolysis process results in methane. and a methanation process that generates water, A combustion step is performed in which a combustion reaction of methane produced in the methanation step is carried out using a combustion gas containing oxygen produced in the water electrolysis step, thereby generating thermal energy and emitting carbon dioxide as a reaction product of the combustion reaction. The system includes a distribution step that separates the carbon dioxide generated in the combustion step into carbon dioxide for the methanation step and carbon dioxide for the combustion step. In the methanation step, the methanation reaction is carried out using carbon dioxide for the methanation step. A method for generating thermal energy, wherein the combustion step involves adding carbon dioxide for the combustion step to the combustion gas and carrying out the combustion reaction.

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