Solid carbon generation system

Abstract

This aims to suppress the increase in thermal energy consumption in solid carbon production systems that use carbon dioxide as a raw material. [Solution] The solid carbon generation system 100 comprises an electrolytic cell 103, a molten salt 101 containing carbonate ions housed in the electrolytic cell 103, a cathode 111 and an anode 113 immersed in the molten salt 101, a power supply 115 connected to the cathode 111 and the anode 113, a supply path 120 for supplying a raw material gas 201 containing carbon dioxide to the electrolytic cell 103, an exhaust path 130 for guiding the exhaust gas 203 from the electrolytic cell 103 to the outside of the electrolytic cell 103, and a heat exchanger 141 arranged on the supply path 120 and the exhaust path 130 for heating the raw material gas 201 with the thermal energy of the exhaust gas 203.

Description

[Technical Field]

[0001] This disclosure relates to a solid carbon production system that uses carbon dioxide as a raw material. [Background technology]

[0002] Conventionally, a method for producing carbon by molten salt electrolysis using carbon dioxide as a raw material is known (see, for example, Patent Documents 1 and 2).

[0003] Patent Document 1 describes a method for depositing diamond on the surface of a cathode by arranging an anode-cathode pair in a mixed molten salt containing at least one of an alkali metal halide and an alkaline earth metal halide in a CO2 atmosphere, and performing electrolysis while controlling the cathode voltage so as not to deposit cations of the mixed molten salt on the cathode side.

[0004] Patent Document 2 describes a method for fixing carbon in carbon dioxide by an electrochemical process using a molten salt. This method involves (a) carbonate ions (CO3 2- The process comprises the steps of (b) preparing an electrolytic bath consisting of a molten salt containing (c) (a), (b) arranging a cathode and an anode in the electrolytic bath, and (c) blowing carbon dioxide into the electrolytic bath and applying a voltage between the cathode and anode that reduces carbonate ions, thereby energizing the system. The energization then decomposes the carbon dioxide and fixes it as carbon on the cathode surface. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-89230 [Patent Document 2] Japanese Patent Publication No. 2010-53425 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In the technologies described in Patent Documents 1 and 2, solid carbon is deposited on the cathode by a reduction reaction of carbonate ions in the cathode. To promote this reduction reaction, it is necessary to maintain the molten salt at a high temperature to promote the dissolution of carbon dioxide supplied to the electrolytic cell into the molten salt. For this reason, it is common to heat the electrolytic cell using an electric furnace, but this presents the problem that a large amount of thermal energy is required to maintain the electrolytic cell at a high temperature.

[0007] Therefore, this disclosure aims to address the challenge of suppressing the increase in thermal energy consumption in a solid carbon production system that uses carbon dioxide as a raw material. [Means for solving the problem]

[0008] To address the above issues, this disclosure utilizes the thermal energy of exhaust gas from the electrolytic cell to suppress the overall thermal energy consumption of the system.

[0009] In other words, one embodiment of the solid carbon generation system disclosed herein is: Electrolytic cell and The electrolytic cell contains a molten salt containing carbonate ions, The cathode and anode immersed in the molten salt, A power supply connected to the cathode and the anode, A supply channel for supplying a raw material gas containing carbon dioxide to the electrolytic cell, A discharge passage for guiding the exhaust gas from the electrolytic cell to the outside of the electrolytic cell, The system includes a heat exchanger positioned on the supply path and the discharge path, which heats the raw material gas using the thermal energy of the exhaust gas. It is characterized by the following:

[0010] With this configuration, the heat exchanger can be used to heat the raw material gas using the thermal energy of the exhaust gas before supplying it to the electrolytic cell. This reduces the amount of thermal energy consumed to maintain the molten salt at a high temperature.

[0011] The aforementioned discharge passage is A carbon dioxide adsorption / desorption device which is arranged downstream of the heat exchanger and can adsorb and desorb unreacted carbon dioxide contained in the exhaust gas, and a return path for returning the carbon dioxide desorbed from the carbon dioxide adsorption / desorption device to the supply path. This is preferable.

[0012] In this configuration, unreacted carbon dioxide contained in the exhaust gas is separated by the carbon dioxide adsorption / desorption device and returned to the supply path through the return path. As a result, unreacted carbon dioxide can be reused, and by returning the carbon dioxide contained in the high-temperature exhaust gas to the supply path, it is also advantageous for increasing the temperature of the raw material gas.

[0013] The exhaust path branches into a first path and a second path downstream of the carbon dioxide adsorption / desorption device, the first path is connected to the upstream side of the heat exchanger in the supply path and functions as the return path, and the second path is connected to a heat accumulator that stores the thermal energy of the exhaust gas that has passed through the carbon dioxide adsorption / desorption device. This is preferable.

[0014] The unreacted carbon dioxide separated from the exhaust gas is returned to the supply path through the first path. On the other hand, since the exhaust gas from which carbon dioxide has been removed is still at a high temperature, its thermal energy is recovered using the heat accumulator. Thus, the thermal energy of the exhaust gas can be used for various heating purposes.

[0015] The exhaust path branches into a first exhaust path and a second exhaust path at a branch point downstream of the heat exchanger, each of the first exhaust path and the second exhaust path includes the carbon dioxide adsorption / desorption device, the first path, and the second path arranged downstream of the branch point, when the carbon dioxide is adsorbed in the carbon dioxide adsorption / desorption device of the first exhaust path, the carbon dioxide is desorbed in the carbon dioxide adsorption / desorption device of the second exhaust path, When carbon dioxide is adsorbed in the carbon dioxide adsorption / desorption device of the second discharge path, desorption of carbon dioxide in the carbon dioxide adsorption / desorption device of the first discharge path is performed. This is preferable.

[0016] In this configuration, one of the carbon dioxide adsorption / desorption devices in the first discharge path and the carbon dioxide adsorption / desorption device in the second discharge path is in a carbon dioxide adsorption state, and the other is in a carbon dioxide desorption state. As a result, unreacted carbon dioxide can be continuously returned to the supply path, which is advantageous for the reuse of carbon dioxide and the heating of the raw material gas.

[0017] The discharge path is arranged downstream of the heat exchanger and includes a regenerator that stores the thermal energy of the exhaust gas. This is preferable.

[0018] In this configuration, the thermal energy of the exhaust gas that has passed through the heat exchanger is recovered using the regenerator. As a result, the thermal energy of the exhaust gas can be more effectively utilized.

[0019] The discharge path is arranged downstream of the regenerator and includes a carbon dioxide adsorption / desorption device capable of adsorbing and desorbing unreacted carbon dioxide contained in the exhaust gas, a first path for returning the carbon dioxide desorbed from the carbon dioxide adsorption / desorption device to the supply path, and a second path for taking out the exhaust gas from which carbon dioxide has been removed by the carbon dioxide adsorption / desorption device to the outside of the system. This is preferable.

[0020] Unreacted carbon dioxide separated from the exhaust gas that has passed through the regenerator is returned to the supply path through the first path and reused. On the other hand, since the exhaust gas from which carbon dioxide has been removed contains oxygen generated at the anode, it can be taken out of the system through the second path and used for various applications such as combustion utilization and fuel cell utilization.

[0021] The heat energy stored in the heat storage device is used to heat the carbon dioxide adsorption / desorption device, and the carbon dioxide adsorbed on the carbon dioxide adsorption / desorption device is desorbed. It is preferable.

[0022] By employing a carbon dioxide adsorption / desorption device that removes carbon dioxide through heating, the thermal energy of the heat storage device can be used to heat the carbon dioxide adsorption / desorption device, thereby further reducing the overall thermal energy consumption of the solid carbon generation system.

[0023] The electrolytic cell is heated using the thermal energy stored in the heat storage device. It is preferable.

[0024] By utilizing the thermal energy of the heat storage device to heat the electrolytic cell, the overall thermal energy consumption of the solid carbon production system can be further reduced. [Effects of the Invention]

[0025] As described above, this disclosure makes it possible to suppress the increase in thermal energy consumption in a solid carbon production system that uses carbon dioxide as a raw material. [Brief explanation of the drawing]

[0026] [Figure 1] A diagram showing the configuration of the solid carbon generation system according to Embodiments 1 to 3. [Figure 2] A diagram showing the gas flow in the solid carbon generation system according to Embodiment 3. [Figure 3] Figure 2 illustrates an example of how to operate the exhaust gas treatment device in the solid carbon generation system. [Figure 4] Figure 2 illustrates an example of how to operate the exhaust gas treatment device in the solid carbon generation system. [Figure 5] A diagram corresponding to Figure 2 showing a solid carbon generation system according to Embodiment 4. [Modes for carrying out the invention]

[0027] Embodiments of the present disclosure will be described in detail below with reference to the drawings. The following description of preferred embodiments is illustrative in nature and is not intended to limit the present disclosure, its applications, or its uses in any way.

[0028] (Embodiment 1) <Solid Carbon Generation System> As shown in Figure 1, the solid carbon generation system 100 according to this disclosure comprises an electrolytic cell 103, a molten salt 101, a cathode 111, an anode 113, a power supply 115, a supply line 120, a discharge line 130, and a heat exchanger 141. The solid carbon generation system 100 may further include an optional vacuum insulated container 105 as needed. Furthermore, as will be detailed in Embodiments 2 and 3, the solid carbon generation system 100 may further include an optional exhaust gas treatment device 100A as needed.

[0029] In this specification, the terms "upstream" and "downstream" are based on the direction of flow of the raw material gas and exhaust gas.

[0030] [Electrolytic cell, molten salt, cathode, anode, and power supply] The electrolytic cell 103, cathode 111, anode 113, and power supply 115 are not particularly limited, and conventionally known general configurations used in molten salt electrolysis using carbon dioxide CO2 as a raw material can be adopted.

[0031] The molten salt 101 contained in the electrolytic cell 103 contains carbonate ions CO3 2- As long as it contains [the specified element], it is not particularly limited, and any conventionally known general molten salt used in molten salt electrolysis using CO2 as a raw material can be used.Specific examples of molten salt 101 include alkali metal carbonates, alkaline earth metal carbonates, etc., and preferably a molten salt containing lithium carbonate Li2CO3 can be used.

[0032] For example, when Li2CO3 is heated to near its melting point (618°C), specifically to a temperature between 500°C and 800°C, the Li2CO3 becomes molten in the electrolytic cell 103. The electrolytic cell 103 may be heated, for example, in an electric furnace (not shown) placed on the outer periphery of the electrolytic cell 103, or, as will be described later, if a heat accumulator 147 is provided, the heating may be carried out using the thermal energy stored in the heat accumulator 147.

[0033] Furthermore, it is preferable that the inside of the electrolytic cell 103 is replaced with an inert gas such as Ar.

[0034] Two electrodes are immersed in the molten salt 101, one serving as the cathode 111 and the other as the anode 113. The cathode 111 and anode 113 are connected to each other by wiring that constitutes an external circuit, and a power supply 115 is located on the external circuit. In other words, both electrodes are connected to the power supply 115.

[0035] [Supply route] The supply path 120 is a gas flow path that supplies raw material gas 201 containing CO2 to the electrolytic cell 103. The supply path 120 comprises an upstream supply path 121 located upstream of the heat exchanger 141 and a downstream supply path 122 located downstream.

[0036] At the upstream end of the upstream supply channel 121, although not intended to be limiting, a gas cylinder 145 containing the raw material gas 201 is connected. The raw material gas 201 supplied through the upstream supply channel 121 may, although not intended to be limiting, be, for example, CO2-containing gas derived from the exhaust of a vehicle or CO2-containing gas derived from an on-board CO2 recovery system. The CO2 content of the raw material gas 201 may, although not intended to be limiting, be, for example, 400 ppm or more and 100% or less.

[0037] In Figure 1, the tip (downstream side) of the downstream supply channel 122 is immersed in the molten salt 101, and the raw material gas 201 is bubbled into the molten salt 101, but the configuration is not limited to this. If the downstream supply channel 122 is connected to the electrolytic cell 103, the tip of the downstream supply channel 122 does not need to be immersed in the molten salt 101. In this case, the raw material gas 201 supplied from the downstream supply channel 122 into the electrolytic cell 103 flows onto the liquid surface of the molten salt 101. From the viewpoint of promoting the dissolution of CO2 into the molten salt 101, supplying the raw material gas 201 by bubbling is preferable.

[0038] [Exhaust channel] The discharge passage 130 is a gas flow path that guides the exhaust gas 203 from the electrolytic cell 103 to the outside of the electrolytic cell 103. The exhaust gas 203 discharged from the electrolytic cell 103 contains oxygen O2 generated at the anode 113 and unreacted CO2.

[0039] The discharge passage 130 comprises an upstream discharge passage 131 located upstream of the heat exchanger 141 and a downstream discharge passage 132 located downstream. The downstream side of the downstream discharge passage 132 is not particularly limited, but it is preferable to have an exhaust gas treatment device 100A, as will be described later in Embodiments 2 and 3.

[0040] [Heat exchanger] The heat exchanger 141 is located on the supply channel 120 and the discharge channel 130. Specifically, the downstream side of the upstream supply channel 121 and the upstream side of the downstream supply channel 122 are connected to the heat exchanger 141. Also, the downstream side of the upstream discharge channel 131 and the upstream side of the downstream discharge channel 132 are connected to the heat exchanger 141. The heat exchanger 141 heats the raw material gas 201 flowing through the supply channel 120 with the thermal energy of the exhaust gas 203 that flows into the heat exchanger 141.

[0041] The heat exchanger 141 is not particularly limited as long as it is capable of heating the raw material gas 201 with the thermal energy of the exhaust gas 203, and a generally known heat exchanger such as a plate heat exchanger can be used.

[0042] [Vacuum-insulated container] The vacuum-insulated container 105 is preferably provided in order to suppress the temperature drop of the exhaust gas 203 in the upstream discharge channel 131 and the raw material gas 201 in the downstream supply channel 122. This allows the thermal energy of the exhaust gas 203 to be efficiently used to heat the raw material gas 201.

[0043] The vacuum insulated container 105 is not particularly limited and can be a generally known configuration such as a stainless steel vacuum insulated container. The area inside the vacuum insulated container 105 that is outside the electrolytic cell 103 is depressurized by, for example, a commercially available vacuum pump.

[0044] [High-temperature molten salt electrolysis] The principle of solid carbon (C) deposition by high-temperature molten salt electrolysis will be explained using the example of molten salt 101 containing lithium carbonate (Li2CO3). The current application conditions in high-temperature molten salt electrolysis are not particularly limited, and conventionally known general conditions used in molten salt electrolysis using CO2 as a raw material can be adopted. The current application conditions may vary depending on the size of the electrodes, but specifically, for example, a condition in which a voltage of about 1-2V is applied between the two electrodes can be used.

[0045] When power is supplied by the power supply 115 to perform electrolysis of the molten salt 101, the reduction reaction shown in equation (1) below proceeds at the cathode 111.

[0046] CO3 2- +4e - →C+3O 2- ...(1) Furthermore, the oxidation reaction shown in equation (2) below proceeds at anode 113.

[0047] 20 2- →4e - +O2···(2) On the other hand, when the raw material gas 201 is supplied into the electrolytic cell 103 through the supply passage 120, the CO2 contained in the raw material gas 201 and the O generated in the above equation (1) are released. 2- The reaction shown in equation (3) below proceeds between them.

[0048] CO2 + O 2- → CO3 2- ···(3) The CO3 generated in Equation (3) 2- is used in the above Equation (1).

[0049] Overall, by continuously supplying the raw material gas 201, seemingly, the electrolysis reaction of the following Equation (4) proceeds continuously.

[0050] CO2 → C + O2 ···(4) As a result, solid carbon C is deposited on the cathode 111. The solid carbon C is, for example, an expensive carbon material such as diamond, graphene, carbon nanotube, carbon nanosheet, etc., although not intended to be limiting. Also, the O2 generated at the anode 113 is discharged outside the electrolytic cell 103 through the discharge path 130 together with the unreacted CO2.

[0051] In addition, in the molten salt 101, the reaction of the following Equation (5) can also proceed.

[0052] 2Li + + O 2- → Li₂O ···(5) When combining the above Equation (1), Equation (2) and Equation (5), the reaction of the following Equation (6) can proceed overall.

[0053] Li₂CO₃ → C + O₂ + Li₂O ···(6) Since the melting point of Li₂O is 1400 °C or higher and it does not melt near the melting point of Li₂CO₃, it precipitates as a solid in the molten salt 101. Then, the O 2- to be used in the reaction of the above Equation (3) is consumed by the reaction of the above Equation (5), and ultimately hinders the progress of the reaction of the above Equation (4).

[0054] The reaction of the above Equation (5) occurs when the reaction rates of the above Equation (1) and the above Equation (2) are greater than the reaction rate of the above Equation (3), and O 2-This becomes excessive and the reaction proceeds particularly rapidly. Therefore, in order to maintain the continuous progress of equation (4) above, it is desirable that the reaction rate of equation (3) above be greater than the reaction rates of equations (1) and (2) above.

[0055] The reaction in equation (3) above can be considered to be rate-determined by the dissolution of CO2 in the source gas 201 into the molten salt 101.

[0056] Conventionally, in order to promote the dissolution of CO2 into the molten salt 101, the electrolytic cell 103 is heated in an electric furnace or the like, but the amount of thermal energy required to maintain the temperature of the electrolytic cell 103 is enormous.

[0057] Therefore, in the solid carbon generation system according to this disclosure, heat exchangers 141 are placed on the supply channel 120 and the discharge channel 130, and the raw material gas 201 flowing through the supply channel 120 is heated by the thermal energy of the exhaust gas 203.

[0058] As described above, the exhaust gas 203 from the electrolytic cell 103 contains O2 generated at the anode 113 and unreacted CO2. Since the temperature of the electrolytic cell 103 is maintained at a high temperature, for example, 500°C to 800°C, the temperature of the exhaust gas 203 is also around the same temperature, specifically, for example, about 750°C. On the other hand, the temperature of the raw material gas 201 in the upstream supply line 121 may be at room temperature, such as 25°C, if it originates from an on-board carbon dioxide capture system. In this configuration, the raw material gas 201 is heated to, for example, about 300°C by the heat exchanger 141 and supplied to the electrolytic cell 103. This reduces the amount of thermal energy consumed to maintain the molten salt at a high temperature.

[0059] Furthermore, since the reaction in formula (3) is an exothermic reaction, the temperature of the electrolytic cell 103 can be maintained by suppressing the temperature drop of the electrolytic cell 103 by heating the raw material gas 201 and by promoting the reaction in formula (3). In this way, heating of the electrolytic cell 103 to maintain the temperature of the electrolytic cell 103 during electrolysis, which was conventionally performed using an electric furnace or the like, becomes unnecessary.

[0060] (Embodiment 2) Other embodiments relating to this disclosure will be described in detail below. In the description of these embodiments, the same reference numerals are used for parts that are the same as in Embodiment 1, and detailed descriptions will be omitted.

[0061] The temperature of the exhaust gas 203 discharged from the electrolytic cell 103 decreases to, for example, about 450°C after passing through the heat exchanger 141, but it is still high. Therefore, it is desirable to make more effective use of the thermal energy of the exhaust gas.

[0062] As an example of a device for effectively utilizing the thermal energy of such exhaust gases, the solid carbon generation system 100 of Embodiment 2 includes an exhaust gas treatment device 100A, as shown in Figure 1. The exhaust gas treatment device 100A is installed on the downstream discharge passage 132 of the solid carbon generation system 100 of Embodiment 1.

[0063] As described above, exhaust gas 203 contains O2 generated at the anode and unreacted CO2. Therefore, by separating CO2 from exhaust gas 203 and returning it to the supply line 120, the temperature of the raw material gas 201 can be effectively increased.

[0064] Specifically, the exhaust gas treatment device 100A is located on the downstream discharge passage 132 and includes a CO2 adsorption / desorption device 152 that adsorbs and desorbs unreacted CO2 contained in the exhaust gas 203. Downstream of the CO2 adsorption / desorption device 152 in the downstream discharge passage 132, the passage branches at a first branching point 130a into a first branching passage 132a (first path, return path) and a second branching passage 132b (second path). The first branching point 130a is provided with a flow path switching member, such as a three-way valve, and is configured to switch the path of the exhaust gas 203 to either the first branching passage 132a or the second branching passage 132b. The first branching passage 132a is connected to the upstream supply passage 121. The second branching passage 132b is connected to a heat accumulator 147 located downstream and an O2 gas cylinder 149 located downstream of the heat accumulator 147.

[0065] The CO2 adsorption / desorption device 152 is a device that can switch between CO2 adsorption and desorption (desorption) by switching predetermined conditions. The CO2 adsorption / desorption device 152 is not particularly limited as long as it has such a function, and a generally known CO2 adsorption / desorption device using methods such as electroswing adsorption (ESA), pressure swing adsorption (PSA), and temperature swing adsorption (TSA) can be used.

[0066] Examples of devices capable of electrochemically adsorbing and desorbing CO2 using ESA include, but are not limited to, a CO2 adsorption / desorption device using an electrochemical cell equipped with a polyanthraquinone-carbon composite electrode and a polyvinylferrocene-carbon composite electrode (S. Voskian et al., Energy Environ. Sci., 2019, 12, 3530). Figure 1 shows an example of a CO2 adsorption / desorption device employing ESA. In this case, an additional power supply 143 is connected to the device. The CO2 adsorption / desorption by the CO2 adsorption / desorption device 152 can then be switched by turning the additional power supply 143 on / off or changing the polarity of the current. For example, in the above example, CO2 can be adsorbed by applying current to the polyanthraquinone-carbon composite electrode as the cathode and the polyvinylferrocene-carbon composite electrode as the anode. CO2 can be desorbed by switching the polarity of both electrodes.

[0067] Examples of CO2 adsorption / desorption devices using PSA include, but are not limited to, devices using zeolite-based adsorbents, inorganic carbon dioxide adsorbents made of amorphous aluminum silicate with a partially imogolite structure, etc. In such PSA-based CO2 adsorption / desorption devices, for example, CO2 can be adsorbed by increasing pressure and desorbed by decreasing pressure.

[0068] Examples of devices capable of adsorbing and desorbing CO2 using TSA include, but are not limited to, zeolite-based adsorbents. In such TSA-based CO2 adsorption and desorption devices, for example, CO2 can be adsorbed within a predetermined temperature range, and CO2 can be desorbed by raising the temperature above that range.

[0069] An example of how to operate the exhaust gas treatment device 100A will be explained.

[0070] First, in the CO2 adsorption operation, the CO2 adsorption / desorption device 152 is set to the CO2 adsorption state, and the flow path switching member at the first branch point 130a is set to the open state towards the second branch 132b side and the closed state towards the first branch 132a side. As a result, CO2 in the exhaust gas 203 is adsorbed by the CO2 adsorption / desorption device 152 and removed from the exhaust gas 203. The exhaust gas 203 (also called "O2-containing gas") that has passed through the CO2 adsorption / desorption device 152 passes through the first branch point 130a and flows through the second branch 132b, as shown by the dashed arrow, and flows into the heat storage device 147.

[0071] The heat storage device 147 has the function of storing the thermal energy of an O2-containing gas. The heat storage device 147 is not particularly limited as long as it has this function, and a generally known heat storage device can be used. Specifically, examples of heat storage devices 147 include calcium oxide (CaO / H2O system (where the substance after " / " indicates the working medium; the same applies hereinafter): heat storage temperature approximately 500°C), ammonium bisulfate (NH4HSO4 / NH3 system: heat storage temperature approximately 470°C), magnesium oxide (MgO / H2O system: heat storage temperature approximately 300~350°C), manganese oxide (Mn2O3 / O2 system: heat storage temperature approximately 450°C) A heat storage device can be used that utilizes chemical heat storage materials such as (up to 550°C), sensible heat storage materials such as silicone oil (heat storage temperature approximately 300-400°C), nitrite-based (heat storage temperature approximately 250-450°C), nitrate-based (heat storage temperature approximately 265-565°C), and carbonate-based (heat storage temperature approximately 450-850°C), and latent heat storage materials such as sodium nitrate (heat storage temperature approximately 300°C) and potassium nitrate (heat storage temperature approximately 330°C). Preferably, a heat storage device using a chemical heat storage material can be used. For example, if the temperature of the O2-containing gas is 400°C or higher, a heat storage device using calcium oxide can be used, and if the temperature of the O2-containing gas is less than 400°C, a heat storage device using magnesium oxide can be used.

[0072] When high-temperature O2-containing gas flows into the heat accumulator 147, the heat from the O2-containing gas is stored in the heat accumulator 147, and the temperature of the O2-containing gas decreases. After the O2-containing gas has cooled down flows out of the heat accumulator 147, it may be used for various purposes such as combustion or fuel cell use, or it may be stored in an O2 gas cylinder 149, for example, and used for various purposes. If a chemical heat storage material using O2 as the working fluid is used as the heat accumulator 147, the O2 stored in the O2 gas cylinder 149, etc., may be used to generate heat in the heat accumulator 147. On the other hand, the thermal energy stored in the heat accumulator 147 can be used, without limitation, for purposes such as heating an electrolytic cell 103 for the purpose of molten salt generation or temperature maintenance.

[0073] Next, in the CO2 desorption operation, the CO2 adsorption / desorption device 152 is set to a CO2 desorption state, and the flow path switching member at the first branch point 130a is set to an open state towards the first branch 132a side and a closed state towards the second branch 132b side. In this way, the CO2 adsorbed by the CO2 adsorption / desorption device 152 in the above CO2 adsorption operation is desorbed and returned to the upstream supply channel 121 through the first branch 132a. By returning this CO2 to the upstream supply channel 121, unreacted CO2 can be reused and the temperature of the raw material gas 201 in the upstream supply channel 121 can be increased.

[0074] According to the solid carbon generation system 100 of this embodiment, the thermal energy of the exhaust gas 203 is efficiently utilized by reusing unreacted CO2 using the CO2 adsorption / desorption device 152 in addition to the heat exchanger 141, thereby effectively suppressing the amount of thermal energy consumed to maintain the molten salt at a high temperature. Furthermore, if the thermal energy of the O2-containing gas is recovered using the heat regenerator 147 and used to heat the electrolytic cell 103, it becomes even more advantageous to reduce the amount of thermal energy consumed.

[0075] (Embodiment 3) In Embodiment 2, the exhaust gas treatment device 100A was configured to include one CO2 adsorption / desorption device, but it may also be configured to include multiple CO2 adsorption / desorption devices.

[0076] Specifically, for example, as shown by the dashed line in Figure 1, the downstream discharge passage 132 may be branched to provide another additional CO2 adsorption / desorption device. That is, in the exhaust gas treatment device 100A of this embodiment, the downstream discharge passage 132 branches at the second branching point 130b, and a second discharge passage 134 is provided. The portion of the downstream discharge passage 132 downstream of the second branching point 130b is sometimes referred to as the first discharge passage 132.

[0077] Figures 2 to 4 illustrate an example of the gas flow and operation method of the exhaust gas treatment device 100A in the solid carbon generation system 100 of this embodiment. For ease of understanding, these figures omit the piping diagrams and only show the gas flow with arrows. Furthermore, the cathode 111, anode 113, and power supply 115 are not shown. The configuration of the exhaust gas treatment device 100A of this embodiment will now be described with reference to Figures 1 to 4.

[0078] The first discharge channel 132 includes a CO2 adsorption / desorption device 152, a first branch point 130a, a first branch channel 132a, and a second branch channel 132b, as described in Embodiment 2.

[0079] On the other hand, the second discharge channel 134 is equipped with an additional CO2 adsorption / desorption device 154. Downstream of the additional CO2 adsorption / desorption device 154 in the second discharge channel 134, the channel branches into an additional first branch channel 134a and an additional second branch channel 134b at an additional first branch point 130c.

[0080] The additional first branch point 130c is provided with a flow path switching member, similar to the first branch point 130a, and is configured to allow switching to either the additional first branch 134a or the additional second branch 134b by operating the flow path switching member.

[0081] The additional first branch 134a is connected to the upstream supply channel 121, similar to the first branch 132a. The additional second branch 134b merges with the second branch 132b at the confluence point 130d.

[0082] The additional CO2 adsorption / desorption device 154 can be the same as the CO2 adsorption / desorption device 152. Preferably, the additional CO2 adsorption / desorption device 154 has the same configuration as the CO2 adsorption / desorption device 152. When both the CO2 adsorption / desorption device 152 and the additional CO2 adsorption / desorption device 154 are CO2 adsorption / desorption devices using ESA, as shown in Figures 1 to 4, for example, an additional power supply 143 can be connected to both, and the CO2 adsorption state and CO2 desorption state of both can be switched by turning the additional power supply 143 on / off, switching the polarity, etc. Note that in these figures, the CO2 adsorption / desorption device 152 and the additional CO2 adsorption / desorption device 154 are connected to one additional power supply 143, but this configuration is not limited to this, and they may be connected to separate power supplies.

[0083] In this embodiment, the exhaust gas treatment device 100A is equipped with two CO2 adsorption / desorption devices. By simultaneously setting one of the devices to a CO2 adsorption state and the other to a CO2 desorption state, the treatment of the exhaust gas 203 can be made more efficient.

[0084] First, if CO2 is to be desorbed using an additional CO2 adsorption / desorption device 154 while CO2 is being adsorbed by the CO2 adsorption / desorption device 152, the operation should be carried out as follows.

[0085] As shown in Figure 3, the CO2 adsorption / desorption device 152 is set to the CO2 adsorption state, and the flow path switching member at the first branch point 130a is set to the open state towards the second branch 132b side and the closed state towards the first branch 132a side. As a result, CO2 in the exhaust gas 203 is adsorbed by the CO2 adsorption / desorption device 152 and removed from the exhaust gas 203. The exhaust gas 203 that has passed through the CO2 adsorption / desorption device 152, i.e., the O2-containing gas, passes through the first branch point 130a and flows through the second branch 132b, as shown by the dashed arrow, and flows into the heat storage device 147.

[0086] Meanwhile, the additional CO2 adsorption / desorption device 154 is set to a CO2 desorption state, the flow path switching member of the additional first branch point 130c is set to an open state toward the additional first branch 134a side and a closed state toward the additional second branch 134b side. In this way, the CO2 adsorbed by the additional CO2 adsorption / desorption device 154 is desorbed and returned to the upstream supply path 121 through the additional first branch 134a.

[0087] Furthermore, when CO2 is adsorbed by the additional CO2 adsorption / desorption device 154, if CO2 desorption is to be performed in the CO2 adsorption / desorption device 152, the operation should be carried out as follows.

[0088] As shown in Figure 4, the additional CO2 adsorption / desorption device 154 is set to the CO2 adsorption state, the flow path switching member of the additional first branch point 130c is set to the open state towards the additional second branch 134b and to the closed state towards the additional first branch 134a. As a result, CO2 in the exhaust gas 203 is adsorbed by the additional CO2 adsorption / desorption device 154 and removed from the exhaust gas 203. The exhaust gas 203 that has passed through the additional CO2 adsorption / desorption device 154, i.e., the O2-containing gas, flows through the additional first branch point 130c, the additional second branch 134b and the confluence point 130d, as shown by the dashed arrows, and flows into the second branch 132b and into the heat storage device 147.

[0089] Meanwhile, the CO2 adsorption / desorption device 152 is set to a CO2 desorption state, and the flow path switching member at the first branch point 130a is set to an open state towards the first branch 132a side and a closed state towards the second branch 132b side. In this way, the CO2 adsorbed by the CO2 adsorption / desorption device 152 is desorbed and returned to the upstream supply path 121 through the first branch 132a.

[0090] Thus, in the exhaust gas treatment device 100A of this embodiment, one of the CO2 adsorption / desorption device 152 and the additional CO2 adsorption / desorption device 154 can be in a CO2 adsorption state, and the other in a CO2 desorption state. This allows unreacted CO2 to be continuously returned to the upstream supply passage 121, which is advantageous for heating the raw material gas 201.

[0091] Note that the second branch point 130b and the confluence point 130d may simply be connected by piping, or they may be equipped with flow path switching members such as three-way valves. Figures 3 and 4 show examples in which flow path switching members are provided at both points. Specifically, in Figure 3, the flow path switching member at the second branch point 130b is open towards the first discharge channel 132 and closed towards the second discharge channel 134, while the flow path switching member at the confluence point 130d is open towards the first discharge channel 132 and closed towards the additional second branch point 134b. In Figure 4, the flow path switching member at the second branch point 130b is closed towards the first discharge channel 132 and open towards the second discharge channel 134, while the flow path switching member at the confluence point 130d is closed towards the first discharge channel 132 and open towards the additional second branch point 134b.

[0092] The exhaust gas treatment device 100A of Embodiment 3 is configured to include two CO2 adsorption / desorption devices, but is not limited to this configuration. The downstream discharge passage 132 may be further branched to include three or more CO2 adsorption / desorption devices. This is effective in improving the efficiency of utilizing the thermal energy of the exhaust gas, for example, when there is a difference between the time required for CO2 adsorption and the time required for desorption.

[0093] (Embodiment 4) Figure 5 is a diagram corresponding to Figure 2 showing a solid carbon generation system 100 according to Embodiment 4. As shown in Figure 5, in the exhaust gas treatment device 100A, the heat regenerator 147 may be placed upstream of the CO2 adsorption / desorption device 152 and the additional CO2 adsorption / desorption device 154, preferably directly downstream of the heat exchanger 141.

[0094] In the example shown in Figure 5, the exhaust gas 203 from the downstream discharge channel 132 first flows into the heat accumulator 147, where the thermal energy of the exhaust gas 203 is stored in the heat accumulator 147. The exhaust gas 203, whose temperature has decreased, flows out of the heat accumulator 147 and into the CO2 adsorption / desorption device 152 or an additional CO2 adsorption / desorption device 154 located downstream of the heat accumulator 147.

[0095] The CO2 adsorption / desorption device 152 or the additional CO2 adsorption / desorption device 154 can be configured in the same way as in Embodiment 3 described above. In the example in Figure 5, as another example of the CO2 adsorption / desorption device 152 and the additional CO2 adsorption / desorption device 154, a zeolite-based CO2 adsorption / desorption device using TSA is employed. The CO2 adsorption / desorption device 152 and the additional CO2 adsorption / desorption device 154 are connected to the heat accumulator 147, and the heat energy stored in the heat accumulator 147 can be used to desorb CO2 from both devices. The heat energy stored in the heat accumulator 147 may be used for heating the electrolytic cell 103 or for various other heating purposes, as in Embodiments 2 and 3.

[0096] The operation method for the CO2 adsorption / desorption device 152 and the additional CO2 adsorption / desorption device 154 can be the same as the operation method described in Embodiment 3. Specifically, by putting one of the CO2 adsorption / desorption device 152 and the additional CO2 adsorption / desorption device 154 into a CO2 adsorption state and the other into a CO2 desorption state, the efficiency of exhaust gas treatment can be improved. In the example shown in Figure 5, the CO2 adsorption / desorption device 152 and the additional CO2 adsorption / desorption device 154 can be put into a CO2 desorption state by heating them using the heat storage device 147.

[0097] The unreacted CO2 separated from the exhaust gas 203 can be returned to the upstream supply channel 121, as in Embodiments 2 and 3. The O2-containing gas separated from the exhaust gas 203 can also be removed from the system via the second branch channel 132b, as in Embodiments 2 and 3, and used for various purposes such as combustion or fuel cell applications. Alternatively, as shown by the dashed line in Figure 5, it can be stored in an O2 gas cylinder 149 or the like for various applications.

[0098] Note that while Figure 5 illustrates a configuration with two CO2 adsorption / desorption devices, similar to Figure 2, the system is not limited to this configuration. It may also be configured with one or three or more CO2 adsorption / desorption devices.

[0099] (Other embodiments) In the above embodiment, the case where a three-way valve is used as the flow path switching member has been described. However, the present invention is not limited to such a configuration, and other members may be used as long as the flow path can be switched. When using a three-way valve, it can be a generally known three-way valve, either a T-port or an L-port, and can be a manual valve or a solenoid valve. When the three-way valve is a solenoid valve, it can be configured to be controlled by a control device (not shown). Further, in the solid carbon generation system 100, for example, components such as a power source 115, a heat exchanger 141, an additional power source 143, a heat accumulator 147, a CO2 adsorption / desorption device 152, an additional CO2 adsorption / desorption device 154, and flow path switching members at each branch point and confluence point can be configured to be controlled by a control device (not shown).

Industrial Applicability

[0100] <UNK> The present disclosure is extremely useful in the field of solid carbon generation systems using carbon dioxide as a raw material.

Explanation of Reference Numerals

[0101] 100 Solid carbon generation system 101 Molten salt 103 Electrolytic cell 111 Cathode 113 Anode 115 Power source 120 Supply path 130 Discharge path 130a First branch point 130b Second branch point 130c Additional first branch point 130d Confluence point[[ID=3)]] 132 Downstream discharge path (first discharge path) 132a First branch path (first path, return path) 132b Second branch path (second path) 134 Second discharge path l34a Additional first branch path (first path, return path) 134b Additional second branch path (second path) 141 Heat exchanger 147 Heat accumulator 152 CO2 adsorption / desorption device (carbon dioxide adsorption / desorption device) 154 Additional CO2 adsorption / desorption equipment (carbon dioxide adsorption / desorption equipment) 201 Raw material gas 203 Exhaust Gas

Claims

1. Electrolytic cell and The electrolytic cell contains a molten salt containing carbonate ions, The cathode and anode immersed in the molten salt, A power supply connected to the cathode and the anode, A supply channel for supplying a raw material gas containing carbon dioxide to the electrolytic cell, A discharge passage for guiding the exhaust gas from the electrolytic cell to the outside of the electrolytic cell, The system includes a heat exchanger positioned on the supply path and the discharge path, which heats the raw material gas using the thermal energy of the exhaust gas. A solid carbon generation system characterized by the following features.

2. In claim 1, The aforementioned discharge passage is A carbon dioxide adsorption / desorption device is provided, which is located downstream of the heat exchanger and capable of adsorbing and desorbing unreacted carbon dioxide contained in the exhaust gas. The system includes a return path that returns the carbon dioxide detached from the carbon dioxide adsorption / desorption device back to the supply path. A solid carbon generation system characterized by the following features.

3. In claim 2, The aforementioned discharge passage branches into a first path and a second path downstream of the carbon dioxide adsorption / desorption device. The first path is connected to the upstream side of the heat exchanger of the supply path and functions as the return path. The second path is connected to a heat storage device that stores the thermal energy of the exhaust gas that has passed through the carbon dioxide adsorption / desorption device. A solid carbon generation system characterized by the following features.

4. In claim 3, The aforementioned discharge passage branches into a first discharge passage and a second discharge passage at a branching point downstream of the heat exchanger. Each of the first discharge path and the second discharge path comprises the carbon dioxide adsorption / desorption device, the first path, and the second path, located downstream of the branching point. When carbon dioxide is adsorbed in the carbon dioxide adsorption / desorption device of the first discharge channel, carbon dioxide is desorbed in the carbon dioxide adsorption / desorption device of the second discharge channel. When carbon dioxide is adsorbed in the carbon dioxide adsorption / desorption device of the second discharge channel, carbon dioxide is desorbed in the carbon dioxide adsorption / desorption device of the first discharge channel. A solid carbon generation system characterized by the following features.

5. In claim 1, The aforementioned discharge passage is located downstream of the heat exchanger and includes a heat storage device that stores the thermal energy of the exhaust gas. A solid carbon generation system characterized by the following features.

6. In claim 5, The aforementioned discharge passage is A carbon dioxide adsorption / desorption device is provided, which is located downstream of the heat storage device and is capable of adsorbing and desorbing unreacted carbon dioxide contained in the exhaust gas. A first path for returning the carbon dioxide detached from the carbon dioxide adsorption / desorption device back to the supply path, The system includes a second path for removing the exhaust gas from which carbon dioxide has been removed by the carbon dioxide adsorption / desorption device. A solid carbon generation system characterized by the following features.

7. In any one of claims 3, 4, and 6, The heat energy stored in the heat storage device is used to heat the carbon dioxide adsorption / desorption device, and the carbon dioxide adsorbed on the carbon dioxide adsorption / desorption device is desorbed. A solid carbon generation system characterized by the following features.

8. In any one of claims 3 to 6, The electrolytic cell is heated using the thermal energy stored in the heat storage device. A solid carbon generation system characterized by the following features.

Images