ELECTROSYNTHESIS SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2022-196714 filed on Dec. 9, 2022, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION
Field of the Invention

The present invention relates to an electrosynthesis system.

Description of the Related Art

In recent years, efforts have been made to substantially reduce waste generation through prevention, reduction, recycling and reuse. Toward the realization thereof, research and development are being carried out in relation to an electrosynthesis system. An electrosynthesis system is a system in which carbon dioxide gas and water vapor are subjected to electrolysis, and hydrocarbon gas such as methane or the like is synthesized based on hydrogen gas and carbon monoxide gas obtained by the electrolysis.

There is a case in which a catalyst is used to synthesize hydrocarbon gas from hydrogen gas and carbon monoxide gas. In this case, there is a tendency for carbon to be deposited on the catalyst due to usage of the catalyst over a prolonged time period. When carbon is deposited on the catalyst, the efficiency of the synthesis of the hydrocarbon gas is decreased.

In JP 2009-095722 A, it is disclosed that, when deposited carbon of a catalyst and air are brought into contact with each other and heated at a predetermined temperature, the deposited carbon vanishes. Accordingly, in the case that carbon is deposited on a catalyst used for synthesizing hydrocarbon gas, the deposited carbon is capable of being removed.

SUMMARY OF THE INVENTION

However, when the deposited carbon of the catalyst and air are brought into contact with each other and heated at a predetermined temperature, there is a tendency for the catalyst to become oxidized. When the catalyst is oxidized, the efficiency of the synthesis of the hydrocarbon gas is decreased.

The present invention has the object of solving the aforementioned problem.

An aspect of the present invention is characterized by an electrosynthesis system comprising an electrolysis device configured to subject carbon dioxide gas and water vapor to electrolysis and thereby generate carbon monoxide gas and hydrogen gas, a synthesizing device configured to use a catalyst to synthesize hydrocarbon gas from the carbon monoxide gas and the hydrogen gas that are discharged from the electrolysis device, a water vapor amount adjustment valve configured to adjust a flow rate of the water vapor supplied to the electrolysis device, a carbon dioxide amount adjustment valve configured to adjust a flow rate of the carbon dioxide gas supplied to the electrolysis device, a carbon dioxide concentration sensor configured to measure a concentration of the carbon dioxide gas within an exhaust gas discharged from the synthesizing device, and a control device, wherein, in a case that the concentration of the carbon dioxide gas within the exhaust gas has fallen below a predetermined carbon dioxide concentration threshold value in a state in which oxygen gas is being supplied to the synthesizing device, the control device opens the water vapor amount adjustment valve without opening the carbon dioxide amount adjustment valve, and thereby supplies the hydrogen gas to the synthesizing device via the electrolysis device.

According to the above-described aspect, the hydrogen gas generated in the electrolysis device by the electrolysis of water vapor can be supplied from the electrolysis device to the synthesizing device. As a result, the catalyst, which has been oxidized by the combustion of carbon deposited on the catalyst, can be reduced by a reaction with the hydrogen gas. As a result, it is possible to suppress a decrease in the efficiency of the synthesis of the hydrocarbon gas by the synthesizing device.

The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the configuration of an electrosynthesis system according to an embodiment;

FIG. 2 is a diagram showing a first gas processing mechanism and a second gas processing mechanism;

FIG. 3 is a diagram showing a case in which a carbon combustion process is carried out in the second gas processing mechanism;

FIG. 4 is a diagram showing a case in which a catalyst reduction process is carried out in the second gas processing mechanism;

FIG. 5 is a diagram showing a case in which a carbon combustion process is carried out in the first gas processing mechanism;

FIG. 6 is a diagram showing a case in which a catalyst reduction process is carried out in the first gas processing mechanism;

FIG. 7 is a diagram showing the transition of gas in a fuel electrode of a first electrolysis device or a second electrolysis device; and

FIG. 8 is a diagram showing one gas processing mechanism according to a modification.

DETAILED DESCRIPTION OF THE INVENTION
Embodiment

FIG. 1 is a schematic diagram showing the configuration of an electrosynthesis system 10 according to an embodiment. The electrosynthesis system 10 is equipped with a water vapor generator 12, a raw material gas concentration device 14, an oxygen-containing gas supplying device 16, a first gas processing mechanism 18A, a second gas processing mechanism 18B, a heat exchanger 20, a dehumidifier 22, and a separator 24.

The water vapor generator 12 is a device that generates water vapor. The water vapor generator 12 causes water that is supplied from a water source to evaporate. The water source may be a water purification facility or may be a water supply tank. The water vapor obtained by the water vapor generator 12 is supplied to the first gas processing mechanism 18A via a first water vapor supply passage 31A. Further, the water vapor obtained by the water vapor generator 12 is supplied to the second gas processing mechanism 18B via a second water vapor supply passage 31B.

The raw material gas concentration device 14 is a device that serves to concentrate the raw material gas. Further, using a pressure swing adsorption method (PSA method), the raw material gas concentration device 14 concentrates the raw material gas within a raw material-containing gas that is supplied from a raw material gas source. The raw material gas is carbon dioxide gas. The raw material gas source may be plant equipment such as a garbage disposal plant or a steel mill, or may be a raw material gas tank. The raw material gas that is concentrated by the raw material gas concentration device 14 is supplied to the first gas processing mechanism 18A via a first raw material gas supply passage 32A. Further, the raw material gas that is concentrated by the raw material gas concentration device 14 is supplied to the second gas processing mechanism 18B via a second raw material gas supply passage 32B.

The oxygen-containing gas supplying device 16 is a device that sends out an oxygen-containing gas that contains oxygen gas. The oxygen-containing gas supplying device 16 may be a blower (air blower). The oxygen-containing gas may be air. The oxygen-containing gas that is sent out from the oxygen-containing gas supplying device 16 is supplied to the first gas processing mechanism 18A via a first oxygen-containing gas supply passage 33A. Further, the oxygen-containing gas that is sent out from the oxygen-containing gas supplying device 16 is supplied to the second gas processing mechanism 18B via a second oxygen-containing gas supply passage 33B.

The first gas processing mechanism 18A and the second gas processing mechanism 18B are mechanisms that selectively implement any one of a hydrocarbon generation process, a carbon combustion process, or a catalyst reduction process. The hydrocarbon generation process is a process of generating hydrocarbon gas from water vapor and carbon dioxide gas using a catalyst. The carbon combustion process is a process in which carbon deposited on the catalyst is reacted with oxygen gas to cause the carbon to burn. The catalyst reduction process is a process in which the catalyst, which has been oxidized by the combustion of carbon, is made to react with the hydrogen gas to reduce the catalyst.

The first gas processing mechanism 18A discharges an exhaust gas obtained by the hydrocarbon generation process, the carbon combustion process, or the catalyst reduction process to a first exhaust gas passage 34A. The second gas processing mechanism 18B discharges an exhaust gas obtained by the hydrocarbon generation process, the carbon combustion process, or the catalyst reduction process to a second exhaust gas passage 34B. In the case that the hydrocarbon generation process is implemented, the hydrocarbon gas, the water vapor, the carbon monoxide gas, and the carbon dioxide gas are included in the exhaust gas. On the other hand, in the case that the carbon combustion process is implemented, the water vapor, the carbon dioxide gas, and the oxygen gas are included in the exhaust gas. Further, in the case that the catalyst reduction process is implemented, the water vapor and the hydrogen gas are included in the exhaust gas. Details of the first gas processing mechanism 18A and the second gas processing mechanism 18B will be discussed later.

An exhaust gas merging passage 35 and a coolant pipe (not shown) pass through the heat exchanger 20. The exhaust gas supplied from the first gas processing mechanism 18A via the first exhaust gas passage 34A, and the exhaust gas supplied from the second gas processing mechanism 18B via the second exhaust gas passage 34B flow into the exhaust gas merging passage 35. A coolant supplied from a coolant tank (not shown) flows through the coolant pipe. The heat exchanger 20 causes heat exchange to take place between the coolant and the exhaust gas, and thereby cools the exhaust gas.

The dehumidifier 22 is arranged in the exhaust gas merging passage 35 at a location downstream of the heat exchanger 20. The dehumidifier 22 extracts moisture within the exhaust gas. According to the present embodiment, the dehumidifier 22 cools the exhaust gas and extracts moisture within the exhaust gas. The dehumidifier 22 discharges the moisture extracted from the exhaust gas into a drainage passage 36. The moisture discharged into the drainage passage 36 may be returned to the water vapor generator 12.

The separator 24 is arranged in the exhaust gas merging passage 35 at a location downstream of the dehumidifier 22. The separator 24 includes one or more adsorbents that adsorb specified gases. According to the present embodiment, the separator 24 includes a hydrogen adsorbent, a carbon monoxide adsorbent, and a carbon dioxide adsorbent. Using the pressure swing adsorption method (PSA method), the separator 24 individually separates the hydrogen gas, the carbon monoxide gas, and the carbon dioxide gas within the exhaust gas. The hydrogen gas separated from the exhaust gas is discharged into a hydrogen gas discharge passage 37, the carbon monoxide gas separated from the exhaust gas is discharged into a carbon monoxide gas discharge passage 38, and the carbon dioxide gas separated from the exhaust gas is discharged into a carbon dioxide gas discharge passage 39.

As noted previously, in the case that the hydrocarbon generation process is carried out in at least one of the first gas processing mechanism 18A or the second gas processing mechanism 18B, hydrocarbon gas is contained in the exhaust gas. In this case, since the hydrogen gas, the carbon monoxide gas, and the carbon dioxide gas in the exhaust gas are separated by the separator 24, the hydrocarbon gas in the exhaust gas is concentrated. The concentrated hydrocarbon gas is discharged into a hydrocarbon gas discharge passage 40.

A control device 26 is a device that controls the electrosynthesis system 10. The control device 26 causes the first gas processing mechanism 18A to carry out the hydrocarbon generation process, the carbon combustion process, or the catalyst reduction process. The control device 26 causes the second gas processing mechanism 18B to carry out the hydrocarbon generation process, the carbon combustion process, or the catalyst reduction process. Details of the controls carried out by the control device 26 will be described later.

FIG. 2 is a diagram showing the first gas processing mechanism 18A and the second gas processing mechanism 18B. The constituent elements of the second gas processing mechanism 18B that correspond to the constituent elements of the first gas processing mechanism 18A are designated by the same numbers with the letter B appended thereto instead of the letter A.

The first gas processing mechanism 18A is equipped with a first heater 50A, a first electrolysis device 52A, a first heat exchanger 54A, a first synthesizing device 56A, and a first gas analyzer 58A as constituent elements thereof. The second gas processing mechanism 18B is equipped with a second heater 50B, a second electrolysis device 52B, a second heat exchanger 54B, a second synthesizing device 56B, and a second gas analyzer 58B as constituent elements thereof.

Each of the above-described constituent elements provided in the first gas processing mechanism 18A and each of the above-described constituent elements provided in the second gas processing mechanism 18B are substantially the same. Further, the connected relationship of the above-described constituent elements provided in the first gas processing mechanism 18A and the connected relationship of the above-described constituent elements provided in the second gas processing mechanism 18B are substantially the same. Accordingly, in the following, descriptions regarding each of the above-described constituent elements provided in the second gas processing mechanism 18B, and the connected relationship of such constituent elements will be omitted.

The first heater 50A is a heating device. The first heater 50A heats the water vapor that is supplied to the first electrolysis device 52A. Further, the first heater 50A heats the raw material gas (the carbon dioxide gas) that is supplied to the first electrolysis device 52A. A downstream end portion of the first water vapor supply passage 31A, a downstream end portion of the first raw material gas supply passage 32A, and an upstream end portion of a first mixed gas supply passage 41A are arranged in the first heater 50A. The downstream end portion of the first water vapor supply passage 31A, and the downstream end portion of the first raw material gas supply passage 32A are connected to the upstream end portion of the first mixed gas supply passage 41A. A downstream end portion of the first mixed gas supply passage 41A is connected to the first electrolysis device 52A.

The first electrolysis device 52A is a device that subjects the carbon dioxide gas and the water vapor to electrolysis. The first electrolysis device 52A includes a plurality of electrolytic cells 61. Each of the electrolytic cells 61 includes an electrolyte membrane 62, a fuel electrode 63, and an oxygen electrode 64. The electrolyte membrane 62 is sandwiched between the fuel electrode 63 and the oxygen electrode 64. The electrolyte membrane 62, for example, is a solid electrolyte membrane such as yttria-stabilized zirconia or the like.

The fuel electrode 63 may be referred to as a cathode. The fuel electrode 63 is connected to the water vapor generator 12 via the first mixed gas supply passage 41A and the first water vapor supply passage 31A. Further, the fuel electrode 63 is connected to the raw material gas concentration device 14 via the first mixed gas supply passage 41A and the first raw material gas supply passage 32A. Furthermore, the fuel electrode 63 is connected to the first synthesizing device 56A via a first mixed gas discharge passage 42A.

The oxygen electrode 64 may be referred to as an anode. The oxygen electrode 64 is connected to the oxygen-containing gas supplying device 16 via the first oxygen-containing gas supply passage 33A. Further, the oxygen electrode 64 is connected to an oxygen discharge unit via a first oxygen-containing gas discharge passage 43A. The oxygen discharge unit may be an oxygen gas tank, or may be an atmospheric space.

The first heat exchanger 54A is disposed between the first electrolysis device 52A and the first synthesizing device 56A. The first mixed gas discharge passage 42A and the coolant pipe (not shown) pass through the first heat exchanger 54A. The first heat exchanger 54A causes heat exchange to take place between the coolant flowing through the coolant pipe and the gas flowing through the first mixed gas discharge passage 42A, and thereby cools the gas supplied to the first synthesizing device 56A. The first heat exchanger 54A is capable of adjusting the degree of cooling of the gas in accordance with a temperature specified by the control device 26 (see FIG. 1). According to the present embodiment, by increasing or decreasing the flow rate of the coolant flowing through the coolant pipe, the first heat exchanger 54A adjusts the degree of cooling of the gas.

The first synthesizing device 56A is a device that synthesizes hydrocarbon gas from carbon monoxide gas and hydrogen gas. In the case that the hydrocarbon generation process is performed in the first gas processing mechanism 18A, the carbon monoxide gas and the hydrogen gas are supplied from the first electrolysis device 52A to the first synthesizing device 56A. The first synthesizing device 56A synthesizes the hydrocarbon gas using a catalyst. The catalyst, for example, is a catalyst containing a metal such as nickel or the like.

A case may occur in which carbon is deposited on the catalyst due to usage of the catalyst over a prolonged time period. In this case, the carbon combustion process is carried out in the first gas processing mechanism 18A. When the carbon combustion process is implemented, oxygen gas is supplied from the first electrolysis device 52A to the first synthesizing device 56A. In this case, in the first synthesizing device 56A, the carbon dioxide gas and water (water vapor) are generated by a combustion reaction between the carbon deposited on the catalyst and the oxygen gas.

There is a tendency for the catalyst to become oxidized due to the reaction between the carbon deposited on the catalyst and the oxygen gas. Therefore, according to the present embodiment, the catalyst reduction process is carried out after the carbon combustion process. When the catalyst reduction process is implemented, the hydrogen gas is supplied from the first electrolysis device 52A to the first synthesizing device 56A. In this case, in the first synthesizing device 56A, water (water vapor) is generated by a reduction reaction between the oxidized catalyst and the hydrogen gas.

The first gas analyzer 58A is disposed in the first exhaust gas passage 34A in close proximity to the first synthesizing device 56A. The first gas analyzer 58A includes a hydrocarbon concentration sensor 71, a carbon dioxide concentration sensor 72, a hydrogen concentration sensor 73, and a water vapor concentration sensor 74. The hydrocarbon concentration sensor 71 detects the concentration of the hydrocarbon gas within the exhaust gas. The carbon dioxide concentration sensor 72 detects the concentration of the carbon dioxide gas within the exhaust gas. The hydrogen concentration sensor 73 detects the concentration of the hydrogen gas within the exhaust gas. The water vapor concentration sensor 74 detects the concentration of the water vapor within the exhaust gas.

Next, a description will be given concerning the control device 26 (FIG. 1) that switches between the hydrocarbon generation process, the carbon combustion process, and the catalyst reduction process.

The control device 26 is a computer that controls the electrosynthesis system 10. The control device 26 is equipped with an operation unit, a storage unit, and a computation unit. The operation unit is an input device that is capable of receiving instructions from an operator. The storage unit may be constituted by a volatile memory and a non-volatile memory. As an example of the volatile memory, there may be cited a RAM or the like. As an example of the non-volatile memory, there may be cited a ROM, a flash memory, or the like. The computation unit includes a processor such as a CPU, an MPU, or the like.

The control device 26 controls a plurality of valves provided in the first gas processing mechanism 18A, and thereby causes the first gas processing mechanism 18A to carry out the hydrocarbon generation process, the carbon combustion process, or the catalyst reduction process. The control device 26 controls a plurality of valves provided in the second gas processing mechanism 18B, and thereby causes the second gas processing mechanism 18B to carry out the hydrocarbon generation process, the carbon combustion process, or the catalyst reduction process. In the drawings, in the case that the valves are open, they are shown in white, and in the case that the valves are closed, they are shown in black.

The plurality of valves provided in the first gas processing mechanism 18A are a first water vapor amount adjustment valve 81A, a first carbon dioxide amount adjustment valve 82A, a first oxygen opening/closing valve 83A, a first switching valve 84A, a first oxygen passage switching valve 85A, and a first mixing passage switching valve 86A. The plurality of valves provided in the second gas processing mechanism 18B are a second water vapor amount adjustment valve 81B, a second carbon dioxide amount adjustment valve 82B, a second oxygen opening/closing valve 83B, a second switching valve 84B, a second oxygen passage switching valve 85B, and a second mixing passage switching valve 86B.

Each of the above-described valves provided in the first gas processing mechanism 18A and each of the above-described valves provided in the second gas processing mechanism 18B are substantially the same. Accordingly, in the following, descriptions regarding each of the above-described valves provided in the second gas processing mechanism 18B will be omitted.

The first water vapor amount adjustment valve 81A is provided in the first water vapor supply passage 31A. The first water vapor amount adjustment valve 81A is a flow rate adjustment valve that adjusts the flow rate of the water vapor supplied to the first electrolysis device 52A. The first water vapor amount adjustment valve 81A closes or opens in accordance with the control of the control device 26. The opening amount of the first water vapor amount adjustment valve 81A may be set by the control device 26, or may be set in advance as a default.

The first carbon dioxide amount adjustment valve 82A is provided in the first raw material gas supply passage 32A. The first carbon dioxide amount adjustment valve 82A is a flow rate adjustment valve that adjusts the flow rate of the carbon dioxide gas supplied to the first electrolysis device 52A. The first carbon dioxide amount adjustment valve 82A closes or opens in accordance with the control of the control device 26. The opening amount of the first carbon dioxide amount adjustment valve 82A may be set by the control device 26, or may be set in advance as a default.

According to the present embodiment, the opening amount of the first water vapor amount adjustment valve 81A and the opening amount of the first carbon dioxide amount adjustment valve 82A are set at a ratio corresponding to the type of the hydrocarbon gas synthesized in the first synthesizing device 56A. For example, in the case that the type of the hydrocarbon gas is methane gas, the opening amount of the first water vapor amount adjustment valve 81A and the opening amount of the first carbon dioxide amount adjustment valve 82A are set at a ratio of “3:1”. Alternatively, in the case that the type of the hydrocarbon gas is methanol, the opening amount of the first water vapor amount adjustment valve 81A and the opening amount of the first carbon dioxide amount adjustment valve 82A are set at a ratio of “2:1”. Alternatively, in the case that the type of the hydrocarbon gas is ethanol, the opening amount of the first water vapor amount adjustment valve 81A and the opening amount of the first carbon dioxide amount adjustment valve 82A are set at a ratio of “3:2”.

The first oxygen opening/closing valve 83A is provided in the first oxygen-containing gas supply passage 33A. The first oxygen opening/closing valve 83A is a solenoid valve. The first oxygen opening/closing valve 83A closes or opens in accordance with the control of the control device 26.

The first switching valve 84A is provided in the first oxygen-containing gas discharge passage 43A. The first switching valve 84A, for example, is a three-way valve whose path can be switched under the control of the control device 26. The first switching valve 84A switches whether or not to supply the oxygen gas to the first synthesizing device 56A. Such switching is controlled by the control device 26.

In the case that the first switching valve 84A switches to supply the oxygen gas to the first synthesizing device 56A, the oxygen gas flows into a first communication passage 44A that branches off from the first oxygen-containing gas discharge passage 43A. In this case, the oxygen gas is supplied to the first synthesizing device 56A via the first mixed gas discharge passage 42A to which a downstream end portion of the first communication passage 44A is connected. On the other hand, in the case that the first switching valve 84A switches not to supply the oxygen gas to the first synthesizing device 56A, the oxygen gas flows toward the downstream of the first oxygen-containing gas discharge passage 43A.

The first oxygen passage switching valve 85A is provided in the first oxygen-containing gas discharge passage 43A at a location downstream of the first switching valve 84A. The first oxygen passage switching valve 85A, for example, is a three-way valve whose path can be switched under the control of the control device 26. The first oxygen passage switching valve 85A switches whether or not to supply the oxygen gas to the second electrolysis device 52B. Such switching is controlled by the control device 26.

In the case that the first oxygen passage switching valve 85A switches to supply the oxygen gas to the second electrolysis device 52B, the oxygen gas flows into a first communication passage 45A that branches off from the first oxygen-containing gas discharge passage 43A. In this case, the oxygen gas is supplied to the second electrolysis device 52B via the second oxygen-containing gas supply passage 33B to which a downstream end portion of the first communication passage 45A is connected. On the other hand, in the case that the first oxygen passage switching valve 85A switches not to supply the oxygen gas to the second electrolysis device 52B, the oxygen gas flows toward the downstream of the first oxygen-containing gas discharge passage 43A. In this case, the oxygen gas is supplied to the oxygen discharge unit.

The first mixing passage switching valve 86A is provided in the first mixed gas discharge passage 42A. The first mixing passage switching valve 86A, for example, is a three-way valve whose path can be switched under the control of the control device 26. The first mixing passage switching valve 86A switches whether or not to supply the oxygen gas to the first synthesizing device 56A. Such switching is controlled by the control device 26.

In the case that the first mixing passage switching valve 86A switches to supply the oxygen gas to the first synthesizing device 56A, the oxygen gas flows from the first communication passage 44A into the first mixed gas discharge passage 42A. In this case, the oxygen gas is supplied to the first synthesizing device 56A. On the other hand, in the case that the first mixing passage switching valve 86A switches not to supply the oxygen gas to the first synthesizing device 56A, the gas discharged from the first electrolysis device 52A into the first mixed gas discharge passage 42A is supplied to the first synthesizing device 56A.

Next, a description will be given concerning a case in which the control device 26 causes the first gas processing mechanism 18A to carry out the hydrocarbon generation process.

In the case that the first gas processing mechanism 18A is made to carry out the hydrocarbon generation process, the control device 26 opens the first water vapor amount adjustment valve 81A, the first carbon dioxide amount adjustment valve 82A, and the first oxygen opening/closing valve 83A (refer to FIG. 2). In this case, in the first electrolysis device 52A, the water vapor supplied from the water vapor generator 12 and the carbon dioxide gas supplied from the raw material gas concentration device 14 are subjected to electrolysis. When the electrolysis is carried out, the carbon monoxide gas and the hydrogen gas are generated at the fuel electrode 63, and the oxygen gas is generated at the oxygen electrode 64.

In the case that the first gas processing mechanism 18A is made to carry out the hydrocarbon generation process, the control device 26 controls the first mixing passage switching valve 86A, and thereby forms a gas passage from the fuel electrode 63 of the first electrolysis device 52A to the first synthesizing device 56A (refer to FIG. 2). In this case, the carbon monoxide gas and the hydrogen gas generated at the fuel electrode 63 are supplied to the first synthesizing device 56A via the first mixed gas discharge passage 42A. In the first synthesizing device 56A, synthesis of the hydrocarbon gas from the carbon monoxide gas and the hydrogen gas is carried out using the catalyst.

In the case that the first gas processing mechanism 18A is made to carry out the hydrocarbon generation process, the control device 26 specifies a first temperature for the first heat exchanger 54A. The first temperature is set to a temperature that is suitable for a reaction for synthesis of the hydrocarbon gas from the carbon monoxide gas and the hydrogen gas. For example, the first temperature is 300° C.

In the case that the first gas processing mechanism 18A is made to carry out the hydrocarbon generation process, the control device 26 controls the first switching valve 84A and the first oxygen passage switching valve 85A, and thereby forms a gas passage from the oxygen electrode 64 of the first electrolysis device 52A to the oxygen discharge unit (refer to FIG. 2). In this case, the oxygen gas generated at the oxygen electrode 64 is supplied to the oxygen discharge unit via the first oxygen-containing gas discharge passage 43A together with the oxygen-containing gas supplied from the oxygen-containing gas supplying device 16. By the oxygen-containing gas being supplied from the oxygen-containing gas supplying device 16 to the oxygen electrode 64, the oxygen gas generated at the oxygen electrode 64 is prevented from stagnating in the electrolytic cells 61.

During the execution of the hydrocarbon generation process in the first gas processing mechanism 18A, the control device 26 compares the hydrocarbon concentration detected by the hydrocarbon concentration sensor 71 of the first gas analyzer 58A with a predetermined hydrocarbon concentration threshold value.

Next, a description will be given concerning a case in which the control device 26 causes the second gas processing mechanism 18B to carry out the hydrocarbon generation process. In the case that the second gas processing mechanism 18B is made to carry out the hydrocarbon generation process, similarly to the case of the first gas processing mechanism 18A, the control device 26 specifies a first temperature for the second heat exchanger 54B. Further, similarly to the case of the first gas processing mechanism 18A, the control device 26 controls the plurality of valves.

More specifically, the control device 26 opens the second water vapor amount adjustment valve 81B, the second carbon dioxide amount adjustment valve 82B, and the second oxygen opening/closing valve 83B (refer to FIG. 2). Further, the control device 26 controls the second mixing passage switching valve 86B, and thereby forms a gas passage from the fuel electrode 63 of the second electrolysis device 52B to the second synthesizing device 56B (refer to FIG. 2). Further, the control device 26 controls the second switching valve 84B and the second oxygen passage switching valve 85B, and thereby forms a gas passage from the oxygen electrode 64 of the second electrolysis device 52B to the oxygen discharge unit (refer to FIG. 2). In this case, similarly to the case of the first gas processing mechanism 18A, electrolysis of the water vapor and the carbon dioxide gas is carried out in the second electrolysis device 52B, and synthesis of the hydrocarbon gas is carried out in the second synthesizing device 56B.

During the execution of the hydrocarbon generation process in the second gas processing mechanism 18B, the control device 26 compares the hydrocarbon concentration detected by the hydrocarbon concentration sensor 71 of the second gas analyzer 58B with a predetermined hydrocarbon concentration threshold value.

Next, a description will be given concerning a case in which the control device 26 switches the process executed by the second gas processing mechanism 18B from the hydrocarbon generation process to the carbon combustion process.

When carbon is deposited on the catalyst of the second synthesizing device 56B, the efficiency of the synthesis of the hydrocarbon gas in the second synthesizing device 56B decreases, and there is a tendency for the concentration of the hydrocarbon gas within the exhaust gas that is discharged from the second synthesizing device 56B to decrease. Accordingly, as the amount of carbon deposited on the catalyst of the second synthesizing device 56B increases, the degree of the decrease in the concentration of the hydrocarbon gas within the exhaust gas discharged from the second synthesizing device 56B increases.

In the case that the hydrocarbon concentration detected by the hydrocarbon concentration sensor 71 of the second gas analyzer 58B has fallen below the hydrocarbon concentration threshold value, the control device 26 determines that it is necessary to remove the carbon deposited on the catalyst of the second synthesizing device 56B. In this case, the control device 26 causes the second gas processing mechanism 18B to carry out the carbon combustion process. FIG. 3 is a diagram showing a case in which the carbon combustion process is carried out in the second gas processing mechanism 18B.

In the case that the second gas processing mechanism 18B is made to carry out the carbon combustion process, the control device 26 closes the second water vapor amount adjustment valve 81B and the second carbon dioxide amount adjustment valve 82B (refer to FIG. 3). In this case, the water vapor and the carbon dioxide gas are not supplied to the fuel electrode 63 of the second electrolysis device 52B. Therefore, in the second electrolysis device 52B, electrolysis of the water vapor and the carbon dioxide gas is not carried out, and in the second synthesizing device 56B, synthesis of the hydrocarbon gas is not carried out.

In the case that the second gas processing mechanism 18B is made to carry out the carbon combustion process, the control device 26 switches the temperature specified for the second heat exchanger 54B from the first temperature to a second temperature. The second temperature is set to a temperature suitable for a combustion reaction between the carbon deposited on the catalyst and the oxygen gas. The second temperature is higher than the first temperature. For example, the second temperature is 500° C.

In the case that the second gas processing mechanism 18B is made to carry out the carbon combustion process, the control device 26 closes the second oxygen opening/closing valve 83B (refer to FIG. 3). Further, the control device 26 controls the first oxygen passage switching valve 85A, and thereby forms a gas passage from the oxygen electrode 64 of the first electrolysis device 52A to the second electrolysis device 52B (refer to FIG. 3). Further, the control device 26 controls the second switching valve 84B and the second mixing passage switching valve 86B, and thereby forms a gas passage from the oxygen electrode 64 of the second electrolysis device 52B to the second synthesizing device 56B (refer to FIG. 3). In this case, the oxygen gas generated in the first electrolysis device 52A is supplied to the second synthesizing device 56B. The oxygen gas flows, in this order, through the first oxygen-containing gas discharge passage 43A, the first communication passage 45A, the second oxygen-containing gas supply passage 33B, a second oxygen-containing gas discharge passage 43B, a second communication passage 44B, and a second mixed gas discharge passage 42B.

At the time of electrolysis in the first electrolysis device 52A, the first electrolysis device 52A reaches a high temperature on the order of 700° C. to 800° C. Therefore, the oxygen gas generated by the first electrolysis device 52A is at a high temperature. By the high temperature oxygen gas passing through the second electrolysis device 52B prior to being supplied to the second synthesizing device 56B, the second electrolysis device 52B during the period that electrolysis is stopped can be heated. Accordingly, compared to a case in which the high temperature oxygen gas does not pass through the second electrolysis device 52B, it is possible to restore the second electrolysis device 52B and to restart electrolysis in the second electrolysis device 52B at an early stage.

When the oxygen gas is supplied to the second synthesizing device 56B, the amount of carbon deposited on the catalyst of the second synthesizing device 56B decreases due to a combustion reaction with the oxygen gas. During the execution of the carbon combustion process in the second gas processing mechanism 18B, the control device 26 compares the carbon dioxide concentration detected by the carbon dioxide concentration sensor 72 of the second gas analyzer 58B with a predetermined carbon dioxide concentration threshold value.

Next, a description will be given concerning a case in which the control device 26 switches the process executed by the second gas processing mechanism 18B from the carbon combustion process to the catalyst reduction process.

In the case that the carbon dioxide concentration has fallen below the carbon dioxide concentration threshold value, the control device 26 determines that the amount of carbon deposited on the catalyst of the second synthesizing device 56B has decreased to such an extent that almost no influence is exerted on the synthesis of the hydrocarbon gas. In this case, the control device 26 causes the second gas processing mechanism 18B to carry out the catalyst reduction process. FIG. 4 is a diagram showing a case in which the catalyst reduction process is carried out in the second gas processing mechanism 18B.

In the case that the second gas processing mechanism 18B is made to carry out the catalyst reduction process, the control device 26 opens the second water vapor amount adjustment valve 81B in a state with the second carbon dioxide amount adjustment valve 82B closed (refer to FIG. 4). In this case, the water vapor is supplied to the fuel electrode 63 of the second electrolysis device 52B, and the carbon dioxide gas is not supplied thereto. Therefore, the water vapor is subjected to electrolysis in the second electrolysis device 52B.

In the case that the second gas processing mechanism 18B is made to carry out the catalyst reduction process, the control device 26 switches the temperature specified for the second heat exchanger 54B from the second temperature to a third temperature. The third temperature is set to a temperature suitable for a reduction reaction to take place between the catalyst oxidized by the carbon combustion process and the hydrogen gas. The third temperature is higher than the first temperature and lower than the second temperature. For example, the third temperature is 400° C.

In the case that the second gas processing mechanism 18B is made to carry out the catalyst reduction process, the control device 26 opens the second oxygen opening/closing valve 83B (refer to FIG. 4). Further, the control device 26 controls the second switching valve 84B, and thereby forms a gas passage from the oxygen electrode 64 of the second electrolysis device 52B to the oxygen discharge unit (refer to FIG. 4). Further, the control device 26 controls the second mixing passage switching valve 86B, and thereby forms a gas passage from the fuel electrode 63 of the second electrolysis device 52B to the second synthesizing device 56B (refer to FIG. 4). In this case, the hydrogen gas generated by electrolysis of the water vapor in the second electrolysis device 52B is supplied to the second synthesizing device 56B via the second mixed gas discharge passage 42B.

When the hydrogen gas is supplied to the second synthesizing device 56B, the catalyst that has been oxidized in the carbon combustion process is reduced by reacting with the hydrogen gas, and gradually returns to its state prior to being oxidized. During the execution of the catalyst reduction process in the second gas processing mechanism 18B, the control device 26 compares the hydrogen concentration detected by the hydrogen concentration sensor 73 of the second gas analyzer 58B with a predetermined hydrogen concentration threshold value.

In the case that the hydrogen concentration exceeds the hydrogen concentration threshold value, the control device 26 determines that the oxidized catalyst has been reduced to such an extent that almost no influence is exerted on the synthesis of the hydrocarbon gas. In this case, the control device 26 causes the second gas processing mechanism 18B to carry out the hydrocarbon generation process.

Moreover, the control device 26 may determine, based on the concentration of the water vapor within the exhaust gas, whether the oxidized catalyst has been reduced to such an extent that almost no influence is exerted on the synthesis of the hydrocarbon gas. In this case, during the execution of the catalyst reduction process in the second gas processing mechanism 18B, the control device 26 compares the concentration of the water vapor detected by the water vapor concentration sensor 74 of the second gas analyzer 58B with a predetermined water vapor threshold value. When the water vapor concentration falls below the water vapor concentration threshold value, the control device 26 causes the second gas processing mechanism 18B to carry out the hydrocarbon generation process.

Next, a description will be given concerning a case in which the control device 26 switches the process executed by the first gas processing mechanism 18A from the hydrocarbon generation process to the carbon combustion process.

In the case that the hydrocarbon concentration detected by the hydrocarbon concentration sensor 71 of the first gas analyzer 58A has fallen below the hydrocarbon concentration threshold value, the control device 26 determines that it is necessary to remove the carbon deposited on the catalyst of the first synthesizing device 56A. In this case, the control device 26 causes the first gas processing mechanism 18A to carry out the carbon combustion process. FIG. 5 is a diagram showing a case in which the carbon combustion process is carried out in the first gas processing mechanism 18A.

In the case that the first gas processing mechanism 18A is made to carry out the carbon combustion process, the control device 26 switches the temperature specified for the first heat exchanger 54A from the first temperature to a second temperature. Further, the control device 26 closes the first water vapor amount adjustment valve 81A and the first carbon dioxide amount adjustment valve 82A (refer to FIG. 5). In this case, in the first electrolysis device 52A, electrolysis of the water vapor and the carbon dioxide gas is not carried out, and in the first synthesizing device 56A, synthesis of the hydrocarbon gas is not carried out.

In the case that the first gas processing mechanism 18A is made to carry out the carbon combustion process, the control device 26 closes the first oxygen opening/closing valve 83A (refer to FIG. 5). Further, the control device 26 controls the second oxygen passage switching valve 85B, and thereby forms a gas passage from the oxygen electrode 64 of the second electrolysis device 52B to the first electrolysis device 52A (refer to FIG. 5). Further, the control device 26 controls the first switching valve 84A and the first mixing passage switching valve 86A, and thereby forms a gas passage from the oxygen electrode 64 of the first electrolysis device 52A to the first synthesizing device 56A (refer to FIG. 5). In this case, the oxygen gas generated in the second electrolysis device 52B is supplied to the first synthesizing device 56A. The oxygen gas flows, in this order, through the second oxygen-containing gas discharge passage 43B, a second communication passage 45B, the first oxygen-containing gas supply passage 33A, the first oxygen-containing gas discharge passage 43A, the first communication passage 44A, and the first mixed gas discharge passage 42A.

When the oxygen gas is supplied to the first synthesizing device 56A, the amount of carbon deposited on the catalyst of the first synthesizing device 56A decreases due to a combustion reaction with the oxygen gas. During the execution of the carbon combustion process in the first gas processing mechanism 18A, the control device 26 compares the carbon dioxide concentration detected by the carbon dioxide concentration sensor 72 of the first gas analyzer 58A with a predetermined carbon dioxide concentration threshold value.

Next, a description will be given concerning a case in which the control device 26 switches the process executed by the first gas processing mechanism 18A from the carbon combustion process to the catalyst reduction process.

In the case that the carbon dioxide concentration has fallen below the carbon dioxide concentration threshold value, the control device 26 determines that the amount of carbon deposited on the catalyst of the first synthesizing device 56A has decreased to such an extent that almost no influence is exerted on the synthesis of the hydrocarbon gas. In this case, the control device 26 causes the first gas processing mechanism 18A to carry out the catalyst reduction process. FIG. 6 is a diagram showing a case in which the catalyst reduction process is carried out in the first gas processing mechanism 18A.

In the case that the first gas processing mechanism 18A is made to carry out the catalyst reduction process, the control device 26 switches the temperature specified for the first heat exchanger 54A from the second temperature to a third temperature. Further, the control device 26 opens the first water vapor amount adjustment valve 81A in a state with the first carbon dioxide amount adjustment valve 82A closed (refer to FIG. 6). In this case, the water vapor is supplied to the fuel electrode 63 of the first electrolysis device 52A, and the carbon dioxide gas is not supplied thereto. Therefore, the water vapor is subjected to electrolysis in the first electrolysis device 52A.

In the case that the first gas processing mechanism 18A is made to carry out the catalyst reduction process, the control device 26 opens the first oxygen opening/closing valve 83A (refer to FIG. 6). Further, the control device 26 controls the first switching valve 84A, and thereby forms a gas passage from the oxygen electrode 64 of the first electrolysis device 52A to the oxygen discharge unit (refer to FIG. 6). Further, the control device 26 controls the first mixing passage switching valve 86A, and thereby forms a gas passage from the fuel electrode 63 of the first electrolysis device 52A to the first synthesizing device 56A (refer to FIG. 6). In this case, the hydrogen gas generated by electrolysis of the water vapor in the first electrolysis device 52A is supplied to the first synthesizing device 56A via the first mixed gas discharge passage 42A.

When the hydrogen gas is supplied to the first synthesizing device 56A, the catalyst that has been oxidized in the carbon combustion process is reduced by reacting with the hydrogen gas, and gradually returns to its state prior to being oxidized. During the execution of the catalyst reduction process in the first gas processing mechanism 18A, the control device 26 compares the hydrogen concentration detected by the hydrogen concentration sensor 73 of the first gas analyzer 58A with a predetermined hydrogen concentration threshold value.

In the case that the hydrogen concentration exceeds the hydrogen concentration threshold value, the control device 26 determines that the oxidized catalyst has been reduced to such an extent that almost no influence is exerted on the synthesis of the hydrocarbon gas. In this case, the control device 26 causes the first gas processing mechanism 18A to carry out the hydrocarbon generation process.

Moreover, the control device 26 may determine, based on the concentration of the water vapor within the exhaust gas, whether the oxidized catalyst has been reduced to such an extent that almost no influence is exerted on the synthesis of the hydrocarbon gas. In this case, during the execution of the catalyst reduction process in the first gas processing mechanism 18A, the control device 26 compares the concentration of the water vapor detected by the water vapor concentration sensor 74 of the first gas analyzer 58A with a predetermined water vapor threshold value. When the water vapor concentration falls below the water vapor concentration threshold value, the control device 26 causes the first gas processing mechanism 18A to carry out the hydrocarbon generation process.

In this manner, according to the present embodiment, while the carbon dioxide gas and the water vapor are being supplied to the first electrolysis device 52A, the control device 26 monitors the hydrocarbon concentration within the exhaust gas that is discharged from the first synthesizing device 56A.

When the hydrocarbon concentration falls below the predetermined hydrocarbon concentration threshold value, the control device 26 closes the first water vapor amount adjustment valve 81A and the first carbon dioxide amount adjustment valve 82A, and stops the supply of the carbon dioxide gas and the water vapor. Thereafter, the control device 26 controls the first switching valve 84A and the first mixing passage switching valve 86A, and thereby supplies the oxygen gas to the first synthesizing device 56A. Consequently, the carbon deposited on the catalyst provided in the first synthesizing device 56A can be made to undergo combustion by the oxygen gas.

Further, according to the present embodiment, while the oxygen gas is being supplied to the first synthesizing device 56A, the control device 26 monitors the carbon dioxide concentration within the exhaust gas that is discharged from the first synthesizing device 56A. When the carbon dioxide concentration falls below the predetermined carbon dioxide concentration threshold value, the control device 26 opens the first water vapor amount adjustment valve 81A without opening the first carbon dioxide amount adjustment valve 82A, and supplies the water vapor to the first electrolysis device 52A. Consequently, the hydrogen gas generated in the first electrolysis device 52A by electrolysis of the water vapor can be supplied from the first electrolysis device 52A to the first synthesizing device 56A. As a result, the catalyst, which has been oxidized by the combustion of carbon deposited on the catalyst, can be reduced by a reaction with the hydrogen gas.

Further, according to the present embodiment, the control device 26 switches the temperature specified for the first heat exchanger 54A depending on the type of the gas supplied to the first synthesizing device 56A. Consequently, each of a plurality of mutually different chemical reactions can be appropriately implemented in the first synthesizing device 56A.

On the other hand, while the carbon dioxide gas and the water vapor are being supplied to the second electrolysis device 52B, the control device 26 monitors the hydrocarbon concentration within the exhaust gas that is discharged from the second synthesizing device 56B. When the hydrocarbon concentration within the exhaust gas that is discharged from the second synthesizing device 56B falls below the predetermined hydrocarbon concentration threshold value, the control device 26 closes the second water vapor amount adjustment valve 81B and the second carbon dioxide amount adjustment valve 82B, and stops the supply of the carbon dioxide gas and the water vapor. Thereafter, the control device 26 opens the second switching valve 84B and thereby supplies the oxygen gas to the second synthesizing device 56B. Consequently, the carbon deposited on the catalyst provided in the second synthesizing device 56B can be made to undergo combustion by the oxygen gas.

Further, according to the present embodiment, while the oxygen gas is supplied to the second synthesizing device 56B, the control device 26 monitors the carbon dioxide concentration within the exhaust gas that is discharged from the second synthesizing device 56B. When the carbon dioxide concentration falls below the predetermined carbon dioxide concentration threshold value, the control device 26 opens the second water vapor amount adjustment valve 81B without opening the second carbon dioxide amount adjustment valve 82B, and supplies the water vapor to the second electrolysis device 52B. Consequently, the hydrogen gas generated in the second electrolysis device 52B by electrolysis of the water vapor can be supplied from the second electrolysis device 52B to the second synthesizing device 56B. As a result, the catalyst, which has been oxidized by the combustion of carbon deposited on the catalyst, can be reduced by a reaction with the hydrogen gas.

Further, according to the present embodiment, the control device 26 switches the temperature specified for the second heat exchanger 54B depending on the type of the gas supplied to the second synthesizing device 56B. Consequently, each of a plurality of mutually different chemical reactions can be appropriately implemented in the second synthesizing device 56B.

FIG. 7 is a diagram showing the transition of gas in the fuel electrode 63 of the first electrolysis device 52A or the second electrolysis device 52B. As noted previously, in the case of transitioning from the hydrocarbon generation process to the carbon combustion process, the first water vapor amount adjustment valve 81A (or the second water vapor amount adjustment valve 81B) and the first carbon dioxide amount adjustment valve 82A (or the second carbon dioxide amount adjustment valve 82B) are closed. According to the present embodiment, a timing T1 at which the first water vapor amount adjustment valve 81A (or the second water vapor amount adjustment valve 81B) is closed is later than a timing T2 at which the first carbon dioxide amount adjustment valve 82A (or the second carbon dioxide amount adjustment valve 82B) is closed.

More specifically, after closing the first carbon dioxide amount adjustment valve 82A (or the second carbon dioxide amount adjustment valve 82B), the control device 26 closes the first water vapor amount adjustment valve 81A (or the second water vapor amount adjustment valve 81B). Consequently, the carbon dioxide gas and the carbon monoxide gas remaining in the fuel electrode 63 can be discharged from the fuel electrode 63 by the water vapor. Accordingly, compared to a case in which the timing at which the adjustment valves are closed is the same, it is possible to increase the efficiency of the water electrolysis at the fuel electrode 63 where the hydrogen gas that is used in the catalyst reduction process which is carried out after the carbon combustion process is generated. As a result, it is possible to shorten the time period of the catalyst reduction process.

[Modifications]

The above-described embodiment may be modified in the following manner.

(Modification 1)

The control device 26 may adjust the flow rate of the oxygen gas that is supplied to the first synthesizing device 56A or the second synthesizing device 56B. In this case, an oxygen concentration sensor and an oxygen amount adjustment valve are provided in each of the first communication passage 44A and the second communication passage 44B. The oxygen amount adjustment valve is arranged at a location downstream of the oxygen concentration sensor.

The oxygen concentration sensor is a sensor that detects the concentration of the oxygen gas in the oxygen-containing gas flowing through the first communication passage 44A or the second communication passage 44B. The oxygen amount adjustment valve is a flow rate adjustment valve that adjusts the flow rate of the oxygen gas that is supplied to the first synthesizing device 56A or the second synthesizing device 56B.

In the case that the second gas processing mechanism 18B is made to carry out the carbon combustion process (refer to FIG. 3), the control device 26 controls the degree of opening of the oxygen amount adjustment valve provided in the second communication passage 44B, by using the oxygen concentration sensor provided in the second communication passage 44B. In this case, as the concentration of the oxygen gas detected by the oxygen concentration sensor increases, the control device 26 decreases the degree of opening of the oxygen amount adjustment valve. Consequently, it is possible to supply the oxygen gas to the second synthesizing device 56B in just the right amount.

On the other hand, in the case that the first gas processing mechanism 18A is made to carry out the carbon combustion process (refer to FIG. 5), the control device 26 controls the degree of opening of the oxygen amount adjustment valve provided in the first communication passage 44A, by using the oxygen concentration sensor provided in the first communication passage 44A. In this case, as the concentration of the oxygen gas detected by the oxygen concentration sensor increases, the control device 26 decreases the degree of opening of the oxygen amount adjustment valve. Consequently, it is possible to supply the oxygen gas to the first synthesizing device 56A in just the right amount.

(Modification 2)

A plurality of sets of the first gas processing mechanism 18A and the second gas processing mechanism 18B may be provided.

(Modification 3)

The control device 26 may cause the carbon combustion process and the catalyst reduction process in the first gas processing mechanism 18A, and the carbon combustion process and the catalyst reduction process in the second gas processing mechanism 18B to be alternately executed in every unit time period. In this case, the hydrocarbon concentration sensor 71 can be removed. Further, since the process in the control device 26 of comparing the hydrocarbon concentration detected by the hydrocarbon concentration sensor 71 with the hydrocarbon concentration threshold value is eliminated, the processing load on the control device 26 can be reduced.

(Modification 4)

One of the first gas processing mechanism 18A or the second gas processing mechanism 18B may be removed. FIG. 8 is a diagram showing one gas processing mechanism 18 according to the modification. In FIG. 8, the terms “first” and “second” and the symbols “A” and “B” that have been attached to the names of the constituent elements in the embodiment are omitted.

According to the present modification, the oxygen gas generated in one of the first gas processing mechanism 18A or the second gas processing mechanism 18B is not supplied to the other one of the first gas processing mechanism 18A or the second gas processing mechanism 18B. Therefore, in the gas processing mechanism 18, the first oxygen passage switching valve 85A (or the second oxygen passage switching valve 85B), the first mixing passage switching valve 86A (or the second mixing passage switching valve 86B), the first communication passage 44A (or the second communication passage 44B), and the first communication passage 45A (or the second communication passage 45B) are removed.

On the other hand, in the gas processing mechanism 18, there is provided a connecting pipe 90 that branches off from an oxygen-containing gas discharge passage 43, and is connected to a synthesizing device 56 via a heat exchanger 54.

Although the control of the control device 26 with respect to the gas processing mechanism 18 is the same as in the above-described embodiment, a brief description thereof will be provided. In the case that the gas processing mechanism 18 is made to carry out the hydrocarbon generation process, the control device 26 specifies a first temperature for the heat exchanger 54. Further, the control device 26 opens a water vapor amount adjustment valve 81, a carbon dioxide amount adjustment valve 82, and an oxygen opening/closing valve 83 (refer to FIG. 8). In addition to this, the control device 26 controls a switching valve 84, and thereby forms a gas passage from the oxygen electrode 64 to the oxygen discharge unit.

When the hydrocarbon concentration within the exhaust gas discharged from the synthesizing device 56 falls below the hydrocarbon concentration threshold value, the control device 26 switches the temperature specified for the heat exchanger 54 from the first temperature to a second temperature. Further, the control device 26 closes the water vapor amount adjustment valve 81 and the carbon dioxide amount adjustment valve 82. Further, the control device 26 controls the switching valve 84, and thereby forms a gas passage from the oxygen electrode 64 to the synthesizing device 56.

When the carbon dioxide concentration within the exhaust gas discharged from the synthesizing device 56 falls below the carbon dioxide concentration threshold value, the control device 26 switches the temperature specified for the heat exchanger 54 from the second temperature to a third temperature. Further, the control device 26 opens the water vapor amount adjustment valve 81 in a state with the carbon dioxide amount adjustment valve 82 closed. Further, the control device 26 controls the switching valve 84, and thereby forms a gas passage from the oxygen electrode 64 to the oxygen discharge unit.

In this manner, even if one of the first gas processing mechanism 18A or the second gas processing mechanism 18B is removed, the control of the control device 26 is the same as in the above-described embodiment. Accordingly, even with only one gas processing mechanism 18, the same advantageous effects as in the above-described embodiment can be obtained.

(Modification 5)

The first communication passage 44A or the second communication passage 44B may be replaced with the connecting pipe 90. In this case, the first mixing passage switching valve 86A or the second mixing passage switching valve 86B can be removed.

A description will be given below concerning the invention and the advantageous effects thereof that are capable of being grasped from the above disclosure.

(1) The present invention is characterized by the electrosynthesis system (10) equipped with the electrolysis device (52, 52A, 52B) that subjects the carbon dioxide gas and the water vapor to electrolysis and thereby generates the carbon monoxide gas and the hydrogen gas, and the synthesizing device (56, 56A, 56B) that uses the catalyst to synthesize the hydrocarbon gas from the carbon monoxide gas and the hydrogen gas that are discharged from the electrolysis device. The electrosynthesis system includes the water vapor amount adjustment valve (81, 81A, 81B) that adjusts the flow rate of the water vapor supplied to the electrolysis device, the carbon dioxide amount adjustment valve (82, 82A, 82B) that adjusts the flow rate of the carbon dioxide gas supplied to the electrolysis device, the carbon dioxide concentration sensor (72) that measures the concentration of the carbon dioxide gas within the exhaust gas discharged from the synthesizing device, and the control device (26). In the case that the concentration of the carbon dioxide gas within the exhaust gas has fallen below the predetermined carbon dioxide concentration threshold value in a state in which the oxygen gas is being supplied to the synthesizing device, the control device opens the water vapor amount adjustment valve without opening the carbon dioxide amount adjustment valve, and thereby supplies the hydrogen gas to the synthesizing device via the electrolysis device.

In accordance with this feature, the hydrogen gas generated in the electrolysis device by the electrolysis of the water vapor can be supplied from the electrolysis device to the synthesizing device. As a result, the catalyst, which has been oxidized by the combustion of carbon deposited on the catalyst, can be reduced by a reaction with the hydrogen gas. As a result, it is possible to suppress a decrease in the efficiency of the synthesis of the hydrocarbon gas by the synthesizing device. In addition to this, the hydrogen gas supplied to the synthesizing device can be heated by the electrolysis device, which becomes high in temperature during electrolysis. As a result, compared to a case in which the hydrogen gas is supplied to the synthesizing device without passing through the electrolysis device, there is no need to use a heater or the like, which is more efficient.

(2) In the present invention, the electrosynthesis system according to the above-described item (1) may further include at least one of the hydrogen concentration sensor (73) that measures the concentration of the hydrogen gas within the exhaust gas, or the water vapor concentration sensor (74) that measures the concentration of the water vapor within the exhaust gas, wherein, in a state in which the oxygen gas is being supplied to the synthesizing device, in the case that the concentration of the hydrogen gas within the exhaust gas exceeds the predetermined hydrogen concentration threshold value, or in the case that the concentration of the water vapor within the exhaust gas falls below the predetermined water vapor concentration threshold value, the control device may open the water vapor amount adjustment valve and the carbon dioxide amount adjustment valve, and thereby start supplying the carbon dioxide gas and the water vapor to the electrolysis device. In accordance with this feature, even if the catalyst is reduced, it is possible to suppress a situation in which the hydrogen gas continues to be supplied. As a result, it is possible to increase the efficiency with which the hydrogen gas is used.

(3) In the present invention, the electrosynthesis system according to the above-described item (1) may further include the hydrocarbon concentration sensor (71) that measures the concentration of the hydrocarbon gas within the exhaust gas, and the switching valve (84, 84A, 84B) that selectively switches whether or not to supply the oxygen gas to the synthesizing device, wherein, in the case that the concentration of the hydrocarbon gas has fallen below the predetermined hydrocarbon concentration threshold value in a state in which the carbon monoxide gas and the hydrogen gas are being supplied to the synthesizing device, the control device may close the water vapor amount adjustment valve and the carbon dioxide amount adjustment valve and thereby stop supplying the carbon dioxide gas and the water vapor to the electrolysis device, and after stopping supplying the carbon dioxide gas and the water vapor, the control device may control the switching valve and thereby supply the oxygen gas to the synthesizing device. In accordance with this feature, the carbon deposited on the catalyst provided in the synthesizing device can be made to undergo combustion by the oxygen gas.

(4) In the present invention, in the electrosynthesis system according to the above-described item (3), the control device may stop supplying the water vapor after having stopped supplying the carbon dioxide gas. In accordance with this feature, the carbon dioxide gas and the carbon monoxide gas remaining in the electrolysis device can be pushed out from the electrolysis device by the water vapor. Accordingly, compared to a case in which the timing at which the supply of the carbon dioxide gas is stopped is the same as the timing at which the supply of the water vapor is stopped, it is possible to increase the efficiency of the water electrolysis by the electrolysis device that generates the hydrogen gas that is used in the catalyst reduction process which is carried out after the carbon combustion process. As a result, it is possible to shorten the time period of the catalyst reduction process.

(5) In the present invention, the electrosynthesis system according to the above-described item (3) may further include the heat exchanger (54, 54A, 54B) that is disposed between the electrolysis device and the synthesizing device, and cools the gas supplied from the electrolysis device to the synthesizing device, wherein the heat exchanger may be capable of adjusting the degree of cooling of the gas in accordance with the temperature specified by the control device, and the control device may switch the temperature specified for the heat exchanger depending on the type of the gas. In accordance with this feature, each of a plurality of mutually different chemical reactions can be appropriately implemented in the synthesizing device.

(6) In the present invention, in the electrosynthesis system according to the above-described item (3), the electrolysis device may be provided in plurality, the synthesizing device may be provided in plurality, and the switching valve may be provided in plurality, the first synthesizing device (56A), which is one of the plurality of synthesizing devices, may use the catalyst to synthesize the hydrocarbon gas from the carbon monoxide gas and the hydrogen gas that are discharged from the first electrolysis device (52A), which is one of the plurality of electrolysis devices, the second synthesizing device (56B), which is another one of the plurality of synthesizing devices, may use the catalyst to synthesize the hydrocarbon gas from the carbon monoxide gas and the hydrogen gas that are discharged from the second electrolysis device (52B), which is another one of the plurality of electrolysis devices, the first switching valve (84A), which is one of the plurality of switching valves, may selectively switch whether or not to supply the oxygen gas, which is generated secondarily by the electrolysis in the first electrolysis device, to the second synthesizing device, the second switching valve (84B), which is another one of the plurality of switching valves, may selectively switch whether or not to supply the oxygen gas, which is generated secondarily by the electrolysis in the second electrolysis device, to the first synthesizing device, and in the case that the concentration of the hydrocarbon gas within the exhaust gas discharged from the first synthesizing device has fallen below the predetermined hydrocarbon concentration threshold value in a state in which the carbon monoxide gas and the hydrogen gas are being supplied to the first synthesizing device, the control device may control the second switching valve and thereby supply the oxygen gas to the first synthesizing device, and in the case that the concentration of the hydrocarbon gas within the exhaust gas discharged from the second synthesizing device has fallen below the predetermined hydrocarbon concentration threshold value in a state in which the carbon monoxide gas and the hydrogen gas are being supplied to the second synthesizing device, the control device may control the first switching valve and thereby supply the oxygen gas to the second synthesizing device.

In accordance with this feature, it is possible to increase the efficiency with which the oxygen gas is used. Further, the oxygen gas, which is heated by the first electrolysis device in which the electrolysis is carried out, can be supplied to the second synthesizing device via the second electrolysis device in a state in which the electrolysis is stopped. Similarly, the oxygen gas, which is heated by the second electrolysis device in which the electrolysis is carried out, can be supplied to the first synthesizing device via the first electrolysis device in a state in which the electrolysis is stopped. Accordingly, it is possible to cause the electrolysis device which is in a state in which the electrolysis is stopped to be restored at an early stage, and to cause the electrolysis device to restart the electrolysis.

Moreover, the present invention is not limited to the above-described disclosure, and various configurations can be adopted therein without departing from the essence and gist of the present invention.

ELECTROSYNTHESIS SYSTEM

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