JP7147705B2 - energy conversion system - Google Patents

Description

The present invention relates to energy conversion systems.

In recent years, the electrification of power sources has attracted attention, and as one means of solving this problem, there is a demand for practical use of a system that converts surplus electric power into fuel such as hydrocarbons and stores it. Patent Literature 1 proposes a fuel synthesizing system that electrolyzes water vapor and carbon dioxide to produce syngas composed of hydrogen and carbon monoxide, and synthesizes hydrocarbons using this syngas.

JP 2014-152219 A

However, the system that converts electric power into fuel, such as that disclosed in Patent Document 1, has not yet achieved a high efficiency suitable for practical use.

SUMMARY OF THE INVENTION In view of the above points, an object of the present invention is to improve fuel synthesis efficiency in an energy conversion system that electrolyzes H ₂ O and CO ₂ to produce H ₂ and CO, and synthesizes hydrocarbons from H ₂ and CO. and

In order to achieve the above object, in the first aspect of the invention, a fuel synthesizing device (10), a power supply device (14), an H ₂ O supply section (20, 22), a CO ₂ supply section (23) are provided. , 25). The fuel synthesizer has an electrolyte (11) having oxygen ion conductivity, a cathode (12) provided on one side of the electrolyte, and an anode (13) provided on the other side of the electrolyte. The power supply supplies power to the fuel synthesizer. The H ₂ O supply unit supplies H ₂ O to the cathode. The CO ₂ supply section supplies CO ₂ to the cathode.

At the cathode electrode, H _{2 O supplied from the H 2 O} supply section and CO ₂ supplied from the CO ₂ supply section flow in a predetermined gas flow direction. _At the cathode, H ₂ O is electrolyzed to produce H ₂ , CO ₂ is electrolyzed to produce CO, and hydrocarbons _are produced using H ₂ and CO. A synthesizing fuel synthesis reaction occurs. The cathode has a plurality of types of catalysts including an H _{2 O electrocatalyst that promotes the H 2 O} electrolysis reaction, a CO _{2 electrocatalyst that promotes the CO 2 electrolysis} reaction, and a fuel synthesis catalyst that promotes the fuel synthesis reaction. is provided.

CO ₂ electrocatalyst, H ₂ O electrocatalyst, and fuel contained in a plurality of types of catalysts for each of the upstream portion (12a), midstream portion (12b), and downstream portion (12c, 12d) in the gas flow direction of the cathode electrode. Each has a different proportion of synthetic catalyst. In the upstream part, the number of moles of CO is the largest among the reaction products consisting of CO generated in the CO ₂ electrolysis reaction, H ₂ generated in the H ₂ O electrolysis reaction, and hydrocarbons generated in the fuel synthesis reaction. . Among the reaction products, the number of moles of H ₂ is the largest in the middle stream. In the downstream part, the number of moles of hydrocarbons is the largest among the reaction products.

This allows as much CO ₂ as possible to be electrolyzed to CO by the CO ₂ electrolysis reaction before H ₂ is produced by the H ₂ O electrolysis reaction. Since the H ₂ O electrolysis reaction occurs in a state where the CO ₂ concentration is decreased and the CO concentration is increased, the occurrence of the reverse water gas shift reaction in which CO ₂ reacts with H ₂ can be suppressed. As a result, H ₂ consumption due to the reverse water gas shift reaction can be suppressed, power consumption used for H ₂ production can be suppressed, and fuel synthesis efficiency can be improved.

In addition, by prioritizing the fuel synthesis reaction in the downstream portion, fuel synthesis can be efficiently performed using CO produced in the upstream portion and H ₂ produced in the midstream portion.

It should be noted that the reference numerals in parentheses of the respective components above indicate the correspondence with specific means described in the embodiments to be described later.

It is a figure showing the whole energy conversion system composition of a 1st embodiment. It is a figure showing composition of a fuel synthesizer of a 1st embodiment. It is a figure which shows the structure of the fuel synthesizer of 2nd Embodiment. FIG. 10 is a diagram showing the configuration of a fuel synthesizing device according to a third embodiment; It is a figure which shows the structure of the fuel synthesis apparatus of 4th Embodiment.

(First embodiment)
An energy conversion system according to a first embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the energy conversion system includes a fuel synthesizer 10 . The fuel synthesizer 10 is a solid oxide electrolysis cell (SOEC). The fuel synthesizing device 10 of the present embodiment can generate H ₂ and CO by electrolysis of H ₂ O and CO ₂ and synthesize hydrocarbons using H ₂ and CO. Hydrocarbons are fuels and can be used, for example, to generate electricity in fuel cells.

The fuel synthesizer 10 includes an electrolyte 11 and a pair of electrodes 12 and 13 provided on both sides of the electrolyte 11 . The pair of electrodes 12 and 13 are a cathode 12 provided on one side of the electrolyte 11 and an anode 13 provided on the other side of the electrolyte 11 .

The electrolyte 11 is a solid material having oxygen ion conductivity, and for example, ZrO ₂ , which is a zirconia-based oxide, can be used. The cathode electrode 12 and the anode electrode 13 are configured as a cermet obtained by mixing and sintering a metal catalyst and ceramics.

Anode 13 is provided with a metal catalyst that promotes a reaction that combines O ²⁻ and electrons to generate O ₂ . The anode 13 is provided with, for example, Ni or Pt as a metal catalyst.

Cathode 12 is provided with a plurality of types of metal catalysts. The multiple types of metal catalysts include metal catalysts that promote the _CO2 electrolysis reaction, metal catalysts that promote the _H2O electrolysis reaction, and metal catalysts that promote the fuel synthesis reaction. Hereinafter, the metal catalyst that promotes the CO ₂ electrolysis reaction is also referred to as the CO ₂ electrocatalyst, the metal catalyst that promotes the H ₂ O electrolysis reaction is also referred to as the H ₂ O electrocatalyst, and the metal catalyst that promotes the fuel synthesis reaction is referred to as the fuel synthesis catalyst. Also called

Cu, for example, can be used as the CO ₂ electrocatalyst. Ni and ruthenium, for example, can be used as the H ₂ O electrocatalyst. Cobalt and Fe, for example, can be used as fuel synthesis catalysts. In the cathode electrode 12, the composition ratio of a plurality of types of metal catalysts is varied for each region along the direction of gas flow. This point will be described later.

Power is supplied to the fuel synthesizing device 10 from a power supply device 14, which is an external power source. In this embodiment, a power generator using natural energy is used as the power supply device 14 . As the power supply device 14, for example, a solar power generation device can be used.

In the fuel synthesizer 10, H ₂ O and CO ₂ are supplied to the cathode 12 while power is being supplied. H ₂ O and CO ₂ are feed gases for synthesizing hydrocarbons. In this embodiment, the internal pressure of the cathode electrode 12 to which H ₂ O and CO ₂ are supplied is approximately atmospheric pressure.

H ₂ O is supplied from the H ₂ O storage unit 20 to the cathode electrode 12 through the H ₂ O supply passage 21 . H ₂ O in a liquid state is stored in the H ₂ O storage unit 20 of the present embodiment. The H ₂ O supply passage 21 is provided with an H ₂ O pump 22 for pumping H ₂ O. H ₂ O may be supplied to the cathode 12 in a liquid state, or may be supplied to the cathode 12 as water vapor. The H ₂ O pump 22 operates based on a control signal from a control device 29 which will be described later. Note that the H ₂ O storage unit 20 and the H ₂ O pump 22 correspond to the H ₂ O supply unit.

CO ₂ is supplied from the CO ₂ storage unit 23 to the fuel synthesizing device 10 through the CO ₂ supply passage 24 . CO ₂ in a liquid state is stored in the CO ₂ storage unit 23 of the present embodiment. The CO ₂ stored in the CO ₂ storage unit 23 is pressurized.

A pressure regulating valve 25 is provided in the CO ₂ supply passage 24 . The pressure regulating valve 25 reduces the pressure of CO ₂ stored in the CO ₂ storage section 23 . The pressure regulating valve 25 is an expansion valve for expanding _CO2 . The pressure regulating valve 25 operates based on a control signal from a control device 29, which will be described later. Note that the CO ₂ storage unit 24 and the pressure regulating valve 25 correspond to the CO ₂ supply unit.

At the cathode 12 of the fuel synthesizer 10, H ₂ is produced by electrolysis of H ₂ O, and CO is produced by electrolysis of CO ₂ . At the cathode electrode 12, hydrocarbons are synthesized from H ₂ and CO produced by electrolysis. The synthesized hydrocarbons are contained in fuel synthesis exhaust gas and discharged from the cathode electrode 12 . The hydrocarbon contained in the fuel synthesis exhaust gas is, for example, methane.

The fuel synthesis exhaust gas passes through the fuel synthesis exhaust gas passage 26 . A fuel separator 27 is provided in the fuel synthesis exhaust gas passage 26 . The fuel separation unit 27 separates hydrocarbons from the fuel synthesis exhaust gas. Separation of hydrocarbons from the fuel synthesis offgas can be carried out, for example, by distillative separation.

The hydrocarbons separated by the fuel separation section 27 are stored in the fuel storage section 28 as fuel. Liquid hydrocarbons are stored in the fuel storage unit 28 of the present embodiment.

The energy conversion system comprises a controller 29 . The control device 29 is composed of a well-known microcomputer including CPU, ROM, RAM, etc. and its peripheral circuits. The control device 29 performs various calculations and processes based on the air conditioning control program stored in the ROM, and controls the operation of various devices to be controlled such as the power supply device 14 , the H ₂ O pump 22 and the pressure regulating valve 25 . Various sensors (not shown) are connected to the input side of the control device 29 .

Next, chemical reactions that occur in the fuel synthesizing device 10 will be described. In the fuel synthesizing device ₁₀ , H ₂ O and CO ₂ are supplied to the cathode ₁₂ while power is being supplied from the power supply device 14 . H ₂ , CO, O ^2- are produced. O ²⁻ produced at the cathode 12 moves to the anode 13 through the electrolyte 11 . At the anode electrode 13, O ²⁻ is combined with electrons to generate O ₂ .

At the cathode electrode ₁₂ , a fuel synthesis reaction occurs in which _CH4 is synthesized from H2 and CO produced by the electrolysis reaction. CH ₄ produced at the cathode 12 is discharged from the fuel synthesizing device 10 through the fuel synthesizing exhaust gas passage 26 as fuel synthesizing exhaust gas. CH ₄ contained in the fuel synthesis exhaust gas is separated in the fuel separation section 27 and stored in the fuel storage section 28 as a hydrocarbon fuel. The remaining fuel synthesis exhaust gas from which _CH4 has been separated is discharged to the outside.

At the cathode electrode 12 of the fuel synthesizer 10, the following H ₂ O electrolysis reaction, CO ₂ electrolysis reaction and fuel synthesis reaction occur.

[H ₂ O electrolytic reaction]
_H2O + ^2e- →H2 ₊ ^O2-
[CO ₂ electrolysis reaction 1]
_CO2 + ^2e- →CO+ ^O2-
[CO ₂ electrolysis reaction 2]
_CO2 +H2→CO _{+ H2O}
[Fuel synthesis reaction]
_{3H2 +} CO→CH4+ _H2O
In the H ₂ O electrolysis reaction, H ₂ O is electrolyzed to produce H ₂ . In the CO ₂ electrolysis reaction, CO is produced by electrolyzing CO ₂ . The CO ₂ electrolysis reaction includes CO ₂ electrolysis reaction 1 and CO ₂ electrolysis reaction 2 .

The CO ₂ electrolysis reaction 2 is a reverse water gas shift reaction, in which H ₂ produced in the H ₂ O electrolysis reaction is consumed and H ₂ O is produced. Among the two types of CO ₂ electrolysis reactions, if the proportion of CO ₂ electrolysis reaction 2 increases, a large amount of electric power is required to generate H ₂ by the H ₂ O electrolysis reaction, resulting in a decrease in system efficiency. Therefore, it is desirable to prevent CO ₂ electrolysis reaction 2 from occurring as much as possible.

_In the fuel synthesis reaction, H2 and CO are used to synthesize _CH4 . In the fuel synthesis reaction, H ₂ O is produced as a by-product along with the synthesis of CH ₄ . H _{2 O produced in the fuel synthesis reaction is electrolyzed in the H 2 O} electrolysis reaction. In order to efficiently synthesize CH ₄ in the fuel synthesis reaction, it is desirable to quickly remove H ₂ O produced as a by-product.

Next, the configuration of the cathode 12 of the fuel synthesizing device 10 will be described with reference to FIG. In FIG. 2, the direction from the left side to the right side is the gas flow direction of the raw material gas composed of H ₂ O and CO ₂ . The direction of gas flow is along the interface between the electrolyte 11 and the cathode electrode 12 .

As shown in FIG. 2, the cathode 12 is provided with an upstream portion 12a, a midstream portion 12b, and downstream portions 12c and 12d in order from the upstream side along the gas flow direction. The downstream portions 12c and 12d are composed of a first downstream portion 12c and a second downstream portion 12d located downstream of the first downstream portion 12c. The upstream portion 12a, the midstream portion 12b, and the downstream portions 12c, 12d have different composition ratios of a plurality of metal catalysts, and different generation ratios of the CO ₂ electrolysis reaction, the H ₂ O electrolysis reaction, and the fuel synthesis reaction.

The upstream portion 12a, the midstream portion 12b, and the downstream portions 12c, 12d are different in reaction to occur preferentially among the CO ₂ electrolysis reaction, the H ₂ O electrolysis reaction, and the fuel synthesis reaction. The CO ₂ electrolysis reaction takes precedence in the upstream portion 12a. The H ₂ O electrolytic reaction takes precedence in the midstream portion 12b. The fuel synthesis reaction takes precedence in the downstream portions 12c and 12d.

In the upstream portion 12a, the number of moles of CO is the largest among the reaction products composed of CO generated by the CO ₂ electrolysis reaction, H ₂ generated by the H ₂ O electrolysis reaction, and hydrocarbons generated by the fuel synthesis reaction. there is In the midstream portion 12b, the molar number of H ₂ is the largest among the reaction products consisting of CO, H ₂ and hydrocarbons. In the downstream portions 12c and 12d, the number of moles of hydrocarbons is the largest among the reaction products composed of CO, H ₂ and hydrocarbons.

In FIG. 2, the priority of each reaction is indicated using inequality signs of “>>” and “>”. In the present specification, the inequality signs ">>" and ">" are defined by the production ratio of reaction products in each reaction. ">>" means that the number of moles of the reaction product of the reaction positioned on the left side is two or more times the number of moles of the reaction product of the reaction positioned on the right side. ">" means that the number of moles of the reaction product of the reaction located on the left side is greater than the number of moles of the reaction product of the reaction located on the right side of ">".

In the upstream portion 12a, the reaction is CO ₂ electrolysis reaction>>H ₂ O electrolysis reaction>fuel synthesis reaction. That is, in the upstream portion 12a, the number of moles of the reaction product CO of the CO ₂ electrolysis reaction is at least twice as large as that of the reaction product H ₂ of the H ₂ O electrolysis reaction, and the number of moles of the reaction product CO of the CO ₂ electrolysis reaction is The number of moles is more than twice that of the reaction product _CH4 of the fuel synthesis reaction. Furthermore, in the upstream portion 12a, the number of moles of the reaction product H ₂ of the H ₂ O electrolysis reaction is greater than the number of moles of the reaction product CH ₄ of the fuel synthesis reaction.

In the upstream portion 12a, the number of moles of the reaction product CO of the CO ₂ electrolysis reaction is 50% or more of the total number of moles of the reaction products of the CO ₂ electrolysis reaction, the H ₂ O electrolysis reaction and the fuel synthesis reaction. In the upstream portion 12a, the number of moles of the reaction product CO of the CO ₂ electrolysis reaction is preferably 80% or more of the total number of moles of the reaction products of the CO ₂ electrolysis reaction, the H ₂ O electrolysis reaction and the fuel synthesis reaction.

In the midstream portion 12b, the H ₂ O electrolysis reaction>>fuel synthesis reaction>CO ₂ electrolysis reaction. That is, in the midstream portion 12b, the number of moles of the reaction product H ₂ of the H ₂ O electrolysis reaction is at least twice the number of moles of the reaction product H ₄ of the fuel synthesis reaction, and the number of moles of the reaction product H 2 O of the H ₂ O electrolysis reaction The number of moles of ₂ is more than double the reaction product CO of the CO ₂ electrolysis reaction. Furthermore, in the midstream portion 12b, the number of moles of the reaction product _CH4 of the fuel synthesis reaction is greater than the number of moles of the reaction product CO of the _CO2 electrolysis reaction.

In the midstream portion 12b, the number of moles of the reaction product H ₂ of the H ₂ O electrolysis reaction is 50% or more of the total number of moles of the reaction products of the CO ₂ electrolysis reaction, the H ₂ O electrolysis reaction, and the fuel synthesis reaction. . In the midstream portion 12b, the number of moles of the reaction product H ₂ of the H ₂ O electrolysis reaction can be 80% or more of the total number of moles of the reaction products of the CO ₂ electrolysis reaction, the H ₂ O electrolysis reaction and the fuel synthesis reaction. desirable.

In the first downstream portion 12c, fuel synthesis reaction>H ₂ O electrolysis reaction>>CO ₂ electrolysis reaction. That is, in the first downstream portion 12c, the number of moles of the reaction product CH ₄ from the fuel synthesis reaction is at least twice the number of moles of the reaction product CO from the CO ₂ electrolysis reaction, and the reaction product H from the H ₂ O electrolysis reaction. The number of moles of ₂ is more than double the reaction product CO of the CO ₂ electrolysis reaction. Furthermore, in the _first downstream portion 12c, the number of moles of the reaction product CH4 of the fuel synthesis reaction is greater _than the number of moles of the reaction product H2 of the _H2O electrolysis reaction.

In the first downstream portion 12c, the total number of moles of the reaction product CH ₄ of the fuel synthesis reaction and the reaction product H ₂ of the H ₂ O electrolysis reaction is the reaction product of the CO ₂ electrolysis reaction, the H ₂ O electrolysis reaction, and the fuel synthesis reaction. It is 80% or more of the total number of moles of the product. In the first downstream portion 12c, the total number of moles of the reaction product CH ₄ of the fuel synthesis reaction and the reaction product H ₂ of the H ₂ O electrolysis reaction is converted into reaction products of the CO ₂ electrolysis reaction, the H ₂ O electrolysis reaction and the fuel synthesis reaction. It is desirable to make it 90% or more of the total number of moles of the product.

In the second downstream portion 12d, fuel synthesis reaction>>H ₂ O electrolysis reaction>CO ₂ electrolysis reaction. That is, in the second downstream portion 12d, the number of moles of the reaction product CH ₄ of the fuel synthesis reaction is at least twice the number of moles of the reaction product H ₂ of the H ₂ O electrolysis reaction, and the number of moles of the reaction product CH 4 of the fuel synthesis reaction The number of moles of ₄ is more than double the reaction product CO of the CO ₂ electrolysis reaction. Furthermore, in the second downstream portion 12d, the number of moles of the reaction product H ₂ of the H ₂ O electrolysis reaction is greater than the number of moles of the reaction product CO of the CO ₂ electrolysis reaction.

In the second downstream portion 12d, the number of moles of the reaction product CH4 of the fuel synthesis reaction is 50% or more of the _total number of moles of the reaction products of the _CO2 electrolysis reaction, the _H2O electrolysis reaction and the fuel synthesis reaction. . In the second downstream portion 12d, the number of moles of the reaction product CH4 of the fuel synthesis reaction may be 80% or more of the _total number of moles of the reaction products of the _CO2 electrolysis reaction, the _H2O electrolysis reaction and the fuel synthesis reaction. desirable.

In this embodiment, the proportions of the CO ₂ electrocatalyst, H ₂ O electrocatalyst, and fuel synthesis catalyst are different for each of the upstream portion 12a, midstream portion 12b, first downstream portion 12c, and second downstream portion 12d. By varying the proportions of these catalysts, the CO ₂ electrolysis reaction, the H ₂ O electrolysis reaction, and the fuel synthesis reaction are performed for each of the upstream portion 12a, the midstream portion 12b, the first downstream portion 12c, and the second downstream portion 12d. The production ratio of each reaction product is made different.

In the upstream portion 12a, the ratio of the CO ₂ electrocatalyst, the H ₂ O electrocatalyst, and the fuel synthesis catalyst is such that the number of moles of CO is two times or more that of H ₂ and the number of moles of CO is two or more times that of CH ₄ . is set to be Furthermore, in the upstream portion 12a, the proportions of the H ₂ O electrocatalyst and the fuel synthesis catalyst are set so that the number of moles of H ₂ is greater than that of CH ₄ .

In the midstream portion 12b, the ratio of the CO ₂ electrocatalyst, the H ₂ O electrocatalyst, and the fuel synthesis catalyst is such that the number of moles of H ₂ is at least twice that of CH ₄ and the number of moles of H ₂ is twice that of CO. It is set to be more than Furthermore, in the midstream section 12b, the ratio of the _CO2 electrocatalyst and the fuel synthesis catalyst is set so that the number of moles of _CH4 is greater than that of _CO2 .

In the first downstream portion 12c, the ratio of the CO ₂ electrocatalyst, the H ₂ O electrocatalyst, and the fuel synthesis catalyst is such that the number of moles of CH ₄ is twice or more that of CO, and the number of moles of H ₂ is two times that of CO. It is set to more than double. Furthermore, in the first downstream portion 12c, the ratio of the H ₂ O electrocatalyst and the fuel synthesis catalyst is set so that the number of moles of CH ₄ is greater than that of H ₂ .

In the second downstream portion 12d, the ratio of the CO ₂ electrocatalyst, the H ₂ O electrocatalyst, and the fuel synthesis catalyst is such that the number of moles of CH ₄ is twice or more that of H ₂ and the number of moles of CH ₄ is that of CO. It is set to double or more. Furthermore, in the second downstream portion 12d, the ratio of the CO ₂ electrocatalyst and the H ₂ O electrocatalyst is set so that the number of moles of H ₂ is greater than that of CO.

Next, chemical reactions that occur when CO ₂ and H ₂ O are supplied to the cathode 12 of the fuel synthesizing device 10 will be described.

At the upstream portion 12a of the cathode electrode 12, the CO ₂ electrolysis reaction occurs preferentially, and as much CO as possible is produced from CO ₂ . In the upstream portion 12a, the H ₂ O electrolysis reaction and the fuel synthesis reaction are suppressed. _{The H2O} electrolysis reaction takes precedence over the fuel synthesis reaction and a small amount of H2 is produced from _H2O . CO produced in the CO ₂ electrolysis reaction, a small amount of H ₂ produced in the H ₂ O electrolysis reaction, and most of H ₂ O not used in the H ₂ O electrolysis reaction are supplied to the midstream section 12b. be.

_In the midstream portion 12b, the _H2O electrolysis reaction occurs preferentially, and as much H2 as possible is produced from _H2O . The fuel synthesis reaction and the CO ₂ electrolysis reaction are suppressed in the midstream portion 12b. _The fuel synthesis reaction takes precedence over the _CO2 electrolysis reaction and a small amount of _CH4 is synthesized from CO and H2. CO supplied from the upstream portion 12a and H ₂ produced by the H ₂ O electrolytic reaction in the midstream portion 12b are supplied to the first downstream portion 12c.

_In the _first downstream portion 12c, a fuel synthesis reaction occurs preferentially and CH4 is synthesized from CO and H2. In the first downstream portion 12c, the H ₂ O electrolysis reaction also preferentially occurs, and the H ₂ O by-produced in the fuel synthesis reaction is electrolyzed. The CO ₂ electrolysis reaction is suppressed in the first downstream portion 12c. CH ₄ synthesized in the fuel synthesis reaction and CO and H ₂ not used in the fuel synthesis reaction are supplied to the second downstream section 12d.

_In the _second downstream portion 12d, a fuel synthesis reaction occurs preferentially and CH4 is synthesized from CO and H2. In the second downstream portion 12d, a fuel synthesis reaction is performed using the remaining CO and H ₂ not used in the fuel synthesis reaction in the first downstream portion 12c.

In the fuel synthesizing device 10 of this embodiment described above, the rate of occurrence of the CO ₂ electrolysis reaction, the H ₂ O electrolysis reaction, and the fuel synthesis reaction at the upstream portion 12a, the midstream portion 12b, and the downstream portions 12c, 12d of the cathode 12 is determined as follows: making it different. Priority is given to the CO ₂ electrolysis reaction in the upstream portion 12a, priority is given to the H ₂ O electrolysis reaction in the midstream portion 12b, and priority is given to the fuel synthesis reaction in the downstream portions 12c and 12d.

This allows as much CO ₂ as possible to be electrolyzed to CO by the CO ₂ electrolysis reaction before H ₂ is produced by the H ₂ O electrolysis reaction. Since the H ₂ O electrolysis reaction occurs in a state where the CO ₂ concentration is decreased and the CO concentration is increased, the CO ₂ electrolysis reaction 2 (reverse water gas shift reaction) in which CO ₂ reacts with H ₂ can be suppressed. As a result, H ₂ consumption by electrolysis reaction 2 can be suppressed, power consumption used for H ₂ production can be suppressed, and fuel synthesis efficiency can be improved.

In addition, by prioritizing the fuel synthesis reaction in the first downstream portion 12c and the second downstream portion 12d, fuel synthesis is efficiently performed using CO produced in the upstream portion 12a and H ₂ produced in the midstream portion 12b. be able to.

Further, in the first downstream portion 12c, priority is given to the H ₂ O electrolysis reaction next to the fuel synthesis reaction. As a result, the fuel synthesizing reaction and the H ₂ O electrolysis reaction occur simultaneously, and the H _{2 O produced as a by-product of the fuel synthesizing reaction can be electrolyzed into H 2 by the H 2 O} electrolysis reaction. As a result, H ₂ O, which is a by-product of the fuel synthesis reaction, can be quickly removed, and the fuel synthesis efficiency can be improved.

Further, a second downstream portion 12d that prioritizes the fuel synthesis reaction is provided downstream of the first downstream portion 12c. As a result, in the second downstream portion 12d, the unreacted CO and H ₂ that have not been used in the fuel synthesis reaction in the first downstream portion 12c can be used for the fuel synthesis reaction, thereby improving the fuel synthesis efficiency. can be done.

(Second embodiment)
Next, a second embodiment of the invention will be described. In the second embodiment, only parts different from the first embodiment will be described.

As shown in FIG. 3, in the second embodiment, a plurality of power supply devices 14a-14c are provided. The first power supply device 14 a applies a voltage between the upstream portion 12 a of the cathode 12 and the anode 13 . The second power supply device 14 b applies a voltage between the midstream portion 12 b of the cathode 12 and the anode 13 . The third power supply device 14 c applies a voltage between the first downstream portion 12 c and the second downstream portion 12 d of the cathode 12 and the anode 13 . These power supply devices 14 a - 14 c are controlled by a control device 29 .

Each power supply 14a-14c can apply a different voltage. The CO ₂ electrolysis reaction and the H ₂ O electrolysis reaction have different effective voltages. The first power supply device 14a applies a voltage suitable for the _CO2 electrolysis reaction. The second power supply device 14b applies a voltage suitable for the _H2O electrolytic reaction. The third power supply device 14c applies a voltage suitable for the _H2O electrolytic reaction.

A voltage suitable for CO ₂ electrolysis reaction is also called CO ₂ electrolysis voltage, and a voltage suitable for H ₂ O electrolysis reaction is also called H ₂ O electrolysis voltage. The _CO2 electrolysis voltage is a higher voltage than the _H2O electrolysis voltage. Specifically, the CO ₂ electrolysis voltage is desirably 1.0 to 2.5V, more desirably 1.0 to 1.4V. The H ₂ O electrolysis voltage is preferably 0.9-2.4V, more preferably 0.9-1.3V.

According to the second embodiment described above, a plurality of power supply devices 14a to 14c are provided, and the upstream portion 12a, the midstream portion 12b, and the downstream portions 12c and 12d of the cathode electrode 12 are respectively prioritized for chemical reactions. Appropriate voltage is applied. This allows the CO ₂ electrolysis reaction to proceed efficiently in the upstream portion 12a. The H ₂ O electrolysis reaction can proceed efficiently in the midstream portion 12b, the first downstream portion 12c, and the second downstream portion 12d.

(Third embodiment)
Next, a third embodiment of the invention will be described. In the third embodiment, only parts different from the above embodiments will be described.

As shown in FIG. 4, a plurality of electrolytes 11 and 15 are provided in the third embodiment. In the example shown in FIG. 4, two electrolytes 11 , 15 are provided on both sides of the cathode 12 . The first electrolyte 11 is set as an electrolyte for _CO2 electrolytic reaction, and the second electrolyte 15 is set as an electrolyte for _H2O electrolytic reaction.

The second electrolyte 15 is thinner than the first electrolyte 11 . In the fuel synthesis reaction, the required number of moles of H ₂ is three times that of CO, and the number of moles of O ²⁻ generated in the H ₂ O electrolysis reaction is also three times that of O ²⁻ generated in the CO ₂ electrolysis reaction. Since the H ₂ O electrolytic reaction produces more O ²⁻ than the CO ₂ electrolytic reaction, it is necessary to efficiently conduct the O ²⁻ produced at the cathode 12 through the second electrolyte 15 . Therefore, in the third embodiment, the thickness of the second electrolyte 15 is reduced to efficiently conduct O ²⁻ generated by the H ₂ O electrolysis reaction.

A first anode 13 is provided on the opposite side of the cathode 12 in the first electrolyte 11 . A second anode 16 is provided on the opposite side of the cathode 12 in the second electrolyte 15 .

Also in the third embodiment, a plurality of power supply devices 14a to 14c are provided as in the second embodiment. The first power supply device 14 a applies a voltage between the upstream portion 12 a of the cathode 12 and the first anode 13 . The second power supply device 14 b applies a voltage between the midstream portion 12 b of the cathode 12 and the second anode 16 . The third power supply device 14 c applies a voltage between the downstream portions 12 c and 12 d of the cathode 12 and the second anode 16 .

In the third embodiment described above, a plurality of electrolytes 11 and 15 are provided, the first electrolyte 11 is used for the _CO2 electrolytic reaction, and the second electrolyte 15 is used for the _H2O electrolytic reaction. As a result, the electrolytes 11 and 15 can be made suitable for the CO ₂ electrolytic reaction or the H ₂ O electrolytic reaction, and the efficiency of each reaction can be improved.

(Fourth embodiment)
Next, a fourth embodiment of the invention will be described. In the fourth embodiment, only parts different from the above embodiments will be described.

As shown in FIG. 5, in the fourth embodiment, the cathode 12 is provided with a plurality of gas separation membranes 12e to 12h. The plurality of gas separation membranes 12e-12h includes a first gas separation membrane 12e, a second gas separation membrane 12f, a third gas separation membrane 12g and a fourth gas separation membrane 12h.

The first gas separation membrane 12e is provided downstream of the upstream portion 12a in the gas flow direction. The second gas separation membrane 12f is provided downstream in the gas flow direction of the midstream portion 12b. The third gas separation membrane 12g is provided downstream of the first downstream portion 12c in the gas flow direction. The fourth gas separation membrane 12h is provided downstream of the second downstream portion 12d in the gas flow direction. The first gas separation membrane 12e corresponds to the upstream gas separation membrane, the second gas separation membrane 12f corresponds to the midstream gas separation membrane, and the third gas separation membrane 12g and the fourth gas separation membrane 12h correspond to the downstream section. It corresponds to a gas separation membrane.

The first gas separation membrane 12e is sandwiched between the upstream portion 12a and the midstream portion 12b. The second gas separation membrane 12f is sandwiched between the midstream portion 12b and the first downstream portion 12c. The third gas separation membrane 12g is sandwiched between the first downstream portion 12c and the second downstream portion 12d.

The gas separation membranes 12e-12h have the function of restricting the permeation of specific types of gases. The first gas separation membrane 12e restricts permeation of _CO2 . The second gas separation membrane 12f, the third gas separation membrane 12g and the fourth gas separation membrane 12h limit the permeation of _H2O .

The gas separation membranes 12e-12h can be made of mesoporous silica, for example. Mesoporous silica can be suitably used as the gas separation membranes 12e to 12h by selecting pores according to the type of gas to be separated.

According to the fourth embodiment described above, in the upstream portion 12a, the first gas separation membrane 12e restricts CO ₂ from flowing downstream. Thereby, the CO ₂ electrolysis reaction can be efficiently performed in the upstream portion 12a.

In the midstream portion 12b, the first downstream portion 12c, and the second downstream portion 12d, the second gas separation membrane 12f, the third gas separation membrane 12g, and the fourth gas separation membrane 12h prevent H ₂ O from flowing downstream. Limited. As a result, the H ₂ O electrolytic reaction can be efficiently performed in the midstream portion 12b, the first downstream portion 12c, and the second downstream portion 12d.

(Other embodiments)
The present invention is not limited to the above-described embodiments, and can be variously modified as follows without departing from the scope of the present invention. Moreover, the means disclosed in each of the above embodiments may be appropriately combined within the practicable range.

For example, in each of the above embodiments, methane was exemplified as the hydrocarbon synthesized by the fuel synthesizing device 10, but different types of hydrocarbons may be synthesized. By varying the type of catalyst and reaction temperature used in the cathode electrode 12, the types of hydrocarbons to be synthesized can be varied. Examples of different types of hydrocarbons include hydrocarbons such as ethane and propane, which have more carbon atoms than methane, and hydrocarbons containing oxygen atoms, such as alcohols and ethers.

Further, in each of the above embodiments, the internal pressure of the cathode 12 is about atmospheric pressure, but the internal pressure of the cathode 12 may be higher than the atmospheric pressure. By increasing the internal pressure of the cathode electrode 12, the reaction rates of the H ₂ O electrolysis reaction, the CO ₂ electrolysis reaction and the fuel synthesis reaction can be increased, and the system efficiency can be enhanced.

In order to make the internal pressure of the cathode 12 high, for example, a back pressure regulating valve for adjusting the internal pressure of the cathode 12 may be provided in the fuel synthesis exhaust gas passage 26 . Then, by supplying H ₂ O from the H ₂ O supply passage 21 in a state of pressure higher than atmospheric pressure and supplying CO ₂ from the CO ₂ supply passage 24 in a state of pressure higher than atmospheric pressure, the inside of the cathode electrode 12 The pressure can be high. Furthermore, it is desirable that the fuel synthesizing device 10 has a pressure-resistant structure. When the internal pressure of the cathode electrode 12 is high, the upper limit is preferably about 100 atmospheres.

Further, in the second embodiment, the thickness of the electrolyte 11 may be varied depending on the upstream portion 12a, the midstream portion 12b, and the downstream portions 12c and 12d of the cathode electrode 12. FIG. Since the H ₂ O electrolytic reaction, which takes precedence in the midstream portion 12b, produces more O ²⁻ than the CO ₂ electrolytic reaction, it is necessary to efficiently conduct the O ²⁻ produced at the cathode electrode 12 to the second electrolyte 15. be. Therefore, by making the thickness of the portion corresponding to the midstream portion 12b in the electrolyte 11 thinner than the portion corresponding to the upstream portion 12a, O ²⁻ can be efficiently conducted.

10 fuel synthesizer, 11 electrolyte, 12 cathode, 12a upstream, 12b midstream, 12c downstream (first downstream), 12d downstream (second downstream), 12e first gas separation membrane (upstream gas separation membrane), 12f second gas separation membrane (midstream gas separation membrane), 12g third gas separation membrane (downstream gas separation membrane), 12h fourth gas separation membrane (downstream gas separation membrane), 13 anode, 14 power supply, 14a first power supply, 14b second power supply, 15 second electrolyte, 20 _H2O reservoir ( _H2O supply), 22 _H2O pump ( _H2O supply) , 23 CO ₂ storage (CO ₂ supply), 25 pressure regulating valve (CO ₂ supply)

Claims (14)

A fuel having an electrolyte (11, 15) having oxygen ion conductivity, a cathode (12) provided on one side of said electrolyte, and an anode (13, 16) provided on the other side of said electrolyte. a synthesizer (10);
a power supply (14) for supplying power to the fuel synthesizer;
H ₂ O supply units (20, 22) for supplying H ₂ O to the cathode;
CO ₂ supply units (23, 25) for supplying CO ₂ to the cathode;
with
At the cathode electrode, H ₂ O supplied from the H ₂ O supply unit and CO ₂ supplied from the CO ₂ supply unit flow in a predetermined gas flow direction,
At the cathode, the H ₂ O electrolysis reaction for electrolyzing H ₂ O to produce H ₂ , the CO ₂ electrolysis reaction for electrolyzing CO ₂ to produce CO, and the H ₂ and CO A fuel synthesis reaction that synthesizes hydrocarbons occurs,
The cathode includes a H _{2 O electrocatalyst that promotes the H 2 O} electrolysis reaction, a CO _{2 electrocatalyst that promotes the CO 2 electrolysis} reaction, and a fuel synthesis catalyst that promotes the fuel synthesis reaction. Catalysts of different types are provided,
The CO ₂ electrocatalyst and the H ₂ contained in the plurality of types of catalysts are added to each of the upstream portion ( 12 a ), the midstream portion ( 12 b ), and the downstream portion ( 12 c, 12 d ) of the cathode in the gas flow direction. the proportions of the O electrocatalyst and the fuel synthesis catalyst are different,
In the upstream portion, the number of moles of CO is the largest among the reaction products consisting of CO generated in the CO ₂ electrolysis reaction, H ₂ generated in the H ₂ O electrolysis reaction, and hydrocarbons generated in the fuel synthesis reaction. Among the reaction products, the number of moles of H ₂ is the largest in the midstream portion, and the number of moles of hydrocarbons among the reaction products is the largest in the downstream portion. energy conversion system. In the upstream portion, the number of moles of CO generated by the CO ₂ electrolysis reaction is at least twice the number of H ₂ generated by the H ₂ O electrolysis reaction, and the number of moles of CO generated by the CO ₂ electrolysis reaction. 2. The energy conversion system of claim 1, wherein is more than twice as many hydrocarbons produced in said fuel synthesis reaction. _3. The energy conversion system according to claim 2, wherein in the upstream portion, the number of moles of H2 produced by the _H2O electrolysis reaction is larger than that of hydrocarbons produced by the fuel synthesis reaction. In the midstream portion, the number of moles of H ₂ produced by the H ₂ O electrolysis reaction is at least twice that of hydrocarbons produced by the fuel synthesis reaction, and the number of moles of H ₂ produced by the H ₂ O electrolysis reaction is 4. The energy conversion system according to any one of claims 1 to 3, wherein the number of moles is at least twice that of CO produced in the _CO2 electrolysis reaction. 5. The energy conversion system according to claim 4, wherein in the midstream portion, the number of moles of hydrocarbons produced by the fuel synthesis reaction is greater than the number of moles of CO produced by the _CO2 electrolysis reaction. The downstream portion includes a first downstream portion (12c) and a second downstream portion (12d) located downstream of the first downstream portion,
In the first downstream portion, the number of moles of hydrocarbons produced in the fuel synthesis reaction is at least twice the number of CO produced in the CO ₂ electrolysis reaction, and the number of moles of H ₂ produced in the H ₂ O electrolysis reaction is 6. The energy conversion system according to any one of claims 1 to 5, wherein the number of moles is at least twice that of CO produced in the _CO2 electrolysis reaction. 7. The energy conversion system according to claim 6, wherein in the first downstream portion, the number of moles of hydrocarbons produced by the fuel synthesis reaction is greater _than the number of moles of H2 produced by the _H2O electrolysis reaction. In the second downstream portion, the number of moles of hydrocarbons produced in the fuel synthesis reaction is at least twice the number of moles of H ₂ produced in the H ₂ O electrolysis reaction, and the number of moles of hydrocarbons produced in the fuel synthesis reaction is 8. The energy conversion system according to claim 6 or 7, wherein the number of moles is at least twice that of CO produced in the _CO2 electrolysis reaction. 9. The energy conversion system according to claim 8, wherein in the _second downstream portion, the number of moles of H2 produced by the _H2O electrolysis reaction is greater than the number of moles of CO produced by the _CO2 electrolysis reaction. The power supply device includes a first power supply device (14a) that applies voltage to the upstream portion of the cathode and a second power supply device (14b) that applies voltage to the midstream portion of the cathode. contains
10. The energy conversion system according to any one of claims 1 to 9, wherein the applied voltage of the first power supply and the applied voltage of the second power supply are different. A plurality of the electrolytes are provided with the cathode interposed therebetween,
11. The plurality of electrolytes according to any one of claims 1 to 10, comprising a first electrolyte (11) used for the _CO2 electrolysis reaction and a second electrolyte (15) used for the _H2O electrolysis reaction. 1. An energy conversion system according to claim 1. 12. The energy conversion system according to any one of claims 1 to 11, wherein an upstream gas separation membrane (12e) for restricting permeation of _CO2 is provided on the downstream side of the upstream part in the direction of gas flow. 13. The energy conversion system according to any one of claims 1 to 12, wherein a midstream gas separation membrane (12f) for restricting permeation of _H2O is provided on the downstream side of the midstream in the gas flow direction. 14. The energy conversion system according to any one of claims 1 to 13, wherein downstream gas separation membranes (12g, 12h) for limiting permeation of _H2O are provided on the downstream side of the downstream portion in the direction of gas flow. .

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