Electricity generation or hydrogen production method and energy conversion system

Abstract

The present invention provides a method for generating electric power or producing hydrogen from a carbon source, and an energy conversion system, the method for generating electric power or producing hydrogen comprising: a chemical conversion step for, in a chemical conversion unit, causing a reaction of a mixture of a carbon source and a solution that contains an intermediate medium, at a temperature at which the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state, such that the carbon source is oxidized and the intermediate medium is reduced; an electrochemical conversion step for causing the intermediate medium that was reduced in the chemical conversion step to make contact with an anode of a battery structure of an electrochemical conversion unit that comprises said battery structure and causing oxygen or air to make contact with a cathode of the battery structure such that electric power is generated, or causing water to make contact with said cathode such that hydrogen is produced; and a recycling step for returning the solution that contains the intermediate medium after the electrochemical conversion step to the mixture.

Description

[Technical field]

[0001] The present invention relates to a method for producing electricity or hydrogen and an energy conversion system. [Background technology]

[0002] Fossil fuels such as high-grade coal and petroleum have been widely used as carbon sources to be converted into electricity at power plants because large amounts of energy can be easily extracted by combustion. However, in recent years, the problem of resource depletion has arisen. On the other hand, hydrogen energy, which has a high exergy rate, has been attracting attention as an alternative energy source to fossil fuels.

[0003] Energy conversion systems and methods have been proposed that have high resource-to-energy conversion efficiency for the production of electricity or (secondary) energy sources with high exergy rates.

[0004] For example, systems and methods are known that utilize waste heat (also called exhaust heat), which is low-temperature energy that could not be used in power plants or the like until now (Patent Documents 1 and 2). Patent Document 1 describes a waste heat hydrogen production device that includes a thermoelectric power generation device that has a high-temperature side exposed to high temperatures and a low-temperature side exposed to low temperatures and converts thermal energy into electrical energy, a steam generation device for obtaining steam, and an electrochemical device that produces hydrogen by electrolysis from the steam obtained in the steam generation device using the electrical energy obtained in the thermoelectric power generation device, and that uses waste heat released in the steelmaking process as its energy source. Patent Document 2 describes a method for recovering exhaust heat, in which exhaust heat at 150 degrees Celsius or less is used in an endothermic reforming reaction of methanol (CH3OH) to produce carbon dioxide (CO2) and hydrogen (H2), and the thermal energy contained in the exhaust heat, which has a low exergy rate, is converted into hydrogen (H2), a combustible substance with a higher exergy rate, and recovered.

[0005] Also known are methods that utilize low-quality carbon sources such as lignite and biomass (see Patent Documents 3 and 4). Patent Document 3 describes a method for producing hydrogen by a thermochemical decomposition reaction of water and carbon using cerium oxide as a reaction medium. Patent Document 4 describes a method for producing hydrogen from biomass and iron oxide, which includes a reduction step in which a mixture of iron oxide particles and biomass is heated to reduce the iron oxide, and a first oxidation step in which a solid phase containing metallic iron and carbon obtained in the reduction step is brought into contact with water vapor at a temperature of 600°C or less to generate hydrogen gas, and the solid phase containing iron oxide obtained in the first oxidation step is supplied to the reduction step, thereby circulating iron and iron oxide.

[0006] Other known methods include electrolyzing water using electrons obtained from an alkali metal and a metal with low ionization tendency to produce hydrogen. For example, Patent Document 5 describes a hydrogen production method including an electrochemical oxidation-reduction step in which an alkali metal is used for the negative electrode and carbon or a metal with a lower ionization tendency than the alkali metal is used for the positive electrode, whereby electrons are released from the alkali metal and a fusion product of the alkali metal and carbon or metal is produced by a cell reaction, a hydrogen generation step in which hydrogen is generated by electrolyzing water using the electrons released in the electrochemical oxidation-reduction step, and a thermochemical reduction step in which the fusion product is heated to reduce it to the alkali metal and carbon or metal. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2011-208242 A [Patent Document 2] Japanese Patent Application Publication No. 05-170401 [Patent Document 3] Japanese Patent Application Publication No. 10-251001 [Patent Document 4] JP 2008-137864 A [Patent Document 5] JP 2016-121036 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, further improvement in energy conversion efficiency is required for all of the devices and methods described in Patent Documents 1 to 5. In particular, there is no known means for efficiently using low-quality carbon sources (such as lignite, peat, and biomass with high moisture content) as energy sources. Furthermore, conventional methods generally target waste heat utilization at high temperatures, such as at 600° C. or higher, and it is difficult to utilize low-temperature waste heat, such as at 350° C. or lower. In addition, in conventional methods for utilizing carbon sources, the carbon source must first be converted into thermal energy, which poses the problem of low energy conversion efficiency. An object of the present invention is to provide a method for producing power generation or hydrogen, and an energy conversion system, which have excellent energy conversion efficiency even when a low-quality carbon source is used and low-temperature waste heat is utilized. [Means for solving the problem]

[0009] In the present invention, power generation or hydrogen production is performed via energy conversion from a carbon source to an intermediate medium by a solution reaction. In this way, in the present invention, power generation or hydrogen production can be performed from a carbon source without passing through the form of thermal energy, and therefore energy conversion efficiency can be improved. In the present invention, the low-temperature waste heat can be used to adjust the environmental temperature of the reaction. Furthermore, it is also possible to further improve the energy conversion efficiency by utilizing temperature changes in the chemical exergy of the carbon source and intermediate medium. Specifically, according to the present invention, by combining a chemical conversion unit that performs an oxidation-reduction reaction between the carbon source and intermediate medium with an electrochemical conversion unit that uses the intermediate medium in a reduced state to generate electricity or produce a secondary energy source with a high exergy rate, and selecting the reaction temperature of the chemical conversion unit, it has been found that the chemical exergy of the intermediate medium in a reduced state can be made smaller than the chemical exergy of the carbon source, thereby solving the above-mentioned problem. The configuration of the present invention, which is a specific means for solving the above problems, and a preferred configuration of the present invention will be described below.

[0010] [1] A method for generating electricity or producing hydrogen from a carbon source, comprising: a chemical conversion step in which a mixture of a solution containing an intermediate medium and a carbon source is reacted in a chemical conversion unit at a temperature where the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state, thereby oxidizing the carbon source and reducing the intermediate medium; an electrochemical conversion step in which a solution containing the intermediate medium reduced in the chemical conversion step is brought into contact with an anode of a battery structure in an electrochemical conversion unit having a battery structure, or a substrate on which the intermediate medium reduced in the chemical conversion step is precipitated is used as the anode of the battery structure, and oxygen or air is brought into contact with the cathode of the battery structure to generate electricity, or water is brought into contact with the cathode to produce hydrogen; and a recycling step in which the solution containing the intermediate medium after the electrochemical conversion step is returned to the mixture. [2] The method for producing electricity or hydrogen described in [1], wherein in the chemical conversion step, the intermediate medium in a reduced state is precipitated on a substrate, and in the electrochemical conversion step, the substrate on which the intermediate medium is precipitated is used as the anode of the battery structure in the electrochemical conversion section. [3] The method for producing electricity or hydrogen according to [1] or [2], wherein the reaction temperature in the chemical conversion step is 350°C or lower. [4] The method for generating electricity or producing hydrogen according to claim [1] or [2], wherein the intermediate medium contains at least one element selected from the group consisting of V, Cr, Mn, Fe, Cu, and Zn. [5] The method for producing electricity or hydrogen described in [1] or [2], further comprising recovering CO2 generated by an oxidation-reduction reaction in the chemical conversion section. [6] An energy conversion system comprising: a chemical conversion unit that oxidizes the carbon source while reducing the intermediate medium from an oxidized state to a reduced state; and an electrochemical conversion unit that includes one electrode, the other electrode, and an electric current connecting the one electrode and the other electrode, and that oxidizes the intermediate medium from a reduced state to an oxidized state at the one electrode while reducing a reduced material at the other electrode, wherein the chemical conversion unit performs a reduction reaction at a temperature at which the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in its reduced state, and the electrochemical conversion unit outputs at least one of the reduced form of the reduced material and electricity to the outside. [7] The energy conversion system described in [6], comprising a plurality of at least one of the chemical conversion units and the electrochemical conversion units. [8] The energy conversion system described in [6], comprising a plurality of electrochemical conversion units, some of which output hydrogen as the reduced material to the outside, and other parts of which output electric power to the outside, and which uses the electric power as auxiliary electric power for outputting the hydrogen to the outside. [9] The energy conversion system described in [6], which recovers CO2 generated by an oxidation-reduction reaction in the chemical conversion section. Effect of the Invention

[0011] In the present invention, power generation or hydrogen production can be performed through energy conversion from a carbon source to an intermediate medium by a solution reaction, without going through the form of thermal energy from the carbon source, and therefore the energy conversion efficiency can be improved. In addition, this energy conversion can also be performed by utilizing low-temperature waste heat. Furthermore, in the present invention, even low-quality carbon sources that are difficult to convert into thermal energy, for example, by combustion, can be used. Furthermore, depending on demand, it is possible to choose between obtaining electricity directly (generating electricity) or producing hydrogen as a secondary energy source. As described above, according to the present invention, it is possible to provide a power generation or hydrogen production method and an energy conversion system that have excellent energy conversion efficiency even when a low-quality carbon source and low-temperature waste heat are utilized. In addition, the CO2 produced by the method of the present invention can be easily recovered with high purity, which reduces the environmental impact and allows for secondary use of the CO2 if necessary. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of an example of an energy conversion system of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of an example of a first preferred embodiment of the energy conversion system of the present invention. [Diagram 3] FIG. 3 is a schematic graph showing the relationship between the temperature and chemical exergy of the intermediate medium used in the first preferred embodiment. [Figure 4] FIG. 4 is a schematic diagram of an embodiment for recovering CO2 gas in the first preferred embodiment. [Diagram 5] FIG. 5 is a schematic diagram comparing the energy conversion efficiency between the conventional method and the proposed method using the first preferred embodiment of the present invention. [Figure 6] Figure 6(a) shows the magnitude relationship of the chemical exergy of the carbon source (brown coal) and intermediate medium at three temperatures. Figure 6(b) is a graph showing the temperature change of the chemical exergy of the carbon source (brown coal) and several intermediate mediums. [Figure 7] FIG. 7 is a schematic diagram of an example of (B-1) power generation during power shortage in the second preferred embodiment of the energy conversion system of the present invention. [Figure 8] FIG. 8 is a schematic diagram of the proposed method for recovering CO2 gas when generating electricity during a power shortage (B-1) in the second preferred embodiment, and a bar graph comparing it with the conventional method. [Figure 9]FIG. 9 is a schematic diagram of an example of (B-2) hydrogen production during excess power in the second preferred embodiment of the energy conversion system of the present invention. [Figure 10] FIG. 10 is a schematic diagram of the proposed method for recovering CO2 gas when producing hydrogen during excess power (B-2) in the second preferred embodiment, and a bar graph comparing it with the conventional method. [Figure 11] Fig. 11(A) is a bar graph showing the yield of generated gas when the reaction temperature of the chemical conversion unit is 300°C. Fig. 11(B) is a bar graph showing the yield of generated gas when the reaction temperature of the chemical conversion unit is 250°C. [Figure 12] Figure 12(A) shows the XRD pattern of the solid product when Cr2(SO4)3 is reduced, and Figure 12(B) shows the XRD pattern of the solid product when Cr(OH)3 is reduced. [Figure 13] Fig. 13(A) is a schematic diagram of the material balance in Evaluation Example 1 of Example 1. Fig. 13(B) is a schematic diagram of the exergy balance in Evaluation Example 1 of Example 1. Fig. 13(C) is a schematic diagram of an example of the exergy balance in a combustion process. [Figure 14] Fig. 14(A) is a schematic diagram of the material balance in Evaluation Example 1 of Example 1. Fig. 14(B) is a schematic diagram of the exergy balance in Evaluation Example 1 of Example 1. Fig. 14(C) is a schematic diagram of an example of the exergy balance in a gasification process. [Figure 15] FIG. 15 is a schematic diagram of an experimental device used in Evaluation Example 3 as the chemical conversion unit in Example 2. [Figure 16] FIG. 16 shows photographs of the sample of the chemically converted portion before and after the reaction under specific reaction conditions in Evaluation Example 3, and a graph showing the relationship between wavelength and absorbance measured with a spectrophotometer. [Figure 17] 17(A) is a graph showing the relationship between the reaction time and the conversion rate XVO 2+ of VO 2+ ions under several reaction conditions in Evaluation Example 3. FIG. 17(B) is a graph showing the relationship between the conversion rate XVO 2+ of VO 2+ ions and the electrochemical conversion E. [Figure 18] Fig. 18(A) is an XRD pattern of the solid product in Evaluation Example 4. Fig. 18(B) is a photograph of the solid product in Evaluation Example 4 under specific conditions. [Figure 19] FIG. 19 is a bar graph showing the yield of generated gas in Evaluation Example 4. [Figure 20] FIG. 20 is a schematic diagram of the model used in the reaction rate analysis of Evaluation Example 5. [Figure 21] FIG. 21 is a graph showing the relationship between the reaction time and the conversion ratio XVO 2+ of VO 2+ ions based on the calculated reaction rate in Evaluation Example 5, in which the experimental values ​​in the demonstration experiment are plotted. [Figure 22] FIG. 22 is a schematic diagram of the reactor design in the chemical conversion section used in Evaluation Example 6. [Figure 23] FIG. 23 is a schematic diagram showing the material balance, power generation efficiency, and reactor size in Evaluation Example 6 of Example 2. [Figure 24] FIG. 24 is a schematic diagram of the energy conversion system used in Evaluation Example 7. [Diagram 25] FIG. 25 is a graph showing the relationship between the efficiency of the electrolytic reaction and the energy conversion efficiency in the energy conversion system used in Evaluation Example 7. [Figure 26] FIG. 26 is a graph showing the relationship between current density and voltage when hydrogen is produced by the method of Example 2 and the conventional method. [Figure 27] Fig. 27(A) is a graph showing the relationship between current density and efficiency of electrolysis reaction when hydrogen is produced by the method of Example 2 and the conventional method. Fig. 27(B) is a graph showing the relationship between current density and energy conversion efficiency when hydrogen is produced by the method of Example 2 and the conventional method. [Figure 28] FIG. 28 is a graph showing the relationship between the reduction rate of VO2+, which is an intermediate medium and has an oxidation number of 4, to V3+, which has an oxidation number of 3, and the measured value of the cell voltage (ECell [V]) and the overall power generation efficiency. [Figure 29] FIG. 29 is a graph (IV curve) showing the relationship between current (I) and voltage (V) during power generation in Evaluation Example 10. [Diagram 30] FIG. 30 is a graph showing the relationship between current density and voltage when hydrogen was produced by the method of Evaluation Example 11 and the conventional method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will be described in detail below. The following description of the constituent elements may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "~" means a range including the numerical values ​​before and after "~" as the lower and upper limits.

[0014] [Power generation or hydrogen production methods] The method for generating electricity or producing hydrogen of the present invention is a method for generating electricity or producing hydrogen from a carbon source, and includes a chemical conversion step in which a mixture of a solution containing an intermediate medium and a carbon source is reacted in a chemical conversion unit at a temperature where the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state, thereby oxidizing the carbon source and reducing the intermediate medium; an electrochemical conversion step in which a solution containing the intermediate medium reduced in the chemical conversion step is brought into contact with an anode of a battery structure in an electrochemical conversion unit having a battery structure, or a substrate on which the intermediate medium reduced in the chemical conversion step is precipitated is used as the anode of the battery structure, and oxygen or air is brought into contact with the cathode of the battery structure to generate electricity, or water is brought into contact with the cathode; and a reuse step in which the solution containing the intermediate medium after the electrochemical conversion step is returned to the mixture.

[0015] (Carbon source) There are no particular limitations on the carbon source. In the present invention, a low-quality carbon source can be used as the carbon source. The carbon source is preferably a low-quality fossil fuel or a carbon source other than fossil fuel such as biomass or plastic, and more preferably lignite, peat, biomass, polymer, plastic, (organic) sludge, or organic waste discharged from the manufacturing industry. Lignite is preferred as a low-grade fossil fuel. Lignite refers to coal with a calorific value of 5800 kcal / kg or more and less than 7300 kcal / kg based on pure coal. Lignite is preferably non-caking, i.e., has no caking properties. Lignite has a carbon content of about 65 to 78% by mass, is brown in appearance, and contains a large amount of moisture. Biomass is a renewable organic resource derived from living organisms, excluding fossil resources, and unlike fossil fuels, which emit large amounts of CO2 into the atmosphere, it is reproducible and carbon neutral. Biomass is broadly divided into dry biomass (wood, bark, waste paper, sawdust, etc.) and wet biomass (sludge, manure, food waste, aquatic plants, etc.). Incidentally, living wood has a moisture content of about 50% by mass. The polymer is not particularly limited, and for example, a polymer compound containing carbon atoms can be used, and examples of the polymer include organic resins, fibers, rubber, and paints. The plastic is preferably a recycled waste plastic, etc. In addition, the waste plastic is preferably one that does not generate gases other than CO2 during the reaction. Organic waste discharged from the manufacturing industry refers broadly to organic waste discharged from the manufacturing industry. The organic waste is not particularly limited, and examples include industrial waste, industrial waste, chemical waste, food waste, etc. Here, the manufacturing industry is a concept that broadly includes the chemical manufacturing industry, metal manufacturing industry, machine manufacturing industry, food manufacturing industry, clothing manufacturing industry, etc., in which things are manufactured. The carbon source used in the present invention is not limited by its water content. For example, even a carbon source having a water content of more than 60% by mass, which is generally considered difficult to use in a combustion reaction, can be used in the present invention. The carbon source is preferably a liquid or solid at room temperature (25° C.). The carbon source is preferably in the form of a solid or an aqueous solution. As a solid, for example, a powder is preferable. The following table shows the moisture content of the solid fuel, which is the carbon source, and the VO 2+Although the reaction rates are shown as examples, these reaction rates are merely shown as an index of the reaction rate of the solid fuel in the present invention, and any solid fuel can be used in the present invention. Also, the carbon source in the present invention is not limited to these.

[0016] [Table 1]

[0017] (Chemical conversion process) The method for generating electricity or producing hydrogen of the present invention includes a chemical conversion step in which a mixture of a solution containing an intermediate medium and a carbon source is reacted in a chemical conversion section at a temperature at which the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state, thereby oxidizing the carbon source and reducing the intermediate medium.

[0018] <Intermediate medium> In the chemical conversion process, a mixture of a solution containing an intermediate medium and a carbon source is used. The intermediate medium may be a material containing a metal element such as a simple metal, a metal compound, or a metal ion, a metal complex, or a mixture containing a metal element. The intermediate medium can be oxidized or reduced, and can take at least two states: an oxidized intermediate medium and a reduced intermediate medium. The oxidized intermediate medium and the reduced intermediate medium can be changed reversibly. The oxidation / reduction of an intermediate refers to a reaction involving a change in the valence of a metallic element. The intermediate medium in the oxidized state and the intermediate medium in the reduced state may be in a relatively oxidized state or a relatively reduced state, respectively. For example, the intermediate medium in the reduced state may contain a metal element whose oxidation number is greater than 0 or a metal element whose oxidation number is 0. More specifically, when the intermediate medium in the oxidized state is a Cr element whose oxidation number is 3, the intermediate medium in the reduced state may be a Cr element whose oxidation number is 2, or may be a simple Cr metal whose oxidation number is 0. The intermediate may have a metal ion as part of a complex, for example as a central metal or a ligand.

[0019] The intermediate medium in the oxidized state is preferably a metal compound, a metal ion, or a mixture containing these, and more preferably a metal compound or a metal ion. The metal compound contained in the intermediate medium in the oxidized state is, for example, a metal oxide (ion). There are no other limitations on the metal element used in the intermediate medium, as long as it can make the chemical exergy of the intermediate medium in a reduced state smaller than the chemical exergy of the carbon source at the reaction temperature of the chemical conversion section. The intermediate medium preferably contains a transition metal element, more preferably contains at least one element of V, Cr, Mn, Fe, Cu, and Zn, and particularly preferably contains at least one element of V, Cr, and Cu. Among these, the metal elements contained in the intermediate medium are converted into VO by the carbon source. 2+ →V 3+ , Cr 3+ →Cr 2+ , Cu 2+ →It is preferable that it is reduced to Cu. Here, the reduction reaction is preferably an exothermic reaction, since the reaction temperature may be maintained by the reaction heat itself and the use of external energy such as waste heat can be minimized. From the viewpoint of capturing and utilizing waste heat as energy, the reduction reaction is an endothermic reaction (for example, Cr 3+ →Cr 2+ ) is preferred. Also, Cr 3+ →Cr 2+ is preferable in that the chemical exergy is greatly improved when the temperature is returned to room temperature from the reduction temperature. On the other hand, VO 2+ →V 3+ In the case of , the change in chemical exergy due to temperature is small, and in fact the higher the temperature the higher the chemical exergy, so it is preferable in that it is possible to carry out efficient chemical and electrochemical conversions while maintaining a high temperature by utilizing waste heat, etc., with an emphasis on reaction speed. However, since the reduction reaction in the chemical conversion section is an exothermic reaction, a method of applying external heating only at the start of the reaction can be adopted. The intermediate medium in the oxidizing state is preferably a liquid or solid at room temperature, and more preferably a liquid.

[0020] <Reduction method (chemical conversion section)> In the chemical conversion process, in the chemical conversion section, a mixture of a solution containing an intermediate medium and a carbon source is reacted at a temperature at which the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state, thereby oxidizing the carbon source and reducing the intermediate medium. The present invention is characterized by the fact that it does not require the conversion of the carbon source into thermal energy, and therefore the energy loss is kept to a minimum (the exergy change is small). In addition, in the present invention, the reaction in the chemical conversion section is carried out at a reaction temperature lower than the temperature generated by the combustion reaction of the carbon source. In this specification, the combustion reaction refers to a reaction in which a carbon source combines with oxygen to emit heat and light.

[0021] Specifically, for example, in the chemical conversion step, in the chemical conversion section, the intermediate medium-containing solution and the carbon source powder (or liquid) are mixed, and the temperature of the mixture is raised to a predetermined temperature. The predetermined temperature is a temperature at which the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state. In addition, the above-mentioned predetermined temperature is preferably as low as possible from the viewpoints that a large chemical exergy difference increases the loss associated with the reaction, and that high pressure is required to prevent the solution from boiling, but it can be set appropriately taking into consideration the reaction rate. In the case of VO, reduction proceeds even at room temperature in terms of chemical equilibrium. 2+ →V 3+ When using a heating element, it is preferable to raise the temperature moderately in order to initiate the reaction and increase the reaction rate. However, when the reduction reaction is an exothermic reaction, external heating is required only at the start of the reaction, and once the reaction has started, the temperature can be maintained by the heat of reaction. Specifically, the reaction temperature in the chemical conversion step is preferably 350°C or lower. The reaction temperature may be determined in consideration of the type of carbon source and intermediate medium, etc. The reaction pressure may be selected at a value at which the aqueous solution does not evaporate. For example, a pressure of 15 MPa (150 atm) is required to prevent the aqueous solution from evaporating at 350°C.

[0022] In the chemical conversion step, the intermediate medium-containing solution is mixed with the carbon source powder (or liquid), and the reaction between the intermediate medium and the carbon source proceeds in the liquid. By proceeding with the reaction in the liquid in this manner, it becomes easy to extract the intermediate medium in a reduced state, and it becomes easy to collect the generated gas without mixing it with the surrounding air. In principle, only CO2 gas is produced by the reaction between the intermediate medium and the carbon source in the chemical conversion section. In actual operation, there is a possibility that CO and water vapor may be mixed in, but this is not a problem as CO gas easily becomes CO2, and water vapor can be easily separated as a liquid by lowering the temperature. As a result, the purity of the obtained CO2 is 99.9% or more, and it is possible to recover 99.99% or more.

[0023] In the chemical conversion step, when the intermediate medium in the reduced state is a solid, the intermediate medium in the reduced state may be precipitated on a substrate separately provided in the chemical conversion unit. In such an embodiment, the intermediate medium in the reduced state precipitated on the substrate and the substrate may be used as an electrode in the electrochemical conversion unit described later. Specifically, for example, an intermediate medium that is a metal ion may be reduced to a metal, which is then precipitated on a substrate.

[0024] In the chemical conversion process, it is not necessary to completely terminate the reduction reaction of the intermediate medium in the mixture. It is sufficient if the necessary amount of exergy from the carbon source can be captured (i.e., if the oxidation of the carbon source proceeds sufficiently). The mixture used here can be repeatedly used in the reaction with the recovered intermediate medium in the reuse process described below, so the unreacted intermediate medium is not immediately lost. Even if the reaction rate of the intermediate medium is low and the reduction reaction is not yet complete, the reaction in the subsequent electrochemical conversion section will proceed sufficiently. Figure 17(b) explains this, and will be described later. Preferred embodiments of the chemical conversion portion will be described in detail below.

[0025] (Electrochemical conversion process) The method for generating electricity or producing hydrogen of the present invention includes an electrochemical conversion step of contacting an anode of a battery structure in an electrochemical conversion unit having a battery structure with a solution containing the intermediate medium reduced in the chemical conversion step, or using a substrate that comes into contact with the intermediate medium reduced in the chemical conversion step as the anode of the battery structure, and contacting oxygen or air with the cathode of the battery structure to generate electricity, or contacting water to produce hydrogen.

[0026] <Power generation method (electrochemical conversion section)> The electrochemical conversion unit has a battery structure including one electrode (anode), the other electrode (cathode), and a current-carrying unit connecting the one electrode and the other electrode. There is no particular limitation on the one electrode and the other electrode. In the present invention, it is preferable that the electrochemical conversion unit is a redox flow type in which the one electrode and the other electrode are each equipped with a pump. Known electrodes can be used as the material for the one electrode and the other electrode. For example, in addition to Pt, carbon can be used as the electrode because of its small overvoltage, but the electrode is not limited to this. In particular, as the anode, a substrate on which an intermediate medium is precipitated by the chemical conversion process may be used. The above battery structure may also use a known separator for water electrolysis.

[0027] In the electrochemical conversion step included in the power generation method, a solution containing the intermediate medium reduced in the chemical conversion step is brought into contact with the anode of the battery structure in an electrochemical conversion section having a battery structure, or a substrate on which the intermediate medium reduced in the chemical conversion step is precipitated is used as the anode of the battery structure. An example of a method for contacting the reduced intermediate medium with the anode is to use a solution containing the reduced intermediate medium obtained by the chemical conversion step as an electrolyte and contact the anode. Examples of a method for using a substrate on which a reduced intermediate medium is precipitated in a chemical conversion process as an anode of the battery structure include a method in which, when the intermediate medium is precipitated in a solid phase in the chemical conversion process, the intermediate medium in a reduced state is precipitated on a substrate in the chemical conversion process, and the substrate on which the intermediate medium is precipitated is used as the anode of the battery structure in the electrochemical conversion section in the electrochemical conversion process. The form of the substrate is not particularly limited, and substrates of any form, such as plate-like, rod-like, mesh-like, etc., can be used. The material of the substrate is not particularly limited, and any known material for an electrode can be used. However, in the case where the intermediate medium is precipitated as a metal, the substrate can be made of the same metal as the intermediate medium. However, when the material of the substrate and the reduced intermediate medium are the same metal, the substrate and the precipitated reduced intermediate medium are inseparable, and the substrate and intermediate medium may function together as both an anode and a reduced intermediate medium.

[0028] When a method is adopted in which a solution containing the intermediate medium in a reduced state obtained by the chemical conversion step is used as an electrolyte to contact the anode, the battery structure in the electrochemical conversion section may be configured as a redox flow battery. As the electrolyte, a solution in which the intermediate medium that has been subjected to reduction treatment in the chemical conversion step has been dissolved, or a solution in which the intermediate medium has been precipitated in the chemical conversion step can be used as it is.

[0029] Here, by supplying oxygen gas or air to the other electrode (cathode), it becomes a battery. In the electrochemical conversion process (when generating electricity), the oxidation of the intermediate medium does not need to be completed completely. Even if some unreacted parts remain, this does not lead to loss because the solution (electrolyte) and the electrode members are repeatedly used between the chemical reaction parts.

[0030] <Hydrogen production method (electrochemical conversion section)> It has a structure similar to that of the above-mentioned battery (power generation method), and hydrogen is generated by supplying water to the cathode side. Depending on the type and state of the intermediate medium, it may be necessary to apply an electrolytic current from outside. Even in this case, the voltage required for water electrolysis is much lower than that of normal water electrolysis, the energy conversion efficiency is high, and the effect of contacting the intermediate medium with the anode is recognized. When applying an external current, the electrolysis voltage is small, so carbon electrodes can also be used. Even in the electrochemical conversion process (when producing hydrogen), the oxidation of the intermediate medium does not need to end completely. Even if some unreacted parts remain, the solution (electrolyte) and electrode members are repeatedly used between the chemical reaction section, so this does not lead to losses. What is important is that the carbon source is consumed in the chemical conversion section.

[0031] <Reuse process> The power generation or hydrogen production method of the present invention includes a recycling step of returning the solution containing the intermediate medium after the electrochemical conversion step back to the mixture. By including the reuse process, the intermediate medium can be used repeatedly in the chemical conversion process and the electrochemical conversion process, there is no need to allow the reduction and oxidation reactions of the intermediate medium to proceed completely, tolerance to changes in reaction conditions is increased, and the carbon source can be consumed efficiently. Furthermore, since the intermediate medium is not consumed in principle, this is also effective in terms of saving resources.

[0032] <Coordination between each process> For example, in the chemical conversion step of the present invention, a carbon source is added to a solution containing an intermediate medium (in an oxidized state), and the solution is kept pressurized and at a predetermined temperature (a temperature range in which the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state) to reduce the intermediate medium. The reduced intermediate medium or a solution containing the intermediate medium is then cooled and supplied to the anode of a battery in the electrochemical conversion step of the present invention to extract electrical energy or produce hydrogen. In the electrochemical conversion step, the intermediate raw material is oxidized, so after extraction, the carbon source is added again and the intermediate raw material is returned to the chemical conversion step (recycling step). When the cooling is performed by a heat pump, the extracted heat can be used to heat the chemical conversion section and maintain the temperature. When the reaction in the chemical conversion unit is carried out in a solution and the intermediate medium in the oxidized state in the electrochemical conversion unit is contained in the solution, the chemical conversion unit and the electrochemical conversion unit can be connected by a pipeline, so that the chemical conversion process, the electrochemical conversion process, and the recycling process can be carried out continuously and in parallel. The chemical conversion unit and the electrochemical conversion unit can be freely combined, and multiple combinations of both can be used as appropriate. In the electrochemical conversion section, multiple cells can be installed to generate electricity and produce hydrogen simultaneously. In this case, the electricity generated here can be used as supplementary energy for hydrogen production.

[0033] In the present invention, it is preferable that a recovery step for recovering CO2 gas is provided after the chemical conversion step, and a step for separating nitrogen gas from the gas obtained in the chemical conversion step is not included. In the present invention, since a combustion reaction is not performed in the chemical conversion step, the reaction proceeds even without introducing a nitrogen-containing gas such as air into the chemical conversion step. When a nitrogen-containing gas such as air is not introduced into the chemical conversion step, the gas obtained in the chemical conversion step contains almost no nitrogen gas in the first place, so that a step for separating nitrogen gas is not required.

[0034] Other preferred aspects of the energy conversion method of the present invention are the same as the preferred aspects of the energy conversion system of the present invention described below.

[0035] [Energy Conversion System] The energy conversion system of the present invention includes a chemical conversion unit that oxidizes a carbon source while reducing an intermediate medium from an oxidized state to a reduced state; an electrochemical conversion unit including one electrode, a second electrode, and a current-carrying unit connecting the one electrode and the other electrode, and oxidizing the intermediate medium from a reduced state to an oxidized state at the one electrode while reducing a reduced material at the other electrode; A reduction reaction is carried out at a temperature at which the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state at the reaction temperature of the chemical conversion unit; The electrochemical conversion unit outputs at least one of the reduced product of the reduced material and electric power to the outside. With this configuration, the system of the present invention has excellent energy conversion efficiency in power generation or in production of secondary energy with a high exergy rate. Here, chemical exergy means the maximum work that a given substance can do before it reaches a state of chemical equilibrium with the atmosphere under standard conditions.

[0036] (Reduced material, reduced form of reduced material) The reduced material obtained in the electrochemical conversion section is not particularly limited, but is preferably a high-quality energy resource. High-quality energy resources are preferably hydrogen, but other examples include hydrocarbons, alcohols, aldehydes, carboxylic acids, and CO. Similarly, the reduced material introduced into the electrochemical conversion unit is not particularly limited. When hydrogen is produced as a reduced form of the reduced material, it is preferable that the reduced material is HO from the viewpoint of obtaining hydrogen with high purity. Preferred embodiments of the present invention will now be described.

[0037] <Outline of the energy conversion system of the present invention> First, an outline of the energy conversion system of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram of an example of the energy conversion system of the present invention. The system shown in FIG. 1 includes a chemical conversion section 11 that reduces an intermediate from an oxidized state to a reduced state at a reaction temperature lower than the temperature generated in the combustion reaction of a carbon source 1 .

[0038] The chemical conversion unit 11 preferably has a reactor for reacting the oxidized intermediate medium with the carbon source. The reactor can realize the temperature and pressure required for the chemical conversion process. It is preferable that the temperature of the reaction vessel can be controlled to a predetermined temperature by waste heat or the like. In the present invention, it is preferable that the chemical conversion unit 11 reacts a solid carbon source in a solution containing an oxidized intermediate medium from the viewpoint of contact between the intermediate medium and the carbon source. In this case, it is preferable that the reactor has a push-out flow for both the liquid phase and the solid phase.

[0039] The energy conversion system shown in Fig. 1 includes a capture unit 31 that captures CO2 gas downstream of the chemical conversion unit 11, but may not include the capture unit 31. Note that, although the chemical conversion unit 11 in Fig. 1 includes a propeller (stirring member), the system may not include a propeller. The energy conversion system shown in FIG. 1 includes an electrochemical conversion unit 21 that includes one electrode 22, another electrode 23, and an electrical current conducting unit 24 that connects the one electrode 22 and the other electrode 23, and that oxidizes an intermediate medium from a reduced state to an oxidized state at the one electrode 22 while reducing a reduced material 4 at the other electrode 23. In the energy conversion system shown in FIG. 1, the electrochemical conversion unit 21 outputs at least one of the reduced form 5 of the reduced material and electricity 6 to the outside. In the energy conversion system shown in Fig. 1, the oxidized intermediate medium 2 is reduced and converted into the reduced intermediate medium 3 in the chemical conversion unit 11, and the reduced intermediate medium 3 is oxidized and converted into the oxidized intermediate medium 2 in the electrochemical conversion unit 21. In the present invention, it is preferable to repeat the above oxidation-reduction by returning the oxidized intermediate medium 2 obtained in the electrochemical conversion unit 21 to the chemical conversion unit 11.

[0040] The electrochemical conversion unit 21 oxidizes the intermediate medium from a reduced state to an oxidized state at one electrode. The electrochemical conversion unit 21 preferably includes a pipe for supplying the reduced intermediate medium to one electrode. The electrochemical conversion unit 21 preferably includes a return pipe for returning the obtained oxidized intermediate medium to the chemical conversion unit 11. The oxidized intermediate medium is reused in the chemical conversion unit 11. The electrochemical conversion unit preferably has a structure capable of outputting at least one of the reduced form of the reduced material and electric power to the outside. The structure for outputting electric power to the outside may be the electric current conducting unit or may be a separate member.

[0041] It is also preferable that the energy conversion system of the present invention includes at least one of the chemical conversion unit 11 and the electrochemical conversion unit 21 in a plurality of units. When a plurality of the chemical conversion units 11 are provided, their configurations, reaction raw materials and reaction conditions carried out therein may be the same or different from each other. When a plurality of electrochemical conversion units 21 are provided, their configurations, reaction raw materials and reaction conditions carried out therein may be the same or different from each other. Here, it is also preferable that a plurality of electrochemical conversion units 21 are provided, and auxiliary power for hydrogen generation is generated and supplied by at least one of the electrochemical conversion units.

[0042] The chemical conversion unit in the energy conversion system of the present invention can be classified into the following four aspects of chemical conversion units a to d. Chemical conversion section a: The oxidation-reduction reaction is an exothermic reaction, and the intermediate medium after reduction dissolves in the reaction solution. Chemical conversion section b: The redox reaction is exothermic and the intermediate medium after reduction is solid Chemical conversion section c: The oxidation-reduction reaction is an endothermic reaction, and the intermediate medium after reduction dissolves in the reaction solution. Chemical conversion section d: The redox reaction is endothermic and the intermediate medium after reduction is solid The electrochemical conversion unit in the energy conversion system of the present invention can be classified into the following six aspects of electrochemical conversion units a to f. Electrochemical conversion section a: The anode is contacted with a solution containing the reduced intermediate medium, and the cathode is contacted with oxygen or air (power generation) Electrochemical conversion section b: A substrate on which an intermediate medium is deposited is used as the anode, and oxygen or air is brought into contact with the cathode (power generation). Electrochemical conversion section c: The anode is in contact with a solution containing the intermediate medium after reduction, and the cathode is in contact with water. No additional power is supplied during hydrogen production (hydrogen production). Electrochemical conversion section d: A substrate on which an intermediate medium is deposited is used as the anode, and the cathode is in contact with water, and no additional power is supplied during hydrogen production (hydrogen production). Electrochemical conversion unit e: The anode is in contact with a solution containing the intermediate medium after reduction, and the cathode is in contact with water, providing additional power during hydrogen production (hydrogen production) Electrochemical conversion section f: A substrate on which an intermediate medium is deposited is used as the anode, and the cathode is in contact with water to supply additional power during hydrogen production (hydrogen production).

[0043] Examples of combinations of a chemical conversion unit and an electrochemical conversion unit in the energy conversion system of the present invention include the following systems 1 to 12. System 1: Chemical conversion unit a and electrochemical conversion unit a System 2: Chemical conversion unit a and electrochemical conversion unit c System 3: Chemical conversion unit a and electrochemical conversion unit e System 4: Chemical conversion unit b and electrochemical conversion unit b System 5: Chemical conversion unit b and electrochemical conversion unit d System 6: Chemical conversion unit b and electrochemical conversion unit f System 7: Chemical conversion unit c and electrochemical conversion unit a System 8: Chemical conversion unit c and electrochemical conversion unit c System 9: Chemical conversion unit c and electrochemical conversion unit e System 10: Chemical conversion unit d and electrochemical conversion unit b System 11: Chemical conversion unit d and electrochemical conversion unit d System 12: Chemical conversion unit d and electrochemical conversion unit f Furthermore, the energy conversion system of the present invention may be a composite system including a plurality of different systems among the above systems 1 to 12.

[0044] <First Preferred Aspect> A first preferred embodiment of the energy conversion system of the present invention is shown below. The first preferred embodiment is a specific example in which there is no additional power supply means during hydrogen production, and is a specific example of the above systems 1, 2, 4, 5, 7, 8, 10, or 11. In particular, a first preferred embodiment of the energy conversion system is preferably an embodiment for highly efficient waste heat utilization utilizing the temperature dependency of chemical exergy. The waste heat utilization includes both the case where the waste heat is utilized for an endothermic reaction in a chemical conversion section (the above systems 7, 8, 10, and 11), and the case where the waste heat is utilized for maintaining and adjusting the environmental temperature (the above systems 1, 2, 4, and 5). FIG. 2 is a schematic diagram of an example of a first preferred embodiment of the energy conversion system of the present invention. In the energy conversion system shown in FIG. 2, the chemical conversion unit 11 further includes a waste heat supply means 33 in the energy conversion system shown in FIG. 1, and waste heat 8 is supplied from the waste heat supply means 33. There are no particular limitations on the waste heat 8 as long as it is heat discarded from a power plant, a factory, a waste disposal site, or the like. An example of waste heat is heat discarded from a heat engine in a power plant, a factory, a waste disposal site, or the like. The temperature of the waste heat is preferably equal to or higher than the reaction temperature of the chemical conversion unit. Note that the chemical conversion unit only needs to have a heat supply means and does not need to be a waste heat supply means. The heat supply means in the chemical conversion unit may be, for example, a solar heat supply means that supplies solar heat. In the example of FIG. 2, HO (or H +) is used to simultaneously produce (co-produce) H2, which is a reduced product 5 of the reduced material, and electricity 6, and in this example, it is also preferable that hydrogen can be produced without generating O2. In the embodiment shown in FIG. 2, the chemical conversion unit may be any of the chemical conversion units a to d. Also, the electrochemical conversion unit may be any of the electrochemical conversion units c or d. That is, the embodiment shown in FIG. 2 corresponds to the above-mentioned systems 2, 5, 8, and 11.

[0045] In a first preferred embodiment of the energy conversion system, the chemical exergy of the intermediate medium in the electrochemical conversion unit is greater than the chemical exergy of the carbon source in the chemical conversion unit. In this case, the chemical exergy in the electrochemical conversion unit and the chemical exergy in the chemical conversion unit are compared in terms of the chemical exergy under each temperature condition. In other words, the comparison is not limited to the comparison in terms of the chemical exergy under the same temperature condition, but may be compared in terms of the chemical exergy under different temperature conditions. In addition, in the first preferred embodiment of the energy conversion system, it is preferable that the chemical exergy of the intermediate medium in the electrochemical conversion unit is greater than the chemical exergy of the intermediate medium in the chemical conversion unit. Fig. 3 is a schematic graph showing the relationship between the temperature and chemical exergy of the intermediate medium used in the first preferred embodiment of the energy conversion system. Fig. 3 shows that by making the chemical exergy of the intermediate medium (in a reduced state) smaller than that of the carbon source (reactant in Fig. 3), and making the chemical exergy of the intermediate medium (in a reduced state) in the electrochemical conversion unit larger than that of the intermediate medium (in a reduced state) in the chemical conversion unit at the reaction temperature of the chemical conversion unit, when the reduction reaction of the intermediate medium is an endothermic reaction, the reaction in the chemical conversion unit can be advanced by introducing waste heat or the like as additional energy to the chemical conversion unit. In this case, the reaction in the electrochemical conversion unit also easily advances, and it can be seen that secondary energy sources with high exergy rates, such as electricity and hydrogen, can be produced with high efficiency. In the first preferred embodiment of the energy conversion system, the reaction in the chemical conversion unit is preferably an endothermic reaction, i.e., the chemical conversion unit c or d is preferred, and the system is preferably 7, 8, 10 or 11.

[0046] In a first preferred embodiment of the energy conversion system, a heat exchange section is provided between the chemical conversion section and the electrochemical conversion section, and the reaction temperature in the electrochemical conversion section is made lower than the reaction temperature in the chemical conversion section, thereby making it possible to utilize more energy. Furthermore, in a first preferred embodiment of the system, it is preferable from the viewpoint of increasing energy conversion efficiency that the system is provided with a heat return pipe that can return the heat recovered in the heat exchange section to the waste heat supply means (or a second heat exchange section that is optionally provided upstream of the chemical reaction section).

[0047] Fig. 4 is a schematic diagram of a first preferred embodiment of the system for recovering CO2 gas. As shown in Fig. 4, in the embodiment in which waste heat is introduced into the chemical conversion section, biomass or lignite used as a carbon source is oxidized, and the intermediate medium in the oxidized state is reduced, and a recovery section for recovering CO2 gas is provided downstream of the chemical conversion section, the gas (CO2-containing gas) obtained in the chemical conversion section does not contain nitrogen, and nitrogen separation is not required, so that high-purity CO2 gas can be easily recovered. Cr as an intermediate in oxidation state (III) In the first preferred embodiment of the system for producing electricity or hydrogen using the above, CO2 gas is recovered (proposed method), and the energy conversion efficiency is much higher than that of the conventional method. Figure 5 is a schematic diagram comparing the energy conversion efficiency of the conventional method and the proposed method using the first preferred embodiment of the system of the present invention. Conventionally, the efficiency of converting the energy of biomass or lignite (assuming this energy is 100) into H2 by gasification is about 70%, and the efficiency of converting CO2 using conventional methods is about 60% when nitrogen separation is also taken into account. In addition, the efficiency of generating electricity using a thermoelectric conversion element from waste heat at about 300°C (139) is about 10% (about 14). In contrast, the proposed method converts the energy of biomass or lignite (100) into Cr by inputting waste heat (139) of about 300°C in the chemical conversion section. (II) The CO2 gas is recovered and converted to Cr by the electrochemical conversion section. (II) During the reoxidation of hydrogen, electricity (31) and H2 (128) can be produced simultaneously. The energy conversion efficiency is 100% x (128 + 31) / (100 + 139) = approximately 67%. Therefore, the energy conversion efficiency of the proposed method (128 + 31 = 159) is approximately twice that of the conventional method with CO2 gas capture (60 + 14 = 74). Therefore, the energy conversion system of the present invention (common to the first and second preferred embodiments) is also a so-called CCUS ready method that can easily be combined with a capture process for capturing CO2 gas. In this specification, preparation to be able to install additional CCUS equipment at an appropriate time in the future is referred to as "CCUS Ready". CCUS is a technology for capturing, utilizing and storing carbon dioxide. In addition, in the capture of CO2 gas, it is required based on laws and guidelines in Japan to separate nitrogen gas from CO2-containing gas to obtain high-purity CO2 gas in the case of ocean dumping of CO2 gas, and there is a problem that the energy and cost required for the process of separating this nitrogen gas is large.

[0048] FIG. 6(a) shows the values ​​of chemical exergy of the carbon source (brown coal) and the intermediate medium at representative temperatures. From FIG. 6(a), it can be seen that when a Cr compound with an oxidation number of 3 changes to a Cr compound with an oxidation number of 2, if the reaction temperature of the chemical conversion section is set to 300°C (calculated to be 255°C or higher), the chemical exergy of the intermediate medium (in a reduced state) can be made smaller than the chemical exergy of the carbon source. Similarly, for example, when a Cr compound with an oxidation number of 3 changes to a Cr compound with an oxidation number of 1 or 0, when a Ni compound with an oxidation number of 2 changes to a Ni compound with an oxidation number of 0, and when a vanadium compound with an oxidation number of 3 changes to a vanadium compound with an oxidation number of 2, the chemical exergy of the intermediate medium can be made smaller than the chemical exergy of the carbon source by setting the reaction temperature at a high temperature. For example, the reaction temperature when a Cr compound with an oxidation number of 3 changes into a Cr compound with an oxidation number of 1 or 0 is 300°C or higher, the reaction temperature when a Ni compound with an oxidation number of 2 changes into a Ni compound with an oxidation number of 0 is 310°C or higher, and the reaction temperature when a vanadium compound with an oxidation number of 3 changes into a vanadium compound with an oxidation number of 2 is 290°C or higher. Figure 6(b) is a graph showing the temperature change in chemical exergy of lignite and the intermediate medium after reduction, and the valence after reduction is shown for all materials except lignite. Furthermore, from Figure 6(b), it can be seen that if the reaction temperature of the electrochemical conversion section is set to 25°C (room temperature), the chemical exergy of the intermediate medium in the reduced state in the electrochemical conversion section can be made greater than the chemical exergy of the intermediate medium in the reduced state in the chemical conversion section (300°C).

[0049] In a first preferred embodiment of the energy conversion system, the reaction in the chemical conversion section (reduction reaction of the intermediate medium) is an endothermic reaction (e.g., Cr 3+ →Cr 2+ ) is preferable. In addition, the reaction in the chemical conversion part is an endothermic reaction, Cr 3+ →Cr 2+ In this case, it is more preferable that the reaction temperature in the chemical conversion section be 255°C or higher and 350°C or lower from the viewpoints of waste heat utilization and the pressure when the reaction in the chemical conversion section is carried out with an aqueous solution, and it is particularly preferable that the reaction temperature be 280°C or higher and 320°C or lower. In addition, the reaction temperature of the chemical conversion section may be any condition under which the chemical exergy of the intermediate medium in a reduced state is smaller than the chemical exergy of the carbon source.

[0050] In a first preferred embodiment of the energy conversion system, the intermediate medium preferably contains a Cr element. The intermediate medium in the oxidation state is Cr with an oxidation number of 3. (III) The intermediate medium in the reduced state is Cr with oxidation number 2. (II) , Cr with oxidation state 1 (I) or Cr with oxidation state 0 (0) More preferably, Cr has an oxidation number of 1. (I) or Cr with oxidation state 0 (0) In general, a higher degree of reduction is preferable in terms of increasing exergy, but an appropriate degree of reduction can be selected in consideration of the relationship with the processing conditions of both the chemical conversion unit and the electrochemical conversion unit.

[0051] <Second Preferred Aspect> A second preferred embodiment of the energy conversion system is one in which the electrochemical conversion unit includes an additional power supply means, receives additional power from the additional power supply means, and outputs the reduced form of the reduced material to the outside. In the following explanation, (B-2) is this embodiment. The second preferred embodiment is a case in which an additional power supply means is provided during hydrogen production, that is, a specific example of electrochemical conversion unit e or f, and is a specific example of the above system 3, 6, 9, or 12. In a second preferred embodiment of the energy conversion system, it is preferable that (B-1) power generation during power shortage and (B-2) hydrogen production during power excess can both be performed. That is, it is preferable that the electrochemical conversion unit outputs power to the outside when the power supply is insufficient relative to the power demand, and that the electrochemical conversion unit outputs the reduced form of the reduced material to the outside when the power supply is in excess of the power demand. Specifically, in a second preferred embodiment of the energy conversion system, the electrochemical conversion unit is equipped with a control unit, and it is more preferable that the control unit controls the electrochemical conversion unit to output power to the outside when the power supply is insufficient relative to the power demand, and to output the reduced form of the reduced material to the outside when the power supply is in excess of the power demand. Here, the electrochemical conversion unit that outputs the electricity to the outside (hereinafter also referred to as "electrochemical conversion unit A") and the electrochemical conversion unit that outputs the reduced form of the reduced material to the outside (hereinafter also referred to as "electrochemical conversion unit B") may be the same or different. When electrochemical conversion unit A and electrochemical conversion unit B are different, they may be included in the same system or in different systems. In other words, the system of the present invention also includes a complex of systems comprising two or more systems each including an electrochemical conversion portion. When electrochemical conversion unit A and electrochemical conversion unit B are formed as the same electrochemical conversion unit, there are advantages such as a smaller system and reduced manufacturing costs. Furthermore, when electrochemical conversion unit A and electrochemical conversion unit B are separate electrochemical conversion units, an electrode structure, catalyst, etc. suitable for outputting electricity to the outside can be selected for electrochemical conversion unit A, and an electrode structure, catalyst, etc. suitable for outputting reductants to the outside can be selected for electrochemical conversion unit B, thereby offering the advantage of greater freedom in design. Furthermore, the numbers of electrochemical conversion units A and electrochemical conversion units B are not particularly limited. For example, the energy conversion system of the present invention can take various forms, such as a system having one electrochemical conversion unit A and multiple electrochemical conversion units B, or a system that is a composite of a system having one electrochemical conversion unit A and multiple systems having one electrochemical conversion unit B.

[0052] (B-1) Power generation during power shortages 7 is a schematic diagram of an example of (B-1) power generation during power shortage in the second preferred embodiment of the system of the present invention. (B-1) is a specific example of the electrochemical conversion unit a or b, and is a specific example of the above-mentioned system 1, 4, 7 or 10. In the system shown in Fig. 7, in addition to the system shown in Fig. 1, electrochemical conversion unit 21 further includes a control unit 41, which controls electrochemical conversion unit 21 to output electric power 6 to the outside when the electric power supply is insufficient for the electric power demand. Note that the system shown in Fig. 7 further includes additional electric power supply means 42, but in (B-1) power generation during electric power shortage, the additional electric power supply means 42 does not need to be used. In the example shown in Figure 7, VO is used as the intermediate medium 2 in the oxidation state in the chemical conversion section. 2+ Using the reduced intermediate medium 3, V 3+ While obtaining the above, the carbon source 1 is oxidized. In the example of FIG. 7, the reaction temperature of the chemical conversion unit can be set to 250° C. or lower. In the example of FIG. 7, in the electrochemical conversion section, O2 is used as the reduced material 4 to obtain H2O, which is the reduced form 5 of the reduced material, while V 3+ The intermediate oxidation state is VO 2+ It regenerates and outputs 6 power.

[0053] Figure 8 is a schematic diagram of the proposed method for recovering CO2 gas when generating electricity during power shortages (B-1), and a bar graph comparing it with the conventional method. As shown in Figure 8, in the case of an embodiment in which biomass or lignite used as a carbon source in the chemical conversion unit is oxidized, the intermediate medium in the oxidized state is reduced, and a recovery unit for recovering CO2 gas is provided after the chemical conversion unit, the gas (CO2-containing gas) obtained in the chemical conversion unit does not contain nitrogen, and nitrogen separation is not required, so that it is easy to recover high-purity CO2 gas.

[0054] An example of a reaction in the chemical conversion section of FIG. 7 is as follows. CH 0.84 O 0.34 +1.66H2O →CO2+4.16H + +4.16e ー VO 2+ +2H + +e ー →V 3+ +H2O CH 0.84 O 0.34 +4.16VO 2+ +4.16H + →CO2+2.5H2O+4.16V 3+ An example of the reaction in the electrochemical conversion unit of FIG. 7 is as follows. V 3+ +H2O →VO 2+ +2H + +e ー 0.337V O2+4H + +4e ー →2H2O 1.23V 4V 3+ +2H2O+O2→4VO 2+ +4H + E0=0.89V Therefore, the theoretical power output of the energy conversion system shown in Figure 7 is 4.16 [mol-e ー / mol-C]×0.89[V]×[96500C / mol-C] =357.3kJ / mol-C. Since the calorific value of lignite is 451.2 kJ / mol-C, the theoretical power generation efficiency of the energy conversion system shown in Figure 7 is 0.79 (=357.3 / 451.2). In this case, the practical power generation efficiency is 0.79 x 0.7 = 0.55, using a coefficient of 0.7 to account for the efficiency of electrochemical conversion and other energy losses.

[0055] (B-1) When generating electricity during power shortages, it is possible to simultaneously solve conflicting issues such as the degradation of fossil fuels due to the depletion of carbon source resources, carbon capture and storage (CCUS), the use of biomass, etc., responding to load fluctuations (including the balance between electricity demand and supply), and improving power generation efficiency. The results of comparing the case of (B-1) (proposed method) with the conventional method (boiler) and IGCC (integrated coal gasification combined cycle power plant) are shown in Table 2 below.

[0056] [Table 2] [2] Cost and Performance Baseline for Fossil Energy Plants, Volume 1b, Rev 2b, DOE / NETL-2010 / 1397

[0057] From Table 2, in the power generation method with combustion (IGCC), the power generation efficiency drops by about 10% when CCUS is introduced, and most of the energy required for introduction is the separation and capture process. This is also the case for the conventional method (boiler). In contrast, in the proposed method (second preferred embodiment of the energy conversion system ((B-1) When generating electricity during power shortages), the gas produced in the chemical conversion unit is CCUS ready, so that the decrease in power generation efficiency when CCUS is introduced can be suppressed. Therefore, it is preferable that the second preferred embodiment of the energy conversion system is equipped with a capture unit that captures CO2 gas downstream of the chemical conversion unit, and a higher power generation efficiency can be obtained compared to conventional methods, especially when separating and capturing CO2.

[0058] The results of the above explanation are summarized in the bar graph on the right side of Figure 8. According to Table 1, the conversion efficiency of the conventional method of converting biomass or lignite energy (this energy is taken as 100) into electricity using a boiler is approximately 20% (10-30%), and when CO2 is captured using the conventional method, the conversion efficiency drops by another 10% to approximately 10%. In contrast, the proposed method can convert the energy of biomass or lignite (100) into electricity at a practical power generation efficiency of 0.55 (55%), as calculated above.

[0059] In a second preferred embodiment of the energy conversion system, the reaction in the chemical conversion unit is preferably an exothermic reaction from the viewpoint that the reaction can be continued by maintaining the temperature with its own reaction heat when there is no heat that can be supplied from the outside. However, the reaction may be an endothermic reaction. In addition, in a second preferred embodiment of the energy conversion system, the reaction temperature in the chemical conversion section is preferably 25°C (room temperature) to 350°C from the viewpoint of pressure when the reaction in the chemical conversion section is carried out with an aqueous solution, is preferably 100°C or higher and 350°C or lower from the viewpoint of reaction rate, and is particularly preferably 220°C or higher and 250°C or lower from the viewpoint of using lignite as a carbon source. In a second preferred embodiment of the energy conversion system, the intermediate medium preferably contains Cu element or V element, and more preferably contains V element from the viewpoint of increasing the energy conversion efficiency at high temperatures in electrochemical conversion. (II) or V with oxidation number 4 (IV) The intermediate medium in the reduced state is Cu with an oxidation number of 0. (0) , V with oxidation number 3 (III) or V with oxidation number 2 (II) It is more preferable that: In a second preferred embodiment of the energy conversion system, the chemical exergy of the reduced intermediate medium in the electrochemical conversion section may be greater than, or may be the same as, or smaller than, the chemical exergy of the carbon source in the chemical conversion section.

[0060] (B-2) Hydrogen production during power surplus FIG. 9 is a schematic diagram of an example of (B-2) hydrogen production during excess power in the second preferred embodiment of the energy conversion system of the present invention. The energy conversion system shown in FIG. 9 is the energy conversion system shown in FIG. 7, in which the control unit 41 controls the electrochemical conversion unit 21 to discharge the reduced body 5 of the reduced material to the outside when the power supply is excessive relative to the power demand. The energy conversion system shown in FIG. 9 further includes an additional power supply means 42, which supplies additional power 7 to the electrochemical conversion unit. The additional power supply is preferably surplus power when the additional power supply is excessive relative to the power demand, and is particularly preferably surplus power derived from renewable energy. In particular, among renewable energies, solar power can be generated in excess of the power demand during the day, and surplus power derived from solar power is preferably used as the additional power of the present invention. Alternatively, power obtained by power generation according to the present invention may be supplied. In the example of FIG. 9, HO (or H + ) is used to produce H2, which is the reduced form 5 of the reduced material.

[0061] FIG. 10 is a schematic diagram of a proposed method for recovering CO2 gas when producing hydrogen during excess power (B-2) in the second preferred embodiment of the energy conversion system, and a bar graph comparing it with the conventional method. Conventionally, the conversion efficiency of biomass or lignite energy (assuming this energy is 100) to H2 by gasification is about 70%, and the conversion efficiency of conventional CO2 capture is about 60% when nitrogen separation is also taken into account. In addition, the efficiency of producing hydrogen from surplus electricity (43) by water electrolysis is about 70% (about 30). In contrast, in the proposed method, the energy of biomass or lignite (100) is converted into V (III) or Cu (0) The CO2 gas is then recovered, and the surplus electricity is introduced into the electrochemical conversion section to produce H2 by reducing water. The energy conversion efficiency of the proposed method is approximately 90% based on Evaluation Example 8 of Example 2 described below. Therefore, the energy conversion efficiency of the proposed method (90 + 39 = 129) is approximately 1.4 times higher than that of the conventional method with CO2 gas capture (60 + 30 = 90). EXAMPLES

[0062] The present invention will be described in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

[0063] [Example 1] The energy conversion system of Example 1, which is capable of performing highly efficient waste heat conversion utilizing the temperature dependency of chemical exergy, was examined. A demonstration experiment of the energy conversion system shown in Figure 2 was carried out in the following procedure, and it was demonstrated that electricity and H2 can be produced simultaneously by supplying waste heat.

[0064] The chemical conversion section was designed to be able to supply waste heat and perform an endothermic reaction at 250-300°C. Lignite was used as the carbon source. In the chemical conversion section, an aqueous solution of Cr(OH)3, a Cr compound with an oxidation number of 3, was used as an intermediate medium in the oxidized state. In the chemical conversion section, lignite was oxidized to CO2, and the intermediate medium in the oxidized state was reduced to CrO with an oxidation number of 2, which is a reduced intermediate medium. Nearly 100% (more than 99% by volume) of the CO2 generated in the chemical conversion section was captured in the capture section (including a separator and capture vessel) connected between the chemical conversion section and the electrochemical conversion section. The reduced intermediate generated in the chemical conversion section was transferred to the electrochemical conversion section.

[0065] The electrochemical conversion unit was of the redox flow type, with a structure including one electrode, the other electrode, and a current-carrying section connecting them. A reduced intermediate medium was supplied to one electrode, and the reduced intermediate medium CrO was oxidized to oxidized Cr(OH)3, and the resulting Cr(OH)3 was returned to the chemical conversion unit through a return pipe for reuse. However, the resulting Cr(OH)3 may be taken out once and then reused in the chemical conversion unit as appropriate. On the other hand, water was used as the reduced material in the electrode, and H2 was produced by reducing the water and taken out. Electricity was taken out from the electrified part. The reaction temperature in the electrochemical conversion section was set to room temperature (25° C.).

[0066] <Demonstration of reaction progress> (Lignite and Cr 3+ Reaction with: Gas Analysis) In the chemical conversion section, lignite is oxidized to produce Cr compounds with oxidation number 3 (Cr (III) The following reaction, in which Cr(III) is reduced to a Cr compound with an oxidation state of 2, was demonstrated by gas analysis. CH 0.84 O 0.34 +4.16Cr 3+ +1.66H2O→CO2+4.16Cr 2+ +4.16H + Figure 11(A) is a bar graph showing the yield of generated gas when the reaction temperature of the chemical conversion section is 300°C. From the left side of the page, Figure 11(A) shows the results of the yield of generated gas for a control without Cr compounds, for Cr2(SO4)3, and for Cr(OH)3. Figure 11(B) is a bar graph showing the yield of generated gas when the reaction temperature of the chemical conversion unit is set to 250°C. Figure 11(B) shows, from the left side of the page, the results of the yield of generated gas in the case of Cr2(SO4)3 and the case of Cr(OH)3. From Figures 11(A) and 11(B), when the reaction temperature of the chemical conversion section is set to 300°C, the ratio of lignite and Cr 3+ It was found that the yield of CO2 was significantly increased by the reaction with Cr(OH)3. In addition, the generation of H2 was confirmed in the case of Cr(OH)3. From these results, it was found that the Cr compound with oxidation number 3 (Cr (III) It was found that lignite is oxidized by

[0067] (Lignite and Cr 3+ Reaction with: Analysis of solid products The reaction temperature of the chemical conversion section is set at 300°C, and lignite is oxidized in the chemical conversion section while Cr compounds with oxidation number 3 (Cr (III)The following reaction, in which Cr(II) is reduced to a Cr compound with oxidation state 2, was demonstrated by analysis of the solid product. CH 0.84 O 0.34 +4.16Cr 3+ +1.66H2O→CO2+4.16Cr 2+ +4.16H + Figure 12(A) shows the XRD pattern of the solid product when Cr2(SO4)3 is reduced. (I) and CrC (0) was found to be produced. Figure 12(B) shows the XRD pattern of the solid product when Cr(OH)3 is reduced. (II) was found to be produced. From Figures 12(A) and 12(B), when the reaction temperature of the chemical conversion section is set to 300°C, the ratio of lignite and Cr 3+ It was found that the yield of CO2 was significantly increased by the reaction with Cr(OH)3. In addition, the generation of H2 was confirmed in the case of Cr(OH)3. From these results, it was found that when the reaction temperature of the chemical conversion section is 300°C, the Cr (III) was found to have been restored.

[0068] <Evaluation Example 1> In evaluation example 1, Cr was used in the energy conversion system of Example 1. (III) An example of a process using the above-mentioned method was compared with a combustion process and evaluated. In evaluation example 1, a process in which the chemical conversion unit was provided with a waste heat supply means and waste heat was supplied from the waste heat supply means was carried out in the energy conversion system of Example 1. Fig. 13(A) is a schematic diagram of the material balance in Evaluation Example 1 of the energy conversion system of Example 1. Fig. 13(B) is a schematic diagram of the exergy balance in Evaluation Example 1 of the energy conversion system of Example 1. As shown in Fig. 13(B), the energy conversion system of Example 1 used in Evaluation Example 1 includes a heat return pipe 34. On the other hand, FIG. 13(C) is a schematic diagram of an example of exergy balance in a combustion process. The results of Evaluation Example 1 show that, compared to a combustion process, the energy conversion system of Example 1 is capable of utilizing waste heat and has small exergy loss.

[0069] <Evaluation example 2> In Evaluation Example 2, in the energy conversion system of Example 1, Cr (III) An example of a process using the above-mentioned method was compared with a gasification process and evaluated. In evaluation example 2, the chemical conversion unit was equipped with a waste heat supply means, and a process in which waste heat was supplied from the waste heat supply means was carried out in the energy conversion system of Example 1. 14(A) is a schematic diagram of the material balance in Evaluation Example 1 of the energy conversion system of Example 1. FIG. 14(B) is a schematic diagram of the exergy balance in Evaluation Example 1 of the energy conversion system of Example 1. On the other hand, FIG. 14(C) is a schematic diagram of an example of the exergy balance in a gasification process. From the results of Evaluation Example 2, it was found that the energy conversion system of Example 1 can utilize waste heat and has a higher yield than the gasification process. Furthermore, it was found that the energy conversion system of Example 1 is advantageous over the gasification process in that it does not require separation of nitrogen from CO2 in the generated gas.

[0070] [Example 2] The energy conversion system of Example 2, which is capable of highly efficient hydrogen production, was examined. The energy conversion system of Example 2 includes a control unit capable of switching between (B-1) power generation during power shortage as shown in Fig. 7 and (B-2) hydrogen production during power surplus as shown in Fig. 9, and was otherwise manufactured in the same manner as the energy conversion system of Example 1. A demonstration experiment of the energy conversion system of Example 2 was carried out according to the following procedure.

[0071] <(B-1) Demonstration of power generation during power shortages> (Evaluation example 3) In Evaluation Example 3, an experimental device shown in Fig. 15 was used. Fig. 15 is a schematic diagram of the experimental device used in Evaluation Example 3 as a chemical conversion unit in the energy conversion system of Example 2. The reaction conditions were as follows: Reaction temperature: 200℃ or 250℃. Reaction time: 10 to 180 minutes. Pressure: 4MPa. Reaction volume: 0.7mL or 7mL. Intermediate medium: VOSO4 aqueous solution. Additive: H2SO4 aqueous solution. Carbon source: lignite (Loy Yang coal) or eucalyptus. The gas analysis methods were as follows. Gas chromatography (Shimadzu, GC-12A) Column: Porapak-Q, Molecular Sieve 5A Detector: TCD, FID The liquid was analyzed as follows. UV-vis-NIR(Shimadzu, UV-3100PC) The analytical method for the solid residue was as follows. CHN(Yanako, MT-6)

[0072] FIG. 16 shows the specific reaction conditions of Evaluation Example 3 (reaction time 250° C., reaction time 25 min, initial VO 2+ Concentration C VO 2+ ,0 = 0.50 mol / L, initial carbon concentration C c,0 = 1.0 mol / L, initial H2SO4 concentration C H2SO4,0 Figure 16 shows the photos of the sample in the chemical conversion section before and after the reaction in the case of VO2+ (oxidation number 4, VO2+ = 3.0 mol / L) and the graph of the relationship between wavelength and absorbance. 2+ The ion is the intermediate of the reduction state, V with oxidation number 3. 3+In other words, the results in Figure 16 suggest that under these specific reaction conditions, the oxidation reaction of the lignite, which is the carbon source, proceeds.

[0073] FIG. 17(A) shows the reaction time and VO 2+ Conversion rate of ions, X VO 2+ From Fig. 17(A), when biomass (eucalyptus) is used as the carbon source, the above VO 2+ Ion to V 3+ It was found that the reduction reaction to VO ions proceeds at least at 125 to 200 °C. In addition, when lignite is used as the carbon source, the above-mentioned VO 2+ Ion to V 3+ It was found that the reduction reaction to ions proceeds at least at temperatures between 125 and 200°C. Also, FIG. 17(B) shows the VO 2+ Conversion rate of ions, X VO 2+ 17(B) is a graph showing the relationship between the electrochemical conversion E (unit: V) and the VO 2+ Conversion rate of ions, X VO 2+ It was found that even when the value of V is as low as 0.2, a sufficient electromotive force of 0.86 V can be obtained in the downstream electrochemical conversion unit. In other words, it is possible to obtain a sufficient voltage in the electrochemical conversion unit even when the reduction of the intermediate medium is insufficient.

[0074] (Evaluation Example 4: Cu and biomass) In Evaluation Example 4, VO was used as the intermediate medium in Evaluation Example 3. 2+ Cu instead of ions 2+ The reaction temperature was 300°C, the reaction time was 120 minutes, and the initial Cu 2+ Concentration C Cu 2+ ,0 = 1.0 mol / L, the initial carbon concentration C c,0= 1.0 mol / L, 0.47 mol / L, or 0.30 mol / L. In Evaluation Example 4, the solid product after the reaction was evaluated by XRD and photography, and the generated gas after the reaction was evaluated by gas analysis. In the chemical conversion section, while oxidizing biomass (cellulose), Cu with oxidation number 2 2+ The reaction in which the ion is reduced to elemental Cu with an oxidation state of 0 is as follows: (C6H 10 O5) n +7H2O →6nCO2+24nH + +24ne - Cu 2+ +2e - →Cu (C6H 10 O5) n +7H2O+12nCu 2+ →6nCO2+24nH + +12nCu

[0075] FIG. 18(A) shows the XRD pattern of the solid product in Evaluation Example 4. FIG. 18(B) shows the XRD pattern of the solid product in Evaluation Example 4 under specific conditions (initial Cu 2+ Concentration C Cu 2+ ,0 = 1.0 mol / L, initial carbon concentration C c,0 = 1.0 mol / L). As shown in Figures 18(A) and 18(B), in the chemical conversion section, the carbon source biomass converts Cu with oxidation number 2, which is an intermediate in the oxidation state. 2+ It was found that the reaction proceeds by reducing the ions to elemental Cu with an oxidation number of 0, which is an intermediate medium for the reduction state. FIG. 19 is a bar graph showing the yield of the generated gas in Evaluation Example 4. From FIG. 19, when the reaction temperature of the chemical conversion unit is set to 300° C., Cu 2+ It was found that while the biomass was reduced to Cu, the Cu in the above reaction was oxidized to CO2. 2+ and the stoichiometric ratio of CO2 = 2.

[0076] The reaction temperatures corresponding to the solid fuel (carbon source) type and medium (intermediate medium) type in the chemical conversion section in the above evaluation examples are shown in Table 3. From Table 3 below, it can be seen that it is possible to utilize waste heat at low temperatures, such as 350°C or less, with various combinations of carbon sources and intermediate media.

[0077] [Table 3]

[0078] (Evaluation example 5) In Evaluation Example 5, the reaction temperature was changed to 250°C and the initial VO 2+ Concentration C VO 2+ ,0 = 1.0 mol / L or 1.8 mol / L, initial carbon concentration C c,0 = 1.8 mol / L, initial H2SO4 concentration C H2SO4,0 = 3.0 mol / L, the reaction rate was evaluated. FIG. 20 is a schematic diagram of the model used in the reaction rate analysis of Evaluation Example 5. The reaction rate r VO 2+ The calculated values ​​were calculated based on the following formula using the model shown in FIG.

number

[0079] k r =0.335 L 3 / (mol 2 mol-C min) k V3+ =60.9 L / mol K=0.00129 L 2 / mol 2 ε0=0.15

[0080] FIG. 21 shows the relationship between reaction time and VO 2+ Conversion rate of ions, X VO 2+The experimental values ​​from the demonstration experiment are plotted on a graph that shows the relationship between the oxidation state and the oxidation number of VO2 with oxidation number 4, which is an intermediate medium in the chemical conversion section. Figure 21 shows that the experimental values ​​and the calculated values ​​are in good agreement. 2+ The ion is the intermediate of the reduction state, V with oxidation number 3. 3+ It was suggested that the oxidation reaction of lignite, which is the carbon source, proceeds due to the reduction of ions to cesium ions.

[0081] (Evaluation Example 6) In the energy conversion system of Example 2, lignite and VO 2+ The reactor size for the process using ions was calculated. FIG. 22 is a schematic diagram of the reactor design in the chemical conversion section used in Evaluation Example 6. The reactor used was an isothermal moving bed reactor. In addition, both the liquid phase and the solid phase were extrusion flows. The reactor used has a structure that can react a solid carbon source in a solution containing an intermediate medium in an oxidized state. Z was designed based on the following formula.

number

[0082] <(B-2) Demonstration of hydrogen production during power surplus> (Evaluation Example 7) In Evaluation Example 7, hydrogen production during power surplus was demonstrated by electrolytic reaction (indirect method) using lignite and Cu. FIG. 24 is a schematic diagram of the energy conversion system used in Evaluation Example 7. In Evaluation Example 7, the electrochemical conversion unit is provided with additional power supply means, additional power is supplied from the additional power supply means, and the electrochemical conversion unit performs a process of discharging the reduced form (H2) of the reduced material (water) to the outside in the system of Example 2. The reaction formula of the electrochemical conversion unit in Evaluation Example 7 is as follows: Anode: Cu →Cu 2+ +2e - E0=0.337V Cathode: 2H + +2e - →H2E0=0V Cu+2H + →Cu 2+ +H2 ΔH r,0 =64.9KJ / mol ΔG r,0 =65.5KJ / mol FIG. 25 is a graph showing the relationship between the efficiency of the electrolytic reaction and the energy conversion efficiency in the energy conversion system used in Evaluation Example 7. Energy Conversion Efficiency =H2 combustion heat [KJ] / (combustion heat of reacted lignite + actual amount of electricity added in electrolysis reaction) [KJ] Efficiency of electrolysis reaction = Thermodynamically minimum energy required [KJ] / Actual amount of power added in electrolytic reaction [KJ] From FIG. 25, it can be seen that when the electrochemical reaction is operated at a typical efficiency of 70%, the overall energy conversion efficiency is 90%.

[0083] (Evaluation Example 8) In evaluation example 8, an example of a hydrogen production process by electrolytic reaction using lignite and Cu in the energy conversion system of Example 2 was evaluated in comparison with a conventional hydrogen production process by water electrolysis reaction using Pt electrodes. The voltage required to achieve the same current density (same hydrogen production rate) in each process was measured and shown in Figure 26. Figure 26 is a graph showing the relationship between current density and voltage when hydrogen is produced by the energy conversion system of Example 2 and the conventional method. Furthermore, the efficiency of the electrolysis reaction and the energy conversion efficiency at the same current density (same hydrogen generation rate) were calculated for each process, and are shown in Figures 27(A) and 27(B). Figure 27(A) is a graph showing the relationship between the current density and the efficiency of the electrolysis reaction when hydrogen is produced by the energy conversion system of Example 2 and the conventional method. Figure 27(B) is a graph showing the relationship between the current density and the energy conversion efficiency when hydrogen is produced by the energy conversion system of Example 2 and the conventional method. 26 and 27(B), it was found that the energy conversion system of Example 2 had an energy conversion efficiency of about 90%, which is higher than that of the conventional hydrogen production process. It was also found that the energy conversion system of Example 2 required a lower voltage than that of the conventional hydrogen production process. As shown in FIG. 27(A), the efficiency of the electrolysis reaction in the energy conversion system of Example 2 was comparable to that of the conventional hydrogen production process.

[0084] (Evaluation Example 9) In Evaluation Example 9, the VO 2+ Ion concentration and V 3+ After preparing electrolyte solutions with adjusted ion concentrations, each electrolyte solution was brought into contact with the anode, and air was supplied to the cathode to confirm the electromotive force and overall power generation efficiency. The cell configuration in the electrochemical conversion section was as shown in Table 4 below. Figure 28 shows the intermediate oxidation state, VO 2+ Ion concentration (C VO2+ ), V with oxidation number 3, which is an intermediate medium for reduced metal-containing materials 3+ Ion concentration (C V3+ ) for the total amount of C V3+ The ratio of (C V3+ / (C VO2+ +C V3+ )) vs. battery voltage (E Cell 1 is a graph showing the relationship between the total power generation efficiency [V] and the total power generation efficiency. From Figure 28, C V3+ / (C VO2+ +C V3+ ) is small, that is, even when the reduction rate is small, sufficient battery voltage and power generation efficiency can be obtained.

[0085] (Evaluation Example 10) In Evaluation Example 10, similar to Evaluation Example 9, VO 2+ Ion concentration and V 3+ After preparing electrolyte solutions with adjusted ion concentrations, each electrolyte solution was brought into contact with the anode, and electricity was generated by supplying air to the cathode, and the changes in current and voltage during power generation were measured. The cell configuration in the electrochemical conversion section was as shown in Table 4 below. FIG. 29 is a graph (IV curve) showing the relationship between current (I) and voltage (V) during power generation in Evaluation Example 10. From Figure 29, VO 2+ Ions are completely V 3+ It can be seen that even if the carbon is not reduced to ions, there is no problem with the power generation characteristics.

[0086] (Evaluation Example 11) In Evaluation Example 11, an example of a hydrogen production process by electrolysis using lignite and V as an intermediate medium in the system of Example 2 was compared with a conventional hydrogen production process by water electrolysis using a Pt electrode, and an evaluation was performed. The cell configuration, medium, and counter electrode (cathode) supply were as shown in Table 4 below. The voltage required to achieve the same current density (same hydrogen generation rate) in each process was measured and is shown in Figure 30. Figure 30 is a graph showing the relationship between current density and voltage when hydrogen was produced by the system of Example 2 and the conventional method in Evaluation Example 11. FIG. 30 shows that the system of Example 2, even when V is used as the intermediate medium, has a large current density even at a low voltage, and is suitable for highly efficient hydrogen production, compared to conventional hydrogen production processes.

[0087] Table 4 shows the generated energy form, cell configuration, medium, cathode supply, applied voltage, and temperature during power generation or hydrogen production in FIGS.

[0088] [Table 4] [Explanation of symbols]

[0089] 1. Carbon source 2. Oxidation state intermediate 3. Reduced state intermediate medium 4 Reducible material 5. Reduced form 6 Electricity 7 Surplus electricity 11 Chemical Transformation Division 21 Electrochemical conversion section 22 One electrode 23 Other electrode 24 Electrical section 31 Collection Department 32 Heat exchange section 33 Waste heat supply means 34 Heat return piping 41 Control section 42 Additional power supply means

Claims

1. 1. A method for generating electricity from a carbon source, comprising: a chemical conversion step in which a mixture of a solution containing an intermediate medium and a carbon source is reacted at a temperature at which the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state in a chemical conversion unit, thereby oxidizing the carbon source and reducing the intermediate medium; a cooling step of cooling the solution containing the reduced intermediate medium that has been subjected to the chemical conversion step; an electrochemical conversion step in which an anode of a battery structure in an electrochemical conversion unit having the battery structure is brought into contact with a solution containing the intermediate medium that has been reduced in the chemical conversion step and has been subjected to the cooling step, and a cathode of the battery structure is brought into contact with oxygen or air to generate electricity; and a recycling step of adding a new carbon source to the solution containing the intermediate medium after the electrochemical conversion step and returning it to the mixture. Power generation method.

2. 1. A method for generating electricity from a carbon source, comprising: a chemical conversion step in which a mixture of a solution containing an intermediate medium and a carbon source is reacted at a temperature at which the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state in the chemical conversion unit, thereby oxidizing the carbon source while reducing the intermediate medium and precipitating the intermediate medium on a substrate; a cooling step of cooling the solution containing the intermediate medium that has been subjected to the chemical conversion step; an electrochemical conversion step in which, in an electrochemical conversion unit having a battery structure, a solution containing the cooled intermediate medium is used as an electrolyte, the base material on which the intermediate medium reduced in the chemical conversion step is precipitated is used as an anode of the battery structure, and oxygen or air is brought into contact with the cathode of the battery structure to generate electricity; and a recycling step of adding a new carbon source to the solution containing the intermediate medium after the electrochemical conversion step and returning it to the mixture. Power generation method.

3. 1. A method for producing hydrogen from a carbon source, comprising the steps of: a chemical conversion step in which a mixture of a solution containing an intermediate medium and a carbon source is reacted at a temperature at which the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state in a chemical conversion unit, thereby oxidizing the carbon source and reducing the intermediate medium; a cooling step of cooling the solution containing the reduced intermediate medium that has been subjected to the chemical conversion step; an electrochemical conversion step of producing hydrogen by contacting an anode of a battery structure in an electrochemical conversion unit having the battery structure with a solution containing the intermediate medium reduced in the chemical conversion step and subjected to the cooling step, and contacting a cathode of the battery structure with water; and a recycling step of adding a new carbon source to the solution containing the intermediate medium after the electrochemical conversion step and returning it to the mixture. A method for producing hydrogen.

4. 1. A method for producing hydrogen from a carbon source, comprising the steps of: a chemical conversion step in which a mixture of a solution containing an intermediate medium and a carbon source is reacted at a temperature at which the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state in the chemical conversion unit, thereby oxidizing the carbon source while reducing the intermediate medium and precipitating the intermediate medium on a substrate; a cooling step of cooling the solution containing the intermediate medium that has been subjected to the chemical conversion step; an electrochemical conversion step in which, in an electrochemical conversion unit having a battery structure, a solution containing the cooled intermediate medium is used as an electrolyte, the base material on which the intermediate medium reduced in the chemical conversion step is precipitated is used as an anode of the battery structure, and water is brought into contact with the cathode of the battery structure to produce hydrogen; and a recycling step of adding a new carbon source to the solution containing the intermediate medium after the electrochemical conversion step and returning it to the mixture. A method for producing hydrogen.

5. The method according to any one of claims 1 to 4, wherein the reaction temperature in the chemical conversion step is 350°C or lower.

6. The method according to any one of claims 1 to 4, wherein the intermediate medium contains at least one element selected from the group consisting of V, Cr, Mn, Fe, Cu, and Zn.

7. CO generated by the oxidation-reduction reaction in the chemical conversion section ２ The method according to any one of claims 1 to 4, wherein

8. a chemical conversion unit that oxidizes the carbon source while reducing the intermediate from an oxidized state to a reduced state; A temperature control mechanism for heating and cooling the solution containing the intermediate medium; an electrochemical conversion unit including one electrode, a second electrode, and a current-carrying unit connecting the one electrode and the other electrode, and oxidizing the intermediate medium from a reduced state to an oxidized state at the one electrode while reducing a reduced material at the other electrode; In the chemical conversion unit, a reduction reaction is carried out at a temperature at which the chemical exergy of the carbon source exceeds the chemical exergy of the intermediate medium in a reduced state; Cooling the reduced intermediate medium and / or solution and supplying it to the electrochemical conversion section; The electrochemical conversion unit outputs at least one of the reduced form of the reduced material and electric power to the outside, The solution containing the intermediate medium oxidized in the electrochemical conversion section is returned to the chemical conversion section. Energy conversion system.

9. The energy conversion system according to claim 8 , comprising a plurality of at least one of the chemical conversion unit and the electrochemical conversion unit.

10. 9. The energy conversion system according to claim 8, comprising a plurality of the electrochemical conversion units, some of the electrochemical conversion units outputting hydrogen as the reduced material to the outside, and other parts of the electrochemical conversion units outputting electric power to the outside, and the electric power is used as auxiliary electric power for outputting the hydrogen to the outside.

11. CO generated by the oxidation-reduction reaction in the chemical conversion section ２ The energy conversion system according to claim 8 ,

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