Fuel manufacturing system and fuel manufacturing method

Abstract

The present invention provides a fuel production system and fuel production method that suppresses the loss of thermal energy in the methane reaction and suppresses the deterioration of the reactor and reaction catalyst by adding steam to the methane reaction system. [Solution] The electrolytic device comprises a solid oxide type electrolytic apparatus 11 that electrolyzes a raw material gas containing at least water vapor, a reactor 30 that synthesizes hydrocarbons using carbon oxide and hydrogen from the electrolytic apparatus 11 as raw materials, a heat exchanger 40 that exchanges heat between the generated gas containing hydrocarbons and water vapor from the reactor 30 and liquid water, a condensation separator 60 that separates condensed water from the generated gas cooled in the heat exchanger 40, and a reactor water vapor supply mechanism 500 that supplies water vapor to the reactor 30. The pressure of the liquid water is set to a lower pressure than the pressure of the generated gas, at least a portion of the water vapor in the generated gas condenses in the heat exchanger 40 to produce condensed water, and at least a portion of the liquid water becomes water vapor, and the electrolytic water vapor supply mechanism 600 supplies at least a portion of the water vapor produced in the heat exchanger 40 to the electrolytic apparatus 11.

Description

[Technical Field]

[0001] The present invention relates to a fuel production system and a fuel production method for synthesizing hydrocarbons using carbon oxide and hydrogen from an electrolytic device as raw materials. [Background technology]

[0002] In recent years, in order to realize a carbon-neutral society, research has been conducted on methods for producing fuels using renewable energy obtained from power generation methods such as solar, wind, and hydroelectric power. However, in the development of such fuel production methods, the low conversion efficiency when converting renewable energy such as electricity into fuel is a challenge, and improving this efficiency is necessary.

[0003] Among these, the SOEC electrolytic fuel generation system is a system that uses electricity to produce fuels such as methane gas, and is being actively researched as a system that can achieve high energy conversion efficiencies of 85% to 90%. The key to achieving this high energy conversion efficiency is to effectively utilize the heat obtained from hydrocarbon synthesis reactions using hydrogen gas obtained by SOEC electrolysis.

[0004] SOEC stands for Solid Oxide Electrolysis Cell. By electrolyzing a mixed gas consisting of carbon dioxide and water vapor using an SOEC, a gas (synthesis gas) mainly composed of hydrogen and carbon monoxide can be obtained. By reacting this synthesis gas on a catalyst, hydrocarbons can be synthesized. In particular, when a methanation catalyst is used, methane, which is the main component of city gas, can be produced. Furthermore, by generating water vapor with the heat produced in the hydrocarbon synthesis reaction and using this water vapor as an electrolytic raw material in the SOEC, high energy conversion efficiency can be achieved. Therefore, the SOEC electrolytic fuel production system is expected to be a means of significantly reducing the cost of synthetic methane production.

[0005] The reaction equation for the reaction that produces hydrogen and carbon monoxide from a mixed gas consisting of carbon dioxide and water vapor during SOEC electrolysis is as follows: CO2+3H2O → CO+3H2+2O2 (Formula 1)

[0006] The reaction equation for the methanation reaction, in which carbon monoxide obtained by SOEC co-electrolysis reacts with hydrogen to produce methane, is as follows: CO+3H2→ CH4+H2O (Formula 2)

[0007] Patent Document 1 describes a technique for increasing the methane concentration in the product gas and removing carbon monoxide gas from the product gas by adding water vapor to the reaction system during a hydrocarbon synthesis reaction using carbon monoxide and hydrogen as raw materials.

[0008] Patent Document 2 discloses an invention concerning an SOEC electrolytic apparatus that generates the water vapor required for SOEC co-electrolysis by utilizing the heat contained in the exhaust gas generated internally.

[0009] Patent Document 3 discloses an invention relating to a hydrocarbon synthesis system that generates raw material steam by heating raw material water using the heat of a product gas containing steam discharged from a hydrocarbon generation apparatus. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2015-124217 [Patent Document 2] Japanese Patent Publication No. 2018-517233 [Patent Document 3] Japanese Patent Publication No. 2024-054766 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] In the invention described in Patent Document 1, the thermal energy of the steam added to the reaction system cannot be effectively utilized, which causes a decrease in energy conversion efficiency.

[0012] Also, in the invention described in Patent Document 2, although steam used for SOEC co-electrolysis is generated by using the heat generated in the hydrocarbon synthesis reaction of the SOEC co-electrolysis fuel generation system, steam is generated using a liquid lower than atmospheric pressure. In this method, the energy related to decompression causes a decrease in energy conversion efficiency.

[0013] Also, in the invention described in Patent Document 3, depending on the reaction conditions of the hydrocarbon synthesis reaction, there is a risk of causing deterioration of the reactor and the reaction catalyst.

[0014] The present invention has been made in view of the above problems, and its object is to provide a fuel production system and a fuel production method that suppress loss of thermal energy in a hydrocarbon synthesis reaction and suppress deterioration of a reactor and a catalyst by adding steam to a hydrocarbon synthesis reactor.

Means for Solving the Problems

[0015] The characteristic configuration of the fuel production system according to the present invention includes a solid oxide electrolyzer that electrolyzes a raw material gas containing at least steam, a reactor that synthesizes hydrocarbons using carbon monoxide and hydrogen from the solid oxide electrolyzer as raw materials, a heat exchanger that heat-exchanges the product gas containing the hydrocarbons and steam from the reactor with liquid water, a condensation separator that separates condensed water from the product gas cooled by the heat exchanger, and a reactor steam supply mechanism that supplies steam to the reactor. The pressure of the liquid water is set to a pressure lower than the pressure of the product gas. In the heat exchanger, at least a part of the steam contained in the product gas condenses to generate condensed water, and at least a part of the liquid water vaporizes to generate steam. It has an electrolysis steam supply mechanism that supplies at least a part of the steam generated in the heat exchanger to the solid oxide electrolyzer.

[0016] The characteristic configuration of the fuel production method according to the present invention includes an electrolysis step in a solid oxide electrolyzer for electrolyzing a raw material gas containing at least water vapor, a reaction step for synthesizing hydrocarbons using carbon dioxide and hydrogen generated in the electrolysis step as raw materials, a heat exchange step for heat-exchanging the product gas containing the hydrocarbons and water vapor generated in the reaction step with liquid water, a condensation separation step for separating condensed water from the product gas cooled in the heat exchange step, and a reactor water vapor supply step for supplying water vapor into the reaction system in the reaction step. The pressure of the liquid water is set to a pressure lower than the pressure of the product gas. In the heat exchange step, at least a part of the water vapor contained in the product gas condenses to generate condensed water, and at least a part of the liquid water vaporizes to generate water vapor. Electrolysis water vapor supply is performed to supply at least a part of the water vapor generated in the heat exchange step to the electrolysis step.

[0017] According to this characteristic configuration, in the heat exchanger, the heat possessed by the product gas generated in the hydrocarbon synthesis reaction can be transferred to liquid water and used for vaporization, and at least a part of the water vapor thus generated can be supplied to the solid oxide electrolyzer. Therefore, using the heat supplied from the high-temperature product gas after the hydrocarbon synthesis reaction, heating the liquid water directly supplied to the solid oxide electrolyzer to generate water vapor can reduce energy loss compared to heating the liquid water indirectly supplied to the solid oxide electrolyzer using another heat medium and then generating water vapor, while heating the liquid water.

[0018] In addition, since the liquid water used when cooling the product gas is at a low pressure compared to the product gas, in the heat exchanger, by realizing different state changes between the same substances with different pressures, that is, condensing the relatively high-pressure and high dew-point water vapor contained in the product gas and vaporizing the relatively low-pressure and low-boiling-point liquid water, the latent heat of the water vapor contained in the product gas can be utilized, so that the energy required for vaporizing the liquid water can be reduced. <00001

[0019] Furthermore, this feature configuration allows for lowering the maximum reaction temperature by adding steam to the raw materials for the hydrocarbon synthesis reaction, thereby suppressing catalyst deactivation and deterioration of the reaction vessel. In addition, the product gas obtained from the hydrocarbon synthesis reaction contains steam, and by cooling and condensing this steam while exchanging heat with low-pressure water, the heat obtained is used to heat liquid water and generate steam for electrolysis in a solid oxide electrolytic device, thereby recovering the energy consumed to produce the steam.

[0020] Furthermore, hydrocarbon synthesis reactions are highly exothermic reactions, causing the temperature inside the reactor to rise due to the reaction heat. Catalysts used in the reaction deteriorate when exposed to high temperatures, such as due to the aggregation of active metals. Also, when using an adiabatic reactor, the temperature of the gas inside the reactor is almost identical to the temperature at the reactor outlet, resulting in high reactor temperatures and the need for expensive, heat-resistant materials. When using a heat exchange reactor, although the reactor outlet temperature is controlled to a constant value, the temperature rises internally due to reaction heat, creating hot spots. In relatively fast reactions, such as methanation, the maximum internal temperature is known to be close to that of an adiabatic reactor. Therefore, catalyst deterioration due to high temperatures can occur even in heat exchange reactors. However, by adding steam to the raw materials using a reactor steam supply mechanism, the temperature rise due to the reaction can be suppressed.

[0021] A further characteristic feature of the fuel production system according to the present invention is that, in the heat exchanger, the pressure of the generated gas is 0.5 MPaG or higher, and the pressure of the liquid water is atmospheric pressure or higher.

[0022] A key feature of the fuel production method according to the present invention is that, in the heat exchange step, the pressure of the generated gas is 0.5 MPaG or higher, and the pressure of the liquid water is at or above atmospheric pressure.

[0023] According to this characteristic configuration, since dew point and boiling point are variables that correlate with pressure, when the pressure difference between the generated gas and liquid water is sufficiently large, the difference between the dew point of the generated gas and the boiling point of the liquid water becomes sufficiently large. Therefore, in the heat exchanger, it is possible to achieve two different phase changes between the same substance at different pressures: condensing the water vapor contained in the generated gas and evaporating the liquid water.

[0024] A further characteristic feature of the fuel production system according to the present invention is that it includes a heating unit for heating the liquid water, wherein the liquid water is heated in the heating unit to a temperature above the boiling point of water minus a predetermined first temperature and below the boiling point of water.

[0025] The characteristic configuration of the fuel production method according to the present invention is that it includes a heating step for heating liquid water, wherein in the heating step, the liquid water is heated to a temperature that is above the boiling point of water minus a predetermined first temperature and below the boiling point of water.

[0026] According to this characteristic configuration, liquid water is heated to a temperature close to its boiling point and receives heat from the generated gas, allowing the supplied heat to be efficiently used for the state change of water from liquid to gas.

[0027] A key feature of the fuel production system according to the present invention is that the temperature of the liquid water after it has been heated in the heating section is set to a temperature obtained by subtracting a predetermined second temperature from the temperature of the generated gas after it has passed through the heat exchanger.

[0028] A further characteristic feature of the fuel production method according to the present invention is that the temperature of the liquid water after heating in the heating step is set to a temperature obtained by subtracting a predetermined second temperature from the temperature of the generated gas after the heat exchange step is completed.

[0029] According to this feature configuration, the temperature of the generated gas after the heat exchange process is completed can be arbitrarily set based on the temperature of the liquid water after it has been heated in the heating section. Since the amount of water that condenses during cooling in a heat exchanger depends on its temperature, the amount of water separated from the generated gas can be adjusted by setting the temperature of the generated gas after the heat exchange process is complete.

[0030] A further characteristic feature of the fuel production system according to the present invention is that the solid oxide electrolytic device is configured to co-electrolyze the raw material gas containing water vapor and carbon dioxide, and the reactor is configured to synthesize the hydrocarbon using hydrogen produced in the electrolytic device and carbon monoxide as the carbon oxide as raw materials.

[0031] A further characteristic feature of the fuel production method according to the present invention is that the electrolysis step is a step of co-electrolyzing the raw material gas containing water vapor and carbon dioxide, and in the reaction step, the hydrocarbon is synthesized using the hydrogen produced in the electrolysis step and carbon monoxide as the carbon oxide as raw materials.

[0032] In the electrolysis process used to generate hydrogen for the reaction, energy loss can be reduced by using the heat generated in the reaction process to produce the water vapor required along with carbon dioxide.

[0033] A further characteristic configuration of the fuel production system according to the present invention is that it comprises a plurality of reactors, the generated gas from at least one reactor is passed through a heat exchanger for cooling, and the generated gas after passing through the heat exchanger is introduced into another reactor and passed through another heat exchanger.

[0034] A further characteristic feature of the fuel production method according to the present invention is that it comprises a plurality of reaction steps, the generated gas produced in at least one of the reaction steps is passed through a heat exchanger in the heat exchange step to cool it, the generated gas after passing through the heat exchanger is used in another reaction step and passed through another heat exchanger after the reaction.

[0035] This characteristic configuration allows for the repeated synthesis reaction of hydrocarbons, and by separating the condensed water generated in the heat exchanger before each subsequent reaction, the purity of the hydrocarbons after the synthesis reaction can be increased.

[0036] A further characteristic feature of the fuel production system according to the present invention is that at least one of the reactors is a heat exchange type reactor through which water as a heat transfer medium is passed, and the steam generated by the evaporation of the water as a heat transfer medium through heat exchange is supplied to at least one of the reactors.

[0037] A further characteristic feature of the fuel production method according to the present invention is that at least one of the reaction steps is a reaction step that uses a heat exchange type reactor through which water as a heat transfer medium is passed, and the steam produced by the evaporation of the water as a heat transfer medium through heat exchange is supplied to at least one of the reaction steps.

[0038] This characteristic configuration allows for the addition of steam, produced by the evaporation of water used as a heat transfer medium in a heat exchange reactor, into the hydrocarbon synthesis reaction system, thereby improving energy efficiency.

[0039] A further characteristic feature of the fuel production system according to the present invention is that the generated gas from which water vapor has been removed in the condenser separator is a gas mainly composed of methane.

[0040] A further characteristic feature of the fuel production method according to the present invention is that the generated gas from which water vapor has been removed in the condensation separation step is a gas mainly composed of methane.

[0041] According to this characteristic configuration, by using the fuel production system according to the present invention, methane with high energy efficiency during production can be obtained. [Brief explanation of the drawing]

[0042] [Figure 1]This graph shows the temperature of the generated gas when a methanation reaction is carried out in an adiabatic reactor at an inlet temperature of 250°C and 2 MPaG, using a gas mixture of carbon dioxide and hydrogen in a volume ratio of 1:4, diluted with various amounts of water vapor. [Figure 2] This graph shows the methane purity in the product gas when a methanation reaction is carried out in an adiabatic reactor using a gas mixture of carbon dioxide and hydrogen in a volume ratio of 1:4, diluted with water, at an inlet temperature of 250°C and 2 MPaG. [Figure 3] This is a flowchart of the process used in the calculations related to the graph in Figure 4. [Figure 4] This graph shows the relationship between the ratio of the amount of water vapor added to the reaction vessel to the amount of carbon dioxide used as a raw material, and the low-pressure steam obtained through heat exchange in the heat exchanger. [Figure 5] This is a diagram illustrating the definition of the first temperature. [Figure 6] This is a diagram illustrating the definition of the second temperature. [Figure 7] This is a process flow diagram of the fuel production system according to Example 1. [Figure 8] This is a process flow diagram of the fuel production system according to Example 2. [Figure 9] This is a process flow diagram of the fuel production system according to Example 3. [Figure 10] This is a process flow diagram of the fuel production system according to Example 4. [Figure 11] This is a process flow diagram of the fuel production system according to Example 5. [Modes for carrying out the invention]

[0043] The following describes embodiments of the fuel production system and fuel production method based on Figures 7 to 11, which are process flow diagrams relating to Examples 1 to 5. The fuel production system 100 of the present invention comprises: a solid oxide electrolytic device 11 having a solid oxide electrolytic cell (not shown) for electrolyzing a raw material gas containing at least water vapor; a first reactor 30 (reactor) for synthesizing hydrocarbons using carbon oxide and hydrogen from the solid oxide electrolytic device 11 as raw materials; a first heat exchanger 40 (heat exchanger) for exchanging heat between the product gas containing hydrocarbons and water vapor from the first reactor 30 and liquid water; a first condensation separator 60 (condensation separator) for separating condensed water from the product gas cooled in the first heat exchanger 40; a reactor water vapor supply mechanism 500 for supplying water vapor to the first reactor 30; and an electrolytic water vapor supply mechanism 600 for supplying at least a portion of the water vapor generated in the first heat exchanger 40 to the solid oxide electrolytic device 11. Furthermore, in the fuel production system 100, the pressure of the liquid water supplied to the first heat exchanger 40 as a heat transfer medium is set to a lower pressure than the pressure of the generated gas. In the first heat exchanger 40, at least a portion of the water vapor contained in the generated gas condenses to produce condensed water, and at least a portion of the liquid water vaporizes to produce water vapor. In this application, carbon oxide refers to carbon monoxide and carbon dioxide.

[0044] <Steam supply mechanism for reactors> The fuel production system according to this embodiment includes a reactor steam supply mechanism 500 for adding steam to the reactor along with the raw materials, carbon oxide and hydrogen, during the methanation reaction. The reactor steam supply mechanism 500 consists of a reactor water supply unit 83, a steam supply pump 501, and a steam supply heater 502. Water supplied from the reactor water supply unit 83 is pressurized by the steam supply pump 501 and heated by the steam supply heater 502 to generate steam. The generated steam is mixed with carbon dioxide 1 and hydrogen 2 supplied from the hydrogen supply unit 81 in the reactor steam supply unit 503. Alternatively, the steam supply heater 502 may heat the water but keep it in a liquid state without vaporizing it, and generate steam by vaporizing this liquid water with heat supplied from a heat exchange reactor or heat exchanger. The generated steam may then be mixed with carbon dioxide 1 and hydrogen 2 in the reactor steam supply unit 503.

[0045] <Electrolytic water vapor supply mechanism> The steam generated when liquid water is heated in the heat exchanger is sent to the solid oxide type electrolytic device 11 by the electrolytic steam supply mechanism 600.

[0046] <Solid oxide electrolyzer> In this embodiment, a solid oxide electrolytic device 11 having a solid oxide electrolytic cell (not shown) is used. The solid oxide electrolytic cell comprises a solid electrolyte that conducts oxygen ions, an anode electrode provided on one side of the solid electrolyte, and a cathode electrode provided on the other side of the solid electrolyte. Examples of solid electrolytes used include yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), ytterbia-stabilized zirconia (YbSZ), and lanthanum gallate (LaGaO3, LSGM).

[0047] The solid oxide electrolytic device 11 is equipped with a solid oxide electrolytic cell housed in a heat-insulating device covered with heat-insulating material. By introducing carbon dioxide and water vapor as raw material gases into the inside of this heat-insulating device and applying a predetermined power (voltage and current) between the two electrodes to carry out an electrolytic reaction, carbon monoxide and hydrogen can be produced. Carbon dioxide is supplied to the solid oxide electrolytic device 11 by a carbon dioxide supply unit 80 (raw material gas supply mechanism) that can adjust the amount of carbon dioxide supplied, and water vapor is supplied to the solid oxide electrolytic device 11 by an electrolytic water vapor supply mechanism 600. Furthermore, if only water vapor is introduced into the heating equipment and an electrolytic reaction is carried out, only hydrogen will be produced. In this case, the carbon dioxide supplied by the carbon dioxide supply unit is mixed with the hydrogen produced by the solid oxide electrolytic device downstream of the solid oxide electrolytic device.

[0048] The electrolytic reaction is usually carried out at around 600°C to 1000°C, preferably around 700°C to 850°C. When the electrolytic reaction temperature is within this range, a sufficient electrolytic current density can be ensured, thus keeping equipment costs low. Furthermore, the degradation of the electrolytic cell is suppressed, resulting in lower operating costs.

[0049] <reactor> In this embodiment, a first reactor 30 is provided for synthesizing methane using a gas containing carbon monoxide and hydrogen produced by the electrolytic reaction in the solid oxide electrolytic apparatus 11 as raw materials (methanation reaction as a hydrocarbon synthesis reaction). Note that the gas containing carbon monoxide and hydrogen produced by the electrolytic reaction may contain unreacted carbon dioxide and water vapor, and these gases may also be supplied to the first reactor 30. As shown in (Equation 2), the methanation reaction produces water simultaneously with the production of methane. Therefore, the product gas produced by the methanation reaction is mainly composed of methane, but also contains water vapor.

[0050] The first reactor 30 is equipped with a methanation catalyst that comes into contact with a gas containing carbon monoxide and hydrogen. Known methanation catalysts such as Ni and Ru can be used as the methanation catalyst.

[0051] The inlet temperature when contacting the methanation catalyst is preferably between 200°C and 350°C. Within this range, a sufficient reaction rate is easily obtained, making it easier to carry out the methanation reaction without using an excessive amount of catalyst, and also making it easier to control the outlet temperature of the methanation reaction, thus ensuring the durability of the catalyst.

[0052] The methanation reaction generates a relatively large amount of heat, so as the reaction progresses, the gas temperature rises, and consequently the equilibrium conversion rate decreases. Therefore, it is usually difficult to obtain the desired conversion rate in a single-stage reaction. When using an adiabatic reactor, it is preferable to cool the outlet gas, whose temperature has risen due to the reaction heat, by heat exchange before introducing it into the next stage reactor. Multiple adiabatic reactors may be connected via cooling heat exchangers, or at least one adiabatic reactor on the inlet side and at least one heat exchange reactor on the outlet side may be connected via a cooling heat exchanger.

[0053] By feeding the gas containing carbon monoxide (carbon oxide) and hydrogen, generated in the solid oxide electrolytic device 11, into the first reactor 30, methane, the main component of city gas, can be produced. Since a large amount of heat is generated during methane production, this heat can be used to heat water and generate steam, which can then be used in the electrolytic reaction in the solid oxide electrolytic device 11, thereby effectively utilizing the heat generated during methane production.

[0054] <Heat exchanger> In this embodiment, a first heat exchanger 40 is provided to exchange heat between the product gas containing hydrocarbons and water vapor from the first reactor 30 and liquid water. As the first heat exchanger 40, any known gas-liquid heat exchanger can be used. In the first heat exchanger 40, heat exchange is performed with liquid water to cool the high-temperature product gas obtained from the methanation reaction, thereby cooling the product gas to a predetermined temperature. During this process, water vapor in the product gas condenses to generate condensed water. Then, in the first heat exchanger 40, the heat contained in the product gas generated by the hydrocarbon synthesis reaction can be transferred to liquid water and used for vaporization. The liquid water vaporizes through heat exchange with the high-temperature product gas and is supplied to the solid oxide type electrolytic device 11 via the electrolytic steam supply mechanism 600 and used as part of the raw material gas. Furthermore, heat exchange between the generated gas and liquid water is carried out using the first heat exchanger 40, with heat being transferred directly between the generated gas and liquid water without the use of any other heat transfer medium. Furthermore, in the examples, when steam generated in a heat exchanger is added as a raw material, there are two or more reactors, but in practice, only one reactor may be used.

[0055] <Simultaneous control of water evaporation and water vapor condensation in heat exchange> During heat exchange, the generated gas is under the same high-pressure conditions as during the methanation reaction. As a result, the condensation temperature of water vapor in the generated gas, i.e., the dew point of the generated gas, is significantly higher than the boiling point of water at normal pressure. Incidentally, it is preferable that there be a difference of 30°C or more between the condensation temperature of water vapor contained in the generated gas, that is, the dew point of the generated gas, and the boiling point of water in its liquid state.

[0056] For example, under a pressure of 10 atmospheres (1.0 MPa), liquid water has a boiling point of 179°C and a specific heat of 4.36 J / g·K (water temperature = 160°C), while the specific heat of water vapor is 2.54 J / g·K (water vapor temperature = 180°C). Meanwhile, the energy of evaporation (enthalpy of evaporation) of water under a pressure of 10 atmospheres is 2015 J / g. Therefore, by cooling the generated gas to a temperature lower than its dew point, a gas-liquid phase change occurs in the water vapor contained in the generated gas, causing the water vapor to condense into water. Compared to the case without a gas-liquid phase change of water vapor, a larger amount of heat is generated, and a greater amount of heat can be supplied to the liquid water.

[0057] It is known that the boiling point of water at 0.5 MPa is 151.1°C, and the boiling point of water at 0.2 MPa is 119.6°C.

[0058] In this invention, liquid water is used as the heat transfer medium to receive heat from the generated gas. The boiling point of liquid water is lower than the condensation temperature of the water vapor contained in the generated gas. Therefore, the liquid water receives the condensation energy associated with the condensation of water vapor contained in the generated gas, causing the liquid water to undergo a phase change and vaporize, generating water vapor. In other words, even though water is used on both the heat supply and heat recipient sides in the heat exchange, a phase change from gas to liquid occurs on the heat supply side due to the condensation of water vapor, while a phase change from liquid to gas occurs on the heat recipient side due to the evaporation of water.

[0059] <Effects of supplying water vapor to the methanation reaction system> Furthermore, by changing the boiling point of water, which is the heat transfer medium, the cooling temperature of the generated gas can be adjusted. This controls the amount of water vapor condensed from the generated gas, which in turn controls the amount of water vapor contained in the reaction system during the methanation reaction that takes place in a subsequent reactor, thereby controlling the reaction temperature of the methanation reaction. In this way, by controlling the amount of water vapor contained in the reaction system and the reaction temperature, it is possible to suppress catalyst degradation due to rising internal reactor temperature, reactor damage, and carbon deposition inside the reactor.

[0060] <Benefits of adding steam to raw materials and appropriate amounts to add> In hydrocarbon-related reactions such as methanation reactions, solid carbon deposition inside the reactor can be a problem. When solid carbon precipitates inside the reactor, it not only degrades the catalyst but also causes problems such as blockage of the reaction tube due to the deposited carbon. It is generally known that carbon deposition is less likely to occur when the amount of water vapor in the reaction gas is high, so adding water vapor to the reactor has the effect of suppressing carbon deposition.

[0061] Furthermore, since the methanation reaction is a highly exothermic reaction, the reaction heat causes the temperature inside the reactor to rise. When the catalyst used in the reaction is exposed to high temperatures, it deteriorates due to the aggregation of the active metal. Also, when an adiabatic reactor is used, the temperature of the gas inside the reactor almost matches the temperature at the reactor outlet, causing the reactor to become very hot, so it is necessary to use expensive materials with high heat resistance. When a heat exchange reactor is used, although the reactor outlet temperature is controlled to a constant value, the temperature rises inside due to the heat generated by the reaction, creating hot spots. In relatively fast reactions such as the methanation reaction, it is known that the maximum temperature inside a heat exchange reactor is close to the maximum temperature inside an adiabatic reactor, so catalyst deterioration due to high temperatures can also occur in a heat exchange reactor. Therefore, from the viewpoint of suppressing the temperature rise caused by the reaction, it is preferable to add water vapor to the methanation reaction mixture to suppress the temperature rise inside the reactor.

[0062] Therefore, from the perspective of the maximum temperature inside the reactor, we used the process simulator Unisim to investigate the appropriate amount of steam to introduce into the methanation reaction system. When a gas prepared by mixing carbon dioxide and hydrogen in a volume ratio of 1:4 was diluted with various amounts of water vapor and a methanation reaction was carried out in the first reactor 30, an adiabatic reactor, at an inlet temperature of 250°C and a pressure of 2 MPaG, the temperature of the resulting gas was calculated and is shown in Figure 1. As the amount of water vapor added increases, the temperature of the generated gas decreases. Therefore, from the perspective of suppressing the rise in reactor temperature, the more water vapor added, the better. When no water vapor is added, the temperature of the generated gas exceeds 760°C. When the amount of carbon dioxide in the raw material is set to 1 and the amount of water vapor added is also set to 1, the temperature of the generated gas is suppressed to 704°C. Furthermore, when the amount of water vapor added is set to 2, the temperature of the generated gas is 659°C, well below 700°C, and when the amount of water vapor added is set to 2.5, the temperature of the generated gas is 639°C, below 650°C. These results indicate that the amount of steam added to the reactor is preferably 1 or more times the amount of carbon dioxide used as a raw material, more preferably 2 or more times, and even more preferably 2.5 or more times.

[0063] Furthermore, when an adiabatic reactor is used as the reactor, adding hydrogen to the reaction raw materials has the effect of improving the purity of the methane produced. Figure 2 shows the calculated results of the methane purity (dry basis) in the produced gas when a gas prepared by mixing carbon dioxide and hydrogen in a volume ratio of 1:4 is diluted with water and a methanation reaction is carried out in an adiabatic reactor at an inlet temperature of 250°C and 2 MPaG.

[0064] Since the purity of methane in the post-reaction gas increases with increasing amounts of water vapor added, when using an adiabatic reactor, it is better to add more water vapor to improve methane purity. In an adiabatic reactor, supplying steam lowers the reactor outlet temperature, shifting the chemical equilibrium and increasing the purity of methane. However, in a heat exchange reactor, the outlet temperature is controlled to a constant value, so increasing the amount of steam added to the raw materials does not improve the purity of methane.

[0065] As described above, the more steam added to the reactor, the lower the maximum temperature inside the reactor, reducing the burden on the reactor and reaction catalyst. Furthermore, in the case of an adiabatic reactor, adding hydrogen to the reaction raw materials can improve the purity of the methane produced. Therefore, a larger amount of steam added to the raw materials is preferable. On the other hand, in this invention, the energy used to produce the steam added to the reaction vessel is the heat recovered in a heat exchanger installed downstream of the reaction vessel. Since the low-pressure steam generated using this heat is used as a raw material in the solid oxide electrolytic device, the more steam added to the reaction vessel, the greater the amount of low-pressure steam obtained. If the amount of low-pressure steam is too large, the excess steam will be discarded, leading to a decrease in the energy conversion efficiency of the process. Therefore, it is preferable that the amount of steam generated by heat exchange with the product gas does not significantly exceed the amount required by the solid oxide electrolytic device.

[0066] Therefore, from the perspective of energy efficiency, we similarly used the process simulator Unisim to investigate the appropriate amount of water vapor to be introduced into the methanation reaction system.

[0067] In conducting this study, we determined the theoretical amount of hydrogen required to increase the purity of the methane produced. To increase the purity of methane produced using carbon monoxide, carbon dioxide, and hydrogen as raw materials, it is desirable that the concentrations of carbon monoxide, carbon dioxide, and hydrogen in the gas (represented as [CO], [CO2], and [H2] respectively) satisfy the following equation. 3×[CO]+4×[CO2]=[H2] (Equation 3) In a water vapor electrolysis SOEC methanation system using a solid oxide electrolytic device that electrolyzes only water vapor, the optimal amount of water vapor to be added to the methanation reaction system, which is appropriate from the standpoint of energy efficiency, is calculated using (Equation 3). Assuming a raw material utilization rate of 70% in the solid oxide electrolytic device and an amount of carbon dioxide supplied to the methanation reactor of 1, the optimal relative amount of water vapor to the carbon dioxide supplied to the solid oxide electrolytic device in order to supply an appropriate amount of hydrogen is 5.7.

[0068] Figure 4 shows the results of calculations regarding the relationship between the ratio of the amount of water vapor added to the reaction vessel to the amount of carbon dioxide used as a raw material, and the low-pressure steam obtained by heat exchange in the heat exchanger, in the model shown in Figure 3. Let's explain the model in Figure 3. Carbon dioxide 1 (10 Nm³) supplied from the carbon dioxide supply unit 80. 3 ( / h) and hydrogen 2 (40Nm³) supplied from hydrogen supply unit 81. 3 A mixed gas of carbon dioxide (1) and hydrogen (2) was pressurized to 2 MPaG using compressor 3. Steam (2 MPaG) supplied from reactor steam supply section 503 of reactor steam supply mechanism 500 was added to the mixed gas of carbon dioxide (1) and hydrogen (2), heated to 250°C with first gas heating heater 20, and introduced into first reactor 30 (heat exchange type) to carry out the methanation reaction. After the reaction was complete, the product gas was removed and passed through the first heat exchanger 40 to cool it to 150°C. The cooled product gas was then cooled to 5°C in the cooler 4, and the condensate 14 produced by the cooling was separated and removed in the first condensation separator 60 to obtain fuel 15 mainly composed of methane. The water used to cool the generated gas in the first heat exchanger 40 was supplied from the heat exchange water supply unit 82, pressurized to 0.01 MPaG by the first pump 70, heated to 102°C by the first water heating heater 50, and then supplied to the first heat exchanger 40. Since the boiling point of water at a pressure of 0.01 MPaG is approximately 102.6°C, the water supplied to the first heat exchanger 40 is liquid. When the first heat exchanger 40 was flowing, some of the water supplied to the heat exchanger was converted into steam by the heat supplied from the generated gas, and the generated steam was supplied to the solid oxide type electrolytic device 11 by the electrolytic steam supply mechanism 600. As shown in Figure 4, if the amount of carbon dioxide used as the raw material is 1, then when the relative amount of water vapor added is 4, the relative amount of low-pressure steam obtained will be 5.8. From these results, it is preferable that, from the viewpoint of thermal energy efficiency, the amount of water vapor added to the reaction vessel be four times or less the amount of carbon dioxide.

[0069] <First Condenser / Separator> In this embodiment, the water vapor contained in the product gas, which has been cooled in the first heat exchanger 40 and from which condensed water has been separated, is separated again in the first condensation separator 60. Specifically, the product gas, which has been cooled in the first heat exchanger 40 and from which condensed water has been separated, is further cooled by the cooler 4 and flows into the first condensation separator 60, where the contained water vapor condenses to produce condensed water. In the first condensation separator 60, the condensed water is separated to obtain a gas mainly composed of methane (synthetic methane).

[0070] The first condenser separator 60 can employ separation methods such as liquefaction separation, membrane separation, and adsorption separation. The first condenser separator 60 may combine one or more of these separation methods.

[0071] Liquefaction separation involves liquefying and separating water-containing components by controlling the temperature to obtain a gas primarily composed of methane.

[0072] Membrane separation involves using a separation membrane that selectively allows water to pass through, thereby separating water-containing components and obtaining a gas primarily composed of methane. The type of separation membrane is not particularly limited, as long as it can allow small molecular sizes to pass through and separate specific components from other components.

[0073] Adsorption separation involves separating water-containing components using an adsorbent to obtain a gas primarily composed of methane. Adsorbents such as silica gel, zeolite, and activated carbon can be used. When employing adsorption separation, a heating device is provided. Heating the adsorbent allows for the desorption of water-containing components from the adsorbent.

[0074] <Synthetic methane (e-methane)> The methane produced using the fuel production system and fuel production method according to this embodiment, with non-fossil energy sources as raw materials, is generally called e-methane.

[0075] <1st temperature> As shown in Figure 5, in this embodiment, the temperature of the liquid water that flows through the first heat exchanger 40 and receives heat from the generated gas is set to be above the boiling point of water minus a predetermined first temperature, and below the boiling point of water. Here, the first temperature is, for example, around 5°C, which is close to the boiling point, and therefore, with the heat supplied by the heat exchanger, a large amount of water vapor can be generated.

[0076] <Second temperature> As shown in Figure 6, in this embodiment, the temperature of the water supplied to the first heat exchanger 40 is set to a temperature obtained by subtracting a predetermined second temperature from the temperature of the generated gas after passing through the first heat exchanger 40. The second temperature is, for example, around 50°C, and by adjusting the temperature of the heated liquid water, the temperature of the generated gas can be cooled to the desired temperature.

[0077] <Temperature control of the generated gas after flow through the heat exchanger> When condensed water is separated from the product gas obtained in a methanation reaction and used as a reaction raw material in the next methanation reaction, the purity of the methane produced in the next step is affected by the amount of water vapor contained in the product gas used as a raw material. Since the amount of water vapor in the product gas increases or decreases with the temperature of the product gas, it is important to appropriately control the temperature of the product gas. The present invention is configured such that liquid water is heated in a heating section to a temperature above the boiling point of the water minus a predetermined first temperature, and below the boiling point of the water, and the temperature of the heated liquid water is set to a temperature obtained by subtracting a predetermined second temperature from the temperature of the generated gas after passing through the heat exchanger, that is, the temperature of the generated gas after passing through the heat exchanger is the temperature of the heated liquid water plus a predetermined second temperature. Therefore, increasing the pressure of the liquid water supplied to the heat exchanger raises the boiling point of the liquid water. Consequently, the temperature of the heated liquid water, which is above the boiling point of the liquid water minus a predetermined first temperature and below the boiling point of water, also increases. Along with this, the temperature of the generated gas after passing through the heat exchanger, which is the temperature of the heated liquid water plus a predetermined second temperature, also increases. Conversely, lowering the pressure of the liquid water supplied to the heat exchanger lowers the boiling point of the liquid water. Consequently, the temperature of the heated liquid water, which is above the boiling point of the liquid water minus a predetermined first temperature and below the boiling point of water, also decreases. Along with this, the temperature of the generated gas after passing through the heat exchanger, which is the temperature of the heated liquid water plus a predetermined second temperature, also decreases. In this way, by adjusting the pressure of the liquid water supplied to the heat exchanger, the temperature of the generated gas after it passes through the heat exchanger can be controlled, and therefore, the amount of water contained in the generated gas can be adjusted.

[0078] Temperature control of the generated gas after it has passed through the heat exchanger using this method is easier to adjust compared to temperature control by adjusting the flow rate of liquid water passing through the heat exchanger or by changing the settings of the heat exchanger.

[0079] <Other variations> Although a pump is used to supply liquid water to the heat exchanger, if the liquid water is subjected to a pressure above atmospheric pressure and flows smoothly through the heat exchanger, a configuration that does not use a pump, such as using a water-tube boiler instead, is also acceptable.

[0080] The embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. (Examples)

[0081] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples. Note that all of the results in this example were calculated using a process simulator (software name: Unisim). (Example 1)

[0082] As shown in Figure 7, carbon dioxide 1 (10 Nm³) supplied from the carbon dioxide supply unit 80. 3 ( / h) and hydrogen 2 (40Nm³) supplied from the solid oxide electrolytic device 11. 3 The mixed gas, which was a mixture of carbon dioxide (1 / h) and hydrogen (2), was pressurized to 2 MPaG using compressor 3. 3 The mixture was heated to 250°C using the first gas heater 20 by adding ( / h) and then introduced into the first reactor 30 (heat exchange type) to carry out the methanation reaction. The maximum temperature inside the first reactor 30 during the methanation reaction was 639°C, but the reactor outlet temperature was reduced to 250°C by removing heat using a heat transfer medium such as water in the heat exchange reactor. After the reaction was complete, the product gas was removed and passed through the first heat exchanger 40 to cool it to 150°C. The cooled product gas was then cooled to 5°C in the cooler 4, and the condensate 14 produced by the cooling was separated and removed in the first condensation separator 60 to obtain fuel 15 mainly composed of methane. The concentrations of each component in the obtained fuel 15 were methane 93.2%, carbon dioxide 1.3%, hydrogen 5.5%, water 0.0%, and carbon monoxide 0.0%.

[0083] The reactor steam supply mechanism 500 adds steam to the mixed gas of carbon dioxide 1 and hydrogen 2 as follows: The water supplied from the reactor water supply unit 83 is pressurized to 2 MPaG by the steam supply pump 501, then heated to 215°C by the steam supply heater 502, and then introduced into the reactor 30 as a heat transfer medium. Since the boiling point of water at a pressure of 2 MPaG is approximately 215.4°C, the water supplied with heat from the first reactor 30 is in liquid form and vaporizes upon receiving heat from the first reactor 30, becoming 250°C steam. The generated steam is added to a mixture of carbon dioxide 1 and hydrogen 2 in a reactor steam supply unit 503 located between the compressor 3 and the first gas heating heater 20.

[0084] The water used to cool the generated gas in the first heat exchanger 40 was supplied from the heat exchange water supply unit 82, pressurized to 0.01 MPaG by the first pump 70, heated to 102°C by the first water heating heater 50, and then supplied to the first heat exchanger 40. Since the boiling point of water at a pressure of 0.01 MPaG is approximately 102.6°C, the water supplied to the first heat exchanger 40 is liquid. When the first heat exchanger 40 was flowing, some of the water supplied to the heat exchanger was converted into steam by the heat supplied from the generated gas, and the generated steam was supplied to the solid oxide type electrolytic device 11 by the electrolytic steam supply mechanism 600. The temperature and flow rate of the steam supplied to the solid oxide electrolytic device 11 were as follows: The temperature is 102.6°C, and the volumetric flow rate is 43.29 Nm³. 3 The amount obtained was 34.79 kg / h. (Example 2)

[0085] As shown in FIG. 8, the carbon dioxide 1 (10 Nm 3 / h) supplied from the carbon dioxide supply unit 80 and the hydrogen 2 (40 Nm 3 / h) supplied from the solid oxide electrolysis device 11 were mixed, and the mixed gas was pressurized to 2 MPaG using the compressor 3. Steam (25 Nm 3 / h) supplied from the reactor steam supply section 503 of the reactor steam supply mechanism 500 was added to the mixed gas of carbon dioxide 1 and hydrogen 2, heated to 250° C. by the first gas heater 20, and then introduced into the first reactor 30 (adiabatic type) to carry out the methanation reaction. The temperature at the outlet of the first reactor 30 and the temperature of the product gas during the methanation reaction were 639° C. After the reaction was completed, the generated gas was passed through the first heat exchanger 40 to be cooled to 280° C., and then passed through the second heat exchanger 41 to be cooled to 150° C. The condensed water 14 generated by the cooling was separated and removed by the first condensate separator 60, heated to 250° C. by the second gas heater 21, and then introduced into the second reactor (heat exchange type) to carry out the methanation reaction. After the reaction was completed, the generated gas was passed through the third heat exchanger 42, cooled to 150° C., and then passed through the cooler 4 to be cooled to 5° C. The condensed water 14 generated by the cooling was separated and removed by the second condensate separator 61 to obtain the fuel 15. The concentrations of the respective components contained in the obtained fuel 15 were 96.4% methane, 0.64% carbon dioxide, 2.9% hydrogen, 0.0% water, and 0.0% carbon monoxide.

[0086] The mechanism by which the reactor steam supply mechanism 500 adds steam to the mixed gas of carbon dioxide 1 and hydrogen 2 is as follows. The water supplied from the reactor water supply unit 83 is pressurized to 2 MPaG by the steam supply pump 501, then heated to 215°C by the steam supply heater 502, and supplied to the first heat exchanger 40. Since the boiling point of water at a pressure of 2 MPaG is approximately 215.4°C, the water supplied to the first heat exchanger 40 is liquid. As it passes through the first heat exchanger 40, it vaporizes due to the heat supplied from the generated gas, becoming steam at 250°C. The generated steam is added to a mixed gas of carbon dioxide 1 and hydrogen 2 in the reactor steam supply unit 503, which is located between the compressor 3 and the first gas heating heater 20.

[0087] The liquid water used in the second heat exchanger 41 and the third heat exchanger 42 was supplied according to the following procedures. Second heat exchanger 41 and third heat exchanger 42: Water supplied from the heat exchange water supply unit 82 is pressurized to 0.01 MPaG by the first pump 70, heated to 102°C by the first water heating heater 50, and then supplied to the second heat exchanger 41 and third heat exchanger 42. Since the boiling point of water at a pressure of 0.01 MPaG is approximately 102.6°C, the water supplied to the second heat exchanger 41 and third heat exchanger 42 is liquid. The steam generated in the second heat exchanger 41 and the third heat exchanger 42 was supplied to the solid oxide type electrolytic device 11 by the electrolytic steam supply mechanism 600. The steam supplied from the second heat exchanger 41 to the solid oxide electrolytic device 11 had a temperature of 102.6°C and a volumetric flow rate of 33.57 Nm³. 3 The yield was 26.98 kg / h. Furthermore, the steam supplied from the third heat exchanger 42 to the solid oxide electrolytic device 11 had a temperature of 102.6°C and a volumetric flow rate of 14.66 Nm³. 3 The yield was 11.78 kg / h.

[0088] (Example 3) As shown in Figure 9, carbon dioxide 1 (10 Nm³) is supplied from the carbon dioxide supply unit 80. 3 ( / h) and hydrogen 2 (40Nm³) supplied from the solid oxide electrolytic device 11. 3The mixed gas, which was a mixture of carbon dioxide (1 / h) and hydrogen (2), was pressurized to 2 MPaG using compressor 3. 3 The mixture was heated to 250°C using the first gas heating heater 20 and then introduced into the first reactor 30 (adiabatic type) to carry out the first methanation reaction. The temperature at the outlet of the first reactor 30 and the temperature of the generated gas during the first methanation reaction were 639°C. After the reaction was complete, the generated gas was passed through the first heat exchanger 40 to cool to 280°C, and then passed through the second heat exchanger 41 to cool to 150°C. The condensed water 14 generated by the cooling was separated by condensation using the first condensation separator 60. The generated gas after condensation separation was heated to 250°C using the second gas heating heater 21, and the second methanation reaction was carried out in the second reactor 31 (adiabatic type). The temperature at the outlet of reactor 31 and the temperature of the generated gas during the second methanation reaction were 604°C. The concentrations of each component in the gas introduced into the second reactor 31 were as follows: methane 15.9%, carbon dioxide 10.3%, hydrogen 47.6%, water 24.1%, and carbon monoxide 2.1%. After the second methanation reaction was completed, the generated gas was passed through the third heat exchanger 42 to cool to 150°C, and the condensed water 14 produced by the cooling was separated by condensation using the second condensation separator 61. The gas after the second condensation separation was heated to 250°C using the third gas heating heater 22 and then introduced into the third reactor 32 (heat exchange type) to carry out the third methanation reaction. The concentrations of each component in the gas introduced into the third reactor were as follows: methane 35.5%, carbon dioxide 6.9%, hydrogen 32.2%, water 24.0%, and carbon monoxide 1.5%. After the reaction was complete, the generated gas was passed through the fourth heat exchanger 43 to cool to 150°C, then cooled to 5°C in the cooler 4, and the condensed water 14 generated by the cooling was separated and removed using the third condensation separator 62 to obtain the fuel 15. The concentrations of each component in the obtained fuel 15 were as follows: methane 97.4%, carbon dioxide 0.42%, hydrogen 2.1%, water 0.0%, and carbon monoxide 0.0%.

[0089] The reactor steam supply mechanism 500 adds steam to the mixed gas of carbon dioxide 1 and hydrogen 2 as follows: Water supplied from the reactor water supply unit 83 is pressurized to 2 MPaG by the steam supply pump 501, heated to 215°C by the steam supply heater 502, and supplied to the first heat exchanger 40. Since the boiling point of water at a pressure of 2 MPaG is approximately 215.4°C, the water supplied to the first heat exchanger 40 is in liquid form. In the first heat exchanger 40, it vaporizes due to the heat supplied from the generated gas and becomes steam at 250°C. The generated steam is added to a mixed gas of carbon dioxide 1 and hydrogen 2 in the reactor steam supply unit 503.

[0090] The liquid water used in the second heat exchanger 41, the third heat exchanger 42, and the fourth heat exchanger 43 is supplied according to the following procedure. Water supplied from the heat exchange water supply unit 82 is pressurized to 0.01 MPaG by the first pump 70 and then heated to 102°C by the first water heating heater 50. This water is supplied to the second heat exchanger 41, the third heat exchanger 42, and the fourth heat exchanger 43. Since the boiling point of water at a pressure of 0.01 MPaG is approximately 102.6°C, the water supplied to the second heat exchanger 41, the third heat exchanger 42, and the fourth heat exchanger 43 is liquid. Furthermore, some of the supplied water vaporizes through heat exchange in each heat exchanger, generating steam. The generated steam is then transferred to the solid oxide type electrolytic device 11 by the electrolytic steam supply mechanism 600.

[0091] The temperature and volume of water vapor generated in the second heat exchanger 41, the third heat exchanger 42, and the fourth heat exchanger 43 are as follows. Heat exchanger 41 (second unit): Temperature: 102.6°C, Volumetric flow rate: 33.57 Nm 3 / h, amount obtained: 26.98kg / h. Third heat exchanger 42... Temperature: 102.6℃, Volumetric flow rate: 20.73Nm 3 / h, amount obtained: 16.66kg / h. Heat exchanger 43 (No. 4): Temperature: 102.6°C, Volumetric flow rate: 7.07 Nm³ 3 / h, amount obtained: 5.68kg / h.

[0092] (Example 4) As shown in Figure 10, carbon dioxide 1 (10 Nm³) is supplied from the carbon dioxide supply unit 80. 3 ( / h) and hydrogen 2 (40Nm³) supplied from the solid oxide electrolytic device 11. 3 The mixed gas, which was a mixture of carbon dioxide (1 / h) and hydrogen (2), was pressurized to 2 MPaG using compressor 3. 3 The mixture was heated to 250°C using the first gas heating heater 20 and then introduced into the first reactor 30 (adiabatic type) to carry out the first methanation reaction. The temperature at the outlet of reactor 30 and the temperature of the generated gas during the first methanation reaction were 639°C. After the reaction was complete, the generated gas was passed through the first heat exchanger 40 to cool to 280°C, and then passed through the second heat exchanger 41 to cool to 145°C. The condensed water 14 generated by the cooling was separated and removed using the first condensation separator 60. The gas obtained by condensation separation of condensed water was heated to 300°C using a second gas heating heater 21 and introduced into a second reactor (heat exchange type) to carry out the second methanation reaction. The maximum temperature inside the second reactor 31 was 631°C, but by removing heat using a heat transfer medium such as water in the heat exchange reactor, the reactor outlet temperature was reduced to 300°C. The composition of the gas introduced into the second reactor was as follows: methane 16.5%, carbon dioxide 10.7%, hydrogen 49.5%, water 21.1%, and carbon monoxide 2.2%. After the second methanation reaction was completed, the generated gas was passed through the third heat exchanger 42 to cool to 110°C, and the condensed water 14 generated by the cooling was separated by condensation using the second condensation separator 61. The generated gas after condensation separation was heated to 300°C using the third gas heating heater 22 and introduced into the third reactor (heat exchange type) to carry out the third methanation reaction. After the third methanation reaction was completed, the generated gas was passed through the fourth heat exchanger 43 to cool to 108°C, and then cooled to 5°C in the cooler 4. The condensed water 14 generated by the cooling was separated and removed using the third condensation separator 62 to obtain the fuel 15. The concentrations of each component in the obtained fuel 15 were 98.2% methane, 0.28% carbon dioxide, 1.5% hydrogen, 0.0% water, and 0.0% carbon monoxide.

[0093] The reactor steam supply mechanism 500 adds steam to the mixed gas of carbon dioxide 1 and hydrogen 2 as follows: The water supplied from the reactor water supply unit 83 is pressurized to 2 MPaG by the steam supply pump 501, heated to 215°C by the steam supply heater 502, and then supplied to the first heat exchanger 40. Since the boiling point of water at a pressure of 2 MPaG is approximately 215.4°C, the water supplied to the first heat exchanger is in liquid form. In the first heat exchanger 40, it vaporizes into 250°C steam due to heat supplied from the generated gas. The generated steam is added to a mixed gas of carbon dioxide 1 and hydrogen 2 in the reactor steam supply unit 503.

[0094] The liquid water used in the second heat exchanger 41, the third heat exchanger 42, and the fourth heat exchanger 43 is supplied according to the following procedure. Second heat exchanger 41: Water supplied from the heat exchange water supply unit 82 was pressurized to 0.25 MPaG by the first pump 70, heated to 139°C by the first water heating heater 50, and then supplied to the second heat exchanger 41. Since the boiling point of water at a pressure of 0.25 MPaG is approximately 139°C, the water supplied to the second heat exchanger 41 is liquid. Third heat exchanger 42: Water supplied from the heat exchange water supply unit 82 was pressurized to 0.02 MPaG by the second water heating pump 71, heated to 104°C by the second water heating heater 51, and then supplied to the third heat exchanger 42. Since the boiling point of water at a pressure of 0.02 MPaG is approximately 105°C, the water supplied to the third heat exchanger 42 is liquid. Fourth heat exchanger 43: Water supplied from the heat exchange water supply unit 82 was pressurized to 0.01 MPaG by the third water heating pump 72, heated to 102°C by the third water heating heater 52, and then supplied to the fourth heat exchanger 43. Since the boiling point of water at a pressure of 0.01 MPaG is approximately 102.6°C, the water supplied to the fourth heat exchanger 43 is liquid.

[0095] The water, which has been pressurized and heated, is supplied to the second, third, and fourth heat exchangers, respectively. Due to heat exchange, a portion of the water evaporates, generating steam. The steam generated in the second, third, and fourth heat exchangers is transferred to the solid oxide type electrolytic device 11 by the electrolytic steam supply mechanism 600. However, a fourth condenser separator 63 and a fifth condenser separator 64 are provided together with expansion valves 7 between the second heat exchanger 41 and the solid oxide electrolytic device 11, and between the third heat exchanger 42 and the solid oxide electrolytic device 11, respectively, and the steam generated in the heat exchanger is depressurized and expanded here. The condensed water 14 generated by the depressurization and expansion of the steam is separated and removed by the fourth condenser separator 63 and the fifth condenser separator 64, respectively.

[0096] The temperature, volumetric flow rate, and amount of water vapor obtained after passing through the fourth condenser separator 63 are as follows. Temperature: 102.6℃, Volumetric flow rate: 42.53Nm 3 / h, amount obtained: 34.18kg / h.

[0097] The temperature, volumetric flow rate, and amount of water vapor obtained after passing through the fifth condenser separator 64 are as follows. Temperature: 102.6℃, Volumetric flow rate: 18.68Nm 3 / h, amount obtained: 15.01kg / h.

[0098] The temperature, volumetric flow rate, and amount of steam obtained from the fourth heat exchanger are as follows: Temperature: 102.6℃, Volume flow rate: 2.51Nm 3 / h, amount obtained: 2.02kg / h. In this embodiment, the cooling temperature of the gas is adjusted to an appropriate value by cooling the gas using water at different pressures. For example, the gas exiting the first reactor 30 is cooled by the first heat exchanger 40, but since this temperature is set to a relatively high 145°C, it still contains 21.1% water even after the separation of condensed water in the first condensation separator 60. As a result, the gas supplied to the second reactor 31 contains a sufficient amount of water, making carbon deposition less likely and suppressing the temperature rise, thereby keeping the maximum temperature inside the reactor to 631°C. (Example 5)

[0099] As shown in Figure 11, synthesis gas containing carbon oxide (50 Nm³) is the raw material for the methanation reaction. 3 The synthesis gas ( / h) is supplied from the solid oxide electrolytic device 11. The concentrations of each component in the synthesis gas are as follows: methane 1.9%, carbon dioxide 5.8%, hydrogen 62.3%, water 16.9%, carbon monoxide 13.0%. The synthesis gas is pressurized to 0.9 MPaG by compressor 3, and steam (20 Nm³) is supplied from the reactor steam supply section 503 of the reactor steam supply mechanism 500. 3 The mixture was heated to 250°C using the first gas heating heater 20 and then introduced into the first reactor 30 (heat exchange type) to carry out the first methanation reaction. The maximum temperature inside reactor 30 during the first methanation reaction was 638°C. After the reaction was complete, the generated gas was passed through the first heat exchanger 40 to cool to 107°C, and the condensed water 14 produced by the cooling was separated and removed using the first condensation separator 60. The product gas, which had undergone condensation and separation, was heated to 250°C using a second gas heating heater 21 and then introduced into a second reactor 31 (heat exchange type) to carry out a second methanation reaction. The concentrations of each component in the product gas introduced into the second reactor were as follows: methane 79.3%, carbon dioxide 1.5%, hydrogen 5.9%, water 13.3%, and carbon monoxide 0.0%. After the second methanation reaction was completed, the generated gas was introduced into the second heat exchanger and cooled to 107°C, and then cooled to 5°C in the cooler 4. The condensed water 14 generated by the cooling was separated by condensation using the second condensation separator 61 to obtain fuel 15. The concentrations of each component in the obtained fuel 15 were 98.3% methane, 0.31% carbon dioxide, 1.3% hydrogen, 0.0% water, and 0.0% carbon monoxide. The reactor steam supply mechanism 500 adds steam to the mixed gas of carbon dioxide 1 and hydrogen 2 as follows: The water supplied from the reactor water supply unit 83 is pressurized to 0.9 MPaG by the steam supply pump 501, heated to 180°C by the steam supply heater 502, and then transferred to the first reactor 30 (heat exchange type) as a heat transfer medium. Since the boiling point of water at a pressure of 0.9 MPaG is approximately 180.1°C, the water supplied to the first reactor 30 is in liquid form. The water transferred as a heat transfer medium vaporizes due to the heat supplied from the reactor, generating steam at 250°C. The generated steam is added to a mixed gas of carbon dioxide 1 and hydrogen 2 in the reactor steam supply unit 503.

[0100] The liquid water used in the first heat exchanger 40 and the second heat exchanger 41 is supplied according to the following procedure. Water supplied from the heat exchange water supply unit 82 is pressurized to 0.01 MPaG by the first pump 70, heated to 102°C by the first water heating heater 50, and then transferred to the first heat exchanger 40 and the second heat exchanger 41. In each heat exchanger, heat is supplied to generate steam, and the generated steam is transferred to the solid oxide type electrolytic device 11 by the electrolytic steam supply mechanism 600.

[0101] The steam generated in the first heat exchanger 40 had a temperature of 102.6°C and a volumetric flow rate of 44.69 Nm³. 3 The yield was 35.92 kg / h. Furthermore, the steam generated in the second heat exchanger 41 had a temperature of 102.6°C and a volumetric flow rate of 2.56 Nm³. 3 The yield was 2.06 kg / h.

[0102] The condensed water 14 separated and removed in the first condenser separator 60 is collected, and after its pressure is reduced to 0.01 MPaG in the expansion valve 7, it is transferred to the second heat exchanger 41. In this way, the amount of water heated by the first water heating heater 50 is reduced, and energy efficiency can be improved. [Explanation of Symbols]

[0103] 2: Hydrogen 11: Solid oxide electrolyzer 30: Reactor (First Reactor) 40: Heat exchanger (1st heat exchanger) 60: Condenser (First Condenser) 100: Fuel production system 500: Steam supply mechanism for reactors 501: Steam supply pump 600: Electrolytic steam supply mechanism

Claims

1. A solid oxide type electrolytic device that electrolyzes a raw material gas containing at least water vapor, A reactor for synthesizing hydrocarbons using carbon oxide and hydrogen from the solid oxide electrolytic device as raw materials, A heat exchanger that exchanges heat between the product gas containing the hydrocarbons and water vapor from the reactor and liquid water, A condensation separator for separating condensed water from the generated gas cooled by the heat exchanger, The reactor is equipped with a reactor steam supply mechanism for supplying steam, The pressure of the liquid water is set to a pressure lower than the pressure of the generated gas. In the heat exchanger, at least a portion of the water vapor contained in the generated gas condenses to produce condensed water, and at least a portion of the liquid water vaporizes to produce water vapor. A fuel production system having an electrolytic steam supply mechanism that supplies at least a portion of the steam generated in the heat exchanger to the solid oxide type electrolytic device.

2. The fuel production system according to claim 1, wherein in the heat exchanger, the pressure of the generated gas is 0.5 MPaG or higher, and the pressure of the liquid water is atmospheric pressure or higher.

3. The fuel production system according to claim 2, further comprising a heating unit for heating the liquid water, wherein the liquid water is heated in the heating unit to a temperature above the boiling point of the water minus a predetermined first temperature and below the boiling point of the water.

4. The fuel production system according to claim 3, wherein the temperature of the liquid water after it has been heated in the heating section is set to a temperature obtained by subtracting a predetermined second temperature from the temperature of the generated gas after it has passed through the heat exchanger.

5. The fuel production system according to any one of claims 1 to 4, wherein the solid oxide electrolytic apparatus is configured to co-electrolyze the raw material gas containing water vapor and carbon dioxide, and the reactor is configured to synthesize the hydrocarbon using hydrogen produced in the solid oxide electrolytic apparatus and carbon monoxide as carbon oxide as at least part of the raw materials.

6. The reactor comprises multiple such reactors, A fuel production system according to any one of claims 1 to 4, wherein the generated gas from at least one reactor is passed through the heat exchanger to cool it, and the generated gas after passing through the heat exchanger is introduced into the other reactors.

7. The fuel production system according to claim 6, wherein at least one of the reactors is a heat exchange reactor through which water as a heat transfer medium is passed, and steam generated by the evaporation of the water as a heat transfer medium due to heat exchange is supplied to at least one of the reactors.

8. The fuel production system according to any one of claims 1 to 4, wherein the fuel produced is a gas mainly composed of methane.

9. An electrolysis process in a solid oxide type electrolytic apparatus that electrolyzes a raw material gas containing at least water vapor, A reaction step for synthesizing hydrocarbons using carbon oxide and hydrogen produced in the electrolysis step as raw materials, A heat exchange step involves exchanging heat between the product gas, which includes the hydrocarbon and water vapor produced in the reaction step, and liquid water. A condensation separation step in which water vapor contained in the generated gas cooled in the heat exchange step is condensed, The reaction step includes a reactor steam supply step for supplying steam into the reaction system, The pressure of the liquid water is set to a pressure lower than the pressure of the generated gas. In the heat exchange step, at least a portion of the water vapor contained in the generated gas condenses to produce condensed water, and at least a portion of the liquid water vaporizes to produce water vapor. A fuel production method comprising supplying steam to supply at least a portion of the steam generated in the heat exchange step to the electrolysis step.

10. The gas production method according to claim 9, wherein in the heat exchange step, the pressure of the generated gas is 0.5 MPaG or higher, and the pressure of the liquid water is atmospheric pressure or higher.

11. The fuel manufacturing method according to claim 10, further comprising a heating step of heating the liquid water, wherein in the heating step the liquid water is heated to a temperature above the boiling point of the water minus a predetermined first temperature and below the boiling point of the water.

12. The fuel production method according to claim 11, wherein the temperature of the liquid water after heating in the heating step is set to a temperature obtained by subtracting a predetermined second temperature from the temperature of the generated gas after the completion of the heat exchange step.

13. The gas production method according to any one of claims 9 to 12, wherein the electrolysis step is a step of co-electrolyzing the raw material gas containing water vapor and carbon dioxide, and the reaction step is a step of synthesizing the hydrocarbon using hydrogen produced in the electrolysis step and carbon monoxide as carbon oxide as at least part of the raw materials.

14. The reaction process comprises multiple such steps, A fuel production method according to any one of claims 9 to 12, wherein the generated gas produced in at least one of the reaction steps is passed through a heat exchanger in the heat exchange step to cool it, and the generated gas after passing through the heat exchanger is used in the other reaction steps.

15. The fuel production method according to claim 14, wherein at least one of the reaction steps is a reaction step using a heat exchange type reactor through which water as a heat medium is passed, and steam generated by the evaporation of the water as a heat medium due to heat exchange is supplied to at least one of the reaction steps.

16. The fuel production method according to any one of claims 9 to 12, wherein the generated gas from which water vapor has been removed in the condensation separation step is a gas mainly composed of methane.

17. Methane produced by the fuel production method according to any one of claims 9 to 12.

18. Methane produced by the fuel production method described in claim 13.

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