Hydrocarbon Production Systems

Abstract

To provide a hydrocarbon production system that can control stable operation of both a catalytic reactor that produces hydrocarbon and a solid oxide type electrolysis cell that performs high-temperature electrolysis.SOLUTION: A hydrocarbon production system includes a solid oxide type electrolysis cell for producing a gas containing methane, hydrogen and carbon monoxide from a gas containing water vapor and carbon dioxide, a catalytic reactor for producing hydrocarbon from the gas produced in the solid oxide type cell, an evaporator for generating the water vapor using heat generated when the hydrocarbon is produced in the catalytic reactor, and an energy supply unit for directly or indirectly supplying thermal energy for generating the water vapor to the evaporator.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydrocarbon production system. [Background technology]

[0002] To curb global warming, there is a need to reduce carbon dioxide emissions, and there is a demand for the expanded introduction of power generation systems using renewable energy. However, when using renewable energy sources such as solar and wind power, the amount of power generated can fluctuate significantly depending on the weather. For this reason, energy storage is necessary to compensate for these fluctuations. For long-term energy storage, such as for days or months, conversion to chemical energy is useful from the perspective of energy density. Hydrocarbons such as methane, ethane, propane, and methanol are promising candidates for conversion because they have high energy density and well-established infrastructure for storage, transportation, and utilization.

[0003] For example, Patent Document 1 describes heating water with the heat of the methanation reaction and using the heated water as a feedstock for steam electrolysis. Similarly, Non-Patent Document 1 considers a system in which steam is directly generated using the heat of the methanation reaction, the steam is used for steam electrolysis, and the resulting hydrogen is returned to the methanation reactor.

[0004] Furthermore, in Patent Document 2, the methanation reaction process is divided into multiple steps, and the raw material is bypassed to the subsequent reaction step, thereby suppressing the temperature rise. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2015-513531 [Patent Document 2] Japanese Patent Application Publication No. 2018-135283 [Non-patent literature]

[0006] [Non-Patent Document 1] Fuel Processing Technology Volume 181(1 December,2018) page 61 Summary of the Invention [Problem to be solved by the invention]

[0007] Although the conventional technology described in Patent Document 1 improves energy efficiency, heat and materials circulate between the steam electrolysis device and the reactor that converts to methane, making it difficult to control the stable operation of the steam electrolysis device and the reactor. Non-Patent Document 1 also reports that it becomes difficult to control the stable operation of the steam electrolysis device and the reactor when they are connected. As shown in the following formulas (1) to (4), the heat of reaction in the reactor and the latent heat of vaporization of the raw material steam become closer in value as hydrocarbons with lower molecular weights are produced, and the amount of energy adjustment decreases.

[0008] Therefore, if the amount of heat recovered in the reactor fluctuates due to fluctuations in the operating state of the reactor, the fluctuations in the amount of heat recovered are not adjusted, and the amount of steam generated is significantly affected. As a result, the amount of H generated in the steam electrolysis device fluctuates, which further fluctuates the operating state of the reactor to which H is supplied. Once such fluctuations in the operating state occur, it becomes difficult to control the stable operation of the steam electrolysis device and the reactor. CO2+4H2→CH4+2H2O(g) ΔH=-165kJ / mol (1) 4H2O(l)→4H2O(g) ΔH= 176kJ / mol (2) 2CO2+7H2→C2H6+4H2O(g) ΔH=-265kJ / mol (3) 7H2O(l)→7H2O(g) ΔH= 308kJ / mol (4)

[0009] Furthermore, in the conventional technology described in Patent Document 2, the reaction process is divided into multiple steps, which makes it difficult to stabilize the amount of heat recovered from the multiple steps.

[0010] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a hydrocarbon production system that enables stable control of the operation of both a catalytic reactor that produces hydrocarbons and a solid oxide electrolysis cell that performs high-temperature electrolysis. [Means for solving the problem]

[0011] In order to achieve the above object, the hydrocarbon production system according to the present invention is characterized by comprising: a solid oxide electrolysis cell that produces a gas containing methane, hydrogen, and carbon monoxide from a gas containing water vapor and carbon dioxide; a catalytic reactor that produces hydrocarbons from the gas produced in the solid oxide electrolysis cell; an evaporator that generates the water vapor by utilizing heat generated when the hydrocarbons are produced in the catalytic reactor; and an energy supply device that directly or indirectly supplies thermal energy for producing the water vapor to the evaporator. [Effects of the Invention]

[0012] According to the hydrocarbon production system of the present invention, it is possible to control the stable operation of the catalytic reactor and the solid oxide electrolysis cell. Other problems, configurations, and effects will become clear from the description of the following embodiments. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram of a hydrocarbon production system according to a first embodiment. [Figure 2] Equilibrium composition diagram of the raw gas with CO2:H2=1:4. [Figure 3] FIG. 10 is a block diagram of a hydrocarbon production system according to a second embodiment. [Figure 4] FIG. 10 is a block diagram of a hydrocarbon production system according to a modified example. [Figure 5] FIG. 1 is a block diagram of a hydrocarbon production system according to an embodiment. [Figure 6] FIG. 2 is a block diagram of a hydrocarbon production system according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that components with the same reference numerals in each embodiment have the same functions in each embodiment unless otherwise specified, and description thereof will be omitted.

[0015] First Embodiment A hydrocarbon production system 1A according to the first embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram showing a schematic configuration of the hydrocarbon production system 1A according to the first embodiment of the present invention.

[0016] As shown in FIG. 1, a hydrocarbon production system 1A according to this embodiment includes an SOEC (solid oxide electrolysis cell) 10, a catalytic reactor 20, an evaporator 30, and an energy supply device 40.

[0017] The hydrocarbon production system 1A has a heat medium passage 50 that circulates a heat medium between the catalytic reactor 20 and the evaporator 30. The heat medium passage 50 has a first heat medium passage 52 that transports the heat medium from the catalytic reactor 20 to the evaporator 30, and a second heat medium passage 54 that transports the heat medium from the evaporator 30 to the catalytic reactor 20. A heat medium pump 95 is provided in the heat medium passage 50, and the heat medium is circulated through the heat medium passage 50 by driving the heat medium pump 95.

[0018] The hydrocarbon production system 1A also includes a steam supply pipe (supply pipe) 70 that supplies steam from the evaporator 30 to the SOEC 10, a water supply pipe 71 that supplies water to the evaporator 30, a gas supply pipe 72 that supplies gas from the SOEC 10 to the catalytic reactor 20, a carbon dioxide supply pipe 74 that supplies carbon dioxide (CO2) to the steam supply pipe 70, a hydrocarbon transfer pipe 76 that removes the hydrocarbons produced in the catalytic reactor 20 from the system, and a water transfer pipe 77 that transfers the water separated in the first condenser 90.

[0019] The catalytic reactor 20 produces hydrocarbons from the gas (i.e., gas containing methane, hydrogen, carbon monoxide, and carbon dioxide) produced in the SOEC 10. For example, the Sabatier reaction is known as a methanation reaction for producing methane synthesized from carbon dioxide and hydrogen, and is represented by the above-mentioned reaction formula (1).

[0020] As shown in Figure 1, the catalytic reactor 20 has a catalyst bed 22 filled with a catalyst and a cooling bed 24 adjacent to but isolated from the catalyst bed 22. The Sabatier reaction is an exothermic, volume-reducing reaction, and therefore the reaction is more likely to proceed at low temperatures and high pressures. The catalyst bed 22 is usually cooled by the cooling bed 24 so that the reaction temperature is around 300°C.

[0021] Gases containing hydrogen, carbon dioxide, and the like are supplied to the catalyst layer 22. In the catalyst layer 22, hydrocarbon production reactions proceed based on the reactions of the above-mentioned reaction formulas (1) and (3), etc. Various materials can be selected for the catalyst packed into the catalyst layer 22 depending on the target hydrocarbon species. For example, Ru, Ni, Cu, etc. can be selected for the active metal, and Al2O3, SiO2, CeO2, ZrO2, etc. can be selected for the active metal support. Furthermore, the catalyst shape can be selected from honeycomb type, pellet type, etc.

[0022] 1, the first condenser 90 and a separator (not shown) separate components other than hydrocarbons, such as water, from the gas reacted in the catalyst layer 22. The water transport pipe 77 transports the separated water, for example, to the outside of the hydrocarbon production system 1A. When water is used to separate components other than hydrocarbons from the gas supplied to the first condenser 90, the water heated by heat exchange in the first condenser 90 may be supplied to the evaporator 30.

[0023] Furthermore, hydrocarbons such as CH4 produced in catalyst layer 22 pass through a pressure adjustment means such as a back pressure valve 93 provided in hydrocarbon transport pipe 76 and are extracted as products. Back pressure valve 93 adjusts the internal pressure of SOEC 10. Note that after the gas reacted in catalyst layer 22 passes through first condenser 90 and a separator (not shown), the gas may be further reacted in a second catalytic reactor (not shown) to produce hydrocarbons. Furthermore, components other than the separated hydrocarbons (for example, water extracted through water transport pipe 77) may be reused.

[0024] A heat transfer medium is supplied to the cooling layer 24 through the second heat transfer medium flow path 54, and the heat generated in the catalyst layer 22 is absorbed by the heat transfer medium in the cooling layer 24, thereby cooling the catalyst layer 22. Various types of heat transfer medium can be selected for the heat transfer medium supplied to the cooling layer 24, such as heat transfer oil or high-pressure water. In this embodiment, water pressurized to a pressure higher than atmospheric pressure is called high-pressure water. When high-pressure water is selected as the heat transfer medium, it is easier to control the pressure of the heat transfer medium circulating through the heat transfer medium flow path 50 compared to when heat transfer oil is selected. In addition, high-pressure water can be handled more safely because there is no risk of combustion. Various shapes can be selected for the catalytic reactor 20, such as a shell-and-tube type or a plate type.

[0025] The evaporator 30 heats water and generates steam by utilizing heat generated when hydrocarbons are produced in the catalytic reactor 20. The evaporator 30 has an evaporation layer 34 in which water evaporates, and a heating layer 32 that is adjacent to but isolated from the evaporation layer 34. Water is supplied to the evaporation layer 34 through a water supply pipe 71 by driving a water pump 94, and the heat medium that has passed through the cooling layer 24 is supplied to the heating layer 32 through a first heat medium flow path 52. The shape of the evaporator 30 can be selected from a variety of shapes, such as a shell-and-tube type or a plate type.

[0026] The energy supply device 40 is provided in the first heat medium passage 52. The energy supply device 40 supplies thermal energy to the heat medium supplied from the catalytic reactor 20 to the evaporator 30 through the first heat medium passage 52, thereby heating the heat medium. In other words, the energy supply device 40 indirectly supplies thermal energy to the evaporator 30 via the heat medium. The energy supply device 40 may heat the heat medium from outside the first heat medium passage 52, or may heat the heat medium from inside the first heat medium passage 52. The energy supply device 40 can be selected from various types, such as an electric heater or a heat exchanger.

[0027] An additional energy supply device other than the energy supply device 40 may be installed in the second heat medium flow path 54 between the outlet of the evaporator 30 and the inlet of the catalytic reactor 20. For example, the optimum lower temperature limit for a Ni-based methanation catalyst is 200 to 250°C, and the boiling point of water at 1.0 MPa is approximately 180°C. For this reason, the heat medium temperature on the outlet side of the evaporator 30 may fall below the optimum lower temperature limit for the catalyst layer 22 of the catalytic reactor 20. In this case, the temperature of the heat medium can be adjusted by the additional energy supply device installed in the second heat medium flow path 54 so that the temperature exceeds the optimum lower temperature limit for the catalyst layer 22.

[0028] The SOEC 10 produces a gas containing methane, hydrogen, and carbon monoxide from a gas containing water vapor and carbon dioxide. The SOEC 10 is supplied with water vapor generated in the evaporator 30 and CO2 transported through a carbon dioxide supply pipe 74. The mixing ratio of water vapor to CO2 can be selected according to the target hydrocarbon. From the viewpoint of suppressing carbon deposition in the SOEC 10, the ratio of the supply amounts of water vapor and CO2 (water vapor / CO2) is preferably 3 or more, and more preferably 3.5 or more.

[0029] The SOEC 10 operates at high temperatures of 500 to 1000°C and is capable of electrolyzing gas containing water vapor and CO2 as raw materials. The SOEC 10 may be preheated by heat exchange of the inlet gas with the outlet gas of the anode and cathode, or may be heated by a heater or the like.

[0030] SOEC10 electrolyzes steam, which has a higher energy state than water, so it requires less energy for electrolysis and operates at high temperatures, resulting in low reaction resistance.For this reason, steam electrolysis using SOEC10 is more energy efficient than water electrolysis.

[0031] Various types of cells can be selected for the SOEC 10. For example, shapes such as flat plate, cylindrical, and flattened cylindrical can be selected. The SOEC 10 has supports such as an electrolyte support, a cathode support, an anode support, and a metal support. The constituent materials of the SOEC 10 can also be selected arbitrarily. A cermet of Ni and electrolyte is generally used as the anode, and a reducing gas must be supplied to the anode to prevent oxidation of the Ni. In the hydrocarbon production system 1A according to this embodiment, a portion of the hydrocarbon product is recycled and mixed with CO2 (not shown). The operating temperature of the SOEC 10 can be selected arbitrarily according to the constituent materials and cell shape. From the viewpoints of the CH4 concentration at equilibrium and heat radiation suppression, a temperature of 800°C or less is desirable.

[0032] The hydrocarbon production system 1A according to this embodiment has a control device (not shown) that controls the value of the current supplied to the SOEC 10. Therefore, by changing the value of the current supplied to the SOEC 10 by the control device, the amount of electrochemical reaction in the SOEC 10 can be controlled.

[0033] When the amount of steam supplied to the SOEC 10 decreases, it is necessary to reduce the current supplied to the SOEC 10 in order to prevent a shortage of H2O and CO2. This reduces the amount of gas supplied to the catalytic reactor 20, and the amount of heat generated in the catalytic reactor 20. This also reduces the amount of heat recovered by the heat transfer medium, further reducing the amount of steam supplied to the SOEC 10.

[0034] In addition to water vapor and carbon dioxide, hydrogen, carbon monoxide, methane, and other hydrocarbons may be supplied to the anode of the SOEC 10. At the anode, electrochemical reactions occur as shown in the following equations (5) and (6). H2O+2e - →H2+O 2-(5) CO2+2e - →CO+O 2- (6)

[0035] Furthermore, on the electrode surface of the SOEC 10, the reactions shown in the following formulas (7), (8), and (9) occur. H2+CO2→CO+H2O(7) CO+3H2→CH4+H2O(8) 2CO → C + CO2(9)

[0036] Figure 2 shows the equilibrium composition of the feed gas at CO2:H2 = 1:4. In Figure 2, the horizontal axis shows the temperature of the SOEC 10, and the vertical axis shows the amount of CH4 generated in the SOEC 10 when the feed gas composition is CO2:H2 = 1:4. Figure 2 shows the amount of CH4 generated depending on the pressure (0.1 MPa, 0.3 MPa, 1.0 MPa) of the feed gas supplied to the SOEC 10.

[0037] As shown in FIG. 2, even at the operating temperature of the SOEC 10 (approximately 600°C to approximately 800°C), CH4 can be produced by the reactions of formulas (1) and (8) under high-pressure conditions higher than atmospheric pressure (0.1 MPa). The conversion rate of CO2 in the feed gas supplied to the SOEC 10 to CH4 is preferably 15% or higher, and more preferably 30% or higher. The reactions of formulas (1) and (8) are exothermic reactions, and the thermal neutral voltage in the SOEC 10 decreases by the amount of thermal energy generated, allowing for reduced electrolysis power. From the perspective of increasing the amount of CH4 produced at equilibrium, the reaction pressure in the SOEC 10 is preferably higher than atmospheric pressure (0.1 MPa), preferably 0.3 MPa or higher, and more preferably 1.0 MPa or higher. The absolute pressure of the gas supplied to the SOEC 10 is adjusted by a back-pressure valve 93 installed in the hydrocarbon transport pipe 76.

[0038] As shown in FIG. 1, the hydrocarbon production system 1A includes a pressure vessel 80 that houses an SOEC 10. The pressure vessel 80 maintains the internal pressure of the pressure vessel 80 so that it is equal to the pressure of the gas supplied to the SOEC 10. From the viewpoint of suppressing gas leakage from the SOEC 10 and reducing stress on the SOEC 10, it is desirable to install the stack of the SOEC 10 inside the pressure vessel 80 and reduce the differential pressure between the SOEC 10 and the pressure vessel 80 as much as possible. The allowable range of the differential pressure depends on the gas seal structure, the material of the sealant, the cell strength, etc., and can be designed as appropriate.

[0039] Carbon deposition due to the disproportionation reaction shown in formula (9) above leads to electrode degradation. Therefore, it is necessary to control the gas composition, gas flow rate, current value, etc. so that carbon deposition does not occur at equilibrium at the composition and temperature of the anode outlet after the reactions of formulas (5) and (6) occur. Specifically, the oxygen atom / carbon atom ratio of the anode outlet gas is preferably 2 or more, and more preferably 3 or more.

[0040] Furthermore, the electrolysis capacity of the SOEC 10 is defined as "(oxygen atom flow rate of the inlet gas) - (carbon atom flow rate of the inlet gas)" relative to the anode inlet gas composition and flow rate. Because the gas flow rate supplied to each cell of the SOEC 10 varies, as does the reaction rate at the anode. Therefore, if a current equivalent to the electrolysis capacity is applied, localized HO and CO shortages may occur, potentially leading to cell degradation or damage. Therefore, the current value should be 90% or less of the electrolysis capacity, more preferably 80% or less. On the other hand, if the electrolysis current is too low, the energy used to preheat the gas to supply it to the SOEC 10 is wasted, resulting in reduced energy efficiency. Therefore, the ratio of the electrolysis current to the electrolysis capacity should be 50% or more, more preferably 70% or more. To prevent carbon deposition and HO and CO shortages, it is necessary to control the current and the gas composition supplied.

[0041] The atmosphere at the cathode of the SOEC 10 must be kept oxidizing to prevent reduction of the cathode material. For example, air or oxygen can be supplied, and gas does not need to be supplied during the electrolysis reaction. The electrical connection (number of series or parallel connections) of multiple cells used in the SOEC 10 can be set as desired.

[0042] The gas containing CH4, H2, and CO generated at the anode of the SOEC 10 is supplied to the catalytic reactor 20. The gas may be supplied directly to the catalytic reactor 20, or may be supplied after adjusting the gas composition. For example, removing H2O using a condenser (not shown) is desirable because it facilitates the reaction of formula (1). To reduce the element ratio H / C in the gas supplied to the catalytic reactor 20, additional CO2 may be supplied, or CH4 may be separated.

[0043] As shown in FIG. 1, the hydrocarbon production system 1A includes a first detection unit (detection unit) 60 provided in the first heat medium flow path 52, and a control unit 64 that controls the operation of the energy supply device 40 based on information detected by the first detection unit 60.

[0044] The first detection unit 60 detects the thermal energy of the heat medium supplied to the evaporator 30. Specifically, the first detection unit 60 detects at least one of the temperature and flow rate of the heat medium as the thermal energy of the heat medium. In other words, the first detection unit 60 detects the temperature and flow rate of the heat medium at the inlet side (first heat medium flow path 52) of the evaporator 30 after being heated in the cooling layer 24 of the catalytic reactor 20. Various types of first detection unit 60 can be selected.

[0045] The detection information of the first detection unit 60 is transmitted to the control unit 64. The control unit 64 controls the amount of thermal energy supplied by the energy supply device 40 based on the information from the first detection unit 60. Specifically, the control unit 64 controls the amount of thermal energy supplied by the energy supply device 40 so that the flow rate of water vapor supplied from the evaporator 30 to the SOEC 10 falls within a desired range. The control unit 64 calculates the thermal energy to be supplied from the heat medium to the evaporator 30 based on the temperature and flow rate of the heat medium and the specific heat of the heat medium obtained in advance, and controls the amount of thermal energy supplied by the energy supply device 40 so that the thermal energy falls within a desired range.

[0046] By controlling the thermal energy supplied to the evaporator 30 within a desired range, the flow rate of the steam supplied to the SOEC 10 falls within a desired range. As a result, even if the amount of heat recovered from the catalytic reactor 20 by the heat transfer medium fluctuates, the thermal energy required to replenish the reduced amount of heat recovered due to the fluctuation can be accurately calculated based on the temperature of the heat transfer medium actually flowing through the first heat transfer medium flow path 52, etc. Therefore, it is possible to prevent excessive supply of thermal energy by the energy supply device 40, thereby improving energy efficiency and stabilizing the amount of steam generated.

[0047] Furthermore, the control unit 64 controls the energy supply device 40 to continue supplying thermal energy while the system is operating. This increases the steady-state amount of thermal energy supplied by the energy supply device 40. Therefore, when the amount of thermal energy supplied by the energy supply device 40 is varied in response to fluctuations in the amount of heat recovered from the catalytic reactor 20 by the heat transfer medium, the proportion of the fluctuation to the steady-state amount of thermal energy supplied decreases. When the proportion of the fluctuation to the steady-state amount of thermal energy supplied decreases, the response delay due to the influence of the heat capacity of the energy supply device 40 (i.e., the delay in the time it takes for the energy supply device 40 to actually supply heat to the heat transfer medium) can be reduced, enabling stable control of the amount of water vapor generated. Of the thermal energy steadily supplied to the evaporator 30, the proportion of energy supplied from the energy supply device 40 is desirably 15% or more, and more desirably 30% or more.

[0048] Furthermore, the hydrocarbon production system 1A may have a second detection unit 62 provided in the second heat medium passage 54, in addition to the first detection unit 60. The second detection unit 62 detects at least one of the temperature and flow rate of the heat medium as the thermal energy of the heat medium. In other words, the second detection unit 62 detects the temperature and flow rate of the heat medium in the second heat medium passage 54, after the heat medium has passed through the heating layer 32 of the evaporator 30.

[0049] The detection information of the second detector 62 is transmitted to the controller 64. Based on the information from the first detector 60 and the second detector 62, the controller 64 controls the amount of thermal energy supplied by the energy supply device 40 so that the flow rate of the water vapor supplied from the evaporator 30 to the SOEC 10 is within a desired range. For example, the controller 64 compares the temperature of the heat medium flowing through the first heat medium passage 52 with the temperature of the heat medium flowing through the second heat medium passage 54, and calculates the thermal energy supplied to the evaporator 30 from the difference between the temperatures. Note that the controller 64 may also compare the flow rates of the heat medium flowing through the first heat medium passage 52 and the second heat medium passage 54 in addition to the temperature of the heat medium, and calculate the thermal energy supplied to the evaporator 30 from the temperature difference and the flow rate difference. This allows for more accurate calculation of the thermal energy supplied to the evaporator 30.

[0050] According to the hydrocarbon production system 1A of this embodiment, heat is supplied to the heat transfer medium by the energy supply device 40. Therefore, even if the amount of heat absorbed by the heat transfer medium in the cooling layer 24 decreases due to fluctuations in the operating state of the catalytic reactor 20, the decreased amount of heat can be replenished by the energy supply device 40. This prevents a decrease in the amount of heat of the heat transfer medium supplied to the heating layer 32 of the evaporator 30, and prevents a decrease in the amount of steam supplied from the evaporation layer 34 of the evaporator 30 to the SOEC 10. As a result, a decrease in the amount of gas generated in the SOEC 10 is prevented. Therefore, even if the operating state of the catalytic reactor 20 fluctuates, a decrease in the amount of gas supplied from the SOEC 10 to the catalytic reactor 20 is prevented, and therefore the operations of the catalytic reactor 20 and the SOEC 10 can be stably controlled.

[0051] Furthermore, by operating the SOEC 10 under high pressure and with CO2 supplied, methane is generated in the SOEC 10. Because methane is generated in the SOEC 10, even if the catalyst layer 22 of the catalytic reactor 20 is downsized to reduce the amount of methane generated in the catalytic reactor 20, a decrease in the amount of methane produced in the hydrocarbon production system 1A can be avoided. In this way, a compact catalytic reactor 20 can be provided without reducing the amount of methane produced. Furthermore, because the catalytic reactor 20 is downsized and the amount of heat generated in the catalytic reactor 20 is reduced, it is easier to suppress temperature increases that cause catalyst degradation, and the catalyst life can be extended.

[0052] Furthermore, the methanation reactions of formulas (1) and (8) are exothermic reactions, and the thermoneutral voltage in the SOEC 10 decreases by the amount of the generated thermal energy, thereby enabling a reduction in the electrolysis power. Because the electrolysis power in the SOEC 10 is reduced, a decrease in the energy efficiency of the hydrocarbon production system 1A can be avoided even if the steady energy supply amount from the energy supply device 40 increases.

[0053] Furthermore, since the steady-state amount of thermal energy supplied by the energy supply device 40 increases, the ratio of the amount of fluctuation to the steady-state amount of thermal energy supplied decreases when the amount of energy supplied by the energy supply device 40 is varied as a means for adjusting for fluctuations in the amount of heat recovered from the catalytic reactor 20. When the ratio of the amount of fluctuation to the steady-state amount of thermal energy supplied is small, it is possible to reduce the response delay caused by the influence of the heat capacity of the energy supply device 40, and it becomes possible to stabilize the amount of water vapor evaporation.

[0054] Furthermore, when the system is started up, the heated heat medium can be circulated through the heat medium flow path 50 by driving the heat medium pump 95 and the energy supply device 40. This makes it possible to warm up the catalytic reactor 20 and the evaporator 30 simultaneously, enabling the hydrocarbon production system 1A to be started up more quickly.

[0055] Second Embodiment Next, a hydrocarbon production system 1B according to a second embodiment of the present invention will be described with reference to Fig. 3. Fig. 3 is a block diagram showing a schematic configuration of the hydrocarbon production system 1B according to the second embodiment of the present invention. In the hydrocarbon production system 1B according to the second embodiment, the same configurations and operations as those of the hydrocarbon production system 1A according to the first embodiment are denoted by the same reference numerals, and descriptions thereof will be omitted. The hydrocarbon production system 1B according to the second embodiment differs from the hydrocarbon production system 1A according to the first embodiment in that the evaporator 30 has a first evaporator 36 and a second evaporator 38, that the energy supply device 40 supplies thermal energy to the second evaporator 38, that the second evaporator 38 generates water vapor, and that the first detection unit 60 detects the flow rate of water vapor supplied to the SOEC 10.

[0056] As shown in FIG. 3 , the evaporator 30 of the hydrocarbon production system 1B according to this embodiment includes a first evaporator 36 that generates steam by utilizing heat generated when hydrocarbons are produced in the catalytic reactor 20, and a second evaporator 38 that generates steam by utilizing thermal energy supplied by an energy supply device 40.

[0057] Water is supplied to the first evaporator 36 through the water supply pipe 71 by driving a water pump 94, and the first evaporator 36 can generate steam using heat from the catalytic reactor 20. Water is supplied to the second evaporator 38 through the water supply pipe 71A by driving a water pump 94A, and the second evaporator 38 can generate steam using thermal energy from the energy supply device 40. The energy supply device 40 directly supplies thermal energy to the second evaporator 38.

[0058] The first evaporator 36 and the second evaporator 38 supply the generated steam to a steam supply pipe 70. The first evaporator 36 is integrated with the catalytic reactor 20, and the first evaporator 36 and the catalytic reactor 20 directly exchange heat. This makes it possible to cool the catalytic reactor 20 with a high heat flux. Furthermore, since the heat medium passage 50 is not required, the hydrocarbon production system 1B can have a simple and compact configuration. The second evaporator 38 may be located close to the first evaporator 36 or may be separate from it.

[0059] The first detection unit 60 detects the flow rate of water vapor flowing through the water vapor supply pipe 70, i.e., the total flow rate of water vapor supplied to the SOEC 10. The control unit 64 controls the amount of thermal energy supplied by the energy supply device 40 based on the detection information (water vapor flow rate) from the first detection unit 60 so that the flow rate of water vapor flowing through the water vapor supply pipe 70 falls within a desired range. In this way, the control unit 64 stably controls the amount of water vapor supplied to the SOEC 10.

[0060] Typically, an evaporator has a higher heat capacity than a heat transfer medium, so even if thermal energy is supplied to the second evaporator 38 by the energy supply device 40, it may take a long time to obtain the desired water vapor flow rate. For this reason, the water vapor flow rate may be measured by the first detection unit 60, and the control unit 64 may control (increase) the amount of thermal energy supplied by the energy supply device 40, taking into account the time lag between the thermal energy supplied to the second evaporator 38 and the water vapor flow rate.

[0061] As with the hydrocarbon production system 1A of the first embodiment, the hydrocarbon production system 1B of this embodiment can reduce the heat value of the catalytic reactor 20 while increasing the steady-state amount of steam generated in the second evaporator 38. Therefore, when the amount of steam generated in the second evaporator 38 is varied to suppress fluctuations in the amount of steam supplied to the SOEC 10, the ratio of the amount of steam fluctuation to the steady-state amount of steam generation decreases. This reduces the response delay (the time delay between when thermal energy is supplied to the second evaporator 38 by the energy supply device 40 and when a desired steam flow rate is obtained) caused by the influence of the heat capacity of the second evaporator 38, enabling stable control of the amount of steam supplied to the SOEC 10. It is desirable that the proportion of the amount of steam steadily supplied to the SOEC 10 supplied from the second evaporator 38 be 15% or more, and more preferably 30% or more.

[0062] <Modification> Next, a hydrocarbon production system 1C according to a modified example of the first embodiment of the present invention will be described with reference to Fig. 4. Fig. 4 is a block diagram showing a schematic configuration of the hydrocarbon production system 1C according to a modified example of the first embodiment of the present invention. In the hydrocarbon production system 1C according to this modified example, the same components and operations as those of the hydrocarbon production system 1A according to the first embodiment are denoted by the same reference numerals, and their description will be omitted. The hydrocarbon production system 1C according to this modified example differs from the hydrocarbon production system 1A according to the first embodiment in that the gas supply piping 72 includes a second condenser 91 and a CH4 separator 96, and the ratio of the gas composition supplied to the SOEC 10 is water vapor amount / carbon dioxide < 4.

[0063] In FIG. 4, the ratio of the gas composition supplied to the SOEC 10 is set to water vapor / carbon dioxide < 4, and the gas supply pipe 72 has a second condenser 91 and a CH4 separator 96, so that the H / C ratio of the gas supplied to the catalytic reactor 20 can be reduced.

[0064] In order to produce high molecular weight hydrocarbons such as CH and CH, the H / C ratio of the gas supplied to the catalytic reactor 20 must be low. However, as described above, supplying a gas with a low H / C ratio, i.e., a gas with a low water vapor / carbon dioxide ratio, to the SOEC 10 may result in carbon deposition within the SOEC 10. In the hydrocarbon production system 1C according to this modification, CH and water are separated in the gas supply pipe 72 on the outlet side of the SOEC 10. This allows the gas supplied to the catalytic reactor 20 to be adjusted to an H / C ratio suitable for producing high molecular weight hydrocarbons such as CH and CH, and these high molecular weight hydrocarbons can be extracted as products. The CH separated in the separator 96 can also be used as a product.

[0065] The present invention will be described with reference to the following examples. Fig. 5 is a block diagram showing a schematic configuration of a hydrocarbon production system according to an example of the present invention. Fig. 6 is a block diagram showing a schematic configuration of a hydrocarbon production system according to a comparative example of the present invention. In a hydrocarbon production system 1D according to this example and a hydrocarbon production system 1E according to a comparative example, the same components and operations as those in the hydrocarbon production system 1A according to the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0066] [Example] In this example, a hydrocarbon production system 1D having a configuration as shown in Fig. 5 was used. High-pressure water was used as the heat medium, and a heat medium flow path 50 was installed to circulate the water from the outlet of the catalytic reactor 20 to the inlet of the catalytic reactor 20. In addition, a high-pressure water pressure regulator 98 was installed in the heat medium flow path 50, and the pressure of the high-pressure water was adjusted to approximately 10 MPa.

[0067] A first heater 42 was installed as the energy supply device 40 in the heat medium flow path 50 (first heat medium flow path 52) on the inlet side of the evaporator 30, and the temperature and flow rate of the heat medium in the first heat medium flow path 52 were measured by a first detection unit 60. In addition, a second heater 44 was installed in the heat medium flow path 50 (second heat medium flow path 54) on the outlet side of the evaporator 30, and the heat medium temperature at the inlet of the catalytic reactor 20 was adjusted to 240°C.

[0068] Another catalytic reactor 20A and a third condenser 92 were installed downstream of the first condenser 90 to adjust the gas composition.

[0069] The catalyst layer 22 of the catalytic reactor 20 was filled with Ni-Al2O3 catalyst, and the catalyst layer of another catalytic reactor 20A was filled with Ru-Al2O3 catalyst.

[0070] The pressure in the gas supply pipe 72 was adjusted using the back pressure valve 93 so that the pressure in the SOEC 10 was 1.0 MPa. The pressure in the pressure vessel 80 was also adjusted to be the same as the pressure in the SOEC 10.

[0071] Carbon dioxide (CO2) flow rate 4m 3 / h was supplied to the steam supply pipe 70 through the carbon dioxide supply pipe 74, where it was mixed with the steam generated in the evaporator 30 and supplied to the SOEC 10 at about 200°C. The water supplied to the evaporator 30 was water that had been supplied to the first condenser 90 and the third condenser 92 and heated by heat exchange with the gas.

[0072] The supply gas and the generated gas were heat exchanged in a heat exchanger inside the SOEC 10, and the supply gas was heated to the cell operating temperature of 700°C by a third heater 46 before being supplied to the cell stack. The average output of the third heater 46 was 2.7 kW. The cell stack had an electrode area of ​​121 cm. 2 It consists of 800 cells and has a current density of 0.4A / cm 2 Electrolysis was performed at an electrolysis voltage of 1.20 V and 46.0 kW per cell. The ratio of the electrolysis current to the amount of electrolysis possible was 80%. The gas produced at the fuel electrode of the SOEC 10 was cooled to 50°C in the second condenser 91 and condensed, and then preheated to 250°C by heat exchange with the outlet gas of the SOEC 10 and supplied to the catalytic reactor 20.

[0073] The gas composition at the outlet of the second condenser 91 was 63% hydrogen, 1% water vapor, 8% carbon monoxide, 10% carbon dioxide, and 18% methane.

[0074] In the catalytic reactor 20, the flow rate of high-pressure water in the cooling layer 24 was controlled using a heat transfer medium pump 95 and a pressure regulator 98 so that the outlet gas of the catalyst layer 22 would be 300°C or less. The amount of heat recovered by the heat transfer medium in the catalytic reactor 20 was 5.1 kW on average. The output of the first heater 42 used to adjust the temperature of the heat transfer medium was 3.1 kW on average, and approximately 38% of the heat consumed by the evaporator 30 was from the first heater 42. The second heater 44 was not used during steady state operation.

[0075] The outlet gas of the catalyst layer 22 of the catalytic reactor 20 was cooled to 50°C in the first condenser 90 and condensed, and then heat-exchanged with the outlet gas of the catalyst layer 22 to preheat it to 200°C or higher, and supplied to another catalytic reactor 20A. The outlet gas of the catalyst layer of the other catalytic reactor 20A was cooled to 50°C in the third condenser 92 and condensed. Thereafter, the gas was pumped through the gas return pipe 73 at a flow rate of 0.4 m / s by using a gas pump 97. 3 / h of the gas was returned as a reducing gas to the inlet of the SOEC10, and the remainder was taken out as a product.

[0076] The gas obtained had a methane (CH4) concentration of 98.3% and a hydrogen (H2) concentration of 0.4%. The combustion heat was 44.2 kW based on the higher heating value. The energy efficiency (= product gas heating value / electricity consumption) was 84%.

[0077] [Comparative Example] In the comparative example, a methanation system having a configuration as shown in Figure 6 was used. The differences from Figure 5 will be mainly explained below.

[0078] The SOEC 10 was not contained in a pressure vessel 80, but was placed under atmospheric pressure of 0.1 MPa. Carbon dioxide (CO2) was supplied at a flow rate of 4 m 3 / h was supplied to the steam supply pipe 70 through the carbon dioxide supply pipe 74, where it was mixed with the steam generated in the evaporator 30 and supplied to the SOEC 10 at about 250°C. The supply gas and the generated gas were heat exchanged in a heat exchanger inside the SOEC 10, and the supply gas was further heated by the third heater 46 to the cell operating temperature of 700°C before being supplied to the cell stack.

[0079] The average output of the third heater 46 was 2.3 kW. The cell stack had an electrode area of ​​121 cm 2 It consists of 640 cells and has a current density of 0.5A / cm 2 Electrolysis was performed at an electrolysis voltage of 1.31 V and 50.3 kW per cell. The ratio of the electrolysis current to the amount of electrolysis possible was 80%. The gas produced at the fuel electrode of the SOEC 10 was introduced into the inlet of the catalyst layer 22 of the catalytic reactor 20 in the same manner as in the examples.

[0080] The gas composition at the outlet of the second condenser 91 was 66% hydrogen, 12% steam, 14% carbon monoxide, 6% carbon dioxide, and 2% methane. The amount of heat recovered by the heat transfer medium in the catalytic reactor 20 was 10.0 kW on average during periods with little fluctuation.

[0081] Neither the first heater 42 nor the second heater 44 was used steadily, but the time average of their intermittent use was 0.3 kW in total, which was about 3% of the heat consumption of the evaporator 30. The gas from the outlet of the catalyst layer 22 of the catalytic reactor 20 was treated in the same manner as in the examples and then extracted as a product.

[0082] The average composition of the product during periods of minimal fluctuation was 85% methane (CH4) and 3% hydrogen (H2), and the combustion heat was 44.3 kW on a higher heating value basis. The energy efficiency was 82%. After startup, the rated output was achieved for a short time, but the voltage of the SOEC10 rose sharply, requiring a reduction in current and other factors, making stable operation at the rated output impossible.

[0083] The produced gas energy and power consumption of the example and the comparative example are shown in Table 1. In the example, the reduction in electrolysis power (4.3 kW) was greater than the increase in output (2.8 kW) of the first heater 42 and the second heater 44 compared to the comparative example, and energy efficiency was improved.

[0084] Table 2 shows the ratio of the first heater 42 and the second heater 44 to the heat quantity of the evaporator 30, and the amount of heat recovered by the heat transfer medium in the catalytic reactor 20, for the Example and the Comparative Example. In the Example, 30% or more of the heat quantity was steadily supplied from the first heater 42 to the evaporator 30, so it is presumed that the amount of water vapor generated in the evaporator 30 was stabilized. In contrast, in the Comparative Example, there was no steady heat supply from the first heater 42 to the evaporator 30, so it is presumed that the amount of water vapor generated in the evaporator 30 could not be stabilized and stable operation at rated capacity was not possible. Furthermore, in the Example, the amount of heat generated in the catalytic reactor 20 (amount of heat recovered by the heat transfer medium) was halved compared to the Comparative Example.

[0085] [Table 1]

[0086] [Table 2]

[0087] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0088] Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be partially or entirely realized by hardware, for example, by designing them as integrated circuits. The above-described configurations, functions, etc. may also be realized by software, in which a processor interprets and executes a program that realizes each function. Information such as the program, tape, and file that realizes each function can be stored in a memory, a recording device such as a hard disk or solid state drive (SSD), or a recording medium such as an IC card, SD card, or DVD.

[0089] In addition, the control lines and information lines shown are those that are considered necessary for the explanation, and do not necessarily show all the control lines and information lines in the product. In reality, it can be assumed that almost all components are interconnected. [Explanation of symbols]

[0090] 1A, 1B, 1C, 1D, 1E Hydrocarbon production system, 10 SOEC (solid oxide electrolysis cell), 20, 20A Catalytic reactor, 30 Evaporator, 36 First evaporator, 38 Second evaporator, 40 Energy supply device, 50 Heat medium flow path, 60 First detection unit (detection unit), 64 Control unit, 70 Steam supply pipe (supply pipe), 80 Pressurized vessel, 93 Back pressure valve (pressure adjustment means)

Claims

1. a solid oxide electrolysis cell that produces a gas containing methane, hydrogen, and carbon monoxide from a gas containing water vapor and carbon dioxide; a catalytic reactor for producing hydrocarbons from the gas produced in the solid oxide electrolysis cell; an evaporator that generates the water vapor by utilizing heat generated when the hydrocarbons are produced in the catalytic reactor; an energy supply device that directly or indirectly supplies, to the evaporator, thermal energy for stabilizing the amount of water vapor generated by the evaporator in addition to the thermal energy supplied from the catalytic reactor to the evaporator; a detector that detects the heat energy supplied to the evaporator; a control unit that controls an amount of thermal energy supplied by the energy supply device based on information from the detection unit so that an amount of the water vapor supplied from the evaporator to the solid oxide electrolysis cell is within a desired range.

2. a heat transfer medium flow path for circulating a heat transfer medium between the catalytic reactor and the evaporator; The hydrocarbon production system according to claim 1 , wherein the energy supply device is provided in the heat transfer medium flow path.

3. The hydrocarbon production system according to claim 2 , wherein the energy supply device supplies the thermal energy to the heat medium supplied from the catalytic reactor to the evaporator.

4. A hydrocarbon production system as described in Claim 3, characterized in that the detection unit detects the thermal energy of the heat transfer medium.

5. The hydrocarbon production system according to claim 4 , wherein the control unit controls the amount of thermal energy supplied by the energy supply device so that the flow rate of the steam falls within a desired range.

6. 6. The hydrocarbon production system according to claim 5, wherein the detection unit detects at least one of a flow rate and a temperature of the heat medium as the thermal energy of the heat medium.

7. 7. The hydrocarbon production system according to claim 6, wherein the heat medium is high-pressure water having a pressure higher than atmospheric pressure.

8. The evaporator comprises: a first evaporator that generates the water vapor by utilizing heat generated when the hydrocarbons are produced in the catalytic reactor; 2. The hydrocarbon production system according to claim 1, further comprising: a second evaporator that generates the steam by utilizing the thermal energy supplied by the energy supply device.

9. a supply pipe that supplies the water vapor generated in the first evaporator and the second evaporator to the solid oxide electrolysis cell; The detection unit detects a flow rate of water vapor flowing through the supply pipe, 9. The hydrocarbon production system according to claim 8, wherein the control unit controls the amount of thermal energy supplied by the energy supply device based on information from the detection unit so that a flow rate of the water vapor flowing through the supply pipe falls within a desired range.

10. 10. The hydrocarbon production system according to claim 4 or 9, wherein the control unit performs control to continue the supply of thermal energy by the energy supply device while the system is operating.

11. a pressurized vessel containing the solid oxide electrolysis cell; 2. The hydrocarbon production system according to claim 1, wherein the internal pressure of the pressurized vessel is maintained equal to the absolute pressure of the gas supplied to the solid oxide electrolysis cell.

12. 12. The hydrocarbon production system according to claim 1, further comprising a pressure adjusting means for adjusting the absolute pressure of the gas supplied to the solid oxide electrolysis cell to a pressure higher than atmospheric pressure.

13. The hydrocarbon production system according to claim 12 , wherein the pressure adjusting means adjusts the absolute pressure of the gas to 0.3 MPa or more.

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