Hydrogen production equipment including solid oxide fuel cell systems

Abstract

To provide a hydrogen production apparatus that can assist a power supply to a water electrolysis hydrogen generator, and economically produce hydrogen while suppressing the amount of emission of a carbon dioxide at the time of hydrogen production.SOLUTION: A hydrogen production apparatus comprises: a water electrolysis hydrogen generator 2 for generating hydrogen and oxygen by water electrolysis; a solid oxide fuel cell system 6 for generating power using a hydrocarbon fuel gas as a raw fuel gas; and a power source controller 18 for controlling a driving power for operating the water electrolysis hydrogen generator 2. The solid oxide fuel cell system 6 comprises: a cell stack for generating power by an electrochemical reaction between a modified fuel gas modified with a hydrocarbon fuel gas and an oxidant gas; and a combustion chamber for burning an anode off-gas from the cell stack. The oxygen generated by the water electrolysis hydrogen generator 2 is delivered to the combustion chamber. The cell generation power generated by the cell stack is delivered to the water electrolysis hydrogen generator 2 through the power source controller 18.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid oxide fuel cell having a cell stack that generates electricity through an electrochemical reaction (fuel cell reaction) between a reformed fuel gas obtained by reforming a fuel gas and an oxidant gas. System included This relates to a hydrogen production device. [Background technology]

[0002] When hydrogen is burned or subjected to an electrochemical reaction (fuel cell reaction) to generate electricity (including hydrogen power generation in fuel cell vehicles), no carbon dioxide (hereinafter also referred to as "CO2") is emitted during the combustion or electrochemical reaction. However, the most common hydrogen production technologies are those that combine the conversion of natural gas into a hydrogen-rich gas using the steam reforming method with gas separation and purification using methods such as the pressure swing method, or those that produce hydrogen as a by-product in the steelmaking process, and these methods result in the emission of carbon dioxide during the production stage.

[0003] For this reason, in recent years, the value of more environmentally friendly hydrogen (hereinafter also referred to as "H2") has been increasing, with attention also being paid to the amount of carbon dioxide emitted during the production stage, and hydrogen with low CO2 emissions, which emits less carbon dioxide during production, is now recognized as having environmental value compared to hydrogen produced by conventional methods.

[0004] Therefore, attention has been focused on a method of producing hydrogen using a water electrolysis hydrogen generator that uses electricity (natural energy-generated electricity) generated by natural energy power generation devices (such as solar power generation devices and wind power generation devices) that utilize natural energy such as sunlight and wind power. Alkaline and solid polymer types of water electrolysis hydrogen generation devices are known, and both are commercially available. Anion exchange membrane water electrolysis and solid oxide steam electrolysis have also been developed as methods of producing hydrogen by electrolysis.

[0005] Due to the high equipment and electricity costs involved in producing hydrogen by water electrolysis, it cannot compete in terms of hydrogen production cost with mainstream methods such as producing hydrogen by reforming natural gas or as a by-product of steelmaking, and is therefore only used in limited applications such as some industrial uses where there is stable local demand for hydrogen, and primarily for technology demonstration purposes. In the long term, it is expected that equipment costs will be reduced through technological development of water electrolysis hydrogen generation equipment, but in the short to medium term, it will be desirable to produce hydrogen cheaply while using expensive water electrolysis hydrogen generation equipment.

[0006] Meanwhile, a known high-efficiency power generation technology for natural gas and other fuels is the solid oxide fuel cell system (hereinafter also referred to as "SOFC system"), which houses a solid oxide cell stack using a solid electrolyte as a membrane that conducts oxide ions in a storage container. In this solid oxide fuel cell system, the cell stack is composed of multiple stacked fuel cells, and each fuel cell has a fuel electrode (anode) on one side of the solid electrolyte and an oxygen electrode (cathode) on the other side. The operating temperature of the cell stack in this solid oxide fuel cell system is high, approximately 700 to 900°C, and at such high temperatures, hydrogen, carbon monoxide, and hydrocarbons in the fuel gas (reformed fuel gas) undergo an electrochemical reaction with oxygen in the air to generate electricity.

[0007] In such SOFC systems, hydrocarbon fuel gas such as natural gas or biofuel gas (a fuel gas composed of a mixture of methane and carbon dioxide) is used as the raw fuel gas. This SOFC system includes a reformer for, for example, steam reforming the hydrocarbon fuel gas, a fuel gas supply means for supplying fuel gas (raw fuel gas) to the reformer, an air supply means for supplying air as an oxidant gas, and a cell stack having a fuel electrode (anode) and an oxygen electrode (cathode), where reformed fuel gas from the reformer is supplied to the fuel electrode of the cell stack, and air from the air supply means is supplied to the oxygen electrode, and power is generated by an electrochemical reaction between the reformed fuel gas and the oxidant gas in the cell stack.

[0008] In this SOFC system, the cell stack and reformer are housed in a high-temperature space, and a high-temperature state is maintained by burning anode off-gas from the fuel electrode (anode) of the cell stack. For example, a combustor is housed in this high-temperature space, and anode off-gas and cathode off-gas from the cell stack are fed to the combustor, and the high-temperature space is maintained at a high temperature by using the combustion heat in the combustor (see, for example, Patent Document 1).

[0009] In such SOFC systems, anode off-gas and cathode off-gas from the cell stack are fed to a combustor and combusted in the combustor, resulting in a combustion exhaust gas containing nitrogen and oxygen in addition to water and carbon dioxide. To recover carbon dioxide from such a combustion exhaust gas, it is necessary to dissolve the carbon dioxide in an alkaline absorption solution and then apply heat to desorb the carbon dioxide (regenerate the absorption solution), which requires thermal energy.

[0010] Furthermore, a method has been proposed that utilizes the high temperature operation of SOFC systems as a method for completely oxidizing anode off-gas from the cell stack of an SOFC system to convert it into water and carbon dioxide (see, for example, Patent Document 2). In this method, an oxygen ion conductor or a mixed conductor that conducts oxygen ions and electrons is used, and the difference in oxygen activity between the anode off-gas and the cathode off-gas causes the oxygen in the cathode off-gas to react with the remaining hydrogen and carbon monoxide in the anode off-gas, resulting in almost complete oxidation, without nitrogen being mixed into the anode off-gas from the cell stack.

[0011] This method using a selectively permeable membrane takes advantage of the high temperature operation of the SOFC system, and because it is driven by the difference in oxygen activity between the anode off-gas and the cathode off-gas, it has the advantage of not proceeding excessively. However, the technological maturity of the selectively permeable membrane is still low, which leads to problems such as high cost and low reliability. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-21596 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-3719 Summary of the Invention [Problem to be solved by the invention]

[0013] When producing hydrogen, using electricity generated by a natural energy power generation device (e.g., a solar power generation device) that utilizes natural energy as the main power source for a water electrolysis hydrogen generation device can reduce the amount of carbon dioxide emitted during hydrogen production, but this creates the problem that the electricity generated by the natural energy power generation device fluctuates depending on natural conditions.

[0014] For example, when a solar power generation system is used, the amount of sunlight that contributes to power generation is small during nighttime hours, rainy or cloudy hours, etc., and the solar power generation system operates with low or almost no power output. Also, when a wind power generation system is used, the wind power that contributes to power generation is weak during times of weak winds, etc., and the wind power that contributes to power generation is weak, and the wind power generation system operates with low or almost no power output.

[0015] When the natural energy power generation device is operating in a low power generation output state, the utilization rate of the hydrogen production equipment is low, making it difficult to produce hydrogen efficiently, resulting in the problem of higher hydrogen production costs.

[0016] It is also possible to use commercial electricity from a grid (commercial power supply) when the power output of a natural energy power generation device (for example, a solar power generation device) is low. However, in such cases, carbon dioxide is emitted when commercial electricity is generated, making it difficult to sufficiently reduce carbon dioxide emissions per unit of hydrogen produced.

[0017] For this reason, when using a natural energy power generation device, it is possible to consider using a secondary battery as an auxiliary means to suppress fluctuations in the power output, but with a solar power generation device, for example, there are long periods of time when the power output is low (at least half a day at night, and even longer periods if it rains), so a secondary battery with a large capacity is required to suppress fluctuations in the power output.This is not a problem for the amount of power needed for a short period of time, such as a few tens of minutes, but when trying to store the power needed for a long period of time, such as several hours, it is not easy to achieve economic viability when considering the cost of the secondary battery.

[0018] An object of the present invention is to provide a hydrogen production device that can assist the supply of power to a water electrolysis hydrogen production device and produce hydrogen economically while minimizing carbon dioxide emissions during hydrogen production. [Means for solving the problem]

[0020] A hydrogen production device according to claim 1 of the present invention comprises a water electrolysis hydrogen generation device that electrolyzes water to generate hydrogen and oxygen, a solid oxide fuel cell system that generates electricity using a hydrocarbon fuel gas as a raw fuel gas, and a power supply controller that controls the driving power for operating the water electrolysis hydrogen generation device, The solid oxide fuel cell system includes a reformer that reforms a raw fuel gas to generate a reformed fuel gas, a cell stack that generates electricity by an electrochemical reaction between the reformed fuel gas from the reformer and an oxidant gas, and a combustor that combusts an anode off-gas from an anode of the cell stack, The oxygen produced in the water electrolysis hydrogen generation apparatus is supplied to the combustor through an oxygen supply line, and the battery-generated power generated in the cell stack is supplied to the water electrolysis hydrogen generation apparatus via the power supply controller.

[0021] In addition, in the hydrogen production device according to claim 2 of the present invention, the rated power output of the solid oxide fuel cell system is 30% or less of the rated power consumption of the water electrolysis hydrogen generation device.

[0022] In addition, in the hydrogen production device described in claim 3 of the present invention, the power generated from a natural energy power generation device that generates power using natural energy, commercial power supply from a grid power source, and the cell-generated power from the solid oxide fuel cell system are supplied to the power supply controller, and the power supply controller preferentially supplies the natural energy-generated power and the cell-generated power to the water electrolysis hydrogen production device.

[0023] In addition, in the hydrogen production apparatus described in claim 4 of the present invention, the solid oxide fuel cell system further includes a condenser that condenses moisture contained in the combustion exhaust gas from the combustor, a gas-liquid separator that separates the condensed water condensed in the condenser, and an exhaust gas recovery and purification line that recovers and purifies the combustion exhaust gas from which the condensed water has been separated by the gas-liquid separator, and carbon dioxide is recovered and purified through the exhaust gas recovery and purification line. [Effects of the Invention]

[0026] According to a first aspect of the present invention, a hydrogen production apparatus includes a water electrolysis hydrogen generator that electrolyzes water to produce hydrogen and oxygen, a solid oxide fuel cell system that generates electricity using a hydrocarbon fuel gas as a raw fuel gas, and a power supply controller that controls the driving power supplied to the water electrolysis hydrogen generator. The oxygen produced in the water electrolysis hydrogen generator is supplied to a combustor of the solid oxide fuel cell system through an oxygen supply line, and the oxygen generated in the water electrolysis hydrogen generator can be supplied to this combustor and effectively used for combustion of anode off-gas. Furthermore, the battery-generated power generated in the cell stack is supplied to the water electrolysis hydrogen generator via the power supply controller, and the power generated in the cell stack can be used as part of the driving power for the water electrolysis hydrogen generator, thereby increasing the driving power of the water electrolysis hydrogen generator and improving its capacity utilization rate.

[0027] Furthermore, according to the hydrogen production device of the present invention, the rated power output of the solid oxide fuel cell system is 30% or less of the rated power consumption of the water electrolysis hydrogen generation device, so that the water electrolysis hydrogen generation device can be operated with an effective facility utilization rate.

[0028] Furthermore, according to the hydrogen production device of the present invention, natural energy-generated power from a natural energy power generation device that generates power using natural energy, commercial power supply from a grid power source, and battery-generated power from a solid oxide fuel cell system are supplied to a power supply controller, and the power supply controller preferentially supplies the natural energy-generated power and battery-generated power to the water electrolysis hydrogen production device, thereby reducing consumption of commercial power supply from the grid power source and reducing carbon dioxide emissions during hydrogen production. Note that natural energy power generation devices include solar power generation devices that use sunlight and wind power generation devices that use wind power.

[0029] Furthermore, according to the hydrogen production device of the present invention, the combustion exhaust gas from the combustor of the solid oxide fuel cell system is fed to a condenser and a gas-liquid separator, the moisture in the combustion exhaust gas is condensed in the condenser, and the condensed water is separated in the gas-liquid separator, after which it is recovered and purified through the exhaust gas recovery and purification line, thereby reducing carbon dioxide emissions from this solid oxide fuel cell system.

[0030] The solid oxide fuel cell system using this hydrogen production device uses hydrocarbon fuel gas as raw fuel gas. This fuel gas is reformed in a reformer to produce reformed fuel gas, which is then sent to the fuel electrode (anode) of the cell stack to generate electricity through an electrochemical reaction. The anode off-gas from the cell stack is then sent to the combustor, and oxygen generated in the water electrolysis hydrogen generator is also sent to the combustor, where it is burned using this oxygen. In this type of SOFC system, the combustion exhaust gas from the combustor contains carbon dioxide, which contains moisture. However, the moisture is condensed in a condenser and then separated in a gas-liquid separator, leaving only the remaining carbon dioxide to flow through the exhaust gas recovery and purification line. Thus, by recovering and purifying the combustion exhaust gas (carbon dioxide) flowing through the exhaust gas recovery and purification line, carbon dioxide emissions from the solid oxide fuel cell system can be reduced. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a block diagram showing a simplified embodiment of a hydrogen production device according to the present invention; [Figure 2] FIG. 2 is a diagram showing a simplified embodiment of a solid oxide fuel cell system used in the hydrogen production device of FIG. 1. [Figure 3] FIG. 1 is a diagram showing a typical example of the relationship between the time of day of a solar power generation device and its relative output. [Figure 4] FIG. 1 is a graph showing the relationship between the ratio of the output power of the SOFC system to the input power of the water electrolysis hydrogen generator and the improvement effect index per SOFC power generation output. [Figure 5] FIG. 1 is a diagram illustrating the difference in capacity factor before and after adding an SOFC system to a water electrolysis hydrogen generation system, and the improvement effect index per SOFC power generation output when an SOFC system is added. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, a solid oxide fuel cell system according to the present invention will be described with reference to the accompanying drawings. including stemThe hydrogen production device will now be described.

[0035] First, one embodiment of a hydrogen production device will be described with reference to Fig. 1. In Fig. 1, the hydrogen production device 1 shown includes a water electrolysis hydrogen generation device 2 that generates hydrogen by electrolysis of water, a solar power generation device 4 that generates electricity using sunlight (constituting a natural energy power generation device that generates electricity using natural energy), and a solid oxide fuel cell system 6 that generates electricity using hydrocarbon fuel gas as raw fuel gas.

[0036] The water electrolysis hydrogen generator 2 may be of various well-known types that generate hydrogen by electrolyzing water, and the hydrogen generated by the electrolysis of water is the target product, which is stored in a hydrogen tank 10 or the like via a hydrogen supply line 8, or is supplied to downstream hydrogen-using equipment (not shown) for consumption. The generated hydrogen can also be used as fuel gas for fuel cell vehicles, industrial or household fuel cells, etc.

[0037] Furthermore, oxygen is produced as a by-product during the electrolysis of water, and as will be described later, this by-product (oxygen) is supplied to the solid oxide fuel cell system 6 through the oxygen supply line 12 at a pressure of, for example, about 200 kPa and consumed, and by using this oxygen in the solid oxide fuel cell system 6, it is possible to effectively utilize the by-product (oxygen) produced during the electrolysis of water. Note that a portion of this by-product (oxygen) (surplus oxygen) may be stored in, for example, an oxygen tank 16 through the oxygen storage line 12.

[0038] Electricity used for electrolyzing water in the water electrolysis hydrogen generator 2 is supplied from a power supply controller 18. This power supply controller 18 is supplied with solar-generated power (power generated by natural energy) from the solar power generation device 4, battery-generated power from the solid oxide fuel cell system 6, and commercial power supply from a grid power supply 21 (so-called commercial power supply of, for example, 200 V), and the power supply controller 18 selects one or more of the solar-generated power, battery-generated power, and commercial power supply as the power required to operate the water electrolysis hydrogen generator 2, and supplies the required power.

[0039] In this embodiment, the power supply controller 18 controls the use of solar-generated power from the solar power generation device 4 and battery-generated power from the solid oxide fuel cell system 6, and controls the use of commercially available power when there is a significant power shortage even after using the solar-generated power and battery-generated power. By controlling in this manner, the solar-generated power and battery-generated power are used preferentially, and as will be understood from the description below, it is possible to reduce the cost of hydrogen production during hydrogen production and also to keep carbon dioxide emissions to a minimum.

[0040] As can be seen from the above description, in order to efficiently produce hydrogen and keep carbon dioxide emissions low, it is sufficient to operate this hydrogen production device 1 using solar power generated by the solar power generation device 4 and cell-generated power from the solid oxide fuel cell system 6. In this case, even when solar power generation from the solar power generation device 4 is not available, the water electrolysis hydrogen generation device 2 will operate using cell-generated power from the solid oxide fuel cell system 6, and therefore oxygen will be produced as a by-product of water electrolysis and will be supplied to the solid oxide fuel cell system 6. In this case, any surplus power can be addressed by reducing the power generation output of the solid oxide fuel cell system 6.

[0041] Next, we will explain the solid oxide fuel cell system 6 (SOFC system) used in this hydrogen production device 1, mainly with reference to Figure 2. In Figure 2, the solid oxide fuel cell system 6 (SOFC system) shown consumes hydrocarbon fuel gas (e.g., city gas, LP gas, biogas, etc.) as raw fuel gas to generate electricity, and includes a reformer 20 for reforming the fuel gas, and a solid oxide cell stack 22 that generates electricity by an electrochemical reaction (fuel cell reaction) between the reformed fuel gas reformed in the reformer 20 and air as an oxidant gas.

[0042] The cell stack 22 is constructed by stacking multiple solid oxide fuel cell cells via interconnector plates for generating electricity through electrochemical reactions, and although not shown, it is equipped with a solid electrolyte 24 that conducts oxygen ions, a fuel electrode 26 (anode) provided on one side of the solid electrolyte 24, and an oxygen electrode 28 (cathode) provided on the other side of the solid electrolyte 24, and the solid electrolyte 24 is made of, for example, zirconia doped with yttria.

[0043] The fuel electrode 26 side of this cell stack 22 is connected to the reformer 20 via a reformed fuel gas supply line 30, and in this embodiment, the reformer 20 is configured as an integrated unit with a vaporizer 32 for vaporizing reforming water. Note that the vaporizer 32 may be configured separately from the reformer 20, and the water vapor vaporized by the vaporizer 32 may be supplied to the reformer 20 via a water vapor supply line (not shown).

[0044] The vaporizer 32 is connected to a water supply source (not shown) (for example, composed of a water tank or a water recovery tank) via a water supply line 34, and reforming water from the water supply source is supplied to the vaporizer 32 through the water supply line 34. The reformer 20 contains a reforming catalyst, for example, alumina supported with ruthenium, and the raw fuel gas supplied via the fuel gas supply line 36 is steam reformed by the reforming catalyst with the steam vaporized in the vaporizer 32.

[0045] In this fuel gas supply line 36, a fuel supply pump 38 (fuel gas supply means), a fuel flow meter 40 (flow rate sensor), a desulfurizer 42, and a shutoff electromagnetic valve 44 are arranged in this order from the vaporizer 32 toward the upstream side. The desulfurizer 42 removes sulfur components contained in the raw fuel gas (sulfur components in the odorant), and the shutoff electromagnetic valve 44 closes to shut off the fuel gas supply line 36 when the supply of raw fuel gas is stopped.

[0046] Furthermore, the fuel supply pump 38 pressurizes the raw fuel gas flowing through the fuel gas supply line 36 and supplies it to the vaporizer 32, the fuel flow meter 40 measures the flow rate of the raw fuel gas flowing through the fuel gas supply line 36, and the system control unit (not shown) of the SOFC system 6 compares the set flow rate value of the raw fuel gas with the measured flow rate value of the fuel flow meter 40, and when this measured flow rate value is smaller (or larger) than the set flow rate value, increases (or decreases) the rotation speed of the fuel supply pump 38, and in this way the supply flow rate of the raw fuel gas is adjusted to the set flow rate value of the SOFC system.

[0047] A water supply pump 46 (water supply means) is provided in the water supply line 34, and this water supply pump 46 supplies reforming water from a water supply source (not shown) to the vaporizer 32 through the water supply line 34. A system control unit (not shown) of the SOFC system 6 controls the rotation speed of this water supply pump 46, and increases (or decreases) the rotation speed of the water supply pump 40 when the supply flow rate of the reforming water is less (or more) than a set flow rate value, thereby adjusting the supply flow rate of the reforming water to the set flow rate value.

[0048] Furthermore, the oxygen electrode 28 side of this cell stack 22 is connected to an air blower 50 (air supply means) via an air supply line 48. The air blower 50 supplies air as an oxidant gas to the oxygen electrode 28 side of the cell stack 22 through the air supply line 48. An air flow meter 52 that measures the air flow rate is disposed in this air supply line 48, and a system control unit (not shown) of the SOFC system 6 compares the set air flow rate value with the flow rate value measured by the air flow meter 52, and increases (or decreases) the rotation speed of the air blower 50 when this measured flow rate value is smaller (or larger) than the set flow rate value, thereby adjusting the air supply flow rate to the set flow rate value of the SOFC system.

[0049] The SOFC system 6 is provided with a combustor 54 that combusts anode offgas from the fuel electrode 26 (anode) of the cell stack 22. More specifically, the discharge side of the fuel electrode 26 of the cell stack 22 is connected to the combustor 54 via an anode offgas feed line 56, and the anode offgas from the cell stack 22 is fed to the combustor 54 via this anode offgas feed line 56. An oxygen feed line 12 from the water electrolysis hydrogen generator 12 is connected to the combustor 54, and an electromagnetic cutoff valve 58 and a mass flow controller 60 (oxygen flow rate control means) are provided on the oxygen feed line 12. The mass flow controller 60 controls the feed flow rate of oxygen flowing through the oxygen feed line 12 as described below, and feeds the oxygen downstream to the combustor 54, and the electromagnetic cutoff valve 58 closes to shut off the oxygen feed line 12 when the supply of oxygen is stopped.

[0050] A first heat exchanger 62 is provided to allow heat exchange between the cathode offgas discharged from the oxygen electrode 28 (cathode) of the cell stack 22 and the air flowing in the air supply line 48. A cathode offgas discharge line 64 is provided on the discharge side of the oxygen electrode 28 of the cell stack 22, and a first heat exchanger 62 is disposed in this cathode offgas discharge line 64. In this first heat exchanger 62, heat exchange occurs between the cathode offgas flowing in the cathode offgas discharge line 64 and the air flowing in the air supply line 48, and the air heated by this heat exchange is supplied to the oxygen electrode 28 side of the cell stack 22.

[0051] Furthermore, a second heat exchanger 66 is provided so that heat exchange occurs between the combustion exhaust gas discharged from the combustor 54 and the air flowing in the air supply line 48. A combustion exhaust gas discharge line 68 is provided on the discharge side of the combustor 54, and a second heat exchanger 66 is disposed in this combustion exhaust gas discharge line 68, and in this second heat exchanger 66, heat exchange occurs between the combustion exhaust gas flowing in the combustion exhaust gas discharge line 68 and the air flowing in the air supply line 48. With this configuration, the air from the air blower 50 is heated by heat exchange with the cathode off-gas in the first heat exchanger 62, and is further heated by heat exchange with the combustion exhaust gas in the second heat exchanger 66, and the air heated in this way in two stages is supplied to the oxygen electrode 28 side of the cell stack 22.

[0052] In this SOFC system 6, the reformer 20 and the vaporizer 32 are disposed in contact with or in close proximity to the combustor 54, and the reformer 20 and the vaporizer 32 are heated and maintained at a predetermined temperature by the combustion heat generated by the combustion of anode off-gas in this combustor 54. Furthermore, the cell stack 22, combustor 54, reformer 20, vaporizer 32, first heat exchanger 62, and second heat exchanger 66 are housed in a high-temperature space 82 surrounded by a heat insulating material (not shown), and the combustion heat from the combustor 54 maintains the interior of this high-temperature space 82 at a high temperature.

[0053] To minimize carbon dioxide emissions, the SOFC system 6 is further configured as follows: A third heat exchanger 70 and a gas-liquid separator 72 are disposed downstream in this order in the combustion exhaust gas discharge line 68. The third heat exchanger 70 functions as a condenser for condensing moisture in the combustion exhaust gas and may be, for example, a heat exchanger used to store the thermal energy of the combustion exhaust gas as hot water in a hot water storage tank (not shown) of a hot water storage device. The third heat exchanger 70 exchanges heat between water from the hot water storage tank (not shown) of the hot water storage device and the combustion exhaust gas flowing through the combustion exhaust gas discharge line 68. This heat exchange cools the combustion exhaust gas from the combustor 54 and condenses the moisture contained therein, while the hot water heated by the heat exchange is stored in the hot water storage tank. Furthermore, the condenser does not have to be the third heat exchanger 70 that exchanges heat with water from such a hot water storage device, but may be one that exchanges heat with, for example, cooling water, or one that exchanges heat with air, as long as it cools the combustion exhaust gas by heat exchange and condenses the moisture contained therein.

[0054] Meanwhile, the combustion exhaust gas cooled by heat exchange flows further downstream through the combustion exhaust gas discharge line 68, and the condensed water condensed in the third heat exchanger 70 is separated by a gas-liquid separator 72. The gas-liquid separator 72 is configured, for example, by a drain separator, and the moisture contained in the combustion exhaust gas is cooled and condensed by heat exchange in the third heat exchanger 70, the condensed water is separated by this gas-liquid separator 72, and the combustion exhaust gas from which the moisture has been separated flows further downstream. The condensed water separated by the drain separator may be recovered, for example, in a water recovery tank (not shown) and reused as reforming water.

[0055] A three-way valve 74 is disposed downstream of the exhaust gas recovery line 68, and an exhaust gas recovery and purification line 76 (specifically, a carbon dioxide recovery and purification line) is connected to one discharge side of the three-way valve 74, and an exhaust gas treatment line 78 is connected to the other discharge side. When this three-way valve 74 is in a first switching state, it connects the combustion exhaust gas discharge line 68 with the exhaust gas recovery and purification line 76, and the combustion exhaust gas from the combustion exhaust gas discharge line 68 flows into the exhaust gas recovery and purification line 76 to be recovered and purified, and when it is in a second switching state, it connects the combustion exhaust gas discharge line 68 with the exhaust gas treatment line 78, and the combustion exhaust gas from the combustion exhaust gas discharge line 68 flows into the exhaust gas treatment line 78 to be treated as required.

[0056] In the solid oxide fuel cell system 6, the operating state is stable during rated operation, so the anode off-gas from the cell stack 22 can be completely combusted in the combustor 54 using oxygen from the water electrolysis hydrogen generator 2, and in such a case the three-way valve 74 is held in the first switching state, and carbon dioxide as the combustion exhaust gas is recovered and purified through the exhaust gas recovery and purification line 76. On the other hand, during startup operation or low-output operation, it is difficult to completely combust the anode off-gas from the cell stack 22 using oxygen in the combustor 54, and in such a case the three-way valve 74 is held in the second switching state, and the combustion exhaust gas flows through the exhaust gas treatment line 78, is treated as required, and is then emitted, for example, into the atmosphere.

[0057] The combustion exhaust gas (CO2) recovered through this exhaust gas recovery and purification line 76 can be used to produce synthetic fuels (jet fuel, liquid fuels such as methanol, gas fuels such as methane and propane), and can also be used to synthesize chemical products such as olefins and urethanes.

[0058] This hydrogen production device 1 can reduce carbon dioxide emissions during hydrogen production, and this SOFC system 6 can also reduce carbon dioxide emissions during power generation operation, as will be described below. Power generation is performed using a hydrocarbon fuel gas (e.g., natural gas, biogas (mainly methane, CO2), etc.) as the raw fuel gas for the SOFC system 6, and when the raw fuel gas is completely oxidized without being mixed with the air supplied to the cell stack 22, the products are carbon dioxide (CO2) and water (H2O). When these products are cooled and the moisture is removed, the carbon dioxide remains in the combustion exhaust gas and can be separated. The separated carbon dioxide can be recovered and purified by being sent to the exhaust gas recovery and purification line 76.

[0059] More specifically, when the fuel utilization rate is, for example, 80% under the operating conditions of the SOFC system 6, oxygen from the oxygen electrode 28 side of the cell stack 22 is supplied to the anode 26 side through the electrolyte 24 so that 80% of the raw fuel gas undergoes an electrochemical reaction. As a result, the gas composition at the exhaust outlet of the anode 26 is such that the reformed fuel gas is partially oxidized with pure oxygen to, for example, 80%, and contains hydrogen (H), carbon monoxide (CO), carbon dioxide (CO), and water (H0). Because the general operating temperature of the cell stack 22 in the SOFC system 6 is 700°C or higher and a large amount of water is present, the methane content is extremely low at less than 0.1%.

[0060] In order to completely oxidize this gas into CO2 and HO, the anode off-gas from the cell stack 22 is fed to the combustor 54, and oxygen generated as a by-product in the water electrolysis hydrogen generator 2 is also fed to the combustor 54, where the anode off-gas is combusted with the oxygen. When the fuel utilization rate of the cell stack 22 is 80%, the amount of oxygen required to combust 20% of the raw fuel gas is fed from the water electrolysis hydrogen generator 2 to the combustor 54 of the SOFC system 6 via the oxygen supply line 12. By controlling the amount of oxygen supplied from the water electrolysis hydrogen generator 2 in this manner, the anode off-gas from the cell stack 22 can be completely oxidized into CO2 and HO.

[0061] When oxygen (so-called pure oxygen) from the water electrolysis hydrogen generator 2 is supplied to the combustor 54 in the high-temperature space 82 of the SOFC system 6, the rate of oxidation degradation of the cell stack 22 due to contact with pure oxygen or high-concentration oxygen is greater than the rate of oxidation degradation due to contact with air. Therefore, it is desirable that the only places that come into contact with pure oxygen are the combustor 54 itself and the supply pipe to it (oxygen supply line 12). Furthermore, it is desirable that the combustion conditions for the anode off-gas in the combustor 54 be stoichiometric combustion, which results in a post-combustion composition of only HO and CO. By doing so, the post-combustion combustion exhaust gas can be cooled to separate the condensed water, and the remaining CO can be recovered through the exhaust gas recovery line 76.

[0062] The above-described hydrogen production system 1, which combines a natural energy power generation system (for example, a solar power generation system 4) and an SOFC system 6 with the water electrolysis hydrogen generation system 2, is particularly effective in reducing the cost of hydrogen production. The power generated by a natural energy power generation system (for example, a solar power generation system 4) fluctuates greatly, and periods of low output in particular last for several hours or more. However, by combining this natural energy power generation system with an SOFC system 6, the battery-generated power from the SOFC system 6 can be supplied to the water electrolysis hydrogen generation system 2, thereby increasing the capacity factor of the water electrolysis hydrogen generation system 2. This increase in capacity factor has a significant effect, especially when the capacity factor of the water electrolysis hydrogen generation system 6 is low.

[0063] Next, the effect of improving the capacity factor (defined here as the capacity factor relative to rated operation over calendar hours) of the water electrolysis hydrogen generation system using cell-generated power from the SOFC system will be described.

[0064] We will explain the case where the goal is to reduce CO2 emissions during hydrogen production. If the power source for the water electrolysis hydrogen generator is, for example, a solar power generation system, fluctuations in the power generation output will determine the capacity factor of the water electrolysis hydrogen generator (defined here as (calendar time) x (utilization factor for rated operation)). This makes it possible to calculate the portion of the fluctuating hydrogen production cost equivalent to the facility cost (yen / Nm3). The relationship between the capacity factor and the portion of the hydrogen production cost equivalent to the facility cost (yen / Nm3) is proportional to 1 / u, where u is the capacity factor. Therefore, for example, if the capacity factor increases from 0.7 to 0.8, the effect will be significantly greater than if the capacity factor increases from 0.3 to 0.4.

[0065] The solar power generation system 4 has large fluctuations in output of solar power generation electricity, and the power output of this solar power generation system 4 may be small, resulting in a low capacity utilization rate of the water electrolysis hydrogen generation system. However, by using the SOFC system 6 as part of the power source for the water electrolysis hydrogen generation system 2 and supplying battery-generated electricity from this SOFC system 6, particularly when the capacity utilization rate is low, it is possible to achieve good results with a relatively small increase in power generation capacity, and the economic efficiency of hydrogen production is likely to be improved despite an increase in the equipment costs related to the SOFC system 6.

[0066] Here, we estimate the economic improvement effect when a water electrolysis hydrogen generation system is combined with a solar power generation system and an SOFC system. Figure 4 shows a typical example of the power generation output of a solar power generation system by time of day. In Figure 4, the solid line A shows the relative output on a sunny day, the dashed line B shows the relative output on a cloudy day, and the dashed line C shows the relative output on a rainy day. Figure 4 is a simplified representation of a typical example, where the maximum power generation output on a sunny day is set to 1.0, and the relative output is shown relative to this maximum power generation output. For example, the New Energy and Industrial Technology Development Organization and others have published detailed databases of solar radiation by region, making it possible to carry out detailed calculations.

[0067] In this calculation, we assumed four sunny days, four cloudy days, and two rainy days over a 10-day period, and calculated the capacity factor (utilization factor per rated time x calendar hours) of the water electrolysis hydrogen generator when the power output of the solar power generator was connected to the water electrolysis hydrogen generator. Although the power output of the solar power generator fluctuates within an hour, these small output fluctuations can be absorbed by a small-capacity power storage function in either the solar power generator or the water electrolysis hydrogen generator. Therefore, we calculated the capacity factor as fluctuating in hourly increments, as shown in Figure 4. In this calculation, the maximum power output of the solar power generator (the power output when sunlight is strongest on a sunny day) was set to 1.0, and the rated input power to the water electrolysis hydrogen generator (i.e., the device capacity) was set to 0.6, 0.4, and 0.2. The calculation also assumed that the water electrolysis hydrogen generator could produce hydrogen proportional to the partial input. That is, if the amount of hydrogen produced when "1" amount of power is supplied to the water electrolysis hydrogen generator is "1," then the calculation was made so that the amount of hydrogen produced when "0.5" amount of power is supplied is "0.5." Then, the capacity factor of the water electrolysis hydrogen generator over 10 days was calculated for the hydrogen production equipment not combined with the SOFC system. After that, the capacity factor of the water electrolysis hydrogen generator over 10 days was calculated for the hydrogen production equipment combined with the SOFC system.

[0068] Figure 5 shows the calculated capacity utilization rate of the water electrolysis hydrogen generation equipment before and after adding the SOFC system. As shown in these calculation results, adding the SOFC system increases the capacity utilization rate of the water electrolysis hydrogen generation equipment, improving the capacity utilization rate.

[0069] Furthermore, the effect of this improvement in capacity factor was calculated by taking the capacity factor as u, (1 / u) as the capital cost improvement index, and the difference in (1 / u) between the presence and absence of the SOFC system as the capital cost improvement index for adding the SOFC system.The improvement effect index per power output of the SOFC system was calculated by dividing this capital cost improvement index for adding the SOFC system by the power output of the SOFC system.The results of this calculation are shown in Figure 5, and the trend of the improvement effect index is shown in Figure 4.

[0070] Figure 5 shows calculations for the rated power consumption of the water electrolysis hydrogen generator set to 0.2, 0.4, and 0.6, with the power output of the solar power generation system (Figure 3) set to 1.0. This calculation shows that even when the relationship between the rated input power of the water electrolysis hydrogen generator and the maximum output power of the solar power generation system changes (varying between 0.2 and 0.6), the improvement in the equipment cost of the water electrolysis hydrogen generator per SOFC system remains largely unchanged, and decreases as the proportion of SOFC systems installed increases. It is clear from past performance and technical characteristics (increasing the power output requires increasing the number of fuel cells) that SOFC systems generally tend to have limited economies of scale in terms of cost and efficiency. While this must be taken into account in the details, the calculation results in Figures 4 and 5 show that in a hydrogen production system combining a solar power generation system and an SOFC system, the power output of the SOFC system relative to the rated power input of the water electrolysis hydrogen generator should be at most 0.3, and preferably 0.2 or less.

[0071] As described above, hydrogen production according to the present invention One embodiment of the device Although the embodiments have been described, the present invention is not limited to these embodiments, and various changes and modifications are possible without departing from the scope of the present invention.

[0072] For example, in the hydrogen production device described above, a water electrolysis hydrogen generation device is combined with a solar power generation device as a natural energy power generation device and an SOFC system. However, instead of this combination, a wind power generation device as a natural energy power generation device and an SOFC system can be combined to obtain the same effects as described above.

[0073] In addition, for example, the above-mentioned hydrogen production In the device The system employs both the technical features of consuming the by-product (oxygen) of the water electrolysis hydrogen generation device in the SOFC system and the technical feature of recovering the combustion exhaust gas (carbon dioxide) emitted from the SOFC system, but it is also possible to employ only one of these technical features. [Explanation of symbols]

[0074] 1. Hydrogen production equipment 2 Water electrolysis hydrogen generator 4. Solar power generation equipment 6 Solid oxide fuel cell system (SOFC system) 12 Oxygen supply line 18 Power Controller 20 Reformer 22 Cell Stack 54 Combustor 60 Mass Flow Controller 70 Third heat exchanger 72 Gas-liquid separation equipment 74 Three-way valve 76 Exhaust gas recovery and purification line 78 Exhaust Gas Treatment Line

Claims

1. The system comprises a water electrolysis hydrogen generator that electrolyzes water to generate hydrogen and oxygen, a solid oxide fuel cell system that generates electricity using a hydrocarbon fuel gas as a raw fuel gas, and a power supply controller that controls the drive power for operating the water electrolysis hydrogen generator, The solid oxide fuel cell system includes a reformer that reforms a raw fuel gas to generate a reformed fuel gas, a cell stack that generates electricity by an electrochemical reaction between the reformed fuel gas from the reformer and an oxidant gas, and a combustor that combusts an anode off-gas from an anode of the cell stack, a hydrogen production apparatus, characterized in that oxygen produced in the water electrolysis hydrogen generation apparatus is supplied to the combustor through an oxygen supply line, and battery-generated power generated in the cell stack is supplied to the water electrolysis hydrogen generation apparatus via the power supply controller.

2. 2. The hydrogen production device according to claim 1, wherein the rated power output of the solid oxide fuel cell system is 30% or less of the rated power consumption of the water electrolysis hydrogen production device.

3. 3. The hydrogen production device according to claim 1, wherein the power supply controller is supplied with natural energy-generated power from a natural energy power generation device that generates power using natural energy, commercial power supply from a grid power source, and the cell-generated power from the solid oxide fuel cell system, and the power supply controller preferentially supplies the natural energy-generated power and the cell-generated power to the water electrolysis hydrogen production device.

4. The hydrogen production device according to any one of claims 1 to 3, characterized in that the solid oxide fuel cell system further includes a condenser that condenses moisture contained in the combustion exhaust gas from the combustor, a gas-liquid separator that separates the condensed water condensed in the condenser, and an exhaust gas recovery and purification line that recovers and purifies the combustion exhaust gas from which the condensed water has been separated by the gas-liquid separator, and carbon dioxide is recovered and purified through the exhaust gas recovery and purification line.

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