Electrolytic system

Abstract

This system efficiently separates the generated hydrogen from the unreacted water vapor contained in the hydrogen electrode off-gas. [Solution] The electrolytic system comprises a solid oxide electrolytic cell, a heat-insulating case for housing the solid oxide electrolytic cell, a gas-liquid separation unit that separates water vapor in the hydrogen electrode off-gas discharged from the hydrogen electrode to the outside of the case by heat exchange with a coolant, an absorption chiller that generates a coolant by repeating a cycle in which liquefied refrigerant is evaporated in an evaporator to cool the coolant, vaporized refrigerant is absorbed into the absorbent in an absorber, the absorbent is heated in a regenerator to regenerate the vaporized refrigerant, and the vaporized refrigerant is cooled and condensed in a condenser, and a hydrogen electrode off-gas supply line that supplies the hydrogen electrode off-gas discharged from the hydrogen electrode to the regenerator as a heat source for the absorbent, and then supplies it to the gas-liquid separation unit.

Description

Technical Field

[0001] This specification discloses an electrolysis system.

Background Art

[0002] Conventionally, there has been proposed a fuel cell system including a solid oxide fuel cell stack, a combustor that burns the anode exhaust gas and the cathode exhaust gas of the solid oxide fuel cell stack, an absorption refrigerator provided in the combustion exhaust gas path of the combustor and heated by the combustion exhaust gas to regenerate a heating section, a first heat exchanger provided in the combustion exhaust gas path so as to be located downstream of the absorption refrigerator and heating reformed water by the heat of the combustion exhaust gas cooled by the regeneration heating section, a condensation section provided in the combustion exhaust gas path so as to be located downstream of the first heat exchanger and condensing water vapor contained in the combustion exhaust gas using the atmosphere or the vaporization section of the absorption refrigerator, a recovered water tank that recovers the water condensed in the condensation section, and a reformed water transmitter that sends the water in the recovered water tank to the first heat exchanger as reformed water (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] 虽上述专利文献1记载了为从燃料电池系统的燃烧废气中回收水而应用吸收式制冷机,但未提及对电解系统的应用。 Although Patent Document 1 described above mentions the application of an absorption refrigerator for the purpose of recovering water from the combustion exhaust gas of a fuel cell system, it does not mention anything about the application to an electrolysis system.

[0005] The main object of the present disclosure is to efficiently separate the produced hydrogen and unreacted water vapor contained in the hydrogen electrode off-gas in an electrolysis process that electrolyzes water vapor supplied to the hydrogen electrode to produce hydrogen. [Means for solving the problem]

[0006] This disclosure employs the following means to achieve the primary objectives described above.

[0007] The electrolytic system of this disclosure comprises: a solid oxide electrolytic cell that generates hydrogen by electrolyzing water vapor supplied to a hydrogen electrode; an insulated case that houses the solid oxide electrolytic cell; a gas-liquid separation unit that separates water vapor in the hydrogen electrode off-gas discharged from the hydrogen electrode to the outside of the case by heat exchange with a coolant; an absorption chiller having an evaporator, an absorber, a regenerator, and a condenser, which generates the coolant by repeating a cycle in which liquefied refrigerant is evaporated in the evaporator to cool the coolant, vaporized refrigerant is absorbed into the absorbent in the absorber, the absorbent is heated in the regenerator to regenerate the vaporized refrigerant, and the vaporized refrigerant is cooled and condensed in the condenser; and a hydrogen electrode off-gas supply line that supplies the hydrogen electrode off-gas discharged from the hydrogen electrode to the outside of the case as a heat source for the absorbent to the regenerator, and then supplies it to the gas-liquid separation unit.

[0008] In the electrolytic system of this disclosure, the hydrogen electrode off-gas discharged from the hydrogen electrode of the solid oxide electrolytic cell to the outside of the case is supplied to the regenerator of the absorption chiller, and then to the gas-liquid separation section, where it is separated into gas and liquid by heat exchange with the coolant cooled in the evaporator of the absorption chiller. This allows for efficient gas-liquid separation of the generated hydrogen and unreacted water vapor contained in the hydrogen electrode off-gas. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the electrolysis system of this embodiment. [Modes for carrying out the invention]

[0010] Next, the forms for implementing this disclosure will be described with reference to the drawings.

[0011] Figure 1 is a schematic diagram of the electrolysis system 10 of this embodiment. As shown in Figure 1, the electrolysis system 10 of this embodiment includes an electrolysis module 20 containing an electrolysis cell stack 21 that generates hydrogen by steam electrolysis, a steam supply system 30 that supplies steam to the electrolysis module 20, a hydrogen supply system 40 that supplies hydrogen to the electrolysis module 20, an air supply system 50 that supplies air as a sweep gas to the electrolysis module 20, and a hydrogen recovery system 60 that recovers the generated hydrogen produced in the electrolysis module 20.

[0012] The electrolytic module 20 includes an electrolytic cell stack 21, a combustor 22, and a heat exchanger (not shown), all of which are housed in an insulated module case 24.

[0013] The electrolytic cell stack 21 comprises a plurality of solid oxide electrolytic cells (SOECs), each containing a solid electrolyte, a hydrogen electrode positioned on one side of the solid electrolyte, and an oxygen electrode positioned on the other side of the solid electrolyte. The electrolytic operation of the electrolytic cell stack 21 is performed by supplying water vapor to the hydrogen electrode and power from the power supply unit 26. At the hydrogen electrode, hydrogen is generated when the water vapor is decomposed into oxygen ions and hydrogen. At the oxygen electrode, oxygen is generated when the decomposed oxygen ions permeate the solid electrolyte and combine with electrons. The power supply unit 26 can be a grid power supply, a renewable energy device (e.g., a solar power generation device), a storage battery, etc.

[0014] Since the electrolytic cell stack 21 operates in a high-temperature environment, for example, 650-800°C, the solid electrolyte, hydrogen electrode, and oxygen electrode are made of ceramic material. Furthermore, because the catalyst decomposes water vapor into oxygen ions and hydrogen, a cermet made of a catalytic metal such as nickel and ceramic is used for the hydrogen electrode. In order to maintain good catalytic activity of the hydrogen electrode, it is necessary to keep the hydrogen electrode in a reducing atmosphere and prevent oxidation of the metal. For this reason, in this embodiment, hydrogen for oxidation prevention is mixed into the water vapor supplied to the hydrogen electrode.

[0015] One end of the hydrogen electrode inlet pipe 21a is connected to the hydrogen electrode inlet of the electrolytic cell stack 21, and the other end of the hydrogen electrode inlet pipe 21a is connected to the steam supply system 30 and the hydrogen supply system 40. One end of the oxygen electrode inlet pipe 21b is connected to the oxygen electrode inlet of the electrolytic cell stack 21, and the other end of the oxygen electrode inlet pipe 21b is connected to the air supply system 50. One end of the hydrogen electrode outlet pipe 21c is connected to the hydrogen electrode outlet of the electrolytic cell stack 21, and the other end of the hydrogen electrode outlet pipe 21c is connected to the hydrogen recovery system 60. One end of the oxygen electrode outlet pipe 21d is connected to the oxygen electrode outlet of the electrolytic cell stack 21, and the other end of the oxygen electrode outlet pipe 21d is connected to the combustor 22. The combustor 22 is connected to the combustion hydrogen supply pipe 43 and the combustion exhaust gas pipe 21e.

[0016] The steam supply system 30 includes a water tank 31 for storing raw water (pure water) supplied via a pure water device (not shown), a steam generator 32 for heating the raw water to generate steam, a water supply pipe 33 connected to the water tank 31 and the steam generator 32, a water pump 34 installed in the water supply pipe 33 for pressurizing the raw water in the water tank 31 to the steam generator 32, and a steam supply pipe 35 for supplying the steam generated by the steam generator 32 to the hydrogen electrode inlet pipe 21a of the electrolysis module 20. In this embodiment, the steam generator 32 is connected to a hydrogen recovery pipe 61, which will be described later and is connected to the hydrogen electrode outlet pipe 21c, and is configured as a heat exchanger that heats the raw water to generate steam by heat exchange with the hydrogen electrode off-gas flowing through the hydrogen recovery pipe 61. The steam introduced from the steam supply system 30 into the hydrogen electrode inlet pipe 21a is heated by heat exchange with combustion exhaust gas etc. in a heat exchange section (not shown) installed in the hydrogen electrode inlet pipe 21a, and then supplied to the hydrogen electrode of the electrolytic cell stack 21.

[0017] The hydrogen supply system 40 includes an oxidation-preventing hydrogen supply pipe 41 with one end connected to the hydrogen electrode inlet pipe 21a, a hydrogen blower 42 installed on the oxidation-preventing hydrogen supply pipe 41, a combustion hydrogen supply pipe 43 with one end connected to the combustor 22, and a hydrogen blower 44 installed on the combustion hydrogen supply pipe 43. By driving the hydrogen blower 42, hydrogen is introduced into the oxidation-preventing hydrogen supply pipe 41, and the introduced hydrogen is supplied to the hydrogen electrode of the electrolytic cell stack 21 as oxidation-preventing hydrogen. Also, by driving the hydrogen blower 44, hydrogen is introduced into the combustion hydrogen supply pipe 43, and the introduced hydrogen is supplied to the combustor 22 as combustion hydrogen. Flow meters (not shown) are installed on both the oxidation-preventing hydrogen supply pipe 41 and the combustion hydrogen supply pipe 43.

[0018] The air supply system 50 includes an air supply pipe 51 connected to the oxygen electrode inlet pipe 21b and an air blower 52 installed on the air supply pipe 51. By driving the air blower 52, the air drawn into the air supply pipe 51 is introduced into the oxygen electrode inlet pipe 21b, where it is heated by heat exchange with combustion exhaust gas, hydrogen electrode off-gas, etc., in a heat exchange unit (not shown) installed in the oxygen electrode inlet pipe 21b, and then supplied to the oxygen electrode of the electrolytic cell stack 21.

[0019] The hydrogen recovery system 60 recovers generated hydrogen from the hydrogen electrode off-gas, which contains generated hydrogen and unreacted water vapor discharged from the hydrogen electrode outlet. The hydrogen recovery system 60 comprises a hydrogen recovery pipe 61 connected to the hydrogen electrode outlet pipe 21c, a condenser 62 (gas-liquid separation unit) installed in the hydrogen recovery pipe 61, and an absorption chiller 70. The condenser 62 condenses the water vapor contained in the hydrogen electrode off-gas flowing through the hydrogen recovery pipe 61 by heat exchange with cooling water, separating the hydrogen electrode off-gas into generated hydrogen and condensed water. The condensed water separated in the condenser 62 is stored in the water tank 31 via the condensed water pipe 64. The condensed water stored in the water tank 31 is used as raw water for generating water vapor for electrolysis.

[0020] The absorption chiller 70 comprises an evaporator 71, an absorber 72, a regenerator 73, and a condenser 74. This absorption chiller 70 has a refrigeration cycle in which liquefied refrigerant is evaporated in the evaporator 71, vaporized refrigerant is absorbed into an absorbent liquid in the absorber 72, the absorbent liquid is heated in the regenerator 73 to regenerate the vaporized refrigerant, and the vaporized refrigerant is cooled and condensed in the condenser 74. A circulation pipe 75 through which cooling water circulates is connected to the evaporator 71 and the condenser 62 (gas-liquid separation section). The absorption chiller 70 generates the cold energy necessary for the condensation of water vapor contained in the hydrogen electrode off-gas in the condenser 62 by cooling the cooling water flowing through the circulation pipe 75 in the evaporator 71 using the heat of vaporization of the refrigerant.

[0021] The regenerator 73 has a first heating heat exchange section 73a, a second heating heat exchange section 73b, and a third heating heat exchange section 73c for heating the absorbent liquid. Unused waste heat (40-60°C) discharged from factories, etc., is supplied to the first heating heat exchange section 73a. Hydrogen recovery piping 61 is connected to the second heating heat exchange section 73b downstream of the steam generator 32 and upstream of the condenser 62, and hydrogen electrode off-gas (80-90°C) that has undergone heat exchange with the raw water in the steam generator 32 is supplied to it. The hydrogen electrode off-gas (60-70°C) that has passed through the second heating heat exchange section 73b is supplied to the condenser 62, where it is separated into gas-liquid and gas-liquid into generated hydrogen and condensed water through heat exchange with cooling water. Furthermore, the combustion exhaust gas piping 21e is connected to the third heating heat exchange section 73c, and combustion exhaust gas (90-100°C) discharged from the combustor 22 to the outside of the module case 24 is supplied to it. The first heating heat exchange section 73a, the second heating heat exchange section 73b, and the third heating heat exchange section 73c are arranged in the order of first heating heat exchange section 73a, second heating heat exchange section 73b, and third heating heat exchange section 73c from the upstream side with respect to the flow of the absorbent liquid, so that heat exchange with the absorbent liquid is in the order of unused waste heat, hydrogen electrode off-gas, and combustion exhaust gas (in order of increasing temperature). This allows the absorbent liquid to be sufficiently heated to regenerate the vaporized refrigerant. Note that the first heating heat exchange section 73a and the third heating heat exchange section 73c may be omitted.

[0022] The condenser 74 has a first cooling heat exchanger section 74a and a second cooling heat exchanger section 74b for cooling the vaporized refrigerant. The first cooling heat exchanger section 74a is connected to the water supply pipe 33 upstream of the steam generator 32, and raw water (20 to 30°C) from the water tank 31 is supplied thereto. Cooling water (30 to 35°C) is supplied to the second cooling heat exchanger section 74b. In order to give as much heat as possible to the raw water, the first cooling heat exchanger section 74a and the second cooling heat exchanger section 74b are arranged in the order of the first cooling heat exchanger section 74a and the second cooling heat exchanger section 74b from the upstream side with respect to the flow of the vaporized refrigerant so as to exchange heat with the vaporized refrigerant in the order of the raw water and the cooling water. Note that the second cooling heat exchanger section 74b may be omitted.

[0023] The reflux pipe 65 branches from the downstream side of the condenser 62 in the hydrogen recovery pipe 61 and is connected to the other end of the hydrogen supply pipe 41 for antioxidant prevention and the other end of the hydrogen supply pipe 43 for combustion. The generated hydrogen flowing through the hydrogen recovery pipe 61 is drawn from the reflux pipe 65 into the hydrogen supply pipe 41 for antioxidant prevention by driving the hydrogen blower 42, and is supplied from the hydrogen supply pipe 41 for antioxidant prevention to the hydrogen electrode of the electrolytic cell stack 21. Further, the generated hydrogen flowing through the hydrogen recovery pipe 61 is drawn from the reflux pipe 65 into the hydrogen supply pipe 43 for combustion by driving the hydrogen blower 44, and is supplied from the hydrogen supply pipe 43 for combustion to the combustor 22.

[0024] The control device 80 is configured as a microprocessor centered on a CPU, and in addition to the CPU, includes a ROM, a RAM, an input / output port, etc. Detection signals from a temperature sensor installed near the electrolytic cell stack 21, a temperature sensor installed in the combustor 22, a flow meter installed in the hydrogen supply pipe 41 for antioxidant prevention, a flow meter installed in the hydrogen supply pipe 43 for combustion, a flow meter installed in the hydrogen recovery pipe 61, etc. are input via the input port. Further, control signals from the control device 80 are output via the output port to the water pump 34, the hydrogen blowers 42 and 44, the air blower 52, etc.

[0025] Next, the operation (electrolysis operation) of the electrolysis system 10 configured in this way will be described.

[0026] During electrolysis, in the electrolysis system 10, the control device 80 controls the water pump 34 to supply water vapor to the hydrogen electrode of the electrolysis cell stack 21 and the air blower 52 to supply air to the air electrode of the electrolysis cell stack 21, and supplies power from the power supply unit 26 to the terminals of the electrolysis cell stack 21 to perform electrolysis. The control device 80 then controls the hydrogen blowers 42 and 44 so that the hydrogen generated by the electrolysis operation is supplied to the hydrogen electrode of the electrolysis cell stack 21 as antioxidant hydrogen via the reflux pipe 65 and also supplied to the combustor 22 as combustion hydrogen.

[0027] When the water pump 34 is driven, the raw water in the water tank 31 passes through the condenser 74 (first cooling heat exchange section 74a) of the absorption chiller 70, where it is heated by heat exchange with the vaporized refrigerant before being supplied to the steam generator 32. The heated raw water then becomes steam through heat exchange with the hydrogen electrode off-gas discharged from the hydrogen electrode of the electrolytic cell stack 21, and is further heated by heat exchange with combustion exhaust gas etc. through the hydrogen electrode inlet pipe 21a before being supplied to the hydrogen electrode. The cold energy (20-30°C) of the raw water is used to condense the vaporized refrigerant in the condenser 74 of the absorption chiller 70, and the heat of the vaporized refrigerant is used to heat the raw water. Furthermore, the heat (140-150°C) of the hydrogen electrode off-gas discharged from the hydrogen electrode to the outside of the module case 24 is used to generate steam. This further reduces the energy required for steam generation and improves the overall energy efficiency of the system.

[0028] Furthermore, the heat (80-90°C) of the hydrogen electrode off-gas that has passed through the steam generator 32 is used to regenerate the vaporized refrigerant from the absorbent liquid that has absorbed the vaporized refrigerant in the regenerator 73 (second heating heat exchange section 73b) of the absorption chiller 70, and the coldness of the absorbent liquid is used to cool the hydrogen electrode off-gas. In addition, in the absorption chiller 70, the low-temperature cooling water (5-10°C) produced in the evaporator 71 is supplied to the condenser 62. The hydrogen electrode off-gas (60-70°C) that has passed through the regenerator 73 is cooled in the condenser 62 by heat exchange with the cooling water, and the water vapor contained in the hydrogen electrode off-gas is condensed. As a result, the generated hydrogen and water vapor contained in the hydrogen electrode off-gas can be separated into liquid and gas phases effectively, and high-purity hydrogen can be efficiently produced.

[0029] In the embodiment described above, the electrolysis system 10 is equipped with an electrolytic cell stack 21 that generates hydrogen by steam electrolysis. However, the electrolysis system 10 may also be configured to use the electrolytic cell stack 21 as a reversibly operated solid oxide cell stack, thereby switching between an electrolysis mode in which hydrogen is generated by steam electrolysis and a power generation mode in which electricity is generated by the reaction of hydrogen as a fuel gas with oxygen contained in the air.

[0030] The above describes the forms for implementing this disclosure using embodiments, but this disclosure is not limited in any way to these embodiments, and can of course be implemented in various forms without departing from the gist of this disclosure. [Industrial applicability]

[0031] This disclosure can be used in industries such as the manufacturing of electrolytic systems. [Explanation of symbols]

[0032] 1 Electrolytic system, 21 Electrolytic cell stack (solid oxide type electrolytic cell), 22 Combustor (combustion section), 24 Module case (case), 32 Steam generator (steam generation section), 33 Water supply pipe (raw water supply line), 35 Steam supply pipe (steam supply line), 61 Hydrogen recovery piping (hydrogen electrode off-gas supply line), 62 Condenser (gas-liquid separation section), 70 Absorption chiller, 71 Evaporator, 72 Absorber, 73 Regenerator, 73b Second heating heat exchange section (first heat exchange section), 73c Third heating heat exchange section (second heat exchange section), 74 Condenser.

Claims

1. A solid oxide type electrolytic cell that generates hydrogen by electrolyzing water vapor supplied to the hydrogen electrode, A heat-insulating case for housing the aforementioned solid oxide electrolytic cell, A gas-liquid separation unit that separates water vapor in the hydrogen electrode off-gas discharged from the hydrogen electrode to the outside of the case by heat exchange with a coolant, An absorption chiller having an evaporator, an absorber, a regenerator, and a condenser, wherein the chiller generates the coolant by repeating a cycle in which liquefied refrigerant is evaporated in the evaporator to cool the coolant, vaporized refrigerant is absorbed into the absorbent in the absorber, the absorbent is heated in the regenerator to regenerate the vaporized refrigerant, and the vaporized refrigerant is cooled and condensed in the condenser, A hydrogen electrode off-gas supply line supplies the hydrogen electrode off-gas discharged from the hydrogen electrode to the outside of the case to the regenerator as a heat source for the absorbent liquid, and then supplies it to the gas-liquid separation unit. An electrolytic system equipped with the following features.

2. The electrolytic system according to claim 1, A steam supply line that supplies steam to the hydrogen electrode, A steam generating unit connected to the aforementioned steam supply line, which heats raw water to generate steam, A raw water supply line that supplies the raw water to the condenser as a cooling source for the vaporized refrigerant, and then supplies it to the steam generation unit, An electrolytic system equipped with the following features.

3. The electrolytic system according to claim 2, The hydrogen electrode off-gas supply line supplies the hydrogen electrode off-gas discharged from the hydrogen electrode to the outside of the case to the steam generation unit as a heat source for the raw water, and then supplies it to the regenerator as a heat source for the absorbent liquid. Electrolytic system.

4. The electrolytic system according to claim 3, A combustion section housed in the aforementioned case for burning flammable gas, A combustion exhaust gas supply line supplies the combustion exhaust gas discharged from the combustion section to the outside of the case to the regenerator as a heat source for the absorbent liquid, Equipped with, The regenerator includes a first heat exchange unit that performs heat exchange between the absorbent liquid and the hydrogen electrode off-gas, and a second heat exchange unit that performs heat exchange between the absorbent liquid and the combustion exhaust gas. The first heat exchange section and the second heat exchange section are provided so that the absorbent liquid exchanges heat with the hydrogen electrode off-gas and the combustion exhaust gas in that order. Electrolytic system.

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