Electrolytic system

Abstract

To further improve the efficiency of hydrogen production in electrolysis systems. [Solution] The electrolysis system comprises a solid oxide electrolytic cell that generates hydrogen by electrolyzing water vapor supplied to the hydrogen electrode and discharges a hydrogen electrode off-gas containing the generated hydrogen and unreacted water vapor from the hydrogen electrode; a hot water tank that stores water in a heat-insulating manner; a heat pump type hot water generator that extracts heat from the hydrogen electrode off-gas to condense the water vapor in the hydrogen electrode off-gas and heats the water in the hot water tank with the extracted heat; a heat pump type steam generator that extracts heat from the water in the hot water tank and heats raw water with the extracted heat to generate water vapor; and a raw water supply passage that supplies the water in the hot water tank as raw water to the steam generator.

Description

Technical Field

[0001] This specification discloses an electrolysis system.

Background Art

[0002] Conventionally, a fuel cell system has been proposed that includes a heat pump in which a compressor, a condenser, an expansion valve, and an evaporator are connected in sequence by a refrigerant circulation line, a fuel cell that generates electricity using fuel reformed by reformed water, and a heating unit that burns the fuel electrode exhaust gas and the air electrode exhaust gas discharged from the fuel cell to heat a reforming catalyst. By exchanging heat between the burner exhaust gas discharged from the heating unit and the refrigerant by the evaporator of the heat pump, the burner exhaust gas is cooled to generate condensed 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] Although Patent Document 1 described above describes a fuel cell system with improved COP of a heat pump, it does not mention applying a heat pump to an electrolysis system. In an electrolysis system equipped with a solid oxide type electrolysis cell, high-temperature steam is electrolyzed to generate hydrogen, so it is necessary to fully consider this when applying a heat pump to an electrolysis system.

[0005] The main object of the present disclosure is to further improve the efficiency of hydrogen generation in an electrolysis system.

Means for Solving the Problems

[0006] The present disclosure has taken the following means to achieve the above main object.

[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 and discharges a hydrogen electrode off-gas containing the generated hydrogen and unreacted water vapor from the hydrogen electrode; a hot water tank that stores water in a heat-insulating manner; a heat pump type hot water generator that extracts heat from the hydrogen electrode off-gas to condense the water vapor in the hydrogen electrode off-gas and heats the water in the hot water tank with the extracted heat; a heat pump type steam generator that extracts heat from the water in the hot water tank and heats raw water with the extracted heat to generate the water vapor; and a raw water supply passage that supplies the water in the hot water tank as the raw water to the steam generator.

[0008] In the electrolysis system of this disclosure, a hot water generator extracts heat from the hydrogen electrode off-gas to produce hot water, and the produced hot water is used as a heat source for a heat pump in a steam generator, as well as as raw water for generating steam. This allows for the extraction of heat from the hydrogen electrode off-gas, which separates the hydrogen off-gas into gas-liquid and condensed water, thereby recovering the hydrogen, and also enables the efficient generation of steam for electrolysis. As a result, the efficiency of hydrogen production in the electrolysis system can be further improved. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the electrolysis system of this embodiment. [Figure 2] This is a schematic diagram of an electrolysis system according to another embodiment. [Modes for carrying out the invention]

[0010] The forms for implementing this disclosure will be explained with reference to the drawings.

[0011] Figure 1 is a schematic diagram of the electrolysis system 10 of this embodiment. The electrolysis system 10 of this embodiment includes an electrolysis module 20 including an electrolysis cell stack 21 that generates hydrogen by steam electrolysis, a steam supply system 30 that generates steam from raw water and supplies it to the electrolysis module 20, an air supply system (not shown) that supplies air as a sweep gas to the electrolysis module 20, a hydrogen recovery system 60 that recovers the hydrogen generated in the electrolysis cell stack 21, and a control device 80 that controls the entire system.

[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 25.

[0013] The electrolytic cell stack 21 comprises a plurality of solid oxide single cells, 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 cell stack 21 is supplied with water vapor from the hydrogen electrode inlet and power from the power supply unit 26, causing the water vapor to be electrolyzed to produce hydrogen at the hydrogen electrode and oxygen at the oxygen electrode. The produced hydrogen (generated hydrogen) is discharged from the hydrogen electrode outlet as a hydrogen electrode off-gas along with unreacted water vapor, and the produced oxygen is discharged from the oxygen electrode outlet as an oxygen electrode off-gas along with air, which is a sweep gas supplied from the oxygen electrode inlet. 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 is mixed into the water vapor supplied to the hydrogen electrode to prevent oxidation.

[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 50. 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. 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.

[0016] The combustor 22 receives a supply of generated hydrogen (hydrogen for combustion) contained in the hydrogen electrode off-gas and the oxygen electrode off-gas as combustible gases, and burns these mixed gases. The electrolytic cell stack 21 is heated by the combustion heat and combustion exhaust gas generated in the combustor 22. The combustion exhaust gas discharged from the combustor 22 exchanges heat with the water vapor flowing through the hydrogen electrode inlet pipe 21a and the air flowing through the oxygen electrode inlet pipe 21b before being discharged outside the electrolytic module 20.

[0017] The steam supply system 30 includes a hot water tank 31 for storing water (pure water) in a heat-insulating manner, a steam generation heat pump 40 for generating steam by evaporating raw water, a raw water supply pipe 32 connecting the hot water tank 31 and the steam generation heat pump 40, and a steam supply pipe 34 connecting the steam generation heat pump 40 and the electrolysis module 20 (hydrogen electrode inlet pipe 21a). A pure water supply pipe 35 is connected to the hot water tank 31, and purified water from a pure water device (not shown) is supplied via the pure water supply pipe 35 as needed. In addition, a combustion exhaust gas pipe 36 is connected to the hot water tank 31 through which combustion exhaust gas discharged from the combustor 22 to the outside of the electrolysis module 20 flows. The combustion exhaust gas that has passed through the combustion exhaust gas pipe 36 exchanges heat with the water in the hot water tank 31 before being discharged to the outside air. This allows the water vapor contained in the combustion exhaust gas to be recovered through heat exchange with the combustion exhaust gas and heated, thereby heating the water in the hot water tank 31.

[0018] The water (hot water) stored in the hot water tank 31 is supplied to the steam generation heat pump 40 via the raw water supply pipe 32 by the drive of the raw water pump 33 installed in the raw water supply pipe 32. After being converted into steam in the steam generation heat pump 40, it is supplied to the electrolytic module 20 via the steam supply pipe 34. The steam supplied to the electrolytic module 20 is then 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.

[0019] The steam generation heat pump 40 extracts heat from the water (hot water) stored in the hot water tank 31, and uses the extracted heat to heat the raw water to generate steam (saturated steam). The steam generation heat pump 40 comprises a heat extraction heat exchanger (evaporator) 41, a compressor 42, a steam generation heat exchanger (condenser) 43, an expansion valve 44, and circulation piping 45 that connects these so that a refrigerant circulates between them. The hot water tank 31 is connected to the heat extraction heat exchanger 41 via a hot water circulation path 47. A circulation pump 48 is installed in the hot water circulation path 47 to circulate the hot water from the hot water tank 31 between the hot water tank 31 and the heat extraction heat exchanger 41. In addition, a raw water supply pipe 32 is connected to the inlet of the steam generation heat exchanger 43, and a steam supply pipe 34 is connected to the outlet of the steam generation heat exchanger 43. The steam generating heat pump 40 generates steam by repeating a heat pump cycle of heat reception, compression, heat release, and expansion using a refrigerant, thereby releasing heat to the hot water (raw water) supplied from the hot water tank 31 via the refrigerant that receives heat from the hot water in the hot water tank 31.

[0020] The air supply system, although not shown in the diagram, includes an air filter and an air blower. The air blower draws air from the air filter and supplies it to the electrolytic module 20. The air supplied to the electrolytic module 20 is heated by heat exchange with combustion exhaust gas, hydrogen electrode off-gas, etc., in a heat exchange section (not shown) installed in the oxygen electrode inlet piping 21b, and then supplied to the oxygen electrode of the electrolytic cell stack 21.

[0021] The hydrogen recovery system 60 recovers the generated hydrogen from the hydrogen electrode off-gas containing the generated hydrogen and unreacted steam discharged from the hydrogen electrode outlet. The hydrogen recovery system 60 includes a hydrogen tank 61, a hydrogen electrode off-gas pipe 62 having one end connected to the hydrogen electrode outlet pipe 21c, a warm water generating heat pump 70 connected to the other end of the hydrogen electrode off-gas pipe 62, and a hydrogen recovery pipe 63 connected to the hydrogen tank 61 and the warm water generating heat pump 70.

[0022] The warm water generating heat pump 70 extracts heat from the hydrogen electrode off-gas to condense the steam contained in the hydrogen electrode off-gas, and at the same time, warms the water in the warm water tank 31 with the extracted heat to generate warm water. The warm water generating heat pump 70 includes a heat extraction heat exchanger (evaporator) 71, a compressor 72, a warm water generating heat exchanger (condenser) 73, an expansion valve 74, and a circulation pipe 75 that connects these so that the refrigerant circulates. The hydrogen electrode off-gas pipe 62 is connected to the inlet of the heat extraction heat exchanger 71, and the hydrogen recovery pipe 63 is connected to the outlet of the heat extraction heat exchanger 71. Further, the warm water tank 31 is connected to the warm water generating heat exchanger 73 via a warm water circulation path 77. A circulation pump 78 for circulating the water in the warm water tank 31 between the warm water tank 31 and the warm water generating heat exchanger 73 is installed in the warm water circulation path 77. The warm water generating heat pump 70 generates warm water by repeating a heat pump cycle of heat reception, compression, heat release, and expansion by the refrigerant, and releasing heat to the water supplied from the warm water tank 31 through the refrigerant that has received heat from the hydrogen electrode off-gas.

[0023] The hydrogen electrode off-gas passes through the warm water generating heat pump 70 (heat extraction heat exchanger 71), whereby the steam in the hydrogen electrode off-gas is condensed and separated into gas-liquid phases into generated hydrogen and condensed water. Then, the generated hydrogen passes through the hydrogen recovery pipe 63 and is pressurized by a booster pump (not shown) and recovered into the hydrogen tank 61. Also, the condensed water is stored in a condensed water tank 65 through a condensed water recovery pipe 64 branched from the hydrogen recovery pipe 63. The condensed water stored in the condensed water tank 65 is supplied to the warm water tank 31.

[0024] <In addition, an exhaust heat recovery heat exchanger 76 is installed between the heat extraction heat exchanger 71 and the compressor 72 in the circulation pipe 75. The exhaust heat recovery heat exchanger 76 exchanges heat between the low-temperature (for example, 80 °C or lower) exhaust heat (unused exhaust heat) that has become unusable and the refrigerant in facilities where a large amount of exhaust heat, such as factory exhaust heat, is generated. As a result, the water in the hot water tank 31 can be further heated using the unused exhaust heat, so that the generation of steam using the hot water in the hot water tank 31 can be performed more efficiently.

[0025] The hydrogen supply system 50 includes an antioxidant hydrogen supply pipe 51 branched from the hydrogen recovery pipe 63 and connected to the hydrogen electrode inlet pipe 21a, a hydrogen blower 52 installed in the antioxidant hydrogen supply pipe 51, a combustion hydrogen supply pipe 53 branched from the hydrogen recovery pipe 63 and connected to the combustor 22, and a hydrogen blower 54 installed in the combustion hydrogen supply pipe 53. A part of the generated hydrogen flowing through the hydrogen recovery pipe 63 is supplied as antioxidant hydrogen to the hydrogen electrode of the electrolytic cell stack 21 through the antioxidant hydrogen supply pipe 51 by driving the hydrogen blower 52. Another part of the generated hydrogen flowing through the hydrogen recovery pipe 63 is supplied as combustion hydrogen to the combustor 22 through the combustion hydrogen supply pipe 53 by driving the hydrogen blower 54.

[0026] Although not shown, the control device 80 is configured as a microprocessor centered on a CPU, and in addition to the CPU, it includes a ROM that stores a processing program, a RAM that temporarily stores data, and input / output ports. Detection signals from temperature sensors installed near the electrolytic cell stack 21, temperature sensors installed in the hot water tank 31, a flow sensor installed in the steam supply pipe 34, a flow sensor installed in the antioxidant hydrogen supply pipe 51, a flow sensor installed in the combustion hydrogen supply pipe 53, etc. are input into the control device 80 via the input ports. On the other hand, control signals from the control device 80 are output to the power supply device 26, the raw water pump 33, the hydrogen blowers 52, 54, the circulation pumps 48, 78, the steam generation heat pump 40, the hot water generation heat pump 70, etc. via the output ports.

[0027] Next, the operation of the electrolytic system 10 of this embodiment, as configured in this way, will be described.

[0028] The control device 80 controls the circulation pump 38 and the raw water pump 33 so that the hot water in the hot water tank 31 circulates through the heat extraction heat exchanger 41 of the steam generation heat pump 40, and the hot water in the hot water tank 31 is supplied to the steam generation heat exchanger 43. As a result, heat is extracted from the hot water in the hot water tank 31 in the steam generation heat pump 40, and steam is generated from the hot water (raw water) in the hot water tank 31 using the extracted heat. The generated steam is supplied to the hydrogen electrode inlet pipe 21a, where it is heated by heat exchange with combustion exhaust gas etc. in the heat exchange section installed in the hydrogen electrode inlet pipe 21a, and then supplied to the hydrogen electrode of the electrolytic cell stack 21. Subsequently, the control device 80 controls the air supply system (air blower) so that air as sweep gas is supplied to the oxygen electrode inlet pipe 21b. The air supplied to the oxygen electrode inlet pipe 21b is heated by heat exchange with hydrogen electrode off-gas, combustion exhaust gas, etc., in a heat exchange section installed in the oxygen electrode inlet pipe 21b, and then supplied to the oxygen electrode of the electrolytic cell stack 21. The control device 80 then controls the power supply unit 26 so that the electrolytic cell stack 21 is supplied with the power necessary for electrolysis.

[0029] The steam supplied to the hydrogen electrode of the electrolytic cell stack 21 is decomposed into hydrogen and oxygen ions by electrolysis at the hydrogen electrode to produce hydrogen, and the oxygen ions permeate the solid electrolyte to produce oxygen at the oxygen electrode. The hydrogen produced at the hydrogen electrode, along with the unreacted steam, is discharged as hydrogen electrode off-gas from the hydrogen electrode outlet of the electrolytic cell stack 21 and supplied to the heat extraction heat exchanger 71 of the hot water generation heat pump 70. The control device 80 controls the circulation pump 78 so that the water in the hot water tank 31 is supplied to the hot water generation heat exchanger 73 of the hot water generation heat pump 70. As a result, heat is extracted from the hydrogen electrode off-gas and, if necessary, from unused waste heat in the hot water generation heat pump 70, and the extracted heat heats the water in the hot water tank 31, thereby producing hot water. The produced hot water is returned to the hot water tank 31. Meanwhile, the hydrogen electrode off-gas supplied to the heat extraction heat exchanger 71 is separated into gas-liquid and gas-liquid components: generated hydrogen and condensed water. The generated hydrogen is recovered into the hydrogen tank 61 via the hydrogen recovery piping 63. The control device 80 controls the hydrogen blowers 52 and 54 so that a portion of the generated hydrogen is supplied to the hydrogen electrode of the electrolytic cell stack 21 as antioxidant hydrogen via the antioxidant hydrogen supply pipe 51, and also supplied to the combustor 22 as combustion hydrogen via the combustion hydrogen supply pipe 53.

[0030] Thus, the electrolysis system 10 generates hot water by extracting heat from the hydrogen electrode off-gas in the hot water generation heat pump 70, and uses the generated hot water as a heat source in the steam generation heat pump 40, as well as as raw water for generating steam. Therefore, by extracting heat from the hydrogen electrode off-gas, the hydrogen electrode off-gas can be separated into gas-liquid and condensed water, allowing for the recovery of generated hydrogen, and steam for electrolysis can be efficiently generated. As a result, the efficiency of hydrogen generation in the electrolysis system 10 can be further improved.

[0031] In the embodiment described above, the hot water tank 31 is connected to a pure water supply pipe 35 and a combustion exhaust gas pipe 36. However, as in the electrolysis system 110 of another embodiment illustrated in Figure 2, a heat exchanger 37 for exchanging heat between pure water and combustion exhaust gas may be installed between the pure water supply pipe 35 and the combustion exhaust gas pipe 36. This allows the pure water supplied to the hot water tank 31 to be heated directly, and steam can be generated more efficiently using the hot water in the hot water tank 31.

[0032] Although the embodiments for implementing this disclosure have been described above, 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]

[0033] This disclosure can be used in industries such as the manufacturing of electrolytic systems. [Explanation of Symbols]

[0034] 10,110 Electrolysis system, 21 Electrolytic cell stack (solid oxide type electrolytic cell), 22 Combustor (combustion section), 31 Hot water tank, 32 Raw water supply pipe (raw water supply route), 40 Steam generation heat pump (steam generation device), 35 Pure water supply piping (water supply route), 36 Combustion exhaust gas piping (combustion exhaust gas supply route), 70 Hot water generation heat pump (hot water generation device), 76 Heat exchanger for exhaust heat extraction (heat exchange section).

Claims

1. A solid oxide electrolytic cell that generates hydrogen by electrolyzing water vapor supplied to the hydrogen electrode, and discharges a hydrogen electrode off-gas containing the generated hydrogen and unreacted water vapor from the hydrogen electrode, A hot water tank that stores water in a way that keeps it warm, A heat pump type hot water generator that extracts heat from the hydrogen electrode off-gas to condense the water vapor in the hydrogen electrode off-gas, and uses the extracted heat to heat the water in the hot water tank, A heat pump type steam generator that extracts heat from the water in the hot water tank and uses the extracted heat to heat the raw water to generate steam, A raw water supply channel that supplies water from the hot water tank as raw water to the steam generator, An electrolytic system equipped with the following features.

2. The electrolytic system according to claim 1, The hot water generating device extracts heat from the hydrogen electrode off-gas and waste heat from outside the system, and uses the extracted heat to heat the water in the hot water tank. Electrolytic system.

3. An electrolytic system according to claim 1 or 2, A combustion section for burning flammable gas, A combustion exhaust gas supply passage supplies the combustion exhaust gas generated in the combustion section to the hot water tank to heat the water in the hot water tank, An electrolytic system equipped with the following features.

4. The electrolytic system according to claim 3, A water supply channel for supplying water to the hot water tank, A heat exchanger that exchanges heat between water flowing through the water supply channel and combustion exhaust gas flowing through the combustion exhaust gas supply channel, An electrolytic system equipped with the following features.

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