Water electrolysis system and synthetic compound production system

Abstract

This water electrolysis system comprises: a water separation tank that is connected to a water electrolysis cell stack and that stores water discharged therefrom; an external water supply path that supplies normal-temperature external water; a water circulation path that is provided with a water circulation pump, that is connected to the water separation tank and the external water supply path, and that circulates the water in the water separation tank via the external water supply path; an ion exchange resin provided on the downstream side of a part where the external water supply path merges with the water circulation path; a cooling unit that cools the water in the water circulation path so that the temperature of the water that merges with the external water and flows into the ion exchange resin, and has a temperature higher than normal temperature, falls below a prescribed ion exchange resin upper limit temperature; and a water supply path that serves as a path separate from the water circulation path, said water supply path being provided with a water supply pump, heating the water from the water separation tank through use of a heating unit, and supplying the heated water to the water electrolysis cell stack.

Description

Water electrolysis system and synthetic compound manufacturing system

[0001] The present invention relates to a water electrolysis system that generates hydrogen and oxygen by electrolyzing water, and a synthetic compound manufacturing system that produces synthetic compounds using hydrogen from this water electrolysis system.

[0002] Conventionally, water electrolysis systems have been proposed that use a water electrolysis cell stack with a solid polymer electrolyte membrane to electrolyze water into hydrogen and oxygen. In such water electrolysis systems, when the water discharged from the water electrolysis cell stack is circulated for use, ions in the circulating water are removed using an ion exchange resin in order to maintain high purity water.

[0003] Generally, the temperature at which ion exchange resins function efficiently is lower than the efficient operating temperature of water electrolysis cell stacks, requiring careful consideration of water temperature.

[0004] For example, in Japanese Patent Publication No. 2002-173788, water separated from oxygen is cooled by a circulating water cooler and sent to a water electrolysis device, with a portion of it branched off to a channel for treatment with ion exchange resin. The water branched off to the channel for treatment with ion exchange resin is further cooled to room temperature by a blowdown water cooler before being used for treatment with ion exchange resin.

[0005] However, in the technology described in Japanese Patent Publication No. 2002-173788, the water is cooled to room temperature in order to accommodate the ion exchange resin, resulting in significant heat loss.

[0006] This invention has been made in consideration of the above facts, and aims to provide a water electrolysis system and a synthetic compound manufacturing system that reduce impurities in raw water while minimizing heat loss.

[0007] A water electrolysis system in the first embodiment includes: a water electrolysis cell stack; a water separation tank connected to the water electrolysis cell stack for separating and storing water discharged from the water electrolysis cell stack from gas; an external water supply channel connected to the water separation tank for supplying external water at room temperature; a water circulation channel equipped with a water circulation pump and connected to the water separation tank and the external water supply channel for circulating water from the water separation tank via the external water supply channel; an ion exchange resin provided downstream of a tank at the confluence of the external water supply channel and the water circulation channel; a cooling unit provided in the water circulation channel for cooling the water in the water circulation channel to a temperature higher than room temperature and lower than a predetermined upper limit temperature of the ion exchange resin when it merges with the external water; and a water supply channel provided with a water supply pump via a separate route from the water circulation channel for heating water from the water separation tank in a heating unit and supplying it to the water electrolysis cell stack.

[0008] According to the first embodiment of the water electrolysis system, the water in the water circulation path is cooled such that the temperature of the water in the cooling section is higher than room temperature, and the temperature of the water that flows into the ion exchange resin after joining with the external water is lower than a predetermined upper limit temperature of the ion exchange resin. Therefore, it is sufficient to cool the water in the water circulation path to a temperature higher than room temperature before joining with the external water at room temperature, thereby reducing heat loss.

[0009] In the second embodiment of the water electrolysis system, a supply water tank is provided at the confluence of the external water supply channel with the water circulation channel or downstream of the confluence, and upstream of the ion exchange resin.

[0010] According to the water electrolysis system of the second embodiment, water can be stably supplied to the ion exchange resin by mixing external water and water in the water circulation path in the supply water tank.

[0011] A third embodiment of the water electrolysis system includes a water temperature measuring unit that measures the water temperature between the confluence and the ion exchange resin, and the cooling unit cools the water in the water circulation path based on the water temperature measured by the water temperature measuring unit so that the temperature of the water flowing into the ion exchange resin becomes a predetermined optimal temperature for the ion exchange resin, which is below the predetermined upper limit temperature of the ion exchange resin.

[0012] According to the third embodiment of the water electrolysis system, cooling in the cooling unit can be performed while taking into account fluctuations in the temperature of the external water.

[0013] In the fourth embodiment of the water electrolysis system, a cation exchange resin with a higher heat resistance than the ion exchange resin is provided upstream of the heating section of the water supply path.

[0014] According to the water electrolysis system of the fourth embodiment, the purity of the water supplied to the water electrolysis cell stack can be increased by providing a cation exchange resin, which generally has a high heat resistance temperature, in the water supply path.

[0015] The fifth embodiment of the synthetic compound production system comprises a water electrolysis system according to any of the first to fourth embodiments, and a reactor that produces a synthetic compound and water using carbon dioxide and hydrogen produced in the water electrolysis cell stack as raw materials, wherein the heating unit is provided upstream of the water electrolysis cell stack in the water supply channel, and heat exchange occurs between the heat medium that recovers the reaction heat from the reactor and the water in the water supply channel.

[0016] According to the synthetic compound production system of the fifth embodiment, the water supplied to the water electrolysis cell stack can be heated using the reaction heat of the reactor.

[0017] According to the present invention, it is possible to reduce impurities in the raw water while minimizing heat loss.

[0018] This is a schematic block diagram showing the configuration of the water electrolysis system according to this embodiment. This is a block diagram showing the connection between the water electrolysis system and the control unit according to this embodiment. This is a schematic block diagram showing the configuration of a modified water electrolysis system according to this embodiment.

[0019] The embodiments for carrying out the present invention will be described below with reference to the drawings.

[0020] [First Embodiment]

[0021] Figure 1 shows a synthetic compound production system 10. The synthetic compound production system 10 includes a water electrolysis system 20 and a synthetic fuel production device 50.

[0022] The water electrolysis system 20 includes a water electrolysis cell stack 22, a water separation tank 24, an ion exchange resin 26, a cooler 38, and a heat exchanger 44.

[0023] The water electrolysis cell stack 22 is formed by stacking water electrolysis cells, each having an electrolyte membrane in between, forming an anode and a cathode. In the water electrolysis cell stack 22, when an electric current is applied, the water supplied to the anode is electrolyzed as shown in equation (1), generating oxygen at the anode and hydrogen at the cathode. The water electrolysis cell stack 22 is connected to the control unit 60 via a DC power supply unit DC, and the amount of current supplied is controlled by the control unit 60, thereby controlling the amount of water electrolysis.

[0024] H ２ O→H ２ + (1 / 2) O ２ (1)

[0025] One end of a water supply channel 42 is connected to the anode-side inlet of the water electrolysis cell stack 22, and water is supplied from the water supply channel 42 to the anode of the water electrolysis cell stack 22. A hydrogen delivery channel 22A is connected to the cathode-side outlet of the water electrolysis cell stack 22, and hydrogen is delivered from the hydrogen delivery channel 22A to the reactor 52 of the synthetic fuel production device 50, which will be described later. One end of a water-oxygen delivery channel 22B is connected to the anode-side outlet of the water electrolysis cell stack 22, and oxygen and water are delivered from the water-oxygen delivery channel 22B. The other end of the water-oxygen delivery channel 22B is connected to a water separation tank 24.

[0026] The water separation tank 24 separates oxygen and water from the water-oxygen delivery passage 22B and stores the separated water. The oxygen delivery passage 24A is connected to the water separation tank 24, and oxygen is delivered from the oxygen delivery passage 24A. The other end of the water supply passage 42 is connected to the water separation tank 24. A water supply pump 48 is provided in the water supply passage 42, and the water supply pump 48 supplies water from the water separation tank 24 to the water electrolysis cell stack 22. The water supply pump 48 is connected to the control unit 60, and its output is controlled by the control unit 60. In this embodiment, the water supply pump 48 is set to flow at a constant flow rate according to the operating load.

[0027] An external water supply channel 32 is connected to the water separation tank 24. The external water supply channel 32 is equipped with, in order from upstream, a control valve 32A, a supply water tank 25, an ion exchange temperature sensor 28, and an ion exchange resin 26. A water level gauge 25A is provided in the supply water tank 25, and when the water level detected by the water level gauge 25A falls below a predetermined level, the control valve 32A is opened, and ambient temperature external water is supplied to the supply water tank 25 from the outside. The control valve 32A and the water level gauge 25A are connected to a control unit 60, and the water level detected by the water level gauge 25A is fed back to the control valve 32A via the control unit 60.

[0028] The ion exchange temperature sensor 28 is installed between the water supply tank 25 and the ion exchange resin 26, and measures the temperature of the water discharged from the water supply tank 25. The ion exchange temperature sensor 28 is connected to the control unit 60, and the measured temperature T is output to the control unit 60.

[0029] An ion exchange resin 26 is provided between the ion exchange temperature sensor 28 of the external water supply channel 32 and the water separation tank 24. The ion exchange resin 26 removes impurities contained in the water by ion exchange treatment and maintains the electrical resistivity at a value close to that of theoretically pure water.

[0030] One end of the water circulation path 30 is connected to the water separation tank 24, and the other end of the water circulation path 30 is connected to the supply water tank 25. A water circulation pump 34 is provided in the water circulation path 30. The water circulation pump 34 discharges water from the water separation tank 24, and the water is returned to the water separation tank 24 via a cooler 38 (described later), the supply water tank 25, and the ion exchange resin 26. The water circulation pump 34 is connected to a control unit 60, and its output is controlled by the control unit 60. In this embodiment, the water circulation pump 34 is set to flow at a constant flow rate.

[0031] A cooler 38 is provided downstream of the water circulation pump 34 in the water circulation path 30. The cooler 38 cools the water flowing through the water circulation path 30 with a heat transfer medium supplied inside. A flow control valve 38A is connected to the control unit 60, and the flow rate of the heat transfer medium supplied into the cooler 38 is adjusted by the flow control valve 38A based on the temperature T.

[0032] Specifically, the cooling of the water in the cooler 38 is performed by adjusting the flow rate control valve 38A so that the temperature T of the water supplied to the ion exchange resin 26 becomes the ion exchange resin appropriate temperature T1 which is the appropriate temperature in the ion exchange resin 26. That is, the flow rate control valve 38A is feedback-controlled by the control unit 60 so that the temperature T becomes the ion exchange resin appropriate temperature T1.

[0033] The ion exchange resin appropriate temperature T1 is set as the temperature (the temperature that can promote ion exchange) at which the ion exchange resin 26 functions efficiently, and is set within the range of 40°C to 70°C. The circulating water flowing into the supply water tank 25 is cooled by the cooler 38 to a temperature T2 higher than the ion exchange resin appropriate temperature T1. Since the external water supplied to the supply water tank 25 is at room temperature, the temperature of the water supplied from the water circulation path 30 to the supply water tank 25 is lowered by the room temperature external water. Therefore, the temperature T2 becomes a temperature higher than room temperature and the ion exchange resin appropriate temperature T1. Note that depending on the conditions of the external water (for example, when the temperature of the external water is very low), the temperature of the circulating water flowing into the ion exchange resin 26 may be lower than the ion exchange resin appropriate temperature T1 only by mixing with the external water. In this case, the cooler 38 becomes unnecessary and cost reduction is possible.

[0034] Also, in the present embodiment, the temperature T of the water supplied to the ion exchange resin 26 is adjusted to be the ion exchange resin appropriate temperature T1 which is the appropriate temperature in the ion exchange resin 26, but the upper limit temperature Tmax at which the ion exchange resin 26 having a temperature higher than the ion exchange resin appropriate temperature T1 can be durable may be set in place of T1. The upper limit temperature Tmax here is the upper limit value of the temperature at which the ion exchange resin 26 can be used.

[0035] As the ion exchange resin 26, for example, a mixed bed product of a strongly acidic cation resin and a strongly basic anion resin, for example, a mixed bed resin of a strongly acidic cation exchange resin having a SO ３ － X ＋ functional group and a strongly basic anion exchange resin having an N ＋ (CH ３ ) ３ ·X － functional group, and a general styrene-based resin matrix can be used.

[0036] Further, as the cooler 38, not only when using cooling water, but also cooling may be performed using air like a radiator. In this case, the degree of cooling can be adjusted by changing the rotational speed of the fan.

[0037] A stack temperature sensor 42T is provided on the downstream side of the water supply pump 48 in the water supply passage 42. The stack temperature sensor 42T detects the temperature T3 of the water flowing through the water supply passage 42 immediately before being supplied to the water electrolysis cell stack 22. The stack temperature sensor 42T is connected to the control unit 60. The temperature T3 measured by the stack temperature sensor 42T is output to the control unit 60. Based on the temperature T3, the flow rate adjustment valve 44A of the heat exchanger 44 described later is adjusted.

[0038] A heat exchanger 44 is provided between the stack temperature sensor 42T and the water supply pump 48 in the water supply passage 42. The heat exchanger 44 performs heat exchange between the heat medium oil from the reactor 52 described later and the water in the water supply passage 42, and heats the water in the water supply passage 42. The flow rate of the heat medium oil supplied to the heat exchanger 44 is adjusted by the flow rate adjustment valve 44A.

[0039] Specifically, the heating of the water in the heat exchanger 44 is performed by adjusting the flow rate adjustment valve 44A so that the temperature T3 of the water supplied to the water electrolysis cell stack 22 becomes the water electrolysis appropriate temperature T4 which is an appropriate temperature for the water electrolysis operation in the water electrolysis cell stack 22. That is, the flow rate adjustment valve 44A is feedback-controlled by the control unit 60 so that the temperature T3 becomes the water electrolysis appropriate temperature T4.

[0040] The synthetic fuel generation device 50 has a reactor 52, and a hydrogen delivery passage 22A and a carbon dioxide supply passage 23 are connected to the reactor 52. Hydrogen electrolyzed in the water electrolysis cell stack 22 is supplied from the hydrogen delivery passage 22A, and carbon dioxide is supplied from the carbon dioxide supply passage 23.

[0041] In the reactor 52, as an example, methane and water are generated by a methane synthesis reaction as shown in the following formula (2).

[0042] 4H ２ + CO ２ → CH４ +2H ２ O (2)

[0043] The synthetic fuel production device 50 is provided with a heat transfer oil circulation path 54. The heat transfer oil circulation path 54 circulates the heat transfer oil between the reactor 52 and the heat exchanger 44. The water in the water supply path 42 is heated by the heat transfer oil sent to the heat exchanger 44 via the heat transfer oil circulation path 54. A heat transfer oil temperature sensor 50T is provided upstream of the reactor 52 and downstream of the heat exchanger 44 in the heat transfer oil circulation path 54. The heat transfer oil temperature sensor 50T detects the temperature T5 of the heat transfer oil that is returned to the synthetic fuel production device 50. The heat transfer oil temperature sensor 50T is connected to a control unit 60 and outputs the detected temperature T5 to the control unit 60.

[0044] A cooler 46 is provided upstream of the temperature sensor 50T in the heat transfer oil circulation path 54 and downstream of the heat exchanger 44. In the cooler 46, the opening of the cooling control valve 46A is adjusted so that the temperature T5 is the appropriate temperature for the synthesis reaction in the reactor 52. The cooling control valve 46A is connected to the control unit 60, and the temperature T5 is fed back and controlled by the control unit 60.

[0045] The synthetic fuel production device 50 is connected to a product gas delivery passage 56, and the product gas produced in the reactor 52, for example, methane and water, is sent to the product gas delivery passage 56.

[0046] As shown in Figure 2, the control unit 60 is connected to a DC power supply DC, a control valve 32A, a water level gauge 25A, a flow rate control valve 38A, a flow rate control valve 44A, an ion exchange temperature sensor 28, a stack temperature sensor 42T, a water circulation pump 34, a water supply pump 48, a heat transfer medium temperature sensor 50T, and a cooling control valve 46A. The control unit 60 is connected to the water electrolysis cell stack 22 via the DC power supply DC. The control unit 60 includes a CPU (Central Processing Unit) 61, a ROM (Read Only Memory) 62, a RAM (Random Access Memory) 63, an input / output interface (I / O) 64, and a storage unit 65.

[0047] The CPU 61, ROM 62, RAM 63, and I / O 64 are connected to each other via the bus 66. Each functional unit, including the storage unit 65, is connected to the I / O 64. These functional units are able to communicate with the CPU 61 via the I / O 64.

[0048] For the storage unit 65, for example, an HDD (Hard Disk Drive), SSD (Solid State Drive), or flash memory may be used. The storage unit 65 stores control programs for controlling each part of the water electrolysis system 20, as well as various data (for example, the optimal temperature T1 for the ion exchange resin and the optimal temperature T2 for water electrolysis). Note that these control programs and various data may also be stored in ROM 62.

[0049] In the water electrolysis system 20 of this embodiment, the water supply path 42 that supplies water to the water electrolysis cell stack 22 and the water circulation path 30, which is equipped with ion exchange resin 26, are separate paths. The water circulation path 30 is connected to an external water supply path, and the water from the water separation tank is circulated via the external water supply path. Therefore, the water temperatures of the water supply path 42 and the water circulation path 30 can be made different. The ion exchange resin 26 is provided downstream of the water circulation path 30 after it merges with the water circulation path 32 of the external water supply path 32, and the cooler 38 is provided in the water circulation path 30. Therefore, the cooler 38 only needs to cool the water to a temperature T2 which is higher than the optimal temperature T1 for the ion exchange resin, so the output of the cooler 38 can be reduced and heat loss can be reduced.

[0050] Furthermore, by mixing external water with water from the water circulation path 30 in the supply water tank 25, water can be stably supplied to the ion exchange resin 26.

[0051] Furthermore, since the cooling in the cooler 38 is feedback-controlled based on the temperature T measured by the ion exchange temperature sensor 28 downstream after the water supply path 32 merges with the water circulation path 30, the cooling in the cooler 38 can be performed while taking into account fluctuations in the temperature of the external water.

[0052] Furthermore, in this embodiment, the water supplied to the water electrolysis cell stack 22 is heated using the reaction heat of the reactor 52, so the reaction heat can be effectively utilized.

[0053] In this embodiment, an ion exchange resin was not provided in the water supply path 42. However, as shown in Figure 3, a cation exchange resin 43 with a higher heat resistance temperature than the ion exchange resin 26 may be provided downstream of the water supply pump 48 and upstream of the heat exchanger 44. By providing the cation exchange resin 43, the purity of the water supplied to the water electrolysis cell stack 22 can be increased. As the cation exchange resin 43, for example, SO ３ － X ＋ A strongly acidic cation exchange resin having functional groups can be used.

[0054] The disclosure of Japanese Patent Application No. 2025-016743 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. A water electrolysis system comprising: a water electrolysis cell stack; a water separation tank connected to the water electrolysis cell stack for separating and storing water discharged from the water electrolysis cell stack from gas; an external water supply channel connected to the water separation tank for supplying external water at room temperature; a water circulation channel equipped with a water circulation pump and connected to the water separation tank and the external water supply channel for circulating water from the water separation tank via the external water supply channel; an ion exchange resin provided downstream of a tank at the confluence of the external water supply channel and the water circulation channel; a cooling unit provided in the water circulation channel for cooling the water in the water circulation channel to a temperature higher than room temperature and lower than a predetermined upper limit temperature of the ion exchange resin when it merges with the external water; and a water supply channel provided with a water supply pump via a separate route from the water circulation channel for heating water from the water separation tank in a heating unit and supplying it to the water electrolysis cell stack.

2. The water electrolysis system according to claim 1, wherein a supply water tank is provided at the confluence of the external water supply channel with the water circulation channel, or downstream of the confluence, and upstream of the ion exchange resin.

3. The water electrolysis system according to claim 2, further comprising a water temperature measuring unit for measuring the water temperature between the confluence and the ion exchange resin, wherein the cooling unit cools the water in the water circulation path to a predetermined ion exchange resin suitable temperature, based on the water temperature measured by the water temperature measuring unit, such that the temperature of the water flowing into the ion exchange resin is below the predetermined upper limit temperature of the ion exchange resin.

4. The water electrolysis system according to claim 1, wherein a cation exchange resin having a higher heat resistance than the ion exchange resin is provided upstream of the heating section of the water supply channel.

5. A synthetic compound production system comprising a water electrolysis system according to any one of claims 1 to 4, and a reactor that produces a synthetic compound and water using carbon dioxide and hydrogen produced in the water electrolysis cell stack as raw materials, wherein the heating section is provided upstream of the water electrolysis cell stack in the water supply channel, and heat exchange occurs between a heat transfer medium that recovers the reaction heat of the reactor and the water in the water supply channel.

Images