Water electrolysis system and synthetic compound manufacturing system

Abstract

To reduce impurities in raw water while minimizing heat loss. [Solution] The water electrolysis system 20 includes a water separation tank 24 connected to the water electrolysis cell stack 22 and storing water discharged from the water electrolysis cell stack 22; an external water supply channel 32 for supplying external water at room temperature; a water circulation channel 30 provided with a water circulation pump 34, connected to the water separation tank 34 and the external water supply channel 32, and circulating water from the water separation tank 34 via the external water supply channel 32; an ion exchange resin 26 provided downstream of the junction of the external water supply channel 32 with the water circulation channel 30; a cooling unit 38 for cooling water in the water circulation channel 30 so that the temperature of the water, which is higher than room temperature and which merges with the external water and flows into the ion exchange resin 26, is lower than a predetermined upper limit temperature of the ion exchange resin; and a water supply channel 42, separate from the water circulation channel 30 and provided with a water supply pump 48, for heating water from the water separation tank 34 in a heating unit 44 and supplying the water to the water electrolysis cell stack 22.

Description

[Technical Field]

[0001] The present invention relates to a water electrolysis system that electrolyzes water to generate hydrogen and oxygen, and a synthetic compound production system that produces a synthetic compound using hydrogen from the water electrolysis system. [Background technology]

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

[0003] Generally, the temperature at which ion exchange resins function efficiently is lower than the efficient operating temperature of a water electrolysis cell stack, and therefore, some ingenuity is required regarding the water temperature. For example, in Patent Document 1, water from which oxygen has been separated is cooled by a circulating water cooler and sent to a water electrolysis device, with a portion of the water being branched off to a flow path for treatment with ion exchange resins. The water branched off to the flow path for treatment with ion exchange resins is further cooled to room temperature by a blow-off water cooler and then sent to treatment with ion exchange resins.

[0004] However, in the technology of Patent Document 1, the water is cooled to room temperature in order to be compatible with ion exchange resins, resulting in a large heat loss. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-173788 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a water electrolysis system and a synthetic compound production system that reduce impurities in raw water while minimizing heat loss. [Means for solving the problem]

[0007] A water electrolysis system according to a first aspect includes a water electrolysis cell stack; a water separation tank connected to the water electrolysis cell stack for separating water discharged from the water electrolysis cell stack from gas and storing the water; an external water supply channel connected to the water separation tank for supplying external water at room temperature; a water circulation channel provided with a water circulation pump, 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; and a water circulation channel at a junction of the external water supply channel and the water circulation channel. Tank installed in the water electrolysis cell stack.

[0008] In the water electrolysis system of the first aspect, the water in the water circulation channel is cooled so that the temperature of the water that is higher than room temperature in the cooling unit and that joins with the external water and flows into the ion exchange resin 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 channel to a temperature higher than room temperature before joining with the external water at room temperature, thereby reducing heat loss.

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

[0010] According to the water electrolysis system of the second aspect, by mixing the external water with the water in the water circulation channel in the supply water tank, water can be stably delivered to the ion exchange resin.

[0011] A water electrolysis system according to a third aspect includes a water temperature measuring unit that measures the temperature of water flowing from the confluence to the ion exchange resin, and the cooling unit determines whether the temperature of the water flowing into the ion exchange resin is equal to or lower than the temperature measured by the water temperature measuring unit. the temperature is lower than the predetermined upper limit temperature of the ion exchange resin The water in the water circulation passage is cooled to a predetermined optimum temperature for the ion exchange resin.

[0012] According to the water electrolysis system of the third aspect, the cooling unit can perform cooling taking into account fluctuations in the temperature of the external water.

[0013] In a fourth aspect of the water electrolysis system, the water supply channel further includes: Higher heat resistance than the ion exchange resin A cation exchange resin is provided.

[0014] According to the water electrolysis system of the fourth aspect, 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 channel.

[0015] A synthetic compound production system of a fifth aspect includes the water electrolysis system of any one of the first to fourth aspects, 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, and the heating unit is provided in the water supply channel upstream of the water electrolysis cell stack and performs heat exchange between a heat medium that recovers reaction heat in the reactor and water in the water supply channel.

[0016] According to the synthetic compound production system of the fifth aspect, the temperature of the water supplied to the water electrolysis cell stack can be increased using the reaction heat of the reactor. [Effects of the Invention]

[0017] According to the present invention, impurities in raw water can be reduced while heat loss is reduced. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a block diagram schematically illustrating the configuration of a water electrolysis system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing connections to a control unit of the water electrolysis system according to the present embodiment. [Figure 3] FIG. 10 is a block diagram schematically illustrating the configuration of a water electrolysis system according to a modified example of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] [First embodiment]

[0021] 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 forming an anode and a cathode with an electrolyte membrane sandwiched between them. In the water electrolysis cell stack 22, when electricity is applied, water supplied to the anode is electrolyzed as shown in formula (1), generating oxygen at the anode and hydrogen at the cathode. The water electrolysis cell stack 22 is connected to a control unit 60 via a DC power supply DC, and the control unit 60 controls the amount of electricity applied and, therefore, the amount of water electrolysis.

[0024] H2O→H2+(1 / 2)O2(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 a reactor 52 of a synthetic fuel generator 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 the water separation tank 24.

[0026] The water separation tank 24 separates the oxygen and water from the water / oxygen delivery channel 22B and stores the separated water. The oxygen delivery channel 24A is connected to the water separation tank 24, and oxygen is delivered from the oxygen delivery channel 24A. The other end of the water supply channel 42 is connected to the water separation tank 24. A water supply pump 48 is provided in the water supply channel 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 a control unit 60, and the output of the water supply pump 48 is controlled by the control unit 60. In this embodiment, the water supply pump 48 is set to deliver a constant flow rate depending on the operating load.

[0027] An external water supply passage 32 is connected to the water separation tank 24. In the external water supply passage 32, an adjustment valve 32A, a supply water tank 25, an ion exchange temperature sensor 28, and an ion exchange resin 26 are provided, in that order from the upstream side. 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 adjustment valve 32A is opened and external water at room temperature is supplied from the outside to the supply water tank 25. The adjustment 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 adjustment valve 32A via the control unit 60.

[0028] The ion exchange temperature sensor 28 is provided between the supply water tank 25 and the ion exchange resin 26, and measures the temperature of the water delivered from the supply water 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 in the external water supply line 32 and the water separation tank 24. The ion exchange resin 26 performs an ion exchange treatment on the water to remove impurities contained in the water and maintain the electrical resistivity at a value close to that of theoretically pure water.

[0030] One end of a 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 sends water out of the water separation tank 24 and returns the water to the water separation tank 24 via a cooler 38, the supply water tank 25, and the ion exchange resin 26, which will be described later. 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 supply a constant flow rate.

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

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

[0033] The optimum ion exchange resin temperature T1 is set as a temperature that allows the ion exchange resin 26 to function efficiently (a temperature that can promote ion exchange), and is set in 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 that is higher than the optimum ion exchange resin temperature T1. Because the external water supplied to the supply water tank 25 is at room temperature, the water supplied from the water circulation path 30 to the supply water tank 25 is cooled by the external water at room temperature. Therefore, the temperature T2 is higher than room temperature and the optimum ion exchange resin 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 become lower than the optimum ion exchange resin temperature T1 simply by mixing with the external water. In this case, the cooler 38 is not required, which can reduce costs.

[0034] In this embodiment, the temperature T of the water supplied to the ion exchange resin 26 is adjusted to be the optimum ion exchange resin temperature T1, which is the optimum temperature for the ion exchange resin 26. However, an upper limit temperature Tmax that the ion exchange resin 26 can withstand, which is higher than the optimum ion exchange resin temperature T1, may be set instead of T1. The upper limit temperature Tmax here is the upper limit of the temperature at which the ion exchange resin 26 can be used.

[0035] The ion exchange resin 26 may be, for example, a mixed bed of a strong acid cation resin and a strong base anion resin, such as SO3 - X + A strong acid cation exchange resin with functional groups and N + (CH3)3·X - The mixed bed resin of the anion exchange resin having functional groups can be a general styrene-based resin matrix.

[0036] The cooler 38 may use air as cooling, like a radiator, instead of cooling water. In this case, the degree of cooling can be adjusted by changing the rotation speed of the fan.

[0037] A stack temperature sensor 42T is provided downstream of the water supply pump 48 in the water supply channel 42. The stack temperature sensor 42T detects the temperature T3 of the water flowing through the water supply channel 42 immediately before it is 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. A flow rate adjustment valve 44A of a heat exchanger 44 (described later) is adjusted based on the temperature T3.

[0038] A heat exchanger 44 is provided in the water supply passage 42 between the stack temperature sensor 42T and the water supply pump 48. The heat exchanger 44 exchanges heat between the heat transfer oil from the reactor 52 (described later) and the water in the water supply passage 42, thereby heating the water in the water supply passage 42. The flow rate of the heat transfer oil supplied to the heat exchanger 44 is adjusted by a flow control valve 44A.

[0039] Specifically, the flow rate control valve 44A is adjusted to heat the water in the heat exchanger 44 so that the temperature T3 of the water supplied to the water electrolysis cell stack 22 becomes the optimum water electrolysis temperature T4, which is the optimum temperature for water electrolysis in the water electrolysis cell stack 22. In other words, the flow rate control valve 44A is feedback-controlled by the control unit 60 so that the temperature T3 becomes the optimum water electrolysis temperature T4.

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

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

[0042] 4H2+CO2→CH4+2H2O (2)

[0043] The synthetic fuel generator 50 is provided with a heat transfer oil circulation path 54. The heat transfer oil circulation path 54 circulates 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 medium temperature sensor 50T is provided on the heat transfer oil circulation path 54 upstream of the reactor 52 and downstream of the heat exchanger 44. The heat transfer medium temperature sensor 50T detects the temperature T5 of the heat transfer oil returned to the synthetic fuel generator 50. The heat transfer medium temperature sensor 50T is connected to the control unit 60 and outputs the detected temperature T5 to the control unit 60.

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

[0045] A product gas delivery line 56 is connected to the synthetic fuel generator 50, and the product gas produced in the reactor 52, such as methane and water, is delivered to the product gas delivery line 56.

[0046] 2 , the control unit 60 is connected to the DC power supply DC, the adjustment valve 32A, the water level gauge 25A, the flow rate adjustment valve 38A, the flow rate adjustment valve 44A, the ion exchange temperature sensor 28, the stack temperature sensor 42T, the water circulation pump 34, the water supply pump 48, the heat medium temperature sensor 50T, and the cooling adjustment 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 a bus 66. The I / O 64 is connected to various functional units including a storage unit 65. These functional units are capable of communicating with the CPU 61 via the I / O 64.

[0048] The storage unit 65 may be, for example, a hard disk drive (HDD), a solid state drive (SSD), or a flash memory. The storage unit 65 stores control programs for controlling the various components of the water electrolysis system 20 and various data (e.g., the optimum temperature T1 for ion exchange resin and the optimum temperature T2 for water electrolysis). The control programs and various data may be stored in the ROM 62.

[0049] In the water electrolysis system 20 of this embodiment, the water supply channel 42 that supplies water to the water electrolysis cell stack 22 and the water circulation channel 30 provided with the ion exchange resin 26 are separate channels, and the water circulation channel 30 is connected to an external water supply channel so that water from the water separation tank circulates via the external water supply channel. This allows the water temperatures of the water supply channel 42 and the water circulation channel 30 to be different. The ion exchange resin 26 is provided downstream of the external water supply channel 32 after it joins with the water circulation channel 30, and the cooler 38 is provided in the water circulation channel 30. This allows the cooler 38 to cool the water to T2, which is higher than the optimum temperature T1 for the ion exchange resin, thereby reducing the output of the cooler 38 and heat loss.

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

[0051] In addition, 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 external water supply path 32 joins the water circulation path 30, so that the cooling in the cooler 38 can be performed taking into account fluctuations in the water temperature of the external water.

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

[0053] In this embodiment, no ion exchange resin is provided in the water supply channel 42. However, as shown in FIG. 3, a cation exchange resin 43 having 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. The cation exchange resin 43 may be, for example, a cation exchange resin containing SO3 - X + A strong acid cation exchange resin having functional groups can be used. [Explanation of symbols]

[0054] 10. Synthetic Compound Manufacturing System 20 Water electrolysis system 22 Water electrolysis cell stack 24 Water Separator Tank 25 Supply water tank 26 Ion exchange resin 30 Water circulation path 32 External water supply channel 34 Water circulation pump 38 Cooler (cooling section) 42 Water supply channel 43 Cation Exchange Resin 44 Heat exchanger (heating section) 50 Synthetic fuel generator 52 Reactor

Claims

1. a water electrolysis cell stack; a water separation tank connected to the water electrolysis cell stack, which separates water discharged from the water electrolysis cell stack from gas and stores the water; an external water supply line connected to the water separation tank and supplying external water at room temperature; a water circulation path provided with a water circulation pump, connected to the water separation tank and the external water supply path, and circulating the water in the water separation tank via the external water supply path; an ion exchange resin disposed downstream of a tank disposed at a junction of the external water supply channel and the water circulation channel; a cooling unit provided in the water circulation path, which cools the water in the water circulation path so that the temperature of the water that is higher than room temperature and that joins the external water and flows into the ion exchange resin is lower than a predetermined upper limit temperature of the ion exchange resin; a water supply channel provided with a water supply pump and separate from the water circulation channel, for heating water from the water separation tank with a heating unit and supplying the heated water to the water electrolysis cell stack; A water electrolysis system equipped with

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

3. a water temperature measuring unit for measuring the water temperature between the confluence and the ion exchange resin; 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 optimum temperature for the ion exchange resin that is lower than the predetermined upper limit temperature of the ion exchange resin. The water electrolysis system according to claim 2 .

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

5. A water electrolysis system according to any one of claims 1 to 4; a reactor for producing a synthetic compound and water using carbon dioxide and hydrogen produced in the water electrolysis cell stack as raw materials; the heating unit is provided in the water supply channel upstream of the water electrolysis cell stack, and performs heat exchange between a heat medium that recovers reaction heat from the reactor and water in the water supply channel. Synthetic compound manufacturing system.

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