Water electrolysis system and method for producing gas by electrolysis of water

Abstract

To provide a technology for supplying high-purity gas by removing impurities from gas containing hydrogen or oxygen produced by electrolysis of water.SOLUTION: A water electrolysis system 2 comprises: a first cooling device 10 that cools gas containing a predetermined gas component generated by electrolysis of water to a high first cooling temperature equal to or higher than the boiling point of the gas component to liquefy a first impurity having a boiling point higher than the first cooling temperature in a separable manner; a gas-liquid separation device 20 that separates the first impurity liquefied by the first cooling device 10 from the gas; and a second cooling device 30 that cools the gas from which the first impurity has been separated to a second cooling temperature lower than the boiling point of the gas component to liquefy the gas component in a separable manner so as to separate a second impurity having a boiling point lower than the second cooling temperature as gas.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present specification relates to a water electrolysis system and a method for producing gas by electrolysis of water. [Background technology]

[0002] This type of water electrolysis system electrolyzes water to produce component gases containing hydrogen or oxygen as gas components, which are then supplied to a fuel cell, etc. In the water electrolysis system, moisture in the component gases is discharged to the outside of the system using a dehumidifying device that uses cooling by heat exchange with a desiccant or refrigerant (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-019061 Summary of the Invention [Problem to be solved by the invention]

[0004] Using a dehumidifier can remove water from gas. However, it cannot remove impurities from hydrogen gas, such as oxygen, which leaks from the oxygen electrode side to the hydrogen electrode side through the electrolyte membrane of the water electrolysis device. Also, it cannot remove hydrogen from oxygen gas, which leaks from the hydrogen electrode side to the oxygen electrode side.

[0005] The present specification provides a technology for removing impurities from a gas containing hydrogen or oxygen produced by electrolysis of water, thereby supplying a high-purity gas. [Means for solving the problem]

[0006] The technology disclosed in this specification is embodied in a water electrolysis system. The water electrolysis system includes a first cooling device that cools a gas containing predetermined gas components produced by water electrolysis to a first cooling temperature equal to or higher than the boiling point of the gas components and liquefies a first impurity having a boiling point higher than the first cooling temperature so as to be separable from the gas components, a gas-liquid separation device that separates the first impurity liquefied by the first cooling device from the gas, and a second cooling device that cools the gas from which the first impurity has been separated to a second cooling temperature lower than the boiling point of the gas components and liquefies the gas components so as to be separable from the second impurity having a boiling point lower than the second cooling temperature.

[0007] In this water electrolysis system, if a first impurity having a boiling point higher than the first cooling temperature is present, it is liquefied and separated by the first cooling device. If a second impurity having a boiling point lower than the second cooling temperature is present, it is gasified and separated by the second cooling device. Since the first impurity and the second impurity are removed from the gas, it is possible to produce a gas containing the specified gas components at a high purity.

[0008] For example, when the predetermined gas component is hydrogen, it is cooled to a first cooling temperature that is equal to or higher than the boiling point of hydrogen (-253°C). As a result, substances with boiling points higher than the first cooling temperature, such as water (boiling point: 100°C) and oxygen (boiling point: -183°C), are liquefied. The liquefied water and oxygen are separated from the hydrogen. Next, the gas from which the water and oxygen have been separated is cooled to a second cooling temperature that is lower than the boiling point of hydrogen. As a result, the hydrogen is liquefied, and if there are impurities with boiling points lower than the second cooling temperature, these will remain as gas. The impurities that remain as gas are separated from the liquid hydrogen.

[0009] For example, when the predetermined gas component is oxygen, the gas is cooled to a first cooling temperature that is equal to or higher than the boiling point of oxygen. As a result, a substance with a boiling point higher than the first cooling temperature, such as water, is liquefied. The liquefied water is separated from the oxygen. Next, the gas from which the water has been separated is cooled to a second cooling temperature that is lower than the boiling point of oxygen. As a result, the oxygen is liquefied, and if there are impurities with a boiling point lower than the second cooling temperature, such as hydrogen, these will remain as a gas. The hydrogen and other impurities that remain as a gas are separated from the liquid oxygen.

[0010] The technology disclosed in this specification is also embodied in a method for producing a liquid material by electrolysis of water. This method includes a first cooling step of cooling a gas containing electrolyzed water supplied from an electrolysis device to a first cooling temperature equal to or higher than the boiling point of the liquid material to liquefy a first impurity having a boiling point higher than the first cooling temperature, a step of separating the first impurity from the gas into gas and liquid, and a second cooling step of cooling the gas from which the first impurity has been separated to a second cooling temperature lower than the boiling point of the liquid material to liquefy the gas component so that a second impurity having a boiling point lower than the second cooling temperature can be separated as a gas.

[0011] According to this manufacturing method, the first impurity is liquefied and separated from the gas in the first cooling step. The gasified liquid material is liquefied and separated from the gas from which the first impurity has been separated in the second cooling step. As a result, a highly pure liquid material is produced. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating an overview of an example of a water electrolysis system. [Figure 2] FIG. 1 is a diagram showing a process for producing electrolytic gas using a water electrolysis system. [Figure 3] FIG. 4 is a diagram showing the relationship between gas components and cooling temperature during hydrogen gas production. [Figure 4] FIG. 4 is a diagram showing the relationship between gas components and cooling temperature during oxygen gas production. [Figure 5]FIG. 10 is a diagram illustrating an outline of another configuration example of a water electrolysis system. DETAILED DESCRIPTION OF THE INVENTION

[0013] The water electrolysis system disclosed in this specification (hereinafter also simply referred to as the present system) comprises a first cooling device that cools a gas containing predetermined gas components produced by water electrolysis to a first cooling temperature that is equal to or higher than the boiling point of the gas components, and liquefies first impurities having a boiling point higher than the first cooling temperature so as to be separable from the gas components; a gas-liquid separation device that separates the first impurities liquefied in the first cooling device from the gas; and a second cooling device that cools the gas from which the first impurities have been separated to a second cooling temperature that is lower than the boiling point of the gas components, and liquefies the gas components so as to be separable from the gas a second impurity having a boiling point lower than the second cooling temperature.

[0014] In one embodiment of the present system, the gas component is hydrogen or oxygen, which are gas components produced by electrolysis of water.

[0015] In one embodiment of this system, the gas component is hydrogen, the first cooling temperature is a temperature equal to or higher than the boiling point of hydrogen and lower than the boiling point of oxygen, and the second cooling temperature is a temperature lower than the boiling point of hydrogen.

[0016] In one embodiment of this system, the gas component is oxygen, the first cooling temperature is a temperature equal to or higher than the boiling point of oxygen, and the second cooling temperature is a temperature lower than the boiling point of oxygen and equal to or higher than the boiling point of hydrogen.

[0017] In one embodiment of this system, the first cooling device includes a first heat exchanger and a cooler that cools the first heat exchanger, and the second cooling device includes a second heat exchanger and a cooler that cools the second heat exchanger.

[0018] The method for producing a liquid material by water electrolysis disclosed in this specification (hereinafter simply referred to as this method) comprises a first cooling step in which water supplied from an electrolysis device is electrolyzed gas, the gas containing the gasified liquefied material is cooled to a first cooling temperature equal to or higher than the boiling point of the liquefied material, and a first impurity having a boiling point higher than the first cooling temperature is liquefied; a step of separating the first impurity from the gas into gas and liquid; and a second cooling step in which the gas from which the first impurity has been separated is cooled to a second cooling temperature lower than the boiling point of the liquefied material, and the gasified liquid material is liquefied so that a second impurity having a boiling point lower than the second cooling temperature can be separated as a gas.

[0019] In this method, the gas components already described in relation to this system correspond to the gasified liquid material. Also, the various embodiments of the first cooling temperature and the second cooling temperature already described in relation to this system can be applied to this method. Furthermore, this system can be used to produce liquid materials by electrolysis of water.

[0020] The present system 2 and the method for producing a liquid material will be described below with reference to the appropriate drawings. Fig. 1 shows an example of the present system 2, Fig. 2 shows the process for producing a liquid material using the present system, and Fig. 3 shows the relationship between the electrolytic gas and the cooling temperature during the production of liquid hydrogen. Figs. 1 to 3 illustrate an example of a system and process for producing liquid hydrogen by water electrolysis. Hydrogen is an example of a predetermined gas component in this specification.

[0021] The first and second cooling temperatures in the first and second cooling devices shown in this specification are both temperatures under 1 atmosphere. However, under high pressure exceeding 1 atmosphere or reduced pressure below 1 atmosphere, the boiling points of gas components such as hydrogen and oxygen change depending on the pressure, and the first and second cooling temperatures also change accordingly.

[0022] The system 2 includes a water electrolysis device 4, a first cooling device 10, a gas-liquid separation device 20, a second cooling device 30, and a tank 40. The system 2 further includes a piping system 50 that allows the electrolytic gas or liquid to circulate between these elements. Although not shown, the system 2 also includes sensors that detect the temperatures of the first cooling device 10, the gas-liquid separation device 20, the second cooling device 30, and the tank 40, and a controller that performs temperature control, thereby controlling the temperatures of these devices.

[0023] The water electrolysis device 4 is not particularly limited as long as it can produce hydrogen or oxygen by electrolysis of water. The water electrolysis device 4 can have a configuration known to those skilled in the art. The water electrolysis device 4 may be a water electrolysis device based on various types of electrolysis, such as alkaline water electrolysis, solid polymer water electrolysis, or solid oxide water electrolysis. Of these, the water electrolysis device 4 is a water electrolysis device using alkaline water electrolysis or solid polymer water electrolysis. The water electrolysis device 4 is configured to be able to supply hydrogen produced by the water electrolysis device 4 to the first cooling device 10.

[0024] The first cooling device 10 includes a heat exchanger 12 and a refrigerator 14. The heat exchanger 12 and the refrigerator 14 are not particularly limited, and a known heat exchanger and refrigerator can be used, respectively. The gas cooled by the first cooling device 10 is configured to be able to be supplied to a gas-liquid separator 20. This gas contains hydrogen as a main component, and may also contain water and oxygen as impurities.

[0025] As shown in Fig. 3, the first cooling device 10 is configured to be able to cool the supplied gas to a first cooling temperature T1 during the production of liquid hydrogen. Here, the first cooling temperature T1 is equal to or higher than the boiling point of hydrogen (-253°C). The first cooling temperature T1 is a temperature at which impurities having a boiling point higher than the first cooling temperature T1 (here, oxygen and water, which are impurities having a boiling point higher than that of hydrogen) can be liquefied. In this embodiment, the temperature is lower than the boiling point of oxygen (-183°C) in order to separate oxygen as a liquid.

[0026] By cooling a gas containing water to the first cooling temperature T1, at least a portion of the impurities having a boiling point higher than the first cooling temperature T1 are liquefied. As shown in FIG. 3, in this embodiment, the impurities are acid and water (boiling point 100°C). The impurities liquefied at the first cooling temperature T1 are an example of the first impurities in this specification. When water and oxygen are targeted as the first impurities, water and oxygen can be liquefied if the first cooling temperature T1 is higher than the boiling point of hydrogen and lower than the boiling point of oxygen. The first cooling temperature T1 is set appropriately depending on the boiling points of the component gases, cooling efficiency, cost, and the boiling points of the impurities to be separated.

[0027] The gas-liquid separator 20 separates the liquid from the gas supplied from the first cooling device 10. Specifically, the gas-liquid separator 20 separates water and oxygen, which are liquid impurities, from a gas containing gaseous hydrogen and impurities liquefied by the first cooling device. The gas from which the impurity liquid has been separated by the gas-liquid separator 20 is supplied to the second cooling device 30. The gas-liquid separator 20 can be appropriately selected from known gas-liquid separators and used.

[0028] The impure liquid separated in the gas-liquid separator 20 is stored in a temporary storage tank 22. The impure liquid in the temporary storage tank 22 is discharged to the outside of the system 2 by closing the valve 24 and opening the valve 26.

[0029] The second cooling device 30 includes a heat exchanger 32 and a refrigerator 34. The heat exchanger 32 and the refrigerator 34 are not particularly limited, and a known heat exchanger and refrigerator can be used, respectively. The gas cooled by the second cooling device 30 is configured to be able to be supplied to a tank 40.

[0030] As shown in FIG. 3, for example, the second cooling device 30 is configured to be able to cool the supplied gas to a second cooling temperature T2 when producing liquid hydrogen. The second cooling temperature T2 is lower than the first cooling temperature T1 and lower than the boiling point of hydrogen (−253°C). The second cooling temperature is a temperature at which second impurities having a boiling point lower than the second cooling temperature T2 (here, impurities having a boiling point lower than that of hydrogen) remain as a gas. Note that, because the freezing point of hydrogen is −259°C, it may be preferable to use a temperature higher than −259°C to avoid freezing of hydrogen.

[0031] By cooling to the second cooling temperature T2, hydrogen is liquefied or solidified from a gaseous state. At least a portion of impurities having a boiling point lower than the second cooling temperature T2 remain as a gas. For example, there is helium (-269°C). Impurities that remain as a gas even at the second cooling temperature T2 are an example of the second impurity in this specification. At least a portion of the second impurity is contained in the liquid hydrogen in a gaseous state. Note that the second cooling temperature T2 is a temperature equal to or higher than the boiling point of the impurity that is desired to remain as a gas. The second cooling temperature T2 is set appropriately depending on the boiling points of the component gases, cooling efficiency, cost, the boiling points of the impurities to be separated, and the like.

[0032] The tank 40 stores the cooled liquid from the second cooling device 30. The tank 40 is configured, for example, to be able to maintain the liquid at the second cooling temperature T2. In this way, impurities that remain in a gaseous state by the second cooling device 30 are stored in the tank 40 together with the liquid hydrogen. Furthermore, the second impurities are separated from the liquid hydrogen by gas-liquid separation in the tank 40. The liquid hydrogen from which the impurities have been separated as a gas is supplied to a hydrogen user by opening the valve 42. In addition to storing liquid hydrogen, the tank 40 also functions as a gas-liquid separator for gasified impurities.

[0033] The system 2 may include a gasification device that gasifies a liquid material such as liquid hydrogen.

[0034] Next, with reference to FIGS. 2 and 3, a process for producing liquid hydrogen, which is an example of a liquid material, by electrolysis of water using the present system 2 will be described.

[0035] 2, in the water electrolysis step S10, water is electrolyzed in the water electrolysis device 4. Hydrogen gas generated by the electrolysis is supplied to the first cooling device 10.

[0036] In the first cooling step S20, the supplied hydrogen gas is cooled to a first cooling temperature T1. By cooling to the first cooling temperature T1, at least a portion of the water and oxygen contained in the hydrogen gas is liquefied, as shown in Fig. 3. The gas cooled in the first cooling device 10 is supplied to the gas-liquid separator 20.

[0037] In the gas-liquid separation step S30, water and oxygen are separated as liquid from the hydrogen gas in which at least a portion of these has been liquefied. The liquid is stored in a temporary storage tank 22 and is discharged outside the system 2 at an appropriate time. The hydrogen gas from which the liquid has been separated is supplied from the gas-liquid separator 20 to the second cooling device 30.

[0038] In the second cooling step S40, the hydrogen gas supplied to the second cooling device 30 is cooled to a second cooling temperature T2. The second cooling temperature T2 is a temperature lower than the boiling point of hydrogen (-253°C). By being cooled to the second cooling temperature T2, the hydrogen gas is liquefied, as shown in FIG. 3. Furthermore, at least a portion of the impurities having a boiling point lower than the second cooling temperature T2 remain in a gaseous state and are contained in the liquid hydrogen. The liquid hydrogen is supplied from the second cooling device 30 to the tank 40.

[0039] In the storage step S50, the liquid hydrogen supplied to the tank 40 is stored while being maintained at the second cooling temperature T2. While the liquid hydrogen is stored in the tank 40, gas impurities are separated from the liquid hydrogen. Such impurity-containing gas is stored as a gas phase in the head space of the tank 40, for example.

[0040] The liquid phase portion of the tank 40 is converted into liquid hydrogen containing higher purity hydrogen by removing impurities (water and oxygen) having a boiling point higher than the first cooling temperature T1 and impurities having a boiling point lower than the second cooling temperature T2. This liquid hydrogen is supplied to a user (site of use) outside the system 2 by opening the valve 42. The liquid hydrogen may be gasified by a gasification device that may be provided in the system 2, or may be gasified at the supply destination.

[0041] Furthermore, by discharging a portion of the gas phase of the tank 40 outside the system 2 and increasing the internal pressure by evaporating gas from the liquid hydrogen, the impurity concentration in the gas phase and therefore in the liquid phase can be further reduced.

[0042] Although the above description has been made on the production of liquid hydrogen or hydrogen gas by water electrolysis, the present system 2 can also be used directly to produce liquid oxygen or oxygen gas, which are examples of liquid materials, from the water electrolysis device 4. That is, the first cooling device 10, gas-liquid separator 20, second cooling device 30, and tank 40 of the present system 2 can be applied to the production of liquid oxygen or oxygen gas. Note that the present system 2 can also be provided with a separate first cooling device, gas-liquid separator, second cooling device, tank, and pipeline system for liquid oxygen, etc.

[0043] The production of oxygen gas using this system 2 can be carried out in the same manner as the production of hydrogen gas described above, except for the first cooling temperature in the first cooling device and the second cooling temperature in the second cooling device. The first cooling temperature in the first cooling device, the second cooling temperature in the second cooling device, and other factors when producing oxygen gas will be described below with reference to Fig. 4. Note that the oxygen gas produced by the water electrolysis device 4 contains oxygen as a main component, and may also contain water and hydrogen as impurities.

[0044] As shown in FIG. 4, in the case of oxygen gas, the first cooling temperature is a temperature equal to or higher than the boiling point of oxygen (-183°C). By cooling to the first cooling temperature T1, at least a portion of impurities having a boiling point higher than the first cooling temperature T1 are liquefied. For example, water (boiling point 100°C). If the first cooling temperature T1 is a temperature higher than the boiling point of oxygen, water can be liquefied. Here, hydrogen as an impurity is in a gaseous state along with oxygen. Note that the first cooling temperature T1 is a temperature lower than the boiling point of water (100°C).

[0045] As shown in FIG. 4, the second cooling temperature T2 is lower than the first cooling temperature T1 and lower than the boiling point of oxygen (-183°C). The second cooling temperature T2 is a temperature equal to or higher than the boiling point of hydrogen. By cooling to the second cooling temperature T2, the oxygen is liquefied. At least some of the impurities having a boiling point lower than the second cooling temperature T2 remain as gas. An example of such impurities is hydrogen (-253°C). At least some of the impurities are contained in the liquefied oxygen in a gaseous state.

[0046] The liquid oxygen cooled to the second cooling temperature T2 is stored in the tank 40 at the second cooling temperature T2. In the tank 40, impurities such as hydrogen are separated into a gas phase from the liquid oxygen by gas-liquid separation. The separated liquid oxygen is supplied to a destination as needed. The liquid oxygen is also gasified as needed.

[0047] As described above, the present system 2 and the method for producing gas by electrolysis of water can also be applied to the production of liquid oxygen and oxygen gas.

[0048] In the above description, the present system 2 includes the first cooling device 10, the gas-liquid separator 20, and the second cooling device 30, but is not limited to this. For example, as shown in FIG. 5, an additional cooling device 60, a gas-liquid separator 70, and a temporary storage tank 72 may be provided. By setting an additional cooling temperature in the additional cooling device 60, for example, when impurities other than water, oxygen, and hydrogen may be contained, it is possible to separate the multiple impurities by converting them into liquid or gas. The additional cooling device 60 may include a heat exchanger 62 and a refrigerator 64.

[0049] Furthermore, for example, as also shown in FIG. 5, an impurity separation device 80 using an adsorbent material that adsorbs impurities such as water, such as a conventional dehumidifying agent, may be provided.

[0050] Although several specific examples have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility either alone or in combination. [Explanation of symbols]

[0051] 2 Electrolysis system, 4 Water electrolysis device, 10 First cooling device, 12 Heat exchanger, 14 Refrigeration machine, 20 Gas-liquid separator, 22 Impurity storage tank, 30 Second cooling device, 32 Heat exchanger, 34 Refrigeration machine, 40 Tank, 50 Pipe system, 60 Additional cooling device, 70 Additional gas-liquid separator, 80 Impurity separator

Claims

1. A water electrolysis system, a first cooling device that cools a gas containing a predetermined gas component generated by electrolysis of water to a first cooling temperature that is higher than or equal to the boiling point of the gas component, thereby liquefying a first impurity having a boiling point higher than the first cooling temperature so as to be separable into a liquid; a gas-liquid separator that separates the first impurities liquefied by the first cooling device from the gas; a second cooling device that cools the gas from which the first impurity has been separated to a second cooling temperature that is lower than the boiling point of the gas component, and liquefies the gas component so that a second impurity having a boiling point lower than the second cooling temperature can be separated as a gas; A system comprising:

2. The system of claim 1 , wherein the gas component is hydrogen or oxygen.

3. the gas component is hydrogen, 3. The system of claim 2, wherein the first cooling temperature is a temperature equal to or greater than the boiling point of hydrogen and less than the boiling point of oxygen, and the second cooling temperature is a temperature less than the boiling point of hydrogen.

4. the gas component is oxygen, 3. The system of claim 2, wherein the first cooling temperature is a temperature equal to or greater than the boiling point of oxygen, and the second cooling temperature is a temperature lower than the boiling point of oxygen and equal to or greater than the boiling point of hydrogen.

5. the first cooling device includes a first heat exchanger and a cooler that cools the first heat exchanger, The system according to any one of claims 1 to 4, wherein the second cooling device includes a second heat exchanger and a cooler that cools the second heat exchanger.

6. A method for producing a liquid material by electrolysis of water, comprising: a first cooling step in which water supplied from an electrolysis device is electrolyzed gas, and the gas containing the gasified liquid material is cooled to a first cooling temperature that is equal to or higher than the boiling point of the liquid material, thereby liquefying a first impurity having a boiling point higher than the first cooling temperature so as to be separable as a liquid; performing gas-liquid separation of the first impurity from the gas; a second cooling step of cooling the gas from which the first impurity has been separated to a second cooling temperature lower than the boiling point of the liquid material to liquefy the gasified liquid material so that a second impurity having a boiling point lower than the second cooling temperature can be separated as a gas; A method comprising:

Images