Methods of producing hydrogen

Abstract

A method for producing hydrogen using a water electrolysis system, wherein the water electrolysis system comprises at least an electrolytic cell and a purification device for removing oxygen from hydrogen gas generated in the electrolytic cell, wherein the method comprises: 2 When the electrolytic cell is operated at a current density of 2.0 kA / m 2 The oxygen concentration of hydrogen introduced into the purification device is Oa when the current density of the electrolytic cell is 0.2 kA / m 2 When the oxygen concentration in the hydrogen gas introduced into the purification device during operation at a current density of 1.50 Å is Ob, control is performed so that Ob / Oa is less than 10.0.

Description

Technical Field

[0001] The present invention relates to a method for producing hydrogen. Background Art

[0002] In recent years, in order to adjust the supply and demand balance of electricity and improve power generation efficiency, research and development of power storage technology has been carried out in the hope of replacing electricity with a form that can be stored and transported. As one of them, research has been carried out on a technology that converts electrical energy into hydrogen that can be stored and transported and uses hydrogen as an energy source or raw material.

[0003] Hydrogen is widely used in industry for oil purification, chemical synthesis, metal purification, etc. In recent years, its use in hydrogen refueling stations for fuel cell vehicles (FCVs), smart communities, hydrogen power plants, etc. has also expanded. Therefore, there are high expectations for the development of technology to obtain hydrogen.

[0004] As a method for producing hydrogen, it can be roughly divided into a method using fossil fuels as raw materials and a method based on the decomposition of water. From the perspective of not generating carbon dioxide, the method based on the decomposition of water, especially the electrolysis (electrolysis) of water, has attracted attention. As a method for electrolyzing water, there are solid polymer water electrolysis, high temperature steam electrolysis, alkaline water electrolysis, etc. Alkaline water electrolysis is considered to be one of the particularly advantageous methods because it has been industrialized for more than decades, can be implemented on a large scale, and is cheaper than other water electrolysis devices.

[0005] In alkaline water electrolysis, water is electrolyzed to generate hydrogen on the cathode side and oxygen on the anode side. In order to prevent the mixing of the generated gases (hydrogen, oxygen), a diaphragm is sandwiched between the cathode side and the anode side, but since the cathode side and the anode side are connected by an electrolyte through the pores of the diaphragm, a trace amount of oxygen is mixed in the hydrogen generated on the cathode side. The oxygen mixed into the hydrogen is removed downstream by a deoxygenation unit (purification device). For example, the deoxygenation catalyst described in Patent Document 1 can be used to react oxygen and hydrogen to convert them into water, and then dehumidification can be performed to obtain high-purity hydrogen. Regarding such a method for producing high-purity hydrogen based on a combination with the electrolysis of water, there are records in Patent Documents 2 and 3.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 58-174239

[0009] Patent Document 2: Japanese Patent No. 2735723

[0010] Patent Document 3: Japanese Patent No. 3604620 Summary of the invention

[0011] Problems to be solved by the invention

[0012] However, the oxygen concentration in the generated hydrogen gas varies depending on the operating conditions of the alkaline water electrolysis. When the oxygen concentration in the hydrogen gas fed to a deoxygenation mechanism such as a purification device increases, various problems may occur.

[0013] For example, when the oxygen concentration in the hydrogen sent to the purification device increases, the temperature of the catalyst will increase locally due to the heat released by the catalytic reaction of the deoxygenation catalyst, and the degradation of the catalyst will easily develop. In addition, in the purification device, the water content generated by the catalytic reaction of hydrogen and oxygen increases, and the interior of the purification device becomes a humid atmosphere. As a result, there will be concerns about the easy development of catalyst degradation, the mixing of water vapor mist in the later stage, and the increase in water discharge. In addition, these will become the cause of changes in the temperature or pressure of the hydrogen in the purification device, which may cause the design of the later stage process to become difficult, or reduce the accuracy of the meters monitoring the purification device or cause their failure.

[0014] Therefore, in order to extend the life of the deoxidation catalyst and prevent a decrease in the measurement accuracy and failure of meters, it is necessary to stably control the oxygen concentration in the hydrogen gas fed to the purification device.

[0015] Therefore, an object of the present invention is to provide a method for producing hydrogen capable of stably controlling the oxygen concentration in hydrogen gas fed to a purification device.

[0016] Means for solving problems

[0017] The gist of the present invention is as follows. [1]

[0019] A method for producing hydrogen using a water electrolysis system, wherein the water electrolysis system comprises at least an electrolytic cell and a purification device for removing oxygen from hydrogen gas generated in the electrolytic cell.

[0020] The manufacturing method is characterized in that

[0021] In the above electrolytic cell, at least 0.5 kA / m 2 When the current density is above 1000 ℃, the oxygen concentration in the hydrogen introduced into the purification device is controlled to be less than 0.5% by volume at all times.

[0022] In addition, the electrolytic cell is set at 2.0 kA / m 2 The oxygen concentration of the hydrogen introduced into the above purification device when the current density is 0.2 kA / m 2When the oxygen concentration in the hydrogen introduced into the above-mentioned purification device during operation at a current density of 1.50, control is performed so that Ob / Oa is less than 10.0. [2]

[0024] The method for producing hydrogen as described in [1], wherein the electrolytic cell is heated at a current of at least 0.2 kA / m 2 When operating at the above current density, the oxygen concentration in the hydrogen gas introduced into the purification device is controlled so as to be always less than 0.5 vol%. [3]

[0026] The method for producing hydrogen as described in [1] or [2], wherein the electrolytic cell is heated at 0.2 kA / m 2 When operating at the above current density, the oxygen concentration in the hydrogen gas introduced into the purification device is controlled so as to be always less than 0.2 vol%. [4]

[0028] The method for producing hydrogen according to any one of [1] to [3], wherein the electrolytic cell is heated to 0.1 kA / m 2 When operating at the above current density, control is performed so that the oxygen concentration in the hydrogen gas introduced into the purification device is always less than 0.5 volume %. [5]

[0030] The method for producing hydrogen according to any one of [1] to [4], wherein the water electrolysis system has a mechanism for controlling the oxygen concentration in the hydrogen gas supplied to the purification device. [6]

[0032] The method for producing hydrogen as described in [5], wherein the mechanism for controlling the oxygen concentration in the hydrogen gas supplied to the purification device is a mechanism for controlling the circulation flow rate of the electrolyte in the electrolytic cell. [7]

[0034] A method for producing hydrogen as described in [6], wherein a mechanism for controlling the circulation flow rate of the electrolyte in the above-mentioned electrolytic cell has at least one of an inverter and an automatic control valve, the inverter is installed on a liquid delivery pump for circulating the electrolyte, and the automatic control valve is installed on a liquid distribution pipe for distributing the electrolyte. [8]

[0036] The method for producing hydrogen according to any one of [5] to [7], wherein the means for controlling the oxygen concentration in the hydrogen gas supplied to the purification device is a means for supplying a part of the hydrogen gas purified by the purification device. [9]

[0038] The method for producing hydrogen as described in any one of [5] to [8], wherein the mechanism for controlling the oxygen concentration in the hydrogen gas supplied to the purification device is a mechanism for controlling the oxygen concentration according to the current density of the electrolytic cell.

[10]

[0040] The method for producing hydrogen as described in any one of [5] to [9], wherein the mechanism for controlling the oxygen concentration in the hydrogen gas supplied to the above-mentioned purification device is a mechanism for controlling the oxygen concentration based on the oxygen concentration in the hydrogen gas supplied to the above-mentioned purification device.

[11]

[0042] The method for producing hydrogen according to any one of [1] to

[10] , wherein the electrolytic cell is used under alkaline conditions.

[12]

[0044] The method for producing hydrogen as described in any one of [1] to

[11] is characterized in that the electrolytic cell includes an electrode chamber and a flow path for supplying an electrolyte to the electrode chamber, and a portion of the flow path is formed of an insulating material.

[0045] Effects of the Invention

[0046] According to the present invention, it is possible to provide a method for producing hydrogen capable of stably controlling the oxygen concentration in hydrogen gas fed to a purification device. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a diagram showing an overview of an example of the alkaline water electrolysis system according to the present embodiment.

[0048] Figure 2 This is a diagram showing an example of an operation method of a water electrolysis system in the method for producing hydrogen according to the present embodiment. Figure 2 In FIG. 1 , the horizontal axis represents the current density, the vertical axis represents the oxygen concentration in the hydrogen gas, the solid line represents the curve in the case of the water electrolysis system of the present embodiment, and the dotted line represents the curve in the case of the conventional water electrolysis system.

[0049] Figure 3 It is a diagram showing an overview of another example of the alkaline water electrolysis system according to the present embodiment.

[0050] Figure 4 This is a diagram showing an overview of still another example of the alkaline water electrolysis system according to the present embodiment. DETAILED DESCRIPTION

[0051] The specific embodiment of the present invention (hereinafter referred to as "this embodiment") will be described in detail below. The present invention is not limited to the following embodiment, and can be implemented in various modifications within the scope of the gist.

[0052] In addition, in the embodiment of the present invention, A (numerical value) to B (numerical value) mean A or more and B or less.

[0053] [Method for producing hydrogen]

[0054] The hydrogen production method of the present embodiment is a method for producing hydrogen using a water electrolysis system, wherein the water electrolysis system comprises at least an electrolytic cell and a purification device for removing oxygen from hydrogen gas generated in the electrolytic cell, and the production method is characterized in that:

[0055] In the above electrolytic cell, at least 0.5 kA / m 2 When the current density is above 1000 ℃, the oxygen concentration in the hydrogen introduced into the purification device is controlled to be less than 0.5% by volume at all times.

[0056] In addition, the electrolytic cell is set at 2.0 kA / m 2 The oxygen concentration of the hydrogen introduced into the above purification device when the current density is 0.2 kA / m 2 When the oxygen concentration in the hydrogen introduced into the above-mentioned purification device during operation at a current density of 1.50, control is performed so that Ob / Oa is less than 10.0.

[0057] It should be noted that in the hydrogen production method of the present embodiment, the oxygen concentration (volume %) in hydrogen gas refers to the volume % of oxygen relative to the total volume of hydrogen and oxygen in the hydrogen gas (O2 / (H2+O2)×100).

[0058] In the hydrogen production method of the present embodiment, hydrogen is produced by electrolyzing alkaline water using, for example, an alkaline water electrolysis system including an electrolytic cell and a purification device for removing oxygen from hydrogen gas generated in the electrolytic cell.

[0059] -Alkaline water electrolysis system-

[0060] The alkaline water electrolysis system that can be used in this embodiment will be briefly described below using the drawings.

[0061] The alkaline water electrolysis system of the present embodiment is not particularly limited as long as it includes an electrolytic cell and a purification device for removing oxygen from hydrogen gas generated in the electrolytic cell.

[0062] Figure 1 An overview of an example of an alkaline water electrolysis system that can be used in the present embodiment is shown.

[0063] like Figure 1As shown, in the alkaline water electrolysis system 70 of the present embodiment, the electrolytic cell 50, the hydrogen separation tank 72h and the purification device 75 are connected by a hydrogen pipeline 100h (through which the hydrogen generated by the cathode of the electrolytic cell 50 passes). The electrolytic cell 50, the hydrogen separation tank 72h and the purification device 75 are preferably, but not particularly limited to, connected in series. By connecting them in series, hydrogen separation and purification can be performed efficiently.

[0064] like Figure 1 As shown, in the alkaline water electrolysis system 70 of the present embodiment, the hydrogen gas generated in the cathode chamber of the electrolytic cell 50 passes through the hydrogen separation tank 72h and the purification device 75 via the hydrogen line 100h.

[0065] The electrolytic cell 50, the hydrogen separation tank 72h, and the purification device 75 are briefly described below.

[0066] --Electrolyzer--

[0067] The electrolytic cell 50 of the present embodiment is not particularly limited as long as it can electrolyze alkaline water and has a mechanism for separating, collecting, and discharging hydrogen generated in the cathode chamber and oxygen generated in the anode chamber.

[0068] The electrolytic cell 50 may be a monopolar type or a bipolar type, and a bipolar type electrolytic cell 50 is preferred in industry. The bipolar type is a method in which a plurality of electrolytic cells (the electrolytic cells include a combination of an anode, a cathode, and a diaphragm disposed therebetween) are arranged in the same direction, connected in series across a partition, and only the two ends are connected to a power source. By using a bipolar type electrolytic cell 50 as the electrolytic cell 50, the amount of power supplied from the power source can be reduced, and hydrogen can be produced in large quantities in a short time by electrolysis of alkaline water.

[0069] It should be noted that the bipolar electrolytic cell 50 can also be understood as having the following structure: it is formed by overlapping a plurality of bipolar elements with a diaphragm sandwiched therebetween, and the bipolar element comprises a cathode as a constituent element of an electrolytic unit, an anode as a constituent element of the electrolytic unit adjacent to the cathode terminal side, a partition separating the cathode and the anode, and an outer frame edging the partition.

[0070] like Figure 1 As shown, the electrolytic cell 50 and the hydrogen separation tank 72h are connected by a hydrogen pipeline 100h, and the mixed phase flow of hydrogen gas and electrolyte generated by the cathode chamber flows out of the electrolytic cell 50 and flows into the hydrogen separation tank 72h through the hydrogen pipeline 100h.

[0071] A flow control valve (not shown), a flow meter 82 and the like may be provided between the electrolytic cell 50 and the hydrogen separation tank 72h as necessary.

[0072] In the electrolytic cell 50, a plurality of electrolytic units are connected to the supply and discharge pipes of the electrolyte called a common header. Generally, the anolyte supply pipe is called the anode inlet header, the cathode liquid supply pipe is called the cathode inlet header, the anolyte recovery pipe is called the anolyte outlet header, and the cathode liquid recovery pipe is called the cathode liquid outlet header. The electrolytic units are connected to each electrolyte supply pipe and each electrolyte recovery pipe through a hose or the like. According to the installation position of the header, it is classified into an internal header type bipolar electrolytic cell and an external header type bipolar electrolytic cell.

[0073] The electrolytic cell may be of any manifold type, and preferably a portion of the flow path for supplying electrolyte to each electrode chamber is formed of an insulating material. By making a portion of the flow path of the insulating material, the leakage current flowing during electrolysis can be reduced, and the oxygen concentration in hydrogen can be reduced.

[0074] The external manifold type bipolar electrolytic cell is configured such that the anode inlet manifold and the cathode inlet manifold are parallel to the electrolytic cell 50 in a direction perpendicular to the current-carrying surface of the electrolytic cell. The anode inlet manifold and the cathode inlet manifold are connected to each electrolytic cell by a hose. For example, it is preferred that a portion of the hose be made of an insulating material.

[0075] The material of the hose is not particularly limited, but it is necessary to use a material that can fully withstand the corrosiveness of the electrolyte used, pressure and temperature and other operating conditions in addition to insulation. Specifically, PTFE, ETFE, PFA, polyvinyl chloride, polypropylene, polyethylene, etc. are preferably used.

[0076] -Hydrogen separation tank-

[0077] The hydrogen separation tank 72h of the present embodiment has a mechanism for separating the hydrogen generated by the electrolytic cell 50 from the electrolyte, and is respectively provided with at least one inlet for allowing the mixed phase of hydrogen generated by the cathode chamber of the electrolytic cell 50 and the electrolyte to flow in, a hydrogen gas flow outlet at the upper layer of the tank for discharging the hydrogen gas, and an electrolyte flow outlet at the lower layer of the tank for discharging the electrolyte.

[0078] In order to improve hydrogen separation performance, the inlet into the hydrogen separation tank 72h is preferably located above the electrolyte surface, but is not limited thereto.

[0079] The hydrogen separation tank 72h may further include a liquid level gauge, a pressure release valve, and the like.

[0080] The electrolyte after separation of hydrogen flows out from the electrolyte outflow port at the bottom of the tank and flows into the electrolytic tank 50 again, thereby forming a circulation path.

[0081] like Figure 1As shown, the hydrogen separation tank 72h and the purification device 75 are connected by a hydrogen pipeline 100h. The hydrogen separated from the electrolyte flows out from the hydrogen gas flow outlet above the tank and flows into the purification device 75 via the hydrogen pipeline 100h.

[0082] A gas concentration meter (e.g., an oxygen concentration meter in hydrogen O2I) 79, a mist separator, a heat exchanger, various control valves, a hydrogen return pipeline for supplying part of the hydrogen or hydrogen, etc. may be provided between the hydrogen separation tank 72h and the purification device 75 as needed.

[0083] --Purification device--

[0084] The purification device 75 of the present embodiment has a purification mechanism for removing oxygen from hydrogen gas, and is provided with at least one hydrogen gas inlet for allowing hydrogen gas containing oxygen to flow in, and a hydrogen gas outlet for allowing hydrogen gas from which oxygen has been removed to flow out.

[0085] As a purification mechanism for removing oxygen from hydrogen, for example, a mechanism for converting oxygen and hydrogen into water by reacting with a deoxidation catalyst can be cited. In order to improve the conversion efficiency, it is preferred to preheat the hydrogen to an appropriate temperature in the range of 100°C to 300°C by using a heat exchanger or the like. The deoxygenated gas is cooled by a heat exchanger when necessary, and after separating the condensed water, it is dehumidified by a dehumidifier to produce high-purity hydrogen.

[0086] In addition, the purification device may be equipped with a control unit capable of manually or automatically controlling the purification mechanism as required. The control unit may be controlled by signals from other components of the alkaline water decomposition system.

[0087] On the downstream side of the hydrogen gas flow outlet of the purification device 75, an oxygen concentration detection unit (for example, an oxygen concentration meter in hydrogen O2I) 80, a meter type 76 for monitoring the purification device 75 (for example, a temperature detector, a pressure detector, etc.), a heat exchanger, a mist separator, a dehumidifier, a hydrogen storage tank 77h for storing purified hydrogen, a compressor, a hydrogen return pipeline for returning part of the hydrogen to the upstream side of the purification device 75, various control valves, etc. can be provided as needed.

[0088] In the alkaline water electrolysis system 70 of the present embodiment, as components other than the above, for example, Figure 1As shown, it may include a liquid delivery pump 71 for circulating the electrolyte, an oxygen pipeline 100o for passing oxygen generated by the anode of the electrolytic cell 50, an oxygen separation tank 72o for separating the electrolyte and oxygen, an oxygen storage tank 77o for storing oxygen, a water supply device 73 for replenishing water consumed by electrolysis, a rectifier 74 for supplying power to the electrodes of the electrolytic cell 50, a flow meter 82, a check valve 93 for preventing backflow of gas, etc. A gas concentration meter, a pressure gauge PI, various control valves, various control devices, a heat exchanger, etc. may also be provided as needed.

[0089] In this embodiment, the components of the alkaline water electrolysis system 70 described above can be used to produce, for example, Figure 1 The alkaline water electrolysis system 70 of the structure shown is used, but is not limited to this.

[0090] -Control of oxygen concentration in hydrogen gas-

[0091] Next, the control of the oxygen concentration in the hydrogen gas on the downstream side of the electrolytic cell 50 in the present embodiment will be described in detail.

[0092] Figure 2 This is a diagram showing an example of an operation method of a water electrolysis system in the method for producing hydrogen according to the present embodiment. Figure 2 In FIG. 1 , the horizontal axis represents the current density, the vertical axis represents the oxygen concentration in the hydrogen gas, the solid line represents the curve in the case of the water electrolysis system of the present embodiment, and the dotted line represents the curve in the case of the conventional water electrolysis system.

[0093] The method for producing hydrogen in this embodiment is characterized in that, in the water electrolysis system, at least 0.5 kA / m 2 When the current density is above 2.0 kA / m, the oxygen concentration in the hydrogen introduced into the purification device 75 is controlled to be less than 0.5 volume % at all times; further, for the water electrolysis system, the electrolytic cell 50 is set to operate at 2.0 kA / m 2 When the current density is 0.2 kA / m 2 When the oxygen concentration in the hydrogen gas introduced into the purification device 75 during the operation at the following current density is Ob (hereinafter also referred to as "oxygen concentration Ob"), control is performed so that Ob / Oa is less than 10.0.

[0094] By applying at least 0.5 kA / m 2When operating at the above current density, control is performed so that the oxygen concentration in the hydrogen introduced into the purification device 75 is always less than 0.5 volume%. The oxygen concentration in the hydrogen introduced into the purification device 75 can be stably controlled, and the degradation of the deoxygenation catalyst and the reduction of the purification efficiency can be prevented, as well as the reduction in accuracy and failure of the metering meter 76 for monitoring the purification device 75, and the design of the subsequent process can be easily performed.

[0095] The above effect is fully effective in constant power operation, but is more effective in variable power operation using variable power such as solar power or wind power to supply power. This is because in variable power operation, the operating conditions of the electrolytic cell 50 frequently change with changes in the supplied power, and as a result, the oxygen concentration in the hydrogen gas fed to the purification device 75 may frequently change.

[0096] In general, in hydrogen production by electrolysis, the current density is 2.0 kA / m 2 The above operating conditions are preferably carried out at a current density of 4.0 kA / m 2 ~20.0kA / m 2 operation, preferably the current density is 6.0 kA / m 2 ~15.0kA / m 2 Since the amount of hydrogen produced increases in proportion to the current density, it can be said that the higher the current density, the higher the operating rate of the equipment. On the other hand, since the electrolysis efficiency decreases according to the current density, there is a preferred current density corresponding to the electrolytic cell 50.

[0097] However, for the electrolytic cell 50, by reducing the power supply, specifically, by intermittent or periodic reduction of the power supply during operation when using a variable power supply, or by certain abnormalities of the components of the alkaline water electrolysis system 70, or by operations when starting or stopping the operation cycle when using a stable power supply, it is possible to make the electrolytic cell 50 operate at a current density of 2.0 kA / m 2 The operation is carried out under the following operating conditions. Generally, in the electrolysis of water, if the current density decreases, the oxygen concentration in the hydrogen increases. Figure 2 As shown by the dotted line, at a current density of 2.0 kA / m 2 In the following region, the oxygen concentration in hydrogen may reach 0.5 vol% or more. The reason for the increase in the oxygen concentration in hydrogen is that the amount of hydrogen generated decreases as the current density decreases, while the amount of oxygen generated does not change due to the influence of leakage current or the influence of dissolved oxygen in the electrolyte.

[0098] On the other hand, in this embodiment, if Figure 2 The solid line indicates that the electrolytic cell 50 is at least 0.5 kA / m 2When operating at the above current density, the oxygen concentration in the hydrogen introduced into the purification device 75 is controlled to be always less than 0.5% by volume. By making the oxygen concentration in hydrogen less than 0.5% by volume, the load of the purification device 75 can be maintained below a certain value, and the accuracy reduction and failure of the meter 76 monitoring the purification device 75 can be prevented.

[0099] In addition, in this embodiment, the electrolytic cell 50 is set to 2.0 kA / m 2 When the current density is 0.2 kA / m 2 When the oxygen concentration in hydrogen is Ob, Ob / Oa is controlled to be less than 10.0. By controlling in this way, even at a current density of 2.0 kA / m 2 Even in the operation in which the low current density region frequently changes, the deoxidation catalyst can be prevented from being degraded, and the design of the subsequent process can be easily performed. For the same reason, Ob / Oa is preferably controlled to be less than 8.0, and more preferably controlled to be less than 5.0.

[0100] In this embodiment, the electrolytic cell 50 is heated to at least 0.5 kA / m 2 When operating at the above current density, it is preferable to control the oxygen concentration in the hydrogen gas introduced into the purification device 75 to be always less than 0.2 volume %, and more preferably to control it to be always less than 0.1 volume %.

[0101] In this embodiment, the electrolytic cell 50 is heated at 0.2 kA / m 2 When operating at the above current density, it is preferred to control the oxygen concentration in the hydrogen introduced into the purification device 75 to be always less than 0.5 volume %, more preferably to be always less than 0.2 volume %, and further preferably to be always less than 0.1 volume %.

[0102] When the oxygen concentration in the hydrogen gas fed to the purification device 75 is within the above range, the purification efficiency can be improved, and the service life of the meter 76 for monitoring the purification device 75 can be extended.

[0103] In this embodiment, the electrolytic cell 50 is heated at 0.1 kA / m 2 Even when operating at the above current density, it is more preferable to control the oxygen concentration in the hydrogen gas introduced into the purification device 75 so as to be always less than 0.5 volume %, and more preferably less than 0.2 volume %.

[0104] When the oxygen concentration in the hydrogen gas fed to the purification device 75 is within the above range, the purification efficiency can be improved, and the service life of the meter 76 for monitoring the purification device 75 can be extended.

[0105] In this embodiment, although not particularly limited, for example, 0.1 kA / m 2 The oxygen concentration in hydrogen gas during operation at a current density of 0.2 kA / m 2 The oxygen concentration in hydrogen gas during operation at a current density of 0.5 kA / m 2 The oxygen concentration in hydrogen gas during operation at a current density of 2.0 kA / m 2 The oxygen concentration in hydrogen gas decreases gradually when the current density is 0.1 kA / m 2 The oxygen concentration in the hydrogen gas during operation at a current density of 0.1 to 2.0 kA / m 2 The maximum value in the range.

[0106] In addition, in this embodiment, although not particularly limited, for example, 0.5 kA / m 2 The oxygen concentration in hydrogen gas during operation at a current density of 2.0 kA / m 2 The oxygen concentration in hydrogen gas during operation at a current density of 0.2 kA / m 2 The oxygen concentration in hydrogen gas when the current density is 0.1 kA / m 2 The oxygen concentration in hydrogen gas when the current density is 0.1 kA / m 2 The oxygen concentration in hydrogen gas during operation at a current density of 0.2 kA / m 2 The oxygen concentration in hydrogen gas during operation at a current density of 0.5 kA / m 2 The oxygen concentration in hydrogen increases gradually when the current density is 0.5 kA / m 2 The oxygen concentration in the hydrogen gas during operation at a current density of 0.1 to 0.5 kA / m 2 The maximum value in the range.

[0107] Whether the oxygen concentration is controlled within the above range can be confirmed by monitoring the oxygen concentration in the hydrogen supplied to the purification device 75. As a monitoring method, the oxygen concentration in the hydrogen supplied to the purification device 75 can be monitored using an oxygen concentration detection unit capable of measuring the oxygen concentration in the hydrogen.

[0108] The oxygen concentration may be monitored continuously or intermittently. For example, the oxygen concentration may be monitored intermittently only when it is estimated to be 0.5 vol% due to low-density current operation or other changes in operating conditions.

[0109] Here, in the present embodiment, the water electrolysis system preferably includes a mechanism for controlling the oxygen concentration in the hydrogen gas supplied to the purification device 75 .

[0110] As a first aspect, the mechanism for controlling the oxygen concentration in the hydrogen gas supplied to the purification device 75 is preferably a mechanism for controlling the circulation flow rate of the electrolytic solution in the electrolytic cell 50 .

[0111] In this embodiment, when the oxygen concentration in the hydrogen gas supplied to the purification device 75 increases due to a decrease in the current density, the oxygen concentration can be suppressed by reducing the circulation flow rate.

[0112] In the first embodiment, it is particularly preferred that the mechanism for controlling the circulation flow rate of the electrolyte in the electrolytic cell 50 has at least one of an inverter and an automatic control valve, wherein the inverter is installed on a liquid delivery pump 71 for circulating the electrolyte, and the automatic control valve is installed on a liquid distribution pipe for distributing the electrolyte.

[0113] As a second aspect, the mechanism for controlling the oxygen concentration in the hydrogen gas supplied to the purifier 75 is preferably a mechanism for supplying a part of the hydrogen gas purified by the purifier 75 .

[0114] In this method, as a direct control method of the oxygen concentration, hydrogen is supplied to the upstream of the purification device 75 to reduce the oxygen concentration.

[0115] The hydrogen supplied to the upstream of the purifier 75 is preferably a part of the hydrogen gas purified by the purifier 75 , but is not limited thereto. For example, the hydrogen gas may be separately prepared in the hydrogen supply tank 81 h or the like for supply.

[0116] In addition, the mechanism for controlling the oxygen concentration in the hydrogen gas supplied to the purification device 75 is preferably a mechanism for controlling the oxygen concentration according to the current density of the electrolytic cell 50 .

[0117] Here, for example, when a decrease in the current density of the electrolytic cell 50 is detected, the circulation flow rate of the electrolyte in the electrolytic cell 50 is controlled, or a part of the hydrogen gas purified by the purification device 75 is supplied, to control the oxygen concentration as described above.

[0118] For example, when the current density of the electrolytic cell 50 reaches or falls below a reference value, the above-mentioned oxygen concentration control may be started. The reference value may be 3.0 kA / m 2 , preferably 2.0 kA / m 2 , more preferably 1.0 kA / m 2 .

[0119] In addition, linear control can be performed according to the current density of the electrolytic cell 50.

[0120] In addition, the mechanism for controlling the oxygen concentration in the hydrogen gas supplied to the purification device 75 is preferably a mechanism for controlling the oxygen concentration according to the oxygen concentration in the hydrogen gas supplied to the purification device 75 .

[0121] Here, for example, when an increase in the oxygen concentration in the hydrogen supplied to the purifier 75 is detected, the circulation flow rate of the electrolyte in the electrolytic cell 50 is controlled, or a portion of the hydrogen purified by the purifier 75 is supplied, to control the oxygen concentration as described above.

[0122] For example, the above-mentioned control of oxygen concentration may be started when the oxygen concentration in the hydrogen gas supplied to the purifier 75 reaches or exceeds a reference value. The reference value may be 0.5% by volume, preferably 0.25% by volume, and more preferably 0.15% by volume.

[0123] In addition, linear control can be performed according to the oxygen concentration in the hydrogen gas.

[0124] Figure 3 2 shows an overview of another example of the alkaline water electrolysis system 70 according to the present embodiment.

[0125] In the following, for Figure 1 In the alkaline water electrolysis system 70 of the example of the present invention shown, the same elements are denoted by the same reference numerals, and the description thereof is omitted.

[0126] Especially in Figure 3 In another example of the alkaline water electrolysis system 70 shown, a flow regulating valve 91 is provided in the bipolar electrolytic cell 50 to control the circulation flow of the electrolyte. In addition, in the system, a bypass line 92 that can serve as a bypass path is provided for the liquid delivery pump 71 to prevent overloading of the liquid delivery pump 71.

[0127] Figure 4 The outline of still another example of the alkaline water electrolysis system 70 according to the present embodiment is shown.

[0128] In the following, for Figure 1 In the alkaline water electrolysis system 70 of the example of the present invention shown, the same elements are denoted by the same reference numerals, and the description thereof is omitted.

[0129] Especially in Figure 4 In the alkaline water electrolysis system 70 of another example shown, the oxygen separation tank 72o and the hydrogen separation tank 72h are connected by a pressure equalizing pipe, so that the pressure difference fluctuation when the output power fluctuates can be suppressed.

[0130] In the above, the control of the oxygen concentration in the hydrogen gas on the downstream side of the electrolytic cell 50 has been described by way of example with reference to the drawings, but the present embodiment is not limited to the above-described example.

[0131] The electrolytic cell 50 can be used under pressurized conditions or normal pressure conditions, or can be used under alkaline conditions.

[0132] -Conditions for alkaline water electrolysis-

[0133] The following is a detailed description of various conditions for performing alkaline water electrolysis using the alkaline water electrolysis system 70 in this embodiment.

[0134] When performing alkaline water electrolysis, the power source for supplying electric power to the electrolytic cell 50 is not particularly limited, and for example, a stable power source, a variable power source, etc. may be used.

[0135] A stable power source is a power source that is generated from non-renewable energy sources or renewable energy sources and has a stable output of system power, etc. Examples of non-renewable energy generation methods that can be used for a stable power source include thermal power generation, nuclear power generation, etc. In addition, examples of renewable energy generation methods that can be used for a stable power source include hydroelectric power generation, geothermal power generation, and biomass power generation.

[0136] A variable power source is a power source that generates electricity from renewable energy and whose output varies in units of seconds to minutes. There is no particular limitation on the renewable energy generation method that can be used for the variable power source, and examples thereof include solar power generation and wind power generation.

[0137] In the method for producing hydrogen according to the present embodiment, the above-mentioned effect becomes remarkable by using a variable power source such as solar power generation and wind power generation.

[0138] The electrolyte used in the alkaline water electrolysis may be an alkaline aqueous solution in which an alkali metal salt is dissolved, and examples thereof include a NaOH aqueous solution and a KOH aqueous solution.

[0139] The concentration of the alkali metal salt in the electrolyte is not particularly limited, but is preferably 20% to 50% by mass, more preferably 25% to 40% by mass. Among them, a 25% to 35% by mass KOH aqueous solution is particularly preferred from the perspectives of ion conductivity, kinematic viscosity, and freezing at low temperatures.

[0140] The temperature of the electrolyte in the electrolytic cell 50 is not particularly limited, but is preferably 60°C to 130°C, more preferably 80°C to 120°C, and even more preferably 90°C to 110°C.

[0141] When the electrolyte in the electrolytic cell 50 is within the above temperature range, it is possible to effectively suppress thermal degradation of components of the electrolytic cell 50 such as the gasket and the diaphragm while maintaining high electrolysis efficiency.

[0142] The current density supplied to the electrolytic cell 50 is not particularly limited, but is preferably 0.1 kA / m 2~20kA / m 2 , more preferably 2kA / m 2 ~20kA / m 2 , more preferably 6kA / m 2 ~15kA / m 2 .

[0143] Particularly when a variable power source is used, it is preferable that the upper limit of the current density be within the above range.

[0144] The pressure in the electrolytic cell 50 is not particularly limited, but is preferably 3 kPa to 3000 kPa, and more preferably 3 kPa to 1000 kPa.

[0145] As the water supplied from the water supply device 73, ordinary tap water can be used, but in consideration of long-term operation, ion exchange water, RO water, ultrapure water, etc. are preferably used.

[0146] The hydrogen production method and the alkaline water electrolysis system of the present embodiment have been described above with reference to the drawings. However, the hydrogen production method and the alkaline water electrolysis system of the present embodiment are not limited to the above examples, and the above embodiment may be modified as appropriate.

[0147] In addition, various conditions of each aspect of the present embodiment can be used alone or in appropriate combination.

[0148] Example

[0149] The present invention is described in more detail below by way of examples, but the present invention is not limited to the following examples.

[0150] An alkaline water electrolysis system was produced as follows.

[0151] -Bipolar element-

[0152] A bipolar element was fabricated as follows.

[0153] --Partition, frame--

[0154] As a bipolar element, an element having a partition wall for partitioning an anode and a cathode and an outer frame surrounding the partition wall was used. All the materials of the parts in contact with the electrolyte such as the partition wall and the frame of the bipolar element were made of nickel.

[0155] -Electrodes, diaphragms-

[0156] As the anode, a nickel expanded substrate that had been subjected to sandblasting treatment in advance was used, and granulated nickel oxide was sprayed onto both surfaces of the conductive substrate by plasma spraying.

[0157] -cathode-

[0158] As the conductive substrate, a substrate in which platinum was supported on a plain woven mesh substrate in which nickel fine wires having a diameter of 0.15 mm were woven into 40 meshes was used.

[0159] -Diaphragm-

[0160] As the separator, a polysulfone porous membrane containing zirconium oxide particles was used. The thickness of the separator was 0.5 mm and the average water permeable pore size was 0.3 mm.

[0161] The two electrodes were adjusted to a 50 cm square (50 cm long x 50 cm wide) by cutting, and the separator was adjusted to a 52.5 cm square (52.5 cm long x 52.5 cm wide) by cutting.

[0162] -Zero pole distance structure-

[0163] The bipolar element is stacked with a spacer holding a diaphragm interposed therebetween to assemble a bipolar electrolytic cell, whereby the cathode and the anode are pressed from both sides of the diaphragm to make them contact, thereby forming a zero-gap structure.

[0164] Only the anode was used on the anode side, and a cathode consisting of a combination of "cathode-conductive elastic body-collector" was used on the cathode side. The above-mentioned components were used as the anode and cathode. The conductive elastic body was fixed to the collector by spot welding.

[0165] -Bipolar Electrolyzer-

[0166] The bipolar electrolyzer is manufactured using bipolar elements according to the following process.

[0167] Use 9 bipolar elements, configure a fixed head, an insulating plate, and an anode terminal element on one end, further arrange the anode side gasket part, a diaphragm, a cathode side gasket part, and the bipolar element in sequence, configure the above-obtained elements into 9 groups, further configure the anode side gasket part, a diaphragm, and a cathode side gasket part, arrange the cathode terminal element, an insulating plate, and a movable head on the other end, then apply pressure from both sides of the fixed head and the movable head to tighten them and stack them, thereby assembling a bipolar electrolytic cell.

[0168] The electrolytic cell has a structure in which 10 pairs of cathode chambers and 10 pairs of anode chambers are connected in series.

[0169] The cathode is mounted on the cathode side of the bipolar frame, and the anode is mounted on the anode side of the bipolar frame to make a bipolar element. In addition, the cathode is mounted on the cathode terminal frame to make a cathode terminal element. The anode is mounted on the anode terminal frame to make an anode terminal element.

[0170] Liquid delivery pump, gas-liquid separation tank, water feeder, etc. are all made of commonly used equipment in the relevant technical field. Figure 1The electrolysis device for alkaline water electrolysis shown in the figure. An inverter is provided in the liquid delivery pump so that the circulation flow rate can be controlled according to the current density. In addition, a flow control valve is provided in the rear section of the liquid delivery pump so that the flow rate can be controlled according to the current density.

[0171] The hydrogen separated by the hydrogen separation tank is released into the purification device. An oxygen concentration meter (O2I) in hydrogen, a pressure gauge, a thermometer and a pressure control valve are installed in the middle.

[0172] The oxygen concentration meter (O2I) in hydrogen is SD-1DOX manufactured by Riken Keiki Co., Ltd. The gas to be measured is sent to the concentration meter sensor unit by a suction pump (not shown), and the concentration meter performs analysis. The oxygen concentration meter is connected in series between the gas-liquid separation tank and the purification device.

[0173] The purification device used was the following device: Al2O3 loaded with 0.5 mass % Pd was used as a deoxidation catalyst, and housed in a housing so that L / D = 2. A heat exchanger was provided at the front stage of the purification device to preheat the hydrogen to 150°C.

[0174] An oxygen concentration meter and a gas temperature detector are installed at the outlet of the purification device.

[0175] The alkaline water electrolysis method using the electrolysis apparatus for alkaline water electrolysis was carried out under the following conditions.

[0176] As the electrolyte, a 30% KOH aqueous solution was used.

[0177] The liquid feeding pump 71 performs circulation among the cathode chamber, the hydrogen separation tank (cathode gas-liquid separation tank), and the cathode chamber, and performs circulation among the anode chamber, the oxygen separation tank (anode gas-liquid separation tank), and the anode chamber.

[0178] For the gas-liquid separation tank, prepare a 1400mm high and 1m3 volume 3 Gas-liquid separation tank.

[0179] Make the liquid volume of the gas-liquid separation tank about 50% of the designed volume.

[0180] From the rectifier to the bipolar electrolyzer, the area of ​​the two electrodes (0.25m 2 ), electrolysis was carried out at the following current density.

[0181] At 4.0kA / m 2 Implement for 24 hours at 2.0kA / m 2 Implement for 1 hour at 4.0kA / m 2 1 hour, 0.5kA / m 2 Implement for 1 hour at 4.0kA / m 2 1 hour, at 0.2kA / m 2Implement for 1 hour at 4.0kA / m 2 1 hour, 0.1kA / m 2 The implementation lasted for 1 hour, for a total of 31 hours.

[0182] The oxygen concentration in the hydrogen supplied to the purification device after 45 minutes was changed at each current density, and the concentration was changed to 2.0 kA / m 2 The following results are shown in Table 1. Table 1 also shows the maximum value of the oxygen concentration in hydrogen at the outlet of the purifier and the maximum value of the hydrogen gas temperature at the outlet of the purifier.

[0183] [Example 1]

[0184] The electrolytic cell is constructed as follows Figure 3 shown.

[0185] As a header structure provided in a bipolar electrolytic cell, an external header type is adopted.

[0186] A PFA hose (inner diameter Ø8 mm, length 0.55 m) was used to deliver liquid from the inlet header (inner diameter Ø40 mm) to each unit. A PFA hose (inner diameter Ø16 mm, length 0.35 m) was used to deliver liquid from each unit to the outlet header (inner diameter Ø40 mm).

[0187] According to the current density of 2.0kA / m 2 The electrolyte circulation flow rate is 630L / hour (100% output) and the current density is 0.1kA / m 2 The frequency of the inverter of the liquid delivery pump is set so that the circulation flow rate of the electrolyte is 63L / hour (10% output) at this time, and the circulation flow rate is linearly controlled according to the current density. During operation, the flow control valve is fully open.

[0188] [Example 2]

[0189] The same electrolytic cell as in Example 1 was used, and the same operation as in Example 1 was performed except that the circulation flow rate of the electrolyte solution was changed to the following control method.

[0190] The electrolyte circulation flow rate is set at a current density of 1.0 kA / m 2 When the above is 630L / hour, the current density is less than 1.0kA / m 2 The flow rate is controlled and operated by a flow control valve at 315L / hour.

[0191] [Example 3]

[0192] The electrolytic cell is constructed as follows Figure 3 shown.

[0193] As a header structure provided in a bipolar electrolytic cell, an internal header type is adopted.

[0194] The circulation flow rate of the electrolyte is always kept at 250L / hour. A portion of the purified hydrogen is supplied and operated according to the oxygen concentration in the hydrogen supplied to the purification device. Specifically, the frequency of the inverter of the hydrogen supply pump is set to 4000NL / hour (100% output) when the oxygen concentration in the hydrogen is 5% by volume and 160NL / hour (4% output) when the oxygen concentration in the hydrogen is 0.2% by volume, and the hydrogen supply amount is linearly controlled according to the oxygen concentration in the hydrogen supplied to the purification device.

[0195] [Example 4]

[0196] In the configuration of Example 3, the operation was carried out in the same manner as in Example 3 except that the hydrogen supply amount was always set to 1000 NL / hour.

[0197] [Example 5]

[0198] The electrolytic cell is constructed as follows Figure 4 shown.

[0199] As a header structure provided in a bipolar electrolytic cell, an internal header type is adopted.

[0200] The circulation of the electrolyte is divided into the cathode chamber and the anode chamber, and circulated separately using two pumps.

[0201] Pressure control valves are installed at the outlets of oxygen and hydrogen to maintain the pressure at 1.5 MPa.

[0202] The circulation flow rate of the electrolyte was always maintained at 250 L / hour.

[0203] The operation was performed while a part of the purified hydrogen gas was constantly supplied at 800 NL / hour.

[0204] [Comparative Example 1]

[0205] In the configuration of Example 5, the operation was carried out in the same manner as in Example 5, except that the operation was carried out without supplying a part of the purified hydrogen gas.

[0206]

[0207] In Examples 1 to 5, at 0.5 kA / m 2 When the current density is above 0.2 kA / m 2 When operating at the above current density, the oxygen concentration in hydrogen is always less than 0.5% by volume, and Ob / Oa is also less than 10.

[0208] In particular, in Example 1, Ob is as follows: 2When the current density is above 0.1 kA / m 2 The current density is less than 0.2% by volume during operation. The oxygen concentration in the hydrogen at the outlet of the purification device is less than 0.01% by volume, and the hydrogen temperature at the outlet of the purification device is also kept very low.

[0209] On the other hand, the results of Comparative Example 1 are as follows: 2 When operating at the above current density, the oxygen concentration in hydrogen was greater than 2.0% by volume, and the oxygen concentration in hydrogen at the outlet of the purification device reached 0.06% by volume. In addition, the hydrogen temperature at the outlet of the purification device increased to 285°C, and there was a concern that the catalyst temperature in the purification device would increase locally.

[0210] Industrial Applicability

[0211] According to the present invention, in water electrolysis using a stable power supply or a variable power supply, the oxygen concentration in the hydrogen sent to the purification device can be stably controlled, and a decrease in purification efficiency, a decrease in measurement accuracy of meters and failures can be effectively prevented.

[0212] 50 Bipolar Electrolyzer

[0213] 70 Alkaline water electrolysis system

[0214] 71 Liquid delivery pump

[0215] 72h Hydrogen Separation Tank

[0216] 72o Oxygen Separation Tank

[0217] 73 Water dispenser

[0218] 74 Rectifier

[0219] 75 Purification Device

[0220] 76 Meters

[0221] 77h Hydrogen storage tank

[0222] 77o Oxygen Storage Tank

[0223] 79 Oxygen concentration meter in hydrogen (O2I)

[0224] 80 Oxygen concentration meter in hydrogen (O2I)

[0225] 81h Hydrogen supply tank

[0226] 82 Flow Meter

[0227] 83 Hydrogen supply pump

[0228] 91 Flow Control Valve

[0229] 92 Bypass line

[0230] 93 Check valve

[0231] 100h Hydrogen pipeline

[0232] 100o Oxygen Line

[0233] PI Pressure Gauge

[0234] TI Thermometer

Claims

1. A method for producing hydrogen, which is a method for producing hydrogen by using a water electrolysis system to change the output according to a variable power supply, the water electrolysis system comprising at least an electrolytic cell, a purification device for removing oxygen from hydrogen generated in the electrolytic cell, and a mechanism for controlling the oxygen concentration in the hydrogen supplied to the purification device. The manufacturing method is characterized in that At a current density of 2.0 kA / m 2 During the operation of the electrolyzer in the low current density region below, at a current density of 0.5 kA / m 2 Above 2.0kA / m 2 Within the following operating range, the oxygen concentration in the hydrogen introduced into the purification device is controlled to be less than 0.5% by volume at all times. In addition, the electrolytic cell is set at 2.0 kA / m 2 The oxygen concentration of the hydrogen introduced into the purification device when the current density is 0.2 kA / m 2 When the oxygen concentration in the hydrogen introduced into the purification device is Ob, Ob is controlled to be lower so that Ob / Oa is less than 8.0, The mechanism for controlling the oxygen concentration in the hydrogen supplied to the purifier is selected from the group consisting of a mechanism for controlling the circulation flow rate of the electrolyte in the electrolytic cell and a mechanism for supplying a part of the hydrogen purified by the purifier to the upstream of the purifier.

2. The method for producing hydrogen according to claim 1, wherein: At a current density of 2.0 kA / m 2 During the operation of the electrolyzer in the low current density region, at a current density of 0.2 kA / m 2 Above 2.0kA / m 2 In the following operating range, control was performed so that the oxygen concentration in the hydrogen introduced into the purification device was always less than 0.5% by volume.

3. The method for producing hydrogen according to claim 1 or 2, wherein: At a current density of 2.0 kA / m 2 During the operation of the electrolyzer in the low current density region, at a current density of 0.2 kA / m 2 Above 2.0kA / m 2 In the following operating range, control was performed so that the oxygen concentration in the hydrogen introduced into the purification device was always less than 0.2% by volume.

4. The method for producing hydrogen according to claim 1 or 2, wherein: At a current density of 2.0 kA / m 2 During the operation of the electrolytic cell in the low current density region below, at a current density of 0.1 kA / m 2 Above 2.0kA / m 2 In the following operating range, control was performed so that the oxygen concentration in the hydrogen introduced into the purification device was always less than 0.5% by volume.

5. The method for producing hydrogen according to claim 1 or 2, wherein: The mechanism for controlling the oxygen concentration in the hydrogen gas supplied to the purification device is a mechanism for controlling the circulation flow rate of the electrolyte in the electrolytic cell.

6. The method for producing hydrogen according to claim 1 or 2, wherein: The mechanism for controlling the circulation flow rate of the electrolyte in the electrolytic cell has at least one of an inverter and an automatic control valve. The inverter is installed on a liquid delivery pump for circulating the electrolyte, and the automatic control valve is installed on a liquid distribution pipe for distributing the electrolyte.

7. The method for producing hydrogen according to claim 1 or 2, wherein: The means for controlling the oxygen concentration in the hydrogen gas supplied to the purification device is a means for supplying a part of the hydrogen gas purified by the purification device to the upstream of the purification device.

8. The method for producing hydrogen according to claim 1 or 2, wherein: The mechanism for controlling the oxygen concentration in the hydrogen gas supplied to the purification device is a mechanism for controlling the oxygen concentration according to the current density of the electrolytic cell.

9. The method for producing hydrogen according to claim 1 or 2, wherein: The means for controlling the oxygen concentration in the hydrogen gas supplied to the purification device is a means for controlling the oxygen concentration according to the oxygen concentration in the hydrogen gas supplied to the purification device.

10. The method for producing hydrogen according to claim 1 or 2, wherein: The electrolytic cell is used under alkaline conditions.

11. The method for producing hydrogen according to claim 1 or 2, wherein: The electrolytic cell includes an electrode chamber and a flow path for supplying an electrolyte solution to the electrode chamber, and a portion of the flow path is formed of an insulating material.

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