Water vapor electrolysis system

Abstract

The present invention provides a steam electrolysis system that suppresses the decrease in the purity of the generated hydrogen. [Solution] A steam electrolysis system 1a comprising: an electrolytic cell stack 2 having a fuel electrode 21 that generates hydrogen from water vapor, an air electrode 22 through which air flows, and a solid electrolyte 23 disposed between the fuel electrode 21 and the air electrode 22; a water vapor supply line 3 that supplies water vapor-containing gas to the fuel electrode 21; a hydrogen discharge line 4 that discharges the generated gas containing hydrogen; an air supply line 5 that supplies air to the air electrode 22; an air discharge line 6 that discharges exhaust air containing oxygen generated at the air electrode 22; and at least one pressure regulating valve 7 disposed in the hydrogen discharge line 4, which adjusts the pressure in the space facing the fuel electrode 21 to be greater than the pressure in the space facing the air electrode 22 when hydrogen is being generated at the fuel electrode 21.

Description

[Technical Field]

[0001] This invention relates to a water vapor electrolysis system. [Background technology]

[0002] A steam electrolysis system described in Patent Document 1 is known. This steam electrolysis system comprises an electrolytic cell stack, a hydrogen chamber, an oxygen chamber, a hydrogen control valve, and an oxygen control valve. The electrolytic cell stack is constructed by stacking multiple electrolytic cells. The electrolytic cells produce hydrogen and oxygen by electrolyzing steam. The electrolytic cells include a fuel electrode that produces hydrogen and oxygen ions from steam, and an air electrode that produces oxygen from oxygen ions.

[0003] A hydrogen chamber is arranged for the passage of a gas containing hydrogen. An oxygen chamber is arranged for the passage of a mixture of air and oxygen. A hydrogen control valve is located downstream of the hydrogen chamber to regulate the pressure of the gas flowing through it. An oxygen control valve is located downstream of the oxygen chamber to regulate the pressure of the gas flowing through it.

[0004] In the technology described in Patent Document 1, the hydrogen control valve and the air control valve are controlled so as to minimize the pressure difference between the fuel electrode and the air electrode. This was expected to suppress the differential pressure so as to satisfy the low differential pressure constraint of the seal portion of the electrolytic cell. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6732950 [Overview of the project] [Problems that the invention aims to solve]

[0006] According to the above technology, there is a concern that if the air flowing through the air electrode leaks into the fuel electrode in the electrolytic cell stack, the purity of the generated hydrogen will decrease.

[0007] This invention has been made in view of the above problems, and aims to provide a steam electrolysis system that suppresses a decrease in the purity of the generated hydrogen. [Means for solving the problem]

[0008] One aspect of the present invention is, An electrolytic cell stack (2) comprises a fuel electrode (21) through which a water vapor-containing gas is supplied and which generates hydrogen from the water vapor, an air electrode (22) through which air flows, and a solid electrolyte (23) disposed between the fuel electrode and the air electrode. A steam supply line (3) is connected to the upstream side of the fuel electrode and supplies the steam-containing gas to the fuel electrode, A hydrogen outlet line (4) connected to the downstream side of the fuel electrode and for discharging the hydrogen-containing generated gas, An air supply line (5) is connected to the upstream side of the air electrode and supplies air to the air electrode, An air discharge line (6) is connected downstream of the air electrode and discharges the exhaust air containing oxygen generated at the air electrode, The steam electrolysis system (1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i) includes at least one pressure regulating valve (7) positioned in the hydrogen output line and adjusting the pressure in the space facing the fuel electrode to be greater than the pressure in the space facing the air electrode when hydrogen is being generated at the fuel electrode. [Effects of the Invention]

[0009] According to one aspect of the present invention, since the pressure in the space facing the fuel electrode is greater than the pressure in the space facing the air electrode, the mixing of air from the air electrode into the fuel electrode can be suppressed. This makes it possible to suppress a decrease in the purity of the hydrogen produced at the fuel electrode.

[0010] As described above, according to the above aspect, it is possible to provide a steam electrolysis system that suppresses a decrease in the purity of generated hydrogen.

[0011] Note that the reference signs in parentheses described in the claims and the means for solving the problem indicate correspondence with specific means described in the embodiments described later, and do not limit the technical scope of the present invention. [Brief Description of the Drawings]

[0012] [Figure 1] A block diagram showing the steam electrolysis system of Embodiment 1. [Figure 2] A time chart showing the operation of the steam electrolysis system of Embodiment 1, wherein (a) is a graph showing the change over time of the gas flow rate, (b) is a graph showing the change over time of the opening degree of the pressure regulating valve, and (c) is a graph showing the change over time of the differential pressure target value. [Figure 3] A block diagram showing the steam electrolysis system of Embodiment 2. [Figure 4] A block diagram showing the steam electrolysis system of Embodiment 3. [Figure 5] A schematic diagram showing the adjustable ranges of the two pressure regulating valves in Embodiment 3. [Figure 6] A time chart showing the operation of the steam electrolysis system of Embodiment 3, wherein (a) is a graph showing the change over time of the gas flow rate, (b) is a graph showing the change over time of the opening degree of the pressure regulating valve, and (c) is a graph showing the change over time of the differential pressure target value. [Figure 7] A block diagram showing the steam electrolysis system of Embodiment 4. [Figure 8] A block diagram showing the steam electrolysis system of Embodiment 5. [Figure 9] A block diagram showing the steam electrolysis system of Embodiment 6. [Figure 10] A schematic diagram for explaining the pressure loss elements of the electrolysis cell in Embodiment 6. [Figure 11]A block diagram showing the steam electrolysis system of Embodiment 7. [Figure 12] A block diagram showing the steam electrolysis system of Embodiment 8. [Figure 13] A block diagram showing the steam electrolysis system of Embodiment 9. [Modes for carrying out the invention]

[0013] (Embodiment 1) 1. Overview of the steam electrolysis system 1a Embodiment 1 of the steam electrolysis system 1a will be described with reference to Figures 1 and 2. The steam electrolysis system 1a of this embodiment 1 comprises an electrolytic cell stack 2, a steam supply line 3, a hydrogen outlet line 4, an air supply line 5, an air discharge line 6, and a pressure regulating valve 7.

[0014] As shown in Figure 1, the electrolytic cell stack 2 comprises a fuel electrode 21 that is supplied with a water vapor-containing gas and generates hydrogen from the water vapor contained in the water vapor-containing gas, an air electrode 22 through which air flows, and a solid electrolyte 23 placed between the fuel electrode 21 and the air electrode 22. The electrolytic cell stack 2 is constructed by stacking multiple electrolytic cells (not shown).

[0015] The steam supply line 3 is connected to the upstream side of the fuel electrode 21 and supplies steam-containing gas to the fuel electrode 21. The hydrogen discharge line 4 is connected to the downstream side of the fuel electrode 21 and discharges the generated gas containing hydrogen.

[0016] The air supply line 5 is connected to the upstream side of the air electrode 22 and supplies air to the air electrode 22. The air discharge line 6 is connected to the downstream side of the air electrode 22 and discharges the exhaust air containing oxygen generated at the air electrode 22.

[0017] At least one pressure regulating valve 7 is located in the hydrogen outlet line 4 and adjusts the pressure so that, when hydrogen is being generated at the fuel electrode 21, the pressure in the space facing the fuel electrode 21 is greater than the pressure in the space facing the air electrode 22.

[0018] As shown in Figure 1, the electrolytic cell stack 2 comprises a fuel electrode 21, an air electrode 22, and a solid electrolyte 23. The solid electrolyte 23 is placed between the fuel electrode 21 and the air electrode 22.

[0019] The electrolytic cell stack 2, although not shown in detail, includes a space through which water vapor-containing gas and generated gases flow. This space is configured facing the fuel electrode 21.

[0020] Furthermore, the electrolytic cell stack 2, although not shown in detail, includes a space through which air and exhaust air circulates. This space is configured facing the air electrode 22.

[0021] The fuel electrode 21 is supplied with water vapor to generate hydrogen. The fuel electrode 21 is porous and electrically conductive. The generated hydrogen and residual water vapor are discharged from the fuel electrode 21.

[0022] The air electrode 22 is configured to desorb oxygen produced by the electrolysis of water vapor supplied to the fuel electrode 21. The air electrode 22 is porous and conductive. Air with an increased oxygen concentration due to the production of oxygen is discharged from the air electrode 22.

[0023] The solid electrolyte 23 is a solid oxide type electrolyte placed between the fuel electrode 21 and the air electrode 22. Therefore, the electrolytic cell stack 2 of this embodiment includes an SOEC (Solid Oxide Electrolytic Cell).

[0024] By heating the electrolytic cell stack 2 to a high temperature and applying a voltage between the fuel electrode 21 and the air electrode 22, water vapor is reduced at the fuel electrode 21, thereby generating hydrogen at the fuel electrode 21 and oxygen at the air electrode 22.

[0025] The steam electrolysis system 1a supplies hydrogen, generated by the electrolysis of steam, to a downstream system 8 that utilizes the hydrogen. As shown in Figure 1, the steam electrolysis system 1a includes an electrolytic cell stack 2, a steam supply line 3, a hydrogen outlet line 4, an air supply line 5, an air discharge line 6, a flow rate control device 91, a pressure control device 92, and a flow path control device 93.

[0026] The water vapor supply line 3 is connected to the upstream side of the fuel electrode 21 of the electrolytic cell stack 2. The water vapor supply line 3 supplies a water vapor-containing gas to the fuel electrode 21. A gas other than water vapor may flow through the water vapor supply line 3. The concentration of water vapor in the water vapor-containing gas is arbitrary. The water vapor supply line 3 is equipped with a nitrogen supply line 3a and a hydrogen supply line 3b, which are connected to the water vapor supply line 3. Therefore, a gas containing one or more selected from the group consisting of water vapor, nitrogen, and hydrogen can flow through the water vapor supply line 3.

[0027] A steam flow control valve 31 is installed in the steam supply line 3 to adjust the flow rate of steam. The steam flow control valve 31 is an example of a flow control valve.

[0028] The nitrogen supply line 3a supplies nitrogen to the fuel electrode 21. The nitrogen supply line 3a is equipped with a nitrogen flow control valve 31a to adjust the flow rate of nitrogen. The nitrogen flow control valve 31a is an example of a flow control valve.

[0029] The hydrogen supply line 3b supplies hydrogen to the fuel electrode 21. By supplying hydrogen to the fuel electrode 21, the fuel electrode 21 can be made into a reducing atmosphere. This suppresses oxidation and deterioration of the fuel electrode 21 even if oxygen-containing gas located on the air electrode 22 side flows into the fuel electrode 21.

[0030] A hydrogen flow control valve 31b is installed in the hydrogen supply line 3b to adjust the hydrogen flow rate. The hydrogen flow control valve 31b is an example of a flow control valve.

[0031] The hydrogen outlet line 4 is connected to the downstream side of the fuel electrode 21. The hydrogen outlet line 4 carries a product gas containing hydrogen produced at the fuel electrode 21. The product gas contains hydrogen and water vapor. The water vapor is unreacted water vapor that was not electrolyzed at the fuel electrode 21.

[0032] The hydrogen outlet line 4 includes a hydrogen-side pressure gauge 41, a cooler 42, a pressure regulating valve 7, and a branching point J. The hydrogen-side pressure gauge 41 is positioned relatively close to the fuel electrode 21 within the hydrogen outlet line 4. The hydrogen-side pressure gauge 41 measures the pressure of the generated gas flowing through the hydrogen outlet line 4.

[0033] The cooler 42 is located downstream of the hydrogen-side pressure gauge 41 in the hydrogen outlet line 4. The cooler 42 cools the generated gas. By liquefying and removing water vapor in the cooler 42, the purity of hydrogen in the generated gas can be increased.

[0034] The pressure regulating valve 7 is located downstream of the cooler 42 in the hydrogen outlet line 4. The pressure regulating valve 7 adjusts the pressure of the generated gas flowing through the hydrogen outlet line 4.

[0035] The branching point J is located downstream of the pressure regulating valve 7. At branching point J, the hydrogen outlet line 4 branches into the downstream supply line 43 and the gas purge line 44.

[0036] The downstream supply line 43 supplies hydrogen to a downstream system 8 that utilizes the hydrogen contained in the generated gas. The downstream system 8 is not particularly limited. Any system can be used as the downstream system 8, for example, an apparatus for producing chemical substances using hydrogen as a raw material, an apparatus for performing reduction treatment in a reducing atmosphere formed by hydrogen, or an apparatus for manufacturing and processing products in a reducing atmosphere formed by hydrogen.

[0037] A flow path switching valve 43a is located in the downstream supply line 43 between the branching point J and the downstream system 8. By opening the flow path switching valve 43a, water contained in the generated gas can be supplied to the downstream system 8. Conversely, by closing the flow path switching valve 43a, the supply of hydrogen to the downstream system 8 can be stopped.

[0038] The end of the gas purge line 44 opposite the branching point J is open to the outside. This allows the gas purge line 44 to release at least one of nitrogen, water vapor, and hydrogen to the outside. A flow path switching valve 44a is located in the gas purge line 44. By opening the flow path switching valve 44a, the generated gas can be released to the outside. Conversely, by closing the flow path switching valve 44a, the release of the generated gas to the outside can be stopped.

[0039] The air supply line 5 is connected to the upstream side of the air electrode 22 of the electrolytic cell stack 2. The air supply line 5 supplies air to the air electrode 22. An air pump 51 is located in the air supply line 5. This pumps the air to a predetermined pressure and supplies it to the air electrode 22. However, a compressor, blower, etc. may be used instead of the air pump 51.

[0040] The air discharge line 6 is connected to the downstream side of the air electrode 22. The end of the air discharge line 6 opposite the air electrode 22 is open to the outside. This allows the air discharge line 6 to release the exhaust air discharged from the air electrode 22 to the outside. The air discharge line 6 is equipped with an air-side pressure gauge 61 and a cooler 62.

[0041] The air-side pressure gauge 61 is positioned relatively close to the air electrode 22 in the air discharge line 6. The air-side pressure gauge 61 measures the pressure of the discharged air flowing through the air discharge line 6.

[0042] The cooler 62 lowers the temperature of the exhaust air circulating in the air discharge line 6 to a predetermined temperature. The exhaust air, cooled to the predetermined temperature, is then released to the outside.

[0043] The flow rate control device 91 includes a processor (not shown) and a memory (not shown). The flow rate control device 91 can individually control the steam flow control valve 31, the nitrogen flow control valve 31a, and the hydrogen flow control valve 31b. As a result, the flow path control device 93 can adjust the steam concentration, nitrogen concentration, and hydrogen concentration in the steam-containing gas flowing through the steam supply line 3, and can also adjust the overall flow rate of the steam-containing gas.

[0044] The pressure control device 92 includes a processor (not shown) and a memory (not shown). The pressure control device 92 acquires the pressure of the generated gas measured by the hydrogen-side pressure gauge 41 and the pressure of the exhaust air measured by the air-side pressure gauge 61. Based on the pressure of the generated gas and the pressure of the exhaust air, the pressure control device 92 controls the pressure regulating valve 7 so that the pressure in the space facing the fuel electrode 21 is greater than the pressure in the space facing the air electrode 22.

[0045] In detail, the pressure control device 92 estimates the pressure in the space facing the fuel electrode 21 located upstream of the hydrogen outlet line 4, based on the pressure of the generated gas flowing through the hydrogen outlet line 4, as measured by the hydrogen-side pressure gauge 41.

[0046] Furthermore, the pressure control device 92 estimates the pressure in the space facing the air electrode 22 located upstream of the air discharge line 6, based on the pressure of the discharged air flowing through the air discharge line 6, which is measured by the air-side pressure gauge 61.

[0047] The pressure control device 92 stores in its memory a target value for the pressure difference between the pressure in the space facing the fuel electrode 21 and the pressure in the space facing the air electrode 22. There may be only one target value, or different values ​​may be set for each operating process of the steam electrolysis system 1a.

[0048] The pressure control device 92 adjusts the pressure regulating valve 7 so that the difference between the estimated pressure in the space facing the fuel electrode 21 and the estimated pressure in the space facing the air electrode 22 becomes a target value. In this way, the pressure control device 92 can control the pressure regulating valve 7 so that the pressure in the space facing the fuel electrode 21 is greater than the pressure in the space facing the air electrode 22.

[0049] The flow path control device 93 includes a processor (not shown) and a memory (not shown). The flow path control device 93 controls whether the generated gas flows to the downstream supply line 43 or to the gas purge line 44 by controlling a flow path switching valve 43a located in the downstream supply line 43 and a flow path switching valve 44a located in the gas purge line 44.

[0050] The pressure control device 92 obtains information from the flow rate control device 91 regarding fluctuations in the overall flow rate of the water vapor-containing gas and fluctuations in the flow rates of each component of the water vapor-containing gas. The pressure control device 92 also obtains information from the flow path control device 93 regarding changes in the flow path. Based on the information regarding changes in the flow rate of the water vapor-containing gas and changes in the flow path of the generated gas, the pressure control device 92 predicts pressure fluctuations in the space facing the fuel electrode 21.

[0051] The pressure control device 92 controls the pressure regulating valve 7 based on the predicted pressure fluctuations so that the pressure fluctuations in the space facing the fuel electrode 21 are reduced.

[0052] Furthermore, the pressure control device 92 changes the above-mentioned target value in accordance with the operating process of the steam electrolysis system 1a, based on information obtained from the flow rate control device 91 and information obtained from the flow path control device 93. However, the pressure control device 92 may also be configured to control the pressure regulating valve 7 based on a single target value.

[0053] 2. Operation process of the steam electrolysis system 1a Next, with reference to Figure 2, the operation process of the steam electrolysis system 1a of this embodiment 1 will be described. Figure 2(a) is a graph showing the time change in the flow rate of the gas supplied to the fuel electrode 21. Figure 2(b) is a graph showing the time change in the opening degree of the pressure regulating valve 7. Figure 2(c) is a graph showing the time change in the target value of the pressure difference between the pressure in the space facing the fuel electrode 21 and the pressure in the space facing the air electrode 22.

[0054] As shown in Figures 2(a) to 2(c), the steam electrolysis system 1a of this embodiment 1 performs five operating steps, from step 1 to step 5.

[0055] 2.1 Process 1 Step 1 aims to purge the electrolytic cell stack 2 and each line 3, 4, 5, 6 with nitrogen when starting the steam electrolysis system 1a. In Step 1, as shown in Figure 2(a), the flow rate control device 91 fully closes the steam flow rate control valve 31, adjusts the opening of the nitrogen flow rate control valve 31a so that the nitrogen flow rate is a predetermined flow rate, and adjusts the opening of the hydrogen flow rate control valve 31b so that the hydrogen flow rate is a predetermined flow rate. As shown in Figure 2(b), in Step 1, the pressure control device 92 adjusts the opening of the pressure control valve 7 to a predetermined opening v 14 This is set to 0. In step 1, as shown in Figure 2(c), the target value of the differential pressure between the pressure in the space facing the fuel electrode 21 and the pressure in the space facing the air electrode 22 is set to 0.

[0056] The hydrogen circulated in step 1 is intended to create a reducing atmosphere within the steam electrolysis system 1a.

[0057] Furthermore, when the air pump 51 is activated, air is supplied from the air supply line 5 to the electrolytic cell stack 2, and air is discharged to the outside from the air discharge line 6. When the output of the air pump 51 is constant, the pressure in the air supply line 5 is substantially constant in processes 1 to 5. Similarly, when the output of the air pump 51 is constant, the pressure in the air discharge line 6 is substantially constant in processes 1 to 5. However, "substantially constant" includes cases where the pressure is constant, as well as cases where the pressure is not constant but can be considered substantially constant. The same applies hereafter. Also, the pressure in the air supply line 5 and the pressure in the air discharge line 6 may be the same or different.

[0058] In step 1, the flow path control device 93 completely closes the flow path switching valve 43a located in the downstream supply line 43 and completely opens the flow path switching valve 44a located in the gas purge line 44. This purges nitrogen and hydrogen to the outside.

[0059] In step 1, since hydrogen is not generated from water vapor, there is no need to consider the mixing of air with the hydrogen. In step 1, by making the pressure in the space facing the fuel electrode 21 the same as the pressure in the space facing the air electrode 22, it is possible to suppress stress on the electrolytic cell stack 2 due to the pressure difference.

[0060] 2.2 Process 2 Step 2 aims to replace the electrolytic cell stack 2 and each line with water vapor. In Step 2, as shown in Figure 2(a), the flow control device 91 increases the opening of the water vapor flow control valve 31 over time, and at the end of Step 2, sets the opening of the water vapor flow control valve 31 to a predetermined opening. The flow control device 91 also decreases the opening of the nitrogen flow control valve 31a over time, and at the end of Step 2, sets the opening of the nitrogen flow control valve 31a to 0%. The flow control device 91 opens the hydrogen flow control valve 31b to a predetermined opening, similar to Step 1.

[0061] The flow path control device 93, similar to step 1, completely closes the flow path switching valve 43a located in the downstream supply line 43 and completely opens the flow path switching valve 44a located in the gas purge line 44. This purges nitrogen, water vapor, and at least one of hydrogen to the outside.

[0062] As shown in Figure 2(c), in step 2, the target value of the differential pressure between the space facing the fuel electrode 21 and the space facing the air electrode 22 is set to 0. This is for the same reasons as in step 1.

[0063] As shown in Figure 2(b), the pressure control device 92 controls the opening degree of the pressure regulating valve 7 to a predetermined opening degree v 14 The pressure is gradually reduced over time, and at the end of step 2, the opening of the pressure regulating valve 7 is set to v 11 Set to v. As described above, the target value of the differential pressure between the space facing the fuel electrode 21 and the space facing the air electrode 22 is 0. However, because pressure fluctuations occur as the gas flowing through the water vapor electrolysis system 1a is replaced from nitrogen to water vapor, the opening degree of the pressure regulating valve 7 is set to v in order to suppress these pressure fluctuations. 14 from v 11 This changes the pressure to a certain extent. This suppresses the stress on the electrolytic cell stack 2 due to the pressure difference.

[0064] 2.3 Process 3 Step 3 aims to change the differential pressure between the space facing the fuel electrode 21 and the space facing the air electrode 22 to a target value. In Step 3, as shown in 2(a), the flow control device 91 adjusts the opening of the water vapor flow control valve 31 so that the water vapor flow rate is constant, maintains the opening of the nitrogen flow control valve 31a at 0%, and adjusts the opening of the hydrogen flow control valve 31b so that the hydrogen flow rate is constant.

[0065] As shown in Figure 2(c), the target value of the differential pressure between the space facing the fuel electrode 21 and the space facing the air electrode 22 is set to 0 at the start of process 3, increases over time, and is set to Δp at the end of process 3.

[0066] As shown in Figure 2(b), the pressure control device 92 controls the opening degree of the pressure regulating valve 7 at the start of process 3. 11 The opening of the pressure regulating valve 7 is gradually reduced over time, and at the end of step 3, the opening of the pressure regulating valve 7 is set to v 12 This is set to allow the pressure in the space facing the fuel electrode 21 to be greater than the pressure in the space facing the air electrode 22 at the end of step 3. In step 3, hydrogen production has not yet started, but before hydrogen production begins, the pressure in the space facing the fuel electrode 21 is set to be greater than the pressure in the space facing the air electrode 22. This suppresses the mixing of gas from the air electrode 22 into the fuel electrode 21 in advance. In addition, impurities such as nitrogen remaining in the water vapor supply line 3 can be expelled from the water vapor supply line 3.

[0067] 2.4 Process 4 Step 4 aims to maintain a state in which the pressure in the space facing the fuel electrode 21 is greater than the pressure in the space facing the air electrode 22. In Step 4, as shown in 2(a), the flow control device 91 adjusts the opening of the water vapor flow control valve 31 so that the water vapor flow rate is constant, maintains the opening of the nitrogen flow control valve 31a at 0%, and maintains the opening of the hydrogen flow control valve 31b at a predetermined amount.

[0068] As shown in Figure 2(c), in step 4, the target value of the differential pressure between the space facing the fuel electrode 21 and the space facing the air electrode 22 is set to Δp. In step 4, hydrogen production has not yet started, but before hydrogen production begins, by maintaining a state in which the pressure in the space facing the fuel electrode 21 is greater than the pressure in the space facing the air electrode 22 for a predetermined time, the mixing of gas from the air electrode 22 to the fuel electrode 21 can be suppressed in advance. In addition, impurities such as nitrogen remaining in the water vapor supply line 3 can be expelled from the water vapor supply line 3.

[0069] 2.5 Process 5 Step 5 is a step of generating hydrogen by electrolyzing water vapor contained in a water vapor-containing gas. In Step 5, as shown in FIG. 2(a), the flow rate control device 91 adjusts the opening degree of the water vapor flow rate adjustment valve 31 so that the flow rate of water vapor becomes constant, maintains the opening degree of the nitrogen flow rate adjustment valve 31a at 0%, and maintains the opening degree of the hydrogen flow rate adjustment valve 31b at a predetermined amount.

[0070] In Step 5, hydrogen is generated from water vapor by applying a voltage to the electrolysis cell stack 2. The voltage applied to the electrolysis cell stack 2 is controlled to increase with time from 0 to a predetermined value at the start of Step 5, and to be maintained at the predetermined value after reaching the predetermined value. As the voltage applied to the electrolysis cell stack 2 increases, the flow rate of hydrogen generated at the fuel electrode 21 increases, and after the voltage is controlled to be constant, the hydrogen generation amount also becomes constant.

[0071] As shown in FIG. 2(c), in Step 4, the target value of the differential pressure between the pressure in the space facing the fuel electrode 21 and the pressure in the space facing the air electrode 22 is set to Δp.

[0072] As shown in FIG. 2(b), as the hydrogen generation amount increases, the pressure control device 92 adjusts the opening degree of the pressure regulating valve 7 from v 12 to v 13 to maintain the differential pressure between the pressure in the space facing the fuel electrode 21 and the pressure in the space facing the air electrode 22 at Δp.

[0073] 3. Functions and Effects of the First Embodiment Next, the functions and effects of the first embodiment will be described. The water vapor electrolysis system 1a of the first embodiment includes an electrolysis cell stack 2, a water vapor supply line 3, a hydrogen lead-out line 4, an air supply line 5, an air discharge line 6, and a pressure regulating valve 7.

[0074] The electrolysis cell stack 2 includes a fuel electrode 21 to which a water vapor-containing gas is supplied and which generates hydrogen from water vapor, an air electrode 22 through which air flows, and a solid electrolyte 23 disposed between the fuel electrode 21 and the air electrode 22.

[0075] The steam supply line 3 is connected to the upstream side of the fuel electrode 21 and supplies steam-containing gas to the fuel electrode 21. The hydrogen discharge line 4 is connected to the downstream side of the fuel electrode 21 and discharges the generated gas containing hydrogen. The air supply line 5 is connected to the upstream side of the air electrode 22 and supplies air to the air electrode 22. The air discharge line 6 is connected to the downstream side of the air electrode 22 and discharges the exhaust air containing oxygen generated at the air electrode 22.

[0076] The pressure regulating valve 7 is located in the hydrogen outlet line 4 and adjusts the pressure so that, when hydrogen is being generated at the fuel electrode 21, the pressure in the space facing the fuel electrode 21 is greater than the pressure in the space facing the air electrode 22.

[0077] According to this embodiment 1, since the pressure in the space facing the fuel electrode 21 is greater than the pressure in the space facing the air electrode 22, it is possible to suppress the mixing of air from the air electrode 22 into the fuel electrode 21. This makes it possible to suppress a decrease in the purity of the hydrogen produced at the fuel electrode 21.

[0078] The steam electrolysis system 1a further includes a hydrogen-side pressure gauge 41, an air-side pressure gauge 61, and a pressure control device 92.

[0079] The hydrogen-side pressure gauge 41 is located on at least one of the water vapor supply line 3 and the hydrogen outlet line 4. The air-side pressure gauge 61 is located on at least one of the air supply line 5 and the air discharge line 6.

[0080] Based on the hydrogen-side pressure obtained from the hydrogen-side pressure gauge 41 and the air-side pressure obtained from the air-side pressure gauge 61, the pressure control device 92 controls the pressure regulating valve 7 so that, when hydrogen is being generated at the fuel electrode 21, the pressure in the space facing the fuel electrode 21 is greater than the pressure in the space facing the air electrode 22.

[0081] According to this embodiment 1, the pressure regulating valve 7 can be controlled with high precision. This further suppresses the mixing of air from the air electrode 22 into the fuel electrode 21. As a result, the decrease in the purity of hydrogen produced at the fuel electrode 21 can be further suppressed.

[0082] The steam electrolysis system 1a of this embodiment 1 further includes a steam flow control valve 31, a nitrogen flow control valve 31a, a hydrogen flow control valve 31b, a flow control device 91, a downstream supply line 43, a gas purge line 44, flow path switching valves 43a, 44a, and a flow path control device 93.

[0083] The steam flow control valve 31, nitrogen flow control valve 31a, and hydrogen flow control valve 31b are located in the steam supply line 3 to adjust the flow rate of the steam-containing gas. The flow control device 91 controls the steam flow control valve 31, nitrogen flow control valve 31a, and hydrogen flow control valve 31b.

[0084] The downstream supply line 43 branches off from the hydrogen outlet line 4 and sends the generated gas to the downstream system 8 that utilizes hydrogen. The gas purge line 44 branches off from the hydrogen outlet line 4 and discharges at least one of nitrogen, water vapor, and hydrogen to the outside. The flow path switching valves 43a and 44a switch whether the generated gas flows to the downstream supply line 43 or to the gas purge line 44. The flow path control device 93 controls the flow path switching valves 43a and 44a.

[0085] According to this embodiment 1, it is possible to adjust the flow rate of the water vapor-containing gas in accordance with the operation process of electrolyzing water vapor, and also to adjust the flow path of the generated gas.

[0086] The pressure control device 92 of this embodiment 1 is configured to control the pressure regulating valve 7 based on a target value for the pressure difference between the water vapor-containing gas in the fuel electrode 21 and the air in the air electrode 22. The target value is set to a different value for each operating process of the water vapor electrolysis system 1a.

[0087] According to this embodiment 1, the pressure difference between the space facing the fuel electrode 21 and the space facing the air electrode 22 can be varied for each operating process of the steam electrolysis system 1a. This allows, for example, the pressure difference between the fuel electrode 21 and the air electrode 22 to be increased in operating processes where it is desired to increase the purity of the hydrogen produced at the fuel electrode 21, and to be decreased in operating processes where the purity of the hydrogen does not need to be considered. This reduces stress on the electrolysis cell stack 2.

[0088] In this embodiment 1, when the flow rate control device 91 changes the flow rate of the water vapor-containing gas by controlling the water vapor flow control valve 31, the nitrogen flow control valve 31a, and the hydrogen flow control valve 31b, or when the flow path control device 93 changes the flow path of the generated gas by controlling the flow path switching valves 43a and 44a, the pressure control device 92 is configured to predict the pressure fluctuation of the water vapor-containing gas at the fuel electrode 21 due to the change in flow rate or flow path, and to control the pressure control valve 7 based on the predicted pressure fluctuation of the water vapor-containing gas so that the pressure fluctuation of the water vapor-containing gas at the fuel electrode 21 becomes smaller.

[0089] According to this embodiment 1, pressure fluctuations in the space facing the fuel electrode 21 can be suppressed based on flow rate changes by the flow rate control device 91 or flow path changes by the flow path control device 93. This makes it easier to control the pressure in the space facing the fuel electrode 21 to a state higher than the pressure in the space facing the air electrode 22, thereby further suppressing a decrease in the purity of hydrogen produced at the fuel electrode 21.

[0090] The electrolytic cell stack 2 of this embodiment 1 includes a solid oxide type electrolytic cell.

[0091] (Embodiment 2) Next, the steam electrolysis system 1b of Embodiment 2 will be described with reference to Figure 3. Note that, among the reference numerals used in Embodiment 2 and later, those that are the same as those used in the previously described embodiments represent the same components as those in the previously described embodiments, unless otherwise specified.

[0092] The steam electrolysis system 1b of this second embodiment includes a recirculation line 45 downstream of the pressure regulating valve 7 in the hydrogen outlet line 4. The recirculation line 45 branches off from branching point J of the hydrogen outlet line 4 and is connected to the steam supply line 3. As a result, a portion of the hydrogen produced at the fuel electrode 21 is supplied to the steam supply line 3 via the recirculation line 45. However, the recirculation line 45 may be configured to branch off from the hydrogen outlet line 4 at a position different from branching point J.

[0093] A reflux pump 45a is located in the reflux line 45 between the branching point J and the steam supply line 3. This reflux pump 45a sends the hydrogen produced at the fuel electrode 21 to the steam supply line 3. However, a compressor or a blower may be installed instead of the reflux pump 45a.

[0094] A recirculating hydrogen discharge line 46 branches off from the recirculating line 45 downstream of the recirculating pump 45a. The recirculating hydrogen discharge line 46 discharges the hydrogen flowing through the recirculating line 45 to the outside. A hydrogen discharge flow rate control valve 46a is installed in the recirculating hydrogen discharge line 46. The hydrogen discharge flow rate control valve 46a is an example of a flow rate control valve. The hydrogen discharge flow rate control valve 46a installed in the recirculating hydrogen discharge line 46 is controlled by a flow rate control device 91. The recirculating hydrogen discharge line 46 allows excess hydrogen to be discharged to the outside.

[0095] A reflux hydrogen flow control valve 45b is located in the reflux line 45 between the reflux hydrogen discharge line 46 and the steam supply line 3. The reflux hydrogen flow control valve 45b is an example of a flow path control valve. The reflux hydrogen flow control valve 45b located in the reflux line 45 is controlled by a flow control device 91.

[0096] According to this embodiment, the hydrogen generated at the fuel electrode 21 of the electrolytic cell stack 2 can be used to maintain the fuel electrode 21 of the electrolytic cell stack 2 in a reducing atmosphere. This makes it possible to reduce manufacturing costs compared to the case where hydrogen for reducing the fuel electrode 21 is prepared separately.

[0097] (Embodiment 3) Next, the steam electrolysis system 1c of Embodiment 3 will be described with reference to Figures 4 to 6. In Embodiment 3, a first pressure regulating valve 71 and a second pressure regulating valve 72 are arranged in parallel with the hydrogen outlet line 4. The capacity coefficients of the first pressure regulating valve 71 and the second pressure regulating valve 72 are different. Except as described above, it is the same as Embodiment 2, so the same reference numerals are used for the same components and redundant explanations are omitted.

[0098] The first pressure regulating valve 71 and the second pressure regulating valve 72 are set to a pressure adjustment range that can be adjusted with a predetermined precision, defined by rangeability. The rangeability of the first pressure regulating valve 71 and the second pressure regulating valve 72 is not particularly limited and can be set arbitrarily. In this embodiment, the rangeability of the first pressure regulating valve 71 and the rangeability of the second pressure regulating valve 72 are set to 20:1. The rangeability of the first pressure regulating valve 71 and the rangeability of the second pressure regulating valve 72 may be different.

[0099] Since the rangeability of the first pressure regulating valve 71 and the second pressure regulating valve 72 is 20:1, the first pressure regulating valve 71 and the second pressure regulating valve 72 are configured to control the pressure with a predetermined accuracy when the valve opening is in the range of 5% to 100%. In other words, when the valve opening is in the range of 0% to 5%, the pressure is controlled with a lower accuracy than the predetermined accuracy.

[0100] In this third embodiment, as shown in Figure 5, the pressure adjustment range of the first pressure regulating valve 71 and the pressure adjustment range of the second pressure regulating valve 72 overlap, at least partially. In this third embodiment, the capacity coefficient Cv at 100% valve opening, which is the upper limit of the pressure adjustment range of the second pressure regulating valve 72, is set to be slightly larger than the capacity coefficient Cv at 5% opening, which is the lower limit of the pressure adjustment range of the first pressure regulating valve 71. As a result, when the opening of the first pressure regulating valve 71 is reduced to less than 5%, the pressure can always be controlled within the pressure adjustment range of each pressure regulating valve 7 by adjusting the pressure using the second pressure regulating valve 72. This suppresses a decrease in the accuracy of pressure adjustment. The capacity coefficient Cv is not particularly limited and can be defined, for example, as the flow rate of 15.6°C clean water flowing while maintaining a differential pressure of 1 psi across the valve, expressed in US gal / min, or it may be based on other definitions.

[0101] Next, the operation of the steam electrolysis system 1c of this embodiment 3 will be explained using Figures 6(a) to 6(c). Note that Figure 6(a) is the same as Figure 2(a) and Figure 6(c) is the same as Figure 2(c), so redundant explanations will be omitted.

[0102] As shown in Figure 6(b), in step 1, the pressure control device 92 sets the opening degree of the first pressure regulating valve 71 and the second pressure regulating valve 72 to a predetermined value v 24 This is set to the same value. In other words, in step 1, the pressure in the space facing the fuel electrode 21 and the pressure in the space facing the air electrode 22 are set to the same value.

[0103] In step 2, as shown in Figure 6(b), the pressure control device 92 sets the opening degree of the first pressure regulating valve 71 to a predetermined value v 24 The opening of the first pressure regulating valve 71 is gradually reduced over time until it is completely closed. The pressure control device 92 gradually reduces the opening of the second pressure regulating valve 72 over time when the opening of the first pressure regulating valve 71 is slightly greater than 5%. At the end of step 2, the opening of the first pressure regulating valve 71 is set to 0%, and the opening of the second pressure regulating valve 72 is set to v 21 Set to this.

[0104] As shown in Figure 6(b), the pressure control device 92 controls the opening degree of the second pressure regulating valve 72 at the start of process 3. 21 Then, the opening degree of the pressure regulating valve 7 is reduced over time, and at the end of process 3, the opening degree of the second pressure regulating valve 72 is set to v 22 This is set to allow the pressure in the space facing the fuel electrode 21 to be greater than the pressure in the space facing the air electrode 22 at the end of process 3.

[0105] In step 4, as shown in Figure 2(b), the opening degree of the second pressure regulating valve 72 is v 22 It is maintained.

[0106] In step 5, as shown in Figure 6(b), as the amount of hydrogen produced increases, the pressure control device 92 adjusts the opening of the second pressure regulating valve 72 to v 22 from v 23 By changing the pressure in this way, the pressure difference between the space facing the fuel electrode 21 and the space facing the air electrode 22 is maintained at Δp.

[0107] In this embodiment 3, the hydrogen outlet line 4 has a first pressure regulating valve 71 and a second pressure regulating valve 72 arranged in parallel with the hydrogen outlet line 4, and the capacity coefficients of the first pressure regulating valve 71 and the second pressure regulating valve 72 are different. This allows for a wider pressure adjustment range compared to when the pressure is regulated by a single pressure regulating valve 7. This makes it easier to control the pressure in the space facing the fuel electrode 21 to be higher than the pressure in the space facing the air electrode 22. As a result, the decrease in the purity of the hydrogen produced at the fuel electrode 21 can be further suppressed.

[0108] Furthermore, in this third embodiment, each of the first pressure regulating valve 71 and the second pressure regulating valve 72 is set to a pressure adjustment range that allows for pressure adjustment with a predetermined accuracy, and at least a portion of the pressure adjustment ranges of the first pressure regulating valve 71 and the second pressure regulating valve 72 overlap with each other. As a result, when switching from the first pressure regulating valve 71 to the second pressure regulating valve 72, it is always possible to control within the pressure adjustment range of each pressure regulating valve 71, 72. This makes it possible to suppress a decrease in the accuracy of pressure adjustment.

[0109] (Embodiment 4) Next, with reference to Figure 7, the steam electrolysis system 1d of Embodiment 4 will be described. In Embodiment 4, a first pressure regulating valve 71, a second pressure regulating valve 72, and a third pressure regulating valve 73 are arranged in parallel with the hydrogen outlet line 4. The capacity coefficients of the first pressure regulating valve 71, the second pressure regulating valve 72, and the third pressure regulating valve 73 are different.

[0110] Furthermore, the pressure adjustment ranges of the first pressure regulating valve 71, the second pressure regulating valve 72, and the third pressure regulating valve 73 partially overlap with each other. Since the rest of the configuration is the same as in Embodiment 3, the same reference numerals are used for the same components, and redundant explanations are omitted.

[0111] With the above configuration, the pressure can be adjusted with high precision over a relatively wide pressure range. This makes it possible to suppress a decrease in the accuracy of pressure adjustment when switching between multiple pressure regulating valves 71, 72, and 73.

[0112] Furthermore, the number of pressure regulating valves arranged in parallel with hydrogen outlet line 4 may be four or more.

[0113] (Embodiment 5) Next, with reference to Figure 8, the steam electrolysis system 1e of Embodiment 5 will be described. In Embodiment 5, the hydrogen-side pressure gauge 41 is located in the hydrogen outlet line 4 connected to the downstream side of the fuel electrode 21. The air-side pressure gauge 61 is connected to the air supply line 5 connected to the upstream side of the air electrode 22.

[0114] According to this embodiment 5, the pressure control device 92 can control the pressure of the water vapor-containing gas in the fuel electrode 21 with greater precision based on the pressure of the generated gas downstream of the fuel electrode 21 and the pressure of the air upstream of the air electrode 22. The pressure of the generated gas downstream of the fuel electrode 21 is lower than the pressure of the water vapor-containing gas upstream of the fuel electrode 21. On the other hand, the pressure of the air upstream of the air electrode 22 is higher than the pressure of the exhaust air downstream of the air electrode 22. Therefore, according to this embodiment, the pressure in the space facing the fuel electrode 21 can be reliably made higher than the pressure in the space facing the air electrode 22, based on the lower pressure in the fuel electrode 21 and the higher pressure in the air electrode 22. This further suppresses the mixing of air from the air electrode 22 into the fuel electrode 21, and thus further suppresses the decrease in the purity of the hydrogen produced in the fuel electrode 21.

[0115] (Embodiment 6) Next, with reference to Figures 9 to 10, the steam electrolysis system 1f of Embodiment 6 will be described. As shown in Figure 9, in Embodiment 6, the hydrogen-side pressure gauge 41 is located in the steam supply line 3 connected to the upstream side of the fuel electrode 21. The air-side pressure gauge 61 is connected to the air supply line 5 connected to the upstream side of the air electrode 22.

[0116] As shown in Figure 10, if there is a pressure loss element 21a downstream of the fuel electrode 21 that causes pressure loss of the water vapor-containing gas, such as when the flow path of the water vapor-containing gas narrows or bends, the pressure of the water vapor-containing gas inside the fuel electrode 21 decreases significantly downstream of the pressure loss element 21a. In this case, the pressure in the water vapor supply line 3 connected upstream of the fuel electrode 21 is considered to be relatively close to the pressure in the space facing the fuel electrode 21. In such cases, by placing the hydrogen-side pressure gauge 41 in the water vapor supply line 3, the pressure in the space facing the fuel electrode 21 can be measured more accurately.

[0117] The same applies when a pressure loss element 22a is present downstream of the air electrode 22, so a redundant explanation will be omitted.

[0118] (Embodiment 7) Next, with reference to Figure 11, the steam electrolysis system 1g of Embodiment 7 will be described. In Embodiment 7, a pneumatic regulating valve is located in the air discharge line 6. The pneumatic regulating valve 64 adjusts the pressure in the space facing the air electrode 22. The pressure control device 92 controls the pneumatic regulating valve 64.

[0119] According to this embodiment 7, the pressure in the space facing the air electrode 22 can also be controlled. This ensures that the pressure in the space facing the fuel electrode 21 is reliably higher than the pressure in the space facing the air electrode 22. As a result, the mixing of air from the air electrode 22 into the fuel electrode 21 can be further suppressed, thereby further suppressing the decrease in the purity of hydrogen produced at the fuel electrode 21.

[0120] (Embodiment 8) Next, with reference to Figure 12, the steam electrolysis system 1h of Embodiment 8 will be described. In Embodiment 8, a differential pressure gauge 74 for measuring the differential pressure between the hydrogen outlet line 4 and the air discharge line 6 is positioned across the hydrogen outlet line 4 and the air discharge line 6.

[0121] The pressure control device 92 of this embodiment 8 obtains the differential pressure between the hydrogen outlet line 4 and the air discharge line 6 from the differential pressure gauge 74, and controls the pressure regulating valve 7 based on the differential pressure so that the pressure in the space facing the fuel electrode 21 is greater than the pressure in the space facing the air electrode 22.

[0122] According to this embodiment 8, the pressure regulating valve 7 can be controlled with high precision by the differential pressure obtained by a single differential pressure gauge 74. As a result, the mixing of air from the air electrode 22 into the fuel electrode 21 can be further suppressed compared to when pressure is obtained by multiple pressure measuring means. Consequently, the decrease in the purity of hydrogen produced at the fuel electrode 21 can be further suppressed.

[0123] The differential pressure gauge 74 may also be positioned across the water vapor supply line 3 and the air supply line 5 to measure the differential pressure between the water vapor supply line 3 and the air supply line 5.

[0124] (Embodiment 9) Next, with reference to Figure 13, the steam electrolysis system 1i of Embodiment 9 will be described. In Embodiment 9, a first differential pressure gauge 74a, which measures the differential pressure between the steam supply line 3 and the air supply line 5, is positioned across the steam supply line 3 and the air supply line 5. In addition, a second differential pressure gauge 74b, which measures the differential pressure between the hydrogen outlet line 4 and the air discharge line 6, is positioned across the hydrogen outlet line 4 and the air discharge line 6.

[0125] The pressure control device 92 of this embodiment 8 acquires a first differential pressure between the steam supply line 3 and the air supply line 5, measured by the first differential pressure gauge 74a, and a second differential pressure between the hydrogen outlet line 4 and the air discharge line 6, measured by the second differential pressure gauge 74b. The pressure control device 92 calculates the average value of the first differential pressure acquired from the first differential pressure gauge 74a and the second differential pressure acquired from the second differential pressure gauge 74b. Based on the average value of the first and second differential pressures, the pressure control device 92 controls the pressure regulating valve 7 so that the pressure in the space facing the fuel electrode 21 is greater than the pressure in the space facing the air electrode 22.

[0126] According to this embodiment 8, the average value of the first differential pressure and the second differential pressure can be calculated. This makes it possible to obtain the average value of the pressure difference within the electrolytic cell stack 2.

[0127] The present invention is not limited to the embodiments described above, and can be applied to various embodiments without departing from its spirit.

[0128] <Other> The features of this invention are as follows. [1] An electrolytic cell stack (2) comprises a fuel electrode (21) through which a water vapor-containing gas is supplied and which generates hydrogen from the water vapor, an air electrode (22) through which air flows, and a solid electrolyte (23) disposed between the fuel electrode and the air electrode. A steam supply line (3) is connected to the upstream side of the fuel electrode and supplies the steam-containing gas to the fuel electrode, A hydrogen outlet line (4) connected to the downstream side of the fuel electrode and for discharging the hydrogen-containing generated gas, An air supply line (5) is connected to the upstream side of the air electrode and supplies air to the air electrode, An air discharge line (6) is connected downstream of the air electrode and discharges the exhaust air containing oxygen generated at the air electrode, A steam electrolysis system (1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i) comprising: at least one pressure regulating valve (7) positioned in the hydrogen output line and adjusting the pressure in the space facing the fuel electrode to be greater than the pressure in the space facing the air electrode when hydrogen is being generated at the fuel electrode. [2] moreover, A hydrogen-side pressure gauge (41) is located in at least one of the steam supply line and the hydrogen outlet line, An air-side pressure gauge (61) is located in at least one of the air supply line and the air discharge line, The steam electrolysis system according to [1], further comprising: a pressure control device (92) that controls the pressure regulating valve based on the hydrogen-side pressure obtained from the hydrogen-side pressure gauge and the air-side pressure obtained from the air-side pressure gauge, such that the pressure in the space facing the fuel electrode is greater than the pressure in the space facing the air electrode when hydrogen is being generated at the fuel electrode. [3] The hydrogen-side pressure gauge is located in the hydrogen outlet line. The steam electrolysis system according to [2], wherein the air-side pressure gauge is located in the air supply line. [4] moreover, A differential pressure gauge (74) for measuring at least one of the differential pressure between the water vapor supply line and the air supply line, and the differential pressure between the hydrogen discharge line and the air discharge line, A steam electrolysis system according to any one of [1] to [3], comprising: a pressure control device that controls the pressure regulating valve based on the differential pressure obtained from the differential pressure gauge such that the pressure in the space facing the fuel electrode is greater than the pressure in the space facing the air electrode. [5] Multiple pressure regulating valves are arranged in parallel with the hydrogen outlet line. A steam electrolysis system according to any one of [1] to [4], wherein the capacity coefficients of the multiple pressure regulating valves are different. [6] Each of the multiple pressure regulating valves is set to a pressure regulating range that allows for pressure adjustment with a predetermined accuracy. The steam electrolysis system according to [5], wherein the pressure adjustment ranges of each of the multiple pressure adjustment valves overlap with each other in at least part. [7] Furthermore, the system includes an air pressure regulating valve (64) positioned in the air discharge line and for adjusting the pressure in the space facing the air electrode, The steam electrolysis system according to [2], wherein the pressure control device controls the pneumatic regulating valve. [8] moreover, A flow control valve (31, 31a, 31b) is arranged in the steam supply line to adjust the flow rate of the steam-containing gas, A flow control device (91) that controls the flow control valve, A downstream supply line (43) branches off from the hydrogen output line and sends the generated gas to a downstream system that utilizes the hydrogen, A gas purge line (44) branches off from the hydrogen outlet line and discharges the generated gas to the outside, A flow path switching valve (43a, 44a) for switching whether the generated gas is flowed to the downstream supply line or to the gas purge line, The steam electrolysis system according to [2], further comprising a flow control device (93) for controlling the flow path switching valve. [9] The pressure control device is configured to control the flow control valve based on a target value of the pressure difference between the water vapor-containing gas in the fuel electrode and the air in the air electrode. The steam electrolysis system according to any one of [3], [4], [7], or [8], wherein the target value is set to a different value for each operating process of the steam electrolysis system.

[10] moreover, A hydrogen-side pressure gauge is provided in at least one of the steam supply line and the hydrogen outlet line, An air-side pressure gauge is provided in at least one of the air supply line and the air discharge line, The system includes a pressure control device that controls the pressure regulating valve based on the hydrogen-side pressure obtained from the hydrogen-side pressure gauge and the air-side pressure obtained from the air-side pressure gauge, such that the pressure in the space facing the fuel electrode is greater than the pressure in the space facing the air electrode when hydrogen is being generated at the fuel electrode. Multiple pressure regulating valves are arranged in parallel with the hydrogen outlet line. The capacity coefficients of the multiple pressure regulating valves are different. Each of the multiple pressure regulating valves is set to a pressure regulating range that allows for pressure adjustment with a predetermined accuracy. The pressure adjustment ranges of each of the multiple pressure regulating valves overlap with each other in at least part, The pressure control device is configured to control the pressure regulating valve based on a target value of the pressure difference between the water vapor-containing gas in the fuel electrode and the air in the air electrode. The steam electrolysis system according to [1], wherein the target value is set to a different value for each operating process of the steam electrolysis system.

[11] When the flow control device changes the flow rate of the water vapor-containing gas by controlling the flow control valve, or when the flow path control device changes the flow path of the generated gas by controlling the flow path switching valve, The pressure control device is Predict the pressure fluctuation of the water vapor-containing gas at the fuel electrode due to the change in flow rate or the change in flow path, A steam electrolysis system according to any one of [8] to

[10] , wherein the pressure regulating valve is controlled to reduce the pressure fluctuation of the steam-containing gas at the fuel electrode based on the predicted pressure fluctuation of the steam-containing gas.

[12] The water vapor electrolysis system according to any one of [1] to

[11] , wherein the electrolytic cell stack comprises a solid oxide type electrolytic cell. [Explanation of Symbols]

[0129] 1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i: Steam electrolysis system, 2: Electrolytic cell stack, 3: Steam supply line, 4: Hydrogen outlet line, 5: Air supply line, 6: Air discharge line, 7: Pressure regulating valve

Claims

1. An electrolytic cell stack (2) comprises a fuel electrode (21) through which a water vapor-containing gas is supplied and which generates hydrogen from the water vapor, an air electrode (22) through which air flows, and a solid electrolyte (23) disposed between the fuel electrode and the air electrode. A steam supply line (3) is connected to the upstream side of the fuel electrode and supplies the steam-containing gas to the fuel electrode, A hydrogen outlet line (4) connected to the downstream side of the fuel electrode and for discharging the hydrogen-containing generated gas, An air supply line (5) is connected to the upstream side of the air electrode and supplies air to the air electrode, An air discharge line (6) is connected downstream of the air electrode and discharges the exhaust air containing oxygen generated at the air electrode, A steam electrolysis system (1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i) comprising: at least one pressure regulating valve (7) positioned in the hydrogen output line, which adjusts the pressure in the space facing the fuel electrode to be greater than the pressure in the space facing the air electrode when hydrogen is being generated at the fuel electrode.

2. moreover, A hydrogen-side pressure gauge (41) is provided in at least one of the steam supply line and the hydrogen outlet line, An air-side pressure gauge (61) is provided in at least one of the air supply line and the air discharge line, The steam electrolysis system according to claim 1, further comprising: a pressure control device (92) that controls the pressure regulating valve based on the hydrogen-side pressure obtained from the hydrogen-side pressure gauge and the air-side pressure obtained from the air-side pressure gauge, such that the pressure in the space facing the fuel electrode is greater than the pressure in the space facing the air electrode when hydrogen is being generated at the fuel electrode.

3. The hydrogen-side pressure gauge is located in the hydrogen outlet line. The steam electrolysis system according to claim 2, wherein the air-side pressure gauge is located in the air supply line.

4. moreover, A differential pressure gauge (74) for measuring at least one of the differential pressure between the water vapor supply line and the air supply line, and the differential pressure between the hydrogen discharge line and the air discharge line, The steam electrolysis system according to claim 1, further comprising: a pressure control device that controls the pressure regulating valve based on the differential pressure obtained from the differential pressure gauge, such that the pressure in the space facing the fuel electrode is greater than the pressure in the space facing the air electrode.

5. Multiple pressure regulating valves are arranged in parallel with the hydrogen outlet line. The steam electrolysis system according to claim 1, wherein the capacity coefficients of the multiple pressure regulating valves are different.

6. Each of the multiple pressure regulating valves is set to a pressure regulating range that allows for pressure adjustment with a predetermined accuracy. The steam electrolysis system according to claim 5, wherein the pressure adjustment ranges of each of the multiple pressure adjustment valves overlap with each other in at least part.

7. Furthermore, the system includes an air pressure regulating valve (64) positioned in the air discharge line and for adjusting the pressure in the space facing the air electrode, The steam electrolysis system according to claim 2, wherein the pressure control device controls the pneumatic regulating valve.

8. moreover, A flow control valve (31, 31a, 31b) is arranged in the steam supply line to adjust the flow rate of the steam-containing gas, A flow control device (91) that controls the flow control valve, A downstream supply line (43) branches off from the hydrogen output line and sends the generated gas to a downstream system that utilizes the hydrogen, A gas purge line (44) branches off from the hydrogen discharge line and discharges at least one of nitrogen, water vapor, and hydrogen to the outside, A flow path switching valve (43a, 44a) for switching whether the generated gas is flowed to the downstream supply line or to the gas purge line, The steam electrolysis system according to claim 2, further comprising a flow path control device (93) for controlling the flow path switching valve.

9. The pressure control device is configured to control the pressure regulating valve based on a target value of the pressure difference between the water vapor-containing gas in the fuel electrode and the air in the air electrode. The steam electrolysis system according to any one of claims 3, 4, 7, or 8, wherein the target value is set to a different value for each operating process of the steam electrolysis system.

10. moreover, A hydrogen-side pressure gauge is provided in at least one of the steam supply line and the hydrogen outlet line, An air-side pressure gauge is provided in at least one of the air supply line and the air discharge line, The system includes a pressure control device that controls the pressure regulating valve based on the hydrogen-side pressure obtained from the hydrogen-side pressure gauge and the air-side pressure obtained from the air-side pressure gauge, such that the pressure in the space facing the fuel electrode is greater than the pressure in the space facing the air electrode when hydrogen is being generated at the fuel electrode. Multiple pressure regulating valves are arranged in parallel with the hydrogen outlet line. The capacity coefficients of the multiple pressure regulating valves are different. Each of the multiple pressure regulating valves is set to a pressure regulating range that allows for pressure adjustment with a predetermined accuracy. The pressure adjustment ranges of each of the multiple pressure regulating valves overlap with each other in at least part, The pressure control device is configured to control the pressure regulating valve based on a target value of the pressure difference between the water vapor-containing gas in the fuel electrode and the air in the air electrode. The steam electrolysis system according to claim 1, wherein the target value is set to a different value for each operating process of the steam electrolysis system.

11. When the flow control device changes the flow rate of the water vapor-containing gas by controlling the flow control valve, or when the flow path control device changes the flow path of the generated gas by controlling the flow path switching valve, The pressure control device is Predict the pressure fluctuation of the water vapor-containing gas at the fuel electrode due to the change in flow rate or the change in flow path, The steam electrolysis system according to claim 8, configured to control the pressure regulating valve so that the pressure fluctuation of the steam-containing gas at the fuel electrode is reduced based on the predicted pressure fluctuation of the steam-containing gas.

12. The steam electrolysis system according to claim 1, wherein the electrolytic cell stack comprises a solid oxide type electrolytic cell.

Images