Hydrogen production system and method for producing hydrogen

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Description in which hydrogen and oxygen are generated from steam by the electrolytic reaction, and an exothermic reaction

Cross-Reference to Related Application by electrical resistance of the electrolytic cell itself become almost equal to each other, it is possible to mini- [0001] This application is based upon and claims the 5 mize energy input from outside, and produce hydrogen benefit of priority from Japanese Patent application No. at high efficiency.

2014-162431, filed on August 8, 2014, the entire content [0009] However, when the renewable energy is used of which is incorporated herein by reference. as an electric power source for the electrolytic reaction, there is a problem that it is difficult to maintain an applied

BACKGROUND OF THE INVENTION 10 voltage to the electrolytic cell around the thermoneutral point since the electric power obtained by the renewable

Field of the Invention energy varies with time.

[0010] Also, when a time-varying electric power source [0002] Embodiments of the present invention relate to is used, the electrolytic cell may be brought into a steam a technique for producing hydrogen in which hydrogen 15 starvation state (steam starvation) or a surplus steam is generated by using high temperature steam electroly- state due to a change in a steam rate used for the elecsis. trolytic reaction. Thus, there is a problem that it is difficult to perform an efficient hydrogen production operation ac-

Related Art cording to the steam rate.

[0003] Realization of a hydrogen energy society using SUMMARY OF THE INVENTION hydrogen as an energy medium has attracted attention.

As one of technologies for producing hydrogen, a high [0011] To solve the above problems, it is an object of temperature steam electrolysis is widely known. The high present invention to provide a technique for producing temperature steam electrolysis is a method in which hy- 25 hydrogen that achieves a highly-efficient hydrogen prodrogen and oxygen are generated by electrolyzing steam duction operation even when a time-varying electric powwith a high temperature (normally, 500°C or more). er source is used.

[0004] The method has an advantage to reduce an [0012] A hydrogen production system according to an amount of electricity required for electrolysis by electro- embodiment of the present invention includes a capacitor lyzing steam under a high temperature environment as 30 inputting electric power energy from a renewable power compared to electrolysis of water. Because of the char- supply, and storing electric power, a pulse voltage genacteristic as described above, an same amount of hydro- eration unit generating a pulse voltage having a set amgen can be obtained by using smaller electricity than that plitude and a set cyclic period by using the electric power of the room temperature water electrolysis by about 30%. stored in the capacitor, and an electrolytic cell applying Thus, hydrogen can be produced at high energy efficien- 35 the generated pulse voltage, and generating hydrogen cy. by high temperature steam electrolysis by using steam [0005] Furthermore, since water is a raw material, it is supplied into the electrolytic cell. possible to produce hydrogen without discharging car- [0013] A method for producing hydrogen according to bon dioxide at all if electric power obtained by renewable an embodiment of the present invention includes the energy that generates no carbon dioxide and a heat 40 steps of: inputting electric power energy from a renewasource that generates no carbon dioxide are used. ble power supply to store electric power in a capacitor; [0006] In the high temperature steam electrolysis, a generating a pulse voltage having a set amplitude and a hydrogen electrode and an oxygen electrode are provid- set cyclic period by using the stored electric power; and ed on both sides of a solid oxide electrolyte to constitute applying the generated pulse voltage to generate hydroan electrolytic cell. High temperature steam is supplied 45 gen by high temperature steam electrolysis in an electo the hydrogen electrode side, and an electrolytic volt- trolytic cell by using steam supplied into the electrolytic age is applied to the both electrodes, so that the steam cell.

is decomposed to hydrogen and oxygen.

[0007] Conventionally, various hydrogen production BRIEF DESCRIPTION OF THE DRAWINGS apparatuses that safely and efficiently produce hydrogen 50 by the high temperature steam electrolysis have been [0014] studied. A technology to generate hydrogen efficiently by the high temperature electrolysis with lower energy Fig. 1 is a configuration diagram of a hydrogen prohas been disclosed (for example, Japanese Patent Laid- duction system according to a first embodiment; Open Nos. 2002-348694, 2005-281716, 2013-49600). 55 Fig. 2A is a graph illustrating a pulse voltage applied [0008] In the above high temperature steam electroly- when electric power supplied from a renewable powsis, by performing an electrolytic reaction at a thermon- er supply is proper, Fig. 2B is a graph illustrating a eutral point at which an endothermic reaction in a process pulse voltage applied when the supplied electric

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power is increased, and Fig. 2C is a graph illustrating electric power energy since the capacitor 12 is less dea pulse voltage applied when the supplied electric teriorated by repetitive use (charging and discharging), power is decreased; and has faster load following capability as compared to Fig. 3 is a flowchart illustrating a control action of the a case in which a chemical battery such as a lead-acid hydrogen production system according to the first 5 battery is used for storing the electric power energy. It is embodiment; also possible to instantly measure the voltage value at Fig. 4 is a configuration diagram of a hydrogen pro- the voltage measurement unit 15.

duction system according to a second embodiment; [0020] The electric power stored in the capacitor 12 is Fig. 5A is a graph illustrating a pulse voltage applied inputted into the pulse voltage generation unit 13, and when a rate of steam is proper, Fig. 5B is a graph 10 the pulse voltage generation unit 13 generates the pulse illustrating a pulse voltage applied when the rate of voltage having a set amplitude, a set cyclic period, and steam is excessive, and Fig. 5C is a graph illustrating a set pulse width. Note that a voltage where a thermona pulse voltage applied when the steam is depleted; eutral point can be maintained during an electrolytic re- Fig. 6 is a flowchart illustrating a control action of the action is previously set as the amplitude in the pulse volthydrogen production system according to the sec- 15 age generation unit 13. The cyclic period and the pulse ond embodiment; width are set based on a relationship between the am- Fig. 7 is a configuration diagram of a hydrogen pro- plitude and electric power required for properly operating duction system according to a third embodiment; and the electrolytic cell 14.

Fig. 8 is a flowchart illustrating a control action of the [0021] In the electrolytic cell 14, a solid oxide electrohydrogen production system according to the third 20 lyte (not shown) is arranged in a center, and a hydrogen embodiment. electrode and an oxygen electrode are formed on both sides of the solid oxide electrolyte.

DESCRIPTION OF THE EMBODIMENTS [0022] The pulse voltage generated in the pulse voltage generation unit 13 is applied to the electrolytic cell

(First Embodiment) 25 14, and the electrolytic cell 14 generates hydrogen and oxygen by the high temperature steam electrolysis by [0015] Hereinafter, embodiments of the present inven- using the steam supplied into the electrolytic cell. tion are described based on the accompanying drawings. [0023] The voltage measurement unit 15 measures a [0016] As shown in Fig. 1, a hydrogen production sys- voltage of the electric power stored in the capacitor 12 tem 10 according to a first embodiment includes a ca- 30 during the electrolytic reaction in the electrolytic cell 14. pacitor 12, a pulse voltage generation unit 13, and an Accordingly, the change in the electric power supplied electrolytic cell 14. Electric power energy from a renew- from the renewable power supply 11 is monitored. able power supply 11 is inputted into the capacitor 12, [0024] The pulse cyclic period adjustment unit 16 and the capacitor 12 stores electric power. The pulse changes the cyclic period of the pulse voltage according voltage generation unit 13 generates a pulse voltage hav- 35 to the change in the measured voltage value. ing a set amplitude and a set cyclic period by using the [0025] To be more specific, when the measured voltelectric power stored in the capacitor 12. The generated age value is increased, that is, when the electric power pulse voltage is applied to the electrolytic cell 14, and the supplied from the renewable power supply 11 is inelectrolytic cell 14 generates hydrogen by high temper- creased, the amplitude of the pulse voltage is maintained ature steam electrolysis by using steam supplied into the 40 constant, and the cyclic period of the pulse voltage set electrolytic cell. in the pulse voltage generation unit 13 is changed to a [0017] The hydrogen production system 10 further in- shorter period. Accordingly, with average electric power cludes a voltage measurement unit 15 and a pulse cyclic consumed in the electrolytic cell 14 being increased, the period adjustment unit 16. The voltage measurement unit electrolytic reaction in the electrolytic cell 14 is main- 15 measures a voltage value of the capacitor 12. The 45 tained at the thermoneutral point. pulse cyclic period adjustment unit 16 changes the cyclic [0026] On the other hand, when the measured voltage period of the pulse voltage according to a change in the value is decreased, that is, when the electric power supmeasured voltage value. plied from the renewable power supply 11 is decreased, [0018] The renewable power supply 11 means an elec- the amplitude of the pulse voltage is maintained constant, tric power source using renewable energy such as wind 50 and the cyclic period of the pulse voltage set in the pulse power, hydraulic power, and solar power. The electric voltage generation unit 13 is changed to a longer period. power energy outputted from the renewable power sup- Accordingly, with the average electric power being deply 11 has a characteristic to change with passage of creased, the electrolytic reaction in the electrolytic cell time. 14 is maintained at the thermoneutral point. [0019] The electric power energy outputted from the 55 [0027] The function of the pulse cyclic period adjustrenewable power supply 11 is inputted into the capacitor ment unit 16 may also be configured so as to be imple- 12, and the capacitor 12 stores the electric power. The mented by executing a predetermined program code uscapacitor 12 can be advantageously used for storing the ing an electronic circuit such as a processor, or without

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being limited to such software processing, a unit or com- to the electrolytic cell 14 to perform the electrolytic reacputer implemented by hardware processing using an tion, and the cyclic period of the pulse voltage is changed electronic circuit such as an ASIC or may be configured according to the change in the electric power supplied as a unit or computer implemented by combining soft- from the renewable power supply 11. Accordingly, even ware processing and hardware processing. 5 when the supplied electric power changes with time, the [0028] Figs. 2A to 2C are graphs for explaining a applied voltage required for maintaining the thermoneuchange in the pulse voltage in association with a change tral point in the electrolytic cell 14 can be held. It is thus in the electric power supplied from the renewable power possible to perform a highly-efficient hydrogen producsupply 11. In the graphs, a solid line indicates the pulse tion operation.

voltage applied to the electrolytic cell 14, and a dashed 10 line indicates the average electric power consumed in (Second Embodiment) the electrolytic cell 14.

[0029] Fig. 2A is a graph illustrating a pulse voltage [0039] Fig. 4 shows the hydrogen production system when the electric power supplied from the renewable 10 according to a second embodiment. Note that compower supply 11 is proper. A voltage Vs where the ther- 15 ponents corresponding to those of the first embodiment moneutral point can be maintained during the electrolytic are assigned same reference numerals, and an overlapreaction is set as the amplitude of the pulse voltage. A ping description is omitted.

cyclic period Ts and a pulse width Tw are set based on a [0040] A current measurement unit 17 is connected to relationship between the voltage Vs and the electric pow- the electrolytic cell 14, and measures a value of a current er required for properly operating the electrolytic cell 14. 20 flowing through the electrolytic cell 14. [0030] Fig. 2B is a graph illustrating a pulse voltage [0041] A pulse amplitude adjustment unit 18 changes when the electric power supplied from the renewable the amplitude of the pulse voltage so as to obtain an power supply 11 is increased. The amplitude of the pulse applied voltage corresponding to a flow rate of the steam voltage is maintained constant at the voltage Vs, and the in the electrolytic cell 14 according to a change in the cyclic period of the pulse voltage is changed to Ts1. Ac- 25 measured current value.

cordingly, the average electric power consumed in the [0042] To be more specific, when the measured curelectrolytic cell 14 is increased. rent value is higher than a current value required for prop- [0031] Fig. 2C is a graph illustrating a pulse voltage erly operating the electrolytic cell 14, the flow rate of the when the electric power supplied from the renewable steam in the electrolytic cell 14 is determined to be in a power supply 11 is decreased. The amplitude of the pulse 30 surplus state, and the amplitude of the pulse voltage is voltage is maintained constant at the voltage Vs, and the changed to a higher voltage value. Accordingly, the eleccyclic period of the pulse voltage is changed to Ts2. Ac- trolytic reaction is promoted corresponding to the surplus cordingly, the average electric power consumed in the state of the steam rate.

electrolytic cell 14 is decreased. [0043] On the other hand, when the measured current [0032] Fig. 3 is a flowchart illustrating a control action 35 value is lower than the proper value, the flow rate of the of the hydrogen production system 10 according to the steam in the electrolytic cell 14 is determined to be in a first embodiment (see Fig. 1 as appropriate). steam starvation state, and the amplitude of the pulse [0033] The pulse voltage generation unit 13 generates voltage is changed to a lower voltage value. Accordingly, the pulse voltage having the set amplitude, cyclic period, the electrolytic reaction is inhibited corresponding to the and pulse width (S10). 40 steam starvation state.

[0034] The generated pulse voltage is applied to the [0044] The function of the pulse amplitude adjustment electrolytic cell 14, and the electrolytic cell 14 generates unit 18 may also be configured so as to be implemented hydrogen by the high temperature steam electrolysis by by executing a predetermined program code using an using the steam supplied into the electrolytic cell (S11, electronic circuit such as a processor, or without being S12). 45 limited to such software processing, a unit or computer [0035] The voltage measurement unit 15 measures the implemented by hardware processing using an electronic voltage value of the capacitor 12 during the electrolytic circuit such as an ASIC or may be configured as a unit reaction in the electrolytic cell 14 (S13). or computer implemented by combining software [0036] The pulse cyclic period adjustment unit 16 processing and hardware processing. changes the cyclic period of the pulse voltage according 50 [0045] Figs. 5A to 5C are graphs for explaining a to the measured voltage value (S14). change in the pulse voltage in association with a change [0037] The electrolytic reaction is performed with the in the current flowing through the electrolytic cell 14. In cyclic period of the pulse voltage being adjusted until a the graphs, a solid line indicates the pulse voltage applied set electrolytic time has elapsed (S15: NO, S10 to S14). to the electrolytic cell 14, and a dashed line indicates the When the electrolytic time has elapsed, the electrolytic 55 current in the electrolytic cell 14. reaction is terminated by stopping the generation of the [0046] Fig. 5A is a graph illustrating a pulse voltage pulse voltage (S15: YES). when the current value is proper, that is, when the steam [0038] As described above, the pulse voltage is applied rate in the electrolytic cell 14 is proper. The voltage Vs

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where the thermoneutral point can be maintained during description is omitted.

the electrolytic reaction is set as the amplitude of the [0057] In the third embodiment, the hydrogen producpulse voltage. A current i corresponding to the applied tion operation is performed by adjusting the cyclic period voltage is measured in the electrolytic cell 14. and the amplitude of the pulse voltage by use of the pulse [0047] Fig. 5B is a graph illustrating a pulse voltage 5 cyclic period adjustment unit 16 and the pulse amplitude when the current value is increased to i+Δi, that is, when adjustment unit 18 during the electrolytic reaction in the the steam flow rate in the electrolytic cell 14 is in the electrolytic cell 14. Note that the pulse amplitude adjustsurplus state. In this case, the electrolytic reaction is pro- ment unit 18 adjusts the amplitude within a range in which moted by increasing the amplitude of the pulse voltage the thermoneutral point is maintained. to Vs+ΔV. 10 [0058] Fig. 8 is a flowchart illustrating a control action [0048] Fig. 5C is a graph illustrating a pulse voltage of the hydrogen production system 10 according to the when the current value is decreased to i-Δi, that is, when third embodiment.

the steam flow rate in the electrolytic cell 14 is in the [0059] The pulse voltage generation unit 13 generates steam starvation state. In this case, the electrolytic reac- the pulse voltage having the set amplitude, cyclic period, tion is inhibited by decreasing the amplitude of the pulse 15 and pulse width (S30).

voltage to Vs-ΔV. [0060] The generated pulse voltage is applied to the [0049] Fig. 6 is a flowchart illustrating a control action electrolytic cell 14, and the electrolytic cell 14 generates of the hydrogen production system 10 according to the hydrogen by the high temperature steam electrolysis by second embodiment. using the steam supplied into the electrolytic cell (S31, [0050] The pulse voltage generation unit 13 generates 20 S32).

the pulse voltage having the set amplitude, cyclic period, [0061] The voltage measurement unit 15 measures the and pulse width (S20). voltage value of the capacitor 12 during the electrolytic [0051] The generated pulse voltage is applied to the reaction in the electrolytic cell 14 (S33). electrolytic cell 14, and the electrolytic cell 14 generates [0062] The pulse cyclic period adjustment unit 16 hydrogen by the high temperature steam electrolysis by 25 changes the cyclic period of the pulse voltage according using the steam supplied into the electrolytic cell (S21, to the measured voltage value (S34). S22). [0063] The current measurement unit 17 measures the [0052] The current measurement unit 17 measures the current value of the electrolytic cell 14 (S35). current value of the electrolytic cell 14 during the elec- [0064] The pulse amplitude adjustment unit 18 changtrolytic reaction in the electrolytic cell 14 (S23). 30 es the amplitude of the pulse voltage according to the [0053] The pulse amplitude adjustment unit 18 chang- measured current value (S36).

es the amplitude of the pulse voltage according to the [0065] The electrolytic reaction is performed with the measured current value (S24). cyclic period and the amplitude of the pulse voltage being [0054] The electrolytic reaction is performed with the adjusted until a set electrolytic time has elapsed (S37: amplitude of the pulse voltage being adjusted until a set 35 NO, S30 to S36). When the electrolytic time has elapsed, electrolytic time has elapsed (S25: NO, S20 to S24). the electrolytic reaction is terminated by stopping the When the electrolytic time has elapsed, the electrolytic generation of the pulse voltage (S37: YES). reaction is terminated by stopping the generation of the [0066] As described above, the pulse voltage is applied pulse voltage (S25: YES). to the electrolytic cell 14 to perform the electrolytic reac- [0055] As described above, the pulse voltage is applied 40 tion, and the cyclic period and the amplitude of the pulse to the electrolytic cell 14 to perform the electrolytic reac- voltage are adjusted. Accordingly, the thermoneutral tion, and the amplitude of the pulse voltage is changed point is maintained in the electrolytic cell 14, and a more according to the change in the current in the electrolytic efficient hydrogen production operation according to the cell 14. Accordingly, even when the steam rate used for steam rate is enabled.

the electrolytic reaction varies due to the change in the 45 [0067] In accordance with the hydrogen production supplied electric power, an efficient hydrogen production system of the aforementioned respective embodiments, operation according to the steam rate is enabled. Since the pulse voltage is applied to the electrolytic cell that driving of the electrolytic cell 14 in the steam depleted performs the high temperature steam electrolysis, and state is suppressed, maintainability of the electrolytic cell at least one of the cyclic period and the amplitude of the 14 can be improved. 50 pulse voltage is adjusted. Thus, even when a time-varying electric power source is used, it is possible to achieve

(Third Embodiment) the highly-efficient hydrogen production operation. [0068] The embodiments of the present invention have [0056] Fig. 7 shows the hydrogen production system thus been described. However, the embodiments have 10 according to a third embodiment. Note that compo- 55 been presented as examples, which are not intended to nents corresponding to those of the first embodiment limit the scope of the invention. The novel embodiments (Fig. 1) and those of the second embodiment (Fig. 4) are can be implemented in various other modes. Various assigned same reference numerals, and an overlapping omissions, replacements, and changes may be made

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within the scope without departing from the gist of the the cyclic period of the pulse voltage according invention. The embodiments and modifications are en- to a change in the measured voltage value; compassed by the scope and gist of the invention, and a current measurement unit measuring a value included in the invention described in claims and the of a current flowing through the electrolytic cell; equivalent scope thereof. 5 and a pulse amplitude adjustment unit changing the amplitude of the pulse voltage according to a

Claims change in the measured current value.

1. A hydrogen production system comprising: 10 5. A method for producing hydrogen comprising the steps of:

a capacitor inputting electric power energy from a renewable power supply , and storing electric inputting electric power energy from a renewapower; ble power supply to store electric power in a caa pulse voltage generation unit generating a 15 pacitor;

pulse voltage having a set amplitude and a set generating a pulse voltage having a set amplicyclic period by using the electric power stored tude and a set cyclic period by using the stored in the capacitor; and electric power; and an electrolytic cell applying the generated pulse applying the generated pulse voltage to genervoltage, and generating hydrogen by high tem- 20 ate hydrogen by high temperature steam elecperature steam electrolysis by using steam sup- trolysis in an electrolytic cell by using steam supplied into the electrolytic cell. plied into the electrolytic cell.

2. The hydrogen production system according to claim 6. The method for producing hydrogen according to 1, further comprising: 25 claim 5, further comprising the steps of:

a voltage measurement unit measuring a volt- measuring a voltage value of the capacitor; and age value of the capacitor; and changing the cyclic period of the pulse voltage a pulse cyclic period adjustment unit changing according to a change in the measured voltage the cyclic period of the pulse voltage according 30 value.

to a change in the measured voltage value.

7. The method for producing hydrogen according to 3. The hydrogen production system according to claim claim 5, further comprising the steps of: 1, further comprising:

35 measuring a value of a current flowing through a current measurement unit measuring a value the electrolytic cell; and of a current flowing through the electrolytic cell; changing the amplitude of the pulse voltage acand cording to a change in the measured current vala pulse amplitude adjustment unit changing the ue.

amplitude of the pulse voltage according to a 40 change in the measured current value. 8. A method for producing hydrogen comprising the steps of:

4. A hydrogen production system comprising:

inputting electric power energy from a renewaa capacitor inputting electric power energy from 45 ble power supply to store electric power in a caa renewable power supply , and storing electric pacitor;

power; generating a pulse voltage having a set amplia pulse voltage generation unit generating a tude and a set cyclic period by using the stored pulse voltage having a set amplitude and a set electric power;

cyclic period by using the electric power stored 50 applying the generated pulse voltage to generin the capacitor; ate hydrogen by high temperature steam elecan electrolytic cell applying the generated pulse trolysis in an electrolytic cell by using steam supvoltage, and generating hydrogen by high tem- plied into the electrolytic cell; perature steam electrolysis by using steam sup- measuring a voltage value of the capacitor; plied into the electrolytic cell; 55 changing the cyclic period of the pulse voltage a voltage measurement unit measuring a volt- according to a change in the measured voltage age value of the capacitor; value;

a pulse cyclic period adjustment unit changing measuring a value of a current flowing through

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description • JP 2014162431 A [0001] • JP 2005281716 A [0007] • JP 2002348694 A [0007] • JP 2013049600 A [0007]