JPH09199155A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely realize the effective and reversible utilization of energy by storing the hydrogen generated by the electrolysis of water in a spent hydrogen storage alloy contaminated by a radioactive material. SOLUTION: Water 12a is fed to the reactor 11 of a fuel cell 10, and a DC voltage is applied to electrodes 11b, 11c. Water 12a is electrolyzed, and the oxygen generated on the positive electrode 11c is stored in an oxygen storage tank 13. The hydrogen generated on the negative electrode 11b is introduced into a hydrogen storage alloy containing means 15. A hydrogen storage alloy 15a is manufactured by utilizing a spent nuclear fuel cover pipe or the like, and it is contaminated with a radioactive material. When the hydrogen 15b is introduced, a large quantity of the hydrogen 15b is stored based on the action of the β-rays generated by the radioactive material in the hydrogen storage alloy 15a. The heat of reaction is deprived of by heating/cooling bodies and accumulated in a heat conducting member 15c, and reaction continuously proceeds. The cost of the hydrogen storage alloy 15a can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell, and more particularly, to a reversible energy storage system using a hydrogen storage alloy contaminated with radioactive materials, which comprises a reactor, a hydrogen storage alloy accommodating means, and the like. The present invention relates to a fuel cell that can be used.

[0002]

2. Description of the Related Art A fuel cell is a power generation system that directly converts chemical energy of a fuel into electric energy by an electrochemical reaction and has the following excellent features.

(1) Since it is not affected by the Carnot's cycle as in the case of the existing thermal power generation system, the power generation efficiency is high and the total energy efficiency reaches about 80% when exhaust heat is used. Highly efficient energy utilization can be achieved.

(2) Even with a relatively small capacity of about 10 ² kW class to about 10 ⁴ kW class, it is possible to obtain a high power generation efficiency of more than 40% as well as a state-of-the-art large capacity thermal power generation system and a partial load. There is little decrease in efficiency during operation.

(3) The emission of air pollutants such as nitrogen oxides, the generation of noise and vibration are small, and the adverse effect on the environment is small.

(4) Hydrogen, natural gas, LP as fuel
It is possible to use hydrocarbons such as G, methanol, naphtha, kerosene, and the like, or a combination thereof, and it is excellent in the variety of energy sources.

(5) Since a large amount of cooling water (seawater) is not required, there are few restrictions on site conditions.

However, even with a fuel cell having many excellent features as described above, not only power generation but also surplus power is stored as chemical energy (fuel),
At present, no progress has been made on the so-called reversible use of stored energy, which is taken out when needed and directly converted into electric energy. One of the causes is that the inexpensive and efficient storage / re-release technology has not been established for the fuel generated in the process of converting electric energy into chemical energy.

In this fuel storage / re-release technology, a method using a so-called hydrogen storage alloy that stores hydrogen (H) gas as a fuel in the form of a metal hydride is known. This method utilizes a phenomenon in which a certain kind of metal or alloy reacts with hydrogen, and this hydrogen is trapped / occluded in the form of a metal hydride, while the hydrogen is released when heated. In the method using this hydrogen storage alloy, solid
Although it is a gas reaction, the reaction proceeds at a relatively high speed and is reversible. Further, some alloys have the ability to store hydrogen at a density equal to or higher than that of liquid hydrogen, and have received much attention.

The following characteristics are generally required for a practical hydrogen storage alloy. 1) Easy activation and large hydrogen storage capacity. 2) The heat of reaction formation is small. 3) The dissociation pressure near room temperature is as small as 2-3 atm. 4) The rate of hydrogen absorption and desorption is high. 5) There is little deterioration in performance even after repeated storage and release of hydrogen. 6) Inexpensive.

At present, many studies have been conducted on hydrogen storage alloys. These are (a) Mg (magnesium), (b) Ti (titanium), (c) rare earth metal,
(D) Other metals such as Zr (zirconium) and alloys based on these metals are roughly classified.

The Mg-based alloy has a large hydrogen storage capacity of 7.6% by weight and is low in density of the alloy, so that it is advantageous for use as a transfer material. On the other hand, the heating temperature for releasing hydrogen is high. High (dissociation pressure 1000 hPa at 287 ° C),
Moreover, there is a problem in that the reaction rate is slow (Reference; Ceramics, 14 [ 4] (1979) Shuichiro Ono, Yasuaki Ohsumi, Metal Hydride, p339).

Further, it is difficult to activate a Ti-based alloy,
That is, since the oxide film, moisture or gas is easily adsorbed on the surface of the alloy, the hydrogen storage performance is easily impaired,
There is also a problem that this hydrogen storage performance is easily affected by the purity of hydrogen (Reference; Carpenter's Trial Report, 30 [ 3]
(1979), Masanori Nakane, Yasuaki Ohsumi, Hiroshi Suzuki, Akihiko Kato, Current status of research on metal hydrides and their new applications, p201).

[0014] Alloy AB ₅ (A is a rare earth metal, B is Ni (nickel), Co (showing a metal such as cobalt)) of the rare earth metal-based series of studies have been performed for this alloy AB ₅ is It has excellent hydrogen absorption and desorption characteristics,
There is a drawback in that it is expensive (reference; Philips Res.
Repts., 25 [ 1] (1970) JHNVan Vucht, FAKuijpers,
HCAMBruning, Reversible Room Temperature Adso
rption of Hydrogen by Intermetallic Compounds, p13
3).

Other metals include Zr and Hf.
(Hafnium), Cu (copper), V (vanadium), Nb
Although investigations of (niobium) -based alloys and the like are being conducted, there are many unclear points regarding their characteristics. As described above, the hydrogen storage alloys at present have some drawbacks, and it can be said that the hydrogen storage alloys that can be used on a practical scale are still under development.

Recently, a technique for controlling and utilizing radiation has been studied, and Japanese Patent Application Laid-Open No. 6-72701 discloses that the abundance of depleted uranium (uranium (U) isotope is less than that of natural uranium (about 0). .2%)) has been proposed as a hydrogen storage alloy. This is a method in which depleted uranium is used as a by-product in the uranium concentration process, and this is heated to about 250 ° C. to occlude hydrogen as a metal hydride of UH ₃ while being heated to about 450 ° C. to release hydrogen. Is.

Further, Japanese Patent Laid-Open No. 6-201868 discloses that
A hydrogen storage alloy such as palladium (Pd) is used as a cathode, the pressing force ratio of the surface water pressure in the artificial microvoid is set to >> 1, and electrolysis is performed under a pressurized liquid phase that suppresses the vapor phase, and H ⁺ The storage capacity of the hydrogen storage alloy is increased by significantly increasing the ion concentration. At the same time, a method is disclosed in which the plasma oscillation frequency generated in deuterium plasma is rapidly increased to the γ-ray region to cause a deuterium thermonuclear reaction burst to control the neutron emission capacity.

Further, Japanese Patent Publication No. 5-53543 proposes that a highly radioactive platinum group element (for example, ruthenium-106) recovered from spent nuclear fuel is supported on an n-type fine particle semiconductor such as titanium oxide. . It is described that when it is contacted with water, it is easily decomposed into hydrogen and oxygen by radiation and catalytic action.

[0019]

In the conventional fuel cells, many kinds of hydrogen storage alloys have been studied for the conventional fuel cells, but as described above, these have low hydrogen storage capacity. There are still some problems such as difficulty in releasing hydrogen, low energy conversion efficiency, high price, etc. Therefore, there is a problem that practical use is difficult.

In the fuel cell using the above-mentioned depleted uranium, it is expected that the depleted uranium will be reused and the price of the hydrogen storage alloy will be reduced accordingly. There was a problem that the energy conversion efficiency was not good because it required a large amount of heat. In addition, the abundance of U isotopes in depleted uranium is low, and there has been a problem that a technology for positively utilizing radiation to enhance the hydrogen storage capacity has not been reached.

Further, in the technique disclosed in Japanese Patent Laid-Open No. 6-201868, the so-called FP effect (Fl
It was mainly done to improve the stability of eishchmann-Pons), and there was a problem that it is difficult to immediately apply this technology to a fuel cell to achieve reversible use of energy.

In the technique disclosed in Japanese Patent Publication No. 5-53543 mentioned above, as described above, the radiation energy is used to decompose water to generate hydrogen as a fuel. There is a problem that this technology cannot be directly used for storage and release of hydrogen in the alloy.

The present invention has been made in view of the above problems, and provides a fuel cell capable of reversibly utilizing energy by efficiently absorbing and desorbing hydrogen by using an inexpensive hydrogen storage alloy. Is intended.

[0024]

[Means for Solving the Problem and Its Effect] In many transition metals and subtransition elements, so-called interstitial hydrides (HBs) in which hydrogen atoms are contained in the metal crystal lattice of this matrix are used.
hydride) is formed. These hydrides are produced by heating transition metals in a stream of hydrogen, and many of these are berthollide compounds that do not follow the valence law.
compound: non-stoichiometric compound). In this beltride compound, H enters as protons (hydrogen nuclei, protons) in the interstices of the metal crystal lattice,
The electron behaves similarly to the case of a bond electron of a metal, and thus has conductivity. Compared to the fact that the specific gravity of salt-like hydrides is higher than that of pure metal,
In such a metal-like hydride, when hydrogen is stored, the metal lattice expands and the specific gravity decreases.

When β rays act on the hydrogen storage alloy, protons p are converted into neutrons n based on the following equation.

P → n + e ⁻ + ν p → n + e ⁺ + ν e ⁻ + e ⁺ → γ where p: proton n: neutron (neutron) e ⁻ : electron e ⁺ : positron ν: neutrino Upon collision, neutrons n and neutrinos ν are generated, and hydrogen is sequentially stored in the metal crystal lattice as neutrons n. In this case, since the neutron n does not have an electric charge, Coulomb interaction does not occur with the ion in the metal crystal lattice, and the hydrogen storage amount is dramatically increased as compared with the case of storing in the form of the proton p. To do. On the other hand, when the hydrogen storage alloy is heated in the presence of strong γ rays, the reaction opposite to the above formula proceeds. That is, an electron pair (e ⁻ + e ⁺ ) is created from γ rays, and neutrons n are converted into protons p to eventually become hydrogen atoms. The present inventors have found out these things and completed the present invention.

To achieve the above object, a fuel cell according to the present invention comprises a reactor, water supplied to the reactor, and water storage means for storing water produced in the reactor, Hydrogen generated in the reactor and hydrogen storage alloy accommodating means for accommodating the hydrogen storage alloy in which hydrogen to be supplied to the reactor is stored, oxygen generated in the reactor, and supply to the reactor A fuel cell comprising an oxygen storage means for storing oxygen, and a DC / AC converter connected to an electrode of the reactor, wherein the hydrogen storage alloy is contaminated with radioactive material. It has a feature.

According to the above fuel cell, a large amount of hydrogen is stored in the hydrogen storage alloy by the action of β-rays generated from the radioactive substance, while the action of γ-rays generated from the radioactive substance causes Hydrogen is easily released from the hydrogen storage alloy at a relatively low heating temperature. Therefore, when water is electrolyzed by using excess power in the reactor, the generated hydrogen can be stored easily and in a large amount in the hydrogen storage alloy accommodating means via the hydrogen storage alloy, and at the same time, oxygen generated at the same time can be stored. Are stored in the oxygen storage means. On the other hand, hydrogen can be efficiently released from the hydrogen storage alloy, and when this hydrogen and oxygen stored in the oxygen storage means are reacted in the reactor, electrons are taken out at the electrode of the reactor, AC power can be generated through the DC / AC converter. Further, since the used metal contaminated with a radioactive substance can be positively used as the hydrogen storage alloy, the cost of the hydrogen storage alloy can be reduced. As a result, efficient and reversible use of energy can be surely realized.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a fuel cell according to the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a fuel cell according to an embodiment.
Reference numeral 1a indicates a container. The electrode 11 is provided in the container 11a.
b, 11c are provided, an electrolyte 11d is filled between the electrodes 11b, 11c, and a filter 11 is provided in the electrolyte 11d.
e is interposed, and a radioactive substance (not shown) leaked from the hydrogen storage alloy 15a by the filter 11e is disposed on the electrode 11c side (water 12a or oxygen 13a) via the electrolyte 11d.
It is designed to prevent leakage to the inside. These electrodes 11b and 11c, electrolyte 11d, filter 11e
The cell 11f is configured to include the
Stack units (both not shown) by stacking a certain number of
Is configured. A reactor 11 as a fuel cell main body is configured by including these containers 11a, cells 11f, a stack unit and the like. Further, the lower part of the container 11a is connected to a water storage tank 12 as a water storage means and an oxygen storage tank 13 as an oxygen storage means via connecting pipes 12b and 13b, and is connected to the water storage tank 12 and the oxygen storage tank 13. Is designed to store water 12a and oxygen 13a, respectively. The electrodes 11b and 11c are connected to the DC / AC converter 14 via lead wires 14a, respectively. Furthermore, the upper part of the container 11a is connected to the hydrogen storage alloy accommodation means 15 via a good thermal conductor member 15c and a connection pipe 15d, and the hydrogen storage alloy accommodation means 15 is connected to the hydrogen storage alloy (hereinafter, A hydrogen storage alloy 15a is stored therein, and the hydrogen storage alloy 15a stores hydrogen 15b as a fuel. This hydrogen storage alloy 15a melts a used nuclear fuel cladding tube (Zr composition is 98% or more) used in, for example, a pressurized water reactor, and a predetermined amount of M
It is manufactured by adding n (manganese).

FIG. 2 is a cross-sectional view for explaining the hydrogen storage alloy accommodating means 15 of the fuel cell according to the embodiment in more detail. In the figure, 15f indicates a container. A plurality of introducing pipes 15g are erected in a container 15f having a substantially circular cross-sectional view, and a plurality of holes (not shown) are formed in the outer peripheral portion of the introducing pipe 15g. The lower end portion is connected to the connecting pipe 15d via the collecting pipe 15h and the valve 15i. On the other hand, a heating / cooling body 15j is arranged around each of the introducing pipes 15g so as to cover the introducing pipes 15g.
The cooling body 15j is adapted to be connected to a good thermal conductor member 15c (FIG. 1). These containers 15f, introduction pipe 1
The hydrogen storage alloy accommodating means 15 is configured to include 5 g, the collecting pipe 15 h, the heating / cooling body 15 j, and the like. A hydrogen storage alloy 15a is provided between the heating / cooling body 15j and the introducing pipe 15g.
And the thickness of the hydrogen storage alloy 15a is set to be substantially constant at any position, so that the hydrogenation reaction proceeds uniformly. And connecting pipe 15
Introducing pipe 15g through d, valve 15i, and collecting pipe 15h
The hydrogen 15b introduced into the hydrogen storage alloy 15a is blown out to the hydrogen storage alloy 15a through the hole of the introduction pipe 15d and stored therein, and the heat generated at this time is removed via the heating / cooling body 15j. On the other hand, when the hydrogen storage alloy 15a is heated by the heat supplied through the heat quantity conductor member 15c and the heating / cooling body 15j, hydrogen 15b is released from the hydrogen storage alloy 15a, and the hydrogen 15b is supplied to the introduction pipe 15d. The gas is supplied to the reactor 11 (FIG. 1) through the holes, the collecting pipe 15h, the valve 15i, and the connecting pipe 15d.

Further, a filter 15e is arranged in the connecting pipe 15d, and the filter 15e prevents the radioactive substance from leaking from the hydrogen storage alloy 15a to the reactor 11 side. Further, the hydrogen storage alloy containing means 15 that easily emits radiation to the outside and the good heat conductor member 15
c, the connecting pipe 15d, and the outer periphery of about half of the reactor 11 are covered with a radiation protection container 16, and the radiation protection container 16, about half of the reactor 11, the water storage tank 12, and oxygen. The storage tank 13 is stored in the storage container 17. These reactor 11 and water storage tank 1
2, the oxygen storage tank 13, the DC / AC converter 14, the hydrogen storage alloy accommodation means 15, the hydrogen storage alloy 15a, the radiation protection container 16, the storage container 17 and the like constitute the fuel cell 10.

In the case of using the fuel cell 10 constructed as above, after supplying the water 12a from the water storage tank 12 to the reactor 11, it is converted through the DC / AC converter 14 using the surplus AC power. DC voltage applied to electrodes 11b, 11c
When applied to, the water 12a is electrolyzed to generate oxygen 13a in the electrode 11c as an anode, and the oxygen 13a is stored in the oxygen storage tank 13 through the connecting pipe 13b.
At the same time, hydrogen 15b is generated in the electrode 11b as the cathode, and this hydrogen 15b is introduced into the hydrogen storage alloy accommodation means 15 through the connecting pipe 15d. Then hydrogen storage alloy 15
A large amount of hydrogen 15b is stored in the hydrogen storage alloy 15a based on the action of β-rays generated from the radioactive substance in a, and the heat of reaction is taken by the heating / cooling body 15j, which is a good conductor of heat. The heat is accumulated in the member 15c and the reaction continuously proceeds.

On the other hand, when the demand for electric power is high, the oxygen 13a stored in the oxygen storage tank 13 is supplied to the connecting pipe 13
It is supplied to the reactor 11 via b. At the same time, by utilizing the heat stored in the good heat conductor member 15c, the heating / cooling body 15
When the hydrogen storage alloy 15a is heated to a predetermined temperature range via j, the hydrogen storage alloy 15a is easily converted into hydrogen 15b based on the interaction between this heat and the γ-ray generated from the radioactive substance in the hydrogen storage alloy 15a. And is supplied to the reactor 11 from the hydrogen storage alloy accommodation means 15 via the connecting pipe 15d. Then, a DC voltage is generated between the electrodes 11b and 11c, and this DC voltage is converted into AC in the AC / DC converter 14 and taken out as AC power. Also,
At this time, the water 12a produced in the reactor 11 is stored in the water storage tank 12.

As is clear from the above description, in the fuel cell 10 according to the embodiment, a large amount of hydrogen 15b is stored in the hydrogen storage alloy 15a by the action of β rays generated from the radioactive substance, while the radioactive Hydrogen 15b is easily released from the hydrogen storage alloy 15a at a relatively low heating temperature by the action of γ rays generated from the substance. Therefore reactor 1
When the water 12a is electrolyzed by using the surplus power or the like in No. 1,
The generated hydrogen 15b can be stored in the hydrogen storage alloy accommodation means 15 through the hydrogen storage alloy 15a easily and in a large amount, and at the same time, the generated oxygen 13a is stored in the oxygen storage tank 13. On the other hand, hydrogen 15b can be efficiently released from the hydrogen storage alloy 15a, and this hydrogen 15b and the oxygen 13a stored in the oxygen storage tank 13 are stored.
When and are reacted in the reactor 11, electrons are extracted at the electrodes 11b and 11c of the reactor 11, and AC power can be generated through the DC / AC converter 14. Further, since the used metal contaminated with the radioactive material can be positively used as the hydrogen storage alloy 15a, the cost of the hydrogen storage alloy 15a can be reduced. As a result, efficient and reversible use of energy can be surely realized.

In the fuel cell 10 according to the above embodiment, the case where hydrogen is used as the fuel has been described, but the fuel is not limited to hydrogen as long as it is a gas containing hydrogen atoms. It may be methane, propane, methanol, ammonia, hydrazine or the like.

Further, in the fuel cell 10 according to the above-described embodiment, the case where the spent nuclear fuel cladding tube is used as the hydrogen storage alloy 15a has been described, but the present invention is not limited to the nuclear fuel cladding tube and the radioactive fuel cladding tube is not limited to the nuclear fuel cladding tube. Another hydrogen storage alloy may be used as long as it is contaminated with a substance.

[0037]

[Examples and Comparative Examples] The results of investigating the chemical formula, the hydrogen content rate, the dissociation pressure, and the heat of formation of the hydride of the hydrogen storage alloy in the fuel cell according to the example will be described below.

As the hydrogen storage alloy of the fuel cell according to the example, the one prepared by adding Mn to the used nuclear fuel cladding tube (Zr 98% or more) contaminated with radioactive material was used. For the fuel cell according to the comparative example, a hydrogen storage alloy manufactured by adding Mn to a nuclear fuel clad tube before use, which was not contaminated with radioactive materials, was used. The results are shown in Table 1 below.

[0039]

[Table 1]

As is clear from Table 1, in the case of the fuel cell according to the comparative example, a relatively large amount of heat was taken for hydrogen absorption / desorption even though the hydrogen content (storage) rate was as low as 1.7%. Needed. On the other hand, in the case of the fuel cell according to the example, it is possible to occlude and release hydrogen with about 1/3 of the heat as compared with the case of the comparative example, and the hydrogen content is increased to 3.5% (a little over twice). I was able to raise it. Although the dissociation pressure was higher than that of the comparative example, it was able to be lower than that of the fuel cell using a general hydrogen storage alloy not shown.

The results of investigating the energy conversion efficiency using the fuel cell according to the example, which is reversibly utilized about 20 times under the following conditions, will be described below.

As the electrolyte 11d of the cell 11f, there was used one in which concentrated phosphoric acid was impregnated in a matrix composed of a kneaded material of silicon carbide and carbon fluoride. Further, as the electrodes 11b and 11c, those in which the surface of a porous carbon member to which a platinum catalyst was added and whose surface was subjected to Teflon waterproofing were used. As the interconnector, a carbon connector having a large number of grooves through which hydrogen 15b or oxygen 13a passes is used. The cell 11f was formed by stacking about 450 layers to form a stack unit having a power generation capacity of 240 kW, and the reactor 11 having a power generation capacity of 4.5 MW was used in which about 20 sets of the stack units were connected in series / parallel. In addition, this stack unit has 5 to 6 cells 11
A pipe (not shown) is embedded in each f, and cooling water is circulated in this pipe to reduce the operating temperature in the reactor 11 to 1
The temperature was maintained at 20 to 190 ° C.

As a result, the energy conversion efficiency of the fuel cell according to the comparative example is about 50% in the reactor 11, and about 40% in the hydrogen storage alloy accommodating means 15 and the DC / AC converter 14. Therefore, the total energy conversion efficiency was 20%. On the other hand, the energy conversion efficiency in the case of the fuel cell according to the embodiment is
Although it is about 50% in the reactor 11, it is as high as about 90% in the hydrogen storage alloy accommodating means 15 and the DC / AC converter 14, and therefore the total energy conversion efficiency is improved to 45%.

In the above-mentioned embodiment, the case where the solid acid type in which the concentrated phosphoric acid is impregnated in the matrix is used as the electrolyte 11d has been described, but even in the case of another embodiment using the molten carbonate electrolyte, It was possible to obtain almost the same result.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing an embodiment of a fuel cell according to the present invention.

FIG. 2 is a cross-sectional view schematically showing a hydrogen storage alloy accommodation means of the fuel cell according to the embodiment.

[Explanation of symbols]

 10 Fuel Cell 11 Reactor 11b, 11c Electrode 12 Water Storage Tank 12a Water 13 Oxygen Storage Tank 13a Oxygen 14 DC / AC Converter 15 Hydrogen Storage Alloy Storage Means 15a Hydrogen Storage Alloy 15b Hydrogen

Claims (1)

[Claims] 1. A reactor, water supplied to the reactor, water storage means for storing water produced in the reactor, hydrogen produced in the reactor, and the reactor. Hydrogen storage alloy housing means for housing a hydrogen storage alloy in which hydrogen to be supplied is stored, and oxygen generated in the reactor,
And a fuel cell comprising oxygen storage means for storing oxygen to be supplied to the reactor, and a DC / AC converter connected to an electrode of the reactor, wherein the hydrogen storage alloy is made of a radioactive material. A fuel cell characterized by being contaminated.