U.S. patent application number 11/297519 was filed with the patent office on 2006-07-20 for system and method for generating high pressure hydrogen.
This patent application is currently assigned to Mitsubishi Corporation. Invention is credited to Hiroyuki Harada.
Application Number | 20060157354 11/297519 |
Document ID | / |
Family ID | 27670908 |
Filed Date | 2006-07-20 |
United States Patent
Application |
20060157354 |
Kind Code |
A1 |
Harada; Hiroyuki |
July 20, 2006 |
System and method for generating high pressure hydrogen
Abstract
The invention provides a system and a method for generating high
pressure hydrogen that is able to efficiently and safely generate
hydrogen by only the electrolysis of water even when using electric
power generated by a frequently varying natural energy, such as
sunlight, without using any compressors. The system comprises an
electrolysis cell using polyelectrolyte membranes, particularly a
double-polarity multi-layered type electrolysis cell having a
specified structure disposed in a vessel for storing generated
hydrogen, preferably for storing cooled hydrogen under a high
pressure hydrogen atmosphere. High pressure hydrogen is generated
by electrolysis of pure water using the electrolysis cell by
suppressing the pressure applied to the cell to a pressure below
the pressure resistance of the cell using a differential pressure
sensor and pressure controller.
Inventors: |
Harada; Hiroyuki; (Tokyo,
JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
Mitsubishi Corporation
Tokyo
JP
|
Family ID: |
27670908 |
Appl. No.: |
11/297519 |
Filed: |
December 9, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10352968 |
Jan 29, 2003 |
7048839 |
|
|
11297519 |
Dec 9, 2005 |
|
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Current U.S.
Class: |
205/637 |
Current CPC
Class: |
Y02P 20/133 20151101;
C25B 15/02 20130101; C25B 15/08 20130101; C25B 9/05 20210101; Y02E
60/36 20130101; C25B 1/04 20130101; C25B 9/19 20210101 |
Class at
Publication: |
205/637 |
International
Class: |
C25B 1/02 20060101
C25B001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 29, 2002 |
JP |
2002-19713 |
Mar 19, 2002 |
JP |
2002-77344 |
May 28, 2002 |
JP |
2002-153961 |
Jun 19, 2002 |
JP |
2002-178415 |
Mar 19, 2002 |
JP |
2002-19314 |
Claims
1-43. (canceled)
44. A method for generating high pressure hydrogen comprising the
steps of: generating hydrogen and oxygen by electrolysis of pure
water using an electrolysis cell comprising polyelectrolyte
membranes and disposing in a high pressure vessel; storing
generated hydrogen in a high pressure vessel comprising the
electrolysis cell disposed therein; and storing oxygen in a high
pressure vessel for storing electrolysis pure water together with
returned pure water.
45. The method for generating high pressure hydrogen according to
claim 44 comprising the step of cooling generated hydrogen.
46. The method for generating high pressure hydrogen according to
claim 44 comprising the step of: discharging generated hydrogen out
of the high pressure vessel through a pipe line; and storing
hydrogen by returning into the high pressure vessel after cooling
with a heat exchanger.
47. The method for generating high pressure hydrogen according to
claim 44 comprising the step of: discharging oxygen and returned
pure water out of the high pressure vessel through a pipe line; and
storing oxygen and returned pure water in the high pressure vessel
for storing electrolysis pure water after controlling the
temperature with a heat exchanger.
48. The method for generating high pressure hydrogen according to
claim 46 or 47, wherein each pipe line comprises a plurality of
fine tubes branched in the high pressure vessel, at least generated
hydrogen being returned to the inside of the high pressure vessel
from the bottom thereof.
49. The method for generating high pressure hydrogen according to
claim 44, wherein pure water is electrolyzed by adjusting the
differential pressure between the inner pressure of the high
pressure vessel for storing hydrogen and the inner pressure of the
high pressure vessel for storing oxygen and pure water below a
pressure of the pressure resistance of the polyelectrolyte membrane
constituting the electrolysis cell.
50. The method for generating high pressure hydrogen according to
claim 49, wherein pure water is electrolyzed by adjusting the inner
pressure of the high pressure vessel for storing hydrogen to be a
little lower than the pressure of the high pressure vessel for
storing oxygen and pure water, and the pure water circulation
system including the electrolysis cell.
51. The method for generating high pressure hydrogen according to
claim 49 or 50, wherein the differential pressure is adjusted by
controlling the hydrogen pressure and oxygen pressure in respective
high pressure vessels and/or by transferring pure water in the
vessels.
52. The method for generating high pressure hydrogen according to
claim 51, wherein pure water is transferred by switching the valves
provided in the pure water pipe lines connecting between respective
high pressure vessels.
53. The method for generating high pressure hydrogen according to
claim 51, wherein pure water is transferred by switching the valves
connected to pure water pipe lines coupling respective high
pressure vessels and provided in respective vessels.
54. The method for generating high pressure hydrogen according to
claim 53, wherein the valves are switched while they are submerged
in pure water in the high pressure vessels.
55. The method for generating high pressure hydrogen according to
claim 51, wherein the valves are automatically switched with a
pressure controller provided in a pure water pipe line coupling
respective high pressure vessels.
56. The method for generating high pressure hydrogen according to
claim 49 or 50, wherein the volume of pure water stored in the high
pressure vessel for storing hydrogen is controlled to be larger
than the volume of oxygen stored in the high pressure vessel for
storing oxygen, and wherein the volume of pure water stored in the
high pressure vessel for storing oxygen is controlled to be larger
than the volume of hydrogen stored in the high pressure vessel for
storing hydrogen.
57. The method for generating high pressure hydrogen according to
claim 49 or 50, wherein the volume of oxygen stored in the high
pressure vessel for storing oxygen is controlled to be within 4% of
the volume of hydrogen in the high pressure vessel for storing
hydrogen.
58. The method for generating high pressure hydrogen according to
any one of claims 44 to 47, wherein pure water having a high
resistivity after de-ionization and containing small number of
bubbles after defoaming is used for electrolysis.
59. The method for generating high pressure hydrogen according to
claim 58, wherein pure water for electrolysis supplied from a high
pressure vessel for storing pure water using a water feed pump and
a pump driving motor provided in the vessel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a system and method for directly
generating high pressure hydrogen (compressed hydrogen) required
for the utilization of hydrogen energy without using any mechanical
pressurizing device, such as a compressor, whereby pure water, such
as deionized water, distilled water and purified water after
filtration are electrolyzed using a polyelectrolyte membrane
(referred to as PEM hereinafter). The invention belongs to
technology related to clean hydrogen energy.
[0003] 2. Description of the Related Art
[0004] Carbon dioxide released by using fossil fuels, such as coal
and petroleum, in recent years are thought to be major causes of
global greenhouse effects. In addition, acid rain caused by
nitrogen oxides and sulfur oxides discharged by the combustion of
the fossil fuels serves as a major cause of the loss of human
health and destruction of forests. Furthermore, there exist
fundamental problems that the estimated amount of fossil fuel
deposits is limited, and they may be depleted sooner or later.
[0005] To suppress these problems from occurring, the development
of novel technologies is urgently desired, whereby the consumption
of the fossil fuels is depressed or brought to an end, and clean
natural energies that are able to be regenerated can be substituted
for the fossil fuels are utilized.
[0006] The most abundant natural energy, as the substitute of
fossil energy, is solar energy. The energy that the earth receives
in one hour from the sun corresponds to or exceeds the energy
consumed by humankind for one year. It is not a dream to cover the
total energy demand of humankind by the solar energy alone, and
many technologies for utilizing solar energy, such as solar
generators have been proposed.
[0007] In the representative well known in the art methods for
utilizing natural energies, such as solar generators,
aerogenerators and hydroelectric generators, natural energy is
taken out and utilized as electric power.
[0008] It is difficult to store and transport electric power
itself. Electric power is usually stored by charging a battery.
However, batteries are heavy, and the charge is consumed by
self-discharge during storage while it is not used.
[0009] The most crucial problem for the future energy is to be free
from the problems as described above, or the energy should be
easily stored and transported while being able to be commonly used
where and when necessary. Hydrogen is a candidate for generating
energy that satisfies the conditions as described above.
[0010] Hydrogen can be readily stored, is able to regenerate its
energy as electric power, is convenient and efficient as an energy
source. Accordingly, it is contemplated to efficiently convert
electric power obtained by natural energy into clean hydrogen
energy by electrolysis of water, and to use a hydrogen energy
source as a substitute of conventional energy sources, such as
petroleum. It is anticipated that a hydrogen economy society using
hydrogen as the energy source would be realized in the 21st
century.
[0011] To realize the hydrogen economy society, the development of
fuel cells using hydrogen as a fuel (Polyelectrolyte Fuel Cell,
abbreviated as PEFC hereinafter) have been actively developed as
means for efficiently utilizing hydrogen as the energy source. In
addition, uses of hydrogen for automobile and home generators have
been also considered. The hydrogen economy society with no anxiety
of the greenhouse effect by carbon dioxide would be realized when
the methods as described above are spread to enable hydrogen
generated by natural energy to be widely utilized.
[0012] Such a society as described above is based on an assumption
that crucial problems for efficiently generating hydrogen are
solved using natural energies, particularly solar energy.
[0013] The most important problem for utilizing hydrogen as the
energy source is how hydrogen gas could be safely transported and
stored in a compact vessel.
[0014] For solving the problems as described above, it has been
attempted to convert hydrogen gas into liquid hydrogen or to allow
hydrogen to be occluded in an occlusive alloy. However, these
methods involve unsolvable problems of spontaneous evaporation and
insufficient occlusion volume. Since lightweight and highly
pressure resistant gas cylinders have been developed in recent
years, safety of high pressure hydrogen is reevaluated.
Consequently, the hydrogen is often stored and transported by
filling in a gas cylinder as compressed hydrogen with a pressure of
as high as 350 atm or more. Such a method is widely noticed as a
technology compatible for the hydrogen economic society.
[0015] When hydrogen is used for fuel cell vehicles using the fuel
cells as described above, compressed hydrogen at a pressure of as
high as 350 atom should be used. Otherwise, the volume of the
hydrogen gas cylinder is large, and the space for the passenger
cabin is reduced. When the volume of the hydrogen gas cylinder is
small, on the other hand, the cruising distance is so shortened
that it is impractical. Accordingly, it is a key point for shifting
the current society to the hydrogen economy society to convert
hydrogen, utilized as the energy source, into highly compressed
hydrogen with a pressure of as high as 350 atm or more.
[0016] While hydrogen has been generated by electrolysis of an
aqueous alkaline solution prepared by dissolving an alkaline
electrolyte such as potassium hydroxide (KOH) in water for a long
period of time, electrolysis using a polyelectrolyte membrane
(abbreviated as PEM electrolysis hereinafter) by which pure water
is directly electrolyzed into hydrogen and oxygen has been noticed
in recent years as a result of developments of the polyelectrolyte
fuel cells (PEFC). In PEFC water is electrolyzed by a reversed
reaction of PEFC using the PEM.
[0017] As widely known in the art, since an alkali, such as
potassium hydroxide, forms accumulated substances on electrodes by
a reaction of the alkali with the impurities, such as carbon
dioxide dissolved in water in electrolysis of the aqueous alkaline
solution, aqueous electrolysis cells should be periodically cleaned
to remove the accumulated substances. A purification device for
removing alkali mists generated together with hydrogen is also
required.
[0018] Since the hydrogen and oxygen generated are separated from
each other with a porous partition membrane, such as a
gas-permeable asbestos, the mixing ratio between them increases
with a decrease in the amount of the generated gas, and the
proportion of hydrogen or oxygen permeating through the porous
membrane is relatively increased. Consequently, the mixed gas
becomes a detonating gas that involves a danger of explosion making
it difficult to arbitrarily stop and start gas generation. It is
not easy to generate hydrogen by electrolysis of the aqueous
alkaline solution using electric power generated by sunlight or
aerodynamic power that frequently varies. Furthermore, since the
pressure of hydrogen generated by electrolysis of the aqueous
alkaline solution is low, use of a gas compressor is required in
order to prepare a highly compressed hydrogen.
[0019] In contrast, pure water is directly electrolyzed to obtain
highly pure hydrogen while hydrogen and oxygen are separated with
PEM that permeates only protons in the PEM electrolysis method.
Therefore, hydrogen and oxygen are not mixed with each other when
electrolysis is suddenly stopped as in electrolysis of the aqueous
alkaline, and start and stop of electrolysis may be arbitrarily
repeated. Consequently, the PEM electrolysis method is excellent
for converting the frequently varying electric power generated by
natural energy into hydrogen.
[0020] The method for generating high pressure hydrogen by PEM
electrolysis is inherently able to generate high pressure hydrogen
and oxygen because of conversion of liquid to gas. Namely, a small
volume is converted to a large volume with no mechanical pressure
increasing device, such as a compressor used in principle.
Eventually, hydrogen with a pressure of as high as 1000 atm or more
may be obtained by only electrolysis. Since no mechanically movable
parts are involved as compared with devices that mechanically
increase pressure, periodic maintenance work with frequent
inspection and replacement of expendables is not needed. Therefore,
maintenance-free and unattended automatic operation for a long
period of time is possible enabling the practical conversion of
natural energy into hydrogen. Furthermore, since the PEM
electrolysis method has a higher compression efficiency as compared
with the method using mechanical pressure-increasing devices, such
as a compressor, it is an advantage of the PEM electrolysis method
that less compression power is required, and much expectation is
concentrated on the generation of high pressure hydrogen by PEM
electrolysis for energy conversion.
[0021] The system for generating hydrogen by PEM electrolysis
comprises electrolysis cells prepared by laminating a plurality of
unit cells with a structure in which the PEM, having catalytic
electrodes such as platinum formed on both surfaces thereof, is
sandwiched with the porous electrode through which pure water and
gases are permeable. Since each cell is laminated in the
electrolysis cell having the structure as described above, the
electrode partitioning of each unit cell is a double-polarity
electrode because the electrode serves as a cathode as well as an
anode. The PEM electrolysis cell comprising laminated unit cells
may be called a double-polarity multi-layered type electrolysis
cell. Much expectation is concentrated on the emergence of a system
for generating high pressure hydrogen by double-polarity
multi-layered type electrolysis cells using PEM.
[0022] However, it is a current problem of electrolysis by
electrolysis cell using PEM that the pressure resistance of the
seal member and PEM of the electrolysis cell is as low as about 4
atm. Hydrogen and oxygen gases with a pressure of only several to
several tens of atm at most may be generated in the electrolyte
cell as described above, and hydrogen with a pressure of as high as
350 atm or more required for energy conversion cannot be generated.
Therefore, hydrogen is required to be compressed using a gas
compressor for efficient storage and transportation.
[0023] For obtaining high pressure hydrogen without using a gas
compressor, liquid hydrogen is evaporated to convert it into the
high pressure hydrogen, and the hydrogen is charged into a gas
cylinder. However, it is a disadvantageous method, because the
liquefaction of hydrogen needs a large amount of energy and liquid
hydrogen diminishes under transportation and storage by
evaporation. Moreover the liquefier needs regular or frequent
maintenance, and is hard to produce liquid hydrogen at a remote
area under automatic operation with a shortage of hands.
[0024] With respect to energy loss, the energy conversion
efficiency is decreased in the production of liquid hydrogen as
compared to the use of compressed hydrogen since much energy is
required in the former case. While about three hundred million
cubic meters of hydrogen is sold annually in this country, several
tenfolds of hydrogen is estimated to be consumed when only ten
percent of domestic automobiles use hydrogen as the fuel. An amount
of energy exceeding the amount of hydrogen energy currently
available in the market may be consumed as the energy required for
liquefying such a vast amount of hydrogen.
[0025] Although enough liquefying machines for liquefying such a
vast amount of hydrogen should be constructed, the additionally
constructed liquefying machines only consume energy without
creating additional energy.
[0026] Therefore, use of liquefied hydrogen as an energy source is
disadvantageous with respect to the energy conversion efficiency,
and facilities that do not create additional energy are forced to
be constructed to realize the use of liquefied hydrogen.
[0027] Accordingly, use of liquefied hydrogen as a high pressure
hydrogen source, or as an energy source, is restrictive, and it is
hardly conjectured that liquid hydrogen is the major energy source
in the hydrogen economy society in the future.
[0028] The gas compressor involves, on the other hand, the problems
of wear of parts as described previously. Moreover, mechanical
pressure increasing devices such as the gas compressor for
generating the high pressure hydrogen with a pressure as high as
350 atm or more is a theme of development. Devices with
satisfactory functions are not available today. For example
commercialized reciprocative compressors cannot make gas over 200
atm and diaphragm compressors need to exchange diaphragms every
1000 hours and its production capacity is 30 N/m.sup.3 at most.
There are no gas compressors with a capacity of 300 N/m.sup.3 and
contamination of hydrogen by the gas compressor itself is another
problem that cannot be ignored.
[0029] When the purity of hydrogen used as the fuel for converting
hydrogen into electric power using the PEM fuel cell is poor, the
electrodes are poisoned and decrease the output power of the cell,
shortening the service life of the cell. Therefore, contamination
of hydrogen is a fatal drawback.
[0030] The most efficient utilization of energy as the major energy
source is accomplished by compressed hydrogen by which the volume
of the hydrogen is compressed under a high pressure to enable the
hydrogen to be readily stored and transported. The hydrogen can be
used as a substitute of the fossil fuels when hydrogen used as an
energy source is converted into high pressure hydrogen by reducing
its volume for the convenience of storage and transport. Various
methods of PEM electrolysis have been studied as suitable methods
for generating the high pressure hydrogen by only electrolysis
without using a gas compressor. Various methods have been proposed
with respect to the device for generating high pressure hydrogen
required for utilizing hydrogen as an energy source by only
electrolysis, particularly for solving the problem of low pressure
resistance of the electrolysis cell.
[0031] For example, it was noticed in Japanese Patent Publication
No. 3,220,607 (U.S. Pat. No. 5,690,797) that the force acting on
the PEM of the double-polarity multi-layered type electrolysis cell
is a differential pressure between hydrogen generated in the
cathode and oxygen generated in the anode, and that the force
acting on the seal member of the cell is a differential pressure
between the combined pressure of hydrogen and oxygen in the cell
and external pressure of the cell. Therefore, the cell is submerged
in pure water in the high pressure vessel for storing pure water
and oxygen in order to control the pressure in the high pressure
vessel for storing hydrogen and the pressure of the high pressure
vessel for storing oxygen to be equal. The differential pressures
acting on the PEM and seal member of the cell are controlled within
the pressure resistance of the cell. Consequently, only a
differential pressure within the pressure resistance of the cell
acts on the cell even when hydrogen and oxygen is generated at a
combined pressure exceeding the pressure resistance of the cell,
thereby enabling high pressure hydrogen to be generated.
[0032] However, corrosion of metallic parts should be considered in
the device for generating the hydrogen and oxygen gases. The
electrolysis cell is submerged in pure water by housing it in the
high pressure vessel while storing oxygen generated at the anode in
the high pressure vessel. Therefore, the electrolysis cell having
the electrodes is sealed in an environment containing high pressure
oxygen, that readily causes corrosion of metals, and water together
as the pressure is increased.
[0033] Furthermore, corrosion of the metallic parts, such as the
electrodes, are liable to occur as the temperature is increased in
the permissible range of heat resistance of PEM. In addition, the
leak current cannot be ignored since the resistivity of pure water
in which the PEM electrolysis cell is submerged decreases. When the
problem of temperature increase is solved by cooling pure water in
which the PEM electrolysis cell is submerged by using a heat
exchanger, the cell is forced to be operated at a temperature of
40.degree. C. or less where the cell efficiency becomes poor, and
the operating condition is disadvantageous for effective
utilization of heat.
[0034] Therefore, this proposal involves inherent problems to be
solved such as electrolytic corrosion by oxygen and leak electric
current by the decrease of resistivity of pure water, in order to
generate high pressure hydrogen required for utilizing hydrogen as
an energy source.
[0035] When abnormalities, such as a break of PEM isolating the
anode compartment of the electrolysis cell from its cathode
compartment, or a break of the seal member of the electrolysis cell
occur, a large amount of hydrogen is mixed with oxygen in the high
pressure cell housing the electrolysis cell, arising a danger of
generating a detonating gas. Therefore, a countermeasure for this
danger is also required.
[0036] Accordingly, while the generation of high pressure hydrogen
with a pressure of as high as several hundreds of atm or more is
possible in principle in this device for generating hydrogen and
oxygen, the device is currently only applicable for generating
hydrogen with a pressure of several tens of atm, and it is not easy
to generate high pressure hydrogen with a pressure of several
hundreds atm that is considered necessary for utilizing hydrogen as
an energy source.
[0037] A part of the electric current flowing in the electrolysis
cell flows in pure water in which the electrolysis cell is
submerged by the decrease of resistivity of pure water, even when
the problem of corrosion of metals is solved, thereby decreasing
electrolysis efficiency due to electric power loss. Moreover, since
pressure resistance and heat resistance of the ion-exchange resin
are low, another problem is that the decreased resistivity as a
result of the decreased purity of pure water in the high pressure
vessel cannot resume its original high resistivity by regenerating
contaminated pure water into pure water using an ion-exchange
resin. In particular, this is a serious problem because the
electrolysis efficiency is enhanced by increasing the temperature
to about 80.degree. C. or more.
[0038] While pure water should always be regenerated with the
ion-exchange resin due to accelerated dissolution of wall
substances of the vessel into pure water when the temperature of
pure water is increased for decreasing resistivity, the pressure of
the cell is restricted because the ion-exchange resin is broken by
treating pure water under a high pressure. Consequently, it was
difficult to generate high pressure hydrogen required for
utilization of hydrogen as a energy source.
[0039] For solving these problems, Japanese Unexamined Patent
Application Publication No. 2001-130901 has proposed a hydrogen
energy feed device constructed so that electrical insulation is not
compromised even at a high electrolysis temperature, wherein
hydrogen and oxygen generated by electrolysis are stored in
separate high pressure tanks while hermetically immersing the
electrolysis cell in an electrically insulating liquid in an
exclusive high pressure vessel in order to prevent corrosion of
metals, such as the electrode, due to coexistence of oxygen and
water at a high temperature and pressure.
[0040] This method not only settles both problems of corrosion by
electrolysis and decrease of resistivity of pure water at once, but
is also able to prevent the detonating gas from being generated
since pure water serves to isolate oxygen from hydrogen even when
the electrolysis cell is broken, thereby greatly improving safety
of the cell.
[0041] However, this method is still difficult to practically
employ since no practically available electrically insulating
liquid for immersing the electrolysis cell in the high pressure
vessel has not been found yet.
[0042] A vast quantity of electrically insulating liquid is needed
for covering the demands of the device for generating enough
hydrogen to be converted into the vast amount of energy that is
supposed to be consumed. However, it is difficult to chemically
synthesize and use a large quantity of the electrically insulating
liquid without any burden to the environment, or so that the
environment, particularly groundwater and soil, is not readily
polluted by leakage. Moreover, the liquid is required to be
incombustible and chemically stable so that the liquid is not
reactive with a minute quantity of oxygen and hydrogen leaking from
the electrolysis cell while having no danger of explosion by
reacting with oxygen even when a large quantity of oxygen is leaked
in the high pressure vessel. Such electrically insulating liquids
that satisfies these conditions have not been found.
[0043] For example, although PCB is a flame-retarded liquid with
excellent performances, its production and use are forbidden from
the view point of public hazard and environmental pollution.
Therefore, all the currently available insulating oils are
inflammable, and involve a potential danger of explosion when
oxygen is leaked.
[0044] In addition, pure water is difficult to use since the
resistivity of pure water changes with time, as described above,
although pure water itself is excellent as a insulating liquid.
[0045] Since pure water has a potential to dissolve all the
substances, the resistivity of pure water is gradually decreased
when pure water is sealed in the high pressure vessel. This
decrease of resistivity not only decreases efficiency of the cell
due to a leak electric current generated, but also hydrogen and
oxygen are generated by the leak electric power in the high
pressure vessel housing the electrolysis cell increasing the
pressure. This increase of the pressure may cause a potential
danger by which the electrolysis cell may be finally crushed by the
pressure, or the mixed gas of hydrogen and oxygen may explode.
Therefore, countermeasures for these potential dangers should be
provided.
SUMMARY OF THE INVENTION
[0046] Accordingly, the object of the invention by the inventors,
considering the situations as described above, is to provide a
system and method for generating high pressure hydrogen, wherein
high pressure hydrogen, in particular having a pressure of as high
as 350 atm or more required for utilizing hydrogen as an energy
source, can be efficiently generated without using a gas
compressor. Such hydrogen can be stably and safely generated only
by electrolysis using electric power generated by a frequently
varying natural energy such as sunlight.
[0047] Accordingly, it was found that high pressure hydrogen can be
generated only by electrolysis comprising the steps of providing an
electrolysis cell using PEM in a high pressure vessel under a
hydrogen atmosphere, electrolyzing pure water using the
electrolysis cell, storing hydrogen generated at the cathode in the
high pressure vessel housing the electrolysis cell, and storing
oxygen generated at the anode in a high pressure vessel for storing
electrolysis pure water together with returned pure water.
Consequently, a system and a method for generating high pressure
compressed hydrogen with a pressure of 350 atm or more, which is
required for utilizing hydrogen energy, have been established.
[0048] In the generation system and method as described above, pure
water is electrolyzed using the electrolysis cell, while adjusting
the differential pressure between the pressure of the high pressure
vessel for storing hydrogen and the pressure of the high pressure
vessel for storing oxygen and electrolysis pure water to be lower
than the pressure resistance of PEM constituting the electrolysis
cell. Hydrogen and oxygen obtained are stored, and pure water is
supplied to the oxygen side of the electrolysis cell after cooling
it with a heat exchanger. In addition, hydrogen generated in the
electrolysis cell is returned into the high pressure vessel after
cooling with the heat exchanger disposed at the outside of the high
pressure vessel. It was found that the process above enables the
electrolysis cell to be more stably operated since the electrolysis
cell is prevented from being heated by energy loss in the
electrolysis process.
[0049] The electrolysis efficiency is more improved as the
temperature is higher in the PEM electrolysis method. Although PEM
used for PEM electrolysis is made of polymer materials having a
relatively high heat resistance comparable to conventional
plastics, its mechanical strength decreases when the temperature
exceeds 100.degree. C. with a rapid decrease at 120.degree. C. or
more. Since the desirable temperature for operating the
electrolysis cell is 80.degree. C. or less, the heat generated by
electric power loss as a result of electrolysis of water is removed
in the operation of the PEM electrolysis cell. In addition, it was
found that the temperature in the PEM electrolysis system can be
efficiently and precisely controlled by forming the piping lines of
hydrogen and oxygen in the heat exchanger, as well as the piping
line of a heating medium, into branched fine tubes in order to
increase heat conductivity with a wide heat conduction area,
thereby ensuring a sufficiently high pressure resistance and heat
conductivity. This is advantageous for electrolyzing at a
prescribed temperature, preferably at about 80.degree. C., by the
electric power generated by solar energy as a clean energy in the
future. Another advantage of this method is to prevent the
temperature of pure water in the cell from decreasing to below
0.degree. C. as the freezing temperate of water when operation of
the electrolysis cell for generating hydrogen by electrolysis of
water is halted at night in cold provinces or in the winter
season.
[0050] A novel method for sealing through-holes for pulling thin
fine tubes out of a thick high pressure vessel has been
additionally invented.
[0051] For suppressing the force acting on the electrolysis cell
within the pressure resistance of the electrolysis cell, the
difference between the pressures of hydrogen and oxygen acting on
the electrolysis cell should be controlled to be within the
pressure resistance of the electrolysis cell. However, since the
pressure resistance of the electrolysis cell is limited, a higher
accuracy for controlling the pressure is required, as shown below,
as the pressures of oxygen and hydrogen acting on the electrolysis
cell increase. The conventional pressure control methods, or
pressure control by transfer of hydrogen and oxygen, may become an
impossible to comply with the requirement. Accordingly, it was
found that the pressure can be effectively controlled by allowing
pure water contained in the high pressure vessels for storing
hydrogen and oxygen to be transferred from a vessel having a higher
pressure to another vessel having a lower pressure, in place of
pressure control by transfer of hydrogen or oxygen as a gas, or by
using both methods together.
[0052] A pressure controller applicable for the pressure control
method has also been developed.
[0053] The following equation (1) is valid among the precision S(%)
for controlling the differential pressure, the pressure resistance
Ps of the electrolysis cell and the pressure P of hydrogen (or
oxygen) generated in the electrolysis cell. This equation means
that a high pressure control accuracy is required in the system and
method for generating the high pressure hydrogen.
S.gtoreq.(Ps/P).times.100 (1)
[0054] The equation (1) above show that it is necessary to increase
either Ps or the precision S(%) for controlling the differential
pressure, or to increase Ps and S, in order to increase the
pressure P of hydrogen or oxygen generated. However, since the
accuracy S for controlling the differential pressure is currently
limited, the pressure P of hydrogen or oxygen available is
eventually determined by the pressure resistance Ps of the
electrolysis cell.
[0055] While the allowable pressure resistance of the currently
available electrolysis cell is generally about 4 atm, the accuracy
for controlling the pressure may be within 4/10, or within 40%,
when the pressure of oxygen or hydrogen generated is about 10 atm.
Accordingly, the method conventionally used for controlling the
pressure can be employed with no danger of breaking the
electrolysis cell. Therefore, a pressure of about 350 atm that is
required for utilizing hydrogen as an energy source can be applied
in the conventional electrolysis cell at present.
[0056] However, a highly precise control of the pressure with an
accuracy of 4/400 or more, or 1% or more, is required for more
stably and safely generating hydrogen at a pressure of 350 atm, or
for generating hydrogen and oxygen at a pressure required
hereinafter, or a pressure of 400 atm for example, using the
electrolysis cell. This accuracy is hardly attainable by the
conventional method for controlling the pressure, and a more strict
control of the pressure would be required, because hydrogen
compressed under a pressure of about 700 atm will be needed in the
future.
[0057] The inventors have investigated a method for excluding the
factors that make the pressure resistance of the electrolysis cell
decrease, as well as the method for controlling the pressure by
transferring pure water, and found that the electrolysis cell
having a novel structure as will be described hereinafter is
effective for improving the pressure resistance of the electrolysis
cell. This structure permits the diameter of the high pressure
vessel housing the electrolysis cell to be small. In addition, the
high pressure vessel can be formed with a wall as thin as possible,
although the thickness of the wall has been required to be thick in
response to the pressure generated, or the thickness of the high
pressure vessel was required to be larger as the pressure is
higher, or the thickness was required to be increased in proportion
to the square of the diameter of the vessel. Therefore, the
improvement of the structure permits easy manufacture and handling
of the vessel, rendering the vessel to be advantageous in its
manufacturing cost.
[0058] It was found that the following structure is effective for
exhibiting the effects as described above:
[0059] (1) the double polarity multi-layered type electrolysis cell
is fixed by compression by a compression pressure of a compressing
member;
[0060] (2) hydrogen and permeating pure water generated at the
cathode are directly discharged into the high pressure hydrogen
vessel from each cathode of the cell by providing a discharge port
communicating with the cathode at the side wall of the double
polarity electrode; and
[0061] (3) pure water to be electrolyzed is supplied through a pure
water feed passageway formed by a hole provided at the center of
the cell.
[0062] A water level meter was also developed, by taking advantage
of a large difference of electrical conductivity between a gas such
as oxygen and pure water, in order to solve the following problems
encountered in the measurement of the water level in the vessel in
the presence of a high pressure gas, and for improving the accuracy
of pressure control.
[0063] While pure water used for electrolysis and oxygen generated
by electrolysis are stored in the high pressure vessel together, it
may be commonly conjectured that water is stored at the bottom half
and oxygen is stored at the top half in the vessel because the
density of oxygen is 1.429.times.10.sup.-3 g/cc at the standard
conditions (0.degree. C. and 1 atm).
[0064] However, oxygen has a density equal to the density of water
at a pressure of 700 atm from the calculation of
1/(1.429.times.10.sup.-1)=700 with the proviso that oxygen is an
ideal gas. This mean that water floats on oxygen at a pressure of
higher than 700 atm, and an empirical rule that a gas is lighter
than water is not valid.
[0065] Fortunately, such inversion of the density does not occur
unless the pressure is 1000 atm or more considering the size of the
oxygen molecule and intermolecular force of oxygen. However, a
widely used float type level meter cannot accurately sense the
water surface due to unstable movement of the float caused by water
stream and other factors when the difference of density between
water and oxygen becomes small. In addition, the durability of the
float to be used in the float type level meter against the pressure
should be taken into consideration, because the float used for the
float type level meter is required to have an apparent specific
gravity of less than 1. Therefore, manufacture of a float durable
to a pressure required in utilization of the hydrogen energy has
been considered to be difficult.
[0066] The inventors have developed a level meter that can be
stably operated under high pressure for solving these problems, in
order to steadily and widely implement the method for generating
high pressure hydrogen according to the invention.
[0067] The invention completed as described above provides a system
for generating high pressure hydrogen comprising an electrolysis
cell disposed in a high pressure vessel that also serves as a
storage tank of hydrogen generated. The electrolysis cell comprises
polyelectrolyte membranes for generating hydrogen and oxygen by
electrolysis of pure water.
[0068] The invention also provides a system for generating high
pressure hydrogen comprising two high pressure vessels including a
high pressure vessel for storing hydrogen generated and a high
pressure vessel for storing electrolysis pure water and oxygen
generated. An electrolysis cell comprising polyelectrolyte
membranes for generating hydrogen and oxygen by electrolysis is
disposed in the high pressure vessel for storing hydrogen
generated, and the high pressure vessel for storing electrolysis
pure water and oxygen generated communicates with the electrolysis
cell.
[0069] Preferably, the system for generating high pressure hydrogen
has a pressure control device for controlling a differential
pressure between the inner pressure of the high pressure vessel for
storing hydrogen and the inner pressure of the high pressure vessel
for storing oxygen to a pressure below the pressure resistance of
the electrolysis cell.
[0070] Preferably, the system for generating high pressure hydrogen
has a pressure control device provided for measuring the pressures
of respective high pressure vessels and adjusting the differential
pressure to a pressure below the pressure resistance of the
electrolysis cell by discharging hydrogen or oxygen through the
valves provided at respective high pressure vessels being switched
based on the measured values.
[0071] Preferably, the system for generating high pressure hydrogen
has a pressure control device provided for adjusting the
differential pressure to a pressure below the pressure resistance
of the electrolysis cell by allowing pure water to be transferred
by switching the valves in the vessels connected to the pipe lines
communicating with pure water in respective high pressure
vessels.
[0072] Preferably, the system for generating high pressure hydrogen
has a pressure control device provided in the pipe line
communicating with pure water filled in each high pressure vessel
and the pressure is controlled by the pressure control device
having a slider that slides depending on the differential pressure
of pure water in each high pressure vessel.
[0073] Preferably, the electrolysis cell in the system for
generating high pressure hydrogen is a double polarity
multi-layered type cell comprising a plurality of laminated double
polarity electrodes having catalyst layers on both surfaces
thereof, and the electrolysis cell is placed on a mounting table in
the high pressure vessel so as to be compressed with compression
jigs from above the table.
[0074] The present invention also provides a method for generating
high pressure hydrogen, wherein an electrolysis cell comprising
polyelectrolyte membranes is disposed in a high pressure vessel,
and hydrogen and oxygen are generated by electrolysis of pure water
using the electrolysis cell. Hydrogen generated is stored in the
high pressure vessel containing the electrolysis cell, and oxygen
is stored in a high pressure vessel for storing electrolysis pure
water together with returned pure water.
[0075] Preferably, hydrogen generated is cooled before storing in
the high pressure vessel containing the electrolysis cell.
[0076] Preferably, the differential pressure between the inner
pressure of the high pressure vessel for storing hydrogen and the
inner pressure of the high pressure vessel for storing oxygen and
pure water is adjusted below a pressure of the pressure resistance
of the polyelectrolyte membrane constituting the electrolysis cell
in the electrolysis process. The pressure is preferably controlled
by adjusting the hydrogen pressure and oxygen pressure in
respective high pressure vessels by discharging hydrogen or oxygen
from the vessels and/or by transferring pure water in the
vessels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0077] FIG. 1 is a schematic diagram showing the overall
constitution of an example of the system for generating high
pressure hydrogen according to the invention;
[0078] FIG. 2 is provided for illustrating an example of pipe lines
disposed for enhancing the cooling effect in the system for
generating high pressure hydrogen shown in FIG. 1 ;
[0079] FIG. 3 is a cross section of a water feed pump powered with
an induction motor as an example of the water feed pump in FIG.
1;
[0080] FIG. 4 shows a schematic drawing provided for describing an
example of a current introduction terminal for feeding a large
electric current to the electrolysis cell;
[0081] FIG. 5 shows a schematic drawing provided for describing an
example of a current introduction terminal for feeding a small
electric current to the water feed pump and level meter;
[0082] FIG. 6 shows a schematic drawing provided for describing an
example of the level meter;
[0083] FIG. 7 shows a schematic drawing provided for describing
another example of the water feed pump;
[0084] FIG. 8 shows a schematic drawing provided for describing an
example of the method for sealing the through-hole formed at the
side wall of the high pressure vessel;
[0085] FIG. 9 is a schematic diagram showing the overall
constitution of another example of the system for generating high
pressure hydrogen according to the invention;
[0086] FIG. 10 is a partial cross section showing the structure of
the differential pressure sensor in FIG. 9;
[0087] FIG. 11a is a cross section showing the structure of the
release valve in FIG. 9;
[0088] FIG. 11b is a side view showing the structure of the release
valve in FIG. 9;
[0089] FIG. 12 is a cross section showing the structure of the
level meter in FIG. 9;
[0090] FIG. 13 is a schematic diagram showing the overall
constitution of the third example of the system for generating high
pressure hydrogen according to the invention;
[0091] FIG. 14a shows a partial cross section of the pressure
controller in FIG. 13;
[0092] FIG. 14b shows a cross section of the pressure controller
along the line A-A' in FIG. 14a;
[0093] FIG. 15 shows a partial cross section of another example of
the pressure controller;
[0094] FIG. 16 shows a partial cross section of a different
pressure controller;
[0095] FIG. 17 is a cross section showing the structure and
attachment of the electrolysis cell according to the invention;
[0096] FIG. 18 shows disassembled perspective views of the
electrolysis cell in FIG. 17; and
[0097] FIG. 19 illustrates a flow pattern of pure water on the
anode of the electrolysis cell shown in FIG. 17.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0098] Preferred embodiments of the system for generating high
pressure hydrogen according to the invention will be described in
detail hereinafter.
[0099] The invention basically provides a system and a method for
generating hydrogen and oxygen by direct electrolysis of pure water
using an electrolysis cell comprising an anode compartment and
cathode compartment isolated from each other with a partition
membrane, such as a polyelectrolyte membrane.
[0100] As described in detail above, the present invention enables
high pressure hydrogen to be safely and stably generated without
the use of gas compressors using a system for generating hydrogen
and oxygen developed by improving the conventional system. Each
member constituting the generation system is principally the same
as the member known in the art.
[0101] FIG. 1 is a schematic diagram showing the overall
constitution of an example of the system for generating high
pressure hydrogen according to the invention. The reference numeral
1 denotes an electrolysis cell placed in a high pressure vessel 10
(also referred to as a high pressure vessel for storing hydrogen
since it also served as a vessel for storing hydrogen as will be
described hereinafter). The electrolysis cell comprises an anode
compartment and a cathode compartment (not shown) partitioned with
polyelectrolyte membranes (PEM) having electrodes at both ends of
PEM. Pure water for electrolysis is supplied to the anode
compartment of the electrolysis cell 1 through a pure water feed
pipe line 3. The electrolysis cell is constructed so that oxygen
and hydrogen are generated in the anode compartment and cathode
compartment, respectively, of the electrolysis cell 1 by feeding
electricity from a power source 9 through a cathode line 5 and an
anode line 7.
[0102] Oxygen generated in the anode compartment is sent to a high
pressure vessel 31 (also referred to as a electrolysis pure water
tank or a high pressure vessel for storing oxygen) for storing
electrolysis pure water through a return pipe line 4 together with
a part of pure water supplied from a pure water feed pipe line 3,
and is stored in a oxygen pool 31a having a small bottom area
provided at the upper part of the electrolysis pure water tank
31.
[0103] Hydrogen generated in the cathode compartment of the
electrolysis cell 1 may be directly discharged into the high
pressure vessel 10 and stored in the high pressure vessel 10.
However, since generated hydrogen is heated by electric power loss
during electrolysis, the electrolysis cell 1 housed in the high
pressure vessel 10 is heated by the heat of hydrogen when hydrogen
is discharged in the high pressure vessel 10 without cooling, and
PEM may be finally broken by the heat.
[0104] For preventing PEM from being broken by the heat, hydrogen
generated in the electrolysis cell 1 is cooled by leading it into
an external heat exchanger 25b outside of the high pressure vessel
10 through a pipe line, and hydrogen is discharged into the high
pressure vessel 10, preferably into the bottom or in the vicinity
thereof, through a hydrogen discharge pipe line 2. Consequently,
the heat generated by the electric power loss of the electrolysis
cell 1 is cooled, and hydrogen is maintained at a temperature
suitable for operating the electrolysis cell.
[0105] Temperatures of hydrogen flowing in and out of the heat
exchanger 25b are measured with thermometers 28a and 29b,
respectively, and the temperature of hydrogen is controlled by
controlling the temperature and volume of cold water sent into the
heat exchanger 25b.
[0106] Since hydrogen discharged from a hydrogen discharge pipe 2
becomes heavier due to a lower temperature than the temperature of
hydrogen stored in the high pressure vessel 10 by cooling the
formed hydrogen with the heat exchanger 25b, cool hydrogen is
collected at the bottom of the high pressure vessel 10. However,
this hydrogen is lifted up by hydrogen flowing in from the hydrogen
discharge pipe line 2, and ascends by reducing its specific gravity
when the temperature is increased by making contact with the
electrolysis cell 1. This ascending hydrogen carries the heat out
of the high pressure vessel 10 through a valve 15 and needle valve
16, and the electrolysis cell 1 is efficiently cooled.
[0107] While the electrolysis cell 1 is cooled with pure water to a
certain extent by feeding pure water that has been cooled at the
heat exchanger 25a to the anode side, the cooling ability of this
pure water is not sufficient as compared with the electrolysis cell
of a known in the art PEM electrolysis system that is submerged in
pure water. Therefore, it is desirable, in the construction in
which the electrolysis cell 1 is housed in the high pressure vessel
10 for storing hydrogen, that hydrogen generated in the
electrolysis cell 1 returns to the high pressure vessel housing the
electrolysis cell 1 after cooling.
[0108] Although it is contemplated to directly discharge hydrogen
into the high pressure vessel 10 by cooling the high pressure
vessel itself, a wide heat conduction area is required for cooling
since the heat is distributed in the high pressure vessel 10. In
addition, the heat conductivity of the vessel becomes poor as the
pressure is increased since the wall of the high pressure vessel 10
is required to be thick. Therefore, this method is not considered
to be excellent in cooling efficiency.
[0109] The electrolysis cell can be efficiently cooled by
discharging hydrogen generated in the electrolysis cell 1 as
described above, since the temperature of hydrogen is not
dissipated anywhere. Since hydrogen may be discharged through fine
tubes having thinner wall thicknesses as compared with the wall of
the high pressure vessel 10, heat conductivity is not compromised
and cooling efficiency is enhanced.
[0110] Accordingly, high pressure hydrogen can be generated without
placing the electrolysis cell 1 in a corrosive environment where
water and oxygen exist together in the invention, while enabling
cool hydrogen to be discharged from the hydrogen discharge pipe
line 2 through the heat exchanger 25b by a spontaneous pressure
increasing function of the electrolysis cell 1 without using a
pump.
[0111] In addition, heat conductivity of hydrogen increases as the
pressure in the high pressure vessel 10 increases, and the ability
for cooling the electrolysis cell 1 is improved.
[0112] It is also evident that high pressure hydrogen can be stably
and efficiently generated in this invention. According to the
present invention, in particular, hydrogen warmed by the
electrolysis cell 1 ascends and reaches the upper part of the high
pressure vessel 10 by returning hydrogen cooled in the heat
exchanger 25b to the bottom of the high pressure vessel 10, and is
released through a valve 15 and needle valve 16 together with
extracted heat. Accordingly, cooling efficiency of the electrolysis
cell is high enough to enable a highly efficient system for
generating high pressure hydrogen to be designed.
[0113] Hydrogen generated in the electrolysis cell 1 as described
above is discharged into the high pressure vessel 10 from the
hydrogen discharge pipe line 2, and collected and stored in the
high pressure vessel 10.
[0114] When electric power is continuously supplied from the power
source 9 to the electrolysis cell 1 through the cathode line 5 and
anode line 7, pure water is continuously electrolyzed to generate
oxygen and hydrogen. Oxygen is collected in the oxygen pool 31a of
the electrolysis pure water tank 31 while hydrogen is collected in
the high pressure vessel 10, and the pressure of the tank and
vessel are elevated.
[0115] The pressures of oxygen and hydrogen are measured by
pressure gauges 39a and 39b, respectively, provided at the
electrolysis pure water tank 31 and high pressure vessel 10,
respectively. The measured values are compared with each other
using an independently provided controller (not shown). When the
pressure of oxygen is higher then the pressure of hydrogen, for
example, a valve 36 is automatically opened by a control signal
from the controller, and oxygen is released through a needle valve
38 to discharge in the air or to be retrieved in the vessel. When
the pressure of oxygen is equal to the pressure of hydrogen, on the
other hand, the needle valve 36 is closed by operating the
controller. The aperture of the needle valve 38 is automatically
controlled by the controller depending on the magnitude of the
differential pressure between oxygen and hydrogen.
[0116] Hydrogen and oxygen are generated in a proportion of 2:1 in
volume by electrolyzing pure water in the electrolysis cell 1. When
pure water is continuously electrolyzed by closing the valves 36
and 37 communicating with the oxygen pool 31a, and by closing the
valves 14 and 15 communicating with the high pressure vessel 10
without discharging hydrogen and oxygen to the outside, the
pressure of hydrogen in the high pressure vessel 10, and the
pressure of oxygen in the oxygen pool 31a formed in the
electrolysis pure water tank 31 are elevated.
[0117] Since the present invention is directed toward the control
of high pressure hydrogen as a hydrogen energy source, it is
preferable that the volume of oxygen collected in the oxygen pool
31a is controlled so that the volume is 4% or less of the volume of
the high pressure vessel 10 by observing the water level 33a, in
order to safely prepare high pressure hydrogen. Excess oxygen is
released through the needle valve 38, and the pressures are
controlled so that the pressure of oxygen is always equal to the
pressure of hydrogen, or so that the differential pressure between
oxygen and hydrogen is at least within the pressure resistance of
the electrolysis cell, or within 2 atm, with the pressure of oxygen
being a little higher than the pressure of hydrogen.
[0118] When the pressures of hydrogen and oxygen reach respective
prescribed pressures, the controller automatically stops the
electric power from the power source 9 to the electrolysis cell 1,
and electrolysis is stopped with a halt of pressure increase.
[0119] The pressures of hydrogen and oxygen in the high pressure
vessel 10 and oxygen pool 31a, respectively, are controlled as
described above with uniform pressures, wherein the oxygen pressure
is a little higher, and the differential pressure between oxygen
and hydrogen is controlled at least within the pressure resistance
of the electrolysis cell. Accordingly, the differential pressure
between the inside and outside of the electrolysis cell 1, and the
pressure acting on the partition membrane (a membrane having
platinum electrodes on PEM) isolating the anode compartment from
the cathode compartment in the electrolysis cell 1 are controlled
to be within the pressure resistance of the membrane. Consequently,
the partition membrane is not broken and there is no leak of
hydrogen and oxygen.
[0120] The partition membrane may happen to be broken, or a part of
the seal member of the electrolysis cell 1 may happen to be broken
for certain reasons. However, the pressure of oxygen can be
balanced with the pressure of hydrogen by permitting a small volume
of pure water in the electrolysis pure water tank 31 to flow into
the high pressure vessel 10, by connecting both the pure water feed
pipe line 3 and return pipe line 4 connected to the electrolysis
cell 1 to the bottom of the electrolysis pure water tank 31, and by
controlling the pressure of oxygen in the oxygen pool 31a to be a
little higher than the pressure of hydrogen in the high pressure
vessel 10. Consequently, excess pure water is prevented from
flowing into the high pressure vessel, and a mixed gas of hydrogen
and oxygen is not formed, thereby rendering the process quite
safe.
[0121] Furthermore, when the volume of hydrogen in the oxygen pool
31a is suppressed to be 4% or less of the volume of the high
pressure vessel 10, it cannot be anticipated that the oxygen in the
electrolysis pure water tank 31 is mixed with hydrogen in the high
pressure vessel 10 even under any predictable breakage
conditions.
[0122] If oxygen in the oxygen pool 31a is accidentally mixed with
hydrogen in the high pressure vessel 10, and the concentration of
hydrogen never exceeds a lower explosion limit of 4%, a gas
explosion never happens.
[0123] The descriptions above are only valid when normal
electrolysis of water is not maintained. Usually, a safety OFF mode
of the power source (see Handbook of Safety Precautions and Control
in Manufacture of Semiconductors, Harada et. al., published by
Realize Co., 1993) functions immediately after the controller
senses an abnormal electric current or abnormal voltage, and
operation of the generation system is stopped to ensure safety.
[0124] Damage greater than breakage of the electrolysis cell 1
cannot happen by at least preventing an explosion caused by the
mixing of hydrogen and oxygen.
[0125] The mixing of oxygen and hydrogen due to an abnormal state
of the electrolysis cell 1, which is a level not detectable as
abnormal by monitoring the current and voltage of the controller,
can be sensed with an oxygen transducer 10a and a hydrogen
transducer 31b, and operation of the hydrolysis cell is urgently
stopped. Therefore, high pressure hydrogen required for utilizing
hydrogen as an energy source can be safely generated.
[0126] Since the electrolysis cell 1, the cathode line 5 and anode
line 7 for feeding electricity to the cell, and the electrode
terminals 6 and 8 are all placed in a high pressure hydrogen
atmosphere, problems of electrolytic corrosion can be avoided.
[0127] When hydrogen is used, the valve 15 attached to the high
pressure vessel 10 is opened by operating the controller, and
hydrogen is controlled so that it slowly flows out by adjusting the
aperture of the needle valve 16.
[0128] A pressure decrease in the high pressure vessel 10 is
immediately sensed by the pressure gauge 39b, and electric current
flows to the electrolysis cell 1 from the power source 9 under the
control of the controller to start electrolysis in the electrolysis
cell 1. Consequently, hydrogen with the same volume as the volume
of hydrogen discharged through the valve 15 and needle valve 16 is
generated, and the pressure of hydrogen resumes its initial
pressure.
[0129] Since the volume of hydrogen flowing out through the valve
15 and needle valve 16 increases by slowly increasing the aperture
of the needle valve 16 the pressure of hydrogen decreases. However,
the pressure decrease is immediately sensed by the pressure gauge
39a, and the amount of the electric current flowing through the
electrolysis cell 1 from the power source 9 increases by operating
the controller, thereby resuming the initial pressure.
[0130] While the volume of hydrogen released through the valve 15
and needle valve 16 is gradually increased by keeping the pressure
to be approximately constant, the pressure does not further
increase even by increasing the aperture of the needle valve 16
when the amount of hydrogen consumed reaches the amount of hydrogen
generated. As a result, the electric current flowing from the power
source 9 to the electrolysis cell 1 stops increasing.
[0131] When the amount of hydrogen consumed exceeds the maximum
amount of hydrogen that can be generated from the hydrolysis cell
1, on the other hand, the amount of generated hydrogen cannot be
increased after the electric current flowing from the power source
9 to the electrolysis cell 1 has reached its maximum, and the
aperture of the needle valve 16 does not further increase.
Therefore, the hydrogen demand exceeds the maximum amount of
hydrogen that can be generated from the hydrolysis cell 1.
[0132] While the pressure of the high pressure vessel 10 is
maintained at a prescribed pressure, the valves 14 and 37 are
opened when the pressure in the high pressure vessel 10 needs to be
urgently decreased in an emergency allowing hydrogen in the high
pressure vessel 10 and oxygen in the oxygen pool 31a of the
electrolysis pure water tank 31 to be urgently discharged.
[0133] The valve 36 is opened by automatically operating the
controller when the differential pressure between hydrogen and
oxygen increases by the release of hydrogen. Oxygen is discharged
through the needle valve 38 so that the pressure of hydrogen in the
high pressure vessel 10 balances the pressure of oxygen in the
oxygen pool 31a of the electrolysis pure water 31, so that the
differential pressure between hydrogen and oxygen at least falls
within the pressure resistance of the electrolysis cell with a
little higher pressure of oxygen than the pressure of hydrogen.
[0134] Although the descriptions above may give an impression that
the apertures of the needle valves 16 and 38 and electric current
flowing from the power source 9 to the electrolysis cell 1 are
controlled too slowly, they are all controlled by a computer at a
high speed. Since the control speed is sufficiently high as
compared with the speed of variation of the natural energy, the
controller can follow the change of the natural energy.
Accordingly, there are no problems in generating hydrogen using the
system for generating high pressure hydrogen according to the
invention even when using electric power generated by natural
energy that is frequently changed.
[0135] While hydrogen is discharged in the high pressure vessel 10
from the hydrogen discharge pipe line 2, the discharged hydrogen
contains a small amount of water, and the water is collected in a
water pool 11 at the bottom of the high pressure vessel 10.
[0136] The amount of water is always monitored with a level meter
12 when a prescribed amount of water is collected a valve 17 is
opened to discharge it into a water reservoir 20 through a needle
valve 18. The discharge of water stops by closing the valve 17 when
the water level descends to a prescribed level.
[0137] Since hydrogen is dissolved in water discharged from the
high pressure vessel 10, hydrogen is also collected in the water
reservoir 20. A controlled flow rate of nitrogen is supplied into
the water reservoir 20 by a needle valve 23 from a pipe line 24
through a filter 22, and the nitrogen is discharged into the air
through a filter 19. Since the water reservoir is designed to be
isolated from the air by the filter 19, microorganisms never mingle
in the water reservoir 20.
[0138] While the feed of pure water into the electrolysis cell 1 is
not particularly restricted, pure water is supplied into the
electrolysis cell by means of a water feed pump 32 disposed in the
electrolysis pure water tank 31 as in the embodiment shown in FIG.
1.
[0139] The water feed pump 32 comprises an induction motor and
propeller type water feed pump integrated into one unit, and
details thereof will be described hereinafter with reference to
drawings.
[0140] Pure water discharged from the water feed pump 32 is sent
into the electrolysis cell 1 after being cooled with the heat
exchanger 25a placed in the midway of the pure water feed pipe line
3.
[0141] The temperatures of pure water supplied to and released from
the heat exchanger 25a are measured with the thermometers 28a and
29a provided so as to cooperate with the heat exchanger 25. The
electrolysis cell 1 is designed so as to be able to electrolyze at
a desired temperature by controlling the amount of cool water
supplied from a refrigerator (not shown) through a cool water feed
pipe line 26a using the controller.
[0142] Since pure water collected in the electrolysis pure water
tank 31 is consumed by being decomposed into hydrogen and oxygen in
the electrolysis cell 1, the water surface is continuously
monitored with the level meter 33, and pure water is replenished
from the pure water replenishing tank 44 considering that the
volume of oxygen in the oxygen pool 31a is preferably within 4% of
the volume of hydrogen in the high pressure vessel 10.
[0143] While replenishment of pure water is controlled with the
controller, the valves 40 and 42 provided between the electrolysis
pure water tank 31 and pure water replenishing tank 41 are closed
at first since the electrolysis pure water tank 31 is communicating
with a pure water storage tank 48 through a feed pipe line 51a and
return pipe line 51b.
[0144] Then, the valve 41 of the feed pipe line 51a and the valve
43 of the return pipe line 51b are opened, and pure water is
circulated through an ion-exchanger tower 46, a filter 45, the pure
water replenishing tank 44, the return pipe line 51b and the pure
water storage tank 48, in this order, by operating a pump 47. When
the resistivity of pure water, as measured with a resistivity meter
49a provided in the pure water replenishing tank 44, indicates a
prescribed resistivity, the valves 41 and 43 are closed and the
pump 47 is stopped, thereby filling the pure water replenishing
tank 44 with pure water having a high resistivity without
containing any bubbles.
[0145] Then, the pure water replenishing tank 44 is pressurized by
the pressure of oxygen in the oxygen pool 31a of the electrolysis
pure water tank 31 communicating with the pure water replenishing
tank by opening the valves 40 and 42. However, since no gas
component is present in the pure water replenishing tank 44 filled
with pure water, substantially no volume change is observed with
negligible changes of the pressure. Therefore, pure water in the
pure water replenishing tank 44 spontaneously falls down into the
electrolysis pure water tank 31 by gravity, and high pressure
oxygen in the electrolysis pure water tank 31 enters the pure water
replenishing tank 44 by replacing pure water.
[0146] The valves 40 and 42 are closed by confirming that pure
water in the pure water replenishing tank 44 has flowed into the
electrolysis pure water tank 31, and that the water level 33a has
returned to its original level using the level meter 33. When the
valve 43 is closed, high pressure oxygen in the pure water storage
tank 48 is discharged into the air through a filter 50, and the
pressure of the pure water storage tank 44 returns to the
atmospheric pressure.
[0147] Subsequently, the valve 41 is open and pure water is
circulated by actuating the pump 47 to fill the pure water
replenishing tank 44 with pure water, thereby replenishing the
electrolysis pure water tank 31 with pure water again.
[0148] Since the pure water storage tank 48 communicates with a
water tank 56 through a feed pipe line 51, a pump 55 is
automatically operated when the water level of the pure water
storage tank 48 descends by replenishing pure water into the pure
water replenishing tank 44. Replenishing water such as city water
is supplied into the pure water storage tank 48 and is converted
into pure water through the ion-exchanger tower 54, filter 53 and
valve 52 provided in the midway of a feed pipe line 51.
[0149] FIG. 2 shows piping in the main part of the system
illustrating an example of piping for enhancing cooling
effects.
[0150] In this example, hydrogen generated is introduced into the
outside of the high pressure vessel 10 through a plurality of fine
tubes 2a, 2b, and so on, branched from the hydrogen discharge pipe
line 2 by means of a branching pipe line 60 disposed at the upper
part of the high pressure vessel 10. Hydrogen is discharged again
into the high pressure vessel 10 from the bottom of the pressure
vessel 10 after allowing it to pass through the heat exchanger 25b
disposed at the midway of the plural fine tubes. Using the fine
tubes permits the heat conduction area to be increased while
enhancing the pressure resistance of the piping itself.
[0151] It is quite important to keep a hermetic property at the
branching points when the hydrogen discharge pipe line 2 is
branched into the fine tubes 2a, 2b, and so on, from the high
pressure vessel 10. Accordingly, a novel method is employed in the
invention, wherein through-holes that penetrate the wall of the
high pressure vessel 10, into which the fine tubes 2a, 2b, and so
on, are inserted, are formed into tapered shapes from the inside of
the high pressure vessel 10, and the fine tubes are hermetically
sealed without welding by sealing the tapered holes with
wedge-shaped cores.
[0152] The temperature of hydrogen flowing in and out of the heat
exchanger 25b is measured with thermometers 28b attached at the
inlet side of the fine tubes 2a, 2b, and so on, to the heat
exchanger 25b, and thermometers 29b attached at the outlet side of
the fine tubes 2a, 2b, and so, from the heat exchanger 25b. The
temperature of hydrogen is controlled by controlling the
temperature and flow rate of cooling water sent into the heat
exchanger 25b.
[0153] Cooling water can be also utilized for cooling hydrogen in
the high pressure vessel 10 by passing cooling water through the
fine tubes provided in the high pressure vessel 10, preventing pure
water in the electrolysis cell 1 and water pool 11 from freezing
during the halting period.
[0154] The temperature of cooling water is usually in the range of
about 10 to 20.degree. C., and cooling water is supplied from a
cooling water tank with a pump. Cooling water may be used for
cooling the electrolysis cell 1 to a temperature of, for example,
80.degree. C. or less when it generates a heat by electrolysis of
water, while also warming the cell at 0.degree. C. or more when
freezing of the electrolysis cell 1 is a concern during the halt
period of the electrolysis cell 1.
[0155] Pure water in the electrolysis pure water tank 31 may be
supplied to the anode side of the electrolysis cell 1 after cooing
it with the heat exchanger 25a. The return pipe line 4 is also
branched into a plurality of fine tubes 4a, 4b, and so on, at a
branching pipe line 64 disposed at the upper part of the high
pressure vessel 10 as shown in FIG. 2 in order to control the
temperature of the electrolysis cell, 1, as in the hydrogen
discharge pipe line 2. The temperatures of pure water as well as
oxygen generated are controlled with thermometers and heat
exchanger 25c, and pure water is supplied to the bottom of the
electrolysis pure water tank 31 and stored there.
[0156] The temperature is controlled not only for the temperature
control of the electrolysis cell 1, but also for preventing pure
water within the electrolysis cell 1, electrolysis pure water tank
31 and fine tubes 4a, 4b, and so on, from freezing.
[0157] For example, when the atmospheric temperature has decreased
below 0.degree. C. at night during the halt of operation, the
controller (not shown) senses the temperature decrease with the
thermometers (denoted by the marks o in the drawing) provided at
the fine tubes 4a, 4b, and so on, and pure water within the
electrolysis cell 1, electrolysis pure water tank 31 and fine tubes
4a, 4b, and so on, is prevented from freezing by flowing pure water
into the return pipe line 4 for pure water and oxygen comprising
the pure water feed pipe line 3 and plural fine tubes 4a, 4b, and
so on, by operating a high pressure pump 32, during the halt period
of the electrolysis cell 1.
[0158] The temperature of cooling water used is usually in the
range of 10 to 20.degree. C., and cooling water is supplied from a
cooling water tank (not shown) with a pump. Cooling water may be
used for cooling the electrolysis cell 1 to a temperature of
80.degree. C. or less when it is generating electricity, while
serving for warming the electrolysis cell to 0.degree. C. or more
when freezing of the electrolysis cell 1 is a concern during the
halt of the electrolysis cell 1.
[0159] A cooling pipe line 64 comprising a plurality of fine tubes
64a, 64b, and so on, is provided in the electrolysis pure water
tank 31 for cooling pure water in the electrolysis pure water tank
31 in the invention. Consequently, the temperature of the
electrolysis cell 1 can be more easily controlled while efficiently
preventing pure water in the electrolysis pure water tank 31 from
freezing.
[0160] FIG. 3 is a cross section showing an example of a water feed
pump driven with an induction motor as a representative example of
the water feed pump 32. In the drawing, the reference numeral 71
denotes the bottom of the electrolysis pure water tank 31, the
reference numeral 72 denotes a pure water exit port, the reference
numeral 73 denotes a water feed blade, the reference numeral 74
denotes a rotation axis, the reference numeral 75 denotes a rotor,
which is manufactured by integrating a laminated iron core
comprising a laminated multilayer of silicon steel plates with a
cage type copper coil and by coating with a resin, the reference
numeral 76 denotes a drive coil prepared by winding a coil on a
multilayer iron core and coating with a resin, the reference
numerals 76a and 76b denote lead wires for supplying an electric
current to the driving coil, the reference numeral 77 denotes a
rotation sensing coil, the reference numeral 77c denotes a rotation
sensing magnet, the reference numerals 77a and 77b denote lead
wires for the rotation sensing coil, the reference numerals 78a to
78c denote bearings, the reference numeral 79 denotes a nut, the
reference numeral 80 denotes a screw, and the reference numeral 81
denotes a bearing member.
[0161] The lead wires 76a, 76b, 77a and 77b are electrically
insulated by being coated with a resin, and are guided to the
outside of the electrolysis pure water tank 31 by means of
electrically insulated electric current introduction terminals
penetrating through the bottom 71.
[0162] The water feed pump 32 so constructed as described above
starts to rotate the rotor 75 by feeding electric power to the
driving coil 76 from a power source at the outside of the
electrolysis pure water tank 31 together with rotation of the
rotation axis 74 fixed to the rotor 75. Consequently, the blade 73
is simultaneously rotated, and pure water in the electrolysis pure
water tank 31 is supplied to the feed pipe line 3 from the pure
water exit port 72.
[0163] A magnet 77c embedded in the rotation axis 74 rotates
together with rotation of the rotation axis 74 to flow an
alternating induction current through the coil 77, and the
controller can monitor the rotation speed from the number of cycles
of the alternating current.
[0164] FIG. 4 shows a schematic drawing provided for describing an
example of a current introduction terminal for feeding a large
electric current to the electrolysis cell 1 of the system for
generating high pressure hydrogen. In the drawing, the reference
numeral 90 denotes a copper conductor, the reference numeral 90a
denotes an inner lead wire, the reference numeral 91 denotes a
resin insulator, the reference numerals 92a and 92b, and 93a and
93b denote sealing o-rings, the reference numeral 94 denotes a
resin disk, the reference numerals 95a and 95b denote metal disks,
the reference numeral 96 denotes a wiring terminal, the reference
numeral 97 denotes a nut, the reference numeral 98 denotes a press
board, reference numeral 99 denotes a screw, the reference numeral
100 denotes a nut, and the reference numeral 101 denotes a vessel
wall of the high pressure vessel 10. Since the conductor 90
penetrates through the vessel wall by being electrically insulated
from the electrolysis pure water vessel 31, electricity can be
transferred from the outside to the inside of the electrolysis pure
water vessel 31.
[0165] FIG. 5 shows a schematic drawing provided for describing an
example of a current introduction terminal for feeding a small
electric current to the water feed pump 32 and level meter 33
constituting the system for generating high pressure hydrogen
according to the invention. In the drawing, the reference numeral
110 denotes a vessel wall of the electrolysis pure water tank 31,
the reference numeral 111 denotes an insulator stuffed with a resin
such as a curable epoxy resin, and the reference numeral 112
denotes a copper wire covered with an enamel coating. This
construction permits a number of electric wires to be introduced
into the electrolysis pure water tank 31.
[0166] FIG. 6 shows a schematic drawing provided for describing an
example of the level meter used in the invention. In the drawing,
the reference numeral 120 denotes the vessel wall of the
electrolysis pure water tank 31, the reference numerals 121 and 124
denote fixing screws, the reference numeral 122 denotes a copper
wire covered with an enamel coating, the reference numeral 123
denotes a press board, the reference numerals 125a to 125c denote
electrodes plated with gold after pealing off the enamel coating,
and the reference numeral 126 denotes a brace. Since the electrical
resistance between the vessel wall 120 and electrode 125a of the
level meter 33 so constructed as described above differs when the
electrode 125a is submerged and not submerged in pure water, the
electrode 125a submerged in pure water can be discriminated from
the electrode 125a not submerged in pure water, enabling it to be
determined whether the electrode 125a is above the water surface or
under the water surface.
[0167] Accordingly, it can be determined whether the water surface
33a is between the electrodes 125a and 125b, between the electrodes
125b and 125c, or above the electrode 125c, enabling the set of
electrodes to serve as a level meter.
[0168] FIG. 7 shows an example of an external water feed pump
powered by electricity provided at the outside of the electrolysis
pure water tank 31, which is different from the water feed pump 32
placed in the electrolysis pure water tank 31. A pair of motors 128
and a pair of magnets 129 is symmetrically disposed relative to a
water feed rotation blade 127. The pump main unit and rotation
blade 127, and ring plate 130 are made of a non-magnetic material
such as stainless steel, and the space between the magnet 129 fixed
on the rotation blade 127 and the magnet 129 fixed on the axis of
the motor 128 are separated with a thin partition wall 131 made of
a heat-resistive plastic, such as a poly(ether-ether-ketone) resin
(PEEK).
[0169] The magnet 129 of the rotation blade 127 attracts the magnet
129 at the motor 128 side by employing the construction as
described above, and the rotation blade 127 floats and is fixed in
the space.
[0170] The blade 127 rotates with rotation of the motor 128. Pure
water flows into bottom of the electrolysis pure water tank 31
connected to the rotation blade 127 side, while oxygen flows into
the upper part of the electrolysis pure water tank 31 connected to
the motor 128 side. However, these portions have the same pressure
since they are in the same electrolysis pure water tank, and no
differential pressure is applied to the partition plate 131.
[0171] While pure water in the electrolysis pure water tank 31 is
sent into the anode side of the electrolysis cell 1, the electric
current is supplied to the motor 128 through electric wires
penetrating through the main unit of the water feed pump via
current introduction terminals as shown in FIG. 4.
[0172] FIG. 8 shows a schematic drawing provided for describing an
example of the method for sealing the through-hole formed at the
side wall of the high pressure vessel 10 or pure water and oxygen
vessel 31. In the drawing, the reference numeral 141 denotes the
side wall of the high pressure vessel 1 or pure water and oxygen
vessel 31, X denotes the inside of the vessel while Y denotes the
outside of the vessel, the reference numeral 140 denote a piping,
the reference numeral 142 denotes a core, the reference numeral 143
denotes a ring, the reference numeral 144 denotes a fixing screw,
and the reference numeral 145 denotes a holder of the fixing
screw.
[0173] The construction as described above permits the core 142 to
be pressed onto the side wall 141 to fit the piping 140 by
compression when the fixing screw 144 is tightened from the
X-direction by holding the holder 145 of the fixing screw. The core
142 is tightened by pressing the fixing screw 144 by the high
pressure in the vessel to the direction for tightening, and the
pipe line is completely sealed in the through-hole.
[0174] While the core 142 is molded into a structure by which it is
fixed by being inserted into the side wall 141 in the description
of FIG. 8, a commercially available connector may be fixed in the
through-hole of the side wall 141 using a tapered screw, and the
pipe line 140 may be sealed with the same core 142 as described in
FIG. 8.
[0175] FIG. 9 is a schematic diagram showing the overall
constitution of another example of the system for generating high
pressure hydrogen according to the invention. This system for
generating high pressure hydrogen is basically the same as that
shown in FIG. 1, and comprises a high pressure hydrogen vessel 202
constructed so that an electrolysis cell 201 is accommodated in a
hydrogen atmosphere generated, a high pressure oxygen vessel 262
for storing returned pure water and oxygen generated, pure water
pipes lines 216a and 216b through which pure water in the high
pressure hydrogen vessel 202 communicates with pure water in the
high pressure oxygen vessel 262, and a differential pressure sensor
253 for sensing the differential pressure between the pressure of
hydrogen in the high pressure hydrogen vessel 202 and the pressure
of oxygen in the high pressure oxygen vessel 262 in order to
control the differential pressure.
[0176] In the system for generating high pressure hydrogen shown in
FIG. 9, pure water to be electrolyzed is sent into the electrolysis
cell 201 from the high pressure oxygen vessel 262 with the pump
207, and pure water is electrolyzed by feeding electric power
required for electrolysis from a power source 261. Hydrogen and
pure water are discharged into the high pressure hydrogen vessel
202 from a hydrogen discharge port 203, oxygen generated and pure
water not electrolyzed are sent into the high pressure oxygen
vessel 262 through a return pipe line 204, and oxygen is stored in
the oxygen pool 252 located at the upper part of the high pressure
oxygen vessel 262.
[0177] The pressures in the high pressure hydrogen vessel 202 and
high pressure oxygen vessel 262 are increased by the hydrogen and
oxygen generated, respectively, to a prescribed pressure of, for
example, 400 atm. The system is in waiting at this pressure by
halting electrolysis when no hydrogen is needed. When hydrogen is
needed, on the other hand, a valve 257 is opened and a needle valve
256 is slowly opened to feed hydrogen from a hydrogen feed port
255.
[0178] When a decrease of the pressure in the high pressure
hydrogen vessel 202 is sensed with a pressure gauge 254 after
feeding hydrogen, the feed of electric power to the electrolysis
cell 201 from the power source 261 is resumed by the instruction of
a controller (not shown) operating in cooperation with the pressure
gauge 254, and electric power is supplied until the pressure
measured by the pressure gauge 254 returns to its original
value.
[0179] The aperture of the needle valve 256 is further increased
when the pressure as measured with the pressure gauge 254 resumes
with an increase of electric power from the power source 261 until
the pressure as measured by the pressure gauge 254 resumes its
original value. Feed of hydrogen continues by maintaining the
aperture of the needle valve and the electric power from the power
source, until the pressure does not decrease by increasing the
aperture of the needle valve, or the electric power supplied from
the power source 261 reaches a maximum allowable power.
[0180] The differential pressure between the pressure of oxygen
stored in an oxygen pool 252 and the pressure of hydrogen in the
high pressure hydrogen vessel 202 is measured with a differential
pressure sensor 253, an example of which is shown in the embodiment
below, during electrolysis and feed of hydrogen. Usually, the
controller (not shown) controls switching of the valve 244 and the
aperture of the needle valve 243. The amount of discharged oxygen
from an oxygen discharge port 245 is controlled so that no
differential pressure signal is emitted from the differential
pressure sensor 253.
[0181] Pure water is electrolyzed while controlling the pressure in
the high pressure hydrogen vessel 202 to be equal to the pressure
in the pure water and high pressure oxygen vessel 262, and hydrogen
is supplied from the hydrogen feed port 255.
[0182] The differential pressure between the high pressure oxygen
vessel 262 and high pressure hydrogen vessel 202 is controlled by
the discharge of oxygen and hydrogen, particularly by the discharge
of oxygen in the system for generating high pressure hydrogen shown
in FIG. 1. However, since the allowable pressure expected from the
pressure resistance of the electrolysis cell 201 is usually about 4
atm, a pressure control with an accuracy of, for example, as high
as 1% or more is required for generating hydrogen and oxygen with a
pressure of 400 atm or more using the electrolysis cell 201.
[0183] A differential pressure exceeding the allowable pressure
resistance of the electrolysis cell 201 may be generated by a
disturbance of the pressure control caused by a variation of the
amount of consumed hydrogen by the system connected to the hydrogen
feed port 255 for feeding hydrogen to the system, or by a variation
of the electric power supplied from the power source 261.
Accordingly, switching valves 208 and 217 are provided in this
system, in order to avoid a differential pressure exceeding the
allowable pressure resistance of the electrolysis cell. These
switching valves are connected to the pure water pipe lines 216a
and 216b, respectively, for communicating pure water in the high
pressure hydrogen vessel 202 with pure water in the high pressure
oxygen vessel 262, and are operated based on the differential
pressure.
[0184] Accordingly, pure water in the high pressure oxygen vessel
262 is discharged into the high pressure hydrogen vessel 202
through the switching valve 208, when the pressure of hydrogen in
the high pressure hydrogen vessel 202 is reduced below the pressure
of oxygen in the high pressure oxygen vessel 262, and when the
differential pressure between them might exceed the allowable
pressure of the cell 201. Consequently, the volume of pure water in
the high pressure oxygen vessel 262 is reduced while the volume of
oxygen in the oxygen pool 252 is increased, thereby reducing the
pressure in the high pressure oxygen vessel 262 while increasing
the pressure in the high pressure hydrogen vessel 202 to maintain a
differential pressure below the allowable pressure resistance.
[0185] Suppose that the volume of hydrogen in the high pressure
hydrogen vessel 202 is 20 L, the volume of oxygen in the high
pressure oxygen vessel 262 is 0.4 L (2% of the volume of hydrogen),
and the pressure of hydrogen generated is 400 atm. Then, 4 cc of
pure water, as 1% of 0.4 L of oxygen, flows out of the high
pressure oxygen vessel 262 and flows into the high pressure
hydrogen vessel 202. Consequently, the pressure of oxygen reduces
to 4 atm, as 1% of 400 atm, and the pressure of hydrogen increases
to 0.08 atm. Accordingly, a differential pressure of 4.08 atm can
be efficiently reduced to below the pressure resistance of the cell
by transfer of water with a volume of only 4 cc.
[0186] Controlling the water surface 251 in the high pressure
oxygen vessel 262 is crucial for generating hydrogen particularly
at a pressure of 350 atm or more. In this invention, the level
meter 250 is disposed in the high pressure oxygen vessel 262 to
always monitor the water surface 251, and pure water in the high
pressure pure water feed tank 241 is allowed to flow into the high
pressure oxygen vessel 262 by taking advantage of gravity by
opening the valve 238 when the water surface 251 descends from a
prescribed level. Flowing pure water into the high pressure oxygen
vessel 262 from the high pressure pure water feed tank 241 permits
the same volume of oxygen to flow into the high pressure pure water
feed tank 241 through the valve 239.
[0187] It is crucial to place the high pressure pure water feed
tank 241 at a higher level than the high pressure oxygen vessel
262, and the pure water feed tank 240 for replenishing pure water
into the high pressure pure water feed tank 241 at the same or
higher level than the high pressure pure water feed tank 241, in
order to flow pure water in the high pressure pure water feed tank
241 into the high pressure oxygen vessel 262 by taking advantage of
gravity.
[0188] Pure water is replenished into the high pressure pure water
feed tank 241 by closing the valves 238 and 239, and by opening the
valves 236 and 237. The high pressure oxygen vessel 262 is isolated
by closing the valves 238 and 239, and pure water in the pure water
replenishing tank 240 is sent into the high pressure pure water
feed vessel with a pump 232 through an ion-exchanger tower 233 and
filter 234.
[0189] The resistivity of pure water is measured with a resistivity
meter 235. Pure water is circulated through the ion-exchanger tower
233 for ion-exchange treatment until the resistivity becomes higher
than the prescribed value, since the catalyst electrode of the
electrolysis cell 201 is poisoned and the service life of the
electrolysis cell 201 is shortened when the resistivity of pure
water is too low.
[0190] The inside of the high pressure pure water feed tank 241 is
filled with pure water while enabling air bubbles to be removed,
when the pure water replenishing tank 240 is placed above the high
pressure pure water feed tank 241. Accordingly, the pressure
variation when the valves 236 and 237 are closed and the valves 238
and 239 are open only depends on the volume changes of pure water,
which may be substantially ignored.
[0191] Since pure water is circulated with the pump 232 at the
atmospheric pressure, the pump 232, ion-exchanger tower 233, filter
234 and resistivity meter 235 are all operated at the atmospheric
pressure.
[0192] Circulation of pure water with the pump 232 is terminated
depending on the resistivity of pure water measured by the
resistivity meter 235.
[0193] When a subsidiary tank having the same performance as the
high pressure pure water feed tank 241 is provided, the feed of
pure water in the high pressure oxygen tank 262 is never delayed by
allowing any one of them to be always ready.
[0194] Pure water in the high pressure oxygen vessel 262 serves as
a material of electrolysis by being sent into the electrolysis cell
201. Accordingly, when pure water stays for a long period of time
and water quality is decreased with a resistivity of, for example,
6 M.OMEGA./cm.sup.2 or less, the catalyst electrode of the
electrolysis cell 201 may be poisoned and the service life of the
electrolysis cell 201 may be shortened. Accordingly, it is
desirable to occasionally replace a part of pure water with fresh
pure water in order to prevent the quality of pure water in the
high pressure oxygen vessel 262 from being deteriorated.
[0195] Pure water in the high pressure oxygen vessel 262 is
exchanged by allowing pure water in the high pressure oxygen vessel
262 to flow into a pure water discharge tank 219 by opening the
valve 218, discharging pure water in the pure water discharge tank
219 into a water reservoir 223 by closing the valve 218 and opening
the valve 221, and replenishing fresh pure water with a volume
corresponding to the volume of discharged water form the high pure
water feed tank 241.
[0196] For reducing the pressure variation in the pure water
exchange work, the volume of the pure water discharge tank 219 is
preferably about 1% of the volume of the oxygen pool 252, and the
frequency of exchange of pure water may be about 10 times per day
(about 10%), although it depends on the amount of pure water
used.
[0197] Pure water permeated into the cathode from the anode of the
electrolysis cell 201 is discharged with the generated hydrogen
from the hydrogen discharge port 203 into the high pressure
hydrogen vessel 202, and pure water is collected at the bottom in
the high pressure hydrogen vessel 202.
[0198] The storage volume of the pure water is preferably about
twice of the volume of the oxygen pool 252 of the high pressure
oxygen vessel 262. The volume is controlled by sensing the water
surface 209 with the level meter 210, and pure water is allowed to
flow into the pure water reservoir 212 by opening the valve 211
when the volume of pure water has increased to above the prescribed
volume. The volume of the pure water reservoir 212 is determined so
that the pressure variation caused by opening the valve 211 and
allowing pure water to flow into the pure water reservoir 212 does
not exceed the allowable pressure resistance determined by the
pressure resistance of the electrolysis cell 201.
[0199] For example, suppose that the maximum pressure of generated
hydrogen in the high pressure hydrogen vessel 202 is 400 atm, the
volume of stored hydrogen is 20 liters, and the allowable pressure
of the electrolysis cell 201 is 4 atm, the pressure variation of
hydrogen in the operation to allow pure water to flow into the pure
water reservoir 212 by opening the valve 211 is calculated to be
400 atm.times.0.01=4 atm, with the proviso that the volume of the
pure water reservoir is 0.2 liters (1% of the volume of the stored
hydrogen).
[0200] Even when a differential pressure of more than 4 atm is
generated by accumulation of some factors, no differential pressure
exceeding the allowable value of the pressure resistance of the
electrolysis cell is generated by the action of the switching
valves 208 and 217.
[0201] In FIG. 9, the reference numeral 205 denotes a heat
exchanger for cooling the heat generated by electrolysis, the
reference numeral 206 denotes a heat exchanger for adjusting pure
water supplied to the electrolysis cell 201 to a desired
temperature, the reference numeral 213 denotes an electrical
resistance type level meter, the reference numeral 215 denotes a
pure water discharge pipe line, the reference numeral 220 denotes
an electrical resistance type level meter, the reference numeral
224 denotes a float type level meter, the reference numeral 225
denotes a water feed port, the reference numeral 227 denotes a
pump, the reference numeral 228 denotes an ion-exchanger tower, the
reference numeral 229 denotes a filter, the reference numeral 230
denotes a pure water resistivity meter, the reference numeral 231
denotes a float type level meter, the reference numeral 246 denotes
an emergency oxygen discharge port, the reference numeral 247
denotes an emergency oxygen discharge port, the reference numeral
248 denotes a pressure gauge, the reference numeral 249 denotes a
gas leak sensor for sensing the concentration of hydrogen in
oxygen, the reference numeral 258 denotes an emergency hydrogen
discharge valve, the reference numeral 259 denotes an emergency
hydrogen discharge port, and the reference numeral 260 denotes a
gas leak sensor for sensing the concentration of oxygen in
hydrogen.
[0202] FIG. 10 is a partial cross section showing the structure of
the differential pressure sensor used in the invention. As shown in
the drawing, the differential pressure sensor 253 comprises a main
unit 300 which has a cylinder 301 whose both ends are sealed with
bellows 306 and 307 expandable in the longitudinal direction by the
pressure of the high pressure hydrogen vessel 202 or high pressure
oxygen vessel 262 and filled with an inert fluid therein; an
internal magnetic body 304 provided to be freely slidable in an
axial direction in close contact with the inner face of the
cylinder 301; an external magnetic body 305 in close contact with
the outer surface of the cylinder 301 to move in cooperation with
the internal magnetic body 304 so as to be slidable; and a sensor
320 for sensing the differential pressure in cooperation with an
external magnetic body 305 slidable by expansion of the bellows 306
and 307.
[0203] The sensor 320 comprises a light shielding plate 319 movable
in cooperation with the external magnetic body 305; a display plate
316 comprising openings 317 and 318 shielded by the light shielding
plate 319; and a photoelectric meter (not shown) for converting the
transmission luminous energy of the light, after permeating through
the openings 317 and 318, into electrical signals.
[0204] In the differential pressure sensor 253 shown in FIG. 10,
hydrogen in the high pressure hydrogen vessel 202 is sent into a
hydrogen pressure compartment 310 through a hydrogen pipe line 312,
and oxygen in the high pressure oxygen vessel 262 is sent into an
oxygen pressure compartment 311 through an oxygen pipe line, and
the pressures in these compartments are transferred to the bellows
306 and 307, respectively.
[0205] Since a fluid such as a machine oil is filled in the bellows
306 and 307, and in the cylinder 301, the volume thereof
substantially shows no change with the pressures. Accordingly, the
bellows 306 and 307 are not crushed under the high pressure of
oxygen and hydrogen sent from the hydrogen pipe line 312 and oxygen
pipe line 313.
[0206] When the pressure of hydrogen sent from the hydrogen pipe
line 312 is equal to the pressure of oxygen sent from the oxygen
pipe line 313, the internal magnetic body 304 remains stopped at
the center of the cylinder 301, since the forces applied to the
bellows 306 and 307 from the hydrogen pressure compartment 310 and
oxygen pressure compartment 311, respectively, are equal.
[0207] However, when the pressure of hydrogen sent from the
hydrogen pipe line 312 is higher than the pressure of oxygen sent
from the oxygen pipe line 313, a spring 314 expands while a spring
315 contracts by the differential pressure, and the internal
magnetic body 305 displaces. to the oxygen pressure compartment 311
side by being pushed by fixing bars 302 and 303 to a position where
the differential pressure balanced with the force by expansion and
contraction of the springs 314 and 315, respectively.
[0208] Since the internal magnetic body 304 and external magnetic
body 305 are magnetically coupled by the magnetic force applied
between them, the external magnetic body 305 displaces in response
to the displacement of the internal magnetic body 304 with the
displacement of the light shielding plate 319 fixed to the external
magnetic body 305 to cover a part of the opening 318 at the oxygen
side. Consequently, the luminous energy passing through the opening
318 is reduced while the luminous energy passing through the
opening 317 remains unchanged.
[0209] When the pressure of hydrogen sent from the hydrogen pipe
line 312 is lower than the pressure of oxygen sent from the oxygen
pipe line 313, on the contrary, a part of the opening 317 at the
hydrogen side is covered with the light shielding plate 319, and
the luminous energy passing through the opening 317 decreases.
[0210] Which of the pressure of hydrogen sent from the hydrogen
pipe line 312 and the pressure of oxygen sent from the oxygen pipe
line 313 is higher, or the differential pressure between them, can
be determined by measuring the luminous energy passing through the
openings 317 and 318. Therefore, the differential pressure may be
adjusted to zero by controlling the amount of discharged oxygen by
controlling, for example, switching of the valve 244 and needle
valve 243 shown in FIG. 9.
[0211] While the method for sensing the position of the internal
magnetic body by measuring the luminous energy was explained in the
description above, this measurement may be performed using a slide
resistor. A slider is fixed to the external magnetic body 305, and
the slider is made to slide on the slide resistor in harmony with
the displacement of the slider integrated with the external
magnetic body 305, thereby measuring the distance of displacement
of the internal magnetic body 304.
[0212] FIGS. 11a and 11b are a cross section and side view,
respectively, showing the structure of a release valve 208 or 217
used in the system. As shown in the drawing, the release valve 208
or 217 comprises a discharge port 332 provided at a cylindrical
main unit of a valve 330; a cylinder 331 provided within the
cylindrical valve; a spring 333 interlocked to the cylinder 331,
the spring 333 being fixed with a screw 335 and a fixing nut 336 so
as to be able to adjust the spring force; a connection pipe line
338 to a pure water pipe line 216a or 216b for allowing pure water
in the high pressure hydrogen vessel 202 or high pressure oxygen
vessel 262 to transfer; and a ventilation port 337.
[0213] The release valve 208 and 217 are provided so as to adjust
the pressing strength of the spring 333 by loosening the fixing nut
336 and turning a screw head 334. Consequently, the cylinder 331
pushed up by the pressure of pure water transferred through the
connection pipe line 338 is located above the discharge port 332,
and enables pure water in the connection pipe line 338 to be
discharged from the discharge port 332 with a desired pressure (a
pressure determined by the allowable pressure of the cell). It is
also possible to tighten the fixing nut 336 so that the setting is
not changed.
[0214] The cylinder 331 starts to displace upward by the
contraction of the spring 333 due to a differential pressure
applied when the pressure in the atmosphere accommodating the main
unit 330 of the valve becomes higher than the pressure of pure
water in the connection pipe line 338. When the pressure of pure
water in the connection pipe line 338 is further increased, the
level of the cylinder 331 exceeds the level of the discharge port
332 to allow pure water in the connection pipe line 338 to be
discharged from the discharge port 332 to consequently reduce the
pressure in the connection pipe line 338. When the discharge port
332 is formed into an inverse triangle, the amount of pure water
discharged is reduced when the differential pressure is large while
it is increased when the differential pressure is small, serving to
promptly alleviate the differential pressure.
[0215] FIG. 12 is a cross section of the level meter taking
advantage of a large difference of electrical conductivity between
a gas such as oxygen and pure water. The level meter is used as the
level meter 250 in FIG. 9. The level meter comprises a main
electrode 350 having a rod-shaped central electrode 350a and a
concentric external electrode 350b disposed at the outside of the
central electrode 350a; and a sub-electrode 351 having the
rod-shaped central electrode 351a covered with an insulating
cylinder except the tip of the electrode and a concentric external
electrode 351b disposed at the outside of the central electrode
351a.
[0216] In the drawing, the reference numeral 352 denotes the
surface of pure water; the reference numerals 353a and 353b denote
ventilation holes; the reference numerals 354a and 345b denote
attachment members of the external electrodes 350b and 351b,
respectively; the reference numerals 355a and 355b denote
attachment members of the central electrodes 350a and 350b,
respectively; the reference numerals 356a and 356b denote
insulators; the reference numerals 357a and 357b denote fixing jigs
for attaching the external electrodes 350b and 351b, respectively;
the reference numeral 358 denotes an attachment flange; the
reference numerals 359a and 359b denote nuts for fixing the fixing
jigs 357a and 357b, respectively; the reference numerals 360a and
360b denote insulating plates; the reference numerals 361a and 361b
denote washers; the reference numerals 362a and 362b denote lead
wires; the reference numerals 363a and 363b denote washers; the
reference numerals 364a and 364b denote nuts for fixing the central
electrodes 350a and 350b; and the reference numerals 365a to 367b
denote o-rings.
[0217] When the central electrode 350a and external electrode 350b
in the level meter 250 so constructed as described above are
submerged into pure water, the resistance Rm of pure water filling
between the central electrode 350a and external electrode 350b can
be measured by connecting an electric resistance meter between the
lead wire 362a and the ground.
[0218] The resistance Rr between the tip of the central electrode
350b exposed without being covered with the insulating cylinder 368
and the external electrode 351b can be measured by measuring the
electrical resistance between the lead wire 362b and the
ground.
[0219] The length of the tip portion of the central electrode 351a
not covered with the insulating cylinder 368 is defined as Lr, and
each length of the central electrode 350a and external electrode
350b submerged in pure water is defined as Lx. Then, Lx is
determined by the following equation; Lx=Lr(Rr/Rm) (1)
[0220] The equation (1) above shows that the level of the surface
of pure water 352 is determined by calculating Lx.
[0221] While the resistivity of pure water is about 18
M.OMEGA./cm.sup.2 at the outlet of the ion-exchange resin tower, it
decreases with time as the concentration of ions are increased by
dissolving the wall of the pure water vessel. However, it is always
possible to sense an accurate water level irrespective of the time
dependent changes of resistivity of pure water, since the level is
corrected by measuring Rr.
[0222] Since the gases such as hydrogen and oxygen are electric
insulators, the electrical resistance between the lead wire 364a
and the ground is determined only by the electrical resistance of
pure water in which the central electrode 350a and external
electrode 350b are dipped, and the effect of the electrical
resistance of oxygen or hydrogen may be ignored.
[0223] Since all the materials as well as the central electrode
350a and external electrode 350b have excellent pressure resistance
in structures and characteristics, the level meter 250 may be used
without any pressure limitations as in the conventional float type
level meter.
[0224] Although the materials of the electrode may be corroded by
electrolysis when electricity is applied between the electrodes in
an environment in which high pressure oxygen and hydrogen exist
together, these problems can be avoided by pulse measurements or by
plating the central electrodes 350a and 351a and external
electrodes 350b and 351b with a precious metal, such as titanium or
platinum, that is resistant to corrosion. Furthermore, since the
electrical resistance Rr between the lead wire 364a and the ground
is measured as the resistivity of pure water, the measured value
can be used for evaluating the quality of pure water for
determining the frequency of exchange of pure water in the high
pressure vessel of pure water and oxygen 262.
[0225] FIG. 13 shows another example of the system for generating
high pressure hydrogen according to the invention. The electrolysis
cell 201 is designed to be accommodated in a hydrogen atmosphere
generated in the high pressure hydrogen vessel 202, as in the
system previously described. While the system also comprises the
high pressure oxygen vessel 262 for storing pure water to be
electrolyzed, returned pure water and oxygen generated, it also
comprises a pressure controller 270 in place of the differential
pressure sensor 253, and the discharge valves 208 and 217 are
omitted therefrom.
[0226] The pressure controller 270 functions to alleviate the
differential pressure by allowing pure water between the high
pressure oxygen vessel 262 and high pressure hydrogen vessel 202 to
move from the vessel having a higher pressure to the vessel having
a lower pressure based on the differential pressure between
them.
[0227] When the pressure in the high pressure oxygen vessel 262
becomes larger than the pressure in the high pressure hydrogen
vessel 202, pure water in high pressure oxygen vessel 262 flows
into the pressure controller 270, and the same volume of pure water
is pushed back to the high pressure hydrogen vessel 202 from the
pressure controller 270. Consequently, the pressure in the high
pressure oxygen vessel 262 is reduced as the volume of pure water
decreases with an increase of the volume of the oxygen pool 252,
and the pressure in the high pressure hydrogen vessel 202 increases
as the volume of pure water is increased, thereby alleviating the
pressure differential.
[0228] The pressure controller 270 senses the transferred volume of
pure water, and controls switching of the valve 244 and needle
valve 243 with the controller (not shown). Consequently, pure water
transferred to the high pressure hydrogen vessel 202 side returns
to the high pressure oxygen vessel 262. Then, the volume of oxygen
discharged from the oxygen discharge port 245 is controlled to
prevent further transfer of pure water in order to even the
pressure.
[0229] Since the method for controlling the amount of hydrogen
generated from the hydrolysis cell 201 so that the pressure of
hydrogen is maintained at a prescribed pressure by controlling the
amount of electricity supplied from the power source 261 to the
electrolysis cell 201, the method for replenishing pure water to
and discharging pure water from the high pressure oxygen vessel
262, and the method for discharging pure water from the high
pressure hydrogen vessel 202 are the same as those described in the
system in FIG. 9, descriptions thereof are omitted.
[0230] FIG. 14a shows a partial cross section of the pressure
controller 270, and FIG. 14b shows a cross section of the pressure
controller along the line A-A' in FIG. 14a. The pressure controller
270 comprises a main unit 390 of the pressure controller having a
hollow cylinder 370 made of a non-magnetic material, an internal
slider 371 sliding in close contact with the inner surface of the
hollow cylinder 370 and made of a magnetic material, and an
external slider 372 sliding in contact with the external surface of
the hollow cylinder 370 and made of a magnetic material; and a
positional sensor 400 for sensing the position of the external
slider 372. Pure water 384 in the high pressure hydrogen vessel 202
is introduced into one half of the hollow cylinder 370 partitioned
by the internal slider 371, and pure water 385 in the high pressure
oxygen vessel 262 is introduced into the other half.
[0231] Pure water 384 in the high pressure hydrogen vessel 202 is
isolated from pure water 385 in the high pressure oxygen vessel 262
by the internal slider 371. Accordingly, pure water 384 is never
mixed with pure water 385. When the pressure in the high pressure
hydrogen vessel 202 is equal to the pressure in the high pressure
oxygen vessel 262 and no differential pressure is generated between
the vessels, the internal slider 371 is set to position at the
center of the hollow cylinder 370.
[0232] Accordingly, when the pressure in the high pressure oxygen
vessel 202 becomes higher than the pressure in the high pressure
oxygen vessel 262, pure water in the high pressure oxygen vessel
202 flows into the hollow cylinder 370 from the pipe line 375 to
reduce the pressure in the high pressure oxygen vessel 202.
Consequently, the internal slider 371 is pushed so as to increase
the volume of pure water 384 by allowing pure water to flow into
the hollow cylinder 370, and pure water 385 overflowing due to the
reduced volume flows into the pure water and high pressure oxygen
vessel 262 through the pipe line 376, thereby automatically
alleviating the generated pressure differential since the pressure
of oxygen is reduced due to the reduced volume of oxygen in the
high pressure oxygen vessel 262.
[0233] The internal slider 371 moves to a position displaced to a
spring 383 side from the center. Since the internal slider 371 is
magnetically coupled with the external slider 372, the external
slider 372 moves to the same position with the same displacement of
a light shielding plate 377 that is fixed to the external slider
372 by a fixing bar 381 to cover a part of an opening 380, thereby
reducing the luminous energy permeating through the opening
380.
[0234] Since the direction and length of displacement of the
internal slider 371 are determined by comparing the luminous energy
permeating through the opening 380 with the luminous energy
permeating through the opening 379, the aperture of the needle
valve 243 is controlled with the controller (not shown) so that the
internal slider 371 returns to the original central position by
comparing the transmission luminous energy of the opening 380 with
the transmission luminous energy of the opening 379.
[0235] The positional sensor 400 for comparing the luminous energy
of the pressure controller 270 has the same construction and
function as those of the sensor 320 of the differential pressure
sensor 253.
[0236] The volume of oxygen discharged from the oxygen discharge
port 245 are controlled by controlling the aperture of the needle
valve 243 so that the internal slider 371 always stays at the
central position as described above. Therefore, high pressure
hydrogen can be generated without applying a differential pressure
to the electrolysis cell 201.
[0237] When the pressure in the high pressure hydrogen vessel 202
remains higher than the pressure in the high pressure oxygen vessel
262, and the displacement of the internal slider 371 cannot be
stopped even after the control as described above, the internal
slider 371 strikes the spring 383. Since the internal slider 371
cannot move any more without pressing the spring 371, no
restriction is imposed on the movement of the internal slider 371
until the internal slider 371 comes to this position. Therefore,
substantially no differential pressure is generated during this
period.
[0238] However, when the internal slider 371 strikes the spring
383, the internal slider 371 cannot move any more unless it pushes
the spring 383. In other words, the differential pressure cannot be
controlled by the movement of the internal slider 371. However,
when a by-pass flow passageway 374 is provided, the spring 383
contracts to permit pure water in the high pressure hydrogen vessel
202 to directly flow into the high pressure oxygen vessel 262
through the by-pass flow passageway 374, thereby preventing the
pressure differential to increase above a prescribed pressure.
[0239] Permitting pure water in the high pressure hydrogen vessel
202 to directly flow into the high pressure oxygen vessel 262
through the by-pass flow passageway 374 indicates that some
abnormal states have emerged making it impossible to control the
operation of the system only by controlling the aperture of the
needle valve 243 by the controller (not shown). Accordingly, an
emergency shut-off switch (not shown) and emergency discharge
valves 247 and 258 are provided for an emergency stop in these
abnormal states, whereby the power source 261 of the electrolysis
cell 201 is shut down while all the valves except the valve 258 are
closed, and generation of hydrogen and oxygen from the hydrolysis
cell 201 is halted in order to promptly decrease the pressure of
the high pressure hydrogen vessel 202.
[0240] A nitrogen pipe line is also provided for purging the
insides of the high pressure oxygen vessel 262 and high pressure
hydrogen vessel 202 with nitrogen, in order to safely stop the
system, although it is not illustrated in FIG. 13.
[0241] It is a countermeasure for protecting the electrolysis cell
201 from being broken by a pressure exceeding the pressure
resistance to set the strength of the springs 382 and 383 so that
the pressure differential for allowing pure water to flow into the
by-pass flow passageways 373 or 374 as a result of pressing the
spring 383 by the internal slider 371 to fall within the allowable
pressure resistance of the electrolysis cell 201.
[0242] When the volume of the hollow cylinder 370, except the
volume of the slider 371, is adjusted to be equal to the oxygen
pool 252 in the high pressure vessel 262, +50% of the pressure
differential may be alleviated before operating the emergency
shut-off mechanism.
[0243] FIGS. 15 and 16 show partial cross sections of different
pressure controllers 270. The pressure controllers 270 shown in
these drawings comprises a pure water pipe line 413 in parallel to
the pressure controller 270 with an intermediate shut-off valve
420, and switches 411 and 412 for switching the valve.
[0244] In the pressure controller 270, the internal slider 371
permits the cut-off valve 420 to open by means of the switches 411
and 412 at both ends, when the differential pressure is increased
beyond the controllable level by the displacement of the internal
slider 371 and the internal slider 371 causes the spring 383 to
contract. For example, pure water in the high pressure hydrogen
vessel 202 is allowed to directly flow into the high pressure
oxygen vessel 262 through the pure water pipe line 413 so that the
differential pressure does not increase above a prescribed
pressure.
[0245] FIG. 17 is a cross section showing the structure and
attachment of the electrolysis cell used in the system 501 for
generating high pressure hydrogen according to the invention.
[0246] The electrolysis cell 503, a double polarity multi-layered
type electrolysis cell, is housed in the high pressure hydrogen
vessel 502 in the vertical direction.
[0247] As is evident in FIG. 17, the electrolysis cell 503
comprises, between a disk-shaped main cathode 504 and main anode
505, a plurality of ring-shaped polyelectrolyte membranes 506
having platinum catalyst layers on both faces thereof, and a
plurality of annular double polarity electrodes 507 made of a
porous electrode 511 laminated with interposition of a division
wall 516 between opposed porous electrodes 511 in the vertical
direction. The electrolysis cell is mounted on a mounting table 517
provided in the high pressure hydrogen vessel 502, and the main
anode 505 is compressed downward with a compression jig 523
compressed with a spring member 519.
[0248] The compression jig 523 comprises a cylindrical main unit
518 of the jig fixed on the electrolysis cell 503, a spring member
519 attached in the main unit 518 of the jig, and a press screw 520
having one end secured in the high pressure vessel 502 so as to
energize the spring member 519. While one set of the compression
jigs is shown in FIG. 17 for the convenience of illustration, a
plurality of compression jigs are symmetrically arranged to evenly
compress the electrolysis cell 503. However, the electrolysis cell
503 may also be compressed by hydraulic pressure.
[0249] The electrolysis cell 503 is formed by laminating a
plurality of double polarity electrodes 507. A discharge passageway
A of oxygen and pure water is provided by forming permeation holes
509 on the outer circumference of each double polarity electrode
507 so as to communicate the holes with each other in the vertical
direction. Discharge ports 512 of oxygen and pure water are formed
at the anode side of each double polarity electrode 507 to face the
gas discharge passageway A, and oxygen generated and pure water not
electrolyzed are discharged to the outside of the high pressure
vessel 502 through the discharge port 512, oxygen and pure water
discharge passageway A and oxygen discharge pipe line 542. A
hydrogen and pure water discharge port 510 is formed, on the other
hand, in the radial direction in order to directly discharge
hydrogen generated from the cathode and permeating pure water into
the high pressure vessel.
[0250] A pure water feed passageway B is formed at the center of
the electrolysis cell 503 for feeding electrolysis pure water
through permeation holes 508, which are formed at the center of
each double polarity electrode 507 so as to communicate with each
other in the vertical direction. This pure water feed passageway B
is connected to a pure water feed pipe line 547 for feeding pure
water from the outside of the high pressure vessel 502, and pure
water is supplied to the porous electrode 511 through pure water
feed ports 508a formed at the anode side in contact with the pure
water feed passageway B.
[0251] A lead wire 532 for supplying an electric power from the
outside is connected at the top of the electrolysis cell 503.
[0252] While the compression force on the polyelectrolyte membrane
506 is adjusted not to crush the polyelectrolyte membrane 506 by
compressing it with the compression jig 523, the allowable range of
adjustment is so narrow that the polyelectrolyte membrane may be
crushed. Accordingly, an annular sheet of a seal member 524 is
placed at the outside on the outer circumference of the
polyelectrolyte membrane 506 so that the polyelectrolyte membrane
506 is not crushed even by applying excess compression force.
[0253] This seal member 524 is thinner and harder than the
polyelectrolyte membrane 506, and is formed into a ring using a
material such as a plastic being excellent in electrical
insulation. While the relation between the thickness of the
polyelectrolyte membrane 506 and the thickness of the seal member
524 should be appropriate for attaining seal characteristics, it
can be confirmed by clamping the polyelectrolyte membrane 506 and
seal member 524 with the double polarity electrodes 507, and by
measuring electric resistance after compressing under a prescribed
pressure.
[0254] When the seal characteristics have been determined to be
inappropriate, the combination of the polyelectrolyte membrane 506
and seal member 524 is changed, or a seal material with a proper
thickness is selected from the plural seal members 524 each having
a different thickness, in order to select a combination with
desirable electrical resistance.
[0255] It is preferable to provide an annular seal member around
the permeation hole 508 constituting the pure water feed passageway
B to improve sealing performance between the pure water feed
passageway B and the electrode.
[0256] For preventing the polyelectrolyte membrane 506 and the
sheet of the seal member 524 from being crushed by the weight of
the double polarity electrode 507, it is desirable to restrict the
number of the laminated double polarity electrodes 507, and to
dispose a plurality of laminated electrodes as a cascade.
[0257] The main cathode 504 may be in electrical continuity with
the high pressure hydrogen vessel 502 by allowing it to contact the
mounting table 517, and the main anode 505 may be insulated from
the high pressure hydrogen vessel 502. When the high pressure
hydrogen vessel 502 is connected to the ground (not shown), the
main cathode 504 is grounded while the main anode 505 is insulated
from the ground potential. Consequently, an electric power is
supplied to the electrolysis cell 503 by connecting a power source
between a current introduction terminal 527 and the ground. Pure
water is supplied from the pure water feed pipe line 547 through
each pure water feed port 508a provided at the anode in contact
with the pure water feed port B to the porous electrode 511, when
electric power necessary for electrolysis of water is supplied to
the main anode from the current introduction terminal 527 through
the lead wire 532. Oxygen generated by electrolysis of pure water,
and pure water not electrolyzed are collected into the oxygen and
pure water discharge passageway A having the plural permeation
holes 509 through each discharge port 512, and returns to a high
pressure vessel (not shown) for storing high pressure oxygen
through the oxygen discharge pipe line 542.
[0258] Hydrogen generated at the cathode and permeated pure water
are directly discharged into the high pressure vessel 502 from the
discharge port 510, and permeated pure water is discharged from a
pure water discharge pipe line 548 and is collected in a waste
water tank (not shown). Hydrogen pooled in the high pressure vessel
502 is retrieved from a hydrogen feed port 538 formed in the high
pressure vessel 502.
[0259] It is possible to reduce the differential pressure acting
between both ends of the polyelectrolyte membrane 506, and the
differential pressure acting at the seal member 524 between the
double polarity electrodes 507 sealed with the polyelectrolyte
membrane 506, to zero, by controlling the oxygen pressure of a high
pressure vessel (not shown) for pooling oxygen to be equal to the
hydrogen pressure in the high pressure vessel 502. Usually, the
differential pressure between hydrogen and oxygen is controlled
within the pressure resistance of the electrolysis cell 503, in
order to protect the polyelectrolyte membrane 506 from being
broken, and in order to prevent oxygen from leaking into the high
pressure vessel 502 from the seal member 524, even when the
hydrogen pressure pooled in the high pressure vessel 502 has
exceeded the pressure resistance of the cell.
[0260] FIG. 18 shows a disassembled perspective view of the
electrolysis cell 503 shown in FIG. 17. The electrolysis cell 503
is composed of the annular polyelectrolyte membranes 506, the
plural annular sheets of seal members 524 provided at the outer
circumference of the polyelectrolyte membrane, and the plural
annular double polarity electrodes 507 having the same diameter as
each other. The polyelectrolyte membranes, seal members and double
polarity electrodes are laminated in the vertical direction between
the main cathode 504 and main anode 505. A discharge port 512 for
discharging oxygen generated and pure water not electrolyzed out of
the high pressure vessel 502 is provided at the anode side of each
member, and a discharge hole 510 for directly discharging hydrogen
generated and permeated pure water into the high pressure vessel
502 is provided at the cathode side of each member.
[0261] A permeation hole 508 for forming the pure water feed
passageway B for feeding electrolysis pure water is provided at the
center of each member except the main anode 505, and a pure water
feed port 508a for feeding pure water to the anode is formed within
each double polarity electrode 507. A seal member 505a for sealing
the terminal of the pure water feed passageway B, a hole and a pure
water feed port 508a connected to the hole, and an oxygen and pure
water discharge port 512 are provided at the main anode 505.
[0262] A discharge port 510 is provided at the side wall of each
double polarity electrode 507 in order to discharge hydrogen
generated at the cathode and permeated pure water into the high
pressure vessel 502.
[0263] Accordingly, as is evident from FIG. 18, pure water supplied
from the pure water feed passageway B formed at the center of the
main cathode 504 is delivered to each porous electrode 511 at the
anode side from the pure water feed port 508a. Oxygen generated at
the anode and pure water not electrolyzed flows into the oxygen
discharge passageway A from the oxygen and pure water discharge
port 512, and is retrieved to the outside of the high pressure
vessel 502 through the oxygen discharge pipe line 542. Hydrogen
generated at the cathode and permeated pure water is directly
discharged into the high pressure vessel 502 from the hydrogen and
pure water discharge port 510.
[0264] The porous electrode 511 comprises a titanium mesh, and both
end faces thereof are fixed to the inner wall of the double
polarity electrode 507 by welding. The surfaces of the mesh for
contacting the polyelectrolyte membrane 506 having platinum
catalyst formed on both surfaces are finished as a smooth surface
by polishing, and comprises a carbon coating film deposited by ECR
plasma deposition on the surface thereof.
[0265] Each member constituting the electrolysis cell 503 in FIG.
18 has positioning grooves 522 at the outer circumference in the
axial direction in order to facilitate assembling of the
members.
[0266] FIG. 19 illustrates a flow pattern of pure water supplied to
the anode of the electrolysis cell. The arrows in the drawing show
pure water streams. Pure water is supplied from the pure water feed
passageway B provided at the center to the pure water feed port
508a, and flows toward the inner circumference wall of the double
polarity electrode 507 by being spread through an angle of
360.degree.. The streams are tapered, and pure water flows into the
oxygen discharge passageway A comprising the permeation holes 509
through the oxygen and pure water discharge ports 512 that are
symmetrically arranged.
* * * * *