U.S. patent application number 11/050931 was filed with the patent office on 2006-06-08 for system for generating hydrogen and method thereof.
Invention is credited to Justin Damien Baltrucki, Lawrence Clinton Moulthrop, Michael Aaron Spaner.
Application Number | 20060118428 11/050931 |
Document ID | / |
Family ID | 36572979 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060118428 |
Kind Code |
A1 |
Baltrucki; Justin Damien ;
et al. |
June 8, 2006 |
System for generating hydrogen and method thereof
Abstract
An electrochemical system having a plurality of discrete
electrochemical cell stacks is described. The system includes a
water-oxygen management system fluidly coupled to the plurality of
electrochemical cell stacks and a hydrogen management system
fluidly coupled to the plurality of electrochemical cells. A means
for ventilating the system and a control system for monitoring and
operating said electrochemical system, said control system
including a means for detecting abnormal operating conditions and a
means for degrading the performance of said electrochemical system
in response to said abnormal condition.
Inventors: |
Baltrucki; Justin Damien;
(Marlborough, CT) ; Spaner; Michael Aaron; (Deep
River, CT) ; Moulthrop; Lawrence Clinton; (Windsor,
CT) |
Correspondence
Address: |
PROTON ENERGY SYSTEM
10 TECHNOLOGY DRIVE
WALLINGFORD
CT
06492
US
|
Family ID: |
36572979 |
Appl. No.: |
11/050931 |
Filed: |
February 4, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11004185 |
Dec 3, 2004 |
|
|
|
11050931 |
Feb 4, 2005 |
|
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Current U.S.
Class: |
205/637 |
Current CPC
Class: |
Y02E 60/36 20130101;
C25B 1/04 20130101; C25B 15/02 20130101; Y02E 60/366 20130101 |
Class at
Publication: |
205/637 |
International
Class: |
C25B 1/02 20060101
C25B001/02 |
Claims
1. A method of generating hydrogen gas comprising the steps of:
disassociating hydrogen from a reactant; forming hydrogen gas;
monitoring a pressure of said hydrogen gas; comparing said pressure
of said hydrogen gas to a threshold parameter; and, generating a
signal in response to said pressure being less than said threshold
parameter.
2. The method of generating hydrogen gas of claim 1, further
comprising the step of monitoring the amount of time said pressure
is below said threshold parameter.
3. The method of generating hydrogen gas of claim 2 further
comprising the step of stopping the generation of said hydrogen in
response to said signal.
4. The method of generating hydrogen gas of claim 3 wherein said
signal is generated if said pressure is below said threshold
parameter for a predetermined amount of time.
5. The method of generating hydrogen gas of claim 4 wherein said
threshold parameter is at least 10% below the desired operating
pressure.
6. The method of generating hydrogen gas of claim 5 wherein said
threshold parameter is 180 psi.
7. The method of generating hydrogen gas of claim 6 wherein said
predetermined amount of time is 200 seconds.
8. A method of generating hydrogen gas comprising the steps of:
electrochemically separating hydrogen from water; forming hydrogen
gas; monitoring a pressure of said gas; comparing said pressure to
a minimum threshold parameter; measuring the length of time said
pressure is less than said minimum threshold parameter; and,
generating a signal if said length of time exceeds a second
parameter.
9. The method of generating hydrogen gas of claim 8 further
comprising the step of stopping said disassociation of said
hydrogen from said water in response to said signal.
10. The method of generating hydrogen gas of claim 9 wherein said
minimum threshold parameter is 10% less than a desired operating
pressure.
11. The method of generating hydrogen gas of claim 10 wherein said
minimum threshold parameter is 180 psi.
12. A system for generating hydrogen gas comprising: at least one
electrochemical cell; a hydrogen management system coupled fluidly
coupled to said at least one electrochemical cell; a pressure
sensor coupled to said hydrogen management system; and, a control
panel electrically coupled to said pressure sensor.
13. The system for generating hydrogen gas of claim 12 wherein said
pressure sensor includes a means for generating a signal indicative
of an actual pressure.
14. The system for generating hydrogen gas of claim 13 wherein said
control panel includes means comparing said actual pressure signal
to a threshold parameter.
15. The system for generating hydrogen gas of claim 14 wherein said
control panel is electrically connected to said at least one
electrochemical cell.
16. The system for generating hydrogen gas of claim 15 wherein said
control panel further includes means for stopping the operation of
said at least one electrochemical cell.
17. The system for generating hydrogen gas of claim 16 wherein said
threshold parameter is 10% less than a desired operating
pressure.
18. The system for generating hydrogen gas of claim 17 wherein said
threshold parameter is 180 psi.
19. The system for generating hydrogen gas of claim 18 wherein said
control panel further includes a timer means for monitoring the
length of time said actual pressure is less than said threshold
parameter.
20. The system for generating hydrogen gas of claim 19 wherein said
control panel timer means further includes a means for generating a
signal when said length of time exceeds a predetermined time
parameter.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a Continuation-In-Part
application and claims priority to patent application Ser. No.
11/004,185 filed on Dec. 3, 2004 which is incorporated herein by
Reference.
FIELD OF INVENTION
[0002] The present disclosure relates to an electrochemical cell
system and especially relates to a system for stopping the
generation of hydrogen in the event of a fault condition.
BACKGROUND OF INVENTION
[0003] Electrochemical cells are energy conversion devices, usually
classified as either electrolysis cells or fuel cells. An
electrolysis cell functions as a hydrogen generator by
electrolytically decomposing water to produce hydrogen and oxygen
gases, and functions as a fuel cell by electrochemically reacting
hydrogen with oxygen to generate electricity. Referring to FIG. 1,
a partial section of a typical proton exchange membrane
electrolysis cells is detailed. In a typical anode feed water
electrolysis cell (not shown), process water is fed into a cell on
the side of the oxygen electrode (in an electrolytic cell, the
anode) to form oxygen gas, electrons, and protons. The electrolytic
reaction is facilitated by the positive terminal of a power source
electrically connected to the anode and the negative terminal of
the power source connected to a hydrogen electrode (in an
electrolytic cell, the cathode).
[0004] The oxygen gas and a portion of the process water exit the
cell, while protons and water migrate across the proton exchange
membrane to the cathode where hydrogen gas is formed. In a cathode
feed electrolysis cell (not shown), process water is fed on the
hydrogen electrode, and a portion of the water migrates from the
cathode across the membrane to the anode where protons and oxygen
gas are formed. A portion of the process water exits the cell at
the cathode side without passing through the membrane. The protons
migrate across the membrane to the cathode where hydrogen gas is
formed. The typical electrochemical cell system includes a number
of individual cells arranged in a stack, with the working fluid
directed through the cells via input and output conduits formed
within the stack structure. The cells within the stack are
sequentially arranged, each including a cathode, a proton exchange
membrane, and an anode.
[0005] In certain conventional arrangements, the anode, cathode, or
both are gas diffusion electrodes that facilitate gas diffusion to
the membrane. Each cathode/membrane/anode assembly (hereinafter
"membrane electrode assembly", or "MEA") is typically supported on
both sides by flow fields comprising screen packs or bipolar
plates. Such flow fields facilitate fluid movement and membrane
hydration and provide mechanical support for the MEA. Since a
differential pressure often exists in the cells, compression pads
or other compression means are often employed to maintain uniform
compression in the cell active area, i.e., the electrodes, thereby
maintaining intimate contact between flow fields and cell
electrodes over long time periods. Pumps are used to move the
reactants and products to and from the electrochemical cell, which
is connected to the liquid and gas storage devices by a system of
pipes. This use of external pumps and storage areas both limits the
ease with which electrochemical cells may be transported, and
complicates the use of electrochemical cells in locations where
pumps and storage tanks are difficult to introduce or operate.
While existing electrochemical cell systems are suitable for their
intended purposes, there still remains a need for improvements,
particularly regarding operation of electrochemical cell systems
with multiple electrochemical cell stacks and their operation.
SUMMARY OF INVENTION
[0006] A method of generating hydrogen gas including the steps of
disassociating hydrogen from a reactant to form hydrogen gas.
Monitoring a pressure of the hydrogen gas and comparing the
pressure of the hydrogen gas to a threshold parameter. Finally
generating a signal in response to the pressure being less than the
threshold parameter.
[0007] A method of generating hydrogen gas including the steps of
electrochemically separating hydrogen from water. Forming hydrogen
gas and monitoring the pressure of the hydrogen gas. Comparing the
hydrogen gas pressure to a minimum threshold parameter. Measuring
the length of time the hydrogen gas pressure is less than the
minimum threshold parameter and finally, generating a signal if
said length of time exceeds a second parameter.
[0008] A system for generating hydrogen gas having at least one
electrochemical cell. A hydrogen management system coupled fluidly
coupled to the electrochemical cell. A pressure sensor coupled to
said hydrogen management system and a control panel electrically
coupled to said pressure sensor.
BRIEF DESCRIPTION OF DRAWINGS
[0009] Referring now to the drawings, which are meant to be
exemplary and not limiting, and wherein like elements are numbered
alike:
[0010] FIG. 1 is a schematic diagram of a partial prior art
electrochemical cell showing an electrochemical reaction;
[0011] FIG. 2 is an illustration in a perspective view of an
exemplary embodiment of a hydrogen generation system;
[0012] FIG. 3 is an illustration of a piping and instrumentation
diagram of the hydrogen generation system of FIG. 2;
[0013] FIG. 4 is a perspective view illustration of the water
management system of FIG. 2;
[0014] FIG. 5 is a perspective view illustration of a oxygen-water
phase separator and water management manifold of FIG. 2;
[0015] FIG. 6 is a plan view illustration of a water deionizing
filter and water restrictor of FIG. 2;
[0016] FIG. 7 is a state transition diagram illustrating an
exemplary embodiment for control methodology in degraded modes of
operation due to excessive LEL levels;
[0017] FIG. 8 is a state transition diagram illustrating an
exemplary embodiment for control methodology in degraded modes of
operation due to high water temperature;
[0018] FIG. 9 is a state transition diagram illustrating an
exemplary embodiment for control methodology in degraded modes of
operation due to high or low electrochemical cell voltage;
[0019] FIG. 10 is a state transition diagram illustrating an
exemplary embodiment for control methodology in degraded modes of
operation due to a power supply failure;
[0020] FIG. 11 is a state transition diagram illustrating an
exemplary embodiment for control methodology in degraded modes of
operation due to low inlet ionized water flow.
[0021] FIG. 12 is a state transition diagram illustrating an
exemplary embodiment for control methodology in low system output
pressure conditions.
DETAILED DESCRIPTION
[0022] Hydrogen gas is a versatile material having many uses in
industrial and energy application ranging from the production of
ammonia, and cooling of electrical generators to the powering of
vehicles being propelled into space. While being the most abundant
element in the universe, hydrogen gas is not readily available, and
must be extracted from other material. Typically, large production
facilities which reform methane through a steam reduction process
are used to create large quantities of hydrogen gas which is then
stored in containers or tanks and shipped to a customer for use in
their application.
[0023] Increasing, due to logistics and security concerns, it has
become more desirable to produce the hydrogen closer to the end
point of use. The most desirable method of production allows the
user to produce the hydrogen as it is needed at the point of use.
To achieve this, hydrogen generators typical disassociate hydrogen
from a reactant fuel source such as water, natural gas, propane, or
methane. In the exemplary embodiment, water electrolysis is used to
produce the hydrogen gas as it is needed. Referring to FIG. 1 and
FIG. 2, and electrochemical system 12 of the present invention is
shown. Electrochemical cells 14 typically include one or more
individual cells arranged in a stack, with the working fluids
directed through the cells within the stack structure. The cells
within the stack are sequentially arranged, each including a
cathode, proton exchange membrane, and an anode (hereinafter
"membrane electrode assembly", or "MEA" 119) as shown in FIG. 1.
Each cell typically further comprises a first flow field in fluid
communication with the cathode and a second flow field in fluid
communication with the anode. The MEA 119 may be supported on
either or both sides by screen packs or bipolar plates disposed
within the flow fields, and which may be configured to facilitate
membrane hydration and/or fluid movement to and from the MEA
119.
[0024] Membrane 118 comprises electrolytes that are preferably
solids or gels under the operating conditions of the
electrochemical cell. Useful materials include, for example, proton
conducting ionomers and ion exchange resins. Useful proton
conducting ionomers include complexes comprising an alkali metal
salt, alkali earth metal salt, a protonic acid, a protonic acid
salt or mixtures comprising one or more of the foregoing complexes.
Counter-ions useful in the above salts include halogen ion,
perchloric ion, thiocyanate ion, trifluoromethane sulfonic opn,
borofuoric ion, and the like. Representative examples of such salts
include, but are not limited to, lithium fluoride, sodium iodide,
lithium iodide, lithium perchlorate, sodium thiocyanate, lithium
trifluoromethane sulfonate, lithium borofluoride, lithium
hexafluorophosphate, phosphoric acid, sulfuric acid,
trifluoromethane sulfonic acid, and the like. The alkali metal
salt,. alkali earth metal salt, protonic acid, or protonic acid
salt can be complexed with one or more polar polymers such as a
polyether, polyester, or polyimide, or with a network or
cross-linked polymer containing the above polar polymer as a
segment. Useful polyethers include polyoxyalkylenes, such as
polyethylene glycol, polyethylene glycol monoether, and
polyethylene glycol diether; copolymers of at least one of these
polyethers, such as poly(oxyethylene-co-oxypropylene)glycol,
poly(oxyethylene-co-oxypropylene)glycol monoether, and
poly(oxyethylene-co-oxypropylene)glycol diether; condensation
products of ethylenediamine with the above polyoxyalkylenesl; and
esters, such as phosphoric acid esters, aliphatic carboxylic acid
esters or aromatic carboxylic acid esters of the above
polyoxyalkylenes. Copolymers of, e.g., polyethylene glycol
monoethyl ether with methacrylic acid exhibit sufficient ionic
conductivity to be useful.
[0025] Ion-exchange resins useful as proton conducting materials
include hydrocarbon and fluorocarbon-type resins. Hydrocarbon-type
ion-exchange resins include phenolic resins, condensation resins
such as phenol-formaldehyde, polystyrene, styrene-divinyl benzene
copolymers, styrene-butadiene copolymers, styrene,
styrene-divinylbenzene-vinylchloride terpolymers, and the like,
that can be imbued with cation-exchange ability by sulfonation, or
can be imbued with anion-exchange ability by chloromethylation
followed by conversion to the corresponding quatemary-amine.
[0026] Fluorocarbon-type ion-exchange resins can include, for
example, hydrates of tetrafluoroethylene-perfluorosulfonyl
ethoxyvinyl ether or tetrafluoroethylene-hydroxylated
(perfluorovinylether) copolymers and the like. When oxidation and
or acid resist is desirable, for instance, at the cathode of a fuel
cell, fluorocarbon-type resins having sulfonic, carboxylic and/or
phosophoric acid functionality are preferred. Fluorocarbon-type
resins typically exhibit excellent resistance to oxidation by
halogen, strong acids, and bases. One family of fluorocarbon-type
resins having sulfonic acid group functionality is NAFION.TM.resins
(commercially available from E.I. du Pont de Nemours and Company,
Wilmington, Del.).
[0027] Electrodes 114 and 116 comprise catalyst suitable for
performing the needed electrochemical reaction (i.e. electrolyzing
water to produce hydrogen and oxygen). Suitable electrodes
comprise, but are not limited to, platinum, palladium, rhodium,
carbon, gold, tantalum, tungsten, ruthenium, iridium, osmium, and
the like, as well as alloys and combinations comprising one or more
of the foregoing materials. Electrodes 114 and 116 can be formed on
membrane 118, or may be layered adjacent to, but in contact with or
in ionic communication with, membrane 118.
[0028] Flow field members (not shown) and support membrane 118,
allow the passage of system fluids, and preferably are electrically
conductive, and may be, for example, screen packs or bipolar
plates. The screen packs include one or more layers of perforated
sheets or a woven mesh formed from metal or strands. These screens
typically comprise metals, for example, niobium, zirconium,
tantalum, titanium, carbon steel, stainless steel, nickel, cobalt
and the like, as well as alloys and combinations comprising one or
more of the foregoing metals. Bipolar plates are commonly porous
structures comprising fibrous carbon, or fibrous carbon impregnated
with polytetrafluoroethylene or PTFE (commercially available under
the trade name TEFLON.RTM. from E.I. du Pont de Nemours and
Company).
[0029] Referring now to FIG. 2 and FIG. 3, after the water is
disassociated in the electrochemical cells 14 into hydrogen and
oxygen gas, the respective gases leave the electrochemical cells 14
for further downstream processing. The oxygen, mixed with process
water which was not decomposed, is directed into a water oxygen
management system 16 (herein after referred to as "WOMS"). The WOMS
16 maintains all of the water fluid functions within the
electrochemical system 12, including separating the oxygen gas from
the water, manifolding of water lines, monitoring of water quality,
deionizing of the water, all of which will be described in more
detail herein.
[0030] The hydrogen gas exits the electrochemical cells 14 along
with a small amount of water which is carried over with the
hydrogen protons during the process of electrolyzing the water.
This hydrogen-water mixture is directed into a hydrogen gas
management system 18 (hereinafter referred to as "HGMS") for
further processing. The HGMS 18 separates the water from the
hydrogen gas and processes the gas using optional drying apparatus
to further minimize water contamination. Finally, the hydrogen gas
exits the system 12 through a port 20 for use in the end
application.
[0031] The electrochemical system 12 includes further subsystems,
such as a ventilation system 22, power supply modules 24, control
panels 26, a user input panel 28 and combustible gas sensor
calibration system 30. If should be noted that the cabinet 32 of
electrochemical system 12 is divided by a partition 34 which
separates the electrical compartment 36 from the gas generation
compartment 38 to prevent any inadvertent exposure of hydrogen gas
to electrical sources.
[0032] The WOMS 16 is best seen in FIG. 4 6. Deionized water is fed
from an external source to the phase separator and water manifold
40 via a water inlet conduit 42. An optional filter 44 may be
coupled to the water inlet conduit 42 to provide additional
protection against contaminants from entering the system 12. Upon
startup of the system 12, water enters via conduit 42 filling the
phase separator body 46 until the desired water level is detected
by sensor 48 causing the solenoid valve 50 to close. During
operation, when the water level sensor 48 detects the water level
in the phase separator drop below a predetermined threshold, the
solenoid valve 50 opens to provide additional water to the system.
The phase separator and water manifold 40 is mounted to the cabinet
by bracket 43.
[0033] Once the appropriate water level is achieved and the system
12 is operating, water is discharged from the phase separator body
46 through conduit 52 to pump 54. An optional heat exchanger 56 may
be used to reduce the temperature of the water. After leaving the
pump 54, the water enters the manifold 58 via conduit 60. A
plurality of outlets 62 and 64 provide water to the electrochemical
cells 14 and the guard bed 66. Outlets 62 feed water via conduits
68 past flow switches 133 to the electrochemical cells 14. Flow
switches 133 are electrically connected to the control circuits of
power supply 24. In the event that flow is interrupted in conduit
68, the flow switch will send a signal to the power supply 24 which
causes the electrical power to be disconnected to the
electrochemical cell 14 which the interrupted conduit was providing
water. Any additional water not directed to the electrochemical
cells 14 exits the manifold 58 via outlet 64 to be filtered by
guard bed 66. As will be explained in more detail herein, the guard
bed 66 includes a restrictor for preventing excess flow through
outlet 64 which prevents the electrochemical cells 14 from being
starved of water which could adversely affect their performance and
reduce their operating life. Manifold 58 also includes a
conductivity sensor 70 which measures the quality of the water in
the system 12. The sensor 70 is typically a water conductivity and
temperature sensor (commercially available as Model RC-20/PS102J2
manufactured by Pathfinder Instruments). Since these types of
sensor require the water to be flowing in order to maintain
accurate measurements, the placement of the sensor 70 is important.
By placing the sensor 70 at the end of the manifold 58 adjacent to
the outlet to guard bed 66, two functions may be accomplished by
sensor 70. First, the sensor 70 will measure the quality of the
water. Once the water quality falls below a predetermined
threshold, typically 1 to 5 microSiemens/cm, the system 12 will be
shut down to prevent contaminants from damaging the electrochemical
cells 14. Additionally, since the sensor 70 requires flowing water
for accurate measurements, if the guard bed, or any of the conduits
or valves attached thereto become plugged, the water will stop
flowing and the conductivity sensor 70 will also read an
erroneously high conductivity, which will indicate to the system 12
that there is a problem and the process should be shut down.
[0034] Once the water enters outlet 64, it moves to the guard bed
66 via conduit 72. The guard bed 66 includes a manifold 73 which
receives the water from conduit 72 and forces the water through a
screen 74 which filter any particulate matter from entering the
main body 75 of the guard bed 66. After being treated in the body
75, the water exits the guard bed 66 through the manifold 73 via a
volume restrictor 76. The restrictor 76 (commercially available
under Model 58.6271.1 manufactured by Neoperl, Inc.) limits the
amount volume that can pass through the guard bed 66 over a wide
range of pressures. By knowing the output of pump 54 and operating
requirements of electrochemical cells 14, the restrictor 76 can be
appropriately sized to maintain a water volume flowing through the
guard bed 66 at a level that maintains adequate water flow to the
electrochemical cells 14. Water returns from the guard bed 66 to
the inlet 79 in return manifold 78 via conduit 77.
[0035] As described herein above, after the water is decomposed
into hydrogen and oxygen gas by electrochemical cells 14, the
oxygen-water mixture returns to the phase separator 40 via conduits
80. Return manifold 78 receives the conduct 80 through inlets 82.
The oxygen-water mixture travels along the return manifold 78 which
empties into the phase separator body 46. As the mixture enters the
body 46, it impinges on the inner walls and surfaces, causing the
water to separate under the influence of gravity and surface
tension out of the gas and collect in the bottom of the separator
body 46. The liberated gas exits the separator body 46 via conduit
84 and exhausts into the cabinet 32 through outlet 86. A
combustible gas sensor 88 monitors the gas exiting the outlet 86 to
warn if any combustible gases exceed predetermined levels. The
separated water in the body 46 is then reused within the system 12
as described herein above.
[0036] Once the electrochemical cells 14 decompose the water, the
hydrogen gas, mixed with water is processed by the HGMS 18. As best
seen in FIG. 3, the HGMS 18 receives the water via manifold 90. A
hydrogen water phase separator 92 causes nearly all the hydrogen
gas to be separated from the liquid water. The hydrogen gas exits
the separator 92 via conduit 94 while the water collects in the
bottom of the separator 92. A back pressure regulator 154 described
herein assures a minimum hydrogen gas pressure for delivery of
product hydrogen gas and for return of water from the phase
separator 92. By virtue of the pressurization a small amount of
hydrogen gas is dissolved in the water. In the preferred
embodiment, the water with dissolved hydrogen exits and is
depressurized via valves 152 and the resultant mixture then flows
via conduit 96 which returns to the oxygen-water phase separator
46. In an alternate embodiment, the water with dissolved hydrogen
exits and is depressurized via valves 152 and conduit 96 and enters
a hydrogen-water phase separator 150. In this alternate embodiment
the resultant hydrogen gas is vented into the cabinet 38 and the
water returns to the oxygen-water phase separator 46 via conduit
151. The hydrogen gas travels via conduit 94 to a dryer 98,99 which
further dries the gas to a desired level, typically to less than 10
parts per million by volume at standard temperature and pressure.
The dryers 98,99 are connected by a manifold 120 which alternates
the hydrogen gas between the two dryers 98,99 on a predetermined
time interval. These dryers, which are typically referred to as
pressure swing or swing-bed type dryers contain a dessicant which
dries the hydrogen gas to a desired level. Periodically, the system
12 will switch the gas flow from one dryer 98 to the other dryer
99. The amount of time the gas will flow through an individual
dryer 98, 99 will depend on how quickly the desiccant in the dryer
98, 99 becomes saturated with water. Prior to this saturation
point, the gas flow and switched and the system 12 will regenerate
the saturated dryer 98, 99 with a small slip stream of
depressurized dry gas processed by the alternate dryer. After
leaving the hydrogen gas driers 98, 99, the pressure of the
hydrogen gas is measured by pressure sensor 155. The pressure
sensor 155 provides a feedback to the control panel 28 for
determining the appropriate amount of electrical power to provide
to the electrochemical cells 14. The amount of electrical power
provided by the control panel 28 determines the production rate of
the electrochemical cells which in turn affects the output pressure
of the hydrogen gas. By locating the pressure sensor 155 upstream
from the pressure regulator 154, the control panel 28 is able to
compensate for pressure fluctuations that result due to the cycling
of the gas driers 98,99, phase separator 92 drain cycles and
changes in customer demand. By controlling the pressure measured at
pressure sensor 155 slightly above the set pressure of pressure
regulator 154, the system 12 is able to maintain an output hydrogen
gas pressure to the end user within .+-.0.5 bar without the use of
a hydrogen buffer tank which was required hereto before. Typically,
the control panel 28 operates to control the pressure at pressure
sensor 155 at a point 0.1 to 3 barg greater than the pressure
regulator 154 set point. The hydrogen gas exits the system 12 via
outlet 20 for use by the end-user.
[0037] As mentioned herein above, the system 12 also includes a
ventilation system 22 which provides fresh air to the interior of
the gas generation compartment 38. A fan 124 adjacent to a louvered
grill 122 draws in external air. The air travels down the duct 126
and enters the interior portion of the gas generation compartment
38 adjacent the electrochemical cells 14. To exit the compartment
38, the air must traverse the length of the compartment 38 and exit
through louvered grill 128. Due to the flow of air, the oxygen
exhausted by the oxygen-water phase separator vent 86 is quickly
removed from the system 12. Any hydrogen which escapes, such as
hydrogen vented from the phase separator 150, is exhausted into the
flow of air, diluted and quickly removed from system 12. Sensor 160
detects a loss of air ventilation and automatically causes the
system 12 to shut down, stopping the production of oxygen and
hydrogen. Additionally, a combustible gas sensor 130 is positioned
adjacent to the exit grill 128. In the event that combustible gas
levels in the vent air stream reach unacceptable levels, the system
12 is automatically shut down for maintenance or repair.
[0038] Combustible gas sensors such as sensors 130 and 88,
typically use a technology referred to as a "catalytic bead" type
sensor (commercially available under the trade name Model FP-524C
by Detcon, Inc.). These sensors monitor the percentage of lower
flammable limit ("LFL") of combustible gas in a product gas stream.
This LFL measurement represents the percentage of a combustible
gas, such as hydrogen, propane, natural gas, in a given volume of
air (e.g. the LFL for hydrogen in air is 4% by volume). These
sensors 88, 130 require periodic calibration to ensure adequate
performance. Calibration procedures typically require a user to use
a bottle of premixed calibration gas which is manufactured with a
predetermined mixture of hydrogen and air. The mixture is usually
25-50% of the lower flammable limit of the combustible gas. In the
preferred embodiment of the present invention, the system 12 is
configured to either automatically calibrate the sensors on a
periodic basis, or to facilitate manual calibration by eliminating
the need for the user to access the gas generation compartment. The
auto-calibration system 30 of the preferred embodiment includes a
bottle of premixed calibration gas 132, a solenoid valve block 134,
an external port 136 and conduits 138, 140, 142, 143.
[0039] In operation, the combustible gas calibration system 30 is
triggered either when activated by the user via the interface panel
28 or at a predetermined interval by the control panel 26. If the
activation is triggered by the interface panel, the user is given
the choice of either manually connecting an external calibration
bottle to port 136 or use the internal calibration gas 132. If the
user selects to use the external bottle, they are instructed by the
interface panel 28 to connect the bottle. If the user selects to
use the internal calibration gas, the control panel 26 opens a
solenoid valve 144 in the valve block 134 to allow the combustible
gas mixture into conduits 138, 140. Orifices 145, 146 in conduits
138 and 140 respectively are sized to allow the appropriate amount
of gas into the conduit. The gas travels along the conduits 138,
140 to the combustible gas sensors 88, 130. The control panel 26
monitors the levels of combustible gas measured by the sensors 88,
130. If the level measured is not equal to the level present in the
premixed calibration gas, the control panel adjusts the combustible
gas sensors 88, 130 until the appropriate levels are reached.
[0040] If the calibration is triggered by the expiration of the
predetermined time limit, the sequence operates essentially the
same as described above. If the calibration settings of out of
adjustment by a predetermined amount, the control panel may
optionally signal a warning to advise the user and/or shorten the
time period between calibrations.
[0041] In the event that abnormal operating conditions or
parameters such as the combustible gas sensor calibration are
detected, the system 12 contains a number of health monitoring
processes which allow for corrective actions to automatically
adjust the operation of the system 12. In the preferred embodiment
of the system 12, a number of the components, such as the
electrochemical cell 14 or the power supplies are modular. This
modularity provides additional benefits in the event that a fatal
error occurs in one module. As will be described in more detail
herein, when a fatal error occurs, the system 12 is enabled to
adjust the operation of the system to accommodate the error and
perform in a degraded mode until repairs or maintenance can be
performed. This allows the end-user to continue operation without a
major impact on their processes.
[0042] In order to perform the prescribed functions and desired
processing, as well as the computations therefore (e.g. the control
algorithms for hydrogen generation, and the like), control panel 26
and the power supplies 24 may include, but not be limited to, a
processor(s), computer(s), memory, storage, register(s), timing,
interrupt(s), communication interface(s), and input/output signal
interfaces, and the like, as well as combinations comprising at
least one of the foregoing. For example, control panel 26 may
include input signal processing and filtering to enable accurate
sampling and conversion or acquisitions of such signals from
communications interfaces. Additional features of control panel 26
and certain processes, functions, and operations therein are
thoroughly discussed at a later point herein.
[0043] During a normal mode of operation, the power supplied from
the power supplies 24 to the control panel 26 and the
electrochemical cells 14 to produce hydrogen gas as described
herein above. In addition to the processing functions previously
discussed, control panel 26 may also include power distribution
components, such as but not limited to, circuit breakers, relays,
contactors, fuses, dc-dc power conditioners, and the like, as well
as combinations comprising at least one of the foregoing. These
power distribution components allow power to be provided to
components, such as pumps, fans and solenoid valves, within the
system 12. During normal mode, current is varied to the
electrochemical cells 14 to provide the appropriate product level
of hydrogen gas required by the user.
[0044] Referring to FIG. 7, a state transition diagram depicting an
exemplary method of control process 200 for the system 12 is
provided. The process 200 includes numerous modes and the
criterion, requirements, events and the like to control changes of
state among the various modes. The process 200 typically operates
in normal mode 210 monitoring and evaluating various sensors and
states to ascertain the status of the system 12. Such monitoring
may include the evaluation of combustible gas levels in the vent
stream from sensors 88, 130. If the percentage of the lower
flammability limit (hereinafter referred to as "LFL") trends
upwards over time and the level of LFL remains below a threshold,
the process 200 transfers to a log mode 212 which records the LFL
data and sends a warning to the user interface 28.
[0045] Should the process 200 detect that the LFL exceeds a
predetermined threshold, which may indicate that repair or
preventative action is needed, the process transfers to diagnostic
mode 214 to evaluate the electrochemical cells 14. To determine if
the high LFL measurement is due to a faulty or worn electrochemical
cell 14, the diagnostic mode 214 operates each electrochemical cell
14 individually while monitoring the LFL measurements from sensor
88, 130. If the LFL measurements is greater than a shutdown level,
or if the LFL measurements do not drop, or if there is only one
electrochemical cell 14 is operating then the process 200 transfers
to shutdown mode 216 to stop the processes of system 12 in an
orderly manner. Process 200 uses alert mode 218 to notify the
user.
[0046] If the diagnostic mode 214 determines which electrochemical
cell 14 is responsible for the high LFL levels, then the process
200 transfers to degraded mode 220. The degraded mode 220 turns off
the appropriate modules in the power supply 24 to remove electrical
power from the faulty electrochemical cell 14 from operation. Log
mode 212 records the appropriate data and alerts the user. Once the
system 12 has been shut down and properly services, process 200 is
reset to a normal mode 210.
[0047] Another error state which may be encountered by the system
12 is excessive water temperature in the manifold 58. Temperature
measurements from the sensor 70 are acquired, monitored and
analyzed by process 200 while in the normal operating mode 210. If
normal mode 210 detects that the temperature is trending upwards
and the actual water temperature is less than a predetermined
threshold, the process 200 transfers to log mode 212 where the
information is recorded and sends warning to the user.
[0048] If the water temperature measured by sensor 70 exceeds a
predetermined threshold, the process 200 transfers to degraded mode
222. In degraded mode 222, the electrical current output of power
supplies 24 is reduced to lower the hydrogen gas output of the
electrochemical cells 14. The process 200 transfers to log mode 212
to log the temperature information and warn the user of the
degraded performance of the system 12. Once the system 12 has been
shut down and properly services, process 200 is reset to a normal
mode 210. If the temperature measured by sensor 70 remains above a
second predetermined threshold, typically equal to the maximum
operating temperature of the guard bed 66, the process 200
transfers to shut down mode 216 to stop the processes of system 12
in an orderly manner. Process 200 uses alert mode 218 to notify the
user.
[0049] Another error condition which may be experienced by the
system 12 is a low voltage or high voltage condition in the
electrochemical cells 14. If normal mode 210 detects an upward or
downward trend in the voltage, the process 200 transfers to log
mode 212 which records the information and sends a warning to the
user. If the voltage required to operate the electrochemical cells
14 drops below a threshold, rises above a threshold and there is
current being drawn by the electrochemical cells 14, the process
200 transfers to diagnostic mode 228 to determine which
electrochemical cell is operating outside of normal parameters. If
there is only one electrochemical cell 14 operating, process 200
transfers to shutdown mode 216 to stop the processes of system 12
in an orderly manner. Process 200 uses alert mode 218 to notify the
user.
[0050] If there are more than two electrochemical cells 14
available, process 200 transfers to degraded mode 226 which
disables the power supplies which provide electrical power to the
faulty electrochemical cell and continues to operate the system 12
with the remaining electrochemical cells. Degraded mode 226 (FIG.
9) continues to monitor and analyze the electrochemical cell
voltages and similar to the operation described above if an upward
or downward trend is detected, the process 200 transfers to log
mode 212 records the information and sends a warning to the user.
Once the system 12 has been shut down and properly services,
process 200 is reset to a normal mode 210. If the voltages once
again rise above the predetermined thresholds, or fall below a
predetermined threshold, the process 200 once again transfers to
diagnostic mode 228 and repeats the sequence describe above once
again. This process continues until the system 12 is repaired or
reset, or until the last electrochemical cell is determined to be
faulty.
[0051] Referring to FIG. 10, another error which the system 12 may
encounter is a faulty power supply module in the power supply 24.
If the process 200 while in normal mode 210 detects a power supply
failure, the process 200 transfers to diagnostic mode 230. The
diagnostic mode 230 interrogates each of the modules in the power
supply 24 to determine which of the individual modules are faulty.
Once the diagnostic mode 230 determines which module is faulty, the
process 200 transfers to degraded mode 232 which disables the
faulty power supply modules and continues operation. It should be
appreciated that if multiple power supply modules are required to
operate a single electrochemical cell 14, then degraded mode 232
will disable all the power supply modules associated with the
faulty module. The process 200 also transfers to log mode 212 to
record the appropriate power supply information and send a warning
to the user. The process 200 then continues the operation of the
system 12 in degraded mode. Once the system 12 has been shut down
and properly services, process 200 is reset to a normal mode 210.
If another power supply should fail, the sequence of modes repeats
when the process 200 transfers back to diagnostic mode 230. In the
event that there are not enough power supply modules remaining to
operate a single electrochemical cell 14, then the process 200
transfers to shutdown mode 216 to stop the processes of system 12
in an orderly manner. Process 200 uses alert mode 218 to notify the
user.
[0052] Another type of error that may be encountered by the system
12 is a low inlet ionized water flow. In order to maintain
operation of the system 12, a steady supply of fresh deionized
water is typically required. If the flow of deionized water should
be reduced or stop due to a problem with the external supply of
water 17 then the system may be damaged if there is not enough
deionized water to supply the electrochemical cells 14. Water flow
from deionizer 17 is determined by measure the amount of time is
required to change the level of water measured by sensor 48 in the
oxygen-water phase separator 46. As shown in FIG. 11, if normal
mode 210 determines that the flow rate of the inlet deionized water
is too low, the process 200 transfers to diagnostic mode 234 which
determines what hydrogen gas production rate can be achieved with
the available deionized water inlet flow. The process 200 then
transfers to degraded mode 236 which reduces the current produced
by the power supplies 24 to reduce the hydrogen production rate of
the electrochemical cells 14. Degraded mode 236 continues to
monitor and analyze the deionized water inlet flow in the manner
described above. Once the system 12 has been shut down and properly
services, or if the flow of deionized water flow returns to a
normal operating state, the process 200 is reset to a normal mode
210. If the water flow continues to trend downward, the process 200
transfers to log mode 212 records the information and sends a
warning to the user.
[0053] If the inlet water flow declines below a second threshold,
the process 200 transfers back to the diagnostic mode 234 and the
sequence repeats as described above until the inlet flow falls
beneath a minimum operating level. Once the minimum operating level
is achieved, the process 200 transfers to shutdown mode 216 to stop
the processes of system 12 in an orderly manner. Process 200 uses
alert mode 218 to notify the user.
[0054] The last example of an error that may be encountered by the
system 12 is low gas output pressure. Referring to FIG. 12, once
the system 12 is at a normal operating state, a drop in output
pressure may indicate a fault condition requiring maintenance or
operator intervention to prevent damage. Output pressure of the
system 12 is measured by pressure sensor 155 which transmits a
signal indicative of the gas pressure to the control panel 28.
During the normal operating mode 210, the control panel 28 monitors
the actual gas pressure signal and compares the signal to a
parameter indicative of a minimum threshold pressure. If the actual
gas pressure drops below a minimum threshold pressure, the process
200 transfers to diagnostic mode 238 which monitors 240 the actual
output pressure for a predetermined amount of time. If the actual
pressure stays below the minimum threshold pressure, process 200
optionally enters log mode 212 and records the information and
sends a warning to the user.
[0055] If the actual gas pressure returns to the desired pressure,
process 200 is reset and transfers back to normal operating mode
210. However, if actual gas pressure measured by pressure sensor
155 remains below the minimum threshold pressure for the
predetermined amount of time, process 200 transfers back to shut
down mode 16 via diagnostic mode 238 to stop the processes of
system 12 in an orderly manner. Process 200 uses alert mode 218 to
notify the user. Preferably, the minimum threshold pressure is
lower than the operating pressure required by the operator, and
more preferably at least 10% lower than the operating pressure. In
the exemplary embodiment, the operating pressure is 200 psi, and
the minimum threshold pressure is 180 psi. It should be appreciated
that the actual values may be set to any that are necessary or
desired by the operator for a given application.
[0056] While preferred embodiments have been shown and described,
various modifications and substitutions may be made thereto without
departing from the spirit and scope of the invention. For example,
while the embodiments shown referred specifically to an
electrochemical system have three electrochemical cells, it would
also equally apply to a system having two, four or more
electrochemical cells. Accordingly, it is to be understood that the
present invention has been described by way of illustrations and
not limitation.
* * * * *