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.

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™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® 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.