Patent Publication Number: US-7217469-B2

Title: Fluid handling device for hydrogen-containing process fluids

Description:
FIELD OF THE INVENTION 
     The present invention relates to fluid handling devices in an electrochemical cell system, and more particularly to a fluid barrier in a hydrogen-containing process fluid handling device in an electrochemical cell. 
     BACKGROUND OF THE INVENTION 
     Electrochemical fuel cells can be used in a vast array of applications as a power source, including as an alternate power source to the internal combustion engine for vehicular applications. An electrochemical fuel cell contains a membrane sandwiched between electrodes. One preferred fuel cell is known as a proton exchange membrane (PEM), where hydrogen (H 2 ) is used as a fuel source or reducing agent at an anode electrode and oxygen (O 2 ) is provided as the oxidizing agent at a cathode electrode, either in pure gaseous form or combined with nitrogen and other inert diluents present in air. During operation of the fuel cell, electricity is garnered by electrically conductive elements proximate to the electrodes via the electrical potential generated during the reduction-oxidation reaction occurring within the fuel cell. 
     Fluid handling devices within the fuel cell circulate the process fluids (e.g. reactant gases, coolant, effluent streams) throughout the system. Fluid handling devices that deliver hydrogen-containing gases to and from the anode pose particular design challenges due to the reactivity of hydrogen and hydrogen-containing gases. The fluid handling device should sufficiently isolate the hydrogen-containing process fluids, so that the hydrogen-containing gases are not released into the surrounding environment. Fluid handling devices, such as pumps, blowers, and compressors, typically have rotating shafts that extend through the housing of a motor compartment to a process fluid compartment. The seals surrounding the shaft and separating the motor and process fluid compartments may fully seal process fluids from the environment. Other fluid handling device configurations may isolate the device from the surrounding environment by encasing it in a sealed (e.g. hermetically) protective housing. The present invention relates to improving the fluid barriers of fluid handling devices that handle reactive, corrosive, and/or combustible process fluids, which must be isolated, such as the anode process fluids handled in a fuel cell system. 
     SUMMARY OF THE INVENTION 
     One preferred embodiment of the present invention relates to a fluid handling device for a hydrogen-containing process fluid that comprises a process fluid compartment having a first pressure, a drive compartment having a second pressure and having a drive unit for moving the process fluid through the process fluid compartment, and an interconnection compartment disposed between the process fluid compartment and the drive compartment, through which the drive unit extends. A barrier gas storage device in fluid communication with the interconnection compartment has a barrier gas. The interconnection compartment is maintained at a third pressure that is greater than respectively, the first pressure and the second pressure. 
     An alternate preferred embodiment of the present invention includes a method of isolating hydrogen-containing process fluid in a fluid handling device. The method comprises monitoring a first pressure in a process fluid compartment, monitoring a second pressure in a drive compartment, and monitoring a third pressure in an interconnection compartment having a barrier gas, wherein all of the compartments are in fluid communication with one another via gas migration across seals. The third pressure is maintained at a value greater than the first pressure and the second pressure respectively, whereby the process fluid in the process fluid compartment is prevented from migrating into the drive compartment as the process fluid moves through the process fluid compartment of the fluid handling device. 
     Another alternate preferred embodiment of the present invention is a method of separating fluids in an anode recirculation fluid handling device in a fuel cell. The method comprises dehumidifying a barrier gas, pressurizing the barrier gas, and supplying the dehumidified and pressurized barrier gas to an interconnection compartment disposed between a process fluid compartment containing hydrogen-containing process fluids and a drive compartment in fluid communication with ambient, wherein the interconnection compartment contains the barrier gas and has a pressure greater than the pressure of the process fluid compartment and the pressure of the drive compartment. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a schematic representation of an exemplary fuel cell system having an anode recirculation; 
         FIG. 2  is a schematic representation showing a fluid barrier sealing system for a fluid handling device according to the present invention; 
         FIG. 3  is a cross sectional view of a fluid handling device having a fluid barrier in accordance with principles of the present invention; 
         FIG. 4  is a cut away perspective view of a shaft and seals of the fluid barrier of  FIG. 3 ; and 
         FIG. 5  is a partial cross sectional view taken along line  5 — 5  of the fluid barrier of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     The present invention contemplates a fluid barrier for a fluid handling device in a fuel cell system to separate the process fluids in a stage compartment from a drive compartment and the ambient. The fluid barrier is provided by an additional compartment separating the process fluid and drive compartments. The additional compartment is preferably filled with a barrier fluid (e.g. gas) that has a higher pressure than the neighboring process fluid and drive compartments to prevent fluid flow between the process fluid and drive compartments. The present invention may be employed in fluid handling devices that circulate both liquid and gas phase process fluids. First, to better understand the present invention, a brief description of an exemplary electrochemical fuel cell system, wherein the present invention is useful, is helpful for understanding various aspects of the present invention. As shown in  FIG. 1 , an individual fuel cell  20  is shown in a stack  22 . The stack  22  may optionally comprise a plurality of connected fuel cells, as is well known in the art, however, for simplicity is shown here with only a single fuel cell. The fuel cell  20  comprises a polymer electrolyte membrane  24  that is sandwiched between two electrodes: a cathode  26  and an anode  28 . Reactant gases are introduced at both the anode  28  and the cathode  26 , in a preferred embodiment, the reactant gas introduced at the anode  28  is hydrogen-containing (a reductant), and the reactant gas introduced at the cathode is oxygen-containing (an oxidant). Fluid handling devices  30 , such as pumps or blowers, circulate reactant gases into the stack  22 . The cathode and anode electrodes  26 ,  28  typically contain catalysts to facilitate the electrochemical reaction between the oxygen and hydrogen. A preferred polymer electrolyte membrane  24  is a proton exchange membrane, which permits transport of protons from the anode  28  to the cathode  26 , thereby generating an electrochemical potential. Polymer electrolyte membranes  24  require humidification, which is generally provided by a humidifier  32  that supplies moisture to reactant oxygen-containing gas entering the stack  22 . 
     Electrochemical reactions within the fuel cell  20  generate product water which is formed on the cathode  26  side. At the anode  28 , hydrogen gas is consumed in proportion to the reactions occurring within the fuel cell  20 . During typical operations, there are few or no reaction byproducts generated at the anode  28 . Many different configurations for fluid handling at the anode  28  are possible, and fresh hydrogen-containing gas delivered to the anode  28  may be “dead-ended” into the stack  22 , where it is assumed that all hydrogen is consumed within the reactions in the fuel cell  20  and anode effluent is not subsequently recycled back into the anode inlet  36 . Such a configuration is generally known as “discontinuous” anode gas circulation. Other discontinuous operating configurations may utilize the anode effluent stream by delivering it to different parts of the system or other processes, but the anode effluent is not returned to the anode inlet  36 . Re-routing it to other processes may entail directing the anode effluent into a hydrogen reforming plant (not shown) or other areas where residual hydrogen contained in the effluent stream will be consumed. An alternate operating concept, as depicted in  FIG. 1 , includes a continuous operating loop  34 , where the anode effluent stream is recirculated or recycled back into the anode inlet  36  by an anode recirculation pump  40 . The recycled anode inlet stream optionally passes through a recirculation loop filter  37  to remove any impurities. Anode gases typically gain moisture while circulating through the fuel cell  20  and are humidified upon exiting the stack  22 . Continuous anode recirculation systems are advantageous to various aspects of fuel cell performance, including for moisture conservation. Anode recirculation systems are frequently incorporated into fuel cell system designs. 
     However, additional handling of hydrogen-containing process gases or fluids, such as anode effluent, can pose operational and quality issues due to the high reactivity of hydrogen. Ignition or other reactive sources may react with the hydrogen in various components in a system, which is problematic. The humidified hydrogen-containing gas leakage into the drive compartment causes corrosion or chemical attack (e.g. passivation) of the various motor components of the motor. Exposing the magnetic materials in the motor of the fluid handling device to hydrogen-containing humidified anode gases appears to detrimentally impact inductive performance and significantly shorten the lifespan of the pump motor. Introduction of additional fluid handling devices (e.g. pumps or blowers) that interface with hydrogen-containing process gases, especially those containing both high humidity and hydrogen, such as the anode recirculation pump  40  in the present context, must be carefully designed to isolate the process fluids. The present invention incorporates conventional mechanical seals, and further provides an additional protective barrier to ensure isolation of the process fluids. 
     One preferred configuration of a fluid barrier sealing system in a fluid handling device according to the present invention is shown in  FIG. 2 . An exemplary fluid handling device, such as the anode recirculation pump  40 , has a process fluid or stage compartment  42  that contains and transports the process fluids. A propulsion device (e.g. an impeller  44 ) provides propulsion for the process fluid as it exits the stage compartment  42 , and is connected to a drive unit comprising a rotatable shaft  46  that extends to a motor or drive compartment  48 . A barrier fluid, which in certain preferred embodiments is a gas, is drawn from a source  52 , and is directed along a barrier gas feed path  54  which supplies a fluid barrier  56  within the anode recirculation pump  40 . The barrier gas source  52  may be a storage tank or cylinder, or in the case of air, the ambient. The barrier gas is directed to an inlet  60  of a compressor  58 , where it is pressurized. The pressurized barrier gas exits the compressor  58  at an outlet  62  and enters a first passage  64 . A valve  66  is located in the first passage  64  to provide isolation and/or regulation of barrier gas flow from the compressor  58 . 
     The barrier gas is directed to a dehumidifier  68  and then through a second passage  70  to a pressurized storage vessel  72 . A check valve  74  located within the second passage  70  is biased to allow flow in the direction of the pressurized storage vessel  72  and to prevent backflow in the direction of the humidifier  68 . As recognized by one of skill in the art, the order of the compressor  58  and the dehumidifier  68  along the barrier feed path  54  may differ from the one shown in  FIG. 2 , and may entail first dehumidifying the barrier gas when it is drawn from the source  52  and then pressurizing the barrier gas in the compressor  58 , to result in substantially similar conditioning of the barrier gas. Further, compressors may already be incorporated into a system for other processes, and such compressors may have additional capacity. In such a case, the compressor  58  may be shared between the present invention and the other processes within the system. The pressurized storage vessel  72  is connected to a third passage  76  which leads to the fluid barrier  56  in an interconnection chamber or compartment  80  disposed between the stage  42  and drive compartments  48 . Pressure gauges  82  are located along the feed path  54 . The various pressure measurements from the pressure gauges  82  are used to monitor and control operations of equipment and valves along the barrier gas feed path  54 . The precise locations of the gauges  82  may vary from those shown, depending on various system design configurations, as recognized by one of skill in the art. 
     As shown in  FIG. 3  the drive compartment  48  of the anode recirculation pump  40  houses the drive unit, which includes the motor  86  that has induction coils  88  that surround the shaft  46  to induce rotation. The shaft  46  of the drive unit ultimately translates motion to the impeller  44  to propel fluids in the stage compartment  42 . The shaft  46  extends axially from the drive compartment  48  into and through the interconnection compartment  80  to the stage compartment  42 . Generally, a second cooling fan  90  is provided in the drive compartment  48 , which draws in ambient air for cooling the motor  86  and its several components. The drive compartment  48  is in fluid communication with the external environment. A housing  92  encases the motor  86  and cooling fan  90  components. The drive compartment  48  is adjacent to the interconnection compartment  80  on a first side  100 . The drive compartment  48  housing wall  94  terminates in a seal  96  circumscribing the shaft  46 . The seal  96  provides a mechanical fluid barrier between the interconnection compartment  80  and the drive compartment  48 . 
     The stage compartment  42  is adjacent to the interconnection compartment  80  on a second side  102  opposite to the first side  100 . Process fluid is introduced to the stage compartment  42  at an inlet  106 ; and exits at an outlet  108 . Such process fluid, in the case of an anode recirculation pump  40 , is typically a humidified hydrogen-containing gas, but the present invention may apply to any combustible, poisonous, reactive, or corrosive fluids that must be contained solely in the process fluid stage compartment  42  of a fluid handling device. The present invention is also applicable as a fluid barrier in other fluid handling devices having separated propulsion and drive compartments, such as compressors, blowers, and the like. 
     According to one preferred embodiment of the present invention, the interconnection compartment  80  is an area disposed between and adjacent to both the drive  48  and process fluid stage  42  compartments along the opposite first and second sides  100 , 102 . The interconnection compartment  80  has a housing  98 , which may share common walls with the drive and/or stage compartments  48 , 42 , in the regions proximate to the drive and stage compartments  48 ,  42 . In alternate preferred embodiments, the interconnection compartment  80  may optionally form an entirely separate housing with independent walls and seals. The third passage  96  ( FIG. 2 ) is connected to an inlet  104  of the interconnection compartment  80 , where barrier fluid is filled and supplied thereto. One aspect of the present invention includes regulating and maintaining the pressure of the interconnection compartment  80  above the pressure of the two neighboring compartments  42 , 48 , as will be described in more detail below. According to preferred embodiments of the present invention, the barrier fluid of the interconnection compartment  80  provides additional means of isolating the process fluids circulating through the stage compartment  42  from the drive compartment  48  and external environment (in addition to the mechanical seals  96  disposed at the junction or boundary between the housing of each compartment and the shaft  46 ). In preferred embodiments of the present invention, the barrier fluid is a barrier gas, which has sufficient pressure to provide fluid isolation, generally where the process fluid is gaseous. In alternate preferred embodiments, the barrier fluid may be a liquid, which can be pressurized to isolate process fluids which may be liquids. 
     Two exemplary labyrinth type seals  96  are depicted generally in  FIG. 4 , with lands  114 , or rotors, fixedly attached to and extending around the entire circumference of the shaft  46 . The lands  114  rotate with the shaft  46  during operation. Corresponding stators, or grooves,  116  are formed along the circumference of the surface of housing walls  118  that circumscribe the shaft  46 . The lands  114  protrude into the corresponding grooves  116  such that a small gap is formed between the surfaces of the lands  114  and grooves  116 , respectively. These small gaps permit rotational movement of the shaft  46 . 
       FIG. 5  shows a detailed cross sectional view of the annular seals  96  along the rotary shaft  46  of both a first boundary  110  between the drive and interconnection compartments,  48 , 80  and a second boundary  112  between interconnection and stage compartments  42 , 80 . The grooves  116  are formed along the circumference of the surface of the housing walls  118  of both the first intercompartment boundary  110  and second intercompartment boundary  112 . A first seal  120  is formed by a first metal land  122  circumscribing the rotary shaft  46  which protrudes into a corresponding first groove  124  formed in a terminal end  126  of a housing wall  128  of the stage compartment  42 . A first interconnection compartment wall  130 , next to the housing wall  128  of the stage compartment  42 , terminates and merges with the stage compartment housing wall  128  at the terminal end  126  to form the first seal  120  configuration. 
     A second seal  130  is formed by a plurality of second metal lands  132  extending around the circumference of the shaft  46 . The corresponding second grooves  134  are formed in a terminal end  136  of a housing wall  138  of the drive compartment  48 , in the same manner as first seal grooves  124 . A second housing wall  142  of the interconnection compartment  80  extends along the length of the drive compartment  48  housing wall  138  until they merge at the terminal end  136  of the drive compartment housing wall  138  to form the second labyrinth seal  130  configuration. 
     Any conventional seals may be used in the present invention, as recognized by one of skill in the art, and the exemplary seal construction shown is non-limiting. As recognized by one of skill in the art, most seals experience some level of fluid migration across the seal. Further, seals with relatively low fluid migration are typically far more expensive to manufacture and costly to maintain. Thus, according to the present invention, a small amount of fluid migration across the seals is incorporated into preferred embodiments of the present invention, which allows for less expensive fabrication and maintenance of the seals. The less expensive sealing configurations which are compatible with the present invention, include for example, non-contact labyrinth seals or contact face seals, and may also include grease barrier or piston-ring sealing. 
     The configuration of double lands  132  and grooves  134  in the second seal  130 , provides additional protection from process fluids potentially entering the drive compartment  48 , which further reduces the quantity of barrier gas potentially flowing into the drive compartment  48 , and correspondingly into the atmosphere. The exemplary first seal  120  configuration shown has a single land  114  and a single groove  116 , which permits greater quantities of barrier gas to migrate to the stage compartment  42 . Such configurations are merely exemplary and are selected based on the relative physical isolation or protection needed for the respective compartments, accounting for the properties of the process and barrier gases, and the selection of the mechanical seals in combination with various aspects of the fluid barrier and according to the present invention. 
     A first pressure within the stage compartment  42  is designated as P 1 . A second pressure within the drive compartment  48  is designated as P 2 , and a third pressure within the interconnection compartment  80  is designated as P 3 . One preferred aspect of the present invention involves maintaining the interconnection compartment chamber pressure, P 3 , at a higher level than the pressure of either of the adjacent compartments (i.e. P 1 , P 2 ), thus providing a fluid barrier  56  that prevents process fluid from migrating from the stage compartment  42  into the drive compartment  48 , or external environment. Preferably, P 3 &gt;P 1  and P 3 &gt;P 2 , where the pressure of the barrier gas in the interconnection compartment  80  exceeds that of the neighboring stage and drive compartments  42 , 48 . 
     Slight quantities of barrier gas migrate across the first and second seals  120 , 130  flowing from the direction of higher pressure to the region of lower pressure, which translates to barrier gas flow into both the stage compartment  42  and the drive compartment  48  originating from the interconnection compartment  80 . The amount of leakage across the seals  96  is dependent on the differential pressure between P 3  and P 1  or P 2 , respectively. The pressure of the anode recirculation loop in a fuel cell is dependent upon the fuel cell system pressure, which is in turn generally a function of the power level output of the fuel cell. Other variables within the fuel cell further limit the operating system pressures, including membrane pressure tolerance levels. The higher interconnection compartment  80  pressure P 1 , enables the fluid sealing barrier  56  of the present invention, by matching or exceeding the overall pressure of the fuel cell, as it operates. Generally, the fluid barrier  56  pressure is designed to be slightly higher than the maximum pressure achieved in the fuel cell system. 
     Barrier gas that leaks into the stage compartment  42  combines with the process fluids, and enters the fuel cell  20  downstream. Selecting the composition of the barrier gas involves evaluating the impact that the barrier gas may have on fuel cell  20  operations. Although the concentration of the quantity of barrier gas flowing into the fuel cell  20  is preferably small or negligible, compatibility with the internal components of the fuel cell  20  is important to avoid poisoning of the electrode catalysts, membrane  24 , or other components. Likewise, the barrier gas also enters the drive compartment  48  where it interfaces with the motor  86  components. Although the quantity of barrier gas entering the drive compartment  48  is preferably negligible or small, appropriate compatibility with the drive compartment  48  components and the external environment is also important. Thus, selection of a suitable barrier gas according to the present invention balances the physical properties of the gas and their impact on the system with relative cost. It is desirable to select a barrier gas that is non-reactive, non-corrosive, non-combustible, and generally safe for handling and dispersing into the surrounding atmosphere, in addition to compatibility with the fuel cell. Generally, inert gases are preferred barrier gases according to the present invention, however, air is also a suitable barrier gas due to its widespread abundance and relatively low reactivity with the fuel cell, motor components, and the environment. Examples of preferred barrier gases in accordance with the present invention include, for example, air (approximately 79% N 2 , 21% O 2 , and other trace diluents), nitrogen, helium, and mixtures thereof. 
     The fluid barrier  56  of the present invention operates by maintaining a positive differential pressure between the barrier gas pressure (P 3 ) in the interconnection compartment  80  and the pressure of the stage compartment  42  pressure (P 1 , which correlates to the pressure of the process fluids in the anode recirculation loop. The pressure for the anode recirculation loop varies from between about 1 to 2.8 bar absolute, for example. The drive compartment  48  pressure (P 2 ) is preferably equilibrated with ambient pressure approximately equal to the surrounding atmospheric pressure of 1 bar absolute. However, it is contemplated that such values are dependent upon fuel cell system design, and may vary greatly. In most fuel cell systems, the fuel cell operating system pressure exceeds ambient pressure, and thus, a primary consideration is the differential pressure between the interconnection chamber pressure, P 3 , and the stage compartment pressure P 1 , rather than with the drive compartment pressure P 2 . 
     According to the present invention, a positive differential pressure is maintained between the interconnection  80  and stage  42  compartments, such that P 3 −P 1 =ΔP 1 , where ΔP 1  is preferably greater than or equal to 0. The barrier gas buffers and blocks process fluid from entering into the interconnection compartment  80  and further forces barrier gas to flow into the stage compartment  42 , when there is fluid communication via fluid migration across the seal. In such a configuration, the differential pressure between the interconnection compartment  80  and the drive compartment  48  is given by P 3 −P 2 =ΔP 2  and ΔP 2  will likewise be maintained at a value greater than or equal to zero that favors barrier gas flowing towards the drive compartment  48 , because P 2  is a lower value. 
     Fuel cell operations fluctuate greatly during various operating conditions, such as start-up or variations in power demand. Hence, the pressure of the fuel cell operating system is likewise dynamic and may undergo transient operational periods. System design according to the present invention, optimizes the differential pressure values of the fluid barrier  56  (i.e., ΔP 1  and ΔP 2 ) to be sufficient when the process fluids are at maximum pressures, accounting for potential pressure spikes in the anode (and hence fuel cell) operations, while not being so great that large quantities of barrier gas are driven into the stage or drive compartments  42 , 48  possibly unfavorably impacting fuel cell or motor operations. 
     As previously discussed, seal leakage (i.e. fluid migration across the seal) is a function of differential pressures and increases in conjunction with increased differential pressure. The quantity of barrier gas leakage into the stage compartment  42  is often expressed as a power loss, meaning that the reduced quantity of hydrogen in the process fluid (displaced by barrier gas) translates to a corresponding power loss in the fuel cell. Such a rate of hydrogen loss is preferably less than or equal to about 100 W. In certain exemplary fuel cell systems, a differential pressure for both ΔP 1  and ΔP 2  is at least 0.1 bar to maintain the integrity of the fluid barrier. Thus, an average differential pressure value between the interconnection  80  and stage  42  compartments, ΔP 1 , is preferably from about 0.1 to 0.5 bar, for example. An average value indicates the differential pressure value maintained over a duration of time, by averaging the instantaneous differential pressure values. At such levels, the differential pressure is relatively small, yet sufficiently high for a fluid barrier. As appreciated by one of skill in the art, many variables in a system may impact the required barrier gas pressure, and thus, both P 3  and the differential pressures ΔP 1  and ΔP 2  may vary greatly depending on system design. The quantity of fluid migration occurring across the seals is preferably small, such as in preferred embodiments where the hydrogen power loss is less than 100 W, which only minimally impacts fuel cell  20  operations. 
     The pressure of the interconnection compartment  80  is maintained by the supply of pressurized barrier gas stored in the storage vessel  72 . In one preferred embodiment of the present invention, the compressed and dried air that is used as reactant for the cathode inlet is diverted from the cathode compressor/blower  30  for use as the barrier gas and introduced into the storage vessel  72 . Subsequently, the barrier gas is introduced into the inlet  104  of the interconnection compartment  80 . The cathode reactant gases are maintained at a higher pressure than the anode side by the compressor  30 . Thus, the compressor  58  operation is coupled to that of the cathode compressor  30  to provide both a cathode reactant and a relatively high pressure barrier gas. Optionally, the dehumidifier  68  may be used on the compressed gas provided by the compressor  30 , or may coupled to another dehumidifier (not shown) in the system. Thus, the present embodiment presents a simplified system, because duplicate gas conditioning systems are not required, and further there is no need for independent pressure instrumentation within the compartments, as the cathode pressure is maintained above the anode pressure for fuel cell operations. 
     In an alternate preferred embodiment, conventional pressure gauges (as shown generally in  FIG. 2  at  82 ) are situated within each of the compartments, preferably in close proximity to the seals  96 . A first pressure gauge  144  is placed within the stage compartment  42  to measure P 1 . A second pressure gauge  146  within the drive compartment  48  measures P 2 , and a third gauge  148  placed within the interconnection compartment  80  measures P 3 . Other pressure gauges  82  within the system, include those placed along the barrier gas feed path  54  ( FIG. 2 ). As recognized by one of skill in the art, additional pressure gauges may be incorporated into the system to provide additional pressure levels and system redundancy, if necessary. The pressure measurement outputs are preferably input into a controller (not shown), e.g. a control processing unit, that preferably also controls the equipment and valve operations along the feed path  54 , including actuating valves  66  and  67  and operating the compressor  58  and humidifier  68 , for example. In view of the extent of the disclosure, a detailed discussion of the construction and operation of the controller need not be provided herein as such controllers are well within the capabilities of one skilled in the art. 
     P 1 , P 2 , and P 3  are input values into the controller, and these input values may be compared to a setpoint to calculate the differential pressure values ΔP 1  and ΔP 2 . Preferably, the setpoint or predetermined control value is calculated as a function of the pressure measurement readings, such that the system can dynamically account for operating pressure fluctuations in the fuel cell. Such a setpoint may be determined by merely using the direct pressure measurements, or by adding an incremental value to the pressure measurements to calculate differential pressure values. For example, if preferred differential pressures for ΔP 1  and ΔP 2  are 0.3 bar, the setpoints may be calculated as P 1 +0.3 bar for setpoint  1 , and P 2 +0.3 bar for setpoint  2 . Thus, the controller subtracts the setpoint  1  from the input value for P 3  and likewise the setpoint  2  from the input value for P 3 , to calculate the actual values for ΔP 1  and ΔP 2 . If the calculated actual value of either ΔP 1  and ΔP 2  approaches zero or becomes a negative value, P 3  will be increased to the reestablish a positive value. In practice, a margin of error (i.e. 5 to 15% above the minimum pressure value for P 3 ) may be incorporated into the setpoint values to correct for control system lag times, under compensation, or system inaccuracies. 
     In preferred alternate embodiments of the present invention, the controller maintains positive ΔP 1  and ΔP 2  by actuating a release valve  150  for the pressurized storage vessel  72  to open when the ΔP 1  or ΔP 2  falls too low. When P 3 ≦P 1  or P 3 ≦P 2  (which may be ascertained directly or based on controller setpoint calculations, such as the exemplary setpoints discussed above), the pressurized storage vessel valve  150  is opened, supplying pressurized barrier gas to increase P 3  to match the setpoint or predetermined control value (i.e. to reestablish the predetermined positive ΔP 1  or ΔP 2  value). In certain preferred embodiments of the present invention, the release valve  150  is actuated prior to P 3  equaling or falling below the values of P 1  or P 2  to avoid reverse flow into the interconnection compartment  80  and possibly the drive compartment  48 . 
     The pressurized storage vessel  72  releases barrier gas through the third supply passage  76  to the interconnection compartment  80  to respond as necessary to the pressure fluctuations occurring in the fuel cell system, and measured by the pressure gauges  82 . In preferred embodiments of the present invention, the storage volume for pressurized gas stored in the pressurized storage vessel  72  is in excess of the actual volume necessary to directly and continuously supply the interconnection compartment  80  to maintain a P 3  that favors positive ΔP 1  and ΔP 2  values. In essence, the pressurized storage vessel  72  has reserve capacity, both as a contingency for any system fluctuations or failures, as well as to allow for discontinuous intermittent compressor  58  operation. Such a volume is specific to an individual system, and is dependent upon barrier gas flow rate and compressor  58  performance. 
     The compressor  58  pressurizes the barrier gas to a designated predetermined pressure, generally selected to be high enough to maintain the interconnection compartment  80  to be at least 0.1 to 0.5 bar above the neighboring compartments  42 , 48 , as previously discussed. Such a pressure may be 3 bar absolute, in an exemplary fuel cell system that operates at a maximum of 2.8 bar absolute where the differential pressure would be 0.2 bar. The compressor  58  may pressurize barrier gas up to about 10 bar absolute or higher, if it is necessary to match a fuel cell system which operates at high pressures. The required maximum pressure of compressed gas is determined by at least equaling (and preferably exceeding) the maximum pressure that a fuel cell system experiences, accounting for start-up and variable power demand situations. The compressor  58  may be operated intermittently (i.e. discontinuously) to supply the pressurized gas from the compressor  58  to the pressurized storage vessel  72 . Further, as previously discussed, the compressor  58  may be shared with the cathode reactant gas compressor  30 . Alternatively, the storage vessel  72  may be connected to the compressor  58 , as well as to the cathode compressor  30 , to provide additional pressurization of the barrier gas, or may serve as a contingent pressurized barrier gas source. In alternate preferred embodiments of the present invention, the barrier gas may be pre-pressurized and stored in tanks, which may constitute the pressurized storage vessel  72 . In such an embodiment, a compressor  58  is not necessary, as the gas is already pressurized to the appropriate level. Further, such a pressurized storage vessel  72  could be interchanged or recharged with new pressurized barrier gas, as the supply decreases. 
     Another advantage of a preferred embodiment of the present invention is that the barrier gas is dehumidified. With renewed reference to  FIG. 2 , the barrier gas may be processed by a dehumidifier  68 , prior to entering the pressurized storage vessel  72 . Any humidified barrier gas that migrates from the interconnection compartment  80  to the drive compartment  48  may contribute to corrosion of the motor  86  components. Thus, in certain preferred embodiments of the present invention, a dehumidifier  68  is used to remove moisture from the barrier gas, prior to entering the pressurized storage vessel  72  and the interconnection compartment  80 . If the source of the barrier gas is a gas storage canister or tank, the gas may be sufficiently pre-dehumidified that it does not require a dehumidification step. Thus, the present invention provides a barrier gas in a fluid barrier  56  that does not react with or attack motor  86  components, while further isolating harmful process fluids from release into the drive compartment  48  and the atmosphere. 
     The present approach alleviates difficulties attendant to efforts to construct better mechanical seals, which are complex designs with many parts that are costly. Further, more complex mechanical seals are expensive to maintain and may have relatively low useful life, and further may not ensure complete physical isolation of the process fluids. The present invention eliminates a need to use such complex mechanical seals that provide complete physical isolation. 
     The present invention may also be contrasted to other methods of isolating process fluids from the other compartments and the surrounding environment by enclosure of the entire pump, including the drive and the process fluid compartments. Such enclosures are generally hermetically sealed to ensure isolation of the process fluids from the external environment. However, such sealing is also expensive and typically exposes the drive compartment to humidified hydrogen-containing gas, in the case of an anode effluent stream, which may cause corrosion or inactivation of the various components of the motor components. Thus, the present invention provides fluid handling devices and methods of isolating process fluids that prevent both migration of process fluids into the surrounding environment, while further protecting the drive compartment from any degradation or attack by the process fluids. The present invention provides a highly effective isolation of process fluids, and can be incorporated into fuel cell systems with relative ease and low cost. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.