Patent Publication Number: US-2009226772-A1

Title: Apparatus, System, and Method For Supplying Fuel To And Removing Waste From Fuel Cells

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/967,104, filed on Aug. 30, 2007, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to fuel cells, and, more particularly, to supplying fuel to and removing waste from fuel cells. 
     BACKGROUND 
     A fuel cell, like an ordinary battery, provides direct current electricity from two electrochemical reactions. These reactions occur at electrodes to which reactants are fed. For example, in an alcohol combustion fuel cell, a negative electrode (i.e., anode) is maintained by supplying an alcohol-based fuel such as methanol, whereas a positive electrode (i.e., cathode) is maintained by supplying oxygen or air. When providing a current, fuel is electrochemically oxidized at an anode electro-catalyst to produce electrons, which travel through an external circuit to a cathode electro-catalyst where they are consumed together with oxygen in a reduction reaction. A circuit is maintained within the fuel cell by the conduction of protons in an electrolyte. 
     A fuel cell stack typically includes a series of individual fuel cells. Each fuel cell includes an anode and cathode pair. A voltage across each fuel cell is determined by the type of electrochemical reaction occurring in the cell. For example, the voltage can vary from 0 V to 0.9 V for a typical alcohol combustion single cell, depending upon the current generated. The current generated in the cell depends on the operating condition and design of the cell, such as electro-catalyst composition/distribution, active surface area of a membrane electrode assembly, characteristics of a gas diffusion layer, flow field design of an anode and cathode plates, cell temperature, reactant concentration, reactant flow and pressure distribution, reaction by-product or waste removal, and so forth. The reaction area of a cell, number of cells in series, and the type of electrochemical reaction in the fuel cell stack determine a current and hence a power supplied by the fuel cell stack. For example, the typical power of an alcohol combustion fuel cell stack can range from a few watts to several kilowatts. A fuel cell system typically integrates a fuel cell stack along with different subsystems for the management of water, fuel, waste, air, humidification, and heat. These subsystems are sometimes collectively referred to as the balance of plant. 
     Fuel cell systems are increasingly being used to power devices, such as forklifts, pallet loaders, automated-guided vehicles, and other material handling equipment. In order to successfully integrate fuel cell systems into an even wider range of devices, it is desirable to efficiently service the fuel cell systems. In particular, refueling and waste removal should be accomplished quickly, so as to reduce the downtime of a device that is powered by a fuel cell system. Also, refueling and waste removal should be accomplished in a manner that meets environmental and safety regulations and does not require extensive operator supervision. 
     It is against this background that a need arose to develop the refueling devices and related systems and methods described herein. 
     SUMMARY 
     One aspect of the invention relates to a refueling device for servicing a fuel cell system. In one embodiment, the refueling device includes a fuel handling unit that includes a fuel port and a fuel conveyance unit connected to the fuel port. The fuel conveyance unit is configured to convey fuel from the refueling device to the fuel cell system via the fuel port. The refueling device also includes a waste handling unit that includes a waste port and a waste conveyance unit connected to the waste port. The waste conveyance unit is configured to convey waste from the fuel cell system to the refueling device via the waste port. The refueling device further includes a communication port and a refueling device controller connected to the fuel handling unit, the waste handling unit, and the communication port. The refueling device controller is configured to establish a communication link with the fuel cell system via the communication port, such that the fuel cell system directs operation of the fuel handling unit and the waste handling unit. 
     In another embodiment, the refueling device includes a common port configured to pass fuel and waste. The refueling device also includes a fuel conveyance unit and a waste conveyance unit that are each connected to the common port. The fuel conveyance unit is configured to convey the fuel along a fuel flow pathway passing through the common port, and the waste conveyance unit is configured to convey the waste along a waste flow pathway passing through the common port. The refueling device further includes a flow pathway selector that is connected between the common port and each of the fuel conveyance unit and the waste conveyance unit, and the flow pathway selector is configured to select between the fuel flow pathway and the waste flow pathway. 
     Another aspect of the invention relates to a fuel cell system. In one embodiment, the fuel cell system includes a fuel input port, a fuel storage unit connected to the fuel input port, a communication port, a first sensor connected to the fuel input port and the communication port, and a second sensor connected to the fuel storage unit. The first sensor is configured to produce a first output indicative of a connection between a refueling device and at least one of the fuel input port and the communication port, and the second sensor is configured to produce a second output indicative of a fuel level of the fuel storage unit. The fuel cell system also includes a fuel cell system controller connected to the first sensor, the second sensor, and the communication port. The fuel cell system controller is configured to direct operation of the refueling device via the communication port, and the fuel cell system controller is configured to direct conveyance of fuel from the refueling device to the fuel storage unit based on the first output and the second output. 
     A further aspect of the invention relates to a method for servicing a fuel cell system using a refueling device. In one embodiment, the method includes detecting a connection between the refueling device and the fuel cell system. The method also includes, responsive to detecting the connection, determining a fuel level of a fuel storage unit included in the fuel cell system. The method also includes, responsive to determining that the fuel level is below a threshold fuel level, initiating conveyance of fuel from the refueling device to the fuel storage unit. The method further includes, responsive to determining that the fuel level is at least the threshold fuel level, terminating conveyance of fuel from, the refueling device to the fuel storage unit. 
     Other aspects and embodiments of the invention are also contemplated. The foregoing summary and the following detailed description are not meant to restrict the invention to any particular embodiment but are merely meant to describe some embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       For a better understanding of the nature and objects of some embodiments of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings. 
         FIG. 1  illustrates an overall system implemented in accordance with an embodiment of the invention. 
         FIG. 2  illustrates a refueling device to service a fuel cell system, according to another embodiment of the invention. 
         FIG. 3  illustrates a state diagram for refueling and waste removal operations, according to an embodiment of the invention. 
         FIG. 4  illustrates a refueling device implemented in accordance with another embodiment of the invention. 
         FIG. 5  illustrates a refueling device implemented in accordance with another embodiment of the invention. 
         FIG. 6  illustrates a refueling device implemented in accordance with another embodiment of the invention. 
         FIG. 7  illustrates a refueling device implemented in accordance with a further embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION  
     Definitions 
     The following definitions apply to some of the components described with respect to some embodiments of the invention. These definitions may likewise be expanded upon herein. 
     As used herein, the singular terms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a sensor can include multiple sensors unless the context clearly dictates otherwise. 
     As used herein, the term, “set” refers to a collection of one or more components. Thus, for example, a set of sensors can include a single sensor or multiple sensors. Components of a set can be referred to as members of the set. Components of a set can be the same or different. In some instances, components of a set can share one or more common characteristics. 
     As used herein, the terms “optional” and “optionally” mean that the described event or circumstance may or may not occur, and that the description includes instances where the event or circumstance occurs and instances in which it does not. 
     As used herein, the terms “connect,” “connected,” and “connection” refer to an operational coupling or linking. Connected components can be directly coupled to one another or can be indirectly coupled to one another, such as via another set of components. 
     Attention first turns to  FIG. 1 , which illustrates an overall system  100  implemented in accordance with an embodiment of the invention. A fuel cell system  102  is implemented as an integral component or as a separate component of a target device  106 , which can be a mobile device such as a vehicle or a device that operates at a fixed location. As illustrated in  FIG. 1 , the fuel cell system  102  includes a fuel storage unit  108 , a set of fuel cells  110 , a waste storage unit  112 , and a fuel cell, system controller  114 . The fuel cells  110  can be implemented as an alcohol combustion fuel cell stack that consumes an alcohol-based fuel, such as ethanol or methanol, and supplies electrical power to a load  104 , such as a thermal or an electrical load. Depending on the particular implementation, little or no waste can be accumulated during operation of the fuel cell system  102 , in which case the waste storage unit  112  can be optionally omitted. 
     As illustrated in  FIG. 1 , the fuel cell system  102  is serviced by a refueling device  116 . In particular, the refueling device  116  supplies fuel to the fuel cell system  102 , such that neither the fuel cells  110  nor the fuel storage unit  108  needs to be removed from the target device  106 . In addition, any accumulated waste is removed from the fuel cell system  102  by the same refueling device  116 . In the illustrated embodiment, the refueling device  116  includes a fuel handling unit  118 , a waste handling unit  120 , and a refueling device controller  122 . During refueling operations, the fuel handling unit  118  conveys fuel from an external fuel storage unit  124  to the fuel storage unit  108  of the fuel cell system  102 . Depending on the particular implementation, the refueling device  116  can store fuel onboard, in which case the external fuel storage unit  124  can be optionally omitted. Also, the fuel handling unit  118  can convey fuel directly to the fuel cells  110 , such as for an implementation in which the fuel cells  110  supply electrical power to the refueling device  116 . During waste removal operations, the waste handling unit  120  conveys waste from the waste storage unit  112  of the fuel cell system  102  to the refueling device  116 , and either stores this waste onboard or conveys it to an external waste storage unit  126 . For implementations in which little or no waste is accumulated by the fuel cell system  102 , the waste handling unit  120  can be optionally omitted. 
     Advantageously, the illustrated embodiment includes control and safety mechanisms to provide safe and regulated operations during refueling and waste removal. In particular, the fuel cell system controller  114  and the refueling device controller  122  operate in conjunction to control the refueling and waste removal operations in a substantially automated manner and in compliance with environmental and safety regulations. The refueling and waste removal operations can occur sequentially or in parallel, the latter of which allows enhanced servicing throughput and reduces the downtime of the target device  106 . In addition, the illustrated embodiment allows multiple fuel cell systems, each having its own distinct refueling and waste removal requirements, to be serviced by the same refueling device  116 , with little or no modification and operator supervision when servicing the fuel cell systems. As further described herein, this can be accomplished by establishing a communication link between the fuel cell system controller  114  and the refueling device controller  122 , thereby allowing the fuel cell system controller  114  to control the refueling device  116  in accordance with particular refueling and waste removal requirements of the fuel cell system  102 . 
     Attention next turns to  FIG. 2 , which illustrates a refueling device  200  to service a fuel cell system  202  according to another embodiment of the invention. 
     In the illustrated embodiment, the refueling device  200  includes a fuel input port  204 , an internal fuel storage unit  206 , a fuel conveyance unit  208 , a fuel filtering unit  210 , a fuel output port  212 , and a set of sensors  214 , which collectively correspond to a fuel handling unit to supply fuel to the fuel cell system  202 . Various components of the fuel handling unit are connected to one another to define a fuel flow pathway extending between the fuel input port  204  and the fuel output port  212 . It should be recognized that the particular implementation of these components is provided by way of example, and these components can be combined, sub-divided, or re-ordered in accordance with another implementation. Also, certain of these components can be optionally omitted for another implementation. 
     Referring to  FIG. 2 , the particular implementation of the fuel input port  204  can vary depending upon whether the refueling device  200  operates at a fixed location or is a mobile device. In the case of the refueling device  200  operating at a fixed location, fuel can be conveyed, via the fuel input port  204 , from an external fuel storage unit (not illustrated), and the fuel input port  204  can be implemented to provide a fixed fluid connection with a manual shut-off mechanism. This fixed implementation allows multiple refueling devices to share a common external fuel storage unit, and to service multiple fuel cell systems for enhanced servicing throughput. In the case of a mobile implementation, the refueling device  200  stores fuel onboard in the internal fuel storage unit  206 , and subsequently conveys the fuel to the fuel cell system  202  in situ. In this case, the fuel input port  204  can be implemented to provide a temporary fluid connection, with a mechanism to facilitate engaging and disengaging with an external fuel storage unit (not illustrated). Similarly, the fuel output port  212  can include a mechanism to facilitate engaging and disengaging with the fuel cell system  202 . In addition, the particular implementation of the fuel output port  212  can depend upon environmental and safety regulations at a location in which the fuel cell system  202  operates. For example, the fuel output port  232  can be implemented to provide a positive-locking, dry-break fluid connection. For enhanced safety, a flow of fuel should not exceed a blocking pressure rating of the fuel output port  212 . 
     The internal fuel storage unit  206  can be implemented as a relatively rigid fuel storage tank or as a relatively non-rigid or expandable fuel storage tank. In the case of the refueling device  200  operating at a fixed location, the internal fuel storage unit  206  can be optionally omitted. In the case of a mobile implementation, the internal fuel storage unit  206  provides onboard storage of fuel, and the fuel conveyance unit  208  conveys the fuel to the fuel cell system  202  in situ. The fuel conveyance unit  208  can be implemented as a pump along with other optional flow control or flow restrictive components to meet safety regulations and a desired level of servicing throughput. In the illustrated embodiment, the fuel conveyance unit  208  conveys fuel along a substantially unidirectional flow pathway passing through the fuel output port  212 . However, it is also contemplated that the fuel conveyance unit  208  can convey fuel along a bi-directional flow pathway. In such manner, the refueling device  200  can. remove substantially all fuel from the fuel cell system  202  to facilitate its shipment to another location. 
     As illustrated in  FIG. 2 , the fuel filtering unit  210  is disposed along the fuel flow pathway, and operates to reduce Or minimize the level of contaminants in fuel supplied to the fuel cell system  202 . In such manner, the fuel filtering unit  210  allows the use of a lower purity or lower grade fuel, thereby providing cost savings. The fuel filtering unit  210  can be implemented as a set of filters to process fuel in-line as it is conveyed to the fuel cell system  202  or as part of separate filtering operations, such as along a re-circulating fuel filtration pathway. Examples of filters that can be used include particulate and ionic filters. Particulate filters are typically passive components including screens or meshes, but can also operate with a centrifugal or another active mechanism. Ionic filters typically involve a chemical or electrochemical mechanism to achieve separation of contaminants. An in-line implementation of the fuel filtering unit  210  can simplify related hardware and control mechanisms. In the case of a re-circulating implementation, the fuel filtering unit  210  can be powered and operated during time intervals prior to servicing the fuel cell system  202 . 
     The sensors  214  are connected to the internal fuel storage unit  206 , the fuel conveyance unit  208 , and the fuel filtering unit  210 , and operate to monitor an operational status of these connected components. The particular implementation of the sensors  214  can vary depending upon the particular implementation of these connected components and the desired complexity for related control mechanisms. For example, the sensors  214  can monitor fault events related to the internal fuel storage unit  206 . In particular, a leak sensor can produce an output indicative of a critical fault event that terminates refueling operations, while a level sensor can produce an output indicative of an empty or low fuel level. In the case of an expandable implementation of the internal fuel storage unit  206 , a pressure sensor can be used in place of a level sensor to monitor fuel levels. For implementations in which fuel is actively pumped or re-circulated, an electrical current or voltage sensor can monitor pumping or re-circulating operations and indicate a fault event, such, as a pump failure, a line blockage, or a vacuum condition. The sensors  214  can also monitor fuel flow rates and pressures, such as using in-line flow meters and pressure gauges. 
     In the illustrated embodiment, the refueling device  200  also includes a waste input port  216 , a waste conveyance unit  218 , a waste filtering unit  220 , an internal waste storage unit  222 , a waste output port  224 , and a set of sensors  226 , which collectively correspond to a waste handling unit to remove waste from the fuel cell system  202 . Various components of the waste handling unit are connected to one another to define a waste flow pathway extending between the waste input port  216  and the waste output port  224 . It should be recognized that the particular implementation of these components is provided by way of example, and these components can be combined, sub-divided, or re-ordered in accordance with another implementation. Also, certain components can be optionally omitted for another implementation. In the illustrated embodiment, the waste flow pathway is separate from the fuel flow pathway to reduce or minimize mixing of waste and fuel. However, it is also possible that the waste flow pathway and the fuel flow pathway can share a common pathway for handling fuel and waste. 
     Referring to  FIG. 2 , the waste input port  216  and the waste output port  224  can be implemented in a similar manner as the fuel output port  212  and the fuel input port  204 , respectively. For example, in the case of the refueling device  200  operating at a fixed location, the waste output port  224  can be implemented to provide a fixed fluid connection, and, in the case of a mobile implementation, the waste output port  224  can be implemented to provide a temporary fluid connection, with a mechanism to facilitate engaging and disengaging with an external waste storage unit (not illustrated). The waste input port  216  can include a mechanism to facilitate engaging and disengaging with the fuel cell system  202 , along with a mechanism to provide a positive-locking, dry-break fluid connection. In the illustrated embodiment, the waste input port  216  is separate from the fuel output port  212 , and serves as a dedicated port for handling waste. However, it is also contemplated that a common port can be used for handling fuel and waste. 
     The internal waste storage unit  222  and the waste conveyance unit  218  can be implemented in a similar manner as the internal fuel storage unit  206  and the fuel conveyance unit  208 , respectively. For example, the internal waste storage unit  222  can be implemented as a relatively rigid waste storage tank or as an expandable waste storage tank. In the case of the refueling device  200  operating at a fixed location, the internal waste storage unit  222  can be optionally omitted. In the case of a mobile implementation, the refueling device  200  stores waste onboard in the internal waste storage unit  222 , and subsequently conveys the waste to an external waste storage unit (not illustrated). Similar to the fuel conveyance unit  208 , the waste conveyance unit  218  can be implemented as a pump along with other optional flow control or flow restrictive components. In the illustrated embodiment, the waste conveyance unit  218  conveys waste from the fuel cell system  202  along a substantially unidirectional flow pathway passing through the waste input port  216 . However, it is also contemplated that the waste conveyance unit  218  can convey waste along a bi-directional flow pathway. In such manner, the waste output port  224  can be optionally omitted, and the refueling device  200  can remove waste from the fuel cell system  202 , via the port  216 , and can subsequently convey the waste, via the same port  216 , to an external waste storage unit (not illustrated). 
     As illustrated in  FIG. 2 , the waste filtering unit  220  is disposed along the waste flow pathway, and operates to reduce or minimize the level of contaminants in waste removed from the fuel cell system  202 . In the case of alcohol combustion, a typical waste is water along with contaminants, such as trace amounts of an alcohol-based fuel, metal ions, and dissolved carbon dioxide. This waste can be filtered to allow its disposal in accordance with environmental regulations or to allow its recycling for use in the fuel filtering unit  210 . Similar to the fuel filtering unit  210 , the waste filtering unit  220  can be implemented as a set of filters to process waste in-line or as part of separate filtering operations, such as along a re-circulating waste filtration pathway. In the case of a re-circulating implementation, the waste filtering unit  220  can be powered and operated during time intervals prior to servicing the fuel cell system  202 . 
     The sensors  226  are connected to the internal waste storage unit  222 , the waste filtering unit  220 , and the waste conveyance unit  218 , and operate to monitor an operational status of these connected components. The sensors  226  can be implemented in a similar manner as the sensors  214 , and can include a particular combination of leak sensors, level sensors, pressure sensors, electrical current or voltage sensors, flow meters, or pressure gauges. 
     Still referring to  FIG. 2 , the refueling device  200  also includes a refueling device controller  228 , which is connected to and directs operation of various components of the refueling device  200 . In the illustrated embodiment, the refueling device controller  228  is implemented as a slave controller that directs refueling and waste removal operations subject to control by the fuel cell system  202 . In conjunction, the refueling device controller  228  tracks the operational status of the refueling device  200  in accordance with outputs of the sensors  214  and  226 , and conveys the operational status to the fuel cell system  202 . This is accomplished via a communication port  234 , which can be implemented to provide a wired connection, such a cable connection, or a wireless connection, such as an optical or radio-frequency connection. A wired connection can allow for both data communication and electrical power to be conveyed between the fuel cell system  202  and the refueling device  200 , while a wireless connection can simplify operator intervention when servicing the fuel cell system  202 . In the vicinity of several refueling devices, as can be found in certain industrial applications, a wired connection can be implemented so as to uniquely identify the particular refueling device  200  connected to the fuel cell system  202 . 
     The refueling device  200  further includes a user interface  230  and a power source  232 , which can be implemented as a battery. The user interface  230  provides indications of operational status to an operator, including alerts regarding any fault events, and the power source  232  supplies electrical power to the refueling device controller  228  and other active components of the refueling device  200 . In general, the refueling device  200  can derive electrical power from any of three sources: (1) the power source  232 ; (2) an external power source (not illustrated), such as an alternating current power source; and (3) the fuel cell, system  202 . In the case of the refueling device  200  operating at a fixed location, electrical power can be supplied by either the fuel cell system  202  or by an external power source, in which case the onboard power source  232  can be optionally omitted. For a mobile implementation of the refueling device  200 , electrical power can be supplied by either the fuel cell system  202  or by the onboard power source  232 . 
     The fuel cell system  202  includes a fuel input port  236  and a fuel storage unit  238 , which are connected to one another to define a fuel flow pathway that supplies fuel to a set of fuel cells  240 . The fuel input port  236  can be implemented in a similar manner as the fuel output port  232 , and can include a mechanism to facilitate engaging and disengaging with the refueling device  200 . The fuel storage unit  238  can be implemented as a relatively rigid fuel storage tank or as an expandable fuel storage tank, A set of sensors  242  are connected to the fuel storage unit  238 , and operate to monitor an operational status of the fuel storage unit  238 . The particular implementation of the sensors  242  can vary depending upon the particular implementation of the fuel storage unit  238  and the desired complexity for related control mechanisms. For example, the sensors  242  can include a level sensor or a pressure sensor to produce outputs indicative of fuel levels. Other implementations of the sensors  242  can include a particular combination of leak sensors, flow meters, or pressure gauges. 
     Referring to  FIG. 2 , the fuel cell system  202  also includes a waste storage unit  244  and a waste output port  246 , which are connected to one another to define a waste flow pathway that removes waste from the fuel cells  240 . The waste output port  246  can be implemented in a similar manner as the waste input port  216 , and can include a mechanism to facilitate engaging and disengaging with the refueling device  200 . In the illustrated embodiment, the waste output port  246  is separate from the fuel input port  236 , and serves as a dedicated port for handling waste. However, it is also contemplated that a common port can be used for handling fuel and waste. The waste storage unit  244  can be implemented as a relatively rigid waste storage tank or as an expandable waste storage tank. A set of sensors  248  are connected to the waste storage unit  244 , and operate to monitor an operational status of the waste storage unit  244 . The particular implementation of the sensors  248  can vary depending upon the particular implementation of the waste storage unit  244  and the desired complexity for related control mechanisms. For example, the sensors  248  can include a level sensor or a pressure sensor to produce outputs indicative of waste levels. Other implementations of the sensors  248  can include a particular combination of leak sensors, flow meters, or pressure gauges. 
     The fuel cell system  202  further includes a fuel cell system controller  250 , which is connected to and directs operation of various components of the fuel cell system  202 . In particular, the fuel cell system controller  250  tracks the operational status of the fuel cell system  202  in accordance with outputs of the sensors  242  and  248 . In the illustrated embodiment, the fuel cell system controller  250  is implemented as a master controller that directs refueling and waste removal operations by controlling the refueling device controller  228 . In conjunction, the fuel cell system controller  250  tracks the operational status of the refueling device  200  as conveyed by the refueling device controller  228 . This is accomplished via a communication port  252 , which can be implemented to provide a wired connection or a wireless connection. It is contemplated that the master-slave assignments can be switched for another implementation, with the refueling device controller  228  serving as a master controller, and the fuel cell system controller  250  serving as a slave controller. 
     A set of sensors  254  are connected to the fuel input port  236 , the communication port  252 , and the waste output port  246 , and operate to monitor a connection status of the ports  236 ,  252 , and  246 . The sensors  254  can include a proximity or contact sensor to produce an output indicative of a fluid connection between the ports  212  and  236  or between the ports  216  and  246 , and a proximity or contact sensor to produce an output indicative of a wired or wireless connection between the ports  234  and  252 . The fuel cell system controller  250  tracks the connection status of the ports  236 ,  252 , and  246  in accordance with outputs of the sensors  254 , so as to automatically detect an operator&#39;s intention to service the fuel cell system  202 . 
     The operation of the fuel cell system controller  250  can be further understood with reference to  FIG. 3 , which illustrates a state diagram for refueling and waste removal operations, according to an embodiment of the invention. 
     Referring to  FIG. 3 , the fuel cell system controller  250  initially directs operation of the fuel cell system  202  in a normal operation state (block  300 ). If the fuel cell system controller  250  first detects a fluid connection to either of, or both, the fuel input port  236  and the waste output port  246 , the fuel cell system controller  250  exits the normal operation state and waits for a wired or wireless connection to the communication port  252  (block  302 ). If the wired or wireless connection is detected within a particular time interval, such as a pre-determined or operator-selectable time interval, the fuel cell system controller  250  establishes a communication link with the refueling device controller  228 . Otherwise, the fuel cell system controller  250  transitions to a fault state (block  312 ). Similarly, if the fuel cell system controller  250  first detects a wired or wireless connection to the communication port  252 , the fuel cell system controller  250  exits the normal operation state and waits for a fluid connection to either of, or both, the fuel input port  236  and the waste output port  246  (block  304 ). If the fluid connection is detected within a particular time interval, such as a pre-determined or operator-selectable time interval, the fuel cell system controller  250  establishes a communication link with the refueling device controller  228 . Otherwise, the fuel cell system controller  250  transitions to the fault state (block  312 ). A communication link can be established using a set of request and acknowledgement messages that are exchanged between the fuel cell system controller  250  and the refueling device controller  228 . Once the communication link is established, the fuel cell system controller  250  transitions to a refueling operation state (block  306 ). 
     In the refueling operation state, the fuel cell system controller  250  tracks the operational status of the fuel cell system  202  as well as the operational status of the refueling device  200 . In particular, the fuel cell system controller  250  determines fuel and waste levels of the fuel cell system  202 . If the fuel level of the fuel cell system  202  is below a threshold fuel level, such as a pre-determined or operator-selectable fuel level, the fuel cell system controller  250  assumes control of the refueling device  200 , via the refueling device controller  228 , and initiates refueling operations (block  308 ). If the waste level of the fuel cell system  202  is at or above a threshold waste level, such as a pre-determined or operator-selectable waste level, the fuel cell system controller  250  initiates waste removal operations (block  310 ). The refueling and waste removal operations can occur sequentially or in parallel. 
     If a fault event is detected while in the refueling operation state, the fuel cell system controller  250  transitions to the fault state, and alerts an operator via the user interface  230  (block  312 ). Examples of fault events include an overcurrent condition of the fuel conveyance unit  208 , an overcurrent condition of the waste conveyance unit  218 , a leak of the internal fuel storage unit  206  of the refueling device  200 , an empty or low fuel level of the internal fuel storage unit  206 , a leak of the internal waste storage unit  222  of the refueling device  200 , a full waste level of the internal waste storage unit  222 , the refueling operations taking longer than a particular time interval, and the waste removal operations taking longer than a particular time interval. In the case of a critical fault event, such as a leak, the fuel cell system controller  250  can substantially immediately terminate the refueling and waste removal operations. In the event of a non-critical fault event, the fuel cell system controller  250  can direct the refueling and waste removal operations to be continued in a safe manner, albeit at a reduced performance level. The fuel cell system controller  250  can reference mass flow characteristics of fuel and waste, characteristics of the fuel and waste handling units, and other information contained in an associated memory to control and monitor the flow of fuel and waste. If the flow characteristics are not within expected ranges, the fuel cell system controller  250  can detect a fault event, and can alert the operator via the user interface  230 . 
     In the absence of a fault event, the fuel cell system controller  250  terminates the refueling operations once the fuel level of the fuel cell system  202  is at or above the threshold fuel level. Also, once the waste level of the fuel cell system  202  is below the threshold waste level, the fuel cell system controller  250  terminates the waste removal operations. The fuel cell system controller  250  then transitions to a refueling wrap-up operation state (block  314 ). 
     In the refueling wrap-up operation state, the fuel cell system controller  250  alerts the operator regarding completion of refueling and waste removal, via the user interface  230 . Also, the fuel cell system controller  250  waits for the operator to disconnect the refueling device  200  with respect to the fuel input port  236 , the communication port  252 , and the waste output port  246 . If disconnection does not take place within a particular time interval, such as a pre-determined or operator-selectable time interval, the fuel cell system controller  250  transitions to the fault state (block  312 ). Otherwise, the fuel cell system controller  250  terminates the communication link with the refueling device controller  228 , and transitions back to the normal operation state (block  300 ). 
     The foregoing provides a general overview of some embodiments of the 
     invention. Attention next turns to  FIG. 4  through  FIG. 7 , which illustrate specific 
     implementations in. accordance with other embodiments of the invention. 
       FIG. 4  illustrates a refueling device  400  implemented in accordance with an embodiment of the invention. In particular, the refueling device  400  is implemented so as to have reduced complexity by omitting internal fuel and waste storage tanks, sensors, and other related components. 
     Referring to  FIG. 4 , the refueling device  400  includes a fuel input port  402 , a fuel pump  404 , and a fuel output port  406 , which are connected to one another to define a fuel flow pathway and collectively correspond to a fuel handling unit. During refueling operations, the fuel pump  404  conveys fuel from an external fuel storage tank  408  to a fuel cell system (not illustrated). The refueling device  400  also includes a waste input port  410 , a waste pump  412 , and a waste output port  414 , which are connected to one another to define a waste flow pathway and collectively correspond to a waste handling unit. The fuel output port  406  and the waste input port  410  are implemented within a common hose or tube  426 , which facilitates simultaneous engagement and disengagement with the fuel cell system. During waste removal operations, the waste pump  412  conveys waste from the fuel cell system to an external waste storage tank  416 . Additional reduction in complexity is accomplished by omitting sensors to monitor an operational state of the fuel pump  404  and the waste pump  412 . Still referring to  FIG. 4 , the refueling device  400  further includes a refueling device controller  418 , which is connected to and directs operation of a user interface  420  and other components of the refueling device  400 . Data communication is established via a communication port  424 , which is implemented to provide a wireless connection between the refueling device controller  418  and the fuel cell system. In the illustrated embodiment, electrical power is supplied by an onboard power source  422 . 
       FIG. 5  illustrates a refueling device  500  implemented in accordance with another embodiment of the invention. In particular, the refueling device  500  is implemented so as to have reduced complexity by omitting a fuel pump, sensors, and other related components. Omission of the fuel pump can reduce the possibility of electrical sparks, and can be desirable for certain hazardous environments. 
     Referring to  FIG. 5 , the refueling device  500  includes a fuel input port  502 , a flow control component  504 , and a fuel output port  506 , which are connected to one another to define a fuel flow pathway and collectively correspond to a fuel handling unit. In the illustrated embodiment, the fuel handling unit operates by gravity, and, during refueling operations, fuel is gravity-fed from an external fuel storage tank  508  and conveyed to a fuel cell system (not illustrated). The flow control component  504  can be implemented as a two-way solenoid valve or another type of controllable valve to gate the flow of fuel to the fuel cell system. The refueling device  500  also includes a waste input port  510 , a waste pump  512 , and an internal waste storage tank  514 , which are connected to one another to define a waste flow pathway and collectively correspond to a waste handling unit. The fuel output port  506  and the waste input port  510  are implemented within a common hose or tube  526 , which facilitates simultaneous engagement and disengagement with the fuel cell system. During waste removal operations, the waste pump  512  conveys waste from the fuel cell system to the internal waste storage tank  514 . When the internal waste storage tank  514  becomes full, the tank  514  is removed, emptied, and then returned to the refueling device  500 . The internal waste storage tank  514  can be formed from a translucent or transparent material and placed at a visible location within the refueling device  500 , thereby obviating the use of sensors to monitor waste levels. Additional reduction in complexity is accomplished by omitting sensors to monitor an operational state of the waste pump  512 . Still referring to  FIG. 5 , the refueling device  500  further includes a refueling device controller  518 , which is connected to and directs operation of a user interface  520  and other components of the refueling device  500 . Data communication is established via a communication port  524 , which is implemented to provide a wireless connection, and electrical power is supplied by an onboard power source  522 . 
       FIG. 6  illustrates a refueling device  600  implemented in accordance with another embodiment of the invention. In particular, the refueling device  600  is implemented so as to provide a bi-directional flow of waste. 
     Referring to  FIG. 6 , the refueling device  600  includes a fuel input port  602 , an internal fuel storage tank  604 , a fuel pump  606 , a fuel output port  608 , and a sensor  610 , which are connected to one another and collectively correspond to a fuel handling unit. During refueling operations, the fuel pump  606  conveys fuel from the internal fuel storage tank  604  to a fuel cell system (not illustrated) via the fuel output port  608 . The sensor  610  monitors fuel levels, and can be implemented as a level sensor or a pressure sensor. When the internal fuel storage tank  604  becomes empty, the fuel pump  606  replenishes the tank  604  with fuel from an external fuel storage tank (not illustrated) via the fuel input port  602 . The refueling device  600  also includes a waste input port  612 , a waste pump  614 , a pair of three-way solenoid valves  616   a  and  616   b,  an internal waste storage tank  618 , and a sensor  630 , which are connected to one another and collectively correspond to a waste handling unit. The solenoid valves  616   a  and  616   b  are controlled to provide a bi-directional flow of waste. During waste removal operations, the waste pump  614  conveys waste from the fuel cell system to the internal waste storage tank  618 , via ports  620   a ′ and  620   a ″ of the solenoid valve  616   a  and via ports  620   b ′ and  620   b ″ of the solenoid valve  616   b.  The sensor  630  monitors waste levels, and can be implemented as a level sensor or a pressure sensor. When the internal waste storage tank  618  becomes full, the waste pump  614  conveys waste from the internal waste storage tank  618  to an external waste storage tank (not illustrated), via ports  620   b ″ and  620   b ′″ of the solenoid valve  616   b  and via ports  620   a ′″ and  620   a ′ of the solenoid valve  616   a.  Still referring to  FIG. 6 , the refueling device  600  further includes a refueling device controller  622 , which is connected to and directs operation of a user interface  624  and other components of the refueling device  600 . In the illustrated embodiment, port  626  is implemented as a common port for data communication and for supplying electrical power from the fuel cell system to various components of the refueling device  600 . 
       FIG. 7  illustrates a refueling device  700  implemented in accordance with a further embodiment of the invention. In particular, the refueling device  700  is implemented so as to have reduced plumbing by including a common port  708  for passing fluid and waste and a flow pathway selector, which is implemented as a three-way solenoid valve  710 . The solenoid valve  710  is controlled to select between a fuel flow pathway and a waste flow pathway passing through the common port  708 . 
     Referring to  FIG. 7 , the refueling device  700  includes an internal fuel storage tank  702 , a fuel pump  704 , and a sensor  706 , which are connected to one another and collectively correspond to a fuel handling unit. During refueling operations, the fuel pump  704  conveys fuel from the internal fuel storage tank  702  to a fuel cell system (not illustrated), along a fuel flow pathway passing through ports  712 ′ and  712 ″ of the solenoid valve  710  and through the common port  708 . The sensor  706  monitors fuel levels and can be implemented as a level sensor or a pressure sensor. When the internal fuel storage tank  702  becomes empty, the tank  702  is removed, replenished with fuel, and then returned to the refueling device  700 . The refueling device  700  also includes a waste pump  714 , a pair of three-way solenoid valves  716   a  and  716   b,  an internal waste storage tank  718 , and a sensor  730 , which are connected to one another and collectively correspond to a waste handling unit. The solenoid valves  716   a  and  716   b  are controlled to provide a bi-directional flow of waste. During waste removal operations, the waste pump  714  conveys waste from the fuel cell system to the internal waste storage tank  718 , along a waste flow pathway passing through the common port  708 , through ports  712 ″ and  712 ″′ of the solenoid valve  710 , through ports  720   a ′ and  720   a ″ of the solenoid valve  716   a,  and through ports  720   b ′ and  720   b ″ of the solenoid valve  716   b.  The sensor  730  monitors waste levels, and can be implemented as a level sensor or a pressure sensor. When the internal waste storage tank  718  becomes full, the waste pump  714  conveys waste from the internal waste storage tank  718  to an external waste storage tank (not illustrated), along a waste flow pathway passing through ports  720   b ″ and  720   b ′″ of the solenoid valve  736   b,  through ports  720   a ′″ and  720   a ′ of the solenoid valve  716   a,  through ports  712 ″′ and  712 ″ of the solenoid valve  710 , and through the common port  708 . 
     Still referring to  FIG. 7 , the refueling device  700  further includes a refueling device controller  722 , which is connected to and directs operation of a user interface  724  and other components of the refueling device  700 . In the illustrated embodiment, port  726  is implemented as a common port for data communication and for supplying electrical power from the fuel cell system to various components of the refueling device  700 . 
     Some embodiments of the invention relate to a computer-readable storage medium having computer code stored thereon for performing various computer-implemented operations. The media and computer code may be those specially designed and constructed for the purposes of the invention, or they may be of the kind well known and available to those having skill in the computer software arts. Examples of computer-readable media include, but are not limited to: magnetic storage media such as hard disks, floppy disks, and magnetic tape; optical storage media such as Compact Disc/Digital Video Discs (“CD/DVDs”), Compact Disc-Read Only Memories (“CD-ROMs”), and holographic devices; magneto-optical storage media such as floptical disks; and hardware devices that are specially configured to store and execute program code, such as Application-Specific Integrated Circuits (“ASICs”), Programmable Logic Devices (“PLDs”), and ROM and RAM devices. Examples of computer code include, but are not limited to, machine code, such as produced by a compiler, and files containing higher-level code that are executed by a computer using an interpreter. For example, an embodiment of the invention may be implemented using Java, C++, or other object-oriented programming language and development tools. Additional examples of computer code include, but are not limited to, encrypted code and compressed code. 
     Some embodiments of the invention can be implemented using computer code in place of, or in combination with, hardwired circuitry. For example, with reference to  FIG. 1 , the refueling device controller  122  and the fuel cell system controller  114  can be implemented using computer code, hardwired circuitry, or a combination thereof. 
     While the invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, or process to the objective, spirit and scope of the invention. All such modifications are intended to be within the scope of the claims appended hereto. In particular, while the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the invention. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not limitations of the invention.