Abstract:
A method and apparatus for providing a balanced fluid supply through multiple feeds are disclosed. The method comprises supplying the fluid through a plurality of feeds from a common fluid accumulator; determining the fluid pressure in a common fluid accumulator; and controlling the fluid pressure in the common fluid accumulator responsive to the fluid pressure sensed therein to maintain the fluid pressure within a predetermined range. The balanced fluid supply comprises a common fluid accumulator; a plurality of feeds from the common fluid accumulator; and a control system capable of controlling the pressure of the fluid supplied from the common fluid accumulator to the feeds responsive to a determined pressure of fluid in the common fluid accumulator.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention pertains to fluid supplies for fuel processors, and, more particularly, to a fluid balance control system for use in a fuel processor.  
           [0003]    2. Description of the Related Art  
           [0004]    Fuel cell technology is an alternative energy source for more conventional energy sources employing the combustion of fossil fuels. A fuel cell typically produces electricity, water, and heat from a fuel and oxygen. More particularly, fuel cells provide electricity from chemical oxidation-reduction reactions and possess significant advantages over other forms of power generation in terms of cleanliness and efficiency. Typically, fuel cells employ hydrogen as the fuel and oxygen as the oxidizing agent. The power generation is proportional to the consumption rate of the reactants.  
           [0005]    A significant disadvantage which inhibits the wider use of fuel cells is the lack of a widespread hydrogen infrastructure. Hydrogen has a relatively low volumetric energy density and is more difficult to store and transport than the hydrocarbon fuels currently used in most power generation systems. One way to overcome this difficulty is the use of “fuel processors” or “reformers” to convert the hydrocarbons to a hydrogen rich gas stream, commonly referred to as “reformate”, which can be used as a feed for fuel cells. Hydrocarbon-based fuels, such as natural gas, LPG, gasoline, and diesel, require conversion processes to be used as fuel sources for most fuel cells. Current art uses multi-step processes combining an initial conversion process with several clean-up processes. The initial process is most often steam reforming (“SR”), autothermal reforming (“ATR”), catalytic partial oxidation (“CPOX”), or non-catalytic partial oxidation (“POX”). The clean-up processes are usually comprised of a combination of desulfurization, high temperature water-gas shift, low temperature water-gas shift, selective CO oxidation, or selective CO methanation. Alternative processes include hydrogen selective membrane reactors and filters.  
           [0006]    Thus, many types of fuels can be used; some of them hybrids with fossil fuels, but the ideal fuel is hydrogen. If the fuel is, for instance, hydrogen, then the combustion is very clean and, as a practical matter, only the water is left after the dissipation and/or consumption of the heat and the consumption of the electricity. Most readily available fuels (e.g., natural gas, propane and gasoline) and even the less common ones (e.g., methanol and ethanol) include hydrogen in their molecular structure. Some fuel cell implementations therefore employ a “fuel processor” that processes a particular fuel to produce a reformate stream used to fuel the fuel cell.  
           [0007]    The handling of fluids is consequently an important component of fuel processor design. Typically, for instance, several aspects of the fuel processor&#39;s operation require a supply of air. Fuel processors therefore frequently have an air supply that feeds air to the parts of the fuel processor needing air. In a typical single-source air supply system, air coming off of a compression device (blower or compressor) is split up to deliver fractions of the supply to various sub-units within the fuel processor. Each air line branching off to each sub-unit is metered and monitored by a flow controller and flow meter or a combination of both in one unit. However, in this configuration, the upstream pressure of the flow controllers (downstream pressure of the compression device) fluctuates when the controllers are opening and closing. As a result, the flows fluctuate, causing an undesirable imbalance in air to fuel ratio. The imbalance causes inconsistency in air flows to the various downstream sub-units, potentially causing upset conditions. Some approaches try to remedy this effect by providing independent air sources for each of the sub-units. However, this leads to more costly components, complicated control schemes, and increased potential breakdown of additional components. Still others have used orifice plates to meter flow to various units. This tends to make the design complicated as orifice plates have to be adjusted once the air demands change. Similar problems are encountered with the handling of other fluids.  
           [0008]    The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.  
         SUMMARY OF THE INVENTION  
         [0009]    A method and apparatus for providing a balanced fluid supply through multiple feeds are disclosed. The method comprises supplying the fluid through a plurality of feeds from a common fluid accumulator; determining the fluid pressure in a common fluid accumulator; and controlling the fluid pressure in the common fluid accumulator responsive to the fluid pressure sensed therein to maintain the fluid pressure within a predetermined range. The balanced fluid supply comprises a common fluid accumulator; a plurality of feeds from the common fluid accumulator; and a control system capable of controlling the pressure of the fluid supplied from the common fluid accumulator to the feeds responsive to a determined pressure of fluid in the common fluid accumulator. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:  
         [0011]    [0011]FIG. 1 illustrates one particular embodiment of a fuel processor assembled and operated in accordance with the present invention;  
         [0012]    [0012]FIG. 2 details the air subsystem of the fuel processor in FIG. 1; and  
         [0013]    [0013]FIG. 3A and FIG. 3B conceptually illustrate a computing apparatus as may be used in the implementation of one particular embodiment of the present invention. 
     
    
       [0014]    While the invention is susceptible to various modifications and alternative forms, the drawings illustrate specific embodiments herein described in detail by way of example. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.  
         [0016]    [0016]FIG. 1 illustrates one embodiment of an apparatus  100  assembled and operated in accordance with the present invention. The apparatus  100  comprises a fuel processor  101 , a fuel cell  103 , and a control system  107 . The fuel cell  103  is preferably a Proton Exchange Membrane (“PEM”) fuel cell, but other types of fuel cells may be used. The invention is not limited by the implementation of the fuel cell  103 . More particularly, in the illustrated embodiment, the fuel processor  100  comprises several modular physical subsystems, namely:  
         [0017]    an autothermal reformer (“ATR”)  102  that performs the oxidation-reduction reaction that reforms the fuel input to the fuel processor  100  into a gas for a fuel cell  103 , and which employs a preferential oxidizer  105  to that end;  
         [0018]    an oxidizer  104 , which is an anode tailgas oxidizer (“ATO”) in the illustrated embodiment, that mixes steam, fuel, and air to create a fuel mixture delivered as a reformate to the ATR  102 ;  
         [0019]    a fuel subsystem  106 , that delivers an input fuel (natural gas, in the illustrated embodiment) to the oxidizer  104  for mixing into the reformate delivered to the ATR  102 ;  
         [0020]    a water subsystem  108 , that delivers water to the oxidizer  104  for mixing into the reformate delivered to the ATR  102 ;  
         [0021]    an air subsystem employing a closed loop, feedback control technique to maintain a constant pressure of air supplied to the ATR  102 , the preferential oxidizer  105 , and the oxidizer  104  from a common air source;  
         [0022]    a thermal subsystem  112 , that regulates the operational temperatures of the ATR  102  and the oxidizer  104 ; and  
         [0023]    a control system  107  capable of controlling the operation of the ATR  102 , the oxidizer  104 , the fuel subsystem  106 , the water subsystem  108 , the air subsystem  110 , and the thermal subsystem  112 .  
         [0024]    Particular implementations of the air subsystem  110  are illustrated in FIG. 2.  
         [0025]    [0025]FIG. 2 depicts one particular implementation of the air subsystem  110 . A compressor  200 , including a motor  202 , receives filtered air from the ambient atmosphere via an air intake  204 , a filter  206 , and a flow meter  208   a  and compresses it into an accumulator  210 . The air from the accumulator  210  is then distributed through two feeds ATO, ATR over the lines  212 ,  214 , including the flow meters  208   b ,  208   c  and control valves  216 ,  218   a  to the oxidizer  104  and the ATR  102 . The air from the accumulator  210  is also distributed through a feed PrOx over the line  220  including a flow meter  208   d  and a control valve  218   b  to the preferential oxidizer  105 . Since the accumulator  210  supplies air to each of the feeds ATO, ATR, and PrOx, the air subsystem  110  provides a common air source for these three feeds.  
         [0026]    Each of the flow meters  208   a - 208   d  includes a respective instrumentation sensor  222   a - 222   d  through which it measures the flow of air therethrough. Note that some embodiments may omit the instrumentation sensors  222   a - 222   d . The accumulator  210  includes a pressure sensor  224 . Each of the motor  202 , control valve  216 , control valves  218   a - 218   b  includes a respective actuator  226   a - 226   d . The line  228  between the compressor  200  and the accumulator  210  includes, in the illustrated embodiment, a diagnostic sensor  230  for measuring the temperature of the air in the line  228 . The instrumentation sensors  222   a - 222   d , pressure sensor  224 , and actuators  226   a - 226   d  are utilized to control the operation of the air subsystem  110  in a manner described more fully below.  
         [0027]    The apparatus  100  also includes the control system  107 . One particular implementation  300  of the control system  107 , first shown in FIG. 1, is illustrated in FIG. 3A and FIG. 3B. Note that, in some embodiments, the control system may be implemented on a computing system comprising a number of computers such as the control system  107 , each of which may control some designated facet of the operation of the fuel processor  101 . However, in the illustrated embodiment, the computing apparatus  300  controls all aspects of the fuel processor  101  operation not under manual control. The computing apparatus  300  is rack-mounted, but need not be rack-mounted in all embodiments. Indeed, this aspect of any given implementations is not material to the practice of the invention. The computing apparatus  300  may be implemented as a desktop personal computer, a workstation, a notebook or laptop computer, an embedded processor, or the like.  
         [0028]    The computing apparatus  300  illustrated in FIG. 3A and FIG. 3B includes a processor  305  communicating with storage  310  over a bus system  315 . The storage  310  may include a hard disk and/or random access memory (“RAM”) and/or removable storage such as a floppy magnetic disk  317  and an optical disk  320 . The storage  310  is encoded with a data structure  325  storing the data set acquired as discussed above, an operating system  330 , user interface software  335 , and an application  365 . The user interface software  335 , in conjunction with a display  340 , implements a user interface  345 . The user interface  345  may include peripheral I/O devices such as a key pad or keyboard  350 , a mouse  355 , or a joystick  360 . The processor  305  runs under the control of the operating system  330 , which may be practically any operating system known to the art. The application  365  is invoked by the operating system  330  upon power up, reset, or both, depending on the implementation of the operating system  330 .  
         [0029]    The present invention employs a closed-loop control for the compressor  200  (or, in some embodiments, an air blower) with feedback from the pressure sensor  224  inside the accumulator  210  to maintain a fixed pressure feed to the ATR  102 , the preferential oxidizer  103 , and the oxidizer  104 . Each individual air supply line  212 ,  214 , and  220  is controlled and monitored by a flow controller (i.e., the control valves  216 ,  218   a - 218   b ) and a flow meter  208   b - 208   d . Inlet pressure to each of these flow controllers  216 ,  218   a - 218   b  is maintained constant, therefore, fluctuations in the flow rates are eliminated. This method enables the ability to quickly meet air flow requests to the process units without cross-interfering and negatively affecting the other process units.  
         [0030]    More particularly, the application  365  (shown in FIG. 3B) residing in the storage  310  is a software implemented control system. The application  310  reads the signal generated by the pressure sensor  224  indicating the pressure in the accumulator  210 . In some embodiments, the application  310  may also read the signals generated by the instrumentation sensors  222   a - 222   d  indicating the pressure in the supply lines  212 ,  214 , and  220 , respectively, although this pressure should be the same as that in the accumulator  210 . Some alternative embodiments may also read the signal generated by the instrumentation sensor pressure sensor  224   a  on the air intake  204 .  
         [0031]    The application  310  signals the actuators  226   a - 226   a  to open and close the control valves  216 ,  218   a - 218   b  to provide air in the desired volumes and pressures to the oxidizer  104 , ATR  102 , and preferential oxidizer  105 , respectively. As will be appreciated by those skilled in the art having the benefit of this disclosure, the desired pressures and volumes will be a function of the operational characteristics of the oxidizer  104 , ATR  102 , and preferential oxidizer  105 . Thus, the precise values will be implementation specific, and are not germane to the practice of the invention. Similarly, although a single pressure may be preferred for each of the oxidizer  104 , ATR  102 , and preferential oxidizer  105 , specifications for pressures are typically pressure ranges. Thus, the object is not so much to achieve a particular pressure, but to maintain the pressure on the inlets to the control valves  216 ,  218   a - 218   b  within a specified range.  
         [0032]    The application  310  also signals the actuator  226   d  to cycle the motor  202  coupled to the compressor  202  to maintain the proper pressure in the accumulator  210  as measured by the pressure sensor  224  and in the supply lines  212 ,  214 , and  220 . In the illustrated embodiment, this determination is made by sensing the pressure in the accumulator  210 , as described above. However, in some alternative embodiments, the determination may be made by sensing the pressure in anywhere between the compressor  220  and the accumulator  210 , i.e., anywhere in the line  228  feeding the accumulator  220 . If the sensed pressure in the accumulator  210  drops below a predetermined level, or, more precisely, outside specified range of pressure, then the application  310  actuates the motor  202  to raise the pressure in the accumulator  210 .  
         [0033]    Thus, in operation, the application  310  is aware of the desired pressure in the accumulator  210  and the volumes of air to be delivered over the supply lines  212 ,  214 , and  220  to the ATR  102 , the preferential oxidizer  103 , and the oxidizer  104 . This information may be, for instance, retrieved from the data structure  325  (shown in FIG. 3B). Through the instrumentation sensors  222   b - 222   d , the application  310  monitors the air flow in the supply lines  212 ,  214 , and  220 . Supplying air to the ATR  102 , oxidizer  104  and PrOx  105  leads to a drop in pressure inside the accumulator  210 . The pressure sensor  224  detects the pressure fluctuation and sends an output signal to the application  310 . When the application  310  detects a signal from pressure sensor  224  and determines that the pressure in the accumulator  210  has deviated from the desired pressure set point, the application  310  signals the actuator  226   d  to increase the speed to the motor  202 . This ramps up the air flow to the accumulator  210 . This maintains the pressure in the accumulator  210  at the desired pressure set point. As the pressure in the accumulator  210  is maintained at the desired set point, the pressure on the inlets to the control valves  216 ,  218   a - 218   b  is maintained steady, regardless of the air flow rates in lines  212 ,  214 , and  220 .  
         [0034]    The air supply by the compressor  200  through the accumulator  210  is therefore controlled in a closed-loop fashion using feedback from the instrumentations pressure sensor pressure sensor  224 . The air supply subsystem  110  employs this closed-loop, feedback control to maintain a constant pressure to control valves  216 ,  218   a - 218   b . Consequently, pressure drop across the orifices of the control valves  216 ,  218   a - 218   b  is also maintained constant. As previously mentioned, the accumulator  210  receives air from the compressor  200  via the line  228  and supplies air to each of the feeds ATO, ATR, and PrOx.  
         [0035]    In this sense, the accumulator  210  acts as an air manifold. However, whereas a manifold has zero dead volume, the accumulator  210  is designed to have enough dead volume to handle pressure fluctuations and to allow time for the signal, sent by pressure sensor pressure sensor  224 , to be received by the actuator  226   d  and for the closed-loop, feedback control to take place, when a fluctuation in pressure takes place inside the accumulator  210 . Pressure fluctuations are more gradual and will not greatly affect flows in lines  212 ,  214 , and  220 .  
         [0036]    Note that the illustrated embodiment handles air, a particular, gaseous fluid. The invention may also be applied to other types of fluids, such as water or fuel for the fuel processor. The differences in the nature of the fluids may permit or necessitate differences in implementation. For instance, to handle a liquid (e.g., water), the compressor  200  in FIG. 2 can be replaced by a pump. Thus, the compressor  200  is but one example of a fluid moving device that may be used to implement various alternative embodiments depending upon the fluid being handled. Other modifications and/or substitutions to the illustrated embodiment may also be desired to accommodate application of the invention to other fluids.  
         [0037]    This concludes the detailed description. The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.