Abstract:
A gas compressor that compresses a gas in a fuel cell system includes a shaft having first and second ends, a first bearing rotatably supporting the shaft at the first end and a second bearing rotatably supporting the shaft between the first and second ends. A sealing arrangement is concentric with the second bearing to inhibit migration of the gas between compartments of the compressor. The gas compressor can be a compressor, blower, pump or supercharger or turbo compressor that transports the gas.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to hydrogen supply systems, and more particularly to a bearing and seal arrangement for a hydrogen supply unit.  
       BACKGROUND OF THE INVENTION  
       [0002]     Fuel cell systems include a fuel cell stack that produces electrical energy based on a reaction between a hydrogen-based feed gas (e.g., pure hydrogen or a hydrogen reformate) and an oxidant feed gas (e.g., pure oxygen or oxygen-containing air). The hydrogen-based feed gas and oxidant feed gas are supplied to the fuel cell stack at appropriate operating conditions (i.e., temperature and pressure) for reacting therein. The proper conditioning of the feed gases is achieved by other components of the fuel cell stack to provide the proper operating conditions.  
         [0003]     The fuel cell system includes a compressor for compressing the hydrogen-based feed gas to an appropriate operating pressure for reaction in the fuel cell stack. The hydrogen-based feed gas inherently effects the durability of the compressor components. As a result, compressor designs attempt to limit contact between the compressor components and the hydrogen-based feed gas. Traditional compressor designs, however, include a bearing that supports an end of a shaft and that is immersed in the hydrogen-based feed gas. Further, traditional compressor designs are not optimally designed and, as a result, are less cost effective, more complex and less durable than desired.  
       SUMMARY OF THE INVENTION  
       [0004]     Accordingly, the present invention provides a gas compressor to compress a gas in a fuel cell system. The gas compressor includes a shaft having first and second ends, a first bearing rotatably supporting the shaft at the first end and a second bearing rotatably supporting the shaft between the first and second ends. A sealing arrangement is concentric with the second bearing to inhibit migration of the gas between compartments of the compressor.  
         [0005]     In one feature, the compressor further includes a compressor impeller fixed for rotation with the shaft and rotatably driven by the shaft in a compressor compartment to compress the gas.  
         [0006]     In another feature, the gas compressor further includes an electric motor disposed in a motor compartment and engaged with the shaft to rotatably drive the shaft.  
         [0007]     In still another feature, the compartments include a compressor compartment and a motor compartment. The sealing arrangement inhibits migration of the gas from the compressor compartment into the motor compartment. The first end of the shaft and the first bearing are disposed within the motor compartment. The second bearing is disposed within the motor compartment.  
         [0008]     In yet another feature, the sealing arrangements includes a barrier-gas sealing system.  
         [0009]     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  
       [0010]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0011]      FIG. 1  is a functional block diagram illustrating an exemplary fuel cell system implementing a recirculation unit according to the principles of the present invention;  
         [0012]      FIG. 2  is a cross-sectional view of the recirculation unit;  
         [0013]      FIG. 3A  is a detailed view of a concentric sealing arrangement of the recirculation according to the principles of the present invention;  
         [0014]      FIG. 3B  is a detailed view of a non-concentric sealing arrangement; and  
         [0015]      FIG. 4  is a detailed view of a concentric barrier-gas sealing system.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0017]     Referring now to  FIG. 1 , a functional block diagram of an exemplary fuel cell system  10  is shown. The fuel cell system  10  includes a fuel cell stack  12 , a hydrogen source  14 , an anode recirculation unit  16  and a cathode supply unit  20 . The anode recirculation unit  16  and cathode unit  20  are generally provided as blowers or compressors. The fuel cell stack  12  produces electric current to power a load (not shown) such as an electric motor. More specifically, in the fuel cell stack  12 , as hydrogen-containing feed gas flows into an anode side of the fuel cell stack  12  a catalyst facilitates separation of the hydrogen-containing feed gas into electrons and hydrogen ions (i.e., protons). The hydrogen ions pass through an electrolyte membrane and combine with oxygen in a cathode side to produce water (H 2 O). The electrons, which cannot pass through the electrolyte membrane, flow from the anode side to the cathode side through an external circuit (e.g., the load). The load consumes the power generated by the fuel cell stack  12 .  
         [0018]     The hydrogen source  14  supplies the hydrogen-containing feed gas for the anode side of the fuel cell stack  12 . In one embodiment, the hydrogen-containing feed gas is essentially pure hydrogen. In such a case, the hydrogen source  14  is a tank containing such hydrogen. In another embodiment, the hydrogen-containing feed gas comprises a hydrogen-containing gas mixture such as reformate that includes hydrogen as one of its components. In such a case, the hydrogen source  14  indicates a reformation system that reforms a hydrocarbon fuel to produce the hydrogen-containing reformate.  
         [0019]     Regardless of the manner in which the hydrogen-containing feed gas is supplied, the hydrogen-containing feed gas is supplied to the anode side of the fuel cell stack  12  for reaction therein. The anode recirculation unit  16  recirculates exhaust gas exiting the fuel cell stack  12  for re-use in the fuel cell stack  12 . The recirculated exhaust gas includes hydrogen, water (both liquid and vapor), nitrogen and other components. The cathode supply unit  20  compresses an oxygen-containing feed gas (e.g., air) to supply the compressed oxygen-containing feed gas to the cathode side of the fuel cell stack  12  at an appropriate pressure.  
         [0020]     Referring now to  FIG. 2 , a cross-sectional view of the anode recirculation unit  16  is shown. The exhaust gas is drawn into the anode recirculation unit  16  at a suction inlet (not shown), is compressed therein and is discharged from the anode recirculation unit  16  at a discharge outlet (not shown). The anode recirculation unit  16  includes a motor compartment  22  and a compressor or blower compartment  24 . The motor compartment is defined by a motor casing  26  and a housing  28 . The blower compartment  24  is defined by the housing  28  and a blower casing  30 . A shaft  32  is rotatably supported between the motor compartment  22  and the blower compartment  24 . The shaft  32  is rotatably driven by a rotor of a motor  34  that is disposed within the motor compartment  22 . A blower impeller  36  or multiple compressor impellers  36  are fixed for rotation with the shaft  32  within the blower compartment  24 . Although the anode supply unit  16  is illustrated as a two-stage radial compressor it is appreciated that the anode supply unit  16  can be of any other type.  
         [0021]     The shaft  32  is rotatably supported by first and second bearings  38 , 40 , respectively. The first bearing  38  seats within a recess  42  of the motor casing  26  and rotatably supports a first end of the shaft  32 . A blower  44  is fixed for rotation with the shaft  32 . Although the blower  44  is shown fixed to a first end of the shaft  32 , it is anticipated that the blower  44  can be positioned in other locations along the shaft  32 . The blower  44  is induced to rotate via rotation of the shaft  32 . The blower  44  induces air flow through a blower housing  46  to cool the motor compartment  22 . The second bearing  40  seats within a recess  48  of the housing  28 . The second bearing  40  rotatably supports the shaft  32  at an intermediate point along the length of the shaft  32 .  
         [0022]     Although the blower  44  is provided for air-cooling of the motor compartment  22 , it is anticipated that the anode supply unit  16  can be water-cooled. In such a case, a water jacket (not shown) is in heat transfer relationship with the anode recirculation unit  16 . Water or coolant flowing through the water jacket cools the anode recirculation unit.  
         [0023]     A sealing system  50  is concentrically disposed about the second bearing  40 . The sealing system  50  seals the blower compartment  24  to prevent leakage of hydrogen-containing feed gas through the second bearing  40  and into the motor compartment  22 . The sealing system  50  illustrated in  FIG. 2  is a generic sealing system that can be one of several kinds known in the art. For example, the sealing system can be a gas-barrier type sealing system discussed in further detail below and discussed in detail in commonly assigned U.S. patent application Ser. No. 10/445,420, filed May 27, 2003 and entitled Fluid Handling Device for Hydrogen-Containing Process Fluids. A pressurized barrier gas resides within the sealing system  50  and is at a higher pressure than either the pressure within the motor compartment  22  or the blower compartment  24 . In this manner, the pressurized barrier gas inhibits fluid flow from the blower compartment  24 , through the sealing system  50  and into the motor compartment  22 . Likewise, the pressurized barrier gas inhibits fluid flow from the motor compartment  22 , through the sealing system  50  and into the blower compartment  24 . It is appreciated that the gas-barrier type sealing system is merely exemplary and other types of sealing systems may be implemented as the sealing system  50  and disposed concentric to the second bearing  40 .  
         [0024]     Referring now to  FIGS. 3A and 3B , the advantages of the bearing and sealing system arrangement of the present invention will be discussed in detail. As illustrated in  FIG. 3A , a distance X is defined between a top face of the second bearing  40  and a bottom edge of the sealing system  50 .  FIG. 3B  illustrates a traditional, non-concentric bearing and sealing system arrangement. A distance Y is defined between a top face of the bearing and a bottom edge of the non-concentric sealing system. As is seen, the distance X is significantly shorter than the distance Y. Therefore, the shaft  32  is shorter than the shaft associated with the traditional, non-concentric bearing and sealing system arrangement.  
         [0025]     Specific benefits are realized as a result of the shaft  32  being shorter than traditionally required. Initially, the impellers  36  are closer to the second bearing  40  which is a support point of the shaft  32 . The moment in the shaft  32  created by the weight of the impellers  36  mounted thereto is decreased over that of a traditional system having impellers located further away. As a result, the shaft  32  is sufficiently supported by only the first and second bearings  38 , 40 . A traditional arrangement, having a larger moment in the shaft, requires a third bearing to support the second end of shaft. Therefore, because a third bearing is not required, component cost is spared. Additionally, the third bearing would be disposed within the blower compartment  24  and exposed to the hydrogen-containing feed gas. Exposure to the hydrogen-containing feed gas is detrimental to the third bearing, reducing the durability of the third bearing and therefore, reducing the durability of the anode recirculation unit  16  as a whole. Because a third bearing is not required, the recirculation unit  16  of the present invention is inherently cheaper and more durable than a traditional supply unit.  
         [0026]     Further, the bending moment through the shaft  32  is decreased as compared to the shaft of a traditional arrangement. As a result, the diameter of the shaft  32  is reduced as compared to the shaft of a traditional arrangement. This provides several distinct advantages. Initially, material cost is saved as the shaft  32  can be manufactured from less material. Further, the sizes of the first and second bearings  38 , 40  can be reduced. The durability of a bearing is a function of its rotational speed, time of rotation and its diameter. For a cyclically loaded supply unit, the rotational speed and time of rotation are constant (i.e., cannot be controlled to effect bearing durability). Therefore, a reduction in bearing diameter enables increased bearing durability. Thus, the concentric bearing and sealing system of the present invention enables increased bearing durability for the first and second bearings  38 , 40 . Because smaller bearings are implemented, a further cost savings is realized.  
         [0027]     Referring now to  FIG. 4 , the sealing system  50  is illustrated as a barrier-gas sealing system  50 ′. Implementation of the barrier-gas sealing system  50 ′ enables a decrease in components and a smaller packaging envelope within the recirculation unit  16  over other traditional sealing systems. The barrier-gas sealing system  50 ′ includes a gasket  61 , a seal head  62  and an O-ring  63 . A ring groove  64  is formed in a face of the seal head  62  and a passage  65  is formed therethrough to enable fluid communication between the center of the barrier gas sealing system  50 ′ and the ring groove  64 . Although the gasket  61  is shown as providing a sealing surface between the blower compartment  24  and the barrier-gas within the sealing system  50 ′, the sealing system  50 ′ can be flipped to the motor compartment side such that the gasket  61  provides a sealing surface between the blower compartment  24  and the barrier-gas within the sealing system  50 ′.  
         [0028]     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.