Abstract:
Disclosed is a fuel cell module provided with a fuel cell stack and a load-applying mechanism. The load-applying mechanism is provided with: a first clamping part that applies a first camping load, in the direction of stacking, to the gas seal part of the fuel cell stack; a second clamping part that applies to an electrolyte/electrode unit, in the aforementioned direction of stacking, a second clamping load that is lighter than the first clamping load; and a third clamping part that is provided on the first clamping part and, separately from the first clamping part, applies a third clamping load to the gas seal part in the aforementioned direction of stacking.

Description:
TECHNICAL FIELD  
       [0001]    The present invention relates to a fuel cell module including a fuel cell stack formed by stacking a plurality of fuel cells and a load applying mechanism for applying the load to the fuel cell stack in the stacking direction. Each of the fuel cells is formed by stacking an electrolyte electrode assembly and a separator. The electrolyte electrode assembly includes an anode, a cathode, and an electrolyte interposed between the anode and the cathode. 
       BACKGROUND ART 
       [0002]    Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (MEA). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, normally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack. 
         [0003]    In the fuel cell stack, it is required to apply a stacking load for tightening the fuel cells in the stacking direction. In order to maintain the desired sealing performance, the required stacking load is high in portions where reactant gases (in particular, the fuel gas) flow in the fuel cell stack. Further, in order to prevent the MEAs from being damaged undesirably, a relatively small load needs to be applied to portions where the MEAs of the fuel cell stack are supported. For this reason, the load applying mechanism for applying the stacking load to the fuel cell stack is required to apply different loads to the portions where gas sealing is performed and the portions where the MEAs are supported. 
         [0004]    In this regard, for example, in a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2007-073359, as shown in  FIG. 10 , in a fuel cell formed by stacking power generation cells  1   a  and separators  2   a,  a tightening load is applied to the fuel cell using tie-rods  3   a  and nuts  4   a  to maintain the desired gas sealing performance. A weight  5   a  is disposed on the power generation cells  1   a,  above the center of the separators  2   a.  Power generation elements of the power generation cells  1   a  tightly contact each other by the load applied by the weight  5   a.    
         [0005]    Further, as shown in  FIG. 11 , a solid polymer electrolyte fuel cell disclosed in Japanese Laid-Open Patent Publication No. 08-088018 includes a fuel cell stack body lb formed by stacking unit cells through electrically conductive separators, and tightening means for tightening the fuel cell stack body  1   b  in the stacking direction. The tightening means includes first tightening means  2   b  for tightening an area where manifolds are provided, and second tightening means  3   b  for tightening an area where power generation is performed. The first tightening means  2   b  includes bolts  4   b,  and the second tightening means  3   b  includes bolts  5   b.    
         [0006]    Further, in a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2006-179402, as shown in  FIG. 12 , a stack body formed by stacking a plurality of unit cells  1   c  is sandwiched between a pair of end plates  2   c,    3   c.  A load is applied to portions of the unit cells  1   c  where sealing is required by applying a tightening load to components between the end plates  2   c,    3   c  using a plurality of through bolts  4   c  and nuts  5   c.    
         [0007]    A load adjuster  6   c  adjusts a pressure force of a spring box  7   c  applied to an end plate  3   c.  By the pressure force of the spring box  7   c,  a tightening load is applied to the power generation area of the unit cell  1   c.    
       SUMMARY OF INVENTION  
       [0008]    Before separators are used, the separators have distortion that is present after production of the separators to form a stack. Therefore, when separators having such distortion are stacked together, due to accumulation of the distortion, the stack may not have dimensions as designed. Further, since the separators have spring characteristics due to the distortion, and the rigidity of the stack is high, a larger load is required at the time of stacking the separators. 
         [0009]    After the fuel cell stack is used in power generation, the separators tend to be deformed to fit with the shape of the fuel cell stack. Therefore, the state of tightening the fuel cell stack changes from the initial state. Further, since the separators and MEAs are expanded or contracted due to the heat during power generation reaction, the stack is also expanded or contracted, and the stacking load changes during operation. 
         [0010]    However, Japanese Laid-Open Patent Publication No. 2007-073359 uses a technique of merely applying a certain load to the power generation area of the power generation cell  1   a  by the weight  5   a.  Therefore, even if it becomes necessary to apply a new load to the fuel cell stack in correspondence with changes in the load during operation, it is not possible to apply the new load. 
         [0011]    Further, in Japanese Laid-Open Patent Publication No. 08-088018, the second tightening means  3   b  applies the tightening load for tightening the area where power generation is performed in the fuel cell stack body  1   b  using the bolts  5   b.  Therefore, it is not possible to change the load in correspondence with changes in the load required during operation of the fuel cell stack. 
         [0012]    Further, in Japanese Laid-Open Patent Publication No. 2006-179402, the tightening load applied to the area where power generation is performed in the unit cell  1   c  depends on the pressure applied by the spring box  7   c.  Therefore, even in the case where the load to the fuel cell stack needs to be changed newly (to increase the tightening load), it is difficult to change the load. 
         [0013]    The present invention has been made to solve the problems of this type, and an object of the present invention is to provide a fuel cell module in which it is possible to easily and reliably handle distortion that is present in separators before the separators are used, and changes in the shape of the separators after power generation reaction, and maintain the desired gas sealing performance and durability. 
         [0014]    The present invention relates to a fuel cell module including a fuel cell stack and a load applying mechanism. The fuel cell stack is formed by stacking a plurality of fuel cells, and providing a first end plate and a second end plate at both ends of the fuel cells in a stacking direction. Each of the fuel cells is formed by stacking an electrolyte electrode assembly and a separator in the stacking direction. Each of the electrolyte electrode assemblies includes an anode, a cathode, and an electrolyte interposed between the anode and the cathode. The load applying mechanism applies a load to the fuel cell stack in the stacking direction. 
         [0015]    The load applying mechanism includes a first tightening load applying unit for applying a first tightening load to a gas sealing portion of the fuel cell stack, a second tightening load applying unit for applying a second tightening load to the electrolyte electrode assembly, and a third tightening load applying unit provided at the first tightening load applying unit for applying a third tightening load to the gas sealing portion in the stacking direction, separately from the first tightening load applying unit. The second tightening load is smaller than the first tightening load. 
         [0016]    In the present invention, the third tightening load applying unit is provided at the first tightening load applying unit for applying the first tightening load to the gas sealing portion of the fuel cell stack in the stacking direction. In the structure, the third tightening load applying unit can apply the third tightening load to the gas sealing portion in the stacking direction, separately from the first tightening load applying unit. Therefore, adjustment of the load can be performed easily. 
         [0017]    Thus, even if distortion is present in the separators before the separators are used, the desired gas sealing performance can be maintained reliably by applying the first tightening load and the third tightening load. 
         [0018]    Further, when the stacking load changes due to the change in the shape of the separators after power generation reaction, the load can be adjusted by the third tightening load applying unit. Therefore, the desired sealing performance and the desired stacking load can be maintained suitably. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]      FIG. 1  is a cross sectional view showing a fuel cell module according to an embodiment of the present invention; 
           [0020]      FIG. 2  is a perspective view schematically showing a fuel cell stack of the fuel cell module; 
           [0021]      FIG. 3  is a cross sectional view showing the fuel cell stack, taken along a line III-III in  FIG. 2 ; 
           [0022]      FIG. 4  is an exploded perspective view showing the fuel cell; 
           [0023]      FIG. 5  is a partially exploded perspective view showing gas flows in the fuel cell; 
           [0024]      FIG. 6  is a plan view showing a separator of the fuel cell; 
           [0025]      FIG. 7  is a cross sectional view schematically showing operation of the fuel cell; 
           [0026]      FIG. 8  is a partially exploded perspective view showing the fuel cell stack; 
           [0027]      FIG. 9  is a cross sectional view showing the fuel cell stack, taken along a line IX-IX in  FIG. 8 ; 
           [0028]      FIG. 10  is a view showing a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2007-073359; 
           [0029]      FIG. 11  is a partial cross sectional view showing the fuel cell disclosed in Japanese Laid-Open Patent Publication No. 08-088018; and 
           [0030]      FIG. 12  is a view showing a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2006-179402. 
       
    
    
     DESCRIPTION OF EMBODIMENTS  
       [0031]    As shown in  FIG. 1 , a fuel cell module  10  according to an embodiment of the present invention is used in various applications, including stationary and mobile applications. For example, the fuel cell module  10  is mounted on a vehicle. The fuel cell module  10  includes a fuel cell stack  12 , a heat exchanger  14  for heating the oxygen-containing gas before it is supplied to the fuel cell stack  12 , an evaporator  15  for evaporating water to produce a mixed fuel of the raw fuel and the water vapor, a reformer  16  for reforming the mixed fuel to produce a fuel gas (reformed gas), and a casing  17  containing the fuel cell stack  12 , the heat exchanger  14 , the evaporator  15 , and the reformer  16 . 
         [0032]    The reformer  16  reforms higher hydrocarbons (C 2+ ) such as ethane (C 2 H 6 ), propane (C 3 H 8 ), and butane (C 4 H 10 ) in the city gas (raw fuel) to produce the fuel gas chiefly containing methane (CH 4 ), hydrogen, and CO by steam reforming as a preliminary reformer, and the reformer  16  is operated at an operating temperature of several hundred degrees Celsius. 
         [0033]    In the casing  17 , a fluid unit  18  including at least the heat exchanger  14 , the evaporator  15 , and the reformer  16  is disposed on one side of the fuel cell stack  12 , and a load applying mechanism  19  for applying a tightening load in the stacking direction indicated by an arrow A is disposed on the other side of the fuel cell stack  12  (see  FIGS. 1 to 3 ). 
         [0034]    The fuel cell stack  12  includes a plurality of fuel cells  12   a.  The fuel cell  12   a  is a solid electrolyte fuel cell. As shown in  FIGS. 4 and 5 , the fuel cell  12   a  includes electrolyte electrode assemblies (MEAs)  26 . Each of the electrolyte electrode assemblies  26  includes a cathode  22 , an anode  24 , and an electrolyte (electrolyte plate)  20  interposed between the cathode  22  and the anode  24 . For example, the electrolyte  20  is made of ion-conductive oxide such as stabilized zirconia. The electrolyte electrode assembly  26  has a circular disk shape. A barrier layer (not shown) is provided at least at the outer circumferential edge of the electrolyte electrode assembly  26  for preventing the entry or discharge of the oxygen-containing gas and the fuel gas. 
         [0035]    In the fuel cell  12   a,  four electrolyte electrode assemblies  26  are sandwiched between a pair of separators  28 . The four electrolyte electrode assemblies  26  are provided on a circle concentrically around a fuel gas supply passage (reactant gas supply passage)  30  extending through the center of the separators  28 . 
         [0036]    As shown in  FIG. 4 , each of the separators  28  includes, e.g., one metal plate of stainless alloy etc., or a carbon plate. A fuel gas supply section (reactant gas supply section)  32  is formed at the center of the separator  28 , and the fuel gas supply passage  30  extends through the fuel gas supply section  32 . Four first bridges  34  extend radially outwardly from the fuel gas supply section  32  at equal intervals, e.g., 90°. The fuel gas supply section  32  is integral with sandwiching sections  36  each having a relatively large diameter, through the first bridges  34 . The centers of sandwiching sections  36  are equally distanced from the center of the fuel gas supply section  32 . 
         [0037]    Each of the sandwiching sections  36  has a circular disk shape, having substantially the same dimensions as the electrolyte electrode assembly  26 . The sandwiching sections  36  are separated from each other. A fuel gas inlet  38  for supplying the fuel gas is formed at the center of the sandwiching section  36 , or at an upstream position deviated from the center of the sandwiching section  36  in the flow direction of the oxygen-containing gas. 
         [0038]    Each of the sandwiching sections  36  has a fuel gas channel  40  on a surface  36   a  which contacts the anode  24 , for supplying a fuel gas along an electrode surface of the anode  24 . Further, a fuel gas discharge channel  42  for discharging the fuel gas partially consumed in the fuel gas channel  40  and a circular arc wall  44  forming a detour path to prevent the fuel gas from flowing straight from the fuel gas inlet  38  to the fuel gas discharge channel  42  are provided on the surface  36   a.    
         [0039]    The circular arc wall  44  has a substantially horseshoe shape. The fuel gas inlet  38  is provided on a distal end side, inside the circular arc wall  44 , and the fuel gas discharge channel  42  is provided on the proximal end side, near the first bridge  34 . On the surface  36   a,  a circumferential protrusion  46  and a plurality of projections  48  are provided. The circumferential protrusion  46  protrudes toward the fuel gas channel  40 , and contacts the outer edge of the anode  24 , and the projections  48  contact the anode  24 . 
         [0040]    The protrusion  46  has a substantially ring shape with partial cutaway at a position corresponding to the fuel gas discharge channel  42 . The projections  48  are made of solid portions formed by, e.g., etching, or hollow portions formed by press forming. 
         [0041]    As shown in  FIGS. 6 and 7 , each of the sandwiching sections  36  has a substantially planar surface  36   b  which contacts the cathode  22 . A plate  50  having a circular disk shape is fixed to the surface  36   b,  e.g., by brazing, diffusion bonding, laser welding, or the like. A plurality of projections  52  are provided on the plate  50 , e.g., by press forming. By the projections  52 , an oxygen-containing gas channel  54  for supplying an oxygen-containing gas along an electrode surface of the cathode  22  is formed on the side of the surface  36   b  of the sandwiching section  36 . The projections  52  function as a current collector. 
         [0042]    Extensions  56  extend from the outer circumferential positions of the respective sandwiching sections  36 . The extensions  56  are used for collecting and measuring generated electrical energy from the fuel cells  12   a,  positioning the electrolyte electrode assemblies  26  to the separators  28 , and detecting the number of fuel cells (see  FIGS. 4 to 6 ). 
         [0043]    As shown in  FIG. 4 , a channel member  60  is fixed to a surface of the separator  28  facing the cathode  22 , e.g., by brazing, diffusion bonding, or laser welding. The channel member  60  has a planar shape. The fuel gas supply passage  30  extends through a fuel gas supply section  62  at the center thereof in the channel member  60 . A predetermined number of reinforcement bosses  63  are formed in the fuel gas supply section  62 . 
         [0044]    Four second bridges  64  extend radially from the fuel gas supply section  62 . Each of the second bridges  64  is fixed to the separator  28  from the first bridge  34  to the surface  36   b  of the sandwiching section  36  to cover the fuel gas inlet  38  (see  FIG. 7 ). 
         [0045]    From the fuel gas supply section  62  to the second bridge  64 , a fuel gas supply channel  66  connecting the fuel gas supply passage  30  to the fuel gas inlet  38  is formed. For example, the fuel gas supply channel (reactant gas supply channel)  66  is formed by, e.g., etching. 
         [0046]    As shown in  FIG. 7 , the oxygen-containing gas channel  54  is connected to the oxygen-containing gas supply passage (reactant gas supply section)  68  for supplying the oxygen-containing gas from a space between an inner circumferential edge of the electrolyte electrode assembly  26  and an inner circumferential edge of the sandwiching section  36  in a direction indicated by an arrow B. The oxygen-containing gas supply passage  68  extends between the inside of the respective sandwiching sections  36  and the respective first bridges  34  in the stacking direction indicated by the arrow A. 
         [0047]    An insulating seal  70  for sealing the fuel gas supply passage  30  is provided between the separators  28 . For example, crustal component material such as mica material and ceramic material, glass material, and composite material of clay and plastic may be used for the insulating seal  70 . The insulating seal  70  seals the fuel gas supply passage  30  from the electrolyte electrode assemblies  26 . For the fuel cells  12   a,  an exhaust gas channel  72  is provided outside (around) the sandwiching sections  36 . 
         [0048]    A flow rectifier member  74  is provided in each space between the adjacent sandwiching sections  36  for rectifying the flow of the oxygen-containing gas supplied from the oxygen-containing gas supply passage  68 , and flowing through the oxygen-containing gas channel  54  along the surface of each electrolyte electrode assembly  26  and rectifying the flow of the fuel gas flowing in the fuel gas channel  40  along the surface of each electrolyte electrode assembly  26 . The flow rectifier member  74  is a plate having a substantially fan shape. A predetermined number of the flow rectifier members  74  are stacked in the direction indicated by the arrow A. The number of the flow rectifier members  74  in a plan view is four, corresponding to positions between the sandwiching sections  36 . 
         [0049]    The flow rectifier member  74  is formed by joining an electrically insulating member of, e.g., mica material, with silicone resin. The flow rectifier member  74  is provided along part of the outer edge of the sandwiching section  36  and part of the circumscribed circle of the separator  28 . One end of the flow rectifier member  74  along the part of the sandwiching section  36  is provided near the joint positions between the sandwiching sections  36  and the first bridges  34 , and an outer circumferential portion  78  as the other end of the flow rectifier member  74  form part of the circumscribed circle of the separator  28 . 
         [0050]    The one end of the flow rectifier member  74  includes a cutout  80  which is cut in a direction away from the oxygen-containing gas supply passage  68  and the fuel gas supply passage  30 . Circular arc portions  82  respectively corresponding to the outer shapes of the sandwiching sections  36  are formed on both sides of the flow rectifier member  74 . 
         [0051]    As shown in  FIGS. 2 and 3 , in the fuel cell stack  12 , an end plate (second end plate)  84   a  having a substantially circular disk shape is provided at one end of the fuel cells  12   a  in the stacking direction. Further, the fuel cell stack  12  includes a plurality of end plates (first end plates)  84   b  and a fixing ring  84   c  at the other end in the stacking direction, through a partition wall  85 . Each of the end plates  84   b  has a small diameter, and a substantially circular shape, and the fixing ring  84   c  has a large diameter, and a substantially ring shape. A plurality of ring members  83  are interposed between the end plate  84   a  and the end plates  84   b.    
         [0052]    The partition wall  85  prevents diffusion of the exhaust gas to the outside of the fuel cell  12   a.  The number of end plates  84   b  is four, corresponding to the positions of stacking the electrolyte electrode assemblies  26 . 
         [0053]    The end plate  84   a  and the fixing ring  84   c  include a plurality of holes  86 . Bolt insertion collar members  87  are integrally inserted into the ring members  83  in the stacking direction. Bolts  88  are inserted into the holes  86  and the bolt insertion collar members  87 , and screwed into nuts  90 . By the Bolts  88  and the nuts  90 , the end plate  84   a  and the fixing ring  84   c  are fixedly tightened together. 
         [0054]    One fuel gas supply pipe  92 , a casing  93 , and one oxygen-containing gas supply pipe  94  are provided at the end plate  84   a.  The fuel gas supply pipe  92  is connected to the fuel gas supply passage  30 . The casing  93  has a cavity  93   a  connected to the respective oxygen-containing gas supply passages  68 . The oxygen-containing gas supply pipe  94  is connected to the casing  93 , and to the cavity  93   a.    
         [0055]    A support plate member  102  is fixed to the end plate  84   a  through a plurality of bolts  88 , nuts  98   a,    98   b,  and plate collar members  100 . A first tightening load applying unit  104  for applying a first tightening load to the fuel gas supply sections  32 ,  62  (gas sealing portions where gas sealing is required), second tightening load applying units  108  for applying a second tightening load to each of the electrolyte electrode assemblies  26 , and a third tightening load applying unit  109  are provided between the support plate member  102  and the end plate  84   a.  The second tightening load is smaller than the first tightening load. Further, the third tightening load applying unit  109  is provided at the first tightening load applying unit  104 , for applying a third tightening load to the fuel gas supply sections  32 ,  62  separately from the first tightening load applying unit  104 . The first tightening load applying unit  104 , the second tightening load applying units  108 , and the third tightening load applying unit  109  form the load applying mechanism  19 . 
         [0056]    The load applying mechanism  19  is provided on the end plate  84   b  side, and the first tightening load applying unit  104  and the third tightening load applying unit  109  support the load in the stacking direction through the end plate  84   a.    
         [0057]    As shown in  FIGS. 2 ,  3 , and  8 , the first tightening load applying unit  104  includes two bolts (first bolts)  110  screwed into the end plate  84   a  extending through the stacked fuel cells  12   a  toward the end plate  84   b,  and a first plate member  112  engaged with the bolts  110 , and a first spring member  116  interposed between the first plate member  112  and a support plate  114  to apply the load in the stacking direction to the fuel gas supply sections  32 ,  62 . 
         [0058]    A presser member  118  is provided at the center of the fuel cells  12   a  (centers of the fuel gas supply sections  32 ,  62 ) for preventing leakage of the fuel gas from the fuel gas supply passage  30 . The presser member  118  is provided near the center of the four end plates  84   b  for pressing the fuel cells  12   a.  A first plate member  112  is provided for the presser member  118 , and a tip end of a first presser bolt  117  contacts the support plate  114 . The first presser bolt  117  is screwed into a first screw hole  119  formed in the support plate member  102 . The position of the first presser bolt  117  is adjustable through a first nut  120 . 
         [0059]    Each of the second tightening load applying units  108  includes a bolt (second bolt)  88  screwed into the end plate  84   a,  the support plate member  102  (second plate member) engaged with the bolt  88 , and a second spring member  122  interposed between the support plate member  102  and the fuel cell  12   a  for applying the load to the electrolyte electrode assemblies  26  in the stacking direction. 
         [0060]    A receiver member  124   a  is provided at the end plate  84   b,  corresponding to each of the electrolyte electrode assemblies  26 . The receiver member  124   a  is positioned on the end plate  84   b  through a pin  126 . One end of the second spring member  122  contacts the receiver member  124   a,  and the other end of the second spring member  122  contacts a receiver member  124   b.  A tip end of a second presser bolt  128  contacts the receiver member  124   b.  The second presser bolt  128  is screwed into a second screw hole  130  formed in the support plate member  102 . The position of the second presser bolt  128  is adjustable through a second nut  132 . 
         [0061]    As shown in  FIGS. 8 and 9 , the third tightening load applying unit  109  includes a pair of bolts (third bolt)  134  screwed into the end plate  84   a,  a pair of presser members  136  interposed between the first plate member  112  and the support plate member  102  for applying a load to the first plate member  112  in the stacking direction. 
         [0062]    A threaded portion  138  is formed in the outer circumference of the bolt  134 , and the threaded portion  138  has a predetermined length from one end of the bolt  134 . The threaded portion  138  is inserted into a hole  140  formed in the support plate member  102 . The presser member  136  externally fitted to the threaded portion  138  has a cylindrical shape, and one end of the presser member  136  contacts the first plate member  112 , and the other end of the presser member  136  contacts a nut member  142 . The threaded portion  138  is screwed into the nut member  142 . 
         [0063]    The first spring member  116  is interposed between the first plate member  112  and the support plate  114  around the presser member  136 . The bolts  134  extend through the first plate member  112  and the support plate  114 . The threaded portions  138  of the bolts  134  are screwed into the nut members  142 , and the nut members  142  are screwed (spirally rotated) in a predetermined direction for allowing the presser members  136  to press the first plate member  112 . Thus, by the presser member  118  which contacts the first plate member  112 , the load in the stacking direction is applied to the center of the fuel cells  12   a.    
         [0064]    Each of the four flow rectifier members  74  has a through hole  144  extending in the stacking direction. A bolt  146  is inserted into each hole  144 , and the bolt  146  is screwed into the end plate  84   a.  A cylindrical presser member  148  is externally fitted to an end of the bolt  146  extending outwardly from the flow rectifier member  74 . One end of the presser member  148  contacts an end surface of the flow rectifier member  74  provided at the outermost position. The bolt  146  is screwed into a nut member  150 . The other end of the presser member  148  contacts the nut member  150 , and the presser member  148  is supported by the nut member  150 . 
         [0065]    As shown in  FIG. 1 , the casing  17  includes a first case unit  160   a  containing the load applying mechanism  19 , and a second case unit  160   b  containing the fuel cell stack  12 . The joint portion between the first case unit  160   a  and the second case unit  160   b  is tightened by screws  162  and nuts  164  through the partition wall  85 . The partition wall  85  functions as a gas barrier for preventing entry of the hot exhaust gas or the hot air from the fluid unit  18  into the load applying mechanism  19 . An end of a ring shaped wall plate  166  is joined to the second case unit  160   b,  and a head plate  168  is fixed to the other end of the wall plate  166 . 
         [0066]    A fuel gas supply pipe  170  is connected to the evaporator  15 . The fuel gas supply pipe  170  is connected to a raw fuel supply unit (not shown) for supplying a raw fuel (methane, ethane, propane, or the like). The outlet of the evaporator  15  is connected to the inlet of the reformer  16 . An exhaust gas pipe  172  is provided adjacent to the fuel gas supply pipe  170 . 
         [0067]    An oxygen-containing gas supply pipe  174  is connected to the head plate  168 , and the oxygen-containing gas supply pipe  174  extends through a channel  176  in the casing  17 , and connects the heat exchanger  14  to the oxygen-containing gas supply passage  68 . 
         [0068]    Operation of the fuel cell module  10  will be described below. 
         [0069]    As shown in  FIG. 1 , the air ejected from an air pump (not shown) as an oxygen-containing gas is supplied from the oxygen-containing gas supply pipe  174  to the channel  176  in the casing  17 . The air is heated by the heat exchanger  14 , and then, the air is supplied through the oxygen-containing gas supply pipe  94  to each of the oxygen-containing gas supply passages  68  through the cavity  93   a.    
         [0070]    A raw fuel (methane, ethane, propane or the like) is supplied from the fuel gas supply pipe  170  to the reformer  16 , and water is supplied from the fuel gas supply pipe  170  to the reformer  16 . The raw fuel flows through the reformer  16 , and the raw fuel is reformed to produce a fuel gas (hydrogen-containing gas). The fuel gas is supplied from the fuel gas supply pipe  92  connected to the end plate  84   a  to the fuel gas supply passage  30 . 
         [0071]    As shown in  FIG. 7 , the fuel gas flows along the fuel gas supply passage  30  of the fuel cell stack  12  in the stacking direction indicated by the arrow A. The fuel gas moves through the fuel gas supply channel  66  formed in each of the fuel cells  12   a  along the surface of the separator  28 . 
         [0072]    The fuel gas flows from the fuel gas supply channel  66  into the fuel gas channel  40  through the fuel gas inlet  38  formed in the sandwiching section  36 . The fuel gas inlet  38  is provided at substantially the central position of the anode  24  of each electrolyte electrode assembly  26 . Thus, the fuel gas is supplied from the fuel gas inlet  38  to substantially the central region of the anode  24 , and flows along the fuel gas channel  40  to the outer circumferential region of the anode  24 . 
         [0073]    Under the rectifying operation of the flow rectifier member  74 , the oxygen-containing gas is supplied to the oxygen-containing gas supply passage  68 , and flows into the space between the inner circumferential edge of the electrolyte electrode assembly  26  and the inner circumferential edge of the sandwiching section  36 , and flows in the direction indicated by the arrow B toward the oxygen-containing gas channel  54 . In the oxygen-containing gas channel  54 , the oxygen-containing gas flows from the inner circumferential edge (center of the separator  28 ) to the outer circumferential edge (outer circumferential edge of the separator  28 ) of the electrolyte electrode assembly  26 . 
         [0074]    Thus, in each of the electrolyte electrode assemblies  26 , the fuel gas flows from the center to the outer circumferential side on the electrode surface of the anode  24 , and the oxygen-containing gas flows in one direction indicated by the arrow B on the electrode surface of the cathode  22 . At this time, oxide ions move through the electrolyte  20  toward the anode  24  for generating electricity by chemical reactions. 
         [0075]    The exhaust gas chiefly containing the air after partial consumption in the power generation reaction is discharged to the outer circumferential region of each of the electrolyte electrode assemblies  26 , and flows through the exhaust gas channels  72  as the off gas, and the off gas is discharged from the fuel cell stack  12  (see  FIG. 1 ). 
         [0076]    In the present embodiment, as shown in  FIGS. 3 ,  8 ,  9 , in addition to the first tightening load applying unit  104  for applying the first tightening load to the fuel gas supply sections  32 ,  62  (gas sealing portions) of the fuel cell stack  12 , the third tightening load applying unit  109  is provided. Thus, the third tightening load applying unit  109  can apply the third tightening load to the fuel gas supply sections  32 ,  62  in the stacking direction, separately from the first tightening load applying unit  104 . Therefore, adjustment of the load can be performed easily. 
         [0077]    Thus, even if distortion is present in the separators  28  before the separators  28  are used, by applying the first tightening load and the third tightening load, the desired sealing performance in the fuel gas supply sections  32 ,  62  is maintained reliably. 
         [0078]    Further, when the stacking load changes due to the change in the shape of the separators  28  after power generation reaction, the load can be adjusted by the third tightening load applying unit  109 . Therefore, the desired sealing performance and the desired stacking load in the fuel gas supply sections  32 ,  62  can be maintained suitably. 
         [0079]    Further, the load applying mechanism  19  is provided adjacent to the end plate  84   b  of the fuel cell stack  12 , and the first tightening load applying unit  104  and the third tightening load applying unit  109  maintain the load in the stacking direction through the end plate  84   a.  Therefore, by using the first tightening load applying unit  104  and the third tightening load applying unit  109 , it is possible to reliably apply the load in the stacking direction to the fuel gas supply sections  32 ,  62 , maintain the sealing performance at all times, and maintain and the load in the stacking direction. 
         [0080]    Further, as shown in  FIGS. 2 and 3 , the first tightening load applying unit  104  includes the bolts  110  screwed into the end plate  84   a  and extending through the fuel cells  12   a  of the fuel cell stack  12  toward the end plate  84   b,  the first plate member  112  engaged with the bolts  110 , and the first spring member  116  interposed between the first plate member  112  and the support plate  114  to apply the load in the stacking direction to the fuel gas supply sections  32 ,  62 . 
         [0081]    The second tightening load applying unit  108  includes the bolt  88  screwed into the end plate  84   a,  the support plate member  102  engaged with the bolt  88 , and the second spring member  122  interposed between the support plate member  102  and the end plate  84   b  for applying the load in the stacking direction to the electrolyte electrode assembly  26 . 
         [0082]    In the structure, the first tightening load applying unit  104  and the second tightening load applying unit  108  can apply the spring load. Even if the load related to the fuel cell stack  12  changes depending on the operating condition of the fuel cell stack  12 , it becomes possible to track such changes in the load, and handle the changes. Thus, damages of the electrolyte electrode assemblies  26  can be suppressed suitably. 
         [0083]    Further, as shown in  FIGS. 8 and 9 , the third tightening load applying unit  109  includes the bolts  134  screwed into the end plate  84   a,  and the presser members  136  externally fitted to the bolts  134 , and interposed between the first plate member  112  and the support plate  114  for applying a load to the first plate member  112  in the stacking direction. Therefore, by adding a slight improvement to the existing load applying mechanism  19 , the third tightening load applying unit  109  can be provided. Thus, production cost can be reduced effectively. 
         [0084]    Further, the presser member  136  has the cylindrical shape, and one end of the presser member  136  contacts the first plate member  112 , and the other end of the presser member  136  contacts the nut member  142 . The threaded portion  138  of the bolt  134  is screwed into the nut member  142 . When the nut member  142  is screwed in a predetermined direction, the presser member  136  can apply the load in the stacking direction to the first plate member  112 . Therefore, with simple and economical structure, the third tightening load applying unit  109  can be provided. 
         [0085]    In the fuel cell stack  12  including the separators  28  which have not been used yet, assuming that the load is firstly applied to the fuel gas supply sections  32 ,  62  by the first tightening load applying unit  104  before operation, and then, the second tightening load is applied to the electrolyte electrode assemblies  26  between the sandwiching sections  36  by the second tightening load applying unit  108 , the desired load may not be applied to the fuel gas supply sections  32 ,  62  due to distortion or the like in the separators  28 . 
         [0086]    The nut member  142  of the third tightening load applying unit  109  is screwed for allowing the presser member  136  to apply the third tightening load to the fuel gas supply sections  32 ,  62  separately. Thus, the gas sealing performance in the fuel gas supply sections  32 ,  62  can be maintained suitably. 
         [0087]    After operation is started, by power generation, the shape of the separators  28  is deformed to fit with the shapes of the other components. Thus, the load applied to the fuel gas supply sections  32 ,  62  is changed (reduced). At this time, by operating the third tightening load applying unit  109 , the desired tightening load can be applied to the fuel gas supply sections  32 ,  62 , and improvement in the sealing performance is achieved easily. 
         [0088]    Even if the load required for the fuel cell stack  12  changes during operation, the desired load can be applied at all times by the spring load of the first tightening load applying unit  104  and the spring load of the second tightening load applying unit  108 . 
         [0089]    Further, as shown in  FIG. 1 , in the fuel cell module  10 , the load applying mechanism  19  is provided adjacent to the end plate  84   b  of the fuel cell stack  12 , and the fluid unit  18  including the heat exchanger  14 , the evaporator  15 , and the reformer  16  is provided adjacent to the end plate  84   a  of the fuel cell stack  12 . In the structure, the fluid unit  18  and the load applying mechanism  19  are provided separately with respect to the fuel cell stack  12 , the load applying mechanism  19  can be separated from the high temperature atmosphere, and improvement in the durability is achieved. 
         [0090]    Further, the separator  28  includes the sandwiching section  36 , the first and second bridges  34 ,  64  connected to the sandwiching section  36 , and the fuel gas supply sections  32 ,  62  connected to the first and second bridges  34 ,  64 . The fuel gas supply passage  30  extends through the fuel gas supply sections  32 ,  62  in the stacking direction. In the structure, the gas sealing portions are formed in the fuel gas supply sections  32 ,  62 . Thus, in the separators  28 , sealing can be performed reliably to prevent leakage of the fuel gas flowing through the fuel gas supply passage  30  formed in the fuel gas supply sections  32 ,  62 .