Patent Publication Number: US-2010112404-A1

Title: Fuel cell system

Description:
TECHNICAL FIELD 
     The present invention relates to a fuel cell system provided with a discharge valve for discharging a fuel off gas or a fluid containing generated water in a circulation system to the outside. 
     BACKGROUND ART 
     Currently, a fuel cell system provided with a fuel cell which receives the supply of reactant gas (a fuel gas and an oxidizing gas) to generate electric power has been proposed and in practical use. For instance, the fuel cell system disclosed in Japanese Patent Application Laid-Open No. 2006-147440 has a circulation system which circulates a fuel off gas discharged from a fuel cell to the fuel cell. The fuel off gas in the circulation system contains generated water, which has been generated from an electrochemical reaction in the fuel cell. The circulation system has a gas-liquid separator which separates the fuel off gas and the generated water. Further, a discharge passage for discharging the generated water to the outside is connected to a water reservoir of the gas-liquid separator, and a discharge valve (drain valve) is installed in the discharge passage. 
     The discharge passage has a double-piping structure in which the generated water passes through an inner pipe thereof, while cooling water from the fuel cell passes through an outer pipe thereof. With this arrangement, the discharge valve is heated by the cooling water which has been warmed by the exhaust heat of the fuel cell, thereby restraining the water in the discharge valve from freezing even when an external temperature is below zero. 
     DISCLOSURE OF THE INVENTION 
     However, no specific construction of the discharge valve has been disclosed in Japanese Patent Application Laid-Open No. 2006-147440. According to Japanese Patent Application Laid-Open No. 2006-147440, the double piping is built in the discharge valve; however, it is structurally difficult to implement the double piping where the discharge valve allows a passage (the inner pipe) between a valve seat and a valve disc to be closed by the valve disc, while to be covered by the outer pipe. Even if such a construction is possible, the structure around the valve seat would be extremely complicated. 
     An object of the present invention is to provide a fuel cell system capable of raising the temperature of a discharge valve so as to restrain freezing in the discharge valve by a simple structure. 
     To achieve the above object, a fuel cell system of the present invention comprises a circulation system which circulate a fuel off gas discharged from a fuel cell to the fuel cell; a discharge valve which discharges a fluid in the circulation system to the outside; and a refrigerant flow path through which a refrigerant is circulated to the fuel cell flows. Further, the discharge valve has a valve body provided with a flow path which interconnects the interior of the circulation system and the outside, and a part of the refrigerant flow path penetrates the valve body so as to be independent of the aforesaid flow path. 
     With this arrangement, the refrigerant flows directly into the valve body, thus allowing the temperature of the valve body to be raised by thermal conduction. This makes it possible to restrain freezing in the flow path for discharging a fluid. Further, the part of the flow path for discharging a fluid and the refrigerant flow path are independent in the valve body, thus allowing the structure of the discharge valve to be simplified. 
     Preferably, the discharge valve may have a valve seat and a valve disc which moves away from or into contact with the valve seat to open or close the flow path for discharging a fluid, and the part of the refrigerant flow path may be provided by penetrating a portion of the valve body near the valve seat. 
     With this arrangement, the refrigerant can be passed near the valve seat, thus making it possible to intensively heat the valve seat involved in freezing. 
     Another fuel cell system in accordance with the present invention comprises a circulation system, a discharge valve, and a refrigerant flow path, as with the case described above. Further, a pipe constituting the refrigerant flow path contacts a surface of a valve body of the discharge valve through a thermally-conductive member. 
     With this arrangement, the heat of a refrigerant flowing through the refrigerant flow path can be transferred to the valve body from the pipe via the thermally-conductive member. Thus, the temperature raising performance of the discharge valve can be improved and the freezing in the flow path for discharging a fluid can be restrained by the simple structure. 
     Preferably, the thermally-conductive member may be a stay which secures the pipe of the refrigerant flow path to the valve body. 
     This arrangement allows a single member to serve as the member for securing the pipe of the refrigerant flow path and also as the member for transferring heat from the refrigerant flow path to the valve body. This permits a simple and compact structure in the neighborhood of the discharge valve. 
     Preferably, the fuel cell may be formed of a fuel cell stack constituted by stacking unit cells, and the valve body may be secured to the fuel cell stack at one point. 
     With this arrangement, there is only one heat bridge through which heat escapes from the valve body to the fuel cell stack, thus making it possible to restrain the heat dissipation from the valve body to the fuel cell stack. Hence, the temperature rise of the valve body can be enhanced. 
     In another preferred mode, the valve body may be bolted to the fuel cell stack through a bracket. The bracket may be spaced away from the fuel cell stack except for a portion bolted to the fuel cell stack. 
     This arrangement allows the area of the heat bridge to be reduced, also permitting enhanced temperature rise of the valve body. 
     Preferably, the valve body may be secured to an end plate of the fuel cell stack. 
     In general, the end plate is provided with a connection for joining the refrigerant flow path to the interior of the fuel cell stack. Therefore, securing the valve body to the end plate permits effective use of the end plate in placing the discharge valve on the fuel cell stack. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a main section of a fuel cell system according to an embodiment. 
         FIG. 2  is a top plan view of an exhaust/drain valve according to the embodiment and a neighborhood thereof. 
         FIG. 3  is a side view of the exhaust/drain valve according to the embodiment and a neighborhood thereof, as observed from the direction of III in  FIG. 2 . 
         FIG. 4  is a sectional diagram taken at IV-IV in  FIG. 2 . 
         FIG. 5  is a sectional diagram taken at V-V in  FIG. 4 . 
         FIG. 6  is a top plan view of an exhaust/drain valve according to a modification example and a neighborhood thereof. 
         FIG. 7  is a top plan view of an exhaust/drain valve according to a modification example and a neighborhood thereof. 
         FIG. 8  is a top plan view of an exhaust/drain valve according to a modification example and a neighborhood thereof. 
         FIG. 9  is a side view of an exhaust/drain valve according to a second embodiment and a neighborhood thereof. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The following will describe a fuel cell system in accordance with preferred embodiments of the present invention with reference to the accompanying drawings. 
     First Embodiment 
     A fuel cell system  1  illustrated in  FIG. 1  is a vehicle-mounted electric power generating system for a fuel cell vehicle. The fuel cell system  1  can be applied to an electric power generating system for any type of mobile body, such as a marine vessel, an airplane, a train, or a walking robot, and can be further applied to a fixed electric power generating system or the like used as electric power generating equipment for a building, a house, or the like. 
     As illustrated in  FIG. 1 , the fuel cell system  1  has a fuel cell  2 , an oxidizing gas piping system  3 , a fuel gas piping system  4 , a refrigerant piping system  5 , and a controller  6 . 
     The fuel cell  2  is, for example, a solid polyelectrolyte type. As illustrated in  FIGS. 2 and 3 , the fuel cell  2  has a stack body  21  which is formed by stacking multiple unit cells, and also has a terminal plate with an output terminal, an insulating plate, and an end plate  22  stacked in sequence on the outer side of unit cells at both ends of the stack body  21 . The end plate  22  is provided with a fluid piping connection for supplying and discharging various types of fluids (an oxidizing gas, a fuel gas, and a refrigerant) into and from the stack body  21 . Incidentally, the terminal plate and the insulating plate are not shown in  FIGS. 2 and 3 . 
     Each of the unit cells has an air electrode on one surface of an electrolyte membrane, a fuel electrode on the other surface thereof, and a pair of separators sandwiching the air electrode and the fuel electrode from both sides. A fuel gas is supplied to a fuel gas passage  2   a  of one separator, while an oxidizing gas is supplied to an oxidizing gas passage  2   b  of the other separator. Further, a refrigerant is supplied to a refrigerant passage  2   c  between the separators. An electrochemical reaction takes place in the unit cell to which the oxidizing gas and the fuel gas have been supplied, thus causing the unit cell to generate electric power. The electrochemical reaction also generates water at the air electrode. A part of the generated water may permeate the electrolyte membrane and move toward the fuel electrode. The electrochemical reaction in the solid polyelectrolyte type fuel cell  2  is a heat-generating reaction, but the supply of the refrigerant maintains the temperature of the fuel cell  2  at approximately 60 to 70° C. 
     The oxidizing gas and the fuel gas are generically referred to as reactant gases. In particular, the oxidizing gas and the fuel gas discharged from the fuel cell  2  are referred to as an oxidizing off gas and a fuel off gas, respectively, and these are generically referred to as reactant off gases. In the following description, air will be taken as an example of the oxidizing gas and a hydrogen gas as an example of the fuel gas. The fuel off gas will be referred to as the hydrogen off gas. 
     The oxidizing gas piping system  3  supplies and discharges the oxidizing gas to and from the fuel cell  2 . The oxidizing gas piping system  3  has a humidifier  30 , a supply flow path  31 , a discharge flow path  32 , an exhaust flow path  33 , and a compressor  34 . The compressor  34  is provided at an upstream end of the supply flow path  31 . The air in the atmosphere introduced by the compressor  34  is pressure-fed to the humidifier  30  through the supply flow path  31 , humidified by the humidifier  30  and then supplied to the fuel cell  2 . The oxidizing off gas discharged from the fuel cell  2  is introduced into the humidifier  30  through the discharge flow path  32 , and then flows through the exhaust flow path  33  so as to be discharged to the outside. 
     The fuel gas piping system  4  supplies and discharges the fuel gas to and from the fuel cell  2 . The fuel gas piping system  4  has a hydrogen tank  40 , a supply flow path  41 , and a circulation flow path  42 . 
     The hydrogen tank  40  is a hydrogen supply source storing a hydrogen gas of a high pressure (e.g., 70 MPa). In place of the hydrogen tank  40 , a combination of a reformer which generates a hydrogen-rich reformed gas from a hydrocarbon-based fuel and a high-pressure gas tank which places a reformed gas, which has been generated by the reformer, in a high-pressure state and accumulates the high-pressure reformed gas may be adopted as a hydrogen supply source. Further, in place of the hydrogen tank  40 , a tank having a hydrogen storing alloy may be adopted. 
     The supply flow path  41  is a flow path for supplying the hydrogen gas in the hydrogen tank  40  to the fuel cell  2 , and consists of a main flow path  41   a  and a mixing flow path  41   b , a merging point A being the boundary thereof. The main flow path  41   a  is provided with a shut valve  43 , a regulator valve  44 , and an injector  45 . The shut valve  43  functions as a supply valve of the hydrogen tank  40 . The regulator valve  44  reduces the gas pressure of the hydrogen gas to a preset secondary pressure. The injector  45  is an electromagnetically driven on-off valve and adjusts with high accuracy the flow rate or the pressure of the hydrogen gas supplied to the mixing flow path  41   b.    
     The circulation flow path  42  is a return pipe for returning the hydrogen off gas discharged through a hydrogen gas outlet of the fuel cell  2  back to the supply flow path  41 . The hydrogen pump  46  pressurizes the hydrogen off gas in the circulation flow path  42  and pressure-feeds the hydrogen off gas to the merging point A. At the merging point A, the new hydrogen gas from the hydrogen tank  40  and the hydrogen off gas from the hydrogen pump  46  are merged, and the mixed hydrogen gas after the merging is passed through the mixing flow path  41   b  and supplied to the fuel cell  2 . Thus, the remaining hydrogen in the hydrogen off gas is recycled for the electric power generation in the fuel cell  2 . 
     The circulation flow path  42  is connected to a discharge flow path  49  through a gas-liquid separator  47  and an exhaust/drain valve  48  provided on the upstream side of the hydrogen pump  46 . The hydrogen off gas passing through the circulation flow path  42  contains the moisture of generated water and a nitrogen gas which have permeated through the electrolyte membrane to the fuel electrode, although the quantities thereof are extremely small, as compared with the quantity of the hydrogen off gas. The gas-liquid separator  47  separates a liquid (moisture) and a gas (hydrogen off gas) in the hydrogen off gas, and temporarily retains the separated moisture. The retained moisture is discharged from the exhaust/drain valve  48  into the discharge flow path  49  so as to be discharged to the outside. Further, a part of the hydrogen off gas after the moisture has been collected is also discharged into the discharge flow path  49  from the exhaust/drain valve  48  so as to be discharged to the outside. 
     Thus, the exhaust/drain valve  48  functions not only as a drain valve for discharging the water as the fluid flowing in the circulation system  10  to the outside but also functions as an exhaust valve for discharging the hydrogen off gas containing impurities to the outside. When the exhaust/drain valve  48  is opened, the generated water accumulated in the gas-liquid separator  47  can be drained and the concentration of the hydrogen in the hydrogen off gas can be increased. The specific structures of the exhaust/drain valve  48  and the neighborhood thereof will be described later. 
     The downstream end of the discharge flow path  49  may be directly open to the atmosphere, or may be connected to a diluter, which is not shown, or the exhaust flow path  33 . Further, the circulation system  10  is a system in which the circulation flow path  42 , the mixing flow path  41 , and the fuel gas passage  2   a  are joined in sequence, and circulates the hydrogen off gas back to the fuel cell  2 . 
     The refrigerant piping system  5  circulates a refrigerant (e.g., cooling water) to the fuel cell  2 . The refrigerant piping system  5  has a cooling pump  50 , a refrigerant flow path  51 , a radiator  52 , a bypass flow path  53 , and a switching valve  54 . The cooling pump  50  pressure-feeds the refrigerant in the refrigerant flow path  51  to circulate the refrigerant to the refrigerant passage  2   c . The end of the piping of the refrigerant flow path  51  is joined to a connection of the end plate  22 . Further, as will be described later, the exhaust/drain valve  48  is heated by a part of the refrigerant flow path  51 . The radiator  52  cools the refrigerant discharged from the fuel cell  2 . The switching valve  54  switches the flow of cooling water between the radiator  52  and the bypass flow path  53 , as necessary. 
     The controller  6  is constituted as a microcomputer incorporating a CPU, a ROM, and a RAM. The controller  6  receives detected information from a current sensor and also detected information of sensors for detecting the pressures, the temperatures, the flow rates and the like of fluids passing through the piping systems. Then, the controller  6  controls various types of equipment (the compressor  34 , the shut valve  43 , the injector  45 , the hydrogen pump  46 , the exhaust/drain valve  48 , the cooling pump  50 , the switching valve  54 , and the like) in the system  1  according to the aforesaid detected information or a required amount of electric power to be generated in the fuel cell  2 , and carries out a purging operation or the like in the circulation system  10 . 
     A description will now be given of the constructions of the exhaust/drain valve  48  and the neighborhood thereof. 
     As illustrated in  FIGS. 4 and 5 , the exhaust/drain valve  48  (discharge valve) is an electromagnetically driven on-off valve and actuated by control signals from the controller  6  to intermittently release a fluid in the circulation system  10  to the discharge flow path  49 . The exhaust/drain valve  48  has an angle-valve structure and comprises a valve body  61 , a valve seat  61   d , and a valve disc  62 . 
     In the valve body  61 , an inflow channel  61   a , an outflow channel  61   b , and a valve chest  61   c  are formed as a flow path  61   e  for the fluids (the water and the hydrogen off gas) discharged from the gas-liquid separator  47 . The inflow channel  61   a  is in communication with the circulation flow path  42  through the gas-liquid separator  47 , while the outflow channel  61   b  is in communication with the outside through the discharge flow path  49 . The valve seat  61   d  is formed on the bottom surface of the valve chest  61   c  and has an opening, which is in communication with the outflow channel  61   b.    
     The valve disc  62  is provided in the valve chest  61   c  such that the valve disc  62  is movable within a predetermined stroke in the direction of an axis line X-X. The valve disc  62  abuts against the valve seat  61   d  to close the opening of the valve seat  61   d  so as to close the flow path  61   e . On the other hand, when the valve disc  62  moves away from the valve seat  61   d , the opening of the valve seat  61   d  is released so as to open the flow path  61   e . A diaphragm  63  is provided between the outer surface of the valve disc  62  and an edge of the valve chest  61   c  and constructed so as to follow the movement of the valve disc  62 . 
     A plunger  64  has the valve disc  62  secured to the distal end thereof, and is biased toward the valve seat  61   d  by a spring  64   a . The plunger  64 , a coil  65  and an iron core  66  constitute a drive unit of a solenoid type actuator for reciprocating the valve disc  62  at a predetermined stroke in the direction of the axis line X-X. Turning ON or OFF the supply of current to the coil  65  of the drive unit basically causes the exhaust/drain valve  48  to be switched between two positions, namely, “open” and “close” thereby to intermittently discharge the fluids (the water and the off gas), which are discharged from the gas-liquid separator  47 , to the discharge flow path  49 . 
     The exhaust/drain valve  48  is provided with, in addition to the aforesaid general structures, a structure which is heated by the refrigerant piping system  5 . More specifically, a part of the refrigerant flow path  51  penetrates the valve body  61 . The refrigerant flow path  51  is formed in a portion of the valve body  61 , which portion does not intersect with the inflow channel  61   a , the outflow channel  61   b , and the valve chest  61   c , such that the refrigerant flow path  51  is independent of or does not interfere with the flow path  61   e . The valve body  61  has the inlet  51   a  and an outlet  51   b  of a refrigerant formed therein, and pipes  51   c  and  51   d  of the refrigerant flow path  51  outside the valve body  61  are connected to the inlet  51   a  and the outlet  51   b . A flow path  51   e  connecting the inlet  51   a  and the outlet  51   b  is an L-shaped flow path passing aslant below the valve chest  61   c , and formed such that the flow path  51   e  penetrates a portion, which is relatively near the valve chest  61   c  and the valve seat  61   d , so as to surround the outflow channel  61   b  from two directions. 
     With this arrangement, when the refrigerant flows through the refrigerant flow path  51  at a low temperature, the heat of the refrigerant is promptly transferred to the valve chest  61   c  and the valve seat  61   d , thus intensively heating the valve chest  61   c  and the valve seat  61   d . This restrains water from freezing at the valve chest  61   c  and the valve seat  61   d . Further, the flow path  51   e  for the refrigerant and the flow path  61   e  for the hydrogen off gas or the like are independent in the valve body  61 , thus accomplishing an extremely simple structure of the exhaust/drain valve  48 , as compared with the double piping structure. Moreover, since the freezing in the flow path  61   e  can be restrained, the flow path  61   e  does not require a large diameter to prevent freezing, thus making it possible to reduce the size and the weight of the exhaust/drain valve  48 . In addition, the inlet  51   a  and the outlet  51   b  of the refrigerant are provided in different directions from the inlet of a fluid into the inflow channel  61   a  and the outlet of a fluid from the outflow channel  61   b , permitting easy routing of pipes outside the valve body  61 . 
     Here, the refrigerant flowing in the valve body  61  is preferably the refrigerant before flowing into the radiator  52 . This is because the temperature of the refrigerant is lowered by the radiator  52 ; therefore, in order to raise the temperature of the exhaust/drain valve  48  more promptly, it is better to use the refrigerant before its temperature is lowered. 
     However, in the case where a low-efficiency operation is performed in a low-temperature environment wherein the temperature of the exhaust/drain valve  48  is below a water-freezing temperature, control may be conducted such that the refrigerant flows into the bypass flow path  53 , bypassing the radiator  52 . This reduces the difference between the temperature of the refrigerant at a supply end and that at a discharge end of the fuel cell  2 , so that either the refrigerant at the supply end or the refrigerant at the discharge end of the fuel cell  2  may be allowed to flow into the valve body  61 . This is because there is no significant difference in the effect for raising the temperature of the valve body  61 . 
     As described above, according to the fuel cell system  1  of the present embodiment, the simple structure allows a refrigerant to circulate through the exhaust/drain valve  48  and also allows the circulation position to be set in the vicinity of the valve seat  61   d . Thus, the exhaust heat of the fuel cell  2  can be used to raise the temperature of the exhaust/drain valve  48  and the freezing of the flow path  61   e  for the hydrogen off gas or the like can be restrained. In particular, when the fuel cell system  1  is started up in a low-temperature environment at below-zero temperatures or the like, even if the flow path  61   e  is partly frozen, the temperature of the exhaust/drain valve  48  can be promptly raised, making it possible to eliminate the partial freezing. 
     Control may be conducted such that the refrigerant is supplied to the valve body  61  only when the temperature is low, e.g., below zero. In this case, the controller  6  may set the circulation by the switching valve  54  such that the refrigerant is supplied to the valve body  61  only in a predetermined low-temperature environment wherein the temperature is below zero or the like according to an external temperature sensor or the like, which is not shown. 
     The following will describe modification examples of the embodiment described above. The description of like aspects as those in the embodiment above will be omitted, and only different aspects will be described. 
     The exhaust/drain valve  48  may be provided at a position apart from the fuel cell  2 , that is, at a position apart from the end plate  22  (refer to  FIG. 1 ). Meanwhile, the exhaust/drain valve  48  may be secured to the end plate  22 . 
     However, simply securing the exhaust/drain valve  48  to the end plate  22  would cause the end plate  22  to take considerable heat from the exhaust/drain valve  48 , the temperature of which is rising. It would be likely to adversely affect the rise of the temperature of the exhaust/drain valve  48 . Therefore, the following will explain two examples of a preferred method for securing the exhaust/drain valve  48  so as to restrain heat dissipation to the end plate  22 . 
     First Example 
       FIG. 2  is a diagram illustrating the plane configurations of an end portion of the stack body  21  and the exhaust/drain valve  48 , and  FIG. 3  is a side view observed from direction III in  FIG. 2 . Incidentally,  FIGS. 2 and 3  illustrate simplified configurations of the stack body  21  and the exhaust/drain valve  48 , the detailed portions thereof being omitted. 
     As illustrated in  FIG. 2  and  FIG. 3 , the exhaust/drain valve  48  is secured to the end plate  22  by a bolt  71  (a fastening member) through a bracket  70 . The bracket  70  has a first plate-like member  72   a  extending in parallel to a surface of the end plate  22  and a second plate-like member  72   b  extending at a right angle from a bottom end of the first plate-like member  72   a . The first plate-like member  72   a  is secured to the end plate  22  by the bolt  71 , and the second plate-like member  72   b  is secured to the valve body  61  of the exhaust/drain valve  48 . 
     The end plate  22  has a spot facing  23  formed adjacently to the surface of the first plate-like member  72   a . The spot facing  23  is shaped to be larger than the contour of the first plate-like member  72   a , and a bottom surface  23   a  thereof has a bearing portion  24  protruding toward the first plate-like member  72   a . The bearing portion  24  is formed at a position corresponding to the position of a bolt hole of the first plate-like member  72   a , and a bearing surface  24   a  is formed around a fastening hole into which the bolt  71  is screwed in. When the valve body  61  is secured to the end plate  22  through the bracket  70 , the portion of the bracket  70  which is in contact with the end plate  22  is only the portion of the bearing surface  24   a.    
     According to the first example, the bracket  70  is spaced away from the end plate  22  except for the portion bolted to the end plate  22 . In other words, the contact surface between the bracket  70  and the end plate  22  is only the bearing surface  24   a , which has a small area. This makes it possible to restrain the heat dissipation from the valve body  61  to the end plate  22 . 
     A modification example of the first example may be, for instance, a mode illustrated in  FIG. 6  or  FIG. 7 . To be specific, as illustrated in  FIG. 6 , a bearing portion  124  may be provided on the first plate-like member  72   a  of the bracket  70 , while omitting the spot facing  23  and the bearing portion  24 . This arrangement also reduces the area of the contact surface, which provides a thermal conduction route from the valve body  61  to the end plate  22 , as with the construction described above. Hence, the heat dissipation from the valve body  61  to the end plate  22  can be restrained. 
     Further, as illustrated in  FIG. 7 , a washer  25 , such as a spring washer or a lock washer, may be provided between the first plate-like member  72   a  and the end plate  22 , while omitting the bearing portion  24 . This construction also reduces the areas of the contact surface between the washer  25  and the first plate-like member  72   a  and of the contact surface between the washer  25  and the end plate  22 , as with the construction described above. Thus, the thermal conduction area is reduced in a like manner, making it possible to restrain the heat dissipation from the exhaust/drain valve  48 , the temperature of which is rising. 
     In any one case of the first example, the bracket  70  may be formed integrally with the valve body  61 . 
     Second Example 
       FIG. 8  is a diagram illustrating the plane configurations of an end portion of the stack body  21  and the exhaust/drain valve  48  similar to those in  FIG. 2 . In the present example, the exhaust/drain valve  48  is secured to the end plate  22  at only one point. More specifically, the exhaust/drain valve  48  is secured to a bracket  270 , and the bracket  270  is secured to the end plate  22 , the bracket  270  and the end plate  22  being fastened at one point by a single bolt  271 . The fastening at one point makes it possible to reduce the amount of heat transferred from the exhaust/drain valve  48 , whose temperature is rising, to the end plate  22 , thus expediting the rise of the temperature of the exhaust/drain valve  48 . 
     The one-point fastening is preferably positioned at the center of gravity of the exhaust/drain valve  48  or in the vicinity thereof. This allows the exhaust/drain valve  48  to be stably supported by the end plate  22  even if the exhaust/drain valve  48  should be subjected to a vibration or an impact due to an external force. Incidentally, the bracket  270  may be integrally formed with a valve body  61 . 
     Second Embodiment 
     Referring now to  FIG. 9 , a second embodiment of the present invention will be described regarding major different aspects. A different aspect from the first embodiment is that the refrigerant flow path  51  is provided in contact with the outer surface of the valve body  61  rather than a part of the refrigerant flow path  51  penetrating the valve body  61 . Components that are common with those of the first embodiment will be assigned like reference numerals and detailed explanation thereof will be omitted. 
     A pipe  151  of the refrigerant flow path  51  is disposed near the valve body  61  and secured to the valve body  61  through a stay  73  (a thermally-conductive member). The stay  73  is a plate-like member, such as a metal member, having thermal conductivity. One end  73   a  of the stay  73  contacts with the surface of the valve body  61  and is secured thereto by a bolt or the like. The surface of the valve body  61  with which the one end  73   a  contacts is preferably near a valve chest  61   c  or a valve seat  61   d . Further, the other end  73   b  of the stay  73  is provided such that the other end  73   b  contacts with the surface of the pipe  151 . The other end  73   b  has, for example, an approximately semi-arcuate section, and contacts with the pipe  151  such that the other end  73   b  covers the half of the outer peripheral surface of the pipe  151 . This arrangement makes it possible to secure certain sizes of an area of contact between the stay  73  and the valve body  61  and an area of contact between the stay  73  and the pipe  151 . 
     According to the second embodiment, the plate surface of the stay  73  contacts with the valve body  61  and the pipe  151 , so that the heat of a refrigerant flowing through the refrigerant flow path  51  is transferred from the pipe  151  to the stay  73  and then from the stay  73  to the valve body  61 . Thus, the structure, which is simpler than that of the first embodiment, makes it possible to improve the performance for raising the temperature of the exhaust/drain valve  48  and to restrain the exhaust/drain valve  48  from freezing. 
     As with the first embodiment, the refrigerant flowing through the pipe  151  may be any refrigerant before flowing into a radiator  52 , and in the case of performing a low-efficiency operation, the refrigerant may be either the refrigerant at the supply side or the one at the discharge side of the fuel cell  2 . Further, the shape and the securing position of the stay  73  may be designed such that the stay  73  does not interfere with other members provided around the valve body  61  and that the neighborhood of the exhaust/drain valve  48  is simple and compact. 
     INDUSTRIAL APPLICABILITY 
     The exhaust/drain valve  48  may be adapted to perform only exhaust or drainage. For example, in the case where a drain valve for discharging water, which has been separated by the gas-liquid separator  47 , to the outside and an exhaust valve for discharging the hydrogen off gas in the circulation flow path  42  to the outside together with impurities are provided separately, adopting the same construction as that of the exhaust/drain valve  48  for each of the drain valve and the exhaust valve makes it possible to restrain these valves from freezing. In such a construction, the drain valve is connected to the gas-liquid separator  47  in the same manner as that of the exhaust/drain valve  48 . Meanwhile, the exhaust valve is installed in a purge channel which is branched and connected to the circulation flow path  42 .