Abstract:
Disclosed is a hydrogen supply apparatus which can mix an odorant with hydrogen gas even at a low temperature and can detect the leakage of the hydrogen gas. The apparatus comprises a gas storage means for storing hydrogen gas therein, an odorant-addition means for adding an odorant to the hydrogen gas fed from the gas storage means, and a temperature control means for controlling the temperature of at least one of the hydrogen gas stored in the gas storage means, the hydrogen gas fed from the gas storage means and the odorant.

Description:
This is a division of application Ser. No. 11/991,666 filed 7 Mar. 2008, which is a 371 national phase application of PCT/JP2006/317670 filed 6 Sep. 2006, claiming priority to Japanese Patent Application No. 2005-259129 filed 7 Sep. 2005, and No. 2006-211730 filed 3 Aug. 2006, respectively, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a hydrogen supply apparatus and a fuel gas supply apparatuses, each of which can be suitably used in a fuel cell system that generates electric energy by an electrochemical reaction in particular. 
     BACKGROUND OF THE INVENTION 
     A fuel cell system for obtaining electric energy by an electrochemical reaction between a hydrogen gas and an oxidation gas is known. The hydrogen gas serving as a fuel for this fuel cell system is flammable and odorless. On the other hand, in handling a hydrogen gas, it is preferable to be able to recognize the presence of the hydrogen gas with certainty. 
     Therefore, a hydrogen supply apparatus that mixes a hydrogen gas with an odorant whose presence is recognizable due to its odor has been provided (see, for example, Patent Document 1). In this hydrogen supply apparatus, since the hydrogen gas and the odorant are mixed, the handling of the hydrogen gas is facilitated. Further, in the case where the leakage of the hydrogen gas has occurred, for example, the leakage of the hydrogen gas can be immediately detected due to the odor of the odorant.
     [Patent document 1] JP 2002-29701 A   [Patent document 2] JP 2002-216812 A   [Patent document 3] JP 2004-111167 A   

     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In order to detect the leakage of the hydrogen gas, the odorant and the hydrogen gas have to be mixed. However, in the case where the hydrogen gas has reached an extremely low temperature, the odorant has sometimes been solidified, and the hydrogen gas and the odorant have not been mixed at an extremely low temperature in some cases. In a system for storing the hydrogen gas in a high-pressure state, such as a high-pressure hydrogen tank in particular, the hydrogen gas has reached an extremely low temperature due to adiabatic expansion during the hydrogen supply, and the hydrogen gas has been supplied while not being mixed with the odorant in some cases. 
     The present invention has been made in view of the various problems mentioned above, and it is an object of the present invention to provide a hydrogen supply apparatus capable of mixing an odorant with a hydrogen gas even at a low temperature, and detecting the hydrogen gas leakage. 
     Means for Solving the Problems 
     In order to solve the above-mentioned problems, the present invention adopts the following means. That is, a hydrogen supply apparatus according to the present invention includes: gas storage portion which stores a hydrogen gas; an odorant addition portion which adds an odorant to the hydrogen gas; and a temperature adjustment portion which adjusts a temperature of at least one of the hydrogen gas, the odorant, and the hydrogen gas to which the odorant has been added. 
     In the hydrogen supply apparatus, upon supply of the hydrogen gas stored in the gas storage portion to the outside thereof, the pressure of the hydrogen gas is reduced, and the hydrogen gas undergoes adiabatic expansion. Thus, the temperature of the hydrogen gas is reduced. When the temperature of the hydrogen gas is reduced to a level equal to or lower than a predetermined temperature, the odorant to be mixed with the hydrogen gas is solidified or liquefied, and may have difficulty in mixing with the hydrogen gas. 
     The hydrogen supply apparatus according to the present invention increases the temperature of at least one of the hydrogen gas and the odorant by the temperature adjustment portion to suppress a temperature reduction in hydrogen gas, thus making it possible to maintain the odorant in a state in which (or at a temperature at which) the odorant can be mixed with the hydrogen gas. The hydrogen gas whose temperature is increased may be a hydrogen gas stored in the gas storage portion, or may be a hydrogen gas supplied to the outside from the gas storage portion. Further, the hydrogen gas supplied to the outside includes a hydrogen gas to which the odorant has been added. It should be noted that the hydrogen gas supply apparatus according to the present invention can add the odorant to the hydrogen gas by including odorant addition portion. The hydrogen gas to which the odorant is to be added may be a hydrogen gas stored in the gas storage portion, or may be a hydrogen gas discharged from the gas storage portion. Further, the hydrogen gas, to which the odorant has been added by the odorant addition portion, is supplied to the supply destination for the hydrogen gas, i.e., a hydrogen gas utilization apparatus such as a fuel cell or a hydrogen engine. 
     Further, a hydrogen supply apparatus according to the present invention may be characterized by further including stored gas temperature detection portion which detects the temperature of the hydrogen gas stored in the gas storage portion, and characterized in that the temperature adjustment portion has a gas temperature reduction suppression portion which suppresses a temperature reduction in hydrogen gas stored in the gas storage portion, when the temperature of the hydrogen gas detected by the stored gas temperature detection portion is equal to or lower than a predetermined temperature. 
     When the temperature of the hydrogen gas is equal to or lower than the predetermined temperature, a temperature reduction in hydrogen gas is suppressed by the gas temperature reduction suppression portion, thus making it possible to maintain the odorant in a state in which (or at a temperature at which) the odorant can be mixed with the hydrogen gas. It should be noted that the hydrogen gas may be one mixed with the odorant. With the use of the hydrogen gas mixed with the odorant, the hydrogen gas mixed with the odorant can be supplied, and the detection accuracy of the hydrogen gas leakage can be improved. The predetermined temperature refers to a temperature below which the odorant is changed into, for example, a solid form incapable of mixing with the hydrogen gas, and is appropriately set in accordance with the properties of the odorant. 
     Further, a hydrogen supply apparatus according to the present invention may be characterized by further including hydrogen gas temperature detection portion which detects the temperature of the hydrogen gas supplied from the gas storage portion, and characterized in that the temperature adjustment portion has a heating portion which increases the temperature of the hydrogen gas supplied from the gas storage portion, when the temperature of the hydrogen gas detected by the hydrogen gas temperature detection portion is equal to or lower than a predetermined temperature. 
     The above-mentioned stored gas temperature detection portion detects the temperature of the hydrogen gas stored in the gas storage portion; on the other hand, the hydrogen gas temperature detection portion detects the temperature of the hydrogen gas, supplied to the outside of the gas storage portion, at the outside of the gas storage portion. That is, the hydrogen gas temperature detection portion is capable of detecting the temperature of the hydrogen gas to be supplied to the outside of the gas storage portion, which has been reduced due to adiabatic expansion. Based on the temperature of the hydrogen gas detected, the temperature adjustment portion increases the temperature of the hydrogen gas supplied from the gas storage portion, thereby making it possible to suppress the liquefaction or solidification of the odorant, resulting from the cooling thereof by the hydrogen whose temperature has been reduced. It should be noted that the heating portion may be any portion as long as it is capable of increasing the temperature of the hydrogen gas, and an example of which may be a heater. 
     Further, the hydrogen supply apparatus according to the present invention may be characterized by further including an odorant temperature detection portion which detects the temperature of the odorant to be added by the odorant addition portion, in which the temperature adjustment portion has a heating portion which increases the temperature of the odorant to be added by the odorant addition portion, when the temperature of the odorant detected by the odorant temperature detection portion is equal to or lower than a predetermined temperature. 
     In order to increase the temperature of the odorant, it is preferable to calculate the vapor pressure of the odorant from the temperature of the odorant detected, and to apply heat to the odorant so that it reaches a necessary vapor pressure. The necessary vapor pressure refers to a pressure at which the odorant added to the hydrogen gas does not liquefy or solidify. The supply of heat to the odorant may be carried out by providing an odorant storage portion which stores an odorant, for example, and by raising the temperature of the odorant storage portion using a heating portion such as a heater. By adjusting the vapor pressure of the odorant in this manner, the liquefaction or solidification of the odorant can be suppressed. It should be noted that the heating portion may be any portion as long as it can increase the temperature of the odorant, and an example of which may be a heater. 
     Further, the hydrogen supply apparatus according to the present invention may be characterized by further including: a hydrogen gas temperature detection portion which detects the temperature of the hydrogen gas supplied from the gas storage portion; and an odorant temperature detection portion which detects the temperature of the odorant added by the odorant addition portion, in which the temperature adjustment portion has a heating portion which increases the temperature of the odorant when at least one of the temperature of the hydrogen gas detected by the hydrogen gas temperature detection portion and the temperature of the odorant detected by the odorant temperature detection portion meets a predetermined condition. 
     In the present invention, the temperature of the odorant is adjusted not only based on the temperature of the odorant detected by the odorant detection portion, but also based on the temperature of the odorant detected by the hydrogen gas detection portion. The predetermined condition portion determines that the temperature of the hydrogen gas detected by the hydrogen gas temperature detection portion is equal to or lower than a predetermined temperature, or the temperature of the odorant detected by the odorant temperature detection portion is equal to or lower than a predetermined temperature. It should be noted that temperatures to be employed may be prioritized, and the temperature of the odorant may be increased based on a high-priority temperature. The heating portion may be any portion as long as it can increase the temperature(s) of the hydrogen gas and/or the odorant, and an example of which may be a heater. 
     Further, a hydrogen supply apparatus according to the present invention may be characterized by further including a hydrogen gas temperature detection portion which detects the temperature of the hydrogen gas supplied from the gas storage portion, and characterized in that the temperature adjustment portion has a heating portion which increases the temperature of the hydrogen gas which is supplied from the gas storage portion and to which the odorant has been added by the odorant addition portion, when the temperature of the hydrogen gas detected by the hydrogen gas temperature detection portion is equal to or lower than a predetermined temperature. 
     According to the present invention, the temperature of the hydrogen gas, to which the odorant has been added by the odorant addition portion, is adjusted, thereby suppressing the liquefaction or solidification of the odorant contained in the hydrogen gas. As described above, upon supply of the hydrogen gas stored in the gas storage portion to the outside thereof, the temperature may be reduced due to adiabatic expansion. However, the causes of the temperature reduction in hydrogen gas are not limited to this, and it may also be possible that the temperature of the hydrogen gas is reduced, for example, by placing the hydrogen gas supply apparatus in a below-freezing environment. Even if the hydrogen gas or odorant is heated, the temperature reduction in hydrogen gas due to such a cause may occur because of the subsequent gradual loss of heat from the hydrogen gas, for example. According to the present invention, the temperature of the hydrogen gas after the addition of the odorant can be increased, and therefore, the liquefaction or the like of the odorant can be prevented even if the hydrogen gas supply apparatus is placed in a below-freezing environment. 
     Further, a hydrogen supply apparatus according to the present invention may be characterized by further including a hydrogen gas supply amount adjustment portion which adjusts a supply amount of the hydrogen gas supplied from the gas storage portion, and characterized in that the temperature adjustment portion decreases the supply amount of the hydrogen gas, supplied from the gas storage portion, by the hydrogen gas supply amount adjustment portion, to thereby suppress a temperature reduction in hydrogen gas. 
     Upon supply of the hydrogen gas from the gas storage portion to the outside thereof, the hydrogen gas inside the gas storage portion is decreased, and the temperature of the hydrogen gas is reduced due to adiabatic expansion. In particular, if the hydrogen gas is stored in a high-pressure state in a high-pressure hydrogen tank, for example, the pressure is sharply reduced, which results in a significant temperature reduction. However, upon decrease in the supply amount of the hydrogen gas, the temperature reduction is decreased. 
     Accordingly, when the temperature of the hydrogen gas is equal to or lower than the predetermined temperature, the supply amount of the hydrogen gas is preferably decreased by the hydrogen gas supply amount adjustment portion, and the temperature reduction can be suppressed to facilitate the mixing of the odorant with the hydrogen gas by decreasing the supply amount of the hydrogen gas. 
     Further, a hydrogen supply apparatus according to the present invention may be characterized in that the predetermined temperature is equal to or higher than a melting point of the odorant. That is, when the temperature of the hydrogen gas detected by the stored gas temperature detection portion or the hydrogen gas temperature detection portion is equal to or lower than the predetermined temperature that is equal to or higher than the melting point of the odorant, the temperature adjustment portion increases the temperature of at least one of the hydrogen stored in the gas storage portion, the hydrogen gas supplied from the gas storage portion, and the odorant. 
     The melting point of the odorant is a temperature at which the odorant changes from a solid form to a liquid form. When the temperature of the odorant is reduced to be lower than the melting point thereof, the odorant is turned into a solid form, which has difficulty in mixing with the hydrogen gas. At such a temperature, the hydrogen gas and the odorant may not be mixed, and the detection accuracy of the hydrogen gas leakage may be degraded. 
     Accordingly, the predetermined temperature is set equal to or higher than the melting point of the odorant so as to suppress a temperature reduction in hydrogen gas when the temperature of the hydrogen gas is equal to or lower than the predetermined temperature, thereby suppressing the solidification of the odorant, and allowing the odorant to be present in a liquid form or in a gaseous form. Generally, it is difficult to mix the odorant in a solid form with the hydrogen gas, and therefore, the odorant is provided in a liquid form or in a gaseous form, thus facilitating the mixing of the odorant with the hydrogen gas. 
     It should be noted that the predetermined temperature is set equal to or higher than the melting point of the odorant because it is suitable for the odorant, which can be mixed with the hydrogen gas or is easily mixed therewith in a liquid state, and this temperature is appropriately changed in accordance with the properties of the odorant. 
     Further, a hydrogen supply apparatus according to the present invention may be characterized in that the predetermined temperature is equal to or higher than a boiling point of the odorant. That is, when the temperature of the hydrogen gas, detected by the gas temperature detection portion, is equal to or lower than the predetermined temperature that is equal to or higher than the boiling point of the odorant, the gas temperature reduction suppression portion increases the temperature of at least one of the hydrogen stored in the gas storage portion, the hydrogen gas supplied from the gas storage portion, and the odorant. 
     The boiling point of the odorant is a temperature at which the odorant changes from a liquid form to a gaseous form. When the temperature of the odorant is reduced to be lower than the boiling point thereof, the odorant is changed into a liquid form, which may have difficulty in mixing with the hydrogen gas depending on the properties of the odorant. The odorant, which will not be mixed with the hydrogen gas or have difficulty in mixing therewith in a liquid state, may degrade the detection accuracy of the hydrogen gas leakage. 
     Accordingly, by suppressing a temperature reduction in hydrogen gas when the temperature of the hydrogen gas is at the predetermined temperature that is equal to or higher than the boiling point of the odorant, the odorant is kept in a gaseous state, thus making it possible to facilitate the mixing of the odorant with the hydrogen gas. 
     It should be noted that the predetermined temperature is set equal to or higher than the boiling point of the odorant because it is suitable for the odorant, which can be mixed with the hydrogen gas or is easily mixed therewith in a gaseous state, and this temperature is appropriately changed in accordance with the properties of the odorant. 
     Further, a hydrogen supply apparatus according to the present invention may be characterized by including: a gas storage portion which stores a hydrogen gas mixed with an odorant; a gas supply portion which supplies the hydrogen gas from the gas storage portion; and a gas temperature detection portion which detects the temperature of the hydrogen gas stored in the gas storage portion; and a gas temperature reduction suppression portion which suppresses a temperature reduction in hydrogen gas stored in the gas storage portion, when the temperature of the hydrogen gas detected by the gas temperature detection portion is equal to or lower than a predetermined temperature. 
     By suppressing a temperature reduction in hydrogen gas using the gas temperature reduction suppression portion when the temperature of the hydrogen gas mixed with the odorant is equal to or lower than the predetermined temperature, the odorant can be maintained in a state in which (or at a temperature at which) it can be mixed with the hydrogen gas. Accordingly, the hydrogen gas mixed with the odorant can be supplied, thus enabling an improvement in the detection accuracy of the hydrogen gas leakage. The predetermined temperature is a temperature below which the odorant is changed into a solid state, for example, which cannot be mixed with the hydrogen gas, and is appropriately set in accordance with the properties of the odorant. 
     Further, a hydrogen supply apparatus according to the present invention may be characterized by further including a hydrogen gas temperature detection portion which detects the temperature of the hydrogen gas supplied from the gas storage portion, and characterized in that the temperature adjustment portion has a heating portion which increases the temperature of the hydrogen gas which is supplied from the gas storage portion and to which the odorant has been added by the odorant addition portion, when the temperature of the hydrogen gas detected by the hydrogen gas temperature detection portion is equal to or lower than a predetermined temperature. Thus, it is possible to increase the temperature of the hydrogen gas, which has been mixed with the odorant, and which is to be supplied to the outside from the gas storage portion. 
     Besides, the hydrogen supply apparatus according to the present invention may be characterized in that the gas temperature reduction suppression portion suppresses a temperature reduction in hydrogen gas by decreasing the supply amount of the hydrogen gas. 
     The hydrogen supply apparatus according to the present invention is satisfactory as long as it can suppress a temperature reduction in hydrogen gas when the temperature of the hydrogen gas is equal to or lower than a predetermined temperature at which the hydrogen gas has difficulty in mixing with the odorant; for example, in addition to the above-mentioned configurations, the apparatus may be provided with a limiter for stopping the supply of the hydrogen gas when the temperature thereof is equal to or lower than the predetermined temperature, so as to prevent a decrease in the hydrogen gas inside a hydrogen storage device, and to suppress a temperature reduction in hydrogen gas, or the apparatus may be provided with a plurality of gas storage portions so as to use the hydrogen gas inside the gas storage portion in which the temperature of the hydrogen gas is higher than the predetermined temperature, without the use of the gas storage portion in which the temperature of the hydrogen gas is lower than the predetermined temperature, thereby maintaining the temperature of the hydrogen gas to be supplied above the predetermined temperature. 
     Actually, each of the hydrogen supply apparatuses described above is an apparatus for supplying a hydrogen gas as a fuel gas. It should be noted that problems that the odorant is not solidified at a low temperature and the hydrogen gas is not mixed with the odorant at an extremely low temperature are not limited to the hydrogen gas, but those problems are possible in general fuel gas. Accordingly, an object of the present invention is to provide a fuel gas supply apparatus capable of mixing an odorant with a fuel gas even at a low temperature, and detecting the fuel gas leakage. 
     In order to solve the above-mentioned problems, the present invention adopts the following portion. That is, a fuel gas supply apparatus according to the present invention is characterized by including: a gas storage portion which stores a fuel gas; an odorant addition portion which adds an odorant to the fuel gas; and a temperature adjustment portion which adjusts the temperature of at least one of the hydrogen gas, the odorant, and the hydrogen gas to which the odorant has been added. 
     The fuel gas supply apparatus according to the present invention has functions equivalent to those of each hydrogen supply apparatus already described above. This is because “fuel gas” is a generic name for a natural gas, a liquefied petroleum gas and the like, and a hydrogen gas is also included in a fuel gas. Accordingly, the configuration of the above-mentioned fuel gas supply apparatus can be described by replacing the hydrogen gas in each hydrogen supply apparatus already described above with a fuel gas. Therefore, the description thereof will be omitted. 
     It should be noted that examples of the fuel gas include a natural gas, and a liquefied petroleum gas (LPG) composed of propane and butane and utilized as a mixture thereof. It should be noted that the natural gas includes a compressed natural gas (hereinafter, referred to as “CNG”). Further, if hydrogen is reformed by a reformer, a resultant reformed gas is also included in the fuel gas. Further, the fuel gas supply apparatus for supplying those fuel gases is applicable to a fuel cell serving as a fuel gas consumption device that consumes a fuel gas, a hydrogen engine, a CNG engine, an LPG engine, and a reformer for reforming a fuel gas, for example. It should be noted that a reformer for reforming a fuel gas refers to a reformer for reforming, for example, a fuel gas to hydrogen. 
     According to the hydrogen supply apparatus of the present invention, a temperature reduction in a hydrogen gas can be suppressed even at a low temperature, an odorant and a hydrogen gas can be mixed, and the hydrogen gas leakage can be detected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  A block diagram of a fuel cell system  10  according to Embodiment 1. 
         FIG. 2  A flow chart illustrating the temperature control of a hydrogen gas in the fuel cell system  10  according to Embodiment 1. 
         FIG. 3  A flow chart illustrating the temperature control of a hydrogen gas in the fuel cell system  10  according to Embodiment 2. 
         FIG. 4  A block diagram of a water fuel cell system  11  according to Embodiment 3. 
         FIG. 5  A flow chart illustrating the temperature control of a hydrogen gas according to Embodiment 3. 
         FIG. 6  A map of a necessary heating amount. 
         FIG. 7  A block diagram of a fuel cell system  12  according to Embodiment 4. 
         FIG. 8  A flow chart illustrating the vapor pressure control of an odorant according to Embodiment 4. 
         FIG. 9  A block diagram of a fuel cell system  13  according to Embodiment 5. 
         FIG. 10  A block diagram of a fuel cell system  14  according to Embodiment 6. 
         FIG. 11  A flow chart illustrating the temperature control of a hydrogen gas according to Embodiment 6. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of hydrogen supply apparatuses according to the present invention will be described in detail with reference to the drawings. 
     Embodiment 1 
       FIG. 1  is a system block diagram of a fuel cell system  10  including a hydrogen supply apparatus according to Embodiment 1. This fuel cell system includes: a fuel cell  1 ; a high-pressure hydrogen tank  2  which stores a hydrogen gas serving as a fuel gas, and which functions as a hydrogen supply apparatus for supplying the hydrogen gas to the fuel cell  1 ; an air supply apparatus  3  for supplying air to the fuel cell  1 ; and an electronic control unit (ECU)  4  for controlling the various apparatuses. 
     The high-pressure hydrogen tank  2  includes: a tank  21  serving as gas storage portion in which the hydrogen gas mixed with an odorant is stored; a main stop valve  22  through which the hydrogen gas is supplied to the fuel cell  1 ; a heater  23  serving as a heating portion for increasing the temperature of the hydrogen gas inside the tank  21 ; and a thermometer  24  serving as a gas temperature detection portion which detects the temperature of the hydrogen gas inside the tank  21 . 
     The fuel cell  1  causes an electrochemical reaction between the hydrogen gas and an oxidation gas via an electrolyte to obtain electric energy. The fuel cell  1  according to Embodiment 1 is a solid polymer electrolyte fuel cell frequently used in an electric automobile that runs using a fuel cell as a power supply. 
     The hydrogen gas stored in the high-pressure hydrogen tank  2  contains methyl acrylate as an odorant. The odorant gives the hydrogen gas an odor by mixing the odorant into an odorless hydrogen gas, and serves to detect the hydrogen gas leakage. The methyl acrylate has a boiling point of about 80° C. and a melting point of about −75° C. 
     The main stop valve  22  serves as a supply port through which the hydrogen gas is supplied from the tank  21  to the fuel cell  1 , and a supply flow rate therethrough is controlled by the ECU  4 . Further, the main stop valve  22  is a solenoid valve, which is heated by passing an electric current therethrough, and which can indirectly heat the hydrogen gas to be supplied to the fuel cell  1 . That is, the main stop valve  22  has a function of a heating portion like the heater  23 . 
     The heater  23  is disposed at a lower part of the tank  21 , and can directly heat the hydrogen gas inside the tank  21  with the control of the ECU  4 . The position at which the heater  23  is placed may be any position as long as the hydrogen gas inside the tank  21  can be heated, and is not limited to the lower part of the tank  21 ; however, when the odorant is in a solid form or in a liquid form, the hydrogen gas is accumulated at the lower part of the tank  21 , and therefore, the hydrogen gas can be efficiently heated by placing the heater  23  at the lower part of the tank  21 . 
     The thermometer  24  serves to detect the temperature of the hydrogen gas inside the tank  21 , and is configured so that the temperature of the hydrogen gas detected is inputted to the ECU  4 . The ECU  4  controls the main stop valve  22  or the heater  23  based on the temperature of the hydrogen gas detected by the thermometer  24 , thereby maintaining the hydrogen gas inside the tank  21  at an appropriate temperature. 
     Hereinafter, the temperature control of the hydrogen gas in the fuel cell system  10  configured as described above will be described in detail. Each of the various controls described below is executed by the ECU  4 , and is a routine repeated at regular intervals. 
     Embodiment 1 provides temperature control prior to the start of supply of the hydrogen gas, and is an embodiment in which when the temperature of the hydrogen gas inside the high-pressure hydrogen tank  2  is equal to or lower than a predetermined temperature, the temperature of the hydrogen gas is increased by the heater  23  or the main stop valve  22  to create a state where the mixing of the odorant with the hydrogen gas is facilitated, thus supplying the hydrogen gas mixed with the odorant to the fuel cell.  FIG. 2  is a flow chart illustrating the temperature control of the hydrogen gas according to Embodiment 1. 
     First, at the start of the supply of the hydrogen gas from the high-pressure hydrogen tank  2  to the fuel cell  1 , the temperature of the hydrogen gas inside the tank  21  is detected by the thermometer  24  (Step  101 ). The detected temperature is inputted to the ECU  4 , and the ECU  4  determines whether the detected temperature is equal to or lower than a predetermined temperature T1 (Step  102 ). 
     In Embodiment 1, methyl acrylate is used as the odorant, and the predetermined temperature T1 is set to −70° C., which is 5° C. higher than −75° C., i.e., the melting point of methyl acrylate. That is, at a temperature higher than the predetermined temperature T1, the methyl acrylate is present as a liquid, and is in a state in which the methyl acrylate is easily mixed with the hydrogen gas. 
     When the temperature of the hydrogen gas detected is equal to or lower than the predetermined temperature T1, the ECU  4  carries out a heating process so as to prevent the odorant from being solidified (Step  103 ). In the heating process, the hydrogen gas may be directly heated by passing an electric current through the heater  24 , or the hydrogen gas to be supplied may be indirectly heated by passing an electric current through the main stop valve  22 . After having carried out the heating process for a certain period of time by any one of methods, the temperature of the hydrogen gas inside the tank  21  is detected again by the thermometer  24  (Step  101 ). 
     It is determined again whether the temperature of the hydrogen gas detected is equal to or lower than T1 (Step  102 ), and the heating process is repeated until it is determined that the temperature of the hydrogen gas inside the tank  21  is higher than the predetermined temperature T1. If the temperature of the hydrogen gas detected by the thermometer  24  is determined to be higher than the predetermined temperature T1 as a result of the determination of Step  102 , it is determined that the methyl acrylate serving as the odorant is in a liquid form and is mixed with the hydrogen gas, thus starting the supply of the hydrogen gas (Step  104 ). 
     It should be noted that if the supply of the hydrogen gas is continued, the temperature thereof is reduced due to the adiabatic expansion of the hydrogen gas, and therefore, the present control is repeated at certain periods of time even after the supply of the hydrogen gas has been started. As described above, according to Embodiment 1, the hydrogen gas can be supplied at a temperature at which the odorant is easily mixed with the hydrogen gas, thus facilitating the mixing of the hydrogen gas with the odorant, and enabling an improvement in the detection accuracy of the hydrogen gas leakage. 
     Further, in Embodiment 1, the temperature control of the hydrogen gas is performed before the start of supply of the hydrogen gas, but the temperature control does not necessarily have to be performed before the start of supply of the hydrogen gas, and may be performed during the supply of the hydrogen gas. It should be noted that when the temperature control is performed during the supply of the hydrogen gas, a hydrogen supply stopping portion which stops the supply of the hydrogen gas may further be provided, if the temperature of the hydrogen gas is equal to or lower than the predetermined temperature T1. By providing the hydrogen supply stopping portion, the supply of the hydrogen gas equal to or lower than the predetermined temperature is stopped, thus making it possible to prevent the hydrogen gas, which is not mixed with the odorant at a low temperature, from being supplied to the fuel cell  1 . 
     Embodiment 2 
     In Embodiment 2, when the temperature of the hydrogen gas inside the high-pressure hydrogen tank  2  is equal to or lower than the predetermined temperature, the flow rate of the hydrogen gas to be supplied to the fuel cell  1  is reduced, thereby preventing a decrease in the hydrogen gas inside the tank  21 . By preventing the decrease in the hydrogen gas inside the tank  21 , the temperature reduction in hydrogen gas due to adiabatic expansion is suppressed. The hydrogen gas temperature control according to Embodiment 2 is the temperature control carried out during the supply of the hydrogen gas. It should be noted that the configuration of the fuel cell system is substantially the same as in Embodiment 1; therefore, the same components are identified by the same reference numerals, and the description thereof will be omitted. 
     In the fuel cell system  10  according to Embodiment 2, the ECU  4 , serving as gas temperature control portion, has a function of adjusting the supply flow rate of the hydrogen gas to be supplied from the high-pressure hydrogen tank  2  to the fuel cell  1 . If the temperature indicated by the thermometer  24  serving as gas temperature detection portion is equal to or lower than a predetermined temperature, the ECU  4  reduces the supply flow rate of the hydrogen gas to suppress the adiabatic expansion of the hydrogen gas inside the tank  21 , and to suppress the temperature reduction in hydrogen gas inside the tank  21 . By suppressing the temperature reduction in hydrogen gas in this manner, the odorant contained in the hydrogen gas can be maintained at a temperature higher than a constant temperature at which the odorant is easily mixed with the hydrogen gas, and the hydrogen gas mixed with the odorant can be furnished to the fuel cell  1 . 
       FIG. 3  is a flow chart illustrating the temperature control of the hydrogen gas according to Embodiment 2. First, the hydrogen gas is supplied from the high-pressure hydrogen tank  2  to the fuel cell  1  at a supply flow rate Q1 (Step  201 ). After a certain period of time has passed since the supply of the hydrogen gas, the temperature of the hydrogen gas inside the tank  21  is detected by the thermometer  24  (Step  202 ). The detected temperature is inputted to the ECU  4 , and the ECU  4  determines whether the temperature of the hydrogen gas detected is equal to or lower than a predetermined temperature T2 (Step  203 ). 
     Also in Embodiment 2, similarly to Embodiment 1, methyl acrylate is used as the odorant. However, the predetermined temperature T2 is set to −65° C., which is 10° C. higher than −75° C., i.e., the melting point of methyl acrylate. The reason the predetermined temperature T2 is set higher than the predetermined temperature in Embodiment 1 is that in Embodiment 1, the temperature reduction to the predetermined temperature T1 or lower is impossible since the hydrogen gas is heated by the heating portion, but in Embodiment 2, the slight temperature reduction to the predetermined temperature T2 or lower is possible since the temperature reduction is suppressed without performing any heating process. Accordingly, the predetermined temperature T2 in Embodiment 2 is set 5° C. higher than the predetermined temperature T1 in Embodiment 1. 
     If the temperature of the hydrogen gas detected is equal to or lower than the predetermined temperature T2, the ECU  4  changes the supply flow rate of the hydrogen gas from Q1 to Q2 (where Q2&lt;Q1) in order to suppress the temperature reduction in hydrogen gas (Step  204 ). By reducing the supply flow rate of the hydrogen gas, the adiabatic expansion of the hydrogen gas inside the tank  21  is suppressed, and the temperature reduction in hydrogen gas is suppressed. 
     After having supplied the hydrogen gas to the fuel cell  1  at the supply flow rate Q2 for a certain period of time, the temperature of the hydrogen gas is detected again (Step  202 ). The ECU  4  determines whether the temperature of the hydrogen gas detected is equal to or lower than the predetermined temperature T2 (Step  203 ), and the hydrogen gas is supplied at the supply flow rate Q2 until the temperature of the hydrogen gas is determined to be higher than the predetermined temperature T2. If the temperature of the hydrogen gas detected by the thermometer  24  is determined to be higher than the predetermined temperature T2 as a result of the determination of Step  203 , the supply flow rate of the hydrogen gas is changed from Q2 to Q1, and the hydrogen gas is supplied at the supply flow rate Q1 (Step  205 ). 
     By detecting the temperature of the hydrogen gas during the supply of the hydrogen gas and reducing the supply flow rate of the hydrogen gas when the temperature of the hydrogen gas is reduced nearly to the melting point in this manner, the hydrogen gas can be supplied at a temperature at which the odorant is easily mixed with the hydrogen gas, thus making it possible to facilitate the mixing of the hydrogen gas with the odorant, and to improve the detection accuracy of the hydrogen gas leakage. 
     Alternatively, in another embodiment, a fuel cell system including the plurality of high-pressure hydrogen tanks  2  may be configured so that, instead of reducing the supply flow rate of the hydrogen gas when the temperature of the hydrogen gas is equal to or lower than the predetermined temperature T2, the high-pressure hydrogen tank, in which the temperature of the hydrogen gas is higher than the predetermined temperature T2, is selected to supply the hydrogen gas from the high-pressure hydrogen tank to the fuel cell. 
     Embodiment 3 
     Next, a fuel cell system  11  including a hydrogen supply apparatus according to Embodiment 3 will be described. In the fuel cell system  10  according to Embodiment 1, the hydrogen gas inside the tank  21  is directly heated by the control of the ECU  4 . On the other hand, in the fuel cell system  11  according to Embodiment 3 heats the hydrogen gas, which has undergone adiabatic expansion and which is to be supplied from the high-pressure hydrogen tank  2 . Upon supply of the hydrogen gas inside the high-pressure hydrogen tank  2  to the outside thereof, the hydrogen gas to be supplied may undergo adiabatic expansion due to pressure drop, and the temperature thereof may be reduced. Further, in a below-freezing environment, the temperature of the hydrogen gas is reduced. Upon reduction of the temperature of the hydrogen gas, there arises a problem that the odorant to be mixed therewith is liquefied or solidified. The fuel cell system  11  according to Embodiment 3 solves such a problem. 
       FIG. 4  is a system block diagram of the fuel cell system including the hydrogen supply apparatus according to Embodiment 3. The fuel cell system  11  includes: the fuel cell  1 ; the high-pressure hydrogen tank  2 ; the air supply apparatus  3 ; the ECU  4 ; an odorant tank  5 ; a buffer tank  6 ; a heater  23   a ; a thermometer  24   a ; a hydrogen gas supply passage  30 ; an air supply passage  31 ; an anode off-gas passage  32 ; a circulating gas passage  33 ; and a hydrogen gas supply branch passage  34 . It should be noted that the components already described above are identified by the same reference numerals, and thus the detailed description thereof will be omitted. 
     The hydrogen gas supply passage  30  is connected, at its one end, to the high-pressure hydrogen tank  2 , and is connected, at its other end, to the anode side of the fuel cell  1  to guide the hydrogen gas to the fuel cell  1 . The hydrogen gas supply passage  30  is provided with a hydrogen flowmeter  27 , the thermometer  24   a , and the heater  23   a  in this order from the upstream side of the flow of the hydrogen gas. 
     The hydrogen flowmeter  27  detects the flow rate of the hydrogen gas supplied from the high-pressure hydrogen tank  2 . The hydrogen flowmeter  27  is electrically connected to the ECU  4 , and the detected hydrogen flow rate is inputted to the ECU  4 . Further, the thermometer  24   a  detects the temperature of the hydrogen gas supplied from the high-pressure hydrogen tank  2 . The thermometer  24   a  is electrically connected to the ECU  4 , and the detected temperature is inputted to the ECU  4 . 
     The heater  23   a  is provided to the hydrogen supply passage  30 , and heats the hydrogen gas, passing through the hydrogen supply passage  30 , by the control of the ECU  4 . The heater  23   a  can be placed, for example, at a lower part of the hydrogen supply passage  30 , but is preferably placed so as to cover the hydrogen gas supply passage  30 . This is because the hydrogen gas passing through the hydrogen gas supply passage  30  can be heated efficiently in such a configuration. 
     The hydrogen gas supply branch passage  34  branches off from the hydrogen gas supply passage  30  at the downstream side of the heater  23   a , and merges with the hydrogen gas supply passage  30  again. Further, the hydrogen gas supply branch passage  34  is provided with a pump  25 , the odorant tank  5 , the buffer tank  6 , and an injector  26  in this order from the upstream side of the flow of the hydrogen gas. 
     The pump  25  adjusts the flow rate of the hydrogen gas to which the odorant is to be added. The odorant tank  5  stores the odorant to be added to the hydrogen gas supplied from the high-pressure hydrogen tank  2 . The buffer tank  6  temporarily retains the hydrogen gas supplied from the high-pressure hydrogen tank  2 , adds the odorant, stored in the odorant tank  5 , to the hydrogen gas, and carries out agitation. Further, the injector  26  is supplied with the hydrogen gas, to which the odorant is added, from the high-pressure hydrogen tank  2 , and mixes this hydrogen gas with the hydrogen gas guided through the hydrogen gas supply passage  30  functioning as a main passage. 
     The air supply passage  31  is connected, at its one end, to the air supply apparatus  3 , and is connected, at its other end, to the cathode side of the fuel cell  1  to guide air to the fuel cell  1 . The anode off-gas passage  32  guides an anode off-gas, discharged from the anode side of the fuel cell  1 , to the outside of the fuel cell system  11 . The circulating gas passage  33  branches off from the anode off-gas passage, and merges with the hydrogen gas supply passage to guide the hydrogen gas, contained in the anode off-gas, to the fuel cell  1  again. 
     Hereinafter, the temperature control of the hydrogen gas in the fuel cell system  11  configured as described above will be described in detail. Each of the various controls described below is executed by the above-mentioned ECU  4 , and is a routine repeated at regular intervals. 
       FIG. 5  is a flow chart illustrating the temperature control of the hydrogen gas according to Embodiment 3. First, the ECU  4  obtains the flow rate of the hydrogen gas supplied from the high-pressure hydrogen tank  2  to the fuel cell  1  (Step  301 ). The flow rate of the hydrogen gas can be obtained by the hydrogen flowmeter  27 . 
     Next, the ECU  4  determines, from a map, a heater heating amount associated with the obtained hydrogen flow rate (Step  302 ). In this regard, a map of a necessary heating amount is shown in  FIG. 6 . As shown in  FIG. 6 , the horizontal axis represents the hydrogen flow rate (NL/min), the vertical axis represents the heater heating amount (W), and the straight line P1 represents a variation in the heater heating amount. Such a map of the necessary heating amount may be stored in advance in a memory or the like of the ECU  4 , for example. 
     Then, the ECU  4  obtains the temperature of the hydrogen gas supplied from the high-pressure hydrogen tank  2  (Step  303 ). The temperature of the hydrogen gas can be obtained by the thermometer  24   a . Subsequently, the ECU  4  determines whether the temperature of the hydrogen gas obtained is sufficiently high (Step  304 ). It should be noted that the sufficiently high temperature of the hydrogen gas portion a temperature at which the odorant to be added does not liquefy or solidify, and may be appropriately set depending on the odorant to be added. If the temperature of the hydrogen gas obtained is determined to be sufficiently high, the ECU  4  ends the temperature control process for the hydrogen gas according to Embodiment 3. 
     On the other hand, if the temperature of the hydrogen gas obtained is not determined to be sufficiently high, the ECU  4  determines whether the temperature of the hydrogen gas obtained is equal to or lower than a predetermined temperature T3 (Step  305 ). If the temperature of the hydrogen gas is determined to be equal to or lower than the predetermined temperature T3, the ECU  4  increases the heating amount (Step  306 ), and ends the temperature control process for the hydrogen gas according to Embodiment 3. It should be noted that the predetermined temperature T3 may be the melting point or the boiling point of the odorant. 
     As described above, in the temperature control of the hydrogen gas according to Embodiment 3, the ECU  4  determines the heater heating amount from the map, and corrects the determined heater heating amount by the obtained temperature. Thus, the ECU  4  can obtain a more accurate heater heating amount. As a result, in the case where the temperature of the hydrogen gas to be supplied is reduced due to adiabatic expansion or the like, the odorant can be prevented from being liquefied or solidified. 
     Embodiment 4 
     Next, a fuel cell system  12  including a hydrogen supply apparatus according to Embodiment 4 will be described.  FIG. 7  is a system block diagram of the fuel cell system  12  including the hydrogen supply apparatus according to Embodiment 4. The configuration of the fuel cell system  12  according to Embodiment 4 is basically similar to that of the fuel cell system  11  according to Embodiment 3 described above. The fuel cell system  12  according to Embodiment 4 is different from the fuel cell system  11  according to Embodiment 3 in that a heater  23   b  and a thermometer  24   b  are provided. It should be noted that the components already described above are identified by the same reference numerals, and thus the detailed description thereof will be omitted. 
     The thermometer  24   b  detects the temperature of the odorant stored in the odorant tank  5 . The detected temperature is inputted to the ECU  4 . The heater  23   b  is provided at a lower part of the odorant tank  5 , and heats the hydrogen gas, stored in the odorant tank  5 , by the control of the ECU  4 . The position at which the heater  23   b  is placed may be any position as long as the odorant stored in the odorant tank  5  can be heated, and is not limited to the lower part of the odorant tank  5 . However, the odorant in a solid form or in a liquid form is accumulated at the lower part of the odorant tank  5 , and therefore, the odorant can be efficiently heated by placing the heater  23   b  at the lower part of the odorant tank  5 . 
     Next, the vapor pressure control of the odorant according to Embodiment 4 will be described.  FIG. 8  is a flow chart illustrating the vapor pressure control of the odorant according to Embodiment 4. First, the ECU  4  obtains the temperature of the odorant, stored in the odorant tank  5 , by the thermometer  24   b  (Step  401 ). 
     Then, the ECU  4  predicts how the temperature of the hydrogen gas, supplied from the high-pressure hydrogen tank  2 , is reduced due to adiabatic expansion (Step  402 ). The temperature variation in the hydrogen gas due to adiabatic expansion is obtained as data beforehand, and based on this data, how the temperature of the hydrogen gas is reduced due to adiabatic expansion can be predicted. Further, the temperature of the hydrogen gas supplied from the high-pressure hydrogen tank  2  may be measured for a certain period of time, and based on this measurement, how the temperature is reduced thereafter may be predicted. 
     Subsequently, the ECU  4  heats the odorant, stored in the odorant tank  5 , by the heater  23   b  so that the odorant reaches a necessary vapor pressure (Step  403 ). The ECU  4  can determine the heater heating amount based on the temperature of the odorant obtained, the prediction of how the temperature of the hydrogen gas is reduced, and the property of the odorant. 
     As described above, by carrying out the control so that the heater heating amount is determined based on the temperature of the odorant, the temperature of the hydrogen gas, and the property of the odorant, the temperature of the odorant to be added to the hydrogen gas is raised in advance, and the odorant reaches a necessary vapor pressure, it is possible to prevent the liquefaction or solidification of the odorant, resulting from the cooling thereof by the hydrogen gas whose temperature has been reduced. 
     Embodiment 5 
     In addition to the above-described embodiments, for example, the hydrogen gas, to which the odorant has been added, may be heated.  FIG. 9  is a schematic block diagram showing a fuel cell system  13  including a hydrogen supply apparatus according to Embodiment 5. The configuration of the fuel cell system  13  according to Embodiment 5 is basically similar to that of the fuel cell system  11  according to Embodiment 3. The fuel cell system  13  according to Embodiment 5 is different in configuration from the fuel cell system  11  according to Embodiment 3 in that a heater  23   c  and a thermometer  24   c  are further provided. The fuel cell system  13  according to Embodiment 3 includes the heater  23   c , thus making it possible to heat the hydrogen gas, to which the odorant has been added through the buffer tank  6 . 
     It should be noted that the heating of the hydrogen gas, to which the odorant has been added, may be carried out by obtaining the temperature of the hydrogen gas to which the odorant has been added, and by heating the hydrogen gas, to which the odorant has been added, to the extent that the odorant will not be liquefied or solidified, in addition to the execution of the control similar to the temperature control of the hydrogen gas according to Embodiment 3, for example. 
     Even if the hydrogen gas is heated by the heater  23   a , the temperature of the hydrogen gas is gradually reduced thereafter in a below-freezing environment or the like. However, the fuel cell system  13  according to Embodiment 5 can heat the hydrogen gas again after the odorant has been added to the hydrogen gas, and can prevent the liquefaction or solidification of the odorant. 
     Embodiment 6 
     Further, in the case where the hydrogen gas mixed with the odorant is stored in the high-pressure hydrogen tank  2 , the hydrogen gas mixed with the odorant may be heated outside of the high-pressure hydrogen tank.  FIG. 10  is a schematic block diagram showing a fuel cell system  14  including a hydrogen supply apparatus according to Embodiment 6. The configuration of the fuel cell system  14  according to Embodiment 6 is basically similar to that of the fuel cell system  10  according to Embodiment 1. The fuel cell system  14  according to Embodiment 6 is different in configuration from the fuel cell system  10  according to Embodiment 1 in that a heater  23   d  and a thermometer  24   d  are provided instead of the heater  23  and the thermometer  24  in Embodiment 1, respectively. The fuel cell system  14  according to Embodiment 6 includes the heater  23   d  and the thermometer  24   d , thus making it possible to heat the hydrogen gas mixed with the odorant and supplied from the high-pressure hydrogen tank  2 . As a result, the odorant can be prevented from being liquefied or solidified. 
     It should be noted that the temperature control of the hydrogen gas mixed with the odorant can be carried out by the ECU  4  based on the temperature of the hydrogen gas mixed with the odorant, detected by the thermometer  24   d .  FIG. 11  is a flow chart illustrating the temperature control of the hydrogen gas according to Embodiment 6. The ECU  4  obtains the temperature of the hydrogen gas, mixed with the odorant, by the thermometer  24   d  (Step  501 ), and determines whether the obtained temperature of the hydrogen gas, mixed with the odorant, is equal to or lower than a predetermined temperature T4 (Step  502 ). Then, if the temperature of the hydrogen gas, mixed with the odorant, is determined to be equal to or lower than the predetermined temperature T4, the ECU  4  heats the hydrogen gas, mixed with the odorant, by the heater  23  (Step  503 ). On the other hand, if the temperature of the hydrogen gas mixed with the odorant is not determined to be equal to or lower than the predetermined temperature T4, the ECU  4  ends the temperature control of the hydrogen gas mixed with the odorant. It should be noted that the predetermined temperature T4 may be the melting point or the boiling point of the odorant. 
     In this manner, since the hydrogen supply apparatus according to the present invention is satisfactory so long as the temperature of the hydrogen gas to be supplied can be maintained at a temperature at which the hydrogen gas is easily mixed with the odorant, the present invention is not limited to the foregoing embodiments, and further includes a combination thereof as far as possible. 
     It should be noted that each of the embodiments has been described using an example in which a hydrogen gas is used as a fuel gas. However, the present invention is not limited thereto, but examples of the fuel gas include a natural gas, and an LPG. Therefore, the present invention may be implemented as a fuel gas supply apparatus. 
     INDUSTRIAL APPLICABILITY 
     The fuel gas supply apparatus according to the present invention is capable of suppressing a temperature reduction in fuel gas even at a low temperature, and is useful for the detection of the fuel gas leakage when an odorant and a fuel gas are mixed. 
     (Note1) 
     A hydrogen supply apparatus characterized by including: a gas storage portion which stores a hydrogen gas mixed with an odorant; a gas supply portion which supplies the hydrogen gas from the gas storage portion; a gas temperature detection portion which detects a temperature of the hydrogen gas stored in the gas storage portion; and a gas temperature reduction suppression portion which suppresses a temperature reduction in hydrogen gas stored in the gas storage portion, when the temperature of the hydrogen gas detected by the gas temperature detection portion is equal to or lower than a predetermined temperature. 
     (Note2) 
     A hydrogen supply apparatus according to Note 1, characterized in that the predetermined temperature is equal to or higher than a melting point of the odorant. 
     (Note3) 
     A hydrogen supply apparatus according to Note 1, characterized in that the predetermined temperature is 
     (Note4) 
     The hydrogen supply apparatus according to any one of Note 1 to Note 3, characterized by further including a heating portion which increases the temperature of the hydrogen gas, in which the gas temperature reduction suppression portion suppresses a temperature reduction in hydrogen gas by the heating portion. 
     (Note5) 
     The hydrogen supply apparatus according to any one of Note 1 to Note 3, characterized in that the gas temperature reduction suppression portion decreases an amount of the hydrogen gas supplied by the gas supply portion, to thereby suppress a temperature reduction in hydrogen gas.