Patent Publication Number: US-2007101647-A1

Title: Hydrogen generating apparatus, method of operating hydrogen generating apparatus, fuel cell system, and method of operating fuel cell system

Description:
TECHNICAL FIELD  
      The present invention relates to a hydrogen generating apparatus, a method of operating the hydrogen generating apparatus, a fuel cell system, and a method of operating the fuel cell system (hereinafter referred to as a hydrogen generating apparatus or the like). More particularly, the present invention relates to a hydrogen generating apparatus or the like which is capable of detecting an excess water state or an excess steam state in the interior(s) of a shift converter and/or a selective oxidation device for decreasing carbon monoxide in a reformed gas.  
     BACKGROUND ART  
      Fuel cell systems are configured to cause a hydrogen-rich reformed gas supplied as a fuel gas to an anode of a fuel cell and air or the like supplied as an oxidizing gas to a cathode of the fuel cell to electrochemically react with each other in the interior of the fuel cell, to thereby generate electric power and heat. One method of generating the hydrogen-rich reformed gas is a steam reforming method. In this method, a material such as a natural gas, a hydrocarbon based gas such as LPG, alcohol such as methanol, or gasoline such as naphtha, and steam are caused to react with each other to generate the hydrogen-rich reformed gas. A hydrogen generating apparatus that generates the reformed gas generally contains a reformer for a steam reforming reaction, a shift converter for a shift reaction, and a selective oxidation device for CO selective oxidation. These components are provided with a reforming catalyst body, a shift reaction catalyst body, and a CO selective oxidation catalyst body, respectively.  
      Correct reaction temperatures of these catalyst bodies are different from each other. Therefore, in order to allow hydrogen to be supplied stably and efficiently, it is necessary to quickly increase the temperatures of the respective catalyst bodies up to the correct temperatures and keep them at the correct temperatures after start-up of the hydrogen generating apparatus.  
      It has been pointed out that, when the steam is supplied excessively to the hydrogen generating apparatus, water condensation may occur, causing hindrance to an increase or stability of the reaction temperature.  
      In order to solve this problem, there has been disclosed a hydrogen generating apparatus that employs a method in which a shift reaction catalyst body contained in a shift converter is heated by a shift converter heater to increase a temperature of a reformed gas supplied from a reformer to the shift converter through a gas passage up to a dew point or higher (see patent document 1). This makes it possible to reduce time required to supply hydrogen stably at the start-up of the hydrogen generating apparatus and to inhibit degradation of activity of a shift converter catalyst which may be caused by water condensation.  
      Patent Document 1: Japanese Laid-Open Patent Application Publication No. 2001-354404 ( FIG. 1 )  
     DISCLOSURE OF THE INVENTION  
     Problems to be Solved by the Invention  
      The patent document 1 fails to disclose a method to detect an excess water state or an excess steam state in the interior of the shift converter or the selective oxidation device. For this reason, the hydrogen generating apparatus of the patent document 1 is incapable of addressing, at correct timings, reduction of a loss of start-up energy in the fuel cell system or reduction of activity of the catalyst in the interior(s) of the shift converter and/or the selective oxidation device. That is, how to surely detect the excess water state or the excess steam state in the interior(s) of the shift converter or the selective oxidation device has not been made clear yet.  
      More specifically, in the hydrogen generating apparatus of the patent document 1, it is difficult to surely detect the event that water for steam reforming is supplied excessively to the reformer, water for causing shift reaction between water and carbon monoxide is supplied excessively to the shift converter, or excess steam or excess condensed water remains in the interior(s) of the reformer, the shift converter, or the selective oxidation device, which may be caused by repeated heating and cooling of the hydrogen generating apparatus due to frequent of start-up and stop of the hydrogen generating apparatus. This may cause the reforming catalyst body, the shift reaction catalyst body or the CO selective oxidation catalyst body to be immersed in excess water for a long time period. As a result, activity of these catalysts may degrade.  
      If the fuel cell system continues to start-up and generate power with the activity of the shift converter catalyst and the activity of the CO selective oxidation catalyst body degraded, carbon monoxide is not fully removed from the reformed gas in the interiors of the shift converter and the selective oxidation device, causing the catalysts of the fuel cell to be poisoned by the remaining carbon monoxide. As a result, the fuel cell may decrease its output power and, further, abnormal stop of the fuel cell system may arise.  
      The present invention has been made to solve the above mentioned problem, and an object of the present invention is to provide a hydrogen generating apparatus or the like which is capable of detecting an excess water state or an excess steam state in the interior of a shift converter or a selective oxidation device by a simple method.  
      Another object of the present invention is to provide a hydrogen generating apparatus or the like which is capable of correctly removing excess water or excess steam from the interior of the shift converter or the selective oxidation device to thereby reduce a loss of start-up energy of the hydrogen generating apparatus and to thereby inhibit degradation of catalytic activity of the shift converter and/or the selective oxidation device.  
     MEANS FOR SOLVING THE PROBLEM  
      In order to solve the above mentioned problems, a hydrogen generating apparatus of the present invention comprises a hydrogen generator including a reformer configured to generate a reformed gas from a material and steam; a shift converter configured to cause the reformed gas supplied from the reformer to be subjected to a shift reaction; and a selective oxidation device configured to decrease a concentration of carbon monoxide in the reformed gas after the shift reaction; a temperature sensor configured to detect one of a temperature of the shift converter and a temperature of the selective oxidation device; and a controller configured to determine that excess water or excess steam exists in an interior of the hydrogen generator when an increasing rate of the temperature detected by the temperature sensor is less than a predetermined threshold.  
      The controller may determine that excess water or excess steam exists in an interior of a shift converter when an increasing rate of the temperature of the shift converter that is detected by the temperature sensor is less than a predetermined threshold. In addition, the controller may determine that excess water or excess steam exists in an interior of the selective oxidation device when an increasing rate of the temperature of the selective oxidation device that is detected by the temperature sensor is less than a predetermined threshold.  
      Thereby, it is possible to accurately detect the excess water state or the excess steam state in the interior(s) of the shift converter and/or the selective oxidation device, and to address the excess state quickly by an operation of the hydrogen generating apparatus described below. As a result, a loss of a start-up energy of the hydrogen generating apparatus is reduced, and degradation of catalytic activity of the shift converter and/or the selective oxidation device is avoided.  
      A hydrogen generating apparatus of the present invention comprises a hydrogen generator including a reformer configured to generate a reformed gas from a material and steam; a shift converter configured to cause the reformed gas supplied from the reformer to be subjected to a shift reaction; and a selective oxidation device configured to decrease a concentration of carbon monoxide in the reformed gas after the shift reaction to a predetermined concentration or less; a temperature sensor configured to detect one of a temperature of the shift converter and a temperature of the selective oxidation device; and a controller configured to perform control to decrease water or steam in an interior of the hydrogen generator when an increasing rate of the temperature detected by the temperature sensor is less than a predetermined threshold.  
      In one example, the hydrogen generating apparatus configured to be controlled to decrease the water or the steam may further comprise a water supply device configured to supply the water or the steam to the hydrogen generator, and the controller may be configured to control the water supply device to decrease an amount of the water or the steam supplied to the interior of the hydrogen generator when the increasing rate of the temperature detected by the temperature sensor is less than the predetermined threshold.  
      In another example, the hydrogen generating apparatus configured to be controlled to decrease the water or the steam further comprise a water discharge device that is equipped in the shift converter and is configured to discharge the water; and the controller may be configured to control the water discharge device to discharge the water from an interior of the shift converter to outside when an increasing rate of a temperature of the shift converter that is detected by the temperature sensor is less than a predetermined threshold. Or, the hydrogen generating apparatus may further comprise a water discharge device that is equipped in the selective oxidation device and is configured to discharge the water; and the controller may be configured to control the water discharge device to discharge the water from an interior of the selective oxidation device to outside when an increasing rate of a temperature of the selective oxidation device that is detected by the temperature sensor is less than a predetermined threshold.  
      In a further example, the hydrogen generating apparatus configured to be controlled to decrease the water or the steam may further comprise an air supply device configured to supply air to the shift converter; and the controller may be configured to control the air supply device to introduce the air to an interior of the shift converter when an increasing rate of the temperature of the shift converter that is detected by the temperature sensor is less than a predetermined threshold. Or, the hydrogen generating apparatus may further comprise an air supply device configured to supply air to the selective oxidation device; and the controller may be configured to control the air supply device to introduce the air to the interior of the selective oxidation device when an increasing rate of the temperature of the selective oxidation device that is detected by the temperature sensor is less than a predetermined threshold.  
      In a further example, the hydrogen generating apparatus configured to be controlled to decrease the water or the steam may further comprise a heating device configured to heat the shift converter; and the controller may be configured to control the heating device to heat an interior of the shift converter when an increasing rate of the temperature of the shift converter that is detected by the temperature sensor is less than a predetermined threshold. Or, the hydrogen generating apparatus may further comprise a heating device configured to heat the selective oxidation device; and the controller may be configured to control the heating device to heat an interior of the selective oxidation device when an increasing rate of the temperature of the selective oxidation device that is detected by the temperature sensor is less than a predetermined threshold.  
      The water discharge device, the air supply device or the heater enables the excess water resulting from the steam or the condensed moisture to be correctly removed from the shift converter and/or the selective oxidation device.  
      A method of operating a hydrogen generating apparatus comprising a hydrogen generator including a reformer configured to generate a reformed gas from a material and steam; a shift converter configured to cause the reformed gas supplied from the reformer to be subjected to a shift reaction; and a selective oxidation device configured to decrease a concentration of carbon monoxide in the reformed gas after the shift reaction to a predetermined concentration or less; and a temperature sensor configured to detect one of a temperature of the shift converter and a temperature of the selective oxidation device, the method comprising: decreasing water or steam in an interior of the hydrogen generator when an increasing rate of the temperature detected by the temperature sensor is less than a predetermined threshold.  
      Or, a method of operating a fuel cell system comprising a hydrogen generator including a reformer configured to generate a reformed gas from a material and steam; a shift converter configured to cause the reformed gas supplied from the reformer to be subjected to a shift reaction; and a selective oxidation device configured to decrease a concentration of carbon monoxide in the reformed gas after the shift reaction to a predetermined concentration or less; a fuel cell configured to generate electric power using the reformed gas supplied from the reformer and an oxidizing gas; and a temperature sensor configured to detect one of a temperature of the shift converter and a temperature of the selective oxidation device, the method comprising: decreasing water or steam in an interior of the hydrogen generator when an increasing rate of the temperature detected by the temperature sensor is less than a predetermined threshold.  
      A hydrogen generating apparatus of the present invention comprises a hydrogen generator including a reformer configured to generate a reformed gas supplied from a material and steam; a shift converter configured to cause the reformed gas supplied from the reformer to be subjected to a shift reaction; a selective oxidation device configured to decrease a concentration of carbon monoxide in the reformed gas after the shift reaction to a predetermined concentration or less; a reformer heater configured to heat the reformer; a combustion sensor configured to detect a combustion state of a combustible gas in the reformer heater; and a controller configured to determine that excess water or steam exists in an interior of the hydrogen generator when a detection signal detected by the combustion sensor reaches, with a frequency of predetermined number of times or more, a numeric value at which a flame vanishes in the reformer heater, during a time period that elapses from when a temperature of the shift converter reaches a shift reaction temperature range until a temperature of the selective oxidation device reaches a selective oxidation reaction temperature range.  
      Thereby, it is possible to accurately detect the excess water state or the excess steam state in the interior of the shift converter or the selective oxidation device, and to address the excess state quickly by an operation of the hydrogen generating apparatus described below. As a result, a loss of a start-up energy of the hydrogen generating apparatus is reduced, and degradation of catalytic activity of the shift converter and/or the selective oxidation device is avoided.  
      A hydrogen generating apparatus of the present invention comprises a hydrogen generator including a reformer configured to generate a reformed gas from a material and steam; a shift converter configured to cause the reformed gas supplied from the reformer to be subjected to a shift reaction; a selective oxidation device configured to decrease a concentration of carbon monoxide in the reformed gas after the shift reaction to a predetermined concentration or less; a reformer heater configured to heat the reformer; a combustion sensor configured to detect a combustion state in the reformer heater; and a controller configured to perform control to decrease water or steam in an interior of the hydrogen generator when a detection signal detected by the combustion sensor reaches, with a frequency of predetermined number of times or more, a numeric value at which a flame vanishes in the reformer heater, during a time period that elapses from when a temperature of the shift converter reaches a shift reaction temperature range until a temperature of the selective oxidation device reaches a selective oxidation reaction temperature range.  
      In one example, the hydrogen generating apparatus configured to be controlled to decrease the water or the steam may further comprise a water supply device configured to supply the water or the steam to the hydrogen generator, and the controller may be configured to control the water supply device to decrease an amount of the water or the steam supplied to the interior of the hydrogen generator when a detection signal detected by the combustion sensor reaches, with a frequency of predetermined number of times or more, a numeric value at which a flame vanishes in the reformer heater, during a time period that elapses from when a temperature of the shift converter reaches a shift reaction temperature range until a temperature of the selective oxidation device reaches a selective oxidation reaction temperature range.  
      In another example, the hydrogen generating apparatus configured to be controlled to decrease the water or the steam may further a water discharge device that is equipped in the shift converter and/or the selective oxidation device and is configured to discharge water; and the controller may be configured to control the water discharge device to discharge water from an interior of the shift converter and/or an interior of the selective oxidation device to outside when a detection signal detected by the combustion sensor reaches, with a frequency of predetermined number of times or more, a numeric value at which a flame vanishes in the reformer heater, during a time period that elapses from when a temperature of the shift converter reaches a shift reaction temperature range until a temperature of the selective oxidation device reaches a selective oxidation reaction temperature range.  
      In another example, the hydrogen generating apparatus configured to be controlled to decrease the water or the steam may further an air supply device configured to supply air to the shift converter and/or the selective oxidation device; and the controller may be configured to control the air supply device to introduce air to an interior of the shift converter and/or an interior of the selective oxidation device when a detection signal detected by the combustion sensor reaches, with a frequency of predetermined number of times or more, a numeric value at which a flame vanishes in the reformer heater, during a time period that elapses from when a temperature of the shift converter reaches a shift reaction temperature range until a temperature of the selective oxidation device reaches a selective oxidation reaction temperature range.  
      In a further example, the hydrogen generating apparatus configured to be controlled to decrease the water or the steam may further comprise a heating device configured to heat the shift converter and/or the selective oxidation device; and the controller may be configured to control the heating device to heat an interior of the shift converter and/or the selective oxidation device when a detection signal detected by the combustion sensor reaches, with a frequency of predetermined number of times or more, a numeric value at which a flame vanishes in the reformer heater, during a time period that elapses from when a temperature of the shift converter reaches a shift reaction temperature range until a temperature of the selective oxidation device reaches a selective oxidation reaction temperature range.  
      The water discharge device, the air supply device or the heating device enables the excess water resulting from the steam or the condensed moisture to be correctly removed from the shift converter and/or the selective oxidation device.  
      A fuel cell system of the present invention comprises the above described hydrogen generating apparatus; and a fuel cell configured to generate electric power using a reformed gas supplied from the hydrogen generator and an oxidizing gas. And, a method of operating a hydrogen generating apparatus comprising a hydrogen generator including a reformer configured to generate a reformed gas from a material and steam; a shift converter configured to cause the reformed gas supplied from the reformer to be subjected to a shift reaction; a selective oxidation device configured to decrease a concentration of carbon monoxide in the reformed gas after the shift reaction to a predetermined concentration or less; a reformer heater configured to heat the reformer; and a combustion sensor configured to detect a combustion state of a combustible gas in the reformer heater; the method comprising: decreasing water or steam in an interior of the hydrogen generator when a detection signal detected by the combustion sensor reaches, with a frequency of predetermined number of times or more, a numeric value at which a flame vanishes in the reformer heater, during a time period that elapses from when a temperature of the shift converter reaches a shift reaction temperature range until a temperature of the selective oxidation device reaches a selective oxidation reaction temperature range.  
      Also, a method of operating a fuel cell system comprising a hydrogen generator including a reformer configured to generate a reformed gas from a material and steam; a shift converter configured to cause the reformed gas supplied from the reformer to be subjected to a shift reaction; a selective oxidation device configured to decrease a concentration of carbon monoxide in the reformed gas after the shift reaction to a predetermined concentration or less; a reformer heater configured to heat the reformer; a fuel cell configured to generate electric power using a reformed gas supplied from the hydrogen generator and an oxidizing gas, and a combustion sensor configured to detect a combustion state of a combustible gas in the reformer heater, the method comprising: decreasing water or steam in an interior of the hydrogen generator when a detection signal detected by the combustion sensor reaches, with a frequency of predetermined number of times or more, a numeric value at which a flame vanishes in the reformer heater, during a time period that elapses from when a temperature of the shift converter reaches a shift reaction temperature range until a temperature of the selective oxidation device reaches a selective oxidation reaction temperature range.  
     EFFECTS OF THE INVENTION  
      In accordance with the present invention, it is possible to achieve a hydrogen generating apparatus or the like that is capable of detecting an excess water state or an excess steam state in the interior of a shift converter or a selective oxidation device.  
      In addition, in accordance with the present invention, it is possible to provide a hydrogen generating apparatus or the like which is capable of correctly removing excess water or excess steam from the interior of the shift converter or the selective oxidation device to thereby reduce a loss of start-up energy of the hydrogen generator and to thereby inhibit degradation of catalytic activity of the shift converter and/or the selective oxidation device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram showing a construction of a fuel cell system according to an embodiment 1 of the present invention;  
       FIG. 2  is a view showing rising temperature characteristics of a reformer, a shift converter, and a selective oxidation device of a hydrogen generator from start-up of the hydrogen generator, under the condition in which steam is supplied normally and excessively;  
       FIG. 3  is a block diagram showing a construction of a fuel cell system according to an embodiment 2 of the present invention;  
       FIG. 4  is a view showing an example of correlation in a normal state between time (start-up time) on an abscissa axis and a detected reformer temperature (KS), a detected combustion temperature (TFG), and a detected combustion flame current (FRG) on a ordinate axis, in which the start-up time represents a time period that elapses from when the hydrogen generator starts start-up operation (to), the detected reformer temperature (KS) is output from a reformer temperature sensor, the detected combustion temperature (TFG) is output from a temperature detecting means used as a combustion sensor, and the detected combustion flame current (FRG) is output from a flame current detecting means used as the combustion sensor;  
       FIG. 5  is a view showing an example of correlation in an abnormal state between time (start-up time) on an abscissa axis and a detected reformer temperature (KSN), a detected combustion temperature (TFN), and a detected combustion flame current (FRN) on a ordinate axis, in which the start-up time represents a time period that elapses from when the hydrogen generator starts start-up operation (to), the detected reformer temperature (KSN) is output from the reformer temperature sensor, the detected combustion temperature (TFN) is output from the temperature sensor used as the combustion sensor, and the detected combustion flame current (FRN) is output from the flame current sensor used as the combustion sensor;  
       FIG. 6  is a flowchart showing an example of a control program of a controller at the start-up of the hydrogen generator;  
       FIG. 7  is a block diagram showing a construction of a fuel cell system according to an embodiment 3 of the present invention;  
       FIG. 8  is a block diagram showing a construction of a fuel cell system according to an embodiment 4 of the present invention; and  
       FIG. 9  is a block diagram showing a construction of a fuel cell system according to an embodiment 5 of the present invention. 
    
    
     EXPLANATION OF REFERENCE NUMERALS  
     
         
           100  reformer  
           101  reforming catalyst body  
           102  reformer heater  
           103  shift converter  
           104  shift reaction catalyst body  
           105  selective oxidation device  
           106  CO selective oxidation catalyst body  
           107  material feed means  
           108  first water supply device  
           109  second water supply device  
           110 ,  206  electromagnetic valve  
           111  combustion fan  
           113  shift converter heater  
           114  selective oxidation device heater  
           115  reformer temperature sensor  
           116  shift converter temperature sensor  
           117  selective oxidation device temperature sensor  
           118  hydrogen generator  
           120  hydrogen generating apparatus  
           200  oxidizing gas supply means  
           201  air supply device  
           202  oxidizing gas humidifier  
           203  fuel cell  
           204  switching valve  
           300  fuel cell system  
           301  first fuel gas passage  
           302  second fuel gas passage  
           303  first reformed gas passage  
           304  second reformed gas passage  
           305  third reformed gas passage  
           306  first branch passage  
           307  second branch passage  
           308  first water passage  
           309  second water passage  
           310  third water passage  
           311  first air passage  
           312  second air passage  
           400 ,  401  discharge valve  
           402 ,  403  discharge passage  
           500 ,  501  air supply pump  
           502 ,  503  dry air supply passage  
           600 ,  601  exhaust gas supply valve  
           602 ,  603  exhaust gas supply passage  
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      Hereinafter, embodiments 1 to 5 of the present invention will be described with reference to the drawings.  
     Embodiment 1  
       FIG. 1  is a block diagram showing a construction of a fuel cell system according to an embodiment 1 of the present invention.  
      A hydrogen generating apparatus  120  mainly comprises a hydrogen generator  118  configured to supply a hydrogen-rich gas to a fuel cell  203 , a controller  205  that is configured to control a feed amount of a hydrocarbon based material such as methane, butane, and a natural gas and to detect the temperature(s) of a shift converter  103  and/or a selective oxidation device  105  of the hydrogen generator  118  to detect and determine whether or not the amount of water or the amount of steam is correct; an oxidizing gas supply means  200  configured to supply air which is the oxidizing gas to the fuel cell  203 , a material feed means  107  configured to feed the material to the hydrogen generator  118 , and first and second water supply devices  108  and  109  configured to supply water to the hydrogen generator  118 .  
      A fuel cell system  300  comprises the above mentioned hydrogen generating apparatus  120  and the fuel cell  203  configured to generate electric power using the hydrogen-rich gas supplied from the hydrogen generating apparatus  120 .  
      The hydrogen generator  118  includes the reformer  100  configured to conduct a steam reforming reaction, the shift converter  103  configured to conduct a shift reaction to convert steam and carbon monoxide into hydrogen and carbon dioxide, and the selective oxidation device  105  configured to conduct CO selective oxidation to decrease a concentration of carbon monoxide to approximately 10 ppm or lower. The reformer  100  is provided with a reforming catalyst body  101  that promotes the steam reforming reaction and a reformer heater  102  that supplies heat for reforming reaction to the reforming catalyst body  101 . The shift converter  103  is provided with a shift reaction catalyst body  104  and a shift converter heater  113  that heats the shift reaction catalyst body  104 . The selective oxidation device  105  is provided with a CO selective oxidation catalyst body  106  and a selective oxidation device heater  114  that heats the CO selective oxidation catalyst body  106 . The heaters  113  and  114  heat the shift converter  103  and the selective oxidation device  105 , respectively, to reduce a time period necessary to increase the temperature at the start-up the hydrogen generator  118 .  
      The oxidizing gas supply means  200  includes an air supply device  201  such as a blower fan and an oxidizing gas humidifier  202  that humidifies air.  
      [Detailed Construction of Hardware of Fuel Cell System] 
      A detailed construction of hardware of the fuel cell system  300  will be described with reference to  FIG. 1 . In the fuel cell  203 , power generation is carried out in such a manner that the hydrogen-rich gas (hereinafter referred to as a reformed gas) introduced to an anode (not shown) and the air introduced to a cathode (not shown) react with each other to generate electric power and heat.  
      First, passages through which the reformed gas is introduced to the anode and the associated gas reaction will be described. The material comprising an organic compound containing at least carbon and hydrogen is controlled to have a correct flow rate by an electromagnetic valve  206  that is provided in a first fuel gas passage  301  to open and close the first fuel gas passage  301  and a material flow rate control valve (not shown) within the material feed means  107 , and then is guided to the reforming catalyst body  101 . Simultaneously, the water or the steam is supplied from the first water supply device  108  to the reforming catalyst body  101  through a first water passage  308 . Thereby, in the reformer  100 , the reforming catalyst body  101  causes the steam reforming reaction to proceed, thereby generating the hydrogen-rich reformed gas from the material and the steam.  
      A second fuel gas passage  302  branches from the first fuel gas passage  301 . An electromagnetic valve  110  is provided in the second fuel gas passage  302 . The material, the flow rate of which has been controlled by the electromagnetic valve  110  and the material flow rate control valve, is fed as a combustion material to a burner of the reformer heater  102  through the passage  302 . A combustion fan  111  supplies combustion air to the burner of the reformer heater  102 .  
      The reformed gas is guided from the reforming catalyst body  101  to the shift reaction catalyst body  104  through a first reformed gas passage  303 , while water is supplied from the second water supply device  109  to the shift reaction catalyst body  104  through a third water passage  310 . This causes the shift reaction to convert carbon monoxide in the reformed gas and the steam into hydrogen and carbon dioxide. In order to decrease the concentration of carbon monoxide in the gas resulting from the shift reaction to a predetermined concentration level (e.g., 10 ppm or less), the reformed gas after the shift reaction is guided to the CO selective oxidation catalyst body  106  through a second reformed gas passage  304  to further decrease the concentration of CO through CO selective oxidation. In this manner, the reformed gas containing hydrogen as a major component, the CO concentration of which has been decreased, is generated in the hydrogen generator  118 .  
      Then, the reformed gas containing hydrogen as a major component flows from the selective oxidation device  105  of the hydrogen generator  118  into a third reformed gas passage  305 . Then, a switching valve  204  provided in the third reformed gas passage  305  causes the hydrogen-rich gas to flow in a first or second branch passage  306  or  307  to allow the hydrogen-rich gas to be supplied to the fuel cell  203  or to the reformer heater  102  through the passage  306  or  307 , respectively. A part of the reformed gas is guided to the anode of the fuel cell  203  through the first passage  306  and is consumed in required amount through an electrode reaction of the anode, and then, the remaining reformed gas is caused to flow to the burner of the reformer heater  102 , as an off gas. Through the second passage  307 , the reformed gas is caused to flow to the burner of the reformer  102  without being guided to the anode.  
      The reformed gas that has flowed to the burner of the reformer heater  102  is combusted with air supplied from the combustion fan  111  in the interior of the reformer heater  102 .  
      Subsequently, passages through which air is guided to the cathode will be described. The air is supplied from the air supply device  201  to the oxidizing gas humidifier  202  through a first air passage  311 . The water is supplied from the first water supply device  108  to the oxidizing gas humidifier  202  through a second water passage  309  that branches from a first water passage  308 . In the oxidizing gas humidifier  202 , air is humidified and is guided to the cathode of the fuel cell  203  through a second air passage  312 . The humidified air which has not been consumed in the cathode of the fuel cell  203  is released to atmosphere.  
      [Configuration of Control System of Fuel Cell System] 
      Subsequently, a configuration of a control system of the fuel cell system  300  will be described with reference to  FIG. 1 .  
      The controller  205  includes an arithmetic unit such as a microcomputer, and is configured to control desired components of the fuel cell system  300  to thereby control the operation of the fuel cell system  300 .  
      As used herein, the term “controller” refers to a controller group in which a plurality of controllers cooperate with each other to control the operation of the fuel cell system  300 , as well as a single controller. Therefore, the controller  205  is not necessarily constituted by the single controller, but may be a plurality of controllers that are distributed and cooperate with each other to control the operation of the fuel cell system  300 .  
      Input sensors of the controller  205  include various types of temperature sensors. To be specific, the temperature sensors include a reformer temperature sensor  115  that detects a temperature of a gas in the reformer  100  (temperature of the gas near the reforming catalyst body  101 ), a shift converter temperature sensor  116  that detects a temperature of a gas in the shift converter  103  (temperature of the gas near the shift reaction catalyst body  104 ), and a selective oxidation device sensor  117  that detects a temperature of a gas in the selective oxidation device  105  (temperature of the gas near the CO selective oxidation catalyst body  106 ).  
      The reformer temperature sensor  115  is attached on the reformer  100  to detect the temperature of the gas on upstream side of the reforming catalyst body  101 . The shift converter temperature sensor  116  is attached on the shift converter  100  to detect the temperature on upstream side of the shift reaction catalyst body  104 . The selective oxidation device temperature sensor  117  is attached on the selective oxidation device  100  to detect the temperature on upstream side of the CO selective oxidation catalyst body  105 .  
      Excess steam condenses to water, which stays at a lower end region of a tubular catalyst body (on downstream side in the flow of the gas). For this reason, catalyst may be exposed to severer environment at the lower end region on downstream side than at an upper end region on upstream side in flow of the gas. Therefore, if it is detected by the temperature sensor disposed on the upstream side of the catalyst that an abnormality due to excess water occurs on the upstream side, then it is definitely determined that the downstream region of the catalyst is exposed to excess water.  
      An output operation portion controlled by the controller  205  includes the flow rate control portion of the first and second water supply devices  108  and  109 , the electromagnetic valve  206  that controls the amount of material fed to the reforming catalyst body  101 , the electromagnetic valve  110  that controls the combustion material fed to the burner of reformer heater  102 , the material flow rate control valve that is built into the material feed means  107  to control the amount of material fed from a source, the shift converter heater  113  that heats the shift converter  103 , the selective oxidation device heater  114  that heats the selective oxidation device  105 , the switching valve  204  that switches the passage of the reformed gas supplied from the hydrogen generator  118 , etc.  
      The controller  205  receives the temperatures which have been detected by the temperature sensors  115 ,  116 , and  117 . Based on these temperatures, the controller  205  causes the flow rate control valve built into the material feed means  107  and the electromagnetic valves  110  and  206  to operate to stabilize the reaction temperatures of the respective catalyst bodies  101 ,  104 , and  106 , and controls the output of the shift converter heater  113  and the output of the selective oxidation device heater  114  to reduce the time required to increase the temperature of the shift converter  103  and the temperature of the selective oxidation device  105  at the start-up of the hydrogen generator  118 . Further, the controller  205  causes the switching valve  204  to operate so that generated gas (reformed gas) supplied from the hydrogen generator  118  is selectively guided to the fuel cell  203  or to the reformer heater  102 .  
       FIG. 2  shows rising temperature characteristics of the reformer  100 , the shift converter  103 , and the selective oxidation device  105 , in which an abscissa axis indicates a time that elapses from when the hydrogen generator  118  starts the start-up operation (time point at which the reformer heater  102  starts heating the reforming catalyst body  101 : to).  
      In  FIG. 2 , KS profile, HSG profile, and JSG profile represent the rising characteristics of detected temperatures of the reformer  100 , the shift converter  103 , and the selective oxidation device  105  in a case where the steam used for the steam reforming reaction is correctly supplied to the reformer  100  of the hydrogen generator  118  and the steam for stably controlling the temperature of the shift converter  103  is correctly supplied to the shift converter  103 .  
      Since set values in the reaction temperature ranges of the reforming catalyst body  101 , the shift reaction catalyst body  104 , and the CO selective oxidation catalyst body  106  are TKs (predetermined temperature in a range of 600 to 700° C.), THs (predetermined temperature in a range of 200 to 400° C.), and TJs (predetermined temperature in a range of 100 to 300° C.), the KS profile, the HSG profile, and the JSG profile reach the set values in the reaction temperature ranges of the catalyst bodies  101 ,  104 , and  106  at approximately t 1 , t 2 , and t 3 , respectively. It may be estimated that the time periods that elapse from when the hydrogen generator  118  starts the start-up operation (t 0 ) until t 1 , t 2 , and t 3  are 20 to 30 minutes, 30 to 40 minutes, and 40 to 50 minutes, respectively.  
      If water or steam is supplied excessively to the interior of the reformer  100  or the shift converter  103  of the hydrogen generator  118 , or otherwise the hydrogen generator  118  is heated and cooled repeatedly due to repeated start-up and stop, then excess steam or excess condensed water may stay in the interior(s) of the shift converter  103  and/or the selective oxidation device  105 , causing the shift converter  103  and/or the selective oxidation device  105  to get wet or to contain water droplets.  
      In such situations, since the rate at which the rising curve of the temperature detected by the shift converter temperature sensor  116  increases and the rate at which the rising curve of the temperature detected by the selective oxidation device sensor  117  increase become low and their rising curves become gentle in contrast to the HSG profile and the JSG profile in the normal state. In  FIG. 2 , HSN profile represents a characteristic of the detected temperature of the shift converter  103  which increases slowly because of the excess steam or the like and JSN profile represents a characteristic of the detected temperature of the selective oxidation device  106  which increases slowly because of the excess steam or the like.  
      It has been confirmed that, since the reformer  100  is positioned on upstream side relative to other components in the flow of the material and in the flow of the steam, it is less susceptible to the excess steam or the like, and there is a small difference in increase between the temperature in the normal state which is detected by the reformer temperature sensor  115  and the temperature in the abnormal state which is detected by the reformer temperature sensor  115 .  
      As shown in  FIG. 2 , each of the set values in the reaction temperature ranges of the shift reaction catalyst body  104  and the CO selective oxidation catalyst body  106  (THs corresponding to the shift reaction catalyst body  104  and TJs corresponding to the CO selective oxidation catalyst body  106 ) has upper and lower limit values. The upper and lower limit values of the shift reaction catalyst body  104  are respectively represented by THsh and THsl. The upper and lower limit values of the CO selective oxidation catalyst body  106  are respectively represented by TJsh and TJsl. The temperature difference between the set value (THs) in the reaction temperature range of the shift reaction catalyst body  104  and the corresponding upper and lower limit values (THsh and THsl) are respectively represented by ΔTHh and ΔTHl. The temperature difference between the set value (TJs) of the CO selective oxidation catalyst body  106  and the corresponding upper and lower limit values (TJsh and TJsl) are respectively represented by ΔTJh and ΔTJl.  
      Under the excess steam condition or the like, the HSN profile of the shift converter  103  and/or the JSN profile of the selective oxidation device  105  do not exceed even the lower limit temperature (THsl corresponding to the shift converter  103  and TJsl corresponding to the selective oxidation device  105 ) during a time period from when the hydrogen generator  118  starts the start-up operation (to) until the time at which the temperature reaches a value between the lower limit value and the upper limit value in the catalyst reaction temperature range (e.g., time t 2  and time t 3  are illustrated in  FIG. 2  as examples of the time) in the normal state (e.g., HSG profile or JSG profile). That is, if the rate at which the detected temperature increases is lower than that in the normal state during a time period from when the hydrogen generator  118  starts the start-up operation until the predetermined time, then, excess water or excess steam may exist in the shift converter  103  or the selective oxidation device  105 . The predetermined time is determined based on the reaction temperature ranges of the catalysts. Specifically, the predetermined time may be time at which the temperature profile in the normal state reaches a value between the lower limit value and the upper limit value in the reaction temperature range (here, the upper limit value is used on assumption that the temperature characteristic rises steeply to exceed the reaction temperature range, overshoot, and the reaches the reaction temperature).  
      Based on the temperature(s) which have been detected by the shift converter temperature sensor  116  that detects the temperature of the shift converter  103  and/or by the selective oxidation device sensor  117  that detects the temperature of the selective oxidation device  105 , the controller  205  detects whether or not excess steam or condensed water exists in the interior(s) of the shift converter  103  and/or the selective oxidation device  105 , and determines that excess steam or water exists if the detected temperature does not reach the lower limit temperature for the catalytic reaction during a time period from the start-up until the predetermined time as described above. If the detected temperature is above at least the lower limit temperature for the catalytic reaction, the respective catalysts function effectively irrespective of the amount of the steam or water. Therefore, the lower limit temperature for the catalytic reaction is used as a reference to determine whether or not the excess water is allowable.  
      In other words, based on the rates at which the detected temperatures from the shift converter temperature sensor  116  and the selective oxidation device temperature sensor  117  increase as indicated by arrows in  FIG. 2 , the controller  205  carries out a determination process below.  
      If it is determined that the increasing rate (arrow indicated by bold dotted line in  FIG. 2 ) of the temperature detected by the shift converter temperature sensor  116  is less than a predetermined threshold, for example, a lower limit value of the increasing rate (arrow indicated by bold solid line in  FIG. 2 ) of the detected temperature in the normal state, the controller  205  detects and determines that excess water or steam exists in the interior of the hydrogen generator  118  (shift converter  103 ). If it is determined that the increasing rate (arrow indicated by bold two-dotted line in  FIG. 2 ) of the temperature detected by the selective oxidation device temperature sensor  117  is less than a predetermined threshold, for example, a lower limit value of the increasing rate (arrow indicated by bold dashed line in  FIG. 2 ) of the detected temperature in the normal state, the controller  205  detects and determines that excess water or steam exists in the interior of the hydrogen generator  118  (selective oxidation device  105 ).  
      As used herein, the term “increasing rate” of the detected temperature refers to a numeric value that is obtained by dividing the temperature corresponding to the reaction temperature range of each catalyst by the time period required for each catalyst to reach the corresponding reaction temperature range from the start-up, in each temperature curve. For example, as shown in  FIG. 2 , in the HSG profile of the shift converter  103  in the normal state, the temperature of the shift converter  103  increases to the THs during a time period from t 0  until t 2 , and therefore, the increasing rate of the detected temperature which is output from the shift converter temperature sensor  116  in the normal state is THs/(t 2 −t 0 ).  
      While the predetermined threshold is the lower limit value of the increasing rate of the detected temperature of the shift converter  103  in the normal state or the lower limit value of the increasing rate of the detected temperature of the selective oxidation device  105  in the normal state, it is not intended to be limited to these, but may be suitably set depending on the construction or type of the hydrogen generator.  
      [Operation of Fuel Cell System from Start of Start-up Until Power Generation] 
      When the steam is supplied suitably in the fuel cell system  300  (under normal state), the detected temperature profiles obtained by the temperature sensors  115 ,  116 , and  117  of the reformer  100 , the shift converter  103  and the selective oxidation device  105  represent characteristics that rise in earlier stage to the set values in the reaction temperature ranges of the reforming catalyst body  101 , the shift reaction catalyst body  104 , and the CO selective oxidation catalyst body  106 , as indicated by the KS profile, the HSG profile, and the JSG profile of  FIG. 2 . In this case, the controller  205  causes the temperatures of the reforming catalyst body  101 , the shift reaction catalyst body  104  and the CO selective oxidation catalyst body  106  to reach stable predetermined temperatures, and suitably controls the material feed means  107 , the electromagnetic valves  110  and  206 , the switching valve  204 , the first and second water supply devices  108  and  109 , and other components to cause the reformed gas for power generation to be supplied to the anode of the fuel cell  203 , and to cause the oxidizing gas to be supplied from the oxidizing gas supply means  202  to the cathode of the fuel cell  203 , thus starting a power generation operation.  
      If the controller  205  determines that excess water or steam exists in the interior of the shift converter  103  or the selective oxidation device  105  (under abnormal state), the detected temperature profiles obtained by the temperature sensors  116  and  117  of the shift converter  103  and the selective oxidation device  105  represent the rising characteristics which are gentle in contract to those in the normal state, as indicated by the HSN profile and the JSN profile in  FIG. 2 . In this case, the controller  205  reduces the supply amount of the material and the steam to an extent to which carbon deposition does not take place (steam/carbon ratio: S/C=2.0 or more) until the detected temperature of the shift converter  103  exceeds the set value in the reaction temperature range of the shift reaction catalyst body  104  and/or the detected temperature of the selective oxidation device  105  exceeds the set value in the reaction temperature range of the CO selective oxidation catalyst body  106 . Since recovery of the components is retarded if the steam is supplied excessively, the upper limit value of the S/C is approximately 5.0, preferably approximately 3.0. Therefore, the controller  205  controls supply of the material and the steam so that S/C is between 2.0 and 5.0, preferably between 2.0 and 3.0 until the detected temperature of the shift converter  103  exceeds the set value in the reaction temperature range of the shift reaction catalyst body  104  and/or the detected temperature of the selective oxidation device  105  exceeds the set value in the reaction temperature range of the CO selective oxidation catalyst body  106 .  
      A specific method of controlling supply of the material and the steam is such that the controller  205  outputs a control signal to the material flow rate control valve built into the material feed means  107  and to the electromagnetic valve  206  that opens and closes the first fuel gas passage  301  to control the flow rate, and outputs a control signal for output control to the flow rate control portions of the first and second water supply portions  108  and  109  to suppress supply of the material and the steam to the reformer  100  to an extent to which deposition of carbon does not take place.  
      When the HSN profile and/or the JSN profile exceed the set value(s) (THs, TJs) in the reaction temperature range(s) of the shift converter  103  and/or the selective oxidation device  105  (represented by tHn and tJN in  FIG. 2 ), the controller  205  outputs a signal to the control valve in the material feed means  107  and the electromagnetic valve  206  to resets the amount of material to that in the normal state, and outputs a signal to the first and second supply means  108  and  109  to resets the amount of steam to that in the normal state. The controller  205  causes the temperatures of the reforming catalyst body  101 , the shift reaction catalyst body  104  and the CO selective oxidation catalyst body  106  to reach the stable predetermined temperatures and correctly controls the material feed means  107 , the electromagnetic valves  110  and  216 , the switching valve  204 , the first and second water supply portions  108  and  109 , and other components to supply the reformed gas for power generation to the anode in the interior of the fuel cell  203  and to supply the oxidizing gas from the oxidizing gas supply means  200  to the cathode in the interior of the fuel cell  203 , thus starting the power generation operation.  
      As describe above, in accordance with this embodiment, it is possible to determine whether or not excess water or steam exists in the interior(s) of the shift converter  103  and/or the selective oxidation device  105 .  
      Since it is possible to surely detect the problem associated with the excess steam or the like in the shift converter  103  and/or the selective oxidation device  105 , the problem is quickly dealt with, so that the activity of the catalyst(s) of the shift converter  103  and/or the selective oxidation device  105  is quickly restored.  
      Furthermore, power generation is not carried out with degraded catalytic activity, and catalyst poisoning of the fuel cell  203  which would be caused by carbon monoxide is avoided.  
      While in this embodiment, the remaining off gas which has not been consumed in the electrode reaction in the fuel cell  203  is caused to flow to the burner of the reformer heater  102  through the passage that is not provided with an auto drain or a condenser that condenses water in the off gas, the technique described in this embodiment is effective to fuel cell systems that are equipped with these components if the total amount of excess steam or condensed water is above the removing abilities of these components.  
     Embodiment 2  
       FIG. 3  is a block diagram showing an example of a construction of a fuel cell system according to an embodiment 2 of the present invention.  
      A construction of a fuel cell system  320  according to this embodiment is identical to that of the fuel cell system  300  of the embodiment 1 except that the reformer heater  102  is equipped with a combustion sensor  207  that detects a combustion state of a combustible gas in the reformer heater  102 .  
      While in the embodiment 1, it is determined whether or not excess water or steam exists in the interior of the hydrogen generator  118  based on the temperatures detected by the shift converter temperature sensor  116  and the selective oxidation device sensor  117 , it is determined whether or not excess water or steam exists in the interior of the hydrogen generator  118  based on a signal detected by the combustion sensor  207  in this embodiment.  
      In  FIG. 3 , the same reference numerals as those in the embodiment 1 ( FIG. 1 ) denote the same or corresponding components which will not be further described.  
      The combustion sensor  207  is inserted into the burner of the reformer heater  102  to detect the combustion state of the combustible gas in the reformer heater  102 . The combustion sensor  207  is coupled to the controller  205 , which receives a signal indicating the combustion state which is output from the combustion sensor  207 .  
      The combustion sensor  207  is configured to convert physical quantity of a flame current or the like which is obtained by using at least one of brightness, temperature (detected by e.g., thermocouple) and rectification (detected by e.g., flame rod) of the flame generated by combustion of the combustible gas in the burner of the reformer heater  102  into an electric signal to detect the combustion state.  
      Below, an operation for detecting the combustion state of the combustible gas in the burner of the reformer heater  102  by the combustion sensor  207  will be described in detail with reference to the drawings.  
       FIG. 4  is a view showing an example of correlation between time (start-up time) on an abscissa axis and a detected reformer temperature (KS), a detected combustion temperature (TFG), and a detected combustion flame current (FRG) on a ordinate axis, in which the time represents a time period that elapses from when the hydrogen generator starts start-up operation (to), the detected reformer temperature (KS) is output from the reformer temperature sensor, the detected combustion temperature (TFG) is output from a temperature detecting means used as the combustion sensor, and the detected combustion flame current (FRG) is output from a flame current detecting means used as the combustion sensor.  
       FIG. 4  shows the detected combustion temperature (TFG) output from the combustion sensor  207  and the detected combustion flame current (FRG) output from the combustion sensor  207  for a case where the water or the steam is supplied suitably from the first and second water supply means  108  and  109  to the interiors of the reformer  100  and the shift converter  102  of the hydrogen generator  118  and the water or the steam exists in correct amount in the interior of the hydrogen generator  118 . As the feed gas, a city gas is used.  
      The temperature curve of the detected combustion temperature (TFG) indicates a profile similar to that of a temperature curve of the detected reformer temperature (KS), but varies slightly lower than the same over a start-up time period after the reformer heater  102  starts combustion of the combustible gas.  
      The current curve of the detected combustion flame current (FRG) indicates a profile that rises up more rapidly than that of the temperature curve of the detected reformer temperature (KS) just after the reformer heater  102  starts combustion of the combustible gas (it should be noted that a numeric value of the detected combustion flame current (FRG) is limit-controlled correctly so as not to exceed an upper limit value (FRh) of a flame current during a normal operation). Such a phenomenon may be due to the fact that concentration of ions in the flame that are caused by methane component in the gas that is exhausted from the hydrogen generator  118  and flows to the reformer heater  102  increases rapidly just after the reformer heater  102  starts combustion of the reformer heater  102 .  
      When the temperature of the reforming catalyst body  101  has increased with an elapse of the start-up time, the methane component contained in the feed gas (city gas) is able to be converted into hydrogen through the reforming reaction in the reforming catalyst body  101 . After the conversion, the methane concentration in the gas that has been exhausted from the hydrogen generator  118  and flows to the reformer heater  102  decreases, whereas concentration of hydrogen in the gas increases. As a result, ionization in the flame of the reformer heater  102  decreases, causing the detected combustion flame current (FRG) to decrease (near t 1 ). That is, the current curve of the detected combustion flame current (FRG) indicates a profile that gradually decreases near the reforming reaction temperature of the reforming catalyst body  101  without falling below a lower limit value (FRI) of the flame current during the normal operation, and thereafter increases a flame current with an increase in the combustion amount and an increase in the material which are associated with power generation of the fuel cell  203 . That is, the flame current decreases according to a conversion near the reforming reaction temperature under a constant material condition, but when the material increases, ionization of the flame per unit volume increases, causing an increase in the flame current flowing in the flame current detecting means.  
      Subsequently, a temperature curve of the detected combustion temperature (TFG) and a current curve of the detected combustion flame current (FRG) will be described for a case where water is supplied excessively to the interior of the reformer  100  and to the interior of the shift converter  103  of the hydrogen generator  118  and excess steam or excess condensed water stays in the interiors of the reformer  100 , the shift converter  103 , and the selective oxidation device  105  because of repeated heating and cooling caused by frequent start-up and stop.  
       FIG. 5  is a view showing an example of correlation between time (start-up time) on an abscissa axis and a detected reformer temperature (KSN), a detected combustion temperature (TFN), and a detected combustion flame current (FRN) on a ordinate axis, in which the start-up time represents a time period that elapses from when the hydrogen generator starts the start-up operation (to), the detected reformer temperature (KSN) is output from the reformer temperature sensor, the detected combustion temperature (TFN) is output from the temperature sensor used as the combustion sensor, and the detected combustion flame current (FRN) is output from the flame current sensor used as the combustion sensor.  FIG. 5  shows the detected combustion temperature (TFN) output from the combustion sensor  207  and the detected combustion flame current (FRN) output from the combustion sensor  207  for a case where the water or the steam is supplied suitably from the first and second water supply means  108  and  109  to the interior of the reformer  100  and to the interior of the shift converter  102  of the hydrogen generator  118  and the water or the steam exists excessively in the interior of the hydrogen generator  118 .  
      Just after the hydrogen generator  118  starts the start-up operation, the gas exhausted from the selective oxidation device  105  is not supplied to the anode of the fuel cell  203 , but to the burner in the interior of the reformer heater  102  by the switching operation of the switching valve  204 . Just after the hydrogen generator  118  starts the start-up operation, there is a low possibility that excess condensed water staying in the interior of the hydrogen generator  118  is mixed into the exhausted gas in the form of the steam (gas) and is supplied to the burner of the reformer heater  102 . For this reason, the temperature curve of the detected reformer temperature (KSN) just after the hydrogen generator  118  starts the start-up operation indicates a profile substantially identical to that of the temperature curve of the detected reformer temperature (KS; see  FIG. 4 ) in the normal state.  
      With an elapse of the start-up time period of the hydrogen generator  118 , the feed gas is heated up to a high temperature by combustion heat from the reformer heater  102 . Thereby, the excess water is gradually mixed into the gas in the form of the steam and is supplied to the burner of the reformer heater  102 .  
      To be specific, the excess water is sent to the burner of the reformer heater  102  as the steam during a time period from a time (t 1 ) when the temperature of the shift reaction catalyst body  104  reaches the set value in the reaction temperature range of the shift reaction catalyst body  104  until a time (t 2 ) when the temperature of the CO selective oxidation catalyst body  106  reaches the set value in the reaction temperature range of the CO selective oxidation catalyst body  106 . This causes the steam in the burner of the reformer heater  102  to become excess. As a result, the combustion state of the combustible gas in the burner of the reformer heater  102  becomes unstable.  
      As shown in  FIG. 5 , the temperature profile of the detected combustion temperature (TFN) output from the combustion sensor  207  indicates a frequent temperature fluctuation (GX) because of the excess steam during a time period from a time (near t 2 ) when the temperature of the shift converter  103  increases to a time (near t 3 ) until the temperature of the selective oxidation device  105  increases.  
      Likewise, the current profile of the detected combustion flame current (FRN) which is output from the combustion sensor  207  indicates a frequent flame current fluctuation (JX) because of the excess steam during the time period from t 2  to t 3 .  
      It has been found that, during the temperature fluctuation (GX), the numeric value of the detected combustion temperature (TFN) frequently falls below the lower limit value (TFl) in the normal state which corresponds to a lower limit value in an allowable range of a normal operation of the reformer heater  102  and frequently falls to a lower limit value (TFlm) in an abnormal state which corresponds to a value at which the flame of the burner of the reformer heater  102  vanishes.  
      Likewise, it has been found that, during the flame current fluctuation (JX), the numeric value of the detected combustion flame current (FRN) frequently falls below the lower limit value (FRl) in the normal state which corresponds to a lower limit value in an allowable range of the normal operation of the reformer heater  102  and frequently falls to a lower limit value (FRlm) in the abnormal state which corresponds to a value at which the flame of the burner of the reformer heater  102  vanishes.  
      If abnormal states other than supply of the excess steam, such as insufficient supply of the material or the combustion air to the reformer heater  102 , takes place, the numeric values of the detected combustion temperature and the detected combustion current do not fall to the value at which the flame of the burner of the reformer heater  102  vanishes so frequently as those associated with the excess steam. From this fact, the inventors or the like considers that it may be determined whether or not the excess steam exists in the interior of the hydrogen generator  118  (shift converter  102  and selective oxidation device  105 ) based on the numeric value of the detected combustion temperature or the detected combustion current. In view of this, the fuel cell system  320  of this embodiment is configured such that the controller  205  monitors the temperature fluctuation (GX) because of the excess steam at the detected combustion temperature (TFN) and the flame current fluctuation (JX) because of the excess steam at the detected combustion flame current (FRN).  
      More specifically, if the numeric value of the detected combustion current (TFN) frequently falls below the lower limit value (TFlm) in the abnormal state or the numeric value of the detected fuel flame current (FRN) frequently falls below the lower limit value (FRlm) in the abnormal state during a time period that elapses from the time (near t 2 ) when the temperature of the shift converter  103  increases until the time (near t 3 ) when the temperature of the selective oxidation device  105  increases, the controller  205  determines that the shift converter  103  or the selective oxidation device  105  is wet or contains water droplets.  
       FIG. 6  is a flowchart showing an example of a control program of the controller at start-up of the hydrogen generator. The control program is stored in a storage portion (not shown) of the controller  205 .  
      Upon the start-up operation of the hydrogen generator  118 , the reformer heater  102  starts heating the reforming catalyst body  101  (combustion of the combustible gas) (step S 1 ).  
      The controller  205  controls the amount of material, the output of combustion fan, the amount of reformer water, and the amount of shift converter water to correctly control the hydrogen generator  118  (step S 2 ).  
      When the controller  205  receives a detection signal indicating a combustion state which is output from the combustion sensor  207  (step S 3 ), it determines whether or not the detection signal becomes the lower limit value (TFlm, FRlm) in the abnormal state which corresponds to the value at which the flame of the burner of the reformer heater  102  vanishes (step S 4 ).  
      If it is determined that the detection signal from the combustion sensor  207  does not become the lower limit value (TFlm, FRlm) (“No” in step S 4 ), the controller  205  repeats the operation in steps S 2  to S 4 .  
      On the other hand, if it is determined that the detection signal from the combustion sensor  207  becomes the lower limit value (TFlm, FRlm) (“Yes” in step S 4 ), the controller  205  advances the process to a subsequent determination step. The controller  205  counts the number of times the detection signal from the combustion sensor  207  falls below the lower limit value (TFlm, FRlm), and determines whether or not the count reaches a predetermined number of times or more per predetermined time (step S 5 ).  
      The detection signal from the combustion sensor  207  frequently falls below the lower limit value (TFlm, FRlm) corresponding to the value at which the flame of the burner of the reformer heater  102  vanishes during the start-up time period of the hydrogen generator  118  in which the temperature fluctuation (GX) or the flame current fluctuation (JX) occurs because of the excess water, i.e., the time period from the time (near t 2 ) when the temperature of the shift converter  103  increases until the time (near t 3 ) when the temperature of the selective oxidation device  105  increases.  
      If it is determined that the detection signal from the combustion sensor  207  falls below the lower limit value (TFlm, FRlm) the predetermined number of times or more per predetermined time period (predetermined unit time period from t 2  to t 3 ) (“Yes” in step S 5 ), the controller  205  determines that excess water exists in the interior of the shift converter  103  or in the interior of the selective oxidation device  105 . That is, the controller  205  detects the excess water state. Then, the controller  205  carries out an abnormal stop operation of the hydrogen generator  118  in order to remove excess water from the shift converter  103  or the selective oxidation device  105  (step S 6 ).  
      If it is determined that the detection signal from the combustion sensor  207  falls below the lower limit value (TFlm, FRlm) the predetermined number of times or more per predetermined time period (“No” in step  5 ), the controller  205  determines that the material or the combustion air is insufficient in the reformer heater  102 , and carries out an abnormal stop operation of the hydrogen generator  118  because of deficiency of the material or the combustion air in the reformer heater  102  (step S 7 ).  
      In accordance with the determination step of the controller  205 , the excess water state, for example, the state in which the shift converter  103  or the selective oxidation device  105  is wet, is correctly determined based on the detection signal from the combustion sensor  207  equipped in the reformer heater  102 , separately from the abnormal state such as deficiency of the material in the reformer heater  102 .  
      It may be determined whether or not the flame has vanished because of the excess water state, for example, the state in which the shift converter  103  or the selective oxidation device  105  is wet, based on difference between actual values detected by a feed gas flow sensor, a sensor that detects the number of rotations of the combustion fan, or a combustion air flow sensor, and their target set values.  
      The controller  205  executes the abnormal stop operation to remove excess water in such a manner that, as described in the embodiment 1, the controller  205  reduces the supply amount of the material and the steam to an extent to which carbon deposition does not take place (steam/carbon ratio: S/C=2.0 or more) until the detected temperature of the shift converter  103  illustrated in  FIG. 2  exceeds the set value in the reaction temperature range of the shift reaction catalyst body  104  and/or the detected temperature of the selective oxidation device  105  illustrated in  FIG. 2  exceeds the set value in the reaction temperature range of the CO selective oxidation catalyst body  106 . This will not be further described.  
      In the manner described above, in accordance with this embodiment, it is correctly determined whether or not the excess water state occurs in the interior of the shifter  103  or the selective oxidation device  105 , for example, the shift converter  103  or the selective oxidation device  105  is wet.  
      Since the abnormality due to the excess steam or the like in the interior of the shift converter  103  or the selective oxidation device  105  is surely detected, it is dealt with quickly, and thus catalytic activity of the shift converter  103  or the selective oxidation device  103  is quickly restored.  
      Furthermore, power generation is not carried out with degraded catalytic activity, and catalyst poisoning of the fuel cell  203  which would be caused by carbon monoxide is avoided.  
      While in this embodiment, the remaining off gas which has not been consumed in the electrode reaction in the fuel cell  203  is caused to flow to the burner of the reformer heater  102  through the passage that is not provided with an auto drain or a condenser that condenses water in the off gas, the technique described in this embodiment is effective to the fuel cell system that is equipped with these components if the total amount of the excess steam or condensed water remaining in the interior of the reformer  100 , the shift converter  103 , and the selective oxidation device  105  is above the removing ability of these components.  
     Embodiment 3  
       FIG. 7  is a block diagram showing a construction of a fuel cell system according to an embodiment 3 of the present invention. In this embodiment, a modified example 1 for removing excess water from the interior of the shift converter  103  or the selective oxidation device  105  will be described.  
      Since the constructions and operations of the hydrogen generator  118 , the oxidizing gas supply means  200 , the fuel cell  203 , the controller  205  and other components are identical to those described in the embodiments 1 and 2, they will not be further described.  
      A fuel cell system  330  of this embodiment differs in construction from the systems of the embodiments 1 and 2 in that the controller  205  controls a shift converter discharge valve  400  coupled to the shift converter  103  so as to discharge excess condensed water remaining in the interior of the shift converter  103  because of the excess steam or the like and a selective oxidation device discharge valve  401  coupled to the selective oxidation device  105  so as to discharge excess condensed water remaining in the interior of the selective oxidation device  105  because of the excess steam or the like. The discharge valves  400  and  401  as discharge means are constructed of electromagnetic valves.  
      Subsequently, an operation of the fuel cell system  330  of the embodiment 3 will be described.  
      As in the embodiment 1, if the water for the steam reforming is suitably supplied to the reformer  100  of the hydrogen generator  118  and the water is suitably supplied to the shift converter  103  to stably control the temperature of the shift converter  103 , the steam is supplied in correct amount to the interiors of the reformer  100 , the shift converter  103 , and the selective oxidation device  105 . Therefore, the detected temperatures of the reformer  100 , the shift converter  103 , and the selective oxidation device  105  indicate the profiles represented by KS, HSG, and JSG in  FIG. 2 . In this case, as in the embodiment 2, the characteristic of the detected reformer temperature (KS) in the normal state, the characteristic of the detected combustion temperature (TFG) in the normal state, and the characteristic of the detected combustion flame current (FRG) in the normal state are obtained as illustrated in  FIG. 4 .  
      If the water is supplied excessively to the interior(s) of the reformer  100  and/or the shift converter  103  of the hydrogen generator  118 , or excess steam or excess condensed water remains in the interiors of the reformer  100 , the shift converter  103  and the selective oxidation device  105  which may be caused by repeated heating or cooling of the hydrogen generator  118  due to frequent start-up and stop of the hydrogen generator  118 , the detected temperature of the shift converter  103  and the detected temperature of the selective oxidation device  105  indicate the temperature curves represented by HSN and JSN in  FIG. 2 . In this case, as in the embodiment 2, the characteristic of the detected reformer temperature (KSN) in the abnormal state, the characteristic of the detected combustion temperature in the abnormal state (TFN), and the characteristic of the detected combustion flame current (FRN) in the abnormal state are obtained as illustrated in  FIG. 5 .  
      When the controller  205  determines that excess steam or condensed water exists in the interior(s) of the shift converter  103  and/or the selective oxidation device  105  based on the temperature(s) which have been detected by the shift converter temperature sensor  116  that detects the temperature of the shift converter  103  and/or the selective oxidation device sensor  117  that detects the temperature of the selective oxidation device  105 , as in the embodiment 1, it stops the operation of the hydrogen generator  118  and carries out an operation for purging the generated combustible gas.  
      Or, when the controller  205  determines that excess steam or condensed water exists in the interior of the shift converter  103  or the selective oxidation device  105  based on the detection signal from the combustion sensor  207  by detecting the number of times the detection signal falls below the value at which the flame of the reformer heater  102  vanishes as in the embodiment 2 (see flowchart in  FIG. 6 ), it causes the hydrogen generator  118  to stop operation and carries out the operation for purging the generated combustible gas.  
      Subsequently, the controller  205  sends control signal to the discharge valves  400  and  401  coupled to the shift converter  103  and the selective oxidation device  105  through discharge passages  402  and  403 , respectively to open the discharge valves  400  and  401 , during a stop period of the hydrogen generator  118 , causing the excess water to be discharged from the shift converter  103  and/or the selective oxidation device  105 . The discharge valves  400  and  401  must be opened to enable the excess water to be removed fully for a time period, for example, several hours to one night. It should be understood that, by supplying an inert gas such as nitrogen from an inert gas device (not shown) to the shift converter  103  and/or the selective oxidation device  105 , internal pressure(s) of the shift converter  103  and/or the selective oxidation device  105  increase, thus facilitating discharging the excess water and drying the interior(s) of the shift converter  103  and the selective oxidation device  105 . As a result, the problem that the interior(s) of the shift converter  103  and/or the selective oxidation device  105  is wet or contains water droplets because of the excess steam is able to be solved earlier.  
      In accordance with this embodiment, since the abnormality due to the excess steam or the like in the interiors of the shift converter  103  and/or the selective oxidation device  105  is surely detected, it is dealt with quickly, and thus catalytic activity of the shift converter  103  and/or the selective oxidation device  103  is quickly restored.  
      Furthermore, power generation is not carried out with degraded catalytic activity, and catalyst poisoning of the fuel cell  203  which would be caused by carbon monoxide is avoided. While at least one of the shift converter  103  and the selective oxidation device  105  is purged using the inert gas such as nitrogen when discharging the excess water, the interior of the shift converter  103  or the selective oxidation device  105  may be heated or air may be supplied to the shift converter  103  or the selective oxidation device  105 . This is because the internal pressures of the components  103  and  105  increase, enabling the excess water to be easily discharged and the interiors of the shift converter  103  and the selective oxidation device  105  to be dried faster. As a result, the shift converter  103  and the selective oxidation device  105  suitably restore to normal states from the excess water state such as wet state.  
     Embodiment 4  
       FIG. 8  is a block diagram showing a construction of a fuel cell system according to an embodiment 4 of the present invention. In this embodiment, a modified example 2 for removing excess water from the interior of the shift converter  103  or the selective oxidation device  105  will be described.  
      Since the constructions and operations of the hydrogen generator  118 , the oxidizing gas supply means  200 , the fuel cell  203 , the controller  205 , and other components are identical to those of the embodiments 1 and 2, they will not be further described.  
      A fuel cell system  340  of this embodiment differs in construction from the systems of the embodiments 1 and 2 in that a shift converter air supply pump  500  which is an air supply device is coupled to the shift converter  103  and is configured to dry and remove excess condensed water remaining in the shift converter  103  because of the excess steam or the like, a selective oxidation device air supply pump  501  which is an air supply device is coupled to the selective oxidation device  105  and is configured to dry and remove excess condensed water remaining in the selective oxidation device  105  because of the excess steam or the like, and the controller  205  controls these air supply pumps  500  and  501 .  
      Subsequently, an operation of the fuel cell system  340  of the embodiment 4 will be described.  
      As in the embodiment 1, if the water for the steam reforming is suitably supplied to the reformer  100  of the hydrogen generator  118  and the water is suitably supplied to the shift converter  103  to stably control the temperature of the shift converter  103 , the steam is supplied in correct amount to the interiors of the reformer  100 , the shift converter  103 , and the selective oxidation device  105 . Therefore, the detected temperatures of the reformer  100 , the shift converter  103 , and the selective oxidation device  105  indicate the profiles represented by KS, HSG, and JSG in  FIG. 2 . In this case, as in the embodiment 2, the characteristic of the detected reformer temperature (KS) in the normal state, the characteristic of the detected combustion temperature (TFG) in the normal state, and the characteristic of the detected combustion flame current (FRG) in the normal state are obtained as shown in  FIG. 4 .  
      If the water is supplied excessively to the interior(s) of the reformer  100  and/or the shift converter  103  of the hydrogen generator  118 , or excess steam or excess condensed water stays in the interiors of the reformer  100 , the shift converter  103  and the selective oxidation device  105  which may be caused by repeated heating or cooling of the hydrogen generator  118  due to frequent start-up and stop of the hydrogen generator  118 , the detected temperatures of the shift converter  103  and the selective oxidation device  105  indicate the temperature curves represented by HSN and JSN in  FIG. 2 . In this case, as in the embodiment 2, the characteristic of the detected reformer temperature (KSN) in the abnormal state, the characteristic of the detected combustion temperature in the abnormal state (TFN), and the characteristic of the detected combustion flame current (FRN) in the normal state are obtained as illustrated in  FIG. 5 .  
      When the controller  205  determines that excess steam or condensed water exists in the interior(s) of the shift converter  103  and/or the selective oxidation device  105  based on the temperature(s) which have been detected by the shift converter temperature sensor  116  that detects the temperature of the shift converter  103  and/or the selective oxidation device sensor  117  that detects the temperature of the selective oxidation device  105 , as in the embodiment 1, it stops the operation of the hydrogen generator  118  and carries out an operation for purging the generated combustible gas.  
      Or, when the controller  205  determines that excess steam or condensed water exists in the interior of the shift converter  103  or the selective oxidation device  105  based on the detection signal from the combustion sensor  207  by detecting the number of times the detection signal falls below the value at which the flame of the reformer heater  102  vanishes as in the embodiment 2 (see flowchart in  FIG. 6 ), it stops the operation of the hydrogen generator  118  and causes the hydrogen generator  118  to stop operation and carries out the operation for purging the generated combustible gas.  
      Then, the controller  205  sends control signals to the air supply pumps  500  and  501  to drive these pumps  500  and  501  so that air is supplied from the air supply pumps  500  and  501  to the shift converter  103  and the selective oxidation device  105  through dry air supply passages  502  and  503 , respectively during a stop period of the hydrogen generator  118 . The air must be supplied to the shift converter  103  and to the selective oxidation device  105  for a time period, for example, several hours to one night to enable the excess water in the interiors to be fully dried. The air is desirably supplied from the air supply pumps  500  and  501  at a flow rate as fast as possible to efficiently dry the water. A flow rate of the air per unit time is required to be at least higher than a flow rate of the normal operation. This makes it possible that the excess water remaining in the shift converter  103  and/or the selective oxidation device  105  is dried and discharged.  
      In accordance with this embodiment, since the abnormality due to the excess steam or the like in the interior of the shift converter  103  and/or the selective oxidation device  105  is surely detected, it is dealt with quickly, and thus catalytic activity of the shift converter  103  and/or the selective oxidation device  103  is quickly restored.  
      Furthermore, power generation is not carried out with degraded catalytic activity, and catalyst poisoning of the fuel cell  203  which would be caused by carbon monoxide is avoided.  
      In this embodiment, since the air is directly applied to the excess water to vaporize water, the catalytic activity is suitably quickly restored.  
     Embodiment 5  
       FIG. 9  is a block diagram showing a construction of a fuel cell system according to an embodiment 5 of the present invention. In this embodiment, a modified example 3 for removing excess water from the interior of the shift converter  103  or the selective oxidation device  105  will be described.  
      Since the constructions and operations of the hydrogen generator  118 , the oxidizing gas supply means  200 , the fuel cell  203 , the controller  205  and other components are identical to those described in the embodiments 1 and 2, they will not be further described.  
      A fuel cell system  350  of this embodiment differs in construction from the systems of the embodiments 1 and 2 in that a shift converter exhaust gas supply valve  600  that heats and dries the excess condensed water remaining in the shift converter  103  because of the excess steam or the like is provided in a shift converter exhaust gas supply passage  602  coupling the reformer heater  102  to the shift converter  103 , a selective oxidation device exhaust gas supply valve  601  that heats and dries the excess condensed water remaining in the selective oxidation device  105  because of the excess steam or the like is provided in a selective oxidation device exhaust gas passage  603  coupling the reformer heater  102  to the selective oxidation device  105 , and the controller  205  controls the gas supply valves  600  and  601  provided in the exhaust gas supply passages  602  and  603  as the heating devices.  
      Subsequently, an operation of the fuel cell system  350  of the embodiment 5 will be described.  
      As in the embodiment 1, if the water for the steam reforming is suitably supplied to the reformer  100  of the hydrogen generator  118  and the water is suitably supplied to the shift converter  103  to stably control the temperature of the shift converter  103 , the steam is supplied in correct amount to the interiors of the reformer  100 , the shift converter  103 , and the selective oxidation device  105 . Therefore, the detected temperatures of the reformer  100 , the shift converter  103 , and the selective oxidation device  105  indicate the profiles represented by KS, HSG, and JSG in  FIG. 2 . In this case, as in the embodiment 2, the characteristic of the detected reformer temperature (KS) in the normal state, the characteristic of the detected combustion temperature (TFG) in the normal state, and the characteristic of the detected combustion flame current (FRG) in the normal state are obtained as illustrated in  FIG. 4 .  
      If the water is supplied excessively to the interior(s) of the reformer  100  and/or the shift converter  103  of the hydrogen generator  118 , or excess steam or excess condensed water remains in the interiors of the reformer  100 , the shift converter  103  and the selective oxidation device  105  which may be caused by repeated heating or cooling of the hydrogen generator  118  due to frequent start-up and stop of the hydrogen generator  118 , the detected temperatures of the shift converter  103  and the selective oxidation device  105  indicate the temperature curves represented by HSN and JSN in  FIG. 2 . In this case, as in the embodiment 2, the characteristic of the detected reformer temperature (KSN) in the abnormal state, the characteristic of the detected combustion temperature in the abnormal state (TFN), and the characteristic of the detected combustion flame current (FRN) in the abnormal state are obtained as illustrated in  FIG. 5 .  
      When the controller  205  determines that excess steam or condensed water exists in the interior(s) of the shift converter  103  and/or the selective oxidation device  105  based on the temperature(s) which have been detected by the shift converter temperature sensor  116  that detects the temperature of the shift converter  103  and/or the selective oxidation device sensor  117  that detects the temperature of the selective oxidation device  105 , as in the embodiment 1, it stops the operation of the hydrogen generator  118  and carries out an operation for purging the generated combustible gas.  
      Or, when the controller  205  determines that excess steam or condensed water exists in the interior of the shift converter  103  or the selective oxidation device  105  based on the detection signal from the combustion sensor  207  by detecting the number of times the detection signal falls below the value at which the flame of the reformer heater  102  vanishes as in the embodiment 2 (see flowchart in  FIG. 6 ), it causes the hydrogen generator  118  to stop operation and carries out the operation for purging the generated combustible gas.  
      Then, the controller  205  outputs a signal to the exhaust gas supply valve  600  provided in the exhaust gas supply passage  602  fluidically coupling the reformer heater  102  to the shift converter  103  to open the exhaust gas supply valve  600 , during a stop period of the hydrogen generator  118 . Likewise, the controller  205  outputs a signal to the exhaust gas supply valve  601  provided in the exhaust gas supply passage  603  fluidically coupling the reformer heater  102  to the selective oxidation device  105  to open the exhaust gas supply valve  601 , during a stop period of the hydrogen generator  118 . Thereby, the excess water remaining in the shift converter  103  and/or the selective oxidation device  105  is heated and dried efficiently by utilizing residual heat of the exhaust gas resulting from combustion in the reformer heater  102 . The shift converter  103  and the selective oxidation device  105  must be heated for a time period, for example, several hours to one night to enable the excess water in the interiors to be fully dried.  
      While in this embodiment, the exhaust gas supply passages  602  and  603  and the exhaust gas supply valves  600  and  601  used to supply the high-temperature exhaust gas to the shift converter  103  have been described as an example of a heating device, they are merely exemplary, and any other components may be used so long as the excess water remaining in the shift converter  103  or the selective oxidation device  105  is heated and dried.  
      For example, the shift converter heater  113  and the selective oxidation device heater  114  may be controlled to increase their outputs so that these heaters  113  and  114  serve as heating devices.  
      While the interior of the shift converter  103  or the selective oxidation device  105  is dried after the operation of the hydrogen generator  118  stops, the shift converter  103  or the selective oxidation device  105  is suitably dried by using the heating devices of this embodiment during an operation of the hydrogen generator  118 , without stopping the operation of the hydrogen generator  118 .  
      In accordance with this embodiment, since the abnormality due to the excess steam or the like in the interior of the shift converter  103  or the selective oxidation device  105  is surely detected, it is dealt with quickly, and thus catalytic activity of the shift converter  103  or the selective oxidation device  103  is quickly restored.  
      Furthermore, power generation is not carried out with degraded catalytic activity, and catalyst poisoning of the fuel cell  203  which would be caused by carbon monoxide is avoided.  
     INDUSTRIAL APPLICABILITY  
      A fuel cell system of this embodiment enables a hydrogen generating apparatus to achieve high performance and is effective as a power generating apparatus for household uses.