Patent Publication Number: US-2022213899-A1

Title: Blower

Description:
TECHNICAL FIELD 
     The present invention relates to a blower, specifically, relates to a blower suitable for boosting and blowing a gas to be blown from a fuel cell, an electrolytic cell and the like. 
     BACKGROUND ART 
     Blowers which can suck and boost a gas to be blown, and which can ensure the uniformity of temperature within various furnaces such as a heat treatment furnace and a firing furnace and the improvement of heating efficiency are conventionally known. 
     Further, in fuel cells which have become widely used as power generation systems in recent years, for example, a Solid Oxide Fuel Cell, when a humidified high temperature exhaust gas (hereinafter, referred to as the anode-off gas) which is discharged from a fuel electrode is recirculated to a fuel cell, there is the advantageous point that unreacted residual fuel in the exhaust gas can be reused, a reaction product water free of impurities can be used in so-called steam reformation, and the power generation efficiency can be increased, thus, a so-called recirculation blower which is a blower that boosts and blows an anode-off gas to the fuel cell so that it may be recirculated has been used. 
     Furthermore, a water electrolysis apparatus having a high electrolytic efficiency for hydrogen production which uses the reverse reaction of a solid oxide fuel cell, for example, a Solid Oxide Electrolysis Cell has been developed in recent years, but even with this kind of apparatus, the hydrogen is produced by high-temperature steam electrolysis, thus, a blower is used in order to compress and recirculate the production gas to the fuel electrode to prevent oxidative deterioration of the fuel electrode. 
     In this kind of blower, a shaft seal structure has been devised so that the gas to be blown is not permitted to leak to the outside from a shaft hole part through which a rotating shaft of an impeller passes. 
     For example, the blower described in PTL 1 comprises a heat resistant impeller cantilevered by a rotating shaft, a bearing which supports the rotating shaft of the impeller to be freely rotatable with respect to a casing, a heat insulating layer disposed between the impeller and the bearing, and a cooling part disposed between the heat insulating layer and the bearing, and by this blower having a first coupling of a pair of magnetic couplings disposed on a rear end part opposite to the impeller of the rotating shaft and a nonmagnetic partition wall disposed between the first coupling and a second coupling of the magnetic joint mounted on a front-end part of the motor shaft for driving, a space surrounding the rotating shaft of the impeller is hermetically sealed off from the outside with the nonmagnetic partition wall and a casing. 
     Further, PTL 2 describes a blower (compressor) which sucks and compresses a process gas from an intake port by the rotation of a rotating body, and uses a dry gas seal in a shaft seal of a rotating shaft of the rotating body while supplying a part of the process gas to the dry gas seal, and flares the gas discharged from narrow gaps between a rotating ring and stationary rings to the atmospheric air side. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1 WO 2004/070209 
         PTL 2 JP-A 2012-107609 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The conventional blower as described in the aforementioned PTL 1 has the advantageous point that a completely gas-tight state can be established in which a space surrounding the rotating shaft of the impeller is hermetically sealed off from the outside by a nonmagnetic partition wall and a casing. 
     However, there is concern that, depending on the operational state of the blower, a humidified anode-off gas may not be able to infiltrate into the shaft hole or reduce bearing performance. 
     On the one hand, the blower described in PTL 2 has the problem that separates from the dry gas seal which uses the process gas, flare processing, etc., of a discharge seal gas containing a seal element which uses an inert gas (nitrogen gas) and a process gas component is necessary to produce a seal which prevents leakage of the process gas to the outside, thus, the configuration is complicated and it is difficult to reduce the cost. 
     The object of the present invention is to provide a blower which can reliably prevent a target gas from infiltrating into the shaft hole with a simple configuration in order to solve the unsolved problems as described above. 
     Solution to Problem 
     (1) In order to obtain the aforementioned object, the blower described in the present invention is provided with a first casing formed by a gas passage for introducing a target gas and a shaft hole in communication with the gas passage, a rotating shaft inserted to be freely rotatable in the shaft hole of the first casing, an impeller housed within the first casing at a front-end side of the rotating shaft and which can rotate integrally with the rotating shaft, a motor which drives the rotating shaft from a rear end side, a second casing having an interior space in communication with the shaft hole and supporting the rotating shaft via a bearing, and a purge gas introduction means which introduces a purge gas having a higher pressure than that in the shaft hole of the first casing into the interior space of the second casing, wherein the inflow of the target gas from the gas passage side of the first casing into the shaft hole is suppressed by introducing the purge gas into the interior space of the second casing. 
     With this configuration, the blower of the present invention introduces the purge gas having a higher pressure than that in the shaft hole in communication with the gas passage of the first casing to the interior space of the second casing supporting the rotating shaft via the bearing to be freely rotatable. Therefore, the purge gas in the interior space side of the second casing suppresses the high temperature gas introduced into the gas passage of the first casing from infiltrating into the shaft hole on the back side of the impeller. Note that, the purge gas pressure may be approximately constant or variable. 
     (2) A preferred embodiment of the present invention may be configured such that when the purge gas introduction means introduces the purge gas into the interior space of the second casing, the purge gas is filled on the shaft hole side from at least the bearing in the interior space while the pressure of the purge gas is maintained at a higher pressure than that within the shaft hole. 
     In this way, when the purge gas is introduced into the interior space of the second casing, the pressure of the purge gas is maintained at a higher pressure than in the shaft hole, thus, the exhaust gas on the gas passage side of the first casing is more effectively suppressed from flowing into the shaft hole. Further, even when the bearing is cooled to the dew point or less, the dry purge gas suppresses condensation in the vicinity of the bearings, and the elution, etc., of the grease for bearing lubrication is effectively suppressed. Note that, the purge gas introduction means should always be operated. 
     (3) A preferred embodiment of the present invention may be configured such that the high temperature gas is discharged from the fuel electrode side of a fuel cell, and the purge gas comprises at least a fuel component of the fuel cell, wherein when the purge gas is introduced into the interior space of the second casing, the purge gas flows to the gas passage side of the first casing through an annular clearance in the periphery of the rotating shaft in the shaft hole. 
     In this case, the exhaust gas (anode-off gas) of the fuel cell is recirculated to the supply path side of the fuel gas together with the H 2 O produced by power generation, but the dry purge gas comprising the fuel component can flow from the interior space of the second casing to the shaft hole of the first casing, and can flow to the gas passage side of the first casing. Therefore, the humidified exhaust gas from the fuel electrode side is effectively suppressed from entering into the interior space of the second casing, and the exhaust gas to be recirculated is not contaminated by the purge gas. 
     (4) A preferred embodiment of the present invention may be configured such that the first casing is provided with a heat insulating part which is a substantially plate-like body positioned on the back side of the impeller and penetrated by the rotating shaft, and a part of the purge gas passage which introduces the purge gas from the bearing within the interior space to the shaft hole side is open in the vicinity of the rear end of the shaft hole on the bearing side of the heat insulating part. 
     In this case, the part of the purge gas passage in the vicinity of the rear end of the shaft hole is open in the vicinity of the rear end of the shaft hole of the rotating shaft, thus, the dry purge gas is properly supplied in the vicinity of the rear end of the shaft hole, and the humidified exhaust gas is more effectively suppressed from entering the interior space of the second casing through the shaft hole. 
     (5) A preferred embodiment of the present invention in which the heat insulating part may have an airtight wall surface having a lower thermal conductivity than the second casing in at least the vicinity of the shaft hole, and the airtight wall surface may have a high temperature side surface portion facing the back surface of the impeller spaced at a predetermined clearance, a cylindrical wall surface portion which forms the shaft hole, and a low temperature side surface portioned in the vicinity of the opening of the purge gas passage. 
     In this way, the airtight wall surface of the heat insulating part, the impeller and the rotating shaft form the gas passage extending to the back side of the impeller from the shaft hole by the airtight wall surface. Therefore, the dry gas seal function of the shaft hole can be sufficiently ensured, and the heat transfer to the bearing can be more effectively suppressed. 
     (6) A preferred embodiment of the present invention may be configured such that a plurality of members comprising at least the heat insulating part, the rotating shaft and the bearing define an annular gas storage chamber which opens a part of the purge gas passage on the rear end side of the shaft hole, and a clearance passage having a smaller clearance dimension than the annular gas storage chamber is formed between the cylindrical wall surface portion of the airtight wall surface of the heat insulating part and the rotating shaft. 
     With this configuration, the air within the gas storage chamber to which the bearing is exposed at the rear end side of the shaft hole can be rapidly replaced with the purge gas in the initial operation and the like, the purge gas can be stably supplied within the annular gas storage chamber of the rear end side of the shaft hole, and regardless of pressure fluctuations on the impeller side due to load fluctuations, the purge gas can stably ensure the dry gas sealing performance. 
     (7) A preferred embodiment of the present invention may be configured such that a part of the purge gas passage which is on the rear end side of the shaft hole and which is on the shaft hole side of the bearing opens on the outer peripheral surface of the front-end side of the rotating shaft and extends to the radial and axial rearward sides of the rotating shaft. 
     In this case, the part of the purge gas passage through which the rotating shaft passes makes it possible for the purge gas to rapidly and reliably flow to the shaft hole side due to the bearing within the interior space of the second casing, and it is possible to more effectively suppress the humidified exhaust gas within the first casing from infiltrating and condensing within the shaft hole and the bearing. 
     (8) A preferred embodiment of the present invention may be configured such that a part of the purge gas passage is on the rear end side of the rotating shaft of the bearing and opens on the end surface extending in the radial direction of the rotating shaft on the radially inward side from the outer peripheral surface of the front-end side of the rotating shaft. 
     In this case, the purge gas is urged radially outward due to the centrifugal force accompanying the rotation of the purge gas passage extending radially on the front-end side of the bearing during the rotation of the rotating shaft, and the sucking of the purge gas from the rear end part side of the purge gas passage is facilitated. 
     (9) A preferred embodiment of the present invention may be configured such that the first casing is provided with a heat insulating part which is a substantially plate-like body positioned on the back side of the impeller and penetrated by the rotating shaft, and a part of the purge gas passage which introduces the purge gas into the shaft hole side of the bearing within the interior space opens radially outward toward an inner peripheral surface of the bearing. 
     In this case, a part of the purge gas passage opens toward the inner peripheral surface of the bearing, thus, it is possible to effectively cool the inner peripheral surface side of the bearing, which is difficult to cool from the casing side. 
     (10) A preferred embodiment of the present invention may be configured such that a part of the purge gas passage comprises a first groove part that opens radially outward toward an inner ring of the bearing and a plurality of second groove parts that extend from the first groove part toward the shaft hole side and open on an outer peripheral surface of the rotating shaft between the heat insulating part and the bearing. 
     With this configuration, the inner ring of the bearing can be effectively cooled by the purge gas flowing through the first groove part and the plurality of second groove parts of the purge gas passage, and it is possible to flow out the purge gas substantially evenly in the periphery of the rotating shaft between the beat insulating part and the bearing from the plurality of the second groove parts, thus, the inner ring side of the bearing can be cooled more effectively. 
     Advantageous Effects of Invention 
     The present invention can provide a blower which can reliably prevent a target gas from infiltrating into a shaft hole with a simple configuration. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side sectional view illustrating a schematic configuration of a blower according to a first embodiment of the present invention. 
         FIG. 2  is a side sectional view of main portions of the blower according to the first embodiment of the present invention. 
         FIG. 3  is a side sectional view of main portions of a separate embodiment for increasing the cooling effect of an impeller rotating shaft and a bearing purge gas in the blower according to the first embodiment of the present invention. 
         FIG. 4  is a side sectional view illustrating the schematic configuration of a blower according to a second embodiment of the present invention. 
         FIG. 5  is a side sectional view of the schematic configuration of a blower according to a third embodiment of the present invention. 
         FIG. 6  is a side sectional view of the schematic configuration of a blower according to a fourth embodiment of the present invention. 
         FIG. 7  is a partially enlarged schematic cross-sectional view of a shaft hole portion and a bearing portion of the blower according to the fourth embodiment of the present invention. 
         FIG. 8  is a cross-sectional view of the bearing inner ring and the rotating shaft as seen on the impeller side in the bearing portion of the blower according to the fourth embodiment of the present invention. 
         FIG. 9  is a side sectional view of the schematic configuration of a blower according to a fifth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Preferred embodiments of the present invention will be described below with reference to the drawings. 
     First Embodiment 
     The blower according to the first embodiment of the present invention is provided as a so-called recirculation blower in a power generation system comprising a fuel cell, for example, a combined power generation system (for example, refer to JP-A 2019-145394, JP-A 2014-107071, etc.) in which a solid oxide fuel cell (hereinafter, referred to as SOFC) is combined with a micro gas turbine (hereinafter, referred to as MGT). 
     First, a summary of the power generation system will be described. 
     As illustrated in the schematic configuration of  FIG. 1 , a power generation system  1  of the present embodiment is provide with a fuel system, an air system and an exhaust gas system, wherein a fuel gas is input to a SOFC2 fuel electrode  2   a  (anode) side which is a fuel cell via a fuel supply line L 1 , and air boosted by an MGT3 compressor  3   a  is input to a SOFC2 air electrode  2   b  (cathode) side by an air supply line L 2  and an air blower  4 . 
     Further, a part of the SOFC2 anode-off gas is boosted by a recirculation blower  5  (blower) on a recirculation line L 3  to be returned to the fuel supply line L 1  side and recirculated to SOFC2. The remaining part of the anode-off gas and the exhaust gas (hereinafter, referred to as the cathode-off gas) from the SOFC2 air electrode  2   b  are supplied to a combustor  6 , and the combustion gas from the combustor  6  is sent to an MGT3 gas turbine  3   b , so as to drive the MGT3 compressor  3   a  and a generator  3   c.    
     A gas blower  8  for sending the remaining part of the anode-off gas to the combustor  6  is provided the upstream side of the combustor  6 , and a heat exchanger  9  for exchanging heat between the combustion gas discharged from the combustor  6  and the air sent from the MGT3 compressor  3   a  to the air supply line L 2  is provided the downstream side of the combustor  6 . Furthermore, a gas flow rate control valve or the like (not shown) is provided on the upstream side of each of the air blower  4 , the gas blower  8  and the recirculation blower  5 . 
     The fuel gas supplied to SOFC2 and the fuel gas supplied to the combustor  6  are respectively manufactured from, for example, natural gas, municipal gas, or, hydrogen, carbon monoxide, methane or other hydrocarbon gases, or, carbonaceous material (oil, coal, and the like) by gasification equipment, and are prepared so that the calorific value is substantially constant. Further, fuel gas heated to a high temperature is supplied to the SOFC2 fuel electrode  2   a  in accordance with the SOFC2 operating temperature (for example, in the range of 700° C. to 1000° C.) 
     Further, by merging with an anode-off gas boosted by the recirculation blower  5 , the fuel gas supplied to the SOFC2 fuel electrode  2   a  side becomes, for example, a high temperature hydrogen rich gas obtained by reforming and reacting water vapor having a volume ratio in the range of 30% to 50% with a hydrocarbon gas of the fuel, and thus, contained hydrogen (H 2 ), carbon monoxide (CO), and lower hydrocarbons (for example, methane (CH 4 )). The oxidizing gas supplied to SOFC2 is a gas containing approximately 15% to 30% oxygen, for example, air, but other than air, a mixed gas of combustion exhaust gas and air, a mixed gas of oxygen and air and the like may be used (hereinafter, the oxidizing gas supplied to SOFC2 is simply referred to as air). 
     Specifically, a predetermined oxidation reaction (2H 2 +2O 2− →2H 2 O+4e −  . . . (1)) between steam reformed high temperature hydrogen rich gas and the oxide ion (O 2− ) in the SOFC2 electrolyte  2   c  occurs on the SOFC2 fuel electrode  2   a  side. On the one hand, a predetermined reduction reaction (O 2 +4e − →2O 2−  . . . (2)) occurs between the oxygen (O 2 ) in the air which is boosted and supplied and the electrons supplied from the fuel electrode  2   a  side via an external circuit on the SOFC2 air electrode  2   b  side. As a result, in the SOFC2, a fuel (H 2 ) can be chemically reacted with oxygen (O 2 ) to generate electricity, and water (H 2 O) can be produced. 
     Note that, steam reformation of the fuel gas is an endothermic reaction which reacts, for example, methane (CH 4 ) which is a main component of the fuel gas with water vapor (H 2 O) to reformulate hydrogen (H 2 ) with carbon monoxide (CO), the CO contained in the reformulated fuel gas can be reacted with the oxide ion (O 2− ) in the electrolyte to produce electrons (CO+O 2− →CO 2 +2e −  . . . (3)), and thus, can be a fuel. 
     The DC power output at the SOFC2 is converted to three-phase AC power, for example, an inverter  7 , and boosted by a transformer together with the three-phase AC power from the MGT3 generator  3   c . Moreover, part of the three-phase AC power from the SOFC2 and the MGT3 is supplied to SOFC2 and MGT3 accessories. Certainly, the DC power output at the SOFC2 can be used as DC. 
     The recirculation blower  5  illustrated in  FIGS. 1 and 2  blows air at an amount and static pressure within predetermined ranges so that the anode-off gas at a high temperature, for example, in the range of 750° C., humidified by the water (H 2 O) produced by the SOFC2 power generation may be recirculated to the SOFC2. 
     As illustrated in  FIG. 1 , the recirculation blower  5  is a centrifugal-compression type air blower which boosts and blows the high temperature anode-off gas discharged from the SOFC2 (fuel cell) fuel electrode  2   a , and is provided with a first casing  11 , a second casing  12 , an impeller  13 , a rotating shaft  14 , a motor  15 , and, a purge gas introduction means  16 . 
     The first casing  11  is configured to include a scroll casing part  11   s  for introducing the anode-off gas into the gas passage  11   c  extending from a suction port  11   a  on the center side to a scroll passage  11   b  around the first casing  11 , and a back-plate collar member  11   p  which is fitted and integrally fixed to the rear side of the scroll casing part  11   s , and defines a storage space of the impeller  13  in the gas passage  11   c.    
     As illustrated in  FIG. 2 , the back-plate collar member  11   p  includes a back-plate part  11   d  facing the back surface of the impeller  13 , a cylindrical part  11   f  forming a shaft hole  11   e  which opens in the center of the back-plate part  11   d , and a support  11   g  which is fixed with a plurality of bolts  17   b  to a front-end portion on the inner peripheral side of a second casing  12 , and a rotating shaft  14  penetrates into the shaft hole  11   e.    
     The back-plate collar member  11   p  is a member having a smaller thermal conductivity than the second casing  12 , at least the back-plate part  11   d  constitutes a substantially plate-shaped heat insulating part positioned on the back side of the impeller  13 , specifically, a substantially annular plate-shaped heat insulating part having an annular stepped surface facing both the outer peripheral surface of the back surface side and the back surface of the impeller  13 . 
     The back-plate part  11   d  and the cylindrical part  11   f  of the back-plate collar member  11   p  are airtight members respectively positioned in the vicinity of the shaft hole  11   e , and the back-plate part  11   d  of the back-plate collar member  11   p  is a high temperature side wall surface portion facing the back surface of the impeller  13  spaced at a predetermined clearance, thus, the cylindrical part  11   f  is the airtight cylindrical wall surface portion which forms the shaft hole  11   e.    
     The scroll casing part  11   s  is fastened to the second casing  12  by a plurality of bolts  17   c  via a fastening flange  11   j  welded so as to project the back side of the outer peripheral portion of the scroll casing part  11   s . Note that, it is considered that the heat insulating layer is provided in an annular space  18  formed between the back-plate collar member  11   p  and the fastening flange  11   j.    
     The second casing  12  has an interior space  21  in communication with the shaft hole  11   e  of the first casing  11  and is a bottomed tubular body which supports the rotating shaft  14  via a pair of bearings  22 A, 22 B, and has a rear end side (motor case portion) which stores a stator  15   s  of the motor  15  having a relatively large diameter relative to the front-end side (bearing box portion) which stores the bearings  22 A, 22 B. On the one hand, the rotating shaft  14  has a gradually reduced diameter from the impeller  13  side to the motor  15  side, and the impeller  13  and the rotating shaft  14  can be detached from the front side with respect to the second casing  12 . 
     As illustrated in  FIG. 3 , by the outer diameter of a rotor  15   r  of the motor  15  being smaller than the inner diameter of the front-end side of the second casing  12 , an integral rotating element whose rotation balance has been adjusted from the impeller  13  to the rotor  15   r  may be detached from the front side (left side in the drawing) with respect to the second casing  12  together with the back-plate collar member  11   p.    
     The second casing  12  is made of, for example, copper, a heatsink  23  having a large cooling area integrally joined to a copper rear end cover part  12   r  is fastened to the rear end of the second casing  12 , and a cooling fan  24  is mounted on the heatsink  23 . 
     The impeller  13  is integrally supported on the front-end side of the rotating shaft  14  while being stored to be freely rotatable in the first casing  11 , and has a wing shape which can boost the pressure in order to suck and recirculate an anode-off gas by integrally rotating with the rotating shaft  14 . 
     In the drawings, the impeller  13  has a plurality of blades  13   a  having a 3-dimensional twisted shape, but it is not limited to a specific shape, and may be any of the well-known centrifugal-compression types. However, a hub back surface part  13   b  of the impeller  13  should be hollow in order to reduce the cross-sectional area that contributes to heat transfer. 
     The rotating shaft  14  is inserted to be freely rotatable in the shaft hole  11   e  of the first casing  11 , and has a large diameter part  14   a  welded to a hub back surface part  13   b  of the impeller  13 , an intermediate diameter part  14   b  fitted to and supported on an inner ring of the pair of bearings  22 A, 22 B, and a small diameter part  14   c  which penetrates a rotation center part of the motor  15  and is integrally joined to the rotor  15   r.    
     Further, the purge gas passage  41  (part of the purge gas passage) which opens on the bearings  22 A, 22 B side relative to the back-plate part  11   d  (heat insulating part) of the back-plate collar member  11   p , and, on the outer peripheral surface in the vicinity of the rear end of the shaft hole  11   e  is formed in the rotating shaft  14 . The purge gas passage  41  forms a passage of the purge gas (hereinafter also referred to as shaft hole route) also in the rotating shaft  14 , apart from a passage of the purge gas (annular clearance, hereinafter also referred to as bearing route) that passes through a clearance between the rotor  15   r  and the stator  15   s  around the rotating shaft  14  and passes through the inside of the bearings  22 A, 22 B to the gas storage chamber  31  when the purge gas from the purge gas introduction means  16  is supplied from the rearward motor  15  side into the interior space  21  of the second casing  12 , so that the supply pressure of the purge gas can be introduced to the forward shaft hole  11   e  side from the bearings  22 A, 22 B. 
     The support  11   g  of the back-plate collar member  11   p  fastened to the second casing  12  is the airtight low temperature side surface portion positioned in the vicinity of the plurality of front-end side openings  41   a  of the purge gas passage  41 . 
     The back-plate collar member  11   p  and the impeller  13  are both made of materials having a high temperature strength and which can suppress deterioration of the material strength due to high temperature steam oxidation in order to be in contact with a humidified high temperature (for example, in the range of 750° C.) anode gas. The rotating shaft  14  may be formed from the same material. Examples of the material include Fe—Ni—Cr based alloy and Ni—Cr—Co based alloy, or, ceramics such as dense silicon carbide (SiC), silicon nitride (Si3N4) and sialon (SiAlON) having a porosity of 10% or less can be used. 
     The motor  15  is an electric rotational drive means which drives the rotating shaft  14  from the rear end side, for example, a 3-phase motor, and may have the well-known stator  15   s  and rotor  15   r . The arrangement of the windings, yoke, magnets, and the like in the motor  15  is not limited to a specific state. 
     The purge gas introduction means  16  introduces a gas having a higher pressure than that inside of the shaft hole  11   e  of the first casing  11  into the interior space  21  of the second casing  12  as a purge gas for removing the anode-off gas from the interior space  21  side, and the purge gas can be introduced into the interior space  21  of the second casing  12  in order to suppress the inflow of the anode-off gas from the gas passage  11   c  side of the first casing  11  into the shaft hole  11   e.    
     Since the SOFC2 anode-off gas contains carbon monoxide and moisture, the purge gas introduction means  16  is configured so as to continuously introduce the purge gas into the interior space  21  of the second casing  12  and continuously introduce the purge gas also into the forward side of the bearings  22 A, 22 B through an axial passage  41   c  described later in the rotating shaft  14  so that the shaft hole  11   e  of the first casing  11  is constantly in a gas-tight seal state. The purge gas introduction means  16  may change the amount of purge gas introduced per unit time, for example, in accordance with the rotational speed [rpm] of the impeller  13  which corresponds to the SOFC2 driving load. 
     Specifically, the purge gas introduction means  16  can fill a purge gas having a predetermined pressure capable of removing a residual gas (at the time of the initial operation, air) on the shaft hole  11   e  side of at least one bearing  22 A in the interior space  21  of the second casing  12 , for example, a fuel gas within the internal space  21  on the shaft hole  11   e  side of at least one of the bearings  22 A, in this case, the entirety of the interior space  21 , and can maintain the purge gas pressure within the interior space  21  at a higher pressure than the pressure of the back side of the impeller  13  within the shaft hole  11   e  and within the gas passage  11   c . Note that, the purge gas introduction means  16  may supply the purge gas at a substantially constant pressure, or the purge gas may be supplied at a pressure that is variably set in a stepwise manner or a pressure that is continuously and variably controlled. 
     The purge gas introduction means  16  will not be described in detail, but contains a fuel supply source which extracts a part of the fuel gas from the supply path, an introduction control valve which may adjust the purge gas pressure in accordance with the rotational speed [rpm] of the impeller  13  specifically, in accordance with the pressure within the interior space  21 , a purge gas introduction passage  42  formed in the rear end cover part  12   r  of the second casing  12 , and airtight pipes, fitting and the like which are not shown. The purge gas introduction passage  42 , the abovementioned airtight pipes and the like constitute the remainder of the purge gas passage positioned on the upstream side of the purge gas passage  41  and the like of two paths (bearing route and shaft hole route) inside and outside of the rotating shaft  14 . 
     The purge gas pressure which opposes the pressure within the shaft hole  11   e  and the pressure on the back side of the impeller  13  within the gas passage  11   c  can be variably set by selectively controlling an introduction control valve of the purge gas introduction means  16  based on the detected results (sensor detection information which is not shown) of the operating conditions, for example, the rotational speed [rpm] of the impeller  13  and the pressure within the interior space  21 , and a data map of the purge gas pressure obtained from the test results in advance within the specified range of operating conditions. 
     In the present embodiment, the target gas for blowing introduced into the gas passage  11   c  and boosted is an anode-off gas discharged from the fuel electrode  2   a  side as the SOFC2 exhaust gas, and the purge gas introduced into the shaft hole  11   e  side through the two paths inside and outside of the rotating shaft  14  in the interior space  21  of the second casing  12  contains the fuel components of the SOFC2. Certainly, the purge gas which is a dry seal gas may be nitrogen gas or another dry seal gas which does not contain the fuel component of the fuel cell. 
     Note that, the purge gas of the present invention is not limited to a fuel gas, and may be other gases such as nitrogen gas, air and the like, the blower of the present invention is not limited to the recirculation blower  5 , and may be the air blower  4  in which the target gas is air, or may be the gas blower  8  in which the target gas is the anode-off gas, and may boost and blow a gas other than the high temperature gas using the fuel cell. Further, the target gas of the present invention means a gas which is the target for blowing having an ordinary temperature, but in the present embodiment, the target gas is a gas heated to a temperature higher than room temperature, for example, is a high temperature gas heated to a temperature of several hundred degrees Celsius. 
     In the present embodiment, an annular gas storage chamber  31  surrounding the rotating shaft  14  on the rear end side of the shaft hole  11   e  is defined by a plurality of members including the back-plate collar member  11   p , the rotating shaft  14 , and the bearing  22 A, and the purge gas passage  41  communicates with the gas storage chamber  31 . Further, a thin cylindrical clearance passage  32  having a smaller radial clearance dimension than the annular gas storage chamber  31  is formed between the cylindrical part  11   f  which is the airtight cylindrical wall surface portion of the back-plate collar member  11   p  and the rotating shaft  14 . Furthermore, a thin plate-shaped clearance  33  expanding in the direction substantially orthogonal to the thin cylindrical clearance passage  32  and bent in a crank shape to the radially outward side is formed between the back surface of the impeller  13  and the back-plate collar member  11   p.    
     Moreover, when the purge gas is introduced in the interior space  21  of the second casing  12 , the aforementioned purge gas pressure is set so that the purge gas flows through the clearance passage  32  around the rotating shaft  14  in the shaft hole  11   e  to the gas passage  11   c  side of the first casing  11  within a predetermined flow amount range. 
     A front-end side opening  41   a  of the purge gas passage  41  is on the front side of the bearing  22 A and opens on the rear end side within the shaft hole  11   e , for example, between the large diameter part  14   a  of the front-end side of the rotating shaft  14  and the intermediate diameter part  14   b , and the other portions of the purge gas passage  41  continuing to the front-end side opening  41   a  extend along the radial and axial rearward sides of the rotating shaft  14 . 
     Specifically, one end side portion of the purge gas passage  41  penetrates in the radial direction and has a plurality of radial passages  41   b  which intersect each other at a predetermined angle (for example, 90°) at equal angular intervals so that the front-end side opening  41   a  opens in a plurality of locations on a stepped outer peripheral surface  14   d  between the large diameter part  14   a  and the intermediate diameter part  14   b  of the rotating shaft  14 , and the other portion is a single axial passage  41   c  extending from the intersecting portion of the plurality of radial passages  41   b  to the rear side in the axial direction of the rotating shaft  14 . 
     The plurality of radial passages  41   b  extend radially outward from a collection passage  41   d  positioned in the center of the large diameter part  14   a  of the rotating shaft  14 , the single axial passage  41   c  penetrates the axial center portion of the intermediate diameter part  14   b  and the small diameter part  14   c  from the collection passage  41   d  and opens on a rear end surface  14   r  of the rotating shaft  14 . In this case, as described above, by the supply pressure of the purge gas from the purge gas introduction means  16 , the purge gas is supplied around the rotating shaft  14  and into the purge gas passage  41  in the rotating shaft  14  within the interior space  21  and is supplied to the annular gas storage chamber  31  on the forward side of the bearing  22 A through a plurality of paths, thus, the parge gas having a predetermined pressure or higher is supplied into the shaft hole  11   e  in communication with the clearance  33  on the back surface side of the impeller  13 . Additionally, during the rotation of the motor  15 , the purge gas is urged radially outward by the centrifugal force accompanying the rotation of the plurality of radial passages  41   b  of the purge gas passage  41 , the sucking of the purge gas into the purge gas passage  41  is facilitated, and the purge gas having a predetermined pressure or higher within the shaft hole  11   e  in communication with the clearance  33  on the back side of the impeller  13  is reliably supplied. Moreover, during the operation of the recirculation blower  5 , regardless of the rotational speed of the rotating shaft  34  (even when rotation is stopped), the supply of the purge gas having a predetermined pressure or higher within the shaft hole  11   e  is maintained, and the internal gas is continuously replaced by the purge gas. 
     As illustrated in  FIG. 3 , a small diameter passage for cooling  41   e  having a smaller passage cross sectional area than both passages  41   c , 41   d  may be formed in the vicinity of the bearing  22 A in the axial direction of the rotating shaft  14  so that the collection passage  41   d  may communicate with the axial passage  41   c  in the vicinity of the center of the rotating shaft  14 . In this way, when the sucking of the purge gas into the purge gas passage  41  is facilitated during the rotation of the rotating shaft  14  in addition to the above-mentioned supply pressure of the purge gas from the purge gas supply means  16 , the flow velocity within the small diameter passage for cooling  41   e  becomes larger than the flow velocities around the axial passage  41   c  and within the collection passage  41   d . As a result, the heat transfer (convection) on the inner wall surface of the small diameter passage for cooling  41   e  is significantly increased, and thus, the bearing cooling efficiency can be increased due to the purge gas. 
     Further, the axial passage  41   c  on the other end side of the purge gas passage  41  is open on the surface extending radially of the rotating shaft  14  on the rear end side of the rotating shaft  14  from the bearing  22 A, for example, on the rear end surface  14   r , so as to be positioned on the radially inward side (rotation center side) from the stepped outer peripheral surface  14   d  on the front-end side of the rotating shaft  14 . Note that, in this case, the axial passage  41   c  of the purge gas passage  41  is open with a small diameter at the center of the rear end surface  14   r  of the rotating shaft  14 , but, for example, a tapered surface having a large diameter toward the rear side may be formed on the rear end inner peripheral part of the rotating shaft  14  so that the opening diameter of the other end becomes larger than the intermediate portion of the purge gas passage  41 . 
     The bearings  22 A, 22 B are, for example, angular ball bearing filled with an appropriate amount of grease, and are supported in the second casing  12  via support rings  25 A, 25 B on the outer sides. 
     Note that, the recirculation blower  5  has been used in the power generation system  1  provided with SOFC2 as an air blower for blowing a high temperature gas, thus, generally, it is necessary that 1) the shaft seal for the shaft hole  11   e  of the rotating shaft  14  of the impeller  13  is completely airtight, 2)since the power generation system  1  may be used as a distributed power source in remote areas, only the power supplied from the system itself is used, and 3) the recirculation blower  5  is compact since it can be installed as a distributed power source in ordinary homes and small apartments. 
     Next, the operation will be described. 
     In the recirculation blower  5  of the present embodiment configured as above, the purge gas having a high pressure is introduced into the interior space  21  of the second casing  12  in particular into the forward gas storage chamber  31  through the two paths inside and outside of the rotating shaft  14  of the impeller  13  by the purge gas introduction means  16 . Therefore, the anode-off gas introduced into the first casing  11  of the recirculation blower  5  can be suppressed from infiltrating within the shaft hole  11   e  of the back side of the impeller  13  by the high-pressure purge gas in the forward gas storage chamber  31  adjacent to the shaft hole  11   e  (annular clearance). 
     Further, in the present embodiment, when the purge gas introduction means  16  initially introduces and thereafter continuously introduces the purge gas into the interior space  21  of the second casing  12 , the pressure of the purge gas can generally be maintained at a higher pressure than the pressure within the shaft hole  11   e . Therefore, the anode-off gas on the gas passage  11   c  side of the first casing  11  is more effectively suppressed from flowing into the shaft hole  11   e  and from flowing into the interior space  21  of the second casing  12 . Further, even in the case when the bearing  22 A was cooled to the dew point (for example, 70° C. to 80° C.) or lower, the humidified anode-off gas does not infiltrate into the shaft hole  11   e  so that condensation in the vicinity of the bearing  22 A is effectively suppressed, and the elution of grease is effectively suppressed. 
     In addition, in the present embodiment, fuel gas is used in the purge gas for sealing, thus, a dedicated sealing fluid is not necessary and there is no need for numerous pipes, valves, and the like for a reliable shaft seal, thus, the recirculation blower  5  has a simple configuration, and the conventional problems that the miniaturization and cost reduction are difficult are eliminated. 
     In addition, the purge gas containing a SOFC2 fuel component flows at a predetermined flow amount through the clearance passage  32  in the periphery of the rotating shaft  14  within the shaft hole  11   e  to the gas passage side of the first casing, and merges with the anode-off gas, thus, the humidified anode-off gas within the first casing  11  is reliably suppressed from passing through the shaft hole  11   e  and entering into the interior space  21  of the second casing  12 , and the anode-off gas recirculated to SOFC2 does not become contaminated by the purge gas. 
     Further, in the present embodiment, the thin cylindrical clearance passage  32  in the shaft hole  11   e , the annular thin plate-shaped clearance  33  and the like expanding to the back side of the impeller  13  are formed on the airtight wall surface by the back-plate collar member  11   p , the impeller  13  and the rotating shaft  14 , thus, the dry gas seal function of the shaft hole  11   e  can be sufficiently ensured. Furthermore, the back-plate collar member  11   p  has an insulation function and the thermal conductivity area from the impeller  13  to the rotating shaft  14  is controlled to be small, thus, the thermal conductivity to the bearing  22 A can be more effectively suppressed. In addition, the second casing  12  and the support rings  25 A, 25 B are each formed of materials having a high thermal conductivity, thus, an effective heat removal from the bearings  22 A, 22 B to the second casing  12  side is possible, and a stable bearing performance can be ensured in combination with the effective suppression of the elution, etc., of grease from the bearings  22 A, 22 B. 
     Further, in the present embodiment, the annular gas storage chamber  31  into which the purge gas passage  41  opens is defined on the rear end side of the shaft hole  11   e , and the clearance passage  32  having a smaller radial clearance dimension than the annular gas storage chamber  31  is formed between the airtight cylindrical wall surface portion of the back-plate collar member  11   p  and the rotating shaft  14 . Therefore, during the initial operation, etc., the air within the gas storage chamber  31  where the bearing  22 A is exposed on the rear end side of the shaft hole  11   e  can be rapidly replaced with the purge gas, and the purge gas can be reliably filled within the gas storage chamber  31 . Further, the predetermined-pressure purge gas is supplied into the gas storage chamber  31  through the two paths inside and outside of the rotating shaft  14  in the interior space  21  by the purge gas introduction means  16 , and the introduction of the purge gas in the shaft hole route depending on the number of rotations of the impeller  13  is facilitated so that the internal residual gas is always replaced by the purge gas at a suitable flow amount. As a result, concerns such as the elution etc., of lubricant from the bearing  22 A due to condensation of the water vapor can be eliminated, and the dry gas seal performance of the shaft hole  11   e  can be stably ensured due to the purge gas regardless of pressure fluctuations of the anode-off gas due to load fluctuations on the impeller  13  side. 
     Further, in the present embodiment, the purge gas passage  41  is open on the outer peripheral surface of the front-end side of the rotating shaft  14  on the rear end side of the shaft hole  11   e  and on the shaft hole  11   e  side of the bearing  22 A, whereas the rear end of the purge gas passage  41  opens in the vicinity of the center of the rear end surface  14   r  of the rotating shaft  14 . Therefore, during the rotation of the rotating shaft  14 , the purge gas is urged radially outward by the centrifugal force accompanying the rotation of the radial passage  41   b  of the purge gas passage  41  on the front-end side of the bearing  22 A so as to be rapidly filled within the annular gas storage chamber  31 , and facilitate the sucking of the purge gas to the purge gas passage  41 . Further, regardless of changes in the number of rotations of the impeller  13 , the purge gas pressure acting within the shaft hole  11   e  can be maintained at the required pressure. Furthermore, the purge gas flows toward the annular gas storage chamber  31  from the back side to the front side in one direction so that the residual gas in the interior space  21  of the second casing  12  is reliably replaced with the purge gas. 
     Therefore, in the recirculation blower of the present embodiment 5, regardless of the operating conditions, it is possible to reliably suppress the humidified high temperature anode-off gas from infiltrating to the shaft hole  11   e  side, and, it is easy to reduce the size and cost. 
     Second Embodiment 
       FIG. 4  illustrates a blower according to a second embodiment of the present invention. 
     Note that, each embodiment described below has a composition and operation similar to the aforementioned first embodiment, thus, the features which are different from the first embodiment will mainly be described, and the features similar to previous embodiments are assigned the same reference numerals as the corresponding component illustrated in  FIGS. 1 and 2 , and a substantially overlapping description have been omitted. 
     As illustrated in  FIG. 4 , the blower of the second embodiment is provided with an approximately disc-shaped heat-insulated wall  37  between the first casing  11  and the second casing and adjacent to the back-plate collar member  11   p , an approximately cylindrical heat-insulated wall  38  surrounding the second casing  12 , an appropriately annular-plate mounting plate  12   f  intervening between the second casing  12  and the heat-insulated wall  37 , and a support cylinder  39  surrounding the cylindrical heat-insulated wall  38 , wherein the second casing  12  is a casing structure which is relatively vertical (long axis small diameter), and the outer peripheral surface is not exposed to the external environment. Further, the cylindrical heat-insulated wall  38  is made of, for example, ceramic fiber, and the predetermined-pressure purge gas is introduced into the cylindrical heat-insulated wall  38  from an outer purge gas passage  12   p  formed on the rear-end cover part  12   r  side of the second casing  12 , thereby effectively preventing the situation where the anode-off gas having high temperature and humidity infiltrates into the second casing  12  from the gas passage  11   c  side around the back-plate part  11   d  of the first casing  11  causing condensation. 
     Further, a rotating shaft  34  for supporting the impeller  13  to be freely rotatable is a large diameter part  34   a  having a maximum diameter at a central portion between the bearings  22 A, 22 B without a gradual decrease in the diameter from the front-end side to the rear end side such as with the rotating shaft  14  of the first embodiment, a pair of intermediate diameter parts  34   b  supported by the bearings  22 A, 22 B on both sides have substantially the same diameter, and small diameter parts  34   c , 34   e  on both sides have a smaller diameter. 
     An intermediate diameter part  34   b  on the front-end side is inserted in the shaft hole  11   e , and the impeller  13  is fastened and fixed to the small diameter part  34   c  on the front-end side. 
     Moreover, a plurality of members including the back-plate collar member  11   p , the rotating shaft  34  and the bearing  22 A defines the annular gas storage chamber  31  surrounding the rotating shaft  34  in the vicinity of the shaft hole  11   e  on the rear end side of the shaft hole  11   e , and a large portion of the annular gas storage chamber  31  is positioned on the outside in the radial direction relative to the thin cylindrical clearance passage  32  within the shaft hole  11   e.    
     A motor  35  which rotatably drives the impeller  13  via the rotating shaft  34  has a rotor  35   r  and a stator  35   s  that are vertically or longitudinally long compared to the motor  15  in the first embodiment. 
     The arrangement of the windings, yoke, magnets, and the like in the motor  35  is not limited to a specific state in the same manner as the motor  15  in the first embodiment. 
     Furthermore, the rear end cover part  12   r  of the second casing is further provided with a hermetic connector  45  for airtightly pulling out and connecting electric wires of the motor  35  to the outside, a temperature sensor  46  for detecting the temperature of the bearings and the motor within the second casing  12  in addition to a purge gas introduction pipe, hose, or the like not shown for connecting the purge gas introduction passage  42  to an external purge gas supply source. 
     In the present embodiment, it is possible to obtain the operation and effect in the same manner as the first embodiment. 
     Third Embodiment 
       FIG. 5  illustrates a blower according to a third embodiment of the present invention. 
     As illustrated in  FIG. 5 , while the blower of the third embodiment is provided with an approximately disc-shaped heat-insulated wall  37  adjacent to the back-plate collar member  11   p , the approximately cylindrical heat-insulated wall  38  surrounding the second casing  12 , and the support cylinder  39  surrounding the cylindrical heat-insulated wall  38  between the first casing  11  and the second casing  12  in the same manner as the second embodiment, the second casing  12  has a relatively short axis and large diameter. Further, the support cylinder  39  is supported on a fixed support stand  36 . 
     Further, the rotating shaft  34  for supporting the impeller  13  to be freely rotatable has a maximum diameter at the central portion of the axis between the bearings  22 A, 22 B in the same manner as the second embodiment, and has substantially the same diameter at the portion supported by the bearings  22 A, 22 B. 
     Furthermore, although in the cases of the first and the second embodiments, the second casing  12  is not cooled by the heatsink  23  and a cooling fan  24  on the rear end side, a plurality of folded cooling passages  43  containing at least a pair of vertical passages  43   a , 43   b  and a horizontal passage  43   c  connected to the pair of vertical passages  43   a , 43   b  are formed in the second casing  12 , and a collection pipe  52 , hoses  53 , 54  and the like which connect these cooling passages  43  to the supply source side of an external medium for cooling are provided. Moreover, the second casing  12  can be cooled by passing a medium for cooling, for example, coolant through the folded cooling passages  43 . 
     Further, the present embodiment is constituted so that the purge gas introduction means  16  opens in the center of the rear end cover part  12   r  of the second casing  12  to mount a purge gas introduction tube  47  extending in the motor rotating shaft direction, and introduces the purge gas into the interior space  21  therethrough. Moreover, a hermetic connector  48  or the like for airtightly pulling out and connecting the wiring of the motor  35  to the outside is mounted on the outer end side of the purge gas introduction tube  47 . 
     In the present embodiment, it is possible to obtain the operation and effect in the same manner as the first embodiment. 
     Fourth Embodiment 
       FIGS. 6 to 8  show a small-size and high-speed blower according to a fourth embodiment of the present invention. 
     The recirculation blower  5  of the present embodiment is configured so as to boost and blow an anode-off gas having a high temperature discharged from the fuel electrode  2   a  of SOFC2. 
     As shown in  FIGS. 6 and 7 , in the blower  5  of the fourth embodiment, the heat-insulated wall  37 , in which the back plate collar member  11   p  made of ceramic fiber or the like and the mounting plate  12   f  are combined, is integrally connected to the second casing  12  by a plurality of bolts  17   b  fitted in the heat-insulated wall  37  on the back side of the first casing  11  for storing the impeller  13 . The first casing  11  and the support cylinder  39  are integrally connected to the second casing  12  that stores the motor  35  via a plurality of bolts  17   d  fastened to the rear end cover part  12   r . The heat-insulated wall  37  is a substantially plate-like body positioned on the back surface side of the impeller  13 , and the rotating shaft  34  penetrates the circular central portion thereof. 
     Further, the rotating shaft  34  for supporting the impeller  13  to be freely rotatable is a large diameter part  34   a  having a maximum diameter on one side portion between the bearings  22 A, 22 B and close to the bearing  22 A, and the rotor  35   r  of the motor  35  is integrally mounted to the other side portion  34   e . Middle diameter parts  34   b  on the inner and outer sides of the bearings  22 A, 22 B have substantially the same diameter and are supported to be freely rotatable by the second casing  12  via the bearings  22 A, 22 B. Further, a small diameter part  34   c  on the front-end side of the rotating shaft  34  is integrally connected to the impeller  13 . 
     Here, the two bearings  22 A, 22 B are arranged in the vicinity of both ends of the stator  35   s  in the axial direction of the motor  35 , and the rotor  35   r  of the motor  35  is supported by both sides with respect to the second casing  12  via both bearings  22 A, 22 B so that the resonance of the impeller  13  and the rotating shaft  34  (rotating portion) in a wide rotational speed range up to a high rotational speed (for example, 100,000 rpm) can be effectively prevented. 
     Further, in the rotating shaft  34 , an axial purge gas passage  41  for introducing the purge gas through the shaft into the shaft hole  11   e  side from the bearings  22 A, 22 B within the interior space  21  is formed, in addition to the purge gas path of the bearing route around the rotating shaft  34 . A part of the purge gas passage  41  is formed so as to open radially outward toward the inner peripheral surface side of the bearing  22 A on one side close to the impeller  13 . 
     Specifically, a part of the purge gas passage  41  positioned on the front side in the axial direction of the rotating shaft  34  near the impeller  13  has a first groove part that opens concavely and radially outward toward an inner ring  22   ir  of the bearing  22 A, for example, an annular groove part  41   g  extending in the circumferential direction and a plurality of vertical groove-shaped second groove parts  41   a  extending from the first groove part  41   g  toward the shaft hole  11   e  side. The plurality of second groove parts  41   a  open on the outer peripheral surface of the rotating shaft  34  exposed between the heat-insulated part  37  and the bearing  22 A, for example, at equal angular intervals of 90 degrees. 
     Further, a part of the purge gas passage  41  is configured to include a plurality of radial passages  41   b  penetrating in the radial direction of the rotating shaft  34  so as to open on the inner bottom surface side of the annular groove part  41   g , and a collection passage  41   d  connected at predetermined angular intervals to the inner end sides of the plurality of radial passages  41   b . The collection passage  41   d  is communicatively connected to the axial passage  41   c  extending on the rear side of the collection passage  41   d  in the axial direction of the collection passage  41   d.    
     Although the plurality of radial passages  41   b  intersect at equal angular intervals of, for example, 90° in the same manner of the plurality of second groove parts  41   a , the arrangement angle positions are different by 45° with respect to the plurality of second groove parts  41   a , respectively. As shown in  FIG. 8 , the purge gas supplied radially outward from the collection passage  41   d  of the purge gas passage  41  through the plurality of radial passages  41   b  is in direct contact with the entire circumference on the inner peripheral surface side with respect to the inner ring  22   ir  of the bearing  22 A so that the inner ring  22   ir  can be cooled. In the figure, for example, assuming that the arrangement angle positions of the plurality of radial passages  41   b  are 0°, 90°, 180°, and 270°, the arrangement angle positions of the plurality of second groove parts  41   a  are 45°, 135°, 225°, and 315°. 
     Further, in the same manner of the third embodiment, the embodiment is provided with the purge gas introduction means  16  that opens in the center of the rear end cover part  12   r  of the second casing  12  to mount the purge gas introduction tube  47  extending in the motor rotating shaft direction, and introduces the purge gas into the interior space  21  via the purge gas passage penetrating, for example, the pipe wall or the like of the purge gas introduction tube  47  not shown in detail. The supply pressure of the purge gas described above is set to the extent that the purge gas can flow into the gas passage  11   c  side of the first casing  11  via the clearance passage  32  around the rotating shaft  14  in the shaft hole  11   e  at a predetermined flow amount (for example, 1 L (liter)-30 L/min) effective for cooling the bearing  22 A when the purge gas (for example, fuel gas at room temperature) is supplied to the interior space  21  of the second casing  12  by the purge gas introduction means  16  and the purge gas is introduced into the gas storage chamber  31  through a plurality of paths inside and outside the rotating shaft  34 . A hermetic connector  48  or the like for airtightly pulling out and connecting the wiring of the motor  35  to the outside is mounted on the outer end side of the purge gas introduction tube  47 . 
     Note that, for example, a plurality of O-rings or the like are externally mounted to the rear-side bearing  22 B on the outer ring side supported by the second casing  12  to restrict the rotation of the outer ring a core float-shaped support ring  25 B in which a lubricant is applied between the O-rings, and further the bearing  22 B is urged toward the bearing  22 A by a thrust load generating ring  28 . Further, the support ring  25 A that supports the outer ring of the bearing  22 A is abutted in the axial direction with respect to the substantially annular plate-shaped mounting plate  12   f  so as to restrict the forward movement of the bearing  22 A, and is prevented from rotating by a positioning pin or the like embedded in the mounting plate  12   f . Therefore, the rotating shaft  34  is configured so that the large diameter part  34   a  that is one side portion between the bearings  22 A, 22 B and the other side portion  34   e  are positioned axially by the bearings  22 A, 22 B, and the rotating shaft  34  is supported to be freely rotatable in an aligned state. 
     In the present embodiment, a plurality of vertical groove-shaped second groove parts  41   a , which are openings on the front-end side of the purge gas passage  41 , open on an outer peripheral surface of the intermediate diameter part  34   b  positioned on the front side of the rotating shaft  34 , on the front side of the bearing  22 A and on the rear end side of the shaft hole  11   e . The annular groove part  41   g , which is connected to the second groove parts  41   a , opens radially outward over the entire circumferential direction of the rotating shaft  34  at a predetermined groove width in the vicinity of the center of the axial length region of the bearing  22 A. The plurality of radial passages  41   b  in communication with the annular groove part  41   g  are communicably connected to the axial passage  41   c  on the rear side in the axial direction via the collection passage  41   d.    
     Therefore, when the purge gas introduction means  16  operates to supply the purge gas to the interior space  21  of the second casing  12  at a supply pressure according to the rotational speed of the motor  35  during operation of the recirculation blower  5 , the purge gas having a predetermined pressure or higher is surely introduced into the shaft hole  11   e  and the gas storage chamber  31  in communication with the clearance  33  on the rear surface side of the impeller  13  through the plurality of paths inside and outside of the rotating shaft  34 . 
     At this time, the purge gas introduced into the purge gas passage  41  directly cools the vicinity of the center of the axial length region of the bearing  22 A while the purge gas is supplied between the shaft hole  11   e  and the bearing  22 A. Further, the internal gas is continuously replaced by the purge gas, and the purge gas having a predetermined pressure is introduced on the right side in  FIG. 1  of the shaft hole  11   e , so that an effective back pressure is generated to oppose the infiltration of the anode-off gas boosted according to the rotational speed of the impeller  13  into the shaft hole  11   e  and the infiltration thereinto of the anode-off gas having high temperature and humidity is effectively suppressed. Further, in the present embodiment, since the purge gas can be a fuel gas, it is possible to flow the purge gas from the shaft hole  11   e  to the gas passage  11   c  side of the first casing  11  at an effective flow amount for cooling the bearing  22 A. 
     As a result, the conventional concern that, depending on the operational state of the recirculation blower  5 , a humidified anode-off gas may infiltrate into the shaft hole  11   e  or reduce the bearing performance can be eliminated, the operation and effect can be obtained in the same manner as the first embodiment, and the cooling efficiency on the inner ring  22   ir  side of the bearing  22 A, which has not been easily cooled, can be remarkably improved. 
     Fifth Embodiment 
       FIG. 9  shows a small-size and high-speed blower according to a fifth embodiment of the present invention. 
     The recirculation blower  5  of the present embodiment is configured to boost and blow the high temperature anode-off gas discharged from the fuel electrode  2   a  of SOFC2. 
     As shown in  FIG. 9 , the blower  5  of the fifth embodiment is provided with a heat-insulated wall  68  in which the back plate collar member  11   p  and a thick mounting plate  67  are integrally formed on the back surface side of the first casing  11  which stores the impeller  13 . The heat-insulated wall  68  is integrally connected to the second casing  12  by a plurality of bolts  17   c.    
     The mounting plate  67  of the heat-insulated wall  68  surrounds the rotating shaft  34  with a predetermined radial clearance from the rotating shaft  34  between the back plate collar member  11   p  and the bearing  22 A, so that the annular gas storage chamber  31  surrounding the rotating shaft  34  is defined between the shaft hole  11   e  of the first casing  11  and the bearing  22 A. 
     The back plate collar member  11   p  of the heat-insulated part  68  is an airtight wall surface that is positioned at least in the vicinity of the shaft hole  11   e  and has a thermal conductivity lower than that of the second casing  12 . Further, in almost the same way of the back plate collar member  11   p  in the first embodiment, the heat-insulated part  68  has a back plate part  11   d  (high temperature side wall surface part) facing the back surface of the impeller  13  with a clearance, a cylindrical part  11   f  (cylindrical wall surface part) forming the shaft hole  11   e , and a support part  11   h  (low temperature side wall surface part) on which the outer ring of the bearing  22 A is abutted and supported. 
     Further, the heat-insulated wall  68  is provided with at least one purge gas introduction passage  61  having an inlet on the outer end side and extending radially (in a radial direction) from the gas storage chamber  31 , and an inner end of the purge gas passage  61  opens in the vicinity of the outer ring abutting part  11   h . The purge gas is introduced directly into the gas storage chamber  31  (without passing through the rotating shaft  34 ) from an external purge gas introduction means  66  through the purge gas introduction passage  61 . 
     In almost the same way of the purge gas introduction means  16  of the first embodiment, the purge gas introduction means  66  introduces a gas having a higher pressure than that in the shaft hole  11   e  of the first casing  11  through the purge gas introduction passage  61  and the gas storage chamber  31  into the second casing  12 , so that when the purge gas is introduced into the gas storage chamber  31 , the inflow of the anode-off gas having high temperature and humidity from the gas passage  11   c  side of the first casing  11  into the shaft hole  11   e  is suppressed. 
     That is, also in the present embodiment, the purge gas having a predetermined pressure is introduced into the inner side (right side in  FIG. 9 ) of the shaft hole  11   e  of the first casing  11  so that an effective back pressure is generated to oppose the infiltration of the anode-off gas boosted according to the rotational speed of the impeller  13  into the shaft hole  11   e , thereby effectively suppress the infiltration of the anode-off gas having high temperature and humidity. Further, it is also possible to flow the purge gas from the shaft hole  11   e  into the gas passage  11   c  side of the first casing  11  by using the purge gas that is a fuel gas. 
     Note that, in the present embodiment, the gas in the interior space  21  can be continuously replaced with the purge gas while the purge gas introduced into the inside of the second casing  12  by the purge gas introduction means  66  via the purge gas introduction passage  61  and the gas storage chamber  31  forms a flow in the opposite direction to that of each of the above-described embodiments. Specifically, the purge gas introduced into the second casing  12  flows in the interior space  21  from the gas storage chamber  31  side to the motor  35  side through the bearing  22 A (a passage that bypasses the bearing  22 A, for example, an inclined passage that opens at both ends in both the radial and axial directions of the bearing  22 A may be used together), and the purge gas is discharged out from a purge gas passage  62  that also serves as the motor wiring hole of the rear end cover part  12   r  through a clearance such as periphery of the rotor  35   r . Further, at least at the start of use, a purge gas replacement outlet  63  is fully opened until the air in the second casing  12  which is a bearing box is replaced with the purge gas. 
     Note that in  FIG. 9 , the rotating shaft  34  is provided with a fastening ring  27  with a brim, which is positioned in the gas storage chamber  31  and fastens and fixes the inner ring of the bearing  22 A to the rotating shaft  34 . With the fastening ring  27  having a brim, it is possible to effectively guide the flow of the purge gas flowing into the gas storage chamber  31  to the bearing  22 A side and generate an effective back pressure to oppose the above-mentioned infiltration of the anode-off gas into the shaft hole  11   e.    
     Also, in this embodiment, the same effect as in each of the above-described embodiments can be obtained. 
     Note that, in each of the above embodiments, it was described that the blower of the present invention recirculates a SOFC anode-off gas, but as stated above, the blower of the present invention may be used as a blower for boosting an anode-off gas other than a recirculation blower or a blower for boosting a high temperature cathode-off gas. Therefore, the purge gas can make the target gas for blowing as a main component, and can use a so-called inert gas such as nitrogen. 
     Furthermore, the blower of the present invention can be applied to a hydrogen production system by a Solid Oxide Electrolysis Cell (SOEC) in which a blower which compresses and recirculates a humidified hydrogen gas to a fuel electrode, and can be applied to other blowers which can boost a target gas, and can ensure the uniformity of the temperature inside various heat treatment furnaces and firing furnaces and improve the heating efficiency. 
     Further, in each of the above-described embodiments, the purge gas supplied at a predetermined supply pressure into the interior space  21  of the second casing  12  is supplied to the gas storage chamber  31  through a plurality of paths including a first supply path (bearing route) around the rotating shaft  14  or  34  integrally coupled with the impeller  13  and a second supply path (shaft hole route) passing through the purge gas passage  41  inside the rotating shaft  14  or  34 . However, for example, when the temperature of the bearing  22 A to be cooled is not so high, it goes without saying that it is also conceivable to form a vertical groove or a purge gas passage passing through the outer side of the bearings  22 A, 22 B in the support pipes  25 A, 25 B supporting the bearings  22 A, 22 B or the second casing  12  that is a bearing box instead of passing the purge gas through the bearings  22 A, 22 B. 
     As described above, the present invention can provide a blower which can reliably suppress a gas to be blown from infiltrating into the shaft hole side, and, a small size and cost reduction is simple, and thus, is useful in all blowers suitable for boosting and blowing a gas to be blown from a fuel cell, an electrolytic cell and the like. 
     REFERENCE SIGNS LIST 
     
         
           1  power generation system 
           2  SOFC (solid oxide fuel cell) 
           2   a  fuel electrode (anode) 
           2   b  air electrode (cathode) 
           3  MGT (micro gas turbine) 
           4  air blower 
           5  recirculation blower (blower) 
           6  combustor 
           7  inverter 
           8  gas blower 
           9  heat exchanger 
           10  first casing 
           11   a  suction port 
           11   b  scroll passage 
           11   c  gas passage 
           11   d  back-plate part (high temperature side surface portion) 
           11   e  shaft hole 
           11   f  cylindrical part (cylindrical wall surface portion) 
           11   g  support (low temperature side surface portion) 
           11   p  back-plate collar member 
           11   s  scroll casing part 
           12  second casing 
           12   r  rear end cover part 
           13  impeller 
           14 ,  34  rotating shaft 
           14   d  stepped outer peripheral surface 
           14   r  rear end surface 
           15 ,  35  motor 
           16  purge gas introduction means 
           21  interior space 
           22 A, 22 B bearing 
           23  heatsink 
           24  cooling fan 
           31  gas storage chamber (annular gas storage chamber) 
           32  clearance passage (thin cylindrical clearance passage) 
           41  purge gas passage (part of purge gas introduction passage) 
           41   a  front-end side opening (second groove part) 
           41   b  radial passage (plurality of radial passage) 
           41   c  axial passage 
           41   d  collection passage 
           41   e  small diameter passage for cooling 
           41   g  annular groove part (first groove part) 
           42  purge gas introduction passage (remainder of purge gas 
         introduction passage) 
           47  purge gas introduction tube 
           48  hermetic connector 
           61  purge gas introduction passage 
           66  purge gas introduction means 
           67  mounting plate 
         L 1  fuel supply line 
         L 2  air supply line 
         L 3  recirculation line