Patent Publication Number: US-10774747-B2

Title: Micro gas turbine system

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a micro gas turbine system. 
     2. Description of the Related Art 
     Conventionally, small gas turbine systems capable of providing a low temperature heat source have been known. For example, Japanese Unexamined Patent Application Publication No. 2001-152871 discloses a small gas turbine apparatus  300  as illustrated in  FIG. 7 . The small gas turbine apparatus  300  includes a first rotating mechanism including a first compressor  303  and a first expansion turbine  307 , and a second rotating mechanism including a second compressor  313  and a second expansion turbine  316 . The second compressor  313  receives and compresses a part of air compressed by and outputted from the first compressor  303 . The second expansion turbine  316  expands the air compressed by the second compressor  313 . Exhaust from the second expansion turbine  316  is usable as a low temperature heat source. 
     As another example, International Publication No. 2011/152049 discloses a gas turbine system  500  suitable for in-vehicle use as illustrated in  FIG. 8 . The gas turbine system  500  includes a gas turbine apparatus  502 , a cooling fluid generating apparatus  505 , an air conditioning unit  506 , and a heat exchanger  507 . The gas turbine apparatus  502  includes a first compressor  521  and a first expansion turbine  523 , which are connected to each other via a first shaft  522 ; a burner  526 ; and a regenerated heat exchanger  527 . Further, the gas turbine apparatus  502  includes a generator  524  connected to the first shaft  522 . The cooling fluid generating apparatus  505  includes a second compressor  551  and a second expansion turbine  553 , which are connected to each other via a second shaft  552 ; a cooler  55 ; and a water separator  556 . Further, the cooling fluid generating apparatus  505  includes a generator  554  connected to the second shaft  552 . The cooling fluid generating apparatus  505  is provided with a carburetor  557  upstream of the cooler  555 . The air conditioning unit  506  includes a mixer  562  and a blower  561 . 
     The first compressor  521  takes in and compresses air taken from atmospheric air. High pressure air discharged from the first compressor  521  flows into the regenerated heat exchanger  527  and then flows into the burner  526 . The combustion gas generated in the burner  526  flows into and expands in the first expansion turbine  523 . Thereby, the pressure of the combustion gas drops down to a level around the atmospheric pressure. The combustion gas discharged from the first expansion turbine  523  flows into the regenerated heat exchanger  527 . In the regenerated heat exchanger  527 , the combustion gas and high pressure air before flowing into the burner  526  exchange heat. The second compressor  551  is connected to one end of an air-extraction passage  504  for extracting air (extracted air) boosted by the first compressor  521  from the gas turbine apparatus  502 . The second compressor  551  receives and compresses the extracted air. High pressure air discharged from the second compressor  551  passes through the carburetor  557  and the cooler  555 . In the carburetor  557 , the temperature of high pressure air discharged from the second compressor  551  drops due to vaporization heat of the fuel. High pressure air flowing out from the cooler  555  flows into and expands in the second expansion turbine  553 . Thereby, the pressure of the high pressure air drops down to a level around the atmospheric pressure. Cool air (cooling fluid) is generated by expansion of the air in the second expansion turbine  553 . The air discharged from the second expansion turbine  553  passes through the water separator  556  and then is fed to the air conditioning unit  506 . The water separator  556  separates moisture from the air discharged from the second expansion turbine  553 . 
     Air discharged from the second expansion turbine  553  is mixed with air supplied from the blower  561  in the mixer  562  and thereby is adjusted to a desired temperature. The adjusted air is fed to the heat exchanger  507 . The heat exchanger  507  causes heat exchange between the adjusted air flowing out from the mixer  562  and the combustion gas flowing out from the regenerated heat exchanger  527  mentioned above and thereby heats the adjusted air flowing out from the mixer  562  to a temperature suitable for air conditioning. Then, the air heated by the heat exchanger  507  is supplied to a cabin. However, when cooling, the air adjusted by the air conditioning unit  506  to a temperature suitable for a demanded temperature in air conditioning also may be supplied directly to the cabin without passing through the heat exchanger  507 . Thus, the air discharged from the second expansion turbine  553  in the gas turbine system  500  is utilized for air conditioning in the cabin. 
     SUMMARY 
     Techniques described in Japanese Unexamined Patent Application Publication No. 2001-152871 and International Publication No. 2011/152049 still have room for improvement from the viewpoint of enhancing the thermal efficiency. In view of this, one non-limiting and exemplary embodiment of the present disclosure provides a micro gas turbine system which is advantageous in enhancing the thermal efficiency. 
     In one general aspect, the techniques disclosed here feature a micro gas turbine system comprising: a micro gas turbine apparatus including: a first compressor that receives and compresses a working fluid; a burner that generates a combustion gas by injecting a fuel into the working fluid discharged from the first compressor; and a first turbine that is connected to the first compressor via a first shaft, and that expands the combustion gas generated by the burner, and an extracting cycle apparatus including: a second compressor that receives extracted air being a part of the working fluid discharged from the first compressor and that compresses the received extracted air as a working fluid; and a second turbine that is connected to the second compressor via a second shaft, and that expands the working fluid discharged from the second compressor, in which the micro gas turbine apparatus uses the working fluid expanded by the second turbine and discharged from the second turbine to cool down at least a portion of the first turbine or to cool down the working fluid to be fed to the first compressor. 
     The above micro gas turbine system is advantageous in enhancing the thermal efficiency. 
     Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefit and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a configuration diagram of a micro gas turbine system according to a first embodiment; 
         FIG. 2  is a perspective cross-sectional view illustrating an inner structure of a first turbine according to the first embodiment; 
         FIG. 3  is a perspective view of a turbine nozzle ring illustrated in  FIG. 2 ; 
         FIG. 4  is a perspective cross-sectional view illustrating an inner structure of a nozzle blade illustrated in  FIG. 3 ; 
         FIG. 5  is a configuration diagram of a micro gas turbine system according to a second embodiment; 
         FIG. 6  is a configuration diagram of a micro gas turbine system according to a third embodiment; 
         FIG. 7  is a configuration diagram of a conventional small gas turbine apparatus; and 
         FIG. 8  is a configuration diagram of a conventional gas turbine system. 
     
    
    
     DETAILED DESCRIPTION 
     Findings Based on Consideration of the Present Inventors 
     Japanese Unexamined Patent Application Publication No. 2001-152871 states that exhaust of a second expansion turbine  316  may be used as a low temperature heat source, but does not make specific consideration on the method of using exhaust of the second expansion turbine  316 . International Publication No. 2011/152049 states that the cool air generated by expanding air in the second expansion turbine  553  is used for air conditioning of the vehicle, but does not make consideration on use of the cool air in applications other than air conditioning of the vehicle. 
     The gas turbine exhibits higher thermal efficiency as a gas turbine inlet temperature (temperature of a combustion gas flowing into the gas turbine) becomes higher. However, when the gas turbine inlet temperature is too high, the turbine located downstream of the burner in a flow of the combustion gas may be burnt and damaged. In this regard, a large gas turbine prevents burning of the turbine by cooling the turbine with a working fluid. Most of large gas turbines are provided with multiple stages of axial compressors and multiple stages of axial turbines. In this case, a working fluid at a specific ratio is extracted from a compressor suitable for a pressure of a working fluid flowing in a turbine to be cooled, and the extracted working fluid bypasses the burner and flows into the turbine suitable for the pressure of the extracted air to cool down the turbine. For example, among the multiple stages of axial turbines, a high pressure turbine disposed just after the burner is cooled down by receiving a flow of a working fluid extracted from a high pressure compressor located at a later stage among the multiple stages of axial compressors. In this case, the working fluid extracted from the high pressure compressor is cooled down as necessary. For example, a low pressure turbine at a later stage among the multiple stages of axial turbines is cooled down by receiving a flow of a working fluid extracted from a low pressure compressor located at an earlier stage among the multiple stages of axial compressors. This is because, in terms of state quantity, the working fluid passing through the low pressure turbine becomes a lower pressure than a pressure of a working fluid passing through the high pressure turbine. 
     On the other hand, the micro gas turbine is an inexpensive ultra-small gas turbine having a small and simplified construction including a high speed generator with a power generation output of approximately 200 kW or lower and the number of revolutions of 80,000 to 120,000 per minute. The micro gas turbine is usually used in an application where power is generated with simple handling. Unlike a large gas turbine, the micro gas turbine has to meet very high requirements of reducing the manufacturing cost and minimizing dimensions. Therefore, a typical micro gas turbine includes a centrifugal compressor and a radial turbine, in other words, a single stage of compressor and a single stage of turbine. When the micro gas turbine is exclusively used for power generation, a turbine inlet temperature needs to be raised to enhance thermal efficiency as in the large gas turbine. However, the turbine inlet temperature in the micro gas turbine is kept lower than the turbine inlet temperature of the large gas turbine. This is because the micro gas turbine is not configured to cool the turbine unlike the large gas turbine. One of the reasons that the micro gas turbine is not configured to cool the turbine is one of characteristics of the centrifugal compressor. The centrifugal compressor can more easily achieve a high pressure ratio in a single stage than the axial compressor. However, when the centrifugal compressor and the axial compressor under the same intake conditions at the same pressure ratio are compared with each other, a mass flow rate of the working fluid of the centrifugal compressor is apt to be smaller than mass flow rate of the working fluid of the axial compressor. If a part of the working fluid which has passed through the centrifugal compressor is extracted for cooling down the turbine, the micro gas turbine may fail to maintain a desired cycle efficiency due to insufficient output of the turbine. Even if a part of the working fluid which has passed through the centrifugal compressor is extracted for cooling down the turbine, the flow rate of the working fluid to be extracted is inevitably low. Conventional micro gas turbines are not provided with an apparatus or a structure that appropriately cools down the extracted working fluid for the purpose of cooling the turbine. For those reasons, it was considered that even if a part of the working fluid which has passed through the centrifugal compressor is extracted, the extracted working fluid does not have a flow rate, flow velocity, pressure, and temperature required to cool down the turbine and therefore cannot cool down the turbine in an appropriate manner. However, the present inventors found that parts of the turbine in the micro gas turbine can be cooled down by using the working fluid discharged from a turbine in an extracting cycle apparatus. The present inventors also found that thermal efficiency of the micro gas turbine system is drastically enhanced by cooling down parts of the turbine in the micro gas turbine with the working fluid discharged from the turbine in the extracting cycle apparatus. In addition, the present inventors found that thermal efficiency of the micro gas turbine system is also enhanced by cooling down a working fluid to be fed to a compressor of the micro gas turbine with a working fluid discharged from the turbine in the extracting cycle apparatus. A micro gas turbine system of the present disclosure is designed based on the findings of the present inventors. 
     A first aspect of the present disclosure provides a micro gas turbine system comprising: a micro gas turbine apparatus including: a first compressor that receives and compresses a working fluid; a burner that generates a combustion gas by injecting a fuel into the working fluid discharged from the first compressor; and a first turbine that is connected to the first compressor via a first shaft, and that expands the combustion gas generated by the burner, and an extracting cycle apparatus including: a second compressor that receives extracted air being a part of the working fluid discharged from the first compressor and that compresses the received extracted air as a working fluid; and a second turbine that is connected to the second compressor via a second shaft, and that expands the working fluid discharged from the second compressor, in which the micro gas turbine apparatus uses the working fluid expanded by the second turbine and discharged from the second turbine to cool down at least a portion of the first turbine or to cool down the working fluid to be fed to the first compressor. 
     Another representation of the first aspect of the present disclosure is a micro gas turbine system comprising:
         a first passage in which a working fluid flows;   a first compressor that is present on the first passages;   a first turbine that is present on the first passage and that is connected to the first compressor via a first shaft;   a burner that is present on the first passage between the first compressor and the first turbine;   a second passage in which the working fluid flows, the second passage branching from a branching point in the first passage, the branching point being located between the first compressor and the burner in the first passage;   a second compressor that is present on the second passage; and   a second turbine that is present on the second passage and that is connected to the second compressor via a second shaft, wherein the first turbine includes   a turbine wheel that is rotatably connected to the first shaft; and   a nozzle blade that is disposed outside the turbine wheel in a radial direction of the turbine wheel and that is located around the turbine wheel,   the nozzle blade has a passage therein,   the passage in the nozzle blade constitutes the second passage, and   the nozzle blade is cooled by the working fluid that has passed through the second turbine.       

     Further another representation of the first aspect of the present disclosure is a micro gas turbine system comprising:
         a first passage in which a working fluid flows;   a first compressor that is present on the first passages;   a first turbine that is present on the first passage and that is connected to the first compressor via a first shaft;   a burner that is present on the first passage between the first compressor and the first turbine;   a second passage in which the working fluid flows, the second passage branching from a branching point in the first passage, the branching point being located between the first compressor and the burner in the first passage;   a second compressor that is present on the second passage;   a second turbine that is present on the second passage and that is connected to the second compressor via a second shaft; and   a heat exchanger that is commonly present on a first part of the first passage and a second part of the second passage, wherein   the first part of the first passage is located upstream of the first compressor in a flowing direction of the working fluid in the first passage, and   the second part of the second passage is located downstream of the second turbine in the flowing direction of the working fluid in the second passage.       

     Further another representation of the first aspect of the present disclosure is a micro gas turbine system comprising:
         a first passage in which a working fluid flows;   a first compressor that is present on the first passages;   a first turbine that is present on the first passage and that is connected to the first compressor via a first shaft;   a burner that is present on the first passage between the first compressor and the first turbine;   a second passage in which the working fluid flows, the second passage branching from a branching point in the first passage, the branching point being located between the first compressor and the burner in the first passage;   a second compressor that is present on the second passage;   a second turbine that is present on the second passage and that is connected to the second compressor via a second shaft; and   a heat exchanger that is commonly present on a first part of the first passage and a second part of the second passage, wherein   the first passage and the second passage are combined with each other at a meeting point, and   the meeting point is located upstream of the first compressor in a flowing direction of the working fluid in the first passage and downstream of the second turbine in the flowing direction of the working fluid in the second passage.       

     According to the first aspect, by using a working fluid expanded by the second turbine and discharged from the second turbine, at least a portion of the first turbine is cooled down or a working fluid to be fed to the first compressor is cooled down. When at least a portion of the first turbine is cooled down by using the working fluid expanded by the second turbine and discharged from the second turbine, this provides more room to raise the turbine inlet temperature of the first turbine, and thereby the thermal efficiency of the micro gas turbine system may be enhanced. Also, when the working fluid to be fed to the first compressor is cooled down by using a working fluid expanded by the second turbine and discharged from the second turbine, the temperature of the working fluid taken into the first compressor is low. Thus, power necessary for operating the first compressor is reduced. As a result, thermal efficiency of the micro gas turbine system may be enhanced. Thus, the micro gas turbine system according to the first aspect is advantageous in enhancing the thermal efficiency. 
     A second aspect of the present disclosure provides a micro gas turbine system, wherein in addition to the first aspect, the second turbine discharges the working fluid with a higher pressure than a pressure of at least a part of the combustion gas flowing in the first turbine, and the micro gas turbine apparatus cools down at least the portion of the first turbine by using the working fluid with the higher pressure discharged from the second turbine. According to the second aspect, at least a portion of the first turbine is cooled down by using the higher-pressure working fluid discharged from the second turbine. This provides more room to raise the turbine inlet temperature of the first turbine. Also, the second turbine discharges a working fluid with a higher pressure than a pressure of at least a part of the combustion gas flowing in the first turbine. Thus, the working fluid discharged from the second turbine may be caused to flow into a flow of the combustion gas. 
     A third aspect of the present disclosure provides a micro gas turbine system, wherein, in addition to the second aspect, the first turbine is a radial turbine including a turbine wheel that is fixed to the first shaft; and a turbine nozzle that includes nozzle blades disposed around the turbine wheel outside the turbine wheel in a radial direction, and the micro gas turbine apparatus cools down the nozzle blades by using the working fluid with the higher pressure discharged from the second turbine. According to the third aspect, the nozzle blades of the turbine nozzle of the radial turbine are cooled down, which provides more room to raise the turbine inlet temperature of the first turbine. 
     A fourth aspect of the present disclosure provides a micro gas turbine system, wherein, in addition to the third aspect, each of the nozzle blades includes a passage which is formed inside the nozzle blade, and through which the working fluid with the higher pressure discharged from the second turbine flows; and a film cooling passage that extends from an inner peripheral surface of the nozzle blade only to an outer peripheral surface of the nozzle blade facing the turbine wheel, and that communicates with the passage and outside of the nozzle blade. According to the fourth aspect, the inner peripheral surface of the nozzle blade may be collision-cooled by a working fluid flowing in a passage formed inside the nozzle blade. The film cooling passage extends from the inner peripheral surface of the nozzle blade only to the outer peripheral surface of the nozzle blade facing the turbine wheel. The pressure of the combustion gas is apt to drop around the outer peripheral surface of the nozzle blade facing the turbine wheel. Thus, the working fluid flowing in the passage is apt to flow out to the outside of the nozzle blade through the film cooling passage. Thus, the outer peripheral surface of the nozzle blade is apt to be film-cooled. 
     A fifth aspect of the present disclosure provides a micro gas turbine system, wherein, in addition to the fourth aspect, the first turbine further includes a back-side passage that communicates with the passages and that extends to a portion of a back face of the turbine wheel radially inside an end of the rear face of the turbine wheel in a radial direction. According to the fifth aspect, the back face of the turbine wheel may be cooled down by the working fluid which has passed through the back-side passage. With this cooling, the turbine wheel in the radial turbine is also cooled down, and this provides more room to raise the turbine inlet temperature of the first turbine. 
     A sixth aspect of the present disclosure provides a micro gas turbine system, wherein, in addition to the first aspect, the micro gas turbine apparatus further includes a heat exchanger that is disposed upstream of an inlet of the first compressor in a flow of the working fluid in the micro gas turbine apparatus, and that causes heat exchange between the working fluid to be fed to the first compressor and the working fluid discharged from the second turbine, and the second turbine discharges the working fluid that has a temperature lower than a temperature of the working fluid to be fed to the first compressor and that has a pressure higher than a pressure of the working fluid to be fed to the first compressor. According to the sixth aspect, the working fluid to be fed to the first compressor is cooled down in the heat exchanger by the working fluid discharged from the second turbine. Therefore, the temperature of the working fluid to be fed to the first compressor is low. Thus, power necessary for operating the first compressor is low. As a result, thermal efficiency of the micro gas turbine system may be enhanced. 
     A seventh aspect of the present disclosure provides a micro gas turbine system, wherein, in addition to the first aspect, the micro gas turbine apparatus further includes a mixer that is disposed upstream of an inlet of the first compressor in a flow of the working fluid in the micro gas turbine apparatus, and that mixes the working fluid discharged from the second turbine with a working fluid supplied from outside of the micro gas turbine system, and discharges the mixed fluid, and the second turbine discharges the working fluid that has a temperature lower than a temperature of the working fluid supplied from the outside of the micro gas turbine system to the mixer, and that has a pressure higher than a pressure of the working fluid supplied from the outside of the micro gas turbine system to the mixer. According to the seventh aspect, the working fluid supplied from the outside of the micro gas turbine system to the mixer is mixed with and cooled down by the working fluid discharged from the second turbine. Therefore, the temperature of the working fluid to be fed to the first compressor is low. Thus, power necessary for operating the first compressor is low. As a result, thermal efficiency of the micro gas turbine system may be enhanced. 
     An eighth aspect of the present disclosure provides a micro gas turbine system, wherein, in addition to any one of the first aspect to the seventh aspect, the extracting cycle apparatus includes an electric motor that is connected to the second turbine via the second shaft, and the electric motor adjusts a pressure of the working fluid to be discharged from the second turbine by adjusting a rotation speed of the second turbine through load adjustment. According to the eighth aspect, the pressure of the working fluid discharged from the second turbine is adjusted in an appropriate manner through load adjustment of the electric motor of the extracting cycle apparatus. 
     A ninth aspect of the present disclosure provides a micro gas turbine system, wherein, in addition to any one of the first aspect to the eighth aspect, the first compressor receives a flow of air with an atmospheric pressure as the working fluid. According to the ninth aspect, the working fluid for operating the micro gas turbine may be obtained in an easy manner. 
     A tenth aspect of the present disclosure provides a micro gas turbine system, wherein, in addition to any one of the first aspect to the ninth aspect, the first compressor is a centrifugal compressor. According to the tenth aspect, the micro gas turbine system may be downsized, and produce the effects described above in the first to ninth aspects. 
     Hereinafter, embodiments of the present disclosure are described with reference to the accompanying drawings. Description below is related to one example of the micro gas turbine system according to the present disclosure, and the present invention is not limited thereby. 
     First Embodiment 
     First, a micro gas turbine system  10   a  according to a first embodiment is described. As illustrated in  FIG. 1 , the micro gas turbine system  10   a  includes a micro gas turbine apparatus  1   a  and an extracting cycle apparatus  2 . The micro gas turbine apparatus  1   a  includes a first compressor  11 , a burner  15 , and a first turbine  12 . The first compressor  11  receives and compresses a working fluid. The burner  15  generates a combustion gas by injecting a fuel into the working fluid discharged from the first compressor  11 . The first turbine  12  is connected to the first compressor  11  via a first shaft  17  and expands the combustion gas generated by the burner  15 . The extracting cycle apparatus  2  includes a second compressor  21  and a second turbine  22 . The second compressor  21  receives an extracted air that is a part of the working fluid discharged from the first compressor  11  and compresses the extracted air as a working fluid. The second turbine  22  is connected to the second compressor  21  via a second shaft  27  and expands the working fluid discharged from the second compressor  21 . The micro gas turbine apparatus  1   a  cools down at least a portion of the first turbine  12  by using the working fluid expanded by the second turbine  22  and discharged from the second turbine  22 . Thus, a turbine inlet temperature (temperature of the combustion gas flowing into the first turbine  12 ) of the first turbine  12  may be raised. For example, the inlet temperature of the first turbine  12  may be raised to 1,300 K or higher. Thus, the micro gas turbine system  10   a  is advantageous in enhancing the thermal efficiency. 
     The first compressor  11 , for example, receives air of atmospheric pressure as a working fluid. The first compressor  11  is, for example, a centrifugal compressor. 
     As illustrated in  FIG. 1 , the micro gas turbine apparatus  1   a  further includes, for example, a motor generator  13 . The motor generator  13  is connected to the first shaft  17 . The motor generator  13  functions as an electric motor when the micro gas turbine apparatus  1   a  is activated, and causes the first compressor  11  to operate by rotating the first shaft  17 . The micro gas turbine apparatus  1   a  further includes, for example, a regenerated heat exchanger  14 . In this case, the high pressure working fluid discharged from the first compressor  11  flows into the regenerated heat exchanger  14 . The working fluid flowing into the regenerated heat exchanger  14  is heated in the regenerated heat exchanger  14  by heat exchange with a combustion gas which has passed the first turbine  12 . The working fluid which has passed the regenerated heat exchanger  14  flows into the burner  15 . 
     As illustrated in  FIG. 1 , a fuel is supplied into the burner  15  through a fuel supply passage  51  and injected into the working fluid in the burner  15 . Inside the burner  15 , for example, a spark electrode (not shown) is disposed to cause combustion in the burner  15  by spark and thereby generate a combustion gas of high temperature. The fuel is, for example, a liquid fuel or a gas fuel. As the liquid fuel, for example, a petroleum-based fuel such as gasoline, kerosene, light oil, and heavy oil, an alcohol-based fuel such as methanol and ethanol, and an alcohol-based mixed fuel containing an alcohol-based fuel may be used. As the gas fuel, for example, compressed natural gas (CNG), liquefied petroleum gas (LPG), methyl tertiary butyl ether (MTBE), hydrogen, or the like may be used. 
     The combustion gas generated in the burner  15  flows into the first turbine  12  and expands in the first turbine  12 . Power is generated as a rotating torque from the combustion gas expanding in the first turbine  12 . The power causes the first compressor  11  to operate, and a surplus power causes the motor generator  13  to generate electric power. The combustion gas discharged from the first turbine  12  flows into the regenerated heat exchanger  14 . As described above, heat exchange between the high-pressure working fluid before flowing into the burner  15  and the combustion gas is caused in the regenerated heat exchanger  14 , and thereby the temperature of the combustion gas drops. The combustion gas flowing out from the regenerated heat exchanger  14  is discharged to the outside of the micro gas turbine apparatus  1   a.    
     As a result that a part of the working fluid discharged from the first compressor  11  is pulled out, an extracted air is generated. As illustrated in  FIG. 1 , the extracted air is supplied to the second compressor  21  through an air-extraction passage  52 . An inlet of the air-extraction passage  52  is formed in the middle of passage of the working fluid that connects an outlet of the first compressor  11  and an inlet of the working fluid in the burner  15  with each other. In a case where the micro gas turbine apparatus  1   a  includes the regenerated heat exchanger  14 , the inlet of the air-extraction passage  52  is typically formed in the middle of passage of the working fluid that connects the outlet of the first compressor  11  and the inlet of the working fluid in the regenerated heat exchanger  14  with each other. Flow rate of the extracted air flowing in the air-extraction passage  52  is not restricted particularly. However, for example, 20% to 50% by mass of the working fluid discharged from the first compressor  11  is extracted as the extracted air. 
     As illustrated in  FIG. 1 , the micro gas turbine system  10   a  further includes, for example, an intermediate cooler  16 . The intermediate cooler  16  is disposed in the middle of the air-extraction passage  52 . The extracted air is cooled down in the intermediate cooler  16  by a heating medium such as, cooling water or the like. Thus, low temperature extracted air cooled down in the intermediate cooler  16  is supplied into the second compressor  21  as a working fluid. Thus, power necessary for operating the second compressor  21  may be reduced. 
     The working fluid flowing into the second compressor  21  is compressed in the second compressor  21  and discharged from the second compressor  21 . As illustrated in  FIG. 1 , the extracting cycle apparatus  2  further includes, for example, a heat exchanger  24 . The heat exchanger  24  causes heat exchange between the working fluid discharged from the second compressor  21  and a fuel before flowing into the burner  15 . Thus, the temperature of the working fluid drops by passing through the heat exchanger  24 , and the working fluid discharged from the second compressor  21  transforms into a low-temperature and high-pressure state. The working fluid turned into the low-temperature and high-pressure state flows into the second turbine  22 . The pressure of the working fluid flowing into the second turbine  22  drops by expanding in the second turbine  22 . At least a portion of the first turbine  12  is cooled down by using the working fluid discharged from the second turbine  22 . For example, as illustrated in  FIG. 1 , passage  53  of the working fluid extends from the outlet of the second turbine  22  up to at least a portion of the first turbine  12 . 
     Although pressure of the working fluid drops in the second turbine  22 , the second turbine  22  discharges, for example, a working fluid with a pressure higher than a pressure of at least a part of the combustion gas flowing in the first turbine  12 . In this case, the micro gas turbine apparatus  1   a  cools down at least a portion of the first turbine  12  by using the higher pressure working fluid discharged from the second turbine  22 . The second turbine  22  discharges a working fluid with a pressure higher than a pressure of at least a part of the combustion gas flowing in the first turbine  12  and therefore causes the working fluid discharged from the second turbine  22  to flow out into the flow of the combustion gas. 
     As illustrated in  FIG. 1 , the extracting cycle apparatus  2  includes an electric motor  23 . The electric motor  23  is connected to the second turbine  22  via a second shaft  27 . The electric motor  23  is typically constituted as a part of a generator motor. The electric motor  23  adjusts the pressure of the working fluid discharged from the second turbine  22  by adjusting a rotation speed of the second turbine  22  through load adjustment. For example, with such function of the electric motor  23 , the second turbine  22  discharges a working fluid with a pressure higher than a pressure of at least a portion of the combustion gas flowing in the first turbine  12 . A known technique related to the electric motor load adjustment method such as control by an inverter may be applied to the load adjustment of the electric motor  23 . 
     As illustrated in  FIG. 2 , the first turbine  12  is, for example, a radial turbine including a turbine wheel  12   a  and a turbine nozzle  12   b . The turbine wheel  12   a  is fixed to the first shaft  17 . The turbine nozzle  12   b  includes nozzle blades  12   c  disposed around the turbine wheel  12   a  outside the turbine wheel  12   a  in a radial direction. The first turbine  12  further includes, for example, a casing  12   j  and a casing  12   k . The turbine wheel  12   a  and the turbine nozzle  12   b  are housed inside the casing  12   j , and the casing  12   j  forms a passage in which the combustion gas flows inward a radial direction toward the turbine wheel  12   a . The combustion gas flowing into the first turbine  12  flows toward the turbine wheel  12   a  through the turbine nozzle  12   b . The casing  12   k  forms a passage for receiving a flow of the combustion gas which has passed the turbine wheel  12   a . The combustion gas flowing into the turbine wheel  12   a  causes the turbine wheel  12   a  to rotate and thereby the power is generated. The micro gas turbine apparatus  1   a , for example, cools down the nozzle blades  12   c  of the turbine nozzle  12   b  by using the high pressure working fluid discharged from the second turbine  22 . Thus, the inlet temperature of the first turbine  12  may be raised. An arrow in  FIG. 2  conceptually indicates a direction in which the working fluid discharged from the second turbine  22  flows. 
     As illustrated in  FIG. 3 , the turbine nozzle  12   b  is formed, for example, by a turbine nozzle ring  19 . The turbine nozzle ring  19  includes a first annular plate  19   a , a second annular plate  19   b , and a predetermined quantity of nozzle blades  12   c  disposed in a circumferential direction. The nozzle blades  12   c  are disposed between the first annular plate  19   a  and the second annular plate  19   b . The turbine nozzle ring  19  is fixed, for example, to the casing  12   j . Thus, a predetermined number of nozzle blades  12   c  are disposed in a circumferential direction so as to enclose the turbine wheel  12   a  outside the turbine wheel  12   a  in the radial direction. 
     As illustrated in  FIG. 4 , each of the nozzle blades  12   c  includes a passage r 1  and a film cooling passage r 2 . The passage r 1  is a passage of the high pressure working fluid discharged from the second turbine  22 , the passage being formed inside the nozzle blade  12   c . The film cooling passage r 2  is a passage which extends from the inner peripheral surface of the nozzle blade  12   c  only to the outer peripheral surface of the nozzle blade  12   c  facing the turbine wheel  12   a  and communicates with the passage r 1  and the outside of the nozzle blade  12   c . The nozzle blade  12   c  has, for example, a tubular structure extending in an axial direction of the turbine nozzle ring  19 . As illustrated in  FIG. 2 , a communication passage  18  is formed inside the casing  12   j . Internal space of the nozzle blade  12   c  is communicated with the passage  53  by the communication passage  18 . The first annular plate  19   a  has a through-hole at a location facing the internal space of each of the nozzle blades  12   c  in a circumferential direction and a radial direction of the turbine nozzle ring  19 . Thus, the high pressure working fluid discharged from the second turbine  22  is supplied to the passage r 1  inside the nozzle blade  12   c  through the passage  53 , the communication passage  18 , and the through-hole of the first annular plate  19   a . Inner peripheral surface of the nozzle blade  12   c  is collision-cooled by the working fluid supplied to the passage r 1 . The working fluid supplied to the passage r 1  is discharged through the outer peripheral surface of the nozzle blade  12   c  facing the turbine wheel  12   a  of the nozzle blade  12   c  through the film cooling passage r 2 . Thus, the outer peripheral surface of the nozzle blade  12   c  facing the turbine wheel  12   a  is film-cooled. The pressure of the combustion gas is apt to drop around the outer peripheral surface of the nozzle blade c facing the turbine wheel  12   a . Thus, the working fluid flowing in the passage r 1  is apt to flow out to the outside of the nozzle blade  12   c  through the film cooling passage r 2 . Thus, the outer peripheral surface of the nozzle blade  12   c  is apt to be film-cooled. 
     For example, as illustrated in  FIGS. 3 and 4 , multiple groups each including multiple film cooling passages r 2  arranged in the axial direction of the turbine nozzle ring  19  are arranged in a circumferential direction of the turbine nozzle ring  19  in each of the nozzle blades  12   c . Two adjacent groups of film cooling passages r 2  are disposed such that the film cooling passages r 2  in one group are shifted in the axial direction of the turbine nozzle ring  19  from the film cooling passages r 2  in the other group. Thus, the outer peripheral surface of the nozzle blade  12   c  is easily film-cooled uniformly. 
     As illustrated in  FIG. 4 , for example, an inner tube  12   d  is disposed inside the nozzle blade  12   c . The passage r 1  is separated into two spaces inside the nozzle blade  12   c  by the inner tube  12   d . The inner tube  12   d  includes multiple through-holes, and a space formed between the inner peripheral surface of the nozzle blade  12   c  and the outer peripheral surface of the inner tube  12   d  communicates with the internal space of the inner tube  12   d . The first annular plate  19   a  has, for example, a through-hole at a location facing the internal space of the inner tube  12   d  disposed inside each of nozzle blades  12   c  in a circumferential direction and a radial direction of the turbine nozzle ring  19 . Thus, a part of the working fluid which has passed through the passage  53  flows into the internal space of the inner tube  12   d  and is supplied to a space formed between the inner peripheral surface of the nozzle blade  12   c  and the outer peripheral surface of the inner tube  12   d  through through-holes of the inner tube  12   d . For example, about 50% of the working fluid which has passed through the passage  53  is supplied into a space formed between the inner peripheral surface of the nozzle blade  12   c  and the outer peripheral surface of the inner tube  12   d . Through-holes of the inner tube  12   d  are formed, for example, at a portion of the outer peripheral surface of the inner tube  12   d  facing the inner peripheral surface of the nozzle blade  12   c  where the film-cooling passage r 2  is not formed. With this configuration, the inner peripheral surface of the nozzle blade  12   c  corresponding to the outer peripheral surface of the nozzle blade  12   c  which is hardly film-cooled by the working fluid supplied to the passage r 1  may be collision-cooled. Thus, the nozzle blade  12   c  may be cooled down in an appropriate manner by combination of collision-cooling and film-cooling. The temperature of the outer peripheral surface of the nozzle blade  12   c  where the film cooling passage r 2  is not formed is apt to be raised by the combustion gas. Thus, thermal barrier coating (TBC) by silicon nitride or the like is preferably formed on the outer peripheral surface of the nozzle blade  12   c  where the film cooling passage r 2  is not formed. 
     As illustrated in  FIG. 2 , the first turbine  12 , for example, further includes a back-side passage r 3 . The back-side passage r 3  communicates with the passage r 1  and extends toward a portion of a back face bf located on a more inner side in radial direction than an end of the back face bf of the turbine wheel  12   a  in a radial direction. Thus, the back face bf of the turbine wheel  12   a  may be cooled down by the working fluid which has passed through the back-side passage r 3 . With this configuration, the turbine wheel  12   a  in the radial turbine is also cooled down, and thereby turbine inlet temperature of the first turbine  12  is apt to be raised. 
     The first turbine  12  further includes, for example, a backplate  12   m  and a heat shield plate  12   n . The backplate  12   m  separates the first compressor  11  and the first turbine  12  from each other. The heat shield plate  12   n  is disposed so as to face the back face bf of the turbine wheel  12   a . At least a portion of the back-side passage r 3  is formed by the backplate  12   m  and the heat shield plate  12   n . The second annular plate  19   b  has a through-hole at a location facing the internal space of each of nozzle blades  12   c  in a circumferential direction and a radial direction of the turbine nozzle ring  19 . For example, the second annular plate  19   b  has a through-hole at a location facing the internal space of the inner tube  12   d  disposed inside each of nozzle blades  12   c  in a circumferential direction and a radial direction of the turbine nozzle ring  19 . For example, the back-side passage r 3  communicates with the passage r 1  through the through-hole formed on the second annular plate  19   b . About 50% of the working fluid which has passed through the passage  53  is supplied to the back-side passage r 3  through the passage r 1 . Multiple through-holes are formed at an end on the inner side of the heat shield plate  12   n  in a radial direction. The working fluid flowing in the back-side passage r 3  passes through the multiple through-holes of the heat shield plate  12   n  and is blown to the back face bf of the turbine wheel  12   a . Thus, the turbine wheel  12   a  is collision-cooled. The working fluid blown to the back face bf of the turbine wheel  12   a  is mixed with the combustion gas flowing in the turbine wheel  12   a  and discharged to the outside of the first turbine  12 . A scallop for reducing the stress is preferably formed on the back face bf of the turbine wheel  12   a.    
     Second Embodiment 
     A micro gas turbine system  10   b  according to a second embodiment is described. The micro gas turbine system  10   b  has the same configuration as the micro gas turbine system  10   a  except for components otherwise described. Components of the micro gas turbine system  10   b  identical or corresponding to components of the micro gas turbine system  10   a  are assigned with same reference numerals, and description thereof is omitted. Description regarding the first embodiment also applies to the second embodiment unless otherwise inconsistent technically. 
     The micro gas turbine system  10   b  cools down a working fluid to be fed to the first compressor  11 , by using a working fluid expanded by the second turbine  22  and discharged from the second turbine  22 . Thus, the temperature of the working fluid taken into the first compressor  11  is low. Thus, power necessary for operating the first compressor  11  is reduced. As a result, the micro gas turbine system  10   b  is advantageous in enhancing the thermal efficiency. 
     As illustrated in  FIG. 5 , the micro gas turbine system  10   b  includes a micro gas turbine apparatus  1   b  in place of the micro gas turbine apparatus  1   a . The micro gas turbine apparatus  1   b  further includes a heat exchanger  30  and has the same configuration as the micro gas turbine apparatus  1   a  except that the micro gas turbine apparatus  1   b  has a passage  55  in place of the passage  53 . The heat exchanger  30  is disposed upstream of the inlet of the first compressor  11  in a flow direction of the working fluid in the micro gas turbine apparatus  1   b , and causes heat exchange between a working fluid to be fed to the first compressor  11  and a working fluid discharged from the second turbine  22 . The second turbine  22  has a temperature lower than a temperature of the working fluid to be fed to the first compressor  11  and discharges a working fluid having a pressure higher than a pressure of the working fluid to be fed to the first compressor  11 . Thus, the working fluid to be fed to the first compressor  11  is cooled down by the working fluid discharged from the second turbine  22 . 
     The passage  55  connects an outlet of the second turbine  22  and the heat exchanger  30  with each other and serves as a passage for supplying the working fluid discharged from the second turbine  22  to the heat exchanger  30 . Although not limited particularly, the heat exchanger  30  is, for example, a plate type heat exchanger. 
     The working fluid supplied to the heat exchanger  30  through the passage  55  is discharged to the outside of the micro gas turbine apparatus  1   b . The pressure of the working fluid to be taken into the first compressor  11  is, for example, equal to the pressure of the environment where the micro gas turbine apparatus  1   b  is placed. For example, the micro gas turbine apparatus  1   b  is placed under the atmospheric pressure, which is the pressure of the working fluid to be taken into the first compressor  11 . In such case, the second turbine  22  discharges a working fluid with a pressure higher than the pressure of the working fluid to be taken into the first compressor  11 . For example, the electric motor  23  of the extracting cycle apparatus  2  adjusts the rotation speed of the second turbine  22  by load adjustment. Thus, the pressure of the working fluid discharged from the second turbine  22  is adjusted so as to become higher than the pressure loss in the passage  55  and the heat exchanger  30  plus the atmospheric pressure. Thus, the working fluid discharged from the second turbine  22  is continuously supplied to the heat exchanger  30 . 
     Third Embodiment 
     A micro gas turbine system  10   c  according to a third embodiment is described. The micro gas turbine system  10   c  has the same configuration as the micro gas turbine system  10   a  except for components otherwise described. Components of the micro gas turbine system  10   c  identical or corresponding to components of the micro gas turbine system  10   a  are assigned with same reference numerals, and description thereof is omitted. Description regarding the first embodiment also applies to the third embodiment unless otherwise inconsistent technically. 
     The micro gas turbine system  10   c  cools down a working fluid to be fed to the first compressor  11 , by using a working fluid expanded by the second turbine  22  and discharged from the second turbine  22 . Thus, the temperature of the working fluid taken into the first compressor  11  is low. As a result, power necessary for operating the first compressor  11  is reduced. Thus, the micro gas turbine system  10   c  is advantageous in enhancing the thermal efficiency. 
     The micro gas turbine system  10   c  includes a micro gas turbine apparatus  1   c  in place of the micro gas turbine apparatus  1   a . The micro gas turbine apparatus  1   c  further includes a mixer  31  and has the same configuration as the micro gas turbine apparatus  1   a  except that the micro gas turbine apparatus  1   c  has a passage  59  in place of the passage  53 . The mixer  31  is disposed upstream of the inlet of the first compressor  11  in the flow direction of the working fluid in the micro gas turbine apparatus  1   c . The mixer  31  passes the working fluid supplied from the outside of the micro gas turbine system  10   c  after mixing with a working fluid discharged from the second turbine  22 . The second turbine  22  discharges a working fluid having a temperature lower than a temperature of the working fluid supplied from the outside of the micro gas turbine system  10   c  to the mixer  31 . The second turbine  22  discharges a working fluid having a pressure higher than a pressure of the working fluid supplied from the outside of the micro gas turbine system  10   c  to the mixer  31 . Thus, the temperature of the working fluid to be fed to the first compressor  11  becomes low. As a result, power necessary for operating the first compressor  11  is reduced, and thereby thermal efficiency of the micro gas turbine system  10   c  is enhanced. 
     For example, the electric motor  23  of the extracting cycle apparatus  2  adjusts the rotation speed of the second turbine  22  by load adjustment. With this adjustment, the pressure of the working fluid discharged from the second turbine  22  becomes higher than a pressure of the working fluid supplied from the outside of the micro gas turbine system  10   c  to the mixer  31 . Thus, the working fluid discharged from the second turbine  22  is continuously supplied to the mixer  31 . The pressure of the working fluid discharged from the second turbine  22  is, for example, 120% to 150% of the pressure of the working fluid supplied from the outside of the micro gas turbine system  10   c  to the mixer  31 . 
     Micro gas turbine systems of the present disclosure may be applied to a stationary emergency generation systems and mobile main and auxiliary generation systems of the small entity.