Patent Publication Number: US-8966878-B2

Title: Gas turbine

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a gas turbine that obtains rotational power by combusting a mixture of fuel and compressed air and supplying generated combustion gas to a turbine. 
     2. Description of the Related Art 
     Generally, a gas turbine includes a compressor, a combustor, and a turbine. Air taken in from an air-intake port is compressed by the compressor to form compressed air with high temperature and high pressure. Fuel is supplied to the compressed air to be combusted in the combustor. The turbine is driven by combustion gas with high temperature and high pressure, and a generator connected to the turbine is driven. The turbine includes a plurality of stator vanes and rotor blades arranged alternately in a casing. The turbine rotationally drives an output shaft coupled with the generator by driving the rotor blades utilizing the combustion gas. The combustion gas driven the turbine is converted to static pressure by a diffuser in an exhaust casing, and is discharged to the atmosphere. In this type of turbine, a turbine shaft to which the rotor blades are fixed is rotatably supported in the casing via bearing portions at inlet casing side and an exhaust casing side, respectively. Lubricant is supplied to each bearing portion and a multistage seal ring is provided near the bearing portion such that the supplied lubricant does not flow out of the bearing portion. By supplying air extracted from the compressor to the seal ring, leakage of the lubricant from the bearing portion is suppressed. 
     Such a gas turbine is described in Japanese Patent Application Laid-Open No. 2005-023812. 
     However, at the exhaust casing side in the gas turbine, an exhaust diffuser that converts the exhaust gas to static pressure to discharge the gas to the outside is provided on an outer peripheral side of the exhaust-side bearing portion, and the bearing portion is heated by exhaust gas with high temperature flowing in the exhaust diffuser. Particularly, when the gas turbine is operated with a low output for a long time, high temperature gas accumulates inside the exhaust diffuser to raise the temperature of the exhaust-side bearing portion, and lubricant supplied to the exhaust-side bearing portion is carbonized to be solidified. As a result, carbide of lubricant adheres on a seal face of the seal ring and the carbide contacts with the turbine shaft, which can generate vibrations. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to at least partially solve the problems in the conventional technology. 
     A gas turbine according to one aspect of the present invention includes a compressor that compresses air to produce compressed air; a combustor that combusts a mixture of fuel and the compressed air to produce combustion gas; a turbine to which the combustion gas is supplied to obtain rotational power; and an exhaust gas passage through which high-temperature gas accumulated in a space partitioned by an exhaust-side bearing portion that rotatably supports a turbine shaft and an exhaust diffuser is discharged. The high-temperature gas is sucked into the exhaust gas passage by exhaust gas flowing in the exhaust diffuser. 
     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross section of an exhaust casing in a gas turbine according to a first embodiment of the present invention; 
         FIG. 2  is a cross section taken along a line II-II shown in  FIG. 1 ; 
         FIG. 3  is a schematic diagram of the gas turbine according to the first embodiment; 
         FIG. 4  is a cross section of an exhaust casing in a gas turbine according to a second embodiment of the present invention; 
         FIG. 5  is a cross section taken along a line V-V shown in  FIG. 4 ; 
         FIG. 6  is a cross section of an exhaust passage in the gas turbine according to the second embodiment; and 
         FIG. 7  is a cross section of an exhaust passage in a gas turbine according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the present invention will be explained in detail below with reference to the accompanying drawings. The present invention is not limited to the embodiments. 
       FIG. 1  is a cross section of an exhaust casing in a gas turbine according to a first embodiment of the present invention.  FIG. 2  is a cross section taken along a line II-II shown in  FIG. 1 .  FIG. 3  is a schematic diagram of the gas turbine according to the first embodiment. 
     As shown in  FIG. 3 , the gas turbine according to the first embodiment includes a compressor  11 , a combustor  12 , a turbine  13 , and an exhaust chamber  14 , in which the turbine  13  is coupled to a generator (not shown). The compressor  11  has an air-intake port  15  for taking in air, a plurality of stator vanes  17  and rotor blades  18  are alternately arranged within a compressor casing  16 , and a bleed manifold  19  is provided on an outside of the compressor  11 . The combustor  12  supplies fuel to compressed air compressed by the compressor  11 , and combusts the fuel by igniting the fuel using a burner. In the turbine  13 , a plurality of stator vanes  21  and rotor blades  22  are alternately arranged within a turbine casing  20 . The exhaust chamber  14  has an exhaust diffuser  23  continuous to the turbine  13 . A rotor (a turbine shaft)  24  is positioned to penetrate the centers of the compressor  11 , the combustor  12 , the turbine  13 , and the exhaust chamber  14 , and an end thereof on the compressor  11  side is rotatably supported by a bearing portion  25 , while an end thereof on the exhaust chamber  14  side is rotatably supported by a exhaust-side bearing portion  26 . A plurality of disk plates are fixed to the rotor  24 , to which each of the rotor blades  18  and  22  is coupled, and a generator (not shown) is coupled to the rotor  24  on the compressor  11  side via a reduction gear. 
     Therefore, air taken in from the air-intake port  15  of the compressor  11  passes through the stator vanes  21  and the rotor blades  22  to be compressed to become compressed air with high temperature and high pressure, and the compressed air is supplied with predetermined fuel to be combusted in the combustor  12 . Combustion gas with high temperature and high pressure as working fluid produced in the combustor  12 , passes through the stator vanes  21  and the rotor blades  22  constituting the turbine  13  to rotationally drive the rotor  24 , and drives the generator coupled to the rotor  24 , while exhaust gas passes through the exhaust diffuser  23  of the exhaust chamber  14  to be discharged rearward. 
     On the exhaust chamber  14  side of the gas turbine thus configured, the exhaust diffuser  23  is provided on an outer periphery side of the bearing portion  26 , and the bearing portion  26  is heated by exhaust gas with high temperature flowing in the exhaust diffuser  23 . Lubricant supplied to the bearing portion  26  is carbonized to be solidified, and carbide of lubricant adheres on a seal face of a seal ring for preventing leakage of lubricant, which can generate vibrations due to contacting of the carbide with the rotor  24 . 
     Therefore, in the gas turbine according to the first embodiment, an exhaust gas passage that sucks high temperature gas accumulated in a space partitioned by the bearing portion  26  that rotatably supports the rotor  24  and the exhaust diffuser  23  utilizing exhaust gas flowing in the exhaust diffuser  23  and discharges the gas, is provided. The first embodiment will be specifically explained below. 
     As shown in  FIGS. 1 and 2 , in the gas turbine according to the first embodiment, the rotor  24  is rotatably supported by a bearing box  32  via a journal bearing  31  constituting the bearing portion  26 , and lubricant is supplied to the journal bearing  31 . The exhaust diffuser  23  is disposed on an outer periphery side of the bearing box  32 . Since the exhaust diffuser  23  is configured to include an outer cylindrical portion (not shown) and an inner cylindrical portion  33 , an exhaust passage  34  is formed, and the outer cylindrical portion is fixed to a casing constituting the exhaust chamber  14 . 
     Three seal rings  35 ,  36 , and  37  are formed at an end portion of the bearing box  32 , and seal faces thereof are positioned on an outer peripheral face of the rotor  24  so as to form a fine clearance. An air hole  38  for supplying seal air is formed on the central seal ring  36  along a diametrical direction of the ring, and an air pipe  39  is coupled to a proximal end of the air hole  38 , while a distal end of the air hole  38  is opened to the seal face. The air pipe  39  is coupled to the bleed manifold  19  of the compressor  11  via a pipe (not shown), which allows supply of bleed air with predetermined pressure. A through-hole  40  opened to a space between the journal bearing  31  and the seal ring  37  is formed in the bearing box  32  along a diametrical direction, and a vapor pipe  41  is coupled to a proximal end of the through-hole  40 . 
     Accordingly, when seal air is supplied from the air pipe  39  to the seal face of the seal ring  36  through the air hole  38 , the supplied seal air passes through the seal face of the seal ring  36  and the outer peripheral face of the rotor  24  to flow toward the seal ring  35  outside the bearing box  32  and the seal ring  37  inside the bearing box  32 . High temperature exhaust gas can be prevented from entering in the bearing box  32  by the seal air that has flowed from the central seal ring  36  toward the seal ring  35  outside the bearing box  32 . On the other hand, leakage of the lubricant from the journal bearing  31  can be prevented by the seal air that has flowed from the central seal ring  36  toward the seal ring  37  inside the bearing box  32 . 
     By coupling an end face of the bearing box  32  and an inner peripheral flange portion  33   a  of the inner cylindrical portion  33  in the exhaust diffuser  23  using a ring-shaped partition wall  42 , a space S is partitioned between the bearing portion  26  and the exhaust diffuser  23 . In this case, an outer peripheral portion of the partition wall  42  comes in close contact with the inner peripheral flange portion  33   a  of the inner cylindrical portion  33  via two ring-shaped seal members  43  and  44 , while an inner peripheral portion thereof is fixed to the bearing box  32  by fastening bolts  45 . By forming a plurality of exhaust holes  46  in the partition wall  42  along a circumferential direction thereof at equal intervals, an exhaust gas passage for discharging high temperature gas accumulated in the space S is provided. 
     Therefore, exhaust gas with high temperature and high pressure that has driven the turbine  13  is converted to static pressure in the exhaust passage  34  of the exhaust diffuser  23  to be discharged. Meanwhile, heat of the exhaust gas is transferred to the inner cylindrical portion  33  of the exhaust diffuser  23  to heat the space S. However, since the exhaust passage  34  communicates with the space S through the exhaust holes  46  formed in the partition wall  42 , a sucking force of exhaust gas flowing in the exhaust passage  34  acts on the space S through each of the exhaust holes  46 , so that the high temperature gas accumulated in the space S is sucked from each of the exhaust holes  46  to be discharged to the exhaust passage  34 . 
     Therefore, the space S is prevented from being heated to an extremely high temperature, so that the lubricant supplied to the journal bearing  31  is not heated to be carbonized. 
     In the gas turbine of the first embodiment, by rotatably supporting the exhaust side end portion of the rotor  24  using the bearing box  32  via the journal bearing  31  serving as the bearing portion  26 , disposing the exhaust diffuser  23  on the outer peripheral side of the bearing box  32 , and coupling the end face of the bearing box  32  and the inner peripheral flange  33   a  of the inner cylindrical portion  33  in the exhaust diffuser  23  to each other using the partition wall  42 , the space S is partitioned between the bearing portion  26  and the exhaust diffuser  23 , and the exhaust gas passage for discharging high temperature gas accumulated in the space S is provided by forming the exhaust holes  46  in the partition wall  42  along the circumferential direction at equal intervals. 
     Accordingly, even if the space S around the bearing portion  26  is heated by high temperature exhaust gas flowing in the exhaust passage  34 , since high temperature gas accumulated in the space S is sucked by exhaust gas flowing in the exhaust passage  34  via each of the exhaust holes  46  serving as exhaust gas passages to be discharged, lubricant on the bearing portion  26  is not carbonized, and occurrence of vibration at the rotor  24  is suppressed, so that the reliability can be improved. 
     The space S is partitioned by the bearing box  32 , the inner cylindrical portion  33  of the exhaust diffuser  23 , and the partition wall  42 , and the exhaust holes  46  are formed in the partition wall  42 . Therefore, by simply forming the exhaust holes  46  in the existing equipment, high temperature gas accumulated around the bearing portion  26  is discharged so that lubricant is not carbonized. 
     Since the partition wall  42  is formed in a ring shape and the exhaust holes  46  are formed in the partition wall  42  along the circumferential direction at equal intervals, high temperature gas accumulated around the bearing portion  26  can be properly discharged from the exhaust holes  46  and a temperature rise of the bearing portion  26  can be reliably suppressed. 
     Second Embodiment 
       FIG. 4  is a cross section of an exhaust casing in a gas turbine according to a second embodiment of the present invention.  FIG. 5  is a cross section taken along a line V-V shown in  FIG. 4 .  FIG. 6  is a cross section of an exhaust passage in the gas turbine according to the second embodiment. According to the second embodiment, same reference numerals denote same parts having functions similar to those in the first embodiment and redundant explanation thereof is omitted. 
     In the gas turbine according to the second embodiment, as shown in  FIGS. 4 and 5 , the rotor  24  is rotatably supported by the bearing box  32  via the journal bearing  31  constituting the bearing portion  26 , and lubricant is supplied to the journal bearing  31 . The exhaust passage  34  is formed by disposing the exhaust diffuser  23  on the outer peripheral side of the bearing box  32 . The seal rings  35 ,  36 , and  37  are formed in the bearing box  32 , seal faces thereof are positioned to form fine clearances between the seal faces and an outer peripheral face of the rotor  24 , and the air hole  38  for supplying seal air is formed in the central seal ring  36  along a diametrical direction. 
     By coupling an end face of the bearing box  32  and the inner cylindrical portion  33  of the exhaust diffuser  23  using the partition wall  42 , the space S is partitioned between the bearing portion  26  and the exhaust diffuser  23 . By forming the exhaust holes  46  in the partition wall  42  along a circumferential direction at equal intervals and fixing exhaust connecting pipes  51  so as to project in the space S corresponding to each of the exhaust holes  46  in the partition wall  42 , exhaust gas passages for discharging high temperature gas accumulated in the space S is provided. 
     That is, each of the exhaust connecting pipes  51  is integrally formed with a pipe portion  53  bent to a mounting flange portion  52  at an approximately right angle, and it is fixed to the partition wall  42  by four fixing bolts  54 . Out of the four exhaust connecting pipes  51 , distal ends of the two pipes that are positioned on an upper side face downward and in a circumferential direction of the partition wall  42 , while distal ends of the remaining two pipes that are positioned on a lower side face downward. 
     Accordingly, exhaust gas with high temperature and high pressure that has driven the turbine is converted to static pressure in the exhaust passage  34  of the exhaust diffuser  23  to be discharged. At that time, heat of the exhaust gas is transferred to the inner cylindrical portion  33  of the exhaust diffuser  23  to heat the space S. However, since the exhaust passage  34  and the space S communicate with each other via the exhaust holes  46  formed in the partition wall  42  and the exhaust connecting pipes  51 , a sucking force of exhaust gas flowing in the exhaust passage  34  acts on the space S through each of the exhaust holes  46 , and high temperature gas accumulated in the space S is sucked from each of the exhaust connecting pipes  51  to be discharged to the exhaust passage  34  through each of the exhaust holes  46 . 
     Accordingly, the space S is prevented from being heated up to an extremely high temperature and lubricant supplied to the journal bearing  31  is not heated to be carbonized. 
     In the gas turbine according to the second embodiment, therefore, the space S is partitioned between the bearing portion  26  and the exhaust diffuser  23  by coupling the end face of the bearing box  32  and the inner cylindrical portion  33  in the exhaust diffuser  23  using the partition wall  42 , and the exhaust gas passages for discharging high temperature gas accumulated in the space S are provided by forming the exhaust holes  46  in the partition wall  42  along the circumferential direction at equal intervals and fixing the exhaust connecting pipes  51  projecting in the space S to each of the exhaust holes  46 . 
     Accordingly, even if the space S around the bearing portion  26  is heated by high temperature exhaust gas flowing in the exhaust passage  34 , since high temperature gas accumulated in the space S is sucked by exhaust gas flowing in the exhaust passage  34  via each of the exhaust holes  46  and each of the exhaust connecting pipes  51  serving as the exhaust gas passages to be discharged, lubricant on the bearing portion  26  is not carbonized, and occurrence of vibration at the rotor  24  is suppressed, so that the reliability can be improved. 
     In this case, since the exhaust connecting pipes  51  fixed corresponding to the exhaust holes  46  project in the space S, a sucking force of exhaust gas flowing in the exhaust passage  34  securely acts on the space S through the exhaust connecting pipes  51 , so that the high temperature gas accumulated in the space S can be securely discharged from the exhaust connecting pipes  51  through the exhaust holes  46 , and discharge performance for high temperature gas can be improved. 
     Since the pipe portions  53  of each of the exhaust connecting pipes  51  are bent such that distal ends thereof face downward, even if foreign materials enter in the space S from the outside, they will not enter into the exhaust connecting pipe  51  against gravity, so that the safety is can be improved. 
       FIG. 7  is a cross section of an exhaust passage in a gas turbine according to a third embodiment of the present invention. According to the third embodiment, same reference numerals denote same parts having functions similar to those in the first and the second embodiments, and redundant explanation thereof is omitted. 
     In the gas turbine according to the third embodiment, as shown in  FIG. 7 , by fixing the exhaust connecting pipes  51  so as to project in the space S corresponding to each of the exhaust holes  46  of the partition wall  42 , the exhaust gas passages for discharging high temperature gas accumulated in the space S is provided, and a cap  61  serving as a flow-rate adjusting unit is attached to each of the exhaust connecting pipes  51 . 
     That is, each of the exhaust connecting pipes  51  is integrally formed with the pipe portion  53  bent to the mounting flange portion  52  at an approximately right angle, and it is fixed to the partition wall  42  by four fixing bolts  54 . A threaded portion  55  is formed on a distal end outer peripheral portion of the exhaust connecting pipe  51 , and the cap  61  can be screwed to be attached to the threaded portion  55  of the exhaust connecting pipe  51 . 
     Accordingly, exhaust gas with high temperature and high pressure that has driven the turbine is converted to static pressure in the exhaust passage  34  of the exhaust diffuser  23  to be discharged. At that time, heat of the exhaust gas is transferred to the inner cylindrical portion  33  of the exhaust diffuser  23  to heat the space S. However, since the exhaust passage  34  and the space S communicate with each other via the exhaust holes  46  formed in the partition wall  42  and the exhaust connecting pipes  51 , a sucking force of exhaust gas flowing in the exhaust passage  34  acts on the space S through each of the exhaust holes  46 , and high temperature gas accumulated in the space S is sucked from each of the exhaust connecting pipes  51  to be discharged to the exhaust passage  34  through each of the exhaust holes  46 . 
     By attaching the caps  61  to an appropriate number of the exhaust connecting pipes  51  of the four exhaust connecting pipes  51  according to a flow rate of exhaust gas flowing in the exhaust passage  34  of the exhaust diffuser  23 , a flow rate of high temperature gas to be discharged from the space S can be adjusted. Therefore, the space S is prevented from being heated up to an extremely high temperature and lubricant supplied to the journal bearing  31  is not heated to be carbonized. 
     In the gas turbine according to the third embodiment, therefore, the space S is partitioned between the bearing portion  26  and the exhaust diffuser  23  by coupling the end face of the bearing box  32  and the inner cylindrical portion  33  in the exhaust diffuser  23  using the partition wall  42 . The exhaust gas passages for discharging high temperature gas accumulated in the space S are provided by forming the exhaust holes  46  in the partition wall  42  along the circumferential direction at equal intervals and fixing the exhaust connecting pipes  51  projecting in the space S to each of the exhaust holes  46 . Further, the caps  61  serving as the flow-rate adjusting units can be attached to the exhaust connecting pipes  51 . 
     Accordingly, even if the space S around the bearing portion  26  is heated by high temperature exhaust gas flowing in the exhaust passage  34 , since high temperature gas accumulated in the space S is sucked by exhaust gas flowing in the exhaust passage  34  via each of the exhaust holes  46  and each of the exhaust connecting pipes  51  serving as the exhaust gas passages to be discharged, lubricant on the bearing portion  26  is not carbonized, and occurrence of vibration at the rotor  24  is suppressed, so that the reliability can be improved. 
     By attaching the caps  61  to an appropriate number of the exhaust connecting pipes  51  according to a flow rate of exhaust gas flowing in the exhaust passage  34  of the exhaust diffuser  23 , the flow rate of high temperature gas discharged from the space S can be adjusted and the temperature in the space S can be stabilized. 
     According to the third embodiment, while the exhaust flow rate of high temperature gas from the space S is adjusted by attaching the caps  61  to a desired number of the exhaust connecting pipes  51  and closing the exhaust holes  46  and the exhaust connecting pipes  51 , each sectional area of the passage in the exhaust connecting pipes  51  can be changed according to a rotation, amount of the caps  61 . 
     According to the present embodiments, the space S is partitioned between the bearing portion  26  and the exhaust diffuser  23  by coupling the end face of the bearing box  32  and the inner cylindrical portion  33  in the exhaust diffuser  23  using the partition wall  42 . However, this invention is not limited to this particular configuration. For example, the space S can be partitioned by deforming the bearing box  32  or a portion of the inner cylindrical portion  33  in the exhaust diffuser  23 . 
     According to an embodiment of the present invention, the exhaust gas passage that sucks high temperature gas accumulated in the space partitioned between the exhaust-side bearing portion that rotatably supports the turbine shaft and the exhaust diffuser by utilizing exhaust gas flowing in the exhaust diffuser to discharge the gas is provided. Therefore, even if the periphery of the exhaust-side bearing portion is heated by high temperature exhaust gas flowing in the exhaust diffuser, high temperature gas accumulated in the periphery is sucked by exhaust gas flowing in the exhaust diffuser through the exhaust gas passage to be discharged, so that the lubricant in the exhaust-side bearing portion is not carbonized and occurrence of vibrations in the turbine shaft is suppressed, thereby improving reliability. 
     Furthermore, according to an embodiment of the present invention, the space is partitioned by the bearing box serving as the exhaust-side bearing portion, the inner cylindrical portion of the exhaust diffuser, and the partition wall coupling the end portions of the bearing box and the inner cylindrical portion on the turbine side, and the exhaust hole is formed in the partition wall as the exhaust gas passage. Therefore, high temperature gas accumulated around the exhaust-side bearing portion can be discharged to prevent carbonization of lubricant in the exhaust-side bearing portion by simply forming the exhaust hole in the existing equipment. 
     Moreover, according to an embodiment of the present invention, since the partition wall is formed in a ring shape and the exhaust holes are formed in the partition wall along a circumferential direction thereof at equal intervals, high temperature gas accumulated around the exhaust-side bearing portion can be properly discharged by the exhaust holes so that the temperature rise of the exhaust-side bearing portion can be suppressed. 
     Furthermore, according to an embodiment of the present invention, the exhaust connecting pipe projecting in the space is fixed to the exhaust hole so that a sucking force of exhaust gas flowing in the exhaust diffuser reliably acts on the space through the exhaust connecting pipe. Accordingly, high temperature gas accumulated in the space can be reliably discharged from the exhaust connecting pipes through the exhaust holes, thereby improving the discharge performance for high temperature gas. 
     Moreover, according to an embodiment of the present invention, since the distal end of the exhaust connecting pipe faces downward, foreign material is prevented from entering in the exhaust connecting pipe, so that the safety can be improved. 
     Furthermore, according to an embodiment of the present invention, the flow-rate adjusting unit is provided to the exhaust hole or the exhaust connecting pipe. Therefore, the temperature in the space, which fluctuates according to operational conditions of the gas turbine, can be stabilized by adjusting the discharge amount of high temperature gas discharged from the space by utilizing the flow-rate adjusting unit. 
     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.