Patent Publication Number: US-8973372-B2

Title: Combustor shell air recirculation system in a gas turbine engine

Description:
FIELD OF THE INVENTION 
     The present invention relates to a combustor shell air recirculation system in a gas turbine engine, wherein the recirculation system is operable during less than full load operation to create a more uniform air temperature distribution within the combustor shell. 
     BACKGROUND OF THE INVENTION 
     During operation of a gas turbine engine, air is pressurized in a compressor section then mixed with fuel and burned in a combustion section to generate hot combustion gases. In a can annular gas turbine engine, the combustion section comprises an annular array of combustor apparatuses, sometimes referred to as “cans” or “combustors”, which each supply hot combustion gases to a turbine section of the engine where the hot combustion gases are expanded to extract energy therefrom to provide output power, which is in turn used to produce electricity. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a gas turbine engine is provided including a longitudinal axis defining an axial direction of the engine. The engine comprises a compressor section where air pulled into the engine is compressed, a combustion section comprising a plurality of combustor apparatuses where fuel is mixed with at least a portion of the compressed air from the compressor section and burned to create hot combustion gases, and a turbine section where the hot combustion gases from the combustion section are expanded to extract energy therefrom. The engine further comprises a casing having a portion disposed about the combustion section, the casing portion comprising a casing wall having a top wall section defining a top dead center, left and right side wall sections, and a bottom wall section defining a bottom dead center. The casing portion further defines an interior volume in which the combustor apparatuses and air compressed by the compressor section are located. The engine additionally comprises a shell air recirculation system. 
     According to a first aspect of the present invention, the shell air recirculation system comprises at least one outlet port located at the bottom wall section of the casing wall and first and second inlet ports located at the top wall section of the casing wall. The inlet ports are circumferentially spaced apart from one another and are located at generally the same axial location. The shell air recirculation system further comprises a piping system that provides fluid communication between the at least one outlet port and the inlet ports, a blower for extracting air from the interior volume of the casing portion through the at least one outlet port and for conveying the extracted air to the inlet ports, and a valve system for selectively allowing and preventing air from passing through the piping system. During a first mode of engine operation, at least some of the air in the interior volume of the casing portion is introduced into the combustor apparatuses for being burned with fuel to create hot combustion gases, and the valve system substantially prevents air from passing through the piping system. During a second mode of engine operation, the valve system allows air to pass through the piping system such that at least a portion of the air in the interior volume of the casing portion is extracted from the at least one outlet port by the blower and conveyed by the blower to the inlet ports for injection into the top wall section of the casing wall. 
     According to a second aspect of the present invention, the shell air recirculation system comprises at least one outlet port located at the bottom wall section of the casing wall and at least one inlet port located at the top wall section of the casing wall. The shell air recirculation system further comprises a piping system that provides fluid communication between the at least one outlet port and the at least one inlet port, a blower for extracting air from the interior volume of the casing portion through the at least one outlet port and for conveying the extracted air to the at least one inlet port, and a valve system for selectively allowing and preventing air from passing through the piping system. During a first mode of engine operation, at least some of the air in the interior volume of the casing portion is introduced into the combustor apparatuses for being burned with fuel to create hot combustion gases, and the valve system substantially prevents air from passing through the piping system. During a second mode of engine operation, the valve system allows air to pass through the piping system such that at least a portion of the air in the interior volume of the casing portion is extracted from the at least one outlet port by the blower and conveyed by the blower to the at least one inlet port. The at least one inlet port is configured such that the air injected thereby flows from the top wall section of the casing wall down the left and right side wall sections of the casing wall toward the bottom wall section of the casing wall. 
     According to a third aspect of the present invention, the combustion section comprises a can annular combustion section comprising an annular array of combustor apparatuses. The shell air recirculation system according to this embodiment comprises at least one outlet port located at the bottom wall section of the casing wall and at least one inlet port located at the top wall section of the casing wall. At least one of the outlet and inlet ports also functions as a steam augmentation pipe to introduce high pressure steam into the interior volume of the casing portion during a first mode of operation. The shell air recirculation system further comprises a piping system that provides fluid communication between the at least one outlet port and the at least one inlet port, a blower for extracting air from the interior volume of the casing portion through the at least one outlet port and for conveying the extracted air to the at least one inlet port, and a valve system for selectively allowing and preventing air from passing through the piping system. During the first mode of engine operation, at least some of the air in the interior volume of the casing portion is introduced into the combustor apparatuses for being burned with fuel to create hot combustion gases, and the valve system substantially prevents air from passing through the piping system. During a second mode of engine operation, the valve system allows air to pass through the piping system such that at least a portion of the air in the interior volume of the casing portion is extracted from the at least one outlet port by the blower and conveyed by the blower to the at least one inlet port for injection into the top section of the casing wall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein: 
         FIG. 1  is a side view, partially in section, of a gas turbine engine including a combustor shell air recirculation system according to an embodiment of the invention; 
         FIG. 2  is a schematic illustration of the combustor shell air recirculation system illustrated in  FIG. 1 ; and 
         FIG. 3  is a sectional view of a portion of a combustor shell air recirculation system according to another aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, specific preferred embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
     Referring to  FIG. 1 , a gas turbine engine  10  constructed in accordance with the present invention is shown. The engine  10  includes a compressor section  12 , a combustion section  14  including a plurality of combustors  16 , also referred to herein as “combustor apparatuses,” and a turbine section  18 . It is noted that only one combustor  16  is illustrated in  FIG. 1  for clarity, but the engine  10  according to the present invention preferably comprises an annular array of combustors  16  that are disposed about a longitudinal axis L A  of the engine  10  that defines an axial direction within the engine  10 . Such a configuration is typically referred to as a “can-annular combustion system”. 
     The compressor section  12  inducts and pressurizes inlet air, at least a portion of which is directed to a combustor shell  20  for delivery to the combustors  16 . The air in the combustor shell  20  is hereinafter referred to as “shell air”. Other portions of the pressured air may be extracted from the compressor section  12  to cool various components within the engine  10 . 
     Upon entering the combustors  16 , the compressed air from the compressor section  12  is mixed with fuel and ignited to produce high temperature combustion gases flowing in a turbulent manner and at a high velocity within the respective combustor  16 . The combustion gases in each combustor  16  then flow through a respective transition duct  22  to the turbine section  18  where the combustion gases are expanded to extract energy therefrom. The energy extracted from the combustion gases is used provide rotation of a turbine rotor  24 , which extends parallel to a rotatable shaft  26  that extends axially through the engine  10 . 
     As shown in  FIG. 1 , an engine casing  30  is provided to enclose the respective engine sections  12 ,  14 ,  18 . A portion  30 A of the casing  30  disposed about combustion section  14  comprises a casing wall  32  that defines the combustor shell  20 , i.e., the combustor shell  20  defines an interior volume within the casing portion  30 A. Referring to  FIG. 2 , the casing wall  32  includes a top wall section  32 A, left and right side wall sections  32 B,  32 C, and a bottom wall section  32 D. The top wall section  32 A defines a top dead center  34  of the casing wall  32 , which comprises an uppermost area of the casing portion  30 A, and the bottom wall section  32 D defines a bottom dead center  36  of the casing wall  32 , which comprises a lowermost area of the casing portion  30 A. 
     A shell air recirculation system  40  according to an aspect of the present invention will now be described. Referring to  FIG. 2 , the shell air recirculation system  40  in the embodiment shown comprises first and second outlet ports  42 A,  42 B located at the bottom wall section  32 D of the casing wall  32 . While the shell air recirculation system  40  according to this embodiment comprises first and second outlet ports  42 A,  42 B, any suitable number of outlet ports can be provided, including a single outlet port. 
     As shown in  FIG. 2 , the outlet ports  42 A,  42 B are circumferentially spaced apart and are located at generally the same axial location, wherein the bottom dead center  36  of the casing wall  32  is located between the outlet ports  42 A,  42 B. According to one aspect of the invention, at least one of the outlet ports  42 A,  42 B may also function as a steam augmentation pipe to channel high pressure steam into the combustor shell  20  to effect an increase in output power of the engine  10 , i.e., by effecting higher combustion gas flow rates through turbine section  18 . 
     The shell air recirculation system  40  further comprises a piping system  44  that is provided to convey shell air that is extracted from the combustor shell  20  through the outlet ports  42 A,  42 B to first and second inlet ports  46 A,  46 B, which are located at the top wall section  32 A of the casing wall  32 . While the shell air recirculation system  40  according to this embodiment comprises first and second inlet ports  46 A,  46 B, any suitable number of inlet ports can be provided, including a single inlet port. 
     As shown in  FIG. 2 , the inlet ports  46 A,  46 B are circumferentially spaced apart and are located at generally the same axial location, wherein the first inlet port  46 A is located near the left side wall section  32 B of the casing wall  32  and the second inlet port  46 B is located near the right side wall section  32 C of the casing wall  32 . According to one aspect of the invention, at least one of the inlet ports  46 A,  46 B may also function as a steam augmentation pipe to channel additional high pressure steam into the combustor shell  20 . 
     The shell air recirculation system  40  still further comprises a valve system  48  comprising first and second valves  48 A,  48 B in the embodiment shown, and a blower  50 . The valve system  48  and the blower  50  are controlled by a controller  52  to selectively allow or prevent shell air from passing through the piping system  44  from the outlet ports  42 A,  42 B to the inlet ports  46 A,  46 B, as will be described in detail below. The blower  50  is provided for extracting the shell air from the combustor shell  20  through the outlet ports  42 A,  42 B and for conveying the extracted shell air to the inlet ports  46 A,  46 B when the valve system  48  is open. 
     A method for utilizing the shell air recirculation system  40  will now be described. During normal operation of the engine  10 , also known as full load or base load operation and also referred to herein as a first mode of engine operation, the first and second valves  48 A,  48 B are closed and the blower  50  is turned off or is otherwise not operational. Hence, the valve system  48  substantially prevents shell air from passing through the piping system  44 . At least a portion of the shell air is provided into the combustors  16  to be burned with fuel as discussed above. Additional portions of the shell air may be used to cool various components within the engine  10 , as will be apparent to those having skill in the art. 
     Upon initiation of a turn down operation, which is implemented to transition the engine  10  to a shut down state or a turning gear state, fuel and shell air supplied to the combustors  16  is gradually ceased, such that the production of high temperature combustion gases in the combustors  16  is gradually decreased to null upon the engine  10  being transitioned to the shut down state or the turning gear state. Once combustion gases are no longer produced in the combustors  16 , rotation of the turbine rotor  24  is not able to be effected by combustion gases. In such a situation, slow rotation of the turbine rotor  24  may be effected by an outside power supply (not shown), such as by a start-up motor, in an operating state referred to herein as a turning gear state. Alternatively, rotation of the turbine rotor  24  may be completely stopped in an operating state referred to herein as a shut down state. In a typical engine  10 , such a turn down operation may take at least about 10-15 minutes to completely transition the engine  10  to a turning gear state, during which time combustion of a gradually decreasing level continues in the combustors  16  to produce high temperature combustion gases, which gases are conveyed into the turbine section  18  to provide rotation of the turbine rotor  24 . The second mode of engine operation, as used herein, is meant to encompass turn down operation, a turning gear state, or a shut down state of the engine  10 . 
     According to an aspect of the present invention, upon the initiation of a turn down operation to transition the engine  10  to either a turning gear state or a shut down state, the controller  52  opens the first and second valves  48 A,  48 B such that the valve system  48  allows air to pass through the piping system  44 . The blower  50  is turned on by the controller  52  during the second mode of operation to extract shell air from the bottom wall section  32 D of the casing wall  32  through the outlet ports  42 A,  42 B. The blower  50  conveys, i.e., pumps, the extracted shell air through the piping system  44  such that the extracted shell air is injected into the top wall section  32 A of the casing wall  32  through the inlet ports  46 A,  46 B. 
     According to another aspect of the invention, the turn down operation may be implemented to transition the engine  10  from full load operation to a turning gear state, which may be run for a predetermined time or until one or more select engine components reaches a predefined temperature, at which point the engine  10  may be transitioned to a shut down state. Under this arrangement, during the turning gear state, the valves  48 A,  48 B are maintained in open positions and operation of the blower  50  is continued to extract shell air from the bottom wall section  32 D of the casing wall  32  through the outlet ports  42 A,  42 B, to convey the extracted shell air through the piping system  44 , and to inject the extracted shell air into the top wall section  32 A of the casing wall  32  through the inlet ports  46 A,  46 B. However, upon the engine  10  entering the shut down state, i.e., after completion of the turning gear state, the blower  50  may be turned off or otherwise disabled to stop the pumping of shell air through the piping system  44 . During the shut down state, the valves  48 A,  48 B may remain opened or the controller  52  may close them, but they would be closed by the controller  52  upon the initiation of an engine start up procedure. 
     As shown in  FIG. 2 , the air injected by the inlet ports  46 A,  46 B into the combustor shell  20  flows from the top wall section  32 A of the casing wall  32  down the respective left and right side wall sections  32 B,  32 C toward the bottom wall section  32 D. The shell air recirculation system  40  thus functions to circulate the shell air within the combustor shell  20  during less than full load operation so as to create a more uniform shell air temperature distribution within the combustor shell  20 . Otherwise, hotter shell air would tend to migrate to the top wall section  32 A, thus resulting in hotter temperatures at the top wall section  32 A than at the bottom wall section  32 D. Further, the shell air toward the bottom wall section  32 D that is extracted through the outlet ports  42 A,  42 B by the blower  50  and injected through the inlet ports  46 A,  46 B is generally cooler than the shell air toward the top wall section  32 A, thus resulting in an even more uniform shell air temperature distribution within the combustor shell  20 . 
     The more uniform shell air temperature distribution within the combustor shell  20  effected by the shell air recirculation system  40  is believed to reduce or prevent issues that might result from components within and around the combustor shell  20  thermally growing at different rates, such as distortion of the engine casing  30  and/or rubbing of turbine blade tips T T  in the turbine section  18  against the casing  30 , thus lengthening a lifespan of these components and maintaining a tight blade tip clearance during full load operation for improved turbine efficiency. It is noted that since the shell air recirculation system  40  according to the present invention injects only shell air into the combustor shell  20 , which shell air is extracted from the bottom wall section  32 D through the outlet ports  42 A,  42 B by the blower  50 , the cost and complexity of the shell air recirculation system  40  is reduced, i.e., compared to a system that uses structure such as an ejector to inject highly pressurized air into the combustor shell  20 . 
     As noted above, one or more of the outlet and inlet ports  42 A,  42 B,  46 A,  46 B may also function as steam augmentation pipes to channel high pressure steam into the combustor shell  20  to effect an increase in output power of the engine  10 . Such steam introduction is typically only performed during full load operation. If any of the outlet and inlet ports  42 A,  42 B,  46 A,  46 B also function as steam augmentation pipes, these ports  42 A,  42 B,  46 A,  46 B preferably extend straight into the casing wall  32  and terminate a short distance into the combustor shell  20 , as shown in  FIGS. 1 and 2 . Using the outlet and inlet ports  42 A,  42 B,  46 A,  46 B as steam augmentation pipes may be especially advantageous if the shell air recirculation system  40  is implemented in an existing engine  10 , i.e., in a retrofit design, as additional pipes that extend through the casing wall  32  would not be required, thus reducing the complexity of installing the shell air recirculation system  40  in an existing engine  10 . 
     If the outlet and inlet ports  42 A,  42 B,  46 A,  46 B are not to function as steam augmentation pipes, one or more of these ports  42 A,  42 B,  46 A,  46 B could have specially configured tips to modify shell air extraction and/or injection from and/or into the combustor shell  20 . For example, referring to  FIG. 3 , a shell air recirculation system  140  constructed in accordance with another embodiment of the invention is shown, wherein structure similar to that described above with reference to  FIGS. 1 and 2  includes the same reference number increased by 100. Further, only structure that differs from the embodiment discussed above with reference to  FIGS. 1 and 2  will be discussed herein for  FIG. 3 . As a point of reference, the view of the shell air recirculation system  140  shown in  FIG. 3  is taken along line  3 - 3  illustrated in  FIG. 1 , and select engine  110  and shell air recirculation system  140  components have been removed from  FIG. 3  for clarity. 
     In this embodiment, the outlet ports  142 A,  142 B have conical shaped tips  142 A 1 ,  142 B 1  to increase the amount of shell air that can be extracted thereby. 
     Further, the inlet ports  146 A,  146 B according to this embodiment have tips  146 A 1 ,  146 B 1  that are angled circumferentially toward one another and are also angled axially in a direction toward the compressor section (not shown in this embodiment) and away from the turbine section (not shown in this embodiment). The inlet ports  146 A,  146 B according to this embodiment are thus configured such that they inject shell air at least partially in the circumferential direction toward one another and toward the top dead center  134  of the casing wall  132 , which is located circumferentially between the first and second inlet ports  146 A,  146 B as shown in  FIG. 3 , i.e., the shell air injected by the inlet ports  146 A,  146 B includes a circumferential velocity component. 
     After flowing to the top dead center  134  of the casing wall  132 , the air injected by the inlet ports  146 A,  146 B flows from the top wall section  132 A of the casing wall  132  down the respective left and right side wall sections  132 B,  132 C toward the bottom wall section  132 D. Since the air injected by the inlet ports  146 A,  146 B according to this embodiment flows to the top dead center  134  of the casing wall  132 , it is believed to be ensured that the shell air at the top dead center  134  of the casing wall  132 , which may be the hottest shell air within the combustor shell  120 , is circulated with the remaining shell air. Further, since the shell air injected by the inlet ports  146 A,  146 B according to this embodiment also flows in the axial direction toward the compressor section of the engine  110 , i.e., the shell air injected by the inlet ports  146 A,  146 B includes an axial velocity component, it is believed to be ensured that a greater amount of the shell air within the combustor shell  120  is circulated. 
     It is noted that the outlet and inlet ports described herein could be located at other axial locations within the casing portion than the locations shown in  FIGS. 1-3 . Further, multiple rows of outlet and inlet ports may be utilized to further improve shell air circulation within the combustor shell. 
     It is also noted that if only a single inlet port is used, i.e., as opposed to using first and second inlet ports in the embodiments discussed above, the single inlet port could be configured to inject air down both the left and right side wall sections of the casing wall. Examples of such an inlet port include a dual tipped inlet port, wherein a first tip is directed to the left side wall section and a second tip is directed to the right side wall section, or the inlet port could have louvers or fins that are provide to inject air in the desired directions. Further, such a single inlet port could be located at the top dead center of the casing wall to provide a more efficient air circulation within the combustor shell. Moreover, such a single inlet port could also be configured such that the shell air injected thereby includes an axial velocity component. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.