Abstract:
An improved inlet bleed heat system for a gas turbine engine is disclosed. The inlet bleed heat system provides improved mixing in an inlet region while permitting the engine to be operated at lower power settings. The inlet bleed heat system comprises a supply conduit, a plurality of feed tubes extending from the supply conduit, and a guide tube for receiving opposing ends of the feed tubes. The plurality of feed tubes each have a plurality of injection orifices and the feed tubes are oriented such that the injection orifices generally face into a flow of oncoming air with the feed tubes being positioned forward of a plurality of sound attenuating baffles.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to gas turbine engines. More particularly, embodiments of the present invention relate to a system and method for providing heated air to the inlet of a gas turbine engine for providing engine turndown and anti-icing capability. 
       BACKGROUND OF THE INVENTION 
       [0003]    Gas turbine engines operate to produce mechanical work or thrust. Specifically, land-based gas turbine engines typically have a generator coupled thereto for the purposes of generating electricity. A gas turbine engine comprises an inlet that directs air to a compressor section, which has stages of rotating compressor blades. As the air passes through the compressor, the pressure of the air increases. The compressed air is then directed into one or more combustors where fuel is injected into the compressed air and the mixture is ignited. The hot combustion gases are then directed from the combustion section to a turbine section by a transition duct. The hot combustion gases cause the stages of the turbine to rotate, which in turn, causes the compressor to rotate. 
         [0004]    The inlet of the gas turbine engine can also include heating devices and noise reduction devices. Specifically, heating devices can include injection devices capable of injecting heated air into the inlet. Noise reduction systems often times includes a plurality of baffles that reduce noise generated by a passing inlet air stream. 
         [0005]    Referring to  FIGS. 1 and 2 , a portion of an inlet bleed heat system  100  of the prior art is depicted. The inlet bleed heat system  100 , which injects heated air into an inlet, comprises a plurality of feed tubes  102  that are positioned aft of and in-line with a silencer baffle  104 . The plurality of feed tubes  102  receive a flow of heated air from a supply pipe  106  that is located above the baffles  104 . As such, the plurality of feed tubes  102  hang in a generally vertical direction behind the baffles  104 . Each of the feed tubes  102  contain a plurality of feed holes  108  that inject the flow of heated air from the feed tube  102  into a passing flow of inlet air. The plurality of feed holes  108  are oriented generally perpendicular to the passing flow of inlet air such that adjacent feed tubes  102  have feed holes  108  directed towards each other, as depicted in  FIG. 2 . 
       SUMMARY 
       [0006]    Embodiments of the present invention are directed towards a system and method for, among other things, providing a supply of heated compressed air to an inlet of a gas turbine engine. An inlet bleed heat system in accordance with the present invention improves a range over which the gas turbine engine can be more effectively operated. Furthermore, the inlet bleed heat system, as disclosed, can provide a more uniform mixture of inlet air and heated compressed air in a shorter distance prior to entering a compressor section of the gas turbine engine. 
         [0007]    In one embodiment of the present invention an inlet bleed heat system comprises a supply conduit, a plurality of feed tubes extending from the supply conduit, and a guide tube for receiving ends of the feed tubes opposite of the supply conduit. The feed tubes each have a plurality of injection orifices and the feed tubes are oriented such that the injection orifices generally face into a flow of oncoming air. 
         [0008]    In another embodiment, a gas turbine engine is provided having a compressor, one or more combustion systems, a turbine, and one or more inlets. The one or more inlets comprise a housing, a plurality of baffles, a supply conduit, a plurality of feed tubes, and a guide tube. In this embodiment, the supply conduit extends generally longitudinally across the housing and has a plurality of openings to which the plurality of feed tubes are coupled. The plurality of feed tubes each have a plurality of injection orifices, and are also received in openings in the guide tube, which is oriented generally parallel to the supply conduit. In this embodiment, the supply conduit, plurality of feed tubes, and guide tube are positioned forward of the plurality of baffles within the inlet, with the plurality of injection orifices oriented in a direction opposite of the baffles. 
         [0009]    In yet another embodiment, a method of providing increased turndown capability to a gas turbine engine is disclosed. Increasing the turndown capability of the engine allows the engine to be operated at a lower power setting than can typically be reached given minimum operating requirements and emissions permitting regulations. The method comprises directing a supply of compressed air from a compressed air source, such as an engine compressor, into a supply conduit, where a portion of the supply conduit is positioned within an inlet of the gas turbine engine. The supply of compressed air is distributed from the supply conduit to a plurality of feed tubes, where it is injected through a plurality of injection orifices into a flow of inlet air. The injection orifices are positioned generally normal to the flow of inlet air. The supply of compressed air initially travels in a direction generally opposite to the flow of inlet air and then turns and travels in a direction generally with the flow of inlet air. As such, the supply of compressed air travels around each of the feed tubes such that mixing with the flow of inlet air is promoted. 
         [0010]    Additional advantages and features of the present invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0011]    The present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0012]      FIG. 1  depicts an elevation view of a portion of an inlet bleed heat system of the prior art; 
           [0013]      FIG. 2  depicts a cross section view of a portion of the inlet bleed heat system of  FIG. 1 ; 
           [0014]      FIG. 3  depicts a perspective view of a gas turbine engine in accordance with an embodiment of the present invention; 
           [0015]      FIG. 4  depicts a perspective view of an inlet portion of a gas turbine engine in accordance with an embodiment of the present invention; 
           [0016]      FIG. 5  depicts a cross section view of a portion of the inlet depicted in  FIG. 4  in accordance with an embodiment of the present invention; 
           [0017]      FIG. 6  depicts a detailed elevation view of a portion of the feed tubes of the inlet depicted in  FIG. 4  in accordance with an embodiment of the present invention; 
           [0018]      FIG. 7  depicts a detailed perspective view of a portion of the feed tubes and supply conduit depicted in  FIG. 4  in accordance with an embodiment of the present invention; and, 
           [0019]      FIG. 8  depicts a partial exploded view of a portion of the supply conduit and a feed tube of  FIG. 7  in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The subject matter of the present invention is described with specificity herein to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventors have contemplated that the claimed subject matter might also be embodied in other ways, to include different components, combinations of components, steps, or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies. 
         [0021]    Referring now to  FIG. 3 , a gas turbine engine  300  in accordance with an embodiment of the present invention is depicted. The gas turbine engine  300  comprises a compressor  302 , which for the embodiment depicted is an axial type compressor. However, other compressor arrangements can be utilized in conjunction with this invention. The gas turbine engine  300  also comprises one or more combustion systems  304  that are in fluid communication with the compressor  302 . For the embodiment depicted in  FIG. 3 , the gas turbine engine  300  utilizes a plurality of can-annular combustion systems. However, the invention is not limited to this combustor arrangement and can include a variety of combustor types (i.e. diffusion, premix, or a combination) that operate on a variety of fuel types (i.e. liquid, gaseous, or both). 
         [0022]    Mechanically coupled to the compressor  302  and in fluid communication with the one or more combustion systems  304  is a turbine  306 . The compressor  302  is coupled to the turbine  306  through a shaft that runs along a centerline of the engine. The turbine  306  receives the hot combustion gases from the one or more combustion systems  304  and the passing of the hot combustion gases across the blades of the turbine  306  turns the turbine  306 , and thereby turns the compressor  302 . 
         [0023]    Air is the primary fluid used by the gas turbine engine  300  for compression, and that is mixed and reacted with a fuel source, so as to create the hot combustion gases used to drive the turbine. One or more inlets  308  are in fluid communication with the compressor  302  and are used to direct the air into the compressor  302 . With reference now to  FIGS. 4-8 , the one or more inlets  308  comprise a housing  310  as well as other components of an inlet bleed heat system  312 . Located within the housing  310  is a plurality of generally axially extending baffles  314 . These baffles  314  are positioned within the housing  310  to reduce noise associated with a flow of inlet air passing through the housing  310 . 
         [0024]    In this embodiment of the present invention, a supply conduit  316  extends through a wall of the housing  310  and generally longitudinally across a lower portion of the housing  310 , as depicted in  FIG. 4 . In order to provide adequate sealing between the housing  310  and the supply conduit  316 , a rope seal is positioned at the their interface to ensure that air directed into the inlet does not leak out of the inlet and into the surrounding atmosphere. 
         [0025]    The supply conduit  316  is coupled to a plurality of feed tubes  318 , which have a first end  320  and a second end  322 , and a plurality of injection orifices  324 . This coupling can occur in a variety of ways. One such way is through a threaded engagement between the supply conduit  316  and the first end  320  of the plurality of feed tubes  318 . This coupling between the supply conduit  316  and the first end  320  of the plurality of feed tubes  318  is depicted in  FIG. 8 . The plurality of feed tubes  318  are coupled in a manner such that they extend in a generally perpendicular direction from the supply conduit  316 . While a threaded engagement has been described, alternate coupling means between the supply conduit  316  and the plurality of feed tubes  318  are also envisioned, such as welding or removable fasteners. 
         [0026]    The plurality of injection orifices  324  are drilled holes into the plurality of feed tubes  318 . A variety of means can be used for placing the plurality of injection orifices  324  into the plurality of feed tubes  318 . Some possible means include standard machine drilling, laser drilling, and electrical discharge machining (EDM). Due to the location and orientation of the plurality of feed tubes  318 , complex injection nozzles in each of the plurality of injection orifices  324  are not required. 
         [0027]    Positioned at the second end  322  of the plurality of feed tubes  318  is a guide tube  326 . The guide tube  326  is oriented generally parallel to the supply conduit  316  and has a plurality of openings for receiving the second end  322  of the plurality of feed tubes  318 . The openings in the guide tube  326  are larger than the diameter of the feed tubes  318  such that the feed tubes are retained within the guide tube  326  while not imparting a load onto the feed tubes  318 . With the first end  320  of the plurality of feed tubes  318  coupled to the supply conduit  316 , it is not desirable to couple the second end  322  to the guide tube  326 . This allows for the plurality of feed tubes  318  to grow thermally towards the guide tube  326  to minimize any thermal stress in the plurality of feed tubes  318 . Furthermore, since the second end  322  of the plurality of feed tubes  318  are not coupled to the guide tube  326  and can therefore rub or slide on the opening in the guide tube  326 , it is possible that either one or both of these components can adversely wear. To limit the amount of wear exhibited by the plurality of feed tubes  318 , an embodiment of the present invention has an area adjacent to the second end  322  of each feed tube  318 , which contacts the opening in the guide tube  326 , coated with a Tungsten Carbide (WC—Co) coating. This coating protects the plurality of feed tubes  318  and directs any wear to the guide tube  326 , which is a simpler and less expensive component to repair and/or replace. 
         [0028]    One such practical embodiment of the present invention utilizes a supply conduit  316  that extends across the housing  310  a length of nearly 12 feet and has eight feed tubes  318  that extend upward from the supply conduit  316 . The supply conduit  316 , plurality of feed tubes  318 , and guide tube  326  are each fabricated from a stainless steel. These feed tubes  318  extend upwards a height of nearly 11 feet and contain over 100 equally spaced injection orifices  324 . The quantity, size, and spacing of the plurality of injection orifices  324  is a function of a variety of factors such as pressure and temperature of the supply of compressed air and desired penetration of the supply of compressed air into the flow of inlet air. The plurality of feed tubes  318  are received within openings in the guide tube  326 , which extends a length similar to that of the supply conduit  316 . 
         [0029]    As shown in  FIG. 4 , the supply conduit  316  extends in a generally horizontal direction, or longitudinally across the lower portion of the housing  310 , and the plurality of feed tubes  318  extend generally perpendicular to the supply conduit  316 , or in a generally vertical direction, which is parallel to the baffles  314 . While this is one embodiment that is convenient from a piping arrangement and for securing the supply conduit  316  to the housing  310 , it is not the only possible arrangement. An alternate configuration of the components of the inlet bleed heat system  312 , namely the supply conduit  316 , plurality of feed tubes  318 , and guide tube  326  would be to orient the inlet bleed heat system 90 degrees to that depicted in  FIG. 4 , such that the supply conduit  316  would be oriented in a generally vertical direction. In this alternate configuration, the plurality of feed tubes  318  would then extend in a generally horizontal direction to a generally vertically extending guide tube  326 . This type of arrangement for the components of the inlet bleed heat system  312  may be necessary depending on the orientation of the baffles  314  and the manner in which a supply conduit  316  can be directed into the housing  310 . It is also possible that the configuration depicted in  FIG. 4  could be inverted 180 degrees such that the supply conduit  316  extends across an upper portion of the housing  310  and the plurality of feed tubes  318  extend downward to a guide tube  326  that extends along a lower portion of the housing  310 . Alternatively, the inlet bleed heat system  312  could be oriented at some angle in between. 
         [0030]    Referring to  FIGS. 4 and 5 , the supply conduit  316 , plurality of feed tubes  318 , and guide tube  326  are positioned forward of the plurality of generally axially extending baffles  314 . As it can be seen in  FIG. 5 , in addition to the axial position of the feed tubes  318  relative to the baffles  314 , the plurality of feed tubes  318  are also positioned such that the plurality of injection orifices  324  are oriented in a direction generally opposite to the baffles  314 . Although depicted forward of the generally axially extending baffles  314 , the supply conduit  316 , plurality of feed tubes  318 , and guide tube  326  can be positioned aft of the baffles  314  as long as the plurality of injection orifices  324  are oriented into the flow of inlet air. 
         [0031]    In an alternate embodiment of the present invention, an inlet bleed heat system  312  is provided. This inlet bleed heat system  312  is typically used in conjunction with the gas turbine engine  300  previously discussed, however can be fabricated and installed separately from the gas turbine engine  300 . The inlet bleed heat system  312  comprises a supply conduit  316  oriented in a generally horizontal direction, a plurality of feed tubes  318 , and a guide tube  326 . More specifically, the plurality of feed tubes  318  have a first end  320 , a second end  322 , and a plurality of injection orifices  324 . The plurality of feed tubes  318  are positioned such that the plurality of injection orifices  324  are oriented generally into a flow of oncoming air (see  FIG. 5 ). The first end  320  of the feed tubes  318  are coupled to the supply conduit  316  and the feed tubes extend in a direction that is generally perpendicular from the supply conduit  316 . A manner by which the plurality of feed tubes  318  are coupled to the supply conduit  316  is through a threaded coupling in that the first end  320  of the feed tubes  318  is threaded so as to engage a corresponding threaded portion  328  of the supply conduit  316  (see  FIG. 8 ). 
         [0032]    The guide tube  326  is spaced a distance apart from the supply conduit  316  and is oriented generally parallel with the supply conduit  316 . The guide tube  326  further comprises a plurality of openings for receiving the second end  322  of the plurality of feed tubes  318 . These openings have a diameter that is larger than that of the plurality of feed tubes  318  so as to provide space to compensate for any thermal growth of the plurality of feed tubes  318 . The inlet bleed heat system  312  is coupled to a source of compressed air, which may or may not be associated with the gas turbine  300 . Examples of the source of compressed air can include an auxiliary compressor or storage tank. 
         [0033]    In yet another embodiment of the present invention, a method of providing increased turndown to a gas turbine engine is disclosed. Turndown, as one skilled in the art will understand, allows an operator of a gas turbine engine to run the engine at lower load settings while maintaining emissions compliance. Often times complex fuel scheduling is required to lower the load settings without violating emissions regulations. However, an alternate manner in which engine turndown can be achieved is through adding pre-heated air to the compressor of the engine. By raising the air temperature to the compressor, the air density is reduced, thereby reducing the mass flow through the engine, and hence the power output of the gas turbine. 
         [0034]    The method comprises directing a supply of compressed air from a compressed air source into a supply conduit. One form of a compressed air source is a plenum of compressed air positioned adjacent the discharge of the engine compressor. However, compressed air can be taken directly from a stage of the compressor if lower pressure air is desired. For an embodiment of the present invention, compressed air taken from the compressor discharge has a pressure of approximately 110 pounds per square inch (psi) and a temperature of approximately 550 degrees Fahrenheit (deg. F.). The compressed air is directed into a supply conduit  316 , of which a portion of the supply conduit  316  is positioned within a housing  310  of the gas turbine engine  300 , as depicted in  FIG. 4 . However, the supply conduit  316  also includes portions that extend between the compressed air source and the inlet  308  of the gas turbine engine as depicted in  FIG. 3 . 
         [0035]    The supply of compressed air is then distributed from the supply conduit  316  to a plurality of feed tubes  318 . As depicted in  FIG. 4 , the plurality of feed tubes  318  extend from the supply conduit across the housing  310 . The supply of compressed air is then injected into a flow of inlet air by a plurality of injection orifices  324  in each of the plurality of feed tubes  318 . As it can be seen by  FIG. 5 , the plurality of injection orifices  324  are positioned generally normal to the flow of inlet air. In operation, the supply of compressed air is injected by the plurality of feed tubes  318  and travels in a direction generally opposite to that of the flow of inlet air. The supply of compressed air then turns and travels in a direction generally with the flow of inlet air. As a result, the supply of compressed air then travels around each of the plurality of feed tubes  318  which propagates mixing. This change in flow direction is depicted by the arrows in  FIG. 5 . The direction of compressed air injection allows the compressed air to penetrate upstream, thereby maximizing the effective mixing length with the flow of inlet air prior to the mixture entering the compressor  302  of the gas turbine engine  300 . As an example, the length required to mix the supply of compressed air with the flow of inlet air is reduced to approximately 14 inches, which is a significantly shorter mixing distance than the prior art. 
         [0036]    The use of an inlet bleed heat system  312  is primarily used for either achieving low power operations (turndown) while maintaining emissions compliance or for anti-icing functions. If ice forms in the housing  310  of the inlet  308  and breaks loose during engine operation, severe damage can occur to the compressor  302 . Therefore, by injecting a supply of compressed air into the housing  310  having an elevated temperature compared to the flow of inlet air, the overall operating temperature of the inlet  308  is increased, thereby preventing ice formation. 
         [0037]    The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments will become apparent to those of ordinary skill in the art to which the present invention pertains without departing from its scope. 
         [0038]    From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages which are obvious and inherent to the system and method. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and within the scope of the claims.