Patent Publication Number: US-7707836-B1

Title: Venturi cooling system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a Continuation of pending U.S. patent application Ser. No. 12/357,029, filed on Jan. 21, 2009. 

   TECHNICAL FIELD 
   The present invention relates to combustors that may be used in combustion turbines. More specifically, the present invention relates to a system for cooling the venturi throat region between the primary and secondary combustion chambers. 
   BACKGROUND 
   Gas turbines play a significant role in a number of applications, such as aircraft propulsion, marine propulsion, power generation and driving processes, such as pumps and compressors. Typically, a gas turbine includes a compressor, a combustor and a turbine. In operation, air is fed into the system where it is compressed by the compressor and mixed with fuel in the combustor. The compressed air and fuel mixture are then burned within the combustor to cause an expansion of the air flow, which is responsible for driving the turbine. 
   Combustion liners define the interior volume of the combustor and serve to protect the combustor casing and remaining engine parts from the extreme temperatures present within the combustor. In order to reduce NO x  emissions and extend the longevity of engine components, it is desirable to use a portion of the compressed air exiting the compressor for cooling various combustor components, including the combustion liner. 
   Combustion liners often include a venturi throat region that is used to influence the flame location within the combustor and to stabilize the combustion flame. In such arrangements, a lowering of the NO x  emissions is achieved by lowering peak flame temperatures through the burning of a lean, uniform mixture of fuel and air. Uniformity is typically achieved by pre-mixing fuel and air in the combustor upstream of the venturi and then firing the mixture downstream of the edge or apex of the venturi into the secondary combustion chamber. The venturi configuration, by virtue of accelerating the flow preceding the throat portion, is intended to keep the flame from flashing back into the pre-mixing region or primary combustion chamber, upstream of the venturi throat. The flame holding region, upstream of the venturi, is also required to be cooled under certain operating conditions. Since flames can reside on each side of the venturi, both sides need to be cooled. However, if the flow of cooling air released downstream of the venturi is too large or is released too close to the venturi, it may adversely affect combustion performance. 
   U.S. Pat. No. 5,117,636 shows a cooling passageway within the venturi that is extended downstream from the venturi apex or throat, such that the cooling air does not re-enter the flame holding zone within the secondary combustion chamber. It is intended that the functions of flame holding and venturi cooling are decoupled. U.S. Pat. No. 6,430,932 shows a cooling chamber within a venturi that directs the cooling flow counter to the combustion flow and dumps cooling air upstream of the venturi. 
   It has been determined that the heat load on the upstream and downstream sides of the venturi are different and the dumping of cooling air near the venturi on either side has an effect on the operation of the combustor. In the prior designs, where the cooling of both sides of the venturi are linked, there has not been a balancing of the heat pickup within the venturi walls nor has there been an accommodation made for pressure drop within the cooling passageway. 
   SUMMARY OF THE INVENTION 
   A combustor is provided for a gas turbine engine of the type having a nozzle assembly located at a first end of the combustor and a combustion chamber defined at a second end of the combustor, downstream of the nozzle. A venturi is positioned between the nozzle and the combustion chamber. The venturi defines a transition between the first end of the combustor and the second end of the combustor. The venturi includes a passageway therein for receipt of a cooling air flow. The passageway has a first side facing the nozzle and a second side facing the combustion chamber. A compressed air source is directed into the passageway with the flow inlet being in communication with both the first and second sides of the venturi passageway. The venturi passageway directs compressed air from the source in opposite directions within the venturi. Thus, the air flow in the first side and second side of the passageway are in opposite directions. 
   A further aspect of the invention may include a secondary passageway that extends upstream of the second side of the venturi passageway. Further, the cooling flow inlet may be positioned closer to the nozzle or closer to the upstream side of the venturi apex. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, there is illustrated a number of embodiments which are presently preferred. 
       FIG. 1  shows a simplified cross-section of a gas turbine combustion system incorporating an embodiment of the present invention. 
       FIG. 2  is a partial cross-sectional view of the venturi throat region of the combustion system illustrated in  FIG. 1 . 
       FIG. 3  is a partial cross-sectional view of a further embodiment of a venturi system for use in a combustion system. 
       FIG. 4  is a partial cross-sectional view of still a further embodiment of a venturi system for use in a combustion system. 
   

   DETAILED DESCRIPTION 
   In the drawings, there is shown a graphical representation of a typical combustor and a number of embodiments of the present invention. The combustor is generally designated by the numeral  10  and is contemplated to be incorporated into a gas turbine (not shown). In  FIG. 1 , the combustor  10  includes a combustion liner  12  that is at least partially surrounded by a heat shield or flow sleeve  14 . Compressed air is provided from an upstream compressor (not shown) and fed into a surrounding channel  16  formed between the heat shield  14  and combustion liner  12 . 
   Within the confines of the combustion liner  12  are provided a plurality of primary fuel nozzles  18  and a secondary fuel nozzle  20 . A combustor flow sleeve  22  is provided surrounding the secondary fuel nozzle  20 , separating the secondary nozzle  20  from the primary nozzles  18 . Fuel  24  is introduced into a controller  26  and fed to the nozzles  18 ,  20 . The area between the combustion liner  12  and combustor flow sleeve  22  defines an upstream or primary combustion chamber  28 . Downstream of the secondary nozzle  20  is a venturi  30  defining an annular restriction within the area defined by the combustion liner  12 . The venturi  30  includes an apex  32  that defines a venturi throat portion. The apex  32  is positioned downstream of the nozzles  18 ,  20 . A downstream or secondary combustion chamber  34  is positioned within the combustor downstream of the venturi apex  32 . 
   In operation, a flame can reside on either side of the venturi  30 , both in the upstream combustion chamber  28  and the downstream combustion chamber  34 . In a primary operation, fuel  24  is provided to the primary nozzles  18 , with combustion occurring in the upstream combustion chamber  28  and directed downstream through the venturi throat  32 . In a lean-lean operation, fuel  24  is provided to the primary nozzles  18  as well as to the secondary nozzle  20 . Combustion occurs in both the upstream combustion chamber  28  as well as the downstream combustion chamber  34 . In addition, the combustor  10  may operate with fuel  24  directed solely to the secondary nozzle  20 , creating combustion in the downstream combustion chamber  34 . Additional fuel  24  may be provided to the primary nozzles  18  without flame being created in the upstream combustion chamber  28 . The fuel and air pre-mix passing through the upstream chamber  28  is directed by the venturi  30  into the downstream combustion chamber  34  creating a pre-mix operation and a significant flame within the downstream chamber  34 . 
   Since flames can reside on either side of the venturi  30 , both sides of the walls of the venturi typically need to be cooled for proper operation and for longevity of the equipment. As shown in  FIG. 1 , cooling air in the surrounding channel  16  is directed on to the rear side of the venturi  30  and then directed along the inside walls of the venturi  30 . The heat load on the upstream and downstream sides of the venturi  30  are contemplated to be different. In addition, movement of the cooling air back into the combustion chambers on either side of the venturi  30  also has an affect on operation of the combustor  10 . 
   In  FIG. 2 , there is shown an enlarged schematic cross-sectional view of one side of the venturi  30  illustrated in  FIG. 1 . Compressed air  36  is directed into a plenum  38  on the back side of the venturi  30 . In this embodiment, the inlet plenum  38  is positioned directly behind the apex  32  of the venturi  30 . The cooling air is directed substantially perpendicular to a horizontal ground plane and is directed to the venturi  30  by the inlet plenum  38 , which is in fluid communication with two channels  40  and  42  that are generally parallel to a first or upstream side  41  of the venturi  30  and a second or downstream side  43  of the venturi  30 . As shown in  FIGS. 2 and 3 , sides  41 ,  43  are preferably not perpendicular to liner  12  but are angled with respect thereto. The cooling air  36  directed into the channel  40  is turned in an opposite direction from the cooling air directed into the channel  42 . The air flow along the upstream channel  40  on the upstream side  41  of the venturi  30  is directed through an upstream exit  44  and into the primary combustion chamber  28 . The cooling flow passing through the downstream channel  42  and along the downstream side  43  is directed through downstream exit  46 , positioned adjacent the combustion liner  12 , and into the downstream combustion chamber  34 . As shown, preferably, upstream exit  44  and downstream exit  46  are at the respective ends of sides  41 ,  43  and may be adjacent liner  12 . In addition, the upstream exit and downstream exit may be at a distal end with respect to the apex. As also shown, the air that exits from upstream exit  44  may be directed towards the first end of the chamber and the air that exits from downstream exit  46  may be directed towards the second end of the chamber. A number of specific forms of exhaust exits for the venturi air are known in the prior art and may be incorporated into the venturi  30  as presently described. 
   In  FIG. 3 , a variation of the structures of the invention is shown. The cooling air  36  is directed from the channel  16  into an inlet plenum  138  having an outlet that is positioned adjacent the downstream side  43  of the venturi  30 . The inlet plenum  138  is in direct fluid communication with the downstream channel  142 . Cooling air is directed in a downstream direction through the channel  142 , towards the downstream exit  46 . An additional flow of cooling air is directed within the downstream channel portion  142   a  in the opposite direction from the downstream exit  46 . Cooling channel portion  142   a  communicates with upstream channel  140 , positioned behind the upstream side  41  of the venturi  30 . The cooling air within the upstream channel  140  is directed through the upstream exit  44  and into the upstream combustion chamber  28 . Positioning the cooling channel on the downstream face of the venturi reduces the cooling required for the downstream portion of the venturi. Alternatively, the inlet plenum  138  may be positioned adjacent the upstream side  41  of the venturi  30 . 
   Thus, the venturi defines a transition between the first and second ends of the combustor. The internal passageway within the venturi includes a first side and a second side on opposite sides of an apex of the venturi. The cooling inlet for the compressed air flow is in fluid communication with the first and second sides of the venturi passageway and the compressed air from the cooling inlet is directed through the venturi passageway in opposite directions within the first side and second side. The cooling inlet may communicate with the venturi passageway at a position in line with or offset from the apex of the venturi. The cooling inlet may be formed as a radial plenum positioned behind the venturi or may take any number of other forms. 
   In  FIG. 4 , a further embodiment of a venturi cooling system is provided. The cooling air  36  is directed from the channel  16  into an inlet plenum  238 . The inlet plenum  238  directs the cooling air into the channels  240 ,  242  on the rear side of the venturi  30 . As illustrated, the inlet plenum  238  is positioned adjacent the rear of the apex  32  of the venturi  30 , with the second passageway or upstream channel  240  directing cooling air along the upstream side  41  and the first passageway or downstream channel  242  directing cooling air along the downstream side  43 . The downstream end of channel  242  is in fluid communication with a liner or secondary passageway  248 . The cooling air within the channel  242  reverses in direction as it enters the secondary passageway  248 . The secondary passageway  248  extends towards the upstream side of the combustor and joins with the upstream channel  240 , adjacent an exhaust channel  250 . The combined flow from the upstream channel  240  and secondary passageway  248  passes through the exhaust channel  250  and is exhausted through the upstream exit  244  into the combustion chamber  28  on the upstream side of the venturi  30 . As shown in  FIG. 4 , the cooling air exit may be positioned upstream of the first side of the venturi. 
   In the embodiment shown in  FIG. 4  (and in the embodiments described above), it is contemplated that inlet plenum  238  may comprise something other than a continuous slot or annular channel. The inlet plenum  238  and secondary passageway  248  may be formed by a series of pipes that cross over one another. Thus, the inlet plenum  238  feeds the back side of the venturi  30  after crossing over the series of pipes that form the passageway  248 . Repositioning of the inlet plenum  238  with respect to the axial position of the apex  32  of the venturi  30  may also be utilized to adjust the cooling effect on the venturi  30 . In addition, as in all of the embodiments discussed herein, the relative size and formation of the channels and passageways may be varied so as to adjust the air flow and pressure drop of the cooling air as it moves inside the venturi walls and is then directed into the combustion chambers. 
   A variety of modifications to the embodiments described will be apparent to those skilled in the art upon review of the present disclosure. Thus, the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.