Abstract:
A combustor of an industrial gas turbine engine having a combustor secured within a combustor casing with a combustor cavity surrounding the combustor, and a flow liner forming a cooling air space between the casing and the flow liner in which high pressure cooling air can be passed to provide insulation to the casing from the high temperature gas surround the combustor. The flow liner can include a TBC or a layer of insulation to limit heat buildup of the cooling air flowing through the space to further insulate the casing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit to U.S. Provisional Application 62/295,811 filed Feb. 16, 2016 and entitled COOLED COMBUSTOR CASE WITH OVER-PRESSURIZED COOLING AIR. 
     
    
     GOVERNMENT LICENSE RIGHTS 
       [0002]    This invention was made with Government support under contract number DE-FE0023975 awarded by Department of Energy. The Government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    Field of the Invention 
         [0004]    The present invention relates generally to an industrial gas turbine engine, and more specifically an industrial gas turbine engine with a combustor flow liner to maintain a relatively low metal temperature of a combustor casing. 
         [0005]    Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98 
         [0006]    In an industrial gas turbine engine, compressed air from a compressor is delivered to a combustor cavity surrounding a combustor, where the compressed air flows into the combustor and is burned with a fuel to produce a hot gas flow that is then passed through a turbine to drive the compressor and an electric generator. The compressed air surrounding the combustor is also in contact with a combustor casing of the engine that is formed of a relatively thick metal material. The combustor casing must be made relatively thick in order to withstand the high pressure of the compressor exit air that surrounds the combustor and eventually flows into the combustor. The high temperature exposed to the combustor casing will limit the life of the casing and thus limit the life of the engine. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    An industrial gas turbine engine has a compressor that delivers high pressure air to a combustor cavity that surrounds a combustor and then flows into the combustor to be burned with a fuel to produce a hot gas flow. A turbine part such as a row of turbine stator vanes includes a cooling circuit in which compressed air is passed through for cooling of the turbine part, and the spent cooling air is delivered to the combustor through the combustor cavity instead of being discharged into the hot gas flow passing through the turbine. The cooling air for the turbine part is pressurized over the compressor discharge pressure so that the cooling air can cool the part and still have enough pressure for discharge into the combustor. The combustor casing part cooling air is cooled using an intercooler, and then the cooled highly pressurized air is passed through a flow liner passage to provide for an insulation to an inner side of the combustor casing to prevent over-heating of the casing. The cooling air used to cool the casing is then discharged into the combustor cavity along with the compressor discharge, and then flows into the combustor. 
         [0008]    The flow liner can be an annular single sheet liner to channel cooling air along the space within the casing, or the liner can be formed as a series of cooling channels each with an inlet and a discharge to discharge the cooling air into the combustor cavity. 
         [0009]    The flow liner can be coated on an outer side with a thermal barrier coating to limit heat transfer from the hot flow liner into the cooling air passing underneath the casing. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]      FIG. 1  shows a cross section view of a combustor case of an industrial gas turbine engine of the present invention. 
           [0011]      FIG. 2  shows a cross section view of a combustor case of an industrial gas turbine engine according to a second embodiment of the present invention. 
           [0012]      FIG. 3  shows a cross section close-up view of a combustor casing and flow liner of an industrial gas turbine engine according to a third embodiment of the present invention. 
           [0013]      FIG. 4  shows a cross section view of a section of a flow liner used in the combustor of the present invention. 
           [0014]      FIG. 5  shows a cross section view of a section of the flow liner with a thermal barrier coating on the cooling air flow side of the present invention. 
           [0015]      FIG. 6  shows a cross section view of a section of the flow liner with an insulator between two walls of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    The present invention is cooled combustor casing of an industrial gas turbine engine in which cooling air pressurized over the compressor exit pressure (referred to as P3) is cooled through a heat exchanger and then used to cool the combustor case so that the heated cooling air can be introduced into the combustor to burn with a fuel. This allows for lower temperature resistant and cheaper metal materials to be used for the combustor casing which must be relatively thick to withstand the high pressure at higher temperature within the combustor cavity. In the industrial gas turbine engine of the present invention, compressed air is supplied to an air cooled turbine part such as a row of stator vanes to provide cooling. The spent cooling air from the cooled turbine part is then discharged into the combustor to be burned with fuel instead of being discharged out into the turbine hot gas flow through film holes in the turbine part. This spent cooling air must be slightly higher in pressure than the compressor outlet pressure (P3) so that the spent cooling air can be discharged into the combustor to merge with the compressed air from the compressor exit at P3 pressure. The compressed air used for cooling of the turbine part can be compressed upstream of the turbine part with enough pressure to flow into the combustor, or the spent cooling air from the turbine part can be further compressed in a fan downstream of the turbine part and upstream of the combustor, and in both examples the compressed air to be used for cooling can be cooled using an intercooler before or after the boost compression occurs. It is this cooled over-pressurized cooling air supply that is passed through the space formed between the combustor casing and the flow liner that eventually flows back into the combustor cavity and then into the combustor combustion chamber. 
         [0017]    To utilize a low cost steel material for the combustor casing such as a steel or steel alloy, this invention proposes the use of a pre-conditioned high pressure, low-temperature cooling air supply from a semi-closed loop Advanced Recirculating Total Impingement Cooling return system. Cooling air fed into the combustor case is pressurized over the compressor exit pressure (P3) and cooled through a heat exchanger to pre-condition the cooling air flow. The use of pre-conditioned over pressurized air (&gt;P3) presents an innovative solution for the state-of-the-art systems which contain low available pressure ratios in combustor case cooling. The present invention, as shown in  FIGS. 1 and 2 , supplies the pre-conditioned cooling air via a plurality of pipes at the static outer casing. The combustor casing  14  must be relatively thick in order to withstand the relatively high pressure of the compressor discharge surrounding the combustor. The flow liner  16  is exposed to even pressure over both sides and thus can be as thin as required. However, the flow liner should be made from a material with low oxidation characteristics such as nickel based alloys but could also be made of the same material as the casing  14 . Cooling of the casing  14  is desirable to around 950 degrees F. in order to maximize the life of the thick casing. 
         [0018]      FIG. 1  shows a first embodiment of the combustor casing cooling design in which preconditioned air is supplied at supply flange  11  with convective cooling through one annular channel or a plurality of circumferential cooling channels  12  flowing from the aft of the case forward. The channel(s) purge spent cooling flow into the combustor cavity  13 . A annular shaped combustor flow liner  16  made from a high temperature resistant material is used to protect the combustor casing  14  which is made of a lower cost and lower temperature resistant metal. A hot air channel  15  surrounding the combustor  17  and transition duct  18  would be too hot for the combustor casing  14  to handle without cooling and thus would shorten the life of the combustor casing  14 . The preconditioned cooling air introduced through the supply flange or pipe  11  would flow is a space formed between the flow liner  16  and the combustor casing  14  to provide insulation to the casing  14  from the hot gas surrounding the combustor  15 . Since the flow liner can be made from a thinner piece of metal than the casing  14 , the flow liner can be made from a more expensive and higher heat resistant metal. Compressed air from the compressor flows into the cavity  15  surrounding the combustor  17  and the transition duct  18  and thus is relatively hot such that if the casing was exposed directly to the hot compressor gas its life would be limited. 
         [0019]      FIG. 2  shows a second embodiment of the combustor casing cooling design which includes convective cooling through a series of axial spaced impingement and circumferential cooling channel segments. Pre-conditioned cooling air can also be fed through a plurality of pipes  21  at the static outer casing  14  at multiple locations as shown in  FIG. 2  to minimize the cooling air heat up through the length of the casing cooling circuit. The cooling air discharged is then returned into the combustor casing for where it can be mixed with fuel to be burned in the combustor. Each of the preconditioned cooling air supply pipes  21  delivers the cooling air to a space formed between the combustor casing  14  and the flow liner  16 . In the  FIG. 2  embodiment, a high temperature resistant annular seal  22  is used to separate adjacent spaces so that the cooling air will be discharged through holes in the flow liner  16  and into the space surrounding the combustor  15 . The benefit to the  FIG. 2  embodiment over the  FIG. 1  embodiment is that fresh cooling air is used for each of the separate cooling flow spaces formed between the liner  16  and the casing  14 . In the  FIG. 1  embodiment, the cooling air will be quite hot when it reaches the end in which all of the cooling air flows into the combustor cavity  13 . The  FIG. 2  embodiment requires more cooling air, but results in a more uniform temperature distribution of the combustor casing  14 . 
         [0020]      FIG. 3  shows a third embodiment of the combustor cooling design in which the one piece annular flow liner with seals of  FIG. 2  is replaced with individual annular flow liners  26  arranged in series with the casing  14 . Each individual flow liner  26  is secured to the underside of the casing  14  to form a separate annular shaped cooling air passage between the flow liner  26  and the casing  14 . The cooling air flow out the forward end of the space and into the combustor cavity  13 . 
         [0021]      FIGS. 4-6  show different embodiment of the flow liner used in the present invention. In  FIG. 4 , the flow liner  16  is a plain metal liner made from a high temperature resistant material that can withstand the high temperature of the gas surrounding the combustor in the cavity  13 .  FIG. 5  shows a TBC  27  on the outer surface of the flow liner exposed to the cooling air flow in the space formed between the flow liner and the casing  14 . The TBC  27  prevents the cooling air from heating up too much so that the casing  14  remains relatively cool.  FIG. 6  shows a flow liner made from two walls  28  and  29  with an insulator  31  formed between the two walls.