Abstract:
A fuel system comprises a fuel nozzle having a first port and a second port, a first manifold connected to the first port, and a first inert gas buffer portion disposed between the first manifold and a source of compressed air.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to gas turbine fuel systems and more particularly to fuel systems for Dry Low Nitrogen Oxide (NOx) combustion systems. 
         [0002]    High hydrogen content low BTU gaseous fuel (synthetic gas) may be derived from a variety of sources including, for example, coal gasification processes or alternative sources such as coke gas and other industrial chemical processes. 
         [0003]    Dry Low NOx (DLN) systems may include the use of synthetic gas or other types of gas having a relatively high hydrogen content that is blended with a high BTU gaseous fuel such as, for example, natural gas. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one aspect of the invention, a fuel system comprises a fuel nozzle having a first port and a second port, a first manifold connected to the first port, and a first inert gas buffer portion disposed between the first manifold and a source of compressed air. 
         [0005]    According to another aspect of the invention, a method of controlling a fuel system comprises purging a first fuel source manifold with an inert gas, purging an inert gas buffer portion of the fuel system with the inert gas, closing a vent valve connected to the inert gas buffer portion, and stopping the purge of the first fuel source manifold. 
         [0006]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0007]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  is exemplary embodiment of a fuel system. 
           [0009]      FIGS. 2-9  illustrate exemplary alignments of the fuel system of  FIG. 1 . 
       
    
    
       [0010]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    Dry Low NOx (DLN) gas turbine systems often use a fuel such as, for example, synthetic gas that has a H2 content less than 5% and a natural gas fuel. The use of a fuel having a higher H2 content (greater than 5%) hereinafter, H2 blend gas increases the risk of undesirable combustion in the piping and manifolds of the fuel system. The system and methods described below include a DLN system that allows H2 blend gas and natural gas to be safely used over a range of gas turbine system operating modes. 
         [0012]      FIG. 1  illustrates an exemplary embodiment of a fuel system  100 .  FIG. 1  shows an example of the fuel system  100  in a turbine light off mode that will be described in detail below. The system  100  includes one or more fuel nozzles  110  that may have a plurality of ports. In the illustrated embodiment the ports include a primary inner port  101 , a primary outer port  103 , a transfer port  105 , and a secondary/pilot port  107 . The ports are each connected to an associated manifold that directs gas to the port. The manifolds include a primary inner manifold  102 , a primary outer manifold  104 , a transfer manifold  106 , and a secondary manifold  108 . Compressor discharge air (CPD)  113  is received from the compressor turbine (not shown) and is delivered to the system  100  via a CPD manifold  114 . The CPD  113  is used to cool the fuel nozzle  110  and to purge manifolds. A first gas supply  120  that may include, for example, natural gas provides a first gas to the fuel nozzle  110  via a first gas supply manifold  124 . The system  100  includes inert gas buffers  116  and  118 . The inert gas buffers receive an inert gas  123  such as, for example N2 or CO2 from an inert gas supply (not shown). The inert gas buffers  116  and  118  may be used to separate the CPD  113  gas from gas received from a second gas supply  122 . The second gas is provided to the fuel nozzle  110  via a second gas supply manifold  126 . The system  100  includes a number of stop valves and flow control valves that control the flow of gas in the system. 
         [0013]      FIG. 1  illustrates an example of the alignment of the system  100  in a light off mode. The shaded valves represent valves in a closed position, while the unshaded valves represent valves in an open position. In this regard, the VS 4 - 1 , VSR- 1  and the VGC- 1  valves are open allowing the primary outer port  103  to receive gas from the first gas supply  120  via the primary outer manifold  104 . The VA 13 - 13 , VA 13 - 14 , VA 13 - 3  and VA 13 - 4  valves are open allowing the primary inner port  101  and the transfer port  105  to receive CPD air  113 . The VGC- 2  valve is closed, isolating the secondary port  107 . 
         [0014]      FIG. 2  illustrates an example of the alignment of the system  100  in a “lean-lean” fuel operating mode. The VGC- 2  valve is open sending the gas from the first gas supply  120  to the secondary/pilot port  107  via the secondary manifold  108 . 
         [0015]      FIG. 3  illustrates an example of the alignment of the system  100  where the transfer port  105  receives fuel. In the illustrated example, the VA 13 - 3  and VA 13   4  valves have been closed stopping the flow of CPD  113  gas to the transfer manifold  106 , while the VA 13 - 16  valve has been opened to vent. The VGC- 3  valve is opened allowing gas from the first gas supply  120  to flow to the transfer port  105  via the transfer manifold  106 . The VGC- 1  valve has been closed preventing fuel from flowing to the primary outer port  103 . 
         [0016]      FIG. 4  illustrates an example of the alignment of the system  100  that prepares the system  100  to receive fuel from the first gas supply  120  and the second gas supply  122  and output the blended fuel via the primary outer port  103 . The VGC  1  valve has been opened, allowing the fuel from the first gas supply  120  to flow to the primary outer port  103 . The VGC- 3  valve has been closed, preventing fuel from the first gas supply  120  from flowing to the transfer port  105 . The valves VA 13 - 3  and VA 13 - 4  have been opened and the VA 13 - 16  valve is closed allowing CPD  113  gas to flow to the transfer port  105 . 
         [0017]      FIG. 5  illustrates an example of the alignment of the system  100  that further prepares the system to output blended fuel via the primary outer port  103 . In the illustrated example, the VAH 1 - 5  valve is opened. Opening the VAH 1 - 5  valve allows inert gas  123  to flow through the inert gas buffer  118  and vent via the VA 13   16  valve. The flow of inter gas  123  through the inert gas buffer  118  purges the inert gas buffer of any non-inert gas such as, for example, gaseous fuel or CPD air  113 . The VAH 1 - 1  valve is opened, purging the second gas supply manifold  126  with inert gas  123  that vents via the VA 13 - 22  valve. The VA 13 - 20  valve is closed, and the VS 4 - 11  valve is opened. 
         [0018]      FIG. 6  illustrates an example of the alignment of the system  100  when the primary outer port  103  is receiving a blend of fuel from the first and second gas supplies  120  and  122 . In the illustrated example, the VA 13 - 17  valve is closed, and the inert gas  123  is maintained at a higher pressure than the CPD air  113 , the first gas  120  and the second gas  122 . The higher pressure of the inert gas  123  prevents non-inert gas from entering the inert gas buffer  118 ; safely isolating the second gas supply  122  from non-inert gas. The VSR- 11  and the VGC- 11  valves are opened allowing fuel from the second gas supply  122  to mix with fuel from the first gas supply  120  and flow to the primary outer port  103 . 
         [0019]      FIG. 7  illustrates an example of the alignment of the system  100  that prepares the system to output blended fuel via the primary inner port  101 . The valve VA 13 - 17  is opened allowing the inert gas buffer  118  to be purged with inert gas  123  that is vented via the VA 13 - 17  valve. The VA 13 - 13  and VA 13 - 14  valves are closed preventing the CPD air  113  from flowing through the primary inner manifold  102 . The VAH 1 - 3  and VA 13 - 15  valves are opened purging the inert gas buffer  118  with inert gas  123  vented via the VA 13 - 15  valve. The VAH 1 - 2  valve is opened, purging the primary inner manifold  102  and primary inner port  101  with inert gas  123   
         [0020]      FIG. 8  illustrates an example of the alignment of the system  100  when the primary inner port  101  is receiving a blend of fuel from the first and second gas supplies  120  and  122 . The VA 13 - 15  valve is closed, pressurizing the inert gas buffer  116  with inert gas  123 . The VAH 1 - 2  valve is closed. The VGC- 4  valve is opened, allowing fuel from the first gas supply  120  to flow to the primary inner manifold  102 . The VS 4 - 12  and VGC- 12  valves are opened allowing fuel from the second gas supply  122  to flow to the primary inner manifold  102  and mix with the fuel from the first gas supply  120 . The mixed or blended fuel flows to the primary inner port  101 . 
         [0021]      FIG. 9  illustrates an example of the alignment of the system  100  when the system is in a “tripped” or secured mode. In the illustrated example, the vent valves including the vent valves VA 13 - 31  and VA 13 - 27  are opened. The valves controlling the flow of the inert gas  123  including the valve VAH  1 - 4  are opened allowing inert gas  123  to purge and vent through ports  101  and  103 , and to purge and vent from the inert gas buffers  116  and  118 . The valves controlling the flow of fuel and CPD air  113  are closed. 
         [0022]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.