Abstract:
The present invention is directed to a lean direct injection (LDI) combustion system for a gas turbine using a shell and tube heat exchanger concept to construct a shell and tube lean direct injector (“LDI”) for the combustion system. One side of the LDI injector, either the shell side or the tube side, carries an oxidizer, such as air, to the combustor, while the other side of the LDI injector carries fuel to the combustor. Straight or angled holes drilled in an end plate of the combustor allow the fuel to enter the combustor and mix with air being injected into the combustor.

Description:
[0001]    The present invention is directed to gas turbines, and more particularly to a lean direct injection (LDI) combustion system using a shell and tube heat exchanger concept to carry fuel and air to the combustor. 
       BACKGROUND OF THE INVENTION 
       [0002]    Most combustion processes have, in some way or another, a recirculating flow field. The recirculating flow field tends to stabilize the combustion reaction zone, but an unnecessarily large recirculation zone can result in high nitrogen oxide (NO x ) emissions for combustion systems. 
         [0003]    Lean direct injection for combustion has been shown to have the potential to reduce NO x  emissions. However, constructing a combustor to simply and uniformly inject many fuel and air streams presents a challenge. Non-premixed combustors typically use multiple fuel passages to inject fuel from a diffusion tip into air passing through an outer ring of the diffuser tip. This requires multiple diffuser tips with multiple separate air and fuel passages all mounted in a complicated head end assembly. 
         [0004]    The shell and tube LDI combustion system of the present invention provides a means for easily constructing a combustion system made up of many LDI injector sets with uniform air and fuel flow through all the passages using a concept similar to a shell and tube heat exchanger design. A shell and tube heat exchanger consists of a shell with a bundle of tubes inside it. One fluid flows through the tubes and another fluid flows over the tubes, through the shell, to transfer heat between the two fluids. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    The present invention is directed to a lean direct injection (LDI) combustion system using a shell and tube heat exchanger concept to construct a shell and tube lean direct injector (“LDI”) used with the combustion system. According to the present invention, one side of the LDI injector, either the shell or the tube, carries an oxidizer, such as air, to a combustor, while the other side of the LDI injector carries fuel to the combustor. The tubes carry the oxidizer (or fuel, or diluent or combinations thereof) to the combustor, while straight or angled holes drilled or otherwise cut into an end plate of the combustor allow the fuel (or oxidizer, or diluent or combinations thereof) to enter the combustor from the shell. Heat exchanger construction techniques, such as brazing or welding, are used to assemble the components of the LDI combustion system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a partial cross-sectional, perspective view of one embodiment of the shell and tube lean direct injection combustion system of the present invention. 
           [0007]      FIG. 2  is another partial cross-sectional, perspective view of the embodiment of the shell and tube lean direct injection combustion system of  FIG. 1  showing holes in the end plate of the combustor for introducing fuel from the shell side and air from the tube side into the combustor. 
           [0008]      FIG. 2A  is a cross-sectional schematic that shows two different methods for cutting fuel and air holes in the end of the combustor. 
           [0009]      FIG. 3  shows an alternative embodiment of the shell and tube LDI combustion system in which progressively larger shells are positioned within each other and are used with corresponding groups of tubes. 
           [0010]      FIG. 4  shows an alternative embodiment of the shell and tube LDI combustion system in which flattened tubes or bars/plates or fin stock is used to form the tubes. 
           [0011]      FIGS. 5A through 5D  show a further alternative embodiment of the shell and tube LDI combustion system which uses a shell and tube LDI assembly that includes a shell assembly within which a tube assembly is inserted. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]      FIG. 1  is a partial cross-sectional, perspective view of one embodiment of the shell and tube lean direct injection combustion system  10  of the present invention. The shell and tube LDI combustion system  10  includes a combustor  12  and a shell and tube lean direct injector  14  that carries fuel and an oxidizer, such as air, to the combustor  12 . 
         [0013]    The shell and tube LDI  14  is comprised of a shell  16  and a bundle or plurality of tubes  18  positioned inside of the shell  16 . In the embodiment of the LDI  14  shown in  FIG. 1 , the fuel is carried to the combustor  12  by the “shell side”  16  of LDI  14 , while the air is carried to the combustor  12  by the “tube side”  18  of LDI  14 . As an alternative, however, either side could contain fuel, air, or diluent, or any combination thereof. 
         [0014]      FIG. 2  is another partial cross-sectional, perspective view of the embodiment of the shell and tube lean direct injection combustion system  10  of  FIG. 1  showing two sets of holes in an end plate of the combustor  12  for injecting fuel from the shell side  16  and air from the tube side  18  into the combustor  12 . 
         [0015]    The plurality of tubes  18  within shell  16  extend completely across the interior of shell  16  from a first end plate  20  of shell  16  to a second end plate  22  of shell  16 . The first end plate  20  has a plurality of holes  24  drilled or otherwise cut into it in which first ends  26  of tubes  18  terminate. The plurality of holes  24  in end plate  20  correspond in number to the plurality of tubes  18  within shell  16 . The second end plate  22  of shell  16  also has a plurality of holes  30  drilled or otherwise cut into it in which second ends  36  of tubes  18  terminate. 
         [0016]    Adjacent to end plate  22  of shell  16  is an end plate or cap  32  of combustor  12 . End plate  32  is shown in phantom in  FIGS. 1 and 2  so that holes within end plate  32  for injecting fuel and air into combustor  12  can be readily illustrated. 
         [0017]    Air enters combustor  12  through the tube side  18  of LDI  14  of the embodiment of the combustion system  10  shown in  FIGS. 1 and 2 . As can be seen in  FIGS. 1 and 2 , a plurality of holes  34  are drilled or otherwise cut into end plate  32 . Holes  34  correspond in number and positioning to holes  30  in end plate  22 . As such, holes  34  are used to inject air into combustor  12 . To this end, the first end plate  20  of shell  16  is joined to an upstream plenum  40  shown in  FIG. 1 . Air from upstream plenum  40  enters into holes  24  in end plate  20  and passes through tubes  18  into combustor  12  through holes  34  in end plate  32 . 
         [0018]    Fuel enters combustor  12  through the shell side  16  of LDI  14 . The shell  16  includes a fuel inlet  28  through which fuel is pumped into shell  16 . The end plate  22  of shell  16  also includes a plurality of fuel holes  29  corresponding to a plurality of fuel holes  38  in end plate  32  of combustor  12 . The fuel flowing through fuel holes  29  and then fuel holes  38  is injected into combustor  12 , where it is mixed with air injected into combustor  12  from air holes  34  connected to tubes  18 . As can be seen from  FIG. 2 , for each air hole  34  in end plate  32  of combustor  12 , there is preferably at least a pair of fuel holes  38  straddling it. The shell side  16 , fuel inlet  28 , fuel holes  29  in end plate  22  and fuel holes  38  through the end plate  32  have been sized to ensure uniform hole sizes throughout for proper fuel delivery to combustor  12 . 
         [0019]    The tubes  18  and shell  16  can be brazed or welded together. The air holes  34  and fuel holes  38  can be drilled or cut through end plate  32  using any conventional method. In the configuration shown in  FIGS. 1 and 2 , the fuel holes  38  start straight and then are angled at their exit in end plate  32  to inject fuel into the air stream coming from air holes  34 . The fuel holes  38  are shown in  FIG. 2  as exiting into the combustor  12 , but they could be cut so as to intersect the air holes within end plate  32 , thus providing some premixing of air and fuel prior to entry into the combustor  12 . It should be noted that fuel and air holes  38  could also be cut either in line with the incoming tubes through end plate  32 , or completely at an angle relative to the incoming tubes through end plate  32 . It should be further noted that the number or location of fuel holes  38  positioned around an air hole  34  could be varied, based on optimizing performance of the combustion system  10 . 
         [0020]      FIG. 2A  is a cross-sectional schematic showing two different methods for cutting fuel and air holes in the end plate  32  of the combustor. The first method is to cut holes  38 A that are straight through end plate  32 , similar to those shown in  FIG. 2 . The second method is to cut the air and fuel holes  38 B at an angle so as to angle the flow entering into the combustor. A combination of different angled tubes around the combustor can be used to impart swirl. 
         [0021]    The shell side  16  of LDI  14  is sized to contain as many LDI injector tubes  18  as desired. The combustion system  10  could contain one large shell and tube LDI  14 , such that the end plate  22  of the LDI  14  is the cap  32  of combustor  12 , or the combustor  10  could contain a number of smaller shell and tube LDI&#39;s  14  mounted adjacent to each other in a pattern about the cap  32  of combustor  12 . 
         [0022]    In one alternative embodiment of combustion system  10 , the fuel would be carried on the tube side  18  and the air carried on the shell side  16 , such that air injects into fuel. Additionally, either the fuel or air side could have a premixed air/fuel mixture instead of using pure fuel or pure air so that mixing of the air and fuel in the combustor  12  is more rapid. The fuel side or the air side could also contain some combination of diluents as a way to introduce diluents into the combustor  12 . 
         [0023]    An alternative embodiment of the combustion system  10  of the present invention could use multiple sets of tubes and/or segregated shell sections (internally partitioned) within the shell and tube LDI  14  to allow for the use of multiple different air/fuel/diluent combinations through multiple different LDI combinations. One example of this kind of embodiment is shown in  FIG. 3 , in which progressively larger shells, e.g., shells  16 A to  16 G, positioned within each other are used with corresponding groups of tubes, e.g.,  18 A to  18 G leading to holes  29 A to  29 G in end plate  22 . 
         [0024]    Further embodiments of the combustion system  10  of the present invention could use flattened tubes  118  leading to air holes  130 , surrounded by a larger number of fuel holes  129 , as shown in  FIG. 4A , or bars/plates or fin stock (thin ruffled sheets of metal)  218  or  318  leading to air holes  230  or  330  surrounded by large numbers of fuel holes  229  or  329 , as shown in  FIGS. 4B and 4C . The bars/plates or fin stock could be brazed together to segregate the different fuel/air/diluent passages. Another embodiment could have progressively larger tubes within each other, with the spaces between the pipes alternately containing air, fuel, diluent, or some combination of each. Yet another embodiment could use a variety of different tube sizes/shapes in any combination to optimize performance. 
         [0025]      FIGS. 5A through 5D  illustrate yet a further embodiment of the shell and tube LDI combustion system of the present invention. The combustion system  50  shown in  FIGS. 5A through 5D  includes a combustor  52  and a shell and tube lean direct injector assembly  54  that delivers fuel and air to the combustor  52 . The shell and tube LDI  54  is comprised of a shell assembly  56  and a tube assembly  58  positioned within the shell assembly  56 . 
         [0026]    The shell assembly  56  is comprised of a large cylinder  60  with a hollow center within which the tube assembly  58  ( FIG. 5C ) is inserted, as shown in  FIG. 5D , and two flanges  62  and  64  that are welded to the outside of tube  60  to provide strength to tube  60 . 
         [0027]    The tube assembly  58  is comprised of a first end plate  66 , a second end plate  68  and a bundle or plurality of tubes  70  extending between end plates  66  and  68 . First end plate  66  has a plurality of holes  72  drilled or otherwise cut into it for receiving air or fuel from an upstream plenum  74 . Second end plate  68  has a plurality of holes  76  and  78  for injecting air and fuel into combustor  62 . The tubes  70  extend between holes  72  and  76 . The configuration of holes  72  and  76  is similar to that of holes  34  and  38  shown in  FIG. 2 . 
         [0028]    Attached to shell assembly  56  are two additional flanges  76  and  78  ( FIGS. 5A and 5B ) for attaching assembly  56  to corresponding flanges  80  and  82  on upstream plenum  69  and combustor  52 , respectively. Shell assembly  56  also includes a fuel inlet  84  through which fuel is pumped into shell assembly  56 . The fuel introduced into shell assembly  56  is, in turn, injected into combustor  52  through holes  78  in end plate  68 . 
         [0029]    The shell and tube LDI combustion system of the present invention provides lower NOx emissions than current MNQC nozzles. Tests have shown NOx levels using the combustion system are less than half those obtained using MNQC nozzles at similar conditions. This could provide a significant emissions advantage and/or reduction in the need for diluents. The combustion system of the present invention also provides better distribution of fuel and air for improved combustion. It allows for scaling down injector sizes to very small sizes or scaling up to large sizes. It can be used in place of current MNQC technology, or in place of current diffusion tips in DLN technology. It can also be used in place of current MNQC nozzles in any sungas engine or in place of diffusion tips in any current DLN combustor. 
         [0030]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.