Abstract:
Dilution sleeves are provided in radially aligned openings in the combustion liner and flow sleeve of a combustor for a gas turbine. The sleeves have a flange for seating on a collar of the flow sleeve about the opening therethrough enabling the dilution sleeve to extend through the aligned openings. A cover is removably mounted on the outer casing and a spring bears between the cover and the dilution sleeve flange to maintain the dilution sleeve in the openings. Dilution sleeves having different cross-sectional flow areas may be provided in lieu of initially installed dilution sleeves upon comparing measured emission levels with desired emission levels and ascertaining the desired increase or decrease in cross-sectional flow area through the dilution sleeves.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to apparatus and methods for adjusting the NO x  level of emissions of heavy-duty gas turbines for emissions compliance without disassembly of the combustors and particularly relates to a mechanical arrangement enabling external access to the dilution air sleeves for the combustion chamber for adjusting the combustor dilution air flow hole areas and methods of adjustment. 
     Heavy-duty gas turbines employing dry low NO x  combustion systems are typically installed with predetermined dilution flow hole areas for flowing compressor discharge air into the combustion liner to shape the gas temperature profile exiting the combustion system and provide reduced NO x  emissions. Dilution air flow sleeves are typically provided and have a predetermined hole area for flowing compressor discharge air into the combustion liner. Not infrequently, however, and after installation of the turbine at the power generation site, the NO x  emissions level is either too high or too low, with corresponding CO emissions level that is too high. This is a result of the normal variability of machine air flow fraction that is delivered to the combustor and the resulting variability of flame temperature in the NO x  producing zones of the combustor. 
     Under those circumstances, the turbine is typically brought into NO x  emissions compliance by removal of the combustion liners from the turbine and resizing the dilution holes to redistribute the combustor air flow. This procedure requires the physical removal of the combustion liner from the turbine with attendant removal of certain piping for fuel, as well as piping for oil and water systems and auxiliary air piping for atomization. It is also necessary to remove the heavy end cover of the combustor to gain access to the dilution holes. Further, there is the possibility of contaminating the fuel system in the process of removing and reassembling the various piping systems. Still further, this process can take between one to two weeks&#39; time, during which there is a gas turbine outage, preventing the electricity provider from producing power during that period of time. Consequently, there is a need for a system which facilitates change of the combustor dilution hole areas without disassembly and subsequent reassembly of major portions of the combustor and in a reduced timeframe. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with a preferred embodiment of the present invention, there is provided a mechanical arrangement enabling external access to the combustion chamber which facilitates changeover of combustor dilution hole areas to adjust the NO x  levels without disassembly of the combustors. To accomplish this, the combustion liner and surrounding air flow sleeve have aligned radial openings at an axial location along the liner for admitting dilution air through dilution sleeves in the aligned radial openings into the combustion chamber. An outer casing surrounds the flow sleeve and defines with the flow sleeve an annular flow passage for flowing compressor discharge air through the dilution sleeves into the combustion chamber. The openings through the flow sleeve are provided with collars which form seats for receiving flanges of the dilution sleeves. The outer casing is also provided with a cylindrical boss or flange in line with the axes of the openings through the combustion liner and flow sleeve, affording access to the dilution sleeves externally of the combustor. A cover is releasably secured to the cylindrical flange, for example, by bolts, and a spring cooperates between the cover and the flange on each dilution sleeve to maintain the dilution sleeve in the aligned openings of the combustion liner and flow sleeve with the flange of the dilution sleeve seated on the collar. 
     Each dilution sleeve has a central opening of a predetermined area. In the event that the NO x  emissions are out of compliance after initial installation of the gas turbine, the access covers to the installed dilution sleeves are removed and dilution sleeves having holes of different areas are inserted to provide more or less compressor discharge air flow through the sleeves into the combustion chamber. Particularly, after the NO x  emissions of the newly installed turbine have been measured at the design operating conditions, the actual measured NO x  emission level is compared with the required NO x  emission level for compliance. If the measured NO x  emissions deviate to the extent the turbine is out of compliance, an increase or decrease in the hole area of the installed dilution sleeves is calculated to arrive at a dilution hole area effective to provide a NO x  emission level within the compliance range. Once the required dilution hole area is determined, the combustion covers are removed and a new set of dilution sleeves conforming to the new required hole area is provided. Alternatively, the initially installed set of dilution sleeves are machined to the required new dilution hole areas. In either case, the dilution sleeves with the required hole areas are inserted through the cylindrical bosses to seat on the collars about the openings in the flow sleeve and extend through the aligned openings through the flow sleeve and the combustion liner. The springs and covers are then reinstalled to secure the dilution sleeves in place with the properly sized dilution hole areas. 
     In a preferred embodiment according to the present invention, there is provided a combustor for a gas turbine comprising an outer casing, a flow sleeve within the outer casing defining an air flow passage with the outer casing, a combustion liner within the flow sleeve for flowing hot gases of combustion, at least one opening in each combustion liner and the flow sleeve, a dilution sleeve removably received within the openings of the combustion liner and the flow sleeve and an access port in the outer casing for access to the dilution sleeve, the dilution sleeve being sized for passage through the access port enabling insertion into or removal of the dilution sleeve from the openings. 
     In a further preferred embodiment according to the present invention, there is provided in a combustor for a gas turbine having a combustion liner defining a hot gas flow path, an outer casing, a flow sleeve between the outer casing and the liner defining a dilution air flow path therebetween, and openings through the flow sleeve and the liner for flowing dilution air in the dilution air flow path into the hot gas flow path, a method of adjusting the level of NO x  emissions comprising the steps of (a) providing a dilution air flow sleeve in the openings having an air flow passage of a predetermined area, (b) measuring the NO x  emissions from the gas turbine at design operating conditions, (c) determining a deviation of the measured NO x  emissions from a predetermined desired level of NO x  emissions, (d) ascertaining a predetermined area of a desired air flow passage through an air flow dilution sleeve based on the deviation and (e) installing an air flow dilution sleeve in the turbine having a flow area sized to provide at least approximately the desired level of NO x  emissions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary cross-sectional view of a combustor for a gas turbine illustrating a dilution sleeve for flowing dilution air into the combustion chamber constructed in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a cross-sectional view thereof taken generally about on line  2 — 2  in FIG. 1; 
     FIG. 3 is a graph of the NO x  emissions versus dilution hole effective area by which the required hole area for NO x  emissions in compliance can be determined; and 
     FIGS. 4A,  4 B and  4 C illustrate a set of dilution sleeves of identical outside diameters and with different inside diameters affording different dilution sleeve flow areas. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, particularly to FIG. 1, there is illustrated a dry low NO x  combustor, generally designated  10 , comprised of a combustor outer casing  12 , a flow sleeve  14 , generally concentrically within the outer casing  12 , and a flow liner  16  for confining the hot gases of combustion in a hot gas flow path  17  (FIG.  2 ). Additionally illustrated are primary and secondary fuel nozzles  18  and  20 , respectively, and a venturi  22 . It will be appreciated that fuel is supplied to the nozzles  18  or  20  and the hot gases of combustion are generated for flow generally axially downstream within the combustion liner  16  and into the first stage of a gas turbine, not shown. As conventional, cooling air is supplied along an annular passage  23  between the combustion liner  16  and flow sleeve  14  for flow into the reaction chamber. A proportion of compressor discharge air also flows in the annular passage  24  between the outer casing  12  and the flow sleeve  14  in the direction of the arrow for supplying dilution air into the reaction chamber. 
     Referring to FIG. 2, the dilution air is provided through openings  26  and  28  in the flow sleeve  14  and combustion liner  16 , respectively. In FIG. 2, two sets of openings  26  and  28  are radially aligned at circumferentially spaced positions about the combustor for receiving the compressor discharge dilution air in annular passage  24 . Dilution flow sleeves  30  extend through the aligned openings  26  and  28  for directing the dilution air into the combustion chamber, the dilution sleeves  30  having central openings  32  of predetermined flow areas. By changing the flow areas of the dilution sleeves  30 , i.e., the flow areas of openings  32 , the level of NO x  emissions can be changed. For this purpose, and as illustrated in FIGS. 4A,  4 B and  4 C, a set of dilution sleeves  34 ,  36 ,  38 , etc. are provided, each sleeve having a central opening of different diameter and hence different cross-sectional area. As illustrated, central openings  40 ,  42 ,  44  of sleeves  34 ,  36 ,  38 , respectively, have different areas and, consequently, when used in the combustor, have the effect of increasing or decreasing the level of emissions. It will be appreciated that while only three flow sleeves having central openings of different areas are illustrated in FIGS. 4A,  4 B and  4 C, any number of flow sleeves  30  with different incremental sizes of the central openings  32  can be provided. Alternatively, a single set of flow sleeves are provided with the initially installed turbine. Those sleeves can be removed from the turbine as set forth herein, machined to provide the desired flow area and reinstalled into the turbine in accordance with the present invention. 
     To enable external access to the dilution sleeves to mechanically adjust the dilution air flow into the combustion chamber, each opening  26  through the flow sleeve  14  is provided with a collar  50  secured to sleeve  14 . The collar  50  forms a seat for receiving the flange  54  of the dilution sleeve  30 , it being appreciated that as illustrated, the cylindrical dilution sleeve  30  extends from flange  54  through openings  26  and  28  in the flow sleeve  14  and combustion liner  16 , respectively, for delivering dilution air to the combustion chamber. To retain the sleeve  30  in the radially aligned openings  26  and  28 , a cylindrical boss or flange  56  is provided on the outer casing  12  about an access port or opening  58 . The opening  58  lies in radial alignment with the openings  26  and  28 . The cylindrical boss  56  terminates at an outer annular end face in bolt holes to receive bolts  60  for securing a cover  62  to the boss  56 . An element  64 , preferably a helical coil spring, extends between the outer casing  12 , and particularly between the cover  62  and the flange  54  of each dilution sleeve  32  to maintain the sleeve seated on collar  50  and extending into the aligned openings  26  and  28 . It will be appreciated that preferably a pair of dilution sleeves, aligned openings, covers, seals and springs are provided as illustrated in FIG. 2 at circumferentially spaced locations about the combustor, each identical to the other. 
     To change over from one set of dilution sleeves having a predetermined flow area to another set of dilution sleeves having a different flow area, it will be appreciated that the covers  62  may be removed by unthreading the bolts  60  from the boss  56 . The springs  64  and sleeves  30  are therefore accessible externally of the combustor and are removed. Thus, the removed sleeves can be replaced by sleeves having the same outside diameters but having appropriately sized openings  32 . Alternatively, the removed sleeves  30  can be machined to provide openings of different cross-sectional area or their openings can be reduced in size by inserting and welding a further sleeve within the dilution sleeve. With the sleeves having the appropriate sized dilution flow openings installed and seated on collars  50 , the covers  62  and springs  64  are then reapplied to the outer casing with the springs maintaining the sleeve in position on collars  50 . It will be appreciated that the compressor discharge air flowing in the annular chamber  24  flows between the collars  50  and bosses  56  past the dilution sleeve flanges  54  and through the openings  32  of the sleeves  30  into the combustion chamber. 
     Upon initial installation of the gas turbine, the NO x  emissions are measured. If the emissions are out of compliance with predetermined required emission levels, dilution sleeves having central openings with different cross-sectional areas are substituted for the dilution sleeves provided initially with the gas turbine or the initially provided dilution sleeves are modified, e.g., by machining, to provide dilution sleeves having central openings of appropriate area. If the deviation between the measured level of NO x  emissions renders the turbine out of compliance, the desired change in dilution hole effective area can be calculated and a new dilution hole area determined. A graph, typical to the graph illustrated in FIG. 3, may also be used to determine the desired change in dilution hole effective area and, consequently, the required dilution hole diameter whereby the extant dilution sleeves can be replaced by properly sized dilution sleeves or modified to obtain the desired dilution flow area. Through calculation or by employing the chart, the change in area of the dilution flow sleeve central openings from the flow area of the initially installed dilution sleeves to flow areas required to obtain a desired emission level can be ascertained. The chart is a plot of NO x  emissions for a Frame  6 B heavy duty gas turbine fired at 2,075° F. in parts per million versus dilution hole effective area in square inches, e.g., the chart being corrected for the firing temperature of 2075° F. Using the equation given on the chart, for a given measured NO x  emission, the dilution hole effective area can be calculated to achieve a desired level of emissions. For example, the log of the measured NO x  divided by dilution hole effective area=0.27399. This implies that for a 10% increase in NO x  emission levels, the increase in dilution hole effective area would be log In (1.10) divided by 0.27399=0.3479 inches 2 . Consequently, with this calculated or graphically obtained increase in dilution hole effective area, the dilution hole area necessary to bring the NO x  emissions level into compliance is obtained. Similar graphs corrected using calculations or experimental data would be applied to larger or smaller gas turbine combustion systems. A set of sleeves having a dilution hole area approximating or corresponding to the desired hole area can then be selected from dilution sleeve sets of different diameters, for example, those illustrated in FIGS. 4A-4C and installed to provide dilution sleeves having desired flow area. Typically, where sets of dilution sleeves are provided, the desired change in area from the extant dilution sleeve will not correspond exactly with the increments in cross-sectional hole areas of the sets of dilution sleeves. Accordingly, given the change in effective area necessary, a set of dilution sleeves which approximates the desired effective area, whether on the high or low side of the calculated change in area, may be used. Alternatively, the extant dilution sleeves may be removed and machined or material added as necessary to achieve the desired flow area. Once the dilution flow sleeves having the desired flow areas are identified, they are installed as previously discussed. 
     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.