HIGH RELIABILITY FUEL OIL NOZZLE FOR A GAS TURBINE

Abstract: A fuel nozzle for a gas turbine in which the air supply por­ tion surrounds the fuel supply portion is conveniently remova­ ble to permit cleaning and the two parts are resiliently disposed to permit differential expansion caused by the thermal differen­ tials during operation.

Description: This invention relates to a fuel nozzle, for a gas turbine and in particular to an atomizing fuel nozzle with particular application to gas turbines. The fuel for a gas turbine is normally atomized in an oil nozzle as shown for example in GB-A-2004050 by means of a small orifice which ejects the fuel under pressure into an air stream. The air stream is normally caused to swirl to rotate about the outer periphery of the nozzle thus improving the atomizing and mixing of the fuel and air. Because of the difficult conditions under which such jets operate, it is usual for deposits to form within the nozzle caused by material in the air supply and such deposits tend to obstruct the air flow through the nozzle. Also, because the oil supplied to one portion of the nozzle is at one temperature and the air surrounding another portion is at a different temperature, the differential in temperature between the oil and the air will cause the differential temperature of the components of the nozzle. In a gas turbine in operation, it is normal for the surrounding air to be at high temperature and the fuel to be relatively low temperature therefore, the various parts of the nozzle are subjected to different temperatures and these differential temperatures, which build up during starting and shut-down, cause relative motion between the various components of the nozzle as the temperature differential causes differential expansion of the components. This differential expansion stabilizes at operating temperature with the result that two critical components of the nozzle that is the fuel and air supply structures remain separated until shut-down. The exposure of the separated surfaces to the environment inside the combustor produces pitting of said surfaces which may therefore not form an airtight seal as they must during each and every start of the gas turbine. It is therefore the principal object of the present invention to provide a fuel nozzle in which pitting of the fuel and air supply components is avoided so that they can be properly sealed in sealing engagement during startup of the turbine for appropriate control of the startup air supply to the nozzle. With this object in view, the present invention resides in a fuel nozzle, for a gas turbine, comprising a nozzle body with an inner tube bearing at its end a nozzle tip having a central orifice adapted for fuel to be ejected under pressure, an outer tube surrounding said inner tube bearing at its end a swirl cap including a plurality of passages through which air is to be ejected under pressure into the stream of fuel from said central orifice and a central aperture in said swirl cap into which said nozzle tip fits and means to maintain said nozzle tip and said swirl cap in contact, said nozzle body having a cavity around said inner tube and the outer tube extending with its inner end opposite said swirl cap into said cavity and carrying a ring adapted to fit into said cavity so as to center said outer tube at its inner end, characterized in that spring means are provided engaging said outer tube at its inner end and projecting axially so as to be compressed upon mounting of said nozzle body onto a gas turbine combustor for maintaining a resilient contact between said swirl cap and said nozzle tip. In this arrangement, all the critical parts of the nozzle are held in engagement with each other by means of spring loading in a manner which permits their disassembly. The disassembly facilitates cleaning of the components and the spring loading maintains relatively constant force between the components thus reducing the pitting and the resultant problems of poor atomization and improper combustion. The invention will now be described, by way of example, with reference to the accompanying drawings in which: The Fig. 1 is a section of an oil nozzle in accordance with the present invention; and Fig. 2 is a section of an oil nozzle showing an alternative arrangement in accordance with the invention. Fig. 1 shows a fuel portion of the nozzle shaped and formed in the conventional manner to receive fuel oil through a central orifice 2 which is connected to a tube 3. A nozzle tip 4 is threadably engaged to the end of tube 3 and sealed thereto by a gasket 5. A very fine opening 6, passes through the nozzle tip and provides a passage for the fuel oil. Atomizing air is provided to the nozzle through orifice 7 which connects with a chamber 8 which surrounds the tube 3. A tube 9 defines an annular passage between its inner surface and the outer surface of tube 3 which annular passage 10 connects with chamber 8 and conducts the atomizing air to the upper portion of the nozzle. A swirl cap 11 threadably engages the upper portion of tube 9 and is locked thereto by a locking washer 12. The swirl cap 11 has a conical aperture at its upper end which conical aperture precisely conforms to the frusto-conical upper portion of the nozzle tip 4 to form an airtight seal and, when threadably engaged with tube 9, is held in firm engagement with the surface of the nozzle tip 4. A plurality of passages 13, at the outer or upper end of the swirl cap provide passage for the air from the annular passage 10 out into the area where the fuel is being sprayed from the nozzle tip. The tube 9 is retained in the body 1 by means of a keeper ring 14, a preloading ring 15 and a conical spring 16. The spring 16 may be composed of one or more layers of conical springs having an internal diameter corresponding to the external diameter of tube 9 and external diameter slightly less than the aperture in base 1. The finished inner and outer peripheries of spring 16 provide a seal between the tube 9 and the body 1. Retaining bolts such as bolt 22 mount the nozzle in the combustor. The device is assembled by mounting the oil nozzle tip 4 on tube 3, mounting the swirl cap 11 on tube 9, slipping tube 9 over tube 3, dropping spring 16 down over tube 9 to fit into the upper opening of body 1, dropping preloading ring 15 over tube 9, and engaging keeper ring 14. The preloading ring is dimensioned and located so as to preload the swirl cap 11 against the nozzle tip 4 with a predetermined force due to the compression of the conical spring 16 when the nozzle body 1 is bolted into its operating position by means of bolts 22. During the operation of the gas turbine, the fuel under pressure is introduced into orifice 2 and the atomizing air, also under pressure, is introduced into orifice 7. As the temperature of the environment inside the combustor increases, the temperature of the tube 9 increases causing differential expansion with reference to tube 3 which is maintained at a relatively low temperature by the supply of fuel oil passing through its inner passage. As these two tubes attain their different temperatures and their different lengths, the force between the nozzle tip 4 and the swirl cap 11 is maintained by virtue of the deflection of the conical spring 16 which has provided a preloading and will permit motion of the two components relative to each other at their lower end whilst maintaining substantially constant force at their upper end. When it is desired to clean the nozzle it is relatively easy to remove the bolts 22 and remove the air portion of the nozzle, that is the outer tube 9 and the swirl cap 11, thus exposing the annular passage 10 and permitting thorough cleaning of the nozzle. This also permits thorough cleaning of the passages 13 in the swirl cap and permits more convenient access to the nozzle tip which may be removed from the tube 3, if desired, to permit cleaning of the interior of tube 3. Fig. 2 shows an alternative embodiment of the invention. Similar parts bear the same designation. It will be seen in this embodiment that tube 9 is sealed to body 1 by a packing 18 rather than the finished peripheral surfaces of the spring 16. The tube 9 is resiliently held in body 1 by springs 19 which are six in number and are regularly arranged around tube 9 in cylindrical indentations 20 in the base of tube 9. The upper ends of springs 19 bear against the combustor coverplate 21. Body 1 is fastened to the combustor coverplate by a plurality of bolts 22. The device is assembled as before with the oil nozzle tip 4 on tube 3 and the swirl cap 11 on tube 9 and tube 9 slipped over tube 3. The springs 19 are now placed in their respective indentations 20 and the assembly bolted to the coverplate 21. As bolts 22 are drawn up, they compress springs 19 and preload the swirl cap 11 against the nozzle tip 4. As in the case of the embodiment shown in Fig. 1, the nozzle may be conveniently disassembled for cleaning and the resilient means, in this case coil springs 19, hold the tip and swirl cap in contact but permit differential expansion of tubes 3 and 9.

Claims: A fuel nozzle, for a gas turbine, comprising a nozzle body (1) with an inner tube (3) bearing at its end a nozzle tip (4) having a central orifice (6) adapted for fuel to be ejected under pressure, an outer tube (9) surrounding said inner tube bearing at its end a swirl cap (11) including a plurality of passages (13) through which air is to be ejected under pressure into the stream of fuel from said central orifice and a central aperture in said swirl cap into which said nozzle tip fits and means to maintain said nozzle tip and said swirl cap in contact, said nozzle body having a cavity around said inner tube and the outer tube extending with its inner end opposite said swirl cap into said cavity and carrying a ring (15; 9,18) adapted to fit into said cavity so as to center said outer tube at its inner end, characterized in that spring means (16,19) are provided engaging said outer tube at its inner end and projecting axially so as to be compressed upon mounting of said nozzle body onto a gas turbine combustor for maintaining a resilient contact between said swirl cap and said nozzle tip. A fuel nozzle as claimed in claim 1 wherein the central aperture in said swirl cap is conical and the nozzle tip has a conical outer surface which fits into and substantially conforms to the conical central aperture in said swirl cap. A fuel nozzle as claimed in claim 2 wherein the air for said nozzle is supplied through the annular passage between said inner and outer tubes. A fuel nozzle as claimed in claim 3 wherein said nozzle tip is demountably attached to said inner tube. A fuel nozzle as claimed in any one of claims 1 to 4, wherein said swirl cap is demountably attached to said outer tube.

Inventors: BENNETT, ALAN. D.
Applicants: WESTINGHOUSE CANADA INC.
Application year: 1986
Main classification: F23D11
IPC codes: F23D11, F23R3