Abstract:
In a fuel lance for spraying liquid and/or gaseous fuels into a combustion chamber, which fuel lance is part of a secondary or tertiary burner, around which a hot-gas jet flows in a main flow direction, and comprises a liquid-fuel passage for supplying liquid fuel and first means for spraying the liquid fuel from the liquid-fuel passage into the combustion chamber, operation characterized by reduced addition of water is made possible owing to the fact that the first means comprise a liquid-fuel nozzle, which sprays the liquid fuel essentially parallel to the main flow direction as a plain jet into the combustion chamber.

Description:
FIELD OF THE INVENTION 
     The present invention relates to fuel lance apparatus and methods for spraying liquid and/or gaseous fuels into a combustion chamber, particularly as used in gas turbines. 
     BACKGROUND OF THE INVENTION 
     Publication DE-A1-43 26 802 discloses a fuel lance which is at present used by the applicant in his gas turbines (in this respect see also publications U.S.Pat. No. 5,431,018, U.S. Pat. No. 5,626,017 and EP-A1-0 620 362). In this case, the nozzles for gaseous fuel and liquid fuel (oil, etc.) are combined. 
     The development of the oil spraying of the primary burners (EV burners) led to the plain-jet principle. In this case, the liquid fuel is sprayed as a jet through a central bore into the burner. The fuel jet disintegrates in the swirl zone of the EV burner (in this respect see, for example, EP-B1-0 321 809). Depending on the adaptation of the impulse ratio between the liquid-fuel jet and the surrounding air flow, the location of the jet disintegration can be set. 
     The known radial spraying of the liquid fuel of the SEV chamber and the atomizing of the liquid fuel by means of an air-blast nozzle leads to a relatively large quantity of water having to be admixed with the liquid-fuel spray jet in order to prevent a flame flashback. 
     SUMMARY OF THE INVENTION 
     The object of the invention is therefore to provide a fuel lance for the spraying of liquid fuel and/or gaseous fuel in a secondary or tertiary burner, which fuel lance avoids the above-described disadvantages of previous lances and permits in particular a reduction in the retention time of the liquid fuel in the premix section and thus a reduction in the admixed proportion of water. 
     The essence of the invention consists in spraying the liquid fuel axially in the main flow direction by means of a plain-jet nozzle. The result of this type of spraying is that the retention time of the liquid fuel in the premix section is reduced and thus less water has to be added in order to prevent a flame flashback. 
     A first preferred embodiment of the fuel lance according to the invention is comprises a central liquid-fuel tube, which is arranged concentrically to a lance axis and encloses the liquid-fuel passage for directing a liquid fuel, and a gas tube, which encloses the liquid-fuel tube and forms between it and the liquid-fuel tube a gas passage for directing a gaseous fuel, and a lance shell, which encloses the gas tube and forms between it and the gas tube an air passage for directing cooling or atomizing air, and also second means for spraying the gaseous fuel from the gas passage into the combustion chamber, and third means for spraying the air from the air passage into the combustion chamber, the lance axis being oriented essentially parallel to the main flow direction. This permits a flexible mode of operation with different fuels or fuel combinations in a compact construction. 
     The axial liquid-fuel jet of the fuel lance according to the invention is preferably surrounded by an air veil. This is achieved in a second embodiment of the invention in that the liquid-fuel nozzle is arranged centrally in the lance axis, and in that the third means comprise first nozzle means which are designed in such a way that the liquid-fuel jet discharging axially through the liquid-fuel nozzle is surrounded in a sheath-like manner by a likewise axially discharging air veil, either the first nozzle means comprising a plurality of axially oriented bores which are arranged in a distributed manner around the liquid-fuel nozzle, or the first nozzle means comprising an annular gap which concentrically surrounds the liquid-fuel nozzle. 
     The air for the air veil around the liquid-fuel jet is preferably utilized at least for the partial cooling of the lance head. This is done in a development of the second embodiment of the invention by the first nozzle means or bores or the annular gap being connected to the air passage via a head passage, running through the lance head, in such a way that the lance head is cooled by the air flowing in the head passage. 
     In a further preferred embodiment of the invention, the gaseous fuel from the gas passage is sprayed radially into the combustion chamber through individual nozzle openings oriented radially to the lance axis, the gas jet from the nozzle openings in each case being surrounded concentrically by an air sheath, and the nozzle openings for the gaseous fuel in each case being formed by a radially arranged guide tube, which is connected to the gas passage and opens into the combustion chamber through a shell opening in the lance shell, and the shell opening, relative to the outside diameter of the guide tube, being selected in such a way that an annular gap remains free for producing the air sheath surrounding the gas jet. 
     A lance according to another preferred embodiment has an especially simple geometry. The gaseous fuel is sprayed concentrically to the liquid fuel as a plain jet essentially parallel to the main flow direction. The two fuel jets are concentrically surrounded by an air sheath. A first annular gap, which concentrically surrounds the liquid-fuel nozzle, is provided for spraying the gaseous fuel. A second annular gap, which concentrically surrounds the first annular gap, is provided for forming the air sheath. 
     The method according to the invention for operating such a fuel lance is characterized in that in each case liquid fuel is sprayed into the combustion chamber through the liquid-fuel nozzle and air is sprayed into the combustion chamber through each of the first and second annular gaps. 
     Furthermore, it is conceivable for the axial part, formed parallel to the main flow direction, of the fuel lance to be shortened if the inflowing swirl zone (of the hot gases) is configured in such a way that no wake zone occurs. An embodiment of the lance in which the liquid fuel is sprayed directly at the radial holder or supporting arm is therefore also conceivable ( 4  in FIG. 1 of DE-A1-43 26 802). This stem may be designed to be profiled in a more or less fluidically favorable manner. According to the invention, the preferred spraying is effected axially via a plain jet, and accordingly perpendicularly to the main flow direction for the air-sheathed gaseous fuel. This embodiment has the advantage that the lance is easier to fit and requires less cooling air. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are illustrated in the accompanying drawings, in which: 
     FIG. 1 shows a longitudinal section of the head region of a fuel lance in a preferred embodiment of the invention, with radial spraying of the gaseous fuel by a gas jet which is formed axially and is then deflected at right angles into a radial guide tube and has air sheathing; 
     FIG. 2 shows a longitudinal section of a modified form of the embodiment analogous to FIG. 1, in which the radial gas jet is formed directly by the guide tube proceeding radially from the gas tube; and 
     FIG. 3 shows a longitudinal section of the head region of a fuel lance in a second modified form of the preferred embodiment of FIG. 1 with axial gaseous-fuel spraying concentric to the liquid fuel jet and concentric air sheathing of both fuel jets. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A preferred embodiment of a fuel lance according to the invention is shown in longitudinal section in FIG.  1 . The fuel lance  10 , which extends along a lance axis  31 , which in turn lies essentially parallel to the main flow direction  33  of a hot-gas flow flowing around the lance, is shown in FIG. 1 only with its head region. A liquid-fuel tube  16 , a gas tube  14  and a lance shell  12  are arranged one inside the other in the fuel lance  10  concentrically to the lance axis  31 . The interior of the liquid-fuel tube  16  forms a liquid-fuel passage  17 , through which liquid fuel, in particular oil or the like, is directed for spraying in the direction of the depicted arrow into the lance head  11 . Formed between the liquid-fuel tube  16  and the gas tube  14  is a gas passage  15 , through which gaseous fuel is directed in the direction of the depicted arrow for spraying into the lance head  11 . Finally, an air passage  13 , through which air is directed into the lance head  11  in the direction of the depicted arrow, is formed between the gas tube  14  and the lance shell  12 . 
     According to the invention, the liquid fuel is sprayed axially in the form of a plain jet into the combustion chamber, into which the fuel lance  10  projects. To this end, the liquid-fuel passage  17  narrows in the lance head  11  to form an axial liquid-fuel nozzle  18 . The liquid-fuel jet discharging from the liquid-fuel nozzle  18  is preferably sheathed (surrounded) with an air veil. To this end, axial bores  20 , through which air can discharge in the axial direction and surround the liquid-fuel jet, are arranged around the liquid-fuel nozzle  18  on a concentric ring. The air required for this purpose is fed in from the air passage  13  via a head passage  19 , which runs in the marginal region through the lance head  11 . This achieves the effect that the lance head  11  is also cooled by the air flowing through. 
     In the exemplary embodiment in FIG. 1, the gaseous fuel is sprayed from the gas passage  15  radially to the lance axis  31  and thus radially to the main flow direction  33  into the combustion chamber. The gas passage  15  is closed by a closure ring  22  before reaching the lance head  11 . Provided in the closure ring  22  around the lance axis  31  are axial bores  23 , through which the gaseous fuel discharges in the form of axial fuel jets. In a following curved deflecting surface  24 , the axial fuel jets are deflected outward at right angles and then in each case enter a radial guide tube  25 , which directs the jet outward unhindered by the air passage  13 . The guide tubes  25 , in their orifice region, at the same time form the nozzle openings  26  for the radially sprayed gaseous fuel. So that the guide tubes  25  can open into the combustion chamber, corresponding shell openings  27 , through which the guide tubes  25  pass, are provided in the lance shell  12 . The shell openings  27 , relative to the outside diameter of the respective guide tube  25 , are selected in such a way that an annular gap remains free for producing a protective air sheath surrounding the gas jet. 
     A modified form of the embodiment of FIG. 1 is shown in FIG.  2 . Here, the radial jets of the air-sheathed gaseous fuel are formed in a slightly different way. To this end, the gas passage  15  is directed right into the lance head  11  and ends there. The guide tubes  25 , which in this case too cross the air passage  13  and open into the combustion chamber through corresponding shell openings  27  in a manner flush with the lance shell  12  and form the nozzle openings  26 , are directly attached to the gas tube  14 , so that axial bores and deflecting surfaces may be dispensed with. This results in a simplified construction of the fuel lance  10 . The liquid fuel is sprayed and sheathed with air in FIG. 2 in the same way as in FIG.  1 . 
     However, it is also conceivable for the air-sheathed gas jet to be made axially, and not radially, in the form of a plain jet. A second modified form of the embodiment in FIG.  3 . In this case, the liquid-fuel feed, gas feed and air feed are constructed concentrically top the lance, axis. The liquid-fuel nozzle  18  is located in the center. The liquid-fuel nozzle  18  is concentrically surrounded by a first annular gap  29 , through which gaseous fuel is sprayed axially. The gaseous fuel is fed in from the gas passage  15  via a connecting passage  28 , in which connecting webs  32  may be arranged for the mutual support of the tubes. The first annular gap  29  is concentrically surrounded by a second annular gap  21 , through which an air sheath is sprayed axially and surrounds the two fuel jets (such an annular gap may incidentally also be used in FIGS. 1 and 2 instead of the bores  20 ). Furthermore, in the configuration according to FIG. 3, a connection between air passage  13  and gas passage  15  in the form of connecting bores  30  may be provided. As a result, it is possible to maintain the spraying impulse of the gas jet even during part-load mass fuel flows by the reduced fuel quantity being replaced by additional air. In addition, during liquid-fuel operation of the fuel lance according to FIG. 3, it is conceivable for air to also be admitted to the first annular gap  29  (i.e. the gas nozzle). 
     On the whole, the invention results in a fuel lance which leads to a reduced demand for added water. In this case, the gas spraying may be effected radially (FIGS. 1,  2 ) or axially (FIG. 3) or also at other angles to the main flow direction  33 , specifically with one or more jets. Pure gas- or liquid-fuel lances are also conceivable. Finally, the axial part, formed parallel to the main flow direction, of the fuel lance may be shortened if the inflowing swirl zone (of the hot gases) is configured in such a way that no wake zone occurs. An embodiment of the lance in which the liquid fuel is sprayed directly at the radial holder is therefore also conceivable. This stem may be designed to be profiled in a more or less fluidically favorable manner. In this case, the preferred spraying is effected axially via a plain jet, and accordingly perpendicularly to the main flow direction for the air-sheathed gaseous fuel. This embodiment has the advantage that the lance is easier to fit and requires less cooling air.