Patent Grant
9726377
This application claims priority under 35 U.S.C. ยง119 to European patent application no. 09160209.4, filed 14 May 2009, the entirety of which is incorporated by reference herein.
Field of Endeavor
The present invention relates to a burner of a gas turbine.
Brief Description of the Related Art
In particular the present invention refers to a sequential combustion gas turbine; these gas turbines are known to include a compressor generating a main compressed air flow and feeding it to a first burner.
In the first burner a fuel is injected in the compressed air flow to form a mixture that is combusted and expanded in a high pressure turbine.
The hot gas flow discharged by the high pressure turbine (that still includes a large amount of air) is then fed to a second burner, where further fuel is injected to form a mixture; this mixture is thus combusted and expanded in a low pressure turbine.
A burner embodying principles of the present invention is advantageously the second burner of the sequential combustion gas turbine and is made of a duct (typically with a rectangular, square or trapezoidal shape) housing a conditioning device for guaranteeing a straightened inflow of the hot gas coming from the high pressure turbine.
The duct also has four vortex generators, each extending from one of its walls and arranged to generate vortices within the hot gas flow.
Downstream of the vortex generators, the duct has a lance made of a stem from which a terminal portion extends; the terminal portion is provided with nozzles for injecting the fuel.
The end portion of the duct defines a mixing zone where the fuel injected by the lance mixes with the hot gas flow.
Nevertheless, as the lance is positioned immediately downstream of the vortex generators, its stem at least partially blocks the vortices generated by the upper vortex generator (i.e., the vortex generator projecting from the same wall as the stem of the lance).
This disturbs the structure of the vortices within the burner and, in practice, decreases the total mixing efficiency, causing high NOx emissions.
In addition, the gas flow (which includes a large amount of air), when passing through the duct, is subjected to a large pressure drop, due in particular to the stem of the lance. This worsens the performance of the gas turbine.
Different burners have been developed which face these drawbacks.
U.S. Pat. No. 5,513,982 discloses a burner having vortex generators that have a tetrahedral shape and are provided with holes or nozzles at their side walls. In a different embodiment of the burner of U.S. Pat. No. 5,513,982, the holes or nozzles are placed along all the width of the side walls.
Nevertheless, in both cases, since the fuel is injected from the vortex generators, it enters recirculating regions with very low axial velocity.
Because of the high temperature of the hot gas flow, it auto ignites within the duct (i.e., before entering the combustion chamber located downstream of the duct), damaging the burner.
One of numerous aspects of the present invention includes a burner by which problems of the known art are addressed.
Another aspect includes providing a burner by which the vortices are increased and, in particular, the vortices are not disturbed or their propagation is not prevented after their formation.
Another aspect relates to a burner by which pressure drops are smaller than that caused by the traditional burners. This allows better performances of the gas turbines to be achieved.
Yet another aspect includes a burner with a reduced flashback risk, because there is no risk that auto ignition of the fuel occurs within the duct of the burner.
Another aspect includes a lance stem which is integrated with one of the vortex generators.
Advantageously, a burner embodying principles of the present invention allows the NOx emission to be reduced relative to traditional burners.
Further characteristics and advantages of the invention will be more apparent from the description of a preferred, but non-exclusive, embodiment of the burner according to the invention, illustrated by way of non-limiting example in the accompanying drawings, in which:
With reference to the figures, a burner of a gas turbine is illustrated, overall indicated by the reference 1.
In particular the burner can be the second burner of a sequential combustion gas turbine.
The burner 1 includes a duct 2 with a rectangular or square or trapezoidal or annular sector shape (in
The duct 2 houses four vortex generators projecting from each of its walls.
A first vortex generator 3 projects from the upper wall of the duct, a second vortex generator 4 projects from the bottom wall of the duct, and two side vortex generators 5 project from the side walls of the duct.
The burner is also provided with a lance 7 which extends from the first vortex generator 3.
The lance 7 carries one or more nozzles 8 for injecting a fuel within the duct 2; in the present embodiment, the lance carries four nozzles that are placed two at one side and the other two at the other side of the lance. It is anyhow clear that the nozzles 8 may also be different in number and may be placed differently on the lance 7.
Advantageously, the nozzles each have their axis perpendicular to an axis 11 of the duct 2, in order to make the fuel distribute in the volume of the duct after injection.
The nozzles 8 are arranged to inject both liquid and gaseous fuel and, in this respect, they are provided with a plurality of coaxial apertures.
A central aperture is arranged to inject a liquid fuel and a first annular aperture encircling the central aperture is arranged to inject a gaseous fuel.
A further annular aperture of the nozzles encircling both the central and the first annular aperture is arranged to inject a shielding air flow.
The lance 7 has a substantially cylindrical body with a longitudinal axis 10 which is substantially parallel to the longitudinal axis 11 of the duct 2.
Preferably, the axis 10 of the lance 7 overlaps the axis 11 of the duct 2 and the lance 7 is made in one piece with the first vortex generator 3.
Moreover, the lance 7 protrudes from the first vortex generator 3 towards an outlet 13 of the duct 2.
The first vortex generator 3 has a substantially tetrahedral shape with a base surface 14 overlapping the wall of the duct 2.
In addition, the first vortex generator 3 has a leading edge 15 perpendicular to the axis 11 of the duct 2 and laying on the wall of the duct 2.
The vortex generator 3 also has a trailing edge 17 perpendicular to the axis 11 of the duct 2 and perpendicular to the wall of the duct 2 (
In a different embodiment the trailing edge 17 of the vortex generator 3 is neither perpendicular to the axis 11, nor to the wall of the duct 2 (
The lance 7 extends from a zone 18 of the first vortex generator 3 where two side surfaces 19 and a top surface 20 converge.
As shown in the figures, the first vortex generator 3 faces the second vortex generator 4.
In a transversal plane (see
The second vortex generator 4 is similar to the first vortex generator 3 and, in this respect, it also has a tetrahedral shape, with a base surface 23 overlapping a wall of the duct 2, a leading edge 24 perpendicular to the axis 11 of the duct 2 and laying on the wall of the duct 2, and a trailing edge 25 perpendicular to the axis 11 of the duct 2 and also perpendicular to the wall of the duct 2.
The trailing edge 17 of the first vortex generator 3 and the trailing edge 25 of the second vortex generator 4 both lay in a transversal plane 27 perpendicular to the axis 11.
Moreover, the two side vortex generators 5 that project from the side walls of the duct 2 also have a tetrahedral shape with a trailing edge 28 substantially perpendicular to the wall of the duct and placed downstream of the trailing edges 17, 25 of the first and second vortex generators 3, 4.
The burner 1 includes a device for removably connecting the first vortex generator 3 within the duct 2; advantageously this allows an increased flexibility for aerodynamic optimization of the flow pattern in the upper/lower part of the burner, since the vortex generator with the lance protruding from it is fully retractable.
In particular, the first vortex generator 3 has a plate 26, preferably made in one piece with it, that extends in the same direction as the lance 7 and is arranged to close a hole of the duct 2 through which the vortex generator 3/lance 7 are introduced within the duct 2.
The plate 26 stretches to completely cover the lance 7.
The working principle of the burner of the invention is apparent from that described and illustrated and is substantially as follows.
The hot gas flow F coming from the high pressure turbine enters the duct 2 and passes through the vortex generators 3, 4, 5, increasing its vorticity.
Afterwards, the hot gas flow F passes around the lance 7 where the fuel is injected from the nozzles 8.
As the lance 7 projects from the vortex generator 3 and the nozzles 8 are close to the tip of the lance 7 (thus the nozzles 8 are far away from the trailing edge 17 of the vortex generator 3), the fuel is injected in a zone of the duct 2 where the vortices are completely formed, with no risk that the fuel will be withheld within a core of the vortices.
In addition, the vortices are more uniform and stronger than with traditional burners, because their propagation has not been disturbed by the stem of the lance.
Moreover, as the fuel is injected perpendicularly to the wall of the duct 2 (i.e., it is injected in the injection plane which is perpendicular to both the axis of the lance 10 and the axis of the duct 11) it spreads over the entire volume of the duct.
This permits a good distribution of the fuel within the hot gas flow to be achieved and, thus, an optimal mixing quality be obtained; the increased mixing quality lets the emissions be improved and in particular the NOx emission be reduced.
In addition, as in traditional burners, the stem of the lance causes a large pressure drop in the hot gas flow passing through the duct, a burner embodying principles of the present invention allows the pressure drop to be reduced and the performances of the gas turbine to be increased.
In practice the materials used and the dimensions can be chosen at will according to requirements and to the state of the art.
While the invention has been described in detail with reference to exemplary embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents. The entirety of each of the aforementioned documents is incorporated by reference herein.
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