EP1754002B1 - Staged premix burner with an injector for liquid fuel - Google Patents

Description

Technical application

The invention relates to a stepped premix burner, in particular for a combustion chamber of a gas turbine, with a swirl generator for a combustion air flow, fuel outlet openings for the stepped introduction of gaseous fuel into the combustion air stream and a central support, the injector with a swirl nozzle for the injection of liquid fuel and a Umbrella air channel has.

State of the art

In gas turbine plants, premix burners are frequently used, in which inflowing combustion air is impinged by a swirl and mixed with the fuel by injecting fuel into a premixing region. When used in gas turbines, the premix burners must cover the entire operating range with sufficient safety. This operating range includes, for example, the startup of the gas turbine, in which when igniting the burner, a fuel / air mixture at combustion pressures and preheating temperatures must be burned near the ambient conditions. To ensure the stability of the burner operation, the burner is in This operating area is usually operated with a pilot stage. For reasons of symmetry, this pilot stage is arranged centrally in the burner flow field, for example in the form of a fuel lance. The fuel is thereby added to the combustion air axially in the flow direction at the tip of the fuel lance via an injector so that fuel-rich zones in the flow field of the burner and thus a stable operation without extinguishing the flame is ensured even at low combustion pressures and temperatures. At higher operating load, the injection of fuel via the pilot stage for reducing pollutants is usually reduced and operated the burner in the advantageous premixing.

Another requirement of premix burners as well as all other modern gas turbine burners is that the burner should optionally be usable for gaseous and liquid fuels. This requires a further arrangement for fuel injection, which is usually also attached to the top of the fuel lance. To avoid fuel-containing gaseous backflows into the fuel feed lines to the fuel lance, the fuel injector on the fuel lance has an annular gap from which a small proportion of air, based on the total burner air flow, flows out. This so-called shielding air shields the two fuel nozzles for liquid and gaseous fuel against undesired backflow.

An example of an embodiment of such a known premix burner is shown in FIG Fig. 1 in side view (left) and top view (right) shown very schematically. The swirl generator 1 is formed in this example of two partial shells, which are assembled into a cone-shaped swirl body. Between the two subshells are air inlet slots 2 for the tangential entry of combustion air, which are indicated in the figure with the arrows recognizable at this point. In pre-mixing operation, gaseous fuel is introduced into the combustion air along these air inlet slots via unrecognizable feeders and fuel outlet openings in order to mix with the combustion air within the volume predetermined by the swirl generator 1. Within the burner, a fuel lance 3 can be seen centrally, at the end of which an injector 4 with nozzle openings for the injection of liquid fuel, of gaseous fuel and for the exit of umbrella air is mounted. The nozzle opening 7 for the introduction of gaseous fuel 7a can be seen here in the right part of the figure in the center of the fuel lance 3. This nozzle opening 7 is surrounded by a gap 5 for the exit of shielding air 5a. The annular nozzle opening 6 for the introduction of liquid fuel 6a in the present case forms the outer area of this injector 4.

In the lower load range of the gas turbine this premix burner is operated exclusively with one of the two pilot stages, ie by the injection of liquid fuel 6a or gaseous fuel 7a via the injector 4 of the fuel lance 3. In the upper load range must be completely switched over to the premix stage in gaseous fuels due to the high pollutant emissions in pilot operation. During the combustion of liquid fuels in the pilot stage, an emulsion of water and oil is burned as a liquid fuel in the upper load range. By introducing the water, the flame temperature is lowered locally in the flow field. This leads to a reduction in pollutant emissions, in particular nitrogen oxide emissions. In addition to the pollutant emissions, combustion pulsations should also be avoided in the upper load range, which can lead to restrictions in the operating range. Particularly stable burning oil / water emulsion flames are hereby produced with swirl injectors, also referred to as pressure swirl injectors. However, due to the high throughput and the limited space available at the tip of the fuel lance, such swirl injectors cause a high pressure drop on the fuel side.

An injector for injecting a liquid fuel into a combustion chamber of a gas turbine engine, which on the one hand ensures a uniform distribution of the fuel, but at the same time should reduce the risk of deposits of fuel residues, is from the document US 3972182 known. In a cylindrical flow channel, a spin is imposed on the liquid fuel in a swirling device. After leaving the flow channel of the expanding fuel vortex bounces while being acted upon by a first combustion air flow against the inner wall of another flow body with extended flow cross-section. In this case, a part of the fuel atomized in the first combustion air flow, while the other part forms a fuel film on the inner wall, which enters after flowing over a downstream tear-off in another swirl-shaped combustion air flow and there is finely distributed.

EP 1 292 795 describes a stepped premix burner with a liquid fuel injector.

Presentation of the invention

The object of the present invention is to provide a premix burner with a liquid fuel injector which achieves a good atomization quality with a low pre-charge of the liquid fuel.

The object is achieved with a premix burner according to independent claim 1. Advantageous embodiments of the premix burner are the subject of the dependent claims or can be found in the following description and the embodiments.

The proposed stepped premix burner has a liquid fuel injector at the tip of a central carrier for a pilot stage. This central support can be designed, for example, in the form of a fuel lance. The premix burner is structurally designed so that the largest possible injector, ie an injector with a possible large widened cross-section of the nozzle-internal swirl generator, can be used. Due to the graded fuel injection can be dispensed with an injection of gaseous fuel at the tip of the carrier as a pilot stage. Rather, such piloting with gaseous fuel is achieved by the staged fuel injection. For this purpose, the premix burner has at least two different groups of fuel outlet openings with separate feeds for the stepped introduction of the gaseous fuel into the combustion air stream. In one embodiment of the premix burner, one of these groups of fuel outlet openings may be formed in a part of the carrier located upstream of the injector. This group of fuel outlets then forms the gaseous fuel pilot stage.

Of course, the different groups of fuel outlet openings for the stepped supply of gaseous fuel can also be arranged elsewhere. This applies, for example, to an embodiment of the premix burner, in which the swirl generator is formed by a plurality of subshells, which surround a pre-mixing chamber in the shape of a cone shell and between which air inlet slots are formed. All or at least part of the fuel outlet openings for the stepped supply of gaseous fuel is formed in the region of the air inlet openings.

The liquid fuel injector includes a swirl nozzle for injecting the liquid fuel as well an umbrella air duct surrounding the swirl nozzle. Under liquid fuel is in this context not only pure fuel, such as oil, but also a mixture or emulsion of this fuel with other substances, in particular an oil / water emulsion to understand.

The swirl nozzle has an internal swirl generator for the liquid fuel flowing through it and widened in the area of the swirl generator to an enlarged flow cross-section, which again reduces towards the outlet opening of the swirl nozzle. The gas-side stepped lance leaves more space for a larger nozzle than conventional injectors, which can reduce the pressure loss. This allows the operation of this low-pressure injector with still good atomization quality.

The nozzle-internal swirl generator is preferably designed as a swirl grid, which may extend, for example, around a central swirl body within the nozzle. Furthermore, it is advantageous to also arrange a swirl generator within the umbrella air duct surrounding the swirl nozzle. The two swirl generators can produce both co-directional as well as opposite swirls. The generation of a relative to the nozzle-internal swirler opposite direction swirl of the screen air can have a positive influence on the atomization quality of the exiting liquid fuel. The strength and direction of the twist can be used to produce an optimum for the particular application of the injection of liquid fuel optimize over the geometric design of the swirl generator.

In one embodiment of the injector, the exit area, i. in particular, the boundary walls of the pressure swirl nozzle and the screen air duct at the injector outlet, designed so that the umbrella air and the liquid fuel exit under approximately parallel flow directions from the injector.

A further embodiment provides for the shielding air to emerge from the injector at an angle of attack to the direction of flow of the liquid fuel, so that shearing forces are exerted on the exiting liquid fuel by the shielding air. This can be achieved by a suitable shaping of the outlet opening for the shielding air, in particular the outer sheath limiting the shielding air duct. The shear rate generated thereby can be used to improve the atomization result when the liquid fuel emerges. Particularly high shear rates between the shielding air and the liquid fuel can be achieved with almost perpendicular to the flow direction of the liquid fuel exiting screen air.

In a further advantageous embodiment of the injector, the swirl nozzle and the outer jacket surrounding it, which together with the swirl nozzle forms the umbrella air channel, are arranged so as to be displaceable relative to one another in the axial direction, ie in the main flow direction of the liquid fuel. This allows the variation of the geometric shape of the outlet opening of the shielding air by the mutual displacement.
When used in a premix burner of a gas turbine combustor, this displacement preferably takes place as a function of the combustion air temperature and thus the load of the gas turbine. In the upper load range, the shield air velocity can be reduced by suitable displacement and thus the atomization, in particular the spray angle and the spray quality, can be changed.

Of course, the latter embodiments can be realized both with and without swirl generator in the shield air duct. When using a swirl generator in the shielding air duct, the swirl angle or the swirl direction can additionally exert an influence on the atomization quality of the liquid fuel.

The present premix burner, due to the special injector, allows operation with reduced fuel side pressure loss on spray formation and, in some embodiments, additionally improved spray formation.

Brief description of the drawings

Fig .1

schematisch ein Beispiel für einen Vormischbrenner gemäß dem Stand der Technik;

Fig. 2

schematisch ein Beispiel für eine Ausgestaltung eines Vormischbrenners mit einem Injektor für Flüssigbrennstoff;

Fig. 3

ein erstes Beispiel für eine Ausgestaltung des Injektors;

Fig. 4

ein zweites Beispiel für eine Ausgestaltung des Injektors; und

Fig. 5

ein drittes Beispiel für eine Ausgestaltung des Injektors.

The premix burner according to the invention with an injector for liquid fuel will be explained in more detail below on the basis of exemplary embodiments in conjunction with the drawings. Hereby show:

Fig .1

schematically an example of a premix burner according to the prior art;

Fig. 2

schematically an example of an embodiment of a premix burner with a liquid fuel injector;

Fig. 3

a first example of an embodiment of the injector;

Fig. 4

a second example of an embodiment of the injector; and

Fig. 5

a third example of an embodiment of the injector.

Ways to carry out the invention

The construction of a premix burner according to the prior art, as shown in the Fig. 1 has been shown schematically, has already been explained in detail in the introduction.

Fig. 2 now shows schematically an example of an embodiment of the present staged premix burner, in which a liquid fuel injector is used. This premix burner has, in a known manner, a swirl generator 1 which is composed of two partial shells which enclose a pre-mixing chamber in the shape of a cone-shaped jacket. Between the two subshells air inlet slots 2 are formed, which are indicated in the right part of the figure in plan view (viewing direction opposite to the flow direction) on the premix burner. In the area of this Air inlet slots 2 are arranged fuel outlet openings 10 for gaseous fuel, which are acted upon by corresponding feeds with this fuel. By introducing the gaseous fuel into the combustion air stream entering tangentially through the air inlet slots 2, mixing of the gaseous fuel with the combustion air is facilitated by the swirl of the combustion air.

In the present example, a group of fuel outlet openings 10 is formed for gaseous fuel in the combustion chamber near the half of the burner, which forms one of two burner stages in the present case. A second group of gaseous fuel fuel discharge ports 9 is disposed in the central fuel lance 3 upstream of the tip of this lance 3. This further stage for the supply of gaseous fuel can serve as a pilot stage during the start-up phase of the gas turbine, in whose combustion chamber this burner is used. Of course, the first-mentioned burner stage can be arbitrarily divided into different stages, which are acted upon independently with gaseous fuel. Of course, these burner stages can also extend over the entire axial length of the swirl generator 1.

At the top of the fuel lance 3, the present injector 4 is arranged, which in the right part of the FIG. 2 can be seen in plan view. The figure shows the central outlet nozzle 6 for the Liquid fuel 6a and the annular outlet nozzle 5 surrounding it for the umbrella air 5a. The stepped design of this premix burner avoids the installation of an additional nozzle for gaseous fuel at the lance tip, so that more space is available for the injector for liquid fuel. This very advantageously allows the use of the proposed injector with the broadened flow cross-section in the region of the nozzle-internal swirl generator.

In the starting operation of the gas turbine, a large part of the fuel is added via the fuel lance 3. Only at higher load, the burner is operated with lower fuel levels over the lance stage, which allow optimization of the pulsation and pollutant emission behavior.

The Fig. 3 to 5 show exemplary embodiments of injectors 4, as in a premix burner according to Fig. 2 can be used. In the embodiment according to Fig. 3 the geometric shape of the swirl nozzle 14 is clearly visible. This swirl nozzle 14 is locally greatly enlarged in the flow cross-section in the region of the nozzle-internal swirl lattice 12. The swirl lattice 12 is in this case formed around a central swirl body 15. Due to the more favorable compared to conventional injectors space in the lance tip a larger nozzle can be installed, whereby the pressure loss is significantly reduced, so that this injector can be operated with reduced form with high atomization performance.

The shielding air channel 11 surrounds the swirl nozzle 14. The shielding air 5a emerges in this application example in the axial direction from the lance tip. This is achieved by the geometric design of the boundaries of the shield air duct 11 at the outlet end, which run parallel to the axial direction. In the shield air duct 11, an additional swirl grille 13 can optionally be arranged with equal or opposite swirl relative to the nozzle-internal swirl grating 12. The adjustment of the helix angle can influence the atomization quality of the liquid fuel as it exits the injector.

Fig. 4 shows another example of the injector 4, in which this is similar to that of the Fig. 3 , The Indian Fig. 4 However, shown injector 4 has different exit directions for the shielding air 5a and the liquid fuel 6a. Due to the inwardly directed formation of the outlet of the umbrella air duct 11, a setting of the umbrella air flow with respect to the flow direction of the liquid fuel 6a is achieved upon exiting the injector. In the present example, a flow field of the shielding air is forced nearly perpendicular to the flow direction of the liquid fuel by the illustrated embodiment, so däss a high shear rate between the shielding air and the liquid fuel is generated. This high shear rate promotes the atomization effect. Again, a swirl grille 13 may be arranged in the shield air duct, which, in particular in the generation of an opposite twist, can further enhance the effect of atomization.

Fig. 5 Finally, another example of an injector 4 comparable to the injector of FIG Fig. 4 is trained. However, in this example, the shielding air channel 11 has a variable geometry, which is achieved by a mutual displaceability of the outer jacket 16 relative to the swirl nozzle 14 in the axial direction. This displacement is indicated in the figure by the double arrows. If the swirl nozzle 14 is displaced with respect to the outer jacket 16, the outlet gap for the umbrella air opens or closes. The displacement is preferably a function of the combustion temperature and thus the load of the gas turbine. Thus, for example, in the upper load range with the help of this injector by increasing the shield air gap, the shield air velocity can be reduced and thus the spray angle and the spray quality can be changed.

The present configuration of the injector or premix burner permits low-emission and pulsation-free operation in the combustion of liquid fuels or fuel emulsions in a gas turbine combustion chamber. This is made possible above all by the combination of a gas-side gas-fueled gas turbine burner, which makes it possible to install the injector in the tip of the spear, which is larger by local broadening of the swirl nozzle. Due to the different configurations of the injector, the atomization or spray behavior can be influenced to optimize the respective applications. <B> LIST OF REFERENCES </ b> 1 swirl generator 2 Air inlet slots 2a 3 fuel lance 4 Injector for liquid fuel 5 Outlet nozzle for screen air 5a shielding air 6 Outlet nozzle for liquid fuel 6a liquid fuel 7 Outlet nozzle for gaseous fuel 7a Gaseous fuel 8th Flow direction or axial direction 9 Outlets for gaseous fuel 10 Outlets for gaseous fuel 11 Screen air duct 12 In-nozzle swirl grid 13 Swirl lattice in the shield air duct 14 swirl nozzle 15 Internal nozzle swirl body 16 Outer sheath

Claims (12)

1. Staged premix burner, in particular for a combustion chamber of a gas turbine, having a swirl generator (1) for a combustion air stream, fuel exit openings (9, 10) with feeds for the staged introduction of gaseous fuel into the combustion air stream, and a central carrier (3), which has an injector (4) with a swirl nozzle (14) for the injection of liquid fuel (6a) and a shielding-air passage (11) for shielding air (5a), the swirl nozzle (14) being surrounded by the shielding-air passage (11) and having an enlarged cross section of flow in the region of a nozzle-internal swirl generator (12) for the liquid fuel (6a), and this enlarged cross section of flow is reduced again toward an exit opening of the swirl nozzle (14).
2. Premix burner according to Claim 1, characterized in that some of the fuel exit openings (9) for introducing gaseous fuel into the combustion air stream are formed in a part of the carrier (3) which is located upstream of the injector (4).
3. Premix burner according to Claim 1, characterized in that the swirl generator (1) is formed by a plurality of part-shells, which surround a premix space in the shape of a cone envelope and between which air entry slots (2) are formed.
4. Premix burner according to Claim 3, characterized in that at least some of the fuel exit openings (10) for introducing gaseous fuel into the combustion air stream are arranged in the region of the air entry slots (2) at the swirl generator (1).
5. Premix burner according to Claim 1, characterized in that the nozzle-internal swirl generator (12) of the injector (4) is designed as a swirl grate.
6. Premix burner according to Claim 5, characterized in that the swirl grate extends around a central swirl body (15).
7. Premix burner according to one of Claims 1 to 6, characterized in that a passage-internal swirl generator (13) is arranged in the shielding-air passage (11) of the injector (4).
8. Premix burner according to Claim 7, characterized in that the passage-internal swirl generator (13) in the shielding-air passage (11) and the nozzle-internal swirl generator (12) are designed in such a way that they generate oppositely directed swirls.
9. Premix burner according to one of Claims 1 to 8, characterized in that the injector (4) is designed in such a way that the liquid fuel (6a) and the shielding air (5a) emerge from the injector (4) with approximately parallel directions of flow in the axial direction of the carrier (3).
10. Premix burner according to Claim 9, characterized in that boundary walls of the swirl nozzle (14) and of the shielding-air passage (11) run approximately coaxially at an exit of the injector (4).
11. Premix burner according to one of Claims 1 to 8, characterized in that the shielding-air passage (11) is designed in such a way, at an exit of the injector (4), that the shielding air (5a) emerges at an angle with respect to the direction in which the liquid fuel (6a) emerges, in order to exert shearing forces on the liquid fuel (6a).
12. Premix burner according to one of Claims 1 to 11, characterized in that the swirl nozzle (14) and an outer casing (16), which in combination with the swirl nozzle (14) forms the shielding-air passage (11), are arranged so as to be displaceable with respect to one another in the axial direction of the carrier (3).

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