EP0401529B1 - Gas turbine combustion chamber - Google Patents

Abstract

In a combustion chamber (A) having the shape of an annular combustion chamber, a series of large and small premix burners (B, C) is arranged along the annular front wall (10). The large premix burners (B), which are the main burners of the combustion chamber (A), and the small premix burners (C), which are the pilot burners of the combustion chamber (A), follow each other in alternating sequence and regularly along the front wall (10), where they also open into the combustion space of the combustion chamber (A). A plurality of air nozzles (D) are positioned between the large premix burners (B) and the small premix burners (C), their injection being directed into the combustion space of the combustion chamber (A). <IMAGE>

Description

Technical field

The present invention relates to a combustion chamber according to the preamble of claim 1.

State of the art

With regard to the prescribed, extremely low NO _x emissions when operating a gas turbine, many manufacturers are adopting premix burners. One of the disadvantages of premix burners is that they extinguish at a very low air ratio, depending on the temperature of the gas turbine compressor at a λ of approx. 2. For this reason, such premix burners must be supported by one or more pilot burners in the partial load operation of a gas turbine. Diffusion burners are usually used for this. This technology enables very low No _x emissions in the area of full load. In contrast, this auxiliary burner system performs at partial load to significantly higher NO _x emissions. The attempt, which has become known variously, to make the diffusion auxiliary burners leaner or to use smaller auxiliary burners must fail because the burnout deteriorates and the C0 / UHC emissions increase very sharply. In technical terms, this condition has become known as CO / UHC-NO _x scissors.

Object of the invention

The invention seeks to remedy this. The object of the invention, as characterized in the claims, is to provide a combustion chamber which, with minimized exhaust gas emissions, enables a wide operating range, while optimizing the quality factor for the temperature profile at the turbine inlet, in the technical term "pattern factor".

For this purpose, it is provided along the entire front wall of the combustion chamber to alternately place a large and a small premix burner, i.e. A small premix burner can be found between two large premix burners. Furthermore, air nozzles are provided between a large and a small premix burner, which bring a certain amount of air into the combustion chamber. This configuration is optimal for an annular combustion chamber, with the front wall then being annular.

The large premix burners, hereinafter referred to as main burners, are related to the small premix burners, hereinafter referred to as pilot burners, with regard to the flow through them Burner air in a size ratio that is determined on a case-by-case basis. The pilot burners work as independent premix burners in the entire load range of the combustion chamber, whereby the air ratio remains almost constant. Because the pilot burners can now be operated in the entire load range with an ideal mixture (premix burner), the NO _x emissions are very low even at partial load. It also shows that, in the interest of "up-prizing" potential for gas turbines with higher turbine inlet temperatures, the proportion of air that cannot be formed by the burners (lean blowoff limit, CO / UHC) is not, because of the pattern factor, should only be used for cooling purposes. A certain proportion of air is introduced via the air nozzles provided here, preferably after the primary combustion zone of the combustion chamber, and there it is ensured that perfect mixing takes place. This has the advantage that the proportion of air that ensures “upprating” and is therefore blown directly into the secondary combustion zone prevents the undesired “leaning out” of the primary zone. Since the air nozzles are located at a point with a very low air speed and only occupy a limited width of the front wall, their influence on the main flow field in the primary area is only very weak. In particular, the air nozzles do not interfere with the cross-ignition between pilot burners and main burners. Another advantage of these air nozzles results from their position on the front wall; this zone would become very hot there without the cooling effect of the air jets. The main advantage of these air nozzles, however, can be seen in the fact that the shear layers occurring between main burners and pilot burners are stabilized. For this reason the "Lean Stability Limit" of the combustion chamber, at which only the pilot burners burn independently, significantly improved by the air nozzles.

An advantageous embodiment of the invention is achieved if the main burners and the pilot burners consist of so-called double-cone burners of different sizes, and if these are integrated in an annular combustion chamber. Because the circulating streamlines in the ring combustion chamber come very close to the vortex centers of the pilot burners in such a constellation, ignition is only possible with these pilot burners. When starting up, the amount of fuel that is supplied via the pilot burner is increased until the pilot burner is activated, i.e. until the full amount of fuel is available. The configuration is chosen so that this point corresponds to the load shedding condition of the gas turbine. The further increase in output then takes place via the main burner. The main burners are also fully controlled at the peak load of the system. Because the configuration of "small" hot vortex centers (pilot burner) between large, cooler vortex centers (main burner) is extremely unstable, very good burnout with low CO / UHC emissions is achieved even with lean operated main burners in the partial load range, i.e. the hot eddies of the pilot burner immediately penetrate into the cold eddies of the main burner.

Advantageous expedient developments of the task solution according to the invention are characterized in the further dependent claims.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawing. All for the immediate Elements not required to understand the invention are omitted. In the different figures, the same elements are provided with the same reference numerals. The flow direction of the media is marked with arrows.

Brief description of the figures

Fig.1

eine schematische Aufsicht auf einen Teil der Frontwand einer Ringbrennkammer, mit ebenfalls schematisch dargestellten Pilot-, Hauptbrennern sowie Luftdüsen,

Fig.2

einen schematischen Schnitt durch eine Ringbrennkammer in der Ebene eines Hauptbrenners,

Fig.3

einen weiteren Schnitt durch eine Ringbrennkammer in der Ebene eines Pilotbrenners,

Fig.4

einen schematischen Axial-Schnitt durch einen Brenner,

Fig.5

einen schematischen Axial-Schnitt im Bereich der Luftdüsen,

Fig.6

einen Brenner in der Ausführung als Doppelkegelbrenner in perspektivischer Darstellung, entsprechend aufgeschnitten,

Fig.7,8,9

entsprechende Schnitte durch die Ebenen VII-VII (Fig.7), VIII-VIII (Fig. 8) und IX-IX (Fig.9), wobei diese Schnitte nur eine schematische, vereinfachte Darstellung des Doppelkegelbrenners gemäss Fig. 6 sind.

It shows:

Fig. 1

2 shows a schematic view of part of the front wall of an annular combustion chamber, with pilot, main burners and air nozzles also shown schematically,

Fig. 2

2 shows a schematic section through an annular combustion chamber in the plane of a main burner,

Fig. 3

another section through an annular combustion chamber in the plane of a pilot burner,

Fig. 4

a schematic axial section through a burner,

Fig. 5

a schematic axial section in the area of the air nozzles,

Fig. 6

a burner in the design as a double-cone burner in perspective, cut open accordingly,

Fig. 7,8,9

corresponding sections through the levels VII-VII (Fig.7), VIII-VIII (Fig. 8) and IX-IX (Fig.9), these sections being only a schematic, simplified representation of the double-cone burner according to FIG. 6.

Description of the embodiments

1 shows a section of a sector of the front wall 10. This shows the placement of the individual main burners B and pilot burners C. These are evenly and alternately distributed over the circumference of the annular combustion chamber A. The size difference shown between main burners B and pilot burners C is only of a qualitative nature. The effective size of the individual burners and their distribution and number on the circumference of the front wall 10 of the annular combustion chamber A, as already explained above, depends on the power and size of the combustion chamber itself. The main burners B and pilot burners C, which are arranged alternately, open out all at the same height in a uniform annular front wall 10, which forms the entry surface of the annular combustion chamber A. Between the individual burners B, C, a number of air nozzles F, here in a schematic representation, are provided, which occupy approximately half the width of the front wall 10 in the radial direction. If the main burner B and pilot burner C produce co-rotating vortices, a circulating flow is formed above and below the burner B and C. To explain this state, we would like to refer to an endless conveyor belt that is kept moving by rollers in the same direction. The role of the roles is here through the co-rotating burner taken over. A vortex center is also created around the respective burner; around the pilot burner C, the vortex centers are small and hot, and inherently unstable. These come to rest between the large, cooler vortex centers from the main burners B. In this area between the small hot and large cooler vortex centers, the air nozzles F act, which decisively improve the stabilization of the two, as has already been appreciated in the foregoing. Even if the main burners B are operated lean, as is the case in part-load operation, a very good burnout with low CO / UHC emissions can be expected.

2 and 3 show a schematic section through an annular combustion chamber A, respectively in the plane of a pilot burner C and. of a main burner B. The annular combustion chamber A shown here is tapered in the direction of the turbine inlet D, as can be seen from the central axis E of the annular combustion chamber A shown. An individual nozzle 3 is allocated to each burner B, C. Already from this schematic representation it can be seen that the burners B, C are at the same time premix burners, that is to say they do without the otherwise usual premix zone. Of course, these premix burners B, C, regardless of their specific design, must be designed such that there is no fear of re-ignition into the premix zone via the respective front panel 10. A premix burner which excellently fulfills this condition is shown comprehensively in FIGS. 6-9 and explained in more detail there, the structure being able to be the same for both burner types (main burner B / pilot burner C), only their size will be different. In the case of an annular combustion chamber A of medium size, the size ratio between main burner B and pilot burner C is selected such that about 23% of the burner air flows through the pilot burner C and about 77% through the main burner B.

4 and 5 schematically show a main burner B, according to section IV-IV from FIG. 1, and the air nozzles F, according to section V-V from FIG. 1, in a positionally coordinated axial section. In this connection, the structure for the air nozzles F which extends far into the combustion chamber with respect to the front wall 10 and which causes the air G to act further downstream in relation to the flame front of the burners B and C must be observed.

In order to better understand the structure of the burner B / C, it is advantageous if the individual sections according to FIGS. 7-9 are used simultaneously with FIG. 6. Furthermore, in order not to make FIG. 6 unnecessarily confusing, the guide plates 21a, 21b shown schematically according to FIGS. 7-9 have only been hinted at in it. In the description of FIG. 6 below, the remaining FIGS. 7-9 are optionally referred to as required.

The burner B / C according to FIG. 6, which can be both a pilot burner C and a main burner B in terms of structure, consists of two half-hollow partial cone bodies 1, 2 which are offset from one another. The offset of the respective central axis 1b, 2b of the partial cone bodies 1, 2 to each other creates a tangential air inlet slot 19, 20 on both sides in a mirror-image arrangement (FIGS. 7-9) through which the combustion air 15 enters the interior of the burner, ie flows into the cone cavity 14. The two partial cone bodies 1, 2 each have a cylindrical initial part 1a, 2a which is also analogous to that Partial cone bodies 1, 2 run offset from one another, so that the tangential air inlet slots 19, 20 are present from the beginning. A nozzle 3 is accommodated in this cylindrical starting part 1a, 2a, the fuel injection 4 of which coincides with the narrowest cross section of the conical cavity 14 formed by the two partial cone bodies 1, 2. The size of this nozzle 3 depends on the type of burner, ie whether it is a pilot burner C or main burner B. Of course, the burner can be made purely conical, that is to say without cylindrical starting parts 1a, 2a. Both partial cone bodies 1, 2 each have a fuel line 8, 9, which are provided with openings 17 through which the gaseous fuel 13, which is mixed with the combustion air 15 flowing through the tangential air inlet slots 19, 20. The position of these fuel lines 8, 9 are attached to the end of the tangential air inlet slots 19, 20, so that the admixture 16 of this fuel 13 with the inflowing combustion air 15 also takes place there. On the combustion chamber side 22, the burner B / C has a plate which forms the front wall 10. The liquid fuel 12 flowing through the nozzle 3 is injected into the cone cavity 14 at an acute angle such that a cone-shaped fuel spray which is as homogeneous as possible is obtained in the burner outlet plane. The fuel injector 4 can be an air-assisted nozzle or a pressure atomizer. Of course, in certain operating modes of the combustion chamber, it can also be a dual burner with gaseous and liquid fuel supply, as is described, for example, in EP-A1 210 462. The conical liquid fuel profile 5 from the nozzle 3 is enclosed by a rotating combustion air stream 15 flowing in tangentially. In axial Direction, the concentration of the liquid fuel 12 is continuously reduced by the mixed combustion air 15. If gaseous fuel 13/16 is burned, the mixture is formed with the combustion air 15 directly at the end of the air inlet slots 19, 20. When the liquid fuel 12 is injected, the optimal, homogeneous fuel concentration is in the area of the vortex bursting, ie in the area of the backflow zone 6 reached the cross section. The ignition takes place at the tip of the return flow zone 6. Only at this point can a stable flame front 7 arise. A flashback of the flame into the interior of the burner, as is latently the case in known premixing sections, while remedial measures are sought there with complicated flame holders is not to be feared here. If the combustion air 15 is preheated, natural evaporation of the liquid fuel 12 occurs before the point at the burner outlet at which the ignition of the mixture can take place is reached. The degree of evaporation is of course dependent on the size of the burner, the drop size distribution in the case of liquid fuel and the temperature of the combustion air 15. Regardless of whether, in addition to a homogeneous drop mixture through combustion air 15 at low temperature or additionally only partial or complete drop evaporation through preheated combustion air 15, the nitrogen oxide and carbon monoxide emissions are low if the air excess is at least 60%, which is one of them additional precaution to minimize NO _x emissions is available. In the case of complete evaporation before entering the combustion zone, the pollutant emission values are lowest. The same also applies to near-stoichiometric operation when the excess air is replaced by recirculating exhaust gas. When designing the partial cone bodies 1, 2 with regard to the taper inclination and the width of the tangential air inlet slots 19, 20, narrow limits must be observed so that the desired flow field of the air with its return flow zone 6 is established in the area of the burner mouth for flame stabilization. In general, it can be said that a reduction in the size of the air inlet slots 19, 20 shifts the backflow zone 6 further upstream, which would cause the mixture to ignite earlier. After all, it must be ascertained here that the backflow zone 6, which is once geometrically fixed, is inherently positionally stable, because the swirl number increases in the direction of flow in the region of the cone shape of the burner. The design of the burner is particularly suitable for changing the size of the tangential air inlet slots 19, 20 for a given overall length of the burner, in that the partial cone bodies 1, 2 are fixed to the end plate 10 by means of a releasable connection. The distance between the two central axes 1b, 2b is reduced or increased by radial displacement of the two partial cone bodies 1, 2 to and from one another, and the gap size of the tangential air inlet slots 19, 20 changes accordingly, as is particularly well shown in FIGS. 7-9 emerges. Of course, the partial cone bodies 1, 2 can also be displaced relative to one another in another plane, as a result of which even an overlap thereof can be controlled. Yes, it is even possible to move the partial cone bodies 1, 2 spirally towards one another by means of a counter-rotating movement. It is therefore in your hands to vary the shape and size of the tangential air inlets 19, 20 as desired, with which the burner can be individually adapted without changing its overall length.

7-9 also shows the position of the guide plates 21a, 21b. They have flow introduction functions, whereby, depending on their length, they extend the respective end of the partial cone bodies 1 and 2 in the direction of flow of the combustion air 15. The channeling of the combustion air into the cone cavity 14 can be optimized by opening or closing the guide plates 21a, 21b about the pivot point 23, in particular this is necessary if the original gap size of the tangential air inlet slots 19, 20 is changed. Of course, the burner can also be operated without baffles.

Claims (9)

1. Combustion chamber of a gas turbine with premixed burner, the premixed burner consisting of at least two hollow partial conical bodies positioned on one another, the centre lines of which partial conical bodies extend offset to one another in their longitudinal direction characterized in that the combustion chamber (A) is provided at the burner air inlet flow end with a number of premixed burners (B, C), in that the premixed burners (B, C) are located adjacent to one another and, with respect to the burner air flowing through them, are of different sizes, in that the large premixed burners (B) and the small premixed burners (C) follow one another alternately and in that air nozzles (F) are placed between the individual premixed burners (B, C).
2. Combustion chamber according to Claim 1, characterized in that the large premixed burners (B) and the small premixed burners (C) are directed in the same swirl direction.
3. Combustion chamber according to Claim 1, characterized in that the large premixed burners (B) are the main burners and the small premixed burners (C) are the pilot burners of the combustion chamber (A).
4. Combustion chamber according to Claim 1, characterized in that the injection of air (G) via the air nozzles (D) is directed into the combustion space (22) of the combustion chamber (A) and takes place downstream of the premixed burners (B, C).
5. Combustion chamber according to Claim 1, characterized in that at least one fuel nozzle (3) is placed at the inlet flow end in the hollow cone-shaped internal space formed by the partial conical bodies (1, 2), with increasing flow cross-section in the flow direction, the fuel spray inlet of which fuel nozzle (3) is located between the mutually offset centre lines (1b, 2b) of the partial conical bodies (1, 2), and in that the mutual offset of the centre lines (1b, 2b) is a measure of the size of the tangential air inlet slots (19, 20) between the partial conical bodies (1, 2).
6. Combustion chamber according to Claim 5, characterized in that the fuel nozzle (3) can be operated with a liquid fuel.
7. Combustion chamber according to Claim 5, characterized in that further fuel nozzles (17) are present in the region of the tangential air inlet slots (19, 20).
8. Combustion chamber according to Claim 7, characterized in that the fuel nozzles (17) can be operated with a gaseous fuel.
9. Combustion chamber according to one of Claims 1-8, characterized in that the combustion chamber (A) is an annular combustion chamber on whose annular front wall (10) the large premixed burners (B), the small premixed burners (C) and the air nozzles (F) emerge.

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