EP1456583B1 - Method for injecting a fuel/air mixture in a combustion chamber - Google Patents

Abstract

The invention relates to a fuel lance, by means of which fuels (6, 11) can be injected alternately or simultaneously at an injection point essentially located at the lance tip (1), through at least two separate channels (5, 10), with which a secure operation without risk of blowback and avoidance of coking may be achieved, whereby the fuel lance also feeds flushing air (9) to the injection point along with fuel and said flushing air (9) is introduced at the injection point between the two fuel systems (6, 11) such that the above are shielded from each other by means of the flushing air (9).

Description

TECHNICAL AREA

The present invention relates to a method for injecting a fuel air mixture into a combustion chamber according to the preamble of claim 1. Such a method is known from the document US-A-6038863 known.

STATE OF THE ART

Premix burners allow, depending on premix quality, a significant reduction in NOx emissions from gas turbines. The problem, however, is the relatively narrow operating range of premix burners. Even with vortex breakdown swirl stabilization, such as in double cone burners, as they are US 4,932,861 are known, or in double-cone burners with downstream mixing section, as shown for example in the EP 0704657 described, an additional flame for the part-load operation is required. This partial load flame or pilot flame is usually diffusion-like and ideally should have as close as possible contact with the (premix) main flame. Furthermore, it is necessary to avoid by aerodynamic measures a recirculation of fuel mixture in the pilot fuel system during the premix operation, as this can ignite and thus can lead to overheating of the fuel lines.

DE-A1-44 24 597 discloses a combustion device. This combustion device is particularly suitable for a gas turbine and comprises a combustion chamber with a plurality of burners operating in parallel. These burners are supplied by means of exchangeable inserted fuel lances from the outside liquid or gaseous fuel via corresponding liquid fuel supply channels or gas supply channels. For easy tuning of the fuel distribution changeable throttle points are provided in the liquid fuel supply channels or gas supply channels of the individual fuel lances of the burner.

DE-A1-195 45 310 discloses a premix burner. This premix burner for mixing fuel and combustion air consists essentially of at least two partial cone shells with associated pitch cone axes and inlet channels for the combustion air. The premix burner is essentially formed from a straight hollow cone which is delimited by an outer conical surface and an inner conical surface and in which at least two inlet channels are arranged tangentially to the inner conical surface and along a straight conical surface line of the conical surface. The pitch cone axes of the part cone shells formed thereby lie on a common cone axis.

US-A-5,782,626 discloses an atomizer nozzle. In this airblast atomizer nozzle for operating a liquid and gaseous fuel powered burner, the intermediate wall between the inner and outer air duct is held by inner and outer support members, which have a sliding seat and can be designed as swirl blades. The atomizer edges of the airblast nozzle are angled in the direction of the nozzle axis. The nozzle is characterized by small dimensions, low pressure loss and low coking tendency.

PRESENTATION OF THE INVENTION

It is an object of the present invention to provide a method for the introduction of two fuels supplied separately from a lance base, which is usually located at the base of the burner, to the injection location on the burner axis upstream of the vortex breakdown. It is therefore a question of providing a method with which at least two fuels separated from one another can be injected alternatively or simultaneously at a point of injection located essentially at the point of the lance into a combustion chamber. The combustion chamber should be able to be operated simultaneously or alternatively with the two fuels, without the risk of re-ignition or coking (in the case of liquid fuel) occurs.

The solution of the problem can be found in the characterizing part of the main claim. The solution is that the liquid fuel injected at the injection in radially outward and directed to the flow of scavenging air in the form of a revolving, the lance tip hollow hollow truncated cone is injected and the gaseous fuel at Eindüsungsort in radially inward and on the stream the scavenging air is injected in a directed manner.

The essence of the invention thus consists in that the scavenging air, which is likewise guided to the lance tip, is guided in such a way between the fuels injected into the combustion chamber at the lance tip that a "protective shield" of purging air prevents the two fuels from crossing one another. In particular, it can thus be prevented during operation of the lance with only one fuel that fuel enters that fuel channel, which is currently not driven by fuel.

According to the invention, the two channels for the fuels and the channel for the scavenging air are formed as substantially concentric cylindrical tubes of different diameters, wherein the three media are guided in the resulting hollow cylindrical or cylindrical spaces to Eindüsungsort. This construction is simple and particularly suitable with regard to the thermal loads in a burner.

The fuel systems are a liquid fuel system and a gaseous fuel system. Typically, the gaseous fuel is used for the partial load range in the gas mode, and the liquid fuel, for. B. in the form of an oil for the entire load range in oil operation. In this case, the liquid fuel is passed through a central, inner tube with the smallest diameter to the lance tip, said inner tube is surrounded by two other, concentrically arranged with the inner tubes and the gaseous fuel, and the scavenging air in the thus formed hollow cylindrical spaces to the lance tip is led to the Eindüsungsort, and further wherein immediately downstream of the injection site, the scavenging air flows in the cavity between the central, inner tube and the middle tube. This ensures that the purge air at the point of injection effectively between the two Fuel flows and in the sense of a shielding shell and the two fuel streams decoupled from each other.

The fuel lance is further characterized in that the purging air is injected into the combustion chamber in a substantially axial and circumferential manner, in the sense of a hollow cylinder at Eindüsungsort. In other words, the purge air enters the zone of combustion parallel to the burner axis. In this case, the injection of the liquid fuel takes place in a slightly radially outward direction and in the axial purge air flow direction, i. E. in the form of a circumferential hollow circular truncated cone opening to the tip of the spear. The liquid fuel can also be injected at this point through a Hohtkegel swirl nozzle or through a multi-hole nozzle. At the injection site, the gaseous fuel is injected in a slightly radially inward direction and in the purge air flow direction, d. H. in the form of a circular hollow circular truncated cone closing to the tip of the lance.

Another preferred embodiment of the inventive method is characterized in that the liquid and the gaseous fuel at the lance base in the inner tube respectively in the cavity between the inner tube and the middle tube are guided, and the purging air in the cavity between the middle tube and the outer Tube is guided. In this case, either directly at the lance base, the scavenging air can be diverted into the cavity between the inner tube and the middle tube, while the gaseous fuel is passed into the cavity between the middle tube and the outer tube, wherein particularly preferably the introduction of the scavenging air in the middle cavity is made by arranged in corresponding radial segments slots or holes. Since usually the lance tip on the lance base can have a larger diameter, this design allows higher flows of purge air and gaseous fuel.

On the other hand, it is possible to cross the scavenging air only at the lance tip with the leadership of the gaseous fuel. This means that the purging air in the cavity between the middle tube and the outer tube is guided to the lance tip, and in the region of the lance tip the purging air is diverted into the central cavity between the inner tube and the middle tube, while the gaseous fuel in the outer Cavity between the middle tube and the outer tube is passed. Although this design usually allows only slightly lower flows of purging air and gaseous fuel due to the lower dimensions of the spearhead, but has the advantage that the scavenging air, which runs in the outermost channel, at the same time has a cooling effect and excessive heating and associated restrike thereby additionally be prevented.

Furthermore, it relates to the use of a method as described above. In particular, it relates to such use for the pilot operation of a premix burner, in particular a double-cone burner with or without a downstream mixing section, in which case the fuel lance is arranged on the axis of the premix burner.

According to a first preferred embodiment of said use, the lance extends substantially over a length of 3/4 of the total length of the double-cone burner with or without a downstream mixing section, the total length being the length of the conical region of the double-cone burner.

BRIEF EXPLANATION OF THE FIGURES

• Fig. 1 einen axialen Schnitt durch eine Brennstofflanze ;
• Fig. 2 einen axialen Schnitt durch eine gesamte Brennstofflanze, bei welcher die Kreuzung an der Lanzenspitze angeordnet ist; und
• Fig. 3 einen axialen Schnitt durch eine Brennstofflanze, bei welcher die Kreuzung an der Lanzenbasis angeordnet ist.

The invention will be explained in more detail with reference to embodiments in conjunction with the drawings. Show it:

• Figure 1 is an axial section through a fuel lance.
• Figure 2 is an axial section through an entire fuel lance, wherein the intersection is located at the lance tip. and
• Fig. 3 is an axial section through a fuel lance, wherein the crossing is arranged on the lance base.

Only the elements essential to the invention are shown. Identical elements are provided in different figures with the same reference numerals. Flow directions are indicated by arrows.

WAYS FOR CARRYING OUT THE INVENTION

Fig. 1 shows the lance tip 1 of a fuel lance in an axial section. The fuel lance consists of an outermost lance tube 2, the lance in the case of. Use in a double-cone burner, as z. B. off US 4,932,861 is known, usually about 3/4 of the length of the burner protrudes into the cavity between the conical Teilkörpem. However, it is also possible to use the proposed fuel lance in a premix burner with vortex breakdown, which additionally has a downstream mixing section (cf. EP 0704657 ).

The fuel lance usually has a circular cross-section. In the cylindrical outermost tube 2 is located coaxially with the outermost tube 2, a middle tube 4, and another, inner tube, the oil tube 3, with the smallest diameter. Through the oil pipe 3 flows liquid fuel, that is oil 6, Gasoline, or the like in the oil guide 5 to the lance tip 1 when the fuel lance with liquid fuel 6 is operated. At the tip of the oil pipe 3 is a central insert 7, which is arranged substantially on the axis of the burner lance, and which causes the flow of oil at the lance tip 1 is deflected radially outwards. The liquid fuel does not occur in the direction of the axis of the fuel lance in the combustion chamber or the cavity in which the combustion is to take place, but in the form of a circular cone-shaped spray cone, which may be closed all around, ie formed circumferentially. The liquid fuel may also be injected at this point through a hollow cone swirl nozzle (not shown in the figures) or through a multi-hole nozzle.

In the cavity between the outermost tube 2 and the middle tube 4 usually gaseous fuel 11 flows to the lance tip 1. The outer tube 2 has at its outermost end directed in the direction of the axis of the fuel lance, circumferential curvature, i. Constriction, which causes the gas flow is deflected just before emerging from the fuel lance in the direction of the axis of the fuel lance. In other words, a conical hollow gas cone is created.

In the intermediate space 8 between the middle tube 4 and the oil pipe 3, scavenging air 9 now flows according to the invention to the spearhead 1. This scavenging air 9 flows essentially axially, ie. H. forming a cylindrical air jacket at the lance tip 1 from. In other words, the scavenging air 9 flows between the two fuels used. According to the invention, both the gaseous fuel 11 and the liquid fuel 6 are directed onto this cylindrical air mantle of purging air 9. This particular arrangement allows a mode of operation in which due to the shielding of the fuel streams by the scavenging air 9, the lance can be operated either with one of the two fuels 6,11, or with both, without causing z. B. when operating with only one fuel would be the danger that fuels 6,11 can get from the controlled fuel channel in the non-operated channel (no fuel reflux).

Typically, such a fuel lance has an outer diameter in the range of 20 to 40 millimeters (outer diameter of the outermost tube 2), the middle tube 4 has an outer diameter of about 2/3 of that of the outermost tube 2, and the oil tube 3 has a diameter of At the lance base 17 of the lance this usually has a larger outer diameter of in the range of 30 to 60 millimeters. The tubes are advantageously made of nickel-based alloys with a wall thickness in the range of 1 to 3 millimeters. The outer tube 2, which has an inward bend in the foremost region, is tapered there over a length of 10 millimeters in the range of 40%, which causes a deflection of the pilot gas 11 in the direction of the central axis of the fuel lance and whereby the outlet opening of the fuel lance Pilot gas 11 comes to rest so that the shielding effect of the scavenging air 9 is maximum.

Typically, such a fuel lance is used for pilot operation of premix burners. If possible, only gaseous fuel 11 is used in pilot operation, wherein typically the fuel lance is used up to approximately 50% load, ie. H. until the premix flame is sufficiently stabilized. If the premix flame is sufficiently stabilized, normally the fuel lance is no longer fueled, but only the fuel nozzles at the inlet slots of the premix burner.

Is now z. For example, if no gaseous fuel 11 is available, the fuel lance according to the invention alternatively allows burner operation using liquid fuel 6. This alternative usability is possible because the purging air 9 prevents that when operating with only one fuel this fuel in the not operated channel into it, and leads there to reignitions. The coat of scavenging air 9 also has the advantage of liquid fuel 6 that coking can be avoided.

Fig. 2 shows a lance in its entire length. Since usually the liquid and the gaseous fuel 6, 11 are supplied to the lance base 17 of the burner in a pilot gas-15 and an oil inlet 16, there is basically the problem, the purge air 9 to lead between these two fuel channels. This can take place in two different ways, FIG. 2 representing the possibility in which the two fuels are first guided in concentric tubes from the lance base 17 into the area of the lance tip 1, and the purging air 9 is arranged in a further intermediate space between the lances middle pipe 4 and an outer tube 2 is guided to this area. The scavenging air 9 is thereby introduced in the region of the lance base 17 at 14 through openings in the intermediate space between the central tube 4 and the outermost tube 2. This scavenging air 9 is usually sucked from an area behind the burner. The inlet openings can be designed as slots, but to prevent the entry of dirt particles, it proves to be advantageous to perform these openings as holes, usually with a diameter in the range of 2 to 4 millimeters. In the area of the lance tip 1, the pilot gas guide 10 is now guided on the one hand in the radially outermost space by the two outer channels are crossed in a region 12. In the area 13, the scavenging air 9 guided in the outermost space between the pipes 2 and 4 is guided into the middle gap 8 between the middle pipe 4 and the inner oil pipe 3. This mutual deflection takes place in segments (with respect to the cross section perpendicular to the axis of symmetry 18 of the fuel lance), three segments for the gas guide and three segments for the scavenging air guide, the segments typically having the same cross section.

The guide of the scavenging air 9 shown in FIG. 2 in the outermost interspace up to the region of the lance tip 1 has the advantage that the lance thereby has good cooling through this purging air channel. Thus, this lance is particularly suitable when it comes to burners, which have a certain risk of kickback.

3 shows another exemplary embodiment of a fuel lance for pilot operation, in which the intersection 19, 20 of the two channels of purging air and pilot gas does not take place at the lance tip 1 but already at the lance base 17. In other words, at the lance base 17, the introduced scavenging air 9 is guided into the space between the middle tube 4 and the oil pipe 3, and accordingly the pilot gas inlet 15 is already guided at the lance base 17 into the space between the middle pipe 4 and the outermost pipe 2. Again, this happens segmentally, that is, the inlet 14 of the scavenging air 9 takes place through slots or holes in three segments while in another three segments, the pilot gas is fed into the outermost channel. Again, it proves to be advantageous to provide holes for the inlet 14 of the scavenging air 9 to prevent the entry of dirt particles.

The embodiment according to FIG. 3 has the advantage that as a result of the larger diameter of the fuel lance at its lance base 17, larger flow cross sections for the pilot gas and the purging air are made possible than when the intersection takes place at the lance tip. Accordingly, in such a fuel lance, higher flows of purge air 9 and pilot gas 11 can be realized.

LIST OF REFERENCE NUMBERS

1

spearhead

2

extreme lance tube

3

oil pipe

4

middle tube

5

oil guide

6

Oil, liquid fuel

7

central use

8th

Zwischenraüm

9

purge air

10

Pilot gas guide

11

Pilot gas, gaseous fuel.

12

Area of the pilot gas guide 10

13

Area of the scavenging air duct

14

Entry of scavenging air 9 into the scavenging air duct (gap 8)

15

Pilot gas inlet

16

oil input

17

lance base

18

Symmetry axis of the lance

19

Crossing the pilot gas duct 10

20

Crossing the scavenging air duct

Claims (6)

1. Method for injecting a fuel/air mixture into a combustion chamber,

   - wherein alternately or simultaneously a liquid and a gaseous fuel (6, 11) and purge air (9) are injected into the combustion chamber by means of a fuel lance which has a lance tip (1) and two passages for fuels (6, 11) as well as a passage for the purge air (9),

   - wherein the liquid fuel (6) is routed to the lance tip (1) via a central, inner tube (3) having the smallest diameter, this inner tube (3) being surrounded by two further tubes (2, 4), which are arranged concentrically with respect to the inner tube, and

   - wherein the purge air (9) flows within the cavity between the central, inner tube (3) and the middle tube (4) and, at the injection location, is routed in a substantially axial and encircling manner, in the sense of a hollow cylinder, between the liquid and gaseous fuel (6, 11), so that the latter are shielded from one another by the purge air (9),

   characterized in that

   - at the injection location the liquid fuel (6) is injected, in a manner directed radially outward and onto the flow of the purge air (9), in the form of a hollow truncated circular cone which runs all the way around and opens out toward the lance tip (1), and

   - at the injection location the gaseous fuel (11) is injected in a manner directed radially inward and onto the flow of the purge air (9).
2. Method according to Claim 1, characterized in that the liquid and gaseous fuels (6, 11), at the lance base (17), are routed in the inner tube (3) and in the cavity between the inner tube (3) and the middle tube (4), respectively, and the purge air (9) is routed in the cavity between the middle tube (4) and the outer tube (2).
3. Method according to Claim 2, characterized in that directly at the lance base (17) the purge air (9) is diverted into the cavity between the inner tube (3) and the middle tube (4), whereas the gaseous fuel (6) is passed into the cavity between the middle tube (4) and the outer tube (2), with the introduction of the purge air (9) into the middle cavity particularly preferably being performed through bores or slots arranged in corresponding radial segments.
4. Method according to Claim 2, characterized in that the purge air (9) is routed to the lance tip (1) in the cavity between the middle tube (4) and the outer tube (2), and in the region of the lance tip (1) the purge air (9) is diverted into the middle cavity between the inner tube (3) and the middle tube (4), whereas the gaseous fuel (11) is routed into the outer cavity (10) between the middle tube (4) and the outer tube (2).
5. Method according to one of the preceding claims, characterized in that the fuel lance is arranged on the axis of a premix burner and the method is used for pilot operation of a premix burner, in particular of a double-cone burner with or without downstream mixing section.
6. Method according to Claim 5, characterized in that the length of the fuel lance is substantially 3/4 of the total length of the double-cone burner and the fuel lance is used for pilot operation of the premix burner.

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