EP2260238B1 - Method of operating a premix burner - Google Patents

Description

Technical area

The present invention relates to the field of combustion technology. It relates to a method for operating a premix burner according to the preamble of claim 1.

State of the art

For a long time burner arrangements are known from the prior art, according to Fig. 1 along a burner axis 15 comprise a premix burner 11 producing an air / fuel mixture 12 in the form of a double-cone burner and a subsequent mixing tube 13 opening into a combustion chamber 14 ( EP-A2-0 704 657 . EP-A1-0 913 630 . US-A-6,045,351 . WO-A1-2006 / 069861 DE-A1-4417538 . EP-A2-0694740 . EP-A2-1207350 ). These known burner arrangements 10, designated as AEV burners, are designed for the combustion of natural gas and / or oil, but are not suitable for the combustion of highly reactive fuels, in particular fuels with a high hydrogen content, because it leads to a reignition (Flashback) can come from the combustion chamber in the interior of the premix burner. Therefore, modifications have already been proposed in which all of the H 2 -rich fuel is injected through holes in the shells of the premix burner 11. This makes it possible to burn high concentrations of hydrogen. On the other hand, however, a high degree of dilution is necessary for this. In addition, a rebound occurred when the air temperature rose to over 460 ° C, which precludes the safe combustion of H2-rich fuels in gas turbines, which relates to each gas turbine, the gas turbine with a combustion chamber or equipped with sequential combustion. But it is also an axially stepped injection of the fuel conceivable, wherein a portion of the fuel injected over the Vormischbrenner forming part body and the rest is injected into the mixing tube.

It has also been proposed to inject H 2 -rich fuels between the swirl generator and the mixing tube in a transition section which serves to transfer an upstream flow. Recent research has shown that safety can be increased if most of the fuel downstream of this transitional section, i. is injected over within the mixing tube. The experimental data and subsequent considerations for designing the burner assembly indicate that very high fuel injection rates are necessary to ensure that the fuel does not adhere to or diffuse on the walls of the mixing tube. The introduction in particular of a highly reactive fuel in the immediate vicinity of the inner walls of the mixing tube must be avoided in any case, especially when it comes to fuels with a high proportion of H2, because otherwise the flashback is almost favored.

• Eine Erhöhung der Brennergeschwindigkeit stromaufwärts der zentralen Rückströmzone am Brennerausgang, um die Wahrscheinlichkeit eines Flammenrückschlags zu verringern.
• Eine Verringerung der Stärke der zentralen Rückströmzone am Brennerausgang, um die Wahrscheinlichkeit eines Rückschlags der Flamme zu verringern.
• Eine Verschiebung der zentralen Rückströmzone weiter stromabwärts, um die Wahrscheinlichkeit eines Rückschlags der Flamme zu verringern.
• Eine Verhinderung der Ausbreitung von Stosswellen, die von Druck- und Massen-Störungen bei der Einbringung der Verbrennungsluft und/oder der Brennstoffe in den Vormischbrenner herrühren, und so die Wahrscheinlichkeit eines Rückschlages der Flamme verringern.

Internal investigations suggest that the mixing tube of a premix burner can be converted from a cylindrical shape to a conically tapered configuration to achieve:

• An increase in burner speed upstream of the central return flow zone at the burner outlet to reduce the likelihood of flashback.
• Reducing the strength of the central backflow zone at the burner outlet to reduce the likelihood of flashback.
• Shifting the central backflow zone farther downstream to reduce the likelihood of flashback.
• Preventing the propagation of shock waves resulting from pressure and mass disturbances in the introduction of combustion air and / or fuels into the premix burner, thus reducing the likelihood of flashback.

These measures are particularly suitable for operation with a conventional gaseous fuel. Concerning H2-rich fuels, on the other hand, there is a concern that, in the event of ignition starting upstream of the nozzle throat, the flame front would be firmly anchored within the premix burner, with the combustion air flow then no longer being able to rapidly displace this flame front downstream of the premix burner

It is in a different context from the WO-A1-2004 / 071637 has become known, for mixing two media, in particular air and a fuel to use a mixing device having in the flow direction successively a converging section, a constriction and a diverging section, wherein upstream of the converging section, a vortex generator is arranged and the second medium (fuel ) is injected in the converging section itself or in front of it.

Presentation of the invention

It is an object of the invention to provide a burner assembly which allows a safe lean premix operation with highly reactive, in particular H2-containing fuels.

The object is solved by the entirety of the features of claim 1. Essential for the invention is a mixing tube which has a constriction, wherein at the height of the constriction means are provided for the injection of highly reactive, in particular H2-rich fuel. Starting from the o.g. conical shape of the mixing tube, in which the constriction is located at the exit of the tube, the constriction (as constriction) can be moved upstream. The highly reactive fuel is then injected directly at the bottleneck.

An embodiment of the invention is characterized in that the mixing tube tapers conically in a first mixing pipe section from the swirl generator to constriction, and that the mixing tube in a second mixing pipe section from the constriction to the combustion chamber in diameter significantly smaller than at the output of the swirl generator Case is ..

The second mixing pipe section, starting at the constriction can have a constant diameter up to the combustion chamber. The second mixing pipe section can also be slightly conical up to the combustion chamber.

It has proved to be favorable for the safe combustion, when the constriction is arranged in a central region of the mixing tube.

According to another embodiment, the means for injecting highly reactive, in particular H2-rich, fuel in the region of the constriction comprise nozzles which take over a fuel feed.

As far as the design of the premix burner is concerned, it is readily possible to provide it without a transition section between the swirl generator and the mixing tube. Such a premix burner goes out EP-A1-0 321 809 out. A further embodiment of the premix burner provides, in a transition region between the swirl generator and the mixing tube, transition channels for transferring a swirl flow formed in the swirl generator into the flow cross section of the mixing tube arranged downstream of these transition channels. Such a design goes out EP-0 704 657 A1 out.

A further embodiment of the premix burner provides to provide a cylindrical or quasi-cylindrical tube, which consists of partial shells, and in which the combustion air flow flows through tangentially arranged air inlet slots or channels in the interior. The desired swirling of the combustion air stream to maximize the desired premix with at least one fuel injected at a suitable point is achieved by a conical or quasi-conically extending in the flow direction of the inner body. mitbewerkstelligt. Such a configuration is for example EP-0 777 081 A1 out.

The inventive method is advantageously used to operate a gas turbine plant with at least one combustion chamber.

In the following embodiments of the invention will be explained in more detail with reference to the drawings. All features not essential to the immediate understanding of the invention are omitted. The same elements are provided in the various figures with the same reference numerals. The flow direction of the various media is indicated by arrows,

The embodiments are illustrative of the invention and should not be taken in a limiting sense in the interpretation of the subject matter as defined by the claims.

Brief explanation of the figures

Fig. 1

in stark schematisierter Darstellung eine an sich bekannte Brenneranordnung eines Vormischbrenners mit einem Drallerzeuger und einem nachfolgenden Mischrohr;

Fig. 2

in einer zu Fig. 1 vergleichbaren Darstellung eine Brenneranordnung gemäss einem ersten Ausführungsbeispiel der Erfindung, und

Fig. 3

in einer zu Fig. 1 vergleichbaren Darstellung eine Brenneranordnung gemäss einem zweiten Ausführungsbeispiel der Erfindung.

It shows:

Fig. 1

in a highly schematic representation of a known burner assembly of a premix burner with a swirl generator and a subsequent mixing tube;

Fig. 2

in one too Fig. 1 Comparative illustration of a burner assembly according to a first embodiment of the invention, and

Fig. 3

in one too Fig. 1 Comparative illustration of a burner assembly according to a second embodiment of the invention.

Ways to carry out the invention

• Eine Erhöhung der Brennergeschwindigkeit stromaufwärts der zentralen Rückströmzone, welche sich im Bereich des Ausgangs des Vormischbrenners, also am Anfang der Brennkammer 14, bildet, womit der Strömungsdynamik eines Flammenrückschlages in das Innere des Vormischbrenners entgegen gewirkt wird.
• Eine Verringerung der Stärke der zentralen Rückströmzone am Brennerausgang, womit der Strömungsdynamik eines Flammenrückschlages in das Innere des Vormischbrenners entgegen gewirkt wird.
• Eine Verschiebung der zentralen Rückströmzone weiter stromabwärts des Vormischbrenners, womit der Strömungsdynamik eines Flammenrückschlages in das Innere des Vormischbrenners entgegengewirkt wird.
• Massnahmen zur Verhinderung der Entstehung und Ausbreitung von Pulsationen, die von Störungen bei der Zuführung der Verbrennungsluft und/oder Eindüsung des Brennstoffes entstehen, womit ebenfalls gegen einem Flammenrückschlages in das innere des Vormischbrenners entgegen gewirkt wird.

In Fig. 2 is in one too Fig. 1 comparable representation reproduced a burner assembly according to a first embodiment of the invention. The burner assembly 16 comprises a premix burner 11 whose shape is from the above-mentioned document EP-A1-0 321 809 evident. The air flowing tangentially into the interior of the premix burner 11 is enriched with a fuel, and the swirling movement forming there forms a mixture 12. A mixing tube 17 adjoins the premix burner 11 downstream, which in two (in this example approximately the same length ) Mixing pipe sections 17a and 17b is divided. Between the two mixing pipe sections 17a, 17b is a Constriction 18 formed. In the first mixing pipe section 17a from the premix burner 11 to the constriction 18, the mixing tube 17 tapers conically or quasi-conically. In the second mixing pipe section 17b from the constriction 18 to the combustion chamber 14, the mixing tube 17 is significantly smaller in diameter than at the beginning (entrance) of the first mixing pipe section 17a, wherein it has a constant or quasikonstanten diameter downstream of said constriction 18. With this configuration, all the advantages listed at the outset of a continuous conical mixing tube can be achieved, namely:

• An increase in the burner speed upstream of the central backflow zone, which forms in the region of the outlet of the premix burner, ie at the beginning of the combustion chamber 14, whereby the flow dynamics of a flashback is counteracted in the interior of the premix burner.
• A reduction in the strength of the central backflow zone at the burner outlet, which counteracts the flow dynamics of a flashback into the interior of the premix burner.
• A shift of the central backflow zone farther downstream of the premix burner, thus counteracting the flow dynamics of a flashback into the interior of the premix burner.
• Measures to prevent the formation and propagation of pulsations caused by disturbances in the supply of combustion air and / or injection of the fuel, which is also counteracted against a flashback into the interior of the premix burner.

At the same time, this configuration (the upstream shifted constriction) allows a safe (i.e., greatly reduced flashback probability) lean premix combustion of highly reactive fuels. The injection of the high-reactive fuel takes place via fuel feeds 19 and nozzles 22 directly or in the vicinity of the constriction 18 (see the arrows), where the air velocities of the combustion air are greatest.

The cylindrical mixing tube portion 17b downstream of the constriction 18 with its significantly reduced diameter is characterized by high air velocities, which prevent flashback. This section also represents at the same time the mixing section, which allows a good air / fuel mixture at the outlet of the burner assembly 17. An additional important feature of this burner assembly 17 is the utilization of the Venturi effect. The lower static pressure at the throat 18, i. at the point where the fuel is injected means that it is possible to achieve sufficient fuel injection and penetration with relatively low fuel pressures, thereby substantially reducing the use of costly fuel compression.

Due to the higher safety, a lower dilution of the fuel with N2 and / or H2O is required.

Another advantage of the invention is that the premix burner is still suitable for lean standard premix operation with natural gas and oil, provided that care is taken that the fuel does not accumulate on the walls of the converging first mixing pipe portion 17a. In other words, the burner assembly 16 according to Fig. 2 enables operation with 3 fuels ("tri-fuel operation").

But it may also be advantageous, according to Fig. 3 in a burner assembly 20 with the mixing tube 21 and the two mixing pipe sections 21 a and 21 b the rear Mixing pipe section 21 b not cylindrical, but to the combustion chamber 14 towards slightly conical or quasi-conically widening form. Such a geometry reduces the tendency of the fuel to accumulate in the immediate vicinity of the walls of the mixing section (21b), thus increasing the resistance to flashback.

It is also advantageous to reduce the pressure difference in the premix burner, in particular with regard to the high speeds along the entire length of the mixing tube

Benefits also arise when an improvement of the radial distribution of the fuel due to the divergent streamlines is sought.

The method for operating a premix burner according to the invention is particularly suitable for hot gas generation in gas turbine plants, in which fuels are burned with a high H2 content.

LIST OF REFERENCE NUMBERS

10,16,20

burner arrangement

11

Premix burner (double cone)

11 a

swirl generator

12

Air / fuel mixture (or air)

13

mixing tube

14

combustion chamber

15

Brenner

17

mixing tube

17a, b

Mixing tube section

18

constriction

19

fuel supply

21

mixing tube

21 a, b

Mixing tube section

22

jet

Claims (11)

1. Method for operating a premix burner with one or more fuels, the premix burner substantially comprising a swirl generator or being equipped with a swirl generator at the head, the premix burner having means for feeding in a fuel and means for introducing a combustion air stream at least into the swirl generator, at least one mixing pipe, which extends into a combustion chamber and has downstream of the swirl generator (11a) associated with the premix burner (11) a cross-sectional constriction (18), acting downstream of the premix burner or swirl generator, and the mouth of the mixing tube into the combustion chamber (14) being provided by an abrupt change in cross section, which forms the combustion front of the combustion chamber with a flowback zone, characterized in that means (19, 22) for spraying in a highly reactive fuel (19) are arranged in the region of this constriction (18), through which means an H₂-rich fuel is sprayed in.
2. Method according to Claim 1, characterized in that the cross section of the mixing pipe (17, 21) narrows conically in a first mixing pipe portion (17a, 21a), from the outlet of the premix burner (11) to the constriction (18).
3. Method according to Claim 2, characterized in that the mixing pipe (17, 21) is much smaller in cross section in a second mixing pipe portion (17b, 21b), from the constriction (18) to the combustion chamber (14), than the cross section at the outlet of the premix burner (11) in the first mixing pipe portion (17a, 21a).
4. Method according to Claim 3, characterized in that the second mixing pipe portion (17b) has a constant cross section.
5. Method according to Claim 3, characterized in that the cross section of the second mixing pipe portion (21b) slightly widens conically up to the combustion chamber (14).
6. Method according to one of Claims 1 to 5, characterized in that the spraying in of the highly reactive fuel in the region of the constriction (18) is performed by nozzles (22) arranged there, and in that the nozzles comprise an associated fuel feed (19).
7. Method according to one of Claims 1-6, characterized in that liquid fuel is introduced by way of a central fuel nozzle (5) and/or gaseous fuel (13) is introduced at the tangential air inlet slits of the respective swirl generator.
8. Method according to one of Claims 1-7, characterized in that transitional channels by means of which a combustion air flow formed in the swirl generator is transferred into the flow cross section of the mixing pipe (13, 17, 21) arranged downstream of the transitional channels are provided in a transitional region between the swirl generator (11a) and the mixing pipe (13, 17, 21).
9. Method according to one of Claims 1 to 8 for operation in a gas turbine installation that can be operated with at least one combustion chamber.
10. Method according to one of Claims 1-8 for operation in a sequentially fired gas turbine installation.
11. Method according to one of Claims 1-8 for operation in a combined installation.

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