EP1601913A1

EP1601913A1 - Premixing burner

Info

Publication number: EP1601913A1
Application number: EP04716606A
Authority: EP
Inventors: Valter Bellucci; Francois Meili; Christian Oliver Paschereit; Bruno Schuermans
Original assignee: Alstom Technology AG
Current assignee: General Electric Technology GmbH
Priority date: 2003-03-07
Filing date: 2004-03-03
Publication date: 2005-12-07
Also published as: US20060101825A1; US7424804B2; WO2004079264A1

Abstract

The invention relates to a premixing burner comprising a swirl generator (4) and characterised in that two perforated flow elements (10, 11) disposed at a defined clearance with respect to each other are arranged in a combustion air admission area (3). The flow elements are preferably disposed in such a way that the main part of the combustion airflow passes therethrough. In the preferred embodiment, the degree of perforation of the flow elements and the clearance therebetween are defined in such a way that it is possible to prevent a reflection of possible combustion frequencies at the burner (1) output towards the combustion chamber (7).

Description

premix

Technical application area

The present invention relates to a premix burner according to the preamble of claim 1.

State of the art

So-called lean premix burners are predominantly used in modern gas turbine technology. The most varied types of lean premix burners are, for example, from US Pat. No. 4,781,030

EP 321 809, EP 780 629, WO 93/17279, EP 945 677 or WO 00/12936 are known. These burners essentially work on the principle of introducing fuel into a highly swirled air stream, in which it forms a homogeneous mixture with the combustion air. The ignition and flame stabilization take place by the swirl flow bursting at the burner outlet, ie at the burner mouth to the combustion chamber. These burners are preferably operated with a sub-stoichiometric fuel-air ratio, typically with air ratios around 2. The formation of stochiometric zones with hot spots in the flame, in which a high nitrogen oxide production takes place, is avoided in this way, and the good premixing usually also leads to a good burnout achieved. These premix burners are often designed for operation in the area of the lean extinguishing limit, which limits the operating range. For operation with below the amount of fuel required for stable premix operation So-called pilot stages or pilot burners are therefore used, via which additional fuel is introduced into the combustion chamber in certain operating areas.

Under certain unfavorable circumstances, all known premix burners may have a tendency to form thermoacoustic vibrations in the combustion chamber. These undesirable vibrations can be reduced on the one hand by appropriate control of the fuel supply and the fuel distribution, and on the other hand by steaming measures within the combustion chamber. For example, US Pat. No. 5,685,157 discloses an acoustic steamer for a combustion chamber, which is formed by a plurality of resonance tubes which are connected to the combustion chamber via a perforated plate. These resonance tubes serve as Helmholtz resonators, which, depending on the size of the resonance volume, dampen individual thermoacoustic vibrations. US 5,431,018 also shows the use of

Helmholtz resonators on a combustion chamber. In this document, an annular air duct for the supply of cooling and combustion air into the combustion chamber is formed around the supply line for fuel to a combustion chamber and is connected to a resonator volume. An arrangement for damping acoustic vibrations in a combustion chamber is known from US Pat. No. 6,164,058, in which the cooling ducts formed on the combustion chamber wall are adjusted in length in such a way that they enter the cooling air at the inlet

Burners have a minimal acoustic impedance. Part of this cooling air is then mixed with the fuel in the burner and reaches the burner outlet the combustion chamber for combustion. Helmholtz resonators can achieve very high attenuations, but only in a very narrow frequency range to which the resonance volume is matched. They are especially for steaming individuals

Vibrations in the low frequency range are suitable, in which the frequency spacing between the unwanted vibrations is relatively large. In modern gas turbine plants that work with premix burners, however, high-frequency and closely adjacent vibrations can also occur in a broad frequency range due to so-called combustion chamber pulsations, which endanger the quality of the combustion process and also the structural integrity of the plants. Helmholtz resonators are hardly suitable for damping such broadband vibrations.

Presentation of the invention

The object of the present invention is therefore to provide a premix burner of the type mentioned at the outset in such a way that the disadvantages of the prior art are avoided. According to one aspect of the invention, the premix burner should be specified in such a way that the burner at the same time enables acoustic combustion chamber pulsations to be damped during operation.

The problem is solved with the premix burner according to claim 1. Advantageous refinements of the subject matter of the invention are the subject of the subclaims or result from the following description and the exemplary embodiments. The essence of the invention, therefore, is to arrange a first perforated throughflow element in the inflow area for the combustion air, and a second throughflow element with a well-defined distance, in a premix burner, which is particularly suitable for a gas turbine system and which comprises a swirl generator for a combustion air stream flowing to the burner to be arranged upstream of the first flow element from the first flow element. The objectives according to the invention are most efficiently achieved if the flow-through elements are arranged in such a way that essentially the entire combustion air flow must flow through the flow-through elements. In a preferred embodiment of the invention, the burner is designed such that the first flow element is a hollow cylinder and the second flow element is a hollow cylinder surrounding the first flow element. These two hollow cylinders are preferably arranged coaxially. In a further development of this embodiment, the swirl generator is arranged within the first hollow cylinder. The end faces of the burner are then most advantageously designed and closed such that between the

Swirl generator and the flow-through elements no combustion air or only an insignificant mass flow can flow.

In one embodiment of the invention, the swirl generator comprises a plurality, in particular two or four, of partial bodies, which in a preferred embodiment essentially have the shape of Have truncated cone sections, and between which side inlet slots are formed for the supply of combustion air. In a preferred embodiment, the longitudinal axes of the individual partial bodies are laterally offset from one another.

Due to the design with two flow elements through which flow flows in series, the unwanted change in the pressure drop for a given mass flow can be changed by changing the

Perforation levels to adjust acoustic damping can be avoided. This means that the degree of perforation of one of the flow elements can be changed and adapted to special requirements without the pressure drop or

To change the total pressure loss coefficient. The second throughflow element arranged upstream can be designed to match the desired acoustic damping with a suitable degree of perforation in order to achieve maximum acoustic damping in a specific one

Frequency range. The pressure drop is set by the first flow element.

A damping of these acoustic vibrations can be achieved by a suitable design of the flow-through elements depending on the combustion chamber pulsations that occur or are to be avoided during operation of a combustion chamber with the premix burner. The perforated flow-through elements act as an acoustically steaming wall in the plane of the burner outlet, whereby in the plane of the burner outlet taking into account the combustion air speed occurring during operation. the reflection-free condition for sound impedance is fulfilled.

The flow elements are preferably matched to one another by changes in the degree of perforation, the thickness and also their spacing from one another such that at least when the burner is operated as intended, the first flow element arranged downstream reflects the acoustic vibrations at least approximately completely; the second flow-through element is designed such that it effects maximum damping of the acoustic vibrations. The reflection free condition for that

Sound impedance can in particular be met in that the distance of the first flow-through element from the second flow-through element, the degree of perforation of the flow-through elements, and the extent of the flow-through elements in the flow-through direction are coordinated with one another in such a way that the complex sound impedance is characteristic of the

Pulsation frequencies of the burner at least approximately corresponds to the product of the density of the combustion air and the speed of sound in the combustion air.

To meet the reflection-free condition of the complex acoustic impedance, the distance of the first flow-through element from the second is preferred

Flow-through element, the degree of perforation of the first flow-through element, and the extent of the first flow-through element in the flow-through direction in such a way coordinated so that the imaginary part of the complex sound impedance essentially becomes 0.

Furthermore, the first flow element arranged downstream is advantageously designed such that the ratio of the degree of perforation to the pressure loss coefficient of the first flow element corresponds at least approximately to the Mach number of the combustion air flowing through.

The degree of perforation is defined here as the ratio of the free flow cross-section to the total cross-section of a perforated element. The inventive design of a

Premix burner, some of the combustion chamber pressure fluctuations are absorbed and thus steamed. The perforated flow elements act as an acoustic damping element. By supplying the combustion air for the swirl generator via the perforated flow-through elements, a constant flow is maintained which, at a sufficient speed, causes a significant increase in the steaming effect compared to steaming elements which do not have such a flow.

When designing the perforated flow-through elements, the reflection-free condition for the sound impedance Z = R + iX = p * c in the plane of the burner outlet is preferably at least approximately met. The real part R of the complex sound impedance Z is referred to as resistance, the imaginary part X as reactance. Geometry also plays a role here of the burner between the housing wall and the burner outlet level. Maintaining a flow of combustion air through the perforated section during operation of the combustion chamber results in different conditions than without such a gas flow. Without a gas flow, the resistance would be non-linear due to the dependence on the convection and dissipation of the acoustically generated vortices, so that it would be very difficult to adjust. In the present case, the constant leads

Flow of the combustion air through the perforation openings, however, makes a linear contribution to the resistance R due to the convection of the vortices caused by this flow. This linear effect outweighs the non-linear effect if the flow rate is greater than the acoustic speed in the perforation holes. In this case the resistance R is described by the following equation: ζ * U / σ (1) where ζ the pressure loss coefficient of the holes, U the flow rate of the combustion air and σ the perforation degree of the perforation, i.e. describe the proportion of the area of the hole cross sections to the total area of the wall. Therefore, for an optimal damping condition (R = p * c) the value

M = σ / ζ (2), where M = U / c is the Mach number of the flow of the combustion air.

In order to maintain the reflection-free condition, it is also necessary that the imaginary part of the sound impedance, the so-called reactance X, is approximately 0. The distance from the first to the second

Flow-through element is used to adjust the reactance X with respect to the frequencies to be steamed. The downstream element serves as a fully reflective wall (without damping) for the acoustic pressure vibrations. This is made possible by the fact that the pressure drop between the first and the second flow elements is split, so that the acoustic areas upstream and downstream of the flow elements are acoustically decoupled from one another. By choosing suitable values for the hole diameter, hole length or wall thickness, as well as the distance of the

The reactance X can be made approximately zero with respect to the frequency to be steamed through flow elements.

From this representation, the person skilled in the art, who is familiar with the field of acoustic vibrations and the equations on which they are based, receives clear teaching on how the flow elements are to be designed and coordinated, and at what distance they are to be arranged in order to provide the best possible damping to achieve expected combustion pulsations.

In a preferred embodiment of the invention, the flow-through elements consist of solid, non-porous components into which are known per se Wise openings, perforations for which combustion air is introduced. In particular, an embodiment is preferred in which the perforation is introduced into the flow-through elements by machining, for example by drilling. For example, a sheet metal blank of suitable thickness is brought into the desired shape by bending or pressing, and the flow openings are introduced into the blanks by a subsequent manufacturing process, in particular by drilling. A perforated sheet can also be used from the start. In another embodiment, a blank is brought into a suitable basic shape by a primary molding process, for example casting or sintering, and the perforation openings are then introduced. Through-flow openings can also be formed during primary shaping. In any case, however, there is the possibility or the need to fine-tune the throughflow opening by machining in order to achieve the required acoustic damping and / or reflection properties. However, the base material of the flow-through elements is very particularly preferably solid, that is to say there are no porosities in the base material. In principle, the use of, for example, sintered porous basic structures, such as metal felts, is also possible; Although this possibility is included in the scope of the invention, this embodiment is not considered to be particularly advantageous since the coordination of the

Perforation openings on the desired properties described above made very difficult. The burner according to the invention can have a geometric shape and a structure, as is known from known premix burners of the prior art. A type of burner is preferred in which the swirl body is composed of several conical section-shaped partial shells, between which time entry slots are formed for the combustion air. Such a burner is known, for example, from US 4,932,861.

The burner according to the invention is suitable for use in combustion devices, and in particular for use in combustion chambers of gas turbine groups.

Brief description of the drawings

The invention is explained briefly below using an exemplary embodiment in conjunction with the drawings. Here show:

Fig. La shows an example of the size of the reflection coefficient r of a plate with a degree of perforation of 2.5% without a fixed flow through the individual perforation holes;

Fig. Lb the phase φ of the acoustic

Reflection coefficient of a plate according to FIG la; Fig. 2a the size of the acoustic

Reflection coefficient r for a plate with a degree of perforation of 2.5%, which maintains a constant flow of 8m / s through the perforation holes;

Fig. 2b, the phase φ of the acoustic

Reflection coefficients in a plate according to FIG. 2a;

3 shows a combustion chamber which comprises a burner according to the invention.

Ways of Carrying Out the Invention

In the following, exemplary embodiments of the present invention as well as those achieved with them are described

Effects explained. Features that are essential for the invention are shown in the drawing. The high and low pressure turbines downstream of the combustion chamber, which are also present when the combustion chamber is used in a gas turbine system, and the upstream compressor stage are not shown, for example.

Figures 1 and 2 show a comparison of the effect of a perforated plate as used as the perforated section of the present burner, with and without the constant flow of combustion air according to the present invention. The solid lines in FIGS. 1 and 2 show the values calculated according to a numerical model, the rectangular boxes measured values. The calculations and measurements were carried out with a perforated plate with a perforation degree of 2.5%. The reflection coefficient r is calculated from r = (Z + p * c) / (Z - p * c). The maximum absorption results here for the resonance frequency, which is characterized in the representation of the phase of the reflection coefficient by the phase jump. The figures show the good agreement of the calculated with the measured values, so that the model used is very well suited for the dimensioning of such perforated sections.

FIG. 2 shows the conditions as prevailing in the present combustion chamber, in which a constant flow of combustion air is maintained through the perforated sections. This flow enables better adjustment of the

Resonance frequency of the damping and, on the other hand, leads to greater damping over a wider frequency range, as can be clearly seen by comparing FIGS. 1a and 2a. With the present burner with the perforated sections in the housing wall, through which the swirl generator is supplied with the combustion air, improved acoustic damping can thus be achieved.

FIG. 3 shows a combustion chamber 7 with a burner 1 according to the invention. The burner 1 comprises a swirl generator 4 which has a conical interior for generating a swirl flow of the combustion air 3 entering from the side. This swirl flow mixes the fuel gas supplied via the feed 2 with the

Combustion air. In this way, a swirl-stabilized is formed at the burner outlet into the combustion chamber 7 Flame 6 with reverse flow in the core. The swirl generator 4 is arranged within two essentially coaxial hollow cylinders 10 and 11. The hollow cylinders 10 and 11 are perforated and represent flow elements flowed through in series. The combustion air 3 flowing to the burner successively flows through the second flow element 11 and then the first flow element 10 before it flows into the swirl generator 4. In the interior of the swirl generator 4, the combustion air is mixed with a fuel supplied by the fuel feeds 2. Due to the swirl flow in the swirl generator, a well premixed fuel-air mixture 5 is created. At the outlet into the combustion chamber 7, the swirl flow bursts and a flame front 6 is formed. Occasional combustion pulsations in the combustion chamber 7 are avoided particularly efficiently if the above-described reflection-free condition is fulfilled for the respective pulsation frequencies in the plane of the burner outlet to the combustion chamber 7, that is to say at the transition from the burner 1 to the combustion chamber. As stated above, this condition can be met by appropriate adjustment of the flow elements 11 and 10. In conjunction with the combustion air mass flow or the flow rate of the combustion air, the distance between the flow elements, the degree of perforation of the first, in the present example inner flow element 10, and its thickness are matched to one another such that the conditions set out above are met. The first flow-through element 10, in the present case the inner hollow cylinder, is in terms of its Perforation and its extension in

Flow direction designed so that it acts acoustically at least approximately completely reflective. The second flow-through element, in the present case the outer hollow cylinder 11, is designed for maximum acoustic damping.

The burner according to the invention has a number of advantages. On the one hand, the arrangement of the flow elements means that

Dirt particles reduced. Furthermore, the inflow to the swirl generator is evened out. In addition, with suitable adjustment of the flow elements and their spacing from one another, combustion pulsations that occasionally occur can be effectively dampened or avoided.

It goes without saying that the premix burner according to the invention can also be realized with swirl generator geometries other than that shown in the exemplary embodiment and known, for example, from EP 0 321 809; In particular, the invention can be implemented in connection with burners and / or swirl generators of the types known from WO 93/17279, EP 0 945 677, WO 00/12936, or EP 0 780 629, this addition in no way being understood as conclusive or restrictive may be.

LIST OF REFERENCE NUMBERS

1 burner

2 Supply for fuel gas 5 3 Combustion air flow

4 swirl generators

5 swirl flow

6 flame

7 combustion chamber, combustion chamber

10 10 first downstream flow element

11 second, upstream

Flow element r reflection coefficient φ phase of the reflection coefficient

15 f frequency

Claims

claims

1. Premix burner (1), especially for one

Gas turbine plant comprising a swirl generator (4) for a combustion air flow (3) flowing to the burner, characterized in that a first perforated flow element (10) is arranged in the inflow region for the combustion air (3), and a second flow element (11) with a defined one Distance to the first flow element is arranged upstream of the first flow element.

2. premix burner according to claim 1, characterized in that the distance between the first flow-through element (10) and the second flow-through element (11), the degree of perforation of the first flow-through element (10), and the extent of the first flow-through element in the flow direction are coordinated with one another in such a way that the complex acoustic impedance Z for characteristic pulsation frequencies of the burner corresponds at least approximately to the product of the density of the combustion air and the speed of sound m of the combustion air.

3. premix burner according to one of the preceding claims, characterized in that the distance of the first flow element from the second flow element, the Degree of perforation of the first

Flow-through element, and the extent of the first flow-through element in the flow-through direction are coordinated with one another in such a way that the imaginary part of the complex sound impedance essentially becomes 0.

4. premix burner according to one of the preceding claims, characterized in that the

Flow-through elements are arranged such that essentially the entire

Combustion air flow must flow through the flow elements.

5. premix burner according to one of the preceding claims, characterized in that the first flow-through element is a hollow cylinder, and the second flow-through element is a hollow cylinder surrounding the first flow-through element.

6. premix burner according to claim 5, characterized in that the swirl generator (4) is arranged within the first hollow cylinder.

7. premix burner according to one of the preceding claims, characterized in that the swirl generator (4) is composed of several conical section-shaped partial shells and has lateral inlet slots for the supply of the combustion air.

8. firing device comprising a combustion chamber (7) and at least one premix burner (1) according to one of the preceding claims.

9. Gas turbine group, with at least one combustion chamber with at least one premix burner according to one of claims 1 to 7.