EP1182398B1 - Process for increasing the fluidic stability of a premix-burner as well as premix-burner for carrying out said process - Google Patents
Process for increasing the fluidic stability of a premix-burner as well as premix-burner for carrying out said process Download PDFInfo
- Publication number
- EP1182398B1 EP1182398B1 EP01120011A EP01120011A EP1182398B1 EP 1182398 B1 EP1182398 B1 EP 1182398B1 EP 01120011 A EP01120011 A EP 01120011A EP 01120011 A EP01120011 A EP 01120011A EP 1182398 B1 EP1182398 B1 EP 1182398B1
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- European Patent Office
- Prior art keywords
- burner
- flow
- cavity
- section
- premix
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C7/00—Combustion apparatus characterised by arrangements for air supply
- F23C7/002—Combustion apparatus characterised by arrangements for air supply the air being submitted to a rotary or spinning motion
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23D—BURNERS
- F23D11/00—Burners using a direct spraying action of liquid droplets or vaporised liquid into the combustion space
- F23D11/36—Details, e.g. burner cooling means, noise reduction means
- F23D11/40—Mixing tubes or chambers; Burner heads
- F23D11/402—Mixing chambers downstream of the nozzle
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23D—BURNERS
- F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
- F23D14/46—Details, e.g. noise reduction means
- F23D14/72—Safety devices, e.g. operative in case of failure of gas supply
- F23D14/74—Preventing flame lift-off
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23D—BURNERS
- F23D17/00—Burners for combustion conjointly or alternatively of gaseous or liquid or pulverulent fuel
- F23D17/002—Burners for combustion conjointly or alternatively of gaseous or liquid or pulverulent fuel gaseous or liquid fuel
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C2900/00—Special features of, or arrangements for combustion apparatus using fluid fuels or solid fuels suspended in air; Combustion processes therefor
- F23C2900/07002—Premix burners with air inlet slots obtained between offset curved wall surfaces, e.g. double cone burners
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23D—BURNERS
- F23D2209/00—Safety arrangements
- F23D2209/20—Flame lift-off / stability
Definitions
- the invention relates to a method for fluid mechanical stabilization of a premix burner, in which a combustion air flow is introduced tangentially into a burner interior, mixed to form a coaxially oriented swirl flow with a injected gaseous and / or liquid fuel and induces a remindströmzone at a burner outlet, which during operation of the burner serves to stabilize the flame. Furthermore, the invention relates to a premix burner for carrying out the method.
- a preferred field of application of the invention is the operation of a gas turbine plant.
- EP 0 321 809 and EP 0 780 629 disclose premix burners of the type discussed herein known. Such burners, which are characterized by very low pollutant emissions, are widely used in combustion chambers of gas turbine plants Hot gas generation used.
- thermoacoustic oscillations often occur in the combustion chambers.
- resulting fluid mechanical instability waves lead to the formation of flow vortex, which strongly influence the entire combustion process and lead to unwanted periodic heat releases within the combustion chamber, which are associated with strong pressure fluctuations.
- the high pressure fluctuations are associated with high vibration amplitudes, which can lead to undesirable effects, such as a high mechanical load of the combustion chamber, increased NO x emissions by inhomogeneous combustion and even to extinguish the flame within the combustion chamber.
- Thermoacoustic oscillations are based at least in part on flow instabilities burner flow, which manifests itself in coherent flow structures, and which influence the mixing processes between air and fuel.
- burner flow which manifests itself in coherent flow structures, and which influence the mixing processes between air and fuel.
- conventional Combustion chambers become cooling air in the manner of a cooling air film over the combustion chamber walls directed.
- the cooling air film also has a sound-absorbing effect and contributes to the reduction of thermoacoustic vibrations.
- the cooling air flow significantly reduced in the combustion chamber and almost all of the air is passed through the burner.
- this also reduces the sound-absorbing effect at the same time Cooling air film, whereby the sound-absorbing effect is reduced and reinforces the problems associated with the unwanted vibrations occur.
- thermoacoustic vibration amplitudes has the disadvantage that the injection of fuel at the head stage can be accompanied by an increase in the emission of NO x .
- thermoacoustic vibrations have shown that such unwanted coherent structures arise in mixing operations. Of particular importance here are those between two mixing Currents forming shear layers that are within the coherent structures be formed. Further details can be found in the following publications: Oster & Wygnanski 1982, "The forced mixing layer between parallel 123, 91-130; Paschereit et al., 1995, “Experimental investigation of subharmonic resonance in an axisymmetric jet ", Journal of Fluid Mechanics, Vol. 283, 365-407).
- the invention is based on the object, a method for increasing the fluid mechanical To provide stability of a premix burner, which the undesirable eddies, posing as coherent pressure fluctuation structures training, efficient and suppressed without additional energy.
- the purpose necessary measures on a premix burner should have a low constructive Create effort and be cost effective in their realization.
- the Furthermore, the measures taken should be completely maintenance-free.
- the object is achieved by a method for increasing the fluid mechanical stability of a premix burner and by a premix burner of the type mentioned in the independent claims.
- the idea of the invention advantageously further features are the subject of the dependent claims.
- the method according to the invention is based on the basic idea of fluid mechanics Stabilization of a premix burner, in which at least one Combustion air flow is introduced tangentially into a burner cavity and forming a coaxial with the burner axis oriented swirl flow with a injected gaseous and / or liquid fuel mixed and at one Cross-section jump at the burner mouth induces a backflow zone, which during operation of the burner serves to stabilize the flame, the swirl flow within of the burner cavity towards the burner mouth at least increasingly radially deforming a peripheral portion and in a non-rotationally symmetric Flow cross-section to enter the combustion chamber, this deformation being at the expense of the free flow cross-section of the burner cavity is produced.
- a premix burner according to the invention is based on a premix burner for use in a heat generator, essentially consisting of a swirl generator with means for tangentially introducing a combustion air flow in a cavity of the swirl generator and means for introducing at least a gaseous and / or liquid fuel in the combustion air stream below Formation of a swirl flow with an axial component of motion towards the Burner mouth, at which the swirl flow inducing a backflow zone bursts.
- a generic burner based on at least two hollow, in Flow direction of the hot gases nested conically widening Partial bodies whose center axes are offset from one another are described in EP 0321809 described.
- Such types of burners also known as cone burners or double-cone burners, have at their burner outlet on a spoiler edge, the edge course of consists of two mutually offset semicircles whose closed edge course However, almost circular and thus approximately rotationally symmetrical to the burner axis is trained.
- Such influence on the flow geometry can by at least a section of the cavity wall take place, which wall section in a downstream end portion of the burner cavity has a lower pitch as in an upstream area.
- This at least one section leads to it opposite those wall sections at the same axis height, this feature do not possess, to a radial deviation from the circular shape in the direction of the Brenner axis.
- FIGS. 1a and 1b show in a highly schematized form the structure and mode of action of a premix burner, as it is the starting point of the invention presented here.
- the premix burner consists of two hollow conically widening part bodies (1) and (2), which are arranged axially parallel and offset from one another such that they form tangential gaps (3) in two mirror-inverted overlapping regions.
- two conically widening partial bodies (1) and (2) are shown by way of example in FIGS. 1a and 1b, other configurations are also conceivable. Thus, these burners are not limited to the arrangement of two partial bodies (1) and (2), nor is their conical configuration absolutely necessary. This is familiar to the expert.
- the resulting from the displacement of the longitudinal axes column (3) serve as inlet channels through which the burner air combustion air (5) flows tangentially into the burner cavity (6).
- injection openings (7) there are injection openings (7), through which a preferably gaseous fuel is injected into the passing combustion air (5).
- the fuel injection preferably takes place within the gap (3) immediately before entry into the burner cavity (6).
- a central nozzle (8) is provided for atomizing a liquid fuel whose capacity and mode of operation are governed by the burner parameters.
- the premix burner On the combustion chamber side, the premix burner has a front plate (10) which acts as an anchorage of the part bodies (1) and (2) and has a number of bores (11) for introducing air into the combustion chamber (12).
- the fuel / air mixture passing through the burner cavity (6) in a swirl flow (9) reaches the optimum fuel concentration across the cross section at the downstream end of the premix line (13) at the burner mouth (14).
- the swirl flow (9) bursts to form a backflow zone (15) with an effect stabilizing against the flame front (17) acting there.
- This aerodynamic flame stabilization acts as a kind of flame holder.
- the dreaded failure of mechanical flame holders due to overheating with possible subsequent serious damage to machine sets is thus excluded.
- the flame loses no heat except on cold walls due to radiation. This also contributes to the uniformity of the flame temperature and thus to low pollutant emissions and good combustion stability.
- measures are now provided to increasingly radially deform the swirl flow (9) within the premix section (13).
- this deformation should be symmetrical. This is not mandatory. It is an essential feature to achieve this deformation at the expense of the free flow cross-section (18).
- the wall (21) of the cavity (6) has, in a downstream region (20), at least one section (22) which has a smaller pitch relative to an upstream region (19) relative to the burner axis (4).
- the approximately circular contour (21) of the burner cavity (6) viewed over the cross section, has a deviation from the circumference of the cavity contour (21) in the direction of the central axis (4), ie the cavity (6) constricts Sections (22), as shown in Fig 2a-2d in longitudinal section schematically reproduced. It has proven to be advantageous in this context, to accompany the deformation of the flow simultaneously with an acceleration of the flow. This measure has a particularly favorable effect on the stability of the burner.
- the cross-sectional shape deviating from the rotational symmetry of the flow (9) emerging from the burner has a disruptive effect on the formation of coherent vortex structures and thus ultimately inhibits the formation of thermoacoustic oscillations.
- FIGS. 2a-2d are intended to explain the concept of the invention on the basis of highly schematic representations.
- FIGS. 2b-2d symbolize the concept of the invention, which for the purpose of deforming the airfoil, the wall (21) of the burner cavity (6) in at least one peripheral portion (22) at the expense of the free flow cross-section (18) in the direction of the burner axis (4) to angle. This can be done symmetrically or asymmetrically by at least one of the flow cross-section constricting portion (22).
- FIGS. 3 to 7 show embodiments of burners designed according to the invention.
- FIG 3 shows a preferred variant of the invention, according to which the burner mouth (14) has a polygonal outlet contour (16).
- the conically widening contour (23) of the burner cavity (6) is broken off in a downstream end region (20) and has a smaller pitch than the preceding region (19) in relation to FIG Longitudinal axis (4) continued.
- the term reduced slope should also include a profile parallel to the longitudinal axis (4) or a convergent profile, as shown in FIGS. To realize this suggestion, a variety of measures are available to the person skilled in the art.
- the circle segments from the free flow cross-section (18) of the burner cavity (6) cut out For each partial body (1) or (2), preferably one to four such plates (28) are welded onto the inner wall (21).
- the burner is formed in an upstream region (19) in a manner known per se from two interleaved partial bodies (1) and (2) of substantially circular cross-section.
- a convex course is particularly advantageous in the case of the arrangement of a small number or only one or two such sections (22).
- Another embodiment is not to provide the burner cavity (6) in its upstream region (19) with a circular cross-section, but to equip the burner with a continuous non-rotationally symmetric contoured cavity (6).
- This embodiment is particularly suitable for polygonal contours (23) of the cavity cross section (18).
- FIGS. 5 and 6 show a premix burner, consisting of a swirl generator (13) for a combustion air stream (5) and means for injecting at least one fuel (7) and / or (8), wherein downstream of the swirl generator (13) has a mixing section (25) is arranged.
- the mixing section (25) bounding housing (26) can be arranged in an even circumferential distribution pointed to the longitudinal axis (4) extending inlet openings (27) for injecting an additional amount of combustion air.
- the exit port (16) occupies a polygonal cross-sectional shape composed of a plurality of rectilinear portions (22). Promising exit contours (16) in the form of a regular or irregular polygon ( Figure 5).
- the individual rectilinear sections (22) of the outlet edge (27) span the outlet opening (16) of the burner.
- FIG. 7 shows a variant embodiment with a cylindrical or convergent nozzle section (24) at the downstream burner end.
- these downstream nozzles (24) serve primarily to accelerate the flow at the burner outlet and thus stabilize the return flow zone (15).
- this desirable acceleration is achieved by increasing and decreasing the cross-sectional area such that this nozzle portion (24) is narrowed in the direction of flow from a substantially circular cross-sectional shape to another cross-sectional shape, such as a regular or irregular polygon or one oval.
- FIG. 8 shows a diagram showing the combustion power along the abscissa of the burner according to FIG. 3 and along the ordinate a scaling that allows the formation of thermoacoustic vibrations as Result in coherent structures within the flow stream in the burner, quantified.
- thermoacoustic vibrations in the 100 Hz range. Comparing a burner with conventional burner outlet according to the embodiment in Figure 1 (see polyline with squares interspersed) with an inventive trained burner outlet according to embodiment in Figure 3 (see figure interspersed with circles), it is clear that in the latter case a considerable lower proportion of thermoacoustic vibrations arises.
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- Engineering & Computer Science (AREA)
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- Combustion & Propulsion (AREA)
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- General Engineering & Computer Science (AREA)
- Gas Burners (AREA)
Description
Die Erfindung bezieht sich auf ein Verfahren zur strömungsmechanischen Stabilisierung
eines Vormischbrenners, in den ein Verbrennungsluftstrom tangential in einen
Brennerinnenraum eingeleitet wird, sich unter Ausbildung einer koaxial orientierten
Drallströmung mit einem eingedüsten gasförmigen und/oder flüssigen Brennstoff
vermischt und an einem Brenneraustritt eine Rückströmzone induziert, welche im
Betrieb des Brenners zur Stabilisierung der Flamme dient. Des weiteren bezieht sich
die Erfindung auf einen Vormischbrenner zur Durchführung des Verfahrens.
Ein bevorzugtes Anwendungsgebiet der Erfindung ist der Betrieb einer Gasturbinenanlage.The invention relates to a method for fluid mechanical stabilization of a premix burner, in which a combustion air flow is introduced tangentially into a burner interior, mixed to form a coaxially oriented swirl flow with a injected gaseous and / or liquid fuel and induces a Rückströmzone at a burner outlet, which during operation of the burner serves to stabilize the flame. Furthermore, the invention relates to a premix burner for carrying out the method.
A preferred field of application of the invention is the operation of a gas turbine plant.
Aus EP 0 321 809 und EP 0 780 629 sind Vormischbrenner der hier diskutierten Art
bekannt. Derartige Brenner, die sich durch sehr niedrige Schadstoffemissionen auszeichnen,
werden weit verbreitet in Brennkammern von Gasturbinenanlagen zur
Heissgaserzeugung eingesetzt.
Beim Betrieb von Gasturbinenanlagen treten in den Brennkammern häufig thermoakustische Schwingungen auf. Am Brenner entstehende strömungsmechanische Instabilitätswellen führen zur Ausbildung von Strömungswirbeln, die den gesamten Verbrennungsvorgang stark beeinflussen und zu unerwünschten periodischen Wärmefreisetzungen innerhalb der Brennkammer führen, die mit starken Druckschwankungen verbunden sind. Mit den hohen Druckschwankungen sind hohe Schwingungsamplituden verknüpft, die zu unerwünschten Effekten, wie etwa zu einer hohen mechanischen Belastung des Brennkammergehäuses, einer erhöhten NOx-Emission durch eine inhomogene Verbrennung und sogar zu einem Erlöschen der Flamme innerhalb der Brennkammer führen können.When operating gas turbine plants, thermoacoustic oscillations often occur in the combustion chambers. At the burner resulting fluid mechanical instability waves lead to the formation of flow vortex, which strongly influence the entire combustion process and lead to unwanted periodic heat releases within the combustion chamber, which are associated with strong pressure fluctuations. The high pressure fluctuations are associated with high vibration amplitudes, which can lead to undesirable effects, such as a high mechanical load of the combustion chamber, increased NO x emissions by inhomogeneous combustion and even to extinguish the flame within the combustion chamber.
Thermoakustische Schwingungen beruhen zumindest teilweise auf Strömungsinstabilitäten der Brennerströmung, die sich in kohärenten Strömungsstrukturen äußern, und die die Mischungsvorgänge zwischen Luft und Brennstoff beeinflussen. Bei herkömmlichen Brennkammern wird Kühlluft in Art eines Kühlluftfilms über die Brennkammerwände geleitet. Neben dem Kühleffekt wirkt der Kühlluftfilm auch schalldämpfend und trägt zur Verminderung von thermoakustischen Schwingungen bei. In modernen Gasturbinenbrennkammern mit hohen Wirkungsgraden, niedrigen Emissionen und einer konstanten Temperaturverteilung am Turbineneintritt ist der Kühlluftstrom in die Brennkammer deutlich reduziert, und nahezu die gesamte Luft wird durch den Brenner geleitet. Jedoch reduziert sich damit zugleich auch der schalldämpfende Kühlluftfilm, wodurch die schalldämpfende Wirkung herabgesetzt wird und die mit den unerwünschten Schwingungen verbundenen Probleme wieder verstärkt auftreten.Thermoacoustic oscillations are based at least in part on flow instabilities burner flow, which manifests itself in coherent flow structures, and which influence the mixing processes between air and fuel. In conventional Combustion chambers become cooling air in the manner of a cooling air film over the combustion chamber walls directed. In addition to the cooling effect, the cooling air film also has a sound-absorbing effect and contributes to the reduction of thermoacoustic vibrations. In modern gas turbine combustion chambers with high efficiencies, low emissions and a constant temperature distribution at the turbine inlet is the cooling air flow significantly reduced in the combustion chamber, and almost all of the air is passed through the burner. However, this also reduces the sound-absorbing effect at the same time Cooling air film, whereby the sound-absorbing effect is reduced and reinforces the problems associated with the unwanted vibrations occur.
Eine Möglichkeit der Schalldämpfung besteht im Ankoppeln so genannter Helmholtz-Dämpfer im Bereich der Brennkammer oder der Kühlluftzufuhr. Jedoch ist bei modernen Brennkammerkonstruktionen das Vorsehen derartiger Helmholtz-Dämpfer aufgrund enger Platzverhältnisse mit großen Schwierigkeiten verbunden.One possibility of soundproofing is the coupling of so-called Helmholtz dampers in the area of the combustion chamber or the cooling air supply. However, in modern day Combustor designs the provision of such Helmholtz damper due to tight space conditions associated with great difficulties.
Daneben ist bekannt, dass den im Brenner auftretenden strömungsmechanischen Instabilitäten und den damit verbundenen Druckschwankungen dadurch entgegengetreten werden kann, indem die Brennstoffflamme durch zusätzliche Eindüsung von Brennstoff stabilisiert werden kann. Eine derartige Eindüsung von zusätzlichem Brennstoff erfolgt über die Kopfstufe des Brenners, in der eine auf der Brennerachse liegende Düse für die Pilot-Brennstoffgaszuführung vorgesehen ist, was jedoch zu einer Anfettung der zentralen Flammstabilisierungszone führt. Diese Methode der Verminderung von thermoakustischen Schwingungsamplituden ist jedoch mit dem Nachteil verbunden, dass die Eindüsung von Brennstoff an der Kopfstufe mit einer Erhöhung der Emission von NOx einhergehen kann.In addition, it is known that the fluid mechanical instabilities occurring in the burner and the associated pressure fluctuations can be counteracted by the fuel flame can be stabilized by additional injection of fuel. Such injection of additional fuel takes place via the head of the burner, in which a nozzle for the pilot fuel gas supply lying on the burner axis is provided, which, however, leads to an enrichment of the central flame stabilization zone. However, this method of reducing thermoacoustic vibration amplitudes has the disadvantage that the injection of fuel at the head stage can be accompanied by an increase in the emission of NO x .
Nähere Untersuchungen zur Ausbildung thermoakustischer Schwingungen haben gezeigt, dass derartig unerwünschte kohärente Strukturen bei Mischvorgängen entstehen. Von besonderer Bedeutung sind hierbei die sich zwischen zwei mischenden Strömungen ausbildenden Scherschichten, die innerhalb der kohärente Strukturen gebildet werden. Nähere Ausführungen hierzu sind folgenden Druckschriften zu entnehmen: Oster & Wygnanski 1982, "The forced mixing layer between parallel streams", Journal of Fluid mechanics, Vol. 123, 91-130; Paschereit et al. 1995, "Experimental investigation of subharmonic resonance in an axisymmetric jet", Journal of Fluid Mechanics, Vol. 283, 365-407).Further studies on the formation of thermoacoustic vibrations have have shown that such unwanted coherent structures arise in mixing operations. Of particular importance here are those between two mixing Currents forming shear layers that are within the coherent structures be formed. Further details can be found in the following publications: Oster & Wygnanski 1982, "The forced mixing layer between parallel 123, 91-130; Paschereit et al., 1995, "Experimental investigation of subharmonic resonance in an axisymmetric jet ", Journal of Fluid Mechanics, Vol. 283, 365-407).
Wie aus den vorstehenden Berichten hervorgeht, ist es möglich, die sich innerhalb der Scherschichten ausbildenden kohärenten Strukturen durch gezieltes Einbringen einer akustischen Anregung derart zu beeinflussen, dass Ihre Entstehung verhindert wird. Eine weitere Methode ist das Einbringen eines akustischen Gegenschallfeldes, so dass das vorhandene unerwünschte Schallfeld durch ein gezielt eingebrachtes, phasenverschobenes Schallfeld regelrecht ausgelöscht wird. Diese Antischall-Technik benötigt jedoch verhältnismäßig viel Energie, die entweder extern dem Brennersystem zur Verfügung gestellt werden muss oder die dem gesamten System an einer anderen Stelle abzuzweigen ist, was jedoch zu einer, wenn auch geringen, aber dennoch vorhandenen Wirkungsgradeinbuße führt.As is clear from the above reports, it is possible that within the shear layers forming coherent structures by targeted introduction To influence an acoustic stimulation in such a way that prevents their formation becomes. Another method is the introduction of an acoustic counter-field, so that the existing unwanted sound field by a deliberately introduced, phase-shifted sound field is virtually extinguished. This anti-noise technique but requires a relatively large amount of energy either externally Burner system must be made available or the entire system to divert elsewhere, but this, albeit minor, but still leads to loss of efficiency.
Neben den vorstehend genannten aktiven Möglichkeiten zur gezielten Einflußnahme
zur Reduzierung sich im Inneren von Brennern ausbildenden kohärenten Strukturen
kann alternativ auch mit passiven Maßnahmen derartigen Störungen in der Brennerströmung
entgegengetreten werden. Passive Maßnahmen, das sind vorwiegend
konstruktive Gestaltungsmerkmale der Brenner, die den Betriebsbereich eines Brenners
in Bezug auf Pulsationen und Emissionen erweitern, sind besonders attraktiv,
da sie, einmal installiert, keiner weiteren Wartung bedürfen. Eine solche Massnahmee
kann in einer Störung der Axialsymmetrie des Brenners bestehen. So offenbart
EP 0 985 876 eine Weiterentwicklung eines Vormischbrenners gemäss EP 0 321
809, welche sich dadurch auszeichnet, dass die die Vormischstrecke bildenden Teilkörper
einen nichtkreisförmigen Querschnitt aufweisen.In addition to the aforementioned active options for targeted influence
for reducing coherent structures forming inside burners
Alternatively, with passive measures such disturbances in the burner flow
be countered. Passive measures, these are predominantly
constructive design features of the burner, the operating range of a burner
in terms of pulsations and emissions expand, are particularly attractive
Once installed, they require no further maintenance. Such a measure
may be a disturbance of the axial symmetry of the burner. So revealed
Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren zur Erhöhung der strömungsmechanischen Stabilität eines Vormischbrenners bereitzustellen, welches die unerwünschten Strömungswirbel, die sich als kohärente Druckschwankungsstrukturen ausbilden, effizient und ohne zusätzlichen Energieaufwand unterdrückt. Die hierzu notwendigen Maßnahmen an einem Vormischbrenner sollen einen geringen konstruktiven Aufwand verursachen und kostengünstig in ihrer Realisierung sein. Die eingesetzten Maßnahmen sollen überdies vollständig wartungsfrei sein.The invention is based on the object, a method for increasing the fluid mechanical To provide stability of a premix burner, which the undesirable eddies, posing as coherent pressure fluctuation structures training, efficient and suppressed without additional energy. The purpose necessary measures on a premix burner should have a low constructive Create effort and be cost effective in their realization. The Furthermore, the measures taken should be completely maintenance-free.
Erfindungsgemäss wird die Aufgabe durch ein Verfahren zur Erhöhung der strömungsmechanischen
Stabilität eines Vormischbrenners sowie durch einen Vormischbrenner
der in den unabhängigen Ansprüchen genannten Art gelöst.
Den Erfindungsgedanken vorteilhaft weiterbildende Merkmale sind Gegenstand der
abhängigen Ansprüche.According to the invention the object is achieved by a method for increasing the fluid mechanical stability of a premix burner and by a premix burner of the type mentioned in the independent claims.
The idea of the invention advantageously further features are the subject of the dependent claims.
Das erfindungsgemässe Verfahren basiert auf dem Grundgedanken, zur strömungsmechanischen Stabilisierung eines Vormischbrenners, in den mindestens ein Verbrennungsluftstrom tangential in einen Brennerhohlraum eingeleitet wird und sich unter Ausbildung einer koaxial zur Brennerachse orientierten Drallströmung mit einem eingedüsten gasförmigen und/oder flüssigen Brennstoff vermischt und an einem Querschnittssprung an der Brennermündung eine Rückströmzone induziert, welche im Betrieb des Brenners zur Stabilisierung der Flamme dient, die Drallströmung innerhalb des Brennerhohlraums in Richtung auf die Brennermündung auf mindestens einem Umfangsabschnitt zunehmend radial zu deformieren und in einem nichtrotationssymmetrischen Strömungsquerschnitt in den Brennraum eintreten zu lassen, wobei diese Deformation zu Lasten des freien Strömungsquerschnitts des Brennerhohlraums erzeugt wird.The method according to the invention is based on the basic idea of fluid mechanics Stabilization of a premix burner, in which at least one Combustion air flow is introduced tangentially into a burner cavity and forming a coaxial with the burner axis oriented swirl flow with a injected gaseous and / or liquid fuel mixed and at one Cross-section jump at the burner mouth induces a backflow zone, which during operation of the burner serves to stabilize the flame, the swirl flow within of the burner cavity towards the burner mouth at least increasingly radially deforming a peripheral portion and in a non-rotationally symmetric Flow cross-section to enter the combustion chamber, this deformation being at the expense of the free flow cross-section of the burner cavity is produced.
Die Ausbildung kohärenter Wirbelstrukturen wird durch eine von der Rotationssymmetrie abweichende Formgebung des Strömungsquerschnitts im Brennerhohlraum und beim Eintritt in den Brennraum gestört. In bestimmten Betriebspunkten ist bei Vormischbrennern nach dem Stand der Technik der Zeitverzug des Brennstoffs vom Eindüsungsort bis zur Flamme konstant. Aus der erfindungsgemässen Deformation des Strömungsquerschnitts resultiert eine breite Verteilung der Verzugszeit. Durch die Verhinderung der Entstehung von Wirbelstrukturen am Brenneraustritt und einen verschmierten Zeitverzug wird auch eine periodische Wärmefreisetzung unterdrückt, die ihrerseits für das Auftreten thermoakustischer Schwingungen verantwortlich ist. Indem die Deformation der Drallströmung durch einengende Abschnitte der Hohlraumkontur erzwungen wird, wie an anderer Stelle noch zu erläutern sein wird, kommt es darüber hinaus zu einer Beschleunigung der Strömung, die sich stabilisierend auf die Rückströmzone auswirkt.The formation of coherent vortex structures is by one of the rotational symmetry Deviating shaping of the flow cross-section in the burner cavity and disturbed when entering the combustion chamber. In certain operating points is at Premix burners according to the prior art, the time delay of the fuel from Eindüsungsort to the flame constant. From the inventive deformation the flow cross section results in a broad distribution of the delay time. By the prevention of the formation of vortex structures at the burner outlet and a smeared time delay, also a periodic heat release is suppressed, which in turn is responsible for the occurrence of thermoacoustic vibrations. By the deformation of the swirl flow through constricting portions of the cavity contour forced, as will be explained later, In addition, there is an acceleration of the flow, which is stabilizing affects the Rückströmzone.
Ein Vormischbrenner gemäss der Erfindung geht aus von einem Vormischbrenner zum Einsatz in einem Wärmeerzeuger, im wesentlichen bestehend aus einem Drallerzeuger mit Mitteln zum tangentialen Einbringen eines Verbrennungsluftstroms in einen Hohlraum des Drallerzeugers sowie Mitteln zum Einbringen von wenigstens einem gasförmigen und/oder flüssigen Brennstoff in den Verbrennungsluftstrom unter Ausbildung einer Drallströmung mit einer axialen Bewegungskomponente hin zur Brennermündung, an der die Drallströmung unter Induzierung einer Rückströmzone aufplatzt. Ein gattungsbildender Brenner, basierend auf mindestens zwei hohlen, in Strömungsrichtung der Heißgase ineinandergeschachtelten sich konisch erweiternden Teilkörpern, deren Mittelachsen zueinander versetzt verlaufen, ist in EP 0321809 beschrieben. Derartige, auch als Kegelbrenner oder Doppelkegelbrenner bezeichnete Brennertypen, weisen an ihrem Brenneraustritt eine Abrisskante auf, deren Kantenverlauf aus zwei zueinander versetzten Halbkreisen besteht, deren geschlossener Kantenverlauf jedoch nahezu kreisrund und somit annähernd rotationssymmetrisch zur Brennerachse ausgebildet ist. Das sich im Brennerhohlraum ausbildende Brennstoff-/Luftgemisch breitet sich in Form einer rotationssymmetrischen Drallströmung mit einer axialen Komponente zur Brennermündung hin aus, mit all ihren bekannten Nachteilen bezüglich der Bildung kohärenter Strukturen und den damit verbundenen thermoakustischen Druckschwankungen.A premix burner according to the invention is based on a premix burner for use in a heat generator, essentially consisting of a swirl generator with means for tangentially introducing a combustion air flow in a cavity of the swirl generator and means for introducing at least a gaseous and / or liquid fuel in the combustion air stream below Formation of a swirl flow with an axial component of motion towards the Burner mouth, at which the swirl flow inducing a backflow zone bursts. A generic burner, based on at least two hollow, in Flow direction of the hot gases nested conically widening Partial bodies whose center axes are offset from one another are described in EP 0321809 described. Such types of burners, also known as cone burners or double-cone burners, have at their burner outlet on a spoiler edge, the edge course of consists of two mutually offset semicircles whose closed edge course However, almost circular and thus approximately rotationally symmetrical to the burner axis is trained. The forming in the burner cavity fuel / air mixture spreads in the form of a rotationally symmetric swirl flow an axial component to the burner mouth out, with all their known Disadvantages of the formation of coherent structures and the associated thermoacoustic pressure fluctuations.
Sorgt man hingegen dafür, dass gezielte radiale Deformationen in den Strömungsfluß des Brennstoff-/Luftgemischs eingebracht werden, so dass sich der Strömungsquerschnitt von dem einer rotationssymmetrischen Strömung unterscheidet, so kann auf diese Weise der Ausbildung kohärenter Strukturen und einem konstanten Zeitverzug des Brennstoffswirksam begegnet werden.On the other hand, it is ensured that targeted radial deformations in the flow flow of the fuel / air mixture are introduced so that the flow cross-section from that distinguishes a rotationally symmetric flow, so can in this way the formation of coherent structures and a constant time delay be countered the fuel.
Eine derartige Einflußnahme auf die Strömungsgeometrie kann durch mindestens einen Abschnitt der Hohlraumwandung erfolgen, welcher Wandabschnitt in einem stromabwärtigen Endbereich des Brennerhohlraums eine geringere Steigung besitzt als in einem stromaufwärtigen Bereich. Dieser mindestens eine Abschnitt führt damit gegenüber jenen Wandabschnitten auf gleicher Achshöhe, die diese Eigenschaft nicht besitzen, zu einer radialen Abweichung von der Kreisform in Richtung auf die Brennerachse. Jedwede von der Kreisform abweichende Teilkonturen im Brennerhohlraum und an der Austrittskante, bspw. geradlinige oder asphärisch gekrümmte Wandabschnitte über den Umfang, tragen zur Reduzierung von Strömungswirbeln bei.Such influence on the flow geometry can by at least a section of the cavity wall take place, which wall section in a downstream end portion of the burner cavity has a lower pitch as in an upstream area. This at least one section leads to it opposite those wall sections at the same axis height, this feature do not possess, to a radial deviation from the circular shape in the direction of the Brenner axis. Any deviating from the circular shape partial contours in the burner cavity and at the trailing edge, for example rectilinear or aspherically curved Wall sections around the circumference, contribute to the reduction of flow vortex at.
Als grundsätzliche Auslegungsregel für die Ausgestaltung der Brenneraustrittskante ist zu beachten, daß die geometrische Abweichung von einer runden Geometrie zumindest so groß zu wählen ist, daß die sich ergebende Distanz zwischen beiden Geometrien größer als die Grenzschichtdicke der Strömung ist, die durch die Austrittsgeometrie hindurchströmt.As a basic design rule for the design of the burner outlet edge It should be noted that the geometric deviation from a circular geometry at least so large is to choose that the resulting distance between the two Geometries greater than the boundary layer thickness of the flow is due to the exit geometry flowing.
Die Erfindung wird nachstehend anhand von Ausführungsbeispielen unter Bezugnahme auf die Zeichnung exemplarisch dargestellt. Es zeigen:
- Fig. 1a
- perspektivische Darstellung eines Vormischbrenners nach dem Stand der Technik, von dem die Erfindung ausgeht
- Fig.1b Fig. 2a-d
- weitere Darstellung eines solchen Brenners in vereinfachter Form stark schematisierte Wiedergabe des Erfindungsgedankens anhand verschiedener Formen von Drallerzeugern
- Fig. 3
- eine Ausführungsform eines erfindungsgemäss abgeänderten Brenners
- Fig. 4-7
- alternative Ausführungsformen der Erfindung
- Fig. 8
- Darstellung der Unterdrückung von Verbrennungsschwingungen durch Unterdrückung von Strömungswirbeln in einem Brenner.
- Fig. 1a
- perspective view of a premix burner according to the prior art, from which the invention proceeds
- Fig.1b Fig. 2a-d
- Further illustration of such a burner in a simplified form highly schematic representation of the inventive idea using various forms of swirl generators
- Fig. 3
- an embodiment of a modified according to the invention burner
- Fig. 4-7
- alternative embodiments of the invention
- Fig. 8
- Representation of the suppression of combustion oscillations by suppression of flow vortices in a burner.
Die Fig. 1a und 1b geben in stark schematisierter Form Aufbau und Wirkungsweise
eines Vormischbrenners wieder, wie er Ausgangspunkt der hier vorgestellten Erfindung
ist.
Der Vormischbrenner besteht aus aus zwei hohlen sich konisch erweiternden Teilkörpern
(1) und (2), die derart achsparallel und zueinander versetzt angeordnet sind,
dass sie in zwei spiegelbildlich gegenüberliegenden Überlappungsbereichen tangentiale
Spalte (3) bilden. Obgleich in den Figuren 1a und 1b zwei sich konisch erweiternde
Teilkörper (1) und (2) beispielhaft dargestellt sind, sind indes auch andere
Konfigurationen denkbar. So sind diese Brenner weder auf die Anordnung von zwei
Teilkörpern (1) und (2) beschränkt, noch ist deren konische Konfiguration zwingend
erforderlich. Dies ist dem Fachmann geläufig. Die aus der Versetzung der Längsachsen
resultierenden Spalte (3) dienen als Eintrittskanäle, durch die im Brennerbetrieb
die Verbrennungsluft (5) tangential in den Brennerhohlraum (6) einströmt. Entlang
der tangentialen Eintrittskanäle (3) befinden sich Eindüsungsöffnungen (7), durch
welche ein vorzugsweise gasförmiger Brennstoff in die vorbeiströmende Verbrennungsluft
(5) eingedüst wird. Im Interesse einer guten Durchmischung erfolgt die
Brennstoffeindüsung vorzugsweise innerhalb der Spalte (3) unmittelbar vor Eintritt in
den Brennerhohlraum (6). In dem Anfangsbereich des Brenners, der auch zylindrisch
ausgebildet sein kann (nicht dargestellt), ist eine zentrale Düse (8) zur Zerstäubung
eines flüssigen Brennstoffes vorgesehen, deren Kapazität und Betriebsart sich nach
den Brennerparametern richten. Der flüssige Brennstoff tritt in einem spitzen Winkel
aus der Düse (8) aus und bildet in dem Brennerhohlraum (6) ein kegelförmiges
Brennstoffprofil, das von der tangential eintretenden und in eine Drallströmung (9)
übergehenden Verbrennungsluft (5) umschlossen und fortlaufend zu einem Gemisch
abgebaut wird, welcher Vorgang durch vorgewärmte Verbrennungsluft oder Zumischung
von rückgeführtem Abgas unterstützt werden kann. Es ist alternativ auch
möglich, die Düse (8) mit gasförmigem Brennstoff zu beaufschlagen. Brennraumseitig
besitzt der Vormischbrenner eine als Verankerung der Teilkörper (1) und (2) fungierende
Frontplatte (10), welche eine Anzahl von Bohrungen (11) zur Lufteinbringung
in den Brennraum (12) aufweist. Das in einer Drallströmung (9) den Brennerhohlraum
(6) durchquerende Brennstoff-/Luftgemisch erreicht am stromabwärtigen
Ende der Vormischstrecke (13) an der Brennermündung (14) die optimale Brennstoffkonzentration
über den Querschnitt. Beim Austritt aus dem Brenner platzt die
Drallströmung (9) auf unter Ausbildung einer Rückströmzone (15) mit einem gegenüber
der dort wirkenden Flammenfront (17) stabilisierenden Effekt. Diese aerodynamische
Flammenstabilisierung übernimmt quasi die Funktion eines Flammenhalters.
Das gefürchtete Versagen mechanischer Flammenhalter aufgrund von Überhitzung
mit eventuell nachfolgenden schwerwiegenden Havarien an Maschinensätzen ist
somit ausgeschlossen. Weiterhin verliert die Flamme ausser durch Strahlung keine
Wärme an kalte Wände. Dies trägt zusätzlich zur Vergleichmässigung der Flammentemperatur
und damit zu geringen Schadstoffemissionen und guter Verbrennungsstabilität
bei.
Erfindungsgemäss werden nun Massnahmen vorgesehen, die Drallströmung (9) innerhalb
der Vormischstrecke (13) zunehmend radial zu deformieren. Vorzugsweise
soll diese Deformation symmetrisch erfolgen. Dies ist indes nicht zwingend. Dabei ist
es ein wesentliches Kennzeichen, diese Deformation zu Lasten des freien Strömungsquerschnitts
(18) zu erzielen. Die Wand (21) des Hohlraums (6) weist in einem
stromabwärtigen Bereich (20) wenigstens einen Abschnitt (22) auf, der gegenüber
einem stromaufwärtigen Bereich (19) eine geringere Steigung, bezogen auf die
Brennerachse (4), besitzt. Das heisst, die über den Querschnitt betrachtet annähernd
kreisrunde Kontur (21) des Brennerhohlraums (6) weist, verteilt über den Umfang,
vom Kreisrund der Hohlraumkontur (21) in Richtung auf die Mittelachse (4) abweichende,
also den Hohlraum (6) einengende Abschnitte (22) auf, wie in Fig.2a - 2d im
Längsschnitt schematisch wiedergegeben. Es hat sich nämlich in diesem Zusammenhang
als vorteilhaft erwiesen, die Deformation der Strömung gleichzeitig mit einer
Beschleunigung der Strömung einhergehen zu lassen. Diese Massnahme wirkt
sich besonders günstig auf die Stabilität des Brenners aus. So wirkt sich zum einen
die von der Rotationssymmetrie abweichende Querschnittsform der aus dem Brenner
austretenden Strömung (9) störend auf die Bildung kohärenter Wirbelstrukturen
aus und hemmt damit letztlich die Entstehung thermoakustischer Schwingungen.
Zum anderen führt die aus der absoluten oder relativen Verengung des Strömungsquerschnitts
(18) resultierende Beschleunigung der Drallströmung (9) am Brenneraustritt
(14) zu einer Stabilisierung der Rückströmzone (15), wodurch Fluktuationen
der Rückströmzone (15), die damit verbundene periodische Wärmefreisetzung und
damit wiederum die Entstehung thermoakustischer Schwingungen gehemmt werden.
Aus der Kombination dieser gleichwirkenden Effekte resultieren Synergieeffekte, die
es in besonders vorteilhafter Weise gestatten, mit einem sehr geringen technischen
Aufwand die strömungsmechanische Stabilität eines Vormischbrenners zu erhöhen.
Die Fig.2a - 2d sollen den Erfindungsgedanken anhand stark schematisierter Darstellungen
erläutern. Fig.2a zeigt eine bekannte Drallerzeugergeometrie, mit der die
Erfindung in günstiger Weise verwirklicht werden kann, wobei- wie an anderer Stelle
erwähnt - die konische Konfiguration des Drallerzeugers (13) indes nicht zwingend
ist.
Die Fig.2b - 2d versinnbildlichen den Erfindungsgedanken, der darin besteht, zum
Zwecke der Deformation des Strömungsprofils die Wandung (21) des Brennerhohlraums
(6) in mindestens einem Umfangsabschnitt (22) zu Lasten des freien Strömungsquerschnitts
(18) in Richtung auf die Brennerachse (4) abzuwinkeln. Dies
kann symmetrisch oder asymmetrisch durch mindestens einen solchen den Strömungsquerschnitt
einengenden Abschnitt (22) erfolgen. In einem stromabwärtigen
Bereich (20) des Hohlraums (6), welcher Bereich (20) beispielsweise bei 2/3 der axialen
Länge einsetzen kann, knickt in wenigstens einem Umfangsabschnitt (22) die
Hohlraumwandung (21) in einem Winkel im Bereich von 2° bis 45°, insbesondere 5°
bis 15°, in Richtung auf die Brennerachse (4) ab. Aus diesen schematischen Darstellungen
erschliesst sich dem Fachmann gleichzeitig ein weiterer Vorteil der Erfindung,
nämlich die mit geringem Aufwand mögliche Nachrüstbarkeit vorhandener Brenner.
Die den Strömungsquerschnitt (18) einengenden Abschnitte (22) können durch nachträglich
aufgebrachte strömungsleitende Einbauten (28) realisiert werden.
Die Figuren 3 bis 7 zeigen Ausführungsformen von gemäss der Erfindung gestalteten
Brennern.
Fig.3 gibt eine bevorzugte Variante der Erfindung wieder, nach der die Brennermündung
(14) eine vieleckige Austrittskontur (16) besitzt. Wie aus den schematischen
Darstellungen der Fig.2 am deutlichsten hervorgeht, wird die sich konisch erweiternde
Kontur (23) des Brennerhohlraums (6) in einem stromabwärtigen Endbereich (20)
abgebrochen und mit einer gegenüber dem vorhergehenden Bereich (19) geringeren
Steigung im Verhältnis zur Längsachse (4) fortgeführt. Der Begriff verringerte Steigung
soll auch einen Verlauf parallel zur Längsachse (4) oder einen konvergenten
Verlauf umfassen, wie aus den Figuren 2 ersichtlich. Zur Realisierung dieser Anregung
bietet sich dem Fachmann eine Vielzahl von Massnahmen an. Nach einer bevorzugten
Ausführungsform werden in die schalenförmigen Teilkörper (1) und (2)
nach dem Stand der Technik ausgebildeter Brenner entsprechend ausgeformte Platten
(28) eingeschweisst, die - planimetrisch betrachtet - Sehnen darstellen, die
Kreissegmente aus dem freien Strömungsquerschnitt (18) des Brennerhohlraums (6)
herausschneiden. Je Teilkörper (1) oder (2) werden vorzugsweise eine bis vier solcher
Platten (28) auf die Innenwandung (21) aufgeschweisst. Bei neuen Brennern
erfolgt die Formgebung der Wandkontur im Herstellungsprozess.
Nach einer anderen aus Fig.4 in Verbindung mit Fig.2c ersichtlichen Ausführungsform
ist der Brenner in einem stromaufwärtigen Bereich (19) in an sich bekannter
Weise aus zwei versetzt ineinandergeschachtelten Teilkörpern (1) und (2) von im
wesentlichen kreisförmigem Querschnitt ausgebildet. In einem Übergangsbereich auf
etwa 2/3 der axialen Länge geht die Innenwand (21) aus ihrer im wesentlichen kreisförmigen
Kontur in eine vieleckige über, die sich im weiteren Verlauf zur Brennermündung
(14) hin zunehmend ausprägt. Diese den Strömungsquerschnitt (18) sehnenartig
einengenden Abschnitte (22) der Hohlraumwandung (21) besitzen eine gegenüber
den stromaufwärtigen Bereichen (19) der Hohlraumwandung (6) geringere
Divergenz in Relation zur Längsachse (4). Der Begriff geringere Divergenz soll dabei
auch die Möglichkeit eines parallelen oder konvergenten Verlaufs zur Längsachse (4)
mit einschliessen. In Betrachtung des Querschnitts weisen die einengenden Abschnitte
(22) in der Regel eine geradlinige Kontur auf. Ein leicht konvexer oder konkaver
Verlauf ist indes ebenfalls möglich. Ein konvexer Verlauf ist insbesondere im
Falle der Anordnung einer geringen Anzahl oder lediglich eines oder zweier solcher
Abschnitte (22) vorteilhaft.
Eine weitere, nicht in einer Figur gezeigte Ausführungsform besteht darin, den Brennerhohlraum
(6) auch in seinem stromaufwärtigen Bereich (19) nicht mit einem kreisförmigen
Querschnitt auszustatten, sondern den Brenner mit einem durchgehend
nicht-rotationssymmetrisch konturierten Hohlraum (6) auszurüsten. Diese Ausführungsform
bietet sich insbesondere für vieleckige Konturen (23) des Hohlraumquerschnitts
(18) an.
Es ist aus dem Stand der Technik an sich bekannt, Brenner, so wie sie vorstehend
definiert sind, zum Zwecke einer verbesserten Durchmischung und Flammenpositionierung
bei schwierigen Brennstoffen mit Düsen (24) oder Mischrohren (25) auszurüsten,
die dem Drallerzeuger (13) nachgeschaltet sind. Auch für derartige Brennervarianten
ist die Erfindung geeignet, durch Störung der Strömungsinstabilitäten und
Erzeugung eines verschmierten Zeitverzugs des Brennstoffs vom Eindüsungsort bis
zur Flamme die strömungsmechanische Stabilität solcher Brenner zu erhöhen.
Die Fig.5 und 6 geben einen Vormischbrenner wieder, bestehend aus einem Drallerzeuger
(13) für einen Verbrennungsluftstrom (5) und Mitteln zur Eindüsung mindestens
eines Brennstoffs (7) und/oder (8), wobei stromab des Drallerzeugers (13) eine
Mischstrecke (25) angeordnet ist. In das die Mischstrecke (25) umgrenzende Gehäuse
(26) können in gleichmässiger Umfangsverteilung spitz zur Längsachse (4) verlaufende
Einlassöffnungen (27) zum Eindüsen einer zusätzlichen Verbrennungsluftmenge
angeordnet sein. Vorzugsweise in einem Bereich stromab der Einlassöffnungen
(27) wird der rotationssymmetrische Strömungsquerschnitt der Mischstrecke (25)
durch den freien Querschnitt (29) verengende Abschnitte (22) abgelenkt und radial
deformiert. Die Austrittsöffnung (16) nimmt eine vieleckige Querschnittsform ein, zusammengesetzt
aus einer Mehrzahl geradliniger Abschnitte (22). Vielversprechend
sind Austrittskonturen (16) in Form eines regelmässigen oder unregelmässigen Vielecks
(Fig.5). Die einzelnen geradlinigen Abschnitte (22) der Austrittskante (27) umspannen
die Austrittsöffnung (16) des Brenners. Indes ist diese Geradlinigkeit, wie an
anderer Stelle bereits erwähnt, nicht zwingend, und diese Abschnitte (22) können
auch konvex oder konkav ausgebildet sein. Fig.6 deutet einen konvex ausgeformten
Wandabschnitt (22) in asymmetrischer Anordnung an.
Fig.7 schliesslich zeigt eine Ausführungsvariante mit einem zylindrischen oder konvergenten
Düsenabschnitt (24) am stromabwärtigen Brennerende. Nach dem Stand
der Technik dienen diese nachgeschalteten Düsen (24) vorrangig einer Beschleunigung
der Strömung am Brenneraustritt und damit einer Stabilisierung der Rückströmzone
(15). Nach einer Ausführungsform der Erfindung wird diese wünschenswerte
Beschleunigung durch eine in Strömungsrichtung einsetzende und zunehmende
Querschnittsverringerung dergestalt erreicht, dass dieser Düsenabschnitt (24) in
Strömungsrichtung aus einer im wesentlichen kreisförmigen Querschnittsform auf
eine andere Querschnittsform eingeengt wird, beispielsweise die eines regelmässigen
oder unregelmässigen Vielecks oder eines Ovals.FIGS. 1a and 1b show in a highly schematized form the structure and mode of action of a premix burner, as it is the starting point of the invention presented here.
The premix burner consists of two hollow conically widening part bodies (1) and (2), which are arranged axially parallel and offset from one another such that they form tangential gaps (3) in two mirror-inverted overlapping regions. Although two conically widening partial bodies (1) and (2) are shown by way of example in FIGS. 1a and 1b, other configurations are also conceivable. Thus, these burners are not limited to the arrangement of two partial bodies (1) and (2), nor is their conical configuration absolutely necessary. This is familiar to the expert. The resulting from the displacement of the longitudinal axes column (3) serve as inlet channels through which the burner air combustion air (5) flows tangentially into the burner cavity (6). Along the tangential inlet channels (3) there are injection openings (7), through which a preferably gaseous fuel is injected into the passing combustion air (5). In the interests of good mixing, the fuel injection preferably takes place within the gap (3) immediately before entry into the burner cavity (6). In the initial region of the burner, which may also be cylindrical (not shown), a central nozzle (8) is provided for atomizing a liquid fuel whose capacity and mode of operation are governed by the burner parameters. The liquid fuel exits the nozzle (8) at an acute angle and forms in the burner cavity (6) a conical fuel profile which is enclosed by the combustion air (5) passing tangentially and into a swirling flow (9) and continuously forming a mixture is degraded, which process can be supported by preheated combustion air or admixture of recirculated exhaust gas. It is alternatively also possible to pressurize the nozzle (8) with gaseous fuel. On the combustion chamber side, the premix burner has a front plate (10) which acts as an anchorage of the part bodies (1) and (2) and has a number of bores (11) for introducing air into the combustion chamber (12). The fuel / air mixture passing through the burner cavity (6) in a swirl flow (9) reaches the optimum fuel concentration across the cross section at the downstream end of the premix line (13) at the burner mouth (14). When emerging from the burner, the swirl flow (9) bursts to form a backflow zone (15) with an effect stabilizing against the flame front (17) acting there. This aerodynamic flame stabilization acts as a kind of flame holder. The dreaded failure of mechanical flame holders due to overheating with possible subsequent serious damage to machine sets is thus excluded. Furthermore, the flame loses no heat except on cold walls due to radiation. This also contributes to the uniformity of the flame temperature and thus to low pollutant emissions and good combustion stability.
According to the invention, measures are now provided to increasingly radially deform the swirl flow (9) within the premix section (13). Preferably, this deformation should be symmetrical. This is not mandatory. It is an essential feature to achieve this deformation at the expense of the free flow cross-section (18). The wall (21) of the cavity (6) has, in a downstream region (20), at least one section (22) which has a smaller pitch relative to an upstream region (19) relative to the burner axis (4). That is to say, the approximately circular contour (21) of the burner cavity (6), viewed over the cross section, has a deviation from the circumference of the cavity contour (21) in the direction of the central axis (4), ie the cavity (6) constricts Sections (22), as shown in Fig 2a-2d in longitudinal section schematically reproduced. It has proven to be advantageous in this context, to accompany the deformation of the flow simultaneously with an acceleration of the flow. This measure has a particularly favorable effect on the stability of the burner. On the one hand, the cross-sectional shape deviating from the rotational symmetry of the flow (9) emerging from the burner has a disruptive effect on the formation of coherent vortex structures and thus ultimately inhibits the formation of thermoacoustic oscillations. On the other hand, resulting from the absolute or relative narrowing of the flow cross section (18) resulting acceleration of the swirl flow (9) at the burner outlet (14) to stabilize the Rückströmzone (15), whereby fluctuations in the Rückströmzone (15), the associated periodic heat release and In turn, the formation of thermoacoustic vibrations are inhibited. The combination of these effects with the same effect results in synergy effects which make it possible, in a particularly advantageous manner, to increase the fluid mechanical stability of a premix burner with very little technical effort. FIGS. 2a-2d are intended to explain the concept of the invention on the basis of highly schematic representations. FIG. 2a shows a known swirl generator geometry with which the invention can be realized in a favorable manner, wherein, as mentioned elsewhere, however, the conical configuration of the
FIGS. 2b-2d symbolize the concept of the invention, which for the purpose of deforming the airfoil, the wall (21) of the burner cavity (6) in at least one peripheral portion (22) at the expense of the free flow cross-section (18) in the direction of the burner axis (4) to angle. This can be done symmetrically or asymmetrically by at least one of the flow cross-section constricting portion (22). Can insert into a downstream portion (20) of the cavity (6), which area (20), for example, at 2/3 of the axial length, the cavity wall (21) bends in at least one peripheral portion (22) at an angle in the range of 2 ° up to 45 °, in particular 5 ° to 15 °, in the direction of the burner axis (4) from. From these diagrammatic representations, a further advantage of the invention is disclosed to the person skilled in the art at the same time, namely the retrofittability of existing burners which is possible with little effort. The flow section (18) narrowing sections (22) can be realized by subsequently applied flow-conducting internals (28). FIGS. 3 to 7 show embodiments of burners designed according to the invention.
3 shows a preferred variant of the invention, according to which the burner mouth (14) has a polygonal outlet contour (16). As can be seen most clearly from the schematic representations of FIG. 2, the conically widening contour (23) of the burner cavity (6) is broken off in a downstream end region (20) and has a smaller pitch than the preceding region (19) in relation to FIG Longitudinal axis (4) continued. The term reduced slope should also include a profile parallel to the longitudinal axis (4) or a convergent profile, as shown in FIGS. To realize this suggestion, a variety of measures are available to the person skilled in the art. According to a preferred embodiment, in the cup-shaped part body (1) and (2) according to the prior art trained burner correspondingly shaped plates (28) welded, which - seen planimetrically - represent tendons, the circle segments from the free flow cross-section (18) of the burner cavity (6) cut out. For each partial body (1) or (2), preferably one to four such plates (28) are welded onto the inner wall (21). For new burners shaping the wall contour takes place in the manufacturing process.
According to another embodiment shown in FIG. 4 in conjunction with FIG. 2c, the burner is formed in an upstream region (19) in a manner known per se from two interleaved partial bodies (1) and (2) of substantially circular cross-section. In a transition region to about 2/3 of the axial length of the inner wall (21) goes from its substantially circular contour over in a polygonal, the through increasingly expresses itself in the further course to the burner mouth (14). These chamfering sections (22) of the cavity wall (21) which constrict the flow cross-section (18) have a lower divergence in relation to the longitudinal axis (4) than the upstream regions (19) of the cavity wall (6). The term lower divergence should also include the possibility of a parallel or convergent profile to the longitudinal axis (4) with. Considering the cross section, the constricting portions (22) usually have a rectilinear contour. A slightly convex or concave profile is also possible. A convex course is particularly advantageous in the case of the arrangement of a small number or only one or two such sections (22).
Another embodiment, not shown in a figure, is not to provide the burner cavity (6) in its upstream region (19) with a circular cross-section, but to equip the burner with a continuous non-rotationally symmetric contoured cavity (6). This embodiment is particularly suitable for polygonal contours (23) of the cavity cross section (18).
It is well known in the art to provide burners as defined above with nozzles (24) or mixing tubes (25) downstream of the swirl generator (13) for improved mixing and flame positioning in difficult fuels , Also, for such burner variants, the invention is adapted to increase the fluid mechanical stability of such burners by disturbing the flow instabilities and generating a blurred time delay of the fuel from Eindüsungsort to the flame.
Figures 5 and 6 show a premix burner, consisting of a swirl generator (13) for a combustion air stream (5) and means for injecting at least one fuel (7) and / or (8), wherein downstream of the swirl generator (13) has a mixing section (25) is arranged. In which the mixing section (25) bounding housing (26) can be arranged in an even circumferential distribution pointed to the longitudinal axis (4) extending inlet openings (27) for injecting an additional amount of combustion air. Preferably, in a region downstream of the inlet openings (27) of the rotationally symmetric flow cross-section of the mixing section (25) by the free cross-section (29) narrowing portions (22) deflected and radially deformed. The exit port (16) occupies a polygonal cross-sectional shape composed of a plurality of rectilinear portions (22). Promising exit contours (16) in the form of a regular or irregular polygon (Figure 5). The individual rectilinear sections (22) of the outlet edge (27) span the outlet opening (16) of the burner. However, as already mentioned, this straightness is not mandatory, and these sections (22) may also be convex or concave. Fig.6 indicates a convex shaped wall portion (22) in an asymmetrical arrangement.
Finally, FIG. 7 shows a variant embodiment with a cylindrical or convergent nozzle section (24) at the downstream burner end. According to the prior art, these downstream nozzles (24) serve primarily to accelerate the flow at the burner outlet and thus stabilize the return flow zone (15). According to one embodiment of the invention, this desirable acceleration is achieved by increasing and decreasing the cross-sectional area such that this nozzle portion (24) is narrowed in the direction of flow from a substantially circular cross-sectional shape to another cross-sectional shape, such as a regular or irregular polygon or one oval.
In Figur 8 ist ein Diagramm dargestellt, das entlang der Abszisse die Verbrennungsleistung des Brenners gemäß Figur 3 aufgetragen zeigt und entlang der Ordinate eine Skalierung, die die Ausbildung von thermoakustischen Schwingungen, die als Folge kohärenter Strukturen innerhalb des Strömungsflusses im Brenner entstehen, quantifiziert. Betrachtet werden thermoakustische Schwingungen im 100 Hz-Bereich. Vergleicht man einen Brenner mit konventionellem Brenneraustritt gemäss Ausführungsform in Fig.1 (siehe Linienzug mit Quadraten durchsetzt) mit einem erfindungsgemäß ausgebildeten Brenneraustritt gemäß Ausführungsform in Fig.3 (siehe Linienzug mit Kreisen durchsetzt), so fällt deutlich auf, dass im letzteren Fall ein erheblich geringerer Anteil thermoakustischer Schwingungen entsteht. FIG. 8 shows a diagram showing the combustion power along the abscissa of the burner according to FIG. 3 and along the ordinate a scaling that allows the formation of thermoacoustic vibrations as Result in coherent structures within the flow stream in the burner, quantified. Considered are thermoacoustic vibrations in the 100 Hz range. Comparing a burner with conventional burner outlet according to the embodiment in Figure 1 (see polyline with squares interspersed) with an inventive trained burner outlet according to embodiment in Figure 3 (see figure interspersed with circles), it is clear that in the latter case a considerable lower proportion of thermoacoustic vibrations arises.
- 11
- Teilkörperpartial body
- 22
- Teilkörperpartial body
- 33
- tangentialer Verbrennungslufteintrittskanaltangential combustion air inlet channel
- 44
- BrennerachseBrenner
- 55
- Verbrennungsluftcombustion air
- 66
- Brennerhohlraumburner chamber
- 77
- Eindüsungsöffnungen für BrennstoffInjection openings for fuel
- 88th
- zentrale Brennstoffdüsecentral fuel nozzle
- 99
- Drallströmungswirl flow
- 1010
- Frontplattefront panel
- 1111
- KühlluftbohrungenCooling air holes
- 1212
- Brennraumcombustion chamber
- 1313
- Drallerzeuger, VormischstreckeSwirl generator, premixing line
- 1414
- Brennermündungburner mouth
- 1515
- Rückströmzonebackflow
- 1616
- Austrittsquerschnitt in den BrennraumOutlet cross section into the combustion chamber
- 1717
- Flammenfrontflame front
- 1818
- Strömungsquerschnitt des BrennerhohlraumsFlow cross-section of the burner cavity
- 1919
- stromaufwärtiger Bereich des Brennerhohlraumsupstream portion of the burner cavity
- 2020
- stromabwärtiger Bereich des Brennerhohlraumsdownstream portion of the burner cavity
- 2121
- Wand des BrennerhohlraumsWall of the burner cavity
- 2222
- Wandabschnittwall section
- 2323
- Innenkontur des BrennerhohlraumsInner contour of the burner cavity
- 2424
- Brennerdüseburner
- 2525
- Mischstreckemixing section
- 2626
- MischstreckengehäuseMixing section housing
- 2727
- Austrittskantetrailing edge
- 2828
- Einbauten fixtures
- 2929
- Strömungsquerschnitt in der MischstreckeFlow cross-section in the mixing section
- 3030
- Wand der MischstreckeWall of the mixed route
- 3131
- stromaufwärtiger Bereich der Mischstreckeupstream section of the mixing section
- 3232
- stromabwärtiger Bereich der Mischstreckedownstream section of the mixing section
- 3333
- Strömungsquerschnitt der BrennerdüseFlow cross-section of the burner nozzle
- 3434
- Wand der DüseWall of the nozzle
- 3535
- stromaufwärtiger Bereich der Düseupstream portion of the nozzle
- 3636
- stromabwärtiger Bereich der Düsedownstream portion of the nozzle
Claims (20)
- Method for increasing the fluidic stability of a premix burner, in which at least one combustion airstream is introduced tangentially into a burner cavity and is mixed with an injected gaseous and/or liquid fuel to form a swirling flow oriented coaxially with the burner axis, inducing a backflow zone, which serves to stabilize the flame when the burner is operating, at a sudden change in the cross section at the burner mouth, characterized in that the swirling flow within the burner cavity is increasingly deformed in the direction of the burner mouth and enters the combustion chamber in a cross section of flow that is not rotationally symmetrical, this deformation being produced at the expense of the free cross section of flow.
- Method according to Claim 1, characterized in that the deformation of the swirling flow is associated with an increase in the flow velocity.
- Method according to Claim 2, characterized in that the deformation is associated with a reduction in the free cross section of flow of the burner cavity.
- Method according to Claim 1, characterized in that the deformation is achieved in such a manner that at least one peripheral portion of the cavity wall has a lower pitch in a downstream region of the burner cavity than in an upstream region.
- Method according to Claim 1, characterized in that the deformed flow profile is symmetrical with respect to at least one axis.
- Method according to Claim 4, characterized in that the flow profile adopts the contour of a polygon.
- Method according to Claim 1, characterized in that it is used for the operation of lean premix burners of a gas turbine installation.
- Premix burner for use in a heat generator, substantially comprising a swirl generator (13) with means (3) for tangentially introducing a combustion airstream (5) into a cavity (6) of the swirl generator (13) and means (7; 8) for introducing at least one gaseous and/or liquid fuel into the combustion airstream (5) to form a swirling flow (9) with an axial movement component towards the burner mouth (14), characterized in that the cavity contour (21) in the direction of flow merges from a substantially rotationally symmetrical cross-sectional shape into a cross-sectional shape that is not rotationally symmetrical as a result of at least one portion (22) of the cavity wall (21), as seen over the periphery, adopting a smaller pitch in relation to the burner longitudinal axis (4) in a downstream end region (20) than in an upstream region (19), at the expense of the free cross section.
- Premix burner according to Claim 8, comprising at least two hollow, conically widening part-bodies, (1) and (2), which are nested inside one another coaxially with respect to the longitudinal axis (4), the centre axes of which run offset with respect to one another and the walls (21) of which, in an overlap region, form tangential inlet passages (3) for combustion air (5), and at least one fuel nozzle (8) within the cavity (6) formed by the part-bodies (1) and (2), characterized in that the flow-limiting wall (21) of at least one of the part-bodies (1) or (2), in a downstream end region (20), has at least one peripheral portion (22) which has a lower pitch in relation to the burner longitudinal axis (4) compared to an upstream region (19).
- Premix burner according to Claim 8 or 9, characterized in that a plurality of, preferably two to eight, portions (22) of this type exist over the periphery.
- Premix burner according to Claim 10, characterized in that the burner has a polygonal contour in an end region (20) including the burner mouth (14).
- Premix burner according to Claim 11, characterized in that the burner has the contour of a regular polygon.
- Premix burner according to Claim 11, characterized in that the burner has the contour of an irregular polygon.
- Premix burner according to Claim 9, characterized in that at least one of the part-bodies (1) or (2) has a convex outlet cross section (16) which deviates from the circular.
- Premix burner according to Claim 14, characterized by an at least approximately symmetrical outlet cross section (16).
- Premix burner according to Claim 8, characterized in that the flow-limiting wall (21) of the burner cavity (6) merges continuously or in one or more steps from one pitch to the other between the upstream region (19) and the downstream end region (20).
- Premix burner according to Claim 8, characterized in that the downstream end region (20) comprises approximately the final third of the length of the burner cavity (6).
- Premix burner according to Claim 8, characterized in that plates (28) which limit the free cross section of flow (18) are welded or secured in some other suitable way to the wall (21) in a downstream region (20) within the burner cavity (6).
- Premix burner according to Claim 8, comprising a swirl generator (13) with means (3) for tangentially introducing a combustion airstream (5) into a cavity (6) of the swirl generator (13) and means (7; 8) for introducing at least one gaseous and/or liquid fuel into the combustion airstream (5) so as to form a swirling flow (9) with an axial movement component towards the burner mouth (14), and a burner nozzle (24) at the combustion chamber end, characterized in that the free cross section of flow (33) of the nozzle (24) is reduced in the direction of flow, with a simultaneous transition from a substantially rotationally symmetrical cross-sectional shape into a cross-sectional shape that is not rotationally symmetrical as a result of at least one peripheral portion (22) of the nozzle wall (34) adopting a shorter distance from the nozzle longitudinal axis (4) in a downstream region (36) than in an upstream region (35).
- Premix burner, comprising at least two hollow, conically widening part-bodies, (1) and (2), which are nested inside one another coaxially to the longitudinal axis (4), the centre axes of which run offset with respect to one another and the walls (21) of which, in an overlap region, form tangential inlet passages (3) for combustion air (5), and at least one fuel nozzle (8) within the cavity (6) formed by the part-bodies (1) and (2), also comprising a mixing section (25) downstream of the swirl generator (13) formed by the part-bodies (1) and (2), which mixing section (25), within a first starting region, has transfer passages, running in the direction of flow, for the swirling flow (9) formed in the cavity (6) and opens out into the combustion chamber (12) at a detachment edge (27), characterized in that the free cross section of flow (29) of the mixing section (25) is reduced in the direction of flow, with a simultaneous transition from a substantially rotationally symmetrical cross-sectional shape into a cross-sectional shape that is not rotationally symmetrical as a result of at least one peripheral portion (22) of the wall (30) which delimits the mixing section being at a shorter distance from the nozzle longitudinal axis (4) in a downstream region (32) than in an upstream region (31).
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE10040869A DE10040869A1 (en) | 2000-08-21 | 2000-08-21 | Method and device for suppressing flow vortices within a fluid power machine |
DE10040869 | 2000-08-21 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1182398A1 EP1182398A1 (en) | 2002-02-27 |
EP1182398B1 true EP1182398B1 (en) | 2005-11-16 |
Family
ID=7653185
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP01120011A Expired - Lifetime EP1182398B1 (en) | 2000-08-21 | 2001-08-20 | Process for increasing the fluidic stability of a premix-burner as well as premix-burner for carrying out said process |
Country Status (4)
Country | Link |
---|---|
US (1) | US6599121B2 (en) |
EP (1) | EP1182398B1 (en) |
JP (1) | JP4819260B2 (en) |
DE (2) | DE10040869A1 (en) |
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-
2000
- 2000-08-21 DE DE10040869A patent/DE10040869A1/en not_active Withdrawn
-
2001
- 2001-08-20 EP EP01120011A patent/EP1182398B1/en not_active Expired - Lifetime
- 2001-08-20 US US09/932,094 patent/US6599121B2/en not_active Expired - Lifetime
- 2001-08-20 DE DE50108063T patent/DE50108063D1/en not_active Expired - Lifetime
- 2001-08-21 JP JP2001250830A patent/JP4819260B2/en not_active Expired - Fee Related
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US6599121B2 (en) | 2003-07-29 |
US20020026796A1 (en) | 2002-03-07 |
JP4819260B2 (en) | 2011-11-24 |
EP1182398A1 (en) | 2002-02-27 |
DE50108063D1 (en) | 2005-12-22 |
JP2002130676A (en) | 2002-05-09 |
DE10040869A1 (en) | 2002-03-07 |
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