EP0851990B1 - Burner, in particular for a gas turbine - Google Patents

Description

The invention relates to a burner with one axis and one with respect to this rotationally symmetrical arrangement of one Outer jacket and a coaxial inner jacket, which an annular gap extending from an entry to an exit for carrying a stream of an oxygen-containing Gases defined, with a plurality of arranged in the annular gap Nozzles for supplying a fuel and a swirl grid arranged in the annular gap.

The invention particularly relates to such Burners for use in a gas turbine.

Such a burner can be found in EP 0 193 838 B1 and the article "An economical solution to the NO _x problem in gas turbines" by H. Maghon, VGB Kraftwerkstechnik 68 (1988), 799. A development of this burner is shown in WO 92/19913 A1.

In this context, EP 0 589 520 A1 and US Patents 5 165 241, 5 251 447, 5 323 604 and 5 351 477 are also of interest. Reference should also be made to the article "Dry Low NO _x -Combustion Systems for GE Heavy-Duty Gas Turbines "by LB Davis, brochure GER-3568C of GE Industrial and Power Systems, Schenectady, NY, USA. All of these documents show burners or combustion parts with burners for use in gas turbines.

Relevant teachings of flow mechanics, which are in the present Context of importance is pointed out on the book "Ventilatoren" by B. Eck, 5th edition, Springer-Verlag Berlin, Heidelberg and New York 1972, Chapter C, pages 283 to 285, as well as the book "Axialkompressoren" by J.H. Horlock, Verlag G. Braun, Karlsruhe 1967, DE, supplement 4.

Both books concern fans, especially fans of the axial type, which are identified by a rotating swirl grid, which a stream of a gas in Form of a swirl-free stream sucked along an axis and in the form of a swirled, accelerated current emits along the axis. With a burner the described Art there is a fixed swirl grille, which of one otherwise accelerated, swirl-free current flows and of which this current with a twist and a certain Pressure loss is released. The configuration of the burner resembles the configuration of one in many ways Fan, and essential theoretical foundations of a Fans can be used immediately. Really important is an effect in the present case that has anything to do with a swirl moving current along an axis Gases and regardless of how this electricity is provided was occurs. This effect is the formation of a Vortex core inside the stream, d. that is, one with one Swirl of moving current tends to become one To form a circular ring so that in a surrounding the axis Central area of a cylindrical tube in which the current is no longer flowing in the direction of the current takes place.

The flow of a gas through a largely arbitrary Arrangement of limits, in particular by a burner, can be calculated using numerical mathematics, for what Corresponding computer programs are now commercially available become. Such computer programs are relevant known to migrant and active persons under the names TASCFLOW and FLUENT.

A burner of the type mentioned in the introduction generally has the purpose of a fuel safely and low in pollutants in one Stream of an oxygen-containing gas, especially in compressed air to burn. To avoid education of pollutants like nitrogen oxides and carbon monoxide premix combustion proved to be favorable; first of all a homogeneous mixture of fuel and oxygen-containing gas is formed, and only this mixture ignited. There is generally the possibility of such a mixture the premature inflammation, especially among the Conditions that can be expected in a gas turbine and especially when a relatively flammable Fuel or one with a high flame speed should be used. Fuels of this type are e.g. B. gases, which contain elemental hydrogen, for example Gases obtained from coal gasification and natural gases, the high proportions of longer chain hydrocarbons, whose ignition temperatures are significantly lower than that Ignition temperature of methane.

In a burner in which such premix combustion is realized what is described in some of the documents cited is, in particular in EP 0 193 838 B1 and the WO 92/19913 A1, further problems may arise if the The burner is not ideally flowed and the mixture of the oxygen-containing gas deteriorates with the fuel. In such a case, combustion results the mixture has an inhomogeneous temperature distribution and accordingly an increased production of nitrogen oxides; moreover, an inhomogeneous mixture favors premature mixing Inflammation. These considerations are a realization premix combustion in a gas turbine in which a highly flammable fuel should be burned, quite opposite. They also show that premix combustion, as it has so far been realized, not without problems was, especially because of premature inflammation a mixture of fuel and oxygenated Gas relatively easily does great damage to an affected person Can cause burners. A widespread method of Preventing a flashback is a narrowing of the Burner outlet and thus an acceleration of the fuel gas at the exit. In the event of a flashback however, the flame can penetrate far into the burner.

It is therefore the object of the invention to provide a burner which is designed so that if possible none Irregularities in the current flowing through it train oxygen-containing gas and thus the risk of avoided premature ignition of fuel in the stream is.

To solve this problem, a burner is specified with a Axis and one with respect to this rotationally symmetrical Arrangement of an outer jacket and an inner jacket coaxial therewith, which one from entry to exit reaching annular gap for guiding a flow of oxygen containing gas defined, with a variety of in the annular gap arranged nozzles for supplying a fuel to the stream and one arranged in the annular gap Swirl grille, the arrangement consisting of the outer jacket and the inner jacket is designed so that the current Annular gap between the swirl grille and the outlet with a essentially constant meridional speed flows through.

The characteristic of the "essentially constant meridional speed" means that the current to flow through Arranging the current a substantially constant meridional flow cross section must oppose. This In many cases, however, the flow cross-section is not, for example perpendicular to an axis of symmetry of the flow Structure, but according to the Current descriptive vector field at an angle to the axis of symmetry and be dimensioned transversely to the vector field.

In this context, a simple calculation model provides which does not have to explicitly take the current into account, one good approximation to determine the flow cross section along the arrangement to be flowed through: into the arrangement Tori inscribed, which covers both the surface of the The outer jacket and the surface of the inner jacket tangentially touch. The points are at which such Torus touches the outer jacket or the inner jacket a circle on the outer jacket or a circle on the inner jacket. One is clamped between these two circles Truncated cone surface; this has an area, which in a good approximation of the effective flow cross-section at the location of the Corresponds to the truncated cone.

Computer programs are also available on a commercial basis With which flows through practically any shape Arrangements are predictable. The relevantly experienced and working people are, for example, the computer programs TASCFLOW and FLUENT known. Preferably a such a computer program used to use one of the simple calculation model described above Optimize structure. Noted on the present case be that this due to the existing rotational symmetry basically treatable in the context of a two-dimensional model is; there are of course no fundamental ones Objections, the present case with a three-dimensional Treat model.

The invention is based on the knowledge that the guarantee a constant meridional speed for the Current behind the swirl grid, i.e. H. ensuring one constant rate of propagation of the current along the axis or in a radial-axial with respect to the axis Level, stabilizing itself in a special way on the current and the mixture of oxygen to be formed in this stream containing gas and the fuel affects. In particular This measure ensures that disruptions due to non-ideal flow to the burner can be suppressed. A necessary pressure drop across the burner has to set, is to a large extent between the Entry and the swirl grille dismantled. That is also the danger prevents disturbances in the Electricity arise.

In the context of a preferred further development of the burner the arrangement of the outer jacket and the inner jacket in such a way designed that the annular gap between the entrance and the swirl grid narrowed. For this purpose, the outer jacket is particularly important designed in such a way that at the entrance Lip or a rounded funnel opens; the inner jacket is at the entrance especially with a rounded Edge. This contributes to homogenization of the current passing through the burner and avoids that disturbances that formed in the stream in front of the burner have to continue into the burner.

It is also preferred that those arranged in the annular gap Nozzles for supplying a fuel are arranged in the swirl grille are. For this purpose, there is in particular the swirl grid from hollow guide vanes in which the nozzles are arranged. In this way, a particularly homogeneous interference of the Fuel in the stream can be achieved during the Combustion even temperature distribution in the Guaranteed electricity and thus the excessive emergence of Effectively prevents nitrogen oxides.

With particular preference, the burner is designed such that one of the swirl grille, a radius of the outer jacket and a radius of the inner jacket to determine both radii on Exit, defined swirl number, which can be calculated as Quotient between an angular momentum as dividend and one Product of a meridional impulse and the radius of the Outer jacket as a divisor, with the angular momentum and the meridional Impulse characterize the current at the outlet, if which flows towards the entrance without swirl, is smaller than one critical swirl number, which is determined by the radii. The requirement that the corresponding design of the burner is known as the "hub criterion of Strscheletzky ".

First of all, it should be noted that the swirl number is off characteristic quantities of the current, namely the size of a meridional component of its momentum as well as its size its angular momentum, which is essentially from the swirl grid is determined, it can be calculated that the swirl number is nevertheless a characteristic parameter of the burner itself is. This results from the fluid mechanics similarity relationships.

The term "critical swirl number" has been coined on based on the observation that located near the axis a current moving with a swirl along the axis forms a so-called vortex core, d. H. an area, from which the current is essentially displaced. root cause centrifugal forces are one example. The diameter this vortex core is amenable to calculation; please refer the books cited. Basically, the diameter increases of the vortex core with increasing swirl number. Should be now the current move in a circular ring which defines is by the radius of the outer jacket of the burner as the outer radius and the radius of the inner jacket as the inner radius, so can only ensure that the flow against the inner jacket be if the to the given outer radius and the given swirl radius of the vortex core is smaller than the inner radius. Is the radius of the vortex core larger than the inner radius, it means that there is too a detachment of the flow from the inner jacket with which immediately apparent risk that it flows back into the burner and into one considerable risk of premature ignition of the fuel in the stream comes. The critical swirl number is in this Context defined as the twist number at which the radius of the vortex core of the current exactly the inner radius, d. H. corresponds to the radius of the inner jacket.

The swirl number of the burner defined as explained is preferred chosen significantly smaller than the critical swirl number; in particular, the number of swirls of the burner is between 75% and 97% of the critical swirl number and lies particularly preferably at about 90% of the critical swirl number. Hereby is between the actual geometry of the burner and a certain of a geometry to be regarded as "critical" Safety distance and thus a quantitative one Security against separation of the flow from the inner jacket given.

The burner of any configuration is preferably provided with a pilot burner. This pilot burner comprises in particular a pilot burner arranged in the inner jacket, which delivers a small, stable burning flame where the mixture formed in the burner itself ignite from oxygen-containing gas and fuel can. This is important when regulating the fuel supply and thus a regulation of heat production the burner is desired. It has been shown that premix combustion without stabilization only in one relative narrow operating range, characterized by a relative exact chemical composition, stable is. Will, however, with an appropriate pilot burner provided additional stabilization, one can important extension of the operating area for practical operation can be achieved.

The burner is particularly qualified for use in a Combustion device of a gas turbine and is in particular qualified for a gas turbine that is relatively flammable Fuels are to be burned. The burner is by no means limited to the combustion of gaseous Fuels; in principle, the burner can be in the appropriate Design with any flowable fuel, especially operated with heating oil and the like become.

In FIG 1

einen Längsschnitt durch einen Brenner;

in FIG 2

ein Schema einer Gasturbine

An embodiment of the invention can be seen from the drawing. This shows:

In FIG. 1

a longitudinal section through a burner;

in FIG. 2

a schematic of a gas turbine

The burner shown in FIG. 1 is with respect to axis 1 rotationally symmetrical. It has an outer jacket 2 and one too this coaxial inner jacket 3. Neither the outer jacket 2 nor the inner jacket 3 must each be made in one piece; it is very possible and, for example, for the sake of rational production, advantageous, the outer jacket 2 and / or the inner jacket 3, as shown, from several parts put together. Define the outer jacket 2 and the inner jacket 3 an annular gap 4, which from an inlet 5 to an outlet 6 from a stream 7 (represented by arrows) an oxygen-containing gas is flowed through. in the An annular swirl 8 is arranged, consisting of a plurality of guide vanes 8, which one of the stream 7 Swirl imprints; this means that the stream 7 behind the Swirl grid 8 makes a helical movement about axis 1 executes. So he doesn't just have velocity vectors, those in radial-axial with respect to axis 1 Layers lie and accordingly according to the professional Terminology is meridional; the speed vectors have components behind the swirl grille 8, the tangential to axis 1 or to circles, their centers lie on axis 1 and lie in planes, which are oriented perpendicular to axis 1 are. Such tangential components can be according to the relevant terminology also referred to as "peripheral components become.

The guide vanes 8 have nozzles 9 through which the Stream 7 is supplied with a fuel, in particular a combustible gas becomes. This initially mixes with the electricity without ignition, and the mixture formed ignites only in the area of the exit 6. The is accordingly Burner a premix burner.

An essential feature of the burner is that the arrangement designed in such a way from the outer jacket 2 and the inner jacket 3 is that the current 7 the annular gap 4 between the swirl grid 8 and the outlet 6 with a substantially constant meridional Speed flows through. This means that stream 7 in its direction of propagation, i.e. H. in a with respect to axis 1 meridional direction, no acceleration or experience delay. This requires a careful design, in particular of the outer casing 2 and the inner shell 3, since it may be desirable and in the illustrated Example is realized that the current 7 itself not just moved parallel to axis 1, but a part executes a movement directed radially inwards to axis 1. This inward movement must be balanced by an appropriate extension of the respective distance between the outer jacket 2 and the inner jacket 3; This is clearly recognizable from the drawing.

In front of the swirl grid 8, the annular gap 4 narrows significantly; this narrowing results mainly from the fact that the Stream 7 is partly led radially inwards to axis 1, so that it is sufficient between the outer jacket 2 and the inner jacket 3 Maintain a largely constant distance. The outer jacket 2 is supportive in the area of the entrance 5 expanded approximately like a funnel, so that it becomes 5 opens like a rounded funnel or lip, and the inner jacket 3 has a rounded at the inlet 5 Edge 10.

On the nozzles 9, which serve to deliver the fuel, has already been pointed out. These nozzles 9 are in the guide vanes 8 arranged, thus a particularly homogeneous interference to ensure the fuel in stream 7 without detaching the flow from the guide vanes 8 is coming. The fuel is supplied to the nozzles 9 through a fuel line 11 and an annular one and arranged on the inside of the inner jacket 3 fuel distribution space 12. From this fuel distribution room 12 Fuel through channels (not shown) in the inner jacket 3 and the guide vanes 8 flow to the nozzles 9.

The geometry of the arrangement of the swirl grille 8, the outer jacket 2 and the inner jacket 3 is, as already detailed above explained, chosen such that a swirl number, which essential indicators of the current 7 determines if this in meridional direction at the entry 5 in the ring channel 4, is smaller than a critical swirl number, which is results from the radius of the outer jacket 2 and the radius of the Inner jacket 3 at the outlet 6. The critical swirl number is defined in such a way that a cylindrical flow through along a channel with the stated radius of the outer jacket 2 the axis 1 flows, forms a vortex core, so a area surrounding axis 1 from which the current displaces which has a radius that is the radius of the inner jacket 3 at outlet 6 corresponds. If the current in the Annular gap 4 has a swirl number that is the critical swirl number exceeds, this means that at the outlet 6 in this flow forms a vortex core that has a larger radius has as the inner jacket 3 in the area of the outlet 6. In in such a case the stream 7 could be in the area of the outlet 6 should no longer rest on the inner jacket 3, but should detach from this. But then would have to on the inner coat 3 form a backflow area, in which gas into the ring channel 4 could flow back. This would be a significant one Risk of premature ignition of the combustible mixture connected to stream 7. The burner is accordingly designed that this danger is excluded.

The geometric structure of the burner has been worked out with the help of common mathematical models. there initially uses the simple calculation model described above found in the between the outer jacket 2 and the inner jacket 3 Tori are inscribed, with the help of approximate values intended for the flow cross sections in the arrangement become. The default for defining the structure is in that the flow cross sections over the entire relevant ring channel 4 must be constant. With the help The structure of the simple calculation model was then developed using the commercially available computer program TASCFLOW regarding the desired consistency of the flow cross section optimized via the ring channel 4.

The inflammable mixture is ignited in stream 7 outside the burner. A pilot burner is provided for this 13 with one inside the inner jacket 3 arranged pilot burner 13. This delivers a small one Flame, which ensures that the combustible mixture ignited in the stream 7. A flame on the pilot burner 13 to ignite and maintain is an igniter 14 intended. In the event that from a special pilot burner 13, 14 is taken for granted a modified igniter to ignite the mixture to provide.

2 shows a schematic illustration of a gas turbine with a compressor part 15 for suction and compression of Air, a combustion part 16, to which the compressed air is supplied which is also the one intended for combustion Receives fuel, and a turbine part 17, in which the of the compressor part 15 and compressed in the combustion part 16 additional heated electricity with submission of mechanical work is relaxed. The burner shown in FIG 1 is provided for installation in a combustion part 16 together with a A number of similar burners.

The burner according to the invention is characterized by features with which a current passing through the burner Gases in a particularly favorable manner for the intended purpose being affected. The burner is characterized by a particularly stable operation and particularly avoids operational Disturbances due to non-ideal inflow or through flashbacks.

Claims (12)

1. Burner with an axis (1) and with an arrangement rotationally symmetrical relative to the latter and consisting of an outer casing (2) and of an inner casing (3) coaxial thereto, the said arrangement defining an annular gap (4) extending from an inlet (5) to an outlet (6) and intended for guiding a stream (7) of oxygen-containing gas, with a multiplicity of nozzles (9) arranged in the annular gap (4) and intended for supplying a fuel to the stream (7) and with a swirl lattice (8) arranged in the annular gap (4), characterized in that the arrangement consisting of the outer casing (2) and of the inner casing (3) is designed in such a way that the stream (7) flows through the annular gap (4) between the swirl lattice (8) and the outlet (6) at an essentially constant meridional velocity.
2. Burner according to Claim 1, in which the arrangement consisting of the outer casing (2) and of the inner casing (3) is designed in such a way that the annular gap (4) narrows between the inlet (5) and the swirl lattice (8).
3. Burner according to Claim 2, in which the outer casing (2) opens at the inlet (5) in the manner of a lip.
4. Burner according to Claim 2 or 3, in which the inner casing (3) has a rounded edge (10) at the inlet (5).
5. Burner according to one of the preceding claims, in which the nozzles (9) are arranged in the swirl lattice (8).
6. Burner according to Claim 5, in which the swirl lattice (8) consists of guide blades (8) and the nozzles (9) are arranged in the guide blades (8).
7. Burner according to one of the preceding claims, in which a) the swirl lattice (8), a radius of the outer casing (2) and a radius of the inner casing (3), the said radii being determined at the outlet (6), define a swirl coefficient which is a quotient between a moment of momentum as the dividend and a product of a meridional momentum and the radius of the outer casing (2) as the divisor, the moment of momentum and the meridional momentum characterizing the stream (7) at the outlet (6) when the latter flows to the inlet (5) without a swirl; b) the swirl coefficient is lower than a critical swirl coefficient which is determined by the radii.
8. Burner according to Claim 7, in which the swirl coefficient is between 75 % and 97 % of the critical swirl coefficient.
9. Burner according to Claim 8, in which the swirl coefficient is approximately 90 % of the critical swirl coefficient.
10. Burner according to one of the preceding claims, which has a pilot-burning device (13, 14).
11. Burner according to Claim 10, in which the pilot-burning device (13, 14) comprises a pilot burner (13) arranged in the inner casing (3).
12. Burner according to the preceding claims, which is used in a combustion part (16) of a gas turbine (15, 16, 17).

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