EP2144000B1 - Burner device - Google Patents

Description

The invention relates to a combustion device having at least one burner, which has a substantially rectangular inlet and a substantially circular mixing tube. Such a combustion device is off US 4,383,820 A known.

In EP 0 463 218 B1 a burner is described which has an inlet with coaxial inlets for fuel and air. The burner inlet is followed by a mixing section in which fuel and air mix before the mixture enters a combustion chamber. Fuel and air have such a flow impulse that combustion takes place only in the combustion chamber.

In the patent application DE 10 2007 036 953 (not prepublished) is described a burner in which the inlet has a substantially rectangular cross section, wherein two parallel walls define a clear width. The mixing section forms a round channel whose width is greater than the clear width between the parallel walls, so that in the flow direction widening transition stages are formed. At the transition stages, crossflows are created which enhance the mixing process by increasing turbulent diffuse transport and inducing convective secondary transport. The combustion air is transferred from a rectangular channel into a channel with a round cross-section. The maximum fuel concentration at the outlet of the mixing section becomes small and the distribution of the fuel over the cross section of the mixing channel is improved. The result is a reduction of thermal nitrogen oxide formation.

In DE 689 23 413 T2 For example, there is described a gas turbine fuel air premixer having a dual cylinder structure of an inner cylinder and an outer cylinder. Between the two cylinders are flow paths, are introduced into the fuel and air, whereby in the flow paths, a fuel-air mixture is formed. Nozzles for injecting the fuel into the flow paths are arranged eccentrically to a longitudinal center plane of the flow path. These nozzles can be controlled independently.

The invention has for its object to provide a combustion device with improved mixing of fuel and air, in which the composition of the mixture of fuel and air, ie the air ratio, is variable, on the one hand to keep the NO emission low and on the other a extinction to avoid the flame.

The combustion device according to the invention is defined by the patent claim 1. It is generally designed in the same way as in US 4,383,820 A However, it differs from this by the characterizing features of claim 1.

In the said earlier patent application it was stated that the degree of mixing in the outlet of the burner nozzle has a significant influence on the subsequent combustion processes in the combustion chamber. This applies in particular with regard to the formation of nitrogen oxide (NO _x ), which in turn is largely determined by the local combustion temperature (Zeldovich or thermal NO). The goal of the best possible reduction of nitrogen oxide emissions can be achieved by keeping the combustion temperature as low as possible by appropriate control of the mixing and combustion processes. In the case of gas turbine combustors, the combustion temperature is regulated by an excess of combustion air through the burner. The relevant characteristic here is the air ratio λ, formed from the molar ratio of air to fuel, based on the stoichiometric composition (λ = 1). For example, for double excess air, λ = 2. In the burner itself, fuel and air are brought together and initially stoichiometric areas are formed even with high excess air. The mixing behavior of a burner can now be characterized by the extent to which occurring λ inhomogeneities in the burner are reduced before entering the combustion chamber. In the best case one obtains a homogeneous profile with the λ-value of the assigned global mixture. The corresponding adiabatic combustion temperature of the global mixture may thus be considered as the lower limit of the optimum maximum combustion temperature to be achieved, provided there is no additional heat extraction. The degree of approximation to this ideal state characterizes the quality of mixing of a burner. This concept was successful for a thermal output of approx. 800 kW with a λ value of 1.6 and an associated power density of approx. 13.6 MW / (m ² bar) based on the surface of the combustion chamber head plate) can be realized on the test bench.

In the present invention, the problem of power modulation is now addressed over the widest possible λ range by fuel variation at a constant air mass flow. The lower λ limit is determined by the maximum tolerable NO emission and thus by the maximum flame temperature. For λ = 1.6, the NO emission is about 10 ppm (based on 15% O ₂ in the combustion chamber outlet). The associated adiabatic flame temperature of the global mixture is approximately 2000 K. At lower λ values, there is a drastic increase in NO emission and CO emissions (equilibrium). It turns out, therefore, that in the low λ range, ie in the full load range, the mixture is extremely important. Furthermore, it seems plausible that when λ is increased, ie when the mixture is lean, the flame will eventually go out. The approach to flame extinction is usually announced by an extremely strong increase in CO emission. This extinction limit, which is defined in this way, is dependent on the particular power density considered under otherwise identical operating conditions. While in the above case the power density of 13.6 MW / (m ² bar) (at λ = 1.6) the quenching limit is already reached at about λ = 1.8, this is almost for a smaller power density of 3.2 MW / (m ² bar) λ 3.0 =. The invention shows one way in which the quenching limit can be shifted upwards even for very high power densities and thus a very broad power modulation can be effected.

As the global λ value increases, in the dependency described above, the ignition delay times increase to such an extent that premature flame extinction occurs. If you like, in this case the mix is "too good". This effect can be counteracted by displacing the fuel lance eccentrically to the mixing tube axis in the direction of the combustion chamber axis. This will be the maximum local Fuel concentration increases and the flame extinguishes only at a correspondingly higher λ. The disadvantage is that in the case of a main load (λ = 1.6) the maximum flame temperature also rises and thus also the thermal NO production. One aspect of the present invention is to combine the respective advantages of centric and eccentric positioning of the fuel input by adding a second fuel lance. Both lances can be supplied with fuel independently of each other via separate supply systems. The distance of the lances from each other and also their radial position with respect to the combustion chamber axis can be varied within a certain range and can each be adapted to specific design requirements. Numerical simulations show that for each operating point, that is to say for each λ, a specific value of the fuel split exists on both lances, which causes a minimum of pollutant emissions during combustion. Another important aspect is that due to suitable fuel staging possibly occurring flame instabilities can be almost completely prevented.

By the invention it is achieved that transverse flows are initiated at the transition stages, by which the mixing process is greatly improved by increasing the turbulent transport and the induction of a convective secondary transport. This is achieved by the combustion air is transferred from a rectangular channel into a channel with a round cross-section. Rectangular channel and round channel are "inline", ie arranged on the same burner axis and form on their transition surface two mutually parallel stages (transition stages). The result is a convective-diffusive transport of the fuel-air mixture and a strong and uniform spread of the fuel in the radial direction. The maximum fuel concentration at the outlet of the mixing section is thus low and the distribution of the fuel over the cross section of the mixing channel is improved. The result is a reduction of thermal nitrogen oxide formation. The transition stages between square and round cross-section cause the induction of four Secondary vortices, each rotating about a parallel to the burner axis, but radially offset, extending vortex axis. The rotations of adjacent secondary vortices have opposite directions of rotation.

The invention is particularly suitable for a combustion device for gas turbines, in which a plurality of burners are arranged in a ring and open into a common combustion chamber.

In the following, embodiments of the invention will be explained in more detail with reference to the drawings.

Figur 1

eine Stirnansicht und eine Seitenansicht eines Brenners mit rechteckiger Mischstrecke und rundem Mischrohr, wobei zwei Brennstofflanzen exzentrisch angeordnet sind,

Figur 2

in gleicher Darstellung wie Figur 1 eine Ausführungsform, bei der eine Brennstofflanze zentrisch und eine andere Brennstofflanze exzentrisch angeordnet ist,

Figur 3

eine Darstellung einer Brennkammer mit mehreren ringförmig angeordneten Brennern, wobei die Positionen der Brennstofflanzen erkennbar sind und

Figur 4

das Prinzip eines modulierenden Brenners mit unterschiedlichen Brennstoffzufuhren zu den beiden Brennstofflanzen.

Show it:

FIG. 1

an end view and a side view of a burner with rectangular mixing section and round mixing tube, wherein two fuel lances are arranged eccentrically,

FIG. 2

in the same representation as FIG. 1 an embodiment in which one fuel lance is arranged centrically and another fuel lance is arranged eccentrically,

FIG. 3

a representation of a combustion chamber with a plurality of annularly arranged burners, wherein the positions of the fuel lances are recognizable and

FIG. 4

the principle of a modulating burner with different fuel supplies to the two fuel lances.

In FIG. 1 a burner 10 is shown, which has a rectangular inlet 11 and subsequently a round mixing tube 12. Between inlet 11 and mixing tube 12 there is a transition 13. The inlet 11 is rectangular Cross-section. It has two parallel longitudinal walls 14,15, between which the center longitudinal plane 16 is defined. The two longitudinal walls are connected by transverse walls 17,18. The diameter of the mixing tube 12 is greater than the transverse extent of the inlet 11, but smaller than the longitudinal extent.

According to FIG. 1 run through the inlet 11 two fuel lances L1, L2. Each of the fuel lances consists of a tube through which fuel can be supplied. The fuel lances L1, L2 each have an inlet 20 and an outlet 21, which opens into the mixing tube 12. Around the fuel lances is an air passage 22 having an inlet 27.

According to FIG. 1 are the two lances L1, L2 arranged at a distance from the longitudinal center plane 16, that is "eccentric". The two fuel lances are provided symmetrically to the longitudinal central axis.

In the embodiment of FIG. 2 is the fuel lance L1 arranged centrally, ie with its axis in the longitudinal center plane 16. The fuel lance L2 is arranged eccentrically, ie at a distance from the longitudinal center plane 16th

FIG. 3 shows an annular burner system as used in stationary gas turbines. Numerous burners 10 of the type described are arranged in a ring shape and open into a common combustion chamber 23. The combustion chamber is round here and has a combustion chamber axis 24. The enemas 11 of the burner 10 are not exactly rectangular here. Instead, they form a ring and are therefore bent about the axis 24. In FIG. 3 are also the mixing tubes 12 shown, which open into the combustion chamber 23. The flames arise in the flow direction behind the mixing tubes 12 in the combustion chamber 23.

According to FIG. 3 Each inlet 11 contains two fuel lances L1, L2 arranged in the same way as in FIG FIG. 1 ,

FIG. 4 shows different operating conditions of a burner 10, the two fuel lances according to FIG. 1 Is provided. The supply of fuel to the fuel lances L1, L2 is each separately controllable. The arrows F1 and F2 denote the fuel supply to the fuel lances and the arrow S indicates the air supply. In FIG. 4 the distribution of the gaseous fuel is plotted on a longitudinal section plane through the burner axis and the combustion chamber axis 24. By proportionally different loading of the two fuel lances can be continuously change the formation and position of the flame front 25. The resulting in the combustion chamber 23 recirculation flow 26 is heated by heat release in the flame front 25 to the extent that the entering into the combustion chamber fuel / air mixture undergoes sufficient preheating. This reduces the ignition delay time and prevents the flame from extinguishing.

In FIG. 4 Figure 11 shows the diagram a) the condition that the outer fuel lance L1 is charged with 100% of the fuel quantity while the inner fuel lance L2 is blocked. The representation b) shows a ratio of 50:50 and the representation c) a ratio of 0: 100. For example, CH _{4 is} used as the fuel. It can be seen that the flame front 25 can be changed by changing the fuel components. This reduces the ignition delay time and prevents the flame from extinguishing. In this way, the flame temperature for each λ can be adjusted so that the flame is not extinguished and at the same time the lowest possible NO production takes place. Particular attention should be paid to the fact that when approaching the extinction limit an extremely strong increase in CO production, in contrast to NO production, sets in and the burnout is no longer complete.

In a simulation example, it has been found that the NO emission in the entire power range is below 10 ppm (based on 15% O ₂ ) and assumes a minimum value of 2.7 ppm at λ = 2.4. Newer simulations with the eccentric arrangement of FIG. 2 indicate that the modulation range can be extended beyond λ = 3.0. Overall, it follows that with the burner according to the invention, the combustion can be classified as very low in pollutants.

Claims (4)

1. A burner device comprising at least one burner (10) including a substantially rectangular intake (11) having two parallel longitudinal walls (14,15) and two parallel transverse walls (17,18), and comprising inlets (20,27) for fuel and air, and at least one fuel lance (L1,L2) extending through the intake (11), said intake (11) being followed by a transition section (13) to a round mixing tube (12) whose axis is arranged on the longitudinal central plane of the intake (11),
   characterized in that said at least one fuel lance (L1,L2) is arranged eccentrically relative to the longitudinal central plane (16) of the intake (11) and that the diameter of the mixing tube (12) is larger than the distance of the longitudinal walls (14,15) of the intake and smaller than the distance of the transverse walls (17,18).
2. The burner device according to claim 1, characterized in that at least two fuel lances (L1,L2) are provided, at least one of them being arranged eccentrically.
3. The burner device according to claim 2, characterized in that the fuel lances (L1,L2) can be supplied with fuel in a controlled manner independently from each other.
4. The burner device according to any one of claims 1-3, characterized in that a plurality of burners (10) are arranged in a ring-shaped configuration and enter a common burning chamber (23) and that, in each burner (10), a fuel lance is arranged at an offset from the longitudinal central plane of the associated intake (11) toward the longitudinal axis (24) of the burning chamber (23).

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