US20150316266A1

US20150316266A1 - Burner with adjustable radial fuel profile

Info

Publication number: US20150316266A1
Application number: US14/265,584
Authority: US
Inventors: Bernd Prade; Mariano Cano Wolff; Boris Ferdinand Kock; Jürgen Meisl; Andreas Diebels; William R. Ryan
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2014-04-30
Filing date: 2014-04-30
Publication date: 2015-11-05
Also published as: WO2015165680A1

Abstract

A burner (1) with a longitudinal burner axis (2) and a mixing channel (3, 4), formed in an annular manner around the longitudinal burner axis (2), for the mixing of fuel and air. Each mixing channel is bounded radially on the inside by a channel hub (5, 6) and radially on the outside by a channel outer wall (7, 8). A fuel concentration distribution in the mixing channel (3, 4) from the channel hub (5, 6) to the channel outer wall (7, 8) being adjustable by adjusting the introduction of fuel to provide an adjustable fuel concentration distribution at respective radial locations across each mixing claimed. Also a combustion system (20) with a burner (1) and to a method for operating a burner (1).

Description

TECHNICAL FIELD

The invention relates to a burner with a radially adjustable fuel profile. The invention also relates to a combustion system with such a burner and to a method for operating such a burner.

TECHNICAL BACKGROUND

The operation of gas turbines is influenced more and more frequently by changing boundary conditions. Apart from the usual changes, such as ambient conditions, these changing conditions also take the form of increasingly greater and more frequent load changes, including sometimes sustained operation under partial load, as well as a varying gas composition, i.e. a varying calorific value or Wobbe index.
Since gas turbines, and in particular also the combustion system, often used to be designed in particular for the rated power output, increasing ‘off-design’ operation sometimes has side effects that may lead to operational restrictions.
For example, in certain power output ranges that have previously not been used on a sustained basis, combustion oscillations or increased pollutant emissions occur, possibly restricting sustained operation in those cases. A change of the fuel composition also leads to disturbances, such as for example combustion oscillations, increased emissions and thermal loading of components.
In the system-specific fine-tuning of parameters (tuning), adjustments that are dependent on the ambient conditions and are sometimes complex, e.g. of the amount of pilot gas, the inlet guide vane (IGV) positioning, and consequently the exhaust gas temperature, are respectively provided in different power output ranges, possibly even differently for subjecting the gas turbine to loading and relieving the gas turbine of loading. This may under some circumstances require that, when there are changing operating requirements, a readjustment of control parameters must be made. The exhaust gas emissions may possibly not be adjusted as desired.
EP 1 394 471 A1 discloses a burner with a fuel concentration distribution that is not constant in a plane perpendicular to the direction of flow of the fuel, in particular changes in the radial direction, in order to avoid combustion instabilities during operation of the burner.
A disadvantage of this is that, when there is a change in concentration, the fuel mass flow as a whole is also changed, and the relative concentration at the fuel jets involved remains substantially the same.

SUMMARY OF THE INVENTION

The object of the invention is therefore to provide a burner, a combustion system and a method for operating a burner with which the best possible tuning of the fuel injection can be performed.
This object is achieved by the burner, the combustion system and the method according to the invention. The following is achieved in the case of a burner with a longitudinal burner axis and a mixing channel, which is formed in an annular manner around the longitudinal burner axis, for the mixing of fuel and air, and which is bounded radially on the inside by a channel hub and radially on the outside by a channel outer wall, wherein a fuel concentration distribution in the mixing channel from the channel hub to the channel outer wall is adjustable.
The fuel profile, and consequently the flame geometry, can be adapted to the operational requirements during the operation of the fuel profile. Neutral adjustment of the fuel flows, i.e. a uniform distribution of the fuel from the channel hub to the channel outer wall, produces a homogeneous field, which is preferred for low fuel emissions, with a high power output, in the case of a high part load, for example, a profile with fuel reduction in the middle of the channel. Depending on the form of the flame, and consequently on the delay time distribution of the fuel/air mixture up to the reaction zone, the strength of the feedback of thermoacoustic oscillations to the flow of the fuel/air mixture can consequently be changed.
“Radially” is understood here as meaning a direction from the channel hub to the channel outer wall in the plane perpendicular to the direction of flow of the fuel/air mixture. If the mixing channel formed in an annular manner around the longitudinal burner axis is conical, then “radially” is not understood as meaning strictly mathematically perpendicular to the longitudinal axis of the burner, but an appropriate inclination is assumed.
In an advantageous embodiment of the invention, the burner comprises a burner stage with two distributing systems, first fuel jets of a first distributing system being arranged substantially radially on the inside and/or radially on the outside in the mixing channel and second fuel jets of a second distributing system being arranged substantially radially in the middle in the mixing channel.
By increasing or reducing the fuel of one distributing system as a proportion of the total amount of fuel in the mixing channel, it is possible in the case of this embodiment to adjust a fuel/air profile in the radial middle of the channel that can be freely changed from lean in fuel to rich in fuel (with respect to the integral mean value of the fuel/air mixture).
The radial positioning (and number) of the freely activatable distributing systems may be chosen according to expediency.
This allows the radial position of the minimum or maximum fuel concentration to be varied, there being the possibility in particular of achieving a local maximum or minimum of the injected amount of fuel within the channel and not only at the peripheries of the channel.
In a further advantageous embodiment of the invention, the burner also comprises a further annular mixing channel, which is surrounded by the mixing channel and has a third distributing system and a fourth distributing system. Third fuel jets of the third distributing system are arranged substantially in the region of a radial middle to radially on the outside in the further mixing channel and fourth fuel jets of the fourth distributing system are arranged substantially in a region of the radial middle to radially on the inside in the further mixing channel.
Consequently, a burner with two concentric mixing channels for the at least partial premixing in each case of air with fuel is obtained. This makes it possible for the air and the fuel to be fed to a pilot flame in the inner channel (pilot channel).
It is advantageous if fuel jets are provided in blades with inner fuel passages in the mixing channel for the injection of fuel of at least one distributing system. This allows on the one hand fuel to be injected into an air stream at exactly the desired locations in the mixing channel and on the other hand a swirl to be imparted to the fuel/air stream to improve the mixing.
The fuel ports may be positioned on the blades on either of the suction side or on the pressure side or on both sides.
For a solution that can be realized in a mechanically simple form, it is expedient if neighboring blades are assigned to different distributing systems.
However, the variant in which the blades are respectively assigned to at least two distributing systems offers a greater potential with regard to achievable fine mixing and is therefore advantageous.
In the case of an advantageous alternative embodiment, fuel jets are provided on the channel hub and/or the channel outer wall for the injection of fuel for at least one distributing system. This makes it possible to dispense with the blades with inner fuel passages, at least for one distributing system.
A further advantageous alternative embodiment provides small tubes with fuel jets for the injection of fuel, the small tubes extending from the channel hub in the direction of the channel outer wall. The small tubes are easier to produce, and consequently less costly, than blades with inner fuel passages.
At the same time, it may be expedient with regard to improved flow control if the small tubes are profiled on their outer wall.
In order to be able to adapt the depth of penetration of the individual distributing systems in a specific manner, it is advantageous if at least one diameter for a fuel jet of one distributing system differs from a second diameter of a fuel jet of another distributing system of the same mixing channel.
The combustion system according to the invention comprises a burner according to the invention as well as a combustion chamber, at one end of which the burner is arranged, and comprises a device for measuring alternating pressure amplitudes in individual frequency bands in the combustion chamber. By means of the device for measuring alternating pressure amplitudes in individual frequency bands, it can be established specifically which pressure or flame oscillations occur in the combustion chamber, so that fuel can be suitably supplied to the distributing systems of the burner in order to reduce the disturbances occurring.
In the inventive method, for operating a burner in which fuel is injected into a mixing channel for fuel and air, the fuel of one burner stage is injected by way of at least two distributing systems with a different fuel profile over a cross section of the mixing channel and, for influencing operation-restricting or operation-enhancing oscillation modes in corresponding load ranges, the fuel distribution to the distributing systems is changed.
It is particularly advantageous in this respect if alternating pressure amplitudes in individual frequency bands in a combustion chamber are continuously measured and, in the case of an increase in the amplitude of a mode above a fixed limit value, the fuel of one distributing system as a proportion of the total amount of fuel is changed.
In this respect, it is advantageous with regard to the suppression of combustion oscillations if the fuel distribution in a mixing channel configured as an annular channel is changed such that a radial fuel profile changes.
In particular, it may be advantageous with regard to the suppression of combustion oscillations if the fuel distribution is changed such that a proportion of fuel in a radial middle of the annular channel is changed with respect to radially inner and outer regions of the annular channel.
Furthermore, it may be advantageous with regard to the suppression of combustion oscillations if the fuel distribution is changed such that a proportion of fuel in a radially inner region of the annular channel is changed in comparison with a radially outer region of the annular channel.
It is most particularly advantageous if the fuel distribution in an annular main channel is changed such that a proportion of fuel in a radial middle of the main channel is changed with respect to radially inner and outer regions of the main channel and the fuel distribution in an annular pilot channel that is surrounded by the main channel is changed such that a proportion of fuel in a radially inner region of the pilot channel is changed in comparison with a radially outer region of the pilot channel.
The respective shifting of the proportions of fuel makes it possible to compensate partially or completely for the influence on the combustion behavior of further operating parameters, such as for example the Wobbe index or gas temperature, and ambient conditions.
What is essential here is the adjustability of a radial fuel-air mixture profile during operation by integration of two or more fuel passages that can be activated separately from one another, by way of corresponding distributing systems. This takes place by the radial arrangement of the individual stages in the mixing channel, preferably on each swirl blade or each fuel injection element.
The arrangement allows in particular a local maximum or minimum of the injected amount of fuel to be achieved within the mixing channel and not only at the peripheries of the channel.
The invention is explained in more detail by way of example on the basis of the drawings, which are schematic and not to scale and in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of a burner according to the invention,

FIG. 2 shows schematically a combustion system according to the invention,

FIGS. 3-5 show an example of the changing of the fuel profile over the main channel,

FIGS. 6-8 show a further example of the changing of the fuel profile over the pilot channel,

FIG. 9 shows blades of a burner according to the invention with fuel jets of two distributing systems each,

FIG. 10 shows blades of a burner according to the invention that are assigned to different distributing systems,

FIG. 11 shows a possible arrangement of the fuel jets of the distributing systems on a blade in section,

FIG. 12 shows a view of a blade with the arrangement of the fuel jets from FIG. 11,

FIG. 13 shows a further arrangement of the fuel jets of the distributing systems on a blade in section and

FIG. 14 shows an alternative arrangement of the fuel jets of the distributing systems on a blade in section.

DESCRIPTION OF EMBODIMENTS

FIG. 1 shows schematically and by way of example a section through a burner 1 according to the invention. The burner 1 has a longitudinal axis 2, and also mixing channels, formed in an annular manner around the longitudinal burner axis 2, a main channel 3 and a pilot channel 4, for the mixing of fuel 24 and air 25. Two concentric, annular mixing channels are illustrated. But, the invention may be used for as few as one mixing channel or for more than two of the elements, as a particular burner is designed and as such control over the distribution of fuel is required in an embodiment of a burner.
Arranged centrally along the longitudinal burner axis 2 is a pilot burner 23. In premixing operation, the pilot burner 23 is operated to support the main burner 9.
The mixing channels 3, 4 of the burner stage 9, which is also referred to as the main burner, and of the pilot burner 23 are bounded radially on the inside by a channel hub 5, 6 and radially on the outside by a channel outer wall 7, 8. Arranged in the mixing channels 3, 4 are blades 18, which extend from the hub 5, 6 to the channel outer wall 7, 8. The blades 18 have inner fuel passages 19, which are assigned to different distributing systems 10, 11, 14, 15. Each distributing system comprises an annular passage extending circumferentially around the inward wall of the respective mixing channel 3, 4. The respective distributing system brings fuel to the inward end of all of the blades radially outward of the distributing system. The distributing system is in turn supplied its fuel from a source, not illustrated. During operation, fuel 24 from the blades is injected by fuel jets 12, 13, 16, 17 into the respective mixing channel 3, 4.
FIG. 2 shows a combustion system 20 according to the invention, with a burner 1 according to the invention and a combustion chamber 21, at the one end of which the burner 1 is arranged. The combustion system 20 also comprises a device 22 for measuring alternating pressure amplitudes or accelerations in individual frequency bands in the combustion chamber 21. Such a device 22 at the burner 1 is likewise conceivable. In the inventive method, alternating pressure amplitudes in the individual frequency bands in the combustion chamber 21 are continuously measured. If the amplitude of a mode increases above a fixed limit value, the fuel of one distributing system 10, 11, 14, 15 as a proportion of the total amount of fuel is changed, i.e. increased or reduced. If the amplitude in the corresponding frequency band falls again below the adjusted limit value, the distribution of fuel can be restored to a basic setting.
In an exemplary embodiment of the invention, in the main channel 3 a fuel-air profile in the radial middle of the channel can be freely changed from lean in fuel to rich in fuel (with respect to the integral mean value of the fuel/air mixture) by two separately adjustable distributing systems 10, 11.
By analogy, the fuel injection of the inner pilot channel 4 can likewise be realized by two separately adjustable distributing systems 14, 15. In the pilot channel 4, it is particularly advantageous to set up the arrangement of the third and fourth fuel jets 16, 17 such that a fuel-air profile that allows an adjustment between preferred radially outer or radially inner injection can be produced. Neutral adjustment of the flows then produces a homogeneous field, which is preferred for low fuel emissions, with a high power output, in the case of a high part load and low part load preferably a profile that is relatively lean in fuel in the outer section.
There follows a more detailed description of the operating behavior for the setup described above (main burner lying concentrically on the outside and pilot burner lying on the inside, with in each case two distributing systems 10, 11, 14, 15 that are adjustable independently of one another). In this case, the arrangement of the distributing systems 10, 11, 14, 15 allows a shifting of the proportion of fuel radially in the mixing channel 3 from the middle to the inside (hub 5) and outside (cone or channel outer wall 7) in the main burner 9 and radially in the mixing channel 4 from the inside (hub 6) to the outside (cone or channel outer wall 8) in the pilot burner 23.
FIG. 3 shows plotted on the right the entire nominal proportion of fuel of the two distributing systems 10, 11. This basic setting is optimized for the compromise between emissions and performance of the burner 1.
FIG. 4 shows in comparison with FIG. 3 an increased proportion of fuel in the radial middle of the mixing channel 3, for influencing an operation-restricting or operation-enhancing mode in certain load ranges or possibly to easily influence the NO_xemissions.
FIG. 5 correspondingly shows a reduced proportion of fuel in the radial middle of the mixing channel 3.
A similar situation applies to the pilot burner 23, the mixing channel 4 of which is shown in FIG. 6 with a nominal fuel distribution of the two distributing systems 14, 15 in the basic setting, which is optimized for the compromise between emissions and performance/stability of the burner.
FIG. 7 shows, in comparison, the case of an increased proportion of fuel radially on the inside (i.e. at the hub 6). This changing of the fuel profile also serves for influencing an operation-restricting or operation-enhancing mode in certain load ranges, or can contribute to improving the NO_xemissions in certain load ranges. The starting behavior of the burner 1 is also possibly improved.
FIG. 8 shows a proportion of fuel that is reduced radially on the inside (hub 6) in comparison with FIG. 7.
The degree of shifting of the proportions of fuel is freely selectable within the operating limits. Depending on the operating state of the machine (starting, part load, base load, etc.), the combination of these cases that is expedient in each case is likewise freely selectable.
FIG. 9 shows a detail as seen when looking into a mixing channel 3 along the longitudinal burner axis. In the exemplary embodiment of FIG. 9, the blades 18 have fuel jets 12, 13 of different distributing systems 10, 11. As an alternative to this, FIG. 10 shows an exemplary embodiment in which neighboring blades 18 are exclusively assigned to different distributing systems 10, 11.
FIGS. 11 and 12 show an embodiment of a blade 18 of a burner 1 according to the invention. FIG. 11 shows the respective section through the plane of the inner fuel passage 19 in the blade 18 that belongs to the respective distributing system 10, 11. FIG. 12 shows the plan view of the blade 18 with the arrangement of the fuel jets 12, 13 corresponding to FIG. 11. It can be seen that the fuel jets 12, 13 can be provided both on the suction side and on the pressure side of the blade 18 and that the pattern of the fuel jets 12, 13 does not have to be symmetrical.
Further alternative arrangements of the fuel jets 12, 13 of the distributing systems 10, 11 are shown in FIGS. 13 and 14, embodiments of the invention that produce fuel profiles other than those shown in FIGS. 3 to 8, as shown in FIG. 14, also being covered by the invention.

Claims

What is claimed is:

1. A burner having a longitudinal burner axis;

a first mixing channel extending annularly around the longitudinal burner axis, and the first mixing channel being configured and operable for mixing of fuel and air in the burner;

a channel hub bounding the first mixing channel radially on an inward side thereof, and a channel outer wall bounding the first mixing channel radially on an outward side thereof; and

a device in the first mixing channel configured for providing an adjustable fuel concentration distribution in the first mixing channel radially from the channel hub to the channel outer wall.

2. The burner as claimed in claim 1, further comprising a burner stage comprising a first and a second distribution system for the mixing channel;

respective first fuel jets of the first distributing system being arranged at at least one of substantially radially inward and substantially radially outward in the first mixing channel; and

respective second fuel jets of the second distributing system being arranged substantially radially in a middle region in the first mixing channel between radially inward and radially outward sides of the first mixing channel.

3. The burner as claimed in claim 2, further comprising a second, annular mixing channel which is surrounded by the first mixing channel;

a third distributing system in the second annular mixing channel, the third distributing system having third fuel jets and the third fuel jets are arranged substantially in a radially middle region to a radially outward region in the second annular mixing channel; and

a fourth distributing system having fourth fuel jets and the fourth fuel jets are arranged substantially in the radial middle region of the second annular mixing channel to a radially inward region in the second annular mixing channel.

4. The burner as claimed in claim 3, further comprising blades in each of the mixing channels, the blades having inner fuel passages of the blades and the inner fuel passages located in the respective mixing channel in which the blades are located, and the fuel passages are configured and operable for injection of fuel by at least one of the distributing systems for the respective mixing channel.

5. The burner as claimed in claim 4, further comprising a plurality of the blades in each of the mixing channels, wherein successive blades of the plurality of the blades in each mixing channel are neighboring one another, and different ones of the respective distributing systems of each mixing channel are assigned to neighboring blades in the mixing channels.

6. The burner of claim 4, wherein each of the blades is respectively assigned to and configured to receive fuel from at least two of the distributing systems.

7. A combustion system including a burner as claimed in claim 2;

the combustion system further comprising a combustion chamber having a first end, a burner arranged in the first end of the combustion chamber; and

a device configured for measuring alternating pressure amplitudes or accelerations in individual frequency bands in at least one of the combustion chamber and the burner.

8. A method for operating a burner in which fuel is injected into a mixing channel for mixing of fuel and air, the method comprising:

injecting fuel of one burner stage via at least two distributing systems, each distributing system having a different fuel profile over a cross-section of the mixing channel; and

selectively influencing operation-restricting or operating-enhancing oscillation modes in corresponding load ranges in fuel distribution to the distributing systems for changing the fuel distribution over the cross-section of the mixing channel.

9. The method as claimed in claim 8, further comprising:

continuously measuring alternating pressure amplitudes or accelerations in individual frequency bands in a combustion chamber or at the burner;

upon an increase in an amplitude of a mode above a fixed limit value, changing the fuel of one of the distributing systems as a proportion of the total amount of the fuel being injected by the two distributing systems for adjusting for the increase in the amplitude of the mode.

10. The method of claim 8, wherein the mixing channel is an annular channel and the method further comprising changing the fuel distribution in the mixing channel such that a selected radial fuel profile is altered.

11. The method as claimed in claim 10, further comprising changing the fuel distribution such that a proportion of fuel in a radial middle region of the annular mixing channel is changed with respect to a radially inner and a radially outer region of the annular mixing channel.

12. The method as claimed in claim 10, further comprising changing the fuel distribution such that a proportion of fuel in a radially inner region of the annular mixing channel is changed with respect to a proportion of fuel in a radially outer region of the annular mixing channel.

13. The method as claimed in claim 11, further comprising:

changing fuel distribution in an annular main channel such that a proportional distribution of fuel in a radial middle region in the main channel is changed with respect to a proportional distribution of fuel to a radially inner and a radially outer regions of the main channel; and

changing fuel distribution in an annular pilot channel that is surrounded by the main channel so that a proportion of fuel in a radially inner region of the pilot channel is changed with respect to a proportion of fuel in a radially outer region of the pilot channel.

14. A method for operating a burner according to claim 1, in which fuel is injected into a mixing channel for mixing of fuel and air, the method comprising: