US20080131824A1

US20080131824A1 - Burner device and method for injecting a mixture of fuel and oxidant into a combustion space

Info

Publication number: US20080131824A1
Application number: US11/978,205
Authority: US
Inventors: Claus Wahl; Manfred Aigner; Harald Schuetz; Oliver Lammel; Rainer Lueckerath
Original assignee: Deutsches Zentrum fuer Luft und Raumfahrt eV
Current assignee: WS Warmeprozesstechnik GmbH
Priority date: 2006-10-26
Filing date: 2007-10-25
Publication date: 2008-06-05
Also published as: DE102006051286A1; EP1918641A3; EP1918641A2

Abstract

A burner device is made available, comprising a combustion chamber with a combustion space and an injection device for injecting a mixture of fuel and oxidant into the combustion space, wherein the injection device has a plurality of nozzles arranged on a circular line, the nozzles each have a nozzle chamber, fuel nozzles or fuel pipes for the coupling in of fuel open into the nozzle chambers, oxidant can be coupled into the nozzle chambers via a feed device for generating a mixture and wherein nozzle apertures of the nozzles in the combustion space are designed as elongated holes.

Description

The present disclosure relates to the subject matter disclosed in German application number 10 2006 051 286.3 of Oct. 26, 2006, which is incorporated herein by reference in its entirety and for all purposes.

BACKGROUND OF THE INVENTION

The invention relates to a burner device, comprising a combustion chamber with a combustion space and an injection device for injecting a mixture of fuel and oxidant into the combustion space, wherein the injection device has a plurality of nozzles arranged on a circular line.
The invention relates, in addition, to a method for injecting a mixture of fuel and oxidant into a combustion space.
A recirculation of exhaust gas may be brought about in the combustion space as a result of such a burner device. The mixture of fuel and oxidant, which is injected into the combustion space via corresponding nozzle jets, can mix with the recirculating exhaust gas. As a result, homogeneous combustion ratios are obtained in the combustion space and these counteract the formation of hot spots. As a result, good exhaust gas values with respect to CO and NOx are, on the other hand, obtained.
A burner system which comprises a combustion chamber and a distributor which has at least one intake for fuel is known from US 2006/0029894 A1. Fuel can be directed into the combustion chamber from a first end in the direction of a second end via the distributor.
U.S. Pat. No. 3,834,627 discloses a fuel injector which has a fuel distribution device. DE 25 28 671 A1 discloses a combustion chamber for liquid fuels and gas fuels which has essentially cylindrical walls and a cover plate arranged at the end. The cover plate has a fuel supply nozzle arranged centrally and several feed apertures for gaseous media which are arranged so as to be inclined at an angle in a tangential direction in relation to the central axis of the combustion chamber.
DE 1 800 612 discloses a combustion chamber with apertures which serve the purpose of admixing cooling air to hot combustion gases. The entry apertures for the cooling air have slit-like cross sections.
WO 2005/080878 A1 discloses a premix burner for the combustion of a lean combustible gas which has a premix air duct which extends along a burner axis and via which combustion air can be supplied.
A lance with guides for the mixing of gases is known from U.S. Pat. No. 3,043,577. EP 0 856 128 B1 discloses a gas appliance for bringing about a transfer of heat to a fluid comprising at least one gas burner with premixing.

SUMMARY OF THE INVENTION

In accordance with the present invention, a burner device is provided, with which a good intermixing of gases in the combustion chamber is obtained even with an increase in the power density.
In accordance with the invention, the nozzles each have a nozzle chamber, fuel nozzles or fuel pipes for the coupling in of fuel open into the nozzle chambers, and oxidant can be coupled into the nozzle chambers via a feed device for generating a mixture and nozzle apertures of the nozzles in the combustion space are designed as elongated holes.
In order to increase the power density of a burner device of the type specified at the outset, the gas flow rate through the nozzles can be increased. This leads, however, to greater losses of pressure and, therefore, to a direct reduction in the degree of effectiveness. In order to reduce the losses of pressure, on the other hand, the diameter of the nozzle apertures can be increased. The increase in the diameter of the nozzle apertures does, however, impair the intermixing of gases in the combustion space because the gas jet is thicker.
In accordance with the invention, with elongated holes as nozzle apertures, the mixture of fuel and oxidant may be injected into the combustion space at the respective nozzles as a band-like jet. Such a band-like jet has a greater surface area in comparison with a jet with a round diameter and the same cross section. As a result, the incorporation into the recirculated exhaust gas is improved. As a result, on the other hand, smaller lambda gradients are obtained in the combustion chamber and the emission of NOx and CO may be reduced in comparison with nozzles with round nozzle apertures.
As a result, an improved intermixing of gases can be achieved even with an increase in the power density.
Fuel nozzles or fuel pipes are provided for coupling fuel into the nozzles. As a result, a mixture of fuel and oxidant may be generated which is injected into the combustion space through the nozzles. This mixture of fuel and oxidant is generated in a nozzle chamber of the nozzles. Emissions of NOx and CO are reduced further as a result of the mixing (in comparison with no preliminary mixing) since the lambda gradient is decreased.
The ratio of hole circumference to hole surface area is greater, in particular, in the case of the elongated holes than in the case of a circular hole with the same hole circumference or same hole surface area. As a result, the intermixing of gases can be improved relative to the same hole surface area. The nozzle apertures may be designed with a smaller surface area and, therefore, in a more space-saving manner relative to the same hole circumference.
The ratio is, in particular, greater by at least a factor of 1.2, preferably by a factor of 1.4 and, in one embodiment, by a factor of 1.5. As a result, an effective intermixing relative to the same cross-sectional surface area may be achieved in comparison with round nozzle apertures.
It is favorable when a length of a nozzle aperture is greater than a greatest width of the nozzle aperture. As a result, the ratio of hole circumference to hole surface area may be increased.
The length of the nozzle aperture is, in particular, at least 1.5 times greater than the greatest width in order to achieve a large hole circumference. A large hole circumference, on the other hand, brings about a large cross-sectional volume in an injected jet of fuel and oxidant.
It has proven to be favorable when the nozzle apertures are aligned with their center line radially or at an angle of less than 30° in relation to the radial direction. As a result, an optimized incorporation into the recirculated exhaust gas is obtained. The center line is, in this respect, located between the longer sides of the nozzle aperture.
It may be provided for the rotational orientation in relation to an axis of a nozzle aperture parallel to the axis of the combustion space to be adjustable at least in an angular range. As a result, this rotational position can be varied in order to obtain optimized mixture ratios and combustion ratios at a combustor device in the combustion space.
A nozzle aperture is, in particular, of a slit-like design in order to generate a band-like jet in the mixture of fuel and oxidant injected.
It is also possible for a nozzle aperture to be of a triangular design.
It is also possible for a nozzle aperture to have one or more curved boundary lines. The boundary lines can be curved once or several times.
It is favorable when the combustion space is of a rotationally symmetric design. As a result, mixture ratios and combustion ratios may be achieved in the combustion space with a high degree of symmetry. This, on the other hand, leads to an improved intermixing of recirculated exhaust gas and injected mixture of fuel and oxidant.
It is favorable when the combustion chamber has an outlet area which has a tapering inner cross section. As a result of this outlet area, a recirculation of exhaust gas may be brought about, as a result of which the injected mixture of fuel and oxidant may, on the other hand, be incorporated into hot recirculated exhaust gas.
It is particularly advantageous when the burner device is designed such that a recirculation of exhaust gas can be formed in the combustion space. As a result, homogeneous mixture and combustion ratios are obtained in the combustion space and hot spots avoided.
It is favorable when the hole surface area of an elongated hole is greater than or equal to a surface area of an outlet aperture of a fuel nozzle or fuel pipe into a nozzle chamber. As a result, the formation of any counterpressure is avoided. A preliminary mixture consisting of fuel and oxidant may thus be generated effectively in the nozzle chamber and this mixture may be coupled into the combustion space.
It is advantageous when a switching device is present, by means of which one or more nozzles can be switched to active or inactive with respect to the injection of a mixture of fuel and oxidant into the combustion space through the respective nozzles. It is possible for the switching device, for example, with the aid of a valve to regulate whether a mixture of fuel and oxidant is injected through a correspondingly activated nozzle or not. As a result, the mass flow of the mixture of fuel and oxidant into the combustion space may be reduced in the case of a variation in power without the ratio of fuel to oxidant in the mixture (lambda ratio) having to be readjusted. The exiting velocity of the mixture out of an active nozzle into the combustion space in the case of a reduced mass flow may be maintained by inactivating one or more nozzles, i.e., the momentum of the mixture of fuel and oxidant during entry into the combustion space need not be modified in the case of any variation in power. In particular, with the switching device it is possible to control the fact that, for example, every second or every third or every fourth etc. nozzle can be inactivated. As a result, symmetric ratios can also be achieved in the case of a reduction in the mass flow in the case of a decrease in power.
It is also possible for several nozzles to be arranged on the circular line one behind the other in a radial direction. At least two nozzles with corresponding nozzle apertures in an elongated form are then seated at a nozzle location on the circular line. Several nozzle apertures are then provided at the corresponding nozzle location instead of a single nozzle aperture. These apertures may be designed with a smaller length than if only one nozzle is present at a nozzle location. With a corresponding configuration, it is possible to obtain a greater ratio of the hole circumference to the hole surface area at the nozzle apertures relative to the overall number of nozzles at a nozzle location. As a result the incorporation into recirculating hot exhaust gas may, on the other hand, be improved. A nozzle at a nozzle location is, so to speak, divided into several nozzles.
In accordance with the invention, a method is provided, with which a good intermixing of gases in the combustion space can be achieved even with an increase in the power density.
In accordance with the invention, fuel and oxidant are coupled into nozzle chambers in order to produce a mixture of fuel and oxidant and the mixture of fuel and oxidant is injected into the combustion space via nozzle apertures adjoining the nozzle chambers, wherein the nozzle apertures are located on a circular line and are designed as elongated holes.
The method in accordance with the invention has the advantages already explained in conjunction with the burner device according to the invention.
Additional, advantageous developments have likewise already been explained in conjunction with the burner device according to the invention.
It is provided, in particular, for the mixture of fuel and oxidant to be injected into the combustion space with a higher velocity than the turbulent flame velocity in the combustion space. As a result, any flashback into the nozzle chamber is avoided.
It is favorable when one or more nozzles are inactivated in order to reduce the mass flow of a mixture of fuel and oxidant which is injected into the combustion space. As a result, the mass flow can be reduced in a simple manner in the case of a variation in power without the mixture in the nozzle chamber needing to be influenced. Furthermore, the exiting momentum at the nozzles in the case of a reduction in the mass flow need not be modified as a result.
The inactivated nozzles are, in particular, selected such that they are distributed symmetrically on the circular line. As a result, symmetric ratios are also obtained in the case of a reduction in the mass flow.
The following description of preferred embodiments serves to explain the invention in greater detail in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic sectional illustration of one embodiment of a burner device according to the invention;

FIG. 2 shows a sectional view of the burner device according to FIG. 1; and

FIG. 3 shows a schematic illustration of various possibilities for the configuration of nozzle apertures.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of a burner device in accordance with the invention, which is shown in FIG. 1 and designated as 10, comprises a combustion chamber 12 with a combustion space 14. The combustion space 14 is designed to be rotationally symmetric around an axis 16.
The combustion space 14 comprises a combustion area 18 which is essentially cylindrical and an outlet area 20 with an outlet aperture 22. The outlet area 20 tapers towards the outlet aperture 22. The outlet area 20 is of a truncated design.
An injection device 24 is arranged at the combustion chamber 12 and a mixture of fuel and oxidant may be injected into the combustion space 14 via this injection device. A gaseous fuel is used as fuel. The oxidant is, in particular, atmospheric oxygen.
The injection device 24 comprises a plurality of nozzles 26 which are arranged on a circular line 28 (FIG. 2). In the embodiment shown in FIG. 2, the nozzles 26 are located on the circular line 28. The nozzles 26 have nozzle apertures 30 which open into the combustion space 14. The nozzle apertures 30 are located in the vicinity of a combustion chamber wall 32 which limits the combustion area 18 of the combustion space 14 and are spaced in relation to this combustion chamber wall 32.
The nozzles 26 are essentially aligned parallel to the axis 16 so that the mixture of fuel and oxidant can be injected into the combustion space 14, which is located essentially parallel to the axis 16, with a main direction of inflow. Nozzle axes 34 are, accordingly, aligned parallel to the axis 16.
Fuel can be injected into the nozzles 26 via a respectively associated fuel nozzle 36 or via a respective small fuel pipe 36. Such a fuel nozzle or such a small fuel pipe 36 has an outlet aperture 38 which opens into a nozzle chamber 40 of the nozzles 26 or is positioned outside the nozzle chamber 40 such that fuel which exits from the respective outlet apertures 38 enters the respective nozzle chamber 40 completely. The diameter of the outlet apertures 38 is correspondingly smaller than the diameter of the nozzle chamber 40.
Furthermore, oxidant and, in particular, air can be coupled into the nozzle chamber 40 via a feed device 42.
Fuel can be supplied to the fuel nozzles 36 via a feed device 44.
In one embodiment, twelve nozzles 26 are arranged on the circular line 28. The diameter of the nozzles 26 at the nozzle chamber 40 is 4.5 mm. The diameter of the outlet apertures 38 of the fuel nozzles 36 is 1 mm. The outlet aperture 38 of the fuel nozzles 36 is, in particular, circular in shape.
An ignition device 46 is arranged at the combustion chamber 12 in order to be able to ignite the mixture of fuel and oxidant in the combustion space 14.
The burner device 10 is designed such that exhaust gas can recirculate in the combustion space 14. The recirculation of exhaust gas is indicated in FIG. 1 by the reference numeral 48. As a result of the recirculation of exhaust gas, a temperature profile with a good degree of homogeneity may be achieved in the combustion space 14 and so hot spots are avoided. As a result, lower amounts of NOx and of CO are contained in the exhaust gas.
In this respect, it is provided, in particular, for the velocity of fuel in the fuel nozzles 36 to be greater than the turbulent flame velocity in the combustion space 14 in order to prevent any flashback of the flame into the injection device 24.
In order to increase the power density in the case of a given combination 10 of gas turbine and combustor device, the throughput of the mixture of fuel and oxidant through the injection device 24 can be increased. This does, however, lead to increased losses of pressure which result in a reduction in the degree of efficiency. In order to keep the loss of pressure small, the cross-sectional surface areas of the nozzle apertures 30 of the nozzles 26 can be increased. As a result of the thicker gas jet which is caused by this and is coupled into the combustion space 14, the intermixing with recirculated exhaust gas in the combustion space 14 will deteriorate.
In accordance with the invention, it is provided for the nozzle apertures 30 for the nozzles 26 to be designed as elongated holes 50 instead of circular nozzle apertures. In the case of the elongated holes 50, the ratio of hole circumference to the hole surface area at the nozzle apertures 30 is greater than in the case of a circular aperture with the same hole surface area and, in particular, is greater by a factor of at least 1.2. It may be advantageous when this factor is at least 1.4 or even at least 1.5.
Furthermore, the elongated holes have a length L which is greater than the greatest width B. This length L is, in particular, greater than the width B by at least 1.5 times.
The elongated holes 50 for the nozzle apertures 30 are aligned parallel to a radial direction 54 with a center line 51 or are located at a small acute angle in relation to the radial direction 54. This small acute angle is, in particular, smaller than 30°.
In this respect, it is, in principle, possible for the orientation of the nozzle aperture 30 in its rotary position relative to an axis of rotation 56 to be adjustable parallel to the axis 16.
For example, the nozzles 26 or corresponding parts of the nozzles 26, which bear the nozzle aperture 30, can be screwed to a holder 58. The position of the axis of rotation 56 is determined by the screw-in position and, with it, the alignment in relation to the radial direction 54.
The mixture of fuel and oxidant may be injected into the combustion space 14 through the elongated hole nozzle apertures 50 in “thin strips”. A high ratio is obtained for the cross-sectional circumference of an injected jet in comparison with its cross-sectional surface area (relative, in particular, to a circular nozzle aperture). As a result, the incorporation into the recirculated hot exhaust gas is improved and the incorporation also takes place more quickly. As a result, on the other hand, smaller lambda gradients occur and the emission of NOx and CO is reduced in comparison with round nozzle apertures with the same hole surface area.
The elongated holes 50 may be of a slit-like design, as indicated in FIG. 3 by the reference numeral 60. Parallel boundary lines are provided for the elongated hole 60.
It is also possible for elongated holes to have curved boundary lines, like the elongated holes 62, 64 and 66 according to FIG. 3. The elongated holes can, as mentioned above, be aligned in a radial direction 54 or be turned relative thereto.
The elongated holes 62 and 64 according to FIG. 3 have boundary lines with a single curvature. The elongated hole 66 has boundary lines which are curved several times.
It is, for example, also possible for an elongated hole to be of a triangular design like the elongated hole 68 according to FIG. 3.
It is also possible for a plurality of nozzles 70, 72 to be arranged on the circular line 28 on a corresponding sector of a circle. The nozzles 70, 72 are located, in particular, radially to one another. They have corresponding nozzle apertures 74, 76 which are elongated hole apertures. The nozzle apertures 74 and 76 are located one behind the other in a radial direction 54 and are aligned so as to be flush with one another.
With this embodiment, a nozzle aperture with a long length is subdivided into several nozzle apertures 74, 76. As a result, separate jets of fuel and oxidant can be coupled into the combustion space 14 at the nozzles 70, 72 with an increased area when the distance between the nozzle apertures 74, 76 is selected accordingly.
In one embodiment, the burner device 10 comprises a switching device 80. This acts on the device 42 for feeding oxidant into the respective nozzle chambers 40. The supply of oxidant for each nozzle or for selected nozzles 26 can be interrupted by this device. For this purpose, on-off valves 82 are, in particular, associated with the corresponding nozzles.
Furthermore, the switching device 80 activates on-off valves 84 which are seated on the small fuel pipes 36 or are seated on small fuel pipes 36 of selected nozzles 26. The supply of fuel into the nozzle chamber 40 of a respective nozzle 26 can be interrupted.
In the case of a selected nozzle 26, an on-off valve 82 is provided for the interruption of the supply of oxidant as well as an on-off valve 84 for the interruption of the supply of fuel; the activation of the corresponding on-off valves 82 and 84 is synchronized by the switching device 80.
A selected nozzle 26 can be inactivated by the switching device 80; no more oxidant and no more fuel are made available to the corresponding nozzle 26 due to the closure of the on-off valves 82 and 84 and also no more mixture of fuel and oxidant can then flow into the combustion space 14.
The mass flow of the mixture of fuel and oxidant into the combustion space 14 may be reduced by the switching device 80 in that one or more nozzles 26 are inactivated. This may be required, for example, in the case of a variation in power. The mass flow may be reduced without any regulation or readjustment of the ratio of fuel to oxidant being necessary at the nozzle or the nozzles, via which a mixture of fuel and oxidant is still being injected. Furthermore, no reduction in the exiting velocity occurs at the nozzles, via which injection takes place, i.e., the exiting momentum is not altered.
In particular, the switching device 80 controls the nozzles 26 on the circular line symmetrically so that, for example, ever second, every third or every fourth etc. nozzle 26 is inactivated depending on the mass flow to be set.
As a result of the solution according to the invention with the provision of elongated holes 50, the area of the jet which is coupled into the combustion space 14 may be increased in comparison with circular nozzle apertures with the same jet surface area. A band-like jet is made available, by means of which a better incorporation into recirculated exhaust gas is achieved.
The method in accordance with the invention functions as follows:
Fuel and oxidant are premixed in the nozzle chambers 40 of the nozzles 26. Oxidant is coupled into the respective nozzle chambers 40 via the feed device 42 and fuel is coupled in via the small fuel pipes 36. This mixture is then injected into the combustion space 14 via the respective elongated hole nozzle apertures 50.
The injection velocity is adjusted such that it is higher than the turbulent flame velocity in the combustion space 14. As a result, a flashback of the flame into the nozzle chambers 40 may be avoided.
The nozzle apertures 30 of the nozzles 26 are arranged on the circular line 28.
The aperture surface area of the outlet apertures 38 into the nozzle chambers 40 is smaller than the respective surface areas of the elongated hole nozzle apertures 50 in order to avoid any counterpressure.
One or more nozzles 26 may be inactivated by the switching device 80, i.e., the supply of oxidant and supply of fuel into the corresponding nozzle chamber 40 will be interrupted via the corresponding on-off valves 82 or 84. As a result, the mass flow of the mixture of fuel and oxidant, which is injected into the combustion space 14, may be reduced, wherein no reduction in the exiting velocity and, therefore, the exiting momentum of the mixture of fuel and oxidant at the nozzles 26, via which injection is still taking place, occurs.

Claims

1. Burner device, comprising:

a combustion chamber with a combustion space; and

an injection device for injecting a mixture of fuel and oxidant into the combustion space;

wherein the injection device has a plurality of nozzles arranged on a circular line;

wherein the nozzles each have a nozzle chamber;

wherein fuel nozzles or fuel pipes for the coupling in of fuel open into the nozzle chambers;

wherein oxidant is able to be coupled into the nozzle chambers via a feed device for generating a mixture; and

wherein nozzle apertures of the nozzles in the combustion space are designed as elongated holes.

2. Burner device as defined in claim 1, wherein the ratio of hole circumference to hole surface area is greater in the case of the elongated holes than in the case of a circular hole with the same hole circumference or same hole surface area.

3. Burner device as defined in claim 2, wherein the ratio is greater by at least a factor of 1.2.

4. Burner device as defined in claim 2, wherein the ratio is greater by at least a factor of 1.4.

5. Burner device as defined in claim 2, wherein the ratio is greater by at least a factor of 1.5.

6. Burner device as defined in claim 1, wherein a length of a nozzle aperture is greater than a greatest width of the nozzle aperture.

7. Burner device as defined in claim 6, wherein the length of the nozzle aperture is at least 1.5 times greater than the greatest width.

8. Burner device as defined in claim 1, wherein the nozzle apertures are aligned with their center line radially or at an angle of less than 30° in relation to the radial direction.

9. Burner device as defined in claim 1, wherein the rotational orientation in relation to an axis of a nozzle aperture parallel to the axis of the combustion space is adjustable at least in an angular range.

10. Burner device as defined in claim 1, wherein a nozzle aperture is of a slit-like design.

11. Burner device as defined in claim 1, wherein a nozzle aperture is of a triangular design.

12. Burner device as defined in claim 1, wherein a nozzle aperture has one or more curved boundary lines.

13. Burner device as defined in claim 1, wherein the combustion space is of a rotationally symmetric design.

14. Burner device as defined in claim 1, wherein the combustion chamber has an outlet area with a narrowing inner cross section.

15. Burner device as defined in claim 1, wherein its design is such that a recirculation of exhaust gas is able to be formed in the combustion space.

16. Burner device as defined in claim 1, wherein several nozzles are arranged one behind the other in a radial direction on the circular line.

17. Burner device as defined in claim 1, wherein a hole surface area of an elongated hole is greater than or equal to a surface area of an outlet aperture of a fuel nozzle or a fuel pipe into a nozzle chamber.

18. Burner device as defined in claim 1, comprising a switching device for switching one or more nozzles to active or inactive with respect to the injection of a mixture of fuel and oxidant through the respective nozzles.

19. Method for injecting a mixture of fuel and oxidant into a combustion space, comprising:

bringing fuel and oxidant into nozzle chambers in order to produce a mixture of fuel and oxidant; and

injecting the mixture of fuel and oxidant into the combustion space via nozzle apertures adjoining the nozzle chambers;

wherein the nozzle apertures are arranged so as to be distributed on a circular line and are designed as elongated holes.

20. Method as defined in claim 19, wherein the mixture of fuel and oxidant is injected into the combustion space with a higher velocity than the turbulent flame velocity in the combustion space.

21. Method as defined in claim 19, wherein one or more nozzles are inactivated for the purpose of reducing the mass flow of the mixture of fuel and oxidant injected into the combustion space.

22. Method as defined in claim 21, wherein the inactivated nozzles are selected such that they are distributed symmetrically on the circular line.