U.S. patent application number 12/663886 was filed with the patent office on 2010-08-05 for non-rotational stabilization of the flame of a premixing burner.
Invention is credited to Mariano Cano Wolff, Patrick Ronald Flohr, Matthias Hase, Martin Lenze, Jurgen Meisl, Paul Pixner, Uwe Remlinger, Kai-Uwe Schildmache, Thomas Alexis Schneider, Jaap van Kampen.
Application Number | 20100192583 12/663886 |
Document ID | / |
Family ID | 39060220 |
Filed Date | 2010-08-05 |
United States Patent
Application |
20100192583 |
Kind Code |
A1 |
Cano Wolff; Mariano ; et
al. |
August 5, 2010 |
Non-rotational stabilization of the flame of a premixing burner
Abstract
A method for stabilizing the flame of a premixing burner,
comprising a reaction chamber containing a fluid is provided. The
method includes injecting an air-fuel mixture into the reaction
chamber at a speed that is different from that of the fluid present
in the reaction chamber, adjusting the speed such that vortices
form at the boundary between the air-fuel mixture and the
surrounding fluid. A premixing burner including a reaction chamber
and at least one premixing spray nozzle opening into the reaction
chamber is also provided. The premixing burner injects an air-fuel
mixture into the reaction chamber at a speed that is different from
that of the surrounding fluid, the speed being adjusted such that
vortices from at the boundary between the air-fuel mixture and the
surrounding fluid.
Inventors: |
Cano Wolff; Mariano;
(Ratingen, DE) ; Flohr; Patrick Ronald; (Mulheim
a.d. Ruhr, DE) ; Hase; Matthias; (Mulheim, DE)
; Lenze; Martin; (Essen, DE) ; Meisl; Jurgen;
(Mulheim an der Ruhr, DE) ; Pixner; Paul;
(Munster/ Westf, DE) ; Remlinger; Uwe;
(Leverkusen, DE) ; Schildmache; Kai-Uwe; (Mulheim
a.d. Ruhr, DE) ; Schneider; Thomas Alexis; (Mulheim
a.d. Ruhr, DE) ; van Kampen; Jaap; (Roermond,
NL) |
Correspondence
Address: |
SIEMENS CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
170 WOOD AVENUE SOUTH
ISELIN
NJ
08830
US
|
Family ID: |
39060220 |
Appl. No.: |
12/663886 |
Filed: |
June 19, 2008 |
PCT Filed: |
June 19, 2008 |
PCT NO: |
PCT/EP08/57757 |
371 Date: |
April 14, 2010 |
Current U.S.
Class: |
60/737 ; 60/749;
60/806 |
Current CPC
Class: |
F23R 2900/00014
20130101; F23R 2900/03282 20130101; F23C 9/006 20130101; F23R 3/26
20130101; F23D 2203/007 20130101; F23D 11/102 20130101; F23R
2900/00013 20130101; F23D 14/02 20130101; F23C 2202/40
20130101 |
Class at
Publication: |
60/737 ; 60/749;
60/806 |
International
Class: |
F23D 14/02 20060101
F23D014/02; F23R 3/18 20060101 F23R003/18; F23D 11/10 20060101
F23D011/10; F23R 3/28 20060101 F23R003/28 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2007 |
EP |
07012207.2 |
Claims
1.-23. (canceled)
24. A method for stabilizing the flame of a premixing burner
including a reaction chamber containing a fluid, comprising:
injecting an air/fuel mixture into the reaction chamber at a first
speed that is different from a second speed of the fluid present in
the reaction chamber wherein the air/fuel mixture injected into the
reaction chamber is in a form of an unswirled spray; setting the
first speed such that a plurality of vortices form at an interface
forming between the air/fuel mixture and the fluid surrounding the
air/fuel mixture, the plurality of vortices faun due to a set speed
difference between a mixture present in the reaction chamber and
the air/fuel mixture; and injecting a fuel or the air/fuel mixture
into the reaction chamber as a pilot fuel using a pilot burner, the
pilot fuel is injected into the reaction chamber with a parallel or
an anti-parallel offset from the air/fuel mixture.
25. The method as claimed in claim 24, wherein a plurality of axes
of the plurality of forming vortices are perpendicular to a
propagation direction of the air/fuel mixture.
26. The method as claimed in claim 24, wherein the air/fuel mixture
is formed by injecting the fuel into an oxidation means in a
premixing spray nozzle at a third speed that is higher than a
fourth speed of the oxidation means.
27. The method as claimed in claim 26, wherein the fuel is injected
into the oxidation means parallel to a flow direction of the
oxidation means.
28. The method as claimed in claim 24, wherein a side of the
reaction chamber where the pilot burner is located is cooled using
the oxidation means which is then fed to the pilot fuel during
injection into the reaction chamber.
29. The method as claimed in claim 26, wherein the oxidation means
is air.
30. A premixing burner, comprising: a reaction chamber; a premixing
spray nozzle opening into the reaction chamber; and a pilot burner,
wherein an air/fuel mixture may be injected into the reaction
chamber at a first speed that is different from a second speed of a
fluid surrounding the air/fuel mixture, wherein the first speed is
set such that a plurality of vortices form at an interface forming
between the air/fuel mixture and the fluid, wherein the plurality
of vortices form due to a set speed difference between a mixture
present in the reaction chamber and the injected air/fuel mixture,
and wherein the pilot burner injects a fuel or the air-fuel mixture
into the reaction chamber with a parallel or an anti-parallel
offset from the air/fuel mixture.
31. The premixing burner as claimed in claim 30, wherein the
premixing spray nozzle includes a fuel nozzle.
32. The premixing burner as claimed in claim 31, wherein the
premixing spray nozzle injects the fuel into an oxidation means
through the fuel nozzle parallel to a flow direction of the
oxidation means located in the premixing spray nozzle.
33. The premixing burner as claimed in claim 31, wherein the fuel
nozzle includes a first inlet opening, which allows injection of
the fuel at a first angle between 0.degree. and 90.degree. to the
flow direction of the oxidation means located in the premixing
spray nozzle.
34. The premixing burner as claimed in claim 30, wherein a second
inlet opening of the premixing spray nozzle opening into the
reaction chamber is round, oval, rectangular, or square or is
embodied as a slot, and/or an opening of the fuel nozzle opening
into the premixing spray nozzle is round, oval, rectangular or
square or is embodied as a slot.
35. The premixing burner as claimed in claim 30, wherein the
premixing spray nozzle includes an element for setting an entry
speed of the oxidation means.
36. The premixing burner as claimed in claim 35, wherein the
element is a valve or a perforated sheet.
37. The premixing burner as claimed in claim 30, wherein the pilot
burner is a rotationally stabilized burner or a spray burner.
38. The premixing burner as claimed in claim 37, wherein a
plurality of premixing spray nozzles are disposed to form a ring or
a plurality of concentric rings around the pilot burner.
39. The premixing burner as claimed in claim 38, wherein the
plurality of premixing spray nozzles are disposed to form a
plurality of concentric rings around the pilot burner, and wherein
the plurality of premixing spray nozzles of the various rings are
disposed with an offset from one another.
40. The premixing burner as claimed in claim 30, wherein the
plurality of premixing spray nozzles are disposed in a row.
41. The premixing burner as claimed in claim 30, wherein the
incident spray directions of the plurality of premixing spray
nozzles are at a second angle between 0.degree. and 90.degree. to
one another in the reaction chamber.
42. The premixing burner as claimed in claim 30, wherein a pilot
burner is disposed between two premixing spray nozzles.
43. The premixing burner as claimed in claim 30, wherein the
premixing spray nozzle is disposed opposite the pilot burner, and
wherein the premixing spray nozzle includes a radial offset from
the pilot burner.
44. The premixing burner as claimed in claim 30, wherein the
premixing burner is surrounded by a fluid channel, the fluid
channel is connected to a cooling fluid inlet.
45. The premixing burner as claimed in claim 44, wherein the
cooling fluid inlet is an air inlet.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2008/057757, filed Jun. 19, 2008 and claims
the benefit thereof. The International Application claims the
benefits of European Patent Office application No. 07012207.2 EP
filed Jun. 21, 2007, both of the applications are incorporated by
reference herein in their entirety.
FIELD OF INVENTION
[0002] The present invention relates to a method for stabilizing
the flame of a premixing burner.
BACKGROUND OF INVENTION
[0003] Combustion oscillations can occur during the combustion of
fuel or an air/fuel mixture in combustion chambers of gas turbines.
Such oscillations are characterized by greatly increased pressure
amplitudes at different frequencies. Combustion oscillations can
occur in the combustion chamber itself as well as in the adjacent
components of the gas turbine and can be measured there. Combustion
oscillations are generally undesirable, as they have a negative
effect on combustion and can damage the entire combustion system.
Combustion oscillations primarily occur in premixing combustion
systems, in other words in systems in which the fuel is mixed with
air prior to ignition. They preferably occur when the flame is
restricted to a relatively small location, in other words the
reaction density is very high. So-called dead times are associated
with such a compact flame with little local extension. If the dead
times are within a specific narrow range, interactions can occur
with the acoustics of the combustion chamber. This can cause
combustion oscillations.
[0004] No system or method, with which combustion oscillations are
completely avoided, is known to date. However there are a plurality
of premixing combustion systems in which an air/fuel mixture is
swirled and the flame is stabilized by recirculation zones. With
such systems fuel is injected into an air flow and both are
swirled, for example with the aid of so-called swirl blades. Once
this mixture has covered a certain distance, it combusts downstream
of the burner in a flame front, which is stabilized spatially by
the flow field. However all these systems are characterized in that
they produce a clearly defined and spatially limited flame.
Therefore combustion oscillations or flame instabilities also
inevitably occur here at certain operating points. These can cause
extreme mechanical loading of the combustion chamber structure and
should therefore be avoided or at least reduced.
[0005] An additional, widely used option for stabilizing the flame
is the use of pilot flames. This is particularly significant during
partial load operation of a gas turbine.
SUMMARY OF INVENTION
[0006] The object of the present invention is to provide an
advantageous method for stabilizing the flame of a premixing
burner. A further object of the invention is to provide an
advantageous premixing burner.
[0007] These objects are achieved by a method for stabilizing the
flame of a premixing burner as claimed in the claims and a
premixing burner as claimed in the claims. The dependent claims
contain further advantageous embodiments of the invention.
[0008] The inventive method for stabilizing the flame of a
premixing burner, which comprises a reaction chamber containing a
fluid, such as the combustion gases, is characterized in that an
air/fuel mixture is injected into the reaction chamber at a speed
that is different from that of the fluid present in the reaction
chamber. The speed is set such that vortices form at the interface
forming between the fuel or the air/fuel mixture and the fluid
surrounding it.
[0009] The vortices forming in this process can be characterized in
particular in that the axes of the vortices are perpendicular to
the propagation direction of the air/fuel mixture. This
differentiates them from the vortices which occur in the
above-mentioned premixing combustion systems, in which an air/fuel
mixture is swirled. The axes of the vortices which result primarily
from the swirling of the air/fuel mixture are parallel to the
propagation direction of the air/fuel mixture. Recirculation
vortices also form as a result of the swirling, their axes being
perpendicular to the propagation direction of the air/fuel mixture.
However in contrast to the vortices resulting during swirling, the
vortices resulting in association with the present invention are
characterized in that no vortices occur with axes parallel to the
propagation direction of the air/fuel mixture.
[0010] One advantage of the present invention is that complex
swirling of the air/fuel mixture is not necessary, the air and fuel
being thoroughly mixed by vorticity. Recirculation also causes the
air/fuel mixture to be mixed with the hot combustion gas resulting
during combustion. This stabilizes the burner as continuous
ignition is thus achieved.
[0011] Fuel or an air/fuel mixture can be injected into the
reaction chamber as pilot fuel for flame stabilization purposes. In
this process the pilot fuel can be injected into the reaction
chamber with a parallel or anti-parallel offset in respect of the
air/fuel mixture. If the pilot fuel is injected into the reaction
chamber with an anti-parallel offset in respect of the air/fuel
mixture, the hot gases of the pilot flame are available to the
premixing sprays for the hot gas intake. This reliably stabilizes
the combustion reaction of the sprays. Since the hot gases also
exit from the combustion chamber counter to the premixing spray
direction, practically all the hot gas is available to ignite and
stabilize the premixing sprays.
[0012] The air/fuel mixture can preferably be formed by injecting
the fuel into an oxidation means in a premixing spray nozzle at a
speed that is higher than that of the oxidation means. In
particular the fuel can be injected into the oxidation means
parallel to the flow direction of said oxidation means. Air, i.e.
the oxygen in the air, can in particular serve as the oxidation
means.
[0013] The side of the reaction chamber on which the pilot burner
is located can also be cooled using an oxidation means, which is
then fed to the pilot fuel during injection into the reaction
chamber. The oxidation means can be air for example.
[0014] The major pressure loss in the premixing spray nozzles means
that a large pressure difference is available for such cooling of
the points that are subject to significant heat loading on the side
of the combustion chamber where the pilot burner is located. This
allows the application of different cooling technologies, such as
impact spray cooling, impact spray cooling with surface enlargement
or fin cooling. Dimple, longitudinal and transverse fins can be
used for example for impact spray cooling with surface enlargement.
Open combustion chamber cooling is then not required.
[0015] The inventive method, in particular the principle of
anti-parallel injection of pilot fuel and air/fuel mixture
described above, can be used both for tubular combustion chamber
systems and annular combustion chamber systems. The pilot burner
used here can be a rotationally stabilized burner or a spray
burner.
[0016] Anti-parallel injection is particularly advantageous when
spray burners disposed in an annular manner are used as the main
burners. Stabilization of a number of spray flames disposed in an
annular manner by a centrally disposed pilot flame with a flow
direction parallel to the spray flames causes the main flow
direction of the pilot flame to be counter to a recirculation flow
around the spray flames, which can be problematic for ignition.
This is because not all the pilot flame is available to ignite and
stabilize the spray flames. The greater the recirculation, the less
the pilot flame is able to ignite and stabilize. However
significant recirculation of the hot combustion gases is essential
for stable operation of the spray flames, in order to allow a hot
gas intake into the sprays. The hot gas intake into the sprays
ignites the spray flames and ensures continuous combustion.
[0017] The exit speed of the air/fuel mixture from the premixing
spray nozzle into the reaction chamber or combustion chamber is
preferably greater than the flame speed. The laminar flame speed is
the speed at which the fresh gas flows to the flame front under
laminar flow conditions during flame reactions. When the burner
flames are laminar the flame front is fixed; when they are
turbulent, as is the case in most technical combustion processes,
the flame front fluctuates about a central position. The flame
speed of the turbulent flame is a multiple of the speed of the
laminar flame.
[0018] The inventive premixing burner additionally comprises a
reaction chamber and at least one premixing spray nozzle opening
into the reaction chamber. It is characterized in that the
premixing spray nozzle is embodied such that an air/fuel mixture
can be injected into the reaction chamber at a speed that is
different from that of the surrounding fluid. The speed here is set
so that vortices form at the interface forming between the air/fuel
mixture and the fluid surrounding it. The inventive premixing
burner essentially offers the advantages described above in
relation to the inventive method.
[0019] The burner is an unswirled premixing burner. The air/fuel
mixture is injected into a reaction chamber in the form of an
unswirled spray. The spray entry speed here can preferably be above
the flame speed. The spray entry speed can also preferably be
higher than the speed of the fluid surrounding the spray. The free
spray of each nozzle penetrates into the reaction chamber and in
doing so absorbs surrounding fluid, predominantly already combusted
air/fuel mixture, by carrying it along with it (so-called
entrainment). This backflow stabilizes the flame. The speed and
extension of the free spray determine the flame length, it being
ensured that all the fuel combusts within the reaction chamber.
[0020] The premixing spray nozzle of the inventive premixing burner
can preferably comprise a fuel nozzle. The premixing spray nozzle
here can be embodied such that the fuel is injected through the
fuel nozzle parallel to the flow direction of an oxidation means
present in the premixing spray nozzle, for example compressor air,
into said oxidation means. Alternatively the premixing spray nozzle
can be embodied such that the fuel nozzle has at least one
injection opening, which allows injection of the fuel at an angle
between 0.degree. and 90.degree. to the flow direction of an
oxidation means present in the premixing spray nozzle.
[0021] In principle the inlet opening of the premixing spray nozzle
opening into the reaction chamber and/or the opening of the fuel
nozzle opening into the premixing spray nozzle can have a round,
oval, rectangular or square form or can be embodied as a slot.
[0022] The premixing spray nozzle can also have an element which
allows the setting of the oxidation means entry speed. This element
for setting the oxidation means entry speed can be a valve or a
perforated sheet for example.
[0023] The inventive premixing burner can comprise at least one
pilot burner. The pilot burner can be a rotationally stabilized
burner or a spray burner. A number of premixing spray nozzles can
also be disposed to faun a ring or a number of concentric rings
respectively around a pilot burner. Where a number of premixing
spray nozzles are disposed to form a number of concentric rings
around a pilot burner, it is advantageous if the premixing spray
nozzles of the various rings are disposed with an offset from one
another. The pilot burner here can in particular also be disposed
such that the flow direction of the pilot flame runs anti-parallel
to the spray direction of the spray flames.
[0024] As an alternative to an annular arrangement, a number of
premixing spray nozzles can also be disposed in one or more rows.
It is also advantageous here if the premixing spray nozzles of the
various rows are disposed with an offset from one another. In any
case it is also possible for the incident spray directions of the
premixing spray nozzles to be at an angle between 0.degree. and
90.degree. to one another.
[0025] It has generally proven advantageous for a pilot burner to
be disposed respectively between two premixing spray nozzles. The
premixing spray nozzles or the premixing spray nozzle can
preferably be disposed opposite the pilot burner and with an offset
from it.
[0026] For the purposes of cooling, in particular for cooling the
rear wall of the reaction chamber on the pilot burner side, the
premixing burner can be surrounded by a fluid channel, which is
connected to a cooling fluid inlet. The cooling fluid inlet can in
particular be an air inlet.
[0027] The advantage of the present invention is the unswirled
injection of an air/fuel mixture into the reaction chamber by way
of nozzles, with optimum distribution of the heat release in the
reaction chamber as a whole being achieved by specific
configuration of the air inlets and gas mixing within the mixing
channels. The improved distribution of the heat release hereby
achieved allows greater combustion stability than conventional
systems due to individual penetration depths. Combustion
oscillations are thus avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Further features, characteristics and advantages of the
present invention are described below based on exemplary
embodiments with reference to the accompanying figures, in
which:
[0029] FIG. 1 shows a schematic diagram of the cross-section
through a part of the rear wall of an inventive premixing burner as
a first exemplary embodiment.
[0030] FIG. 2 shows a schematic diagram of the propagation
direction of the air/fuel mixture and a resulting vortex.
[0031] FIG. 3 shows a schematic diagram of a vortex produced by
swirling.
[0032] FIG. 4 shows a schematic diagram of the arrangement of the
inlet openings around the pilot burner on the rear wall of an
inventive premixing burner.
[0033] FIG. 5 shows a schematic diagram of the cross-section
through a part of the rear wall of an inventive premixing burner as
a second exemplary embodiment.
[0034] FIG. 6 shows a schematic diagram of the arrangement of inlet
openings and pilot burners on the rear wall of an inventive
premixing burner as a third exemplary embodiment.
[0035] FIG. 7 shows a schematic diagram of the cross-section
through an inventive premixing burner in a longitudinal direction
as a fourth exemplary embodiment.
[0036] FIG. 8 shows a schematic diagram of the cross-section
through an inventive premixing burner in a longitudinal direction
as a fifth exemplary embodiment.
[0037] FIG. 9 shows a schematic diagram of a section through an
inventive premixing burner along the sectional plane IX-IX shown in
FIG. 8.
DETAILED DESCRIPTION OF INVENTION
[0038] The first exemplary embodiment of the present invention is
described below with reference to FIGS. 1 to 4.
[0039] FIG. 1 shows a schematic diagram of the cross-section
through a part of the rear wall of a largely rotationally
symmetrical premixing burner 1. The center line 2 shows the axis of
symmetry of the premixing burner 1. The premixing burner 1
comprises a housing 3, a pilot burner 4, a reaction chamber 5 and a
premixing spray nozzle 6. The premixing spray nozzle 6 has an inlet
opening 13, which opens into the reaction chamber 5. The pilot
burner 4, which in the present exemplary embodiment is a
rotationally stabilized burner, is located in the center of the
rear wall of the premixing burner 1. It is concentrically
surrounded by a number of premixing spray nozzles 6, which are
likewise located on the rear wall of the premixing burner 1.
[0040] The premixing spray nozzle 6 contains a fuel nozzle 8, which
is surrounded by an air inlet channel 37. The air inlet channel 37
and the pilot burner 4 open into the reaction chamber 5. A
perforated sheet 14 is present in the interior of the air inlet
channel 37. The perforated sheet 14 serves to regulate the speed of
the inflowing oxidation means, which in the present exemplary
embodiment is compressor air. The flow direction of the air flowing
through the air inlet channel 37 is shown by arrows 7.
[0041] Fuel is directed through the fuel nozzle 8 into the front
part, i.e. the part facing the reaction chamber 5, of the premixing
spray nozzle 6. The flow direction of the fuel is shown by an arrow
9.
[0042] In the front part of the premixing spray nozzle 6 the
inflowing air mixes with the fuel flowing in through the fuel
nozzle 8. This mixture is injected into the reaction chamber 5
through the inlet opening 13. Injecting this mixture at high speed
into the reaction chamber 5 causes an interface 11 to form between
the gas present in the reaction chamber 5, in the present exemplary
embodiment already at least partially combusted air/fuel mixture,
and the injected air/fuel mixture. Vortices 10 are produced at this
interface 11 due to the speed difference between the mixture
present in the reaction chamber 5 and the injected air/fuel
mixture. These vortices 10 cause the injected air/fuel mixture to
mix with the gas mixture present in the reaction chamber, said gas
mixture containing in particular hot combustion gases, which help
to stabilize the flame.
[0043] The air is preferably injected through the air inlet channel
37 into the front part of the premixing spray nozzle 6 at a lower
speed than the speed of the fuel injected through the fuel nozzle 8
into the front part of the premixing spray nozzle 6. This causes
the air to be carried along by the fuel, encouraging the mixing of
air and fuel due to so-called entrainment. To this end the air can
be injected into the reaction chamber 5 in particular parallel to
the fuel.
[0044] FIG. 2 shows a schematic outline of a vortex 10 resulting
from the inventive method. FIG. 2 shows the propagation direction
31, which is the same as the main flow direction, of the air/fuel
mixture in the reaction chamber 5 and a resulting vortex 10 by way
of example. The axis 32 of the vortex 10 is also outlined. The
vortex axis 32 of the resulting vortex 10 here runs perpendicular
to the propagation direction 31 of the air/fuel mixture. This
differentiates the vortices resulting in the context of the present
invention from the vortices which are primarily caused by
swirling.
[0045] By way of a comparison FIG. 3 shows vortices 33 and 44,
which were caused by swirling. The axis of the vortex 33 primarily
produced by swirling is characterized in that it is largely
parallel to the propagation direction 31 of the swirled air/fuel
mixture also outlined in FIG. 3. Swirling also causes the formation
of recirculation vortices 44, the axes of which are perpendicular
to the propagation direction 31 of the air/fuel mixture, as shown
schematically in FIG. 3.
[0046] The arrangement of the inlet openings 13 around the pilot
burner 4 is outlined in FIG. 4. FIG. 4 shows a schematic diagram of
the upper half-plane of a section along the IV-IV sectional plane
through the rear wall of the premixing burner 1 shown in FIG. 1.
The center line shown with the reference character 26 in FIG. 4 is
perpendicular to the axis of symmetry shown with reference
character 2 in FIG. 1. FIG. 4 shows the pilot burner 4 and numerous
first inlet openings and second inlet openings of premixing spray
nozzles, said inlet openings being shown with the reference
characters 13 and 15.
[0047] The first inlet openings 13 are disposed on a concentric
circle around the pilot burner 4. The second inlet openings 15 are
likewise disposed on a circle positioned concentrically around the
pilot burner 4, the second inlet openings 15 being at a greater
distance from the pilot burner 4 than the first inlet openings 13.
The second inlet openings 15 are also disposed with an offset from
the first inlet openings 13. Alternatively any number of inlet
openings can also be disposed on just one circle around the pilot
burner 4. Additionally or alternatively pilot burners can be
disposed on a circle, the radius of which is different from the
radius of the circles on which the first and second inlet openings
13 and 15 are disposed. The first inlet openings 13, the second
inlet openings 15 and/or the pilot burners can likewise be disposed
with an axial offset from one another. A second exemplary
embodiment of the present invention is described in more detail
below with reference to FIG. 5. Elements corresponding to elements
described in the first exemplary embodiment are given the same
reference characters and are not described again.
[0048] The particular features of the second exemplary embodiment
for the premixing burner are shown in FIG. 5. FIG. 5 shows a
schematic diagram of the cross-section through a part of the rear
wall of a largely rotationally symmetrical premixing burner. FIG. 5
shows the axis of symmetry 2 running through the center of the
premixing burner. In the center of the rear wall is a pilot burner
4, which, as in the first exemplary embodiment, is embodied as a
rotationally stabilized premixing burner and is surrounded
concentrically by premixing spray nozzles 6. Fuel nozzles 8 are
present in the premixing spray nozzles 6. The fuel nozzles 8 are
surrounded by air inlet channels 37. Fuel and air 16 are injected
into the reaction chamber 5 with the aid of the inlet openings 13
and 15. To this end fuel is first injected through the fuel nozzle
8 into the front part of the premixing spray nozzles 6, where it is
mixed with air 16 from the air inlet channels 37, and then directed
on or injected into the reaction chamber 5.
[0049] In the present exemplary embodiment the fuel nozzles 8 are
characterized in that they have openings 34 on their sides facing
the reaction chamber 5, to allow the fuel to exit at an angle to
the flow direction of the air flowing in through the air inlet
channels 37. The flow direction of the fuel is shown by arrows 9 in
FIG. 5, the flow direction of the air flowing through the air inlet
channels 37 being shown by arrows 7. FIG. 5 shows that the flow
direction of the fuel 9 when exiting through the openings 34 is at
an angle to the flow direction of the air 7 flowing through the air
inlet channels 37. This angle can be set as desired by
corresponding configuration of the openings 34. An angle between
0.degree. and 45.degree. between the flow direction of the exiting
fuel 9 and the flow direction of the inflowing air 9 is
particularly expedient here. The fuel is preferably injected into
the air inlet channels 37 at a higher speed than the air. This
favors penetration of the fuel into the air flow and thus the
mixing of fuel and air.
[0050] In the present exemplary embodiment the air/fuel mixture is
injected into the reaction chamber 5 through first inlet openings
13 parallel to the center line 2. In contrast the air/fuel mixture
is injected into the reaction chamber 5 through second inlet
openings 15 at an angle to the center line 2. Vortices 10 again
form at the interfaces 11 between the injected air/fuel mixture and
the air present in the reaction chamber 5. These vortices 10 have
the characteristics described in the previous exemplary
embodiment.
[0051] A third exemplary embodiment of the present invention is
described below with reference to FIG. 6. Elements which correspond
to the elements described in the first two exemplary embodiments
are given the same reference characters and are not described
again.
[0052] The premixing burner of the third exemplary embodiment is
characterized by a different arrangement of inlet openings and
pilot burners compared with the first two exemplary embodiments.
FIG. 6 shows a schematic diagram of an alternative arrangement of
inlet openings and pilot burners to the one in FIG. 4. FIG. 6 shows
a top view 17 of the rear side of the reaction chamber 5 viewed
from the reaction chamber. Both the pilot burners 4 and the inlet
openings 18 are disposed concentrically around the center point of
the rear wall of the reaction chamber 5. The pilot burners 4 and
the inlet openings 18 here are at the same distance from the center
point. The four pilot burners shown and the eight inlet openings 18
shown in FIG. 6 are disposed such that the inlet openings 18
respectively are adjacent to a pilot burner 4. The inlet openings
18 are also characterized in that in contrast to the previously
described exemplary embodiments they are not round but are embodied
as rectangular slots with rounded corners. Any number of pilot
burners and inlet openings can of course be used instead of four
pilot burners 4 and eight inlet openings 18.
[0053] The described arrangement has the advantage that the
arrangement of a number of pilot burners means that the ignition
paths are shorter than in the previously described exemplary
embodiments with a central pilot burner. A further advantage is
that the plurality of pilot burners allows flexible control of the
burning off of the air/fuel mixture. Also the individual flames can
be stabilized specifically with the aid of the various pilot
burners.
[0054] A fourth exemplary embodiment of the present invention is
described in more detail below with reference to FIG. 7. Elements
which correspond to the elements described in the first three
exemplary embodiments are given the same reference characters and
are not described again.
[0055] FIG. 7 shows a schematic diagram of the cross-section
through a premixing burner in a longitudinal direction. The
premixing burner shown in FIG. 7 contains in its interior a
reaction chamber 5, which has an outlet 35 for the combustion gases
facing the turbine. The reaction chamber 5 is surrounded by a
peripheral channel 19. At the end of the reaction chamber 5 away
from the outlet 35 is a pilot burner 4. The outlet 35 of the
reaction chamber 5 is surrounded in an annular manner by inlet
openings 13 of premixing spray nozzles 6. The inlet openings 13 are
disposed opposite the pilot burner 4 and with a radial offset from
it.
[0056] The pilot burner 4, which in the present exemplary
embodiment is embodied as a rotationally stabilized burner, is
supplied with pilot fuel through a pilot fuel inlet 36. The flow
direction of the pilot fuel is shown by an arrow 20. The pilot fuel
is injected into the reaction chamber 5 by way of the pilot burner
4 and combusted there. Air is also supplied to the pilot burner
from the peripheral channel 19. To this end air from a compressor
passes into the peripheral channel 19. One portion of this air is
directed out from there to the pilot burner 4 with another portion
passing by way of the peripheral channel 19 to the inlet openings
13. The flow direction of the air coming from the compressor is
shown by the arrows 24. The air flowing on to the pilot burner 4 is
shown by the arrows 23. The air reaching the premixing spray
nozzles 6 is shown by the arrows 25.
[0057] At the same time the rear side 21 of the reaction chamber 5
is cooled by the air flowing to the pilot burner 4. The rear side
21 is exposed to greater thermal loads than conventional burners
due to the inlet openings 13 opposite it, through which an air/fuel
mixture is injected at high speed into the reaction chamber 5.
Corresponding cooling is therefore advantageous.
[0058] Each premixing spray nozzle 6 in FIG. 7 comprises a fuel
nozzle 8. The fuel nozzle 8 opens into the front part of the
premixing spray nozzle 6, which in turn opens into the reaction
chamber 5 by way of an inlet opening 13. Fuel is directed into the
fuel nozzle 8. The flow direction of the fuel is shown by arrows
27. The fuel is injected by way of the fuel nozzles 8 into the
front part of the premixing spray nozzle 6. Air is mixed with the
fuel there. The flow direction of the air is shown by arrows 25.
The air used passes from the compressor by way of the peripheral
channel 19 into the premixing spray nozzle 6.
[0059] The flow direction of the air/fuel mixture injected into the
reaction chamber 5 by way of the inlet opening 13 is shown with
arrows 29. The high speed of the injected air/fuel mixture causes
vortices to form at the interface between the injected air/fuel
mixture and the gas surrounding it. The flow direction of the
vortices is shown by arrows 30. The vortices cause the injected
air/fuel mixture to be mixed with the gas present in the reaction
chamber 5. This gas is air and hot gas resulting from the
combustion of the pilot flame. The hot gas flowing from the pilot
burner toward the turbine assists with the formation of such
vortices here. At the same time the entire pilot flame present in
the reaction chamber 5 is available to ignite and stabilize the
spray flames. This is achieved in that the pilot burner 4 and the
inlet openings 13 are disposed anti-parallel to one another and
with a radial offset.
[0060] The main flow direction of the fuel and hot gas of the pilot
flame is shown by arrows 22. This main flow direction 22 of the hot
gas of the pilot flame assists recirculation around the premixing
sprays. The high degree of mixing thus achieved in the reaction
chamber 5 promotes stable combustion in the reaction chamber,
thereby preventing undesirable combustion oscillations.
[0061] Further possible variants of the present invention are
described below as a fifth exemplary embodiment with reference to
FIGS. 8 and 9. Elements which correspond to the elements described
in the first four exemplary embodiments are given the same
reference characters and are not described again.
[0062] FIG. 8 shows a schematic diagram of the cross-section
through an inventive premixing burner in a longitudinal direction
as a fifth exemplary embodiment. FIG. 8 also shows the axis of
symmetry 2, the housing 3 of the premixing burner, a premixing
spray nozzle 6 and a centrally disposed pilot burner 4, which is
intended to ensure ignition of the air/fuel mixture. The pilot
burner 4 is set back axially by way of a cone 43. A number of
premixing spray nozzles 6 are disposed with rotational symmetry
around the axis of symmetry 2, in other words also around the pilot
burner 4.
[0063] The premixing burner comprises a reaction chamber 5 with an
outlet 35 leading to the turbine and a plenum 42, which is opposite
the outlet 35 and is separated spatially from the reaction chamber
by a top plate 41. The plenum 42 contains compressor air, which is
injected into the reaction chamber 5 by the premixing spray nozzles
6. The flow direction of the air is shown by arrows 7.
[0064] A fuel distributor 12 is also disposed in the plenum 42,
being connected to a spur line 39. In FIG. 8 the fuel distributor
12 is disposed at a greater radius from the axis of symmetry 2 than
the spur line 39. Of course the spur line 39 can also be disposed
at a greater radius than the fuel distributor 12. The spur line 39
is used to inject fuel into the premixing spray nozzle 6. The fuel
mixed with the compressor air is injected into the reaction chamber
5 by way of the premixing spray nozzle 6 and combusted there. The
free spray of the resulting flame is shown with the reference
character 40.
[0065] FIG. 9 shows a schematic diagram of a section through the
premixing burner shown in FIG. 8 along the sectional plane IX-IX
indicated there. FIG. 9 again shows the reaction chamber 5, which
is separated from the plenum 42 by the top plate 41. Incorporated
in the top plate 41 is a premixing spray nozzle 6, by way of which
an air/fuel mixture is injected into the reaction chamber 5. In the
plenum 42 is a spur line 39, which can be used to inject fuel into
the premixing spray nozzle 6. The flow direction of the fuel is
shown by arrows 9.
[0066] The reaction chamber 5 of the fifth exemplary embodiment
essentially consists of a cylinder, to one side of which air and
fuel are supplied by way of the top plate 41. In addition to the
fuel distributor 12 flow channels can also be positioned in the
plenum 42, allowing the air and fuel flow to be guided and aligned.
Also a number of pilot burners can be present instead of just one
pilot burner. One or a number of pilot flames should guarantee the
burning off or ignition of the mixture here. It is also possible to
combust the fuel just by way of the pilot burner(s) 4 at low fire
powers.
[0067] The air/fuel mixture can enter the reaction chamber 5 by way
of radial slots, as described in conjunction with FIG. 6. Flow
channels are positioned on the slots, which are used to direct the
flow and in which fuel and air are mixed. Various arrangements of
the premixing spray nozzles 6 and pilot burners 4 in the top plate
41 are possible here.
[0068] In a first variant the premixing spray nozzles 6 can be
positioned around a centrally located pilot burner 4 as described
in conjunction with FIG. 4. They only extend over part of the
annular surface in a radial direction and fount two groups, which
are offset peripherally and radially. The pilot burner 4 can be set
back axially by way of a cone 43 as in FIG. 8. However a flush
structure can also be realized. Both the inner and outer rings of
premixing spray nozzles 6 have their own fuel inlet, so that the
fuel can be staggered.
[0069] As a second variant the premixing spray nozzles 6 can be
positioned in just one ring around a central pilot burner 4, as
shown in FIG. 8. This variant is structurally simpler than the
first variant.
[0070] A third variant has three (alternatively four or any other
number greater than one) pilot burners 4 and six (alternatively
eight or any other number greater than one) premixing spray nozzles
6. The premixing spray nozzles 6 and the pilot burners 4 are
positioned on the same circumference, as described in conjunction
with FIG. 6. The region of the burner in proximity to the axis is
unaffected in this variant and can therefore serve to recirculate
or feed back already reacted gas. Fuel injection in principle takes
place in a similar manner to the variants mentioned above. The fuel
supply can be staggered using two fuel distributors, respectively
supplying every second inlet opening.
[0071] The proposed arrangements allow fuel to be injected into the
air using simple structural methods. This is advantageous compared
with variants in which a large number of circular premixing spray
nozzles 6 are used. The first variant has the advantage that the
two rows of premixing spray nozzles 6 allow the air flow and fuel
quantities to be coordinated. It is also simple to stagger or
displace the fuel quantity axially, so that the radial fuel
distribution can be manipulated if required. The third variant has
the advantage that the arrangement of three (or four or any other
number greater than one) pilot burners 4 means that the ignition
paths are shorter than with the first two variants with a central
burner.
[0072] To summarize, in the context of the present invention the
reaction is distributed spatially by appropriate flow guidance. It
is thus possible largely to avoid combustion-induced instabilities.
The air/fuel mixture is injected into the reaction chamber at high
speed. The resulting high level of turbulence and significant flow
shearing prevents oxidation of the mixture by way of a flame. The
reaction or oxidation is thus distributed over the reaction
chamber. Nitrogen oxide production is thus minimal due to extensive
premixing.
* * * * *