U.S. patent application number 11/503163 was filed with the patent office on 2007-02-22 for premix burner arrangement for operating a combustion chamber and method for operating a combustion chamber.
This patent application is currently assigned to ALSTOM Technology Ltd. Invention is credited to Elena De Marcos, Christian Steinbach, Nicolas Ulibarri, Martin Andrea Von Planta.
Application Number | 20070042307 11/503163 |
Document ID | / |
Family ID | 34842438 |
Filed Date | 2007-02-22 |
United States Patent
Application |
20070042307 |
Kind Code |
A1 |
De Marcos; Elena ; et
al. |
February 22, 2007 |
Premix burner arrangement for operating a combustion chamber and
method for operating a combustion chamber
Abstract
A premix burner is disclosed for operating a combustion chamber
with a gaseous and/or liquid fuel, having a swirl generator for
inducing a swirl flow in an incoming combustion air flow and a
device for injecting fuel into the swirl flow, the swirl generator
having at least two cone shell segments which fit together to form
a flow body and together enclose a conically formed swirl space
with a cone angle .gamma. and air inlet slits directed tangentially
to the length of the cone. At least at the downstream end region of
the swirl generator, a shaped element enclosing the cone shell
segments with an inside wall facing the cone shell segments is
provided, and that the cone shell segments end in the inside wall
in a flush manner while maintaining their shape.
Inventors: |
De Marcos; Elena; (Buenos
Aires, AR) ; Steinbach; Christian; (Birmenstorf,
CH) ; Ulibarri; Nicolas; (Baden, CH) ; Von
Planta; Martin Andrea; (Oetwil A.D.L, CH) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
ALSTOM Technology Ltd
Baden
CH
|
Family ID: |
34842438 |
Appl. No.: |
11/503163 |
Filed: |
August 14, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP05/50579 |
Jan 12, 2004 |
|
|
|
11503163 |
Aug 14, 2006 |
|
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Current U.S.
Class: |
431/350 ;
431/183; 431/187; 431/8 |
Current CPC
Class: |
F23D 17/002 20130101;
F23C 2900/07002 20130101; F23R 3/286 20130101 |
Class at
Publication: |
431/350 ;
431/008; 431/187; 431/183 |
International
Class: |
F23C 5/00 20060101
F23C005/00; F23M 9/00 20060101 F23M009/00; F23C 7/00 20060101
F23C007/00; F23D 14/46 20060101 F23D014/46 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2004 |
CH |
00210/04 |
Claims
1. A premix burner for operating a combustion chamber with a
gaseous and/or liquid fuel, comprising: a swirl generator for
inducing a swirl flow in an incoming combustion air flow; and means
for injecting fuel into the swirl flow, the swirl generator having
at least two cone shell segments which fit together to form a flow
body and together enclose a conically formed swirl space with a
cone angle .gamma. and air inlet slits directed tangentially to the
length of the cone, wherein the cone angle .gamma. is greater than
or equal to 20.degree. and the swirl generator has a downstream
burner diameter of greater than 180 mm, and wherein, at least at
the downstream end region of the swirl generator, a shaped element
enclosing the cone shell segments with an inside wall facing the
cone shell segments is provided, and wherein the cone shell
segments end in the inside wall in a flush manner while maintaining
their shape.
2. The premix burner as claimed in claim 1, wherein the shaped
element encloses the cone shell segments at their downstream end
region in an annular manner in such a way that the inside wall of
the shaped element is connected in each case to the cone shell
segment by means of a line of intersection through the respective
cone shell segment, along which the cone shell segment virtually
penetrates the inside wall while maintaining its shape.
3. The premix burner as claimed in claim 1, wherein the inside wall
is frustoconically formed and has a contour tapering conically in
the direction of flow.
4. The premix burner as claimed in claim 1, wherein the inside wall
has adjoining the swirl generator directly downstream an inflow
region in which the inside wall is formed tapering in a
funnel-shaped manner in the direction of flow.
5. The premix burner as claimed in claim 4, wherein the inside wall
has in the inflow region a curvature contour formed in longitudinal
section as a quarter ellipse.
6. The premix burner as claimed in claim 4, wherein downstream of
the inflow region the inside wall goes over into a flow portion
which has a flow cross section remaining the same in the direction
of flow.
7. The premix burner as claimed in claim 1, wherein the inside wall
is cylindrically formed.
8. The premix burner as claimed in claim 3, wherein the first
shaped element is adjoined in the direction of flow by a further
shaped element, with a further inside wall, which axially has a
constant flow cross section.
9. The premix burner as claimed in claim 1, wherein at least four
cone shell segments are provided to form the swirl space.
10. The premix burner as claimed in claim 1, in combination with a
silo combustion chamber, wherein the premix burner is configured to
fire the silo combusion chamber.
11. The premix burner as claimed in claim 2, wherein the inside
wall is frustoconically formed and has a contour tapering conically
in the direction of flow.
12. The premix burner as claimed in claim 2, wherein the inside
wall has adjoining the swirl generator directly downstream an
inflow region in which the inside wall is formed tapering in a
funnel-shaped manner in the direction of flow.
13. The premix burner as claimed in claim 5, wherein downstream of
the inflow region the inside wall goes over into a flow portion
which has a flow cross section remaining the same in the direction
of flow.
14. The premix burner as claimed in claim 2, wherein the inside
wall is cylindrically formed.
15. The premix burner as claimed in claim 7, wherein the first
shaped element is adjoined in the direction of flow by a further
shaped element, with a further inside wall, which axially has a
constant flow cross section.
16. The premix burner as claimed in claim 5, wherein at least four
cone shell segments are provided to form the swirl space.
17. The premix burner as claimed in claim 6, wherein at least four
cone shell segments are provided to form the swirl space.
18. The premix burner as claimed in claim 5, in combination with a
silo combustion chamber, wherein the premix burner is configured to
fire the silo combusion chamber.
19. The premix burner as claimed in claim 6, in combination with a
silo combustion chamber, wherein the premix burner is configured to
fire the silo combusion chamber.
Description
RELATED APPLICATIONS
[0001] This application is based on and claims priority under 35
U.S.C. .sctn.119 to Swiss Application No. 00210/04, filed Feb. 12,
2004 and is a continuation application under 35 U.S.C. .sctn.120 of
International Application No. PCT/EP2005/050579, filed Feb. 9, 2005
designating the U.S., the entire contents of both of which are
hereby incorporated by reference.
BACKGROUND
[0002] A premixer is disclosed for operating a combustion chamber
with a gaseous and/or liquid fuel, having a swirl generator for
inducing a swirl flow in an incoming combustion air flow and means
for injecting fuel into the swirl flow, the swirl generator having
at least two cone shell segments which fit together to form a flow
body and together enclose a conically formed swirl space with a
cone angle .gamma. and air inlet slits directed tangentially to the
length of the cone.
[0003] Premix burners of the aforementioned generic type are known
from many prior publications, such as for example from EP 0 210 462
A1 and EP 0 321 809 B1, the contents of which are hereby
incorporated by reference in their entireties, to mention just two.
Premix burners of this type are based on the general operating
principle of generating within a generally conically formed swirl
generator, which provides at least two cone shell segments fitted
together in such a way that they appropriately overlap one another,
a swirl flow which comprises a mixture of fuel and air and is
ignited within a combustion chamber downstream of the premix burner
in the direction of flow, thereby forming a premix flame which is
spatially as stable as possible. In this case, the spatial position
of the premix flame is determined by the aerodynamic behavior of
the swirl flow, the swirl coefficient of which increases with
increasing propagation along the burner axis, consequently becomes
unstable and ultimately, as the result of a discontinuous
cross-sectional transition between the burner and the combustion
chamber, breaks down into an annular swirl flow with the formation
of a backflow zone, in the forward region of which, in the
direction of flow, the premix flame forms.
[0004] The aerodynamic stability of the backflow zone forming
depends on the design, shape and size of the swirl generator. For
example, if the forwardmost front in the direction of flow of the
backflow zone forming is not spatially stabilized successfully,
thermoacoustic vibrations or pulsations can occur to an increased
extent within the combustion system, impairing the overall
combustion and the release of heat.
[0005] In consideration of this fact, the premix burner systems
previously known and in use are restricted to overall sizes in
which the maximum burner diameter at the burner outlet is only 180
mm. Premix burners of this type additionally have a relatively
pointed, i.e. small, cone angle, of less than or equal to
18.degree., so that the length of the burner tends to be great in
relation to the diameter of the burner facing downstream, but is
still well able to be handled for assembly and maintenance
purposes.
[0006] However, whenever combustion chambers of large dimensions
are to be fired, so far use has been made of so-called multiple
burner arrangements, which provide for use of the above premix
burners. Multiple burner arrangements of this type are disclosed
for example by DE 42 23 828 A1 or DE 44 12 315 A1, the contents of
which are hereby incorporated by reference in their entireties. To
operate multiple burner arrangements of this type, which are
suitable for example for firing a silo combustion chamber, a
sophisticated arrangement of the large number of premix burners
respectively serving as main burners or pilot burners is required
to achieve the end effect of allowing the combustion chamber to
continue to be operated with lowest possible emission values in the
entire load range.
[0007] However, there is the desire to reduce the complexity and
with it also the number of the individual premix burners that are
required for firing combustion chambers of large dimensions,
without losses of quality in the combustion process having to be
accepted at the same time. In addition, for reasons concerning the
increasingly stringent environmental standards with regard to the
reduction of emission values, the aim is to replace the previously
operated single diffusion burners that are primarily used for
firing silo combustion chambers of large dimensions by more modern,
environmentally more acceptable burner systems. In particular with
regard to the avoidance of high conversion and first-time
acquisition costs, it is desirable to provide premix burners of the
largest possible dimensions, in order for example to be able to
continue to maintain the operation of such silo combustion chambers
of large dimensions with only a single premix burner.
[0008] Theoretical studies and trials have shown that simply
scaling for example a double cone burner known from EP 0 321 809 B1
does not achieve the objective, especially since, as already
mentioned above, the length of the burner would increase
disproportionately. Added to this is the fact that the width of the
air inlet slits which extend tangentially in the burner axis and
through which incoming combustion air flows into the swirl
generator to generate the desired swirl flow would likewise
increase proportionately, so that good mixing of the fuel and
incoming combustion air with adequate quality can no longer be
ensured.
[0009] A further very important and at the same time critical
aspect of a desired increase in size or increase in output of the
previously known premix burner systems concerns the downstream
termination of the cone shell segments enclosing the swirl space of
the swirl generator, which in the example of the double cone burner
described in EP 0 321 809 B1 end in axially directed blocking-off
elements. These blocking-off elements contribute to the formation
of undesired separation vortices which, as coherent vortex
structures, lead to combustion instabilities and, associated
therewith, to thermoacoustic vibrations or pulsations.
[0010] There are also known premix burner arrangements (for example
U.S. Pat. No. 5,588,826, also incorporated herein by reference)
which, as a difference from the premix burner described above, have
a transitional geometry interposed between the swirl generator and
the combustion chamber, for example in the form of a
hollow-cylindrically formed mixing tube. However, transitional
geometries of this type are extremely sensitive aerodynamically,
since flow separations in this zone can lead to flashback or
spontaneous ignition. Similarly, because of their complex
production, transitional geometries of this type contribute
decisively to the production costs.
SUMMARY
[0011] A premix burner is disclosed wherein, in spite of the
increase in size of the burner dimensions, the optimized burner
properties in the case of previously known premix burners can be
retained virtually unchanged. In exemplary embodiments, the aim is
to increase the size of the burner of previously known premix
burner systems can be increased in order to reduce the number of
burners in multiple burner arrangements, as described at the
beginning, and also to reduce the associated system costs.
Similarly, with the larger premix burner systems, previously known
single diffusion burners, as are used for example for the firing of
silo combustion chambers, can be replaced by a single premix
burner.
[0012] According to an exemplary embodiment, a premix burner is
developed in such a way that, at least at the downstream end region
of the swirl generator, a shaped element enclosing the cone shell
segments with an inside wall facing the cone shell segments is
provided, and the cone shell segments end in the inside wall in a
flush manner while maintaining their shape.
[0013] A large number of theoretical studies and experimentally
conducted trials to increase the size of the previously known form
of premix burners, which usually have a maximum burner diameter on
the burner outlet side of 180 mm, led to the realization that the
downstream end structure of the cone shell segments can have a
significant influence on the stability of the premix burner flame
forming, in particular in the endeavor to form the premix burner
with as large a volume as possible.
[0014] So it is found that in most cases of the premix burners that
are in use the end regions of the cone shell segments go over in
the direction of flow into a hollow-cylindrical flow channel, which
is adjoined either directly by the combustion chamber or by an
additional mixing zone in the form of a mixing tube. To avoid the
separation vortices following on directly from the cone shell
segments in the direction of flow, it has been realized that,
immediately after leaving the swirl generator, the swirl flow is
able to spread out largely without making the swirl flow unstable
if, while maintaining their shape, the individual cone shell
segments keep in close contact with the inside wall of the flow
channel adjoining the swirl generator. The concept of "maintaining
their shape" means for the purposes of the invention that the shape
of the cone shell segments formed in the manner of segments of a
cone remains unchanged in the region where they come into contact
with the inside wall of the shaped element enclosing the cone shell
segments, as though the cone shell segments would penetrate
unhindered through the shaped element in a radially outward
direction.
[0015] The inside wall of the shaped element also serves for
forming a flow channel adjoining the cone shell segments
downstream. Depending on the shape and size of the shaped element,
it also serves as a mixing tube or as a joining element, in the
sense of a flanged piece, by means of which the swirl generator can
be connected to a combustion chamber following on in the direction
of flow, such as for example a silo combustion chamber, or some
other channel structure.
[0016] To be able to make the premix burner as compact as possible,
i.e. with a burner length that is as small as possible, cone angles
of at least 11.degree., but preferably in the range of 20.degree.
and greater, are used, at which angles the cone shell segments
surround the swirl space in a conically widening manner. For
example, burners with a burner diameter in the outlet region of
greater than 500 mm which have a burner length of well below one
meter can be made possible. To ensure good mixing of the mixture of
fuel and air within the swirl generator, it is also advantageous to
increase the number of cone shell segments and, associated with it,
the number of air inlet slits, in order in this way to achieve the
smallest possible slit width per air inlet slit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Without restricting the general idea of the invention, the
invention is described below by way of example on the basis of
exemplary embodiments with reference to the drawings, in which:
[0018] FIGS. 1 and 2 show a perspective representation of an
exemplary premix burner with a cylindrically formed shaped
element,
[0019] FIGS. 3 and 4 show a perspective representation of an
exemplary premix burner with a frustoconically formed shaped
element,
[0020] FIG. 5 shows a sectional representation through an exemplary
premix burner with a frustoconically formed shaped element, and
[0021] FIGS. 6 and 7 show a perspective representation of an
exemplary premix burner with a shaped element having an inlet
region formed in a funnel-shaped manner.
DETAILED DESCRIPTION
[0022] Shown in FIG. 1 is a perspective representation of a premix
burner, with the viewing direction from the downstream side into
the swirl space of a swirl generator 2 that is enclosed by a
multiplicity of cone shell segments 1. FIG. 2 shows the same premix
burner, but from a different viewing angle, that is looking at the
swirl generator 2 from the outside, said generator being enclosed
by eight cone shell segments 1 in the exemplary embodiment
represented. The further refinements of the exemplary embodiment
represented in FIGS. 1 and 2 are the same in each case, so that
there is no further distinction between FIG. 1 and FIG. 2.
[0023] The premix burner represented has a central receiving unit
3, which takes the form of a receiving sleeve and is intended for a
central fuel supply unit, for example in the form of a fuel nozzle
for liquid fuels or fuel lance for a pilot flame (not represented),
to be pushed in and held. The cone shell segments 1, connected by
their upstream ends to the receiving unit 3, mutually enclose air
inlet slits 4 and are placed with respect to a burner axis A
extending centrally through the premix burner in such a way that
they delimit a swirl space widening conically in the direction of
flow at a cone angle .gamma.. Each individual cone shell segment 1
has, moreover, depending on the type of fuel, at least one fuel
supply line 5, by means of which fuel can be admixed into the
incoming combustion air flow passing through the air inlet slits
2.
[0024] While maintaining their shape, the individual cone shell
segments 1 open out with their downstream end on an inside wall 6
of a cylindrically formed shaped element 7 surrounding the cone
shell segments 1. The individual cone shell segments 1 are
connected to the inside wall 6 of the shaped element 7 along a line
of intersection 8, which is obtained by a virtual penetration of
each individual cone shell segment 1 with the inside wall 6 of the
cylindrical shaped element 7. In this way, the swirl flow formed
inside the swirl generator 2 does not undergo any disturbance after
flowing over the individual cone shell segments 1.
[0025] Provided upstream of the shaped element 7, for purposes of
an improved incoming air flow through the air inlet slits 4 of the
swirl generator 2, is a second shaped element 9, which is likewise
formed in a hollow-cylindrical manner and has a greater inside
diameter than the first shaped element 7. The transition between
the inside diameters of the shaped elements 7 and 9 takes place by
means of a discontinuous stage 10, which is adjoined, moreover, by
the fuel supply lines 5 of each individual cone shell segment
1.
[0026] The downstream contour of the shaped element 7 is formed in
a cylindrical manner and offers the possibility of a
constructionally simple connection, for example to a combustion
chamber (not represented) arranged downstream in the direction of
flow of the premix burner represented.
[0027] Shown in a perspective representation in FIGS. 3 and 4 is a
further exemplary embodiment of a premix burner formed according to
the invention, in which, as a difference from the exemplary
embodiment that is represented in FIGS. 1 and 2, the region of the
shaped element 7 is formed as a frustoconical portion tapering
conically in the direction of flow. To avoid repetition, the
reference numerals that have already been introduced are not
described. The exemplary embodiment represented in FIGS. 3 and 4
has in the region of the shaped element 7 an inside wall 6, which
is hatched in the perspective representations and is adjoined by
the downstream ends of the cone shell segments 1, while maintaining
their shape. Adjoining the inside wall 6 of the shaped element 7
downstream is a shaped element 11 which is formed in a
hollow-cylindrical manner and serves as a coupling piece or flanged
piece for a following combustion chamber. The inside wall 6 placed
with respect to the cone shell segments 1 has the effect that the
lines of intersection 8 of the cone shell segments 1 with which
they adjoin the inside wall 6 are smaller or shorter in the
direction of flow than in the case of the aforementioned exemplary
embodiment, in which the cone shell segments adjoin along a
cylindrically formed inside wall directed coaxially in relation to
the burner axis.
[0028] A graphic cross-sectional representation of the embodiment
shown in FIGS. 3 and 4 can be seen in FIG. 5. Clearly evident is
the shape-maintaining adjoinment of each individual cone shell
segment 1 to the inside wall 6 of the shaped element 7 tapering
conically in the direction of flow in the form of a cone, which
element goes over in the direction of flow into a
straight-cylindrical region 11.
[0029] Depicted in FIGS. 6 and 7 is a further exemplary embodiment
of a premix burner, provided with a shaped element 7 which has an
upstream region, the so-called inflow region 12, which has an
inside wall 6 tapering in the form of a funnel in the direction of
flow. The curvature of the inside wall 6 in this inflow region 12
corresponds approximately to the contour of a quarter ellipse. The
inflow region 12 is adjoined in the direction of flow as part of
the shaped element 7 by a flow region 12' with a largely constant
flow cross section, to which finally an inlet flange of a
combustion chamber can be attached (not represented). As also in
the variants described above, while retaining their cone shell
segment shape, the cone shell segments 1 of the swirl generator 2
end in the adjoining inside wall 6 of the shaped element 7 in a
flush manner, as though the cone shell segments would penetrate
unhindered through the inside wall 6, but the cone shell segments 1
terminate respectively by means of the lines of intersection 8 at
the inside wall 6. In the case of the inflow region 12 formed as a
quarter ellipse, the downstream end regions of the cone shell
segments 1 closely follow the elliptical curvature of the inside
wall 6 in this region 12. For the meaning of the reference numerals
that have already been introduced and are additionally provided in
FIGS. 6 and 7, reference is made to the aforementioned figures.
[0030] The connection of each individual cone shell segment by its
downstream end region to an inside wall of a shaped element
surrounding the cone shell segments, while maintaining its shape,
leads to minimal irritation of the swirl flow passing through the
cone shell segments. As a difference from the previously known
premix burners, there are no blocking-off effects in the axial
direction through the burner axis associated with the way according
to the invention in which the cone shell segments end in the
corresponding inside wall while maintaining their shape.
[0031] It will be appreciated by those skilled in the art that the
present invention can be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
presently disclosed embodiments are therefore considered in all
respects to be illustrative and not restricted. The scope of the
invention is indicated by the appended claims rather than the
foregoing description and all changes that come within the meaning
and range and equivalence thereof are intended to be embraced
therein.
LIST OF REFERENCE NUMERALS
[0032] 1 cone shell segments [0033] 2 swirl generator [0034] 3
receiving unit [0035] 4 air inlet slits [0036] 5 fuel supply line
[0037] 6 inside wall [0038] 7 shaped element [0039] 8 plane of
intersection [0040] 9 shaped element [0041] 10 step [0042] 11
hollow-cylindrically formed shaped element [0043] 12 inflow
region
* * * * *