Title of Invention

AN IMPROVED BURNER

Abstract This invention relates to an improved burner (100) having a combustion air duct (104), in which a swirl generator (109), which is formed from a number of swirl generator elements (108), is arranged in such a way that the swirl generator (109) can increase the mean velocity at which combustion air (112) flows through the swirl generator (109) to a Mach number of at least 0.4. This results in flow-acoustic decoupling of the combustion area from the combustion-air feed area. This leads to effective suppression of the combustion oscillations. The invention is widely used in the industries such as: industry for making glass and steel products.
Full Text The invention relates to a burner having a
combustion-air feed duct.
Section 3.4 of the book "Berechnung der
Schallausbreitung in durchstromten Kanalen von
Turbomaschinen unter besonderer Beriicksichtingung der
Auslegung von Drehtonschaltern" ["Calculation of the
sound propagation in flow ducts of turbomachines,
taking particular account of the design of rotational
sound switches"] by Christian Faber, Verlag Shaker,
Aachen 1993 illustrates how discontinuities in flow
ducts influence the propagation of sound in a fluid
flowing in these flow ducts. Scatter, reflection and
transmission factors are derived, by means of which it
is possible to calculate which part of incident sound
energy passes the discontinuity and which part is
reflected.
DE 44 30 697 C1 shows an incoming-air sound absorber.
The incoming-air sound absorber comprises a flow line
which is surrounded by an impervious wall and through
which a gaseous medium flows at subsonic speed. A
device for suppressing airborne sound emissions is
arranged in the flow line. As seen in the direction of
flow of the medium, this device is arranged upstream of
a sound-emitting noise source and is used to suppress
the emissions of airborne sound in the opposite
direction to the direction of flow. The device has a
constriction, which is similar to a laval nozzle, in
the flow line. This constriction, in the form of a
laval nozzle, accelerates the velocity of the gaseous
medium to the speed of sound. This builds up a
reflection barrier to the airborne sound.
Combustion oscillations may occur in combustion
systems. Combustion oscillations of this type are
described in the article "Combustion-Driven-
Oscillations in Industry" by Abbott A. Putnam, American
Elsevier,
New York 1971. In accordance with the Rayleigh
criterion, a combustion oscillation is built up when
heat is periodically supplied to a quantity of air in a
combustion chamber if this supply of heat takes place
as a periodic combustion output release in phase with a
characteristic oscillation of the air in the combustion
chamber. Accordingly, the combustion oscillation can be
suppressed by a release of power of the opposite phase.
Combustion oscillations of this type may lead to
considerable noise pollution and even to mechanical
damage to components of the combustion device. It is
stated in the above article, on page 4 under the
paragraph "Pulsations in supply rate" that the
combustion oscillation may be coupled to an air or fuel
supply. To avoid the propagation of pulsations in the
supply systems, it has been proposed to bring about a
considerable pressure loss in the supply systems, in
order in this way to construct a reflection barrier.
However, it has already been pointed out that a
pressure loss of this type is generally unacceptable.
The article "Ma├čnahmen zur Vermeidung von Verbrennungs-
schwingungen-Kennzahl zur stromungsakustischen
Entkopplung am Brenner" [Measures aimed at avoiding
combustion oscillations - characteristic variable for
flow-acoustic decoupling at the burner"] by D. Schroder,
Gaswarme International, Vol. 41, section 1, January 1992
has developed a flow-acoustic limit value criterion for
decoupling a combustion chamber from a coupled system
of pipes. The decoupling is effected by a reflection
area, which is produced in particular at the burner by
means of a narrowing of the cross section of a feed
pipe and, if appropriate, in addition by a perforated
plate arranged at this cross-sectional narrowing.
However, these measures have the drawback of a
considerable pressure loss for the medium which is fed
to the burner.
US-A 4,483,138 shows a burner with a combustion air
duct in which a swirl-blade ring, which is formed from
a number of swirl blades, is arranged, the passage
cross-sectional area between two swirl blades
narrowing, followed by an abrupt increase in the
passage cross-sectional area. A reduction in the flow
velocity is not desired.
US-A 5,451,160 shows a burner having a combustion air
duct in which a number of swirl-generator elements are
arranged. The swirl-generator elements are only
diagrammatically illustrated, and consequently a
profile of the passage cross section between two
swirl-generator elements is not known.
US-A 5,5 558,515 shows a burner having a combustion air
duct in which swirl-generator elements are arranged,
the passage cross-sectional area narrowing between two
swirl-generator element, followed downstream by an
abrupt increase in the passage cross-sectional area.
The swirl-generator elements have a separation edge in
the downstream direction. Following the swirl-generator
element there is a venturi element which accelerates
the flow again.
It is an object of the invention to provide a burner in
which a combustion zone into which the burner opens out
is decoupled from a feed line for combustion air for
the burner
in terms of flow acoustics, this decoupling at most
resulting in an acceptable additional pressure loss in
the combustion air.
According to the invention, this object is achieved by
a burner having a combustion air duct, in which a swirl
generator, which is formed from a number of
swirl-generator elements, is arranged in such a way
that the swirl generator increases the mean velocity at
which the combustion air passes through the swirl
generator to a Mach number of at least 0.4, in
particular at least 0.6. The swirl-blade ring has first
and second blades, which alternate with one another in
the circumferential direction of the swirl-blade ring,
the second blades being offset with respect to the
first blades in the opposite direction to a direction
of flow of the combustion air.
According to the invention, this object is also
achieved by a burner having a combustion air duct in
which a swirl generator, which is formed from a number
of swirl generator elements, is arranged in such a way
that the swirl generator increases the mean velocity of
combustion air flowing through the swirl generator to a
Mach number of at least 0.4, in particular at least
0.6.
At the same time, the profile of the additional swirl
blades is designed in such a way that pressure is
recovered in the combustion air. This is achieved by
means of a passage cross section which widens
gradually. This gradual widening is to be designed in
such a way that there is no flow separation along the
swirl blades.
The mean velocity of flow in this context is the mean
formed for the velocity over a cross section of the
combustion air duct.
Swirl generators are often used in a burner to impart a
swirl, which stabilizes the combustion flame, to the
combustion air entering the combustion chamber. A
reflection barrier for sound waves is built up using
the swirl generators by means of simultaneous
acceleration of the combustion air by means of the
swirl generators to a Mach number of at least 0.4. This
weakens or even suppresses the propagation of
combustion oscillations into the feed line system for
combustion air. By building up the reflection barrier
by means of the swirl generator, a pressure loss in the
combustion air can be kept at a low level. Therefore,
the acoustic decoupling has at most a slight negative
effect on the efficiency of a combustion device in
which the burner is integrated.
It is preferable for a swirl-blade ring comprising
swirl blades for imparting a swirl to the combustion
air to be arranged in the combustion air duct. It is
also preferable for the swirl generator to be formed by
the swirl-blade ring. Therefore, instead of providing
additional swirl generators for acoustic decoupling,
a swirl-blade ring which is present in any case is
designed as an acoustically decoupling swirl generator.
Designing the swirl-generating elements as swirl blades
results in a measure which is easy to implement in
order to keep the pressure loss in the combustion air
at a low level. This is because acceleration of the
combustion air when it enters the swirl-blade ring as a
result of an effective narrowing of the cross section
is followed again by a widening, by means of which
pressure is recovered in the combustion air, on account
of the blade profiles which narrow in the direction of
flow. Therefore, designing the flow generator as a
swirl-blade ring has the advantage both that a means
which is already present is provided for generating a
combustion-stabilizing swirl, and that pressure
recovery, which has a favorable effect on efficiency,
becomes possible in the combustion air.
The swirl-blade ring preferably has first and second
blades which alternate with one another over the
circumferential direction of the swirl-blade ring, the
second blades being offset with respect to the first
blades in the opposite direction to a direction of flow
of the combustion air. The first blades preferably have
a first maximum profile thickness and the second blades
preferably have a second maximum profile thickness, the
first maximum profile thickness being greater than the
second maximum profile thickness. The first blades have
a first chord length and the second blades have a
second chord length. In this context, the first chord
length is preferably shorter than the second chord
length. The swirl generator is therefore formed to a
certain extent from two partial blade rings which
engage in one another in an offset manner in the
direction of flow. The blades of one of the partial
rings are preferably longer and thinner than the blades
of the other partial ring, and specifically it is
preferable for the blades of that partial ring which is
arranged in front of the other partial ring, as seen in
the direction of flow, to be longer and thinner. This
design enables the two methods of operation
of the swirl-blade ring to be optimized, i.e. both the
function of swirl generation and the function of
acoustic decoupling can be fulfilled to a sufficient
extent by suitable dimensioning and matching of the
partial rings to one another. Moreover, this structure
results in a simple way of retrofitting a swirl-blade
ring in a burner in such a way that it subsequently
allows the desired acoustic decoupling. For this
purpose, it is simply necessary for a further
swirl-blade ring to be inserted into the existing
swirl-blade ring. This is achieved by arranging an
additional swirl blade between in each case two
existing swirl blades. Suitable dimensioning of the
additional swirl blades results in the desired
acceleration of the combustion air to a Mach number of
over 0.4, preferably over 0.6, more preferably over
0.8. At the same time, the profile of the additional
swirl blades is designed in such a way that a recovery
of pressure is achieved in the combustion air. This is
preferably achieved by means of a gradually widening
passage cross section. In particular, this gradual
widening is to be designed in such a way that there is
no flow separation along the swirl blades.
The combustion air duct is preferably of annular
design.
Preferably, fuel can be admitted to the combustion air
duct, and in the process this fuel is intensively mixed
with the combustion air prior to combustion.
Furthermore, it is preferable for it to be possible for
the fuel to be admitted from at least some of the
swirl-generating elements. The intensive mixing of the
fuel with the combustion air prior to combustion
(premix burner) leads to a reduction in the emissions
of nitrogen oxides. This is achieved by making the
flame temperature more uniform on account of intimate
mixing, since the emissions of nitrogen oxides rises
exponentially with the flame temperature. A further
advantage of the acoustic decoupling
by means of the swirl generator is additional mixing of
fuel and combustion air, since, on account of the
pronounced acceleration of the combustion air and of
the adjoining zone of pressure recovery, additional
turbulence in the combustion air leads to a further
improvement in the mixing of combustion air and fuel.
If appropriate, the swirl generator may also be
dimensioned in such a way that some of the pressure
recovery is dispensed with in favor of mixing which is
improved by increased turbulence.
The burner preferably has an additional pilot burner,
which is used to stabilize combustion of the
fuel/combustion air mixture emerging from. the
combustion air duct. If the pilot burner operates as a
diffusion burner, i.e. fuel and combustion air in the
pilot burner are only mixed at the location of
combustion, the burner is also known as a hybrid
burner, in which both premix combustion and diffusion
combustion takes place.
The burner is preferably designed as a gas turbine
burner. Particularly in the case of a high power
conversion of a gas turbine, combustion oscillations
with very high amplitudes and possibly considerable
damaging effects may occur. The flow-acoustic
decoupling from the combustion-air supply system is of
particular importance in this context. This applies in
particular to stationary gas turbines.
The invention is explained in more detail by way of
example with reference to the accompanying drawing,in which, in
some cases diagrammatically and not to scale:
FIG. 1 shows a gas turbine,
FIG. 2 shows a burner, and
FIG. 3 shows swirl blades of a swirl-blade ring.
Identical reference symbols have the same meaning
throughout the various figures.
FIG. 1 shows a longitudinal section through a gas
turbine 301. A compressor 303, a combustion chamber 305
and a turbine part 307 are arranged one behind the
other along a turbine axis 302. The combustion chamber
305 opens out into the burner 100, which comprises an
annular combustion air duct 104 and a central pilot
burner 106, which is surrounded by the combustion air
duct 104. The pilot burner 106 is designed as a
diffusion burner, in which fuel 114 and combustion air
112 are mixed and burnt in a combustion zone 311. Fuel
114 is admixed with the combustion air 112 from the
compressor 303 in the combustion air duct 104, upstream
of the combustion zone 311. Therefore, the combustion
air 112 is initially intimately mixed with the fuel
114, before likewise being burnt in the combustion zone
311 within the combustion chamber 305. This process,
which is known as premix combustion, is stabilized by
the diffusion combustion of the pilot burner 106.
During the combustion in the combustion chamber 305,
hot exhaust gas 315 is generated and is fed to the
turbine part 307. The energy of the hot exhaust gases
315 is converted into rotational energy of a turbine
shaft (not illustrated in more detail) by an
arrangement of blades and vanes in the turbine part
307, which are not shown in more detail.
Fluctuations in the combustion flame 313 result in
propagation of sound waves within the combustion
chamber 305, these sound waves being reflected by the
combustion-chamber walls and in turn causing
fluctuations in the flame 313 at the location of
combustion 311. At certain frequencies of the
fluctuations, this interaction makes it possible to
build up a stable combustion-chamber oscillation in the
combustion chamber 305, which may lead to considerable
noise being produced or even to damage to components of
the gas turbine 301. These combustion oscillations also
propagate through the combustion air duct 104.
Therefore,
an additional volume, which can additionally promote
the formation of combustion-chamber oscillations, is
coupled to the combustion chamber 305 through the
combustion air duct 104. Moreover, under certain
circumstances components upstream of the combustion
chamber 305 are also exposed to damaging vibrations.
Therefore, it is desirable for the combustion air duct
104 to be decoupled from the combustion chamber 305 in
terms of flow acoustics. For this purpose, it is
necessary to build up a reflection barrier for the
sound waves from the combustion chamber 305. However, a
simple narrowing of the cross section or the use of a
perforated plate or the like would impair the
efficiency of the gas turbine 301 to such an extent
that economic operation would no longer be possible.
One possible way of acoustically decoupling combustion
chamber 305 and combustion air duct 104 by means of a
burner 100 which is simple and acceptable in terms of
the pressure loss is shown in FIG. 2.
FIG. 2 shows a partially sectional, perspective view of
a burner 100 which is directed along a combustion axis
98. An annular combustion air duct 104 is formed by an
inner wall 101 and an outer wall 102. This duct
surrounds a centrally arranged pilot burner 106, which
is not shown in detail. A swirl generator 109, which is
designed as a swirl-blade ring, is arranged in the
combustion-air duct 104. This swirl generator is formed
from swirl-generator elements 108 which are designed as
swirl blades. The position of the swirl blades 108 can
be adjusted by means of adjustment bolts 110 in the
outer wall 102. The swirl-blade ring 109 is formed from
different swirl blades 108 which alternate with one
another along its circumferential direction U. A first
swirl blade 108B is in each case followed by a second
swirl blade 108A. The first swirl blades 108B are
offset with respect to the second swirl blades 108a,
and are designed to be both shorter and thicker. This
is explained in more detail below with reference to
FIG. 3.
Fuel 114 is admitted to the combustion air duct 104,
via openings, in particular around the blade-inlet
edge, from some, preferably all of the swirl blades
108, by means of a fuel duct, which runs inside the
swirl blade 108 and cannot be seen in this figure.
Combustion air 112 flows through the combustion air
duct 104. This air is mixed intensively with the fuel
114. The dimensioning of the swirl blades 108
accelerates the combustion air 112 to a Mach number of
over 0.4. As a result, a reflection barrier for sound
waves is built up. This leads to acoustic decoupling of
the combustion chamber 305, into which the burner 100
opens, and that part of the combustion air duct 104
which lies upstream of the swirl generator 109. The
combustion air 112 is accelerated by a narrowing in the
passage cross section for the combustion air 112. On
account of the design of the profile of the swirl blade
108, this narrowing is adjoined by a widening of this
passage cross section, in such a way that as far as
possible there is no flow separation for the combustion
air 112. This ensures a high recovery of pressure in
the combustion air 112, so that there are at most
slight losses in efficiency.
FIG. 3 shows a cross section through three of the swirl
blades 108, specifically second swirl blades 108A and
an intervening first swirl blade 108B. The first swirl
blade 108B has a blade front-edge point 200B, a blade
rear-edge point 202B, a skeleton line 204B, a maximum
profile thickness 206B and an adjustment engagement
feature 208B. In a corresponding way, every second
swirl blade 108A has in each case a blade front-edge
point 208A, a blade rear-edge point 202A, a skeleton
line 204A, a maximum profile thickness 206A and an
adjustment engagement means 208A. Combustion air 112
flows in the direction of flow 210 between the first
swirl blade 108B and one of the second swirl blades
108A. Along this direction of flow 210, the first swirl
blade 108B is set back with respect to the second swirl
blades 108A, so that a distance L1 results between the
tangents on the respective blade front-edge points
200B,
200A. A passage cross section Fl for the combustion air
112 flowing between the swirl blades 108 is reduced to
a maximum constriction, which is characterized by a
minimum distance L4 between the first swirl blade 108B
and the second swirl blade 108A. After this maximum
constriction, the passage cross section F2 increases
again, specifically in such a moderate way that there
is no flow separation and therefore no pressure losses
on account of the formation of turbulence. This ensures
a high recovery of pressure in the combustion air 112.
Between the blade rear-edge points 202B, 202A, the
combustion air 112 emerges again between the two blades
108. The blade rear-edge points 202B, 202A are
separated from one another by the distance L3. The
first swirl blades 108B have both a greater maximum
profile thickness 206B and a shorter profile chord 204B
compared to the maximum profile thicknesses 206A and
the profile chords 204A of the second swirl blades
108A. This alternating design of the blades in the
swirl-blade ring 109 makes it possible both to set a
sufficiently high swirl to stabilize combustion and
also the desired acoustic decoupling effect by
acceleration of the combustion air 112 and subsequent
pressure recovery.
In their front region, i.e. along the skeleton line
204A from the blade front-edge point 200A, the second
swirl blades 108A have, in the first quarter, feed
passages 212, through which fuel 114 which is guided in
the interior of the swirl blades 108A can be released
into the combustion air 112. This leads to particularly
intimate mixing of combustion air 112 and fuel 114 even
in the region of the swirl generator 109. Moreover, the
location of combustion is separated from the location
where the mixture is formed, since the decoupling
constriction lies downstream of the fuel supply. As a
result, the fuel supply, which in general can often be
regarded as the cause of fluctuations, is acoustically
decoupled from the combustion. This acoustic decoupling
of the
cause of combustion oscillations leads to combustion
oscillations being suppressed particularly effectively.
The following values are preferably set for the
dimensions of the swirl blades 108 and the distances
between them:
L1 = distance between the tangents on the blade
front-edge points 200B, 200A = 1 to 5 cm,
L2 = distance between the blade front-edge points 200B,
200A = 2 to 8 cm,
L3 = distance between the blade rear-edge points 202B,
202A = 1 to 5 cm,
L4 = minimum distance between the first swirl blades
108B and the second swirl blades 108A = 0.3 to 3 cm,
maximum profile thickness 206B of the first swirl
blades 108B = 2 to 6 cm,
length of the skeleton line 204B of the first swirl
blade 108B = 5 to 17 cm,
maximum profile thickness 206A of the second swirl
blade 108A = 0.5 to 4 cm,
skeleton line length of the profile chord 204A of the
second swirl blade 208A = 8 to 20 cm.
WE CLAIM;
1. An improved burner (100) having a combustion air duct (104),
in which a swirl generator (109), which is formed from a
number of swirl-generator elements (108), characterized in that
the said swirl generator is arranged in such a way that the
swirl generator (109) can be used to increase the mean velocity
at which the combustion air (112) passes through the swirl
generator (109) to a Mach number of at least 0.4.
2. The burner (100) as claimed in claim 1, wherein a swirl-blade
ring (109) comprising swirl blades (108) for imparting a
combustion-stabilizing swirl to the combustion air (112) is
arranged in the combustion air duct (104).
3. The burner (100) as claimed in claim 2, wherein the swirl
generator (109) is formed by the swirl-blade ring (109), the
swirl-generating elements (108) being formed by the swirl
blades (108).
4. The burner (100) as claimed in claim 3, wherein the
swirl-blade ring (109) is formed from first swirl blades (108B)
and from second blades (108A), which follow one another
alternately in the circumferential direction (U) of the
swirl-blade ring (109), the second swirl blades (108A) being
offset with respect to the first swirl blades (108B) in the
opposite direction to a direction of flow (210) of the combustion
air (112).
5. The burner (100) as claimed in claim 4, wherein the first swirl
blades (108B) have a maximum profile thickness (206B) and
the second swirl blades (108A) have a second maximum profile
thickness (206A), the first maximum profile thickness (206B)
being grater than the second maximum profile thickness
(206A).
6. The burner (100) as claimed in claim 4 or 5, wherein the first
swirl blades (108B) have a first profile chord length (204B) and
the second swirl blades (108A) have a second profile chord
length (204A), the first profile chord length (204B) being
shorter than the second profile chord length (204A).
7. The burner (100) as claimed in any one of the preceeding
claims, wherein the flow velocity is increased by narrowing a
free passage cross section (Fl) for the combustion air (112) and
a subsequent recovery of pressure in the combustion air (112)
is achieved by a free passage cross section (F2) which widens
gradually in such a way that the combustion air (112) flows
between the swirl-generating elements (108) substantially
without a flow separation.
8. The burner (100) as claimed in any one of the preceeding
claims, wherein the combustion air duct (104) is of annular
design.
9. The burner (100) as claimed in any one of the preceeding
claims, wherein fuel (114) can be admitted to the combustion
air duct (104) and, when this happens, the fuel is mixed
intensively with the combustion air (112) prior to combustion.
10. The burner (100) as claimed in claim 9, wherein the fuel (114)
can be admitted from at least some of the swirl-generating
elements (108).
11. The burner (100) as claimed in any one of the preceeding
claims, which comprises an additional pilot burner (106), by
means of which combustion of the fuel/combustion air
mixture emerging from the combustion air duct (104) can be
stabilized.
12. The burner (100) as claimed in any one of the preceeding
claims, which is designed as a gas turbine burner (100).
This invention relates to an improved burner (100) having a
combustion air duct (104), in which a swirl generator (109), which is
formed from a number of swirl generator elements (108), is arranged
in such a way that the swirl generator (109) can increase the mean
velocity at which combustion air (112) flows through the swirl
generator (109) to a Mach number of at least 0.4. This results in
flow-acoustic decoupling of the combustion area from the
combustion-air feed area. This leads to effective suppression of the
combustion oscillations. The invention is widely used in the
industries such as: industry for making glass and steel products.

Documents:

IN-PCT-2002-506-KOL-CORRESPONDENCE.pdf

IN-PCT-2002-506-KOL-FORM-27.pdf

in-pct-2002-506-kol-granted-abstract.pdf

in-pct-2002-506-kol-granted-claims.pdf

in-pct-2002-506-kol-granted-correspondence.pdf

in-pct-2002-506-kol-granted-description (complete).pdf

in-pct-2002-506-kol-granted-drawings.pdf

in-pct-2002-506-kol-granted-examination report.pdf

in-pct-2002-506-kol-granted-form 1.pdf

in-pct-2002-506-kol-granted-form 18.pdf

in-pct-2002-506-kol-granted-form 2.pdf

in-pct-2002-506-kol-granted-form 3.pdf

in-pct-2002-506-kol-granted-form 5.pdf

in-pct-2002-506-kol-granted-gpa.pdf

in-pct-2002-506-kol-granted-priority document.pdf

in-pct-2002-506-kol-granted-reply to examination report.pdf

in-pct-2002-506-kol-granted-specification.pdf

in-pct-2002-506-kol-granted-translated copy of priority document.pdf

IN-PCT-2002-506-KOL-OTHER PATENT DOCUMENTS.pdf

IN-PCT-2002-506-KOL-PA.pdf


Patent Number 225487
Indian Patent Application Number IN/PCT/2002/506/KOL
PG Journal Number 46/2008
Publication Date 14-Nov-2008
Grant Date 12-Nov-2008
Date of Filing 22-Apr-2002
Name of Patentee SIEMENS AKTIENGESELLSCHAFT
Applicant Address WITTTELSBACHERPLATZ 2, D- 80333 MUNCHEN, DEUTSCHLAND
Inventors:
# Inventor's Name Inventor's Address
1 OLAF HEIN AM ALTEN BAHNHOF 32, 45481, MULHEIM
PCT International Classification Number F23C 7/00
PCT International Application Number PCT/EP00/10167
PCT International Filing date 2000-10-16
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 99121577.3 1999-10-29 EUROPEAN UNION