Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BURNER
TECHNICAL FIELD
The present disclosure relates to the subject matter set forth in the claims.
In
particular, it relates to a burner. It further relates to a corribustor and a
gas turbine
engine incorporating the burner.
BACKGROUND OF THE DISCLOSURE
From the art, combustion systems and burners are known for the combustion of a
fuel with low nitric oxide generation. For this purpose, the fuel, in
particular a
gaseous fuel, is generally provided for combustion in an intensely premixed,
lean
fuel-oxidant mixture. The oxidant is most commonly air. For improved
readability
and ease of nomenclature, in the present disclosure the term "air" will be
used to
generically denote any oxidant. The skilled person will, by virtue of the
aforesaid,
readily understand the mention of air in the following as a disclosure of a
generic
oxidant. "Air", to this extent, shall be broadly construed to represent a
generic
oxidant.
Lean premixed flames yield the issue of combustion stability, as they are
generally
operated at an equivalence ratio rather close to the lower extinction limit.
Hence, in
certain operation modes, the premix flames, or some of the premix flames, are
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replaced with, or supported by, so-called piloting flames. These are flames
combusting less intensely premixed or even essentially non-premixed fuel-air
mixtures, comprising zones of richer fuel-air mixture and thus providing for
higher
local combustion temperatures and yielding a combustion less sensitive to
external influences. On the downside, however, nitric oxide formation
increases
disproportionally with the combustion temperature, and hence a balance needs
to
be found between nitric oxide formation and combustion stability. Diffusion
flames,
corn busting a stream of fuel and air with zones having equivalence ratios
close to
1, i.e. near stoichiometric zones, yield excellent combustion stability, but
with high
nitric oxide formation. It is hence a goal in burner development and
combustion
engineering to design burners and operation concepts which yield minimum
combustion instabilities in lean premix combustion and/or enable combustion
over
a large range of operation with as little piloting as possible.
Another aspect to be considered in the design of burners and combustion
systems
is an increasing demand for fuel flexibility. The combustion of so-called
"blue" and
"green" hydrogen, which is generated using renewable energy, may be found a
suitable way to store and transport energy harvested from, for instance, solar
and
wind power plants. The operation of premix burners on fuels which yield a
higher
reactivity than natural gas, such as for instance, while not limited to, CO
and
hydrogen, or gas mixtures comprising high contents of C2+ species, i.e.,
hydrocarbon species having two or more carbon atoms, CO or hydrogen thereof,
for a non-limiting instance 50% and more by volume, requires further
considerations. Hydrogen, for instance, yields a short autoignition time,
significantly higher flame velocity, and a wide flammability range. Thus, the
operation of premix burners on, for instance, hydrogen or hydrogen-rich
mixtures
as fuel increases the risk of flame flashback and burner overheating, which
need
to be accounted for. The same is true for other fuels yielding, generally
spoken,
higher flammability than for instance natural gas. The combustion of hydrogen
can
yield locally higher flame temperatures when compared to the combustion of
natural gas, which might result in an increased formation of nitric oxides.
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US 6,267,585 suggests the combustion of hydrogen by directly injecting
hydrogen
into air jets from perforated blades, by which the hydrogen is combusted in
micro
diffusion flames. The document states that in reducing the perforation matrix
size
of the perforated blades nitric oxide levels of as low as 10 ppmv (parts per
million,
volumetric) can be achieved. A burner type sometimes referred to as cluster
burner or micro tube cluster burner is known in the art and suggested for the
combustion of hydrogen. These generally comprise mixing tubes which are
intended to be flown through by air and which extend through a fuel plenum.
The
mixing tubes are in fluid communication with the fluid plenum, whereby the
fuel
can be mixed into the combustion air stream through the mixing tubes.
US 2013/0232979 discloses a burner comprising mixing tubes which extend
through a fuel plenum. Nozzles extend into the mixing tubes for discharging
fuel
from the fuel plenum into the mixing tubes. WO 2015/182154 and
US 2010/0218501 disclose further examples of burners of similar structure and
function. US 2016/033133 suggests an arrangement of a multitude of individual
cluster burner modules side by side, wherein each cluster burner module
comprises an individual fuel plenum and is equipped with an individual supply
line.
US 2015/076251 describes a cluster burner in which the mixing tubes are
combined with a fuel cartridge. Furthermore, a cooling air plenum is provided
downstream of the fuel plenum. The cooling air plenum discharges the cooling
air
through the downstream front wall of the burner for effecting effusion and
film
cooling and is not fluidly connected to the mixing tubes. US 4,100,733
suggests a
microtube cluster burner in which radially inner and radially outer micro
tubes are
arranged to be fed with fuel from distinct fuel plenums. In embodiments, the
fuel
plenums are stacked along the throughflow direction of the microtubes. A
further
cluster burner wherein fuel is discharged from fuel plenums into tubes which
extend through the plenums is known from US 2013/074510.
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OUTLINE OF THE SUBJECT MATTER OF THE PRESENT DISCLOSURE
It is an object of the present disclosure to provide a burner as initially
mentioned.
In aspects, a burner shall be disclosed which avoids the drawbacks of the art
outlined above. In more specific aspects, a burner shall be proposed which
enables the combustion of hydrogen or hydrogen rich fuel or other highly
reactive
fuel gases or fuel gas mixtures in a wide load range and with minimized
flashback
risk and nitric oxide formation. Such gases and gas mixtures are, generally
spoken, characterized by at least one of a significantly shorter autoignition
time,
significantly higher flame velocity, and a significantly broader range of the
equivalence ratio in which they are flammable. In another aspect, a burner
shall be
proposed which allows robust lean premix operation over a wide load range with
minimized flame blowoff risk. In still other aspects, the burner shall be
suitable for
operation on a wide range of fuels. In further aspects, the burner shall
enable the
use of, in addition to fuel, inert fluids for purposes of, for instance, while
not limited
to, reducing nitric oxide formation, mitigating potential flashback issues,
and other
purposes.
In still another aspect, the burner shall be suitable to replace existing
burners in
legacy combustors or combustion appliances, like for instance, while not
limited to,
gas turbine combustors. Such upgrading of legacy combustors may enable those
combustors to be operated on fuels for which the legacy burners to be replaced
were not suitable or inhibited limitations. Such upgrading may also be
suitable to
enhance fuel flexibility, emissions, operating range and other characteristics
of a
legacy combustor. For one, non-limiting instance, a legacy corn bustor may be
upgraded for the combustion of hydrogen.
These objectives are achieved by the subject matter set forth in claim 1
and/or the
specifics outlined in the dependent claims.
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Further effects and advantages of the disclosed subject matter, whether
explicitly
mentioned or not, will become apparent in view of the disclosure provided
below.
Accordingly, disclosed is a burner comprising a first, upstream front wall and
a
5 second, downstream front wall. A general airflow direction is defined
from the first,
upstream front wall to the second, downstream front wall. Hence, the terms
upstream and downstream used in the context of the herein described burner
shall
be understood as referring to the general airflow direction from the first,
upstream,
front wall to the second, downstream front wall, unless defined differently in
the
specific context. It is noted that generally a skilled person will be able to
determine
which of the front walls is intended to serve as the downstream front wall.
The
downstream front wall generally is, implicitly, intended to be provided
bordering a
combustion space and may thus define in terms of material use, cooling
features,
coatings and other features characteristic of a downstream front wall of a
burner
and by which the skilled person will readily distinguish the downstream front
wall
from the upstream front wall. At least one partition wall extends across the
general
airflow direction and between the first and second front walls, whereby the at
least
one partition wall divides a space between the upstream front wall and the
downstream front wall into at least two separate fluid plenums stacked along
the
general airflow direction. The front walls and partition walls may in the
following
also be referred to as the "transverse walls". The burner further comprises at
least
one peripheral wall extending between at least one of: the two front walls, at
least
two partition walls, and/or a front wall and a partition wall. The peripheral
wall may
in particular be leak-proof connected to the transverse walls to which it
extends
along the circumference of the respective transverse wall, thus forming an
essentially closed plenum between the respective transverse walls. For the
sake
of clarity it is noted that within the framework of the present disclosure
each space
between two of the transverse walls inside the burner shall be understood as a
plenum or fluid plenum, irrespective whether the space is further enclosed by
a
peripheral wall or not. A plenum or fluid plenum may be referred to as a
"closed
plenum" if further enclosed by a peripheral wall or an "open plenum"
otherwise. In
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particular embodiments, the peripheral wall may extend from the upstream front
wall to the downstream front wall and be leak-proof connected to the upstream
and downstream front walls along their respective circumference and further in
particular to all partition walls along their respective circumference. In
another
example, the peripheral wall may extend from the upstream front wall to the
most
downstream partition wall and be leak-proof connected to the upstream front
wall
and the most downstream partition wall along their respective circumference,
and
further in particular to all interposed partition walls along their respective
circumference. It is understood that the most downstream plenum formed between
the most downstream partition wall and the downstream front wall may in
particular be intended to be used as a cooling air plenum and may hence be
open
at the periphery to receive air from the outside. Plenums intended to be used
with
fuel or other agents different from air, or more generally spoken, different
from the
oxidizing agent provided to the burner, may in contrast be closed by the
peripheral
wall and be provided with fluid supply connectors. It will be understood that
at least
the closed plenums comprise fluid supply connectors and are intended to be
connected to supply lines fluidly connected to the plenums. A multitude of
passages are provided through the upstream and downstream front walls and the
at least one partition wall. These passages are provided by openings in the
transverse walls, wherein openings in each transverse wall are aligned so as
to
form a passage through which another member may be formed or extend. A
multitude of ducts are provided and extend through at least some of the
passages
and thereby through the fluid plenums, wherein the duct walls are leak-proof
connected to the first front wall, the second front wall and the interposed
partition
walls. In particular, the ducts may extend from the upstream front wall to the
downstream front wall. Such, the ducts provide fluid connection between an
upstream side of the burner adjacent the first front wall and a downstream
side of
the burner adjacent the second front wall. Each duct has a first, upstream end
adjacent the first, upstream front wall and a second, downstream end adjacent
the
second, downstream front wall. The first, upstream end of each duct opens out
to
the upstream side of the burner and the second downstream end of each duct
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opens out to the downstream side of the burner A longitudinal direction is
defined
between said ends of each duct. At their upstream ends, the ducts may be
provided with a smooth inflow geometry, for instance a trumpet-shaped
funnelling
geometry or otherwise comprise a rounded transition geometry to the upstream
front blade, so as to minimize losses of total pressure of the fluid intended
to flow
through the ducts. The ducts are intended to flow the oxidizing agent, most
commonly combustion air, therethrough from the upstream side of the burner to
the downstream side of the burner. The burner comprises discharge means for
providing fluid communication between at least one of the fluid plenums and
the
interior of at least one of the ducts, the discharge means being configured
for
discharging a fluid from a respective fluid plenum into the duct. At least one
of the
discharge means is provided as at least one through hole through a duct wall
and
be hereinafter also be referred to as a "wall-opening type discharge means",
and
at least one of the discharge means is a discharge nozzle which is suspended
in a
duct by a tube or by tubes and may hereinafter also be referred to as a
"nozzle
type discharge means". The tube or tubes extend from a fluid plenum to the
discharge nozzle and provide fluid communication between said fluid plenum and
the discharge nozzle. It may be said that the nozzle is suspended inside the
duct.
Multiple through holes or a group of through holes through the wall of a duct
may
jointly form one discharge means. The discharge nozzle may for instance be
tube-,
drop-, tear-, cone- or pyramid-shaped, while not limited to said exemplarily
given
geometries, and be arranged with a longitudinal axis at least essentially
parallel to
or coaxial with a longitudinal axis of the duct. The nozzle comprises at least
one
discharge opening through which fluid originating from a fluid plenum and
conveyed to the nozzle may be discharged into the respective duct. A discharge
opening may be provided at an axial front face of the nozzle, in particular at
a front
face pointing towards the downstream end of the duct in which the nozzle is
arranged, or on a side wall of the nozzle, in particular in a downstream
region of
the nozzle or adjacent the downstream front face of the nozzle. At least one
of the
ducts is provided with at least two discharge means, each discharge means
fluidly
connecting a fluid plenum out of the at least two fluid plenums to the
interior of the
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duct. The at least two discharge means are provided to discharge a fluid from
inside the respective fluid plenum at different positions along a longitudinal
direction of the duct. Said discharge positions may in particular be
referenced to
and measured from the downstream end of the respective duct, and to a
downstream edge or opening forming the discharge means. Said different
longitudinal discharge positions for one and the same duct may differ from
each
other by for instance at least 2%, at least 5% or at least 10%, or even at
least 20%
of the length of the respective duct. As will be set forth below, it might be
the case
that two discharge means out of the at least two discharge means connect to
one
and the same plenum or to different plenums.
By virtue of the subject matter set forth above it is possible to discharge
multiple
fuel and non-fuel fluids into the combustion air flow through a duct of a
micro-tube
burner and discharge fluids into one and the same duct at different
longitudinal
positions of the duct, thus achieving specific and different mixing of the
fluid and
the combustion air at the downstream end of the duct. This allows superior
versatility when operating the burner.
The outer geometry of the ducts corresponds to that of the passages. The inner
cross-section of the ducts is in embodiments rounded and more in particular
circular. In other embodiments, however, an inner cross-section of a duct may
be
oval, elliptical, or polygon-shaped, wherein in more particular examples the
inner
cross-section of a duct may have the shape of an equilateral polygon. It is
understood that the ducts of the burner of the herein disclosed type are
referred to
a "microtubes" in the art, and hence imply to have comparatively small cross-
sectional dimensions. A cross-sectional area of a single duct may be 2000 mm2
or
less, 1500 mm2 or less, 1000 mm2 or less, 500 mm2 or less, 300 mm2 or less,
100
mm2 or less, or 64 mm2 or less. In other aspects, the hydraulic diameter,
defined
as four times the cross-sectional area divided by the length of the inner
circumference of a duct, may be 50 mm or less, 40 mm or less, 35 mm or less,
25
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mm or less, 20 mm or less, 10 mm or less, or 8 mm or less.
The skilled person will appreciate that the more upstream inside a duct, i.e.
the
further from the respective downstream end of the duct, a fluid is discharged
into
the duct the more intensely it is premixed with the combustion air, or other
oxidizer, flowing through the duct, when it exits from the duct at the
downstream
end thereof. Accordingly, a fuel discharged at a relatively downstream
position of a
duct may be combusted in a relatively stronger diffusion combustion
characteristic,
while a fuel discharged at a relatively upstream position of a duct may be
combusted in a relatively stronger premix combustion mode. In other words, the
combustion of a fuel discharged at a relatively downstream position of a duct
will
generally spoken be more robust, i.e., less susceptible to flame extinction,
when
compared to the combustion of a fuel discharged at a relatively upstream
position
of a duct, while the latter generally spoken produces less nitrogen oxides.
The term "longitudinal direction", as herein used, is not to be understood as
vectored, but shall generally be understood as the orientation of a
longitudinal
extent in space, and may be equivalent to an axial direction, for instance, of
a
duct. However, a duct may be curved, whereby it has, strictly spoken, no axis,
which might implicitly be understood as being straight, but has a curved
longitudinal direction. An axis of a duct or passage may in particular extend
parallel to the longitudinal direction of the duct or passage. A "longitudinal
position"
shall denote the position along said longitudinal direction measured from a
specific
reference position, such as a downstream end of a duct or passage.
It is noted that within the framework of the present disclosure the use of the
indefinite article "a" or "an" does in no way stipulate a singularity nor does
it
exclude the presence of a multitude of the named member or feature. It is thus
to
be read in the sense of "at least one" or "one or a multitude of".
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It is moreover noted that in the context of the present disclosure the terms
"neighbouring" and "adjacent" are considered as synonyms.
In some embodiments, a cartridge may be provided in or may extend through at
5 least one of the passages. At least one cartridge may in more particular
embodiments be provided for providing a liquid agent like liquid fuel or water
into a
combustion space therethrough, and may more particularly comprise an atomizer,
in particular at a distal end of the cartridge which points towards the
combustion
space. The cartridge may also be intended for providing steam, piloting fuel
gas,
10 or other gaseous agents therethrough. The cartridge may be a separate
member
and may be retractable from the burner. The cartridge may be provided directly
through the passages, whereby an outer circumference of the cartridge seals
with
the transverse walls of the burner. In other embodiments, the cartridge may be
inserted into a duct which in turn extends through a passage. It is
appreciated that
in said embodiment the duct through which the cartridge extends may be
provided
without discharge means for providing fluid communication with a fluid plenum.
However, in other embodiments, such discharge means may be provided such
that fluid from a fluid plenum may be discharged downstream a tip of the
cartridge
or in an annular space provided between the outer wall of the cartridge and
the
inner wall of the duct.
In particular, each of the passages may be provided with either a duct or a
cartridge therein or therethrough.
The outer surfaces of the ducts or cartridges extending through the passages
may
seal gas-proof with the transverse walls through which they extend.
As will be appreciated and noted above, if a fluid is discharged into a duct
at a
relatively upstream position, it has a longer path to mix with, for instance,
combustion air flowing through the duct before it is discharged into a
combustion
space at the downstream end of the duct when compared to a fluid which is
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discharged into the duct at a relatively downstream position. Thus, if for
instance a
gaseous fuel is discharged more upstream it may be considered as a premix
fuel,
while the fuel discharged more downstream is cornbusted in a relatively
diffusion
flame characteristic, hence providing additional robustness to the combustion
of
the premix fuel, in particular at low premix equivalence ratios. On the
downside,
the combustion of less intensely premixed piloting fuel will result in
comparatively
higher nitrogen oxide formation. However, one advantage of a micro-tube burner
of the kind herein disclosed is the relatively small dimension of the
individual flame
emanating from an individual duct, and hence the relatively low residence time
of
the species at the elevated temperature level fostering nitrogen oxide
formation.
Discharge of fuel at a relatively upstream location and discharge of fuel at a
relatively downstream location may take place simultaneously, and in one or in
different ducts. The combustion of the less premixed fuel supports combustion
of
the more premixed fuel.
In non-limiting embodiments, at least one duct out of the multitude of ducts
is in
fluid communication with at least two fluid plenums, wherein at least one
first
discharge means is provided for providing fluid communication with a first one
of
said at least two fluid plenums and at least one second discharge means is
provided for providing fluid communication with a second one of said at least
two
fluid plenums. This allows fluids to be selectively discharged into the duct
from
either of the thereto connected plenums. It will thus be found advantageous if
supply lines to the plenums are equipped with individual control valves which
allow
controlling the supply of fluid to the plenums individually.
It may further be provided that at least one duct out of the multitude of
ducts is
configured with a first discharge means which is provided as a wall-opening
type
discharge means and further with a second discharge means which is nozzle type
discharge means. This provides enhanced flexibility in discharging fluid into
a duct.
In particular, it will be appreciated that a fluid discharged into a duct
through a
nozzle-type discharge means may generally be discharged in or close to the
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centre of the duct, while fluid discharged through a wall-opening type
discharge
means is discharged into a boundary layer along the duct wall, and, dependent
upon the momentum of the discharged fluid, may or may not penetrate the
boundary layer. It will further be appreciated that if a fluid is discharged
into a duct
through a nozzle type discharge means the actual discharge position may be
shifted along the general airflow direction, or the longitudinal direction of
the duct,
respectively, while in the case of a wall-opening type discharge means the
discharge position is coupled to the position of the respective fluid plenum.
In order
to take advantage of this flexibility it might thus be provided that the first
discharge
means is in fluid communication with a first fluid plenum and the second
discharge
means is in fluid communication with a second fluid plenum, wherein the first
fluid
plenum is arranged downstream from the second fluid plenum along the general
airflow direction. A discharge position of the second, nozzle type, discharge
means
providing fluid communication between the duct and the second, relatively
upstream, fluid plenum may be positioned downstream the discharge position of
the first discharge means. Thus, fluid from a relatively upstream fluid plenum
may
be discharged into the duct downstream from fluid originating from a
relatively
downstream plenum. In more specific embodiments, the discharge position of the
second, nozzle type, discharge means may be at maximum 2 times the minimum
hydraulic diameter of the duct downstream the discharge position of the first
discharge means. In other specific and non-limiting embodiments, it may be
provided that the discharge position of the second, nozzle type, discharge
means
is upstream of the discharge position of the first discharge means by at
maximum
5 times the minimum hydraulic diameter of the duct and downstream the
discharge
position of the first discharge means by at maximum 2 times the minimum
hydraulic diameter of the duct. The definition of the hydraulic diameter is
outlined
above. It will be appreciated that the duct may be provided with narrowing and
widening cross-section passages along its longitudinal extent. Thus, the
hydraulic
diameter of the duct may vary along its longitudinal extent. Reference is made
to a
minimum hydraulic diameter of the duct.
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In other embodiments the discharge position of any discharge nozzle is
positioned
at a longitudinal position of the duct inside which the discharge nozzle is
arranged
which corresponds to at maximum 20 minimum hydraulic diameters of the
respective duct when measured from a downstream end of the duct and along the
longitudinal direction of the duct.
In non-limiting exemplary embodiments, at least two discharge means of one
duct
may fluidly connect to one and the same fluid plenum and are provided to
discharge the fluid from the fluid plenum at two different positions along a
longitudinal direction of the respective duct. The one duct may then discharge
a
fraction of relatively more intense premixed fuel together with a fraction of
relatively less premixed fuel into a combustion space, which may serve to
support
combustion of the relatively more intense premixed fuel. It is noted that
fluid from a
particular plenum may likewise be discharged into ducts at more than two
longitudinal positions inside the respective duct, which will yield more or
less
pronounced premix of diffusion flame characteristic of a resulting flame
emanating
from the respective duct. In non-limiting embodiments, a first duct may be
provided
with a first discharge means fluidly connecting the first duct to a first
plenum and a
second duct is provided with a second discharge means fluidly connecting the
second duct to the first fluid plenum, wherein the first discharge means is
arranged
to discharge the fluid from the first fluid plenum into the first duct at a
first
longitudinal position of the first duct when measured from the downstream end
of
the first duct and the second discharge means is arranged to discharge the
fluid
from the first fluid plenum into the second duct at a second longitudinal
position of
the second duct when measured from the downstream end of the second duct.
Further the second duct, in this non-limiting embodiment, is free from a
discharge
means fluidly connecting to the first fluid plenum. Hence, certain ducts may
be
operated as ducts with different premix characteristics of the fuel discharged
from
the first fluid plenum at the downstream end of the ducts. In addition, the
first duct
may be free from a discharge means fluidly connecting to the first fluid
plenum and
arranged to discharge the fluid from the first fluid plenum into the first
duct at the
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second longitudinal position of the first duct when measured from the
downstream
end of the first duct. The more intensely premixed fuel and the less premixed
fuel,
in these embodiments, are provided from one and the same plenum, and the mass
flow ratio of the more intensely premixed fuel and the less premixed fuel thus
is
fixed.
In still further embodiments, a first duct is provided with a first discharge
means
fluidly connecting the first duct to a first fluid plenum and arranged and
configured
for discharging into the first duct at a first position when measured from the
downstream end of the first duct and a second duct is provided with a second
discharge means fluidly connecting the second duct to a second fluid plenum
and
arranged and configured for discharging into the second duct at a second
position
when measured from the downstream end of the second duct. The first duct may
be fluidly isolated from the second fluid plenum and the second duct may be
fluidly
isolated from the first fluid plenum. In yet other aspects, a first duct is
provided with
a first discharge means fluidly connecting the first duct to a first fluid
plenum and
arranged and configured for discharging into the first duct at a first
position when
measured from the downstream end of the first duct and the first duct is
further
provided with a second discharge means fluidly connecting the first duct to a
second fluid plenum and arranged and configured for discharging into the first
duct
at a second position when measured from the downstream end of the first duct.
The second position is in both cases different from the first position,
wherein the
positions may be expressed in absolute dimensions or in multiples of a minimum
hydraulic diameter of the respective duct. The mass flow of fluid discharged
from
the plenums at the different first and second positions can be controlled
independently from each other in providing independent control valves in the
supply lines to the plenums. Thus, the mass flow ratio of the more intensely
premixed fuel and the less premixed fuel can be controlled.
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While it is presumed to be self-evident, it is noted that generally a duct may
be
provided with discharge means for discharging fluid into the duct at more than
two
longitudinal positions of the duct.
5 The concept of axial staging of fuel discharge into a duct ¨ i.e., the
further
upstream in a duct the fuel is discharged into the duct the more intensely
mixed
the fuel will be with combustion air upon exiting the duct, yielding a more
premix
type combustion and related low nitrogen oxides emissions, vs. fuel being
discharged into the duct further downstream yielding a more diffusion type
10 combustion and related higher nitrogen oxides generation, which on the
other
hand is less susceptible to interference ¨ has been outlined in some detail
above.
In embodiments, the herein proposed burner comprises a duct which is
dedicatedly configured as a piloting duct and is in fluid communication with a
fluid
plenum different from the most downstream fluid plenum through discharge means
15 configured to discharge into the piloting duct at a longitudinal
distance, when
measured from the downstream end of the duct and along a longitudinal extent
of
the duct, corresponding to at maximum five times the minimum hydraulic
diameter
of the duct. Hence, the fuel may be virtually unmixed with the combustion air
upon
exiting from the duct and is combusted in a diffusion flame. In more specific
exemplary embodiments, a multitude of piloting ducts are provided and each
piloting duct is arranged in the centre of adjacent, i.e. immediately
neighbouring,
non-piloting ducts. Non piloting ducts, in this respect, are ducts which are
in fluid
communication with a fluid plenum different from the most downstream fluid
plenum through discharge means configured to discharge into the non-piloting
duct at a longitudinal distance, when measured from the downstream end of the
respective duct and along a longitudinal axis of the respective duct,
corresponding
to more than five times the minimum hydraulic diameter of the respective duct,
in
particular six or more times, seven or more times, or ten or more times the.
minimum hydraulic diameter of the respective duct. The non-piloting ducts may
in
particular be arranged on a concentric hexagon around the piloting duct. In
more
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particular embodiments, 6n non-piloting ducts may be arranged adjacent the
piloting duct, wherein n is a natural number.
Each three neighbouring passages may be arranged on the corners of an
equilateral triangle. On an overall scale, this arrangement results in the
passages
being provided on an equidistant pattern, wherein each two neighbouring
passages have the same distance from each other, and the mutual influence of
the flows and flames emanating from them can easily be transposed from one
pair
of neighbouring passages to another pair of neighbouring passages. In more
particular embodiments, this may result in an arrangement wherein a burner
comprises a central passage which is encircled by a number of hexagonal rings
in
which further passages are arranged. Generally, on the nth hexagonal ring
encircling a central passage, when counted from the central passage, 6n
passages are provided. Apart from the passages of the outer ring, each passage
is encircled by six neighbouring passages on a hexagonal ring. For instance,
one
duct provided as a dedicated piloting duct for a specific fuel may be
encircled by
six neighbouring ducts provided as dedicated premix ducts for said specific
fuel.
Likewise, a nozzle or cartridge may be arranged in or through a passage which
is
encircled by six other passages. In this embodiment, the nozzle or cartridge
may
comprise an atomizer and may be intended for supplying liquid fuel
therethrough,
while, on the liquid fuel operation, the six neighbouring ducts may be
intended for
providing the combustion air when the burner is operated on liquid fuel. Other
arrangements not explicitly mentioned are readily conceived by a skilled
person.
The self-similar arrangement of passages, or ducts and/or cartridges,
respectively,
facilitates scalability of the burner. Moreover, providing the burner as an
overall
hexagon facilitates replacing existing burners of a legacy combustor with a
number
of burners of the type herein disclosed arranged beside each other.
In aspects, all ducts of the burner are parallel to each other. More in
particular, the
ducts may be parallel to a burner axis, wherein said burner axis is defined as
a
virtual axis perpendicular to the outer surface of the downstream front wall,
or
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downstream face of the burner, which is intended to face a combustion space
arranged downstream the burner. It may in other aspects be provided that at
least
a subset of the multitude of passages are arranged in at least one concentric
hexagonal ring around a midpoint. Said concentric hexagonal ring may be
provided as an equilateral hexagon, comprising in particular 6n passages,
wherein
n is a natural number. The passages arranged in the at least one concentric
hexagonal ring are oriented such that fluid discharged at the downstream side
of
the burner from the passages in the concentric hexagonal ring has a velocity
component which is tangential to a circle defined around the midpoint of the
hexagonal ring. For instance, if a downstream face of the burner, which is the
outer face of the downstream wall not facing a plenum, is a plain surface the
passages, and accordingly any duct or cartridge provided therethrough, are
accordingly inclined with respect to a normal to the downstream face. In
particular,
all passages in a given hexagonal ring may be inclined at an identical angle.
As
the skilled person will readily appreciate, said configuration is suited to
generate a
macroscopic vortex downstream the burner.
It is noted that the expression "subset" of passages or ducts, as used within
the
framework of this document, may as a special case also mean all passages or
ducts of the burner, if, in a specific embodiment, the attributes conjugated
with the
subset apply to all passages or ducts.
In a discharge means, to the extent it comprises at least two discharge
openings,
the discharge openings may be provided such that the velocity vectors of all
streams of fluid to be emanated from the discharge openings meet at or
virtually
originate from a common point in a view on a cross-section of a duct. For
instance,
if the duct inner cross-section is circular or elliptical or has the shape of
an
equilateral polygon, they may meet on or virtually originate from a centre of
the
duct cross-section. Likewise, a single discharge opening of a discharge means
may be provided such that the velocity vector of a stream of fluid emanating
from
said opening is directed towards or virtually originates from a duct centre.
It will be
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appreciated that geometric relations with respect to the duct in this context
strictly
relate to the open inner cross-section of the duct. In other embodiments,
however,
at least one discharge opening of a discharge means may be provided such the
fluid is discharged with a tangential velocity component relative to the duct
cross-
section.
Further, a discharge opening of a discharge means may be provided so as to
discharge fluid in a direction perpendicular to the longitudinal direction of
the duct.
It may also be inclined so as to discharge the fluid with a velocity component
into
the upstream or downstream direction of the duct.
In embodiments, vortex generators and/or blades may be arranged inside a duct.
Vortexes in the flow of combustion air through a duct may serve to intensify
mixing
of fuel and other fluids discharged into the duct through discharge means of
the
duct with the flow of combustion air. A number of blades may be arranged along
the circumference of the duct to generate a swirl of the combustion air inside
the
duct. In embodiments, the vortex generators and/or row of blades are arranged
in
an upstream section of a duct, for instance in the upstream 30% of the
longitudinal
extent of the duct, in the upstream 20% thereof, or in the upstream 10%
thereof.
The vortex generators and/or row of blades may be arranged upstream of any
discharge means inside the duct. However, they may also be arranged
differently
with respect to the discharge means, for example between discharge means in
the
intended direction of combustion air flow or downstream thereof, according to
the
needs. It may moreover be the case that vortex generators and/or rows of
blades
may be provided at more than one longitudinal position of a duct and/or
longitudinal position relative to discharge means.
At least three fluid plenums may be stacked along the general airflow
direction.
Plenums may be provided for the supply of different fluids, e.g., different
fuels. For
a specific fuel, two or more plenums may be provided so as to control the
supply
of said specific fuel to different ducts or the supply of said specific fuel
at different
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longitudinal positions of the ducts for controlling, for instance, piloting.
Further
plenums may be added for supplying inert fluids like steam or nitrogen, which
might be useful for flashback control, or for supplying, through internal
atomizing
nozzles inside on or more ducts, water or liquid fuel or another liquid agent
into the
flow through said one or more ducts. The herein proposed burner thus provides
superior versatility for multi-fuel operation capability and the possibility
to add other
fluids, in that simply another plenum needs to be added to the stack of
plenums.
The most downstream fluid plenum may be intended to be used as a coolant
plenum. The most downstream fluid plenum may be provided with at least one of
a
fluid connection into at least some of the ducts, so as to discharge fluid
from the
most downstream fluid plenum into said at least some of the ducts, and/or with
front wall through holes extending through the second, downstream front wall,
different from the passages through the downstream front wall, so as to
discharge
fluid from the most downstream fluid plenum into an area downstream of the
burner and to cool the downstream front plate by effusion cooling. The most
downstream plenum may in particular be in fluid communication with at least
one
or with a fraction of the ducts or with all ducts through wall-opening type
discharge
means. The discharge means providing fluid communication between the most
downstream plenum and a duct may be configured so as to discharge fluid from
the most downstream plenum into the duct with a downstream velocity component
tangential to the inner surface of the duct wall. The coolant then forms an
inert
boundary layer at the downstream end of the duct which helps to avoid
flashback
into the duct. It is noted that the most downstream fluid plenum may in
embodiments be supplied with other coolant than air, such as for instance,
while
not limited to, steam.
Further, it may be provided, in non-limiting exemplary embodiments, that the
second fluid plenum, when counted from the downstream side of the burner, is
in
fluid communication with the fluid surrounding the burner on its lateral
sides. To
this extent, in one aspect, no peripheral wall may be provided enclosing the
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second fluid plenum counted from the downstream side of the burner, such that
said plenum is an open plenum. In another aspect, said plenum may be enclosed
by a perforated peripheral wall extending between the transverse walls
adjacent
said plenum. Thus, when the burner is installed in a combustion appliance,
said
5 second fluid plenum counted from the downstream side of the burner is in
fluid
communication with a burner hood chamber inside which combustion and cooling
air is provided. The most downstream fluid plenum then may be in fluid
communication with said second fluid plenum when counted from the downstream
side of the burner through openings in the partition wall delimiting the most
10 downstream fluid plenum from the second fluid plenum when counted from
the
downstream side of the burner. Thus, for instance, impingement cooling of the
downstream wall of the burner, which faces the combustion chamber, may be
achieved. The most downstream fluid plenum, in this embodiment, may further be
in fluid communication with the downstream side of the burner through the
15 downstream front wall, in particular through openings provided
therethrough, to
provide further cooling of the downstream wall of the burner. The used cooling
fluid is thus discharged into the combustion chamber. The most downstream
fluid
plenum may alternatively or in addition be configured to discharge the cooling
air
into the downstream part of at least one duct or at least some ducts.
In embodiments, at least a subset of the multitude of passages are arranged as
outer passages on a concentric hexagonal ring around and adjacent at least one
inner passage, wherein at least one inner duct is provided in the at least one
inner
passage and at least one outer duct is provided in the outer passages. In
embodiments, the at least one inner passage might be one single central
passage.
In other embodiments, the at least one inner passage is arranged on an inner
hexagon which is surrounded by an outer hexagon on which the outer passages
are arranged. The at least one inner duct has a most downstream discharge
position at which a discharge means in fluid communication with a fluid plenum
different from the most downstream fluid plenum is configured to discharge
into
the at least one inner duct which is positioned at a first longitudinal
distance from
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the downstream end of the at least one inner duct. The at least one outer duct
has
a most downstream discharge position at which a discharge means in fluid
communication with a fluid plenum different from the most downstream fluid
plenum is configured to discharge into the at least one outer duct which is
positioned at a second longitudinal distance from the downstream end of the at
least one outer duct. The second longitudinal distance is larger than the
first
longitudinal distance. Hence, a more intensely premixed fuel-air mixture exits
from
the at least one outer duct compared to the fuel-air mixture which exits from
the at
least one inner duct.
Each cross-section taken along the longitudinal extent of each duct, and more
in
particular perpendicular to the axis of the duct, out of the multitude of
ducts may
have one of a circular or polygonal shape.
If a fluid plenum is provided as a closed fluid plenum as defined above,
supply
connectors must be provided in fluid connection with the closed fluid plenum.
In
embodiments of the burner, the burner thus comprises supply connectors
configured for fluid supply to at least some of the fluid plenums. In more
specific
embodiments, at least two of the fluid plenums are fluidly connected to a
respective individual supply connector, wherein at least two supply connectors
of
different fluid plenums are arranged concentrically and coaxially.
The burner may be integrally formed by additive manufacturing. That means, the
transverse walls, peripheral walls, duct walls, discharge means and, as the
case
may be, further elements like the above-mentioned vortex generators and
blades,
are provided as a seamless, monolithic one-piece member. The entire burner may
be an additively manufactured seamless, monolithic one-piece member. In other
embodiments, the burner may be assembled from layers, wherein each layer
comprises at least two transverse walls and at least one plenum between the
transverse walls. The burner may be assembled from seamless, monolithic one-
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piece members, each member comprising at least one plenum enclosed by two
transverse walls and, optionally, by a lateral wall, stacked upon each other.
At least one of the through holes arranged in the wall of a duct out of the
multitude
of ducts for providing fluid communication with a fluid plenum may have an
elliptically shaped cross-section, wherein in particular the long axis of the
ellipse
includes an angle of at maximum 30 degrees with one of a longitudinal axis of
the
duct, the general airflow direction or a burner axis, and wherein further in
particular
the ratio of the length of the longer ellipse axis to the length of the short
ellipse
axis is 1.25 or more. In the case that a duct is curved, the above-specified
angle
shall be measured against a local axis at the location of the through hole. A
burner
axis may be defined as an axis perpendicular to at least one of the upstream
wall
or a downstream wall. It may be found advantageous if the long axis of the
ellipse
is oriented at least approximately along a building direction of the burner
during
additive manufacturing of the burner. In applying such a geometry overhanging
structures in the boundary of the through hole are reduced, which considerably
facilitates applying an additive manufacturing process. The building direction
might
be chosen along the duct axis or the general air flow direction of the burner.
At least one of the through holes arranged in the wall of a duct out of the
multitude
of ducts for providing fluid communication with a fluid plenum may have a
polygonal shaped cross-section having a polygonal shaped boundary, the
polygonal shaped boundary comprising straight boundary segments, wherein said
polygonal shaped boundary comprises an upstream boundary section and a
downstream boundary section, wherein at least one of the upstream boundary
section and the downstream boundary section is shaped such that an angle
included between each straight segment of the respective boundary section and
one of a longitudinal axis of the duct, the general airflow direction or a
burner axis
is smaller than or equal to 45 degrees. The statements as to the longitudinal
axis
of the duct and the burner axis made above apply. Also this shape of duct wall
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through holes reduces overhanging structures in the boundary of the through
hole,
which considerably facilitates applying an additive manufacturing process.
In aspects of the present disclosure, the burner may comprise at least some
ducts
differing form each other as to the minimum hydraulic diameter of the ducts.
In still further aspects, at least a subset of ducts out of the multitude of
ducts are
provided with a nozzle type discharge means inside the respective duct,
whereby
an outer boundary of a respective discharge nozzle provided inside a duct
defines
a closest residual flow cross-section between the discharge nozzle and the
inner
wall of the duct. At least two ducts out of the subset of ducts may be
provided with
different residual flow cross-sections. Generally spoken, a residual flow
cross-
section between a nozzle and an inner duct wall will represent a narrowest
flow
cross-section inside the duct, i.e. a metering section. Thus, the mass flow or
volume flow through individual ducts of said subset of ducts may be adjusted
by
the choice of this residual flow cross-section. Said purposeful choice
residual flow
cross-sections may be achieved by a choice of the interacting geometries of
the
nozzle and the inner wall of the duct, i.e. by choice of size and/or shape.
It may in embodiments be provided that at least one duct out of the multitude
of
ducts comprises at least one tapering cross-section longitudinal portion,
wherein
within a tapering cross-section longitudinal portion the cross-sectional area
of the
at least one duct tapers downstream the general airflow direction, or in a
direction
from an upstream end of the duct towards the downstream end of the duct,
respectively, from a first cross-sectional area to a second cross-sectional
area
smaller than the first cross-sectional area. A discharge nozzle is provided
within
said at least one duct with a downstream end of said discharge nozzle,
relative to
the intended flow direction of the duct and/or the general airflow direction,
is
positioned within a tapering cross-section longitudinal portion. Provided that
the
discharge nozzle is configured to discharge at the downstream end, or adjacent
the downstream end, fluid from the discharge nozzle is discharged into an
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accelerated flow. Said tapering cross-section longitudinal portion, in which
the
downstream end of said discharge nozzle is provided, may be configured such
that the hydraulic diameter of the duct at the position where the duct has the
first
cross-sectional area is 1.12 times or more and 2.5 times or less the hydraulic
diameter of the duct at the position where the duct has the second cross-
sectional
area.
For an even more specific instant, the downstream end of nozzles may be
provided at different positions within the tapering cross-section longitudinal
portions of different ducts, thus yielding different residual flow cross-
sections and
hence different mass or volume flows through the different ducts.
It may be provided, in non-limiting embodiments, that out of two fluid plenums
arranged upstream of the most downstream fluid plenum the one which is
arranged further upstream is fluidly connected through discharge means to a
larger number of ducts than the one arranged more downstream. It may be
intended to supply both of these fluid plenums with the same fuel.
It should be mentioned that in principle a plenum, as defined between two
adjacent transverse walls, may be subdivided into sub-plenums in a direction
across the burner axis, or over the cross-section of the burner, respectively.
Such,
the supply of fluids to the ducts may not only be controlled along the general
airflow direction or burner axis, but also about the cross-section of the
burner.
In other aspects, inserts may be provided inside at least one of the plenums,
so as
to mitigate eventual non-uniformity of the volume flow to the various
discharge
means with which the plenum is in fluid communication.
Further disclosed is a combustor comprising a combustion space and further
comprising at least any embodiments of a burner as set forth above, wherein
the
second, downstream, front wall of the burner faces the combustion space and
the
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most downstream of the fluid plenums adjacent the second, downstream front
wall
is provided as a coolant plenum. The coolant plenum may be connectable, or
connected, to a source of cooling air. In other aspects, the coolant plenum
may be
connectable, or connected, to a source of an alternative coolant like for
instance,
5 while not limited to, steam. Connectable, in this context, means that a
connection
line or feed line for connecting is present, but may be equipped with a stop
and/or
control device, so that fluid communication is not necessarily always present.
At least one fluid plenum may be fluidly connectable to a source of
combustible
10 gas. At least one fluid plenum may be connectable to a source of fuel
containing at
least 50% by volume of hydrogen. At least one fuel plenum may be connectable
to
a source of an inert fluid. In particular, if one plenum is connectable to a
source of
hydrogen-rich fuel or other highly reactive fuel, when compared to natural
gas, it
may be found useful if a plenum downstream therefrom is connectable to a
source
15 of an inert fluid in order to mitigate flashback risk.
At least plenums which are connectable to sources of combustible fluid may
advantageously also be provided connectable to a purging fluid source, such as
air or inert fluid, so as to avoid flashback into the plenum when not
pressurized.
Further disclosed is a gas turbine engine comprising a combustor of the kind
set
forth above.
It is understood that the features and embodiments disclosed above may be
combined with each other. It will further be appreciated that further
embodiments
are conceivable within the scope of the present disclosure and the claimed
subject
matter which are obvious and apparent to the skilled person by virtue of the
present disclosure.
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BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter of the present disclosure is now to be explained in more
detail
by means of selected exemplary embodiments shown in the accompanying
drawings. The figures show
Fig. 1 shows an embodiment of the herein disclosed burner
in a
sectional view;
Fig. 2 illustrates a nozzle-type discharge means;
Fig. 3 shows a second embodiment of the herein disclosed burner in a
sectional view;
Fig. 4 shows a third embodiment of the herein disclosed
burner in a
sectional view;
Fig. 5 shows an embodiment of the herein disclosed burner
with a
cartridge inserted through one passage in a sectional view;
Fig. 6 shows an embodiment of the herein disclosed
burner, wherein
ducts have different minimum cross-sectional areas, in a sectional
view;
Fig. 7 shows an embodiment of the herein disclosed
burner, wherein
nozzle-type discharge means extend differently far into tapering
sections of the ducts, in a sectional view;
Fig. 8 shows an embodiment of the herein disclosed
burner, wherein two
plenums are connected to coaxial and concentric supply
connectors, in a sectional view;
Fig. 9 illustrates the possible streamwise orientation of discharge means;
Fig. 10 illustrates a duct of a burner in a cross-
sectional view, wherein
discharge means are arranged to discharge the fluid from a
plenum with a tangential velocity component;
Fig. 11 outlines the arrangement of blades at the inlet of
a duct to induce
a vortex flow of combustion air inside the duct;
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Fig.12 illustrates the possible relative longitudinal
discharge positions of a
nozzle-type discharge means and a wall-opening type discharge
means;
Fig. 13 outlines the hexagonal arrangement of passages and
ducts and/or
fuel nozzles of cartridges in embodiments of the herein disclosed
burner;
Fig. 14 illustrates possible arrangements of piloting
ducts, liquid fuel
combustion nozzles or cartridges, steam or water injection nozzles
or cartridges and the like with respect to a generally hexagonal
passage arrangement;
Fig. 15 illustrates tilted passages for inducing a
macroscopic vortex
downstream the burner;
Fig. 16 shows an embodiment of the herein disclosed burner
with coolant
discharge into the ducts in a sectional view;
Fig. 17 illustrates an exemplary elliptical wall opening in a duct wall;
Fig. 18 illustrates an exemplary polygonal wall opening in
a duct wall; and
Fig. 19 outlines geometric details of the polygonal wall
opening of fig. 18.
It is understood that the drawings are highly schematic, and details not
required for
instruction purposes may have been omitted for the ease of understanding and
depiction. It is further understood that the drawings show only selected,
illustrative
embodiments, and embodiments not shown may still be well within the scope of
the herein disclosed and/or claimed subject matter.
EXEMPLARY MODES OF CARRYING OUT THE TEACHING OF THE PRESENT
DISCLOSURE
Figure 1 shows an exemplary embodiment of a burner 1. The burner may be
particularly suitable for the combustion of hydrogen or hydrogen rich fuels
and
other, compared to natural gas, highly reactive fuels, while not being limited
to this
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application. Burner 1 comprises upstream front wall 11 and downstream front
wall
12. On an upstream side 2 of burner 1 a combustion air plenum may be located.
On the downstream side 3 the combustion space is intended to be arranged. The
combustion air plenum may for a non-limiting instance be provided to be
supplied
with compressed air from the compressor of a gas turbine engine, while the
combustion space may be arranged to discharge into the expansion turbine of a
gas turbine engine. Further, as noted above, "air" is to be understood as
being
representative of any oxidation agent, or fluid comprising an oxidation agent,
which is suitable for the combustion of a fuel, and said oxidation agent or
fluid
comprising an oxidation agent is generically disclosed to a skilled person,
although
for the ease of description air is used as a common example representative of
generic oxidation agents or suitable fluids containing oxidation agents. A
general
airflow direction is defined from the upstream wall 11 to downstream wall 12.
Partition walls 21, 22 and 23 are interposed between upstream front wall 11
and
downstream front wall 12 and extend across the general airflow direction.
Front
walls 11 and 12 and partition walls 21, 22 and 23 may generically be referred
to as
transverse walls, as they extend transverse to or across the general airflow
direction of the burner. A space between upstream front wall 11 and downstream
front wall 12 is divided into four plenums by the partition walls, namely most
upstream plenum 31 between upstream front wall 11 and partition wall 21,
plenum
32 between partition walls 21 and 22, plenum 35 between partition walls 22 and
23
and most downstream plenum 33 between partition wall 23 and downstream front
wall 12. Lateral wall 28 further encloses plenums 31 and 32, while lateral
wall 29
encloses most downstream plenum 33. Plenum 35, in contrast, is not enclosed by
a lateral wall and is thus in direct fluid communication with fluid provided
on the
sides of burner 1, which in most common, while not limiting, cases is
identical with
the fluid on the upstream side 2 of burner 1. Plenums 31, 32 and 33 may thus
be
referred to as closed plenums, which require a supply line to be supplied with
a
fluid, while plenum 35 is referred to as an open plenum which may be supplied
with fluid through open lateral sides. Plenum 35 might be in direct fluid
communication with a combustion air plenum inside which the burner is
installed.
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Most downstream plenum 33 is preferably used as a coolant plenum in order to
cool downstream front wall 12 which is exposed to heat from a combustion space
at the downstream side 3 of burner 1. Plenum 33 is fed form a coolant supply
through coolant feed connectors 331, whereby generally an air flow bled from
the
combustion air may be used for cooling purposes. Also steam or any other
suitable cooling fluid may be applied. It may be provided that coolant plenum
33 is
not enclosed by a lateral wall and is thus configured as an open plenum and
may
be placed inside a larger air plenum of the combustor, such that cooling air
may
flow into cooling air plenum 33 form the entire circumference thereof. This
may
also be achieved in that lateral wall 29 of plenum 33 is perforated. Plenum 31
may
be supplied with a fluid through supply connector 311 which joins into plenum
31
from the upstream side of the burner. Plenum 32 may be supplied through a
fluid
supply connector 321 which extends form the upstream side of the burner and
through plenum 31. As will be appreciated by virtue of figure 1, transverse
walls
11, 21, 22, 23 and 12 are provided with multiple sets of aligned openings,
such
that passages 40, of which only some are designated by reference numbers, are
formed and extend through burner 1 from the upstream side 2 to the downstream
side 3. Ducts 41, 42 and 45 extend through passages 40, through transverse
walls
11, 21, 22, 23 and 12 and through the plenums 31, 32, 35 and 33. The duct
walls
are provided gas-leak proof with the transverse walls. It should be noted that
in
embodiments the ducts are seamlessly joined with the transverse walls, in that
the
duct walls and the transverse walls are manufactured in one monolithic piece.
This
may be achieved by additive manufacturing, while any suitable manufacturing
method may be applied to manufacture burner 1. Ducts 41, 42 and 45 provide
fluid
communication from the upstream side 2 to the downstream side 3 of the burner
along their longitudinal directions. In operation, combustion air flows
through ducts
41, 42 and 45 from the combustion air plenum of a combustion appliance, or the
upstream side 2 of burner 1, to the combustion space, or the downstream side 3
of
burner 1. Through holes 51, only some of which are designated by reference
numbers, are provided through the duct walls and provide fluid communication
between plenum 31 and ducts 41 and 45. Through holes 51 are discharge means
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for discharging a fluid from plenum 31 into ducts 41 and 45. Through holes 52
are
provided through duct walls of ducts 45 and provide fluid communication
between
plenum 32 and ducts 45. In addition, duct 42 if fluidly isolated from plenum
31, and
is fluidly connected to plenum 32 by a discharge means which is a nozzle 62
5 suspended inside duct 42. It is noted that the herein proposed burner is
not limited
to just one single duct of the type of duct 42, which is fluidly connected to
only one
plenum through a nozzle-type discharge means 62.
A nozzle type discharge means comprising a nozzle 62 suspended inside a duct
10 42 is shown in figure 2. Nozzle 62 suspended inside duct 42 by tubes
132, which
provide a mechanical connection between the nozzle and the wall of the duct.
Tubes 132 provide fluid communication between nozzle 62 and plenum 32. While
two suspension tubes 132 are shown, or visible, respectively, in the exemplary
embodiment, it is understood that more suspension tubes could be arranged,
while
15 in other embodiments only a single suspension tube may be provided. The
suspension tube or suspension tubes may also be supplemented by suspension
struts, which provide mechanical fixation to the duct wall, but otherwise do
not
serve to supply fluid to the nozzle. The nozzle, in the shown embodiment, is
arranged coaxial with axis 451 of duct 42 and provided centrally within the
duct.
20 The nozzle is provided with an opening at a front face of the nozzle
which is
downstream with respect to the flow of combustion air 4 through duct 42. Fluid
from plenum 32 may thus be injected into the flow of combustion air 4 at the
downstream end of nozzle 62. A half angle a of injection may be 30 degrees or
less. In embodiments, however, discharge from the nozzle may be effected
25 through differently arranged discharge openings. In still further
embodiments
nozzle 62 may be equipped with a liquid agent atomizer.
It will be appreciated that the injection of a fluid into a duct through a
nozzle 62
yields different characteristics than the discharge through openings in the
duct
30 wall. For instance, nozzle 62 discharges a fluid into a core flow
through duct 42
rather than into a boundary layer at the duct wall, as is the case with
discharge
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openings in the duct wall. In another aspect, the penetration of fluid
discharged
into a duct through a wall opening may strongly vary depending on the
differential
pressure between the respective duct and fluid plenum, and thus depend on the
mass flow or volume flow of discharged fluid. The fluid discharged from wall
openings 51 and 52 in figure 1 may penetrate differently deep into the axial
flow
through a duct dependent upon the mass flow or volume flow of discharged
fluid.
As will be appreciated, this is not the case if a fluid is discharged from
plenum 32
through nozzle 62 in the embodiment of figure 2. However, if the fluid is
discharged from nozzle 62 with a comparatively high momentum ¨ i.e., high
volume flow - and at a low cone angle, it might be the case that a streak of
relatively unmixed fluid travels downstream the duct, while, if the fluid is
discharged from wall openings 51, 52 at a comparatively high momentum ¨ i.e.,
high volume flow ¨ it will penetrate deeper into the axial flow and can in
some
cases mix more intensely than at low volume flows. Further, as will be
appreciated, the position of discharge from a wall opening is coupled to the
position of the respective plenum, while a nozzle 62 may extend further
downstream, or also upstream, inside the duct and allow the fluid from a
plenum to
be discharged into the duct remote from the position of the plenum from which
the
fluid originates. Further, a nozzle inside a duct results in a constriction of
the flow
cross-section through the duct, and may hence yield downstream eddies, which
may foster mixture of the discharged fluid with the axial flow of, e.g.,
combustion
air through the duct. Thus, providing discharge means from plenums to ducts in
a
burner of the type outlined above may result in excellent results when
appropriately combining both types of discharge means in different ducts, at
different distance from the downstream ends of the ducts. The absolute
velocity or
momemtum of the fluid upon being discharged from the discharge means may
moreover have a significant impact on the premixing behaviour, as a person
having skill in the art will readily appreciate.
It is noted that more than one fluid plenum may be provided in fluid
communication
with a duct through nozzle-type discharge means, of the type like discharge
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means 62 shown in figure 1, and that more than one nozzle-type discharge means
may be provided inside one duct. Also, more than one fluid plenum may be
fluidly
connected to one or more ducts through nozzle-type discharge means, and one or
more ducts may be fluidly connected to one or more plenums through nozzle-type
discharge means.
Referring again to figure 1, it will further be appreciated that fluid
discharged from
fluid plenum 31 through wall openings 51 into ducts 41 and 45 travels a longer
distance within the ducts before being discharged on the downstream side 3 of
burner 1 that fluid discharged through discharge means 52 and 62. If for
instance
the same type of fuel, for a more specific instance gaseous fuel, is supplied
to both
plenums 31 and 32, the fluid provided through plenum 32 and discharged into a
duct at a relatively downstream location may be less intensely premixed inside
a
duct than fuel discharged into a duct at a relatively upstream location. For
one
instance ¨ dependent upon other parameters of the burner and the fuel ¨ fuel
discharged from plenum 32 may support, by a relatively diffusion type
combustion
in downstream space 3, combustion of more intensely premixed fuel from plenum
31. This can be important in particular at low, understochiometric, overall
fuel/air
ratios, which might result in the extinction of a completely premixed flame.
Dependent upon the particular requirements, all or only some of the ducts may
be
equipped with discharge means intended to supply fuel for combustion of an
intensely premixed fuel/air mixture, i.e. positioned relatively upstream in
the duct.
Likewise, all or only some of the ducts may be equipped with discharge means
intended to supply fuel for more diffusion type combustion, i.e. positioned
relatively
downstream in the duct. As seen in figure 1, some ducts may be intended only
for
relatively far upstream, or premix type, fuel supply, while others may be
intended
only for relatively far downstream, or diffusion type, fuel supply, while yet
other
ducts may be equipped with discharge means for both. It is noted that the mass
flow of fuel through plenums 31 and 32 may be controlled through control means
provided upstream of the fluid supply connectors 311 and 321. While the
control
means are not shown, they are familiar to a skilled person. The fuel mass flow
to
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plenums 31 and 32 may thus be controlled individually, and thus the ratio
between
the mass flow or fuel discharged into the ducts relatively upstream and
relatively
downstream may be individually controlled. In other embodiments, however,
discharge means may be provided in fluid communication with one and the same
plenum and configured to discharge fluid from the plenum into one and the same
duct or into different ducts, or a combination thereof, at different distances
from the
downstream end of a duct, which results in a fixed mass flow ratio of
differently
mixed fluids at the downstream end of the ducts.
Most downstream arranged coolant plenum 33 is fluidly isolated from the ducts
and discharges the coolant though effusion cooling holes 121 in the downstream
front wall and into downstream space 3, i.e., into the combustion space, thus
effecting cooling of downstream front wall 12.
In the embodiment of figure 1, the ducts are shown to be slightly divergent at
their
downstream ends. Such flared outlet of the ducts may be useful to reduce exit
velocity of the flow from a duct and hence reduce the risk of flame lift-off
of the
microjet flames and hence to ensure stabilization of the microjet flames.
However,
the shape of the ducts at the downstream end might be chosen as needed to meet
requirements, for instance, as to the velocity of the gas flow emanating from
a duct
into downstream space 3. The upstream end of the duct may in instances be
rounded or trumpet-shaped to reduce pressure losses.
The device shown in figure 3 differs from the embodiment of figure 1 mainly in
comprising ducts 43 which are equipped with wall-opening type discharge means
51 fluidly connecting ducts 43 to upstream plenum 31, while they are further
equipped with nozzle-type discharge means 62 fluidly connecting ducts 43 with
plenum 32 downstream from the position of wall-opening type discharge means
51.
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It should be noted that a duct may as well be equipped with more than one
nozzle-
type discharge means, which may further be configured to discharge into the
duct
at different longitudinal positions of the duct. Two nozzle-type discharge
means
provided in one and the same duct may further be fluidly connected to one and
the
same fluid plenum or to different fluid plenums. It is further noted that in
the
framework of the present document a longitudinal or upstream-downstream
position within a duct, or any other reference to a longitudinal position
within a
duct, is generally referenced to and measured from the downstream end of the
respective duct, adjacent downstream plate 12. Said dimension defines the
distance for mixing of fluids within a duct before discharging fluid into a
combustion space and thus is a relevant parameter for a duct of the burner.
Longitudinal dimensions inside a duct may further be expressed in multiples of
the
minimum hydraulic diameter of a duct along its longitudinal extent, wherein
the
hydraulic diameter is determined as four timed the local cross-sectional area
divided by the circumference of a wall encircling said cross-sectional area.
The burner 1 shown as another exemplary embodiment in figure 4 comprises
ducts 48 and 49 which are configured as dedicated piloting ducts and which are
characterized in that the position of a downstream discharge location into
ducts
48, 49 from a plenum different form most downstream plenum 33, wherein said
most downstream plenum is configured as a coolant plenum, is provided 5 times
or less the minimum hydraulic diameter of the respective duct upstream from
the
downstream end of the duct. This is so close to the downstream end of the
respective duct that fuel discharged from any of wall-opening type discharge
means 54 provided in ducts 48 or from nozzle-type discharge means 65 provided
in piloting duct 49 will exit from the duct into combustion space or
downstream
space 3 virtually unmixed with the combustion air flowing through the
respective
duct and will thus yield in a markedly diffusion-type flame at the exit of the
duct. As
outlined above, such flames yield higher nitrogen oxide formation, but on the
other
hand superior robustness of combustion. Said marked pilot flames may support
combustion of fuel discharged into ducts 41, 48 and 49 relatively far upstream
in
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the ducts through discharge means 51, and thus intensely premixed when exiting
the ducts, in particular at low fuel/air ratios. In the shown exemplary
embodiment,
each piloting discharge means, positioned less than five minimum hydraulic
diameters upstream form the downstream end of the respective duct, is provided
5 in a duct also comprising an upstream discharge means 51. This is not
necessarily
the case. A piloting duct may also be provided as a standalone piloting duct
having
no other discharge means upstream from the piloting discharge means. However,
distributing the most upstream discharge means in as many ducts as possible
may
yield advantages in that a given fuel mass flow through these upstream
discharge
10 means may be distributed into a maximum fraction of the combustion air,
which
results in good conditions to reduce nitrogen oxides emissions when operating
the
burner at high loads, i.e. with an comparatively high overall fuel/air ratio.
The skilled person will, in the light of the present description, readily
appreciate
that the herein disclosed burner is not limited to be provided with three
plenums,
15 but more generally may be usefully provided with any number of plenums
of two
and larger. For instance, the burner shown in figure 1 may be supplemented
with
two additional plenums which respectively are merely connected to ducts
through
relatively upstream discharge means and relatively downstream discharge means
like ducts 41 and 42 in figures 1 and 3. It may likewise be supplemented with
a
20 combined piloting/premix duct as shown at 48 and 49 in figure 4. In
being fluidly
connected to different plenums the same ducts may thus be supplied with either
natural gas and/or a different combustible, like, for instance, hydrogen.
Thus,
achieved is a highly versatile burner which is suitable for instance for the
combustion of hydrogen or a hydrogen rich or other highly reactive fuel and
for the
25 combustion of natural gas in a variable premix/piloting operation,
through the
same ducts. The order in which the different plenums are arranged along a
general airflow direction of the burner from the upstream side defined by
upstream
front wall 11 to the downstream side defined by downstream from wall 12, or
the
longitudinal position at which fluid from a specific plenum is discharged into
the
30 duct, will be determined by the skilled person in applying his general
knowledge
and taking into account the effect of the mixing distance of a fluid inside
the duct
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from the discharge position of the fluid to the downstream end of the duct.
The
skilled person will readily appreciate that modules comprising fluid plenums
intended for discharging a specific fluid into at least some of the ducts may,
in a
virtually modular manner, be stacked upon each other. This can be achieved in
manufacturing burners with a different number of "slices" comprising a fluid
plenum, sections of the ducts, appropriate discharge means for fluidly
connecting
the plenum to the interior of the ducts, and, optionally, a fluid supply
connector for
supplying fluid to the plenum. It might be considered to actually build the
burner
from stacked modules. The number of plenums is in principle not limited.
Limiting
factors might be seen in the increasing length of the ducts and thus
increasing
pressure losses, and other issues which might arise if fluids are discharged
too far
upstream of the downstream end of the duct. The fluid plenums, with their
specific
discharge means through which they are fluidly connected to at least one duct,
can be stacked in any order a skilled person may find suitable to fulfil a
certain
purpose. However, it might be found advantageous if the most downstream
plenum is a coolant plenum. It will be appreciated that due to the versatility
of the
herein disclosed burner a comprehensive description of possible embodiments is
not practical. However, in understanding the principle behind the stacked
micro
duct burner herein disclosed, and the function and merits of certain specific
embodiments of "modules", the skilled person receives a comprehensive
teaching.
Figure 5 outlines an embodiment of a burner 1 in which a cartridge 60 is
provided
through a passage 40. Cartridge 60 may in embodiments be a separate and
retractable member. Cartridge 60 may be provided instead of or inside a duct.
If
cartridge 60 is provided instead of a duct, it is understood that cartridge 60
is
preferably configured to achieve a gas-leak proof sealing of the plenums. In
the
embodiment shown, cartridge 60 extends through a duct, whereby sealing of the
plenums is achieved by the duct wall which may be seamlessly manufactured with
front walls 11 and 12 and partition walls 21, 22 and 23 in the primary forming
process. Longitudinally extending or spiralling flutes may optionally be
provided on
an outer surface of the cartridge and/or the inner side of the wall of the
duct
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through which cartridge 60 extends. Combustion air may be provided through the
flutes. The flutes may be spiralling, at least at their downstream ends
adjacent
downstream front wall 12 and when opening out to the downstream space 3, so as
to generate a swirling flow of combustion air at or around the downstream end
of
cartridge 60. A fluid 6 may be provided to downstream space 3 through
cartridge
60. Said fluid may be steam, or a gaseous fuel, or mixture of gaseous fuel and
other gaseous agent, which may for instance be intended for diffusion-type
combustion. The gaseous agent may be discharged with a swirl, which may co- or
counter-rotate with a swirl of combustion air. In other embodiments, cartridge
60
may comprise a liquid atomizing nozzle, thus discharging fluid 6 as a spray
cone
5. The liquid may be liquid fuel or water or a mixture thereof. It is
understood that
further agents, for instance atomizing air or steam, may be provided to and
discharged through cartridge 60. A burner of the herein disclosed type may
comprise more than one cartridge 60. Burner 1 of figure 5 further comprises
ducts
43 which are equipped with relatively upstream nozzle type discharge means 61
in
fluid communication with plenum 31 and relatively downstream wall-opening type
discharge means 52 in fluid communication with plenum 32.
Figure 6 shows an exemplary embodiment in which some of the ducts have
different diameters. For instance, ducts 41a and 41b, which are equipped with
relatively upstream wall-opening type discharge means 51 and in fluid
communication with plenum 31 only, have different minimum hydraulic diameters.
It will be appreciated that in a duct without an insert the longitudinal
section having
said minimum hydraulic diameter defines a metering section. These different
diameters, as will be readily appreciated, have an impact on the mass flow of
combustion air through the respective ducts. If discharge means 51 provided in
ducts 41a and 41b have the same integral cross-section per duct, it will be
appreciated that the flow through duct 41b exhibits a higher fuel/air ratio
from fuel
discharged from plenum 31 than the flow through ducts 41a. If, however, the
integral cross-section of discharge means 51 of ducts 412 is larger than the
integral cross-section of discharge means 51 in ducts 41b, the equivalence
ratios
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may - or may not - be the same, and due to the different minimum hydraulic
diameters the thermal load over the downstream surface of the burner adjacent
downstream wall 12 may be varied. In ducts 42 and 43, however, a residual
cross-
section between an inner wall of the duct and an outer wall of nozzles 62 may
define the metering section. The mass flow through ducts 42 and 43 may thus be
varied in providing different hydraulic diameters of ducts 42 and 43 around
nozzles
62, different outer diameters of nozzles 62, or both.
In the embodiment of figure 7, ducts 44a, 44b and 44c are fluidly connected to
plenum 32 through wall-opening type discharge means 52, while plenum 31 is
fluidly connected to ducts 44a, 44b and 44c through nozzle-type discharge
means
61a, 61b and 61c, respectively. In the region of the nozzle-type discharge
means,
each duct exhibits a tapering cross-section longitudinal portion in which the
duct
tapers downstream the general airflow direction, i.e., in a direction from
first front
wall 11 to second front wall 12, from a first cross-sectional area to a second
cross-
sectional area smaller than the first cross-sectional area. Nozzle-type
discharge
means 61c extend further into the tapering cross-section longitudinal portion
of
ducts 44c than nozzle-type discharge means 61b into ducts 44b, and nozzle-type
discharge means 61b extend further into the tapering cross-section
longitudinal
portion of ducts 44b than nozzle-type discharge means 61a into duct 44a.
Accordingly, the minimum flow cross-section, defined as a residual cross-
section
between the inner wall of a duct and the outer wall of a nozzle, is smaller in
duct
44c than in duct 44b, and the minimum flow cross-section is smaller in duct
44b
than in duct 44a.
The device shown in figure 8 outlines how two supply connectors 311 and 321
provided for feeding two plenums may be arranged concentrically and coaxially.
As illustrated in figure 9, wall-opening type discharge means may be arranged
and
configured to discharge the fluid form a plenum into a duct either
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= perpendicular to the longitudinal direction 451, as for instance
discharge
means 56 of plenum 36;
= upstream the flow direction of combustion air 4, or inclined in the
upstream
direction of duct 46, respectively, as for instance discharge means 57 of
plenum 37; or
= downstream the flow direction of combustion air 4, or inclined in the
downstream direction of duct 46, respectively, as for instance discharge means
58 of plenum 38.
The direction along which the fluid is discharged into duct 46 from the
respective
discharge means 56, 57, 58 is indicated by the arrows originating from the
discharge means. It is noted that the application of said teaching is not
limited to
wall-opening type discharge means.
Figure 10 shows a cross-section through an even more particular example of the
embodiment shown in figure 9 along line X-X. The discharge means may be
arranged and configured such that the fluid is discharged from plenum 36 into
duct
46 with a tangential velocity component so as to form a vortex flow of
discharged
fluid as indicated by the circular arrows in figure 10. It is noted that such
a
configuration of the discharge means is not limited to the embodiment of
figure 9
or any embodiment similar thereto. Such configuration suited to generate a
vortex
flow of fluid discharged from a plenum into a duct may be applied, for
instance,
while not limited to, discharge means discharging the fluid in an upstream or
downstream direction of the combustion air flow inside a duct, as for instance
depicted at 57 and 58 in figure 9, or a nozzle-type discharge means.
In further aspects, illustrated in figure 11, at least one duct 46 may be
provided
with a row of vanes 452 disposed inside duct 46 and disposed around the
circumference of duct 46 and inclined at an angle y with respect to the
longitudinal
direction 451 of duct 46, so as to induce a vortex flow as indicated at 401
onto the
flow of combustion air 4. The vanes may in particular be provided at the
upstream
end of duct 46 such that the vortex flow of combustion air is present
essentially
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throughout the longitudinal extent of duct 46. However, in other aspects,
vanes
452 may be arranged further downstream, so as to discharge fluids from certain
plenums into a purely axial flow of combustion air, while others may be
discharged
into a vortex flow of combustion air. The row of vanes 452 may be provided at
the
5 downstream end of duct 46. While it should be readily apparent to a
person having
skill in the art, it shall be mentioned that a vortex flow of combustion air
may be
combined with a tangential injection of at least one fluid from at least one
plenum,
as outlined in connection with figure 10. The vortexes of combustion air and
of
discharged fluid may be co- or counterrotating and may be affected with at
least
10 essentially equal tangential velocity components or different tangential
velocity
components and with essentially identical or different swirl numbers, as found
suitable by a person having skill in the art when applying her or his common
knowledge. The vanes 452 are in particular provided integrally and in one
piece,
i.e., seamless, with the burner, or the inner wall of a duct. It will be
appreciated
15 that in particular manufacturing the burner with additive manufacturing
methods
enables providing such rather small and complex geometries in one integral
workpiece.
It is apparent to a person having skill in the art that the relative
velocities of the
20 combustion air and the fluid discharged into the flow of combustion air
inside a
duct may have a major impact on the mixing of the fluids and may be applied to
tune mixing and hence combustion behaviour.
Figure 12 illustrates a detail of a further possible embodiment of the herein
25 disclosed burner. Figure 12 shows a section of a burner with plenums 36
and 37
and duct 141 extending therethrough. 4 denotes the flow of combustion air
through
duct 141. Plenum 36 is in fluid communication with duct 141 through nozzle-
type
discharge means 162, while plenum 37 is in fluid communication with duct 141
through wall-opening type discharge means 152. Nozzle-type discharge means
30 162 is configured to discharge fluid from plenum 36 at a position s1
measured
from the downstream end of duct 141, while wall-opening type discharge means
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152 is configured to discharge fluid from plenum 37 at a position s2 measured
from the downstream end of duct 141. Although plenum 36 is positioned upstream
from plenum 37, fluid from plenum 37 is discharged into duct 141 downstream
from the discharge position s2 of fluid from downstream plenum 37. This
illustrates
the flexibility a nozzle-type discharge means offers with respect to the
discharge
location of a fluid from, a specific plenum into a duct.
Figures 13a through 13d show plan views on front faces of burners having
different numbers of passages. As can easily be seen, in each burner each
three
neighbouring passages are provided on the corners of an equilateral triangle.
All
shown embodiments, irrespective of the number of passages, have in common
that a centre passage 40a is concentrically encircled by concentric hexagonal
rings of passages. The embodiment of figure 13a exhibits 7 passages, wherein a
centre passage 402 is encircled by six passages 40b in a hexagonal
arrangement.
Each two neighbouring passages 40b have the same distance from each other
than from central passage 40a. The embodiment of figure 13b exhibits 19
passages, wherein a central passage 40a is encircled by six passages 40b in a
first hexagonal ring and 12 passages 40c of a second hexagonal ring. As is
apparent when further considering figures 13c and 13d, the burner can easily
be
scaled by adding further concentric hexagonal rings of passages, wherein each
additional hexagonal ring comprises 6 passages more than the adjacent inner
hexagonal ring. Each passage, apart from the passages on the outermost
hexagonal ring, may in turn be considered to form the centre of another
hexagon
of surrounding passages. In embodiments, centre passage 40a may be omitted.
This self-similarity of the arrangement of passages, along with the
equidistant
arrangement of all neighbouring passages, facilitates scaling of the burner. A
burner may, on the one hand, be adapted to different burner sizes in adding
additional hexagonal rings of passages of the same size and distance from each
other. A burner of a given size may, on the other hand, be provided with
different
cross-sectional dimensions of the passages, or ducts, respectively. It shall
be
noted that the ducts, or some of the ducts, may have a polygonal rather than a
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circular or, more generally spoken, rounded cross-sectional shape. In
particular
embodiments, at least some of the ducts may exhibit the cross-sectional shape
of
an equilateral hexagon.
Figures 14a through 14c illustrate possible arrangements of piloting ducts,
liquid
fuel nozzles, water or steam injection nozzles and so forth, in a burner of
the
described type. It is well understood and goes without saying that said ducts,
nozzles and the like extend through passages of the burner. For one instance,
as
illustrated in figure 11a, a piloting duct 49, represented by the filled dot,
may be
arranged in a central passage, while all other passages may be provided with
any
other type of duct. The burner of figure 14b exhibits six piloting ducts
arranged
adjacent to each other on an equilateral hexagon. In the embodiment of figure
14c
a piloting duct is provided in the centre of each hexagonal arrangement of
neighbouring non-piloting ducts. The skilled person will appreciate that in
the
embodiments of figure 14 for instance cartridges for the supply of water,
steam,
liquid fuel, piloting gas and so forth may be arranged in the place of the
piloting
ducts 49.
Figure 15 illustrates how the passages 40b and 40c of the hexagonal rings,
and,
consequently, any means provided therethrough, may be inclined relative to a
burner axis 101, so as to discharge the flow emanating from said passages, or
ducts, respectively with a macroscopic tangential component relative to the
burner
axis. Burner axis 101 is defined at least essentially perpendicular to the
downstream front face of the burner. The longitudinal direction of central
passage
40a, or duct respectively, is in particular aspects at least essentially
parallel to
burner axis 101, while the longitudinal axis of passages 40b and 40c are
inclined
about an angle 11 relative to the burner axis, so as to generate a vortex flow
indicated at 102 downstream the burner, or, more specifically, in the
combustion
space. In certain embodiments, no central passage may be present. References
may in this case be made, for instance, to a midpoint of the hexagonal ring.
It is
understood that the inclination angle 11 of the passages may vary dependent on
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the distance of a respective passage from central passage 40a. For one
instance,
inclination angle I. may increase with increasing distance from central
passage
40a or from burner axis 101, or, in other aspects, from a midpoint of the
hexagonal
ring. Of course, it is not excluded that, in embodiments, the inclination
angle 11 may
decrease or may remain the same with increasing distance from central passage
40a or from burner axis 101, or, in other aspects,from a midpoint of the
hexagonal
ring. Due to the self-similarity of the arrangement of the passages, one
burner may
be subdivided into smaller areas, wherein each aera defines a local centre and
an
encircling hexagonal passage arrangement, wherein the passages encircling a
specific centre may be inclined to provide a vortex around said local central
passage. In other words, the passages in a concentric hexagonal ring are
configured such that fluid discharged at the downstream side of the burner
form
the passages in the concentric hexagonal ring has a velocity component which
is
tangential to a circle defined around the midpoint of the hexagonal ring. An
embodiment in which a macroscopic vortex is generated may be found useful for
instance when replacing vortex burners in a legacy combustion appliance.
The example of figure 16 relates to a specific embodiment of the cooling of
the
burner. In the exemplary embodiments, plenums 31 and 32 are configured to
discharge into ducts 47 through wall-opening type discharge means 51 and
nozzle-type discharge means 62, respectively. Wall 23 is provided with through
holes 122 fluidly connecting open plenum 35 and most downstream plenum or
cooling plenum 33. As outlined above, open plenum 35 is in fluid communication
with a space surrounding burner 1, i.e., for instance with a reservoir of air.
Air
from open plenum 35 flows through opening 122 into cooling plenum 33.
Through jets of cooling air entering plenum 33 through holes 122 impingement
cooling of adjacent areas of downstream wall 12 may be effected. Other areas
of
downstream wall 12 are effusion cooled by cooling air which is discharged into
downstream space 3 through through holes 121. A further fraction of the
cooling
fluid is discharged into the downstream part of the ducts through coolant
discharge means 53. For the sake of completeness it is noted that coolant
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discharge means which provide fluid communication between the most
downstream plenum and the interior of a duct may also be used in connection
with embodiments in which coolant is supplied to plenum 33 through coolant
feed
connectors.
While the above shown exemplary embodiments all exhibit two fluid plenums in
connection with the ducts, apart from the most downstream plenum which is
configured as a cooling plenum to provide appropriate cooling for the
thermally
highly loaded downstream wall, the skilled person will appreciate that more
plenums may be provided in fluid communication with at least one duct, and be
intended for providing different types of fuel, fuel intended for different
premixing
prior to combustion, or steam or other inert fluids. In embodiments, a nozzle-
type
discharge means may be equipped with an atomizer, such that also liquids,
like,
for instance, liquid fuel or water, may be discharged into a duct through said
nozzle-type discharge means. In embodiments, the burner may be modular,
each module comprising at least a fluid plenum between two transverse walls, a
duct segment or duct segments extending through the transverse walls and the
plenum or the plenums, a discharge means to provide fluid from the plenum or
the plenums to the duct segment or the duct segments, and, optionally, a fluid
supply connector or fluid supply connectors in fluid communication with the
fluid
plenum or fluid plenums.
Figure 17 depicts a detail from an exemplary embodiment of a burner of the
herein described type. A through hole 52a through the wall of duct 142 for
providing fluid communication with plenum 32 is elliptically shaped, with a
long
ellipse axis 528 and a short ellipse axis 529. An angle included between the
long
ellipse axis 528 and the longitudinal direction of the duct 451, the general
airflow
direction, or a burner axis, is in particular embodiments chosen to be 30
degrees
or less, and in more particular embodiments, as shown in figure 17, an angle
included between the long ellipse axis 528 and the longitudinal direction of
the
duct 451 is at least essentially zero. Moreover, the ratio between the length
a of
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the long ellipse axis and the length b of the short ellipse axis may be chosen
to
be 1.25 or more. This configuration yields advantages in particular if the
burner
or a burner module is manufactured by additive manufacturing, wherein the
building direction may be chosen at least approximately parallel to the
general
5 airflow direction, the duct axis or burner axis. The elliptic shape of
the opening
may facilitate said manufacturing in that overhanging structures during
manufacturing are largely reduced. In other embodiments, the through hole may
for the same reason be lancet-shaped or shaped as a pointed arch with the apex
pointing at least essentially in the building direction of the additively
10 manufactured structure.
Essentially the same advantages may be achieved, for instance, with a polygon-
shaped wall opening 52b as shown in figures 18 and 19. Wall opening 52b as
shown has a base and an apex pointing against the intended flow of combustion
15 air 4. As outlined in more detail in figure 19, polygon-shaped wall
opening 52b
has a polygon-shaped boundary which comprises straight boundary segments
521, 522, 523, 524 and 525. The boundary may also be considered as
comprising an upstream boundary section 526 edging the opening in a direction
against the flow of combustion air 4 and a downstream boundary section 527
20 edging the opening in the direction of the flow of combustion air.
Upstream
boundary section 526 comprises straight boundary segments 522 and 523, while
downstream boundary section 527 comprises straight boundary segments 521,
524 and 525. Straight boundary segments 522 and 523 of upstream boundary
section 526 form an apex of opening 52b pointing upstream relative to the flow
of
25 combustion air. Straight boundary segments 522 and 523 include inner
angles 6
and E with the longitudinal direction 451 of duct 142 which are 45 degrees or
less. The exemplarily shown opening is particularly suitable in connection
with a
component which is additively manufactured with a building direction against
the
intended flow of combustion air 4. Generally, an opening being defined within
a
30 boundary having an apex pointing into the building direction of the
component
and the apex being enclosed between two straight boundary segments edging
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46
the opening in the building direction, wherein those two boundary segments
include an angle of 45 degrees or less with a parallel to the building
direction,
may be found beneficial in connection with an additively manufactured
component. Also a geometry with two apexes, like e.g. a diamond-shaped
geometry, might be applied.
While the subject matter of the disclosure has been explained by means of
exemplary embodiments, it is understood that these are in no way intended to
limit the scope of the claimed invention. It will be appreciated that the
claims
cover embodiments not explicitly shown or disclosed herein, and embodiments
deviating from those disclosed in the exemplary modes of carrying out the
teaching of the present disclosure will still be covered by the claims.
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