U.S. patent application number 13/489029 was filed with the patent office on 2013-12-05 for combustion head for a low nox liquid fuel burner.
This patent application is currently assigned to RIELLO S.p.A.. The applicant listed for this patent is Nicola Bianchini, Emil Calzolari, Davide Martini, Alessio Visentin. Invention is credited to Nicola Bianchini, Emil Calzolari, Davide Martini, Alessio Visentin.
Application Number | 20130323660 13/489029 |
Document ID | / |
Family ID | 49670657 |
Filed Date | 2013-12-05 |
United States Patent
Application |
20130323660 |
Kind Code |
A1 |
Bianchini; Nicola ; et
al. |
December 5, 2013 |
COMBUSTION HEAD FOR A LOW NOx LIQUID FUEL BURNER
Abstract
A combustion head for a burner provided with a nozzle for
atomizing a liquid fuel; the head has a first body adapted to
receive a primary comburent flow and having a frontal wall arranged
to produce a swirl in the primary comburent flow; and a second body
adapted to receive a secondary comburent flow, to convey it towards
a combustion chamber and to produce a swirl therein; a duct and an
intermediate body which define a channel, adapted to feed a
tertiary comburent flow into the combustion chamber and having a
tapered end profile which converges towards the first body and the
second body; and a frontal surface of the intermediate body
substantially lies on the plane defined by the frontal wall of the
first body.
Inventors: |
Bianchini; Nicola; (Legnago,
IT) ; Calzolari; Emil; (Bevilacqua, IT) ;
Martini; Davide; (Sanguinetto, IT) ; Visentin;
Alessio; (Terrazzo, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bianchini; Nicola
Calzolari; Emil
Martini; Davide
Visentin; Alessio |
Legnago
Bevilacqua
Sanguinetto
Terrazzo |
|
IT
IT
IT
IT |
|
|
Assignee: |
RIELLO S.p.A.
Legnago
IT
|
Family ID: |
49670657 |
Appl. No.: |
13/489029 |
Filed: |
June 5, 2012 |
Current U.S.
Class: |
431/354 |
Current CPC
Class: |
F23D 11/36 20130101;
F23D 11/40 20130101 |
Class at
Publication: |
431/354 |
International
Class: |
F23D 11/40 20060101
F23D011/40; F23D 11/36 20060101 F23D011/36 |
Claims
1. A combustion head (1) for a fuel burner, which comprises a
central duct fed with a liquid fuel, having a longitudinal symmetry
axis (X), and is provided, at one end, with a nozzle for the
atomization of said liquid fuel into a combustion chamber (CC); the
combustion head comprises: a first body having a cylindrical
extension and coaxial to the longitudinal symmetry axis (X); the
first body being mounted on the central duct to receive at an inlet
thereof a primary flow (F1) of comburent and to convey the primary
flow (F1) towards the nozzle, the first body having a frontal wall
provided with a plurality of spaced apart peripheral indentations
suited to produce a swirl in said primary flow (F1) of comburent;
and a second body having a cylindrical extension and coaxial to the
longitudinal symmetry axis (X); the second body being mounted on
the first body so as to receive at an inlet thereof a secondary
flow (F2) of comburent and to convey the secondary flow (F2)
towards the combustion chamber (CC), the second body having a
plurality of openings which are suited to produce a swirl in said
secondary flow (F2) of comburent; a swirl regulation assembly to
control the swirl produced in said primary flow (F1) of comburent
and in said secondary flow (F2) of comburent; the swirl regulation
assembly comprising a duct positioned coaxially to the longitudinal
symmetry axis (X) and externally of the second body with the
interposition of an intermediate body there between that is also
coaxial to the longitudinal symmetry axis (X); the duct and the
intermediate body defining a channel (C1) there between through
which a tertiary flow (F3) of comburent is fed into the combustion
chamber (CC); the intermediate body including a frontal surface
positioned substantially on a plane defined by a frontal wall of
the first body, so that the nozzle is positioned directly facing
the combustion chamber (CC); and, at an end section of the swirl
regulation assembly adjacent the combustion chamber (CC), the
channel (C1) has a tapered profile which converges towards the
first body and the second body.
2. The combustion head according to claim 1, wherein the end
section the channel (C1) is defined by a front portion of the duct,
which is shaped as a truncated cone coaxial to the longitudinal
symmetry axis (X) and faces a truncated cone-shaped surface of the
intermediate element, which is also coaxial to the longitudinal
symmetry axis (X).
3. The combustion head according to claim 1, wherein the duct is
movable with respect to the intermediate body between a position of
maximal closure, corresponding to a tertiary flow (F3) of comburent
with a minimum flow rate, preferably equal to zero, and a position
of minimum closure, corresponding to a tertiary flow (F3) of
comburent with a maximum flow rate.
4. The combustion head according to claim 3, wherein the duct
comprises a plurality of internal projections, which are
distributed about the longitudinal symmetry axis (X); the
projections being in contact with and, when in use, slide on an
external surface of the intermediate body, so as to allow a
translation motion of the duct with respect to the intermediate
body between the position of maximal closure and the position of
minimum closure.
5. The combustion head according to claim 1, wherein the
intermediate body has a rear surface shaped as a truncated cone, is
coaxial to the longitudinal symmetry axis (X), and is tapered
towards the first body; the rear surface being suited to increase
the average axial speed of the primary flow (F1) of comburent and
of the secondary flow (F2) of comburent at the inlet of the first
body and of the second body, respectively.
6. The combustion head according to claim 1, wherein the frontal
wall is provided with a through hole that is coaxial to the
longitudinal symmetry axis (X).
7. The combustion head according to claim 6, wherein a cylindrical
lateral wall of said first body is free of through holes and the
primary flow (F1) of comburent at the outlet of the first body is
only divided into a primary swirled comburent flow and a primary
axial comburent flow.
8. The combustion head according to claim 1, wherein each
indentation has a pair of facing lateral walls that are inclined by
a first angle (.alpha.) with respect to a plane defined by a front
flat surface of the frontal wall.
9. The combustion head according to claim 8, wherein the first
angle (.alpha.) ranges between 42.degree. and 48.degree..
10. The combustion head according to claim 1, wherein each of the
plurality of openings is defined by a pair of facing lateral walls
that are inclined by a second angle (.beta.) with respect to a
plane defined by a rear flat surface of the second body.
11. The combustion head according to claim 8, wherein the second
angle (.beta.) ranges between 42.degree. and 48.degree..
12. The combustion head according to claim 10, wherein the second
body comprises a front portion and a rear portion with the front
and rear portions both being cylindrical in shape and positioned
coaxially to the longitudinal symmetry axis (X), but having
different diameters; the plurality of openings being located in the
rear portion.
13. A liquid fuel burner provided with a combustion head
comprising: a first body having a cylindrical extension and coaxial
to the longitudinal symmetry axis (X); the first body being mounted
on the central duct to receive at an inlet thereof a primary flow
(F1) of comburent and to convey the primary flow (F1) towards the
nozzle, the first body having a frontal wall provided with a
plurality of spaced apart peripheral indentations suited to produce
a swirl in said primary flow (F1) of comburent; and a second body
having a cylindrical extension and coaxial to the longitudinal
symmetry axis (X); the second body being mounted on the first body
so as to receive at an inlet thereof a secondary flow (F2) of
comburent and to convey the secondary flow (F2) towards the
combustion chamber (CC), the second body having a plurality of
openings which are suited to produce a swirl in said secondary flow
(F2) of comburent; a swirl regulation assembly to control the swirl
produced in said primary flow (F1) of comburent and in said
secondary flow (F2) of comburent; the swirl regulation assembly
comprising a duct positioned coaxially to the longitudinal symmetry
axis (X) and externally of the second body with the interposition
of an intermediate body there between that is also coaxial to the
longitudinal symmetry axis (X); the duct and the intermediate body
defining a channel (C1) there between through which a tertiary flow
(F3) of comburent is fed into the combustion chamber (CC); the
intermediate body including a frontal surface positioned
substantially on a plane defined by a frontal wall of the first
body, so that the nozzle is positioned directly facing the
combustion chamber (CC); and, at an end section of the swirl
regulation assembly adjacent the combustion chamber (CC), the
channel (C1) has a tapered profile which converges towards the
first body and the second body.
14. The combustion head according to claim 8, wherein the first
angle (.alpha.) is preferably equal to 45.degree..
15. The combustion head according to claim 10, wherein the second
angle (.beta.) is preferably equal to 45.degree..
Description
[0001] The present invention relates to a combustion head for a
liquid fuel burner, and particularly suited for low NOx
emission.
BACKGROUND OF THE INVENTION
[0002] In liquid fuel burners, the combustion reaction between the
liquid fuel and the comburent is known to occur by means of a
combustion head. The comburent is conveyed through the combustion
head into a combustion chamber, where it is mixed with the liquid
fuel which is atomized by means of a nozzle. Within the combustion
chamber, close to and downstream of the combustion head, an
ignition device is arranged, adapted to trigger the mixture of
liquid fuel and comburent so as to start the combustion
process.
[0003] There is an increasing need to reduce the nitrogen oxides
NOx which are generated during the combustion process and which
cause pollution.
[0004] When designing combustion heads, a first solution considers
that the related studies have shown that the nitrogen oxides NOx
are especially generated when the flame temperature is high.
[0005] For this reason, burners have been fine-tuned, which are
equipped with combustion heads in which the abatement of the flame
temperature occurs by recirculating a part of the fumes generated
by the combustion into the combustion head and at the flame itself.
In order to recirculate the fumes inside the flame, the high outlet
speed of the air from the burner head is exploited, which causes a
phenomenon notoriously known in technical language as
"recirculation". Due to this phenomenon, the fumes in the
combustion chamber are recalled into the flame and as they do not
participate in the combustion reaction, they absorb heat by cooling
the flame itself, thus decreasing the nitrogen oxide NOx
emissions.
[0006] Patent application EP-A1-1705424 describes a combustion head
for liquid fuel burners, which comprises a central duct fed with a
liquid fuel, has a longitudinal symmetry axis and is provided, at
one end, with a nozzle for atomizing said liquid fuel into a
combustion chamber. The combustion head comprises a first body with
cylindrical extension and coaxial to the longitudinal symmetry
axis, which is arranged to receive, at the inlet, a primary flow of
comburent and has a frontal wall provided with a plurality of
peripheral indentations for producing a swirl in said primary flow
of comburent. The combustion head comprises a second body with
cylindrical extension and coaxial to the longitudinal symmetry
axis, which is fitted on the central duct and on which the first
body with cylindrical extension is coaxially arranged, is adapted
to receive, at the inlet, a secondary flow of comburent and has a
plurality of openings which are adapted to produce a swirl in the
secondary flow of comburent. The combustion head then comprises
means for regulating the swirl produced both in the primary flow
and in the secondary flow of comburent, which comprise a duct
coaxial to the longitudinal symmetry axis and external to the
second body with the interposition of an intermediate body, the
latter being also coaxial to the longitudinal symmetry axis.
Between the duct and the intermediate body a channel is defined,
which is adapted to feed a tertiary flow of comburent into the
combustion chamber.
[0007] The combustion process carried out through the combustion
head described in EP-A1-1705424 generates the overall effect of
curbing the formation of thermal NOx due to reduced flame
temperatures. The reduction flame temperatures is obtained by means
of a side leak of a portion of the comburent flow. In particular,
such a portion of comburent leaks through a plurality of radial
holes which are obtained in the first body with cylindrical
extension. Thereby, the flame does not exclusively develop from the
frontal surface of the nozzle, but it evenly spreads inside the
combustion chamber.
[0008] However, it has been noted that zones of primary combustion
are established close to the nozzle, which result in the formation
of thermal NOx.
[0009] Moreover, the above-described combustion head for liquid
fuel burners has no application in small boilers, in particular for
household and residential use, as combustion flames with a high
axial extension are generated, which are to be developed inside
boilers of large volume.
[0010] Instead, document U.S. Pat. No. 4,798,330 describes a
combustion head for a burner which is fed with a fuel comprising a
plurality of coaxial bodies fitted onto one another. The combustion
head is provided so as to keep the frontal surface of the
combustion head clean and to keep the combustion flame stable.
However, the combustion head provided according to the dictates of
U.S. Pat. No. 4,798,330 does not curb the formation of thermal
NOx.
SUMMARY OF THE INVENTION
[0011] Therefore, the object of the present invention is to provide
a combustion head which allows the formation of NOx to be minimized
during the combustion process, which may also be applied to small
boilers, in particular for household and residential use, while
being easy and cost-effective to be provided.
[0012] According to the present invention, a combustion head for a
burner for liquid fuels is provided as described and claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present invention will now be described with reference
to the accompanying drawings, which show a non-limiting embodiment
thereof, in which:
[0014] FIG. 1 shows a front perspective view of a first component
of a combustion head provided in accordance with the present
invention;
[0015] FIG. 1A is an enlarged partial view;
[0016] FIG. 2 shows a front perspective view of a second component
of the combustion head provided in accordance with the present
invention, which is fitted onto the first component in FIG. 1;
[0017] FIG. 3 shows a front perspective view of a third component
of the combustion head provided in accordance with the present
invention, arranged outside the second component in FIG. 2;
[0018] FIG. 4 shows a front perspective view of a fourth component
of the combustion head provided in accordance with the present
invention, arranged outside the third component in FIG. 3;
[0019] FIGS. 5 and 6 show rear and front perspective views,
respectively, of a combustion head assembly provided in accordance
with the present invention, by assembling the components in figures
from 1 to 4; and
[0020] FIG. 7 is a sectional view of the combustion head assembly
in FIGS. 5 and 6.
DETAILED DESCRIPTION OF THE INVENTION
[0021] In FIGS. 1 to 6, numeral 1 indicates as a whole a combustion
head where a liquid fuel, such as gas oil, is fed to a nozzle 2 (of
known type) by means of a central duct 3 having a longitudinal
symmetry axis X. Nozzle 2 is adapted to atomize the liquid fuel in
a combustion chamber CC (of known type as well and not disclosed in
detail).
[0022] The combustion head 1 is fitted onto the central duct 3 and
comprises a plurality of components assembled with one another,
which are coaxial to one another and to the longitudinal symmetry
axis X.
[0023] Connected to the central duct 3 is a so-called primary swirl
body 4, with cylindrical symmetry and which is hollow inside and
coaxial to the longitudinal symmetry axis X. In particular, body 4
comprises an external, cylindrical lateral wall 5 which is coaxial
to the longitudinal symmetry axis X, and a frontal wall 6 which is
provided with a through hole 7 to allow the central duct 3 and
nozzle 2 to be inserted. The frontal wall 6 of body 4 has a
plurality of indentations 8 which are evenly spaced about the
longitudinal symmetry axis X; each pair of reciprocally adjacent
indentations 8 defines a partition 9 in which the frontal wall 6 is
divided. In particular, according to the embodiment shown in FIG.
1, body 4 is divided into six partitions defined by just as many
indentations 8 which are evenly spaced about the longitudinal
symmetry axis X. Each indentation 8 is defined by a portion 10 of
base wall and by a pair of lateral walls 11, which face each other
and are inclined by a first angle .alpha. with respect to the plane
defined by a frontal flat surface 12 of the frontal wall 6 as shown
in FIG. 1A.
[0024] According to a preferred variant, angle .alpha. is between
42.degree. and 48.degree., and the angle is preferably equal to
45.degree.. Indentations 8 are in direct communication with the
through hole 7.
[0025] Assembled on body 4 is a so-called secondary swirl body 13
(shown in FIG. 2), with cylindrical symmetry, which is hollow
inside and coaxial to the longitudinal symmetry axis X. In
particular, secondary swirl body 13 comprises an internal
cylindrical surface 14 coaxial to the longitudinal symmetry axis X
which defines a through opening within which the body 4 is
accommodated. The diameter of the internal cylindrical surface 14
is substantially approximate to an external volume diameter of body
2. Body 13 is divided into a rear cylindrical portion 15 and a
front cylindrical portion 16; the rear cylindrical portion 15 has
an overall external volume diameter which is greater than the
overall external volume diameter of the front cylindrical portion
16. The rear cylindrical portion 15 has a plurality of openings 17.
In particular, according to the embodiment shown in FIG. 2, the
rear cylindrical portion 15 has eight openings 17 which are evenly
spaced about the longitudinal symmetry axis X.
[0026] Each opening 17 is defined by a base wall 18 and by a pair
of lateral walls 19, which face each other and are inclined by an
angle .beta. with respect to the plane defined by a rear flat
surface of the rear cylindrical portion 15. According to a
preferred variant, angle .beta. is between 42.degree. and
48.degree., and angle .beta. is preferably equal to 45.degree.. The
openings 17 are not in direct communication with the through hole
of body 13.
[0027] An intermediate body 20 is fixed in turn on body 13, which
has cylindrical symmetry, is hollow inside and coaxial to the
longitudinal symmetry axis X. In particular, the intermediate body
20 comprises an internal cylindrical surface 21 coaxial to the
longitudinal symmetry axis X which defines a through opening within
which body 13 is accommodated. The diameter of the internal
cylindrical surface 21 is substantially approximate to an external
volume diameter of the rear portion 15 of body 13.
[0028] The intermediate body 20 is also divided into a rear portion
22 and a front portion 23. The rear portion 22 has an external
cylindrical surface, which has an overall external volume diameter
which is greater than the overall external volume diameter of the
front portion 23. Moreover, the rear portion 22 has a rear
truncated cone-shaped surface 24 and a frontal truncated
cone-shaped surface 24**, which are both coaxial to the
longitudinal symmetry axis X. As shown in greater detail in FIGS. 3
and 7, a plurality of calibrated through holes 24* are obtained on
the rear portion 22, for the flame probe and the ignition
electrodes to pass. In addition, the front portion 23 comprises a
lateral cylindrical wall 23* coaxial to axis X and a ring-shaped
portion 23** of frontal wall coaxial to axis X.
[0029] It is worth noting that the intermediate body 20 acts as a
supporting element for primary swirl body 4, secondary swirl body
13 and central duct 3.
[0030] It is also worth noting that a frontal surface (defined in
this case by the annular portion 23** of frontal wall) of the
intermediate body 20 substantially lies on the plane defined by the
frontal wall 6 of the primary swirl body 4. Nozzle 2 is placed
directly facing the combustion chamber CC and, in use, the liquid
fuel is directly atomized into the combustion chamber CC.
[0031] Duct 25 is fixed in turn to the intermediate body 20, which
has a substantially cylindrical symmetry, is hollow inside and
coaxial to the longitudinal symmetry axis X.
[0032] Duct 25 is divided into a rear cylindrical portion 26 and a
front portion 27. The rear cylindrical portion 26 has an external
cylindrical surface and an internal cylindrical surface 28, which
are both coaxial to the longitudinal symmetry axis X. In addition,
the front portion 27 has a truncated cone extension which is
coaxial to the longitudinal symmetry axis X and is tapered towards
the free end facing the combustion chamber CC. Furthermore, a
plurality of indentations 27* are obtained on the front portion 27
for the flame probe and the ignition electrodes to pass.
[0033] Duct 25 then comprises a plurality of projections 29 which
are connected to the internal cylindrical surface 28 of the rear
portion 26 in a position close to the front portion 27 and extend
inwards from duct 25. The projections 29 are evenly spaced about
the longitudinal symmetry axis X, extend in the longitudinal
direction over a section of the rear portion 26. According to a
preferred variant, duct 25 comprises six projections 29 spaced
60.degree. apart from one another. Duct is adapted to translate in
one of the two longitudinal directions indicated by arrow P. In
order to allow the translation of duct 25, a control (manually
actuated or by means of an actuator of known type) is provided; the
projections 29 rest with contact and, in use, slide on the external
surface of the intermediate body 20 to allow the movement of duct
25.
[0034] It is worth noting that such a compact geometry of
combustion head 1 allows the size of the combustion flame to be
contained, as better described below.
[0035] In use, a blower (of known type and not shown) provides a
flow F of comburent, such as air, which is conveyed into duct 25
which indeed encloses the whole combustion head 1, and from here it
is then divided into a number of comburent flows.
[0036] In particular, as shown in detail in FIG. 7, the comburent
flow at the inlet of combustion head 1 is divided into three
partial flows indicated as primary comburent flow F1, secondary
comburent flow F2 and tertiary comburent flow F3, respectively, due
to the particular geometry of the combustion head 1 itself.
[0037] The primary comburent flow F1 flows into the primary swirl
body 4 in the longitudinal direction. When the primary comburent
flow F1 meets indentations 8, the flow lines F1 take n a helical
and no longer longitudinal flow, and the speed at which flow F1
exits the primary swirl body 4 has a high tangential motion (swirl)
component. The indentations 8 are hence arranged to produce a swirl
in the primary comburent flow F1. The primary comburent flow F1 is
then further exclusively divided into a primary swirled comburent
flow which exits the indentations 8, and an axial primary comburent
flow which exits the section left free from the nozzle into the
through hole 7.
[0038] The secondary comburent flow F2 flows into the secondary
swirl body 13 in the longitudinal direction. The flow rate of the
secondary comburent flow F2 is determined by the number and section
of the openings 17 made in the rear cylindrical portion 15, and is
usually greater than the primary comburent flow F1. Also in this
case, due to the passage of the secondary comburent flow F2 through
the openings 17, the flow lines F2 take on a helical and no longer
longitudinal flow, and the speed at which flow F2 exits the
secondary swirl body 13 has a high tangential motion (swirl)
component. The openings are hence arranged to produce a swirl in
the secondary comburent flow F2.
[0039] The truncated cone-shaped profile of the rear surface 24 of
the intermediate body 20 allows both the average speed of flow F1
at the inlet of the primary swirl body 4 and the average speed of
flow F2 at the inlet of the secondary swirl body 13 to be
increased. The increase the aforesaid average speeds results in an
increase of the tangential motion (swirl) components of both the
speed at which flow F2 exits the secondary swirl body 13 and the
speed at which flow F1 exits the primary swirl body 4.
[0040] On the other hand, the tertiary comburent flow F3 is
transported through a channel C1 defined between duct 25 and
intermediate body 20. It is apparent that the final flow rate of
the tertiary comburent flow F3 is determined by the distance
between the front, truncated cone-shaped portion 27 of duct 25 and
the intermediate body 20, which can vary due to the translation
motion of duct 25.
[0041] The tertiary comburent flow F3 flows in channel C1 along a
direction parallel to the longitudinal axis X.
[0042] At an end section thereof, close to the combustion chamber
CC, channel C1 has a tapered profile which converges towards the
primary swirl body 4 and towards the secondary swirl body 13. In
particular, the end section has a truncated cone-shaped profile
defined by the front portion 27 of duct 25, being the same as that
of the rear portion 22 of intermediate body 20.
[0043] The profile of channel C1 is obtained so as to accelerate
the tertiary comburent flow F3 before being fed into the combustion
chamber and so as to direct the tertiary comburent flow F3 directly
towards the primary comburent flow F1 and towards the secondary
comburent flow F2 to limit the spatial area downstream of the
combustion head 1, there the combustion flame develops.
[0044] Duct 25 is movable between a maximal closure position,
corresponding to a tertiary comburent flow F3 with minimum flow
rate, preferably equal to zero, and a minimum closure position
corresponding to a tertiary comburent flow F3 with maximum flow
rate.
[0045] In the minimum closure position, the axial component of the
tertiary comburent flow F3 directly directed towards the primary
comburent flow F1 and towards the secondary comburent flow F2
opposes the swirl generated by primary swirl body 4 and secondary
swirl body 13; moreover, in this case, the profile of the
intermediate body 20 on which the tertiary comburent flow F3 runs
adherent due to the "Coanda effect" allows the combustion flame to
have a prevalently axial flow.
[0046] In the maximal closure position, the tertiary comburent flow
F3 does not influence the swirl generated by primary swirl body 4
and secondary swirl body 13; in this case, the combustion flame has
a significantly small axial development.
[0047] The combustion process sequentially includes the following
steps: [0048] atomizing the liquid fuel through nozzle 2; [0049]
mixing the atomized liquid fuel with the primary comburent flow F1;
the atomized liquid fuel has a high kinetic energy and only a small
portion is involved in the primary comburent flow F1; [0050] mixing
the secondary comburent flow F2 with the remaining portion of
liquid fuel not mixed with the primary comburent flow F1; [0051]
spatially confining the combustion flame by means of the tertiary
comburent flow F3 adapted to control the swirl effect.
[0052] It is known from literature that the intensity of the swirl
obtainable with a combustion head 1 has relevant effects on the
polluting emissions of a combustion process. Moreover, it has been
verified that the intensity of the swirl is quantifiable through
the number of swirls and a combustion process with low levels of
NOx emissions can be obtained for a swirl number greater than
1.
[0053] In essence, the combustion head 1 described hereto comprises
four bodies indicated with numerals 4, 13, 20 and 25, respectively,
which are assembled together and may be fitted onto any duct 3 with
axial symmetry.
[0054] It is also worth noting that duct 25 and intermediate body
20 which determine the tertiary comburent flow F3 also influence
the primary comburent flow F1 and the secondary comburent flow F2
due to the dynamic characteristics (i.e. due to flow rate and speed
range) of the tertiary comburent flow F3.
[0055] In greater detail: [0056] the primary comburent flow F1 is
generated due to the primary swirl body 4. By reasoning, without
the secondary F2 and tertiary F3 comburent flows, the radial and
tangential components of the primary comburent flow F1 would
excessively open the cone of the comburent speed range.
Accordingly, the combustion flame would have an excessive opening
and a weak intensity, such as not to ensure the complete combustion
of the harmful residues generated in the first combustion step and
conveyed into the zone involved by the combustion flame due to the
recirculating mechanism by primary swirl body 4 and secondary swirl
body 13. [0057] The secondary comburent flow F2 is generated by the
secondary swirl body 13. As seen above, the secondary comburent
flow F2 is adapted to determine a geometrical confinement of the
primary comburent flow F1 in order to improve the efficiency of the
combustion flame. [0058] The tertiary comburent flow F3 is
developed in the geometrical domain delimited by duct 25 and
intermediate body 20. The tertiary comburent flow F3 only has one
axial component (since no element for deviating the tertiary flow
F3 in the tangential direction is provided). The object of the
tertiary flow F3 is to confine the secondary comburent flow F2 (and
therefore the primary comburent flow F1) in a controllable manner
by means of an axial translation of duct 25. By means of the
movement generated in duct 25, the tertiary comburent flow F3 may
increase in flow rate thus determining an extension of the flame in
the axial direction and a decrease of the radial extension, and
vice versa.
[0059] Thereby, the formation of thermal NOx can be curbed by means
controlling the axial and tangential components of the comburent
flows F1, F2 and F3.
[0060] It has been experimentally verified that the number of
swirls obtainable by means of the combustion head 1 described
hereto (with a primary swirl 4 and a secondary swirl 13) is
substantially high, in the order of 5.45, and such as to ensure a
low level of NOx emissions.
[0061] Moreover, the opportunity to control the intended swirl
level allows a yellow-blue colouring of the flame to be kept, which
is easily detected by an optical sensor with a light dependent
resistor and which is more reliable and less costly than those with
ultraviolet radiation usually used in applications of this
kind.
* * * * *