EP3734154A1

EP3734154A1 - A combustion head with internal recirculation

Info

Publication number: EP3734154A1
Application number: EP20165995.0A
Authority: EP
Inventors: Stefano PESCE
Original assignee: Shanghai Quanjie Envir Co Ltd
Current assignee: Shanghai Quanjie Envir Co Ltd
Priority date: 2019-04-29
Filing date: 2020-03-26
Publication date: 2020-11-04
Also published as: IT201900006424A1; CN111853775A

Abstract

A combustion head (1) with internal recirculation for a burner (100) of a combustion chamber (26) comprising
- a nozzle (8) which is coaxially aligned with the first portion (K) comprising
o a first or second primary internal recirculation chamber (9a; 9b) comprising a first entry aperture (31a) which is connected in fluid-dynamic terms downstream of the diffuser element (7) or the primary flame (17) and a first discharge aperture (31b) which is connected in fluid-dynamic terms upstream or downstream of the diffuser element (7) for the primary internal exhaust gas (I1) and/or the secondary internal exhaust gas (12) which is formed so as to have at least a first or second interference surface (X1a; X1b) with respect to the first and/or second primary supply gas (11', 14) which is suitable for producing a first low-pressure detachment zone (28a) for the primary supply gas (11') and/or for the second primary supply gas (air) (14) and/or
o a secondary internal recirculation chamber (10) comprising a second entry aperture (32a) which is connected downstream of the diffuser element (7) or the secondary flame (18) and a second discharge aperture (32b) which is connected upstream of the secondary flame (18) for the secondary internal exhaust gas (12) which is formed so as to have at least a third interference surface (X3) with respect to the first and/or second secondary supply gas (12', 15) which is suitable for producing a second low-pressure detachment zone (28b) for the first secondary supply gas (12') and/or for the second secondary supply gas (15) so as to produce an internal recirculation of the primary and/or secondary internal exhaust gas (11, 12).

Description

Technological field

The present invention relates to a combustion head with internal recirculation for a burner and a burner comprising such a combustion head.

Technological background

It is known that, in the field of using boilers which are supplied by means of fossil fuels, there are generated emissions of pollution which are dangerous to the environment, in particular in the form of nitrogen oxides (for example, NO, NO₂) which are generally identified using the abbreviation NOx. The emissions of pollution can be influenced or reduced by the design of the combustion plants and in particular by the burners which are used.
In the case of burners, it is well-known that the combustion produces NOx contaminants in quantities which are directly proportional to the temperature of flame produced and design solutions for such burners have been proposed in order to reduce the flame temperature.
In a general sense, the reduction or lowering of the NOx in industrial burners has always been a desirable objective. A lowering of the NOx has been achieved in the past by using a lean primary air/gas mixture connected with a distribution of the gaseous fuel in stages. The lean primary fuel mixture is potentially desirable in some applications because the air in excess produces a charge for reducing the flame temperature in order to reduce the NOx. The gas can then be introduced into the combustion zone either by means of jets which are arranged around the periphery of the burner or by a central jet which protrudes through the final portion of the central gas tube. The secondary fuel is burnt with the air in excess in an environment in which the combustion fumes are present and act as a dilution. This technology has not always been capable of ensuring the levels of NOx desired or prescribed by the current laws.
In specific situations, a lean primary mixture is introduced through the combustion chamber at a relatively high velocity as a result of the extra mass of air in excess. This velocity can sometimes be so high that it exceeds the flame velocity, causing an unstable flame situation. When the flame becomes unstable, it is no longer possible to continue.
For example, the document DE 3811477 A1 describes a gas burner in which an air/gas mixture is supplied at the inlet end of a combustion chamber through various mixing tubes. The gas is directed into the inlet ends of the mixing tubes by respective jets so that the air is drawn by the gas. The inlet ends of the inlet tubes are in different planes, for example, with the mixing tubes directed radially with respect to the burner chamber.

Summary of the invention

A scope of the present invention is to provide a combustion head with internal recirculation for a burner or a burner comprising the above-mentioned combustion head which is structurally and functionally configured to at least partially overcome at least one of the disadvantages of the cited prior art.
Within this scope, an object is to improve the operation of the combustion head (or the burner or the boiler associated therewith), ensuring high performance levels.
This object is at least partially achieved as a result of a combustion head with internal recirculation for a burner of a combustion chamber comprising

a casing which at least partially projects towards the inner side of the combustion chamber and which has a main extent which is substantially cylindrical about a longitudinal axis,
a first portion coaxial with respect to and contained in the casing comprising
- ∘ a first pipe which comprises a primary jet for a first primary supply gas of a primary flame and/or a secondary jet for a first secondary supply gas of a secondary flame,
- ∘ a collector for a second primary supply gas (for example, primary air) of the primary flame,
- ∘ a diffuser element which is positioned downstream of and which interacts in fluid-dynamic terms with the first pipe,
- ∘ a nozzle for a second secondary supply gas, secondary air.

In this context, the term "diffuser element" indicates an element which performs the function of generating a turbulence and mixing between primary air and primary gas. Preferably, this diffuser element is a disc or an element of a different shape with or without holes or a turbine element which comprises blades which provide a rotation for the central flow of air. Preferably, the casing, the first pipe comprising the primary jet, the collector and the diffuser element are formed or arranged so as to be able to generate the primary flame downstream of the diffuser element, thereby producing primary internal exhaust gas, and the casing, the first pipe comprising the secondary jet and the nozzle being formed or arranged so as to be able to generate the secondary flame downstream of the nozzle, thereby producing secondary internal exhaust gas. According to an embodiment, the combustion head comprises

a nozzle which is preferably coaxially aligned with the first portion, comprising
- ∘ a first or second primary internal recirculation chamber comprising a first entry aperture which is connected in fluid-dynamic terms downstream of the diffuser element or the primary flame and a first discharge aperture which is connected in fluid-dynamic terms upstream or downstream of the diffuser element for the primary internal exhaust gas and/or the secondary internal exhaust gas which is formed so as to have at least a first or second interference surface with the first and/or second primary supply gas which is suitable for producing a first low-pressure detachment zone for the primary supply gas and/or for the second primary supply gas (air) and/or
- ∘ a secondary internal recirculation chamber comprising a second entry aperture which is connected downstream of the diffuser element or the secondary flame and a second discharge aperture which is connected upstream of the secondary flame for the secondary internal exhaust gas which is formed so as to have at least a third interference surface with the first and/or second secondary supply gas which is suitable for producing a second low-pressure detachment zone for the first secondary supply gas and/or for the second secondary supply gas so as to produce an internal recirculation of the primary and/or secondary internal exhaust gas.

It is thereby possible to produce a combustion head which is capable of producing a reduced-pressure zone which is positioned upstream of, at or downstream of the primary flame or the diffuser element with respect to a value of the greater pressure present in the combustion chamber.
Similarly, this technical solution can also be carried out upstream of, at or downstream of the secondary flame.
Preferably, the production of the pressure difference is brought about by means of detachment of the air vein from a specific surface. In this context, this surface is identified as the first, second or third interference surface with respect to the first and/or second primary or secondary supply gas.
It is advantageous to note that this reduced pressure does not form as a result of a phenomenon based on the Venturi effect, but instead on the turbulence (and therefore pressure reduction associated therewith) produced as a result of a specific interference surface which is inserted inside a flow.
In this context, the term "burner" is intended to be understood to refer to the whole comprising a ventilation fan, a combustion head and the electronic system dedicated thereto. This condition therefore allows an induced effective recirculation of the internal fumes to be carried out (and in particular of the non-depleted internal fumes), thereby allowing an increase in the lowering of the NOx fumes.
According to an embodiment, the second primary supply gas and/or the second secondary supply gas is/are air.
This condition is advantageously effective in producing desired gaseous combustion mixtures and thus in the resultant operation of the combustion head itself.
Preferably, the first pipe coincides with the longitudinal axis and is connected in fluid-dynamic terms to at least a second pipe which is radially spaced apart from the first pipe and which has a main extent which is substantially parallel therewith.
As a result of this technical solution, it is possible to distribute the first and/or second primary supply gas in an optimally uniform manner inside the combustion chamber, thereby further increasing the efficiency of the combustion head itself. Preferably, the combustion head comprises four second pipes which are circularly equidistant from each other, that is to say, which are positioned with spacing from each other over a circumference.
This solution allows the production of an additional optimum distribution of the first and/or the second primary supply gas. According to an embodiment, the first interference surface with respect to the first and/or second primary supply gas is a radially external surface which is proximal to the first recirculation chamber or the second interference surface is the radially internal surface of the first recirculation chamber. Furthermore, preferably, this second interference surface is contained in a cylindrical main body which is coaxial with the combustion head which further includes a plurality of through-pipes which project radially from the main body until intersecting with the nozzle.
According to an embodiment, the first or second interference surface is inclined substantially at a first angle which is equal to approximately 90° with respect to the longitudinal axis. It is thereby possible to obtain an efficient detachment of the fluid vein, thereby producing a desired reduced pressure downstream of the first or second or third interference surface. Preferably, the first recirculation chamber comprises

a first central or main body which is defined between a distal surface and a proximal surface of a structure which is structurally substantially similar to a hollow cylinder which is parallel with the longitudinal axis,
an arm which projects radially from the first central body and which intersects with the first nozzle.

As a result of this technical solution, there is produced a recirculation chamber which is arranged so as to be radially spaced apart from the longitudinal axis. In this manner, the recirculation gas is prevented from being able to pass through the central portion of the head in the region of the longitudinal axis.
Preferably, the combustion head comprises four first recirculation chambers which are equidistant from each other.
These first recirculation chambers therefore produce or identify a sort of plurality of cylindrical sectors which are arranged substantially around a circumference and radially spaced apart from the longitudinal axis. The Applicant has found that the number equal to four first recirculation chambers corresponds to an ideal compromise solution between the space occupied by the chambers themselves and the space left free for the passage of other gaseous fluids and/or for simpler access to mechanical components for the purposes of maintenance or replacement. Preferably, the second recirculation chamber comprises

a central body which has a cylindrical extent which is coaxial with the longitudinal axis,
a plurality of arms which project radially from the central body and which intersect with the nozzle.

As a result of this technical solution, it is possible to provide a recirculation chamber which has a single central body which is aligned with the longitudinal axis and which comprises only projecting portions which are capable of intersecting with the nozzle, thereby defining the course which can be travelled by the recirculation exhaust gases (primary and/or secondary). According to an embodiment, the plurality of arms is equal to four.
Preferably, the first primary internal recirculation chamber comprises a first aperture which is positioned in fluid-dynamic terms upstream of the first interference surface and a choke plate which is secured to the first primary internal recirculation chamber with permitted translation movement with respect to the first aperture.
As a result of this technical solution, it is possible to choke by means of translation, and therefore to make proportional in a selectively predefined manner, the quantity of the second primary or secondary supply gas with respect to the quantity of the first primary or secondary supply gas.
In this manner, it is further possible to optimize the distribution and stability of the primary and/or secondary flame by defining as desired the quantity of recirculation exhaust gas which is introduced into the flame itself.
According to an embodiment, the second primary internal recirculation chamber comprises a second aperture which is positioned in fluid-dynamic terms upstream of the second interference surface and a choke disc which is secured to the second primary internal recirculation chamber with permitted rotation with respect to the second aperture. In this manner, there is produced a technical solution which allows the implementation of a choking action, by rotating the disc, of the quantity of the second primary or secondary supply gas with respect to the quantity of the first primary or secondary supply gas.
Preferably, the combustion head comprises a movable cylindrical band which is positioned to be coaxial with the outer surface of the nozzle and which is secured thereto with permitted translation movement in order to close or choke the second entry aperture of the secondary internal recirculation chamber.
It is thereby possible to further define in a precise manner what quantity of recirculation exhaust gas (primary and/or secondary) will reach the primary and/or secondary flame.
This technical solution can also Preferably be translated or replicated in the region of the apertures in the nozzle which identify the intersection between it and the first recirculation chamber.

Brief description of the drawings

The features and advantages of the present invention will be better appreciated from the detailed description of a preferred embodiment thereof which is illustrated by way of non-limiting example with reference to the appended drawings, in which:

Figure 1 is a schematic side view of a combustion head and a portion of the combustion chamber according to the present invention,
Figure 2 is a schematic side view of the combustion head and the portion of the combustion chamber of Figure 1,
Figure 2a is a detailed side view of the combustion head of Figure 2,
Figures 3a and 3a' are a side view and front view of an embodiment of the combustion head according to the present invention, respectively,
Figures 3b and 3b' are a side view and front view of an additional embodiment of the combustion head according to the present invention, respectively,
Figure 4a is a perspective view of the embodiment of Figure 3a,
Figure 4b is a perspective view of the embodiment of Figure 3b,
Figure 5a is a schematic perspective view of a first primary internal recirculation chamber of the head of Figure 4a,
Figure 5b is a schematic perspective view of a second primary internal recirculation chamber of the head of Figure 4b,
Figure 6 is a schematic perspective view of a first primary internal recirculation chamber of the head of Figure 4a,
Figures 7a, 7b and 7c relate to the first primary internal recirculation chamber of Figure 5a,
Figure 8a is a perspective view of the first primary internal recirculation chamber of Figure 5a,
Figure 8b is a perspective view of the first primary internal recirculation chamber of Figure 5b,
Figure 9a is a front view of a combustion head constructed according to the prior art,
Figure 9b is a front view of a combustion head constructed according to the present invention.

Preferred embodiment of the invention

In the Figures, there is designated 1 a combustion head with internal recirculation for a burner 100 of a combustion chamber 26 comprising - a casing 1' which at least partially projects towards the inner side of the combustion chamber 26 and which has a main extent which is substantially cylindrical about a longitudinal axis L.
According to an embodiment, the combustion head 1 is constructed from a ceramic or metal material, preferably from steel which is further preferably austenitic.
Preferably, the combustion head 1 is applied to a combustion chamber 26 which already exists. Should it be necessary, it is possible to dimension a hole of the combustion chamber 26 so as to be able to at least partially receive the combustion head 1 in a simple and efficient manner inside the combustion chamber 26.
Alternatively, it is possible to position a second nozzle 23 which is radially distal with respect to the nozzle 8 and which is formed so as to be inserted inside the hole of the combustion chamber, defining the necessary fluid paths for recirculation exhaust gas.
According to an embodiment, the casing 1' has a prismatic form with a hexagonal, octagonal base and the like.
Preferably, the combustion head 1 comprises

a first portion K coaxial with respect to and contained in the casing 1' comprising
- ∘ a first pipe 20 which comprises a primary jet 6a, 6a' for a first primary supply gas 11' of a primary flame 17 and/or a secondary jet 6b for a first secondary supply gas 12' of a secondary flame 18,
- ∘ a collector 5 for a second primary supply gas (primary air) 14 of the primary flame 17,
- ∘ a diffuser element 7 which is positioned downstream of and which interacts in fluid-dynamic terms with the first pipe 20,
- ∘ a nozzle 8 for a second secondary supply gas (secondary air) 15.

With reference to Figure 2, the diffuser element 7 is preferably constructed from austenitic steel, comprising a central body which has a substantially circular form or which has circular symmetry with predefined recesses, and from which a portion which is also circular and preferably inclined with respect to the longitudinal axis L Preferably extends.
According to an embodiment, the combustion head 1 comprises - the casing 1', the first pipe 20 comprising the primary jet 6a, 6a', the collector 5 and the diffuser element 7 which are formed or arranged so as to be able to generate the primary flame 17 downstream of the diffuser element 7, thereby producing primary internal exhaust gas I1, - the casing 1', the first pipe 20 comprising the secondary jet 6b and the nozzle 8 which are formed or arranged so as to be able to generate the secondary flame 18 downstream of the nozzle 8, thereby producing secondary internal exhaust gas 12.
It is important to note that inside the combustion chamber 26 the above-mentioned primary internal exhaust gas I1 and the secondary internal exhaust gas I2 (produced by the primary flame 17 and the secondary flame 18, respectively) can be freely mixed so as to circulate inside the accessible volumes.
This concept will be discussed in greater detail below in relation to a first or second primary internal recirculation chamber 9a, 9b and a secondary internal recirculation chamber 10. According to an embodiment, the first pipe 20 is a steel tube having a dimeter between 25 and 35 mm, preferably equal to 30 mm for a combustion head for a power to be supplied similar to 2500 kW. Naturally, a construction type will have dimensions which are proportionally greater in accordance with the power used. Preferably, and with reference to Figures 2, 3a, 3a', 3b, 3b', the primary jet 6a and 6a' are dedicated jets which are optimized for the introduction of the first primary supply gas 11' of the primary flame 17 while the secondary jet 6b is dedicated and optimized for the introduction of the first secondary supply gas 12' of the secondary flame 18.
These primary jets 6a; 6a' and secondary jets 6b are preferably formed in a cylindrical manner with a through-hole along the axis of the cylinder or in the wall of the cylinder in order to ensure a directional ejection of the first primary and secondary supply gas.
Preferably, the combustion head 1 comprises

a nozzle 8 which is coaxially aligned with the first portion K comprising
- ∘ a first or second primary internal recirculation chamber 9a; 9b comprising a first entry aperture 31a which is connected in fluid-dynamic terms downstream of the diffuser element 7 or the primary flame 17 and a first discharge aperture 31b which is connected in fluid-dynamic terms upstream or downstream of the diffuser element 7 for the primary internal exhaust gas 11 and/or the secondary internal exhaust gas 12 which is formed so as to have at least a first or second interference surface X1a; X1b with the first and/or second primary supply gas 11', 14 which is suitable for producing a first low-pressure detachment zone 28a for the primary supply gas 11' and/or for the second primary supply gas air 14 and/or
- o a secondary internal recirculation chamber 10 comprising a second entry aperture 32a which is connected downstream of the diffuser element 7 or the secondary flame 18 and a second discharge aperture 32b which is connected upstream of the secondary flame 18 for the secondary internal exhaust gas I2 which is formed so as to have at least a third interference surface X3 with respect to the first and/or second secondary supply gas 12', 15 which is suitable for producing a second low-pressure detachment zone 28b for the first secondary supply gas 12' and/or for the second secondary supply gas 15 so as to produce an internal recirculation of the primary and/or secondary internal exhaust gas I1, I2.

As set out above and also illustrated in Figure 2, the primary and secondary internal exhaust gas I1, I2 can be mixed or mixed with each other and can be re-introduced by means of the first or second primary internal recirculation chamber 9a, 9b and/or the secondary internal recirculation chamber 10.
It will be appreciated that these primary and secondary internal exhaust gases I1, I2 can be simply identified when they are produced as exhaust emissions by the primary and secondary flames, respectively. It is advantageous to note that this composition of the exhaust gas is not intended to be maintained in a necessarily constant manner, in fact the purpose itself of the internal recirculation of these fumes is to lower or reduce significantly the content thereof in terms of NOx in order to make the combustion process cleaner and more efficient.
For each internal recirculation, the primary and secondary exhaust gas I1, I2 can be re-mixed with each other, then defining, during the subsequent flame combustion step, new primary and secondary exhaust gas I1, I2.
It is significant to note that the first, second and third interference surfaces X1a, X1b, X3 are arranged so as to generate a deviation (preferably abrupt) in the direction of the flow of the second primary supply gas 14 and/or the second secondary supply gas 15 (preferably air), and a loss of pressure of the flow itself so as to generate a pressure difference which is sufficient to mobilize a flow from the outer side to the inner side of the combustion head 26, passing through the first entry aperture 31a and/or the second entry aperture 32a.
In order to obtain a deviation of the flow, a component of those interference surfaces is Preferably arranged transversely or perpendicularly with respect to the main longitudinal direction of advance of the air flow (substantially parallel with the longitudinal axis L).
In this manner, the charge loss generated and the quantity of primary and secondary exhaust gas flow I1, I2 which is recirculated are directly proportional to the dimensions of the perpendicular components of these interference surfaces.
The Applicant has found that it is possible to obtain this deviation of the flow by means of a surface which has at least one axis perpendicular to the longitudinal axis L.
In other words, in the simplified case in which the above-mentioned interference surface is a plane, this plane can have both the constituent axes perpendicular to the longitudinal axis L, or only one of them then being transverse with respect to the above-mentioned longitudinal axis in a vertical or horizontal direction.
By way of merely exemplary and non-limiting reference, there may be considered a desire to obtain a recirculation flow of the primary and secondary exhaust gas which is sufficiently intense to lower the values of NOx of the combustion below the performance of a normal low NOx combustion head.
At this point, there is now a comparison of the ratio between the air passage surface and the interference surfaces considering a section which is orthogonal with respect to the longitudinal axis L of the passage of air which is connected in fluid-dynamic terms.
For a combustion head without recirculation chambers and interference surfaces constructed according to the prior art, the ratio between the air passage surface (that is to say, the second primary supply gas 14 and/or the second secondary supply gas 15, the fluid passing through these portions of pipes or chambers) and the total cross-section of the nozzle is typically above 40%, also being up to 65% for combustion heads with a low charge loss (cf. Figure 9a). In order to make these arguments even clearer, the passage surface of the second primary supply gas 14 and/or the second secondary supply gas 15 is shown in Figures 9a and 9b with solid parallel lines.
For a combustion head which has internal recirculation and which is provided with recirculation chambers, in order to obtain charge losses which are sufficiently great to obtain a recirculation flow, the ratio between the passage surface of the air and the total cross-section of the nozzle preferably involves values approximately between 12% and 30%. More preferably, the ratio between the surfaces of the first outlet aperture 31b and the second outlet aperture 32b of the primary and secondary exhaust gas I1, I2 (which correspond to the projection onto the plane perpendicular to the longitudinal flow L) and the total cross-section of the nozzle (8) is between values between 30% and 45% (cf. Figure 9b).
Preferably, the second primary supply gas 14 and/or the second secondary supply gas 15 is/are air. Preferably, this type of gas comprises oxygen.
According to an embodiment, the first nozzle 8 has a substantially cylindrical extent.
Preferably, there are defined in the first nozzle 8 the first entry aperture 31a of the first or second primary internal recirculation chamber 9a; 9b and the second entry aperture 32a of the secondary internal recirculation chamber 10.
According to an embodiment shown by way of example in Figure 2, the first pipe 20 coincides with the longitudinal axis L and is connected in fluid-dynamic terms to at least one second pipe 21 which is radially spaced apart from the first pipe 20 and which has a main extent which is substantially parallel therewith.
According to an embodiment and again with reference to Figure 2, the combustion head 1 comprises four second pipes 21 which are circularly equidistant from each other.
Preferably, the first pipe 20 is connected upstream of the combustion head 1 by means of an entry tube 19.
Preferably and with reference to Figures 2 and 3a, the first interference surface X1a with the first and/or second primary supply gas 11', 14 is a radially external surface which is proximal relative to the first recirculation chamber 9a. According to an embodiment and with reference to Figure 3b, the second interference surface X1b is the radially internal surface of the first recirculation chamber 9b.
More preferably, this second interference surface X1b is contained in a main body 60 which is substantially cylindrical and which is coaxial relative to the combustion head 1, further including a plurality of transverse pipes 61 which project radially from the main body until intersecting with the nozzle 8. According to an embodiment, the first or second or third interference surface X1a; X1b, X3 is inclined through a first angle α1 equal to approximately 90° with respect to the longitudinal axis L.
Preferably, and again with reference to Figures 2, 3a, 4a, 5a, 7a, 7b and 7c, the first recirculation chamber 9a comprises

a first central body 9a1 which is defined between a distal surface and a proximal surface of a hollow cylinder which is parallel with the longitudinal axis L,
an arm 9a2 which projects radially from the first central body 9a1 and which intersects with the nozzle 8.

More preferably, the combustion head 1 comprises four first recirculation chambers 9a which are equidistant from each other.
According to an embodiment and with reference to Figures 3b, 4b and 5b, the second recirculation chamber 9b comprises

a central body 9b1 which has a cylindrical extent which is coaxial with the longitudinal axis L,
a plurality of arms 9b2 which project radially from the central body 9b1 and which intersect with the nozzle 8. Preferably, the plurality of arms 9b2 is equal to four.

According to an embodiment and with reference to Figures 3a, 7a, 7b and 7c, the first primary internal recirculation chamber 9a comprises a first aperture 16a which is positioned in fluid-dynamic terms upstream of the first interference surface X1a and a choke plate 34a which is secured to the first primary internal recirculation chamber 9a with permitted translation movement with respect to the first aperture 16a.
The choke plate 34a is secured, for example, by means of screws which allow it to be fixed in a secure manner to the first recirculation chamber 9a and allow it to be moved reversibly as desired or as required.
Preferably, the first aperture has a substantially rectangular form and is positioned on a rear surface which is substantially perpendicular or transverse to the longitudinal axis L. Preferably, the second primary internal recirculation chamber 9b comprises a second aperture 16b which is positioned in fluid-dynamic terms upstream of the second interference surface X1b and a choke disc 34b which is secured to the second primary internal recirculation chamber 9b with permitted rotation with respect to the second aperture 16b.
The choke disc 34b is secured, for example, by means of screws which allow it to be fixed in a secure manner to the second recirculation chamber 9b and allow it to be moved reversibly as desired or as required.
Preferably, the second aperture 16b has a shape similar to a circular sector or segment and is positioned on a rear surface which is substantially perpendicular or transverse to the longitudinal axis L.
According to alternative embodiments, the first aperture 16a can be constructed in the second primary internal recirculation chamber 9b and the second aperture 16b can be constructed in the first primary internal recirculation chamber 9a.
Preferably, the combustion head 1 comprises a movable cylindrical band 30 which is positioned to be coaxial with the external surface of the nozzle 8 and secured thereto with permitted translation movement in order to close or choke the second entry aperture 32a of the secondary internal recirculation chamber 10.

Claims

A combustion head (1) with internal recirculation for a burner (100) of a combustion chamber (26) comprising
- a casing (1') which at least partially projects towards the inner side of the combustion chamber (26) and which has a main extent which is substantially cylindrical about a longitudinal axis (L),

- a first portion (K) coaxial with respect to and contained in the casing (1') comprising
∘ a first pipe (20) which comprises a primary jet (6a, 6a') for a first primary supply gas (II') of a primary flame (17) and a secondary jet (6b) for a first secondary supply gas (12') of a secondary flame (18),

∘ a collector (5) for a second primary supply gas (14) of the primary flame (17),

∘ a diffuser element (7) which is positioned downstream of and which interacts in fluid-dynamic terms with the first pipe (20),

∘ a nozzle (8) for a second secondary supply gas (15),

- the casing (1'), the first pipe (20) comprising the primary jet (6a, 6a'), the collector (5) and the diffuser element (7) being formed or arranged so as to be able to generate the primary flame (17) downstream of the diffuser element (7), thereby producing primary internal exhaust gas (I1),

- the casing (1'), the first pipe (20) comprising the secondary jet (6b) and the nozzle (8) being formed or arranged so as to be able to generate the secondary flame (18) downstream of the nozzle (8), thereby producing secondary internal exhaust gas (I2),
characterized in that the combustion head (1) comprises

- the nozzle (8) which is coaxially aligned with the first portion (K) comprising
∘ a first or second primary internal recirculation chamber (9a; 9b) comprising a first entry aperture (31a) which is connected in fluid-dynamic terms downstream of the diffuser element (7) or the primary flame (17) and a first discharge aperture (31b) which is connected in fluid-dynamic terms upstream or downstream of the diffuser element (7) for the primary internal exhaust gas (I1) and/or the secondary internal exhaust gas (I2), the first or second primary internal recirculation chamber (9a; 9b) being formed so as to have at least a first or second interference surface (X1a; X1b) with the first and/or second primary supply gas (11', 14) which is suitable for producing a first low-pressure detachment zone (28a) for the primary supply gas (11') and/or for the second primary supply gas (14) and/or

∘ a secondary internal recirculation chamber (10) comprising a second entry aperture (32a) which is connected downstream of the diffuser element (7) or the secondary flame (18) and a second discharge aperture (32b) which is connected upstream of the secondary flame (18) for the secondary internal exhaust gas (I2) which is formed so as to have at least a third interference surface (X3) with respect to the first and/or second secondary supply gas (12', 15) which is suitable for producing a second low-pressure detachment zone (28b) for the first secondary supply gas (12') and/or for the second secondary supply gas (15) so as to produce an internal recirculation of the primary and/or secondary internal exhaust gas (II, I2).
A combustion head (1) according to the preceding claim, wherein the second primary supply gas (14) and/or the second secondary supply gas (15) is/are air.
A combustion head (1) according to one or more of the preceding claims, wherein
- the first nozzle (8) has a substantially cylindrical extent.
A combustion head (1) according to one or more of the preceding claims, wherein the first pipe (20) coincides with the longitudinal axis (L) and is connected in fluid-dynamic terms to at least a second pipe (21) which is radially spaced apart from the first pipe (20) and which has a main extent which is substantially parallel therewith.
A combustion head (1) according to the preceding claim, comprising four of the second pipes (21) which are circularly equidistant from each other.
A combustion head (1) according to one or more of the preceding claims, wherein the first interference surface (X1a) with the first and/or second primary supply gas (11', 14) is a radially external surface which is proximal to the first recirculation chamber (9a) or the second interference surface (X1b) is the radially internal surface of the first recirculation chamber (9b).
A combustion head (1) according to one or more of the preceding claims, wherein the first or second interference surface (X1a; X1b) is inclined at a first angle (α1) which is preferably equal to approximately 90° with respect to the longitudinal axis (L).
A combustion head (1) according to one or more of the preceding claims, wherein the first recirculation chamber (9a) comprises
- a first central body (9a1) which is defined between a distal surface and a proximal surface of a hollow cylinder which is parallel with the longitudinal axis (L),

- an arm (9a2) which projects radially from the first central body (9a1) and which intersects with the first nozzle (8).
A combustion head (1) according to the preceding claim, comprising four first recirculation chambers (9a) which are equidistant from each other.
A combustion head (1) according to one or more of the preceding claims, wherein the second recirculation chamber (9b) comprises
- a central body (9b1) which has a cylindrical extent which is coaxial with the longitudinal axis (L),

- a plurality of arms (9b2) which project radially from the central body (9b1) and which intersect with the nozzle (8).
A combustion head (1) according to the preceding claim, wherein the plurality of arms (9b2) is equal to four.
A combustion head (1) according to one or more of the preceding claims, wherein the first primary internal recirculation chamber (9a) comprises a first aperture (16a) which is positioned in fluid-dynamic terms upstream of the first interference surface (X1a) and a choke plate (34a) which is secured to the first primary internal recirculation chamber (9a) with permitted translation movement with respect to the first aperture (16a).
A combustion head (1) according to one or more of the preceding claims, wherein the second primary internal recirculation chamber (9b) comprises a second aperture (16b) which is positioned in fluid-dynamic terms upstream of the second interference surface (X1b) and a choke disc (34b) which is secured to the second primary internal recirculation chamber (9b) with permitted rotation with respect to the second aperture (16b) .
A combustion head (1) according to one or more of the preceding claims, comprising a movable cylindrical band (30) which is positioned to be coaxial with the outer surface of the nozzle (8) and which is secured thereto with permitted translation movement in order to close or choke the second entry aperture (32a) of the secondary internal recirculation chamber (10) .
A combustion head (1) according to one or more of the preceding claims, wherein a ratio between a passage surface of the second primary supply gas (14) and/or the second secondary supply gas (15) and a total cross-section of the nozzle (8) preferably involves values between approximately 12% and 30%.