CN116293678A

CN116293678A - Burner head with internal recirculation and burner comprising a burner head

Info

Publication number: CN116293678A
Application number: CN202211107189.5A
Authority: CN
Inventors: 斯特凡诺·佩谢
Original assignee: Shanghai Quanjie Environment Equipment Co ltd
Current assignee: Shanghai Quanjie Environment Equipment Co ltd
Priority date: 2021-09-10
Filing date: 2022-09-09
Publication date: 2023-06-23
Also published as: IT202100023477A1

Abstract

A burner head with internal recirculation for a burner of a combustion chamber, the burner head comprising: a housing, a manifold, a primary pipe, a secondary pipe, and a recirculation zone. The housing comprises an inlet through which a first combustion-supporting gas flow can flow into the interior of the housing, the first combustion-supporting gas flow being intended to be divided into at least a second combustion-supporting gas flow and a third combustion-supporting gas flow. The manifold includes an outer jacket directly facing the combustion chamber, with at least one radial opening formed in the outer jacket, and the second combustible gas stream can flow in the secondary duct such that the second combustible gas stream can flow inside the manifold and can be discharged from the radial opening. The radial openings are configured such that the second combustible gas stream is impinged by the exhaust gas stream from the combustion chamber, thereby mixing with the exhaust gas stream.

Description

Burner head with internal recirculation and burner comprising a burner head

Technical Field

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

Background

It is known that in the field of boilers supplied by means of fossil fuels, emissions of pollutants harmful to the environment occur, in the form of in particular nitrogen oxides (for example NO, NO 2), generally identified by the abbreviation NOx. The pollutant emissions can be influenced or reduced by the design of the combustion device, in particular the design of the burner used.

In the case of burners, it is well known that the amount of NOx pollutants produced by combustion is proportional to the flame temperature produced, and designs for such burners have been proposed to reduce flame temperature. These NOx produced in the region where the flame temperature is high are generally referred to as thermal NOx.

In a general sense, reducing or lowering NOx in industrial burners has been a desired goal. In the past, NOx reduction was achieved by using a lean primary air/gas mixture associated with a staged distribution of gaseous fuel. In some applications, a lean primary fuel mixture may be required in order to reduce flame temperature and thus NOx, because excess air may create charge. The gas may then be introduced into the combustion zone by means of nozzles arranged around the circumference of the burner or by means of a central nozzle protruding through the last part of the duct of the gas device. The secondary fuel is combusted with excess air in an environment where a flame is present that has been combusted and serves as a dilution. This technique is not always able to ensure the required or prescribed NOx levels for compliance.

In addition to staged combustion, other technologies have been developed over the years to reduce the value of pollutants to increasingly lower levels, including combustion technologies based on internal recirculation of exhaust gas present inside the combustion chamber. The exhaust gas is forced into the burner head creating a zone of lesser pressure upstream in front of the flame through a zone of higher air velocity, a zone of local turbulence, or any other fluid dynamic form that can cause pressure drop and flow of the flame to the central zone of the burner head. The resulting internal recirculation serves to again draw the recirculation gas into the interior of the recirculation chamber, which is then mixed with the combustion air flow and pushed down to the combustion chamber.

The exhaust gas present inside the combustion chamber is considered to be an inert gas and therefore, without any oxygen or with only a minimum percentage of oxygen, does not actively participate in the combustion and serves to dilute the percentage of oxygen in the mixture formed by the exhaust gas with the second combustion gas stream and the second combustible gas stream. The dilution and absorption effects of the heat generated by the combustion result in a reduction of the flame temperature, thus reducing the value of polluting emissions.

Examples of the above combustion techniques are described in patent applications US 5 284 438, US 5 542 840, EP 0 194 079 A1, EP 0857915 A3, WO 2017209503 A1, EP 0386732 A3 and EP 3 734 154 A1.

Another technique used by many burner manufacturers in the prior art is to mix the combustible gas with the inert exhaust gas before combustion occurs, thereby diluting the combustible mixture with inert components, resulting in combustion with reduced temperature peaks.

The patent invented on the basis of this technique is US6626661, in which a combustible gas is injected into a zone without any combustion gas, the combustible gas stream having an incidence direction with respect to the combustion gas stream, but before the combustible gas stream is mixed with the combustion gas stream, the combustible gas stream is restricted to pass through a zone where only exhaust gases are present, which process results in dilution of the combustible gas and subsequent combustion at a reduced temperature. The combustible gas is injected at a higher velocity to direct the jet in the desired direction, which results in a larger pressure loss at the nozzle.

The continuing market demand for reduced emissions sometimes makes the above-described technology inadequate to achieve the desired values. Furthermore, various compromises are necessary in order to obtain efficient operation of the above-described techniques.

Disclosure of Invention

It is an object of the present invention to provide a burner head with internal recirculation for a burner or a burner comprising the same, which burner head is structured and functionally to at least partially overcome at least one of the drawbacks of the cited prior art and to obtain a less emission of NOx pollutants than the prior art.

With this aim, the aim is to improve the operation of the burner head, or of the burner, or of the boiler associated with the burner, so as to ensure a higher level of performance.

This object is at least partly achieved by a burner head with internal recirculation, which burner head comprises one or more of the features mentioned in claim 1, and a burner comprising one or more of the features mentioned in claim 14.

According to a first aspect of the present invention, there is provided a burner head with internal recirculation for a combustion chamber. Preferably, the combustion head comprises: a housing, a manifold, a primary pipe, a secondary pipe, and a recirculation zone. Advantageously, the housing has a generally tubular portion about a longitudinal axis and comprises a first portion and a second portion. Preferably, the first portion protrudes into the combustion chamber interior and comprises a recirculation opening. Advantageously, the second portion is positioned outside the combustion chamber and comprises an inlet of the housing through which the first combustion air flow can flow into the interior of the housing in a direction of travel substantially parallel to the longitudinal axis of the housing. Preferably, the first combustion air flow is intended to be divided into at least a second combustion air flow and a third combustion air flow in the direction of travel. Advantageously, the manifold has a longitudinal portion thereof and comprises an outer sheath directly facing the combustion chamber, in which at least one radial opening is formed, interposed between the recirculation opening and the outlet of the casing. Preferably, the primary duct in which the first combustible gas stream can flow comprises a primary nozzle from which the first combustible gas stream can be discharged and by mixing with the third combustion air stream, a primary flame can be produced. Advantageously, the second combustible gas stream may flow in the secondary duct such that the second combustible gas stream may flow inside the manifold and may be discharged from the radial openings. Preferably, the radial openings are configured such that the second combustible gas flow is impinged by the exhaust gas flow from the combustion chamber so as to be mixed with the exhaust gas flow and conveyed together with the exhaust gas flow through the recirculation opening into the recirculation zone in a direction opposite to the direction of travel. Advantageously, the recirculation zone is located inside the housing in the region of the recirculation opening. Preferably, the recirculation zone comprises a longitudinal inlet portion through which the second combustion air stream can be introduced into the recirculation zone.

Preferably, a portion of the first combustion air flow can be introduced into the recirculation zone through the longitudinal inlet portion, so as to divide the first combustion air flow into a second combustion air flow and a third combustion air flow in the direction of travel, the second combustion air flow advantageously corresponding to the above-mentioned portion of the first combustion air flow.

Preferably, the recirculation zone comprises a passage portion through which the second combustible gas stream mixed with the exhaust gas stream and the second combustion gas stream can be discharged, so as to be able to generate a secondary flame.

It will thus be appreciated that the burner head of the present invention allows to obtain an internal recirculation of the exhaust gas flow and of the combustible gas.

In particular, premixing between the combustible gas stream and the exhaust gas stream is obtained before the premix flow is introduced into the recirculation zone.

This premixing is done outside the burner head so that the two streams can be mixed without any physical elements of the burner head impeding or disrupting the movement of the two streams.

Whereby an optimal premix flow is obtained by optimizing the performance level of the head and allowing a reduction of the NOx level with respect to known solutions. Preferably, the second combustible gas stream mixed with the exhaust gas stream may also be referred to as a recycle stream. Advantageously, the recirculation flow mixed with the second combustion air flow can also be referred to as chamber flow.

Preferably, the direction of travel has a direction of travel from the second portion to the first portion of the housing.

Preferably, the recirculation zone is formed such that a pressure zone is created in the recirculation zone that is lower relative to the internal pressure of the combustion chamber. The recirculation zone is thus advantageously formed to create a negative pressure differential, thereby allowing the exhaust gas stream and the second combustible gas stream to flow out of the combustion chamber into the interior of the recirculation zone. Preferably, the pressure difference is created by separating the combustion air flow from a specific surface contained in the recirculation zone. Preferably, the specific surface may be an interference surface that generates local turbulence or a conical or annular surface that generates a venturi effect. It is thereby possible to construct a combustion head capable of creating a decompression zone.

In some embodiments, this pressure reduction may occur after a phenomenon based on the venturi effect.

In some embodiments, the recirculation zone is defined by one or more recirculation chambers. Preferably, the recirculation chamber is formed with at least one interference surface. Advantageously, when the interference surface is impacted by the combustion air flow, preferably by the second combustion air flow, a pressure reduction is generated in the recirculation zone. The pressure reduction advantageously causes the recirculation flow to be introduced into the recirculation chamber interior.

Advantageously, the rear wall of the recirculation chamber comprises an interference surface for the second combustible gas flow, which interference surface is capable of generating a pressure reduction in the recirculation chamber.

Preferably, the interference surface is arranged to produce a redirection, advantageously a sudden redirection, of the second combustion air flow and a pressure loss of the flow, thereby producing a pressure loss sufficient to enable the recirculation flow from the combustion chamber into the interior of the recirculation chamber by passing through the recirculation opening.

In order to obtain a particularly efficient redirection of the flow, the component parts of the interference surface are advantageously arranged transverse or perpendicular to the direction of travel. In this way, the pressure drop generated is proportional to the size of the portion of the interference surface perpendicular to the direction of travel.

The combustion head according to the invention thus allows to obtain reduced emission levels, in particular reduced emission levels of NOx, while allowing to simplify the production process for obtaining reduced emission levels.

Preferably, the combustion-supporting gas is air. Advantageously, this type of gas comprises oxygen.

In a preferred embodiment, the first and second combustible gas streams may be formed from the same gas, for example from natural gas or any other type of gas supplied via a common distribution network.

Advantageously, the burner head according to the invention allows mixing between the exhaust gas flow and the second combustible gas flow before the secondary flame is formed. This condition is advantageously effective to produce the desired gas combustion mixture and thus operate the combustion head itself.

Preferably, the second combustible gas stream is discharged radially through radial openings in the following areas of the combustion chamber: in which the exhaust flow has a direction substantially opposite to the direction of travel. Advantageously, in this region of the combustion chamber, the exhaust stream does not contain oxygen or contains a negligible percentage of oxygen below the flammability range of the combustible gas before it is introduced inside the recirculation zone, so that the second combustible gas stream and the exhaust stream do not produce any flame. Preferably, the exhaust gas stream is drawn into the recirculation zone together with the second combustible gas stream. Advantageously, the exhaust gas and the combustible gas are mixed with each other in the following percentages: this percentage allows the volumetric relation between the combustible gas and the exhaust gas to vary between one third and one twentieth, even more preferably between one third and one tenth to one. Preferably, the mixing of the combustible gas with the exhaust gas produces a combustible mixture in which the combustible gas is partially diluted in the recirculating flame, thus obtaining a more uniform combustion with smaller temperature peaks, thus obtaining reduced thermal NOx. Advantageously, the second combustible gas stream is already mixed with the exhaust gas stream outside with respect to the burner head before being mixed with the second combustion gas stream in the recirculation zone and generating the secondary flame. A premixed gas stream with inert recycle gas and thus with diluted gas is thus obtained.

The burner head is therefore characterized by a high simplicity of construction, since it is not necessary to use a nozzle, for example, located externally with respect to the housing.

Thanks to the burner head according to the invention, it is advantageously possible to distribute the combustible gas and the comburent gas in a uniform manner inside the combustion chamber, thus further improving the efficiency of the burner head itself and the stability of the flame.

According to another aspect of the invention, a burner comprising a burner head according to the invention is provided.

According to yet another aspect, there is provided a boiler comprising a combustion chamber comprising a burner constructed according to the above aspects.

It will be appreciated that preferred and advantageous features set forth in relation to one of the aspects of the invention may also be used in relation to the other aspects of the invention.

Drawings

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

fig. 1 is a longitudinal section of a burner head and a burner comprising a burner head shown in a schematic way;

FIG. 2 is a longitudinal section of the burner head;

FIG. 3 is a front view of the burner head;

FIG. 4 is a rear view of a cross section of the burner head;

FIG. 5 is a perspective rear view of a cross section of a combustion head;

FIG. 6 is a top view of the recirculation chamber of the burner head;

FIG. 7 is a longitudinal section of the recirculation chamber of the burner head;

FIG. 8 is a front view of the recirculation chamber of the burner head;

fig. 9 is a rear view of the recirculation chamber of the burner head.

Detailed Description

In the figures, the burner 100 for the combustion chamber 26 is designated 1 as a burner head with internal recirculation.

According to a first aspect of the invention, a burner 100 of a combustion chamber 26 is provided with a burner head 1 with internal recirculation.

Preferably, the combustion head 1 comprises: housing 5, manifold 70, primary pipe 20, secondary pipe 30, and recirculation zone 4. Advantageously, the housing 5 has a substantially tubular portion about the longitudinal axis L, and the housing 5 comprises a first portion 51 and a second portion 52. Preferably, the first portion 51 protrudes inside the combustion chamber 26 and comprises a recirculation opening 3 extending along the opening axis T of the combustion chamber 26. Advantageously, the second portion 52 is positioned outside the combustion chamber 26 and comprises an inlet 54 of the housing 5 through which the first combustion air flow 13 can flow inside the housing 5 along a travel direction a substantially parallel to the longitudinal axis L of the housing 5. Preferably, the first combustion air flow 13 is intended to be divided into at least a second flow 14 and a third flow 15 of combustion air in the travelling direction a. Advantageously, the manifold 70 has a longitudinal portion K and comprises an outer jacket 71 directly facing the combustion chamber 26, and a radial opening 7 is formed in the outer jacket 71, the radial opening 7 being interposed between the recirculation opening 3 of the housing 5 and the outlet 61.

Preferably, the primary duct 20, in which the first combustible gas stream 11 can flow, comprises a primary nozzle 6, from which the first combustible gas stream 11 can be discharged, and by mixing with the third combustion air stream 15 a primary flame 17 can be generated. Advantageously, the second combustible gas stream 12 may flow in the secondary duct 30, so that the second combustible gas stream 12 may flow inside the manifold 70 and may be discharged from the radial openings 7. Preferably, the radial openings 7 are configured such that the second combustible gas flow 12 is impinged by the exhaust gas flow 19 from the combustion chamber 26 so as to be mixed with the exhaust gas flow 19 and conveyed together with the exhaust gas flow 19 through the recirculation opening 3 into the recirculation zone 4 in a direction opposite to the travelling direction a.

It should be appreciated that the radial openings 3 need not be configured to produce a fully radial flow. In fact, the radial openings 3 are arranged so as to form oblique flows with respect to the following directions: the direction is completely radial with respect to the manifold 70, provided that the oblique flow is directed away from the outer wall of the manifold and thus has at least one radial component.

Furthermore, even though in the present embodiment a plurality of radial openings 7 are defined, it is also possible to provide for the use of a single radial opening 7, which radial opening 7 is suitably shaped to provide the required air flow.

Advantageously, the recirculation zone 4 is defined by at least one recirculation chamber 4A, which recirculation chamber 4A is positioned at the recirculation opening 3 inside the housing 5. Advantageously, the recirculation chamber 4A comprises a longitudinal inlet portion 41 through which the second combustion air stream 14 can be introduced into the recirculation chamber 4A and a passage portion 44 through which the second combustible air stream 12 mixed with the exhaust air stream 19 and the second combustion air stream 14 is discharged to enable the generation of the secondary flame 18.

In other words, a portion of the first combustion air flow 13 may pass through the longitudinal inlet portion 41, so that the portion of the first combustion air flow 13 is divided into two parts, that is to say, the portion of the first combustion air flow 13 is divided into the second combustion air flow 14 and the third combustion air flow 15, so that the second combustion air flow 14 coincides with the portion of the first combustion air flow 13 passing through the longitudinal inlet portion 41.

According to one embodiment, the burner head 1 is made of a ceramic or metallic material, preferably the burner head 1 is made of steel, preferably the burner head 1 is made of austenitic steel.

Advantageously, the burner head 1 is used in an already existing combustion chamber 26.

Advantageously, the primary nozzle 6 is positioned in the first portion 51 of the housing 5. Preferably, the primary nozzles 6 are dedicated and optimized for introducing the first combustible gas stream 11 inside the combustion chamber 26 to obtain a particularly stable primary flame 17. Advantageously, the primary nozzle 6 is formed in a cylindrical manner and has one or more through holes along the axis of the cylindrical member or in the side walls of the cylindrical member, to ensure the directional discharge of the first combustible gas flow 11.

Advantageously, the second combustible gas stream 12 mixed with the exhaust gas stream 19 may also be referred to as a recycle stream 99.

Preferably, the recycle stream 99 mixed with the second combustion air stream 14 may also be referred to as a chamber stream 98.

Advantageously, exhaust stream 19 may include a primary exhaust stream and a secondary exhaust stream. Preferably, the primary exhaust flow is generated by combustion of the primary flame 17 and the secondary exhaust flow is generated by combustion of the secondary flame 18. Advantageously, the primary and secondary exhaust streams may be combined or mixed with each other. It will be appreciated that these exhaust streams are simply identifiable in that they are generated as exhaust from the primary flame and the secondary flame, respectively. Notably, this composition of the exhaust gases is not intended to be maintained in a necessarily constant manner, in fact the purpose of the internal recirculation of these exhaust gases itself is to significantly reduce or reduce the NOx content in the exhaust gases, so as to make the combustion process cleaner and more efficient. With each internal recirculation, the primary and secondary exhaust gases may be recombined with each other, and then new primary and secondary exhaust gases are defined during a subsequent flame combustion step.

Preferably, the combustion-supporting gas is air. Advantageously, the combustion-supporting gas of this type comprises oxygen. Advantageously, the combustion air flows 13, 14, 15 are air. In some embodiments, the first combustion air stream 13 may be split into additional combustion air streams. The further combustion air flow is preferably air.

In a preferred embodiment, the first and second combustible gas streams may be formed from the same gas, for example from natural gas or any other type of gas supplied via a common distribution network. In any event, it should be understood that the present invention may be used with any type of combustible gas.

Preferably, the travelling direction a has a direction extending from the second portion 52 to the first portion 51 of the housing 5.

The first combustible gas stream 11 advantageously flows in the primary duct 20 in the travelling direction a. Advantageously, the first tube 20 is connected upstream of the burner head 1 by means of an inlet duct system, not shown.

Preferably, the housing 5 has a tubular shape extending around a longitudinal axis L of the housing 5, even more preferably the housing 5 has a circular cross section. Preferably, the outlet 61 of the housing 5 is accommodated in the first portion 51 of the housing 5. Advantageously, the outlet 61 is located at the end of the housing 5 that protrudes furthest into the combustion chamber 26.

Preferably, the manifold 70 has a generally tubular portion about the longitudinal axis L of the housing 5. Preferably, the longitudinal portion K of the manifold 70 is substantially equal to at least half of the total longitudinal portion of the housing 5. Advantageously, the manifold 70 is delimited longitudinally by a first transverse wall 74 and a second transverse wall 75. Preferably, the manifold 70 includes an inner sheath 72 positioned inside the housing 5. Advantageously, the manifold 70 has a generally hollow cylindrical shape. Preferably, the manifold 70 includes a cavity 55, the cavity 55 being disposed between an outer sheath 71 and an inner sheath 72. Advantageously, the cavity 55 is able to receive the second combustible gas flow 12 by means of the secondary duct 30.

Advantageously, the manifold 70 is positioned such that at least 90% or more of the longitudinal portion K of the manifold 70 is located in the first portion 51 of the housing 5. Preferably, the sheath of the first portion 51 of the housing 5 is substantially coincident with the outer sheath 71 of the manifold 70.

The radial opening 7 is preferably configured in the first portion 51 of the housing 5. In a preferred embodiment, a set of radial openings 7 is provided, wherein the radial openings 7 are distributed circumferentially over the outer jacket 71 of the housing 5. Advantageously, the radial openings 7 are distributed equidistant from each other on the outer jacket 71 of the housing 5. Preferably, a plurality of sets of radial openings are provided. Advantageously, the sets of radial openings 7 are equidistant from each other in the longitudinal direction.

Preferably, the outer sheath 71 of the manifold 5 faces directly towards the combustion chamber 26. The term "directly" is intended to be understood as meaning that no obstacle is provided in front of the outer sheath 71. Thus, when the second combustible gas stream 12 is discharged from the manifold through the radial openings 7, it does not strike any obstacle located directly in front of the radial openings 7. In this way, the second combustible gas stream 12 discharged from the radial openings 7 can be directly impacted and conveyed by the exhaust gas stream 19. This allows the construction of the burner head 1 to be simplified, since no element, such as for example a mouth, is provided outside the housing 5.

Preferably, the recycle stream 99 flows toward the interior of the recycle chamber 4A without contacting oxygen or with a minimum percentage of oxygen. The exhaust gas stream 19 is formed of inert gas and thus is devoid of any oxygen or has only a minimum percentage of oxygen, since the exhaust gas stream does not actively participate in combustion and serves to dilute the percentage of oxygen in the mixture formed with the second combustion gas stream 14 and the second combustible gas stream 12.

The presence of combustion-supporting gas and thus the presence of oxygen may lead to undesired and unstable combustion operations, for example in the manifold 70 or in the recirculation chamber 4A.

Advantageously, the radial openings 7 are configured so that the second combustible gas stream 12 is discharged at a limited rate. Preferably, the velocity is such that the second combustible gas stream 12 may be directed entirely by the exhaust gas stream 19.

Preferably, the recirculation opening 3 has a substantially tubular shape and extends around an opening axis T of the recirculation opening 3, even more preferably the recirculation opening 3 has a circular cross section. Preferably, the recirculation openings 3 are through holes in the outer and

inner jackets

71, 72 of the manifold 70. Advantageously, the recirculation opening 3 is delimited by a side surface 73. Preferably, the cavity 55 of the manifold 70 is delimited by the outer jacket 71, the inner jacket 72, the first transverse wall 74, the second transverse wall 75 of the manifold 70 and the side surfaces 73 of the recirculation opening 3.

Preferably, the recirculation opening 3 is interposed between the radial opening 7 and the second portion 52 of the housing 5.

Advantageously, the opening axis T of the recirculation opening 3 is the longitudinal axis of the recirculation opening 3. Preferably, the opening axis T extends in a radial direction of the housing 5. Advantageously, the opening axis T is perpendicular to the longitudinal axis L of the housing 5 and lies in a transversal plane with respect to the longitudinal axis L of the housing 5.

Preferably, the recirculation chamber 4A is positioned inside the first portion 51 of the housing 5. Advantageously, the recirculation chamber 4A comprises two lateral walls 43, a lower wall 56 and a rear wall 57. Preferably, the longitudinal inlet portion 41 of the recirculation chamber is formed on the rear wall 57. Preferably, the longitudinal inlet portion 41 has a square shape.

Advantageously, the lower wall 56 has a curvature substantially corresponding to the curvature of the housing 5.

Preferably, the recirculation chamber 4A, or more generally the recirculation zone 4, is formed such that a low pressure zone is created in the recirculation chamber 4A relative to the internal pressure of the combustion chamber 26. Thus, recirculation zone 4 is advantageously formed to create a negative pressure differential, thereby allowing exhaust stream 19 and second combustible gas stream 12 to exit combustion chamber 26 and flow into the interior of recirculation zone 4.

In a preferred embodiment, the recirculation chamber 4A is formed with at least one interference surface. Advantageously, when the interference surface is impacted by the combustion air flow, preferably by the second combustion air flow 12, a pressure reduction is generated in the recirculation zone 4. The pressure reduction advantageously results in the recycle stream 99 being introduced into the interior of the recycle zone 4. Advantageously, the rear wall 57 of the recirculation zone 4 comprises an interference surface.

Preferably, the combustion head 1 comprises a primary channel 63, the primary channel 63 being interposed between the primary duct 20 and the lower wall 56 of the recirculation chamber 4A. Advantageously, the third combustion air flow 15 flows in the primary channel 63. Preferably, the primary channels 63 are located in a central region of the housing 5, such that the third combustion air flow 15 is concentrated in the central region of the housing 5. Advantageously, the primary channel 63 is configured so that the third combustion air flow 15 is discharged from the casing 5 at the following speeds: the speed is such that the third combustion air flow 15 is located in a region of the combustion chamber 26 remote from the location where the burner head 1 is arranged. In this way, the third combustion air flow 15 is limited to form a very wide circle before returning to the vicinity of the combustion head 1. Preferably, the third combustion air stream 15 is discharged by this kinetic energy to prevent the third combustion air stream 15 from returning and mixing with the recycle stream 99. Preferably, the combustion head 1 comprises a plurality of recirculation openings 3 and respective recirculation chambers 4A. Advantageously, the recirculation openings 3 are arranged equidistant from each other. The term equidistant is intended to be understood as meaning that the opening axes T of successive recirculation openings 3 are spaced apart from each other by a first angle α. Preferably, the first angle α is defined in a plane transverse to the longitudinal axis L of the housing 5 and accommodating the opening axis T of the recirculation opening 3. Preferably, the term "continuous recirculation opening 3" is intended to be understood to mean a recirculation opening 3 which is continuous in the circumferential direction.

Advantageously, a recirculation chamber 4A is associated with each recirculation opening 3. Thus, successive recirculation chambers 4A are also spaced apart from each other by the first angle α. Preferably, the term "continuous recirculation chamber 4A" is intended to be understood as meaning a recirculation chamber 4 which is continuous in the circumferential direction.

In a preferred embodiment of the invention, four recirculation openings 3 and four corresponding recirculation chambers 4A are provided. In this case, the first angle α is about 90 °.

Preferably, the two side walls 43 of the recirculation chamber 4A are formed so as to obtain a secondary channel 62, which secondary channel 62 is interposed between two adjacent side walls 43 of the respective successive recirculation chamber 4A. Advantageously, the secondary channel 62 tapers in the direction of travel a.

The provision of the secondary channel 62 allows the recirculation chamber 4A to be inserted into the housing 5/removed from the housing 5 to be easier. This may be found to be particularly advantageous in the case where the recirculation chamber 4A is connected to the housing 5 by means of a threaded connection.

In other embodiments, the recirculation chamber 4A may advantageously be connected to the housing 5 by means of welding. In this case, alternative embodiments may be provided, for example, in which the secondary channel 62 may take a non-tapered form.

The additional combustion air stream preferably includes a fourth combustion air stream 16. The fourth combustion air stream 16 may advantageously pass in the secondary channel 62.

Advantageously, the secondary channel 62 is configured so that the fourth combustion air flow 16 is discharged from the casing 5 at the following speeds: the speed is such that the fourth combustion air flow 16 is located in the region of the combustion chamber 26 remote from the location where the burner head 1 is located. In this way, the fourth combustion air stream 16 is constrained to form a very wide circle before returning to the vicinity of the burner head 1. Preferably, the fourth combustion air stream 16 is discharged by this kinetic energy to prevent the fourth combustion air stream 16 from returning and mixing with the recycle stream 99.

Preferably, the rear wall 57 of the recirculation chamber 4A is substantially parallel to the following inclined plane: the inclined plane is formed with respect to a plane transverse to the longitudinal axis L of the housing 5 such that the value of the second angle β between the two planes is between about 10 ° and 45 °.

Preferably, the configuration of the rear wall 57 allows the interference surface of the rear wall 57 to be positioned so that a particularly abrupt reorientation of the second combustion-supporting gas flow 12 occurs. The resulting pressure loss of the second combustion air stream 12 advantageously allows a pressure differential to be generated sufficient for the recirculation flow 99 to flow from the combustion chamber 26 through the recirculation opening 3 to the interior of the recirculation zone 4.

The applicant has found that a particularly effective redirection of the second combustible gas stream 12 can advantageously be obtained by the interference surface thanks to a value of the second angle β comprised between 10 ° and 45 °. The resulting pressure drop is in fact proportional to the size of the interference surface with respect to the perpendicular component of the direction of travel a.

Preferably, the recirculation opening 3 has a longitudinal portion V equal to one third of the longitudinal portion K of the manifold 70.

Advantageously, if the recirculation opening 3 has a substantially annular cross section, the longitudinal portion V of the recirculation opening 3 corresponds substantially to the diameter of the cross section.

The longitudinal distance M between the opening axis T and the housing outlet 61 of the housing 5 is approximately equal to two-thirds of the longitudinal portion K of the manifold 70. In this way, the guiding of the recirculation flow 99 in the recirculation zone 4 can be further optimized.

Preferably, the recirculation chamber 4A includes an upper wall 58. Advantageously, the upper wall 58 comprises radial inlets 40, the radial inlets 40 being placed at the respective recirculation openings 3.

The term "corresponding recirculation opening 3" is advantageously intended to be understood as an opening associated with the recirculation chamber 4A. Preferably, a recirculation chamber 4A and possibly a respective radial inlet 40 are associated with each recirculation opening 3.

Advantageously, the upper wall 58 has a curvature substantially corresponding to the curvature of the housing 5.

The upper wall 58 has been found to be particularly advantageous if the recirculation chamber 4A can be assembled in the housing 5/disassembled from the housing 5, for example by means of a threaded connection. In some embodiments where the side walls 43 and the rear wall 57 are welded to the inner jacket 72 of the housing 5, the upper wall 58 may be optional, as the inner jacket 72 of the housing 5 may in this case serve as the upper wall of the recirculation chamber 4A.

Preferably, the radial inlets 40 of the upper wall 58 allow the second combustible gas stream 12 mixed with the exhaust gas stream 19 to be introduced into the respective recirculation chamber 4A via the respective recirculation opening 3.

Advantageously, the radial inlet 40 has a tubular form, even more preferably the radial inlet 40 has a circular cross section. Preferably, the radial inlets 40 extend along the opening axis T of the respective recirculation opening 3. In this way, the recirculation opening 3 and the corresponding radial inlet 40 are coaxial with respect to the same opening axis T.

Advantageously, the longitudinal portion of the radial inlet 40 is slightly smaller than the longitudinal portion V of the corresponding recirculation opening 3. The radial inlets 40 can thus be inserted into the recirculation openings 3 by moving the outer surfaces 74 of the radial inlets 40 against the side surfaces 73 of the respective recirculation openings 3. This promotes the introduction of the recirculation flow 99 inside the recirculation chamber 4A and prevents the loss of flow in the housing 5.

Preferably, the radial opening 7 is positioned at a longitudinal distance B from the outlet 61 of the housing 5, which is approximately between two-thirds and three-thirds of the longitudinal portion K of the manifold 70.

Advantageously, the guiding of the second combustible gas stream 12 away from the radial opening 7 can thereby be further optimized. The second combustible gas stream 12 will therefore advantageously be mixed with the exhaust gas stream 19 for subsequent introduction into the recirculation zone 4 through the recirculation opening 3.

In a preferred embodiment, the radial opening 7 is positioned at a longitudinal distance B from the outlet 61 of the housing 5 equal to about half of the longitudinal portion K of the manifold 70.

Preferably, the diameter of the radial opening 3 varies according to the length of the manifold 70, so as to increase with an increase in the length of the manifold.

Preferably, the primary tube 20 of the burner head 1 extends along the longitudinal axis L of the housing 5. Advantageously, the secondary duct 30 comprises a first secondary duct 31 and a second secondary duct 32. Preferably, the first secondary pipe 31 is coaxial with the primary pipe 20. Advantageously, the second secondary pipe 32 connects the manifold 70 and the first secondary pipe 31.

Advantageously, the primary duct 20 and the secondary duct 30 may be completely separated so that only the first combustible gas stream 11 may flow in the primary duct 20 and only the second combustible gas stream 12 may flow in the secondary duct 30. The first combustible gas stream 11 and the second combustible gas stream 12 can be controlled particularly effectively by means of the two

separate pipes

20, 30. Preferably, the combustible gas flow in the

respective tube

20, 30 can be controlled by means of butterfly valves. Advantageously, one butterfly valve may be used for each

tube

20, 30.

Preferably, the first secondary pipe 31 extends around the primary pipe 20 to surround the primary pipe 20. Advantageously, both the first secondary tube 31 and the primary tube 20 have a tubular form, even more advantageously a circular cross section.

According to a preferred embodiment, the burner head 1 comprises a plurality of second secondary tubes 32. Preferably, the second secondary pipes 32 are equidistant from each other. Advantageously, four second secondary pipes 32 are provided.

In alternative embodiments, a common duct may be provided in which both the first 11 and second 12 combustible gas streams flow. Preferably, the common pipe may branch in the primary pipe 20 and the secondary pipe 30. From a constructional point of view, this solution is simpler and more economical than a solution with two

pipes

20, 30 completely separated. However, this solution may not be as fine as a solution with two completely

separate pipes

20, 30, because it is not possible to control the first 11 and the second 12 combustible gas streams separately, for example by means of butterfly valves.

Preferably, the combustion head 1 comprises a diffuser element 60, which diffuser element 60 is positioned in the region of the primary nozzle 6 and interacts with the first tube 20 in a hydrodynamic manner.

The term "diffuser element" is intended to be understood as meaning the following elements: the element performs the function of creating turbulence and mixing between the combustion gas and the combustible gas. Preferably, the diffuser element 60 is a disk with or without holes, or a turbine-like element comprising blades that cause the rotation of the combustion gas and the final mixing between the combustion gas and the combustible gas.

Advantageously, the diffuser element 60 is made of austenitic steel. Preferably, the diffuser element 60 comprises a central body from which a portion of the diffuser element 60 extends, even more preferably having a substantially annular form, and also more preferably having an annular shape and advantageously inclined with respect to the longitudinal axis L of the housing 5.

In some embodiments, the diffuser element 60 may be a vortex member. Advantageously, the swirl means allow to control the combustion air flow, in particular the third combustion air flow 15. This control of the combustion air flow, together with the control of the first combustible air flow 11 discharged from the primary nozzles 6, allows to produce a stable primary flame 17 with a smaller size, similar to a pilot flame. The primary flame 17 having a smaller size is advantageously not disturbed by the recirculation flow, which may otherwise destabilize the primary flame 17 due to being inert. However, the secondary flame 18 may be advantageously mixed with the recycle stream 99.

The present invention thus solves the problem posed, providing a number of advantages at the same time. In particular, the combustion head 1 allows a particularly limited emission of NOx pollutants to be achieved, in particular due to the internal recirculation of the exhaust gas stream 19 in conjunction with the internal recirculation of the second combustible gas stream 12. In this way, in fact, premixing can be achieved between the streams before introducing the premix streams into the recirculation zone 4. Furthermore, the burner head ensures a higher level of performance, while at the same time ensuring a higher level of structural simplicity.

Claims

1. A burner head (1) with internal recirculation, the burner head (1) being for a burner (100) of a combustion chamber (26), the burner head (1) comprising:

-a housing (5), the housing (5) having a substantially tubular portion around a longitudinal axis (L), and the housing (5) comprising:

a first portion (51), the first portion (51) being configured to protrude inside the combustion chamber (26), and the first portion (51) comprising a recirculation opening (3), an

-a second portion (52), the second portion (52) being configured to be positioned outside the combustion chamber (26), and the second portion (52) comprising an inlet (54) of the housing (5), a first combustion air flow (13) being able to flow inside the housing (5) through the inlet (54) along a travelling direction (a) substantially parallel to the longitudinal axis (L) of the housing (5), the first combustion air flow (13) being used to divide into at least a second combustion air flow (14) and a third combustion air flow (15) along the travelling direction (a);

a manifold (70), the manifold (70) having a longitudinal portion (K), and the manifold (70) comprising:

-an outer sheath (71), the outer sheath (71) facing directly the combustion chamber (26), at least one radial opening (7) being formed in the outer sheath (71), the radial opening (7) being interposed between the recirculation opening (3) and the outlet (61) of the housing (5);

-a recirculation zone (4), the recirculation zone (4) comprising a longitudinal inlet portion (41), a portion of the first combustion air flow (13) being able to be introduced into the recirculation zone (4) through the longitudinal inlet portion (41), so as to divide the first combustion air flow (13) along the travelling direction (a) into at least a second combustion air flow (14) and a third combustion air flow (15), the second combustion air flow (14) corresponding to the portion of the first combustion air flow (13) able to be introduced into the recirculation zone (4);

-a primary duct (20), inside which primary duct (20) a first combustible gas flow (11) can flow, and said primary duct (20) comprises a primary nozzle (6), from which primary nozzle (6) said first combustible gas flow (11) can be discharged and by mixing with said third combustion air flow (15) a primary flame (17) can be generated;

-a secondary duct (30) inside which a second combustible gas flow (12) can flow, so that the second combustible gas flow (12) can flow inside the manifold (70) and can be discharged from the radial opening (7), the radial opening (7) being configured so that the second combustible gas flow (12) is impacted by an exhaust gas flow (19) from the combustion chamber (26) to mix with the exhaust gas flow (19) and to be conveyed together with the exhaust gas flow (19) into the recirculation zone (4) through the recirculation opening (3) in a direction opposite to the travelling direction (a);

the recirculation zone (4) is positioned inside the housing (5) in the region of the recirculation opening (3) and comprises a passage portion (44), through which passage portion (44) the second combustible gas stream (12) mixed with the exhaust gas stream (19) and the second combustion gas stream (14) can be discharged to enable the generation of a secondary flame (18).

2. The combustion head (1) according to any one of the preceding claims, comprising a plurality of said radial openings (7).

3. The combustion head (1) according to the preceding claim, wherein the radial opening (7) is positioned at a longitudinal distance (B) from the outlet (61) of the housing (5), the longitudinal distance (B) being approximately between two-thirds and three-thirds of the longitudinal portion (K) of the manifold (70).

4. The burner head (1) according to any one of the preceding claims, wherein the primary tube (20) extends along the longitudinal axis (L) of the housing (5) and the secondary tube (30) comprises a first secondary tube (31) and a second secondary tube (32), the first secondary tube (31) being coaxial with the primary tube (20), the second secondary tube (32) connecting the manifold (70) and the first secondary tube (31).

5. The combustion head (1) according to any one of the preceding claims, comprising a diffuser element (60), the diffuser element (60) being positioned in the region of the primary nozzle (6) and being hydrodynamically interacted with the first tube (20).

6. The combustion head (1) according to any one of the preceding claims, wherein the recirculation zone (4) is defined by at least one recirculation chamber (4A) formed in the manifold (70).

7. The combustion head (1) according to the preceding claim, wherein a plurality of recirculation openings (3) and corresponding recirculation chambers (4A) are provided.

8. The combustion head (1) according to the preceding claim, wherein the recirculation openings (3) are arranged equidistant from each other.

9. The burner head (1) according to any one of claims 7 to 8, wherein each of the recirculation chambers (4) comprises two side walls (43), said side walls (43) being shaped so as to obtain a secondary channel (62), said secondary channel (62) being interposed between two adjacent side walls (43) of the respective consecutive recirculation chamber (4A).

10. The combustion head (1) according to the preceding claim, wherein the secondary channel (62) is tapered in the travelling direction (a).

11. The combustion head (1) according to any one of claims 6 to 10, wherein the recirculation chamber (4A) comprises a rear wall (57), the rear wall (57) being substantially parallel to a plane inclined with respect to a transversal plane to the longitudinal axis (L) of the housing (5), such that an angle (β) between the transversal plane and the plane has a value of approximately between 10 ° and 45 °.

12. The burner head (1) according to any one of the preceding claims, wherein said recirculation opening (3) has a longitudinal portion (V) equal to about one third of said longitudinal portion (K) of said manifold (70).

13. The combustion head (1) according to any one of claims 6 to 12, wherein the recirculation chamber (4A) comprises an upper wall (58), the upper wall (58) comprising a radial inlet (40) placed at the respective recirculation opening (3).

14. The combustion head (1) according to any one of the preceding claims, wherein the radial opening (7) is configured such that: the exhaust gas flow (19) and the second combustible gas flow (12) are mixed in such a way as to obtain a percentage of the volume relationship between the combustible gas flow (12) and the exhaust gas flow (19) of between one third and one twentieth, even more preferably the radial openings (7) are configured such that: the exhaust gas stream (19) and the second combustible gas stream (12) are mixed in such a way that a percentage of the volume relation between the combustible gas stream (12) and the exhaust gas stream (19) is obtained between one third and one tenth.

15. A burner (100), the burner (100) comprising a burner head (1) according to any one of the preceding claims.