Patent Description:
In particular, the end apparatus for a burner that is the object of the present invention is adapted to be applied to burners that have to be installed in a combustion chamber, particularly on boilers for generating hot water or steam, diathermic oil boilers, kilns, dryers, etc. but can also be applied to air duct solutions. Generally, the burners can be supplied with combustion gas or diesel or mixtures (gas and diesel or gas and naphtha or yet another mixture that is not expressly indicated here).

The burners generally comprise a fan or a supply conduit for supplying the comburent, a supply conduit for supplying the fuel and a combustion head, i.e. the front part of the burner adapted to generate and support the flame, optimising mixing of the fuel and the comburent and maintaining stability thereof during operation.

Currently, various conformations are known for end apparatuses for blown air burners that generally have in common the presence of an outer tubular body and an inner tubular body supplying the gas, fixed to the body of the burner and ending in the front part with a distributor of the gas. In other words, the two tubular bodies are coaxial and the comburent air is supplied therebetween.

The end apparatus comprises the combustion head that has in the zone adapted to generate the flame a diffuser that is usually of discoid or truncated conical shape.

The diffuser is normally provided with uniformly distributed passage holes or gaps that enable the comburent air to pass into the mixing zone with the fuel and the flame to be ignited and maintained.

Substantially, the diffuser retains the flame near the end part of the combustion head to enable the flame to be supported.

The outer tubular casing conveys, with the cylindrical body thereof, the comburent air blown by the fan of the burner.

Some examples of prior art are disclosed in documents <CIT> and <CIT>. <CIT> shows an end apparatus according to the preamble of claim <NUM>.

Disadvantageously, the technical solutions described above often do not enable the burners to so contain the emissions as to maintain the emissions below current emission limits for NOx (nitrogen oxides) specified by recent regulations that set increasingly strict limits (also below <NUM> ppm) for burners for domestic and industrial use.

In this situation, the object of the present invention is to make an end apparatus for a burner and a burner that obviate the aforementioned drawbacks.

A particular object of the present invention is to make an end apparatus for a burner and a burner that enables NOx emissions to be reduced.

An object of the present invention is moreover to make an end apparatus for a burner and a burner without the use of techniques for recirculating burnt fumes to the flue that are expensive and often involve a reduction in efficiency (and consequently dispensed power) of the machine.

A still further object of the present invention is to make an end apparatus for a burner and a burner that enable NOx emissions to be reduced without however increasing the value of other polluting substances (like for example carbon monoxide), on the contrary maintaining other polluting substances as low as possible.

A yet further object of the invention is to make an end apparatus that can maintain the advantages set out above but with significant adjusting elasticity of the fuel/comburent mixture (range of extended excess air approximately comprised between <NUM> <λ< <NUM>).

The objects indicated are substantially attained by an end apparatus for a burner and a burner according to what is described in the appended claims.

Further characteristics and the advantages of the present invention will appear more clearly from the detailed description of some preferred, but not exclusive, embodiments illustrated in the appended drawings, wherein:.

With reference to the appended drawings, the reference number <NUM> has been used to generally designate an end apparatus for a burner, which will be referred to here as apparatus <NUM> for the sake of descriptive simplicity.

The apparatus <NUM> comprises a combustion head <NUM> connectable to supply means for supplying a fuel <NUM> and having at least one inlet opening <NUM>, adapted to enable a fuel to enter, and a plurality of outlet openings <NUM> adapted to enable an outflow of fuel.

It should be noted that between the fuel inlet and the inlet opening <NUM> a butterfly adjusting valve can be housed (not shown in the drawings).

For example, the fuel supplied by the supplying means for supplying a fuel <NUM> can be natural gas or other gaseous fuels, like LPG, biogas, hydrogen or mixtures with variable H2 content.

The apparatus <NUM> further comprises a comburent supply conduit <NUM> configured to convey a comburent to the combustion head <NUM> and extending between a comburent introduction opening <NUM> of the comburent and an emission opening <NUM> thereof along a main extension direction "X".

Advantageously, the combustion head <NUM> can have a passage conduit <NUM> defining an inlet <NUM> and an outlet <NUM> through which a flow of comburent "C" can flow.

Further, the apparatus <NUM> can comprise flame ignition means <NUM>, the means being adapted to promote the ignition of the mixture and usable both for the fuel supplied by the supplying means <NUM>, and for the fuel supplied by the further supply conduit <NUM> (e.g. diesel) which will be discussed subsequently. According to one possible embodiment of the present invention and as illustrated in the appended figures, the combustion head <NUM> is at least partially inserted into the supply conduit <NUM>, at the emission opening <NUM>, so as to define a passage gap <NUM> between the combustion head <NUM> and the supply conduit <NUM> for the flow of comburent "C".

In other words, the flow of comburent "C" can comprise a component passing through the outlet <NUM> and/or a component passing through the passage gap <NUM>.

Advantageously, the combustion head <NUM> can be movable (both in one direction and the opposite direction) relative to the supply conduit <NUM> along a movement direction parallel to, preferably coincident with, the main extension direction "X" so as to permit adjustment of the dimensions of the passage gap <NUM> and thus, of the speed of the flow of comburent "C".

In this manner, the apparatus <NUM> enables the conformation of the flame to be modified and the extension of the flame to be varied along a direction prevalently parallel to the main extension direction "X".

In other words, the relative movement between the combustion head <NUM> and the supply conduit <NUM> enables the shape of the flame to be varied. Advantageously, further, the supply conduit <NUM> can have an end portion <NUM> defining a convergent profile near the emission opening <NUM>.

In particular, the end portion <NUM> determines the convergence of the flow of comburent "C" to the centre of the head, promoting the flame detachment from the surface thereof, apart from the retaining surface <NUM> that will be disclosed below.

In greater detail, the end portion <NUM> interacting with the combustion head <NUM> (as will be described in greater detail below) conveys the flow of comburent "C" such that the flame extends and is sustained at a greater distance from the end part of the combustion head <NUM> relative to prior art apparatuses. Advantageously, the combustion head <NUM> comprises a plurality of outer openings <NUM> configured to emit a first flow of fuel "F1" outside the flow of comburent "C".

In particular, the outer openings <NUM> are arranged outside the passage gap <NUM> according to a direction that is radial to the main extension direction "X". The fuel introduced from the openings <NUM> preferably follows the direction "X".

In other words, the outer openings <NUM> are arranged outside the supply conduit <NUM>.

Preferably, the outer openings <NUM> are arranged on the perimeter of the supply conduit <NUM>.

Still more preferably, the outer openings <NUM> are distributed uniformly on the perimeter of the end portion <NUM> of the supply conduit <NUM>.

Further, the combustion head <NUM> comprises a plurality of inner openings <NUM> arranged at and/or inside the passage gap <NUM> according to a direction that is radial to the main extension direction "X".

In particular, the inner openings <NUM> are adapted to introduce a second flow of fuel "F2', F2"" inside the flow of a comburent "C".

The presence of the first flow of fuel "F1" and of the second flow of fuel "F2', F2"" that join in the flow of comburent in different positions enable the flame to be developed in different zones. In detail, the first flow of fuel "F1" promotes "delayed" mixing that is achieved forwards in the combustion chamber in direction "X", owing to the fact that it introduces the comburent by means of relatively big sections (by way of purely non-limiting example, sections having a diameter equal to <NUM> millimetres) in a zone lacking comburent. The second flow of fuel "F2"", owing to the shaped nozzles thereof and with a profile substantially parallel to the end portion <NUM>, tends to diffuse the gas in a rear/radial zone through a recirculating effect with flow reversal.

The second flow ʺF2‴ facilitates the retention of the flame by promoting fast mixing with the comburent "C" in a low pressure zone that is substantially arranged at the connecting surface <NUM> that will be described in greater detail below.

According to one possible embodiment and as illustrated in the appended figures, the combustion head <NUM> can comprise a central body <NUM> extending between a first end <NUM>, defining the inlet opening <NUM>, and a second end <NUM>, distal from the inlet opening <NUM>, along an extension direction "E".

In particular, the extension direction "E" can be parallel to, preferably coincident with, the main extension direction "X".

The central body <NUM> can be at least partially inserted into the supply conduit <NUM>.

Further, the second end <NUM> can define with the supply conduit <NUM> at least partially the passage gap <NUM>.

Preferably, the second end <NUM> can define with the end portion <NUM> of the supply conduit <NUM> at least partially the passage gap <NUM>.

Advantageously, the central body <NUM> can have an extension that is substantially axially symmetric relative to the extension direction "E".

In this manner, the central body <NUM> can define with the supply conduit <NUM> a passage gap <NUM> having a conformation that is at least partially annular that confers stability and uniformity on the flow of comburent "C" and, thus, on the flame.

According to one possible embodiment and as illustrated in the appended figures, the central body <NUM> can have a housing <NUM> that is adapted to receive in a reversibly inserted manner a supply conduit <NUM> for supplying a fuel.

In particular, the housing <NUM> can extend between the first end <NUM> and the second end <NUM> parallel to the extension direction "E".

According to one possible embodiment of the present invention, the conduit passage conduit <NUM> and the central body <NUM> are operationally connected so as to define a prolongation of the housing <NUM>. In this manner, the housing <NUM> can extend substantially between the inlet <NUM> of the passage conduit <NUM> and the second end <NUM> of the central body <NUM>.

The further supply conduit <NUM> can enable the supply of a fuel that is different from the one supplied by the supply conduit <NUM>, for example diesel or fuel oil, ensuring great operating flexibility for the apparatus <NUM>.

Further, the apparatus <NUM> can comprise at least one switch-on conduit <NUM> in fluid communication with the supply conduit <NUM> and passing through the central body <NUM> adapted to insert the aforesaid flame ignition means <NUM> according to one possible embodiment of the present invention.

In this case, flame ignition means <NUM> can exit suitable switch-on openings 18a of the switch-on conduit <NUM>.

According to some possible embodiments not illustrated in the appended figures, these switch-on openings 18a can have different positioning along the extension direction "E" without the inventive concept at the basis of the present invention being altered.

For example, the switch-on openings 18a can be arranged upstream of the plurality of outflow holes 20b-that will be described in greater detail below. Advantageously, the second end <NUM> of the central body <NUM> can have a convergent portion <NUM>, for example truncated conically shaped, along the extension direction "E" and defining with the supply conduit at least partially the passage gap <NUM>.

This shaping promotes the detachment of the flame from the second end <NUM>, contributing to move the second end <NUM> away from the combustion head <NUM> and at the same time ensuring, also owing to the particular divergent geometry of the profile <NUM>, a zone of minimum flame retention on the retaining surface <NUM>.

The convergent portion <NUM> can have a plurality of outflow holes 20a adapted to introduce at least partially the second flow ʺF2‴ of fuel inside the flow of a comburent "C".

In other words, the central body <NUM> can have a plurality of outflow holes 20a, 20b for introducing at least partially the second flow ʺF2‴ of fuel in the flow of a comburent "C".

In particular, the aforesaid plurality of outflow holes 20a defines at least partially the inner openings <NUM>.

Purely by way of non-limiting example, the plurality of outflow holes 20a, 20b can have a diameter equal to <NUM> millimetres.

The convergent <NUM> and divergent <NUM> portions, together with the plurality of outflow holes 20a, 20b contribute to limiting the turbulent formation of components in the flow of comburent "C" and concomitant with the introduction of the second flow of fuel "F2'" inside the flow of comburent "C". Optimum mixing between fuel and comburent in this stage occurs near the surface <NUM>, thus ensuring increased stability of the flame in this zone and thus ensuring reliability, safety and operating elasticity for the burner during the operating step. This elasticity characteristic enables operation with very extensive λ factors (in which λ indicates the excess air coefficient).

This stability, permitted by the flame anchoring zone at the retaining surface <NUM>, enables the flame to be maintained distant from the combustion head <NUM> and the need for the diffuser (the aforesaid disc or truncated conical element) in the end zone of the combustion head <NUM> to be overcome.

In other words, the apparatus <NUM> can be devoid of the traditional flame retention diffuser.

Further, the absence of the diffuser enables the generation of turbulent zones to be avoided that result in great mixing, enabling the flame to be moved further away from the combustion head <NUM> and diffusing the flame homogeneously in the volume of the combustion chamber. The reduction of the specific thermal load (W/m3) and the reduction of the temperature of the flame near the head <NUM> favour a great reduction of the emissions of thermal NOx.

Further, this effect enables the influence of thermal stress factors to be reduced, permitting an improvement to the life of the components and the possible application of less noble and expensive materials.

According to one possible embodiment and as illustrated in the appended drawings, the second end <NUM> can have at least one divergent portion <NUM> along the extension direction "E".

In particular, the divergent portion <NUM> can be arranged at least partially inside the convergent portion <NUM>.

Advantageously, the further supply conduit <NUM> can be at least partially insertable from the inlet <NUM> as far as inside the divergent portion <NUM>, permitting dispensing of the further fuel at the zone of the combustion head <NUM> adapted to the generation of the flame.

The divergent geometry of the profile <NUM> enables the cone of the spray of the atomizer to be followed, preferably at a solid spray angle comprised between <NUM>° and <NUM>°, ensuring an optimal flame extension of the secondary fuel. Also in this case, the principle of partial flame detachment with partial retention near the retaining surface <NUM> enables NOx emissions to be kept very small.

Further, this insertion enables the overall operating dimensions to be reduced that are induced by the presence of the further supply conduit <NUM>. As illustrated in the appended drawings, the plurality of outflow holes 20b can be obtained at least partially on the divergent portion <NUM> to introduce at least partially the second flow of fuel "F2'" inside the flow of a comburent "C".

According to one possible embodiment of the present invention that is not illustrated in the appended figures, the plurality of outflow holes 20a, 20b can be provided only on the divergent portion <NUM> without altering the inventive concept underlying the present invention.

It is emphasised that the outflow holes 20a are made on the convergent portion <NUM>. Preferably, both the pluralities of outflow holes 20a, 20b as illustrated in appended figures are present.

Alternatively, only the plurality of outflow holes 20b and not the outflow holes 20a can be present.

Further, the second end <NUM> has at least one retaining surface <NUM> (previously mentioned) adapted to connect the divergent portion <NUM> and the convergent portion <NUM>.

In particular, the retaining surface <NUM> can be perpendicular to the extension direction "E".

Advantageously, the retaining surface <NUM> can be at least partially lobe-shaped.

As illustrated in the appended drawings, the aforesaid flame ignition means <NUM> can be arranged at least partially inside the divergent portion <NUM> so as to promote the generation of the flame near the retaining surface <NUM>. According to one possible embodiment of the present invention and as illustrated in the appended drawings, the combustion head <NUM> comprises a plurality of outflow conduits <NUM> branching off from the first end of the central body <NUM>.

Further, the plurality of outflow conduits <NUM> extends at least partially along a direction parallel to the extension direction "E".

In particular, the plurality of outflow conduits <NUM> defines at least partially the aforesaid plurality of outer openings <NUM>.

Preferably, the combustion head <NUM> can comprise at least one inner nozzle <NUM>, still more preferably a plurality of inner nozzles <NUM>, arranged inside the supply conduit <NUM> according to a direction that is radial to the main extension direction "X".

In other words, the at least one inner nozzle <NUM> can be interposed between the central body <NUM> and the supply conduit <NUM> and, preferably, inside the end portion <NUM> and the passage gap <NUM>.

In particular, the inner nozzles <NUM> define a part of said plurality of inner openings <NUM>.

According to one possible embodiment of the present invention, the inner nozzles <NUM> can have a diameter equal to about <NUM> millimetres.

Further, the at least one inner nozzle <NUM> can have different conformations, for example, circular, oval elliptic or the like without altering the inventive concept underlying the present invention.

Advantageously, the at least one inner nozzle <NUM> can have an extension axis tilted relative to the extension direction "E".

In this manner, the inner nozzle <NUM> limits the turbulent formation of components inside the flow of comburent "C" and/or the second flow "F2"" promoting the introduction of the second flow "F2"" along a direction substantially parallel to the surface of the convergent portion <NUM> and <NUM>. Preferably, the combustion head <NUM> comprises a plurality of inner nozzles <NUM> having an extension that is transverse to the extension direction "E" such that the second flow "F2"" is at least partially convergent along the extension direction "E".

Preferably, the combustion head <NUM> further comprises a plurality of outer nozzles <NUM> in fluid communication with the inlet opening <NUM>.

In particular, the outer nozzles <NUM> can be arranged outside the supply conduit <NUM> according to a direction that is radial to the main extension direction "X".

Specifically, the outer nozzles <NUM> can define at least partially the plurality of outer openings <NUM>.

Advantageously, the outer nozzles <NUM> can have an extension substantially parallel to the main extension direction "X" such as to emit the aforesaid first flow "F1" of fuel outside the flow of comburent "C".

In this manner, the first flow "F1" contributes to delaying mixing by enabling the flame to be moved away from the end part of the combustion head <NUM> according to what has been set out previously.

According to one possible embodiment and as illustrated in the appended drawings, the outer nozzles <NUM> can be arranged perimetrically to the supply conduit and near the emission opening <NUM>.

Preferably, the inner nozzles and/or the outer nozzles can be an end portion of a respective outflow conduit <NUM>.

According to a further aspect, the present invention refers to a burner <NUM> comprising an apparatus <NUM> according to what has been previously disclosed and suction means <NUM> configured to suck at least one quantity of comburent from an environment outside the burner <NUM> and to move the quantity from the introduction opening <NUM> to the emission opening <NUM>. Further, the burner can comprise supplying means for supplying a fuel <NUM> adapted to supply a fuel to the combustion head <NUM>.

It is thus observed that the present invention achieves the proposed objects by making an end apparatus for a burner able to reduce NOx emissions owing to the presence of a plurality of outer openings arranged outside the passage gap of the flow of comburent and a plurality of inner openings arranged at and/or inside the passage gap of the comburent operationally connected to move the flame away from the end part of the combustion head.

Claim 1:
An end apparatus (<NUM>) for a burner configured to generate a flame, comprising:
- a combustion head (<NUM>) connectable to supply means for supplying a fuel and having at least one inlet opening (<NUM>), adapted to enable a fuel to enter, and a plurality of outlet openings (<NUM>), adapted to enable an outflow of fuel;
- a comburent supply conduit (<NUM>) configured to convey a comburent to said combustion head (<NUM>) and extending between a comburent introduction opening (<NUM>) and an emission opening (<NUM>) along a main extension direction (X);
wherein said combustion head (<NUM>) is at least partially inserted into said supply conduit (<NUM>), at the emission opening (<NUM>), so as to define a passage gap (<NUM>) between said combustion head (<NUM>) and said supply conduit (<NUM>) for a flow of comburent (C);
wherein said combustion head (<NUM>) comprises:
- a plurality of outer openings (<NUM>) arranged outside said passage gap (<NUM>) according to a direction that is radial to said main extension direction (X) and configured to emit a first flow of fuel (F1) outside said flow of a comburent; and
- a plurality of inner openings (<NUM>) arranged at and/or inside said passage gap (<NUM>) according to a direction that is radial to said main extension direction (X), said inner openings (<NUM>) being adapted to introduce a second flow of fuel (F2', F2") inside said flow of a comburent;
wherein said combustion head (<NUM>) comprises a central body (<NUM>) at least partially inserted into said supply conduit (<NUM>) and extending between a first end (<NUM>), defining said inlet opening (<NUM>), and a second end (<NUM>) along an extension direction (E); said second end (<NUM>) defining with said supply conduit (<NUM>) at least partially said passage gap (<NUM>);
wherein said second end (<NUM>) has a convergent portion (<NUM>), preferably truncated conically shaped, along said extension direction (E) and defines with said supply conduit (<NUM>) at least partially said passage gap (<NUM>);
wherein said second end (<NUM>) has at least one divergent portion (<NUM>) along said extension direction
characterized in that said divergent portion (<NUM>) is arranged at least partially inside said convergent portion (<NUM>).