ES2720031T3 - Air / gas mixing apparatus for premix burners and premix burner provided with such apparatus - Google Patents

Abstract

Air / gas mixing apparatus (10) for premix burners; including the apparatus (10): a means (12A) for supplying combustion air to a mixing chamber (12); a means (14) for feeding and distributing a combustible gas to said mixing chamber (12) in order to achieve the desired air / gas mixture; wherein said means (14) for the admission and distribution of fuel gas includes: (a) a first vertical part (14C), which extends symmetrically around an axis of vertical longitudinal symmetry (Y); (b) a second horizontal part (14D), which has an axis of horizontal longitudinal symmetry (X) perpendicular to said axis (Y), spatially oriented towards an air inlet opening (12A) in said means (14) for the admission and distribution of a gas; said second horizontal part (14D) being adapted to introduce to said means (14) for the admission and distribution of gas a first quantity of combustible gas in countercurrent with respect to the air flow, in order to form a first air mixture / gas; and (c) a third horizontal part (14S), aligned with said second horizontal part (14D) along said axis (X), spatially oriented towards an air / gas mixture outlet opening (12B); said third horizontal part (14S) being able to introduce, in parallel current with respect to the flow of said first air / gas mixture, into said means (14) for the admission and distribution of a gas, a second quantity of combustible gas for the purpose of forming a second air / gas mixture; and wherein said second horizontal part (14D) and said third horizontal part (14S) are respectively provided with a first gas distribution set (15) and a second gas distribution set (16); The mixing apparatus (10) is characterized in that each of said first gas distribution set (15) and said second gas distribution set (16) includes a pair of respectively parallel plates (15A, 15B) (16A, 16B ); a sheet of each pair of an axial horizontal hole (15A **), respectively (16A **) being provided, to allow the passage of combustible gas fed by said intake and distribution means (14).

Description

DESCRIPTION

Air / gas mixing apparatus for premix burners and premix burner provided with such an apparatus The present invention relates to an air / gas mixing apparatus for premix burners and a premix burner provided with such apparatus.

The invention also relates to a method for preparing an air / gas mixture in an air / gas mixing apparatus for premix burners.

In particular, methane or LPG can be used as combustible gas.

In the combustion field, burners traditionally called "premixers" (also known as "premix burners") are known, where the air / gas mixture takes place upwards of the combustion head in the strictest sense of the term; the mixing of the two components takes place in a suitable mixing apparatus. Among other things, these burners are characterized in that they are capable of achieving a wide modulation of the heat output generated in the combustion head.

For example, reference is made to an apparatus of the type of premix described in EP-B1-1 462 716 (of the same Applicant).

This document describes an air / gas mixing apparatus for a premix burner where the gas supply tube (also known as "gas sleeve") is 90 ° elbow shaped and interposed within the supply cylinder of air (also called “air sleeve”), between two fixed metal propellers.

The air coming from a fan, which passes through the first propeller, acquires a tangential velocity component, so that it moves with a helical movement inside the air sleeve.

Such a flow of air collides in the gas hose, at which end, through a series of radially arranged cylindrical tubes, the fuel gas that is affected by a first mixture escapes.

Down the gas hose, the second propeller gives this air / gas flow another tangential velocity component, thereby increasing the degree of mixing of the two components.

By means of the present invention it is possible to improve certain aspects of the apparatus described and illustrated in EP-B1-1 462716, and in particular the following points:

- the degree of air / gas mixture; achieving a more uniform flow of the two components, thereby obtaining a better physicochemical condition for the development of a flame that has good thermal efficiency and reduced nitrogen oxide (NOx) emissions; Y

- an easier and cheaper construction of the metal components to perform the air / gas mixture.

US-B1-7 897 121 (HUGHES et al.) Describes an air / gas mixing apparatus according to the preamble part of claim 1.

Accordingly, the main purpose of the present invention is to make an air / gas mixing apparatus for premix burners with better air / gas mixing compared to the same type apparatus on the market today.

For this reason, according to the present invention, an air / gas mixing apparatus for premix burners according to claim 1 is provided.

Another purpose of the present invention is to provide a premix burner (premix) provided with such an air / gas mixing apparatus.

For a better understanding of the present invention, a preferred embodiment will now be described by way of non-limiting example and with reference to the accompanying drawings, where:

Figure 1 represents a perspective view (in longitudinal and partially exploded cross-section) of an air / gas mixing apparatus for premix burners, made according to the idea of the present invention. Figure 2 represents an enlargement of a fuel gas distribution device used in the air / gas mixing apparatus according to Figure 1.

Figure 3 represents an exploded three-dimensional view of the fuel gas distribution device shown in Figure 2.

Figure 4 represents a first group of elements mounted together, such group being included in the fuel gas distribution device illustrated in Figures 2 and 3.

And Figure 5 represents a second group of elements mounted together. Such group is included in the fuel gas distribution device illustrated in Figures 2 and 3.

In Fig. 1, reference number 10 globally indicates an air / gas mixing apparatus for premix burners according to the ideas of the present invention.

The apparatus 10 includes a circular opening 12A for supplying combustion air to an air / gas mixing chamber 12. The circular opening 12A (made in the housing (CRT) of the mixing chamber 12) and the mixing chamber 12 have a common horizontal longitudinal symmetry axis (X).

The circular opening 12A is advantageously, although not necessarily, provided with a respective metal helix (EL) to give the incoming air to the mixing chamber 12 a substantially helical and swirling (swirling) motion.

In addition, an intake and distribution device 14 of a combustible gas (methane, LPG, etc.) extends inside the mixing chamber 12.

As shown in Fig. 1, in the wall of the air / gas mixing chamber 12 in front of the wall in which the circular opening 12A has been formed, there is an opening 12B through which in use the mixture of air / gas leaving said mixing chamber 12 (see below).

In an embodiment not shown, the opening 12B may be provided with an impending propeller (or similar device) suitable for imparting a substantially spiral eddy movement to the air / gas mixture before it enters the combustion head (not shown). ).

In actual use, in the wall in which the opening 12B is formed, a combustion head of the known and unrepresented type has been mounted (by known means not shown).

As is known, the assembly of the mixing apparatus 10 and the combustion head is known as "premix burner".

According to the embodiment shown in Figure 1, the intake and distribution device 14 is placed, in actual use, on a lower wall 12F of the air / gas mixing chamber 12, so that the circular base 14 of a body central cylindrical main 14C of device 14 coincides with a circular opening 12C formed in said lower wall 12F.

The device 14 is fixed to the bottom wall 12F by mechanical means of the known type and not shown. It may be noted that, in order to increase the clarity of the design, the device 14 shown in Figure 1 has been raised from the bottom 14F.

The device 14, in the particular embodiment illustrated in Figures 1,2 and 3, therefore includes:

(a) a first vertical part of cylindrical tubular shape represented by said central cylindrical main body 14C that extends symmetrically about a vertical axis of longitudinal symmetry (Y) substantially perpendicular to said horizontal axis (X);

(b) a second horizontal part 14D (having a cylindrical tubular shaft (X)) spatially oriented to the circular opening 12A and the metal propeller (EL); the second horizontal part 14D being connected with said cylindrical central main body 14C; said second horizontal part 14D being suitable for introducing to the device 14 a first quantity of fuel in countercurrent with respect to the air flow in order to form a first air / gas mixture;

(c) a third horizontal part 14S (having the axis (X)) of a cylindrical tubular shape spatially oriented to the opening 12B and the combustion head (not shown); the third horizontal part 14S is also connected with the cylindrical central main body 14C and with the second horizontal part 14D; said third horizontal part 14S being suitable for introducing, in parallel current with the flow of said first gas / air mixture, to the device 14, a second quantity of combustible gas in order to form a second air / gas mixture.

The three portions 14C, 14D and 14F are in fluid communication with each other and form a substantially asymmetric T.

It can be indicated that one part can be considered the ideal continuation of the other along said horizontal axis (X) since the second horizontal part 14D and the third horizontal part 14S are aligned along the same horizontal axis (X) .

In other words, the vertical cylindrical central main body 14C ends (at its upper end) with the two horizontal portions 14D, 14S placed as a mirror image with respect to the vertical axis (Y) in order to form an asymmetric T (given the different dimensions of the two horizontal portions 14D, 14 S).

It can also be indicated that, although the second horizontal part 14D is directed towards the circular supply opening 12A of the combustion air, the third horizontal part 14S is oriented to the opening 12D (and therefore, ultimately, to the combustion head) from which the air / gas mixture leaves the air / gas mixing chamber 12. Looking at figures 1, 2 and 3, it can be seen that the third horizontal part 14S differs, in terms of size, from the second horizontal part 14D ; in particular, the third horizontal part 14S is smaller than the second horizontal part 14D, since it has been found experimentally that, for optimum combustion (i.e., with a low NOx content), it is necessary that the volumetric amount of gas fuel that looks into the incoming air is larger than the volumetric amount of fuel gas that is mixed in a second phase with the first air / gas mixture.

As shown in particular in Figure 3, the outlet opening 14D * of the first quantity of combustible gas of the device 14 is associated with a first gas distribution group 15.

Said first gas distribution group 15 includes two circular plates 15A and 15B, parallel to each other, of equal diameter, in use, spaced by a plurality of cylindrical spacers 15C, each of which is longitudinally crossed by a through hole corresponding axial 15C *.

More specifically, while the circular plate 15B has the appearance of a circular disk, the circular plate 15A is in the form of a circular crown (closed ring) which therefore has a central through hole 15A ** (Figure 3) .

The first gas distribution group 15 is completed with a sleeve 15D provided with a flange 15E, the latter oriented, in use, towards the circular plate 15A.

Looking at Figure 3 it can be noted that the three elements 15A, 15B, 15D have respective through holes 15A *, 15B *, 15D *, in use aligned with each other and with the respective axial through holes 15C * (along axes respective horizontals substantially parallel to the axis (X)).

With respect to each set consisting of through holes 15A *, 15B, 15C *, 15D * it is possible to use a respective screw (not shown) to mechanically fix the first gas distribution group 15 to the second horizontal part 14D of the device 14 .

Therefore, in actual use, an operator, after having assembled the elements 15A, 15B, 15C, 15D so that they form the first gas distribution group 15, can fix said first gas distribution group 15 to the device 14 using known mechanical means, such as, for example, a plurality of screws.

As will be seen later, where the general operation of the apparatus 10 is explained, when the first part of combustible gas flows from the sleeve 15D in the direction of the central through hole 15A ** to the interspace 20 (created between the two plates 15A, 15B spaced from each other by the plurality of cylindrical spacers 15C), four radial flows of said gas are formed that mix with the primary air entering through the opening 12A (after being swirled by the metal propeller (EL)).

This first mixture is pushed forward towards the combustion head again by the action of the air fan.

As shown again in FIG. 3, a second gas distribution group 16 is associated in the outlet opening 14S * of the second quantity of combustible gas 16, similar, but not the same as the first distribution group of gas 15 described.

In fact, the second gas distribution group 16 includes two circular plates 16A and 16B, parallel to each other, of equal diameter, in use, spaced by a plurality of cylindrical spacers 16C, each of which is longitudinally crossed by a corresponding axial through hole 16C *.

More specifically, while the circular plate 15B has the appearance of a circular disk, the circular plate 16A is in the form of a circular crown (closed ring), therefore having a central through hole 16A ** (Figure 3) .

However, in the second gas distribution group 16, there is no sleeve with flange.

The two gas distribution groups 15, 16 can be made, at least partially, using suitable metals and / or plastic.

It should also be noted that the sleeve with flange 15D creates a type of venturi effect, which ensures an appropriate division into two parts of the gas flow entering from the central supply sleeve, so that one part is always directed towards the gas distribution group 15, which is located below with respect to the air coming from the fan.

Looking at Figure 3 it can also be seen that the two elements 16A, 16B have respective through holes 16A *, 16B *, in use aligned with each other and with the respective axial through holes 16C * (along substantially parallel horizontal respective axes to the axis (X)).

With each set consisting of through holes 16A *, 16B, 16C *, 16D * it is possible to use a respective screw (not shown) to mechanically fix the second gas distribution group 16 to the third horizontal part 14S of the device 14.

Therefore, in use, an operator, having assembled the elements 16A, 16B, 16C forming the second gas distribution group 16, can fix said second gas distribution group 16 to the device 14 using known mechanical means, such as, for example, a plurality of screws.

As will be seen later, where the general operation of the apparatus 10 is explained, when the second part of the combustible gas leaves the third horizontal part 14S, it joins the first mixture (which, as we have said previously, was formed in the first distribution group 15) mixing, in turn, with it forming a second, and final, air / gas mixture flowing towards the combustion head (not shown) where it is inflamed by a special electrode (not shown).

In particular, in the interspace 30 (which is created between the two plates 16A, 16B spaced from each other by the plurality of cylindrical spacers 16C) also in this case four radial flows of said combustible gas are formed which are mixed with the first mixture of air / gas arriving from the first mixing zone, the zone substantially corresponding to the internal space oriented to the second horizontal part 14D.

The operation of the air / gas mixing apparatus 10 for premix burners according to the present invention is as follows:

(s1) As shown in Figure 1, the primary combustion air enters the mixing chamber 12 through the circular opening 12A (arrow (F1)), advantageously, but not necessarily, provided with a metal propeller (E ^l ) ; primary air is driven by a fan (not shown);

(s2) The combustible gas enters the device 14 through the circular base 14A of the cylindrical central main body 14C (arrow (F2)); the combustible gas is also moved by a respective fan (not shown); (s3) After rising vertically through the entire cylindrical central main body 14C, the combustible gas is diverted to the second horizontal part 14D (arrow (F3)) and to the third horizontal part 14S (arrow (F4));

(s4) Consequently, a first part of the combustible gas leaves radially from the first gas distribution group 15 according to the directions indicated by the arrows (F5) and is mixed with the incipient primary air forming a mixture of primary air / gas in the area surrounding the first gas distribution unit 15;

(s5) The first mixture is thus pushed towards the opening 12B, still inside the mixing chamber 12, where it joins a second part of combustible gas at the radial outlet of the second gas distribution group 16 (arrows F6) forming a second, and last, air / gas mixture in the area surrounding the second gas distribution group 16;

(s6) said second air / gas mixture then flows to the opening 12B (arrow (F7)) in which the combustion head (not shown) is mounted.

The advantages of the apparatus of the present invention can be summarized in the following points:

- the achievement of a better mixture of air and fuel, for the benefit of the combustion head efficiency, and with a substantial decrease in the formation of harmful combustion products such as NOx; Y

- an easier and cheaper construction of the metal components to perform the air / gas mixture.

Claims (6)

1. Air / gas mixing apparatus (10) for premix burners; including the device (10): means (12A) for supplying combustion air to a mixing chamber (12); a means (14) for feeding and distributing a combustible gas to said mixing chamber (12) in order to achieve the desired air / gas mixture; where said means (14) for the admission and distribution of fuel gas includes: (a) a first vertical part (14C), which extends symmetrically around an axis of vertical longitudinal symmetry (Y); (b) a second horizontal part (14D), which has an axis of horizontal longitudinal symmetry (X) perpendicular to said axis (Y), spatially oriented towards an air inlet opening (12A) in said means (14) for the admission and distribution of a gas; said second horizontal part (14D) being adapted to introduce to said means (14) for the admission and distribution of gas a first quantity of combustible gas in countercurrent with respect to the air flow, in order to form a first air mixture / gas; Y (c) a horizontal third part (14S), aligned with said second horizontal part (14D) along said axis (X), spatially oriented towards an air / gas mixture outlet opening (12B); said third horizontal part (14S) being able to introduce, in parallel current with respect to the flow of said first air / gas mixture, into said means (14) for the admission and distribution of a gas, a second quantity of combustible gas for the purpose of forming a second air / gas mixture; Y wherein said second horizontal part (14D) and said third horizontal part (14S) are respectively provided with a first gas distribution set (15) and a second gas distribution set (16); The mixing apparatus (10) is characterized in that each of said first gas distribution set (15) and said second gas distribution set (16) includes a pair of respectively parallel plates (15A, 15B) (16A, 16B ); a sheet of each pair of an axial horizontal hole (15A **), respectively (16A **) being provided, to allow the passage of combustible gas fed by said intake and distribution means (14). 2. Apparatus (10) according to claim 1, characterized in that the radial distributions of the combustible gas within said mixing chamber (12) are implemented by means of said first gas distribution set (15) and said second set of gas distribution (16). 3. Apparatus (10) according to any of the preceding claims, characterized in that said first gas distribution assembly (15) is further provided with a sleeve with flange (15D). 4. Apparatus (10) according to any of the preceding claims, characterized in that said second part (14D) is dimensionally larger than said third part (14S). 5. Apparatus (10) according to any of the preceding claims, characterized in that said means (12A) for supplying combustion air to said mixing chamber (12) is provided with means (EL) for imparting a helical and swirling movement. to the air inlet. 6. Premix burner provided with at least one air / gas mixing apparatus according to claims 1-5 and at least one combustion head.