EP0223634B1 - Gas burner of the air-gas premix type - Google Patents

Abstract

1. A gas burner of the gas/air pre-mixture type feeding a distributor box comprising at least one flame bar, the said burner consisting of a stacked structure (2, 4, 7, 27, 17) comprising the said distributor box (2) which is of elongate flattened form and which receives above it a flame grille (4) in the form of a panel of small thickness with a top surface (14) and a bottom surface (24), the said grille comprising at least one series of orifices (6) in the form of depressions provided in the bottom surface (24) of the grille, the said orifices which are regularly distributed towards the periphery of this grille, at least over its length, communicating with the interior space (12) inside the distributor box (2), the said burner being characterized : in that the depressions (6) disposed in the bottom surface (24) of this grille are of substantially rectangular cross-section which flares out in the direction of flow of the gaseous mixture, orifices (5) which are likewise in the form of depressions but which are of substantially rectangular and constant cross-section being disposed in the top surface (14) of this same grille, which has above it a panel (7, 17) of small thickness which forms a cover which fits over it, and in that the top and bottom surfaces of the grille communicate inter se through a slot (34) disposed through the grill in such a way as to form a communicating passage between the interior space (12) of the box (2) and the cover.

Description

The present invention relates to a burner of the gas / air premix type.

At present, premixed and atmospheric induction burners with partitioned outlet section are known, the relatively simple manufacture of which allows the multiplication of heating points in a hearth. Such burners are commonly used for domestic use, for example water heaters or restaurant hobs, and are often arranged in the form of a ramp. However, it has the drawbacks of having a low specific power in relation to their size, and of giving rise to flames which can sometimes be unstable. In addition, their adjustments are delicate and they can, in practice, operate with satisfactory yields only for a determined feeding regime, which most often requires regulation everywhere or nothing.

Besides this category of burners, conventional type atmospheric induction burners are known, the flexibility and reliability of operation of which lead to their domestic use, for example on current type stoves. However, this technique leads to burners whose specific power is relatively reduced and whose arrangement of the combustion heads results in a high concentration of heat fluxes. Also, their industrial use is reduced.

Among all of the known burners, one can in particular note that of US-A 2,494,243, insofar as it is a burner with premix combustible gas and combustion air comprising a distribution box, for the 'premix supply, and a flame grid provided in its underside with slots in the form of slots, which are in communication with the interior volume of the distribution box.

For information, we can also note the burner of patent GB-A 1 222 354 in that it is of the stacked structure type comprising a distribution box supplied with a gas / air premix, as well as a flame grid. which may be in the form of a series of superimposed corrugated plates.

However, such burners are difficult to adapt to the preferred field of application of the invention; namely boilers for distilling alcohols, and problems of operating flexibility, both at high and low temperatures, still arise.

The gas / air premix burner in accordance with the present invention makes it possible to solve the difficulties mentioned by proposing a burner of simple, robust construction, of small size, and making it possible to modulate the heat flow, thanks to its great flexibility of operation, by delivering significant specific power.

More specifically, the gas burner according to the invention which is of the gas / air premix type supplying a distribution box and consists of a stacked structure comprising said distribution box which has an elongated, flattened shape and which receives, above it, a grid of flames in the form of a thin plate with an upper face and a lower face, said grid comprising at least one series of orifices in the form of slots formed in the lower face of the grid, said orifices which are regularly distributed towards the periphery of this grid, at least along its length, communicating with the interior volume of the distribution box, is characterized in that the slots formed in the underside of this grid have a substantially rectangular section which goes by flaring in the direction of flow of the gas mixture, orifices also in the form of notches, but of substantially rectangular and constant section being formed in the upper face of the same grid, which receives above it a plate of reduced thickness forming a cap from the cap, and in that the upper and lower faces of the grid communicate with each other by a slot made through the grid, so as to form a communication passage between the interior volume of the box and the cap. Thus we will be able to ensure fine modulation of the heat flow and precise control of the flames, whatever the operating regime of the burn.

• - la figure 1 est une vue schématique de côté du brûleur,
• - la figure 2 est une vue en coupe selon la ligne II-II de la vue présentée à la figure 1,
• - la figure 3 est une vue de dessus de la grille du brûleur présenté à la figure 1,
• - la figure 4 est une vue de dessous de cette même grille,
• - la figure 5 est une vue de côté d'une variante de la plaque formant chapeau,
• - la figure 6 est une vue de dessus d'une plaque intermédiaire disposée entre le chapeau et la grille,
• - la figure 7 est une vue de côté du tube diffuseur présenté à la figure 1.

The invention will appear more clearly from the description which follows, made with reference to the accompanying drawings in which:

• - Figure 1 is a schematic side view of the burner,
• FIG. 2 is a sectional view along line II-II of the view presented in FIG. 1,
• FIG. 3 is a top view of the burner grid shown in FIG. 1,
• FIG. 4 is a bottom view of this same grid,
• FIG. 5 is a side view of a variant of the cap plate,
• FIG. 6 is a top view of an intermediate plate disposed between the cap and the grid,
• - Figure 7 is a side view of the diffuser tube shown in Figure 1.

Referring first to Figure 1, we see a burner, according to the invention, identified as a whole 1 and which is constituted by a box 2 forming distribution box in which is disposed a supply tube 3 in a combustible gas mixture, which tube is pierced with orifices 33, 43 through which said combustible mixture flows towards a grid 4 on which slots 5, 6 are formed; said grid being capped with a plate 7 forming a cap.

The tube 3 can in particular be screwed, towards the inlet end 23, and substantially in the axis 63 of the box, on the inner wall of the tubular part 53 projecting from said box.

The combustible gas mixture (gas / air) which feeds the burner 1 comes from a premix chamber (not shown) connected to the feed tube 3, towards the end 23, via a distribution sheath ( not shown).

In order to facilitate the description, the path of the gas mixture inside the burner has been matted indicated by arrows in Figures 1 and 2.

Referring to any one of these two figures, it can be seen that the distribution box 2 has an elongated shape, relatively flattened and of section substantially in "U" shape. It can in particular be manufactured in a foundry or by stamping, thus offering an embodiment which is both simple and inexpensive.

The free interior volume forming chamber 12 of the box communicates, through a passage or an elongated slot 22 with the grid 4 and the cap 7.

The cohesion of the stacked structure formed by the burner 1 can be ensured by screws which successively link the constituent elements of the burner. This type of assembly being known, only the locations 11 of the screws are advantageously located towards the ends of the burner.

With particular reference to Figures 3 and 4, it is noted that the grid 4 is in the form of a plate, preferably metallic substantially rectangular and thin (of the order of a centimeter).

In this grid are formed series of orifices 5, 6 advantageously formed in slots and which communicate with the interior volume 12 of the box 2. In the embodiment adopted, this communication is ensured by an opening 34 formed towards the central part of the grid and which thus forms a passage between the interior volume 12 and the plate 7 forming a cap; said opening being disposed opposite passage 22 formed in box 2.

Advantageously, the slots 5, 6 are provided, respectively, on each of the opposite faces 14, 24 of the grid. The slots 5 have a substantially rectangular and constant section, while the slots 6 have a section which is initially rectangular but widens in the direction of flow of the gas mixture, forming expansion chamber 16; said slots 6 having a depth less than that of slots 5, and all being substantially of the same section.

In addition, in order to ensure good homogenization of the gaseous mixture and allow good combustion thereof, the slots 5 and 6 are distributed substantially regularly at the periphery and along the length of the grid 4 opposite the passage 34. L orientation of the slots 5 and 6 is such that they are formed substantially perpendicularly on either side of the longitudinal axis 44 of the support grid 4. In addition, the slots 5 and 6 are preferably of the same number .

When the burner 1 is placed in its optimal operating position, that is to say substantially horizontally so that the constituent elements of the burner form a stacked structure based on the box 2 which receives, above it, the grid 4 capped with its cap 7, the slots 5 are arranged on the upper face 14 of the grid; the slots 6 then being formed symmetrically on the underside 24 thereof.

It should be noted that good operating conditions of the burner according to the invention are obtained when the position of the latter is such that it forms, with a horizontal plane, an angle less than or equal to 45 _° .

Referring now to Figures 7 and 2, it is noted that the diffuser tube 3, the end opposite to the inlet is closed by a wall, is supplied with a gaseous mixture (gas / air) and is provided with orifices 33 , 43. These orifices are substantially regularly distributed in two series 33, and 43 along the major part of said tube. More specifically and advantageously, the orifices of each of the series are distributed linearly and substantially parallel to the longitudinal axis 13 of the tube 3; each series of orifices being further apart angularly about 90 _° . Advantageously, the orifices are directed towards the bottom 42 of the box (2). It can be noted that, when the tube 3 is arranged, substantially coaxially in the box 2, the orifices of each of the series 33, 43 are oriented so that they form, with the transverse axis 32 of the box, an angle a substantially equal to 45 _° .

In order to ensure a substantially uniform distribution of the combustible gas mixture over the length of the burner, the orifices 33, 43 of the distributor tube are arranged so that the first orifice is disposed, relative to the wall of the box towards its end d admission 23, at a distance of the order of twice the distance separating two successive orifices, the last orifice being disposed, with respect to the opposite wall 23 ′ of the box, at a distance of the order of four times this gap.

Towards one end of the burner box, there is a system for igniting the mixture. One can in particular provide an electric ignition device, of known type, and an ionization probe for the control of flames resulting from combustion.

Referring again to Figure 1, we note that the cap 7 which covers the slots 5 of the grid 4, can be in the form of a rectangular metal plate of small thickness and whose dimensions are substantially those of the covered grid. The cap plate 7 can, for example, be made of copper.

So that the burner of the invention delivers its optimal nominal power and offers its best operating flexibility, provision is made, according to a variant of the invention, for the grate 4 to be surmounted by a part 27, and by a cap 17 having a wall 28 formed back, for example a few millimeters; the intermediate part 27, in the form of a flat plate, coming to be inserted between the grid 4 and the cap 17.

This hat is in the form of substantially a thin rectangular plate whose dimensions are substantially equal to those of the grid which it covers. The wall 28 of the cap 17 is formed back from its face 18 directed towards the grid. This wall extends over the entire width of the plate 17 forming a cap and over most of its length. The intermediate piece 27 comprises, towards its central part, an oblong longitudinal slot 38, which extends over most of the length of the intermediate plate and passes through it over its entire thickness. The slot 38 is arranged opposite the passage 22 of the box 2 and the communication slot 34 of the grid 4.

This intermediate piece 27 can optionally be omitted; the grid 4 is no longer then capped only by the cap 17 or else, as shown in FIG. 1, by the cap in the form of a flat plate 7 whose thickness is substantially constant.

However, the combined use of the cap 17 and the intermediate plate 27 leads to an improvement in the calorific power delivered of the order of 10%.

The burner which has just been described operates in the following manner: - the distributor tube 3 of the burner 1 is supplied with premix. This air / gas premix can be carried out using a mixer of any known type. The air necessary for combustion is induced by the gas pressure, thus achieving stoichiometric mixing. This mixture is then distributed inside the box 2 in the internal volume 12, forming a distribution chamber, via the tube 3 in which the orifices 33, 43 are pierced. The gas mixture then flows towards the grid 4, the communication passage 22 ensuring its flow from the interior volume 12 to the slots 5, 6 of the grid 4. The flow rate of the gaseous mixture which ignites thanks to the igniter (not shown) provided for this purpose, is distributes substantially uniformly over the length of the grid, in the upper 5 and lower 6 slots, the flames catching on the outside of the burner, near said slots. The slots 6 can in particular play the role, thanks to their expansion chamber 16, of piloting the flames; the main flames of the burner then being attached to the outside of the slots 5.

It should be noted that when the grid 4 is surmounted by the intermediate plate 27 and the cap 17, the gas mixture flows through the slot 38 of the plate and the withdrawal 28 from the cap, a second flame control being able to be ensured. by these means.

A burner according to the invention, and presented by way of nonlimiting example, may, in particular, include a box 2 whose internal volume 12 of distribution of the mixture is of the order of 150 to 250 cm ³ and preferably equal to about 200 cm ³ .

In this case, the distributor tube 3 is advantageously provided with 26 orifices 33, 43, distributed in two series of 13 and pierced at an apex angle of about 90 _° ; said holes having a diameter of the order of 3 mm and being substantially regularly separated by a distance of approximately 15 mm.

A good distribution of the gaseous mixture, over the length of the burner, is ensured when the first hole in each series is housed about 30 mm from the internal wall limiting the interior volume of said box, towards its inlet 23; the last hole being made about 60 mm from the opposite internal wall, towards the end 23 '.

If the dimensional characteristics which have just been indicated are substantially observed, the upper slots 5 may be 2 × 55, and with a rectangular section of the order of 2 × 3 mm; the lower slots 6, of the same number, first having a rectangular section of approximately 2 x 1.2 mm and then, at the outlet of the expansion chamber 16, a section of approximately 4 x 1.2 mm.

The burner that has just been presented can deliver a nominal power of the order of 40 kW / PCS by being supplied with atmospheric induction with natural gas at a pressure of approximately 0.1 to 1.2 bar, or in liquefied petroleum gas at a pressure ranging from about 0.1 to 0.7 bar.

Also, given the dimensions, the power delivered is important. In addition, the flexibility of operation of such a burner allows a modification of the specific power delivered in a ratio of the order of 1 to 20. This makes it possible to design devices for producing heat at low temperature, in particular boilers with distill spirits. At the same time, the good distribution of the heat flow allows the application of such burners, in particular for the heating of molds used in foundries or for the manufacture of ceramics.

A particularly advantageous use of the burner of the invention in the industrial field can result from the association of several groups of burners. It is possible in particular to provide groups of two or three burners arranged in parallel, each group having its admission in gaseous mixture and its premix chamber. The groups thus formed will then be distributed over the surfaces to be heated, thus providing a uniform distribution of the heat flow.

By way of example, it may be noted that an installation of this type comprising twenty four burners per series of three, can deliver a power of the order of 800 kW distributed substantially over the entire surface to be heated of a alcohol distillation tank.

By way of a variant of the invention, it is possible in particular to provide that the burner is arranged and operates in the inverted position, that is to say, upside down, the stack then having the cap as a base; this configuration can further improve the efficiency of the burner by recovering the heat of condensation of the water vapor delivered by combustion.

Furthermore, in order to favor, especially when the burners of the invention are associated in parallel by group, the interignition of these, provision may be made for the grid 4 to include slots 15 for passage of said combustible gas mixture.

These slots are preferably arranged on the face 14 of the grate, towards the end 23 ′ of the burner opposite the inlet 23, and between the two rows of slots 5 formed on either side of the axis 44, said slots forming a corolla.

Finally, provision can be made for the end part of the supply tube 3, opposite the inlet 23, to extend inside a tubular cavity 53 _' projecting from the box 2; said tube being able to be hollow at its two ends, a plug (not shown) closing its opposite end to the inlet, for example, by screwing on a thread provided for this purpose on the external wall of the cavity 53 '.

Claims (7)

1. A gas burner of the gas/air pre-mixture type feeding a distributor box comprising at least one flame bar, the said burner consisting of a stacked structure (2, 4, 7, 27, 17) comprising the said distributor box (2) which is of elongate flattened form and which receives above it a flame grille (4) in the form of a panel of small thickness with a top surface (14) and a bottom surface (24), the said grille comprising at least one series of orifices (6) in the form of depressions provided in the bottom surface (24) of the grille, the said orifices which are regularly distributed towards the periphery of this grille, at least over its length, communicating with the interior space (12) inside the distributor box (2), the said burner being characterised: in that the depressions (6) disposed in the bottom surface (24) of this grille are of substantially rectangular cross-sectioin which flares out in the direction of flow of the gaseous mixture, orifices (5) which are likewise in the form of depressions but which are of substantially rectangular and constant cross-section being disposed in the top surface (14) of this same grille, which has above it a panel (7, 17) of small thickness which forms a cover which fits over it, and in that the top and bottom surfaces of the grille communicate inter se through a slot (34) disposed through the grille in such a way as to form a communicating passage between the interior space (12) of the box (2) and the cover.

2. A burner according to Claim 1, characterised in that the depressions (5) which are formed in the top surface (14) of the grille are of larger cross-section than those (6) which are formed in the bottom surface (24) of this same grille, the said depressions (5, 6) all having a cross-section which is substantially identical in each surface.

3. A burner according to any one of the preceding Claims, characterised in that the distributor box (2) comprises a tube (3) for supplying gaseous mixture and provided with discharge orifices (33, 43) which open out into the space (12) inside the said box (2), the said supply tube (3) being disposed substantially coaxially with the said box.

4. A burner according to Claim 3, characterised in that the said discharge orifices (33, 43) are distributed lineally in two series which are offset angularly by approx. 90_° being substantially evenly distributed along at least a part of the said supply tube (3).

5. A burner according to any one of the preceding Claims, characterised in that the cover (17) is such that its surface (18) which is towards the grille (4) comprises a wall (28) which is set back and which extends over all the width of the cover and over the greater part of its length.

6. A burner according to any one of the preceding Claims, characterised in that it comprises an intermediate member (27) in the form of a panel, disposed between the grille (4) and the cover (17) and which has an elongated slot (38) formed opposite the said communicating passage (34), passing through the entire thickness of the said intermediate member.

7. A burner according to any one of Claims 1 to 4, characterised in that the panel which forms a cover (17) is flat and of substantially constant thickness.

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