Deflagration-Proof And Detonation-Proof Surface Combustion Gas Burner

This invention relates to a surface combustion gas burner, in particular a hydrogen burner. Such a burner is in particular intended to be used in domestic or industrial heating apparatuses, to heat a fluid circulating in an exchanger.

There have been two main successive generations of gas burners, namely atmospheric burners and fan burners.

In atmospheric burners, the pressurized gas is emitted through a nozzle and causes a flow of air via a convergent-divergent device. Such a burner has the drawback of emitting polluting discharge into the atmosphere.

Among fan burners, air/gas premixture burners or “premix” burners allow total control of the premixing of gas and air (see for example the burner described in document WO2014006103). Polluting discharge is thus considerably reduced.

However, in the case of premix burners, combustion takes place at the outer surface of the burner. In order to avoid rapid ageing of the burner by exposing its jacket to reddening (which is the case if the flame comes too close to the surface of the jacket), the range of power variation of such a premix burner is in the order of 1 to 3, or even a maximum of 1 to 10, if the jacket is made of a material resistant to high temperatures or includes a specifically developed design such as the burner described in document WO2014006103.

Moreover, during the operation of this air/gas premix burner, the flow rate of the air and gas mixture must be varied so as to avoid the uprooting of the flame due to excessive flow and conversely, to avoid the flame returning into the burner due to the lack of a sufficient flow, thus causing a flashback.

Such a flashback can specifically lead to a deflagration, or even to a detonation.

For a given burner, the range of modulation of its power is therefore regulated by its maximum flow rate, which corresponds to an gas outlet speed less than the uprooting of the flame, and by its minimum flow rate, which corresponds to a gas outlet speed greater than the flashback speed.

In addition, these two extreme limits of the speed of the air and gas mixture are related to the propagation speed of the flame of the gas under consideration, in other words, to the kind of gas. Thus, one and the same air/gas premix burner will offer a different operating range as a function of the kind of gas used and its propagation speed.

By way of illustration, natural gas has an average propagation speed of 0.37 meters/second and hydrogen an average propagation speed in the order of 2.6 meters/second, i.e. nearly seven times faster.

Surface combustion burners of the prior art are therefore also not very suited to the use of hydrogen gas, if one wishes to be able to use such a burner over a wide range of power variations.

However, in order to comply with the environmental and ecological criteria, hydrogen could be a beneficial alternative as fuel for supplying these burners.

One aim of the invention is therefore to make provision for a surface combustion burner which can operate in particular with hydrogen, while being reliable, i.e. avoiding the flashback phenomenon and the associated risks while also being able to be used over a wide range of power variations.

For this purpose, the invention relates to a deflagration-proof and detonation-proof surface combustion gas burner.

In accordance with the invention, this burner comprises a burner body made of metal or refractory material and a gas distributor, the burner body delimits an inner cavity connectable to an air supply source and has an outer face and an inner face, the burner body is perforated by a series of orifices, each of which is extended by a rim, which projects from this outer face and the central axis of which is normal to this outer face, these orifices being disposed in several rows of aligned orifices, the gas distributor comprises a distributor body which delimits a housing connectable to a gas supply source, the distributor body comprises a plurality of longitudinal gas distribution branches, each branch comprising two longitudinal walls, spaced apart from one another in such a way as to define between each other a longitudinal lamellar gas distribution space, which opens at its inner longitudinal end into said housing, the two walls of each branch meeting to form an outer longitudinal edge, a closed front end and a closed rear end of said branch, each branch is perforated by a series of orifices aligned along its outer longitudinal end, each orifice being bordered by a rim which projects over the outer face of said longitudinal edge and each orifice having a central axis normal to this outer face of said longitudinal edge, the distributor body is disposed in the inner cavity of the burner body so that each orifice of the distributor body is coaxial with an orifice of the burner body, the distributor body and the burner body are dimensioned so that the inner diameter Dof an orifice of the burner body is greater than the outer diameter Dof the apex of the rim of an orifice of the distributor body disposed facing this same orifice, so that there is a gap for the passage of air between the apex of the outer longitudinal edge of each branch and the inner face of the burner body, and so that the apex of the rim of each orifice is in immediate proximity to the inlet mouth of the orifice facing which it is placed, so that when the burner body is connected to an air supply source and the distributor body to a gas supply source, the air penetrates the burner body, circulates between the branches of the distributor body and in the gap and escapes from the burner through the rims of the burner body, while the gas penetrates the housing of the distributor body, circulates in the lamellar space of the branches then through the orifices and rims of this distributor body and finally through the rims of the burner body within which it meets the air and is mixed with this one.

Owing to these features of the invention, the gas and air circulate in the burner where the load losses are extremely small, through separate circuits, and are only mixed at the last moment inside the rims of the burner body. These rims thus constitute microchambers for mixing the gas and air and the combustion takes place at the surface, i.e. on exiting these rims, thus preventing any flashback.

Such a burner is therefore particularly suitable for use with hydrogen, a gas which has a high flame propagation speed, since flashback is prevented and therefore any risk of detonation or deflagration also.

In addition, the mixed volumes of gas and air are controlled and make it possible to obtain a wide modulation range.

According to other advantageous and non-limiting features of the invention, taken alone or in combination:

In the remainder of the description, the surface combustion gas burnerin accordance with the invention is described as operating with a gas which is preferably hydrogen. However, it could also operate with another gas, for example natural gas, without however departing from the scope of the invention.

In the remainder of the description and claims, by convention, the term “front” denotes elements that are located or pointing toward the end of the burner through which the air is introduced into it (i.e. on the left on) and the term “rear” denotes elements that are located or pointing in the opposite direction (i.e. on the right on).

In general, the gas burner comprises a burner bodyconnectable to an air supply source and a gas distributorconnectable to a gas supply source.

According to a preferred (and therefore not exclusive) embodiment of the invention, which will now be described in more detail, the burner bodyand the gas distributorare of generally cylindrical shape.

On, it can be seen that the burner bodyis shut off at its rear endby a back walland is equipped at its front endwith a front wall flange, and that the gas distributoris shut off at its rear end by a back walland is equipped at its front end with a front flange. These different elements will now be described.

The burner bodyis formed of a hollow cylindrical shellextending around a central longitudinal axis X-X′, which also constitutes the central longitudinal axis of the burner. This shellpreferably consists of a thin metal sheet.

This bodydelimits a cylindrical inner body.

Said shell is perforated by a plurality of orifices, each of which extends outward as a rim, (see in particular). The rimsurrounds the periphery of the orifice. Each rimprojects over the outer faceof the body. Each orificeand its rimhave a central axis Z-Z′which is normal to this outer face(see). The inner face of the shell is referenced′.

The rim(and more particularly its free end) can advantageously be toothed so as to have notches′. These notches′ are used to create turbulences at the outlet of the bodyand thus to reinforce the flame-holding effect and to avoid the uprooting of the flame.

The orificesand the rimsare for example “punched holes”, obtained by stamping or punching of a flat metal sheet, which is then bent to form the cylindrical bodyand both edges of which are welded.

These orificesare circular or substantially circular and the rimsare cylindrical or substantially cylindrical.

Furthermore, the orifices(and therefore the rims) are aligned so as to form several axial rowsof orifices. These rowsextend parallel to one another and also parallel to the central longitudinal axis X-X′ of the body. Furthermore, preferably, the different rowsare evenly distributed over the entire circumference of the burner body.

In a given row, the different orificescan be evenly spaced apart from one another or contrariwise be grouped to form a pattern, for example grouped two-by-two as can be seen on the figures.

The back wallis composed of a solid disc, equipped with a peripheral annular rim. The diameter of this back wallis adapted to the diameter of the burner body(here to the shell), so that its peripheral rimcan be welded to the rear endof the body, preferably inside this body, as can more clearly seen on the section of. The back walland the bodyare thus welded in a gastight manner by a circular weld.

Furthermore, the back wallis equipped with at least one locator pin, preferably three pins, which project from the front faceof the disc, in the direction of the inside of the cavity, when this back wall is assembled with the body. Their role will be detailed below.

As can be seen on, the front wall flangeis an annular element intended to be welded to the front endof the burner body, to allow the connection of this bodyto an air supply source (not shown on the figures), required for the combustion of the gas. The flangefor example comprises a ringwelded to the inside of this bodyand which extends forward as a radial flangefor attaching the body.

The gas distributorhas the function of distributing the gas, in particular hydrogen, as near as possible to the orificesof the burner bodyand also of distributing the air circulating in the body, as will be described in more detail further on.

The distributoris intended to be inserted axially into the burner body.

As can be seen more clearly on, the distributorcomprises a distributor body, the back walland the front flange.

The bodycomprises a hollow cylinder, of central longitudinal axis X-X′. This axis X-X′is coaxial with the axis X-X′ of the burnerwhen the distributoris mounted in the body. The cylinderis equipped with a plurality of radial branches, disposed in a star around the cylinder. The cylinderdelimits a cylindrical central housing. Each branchextends both radially outward with respect to the central axis X-X′ and over the entire length of the cylinder.

As can be seen more clearly in, each branchcomprises two flat walls,′, parallel or substantially parallel to one another and spaced apart so as to fashion between themselves a lamellar spacewhich opens at its radially inner end into the cylindrical central housing. The two walls,′ meet one another, at their radially outer ends, by a joining area which defines the radially outer longitudinal edgeof each branch. This edgeis preferably of incurvated shape along its cross section, its concavity being turned toward the lamellar space.

Preferably, the bodyis composed of a strip of metal sheet, bent to form the cylinderand folded over on itself several times to form each branchopening into the housing.

As can be seen on, each branchis closed in a gas-tight manner at its front endand at its rear end′, for example by pinching the two walls,′, then welding the edges of these walls to one another.

Finally, the radially outer longitudinal edgeof each branchis perforated by a plurality of orifices, each of them extending by a rim, (see). The rimsurrounds the periphery of the orifice. Each rimprojects outward, from the radially outer faceof the edge. Each orificeand its rimhave a central axis Z-Z′, which is normal to the outer face.

The rimcan advantageously be toothed so as to have notches′ making it possible to create turbulences on exiting the rimand thus improve the air/gas mixture which penetrates the orificeand then the rim.

The orificesand rimsare for example “punched holes”, obtained by stamping a metal sheet. These orificesare circular or substantially circular and the rimsare cylindrical or substantially cylindrical.

The distributor bodycomprises at the most as many branchesas there are rowsof orificesin the burner body. There can be fewer branchesthan there are rowsof orifices and in this case, only air will exit the rowsof orifices. Preferably, there are as many branchesas there are rowsof orifices.

The orifices(and therefore the rims) are axially aligned along the longitudinal edge. Moreover, on each longitudinal edgeof each branch, there are as many orificesas there are orificesin one rowof the burner body. On a given longitudinal edge, the different orificescan be evenly spaced apart from one another or contrariwise be grouped into groups of several orifices, so as to form a pattern, for example grouped two-by-two, as can be seen on the figures.

The back wallis a disc, the outer diameter of which is equal to that of the inner diameter of the cylindrical central housing, and it is welded in a gas-tight manner to the cylinder, so as to shut off said housing.

The front flangemakes it possible to connect the distributor bodyto a pressurized gas (hydrogen) supply source (not shown on the figures).

The front flangepreferably comprises a discperforated by a central hole. The outer diameter of the discis equal to the inner diameter of the cylindrical central housingand this discis welded at its periphery to the front end of the cylinder, in a gastight manner, as can be seen on. This discextends forward as a tube, of longitudinal axis X-X′, which allows the connection of the front flangeto the gas supply source (not shown on the figures).