EP0921349B1 - Fuel atomisation burner and combustion process carried out with such a burner - Google Patents

Abstract

The combustion process is for melting glass. Feeding of a fuel is assured by a burner equipped with at least one injector (1). Each injector is made up of a first conduit (2) fed with liquid fuel presenting at least one internal wall (25) and a second conduit (3) fed with an atomized fluid arranged concentrically with respect to the conduit fed with liquid fuel. Immediately before the injection of the liquid fuel into its feed conduit it is put into the form of a hollow jet essentially adopted to that of the internal wall. The burner used in this combustion process and its use for reducing NOx emissions are also claimed.

Description

The present invention relates to a combustion method and device in which the fuel supply is provided by at least one burner equipped with at least one injector.

The invention will be more particularly described for use for the glass melting in glass furnaces, especially furnaces for manufacturing flat float glass or furnaces for making hollow glass packaging, for example ovens operating in the reverse type using regenerators (energy recuperators) but it is not for as much limited to such applications.

Most combustion processes of the aforementioned type, in particular those used in glass furnaces are faced with problems of unwanted emission of NO _x in combustion fumes.

NO _x has a harmful influence on both humans and the environment. On the one hand, NO ₂ is an irritant gas at the source of respiratory diseases. On the other hand, in contact with the atmosphere, they can gradually form so-called acid rain. Finally, they cause photochemical pollution since, in combination with volatile organic compounds and solar radiation, NO _x are at the origin of the formation of so-called tropospheric ozone, the increase in concentration of which at low altitude becomes harmful for human being. especially in hot weather.

For all these reasons, the standards in force regarding NO _{x are} becoming more and more demanding. However, by the very existence of these standards, oven manufacturers. such as those in glass furnaces, are constantly concerned with limiting NO _x emissions as much as possible, preferably at a rate lower than 500 mg / m ³ of smoke.

The parameters that influence the formation of NO _x have already been analyzed. This is essentially the temperature, because beyond 1300 ° C the emission of NO _x increases exponentially in excess air since the concentration of NO _x depends on the square root of that of the oxygen or the N ₂ concentration.

Many techniques have already been proposed to reduce the emission of NO _x .

A first technique consists in using a reducing agent on the gases emitted so that the NO _x are converted into nitrogen. This reducing agent can be ammonia but we know the disadvantages caused such as the difficulty of storing and handling such a product. It is also possible to use natural gas as a reducing agent, but this is to the detriment of the consumption of the oven and increases the CO ₂ emissions.

It is therefore preferable, without this being compulsory, to get rid of this technique by adopting so-called primary measures.

These measures are thus called because it is not sought to destroy the NO _x already formed, as in the technique described above, but rather to prevent their formation, for example at the level of the flame. These measures are also simpler to implement and therefore more economical. They may however not completely replace the aforementioned technique but come to complement it advantageously. These primary measurements are in any case an essential prerequisite for reducing the consumption of reagents for secondary measurements.

• une première catégorie consiste à réduire la formation de NO_x à l'aide de la technique dite de "reburning" par laquelle on crée une zone en défaut d'air au niveau de la chambre de combustion d'un four. Cette technique présente en outre l'inconvénient d'augmenter la température au niveau des empilages de régénérateurs et, le cas échéant, de prévoir une conception spécifique des régénérateurs et de leurs empilements, tout particulièrement en termes d'étanchéité et de résistance à la corrosion.
• une deuxième catégorie consiste à agir sur la flamme en empêchant, à tout le moins en réduisant, la formation des NO_x à son niveau. Pour cela, on peut par exemple chercher à réduire l'excès d'air de combustion. Il est également possible de chercher à limiter les pics de température en maintenant la longueur de flamme, et à augmenter le volume du front de flammes pour réduire la température moyenne au sein de la flamme. Une telle solution est par exemple décrite dans les demandes de brevet français FR 2750977 et internationale WO 9802386 respectivement déposées le 11 juillet 1996 et le 09 juillet 1997. Elle consiste en un procédé de combustion pour la fusion du verre, dans lequel l'alimentation en combustible et l'alimentation en carburant s'effectuent toutes deux de manière à étaler dans le temps le contact combustible/comburant et/ou à augmenter le volume de ce contact en vue de réduire l'émission des NO_x.

We can, in fact. non-limiting classification of existing measures into several categories:

• a first category consists in reducing the formation of NO _x using the technique known as "reburning" by which an air-defective zone is created at the combustion chamber of an oven. This technique also has the drawback of increasing the temperature at the regenerator stacks and, if necessary, of providing a specific design of the regenerators and their stacks, particularly in terms of sealing and corrosion resistance. .
• a second category consists in acting on the flame by preventing, at the very least by reducing, the formation of NO _x at its level. For this, one can for example seek to reduce the excess combustion air. It is also possible to seek to limit the temperature peaks by maintaining the flame length, and to increase the volume of the flame front to reduce the average temperature within the flame. Such a solution is for example described in the French patent applications FR 2750977 and international WO 9802386 respectively filed on July 11, 1996 and July 09, 1997. It consists of a combustion process for the melting of glass, in which the supply of fuel and the fuel supply are both carried out so as to spread the fuel / oxidant contact over time and / or to increase the volume of this contact in order to reduce the emission of NO _x .

The object of the invention is to propose a new combustion method and device, in which the fuel is a liquid fuel, which make it possible to lengthen the flame and / or to decrease the temperature peaks inside it in order to reduce the formation of NO _x .

Another object of the invention is to propose a combustion process and a related device, suitable for all glass furnace configurations which allow optimal heat transfer, in particular by providing a flame of adequate length and sufficient volume important to promote maximum bath coverage of batch materials in fusion.

GB 1188761 teaches a burner equipped with an injector, comprising a duct of liquid fuel supply, having an internal wall and a supply supply duct spraying fluid disposed concentrically with respect to said supply duct of liquid fuel, said liquid fuel supply conduit comprising a nozzle to eject the liquid fuel, said spray fluid supply duct is ending with a block pierced with an orifice ejecting the spray fluid, the nozzle being inserted in said block, said liquid fuel supply duct comprising means for putting the liquid fuel in the form of a hollow jet substantially matching said internal wall, immediately before ejecting it from its supply duct, the terminal part of the nozzle not being aligned in the plane defined by the face of the block. With such configuration, the spraying fluid is in contact with said face of the block on which opens the opening. This burner produces a very fine spray.

The subject of the invention is a burner equipped with at least one injector, comprising a liquid fuel supply duct, of the fuel oil type, having at least one internal wall and a fluid supply duct spraying arranged concentrically with respect to said fuel supply duct liquid, said liquid fuel supply conduit comprising a nozzle for eject the liquid fuel, said spray fluid supply duct is ending with a block pierced with an orifice ejecting the spray fluid, at the at least part of the nozzle fitting into said block, said supply conduit of liquid fuel comprising at least one means for putting the liquid fuel in the form of a hollow jet mating substantially with said internal wall, immediately before ejecting it from its supply duct. According to the invention, the terminal part of the nozzle is aligned in the plane defined by the face of the block without contact with the fluid of spraying and on which the orifice opens.

The invention also relates to a combustion method, in particular used for glass melting, in which the fuel supply is provided by at least the burner according to the invention. According to the invention, immediately before ejecting the liquid fuel from its supply duct, we put it in the form of a hollow jet marrying substantially said inner wall.

The solution according to the invention perfectly meets the problem posed. In fact, by thus creating a very specific flow of liquid fuel just before it emerges from its supply duct, it makes possible an increased mechanical spraying of the liquid fuel by the spraying fluid at its outlet from the duct, which makes it possible to obtain a very large heterogeneity of the droplets of this same fuel, and therefore to prevent their burning from taking place with too great a speed, a source of formation of NO _x .

Consequently, for a desired flame temperature, it is very advantageous to allow ourselves to bring less oxidizer at the inlet, and therefore at the flame root, which further reduces the risks of NO _x formation. .

The solution according to the invention does not necessarily replace the existing techniques mentioned in the preamble and comes, if necessary, to supplement them very advantageously.

According to an advantageous characteristic of the invention, the liquid fuel with a supply driving pressure of at least 1.2 MPa.

This ensures, whatever the particular configuration of the oven in which the method according to the invention is implemented, for sure, of a fragmentation of the liquid fuel necessary to avoid, as specified more high, too high a burning speed.

Preferably, the liquid fuel is ejected at a temperature between 100 and 150 ° C, more preferably between 120 and 135 ° C.

Such a range of temperatures makes it possible to bring any type of liquid fuel used in current installations, in particular glass furnaces, to the viscosity required immediately before it is ejected from its supply duct. This viscosity can advantageously be at least equal to 5.10 ^-6 m ² / s, in particular between 10 ^-5 and 2.10 ^-5 m ² / s.

According to another characteristic of the invention, the fuel is ejected liquid according to a cone with an opening angle of at least 10 °, in particular included between 10 ° and 20 °.

Such values allow, regardless of the geometry of the duct of liquid fuel supply and its dimensioning, not only to systematically have an interference between the spray fluid jet and droplets of liquid fuel, interference required in connection with the invention, but also a dispersion of the size of these same droplets optimal such that the resulting flame is uniform in temperature over all its length.

As regards the spraying fluid, it is ejected, very advantageously at a flow rate of at most 40 Nm ³ / h.

Obviously, the value of the spray fluid flow rate is correlated to that of the pressure of this same fluid, pressure which should be limited to maximum. By having a maximum flow value like the one mentioned above, we manage to obtain a sufficient flame length for all existing glass furnace configurations.

The invention also relates to a burner equipped with at least one injector, in particular capable of implementing the method described above, comprising a liquid fuel supply duct, of the fuel oil type, having at least one internal wall and a spray fluid supply duct arranged concentrically with respect to the fuel supply pipe liquid. It is remarkable in that the liquid fuel supply duct has at least one means for putting the liquid fuel into the form of a hollow jet mating substantially with the internal wall, immediately before to eject it.

According to one embodiment, the liquid fuel supply duct includes at least one cylindrical tube.

According to this embodiment, the aforementioned means comprises advantageously a nozzle fixed, preferably by screwing, to the end of the tube cylindrical. A nozzle geometry particularly suitable for the burner according to the invention is such that it includes a gyration chamber at its downstream end frustoconical in shape extended by a nozzle whose internal wall is cylindrical.

It is specified, within the framework of the invention, that the terms "downstream" and "upstream" must be understood by reference to the direction of supply of the liquid fuel.

Thus the downstream end of the nozzle designates the end which is the farthest from the liquid fuel supply source and therefore closest to the place where the fuel is ejected from its supply line. In a way particularly preferred, the angle at the top of the gyration chamber is at least minus 30 °, preferably equal to 60 °, which minimizes the loss of charge of flowing liquid fuel.

According to a preferred variant of the invention, the aforementioned means comprises at least one element substantially sealing off the fuel supply duct liquid and pierced with channels, in particular cylindrical, oblique to the liquid fuel supply direction.

This element is decisive in the context of the invention, because it is he who, by its particular geometry, gives the liquid fuel a flow conforms to the above and gives it a level of mechanical energy high enough that it can be sprayed out of its conduit supply in the form of droplets whose dispersion of size is optimal.

The channels can advantageously be uniformly distributed over! A circumference of the element.

This element is shaped allowing its insertion into the supply duct liquid fuel and can for example be a cylinder, preferably two faces substantially parallel to each other. These faces are also oriented preferably in a direction perpendicular to the direction of supply of the liquid fuel.

More advantageously, the orientation of each of the channels is chosen so that their generator makes an angle α of at least 10 °, in particular between 15 and 30 °, preferably equal to 20 °, with the direction liquid fuel supply.

This particular orientation allows to obtain a synergy between all "divided" jets of liquid fuel as they exit the corresponding channels of so that when they strike the downstream part of the supply duct, in especially the gyration chamber of the aforementioned nozzle, they do not interfere between them and contribute to the creation, downstream, of a single hollow jet hugging the wall internal.

According to an additional characteristic, the element can be mounted, in upstream of the nozzle, in a sealed manner in the fuel supply duct liquid, preferably against the gyration chamber.

Regarding the spray fluid supply duct, it preferably comprises at least one cylindrical tube at the end of which is fixed, preferably by screwing, a block pierced with an orifice into which is inserted at at least part of the nozzle according to the invention.

Preferably, the orifice of the block and the external wall of the part of the nozzle which fits into it are arranged concentrically. This provision preferred can also be obtained by the aforementioned screwing capable of ensuring the self-centering of the elements described above, namely the orifice of the block by compared to the part of the nozzle that fits into it.

This concentricity is advantageous insofar as in its absence there is has a risk of forming very large droplets of liquid fuel, fuel oil type, on the periphery of the hollow jet, which can cause combustion poor with in particular an increase in the threshold for the appearance of CO.

Similarly, it is necessary that the terminal part of the nozzle is aligned and preferably perfectly aligned in the plane defined by the face of the block without contact with the spraying fluid and on which the orifice opens. In fact, an incorrect alignment implies a modification of the aerodynamics of liquid fuel and spraying at the exit of their respective supply duct.

Advantageously, the injector according to the invention which has just been described is mounted in a sealed manner in a block of refractory material using a sealing device comprising a plate provided with fins cooling. Such a watertight mounting prevents any entry of parasitic air to the level of the downstream end of the injector, particularly harmful parasitic air in the extent that it increases the oxygen content in the flame root which is the hottest part of it.

According to another characteristic, the burner according to the invention comprises furthermore an adjustable support on which the injector described above is fixed and a ventilation nozzle oriented towards the downstream end of the injector, plus particularly towards the aforementioned plate.

The support is preferably adjustable in inclination, azimuth and translation in particular to come to rest on the plate of the device sealing.

The ventilation nozzle. as for her. blows air, which avoids excessive local overheating at the downstream end of the injector.

The invention finally relates to a burner equipped with at least one injector comprising a liquid fuel supply duct, of the fuel oil type, having at least one internal wall and a spray fluid supply duct arranged concentrically with respect to the fuel supply pipe liquid remarkable in that the liquid fuel supply duct has at least one diffuser.

The advantages brought by the burner described above are undeniable. In addition to the fact that it generates much less NO _x than before in the combustion chamber, for example an oven, its operation is ensured with a much lower spray fluid flow rate which makes possible a wider and more flexible use of the oxidizer and, therefore, ultimately allows obtaining better results from an energy point of view.

The invention applies to all types of oven configurations, in particular glassware, such as loop ovens, with transverse burners. inversion ... It is used more particularly to reduce the emission of NO _x .

Finally, it very advantageously complements the technique described in French patent applications FR 2 750 977 and international WO 9 802 386 mentioned above, a technique belonging in particular to the technology developed by the SAINT-GOBAIN VITRAGE company under the name "FENIX".

• figure 1 : une vue schématique en coupe partielle d'un injecteur selon l'invention,
• figure 2 : une vue en coupe verticale d'une paroi d'un four de verrerie comportant un brûleur équipé de l'injecteur selon la figure 1.

Other details and advantageous characteristics of the invention will emerge below on reading a non-limiting embodiment, described with reference to the figures, which represent:

• FIG. 1 : a schematic view in partial section of an injector according to the invention,
• FIG. 2 : a view in vertical section of a wall of a glass furnace comprising a burner equipped with the injector according to FIG. 1.

First of all, it should be noted that, for the sake of clarity, Figures 1 and 2 are schematic and do not respect the relative proportions between the different elements.

Figure 1 shows a partial sectional view of an injector 1 conforming to the invention.

This injector 1 is made up of two fluid supplies, namely respectively the liquid fuel 2 and the fluid supply duct spray 3.

The liquid fuel used in the context of the invention is a liquid fossil fuel commonly used in combustion devices to heat the batch materials in a glass furnace. He can for example be heavy fuel oil. The spray fluid is, similarly, that which is found usual in current installations and which is used to spray the the aforementioned liquid fuel. This can for example be air (called in this primary air as opposed to secondary air which serves as the main oxidizer). It can also be gas, oxygen (in the case of oxycombustion) or steam.

Liquid fuel and spray fluid supply lines aforementioned are respectively connected, upstream of the flow of each of the two fluids, to a circuit from a liquid fuel source and a source of spray fluid not shown.

The liquid fuel supply duct 2 essentially consists a cylindrical tube 21 at the end of which is screwed a nozzle 22.

This comprises at its downstream end a gyration chamber 23 of frustoconical shape extended by an end piece 24 of cylindrical inner wall 25. The angle at the top  of the gyration chamber 23 is equal to 60 °, chosen value for the reasons explained below.

Inside the aforementioned nozzle 22 is arranged a cylinder 4 mounted tightly in abutment against the turning chamber 23.

The cylinder 4 has channels 41 uniformly distributed over its circumference and has two faces 42, 43 parallel to each other and substantially perpendicular to the liquid fuel supply direction symbolized by the arrow f in FIG. 1, direction otherwise identical to that of the spray.

Channels 41 are cylindrical, their generatrix making an angle α of 20 ° with the direction mentioned above.

The spray fluid supply duct 3, for its part, consists essentially a cylindrical tube 31 at the end of which is screwed a block 32 of which the inner shoulder 33 abuts against the downstream end of the tube 31.

The block 32 is pierced with an orifice 34 of shape allowing the nesting part of the nozzle 22.

The block 32 also has a protruding part on the side of the orifice 34 35 which allows by screwing the block 32 on the cylindrical tube 31 to ensure a perfect self-centering of the external wall 26 of the end piece 24 inside the orifice 34.

In other words, because of their complementary forms, the concentricity of two elements 26, 34 above is perfectly assured, which avoids, as it will be explained below, to have an unwanted change in the dispersion of size of the droplets of liquid fuel as they exit the duct 2.

The dimension d of the part of the block 32 in contact with the cylindrical tube 31 must be calculated with precision, so that the alignment of the part end 36 of the nozzle in the plane (Π) is perfectly realized. This plan Π is that defined by the external face 37 of the block, that is to say that without contact with the spray fluid and onto which the orifice 34 opens.

Such an arrangement contributes to preserving the aerodynamics of the two fluids at the exit of their respective supply duct.

We now refer to Figure 2 which shows a sectional view vertical of a wall of a glass furnace comprising a burner 5 equipped with the injector according to figure 1.

In this particular configuration, it can be seen that the burner 5 comprises a support 6 adjustable in inclination, azimuth and translation.

On this adjustable support 6 is fixed the injector 1 which comes to rest against the walls of a block 7 of refractory material. via a plate 8 fitted with cooling fins. The block 7 of refractory material is itself mounted in an opening in the wall of the oven 9.

The burner 5 also includes a ventilation nozzle 10 oriented towards the aforementioned plate.

Finally, we see two flexible supply pipes 11, 12 connected respectively sources of liquid fuel and spray fluid, sources not shown.

The operation of the burner will now be explained below.

At the crossing of the cylinder 4 the liquid fuel, brought via the tube cylindrical 21, is divided into as many individual jets as there are channels tangentials 41.

The individual jets then arrive in the gyration chamber 23 from strike its walls, with a minimum of pressure losses due to the very value of the angle at the top  equal to 60 °.

The uniform distribution of the tangential channels 41 and the inclination α equal to 20 ° of the generator on the entire circumference of the cylinder 4 of each of these channels result in centrifugation of all jets individually against the wall of the gyration chamber 23 without, however, that they interfere with each other.

This centrifugation at the gyration chamber contributes downstream. that the fuel follows a helical trajectory by getting under the shape of a hollow jet almost perfectly matching the internal wall 25 of the nozzle 24.

At the outlet of the nozzle 24, the liquid fuel has thus acquired energy maximum mechanical and, under the influence of the spray fluid, it bursts genuinely in very fine droplets whose size dispersion is optimal. Such a dispersion makes the flame from the burner and once activated by the main oxidizer very uniform in temperature over its entire length.

What is more, such spraying of fuel lengthens considerably, for the same fuel flow, the flame compared to a spray which would be caused by the same injector 1 without cylinder 4.

The dimensioning of cylinder 4 must be carried out in such a way that the filling is never carried out and that is obtained in accordance with the invention, always a hollow jet substantially matching this wall internal.

The different parameters that are the number, the inclination α and the sizing of channels 41. must be determined according to the flow of the desired injector 1.

This desired flow rate is itself determined from the type of oven on which we want to install the injector, its operating parameters such as the pulled. as well as the nature of the liquid fuel used.

Obviously, these values can be established empirically without any difficulty by those skilled in the art who can also establish abacuses by performing tests.

Those skilled in the art will also take care to choose a surface condition respectively the gyration chamber, the channels, and the end of the walls internal, cared for in order to ensure a minimum of pressure losses due to the friction of the jet (s) of liquid fuel sweeping these same high speed elements.

The injector which has just been described is of simple and inexpensive design. It is. in addition, fully and easily removable and adaptable on already existing installations.

The oven previously described emits much less NO _x , without fear of a reducing combustion which may be harmful to the tint of the glass.

The combustion method and the burner according to the invention are particularly suitable for the production of high quality glass in particular optical, such as flat glass produced by floating.

The invention is particularly applicable to fuels of the heavy fuel type and it makes it possible to circulate very large flows (500 to 600 kg / h) of this type of fuel on a single injector according to the invention.

Of course, various modifications can be made without as well depart from the scope of the invention, namely spraying a fuel liquid put in the form of a hollow jet immediately before being ejected using a spraying fluid such as air, the conduct of which is ensured so so that it comes out exclusively along the axis of the internal wall of the supply duct fuel without any helical component.

Claims (15)

1. Burner (5) equipped with at least one injector (1), comprising a pipe (2) for supplying liquid fuel of the fuel oil type, having at least one internal wall (25) and a pipe (3) for supplying atomisation fluid disposed concentrically with respect to the said liquid fuel supply pipe, the said liquid fuel supply pipe (2) comprising a nozzle (22) for ejecting the liquid fuel, the said atomisation fluid supply pipe terminating in a block (32) with an orifice (34) in it ejecting the atomisation fluid, at least part of the nozzle fitting in the said block, the said liquid fuel supply pipe comprising at least one means (4) for putting the liquid fuel in the form of a hollow jet substantially following the shape of the said internal wall, immediately before ejecting it from its supply pipe, characterised in that the end part (36) of the nozzle is aligned in the plane defined by the face of the block with no contact with the atomisation fluid and on which the orifice opens out.
2. Burner according to the preceding claim, characterised in that the liquid fuel supply pipe comprises at least one cylindrical tube (21) to which the nozzle is fixed.
3. Burner according to the preceding claim, characterised in that the nozzle has at its downstream end a gyration chamber (23) with a frustoconical shape, extended by an end piece (24) whose internal wall (25) is cylindrical.
4. Burner according to the preceding claim, characterised in that the angle at the apex  of the gyration chamber is at least 30°, and preferably equal to 60°.
5. Burner according to one of the preceding claims, characterised in that the said means comprises at least one element (4) substantially closing off the liquid fuel supply pipe and with channels (41) in it, in particular cylindrical, slanting with respect to the direction of supply of the liquid fuel.
6. Burner according to the preceding claim, characterised in that the channels are uniformly distributed over the circumference of the element.
7. Burner according to one of the two preceding claims, characterised in that the said element is a cylinder, preferably with two faces (42, 43) substantially parallel to each other.
8. Burner according to one of Claims 5 to 7, characterised in that the generatrix of each of the said channels forms an angle α of at least 10°, in particular between 15° and 30°, preferably equal to 20°, with the direction of supply of the liquid fuel.
9. Burner according to any one of Claims 5 to 8, characterised in that the said element is mounted upstream of the nozzle in a fluidtight manner in the liquid fuel supply pipe, preferably in abutment against the gyration chamber.
10. Burner according to one of the preceding claims, characterised in that the atomisation fluid supply pipe (3) comprises at least one cylindrical tube (31) at the end of which there is fixed, preferably by screwing, the block (32) with an orifice (34) in it.
11. Burner according to the preceding claim, characterised in that the orifice (34) of the block and the external wall (26) of the part of the nozzle which fits in it are disposed concentrically.
12. Burner according to one of the preceding claims,
    characterised in that the said injector (1) is mounted in a fluidtight manner in a block (7) made from refractory material by means of a sealing device comprising a plate (8) provided with cooling fins.
13. Burner according to any one of the preceding claims, characterised in that it also comprises an adjustable support (6) to which the said injector is fixed and a ventilation fluid nozzle (10) oriented towards the downstream end of the said injector.
14. Combustion method, in particular used for melting glass, in which the fuel supply is provided by at least one burner according to one of the preceding claims.
15. Use of the method according to the preceding claim or of the burner according to one of Claims 1 to 13 for reducing NO_x emissions, in particular in a glassworks furnace.

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