EP0994302B1 - Liquid fuel burner suitable for a furnace to reheat steel industry products - Google Patents

Abstract

The burner, producing an axially-symmetrical flame with axial development, has a broad combustion tunnel (10) with oxidant and fuel injection orifices (13, 14) lying parallel to its longer axis of symmetry. The tunnel can be rectangular or oval in shape, or a combination of these, with the axes of the injection orifices lying in planes parallel to the plane of the products to be treated.

Description

The present invention relates to a fluid fuel burner in particular for furnaces for heating steel products. The purpose of this invention is design of a spread flame burner which improves the distribution of heat fluxes generated by said flame, in order to reduce the heterogeneity of temperature induced in the products to be heated.

It is known that heat treatment furnaces, in particular reheating, hold are intended to carry products, including slabs, blooms and similar, at temperatures required for example for rolling or for obtaining a given metallurgical structure.

It is also known that the quality of the processing of a product, for example a rolling or heat treatment, requires a precise and uniform temperature at inside the product, this temperature depending on the type of treatment desired or the chemical composition of the product to be treated.

For example, in furnaces for heating metallurgical products, the level of average temperature is obtained by passing the products through so-called zones which are characterized by a significant thermal input in a relatively short time, which generates great thermal heterogeneity in reheated products. In order to obtain the required temperature uniformity for their further treatment, the products leaving the heating zones pass through an equalization zone in which the heat input is very low, which provides equalization of temperatures within products.

In Figure 1 of the accompanying drawings, there is shown schematically, in side elevation and vertical section, an embodiment of a reheating of known type steel products. This oven is of the lower and upper heating.

As can be seen in FIG. 1, the products to be heated, designated by the reference 1 are supported and transported inside the oven by a system of beams fixed 2 and mobile 3, the mobile side rails 3 being moved by actions combined with a travel chassis 4 and a lifting chassis 5 giving the products 1 a pilgrim's movement so as to lead them from the entrance to the oven outlet. This is a system well known to those skilled in the art, which does not is not part of the present invention and therefore need not be described in detail.

The oven consists of a heat-insulated enclosure 6, comprising respectively heating zones and equalization zones and on which are arranged upper 7 and lower 7 'heating burners as well as burners equalization 8 installed in the oven roof as can be clearly seen on the Figure 1. In this exemplary embodiment, the burners of the heating zones 7 and 7 'which are located on the side walls of the oven are flame burners axisymmetric, with axial development. The products to be treated are placed in a horizontal plane parallel to the axes of the burners. These can be implanted either in a plane situated above the plane of the product bed (upper burners 7), either in a plane located below the plane of the product bed (lower burners 7 '). The height of the oven enclosure 6 is defined by the distance between the plane of the products 1 of the oven floor and by the distance separating the plane of said products from the vault of the oven. This height is determined according to the characteristics and flame dimensions of burners 7 and 7 ′ located in the side walls of the oven.

In Figure 2 of the accompanying drawings, there is shown schematically, the distribution of the heat flux produced by the burners 7, 7 'with axisymmetric flames with axial development. In this figure, the reference B designates a burner, P the plane of the product bed and I the image of the heat flows transmitted. We see that the flow thermal has heterogeneities in the perpendicular vertical planes and parallel to the axis of the flame. These heterogeneities are caused by the gradual development of combustion at the root of the flame or by the presence of hot zones in this flame, characteristics of this type of known burner.

In this exemplary embodiment, the oven also includes burners 8 located on the roof of the oven in the equalization areas of the latter. It's about flame burners with low axial impulse and high rotation of the flame (important "swirl"). The heat flow transmitted to the products to be heated is constant over a certain diameter, in a plane perpendicular to the axis of the burner 8 and parallel to the bed of products 1. These burners generate limited thermal heterogeneities in these products, however the surface homogeneous radiative exchange created by each burner is limited to a low unit area, which requires the installation of a large number of burners such as 8 to ensure uniform heating of the entire surface of the products. Schematically shown in Figure 3, the location of the burners 8 in the vault of the oven. In this figure, the reference Z designates the main area of heating of each burner 8 on the roof of the furnace, Pv designates the plane of the roof of the furnace and Ip denotes the image of the heat fluxes transmitted on the plane of the bed products.

Finally, the lower burners 7 ′ which are located under the plane of the products 1 do not can be replaced by burners with low axial impulse and high setting flame rotation because their implantation in the oven bottom is impossible in reason for the presence of product and fall support equipment of part of the oxides that form during reheating on the surface of these products. Lower burners such as 7 'equalization zones cannot so be that axisymmetric flame burners, with axial development, despite the thermal flow distribution defects inherent in this type of burner.

WO 90/02907 describes a burner with a fuel / oxidizer nose mixture enriched so as to obtain a high luminosity flame. This burner has a combustion tunnel, equipped with oxidant and fuel injection ports evenly distributed around the geometric axis of the burner so that the flame produced will have a shape of revolution around the geometric axis, and not a spread out shape. This type of burner is used for cracking products injected with combustion air at very high temperatures for example, to purify them.

US-A-5,725,367 describes a burner with a single oxidizer inlet channel and a single fuel inlet channel. We do not find a layout with channels injection lines distributed around the axis of the burner.

US-A-3,676,048 relates to a burner in which the admission of oxidant, to air, is provided by a single duct generally constituting a slit annular in shape and not by injection orifices distributed around the axis of the burner. The pilot flame of this burner is generated by injections of fuel and oxidizer in the combustion tunnel and not by a special arrangement of injectors inducing a difference in the distribution of products of combustion and a recirculation of smoke at the nose of the tunnel combustion.

It is clear from the above that obtaining good homogeneity temperature of products reheated in a product reheating oven metallurgical or in a heat treatment furnace, is limited by the current technology of axisymmetric flame type burners with axial development, or that it is only partially possible by setting space, complex and expensive, of a large number of low-type burners axial impulse and strong rotary movement of the flame on the roof of the oven.

Based on this state of the art, the present invention proposes to provide a burner limiting the heterogeneities of distribution of the heat flow in planes vertical parallel and perpendicular to the flame axis, spreading the surface of exchange between the flame and the plane of the bed of the products to be treated.

In order to clearly understand the result made possible by the present invention, reference is made to FIG. 4 which represents the distribution of the heat flux of the flame of a burner produced in accordance with the provisions of this invention. As in Figure 2, reference B designates the burner, reference P designates the bed of the products and the reference I the image of the heat flows transmitted. This Figure 4 clearly shows that the burner according to the invention develops a flame spread parallel to the bed of products and whose flow is preferably in the plane of the major axis of symmetry of the tunnel, parallel to the product plan. A comparison between this figure 4 and figure 2 commented above clearly shows the technical progress brought by the invention vis-à-vis the burners according to the prior art.

The result thus illustrated is achieved by a burner according to the present invention which is equipped with a combustion tunnel and oxidant injection channels and fuel distributed around the axis of the burner, and characterized in that the tunnel combustion has an enlarged shape of dimensions L and H with a UH ratio greater than 1, with a major axis of symmetry included in a PS plane and arranged substantially parallel to the plane P of the products to be treated, the axes of the channels of oxidant injection are substantially parallel to the plane PS and are inclined relative to the axis of the burner, so as to create a difference in the distribution of combustion products and fumes, producing a spread flame ensuring a homogeneous distribution of the heat flow parallel to the PS plane.

According to the present invention, said combustion tunnel has a shape rectangular, oval, or any combination of these two shapes.

According to another characteristic of the invention, the axes of the injection orifices of the oxidizer and / or fuel are located in planes substantially parallel to the plan of the products to be treated.

• d'une part, une alimentation en comburant munie de canaux d'injection débouchant dans le tunnel de combustion par l'intermédiaire desdits orifices d'injection, ces derniers étant répartis autour de l'axe du brûleur et ayant des axes qui sont situés dans des plans sensiblement parallèles au plan des produits à traiter et,
• d'autre part, une alimentation en carburant disposée centralement et munie de canaux d'injection qui sont répartis autour de l'axe du brûleur, leurs axes étant situés dans des plans sensiblement parallèles au plan des produits.

According to a nonlimiting embodiment of the invention, the burner comprises:

• on the one hand, an oxidant supply provided with injection channels opening into the combustion tunnel via said injection orifices, the latter being distributed around the axis of the burner and having axes which are located in planes substantially parallel to the plane of the products to be treated and,
• on the other hand, a fuel supply arranged centrally and provided with injection channels which are distributed around the axis of the burner, their axes being located in planes substantially parallel to the plane of the products.

According to the invention, the injection channels open into the tunnel through the orifices fuel injection or, in the case where the invention is applied to burners with separate fuel injection pipes, fuel injection channels and ports fuel are located in the injection pipe.

Thanks to these characteristics, a low or zero rotation of the gases is obtained which ensures a distribution of the heat flow over a large area (or conversely), the flame, at the exit of the developing combustion tunnel preferably in the plane of the major axis of symmetry of the tunnel, substantially parallel to the product plan.

According to another embodiment, the burner includes modulation means of the surface on which the burner flame is distributed, these means being able be made by delivering the oxidant and / or fuel in at least two groups separated.

The invention also relates to an oven provided with burners having the characteristics defined above, in particular an oven for heating steel products. This oven may have a radiant wall or exchange wall, arranged substantially parallel to the plan of the products to be treated, opposite the plan of spreading of burner flames. These burners are arranged so that the spreading plane flame is substantially parallel to one of the walls of the furnace. According to the invention, the burners can be installed on the side walls of the oven, on one at less of these front walls, above and / or below the plane of the products to treat.

Other characteristics and advantages of the present invention will emerge from the description given below with reference to the accompanying drawings which illustrate exemplary embodiments devoid of any limiting character.

• La figure 1, qui a été discutée ci-dessus, représente en élévation latérale et coupe verticale, un exemple de réalisation d'un four auquel peut s'appliquer la présente invention ;
• La figure 2 illustre la répartition du flux thermique produit par des brûleurs actuellement connus, du type discuté ci-dessus ;
• La figure 3, discutée ci-dessus, est un schéma illustrant la répartition des brûleurs de voûte prévus dans les zones d'égalisation du four connu illustré par la figure 1 ;
• La figure 4 représente la répartition du flux thermique de la flamme d'un brûleur selon la présente invention,
• La figure 5 est une vue schématique du brûleur selon un premier exemple de réalisation de l'invention, en coupe par un plan parallèle aux plans P et PS de la figure 6 ;
• La figure 6 est une vue de ce même brûleur, depuis l'intérieur du four et,
• La figure 7 est une vue similaire à la figure 5 illustrant un second exemple de réalisation du brûleur, objet de la présente invention.

In the drawings:

• Figure 1, which has been discussed above, shows in side elevation and vertical section, an embodiment of an oven to which the present invention can be applied;
• FIG. 2 illustrates the distribution of the heat flux produced by currently known burners, of the type discussed above;
• FIG. 3, discussed above, is a diagram illustrating the distribution of the vault burners provided in the equalization zones of the known oven illustrated in FIG. 1;
• FIG. 4 represents the distribution of the heat flow of the flame of a burner according to the present invention,
• Figure 5 is a schematic view of the burner according to a first embodiment of the invention, in section through a plane parallel to the planes P and PS of Figure 6;
• FIG. 6 is a view of this same burner, from inside the oven and,
• Figure 7 is a view similar to Figure 5 illustrating a second embodiment of the burner, object of the present invention.

We refer to Figures 5 and 6 which illustrate a first embodiment of a burner according to the present invention. We see that this burner has a tunnel of combustion 10, of enlarged shape, rectangular in the exemplary embodiment not limiting illustrated by these figures, of dimensions L and H and whose major axis of symmetry included in the plane PS is arranged substantially parallel to the plane P of products 1 to be treated. Of course, this is only an embodiment which has no limiting character, the combustion tunnel 10 can be made according to any other enlarged shape, such as for example oval or any combination of an oval and a rectangular shape with an L / H ratio greater than 1.

The walls of the combustion tunnel 10 can be flared to the depth F as illustrated in figure 5.

The supply of fuel, of gas in this nonlimiting exemplary embodiment, is connected to the burner at 12, this fuel being injected via orifices 14. The supply of oxidant, air in this embodiment not limiting, is connected to the burner at 11, the injection by oxidant being effected by through holes 13.

The fuel injection and oxidizer channels are distributed around the axis of the burner. Their axes are arranged in planes substantially parallel to the plane PS in order to ensure a privileged distribution of each fluid which causes spreading the flame in a plane substantially parallel to the PS and P planes.

The burner thus produces at the exit of the tunnel 10, a spread flame with a homogeneous distribution of heat flow in a plane substantially parallel to the plane PS. The distribution of the heat flux obtained is consistent with the representation of the figure 4.

According to another characteristic of the present invention, the burner can be provided devices for modulating the surface on which the heat flux is distributed of the flame of this burner. An embodiment of such a device is illustrated by figure 7.

In this figure, we find the different constituent parts of the burner according to the invention as described above with reference to Figures 5 and 6. In this variant which has no limiting character, the oxidizer is delivered in two separate groups 11A and 11B respectively supplying two groups of channels injection lines 13A and 13B, the axes of the injection channels 13A and 13B are substantially parallel to the PS plane. The two groups of channels can be inclined with respect to the axis of the burner, in the same or different way.

Modulation of the ratio of flow rates and pressures of the two oxidant flows passing through the two groups of injection channels 13A and 13B makes it possible to modulate the surface on which the flame spreads. Of course, the same arrangement can be adopted with regard to the fuel supply, which may be also carried out in separate groups in order to control and modulate the surface on which the thermal flow of the burner is distributed.

The burner object of the present invention and described above can equip in particular an oven for reheating steel products, a holding oven or a heat treatment oven, it being understood that these application examples have not no limiting character. The burners are arranged in these ovens so that the flame spreading plan is substantially parallel to one of the walls of the oven in order to obtain a radiant wall substantially parallel to the plane of the products treat.

The burners which are the subject of the present invention can be installed on the walls sides of an oven as shown in Figure 1, above and below of the plan P of the products as illustrated in 7 and 7 ′ in this figure 1, in order to heat up said products homogeneously on their upper and lower faces.

The burners according to the invention can also be arranged on at least one front walls of the oven, above and / or below the plane P of the products to treat. FIG. 8 illustrates several known examples of frontal implantation of burners in a reheating oven of the type according to figure 1. The burners 15 can be installed on the end walls of the oven, above or below of the plane P of the products, the burners 16 can be installed at any point of the length of the oven, below the plane P of the products and the burners 17 can be located at all points along the length of the oven, above the plane P of the products.

• de réduire la durée de la phase d'égalisation des températures des produits, donc la longueur de la zone des fours de réchauffage dans laquelle cette égalisation de température est opérée.
• de limiter les risques de surchauffe localisée du produit grâce à l'absence de zone chaude ou de point chaud dans la flamme. Cette caractéristique permet l'amélioration de l'état métallurgique final du produit traité.
• de répartir la combustion sur une surface plus importante, ce qui permet de mieux contrôler le mélange de ces fluides donc la composition de l'atmosphère du four et des fumées. Ceci réduit les émissions de polluants générés par la combustion et réduit la formation d'oxydes à la surface des produits réchauffés.
• de réduire la hauteur du laboratoire du four grâce à la réduction de la dimension de la flamme perpendiculairement au plan des produits ou à la réduction du nombre de brûleurs.
• de remplacer un nombre important de brûleurs implantés sur la voûte du four par un nombre plus réduit de brûleurs implantés sur les parois du four. Le circuit de distribution de carburant et de comburant est plus réduit et il est réalisé pour un coût plus faible.

As will be understood, the present invention provides a spread flame burner making it possible to limit the temperature gradient at the surface of the products which are positioned in the oven fitted with such burners and, consequently, in their mass, in a quantity of identical transmitted heat. The decrease in the heterogeneities of distribution of the heat flux in vertical planes parallel and perpendicular to the axis of the flame, obtained by spreading the exchange surface between the flame and the plane of the bed of the products makes it possible in particular:

• reduce the duration of the product temperature equalization phase, therefore the length of the zone of the reheating ovens in which this temperature equalization is carried out.
• to limit the risks of localized overheating of the product due to the absence of a hot zone or hot spot in the flame. This characteristic allows the improvement of the final metallurgical state of the treated product.
• to distribute the combustion over a larger surface, which allows better control of the mixture of these fluids and therefore the composition of the atmosphere of the furnace and the fumes. This reduces the emission of pollutants generated by combustion and reduces the formation of oxides on the surface of the heated products.
• reduce the height of the oven laboratory by reducing the size of the flame perpendicular to the plane of the products or by reducing the number of burners.
• replace a large number of burners located on the top of the oven with a smaller number of burners located on the walls of the oven. The fuel and oxidizer distribution circuit is more reduced and it is produced at a lower cost.

The advantages mentioned above relate to the upper faces and bottom of the product, the burner object of the present invention can be implanted in plans located either above or below the products as seen above with reference to Figure 1.

Claims (17)

1. Fluid-fuel burner of the axisymmetrical flame type with axial development provided with a combustion tunnel (10) and channels for injecting oxidant (13) and fuel (14) distributed around the axis of the burner, characterised in that:

   the combustion tunnel (10) has a broadened shape of dimensions L and H with a ratio L/H greater than 1, with a major symmetry axis included in a plane PS and disposed substantially parallel to the plane (P) of the products to be treated, the axes of the oxidant-injection channels (13) are substantially parallel to the plane (PS) and are inclined with respect to the axis of the burner, so as to create a difference in distribution of the combustion products and fumes, producing a spread flame providing an even distribution of the heat flow parallel to the plane (PS).
2. Burner according to Claim 1, characterised in that it is provided with a rectangular-shaped combustion tunnel (10).
3. Burner according to Claim 1, characterised in that it is provided with an oval-shaped combustion tunnel (10).
4. Burner according to Claim 1, characterised in that the shape of the combustion tunnel (10) is any combination of rectangular and oval shapes.
5. Burner according to any one of the preceding claims, characterised in that the axes of the fuel-injection orifices (14) are situated in planes substantially parallel to the plane (P) of the products to be treated (1).
6. Burner according to any one of the preceding claims, characterised in that it comprises a fuel supply (12) disposed centrally and provided with injection channels which are distributed around the axis of the burner, the axes being situated in planes substantially parallel to the plane (P) of the products to be treated.
7. Burner according to any one of the preceding claims, characterised in that the fuel-injection channels open out in the combustion tunnel (10) through the said injection orifices (14).
8. Burner according to any one of Claims 1 to 6, characterised in that it is of the type with a separate fuel injection pipe, the fuel-injection channels and orifices being situated in the injection pipe.
9. Burner according to any one of the preceding claims, characterised in that the oxidant and/or fuel are delivered in at least two separate groups.
10. Burner according to Claim 9, characterised in that the oxidant is delivered in two separate groups (11A, 11B) supplying respectively two groups of injection channels (13A, 13B), the axes of the said injection channels being substantially parallel to the plane (P) of the products.
11. Burner according to Claim 10, characterised in that the two groups of injection channels are inclined with respect to the axis of the burner, identically or differently.
12. Burner according to any one of the preceding claims, characterised in that the walls of the combustion tunnel (10) are splayed over its depth (F).
13. Furnace, in particular for heating steel-making products, characterised in that it is equipped with burners according to any one of the preceding claims.
14. Furnace according to Claim 13, characterised in that it comprises a radiant wall or exchange wall, disposed substantially parallel to the plane (PS) of the products to be treated, opposite the plane of spread of the flames of the said burners.
15. Furnace according to one of Claims 13 or 14, characterised in that the said burners are disposed so that the plane of spread of the flame is substantially parallel to one of the walls of the furnace.
16. Furnace according to any one of Claims 13 to 15, characterised in that the burners are located on its side walls, above and/or below the plane (P) of the products to be treated.
17. Furnace according to any one of Claims 13 to 16, characterised in that it also comprises burners disposed on at least one of its front walls, above and/or below the plane (P) of the products to be treated.

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