EP0978685A1 - Improvement to burners with fluegas recirculation and low nitric oxide emissions - Google Patents

Abstract

The burner has at least one central liquid or gas fuel feed duct (10) surrounded by a concentric air duct (31), a peripheral air duct (5) of annular section surrounding the central air duct, a series of peripheral ejection nozzles (18) for secondary air, and peripheral gas fuel feed ducts (13) extending at least partly along the annular air duct and ending in ejection nozzles (14). The air ejection nozzles (18) are separated from the gas nozzles (14), each of which is linked to a section of recirculation duct (22) situated in front of it.

Description

The present invention relates to improvements brought to industrial burners with liquid or gaseous fuel.

The technical sector of the invention is the field of manufacture of industrial burners.

The document EP 675 321 describes a gas fuel burner which has several central fuel transport conduits gaseous, arranged in the central part of an air supply channel, called primary injection means; these means consist of rods, the ends of which are folded outwards and arranged under the slots of a flame stabilizer; the ends of the rods are holes through which combustible gas is injected into the fireplace through the slots in the stabilizer.

The burner also comprises several peripheral conduits of transport of gaseous fuel, and means for mixing this fuel with combustion fumes produced in the home, as well as means for recirculating smoke; this burner has indeed means (called secondary) of fuel injection gas, which consist of rods ending in a nozzle each opening into a smoke recirculation duct produced in the home; according to this document, all of the means secondary injection, as well as the associated recirculation conduits, are located inside the air channel (called primary), to ensure their cooling.

Each peripheral fuel injection nozzle is arranged inside a recirculation duct which communicates by its two ends with the hearth; this allows by ejection effect to achieve a recirculation of the fumes which mix with the combustible gas and reduce the formation of nitrogen oxides; to complete this effect of reduction by increasing the combustion stage, the burner includes means (called tertiary) for injecting gaseous fuel, constituted by rods crossing the wall of the enclosure of the hearth; each rod is associated with an air intake channel surrounding the rod.

The burner described in this document presents some disadvantages; in fact, the gas streams delivered by the canes and the air channels associated with these tertiary injection means are likely to form gas streams and / or a curtain surrounding the secondary means of fuel gas injection, which is likely to disrupt and limit the effectiveness of the smoke recirculation by secondary injection means gaseous fuel; another disadvantage results from the difficulty of adjust and control the effect produced by the air jets surrounding the jets of gas from tertiary means of injection, and in particular to control these coaxial jets and their mixture necessary for good combustion with the other jets caused by this burner, which is equipped with three separate gas fuel injection systems and two separate air transport and injection systems in the burner (and the home).

In addition, a drawback related to this device equipped with three means for injecting gaseous fuel, which includes canes extending through the walls delimiting the enclosure of the hearth, resides in the large size of this system and the difficulty in repair, maintain and / or modify such a system partially embedded in the perimeter wall of the foyer.

Patent EP 675 321 also describes a burner devoid of tertiary fuel injection means, whose performance are reduced.

An objective of the present invention is to provide a burner improved and partially remedy at least the disadvantages of known burners while improving their performance in the reduction in the formation of nitrogen oxides.

An objective of the present invention consists in particular in improve the self-recirculation of smoke.

An objective of the present invention is also to propose a compact, simple, inexpensive and improved burner.

• au moins un conduit central de transport de combustible liquide ou gazeux,
• un conduit central de transport d'air (dit primaire) entourant ledit conduit central de transport de combustible,
• un conduit périphérique de transport d'air (dit secondaire) de section annulaire, entourant ledit conduit central de transport d'air,
• plusieurs buses périphériques d'éjection d'air secondaire délivré par ledit conduit périphérique de transport d'air.

According to a first aspect, the invention consists in proposing a burner with liquid or gaseous fuel which comprises:

• at least one central conduit for transporting liquid or gaseous fuel,
• a central air transport duct (called primary) surrounding said central fuel transport duct,
• a peripheral air transport duct (called secondary) of annular section, surrounding said central air transport duct,
• several peripheral nozzles for ejecting secondary air delivered by said peripheral air transport duct.

Each of said air ejection nozzles causes the formation an air jet entering the enclosure delimiting the hearth through the orifice outlet of the nozzle which is located in the vicinity of the internal face of the wall of the enclosure, substantially flush and the latter and preferably slightly protruding, in particular from a distance on the order of radius or nozzle diameter; each jet of air causes depression at vicinity of said outlet, which causes the suction of smoke which are then entrained by the air jet with which they mix to form a gas mixture whose oxygen concentration is lower than that of air; this oxidizing gas mixture leads to a low production of nitrogen oxides during combustion.

The nozzles are preferably constructed in the form of simple short sections of tube, which are preferably parallel to the axis longitudinal of the burner, the outlet openings of which preferably in at least one transverse plane (with reference to the axis length of the burner) which is (are) set back (upstream) from the outlets of the central fuel transport conduits and primary air; due to the fact that these air nozzle orifices are located in rear of the outlet (end) ports of the central air ducts and of fuel, and thanks to the mixture of air ejected by the nozzles with the smoke, avoiding contacting of secondary air (ejected by nozzles) "pure" with the combustion zone, while making it possible to obtain a compact structure where the air nozzles are located at a short distance of the longitudinal axis of the burner.

The length of the tube sections forming the nozzles is generally close to their radius or diameter.

So that the tube sections forming the nozzles play their role, their cumulative section must be less than the section of the duct air transport device to cause air acceleration as they pass.

These tube sections also serve to guide the air in nozzle outlet; the sections are preferably welded by their "upstream" end to a sheet or plate in the shape of a crown connecting the ferrules of said central and peripheral air transport ducts, the sheet being pierced with holes corresponding in shape and size to that tube sections.

The presence of the peripheral air ejection nozzles contributes to improve combustion by causing both "staging" of the air intake and setting in motion (called "recirculation") of the fumes resulting in the creation of a gas mixture at low rate oxygen.

Said air nozzles are preferably identical, arranged at equal distance from the longitudinal axis of the burner (i.e. on a circle) and according to a symmetry of revolution (i.e. angularly equidistant).

• au moins un conduit central de transport de combustible liquide ou gazeux,
• un conduit central de transport d'air (dit primaire) entourant ledit conduit central de transport de combustible,
• un conduit périphérique de transport d'air (dit secondaire) de section annulaire, entourant ledit conduit central de transport d'air,
• plusieurs buses périphériques d'éjection d'air secondaire délivré par ledit conduit périphérique de transport d'air,
• plusieurs conduits périphériques de transport de combustible gazeux s'étendant en partie au moins dans ledit conduit périphérique de transport d'air, de préférence parallèlement à celui-ci, et terminés chacun par une buse périphérique d'éjection du combustible gazeux ; lesdites buses périphériques d'éjection de combustible gazeux sont dissociées desdites buses d'éjection d'air.

According to another aspect, the invention consists in proposing a burner with liquid and gaseous fuels or else with gaseous fuel only, which comprises:

• at least one central conduit for transporting liquid or gaseous fuel,
• a central air transport duct (called primary) surrounding said central fuel transport duct,
• a peripheral air transport duct (called secondary) of annular section, surrounding said central air transport duct,
• several peripheral nozzles for ejecting secondary air delivered by said peripheral air transport duct,
• a plurality of peripheral gas transport conduits extending at least partly in said peripheral air transport conduit, preferably parallel thereto, and each terminated by a peripheral nozzle for ejecting the gaseous fuel; said peripheral fuel ejection nozzles are dissociated from said air ejection nozzles.

Thanks to the fact that the peripheral air ejection nozzles are dissociated, that is to say separated and / or arranged at a distance from the nozzles gaseous fuel ejection devices, each of the air jets produced by these air nozzles and each of the gaseous fuel jets produced by these gas fuel ejection nozzles, leads to neighborhood of each nozzle, a depression causing the aspiration of a part of the smoke present in the fireplace; the fumes mix like this with each jet of air and each jet of gaseous fuel delivered by these nozzles, then are driven by each of these jets; so we improve notably the recirculation of the fumes and consequently one decreases the formation of nitrogen oxide; in addition, the different jets of fuel and air do not interfere with each other in a first time (in the vicinity of the nozzles), which means that the is more stable and easier to adjust, and this delays the air / fuel mixture, which only occurs after mixing with the fumes. Combustion thus occurs in a dilute atmosphere with a reduced oxygen level and therefore leads to a high reduction of nitrogen oxides.

In addition, the fact that said central and peripheral conduits transport of air and fuel fall within the defined volume by the peripheral air transport duct, which is of section cylindrical, and generally delimited by a cylindrical sheet ferrule of steel, the burner according to the invention is compact and can be easily installed in a hole (of corresponding section) provided in the wall of a fireplace, without requiring the creation of orifices separate devices for the passage of air injection canes and / or of fuel.

Preferably, the peripheral gas injection nozzles are three to twelve, especially six to eight, arranged in a crown, regularly (angularly) distributed around the longitudinal axis (of general symmetry) of the burner, and the number of peripheral air ejection nozzles is equal to or double the number of peripheral nozzles for ejecting combustible gas; we can thus arrange the peripheral fuel nozzles and the nozzles air devices nested inside a single crown, the air and gas nozzles being alternated and distant to form separate jets regularly distributed in a ring around of the central part of the burner.

Although the longitudinal axes of the peripheral air and gases can expand in a diverging conical fashion, it is preferable that said axes are substantially parallel to the longitudinal axis of the burner and / or slightly inclined relative thereto.

According to one of the preferred characteristics, the means of smoke recirculation by the jets of combustible gas produced by the peripheral ejection nozzles, have a straight section of cylindrical conduit (or tube) arranged in the extension of each nozzle and at a distance (in front) thereof; said distance is preferably of the same order of magnitude as the radius or the diameter of the section of recirculation tube, in particular less than or equal to three times the diameter of the tube section, preferably less than or equal to two times the diameter of the tube section, for example of the order of 2 to 20 centimeters; thus, the free space between the nozzle and the inlet (the end upstream) of the recirculation duct facilitates the suction and mixing of the combustible gas with the fumes present in the hearth, delimiting a passage section for smoke of considerably larger dimensions larger than that delimited by the peripheral opening of the recirculation described in document EP 675 321; furthermore, this arrangement allows and / or facilitates adjustment, during assembly or the installation of the burner, this distance, which optimizes suction, mixing and entrainment of fumes by gas jets combustible.

It has been found that, surprisingly, the presence of a recirculation duct associated with each peripheral ejection nozzle of combustible gas, improves the recirculation of smoke, and is generally needed to get training and mixing significant of the fumes by the jet of combustible gas, when it is not not the same as regards the entrainment of fumes by the jets air: it is indeed possible to obtain a satisfactory training using the air jet leaving a peripheral ejection nozzle, without associate with this nozzle a smoke recirculation tube; of course it however, it is possible to provide one.

It has also been found that, also surprisingly, the functioning of gas smoke recirculation systems fuel using the nozzles and the recirculation tube, is significantly improved by providing nozzles and / or different dimensions; practically, two types of ejection nozzles combustible gases of different dimensions can be provided for this effect.

To prevent air jets from disturbing and interfering with the smoke entrainment caused by the jets of combustible gas, it it is preferable that the end of the air nozzle extends in front of, or in the same transverse plane as, the inlet opening of the tube recirculation arranged in the extension of the peripheral nozzle fuel gas ejection.

• le rapport du diamètre du conduit d'air secondaire au diamètre du conduit d'air primaire est supérieur à 1 et inférieur ou égal à 2, en particulier supérieur ou égal à 1,5 et inférieur ou égal à 2 ;
• le rapport de la longueur des conduits de recirculation associés aux buses d'éjection de gaz, à leur diamètre, est supérieur à 1 et inférieur ou égal à 10, en particulier voisin de 2 à 4 ;
• les buses périphériques d'éjection de gaz sont disposées sensiblement affleurantes ou de façon peu saillante sur la face interne des parois de l'enceinte du foyer, les buses périphériques d'éjection d'air étant elles disposées proéminentes par rapport à ladite face interne, et par rapport auxdites buses d'éjection de gaz ;
• l'orifice de sortie du conduit central d'air est saillant à l'intérieur de l'enceinte du foyer, et les extrémités avant des conduits de recirculation situés dans le prolongement des buses d'éjection de gaz combustible, sont disposées sensiblement dans le même plan que ledit orifice de sortie du conduit central d'air ;
• les tubes de recirculation associés aux buses d'éjection de gaz combustible, sont fixés sur la virole du conduit central d'air, sur la surface externe de celle-ci, et s'inscrivent à l'intérieur du diamètre du conduit périphérique annulaire de transport d'air secondaire.

According to other preferred characteristics, which contribute to improving the compactness, simplicity and efficiency of the burner:

• the ratio of the diameter of the secondary air duct to the diameter of the primary air duct is greater than 1 and less than or equal to 2, in particular greater than or equal to 1.5 and less than or equal to 2;
• the ratio of the length of the recirculation conduits associated with the gas ejection nozzles, to their diameter, is greater than 1 and less than or equal to 10, in particular close to 2 to 4;
• the peripheral gas ejection nozzles are arranged substantially flush or slightly protruding on the internal face of the walls of the enclosure of the hearth, the peripheral air ejection nozzles being arranged prominent relative to said internal face, and with respect to said gas ejection nozzles;
• the outlet opening of the central air duct protrudes inside the hearth enclosure, and the front ends of the recirculation ducts located in the extension of the fuel gas ejection nozzles, are arranged substantially in the same plane as said outlet port of the central air duct;
• the recirculation tubes associated with the fuel gas ejection nozzles, are fixed to the ferrule of the central air duct, on the external surface thereof, and fit inside the diameter of the annular peripheral duct of secondary air transport.

One of the results of the invention is to combine the means allowing the staging of the combustion by delivery of the fuel in different areas, by supplying combustion air also by different circuits, as well as the recirculation of the fumes by driven by jets of combustible gas, and the recirculation of smoke further by entrainment by jets of combustion air, which optimizes burner operation and reduces particularly the production of nitrogen oxide.

The advantages of the invention will be better understood from through the following description which refers to the accompanying drawings, which illustrate without any limiting character preferential modes of realization of the invention.

In the drawings, identical or similar elements bear, unless otherwise indicated, the same references from one figure to another.

Figure 1 illustrates in schematic perspective view the arrangement of the air and combustible gas ejection nozzles fitted a liquid and / or gaseous fuel burner according to the invention.

Figure 2 illustrates in cross-sectional view through two half-planes longitudinal intersecting along the longitudinal axis, and is a view according to II - II of Figure 3.

FIG. 3 is a front view of the front end of the burner and is a view along III of FIGS. 1 and 2.

Figures 4 and 5 illustrate views respectively identical to those of FIGS. 2 and 3, a liquid fuel burner or gaseous equipped with air ejection nozzles according to the invention; the Figure 5 is a view along V of Figure 4 and Figure 4 is a section according to IV-IV of Figure 5.

The burner 1 has a first cylindrical shell 2 with an axis longitudinal 3 horizontal, a second cylindrical shell 4 coaxial with the first, which delimits with the ferrule 2 a duct 5 of section annular; the ferrule 2 defines a central duct 31 for air passage primary.

The burner extends through a cylindrical orifice 6 provided in the wall 7 separating the hearth 8 from the outside 9 of the enclosure.

The burner comprises in the central part a central rod 10 of transport of combustible gas (in particular such as heavy fuel oil, diesel, petrol, oils, waste liquids ...) up to the burner head equipped with a central nozzle 11 and a flame stabilizer 12, which are arranged at the front end of the duct 31 and of the ferrule 2, and are protruding inside the fireplace 8.

The burner comprises a bundle of six peripheral tubes 13 of transport of combustible gases, which are each equipped at their end front of a nozzle 14 disposed substantially flush (for example 1 cm prominent) on the inner face 15 of the wall 7.

A part of the tubes 13 extends parallel to the axis 3 to the interior of the secondary air transport duct 5; the tubes 13 are supplied by a common collector 16, and pass through a annular flange 17 connecting the ferrules 2 and 4 and in which are provided six circular nozzles 18 for ejecting air; as illustrated in figures 1 and 3, the six identical nozzles 18 are spaced angularly by 60 degrees, same as the six nozzles 14 for ejecting combustible gas and are arranged in between (alternating): the angular space 19 between a nozzle 14 and an adjacent nozzle 18 is in this case close to 30 degrees.

The respective longitudinal axes 20, 21 of the nozzles 14, 18, which are parallel to axis 3, are located on identical or neighboring radii.

Six straight sections 22 of circular section tubes, cut to right angles at their two ends 23, 24, are arranged in the extension of the gas ejection nozzles 14, and are welded along of one of their generators on the external face of the end part before the shell 2, according to generators thereof.

The axis of the tubes 22 coincides with the axis of the nozzles 14 and the rear end 24 of identical sections 22 is disposed at a distance 25 from the corresponding nozzle 14, which distance is by example close to 50 millimeters.

Said rear end 24 extends substantially in the plane containing the orifice 26 for the outlet of the air ejection nozzles 18.

With reference to Figures 4 and 5, the burner 1 has a structure similar to that of Figures 1 to 3; however, the burner of Figures 4 and 5 does not have a peripheral conduit (as identified 13 Figures 1 to 3) transport of gaseous fuels, nozzles 14 or conduit 22 associated.

We find in Figures 4 and 5 the central conduits 10 of fuel transport and 31 primary air transport, as well as the duct peripheral 5 extended by the nozzles 18 for ejecting secondary air, the outlet orifice 26 of which is arranged upstream (by reference to the direction air and fuel flow) - i.e. right (figure 4) - from the projecting end of the shell 2 and of the conduits 10 and 31 central.

Claims (10)

Burner (1) characterized in that it comprises: at least one central conduit (10) for transporting liquid or gaseous fuel, a central air transport duct (31) surrounding said central fuel transport duct, a peripheral air transport duct (5) of annular section, surrounding said central air transport duct, several peripheral nozzles (18) for ejecting secondary air delivered by said peripheral air transport duct, the end (26) of which extends behind the outlet orifices of the central ducts (10, 31) which are protruding into the foyer, several conduits (13) for transporting gaseous fuel extending in part at least in said conduit (5) for peripheral air transport and each terminated by a nozzle (14) for ejection, in that the air ejection nozzles (18) are dissociated from the peripheral nozzles (14) for ejecting gaseous fuel, and in that it comprises a recirculation duct section (22) associated with each nozzle ( 14) and ejecting combustible gas in front of it. Burner according to claim 1, in which the sections of recirculation conduit (22) associated with each nozzle (14) are arranged in the extension of these, at a distance from them which is less than or equal to three times the diameter of said sections, preferably less than or equal to twice this diameter. Burner according to any one of claims 1 or 2, in which the recirculation sections (22) are fixed to the shell of the central air duct (31) and fit inside the diameter of the secondary air transport duct (5). Burner according to any one of claims 1 to 3, which has no recirculation ducts for the air ejection nozzles, and in which the air ejection nozzles have outlet openings of air of non-circular section. Burner according to any one of Claims 1 to 4, wherein said central and peripheral air transport ducts and fuel are part of the volume delimited by the duct air transport device, which is of cylindrical section, and delimited by a cylindrical ferrule (4) made of sheet steel. Burner according to any one of claims 1 to 5, which has three to twelve peripheral gas ejection nozzles (14) fuel, which has three to twenty-four nozzles (18) air ejection devices, which air and gas nozzles fuel are arranged alternately and in a ring. Burner according to any one of claims 1 to 6, which has two types of gas ejection nozzles of dimensions different. Burner according to any one of Claims 1 to 7, wherein the end (26) of the air ejection nozzles extends forward or in the same transverse plane as the inlet orifice (24) of the conduit (22) recirculation associated with the fuel gas ejection nozzle. Burner according to any one of Claims 1 to 8, in which the secondary air ejection nozzles (18) are arranged substantially flush with the wall of the fireplace, and preferably a little protruding. Burner according to any one of Claims 1 to 9, wherein the ratio of the length of the recirculation conduit (22) associated with the gas ejection nozzles, their diameter is greater than 1 and less than or equal to 10, and in which the ratio of the diameter of the duct (5) of secondary air to the diameter of the primary air duct (31) is greater than 1 and less than or equal to 2.

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