EP1074790A1 - Burner with exhaust recirculation - Google Patents

Abstract

Gas burner (1) has central conduits for gas (100) and liquid (10) combustible, surrounded by an air conduit (2) and additional gas conduits (13) running through the air conduit. Exhaust gases conduits (22) are fixed on the exterior face of the air conduit by linkage (101), which has heat transfer properties. An Independent claim is also included for the heater of turbine exhaust gases using the new burner.

Description

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

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

The present invention more particularly relates to improvements to very low emission gaseous fuel burners of nitrogen oxide comprising primary gas injection means fuel placed in the center of the burner and injection means secondary peripherals, and intended to be mounted either in an orifice provided for this in the wall of an enclosure, such as the bedroom combustion or hearth of an oven or a boiler, either in the central part of a turbine exhaust gas circulation duct of a installation of co-generation of electrical and thermal energy, in order to reheat these exhaust gases.

To reduce the nitrogen oxide content of the fumes, it is known to reduce the free oxygen content of the gases in the flame to avoid too strong combination of it with nitrogen from the air, and limit the maximum flame temperature. To reduce the oxygen content in the flame and to reduce the flame temperature, one solution is to recycle some of the smoke present in the fireplace: it is known to achieve this recirculation by means of ejection systems which use the depression created by fuel ejection.

Furthermore, it is known that, in order to limit the maximum temperature of flame, we can stage the combustion, that is to say that instead of putting in a single zone, all of the fuel and oxidizer, we proceed in stages: either we stage the injection of the oxidant without modifying the fuel injection, on the contrary, we store fuel injection without staging that of the oxidant; the injection oxidizer stage also causes a drop in oxygen content free, unlike staged fuel injection only.

The present invention relates more particularly to a burner in which combines the above two smoke recirculation processes, on the one hand, and staging of the fuel supply, on the other.

US Patent 5,073,105 describes a burner mounted on a wall of a oven, which includes a block pierced with openings receiving sprinklers primary and secondary fuel, and delimiting an area of primary combustion; air enters this area through a perforated plate and mixes with horizontal and / or radial fuel jets mixed with the smoke sucked in by the depression resulting from these jets at through corresponding openings provided in the block; jets vertical of fuel mixed with smoke sucked through other openings, exit at the downstream end of the block, in another zone of combustion.

US Patent 5,284,438 describes a burner of similar structure but more complex, in which the burner block defines a convergent and a divergent separated by a constriction, and has conduits smoke extraction by fuel jets which, by their dimensions, their flared shape at the inlet, their inclined position and their outlet located in the block diverging, are supposed to ensure a definite dosage of the mixture fuel - smoke and its injection into an air mixing zone, which is located in the divergent; this burner has a central duct fuel injection system equipped with a nozzle, and a fuel stabilizer flame ; this structure causes the formation of jets (of a mixture fuel - smoke) turbulent and swirling, and causes their mixing with air in the mixing zones delimited by the block.

These burners whose smoke suction channels are formed in thick blocks generally made of refractory concrete, are fragile, bulky, expensive, and difficult to maintain.

The document EP 675 321 describes a gas fuel burner which has several primary fuel injection pipes, arranged in the central part of an air intake channel defined by the body burner tubular; the ends of the rods are folded outwards, arranged under the slots of a flame stabilizer, and the ends of the canes are drilled with holes through which combustible gas is injected into the focus through the stabilizer slots; the burner has in addition to (secondary) gas fuel injection rods, which are distributed around the primary injection rods, and which end in a single nozzle each opening into a recirculation duct for smoke produced in the home; these secondary injection rods, as well that the associated recirculation conduits are located inside the channel air, to ensure their cooling by the air which circulates there.

Each recirculation duct opens into the fireplace in parallel to the air channel, and communicates at its other end with the hearth by a hole drilled in the wall of the air channel, at the outer periphery of the burner; these holes allow, by suction and drive effect, to recirculate the fumes which mix with the gas combustible and reduce the formation of nitrogen oxides; to complete this reduction by increasing the staging of combustion, the burner includes (tertiary) fuel injection rods crossing the wall of the hearth enclosure; each rod is associated with a air intake channel surrounding the cane.

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

The burner described in this document has certain drawbacks: the gas streams delivered by the canes and the air channels associated with these tertiary means of injection, are likely to form a curtain surrounding the secondary fuel gas injection means, which is likely to disrupt and limit the efficiency of the recirculation system smoke by the secondary means of injecting gaseous fuel; a another disadvantage results from the difficulty of adjusting and controlling the effect produced by the air jets surrounding the gas jets of the tertiary means 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 injection systems gaseous fuel and two separate transport and injection systems air in the burner (and the fireplace); in addition, a drawback related to canes extending through the walls delimiting the enclosure of the hearth, resides in the large size of this system and the difficulty in repairing it, maintain and / or modify such a system partially embedded in the wall of the home.

An objective of the present invention is to provide a burner improved and partially remedy at least the disadvantages of burners known while improving their performance in reducing 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 burner capable of being used in a duct for transporting exhaust gas from turbine (s).

According to a first aspect, the invention consists in proposing a burner with gaseous fuel which includes a central conduit for transporting fuel, a central air transport duct surrounding said duct central fuel, several peripheral conduits for transporting gaseous fuel extending at least in part outside the duct central air transport, preferably parallel to it, and finished each by a fuel ejection nozzle; the burner has in addition to a straight section of cylindrical conduit (or tube) of smoke recirculation, which is arranged in the extension of each nozzle and at a distance (in front) thereof; the air transport duct and the smoke extraction ducts are metallic, substantially parallel between them, and preferably open substantially in the same plane perpendicular to the longitudinal axis of the burner; the suction ducts of fumes are fixed on the metal body of the burner, preferably on the air transport duct, by a metallic connection which contributes to ensure, by conduction, the cooling of the suction ducts by the burner body (especially through the air duct) which is itself cooled by the air it carries.

Since the smoke circulation pipes are not the reverse of the burner described in patent EP 675 321, protuberants at inside the air duct, they do not disturb the operation of the burner, especially when the latter - fitted with a central rod for this purpose liquid fuel injection - is supplied with liquid fuel only.

Tests have shown that such a burner causes low emission nitrogen oxides.

The position of the smoke circulation ducts arranged at the outside of the air duct results in separation of the jets from the mixture fuel / smoke compared to the air flow carried by the duct central (main); mixing these jets with the flame resulting from the combustion of the fuel delivered by the central duct intervenes gradually and further (by comparison with the structure described in EP 675 321) downstream of the burner nose, which enhances the effect fuel injection staging.

The effect of suction and entrainment of fumes by gas jets fuel delivered by the peripheral nozzles is improved by the fact that the smoke inlet at the upstream end of the recirculation ducts takes place over the entire periphery thereof; a greater amount of smoke is thus sucked up and mixed with each jet of fuel.

In addition, the jet of fuel / smoke mixture leaving each peripheral recirculation duct causes, due to its speed, a additional smoke training.

The distance from each peripheral fuel nozzle to the inlet opening of the associated recirculation tube is preferably same order of magnitude as the radius or diameter of the pipe section recirculation, for example of the order of 2 to 20 centimeters; so the space free between the nozzle and the inlet (the upstream end) of the recirculation facilitates the extraction of smoke and gas mixing fuel 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 cooling of the flue gas recirculation ducts with the central duct air transport is sufficient to avoid deterioration of these ducts although these flues are arranged in the fireplace (and / or are subjected to intense heating by direct radiation of the flame); preferably, for this purpose, the metal connection serving as a heat sink extends over a large area, in particular substantially over the entire length of recirculation ducts; this link is preferably obtained by welding.

In fact, in the burner according to the invention, the cooling of the smoke circulation tubes cannot be obtained by convection with an air flow (relatively cold) as is the case in patent EP 675 321 and in patent application FR 98/10350 filed on August 7, 1998 by the Applicant; in this document indeed, peripheral nozzles air injection are arranged nested with the peripheral nozzles fuel injection.

• 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 ;
• 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 soudés sur la virole du conduit central d'air, sur la surface externe de celle-ci.

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

• 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 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 welded to the shell of the central air duct, on the external surface thereof.

Said peripheral nozzles and the associated suction ducts are preferably identical, arranged at equal distance from the axis longitudinal of the burner (i.e. on a circle) and according to a symmetry of revolution (that is to say angularly equidistant).

Preferably, the peripheral gas injection nozzles fuel, as well as the associated smoke tubes, are among three to twelve, in particular six to eight, arranged in a crown, regularly (angularly) distributed around the longitudinal axis (from general symmetry) of the burner.

Although the longitudinal axes of the peripheral nozzles and associated flues can extend in a divergent conical fashion (at most 5 degrees), it is preferable that these axes are substantially parallel to the longitudinal axis of the burner.

According to another aspect, the invention consists of a gas heater turbine, which comprises a burner according to the invention which is mounted in the central part of a turbine gas transport duct which is equipped with partial closing flaps.

In this particular use of the burner according to the invention, the external position of the smoke circulation tubes avoids disturbing the combustion of the fuel delivered in the central part.

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, except otherwise indicated, the same references from one figure to another.

FIG. 1 illustrates in longitudinal section view a burner with liquid and gaseous fuel according to the invention.

Figure 2 is a front view of the front end of the burner of the Figure 1 and is a view along II of Figure 1.

Figure 3 illustrates in longitudinal section view a heater turbine outlet gas according to the invention.

Burner 1 (Figures 1 and 2) has a first ferrule cylindrical 2 with longitudinal axis 3 horizontal, and a second ferrule cylindrical 4 coaxial with the first, which delimits a conduit 5; ferrule 2 delimits a central air passage duct 31, which extends the duct 5 air inlet.

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 liquid fuel (in particular such as heavy fuel oil, diesel, petrol, oils, waste liquids ...) up to the head of the equipped burner 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 projecting at the interior of the hearth 8; the burner further comprises a central rod 100 gaseous fuel injection.

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 protruding (for example protruding by 1 centimeter) on the internal face 15 of the wall 7.

A part of the tubes 13 extends parallel to the axis 3 inside the air transport duct 5; the tubes 13 are supplied by a common collector 16, and pass through an annular flange 17 connecting the ferrules 2 and 4; as illustrated in figure 2, the six identical nozzles 14 fuel gas discharge points are angularly spaced 60 degrees apart.

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

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 a from their generators to a full metal bar 101, associated with each conduits, which extends parallel to the conduit 22 and which is itself welded (over its entire length) to the outer 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 end rear 24 of identical sections 22 is arranged at a distance 25 from the corresponding nozzle 14, which distance is close to 50 millimeters, and corresponding to the diameter of the tubes 22.

The front end 23 of the tubes 22 extends in the plane 112 containing the outlet of the central duct 31.

With reference to FIG. 3, the burner 1 is mounted in a duct 200, of axis coinciding with axis 3 of the burner, delimited by walls 201 (in the case where several burners are mounted in the duct 200, their axes 3 are parallel to that of the conduit).

The conduit 200 transports (according to the arrows 103) gas leaving a turbine, whose temperature is around 500 ° C or, when the turbine is stopped, air; in the latter case, flaps 104, which are pivotally mounted in the conduit 200 along axes 105, obturate partially - in the position shown in solid lines - the section of passage of the conduit 200 leaving the passage free - according to the arrows 102 - through the burner pipe 2; the (open) position of the flaps illustrated in dashed lines corresponds to the case where the turbine gases are present.

The burner is fixed in the duct 200 by supports not represented.

In both operating cases, an outside air supply (corresponding to 5% of the total air) is introduced through a pipe 106 to cool the central part of the burner, in particular where the stabilizer 105 of the central (main) flames of gas combustion injected through the central conduits 100 which pass through a deflecting rosette 104; the conduits 100 are supplied by a collector 107.

Furthermore, the peripheral conduits 13 are supplied with gas fuel through a second manifold 16; the flow of gaseous fuel injected by the peripheral nozzles generally represents around 90 at 95% of the total fuel flow. An advantage of the burner is that mixing jets coming out of the tubes 22 help to lengthen the flame, which improves the efficiency of the gas heater and the installation of heat recovery, located downstream of the burner.

Claims (9)

Gaseous fuel burner (1) which has a duct central (10,100) fuel transport, a central conduit (2) of air transport surrounding said central fuel duct and several peripheral conduits (13) for transporting gaseous fuel, characterized in that said peripheral conduits extend in part at least to the outside of the central air transport duct, in that the burner further comprises a straight section of conduit (22) for circulation of smoke which is arranged in the extension of each nozzle (14) fitted the peripheral conduits (13), and in that the suction conduits (22) smoke are fixed by a link (101) on the conduit (2) of transport of air, outside of it and are not in contact with an air flow, their cooling being carried out by conduction via said link (101). Burner according to claim 1, in which the conduits (22) are welded by one of their generators to a metal bar (101) of connection which is welded to a generator of the conduit (2), parallel to this one. Burner according to either of Claims 1 and 2, which includes a flame stabilizer (105) and a deflecting rosette (106) arranged in the air duct (2, 31) in the vicinity of its end plane (112). Burner according to any one of claims 1 to 3, in which the upstream orifice (24) of each conduit (22) is disposed at a distance (25) of the corresponding nozzle (14), which is of the order of the diameter of the conduit (22). Burner according to any one of claims 1 to 4, in which the outlet opening (23) of the conduits (22) extends substantially in the transverse plane (112) of outlet from the duct (2). Burner according to any one of claims 1 to 5, in which the nozzles (14) and the conduits (2, 22) are projecting inside the fireplace (8). Burner according to any one of claims 1 to 6, in which the smoke circulation conduits (22) and the conduit (2) of air transport are metallic. Turbine gas heater transported by a conduit (200) equipped with shutters (104) shutter, characterized in that it comprises a burner according to any one of claims 1 to 7. A heater according to claim 8, which has a duct (106) air supply for cooling the burner.

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