EP1074790B1 - Burner with exhaust recirculation - Google Patents

Description

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

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

The present invention more particularly relates to improvements in low-emission gaseous fuel burners nitrogen oxide having primary gas injection means fuel arranged in the center of the burner and injection means secondary devices, and intended to be mounted either in an orifice intended for that in the wall of an enclosure, such as the chamber of combustion or hearth of a furnace or boiler, that is, in the central part of a turbine exhaust gas flow duct of a installation of co-generation of electrical and thermal energy, in order to warm up 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 a too strong combination of it with the nitrogen of the air, and limit the maximum temperature of the flame. To reduce the oxygen content in the flame and to reduce the flame temperature, one solution is to to recycle some of the fumes present in the hearth: it is known to perform this recirculation by means of ejection systems that use the depression created by the ejection of the fuel.

Moreover, it is known that to limit the maximum temperature of flame, one can stagger the combustion, that is to say that instead of putting the presence in a single zone of all the fuel and oxidant, one proceeds in stages: either one stages the injection of the oxidizer without modifying the injection of the fuel, either on the contrary, one floor fuel injection without storing that of the oxidizer; injection staged oxidizer also causes a drop in oxygen content free, unlike staged injection of fuel alone.

The present invention has more particularly concerned a burner in which combines the two above methods of flue gas recirculation, on the one hand, and staging of the fuel supply, on the other hand.

US Pat. No. 5,073,105 discloses a burner mounted on a wall of a oven, which comprises a block pierced with openings receiving sprinklers primary and secondary fuel, and delimiting a zone of primary combustion; air enters this area through a perforated plate and mixes with horizontal and / or radial fuel jets mixed with the fumes sucked by the depression resulting from these jets at through corresponding openings in the block; jets of fuel mixed with fumes sucked through other openings, go out at the downstream end of the block, into another zone of combustion.

US Pat. No. 5,284,438 describes a burner of similar structure but more complex, in which the burner block delimits a convergent and a divergent separated by a constriction, and includes conduits fumes extraction by fuel jets which, by their dimensions, their flared shape at the entrance, their inclined position and their exit located in the divergent from the block, are supposed to ensure a defined dosage of the mixture fuel - fumes and its injection into a mixing zone with air, which is situated in the divergent; this burner comprises a central duct injection nozzle equipped with a nozzle, and a stabilizer of flame ; this structure causes the formation of jets (of a mixture fuel - smoke) turbulent and swirling, and causes them to mixing with the air in the mixing zones delimited by the block.

These burners whose fume extraction channels are formed in thick blocks generally made of refractory concrete, are fragile, bulky, expensive, and difficult maintenance.

EP 675 321 discloses a gaseous fuel burner which has several primary fuel injection rods arranged in the central part of an air duct delimited by the body tubular burner; the ends of the rods are bent outwards, arranged under the slots of a flame stabilizer, and the ends of rods are pierced with holes through which fuel gas is injected in the focus through the slits of the stabilizer; the burner has in in addition to (secondary) gaseous fuel injection rods, which are distributed around the primary injection rods, and which end with a single nozzle each opening into a recirculation duct smoke produced in the home; these secondary injection canes, as well that the associated recirculation ducts, are located inside the canal of air, to ensure their cooling by the air circulating there.

Each recirculation duct opens into the firebox in parallel to the air channel, and communicates at its other end with the hearth by a orifice pierced in the wall of the air channel, at the outer periphery of the burner; these orifices allow, by suction effect and drive, to recirculate the fumes that mix with the gas fuel 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 cane 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 disadvantages: the gaseous currents delivered by the rods and the air channels associated with these tertiary means of injection, are likely to form a curtain surrounding the secondary means of fuel gas injection, which is likely to disturb and limit the efficiency of the recirculation system smoke by secondary means for injecting gaseous fuel; a Another disadvantage is the difficulty of regulating and controlling the effect produced by the jets of air surrounding the gas jets of tertiary means injection, and in particular to control these coaxial jets and their mixture necessary for good combustion with 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 hearth); in addition, a disadvantage related to canes extending through the walls delimiting the enclosure of the home, lies in the large size of this system and the difficulty of repairing it, maintain and / or modify such a system partially embedded in the wall of the hearth of the hearth.

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

An object of the present invention is in particular to improve the self-recirculation of fumes.

An object of the present invention is also to propose a compact burner, simple, inexpensive and likely to be used in a Turbine exhaust gas transport duct (s).

According to a first aspect, the invention consists in proposing a burner gaseous fuel which comprises a central transport duct fuel, a central air duct surrounding said duct central fuel, several gaseous fuel extending at least partly outside the duct central air transport, preferably parallel to it, and completed each by a fuel ejection nozzle; the burner has in in addition to a rectilinear section of cylindrical conduit (or tube) of recirculation of fumes, 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 The fumes are fixed on the metal body of the burner, preferably on the air transport duct, by a metal connection which contributes to ensure, by conduction, the cooling of the suction ducts by the burner body (especially by the air duct) which is itself cooled by the air it carries.

Because the flue ducts are not, at the opposite of the burner described in patent EP 675 321, protuberant to inside the air duct, they do not disturb the operation of the burner, especially when the latter - equipped for this purpose with a central cane liquid fuel injection - is fueled with liquid fuel only.

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

The position of the flue pipes arranged to the outside of the air duct results in a separation of the jets of 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 (compared to the structure described in EP 675 321) downstream of the nose of the burner, which reinforces the effect staging of the fuel injection.

The effect of suction and entrainment of fumes by gas jets fuel delivered by the peripheral nozzles is improved by the fact that the flue gas inlet at the upstream end of the recirculation ducts is carried out on the whole periphery of these; a greater amount of The fumes are thus sucked up and mixed with each fuel jet.

In addition, the jet of fuel / fume mixture coming out of each recirculation device leads, due to its speed, to a additional training of fumes.

The distance separating each peripheral fuel nozzle from the inlet of the associated recirculation tube is preferably same order of magnitude as the radius or diameter of the pipe section of recirculation, for example of the order of 2 to 20 centimeters; thus, the space between the nozzle and the inlet (the upstream end) of the recirculation facilitates the extraction of fumes and the mixing of gas combustible with the fumes present in the hearth, delineating a passage section for smokes of significantly larger dimensions large than that defined by the peripheral opening of the tubes of recirculation described in EP 675 321; in addition, this provision allows and / or facilitates the adjustment, during assembly or the installation of the burner, this distance, which makes it possible to optimize suction, mixing and entrainment of fumes by gas jets combustible.

It has been found that, surprisingly, the cooling of Conducted flue gas recirculation ducts with the central duct air transport is sufficient to prevent deterioration of these ducts although these flues are located in the fireplace (and / or are subjected to intense heating by the direct radiation of the flame); preferably, for this purpose, the metal link serving as a heat sink extends over a large area, particularly substantially over the entire length of the recirculation ducts; this link is preferably obtained by welding.

Indeed, in the burner according to the invention, the cooling of flue gas tubes can not be obtained by convection with a flow of air (relatively cold) as is the case in EP 675 321 and in the patent application FR 98/10350 filed August 7, 1998 by the Claimant; in this document indeed, peripheral nozzles of 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 features, which contribute to improving the compactness, simplicity and efficiency of the burner:

• the ratio of the length of the recirculation ducts 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 inner face of the walls of the hearth enclosure;
• the outlet orifice 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 outer surface thereof.

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

Preferably, the peripheral gas injection nozzles fuel and the associated flue gas pipes are three to twelve, in particular six to eight, arranged in a crown, regularly (angularly) distributed around the longitudinal axis (of general symmetry) of the burner.

Although the longitudinal axes of the peripheral nozzles and associated flues may extend cone divergently (at most 5 degrees), it is preferable that these axes are substantially parallel to the longitudinal axis of the burner.

In 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 closure shutters.

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 provided by the invention will be better understood at through the following description which refers to the accompanying drawings, which illustrate without any limiting character the preferential modes of embodiment of the invention.

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

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

FIG. 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.

FIG. 3 illustrates in longitudinal sectional view a heater of turbine outlet gas according to the invention.

The burner 1 (FIGS. 1 and 2) comprises a first ferrule cylindrical 2 longitudinal axis 3 horizontal, and a second ferrule cylindrical 4 coaxial with the first, which delimits a duct 5; the ferrule 2 defines a central duct 31 for air passage, 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 central part a central rod of transport of liquid fuel (in particular such as heavy fuel oil, diesel fuel, gasoline, oils, residual liquids ...) up to the equipped burner head a central nozzle 11 and a flame stabilizer 12, which are arranged at the front end of the duct 31 and the ferrule 2, and are salient at inside the fireplace 8; the burner further comprises a central rod 100 injection of gaseous fuel.

The burner comprises a bundle of six peripheral tubes 13 of transport of fuel gas, which are each equipped at their end before a nozzle 14 arranged protruding (for example prominent 1 centimeter) to the inner face 15 of the wall 7.

Part of the tubes 13 extends parallel to the axis 3 inside duct 5 for air transport; the tubes 13 are powered by a common collector 16, and pass through an annular flange 17 connecting ferrules 2 and 4; as illustrated in FIG. 2, the six identical nozzles 14 fuel gas ejection are angularly spaced 60 degrees.

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

Six straight sections 22 of circular section tubes, cut to right angle 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 ducts, which extends parallel to the duct 22 and which is itself welded (over its entire length) to the outer face of the end portion before the ferrule 2, according to generators thereof.

The axis of the tubes 22 coincides with the axis of the nozzles 14 and the end rear 24 identical sections 22 is disposed 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 orifice of the central duct 31.

With reference to FIG. 3, the burner 1 is mounted in a duct 200, of axis coincides with the 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 duct).

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

The burner is fixed in the duct 200 by means represented.

In both cases of operation, a supply of outside air (corresponding to 5% of the total air) is introduced via a conduit 106 for cool the central part of the burner where are located in particular the Stabilizer 105 of central (main) gas combustion flames injected through the central ducts 100 which pass through a deflecting rosette 104; the ducts 100 are fed by a collector 107.

In addition, the peripheral ducts 13 are supplied with gas fuel by a second collector 16; the flow of gaseous fuel injected by the peripheral nozzles is generally of the order of 90 95% of the total fuel flow. An advantage of the burner is that the jets of mixture coming out of the tubes 22 contribute to lengthen the flame, which which improves the efficiency of the gas heater and the installation of heat recovery, arranged downstream of the burner.

Claims (9)

1. Gaseous fuel burner (1), which comprises a central fuel transporting duct (10, 100), a central air transporting duct (2) surrounding the said central fuel duct, and several peripheral gaseous fuel transporting ducts (13), characterized in that the said peripheral ducts extend at least partly to the outside of the central air transporting duct, in that the burner further includes a straight portion of flue gas circulation duct (22) that lies in the extension of each nozzle (14) with which the peripheral ducts (13) are equipped and in that the flue gas intake ducts (22) are fixed by a link (101) to the air transporting duct (2), on the outside of the latter, and are not in contact with a stream of air, the ducts (22) being cooled by conduction via the said link (101).
2. Burner according to Claim 1, in which the ducts (22) are welded along their generatrices to a metal linking bar (101) which is welded to a generatrix of the duct (2), parallel to the latter.
3. Burner according to either of Claims 1 and 2, which includes a flame stabilizer (105) and a deflector (106) that are placed in the air duct (2, 31) near its end plane (112).
4. Burner according to any one of Claims 1 to 3, in which the upstream orifice (24) of each duct (22) is placed at a distance (25) from the corresponding nozzle (14) that is of the order of the diameter of the duct (22).
5. Burner according to any one of Claims 1 to 4, in which the outlet orifice (23) of the ducts (22) lies approximately in the transverse outlet plane (112) of the duct (2).
6. Burner according to any one of Claims 1 to 5,' in which the nozzles (14) and the ducts (2, 22) project into the hearth (8).
7. Burner according to any one of Claims 1 to 6, in which the flue gas circulation ducts (22) and the air transporting duct (2) are made of metal.
8. Heater for heating turbine gases transported by a duct (200) fitted with closure flaps (104), characterized in that it includes a burner according to any one of Claims 1 to 7.
9. Heater according to Claim 8, which includes a duct (106) for supplying air in order to cool the burner.

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