FR2766557A1 - LIQUID AND GASEOUS FUEL BURNERS WITH LOW EMISSION OF NITROGEN OXIDES - Google Patents

Abstract

A burner for liquid and gaseous fuel comprises a duct and central orifice for supplying primary air (4), means for injecting (8) of liquid fuel into a hearth (2) and arranged inside said orifice (4 ) central in the axis of the latter, a flame stabilizer (5) arranged coaxially inside this orifice (4) central, at least one orifice (13) for supplying secondary air situated outside the injection means (8) of liquid fuel and of the central primary air orifice (4), and injection means (7) of gaseous fuel arranged in a ring between the injection means (8) of fuel liquid and the at least one orifice (13) for supplying secondary air. According to the invention, said burner comprises a recirculation circuit (9, 10, 11) of the fumes from the hearth (2) by suction thereof outside the at least secondary air supply orifice (13) and reinjection into the hearth at the injection means (7) of the gaseous fuel.

Description

l

  LIQUID AND GASEOUS FUEL BURNERS

LOW EMISSION OF NITROGEN OXIDES

  The present invention relates to fuel burners

  liquids and gases with low emission of nitrogen oxides.

  The main application of the invention is its use to burn both a liquid fuel and a gaseous fuel while reducing the formation of nitrogen oxides for each of these fuels, which burner being intended to be mounted in the wall an enclosure such as the combustion chamber or hearth of an oven

or a boiler.

  Certain types of burners are certainly known in which the arrangement of the various supply and injection circuits are designed to minimize the formation of nitrogen oxides NO, NO2, but which are generally designed to burn essentially only one basic fuel either liquid or gaseous. We can cite for this, for example, patent applications filed by the same present applicant such as, as regards a gas fuel burner, patent application FR2718222 published on October 6, 1995 on "improvements to gas fuel burners with very low emission of nitrogen oxides "; in the introduction to this patent application, it is recalled, as for the present invention, that the nitrogen oxides are due to two different origins which are, one based on the oxidation of nitrogen from the air combustion itself (called thermal nitrogen oxide) which is the one essentially produced with gaseous fuels, and the other due to the oxidation of nitrogen compounds existing in the fuel during pyrolysis inside the flame (called nitrogen oxide

  fuel) and which mainly concerns liquid fuels.

  Thus, in the case of the patent application recalled above which applies to gaseous fuels, it has mainly been sought to reduce the thermal nitrogen oxide, on the one hand by reducing the temperature of the flame by a staging of the combustion thanks to separate fuel inlets and on the other hand, by reducing the oxygen content of the flame by recombining and recirculating the fumes produced in the hearth with the combustion air according to an arrangement

  particular injection ports.

  In other patent applications such as EP774620 entitled "Burner with liquid or gaseous fuel with very low emission of nitrogen oxides", the main objective is to reduce the combustible nitrogen oxide especially for use with fluid fuel by using, on the one hand, air supply staging devices, and on the other hand by separating the injection of the fuel into several independent and divergent flames so that they receive an air flow additional after a first combustion phase thanks to the air supply stage; in this patent application, it is certainly mentioned that it is also possible to add gas fuel rods, but the burner does not include any specific device for reducing thermal nitrogen oxide, which makes such a device less

  effective in mixed use.

  The problem posed is in fact to be able to produce a burner which is truly mixed, that is to say both liquid and gaseous fuel, which can operate separately or at the same time, and in which the formation of nitrogen oxides both of thermal origin and combustible for gas and for liquid, is minimized with performances which one obtains with no

device known to date.

  A solution to the problem posed is a liquid and gaseous fuel burner comprising a central primary air supply duct and orifice, means for injecting liquid fuel into a hearth and disposed inside said central orifice in the axis of the latter, a flame stabilizer disposed coaxially inside this central orifice, at least one secondary air supply orifice situated outside the means for injecting liquid fuels and the central orifice of primary air, and means for injecting gaseous fuels arranged in a ring between the means for injecting liquid fuels and the at least orifice for supplying secondary air; according to the invention this burner comprises

  a circuit for recirculating the smoke from the hearth by suctioning it

  ci outside the at least secondary air supply orifice and reinjection into the hearth at the injection means of the

gaseous fuel.

  It will be noted that such a solution borrows part of the elements described and known in patent application EP774620 which can be considered as the closest prior art, and in which a circuit for recirculating the smoke from the hearth which was combined was combined. known otherwise such as patent application FR2718222 but according to a specific provision making it possible to obtain a real mixed burner, while the previous devices, using the recirculation of the fumes, were dedicated only to gas fuel burners. In particular, it will be noted in the embodiments described below, that the suction of the fumes is carried out externally to any fuel and air injection pipe. In addition, according to a preferred embodiment, the smoke recirculation circuit of the hearth according to the present invention comprises at least one common wall of heat exchange with the secondary air supply and distribution circuit, which makes it possible to cool. such fumes before they are reinjected into the hearth and therefore improves the performance of the burner. The result is new mixed burners for liquid and gaseous fuels, not liquid or gaseous, which offer both thermal and combustible nitrogen oxide reduction characteristics, thus combining the effects of all the demands of patents such as those cited above, with an additional resulting effect since allowing to operate such a burner, not only with one of the gaseous or liquid fuels, but also with both at the same time, while limiting the nitrogen production from both fuel sources. Such burners can also be used with only one of the two fuel sources, making the latter benefit from the supply arrangements which were originally intended for the other fuel but which can only be beneficial for the other. In particular, for use as a gas burner alone, the staging of air in addition to that of the gas supply, although not specifically necessary for such a fuel, however improves its performance: in fact it reduces also the production of combustible nitrogen oxide in addition to that of thermal origin, the production of which is also reduced thanks to the recirculation of the fumes and by the staging of the injection of the

fuel itself.

  We could cite other advantages of the present invention but those cited above already show enough to prove the

novelty and interest.

  The description and the figures below represent an example of

  embodiment of the invention but are not limiting in nature: other embodiments are possible within the scope of the scope of this invention, in particular by using supply systems

  in primary air as well as in gaseous fuels etc ... different.

  Figure 1 is a simplified sectional view along II 'of the figure

  2 and passing through the longitudinal axis XX 'of the burner according to the invention.

  Figure 2 is a front view of the burner of Figure 1 from

inside the foyer.

  Such a burner comprises, in a known manner as described in patent application EP774620, a duct with a central orifice for supplying primary air 4, means 8 for injecting liquid fuel into the hearth 2 and arranged at the inside said central orifice 4 in the axis of the latter, a flame stabilizer 5 arranged coaxially inside this central orifice 4, and at least one orifice 13 for supplying secondary air situated outside the means of injection 8 of liquid fuel and of the central primary air orifice 4; injection means 7 for gaseous fuel are also arranged, but here without being optional since they are necessary, in a ring between the injection means 8 for liquid fuel and the at least

  orifice 13 for supplying secondary air.

  Said orifice 13 for supplying secondary air may be constituted by a single annular passage or made up of several supply conduits also disposed along the same diameter in a ring, outside said injection means 7, 8,

  gaseous and liquid fuels respectively.

  As shown in Figures i and 2, said liquid and gaseous fuel burner according to the invention, comprises a ring 31 of refractory material comprising all of the air supply, fuel injection and recirculation orifices smoke, it is mounted through the refractory wall 1 of the hearth 2 so that its front face, through which open said

  orifices, or projecting therefrom.

  According to the accompanying figures, the secondary air supply is carried out by multiple orifices 13 which are placed peripherally in staggered rows between the orifices 14 for sucking the fumes in the hearth 2; these suction orifices 14 can themselves be replaced by a single peripheral annular passage, but the arrangement in multiple orifices staggered makes it possible to avoid re-aspirating the secondary air in said smoke suction orifices and vice versa. avoid this secondary air supply preventing said fumes from being sucked up to be recirculated in the head

of the burner.

  On the other hand, according to the invention, these two fluids exchange their calories, but inside the burner, thanks in particular to at least one common wall 10 separating: - on the one hand a box 10 for distributing said fumes recirculated, fed on one side by the suction orifices 11 of said smoke in the hearth 2, and reinjecting the latter, after therefore cooling, in conduits 9 for reinjection into the hearth, through which also the means of injection 7 of the gaseous fuel, - on the other hand, a distribution box 14 for the secondary air, which on one side is supplied by a supply duct 12 and a

  on the other hand, after this secondary air has warmed up, injects it

  ci in the hearth by the orifices 13 as defined above.

  Said means 7 for injecting gaseous fuel and said means for re-injecting fumes which preferably are coaxial and have their orifices 9 combined, are located in a peripheral ring around the flame stabilizer 5 of the liquid fuel. To create a staging of the air intake with respect to the flame of the liquid fuel, all of the injection orifices for this fuel as well as those for the gaseous fuel, and for the supply of primary air, opens out at the bottom d 'a bowl 6; the latter is disposed in a hollow relative to the refractory wall 3 which surrounds it and through which open said secondary air supply orifices 13 and the fumes from the hearth 2 are also sucked in. Said bowl can be of different shapes, as in section according to Figure 1 in a truncated cone, and as the rest this is described in the patent application

EP774620.

  The injection means 7 for the gaseous fuel can be, on the one hand, separate supply rods arranged in a ring around the injection means 8 for the liquid fuel as shown in FIG. 1; said injection rods 7 can be located in the primary air supply duct 4, or be replaced by nozzles mounted on a single ring also disposed peripherally in a ring around the injection means 8 of the

  liquid fuel, and supplied by a single supply rod 7.

  As regards the means 8 for injecting the liquid fuel, these may include multiple orifices thus creating several independent flames in the hearth 2 which can either be directed parallel to the axis XX 'of the burner, or divergent and oriented towards the supply ports 13 for secondary air to improve the combustion of said liquid fuel after a first phase of combustion with primary air; such a divergence of flames, being less necessary as regards the gaseous fuel. Other improvements and additional devices could be added to such a burner according to the invention, using characteristics already described in the previous patent applications of the same applicant such as those mentioned in the introduction: such additional characteristics being already described in these requests for

  patent, need not be repeated in this description but

  could in no case be considered as patentable improvements, since any person skilled in the art knowing all of this prior art, could make such improvements without departing from the scope of this patent application and

  without showing inventive step.

Claims (10)

  1. Burner for liquid and gaseous fuel comprising a duct and central orifice for supplying (4) primary air, means for injecting (8) of liquid fuel into a hearth (2) and disposed inside said orifice ( 4) central in the axis of the latter, a flame stabilizer (5) arranged coaxially inside this central orifice (4), at least one orifice (13) for supplying secondary air located outside injection means (8) of liquid fuel and the central primary air orifice (4), and injection means (7) of gaseous fuel arranged in a ring between the injection means (8) of liquid fuel and the at least orifice (13) for supplying secondary air, characterized in that it comprises a recirculation circuit (9, 10, 11) of the flue gases from the hearth (2) by suction of these to the of the at least secondary air supply orifice (13) and reinjection into the hearth at the level of the means   injection (7) of the gaseous fuel.   2. Burner according to claim 1, characterized in that the injection means (7) of gaseous fuel open into the   orifices (9) for reinjecting the fumes into the hearth (2).   3. Burner according to any one of claims 1 or 2,   characterized in that the smoke recirculation orifices (9) are   located in the peripheral ring around the flame stabilizer (5).   4. Burner according to any one of claims 1 to 3,   characterized in that all of the injection ports for liquid and gaseous fuels and for supplying primary air open out at the bottom of a cavity (6) disposed in hollow relative to the refractory wall (3) which surrounds and through which the orifices (13) of secondary air supply open and the fumes are sucked of the hearth (2).   5. Burner according to any one of claims 1 to 4,   characterized in that the means (8) for injecting liquid fuel have multiple orifices creating several flames independent in the foyer (2).   6. Burner according to claim 5, characterized in that the said independent flames are divergent and oriented towards the   secondary air supply ports (13).   7. Burner according to any one of claims 1 to 6, characterized in that the injection means (7) of the gaseous fuel   have separate supply rods arranged in a ring around the injection means (8) of the liquid fuel. 8. Burner according to any one of claims 1 to 7, characterized in that the smoke recirculation circuit of the hearth (2)   has at least one common wall (101) for heat exchange with the secondary air supply and distribution circuit (4). 9. Burner according to any one of claims 1 to 8,   characterized in that the secondary air supply orifices (13) are placed peripherally in staggered rows between the orifices (14)   smoke extraction in the fireplace (2). 10. Burner according to any one of claims 1 to 9,   characterized in that it comprises a ring (31), made of refractory material characterized in that lomotunana (3) enmerareacae comprising all of the air supply orifices, fuel injection and smoke recirculation orifices, which ring (31), being   mounted through the refractory wall of the hearth (2) so that its front face projects from it.