FR2641365A1 - METHODS AND DEVICES FOR FINALLY SPRAYING LIQUID FUEL AND BURNERS EQUIPPED WITH SUCH DEVICES - Google Patents

Abstract

The invention relates to methods and devices for finely atomizing a liquid fuel and to burners equipped with these devices. A burner according to the invention comprises a primary spray head 1 which delimits a chamber 2 in which a liquid fuel is mixed with a compressed auxiliary fluid, which head is equipped with primary nozzles 3 from which a jet 4 of atomized fuel emerges. The burner further comprises a secondary spray head 5 which is provided with secondary nozzles 6 which are coaxial with the primary nozzles and which have a diameter greater than that of the primary nozzles. The two heads define between them an intermediate space 7 and the burner comprises means for sending an auxiliary fluid into this space which fluid expands through the secondary nozzles. One application is the construction of pulverized solid fuel burners avoiding liquid unburnt.

Description

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  Methods and devices for finely atomising liquid fuel and equipped burners

of these devices.

DESCRIPTION

  The present invention provides methods and devices for finely spraying liquid fuel and liquid fuel burners equipped with a liquid fuel device.

Advanced spraying.

  The technical field of the invention is that of the construction of burners of liquid fuel sprayed by an auxiliary fluid. Pulverized liquid fuel burners are known or

atomized by an auxiliary fluid.

  Such burners are described, for example, in patent FR A 1 305 391, in the publication FR A 2 288 940 and FR A 2 520 484.

  (General Industrial Heating Company Pillard).

  All these burners comprise one or more internal mixing chambers or mixing channels into which the liquid fuel and a pressurized auxiliary fluid which is

  usually compressed air or water vapor.

  The mixing chamber or the mixing channels open into a combustion chamber through orifices from each of which emits a spray of atomized or atomized fuel. The spraying of the liquid is due to a significant difference in velocity between the auxiliary fluid, of low density, which is strongly compressed and which relaxes under the effect of the pressure difference between the mixing chamber and the combustion chamber and the liquid fuel, higher density. It is actually a di-phasic flow, composed of very fine droplets of liquid suspended in the gas. The difference between the speeds of the two phases causes a tearing of the liquid film which bursts into fine droplets. The mixture thus obtained is sometimes called, wrongly, an emulsion whereas it is, in fact, an aerosol, that is to say a

  suspension of liquid droplets in a gas.

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  The quality of combustion, especially the proportion of unburnt carbonaceous solids found in soot, depends very much on the quality of the spray and the fineness of the droplets.

liquid fuel.

  Studies have shown that most of the mass of unburnt carbonaceous solids resulting from the combustion of pulverized liquid fuels consists of large diameter hollow carbonaceous particles, known as "cienospheres", which result from gasification and thus incomplete combustion of gases. larger liquid droplets. The complete combustion time of a droplet of liquid fuel depends on the diameter of the latter and

the nature of the fuel.

  Thus, in cold-walled fireplaces, the larger droplets do not burn fast enough to be completely burned before reaching the cold walls and they give rise to uncombusted carbon residues by a quenching effect. This phenomenon is

  all the more important as the liquid fuel is heavier.

  It is therefore well known to thermists that to reduce the rate of unburnt solids generated by a sprayed liquid fuel burner, it is necessary to use improved spraying means that avoid or minimize the production of large diameter droplets. for example droplets having a diameter of the order of 30 to 100 pm and reduce the maximum diameter of the droplets. Thus, if the diameter of the larger droplets is reduced, the quenching effect is reduced in contact with the cold walls and the reduction of the unburnt carbon content is all the more important when the flame is in a combustion chamber. cooled walls, that the walls are closer to the flame and that the fuel

is heavier.

  In the known burners, the outlets of the jets of pulverized liquid fuel are generally located at the end of a duct or nozzle of varying length in which a wall effect occurs which causes the formation of a film of fuel.

  liquid against the wall of the duct or nozzle.

  As a result of a capillary action and surface tension this film has a tendency to collect liquid while it is sought on the contrary to divide it into fine droplets. This film moves towards the outlet orifice and is drawn towards the combustion chamber in the form of droplets whose diameter is much greater than that of the droplets contained in the jet that leaves through the orifice. For example, the droplets of the jet have a diameter of 5 or 10 pun while the droplets due to the film drive have a diameter of 30 to 100 pm. Most of the larger droplets entering the building chamber are due to this wall effect. In addition, when it arrives in the combustion chamber, the liquid film tends to follow the internal walls of the combustion chamber where it escapes the drive by the jet. If it is a heavy or extra heavy fuel then it gives birth around the nose of the burner to deposits of coke or unburned tar agglomerates. In order to improve the quality of the spraying, spray nozzles have been proposed in which the liquid fuel is injected axially - and the auxiliary fluid is injected tangentially so that a helical movement occurs.

in the nozzle.

  This helical movement creates a centrifugal force which tends to cause drops of liquid against the wall where they form a

  film that eventually leads to the formation of large droplets.

  The object of the present invention is to provide improved spraying means and burners equipped with these spraying means which make it possible to improve the fineness of the fuel droplets, to reduce the amount of droplets of

  large diameter and the diameter of the largest droplets.

  A method according to the invention for finely pulverizing a liquid fuel is of the known type according to which said liquid fuel is mixed with a compressed auxiliary fluid in a chamber or in mixing ducts, which chamber or which ducts have outlet orifices which open out. in a combustion chamber and from each of which emerges a jet of pulverized fuel. The object of the invention is achieved by a method according to which there is disposed, in front of each of the outlet orifices, a secondary nozzle which has a diameter greater than that of said outlet orifice.

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  and which is coaxial with said orifice and injected into said secondary nozzle a compressed auxiliary fluid at a pressure sufficient to expand with a speed greater than the speed of the peripheral layers of the pulverized fuel jet exiting said orifice. A liquid fuel sprayer according to the invention is of the known type comprising one or more primary nozzles from which jets of pulverized fuel emerge, and it is characterized in that it further comprises, in front of each of the primary nozzles, a secondary nozzle which is coaxial with the primary nozzle and which has a diameter greater than the diameter of the primary nozzle and further comprises means for injecting into the secondary nozzles an auxiliary fluid sufficiently compressed to relax with a speed higher than the speed of the layers

  outflow devices from the primary nozzle.

  A burner according to the invention is of the known type comprising a primary spraying head which delimits a mixing chamber in which said liquid fuel and a pressurized auxiliary fluid are introduced, and further comprising primary spray nozzles each having an orifice. exit from which a jet comes out

of pulverized fuel.

  A burner according to the invention further comprises a secondary spray head which envelops said primary spray head, which secondary head carries a plurality of secondary nozzles, each of the secondary nozzles being coaxial with a primary nozzle and having a diameter greater than the diameter of the outlet orifice of said primary nozzle and said burner further comprises means for injecting an auxiliary fluid into said nozzles

  secondary, around the jets coming out of the primary nozzles.

  The invention results in fuel sprays

  Advanced liquid and burners equipped with these sprayers.

  The sprayers according to the invention make it possible to atomize the droplets which are at the periphery of the jets issuing from the primary nozzles and thus to obtain jets of pulverized fuel in which the quantity and the diameter of the largest droplets are reduced, which allows to reduce unburned solids

  soot generators and deposits.

  The following description refers to the accompanying drawings which

  represent, without any limiting nature, exemplary embodiments of sprayers according to the invention and heads of

  burners equipped with these sprayers.

  Figure 1 is an axial half-section of a sprayer according to the invention. FIG. 2 is an axial section of a burner head according to

The invention.

  FIG. 3 is an axial section of the spray head of FIG.

burner according to Figure 2.

  Figures 4 and 5 are an axial section and a half view of

  face of the distributor of a burner according to Figure 2.

  FIG. 6 is an axial section of a second embodiment of FIG.

  production of a burner according to the invention.

  Figure 7 is an axial section of the burner distributor

according to Figure 6.

  Figures 8 and 9 are front views of the dispenser according to

VIII and IX IX of Figure 7.

  FIG. 10 is an axial section of a first variant of FIG.

  production of a burner head according to FIG.

  Figure 11 is an axial section of a second variant.

  Figure 12 is an axial section of a third variant.

  Figure 13 is a fourth variant axial section.

  Figure 14 is an axial section of a spray head.

  FIG. 1 represents a partial axial half-section of a spray head 1 situated at the front end of an axis burner xxi. The head 1 defines a mixing chamber 2 into which is sent, by any known means, a liquid fuel and a pressurized auxiliary fluid. The head comprises nozzles or nozzles or injection ducts 3 which open out through an outlet orifice 3a into a combustion chamber where a pressure is generally close to the atmospheric pressure and in all cases substantially less than the pressure of the auxiliary fluid contained in the mixing chamber 2. Under the effect of the pressure difference the auxiliary fluid expands through the nozzles 3 so that it leaves each of these

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  nozzles a jet 4 of pulverized fuel that is a suspension of

  fine droplets of liquid in a jet of gas.

  An improved sprayer according to the invention further comprises an auxiliary head 5 which is placed in front of the usual head 1. The auxiliary head 5 carries secondary nozzles 6 which have a diameter greater than the diameter of the outlet orifices 3a and which are coaxial with the conduits or nozzles 3 so that the jets 4 from the orifices 3a pass through the secondary nozzles 6 to penetrate

in the combustion chamber.

  The auxiliary head 5 delimits, with the head 1, an auxiliary chamber 7 into which an additional auxiliary fluid is sent which may be the same as the auxiliary fluid sent into the mixing chamber 2. This auxiliary fluid expands through the auxiliary nozzles 6 and it is compressed at a pressure such that its speed

  output is greater than the peripheral speed of the jet 4 that is

  say at the speed of the layers located at the periphery of the jet.

  Thus, the spraying defects of the jet leaving the orifice 3a are corrected by the expansion of the additional auxiliary fluid whose effect is concentrated on the periphery of the initial jet.

  localized droplets of larger diameter.

  This method is applicable to any type of auxiliary fluid sprayer and outlet nozzles to improve the smoothness of the spray. Figure 2 is an axial section of a fuel burner

  liquids equipped with a spray head according to the invention.

  This burner comprises in known manner a body 8 which is pierced

an axial channel 9.

  The rear end of the axial channel 9 communicates with a pipe 10 through which a liquid fuel arrives, by

  example of fuel oil or heavy oils.

  The body 8 has two series of parallel channels 11 and 12

  which are arranged on two circles.

  The rear ends of the ducts 11 and 12 open into circular chambers which communicate with a second pipe 13 through which a highly auxiliary fluid arrives.

  compressed, for example compressed air or water vapor.

  The burner further comprises a spray head 14 located at the front end and a distributor 15 interposed between the spray head 14 and the body 8. It comprises a cap 16 which is screwed onto the body 8 and which carries a shoulder 17 which is supported against the periphery of the spray head 14. It consists of two parts a primary multi-nozzle head 18 and a secondary multi-nozzle head 19 which is placed in front of the primary head and

  which comes to bear against a shoulder of it.

  The shoulder 17 of the assembly cap bears against

  the periphery of the secondary head 19.

  The primary multi-nozzle head 18 delimits a cavity 20 from which a plurality of cylindrical nozzles 21 extend which are arranged on a cone which diverges forwards. Channels 22 are drilled in the thickness of the body of the primary head and each of the channels 22

opens into one of the nozzles 21.

  The liquid fuel that fills the chamber 20 passes through the nozzles 21 where it mixes with the auxiliary fluid arriving via the ducts 22, which produces the spraying of the liquid coming out of the tubes.

  primary nozzles 21 in the form of jets. Such burners are known.

  A burner according to the invention further comprises a secondary multi-nozzle head 18 which carries a plurality of secondary cylindrical nozzles 23. The number of secondary nozzles 23 is equal to the number

primary nozzles 21.

  The secondary nozzles have a diameter greater than the diameter of the primary nozzles. The secondary nozzles are arranged opposite

  primary nozzles and are coaxial with these.

  The secondary head 19 delimits with the primary head 18 an intermediate space 24 which has the shape of a conical chamber in

  which open the primary nozzles and the secondary nozzles.

  Figures 4 and 5 represent respectively an axial section

  and a half front view of the dispenser 15.

  The dispenser is in the form of a cylindrical ring which is traversed from one end to the other by two series of longitudinal channels 25

and 26 arranged on two circles.

  At its front end the distributor has two concentric circular grooves, a groove 25a into which the

  channels 25 and a groove 26a in which the channels 26 open.

  At its rear end the distributor 15 also comprises two concentric circular grooves 25b and 26b in which

  respectively open channels 25 and 26.

  The groove 25b communicates with the channels 12 of the body while the groove 26b communicates with the channels 11 of the body. The groove 25a communicates with the channels 22 of the primary head and feeds them with auxiliary fluid. The groove 26a communicates with the conical chamber 24 and also feeds it with auxiliary fluid. The number of channels 25 is greater than the number of channels 26, by

  example the distributor comprises 18 channels 25 and 12 channels 26.

  The pressure drop experienced by the auxiliary fluid circulating in the channels 25 and 22 is greater than the pressure drop of the auxiliary fluid circulating in the channels 26 so that the pressure of the fluid in the chamber 24 is such that the expansion of the auxiliary fluid through the secondary nozzles 23 is at a speed

  greater than the speed of the jets exiting the primary nozzles 21.

  FIG. 6 is an axial section of an alternative embodiment of a burner according to FIG. 2. The homologous parts are designated

by the same references.

  The injection head comprises a primary head 18 which defines a mixing chamber 20 which receives on the one hand a liquid fuel which circulates in an axial duct 9 and which penetrates axially into the chamber 20 and on the other hand an auxiliary fluid which circulates in conduits 12 and which penetrates tangentially into the chamber 20 in

  which it enters passing between fins 27.

  The primary head 18 carries a plurality of cylindrical nozzles 21

  from which jets of pulverized fuel emerge.

  The injection head further comprises a secondary head 19 which is provided with a plurality of cylindrical nozzles 23 which are aligned with the nozzles 21 and which have a diameter greater than that of the nozzles 21. The primary and secondary heads define between them a chamber 24 into which the primary nozzles 21 and the

secondary nozzles 23.

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  The auxiliary fluid that arrives through the ducts 12 penetrates radially into the intermediate chamber 24 via a passage

  device that is equipped with fins 28.

  The passages equipped with fins 27 and 28 are part of a room 29 called emulsifier which is immediately behind the head

  injection and around the mixing chamber.

  Figure 7 shows an axial section of the part 29 on which we see the mixing chamber 20 and the passages equipped with fins 27 and 28. Figures 8 and 9 show side views

of Figure 7.

  FIG. 10 is an axial section of an alternative embodiment of a burner according to FIG. 6. The only difference lies in the fact that the primary nozzles 21 and the secondary nozzles 23 are tapered and converge towards the front, which allows to obtain better results than those obtained with cylindrical nozzles. FIG. 11 is an axial section of another alternative embodiment of a burner according to FIG. 6. In this variant, the primary spraying head 19 carries primary nozzles 21 which are conical and which converge forward while the secondary spray head 18 carries secondary nozzles 23 which are also conical but which diverge forwards. Advantageously, the angle of conicity of the secondary nozzles 23 is substantially equal to the opening angle of the jets exiting the primary nozzles. This inverted arrangement of the conicity of the nozzles makes it possible to optimize the secondary spraying and the exchange of the qualities of movement between the primary jet and the additional auxiliary fluid which expands at

through the secondary nozzles.

  The choice of auxiliary fluid passage sections through the passage 28 and the sections of the secondary nozzles 23 makes it possible to adjust and optimize the auxiliary fluid consumption.

  secondary and the quality of the spray.

  The fact that the burner comprises a separate and interchangeable part 29 makes it possible to easily modify the passage section of the

auxiliary fluid.

  Figure 12 shows an axial section of a third

  variant embodiment of a burner according to FIG.

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  According to this variant, the primary spraying head 18 which surrounds the mixing chamber 20 as well as the secondary head 19 both have a hemispherical and concentric general shape, which makes it possible to produce the primary nozzles 21 and the secondary nozzles 23 by drilling holes. and by varying the angle a that the axes of the holes make with the axis xx1 of the burner as well as the diameters dl

  primary nozzles and d2 secondary nozzles.

  FIG. 13 represents an alternative embodiment of a burner according to FIG. 12 in which the primary and secondary injection heads comprise a first group of n1 primary nozzles 211 and secondary nozzles 231 which are arranged on an opening cone and a second group of n2 primary nozzles 212 and secondary 232 which are arranged on a second opening cone 3 angle B being different

from the angle a.

  This arrangement allows staging the combustion. If the sections of the secondary nozzles 231 and 232 are identical, the absolute output speeds of the auxiliary fluid are also identical, on the other hand, the axial components V1 and V2 of the streams leaving the two groups of

  secondary nozzles are not the same.

  Fuel injection can be staged by choosing the numbers n1 and n2 of nozzles in each group, the nozzle sections of the two groups and the angles a and p so as to reduce the production of nitrogen oxides, for example by increasing the axial velocity Vl of the jets exiting the nozzles of the first group which correspond to a lower angle α and decreasing the axial velocity V2 of the jets coming out of the nozzles of the second group which correspond to a larger angle F. According to one embodiment, the diameters of the primary nozzles (211, 212) of the two groups are different as are the diameters of the secondary nozzles (231, 232). According to another embodiment, all the primary nozzles (231, 232) have the same diameter and the

  The diameters of the secondary nozzles (231, 232) are different.

  Figure 14 is an axial section of a spray head according to the invention which is composed of a primary head 18 and a secondary head 19 which surrounds the primary head. The primary head delimits a mixing chamber 20 which carries the primary nozzles 21 while the secondary head carries secondary nozzles

  23 aligned with the primary nozzles.

  The chamber 20 is limited by a flat bottom 20a which is perpendicular to the axis xx1 of the burner and the inlet orifices of the primary nozzles 21 are advantageously located as close as possible to the flat bottom 20a, that is to say on the periphery of the this one, where the

  flat bottom is attached to the inclined walls that delimit the room.

  This position has the advantage of avoiding flow

pulsatory and di-phasic.

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Claims (15)

  A method for finely pulverizing a liquid fuel in which a pressurized auxiliary fluid is mixed in a chamber (2) or ducts with said liquid fuel, which chamber or ducts have outlet orifices (3a) which open into the chamber. a combustion chamber and each of which outputs a jet of pulverized fuel characterized in that is disposed in front of each of the outlet ports (3a) a secondary nozzle (6) which has a diameter greater than that of said orifice outlet (3a) and which is coaxial therewith, and is injected into said secondary nozzle a compressed auxiliary fluid whose output speed is greater than the peripheral speed of the jet out of said orifice. 2. A pulverized liquid fuel burner, of the type comprising a primary spraying head (18) defining a mixing chamber (20) in which said liquid fuel and a pressurized auxiliary fluid are introduced, and comprising primary spray nozzles ( 21) each having an outlet orifice from which a jet of pulverized fuel is discharged, characterized in that said burner comprises a secondary spray head (19) which envelops said primary spray head, which secondary head carries a plurality of secondary nozzles (23). , each of the secondary nozzles being coaxial with a primary nozzle and having a diameter greater than the diameter of the outlet orifice of a primary nozzle and said burner further comprises means for injecting an auxiliary fluid into said secondary nozzles, around outgoing jets primary nozzles.   3. Burner according to claim 2 characterized in that the secondary fluid which is injected through said secondary nozzles is compressed to a sufficient pressure so that it relaxes in said secondary nozzles with a speed greater than the speed   peripheral layers of said jets.   4. Burner according to any one of claims 2 and 3   characterized in that said secondary spray head (19) delimits with said primary spray head (18) an intermediate cavity (24) into which said primary nozzles (21) and from which said secondary nozzles (23) bear, and said burner comprises means for sending into said cavity the same auxiliary fluid as that which is sent into said primary nozzles.   5. Burner according to any one of claims 2 and 4   characterized in that said primary (21) and secondary nozzles (23) are cylindrical.   Burner according to one of Claims 2 and 3   characterized in that said primary nozzles (21) are frustoconical and converge towards the outlet and said secondary nozzles (23) are   also frustoconical and converge towards the exit.   Burner according to one of Claims 2 to 4   characterized in that said secondary nozzles (23) are   frustoconical and diverge towards the exit.   Burner according to Claim 7, characterized in that the angle of conicity of the secondary nozzles is substantially equal to   the opening angle of the jets (4) coming out of the primary nozzles.   Burner according to one of Claims 2 to 8   characterized in that said mixing chamber (20) has a flat bottom (20a) which is perpendicular to the axis (xxl) of the burner and the inlet ports of said primary nozzles (21) are in contact with the periphery said flat bottom (20a) so as to avoid flow pulsatory and di-phasic.   Burner according to one of Claims 2 to 8   characterized in that the front wall of said primary head (18) and the front wall of said secondary head 19 are portions of concentric spheres.   Burner according to Claim 10, characterized in that the said primary and secondary injection heads comprise two groups of nozzles, the axes of which are arranged on conical surfaces forming with the axis (xx1) of the burner of the angles. ) different. Burner according to Claim 11, characterized in that the   nozzle diameters of the two groups are different.   13. Burner according to claim 11 characterized in that the diameters of the primary nozzles (21) of the two groups are identical while the diameters of the secondary nozzles (23) of the two groups are different.   14. Burner according to any one of claims 4 to 13   characterized in that it comprises, at the rear of the spray head, an interchangeable distributor (15, 29) which comprises passages (25, 26, 27, 28) for an auxiliary fluid supplying on the one hand said cavity intermediate (24) and on the other hand said mixing chamber (20) or channels (22) which open into said primary nozzles (21).   15. A liquid fuel sprayer comprising one or more primary nozzles (3) from which jets (4) of sprayed liquid zombustible, characterized in that it comprises, in front of each of said primary nozzles, a secondary nozzle (6) which is coaxial with said primary nozzle and which has a diameter greater than that of said primary nozzle and it further comprises means for injecting into said secondary nozzles an auxiliary fluid sufficiently compressed to expand with a speed greater than the speed of the peripheral layers of said jet (4) coming out of the primary nozzle.