Burner for the combustion of fluid fuels

Abstract: According to the invention the burner for the combustion of combustible fluids foresees below the atomizing nozzle (2) and in correspondence with the area of the combustion flue a plurality of slits (8, 68, 78) which are aligned along their longer axis in the circumferential direction of the combustion flue and are arranged in one or more rows near the area of maximum depression. According to a preferred embodiment , the slits are made in the combustion flue. According to another embodiment the slits (78) are made in correspondence with the transversal cross-section, wherein the combustion flue (75) joins the inlet duct (74). According to another embodiment the slits (68) are made in a ring-shaped crown arranged in correspondence with the transversal cross-section, wherein the combustion flue (65) joins the inlet duct (64).

Description: The invention concerns a burner for the combustion of fluid fuels. It is a known fact that one of the methods used in order to decrease the amount of NO x in the combustion fumes is to recycle the fumes themselves within a combustion chamber of the burner, so as to burn up the uncombusted particles present in the fumes. With this purpose burners with an extended head have been developed, wherein the flue of the burner presents a series of openings distributed along the periphery in correspondence with a right section, through which a part of the fumes produced by the combustion process goes back into the burner. Thereby a reduction of the partial oxygen pressure is obtained with a corresponding decrease of the flame temperature and a decrease of the amount of NO x of thermic origin. The burner built following the mentioned principles is known and it constitutes the object of the patent application EP-A-410135. Said burner presents a plurality of slits, made around the periphery of the combustion flue and arranged in the area near the diaphragm separating the combustion flue from the air inlet duct, said slits being arranged with their longitudinal axis parallel to or slanted in relation to the longitudinal axis of the combustion flue. However, a burner built following the teachings of the mentioned patent application does not yet guarantee an optimum performance, although it reaches the purpose of decreasing the production of NO x . In fact, it is a known fact that the pressure in the combustion flue varies at different levels and it presents a minimum (negative) value near the choke of the diaphragm, a positive value near the outlet of the combustion flue and a null value in correspondence with an inversion spot located at an intermediate position of the combustion flue itself. More specifically, starting from the minimum negative value of the pressure, the latter increases gradually in the longitudinal direction of the flue, starting from the diaphragm and going toward the outlet. However, when the slits are arranged with their longitudinal axis aligned with the longitudinal axis of the combustion flue, the depression value permitting the re-cycling of the fumes through the slits is the average depression value existing at each of the spots corresponding with the light of the slits. When, however, the slits - their length remaining the same - are arranged at a slanted position in relation to the axis of the combustion flue, said average depression value increases slightly, but is, however, always lower than the maximum depression value which is present near the diaphragm. The purpose of the present invention is to obtain an improved burner for the combustion of fluid fuels which, in accordance with the main claim includes; a nozzle for the atomizing of the fuel connected with the external distribution main and a duct for the inlet of the combustion air surrounding the nozzle for the conveyance of the air/fuel mixture to a combustion flue, which is co-axial and aligned with the inlet duct; a diaphragm arranged transversally in relation to the inlet duct and the combustion flue, complete with a choke having a smaller cross-section than the diameter of the duct and of the flue and arranged co-axially in relation to the atomizing nozzle; a plurality of slits within the burner below the choke of the diaphragm after the atomizing nozzle, said slits creating the communication between the outside environment and the interior of the combustion flue, and is characterized in that said slits belong to the combustion flue and are aligned along their longer longitudinal axis in the circumferential direction with the combustion flue and are arranged in one or more rows near the area of maximum depression. According to a preferred embodiment the inlet duct and the combustion flue have the same diameter and the slits are arranged in a single row on the lateral surface of the combustion flue. According to a different embodiment, the inlet duct presents a smaller diameter than the combustion flue and the slits are arranged in correspondence with the transversal cross-section wherein the combustion flue joins the inlet duct, the air space which is thus created between them being divided by spacing elements arranged radially between the duct and the flue and attached to them. According to yet another embodiment, the inlet duct presents a smaller diameter than the combustion flue and the slits are arranged in a ring-shaped crown arranged in correspondence with the transversal cross-section, wherein the combustion flue and the inlet duct join together. In this embodiment, too, the slits are located near the straight section where the depression is at its maximum value. In all the described embodiments the slits are located near the straight section of the burner, where the depression is at its maximum value. Advantageously, within the thus improved burner according to the invention, the re-cycling of the combustion fumes is improved and immediate and, as a consequence, there occurs a decrease of the NO produced, as compared with equivalent burners. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description and from the drawings, wherein: Fig. 1 shows in a transversal cross-section the burner according to the invention; Fig. 2 represents the course of pressure build-up in the longitudinal direction of the burner of Fig. 1; Fig. 3 shows a different embodiment of the burner according to the invention; Fig. 4 represents another view of the different embodiment of Fig. 3; Fig. 5 shows yet another embodiment of the burner of the invention; Fig. 6 represents another view if the embodiment of Fig. 5. As can be observed in Fig. 1, the improved burner according to the invention, indicated as a whole with 1, consists essentially of an atomizing nozzle 2 which is connected with the outside fuel distribution main through a duct 3. A duct 4 for the inlet of the combustion air surrounds the nozzle and conveys the air/fuel mixture into a combustion flue 5, which is arranged co-axially to and aligned with the inlet duct 4. A diaphragm 6, complete with a choke 7 having a smaller cross-section than the diameters of the duct and the flue in correspondence with the atomizing nozzle 2 is positioned within the burner 1 and arranged transversally in relation to the same in correspondence with the cross-section wherein the inlet duct 4 joins the combustion flue 5. As has previously been mentioned, in order to obtain a decrease of the NO x amount in the fumes which are exhausted into the environment, it is necessary to re-cycle at least in part the fumes produced by the combustion. It is for this purpose that a plurality of slits 8 are made around the periphery of the combustion flue 5, in correspondence with one of its circumferential cross-sections and going through it. Through said slits a part of the fumes let out of the combustion flue 5 following the direction indicated by arrow 9 re-enter through said slits 8 following the direction indicated by arrow 10. As for the arrangement of said slits 8 which present essentially the shape of slots (11), it is interesting to observe the diagram represented in Fig. 2, wherein the course of the pressure build-up in the longitudinal direction in relation to the burner, starting from the nozzle 2, presents a maximum depression 20, slightly below the choke 7 of diaphragm 6 and a positive value 30 in correspondence with the outlet of the combustion flue 5. Because of the inevitable losses of the load charges along the combustion flue 5, represented in the diagram by the stretch 31, at one spot of the intermediate stretch of the combustion flue 5 there is a maximum pressure value 40, which is higher than pressure 30 in correspondence with the outlet and, as a consequence, there is an inversion spot 50 having null pressure. Therefore, there is a depression along the entire stretch 21 of the diagram of Fig. 2, which facilitates the recalling through the slits 8 of the combustion fumes which are re-cycled and which, as has already been mentioned, enter through said openings following the directions indicated by the arrows 10. It is obvious that the closer the slits 8 are to the point of the maximum depression 20, the larger the flow through them and it is for this reason that in the improvement according to the invention, the slits have the shape of slots (11), that they are arranged aligned along the direction 13, circumferentially to the flue 5 considering their longer longitudinal axis 12, that they are made in correspondence with one transversal cross-section of the combustion flue 5 and that they are located as close as possible to the choke 7 of the diaphragm 6, wherein the maximum depression is to be found. From a constructive point of view said slits 8 are made as close as possible to the junction point of the diaphragm 6, between the inlet duct 4 and the combustion flue 5, compatibly with the constructive requirements. In the described embodiment the slits 8 are arranged in a single row, but they can also be arranged in two or more rows. On the basis of what has been described, it is easy to understand that, since the slits 8 are arranged following the direction of their longitudinal axes 12, when compared with slits of equal length belonging to analogous burners, they concentrate their total suction area, which corresponds essentially with the area of the choke 7 of diaphragm 6, in an area of maximum depression, thereby optimizing the re-cycling of the fumes. A variation of embodiment of the invention is represented in the Figs. 3 and 4, wherein it will be observed that the combustion flue 75 presents a larger diameter than the inlet duct 74. In this embodiment the slits 78 are obtained in correspondence with the transversal cross-section wherein the combustion flue 75 joins the inlet duct 74, the passage area comprised between the outer surface of the inlet duct and the inner surface of the combustion flue 75 being divided through the interposition of spacing elements 76, which are attached to the duct and the flue, which are arranged radially to the same. In this embodiment, too, the slits 78 are arranged with their larger axis aligned along the direction 73 circumferentially to the combustion flue 75. Yet another variation of embodiment of the burner according to the invention is represented in the Figs. 5 and 6, wherein it will be observed that the combustion flue 65 presents, in this case too, a larger diameter than the inlet duct 64 and the slits 68, which have the shape of a slot 66, are in this case obtained in a circular crown 61 placed in correspondence with the transversal cross-section, wherein the combustion flue 65 joins the inlet duct 64. Said slits 68 are arranged with their longer axis 62 aligned along the direction 63 circumferentially to the combustion flue. As for the circular crown 61, it can be obtained en bloc with the combustion flue 65 or it can be made en bloc with the inlet duct 64 or it can constitute a separate part which is then applied to said duct or flue. The thus made slits also reach the proposed purposes. During the construction stage different modifications may be made, such as, for instance, different profiles of the slits, as long as their concentration remains as close as possible to the area of maximum depression, compatibly with the constructive requirements.

Claims: A burner for the combustion of fluid fuels comprising: a nozzle (2) for the atomizing of the fuel connected with the external distribution main and a duct (4, 64, 74) for the inlet of the combustion air surrounding the nozzle (2) for the conveyance of the air/fuel mixture to a combustion flue (5, 65, 75), which is co-axial and aligned with the inlet duct; a diaphragm (6) arranged transversally between the inlet duct (4, 64, 74) and the combustion flue (5, 65, 75), complete with a choke (7) having a smaller cross-section than the diameters of the duct and of the flue and arranged co-axially in relation to the atomizing nozzle (2); a plurality of slits (8, 68, 78) within the burner below the choke (7) of the diaphragm (6) after the atomizing nozzle (2), said slits creating the communication between the outside environment and the interior of the combustion flue (5, 65, 75); characterized in that said slits (8, 68, 78) belong to the combustion flue (5, 65, 75) and are aligned along their longer longitudinal axis (12, 62) in the circumferential direction (13, 63, 73) to the combustion flue (5, 65, 75) and are arranged in one or more rows near the area of maximum depression. A burner according to claim 1, wherein the combustion flue (75) presents a larger diameter than the inlet duct (74), characterized in that the slits (78) are arranged in correspondence with the transversal cross-section wherein the combustion flue (75) joins the inlet duct (74), the air space which is thus created between the external surface of the inlet duct (74) and the inner surface of the combustion flue (75) being divided by spacing elements (76) arranged radially between the duct and the flue and attached to them. A burner according to claim 1, wherein the combustion flue (65) presents a larger diameter than the inlet duct (64), characterized in that the slits (68) are arranged in a ring-shaped crown (61) arranged in correspondence with the transversal cross-section, wherein the combustion flue (65) and the inlet duct (64) join together. A burner according to claim 3, characterized in that the ring-shaped crown (61) belongs to the combustion flue (65) A burner according to claim 3, characterized in that the ring-shaped crown (61) belongs to the inlet duct (64). A burner according to claim 3, characterized in that the ring-shaped crown (61) is applied both on the combustion flue (65) and on the inlet duct (64).

Inventors: MAGNANI ALFREDO, TAGLIAFERRO BRUNO, TONINI EDOARDO, MAGNANI, ALFREDO, TAGLIAFERRO, BRUNO, TONINI, EDOARDO
Applicants: RBL SPA, R.B.L. RIELLO BRUCIATORI LEGNAGO SPA
Application year: 1992
Main classification: F23C9
IPC codes: F23D11, F23C9