COMBUSTION PROCESS AND GAS BURNER WITH LOW NOx, CO EMISSION

Abstract: The process obtains a plurality of small flames which become violet when combusting natural gas. In particular the amount of primary air induced is at least 80 % of the air stoichiometrically required for combustion; the secondary air laps all sides of each single small flame (F) arising from each small group (5) of slots (7, 7') on the burner body (1), in the area where each flame leaves the surface of the burner body (1) so as to swell it making its width at least as big as its height and/or alternatively the contact surface between each flame and the secondary air is increased right from the first steps in combustion, so that each small group (5) creates a small flame with two divergent bladed wings, similar to ''butterfly wings''.

Description: Combustion process and gas burner with low NO x , CO emission. This invention regards a process and equipment to obtain th combustion of gas by means of an atmospheric burner. Several kinds o burners are known: for solid, liquid and gaseous fuels. The burners for gaseous fuels are divided into fan assisted burner and atmospheric burners. In general by using the atmospheric burner an imperfect combustion may occur with harmful emissions of carbo monoxide and nitric oxides, which cause atmospheric pollution. The object of this invention is a process and an equipment to obtai a combustion having a very low level of harmful emissions of at leas 40 of gas capacity per square cm of combustion chamber measured i a plan view. This object has been reached by obtaining a plurality of small flam which become violet when combusting natural gas, that means in t visible spectrum radiations with a wave length, below 0,42 micron. The above is obtained by acting so that the quantity of primary ai inducted inside the burner from the gas jet by means of the sucti tube, usually a Venturi tube, reaches at least 80% of the a stoichiometrically required for combustion; and by acting so that t secondary air laps all sides of every single small flame of t plurality of small flames which come out from the burner's body, in zone close to the external surface of the burner so as to swell ea flame making its width at least as big as its height; and/or alternatively by increasing the contact surface between flame and secondary a right from the first combustion steps, thus producing a small fla with two divergent wings, similar to "butterfly wings". Moreover, preferably, it is foreseen to spread out the flames so th the halo height, on top of the flames, follows the shape of the he exchanger. The atmospheric burner according to the present invention has specific combustion capacity which never exceeds 1,1 KW for each c of the ports area on the burner's body. The sucked air gas mixture maintains a uniform acceleration throu the Venturi tube mouthpiece, which has a parabolic form without sha edges; besides that the maximum average mixture speed must not exce 4,5 m/sec, preferably4,l m/sec. Preferably, the burner's bo sections are wide enough to maintain the average speed of the mixtu lower than 2,5 m/sec, preferably 2 m/sec. If the air intake is not coaxial to the Venturi tube, preferably th latter should be slightly bent compared to the injector axis, order to obtain concentricity with the real diverted mixture flow. In some cases, in order to facilitate the backflow of the mixtu coming out from the Venturi tube, on this latter louvers are open obtain a gradual backflow. In particular , these louvers are open the Venturi tube in zones far from the flame ports of the burner' body. In order that the secondary air laps all sides of the small flame slots are provided in small groups, each one producing a small fla (with or without wings) in rows perpendicular to the burner's bo axis, leaving on the row a distance between every small group least equal to 0,65 b, where "b" is the length of the longest slot the small group, and between the two adjacent rows the distance mus be at least nd/2, where "d" is the width (axially measured) of al the slots of a small group, and "n" is either the number of smal groups foreseen in a row or the number of small groups in tw adjacent rows, when these groups are offset thus forming chess-board configuration. In fact, a chess-board configuration as above described i particularly favourable. Preferably, the upper part of the burner's body, where the slots i small groups are located, has a bending radius bigger to the one the lower part. Preferably, the number of slots in each group of a row decreas towards the burner's vertical symmetry plane. Moreover the slots c be parallel to each other. To obtain a flame with two divergent bladed wings, similar "butterfly wings" a small group of slots split in two sub-group each formed by a plurality of slots very close to each other, particular the sub-groups consist of two to maximum five slots; o sub-group is 2,4 to 2,8 mm from the other. In particular, small groups are created by slots of differe lengths, outwards decreasing, for example the area occupied by small group can be a rhombus. This is favorable in general a particularly with a chess-board configuration. So that the halo may follow the shape of the heat exchanger, the ro made up of small groups are longitudinally located at a variab distance. It is also possible to vary the distance among the grou of a single row. Moreover each group can have a different ports are The flame lift preventing holes are numerous and at a certain mutu distance according to need. In particular the may be placed at t apexes of a square and/or equilateral triangle at a distance of 1 to 1,5 mm, preferably 1,4 mm. The present invention will now be better described on the basis some exemplary embodiments illustrated in the attached drawings, which: Fig. 1 shows a longitudinal sectional view of a burner; Fig. 2 shows a cross-sectional view along the line A-A in figure 1; ; ^_ Figs. 3a and 3b show views of possible variations in the slot grou Fig. 4 shows a view of a possible arrangement of the slot groups; Fig. 5 shows a variant of figure 4; Fig. 6 shows a plan view of the upper part of a burner; Fig. 7 shows a side view of a variant of the burner in figure 6; Figs. 8 and 9 show variants of fig. 2; Figs. 10a, 10b, 10c and lOd show views of possible variants of t sub-groups of holes in which the mutual positions of a sub-group slots and a sub-group of holes is shown. Figures 1 and 2 show a burner consisting of a burner body containing inside it a Venturi tube 2, which has a smoot funnel-shaped mouthpiece 3 with a parabolic form. The Venturi tube leaves a free area (hatched in figure 2, 8 and 9) inside the burn body 1, such as to give an average air/gas mixture speed n exceeding 2m/sec. The upper part of the burner body has holes out which comes a series of small flames F. The section of the burn body 1 where the holes are located is convex, with a bending radi greater than the bending radius of the lower part. The holes consi of small groups 5 of slots 7, each consisting of two sub-groups forming a flame F with two wings (fig. 7) . The small groups 5 a arranged in rows 8 perpendicular to the burner axis 10. Flame li preventing holes 6 are provided between the various small groups (Figs. 10a to lOd). The rows of small groups can be arrang alongside one another with the small groups lined up as shown figure 4, the distance "a" between the small groups 5 in this ca being at least 0.65b, where "b" is the maximum length of the slots a group, while the distance "c" between the rows is at least nd/ where "n" is the number of small groups making up the row and "d" the width of the totality of slots 7 forming a small group Alternatively the rows 8 of small groups 5 can be offset with respe of rows 8' , as shown in figure 5. With this chess-boa configuration, the distances "a" and "c" must comply with t conditions described earlier; "n" in this case is the sum of t small groups in the two adjacent, offset rows 8 and 8'. The distan between the sub-groups 4 of each small group 5 is 2.4 - 2.8 mm. Each sub-group may consist of slots 7, equal in length and parall (figures 3a, 4 and 6); the number of slots can be two, three or fou Alternatively the sub-group (fig. 3b) may consist of slots 7' different lengths (decreasing from the center of the group outward so that the area occupied by each group corresponds to a rhombus. this case the number of slots making up the sub-group may be tw three, four or a maximum of five. Tfre flame lift preventing holes 6 can be arranged as illustrated figures 10a to lOd, i.e at the apexes of a square and/or an ide equilateral triangle, their center distance I being from 1.3 to 1 mm., preferably 1.4 mm. Lastly, in the burner shown in figure 7 the rows of small groups are arranged at a variable distance Dl, D2, D3, D4, D5, D6. This makes it possible to adapt the flame halo 11 to follow the sha of the heat exchanger. A similar adptation is achieved transversal to the burner by varying the number of slots in each small gro (fig. 9) or spacing out the small groups of a single row. Louvers 12 are provided far from small groups 5 in order distribute the backflow along the burner body 1. The particular shap and colour of the flame makes it possible to achieve combustion of high capacity of gas - 40 W per square cm of combustion chambe measured in a plan view - with a very low level of harmful emissions

Claims: C L A I S 1. Process to obtain the combustion of gas with very low cont of harmful emission (NO , CO) by means of an atmospheric burn characterized in that a plurality of small flames are foreseen which become violet w combusting natural gas, that means in the visible spectrum radiati they have a wave length which is less than 0,42 micron. 2. Process to obtain the combustion of gas with very low cont of harmful emission (NO , CO) by means of an atmospheric bur characterized in a) that inside the burner it is sucked a quantity of primary which is at least 80% of the air stoichiometrically required for combustion; b) that the secondary air laps all sides of every single small fl (F) exiting from each group (5) of slots (7, 7') foreseen on burner's body (l),in a zone close to the external surface of burner's body (1) so as to swell each small flame by making its wi at least as big as its height; and/or alternatively c) that from the very first combustion steps, the contact surf between flame and secondary air is increased, so that each slot gro (5) produces a small flame (F) with two divergent bladed wing similar to "butterfly wings". 3. Process according to claim 1 or 2, characterized in that t distance between the small flames (F) can be made greater or small so that the halo height on top of the flames follows the shape of t heat exchanger (S). 4. Burner set up with a suction tube (in particular a Ventu tube) built in a slotted and eventually also pierced burner's bo (1) characterized in that the specific combustion capacity nev 2 exceeds 1, 1 KW per each cm of ports area on the burners body. 5. Burner according to claim 4 characterized in that the Ventu tube mouthpiece is parabolic so that the sucked air maintains uniform acceleration throughout the mouthpiece, the maximum avera mixture speed being less than 4,5 m/sec, preferably 4 m/sec, whi the burner's body sections are wide enough to maintain the avera speed of the flowing mixture under 2,5 m/sec, preferably 2m/sec. 6. Burner according to claim 4 or 5 characterized in that th burner's body (1) has small groups (5) of slots and preferably als flame lift preventing holes (6), located in rows perpendicular to th burner's body axis (10) leaving on the row a distance between smal groups of at least 0,65 b, where "b" is the length of the longes slot of the small group (5), and leaving between the two adjacen rows the distance of at least nd/2 where "d" is the width (in axia direction) of the slots forming a small group (5), and "n" is eithe the number of small groups foreseen in a row or the number of sma groups in two adjacent rows when the rows are offset. 7. Burner according to claim 4, 5 or 6 characterized in that t row of small groups (5) are offset, thus forming a chess-boa con iguration. 8. Burner according to claims 4, 5, 6 or 7 characterized in th the small groups (5) of slots are split in two sub-groups (4) eac formed preferably by two to maximum five slots (7, 7') very close each other, one sub-group being 2,4 - 2,8 mm far from the other. 9. Burner according to one of the claims 4 to 8 characterized i that the small groups (5) are created by parallel slots havin different lengths, the longest length being foreseen inside the grou and the shortest length outside it. 10. Burner according to any claim from 4 to 9, characterized i that the distance (D , D , D , D , D , D ) between the rows i 1 2 3 4 5 6 variable longitudinally along the burner. 11. Burner according to any claim from 4 to 10 characterized i that the distance between the small groups (5) is variable across t burner's body (1). 12. Burner according to any claim from 4 to 11, characterized i that the ports area of the small groups (5) decreases towards th vertical symmetry plane (13) of burner's body (1). 13. Burner according to any claim from 4 to 12 characterized i that the suction tube, particularly the Venturi tube (2), is sligh bent compared to the jet axis in order to obtain the concentric with the real diverted flow of the mixture air/gas. 14. Burner according to any claim from 4 to 13 characterized that on the Venturi tube louvers (12) are open to obtain a grad backflow. 15. Burner according to any claim from 4 to 14 characterized that the upper part of the burner's body, where the slots (7, 7') small groups (5) are located, has a bending radius bigger than one of the lower part. 16. Burner according to any claim from 4 to 15 characterized that the holes (6) are placed at the apexes of a square and/or ideal equilateral triangle at ' a distance (I) comprised between 1 and 1,5 mm, preferably 1,4 mm.

Inventors: SEBASTIANI ENRICO, SEBASTIANI, ENRICO
Applicants: WORGAS BRUCIATORI SRL, WORGAS BRUCIATORI S.R.L.
Application year: 1987
Main classification: F23D14
IPC codes: F23C99, F23D14