LOW-NOx-BURNER

Abstract

The invention relates to a burner, particularly Low-NO.sub.X-burner, for generating a flame by combustion of a fuel, comprising: a tile (15, 15a, 15b) surrounding an opening (2, 2a, 2b) of the tile (15, 15a, 15b) extending along a burner axis (12), the tile (15, 15a, 15b) further comprising a front side (20) and a rear side (21) facing away from the front side (20), wherein the rear side (21) comprises an air inlet (10, 10a, 10b) connected to said opening for feeding air (A, A′, A″) into said opening (2, 2a, 2b), and wherein said front side (20) comprises a discharge outlet (9, 9a, 9b) connected to said opening (2, 2a, 2b) for discharging a flame (30) generated by the burner (1) into a surrounding area (S), and wherein the tile (15, 15a, 15b) further comprises an inside (22) facing said opening (2, 2a, 2b) as well as an outside (23) facing away from said opening (2, 2a, 2b). According to the invention the burner (1) further comprises at least one oxygen lance (5) extending along the burner axis (12) in a first recess (17) of said tile (15, 15a, 15b), the at least one oxygen lance (5) having an ejection nozzle (6) at an end region of the at least one oxygen lance (5) for ejecting oxygen (O), particularly such that the oxygen (O) is at first ejected into a colder flue gas region (31) surrounding the relatively hotter flame (30) generated by the burner (1). Further, the invention relates to a method for generating a flame (30).

Claims

1. A burner for generating a flame by combustion of a fuel, comprising: a tile surrounding an opening of the tile extending along a burner axis, the tile further comprising a front side and a rear side facing away from the front side, wherein the rear side comprises an air inlet connected to said opening for feeding air into said opening, and wherein said front side comprises a discharge outlet connected to said opening for discharging a flame generated by the burner into a surrounding area, and wherein the tile further comprises an inside facing said opening as well as an outside facing away from said opening, the burner further comprising at least one oxygen lance extending along the burner axis in a first recess of said tile, the at least one oxygen lance having an ejection nozzle at an end region of the at least one oxygen lance for ejecting oxygen, characterized in that the first recess for receiving the at least one oxygen lance is formed as a slot formed in the outside of the tile.

2. The burner according to claim 1, characterized in that the at least one oxygen lance is mounted such that the position of its ejection nozzle along the burner axis is adjustable, between an uppermost position and a lowermost position, via a zero-position in between the uppermost and the lowermost position, wherein in said zero-position, the ejection nozzle of the at least one oxygen lance resides in a plane spanned by said front side of the tile, and wherein in the uppermost position the ejection nozzle of the at least one oxygen lance protrudes beyond said plane along the burner axis, and wherein in the lowermost position the ejection nozzle is positioned in front of said plane along the burner axis and does not protrude past said plane along the burner axis.

3. The burner according to claim 1, characterized in that the ejection nozzle of the at least one oxygen lance is designed to eject oxygen under an ejection angle with respect to a centerline of the at least one oxygen lance, wherein said ejection angle ranges between −30° and 30° with respect to said centerline.

4. The burner according to claim 1 characterized in that said slot ends in a second recess of the tile formed in the outside of the tile in an upper region of the tile, which upper region of the tile delimits said discharge outlet, such that the end region of the at least one oxygen lance protrudes out of said slot into said second recess.

5. The burner according to claim 4, characterized in that said second recess comprises a planar lateral surface extending parallel to the burner axis, which planar lateral surface merges in a bottom surface of the recess into which said slot ends, which bottom surface comprises a concave curvature.

6. The burner according to claim 1, characterized in that, the tile of the burner is designed to be mounted in a wall of a furnace, such that the slot ends at an inside of said wall, which inside faces an internal space of the furnace, or above said inside of the wall so that the slot extends past said inside into said internal space along the burner axis.

7. The Burner according to claim 1, characterized in that the burner comprises a primary fuel gas lance comprising an ejection nozzle at an end region of the primary fuel gas lance, which ejection nozzle of the primary fuel gas lance is designed to eject a primary fuel gas for generating said flame when the ejected primary fuel gas is combusted, wherein the ejection nozzle of the primary fuel gas lance is arranged in said opening of the tile and surrounded by the tile, and wherein particularly the burner further comprises a number of secondary fuel gas lances each having an ejection nozzle at an end region of the respective secondary fuel gas lance, which ejection nozzles of the secondary fuel gas lances are arranged along the front side of the tile and are designed to eject a secondary fuel gas for generating said flame when the ejected secondary fuel gas is combusted.

8. The burner according to claim 1, characterized in that said tile is an inner tile of the burner, and wherein said air inlet is a primary air inlet of the inner tile, and wherein particularly the burner comprises an outer tile surrounding an opening of the outer tile extending along the burner axis, wherein the outer tile further comprises a front side and a rear side facing away from the front side, wherein the rear side of the outer tile comprises a secondary air inlet connected to said opening of the outer tile for feeding secondary air into said opening of the outer tile, and wherein said front side of the outer tile comprises a discharge outlet for discharging a flame generated by the burner into a surrounding area, the discharge outlet of the outer tile being connected to the opening of the outer.

9. The burner according to claim 1, characterized in that said tile is an outer tile, wherein said air inlet is a secondary air inlet of the outer tile, and wherein the burner further comprises an inner tile surrounding an opening of the inner tile, which opening of the inner tile extends along the burner axis, the inner tile further comprising a front side and a rear side facing away from the front side, wherein the rear side of the inner tile comprises a primary air inlet connected to said opening of the inner tile for feeding primary air into said opening of the inner tile, and wherein said front side of the inner tile comprises a discharge outlet for discharging a flame generated by the burner into a surrounding area, the discharge outlet being connected to the opening of the inner tile.

10. The burner according to claim 8, characterized in that the burner comprises a fuel oil lance comprising an ejection nozzle at an end region of the fuel oil lance, which ejection nozzle of the fuel oil lance is designed to eject a fuel oil for generating said flame when the ejected fuel oil is combusted, wherein the ejection nozzle of the fuel oil lance is arranged in said opening of said inner tile and surrounded by the inner tile.

11. The burner according to claim 8, characterized in that the burner comprises at least one fuel gas lance comprising an ejection nozzle at an end region of the at least one fuel gas lance, which ejection nozzle of the at least one fuel gas lance is designed to eject a fuel gas for generating said flame when the ejected fuel gas is combusted, wherein the ejection nozzle of the at least one fuel gas lance is arranged in said opening of the outer tile outside the opening of the inner tile.

12. A method for generating a flame by combustion of a fuel using a burner comprising: a tile surrounding an opening of the tile extending along a burner axis, the tile further comprising a front side and rear side facing away from the front side, wherein the rear side comprises an air inlet connecter to said opening for feeding air into said openings and wherein said front side comprises a discharge outlet connected to said opening for discharging a flame generated by the burner into a surrounding area, and wherein the tile further comprises an inside facing said opening as well as an outside facing away from said opening, the burner further comprising at least one oxygen lance extending along the burner axis in a first recess of said tile, the at least one oxygen lance having an ejection nozzle at an end region of the at least one oxygen lance for ejecting oxygen, characterized in that the first recess for receiving the at least one oxygen lance is formed as a slot formed in the outside of the tile wherein oxygen is ejected by means of the at least one oxygen lance into a flue gas region adjacent said generated flame, the flue gas being generated by said combustion of said fuel.

13. The method according to claim 12, characterized in that the flow rate of oxygen ejected by means of the at least one oxygen lance is equal to or larger than the flow rate of excess oxygen in the flue gas generated upon combustion of said fuel, so as to yield a stoichiometric or sub stoichiometric combustion of the fuel in the tile, in the inner tile.

14. The method according to claim 12, characterized in that the oxygen is ejected at a velocity at or below sonic velocity.

Description

[0047] The above described invention will be explained in detail in consideration of the Figures and the technical field. The Figures show preferred embodiments of the invention. However, the invention is not limited by the drawings. It is shown in

[0048] FIG. 1: a front view of a conventional refractory burner tile;

[0049] FIG. 2: a longitudinal section through the conventional burner tile according to FIG. 1;

[0050] FIG. 3: a front view of a burner tile according to the invention;

[0051] FIG. 4: a longitudinal cross section through the tile of FIG. 3;

[0052] FIG. 5: a detail of the tile according to the invention showing a slideable oxygen lance;

[0053] FIGS. 6-8: two embodiments of a staged air burner according to the invention;

[0054] FIGS. 9-10 a staged fuel burner according to the invention.

[0055] FIG. 1 shows a conventional burner tile 15 out of a refractory material such as Alumina based refractory having a central air inlet 10.

[0056] In FIG. 2 a cross sectional view along plane 16 of FIG. 1 of the conventional burner tile 15 is shown. The air inlet 2 is in flow connection to a central opening 2 of the tile 15, which opening 2 extends along a burner axis 12 and ends at a discharge outlet 9 for discharging a flame generated by the burner.

[0057] In detail, the tile 15 further comprises a front side 20 and a rear side 21 that faces away from the front side 20 of the tile 15, wherein the rear side 21 delimits said air inlet 10, and wherein the front side 20 delimits said discharge outlet 9. The air inlet 10 is in flow connection to an air source for feeding air into said opening 2 of the tile 15 that is needed for combustion of fuel. The tile 15 further comprises an inside 22 facing said central opening 2 as well as an outside 23 facing away from said opening 2.

[0058] FIGS. 3 to 5 show a tile 15 according to the invention which has a configuration as the conventional tile 15 described above, but further comprises at least one oxygen lance 5 that extends along the burner axis 12 in a first recess 17 of the tile 15. The at least one oxygen lance 5 comprises an ejection nozzle 6 at an end region of the at least one oxygen lance 5 for ejecting pure oxygen O, wherein particularly the at least one oxygen lance 5 is configured to eject the oxygen O into a colder flue gas region 31 surrounding the relatively hotter flame 30 generated by the burner 1 (cf. FIGS. 6 to 7).

[0059] Particularly, the first recess 17 for receiving the oxygen lance 5 is formed as a slot or groove in the outside 23 of the tile 15, which slot 17 runs parallel to the burner axis 12. The slot 17 ends in an associated second recess 4 of the tile 15 that is formed in the outside 23 of the tile 15, namely in a circumferentially extending upper region 19 of the tile 15 as shown in FIGS. 4 and 5. Thus, the end region of the oxygen lance 5 protrudes with its ejection nozzle 6 out of the slot 17 into the adjacent second recess 4. Of course, several oxygen lances 5 may be provided in associated slots 17 and second recesses 4.

[0060] In detail, the second recess 4 comprises a planar lateral surface 4a that extends parallel to the burner axis 12 and meets a bottom surface 4b of the recess 4 into which said slot 17 ends. Particularly, the bottom surface 4b comprises a concave curvature.

[0061] Furthermore, as indicated in FIG. 5 by the solid and dashed lines, the burner tile 15 is designed to be mounted in a wall 18 of a furnace (e.g. of a firebox), such that the slot 17 ends at an inside 18a of said wall (as indicated by the solid line), which inside 18a faces an internal space S of the furnace, or such that the slot 17 ends above said inside 18a of the wall 18 (as indicated by the dashed line) so that the slot 17 extends into said internal space S along the burner axis 12.

[0062] The tile 15 (as well as the inner and outer tile 15a, 15b described below) are also particularly made out of a refractory material (e.g. see above).

[0063] Furthermore, the oxygen lance 5 is slideable along its direction of longitudinal extension 7 which particularly runs parallel to the burner axis 12 as well as perpendicular to the plane of the discharge outlet 9. Thus, the nozzle 6 of the oxygen lance 5 can be arranged to end within the second flue gas recirculation recess 4, at a zero position 8 in a plane spanned by the front side 20 or said discharge outlet 9 or behind this plane thus extending further into the internal space S (e.g. of a furnace). Here, the ejection angle 11 of the oxygen lance 5 ranges between ±30° with respect to the centerline 7a of the oxygen lance 5. Thus, oxygen O can be ejected towards the flame 30, namely towards the burner axis 12 (positive angle 11) or away from the flame 30/burner axis 12 (negative angle).

[0064] Generally, any fuel gas or fuel oil fired burner can be equipped or retrofitted with a tile 15 according to the invention.

[0065] FIG. 6 shows a staged air burner 1 according to the invention which may be used especially for oil fired applications.

[0066] Such a staged air burner 1 comprises an inner tile 15b that surrounds an opening 2b of the inner tile 15b, wherein the inner tile 15b further comprises, as already described above, a front side 20 delimiting a discharge opening 9b being in flow connection with the opening 2b as well as a primary air inlet 10b at the rear side 21 for feeding primary air A′ into the inner tile 15b. The burner 1 further comprises an outer tile 15a which may surround the inner tile 15a. The two tiles 15a, 15b are arranged coaxially with respect to the burner axis 12, wherein the outer tile 15a comprises a larger diameter than the inner tile 15b. The outer tile 15a comprises a central opening 2a as well which extends along the burner axis 12 from a secondary air inlet 10b on a rear side 21 of the outer tile 15a towards a discharge outlet 9a of the outer tile 15a at the front side 20 of the outer tile 15a. Particularly as can be seen from FIG. 6, the inner tile 15b is arranged in the opening 2a of the outer tile 15a so that an e.g. circumferentially extending gap is formed between an outside of the inner tile 15b and an inside of the outer tile 15a that is connected to said secondary air inlet 10a so that secondary air A″ can be passed through said gap into the burner 1. The inner tile 15b further comprises an inside facing the opening 2b of the inner tile 15b. Further, the outer tile 15a comprises an outside facing away from the inside of the outer tile 15a.

[0067] For the combustion of fuel, the burner 1 according to FIG. 6 further comprises a fuel oil lance 5c coinciding with the burner axis 12 and comprising an ejection nozzle 6c at an end region of the fuel oil lance 5c designed to eject a fuel oil F for generating a flame 30 upon combustion of the fuel oil F. The fuel oil lance 5c can also be a fuel oil gun. In the latter an atomization media (steam or air) is used to spray the liquid into the flame. The ejection nozzle 6c of the fuel oil lance 5c is arranged in an opening of a central tile 15c, which central tile 15c in turn is arranged in the opening 2b of the inner tile 15b and surrounded by the inner tile 15b. Furthermore, the burner 1 comprises fuel gas lances 5d each comprising an ejection nozzle 6d at an end region of the respective fuel gas lance 5d, which ejection nozzles 6d are designed to eject a fuel gas G for generating said flame 30 when the ejected fuel gas G is combusted. The ejection nozzles 6d are e.g. arranged in a circumferential gap between the inner tile 15b and the central tile 15c.

[0068] As described above, the staged air burner 1 comprises at least a primary and a secondary air inlet 10a, 10b and eventually a tertiary air inlet via which the total air A′, A″ (and eventually tertiary air) that is needed for combusting the fuel F,G is injected into the burner 1, particularly according to the following exemplary portions: primary air A′ 15% to 25%, secondary air A″ 25% to 35% and tertiary air A′″ 40% to 55%. In case of primary and secondary air A′, A″ only, primary air can be around 40%, and secondary air around 60%, for instance. Other rations are also possible.

[0069] All fuel oil F and fuel gas G is injected via the fuel oil and gas lances 5c, 5d into a primary combustion zone of the flame 30 with a portion of the total air (e.g. see above). Due to lack of air in said zone, a portion of the fuel oil and fuel gas F, G does not combust resulting in a lower flame temperature causing a lower thermal NO.sub.x production. Further fuel NO.sub.x is limited due to the fact that fuel oil/gas molecules dissociate under fuel oil/gas rich (reducing) conditions. The fuel oil/gas combustion is at least partially completed in a secondary combustion zone of the flame 30. Further, tertiary air (see above) may be injected via at least one corresponding inlet 10c outside the outer tile 15a into a tertiary combustion zone of the flame 30 in which combustion is completed.

[0070] Now, to further reduce NO.sub.x emission in a staged air burner 1 the inner tile and/or the outer tile 15b, 15a are formed like the tile 15 described above in conjunction with FIGS. 3 to 5. This is shown in FIGS. 7 and 8.

[0071] In FIG. 7 the at least one oxygen lance 5 is arranged in a first and a second recess 4, 17 of the inner tile 15b as described with respect to FIGS. 3 to 5 regarding tile 15, wherein the inner tile 15b protrudes in the direction of the burner axis 12 (e.g. direction of longitudinal extension 7) with a portion of height H past the outer tile 15a, which portion of the inner tile 15b comprises said planar lateral surface 4a and particularly bottom surface 4b.

[0072] Alternatively, in FIG. 8 the at least one oxygen lance 5 is arranged in a first and a second recess 4, 17 of the outer tile 15a as described with respect to FIGS. 3 to 5 regarding tile 15, wherein the outer tile 15a protrudes in the direction of the burner axis 12 (e.g. direction of longitudinal extension 7) with a portion of height H past the inner tile 15b, which portion of the outer tile 15a comprises said planar lateral surface 4a and particularly bottom surface 4b.

[0073] Due to the injection of oxygen O via the oxygen lances 5, particularly into a relatively colder flue gas region 31 containing the relatively colder flue gas, which region 31 surrounds the flame 30, particularly using the ejection angle, oxygen rate and ejection speed described above, the recirculation of flue gases is enhanced along the bottom surface 4b and lateral surface of the second flue gas recirculation recess 4 into the flame 30 yielding a further reduction of NO.sub.x due to the fact that the inert flue gas cools the flame 30 and reduces the partial pressure of oxygen O.

[0074] Further, FIGS. 9 and 10 show a burner 1 according to the invention in the form of a staged fuel burner 1.

[0075] Here, only a single tile 15 is present which is configured as described in conjunction with FIGS. 3 to 5 above. The burner 1 shown in FIGS. 9 and 10 further comprises a primary fuel gas lance 5a that coincides with the burner axis 12 and comprises an ejection nozzle 6a at an end region of the primary fuel gas lance 5a, wherein said nozzle 6a is designed to eject a primary fuel gas G′ for generating a flame 30 when the ejected primary fuel gas G′ is combusted. The ejection nozzle 6a of the primary fuel gas lance 5a is arranged in the opening 2 of the tile 15 and surrounded by the tile 15. Furthermore, the burner 1 comprises a number of secondary fuel gas lances 5b (e.g. four such lances 5b) each having an ejection nozzle 6b at an end region of the respective secondary fuel gas lance 5b. The secondary fuel gas lances 5b may be arranged in corresponding apertures of the tile 15 so that the ejection nozzles 6b of the secondary fuel gas lances 5b are arranged along the front side 20 of the tile 15 for ejecting a secondary fuel gas G″ downstream the tile 15 for generating said flame 30 when the ejected secondary fuel gas G″ is corn busted.

[0076] In such a staged fuel burner 1 the air A enters the primary combustion zone of the flame 30 via the air inlet 10 of the tile 15. Particularly, the air A is then passed through a swirling device 40 which deflects the air A so as to generate an air swirl 41 along the plane of the front side 20 of the tile 15 and along the periphery of the tile 15.

[0077] Only a portion of the fuel gas, namely the primary fuel gas G′, is injected into the primary zone of the flame 30 by means of the central primary fuel gas lance 5a. Combustion of the primary fuel gas G′ is thus completed with an overabundance of air A in the tile 15. The majority of the fuel gas, namely the secondary fuel gas G″, is released in the secondary stage, i.e., via the secondary fuel gas lances 5b outside the opening 2 of the tile 15 and combusted with the remaining air A in a secondary combustion zone of the flame 30.

[0078] Particularly, as shown in FIG. 9, the staged fuel burner 1 comprises four oxygen lances 5 arranged equidistantly in the tile 15. These oxygen lances 5 may also be configured to eject oxygen O such that the generation of an oxygen swirl 50 along the plane of the front side 20 of the tile 15 is achieved, which oxygen swirl 50 may have the same direction as the air swirl 41 or the opposite direction.

[0079] For this, the oxygen lances 5 may comprises two nozzles. Wherein the nozzle 6 described above ejects oxygen as described above with respect to FIG. 5, and wherein the further nozzle is designed to eject oxygen along the periphery of the tile (e.g. in a direction parallel to a respective tangent of the periphery), so that said oxygen swirl 50 is created.

[0080] Usually 20% to 40% of the total fuel (corresponding to the primary fuel gas G′) is mixed with 100% of the total air A. The excess oxygen from the primary zone provides the oxygen necessary to complete the combustion of the remaining fuel gas (secondary fuel gas G″). This yields a relatively low peak flame temperature and therefore a reduced emission of thermal NO.sub.x.

[0081] In order to further reduce NO.sub.x emission according to the invention, the tile 15 of the burner 1 shown in FIGS. 9 and 10 is configured as described in conjunction with FIGS. 3 to 5, so that oxygen O can be injected via the oxygen lances 5, particularly into a relatively colder flue gas region 31 containing the relatively colder flue gas, which region 31 surrounds the hotter flame 30, particularly using the ejection angle, oxygen rate and ejection speed described above. As already described, this enhances recirculation of flue gases along the bottom surface 4b and lateral surface 4a of the second flue gas recirculation recess 4 into the flame 30 yielding a further reduction of NO.sub.x due to the fact that the inert flue gas cools the flame 30 and reduces the partial pressure of oxygen O (see above).

[0082] In summary the invention allows to retrofit existing burners; a modification of existing furnace structures is not necessary. Further, the invention is applicable to all kind of furnace set-ups, including natural draft systems.

[0083] The invention allows extended operating range of the furnace normally limited by the available draft in order to keep the firing box in slight negative pressure. The draft in the firing box is generated by the stack effect or by an induced draft fan. When the maximum pressure at the furnace soil is reached, then more fuel cannot be burned in the system. The invention allows higher firing rate into a given process furnaces (above the limit due to the draft limitation) without modifications to the fuel gas extraction system and without increasing the emissions. This means the invention will allows extend the potential of the existing asset, still operating under safe conditions.

REFERENCE NUMERALS

[0084]

TABLE-US-00001 1 Burner 2, 2a, 2b Opening 3 Tertiary air inlets 4 Second Recess 4a Planar lateral surface 4b Bottom surface 5 Oxygen lance 5a Primary fuel gas lance 5b Secondary fuel gas lance 5c Fuel oil lance 5d Fuel gas lance 6, 6a, 6b, 6c, 6d Ejection nozzle 7 direction of longitudinal extension 7a Centerline 8 zero-position 8a Uppermost position 8b Lowermost position 9, 9a, 9b, 9c Discharge outlet 10 Air inlet 10a Secondary air inlet 10b Primary air inlet 10c Tertiary air inlet 11 ejection angle 12 Burner axis 14 Refractory burner Tile 15 conventional refractory burner tile 15a Outer refractory burner tile 15b Inner refractory burner tile 15c Central tile 16 sectional plane 17 First recess or slot for oxygen lance 18 Wall of furnace 19 Upper region of tile 20 Front side 21 Rear side 22 Inside 23 Outside 30 Flame 31 Flue gas region 40 Swirling device 41, 50 Swirl F Fuel oil G Fuel gas G′ Primary fuel gas G″ Secondary fuel gas O Oxygen A Air A′ Primary air A″ Secondary air H height