RECUPERATIVE BURNER

Abstract

A recuperative burner having a burner base and a combustion chamber tube in which at least one burner nozzle is positioned. An exhaust gas recirculation device has a jet pump operated by combustion air and comprises a jet nozzle. A jet pump annular gap is provided for the intake of exhaust gases from outside the combustion chamber tube via an annular driving jet. The exhaust gas recirculation device being configured upstream of the mixing plane of the fuel gases flowing into the combustion chamber tube, between the burner base and the combustion chamber tube and comprises at least one endless exhaust gas intake opening and/or a peripheral, self-contained arrangement of a plurality of exhaust gas intake openings, from which at least one flow path leads into the interior of the combustion chamber tube. A recuperator is arranged upstream of the combustion chamber tube and has a heat transfer body.

Claims

1. A recuperative burner comprising: a burner base; a combustion chamber tube, in which at least one burner nozzle is positioned, at which at least one fuel gas line opens; an exhaust gas recirculation device with a jet pump which is operated by combustion air and comprises a jet nozzle, a cross section of which decreases in a flow direction, and comprises a jet pump annular gap for an intake of exhaust gases from outside a combustion chamber tube via an annular driving jet, the exhaust gas recirculation device being configured upstream of a mixing plane of the fuel gases flowing into the combustion chamber tube, between the burner base and the combustion chamber tube; at least one endless exhaust gas intake opening and/or a peripheral, self-contained arrangement of a plurality of exhaust gas intake openings, from which at least one flow path leads into an interior of the combustion chamber tube; and a recuperator arranged upstream of the combustion chamber tube, with a heat transfer body which has at least two separate throughflow channels provided to conduct counterflowing fluids, wherein at least two fluids enter/exit via inlet and outlet openings of the throughflow channels in the heat transfer body and, of the fluids, one is formed by combustion air to be preheated and the other is formed by the exhaust gas of the recuperative burner, and wherein the jet nozzle is formed at a combustion air outlet opening of the recuperator.

2. The recuperative burner according to claim 1, wherein the base is connected to an inner tube with an inner cavity, which is passed through the combustion chamber tube and/or through the heat transfer body, wherein the combustion air outlet opening of the combustion air throughflow channel extends around the outside of the inner tube, wherein the nozzle of the jet pump is formed inwards by the inner tube and externally by the conical nozzle ring, a tapered end of which is extended to the outside of the inner tube, wherein, between the inner tube and the nozzle ring, the jet pump annular gap is formed, and wherein at least one exhaust gas inlet opening for the exhaust gas throughflow channel of the combustion chamber tube and/or the heat transfer body is arranged outside the nozzle ring.

3. The recuperative burner according to claim 1, wherein the inner tube opens into or at an inlet opening of an eductor which is expanded in diameter relative to the combustion chamber tube, to which the combustion chamber tube is connected, and wherein, between the outside of the inner tube and the edge of the inlet opening of the eductor, the annular exhaust gas intake opening is formed.

4. The recuperative burner according to claim 1, further comprising an inner tube with an inner cavity that is passed through the heat transfer body, wherein the jet pump annular gap and the exhaust gas intake opening are formed in a section of the inner tube located within the heat transfer body.

5. The recuperative burner according to claim 4, wherein in the inner cavity, a conical combustion chamber tube with a trumpet-shaped burner mouth element is arranged, which extends to the front face of the heat transfer body, wherein a flow reversal chamber is formed between the outlet openings of the throughflow channels serving as air supply ducts and the burner mouth element, wherein, between an inner wall of the heat transfer body and an outer wall of the combustion chamber tube, an annular nozzle gap is formed, to which a jet pump annular gap is connected which widens in cross section in the flow direction, wherein, from the exhaust gas intake openings on the outside of the heat transfer body a first flow path leads directly into the jet pump annular gap and a further path leads into one of the throughflow channels in the heat transfer body serving as an exhaust extraction duct, and wherein the jet pump annular gap extends to a deflection point at the rear, open end of the combustion chamber tube.

6. The recuperative burner according to claim 5, wherein the burner mouth element connects to the heat transfer body such that it is positioned in front of inner mouth openings of the throughflow channels serving as air supply ducts and the external exhaust gas intake openings on the heat transfer body are exposed outside the burner mouth element.

7. The recuperative burner according to claim 5, wherein recesses are provided on the burner mouth element in an area of the flow reversal chamber.

8. The recuperative burner according to claim 1, wherein the mouth of the jet pump annular gap is positioned within the cross section of the endless exhaust gas intake opening or within the closed arrangement of a plurality of exhaust gas intake openings.

9. The recuperative burner according to claim 1, wherein the jet pump annular gap and/or the exhaust gas intake opening each has a meandering course.

10. The recuperative burner according to claim 1, wherein an additional exhaust gas recirculation device is provided with a jet pump which is operated by a mixture of fuel gas, combustion air and the recirculating exhaust gas obtained from the jet pump of the first exhaust gas recirculation device and which is formed downstream of the mixing plane of the fuel gases flowing into the combustion chamber upstream of the mouth of the combustion chamber tube.

11. The recuperative burner according to claim 10, wherein the further exhaust gas recirculation device is arranged in the flow direction upstream of a burner nozzle cone of the burner and is arranged with the combustion chamber tube in a common jet tube.

12. The recuperative burner according to claim 10, wherein the additional exhaust gas recirculation device comprises a venturi nozzle module, the inlet opening of which is arranged behind the burner nozzle cone.

13. The recuperative burner according to claim 10, further comprising at least one segmented flame tube arranged downstream behind the venturi nozzle module in the jet tube.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0048] FIG. 1 is a recuperative burner with exhaust gas recirculation device and recuperator in a side view;

[0049] FIG. 2 is a recuperative burner according to FIG. 1 in a longitudinal perspective sectional view;

[0050] FIG. 3 is an enlarged section of FIG. 2;

[0051] FIG. 4 is parts of the exhaust gas recirculation device on the recuperative burner in a partially cut perspective view, seen from the front;

[0052] FIG. 5 is parts of the exhaust gas recirculation device on the recuperative burner in a partially cut perspective view, seen from the rear;

[0053] FIG. 6 is the recuperative burner with a complete burner base in a perspective sectional view in a longitudinal section;

[0054] FIG. 7 is the recuperative burner in a perspective sectional view in a longitudinal section in a section plane rotated by 90 as compared to FIG. 6;

[0055] FIG. 8 is a recuperator for a recuperative burner according to an example of the invention;

[0056] FIG. 9 is a sectional view along the line X-X in FIG. 8;

[0057] FIG. 10 is a recuperative burner according to an example of the invention in perspective sectional view;

[0058] FIG. 11 is the recuperative burner according to FIG. 10 with flow paths drawn; and

[0059] FIG. 12 is a burner with an exhaust gas recirculation device according to an example in a perspective sectional view in a longitudinal section;

DETAILED DESCRIPTION

[0060] FIG. 1 shows a recuperative burner 100 according to the invention in a side view, which is designed as a recuperative burner. A burner base 10 with a combustion chamber flange 11 is used to attach to a furnace wall of a furnace chamber. The parts located in the wall feed-through of the furnace chamber, as well as the parts outside the furnace chamber, which connect to the combustion chamber flange 11 on the right of a recuperative burner installed in a furnace, are not shown here.

[0061] A recuperator 20 with an internal heat exchanger is connected to the burner base 10, in which the incoming combustion air and the outflowing exhaust gases are guided in opposite directions in separate throughflow channels, so that the incoming combustion air is preheated therein by the outflowing exhaust gas. The recuperative burner 100 flows into a combustion chamber in a combustion chamber tube 30, which tapers at the end at a burner mouth cone 31.

[0062] In the example of the invention shown in FIG. 1, the recuperator 20 and the combustion chamber tube 30 do not merge directly into each other. Rather, the combustion chamber tube 30 has an expansion of the diameter at its end facing the recuperator 20, which is effected by an eductor 32 inserted in between. The combustion chamber tube 30 is kept at a distance from the recuperator 20 by inserted spacer elements 36. At the same time, the inner diameter of the eductor 32 is greater than the outer diameter of a nozzle ring 25 at the downstream end of the recuperator 20. The nozzle ring 25 separates the flow paths of the combustion air flowing into the combustion chamber tube 30 and the exhaust gas drawn in via an exhaust gas inlet opening 24 at the recuperator 20. Due to the axial distance of the eductor 32 and the recuperator 20 as well as the difference in diameter between them, an opening extending over the entire circumference is formed between them. This serves as the exhaust gas intake opening 34 for the combustion chamber tube 30.

[0063] At a short axial distance to the exhaust gas intake opening 34, a jet pump annular gap 26 is formed, from which combustion air escapes at high speed and with a largely laminar flow from the corresponding throughflow channel in the recuperator 20. As a result, a jet pump is formed in the opening between the eductor 32 and the recuperator 20, which leads to the intake of parts of the exhaust gas flowing in the opposite direction into the exhaust gas intake opening 24; this partial flow of the exhaust gas is directed together with the combustion air into the combustion chamber in the combustion chamber tube 30, so that a reduction in nitrogen oxides is caused by the recirculation of the exhaust gas and a reduction in the oxygen partial pressure in the combustion chamber. Furthermore, the temperature in the combustion chamber can be reduced by diluting the combustion air, especially when hydrogen is burned.

[0064] FIG. 2 shows a perspective cross sectional representation of the burner 100. In order to maximize the metallic surfaces of the throughflow channels that can be used for heat exchange, the heat transfer body 21 of the recuperator 20 has a very complex spatial geometry for exhaust gas and combustion air and is shown here only in a simplified form, wherein the dotted line indicates the internal separation of the throughflow channels 101, 102. On the side of the heat transfer body facing the eductor 32 there is an annular combustion air outlet opening 23 on the inside and an annular exhaust gas inlet opening 24 with the conical nozzle ring 25 in between on the outside.

[0065] In the center, the heat transfer body 21 has a continuous inner tube 22 with a cavity 27 over its length, which makes it possible to insert a burner insert 40 from the side of the burner base 10 until the burner nozzle 41 is positioned in the combustion chamber tube 30. The burner nozzle 41 divides the combustion chamber tube 30 into a burner chamber 33 and an intermediate chamber 35.

[0066] In the example shown, the nozzle insert 40 comprises a fuel gas line 42 for the supply of methane and another fuel gas line 43 for the supply of hydrogen. An inspection tube 49 is also part of the burner insert 40 in order to be able to observe the flame visually and/or sensorially at the burner nozzle 41. Not visible in the cross-sectional representation of FIG. 2 is a bypass tube through which additional combustion air can be directed into the intermediate chamber 35, as will be described in detail below.

[0067] In order to better illustrate the formation of the jet pump provided according to the invention and the flow conditions in the area between the combustion chamber tube 30 and the recuperator 20, FIG. 3 shows an enlarged section of the cross-sectional representation in FIG. 2.

[0068] The hatched arrows indicate the exhaust gas flow. A major part of the exhaust gas flow is drawn out of the furnace chamber into the exhaust gas inlet opening 24 of the recuperator 20 by an external extraction device acting on an exhaust outlet opening at the base 10. A bypass flow is drawn into the side of the exhaust gas intake opening 34 by the jet pump formed at the junction between combustion chamber tube 30 and recuperator 20.

[0069] The arrows without hatching refer to the combustion air that comes out of the combustion air outlets 23 of the recuperator 20. The air flow is bundled in a narrow jet pump annular gap 26, which is formed between the outer wall of the inner tube 22 and the inner wall of the conical, outer nozzle ring 25. The inner tube 22 extends axially further in the direction of the combustion chamber tube 30 than the conical nozzle ring 25, in particular at least to the axial position at which the eductor 32 begins. The air jet exiting from the jet pump annular gap 26 is supported by the extended inner tube 22 and fed into the combustion chamber tube 30 with little or no turbulence. The annular air flow supported in this way on the inner circumference is exposed exactly at the transition between the nozzle ring 25 and the eductor 32 on its outside, so that exhaust gas is carried along from there and the combustion air diluted by exhaust gas flows into the combustion chamber tube 30. The combustion air diluted by exhaust gas is symbolized by the arrows with point hatching.

[0070] FIG. 4 shows the heat transfer body 21 with an eductor 32 cut open in half. The combustion air outlet openings are covered by the conical nozzle ring 25 and are therefore not visible. An exhaust gas intake opening 24 is formed by an annular arrangement of a plurality of individual exhaust gas intake openings, which lies radially outside the nozzle ring 25. The exhaust gas inlet opening 24 is open to the furnace chamber in a recuperative burner installed in a furnace.

[0071] FIG. 4 also clearly shows the very small radial width of the jet pump annular gap 26 and the axial offset between the nozzle ring 25 on the outside and the inner tube 22 on the inside.

[0072] FIG. 5 is another perspective section, namely as a view from diagonally above at the rear of the transition between the heat transfer body 21 and the eductor 32. The radial width of the exhaust gas intake opening 34 is large, so that from the perspective it is even possible to look inside the combustion chamber tube 30 with a fuel gas line 42 running through it. The gap width is deliberately chosen so large that the flow resistance for the incoming exhaust gas is low and thus a high efficiency of the jet pump is given.

[0073] FIG. 6 shows the recuperative burner 100 according to the invention in a perspective sectional view, in its full length, i.e., including the sections of the burner base 10 beyond the combustion chamber flange 11. The cutting plane is rotated by 90 relative to FIGS. 2 and 3, so that only one fuel gas line 42 is visible.

[0074] The normal path of the combustion air leads from an external blower via an air inlet duct 13 into a combustion air chamber 14 and from there into the radial internal flow path in the heat transfer body 21 of the recuperator 20. Exhaust gas enters at the exhaust gas inlet opening 24 into the radial outer throughflow channels 101, 102 in the heat transfer body 21 and flows through them to an exhaust chamber 15, which surrounds the combustion air chamber 14. Extraction from the exhaust chamber 15 is carried out by an external blower. Due to the jet pump annular gap 26 provided for in the invention, part of the exhaust gas is taken in directly from the furnace chamber back into the combustion chamber tube 30 at the exhaust gas intake opening 34.

[0075] The flow conditions described above correspond to the normal operation of the recuperative burner 100. However, the fuel gas-air mixture diluted by exhaust gas in the combustion chamber 33 is too lean for start-up operation, so that an ignited flame is quickly extinguished again.

[0076] Since it is not possible to temporarily close the jet pump annular gap 26 by mechanically adjustable flaps or the like due to the high temperature load in the recuperative burner 100, a control device for carrying out a start-up process in the form of a lockable bypass line is provided. The bypass line comprises a bypass line tube 46, which also forms part of the burner insert 40, which can be inserted through the cavity 27 in the inner tube 22. The bypass line tube 46, as well as the inspection tube 49, is routed to a rear end flange 19 of the burner base 10. There, it is connected to the combustion air chamber 14 via a bypass line tube bend 17, wherein the flow path between the bypass line tube 46 and the combustion air chamber 14 can be closed via a valve 18.

[0077] The fuel gas lines, the inspection tube 49 and the bypass line tube 46 run through the combustion air chamber 14. However, to prevent the combustion air from entering the cavity 27 of the inner tube 22, the various lines of the burner insert 40 are bundled by a common bulkhead plate 47, through which an airtight barrier is created in the inner tube 22, which can be bypassed by the bypass line tube 46 running through the bulkhead plate 47.

[0078] By opening the valve 18, combustion air flows through the bypass line tube 46 to the intermediate chamber 35, and thus the immediate vicinity of the burner nozzle 41. Since the flow resistance in the throughflow channel for the combustion air within the heat transfer body 21 is much higher than in the bypass line, the air flow flowing through the heat transfer body 21 is significantly weakened, which also reduces the effect of the jet annular pump and consequently only a small amount of exhaust gas is sucked in. A rich gas-air mixture with only a small fraction of exhaust gas is burned, resulting in a stable flame in the burner chamber 33.

[0079] The recuperative burner 100 heats up as the burning time increases, if only through heat conduction and radiation. Since the air paths through the heat transfer body 21 are not completely interrupted even during start-up operation with the bypass line open, and air is also preheated in the combustion air chamber 14 surrounded by the exhaust chamber 15, the combustion air supplied by the bypass line tube 46 also heats up increasingly.

[0080] The valve 18 can be completely closed when a certain minimum temperature is reached in the combustion chamber 33. It is also possible to successively reduce the airflow through the bypass line by means of a motor-driven valve that can be adjusted via a control device, whereby the flow velocity at the jet pump annular gap 26 increases progressively and the fraction of exhaust gas in the combustion chamber 33 increases until the start-up process is completed and the bypass line can be completely closed.

[0081] FIG. 7 shows the recuperation burner 100 with the burner base 10 again in a cutting plane rotated by 90 relative to FIG. 6, wherein this view is shortened by the combustion chamber tube adjoining the eductor 32.

[0082] The cutting plane intersects the bypass line tube 46 over its entire length. The branch of the bypass line tube bend 17 on the underside of the combustion air chamber 14 is also visible. In particular, the formation of an exhaust chamber 15 surrounding the combustion air chamber 14 can be seen, to which an exhaust outlet flange 16 with a large diameter is connected to the side, through which effective extraction of the exhaust gas is caused.

[0083] FIG. 8 shows parts of another example of a recuperative burner with an exhaust gas recirculation device in a perspective longitudinal section. In a recuperator 220, an inner tube 222 with an inner cavity 227 passes through a heat transfer body 221. In alignment with the inner tube 222, a combustion chamber tube 230 is arranged, which has the same inner diameter.

[0084] The special feature of this example of a recuperative burner according to the invention lies in the fact that an exhaust gas recirculation device with an exhaust gas suction jet pump is formed at the transition between the inner tube 222 and the combustion chamber tube 230, wherein this transition is located within the area surrounded by the heat transfer body 221. The jet pump is therefore integrated directly into the heat transfer body 221. A jet pump annular gap 226 is formed between an inner conical nozzle ring 228 and an outer, also conical nozzle ring 225.

[0085] Two throughflow channels 201, 202 are formed in the heat transfer body 221, wherein combustion air is supplied in the inner throughflow channel 201, which flows through the jet pump annular gap 226 into the combustion chamber tube 230. The exhaust gas enters the heat transfer body 221 at at least one exhaust gas inlet opening 224 and flows in the opposite flow direction to the combustion air in the outer throughflow channel 202 towards a burner base. Part of the exhaust gas flow is sucked in by means of the driving jet formed from fresh air at the jet pump annular gap 226 at an annular exhaust gas intake opening 234 and fed into the combustion chamber tube 230.

[0086] In order to return the flow from the widened diameter area in the area of the jet pump annular gap 226 to the cross section of the combustion chamber tube 230, a conical eductor 232 is integrated into the heat transfer body 221.

[0087] The complex shape of the heat transfer body 221, in which both the throughflow channels 201, 202 with maximized heat exchange surface and the exhaust gas recirculation device with the nozzle rings 225, 228 and the eductor 232 are integrated, possibly also the inner tube 222 and the combustion chamber tube 230 as further integral components, is realized by means of an additive manufacturing process.

[0088] FIG. 9 shows another perspective sectional view, with the section plane running transversely to the center axis, namely along the X-X section line in FIG. 8. The view is directed into the jet pump annular gap 226. Only the inner nozzle ring 228 is visible. The outer nozzle ring is concealed in this line of sight.

[0089] FIG. 10 shows a recuperative burner 300 in a perspective, sectional view, in which, similar to the example presented in FIG. 8, a jet pump is formed in the interior of a recuperator 320.

[0090] A heat transfer body 321 of the recuperator 320 has an inner tube 322 with an inner cavity 327. In it, a combustion chamber insert is positioned at one end of the heat transfer body 321 facing a combustion chamber 333, which can be formed of a conical combustion chamber tube 330 and a trumpet-shaped burner mouth element 331. The outer rim of the burner mouth element 331 connects to the heat transfer body 321 in such a way that it is positioned in front of the internal outlet openings 323 of the air supply channels 301 and at the same time the external exhaust gas intake openings 334 on the heat transfer body 321 are exposed outside the burner mouth element 331.

[0091] A flow reversal space 328 is formed between the mouth openings 323 of the air supply ducts and the burner mouth element 331. The burner mouth element 331 has a concave curvature on the side facing the flow reversal space 323 in order to divert the flow of the combustion air supplied via air supply channels 301 by almost 180 to a bottleneck 325.

[0092] The bottleneck 325 is formed between an inner wall of the inner tube 322 in the heat transfer body 321 and an outer wall of the combustion chamber tube 330. The bottleneck 325 is adjoined by an annular space widening in the flow direction with a cone angle of approx. 5 to 15, which forms a jet pump annular gap 326 and ends at a deflection point 351 at the rear end of the combustion chamber tube 330. The jet pump annular gap 326 is formed in particular by the cylindrical inner tube 322 in the heat transfer body 321 and the outside of a conical combustion chamber tube 330 and, due to its convergent-divergent cross-sectional course, forms a jet nozzle that is driven by the supplied combustion air.

[0093] Via the annular jet nozzle formed in this way, exhaust gas is sucked in from the combustion chamber via intake openings 324 on the heat transfer body. The exhaust gas intake channels 302 on the heat transfer body 321 branch in such a way that a first flow path is led directly into the jet nozzle from the exhaust gas intake openings 334, and in particular directly, as viewed in the flow direction, behind the said bottleneck 325. A further path leads via an exhaust gas inlet opening 302 into an exhaust gas extraction duct 302 in the heat transfer body 321, where the combustion air supplied via the air supply channels 301 is preheated in countercurrent operation.

[0094] The mixture of combustion air and exhaust gas sucked in from the combustion chamber via the exhaust gas intake openings 334 exits the annular jet nozzle formed between the heat transfer body 321 and the combustion chamber tube 330 at the rear end of the combustion chamber tube 330 and reaches a deflection element 350 that is also trumpet-shaped, which closes the inner free cross section of the cavity 327 in the heat transfer body 321 and which, with a concave curvature section 351, causes flow deflection into the interior of the combustion chamber tube 330. There, it flows from behind through the flow-permeable burner nozzle 40 and burns there together with the supplied fuel gas. The section of the combustion chamber tube 330 located between the curvature section 351 and the burner nozzle 41 has a divergent cross section, so that there is a widening of the cross section over the entire flow path, which begins at the bottleneck 325 and ends at the burner nozzle 41. This section is referred to as intermediate chamber 335.

[0095] The concave curvature section 351 tapers inwards and forms a burner tube guide 352 in which a central tube of the burner insert 40 is guided and sealed.

[0096] In the example shown in FIG. 10, primary air holes 332 are provided on the burner mouth element 331 in the area of the flow reversal space, in particular at the apex of the trumpet-shaped funnel forming the burner mouth element 331. Via the primary air holes 332, part of the supplied primary air can be directed into the combustion chamber upstream of the burner nozzle 41. The primary air flow thus caused forms an annular air flow that encloses the combustion chamber 333 and the flame emerging from it, stabilizing the flame and improving the efficiency of combustion as well as nitrogen oxide reduction.

[0097] FIG. 11 is basically the same as FIG. 10, with the path of the combustion air supplied being indicated as a dotted line and the path of the exhaust gas being discharged with dotted lines.

[0098] Distributed around the circumference, all flow paths of air and exhaust gas occur a plurality of times, so that air and exhaust gas flows exist next to each other at a plurality of points. As a result, an air-exhaust gas mixture is formed in the area of the diverging annular gap 326 without turbulence, which is fed to the burner nozzle 41.

[0099] FIG. 12 shows a recuperative burner 100, which is supplemented by a second exhaust gas recirculation device 400. The combustion chamber tube 30 and the second exhaust gas recirculation device 400 are arranged in a common jet tube 401. The exhaust gas recirculation device 400 comprises a venturi nozzle module 402 which is arranged in the flow direction in front of the burner mouth cone 31 of the recuperative burner 100 and whose inlet opening 406 is located behind the outlet opening of the burner mouth cone 31, leaving an annular gap between them. Downstream behind the Venturi nozzle module 402, a plurality of segment flame tubes 403 are arranged in series one after the other. The segment flame tubes 403 are used to guide the hot flue gases in the jet tube 401. The exhaust gas recirculation device 400 is terminated by a cross-shaped spacer 405, which ensures optimal dimensioning of a recirculation gap between the segmented flame tube 403 and the jet tube 401.

[0100] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.