DEVICE AND METHOD FOR SUPPLYING COMBUSTION AIR AND FOR RECIRCULATING EXHAUST GAS FOR A BURNER

Abstract

The invention relates to a device (2) and a method for supplying combustion air and for recirculating exhaust gas for a burner (1) comprising a combustion chamber (10) and to a burner (1) comprising a device (2) for supplying combustion air and for recirculating exhaust gas. Multiple drive nozzles (21) distributed about a central axis (A) are used to supply combustion air to a mixing chamber (22) arranged downstream of the drive nozzles (21) by suctioning exhaust gases out of the combustion chamber (10); the combustion air exiting the drive nozzles (21) is mixed with exhaust gases in the mixing chamber (22) in order to form a combustion air/exhaust gas mixture, said exhaust gases flowing out of the combustion chamber (10) and being backflushed by means of the drive nozzles (21); and the combustion air/exhaust gas mixture is supplied to a reaction zone downstream of the mixing chamber (22).

Claims

1. A device for supplying combustion air and for recirculating exhaust gas for a burner having a burner chamber, wherein the device comprises a plurality of driving nozzles which are distributed about a central axis and are fluidically connected to a combustion air supply, wherein a mixing chamber arranged downstream of the driving nozzles is provided, the driving nozzles and the mixing chamber forming a jet pump, and, wherein in the mixing chamber, combustion air emerging from the driving nozzles is mixable with exhaust gases, which flow out of the combustion chamber and are sucked back by means of the driving nozzles, to form a combustion air/exhaust gas mixture, and the combustion air/exhaust gas mixture is suppliable to a reaction zone downstream of the mixing chamber.

2. The device as claimed in claim 1, wherein the mixing chamber has an annular cross section.

3. The device as claimed in claim 1 wherein eight or more driving nozzles which are distributed uniformly about the central axis are provided.

4. The device as claimed in claim 1, wherein a cross-sectional ratio of the mixing chamber and the driving nozzles is smaller than or equal to 20.

5. The device as claimed in claim 1, wherein a bypass duct is provided by means of which combustion air can be supplied to the reaction zone, bypassing the driving nozzles, wherein preferably nozzle openings are provided at an outlet end of the bypass duct.

6. The device as claimed in claim 5, wherein an adjustable bypass valve is provided in the bypass duct, the bypass valve preferably being adjustable continuously or infinitely variably.

7. The device as claimed in claim 1, wherein an adjustable valve is provided in an intake opening for the sucked-back exhaust gas, the valve preferably being adjustable continuously or infinitely variably.

8. The device as claimed in claim 1, wherein a probe is provided for measuring oxygen, preferably upstream of outlet openings of a fuel supply, and/or a measurement sensor is provided for measuring the temperature of the recirculated exhaust gas.

9. A burner comprising a device as claimed in claim 1, and a fuel lance which is arranged coaxially with respect to the central axis and has outlet openings.

10. The burner as claimed in claim 9, wherein a flame tube is provided which delimits the combustion chamber transversely with respect to the direction of flow.

11. The burner as claimed in claim 9, wherein the fuel supply comprises an ignition device or a pilot burner.

12. A method for supplying combustion air and for recirculating exhaust gas for a burner having a combustion chamber, wherein combustion air is supplied by means of a plurality of driving nozzles, which are distributed about a central axis, to a mixing chamber arranged downstream of the driving nozzles with exhaust gases being sucked up from the combustion chamber, and, in the mixing chamber, the combustion air emerging from the driving nozzles is mixed with exhaust gases, which flow out of the combustion chamber and are sucked back by means of the driving nozzles, to form a combustion air/exhaust gas mixture, and the combustion air/exhaust gas mixture is supplied to a reaction zone downstream of the mixing chamber.

13. The method as claimed in claim 12, wherein combustion air is selectively supplied via a bypass duct to the reaction zone, bypassing the driving nozzles.

14. The method as claimed in claim 13, wherein an oxygen content of a mixture of the combustion air supplied selectively via the bypass duct and the combustion air/exhaust gas mixture is monitored and a quantity of the combustion air supplied via the bypass duct is adjusted to maintain a defined oxygen content.

15. The method as claimed in claim 12, wherein a temperature of the recirculated exhaust gas is detected and a quantity of the combustion air supplied via the bypass duct is adjusted depending on the detected temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Further advantages and aspects of the invention emerge from the claims and from the description of exemplary embodiments of the invention that are explained below with reference to the figures, in which:

[0035] FIG. 1: shows a sectioned side view of a burner with a device for supplying combustion air and for recirculating exhaust gas;

[0036] FIG. 2: shows the burner according to FIG. 1 in a sectioned top view according to a marking II-II in FIG. 1;

[0037] FIG. 3: shows a sectioned side view of a burner similarly to FIG. 1 with a device for supplying combustion air and for recirculating exhaust gas;

[0038] FIG. 4: shows the burner according to FIG. 3 in a sectioned top view according to a marking IV-IV in FIG. 3;

[0039] FIG. 5: shows a burner similarly to FIG. 1 in a sectioned side view with a chamber.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0040] FIGS. 1 and 2 show a burner 1 having a combustion chamber 10 and having a device 2 for supplying combustion air and for recirculating exhaust gas in a sectioned side view or in a sectioned top view according to a marking II-II in FIG. 1.

[0041] The burner 1 which is illustrated has a fuel supply 3 with a supply nozzle 30, a fuel lance 31 running coaxially with respect to a central axis A, and outlet nozzles 32. In the exemplary embodiment which is illustrated, a flame holder 4 for stabilizing a flame front is provided upstream of the outlet nozzles 31. The fuel supply 3 which is illustrated furthermore comprises an internal pilot burner or ignition device 34. The ignition device 34 is arranged in a tube 35 which delimits a duct for supplying fuel in the fuel lance 31 of the fuel supply. The combustion chamber 10 is delimited transversely with respect to the direction of flow by a flame tube 12.

[0042] The device 2 comprises a combustion air supply with a supply nozzle 20, a plurality of driving nozzles 21, sixteen in the exemplary embodiment illustrated, which are fluidically connected to the combustion air supply and are distributed about the central axis A and about the fuel lance 31, and a mixing chamber 22 arranged downstream of the driving nozzles 21. The driving nozzles 21 and the mixing chamber 22 form a jet pump. The combustion air supplied by means of the driving nozzles 21 is used here as a driving medium which generates a pumping action such that an exhaust gas flowing out of the combustion chamber 10 is sucked up via an intake opening 25 provided between the driving nozzles 21 and the mixing chamber 22. In the mixing chamber 22, the combustion air emerging from the driving nozzles 21 is mixed with the exhaust gases, which flow out of the combustion chamber 10 and are sucked back by means of the driving nozzles 21, to form a combustion air/exhaust gas mixture, and the combustion air/exhaust gas mixture is supplied to a reaction zone in the combustion chamber 10 downstream of the mixing chamber 22.

[0043] The mixing chamber 22 of the illustrated device 2 has an annular cross section and surrounds the fuel lance 31. The flame tube 12 adjoins the mixing chamber 22. In the exemplary embodiment illustrated, the flame tube 12 and the mixing chamber 22 are realized by a common component. In other embodiments, separate components are provided.

[0044] The device 2 which is illustrated in FIGS. 1 and 2 furthermore has a bypass duct 23 by means of which combustion air can be supplied to the reaction zone, bypassing the driving nozzles 21. In the exemplary embodiment which is illustrated, the bypass duct 23 is configured as an annular duct running coaxially with respect to the central axis A between the fuel lance 31 and the mixing chamber 22. The bypass duct 23 ends downstream of the mixing chamber 22 and upstream of the flame holder 4. For rapid and complete thorough mixing of the combustion air supplied via the bypass duct 23 with the combustion air/exhaust gas mixture coming from the mixing chamber 22, nozzle openings 230 are provided at an outlet end of the bypass duct 23 in the exemplary embodiment which is illustrated. In the exemplary embodiment which is illustrated, a bypass valve 232 which is adjustable continuously or infinitely variably is provided in the bypass duct 23.

[0045] A probe 5 for measuring oxygen is provided downstream of the mixing chamber 22 and, in the exemplary embodiment which is illustrated, downstream of the outlet end of the bypass duct 23 and upstream of the flame holder 4 and of the outlet nozzles 32 of the fuel supply 3.

[0046] Furthermore, a measurement sensor 6 for measuring the temperature of the recirculated exhaust gas is provided. In the exemplary embodiment which is illustrated, the measurement sensor 6 is arranged in the region of the intake opening 25 of the jet pump formed by the mixing chamber 22 and the driving nozzles 21.

[0047] An exhaust gas return ratio of the combustion air/exhaust gas mixture conveyed by the jet pump depends on a cross-sectional ratio of the mixing chamber 22 and of the driving nozzles 21 and on operating parameters, such as a temperature of the recirculated exhaust gas.

[0048] In order to lower a flame temperature to 1500 C., an exhaust gas return ratio of 1 to 1.5 is required depending on the temperature of the returned exhaust gas. A cross-sectional ratio of the mixing chamber 22 and of the driving nozzles 21 is correspondingly suitably configured by a person skilled in the art for a temperature range of the returned exhaust gas. In the exemplary embodiment which is illustrated, the cross-sectional ratio is selected to be smaller than 20. The mixing chamber 22 which is illustrated has funnel-shaped inflow and outflow regions. A cross section of the mixing chamber 22 is determined here in a section located in between with a constant cross section.

[0049] If an exhaust gas return ratio has to be reduced during the operation in order to obtain flame stability, for example because of deviations in the temperature of the returned exhaust gas, some of the combustion air can be supplied via the bypass duct 23 in the exemplary embodiment which is illustrated. The probe 5 can be used to detect an oxygen content and adjust it to a certain value using the bypass valve 232.

[0050] FIGS. 3 and 4 show a burner 1 having a combustion chamber 10 and having a device 2 for supplying combustion air and for recirculating exhaust gas in a sectioned side view or in a sectioned top view according to a marking II-II in FIG. 1. The burner 1 according to FIGS. 3 and 4 are similar to the burner 1 according to FIGS. 1 and 2, and uniform reference signs are used for identical components. A detailed description of components which have already been described is omitted.

[0051] In contrast to the exemplary embodiment according to FIGS. 1 and 2, the device 2 according to FIGS. 3 and 4 does not have a bypass duct 23. Instead, a continuously or infinitely variably adjustable valve 27 is provided in the intake opening 25 for the sucked-back exhaust gas. If an exhaust gas return ratio has to be reduced during the operation in order to obtain flame stability, in the exemplary embodiment according to FIGS. 3 and 4 return of exhaust gas can be reduced by means of the valve 27. In this case, analogously to the exemplary embodiment according to FIGS. 1 and 2, the probe 5 can be used to detect an oxygen content of the combustion air/exhaust gas mixture upstream of the outlet nozzles 32 of the fuel supply andin contrast to the exemplary embodiment according to FIGS. 1 and 2to adjust same to a certain value with the aid of the valve 27. In the exemplary embodiment which is illustrated, an annular cavity which can be used, for example, for wiring of the probe 5 remains between the fuel lance 31 of the fuel supply 3 and the mixing chamber 22. In other embodiments, an inside diameter of the annular mixing chamber 22 is identical to an outside diameter of the duct 31, thus not leaving a cavity.

[0052] FIG. 5 shows the burner 1 according to FIG. 1 and a heating chamber 7 which is delimited by a housing 70. A double-walled housing 70 is provided in the exemplary embodiment which is illustrated. Arranged in the double-walled housing 70 is a tube coil 71 through which a medium to be heated is guided. The exhaust gas or combustion gas is guided through the double-walled housing 70 to an outlet 72 and, in the process, heats the medium guided in the tube coil. In addition, to avoid thermal formation of nitrogen oxides, some of the exhaust gas is sucked up by the jet pump, which is formed by the driving nozzles 21 and the mixing chamber 22, and mixed with the combustion air.

[0053] In contrast to the embodiment according to FIGS. 1 and 2, in the embodiment according to FIG. 5, for operation with fuels with a low reaction rate, for example natural gas, an extended flame tube 112 is provided for an extended dwell period in order to ensure burnout.