Apparatus and method for supplying combustion air for a burner and recirculating exhaust gases

Abstract

The present invention relates to an apparatus (2) and method for supplying combustion air and recirculating exhaust gases for a burner (1) including a combustion chamber (10), as well as a burner (1) including the apparatus (2) for supplying combustion air and recirculating exhaust gases. A plurality of motive nozzles (21) arranged around a central axis (A) are used to supply combustion air to a mixing chamber (22) located downstream of the motive nozzles (21) by aspirating exhaust gases from the combustion chamber (10). The combustion air from the motive nozzles (21) is mixed in the mixing chamber (22) with exhaust gases exiting the combustion chamber (10) and backflushed by the motive nozzles (21) to form a combustion air / exhaust gas mixture, which is then supplied to a reaction zone downstream of the mixing chamber (22).

Description

[Technical Field]

[0001] The present invention relates to a device and method for supplying combustion air and recirculating exhaust gases for a burner, and to a burner having a device for supplying combustion air and recirculating exhaust gases. [Background technology]

[0002] Hydrogen obtained from renewable energies, such as wind, solar, and hydroelectric power, or by water separation from biomass—specifically so-called green hydrogen—is becoming increasingly important as an energy source, first as an adjunct to natural gas and later as a pure gas. Although hydrogen burns virtually without any emissions, oxygen and nitrogen are components of the combustion air, and therefore nitrogen oxides can form even during hydrogen use. Thermal formation of nitrogen oxides begins at high temperatures and then increases exponentially with temperature. Due to the rapid reaction rate of hydrogen, the amount of thermal formation of nitrogen oxides increases significantly with hydrogen compared to pure natural gas. For example, unless special measures are taken, nitrogen oxides in the exhaust gas from a burner using natural gas (CH4) are approximately 50 ppm, and in the exhaust gas from a burner using hydrogen, nitrogen oxides exceed 100 ppm.

[0003] It is known that exhaust gas recirculation or exhaust gas return is an effective measure against the thermal formation of nitrogen oxides in the exhaust gases of combustion plants. Returning the exhaust gas reduces the oxygen content and thus the flame temperature. In the context of this application, the exhaust gas return ratio (EGR) is defined as the mass flow ratio (m ) of the recirculated or returned exhaust gas to the supplied combustion air. A / m L Exhaust gas is also called flue gas or combustion gas.

[0004] A distinction is usually made between external and internal exhaust gas recirculation. In the case of internal exhaust gas recirculation, the exhaust gas is led out of the combustion chamber, and a partial flow of the exhaust gas in the exhaust gas pipe is taken off, for example in a chimney, and added to the combustion air or fuel before or during its entry into the combustion chamber. By means of a suitable controller, the EGR can be adjusted to the desired ratio. A substantial disadvantage of external exhaust gas recirculation is the increased amount of exhaust gas, which in turn requires a corresponding increase in the size of the area for heat extraction.

[0005] In the case of internal exhaust gas recirculation, the exhaust gas or combustion gases present in the combustion chamber are recirculated into the reaction zone by pulses of combustion air. If the temperature in the combustion chamber exceeds the ignition temperature of the fuel, the exhaust gas return ratio can be increased as desired, since flame stability is not important.

[0006] For example, in the case of a method and apparatus for burning fuel in a combustion chamber disclosed in Patent Document 1, combustion air coming out of a nozzle means having a plurality of nozzles arranged in a ring shape can be mixed with partially cooled and sucked back exhaust gas in the combustion chamber at an exhaust gas return ratio EGR≧2 while forming a combustion air / exhaust gas mixture having at least an ignition temperature.

[0007] In contrast, if the temperature in the combustion chamber falls below the ignition temperature, the exhaust gas return rate must be limited to avoid the flame going out. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] European Patent Application Publication No. 0463218 Summary of the Invention [Problem to be solved by the invention]

[0009] The problem addressed by the invention is to provide combustion air and internal recirculation of exhaust gases with a defined exhaust gas return ratio, in particular for burners for low-temperature processes. [Means for solving the problem]

[0010] According to a first aspect, an apparatus for supplying combustion air and recirculating exhaust gas for a burner having a combustion chamber is provided, the apparatus including a plurality of motive nozzles arranged about a central axis and fluidly connected to a combustion air supply, and a mixing chamber arranged downstream of the motive nozzles, the motive nozzles and the mixing chamber forming an injection pump, and within the mixing chamber, combustion air from the motive nozzles can be mixed with exhaust gas flowing from the combustion chamber and sucked back by the motive nozzles to form a combustion air / exhaust gas mixture, and the combustion air / exhaust gas mixture can be supplied to a reaction zone downstream of the mixing chamber. [Effects of the Invention]

[0011] The chamber separated from the surroundings and having a cross section and located between the motive nozzle and the reaction zone of the combustion chamber is called a mixing chamber. The cross section of the mixing chamber can be selected by a person skilled in the art depending on the application. In a preferred embodiment, the cross section in the flow direction is constant, and in one embodiment, a converging or diverging cross section is provided in the inlet and / or outlet region to improve the inflow or outflow.

[0012] The arranged motive nozzle and the mixing chamber form an injection pump, and the exhaust gas return ratio of the combustion air / exhaust gas mixture conveyed through the injection pump depends on the cross-sectional ratio of the mixing chamber and the motive nozzle and on the operating parameters, for example, the temperature of the recirculated exhaust gas. The exhaust gas return ratio can thus be determined by a person skilled in the art in accordance with the predetermined operating parameters by appropriately configuring the mixing chamber and the motive nozzle, for example, up to the flame stability limit. In other words, the cross-section of the mixing chamber is matched to the outlet cross-section of the motive nozzle and the number of motive nozzles.

[0013] In one embodiment, the end of the mixing chamber facing the motive nozzle is at least partially spaced in the flow direction from the wall on which the motive nozzle is arranged, forming an annular or discontinuous gap, which serves as an intake opening for the injection pump, through which exhaust gases can be sucked back and transferred into the mixing chamber. In another embodiment, an intake chamber having an opening for sucking up exhaust gases is provided upstream of the mixing chamber. In use, the end of the mixing chamber facing the combustion chamber is located upstream of the outlet opening of the fuel supply. The distance can be selected appropriately by a person skilled in the art depending on the application.

[0014] As with external exhaust gas recirculation, the combustion air and exhaust gases are mixed before mixing with the fuel at a defined exhaust gas return ratio, which can depend on the operating parameters, so that the amount of exhaust gas in the exhaust line does not increase, as would be the case with external exhaust gas recirculation.

[0015] Exhaust gas recirculation reduces flame temperatures. The rate of nitrogen oxide formation at flame temperatures of approximately 2000°C for conventional fuels is approximately 10 4 ppm / s, decreasing to approximately 10 ppm / s at 1500° C. At low flame temperatures and residence times in the range of a few tenths of a second, nitrogen oxide values obtained in the exhaust gas are thus in the single digits.

[0016] An arrangement of motive nozzles arranged around a central axis is also referred to as a ring arrangement in the context of this application. In one embodiment, the motive nozzles are arranged in parallel. In another embodiment, the axes of the motive nozzles are inclined relative to the central axis. The configuration of an injection pump with multiple motive nozzles arranged around the central axis and a mixing chamber arranged downstream of the motive nozzles forms a compact injection pump. This compact injection pump can be incorporated into existing burners with conventional dimensions. Therefore, the device is also suitable for retrofitting existing plants.

[0017] The device with the injection pump formed by the mixing chamber and the driving nozzle is suitable for burners in the power range of several kW as well as in the MW power range.

[0018] In one embodiment, the mixing chamber has an annular cross section, the inner diameter of the mixing chamber being selected herein so that, in use, the mixing chamber can be positioned around a fuel lance disposed coaxially relative to the central axis.

[0019] The number of motive nozzles can be determined by those skilled in the art depending on the application and the number of burners. In one embodiment, eight or more motive nozzles are provided, evenly arranged around the central axis. This provides a good suction effect, especially for mixing chambers with a supply opening in the form of an annular gap.

[0020] The cross-sectional area ratio of the mixing chamber of the injection pump to the motive nozzle is configured to obtain a predetermined exhaust gas return ratio (EGR), and the resulting cross-sectional area of all the motive nozzles is referred to as the cross-sectional area of the motive nozzle. In one embodiment, the cross-sectional area ratio of the mixing chamber to the motive nozzle is 20 or less.

[0021] As mentioned above, the optimal EGR ratio for avoiding pollutants also depends on the operating parameters. For example, depending on the temperature of the recirculated exhaust gas, a flame temperature reduction of 1500°C requires an EGR ratio of 1 to 1.5 and an oxygen content of the combustion air / exhaust gas mixture of approximately 10% to approximately 12%.

[0022] In one embodiment, therefore, a bypass duct is provided. The bypass duct allows combustion air to be supplied to the reaction zone while bypassing the motive nozzle. As a result, for example, EGR can be reduced for flame stability by directing some of the combustion air through the bypass duct and through the motive nozzle. In one embodiment, the bypass duct is configured as an annular gap duct that, in use, is disposed around the fuel lance and extends partially between the mixing chamber and the fuel lance. In one embodiment, a nozzle opening is provided at the outlet end of the bypass duct to rapidly and thoroughly mix the combustion air supplied through the bypass duct with the combustion air / exhaust gas mixture of the injection pump.

[0023] In one embodiment, an adjustable bypass valve is provided in the bypass duct. In one embodiment, the bypass valve is adjustable only between an open position and a closed position. In another embodiment, a continuously or steplessly adjustable bypass valve is provided. In an embodiment, the bypass valve is adjusted by a controllable or adjustable actuation means, and depending on the embodiment, the bypass valve is opened or closed, or the passage is changed by adjustment or control intervention. For flame stability, the oxygen content of the combustion air / exhaust gas mixture for combustion can be changed and maintained within a specifically defined range by variable supply of additional combustion air via the bypass valve.

[0024] Instead of or in addition to a bypass duct, in one embodiment an adjustable valve is provided in the intake opening for the sucked-back exhaust gases. The valve is preferably continuously or steplessly adjustable. For flame stability, the oxygen content of the combustion air / exhaust gas mixture for combustion can be varied and maintained within a specifically defined range by variable exhaust gas supply via the valve provided in the intake opening for the sucked-back exhaust gases.

[0025] In one embodiment, a probe is provided to measure oxygen, preferably upstream of the outlet opening of the fuel supply and thus upstream of the flame. The oxygen content of the mixture of combustion air / exhaust gas mixture supplied by the injection pump and, if appropriate, combustion air supplied via the bypass duct, is determined by the probe and can be determined and varied by adjusting or controlling the bypass valve and / or a valve provided in the intake opening for the sucked-back exhaust gas.

[0026] Alternatively or additionally, in one embodiment, a measurement sensor is provided to measure the temperature of the recirculated exhaust gas. The optimized exhaust gas return ratio can be determined in relation to the exhaust gas temperature and adjusted by regulating or controlling the bypass valve and / or the valve in the intake opening, preferably while measuring the oxygen content.

[0027] According to a second aspect, a burner is provided that includes a device for supplying combustion air and recirculating exhaust gases, the device including an injection pump, the injection pump preferably having an annular gap-shaped mixing chamber, a plurality of motive nozzles arranged in a ring around a central axis, and a fuel lance arranged coaxially with the central axis and having an outlet opening. The outlet opening is located downstream of the outlet opening of the mixing chamber. The spacing can be selected appropriately by those skilled in the art. In one embodiment, a baffle is provided upstream of the outlet opening of the fuel lance to improve flame stability. The burner thus provided can be installed in a conventional chamber.

[0028] In one modified embodiment, a flame tube is provided, which delimits the reaction zone transversely to the flow direction. The exhaust gases can flow to the injection pump and / or to the exhaust gas outlet in the annular gap between the chamber wall and the flame tube. In one embodiment, the flame tube is arranged directly adjacent to the mixing chamber. The length of the flame tube can be selected by those skilled in the art depending on the fuel. In one embodiment, when operating with a fuel with a low reaction rate, such as natural gas, an extended flame tube is selected to increase the residence time to ensure combustion. However, since the residence time also influences the formation of nitrogen oxides, a shorter flame tube is provided in another embodiment.

[0029] In one embodiment, the fuel lance includes an ignition means or pilot burner, the outlet opening of which is preferably offset relative to the outlet opening of the fuel lance for normal operation.

[0030] According to a third aspect, there is provided a method for supplying combustion air and recirculating exhaust gases for a burner having a combustion chamber, the method comprising: supplying combustion air by a plurality of motive nozzles arranged around a central axis while sucking exhaust gases from the combustion chamber into a mixing chamber arranged downstream of the motive nozzles; and mixing the combustion air from the motive nozzles in the mixing chamber with exhaust gases flowing out of the combustion chamber and sucked back by the motive nozzles to form a combustion air / exhaust gas mixture, and supplying the combustion air / exhaust gas mixture to a reaction zone downstream of the mixing chamber.

[0031] The motive nozzle and the mixing chamber form an injection pump by means of which a combustion air / exhaust gas mixture with a defined EGR can be delivered to the reaction zone according to predetermined operating parameters.

[0032] In one embodiment, selective combustion air is supplied to the reaction zone via a bypass duct, bypassing the motive nozzles. The content of the combustion air supplied via the bypass duct is preferably variable to allow adjustment in response to predetermined operating parameters.

[0033] To this end, in one embodiment, the oxygen content of a mixture of combustion air supplied through the bypass duct and the combustion air / exhaust gas mixture is monitored, and the amount of combustion air supplied through the bypass duct is adjusted to maintain a predetermined oxygen content.

[0034] Alternatively or additionally, in another embodiment, the temperature of the recirculated exhaust gas is detected and the amount of combustion air supplied through the bypass duct is adjusted in response to the detected temperature.

[0035] Further advantages and features of the invention will become apparent from the claims and from the following description of embodiments of the invention which proceeds with reference to the drawings. [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 is a cross-sectional side view of a burner having a device for supplying combustion air and recirculating exhaust gases. [Figure 2] FIG. 2 is a cross-sectional view of the burner according to FIG. 1 taken along the line II-II in FIG. [Figure 3] FIG. 3 is a cross-sectional side view of a burner similar to that of FIG. 1, having means for supplying combustion air and recirculating exhaust gases. [Figure 4] FIG. 4 shows a top cross-sectional view of the burner according to FIG. 3 along the line IV-IV in FIG. [Figure 5] FIG. 5 is a cross-sectional side view of a burner similar to that of FIG. 1, but having a chamber. DETAILED DESCRIPTION OF THE INVENTION

[0037] 1 and 2 show a burner 1 having a combustion chamber 10 and a device 2 for supplying combustion air and recirculating exhaust gases in a cross-sectional side view or a cross-sectional top view along the line II-II in FIG. 1.

[0038] The illustrated burner 1 comprises a fuel supply 3 with a supply nozzle 30, a fuel lance 31 extending coaxially relative to a central axis A, and an outlet nozzle 32. In the illustrated exemplary embodiment, a flame holder 4 is provided upstream of the outlet nozzle 31 to stabilize the flame front. The illustrated fuel supply 3 further comprises an internal pilot burner or ignition means 34. The ignition means 34 is arranged in a tube 35, which delimits a duct for feeding fuel into the fuel lance 31 of the fuel supply. The combustion chamber 10 is bounded transversely to the flow direction by a flame tube 12.

[0039] The apparatus 2 includes a combustion air supply with a supply nozzle 20 and a plurality of, in the illustrated exemplary embodiment, sixteen motive nozzles 21, which are fluidly connected to the combustion air supply and arranged around a central axis A and around a fuel lance 31, with a mixing chamber 22 arranged downstream of the motive nozzles 21. The motive nozzles 21 and the mixing chamber 22 form an injection pump. The combustion air supplied by the motive nozzles 21 is used here as a driving medium to generate the pumping action, and the exhaust gases leaving the combustion chamber 10 are sucked up through a suction opening 25 provided between the motive nozzles 21 and the mixing chamber 22. In the mixing chamber 22, the combustion air leaving the motive nozzles 21 is mixed with the exhaust gases leaving the combustion chamber 10 and sucked back by the motive nozzles 21 to form a combustion air / exhaust gas mixture, which is then fed downstream of the mixing chamber 22 to a reaction zone in the combustion chamber 10.

[0040] The mixing chamber 22 of the illustrated device 2 has an annular cross section and surrounds the fuel lance 31. The flame tube 12 is adjacent to the mixing chamber 22. In the illustrated exemplary embodiment, the flame tube 12 and the mixing chamber 22 are realized by a common component. In other embodiments, separate components are provided.

[0041] 1 and 2 further comprises a bypass duct 23, by means of which combustion air can be supplied to the reaction zone while bypassing the motive nozzle 21. In the illustrated exemplary embodiment, the bypass duct 23 is configured as an annular duct extending coaxially with the central axis A between the fuel lance 31 and the mixing chamber 22. The bypass duct 23 terminates downstream of the mixing chamber 22 and upstream of the flame holder 4. In order to quickly and thoroughly mix the combustion air supplied via the bypass duct 23 with the combustion air / exhaust gas mixture coming from the mixing chamber 22, in the illustrated exemplary embodiment, a nozzle opening 230 is provided at the outlet of the bypass duct 23. In the illustrated exemplary embodiment, a continuously or steplessly adjustable bypass valve 232 is provided in the bypass duct 23.

[0042] Downstream of the mixing chamber 22 is a probe 5 for measuring oxygen, which in the illustrated exemplary embodiment is downstream of the outlet end of the bypass duct 23 and upstream of the outlet nozzle 32 of the flame holder 4 and fuel supply 3.

[0043] Furthermore, a measurement sensor 6 is provided for measuring the temperature of the recirculated exhaust gases. In the illustrated exemplary embodiment, the measurement sensor 6 is arranged in the region of the suction opening 25 of the injection pump formed by the mixing chamber 22 and the driving nozzle 21.

[0044] The exhaust gas return ratio of the combustion air / exhaust gas mixture delivered by the injection pump depends on the cross-sectional ratio of the mixing chamber 22 and the motive nozzle 21 and also on the operating parameters, for example the temperature of the recirculated exhaust gases.

[0045] To reduce the 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. The cross-sectional area ratio of the mixing chamber 22 to the motive nozzle 21 can be appropriately configured by a person skilled in the art for the temperature range of the returned exhaust gas. In the illustrated exemplary embodiment, the cross-sectional area ratio is selected to be less than 20. The illustrated mixing chamber 22 has funnel-shaped inlet and outlet regions. The cross-section of the mixing chamber 22 is determined within a centrally located section with a constant cross-section.

[0046] If the exhaust gas return ratio has to be reduced during operation to obtain flame stability, for example because the temperature of the returned exhaust gases deviates, in the illustrated exemplary embodiment some of the combustion air can be supplied via the bypass duct 23. The probe 5 can be used to detect the oxygen content and the bypass valve 232 can be used to adjust the oxygen content to a predetermined value.

[0047] Figures 3 and 4 show a burner 1 with a combustion chamber 10 and with a device 2 for supplying combustion air and recirculating exhaust gases in a sectional side view or in a sectional top view along the line II-II in Figure 1. The burner 1 according to Figures 3 and 4 is similar to the burner 1 according to Figures 1 and 2, and the same reference numerals are used for the same components. A detailed description of the components already described will not be given.

[0048] 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 steplessly adjustable valve 27 is provided in the intake opening 25 for the sucked-back exhaust gas. If the exhaust gas return ratio must be reduced during operation to achieve flame stability, the valve 27 can be used to reduce the amount of exhaust gas return in the exemplary embodiment according to FIGS. 3 and 4. In this case, as in the exemplary embodiment according to FIGS. 1 and 2, the probe 5 is used to detect the oxygen content of the combustion air / exhaust gas mixture upstream of the fuel supply outlet nozzle 32, and in contrast to the exemplary embodiment according to FIGS. 1 and 2, the oxygen content can be adjusted to a predetermined value by the valve 27. In the illustrated exemplary embodiment, an annular cavity remains between the fuel lance 31 of the fuel supply 3 and the mixing chamber 22, which can be used, for example, for wiring the probe 5. In another embodiment, the inner diameter of the annular mixing chamber 22 is the same as the outer diameter of the duct 31, thus leaving no cavity.

[0049] 5 shows the burner 1 according to FIG. 1 and the heating chamber 7, which is separated by a housing 70. In the illustrated exemplary embodiment, a double-walled housing 70 is provided. A tube coil 71 is arranged in the double-walled housing 70, through which the medium to be heated is guided. Exhaust gases or combustion gases are guided through the double-walled housing 70 to an outlet 72 and in the process heat the medium guided in the tube coil. In addition, to avoid the thermal formation of nitrogen oxides, the exhaust gases are sucked up by an injection pump formed by the driving nozzle 21 and the mixing chamber 22 and mixed with the combustion air.

[0050] In contrast to the embodiment according to Figures 1 and 2, the embodiment according to Figure 5 provides an extended flame tube 112 for extended residence time to ensure burnout for operation with fuels with low reaction rates, such as natural gas. [Aspect 1] 1. An apparatus for supplying combustion air to a burner (1) having a combustion chamber (10) and recirculating exhaust gases, the apparatus (2) comprising a plurality of motive nozzles (21) arranged about a central axis (A) and fluidly connected to a combustion air supply, 1. An apparatus for supplying combustion air to a burner (1) and for recirculating exhaust gases, characterized in that it comprises a mixing chamber (22) arranged downstream of the motive nozzle (21), the motive nozzle (21) and the mixing chamber (22) forming an injection pump, in which the combustion air issuing from the motive nozzle (21) can be mixed with the exhaust gases issuing from the combustion chamber (10) and sucked back by the motive nozzle (21) to form a combustion air / exhaust gas mixture, which can be fed to a reaction zone downstream of the mixing chamber (22). [Aspect 2] 2. The apparatus of claim 1, wherein the mixing chamber (22) has a circular cross section. [Aspect 3] 3. The apparatus according to aspect 1 or 2, wherein there are eight or more motive nozzles (21) uniformly arranged around the central axis (A). [Aspect 4] Aspect 4. The apparatus according to any one of aspects 1 to 3, characterized in that the cross-sectional area ratio between the mixing chamber (22) and the motive nozzle (21) is 20 or less. [Aspect 5] 5. The apparatus of any one of aspects 1 to 4, further comprising a bypass duct (23) through which the combustion air can be supplied to the reaction zone while bypassing the motive nozzle (21), preferably comprising a nozzle opening (230) at an outlet end of the bypass duct (23). [Aspect 6] 6. The device according to aspect 5, wherein an adjustable bypass valve (231) is provided in the bypass duct (23), preferably the bypass valve (231) being continuously or steplessly adjustable. [Aspect 7] 7. The device according to any one of aspects 1 to 6, characterized in that an adjustable valve (27) is provided in the suction opening (25) for the sucked back exhaust gas, preferably the valve (27) being continuously or steplessly adjustable. [Aspect 8] 8. The device according to any one of aspects 1 to 7, characterized in that a probe (5) is provided, preferably upstream of the outlet opening of the fuel supply (3), for measuring oxygen and / or a measurement sensor (6) is provided for measuring the temperature of the recirculated exhaust gas. [Aspect 9] A burner comprising the apparatus of any one of aspects 1 to 8 and a fuel lance (31), the fuel lance being disposed coaxially with respect to the central axis (A) and having an outlet opening (32). [Aspect 10] A burner, characterized in that it is provided with a flame tube (12, 112), which delimits the combustion chamber (10) transversely to the flow direction. [Aspect 11] A burner according to aspect 9 or 10, characterized in that the fuel supply (3) comprises an ignition means (34) or a pilot burner. [Aspect 12] A method for supplying combustion air to a burner (1) having a combustion chamber (10) and recirculating exhaust gases, the method comprising: sucking exhaust gases from the combustion chamber (10) while supplying the combustion air by a plurality of motive nozzles arranged around a central axis (A) to a mixing chamber (22) arranged downstream of the motive nozzles (21); in the mixing chamber (22), the combustion air exiting the motive nozzles (21) is mixed with exhaust gases flowing out of the combustion chamber (10) and sucked back by the motive nozzles (21) to form a combustion air / exhaust gas mixture; and supplying the combustion air / exhaust gas mixture downstream of the mixing chamber (22) to a reaction zone. A method for supplying combustion air and recirculating exhaust gases for a burner (1) having a combustion chamber (10). [Aspect 13] 13. The method of claim 12, wherein the combustion air is supplied to the reaction zone selectively via a bypass duct (23) while bypassing the motive nozzle (21). [Aspect 14] 14. The method of claim 13, wherein an oxygen content of a mixture of the combustion air supplied through the bypass duct (23) and the combustion air / exhaust gas mixture is monitored, and the amount of combustion air supplied through the bypass duct (23) is adjusted to maintain a predetermined oxygen content. [Aspect 15] 15. The method according to any one of aspects 12 to 14, characterized in that a temperature of the recirculated exhaust gas is detected and the amount of the combustion air supplied through a bypass duct (23) is adjusted in response to the detected temperature.

Claims

1. 1. An apparatus for supplying combustion air to a burner (1) having a combustion chamber (10) and for recirculating exhaust gases, said apparatus (2) comprising a plurality of motive nozzles (21) arranged about a central axis (A) and fluidly connected to a combustion air supply, comprising: a mixing chamber (22) arranged downstream of the motive nozzle (21), the motive nozzle (21) and the mixing chamber (22) forming a jet pump, in which the combustion air coming out of the motive nozzle (21) can be mixed with the exhaust gases coming out of the combustion chamber (10) and sucked back by the motive nozzle (21) to form a combustion air / exhaust gas mixture, and the combustion air / exhaust gas mixture can be fed to a reaction zone downstream of the mixing chamber (22); 1. An apparatus for supplying combustion air to a burner (1) and recirculating exhaust gases, characterized in that a bypass duct (23) is provided by which the combustion air can be supplied to the reaction zone while bypassing the motive nozzle (21), the bypass duct (23) terminating downstream of the mixing chamber (22).

2. 2. The device according to claim 1, characterized in that the mixing chamber (22) has an annular cross section.

3. 3. Device according to claim 1 or 2, characterized in that there are provided eight or more than nine motive nozzles (21) uniformly distributed around the central axis (A).

4. 4. Device according to any one of claims 1 to 3, characterized in that the cross-sectional area ratio between the mixing chamber (22) and all the motive nozzles (21) is less than or equal to 20.

5. An apparatus as described in any one of claims 1 to 4, characterized in that a nozzle opening (230) is provided at the outlet end of the bypass duct (23).

6. 6. The device according to claim 5, characterized in that an adjustable bypass valve (231) is provided in the bypass duct (23), preferably the bypass valve (231) being continuously or steplessly adjustable.

7. 7. The device according to claim 1, wherein an adjustable valve (27) is provided in the intake opening (25) for the exhaust gases sucked back, the valve (27) preferably being continuously or steplessly adjustable.

8. An apparatus as described in any one of claims 1 to 7, characterized in that a probe (5) is provided for measuring oxygen and / or a measurement sensor (6) is provided for measuring the temperature of the recirculated exhaust gas.

9. 9. A burner comprising the device according to any one of claims 1 to 8 and a fuel lance (31), the fuel lance being arranged coaxially with respect to the central axis (A) and having an outlet opening (32).

10. 10. Burner according to claim 9, characterized in that a flame tube (12, 112) is provided, said flame tube delimiting said combustion chamber (10) transversely to the flow direction.

11. Burner according to claim 9 or 10, characterized in that the fuel supply (3) comprises ignition means (34) or a pilot burner.

12. A method for supplying combustion air to a burner (1) having a combustion chamber (10) and recirculating exhaust gases, the method comprising: sucking exhaust gases from the combustion chamber (10) while supplying the combustion air by a plurality of motive nozzles arranged around a central axis (A) to a mixing chamber (22) arranged downstream of the motive nozzles (21); in the mixing chamber (22), the combustion air exiting the motive nozzles (21) is mixed with exhaust gases flowing out of the combustion chamber (10) and sucked back by the motive nozzles (21) to form a combustion air / exhaust gas mixture; the combustion air / exhaust gas mixture is supplied to a reaction zone downstream of the mixing chamber (22); the combustion air is optionally supplied to the reaction zone via a bypass duct (23) while bypassing the motive nozzles (21), the bypass duct (23) terminating downstream of the mixing chamber (22). A method for supplying combustion air and recirculating exhaust gases for a burner (1) having a combustion chamber (10).

13. 13. The method according to claim 12, characterized in that the oxygen content of the mixture of the combustion air supplied selectively through the bypass duct (23) and the combustion air / exhaust gas mixture is monitored and the amount of combustion air supplied through the bypass duct (23) is adjusted to maintain a predetermined oxygen content.

14. 14. The method according to claim 12 or 13, characterized in that the temperature of the recirculated exhaust gas is detected and the amount of combustion air supplied via the bypass duct (23) is adjusted depending on the detected temperature.

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