Burner for reducing NOx emissions and method for operating the burner

Abstract

A burner for heating a heating space with a reduction of NOx emissions is provided. The burner includes a mixing and combustion chamber, a mixing and igniting device disposed in the mixing and combustion chamber, and a fuel feed connected to the mixing and igniting device and configured for feeding fuel to the mixing and igniting device. Further, an air feed is provided, which is configured for feeding at least one partial air flow to the mixing and combustion chamber. A combustion chamber opening opens the mixing and combustion chamber towards a heating space to be heated. Furthermore, control means are configured for controlling a fuel flow via the fuel feed and for controlling at least one partial air flow via the air feed.

Claims

1. A method for operating a burner for heating a heating space with a reduction of NOx emissions, the burner comprising: a mixing and combustion chamber; a mixer-igniter disposed in the mixing and combustion chamber; a fuel feed connected to the mixer-igniter mixing and igniting device and adapted to feed fuel to the mixer-igniter; an air feed adapted to feed at least one partial air flow to the mixing and combustion chamber; a combustion chamber opening adapted to open the mixing and combustion chamber towards a heating space to be heated; a controller adapted to control a fuel flow via the fuel feed and for controlling at least one partial air flow via the air feed, wherein the burner and the controller operate the burner with a stable flame extending from the mixer-igniter through the combustion chamber opening into the heating space; and a cross-section of the combustion chamber opening relative to the burner output is in a range of between 1.5 mm.sup.2/kW and 10 mm.sup.2/kW, the method comprising: subsequent to a parameter value reaching a prescribed value, increasing, by the controller, the fuel flow via the fuel feed while maintaining the air flow via the air feed substantially the same as prior to increasing the fuel flow so that a ratio of the fuel flow to the airflow is changed from 1:20 to 1:10 without extinguishing the stable flame.

2. The method according to claim 1, wherein the cross-section of the combustion chamber opening relative to the burner output is further limited to in the range of between 1.5 mm.sup.2/kW and 8 mm.sup.2/kW.

3. The method according to claim 1, wherein the air feed is formed by an air feed pipe, within which the mixer-igniter is disposed in such a way that the mixing and combustion chamber is formed, and that the air feed pipe forms the combustion chamber opening.

4. The burner method according to claim 1, wherein the cross-section of the combustion chamber opening relative to the burner output is further limited to in the range of between 1.5 mm.sup.2/kW and 5 mm.sup.2/kW.

5. The method according to any one of the claim 1, wherein it includes a recuperator, which at least partially surrounds the air feed and via which a second partial air flow can be fed to the mixing and combustion chamber or the heating space outside the mixing and combustion chamber.

6. The method according to claim 5, wherein the air feed is formed by an air feed pipe, within which the mixer-igniter is disposed in such a way that the mixing and combustion chamber is formed, and that the recuperator forms the combustion chamber opening, while the second partial air flow is guided from the recuperator into the mixing and combustion chamber.

7. The method according to claim 6, wherein the cross-section of the combustion chamber opening relative to the burner output is further defined to be in between 3 mm.sup.2/kW and 10 mm.sup.2/kW.

8. The method according to claim 1, wherein the parameter is a temperature in a space to be heated.

9. The method according to claim 8, wherein the temperature is between 200 C. and 500 C.

10. The method according to claim 1, wherein the burner further comprises a flame detector, wherein flame detector is configured for detecting a flame in the region of the mixer-igniter, in the mixing and combustion chamber, and wherein the method further comprises: detecting a flame by the flame detector.

11. The method according to claim 1, wherein the cross-section of the combustion chamber opening relative to the burner output is further limited to in the range of between 1.5 mm.sup.2/kW and mm.sup.2/kW.

12. The method according to claim 1, wherein the cross-section of the combustion chamber opening relative to the burner output is further limited to in the range of between 2.5 mm.sup.2/kW and 3.5 mm.sup.2/kW.

13. The method according to claim 6, wherein the cross-section of the combustion chamber opening relative to the burner output is further defined to be in a range of between 3 mm.sup.2/kW and 6 mm.sup.2/kW.

14. The method according to claim 8, wherein the temperature is between 200 C. and just below the temperature for flameless oxidation.

Description

(1) In the drawings:

(2) FIG. 1 shows a schematic cross-section through a first embodiment of a burner according to an embodiment;

(3) FIG. 2 shows an illustration of an embodiment of control means for controlling a burner in a flow chart;

(4) FIG. 3 shows a schematic cross-section through a second embodiment of a burner according to an embodiment; and

(5) FIG. 4 shows a schematic cross-section through a third embodiment of a burner according to an embodiment.

(6) FIG. 1 schematically shows a first embodiment of a burner 10 according to the invention, based on which the essential features of the invention are to be explained. However, the structure of the burner is not to be understood to be limiting, and FIG. 1 presents, in particular, only a schematic representation of the components and component dimensions. The same also applies to the FIGS. 3 and 4 that show further embodiments. Designs without a recuperator are also included.

(7) The burner 10 is built into a furnace wall 20 and generates a flame 56 with which a heating space 55 is to be heated. In this embodiment, this is an open flame directly heating the heating space 55. However, other embodiments with indirect heating are possible, in which a radiant tube is used. FIG. 4 shows such an embodiment.

(8) The burner 10 has a mixing and combustion chamber 54 which is formed by an air feed 30 in the form of an air feed pipe. Combustion air is introduced (not shown) into this air feed 30 and flows into the mixing and combustion chamber 54 as a first partial air flow L1. An igniting and mixing device 51 connected to a fuel feed 50 through which fuel is fed to the igniting and mixing device 51 is secured within this air feed pipe 30. The fuel is natural gas, for instance.

(9) The igniting and mixing device 51 is configured in a suitable manner such that the fuel exits it in such a way that a stable flame 56 can be produced by igniting the mixture of the fuel flow B and the first partial air flow L1. In the schematic representation of FIG. 1, several fuel flows exit the igniting and mixing device 51 laterally at an angle for this purpose, but this is not to be understood as limiting. Any other suitable igniting and mixing device 51 may also be used.

(10) In this embodiment, the burner further includes a recuperator 40 surrounding the air feed pipe 30. Hot waste gases A1 are drawn from the heating space 55 into the recuperator 40, and a second partial air flow L2 is heated in the counter flow. Optionally, the first partial air flow L1 may also have been preheated in the recuperator 40. The second preheated partial air flow L2 is fed to the heating space 55. This takes place in the region of an elongated flame 56, this flame 56 having different flame zones. A first flame zone 56a is located within the mixing and combustion chamber 54, wherein the air feed pipe 30 forms a combustion chamber opening 53 through which the flame 56 extends from the igniting and mixing device 51. A second flame zone 56b is formed in the heating space 55 in front of the combustion chamber opening 53. The second preheated partial air flow L2 is fed to the flame zone 56b from the recuperator 40. At the same time, hot waste gases A2 are suctioned from the heating space 55 into the flame zone 56b.

(11) In this burner configuration, the cross-section of the combustion chamber opening 53 relative to the burner output is in the range of between 1.5 mm.sup.2/kW and 5 mm.sup.2/kW, particularly preferably between 2.5 mm.sup.2/kW and 3.5 mm.sup.2/kW, for instance. This leads to high exit speeds at the combustion chamber opening 53, which cause low NOx values in the flame zone 56b. Together with the NOx formation of the flame 56 within the mixing and combustion chamber, low NOx values, on the whole, in the range of 5 to 100 mg/Nm.sup.3 relative to 3% O.sub.2 in dry waste gas can be obtained with direct firing. Moreover, the flame 56 is easily monitored, wherein an ionization bar 52, with which the presence of the flame 56 can be detected, is provided in the mixing and combustion chamber 54 for this purpose.

(12) In order to bring the burner into the operating state of FIG. 1, a heating-up phase with a certain control of the fuel flow B and the partial air flows L1, L2 preferably takes place in order to be able to generate a stable flame 56 even in the case of a cold burner 10. Control means 60, whose configuration can be gathered by way of example from FIG. 2, are provided for this purpose. A burner 10 is equipped with control means 60 that enable the burner 10 to be supplied with fuel and air. Hereinafter, the fuel is simply referred to as gas. Starting from the burner 10, a series of an adjusting valve 61, a gas valve 63, a compensator 64 and a spherical valve 65 for connection to a gas supply (not shown) is provided for the gas flow. Starting from the burner 10, a series of an adjusting valve 66, an air valve 67, a compensator 68 and a gate valve 69 for connection to an air supply (not shown) is provided for the air flow. A balanced pressure regulator 62 with a gas valve and a further gas valve 62a in a bypass are provided in a parallel connection between the adjusting valve 61 and the gas valve 63. Between the adjusting valve 66 and the air valve 67, an impulse line 70 branches off towards the balanced pressure regulator 62 with the gas valve.

(13) With these control means the burner can be started up, at first in a cold state, with a fuel-to-air ratio of about 1:20, which enables the formation of a stable flame 56. In the process, the full amount of air is already made available, whereas the fuel flow is at first reduced by means of the valve 62a. Depending on the configuration of the burner 10 and the ambient conditions in a furnace, the fuel flow may be increased from a predetermined temperature, because the flame 56 now stabilizes even at a higher fuel percentage. From this temperature on, a switch is made for the fuel flow from the valve 62a to the valve 62, the fuel flow is thus increased, and a fuel-to-air ratio of approximately 1:10 is set in the process, for example.

(14) FIG. 3 shows an alternative embodiment of the burner 11 according to the invention, in which, however, the recuperator 40 forms the combustion chamber opening 53. Thus, the second partial air flow L2 preheated in the recuperator 40 leads into the mixing and combustion chamber 54 together with the first partial air flow L1. However, the flame 56 with the two flame zones 56a and 56b is formed in an analogous manner, and the other components also correspond to the embodiment of FIG. 1. Only the cross-section of the combustion chamber opening 53 relative to the burner output is in this case in the range of between 3 mm.sup.2/kW and 10 mm.sup.2/kW, particularly preferably between 3 mm.sup.2/kW and 6 mm.sup.2/kW.

(15) FIG. 4 shows a burner 12 according to the embodiment of FIG. 3, in which a heating space 55 to be heated is disposed within a flame tube 42. The flame tube 42 is surrounded by a radiant tube 41 which protrudes from the furnace wall 20 into a furnace interior space for indirect heating. The flame tube 42 within the radiant tube 41 permits the flow of hot waste gases A3 back to the burner 12, wherein they are either fed as waste gases A1 to the recuperator, or suctioned in as waste gases A2 by the flame zone 56b. If an SER radiant tube is used, for example, NOx values in the range of 50 to 150 mg/Nm.sup.3 relative to 3% O.sub.2 in dry waste gas can be obtained with the invention.

LIST OF REFERENCE NUMERALS

(16) 10, 11, 12 Burner 20 Furnace wall 30, 30 Air feed, air feed pipe 40, 40 Recuperator 41 Radiant tube 42 Flame tube 50 Fuel feed 51 Mixing and igniting device 52 Flame monitoring means, ionization bar 53 Burner chamber opening 54, 54 Mixing and combustion chamber 55, 55 Heating space 56 Flame 56a, 56b Flame zone 60 Control means 61 Adjusting valve gas 62 Balanced pressure regulator with gas valve V2 62a Gas valve bypass 63 Gas valve V1 64 Compensator 65 Spherical valve 66 Adjusting valve air 67 Air valve 68 Compensator 69 Gate valve 70 Impulse line L1 Partial air flow L2 Partial air flow, preheated B Fuel flow A1 Waste gas flow in recuperator A2 Waste gas flow in flame A3 Waste gas flow return feed