Burner for the reduction of nitrogen oxide emissions and air nozzle for this burner

Abstract

The invention relates to a burner (1), in particular a flat flame burner, with a fuel gas nozzle (2) for the supply of a fuel gas (4) and with multiple air nozzles (3) for the supply of combustion air (10) and which are arranged substantially in a ring around the fuel gas nozzle (2). According to the invention, the air nozzles (3) each have at least one opening (12) in a lateral nozzle wall (13), via which blocking air (9) can be supplied to the combustion air (10), so that the blocking air (9) strikes the combustion air (10) in a substantially perpendicular direction. The invention also relates to a corresponding air nozzle (13).

Description

[0001] BURNER FOR REDUCING NITROGEN OXIDE EMISSIONS AND AIR NOZZLE YOUR THIS BURNER

[0002] The subject of this invention is a burner, in particular a flat-flame burner, with a burner gas nozzle for supplying a fuel gas, for example natural gas or hydrogen, and several air nozzles for supplying combustion air, which are arranged in a ring around the fuel gas nozzle. The subject of this invention also is an air nozzle for this burner.

[0003] Burners, particularly for industrial applications, are often operated with natural gas. The required combustion air is supplied via several air nozzles, which are usually arranged in a ring around the gas outlet. These burners are usually designed for a certain burner output, but they often have to be operated at a lower output. Experience has shown that the emission rate of nitrogen oxides from an industrial burner increases if the operating mode deviates from the design point. Reducing the combustion output usually leads to higher emissions of nitrogen oxides. This can be explained by the fact that the flow impulse at the burner nozzle decreases as a result of the decreasing mass flow, which influences the kinetics of the chemical reactions in the flame.

[0004] Investigations have shown that, for example, the new values ​​for a natural gas burner from ANDRITZ with a nominal burner capacity of 300 kW increase by 450% if this burner is operated at only 25% of its nominal burner capacity. The NO x The NOx concentration rises to approximately 70 ppm. This increase is considered uncritical in view of the permitted NOx concentration, which is below 100 ppm. However, the situation becomes more critical when these burners are operated with hydrogen. Using hydrogen instead of natural gas leads to higher combustion temperatures and thus also to higher NOx X - values, since the formation of nitrogen oxides is favored by higher temperatures. For example, the NO x -Concentration at a nominal burner output of 300 KW is already ~ 50 ppm and increases by over 300% at a burner output of 25% of the nominal burner output. Here, the NO x-Concentration well above 150 ppm.

[0005] The aim of the invention is to provide a burner which has lower nitrogen oxide emissions than more conventional burners when operated below the nominal burner power.

[0006] The flow impulse of a nozzle is the product of the mass flow and the flow outlet velocity. Accordingly, the flow impulse decreases with decreasing mass flow. If a conventional burner is operated at lower power, not only the fuel gas but also the combustion air supplied via the air nozzles is reduced. This also reduces the flow impulse at the air nozzle and the NO x -values ​​increase. This loss can be compensated by increasing the flow velocity of the combustion air.

[0007] The invention is therefore based on the object of increasing the flow velocity of the combustion air in partial load operation of a burner in order to reduce the N0 x - To reduce emissions without requiring mechanical action on the nozzle cross-section. This object is achieved by a burner, in particular a flat flame burner, according to claim 1.

[0008] According to the invention, the air nozzles of the burner each have at least one opening in their lateral nozzle wall through which sealing air can be supplied to the combustion air, so that the sealing air strikes the combustion air essentially perpendicularly.

[0009] The subject of this invention is therefore the concept of applying sealing air (compressed air) to the air nozzles to change the flow characteristics of the gas in front of the burner.

[0010] The functional principle of the air nozzle according to the invention with sealing air supply is illustrated in Figure 2.

[0011] Preferably, the opening in the lateral nozzle wall of the air nozzle is slit-shaped and extends at least over a partial circumference of the nozzle wall. It is also conceivable for the opening to extend over the entire circumference of the nozzle wall.

[0012] The air nozzles can have a circular cross-section, a rectangular cross-section or a polygonal cross-section.

[0013] It is advantageous if the air nozzles taper in front of the opening for the sealing air supply, as viewed in the direction of combustion air flow. It is advantageous if the reduction angle C, at which the air nozzles taper in front of the opening, is between 20° and 50°. It is advantageous if the opening in the nozzle wall is located in the area of ​​the air nozzle with the smallest free cross-section, i.e., at the point where the flow experiences the maximum acceleration.

[0014] The invention also provides an air nozzle for supplying combustion air for use in a burner, in particular a flat-flame burner. According to the invention, the air nozzle has an opening in its lateral nozzle wall through which sealing air can be supplied to the combustion air, the sealing air striking the combustion air essentially perpendicularly.

[0015] In the following, exemplary embodiments of the invention are described with reference to the drawings. They show:

[0016] Fig. 1 is a schematic sectional view through a burner according to the invention, which here is a flat flame burner;

[0017] Fig. 2 is a detailed view of the air nozzle of the burner from Figure 1;

[0018] Fig. 3 shows the flat flame burner according to the invention from Fig. 1;

[0019] Fig. 4 and 5 show the operation of the air nozzle according to the invention;

[0020] Fig. 6 shows some geometric parameters of an embodiment of the air nozzle; Figure 1 shows a burner 1 according to the invention in the form of a flat flame burner. Combustion gas 4, for example natural gas or hydrogen, is fed to the combustion gas nozzle 2 via a combustion gas channel 11. The combustion gas nozzle 2 is surrounded by a plurality of air nozzles 3. Combustion air 10 is supplied to the air nozzles 3 via the combustion air supply 5 and the combustion air channel 8. In addition, sealing air 9 is supplied to the air nozzles 3 via the sealing air supply 6 and the sealing air channel 7. The sealing air 9 is fed to the combustion air 10 through the opening 12 in the nozzle wall 13.

[0021] Figure 2 shows the air nozzle from Figure 1 in detail. The opening 12 in the nozzle wall 13 can be clearly seen. This opening 12 is slit-shaped in this exemplary embodiment. The cross-section of the air nozzles 3 is essentially square in this example, as can be clearly seen from Figure 3. There you can also clearly see the slit-shaped opening 12 in the nozzle wall 13, which here extends parallel to the inner side edge of the nozzle wall 13 (facing the fuel gas nozzle). The burner 1 shown here has ten air nozzles 3 which are arranged in a ring around the fuel gas nozzle 2. Extensive tests have shown that the air nozzle 3 shown in Figure 2 delivers particularly good results if certain geometric requirements are met.

[0022] It works particularly well when the following relationship holds :

[0023] 0 , 3 < X / Z < 0 , 5 Where X is the distance of the opening 12 from the outlet end 16 of the air nozzle 3 and Z is the diameter of the air nozzle 3 at the outlet end 16 .

[0024] In the present example, the air nozzle 3 also has a taper 15 in front of the opening 12 for the sealing air 9. The nozzle diameter thus decreases towards the opening 12. The reduction angle C of the taper 15 is in the range of 20° or more. In the present example, the air nozzle 3 tapers only on the side where the sealing air 9 is also supplied.

[0025] The functional principle of the air nozzle 3 according to the invention is explained in Figures 4 and 5. Figure 4 shows the flow conditions of an air nozzle 3 when the burner 1 is operating at its nominal combustion output. The burner 1 is generally designed for this operating point, and the flow conditions for the combustion air 10 are optimal. A supply of sealing air 9 is not necessary here.

[0026] Figure 5 shows an operating state of an air nozzle 3 in a burner 1 operating at a lower burner output than the nominal burner output. Sealing air 9 is now supplied to the air nozzle 3 via the opening 12. The opening 12 is located at the point where the air nozzle 3 has the smallest free cross-section and where the air flow experiences the maximum acceleration.

[0027] In the present example, the air nozzle 3 has a circular cross-section, and the opening 12 in the nozzle wall 13 is annular. The sealing air 9 pushes the combustion air 10 inwards, thus causing a curvature of the flow of the combustion air 10. The free cross-section for the combustion air 10 is thereby reduced, and the flow velocity and thus also the flow momentum are increased. In the area in which the combustion air 10 is pushed inwards, vortices and a negative pressure are created, through which ambient air 14 is sucked in in the area of ​​the outlet opening. This is shown schematically in Figure 5.

[0028] The sealing air supply 6 can thus increase the flow momentum of the combustion air 10 in burners 1 operating at a lower power than the nominal burner power, thus positively influencing the kinetics of the chemical reactions of the flame. This leads to a reduction in the formation of nitrogen oxides.

[0029] In the exemplary embodiments in Figures 1 to 3, the sealing air 9 is supplied from only one side of the nozzle wall 13. The flow of combustion air 10 is thereby compressed from one side.

[0030] In the embodiments shown in Figures 4 to 6, the opening 12 in the nozzle wall 13 is annular gap-shaped. The flow of combustion air 10 is thus compressed from all sides. In all embodiments, the supply of sealing air 9 leads to a reduction in the effective free cross-section of the air nozzle 3 and, accordingly, to a flow acceleration through the air nozzle 3.

[0031] Figure 6 shows the air nozzle 3 with the annular gap-shaped opening 12 from Figures 4 and 5 with geometric parameters. It has been shown that this air nozzle 3 functions particularly well when the following relationship applies:

[0032] 0 , 1 < B 2 / A < 0 , 32 Where B is the distance of the opening 12 from the outlet end 16 of the air nozzle 3 and A is the diameter of the air nozzle 3 at the

[0033] Exit end 16 .

[0034] Reference symbol

[0035] 1 burner

[0036] 2 fuel gas nozzle

[0037] 3 Air nozzle

[0038] 4 Fuel gas

[0039] 5 Combustion air supply

[0040] 6 Sealing air supply

[0041] 7 Sealing air duct

[0042] 8 Combustion air duct

[0043] 9 Sealing air

[0044] 10 Combustion air

[0045] 11 Fuel gas channel

[0046] 12 Opening for sealing air

[0047] 13 Nozzle wall

[0048] 14 Ambient air

[0049] 15 Rejuvenation

[0050] 16 Outlet end of the air nozzle 3

Claims

Patent claims 1. Burner (1), in particular a flat flame burner, with a fuel gas nozzle (2) for supplying a fuel gas (4), for example natural gas or hydrogen, and with a plurality of air nozzles (3) for supplying combustion air (10), which are arranged substantially in a ring around the fuel gas nozzle (2), characterized in that the air nozzles (3) each have at least one opening (12) in a lateral nozzle wall (13), via which sealing air (9) can be supplied to the combustion air (10), so that the sealing air (9) strikes the combustion air (10) essentially perpendicularly.

2. Burner (1) according to claim 1, characterized in that the opening (12) in the lateral nozzle wall (13) of the air nozzles (3) is slit-shaped and extends at least over a partial circumference of the nozzle wall (13).

3. Burner (1) according to claim 2, characterized in that the opening (12) extends over the entire circumference of the nozzle wall (13).

4. Burner (1) according to one of claims 1 to 3, characterized in that the air nozzles (3) have a circular cross-section.

5. Burner (1) according to claim 4, characterized in that the following relationship applies: 0.3 < X / Z < 0.5 where X is the distance of the opening (12) from the outlet end (16) of the air nozzle (3) and Z is the diameter of the air nozzle (3) at the outlet end (16).

6. Burner (1) according to one of claims 1 to 3, characterized in that the air nozzles (3) have a polygonal, in particular a rectangular or square cross-section.

7. Burner (1) according to claim 6, characterized in that the following relationship applies: 0, 1 < B 2 / A < 0.32 where B is the distance of the opening (12) from the outlet end (16) of the air nozzle (3) and A is the diameter of the air nozzle (3) at the outlet end (16).

8. Burner (1) according to one of claims 1 to 7, characterized in that the air nozzles (3) taper in front of the opening (12) for the supply of the sealing air (9), viewed in the flow direction of the combustion air (10).

9. Burner (1) according to claim 8, characterized in that the reducing angle (C) with which the air nozzles (3) taper in front of the opening (12) is between 20° and 50°.

10. Burner (1) according to one of claims 1 to 9, characterized in that the opening (12) in the nozzle wall (13) is arranged in the region of the air nozzle (3) with the smallest free cross-section.

11. Air nozzle (3) for the supply of combustion air (10) for use in a burner (1), in particular a flat flame burner, characterized in that the air nozzle (3) has at least one opening (12) in its lateral nozzle wall (13) through which the sealing air (9) of the Combustion air (10) can be supplied so that the sealing air (9) strikes the combustion air (10) essentially perpendicularly.

12. Air nozzle (3) according to claim 11, characterized in that the opening (12) in the lateral nozzle wall (13) of the air nozzle (3) is slit-shaped and extends at least over a partial circumference of the nozzle wall (13).

13. Air nozzle (3) according to claim 12, characterized in that the opening (12) extends over the entire circumference of the nozzle wall (13).

14. Air nozzle (3) according to one of claims 11 to 13, characterized in that the air nozzle (3) has a circular cross-section.

15. Air nozzle (3) according to claim 14, characterized in that the following relationship applies: 0.3 < X / Z < 0.5 where X is the distance of the opening (12) from the outlet end (16) of the air nozzle (3) and Z is the diameter of the air nozzle (3) at the outlet end (16).

16. Air nozzle (3) according to one of claims 11 to 13, characterized in that the air nozzle (3) has a polygonal cross-section.

17. Air nozzle (3) according to claim 16, characterized in that the following relationship applies: 0, 1 < B 2 / A < 0.32 where B is the distance of the opening (12) from the outlet end (16) of the air nozzle (3) and A is the diameter of the air nozzle (3) at the outlet end (16).

18. Air nozzle (3) according to one of claims 11 to 17, characterized in that the air nozzle (3), viewed in the flow direction of the combustion air (10), tapers upstream of the opening (12) for the supply of the sealing air (9).

19. Air nozzle (3) according to claim 18, characterized in that the reduction angle (c) with which the air nozzle (3) tapers upstream of the opening (12) is between 20° and 50°.

20. Air nozzle (3) according to one of claims 11 to 19, characterized in that the opening (12) in the nozzle wall (13) is arranged in the region of the air nozzle (3) with the smallest free cross-section.

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