Method and burner head for the staged combustion of fuel

Abstract

A method for combusting fuel in stages by feeding combustion air (28) into a burner tube (12). A first fuel quantity is fed to form a primary flame (24) in the burner tube. A second fuel quantity is fed downstream to form a main flame front (26). The main flame front (26) stabilizes downstream of the burner tube (12) and is spaced apart from the burner tube (12). The fuel feed is designed such that the primary flame (24) burns at a stoichiometric ratio greater than 1.5, in particular greater than 2.0.

Description

Technical Field

[0001] The invention relates to a method for the staged combustion of fuel and a burner head for the staged combustion of fuel. Background Art

[0002] When burning fossil fuels in combustion plants, nitrogen oxides, such as NO and NO₂, are produced in addition to the processing of other combustion products. Hereinafter, they are collectively referred to as NO. Emissions of these and other harmful substances can be influenced and reduced through structural measures in the burner. The reaction mechanisms that lead to these nitrogen oxides are generally known and are generally distinguished between thermal and transient NO formation, as well as NO formation described as oxidation of nitrogen chemically bound in the fuel.

[0003] It is known that, according to the so-called Zeldovich mechanism, hot NO is dependent on the residence time of the reaction components in the combustion zone, on the one hand, and on the other hand, to a large extent on the combustion temperature itself. The combustion temperature is correlated with the fuel / air ratio λ. The maximum combustion temperature is set at a fuel / air ratio λ=1. This fuel / air ratio is also called the stoichiometric ratio. There is just enough oxygen in the combustion air to ensure complete combustion of the fuel. A fuel / air ratio λ<1 is considered a rich mixture because there is too much fuel. A fuel / air ratio λ>1 is considered a lean mixture because there is too much air. In both cases, the combustion temperature drops again, so less hot NO is formed.

[0004] In addition to thermal NO, the formation of prompt NOx is also important. Prompt NO is generated by hydrocarbon radicals (CH) formed intermediately within the flame as an intermediate product during the combustion of carbon-containing fossil fuels. CH radicals react with atmospheric nitrogen to form hydrocyanic acid (HCN), which is then converted to NO in a very rapid reaction. Lean combustion, or combustion above the stoichiometric ratio, is an effective method to suppress the formation of free CH radicals and thus prompt NO. Lean combustion refers to combustion with excess air, i.e., with a lambda ratio greater than 1.

[0005] Prompt NO is produced in smaller quantities compared to thermal NO, but is crucial for minimizing NO formation especially in ultra-low NO applications.

[0006] It is also known that recirculating or recovering the exhaust gas produced during combustion can help reduce nitrogen oxide formation. Recirculating cooled exhaust gas lowers the flame temperature itself and also reduces the O2 partial pressure in the combustion zone. Both effects contribute to reducing NO formation. However, the introduction of increasing amounts of exhaust gas tends to destabilize the ongoing combustion process.

[0007] EP 1 754 937 B1 and EP 2 037 173 B1 describe combustion heads for achieving NO reduction. These primarily involve single-stage combustion methods that only achieve further NO optimization and flame stabilization to a limited extent. DE 195 09 219 A1 describes a combustion head for two-stage combustion using an air-gas mixture above stoichiometric in the first stage and below stoichiometric in the second stage.

[0008] A distinction can generally be made in the combustion head between a so-called mixing zone and a so-called combustion zone.

[0009] In the mixing zone, different fluids mix, but the fluids are not (yet) combusted. In the mixing zone, the conditions necessary for combustion are usually not met. This can be the case, for example, when the flow velocity of the ignitable mixture is significantly higher than the flame velocity.

[0010] The combustion zone is a region where the conditions necessary for combustion exist. A combustion zone is created when an ignitable mixture (e.g., a fuel-combustion air mixture, a fuel-combustion air-exhaust gas mixture, a fuel-oxidizer mixture, a fuel-oxidizer-exhaust gas mixture) is present, the flow velocity and flame velocity of the ignitable mixture are substantially equal, and a temperature equal to or greater than the ignition temperature of the ignitable mixture exists. The general term "oxidizer" encompasses the term "combustion air," but also includes, for example, ambient air enriched with additional oxygen. Ignition or combustion is not possible in regions where these conditions are not met. Typically, the mixing zone transitions into the combustion zone without significant spatial separation. Summary of the Invention

[0011] The present invention is therefore needed. It may be an object of the present invention to be able to dispense with external measures for NO reduction, such as external recirculation. It may be an object of the present invention to keep energy consumption as low as possible. It may be an object of the present invention to provide an energetically advantageous combustion with minimized NO emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The objects and features of the present invention are set forth in the following description of embodiments with reference to the accompanying drawings, in which:

[0013] Figure 1 A side view of the combustion head is shown highly schematically;

[0014] Figure 2 The components of the combustion head are shown in a schematic perspective view from the fuel input side;

[0015] Figure 3 A schematic perspective view from the flame side is shown Figure 2 Components of the combustion head;

[0016] Figure 4 A side view of a combustion head is schematically shown;

[0017] Figure 5 A cross-sectional view schematically shows the front section of the combustion head; and

[0018] Figure 6 A front view of the burner head is shown schematically. DETAILED DESCRIPTION

[0019] The various aspects and embodiments are described below with reference to the accompanying drawings, wherein the same or similar reference numerals are generally used to refer to the same or similar elements. In the following description, many specific details are set forth to provide a basic understanding of one or more aspects of the embodiments. However, it is apparent to those skilled in the art that one or more aspects of the embodiments may be implemented using fewer specific details. In other cases, elements are shown in schematic shapes to simplify the description of one or more aspects of the embodiments. Therefore, the following description should not be considered restrictive. It should be noted that the different elements in the drawings are not necessarily represented in scale.

[0020] Directional terms used in the description with reference to the accompanying drawings, such as "upper," "lower," "upper side," "lower side," "left," "right," "front side," "back side," "vertical," "horizontal," and the like, are not to be construed as limiting. Components of the embodiments may be positioned in a variety of different orientations, and the directional terms are used for descriptive purposes only. It should be understood that other embodiments may be used and that structural or logical changes are contemplated without departing from the scope of the present invention.

[0021] Multi-stage combustion processes are already well known in practice. However, the previously known solutions are currently insufficient to meet the ever-increasing NOx requirements for combustion plant operation over the long term. According to the present disclosure, staged combustion can achieve even more significant NOx reduction. Due to the corresponding adjustability, NOx reduction can also be ensured over a wide load range and / or for different fuels and / or for different combustion chambers.

[0022] A method for staged combustion of fuel by supplying combustion air into a burner tube according to claim 1 is provided. The fuel can be a gaseous or liquid fuel. A first fuel quantity is supplied to form a primary flame in the burner tube. A second fuel quantity can be supplied downstream to form a main flame front. The main flame stabilizes downstream of the burner tube and is spaced apart from the burner tube. The fuel supply is designed such that the primary flame burns at a stoichiometric ratio greater than 1.5, in particular greater than 2.0. This allows very low flame temperatures to be achieved. Virtually no prompt NO is formed. The main flame is slightly above the stoichiometric ratio. The stoichiometric ratio can be between 1.03 and 1.18. The temperature of the main flame can be significantly reduced by exhaust gas recirculated within the combustion chamber.

[0023] In one embodiment, the first fuel quantity is adjusted independently of the second fuel quantity, thereby ensuring a primary flame above the stoichiometric ratio over a wide load range.

[0024] In one embodiment, the first fuel amount input may be significantly lower than the second fuel amount input. For example, the first fuel amount may be between approximately 3% and 15% of the total fuel amount, i.e., the sum of the first and second fuel amounts. Preferably, the first fuel amount is between 5% and 10% of the sum of the first and second fuel amounts.

[0025] In another embodiment, a portion of the combustion air is twisted. This produces swirling combustion air. A first portion of the first combustion quantity is delivered into the region of the air vortex. This produces a swirling, lean air / fuel mixture. This allows for very good mixing. In this region, the flow velocity is high and the mixture is lean, so that ignition conditions are not met. The flow velocity of the swirling, lean air / fuel mixture is reduced in a subsequent step. A second portion of the first fuel quantity is supplied to the decelerated, swirling, lean air / fuel mixture.

[0026] A combustion head for staged combustion of fuel according to claim 7 is also provided. The provided combustion head is capable of carrying out the method. The combustion head is designed to combust a first amount of fuel input in a primary flame at a ratio above the stoichiometric ratio, and a second amount of fuel input in a main flame at a ratio slightly above the stoichiometric ratio.

[0027] The supply of the first quantity of fuel and the supply of the second quantity of fuel are preferably adjustable independently of one another, thus ensuring very low-nitrogen oxide combustion over a wide load range.

[0028] The following figures show, by way of example, the design of a burner head according to the invention, with which the method according to the invention for the staged combustion of fuel can be carried out.

[0029] Figure 1 A side view of a burner head 10 is shown in highly schematic form. The burner head 10 comprises a burner tube 12, a swirl device 14, first fuel nozzles 16a, 16b, a second fuel nozzle 18, a first fuel inlet 20 and a second fuel inlet 22. The arrows symbolically represent the inflow of fuel. In operation, a primary flame 24 with a higher than stoichiometric ratio is formed in the swirl device 14 and a main flame or main flame front 26 is spaced apart from the burner head 10, the two being respectively Figure 1The flames in the burner are shown symbolically. The burner head 10 is thus used for staged combustion of fuel. The fuel can be gaseous. The fuel can be natural gas. The fuel can also include hydrogen. In addition to being used as a pure gas burner, a dual-fuel burner is also possible, in which liquid fuels can be burned in addition to gaseous fuels. Burners designed solely for liquid fuels are also possible. The remaining description generally relates to the embodiment as a gas burner, without limitation.

[0030] exist Figure 1 In the schematic diagram, combustion air 28 is introduced into the burner tube 12 from the right. Therefore, the right end of the burner tube 12 in this schematic diagram is the upstream end. The burner tube 12 can be essentially cylindrical. The combustion air 28 flows through the burner tube 12 and exits the burner tube at the open end on the left side in the schematic diagram, i.e., at the downstream end. The main flame front 26 forms downstream of the burner head 10. A combustion chamber or combustion cavity (not shown in further detail) is located here.

[0031] The amount of fuel ejected from the first fuel nozzles 16a, 16b can be less than the amount of fuel ejected from the second fuel nozzle 18. If only a small amount of fuel is burned significantly above the stoichiometric ratio in the primary flame 24, a second substoichiometric combustion stage is not necessary. Therefore, the spaced-apart main flame 26 can also be above the stoichiometric ratio overall. The burner head 10 according to the present invention does not produce the typical substoichiometric combustion zones that are present in staged combustion, which has substoichiometric and superstoichiometric combustion zones and the gas residence times in these zones required for NO reduction. The method according to the present invention provides a significantly above-stoichiometric primary flame and a slightly above-stoichiometric main flame.

[0032] The swirl device 14 is disposed within the burner tube 12. The swirl device 14 may be open at both ends. The longitudinal axis of the burner tube 12 and the longitudinal axis of the swirl device 14 may be arranged parallel to or one after the other, such that the swirl device 14 is centrally located within the burner tube 12 and uniformly spaced radially from the inner wall of the burner tube. A portion of the combustion air 28 flows through the burner tube 12 outside the swirl device 14, while another portion of the combustion air 28 flows through the swirl device 14.

[0033] The swirl device 14 includes a swirl body 30, swirl blades 32, and perforated partitions 34. The swirl body 30 may be substantially cylindrical. The perforated partitions 34 may extend substantially perpendicular to the longitudinal axis of the swirl body 30 and divide the interior space of the swirl body 30 into a first region 36 and a second region 38. The first region 36 may be located upstream of the second region 38. The perforated partitions 34 may cause a pressure loss. Thus, the perforated partitions may cause a localized decrease in flow velocity downstream of the perforated partitions 34.

[0034] The swirl vane 32 may be arranged only in the first region 36. The second region downstream of the partition wall 34 may be free of the swirl vane 32. A plurality of swirl vanes 32 may be provided.

[0035] The swirling body 30 has a larger diameter in the first region 36 than in the second region 38. A conical section can be provided in the transition between the first region 36 and the second region 38.

[0036] The first fuel nozzles 16a, 16b are arranged in the swirling body 30. The first fuel nozzles are connected to a first fuel input 20. The first fuel input 20 allows the amount of fuel / gas flowing to the first fuel nozzles 16a, 16b to be adjusted, as in Figure 1 This is indicated by reference numeral 40. This regulation is separate and independent of the regulation 42 in the second fuel inlet 22.

[0037] The first fuel nozzles 16a, 16b may include primary fuel nozzles 16a, also referred to as primary gas nozzles, which are located in a second, downstream region 38 of the swirl device 14. The first fuel nozzles 16a, 16b may include further fuel nozzles, hereinafter referred to as auxiliary fuel nozzles or auxiliary gas nozzles 16b, which are located in a first, upstream region 36 of the swirl device 14.

[0038] The pilot fuel nozzles 16b can be evenly distributed between the swirl vanes 32. The pilot fuel nozzles 16b can be arranged substantially parallel to the longitudinal axis of the burner tube 12. The swirl vanes 32 create a strong swirl in the combustion air 28. As a result, the fuel, also known as pilot gas, flowing out of the pilot fuel nozzles 16b is efficiently premixed with the portion of the combustion air 28 intended for the primary flame 24. This creates a swirling fuel / combustion air mixture. The fuel supply through the pilot fuel nozzles 16b can be designed to form a swirling, lean air / fuel mixture. The pilot fuel nozzles 16b can discharge a first portion of a first fuel quantity. The pilot fuel nozzles 16b can have holes for discharging the fuel. The holes can be arranged so that the fuel is at least partially discharged substantially radially inward, i.e., in a direction substantially perpendicular to the wall of the swirling body 30. Due to the high flow velocity of the swirling combustion air and the high air fraction relative to the fuel or gas quantity, ignition conditions for the swirling fuel / combustion air mixture are not yet achieved in the region of the swirl vanes 32, i.e., in the upstream region 36.

[0039] The partition wall 34 can be designed to decelerate the swirling fuel / combustion air mixture. For this purpose, the partition wall 34 can have openings. For this purpose, the partition wall can be designed essentially in a grid-like manner. The geometry of the partition wall 34 can be designed to reduce the flow velocity of the swirling fuel / combustion air mixture while minimizing disruption to the eddy flow. The partition wall 34 reduces the absolute flow velocity of the swirling flow and the premixed primary air, thereby ensuring ignition of the primary flame 24, which additionally contains the second portion of the first fuel quantity in this region.

[0040] The primary fuel nozzles 16a can be evenly distributed in the downstream region 38. Thus, the primary fuel nozzles 16a are located in a region downstream of the partition wall 34 where the flow velocity is lower. The primary fuel nozzles 16a can be arranged substantially perpendicular to the longitudinal axis of the burner tube 12. The primary fuel nozzles 16a can be evenly distributed within the halo. A plurality of primary fuel nozzles 16a can be provided. In the downstream region 38, the primary fuel nozzles 16a deliver a second portion of the first fuel quantity to the fuel-air mixture formed in the bladed portion of the swirling body 30, or in other words, in the first region 36, thereby producing an ignitable mixture to form the primary flame 24. This second portion of the first fuel quantity is referred to as primary gas. The primary fuel nozzles 16a can have holes for delivering the fuel. The holes can be arranged on the sides of the primary fuel nozzles 16a. The side holes can be arranged so that the fuel is delivered substantially in a tangential direction.

[0041] The ratio of the total opening area of ​​the holes in the primary fuel nozzle 16a to the total opening area of ​​the holes in the pilot fuel nozzle 16b can determine the ratio of primary gas to pilot gas, taking into account the feed lines to the primary fuel nozzle 16a and the pilot fuel nozzle 16b. This ratio can be selected based on the overall geometry and the fuel quality or composition. The ratio can be approximately 1:1. Approximately half of the fuel flowing through the first fuel inlet 20 can be output via the primary fuel nozzle 16a in area 38, and approximately half of the fuel flowing through the first fuel inlet 20 can be output via the pilot fuel nozzle 16b in area 36.

[0042] The individual controllability of the primary gas and the pilot gas by the control device 40, compared to the controllability of the second fuel quantity and the main fuel quantity flowing through the second fuel inlet 22, and the design of the swirl body 30, the primary and pilot fuel nozzles 16a, 16b, and the partition wall 34, allows the generation of a primary flame 24 with a stoichiometric ratio λ>>1 over a different load range. In one embodiment, the stoichiometric ratio of the primary flame 24 is λ>1.5. In another embodiment, the stoichiometric ratio of the primary flame 24 is λ>2.

[0043] It has been shown that, due to the very low combustion temperature, virtually no thermal NO and no prompt NO are produced in the primary flame 24 .

[0044] However, such low combustion temperatures also always lead to flame instabilities, which must be prevented. The reaction rate is exponentially dependent on the temperature and turbulence in the flame zone. Inadequate mixing of fuel and oxidant reduces the reaction rate. Flame instabilities occur when the axial flow velocity exceeds the turbulent flame speed.

[0045] For a stable primary flame 24, the pre-introduction of the auxiliary gas into the swirling combustion air via the auxiliary fuel nozzle 16b and the addition and premixing of the primary air with the fuel, the type and location of the primary gas, the ratio of the auxiliary gas to the primary gas, and the geometry and location of the partition wall 34 in the non-bladed portion 38 of the swirling body 30 are important in the illustrated embodiment. Other means may be provided to achieve a stable primary flame with a stoichiometric ratio greater than 1, particularly greater than 1.5, or greater than 2.

[0046] The cylindrical portion of the swirling fluid 30 where no blades are installed, i.e. Figure 1 The region 38 in FIG. 1 is designed such that the primary flame 24 forms in a defined region which is protected by the remaining combustion air 28 which flows through the burner tube 12 outside the swirl body 30 .

[0047] The second fuel nozzle 18, also called the main gas nozzle, is located outside and downstream of the swirl device 14. The second fuel nozzle 18 is connected to a second fuel input 22. The second fuel input 22 allows the amount of fuel / gas flowing to the second fuel nozzle 18 to be adjusted. In this case, the second fuel amount comprises the majority of the total fuel amount and is therefore also called the main fuel amount or main gas. Figure 1 The regulation of the main gas is shown at 42 .

[0048] The second fuel nozzles 18 are located within the burner tube 12. The second fuel nozzles 18 may be located at the downstream end of the burner tube 12 and flush therewith. The second fuel nozzles 18 may be evenly distributed on the inner circumference of the burner tube 12. Figure 1 Not shown is an annular Delta disk that can fill the space between the burner tube 12 and the second fuel nozzle at the downstream end of the burner tube. Figure 4-6 Detailed description.

[0049] The second fuel nozzle 18 can be designed to ensure a high fuel discharge velocity. The resulting pulse transports the fuel as far as possible into the combustion chamber and forms a combustion zone spaced apart from the burner head 10. The primary gas can be discharged essentially in the flow direction, i.e., parallel to the longitudinal axis of the burner tube 12. To this end, the second fuel nozzle 18 can have an opening on one end. A shutter can define this opening on the end. The design of the second fuel nozzle 18 forms a main flame or main flame front 26, which is spaced apart from the downstream end of the burner head 10 and firmly formed in the combustion chamber (not shown in detail). Due to the coaxial outflow direction of the second fuel nozzle with respect to the burner tube axis, the main flame 26 can have an elongated, extended flame shape. Internal exhaust gas recirculation, which will be described in detail below, can inject exhaust gas into the hot zone of the main flame 26 and thus into the area of ​​maximum NO production. This reduces NO production in the main flame.

[0050] The fuel input can be designed and arranged to provide ignition energy for a spaced main flame 26 consisting of a primary flame and recirculated exhaust gas to ignite the mixture of main fuel, combustion air or general oxidant and recirculated exhaust gas and ensure continuous and stable progress of the oxidation reaction.

[0051] In the illustrated embodiment, the two gas connections, namely the fuel inlet 20 for the primary gas and pilot gas of the primary flame 24 and the fuel inlet 22 for the main gas of the main flame 26, are individually regulated by gas regulating devices 40 and 42. This allows the gas quantities in the primary flame 24 and the main flame 26 to be adjusted separately from one another, thus allowing the stoichiometric ratios in the respective fuel zones to be adjusted separately. This allows for the provision of a stable, above-stoichiometric primary combustion zone, the formation of a virtually NOx-free primary flame 24 over a wide load range, and the adaptation of various combustion chambers.

[0052] Figure 2 The burner head 10a is schematically shown in a perspective view as a part of the fuel inlet side. Figure 1 The same features as those described for the burner head 10 shown in FIG. The burner head 10a can be represented as an embodiment of the burner head 10. Figure 1 The same reference numerals are used in the drawings. Figure 2 The description is basically limited to Figure 1 Details not shown in the schematic diagram. Figure 2 The burner tube 12 is not shown.

[0053] The second fuel inlet 22 of the burner head 10a is embodied as a tube having a connecting flange 44 for connection to a fuel supply. A smaller tube 46, or main gas lance 46, extends from the second fuel inlet 22. The main gas lance 46 guides the fuel from the second fuel inlet 22 to the second fuel nozzles 18 and terminates there. In the illustrated embodiment, the burner head 10a has six second fuel nozzles 18. The main gas lance 46 extends outside the swirling body 30.

[0054] The second fuel inlet 22 merges into a fuel pipe 48, which can pass through the swirling body 30 centrally, parallel to the longitudinal axis of the swirling body 30. The fuel pipe 48 is preferably designed as a central fuel pipe. The fuel pipe 48 conducts the primary gas in a first, upstream region. Downstream of the branching of the primary gas lance 46, a gas separator 50 seals the second fuel inlet 22 from the subsequent fuel pipe 48. The gas separator 50 is arranged in the second fuel inlet 22 / fuel pipe 48 and is substantially perpendicular to the longitudinal axis of the second fuel inlet 22 / fuel pipe 48.

[0055] Downstream of the gas baffle 50, the first fuel inlet 20 opens into the fuel pipe 48. Downstream of the gas baffle 50, the fuel pipe 48 is used to conduct a first fuel quantity. Downstream of the gas baffle 50, a smaller pipe 52, a so-called pilot gas lance, extends. The pilot gas lance 52 directs fuel from the first fuel inlet 20 to the pilot gas nozzles 16b. In the illustrated embodiment, the burner head 10a has three pilot gas nozzles 16b. The pilot gas nozzles 16b are located within the swirl body 30. In addition to the pilot gas nozzles 16b, the swirl vanes 32 are also visible.

[0056] Figure 2 The exemplary shape of the swirl body 30 can also be seen. In the first region 38 having the swirl vanes 32 and the auxiliary gas nozzle 16b, the swirl body 30 is designed as a cylinder with a first diameter. In the second region 38 without the swirl vanes, the swirl body 30 is designed as a cylinder with a second diameter. In one embodiment, the first diameter is greater than the second diameter. The two regions 36, 38 can then be connected by a conical region.

[0057] The swirl body 30 can be mounted movably on the fuel pipe 48 via the swirl body inner tube 54, which allows, for example, adaptation to different combustion chamber geometries and process parameters. Axial movement of the swirl body 30 on the fuel pipe 48 can influence to a limited extent the ratio of the amount of air flowing through the swirl body 30 and being discharged from the gap formed by the outer diameter of the swirl body in the region 38 and the inner diameter of the delta disk 66.

[0058] Even in Figure 2 The combustion tube 12 is not shown in FIG. Figure 2In the schematic diagram of FIG, the combustion air 28 flows from the front right to the rear left, that is, flows through the swirling body 30 and flows outside the swirling body 30. The main gas lance 46 is located in the air flow.

[0059] Figure 3 The burner head 10a is shown schematically in a perspective view from the flame side. Figure 1 and Figure 2 All features described so far also apply to Figure 3 The burner head 10a shown in FIG. Figure 3 In FIG. 3 , the conical portion of the swirling body 30 is not shown and the portion of the swirling body 30 surrounding the downstream region 38 is cut away so that the components located within the swirling body 30 can be shown. Figure 2 As in FIG, the combustion tube 12 is not shown.

[0060] To start the combustion process, a direct electric ignition device 56 may be provided. This ignition device is used only for initial (e.g., one-time) ignition. Once a flame has formed and stabilized, further ignition of the fuel-air mixture occurs via reaction in the flame. In one embodiment, the ignition device 56 is attached to one of the pilot gas nozzles 16b.

[0061] In the illustrated embodiment, the fuel line 48 ends downstream in a cylindrical fuel distributor 58. The fuel distributor 58 can also be referred to as a primary gas distributor 58, since the fuel line 48 only conducts primary gas. In this embodiment, four primary gas nozzles 16a are arranged in a jet pattern on the outer surface of the primary gas distributor 58. The primary gas nozzles 16a are arranged at regular intervals and extend from the fuel line 48 or the primary gas distributor 58 to the burner tube 12 (not shown).

[0062] The primary gas nozzle 16a may have holes 60. Each primary gas nozzle 16a may have multiple holes 60. Two holes 60 are shown, but more or fewer holes are possible. The holes 60 are arranged in the primary gas nozzle 16a so that the primary gas flows out substantially in a tangential direction. The orientation of the holes 60 can be coordinated with the arrangement and design of the swirl vanes 32 so that the primary gas is discharged along with the flow of the fuel / combustion air mixture swirling in the first region 36. The primary gas flows out of the lateral holes in a tangential direction, with the tangential direction being predetermined by the swirl direction. Additionally or alternatively, the primary gas nozzle 16a may have axial holes, through which the primary gas also flows out.

[0063] The secondary fuel nozzles 18 or primary gas nozzles are arranged in a circle around the downstream end of the swirl body 30. The secondary fuel nozzles have holes 62 on their end sides. The holes 62 are designed to ensure a high fuel discharge velocity of the primary gas so that the main flame front 26 is spaced apart from the combustion head.

[0064] Figure 4 A side view of a burner head 10b is schematically shown. The burner head 10b may correspond to the burner head 10 and / or the burner head 10a. Figures 1 to 3 The components depicted will not be described again in detail. Some components have been cut away in the side view to better illustrate the details. The portion of the swirling body 30 that faces the viewer is cut away, allowing the internal structure to be seen. The area where the first fuel inlet 20 opens into the fuel pipe 48 is cut away.

[0065] exist Figure 4 The hole 64 of the primary gas nozzle 16a can be seen in the side view of FIG. The hole 64 is designed so that the fuel is output essentially in the radial direction. Additionally or alternatively, the primary gas nozzle can also have an axial hole.

[0066] exist Figure 4 The burner tube 12 is also shown in FIG. The burner tube 12 can be closed at its downstream end by an annular delta disk 66 that extends radially inward from the burner tube 12. In the embodiment shown, the delta disk 66 has a plurality of radially inwardly directed guides 68. The opening of the second fuel nozzle 18 can terminate flush with the delta disk 66. Figure 6 The design of the delta disk 66, described in detail, serves to recirculate the exhaust gas internally within the main flame 26. Recirculation is induced by the portion of the combustion air 28 that flows through the swirl device 14 and directly impinges on the ring of the annular delta disk 66. This creates low-pressure and eddy current zones on the outflow side of the guide device 68, i.e., on the side of the guide device 68 that faces into the combustion chamber. The exhaust gas thus recirculated is then injected into the hot zone of the main flame 26. In this zone, the recirculated exhaust gas reduces the temperature and the O2 partial pressure. Both effects contribute to reducing or promoting NO formation.

[0067] The amount of fuel from the primary and secondary gas nozzles 16a and 16b is smaller than the amount of fuel ejected from the second fuel nozzle 18. The amount of fuel from the primary and secondary gas nozzles is preferably 3% to 15%, particularly preferably 5% to 10% of the total fuel amount.

[0068] In various embodiments, the excess air required to fully combust the fuel from the primary gas nozzle 16a, the secondary gas nozzle 16b, and the portion of the fuel from the fuel nozzle 18 may be between 1.075 and 1.2. The combustion zones of the primary flame and the spaced-apart main flame are each above the stoichiometric ratio. Due to the axial flow of fuel entering the combustion chamber from the secondary fuel nozzle 18, a zone below the stoichiometric ratio may locally form before the fuel gas, air, and recirculated exhaust gas are fully mixed.

[0069] The reduction in NO values ​​is achieved by burning a small amount of external NO in a partially premixed, very lean primary flame in combination with a spaced-apart main flame. The main flame, by sufficiently mixing the internally recirculated exhaust gas and reducing the O2 partial pressure in the mixture, does not achieve high temperatures that are detrimental to NO formation. Advantageously, a narrow, but not excessively long, flame is formed, which allows the heat released to the cooled annular wall of the combustion chamber by chemical enthalpy conversion during the combustion of the fuel to be efficiently coupled out by radiation and convection.

[0070] Figure 5 A cross-sectional view of the front section of the burner head 10b is shown schematically. Figures 1 to 4 The components mentioned will not be described again in detail.

[0071] The swirl body inner tube 54 can be seen, which is guided on the fuel tube 48. The swirl body is thus movable longitudinally and can be fixed in place by means of screws 70. This movability allows for better adaptation to different combustion chambers in which the main flame front 26 is formed.

[0072] The perforated partition walls 34 are arranged in the region 38. The perforated partition walls 34 are positioned and designed such that the primary flame 24 is reliably fixed or held in the region 38 of the swirling body 30 in this embodiment.

[0073] Figure 6 A front view of the burner head 10b is schematically shown from the flame side, or in other words, from the combustion chamber. A fuel distributor 58 is arranged in the center, and the primary gas nozzle 16a with its orifice 60 extends away from the fuel distributor. A perforated partition wall 34 is located behind it. In the illustrated embodiment, the indentation is formed by two concentric rows of holes, each of which is a perfect circle. It should be understood that the indentation may also have other shapes. The ratio of the open area to the total area may differ from that shown. The perforated partition wall 34 serves to reduce the flow velocity of the swirling air / fuel mixture in the region 36 of the swirling body 30. The partition wall 34 is defined by the wall of the swirling body 30. The auxiliary gas nozzle 16b located behind it can be seen through the indentation.

[0074] The second fuel nozzles 18 with holes 62 are arranged at uniform intervals on the circumference around the central axis of the swirl body 30. Surrounding it is an annular delta disk 66, which encloses the burner tube 12. The guide devices 68 extend inwardly from the inner circumference of the delta disk 66 in the radial direction. In the embodiment shown, there are three guide devices 68. These three guide devices 68 are evenly distributed on the inner circumference. The burner head 10b can also have more or fewer guide devices 68, which can also be evenly distributed on the inner circumference. In the embodiment shown, the guide devices 68 are triangular in shape and point inwardly in the radial direction with a tip. The tip of the triangle is away from the annular delta disk 66. As shown from Figure 5 As can be seen in FIG, the guide device 68 is not located Figure 6 The guide means are not in the plane of the drawing but rather point away from the swirling body 30. The guide means are angled.

[0075] The guide device is configured by means of delta disk 66 so that it forms a low-pressure zone that draws exhaust gas from the combustion chamber. Thus, delta disk 66 and guide device 68 create internal exhaust gas recirculation. The angled, triangular shape pointing away from the swirling body creates a "stationary vortex" on guide device 68, which helps stabilize the main flame front 26. The recirculated exhaust gas is thus injected into the hot zone of the main flame and, therefore, into the region of maximum NO production.

[0076] The geometry of the guide devices 68 is optimized as much as possible so that the highest possible amount of internal exhaust gas is drawn into the main flame 26. The number and geometry of the guide devices 68 are taken into account for the NO reduction effect and for stabilizing the main flame.

[0077] The annular delta disk 66 may have a plurality of ridges 72 on its inner circumference between the guides 68. The ridges 72 form a tooth-shaped geometric structure. Figure 6 , a semicircular protrusion is shown, but the teeth may be configured with other geometric configurations. The teeth 72 are designed to create a larger surface area. This larger surface area provides a larger contact area between the exhaust gas, combustion air, and main fuel, thereby resulting in a more complete and uniform mixing of the fuel-air-exhaust gas mixture. This results in a more evenly distributed combustion zone in the main flame 26 that is rich in exhaust gas and, therefore, has a more favorable stoichiometric ratio. The inventors have discovered that this further reduces the formation of thermal NO overall.

[0078] As already mentioned, the second fuel nozzles 18 are designed to achieve the highest possible discharge velocity. For this purpose, a shutter can be provided in front of the axial opening of the fuel nozzle. The high pulse of the outflowing gas further increases the intensity of the mixing of the internally recirculated exhaust gas and fuel. This is further optimized by coordinating the position of the second fuel nozzles 18 with the geometry of the guide devices 68. The second fuel nozzles 18 are evenly distributed between the guide devices 68.

[0079] During operation, advantageous low-NOx combustion is achieved by first supplying combustion air 28 to the burner tube 12, which has an open end located downstream. A portion of the combustion air 28 swirls in the swirl device 14 arranged in the burner tube 12. A first fuel quantity is supplied directly to the swirl body 30 and mixed there with the swirling combustion air 28. A primary flame forms within the swirling fuel / combustion air mixture. A second combustion quantity is supplied downstream to the swirl device 14. This forms a main flame front, which stabilizes downstream of the burner tube and spaced apart from it. The first fuel quantity is adjusted independently of the second fuel quantity.

[0080] Individual fuel regulation enables very low NOx emissions over a wide load range. At lower loads, a different ratio of the first to second fuel quantities than at higher loads can be optimal. If the ratio of the two fuel quantities to each other is set to a fixed value, low NOx emissions cannot be guaranteed over the entire load range of the burner. In the burner head according to the invention, for example, a smaller percentage of primary / auxiliary gas can be supplied at lower loads than at higher loads. With unseparated regulation, the first fuel quantity can be reduced less than the air quantity flowing through the swirl body at lower loads due to flow limitations, so that NOx emissions at lower loads can also increase in the case of a primary flame that is above the stoichiometric ratio.

[0081] Although specific embodiments are shown and described, it will be understood by those skilled in the art that multiple alternative and / or equivalent embodiments may be substituted for the specific embodiments shown and described without departing from the basic concept of the invention. This application shall include all modifications or variations of the specific embodiments discussed herein.

Claims

1. A method for combusting fuel in a staged manner by introducing combustion air (28) into a combustion tube (12), the method comprising: - inputting a first fuel quantity to form a primary flame (24) in the combustion tube (12) having a significantly higher than stoichiometric ratio of more than 1.5; - a second fuel quantity is fed downstream to form a main flame (26) in the combustion chamber at a slightly above stoichiometric ratio of between 1.03 and 1.18, wherein the temperature of the main flame (26) is reduced by exhaust gas recirculated within the combustion chamber, and wherein the main flame (26) is stabilized downstream of the burner tube (12) and spaced apart from the burner tube (12), The method further comprises: - causing a portion of the combustion air (28) to swirl to produce swirling combustion air; - feeding a first partial quantity of the first fuel quantity into the region of the swirling combustion air to form a swirling lean air / fuel mixture; - Reduce the velocity of the lean, swirling air / fuel mixture; and - feeding a second partial quantity of the first fuel quantity into the slowed, swirling, lean air / fuel mixture.

2. The method according to claim 1, further comprising: The first fuel quantity is controlled independently of the second fuel quantity, wherein the control is performed such that the first fuel quantity is between 3% and 15% of the sum of the first fuel quantity and the second fuel quantity.

3. The method according to claim 1 or 2, wherein: At least a portion of the first partial quantity of the first fuel quantity is fed inwardly in a radial direction.

4. The method according to claim 1 or 2, wherein: At least a portion of the second partial amount of the first fuel amount is fed in a tangential direction with the flow of the swirling fuel / combustion air mixture.

5. The method according to claim 1 or 2, further comprising: - In the region of the supply of the second fuel quantity, a vortex is formed, whereby the exhaust gases are directed back into the hot zone of the main flame (26).

6. A combustion head (10) for the staged combustion of fuel, wherein: The burner head (10) is designed to burn a first amount of fuel supplied in a primary flame (24) at a ratio above the stoichiometric ratio in a burner tube (12) and to burn a second amount of fuel supplied in a main flame (26) at a ratio slightly above the stoichiometric ratio of between 1.03 and 1.18 in a combustion chamber spaced apart from the burner tube (12), wherein the fuel supply is designed such that the primary flame (24) burns at a stoichiometric ratio greater than 1.5, wherein the burner head (10) is further designed such that the temperature of the main flame (26) is reduced by exhaust gas recirculated within the combustion chamber and the main flame (26) is stabilized downstream of the burner tube (12) and spaced apart from the burner tube (12). Therein, the burner head is designed to supply a first portion of the first fuel quantity to a highly swirling portion of the combustion air to form a fuel / combustion air mixture and to supply a second portion of the first fuel quantity to the decelerated fuel / combustion air mixture.

7. The burner head (10) according to claim 6, wherein The supply of the first fuel quantity and the supply of the second fuel quantity can be adjusted independently of one another, wherein the adjustment is performed such that the first fuel quantity is between 3% and 15% of the sum of the first fuel quantity and the second fuel quantity.

8. A combustion head (10) for staged combustion of fuel, comprising: A combustion tube (12) is configured to have combustion air (28) flow through it, wherein: The combustion tube (12) has an open end located downstream; a swirl device (14) arranged in the combustion tube (12) so as to be flowed through by a portion of the combustion air (28), the swirl device having a swirl body (30) surrounding a first and a second region, wherein the first region (36) is located upstream of the second region, and swirl blades (32) are arranged only in the first region; a first fuel nozzle (16a, 16b) arranged in the swirling body (30) to input fuel, thereby forming a primary flame (24) in the swirling body (30); a second fuel nozzle (18) arranged downstream of the swirl device (14) for supplying fuel to form a free main flame (26), wherein the main flame (26) is stabilized downstream of the burner head (10) and spaced apart from the burner head (10); a first fuel input (20) connected to the first fuel nozzle (16a, 16b); and A second fuel inlet (22) is connected to the second fuel nozzle (18), wherein the swirl body (30) and the first fuel nozzle (16a, 16b) are designed to obtain a primary flame (24) with a stoichiometric ratio greater than 1.

5.

9. The burner head according to claim 8, wherein The fuel quantities of the fuel supplied via the first fuel supply (20) or via the second fuel supply (22) can be adjusted independently of each other.

10. The burner head according to claim 8, wherein The swirl device (14) has a perforated partition wall (34) between the first region (36) and the second region (38).

11. The burner head according to claim 8, wherein The first fuel nozzle (16a, 16b) includes a primary fuel nozzle (16a) and a secondary fuel nozzle (16b), wherein the primary fuel nozzle (16a) is arranged in the second region (38) of the swirling body (30), and the secondary fuel nozzle (16b) is arranged in the first region of the swirling body (30).

12. The burner head according to claim 11, wherein The auxiliary fuel nozzles (16b) are evenly distributed between the swirl blades (32) and are designed to discharge fuel inward in a radial direction so as to form a swirling fuel / combustion air mixture.

13. The burner head according to claim 11, wherein The primary fuel nozzles (16a) are evenly distributed in the halo and are designed to discharge fuel in a tangential direction along the flow of the swirling fuel / combustion air mixture.

14. A burner head according to any one of claims 8 to 13, wherein In a first fuel nozzle, at least a portion of the fuel is discharged from the fuel nozzle (16a) via a lateral opening (60).

15. A burner head according to any one of claims 11 to 13, wherein The first fuel inlet (20) is connected to the primary fuel nozzle (16a) via a fuel line (48) in the swirl body (30), wherein the fuel line (48) is flush with a fuel distributor (58) to which the primary fuel nozzle (16a) is fastened.

16. The burner head according to claim 15, wherein The swirling body (30) is arranged on the fuel pipe (48) so as to be movable in the longitudinal direction.

17. The burner head according to claim 16, further comprising: An annular delta disk (66) extends radially inward from a downstream end of the burner tube (12) and has a plurality of radially inwardly directed guides (68).

18. A burner head according to claim 17, wherein The annular delta disk (66) has a plurality of ridges (72) on its inner circumference between the guides (68).

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