CN113915613A - Method and burner head for staged combustion of fuel - Google Patents

Abstract

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

Description

Method and burner head for staged combustion of fuel

Technical Field

The invention relates to a method for staged combustion of fuel and to a burner head for staged combustion of fuel.

Background

When fossil fuels are burned in a combustion plant, nitrogen oxides, such as NO, NO2, are also produced in addition to other combustion products. Hereinafter collectively referred to as NO only. These and other harmful emissions can be influenced and reduced by structural measures in the burner. The reaction mechanisms leading to such nitrogen oxides are basically known and are generally distinguished by thermal NO formation and prompt NO formation, and NO formation described as due to chemically bonded nitrogen oxides in the fuel.

It is known for this purpose that the hot NO is dependent on the one hand on the residence time of the reaction components in the combustion zone and on the other hand largely on the combustion temperature itself, according to the so-called Zeldovich (Zeldovich) mechanism. The combustion temperature is associated with the fuel/air ratio lambda. The maximum combustion temperature is set at the fuel/air ratio λ 1. This fuel/air ratio is also referred to as the stoichiometric ratio. There is just so much oxygen in the combustion air that the fuel is completely burned. The fuel/air ratio λ < 1 is referred to as a rich mixture because there is too much fuel. A fuel/air ratio λ >1 is referred to as a lean mixture because of the excess air. In both cases, the combustion temperature drops again, so that less hot NO is also formed.

In addition to the hot NO, the formation of prompt NOx is also important. Prompt NO is produced by the intermediate formation of hydrocarbon radicals CH in the flame as an intermediate product in the combustion of carbonaceous fossil fuels. The CH groups react with atmospheric nitrogen to form hydrocyanic acid (HCN), which is converted further to NO in a very rapid formation reaction. To suppress the formation of free CH groups and thus prompt NO formation, an effective method is lean combustion or combustion above the stoichiometric ratio. Lean combustion means combustion with excess air, i.e., λ >1.

Prompt NO produces a smaller amount than hot NO, but is crucial to minimize NO formation, especially in ultra-low NO applications.

It is also known that the recirculation or recovery of the exhaust gases produced during combustion is advantageous for reducing the formation of nitrogen oxides. In this regard, the recirculated cooled exhaust gas lowers the flame temperature itself, as well as lowering the partial pressure of O2 in the combustion zone. Both effects contribute to the reduction of NO formation. But the mixing in of more and more exhaust gases will tend to make the continuous combustion process unstable.

EP 1754937B 1 and EP 2037173B 1 show burner heads for achieving NO reduction. Of these, primarily a single-stage combustion process, which only to a limited extent achieves further NO optimization and flame stabilization. DE 19509219 a1 shows a burner head for two-stage combustion using an air-gas mixture above the stoichiometric ratio in the first stage and an air-gas mixture below the stoichiometric ratio in the second stage.

The burner head can usually be distinguished between a so-called mixing zone and a so-called combustion zone.

In the mixing zone the different fluids are mixed and the fluids (also) are not combusted. The conditions necessary for combustion are generally not met in the mixing zone. This may be the case, for example, when the flow velocity of the ignitable mixture is significantly higher than the flame velocity.

The combustion zone is a region where conditions required for combustion exist. The combustion zone is provided in the presence of an ignitable mixture (e.g., fuel-combustion air-mixture, fuel-combustion air-exhaust gas-mixture, fuel-oxidant-exhaust gas-mixture) having a flow velocity and a flame velocity that are substantially equal and having a temperature equal to or greater than an ignition temperature of the ignitable mixture. The general term "oxidant" includes the term "combustion air", but also includes, for example, ambient air enriched with additional oxygen. And ignition or combustion cannot be performed in a region where these conditions are not satisfied. Typically the mixing zone transitions to the combustion zone without significant spatial separation.

Disclosure of Invention

There is therefore a need for the present invention. It may be an object of the invention to be able to eliminate external measures for NO reduction, for example, to eliminate external recirculation. The aim of the invention can be to keep the energy application as low as possible. It may be an object of the present invention to provide an energetically favorable combustion with minimized NO emissions.

Drawings

Objects and features of the present invention are set forth in the following description of embodiments with reference to the accompanying drawings, in which:

FIG. 1 shows a highly schematic side view of a burner head;

FIG. 2 shows the components of the burner head in a schematic perspective view from the fuel input side;

FIG. 3 shows parts of the burner head of FIG. 2 in a schematic perspective view from the flame side;

FIG. 4 schematically illustrates a side view of the burner head;

FIG. 5 schematically illustrates a cross-sectional view of a forward section of a combustion head; and

fig. 6 schematically illustrates a front view of the burner head.

Detailed Description

Aspects and embodiments are described below with reference to the drawings, wherein like or similar reference numerals are generally used to refer to like or similar elements. In the following description, numerous specific details are set forth in order to provide a basic understanding of one or more aspects of the embodiments. It will be apparent, however, to one skilled in the art that one or more aspects of the embodiments may be practiced with less specific details. Elements are shown in schematic shapes in other instances in order to simplify the description of one or more aspects of the embodiments. The following description is, therefore, not to be taken in a limiting sense. It should be noted that the various elements of the drawings are not necessarily shown to scale.

Directional terms used in the description with reference to the drawings, such as "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", and the like, are not restrictively understood. The components of the embodiments can be positioned in a number of different orientations and the directional terminology is used for purposes of illustration only. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the spirit of the present invention.

In practice, multi-stage combustion processes have long been known. However, the solutions known to date are currently not sufficient to be able to continuously meet the continuously increasing NO requirement for the operation of the combustion plant for a long time. According to the present disclosure, NO may be reduced more significantly by staged combustion. By means of the corresponding adjustability, a NO reduction can also be ensured over a wide load range and/or for different fuels and/or for different combustion chambers.

A method according to claim 1 is provided for staged combustion of fuel by feeding combustion air into the combustion tube. The fuel may be a gaseous or liquid fuel. A first amount of fuel is input to form a primary flame within the combustion tube. A second amount of fuel may be input downstream to form a main flame front. The main flame is stabilized downstream of the burner tube and spaced apart from the burner tube. The fuel inlet is configured such that the primary flame burns at a stoichiometric ratio of more than 1.5, in particular more than 2.0. Very low flame temperatures can thereby be achieved. Practically NO prompt NO is formed. The main flame is slightly above stoichiometric. The stoichiometric ratio may be between 1.03 and 1.18. The temperature of the main flame can be significantly reduced by the exhaust gas recirculated inside the combustion chamber.

In one embodiment, the first fuel amount is adjusted independently of the second fuel amount. A higher than stoichiometric primary flame can thereby be ensured over a wide load range.

In one embodiment, the first fuel amount input may be significantly lower than the second fuel amount input. The first fuel amount may be, for example, between about 3% and 15% of the total fuel amount, i.e., the sum of the first fuel amount and the second fuel amount. Preferably, the first fuel amount is between 5% and 10% of the sum of the first fuel amount and the second fuel amount.

In another embodiment, a portion of the combustion air is distorted. Thereby creating swirling combustion air. A first portion of the first combustion quantity is output into the region of the air vortex. Thereby creating a swirling lean air/fuel mixture. Very good mixing can be achieved. In this region, the flow velocity is high and the mixture is lean, so that no ignition conditions are provided. The flow velocity of the swirling lean air/fuel mixture is reduced in the next step. A second portion of the first fuel quantity is delivered to the decelerated swirling lean air/fuel mixture.

There is also provided a burner head for burning fuel in stages according to claim 7. A burner head is provided that is capable of performing the method. The burner head is designed to burn a first input amount of fuel in a primary flame above stoichiometry. The second input amount of fuel is combusted in the main flame slightly above stoichiometry.

The input of the first quantity of fuel and the input of the second quantity of fuel are preferably adjustable independently of one another, so that a very low nitrogen oxide combustion is ensured over a wide load range.

The following figures show exemplary embodiments of the burner head according to the invention with which the method according to the invention for staged combustion of fuel can be carried out.

Fig. 1 shows a side view of a burner head 10 in highly schematic form. The burner head 10 includes a burner tube 12, a swirler 14, first fuel nozzles 16a, 16b, second fuel nozzles 18, a first fuel input 20, and a second fuel input 22. The arrows symbolically represent the inflowing fuel. In operation, a primary flame 24 above the stoichiometric ratio is formed in the swirling device 14 and the main flame or main flame front 26 is spaced apart from the burner head 10, both of which are symbolically illustrated by the flame in fig. 1. The burner head 10 is thus used to burn the fuel in stages. The fuel may be gaseous. The fuel may be natural gas. The fuel may include hydrogen. In addition to the use as a pure gas burner, dual burners are also possible, in which liquid fuels can also be burned in addition to gaseous fuels. Burners for liquid fuel only are also possible. Other descriptions relate generally, without limitation, to embodiments as gas burners.

In the schematic illustration of fig. 1, combustion air 28 is fed into the combustion pipe 12 from the right. Therefore, the right-side end portion of the combustion pipe 12 is the end portion located upstream in this schematic view. The burner tube 12 may be substantially 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 view of the burner tube 12, i.e. at the end located downstream. A main flame front 26 is formed downstream of the burner head 10. A combustion chamber or combustion chamber, not further shown, is located here.

The amount of fuel injected from the first fuel nozzles 16a, 16b may be less than the amount of fuel injected from the second fuel nozzle 18. When only a small amount of fuel is burned in the primary flame 24, which is significantly above the stoichiometric ratio, no second, sub-stoichiometric combustion stage is necessary. The spaced apart main flames 26 may also be above stoichiometric overall. With the combustion head 10 according to the invention, NO substoichiometric combustion zone is produced, as is usual in staged combustion with substoichiometric and higher combustion zones and with the residence time of the gases in the zone required for the reduction of NO. The process according to the invention provides a primary flame which is significantly above the stoichiometric ratio and a main flame which is slightly above the stoichiometric ratio.

The swirling device 14 is arranged inside the burner tube 12. The swirling device 14 may be open at both ends. The longitudinal axis of the burner tube 12 and the longitudinal axis of the swirling device 14 may be arranged parallel or in succession to each other, so that the swirling device 14 is in the middle of the burner tube 12 and is evenly spaced radially from the inner wall of the burner tube. A portion of the combustion air 28 flows through the burner tube 12 outside of the swirling device 14, and another portion of the combustion air 28 flows through the swirling device 14.

The swirling device 14 comprises a swirling body 30, swirl vanes 32 and a perforated partition wall 34. The cyclone body 30 may be substantially cylindrical. Perforated partition 34 may extend substantially perpendicular to the longitudinal axis of cyclone body 30 and divide the interior space of cyclone 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 partition 34 may cause a pressure loss. Thus, the perforated partition may cause a local reduction in flow velocity downstream of the perforated partition 34.

The swirl vanes 32 may be disposed only in the first region 36. A second region downstream of the bulkhead 34 may be free of the swirl vanes 32. A plurality of swirl vanes 32 may be provided.

Cyclone body 30 has a larger diameter in first region 36 than in second region 38. A tapered section may be provided in the transition between the first region 36 and the second region 38.

The first fuel nozzles 16a, 16b are arranged within the swirling body 30. The first fuel nozzle is connected to a first fuel inlet 20. The first fuel input 20 allows for the regulation of the fuel/gas quantity flowing to the first fuel nozzles 16a, 16b, as indicated in fig. 1 with reference 40. This adjustment is separate and independent from the adjustment 42 in the second fuel input 22.

The first fuel nozzles 16a, 16b may include a primary fuel nozzle 16a, also referred to as a primary gas nozzle, located in a downstream second region 38 of the swirling device 14. The first fuel nozzles 16a, 16b may include other fuel nozzles, hereinafter referred to as secondary fuel nozzles or secondary gas nozzles 16b, located in a first region 36 of the swirler 14 upstream.

The secondary fuel nozzles 16b may be evenly distributed between the swirler vanes 32. The secondary fuel nozzles 16b may be arranged substantially parallel to the longitudinal axis of the combustion tube 12. The swirl vanes 32 induce a strong swirl of the combustion air 28. Thus, the fuel, also referred to as secondary gas, flowing from the secondary fuel nozzle 16b is premixed efficiently with the portion of the combustion air 28 for the primary flame 24. A swirling fuel/combustion air mixture is created. The fuel input through the auxiliary fuel nozzle 16b may be designed to create a swirling lean air/fuel mixture. The secondary fuel nozzle 16b may output a first fractional amount of the first fuel quantity. The secondary fuel nozzle 16b may have holes for outputting fuel. The holes may be arranged such that the fuel is at least partly output substantially inwards in a radial direction, i.e. towards a direction substantially perpendicular to the wall of the cyclone body 30. Due to the high flow speed of the swirling combustion air and due to the high air content relative to the fuel or gas quantity, ignition conditions of the swirling fuel/combustion air mixture are not yet realized in the region of the swirl vanes 32, i.e. in the upstream region 36.

The partition wall 34 may be designed to decelerate the swirling fuel/combustion air mixture. The partition 34 may have openings for this purpose. The partition walls can be designed substantially in the form of a grid. The geometry of the partition wall 34 may be designed to reduce the flow velocity of the swirling fuel/combustion air mixture and at the same time to disturb the swirl as little as possible. The partition wall 34 reduces the absolute flow velocity of the swirling and premixed primary air and thereby ensures ignition of the primary flame 24, which additionally has a second portion of the first fuel quantity in this region.

The primary fuel nozzles 16a may be evenly distributed in the downstream region 38. Whereby the primary fuel nozzles 16a are located in a region downstream of the partition wall 34 where the flow velocity is low. The primary fuel nozzles 16a may be arranged substantially perpendicular to the longitudinal axis of the combustion tube 12. The primary fuel nozzles 16a may be evenly distributed in the halo. A plurality of primary fuel nozzles 16a may be provided. The primary fuel nozzle 16a outputs a second portion of the first fuel quantity, which is referred to as primary gas, in the downstream region 38 to the fuel-air mixture formed in the bladed portion of the swirl body 30 or in other words in the first region 36 and thus produces an ignitable mixture to form the primary flame 24. The primary fuel nozzle 16a may have holes for outputting fuel. The holes may be arranged on the sides of the primary fuel nozzle 16 a. The holes of the side faces may be arranged such that the fuel is output in a substantially tangential direction.

The ratio of the total opening area of the holes in the primary fuel nozzle 16a to the total opening area of the holes of the secondary fuel nozzle 16b may be determined in consideration of the input lines to the primary fuel nozzle 16a and the secondary fuel nozzle 16 b. The ratio may be selected based on the overall geometry and fuel quality or fuel composition. The ratio may be about 1: 1. About half of the fuel flowing through the first fuel input 20 may be output via the primary fuel nozzles 16a in the region 38, and about half of the fuel flowing through the first fuel input 20 may be output via the secondary fuel nozzles 16b in the region 36.

The individual adjustability of the primary and secondary gases by the adjusting device 40, in comparison to the adjustability of the secondary and main fuel quantities flowing through the secondary fuel feed 22 and the design of the swirling body 30, the primary and secondary fuel nozzles 16a, 16b and the partition 34, makes it possible to generate a primary flame 24 with a stoichiometric ratio λ > >1 over a further 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.

It is confirmed that, due to the very low combustion temperature, little thermal NO and NO prompt generation of NO occurs in the primary flame 24.

However, such low combustion temperatures also always produce flame instability, which must be blocked. The reaction velocity is exponential with the temperature in the flame zone and with the turbulence in the flame zone. The reaction rate is reduced due to insufficient mixing of the fuel and the oxidant. Flame instability occurs when the flow velocity in the axial direction is greater than the turbulent flame velocity.

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

Furthermore, the cylindrical, non-bladed part of the swirl body 30, i.e. the region 38 in fig. 1, is designed in such a way that the primary flame 24 is formed 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.

The secondary fuel nozzles 18, also referred to as primary gas nozzles, are located outside and downstream of the swirler device 14. The second fuel nozzle 18 is connected to a second fuel inlet 22. The second fuel input 22 allows for adjustment of the amount of fuel/gas flow to the second fuel nozzle 18. The second fuel quantity comprises a majority of the total fuel quantity, and is therefore also referred to as main fuel quantity or main gas. The adjustability of the primary gas is shown in fig. 1 by reference numeral 42.

A second combustion nozzle 18 is within the combustion tube 12. The second fuel nozzle 18 may be located at and flush with the downstream end of the combustion tube 12. The second fuel nozzles 18 may be evenly distributed on the inner circumference of the combustion tube 12. The annular Delta disk, which may fill the spacing between the burner tube 12 and the second fuel nozzle at the downstream end of the burner tube, is not shown in fig. 1. The delta tray is described in detail with reference to fig. 4-6.

The second fuel nozzle 18 may 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 may be output substantially in the flow direction, i.e., parallel to the longitudinal axis of the combustion tube 12. For this purpose, the second fuel nozzle 18 may have an opening on one end side. The shroud may define an opening on the end side. The second fuel nozzle 18 is designed such that a main flame or main flame front 26 is formed, which is spaced apart from the downstream end of the burner head 10 and is formed firmly in a combustion chamber, not shown in detail. The main flame 26 may have an elongated and extensionally formed flame shape based on the arrangement of the second fuel nozzles with respect to the coaxial outflow direction of the burner tube axis. Internal exhaust gas recirculation, which will also be described in detail below, may inject exhaust gas into the hot zone of the main flame 26 and further into the region of maximum NO production. Thereby reducing NO production in the main flame.

The fuel input may be designed and arranged to provide ignition energy to the spaced apart primary flames 26, consisting of primary flames and recirculated exhaust gas, in order to ignite the mixture of primary fuel, combustion air or generally oxidant and recirculated exhaust gas and ensure a continuous, stable course of the oxidation reaction.

In the embodiment shown, the two gas connections, namely the fuel feed 20 for the primary gas and the auxiliary gas of the primary flame 24 and the fuel feed 22 for the main gas of the main flame 26, are regulated individually by gas regulating devices 40 and 42. It is thereby possible to set the gas quantities in the primary flame 24 and in the main flame 26 separately from one another, thus adjusting the stoichiometry in the respective fuel zones separately. This allows the provision of a stable and above stoichiometric primary combustion zone and the formation of a nearly NO-free primary flame 24 over a wide load range and the matching of different combustion chambers.

Fig. 2 schematically shows a portion of the burner head 10a from the fuel inlet side in a perspective view. The burner head 10a may have the same features as described for the burner head 10 shown in fig. 1. The burner head 10a may represent one embodiment of the burner head 10. The same reference numerals are used as in fig. 1. The description of fig. 2 is substantially limited to details not present in the schematic diagram of fig. 1. The burner tube 12 is not shown in fig. 2.

The second fuel supply 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 secondary fuel input 22. The main gas lance 46 directs fuel from the secondary fuel input 22 to the secondary fuel nozzle 18 and terminates there. In the embodiment shown, the burner head 10a has six second fuel nozzles 18. The main gas lance 46 extends beyond the cyclone body 30.

The second fuel inlet 22 merges into a fuel pipe 48, which can extend centrally through the swirling body 30 parallel to the longitudinal axis of the swirling body 30. The fuel pipe 48 is preferably embodied as a central fuel pipe. The fuel pipe 48 directs the primary gas in a first region located upstream. Downstream of the branching of the main gas lance 46, a gas barrier 50 seals the second fuel input 22 from the subsequent fuel pipe 48. The gas barrier 50 is disposed in the second fuel input 22/fuel tube 48 and is substantially perpendicular to the longitudinal axis of the second fuel input 22/fuel tube 48.

Downstream of the gas separator 50, the first fuel inlet 20 opens into the fuel pipe 48. Downstream of the gas barrier 50, the fuel pipe 48 is used to conduct a first amount of fuel. Downstream of the gas baffle 50, smaller tubes 52, so-called auxiliary gas lances, project. The secondary gas lance 52 directs fuel from the first fuel input 20 to the secondary gas nozzle 16 b. In the embodiment shown, the burner head 10a has three secondary gas nozzles 16 b. The secondary gas nozzle 16b is located within the cyclone body 30. In addition to the secondary gas nozzles 16b, swirl vanes 32 are also visible.

Fig. 2 also shows an exemplary shape of the swirling body 30. In a first region 38 with swirl blades 32 and auxiliary gas nozzle 16b, swirl body 30 is designed as a cylinder with a first diameter. In the second region 38, which is free of 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 now be connected to one another by means of a conical region.

The swirl body 30 can be movably mounted on the fuel pipe 48 via a swirl body inner pipe 54, which can, for example, be adapted to different combustor geometries and process parameters. The ratio of the amount of air flowing through swirl body 30 and exiting the gap formed by the outer diameter of the swirl body in region 38 and the inner diameter of the delta tray 66 can be limitedly influenced by the axial movement of swirl body 30 in fuel tube 48.

Even though the burner tube 12 is not shown in fig. 2, it will be appreciated that in the schematic view of fig. 2 the combustion air 28 flows from right front to left back, i.e. through the swirling body 30 and out of the swirling body 30. The primary gas injection lances 46 are located in the air stream.

Fig. 3 shows the burner head 10a in a perspective view, schematically from the flame side. The components already described with reference to fig. 1 and 2 are not described again in detail. All of the features described so far also apply to the burner head 10a shown in fig. 3. In fig. 3, the conical part of the cyclone body 30 is not shown and the part of the cyclone body 30 surrounding the downstream region 38 is cut away to be able to show the components located inside the cyclone body 30. As in fig. 2, the burner tube 12 is not shown.

A direct electrical ignition device 56 can be provided for starting the combustion process, which ignition device is used only initially (for example, for a single ignition). If a flame has been formed and stabilized, further ignition of the fuel-air mixture is achieved by a reaction in the flame. In one embodiment, the ignition device 56 is secured to one of the secondary gas jets 16 b.

In the illustrated embodiment, the fuel tubes 48 terminate downstream in a cylindrical fuel distributor 58. The fuel distributor 58 may also be referred to as a primary gas distributor 58, since here the fuel pipe 48 also conducts only primary gas. In this embodiment, four primary gas nozzles 16a are arranged in a beam-like manner on the outer surface of the primary gas distributor 58 on the primary gas distributor 58. The primary gas nozzles 16a are arranged at uniform distances and are spaced apart from the fuel pipes 48 or from the primary gas distributor 58 as far as the not shown combustion pipe 12.

The primary gas nozzle 16a may have an aperture 60. Each primary gas nozzle 16a may have a plurality of holes 60. Two holes 60 are shown. But may be more or fewer holes. The holes 60 are arranged on the primary gas nozzle 16a such that the primary gas flows out in a substantially tangential direction. The orientation of the holes 60 may be coordinated with the arrangement and design of the swirl vanes 32 such that the primary gas is output with the flow of the swirling fuel/combustion air mixture in the first region 36. The primary gas flows out of the lateral openings in a tangential direction, which is predetermined by the swirl direction. Additionally or alternatively, the primary gas nozzle 16a may have an axial bore from which the primary gas also flows.

The secondary fuel nozzles 18 or the primary gas nozzles are arranged in a circle around the downstream end of the swirler 30. The second fuel nozzle has a bore 62 on its end face. The holes 62 are designed to ensure a high fuel exit velocity of the primary gas so that the primary flame front 26 is spaced from the burner head.

Fig. 4 schematically shows a side view of the burner head 10 b. The burner head 10b may correspond to the burner head 10 and/or the burner head 10 a. The components already described with reference to fig. 1 to 3 are not described again in detail. Individual parts are cut away in side view to better show details. The part of the cyclone body 30 directed towards the viewer is cut away, whereby the inner structure is visible. The region of the first fuel inlet 20 opening into the fuel pipe 48 is cut away.

The holes 64 of the primary gas nozzle 16a are visible in the side view of fig. 4. The holes 64 are designed such that the fuel is output substantially radially inward. Additionally or alternatively, the primary gas nozzle may also have an axial bore.

The burner tube 12 is also shown in fig. 4. The burner tube 12 may be closed at its downstream end by an annular delta tray 66 extending radially inwardly from the burner tube 12. In the illustrated embodiment, the delta tray 66 has a plurality of radially inwardly directed guides 68. The opening of the second fuel nozzle 18 may terminate flush with the delta tray 66. The design of the delta tray 66 described in detail with reference to fig. 6 is used for internal exhaust gas recirculation in the main flame 26. Here, recirculation may be caused by the portion of the combustion air 28 flowing through the swirling device 14 and impinging directly on the ring of annular Deler trays 66. As a result, a low-pressure region and a swirl region are formed on the guide device 68 on the outflow side, i.e., on the side of the guide device 68 pointing into the combustion chamber. The exhaust gases thus led back are here injected into the hot zone of the main flame 26. In this zone, the temperature is reduced by the recirculated exhaust gas and the partial pressure of O2 is reduced. Both effects contribute to the reduction of NO formation or to NO formation.

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

In various embodiments, the air margin required to completely combust portions of the fuel quantities from the primary gas nozzles 16a, the secondary gas nozzles 16b, and from the fuel nozzles 18 may be between 1.075 and 1.2. The combustion zones of the primary flame and the spaced main flame are above the stoichiometric ratio, respectively. Based on the flow of fuel axially into the combustion chamber from the second fuel nozzle 18, a sub-stoichiometric region may be locally formed before the fuel gas and air and recirculated exhaust gas are thoroughly mixed.

The reduction of the NO value is achieved by combustion of an external small amount of NO in a partially premixed, very lean primary flame in combination with a spaced apart main flame which can be made to form NO at detrimentally high temperatures by adequately mixing in the internally recirculated exhaust gas and reducing the partial pressure of O2 in the mixture. Advantageously, an elongated, but not excessively long flame is formed, which allows the heat released by chemical enthalpy when burning the fuel to the cooled annular wall of the combustion chamber to be efficiently coupled out by radiation and convection.

Fig. 5 schematically shows a sectional view of the front section of the burner head 10 b. The components already mentioned with reference to fig. 1 to 4 are not described again in detail.

The swirl body inner tube 54 is visible and is guided over the fuel tube 48. Thereby, the cyclone body is longitudinally movable and may be fixed in position by means of screws 70. The movability allows a better adaptation to different combustion chambers in which the main flame front 26 is formed.

Perforated partition 34 is disposed in region 38. The perforated partition 34 is positioned and designed such that in the described embodiment the primary flame 24 is reliably stabilized or held in the region 38 of the swirling body 30.

Fig. 6 shows a front view of the burner head 10b schematically from the flame side, or in other words from the combustion chamber. The fuel distributor 58 is arranged in the middle, with the primary gas nozzle 16a with its bore 60 extending away from the fuel distributor. Behind which is located a perforated partition 34. In the embodiment shown, the indentations are realized by two concentric rows of holes, wherein the holes are perfectly circular. It should be understood that the indentations may have other shapes. The ratio of open area to total area may be different than shown. The perforated partition wall 34 serves to reduce the flow velocity of the air/fuel mixture from the swirling flow in the region 36 of the swirling body 30. The partition wall 34 is defined by the walls of the cyclone body 30. The secondary gas nozzle 16b located at the rear can be seen through the cutout.

The second fuel nozzles 18 with holes 62 are arranged at even intervals on a circumference around the central axis of the cyclone body 30. Around its periphery is an annular delta tray 66 which encloses the burner tube 12. The guide 68 extends inwardly in a radial direction from the inner circumference of the delta tray 66. In the embodiment shown, three guide devices 68 are provided. The three guides 68 are evenly distributed over the inner circumference. The burner head 10b can also have a greater or lesser number of guides 68, which can likewise be distributed uniformly over the inner circumference. In the illustrated embodiment, the guide 68 is triangularly shaped and points inward in a radial direction with a pointed end. The apex of the triangle is distal from the annular delta tray 66. As can be seen from fig. 5, the guide 68 does not lie in the plane of the drawing in fig. 6, but is directed away from the cyclone body 30. The guide means are angled.

The directing means are configured by means of a delta tray 66 such that the directing means form a low pressure zone which draws off gas from the combustion chamber. Thus, the delta trays 66 and guides 68 cause internal exhaust gas recirculation. The angled, triangular-shaped profile pointing away from the swirling body induces a "stationary vortex" on the guide 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 further into the region of maximum NO production.

The geometry of the guide 68 is optimized as much as possible, so that as high an internal exhaust gas quantity as possible is drawn into the main flame 26. The number and geometry of the guides 68 are taken into account here for the NO-reducing effect and for the stabilization of the main flame.

The annular delta tray 66 may have a plurality of ridges 72 on its inner circumference between the guides 68. The ridges 72 form a tooth geometry. In fig. 6, a semicircular ridge is shown, but the teeth can be configured with other geometries. The teeth 72 are designed to produce a large surface. The larger surface allows for a larger contact surface between the exhaust gas, the combustion air and the main fuel, thereby creating a more thorough and uniform mixing of the fuel-air-exhaust gas mixture. A combustion zone can thereby be formed in the main flame 26 which is more evenly distributed and is rich in exhaust gases and therefore more favorable in stoichiometry. The inventors have found that the formation of hot NO is thereby further reduced overall.

As already mentioned, the second fuel nozzle 18 is shaped such that the highest possible discharge velocity is achieved. To this end, a shroud may be provided in front of the axial opening of the fuel nozzle. The intensity of the internal recirculating exhaust gas and fuel mixing can be further increased by high pulsing of the effluent gas. Further optimization is achieved by coordinating the position of the second fuel nozzle 18 with the geometry of the pilot device 68. The second fuel nozzles 18 are evenly distributed between the guides 68.

In operation, advantageous low-nitrogen combustion is achieved by first delivering combustion air 28 to the burner tube 12 with the open end located downstream. A portion of the combustion air 28 swirls in the swirling device 14 arranged in the combustion tube 12. The first fuel quantity is fed directly into the swirling body 30 and is mixed there with the swirling combustion air 28. A primary flame is formed in the swirling fuel/combustion air mixture within the swirling body. The second combustion quantity is fed downstream to the swirling device 14. A main flame front is formed which is stabilized downstream of and spaced apart from the combustion tube. The first fuel quantity is set independently of the second fuel quantity.

The individual fuel adjustments enable very low NO emissions to be achieved over a large load range. At lower loads, a different ratio of the first fuel amount to the second fuel amount than at high loads may be optimal. When the ratio of the two fuel quantities to each other is set to be fixed, a low NO emission cannot be ensured over the entire load range of the burner. In the burner head according to the invention, a smaller percentage of primary/secondary gas can be delivered at low loads than at high loads, for example. In the case of an undivided regulation, the first fuel quantity is reduced less flow-technically than the air quantity flowing through the swirl body at lower loads, so that the NO emissions at lower loads can also be increased in the primary flame above the stoichiometric ratio.

Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the basic concepts of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

Claims (20)

1. Method for staged combustion of fuel by feeding combustion air (28) into a combustion tube (12), the method comprising:

-feeding a first quantity of fuel to form a primary flame (24) in the combustion tube (12) that is significantly above the stoichiometric ratio, preferably a stoichiometric ratio greater than 1.5, in particular greater than 2.0;

-feeding a second fuel quantity downstream to form a main flame (26) slightly above the stoichiometric ratio in the combustion chamber, preferably between 1.03 and 1.18 stoichiometric ratio, wherein the temperature of the main flame (26) is lowered by the exhaust gas recirculating inside the combustion chamber, and wherein the main flame (26) is stabilized downstream of the combustion pipe (12) and spaced apart from the combustion pipe (12).

2. The method of claim 1, further comprising:

-adjusting the first fuel quantity independently of the second fuel quantity, wherein the adjustment is performed in such a way that the first fuel quantity is approximately between 3% and 15%, preferably between 5% and 10%, of the sum of the first fuel quantity and the second fuel quantity.

3. The method of claim 1 or 2, further comprising:

-swirling a portion of the combustion air (28) to produce swirled combustion air;

-inputting a first partial quantity of the first fuel quantity into a region of the swirled combustion air to form a swirled lean air/fuel mixture;

-reducing the flow velocity of the swirling lean air/fuel mixture; and

-feeding a second partial quantity of the first fuel quantity into the slowed, swirled lean air/fuel mixture.

4. The method according to any of the preceding claims, wherein at least a part of the first partial quantity of the first fuel quantity is input inwards in a radial direction.

5. The method according to any of the preceding claims, wherein at least a part of the second partial quantity of the first fuel quantity is fed in a tangential direction with the flow of the swirling fuel/combustion air mixture.

6. The method of any preceding claim, further comprising:

-forming a vortex, in particular a stationary vortex, in the region of the input of the second fuel quantity, thereby directing exhaust gas back into the hot zone of the main flame front (26).

7. Burner head (10) for staged combustion of fuel, wherein the burner head (10) is designed, combusting the first input amount of fuel in a primary flame (24) above the stoichiometric ratio within the combustion tube (12), and combusting the second input fuel quantity in the combustion chamber at a distance from the combustion pipe (12) in a main flame (26) slightly above the stoichiometric ratio, preferably between 1.03 and 1.18, wherein the fuel inlet is designed such that the primary flame (24) burns at a stoichiometric ratio of more than 1.5, in particular more than 2.0, wherein the burner head (10) is also designed to reduce the temperature of the main flame (26) by means of exhaust gases recirculated inside the combustion chamber, and stabilizing the main flame (26) downstream of the combustion tube (12) and spaced apart from the combustion tube (12).

8. The burner head (10) according to claim 7, wherein the input of the first quantity of fuel and the input of the second quantity of fuel are adjustable independently of each other, wherein the adjustment is made in such a way that the first quantity of fuel is approximately between 3% and 15%, preferably between 5% and 10%, of the sum of the first quantity of fuel and the second quantity of fuel.

9. The burner head (10) according to claim 8, wherein the burner head is designed to deliver a first portion of the first quantity of fuel to the portion of the combustion air generating the strong vortex to form a fuel/combustion air mixture and to deliver a second portion of the first quantity of fuel to the decelerated fuel/combustion air mixture.

10. Burner head (10) for staged combustion of fuel, having:

a combustion tube (12) configured to be flowed through by combustion air (28), wherein the combustion tube (12) has an open end downstream;

a swirling device (14) arranged within the burner tube (12) to be flowed through by a portion of combustion air (28), the swirling device having a swirling body (30) surrounding a first and a second region, wherein the first region (36) is located upstream of the second region and swirl vanes (32) are arranged only in the first region;

a first fuel nozzle (16a, 16b), the first fuel nozzle (16a, 16b) being arranged within the swirling body (30) for feeding fuel to form a primary flame (24) within the swirling body (30);

a second fuel nozzle (18), said second fuel nozzle (18) being arranged downstream of said swirling device (14) for feeding fuel to form a free main flame front (26), wherein said main flame front (26) is stabilized downstream of said burner head (10) and spaced apart from said burner head (10);

a first fuel inlet (20), the first fuel inlet (20) being connected to the first fuel nozzle (16a, 16 b); and

a second fuel supply (22), which second fuel supply (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) having a stoichiometric ratio of more than 1.5, in particular more than 2.0.

11. The burner head according to claim 10, wherein the fuel amounts of the fuels fed through the first fuel feed (20) or through the second fuel feed (22) are adjustable independently of one another.

12. A burner head according to claim 10 or 11, wherein the swirling device (14) has a perforated partition wall (34) between the first zone (36) and the second zone (38).

13. The burner head according to any of claims 10 to 12, wherein the first fuel nozzle (16a, 16b) comprises a primary fuel nozzle (16a) and a secondary fuel nozzle (16b), the primary fuel nozzle (16a) being arranged in the second region (38) of the swirling body (30) and the secondary fuel nozzle (16b) being arranged in the first region of the swirling body (30).

14. The burner head according to claim 13, wherein the secondary fuel nozzles (16b) are evenly distributed between the swirl vanes (32) and are designed to output fuel inwards in a radial direction so as to form a swirling fuel/combustion air mixture.

15. The burner head according to claim 13 or 14, wherein the primary fuel nozzles (16a) are evenly distributed in a halo and are configured to output fuel in a tangential direction with the flow of the swirling fuel/combustion air mixture.

16. The burner head according to any of claims 10 to 15, wherein at least a portion of the fuel is discharged from the fuel nozzle (16a) via a lateral hole (60) in a first fuel nozzle.

17. Burner head according to any of claims 10 to 16, wherein the first fuel input (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), the primary fuel nozzle (16a) being fixed to the fuel distributor (58).

18. Burner head according to claim 17, wherein the swirl body (30) is movably arranged in a longitudinal direction on the fuel pipe (48).

19. The burner head of any preceding claim, further having:

an annular delta tray (66), said delta tray (66) extending radially inward from a downstream end of said burner tube (12) and having a plurality of radially inwardly directed guides (68).

20. The burner head of claim 19, wherein the annular delta tray (66) has a plurality of ridges (72) on its inner circumference between the guides (68).

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