EP3940293A1 - Method for staged combustion of a fuel and combustion head - Google Patents

Abstract

Process Combustion head for the staged combustion of a fuel with the supply of combustion air (28) into a burner tube (12). A first quantity of fuel is supplied to form a primary flame (24) within the burner tube. A second quantity of fuel is introduced downstream to form a main flame front (26). The main flame front (26) stabilizes downstream of the burner tube (12) and spaced from the burner tube (12). The fuel feeds are designed in such a way that the primary flame (24) burns with a stoichiometry greater than 1.5, in particular greater than 2.0.

Description

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

When burning fossil fuels in furnaces, nitrogen oxides, e.g. NO, NO2, are produced in addition to other combustion products. In the following, only NO is referred to in summary. These and other pollutant emissions can be influenced and reduced by design measures in the burners. The reaction mechanisms that lead to such nitrogen oxides are widely known and are generally divided into thermal and prompt NO formation, and described as NO formation as a result of the oxidation of the nitrogen chemically bound in the fuel.

It is known that the thermal NO is dependent on the so-called Zeldovich mechanism on the one hand on the residence time of the reactants in the combustion zone and on the other hand to a large extent on the combustion temperature itself. The combustion temperature is linked to the fuel/air ratio λ. The maximum combustion temperature occurs at a fuel/air ratio of λ=1. This is also referred to as the stoichiometric ratio. There is just enough oxygen in the combustion air for the fuel to burn completely. A fuel/air ratio of λ < 1 is referred to as a rich mixture; there is too much fuel. A fuel/air ratio λ > 1 is referred to as a lean mixture, there is excess air. In both cases, the combustion temperature drops again and consequently less thermal NO is formed.

In addition to thermal NO, the formation of prompt NOx also plays a not insignificant role. The prompt NO arises from hydrocarbon radicals CH formed as intermediates in flames, which are present as intermediate products during the combustion of carbonaceous fossil fuels. The CH radicals react with atmospheric nitrogen to form hydrocyanic acid (HCN), which is further converted to NO in very rapid formation reactions. A proven method to suppress the formation of free CH radicals and thus the formation of prompt NO is lean combustion or lean combustion. Lean combustion refers to combustion with excess air, i.e. with λ > 1.

The prompt NO is formed in small amounts compared to the thermal NO, but is also crucial for the reduction of the NO formation, especially in ultra-low NO applications.

It is also known that the recirculation or recirculation of exhaust gases produced during combustion has a positive effect on reducing the formation of nitrogen oxides. The recirculated, cooled exhaust gas reduces both the flame temperature itself and the O2 partial pressure in the combustion zone. Both effects contribute to the reduction of NO formation. However, mixing in increasing amounts of exhaust gas tends to destabilize the continuous combustion process.

EP 1 754 937 B1 and EP 2 037 173 B1 show burner heads with which NO reduction is achieved. These are primarily single-stage combustion processes that only allow further NO optimization and flame stabilization to a limited extent. DE 195 09 219 A1 shows a combustor for two-stage combustion with a hyper-stoichiometric air-gas mixture in the first stage and a sub-stoichiometric air-gas mixture in the second stage.

In the case of a combustion head, a distinction can usually be made between so-called mixing zones and so-called combustion zones.

Different fluids that are not (yet) burned are mixed in a mixing zone. In a mixing zone, the conditions that must be present for combustion are usually not met. This can be the case, for example, when the flow rate of the ignitable mixture is significantly higher than the flame speed.

A combustion zone is an area where the conditions required for combustion exist. A combustion zone exists when an ignitable mixture (eg, fuel-combustion air mixture, fuel-combustion air-exhaust mixture, fuel-oxidant mixture, fuel-oxidant-exhaust mixture) is present, the flow rate of the ignitable mixture, and the flame velocity are essentially the same and have a temperature that is equal to or greater than the ignition temperature of the ignitable mixture. The more general term oxidizing agent includes the term combustion air, but also includes, for example, ambient air enriched with additional oxygen. Ignition or combustion cannot take place in areas where these conditions are not met. Mixed zones often merge into combustion zones without any clear spatial separation.

For these and other reasons, there is a need for the present invention. It may be an object of the invention to be able to dispense with external measures for reducing NO, for example external exhaust gas recirculation. It can be an object of the invention to keep the use of energy as low as possible. It may be an object of the invention to provide energetically advantageous combustion with minimized NO emissions.

• Fig. 1 stark schematisiert eine Seitenansicht eines Brennkopfs zeigt;
• Fig. 2 schematisch perspektivisch Teile eines Brennkopfs von einer Brennstoffzuführungsseite zeigt;
• Fig. 3 schematisch perspektivisch Teile des Brennkopfs von Fig. 2 von einer Flammenseite zeigt;
• Fig. 4 schematisch eine Seitenansicht eines Brennkopfs zeigt;
• Fig. 5 schematisch eine Schnittansicht eines vorderen Abschnitts eines Brennkopfs zeigt; und
• Fig. 6 schematisch eine Vorderansicht eines Brennkopfs zeigt.

The aims and characteristics of the present invention will become clear in the following description of exemplary embodiments, made with reference to the attached figures, in which:

• 1 shows a highly schematic side view of a combustion head;
• 2 shows schematically in perspective parts of a combustion head from a fuel supply side;
• 3 schematic perspective parts of the burner head from 2 showing from a flame side;
• 4 shows schematically a side view of a combustion head;
• figure 5 shows schematically a sectional view of a front portion of a combustion head; and
• 6 schematically shows a front view of a combustion head.

Aspects and embodiments are described below with reference to the drawings, wherein the same or similar reference numbers are generally used to refer to the same or similar elements. In the following description, numerous specific details are set forth in order to provide a thorough understanding to provide understanding of one or more aspects of the embodiments. However, it may be apparent to one skilled in the art that one or more aspects of the embodiments may be practiced with a lesser degree of the specific details. In other instances, elements are shown in schematic form in order to facilitate describing one or more aspects of the embodiments. The following description should therefore not be taken in a limiting sense. It is noted that the representations of the various elements in the figures are not necessarily to scale.

Directional terminology used in the description with reference to the drawings, such as, for example, "top", "bottom", "top", "bottom", "left", "right", "front", "back", "vertical" , "horizontal" etc. is not meant to be limiting. Components of embodiments can be positioned in a number of different orientations, the directional terminology is used for explanation only. It is understood that other embodiments may be employed and structural or logical changes may be made without departing from the concept of the present invention.

Multi-stage combustion processes have been known in practice for a long time. At present, however, the approaches known to date are not sufficient to be able to continue to meet the steadily increasing NO requirements for the operation of combustion plants in the long term. A more intensive NO reduction is possible through a staged combustion according to the disclosure. With appropriate controllability, the NO reduction can also be guaranteed over a wide load range and/or for different fuels and/or for different combustion chambers.

A method for the staged combustion of a fuel while supplying combustion air into a burner tube according to claim 1 is provided. The fuel can be a gas or a liquid fuel. A first quantity of fuel is introduced to form a primary flame within the burner tube. A second amount of fuel may be added downstream to form a main flamefront. The main flame stabilizes downstream of the burner tube and spaced from the burner tube. The fuel feeds are designed in such a way that the primary flame burns with a stoichiometry greater than 1.5, in particular greater than 2.0. This allows a very low flame temperature to be achieved. It forms practically none prompt NO. The main flame is slightly lean of stoichiometry. The stoichiometry can be between 1.03 ... 1.18. The temperature of the main flame can be significantly reduced by flue gases recirculated inside the combustion chamber.

In one embodiment, the first amount of fuel may be regulated independently of the second amount of fuel. A hyper-stoichiometric primary flame can thus be guaranteed over a wide load range.

In one embodiment, the first amount of fuel supplied can be significantly less than the second amount of fuel supplied. The first amount of fuel can be between 3% and 15% of the total amount of fuel, i.e. the sum of the first amount of fuel and the second amount of fuel. The first amount of fuel is preferably between 5% and 10% of the sum of the first amount of fuel and the second amount of fuel.

In a further embodiment, part of the combustion air is twisted. This creates turbulent combustion air. A first partial quantity of the first quantity of fuel is released into the area of the air turbulence. This creates a turbulent lean air/fuel mixture. Very thorough mixing can be achieved. In this range, the flow velocity is high and the mixture is lean, so that there are no ignition conditions. The flow rate of the swirled lean air/fuel mixture is reduced in the next step. A second portion of the first amount of fuel is introduced into the decelerated swirled lean air/fuel mixture.

There is further provided a combustor for staged combustion of a fuel according to claim 7. The burner head provided enables the procedure to be carried out. The combustor is configured to combust a first supplied amount of fuel in a lean-of-stoichiometric primary flame. A second quantity of fuel supplied is combusted in a slightly over-stoichiometric main flame.

A supply of the first quantity of fuel and a supply of the second quantity of fuel can preferably be regulated independently of one another and thus ensure combustion with a very low level of nitrogen oxides over a wide load range.

The following figures show exemplary configurations of combustion heads according to the invention, with which the method according to the invention for the staged combustion of a fuel can be carried out.

1 shows a highly schematic side view of a burner head 10. The burner head 10 comprises a burner tube 12, a swirl device 14, first fuel nozzles 16a, 16b, second fuel nozzles 18, a first fuel feed 20 and a second fuel feed 22. Arrows symbolize the inflowing fuel. In operation, a lean primary flame 24 forms within the swirler 14 and a main flame or main flame front 26 spaced from the combustor 10, both of which are defined by a flame in the 1 are represented symbolically. Combustion head 10 thus serves to burn fuel in stages. The fuel can be gaseous. The fuel can be natural gas. The fuel may include hydrogen. In addition to use as a pure gas burner, a dual-fuel burner is also possible, in which liquid fuel can also be burned in addition to gaseous fuel. A liquid fuel only burner is also possible. The further description generally relates to an embodiment as a gas burner in a non-limiting manner.

The burner tube 12 is shown in the illustration 1 Combustion air 28 supplied from the right. The end of the burner tube 12 on the right in the illustration is therefore the upstream end. The combustor tube 12 may be substantially cylindrical. The combustion air 28 flows through the burner tube 12 and leaves it at the open end of the burner tube 12 on the left in the illustration, the downstream end. The main flame front 26 is formed downstream of the combustion head 10. Here is the combustion chamber or furnace, not shown.

The amount of fuel from the first fuel nozzles 16a, 16b may be small in relation to the amount of fuel exiting the second fuel nozzles 18. If only a small amount of fuel is burned well lean of stoichiometry in the primary flame 24, a second lean of stoichiometry combustion stage is not necessary. Therefore, the spaced main flame 26 can also be overall lean of stoichiometry. A general under-stoichiometric combustion zone, as in the case of staged combustion with under-stoichiometric and over-stoichiometric combustion zones and the residence time of the gases in these zones necessary for NO reduction, is not produced with the combustion head 10 according to the invention. The inventive method provides a heavily over-stoichiometric primary flame and a slightly over-stoichiometric main flame.

The swirl device 14 is arranged within the burner tube 12 . The twister 14 can be open at both ends. A longitudinal axis of the burner tube 12 and a longitudinal axis of the swirl device 14 can be parallel to one another or lie on top of one another, so that the swirl device 14 is located centrally in the burner tube 12 and is radially evenly spaced from the inner wall of the burner tube. Part of the combustion air 28 flows outside the swirl device 14 through the burner tube 12, another part of the combustion air 28 flows through the swirl device 14.

The swirl device 14 comprises a swirl body 30, swirl vanes 32 and a perforated partition 34. The swirl body 30 can be essentially cylindrical. The perforated dividing wall 34 can run essentially perpendicularly to the longitudinal axis of the swirl body 30 and divide an interior space of the swirl body 30 into a first area 36 and a second area 38 . The first region 36 may be upstream of the second region 38 . The broken partition wall 34 can cause a pressure loss. It can thus locally reduce the flow speed downstream of the partition wall 34 that has been perforated.

The swirl vanes 32 can only be arranged in the first region 36 . The second area downstream of the partition wall 34 can be free of swirl vanes 32 . A plurality of swirl vanes 32 can be provided.

The swirl body 30 can have a larger diameter in the first area 36 than in the second area 38. In the transition between the first area 36 and the second area 38, a conical section can be provided.

The first fuel nozzles 16a, 16b are arranged inside the swirl body 30. You are connected to the first fuel feed 20 . The first fuel supply 20 permits regulation of the amount of fuel/combustion gas flowing to the first fuel nozzles 16a, 16b, as indicated by a symbol 40 in 1 shown. This control is separate and independent of a control 42 in the second fuel feed 22.

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

The support fuel nozzles 16b can be distributed evenly between the swirl vanes 32 . The auxiliary fuel nozzles 16b can be arranged essentially parallel to a longitudinal axis of the burner tube 12 . The swirl vanes 32 cause a strong turbulence of the combustion air 28. The fuel flowing out of the support fuel nozzles 16b, which is also referred to as support gas, is thus highly efficiently premixed with part of the combustion air 28 for the primary flame 24. A twisted fuel/combustion air mixture is created. The fuel supply through the auxiliary fuel nozzles 16b can be designed in such a way that a turbulent lean air/fuel mixture is formed. The auxiliary fuel nozzles 16b can deliver a first subset of the first quantity of fuel. The auxiliary fuel nozzles 16b can have bores for dispensing the fuel. The bores can be arranged in such a way that the fuel is discharged at least partially inwards in a substantially radial direction, i.e. in a direction substantially perpendicular to the wall of the swirler 30. Due to the high flow velocities of the swirled combustion air and due to the high proportion of air in the ratio The ignition conditions of the swirled fuel/combustion air mixture in the region of the swirl vanes 32, ie in the upstream region 36, are not yet given in relation to the fuel or gas quantity.

The partition wall 34 can be designed to decelerate the swirled fuel/combustion air mixture. The partition wall 34 can have openings for this purpose. For this purpose, the dividing wall can be configured essentially in the manner of a lattice. A geometry of the dividing wall 34 can be designed to reduce the flow velocity of the swirled fuel/combustion air mixture while leaving the turbulence largely undisturbed. The partition 34 reduces the absolute flow rate of the swirled and premixed primary air and thus ensures the ignition of the primary flame 24, which is additionally enriched in this area with a second portion of the first amount of fuel.

The primary fuel nozzles 16a may be evenly distributed in the downstream area 38 . The primary fuel nozzles 16a are thus located downstream of the partition wall 34 in an area with a lower flow velocity. The primary fuel nozzles 16a may be arranged substantially perpendicular to a longitudinal axis of the combustor tube 12 . The primary fuel nozzles 16a can be evenly distributed in a corona. A plurality of primary fuel nozzles 16a may be provided. In the downstream region 38, the primary fuel nozzles 16a deliver the second part of the first quantity of fuel, which is referred to as the primary gas, to the fuel-air mixture formed in the bladed part of the swirl body 30 or, in other words, in the first region 36, and thus produce the ignitable mixture for the formation of the primary flame 24. The primary fuel nozzles 16a can have bores for dispensing the fuel. The bores can be arranged laterally on the primary fuel nozzles 16a. The lateral bores can be arranged in such a way that the fuel is discharged essentially in a tangential direction.

The ratio of the opening area of the entirety of the bores in the primary fuel nozzles 16a to the opening area of the entirety of the bores in the support fuel nozzles 16b can determine a ratio of primary gas to support gas, taking into account the supply lines to the primary fuel nozzles 16a and the support fuel nozzles 16b. The ratio can be chosen depending on the overall geometry and the fuel quality or the fuel composition. The ratio can be around 1:1. About half of the fuel flowing through first fuel guide 20 may be delivered via primary fuel nozzles 16a in region 38, and about half of the fuel flowing through first fuel guide 20 may be delivered via support fuel nozzles 16b in region 36.

The separate controllability of the primary and support gas by the control device 40 in relation to the controllability of the second and main fuel quantity flowing through the second fuel supply 22 and the design of the swirler 30, primary and support fuel nozzles 16a, 16b and partition 34 can provide a primary flame 24 with a Generate stoichiometry λ>>1 over a wide load range. In one embodiment, the stoichiometry of the primary flame 24 is λ>1.5. In another embodiment, the stoichiometry of the primary flame 24 is λ>2.

Due to the resulting very low combustion temperatures, it has been proven that almost no thermal and no prompt NO is produced within the primary flame 24 .

However, such low combustion temperatures always produce flame instabilities that must be intercepted. The reaction rate is exponentially dependent on the temperature in the flame zone and on the turbulence in the same. The reaction speed is reduced by imperfect mixing of fuel and oxidizer. 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 previous supply of the support gas via the support fuel nozzles 16b into the swirled combustion air and thus the enrichment and premixing of the primary air with fuel, the type and position of the introduction of the primary gas, the ratio of support and primary gas and the geometry and Position of the partition wall 34 in the bladeless part 38 of the swirler 30 in the illustrated embodiment of importance. Other means can be provided in order to achieve a stable primary flame with a stoichiometry greater than 1, in particular greater than 1.5 or even greater than 2.

Furthermore, the cylindrical, bladeless part of the swirl body 30, the area 38 in 1 , Designed so that the primary flame 24 forms in a defined area that is protected from the remaining combustion air 28 that flows through the burner tube 12 outside of the swirl body 30 .

The second fuel nozzles 18, also referred to as main gas nozzles, are located outside and downstream of the swirl device 14. The second fuel nozzles 18 are connected to the second fuel feed 22. The second fuel feed 22 allows the amount of fuel/combustion gas flowing to the second fuel nozzles 18 to be regulated. The second amount of fuel comprises the majority of the total amount of fuel and is therefore also referred to as the main amount of fuel or main gas. The adjustability of the main gas is marked with the symbol 42 in 1 shown.

The second fuel nozzles 18 are located within the combustor tube 12. The second fuel nozzles 18 may be located at the downstream end of the combustor tube 12 and terminated therewith. The second fuel nozzles 18 can evenly over the Inner circumference of the burner tube 12 are distributed. In 1 not shown is an annular delta disk that can fill a gap between burner tube 12 and second fuel nozzles 18 at the downstream end of the burner tube. The delta disc is with reference to Figures 4-6 explained in more detail.

The second fuel nozzles 18 can be designed to ensure a high fuel exit velocity. The resulting impulse transports the fuel as far as possible into the combustion chamber and forms a combustion zone spaced apart from the combustion head 10 . The main gas can be discharged essentially in the direction of flow, ie parallel to the longitudinal axis of the burner tube 12 . For this purpose, the second fuel nozzles 18 can have an opening on one end face. A panel can determine the opening at the front. The configuration of the second fuel nozzles 18 results in the formation of the main flame or main flame front 26 which is spaced from the downstream end of the combustion head 10 and is stably formed in the combustion chamber, not shown in detail. Due to the arrangement of the second fuel nozzles with a coaxial outflow direction in relation to the axis of the burner tube, the main flame 26 can have a slim and elongated flame shape. An internal exhaust gas recirculation, which is explained in more detail below, can inject exhaust gases into the hot zones of the main flame 26 and thus into the areas of greatest NO production. This reduces NO production in the main flame.

The fuel feeds can be designed and arranged in such a way that ignition energy for the spaced-apart main flame 26 from the primary flame and recirculated exhaust gases is made available in order to ignite the mixture of main fuel, combustion air or generally oxidant and recirculated exhaust gas and ensure a continuous, stable progression of the ensure oxidation reactions.

Both gas connections, ie fuel supply 20 for the primary and supporting gas for the primary flame 24 and fuel supply 22 for the main gas for the main flame 26 are regulated separately by gas control devices 40 and 42 in the embodiment shown. As a result, the quantity of gas in the primary flame 24 and in the main flame 26 can be set separately from one another and the stoichiometry in the respective combustion zone can thus be regulated individually. This allows the setting of a stable and over-stoichiometric primary combustion zone and thus the formation of an almost NO-free primary flame 24 over a wide load range and adaptation to different combustion chambers.

2 shows schematically in a perspective view parts of a combustion head 10a from a fuel supply side. Combustion head 10a can have the same features as for the in 1 illustrated combustion head 10 described. Combustion head 10a may represent an implementation of combustion head 10 . The same reference numbers are therefore used as in 1 used. The description of 2 is essentially limited to details arising from the presentation of the 1 not emerge. In the 2 the burner tube 12 is not shown.

The second fuel feed 22 of the combustion head 10a is designed as a tube which has a connection flange 44 for connection to a fuel supply. Smaller pipes 46 or main gas lances 46 lead from the second fuel feed 22 . The main gas lances 46 direct the fuel from the second fuel feed 22 to the second fuel nozzles 18 and close with them. In the illustrated embodiment, the combustion head 10a has six second fuel nozzles 18 . The main gas lances 46 run outside the swirl body 30.

The second fuel feed 22 transitions into a fuel pipe 48 which can run through the swirl body 30 in the middle parallel to the longitudinal axis of the swirl body 30 . The fuel pipe 48 is preferably designed as a central fuel pipe. The fuel tube 48 carries the main gas in the first upstream region. Downstream of where the main gas lances 46 branch off, a gas separating plate 50 seals off the second fuel feed 22 from the subsequent fuel pipe 48 . The gas separating plate 50 is arranged in the second fuel feed 22/the fuel pipe 48 and is essentially perpendicular to a longitudinal axis of the second fuel feed 22/the fuel pipe 48.

Downstream of the gas separating plate 50, the first fuel feed 20 opens into the fuel pipe 48. Downstream of the gas separating plate 50, the fuel pipe 48 is therefore used to guide the first quantity of fuel. Smaller tubes 52, the so-called support gas lances, branch off downstream of the gas separating plate 50. The supporting gas lances 52 conduct the fuel from the first fuel feed 20 to the supporting gas nozzles 16b. In the illustrated embodiment, the combustion head 10a has three supporting gas nozzles 16b. The support gas nozzles 16b are inside the swirl body 30. The swirl vanes 32 can be seen next to the supporting gas nozzle 16b.

2 An exemplary shape of the swirl body 30 can also be found in FIG. In the first area 38 with the swirl vanes 32 and the support gas nozzles 16b, the swirl body 30 is configured cylindrically with a first diameter. In the second region 38 without swirl vanes, the swirl body 30 is cylindrical with a second diameter. In one embodiment, the first diameter is larger than the second diameter. Both areas 36, 38 can then be connected to one another by a conical area.

Swirl body 30 is displaceably mounted on fuel pipe 48 via a swirl body inner tube 54, which allows, for example, an adjustment to different combustion chamber geometries and process parameters. By axially shifting the
Swirl body 30 on the fuel pipe 48, the ratio of the amounts of air which flows through the swirl body 30 and which exits from the gap formed by the outer diameter of the swirler in area 38 and the inner diameter of the delta disc 66 can be influenced within limits.

Even if in 2 the burner tube 12 is not shown, it is to be understood that the combustion air 28 in the illustration of FIG 2 flows from the front right to the left rear, both through the swirl body 30 and outside of the swirl body 30. The main gas lances 46 are located in the air flow.

3 shows schematically in a perspective view the combustion head 10a from a flame side. Already referring to figures 1 and 2 illustrated parts will not be described again in detail. All features described so far also apply to the burner head 10a as in 3 shown. In 3 The conical portion of the swirler 30 is not shown and portions of the swirler 30 enclosing the downstream region 38 are cut away to allow portions within the swirler 30 to be shown. As in 2 the burner tube 12 is not shown.

To start the combustion process, a direct, electrical ignition 56 can be provided, which is only used initially for (eg for the first time) ignition. Once a flame has formed and stabilized, the fuel-air mixture continues to ignite by reaction from the flame. In one embodiment, the ignition device 56 is attached to one of the support gas nozzles 16b.

In the illustrated embodiment, the fuel pipe 48 ends downstream in a cylindrical fuel distributor 58. The fuel distributor 58 can also be referred to as the primary gas distributor 58 since at this point the fuel pipe 48 only carries the primary gas. In the embodiment, four primary gas nozzles 16a are arranged radially on a lateral surface of the primary gas distributor 58 on the primary gas distributor 58 . The primary gas nozzles 16a are arranged at equal intervals and point away from the fuel pipe 48 or from the primary gas distributor 58 towards the burner pipe 12 (not shown).

The primary gas nozzles 16a can have bores 60 . Each primary gas nozzle 16a can have a plurality of bores 60 . Two bores 60 are shown. However, there can also be more or fewer bores. The bores 60 are arranged on the primary gas nozzles 16a in such a way that the primary gas essentially flows out in a tangential direction. The orientation of the bores 60 can be matched to the arrangement and configuration of the swirl vanes 32 in such a way that the primary gas is discharged with the flow of the fuel/combustion air mixture swirled in the first region 36 . The primary gas flows out of the lateral bores in a tangential direction that is determined by the direction of the swirl. Additionally or alternatively, the primary gas nozzles 16a can have an axial bore, from which the primary gas also flows.

The second fuel nozzles 18 or main gas nozzles are arranged in a circle around the downstream end of the swirl body 30 . They have holes 62 on their end faces. The bores 62 are designed to ensure a high fuel exit velocity of the main gas, so that the main flame front 26 forms at a distance from the combustion head.

4 shows schematically a side view of a combustion head 10b. Combustion head 10b may correspond to combustion head 10 and/or combustion head 10a. Already referring to Figures 1 to 3 illustrated parts will not be described again in detail. In the side view, parts have been cut away to show details better. The part of the swirl body 30 pointing towards the viewer has been cut away so that the internal structure can be seen is. The area where the first fuel feed 20 opens into the fuel pipe 48 has been cut open.

In the side view representation of the 4 holes 64 are visible on the primary gas nozzles 16a. The bores 64 are configured to discharge the fuel substantially radially inward. In addition or as an alternative, the primary gas nozzles can also have axial bores.

In 4 the burner tube 12 is also shown. The combustor tube 12 may be terminated at its downstream end by an annular delta disc 66 extending radially inward from the combustor tube 12 . In the embodiment shown, the delta disc 66 has a plurality of guide devices 68 pointing radially inwards. The openings of the second fuel nozzles 18 can end flush with the delta disc 66 . The design of the delta disc 66 with reference to 6 is described in more detail, is used for internal exhaust gas recirculation in the main flame 26. The recirculation can be effected by the portion of the combustion air 28 that flows past the swirl device 14 and hits the ring of the annular delta disk 66 directly. As a result, negative pressure zones and vortex areas are formed on the guide devices 68 on the downstream side, that is to say on the sides of the guide devices 68 pointing into the combustion chamber. The exhaust gases thereby recirculated are injected into the hot zones of the main flame 26 . In these zones, the recirculated exhaust gas lowers the temperature and reduces the O2 partial pressure. Both effects contribute to the reduction of NO formation or NO formation.

The amount of fuel from the primary gas nozzles 16a and the support gas nozzles 16b is small in relation to the amount of fuel which exits from the second fuel nozzles 18 . It is preferably 3% to 15%, particularly preferably 5% to 10% of the total amount of fuel.

The excess air required for the complete combustion of the partial fuel quantities from the primary gas nozzles 16a, the supporting gas nozzles 16b and from the fuel nozzles 18 can be between 1.075 and 1.2 in embodiments. The combustion zones of the primary flame and the spaced main flame are each lean of stoichiometry. Locally, due to the flow of fuel entering the combustion chamber axially, it can from the second Fuel nozzles 18 come to form sub-stoichiometric zones before fuel gas and air and recirculated exhaust gas have been sufficiently mixed.

The reduction in the NO values results from the extremely low-NO combustion in the partially premixed, very lean primary flame in combination with the main flame at a distance, which, due to the intensive mixing in of internally recirculated exhaust gases and the lowering of the O2 partial pressure in the mixture, has no effect on the NO Formation can form harmful high temperatures. The formation of a slim but not too long flame is advantageous, which efficiently decouples the heat released during the combustion of the fuel from the conversion of the chemical enthalpy to the cooled surrounding walls of the combustion chamber through radiation and convection.

figure 5 Fig. 12 schematically shows a sectional view of a front portion of the combustion head 10b. Already referring to Figures 1 to 4 illustrated parts will not be described again in detail.

The swirl body inner tube 54, which is routed over the fuel tube 48, is visible. The swirl body can thus be displaced longitudinally and can be fixed in its position with a screw 70 . The displaceability allows better adaptation to different combustion chambers in which the main flame front 26 is formed.

The perforated partition 34 is arranged in the area 38 . The breached partition 34 is positioned and configured such that the primary flame 24 is securely stabilized or retained within the region 38 of the swirler 30 in the described embodiment.

6 Fig. 12 schematically shows a front view of the combustion head 10b from the flame side, or in other words from the combustion chamber. Arranged in the center is the fuel distributor 58, from which the primary gas nozzles 16a with their bores 60 extend. Behind it is the perforated partition wall 34. In the exemplary embodiment shown, the perforations are realized by two concentric rows of holes, the holes being circular. It is to be understood that the openings can also have a different shape. The ratio of the opening areas to the total area can also be different than shown. The perforated partition wall 34 serves to reduce the flow velocity of the swirled air/fuel mixture from the area 36 of the Swirl body 30. The partition 34 is limited by the wall of the swirl body 30. The support gas nozzles 16b located behind them can be seen through the openings.

The second fuel nozzles 18 with their bores 62 are arranged at regular intervals on a circle around the central axis of the swirl body 30 . Around it is the annular delta disc 66 which closes off the burner tube 12 . From the inner circumference of the delta disc 66, the guide devices 68 extend inward in the radial direction. In the illustrated embodiment, three baffles 68 are provided. The three guide devices 68 are evenly distributed over the inner circumference. The combustion head 10b can also have more or fewer guide devices 68, which can then likewise be distributed uniformly over the inner circumference. In the exemplary embodiment shown, the guide devices 68 are triangular in shape and have a tip pointing inwards in the radial direction. The triangles point away from the annular delta disc 66 with an apex. How out figure 5 seen, the guide devices 68 are not in the plane of the 6 , but point away from the swirl body 30 . They are angled.

The guide devices 68 with the delta disc 66 are designed in such a way that they cause the formation of a vacuum zone which draws in exhaust gases from the combustion chamber. Delta disk 66 and guide devices 68 thus lead to an internal exhaust gas recirculation. The shape in the manner of an angled triangle pointing away from the swirler leads to "standing vortices" on the guide devices 68, which contribute to the stabilization of the main flame front 26. Consequently, the recirculated exhaust gases are injected into the hot zones of the main flame and thus into the areas of greatest NO production.

The geometry of the guide devices 68 has been optimized in such a way that as high an internal exhaust gas quantity as possible is drawn into the main flame 26 . Both the number and the geometry of the guiding devices 68 must be taken into account both for the effect of the NO reduction and for the stability of the main flame.

The annular delta disc 66 can have a multiplicity of bulges 72 on its inner circumference between the guide devices 68 . The bulges 72 form an interlocking geometry. In 6 Semi-circular lobes are shown, but the teeth can be formed with other geometries. The serration 72 is designed to create a larger surface area. The larger surface area results in a larger contact area between exhaust gas, combustion air and main fuel, a more intensive and uniform mixture of the fuel-air-exhaust gas mixture is produced. As a result, a more uniform distribution of combustion zones enriched with exhaust gas and thus stoichiometrically more favorable can form in the main flame 26 . The inventors have found that this further reduces the overall formation of thermal NO.

As already mentioned, the second fuel nozzles 18 are shaped in such a way that the highest possible exit velocities are achieved. For this purpose, an aperture can be provided in front of the axial opening of the fuel nozzle. Due to the high momentum of the outflowing gas, the intensity of the mixture of internally recirculated exhaust gas and fuel can be further advanced. A further optimization takes place through the position of the second fuel nozzles 18 in coordination with the geometry of the guide devices 68. The second fuel nozzles 18 are evenly distributed between the guide devices 68.

In operation, the advantageous low-nitrogen combustion is achieved by first introducing combustion air 28 into the burner tube 12 with an open end downstream. A part of the combustion air 28 is twisted in the twisting device 14 arranged in the burner tube 12 . A first quantity of fuel is fed directly into the swirl body 30 and mixed there with the swirled combustion air 28 . A primary flame is formed in the swirled fuel/combustion air mixture within the swirler. A second quantity of fuel is supplied downstream of the swirl device 14 . A main flame front is formed which stabilizes downstream of the combustor tube and spaced from the combustor tube. In this case, the first quantity of fuel is regulated independently of the second quantity of fuel.

The separate fuel control makes it possible to achieve very low NO emissions over a wide load range. At a lower load, a different ratio of the first quantity of fuel to the second quantity of fuel can be optimal than at a high load. If the ratio of the two fuel quantities to one another is fixed, low NO emissions cannot be guaranteed over the entire load range of the burner. In the combustion head according to the invention, for example, at low load, less primary gas/support gas can be supplied as a percentage of the main gas than at high load. In the case of non-separate controllability, the first amount of fuel decreases to a lesser extent than the amount of air through the swirler at lower loads, due to flow technology flows, so NO emissions can increase at lower loads even with a lean primary flame.

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

Claims (20)

Method for the staged combustion of a fuel with the supply of combustion air (28) into a burner tube (12), comprising: - Supplying a first amount of fuel to form a highly over-stoichiometric primary flame (24) within the burner tube (12), preferably with a stoichiometry greater than 1.5, in particular greater than 2.0; - supplying a second quantity of fuel downstream to form a slightly over-stoichiometric main flame (26), preferably with a stoichiometry between 1.03 and 1.18, in a furnace, wherein a temperature of the main flame (26) is reduced by exhaust gases recirculated within the furnace, and wherein the main flame (26) stabilizes downstream of the burner tube (12) and spaced from the burner tube (12). The method of claim 1, further comprising: - Controlling the first amount of fuel independently of the second amount of fuel, the control being such that the first amount of fuel is approximately between 3% and 15%, preferably between 5% and 10% of the sum of the first amount of fuel and the second amount of fuel. The method of claim 1 or 2, further comprising: - Swirling part of the combustion air (28) to produce a swirled combustion air; - Supplying a first portion of the first amount of fuel in the region of the swirled combustion air to form a swirled lean air / fuel mixture; - reducing a flow velocity of the swirled lean air/fuel mixture; and - Introducing a second portion of the first amount of fuel into the slowed swirled lean air/fuel mixture. Method according to one of the preceding claims, wherein the supplying of at least part of the first partial quantity of the first quantity of fuel takes place in the radial direction inwards. Method according to one of the preceding claims, wherein the supplying of at least part of the second partial quantity of the first quantity of fuel takes place in a tangential direction with the flow of the swirled fuel/combustion air mixture. A method according to any one of the preceding claims, further comprising: - Formation of vortices, in particular standing vortices in the area where the second quantity of fuel is supplied, so that exhaust gases are returned to the hot zones of the main flame front (26). Combustion head (10) for the staged combustion of a fuel, wherein the combustion head (10) is designed to burn a first quantity of fuel supplied in a hyperstoichiometric primary flame (24) within a burner tube (12), and a second quantity of fuel supplied in a to burn a slightly over-stoichiometric main flame (26), preferably with a stoichiometry between 1.03 and 1.18, in a combustion chamber at a distance from the burner tube (12), the fuel feeds being designed in such a way that the primary flame (24) has a stoichiometry greater than 1 5, in particular greater than 2.0, wherein the combustion head (10) is also designed to reduce a temperature of the main flame (26) by exhaust gases recirculated inside the combustion chamber, and the main flame (26) downstream of the burner tube (12) and at a distance from the burner tube (12) to stabilize. Combustion head (10) according to Claim 7, in which the supply of the first quantity of fuel and the supply of the second quantity of fuel can be regulated independently of one another, the regulation being carried out in such a way that the first quantity of fuel is between approximately 3% and 15%, preferably between 5% and 10% of the sum of the first amount of fuel and the second amount of fuel. A combustor (10) according to claim 8, wherein the combustor is configured to deliver a first portion of the first quantity of fuel to a highly turbulent portion of the combustion air supply to form a fuel / combustion air mixture and supply a second part of the first amount of fuel to the decelerated fuel / combustion air mixture. Combustion head (10) for the staged combustion of a fuel, having: a burner tube (12) adapted to have combustion air (28) therethrough, the burner tube (12) having an open end downstream; a swirl device (14), which is arranged within the burner tube (12) in order to be flowed through by part of the combustion air (28), with a swirl body (30) which encloses a first and a second region, the first region ( 36) is upstream of the second region (38) and swirl vanes (32) are disposed only in the first region; first fuel nozzles (16a, 16b) disposed within the swirler (30) for supplying fuel to form a primary flame (24) within the swirler (30); second fuel nozzles (18) located downstream of the swirler (14) for supplying fuel to form a free main flamefront (26), the main flamefront (26) stabilizing downstream of and spaced from the combustor (10); a first fuel supply (20) connected to the first fuel nozzles (16a, 16b); and a second fuel feed (22), which is connected to the second fuel nozzles (18), the swirl body (30) and the first fuel nozzles (16a, 16b) being configured, the primary flame (24) having a stoichiometry greater than 1.5, in particular greater than 2.0. Combustion head according to Claim 10, in which the fuel quantities of the fuel supplied through the first fuel supply (20) or through the second fuel supply (22) can be regulated independently of one another. Combustion head according to claim 10 or 11, wherein the swirl device (14) has a perforated partition wall (34) between the first region (36) and the second region (38). Combustion head according to one of claims 10 to 12, wherein the first fuel nozzles (16a, 16b) comprise primary fuel nozzles (16a) arranged in the second region (38) of the swirler (30) and auxiliary fuel nozzles (16b) arranged in the first region of the swirler (30) are arranged. A combustor according to claim 13, wherein the support fuel nozzles (16b) are evenly distributed between the swirl vanes (32) and are configured to discharge fuel radially inward to form a swirled fuel/combustion air mixture. Combustion head according to Claim 13 or 14, in which the primary fuel nozzles (16a) are uniformly distributed in a corona and are designed to discharge fuel in a direction tangential to the flow of the swirled fuel/combustion air mixture. Combustion head according to one of Claims 10-15, in which at least part of the fuel exits from the first fuel nozzles (16a) via lateral bores (60) in the first fuel nozzles. Combustion head according to one of claims 10-16, wherein the first fuel feed (20) is connected to the primary fuel nozzles (16a) and the support fuel nozzles (16b) via a fuel pipe (48) in the swirl body (30), the fuel pipe (48) having a fuel manifold (58) to which the primary fuel nozzles (16a) are attached. Combustion head according to Claim 17, in which the swirl body (30) is arranged so as to be displaceable in the longitudinal direction on the fuel pipe (48). A combustor according to any one of the preceding claims, further comprising:
an annular delta disc (66) extending from the downstream end of the Burner tube (12) extends radially inwardly and has a plurality of radially inwardly directed baffles (68). Combustion head according to Claim 19, in which the annular delta disc (66) has a multiplicity of bulges (72) on its inner circumference between the guide devices (68).

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