Burner head, burner system and method for operating a burner system

Abstract

Burner head (10) for supplying oxidizer and fuel to a combustion chamber (50) of a burner system (1), in particular for use in a gas turbine arrangement, with an end face (20) adjoining the combustion chamber (50), with an oxidizer supply having at least one outlet opening (182) arranged on a ring around a central axis (M) of the burner head (10) at the front face (20), which is designed to supply oxidizer without swirl with such a high axial impulse into the combustion chamber (50) that a pronounced, in particular internal, recirculation zone (54) with recirculated exhaust gas is formed within the combustion chamber (50) during operation, wherein the outlet velocity is 60 m / s or more, and with a fuel supply (30) with at least one fuel nozzle (15) for supplying the fuel into the combustion chamber (50), characterized by that the fuel nozzle (15) is arranged outside the oxidizer supply and radially inside the ring, in particular for the unmixed supply of fuel to the combustion chamber (50), that a secondary oxidizer supply with at least one secondary outlet opening (192) arranged radially between the outlet opening (182) and the fuel nozzle (15) is provided for the swirl-free addition of secondary oxidizer into the combustion chamber (50), that the fuel nozzle (15) opens axially back from the outlet opening (182) in a recess (24) in the front face (20), in particular at the level of a bottom surface (242) of the recess (24), that the secondary outlet opening (192) is arranged axially at the level of or upstream of the fuel nozzle (15) in the recess (24) and that the secondary outlet opening (192) and / or the outlet opening (182) are formed in a slit-like manner around the central longitudinal axis (M).

Description

[0001] The invention relates to a burner head for supplying oxidizer and fuel to a combustion chamber of a burner system, particularly for use in a gas turbine arrangement, comprising an end face adjacent to the combustion chamber, an oxidizer supply with at least one outlet opening arranged on a ring around a central axis of the burner head at the end face, which is designed to supply the oxidizer into the combustion chamber without swirl and with such a high axial impulse that a pronounced, particularly internal, recirculation zone with recirculated exhaust gas forms within the combustion chamber during operation, and a fuel supply with at least one fuel nozzle for supplying the fuel into the combustion chamber. The invention further relates to a burner system and a method for operating a burner system.

[0002] Burner systems with burner heads of the type mentioned above, as specified, for example, in DE 10 2012 216 080 A1, are classified according to the so-called FLOX principle due to the stabilization process of the combustion reaction. In this process, the oxidizer, usually air, is injected into the combustion chamber with a high axial impulse (generally at speeds exceeding 80 m / s), thereby creating a pronounced internal recirculation zone with, for example, more than 50% of the exhaust gas recirculated within the combustion chamber. FLOX technology is known for its stable, low-emission combustion and is used, for example, in micro gas turbines (power range ≤ 1 MW).

[0003] In such burner systems operating with liquid fuel, the fuel is typically added in a spray form (i.e., atomized) into the airflow within the oxidizer feed, which is formed by air supply channels within the burner head. Subsequently, partial vaporization and premixing occur in the flow upstream of the addition into the combustion chamber. Combustion takes place in the combustion chamber along the shear layer between the incoming air-fuel mixture and the recirculation zone.

[0004] Fuel atomization within the feed channels is typically achieved using pressure atomizers with an axial-radial spray angle greater than 0°, which usually results in the fuel spray wetting the walls of the air supply channels. This can lead to undesirable effects due to spray-wall interaction (e.g., film formation, secondary atomization, coking, etc.), which negatively impact combustion quality. Particularly at high air temperatures, such as those found in micro gas turbines with heat recovery (so-called "recuperated" micro gas turbines), coking of the fuel atomizer nozzles can occur. To prevent this, the number of fuel nozzles can be reduced, which can negatively affect combustion quality, especially at low power outputs like those of micro gas turbines, when using liquid fuels.

[0005] DE 25 17 756 A1 discloses a device for atomizing and burning liquid fuels, comprising a two-component swirl nozzle. A gaseous oxygen carrier is supplied between the swirl nozzle and a pipe wall surrounding a combustion chamber. Fuel is supplied via a central feed to the swirl nozzle, and primary air is supplied via a further feed surrounding the central feed, through guide elements to create the swirl, all under intense swirl flow.

[0006] DE 33 09 905 A1 discloses a device and a method for burning solid fuels, in which a fuel emulsion is injected into a combustion chamber through an approximately annular inlet opening, creating an approximately hollow-conical flow profile. Gas inlet openings are provided in the front face of the combustion chamber, through which gas or air flows out, its flow path being concentric and helical relative to the axis of the inlet opening for the fuel emulsion leading into the combustion chamber. These measures enable an extremely long particle path over a very short distance along the central axis of the combustion chamber.

[0007] US Patent 4,023,921 A discloses a device and method for burning liquid fuels, wherein a relatively limited primary flame zone near a burner nozzle and a relatively long secondary flame zone are produced. A stream of liquid fuel supplied via a central feed is atomized by a relatively high-velocity gas stream supplied in an annular pattern via a surrounding feed to form the primary flame zone.

[0008] DE 41 18 284 C2 discloses a burner for a vehicle gas turbine with a starting device and flame holder, which is trumpet-shaped and has a fuel atomizing nozzle in its center for introducing starting fuel in the form of a conical shell. The atomizing nozzle is surrounded by an annular gap for introducing swirled starter air.

[0009] DE 10 2015 205 069 A1 discloses a combustion device with secondary fuel inlets arranged within a nozzle ring.

[0010] DE 197 37 311 A1 discloses a method and a device for supplying combustion gases to the mixing device of burners without effectively affecting flame stability. The flame tube is divided into at least two coaxially arranged partial tubes.

[0011] The invention is based on the objective of providing a burner head based on the FLOX principle for optimized operation with liquid fuels, a corresponding burner system and a corresponding method.

[0012] The problem is solved for the burner head with the features of claim 1 and for the method with the features of claim 12.

[0013] The burner head is designed so that the fuel nozzle is located outside the oxidizer supply and radially inside the ring, particularly for the unmixed supply of fuel to the combustion chamber.

[0014] The one or more outlet openings are preferably arranged symmetrically around a ring (i.e., on an imaginary circular ring) for symmetrical, low-emission combustion, with, for example, one annular outlet opening or several outlet openings, particularly those spaced evenly around the ring. The outlet openings can be located on the end face at the level of the front surface or projecting beyond it, and in particular, be oriented orthogonally to the central axis (i.e., lying in a plane orthogonal to the central axis). Several fuel nozzles can also be provided for fuel injection.

[0015] By introducing the fuel without premixing it and mixing it into the oxidizer outside the burner head, particularly in the combustion chamber, undesirable wall wetting inside the burner head and its associated negative effects are avoided. In addition to using liquid fuel, operation with gaseous fuel is also possible, allowing, for example, switching between gaseous and liquid fuel operation (if necessary, with modification of the burner head). Introducing the fuel from a position radially inside the ring, i.e., from the center of the burner head, causes the fuel to mix into the oxidizer flow on the radial inner side. Combustion stabilizes in the radially inner shear layer between the oxidizer and the recirculating hot exhaust gases.This allows a significantly colder gas flow to form in the outer area of ​​the combustion chamber, surrounding the combustion zone and adjacent to the inner wall of the perimeter wall, which advantageously reduces the heat load on the perimeter wall.

[0016] The aforementioned advantages are particularly evident when the fuel supply is designed for the addition of liquid fuel, whereby the fuel is atomized by an atomizing device encompassing the fuel nozzle. The atomizing device can be a commercially available atomizing device, for example, a (hollow cone) pressure atomizer, e.g., for kerosene, or an atomizing device for atomization using air ("air-assisted").

[0017] In a preferred design variant for efficient and targeted distribution of the fuel spray into the combustion chamber, the fuel nozzle is shaped such that, during operation, the fuel flows outwards at an axial-radial angle β after exiting the nozzle. The fuel flow can be swirly, meaning it may have an additional tangential directional component. A hollow conical shape has proven particularly advantageous for precisely introducing the fuel droplets. By selecting the angle β during the design process, the point of impact of the maximum fuel spray ("spray maximum") on the oxidizer can be adjusted, thereby influencing the combustion process.

[0018] According to the invention, the fuel nozzle opens axially back from the outlet opening into a recess in the front face, particularly at the level of a base surface of the recess. The recess can be conically shaped, with a symmetrical, circular cross-section, and arranged coaxially to the central axis to ensure uniform flow, which promotes consistent, clean combustion. This allows for preheating and partial vaporization of the fuel spray by the influence of the recirculating hot exhaust gases, some of which enter the recess, before the fuel spray impacts the oxidizer in the combustion chamber. This contributes to a shorter combustion zone and more uniform, low-emission combustion.

[0019] Preferably, a circumferential surface of the recess between a bottom and an opening of the recess into the combustion chamber is oriented axially-radially at an angle α, wherein the angle α and the angle β are coordinated such that the main flow direction of the fuel (the direction of the region with the maximum spray or droplet density, i.e., the spray maximum) is directed into the combustion chamber, not towards the circumferential surface. Preferably, the angle α is chosen to be large enough that as few droplets as possible, e.g., less than 20% or 10%, are directed with their trajectories towards the circumferential surface. The angle α is, for example, between 10° and 70°, between 20° and 60°, or between 40° and 50°, and can, in particular, substantially correspond to the angle β (e.g., with a deviation of ±5° or ±10°).This design helps to prevent the circumferential surface from being wetted with fuel spray and the associated undesirable effects of spray-wall interaction. The fuel then encounters the oxidizer outside the recess, where the mixture between fuel and oxidizer and the combustion reaction take place.

[0020] In the embodiment according to the invention, a secondary oxidizer supply is provided, comprising at least one secondary outlet arranged radially between the (primary) outlet opening and the fuel nozzle, for the addition of secondary oxidizer to the combustion chamber. The addition of secondary oxidizer between the fuel spray and the (primary) oxidizer serves, for example, to support the desired fuel flow pattern for targeted impact and mixing of fuel and oxidizer, whereby the secondary oxidizer can act as a kind of "support air" for the fuel flow. Furthermore, the position, orientation, and velocity of the secondary oxidizer flow can influence the flow of the primary oxidizer. For example, the primary oxidizer flow can be directed radially outwards, so that it adheres to the circumferential wall of the combustion chamber.

[0021] According to the invention, the secondary outlet opening and / or the (primary) outlet opening are designed as slits circumferentially around the central longitudinal axis. This results, for example, in one or two (circular) annular slits, which can be arranged, in particular, coaxially to the central axis for symmetrical combustion. With two coaxially arranged annular slits, a type of "double-slit burner" is formed. The slits are preferably formed substantially circumferentially, and may be interrupted, for example, by fastening means (e.g., axially extending webs). The slit-like design results in a comparatively homogeneous velocity distribution along the (ring) circumference, i.e., around the fuel nozzle. This avoids areas with low axial velocity and thus prevents the passage of radially outwardly directed fuel droplets and their impact, for example, on the combustion chamber.This is counteracted on the circumferential surface of the recess or on the inner surface of the circumferential wall of the combustion chamber or combustion chamber. This improves the supporting air effect of the secondary oxidizer. Furthermore, the slit-like design of the (primary) outlet opening allows for a comparatively flat airflow with low radial thickness, resulting in a significantly more compact recirculation zone compared to a design with individual nozzles, as in a conventional FLOX burner.

[0022] In a preferred embodiment, the secondary outlet opening is arranged axially at the level of or upstream of the fuel nozzle in the recess. In particular, the axial outlet position of the secondary oxidizer can correspond to the axial outlet position of the fuel. In this way, the fuel is surrounded by the secondary oxidizer immediately after exiting the fuel nozzle. The secondary oxidizer can thus act as a kind of shielding air, i.e., as a barrier between the fuel spray and the surrounding environment, such as the wall. This allows for more controlled design of the point of impact of the fuel spray on the oxidizer flow and, consequently, the combustion process.

[0023] Preferably, the secondary oxidizer supply has at least one secondary feed channel that opens into the secondary outlet opening and is designed such that the main flow direction of the secondary oxidizer upon exiting the secondary outlet opening corresponds axially and radially to an angle α. This can be achieved, for example, by appropriately shaping the inner wall surfaces of the secondary feed channel. "Substantially" means that, for example, a deviation of + / - 5° or up to + / - 10° is permissible. Thus, due to the presence of the radial (in addition to the axial) directional component, the secondary oxidizer, upon entering the combustion chamber, can deflect the primary oxidizer or the resulting overall flow radially outwards, thereby causing the flow to "open up." This positively influences the shape of the recirculation zone and can result in the flow (at least partially) adhering to the circumferential wall.

[0024] Preferably, the secondary outlet opening is arranged radially within the circumferential surface and, in particular, borders the circumferential surface. In this way, the secondary oxidizer, especially when exiting at an angle substantially corresponding to angle α, can be guided along the circumferential surface of the recess and serve as a barrier between the fuel spray and the circumferential surface to prevent wetting and the associated undesirable effects.

[0025] In a preferred embodiment, the (primary) outlet opening is arranged around the opening of the recess essentially adjacent to the circumferential surface, i.e., with an interposed wall thickness to provide fluid-mechanical separation between the oxidizer supply and the recess. In this way, the outlet opening of the primary oxidizer opens radially close to the circumferential surface. The radius of the opening plus the outer radius of the interposed wall thickness thus yields the inner radius of the (primary) outlet opening. The wall thickness should be sufficient to ensure adequate thermal stability. This arrangement allows the secondary oxidizer and / or the fuel spray to impinge on the primary oxidizer close to the (primary) outlet opening. It would also be conceivable, for example, to achieve a longer fuel vaporization time, to deliberately position the primary outlet opening radially away from the opening.For a longer evaporation time, the axial length of the recess can be made larger, either additionally or alternatively, with the bottom positioned relatively far upstream, thus increasing the axial distance between the bottom and the opening. The secondary oxidizer, when imbued with an additional radial impulse, introduces an additional radial directional component into the resulting overall or mixed flow. This additional radially outward-directed component in the flow results in a more axially compact recirculation zone within the combustion chamber.Particularly through the combination of the slit-like design of the primary and / or secondary outlet opening with the additional radial directional component of the secondary oxidizer and the hollow-cone-shaped fuel spray, positive effects can be achieved: The interaction of the annular gap and the atomizing device results in a comparatively very homogeneous temperature field, enabling a very low level of pollutants. The geometries of the oxidizer feeds allow for the targeted design of the distribution or ratio between the primary and secondary oxidizers, thereby influencing the temperature field as well as the position and extent of the recirculation zone, and thus the combustion process. For example, ratios of primary to secondary oxidizer between 1.5 and 3 have proven advantageous.

[0026] If the outlet opening is arranged on a ring rotating around the central axis, the radius of which (with respect to the radial centerline of the outlet opening) is between 0.3 and 0.75 times the radius of the outer circumference of the end face (where the circumferential wall of the combustion chamber connects to the burner head), a reaction zone is created that is spaced away from the circumferential wall. This, especially in conjunction with a radially opening flow path, promotes the formation of the comparatively cooler gas film and thus reduces the thermal stress on the circumferential wall. The radius of the secondary outlet opening (with respect to the radial centerline) to that of the primary outlet opening can, for example, have a ratio between 0.3 and 0.75. By combining the design of the radius and the orientation of the flow path (especially by the angle α) at ​​the secondary outlet opening, the impact position on the primary oxidizer flow can be optimized.The radial height of the secondary outlet opening can significantly influence the velocity and division of the oxidizer flow in the secondary and primary oxidizer flows.

[0027] A simple and robust design can be achieved if the burner head comprises a base body into which the oxidizer supply, and optionally the secondary oxidizer supply, is / are integrated. The base body can have several parts, for example, an outer part, a middle part, and an inner part. Preferably, the primary outlet opening with the primary supply channel is arranged between the outer and middle parts, and the secondary outlet opening with the secondary supply channel is located between the middle and inner parts. The inner part preferably also has a recess for receiving the atomizer, which opens into the recess or the combustion chamber. The base body and the structures integrated therein can be manufactured, for example, using an additive manufacturing process, in particular selective laser melting.

[0028] For a burner system of low complexity, the burner head is designed for single-stage combustion operation. This advantageously requires only one fuel supply with corresponding fuel peripherals. Investigations have shown that the burner head according to the invention can be operated advantageously, stably, and reliably in single-stage operation.

[0029] In the burner system according to the invention, comprising a burner head according to one of the embodiments described above and a circumferential wall encompassing a combustion chamber, the circumferential wall preferably has at least one inlet opening for the radial addition of oxidizer to the combustion chamber. This inlet opening is arranged axially downstream of a reaction zone and upstream or, preferably, at a stagnation region of the recirculation zone, i.e., at the downstream end of the recirculation zone (where the flow velocities reverse as they pass through zero). Investigations have shown that an additional radial introduction of oxidizer, particularly at or within the stagnation region, can positively influence the combustion process. By adding the oxidizer via the inlet opening positioned in this way, the radially added oxidizer is transported upstream by the recirculation and incorporated into the combustion process.This results in a leaner combustion process, i.e., an increased excess of oxidizer during combustion. For symmetrical introduction, several addition openings (positioned symmetrically in the circumferential direction), e.g., in the form of bores, can preferably be provided in the circumferential wall. The additional oxidizer can, in particular, be branched off from an oxidizer flow around the circumferential wall, which flows around the outside of the circumferential wall in a counter-current flow, i.e., towards the burner head, and is directed to the burner head for use as a primary and / or secondary oxidizer.

[0030] Advantageous embodiments of the method according to the invention are explained analogously in connection with the preceding statements regarding the burner head.

[0031] The invention will now be explained in more detail using an exemplary embodiment and with reference to the drawing. It shows: Fig. 1 a burner system with a burner head according to the invention in a perspective sectional view along a central axis.

[0032] Fig. Figure 1 shows a burner system 1 with a burner head 10 and a circumferential wall 52 adjoining the burner head 10 (partially indicated). The burner system 1 is optimized for the combustion of liquid fuel, particularly due to the design of the burner head 10. The circumferential wall 52 is cylindrical for combustion with uniform, symmetrical combustion and comprises a combustion chamber 50 of the burner system 1. At its downstream end, the combustion chamber 50 transitions into a fuel gas outlet (not shown here). According to one embodiment, the circumferential wall 52 has several, e.g., three, addition openings 56 for the radial addition of oxidizer into the combustion chamber 50, which are preferably arranged radially symmetrically around the circumference. The addition openings 56 are located axially downstream of a reaction zone 54 and upstream or, preferably, at a stagnation area 58 of the recirculation zone 54.arranged in the area where the flow velocities reverse upon passing through the 0 point.

[0033] The burner head 10 is arranged with an end face 20 at the inlet of the combustion chamber 50, from which the circumferential wall 52 extends around the combustion chamber 50. The burner head 10 includes a primary oxidizer supply, hereinafter also referred to as the primary air supply 18. The primary air supply 18 comprises a slit-like outlet opening 182, which is arranged on the end face 20 essentially circumferentially on an imaginary ring, preferably circular for symmetrical combustion, coaxial to a central axis M. The outlet opening 182 is arranged in a plane orthogonal to the central axis M.

[0034] The primary air supply 18 is designed to introduce oxidizer from a plenum 40 into the combustion chamber 50 with a high axial impulse and without swirl, creating a pronounced internal recirculation zone 54 with recirculated exhaust gas to stabilize the combustion process during operation. Due to this type of flame stabilization, the burner head can be classified as using FLOX technology. Typical outlet velocities can be, for example, 60 to 130 m / s (or even higher), e.g., more than 80 m / s. The oxidizer can consist primarily of air, which may contain further additives (e.g., externally recirculated exhaust gas, process gas, etc.). The slit-like design of the outlet opening 182, i.e., a significantly larger tangential than radial dimension, e.g., more than three times larger, results in a comparatively small radial thickness of the oxidizer flow entering the combustion chamber 50.This can result in a significantly more axially compact recirculation zone 54 compared to known burner types based on FLOX technology.

[0035] Furthermore, the burner head 10 comprises a fuel supply 30 with a fuel nozzle 15 for supplying the fuel to the combustion chamber 50 without premixing. The fuel supply 30 can further include a nozzle 32 with a portion of a fuel channel 34, which directs the fuel from a fuel supply (not shown) to the burner head 10 to supply the fuel nozzle 15. The fuel nozzle 15 is arranged radially within the ring of the outlet opening 182, in the center of the burner head 10. For stable, low-emission combustion, the fuel nozzle 15 is preferably positioned symmetrically, in this case on the central axis M. Multiple fuel nozzles 15, arranged symmetrically around the central axis M, e.g., on an imaginary ring, are also conceivable. The fuel nozzle 15 is designed as part of an atomizing device 16 for adding liquid fuel in the form of a fuel spray.The atomizing device 16 can be designed, for example, as a pressure atomizer known from the prior art or as an air-assisted atomizer. When the fuel is discharged into the combustion chamber 50 during operation, a conical fuel spray is formed, the main flow direction of which (spray maximum) is axially-radially oriented at an angle β to the central axis M. Preferably, the atomizing device 16 is designed to form a hollow cone shape for the spray in order to introduce the fuel droplets as precisely as possible, particularly into a shear layer between recirculating exhaust gas and the secondary oxidizer. The fuel flow can be swirled to aid atomization.

[0036] The fuel nozzle 15 is axially recessed from the outlet opening 182, in a recess 24 in the end face 20, which is itself axially recessed from the outlet opening 182. The recess 24 is conically shaped and has a base with a base surface 242, an opening 243 as a transition to the combustion chamber 50, and a circumferential surface 241 extending between the base and the opening 243. The base surface 242 and the opening 243 are arranged orthogonally to the central axis M. The circumferential surface 241 is axially and radially oriented at an angle α, which is matched to the angle β of the fuel cone such that the maximum spray of the fuel does not impinge on the circumferential surface 241, but can flow through the opening 243 into the combustion chamber 50. The angle α is preferably between 10° and 70°, for example between 20° and 60°, e.g. between 40° and 50°.The opening 243 has a circular outline and is surrounded by the ring with the outlet opening 182, with an intermediate wall layer for the fluid-mechanical separation of the primary air supply 18 from the recess 24.

[0037] In addition to the primary air supply 18, the burner head 10 has a secondary oxidizer supply, hereinafter also referred to as the secondary air supply 19. The secondary air supply 19 includes a secondary outlet opening 192, which is arranged slit-like and symmetrically around the central axis M on a circular ring. The outlet opening 192 is arranged radially between the fuel nozzle 15 and the outlet opening 182 and is positioned axially at the level of the fuel nozzle 15's opening in the recess 24. An arrangement upstream of the fuel nozzle 15 would also be conceivable. With this arrangement, secondary oxidizer, in particular air, flowing in through the secondary outlet opening 192 during operation can act as a kind of shielding air between the fuel spray and the circumferential surface 241, forming a fluid-mechanical barrier between the fuel spray and the circumferential surface 241.The secondary outlet opening 192 forms part of the base of the recess 24, with the radially inner boundary of the secondary outlet opening 192 being formed by the outer outline of the base surface 242; that is, the outlet opening 192 abuts the base surface 242 radially. The radially outer boundary of the secondary outlet opening 192 is formed by the circumferential surface 241, which is thus arranged radially adjacent to the secondary outlet opening 192. The circumferential surface 241 extends from the secondary outlet opening 192 to the opening 243 of the recess 24 adjacent to the combustion chamber 50.

[0038] The secondary air supply 19 has a secondary supply channel 191 that opens into the secondary outlet opening 192. The secondary supply channel 191 has a radially inner inner wall surface 194 and a radially outer outer wall surface 193, which, opposing each other, define an annular flow cross-section. To impart an axial-radial impulse essentially corresponding to the orientation of the circumferential surface 241, the wall surfaces 193 and 194 are shaped accordingly, with the inner wall surface 194 and the outer wall surface 193 being further apart in an inlet region than in an outlet region with the secondary outlet opening 192. In the outlet region, the two wall surfaces 194 and 193 continuously approach each other for favorable flow guidance. However, a constant distance, with a constant flow cross-section of the gap, is also conceivable.The wall surfaces 194, 193 run at an angle α, at least in the outlet area adjacent to the secondary outlet opening 192. This orientation continues upstream of the secondary outlet opening 192 to such an extent that inlet effects of the secondary oxidizer are avoided when the secondary outlet opening 192 flows into the recess 24. Thus, during operation, a uniform, swirl-free oxidizer or airflow can be generated along the circumferential surface 241 of the recess 24, preventing wall wetting with the fuel spray, e.g., by spray components away from the fuel maximum. Undesirable effects of the associated spray-wall interaction (e.g., film formation, secondary atomization, coking, etc.) can be particularly effectively avoided by this design of the secondary air supply 19, in combination with the orientation of the circumferential surface 241, which is aligned with the spray maximum.

[0039] In the same way as the primary outlet opening 182, the secondary outlet opening 192 is fed from the plenum 40, which is arranged upstream of the burner head 10 as a gas-carrying oxidizer chamber for supplying the burner system 1 with oxidizer. The ratio of primary oxidizer through the primary air supply 18 to secondary oxidizer through the secondary air supply 19 is determined by the geometries of the primary air supply 18 and the secondary air supply 19. In addition to the outlet opening 182, the primary air supply 18 has a primary supply channel 181 that opens into the primary outlet opening 182. For optimized oxidizer flow, the transitions from the plenum 40 to the supply channels 181 and 191 are preferably rounded.

[0040] Due to the arrangement of the primary outlet opening 182 essentially radially adjacent to the opening 243 of the recess 24, the flow of the secondary oxidizer after exiting the opening 243 into the combustion chamber 50 meets the axially directed flow of the primary oxidizer.

[0041] For a compact and, in particular, thermally resistant design, the burner head 10 comprises as an essential component a base body 12 which, corresponding to the circumferential shape of the combustion chamber 50, is essentially cylindrical in its basic form. The base body 12 and structures incorporated therein can be manufactured, for example, by an additive manufacturing process, in particular by selective laser melting.

[0042] The two air inlets 18, 19 and the recess 24 are incorporated into the base body 12. The base body 12 also includes an outer part 121, to the outer circumference of which, for example, resting on a radially circumferential shoulder, the circumferential wall 52 of the burner system 1 is attached. The outer part 121 further comprises an outer end face 22 of the end face 20, which is arranged radially around the primary outlet opening 182 on the combustion chamber side and lies in a plane orthogonal to the central axis M.

[0043] Furthermore, the base body 12 comprises a central part 122, which is positioned radially inside the outer part 121. On the combustion chamber side, the central part 122 includes the circumferential surface 241 of the recess 24, which forms part of the end face 20.

[0044] Between the central section 122 and the outer section 121, the primary feed channel 181 is formed in a ring-like fashion within the base body 12. The primary feed channel 181 has a flow cross-section that is essentially constant in the flow direction, with wall surfaces running parallel to each other. The radially outer wall surface is associated with the outer section 121, and the radially inner wall surface is associated with the central section 122. A flow cross-section of the feed channel 181 that changes along its length is conceivable, e.g., similar to the secondary feed channel 192, which could be used, in particular, to influence the ratio between the primary and secondary oxidizers. The outer section 121 and the central section 122 are held in position relative to each other by means of fastening elements 14. In this example, the fastening elements 14 are designed as struts extending axially in the feed channel 181, four in number, to ensure a stable and at the same time low-resistance fastening.To promote a symmetrical flow pattern, the struts are evenly distributed in the annular-gap-like supply channel 181, here at an angular distance of 90°.

[0045] Radially within the central section 122, the base body 12 has an inner section 123. Between the central section 122 and the inner section 123, the secondary feed channel 191 is formed in a ring-like fashion within the base body 12. The outer wall surface 193 is assigned to the central section 122, and the inner wall surface 194 to the inner section 123. The two wall surfaces 193 and 194, and thus the respective shapes of the central section 122 and the inner section 123, are designed to reduce the flow cross-section along the secondary feed channel 191 in the flow direction, as described above. The central section 122 and the inner section 123 are positioned relative to each other by means of fastening elements 14. These are, for example, also designed as struts extending axially within the feed channel 191; for reliable and aerodynamically efficient fastening, four struts are used.To promote symmetrical flow, the struts are evenly distributed in the annular feed channel 191, with four struts spaced at an angular interval of 90°. To reduce the influence on the velocity distribution upon exiting into the combustion chamber 50, the struts between the outer part 123 and the middle part 122, as well as the struts between the middle part 122 and the inner part 123, are arranged tangentially offset from each other, for example by 45° in the case of four struts.

[0046] The inner part 123 has a recess 17 arranged coaxially to the central axis M for receiving the atomizing device 16, which is positioned there in the operational state. The recess 17 is shaped to receive the atomizing device 16 and is open towards the recess 24. The design is such that the fuel nozzle 15 of the atomizing device 16 for introducing the fuel into the combustion chamber 50 (in particular through the recess 24) is arranged on or symmetrically around the central axis M. In particular, at least part of the end face of the atomizing device 16 forms part of the base surface 242. The other part of the base surface 242 is formed by the side of the inner part 123 facing towards the end face 20.For a uniform, essentially smooth base surface 242, the part of the base surface 242 assigned to the atomizing device 16 and the part assigned to the inner part 123 are axially coplanar to each other.

[0047] As in Fig. As shown in Figure 1, the recess 17 is designed such that the nozzle 32 of the fuel supply 30 can also open into the recess 17. For example, the part of the atomizing device 16 facing away from the end face 20 can be inserted into the downstream end of the nozzle 32, for instance by screwing, plugging, or pressing. The downstream end of the nozzle 32 with the atomizing device 16 can, in turn, be inserted into the recess 17, for example by plugging, screwing, or pressing. In particular, a modular design is advantageously achieved by a detachable fastening of the nozzle 32 and the atomizing device 16 in the recess 17, in which the atomizing device 16 can be replaced as needed.

[0048] During operation, oxidizer, in particular air, flows counter-currently to the main flow direction within the combustion chamber 50 along the circumferential wall 52 towards the burner head 10. Additional oxidizer branches off from this flow and flows radially through the addition openings 56 into the combustion chamber 50. The flow path is in Fig. The recirculation zone 54 is indicated by arrows, with the recirculation zone 54 only shown in the upper half of the combustion chamber 50 for clarity. By positioning the addition openings 56 at and / or upstream of a stagnation area 58 (which forms the downstream end of the recirculation zone 54), the additional oxidizer is transported upstream through the recirculation zone 54 and incorporated into the combustion process. This results in a leaner mixture within the combustion process, i.e., a higher oxidizer content. Studies have shown that this can have a positive effect on the combustion process.

[0049] The remaining oxidizer flows through the plenum 40 to the burner head 10. Part of the oxidizer flows through the primary air supply 18, and the other part through the secondary air supply 19, into the combustion chamber 50 via the burner head 10. The ratio of the oxidizer components to each other, or rather their respective proportions of the total oxidizer flowing into the combustion chamber 50, is determined by the design of the geometries of the primary air supply 18 and the secondary air supply 19, which in turn determines the pressure loss ratio across the air supplies 18 and 19. A variable geometry and thus a different distribution of the oxidizer is also possible.

[0050] The portion of oxidizer flowing through the primary air supply 18 enters the combustion chamber 50 through the outlet opening 182 with high axial momentum and without axial swirl or radial directional component. The outlet velocity is, for example, between 60 m / s and 130 m / s or more, e.g., more than 80 m / s. Compared to a burner system with swirl-stabilized combustion, the velocity is, for example, approximately twice as high. The flow pattern creates a pronounced internal recirculation zone 54 with exhaust gas recirculating within the combustion chamber 50, which stabilizes the combustion process. Due to the slit-like design of the outlet opening 182, without the individual nozzles typical of known FLOX-based burner systems, a comparatively radially flat, annular flow results, contributing to a significantly more axially compact recirculation zone 54.

[0051] The portion of secondary oxidizer flowing through the secondary air supply 19 enters axially, without swirl, and with a radial directional component through the outlet opening 192, first into the recess 24 and then downstream into the combustion chamber 50. Due to the design of the supply channel 191, with the corresponding shaping of the outer wall surface 193 and the inner wall surface 194 in the outlet area, the oxidizer flow upstream of the outlet opening 192 is given an impulse that, in the axial-radial direction, essentially corresponds to the axial-radial orientation of the circumferential surface 241, i.e., the angle α. In this way, the secondary oxidizer can form an air or gas film within the recess 24 along the circumferential surface 241.

[0052] As the secondary oxidizer flows from opening 243 into the combustion chamber 50, it encounters the primary oxidizer, which flows into the combustion chamber 50 from the primary outlet opening 182 surrounding opening 243. Due to the close proximity of the primary outlet opening 182 to opening 243, separated only by a wall thickness, the axial point of impact is relatively close to the primary outlet opening 182. The radial momentum of the secondary oxidizer deflects the primary oxidizer radially outwards when the two oxidizer flows meet. Thus, at the point of convergence, the total oxidizer flow is axially and radially directed. By selecting the ratio between the primary and secondary oxidizers, the radial deflection and, consequently, the position and extent of the recirculation zone 54, as well as the temperature field, can be adjusted.Further degrees of freedom in this regard are the angle α of the circumferential surface 241 and / or the (possibly related) angle β of the fuel spray, as well as the radial distance of the outlet opening 182 from the opening 243 of the recess. The radial directional component of the overall outward flow is conducive to a more axially compact recirculation zone 54.

[0053] The liquid fuel is introduced separately from the oxidizer, i.e., not premixed, via the fuel supply 30 with the fuel nozzle 15 in the center of the burner head 10, initially into the recess 24. In this case, the fuel nozzle 15 is positioned axially at the level of the base surface 242 and radially on the central axis M. Multiple fuel nozzles 15 would also be possible, arranged in particular symmetrically around the central axis M.

[0054] During the addition of fuel, a cone-shaped fuel spray is generated, the axial-radial angle β of which is such that the spray maximum is directed in the flow direction from the opening 243 into the combustion chamber 50. The air film formed by the secondary oxidizer additionally prevents the fuel from wetting the wall within the recess 24. In this way, undesirable spray-wall interaction with secondary evaporation effects is prevented. By initially adding the fuel axially back into the recess 24, preheating and partial pre-evaporation of the liquid fuel spray can be achieved before it enters the combustion chamber 50 through the action of the hot, recirculating exhaust gas, which partially flows into the recess 24.The influence of the recirculation zone 54 on the droplet trajectories of the fuel spray is kept to a minimum, as the droplets move primarily between the secondary oxidizer and the recirculating exhaust gas. Thus, due to this design and process, the fuel, even when flowing into the combustion chamber 50 downstream of the recess 24, is essentially unmixed or at most partially premixed with the oxidizer.

[0055] Outside the opening 243, the fuel spray encounters the annularly flowing primary oxidizer. The relatively homogeneous, circumferential velocity distribution of the primary oxidizer flow prevents areas with low axial velocities. This counteracts the passage of radially outward-flying fuel droplets and their impact on the inner surface of the circumferential wall 52. Thus, undesirable secondary vaporization effects are also avoided within the combustion chamber 50.

[0056] The fuel spray initially impacts the radial inner surface of the annular primary oxidizer. There, the fuel spray mixes with the secondary oxidizer and into the primary oxidizer. This further stabilizes the combustion process radially within the annular primary oxidizer flow, particularly in the inner shear layer between the incoming primary oxidizer and the hot recirculating exhaust gases. Due to the combustion zone being shifted inwards, a comparatively cooler gas film can form radially outwards along the inner surface of the circumferential wall 52, thus reducing the thermal load on the circumferential wall 52.

[0057] Due to the axial offset of the fuel injection position and the associated partial preheating and vaporization of the fuel spray, rapid and complete vaporization and subsequent combustion of the fuel occurs after mixing the fuel spray into the oxidizer. This results in a compact reaction zone compared to other liquid burner systems.

[0058] Investigations have shown that the interaction of the two annular-gap-like outlet openings 182, 192 and the atomizing device 16, and their design and arrangement, achieves the flow pattern described above, resulting in a very homogeneous temperature field within the combustion zone. This reduces the formation of pollutants, particularly nitrogen oxides. Furthermore, the non-swirling flow pattern of the oxidizer results in a low pressure loss and thus a lower power loss of the burner system 1 compared to typical burner systems with swirl-stabilized combustion (pressure losses of, for example, approximately 3% compared to approximately 5%). In this way, especially in conjunction with the avoidance of secondary vaporization effects, a reliable, low-emission burner head 10 and a corresponding burner system 1 for the combustion of liquid fuels are provided.

Claims

[1] Burner head (10) for supplying oxidizer and fuel into a combustion chamber (50) of a burner system (1), in particular for use in a gas turbine arrangement, with an end face (20) adjoining the combustion chamber (50), with an oxidizer supply having at least one outlet opening (182) arranged on a ring around a central axis (M) of the burner head (10) at the front face (20), which is designed to supply oxidizer without swirl with such a high axial impulse into the combustion chamber (50) that a pronounced, in particular internal, recirculation zone (54) with recirculated exhaust gas is formed within the combustion chamber (50) during operation, wherein the outlet velocity is 60 m / s or more, and with a fuel supply (30) with at least one fuel nozzle (15) for supplying the fuel into the combustion chamber (50), characterized by , that the fuel nozzle (15) is arranged outside the oxidizer supply and radially inside the ring, in particular for the unmixed supply of fuel to the combustion chamber (50), that a secondary oxidizer supply with at least one secondary outlet opening (192) arranged radially between the outlet opening (182) and the fuel nozzle (15) is provided for the swirl-free addition of secondary oxidizer into the combustion chamber (50), that the fuel nozzle (15) opens axially back from the outlet opening (182) in a recess (24) in the front face (20), in particular at the level of a bottom surface (242) of the recess (24), that the secondary outlet opening (192) is arranged axially at the level of or upstream of the fuel nozzle (15) in the recess (24) and that the secondary outlet opening (192) and / or the outlet opening (182) are formed in a slit-like manner around the central longitudinal axis (M). [2] Burner head (10) according to claim 1, characterized by , that the fuel supply (30) is designed for the addition of liquid fuel, wherein the fuel is atomized via an atomizing device (16) comprising the fuel nozzle (15). [3] Burner head (10) according to claim 1 or 2, characterized by , that the fuel nozzle (15) is designed such that, during operation, the fuel flows outwards at an angle (β) axially-radially after exiting the fuel nozzle (15). [4] Burner head (10) according to claim 3, characterized by , that a circumferential surface (241) of the depression (24) between the bottom and an opening (243) of the depression (24) into the combustion chamber (50) is aligned axially-radially at an angle (α), wherein the angle (α) and the angle (β) are aligned such that the main flow direction of the fuel is directed into the combustion chamber (50). [5] Burner head (10) according to claim 4, characterized by, that the secondary oxidizer supply has at least one secondary supply channel (191) which opens into the secondary outlet opening (192) and which is designed such that the main flow direction of the secondary oxidizer upon exit from the secondary outlet opening (192) corresponds axially-radially to the angle (α). [6] Burner head (10) according to claim 4 or 5, characterized by , that the secondary outlet opening (192) is arranged radially within the circumferential surface (241), and in particular borders the circumferential surface (241). [7] Burner head (10) according to any one of the preceding claims, characterized by , that the outlet opening (182) is arranged around the opening (243) of the recess (24) substantially adjacent to the circumferential surface (241), i.e. with an intermediate wall thickness for fluid-mechanical separation of the oxidizer supply from the recess (24). [8] Burner head (10) according to any one of the preceding claims, characterized by , that the outlet opening (182) is arranged on the ring rotating around the central axis (M), the radius of which is between 0.3 and 0.75 of the radius of the outer circumference of the front face (20). [9] Burner head (10) according to any one of the preceding claims, characterized by , that the burner head (10) comprises a base body (12) into which the oxidizer supply, and if applicable the secondary oxidizer supply, is inserted. [10] Burner head (10) according to any one of the preceding claims, characterized by , that the burner head (10) is designed for single-stage combustion operation. [11] Burner system (1) with a burner head (10) according to one of the preceding claims and a circumferential wall (52) comprising a combustion chamber (50), wherein at least one addition opening (56) for radial addition of oxidizer into the combustion chamber (50) is provided in the circumferential wall (52), which is arranged axially downstream of a reaction zone and upstream or at a stagnation area of ​​the recirculation zone (54) in which the flow velocities reverse upon passing through the zero point. [12] Method for operating a burner system (1) with a burner head (10) according to one of claims 1 to 10, in which oxidizer is supplied axially without swirl to a combustion chamber (50) of the burner system (1) via an oxidizer supply with at least one outlet opening (182) arranged on a ring around a central axis (M) of the burner head (10), wherein a recirculation zone (54) with recirculated exhaust gas is formed within the combustion chamber (50) to stabilize the combustion process, and where the fuel is supplied in liquid form for combustion in the combustion chamber (50), characterized by , that the fuel for a non-premixed addition is mixed to the oxidizer outside the oxidizer feed, wherein the fuel is fed centrally, radially within the annular outlet opening (192), to the combustion chamber (50), and that secondary oxidizer is supplied into the combustion chamber without swirl by means of a secondary oxidizer supply with at least one secondary outlet opening (192) arranged radially between the outlet opening (182) and the fuel nozzle (15).

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