Ultra-lean flashback-free multi-fuel highly efficient modular-design partially premixed swirl burner

Abstract

The present patent introduces modifications that upgrade the approved claims in WO 2023 / 131386 A1. These modifications include: (i) the inclusion of a new air supply and distribution system permits precise control of the air mass flow rate, adaptive degree of air swirl within a central premix chamber and self-cooling of the burner body and its internal parts, (ii) the adoption of a modular design concept permits mass production of parts, easy assembly and / or spare parts replacement leading to lower manufacturing, maintenance cost, and life time operability, (iii) Operational flexibility due to selection of location, mass flow rate, the magnitude and direction injection velocity of the fuel at different loading conditions that opens the way to the use of different and / or multiple fuels including hydrogen rich fuels enhancement of environmental decarburization, (iv) Ensures the safely and efficient operation down to an ultra-lean mixtures (φ < 0.1) with no concern regarding flashback.

Description

Ultra-Lean Flashback-Free Multi-Fuel Highly Efficient Modular-Design Partially Premixed Swirl Burner

[0001] The present invention is an industrial partially premixed burner for burning multiple fuels to efficiently generate thermal energy and conform to the stringent emission regulations for clean environment. The burner is operable at ultralean equivalence ratio with little or no concern regarding flashback.

[0002] The present patent comes in line with the formulated strategy of the dry low NOx that introduced a generic change in concept.

[0003] This strategy addressed two pillars namely: (i) the need for the development of a new lean premixed combustion and premix burner technology for gas turbine combustors and (ii) the development of the annular combustor technology.

[0004] Pillar 1 of the strategy aims at the avoidance of high flame temperature via the operation closer to the extinction limit through the reduction of the combustor cooling air and the redirection of the air to the burner plane.

[0005] Pillar 2 of the strategy aims at improving the liner wall cooling with new impingement film and convective cooling concepts as well as permitting: (i) the use of distributed multi-burner systems, (ii) allowance of burner switching for load control, (iii) reliance on the piloting concept for safe operation and (iv) adoption of staged burners.

[0006] The introduction and commercialization of the dry low NOx burner technology for advanced low NOx were commenced in 1980. In that respect, three technologies had emerged regarding staged burners, namely: (i) Air-Staging: (Rich burn, Quick mix, lean burn “RQL”), (ii) fuel staging: axial fuel staging (sequential), radial fuel staging and dual stage lean premixed (DLPM) and (iii) the combined Air-Fuel staging (lean premixed combustion, LPM).

[0007] The first lean premixed combustion in gas turbine was commercialized in (1984)and the world’s first compact annular multi-burner combustor was subsequently introduced in (1988). Subsequently, two methodologies of lean premixed combustion had emerged, namely (a) the concept of “Low Swirl Combustion”, (LSC), and (b) the “Enhanced Vortex” (EV) burner that were introduced close to the end of last century.

[0008] The gaseous fuel and air are partially premixed inside the burner gun and a premixed flame is stabilized at the immediate exit of the burner whereby the flow velocity equals the burning velocity of the outgoing fuel / air mixture. In the former method, an annular vane swirler with a central perforated disc intercepts the incoming reactants at a swirl recess length before the burner gun exit.

[0009] (EV burner), the burner is comprised of a central conical premix chamber with circumferential air swirling slots (two or multi slots) and the gaseous fuel is injected from several injection holes at the entry of the conical premix chamber. This burner is also equipped with a central pilot to enrich the mixture at startup or air to assist in anchoring the flame at the burner exit and prevent possible flashback. This enhanced vortex burner underwent several developments starting from (i) the conventional pilot / premix 2-slots EV burner to (ii) the internally staged EV burner to (iii) the advanced EV burner (AEV) and (iv) the EV burner for Syngas (hydrogen rich fuel). In the latter case the gas injection holes are circumferentially arranged at the exit of the conical of the premix chamber to facilitate elimination of flashback.

[0010] It is worth mentioning that extensive R&D efforts had taken place throughout the first two decades of this century to mitigate the flashback phenomena at lean and / or ultra-lean operational conditions. These efforts mainly concentrate on developing active electronic control systems for aviation gas turbines, which at the end of the day could not be trusted together with the associated difficulties with repairing. Active control systems are only recommended for large stationary gas turbine power stations.

[0011] The operational characteristics in the present patent included:

[0012] The introduction of a new air supply and distribution system that replaced the old protruding air admission pipes, (given in the granted patent WO2023 / 131386 A1), and hence facilitates coaxial air admission to ensure smooth and uniform air distribution through the swirling air passages, control of the swirl number through a 90orotation of the fuel injection chambers, control of the incoming air flow rate via a new (internally- mounted) double cone air damper.

[0013] The development of an integrated fuel injection system that permits greater flexibility in burning safely single or multiple gaseous fuels irrespective of the fuel density and burning velocity including hydrogen rich fuels, and / or hydrogen through adequate selection of the fuel injection location, injection velocity (magnitude and direction), injection pattern inside the central virtual premix chamber.

[0014] The adoption of the diecasting methodology in manufacturing the set fuel injection chambers that not only allow accurate and mass production but also permits tailoring the execution of the fuel injection pattern within the matrix (row and / or column) of the fuel injection chambers depending on the fuel type.

[0015] The unbounded flexibility in tailoring the burner design to suit any industrial application via the selection and assembly of the burner internal parts. Also, faulty parts are easily replaced.

[0016] The patent under review addresses the technology using the lean partially premixed flames more than 3 decades ago as an alternative to the use of the high swirl turbulent diffusion flames that was employed in 1939 in can combustor of gas turbines at the time. The technology of high swirl diffusion flames while ensuring high thermal efficiency flame, excellent stability and high turndown ratio resulted unfortunately to high NOx(poisonous gas) in the exhaust gases that destroy the environmental and human health. Despite all the research effort to treat this problem following the methodology of “end of pipe solution” that include exhaust gas recirculation, use of catalytic converters, water or steam injection failed to meet the stringent emission regulations of ultralow NOx and CO emissions of the order of (4-7 ppm@15% O2). On this basis, the conventional diffusion flame concept was totally rejected and being replaced by a new design concept based onlean premixed flamesthat allows burning at an overall low or ultralow equivalence ratio (near lean blowout limit while maintaining flame stability and high turndown ratio.

[0017] The proper location of the base of the stabilized flame.

[0018] Increasing the degree of homogeneity of the prepared mixture.

[0019] The fulfillment of the targeted level of emissions of NOx and CO to comply with international regulations.

[0020] The complete avoidance of flashback (or increasing the flashback resistance).

[0021] The flexibility and adaptivity of operation.

[0022] The potential to use high reactive fuels and / or multiple fuels.

[0023] Increase lifetime and avoidance of thermal stresses on the burner body.

[0024] It is evident from the above-mentioned that:

[0025] The mixing process is separated from the combustion process.

[0026] The combustion process is performed under very lean conditions (lean premixed combustion) where the fuel and air are mixed upstream of the burner exit within the mixing length (inside the burner premixing chamber) whereby increased levels of flame instabilities are anticipated.

[0027] The flame must be stabilized at the vicinity of the burner gun at a location where the flow velocity of the mixed reactants matches (at all times) the burning velocity of the fuel / air mixture that possess varying values of the mixture equivalence ratio depending on the operation condition.

[0028] The operation at ultra-lean conditions is susceptible to flame blowout including the sudden occurrence of sudden flashback that may damage the combustion system. Thus, the mixing process inside the burner premix chamber must ensure, (i)) the formation of a homogeneous mixture and (ii) the elimination of the possibility of flashback resulting from upstream flame propagation into the burner. The later takes place when the local flame speed exceeds the flow speed where the local equivalence ratio of the fuel / air mixture lies within the flammable range. This flashback takes several modes that are associated with different mechanisms that broadly includeauto ignitionandflashback due to upstream flame propagation. The later includes combustion instabilities, flame propagation in the core flow, flame propagation within the boundary layer andcombustion induced vortex breakdown (CIVB).

[0029] On the above-mentioned bases, this patent must not focus on the elements of burner but on how these integrated elements provide safe and adequate operation and performance.

[0030] A fuel injection system of different designs and injection location and direction of fuel injection relative to swirling air.

[0031] The main difference between the present ultra efficient burner and other previously invented or modified partially premixed burners is that air - fuel mixing is taking place under high pressure inside mixing zone due to the small area of the refractory hole that feeds the flame, as well as the minimum mixing cavity volume, leaving zero possibility of zero back-pressure, maximizing flame turn-down ratio and minimizing air-fuel residence time.

[0032] The novel geometry of the air-fuel mixing cavity that have: (i) a very narrow longitudinal slope (≤14ototal angle) close to a flat cylinder and (ii) a progressive increase of the exiting area of the swirling air passage along the premix chamber from bottom to top. This geometrical configuration leads to a progressive decrease of the air velocity and a progressive increase of the air flow rate along the premix chamber from bottom to top. This is also coupled with the tight eclosure of the burner top housing plate that directs and accelerates the flow of the partially premixed mixture towards the central circular exit. This simple explanation clearly indicates that partial premixing is totally occurring at almost zero pressure within the compact volume of the premix chamber, leading to no possibility of flashback.

[0033] The new geometrical configuration, positioning, and function of the multi- fuel injectors. Firstly, these comma shape injectors have a very advanced aerodynamic frame with six faces each leading to a very steady and homogeneous air-fuel mixing and swirling process. Secondly, the initiative positioning of the fuel injectors relative to each other, where the tails of the comma injectors intercept a lateral- oblique pressurized air stream with an adaptive interception span, that accelerates the swirling process inside the air-fuel mixing cavity at low flow residence time, unlike most flow deviators that faces air inlets with the bulk core and not with tail. Thirdly, the internal hollow structure of the fuel injectors enables a constant fuel back pressure and simultaneous injection of the different fuels safely. (including highly explosive fuels like hydrogen and acetylene).

[0034] The present invention is further explained by means of different embodiments and with reference to the attached drawings to the ultra-lean flashback-free multi-fuel highly efficient modular-design partially premixed swirl burner of the present upgraded version.Fig. 1

[0035] [Figs.1a and 1b] illustrates backward assemble and disassemble of the burner according to an embodiment of the present invention.Fig. 2

[0036] [Figs. 2a and 2b] present the forward assemble and disassemble of the burner according to another embodiment.Fig. 3

[0037] presents a vertical section of the burner according to another embodiment.Fig. 4

[0038] [figs.4a and 4b] illustrates a forward and backward horizontal section of the burner.Fig. 5

[0039] Figs. 5a ,5b and 5c] illustrates various details of one column of the of the die-casted internally portioned fuel injection chambers together with the array of the fuel injection holes and the quarter circle bottom base according to another embodiment of the present upgraded invention.Fig. 6

[0040] [Figs. 6a, 6b and 6c] illustrates the different types of the premix chambersFig. 7

[0041] illustrates the side and the upper sectional views of the invented burner.

[0042] PartDescriptionFuel Supply, Distribution and Injection System1Cylindrical gaseous fuels reservoir having multiple concentric chambers, multiple radially positioned holes for fuels admission and central hole for a central pilot injector.2Top thread mounted cover for the cylindrical fuel reservoir with top fitted fuel distribution tubes to different fuel injection chambers.3Fuel supply tubes (with fast sealing joint) for different gaseous fuels.4Fuel distribution tubes (with fast sealing joint) to different fuel injection chambers.5Bottom quarter circle plates welded to the bottom base of the set of the fuel injection chambers.6Profiled partition plates placed on top of the bottom row of the fuel injection chambers.7Profiled partition plates placed on top of the intermediate bottom row of the fuel injection chambers.8Internally segmented fuel injection chambers.9Directional fuel injection nozzles matrix10Virtual premix chamber.11Feeding pipe for central admission of air and / or fuel / air mixture.12Assembly ring of the burner internal componentsAir Supply, Metering and Swirl Adjustment13Cylindrical envelop of the burner body housing the axially admitted air to the swirling air passages formed between the Arabic comma shaped fuel injection chambers.14Hollow outer rotating conical body with circumferential rectangular gates to admit and regulate the air mass flowrate.15Inner fixed conical body having circumferential rectangular air entry slots (each is located at the frontal edge of the outer concave surface of the fuel injection chambers) to path the incoming air into the air swirling passages.16Winged directional air passages with side trapezoidal opening to direct the axially admitted air to the entry slots on the circumference of the inner fixed conical body.17Top assembly screw mounted flange into the outer casing cylindrical envelop.18Top cylindrical housing plate with a central outlet bore for the discharge of the partially premixed fuel / air mixture formed in the virtual premix chamber.19Mounting screws of top cylindrical plate into the upper surface of assembly flange to tightly cap the upper surface of the multi-annular fuel injection chambers.20Top mounted premix- chamber (taking the shape of cylinder, diffuser, nozzle, swirling blades,…) at burner exit.

[0043] The provided design of the present burner fulfills all requirements needed to comply with the stringent environmental regulations together with the top performance in terms of High Turndown ratio, running at ultra lean fuel / air mixture permitting the use of pure hydrogen and / or green hydrogen for applications in diverse industries including stationary and aviation gas turbines, water desalination, casting of metals, boilers and furnaces, crop drying, air conditioning (Chillers), Food industries,……..etc..

[0044] The given design is based on the modular concept in manufacturing, permitting fast assembly and disassembly, ease in replacing parts, low cost, ease of control, safe operation (eliminating flashback), use of diverse types of fuels.Patent Literature

[0045] The present patent presents an updated version with several design modifications that yield not only to notable upgrading in the operational characteristics but also in the manufacturing strategy when compared to the awarded claims given in the previously granted patent.

[0046] PTL: WO 2023 / 131386 A1

Claims

The new introduction of a universal design concept of an ultra-lean partially premixed burner that permits simultaneous, efficient and safe cofiring of multiple gaseous fuels and / or fuel / air mixtures including hydrogen-rich fuels and / or hydrogen while conforming to nowadays emission regulations with no concern regarding flashback. Furthermore, the modular design methodology is adopted and as such it facilitates easy assembly and disassembly, maintenance and / or replacement of parts opening the way to lifetime operability.The inclusion of an integrated air supply and distribution system, metering and swirl control systems that facilitate smooth and uniform air distribution through the swirling air passages formed by the surfaces of the fuel injection chambers. In that respect: (i) Air is supplied coaxially through the cylindrical burner gun, opening the way to the implementation of the compact annular multi-burner combustor configuration in a heavy-duty gas turbine. (ii) Control of the incoming air flow rate is facilitated through a double coaxial hollow conical arrangement whereby the cross-sectional area of each of the entry of the air damper slots is varied via the rotation of the outer conical body relative to the air entry passages on an inner stationary cone and (iii) The variation of the air swirl number is facilitated through the rotation (0 to 90o, manual or automatic) of the fuel injection chambers relative to the rectangular air entry slots at the surrounding inner conical body. This rotation is facilitated through angular movement of the bottom-based fuel supply reservoir as being solidly connected to the fuel injection chambers.The adoption of a new modular design concept of the fuel supply, distribution and injection system that not only permits unbounded flexibility in the use of single or multi gaseous fuels but also allows the selection of the fuel injection location (at the inside face of each fuel chamber) within the matrix (row and / or column) of the fuel injection chambers depending on the fuel density and burning velocity.The adoption of a die casting methodology to manufacture the fuel injection chambers. A single die can be used for mass production of the whole sets of fuel injection chambers together with great flexibility to suit: (i) The use of a single gaseous fuel and / or multi-gaseous fuels, (ii)The injection location along the burner premix chamber; depending on the burning velocity of any one fuel, (iii)The distribution, magnitude and direction of the injected gaseous fuel jet velocities, and (iv)The gas flow rate from each fuel injection chamber, depending on the number, diameter, distribution and injection angle of the gas injection holes. As such, the production of a burner for a particular gaseous fuel(s) can be tailored, relying on the same basic elements, to suit diverse industrial applications, opening the way for low production cost, ease of maintenance, conforming to the international stringent emission regulations together with sizable fuel savings and / or utilizing hydrogen rich fuels (Syn gas, ammonia and cracked ammonia) as well as hydrogen.The novel geometry of the air-fuel mixing cavity that have: (i) a very narrow longitudinal slope (≤14ototal angle) close to a flat cylinder and (ii) a progressive increase of the exiting area of the swirling air passage along the premix chamber from bottom to top. This geometrical configuration leads to a progressive decrease of the air velocity and a progressive increase of the air flow rate along the premix chamber from bottom to top. This is also coupled with the tight eclosure of the burner top housing plate that directs and accelerates the flow of the partially premixed mixture towards the central circular exit. This simple explanation clearly indicates that partial premixing is totally occurring at almost zero pressure within the compact volume of the premix chamber, leading to no possibility of flashback.The inclusion of a premix chamber (conical diffuser, nozzle, cylindrical, set of swirling blades…) on top of the burner outgoing central exit to enhance the uniformity of the already formed partially premixed mixture, leading to extending the lean blowout limit down to an ultra-lean equivalence ratio (φ) ≤ 0.1 in one hand and tailor the flame geometry (e.g. flame length and width) to suit diverse industrial applications. This also opens the way not only to safe utilization of pure hydrogen and / or hydrogen-rich fuels with no concern regarding flashback but also ensures ultralow emissions of NOx and CO in case of burning hydrocarbon fuels down to a single digit.

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