Combustion chamber with a lean-burn pre-nozzle fuel injection system

Abstract

Combustion chamber (100) for burning a fuel stream (30) and an air stream (20), comprising: several fuel nozzles (120), a lean-burn pre-nozzle fuel injection system (270) for premixing a premix fuel (300) and an air stream (20), and an attachment deflector element (210) and a housing (220) radially outwardly enclosing the attachment deflector element (210), wherein the attachment deflector element (210) and the housing (220) define therebetween a premixing ring (250) which is arranged upstream of the fuel nozzles (120), wherein the lean-burn pre-nozzle fuel injection system (270) is disposed radially outwardly adjacent the top deflector (210), and wherein the premixing ring (250) extends downstream of the lean-burn pre-nozzle fuel injection system (270) toward an end cover (240) to premix the premix fuel (300) and the air stream (20) along the length of the premixing ring (250), and wherein the premixing ring (250) has a radially inwardly curved turnaround section (260) adjacent to the end cover (240) and upstream of the fuel nozzles (120) in which the top deflector element (210) and the housing (220) extend in a radially inwardly curved manner.

Description

FIELD OF THE INVENTION

[0001] The present application relates generally to gas turbines and, more particularly, to a combustor having a lean-burn pre-nozzle fuel injection system for mixing fuel and air ahead of the fuel nozzles. GENERAL STATE OF THE ART

[0002] In a gas turbine, operating efficiency generally increases as the temperature of the combustion stream increases. However, at higher combustion stream temperatures, a higher content of nitrogen oxides (“NO x ") and other emissions that may be subject to regulation at both the federal and state levels in the United States and may also be subject to similar regulations abroad. Operating the gas turbine within an effective temperature range while ensuring that the emission of NO x and other regulated emissions remain below the prescribed values, thus represents a balancing act.

[0003] In several types of known gas turbine designs, such as those using dry, low NO combustors x -emission (“DLN” combustors), the fuel streams and the air streams are generally premixed before a reaction or combustion zone via several fuel premixing nozzles to reduce the NO x emissions. This premixing reduces the overall combustion temperature and thus the NO x -Emissions and the like reduced.

[0004] However, several process-relevant problems can occur during premixing, such as shallow flames, flashback, spontaneous combustion, and the like. These problems can be particularly significant when using highly reactive fuels. For example, it is possible that a flame containing a significant amount of hydrogen or other fuel types is sustained in the inlet section upstream of the fuel nozzles. Any form of fuel-rich bubble can therefore sustain a flame and damage the combustion chamber. Other premixing problems can be due to irregularities in the fuel and air flows.

[0005] An improved combustion chamber design is therefore desirable. Such a combustion chamber design should promote improved fuel-air premixing, especially when using highly reactive fuels. These combustion chamber designs should promote good mixing of the components while simultaneously keeping emissions below the prescribed levels and avoiding or limiting problems such as near-surface flames, flashback, spontaneous combustion, and the like.

[0006] US 2007 / 0 089 395 A1 describes a combustion chamber for burning air and fuel. The combustion chamber has an inner cylinder enclosed by an outer casing. A premixing ring is formed between the two. Premixing injection nozzles are arranged upstream of the premixing ring. The premixed fuel injected there can mix with an air flow, reverse the flow direction around the inner cylinder, and finally flow into the combustion chamber via main injection nozzles. A similar combustion chamber is also known from US 5 901 555 A.

[0007] The combustion chamber described in DE 694 10 511 T2 has premixed fuel nozzles which are arranged in direct alignment with an inner combustion chamber housing in the direction of flow. SUMMARY OF THE INVENTION

[0008] The present application thus provides a combustor for combusting a fuel stream and an air stream according to the features of claim 1. These and other features and improvements of the present application will be apparent to one of ordinary skill in the art from the following detailed description taken in conjunction with the several drawings and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a simplified representation of a known gas turbine. Fig. Figure 2 is a cross-sectional side view of a known combustion chamber. Fig. Figure 3 is a side cross-sectional view of a combustion chamber with a lean-burn pre-nozzle fuel injection system described herein. Fig. 4 is a side cross-sectional view of a fuel nozzle for use in the combustor with the lean burn pre-nozzle fuel injection system of Fig. 3. DETAILED DESCRIPTION

[0009] Referring now to the drawings, wherein like reference characters designate like elements throughout the different views, Fig. 1 is a simplified representation of a gas turbine 10 described herein. The gas turbine 10 may include a compressor 15. The compressor 15 compresses an incoming air stream 20. The compressor feeds the compressed air stream 20 to a combustor 25. The combustor 25 mixes the compressed air stream 20 with a compressed fuel stream 30 and ignites the mixture to produce a combustion gas stream 35. While only a single combustion chamber 25 is shown, the gas turbine 10 may include any number of combustion chambers 25. The combustion gas stream 35 is, in turn, fed to a turbine 40. The combustion gas stream 35 drives the turbine 40, thereby performing mechanical work. The mechanical work performed in the turbine 40 drives the compressor 15 and an external load 45, such as an electrical generator and the like.

[0010] The gas turbine 10 may utilize natural gas, various types of syngas, and / or other types of fuels. The gas turbine 10 may be any of several different gas turbines offered by General Electric Company of Schenectady, New York. The gas turbine 10 may have various configurations and may utilize different types of components. Other types of gas turbines may also be used herein. Multiple gas turbines, other types of turbines, and other types of power generation technology may also be used together herein.

[0011] Fig. 2 shows a simplified example of a known combustion chamber 25. Generally speaking, the combustion chamber 25 may include a combustion chamber 50 in which a plurality of fuel nozzles 55 are positioned. The fuel nozzles 55 may be premixing nozzles with one or more swirlers 60 attached. The swirlers 60 promote the premixing of the air stream 20 and the fuel stream 30. An inlet air path 65 may be defined between an insert 70 of the combustion chamber 50 and a housing 75. A transition piece 80 may be positioned behind the combustion chamber 50. Other types of combustion chamber arrangements are known.

[0012] The air stream 20 can flow from the compressor 15 into the combustor 25 via the inlet air path 65. The air stream 20 can change direction and be premixed with the fuel stream 30 around the fuel nozzles 55 and the swirlers 60. The mixture of the air stream 20 and the fuel stream 30 can be combusted in the combustion chamber 50. The combustion gas stream 35 can then be expelled through the transition piece 80 toward the turbine 40. Depending on the nature of the combustion chamber 25, the combustion chamber 25 can use a first fuel, which can be a fuel gas that flows through the swirlers 60, a second fuel and a third fuel, which can be a premixed fuel gas, and a lean-burn pre-nozzle fuel injection system, which can inject a small amount of fuel directly upstream of the swirlers 60. Other types of fuel cycles and configurations are also known.

[0013] Fig. 3 and Fig. 4 show a combustion chamber 100 described herein. Similar to the previously described combustion chamber 25, the combustion chamber 100 includes a combustion chamber 110 in which a plurality of fuel nozzles 120 are positioned. In this example, a central nozzle 130 may be surrounded by a plurality of outer nozzles 140. Any number of fuel nozzles 120 may be used herein.

[0014] Generally described, each of the fuel nozzles 120 may include a central fuel passage 150, generally for a liquid fuel. The fuel nozzles 120 may also include a plurality of fuel injectors 160. The fuel injectors 160 may be positioned around one or more swirlers 170. The fuel injectors 160 may be used with a premixed fuel and the like. Other types of fuel circuits may be used herein. The fuel nozzles 120 may also include a funnel 180 at a forward end thereof for the incoming air stream 20. Any number or shape of the funnels 180 may be used.

[0015] The combustor 100 also includes an inlet air path 200. The inlet air path 200 may be defined between an insert or an end deflector 210 and a housing 220. The end deflector 210 may be attached to a cap 230 and may widen toward the end cap 240 with a flared shape 245. The housing 220 may also be flared such that the housing 220 has a larger diameter in the direction of flow toward the end cap 240. The end deflector 210 and the housing 220 may define a premixing ring 250. The overall mixing ring 250 thus also widens toward the end cap 240. The premixing ring 250 may have a smooth turnaround section 260 around the end cap 240 toward the fuel nozzles 120. The premixing ring 250 may or may not provide diffusion. Other arrangements may be used.

[0016] A lean-burn pre-nozzle fuel injection system 270 may also be placed around the inlet air path 200 between the top deflector 210 and the housing 220 around the end cap 230. The lean-burn pre-nozzle fuel injection system 270 may include a plurality of fuel injectors 280. The fuel injectors 280 may have an aerodynamic wing-like or streamlined shape 285 for optimal resistance to near-surface flames. The fuel injectors 280 may each have a plurality of injector holes 290 therein. The number of fuel injectors 280 and the number of injection holes 290 may be optimized for premixing. Other arrangements may be used here. A premixed fuel 300 may flow therein.

[0017] During operation, the premixed fuel 300 is injected via the fuel injectors 280 of the lean-burn pre-nozzle fuel injection system 270 into the incoming air stream 20 traversing the inlet air path 200. The aerodynamic wing-like shape 285 of the fuel injectors 280 minimizes the risk of flame formation at or behind the injectors 280. The premixed fuel 300 and the air stream 20 are thus premixed into a premixed stream 310 along the length of the premixing ring 250. Because both the top deflector 210 and the housing 220 flare toward the end cover 240, the premixing ring 250 decelerates the air and recovers some of the static pressure. With this flared shape, more diffusion is therefore possible than with a typical cylindrical housing.Premixing also eliminates any fuel-rich bubbles that could sustain a flame. The length of the premixing ring 250, together with the number and spacing of the injectors 280, thus provides improved premixing within the premixing ring 250. The premixed stream 310 is fully mixed before leaving the ring 250.

[0018] The premixed stream 310 then reverses at the turnaround section 260 and flows into the fuel nozzles 120. Because the air flow 20 slows down in the premixing ring 250, the premixed stream 310 smoothly turns at the turnaround section 260 and into the fuel nozzles 120 without recirculation or flow losses. Therefore, the fuel nozzles 120 can utilize the funnels 180 instead of a conventional flow straightener, which can result in a lower pressure drop. The premixed stream 310 further mixes with the normal fuel stream 30 from the fuel injectors 160 or otherwise before being combusted in the combustion chamber 110.

[0019] A high percentage of the total fuel flow can flow through the premixing ring 250 without negatively impacting emissions. Likewise, by purging the fuel nozzles 120, i.e., removing fuel, the overall near-surface flame generation behavior of the fuel nozzles can be improved. With the ability to adjust the percentage of total fuel delivered to the lean-burn pre-nozzle fuel injection system 270 over a wide range, the pressure ratio can be controlled to cope with fluctuations in fuel composition. The overall pressure ratio of the fuel nozzles 120 can be optimized for dynamics without changing the nozzle equivalence ratio and the like. The size of the fuel injectors 160 can also be reduced.

[0020] By using the fuel injectors 280 of the lean-burn pre-nozzle fuel injection system 270 and the premixing ring 250, NO x Emissions are reduced, pressure drop is reduced, and fuel flexibility is increased in terms of both MWI (Modified Wobbe Index) and fuel reactivity. The lean-burn pre-nozzle fuel injection system 270 can thus be fuel-flexible, including the use of highly reactive fuels such as hydrogen, ethane, propane, etc.

[0021] It should be understood that the foregoing description relates only to certain embodiments of the present application and that numerous changes and modifications may be made by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined in the following claims and their equivalents.

[0022] The present application provides a combustion chamber 100 for combusting a fuel stream 30 and an air stream 20. The combustion chamber 100 may include a plurality of fuel nozzles 120, a lean-burn pre-nozzle fuel injection system 270 positioned upstream of the fuel nozzles 120, and a premixing ring 250 positioned between the fuel nozzles 120 and the lean-burn pre-nozzle fuel injection system 270 to premix the fuel stream 30 and the air stream 20. LIST OF REFERENCE SYMBOLS 10 gas turbines 15 Compressor 20 Airflow 25 Combustion chamber 30 Fuel flow 35 Combustion gas stream 40 turbines 45 load 50 combustion chamber 55 fuel nozzles 60 swirl bodies 65 Airway 70 deployment 75 housings 80 transition piece 100 combustion chamber 110 combustion chamber 120 fuel nozzles 130 Center nozzle 140 Outer nozzles 150 fuel channel 160 fuel injectors 170 swirl bodies 180 funnels 200 Inlet air path 210 Attachment deflection element 220 housings 230 final piece 240 end cover 245 Tapered shape 250 premixing ring 260 turning section 270 Lean-burn pre-nozzle fuel injection system 280 fuel injectors 285 Aerodynamic wing-like shape 290 injection holes 300 premixed fuel 310 Premixed stream

Claims

[1] Combustion chamber (100) for burning a fuel stream (30) and an air stream (20), comprising: several fuel nozzles (120), a lean-burn pre-nozzle fuel injection system (270) for premixing a premix fuel (300) and an air stream (20), and an attachment deflector element (210) and a housing (220) radially outwardly enclosing the attachment deflector element (210), wherein the attachment deflector element (210) and the housing (220) define therebetween a premixing ring (250) which is arranged upstream of the fuel nozzles (120), wherein the lean-burn pre-nozzle fuel injection system (270) is disposed radially outwardly adjacent the top deflector (210), and wherein the premixing ring (250) extends downstream of the lean-burn pre-nozzle fuel injection system (270) toward an end cover (240) to premix the premix fuel (300) and the air stream (20) along the length of the premixing ring (250), and wherein the premixing ring (250) has a radially inwardly curved turnaround section (260) adjacent to the end cover (240) and upstream of the fuel nozzles (120) in which the top deflector element (210) and the housing (220) extend in a radially inwardly curved manner. [2] Combustion chamber (100) according to claim 1, wherein each of the fuel nozzles (120) comprises a fuel injector (160) and a swirl body (170). [3] Combustion chamber (100) according to claim 1, wherein each of the fuel nozzles (120) comprises a plurality of fuel nozzles (140). [4] Combustion chamber (100) according to claim 1, wherein the fuel nozzles (120) have a funnel (180). [5] The combustor (100) of claim 1, wherein the top deflector (210) and the housing (220) have a conically flared shape (245) that widens toward the plurality of fuel nozzles (120). [6] The combustion chamber (100) of claim 1, wherein the lean-burn pre-nozzle fuel injection system (270) includes a plurality of said fuel injectors (280). [7] The combustion chamber (100) of claim 6, wherein each of the plurality of fuel injectors (280) has a streamlined vane-like shape (285). [8] The combustion chamber (100) of claim 6, wherein each of the plurality of fuel injectors (280) has a plurality of injector holes (290).

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