EP1793170A2 - Opposed flow combustor - Google Patents

Abstract

In accordance with one embodiment of the present invention a combustor (10) is provided. The combustor (10) includes a combustion chamber (14), a first inlet (22) adapted to provide a first air flow (20) to the combustion chamber (14) in a first direction, a fuel controller (32) adapted to provide a fuel flow (34) to the combustion chamber (14) in the first direction, an opposing inlet (28) adapted to provide an opposing air flow (26) to the combustion chamber (14) in a second direction generally in opposition to the first direction, and wherein the first air flow (20) and the fuel flow (34) interact with the opposing air (26) flow to form a stagnation zone (38) in the combustion chamber (14).

Description

• The present invention relates generally to gas turbine devices and, in particular, to a system and method for providing opposed flows of fuel and air in a combustor.
• In traditional gas turbine devices, air is drawn from the environment, mixed with fuel and, subsequently, ignited to produce combustion gases, which may be used to drive a machine element or to generate power, for instance. Traditional gas turbine devices generally include three main systems: a compressor, a combustor and a turbine. The compressor pressurizes air and sends this air towards the combustor. The compressed air and a fuel are delivered to the combustor. The fuel and air delivered to the combustor are ignited, with the resulting combustion gases being employed to actuate a turbine or other mechanical device. When used to drive a turbine, the combustion gases flow across the turbine to drive a shaft that powers the compressor and produces output power for powering an electrical generator or for powering an aircraft, to name but few examples.
• Gas turbine engines are typically operated for extended periods of time, and exhaust emissions from the combustion gases are a concern. For example, during combustion, nitrogen combines with oxygen to produce oxides of nitrogen (NOx), and these NOx emissions are often subject to regulatory limits and are generally undesired. Traditionally, gas turbine devices reduce the amount of NOx emissions by decreasing the fuel-to-air ratio, and these devices are often referred to as lean devices. Lean devices reduce the combustion temperature within the combustion chamber and, in turn, reduce the amount of NOx emissions produced during combustion.
• Some regions of the United States require as little as three parts per million (ppm) N0x levels in natural gas operation. N0x emissions from a gas turbine have been significantly reduced using premixed combinations of natural gas. The degree of premixing has a strong impact on N0x reduction. However, highly premixed flames demonstrate increased instability and have proven difficult to anchor. Conventional premixed systems do not adequately reach N0x emission targets or theoretical limits so selective catalytic reduction (SCR) of N0x through ammonia injection has been employed. SCR is an expensive approach and improvements to the combustion system would reduce operating costs, such as the cost of electricity for operating the system. In systems powered by syngas or hydrogen, a diffusion flame has been used because high flame velocities associated with the hydrogen content may result in flashback into the premixer. Diluents are added at the injection tip to potentially reduce N0x emissions.
• In addition to natural gas, combustors may employ other fuels, such as syngas (synthetic gas) or hydrogen. Syngas poses challenges to flame stabilization and emission reduction at high firing temperatures. Premixed hydrogen combustion may result in a risk of flashback and typically produces significant N0x without premixing. Thus, there exists a need to provide an improved system and method to reduce the temperature of combustion in gas turbine systems to facilitate a reduction in NOx emissions from such systems.
• Briefly, in accordance with one embodiment of the present invention, a combustor is provided. The combustor comprises a combustion chamber, a first inlet adapted to provide a first air flow to the combustion chamber in a first direction, a fuel controller adapted to provide a fuel flow to the combustion chamber in the first direction, an opposing inlet adapted to provide an opposing air flow to the combustion chamber in a second direction generally in opposition to the first direction and wherein the first air flow and the fuel flow interact with the opposing air flow to form a stagnation zone in the combustion chamber.
• A method of operating a combustion chamber in accordance with an exemplary embodiment of the present invention is also provided. The method comprises injecting a first air flow and a fuel flow into the combustion chamber in a first direction, and injecting an opposing air flow into the combustion chamber in opposition to the first air flow to form a stagnation zone in the combustion chamber.
• Various features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
• FIG. 1 is a diagrammatic representation of a gas turbine device, in accordance with an exemplary embodiment of the present invention;
• FIG. 2 is a partial and diagrammatic, cross-sectional view of a combustor assembly, in accordance with an exemplary embodiment of the present invention;
• FIG. 3 is a partial and diagrammatic, cross-sectional view of a combustor assembly, in accordance with another exemplary embodiment of the present invention;
• FIG. 4 is a partial and diagrammatic, cross-sectional view of a combustor assembly, in accordance with yet another exemplary embodiment of the present invention;
• FIG. 5 is a partial and diagrammatic, cross-sectional view of a combustor assembly, in accordance with still another exemplary embodiment of the present invention; and
• FIG. 6 is a flowchart illustrating an exemplary process for establishing an opposing flow in a combustor in accordance with an exemplary embodiment of the present invention.
• As a preliminary matter, the definition of the term "or" for the purpose of the following discussion and the appended claims is intended to be an inclusive "or." That is, the term "or" is not intended to differentiate between two mutually exclusive alternatives. Rather, the term "or" when employed as a conjunction between two elements is defined as including one element by itself, the other element itself, and combinations and permutations of the elements. For example, a discussion or recitation employing the terminology "A" or "B" includes: "A", by itself "B" by itself and any combination thereof, such as "AB" and/or "BA."
• A flexible fuel combustor in accordance with an exemplary embodiment of the present invention is capable of burning hydrogen, natural gas or syngas in a gas turbine while maintaining low N0x emissions and low dynamics. Such systems may utilize opposed flows of fuel-air mixtures to create aerodynamic flame stabilization and to produce a highly stable flame zone in a combustor. Embodiments of the present invention may be compact in size and may provide low peak flame temperatures to help reduce undesirable N0x emissions.
• In an exemplary embodiment of the present invention, the combustor flame stabilization zone is removed from the burner. Reactants from the combustion process entrained the diluent rich products in the combustor before reacting. The flame is aerodynamically stabilized by an opposed flow of an ultra-lean fuel-air mixture, which creates a stagnation zone. The opposed flow also cools the combustor wall close to the stagnation zone. The combustion products flow toward the burner and then flow into the turbine hot section.
• Turning now to the drawings, FIG. 1 is a diagrammatic representation of a gas turbine device in accordance with an exemplary embodiment of the present invention. In FIG. 1, the gas turbine device is generally referred to by thereference numeral 10. Thegas turbine device 10 comprises one ormore compressor stages 12, acombustor 14 and one ormore turbine stages 16. Thecompressor stages 12 provide afirst air flow 20, which is adapted by the shape of a firstair flow chamber 18 to flow into thecombustor 14 via afirst inlet 22. Thecombustor 14 also includes anopposing airflow chamber 24 to accommodate anopposing air flow 26. Moreover, the output of thecompressor stages 12 is split to form thefirst air flow 20 and theopposing air flow 26. In the embodiment illustrated in FIG. 1, theopposing air flow 26 is delivered to thecombustor 14 via anopposing inlet 28.
• Afuel source 30 provides fuel to afuel controller 32. Thefuel controller 32 delivers afirst fuel flow 34 to thecombustor 14 via thefirst inlet 22. Thefirst airflow 20 and thefirst fuel flow 34 may be partially premixed. Thefirst airflow 20 and thefirst fuel flow 34 are directed into thecombustor 14 in a first direction, as indicated by thearrow 34 that represents the fuel flow. Theopposing airflow 26 enters thecombustor 14 in a second direction that is generally opposition to the first direction followed by thefirst airflow 20 and thefirst fuel flow 34.
• Aperforated plate 36 may be disposed inside thecombustor 14 between thefirst inlet 22 and theopposing inlet 28. The opposition between thefirst air flow 20 and theopposing air flow 26 creates a stagnation zone in thecombustor 14. The stagnation zone, which may also be referred to as a reaction/combustion zone, is identified in FIG. 1 by thereference numeral 38. When combustion occurs, the combustion tends to happen near thestagnation zone 38.
• The air-fuel mixture in thecombustor 14 is ignited to produce a combusted gas flow, as indicated by thearrow 40. The combustedgas flow 40 exits thecombustor 14 and is delivered to theturbine stages 16. The reactants from the combustion process are directed toward theperforated plate 36 with an effusion flow of ultra-lean fuel-air. The jet thus created entrains hot products of combustion and the fuel does not ignite until the jet is very diluted with the hot combustion products. This action lowers peak flame temperatures and N0x production without requiring premixing. Thestagnation zone 38 stabilizes the combustion process under lean conditions and reduces dynamic instabilities.
• An exemplary embodiment of the present invention may employ syngas and hydrogen combustion without the use of diluents. This approach provides a stable combustion zone and reduces dynamics in the system. Reduced combustor cooling is enabled by reduced combustor size and lower peak gas temperatures.
• FIG. 2 is a partial and diagrammatic cross-sectional view of a combustor assembly, in accordance with an exemplary embodiment of the present invention. In the embodiment illustrated in FIG. 2, thefirst air flow 20 and thefirst fuel flow 34 are delivered to thecombustor 14 coaxially via thefirst inlet 22 from the left-hand side of FIG. 2. Thefirst air flow 20 and thefirst fuel flow 34 form a jet that travels across thecombustor 14, entraining hot products from combustion. In the embodiment illustrated in FIG. 2, a second jet of fuel and air comprising the opposingair flow 26 and an opposingfuel flow 42 is desirably premixed and injected into thecombustor 14 via the opposinginlet 28, as shown at the right-hand side of FIG. 2. The premixing of the opposingair flow 26 and the opposingfuel flow 42 may be either full or partial. The opposinginlet 28 may comprise multiple openings in the right-hand side wall.
• In the embodiment illustrated in FIG. 2, thefirst air flow 20 and thefirst fuel flow 34 exhibit a flammability that is greater than the lean flammability limit for the system. The opposingairflow 26 and opposingfuel flow 42 exhibit a flammability that is less than the lean flammability limit. The jet entering the combustor 14 from the left hand side is at a relatively high velocity. A stagnation control pressure p_sc is defined to be the pressure in thecombustion chamber 14 in the region around the entry point of the opposingairflow 26, but prior to the point where the opposingairflow 26 encounters theperforated plate 36. As illustrated in FIG. 2, the stagnation control pressure p_sc is greater than a stagnation zone pressure p_stagnation. Inside thecombustor 14, the flame stabilizes in the stagnation region between the two flows and hot products flow back to the opening on the left hand side, as illustrated by the arrow representing the combustedgas flow 40. In the exemplary embodiment illustrated in FIG. 2, the combustedgas flow 40 exits thecombustion chamber 14 upstream relative to the first direction (as indicated by the arrow 34) from thestagnation zone 38. Moreover, the exit of the combustedgas flow 40 is not coaxial with the first direction (as indicated by the arrow 34) in the exemplary embodiment illustrated in FIG. 2.
• The opposing fuel flow may be provided by a fuel controller (see FIG. 1). The amount and velocity of fuel injected into thecombustor 14 via the opposingfuel flow 42 is desirably variable. It may be controlled in by fluidic means or the like to cause a uniform temperature distribution within thecombustor 14. In fluidic control, an area of a flow, which is proportional to its velocity, is changed by introducing a second flow in the general region such as through the same inlet. In such a manner, the magnitude of the opposingairflow 26 and/or the opposingfuel flow 42 may be adjusted to move the stagnation zone leftward in thecombustion chamber 14. By moving the stagnation zone away from the right-hand side of FIG. 2 in this manner, the temperature of the right-hand wall of thecombustor 14 adjacent to the opposinginlet 28 may be desirably reduced.
• FIG. 3 is a partial and diagrammatic, cross-sectional view of a combustor assembly in accordance with another exemplary embodiment of the present invention. In the exemplary embodiment illustrated in FIG. 3, thefirst fuel flow 34 and opposingfuel flow 42 are omitted for clarity. Thecombustor 14 is disposed at an angle θ relative to the horizontal. Thefirst inlet 22 and the opposinginlet 28 extend outwardly into thecombustion chamber 14.
• The value of θ may be in the range of 0 degrees to 90 degrees depending on design criteria for thecombustor 14. At a θ of 0 degrees, the combustor may extend too far into space to be practical. At a θ value of 90 degrees, escaping gases may have a more direct path to the turbine stages 16.
• FIG. 4 is a partial and diagrammatic, cross-sectional view of a combustor assembly in accordance with yet another exemplary embodiment of the present invention. In the embodiment illustrated in FIG. 4, thefirst airflow 20 enters the combustor 14 from a relatively central location. The combustedgas flow 40 exits the combustor 14 from a radially removed location relative to the position of thefirst inlet 22, as indicated by thearrow 40.
• FIG. 5 is a partial and diagrammatic, cross-sectional view of a combustor assembly in accordance with still another exemplary embodiment of the present invention. In the embodiment illustrated in FIG. 5, thecombustor 14 is connected to the turbine stages (not shown) via ahorn seal 44. Those of ordinary skill in the art will appreciate that thehorn seal 44 facilitates the detachment of thecombustion chamber 14 for maintenance.
• With FIG. 1 in mind, FIG. 6 is a flowchart illustrating an exemplary process for establishing an opposing flow in a combustor in accordance with an exemplary embodiment of the present invention. The process is generally referred to by thereference numeral 44. Atblock 46, a first air flow and a fuel flow are injected into a combustion chamber in a first direction. Atblock 48, an opposing air flow is injected into the combustion chamber in opposition to the first air flow and the fuel flow to form a stagnation zone in the combustion chamber. Further, the first air flow and the fuel flow interact with the opposing air flow to form a vortex flow inside the combustion chamber.
• While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
PARTS LIST

• 10	combustor
  12	Compressor stages
  14	Combustion chamber
  16	Turbine stages
  18	Air flow chamber
  20	First air flow
  22	First inlet
  24	Opposingairflow chamber
  26	Opposingairflow chamber
  28	Opposinginlet
  30	Fuel source
  32	Fuel controller
  34	First fuel flow
  36	Perforated plate
  38	Reaction/combustion zone/stagnation zone
  40	Combusted gas flow
  42	Opposing fuel flow

Claims (10)

1. A combustor (10), comprising:

   a combustion chamber (14);

   a first inlet (22) adapted to provide a first air flow (20) to the combustion chamber (14) in a first direction;

   a fuel controller (32) adapted to provide a fuel flow (34) to the combustion chamber (14) in the first direction;

   an opposing inlet (28) adapted to provide an opposing air flow (26) to the combustion chamber (14) in a second direction generally in opposition to the first direction; and

   wherein the first air flow (20) and the fuel flow (34) interact with the opposing air (26) flow to form a stagnation zone (38) in the combustion chamber (14).
2. The combustor (10) as recited in claim 1, wherein the fuel controller (32) is adapted to provide an opposing fuel flow (42) to the combustion chamber (14) in the second direction.
3. The combustor (10) as recited in claim 2, wherein the opposing air flow (26) and the opposing fuel flow (42) are premixed before being provided to the combustion chamber (14).
4. The combustor (10) as recited in claim 2, wherein the opposing air flow (26) and the opposing fuel flow (42) are partially premixed before being provided to the combustion chamber (14).
5. The combustor (10) as recited in claim 2, wherein the opposing air flow (26) and the opposing fuel flow (42) are fully premixed before being provided to the combustion chamber (14).
6. A method (44) of operating a combustion chamber (14), the method (44) comprising:

   injecting (46) a first air flow (20) and a fuel flow (34) into the combustion chamber (14) in a first direction; and

   injecting (48) an opposing air flow (26) into the combustion chamber (14) in opposition to the first air flow (20) to form a stagnation zone (38) in the combustion chamber (14).
7. The method (44) recited in claim 6, comprising injecting an opposing fuel flow (42) into the combustion chamber (14) in opposition to the first air flow (20).
8. The method (44) recited in claim 7, comprising premixing the opposing air flow (26) and the opposing fuel flow (42).
9. The method (44) recited in claim 7, comprising partially premixing the opposing air flow (26) and the opposing fuel flow (42).
10. The method (44) recited in claim 7, comprising fully premixing the opposing air flow (26) and the opposing fuel flow (42).

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