Patent Application
20120312890
The present disclosure generally relates to a fuel nozzle for a gas turbine, and more particularly relates to a fuel nozzle with swirling vanes.
A gas turbine generally includes a compressor, a combustion system, and a turbine section. Within the combustion system, air and fuel are combusted to generate a heated gas. The heated gas is then expanded in the turbine section to drive a load.
Historically, combustion systems employed diffusion combustors. In a diffusion combustor, fuel is diffused directly into the combustor where it mixes with air and is burned. Although efficient, diffusion combustors are operated at high peak temperatures, which creates relatively high levels of pollutants such as nitrous oxide (NOx).
To reduce the level of NOx resulting from the combustion process, dry low NOx combustion systems have been developed. These combustion systems pre-mix air and fuel to create a relatively lean air-fuel mixture that is combusted at relatively lower temperatures, generating relatively lower levels of NOx.
One problem with dry low NOx combustion is flame instability. Leaner air-fuel mixtures and lower temperatures tend to weaken and destabilize the flame. The flame may detach from its anchor point within the combustor, resulting in flameout. From the above, it is apparent that a need exists for a dry low NOx combustion system that exhibits improved flame stability, so that NOx emissions can be lowered without the corresponding risk of flameout.
A fuel nozzle includes a swirler and a fuel injector positioned upstream from the swirler. The swirler includes an inner hub, an intermediate dividing wall, an outer shroud, a number of inner swirling vanes, and a number of outer swirling vanes. The intermediate dividing wall is concentrically positioned about the inner hub. The outer shroud is concentrically positioned about the intermediate dividing wall. Each inner swirling vane extends between the inner hub and the intermediate dividing wall, and each outer swirling vane extends between the intermediate dividing wall and the outer shroud.
Other systems, devices, methods, features, and advantages of the disclosed fuel nozzle will be apparent or will become apparent to one with skill in the art upon examination of the following figures and detailed description. All such additional systems, devices, methods, features, and advantages are intended to be included within the description and are intended to be protected by the accompanying claims.
The present disclosure may be better understood with reference to the following figures. Matching reference numerals designate corresponding parts throughout the figures, and components in the figures are not necessarily to scale.
Described below are embodiments of a fuel nozzle that improves flame stability within a combustor. The flame stability nozzle generally includes two sets of swirling vanes that are concentrically positioned with reference to each other. The vanes may cause an air-fuel mixture exiting the nozzle to develop a shear layer within the mixture, anchoring the flame within the combustor. The vanes also may increase the swirl of the air-fuel mixture, strengthening the recirculation zone along a centerline of the fuel nozzle where the flame tends to anchor. Increased flame instability may result, which permits optimizing the combustor for reduced NOx generation without the corresponding risk of flameout. For example, the combustor may be operated with leaner air-fuel mixtures or at lower temperatures.
An embodiment of a combustor is shown in
Although only one combustor 100 is shown in
In some embodiments, the combustor 100 is a dual-mode combustor having a first chamber and a second chamber. The first chamber may receive air and fuel through a number of primary fuel nozzles, and the second chamber may receive air and fuel through a secondary fuel nozzle. The combustor can be operated in diffusion and pre-mixing modes, as described in U.S. Pat. No. 4,292,801. In other embodiments, the combustor 100 is a single-mode combustor having one chamber, which is typically operated in a pre-mixing mode. In such embodiments, the one chamber receives air and fuel through fuel nozzles positioned about the combustor.
The flame stability nozzle described herein can be employed in either a single-mode combustor or a dual-mode combustor, as either a primary fuel nozzle or a secondary fuel nozzle. In
Turning to
Upstream from the swirler 110, a fuel provider 118 is positioned in the internal passageway 108. The fuel provider 118 communicates fuel into the internal passageway 108 from a fuel source. For example, the fuel provider 118 may be a fuel peg as shown, although other suitable structures can be employed. The fuel provider 118 may be positioned upstream from the swirler 110 so that a mixing area 119 is defined therebetween. Providing the mixing area 119 upstream of the swirler 110 facilitates stabilizing the flame closer to the swirler 110 with reduced thermal stress on the nozzle body 106. Also, because the fuel is provided upstream of the vanes, the vanes may be solid, as the vanes need not have hollow interiors that define fuel plenums.
In operation, a flow of air is directed along the flame stability nozzle 102 through the interior passageway 108. As the flow of air passes the fuel provider 118, fuel is injected into the flow of air. As the air and fuel travel forward through the mixing area, the air and fuel mix to create an air/fuel flow 120. Upon reaching the swirler 110, the air/fuel flow 120 is separated by the dividing wall 116 into an inner air/fuel flow 122 and an outer air/fuel flow 124. The inner air/fuel flow 122 is turned by the inner set of swirling vanes 112, and the outer air/fuel flow 124 is turned by the outer swirling vanes 114. The inner and outer air/fuel flows 122, 124 then travel downstream of the swirler 110 forward toward the chamber.
Swirling the inner and outer air/fuel flows separately improves flame stability in the combustor. A low velocity region may be created between the flows, and the low velocity region may hold the flame. For example, at any given circumferential location about the swirler 110, the inner air/fuel flow 122 exiting the inner vanes 112 may have a different angular velocity or momentum than the outer air/fuel flow 124 exiting the outer vanes 114, resulting in the development of a shear layer 126 between the two flows. The shear layer 126 acts as a flame anchor point in the flow, increasing the stability of the flame. The inner air/fuel flow 122 also may exhibit increased swirl in comparison to than the outer air/fuel flow 124, such as in embodiments in which the inner swirling vanes 112 have a higher angle of incidence than the outer swirling vanes 124, creating a stronger recirculation zone 128 near the centerline of the fuel nozzle 102. The strengthened recirculation zone 128 facilitates flame stability on the centerline, where the flame tends to anchor.
Mixing the air and fuel upstream of the swirler 110 facilitates maintaining the flame relatively close to the swirler 110 with reduced thermal distress on the burner tube 106. The technical effect is that the stability of the flame is improved without a corresponding increase in undesirable flame holding. This result would not be achieved in a swozzle having fueled vanes, which requires a mixing area disposed downstream from the swirler.
To achieve these results, the inner and outer swirling vanes can have a variety of configurations. The inner vanes may rotate in the same direction as the outer vanes, or in a different direction. The inner vanes and the outer vanes may have the same angle of incidence with reference to the passing flow, or the inner and outer vanes may have different angles of incidence. The inner vanes also may align with the outer vanes, such as along their leading edges, or the inner vanes may be staggered with reference to the outer vanes. Examples configurations are described below.
The swirler 600 creates inner and outer flows that oppose each other, resulting in a shear layer between the flows that promotes flame holding. The interaction between the inner and outer flows can be controlled by varying the difference between the swirl angles, the interaction increasing with greater differences in swirl angle. The interaction between the inner and outer vanes also can be controlled by varying the stagger of the vanes, which varies the stagger of the velocity profiles between the inner and outer flow, creating another area of flow interaction. Even if the inner and outer vanes have the same swirl angle, the flows have different momentums due to the offset velocity profiles, providing potential flame attachment points.
Any of the swirlers described with reference to
The fuel stability nozzle described herein facilitates flame stability, which enables operating the combustor in a manner that reduces NOx generation. For example, the combustor may employ a leaner air-fuel mixture or reduced temperatures with reduced occurrences of flameout.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
