Patent Application
20120085834
The invention relates to a combustor fuel nozzle and, more particularly, to a combustor fuel nozzle including features to reduce flame holding risk inside primary fuel nozzle vanes on high reactivity low wobbe fuel operation.
Gas turbines are widely used in commercial operations for power generation.
During full speed base load operations, the flow rate of the fuel and compressed working fluid mixture through the primary 28 and secondary 30 nozzles is sufficiently high so that combustion occurs only in the downstream chamber 36. During reduced power operations, however, the primary nozzles 28 operate in a diffusion mode in which the flow rate of the fuel and compressed working fluid mixture from the primary nozzles 28 is reduced so that combustion of the fuel and the compressed working fluid mixture from the primary nozzles 28 occurs in the upstream chamber 34.
Lower reactivity fuels, such as natural gas, typically have lower flame speeds. Due to lower natural gas flame speed, the flow rate of the fuel and compressed working mixture from the primary nozzles 28 operated in diffusion mode is sufficiently high so that combustion in the upstream chamber 34 occurs at a sufficient distance from the primary nozzles 28 to prevent the combustion from excessively heating and/or melting the primary nozzles 28. However, higher reactivity fuels, such as synthetic gas, hydrogen, carbon monoxide, ethane, butane, propane, or mixtures of higher reactivity hydrocarbons, typically have higher flame speeds. Increased flame speed of the higher reactivity fuels moves the combustion in the upstream chamber 34 closer to the primary nozzles 28. Local flame temperature under diffusion mode operation in the upstream chamber 34 can be much greater than the melting point of the primary nozzle 28 materials. As a result, primary nozzles 28 operated in diffusion mode may experience excessive heating, resulting in premature and/or catastrophic failure.
Fuel ports are typically located between vanes to inject the fuel between the vanes into the incoming air. The space between the vanes is limited, and on high reactivity fuels, during diffusion mode operation, there are increased chances of flame holding in the fuel jets that can cause damage to the nozzles, thereby limiting the fuel flexibility of the combustion system.
In an exemplary embodiment, a fuel nozzle includes a nozzle cavity with a side wall and a front wall defining an annular cavity, and swirler vanes arranged circumferentially around an outer surface of the nozzle cavity. A plurality of ports are formed in one of the side wall and the front wall and are circumferentially spaced therearound. The plurality of ports provide fluid communication through the side wall or the front wall. The plurality of ports are at least one of positioned or oriented such that fuel jets defined in and communicated through the side wall or the front wall are communicated downstream of the swirler vanes.
In another exemplary embodiment, a fuel nozzle includes a nozzle cavity with a side wall defining an annular cavity, where the side wall is tapered such that the nozzle cavity is part-conical shaped. Swirler vanes are arranged circumferentially around an outer surface of the nozzle cavity. A plurality of ports are formed in the side wall and are circumferentially spaced therearound. The plurality of ports provide fluid communication through the side wall. The plurality of ports are oriented at an angle that is greater than 90° in an axial direction relative to the side wall.
In yet another exemplary embodiment, a method of reducing flame holding risk inside primary fuel nozzle vanes includes the steps of (a) forming a nozzle cavity including a side wall and defining an annular cavity; (b) arranging swirler vanes circumferentially around an outer surface of the nozzle cavity; and (c) forming a plurality of ports in the side wall and circumferentially spaced therearound, the plurality of ports providing fluid communication through the side wall, where the plurality of ports are at least one of positioned or oriented such that fuel jets defined in and communicated through the side wall are communicated downstream of the swirler vanes.
Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention.
The nozzle body 42 includes a side wall 52 that defines a shape of the annular cavity 44. A plurality of orifices 58 or ports are formed in the side wall 52 and are circumferentially spaced around the side wall 52 to provide fluid communication through the side wall 52.
In the conventional construction, fuel in the annular cavity 44 is ejected via orifices 58 to mix with the air in the swirler vanes 46 (see arrows A and B in
With reference to
An alternative construction is shown in
The ports 258, 358 may still further be oriented with a compound angle such that the fuel jets are communicated downstream of the swirler vanes 246, 346 and radially inward or outward. The compound angle promotes better mixing of the fuel and air prior to combustion.
The sidewall 152, 252, 352 is preferably tapered such that the nozzle cavity 144, 244, 344 is part-conical shaped. In the embodiment shown in
With the structure of the described embodiments, fuel jets are communicated downstream of swirler vanes to thereby reduce flame holding risk that can lead to hardware damage. The redirected fuel jets also reduce air blockage caused due to penetration of fuel jets, allowing more air for premixing. That is, as the fuel is injected outside of the swirler vanes, particularly for low wobbe fuels, the structure poses less blockage to the incoming swirler air intended for premixing. Air flow can also be reduced for very low reactivity wobbe fuels to allow more space for the fuel injection ports.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
