Patent Application
20120167586
The invention relates generally to gas turbines and, more particularly, to a fuel nozzle for a gas turbine engine including a cooling circuit that utilizes passive purge flow for fuel nozzle tips supplied from end cap cooling flow before quat fuel injection.
Conventional quat fuel injection systems utilize CdC air mixed with quat fuel for passive purge feeds. The presence of fuel in the passive purge feed elevates a risk of flame holding in the passive purge cavities and within the fuel nozzle tips. It would be desirable to use the end cap purge feed that is free of quat fuel to provide an alternate means to purge the fuel nozzle tips and eliminate the flame holding risk from the design.
In an exemplary embodiment, a cooling circuit for a fuel nozzle in a gas turbine includes an annulus receiving compressor discharge air, a quat cap including a fuel passage through which quat fuel is injected toward the fuel nozzle, and an air passage formed in the quat cap and receiving the compressor discharge air from the annulus. The air passage is positioned upstream of the fuel passage such that the compressor discharge air is not mixed with quat fuel. Purge passages in the fuel nozzle receive the compressor discharge air from the air passage. The purge passages direct the compressor discharge air to the fuel nozzle for tip cooling.
In another exemplary embodiment, a method of cooling a fuel nozzle in a gas turbine includes the steps of (a) receiving compressor discharge air in an annulus; b) directing the compressor discharge air from the annulus to an air passage formed in a quat cap, where the air passage is positioned upstream of a quat fuel passage such that the compressor discharge air in the air passage is not mixed with quat fuel; and (c) receiving the compressor discharge air from the air passage in purge passages in the fuel nozzle, the purge passages directing the compressor discharge air to the fuel nozzle for tip cooling.
In yet another exemplary embodiment, a cooling circuit for a fuel nozzle in a gas turbine includes an end cap cavity receiving passive purge flow from a compressor of the turbine, and fuel nozzle swozzles disposed in a swozzle shroud that impart swirl to incoming fuel and air. Purge slots are formed in the swozzle shroud and through the fuel nozzle swozzles in fluid communication with the end cap cavity. The purge slots are positioned upstream of a quat fuel injection passage, and the passive purge flow enters fuel nozzle tip cavities of the fuel nozzle to provide tip cooling and tip purge volume without mixing the passive purge flow with quat fuel.
A casing surrounds each combustor 14 to contain the compressed working fluid from the compressor 12. Nozzles are arranged in an end cover, for example, with outer nozzles radially arranged around a center nozzle. The compressed working fluid from the compressor 12 flows between the casing and a liner to the outer and center nozzles, which mix fuel with the compressed working fluid, and the mixture flows from the outer and center nozzles into upstream and downstream chambers where combustion occurs.
As noted, prior designs have used quat mixed CdC air to feed passive purge for fuel nozzle tips. The presence of fuel in the passive purge feed, however, elevates a risk of flame holding in the passive purge cavities and within the fuel nozzle tips. With reference to
The cooling circuit 20 includes an air passage 30 formed in the quat cap 26 that receives the compressor discharge air from the annulus 24. As shown in
As shown, the purge passages 32 are formed in the swozzle assembly 28. Preferably, the purge passages 32 comprise slots formed in the swozzle 28.
In a typical construction, the combustor includes several outer nozzles circumferentially surrounding a center nozzle.
With continued reference to
The flow path of the compressor discharge air is shown by arrows in
With the described embodiments, the fuel nozzle swozzles have purge slots on the outside of the swozzle shroud to allow passive purge cooling air from the end cap cavity to enter into the fuel nozzle tip cavities and provide tip cooling and tip purge volume. The cap feed air is before quat injection, thereby reducing or eliminating the risk of a flame holding event caused by passive purge air mixed with fuel in prior designs.
The added purge slots eliminate the need to provide purge air from the end cover side of the combustion chamber for cooling, this air typically has been mixed with fuel. Additionally, the purge slots simplify the design, eliminating a need to take a feeder pipe in the compressor discharge circuits and feed each end cover on the back end, which would require additional circuitry to direct air to the nozzles. The design still further reduces the fuel nozzle complexity by simplifying the number of fluid circuits required at the flange interface allowing for improved durability and lower cost.
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.
