Patent Application
20070101725
This application relates generally to gas turbine engines and, more particularly, to methods and apparatus for injecting fluids into turbine engines.
Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. These same standards have caused turbine engine manufacturers to design more efficient engines, as well as design improved retrofit components that enable engines to operate more efficiently, with improved emissions, and/or with extended useful life and reliability. Moreover, the generally high capital costs associated with the purchase and maintenance of turbine engines, such as revenue losses generated during engine outages, have caused the same engine manufacturers to attempt to design engines that are more reliable and that have extended useful life.
Controlling the mixture of fluids, i.e. gas and steam, delivered to a gas turbine engine may be critical to the engine's performance. Typically, gas turbine engines operating with gas and steam do not meet emissions requirements at all operating conditions, and in particular, such engines generally do not satisfy carbon monoxide (CO) emission requirements as well as other known engines. For example, at least some known gas turbine engines utilizing gas and steam generate higher CO emissions than gas turbine engines utilizing gas and water. More specifically poor mixing of the gas and steam may cause fuel to remain inboard, leading to higher CO emissions being generated. Moreover, poor mixing may cause the recirculation stability zone within the combustor to be shifted downstream, which may cause the flame to become detached, resulting in the generation of CO emissions.
In one aspect, a method of operating a gas turbine engine is provided. The method comprises supplying primary fuel to a chamber within a nozzle, supplying steam to the chamber, and mixing the primary fuel and steam in the chamber prior to discharging the mixture into the combustor from at least one outlet spaced circumferentially around, and extending outward from, a centerline extending through the nozzle.
In another aspect, a nozzle tip for a turbine engine fuel nozzle is provided. The tip includes an annular body including two chambers, at least one pilot fuel outlet, and at least one fuel mixture outlet. The at least one pilot fuel outlet is configured to discharge pilot fuel from one of the two chambers within the fuel nozzle tip. The at least one fuel mixture outlet is configured to discharge a mixture of primary fuel and steam from the second chamber of the fuel nozzle tip. The second chamber is configured to pre-mix the primary fuel and steam prior to discharging the mixture from the fuel nozzle tip.
In a further aspect, a gas turbine engine is provided. The gas turbine engine includes a combustor and a fuel nozzle including a fuel nozzle tip. The fuel nozzle tip includes an annular body including two chambers, at least one pilot fuel outlet, and at least one fuel mixture outlet. The at least one pilot fuel outlet is configured to discharge pilot fuel to the combustor only during pre-selected engine operations. The at least one fuel outlet is configured to release a mixture of primary fuel and steam into the combustor when more power is demanded by the gas turbine engine.
In operation, air flows through low pressure compressor 12 supplying compressed air from low pressure compressor 12 to high pressure compressor 14. The highly compressed air is delivered to combustor 16. Airflow from combustor 16 is channeled through a turbine nozzle to drive turbines 18 and 20, prior to exiting gas turbine engine 10 through an exhaust nozzle 24. As is known in the art, gas turbine engines further include fuel nozzles (not shown) which supply fuel to the combustor 16.
In the exemplary embodiment, pilot fuel outlets 102 are oriented obliquely with respect to centerline 114 extending through nozzle tip 100. As such, pilot fuel discharged from outlets 102 is expelled outward from tip 100 at an oblique angle θ away from centerline 114 and toward fuel mixture being discharged from fuel mixture outlets 104. In the exemplary embodiment, nozzle tip 100 includes four pilot fuel outlets 102. In alternative embodiments, nozzle tip 100 includes more or less then four pilot fuel outlets 102. As will be appreciated by one of ordinary skill in the art, the number of pilot fuel outlets 102 varies depending on the application of fuel nozzle tip 100.
Fuel mixture outlets 104 are spaced circumferentially around, and radially outward from, pilot fuel outlets 102. Furthermore, fuel mixture outlets 104 are configured to discharge a fuel/steam mixture from a chamber 160 (shown in
During operation pilot outlets 102 discharge pilot fuel into the combustor during start up or idle operations of the gas turbine engine. When additional power is demanded, primary fuel and steam are mixed within chamber 160 and discharged through fuel mixture outlet 104 into a combustion zone defined in the combustor of a gas turbine engine. Because primary fuel and steam are mixed prior to being discharged into the combustion zone, the lean mixture provides lower emissions than a non-premixed nozzle tip. Accordingly, the enhanced mixing of primary fuel and steam within nozzle tip 100 facilitates maintaining a more stable flame within the combustion zone defined in the combustor. Generally, controlling the stability of the flame facilitates reducing generation of CO emissions within the combustor.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.
The above described fuel nozzle tip for a gas turbine engine provides an engine capable of meeting emissions standards. The fuel nozzle tip includes a chamber wherein the primary fuel and steam can be premixed before being discharged into the combustor. As a result, a more stable flame is maintained with the combustion zone defined with the combustor, which facilitates reducing the generation of CO emissions.
Although the methods and systems described herein are described in the context of supplying fuel to a gas turbine engine, it is understood that the fuel nozzle tip methods and systems described herein are not limited to gas turbine engines. Likewise, the fuel nozzle tip components illustrated are not limited to the specific embodiments described herein, but rather, components of the fuel nozzle tip can be utilized independently and separately from other components described herein.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
