Patent Application
20060150634
The present invention relates generally to gas turbine combustors and more specifically to an apparatus and method for reducing carbon monoxide emissions from gas turbine combustors.
In recent years government officials have passed more restrictive regulations regarding powerplant emissions, especially those for oxides of nitrogen (NOx) and carbon monoxide (CO). Each of these emissions are well known to contribute to air pollution and regulators continue to set lower levels of acceptable emissions. There are various means to comply with these lower emissions requirements, which vary depending on the powerplant location. Such means include passing the exhaust gases through a catalyst, which serves to transform the carbon monoxide and remaining hydrocarbons into water and carbon dioxide, utilizing lower flame temperature combustors, or limiting the amount of operating time of the powerplant. The latter is the most unfavorable option as it limits the amount of revenue that can be generated. However, the other technologies such as a catalyst and lower flame temperature combustors can be expensive as well.
Complying with environmental requirements is especially a concern when the powerplant is operating at a load point other than its preferred condition. Powerplants are designed to operate most efficiently at the “full-load” condition, that is when they are generating the most power possible, and it is at this condition that they are designed to produce the lowest emissions. However, there are many times when power demand is lower and it is more desirable to operate at a lower power setting, such that only the power demanded is actually supplied, thereby saving on fuel costs. It has been determined that when powerplants operate at conditions other than their most efficient, or design point, emission levels can go out of compliance with local regulations. This is especially true for NOx and CO and the present invention described herein addresses CO emissions reductions. Carbon monoxide from gas turbine combustion systems can typically be caused by a number of factors including inadequate burning rates, inadequate mixing of fuel and air prior to combustion, or quenching of the combustion products in surrounding cooling air. When combustion gases migrate towards a region containing cooler air, the temperature of this air, which is cooler than that of the hot combustion gases, prevents any further chemical reactions from occurring and CO will remain in the exhaust gases.
In order for powerplants to run at lower load conditions, where emission levels can be higher, it is necessary to be able to control the amount of emissions that will result when the combustion system is not operating at its preferred design point. A condition at which higher CO emissions are especially prevalent is at lower power settings. At these lower power settings, the combustion systems are operating at a lower fuel flow and often times burning in a different region than that of the full power condition that may not be as efficient. Therefore, in order to operate a powerplant with reduced CO emissions throughout its operating envelope, it is necessary for the combustion system to be able to provide adequate mixing such that the CO is not quenched and the combustion reactions are completed.
The present invention seeks to overcome the shortcomings of the prior art by providing an apparatus and method of reducing carbon monoxide emissions for a gas turbine combustion system.
The present invention discloses an apparatus and method for reducing the carbon monoxide emissions emitted by a pilot injector of a gas turbine combustor. The pilot injector provides the main flame source for igniting a fuel/air mixture in the combustor and at lower power settings is the only source of hot combustion gases necessary to drive the turbine. The preferred embodiment of the pilot injector comprises a radial swirler, at least one fuel injector, a passageway formed between first and second spaced walls, a means for establishing a recirculation area adjacent to the pilot injector, and a generally annular extension protruding into the combustor thereby providing a region for the CO to burnout prior to interacting with surrounding air flows and becoming quenched. It is in this recirculation area, of lower pressure, that the pilot flame will anchor and burn. As a result, the pilot flame is anchored separate from the main fuel air mixture, which would quench the reaction processing CO emissions from the pilot flame. Furthermore, the pilot flame is anchored further upstream so as to establish a greater residence time in which the pilot flame is to burn and complete the reactions to minimize CO formation.
The present invention will now be described in detail with reference to
Referring to
During typical gas turbine combustor operation, fuel and compressed air are mixed together and the premixture is then ignited to form hot combustion gases to drive a turbine. One measure of combustor, and engine, performance is emissions levels, and more specifically, carbon monoxide (CO) levels. One skilled in the art of gas turbine combustion will understand that CO formation is a multi-step process of breaking down the carbon molecules in the fuel. More specifically, high temperatures, concentrations of O2, and large residence times are required for CO oxidation. However, this multi-step process can be interrupted by a quenching effect due to the combustor design. That is, the remaining oxygen atoms designed to react with the CO molecules to complete the reaction and form CO2 are quenched or cooled prematurely. This typically occurs in regions where additional cooling air is mixed into the process. A means to ensure that this combustion process is completed, despite the addition of potential quenching effects, is to provide a mechanism for increasing the time in which CO is consumed. The present invention provides this mechanism.
In operation, air under pressure passes around the outside of liner 13 and is directed towards inlet 19. The air then passes through radial swirler 15 and mixes with a fuel from first injector 22. The fuel and air mixture is then directed through passageway 18 and towards outlet 20. Additional fuel may be provided from a second injector 23, as shown in the preferred embodiment in
A first alternate embodiment of the present invention is shown in
A second alternate embodiment of the present invention is shown in
While the invention has been described in what is known as presently the preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment but, on the contrary, is intended to cover various modifications and equivalent arrangements within the scope of the following claims.
