Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1999-02-19
2001-02-27
Thorpe, Timothy S. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C060S733000, C060S738000, C060S739000, C060S746000
Reexamination Certificate
active
06192688
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to gas and liquid fuel turbines and, more specifically, to combustors in industrial gas turbines used in power generation plants.
Gas turbine manufacturers, including General Electric, are currently involved in research and engineering programs to produce new gas turbines that will operate at high efficiency without producing undesirable air polluting emissions. The primary air polluting emissions usually produced by gas turbines burning conventional hydrocarbon fuels are oxides of nitrogen, carbon monoxide and unburned hydrocarbons. It is well known in the art that oxidation of molecular nitrogen in air breathing engines is highly dependent upon the maximum hot gas temperature in the combustion system reaction zone and the residence time for the reactants at the highest temperatures reached within the combustor. The level of thermal NOx formation is minimized by maintaining the reaction zone temperature below the level at which thermal NOx is formed or by maintaining an extremely short residence time at high temperature such that there is insufficient time for the NOx formation reactions to progress.
One preferred method of controlling the temperature of the reaction zone of a heat engine combustor below the level at which thermal NOx is formed is to premix fuel and air to a lean mixture prior to combustion. U.S. Pat. No. 4,292,801 dated October 1981, the disclosure of which is hereby incorporated by reference, describes a dual stage-dual mode low NOx combustor for gas turbine application which is one of the pioneering combustor designs based on lean premixed combustion technology. U.S. Pat. No. 5,259,184 dated November 1993, the disclosure of which is also hereby incorporated by reference, describes a dry low NOx single stage dual mode combustor construction for a gas turbine. The thermal mass of the excess air present in the reaction zone of a lean premixed combustor absorbs heat and reduces the temperature rise of the products of combustion to a level where thermal NOx is not formed. Even with this technology, for the most advanced high efficiency heavy duty industrial gas turbines, the required temperature of the products of combustion at the combustor exit/first stage turbine inlet at maximum load is so high that the combustor must be operated with peak gas temperature in the reaction zone which exceeds the thermal NOx formation threshold temperature resulting in significant NOx formation even though the fuel and air are premixed lean. The problem to be solved is to obtain combustor exit temperatures high enough to operate the most advanced, high efficiency heavy duty industrial gas turbines at maximum load without forming a significant amount of thermal NOx.
Lean premixed combustion of hydrocarbon fuels in air is widely used throughout the gas turbine industry as a method of reducing air pollutant levels, in particular thermal NOx emissions levels, for gas turbine combustors. Lean direct injection (LDI) of hydrocarbon fuel and air has also been shown to be an effective method for reducing NOx emission levels for gas turbine combustion systems although not as effective as lean premixed combustion. An example of an LDI fuel injector assembly is described in an article from the 1987 Tokyo International Gas Turbine Congress entitled “Lean Primary Zones: Pressure Loss and Residence Time Influences on Combustion Performance and NOx Emissions,” the disclosure of which is hereby incorporated by reference. The present invention combines these two technologies; i.e., lean premixed combustion and lean direct fuel injection, in a novel and unique manner in order to achieve extremely low air pollutant emissions levels, particularly oxides of nitrogen, when operating an advanced, high efficiency, heavy duty industrial gas turbine at high load.
BRIEF SUMMARY OF THE INVENTION
There is thus a particular need to combine premixed combustion of a lean mixture of hydrocarbon fuel and air with lean direct injection of hydrocarbon fuel and a carrier fluid such as air or inert gas or a mixture of air and inert gas into the products of lean premixed combustion late in the combustion process, and thereby produce a combustion system that will yield very low emissions of air pollutants, in particular oxides of nitrogen, when operating an advanced, high efficiency, heavy duty industrial gas turbine at high load. Moreover, this invention is intended to accomplish this objective while operating the premixed combustion reaction zone with a fuel/air mixture that is lean enough to ensure that the thermal NOx formation in the reaction zone is negligible and while operating the entire combustion system at an overall fuel/air mixture strength that exceeds that of the premixed reaction zone by the amount necessary to meet the inlet temperature demands of the gas turbine. This invention is particularly advantageous in applications where the inlet temperature demands of the turbines are so high as to preclude the possibility of achieving very low thermal NOx emissions levels by lean premixed combustion alone.
These and other advantages are achieved by providing a combustor for a gas turbine including a primary combustion system operable in a plurality of gas turbine modes, the gas turbine modes being determined based on a load range on the gas turbine, and a secondary combustion system selectively operable in a high load range mode of the plurality of gas turbine modes.
The combustor may further be provided with a combustor casing having an open end and an end cover assembly secured to another end thereof, a flow sleeve mounted within the casing, and a combustion liner within the flow sleeve and defining at least a primary reaction zone. The primary combustion system preferably includes a sleeve cap assembly secured to the casing and located axially downstream of the end cover assembly, and at least one start up fuel nozzle and premixing fuel nozzles communicating with the primary reaction zone. In this regard, each premixing fuel nozzle preferably includes a swirler including a plurality of swirl vanes that impart rotation to entering air, and a plurality of fuel spokes that distribute fuel in the rotating air stream. The combustion liner may also define a secondary reaction zone downstream of the primary reaction zone. In this context, the secondary combustion system includes a lean direct injection (LDI) fuel injector assembly communicating with the secondary reaction zone. The LDI fuel injector assembly preferably includes an air manifold, a fuel manifold, and a plurality of fuel/air injection spokes communicating with the air manifold and the fuel manifold. The plurality of fuel/air injection spokes penetrate the combustion liner and introduce fuel and carrier fluid into the secondary reaction zone.
In accordance with another aspect of the invention, there is provided a gas turbine including a compressor section that pressurizes inlet air, a combustion section disposed downstream of the compressor section that receives the pressurized inlet air, and a turbine section disposed downstream of the combustion section and receiving hot products of combustion from the combustion section. The combustion section includes a circular array of circumferentially spaced combustors according to the invention.
In accordance with still another aspect of the invention, there is provided a method of combustion in a gas turbine combustor according to the invention. The method includes the steps of (a) in a low range turbine load mode, supplying fuel to start up fuel nozzles and mixing the fuel with air in a primary reaction zone, (b) in a mid-range turbine load mode, supplying fuel to premixing fuel nozzles and premixing the fuel with air prior to entering the primary reaction zone, and (c) in a high-range turbine load mode, carrying out step (b) and then supplying secondary fuel and carrier fluid to a secondary combustion system and introducing fuel and carrier fluid into a secondary reaction zone.
REFERENCES:
patent: 2944388 (1960-07-01), Bayer
patent: 3934409 (1976-01
General Electric Co.
Nixon & Vanderhye
Thorpe Timothy S.
Tyler Cheryl J.
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