Patent Application
20120011855
The present invention relates to operation of a combustor apparatus in a gas turbine engine.
Gas turbine power plant operators are often faced with an economic dilemma of whether or not to operate their plants during low power demand times. By operating continuously, the plant will be available to quickly produce base load power when the power demand becomes high. The plant maintenance cost will also be reduced with fewer plant starts and stops. However, operation during these low power demand times often results in negative profit margins, or losses, for the plant operator because the low cost of power does not offset the cost of fuel.
The logical solution for the plants that choose to operate continuously is to minimize the losses by minimizing fuel consumption during operation at minimum power demand. Industrial gas turbine engines are designed to operate at a constant design turbine inlet temperature under any ambient air temperature (i.e., the compressor inlet temperature). This design turbine inlet temperature allows the engine to produce maximum possible power, known as base load or a full load operating mode. Any reduction from the maximum possible base load power, such during a plant turn down, is referred to as a part load operating mode. That is, part load entails all engine operation from 0% to 99.9% of base load power. However, operation of the plant is restricted by its exhaust gas emissions permit. Since emissions such as nitrous oxides (NOx) and carbon monoxide (CO) typically increase on a volumetric basis as the gas turbine power decreases, this limits how much the plant can turn down, or reduce power, during the low power demand times.
In particular, part load operation may result in the production of high levels of carbon monoxide (CO) during combustion. One known method for reducing part load CO emissions is to bring the combustor exit temperature or the turbine inlet temperature near that of the base load design temperature. It should be noted that, for purposes of this disclosure, the terms combustor exit temperature and turbine inlet temperature are used interchangeably. In actuality, there can be from about 30 to about 80 degrees Fahrenheit difference between these two temperatures due to, among other things, cooling and leakage effects occurring at the transition/turbine junction. However, with respect to aspects of the present invention, this temperature difference is insubstantial.
To bring the combustor exit temperature closer to the base load design temperature, the mass flow of air through a turbine engine can be restricted by closing compressor inlet guide vanes (IGV), which act as a throttle at the inlet of a compressor for the gas turbine engine. When the IGVs are closed, the trailing edges of each of the vanes rotate closer to the surface of an adjacent vane, thereby effectively reducing the available throat area. Reducing the throat area reduces the flow of air which the first row of rotating blades can draw into the compressor. Lower flow to the compressor leads to a lower compressor pressure ratio being established in the turbine section of the engine. Consequently, the compressor exit temperature decreases because the compressor does not input as much energy into the incoming air. Also, the mass flow of air through the turbine decreases, and the combustor exit temperature increases.
While controlling emissions during plant turn down is effectively controlled by closing the IGVs, this has limited capability. Constant speed compressors, such as those used for industrial gas turbines, have limitations on the amount that the mass air flow into the compressor may be reduced using the IGVs before running into structural and/or aerodynamic issues. Further, CO emissions increase rapidly as gas turbine engine load is reduced below approximately 60%. Once the IGVs have been closed to their limit, and the engine's exhaust temperature limit has been reached, then power typically may be reduced only by decreasing turbine inlet temperature. Turbine inlet temperature reduction corresponds to a decrease in the combustion system's primary zone temperature, resulting in CO and unburned hydrocarbons (UHC) being produced due to quenching of the combustion reactions in the turbine hot gas path.
In accordance with a first embodiment of the present invention, a method is provided of operating a combustor apparatus in a turbine engine. The method comprises transitioning from a first operating mode to a second operating mode corresponding to a lesser load than the first operating mode. An amount of fuel provided to a primary fuel injection system of the combustor apparatus is reduced, wherein the primary fuel injection system provides fuel to a main combustion zone. An amount of fuel provided to a secondary fuel/air injection system of the combustor apparatus is reduced, wherein the secondary fuel/air injection system provides fuel to a secondary combustion zone downstream from the main combustion zone. A total amount of air provided to the combustor apparatus is reduced, wherein a first portion of the air is provided to the primary fuel injection system and a second portion of the air is provided to the secondary fuel/air injection system. Upon reaching operating parameters corresponding to the second operating mode, the amount of fuel provided to the primary fuel injection system is increased, the amount of fuel provided to the secondary fuel/air injection system is reduced to a predetermined value, and the total amount of air provided to the combustor apparatus is increased.
In accordance with a second embodiment of the invention, a method is provided of operating a combustor apparatus in a turbine engine. The method comprises transitioning from a full load operating mode to a part load operating mode. An amount of fuel provided to a primary fuel injection system of the combustor apparatus is reduced, wherein the primary fuel injection system provides fuel to a main combustion zone. An amount of fuel provided to a secondary fuel/air injection system of the combustor apparatus is reduced, wherein the secondary fuel/air injection system provides fuel to a secondary combustion zone downstream from the main combustion zone. A total amount of air provided to the combustor apparatus is reduced, wherein a first portion of the air is provided to the primary fuel injection system and a second portion of the air is provided to the secondary fuel/air injection system, and wherein the second portion of air is distributed to the secondary combustion zone via at least one outlet of the secondary fuel/air injection system located at the secondary combustion zone. Upon reaching operating parameters corresponding to the part load operating mode, the amount of fuel provided to the primary fuel injection system is increased, the amount of fuel provided to the secondary fuel/air injection system is reduced to a predetermined value, and the total amount of air provided to the combustor apparatus is increased.
While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein:
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, specific preferred embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention.
Referring to
The combustion section 14 includes a combustor shell 28 for receiving the compressed air from the compressor section 12, also known as combustor shell air, and one or more combustor apparatuses 30 for receiving and mixing fuel with the combustor shell air and igniting the air/fuel mixture(s) to produce hot working gases, also known as combustion gas.
The combustion gas flows out of the combustion section 14 to the turbine section 16 via a transition section 32 comprising a transition duct 32A (see
As noted above, the combustion section 14 may comprise one or more combustor apparatuses 30. According to one aspect of the invention, the combustion section 14 comprises a plurality of combustor apparatuses 30 spaced circumferentially apart about the turbine rotor 34. Referring to
The combustor apparatus 30 comprises a combustor casing 60, a liner 64 coupled to a cover plate 66 via a plurality of liner support structures 68, a primary fuel injection system 70, also referred to herein as a first fuel injection system, a secondary fuel/air injection system 72, also referred to herein as a second fuel injection system, and the corresponding transition duct 32A.
In the illustrated embodiment, an annular gap 80 is formed between the combustor casing 60 and the liner 64. Compressed air supplied from the compressor section 12 to the combustor shell 28 enters the combustor apparatus 30 through the annular gap 80. As the compressed air approaches the cover plate 66, it turns 180 degrees and flows toward a main combustion zone 82 defined by a portion of the liner 64. As will be described in detail herein, a first portion of this compressed air is delivered to the primary fuel injection system 70 and a second portion of this compressed air is delivered to the secondary fuel/air injection system 72.
As shown in
A base plate 90, illustrated in
In the embodiment shown, the secondary fuel/air injection system 72 comprises a plurality of fuel/air passages 92 extending axially from the base plate 90 through the main combustion zone 82 to a secondary combustion zone 94 located downstream from the main combustion zone 82 see
Referring to
The fuel/air passages 92 of the secondary fuel/air injection system 72 include fuel supply tubes 93, illustrated in
The fuel/air passages 92 also receive the second portion of the compressed air via corresponding openings 95 (see
As noted above, the fuel/air passages 92 are schematically shown in
A method of operating a combustor apparatus, such as the combustor apparatus 30 described above with reference to
According to one aspect of the invention, during full load operating mode of the engine 10, fuel is delivered to both the primary fuel injection system 70 and the secondary fuel/air injection system 72 and air is delivered to the combustor apparatus 30 according to the graphs illustrated in
The engine 10 is transitioned from the full load operating mode 200 to a part load operating mode, also referred to as a second operating mode and corresponding to, for example, about 50-70% load of the engine 10. The part load operating mode corresponds to a lesser load than the full load operating mode 200. Part load operating mode is designated by the reference number 202 in
During the transition from the full load operating mode 200 to the part load operating mode 202, the amount of fuel provided to both the primary fuel injection system 70 and the secondary fuel/air injection system 72 is concurrently decreased, i.e., from point 100 to point a 120 lower than the third amount of fuel 110 for the primary fuel injection system 70 and from point 102 to a point 122 greater than the fourth amount of fuel 112 for the secondary fuel/air injection system 72. The amount of fuel provided to the primary fuel injection system 70 and the secondary fuel/air injection system 72 is continuously decreased, such as corresponding linear decreases with a decreasing load as depicted by the graph shown in
Concurrently with reducing the amount of fuel provided to both the primary fuel injection system 70 and the secondary fuel/air injection system 72 during the transition from the full load operating mode 200 to the part load operating mode 202, a total amount of air provided to the combustion section 14 and therefore to the combustor apparatus 30 is reduced i.e., from point 104 to a point 124 lower than the second amount of air 114 in
Upon reaching the operating parameters corresponding to the part load operating mode 202, the amount of fuel provided to the primary fuel injection system 70 is increased, as depicted by point 110 in
Also upon reaching the operating parameters corresponding to the part load operating mode 202, the total amount of air provided to the combustor apparatus 30 is increased, as depicted by point 114 in
According to another aspect of the invention, the engine 10 may be transitioned from the part load operating mode 202 to a third operating mode corresponding to, for example, less than about 30% load of the engine 10. The third operating mode corresponds to a lesser load than the part load operating mode 202, and is designated by the reference number 204 in
During the transition from the part load operating mode 202 to the third operating mode 204, the amount of fuel provided to the primary fuel injection system 70 is decreased from point 110 to point 130 and the amount of fuel provided to the secondary fuel/air injection system 72 is maintained at a predetermined value, e.g., zero. The amount of fuel provided the primary fuel injection system 70 may be continuously decreased, such as a linear decrease with a decreasing load as depicted by the graph shown in
Concurrently with reducing the amount of fuel provided to the primary fuel injection system 70, the total amount of air provided to the combustor apparatus 30 is reduced from point 114 to point 134, as shown in
It is noted that the load percentages corresponding to the full load operating mode 200, the part load operating mode 202, and the third operating mode 204 can vary from those as described herein without departing from the spirit and scope of the invention.
Injecting fuel in two fuel injection locations, i.e., via the primary fuel injection system 70 and the secondary fuel/air injection system 72, may reduce the production of NOx by the combustion section 14. For example, since a significant portion of the fuel, e.g., about 15-25% of the total fuel supplied by the primary fuel injection system 70 and the secondary fuel/air injection system 72, is injected in a location downstream of the main combustion zone 82, i.e., by the secondary fuel/air injection system 72, the amount of time that the portion of the combustion gas produced at the secondary combustion zone 94 is at a high temperature is reduced as compared to combustion gas resulting from the ignition of fuel injected by the primary fuel injection system 70. Since NOx production is increased by the elapsed time the combustion gas is at a high combustion temperature, combusting a portion of the fuel downstream of the main combustion zone 82 reduces the time the combustion gas resulting from the fuel provided by the secondary fuel/air injection system 72 is at a high temperature, such that the amount of NOx produced by the combustion section 14 may be reduced.
Further, the temperature of the combustion gas can be reduced by leaning out the fuel/air mixture, corresponding to a reduction in the fuel/air ratio (FAR). Since lowering the temperature of the combustion gas effectively reduces NOx emissions, reducing the FAR with a corresponding reduction in the temperature of the combustion results in a reduction in NOx emissions. However, if the temperature of the combustion gas becomes too low, carbon monoxide (CO) emissions may increase, wherein the CO emission rate of the combustion gas may exceed an acceptable level. In order to maintain acceptable emission rates for both NOx and CO, a target range for the FAR is provided, as illustrated in
At full load operating mode 200, as described above, the combustor apparatus 30 may be operated with the FAR in a portion of the ideal range 302, depicted by range A in
As the engine 10 is transitioned from the full load operating mode 200 to the part load operating mode 202, the amount of fuel provided to both the primary fuel injection system 70 and the secondary fuel/air injection system 72 is decreased and the total amount of air provided to the combustor apparatus 30 is reduced, as described above. Just prior to this transition, the FAR for combustor apparatus 30 may approach the lower limit 304, as depicted by range B in
As the FAR reaches the lower limit 304, or, more preferably, prior to the FAR reaching the lower limit 304, the operating parameters corresponding to the part load operating mode 202 are met, at which point the fuel provided to the primary fuel injection system 70 is increased and the fuel provided to the secondary fuel/air injection system 72 is reduced or discontinued, as described above. Concurrently, the total amount of air provided to the combustor apparatus 30 is increased, also described above. During these steps, the FAR for combustor apparatus 30 may increase and approach the upper limit 306, as depicted by range C in
In some instances, it is desirable to maintain the engine at the part load operating mode 202. In other instances, it may be desirable to further reduce the load of the engine 10, i.e., by transitioning from the part load operating mode 202 to the third operating mode 204. Even during transition from the part load operating mode 202 to the third operating mode 204, the FAR is maintained in the ideal range 302. Specifically, as the amount of fuel provided to the primary fuel injection system 70 is reduced, the total amount of air provided to the combustor apparatus 30 is also reduced, thus preventing the FAR of the combustor apparatus 30 from exceeding the lower and upper limits 304 and 306. Just prior to reaching the third operating mode 204, which may correspond to operation of the turbine at a point 204a (see
It is noted that the third operating mode 204 corresponds to a maximum closed position of the IGVs 18, wherein the total amount of air provided combustor apparatus 30 may not be able to be further reduced. Hence, reducing the amount of fuel provided to the primary fuel injection system 70 any further may result in the FAR falling below the lower limit 304 and a corresponding increase in CO emission above an acceptable value. It is also noted that in
It may also be noted that during operation at part load operation at the part load operating mode 202 and during the transition from the part load operating mode 202 to the third operating mode 204, a second portion of air is distributed to the secondary combustion zone 94, thus effectively reducing the percentage of total air supplied for combustion in the combustor apparatus 30, i.e., only the first portion of air is supplied for combustion in the main combustion zone 82 and the secondary combustion zone 94 is effectively “turned off”, as no fuel is provided thereto from the secondary fuel/air injection system 72. Hence, a reduced total amount of fuel may be provided to the combustor apparatus 30, as determined relative to the first portion of air, to provide additional turndown capability during part load operation.
With this control strategy, the turndown capability of the engine 10 may be increased while maintaining the FAR within the ideal range 302 and thus maintaining NOx and CO at acceptable levels.
While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
