Patent Application
20140075953
The present subject matter relates generally to gas turbines and particularly to combustors disposed in gas turbines. More particularly, the present subject matter relates to a system and method for detecting and controlling flashback and flame holding within a combustor.
In order to reduce the formation of air polluting emissions, such as NOx, combustors in a gas turbine often include a lean-premixed combustion system, wherein fuel and air are mixed in a plurality of premixed fuel nozzle assemblies disposed upstream of a combustion chamber in the combustor. However, the use of a lean-premixed combustion system also increases the propensity for flashback events, which occur when the flame within the combustion chamber flashes upstream into the premixing zone of the fuel nozzle assembly. The likelihood of flashback events occurring may be increased further when highly reactive fuels are used to fuel a gas turbine, such as hydrogen augmented fuels and fuels derived from liquefied natural gas. These flashback events often lead to flame holding, wherein the flame “holds” or remains supported within the fuel nozzle assembly. Flame holding can result in significant damage to the fuel nozzle assembly, as increased temperatures within the fuel nozzle exceed the design temperatures of the nozzle materials. Additionally, prolonged flame holding may cause the nozzle material to melt away. This can lead to serious damage to the turbine blades, as melted portions of the fuel nozzle assembly flow through a combustor and into the turbine section of a gas turbine.
In order to prevent such damage, various devices have been proposed to detect flashback and flame holding in a fuel nozzle assembly. For example, some detection devices use thermocouples to detect temperature changes. However, thermocouples only provide flashback and flame holding detection at single points within a fuel nozzle assembly. Accordingly, it is quite complex and costly to place thermocouples in every location within a fuel nozzle assembly where flame holding may occur. Other devices are known that utilize an electric field to detect flames within the fuel nozzle assembly. However, this requires electrical wiring running to each nozzle in order to achieve nozzle-level detection. Moreover, it has been found that there are both cost and reliability issues associated with the use of electric fields to detect flames.
Accordingly, there is a need for a system and method for detecting and controlling flashback and flame holding within a combustor that is reliable, relatively simple and effective without being cost-prohibitive.
Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In one aspect, the present subject matter provides a unique system for detecting and controlling flashback and flame holding in a combustor of a gas turbine. The system includes at least one flame indicator disposed in a combustor and at least one detector disposed downstream from the flame indicator. The flame indicator may be configured to produce light when exposed to a flame and the detector may be configured to detect the light produced by the flame indicator.
In another aspect, the present subject matter provides a gas turbine capable of detecting and controlling flashback and flame holding. The gas turbine may include a compressor section for pressurizing air and a combustor section configured to receive the pressurized air, mix the air with fuel to form an air/fuel mixture and combust the air/fuel mixture. A turbine section may be disposed downstream of the combustor section and can be configured to receive hot gases of combustion flowing from the combustor section. Additionally, the gas turbine may include the system discussed above and described in greater detail herein.
In a further aspect, the present subject matter provides a method for detecting and controlling flashback and flame holding within a combustor of a gas turbine. The method includes the steps of indicating the existence of flame holding in a combustor by producing light of a specific color, detecting the light produced, notifying a gas turbine control system of the detected light and determining whether flame holding exists within the combustor.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
Referring to
Still referring to
Each combustor 16 may also include a quaternary fuel system 38 that injects a small amount of fuel into the pressurized airflow upstream of the premixed fuel nozzle assemblies 28 in order to control the combustion dynamics of the lean-premixed combustion system. The quaternary fuel system 38 may include a plurality of quaternary pegs 40 disposed circumferentially around the inside of the combustion casing 24. Each quaternary peg 40 may be supplied fuel by a quaternary fuel manifold 42, defining fuel circuit Q, disposed around the outer circumference of the combustion casing 24.
Referring to
It should also be appreciated that each combustor 16 in a gas turbine 10 may include any number of premixed fuel nozzle assemblies 28. For example,
As is generally known, damage may occur to a premixed fuel nozzle assembly 28 or to other components of a gas turbine 10 when the flame within the combustion chamber 36 flashes back into the fuel nozzle assembly 28. Additionally, if the air/fuel mixture within the premixing annulus 60 is sufficient to support the flame, the flame can “hold” within the fuel nozzle assembly 28. This can result in significant damage and costly downtime. However, it should be appreciated that, although flashback and flame holding are primarily discussed herein with respect to fuel nozzle assemblies 28, these conditions may occur in other locations within a combustor 16. For example, flashback and flame holding may occur adjacent to or at the quaternary pegs 40 of the quaternary fuel system 38. Flashback and flame holding may also occur in or adjacent to a secondary combustion system (not illustrated) of a gas turbine 10, such as a late lean injection system or a lean direct injection system.
In accordance with an aspect of the present subject matter,
Generally, the flame indicator 66 of the present subject matter may have any configuration that allows the indicator 66 to produces light when exposed to a flame. As such, the flame indicator 66 may be used to signify the existence of flame holding within a combustor 16 by producing a detectable, signature light when in the presence of a flame. In one embodiment, illustrated in
As indicated above, the protective layer(s) 70 of the present subject matter may be configured to ablate in the presence of a flame. For example, the protective layer(s) 70 may be configured to rapidly melt or oxidize away when exposed to a high temperature flame in order to reveal the witness layer underneath 72. Thus, the protective layer(s) 70 may be composed of any material that is capable of withstanding normal operating temperatures within the areas of a combustor 16 not designed for high temperatures (e.g. the premixing annulus 60 or the area adjacent to the quaternary fuel pegs 40), but ablates when exposed to higher temperatures due to flashback and flame holding. In one embodiment, the protective layer(s) 70 may be composed of a metal with a relatively low melting point (e.g. 304 stainless steel, 316 stainless steel, or aluminum) or a high temperature paint (e.g. alumina-based high temperature paint) that will rapidly melt or oxidize in the presence of flame.
Additionally, each protective layer 70 may be applied to a witness layer 72 by any suitable means so that the protective layer 70 provides a protective coating for each witness layer 72. For example, the protective layer(s) 70 may be painted or plated (e.g. by electroplating) on to the witness layer 72. Moreover, as it may be desirable for each protective layer 70 to rapidly ablate away in the presence of a flame, the protective layer(s) 70 may be applied as a relatively thin coating. For example, in one embodiment, the thickness of the protective layer(s) 70 may be less than 0.005 cm, such as less than 0.003 cm. However, it should be appreciated that the desired thickness of the protective layer(s) 70 may vary significantly depending on numerous factors including, but not limited to, the material used to make the witness layer and the operating temperatures of a particular gas turbine 10.
Once a protective layer 70 has ablated away so as to expose an underlying witness layer 72 to a flame, the witness layer(s) 72 of the present subject matter may be generally configured to produce light of a specific color. Thus, the witness layer(s) 72 may be composed of any metal, metal salt, or other compound that produces light of a particular wavelength range via chemiluminescence when exposed to a flame. For example, the witness layer 72 may include sodium such that a yellow-colored light is produced when the layer is exposed to a flame. Alternatively, the witness layer 72 may include cobalt to produce a blue-colored light. It should be readily appreciated that various combinations of metals, metal salts, or compounds may be chosen such that a witness layer 72 can produce light of any desired color when exposed to a flame. Additionally, the thickness of each witness layer 72 may vary depending on the desired duration of the detection event. For instance, the witness layer 72 may have a certain thickness so as to produce several minutes of light when exposed to a flame at maximum operating pressures and temperatures within a combustor 16.
The layered flame indicator 66, discussed above, may be generally disposed at any location within a combustor 16. Particularly, it may be desirable for a flame indicator 66 to be disposed at any location within a combustor 16 that may be subject to flashback and flame holding conditions. Accordingly, it should be appreciated that the system of the present subject matter may comprise a plurality of flame indicators 66 placed at various locations within a combustor 16. For example, a flame indicator 66 may be disposed in every premixed fuel nozzle assembly 28 within a gas turbine 10, one of which is illustrated in
As shown in
Additionally, as shown in
As previously indicated, the system of the present subject matter also includes at least one detector 68 disposed downstream from the flame indicator(s) 66 that may be configured to detect the light produced by the indicator(s) 66. As shown in
In one embodiment, illustrated in
In a preferred embodiment, the system of the present subject may be configured such that the offending fuel circuit (i.e. the circuit supplying fuel to the location at which the flame holding event may be occurring) can be determined. For example, each combustor 16 in a gas turbine 10 may include one or more flame indicators 66 disposed within each premixed fuel nozzle assembly 28 (
This configuration can allow the system of the present subject matter to effectively detect and control flame holding by discriminating both the combustor 16 in which the flame holding event may be occurring and also the offending fuel circuit. Specifically, the turbine control system 74 may be configured to analyze the signal transmitted from the detector 68 to determine the specific color of light sensed by the detector 68. Thus, when a detector 68 detects colored light corresponding to a particular fuel circuit, the turbine control system 74 may be configured to perform a corrective action directed solely to the offending fuel circuit.
It should be appreciated that the corrective action performed by the turbine control system 74 may generally comprise any action designed to eliminate a flame holding event. In one embodiment, the corrective action may include reducing the amount of fuel flowing through the offending fuel circuit. This can be accomplished by either reducing the flow of fuel through the offending fuel circuit without adjusting the amount of fuel flowing through the other circuits, thereby reducing the total amount of fuel supplied to the combustors 16, or by adjusting the percentage of fuel flow to the other fuel circuits to accommodate the reduction in fuel flowing through the offending fuel circuit. In another embodiment, the corrective action may include cutting off the supply of fuel to the offending fuel circuit. If such an action is performed, the turbine operators or the turbine control system 74 may then determine a further course of action, such as holding the fuel load until it is convenient to shutdown the gas turbine 10 or re-loading the circuit to see if the flame holding event has cleared. In a further embodiment, the corrective action may include shutting down the machine to ensure that damage to the gas turbine 10 is minimized.
Additionally, it should be appreciated that the present subject matter also encompasses a gas turbine 10 capable of detecting and controlling flashback and flame holding within a combustor 16. The gas turbine may include a compressor section 12 configured to pressurize air flowing into the gas turbine 10. A combustor section 14 may be disposed downstream from the compressor section 12 and may be configured to receive the air discharged from the compressor section 12. The combustor section 14 may comprise a plurality of combustors 16 configured to mix the pressurized air with fuel to form an air/fuel mixture and combust the air/fuel mixture. A turbine section 18 may be disposed downstream of the combustor section 14 and may be configured to receive hot gases of combustion flowing from each of the combustors 16. Additionally, the gas turbine 10 may include the system described above and illustrated herein.
It should also be appreciated that the present subject matter encompasses a method for detecting and controlling flashback and flame holding within a combustor 16 of a gas turbine 10. The method generally includes the steps of indicating the existence of flame holding in a combustor 16 by producing light of a specific color, detecting the light produced, notifying a gas turbine control system 74 of the detected light and determining whether flame holding exists within the combustor 16.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
