Flashback detection sensor for lean premix fuel nozzles

Details Flashback detection sensor for lean premix fuel nozzles Flashback detection sensor for lean premix fuel nozzles

2000-06-02

2002-08-06

Soderquist, Arlen (Department: 1743)

Chemistry: analytical and immunological testing

Measurement of electrical or magnetic property or thermal...

Of an ionized gas

C048S192000, C250S374000, C250S379000, C324S464000, C324S468000, C422S054000, C422S089000, C431S007000, C431S078000, C431S079000, C431S090000, C431S202000, C436S154000

Reexamination Certificate

active

06429020

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to lean premix combustion systems in general, and to the detection of a flashback condition in lean premix fuel nozzles of gas turbine combustion systems in particular.
2. Brief Discussion of the Related Art
Many advanced gas turbine combustion systems use lean premix nozzles in pursuit of lower emissions and higher efficiency. Unfortunately, many of these systems have experienced problems associated with instabilities and flashback. Flashback occurs when the flame normally contained to the combustion zone of the gas turbine combustion system, moves back into the fuel nozzle.
When flashback occurs in the fuel nozzle, the temperatures inside the nozzle rise above the design temperature for the nozzle material causing costly damage. Also, upon occurrence of a severe flashback condition, fragments of the nozzle material, usually metal, tend to pass through the turbine system usually causing severe damage to the turbine blades. This type of failure, regardless of frequency, can be catastrophic in terms of down time, maintenance costs and lost revenue.
In order to prevent such damage, many devices have in the past been used to detect flashback in fuel nozzles. However, all previous devices tend to exhibit undesirable characteristics such as slow response time, and point type or line of site measurements.
For example, thermocouples and bimetallic elements when used as flashback detectors in fuel nozzles, suffer from the disadvantages of providing only localized point measurements and generally slow reaction times (typically 2 to 3 minutes), which can lead to failure of the fuel nozzle before detection. Another disadvantage of these sensors is that, since they only detect heat, they are unable to distinguish between heat generated by the flame of a flashback condition and the heat radiated by the normal combustion process of the gas turbine combustion system.
Similarly, flame rods must be in direct contact with the flame in order to function properly. Unfortunately, it is not always known exactly where in the fuel nozzle of a gas turbine combustion system flashback will occur, and unless the flame rods are in the precise location, flame rods would be useless for detecting the flame occurring during a flashback condition.
Attempts to use radiation type flame sensors as flashback detectors have also been made. For this type of detector, a photocell is used as the actual detector. At least one element of the photocell is coated with a sulfide compound, such as cadmium-sulfide or lead-sulfide, so as to be sensitive to the particular wavelengths of light emitted by a flame occurring during a flashback condition. For instance, the electrical resistance of cadmium-sulfide decrease directly with increasing intensity of light, and like lead-sulfide, will function as a variable resistor. However, when used to detect the presence of a flame, a cadmium-sulfide photocell is useful only for sensing that portion of the flame occurring in the visible light wavelengths. Unfortunately, the cadmium-sulfide photocell will not respond to gas flames, and therefore can only be used to detect the presence of oil flames.
On the other hand, a lead-sulfide photocell provides detection in the infrared wavelength regions. Similar to the cadmium-sulfide photocell, the lead-sulfide photocell can change its resistance inversely to the infrared radiation it is subjected to, and the current flow generated by the lead-sulfide photocell serves as a measure of flame strength. However, the “shimmering effect” caused by movement of hot gases between a refractory surface and the lead-sulfide photocell can erroneously deceive the photocell into indicating the presence of a flame, which makes this type of photocell unreliable for use as a flashback detector.
To overcome these problems, a suitable flashback detector must be able to reliably and dependably detect the flame of a flashback condition anywhere inside the fuel nozzle and provide a clear indication that a flashback condition exists.
It is well known that a flame, being the result of a chemical reaction between a fuel and oxygen, liberates a large number of electrons. Because of this ionization, the flame is capable of conducting an electrical current. Moreover, a flame can conduct both direct and alternating current, either of which could be utilized to establish an electrical circuit.
Conduction occurs when ionization takes place. The electrons that are liberated from the burning fuel and oxygen molecules are free to move about, thus constituting the current. In addition to the freed electrons, a negative electrode properly situated in the vicinity of the flame would in the process of repelling the freed electrons, also would tend to lose some of its own electrons provided that there were a sufficient number of positive ions, such as from a positive electrode, in the vicinity to attract them. Accordingly, the number of electrons leaving the negative electrode and entering the positive electrode determines the rate of current flow. It is apparent that the current flow depends on the number of positive ions that get near enough to the negative electrode. If the area of one electrode is made several times larger than the other, and that electrode is negative, it will accommodate a larger number of positive ions. This in turn will increase the flow of electrons to the positive electrode. Accordingly, an electrode immersed in the flame would act as one electrode and the combustion chamber wall act as the other electrode.
Hence, an electrode strategically placed in a fuel nozzle, in the vicinity of a location likely to experience flashback, will detect the existence of the flame associated with the flashback condition by way of this flame ionization process. Then, an electrical signal produced by the sensor detecting the existence of the flame would in turn be relayed to the various controllers associated with the proper operation of the gas turbine combustion system.
Therefore, advantageous use of flame ionization techniques could be employed to detect the flame present during a flashback condition. A sensor employing these techniques would make an ideal flashback sensor. The responsive nature of the sensor will also facilitate measurements of flame flicker in the nozzle during operation, should they occur.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a flashback detector for a lean premix combustion system.
It is an additional object of the invention to provide a flashback detector for a lean premix system capable of detecting a flashback condition in a lean premix fuel nozzle.
It is another object of the present invention to provide a flashback detector capable of providing real-time detection of a flame associated with a flashback condition occurring anywhere along the entire length of the fuel nozzle of a combustion system.
It is a further object of the invention to provide a flashback detector that isolates the combustion region of a gas turbine combustion system from the sensor electrode thereby minimizing false indication of flashback.
It is still another object of the invention to provide a reliable flashback detector for a gas combustion system that uses inexpensive electronics and uncomplicated peripheral hardware.
It is yet another object of the invention to provide a flashback detector for a gas turbine combustion system that can easily incorporate the detector in new fuel nozzle designs as well as in existing fuel nozzle designs.
It is yet a further object of the invention to provide detection of flame in the fuel nozzle of a gas turbine combustion system within a time frame that will prevent damage to any part of the gas turbine combustion system.
These and other objects, aspects and advantages will be better understood from the following detailed description of preferred embodiments of the invention with reference to the appended claims.
Basically, the present invention is a system for detecting a flashback condition in a fuel nozzle of a l

Affiliated with

Also associated with

Rating

Flashback detection sensor for lean premix fuel nozzles does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Flashback detection sensor for lean premix fuel nozzles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flashback detection sensor for lean premix fuel nozzles will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2899055