Patent Application
20070207423
This invention relates to fossil fueled fired burners and more particularly to the tripping of those burners.
Flame scanners are important instruments in the operation of the combustion systems of fossil fuel-fired steam generators. To this end, flame scanners are one of the primary inputs into the burner management system normally provided with the steam generator. The principal function of a flame scanner is to monitor the combustion process in the steam generator and to provide, when a stable flame exists, a signal which gives an indication that it is safe to continue feeding fossil fuel into the combustion chamber of the steam generator.
In the event that the flame becomes unstable, or the flame is lost completely, the flame scanner is designed to provide a loss of flame signal to the burner management system. In response to the loss of flame signal, the burner management system shuts off the fossil fuel to the steam generator before an unsafe operating condition develops within the steam generator.
Burner management systems presently initiate a shut off, also known as a trip, of the burner flame if either the intensity or the frequency portion of the analog flame signal from the flame scanner fall below an associated preselected minimum signal strength. The use of these signals to trip the burner flame has worked exceptionally well for many years.
In addition to the two tripping components of the flame signal, that is, intensity and frequency, some burner management systems also include a monitoring signal called flame quality. The flame quality signal is calculated based on the intensity and frequency and to date has been used only as a status indicator to the user and has not been part of the automatic control of the burner.
However, we have determined that signal quality (the product of for example the intensity quality times the flicker frequency quality) can be used as an advanced warning to trip a burner preemptively. This is because a low quality signal will reveal a poor flame state before an individual component of the quality signal (such as for example intensity or flicker frequency or in some systems the AC amplitude of the analog flame signal or some other signal arising from the analog flame signal that is representative of temporal combustion) reaches a trip point. These observations lead us to develop the tripping function of the present invention which is based on the quality signal. In some applications, such as some cyclone burners, this type of tripping is superior to merely tripping on the strength of one signal representative of temporal combustion.
A method for preemptively tripping a fossil fuel fired burner of a steam generator before said burner is tripped when the amplitude of any one of a plurality of signals representative of a property of temporal combustion reaches an associated preselected signal strength comprising:
preemptively tripping said burner when a signal related to a predetermined combination of each of said plurality of signals representative of a property of temporal combustion of a flame in said burner reaches a preselected signal strength.
A computer program product for preemptively tripping a fossil fuel fired burner of a steam generator before said burner is tripped when the amplitude of any one of a plurality of signals representative of a property of temporal combustion reaches an associated preselected signal strength, said computer program product comprising:
computer usable program code configured to preemptively trip said burner when a signal related to a predetermined combination of each of said plurality of signals representative of a property of temporal combustion of a flame in said burner reaches a preselected signal strength.
A system for preemptively tripping a fossil fuel fired burner of a steam generator before said burner is tripped when the amplitude of any one of a plurality of signals representative of a property of temporal combustion reaches an associated preselected signal strength, said system comprising:
a computing device having therein program code usable by said computing device, said program code comprising:
code configured to preemptively trip said burner when a signal related to a predetermined combination of each of said plurality of signals representative of a property of temporal combustion of a flame in said burner reaches a preselected signal strength.
As will be appreciated by one of ordinary skill in the art, the present invention may be embodied as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.”
Furthermore, the present invention may take the form of a computer program product on a computer-usable or computer-readable medium having computer-usable program code embodied in the medium. The computer-usable or computer-readable medium may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device and may by way of example but without limitation, be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium or even be paper or other suitable medium upon which the program is printed. More specific examples (a non-exhaustive list) of the computer-readable medium would include: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a transmission media such as those supporting the Internet or an intranet, or a magnetic storage device.
Computer program code for carrying out operations of the present invention may be written in an object oriented programming language such as Java, Smalltalk, C++ or the like, or may also be written in conventional procedural programming languages, such as the “C” programming language or in assembly language. The program code may execute entirely on the user's computing device, partly on the user's computing device, as a stand-alone software package, partly on the user's computing device and partly on a remote computing device or entirely on the remote computing device or server. In the latter scenario, the remote computing device may be connected to the user's computing device through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computing device (for example, through the Internet using an Internet Service Provider).
Referring now to
Controllers 16a to 16d may also be computing devices.
The flame in each of the burners 12a to 12d is observed by the flame scanner sensing system 30 shown in
Lens system 32, which is embodied as a plano-convex lens, focuses on a small area of the burner flame where the resulting flicker frequency is characteristic of a limited number of combustion pockets in which fuel and air mix and burn. The lens system 32 in this embodiment is shown in
A fiber-optic cable 33 transmits the flame wavelength energy from lens system 32 to optical filter system 36. Optical filter system 36 is optional and is not necessary for the operation of the present invention.
As an alternative, the fiber-optic cable 33 could be replaced with a system where just the filtered flame wavelength energy is focused on the silicon photodiode 38 by a single plano-convex lens or a multiple lens arrangement.
Flame wavelength energy passing through the optical filter system 36, impinges on the silicon photodiode 38 and generates an analog signal representing properties of temporal combustion. Substituting other detectors for the silicon photodiode 38, such as a photoconductive or photovoltaic cell, may generate this same analog signal.
The analog signal generated by the detector spans 4 or 5 decades of amplitude and requires amplification over the entire range without loss of signal to saturation.
The flame scanner electronics 34 shown in
Referring now to
System 50 includes a signal processing function block 52 which is responsive to the signal at input 52c from the flame scanner to provide in a manner well known to those of ordinary skill in the art a signal at output 52a related to the intensity of the flame and a signal at output 52b related to the flicker frequency levels in the signal from the flame scanner. The intensity and flicker frequency related signals at outputs 52a and 52b respectively are inputs 54a and 54b, respectively, to a trip function block 54 which compares each of those signals to an associated preselected trip set point at input 54d for the intensity and at input 54e for the flicker frequency. In a manner well known in the art, block 54 provides at output 54c a signal to trip the associated burner when either the intensity related signal at input 54a approaches the preselected intensity set trip point at input 54d or the flicker frequency related signal at input 54b approaches the preselected frequency trip set point at input 54e. It should be appreciated that the trip set points for both the intensity and flicker frequency are usually set by a technician working for the entity that has sold the present invention to the end user but may also be set by a technician working for or on behalf of the end user.
System 50 further includes quality processing function block 56 which is responsive to the intensity related signal at input 56a, the flicker frequency related signal at input 56b, the intensity and flicker frequency normalization factors at input 56c and the preselected Intensity and Frequency trip points at inputs 56d and 56e which are connected to inputs 54d and 54e of block 54, respectively, to provide, as is described below, at output 56d a quality signal as a function of the flame scanner intensity and flicker frequency related signals for use solely for performance monitoring as a status indicator. It should be appreciated that the normalization factors for both the intensity and flicker frequency are usually set by a technician working for the entity that has sold the present invention to the end user but may also be set by a technician working for or on behalf of the end user.
Quality is a factor calculated using three factors; the present signal levels for Intensity and Frequency at inputs 56a and 56b of block 56, the preselected Intensity and Frequency trip points at inputs 56d and 56e, respectively, and the Intensity and Frequency Normalization values at input 56c of block 56. Typically, the Quality signal ranges from zero at burner trip to 100% at full load.
In order to make Quality a useful indicator, the Quality Normalization Factors must be properly selected. The normalization values for Intensity or Frequency represent the difference between the Intensity or Frequency signal at the “full load, best burner” and the associated trip point during normal operation. One example is given below of the calculation for selecting the quality normalization factor for both intensity and frequency.
Consider an Intensity Trip Point of 35% and an Intensity normalization term of 20. The Quality signal will equal zero when the Intensity signal equals a value of 35% (an Intensity Trip), whereas an Intensity value of 55% (35%+20) represents a Quality value of 100%. Looking at it another way, if high load Intensity at the “best burner” is 55% and the trip point is set at 35%, the Intensity Normalization term is calculated as 55%−35% or 20.
Consider a Frequency Trip Point of 20 Hz and a Frequency normalization term of 25. The Quality signal will equal zero when the Frequency signal equals a value of 20 Hz (a Frequency Trip), whereas a Frequency value of 45 Hz (20 Hz+25) represents a Quality value of 100%. Looking at it another way, if high load Frequency at the “best burner” is 45 Hz and the trip point is set at 20 Hz, the Frequency Normalization term is calculated as 45 Hz−20 Hz or 25.
Referring now to
As is described above, block 64 is responsive to the quality signal at input 64f to provide at output 64c a signal to trip the burner if the quality signal approaches a preselected preemptive quality trip set point at input 64g. As with block 54 of
System 60 further includes quality processing function block 66 which performs the same function as block 56 of
The use of the quality signal to preemptively trip the associated burner is now described in detail. Before using the quality signal for preemptive tripping, the trip points for intensity and flicker frequency need to be determined using industry standard practices, well known to those of ordinary skill in the art, with, in this embodiment of the present invention the preemptive tripping mode turned off. It should be appreciated that in another embodiment of the present invention the preemptive tripping may be left on when the trip points are determined.
After the Frequency and Intensity trip points have been preselected and programmed into the computing device such as for example controller 20 of
where:
I=Current intensity value
ID=Intensity drop out
IN=Intensity normalization value
F=Current frequency value
FD=Frequency drop out
FN=Frequency normalization value
The following special conditions apply to equation (1):
a. If either of the first two terms, (I−ID) or (F−FD), are zero or negative, the quality value will go to zero.
b. The maximum value of any of the first two terms is 1.
The following practice, well known to those of ordinary skill in the art, with, in this embodiment of the present invention, the preemptive tripping mode turned off is used to determine the intensity and frequency normalization factors for a specific burner installation (it should be appreciated that in another embodiment of the present invention the preemptive tripping may be left on when the normalization factors are determined):
A. Record the Trip Point setting for Intensity, for example 40%.
B. Note the Intensity signal at full load, for example 65%.
C. Subtract the two values and use that number for the Intensity Normalization factor, which in this example is 25.
D. Repeat the above procedure for Frequency.
In some situations where high limits also exist, there are corresponding high normalization factors as follows:
where:
IH=Intensity high limit
INH=Intensity normalization high value
FH=Frequency high limit
FNH=Frequency normalization high value
Where there are high limits, the high normalization factors are typically as follows:
where X usually ranges from 5 to 10.
After the adjustment of the intensity and frequency normalization values, the quality signal should be a live, active signal in the ninety percent range at full load. It is allowable to have an occasional quality signal pegged at 100% for short periods of time, for example, three to five seconds, but the overall effect to the observer is that the quality signal, for any burner, is an active signal (i.e. not pegged at 100%). Since the Quality Signal is used as performance feedback, having the signal pegged for long periods of time limits its usefulness as an indicator of performance. Increasing the normalization factors will prevent pegging the signal at 100%. It is also allowable to have an occasional drop in quality below 70% at full load for any individual burner, but this should occur infrequently.
The result of the above procedure is to give a quality signal that is 100% only when both the Intensity and Frequency signals are at their maximums (the maximums were defined when the Normalization terms were calculated). In the case where high limits are also used [equation (2)], the quality signal will be at 100% when intensity and frequency are near the exact middle of the low and high limits.
After the procedures described above are completed the user must determine what quality level is appropriate for a burner trip. Some experimentation with the actual burner is necessary to determine how early the burner should trip before the actual intensity and frequency trip points are reached.
The typical preemptive trip point settings are for a quality signal that is at between 20% and 30%. However, this can vary based on the normalization values established in earlier steps.
The intensity and frequency Normalization values allow the user to increase or decrease the sensitivity of the Quality calculation. For example:
Low normalization values cause less sensitivity. With very low values, the Quality value may rapidly change from 100% to 0%. This rapid change may provide very little warning of a problem before a Flame Trip, that is an Intensity or Frequency Trip, signal is given. Low normalization values may require higher preemptive trip point settings in order to effectively use the quality signal to trip before the occurrence of a flame trip.
High normalization values cause increased sensitivity. With higher values, the Quality value changes by small increments. Operators are able to detect small changes in flame signal quality and are more likely to be able to spot combustion problems before they lead to a flame out condition. It should be noted that if the normalization value is too high, quality never reaches 100%. In this case, the preemptive trip point settings need to be lower than the setting for a typical quality signal of 20% to 30% since the quality is always low.
If the preemptive tripping feature keeps causing nuisance trips no matter how much the trip point is adjusted, it is likely that the normalization values are too high. If the preemptive tripping is not tripping soon enough no matter how much the trip point is adjusted, the normalization values are probably too low. If either of these cases exists, the normalization factors determined in the previous step need readjustment before the preemptive trip value can be finally determined.
If the total quality signal is not stable, the quality smoothing factor may also need adjustment to avoid nuisance trips. The smoothing factor is used to change how much the quality output will be filtered, so that rapid changes are smoothed out using a standard Infinite Impulse Response filter, box-car filter, or any similar technique.
Lastly, after the quality signal value is tuned according to the above procedure, the preemptive tripping mode can be turned on. This causes the system to have two quality values, one for tripping at the output of block 66 and the other at the output of block 68 for monitoring. The new quality value at the output of block 66 is called the preemptive quality, and the signal quality equation is modified in block 68 as is described below to arrive at the “Total” signal quality equation (5).
When the preemptive tripping mode is turned on, the preemptive quality (i.e. the output of block 66) is now given by equation (1), with only intensity and frequency affecting its value. The “total” signal quality (i.e. the output of block 68) is now given by equation (5). After turning on preemptive tripping, the preemptive quality trip points must be set.
When the preemptive tripping mode is turned on, the “total” signal quality is now based on the following equation:
where:
PQ=Current preemptive quality value, that is, the output of block 66
PQD=Preemptive quality drop out, that is, the preemptive trip set point
PQN=Preemptive quality normalization value
The preemptive quality normalization value is determined using the same procedure described above for the other normalization factors.
It should be appreciated that two key differences between “total” signal quality and preemptive quality are:
a. Preemptive quality is based on two inputs: intensity and frequency. “Total” signal quality is based on three components: intensity, frequency and preemptive quality.
b. Preemptive quality has trip points, whereas “total” signal quality does not.
It should be appreciated that while the present invention is described above in a system that uses the intensity and frequency portion of the analog flame signal to trip the associated burner when a preselected condition is met that the present invention may also be used with other systems such as those that use, without limitation, the AC amplitude of the analog flame signal to trip the associated burner when a preselected trip point associated with AC amplitude is reached by that signal.
It should also be appreciated that while the present invention is described herein in connection with trip points that are the low trip point that a high trip point as mentioned herein may also be used with the present invention. It should further be appreciated that there are the following combinations of trip points: only low trip point, low and high trip points or only high trip point.
It is to be understood that the description of the foregoing exemplary embodiment(s) is (are) intended to be only illustrative, rather than exhaustive, of the present invention. Those of ordinary skill will be able to make certain additions, deletions, and/or modifications to the embodiment(s) of the disclosed subject matter without departing from the spirit of the invention or its scope, as defined by the appended claims.
